阅读说明：本技术 纳米结构复合电极 (Nanostructured composite electrodes ) 是由 费尔南多·帕托洛斯基 居伊·大卫迪 尼姆罗德·哈帕克 于 2018-10-31 设计创作，主要内容包括：本文描述了数种复合电极,所述复合电极包含一不锈钢基板及数个含硅纳米结构,所述纳米结构自所述基板延伸。本文亦描述了通过预处理所述不锈钢而不需要一催化剂地制备所述电极的过程。所述含硅纳米结构的至少一部份以下述为特征：基本上不具有一非硅催化剂材料及/或一贵金属；及/或沿着它的长度包括一金属成分,所述金属成分源自所述不锈钢基板；及/或包括一金属硅化物,所述金属硅化物延伸自所述基板及沿着所述基板的长度的至少一部分延伸；及/或在由所述基板的一表面移除的一位置处被与至少一个其它的含硅纳米结构融合,以形成一海绵状三维结构；及/或是不锈钢纳米结构,所述不锈钢纳米结构有一硅层沉积在其上。(Composite electrodes are described herein that include a stainless steel substrate and silicon-containing nanostructures extending from the substrate. Also described herein is a process for preparing the electrode by pretreating the stainless steel without a catalyst. At least a portion of the silicon-containing nanostructures are characterized by: substantially free of a non-silicon catalyst material and/or a noble metal; and/or a metal component along its length, said metal component being derived from said stainless steel substrate; and/or comprises a metal silicide extending from the substrate and along at least a portion of the length of the substrate; and/or fused with at least one other silicon-containing nanostructure at a location removed from a surface of the substrate to form a spongy three-dimensional structure; and/or stainless steel nanostructures having a layer of silicon deposited thereon.)

1. A composite electrode, characterized by: the composite electrode comprises

A stainless steel substrate; and

a plurality of silicon-containing nanostructures extending from the stainless steel substrate, wherein in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is characterized by at least one of:

substantially free of a non-silicon catalyst material; and/or

Substantially free of a noble metal; and/or

Comprises a metal component along its length, said metal component being derived from said stainless steel substrate; and/or

Comprising a metal silicide extending from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate; and/or

Fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a spongy three-dimensional structure; and/or

Is a stainless steel nanostructure having a layer of silicon deposited thereon.

2. The composite electrode of claim 1, wherein: in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is characterized by at least one of:

substantially free of a non-silicon catalyst material; and/or

Substantially free of a noble metal; and/or

Comprises a metal component along its length, said metal component being derived from said stainless steel substrate; and/or

Comprising a metal silicide extending from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate; and/or

Is fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a sponge-like three-dimensional structure.

3. A composite electrode according to claim 1 or 2, wherein: at least a portion of the silicon-containing nanostructures are substantially free of a metallic material that may be used as a non-silicon catalyst in a vapor-liquid-solid growth of silicon nanostructures.

4. The composite electrode of claim 3, wherein: the metal material comprises a noble metal.

5. A composite electrode according to claim 1 or 2, wherein: at least a portion of the silicon-containing nanostructures are substantially free of a noble metal.

6. A composite electrode according to any one of claims 1 to 5, wherein: each of the plurality of silicon-containing nanostructures is substantially free of a non-silicon catalyst material.

7. The composite electrode of claim 6, wherein: the non-silicon catalyst material is useful in a gas-liquid-solid growth of a plurality of silicon nanostructures.

8. The composite electrode of claim 6 or 7, wherein: the non-silicon catalytic material is a metal catalyst material.

9. The composite electrode of claim 6, wherein: the metal catalyst material comprises a noble metal.

10. The composite electrode of any one of claims 1 to 7, wherein: each of the plurality of silicon-containing nanostructures is substantially free of a noble metal.

11. A composite electrode according to any one of claims 4, 5, 9 and 10, wherein: the noble metal comprises gold.

12. A composite electrode according to any one of claims 1 to 11, wherein: in at least a portion or all of the plurality of silicon-containing nanostructures, each silicon-containing nanostructure includes one or more metal constituents along its length, the metal constituents being derived from the stainless steel substrate.

13. The composite electrode of claim 12, wherein: the metal component is selected from nickel, copper and iron.

14. A composite electrode according to any one of claims 1 to 12, wherein: in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures comprises a metal silicide that extends from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate.

15. A composite electrode according to any one of claims 1 to 14, wherein: in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is fused with at least one other silicon-containing nanostructure at a location removed from a surface of the stainless steel substrate to form a sponge-like three-dimensional structure.

16. A composite electrode according to any one of claims 1 to 15, wherein: the plurality of silicon-containing nanostructures form a three-dimensional network of a plurality of cross-chains.

17. A composite electrode according to any one of claims 1 to 16, wherein: in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures includes a crystalline core and a semi-amorphous shell.

18. A composite electrode according to any one of claims 1 to 17, wherein: each of the silicon-containing nanostructures has a length of between 20 and 300 microns in at least a portion or all of the plurality of silicon-containing nanostructures.

19. A composite electrode according to any one of claims 1 to 18, wherein: each of the silicon-containing nanostructures has a diameter between 10 nanometers and 300 nanometers in at least a portion of, or all of, the plurality of silicon-containing nanostructures.

20. A composite electrode according to any one of claims 1 to 19, wherein: at least a portion of the silicon-containing nanostructures comprises a plurality of silicon nanowires.

21. A composite electrode, characterized by: the composite electrode comprises:

a stainless steel body, an outer surface of the stainless steel body comprising a plurality of elongated stainless steel nanostructures extending from the stainless steel body; and

a silicon layer deposited on each of the plurality of elongated stainless steel nanostructures.

22. The composite electrode of claim 21, wherein: the silicon layer substantially coats an outer surface of at least a portion or each of the plurality of stainless steel nanostructures.

23. A composite electrode according to claim 21 or 22, wherein: the silicon layer has a thickness from about 6 nanometers to about 200 nanometers.

24. A composite electrode according to any one of claims 21 to 23, wherein: the plurality of elongated stainless steel nanostructures form a sponge-like nanoporous stainless steel network at the outer surface of the stainless steel body.

25. A composite electrode according to any one of claims 21 to 24, wherein: the plurality of elongated stainless steel nanostructures have a length between 20 microns and 300 microns.

26. A composite electrode according to any one of claims 21 to 25, wherein: each of the number of stainless steel nanostructures has a diameter between 30 nanometers and 90 nanometers.

27. A method of making a composite electrode, comprising: the method comprises the following steps:

contacting a stainless steel substrate with hydrofluoric acid (HF); and

after the contacting, the substrate is subjected to conditions for growing a silicon nanostructure extending from the substrate.

28. The method of claim 27, wherein: after said contacting, obtaining a nanoporous surface structure on said stainless steel substrate, said nanoporous surface structure comprising a plurality of nanostructure growth seed locations, and growing said silicon nanostructure is from at least a portion or each of said plurality of nanostructure growth seed locations.

29. The method of claim 27 or 28, wherein: the contact is with an aqueous solution of monohydrofluoric acid.

30. The method of claim 29, wherein: a concentration of the hydrofluoric acid ranges from 5% to 15% by weight.

31. The method of any one of claims 27 to 30, wherein: the contacting is for a period of time from 10 minutes to 60 minutes.

32. The method of any one of claims 27 to 31, wherein: the growth of the silicon nanostructures is performed by vapor deposition using a silicon precursor.

33. The method of claim 32, wherein: the vapor deposition is performed at a temperature between 400 degrees and 500 degrees.

34. The method of any one of claims 32 to 33, wherein: the vapor deposition is performed for between 5 minutes and 90 minutes.

35. The method of any one of claims 27 to 34, wherein: after growing the nanostructures, further comprising: subjecting the nanostructure to a thermal treatment.

36. The method of claim 35, wherein: the heat treatment is performed in a hydrogen atmosphere or in a vacuum.

37. The method of claim 35 or 36, wherein: the heat treatment is continued for a period of time from 2 to 8 minutes.

38. The method of any one of claims 35 to 37, wherein: the heat treatment occurs at a temperature between 650 degrees and 850 degrees.

39. The method of any one of claims 27 to 38, wherein: the conditions provide a silicon nanostructure having at least one dimension characteristic from about 10 nm to about 200 nm.

40. The method of any one of claims 27 or 39, wherein: the composite electrode is as claimed in any one of claims 1 to 20.

41. A method of making a composite electrode, comprising: the method comprises the following steps:

contacting a stainless steel body with a gaseous environment containing hydrogen gas and a temperature from about 850 degrees to about 1200 degrees, thereby growing a plurality of elongated stainless steel nanostructures extending from the stainless steel body by exposure to the environment; and

a silicon layer is formed on each of the plurality of elongated stainless steel nanostructures.

42. The method of claim 41, wherein: a concentration of the hydrogen gas in the gaseous environment is from 1 to 10% by volume.

43. The method of claim 41 or 42, wherein: the gaseous environment further comprises at least one of nitrogen or argon.

44. The method of any one of claims 41 to 43, wherein: the contacting is for a period of time of about at least 30 minutes.

45. The method of any one of claims 41 or 44, wherein: forming the silicon layer includes: vapor depositing silicon at a temperature from about 380 degrees to about 550 degrees.

46. The method of any one of claims 41 or 45, wherein: forming the silicon layer includes: the silicon is vapor deposited for a period of time from about 30 minutes to about 180 minutes.

47. The method of any one of claims 41 or 46, wherein: forming the silicon layer includes: a silane gas precursor is used to vapor deposit silicon.

48. The method of any one of claims 41 or 47, wherein: forming the silicon layer includes: the silicon is vapor deposited at a pressure from about 1 torr to about 25 torr.

49. The method of any one of claims 41 or 48, wherein: the silicon layer has a thickness from about 6 nanometers to about 200 nanometers.

50. The method of any one of claims 41 or 49, wherein: the composite electrode is as claimed in any one of claims 21 to 26.

Technical field and background

The present invention, in some embodiments thereof, relates to electrochemistry, and more particularly, but not by way of limitation, to silicon-based electrodes that may be used, for example, in energy storage devices such as lithium ion batteries.

One of the most common energy storage devices is the battery pack (battery), and fuel cells and capacitors. One of the most studied areas regarding batteries is the search for new materials as anodes or cathodes with increased capacity, cycle life and overall performance improvements over current technologies. Lithium ion batteries, in particular, are of considerable interest.

Commercial lithium ion batteries typically have graphite as their anode material, reaching a theoretical capacity of 372 milliamp-hours per gram (mAh/g). Although graphite is characterized by high stability and long cycle life due to relatively low volume change, it has been recognized that the substitution of silicon for graphite may help to meet the requirements for higher electrical capacity. Silicon is abundant and has a capacitance of up to 4200 milliamp-hours/gram, which is an order of magnitude higher than the theoretical capacitance of graphite, relative to the theoretical capacitance of lithium.

One such disadvantage of silicon, however, is the large volume change (about 320% volume expansion) of the silicon structure during the lithiation and delithiation stages [ Beaulieu et al, jelutrochem Soc,150: a1457-a1464, 2003 ] these changes in volume cause cracking and shattering of the anode, resulting in rapid degradation of the silicon anode [ Beaulieu et al, Electrochem Solid-State L ett,4: a137-a140, 2001; Besenhard et al, J Power Sources,68:87-90, 1997; Ryu et al, electrochemobond-State L ett,7: a306-a309, 2004 ] furthermore, the volume expansion that causes cracking and shattering also allows the formation of a new Solid Electrolyte Interface (SEI) [ dielectric material, J electrolyte, Soc 126, 1977: a309, 2004 ] which also causes the resistance of the cell stack to decay and the resistance of the cell stack to increase and the insulation layer to decay all the time as a result of the cell stack degrades.

One way to handle the considerable comminution of silicon anodes is to reduce the size of the silicon material to the nanometer scale, rather than using bulk silicon. The high surface to volume ratio of the nanoscale silicon objects increases the ability of the structure to withstand stress, thus limiting the effect of cracking of the material [ Deshpande et al, J Power Sources,195: 5081-. Many types of silicon nanostructures (SiNS) have been studied, including silicon nanoparticles (sinps), silicon nanotubes (sints), core-shell structures, and silicon nanowires (sinws).

L iu et al [ ACS Nano,6:1522-1531, 2012] report that at the first lithiation of several silicon nanoparticles (observed via transmission electron microscopy), particles larger than about 150 nm exhibit cracks on the surface.

Cracking of the silicon particles may cause loss of contact with the current collector and further SEI formation, eventually leading to rapid decay of the capacitance. One significant disadvantage of using SiNP as an anode material is that harvesting SiNP less than 150 nm from a bulk material requires grinding, milling and clean extraction to successfully use these nanoparticles for battery applications. Furthermore, the need for a bonding material to make good and electrically conductive electrical contact with the current collector also limits the process once the SiNP is ready for use.

SiNW and SiNT also pose some limitations in the size of the silicon structure due to their greater compressive resistance.

Wu et al, Nat Nanotechnol,7: 310-. Polymer nanofibers are prepared by electrospinning, followed by a carbon and silicon coating, followed by heating to remove the carbon layer and create a thicker oxide layer.

While very high cycling stability (cyclability) is achieved in their lithium ion batteries, the Wu et al approach is not practical for several reasons: (i) fabrication of SiNT as described therein, and by alternative techniques (e.g., as described by [ Ben-Ishai ]&Patolsky, J Am Chem Soc,131:3679-]The described techniques) manufacturing SiNT is complex and requires several stages to complete, thus compromising the scalability of the process; and (ii) the reported density of the SiNT corresponds to about 0.015 milliampere-hour per square centimeter (mAh/cm)²) An electrode capacity, which is very low for a practical lithium ion battery.

Chan et al Nat Nanotechnol,3:31-35, 2008 report a high capacity lithium ion battery using SiNW grown directly on the current collector, allowing direct electrical transmission and good electrical contact. Very high capacitances are reported, the theoretical capacitance being reached in the first charge cycle at C/20 rate. However, only about 90% of a coulomb efficiency is reported.

Peled et al [ Nano L ett,15:3907-3916, 2015 ] describe the growth of SiNW on an SG L25 AA carbon fiber using CVD and gas-liquid-solid (V L S) as a three-dimensional (3D), open structured surface on which gold nanoparticles are attached via electrostatic interaction using poly-L-lysine (poly-L-lysine).

Other background art includes Chou et al [ Scr Metal Mater,25:2203 & 2208, 1991 ], Istratov et al [ Appl Phys A,13-44, 1999 ]; Kim et al [ Materials L ett,64:2306 & 2309, 2010 ]; Kim et al [ Chem Mater,27:6929 & 6933, 2015 ]; L i et al [ Adv Energy Mater,2:87-93, 2012 ]; and Peled & Menkin [ J Electrochem Soc,164: A1703-A1719, 2017 ], and U.S. Pat. Nos. 7,683,359, 8,017,430 & 8,637,185.

Disclosure of Invention

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising:

a stainless steel substrate; and

a plurality of silicon-containing nanostructures extending from the stainless steel substrate,

wherein in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is characterized by at least one of:

substantially free of a non-silicon catalyst material; and/or

Substantially free of a noble metal; and/or

Comprises a metal component along its length, said metal component being derived from said stainless steel substrate; and/or

Comprising a metal silicide extending from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate; and/or

Fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a spongy three-dimensional structure; and/or

Is a stainless steel nanostructure having a layer of silicon deposited thereon.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising:

a stainless steel body, an outer surface of the stainless steel body comprising a plurality of elongated stainless steel nanostructures extending from the stainless steel body; and

a silicon layer deposited on each of the plurality of elongated stainless steel nanostructures.

According to an aspect of some embodiments of the present invention, there is provided a method of making a composite electrode, the method comprising:

contacting a stainless steel substrate with hydrofluoric acid (HF); and

after the contacting, the substrate is subjected to conditions for growing a silicon nanostructure extending from the substrate.

According to an aspect of some embodiments of the present invention, there is provided a method of making a composite electrode, the method comprising:

contacting a stainless steel body with a gaseous environment containing hydrogen gas and a temperature from about 850 degrees to about 1200 degrees, thereby growing a plurality of elongated stainless steel nanostructures extending from the stainless steel body by exposure to the environment; and

a silicon layer is formed on each of the plurality of elongated stainless steel nanostructures.

According to some of any of the embodiments of the invention, in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is characterized by at least one of:

substantially free of a non-silicon catalyst material; and/or

Substantially free of a noble metal; and/or

Comprises a metal component along its length, said metal component being derived from said stainless steel substrate; and/or

Comprising a metal silicide extending from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate; and/or

Is fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a sponge-like three-dimensional structure.

According to some of any of the embodiments of the invention, at least a portion of the silicon-containing nanostructures are substantially free of a metallic material that may be used as a non-silicon catalyst in a vapor-liquid-solid growth of silicon nanostructures.

According to some of any of the embodiments of the invention relating to a metallic material, the metallic material comprises a noble metal.

According to some of any of the embodiments of the invention, at least a portion of the silicon-containing nanostructures are substantially free of a noble metal.

According to some of any of the embodiments of the invention, each of the plurality of silicon-containing nanostructures is substantially free of a non-silicon catalyst material.

According to some of any of the embodiments of the present invention relating to a non-silicon catalyst material, the non-silicon catalyst material is useful in a gas-liquid-solid growth of silicon nanostructures.

According to some of any of the embodiments of the invention relating to a non-silicon catalytic material, the non-silicon catalytic material is a metal catalytic material.

According to some of any of the embodiments of the invention, each of the plurality of silicon-containing nanostructures is substantially free of a noble metal.

According to some of any of the embodiments of the invention with respect to a noble metal, the noble metal comprises gold.

According to some of any of the embodiments of the invention, in at least a portion or all of the plurality of silicon-containing nanostructures, each silicon-containing nanostructure includes one or more metal constituents along its length, the metal constituents being derived from the stainless steel substrate.

According to some of any of the embodiments of the invention relating to a metal composition, the metal composition is selected from the group consisting of nickel, copper and iron.

According to some of any of the embodiments of the invention, in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures comprises a metal silicide that extends from the stainless steel substrate and along at least a portion of a length of the stainless steel substrate.

According to some of any of the embodiments of the invention, in at least a portion or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is fused with at least one other silicon-containing nanostructure at a location removed from a surface of the stainless steel substrate to form a sponge-like three-dimensional structure.

According to some of any of the embodiments of the invention, the plurality of silicon-containing nanostructures form a three-dimensional network of a plurality of cross-chains.

According to some of any of the embodiments of the invention, each of the silicon-containing nanostructures comprises a crystalline core and a semi-amorphous shell in at least a portion or all of the plurality of silicon-containing nanostructures.

According to some of any of the embodiments of the invention, each of the silicon-containing nanostructures in at least a portion or all of the plurality of silicon-containing nanostructures has a length between 20 microns and 300 microns.

According to some of any of the embodiments of the invention, each of the silicon-containing nanostructures in at least a portion or all of the number of silicon-containing nanostructures has a diameter between 10 nanometers and 300 nanometers.

According to some of any of the embodiments of the invention, at least a portion of the silicon-containing nanostructures comprise a plurality of silicon nanowires.

According to some of any of the embodiments of the invention with respect to a silicon layer, the silicon layer substantially coats an outer surface of at least a portion or each of the plurality of stainless steel nanostructures.

According to some of any of the embodiments of a silicon layer of the present invention, the silicon layer has a thickness from about 6 nanometers to about 200 nanometers.

According to some of any of the embodiments of the invention with respect to the plurality of stainless steel nanostructures, the plurality of silicon-containing nanostructures form a three-dimensional network of a plurality of cross-chains.

According to some of any of the embodiments of the invention with respect to stainless steel nanostructures, the elongated stainless steel nanostructures form a sponge-like nanoporous stainless steel network at the outer surface of the stainless steel body.

According to some of any of the embodiments of the invention with respect to the plurality of stainless steel nanostructures, the plurality of elongated stainless steel nanostructures have a length of between 20 microns and 300 microns.

According to some of any of the embodiments of the invention with respect to the number of stainless steel nanostructures, each of the number of stainless steel nanostructures has a diameter between 30 nanometers and 90 nanometers.

According to some of any of the embodiments of the invention relating to contacting with hydrofluoric acid, after said contacting, a nanoporous surface structure on said stainless steel substrate is obtained, said nanoporous surface structure comprising a plurality of nanostructure growth seed locations, and growing said silicon nanostructure is from at least a portion or each of said plurality of nanostructure growth seed locations.

According to some of any of the embodiments of the invention relating to contacting with hydrofluoric acid, the contacting is with an aqueous solution of hydrofluoric acid.

According to some of any of the embodiments of the invention relating to contacting with hydrofluoric acid, a concentration of the hydrofluoric acid ranges from 5% to 15% by weight.

According to some of any of the embodiments of the invention with respect to contacting with hydrofluoric acid, the contacting is for a period of time from 10 minutes to 60 minutes.

According to some of any of the embodiments of the invention relating to silicon-containing nanostructures, the growth of the silicon nanostructures is performed by vapor deposition using a silicon precursor.

According to some of any of the individual embodiments of the invention, the silicon precursor is 99.5% silane.

According to some of any of the embodiments of the invention relating to vapor deposition, the vapor deposition is performed at a temperature between 400 degrees and 500 degrees.

According to some of any of the embodiments of the invention with respect to vapor deposition, the vapor deposition is performed at a pressure of at least 1 torr.

According to some of any of the embodiments of the invention with respect to vapor deposition, the vapor deposition is performed for between 5 minutes and 90 minutes.

According to some of any of the embodiments of the invention with respect to a method, the process further comprises, after growing the nanostructures: subjecting the nanostructure to a thermal treatment.

According to some of any of the embodiments of the invention relating to a heat treatment, the heat treatment is in a hydrogen atmosphere or in a vacuum.

According to some of any of the embodiments of the invention relating to a heat treatment, the heat treatment lasts for a period of time between 2 and 8 minutes.

According to some of any of the embodiments of the invention relating to a heat treatment, the heat treatment occurs at a temperature between 650 degrees and 850 degrees.

According to some of any of the embodiments of a method according to the present invention, the conditions provide a silicon nanostructure having at least one dimension characteristic from about 10 nm to about 200 nm.

According to some of any of the embodiments of the invention relating to a method of making a composite electrode, the composite electrode is as described herein, according to any of the respective embodiments.

According to some of any of the embodiments of the invention relating to a gaseous environment, a concentration of the hydrogen gas in the gaseous environment is from 1 to 10% by volume.

According to some of any of the embodiments of the invention with respect to a gaseous environment, the gaseous environment further comprises at least one of nitrogen or argon.

According to some of any of the embodiments of the invention relating to contact with a gaseous environment, the contact is for a period of time of about at least 30 minutes.

According to some of any of the embodiments of the invention with respect to a silicon layer, forming the silicon layer comprises: vapor depositing silicon at a temperature from about 380 degrees to about 550 degrees.

According to some of any of the embodiments of the invention with respect to a silicon layer, forming the silicon layer comprises: the silicon is vapor deposited for a period of time from about 30 minutes to about 180 minutes.

According to some of any of the embodiments of the invention with respect to a silicon layer, forming the silicon layer comprises: a silane gas precursor is used to vapor deposit silicon.

According to some of any of the embodiments of the invention with respect to a silicon layer, forming the silicon layer comprises: the silicon is vapor deposited at a pressure from about 1 torr to about 25 torr.

Unless defined otherwise, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, exemplary methods and/or materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be necessarily limiting.

Unless defined otherwise, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, exemplary methods and/or materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be necessarily limiting.

Methods and/or systems implementing embodiments of the present invention may involve performing or completing selected tasks manually, automatically, or a combination thereof. Also, according to the actual instrumentation and equipment of embodiments of the method and/or system of the present invention, several selected operations may be implemented using an operating system, either by hardware, by software, or by firmware, or by a combination thereof.

For example, the hardware used to perform selected operations according to embodiments of the invention may be implemented as a chip or a circuit. As software, selected operations according to embodiments of the present invention may be implemented as software instructions executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more operations according to exemplary embodiments of the methods and/or systems described herein are performed by a data processor, such as a computing platform, for executing instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile storage, such as a magnetic hard disk and/or removable storage, for storing instructions and/or data. Optionally, a network connection is also provided. A display and/or a user input device such as a keyboard or mouse may also optionally be provided.

Drawings

Some embodiments of the invention are described herein, by way of example only, with reference to the accompanying drawings. With the specification in mind the details of the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the embodiments of the present invention. In this regard, the description taken with the drawings will make apparent to those skilled in the art how the embodiments of the present invention may be practiced.

In the illustration:

fig. 1 depicts a battery including a silicon-based electrode, according to some embodiments of the present invention.

FIGS. 2A-2D show optical microscopy images (FIGS. 2A and 2B; dark field image, embedded bright field image) and high resolution scanning electron microscopy images (FIGS. 2C and 2D) of a stainless steel mesh treated with 40% hydrofluoric acid for 30 minutes (FIGS. 2B and 2D) and untreated (e.g., received) stainless steel mesh (FIGS. 2A and 2C); the scale bar in fig. 2 and 2D represents 10 microns, except that in the inset of fig. 2D the scale bar represents 1 micron (the inset image is at a higher resolution in all figures).

FIGS. 3A to 3C present X-ray photoelectron spectroscopy spectra of stainless steel (grade 316) treated with 40% hydrofluoric acid for 30 minutes; fig. 3B shows the portion of the spectrum in fig. 3A that includes nickel peaks, and fig. 3C shows the portion of the spectrum in fig. 3A that includes copper peaks (the inset represents the corresponding spectrum for the untreated control group steel).

FIGS. 4A and 4B present scanning electron micrographs of stainless steel mesh treated with 40% hydrofluoric acid for 30 minutes (FIG. 4B) or without (FIG. 4A) followed by chemical vapor deposition of silicon for 1 hour; the silicon density in fig. 4B is 1.18 mg/cm; the scale bar represents 100 microns, except for the inset where the scale bar represents 1 micron (fig. 4A) or 10 microns (fig. 4B).

FIGS. 5A-5D present a stainless steel mesh treated with 40% hydrofluoric acid for 30 minutes followed by chemical vapor deposition of silicon for 7 minutes (460 degrees, 25 Torr, 5sccm (standard milliliters per unit time) silane, 20sccm argon); the scale bar represents 10 microns in fig. 5A, 1 micron in fig. 5B and 10 nanometers in fig. 5C and 5D.

Fig. 6A-6D present dark field engineered micrographs (all inset at higher magnification) of stainless steel mesh obtained after 30 minutes of treatment with 40% hydrofluoric acid followed by chemical vapor deposition of silicon until a silicon density of 0.5 mg/cm (fig. 6A), 1.09 mg/cm (fig. 6B), 3.07 mg/cm (fig. 6C), or 5.11 mg/cm (fig. 6D) was obtained.

Fig. 7A to 7D present high resolution scanning electron microscopy images of the same stainless steel mesh sample with deposited silicon shown in fig. 6A to 6D, respectively; the scale bar represents 100 microns in fig. 7A and 7D, and 10 microns in fig. 7B and 7C and the inset in all figures.

Figures 8A and 8B present TOF-SIMS (time of flight secondary ion mass spectroscopy) spectra of silicon nanostructures comprising intrinsic silicon (figure 8A) or boron doped P-type silicon (figure 8B) grown on a stainless steel mesh after treating the mesh with 40% hydrofluoric acid for 30 minutes.

Figure 9 presents a schematic depiction of the formation of an aluminum oxide coating on silicon by atomic layer deposition in accordance with some embodiments of the present invention.

FIGS. 10A-10D present transmission electron microscopy images of several exemplary silicon structures grown on a stainless steel substrate and coated with a layer of aluminum oxide (about 5 nm) by "exposed" atomic layer deposition; FIGS. 10A and 10D show a clear crystalline core (FIG. 10D is presented in the sample shown in FIG. 10A, a fast Fourier transform shows crystallinity in the direction [111 ]), and FIGS. 10B and 10C show exemplary connected structures; the scale bar represents 20 nm in fig. 10A (structure diameter of 78 nm) and fig. 10B, and 50 nm in fig. 10C.

Fig. 11 presents a transmission electron micrograph of several exemplary silicon structures grown on a stainless steel substrate and subjected to two lithiation/delithiation cycles.

Fig. 12A and 12B present transmission electron microscopy images of several exemplary silicon structures grown on a stainless steel substrate and coated with two layers of alumina, followed by two lithiation/delithiation cycles.

FIGS. 13A-13C present several graphs showing charge and discharge capacity (FIGS. 13A and 13B) and coulombic efficiency (FIG. 13B; light colored squares) as a function of electrochemical cycle number (cycling at 1 milliamp, occasionally cycling at 0.1 milliamp) for an exemplary anode comprising 1.18 milligrams of silicon per square centimeter coated with alumina, and voltage as a function of capacity at 50, 150, 250, 350, and 450 cycles (electrochemical cell at 85% 1M L iPF in 1:1EC: DEC (1:1 ethylene carbonate: diethyl carbonate) with 2% VC (vinylene carbonate) and 15% FEC (fluoroethylene carbonate) ("1: 1 ethylene carbonate: diethyl carbonate))₆Constructed).

FIGS. 14A and 14B present a dQ/dV plot comprising 1.18 mg/cm silicon, cycled at 1 milliamp current (FIG. 14A) or 0.1 milliamp current (FIG. 14B) with an exemplary anode coated with alumina (electrochemical cell at 85% 1M L iPF in 1:1EC: DEC and 2% VC + 15% FEC)₆Constructed).

Fig. 15A-15D present scanning electron micrographs (fig. 15A) and transmission electron micrographs (fig. 15B-15D) of several silicon structures (fig. 15D) and Solid Electrolyte Interface (SEI) of an exemplary anode coated with alumina after 700 cycles comprising 1.18 mg silicon per square centimeter; fig. 15B shows the structure with a complete alumina coating, fig. 15C shows the structure separated from the alumina coating, fig. 15D shows the alumina shell separated in SEI, the alumina shell is enlarged in the inset; the scale bar represents 50 microns in fig. 15A, 50 nanometers in fig. 15B and 15C, and 200 nanometers in fig. 15D and 5 nanometers in the inset in fig. 15D.

Fig. 16 depicts a model of Solid Electrolyte Interface (SEI) formation on a silicon nanoparticle after repeated charging and discharging, according to some embodiments of the invention.

FIGS. 17A-17D present several graphs showing several P-type silicon nanowire structures grown on a native silicon substrate (AuNP-grown SiNW) using 20 nanometer gold nanoparticles as catalysts, or silicon structures grown on stainless steel before or after 650 degree annealing for 2 hours, at zero gate voltage (FIGS. 17A and 17B, differing only in the Y-axis dimension), as V_sdI (source-drain voltage) as a function_sd(source-drain current), and a scanning electron micrograph of an exemplary silicon structure between the source and drain electrodes (fig. 17C) and a high resolution transmission electron micrograph of a polysilicon structure after annealing (fig. 17D) and fast fourier transform (inset of fig. 17D); the scale bar represents 5 microns in fig. 17C and 20 nanometers in fig. 17D.

Fig. 18 presents an image of a 3D spongy nanoporous silicon coated stainless steel network (one meter by 30 cm) having a silicon density of 0.6 mg/cm, in accordance with some embodiments of the present invention; the stainless steel (steel grade 316) was treated with hydrofluoric acid followed by silicon deposition using a 4 inch chemical vapor deposition apparatus.

Fig. 19 presents high resolution scanning electron microscopy images of untreated (e.g., received) stainless steel (304) mesh at various magnifications.

Fig. 20A to 20E present high resolution scanning electron microscopy images of stainless steel (304) mesh after 30 minutes of treatment with hydrofluoric acid at various magnifications.

Fig. 21 presents scanning electron micrographs of stainless steel (304) mesh (25 microns) after treatment with hydrofluoric acid for 30, 45, and 60 minutes.

Fig. 22 presents scanning electron micrographs of stainless steel (304) mesh (50 microns) after treatment with hydrofluoric acid for 30, 45, and 60 minutes.

Fig. 23 presents a scanning electron micrograph of stainless steel (304) after 30 minutes of treatment with hydrofluoric acid.

FIGS. 24A and 24B show elemental analysis by energy dispersive X-ray spectroscopy (energy dispersive X-ray spectroscopy) of stainless steel (304) after 30 minutes of hydrofluoric acid treatment.

Fig. 25A-25F present transmission electron microscopy images of several exemplary silicon nanostructures comprising a crystalline core and an amorphous silicon shell (the inset in fig. 25A, 25C, and 25F present fast fourier transforms).

Fig. 26A-26E present high resolution scanning electron microscopy images of p-type silicon nanostructures grown by CVD for 140 minutes on a stainless steel mesh (25 microns) pretreated with hydrofluoric acid for 30 minutes. (domain mean diameter 232.5. + -. 3.5 nm)

Fig. 27 presents a high resolution scanning electron micrograph of soldered silicon contacts of a silicon network after high temperature annealing in accordance with some embodiments of the present invention.

Fig. 28A-28D present images of a hydrofluoric acid treated stainless steel mesh (25 microns) rolled into a cylinder (about 1.5 cm in diameter), before (fig. 28A) and after (fig. 28B-28D) subjected to CVD (at 25 torr and 460 degrees for 90 minutes) to deposit a number of silicon nanostructures.

Fig. 29A and 29B each present an image of a stainless steel sheet (25 microns) treated with hydrofluoric acid, rolled and subjected to CVD (as described for fig. 28), taken at medium (fig. 29A) and high (fig. 29B) magnifications, at different lengths from the roll (left corresponding to upstream and right corresponding to downstream relative to silane flow) (HV 15.0kV, WD 11.0-11.3 mm, magnifications of about 500 in fig. 29A, and about 2000 in fig. 29B).

Fig. 30A-30F show scanning electron micrographs of a stainless steel web after heat treatment in a hydrogen-containing atmosphere at a temperature in a range of 950 degrees to 1100 degrees, according to some embodiments of the present invention.

FIGS. 31A-31E show transmission electron micrographs (FIGS. 31A, 31C and 31D), an EDX spectroscopy spectrum (FIG. 31B) and a fast Fourier transform (FIG. 31E; fast Fourier transform of the sample shown in FIG. 31D) of a metal base structure on a stainless steel web after heat treatment in a hydrogen-containing atmosphere at a temperature in a range of 950 to 1100 degrees according to some embodiments of the present invention (scale bar represents 20 nanometers).

FIGS. 32A-32F show transmission electron micrographs (scale bar represents 20 nm) of a silicon-coated metal substrate structure on stainless steel mesh after heat treatment in a hydrogen-containing atmosphere and deposition of silicon by chemical vapor deposition at a temperature in a range of 950 to 1100 degrees, according to some embodiments of the present invention; the inset of fig. 32C-32F exhibits a fast fourier transform.

FIG. 33 depicts a Landerris circuit model for analysis.

FIGS. 34A and 34B present graphs showing silicon nanostructure anodes (0.77 mg P per square centimeter on stainless steel mesh [1:4000]Silicon) capacity (in milliamp-hours per square centimeter or per anode (fig. 34A) or per gram of silicon (fig. 34B) and coulombic efficiency (fig. 34B) (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC) as a function of electrochemical cycle number (cycle index) upon charging or discharging, in the range of 0.05 to 1 volt₆)。

Figure 35 presents a graph showing the capacitance (in milliamp-hours per gram of silicon) as a function of the number of electrochemical cycles (cycle index) when charging and discharging a P-doped and intrinsic silicon nanostructure anode (alumina coated silicon on stainless steel mesh).

FIG. 36 presents a graph showing the capacitance (in the range of 0.05 to 1 volt as a function of electrochemical cycle number (cycle index)) of a silicon nanostructured anode (0.78 square centimeter, 0.7 milligrams of silicon on stainless steel mesh) and a conventional carbon ink upon charging or dischargingMilliamp hours/cm and milliamp hours per anode) (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC₆) (ii) a The average CE (coulomb efficiency) was 99.24%.

FIG. 37 presents a graph showing the capacitance (in milliamp hours per square centimeter and in milliamp hours per anode) as a function of the number of electrochemical cycles (cycle index) in the range of 0.05 to 1 volt (0.78 square centimeter, 1.4 milligrams of silicon on stainless steel mesh) for a silicon nanostructured anode (0.78 square centimeter, 1.4 milligrams of silicon on stainless steel mesh) and a conventional carbon ink upon charging and discharging (electrolyte is 0.85M L iPF M in EC: DEC + 2% VC + 15% FEC)₆) (ii) a The average CE was 99.04%.

FIG. 38 presents a graph showing the capacitance of two silicon nanostructured anodes (1.13 square centimeters, 2.26 milligrams of silicon on stainless steel mesh) and a TUBA LL carbon nanotube carbon ink as a function of electrochemical cycle number (cycle index) in the range of 0.05 to 1 volt (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC) when charged or discharged₆)。

FIG. 39 presents a graph showing the capacitance of a carbon ink-free silicon nanostructured anode (0.78 square centimeter, 0.7 milligrams of silicon on stainless steel mesh) as a function of electrochemical cycle number (cycle index) in the range of 0.05 to 1 volt (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC) upon charging and discharging₆)。

Fig. 40 presents a graph showing the capacitance of 4 silicon nanostructure anodes coated or uncoated with carbon ink (0.93 mg/cm) as a function of electrochemical cycle number (cycle index).

Fig. 41 presents a graph showing the capacitance of 4 silicon nanostructures coated or uncoated with carbon ink as a function of the number of electrochemical cycles (cycle index) of the anode relative to lithium metal (2.2 mg/cm).

Fig. 42 presents a graph showing the capacitance of 4 silicon nanostructure anodes coated with SWCNT carbon ink) as a function of electrochemical cycle number (cycle index) versus lithium metal (2.2 mg/cm).

Fig. 43 presents a graph showing capacitance as a function of electrochemical cycle number (cycle index) relative to lithium metal (2.2 mg/cm) for a silicon nanostructure anode coated with SWCNT carbon ink when charged or discharged.

FIG. 44 presents a graph showing the capacitance of 3 silicon nanostructure anodes coated with SWCNT carbon ink (1.13 square centimeter, 1 mg silicon) in the range of 0.05 to 1 volt as a function of electrochemical cycle number (cycle index) when charged or discharged (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC)₆) (ii) a The batteries #1 to #2 suffer from an error in the program and the battery #3 can still operate.

Fig. 45A and 45B present impedance nyquist plots for a silicon nanostructure anode versus lithium metal charging (fig. 45A) and discharging (45B).

Fig. 46A and 46B present graphs showing the capacity (in milliamp-hours/square centimeter or milliamp-hours per anode (fig. 46A) or milliamp-hours per gram silicon (fig. 46B)) and coulombic efficiency (light colored square in fig. 46B) (electrolyte is 0.85M L iPF) of a silicon nanostructured anode (0.78 square centimeter, 0.94 milligrams of silicon on stainless steel mesh) as a function of the number of electrochemical cycles (cycle index) relative to an NCA anode (from tadilan) in the range of 2.8 to 4 volts when charged and discharged (electrolyte is 0.85M L iPF₆+ in EC: DMC: FEC: PC [3:3:3:1]0.05M L IBOB).

FIG. 47 presents a graph showing the capacitance (C) of several NCA anodes (1.77 square centimeter, 19 mg/square centimeter) as a function of electrochemical cycle number in the range of 4.4 to 3.5 volts (cells 5 to 7) or 4.2 to 3.5 volts (cells 1,3, 4) (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC₆)。

FIG. 48 presents a graph showing the capacitance of an NCA anode (1.77 square centimeters) versus lithium metal in the range of 4.2 to 4.6 volts upon charging as a function of the number of electrochemical cycles (cycle index) using 0.85M L iPF in EC: DEC + 2% VC + 15% FEC₆TAU duplicate samples) or 0.85M L iPF₆+ in EC: DMC: FEC: PC [3:3:3:1]0.05M L IBOB ("Tadlan" replicate specimen) in (E.coli) as electrolyte。

FIG. 49 presents a graph showing the capacitance of 4 silicon nanostructure anodes coated with SWCNT carbon ink (2 mg silicon/square centimeter) in the range of 4 to 3 volts when charged or discharged as a function of the number of electrochemical cycles (cycle index) relative to the NCA anode in a full cell (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC)₆)。

FIG. 50 presents a graph showing the capacity of a silicon nanostructure anode coated with SWCNTs in the range of 0.05 to 1 volt upon charge or discharge as a function of the number of electrochemical cycles (cycle index) in the full cell relative to an L FP anode (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC)₆) (ii) a The average CE was 99.93%.

FIGS. 51A and 51B present graphs showing the capacity (in milliamp-hours per square centimeter or per anode (FIG. 51A) or per gram of silicon (FIG. 51B)) and coulombic efficiency (light colored squares in FIG. 51B) (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC) as a function of electrochemical cycle number (cycle index) in the range of 0.05 to 1 volt at charge or discharge for a silicon nanostructured anode (0.78 square centimeter, 0.94 mg silicon, 0.2 mg alumina on stainless steel mesh) of the (coated alumina) silicon₆) (ii) a The average CE was 99.4%, and the cell was still active.

FIG. 52 presents a graph showing the capacitance of a silicon nanostructure anode (coated with alumina) (0.78 square centimeter, 1.7 milligrams of silicon on stainless steel mesh) coated with a conventional carbon ink as a function of electrochemical cycle number (cycle index) in the range of 0.05 to 1 volt (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC) when charged or discharged₆) (ii) a The average CE was 99.14%.

FIG. 53 presents a graph showing the capacity of 2 (alumina coated) silicon nanostructured anodes (0.5 mg silicon per square centimeter, about 5 nm alumina, on stainless steel mesh) coated with conventional carbon ink as a function of the number of electrochemical cycles (cycle index) in a full cell relative to the NCA anode (electrolyte is in EC: DEC + 2% VC + 15%) when charged or discharged in the range of 4 to 3 volts0.85M L iPF in FEC₆)。

FIG. 54 presents a graph showing the capacitance of 4 (alumina coated) silicon nanostructured anodes (2.1 mg silicon per square centimeter, about 5 nm alumina, on stainless steel mesh) coated with conventional carbon ink, in the range of 4 to 3 volts when charged, as a function of the number of electrochemical cycles (cycle index) relative to the NCA anode in a full cell (electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC), in an electrochemical cell₆)。

Fig. 55 presents a graph showing the alumina formed by 35 cycles of a L D (about 5 nm) or by 70 cycles of a L D (about 10 nm) coated with a silicon nanostructured anode coated with SWCNT carbon ink (1.13 square centimeter, 2.7 milligrams of silicon on stainless steel mesh) as a function of the number of electrochemical cycles (cyclic capacity index) when charged or discharged.

Fig. 56A and 56B present graphs showing the capacitance as a function of electrochemical cycling (cycle index) when charged or discharged for silicon nanostructure anodes (2.4 mg silicon/cm in fig. 56A and 2.1 mg silicon/cm in fig. 56B) with or without alumina-coated alumina formed by a L D of either 30 cycles (fig. 56B) or 70 cycles (fig. 56A).

Fig. 57A and 57B present scanning electron micrograph images of several silicon nanostructures (1.8 mg silicon/cm) with (fig. 57B) and without (fig. 57A) annealing at 400 degrees for 2 hours.

Figure 58 presents a graph showing capacitance of 8 silicon nanostructure anodes as a function of electrochemical cycle number (cycle index); the filled symbols represent annealed anodes and the open symbols represent non-annealed anodes.

Fig. 59 presents a graph showing capacitance as a function of electrochemical cycle number (cycle index) versus lithium for a silicon nanostructure anode when charged or discharged; the red and black symbols represent the anodes subjected to annealing, and the blue and green symbols represent the control anodes not annealed.

FIG. 60 presents a graph showing the presence or absence of a polymer coating (L iPAA, NaCMC, or alginate)) The silicon nanostructured anode of (1.13 square centimeter, 0.9 milligrams of silicon on stainless steel mesh), in the range of 0.05 to 1 volt upon charging or discharging, the capacitance as a function of the number of electrochemical cycles (cycle index) (the carbon coating is SB carbon, the electrolyte is 0.85M L iPF in EC: DEC + 2% VC + 15% FEC)₆)。

FIGS. 61A-61B present scanning electron microscopy images (at different magnifications) of silicon nanostructures deposited on stainless steel mesh at 15 Torr and 430 ℃ for 20 minutes using disilane (3sccm) and hydrogen (10 sccm).

FIGS. 62A and 62B present scanning electron microscopy images (at different magnifications) of silicon nanostructures deposited on stainless steel mesh at 15 Torr and 420 degrees for 20 minutes using disilane (3sccm) and hydrogen (10 sccm).

FIGS. 63A and 63B present scanning electron microscopy images (at different magnifications) of silicon nanostructures deposited on stainless steel mesh using disilane (3sccm) hydrogen (5sccm) and argon (5sccm) at 25 Torr and 410 ℃ for 20 minutes.

Fig. 64 presents a graph showing the voltage of the working electrode (Ewe), counter electrode (Ece), and cell (Ecell) as a function of time during cycling for a silicon nanostructure-NCA cell, determined using a 3-electrode cell with a lithium reference.

Fig. 65 presents a graph showing the capacity as a function of electrochemical cycle number (cycle index) upon charging or discharging in a 3-electrode cell with a lithium reference for a silicon nanostructure-L FP cell.

Fig. 66 presents a graph showing the capacity as a function of electrochemical cycle number (cycle index) upon charging or discharging in a 3-electrode cell with a lithium reference, a silicon nanostructure-NCA cell.

Fig. 67 presents a graph showing terminal voltage as a function of cycle number (cycle index) at electrochemical cycling relative to L FP or NCA anodes measured in a 3-electrode cell on a silicon nanostructured anode.

Figure 68 presents a photograph of three 1/3AAA silicon nanostructured NCA cells (coins used as dimensional references have an 18 mm diameter) prepared according to some embodiments of the present invention.

Figure 69 presents a graph showing the capacity as a function of the number of electrochemical cycles (cycle index) at a rate of C/20 or C/6, when charged or discharged, for three 1/3AAA silicon nanostructured NCA cells prepared according to some embodiments of the present invention.

Figure 70 presents a graph showing the capacity (when charged) of nine 1/3AAA silicon nanostructure NCA cells prepared according to some embodiments of the present invention as a function of the number of electrochemical cycles (cycle index), which is a rate at C/3.

Figure 71 presents a graph showing the capacity (when charged or discharged) as a function of electrochemical cycle number (cycle index) for two 1/3AAA silicon nanostructured NCA cells prepared according to some embodiments of the present invention.

Fig. 72 presents a graph showing capacitance of silicon nanostructure anodes (in one sample) with and without (reference set) a SWCNT double coating followed by thermal cracking as a function of electrochemical cycle number (cycle index).

Fig. 73A and 73B present scanning electron microscopy images of silicon nanostructures coated on both sides with SWCNTs, with (fig. 73B) or without (73A), subjected to thermal cracking (in argon/hydrogen) at 750 ℃ for 1 hour.

Fig. 74 presents a graph showing the capacitance of a silicon nanostructure anode (control group not immersed) as a function of the number of electrochemical cycles (cycle index) (upon charging or discharging) after immersion in a suspension of carbon nanotubes in water or water/ethanol.

FIG. 75 presents a graph showing silicon nanostructure anodes double-coated (i.e., coated on both sides) with (pyro) or (DC) -free thermally cracked carbon nanotube carbon inks, or carbon nanotube carbon inks diluted in water (W) or water/ethanol (WE), in the range of 4 to 3 volts, with capacitance as a function of electrochemical cycle number (cycle index) relative to NCA anodes (control group anodes coated only on the collector side, electrolyte in EC: DEC + 2% VC + 15% F0.85M L iPF in EC₆)。

FIG. 76 presents a photograph of an in situ tensile test instrument (magnified in the left).

Fig. 77 presents a graph showing the stress-strain curves of Stainless Steel (SS) 316L web itself, and after treatment with 30% hydrofluoric acid, and after deposition of silicon nanostructures on the surface (4 samples, batches 1-4).

Fig. 78A and 78B present (after a tensile test) scanning electron micrographs of a sample of silicon nanostructures on a stainless steel mesh at a fracture point.

Fig. 79A and 79B present a scanning electron micrograph of the layers (fig. 79A) and bar graphs showing the silicon levels of the layers in the taped silicon nanostructures on stainless steel (fig. 79B) as determined by energy dispersive X-ray spectroscopy.

Figures 80A-80D present several graphs (figures 80A-80C) and a table (figure 80D) showing capacitance of several silicon nanostructure anodes before and after rolling as a function of electrochemical cycle number; the sample in FIG. 80A (Lot 1, characteristic of relatively strong adhesion between layers) has 2.1 mg silicon/sq cm, the sample in FIG. 80B (Lot 2, characteristic of relatively weak adhesion between layers) has 2 mg silicon/sq cm, and the sample in FIG. 80C (Lot 3) has 1.3 mg silicon/sq cm.

Fig. 81A and 81B present scanning electron microscopy images of silicon nanostructures on steel mesh coated (except at one corner) with Solid Polymer Electrolyte (SPE) with (fig. 81B) or without (fig. 81A) alumina, according to some embodiments of the present invention.

Figure 82 presents a graph showing voltage as a function of capacitance for the first three cycles of a silicon nanostructure anode with SPE.

FIG. 83 presents a graph showing voltage as a function of capacitance for a silicon nanostructure anode with SPE comprising alumina or silica.

Detailed Description

The present invention, in some embodiments thereof, relates to electrochemistry and more particularly, but not by way of limitation, to silicon-based electrodes that may be used, for example, in energy storage devices such as lithium ion batteries.

The inventors have discovered a catalyst-free and low-cost Chemical Vapor Deposition (CVD) process that results in dense (and mostly amorphous) silicon nanostructures, three-dimensional (3D) growth on conductive stainless steel networks. Prior to silicon deposition, the steel substrate is treated by exposure to hydrofluoric acid, which treatment results in silicon nanostructures growing on the substrate at CVD. Alternatively, the steel substrate is subjected to a heat treatment which results in the formation of metal-based nanostructures which may then be coated with silicon via CVD.

Exemplary silicon nanostructures exhibit more than 500 cycles with less than 50% capacity loss and a capacity of about 2000 milliamp hours per gram of silicon for lithium half cells at a cycling rate of about 0.05 C.an exemplary full cell comprising a silicon nanostructure anode and NCA (lithium nickel cobalt aluminum oxide) or L FP (lithium iron phosphate) commercial cathode exhibits more than 300 to 400 full cycles with 100% DOD (depth of discharge) and with less than 40% capacity loss.

The materials and methods described herein can overcome the previously described deficiencies of electrodes for lithium ion batteries (e.g., as described in Chan et al Nat Nanotechnol,3:31-35, 2008); for example, low coulombic efficiency associated with planar substrates, low electrical capacity per unit electrode area, insufficient expansion space associated with lithiation of planar substrates, and/or the need for a catalyst such as gold (which increases cost and limits scalability to industrial scale).

In contrast, the methods described herein can optionally result in a high surface area of active material by a simple, easily scalable, two-stage process (treating stainless steel followed by deposition of silicon) without relying on the addition of a catalyst.

Composite electrode comprising silicon-containing nanostructures

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising a stainless steel substrate, and a plurality of silicon-containing nanostructures extending from the stainless steel substrate.

The term "silicon-containing nanostructure" refers to nanostructures comprising silicon as a major constituent, as well as nanostructures comprising silicon as a core or layer, e.g., a layer overlying a metal core.

For the sake of brevity, silicon-containing nanostructures containing silicon as a major component are interchangeably referred to herein as "silicon nanostructures.

Similarly, silicon-containing nanostructures comprising a layer of silicon on stainless steel are interchangeably referred to herein as "stainless steel nanostructures.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising a self-catalytic stainless steel substrate, and a plurality of silicon-containing nanostructures extending from the stainless steel substrate.

As used herein, the term "autocatalytic" means a substrate (e.g., a stainless steel substrate) capable of catalyzing the growth of silicon nanostructures (e.g., nanowires) on a surface of the substrate, for example, under conditions of silicon chemical vapor deposition (e.g., according to any of the respective embodiments described herein). It should be understood that the term "autocatalytic" does not exclude the processing of a substrate to obtain an autocatalytic substrate if the processing does not rely on the addition of an additional material as a catalyst.

According to an aspect of some embodiments of the present invention, there is provided a catalyst-free composite electrode, including: a stainless steel substrate, and a plurality of silicon-containing nanostructures extending from the stainless steel substrate (i.e., substantially free of a catalyst material, as defined herein)

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising: a stainless steel substrate, and a plurality of silicon-containing nanostructures extending from the stainless steel substrate, wherein the silicon-containing nanostructures are grown via a gas-solid mechanism.

As used herein, the terms "gas-solid" and "VSS" are used interchangeably herein to refer to a mechanism for growing structures (e.g., nanowires) by chemical vapor deposition, wherein a catalytic solid state (optionally, part of an autocatalytic solid state substrate) induces growth at the interface of a solid substrate and the catalytic solid state VSS mechanism is different from V L S mechanism, which is discussed below.

The phrase "extending from" as used herein means a first structure (e.g., a silicon-containing nanostructure as described herein) that is connected to a second structure (e.g., a steel substrate), wherein the region where the two structures are connected is shorter in at least one dimension (optionally in all dimensions) than the length of the first structure in one dimension, which is a dimension along the surface of the second structure.

It should be noted that the growth of such silicon-containing nanostructures need not be catalyzed on all portions of the substrate, but only on a portion of the substrate. For example, the portion of the substrate from which nanostructures may be grown may be in the form of a number of unconnected small regions, each of which is also referred to herein as a "seed location".

As used herein, the term "stainless steel" means an alloy of iron and carbon (referred to in the art as "steel") that further includes a concentration of chromium of at least 10.5 weight percent. The concentration of carbon is typically in a range from 0.002 to 2.14 weight percent.

It is expected that during the life of a patent counting since this application, many relevant types of stainless steel (e.g., steel grade) will be developed and the scope of the term "stainless steel" is intended to include all such new technologies a priori.

In some of any of the individual embodiments described herein, a concentration of chromium in the stainless steel is at least 14 weight percent (e.g., from 14 to 22 weight percent), optionally at least 16 weight percent (e.g., from 16 to 20 weight percent), and optionally at least 18 weight percent (e.g., to 18 to 20 weight percent).

In some of any of the individual embodiments described herein, the stainless steel comprises nickel. In some embodiments, a concentration of nickel in the stainless steel is at least 6 weight percent (e.g., from 6 to 14 weight percent), optionally at least 8 weight percent (e.g., from 8 to 12 weight percent), and optionally at least 10 weight percent (e.g., from 10 to 12 weight percent).

In some of any of the individual embodiments described herein, the stainless steel comprises molybdenum. In some embodiments, a concentration of molybdenum in the stainless steel is at least 1 weight percent (e.g., from 1 to 4 weight percent), and optionally at least 2 weight percent (e.g., from 2 to 3 weight percent).

In some of any of the individual embodiments described herein, the stainless steel is an austenitic stainless steel, i.e., includes a face centered cubic crystal structure. Such a crystalline structure may be obtained, for example, by alloying with sufficient nickel and/or manganese and nitrogen.

Examples of suitable stainless steels include, without limitation, 316L stainless steel (comprising: 16 to 18 weight percent chromium, 10 to 12 weight percent nickel, 2 to 3 weight percent molybdenum, and no more than 0.03 weight percent carbon) and 304 stainless steel (comprising: 18 to 20 weight percent chromium, 8 to 10.5 weight percent nickel, and no more than 0.08 weight percent carbon). 316L and 304 stainless steel are austenitic.

According to some of any of the embodiments described herein, at least a portion (e.g., at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 99%) and preferably all of the nanostructures are elongated nanostructures.

As used herein, an "elongated nanostructure" generally means a three-dimensional object that is made of a solid substance and that has at least one cross-sectional dimension, and in some embodiments two orthogonal cross-sectional dimensions, at any point along its length, of less than 1 micron, or less than 500 nanometers, or less than 200 nanometers, or less than 150 nanometers, or less than 100 nanometers, or even less than 70 nanometers, less than 50 nanometers, less than 20 nanometers, or less than 10 nanometers. The cross-section of the elongated nanostructures may have any arbitrary shape, including, but not limited to, circular, square, rectangular, oval, star, and tubular. Both regular and irregular shapes are included.

In some of any of the embodiments described herein, an average length of the number of silicon-containing nanostructures (according to any individual embodiment described herein) ranges from 5 to 1000 microns, or from 10 to 500 microns, or from 20 to 300 microns, or from 30 to 200 microns, including any intervening subranges and values therebetween.

In any embodiment described herein with respect to a "ratio", the ratio is at least 10%, and optionally at least 20%, or at least 30%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or even at least 99%.

In some of any of the embodiments described herein, a length of at least a portion of the plurality of silicon-containing nanostructures (optionally, each of the plurality of silicon-containing nanostructures), according to any individual embodiment described herein, ranges from 5 to 1000 microns, or from 10 to 500 microns, or from 20 to 300 microns, or from 30 to 200 microns, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, an average diameter of the number of silicon-containing nanostructures (according to any individual embodiment described herein) ranges from 5 to 1000 microns, or from 10 to 500 microns, or from 20 to 300 microns, or from 30 to 100 microns, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, at least a portion of the plurality of silicon-containing nanostructures (according to any individual embodiment described herein) (optionally, each of the plurality of silicon-containing nanostructures) has a diameter in a range from 5 to 1000 microns, or from 10 to 300 microns, or from 20 to 200 microns, or from 30 to 100 microns, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, for at least a portion (optionally, for all) of the plurality of silicon-containing nanostructures, regions of the substrate surface to which the plurality of nanostructures are attached to the substrate are not attached, that is, the plurality of nanostructures are separated by a portion of the substrate surface that is not attached to silicon.

In some of any of the embodiments described herein, the plurality of elongated nanostructures are substantially parallel to each other, at least in a range proximate to a surface of the substrate from which the plurality of elongated nanostructures extend (e.g., to a range of 1 micron from the surface).

In some of any of the embodiments described herein, the plurality of elongated nanostructures are aligned substantially perpendicular to a surface of the substrate, at least in a region proximate to the surface of the substrate (e.g., to a region 1 micron from the surface).

In some of any of the embodiments described herein, the plurality of elongated nanostructures are substantially parallel to each other and aligned substantially perpendicular to a surface of the substrate, at least in a region proximate to the surface of the substrate (e.g., to a region 1 micron from the surface).

In some of any of the embodiments described herein, an average distance between the number of nanostructures (e.g., an average of a number of distances between each nanostructure and the closest other number of nanostructures) ranges from 10 nanometers to 10000 nanometers, or from 10 nanometers to 5000 nanometers, or from 10 nanometers to 2000 nanometers, or from 10 nanometers to 500 nanometers, including any intervening subranges and values therebetween.

The number of elongated nanostructures according to some of the present embodiments are collectively referred to herein as "nanowires". The nanowires may optionally be hollow, e.g., shaped as a hollow tube (in this case, they may be referred to as "nanotubes"), or solid (i.e., not hollow, as defined herein).

In some of any of the embodiments described herein, the nanowire is solid (i.e., not hollow).

Herein, a "solid" nanowire is a nanowire in which void space constitutes no more than 20% (optionally no more than 10%) of the volume of the nanowire, and in which the void space does not extend continuously through most (i.e., more than 50%) or all of the length of the nanowire.

In some of any of the embodiments described herein, the stainless steel substrate is a self-catalyzing stainless steel substrate as defined herein.

In some of any of the individual embodiments described herein, the autocatalytic stainless steel substrate comprises a nanoporous surface structure.

As used herein, the term "nanoporous" means a porous structure comprising, among other things, a plurality of pores having a diameter of less than 1 micron, and optionally less than 100 nanometers.

In some embodiments, the nanoporous surface structure is characterized by a plurality of nanostructure growth seed locations, that is, a plurality of nanostructures are grown in a plurality of regions comprising the plurality of pores mentioned above, the plurality of pores having a diameter of less than 1 micron. The plurality of seed locations of an autocatalytic stainless steel substrate are comprised of materials derived from the stainless steel (e.g., specific metallic elements and/or specific structures of the steel) rather than being produced from a catalytic material (as defined herein). In some such embodiments, the plurality of silicon-containing nanostructures (according to any of the individual embodiments described herein) extend from the plurality of nanostructure growth seed locations on the autocatalytic stainless steel substrate, e.g., each nanostructure extends from a respective growth seed location.

In view of the autocatalytic properties of stainless steels according to some embodiments of the invention, several nanostructures may be prepared without the presence of any added catalyst.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures (according to any individual embodiment described herein) is substantially free of a catalyst material in at least a portion of the plurality of silicon-containing nanostructures (e.g., at least 50%, or at least 75%, or at least 90% of the plurality of nanostructures). In some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of a catalyst material.

Herein, the phrase "catalyst material" means a material capable of catalyzing the growth of silicon nanostructures (e.g., nanowires).

As used herein, stainless steel composition, i.e., any material contained by the stainless steel in the stainless steel bulk (e.g., outside of the plurality of nanostructures extending from the substrate), is excluded from the term "catalyst material", even if the material is not integrated in the stainless steel substrate bulk (e.g., if present on or in a silicon-containing nanostructure) would be considered a catalyst material. In other words, the composition of the stainless steel block does not prevent a substrate from being considered "substantially free of a catalyst material" as defined herein.

It is expected that during the life of a patent counting from this application many relevant catalysts will be developed and the scope of the term "catalytic material" is intended to include all such new technologies a priori.

In some of any of the embodiments described herein with respect to a catalytic material, the catalytic material is a metallic material.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures (according to any of the respective embodiments described herein) in at least a portion of the plurality of silicon-containing nanostructures (e.g., at least 50%, or at least 75%, or at least 90% of the plurality of nanostructures) is substantially free of a catalyst material that is useful in a gas-liquid-solid growth of the plurality of silicon nanostructures, i.e., capable of catalyzing a gas-liquid-solid growth of silicon. In some embodiments, each of the plurality of silicon nanostructures is substantially free of a catalyst material that is usable in a gas-liquid-solid growth of the plurality of silicon nanostructures, i.e., capable of catalyzing the gas-liquid-solid growth of silicon.

As used herein, the terms "gas-liquid-solid" and "V L S" and the like, as used interchangeably herein, refer to a mechanism for growing structures (e.g., nanowires) by chemical vapor deposition, wherein a catalytic liquid phase initiates growth (e.g., from seeds of nucleation) at the interface between a solid substrate and the liquid phase, for example, by collecting vapor entering the liquid phase to produce a higher concentration of the species exiting than in the gaseous phase.

Typically, a liquid catalyst (e.g., in the form of micro-droplets) that grows as a gas, liquid, and solid remains at a tip of the structure (away from the substrate) during the growth process.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures (according to any individual embodiment described herein) in at least a portion of the plurality of silicon-containing nanostructures (e.g., at least 50%, or at least 75%, or at least 90% of the plurality of nanostructures) does not substantially have a substance that, in admixture with silicon in any proportion (e.g., at a eutectic point with silicon), has a melting point below 600 degrees and a boiling point above 600 degrees (at a pressure of 20 torr). In some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of a substance that is in admixture with silicon, has a melting point below 600 degrees and a boiling point above 600 degrees (at a pressure of 20 torr).

Without being bound by any particular theory, it is believed that a melting point below 600 degrees and a boiling point above 600 degrees at a pressure of 20 torr indicates that a substance is a liquid under conditions suitable for chemical vapor deposition of silicon.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures (according to any of the individual embodiments described herein) is substantially free of a catalyst material that is a non-silicon catalyst material in at least a portion of the plurality of silicon-containing nanostructures (e.g., at least 50%, or at least 75%, or at least 90% of the nanostructures). That is, in such embodiments, a catalyst material that is a form of silicon does not prevent a substance from being considered "substantially free of a catalyst material. In some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of a catalyst material.

Herein, the phrase "catalyst material" means a material capable of catalyzing the growth of a plurality of silicon nanostructures (e.g., a plurality of nanowires).

As used herein, stainless steel composition, i.e., any material contained by the stainless steel in the stainless steel bulk (e.g., outside of the plurality of nanostructures extending from the substrate), is excluded from the term "catalyst material", even if the material is not integrated in the stainless steel substrate bulk (e.g., if present on or in a silicon-containing nanostructure) would be considered a catalyst material. In other words, the composition of the stainless steel block does not prevent a substrate from being considered "substantially free of a catalyst material" as defined herein.

In some of any of the embodiments described herein, each of the number of silicon-containing nanostructures (according to any individual embodiment described herein) is substantially free of gold, silver, copper, indium, bismuth, gallium, zinc, aluminum, tin, iron, molybdenum, chromium, manganese, and/or nickel in at least a portion of the number of silicon-containing nanostructures (e.g., in at least 50%, or at least 75%, or at least 90% of the number of nanostructures). In some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of gold, silver, indium, bismuth, gallium, zinc, aluminum, tin, iron, molybdenum, chromium, manganese, and/or nickel. In some embodiments, each of the plurality of silicon-containing nanostructures in the aforementioned portion, or each of the plurality of silicon-containing nanostructures, is further substantially free of (other than gold and silver) all noble metals as defined herein.

In some of any of the embodiments described herein, each of the number of silicon-containing nanostructures (according to any individual embodiment described herein) in at least a portion of the number of silicon-containing nanostructures (e.g., at least 50%, or at least 75%, or at least 90% of the number of silicon-containing nanostructures) is substantially free of gold, silver, copper, indium, bismuth, gallium, zinc, aluminum, tin, and/or manganese. In some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of gold, silver, copper, indium, bismuth, gallium, zinc, aluminum, tin, and/or manganese. In some embodiments, each of the number of silicon-containing nanostructures in the portions described above, or each of the number of silicon-containing nanostructures, is further substantially free of (other than gold and silver) all noble metals as defined herein.

In some of any of the embodiments described herein, each of the number of silicon-containing nanostructures (according to any individual embodiment described herein) in at least a portion of the number of silicon-containing nanostructures (e.g., in at least 50%, or at least 75%, or at least 90% of the number of nanostructures) is substantially free of gold. In some embodiments, each of the plurality of silicon-containing nanostructures in the portion is substantially free of a noble metal.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures (according to any of the individual embodiments described herein) is substantially free of gold, and in some embodiments, each of the plurality of silicon-containing nanostructures is substantially free of a noble metal.

The term "noble metal" as used herein means gold, platinum, iridium, osmium, silver, palladium, rhodium and ruthenium.

Throughout this document, "substantially free" means a concentration of a substance (e.g., in a nanostructure) that is less than 10 parts per million by weight. As described herein, in some of any embodiments relating to nanostructures substantially free of a substance, a concentration of the substance is less than 1 part per million by weight, or less than 0.1 part per million by weight, or less than 0.01 part per million by weight (i.e., less than 10 parts per billion).

In some of any of the embodiments described herein, at least a portion of the plurality of silicon nanostructures, and optionally all of the plurality of silicon nanostructures, comprise, for example, a metal component derived from the stainless steel substrate dispersed along the length (major axis) of the nanostructures. In some embodiments, a concentration of the metal component is greater at a core of the nanostructure(s) than at a surface of the nanostructure(s).

In some of any of the embodiments described herein, at least a portion of the plurality of silicon-containing nanostructures, and optionally all of the plurality of silicon-containing nanostructures, consist essentially of silicon and one or more metal constituents (the one or more metal constituents being derived from the stainless steel substrate), and optionally, for example, also of alumina (e.g., in a coating layer as described herein), with no catalyst material being included therein. In some embodiments, at least a portion of the plurality of silicon-containing nanostructures, and optionally all of the plurality of silicon-containing nanostructures, consist of silicon and one or more metal components derived from the stainless steel substrate, and optionally also of aluminum oxide.

Several examples of metal components that can be derived from a steel substrate include, but are not limited to, nickel, copper, chromium, and iron.

In some of any of the embodiments described herein, a metal silicide (e.g., an iron silicide, a nickel silicide, a chromium silicide, and/or a copper silicide) extends from and along at least a portion of the length of the autocatalytic stainless steel substrate in at least a portion of the number of silicon nanostructures, and optionally in all of the number of silicon nanostructures. Optionally, a metal silicide where a nanostructure meets the metal substrate strengthens the mechanical and/or electrical bond between the silicon and the steel in the nanostructure.

As used herein, a "metal silicide" means a compound comprising: silicon and metal atoms.

In some embodiments, the metal silicide forms a core of the nanostructure(s), surrounded by silicon.

In some embodiments, the metal composition and/or metal silicide in the core and surrounding silicon exhibits a gradient (perpendicular to a long axis of the nanostructure) over a mixture of silicon and metal atoms, whereby a concentration of metal atoms decreases and a concentration of silicon atoms increases in a direction from the core of the nanostructure to a surface of the nanostructure. Optionally, there is no clear boundary between the "metal silicide" and the "silicon".

In some of any of the embodiments described herein, at least a portion of the plurality of silicon-containing nanostructures form a three-dimensional network of a plurality of cross-chains. The number of cross-chains can include a number of nanostructures (e.g., a number of elongated nanostructures) that are fused to each other and/or are not fused to each other (e.g., adjacent to and/or in contact with each other).

In some of any of the embodiments described herein, at least a portion of the plurality of silicon-containing nanostructures, and optionally each of the plurality of silicon-containing nanostructures, are fused with at least one other silicon-containing nanostructure at a location removed from a surface of the stainless steel substrate. In some embodiments, the fusion of the plurality of silicon-containing nanostructures forms a sponge-like three-dimensional structure.

As used herein, the term "sponge-like" means a structure having a porosity of at least 50% (i.e., the voids constitute at least 50% of the volume of the structure).

In some of any of the embodiments described herein with respect to a sponge-like structure, the porosity of the sponge-like structure is at least 75%, or at least 90%, or at least 95%, or at least 98%, or at least 99%.

As exemplified herein, the fusion of the plurality of silicon nanostructures may be achieved by, for example, a thermal treatment (also referred to herein as "annealing") according to any of the respective embodiments described herein at a temperature of at least 600 degrees (e.g., from 600 degrees to 900 degrees) and optionally at least 650 degrees (e.g., from 650 degrees to 850 degrees).

In some of any of the embodiments described herein, in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is characterized by at least one of:

(a) substantially free of a non-silicon catalyst material (according to any of the respective embodiments described herein); and/or

(b) Substantially free of a noble metal (according to any of the respective embodiments described herein); and/or

(c) Comprises a metal composition along its length, said metal composition being derived from said stainless steel substrate (according to any of the individual embodiments described herein); and/or

(d) (in accordance with any of the respective embodiments described herein) comprises a metal silicide extending from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate; and/or

(e) Is fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a spongy three-dimensional structure (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein, in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is characterized by at least any two of the features (a) through (e) described above, optionally by at least any three of the features (a) through (e) described above, optionally by at least any four of the features (a) through (e) described above, and optionally by all of the features (a) through (e) described above.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode, comprising:

a self-catalyzed stainless steel substrate, the self-catalyzed stainless steel substrate comprising: a nanohole surface structure having features of a plurality of nanostructure growth seed locations (according to any of the respective embodiments described herein); and

a plurality of silicon nanostructures extending from the plurality of nanostructure growth seed locations on the autocatalytic stainless steel substrate.

In some of any of the embodiments described herein for this aspect, at least a portion of or each of the plurality of silicon nanostructures is substantially free of a non-silicon catalyst material (according to any of the individual embodiments described herein). In some embodiments, the non-silicon catalyst material is useful in a gas-liquid-solid growth of a number of silicon nanostructures (according to any of the individual embodiments described herein). In some embodiments, the non-silicon catalyst material is a metal catalyst material (according to any of the respective embodiments described herein).

In some of any of the embodiments described herein for this aspect, at least a portion of or each of the plurality of silicon-containing nanostructures is substantially free of a noble metal (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect, at least a portion of or each of the plurality of silicon nanostructures is substantially free of a metal material (according to any of the respective embodiments described herein) that may be used as a non-silicon catalyst in a gas-liquid-solid growth of the plurality of silicon nanostructures.

In some of any of the embodiments described herein (in accordance with any individual embodiment described herein), each of the silicon nanostructures in at least a portion or all of the number of silicon nanostructures includes one or more metal constituents along its length, the metal constituents being derived from the stainless steel substrate.

In some of any of the embodiments described herein (in accordance with any of the individual embodiments described herein), each of the silicon nanostructures comprises a metal silicide extending from the autocatalytic stainless steel substrate and along at least a portion of the length of the autocatalytic stainless steel substrate in at least a portion or all of the number of nanostructures.

In some of any of the embodiments described herein (in accordance with any individual embodiment described herein), in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is fused with at least one other silicon-containing nanostructure at a location removed by the nanohole surface structure of the stainless steel substrate.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising:

a stainless steel substrate; and

a plurality of silicon nanostructures extending from the stainless steel substrate;

wherein each of the plurality of silicon nanostructures is substantially free of a non-silicon catalyst material (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect, the non-silicon catalyst material is useful in a gas-liquid-solid growth of a number of silicon nanostructures (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect, the non-silicon catalyst material is a metal catalyst material (according to any of the individual embodiments described herein). In some embodiments, the metal catalyst material comprises a noble metal.

In some of any of the embodiments described herein (in accordance with any individual embodiment described herein), each of the silicon nanostructures in at least a portion or all of the number of silicon nanostructures includes one or more metal constituents along its length, the metal constituents being derived from the stainless steel substrate.

In some of any of the embodiments described herein (in accordance with any of the individual embodiments described herein), each of the silicon nanostructures comprises a metal silicide extending from the autocatalytic stainless steel substrate and along at least a portion of the length of the autocatalytic stainless steel substrate in at least a portion or all of the number of nanostructures.

In some of any of the embodiments described herein (according to any individual embodiment described herein), in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is fused with at least one other silicon nanostructure at a location removed by the nanohole surface structure of the stainless steel substrate.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising: a stainless steel substrate; and

a plurality of silicon nanostructures extending from the stainless steel substrate,

wherein each of the plurality of silicon nanostructures is substantially free of a noble metal (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect, the noble metal comprises gold.

In some of any of the embodiments described herein (in accordance with any individual embodiment described herein), each of the silicon nanostructures in at least a portion or all of the number of silicon nanostructures includes one or more metal constituents along its length, the metal constituents being derived from the stainless steel substrate.

In some of any of the embodiments described herein for this aspect (in accordance with any of the individual embodiments described herein), each of the silicon nanostructures comprises a metal silicide extending from the autocatalytic stainless steel substrate and along at least a portion of the length of the autocatalytic stainless steel substrate in at least a portion or all of the number of nanostructures.

In some of any of the embodiments described herein for this aspect (according to any individual embodiment described herein), in at least a portion or all of the number of silicon-containing nanostructures, each of the silicon-containing nanostructures is fused with at least one other silicon-containing nanostructure at a location removed by the nanohole surface structure of the stainless steel substrate.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising: a stainless steel substrate; and

a plurality of silicon nanostructures extending from the stainless steel substrate,

wherein (in accordance with any of the individual embodiments described herein) in at least a portion or all of the plurality of silicon nanostructures, each of the silicon nanostructures comprises a metal constituent along its length, the metal constituent being derived from the stainless steel substrate.

In some of any of the embodiments described herein for this aspect, each of the plurality of silicon nanostructures is substantially free of a non-silicon catalyst material and/or a noble metal in at least a portion or all of the nanostructures (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect, each of the silicon nanostructures comprises a metal silicide in at least a portion or all of the plurality of nanostructures, the metal silicide extending from and along at least a portion of the autocatalytic stainless steel substrate (in accordance with any of the individual embodiments described herein).

In some of any of the embodiments described herein for this aspect (according to any individual embodiment described herein), in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is fused with at least one other silicon nanostructure at a location removed by the nanohole surface structure of the stainless steel substrate.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising: a stainless steel substrate; and

a plurality of silicon nanostructures extending from the autocatalytic stainless steel substrate,

wherein in at least a portion or all of the plurality of silicon nanostructures, each of the silicon nanostructures comprises a metal silicide extending from and along at least a portion of the autocatalytic stainless steel substrate (in accordance with any of the respective embodiments described herein).

In some of any of the embodiments described herein for this aspect, each of the plurality of nanostructures is substantially free of a non-silicon catalyst material and/or a noble metal in at least a portion or all of the plurality of nanostructures (according to any of the respective embodiments described herein).

In some of any of the embodiments described herein for this aspect (in accordance with any of the individual embodiments described herein), in at least a portion or all of the plurality of silicon nanostructures, each of the silicon nanostructures includes a metal constituent along its length, the metal constituent being derived from the stainless steel substrate.

In some of any of the embodiments described herein for this aspect (according to any individual embodiment described herein), in at least a portion or all of the number of silicon nanostructures, each of the silicon nanostructures is fused with at least one other silicon nanostructure at a location removed by the nanohole surface structure of the stainless steel substrate.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising: a stainless steel substrate; and

a plurality of silicon nanostructures extending from the stainless steel substrate,

wherein each of the silicon nanostructures is fused with at least one other silicon nanostructure at a location removed from a surface of the stainless steel substrate to form a sponge-like three-dimensional structure (according to any of the respective embodiments described herein) in at least a portion or all of the plurality of silicon nanostructures.

In some of any of the embodiments described herein for this aspect, each of the plurality of nanostructures is substantially free of a non-silicon catalyst material and/or a noble metal in at least a portion or all of the plurality of nanostructures (according to any of the respective embodiments described herein).

In some of any of the embodiments described herein for this aspect (in accordance with any of the individual embodiments described herein), in at least a portion or all of the plurality of silicon nanostructures, each of the silicon nanostructures includes a metal constituent along its length, the metal constituent being derived from the stainless steel substrate.

In some of any of the embodiments described herein for this aspect, in at least a portion or all of the plurality of silicon nanostructures, each of the silicon nanostructures comprises a metal silicide that extends from the stainless steel substrate and along at least a portion of the length of the stainless steel substrate (in accordance with any of the respective embodiments described herein).

As mentioned above, the plurality of silicon-containing nanostructures according to some embodiments of the invention may be in the form of a plurality of nanostructures comprising a layer of silicon on stainless steel, also referred to herein as "stainless steel nanostructures.

According to an aspect of some embodiments of the present invention, there is provided a composite electrode comprising:

a stainless steel body, an outer surface of the stainless steel body comprising a plurality of elongated stainless steel nanostructures extending from the stainless steel body; and

a silicon layer deposited on each of the plurality of elongated stainless steel nanostructures.

As used herein, the term "elongated stainless steel nanostructure" means (as defined herein) an elongated nanostructure composed of stainless steel.

In some of any of the embodiments described herein, an average length of the number of stainless steel nanostructures (according to any individual embodiment described herein) is from 5 to 1000 microns, or from 10 to 500 microns, or from 20 to 300 microns, or from 30 to 200 microns, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, at least a portion of the plurality of stainless steel nanostructures (according to any individual embodiment described herein), optionally each of the plurality of stainless steel nanostructures, has a length from 5 to 1000 micrometers, or from 10 to 500 micrometers, or from 20 to 300 micrometers, or from 30 to 200 micrometers, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, an average diameter of the plurality of stainless steel nanostructures (according to any individual embodiment described herein) is from 5 nanometers to 1000 nanometers, or from 10 nanometers to 300 nanometers, or from 20 nanometers to 200 nanometers, or from 30 nanometers to 90 nanometers, including any intervening subranges and values therebetween.

In some of any of the embodiments described herein, at least a portion of the plurality of stainless steel nanostructures (according to any of the respective embodiments described herein) (optionally each of the plurality of stainless steel nanostructures) has a diameter from 5 nanometers to 1000 nanometers, or from 10 nanometers to 300 nanometers, or from 20 nanometers to 200 nanometers, or from 30 nanometers to 90 nanometers, including any intervening subranges and values therebetween.

Optionally, the silicon layer substantially coats an outer surface of at least a portion or each of the plurality of stainless steel nanostructures. By "substantially coated" is meant that at least 50% of the surface of the stainless steel nanostructure, for example, at least 75% of the surface, or at least 90% of the surface, or at least 95% of the surface, is coated with silicon.

In some of any of the embodiments described herein, the (average) thickness of the silicon layer is in a range from about 6 nanometers to about 200 nanometers, or from about 6 nanometers to about 40 nanometers, or from about 40 nanometers to about 200 nanometers, or from about 20 nanometers to about 100 nanometers.

In some of any of the embodiments described herein, at least a portion of the plurality of elongated stainless steel nanostructures form a three-dimensional network of a plurality of cross-chains. The number of cross-chains may include a number of nanostructures (e.g., elongated nanostructures) that are fused to each other and/or are not fused to each other (e.g., adjacent to each other and/or in contact with each other).

The fusing of the plurality of elongated stainless steel nanostructures may optionally be achieved by fusing of the plurality of silicon layers that cover them, e.g., without fusing the stainless steel components of the plurality of nanostructures. The fusion of the plurality of silicon layers may be achieved, for example, when depositing silicon on the adjoining plurality of stainless steel nanostructures, and/or by annealing (according to any of the individual embodiments described herein).

In some of any of the embodiments described herein, the plurality of elongated stainless steel nanostructures form a sponge-like structure (as defined herein) and/or a nanoporous stainless steel network (as defined herein) at the outer surface of the stainless steel body.

Thus, a sponge-like stainless steel structure has a porosity of at least 50%, and optionally at least 75%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, wherein the silicon layers are considered to be part of the pores/voids in the stainless steel structure.

In some of any of the embodiments described herein, each of the plurality of silicon-containing nanostructures comprises a crystalline core and a semi-amorphous shell in at least a portion or all of the plurality of silicon-containing nanostructures. In some embodiments a crystallinity of the silicon in the nanostructure (as a whole, including core and shell) is at least 4%, or at least 10%, or at least 20%, or at least 50%, or at least 75%, or even at least 90%.

As used herein, the term "semi-amorphous" means a material in which at least a portion of the material is amorphous such that the material has a crystallinity of less than 100%, for example, less than 90%, less than 75%, less than 50%, less than 20%, and even 0%.

Crystallinity can optionally be determined (e.g., quantitatively) by X-ray diffraction according to standard procedures used in the art.

As exemplified herein, the crystallinity of the plurality of silicon-containing nanostructures may be enhanced by, for example, a heat treatment (also referred to herein as "annealing") according to any of the respective embodiments described herein at a temperature of at least 600 degrees (e.g., from 600 degrees to 900 degrees) and optionally at least 650 degrees (e.g., from 650 degrees to 850 degrees).

In some of any of the embodiments described herein, the silicon of the number of silicon-containing nanostructures is doped with donor or acceptor atoms referred to as "dopants". The present embodiments contemplate doping to achieve both N-type (more electrons than a lattice structure that completes a lattice structure) and P-type (less electrons than a lattice structure that completes a lattice structure) doping. The extra electrons in the N-type material or the holes left behind (lack of electrons) in the P-type material act as negative and positive charge carriers, respectively.

Atoms suitable as P-type dopants and as N-type dopants are well known in the art. For example, the nanostructures may be comprised of silicon doped with, for example, boron (typically, but not necessarily, by exposure to diborane), gallium or aluminum to provide a P-type silicon containing nanostructure, or silicon doped with phosphorus (typically, but not necessarily, by exposure to phosphane), arsenic or antimony to provide an N-type semiconductor nanostructure.

In some of any of the embodiments described herein, the silicon is intrinsic silicon, i.e., silicon that is not doped with P-type or N-type dopants.

In some of any of the embodiments described herein, in at least a portion of or all of the plurality of silicon-containing nanostructures, each of the silicon-containing nanostructures is coated with an aluminum oxide layer. The (average) thickness of the aluminum oxide layer is optionally in a range from 1 to 50 nanometers, or from 2 to 25 nanometers, or from 3 to 15 nanometers. Exemplary aluminum oxide layers have a thickness of from about 5 nm to about 10 nm.

As exemplified in the example paragraphs herein, the aluminum oxide layer is optionally formed by atomic layer deposition.

The plurality of silicon-containing nanostructures coated with an aluminum oxide layer may optionally have aluminum oxide coating at least 50% of the surface of a silicon nanostructure or a stainless steel nanostructure (with a silicon layer), or at least 75% of the surface, or at least 90% of the surface, or at least 95% of the surface.

Method for preparing a composite electrode comprising several silicon nanostructures

According to an aspect of some embodiments of the present invention there is provided a method of making a composite electrode, the composite electrode comprising: a plurality of silicon nanostructures on a stainless steel substrate, according to any of the individual embodiments described herein.

The method comprises contacting a stainless steel substrate (according to any of the respective embodiments described herein) with hydrofluoric acid (HF); and subjecting (after contact with hydrofluoric acid) the substrate to conditions for growing a silicon nanostructure (e.g., extending from the substrate).

In some embodiments, contacting with the hydrofluoric acid results in a nanoporous surface structure (as defined herein), for example, comprising a plurality of nanostructure growth seed locations on the stainless steel substrate. The growth of the silicon nanostructures is optionally followed by the growth of at least a portion of or each of the seed sites from the plurality of nanostructures.

In some of any of the individual embodiments described herein, the substrate is contacted with an aqueous hydrofluoric acid solution. In some embodiments, the aqueous hydrofluoric acid solution comprises a concentration of hydrofluoric acid of at least 5 weight percent, for example, a concentration of hydrofluoric acid from 5 to 40 weight percent. In some embodiments, the hydrofluoric acid concentration is in a range from 5 to 15 weight percent. In some embodiments, the hydrofluoric acid concentration is in a range from 25 to 40 weight percent, such as about 30 weight percent.

In some of any of the individual embodiments described herein, hydrofluoric acid is contacted with the stainless steel substrate for a period of time from 10 minutes to 60 minutes, or from 20 minutes to 40 minutes.

Following hydrofluoric acid treatment, the stainless steel substrate is subjected to vapor deposition of silicon to thereby obtain the plurality of silicon nanostructures. The vapor deposition may optionally be implemented according to any of the embodiments described in the paragraphs herein regarding vapor deposition of silicon.

A method for preparing a composite electrode comprising several stainless steel nanostructures:

according to an aspect of some embodiments of the present invention, there is provided a method for preparing a composite electrode, according to any of the respective embodiments described herein, comprising: a plurality of elongated stainless steel nanostructures and a silicon layer on the plurality of stainless steel nanostructures.

The method comprises the following steps: a stainless steel body is contacted (optionally at about atmospheric pressure) with a gaseous environment containing hydrogen at a temperature of from about 850 degrees to about 1200 degrees, whereby a plurality of elongated stainless steel nanostructures extend from the stainless steel body by exposure to the environment.

In some embodiments, the contacting with the gaseous environment described herein is at a temperature of about 950 degrees to about 1100 degrees.

In some of any of the individual embodiments described herein, the gaseous environment further comprises a non-oxidizing gas other than hydrogen, such as nitrogen and/or argon.

In some of any of the individual embodiments described herein, a concentration of hydrogen in the gaseous environment is at least 1%, optionally from 1 to 10% (e.g., determined by a partial pressure of the hydrogen relative to a total pressure of the gaseous environment, and/or determined by a volume of the hydrogen introduced into the gaseous environment relative to a total volume of the number of gases (under the same number of conditions) in the gaseous environment

In some of any of the individual embodiments described herein, the contacting (at the indicated temperature) with the gaseous environment described herein is effected for a period of at least 30 minutes, for example, from 30 minutes to 5 hours.

The method further includes forming a silicon layer on the plurality of stainless steel nanostructures. In some embodiments, the silicon layer is formed by vapor deposition of silicon to thereby obtain the silicon layer according to any of the individual embodiments described herein. The vapor deposition may optionally be implemented according to any of the embodiments described in the paragraphs herein regarding vapor deposition of silicon.

Silicon vapor deposition:

vapor deposition of silicon using a silicon precursor may optionally be used to grow silicon nanostructures (according to any of the various embodiments described herein) and/or to form a silicon layer on a steel nanostructure (according to any of the various embodiments described herein).

As used herein, the term "silicon precursor" means a compound that, in vapor form, can form deposited silicon (e.g., under the conditions described herein). Silane (SiH)₄) And disilane (Si)₂H₆) Is an exemplary silicon precursor.

A purity of one or more silicon precursors (silane and/or disilane) used in vapor deposition is optionally at least 99%, optionally at least 99.5%, optionally at least 99.8%, and optionally at least 99.9%.

The silicon precursor may be mixed with a carrier gas, such as argon or hydrogen (the carrier gas is not considered in determining the purity of the silicon precursor).

In some of any of the individual embodiments described herein, the vapor deposition is effected at a temperature from about 380 degrees to about 550 degrees. In some embodiments, the temperature is from about 400 to 500 degrees. In some embodiments, the temperature is from about 400 to 460 degrees. In some embodiments, the temperature is from about 400 to 440 degrees. In some embodiments, the temperature is from about 400 to 420 degrees.

As exemplified herein, the temperature of vapor deposition may depend on the silicon precursor. For example, a temperature for deposition using silane may optionally be about 460 degrees, and a temperature for deposition using disilane may optionally be about 400 degrees to about 440 degrees (e.g., from about 410 degrees to about 430 degrees).

In some of any of the individual embodiments described herein, vapor deposition is effected at a sub-atmospheric pressure, for example, at a pressure of no more than 100 torr, and optionally no more than 50 torr.

In some of any of the individual embodiments described herein, vapor deposition is effected at a pressure of at least about 1 torr, for example, at a pressure of from about 1 to about 100 torr, or from about 1 to about 25 torr. In some embodiments, the pressure is at least about 5 torr, or at least about 10 torr, or at least about 20 torr. Several exemplary pressures for silicon vapor deposition are in a range from about 10 to about 25 torr.

The silicon precursor may optionally be introduced into an environment of the target surface (e.g., into an enclosed container in which the target surface is contained) at a flow rate of from 1 to 50sccm (standard cubic centimeters per minute), and optionally at a rate of from 2 to 25 sccm. An exemplary gas flow rate for a silicon precursor is from about 3sccm to about 15 sccm.

The skilled artisan will appreciate that a suitable gas flow rate may depend on the number of silicon atoms in the silicon precursor, for example, disilane may be introduced at a lower rate (e.g., about 3sccm) than silane (e.g., about 5sccm) to achieve similar results.

A carrier gas (as described above) may optionally be introduced into an environment of the target surface at a suitable gas flow rate, for example, from 3 to about 500 seem. An appropriate gas flow rate may optionally be given for a given environment based on a desired total pressure (which may be affected by, for example, the strength of the vacuum pump, the volume of the vessel, etc.).

In some of any of the individual embodiments described herein, the vapor deposition is effected over a period of time from 5 minutes to 180 minutes, or over a period of time from 5 minutes to 90 minutes, or over a period of time from 5 minutes to 60 minutes, or over a period of time from 5 minutes to 30 minutes. In some embodiments, such a period is used to form a silicon nanostructure.

In some of any of the individual embodiments described herein, the vapor deposition is effected over a period of at least 30 minutes, for example, from 30 minutes to 180 minutes. In some embodiments, such a period is used to form a silicon layer on a steel nanostructure (e.g., a silicon layer having a thickness from about 6 nanometers to about 200 nanometers according to any of the respective embodiments described herein).

The conditions (e.g., time, temperature, pressure, and/or gas flow) of silicon vapor deposition are optionally selected so as to provide a silicon nanostructure having features with at least one dimension in a range (from about 10 nanometers to about 200 nanometers) according to any of the respective embodiments described herein and/or having a silicon layer with a thickness (e.g., from about 6 nanometers to about 200 nanometers) according to any of the respective embodiments described herein.

Annealing:

in some of any of the individual embodiments described herein (according to any aspect described herein), the plurality of silicon-containing nanostructures according to any of the individual embodiments described herein (preferably after formation of the plurality of nanostructures) are subjected to a thermal treatment, also referred to herein as "annealing". In some such embodiments, the nanostructure is a silicon nanostructure (e.g., as opposed to a stainless steel nanostructure having a silicon layer).

In some of any of the individual embodiments described herein, the heat treatment is effected at a temperature of at least 600 degrees (e.g., from 600 to 900 degrees), and optionally at least 650 degrees (e.g., from 650 to 850 degrees).

The heat treatment is optionally effected for a period of at least one minute, and optionally at least two minutes, for example from 2 to 8 minutes.

In some of any of the individual embodiments described herein, the heat treatment is effected under non-oxidizing conditions, for example, in an atmosphere of hydrogen or in a vacuum.

Without being bound by a particular theory, it is believed that annealing may provide one or more of the following several features:

physical soldering and mechanical strengthening of the plurality of silicon networks and their physical attachment to the underlying stainless steel substrate;

crystallization of several silicon nano-domains; and/or

The diffusion into the silicon-based structures through the metal centers enhances the conductivity of the silicon-to-stainless steel junctions, wherein the formation of short segments of metal silicide at the bottom of the nanostructures improves the electrical contact between the silicon nanostructures and the underlying stainless steel substrate, thereby improving current collection capability (e.g., when functioning as an anode in a lithium ion battery).

Additional features and applications of the composite electrode:

in some of any of the embodiments described herein, an amount of silicon on a surface of the electrode is at least 0.5 mg/cm, optionally at least 1 mg/cm and optionally at least 2 mg/cm. For example, the silicon or amount may be from 0.5 to 20 mg/cm, or from 0.5 to 12 mg/cm, or from 0.5 to 3 mg/cm. In such calculations, the surface of the electrode means microscopic dimensions (e.g., ignoring recesses having a width of 1 mm or less), such that pores in the electrode (e.g., as in a mesh) provide more attachment points for silicon without a corresponding increase in the surface area of the electrode.

As exemplified herein, at least a portion of the composite electrode (e.g., at least a portion of the plurality of nanostructures therein) is optionally coated with a carbonaceous coating (which is preferably electrically conductive), such as carbon black and/or carbon nanotubes (e.g., single-walled carbon nanotubes). The coating may optionally be formed by simple contact with a liquid (e.g., a suspension) containing the carbon and a solvent (e.g., an aqueous solvent and/or an organic solvent) that wets the electrode surface, and optionally followed by thermal cracking. The coating may optionally be used to enhance conduction between the silicon and a current collector, and/or between the anode and a cathode. In some embodiments, an average thickness of the plurality of carbonaceous coating layers is from 1 nm to 1000 nm.

The stainless steel substrate and/or stainless steel body described herein may optionally have a continuous (e.g., flat) bulk structure or may comprise a plurality of stainless steel components, for example, in the form of a woven or non-woven mesh.

In addition to serving to provide a substrate for nanostructures (according to any of the respective embodiments described herein), the stainless steel substrate and/or stainless steel body described herein may optionally serve as a current collector for electrochemical reactions (thus enhancing the conductivity of the electrode)

Additionally or alternatively, the stainless steel substrate and/or stainless steel body and associated plurality of nanostructures described herein (according to any of the individual embodiments described herein) may optionally be characterized by thinness, which may be associated with relatively low weight, high capacitance-to-volume ratio, and/or electrode elasticity, or by porosity (e.g., in embodiments comprising a steel mesh); the porosity may be associated with (due to the higher surface area) increased capacitance and/or electrode elasticity.

Electrode flexibility is advantageous, for example, when facilitating the preparation of electrochemical cells comprising a large electrode area (e.g., by folding and/or rolling up a flexible electrode in a defined volume).

As exemplified herein, several electrodes prepared as described herein can easily have several large, enlarged areas.

In some of any of the embodiments described herein, an area of a composite electrode (according to any of the embodiments described herein) is at least 10 square centimeters, or at least 100 square centimeters, or at least 1000 square centimeters, or at least 1 square meter (10000 square centimeters), or at least 10 square meters.

In some of any of the embodiments described herein, an anode having a capacitance of at least 3 milliampere-hours (mAh) per square centimeter (e.g., from 3 to 4 or from 3 to 5 milliampere-hours per square centimeter) (of the surface of the electrode) is obtained, and in some embodiments, a capacitance of at least 4 milliampere-hours per square centimeter, or at least 6 milliampere-hours per square centimeter, or at least 8 milliampere-hours per square centimeter, or at least 10 milliampere-hours per square centimeter, or at least 12 milliampere-hours per square centimeter, or even 15 milliampere-hours per square centimeter is obtained.

In some of any of the embodiments described herein, there is at least 1000 milliamp-hours per gram silicon (mAh/g)_Si) An electrical capacity of at least 2000 milliamp hours per gram of silicon, or at least 3000 milliamp hours per gram of silicon, in some embodiments. In contrast, the theoretical capacity of graphite (used in many commercial lithium anodes) is 372 milliamp hours per gram.

In some of any of the embodiments described herein, an anode having an irreversible capacity loss (loss of capacity at the beginning of an electrochemical cycle) of no less than 20% (e.g., from 7 to 15%) is obtained, and in some embodiments, an irreversible capacity loss of less than 15%, or less than 10%, or less than 7%, or even less than 5% is obtained.

In some of any of the embodiments described herein, an anode having a coulombic efficiency (determined by the relationship between the capacitances upon charging and discharging) of at least 99% is obtained, and in some embodiments, a coulombic efficiency of at least 99.5%, or at least 99.8%, or even at least 99.9% is obtained.

Capacitance, irreversible capacity loss, and coulombic efficiency (according to any of the embodiments described herein) refer to a number of lithiation and delithiation cycles relative to an appropriate lithium ion cathode. Cycling is optionally performed at a rate of C/20 (i.e., at a rate of 1/20 hours for the capacitance). The coulombic efficiency is optionally determined based on an average efficiency over many (e.g., 100 or more) cycles (e.g., at C/20). Capacitance and irreversible capacitance loss are optionally determined using an initial cycle (or two or three cycles) at a rate of about C/2, which may optionally (e.g., as exemplified herein) be followed by C/20 cycles.

In some of any of the embodiments described herein, an anode and/or full cell (according to any of the individual embodiments described herein) has a cycle life of at least 400 cycles, or at least 500 cycles, or at least 600 cycles, or at least 700 cycles.

As used herein, a "cycle life" means the number of cycles of lithiation and delithiation until a 30% reduction in capacitance (excluding the irreversible capacitance loss at the beginning of the cycle). Anode cycle life is determined by cycling the anode (e.g., according to the procedures exemplified herein) with respect to lithium metal. Full cell cycle life is determined by cycling the anode and the cathode of the full cell.

Capacitance is optionally determined by one cycle at a rate of about C/2 (e.g., to measure starting capacitance and capacitance at the end of the cycle life), while intervening cycles are optionally at a rate of about C/20 (e.g., as exemplified herein).

Electrodes according to embodiments described herein may optionally be included in batteries, such as lithium ion batteries (e.g., in electric vehicles) and other energy storage devices, ultracapacitors, portable and/or wearable devices such as mobile phones, etc., where size and weight are important limiting factors. In addition, it is noted that silicon/lithium alloys have a high melting point that enhances safety (e.g., relative to lithium metal devices).

According to an aspect of some embodiments of the present invention, there is provided an energy storage device, comprising: an electrolyte and at least one composite electrode according to any of the individual embodiments described herein. The energy storage device may optionally be a battery (e.g., a lithium ion battery) comprising one or more full cells (i.e., comprising an anode and cathode); or a capacitor.

The energy storage device (e.g., battery) may comprise any number (i.e., one or more) of electrochemical cells, optionally any number of lithium ion cells, some or all of which comprise at least one composite electrode according to any individual embodiment described herein.

Herein, "lithium ion battery (lithium ion cell)" and "lithium ion battery (lithium ion battery)" refer to a battery (cell) or battery (battery), respectively, wherein an electrochemical reaction that stores and/or releases at least a portion of the electrical energy stored therein (e.g., when the battery is charged) includes the movement of lithium ions from one electrode to another (e.g., from an anode to a cathode or vice versa).

The term "electrolyte" also includes an "electrolyte solution" throughout the present specification.

It is expected that during the life of a patent counting since this application, many relevant electrolytes (solid and/or liquid electrolytes) will be developed and the scope of the term "electrolyte" is intended to include all such new technologies a priori.

Examples of suitable liquid electrolytes for a lithium ion battery include, but are not limited to, those comprising a lithium salt, such as L iPF₆、LiBF₄、LiClO₄Lithium bis (trifluoromethanesulfonyl) imide (L iTFSI) and/or lithium bis (oxalato) borate (L IBOB), and a solvent such as Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), Vinylene Carbonate (VC), fluoroethyl carbonate (FEC) and/or Propylene Carbonate (PC).

Several further examples of liquid electrolytes include room temperature ionic liquids, optionally containing: a cation, such as a1, 3-dialkylimidazolium salt (e.g., 1-ethyl-3-methylimidazole, 1-butyl-3-methylimidazole and/or-hexyl-3-methylimidazole), a1, 2, 3-trialkylimidazole salt (e.g., 1-butyl-2, 3-dimethylimidazole), a1, 3-dialkylpyridinium salt, an N-alkylpyridinium salt (e.g., N-octylpyridinium salt), an N-alkylisoquinolinium, an N-alkylpyrrolinium, an N, N-dialkylpyrrolinium (e.g., 1-methyl-1-propylpyrrolinium, 1-methyl-1-butylpyrrolinium, and/or 1-methyl-1-octylpyrrolinium); and/or an anion such as bis (trifluoromethanesulfonyl) imide ("bisthioimide"), tetrafluoroborate, hexafluorophosphate and/or halide; and/or any combination of the above.

Examples of solid electrolytes include, but are not limited to, solid polymer electrolytes comprising a polymer, such as polyethylene glycol (e.g., comprising from about 500 to about 10000 polyethylene glycol units), and/or a ceramic, such as silica or alumina.

A schematic representation of an exemplary combined configuration of an electrochemical cell 10 (also interchangeably referred to herein as a "full cell") according to some embodiments of the invention is shown in fig. 1.

The electrochemical cell 10 comprises: a composite electrode 20 (according to any of the respective embodiments described herein) comprising silicon, the composite electrode 20 acting as an anode. The electrochemical cell 10 comprises: a cathode 30, the cathode 30 can be any suitable cathode known in the art (e.g., for a lithium ion battery). The electrode (anode) 20 and/or the cathode 30 may optionally further comprise an electrically conductive coating according to any of the respective embodiments described herein, for example a carbonaceous coating (optionally comprising carbon nanotubes).

Several examples of lithium ion cathodes (i.e., cathodes suitable for use in a lithium ion battery) include, but are not limited to, NMC (lithium nickel manganese cobalt oxide, i.e., L iNi)_xMn_yCo_zO₂) Cathode, lithium cobalt oxide (L iCoO)₂) Cathode, NCA (lithium nickel cobalt aluminum oxide, i.e., L iNiCoAlO)₂) Cathode L MO (lithium manganese oxide, i.e., L iMn)₂O₄) Cathode L FP (lithium iron phosphate, i.e., L iFePO)₄) A cathode; and lithium/sulfur cathodeNMC, L MO, lithium cobalt oxide and/or NCA cathodes are particularly suitable for use in anode 20 in several exemplary embodiments, cathode 30 comprises an NCA cathode.

It is expected that throughout the life of a patent counting since this application many relevant cathodes will be developed and the scope of the words "cathode" and "lithium ion cathode" is intended to include all such new technologies a priori.

Electrochemical cell 10 further comprises an electrolyte 40, which electrolyte 40 may be a solid and/or a liquid electrolyte between electrode (anode) 20 and cathode 30 (e.g., according to any of the individual embodiments described herein), and optionally in contact with electrode (anode) 20 and cathode 30.

The electrochemical cell 10 optionally further comprises: a current collector 22, the current collector 22 being configured to electrically connect the anode 20 to an electrical device to be driven by the electrochemical cell 10, and/or a current collector 32 being configured to electrically connect the cathode 30 to an electrical device that is electrically wired to be driven by the electrochemical cell 10. The plurality of current collectors 22 and/or 32 may optionally be configured to secure electrical contacts in a standard configuration (e.g., in a commercial device) for securing a plurality of power sources, such as a plurality of batteries.

Electrochemical cell 10 is optionally free of cathode excess, i.e., the electrical capacity of cathode 30 (e.g., within experimental error) does not exceed the electrical capacity of anode 20, for example, as determined by the respective lithiation and delithiation of the anode and the cathode (e.g., relative to excess lithium metal), that is, outside of cell 10. In some such embodiments, electrochemical cell 10 has an anode excess, and the electrical capacity of cathode 30 is less than the electrical capacity of anode 20.

A plurality (not shown) of electrochemical cells 10 may optionally be configured in series (e.g., to obtain a voltage corresponding to the sum of the voltages of the individual cells), optionally encased in a single housing to form a battery.

An electrochemical cell according to the present embodiments may follow any design known in the art, and may include one or more anodes and/or cathodes. Several exemplary designs include, but are not limited to, several rotating disk electrodes, several ultramicroelectrodes, or several screen printed electrodes.

The configuration of the several components of electrochemical cell 10 as presented in fig. 1 is for illustrative purposes only and is not to be considered limiting in any way.

In some of any of the individual embodiments described herein, an energy density of a lithium ion battery is at least 250 watt-hours per kilogram (Wh/kg), and optionally at least 300 watt-hours per kilogram (e.g., from 300 to 400 watt-hours per kilogram), or at least 350 watt-hours per kilogram, or even at least 400 watt-hours per kilogram. In contrast, the energy density of commercial lithium ion batteries is typically 150 to 250 watt-hours per kilogram.

In some of any of the individual embodiments described herein with respect to a lithium ion battery, the lithium ion battery is rechargeable, i.e., designed and/or identified for reuse when recharging the battery, by applying an appropriate potential.

As used herein, the term "about" means ± 20%. In any of the embodiments described herein where the word "about" is used, that word means ± 20%.

The terms "comprising", "including", "having" and variations thereof mean "including but not limited to".

The phrase "consisting of …" is intended to include and be limited to ("including and limited").

The phrase "consisting essentially of …" means that the composition, method, or structure may include several additional components, steps, and/or portions, but only if the several additional components, steps, and/or portions do not materially alter the basic and novel characteristics of the claimed composition, method, or structure.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" can include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of the present invention may be presented in a range format. It should be understood that the description of the range format is for convenience and brevity only and should not be construed as an inflexible limitation on the scope of the invention. Thus, the description of a range should be considered to have specifically disclosed all the possible sub-ranges and individual numerical values within that range. For example, a description of a range such as from 1 to 6 should be considered to have specifically disclosed several sub-ranges such as from 1 to 3, from 1 to 4, from 2 to 6, from 3 to 6, etc., and several individual numbers within that range, for example, 1,2,3, 4, 5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is intended to include any number (decimal or integer) recited within the indicated range. Ranges between a first indicating number and a second indicating number and ranges from a first indicating number to a second indicating number are used interchangeably herein and are intended to include the first and second indicated numbers and all fractional and integer numbers therebetween.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Several particular features described in the context of various embodiments are not necessarily required to be features of those embodiments, unless the embodiments are inoperable without the elements.

As described hereinabove and as claimed hereinafter, various embodiments and aspects of the invention find experimental support in the following examples.

Examples of the invention

Reference is now made to the following several examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting manner.

Materials and methods

Materials:

hydrofluoric acid (HF) was obtained from Sigma Aldrich (Sigma-Aldrich).

Stainless steel mesh (304 or 316L steel grade) containing fibers of 25 or 50 microns in width is used.

A 9:1 mixed carbon ink was obtained from sigma-oredge.

Lithium foil is available from Rockwood lithium corporation, Inc (Rockwood L ithium Inc.).

Chemical vapor deposition:

stainless steel samples are placed in a quartz tube, and the chamber is evacuated to a base pressure of 0.005 torr, then indicated gases (e.g., silane and argon and/or hydrogen) are introduced at indicated gas flow rates. To deposit P-type silicon, diborane is also introduced (at a rate of 6.25 sccm). The several stainless steel samples were weighed before and immediately after deposition to determine the amount and density of silicon (amount per unit area).

Assembling the battery:

several electrochemical cells were assembled in an argon-filled glove box. Several silicon-containing samples were cut into several 10 mm diameter discs and a drop of indicated carbon ink was applied to one side in order to improve electrical contact with the current collector. The carbon-treated anode obtained is typically placed in a vacuum oven overnight at 50 degreesThen heated to 100 degrees for 2 hours before assembly. A CR2032 coin cell having the indicated electrodes is assembled, the coin cell comprising: 2a spacer, a plurality of silicon-containing nanostructures on stainless steel, a separation film (2400) And a lithium cathode (cut from lithium foil, 15 mm diameter).

X-ray photoelectron spectroscopy (XPS):

x-ray photoelectron spectroscopy measurements were performed using a 5600 Multi-technology System (PHI, USA).

Example 1

Effect of hydrofluoric acid treatment on silicon growth on stainless Steel

Initial attempts to grow silicon structures on the stainless steel were made by inserting a fresh, e.g., received stainless steel mesh into a CVD (chemical vapor deposition) system. The stainless steel mesh as received is shown in fig. 2A and 2C. As demonstrated therein, the stainless steel substrate had few flaws. However, several minor imperfections are created when the substrate is handled, e.g., creases, scratches, pincer imperfections, and the like.

As shown in fig. 4A, very few silicon structures were observed to grow near the number of contact points of the stainless steel mesh, showing that they grew from inside the number of flaws of the substrate.

This result indicates that although the stainless steel contains primarily iron and chromium elements at the surface of the stainless steel, the number of unintentional flaws may expose a number of other metallic elements, such as nickel and copper, which have a positive effect on the growth of the number of silicon structures on the substrate.

Immersing the stainless steel in hydrofluoric acid (HF) strongly promotes cracking of the steel to the point where a number of nano-islands (nano-islands) are formed on the surface of the substrate. Further, the color of the steel changes from gray to black.

Hydrofluoric acid treated stainless steel mesh is shown in fig. 2B and 2D.

As shown in fig. 2D, hydrofluoric acid treatment increased the roughness of the steel surface, indicating a possible increase in nucleation points.

As shown in fig. 4B, several silicon nanostructures were grown uniformly on the hydrofluoric acid treated stainless steel mesh.

Without being bound by any particular theory, it is believed that an increase in roughness and potential nucleation points contributes considerably to the uniform silicon growth promoted by hydrofluoric acid treatment.

Several stainless steel substrates were used for XPS analysis. The substrates were cleaned in a 100 watt oxygen plasma for 10 minutes to remove carbon and organic related contaminants.

Table 1 atomic percent of several elements as received, untreated 316L stainless steel and 316L stainless steel treated with 40% hydrofluoric acid for 30 minutes, as determined by XPS analysis (surface only, no sputtering).

Element(s)	Untreated stainless Steel (%)	Hydrofluoric acid-treated stainless Steel (%)
			C	19.78	24.47
O	52.14	46.73
			N	1.32	Can not be measured
F	5.31	5.17
			Fe	8.95	9.84
Cr	2.03	4.02
			Ni	1.18	4.75
Na	0.93	-
			Ca	0.94	-
Si	5.45	-
			S	1.96	-
Cu	-	2.73
			Mo	-	2.31

The XPS spectrum of a sample of stainless steel treated with 40% hydrofluoric acid for 30 minutes is depicted in fig. 3A, and the elemental composition determined by XPS is presented in table 1.

As shown in table 1, hydrofluoric acid treatment increased the ratio of several non-ferrous elements, such as chromium, nickel, and copper and molybdenum, at the surface of the stainless steel substrate while also successfully cleaning the substrate of many inorganic contaminants, such as sodium, calcium, and sulfur.

Similarly, as shown in fig. 3B, hydrofluoric acid treatment resulted in NiO₂A clear increase in peak size as observed in the portion of the XPS spectrum associated with nickel.

Furthermore, as shown in fig. 3A and 3C, several peaks associated with copper appear in the XPS spectrum upon hydrofluoric acid treatment, and such several peaks are not visible prior to hydrofluoric acid treatment.

These results show that hydrofluoric acid treatment increased the amount of several nonferrous metals present in the stainless steel on the surface of the treated stainless steel.

As further shown in table 1, hydrofluoric acid treatment did not increase the amount of fluorine on the substrate surface. The appreciable amount of fluorine in the untreated sample may be associated with a chemical treatment performed on the stainless steel during its production, since the untreated sample is not in contact with any contaminated objects (the treated sample is handled with different tweezers and never comes into contact with the untreated sample).

Further XPS analysis showed that none of the several metals exposed and concentrated after the hydrofluoric acid treatment contained any indication of metal-fluorine bonding. The iron XPS spectrum alone showed FeF₂A possible signal of, its parameterThe energy of the test is observed on a scale of 711.3-711.4 electron volts, and is related to the Fe₂O₃Peak correlation.

These results show that the only metal affected by the hydrofluoric acid treatment is iron that is dissolved during the process. This is consistent with the results of table 1, which show that all several metals are concentrated on the surface (except for iron, the level remains substantially unchanged).

The effect of process time (in hydrofluoric acid) on silicon density was measured by treating a stainless steel web with 40% hydrofluoric acid for various periods of time, followed by deposition of intrinsic silicon by exposure to silane at a flow rate of 5sccm (standard cubic centimeters per minute) and argon at a pressure of 460 degrees and 25 torr (flow rate of 20 sccm). Both 25 micron and 50 micron mesh samples were tested.

Table 2: average silicon density measured after immersing 25 and 50 micron stainless steel substrates in 40% hydrofluoric acid for various times (after 60 minutes, 50 micron stainless steel began to free).

As shown in table 2, the hydrofluoric acid pretreatment greatly increased the silicon density on the stainless steel mesh.

As further shown in table 2, in a number of untreated samples, the silicon density was close to zero, and the number of 25 micron samples had more silicon than the number of 50 micron samples.

This result shows that silicon growth without hydrofluoric acid treatment is associated with defect sites, and that the 50 micron sample, which is thicker, is less prone to deformation than the 25 micron sample, which is thinner, when handled.

Table 3 presents the results of an experiment using several 25 micron stainless steel mesh samples placed on top of each other in a 4 inch CVD apparatus. Each mesh sample was treated with a different hydrofluoric acid concentration, from 25% to 40%, placed in the order from 40% down the top.

As shown in table 3, the samples treated with 30% hydrofluoric acid exhibited a higher silicon density than the samples treated with higher hydrofluoric acid concentrations, although the 30% hydrofluoric acid samples were less exposed to vapor deposition.

30 minutes was therefore selected as the hydrofluoric acid treatment time for several experiments in the future regarding electrode creation.

Table 3: average silicon density as a function of hydrofluoric acid concentration (all samples were immersed for 30 minutes and stacked 3 hours above each other at 460 degrees and 10 torr in a 4 inch CDV apparatus at 200 seem argon flow, 15 seem silane flow).

Concentration of hydrofluoric acid	Average silicon Density (mg/sq cm)
		25％	0.84
30％	0.95
		35％	0.76
40％	0.71

In addition, several hydrofluoric acid concentrations as low as 5% promoted the growth of several silicon structures when the hydrofluoric acid treatment time exceeded 2 hours (data not shown).

These results show that higher hydrofluoric acid concentrations do not necessarily result in higher silicon densities, and that the metal-fluorine bonds created during the hydrofluoric acid treatment inhibit further dissolution of the surface and create some form of passivation layer. Several higher concentrations (> 30%) of hydrofluoric acid create fluorine-containing bonds more rapidly on the surface, thus reducing the efficiency of the hydrofluoric acid in the process, while several lower concentrations (< 30%) have a weaker dissolving effect on the surface due to less acid contacting the surface.

Table 4: average silicon density when several 25 and 50 micron stainless steel substrates were subjected to different CVD times (all several samples were pretreated with 40% hydrofluoric acid for 30 minutes).

As shown in table 4, the silicon density increased significantly during the period of 7-15 minutes of vapor deposition, and continued to increase at a more gradual rate during the period of 15-60 minutes of vapor deposition (in the several 50 micron samples, the significant decrease in density between 30 and 60 minutes was due to weighing errors, and could be ignored).

The results show that the primary nucleation process occurs in the period of up to about 7 minutes, and rapid growth begins thereafter.

As further shown in table 4, thicker (50 micron) substrates tend to result in higher silicon density than thinner (25 micron) substrates subjected to the same deposition conditions, although they reach a plateau faster than the thinner substrates.

This result shows that hydrofluoric acid treatment is more effective in the several 50 micron samples because these samples have less surface area than the several 25 micron samples, thus greatly promoting silicon structure growth, so that further treatment does not affect the silicon coverage and nucleation in the growth phase.

Similarly, pure 40% hydrofluoric acid at 60 minutes began to completely dissociate the stainless steel samples (but not in the thinner samples) due to the greater effectiveness of hydrofluoric acid on the thicker samples.

Taken together, the results described above show that the silicon density can be controlled by varying several parameters, such as the period of exposure to hydrofluoric acid and the period of chemical vapor deposition, allowing a high silicon density to be obtained.

Several silicon structures grown on a hydrofluoric acid treated stainless steel surface were imaged by electron microscopy.

Fig. 5A and 5B show the presence of several silicon nanostructures, including several line-like structures, using scanning electron microscopy.

Without being bound by any particular theory, it is believed that this phenomenon may be caused by the manner in which the hydrofluoric acid pretreatment creates the several nano-islands (acting as catalysts in later processes). During the growth process, the silane gas is dissociated into pure silicon and then diffused into the stainless steel. Closely spaced catalytic islands may lead to integration of many growing silicon structures, thus creating thicker and shorter structures than more isolated catalytic islands.

As shown in fig. 5C and 5D, no catalyst (by high resolution transmission electron microscopy) was observed on top of the several elongated silicon structures.

Similarly, fig. 5A and 5B show a lack of catalyst from many silicon structures, as determined by scanning electron microscopy.

These results show that the silicon structures grow through a gas-solid (VSS) mechanism, while the silicon is continuously extended from the stainless steel surface.

However, by individually examining a phase diagram for each of the several metals that the stainless steel with silicon comprises, no eutectic point is found for a temperature below about 800 degrees. It is therefore assumed that silicon growth is promoted by the course of several metal silicides as the silane dissociates on the stainless steel network phase.

It is believed that the previously reported methods for growing silicon nanowires on stainless steel (e.g., as described by Chan et al, [ Nat Nanotechnol,3:31-35, 2008 ]; Kim et al [ Materials L ett,64: 2306-.

As shown in fig. 6A to 7D, the voids between the stainless steel fibers were gradually closed as silicon growth proceeded in several samples pretreated with 40% hydrofluoric acid for 30 minutes as observed by optical microscopy (fig. 6A to 6D) and scanning electron microscopy (fig. 7A to 7D).

These results show that the several silicon line-like structures can be grown to as large as tens of microns in length, and that the porosity can be significantly reduced when silicon growth is carried out using the several methods described herein.

For example, fig. 7A shows a stainless steel mesh having a density of 0.5 mg/cm of silicon. Even at this density, the several silicon structures were grown to as large as 10 microns in length while maintaining about 30 nanometers in diameter.

In contrast, fig. 7D shows a stainless steel mesh having a density of 5.11 mg/cm of silicon. At this density, the porosity of the potential anode material has been greatly reduced.

As shown in fig. 8A, the level of copper in the several silicon structures reaches about 10 per cubic centimeter of silicon, as determined by TOF-SIMS²⁰Copper atoms, said levels corresponding to an atomic proportion of up to about 0.2%, indicating diffusion of copper from said stainless steel substrate into said silicon during said growth phase.

The amount of copper in newly manufactured stainless steel is minimal, but silicon is susceptible to copper contamination because of the high diffusion coefficient of copper in silicon (even at low temperatures) [ Istratov & Weber, J Electrochem Soc,149: G21-G130, 2002 ].

As shown in fig. 8B, P-type (boron-doped) grown silicon also contains iron and boron in addition to copper.

This result shows that, due to the donor character of iron in silicon, the atomic proportion of iron is significantly reduced due to its ionizing nature, thus greatly increasing its diffusion coefficient, even at low temperatures.

Without being bound by any particular theory, it is believed that copper has a much greater diffusion coefficient in intrinsic silicon, thus creating a diffusion barrier for any other element in the stainless steel; in a highly boron-doped environment, the solubility of iron increases significantly due to the very strong pairing of iron with boron (FeB), and this solubility and diffusion coefficient increases significantly at low temperatures (see, for example, Istratov et al, Appl Phys A,69:13-44, 1999).

A further advantage of hydrofluoric acid treatment is that it eliminates most of the contaminants on the surface by etching. Several silicon structures can thus be grown on the 3D stainless steel network without a cleaning process.

Treatment with several acids other than hydrofluoric acid (e.g., nitric (65%), sulfuric (95%), phosphoric (85%) and chloric (32%)), or with acetone was also attempted (data not shown). These treatments do not provide the same results as hydrofluoric acid, for example, a change in the appearance of the stainless steel or the amount of several silicon nanostructures grown on the surface of the stainless steel. Conversely, such a treatment may promote passivation of the stainless steel (which inhibits silicon nanostructure growth) via the formation of several thin oxide layers. As revealed by XPS studies, nitric acid promotes the accumulation of more chromium on the surface of the stainless steel. However, it is clear that the nitric acid treatment results in a similar type of silicon growth (as described above) as on the as-received stainless steel due to lack of cracking and exposure of several different elements.

Taken together, the processes described herein can be used to fabricate nanoporous spongy silicon networks on several stainless steel surfaces using relatively low temperatures (e.g., 350 to 450 degrees) without resorting to expensive several noble metal catalysts.

Example 2

Coating a plurality of silicon nanostructures with an aluminum oxide layer

To increase mechanical support and resistance to cracking during lithiation, a layer of alumina was deposited on silicon structures (prepared according to the method described in example 1) via atomic layer deposition (A L D) using a Trimethylaluminum (TMA) catalyst and deionized water (dH)₂O) as schematically depicted in fig. 9.

The alumina deposition method was performed using "exposure" cycles, i.e., the TMA and dH₂Both O-gas were left in the chamber for 7 and 25 seconds each in its respective round before opening the vacuum valve. Because the consistency of the shell formation is the diffusion-limited rate by the two gases, allowing the gases to diffuse at high temperatures (150 degrees) is believed to result in greater permeability into the 3D sample, thus allowing conformal alignment of the alumina shell up to the core of the stainless steel despite the relatively high density of silicon (e.g., as illustrated in fig. 4B).

In a typical process, several samples were placed in an A L D system and held elevated at the bottom surface of the system to allow maximum diffusion through the entire 3D network the samples were exposed to Trimethylaluminum (TMA) for 0.015 seconds while the vacuum valve was closed for 7 seconds followed by a chamber vacuum for 25 seconds the samples were then exposed to dH₂O vapor 0.02 seconds and the vacuum pump was turned off for 25 seconds followed by a chamber vacuum for 30 seconds. The samples were exposed to alumina followed by dH₂Each exposure of O is defined as a 1a L D cycle.

An aluminum oxide capping layer of about 5 nm thickness, conformally coating the exposed SiNS surface regions, was obtained after 35a L D cycles.

Several representative alumina-coated wire-like silicon structures are shown in fig. 10A-10D via transmission electron microscopy.

As shown in fig. 10B and 10C, many of the several silicon structures are connected to each other.

The interconnection of several silicon structures may provide increased mechanical support and resistance to cracking (e.g., in addition to the effect of the aluminum oxide layer).

In addition, the effect of the gas (as discussed above) remaining in the chamber on the conformality of the overcoat on the alumina was tested. With respect to the process described above, the gas is not allowed to remain in the chamber, i.e. the vacuum pump is always on. In addition, more deposition cycles are performed (per process 200 cycle).

When the gas is not allowed time to diffuse further, the resulting alumina coating follows the roughness of the silicon structure; while in the "exposure" process described above, the alumina coating is more consistent in terms of roughness.

These results confirm the effectiveness of the "exposure" process of the several experiments described herein.

Several silicon nanostructures were grown on stainless steel mesh (5sccm silane and 20sccm argon for 80 minutes at 460 degrees and 25 torr) and then subjected to RTP (rapid thermal treatment) to promote crystallization of the silicon (increasing the temperature for about 13 seconds, increasing the temperature to 650 degrees at a rate of 50 degrees/second, then 4 minutes at 650 degrees) followed by deposition of alumina by a 35a L D cycle to obtain a crystalline silicon core and amorphous shell.

As shown in fig. 11, some structures do not exhibit crystallinity and are coated by a Solid Electrolyte Interface (SEI), which cannot be removed.

The transition from a crystalline silicon core to amorphous silicon shows that the penetration of the lithium occurs along the entire nanostructure, including through the alumina shell.

As shown in fig. 12A and 12B, after two cycles of lithiation/delithiation, many nanowire structures exhibit SEI formation and cracking along the nanowires; several alumina shells were still visible, indicating that they were not removed by two cycles.

The average diameter before lithiation (for several control structures) was 85.56 ± 16.21 nanometers, and the average diameter (in the delithiated state) for several structures cycled was 108.40 ± 13.93 nanometers, with relatively little change in volume (about 27%).

This result shows that the alumina shell limits the volume change relative to the typical 400% volume change of silicon.

Furthermore, some alumina-coated silicon nanostructures exhibited no damage after two lithiation/delithiation cycles, which may indicate incomplete wettability.

Example 3

Electrochemical characterization of several silicon nanostructures

By using electrochemical characterization of a coin-type cell configured to have 10 mm anodes, stainless steel mesh with alumina coated silicon structures (prepared according to the procedure described in example 2) was evaluated for potential utility as an anode. Several cells were cycled over the first three cycles using a constant current of 0.1 milliamps (mA) at 30 degrees to obtain the maximum capacity of the cells, followed by aging tests using a constant current of 1 milliamp.

The results for a representative cell comprising alumina coated silicon, and a silicon density of 1.18 grams per square centimeter, are shown in fig. 9A-9C.

As shown in fig. 13A and 13B, at 0.1 milliamp current, the initial capacity of the battery under test reached about 3.6 milliamp-hours per square centimeter (about 3000 milliamp-hours per gram of silicon).

It is noted that such a capacitance value may be acceptable for electric vehicles.

As further shown in the figure, at a more rapid charge/discharge rate of 1 milliamp, the initial capacitance measured was about 2.6 milliamp-hours per square centimeter (about 2300 milliamp-hours per gram of silicon) and decayed to about 1 milliamp-hours per square centimeter after 200 cycles (about 875 milliamp-hours per gram of silicon) and to about 0.6 milliamp-hours per square centimeter after 500 cycles (about 500 milliamp-hours per gram of silicon).

Several of the results above show that the capacity is about 1.5 times the capacity of graphite even after 500 cycles.

As further shown in the figure, the maximum capacity of the cell (measured over an interval of 0.1 milliamp current) reached 2.3 milliamp-hours per square centimeter after 500 cycles, representing a 36% capacity loss after 500 cycles.

Stainless steel does not have lithiation capacity by itself, and it is reasonable to assume that the silicon alone contributes to the overall capacity of the cell.

As illustrated in fig. 13C, a stable decay of the battery can be observed in the voltage pattern. A more significant reduction in capacitance occurs between cycles 150 and 250.

Fig. 14A and 14B show several individual lithiation and delithiation peaks of silicon, which gradually widen during the charging phase, the above figure also showing several sharp lithiation peaks at about 0.25 volts.

Without being bound by any particular theory, it is believed that because the several silicon structures are largely amorphous, several of the observed dQ/dV peaks represent the two lithium rich phases, Si L i_2.3And Si L i_3.25A balance between them. Further, it is believed that the several sharper lithiation peaks near 0.25 volts may be associated with a diffusion barrier caused by SEI (solid electrolyte interface) formation accompanying the aluminum oxide layer.

After 700 cycles (an additional 200 cycles at 0.5 milliamps), the several silicon nanostructures were examined by electron microscopy.

As shown in fig. 15C and 15D, after 700 cycles, the aluminum oxide layer is detached from the silicon (possibly due to the pressure applied by the silicon as it partially expands and contracts as it is lithiated/delithiated) and is accumulated in the SEI.

This result shows that the aluminum oxide layer may contribute to a larger than usual diffusion barrier.

Kim et al [ Chem Mater,27:6929-6933, 2015]Reporters several thicker TiO on several silicon nanowires undergoing lithiation and delithiation₂The coating (larger coating thickness to core diameter ratio, t/D) results in less radial expansion than a thinner coating, but due to TiO_2-The grain-to-grain bonding with the plurality of silicon nanowires is weak, increasing the possibility of cracking.

The alumina shell described herein (considering an average core diameter of 80 nanometers and a shell thickness of 5 nanometers) has a t/D value of about 0.06, which is expected to have little effect on radial expansion. However, due to the amorphous nature of the several silicon structures and the aluminum oxide layer described herein, the particle-to-particle bonding between the two materials is expected to be stronger than in the several nanowires in Kim et al [ Chem Mater,27:6929-6933, 2015 ], and the amorphous nature of the aluminum oxide is expected to allow for greater elasticity of the shell [ Chou et al, Scr Metal Mater,25:2203-2208, 1991 ], thus making it less prone to cracking.

Table 5: characterization of several 3D silicon networks with various silicon densities by electrochemical cycling (several networks are not necessarily non-functional after the indicated number of cycles)

As shown in table 5, while the only one cell that reached 500 cycles was one that included an alumina coating, the presence or absence of an alumina coating had no clear effect on the several electrochemical parameters measured.

In addition, fig. 15B (via transmission electron microscopy) shows that after 700 cycles, some of the silicon nanostructures were still completely encapsulated in an aluminum oxide shell, showing that a silicon nanostructure electrode could reach the end of its life before all of the silicon was consumed.

As shown in fig. 15A, several silicon nanostructures began to separate from several stainless steel fibers after 700 cycles.

The surface of several silicon nanostructure anodes after cycling was subjected to a single element analysis by energy-dispersive X-ray spectroscopy after being washed with water or DMC (dimethyl carbonate), and the results are presented in table 6 below.

Table 6: elemental analysis of the surface of several silicon nanostructures after electrochemical cycling and after cleaning with DMC or water

As represented in table 6, cleaning with water removed carbon, oxygen, and phosphorous from the surface relative to cleaning with DMC (which was not expected to substantially remove SEI), and resulted in an increase in observed silicon.

This result shows that an SEI containing phosphorus, oxygen and organic materials is formed during several electrochemical cycles of the silicon nanostructure.

Taken together, the several results above show that the main degradation mechanism of the anode is thickening of the SEI (until it becomes impermeable to lithium ions), mainly at the surface and between the several stainless steel fibers, before reaching several silicon structures deeper until the cell completely fails. Such a mechanism is schematically depicted in fig. 16.

As further shown in table 5, the several tested cells (with several silicon-containing anodes prepared as described herein) generally exhibited high capacitance and low irreversible capacitance throughout hundreds of cycles.

These results show that several anodes containing several silicon nanostructures as described herein can consistently exhibit very low capacitance loss between hundreds of cycles, while still maintaining higher capacitance than currently available graphite anodes.

Several cells comprising several highly doped (1:4000 boron: silicon) P-type silicon structures are compared to several cells comprising intrinsic silicon in order to obtain further insight into the mechanism of attenuation. The porosity of P-type silicon structures prepared (according to the process described herein) on stainless steel, with or without a subsequent annealing treatment (at 650 degrees), was also compared to the porosity of P-type silicon nanowires grown using gold nanoparticles as a catalyst.

As demonstrated in example 1 (and in particular in fig. 8B), iron diffuses in P-type silicon in a relatively high amount (about 0.2%), which obviously reduces the diffusivity of lithium in the silicon, and therefore the capacitance. While the additional iron may reduce the capacity of the cell, the direct conductivity of the P-type silicon is increased due to the ionic state of the iron in the silicon structure.

As shown in 17A and 17B, the number of P-type silicon nanostructures on stainless steel exhibit little conductivity without annealing; after annealing, however, the conductivity is even higher than that of several P-type silicon nanowires grown using several gold nanoparticles.

As shown in fig. 17D, the anneal results in several silicon structures being polycrystalline.

Fig. 17C shows an exemplary silicon nanostructure between a plurality of sources and a plurality of drains.

These results show that the absence of amorphous nature and a continuous crystalline core of silicon results in a lack of conductivity prior to annealing, which enhances conductivity by introducing crystallinity.

Annealing the silicon, whether P-type silicon or intrinsic silicon, may facilitate out-diffusion of the copper and iron to the surface of the silicon, thus reducing a suitability of the silicon for use in battery devices. This problem may be overcome by rapid heating.

As illustrated in fig. 18, according to an exemplary embodiment of the present invention, the grown 3D nano-pore silicon on a stainless steel network can be easily enlarged to large samples (e.g., one meter long in fig. 18) having stainless steel coated throughout the silicon for anode fabrication. Due to the porous nature of the stainless steel used, the density remains unaffected by rolling and/or placing several samples on top of each other — thus an unlimited size silicon-coated stainless steel anode can be achieved.

Example 4

Silicon nanostructure growth and annealing

According to the process described in example 1, several silicon nanostructures were fabricated on hydrofluoric acid treated stainless steel.

Several hydrofluoric acid treatment times between 10 and 60 minutes were tested, while several good results were obtained at several hydrofluoric acid concentrations of 5 to 15% for 20 to 30 minutes of etching.

Boron doped silicon in a CVD reactor using SiH₄Gas as precursor (flow rate 5sccm), B₂H₆(flow rate 6.25sccm) and dilution with an Ar gas carrier (flow rate 10sccm) at 460 degrees and 25 torr for a period of 30 to 90 minutes via the VSS mechanism, thereby controlling the thickness of the conformal layer of silicon nanoholes and the silicon loading of the anodes as a finished product.

The growth of the silicon nanostructures is followed by a high temperature annealing step at several temperatures between 650 to 850 degrees, in the presence of an atmosphere of hydrogen or in a vacuum environment, for a period of 2 to 8 minutes.

Fig. 20A-20E and 23 show the etching effect of a30 minute hydrofluoric acid treatment of 304 stainless steel (compared to, for example, untreated stainless steel in fig. 19).

Fig. 21 and 22 show the progress of etching over time as a result of hydrofluoric acid treatment of 304 stainless steel.

As shown in fig. 25A-25F, several silicon nanostructures exhibit a crystalline core and an amorphous silicon shell.

Fig. 26A to 26E show the growth of example P-type silicon on a stainless steel mesh.

As shown in fig. 27, annealing by heat treatment results in several silicon nanostructures being welded together.

Several samples of stainless steel (treated with hydrofluoric acid) may optionally be conveniently rolled up to facilitate the CVD process, as depicted in fig. 28A-28D.

As shown in fig. 29A and 29B, the several silicon nanostructures are effectively grown on a rolled sample. Nanostructure growth was similar in several different parts of the sample, except for the most downstream part (where the silicon concentration was lowest): in the most downstream part, the silicon density is slightly lower than in the other parts.

Example 5

Silicon stainless steel core-shell nano-pore spongy network

As an alternative to the hydrofluoric acid treatment, stainless steel base substrates are first heat treated and annealed in a hydrogen-containing atmosphere (1 to 5% hydrogen in a nitrogen carrier at atmospheric pressure) at temperatures between 950 and 1100 degrees for periods of time from 0.5 to 5 hours. This pre-annealing step results in the formation of conformal spongy nanoporous stainless steel structures on the planar native substrates, except for the H₂/N₂The flow of gas does not require any chemical reactants to be provided to the CVD growth chamber.

As a result, the "reactant-free" process for the formation of the metal substrate sponge network is controlled by the temperature and several annealing times under given several conditions.

The resulting several networks of spongy metal substrates were obtained within the several ranges of temperature and gas composition and pressure mentioned above. No formation of a sponge-like structure was observed outside the range of these several conditions.

As shown in fig. 30A-30F, the "reactant-free" growth method resulted in the formation of several metal-based spongy nanoporous networks in communication with several stainless steel conductor surfaces.

As shown in fig. 31B, the several networks are characterized by the presence of metal (such as chromium and copper) and oxygen atoms (as determined by EDX (energy dispersive X-ray)).

As shown in fig. 31A and 31D, the plurality of networks contain a plurality of metal base structures having typical diameters in a range of about 50-100 nanometers.

Electrical measurements of a plurality of single metal-based nanowires harvested from the plurality of sponge layers are performed, exhibiting a plurality of conductivity values that are relatively high.

During the first high temperature annealing step, a 3D spongy metal-based conductive network associated with the original stainless steel substrate and mechanically highly stable is obtained. This 3D conductive sponge layer comprises a significantly increased active surface and thus is an excellent candidate for further deposition of several thin thickness control silicon active shells.

The metallic substrate sponge surfaces are used as a substrate for further thermal cracking deposition of a conformal layer of amorphous silicon. After the first annealing step and the formation of the metal-based spongy network structure layer, a thin thickness control layer of amorphous silicon is conformally deposited on the plurality of metal-based spongy network surfaces, resulting in a mesoscopic large-scale silicon conformal shell layer coating the entire metal-based spongy network surface.

As a general procedure, the conformal layer of silicon is created in situ for periods of 30 to 180 minutes in the CVD at temperatures set in a range of 380 to 550 degrees depending on the desired loading level of silicon (e.g., based on the final cell application). Silane gas precursor in an argon or hydrogen carrier atmosphere is flowed at a rate of about 5 or about 12sccm at pressures in a range of 1 to 25 torr, respectively.

This general process results in the formation of one-dimensional conductive metal substrate cores upon the first high temperature annealing step, the cores conformally coated with a load control silicon layer, suitable (e.g., in a lithium ion battery anode) as the active material for lithiation/delithiation devices.

Silicon loadings in the range of 0.1 to 15 mg/cm are available for silicon layers having a thickness in a range of 6 to 200 nanometers.

The resulting metallic silicon sponge core-shell structure exhibits a controlled loading of conformal silicon cladding layers, high mechanical stability, short lithium ion diffusion length through a silicon shell layer, high metal core chemical stability to lithiation reactions, high conductivity of metal-based core networks and high mechanical stability when expressed as a battery anode element.

As shown in fig. 32A to 32F, an amorphous silicon shell was deposited on the several (crystallized) metal base nanostructures as determined using high resolution transmission electron microscopy (for comparison, the magnifications are similar to those in fig. 31A, 31C and 31D).

The thickness of the silicon layer is typically in a range of about 10 to 20 nanometers.

Example 6

Electrochemical characterization of 3D silicon nanostructures in half-cells with respect to lithium metal anodes

An electrochemical study of the electrode materials is performed by analysis of impedance spectroscopy and cycling of the electrochemical cells. The first stage of material research is the characterization of the electrode under study to a lithium metal counting reference electrode. This set of tests enables the investigation of the several electrode material parameters to be performed without the complexity associated with the limitations of a cathode. In this study, the half-cell consisted of an electrode comprising SiNS (silicon nanostructures) on a stainless steel mesh (prepared according to the procedure described in example 1) against a lithium metal electrode. The half cell configuration described hereinabove allows an evaluation of the alloying-dealloying process of a silicon nanostructure anode to be performed.

Several parameters were studied as follows:

1. capacitance-reversible, irreversible and differential analysis (dq/dv)

2. impedance-EIS (electrochemical impedance Spectrum) at 1MHz to 0.01mHz

3. Rate discharge capability in the range of C/40 to 5C

4. Cycle life cycling at about 1C rate

The next procedure is used to evaluate whether a battery is acceptable as part of the study. An unacceptable cell is typically one that is damaged during SiNS anode fabrication or during cell assembly.

(a) EIS: the measurement is typically made every 100 cycles (after charging and discharging 100) with a scanner (e.g., Solartron)^TMOr Bio-L ogic^TMScanner) is performed at a frequency range of 1MHz to 0.01MHz and an amplitude of 20 Mv. Spectral analysis is used to determine Rb, R_SEIDiffusion, Rt. The randrey circuit model used for analysis is depicted in fig. 33.

(b) The electrochemical cycling process for the study of several half-cells is summarized in tables 7 to 9.

Table 7: cyclic process for initial capacitance measurement

Table 8: cycling process for determining half-cell cycle life

Table 9: cycling process for determining rate discharge capability of half-cell

The doping effect is as follows:

several anodes (according to the procedure described in example 1) were prepared by growing P-type silicon (relative to intrinsic silicon) and then identified as described above. The several anodes were then tested in several half-cells relative to lithium metal CE-RE electrodes. The results are presented in fig. 34A to 35.

As shown in fig. 35, the overall performance of the phosphorus-doped silicon is worse than that of the intrinsic silicon.

In view of these results, future studies use intrinsic silicon anodes as a reference point.

According to the literature, doping is expected to increase stability, contrary to the results described above. Without being bound by any particular theory, it is believed that boron ions in P-type silicon may migrate from the bulk of the structures to the surface during lithiation and delithiation, forming a glassy oxide that inhibits lithium diffusion.

Effect of silicon loading:

several silicon nanostructure anodes with several different degrees of silicon loading were identified using the process described above. The cycle life (defined as the number of cycles before the cell reaches 70% of its initial capacity) of several anodes containing several intrinsic silicon nanostructures on a stainless steel mesh was determined in several half-cells relative to a lithium metal CE-RE electrode (counter electrode reference electrode).

As shown in fig. 36 and 37, the cycle life for several representative samples was longer than 100 cycles (fig. 36) when the silicon loading was 0.9 mg/cm at 1.28 milliamp/cm cycles, but significantly shorter at a higher silicon loading of 1.8 mg/cm (fig. 37).

These results show that a combination of relatively high silicon loading and relatively high current density promotes degradation, possibly due to promoted SEI growth upon cycling.

In an additional experiment, the cycle life of several electrodes with a silicon loading of 2 mg/cm was tested in one half cell versus lithium metal.

As shown in fig. 38, the cycle life of the several tested cells (with a silicon load of 2 mg/cm) was significantly shorter than the cycle life of several half cells with lower silicon loads (e.g., as shown in fig. 36).

However, as shown in fig. 49, anodes from the same series as shown in fig. 38 exhibit a durable cycle life of over 400 cycles in full cells to NCA (lithium nickel cobalt aluminum oxide) cathodes.

These results show that higher silicon loading is associated with increased cycling instability, which is exhibited primarily in the half cell. Half-cells including electrodes with a relatively high silicon loading (e.g., as shown in fig. 37, and in fig. 41 and 43) exhibit shorter cycle life than half-cells including electrodes with a lower silicon mass loading (e.g., as shown in fig. 36, and in fig. 40).

In several half-cells, the lithium metal electrode is in excess, leaving the silicon anode fully lithiated and delithiated. Complete lithiation, due to the sharp voltage change between charge and discharge states (associated with the pulverization of the silicon anode), may be responsible for a short cycle life.

Furthermore, typically in post-mortem analysis (post mortem analysis) of several half cells, a black precipitate was found on the lithium metal surface, indicating the formation of dendrites (dendrites) on the lithium. A dendritic lithium anode may promote rapid deterioration of the several cells. However, this phenomenon does not interfere with the development since the main end goal is to integrate a SiNS anode into a lithium ion full cell.

Effect of the current collector:

to create a current collector for the SiNS on stainless steel mesh, the back side of the electrode was (except when testing alternative methods and materials for creating current collectors) roughly coated with carbon paste according to the following procedure:

the current collector layer was prepared by coating the back surfaces of the several anodes with a layer of conductive carbon paste containing Shawinigan carbon Black (Shawinigan Black), a binder and toluene before vacuum drying. To investigate the effect of the current collector, the several anodes were tested without a conductive agent coating and with a SWCNT coating (from PVP water solution). The performance of several anodes without carbon coating was then evaluated.

As shown in fig. 39, the several uncoated anodes tested performed poorly, especially at 1 milliamp.

As shown in fig. 40 and 41, several carbon-coated SiNS electrodes (coated on only one side of the current collector) exhibited superior performance in several half-cells versus lithium metal relative to the corresponding uncoated SiNS electrodes.

This result shows that the carbon ink does play an important role in current conductivity, especially after the SEI builds up and forms additional insulation on the back side of the anode. Clearly, the chance of a cell without carbon ink providing high capacitance at 1 milliamp is less.

Further tests were performed to evaluate the performance of a SWCNT (single-walled carbon nanotube) coating as a current collector.

Fig. 42 shows cycling of four (replicated) SWCNT-coated SiNS electrodes (1.15 mg silicon/cm) in half-cells versus lithium metal.

Fig. 43 shows the cycling of SWCNT-coated SiNS electrodes (2.2 mg silicon/cm) in half-cells versus lithium metal.

These results show that SWCNT coatings are suitable as current collectors and can replace carbon coatings. Replacing the carbon coating with SWCNTs is generally advantageous because the latter is a commercial solution with improved adsorption to the stainless steel mesh; conversely, poor adsorption of the carbon coating to the mesh may result in short circuits.

The results of fig. 40-43 also show that, as discussed above, relatively high silicon loading is associated with reduced cycling stability.

The application of a SWCNT coating from a dispersion of an N-methyl-2-pyrrolidone (NMP) substrate (obtained from OCSiAl) was then tested in several samples with a silicon loading of 1 mg/square centimeter.

As shown in fig. 44, electrodes (approximately 1 mg/square centimeter silicon loading) were coated with NMP-based dispersion of half-cells exhibiting improved stability relative to similar SWCNT-coated electrodes (e.g., as shown in fig. 42). One of several samples tested (#3) did not reach the end of cycle life after more than 200 cycles.

These results show that the application of a current collector using an NMP based dispersion results in a tighter contact of the current collector, resulting in a considerable improvement of the stability of the anode.

Example 7

Mechanisms for Solid Electrolyte Interface (SEI) formation and growth for silicon anodes

Fig. 45A and 45B present nyquist plots of charge (fig. 45A) and discharge (fig. 45B) of one half-cell containing several exemplary intrinsic silicon nanostructures, as determined by impedance spectroscopy, versus lithium metal.

As shown in fig. 45A, the resistance at the time of charging grows as the voltage increases.

Such a phenomenon is consistent with a breakdown and repair mechanism of the SEI on the SiNS anode, such as described in Peled et al [ Nano L ett,15: 3907-.

As shown in fig. 45A, the impedance at the time of discharge decreases with a decrease in potential.

Upon discharge (alloying of the SiNS electrode with lithium), the lithium is intercalated into the silicon electrode, causing volume expansion and cracking in the second porous layer of the SEI. Exposure of the thinner primary SEI reduces the resistance with decreasing potential. Upon charging (de-alloying of the silicon electrode with lithium), the alloy volume decreases and the opposite occurs.

Without being bound by any particular theory, it is believed that capacitance degradation is primarily due to the thickening of the SEI and the accompanying increase in resistance. The persistent SEI growth is due to the reduction of the electrolyte salt and solvent resulting in the precipitation of solids, and the drying of the battery. Further, it is believed that the thickness of a newly formed SEI on lithium (or on other substrates) is only a few nanometers (in the tunneling range of electrons), but under open circuit voltage conditions the thickness and the resistance of the SEI grow over time, and this phenomenon is exacerbated upon cycling. Electrons diffuse and migrate from the lithium, or from the lithiated anode, through the SEI to the electrolyte. The electrons reduce the solvent and the electrolyte, resulting in the formation of insoluble products, including lithium carbonate, lithium oxide, lithium fluoride, and several polymers. These by-products precipitate on the anode, significantly increasing the thickness of the compact layer of SEI, or forming a porous second layer.

Furthermore, the SEI impedance (R) was measured by impedance spectroscopy and spectral analysis (as described herein)_SEI) Reduced upon lithiation, particularly occurring around 0.25 volts (vs L i), silicon to α -L i₂The first phase of Si is transformed.

This result may be explained by a fresh, and thus low resistance SEI, formed due to the expansion of the SiNSs and by the increase in the surface area of the SiNSs.

These results show that an insufficiently stable SEI layer is a major contributor to the observed capacitance loss.

Example 8

Electrochemical characterization of 3D silicon nanostructures in full battery cells relative to commercial lithium ion cathodes

Several complete lithium ion battery cells are assembled. The cells were made from a commercial NCA (lithium nickel cobalt aluminum oxide) cathode (tadilan) and a SiNS anode (prepared according to the procedure described in example 1, silicon nanostructures on stainless steel mesh, 0.78 square centimeter area and 0.94 mgSilicon) the electrolyte was 0.95M L iPF₆+ in EMC DMC FEC PC (methyl ethyl carbonate dimethyl carbonate fluoroethyl carbonate propylene carbonate) [3:3:3: 1]]0.05M L IBOB (lithium bis oxalato borate) (obtained from 3M) the several cells were cycled between 0.128 milliamps and 1.28 milliamps at 4 volts and 2.8 volts.

As shown in fig. 46A and 46B, the tested cells exhibited poor performance, had a cycle life of less than 10 cycles and very low efficiency.

The cells mentioned above are unbalanced, meaning that there is a cathode excess resulting from sub-optimal silicon loading. The motivation for the cathode excess in several full cells was to load the cell with enough lithium, originating from the cathode, to achieve a balanced cell after SEI formation.

However, the above results show that cathode overdosing may shorten the cycle life of the several full cells.

Without being bound by any particular theory, it is believed that the following degradation mechanism occurs in several full cells with excess cathode material and silicon anodes: the capacitance of the silicon anode decreases upon cycling, causing the minimum voltage on the anode to increase and as a result, and causing the maximum voltage on the cathode to increase. Increasing the maximum voltage on the cathode beyond the stable range results in rapid degradation of the cathode material and, as a result, shortens the cycle life of the full cell.

In addition, a study of the cathode was performed. Several half cells of NCA versus lithium metal were cycled between 4.4 and 3.5 volts and between 4.2 and 3.5 volts at current densities of 0.06 milliamps/cm and 0.6 milliamps/cm.

As shown in figure 47, the irreversible capacities of the several tested NCA half-cells were higher in the range of 4.4 and 3.5 volts than in the range of 4.2 and 3.5 volts.

These results show that when cycled to higher voltages, more lithium is extracted from the cathode, resulting in higher capacitance.

As shown in fig. 48, several exemplary NCA cathodes performed equally well using different tested electrolytes.

Thus, several NCA-SiNS full cells with an anode excess cycled between 4 and 3 volts were tested.

Several full cells were constructed using SiNS anode (2 mg silicon/cm) and NCA cathode, the carbon current collector was SWCNT carbon ink, and the electrolyte was 0.85M L iPF in EC: DEC (ethylene carbonate/diethyl carbonate) with 2% VC (vinylene carbonate) and 15% FEC (fluoroethylene carbonate)₆. The several cells were cycled between 4 and 3 volts for 500 cycles at 0.88 milliamps per square centimeter, and for 4 cycles at 0.088 milliamps per square centimeter per 100 cycles.

As shown in fig. 49, at 400 cycles, the cells had lost about 44% of the initial capacity (determined at 0.1 milliamp current density), a relatively low rate of capacity reduction, and the series of 4 cells exhibited high reproducibility.

Similarly, as shown in FIG. 50, with a SiNS anode (0.88 mg/cm) pair

An exemplary cell with L FP (lithium iron phosphate) cathode exhibits a cycle life of over 400 cycles with 32% capacity loss.

The increased stability of the L FP-based cell was attributed to the increased stability of the L FP cathode.

To study the voltage distribution between the electrodes in a full cell, a 3-electrode cell was assembled in an E L CE LL REF device and consisted of an NCA cathode as Working Electrode (WE), an SiNS anode as Counter Electrode (CE), and a lithium metal Reference Electrode (RE).

It was observed in this experiment that when the cathode was in excess, the silicon anode was lithiated beyond its usable capacity and there was a precipitation of lithium metal on the silicon anode after lithiation was complete.

At the end of the charging, a voltage reduced to about-0.01 volts was observed at the anode (CE), at which time there was about 4 volts at the cathode and about-0.01 volts at the anode.

As exemplified above, the cathode is stable up to at least 4.4 volts. Without being bound by any particular theory, it is believed that the voltage on the silicon substrate anode should not be less than about 50 millivolts.

This result shows that a low voltage on the silicon anode may cause rapid degradation of the full cells compared to the SiNS lithium metal half cells.

The above results show that cell degradation is constituted by said voltage increase on both electrodes, and in order to accurately test said actual cycle life of said several SiNS anodes in several full cells, it is necessary to build several balanced cells either by using a higher silicon load, or by using several cathodes with lower capacity (for example, by using thinner electrodes).

A complete NCA-SiNS cell in a 2-electrode configuration was assembled and cycled between 4 and 3 volts at 0.128 milliamps/cm (normalized per unit SiNS electrode area). The battery passes the acceptance criteria and is then cycled to establish cycle life. However, since up to now the highest silicon loading deposited was 2.2 mg/cm (about 2 mh/cm) and the commercial cathodes used had a capacity of 2.6 mh/cm, such full cells still had cathode excess.

Without being bound by any particular theory, it is believed that in the case of cathode overdose, the failure mechanism described previously occurs: the excess lithium from the cathode is deposited on the anode, and lithium metal particles and dendrites are formed, causing additional irreversible capacitance due to SEI growth on the newly exposed lithium surface. Once the capacitance of the anode is reduced, the minimum voltage on the anode rises when charging and, as a result, the maximum voltage on the cathode rises when charging. As a result, the cathode is excessively excessive to cause deterioration of the battery and shorten the cycle life.

Example 9

Effect of silicon nanostructure modification via alumina deposition

Several intrinsic silicon nanostructured anodes were coated with alumina a L D coating layer (35 cycles-5 nm thickness) and identified as described in example 2 above, the cycle life (defined as the number of cycles before the cell reached 70% of its initial capacity) of the several silicon substrate anodes on a stainless steel mesh (coated with alumina) in several half-cells relative to a lithium metal CE-RE electrode was determined.

As illustrated in fig. 51, an exemplary battery having a silicon load of 1.2 mg/cm loses 30% of its capacity after about 500 cycles at 0.128 milliamps/cm; at a higher current density of 1.28 milliamps/cm, the cell capacity was reduced to 70% of its initial capacity at about 200 cycles.

In contrast, as illustrated in fig. 52, an exemplary battery having a silicon load of 2.2 mg/cm loses less than 30% of its capacity after about 200 cycles at 0.128 milliamps/cm; at a higher current density of 1.28 milliamps/cm, the cell capacity was reduced to 70% of its initial capacity at about 40 cycles.

The above results show that both relatively high current density and relatively high silicon loading are associated with reduced cycling stability.

As described above, several SiNS anodes (2.4 mg/cm) were coated with alumina by atomic layer deposition, and a carbon coating was achieved by using SWCNTs. The thickness of the alumina coating is 5 nm (35 coating cycle) or 10 nm (70 coating cycle).

As shown in fig. 55, a silicon anode coated with a 10 nm alumina coating exhibited better stability than a silicon anode coated with a 5 nm alumina coating.

These results show that the deposited alumina coating improves anode performance, particularly with respect to stability and cycle life.

As shown in fig. 56A and 56B, a deposited aluminum oxide coating reduced the capacitance of silicon anodes relative to uncoated anodes in an electrochemical full cell, the degree of reduction being related to coating thickness, without a significant difference in stability between the several coated and uncoated anodes.

Without being bound by any particular theory, it is believed that because the anode capacity is nearly twice that of the several cells tested, which are limited by the cathode, the silicon may not be fully lithiated to allow a limiting protective layer to improve performance. Further, it is believed that the use of different electrolytes in these samples is not responsible for the variation, as they have proven quite similar in the past.

Example 10

Effect of Heat treatment on silicon nanostructure Anode Performance

Heat treatment is achieved to improve electrode elasticity and release internal pressure. The several heat treatment processes are presented in table 10 below.

Table 10: exemplary Heat treatment Process

As shown in fig. 57A and 57B, the annealed electrodes exhibited a linear morphology (fig. 57B), while the un-annealed electrodes exhibited a more granular morphology (fig. 57A). It is noted that fig. 57A and 57B present regions exhibiting large morphological variations, which are not necessarily representative.

However, the morphological variation is not due to the annealing process, but is present before annealing, since the electrodes are cut from several different regions of the original sample (prepared as described above).

The capacitance of various annealed (solid dots) and unannealed (open dots) anodes upon cycling is presented in fig. 58.

As shown in fig. 58 and 59, while the several tested unannealed anodes typically exhibited a relatively sharp degradation between cycle 4 (when the current density increased to about 1C) to cycle 20 (after which there was generally only a moderate degradation), such degradation was not observed in the several tested annealed anodes.

Furthermore, as shown in fig. 59, the annealed anodes with a wire-like morphology exhibited a capacitance loss that was an order of magnitude less (0.0094% versus 0.26% per cycle) than that of the unannealed anodes, although the improvement may also be associated with the difference in morphology.

These results show that the annealing process alters the degradation mechanism in a way that may greatly extend cycle life, although the alteration may also be associated with the difference in morphology.

Further experiments can determine whether annealing, or the morphology, is the dominant factor in extending cycle life by testing each parameter separately.

Example 11

Effect of polyelectrolyte Wet coatings on silicon nanostructured Anode Performance

The goal of the wet coating is to form a conformal polyelectrolyte layer that will be selected as the polyelectrolyte layer from L iPAA (lithium salt of polyacrylic acid), NaCMC (sodium carboxymethylcellulose), and sodium alginate, which are artificial SEIs, a single ion conductor (lithium or sodium) that is soluble in water.

As shown in fig. 60, the L iPAA, NaCMC, or alginate coatings did not exhibit significant effects on anode cycling or capacitance.

Such coatings may be useful to stabilize the anodes in certain embodiments, although the anode capacitance is not affected.

Several polymer electrolytes in higher concentrations in aqueous solution, and several other polymers (e.g., PVP) dissolved in organic solvents, and tested as wet-modified solutions.

Example 12

Use of disilane as precursor gas for preparing silicon nanostructures

Several silicon nanostructures were prepared on a steel mesh according to a procedure such as described in example 1, except Silane (SiH)₄) The precursor gas is disilane (Si)₂H₆) And (4) substitution. Disilane is heavier and more reactive than silane, resulting in a reduction in the necessary temperature and growth time to prepare the plurality of anodes, and also gives the catalytic reaction of the gas on the stainless steel surface a preference over the thermal cracking reaction. This increases the efficiency of the overall growth process.

As shown in fig. 61A-63B, the morphology of the SiNSs grown with disilane was dependent on the several growth conditions.

These results show that the morphology (e.g., thinner, longer, and more uniform lines) and silicon loading obtained using disilane can be controlled based on a number of growth conditions (e.g., gas flow rates and/or temperatures) in a range of, for example, 380 to 460 degrees, pressures of 1 to 25 torr, and as low as 1sccm disilane gas flow.

Example 13

Effect of cathode type on silicon nanostructured anodes

To further evaluate the degradation mechanism and to compare the degradation in cells with different types of cathodes, 3-electrode cells were assembled in a coin cell comprising a silicon nanostructure (SiNS) anode and a NCA cathode or an L FP cathode.

As shown in fig. 64, cell degradation was associated with a rise in minimum voltage on the silicon-containing anode and a rise in the maximum voltage of the cathode (NCA) as determined using a 3-electrode cell versus cell capacity.

This result shows that the rise in the minimum voltage on the silicon anode is due to degradation of the silicon anode and reduction in capacitance due to several degradation mechanisms previously discussed, and that the maximum voltage of the cathode rises in the same manner as the minimum anode voltage, resulting in further degradation of the cathode and increased cell degradation.

As shown in fig. 65 and 66, a full cell with SiNS anode and L FP cathode deteriorated more rapidly than a full cell with SiNS anode and NCA cathode, although a L FP cathode is generally considered to be a more stable cathode.

To understand the causes of the different degradation rates of different cathodes, the several voltages of the several electrodes relative to the control were examined. In particular, the several terminal voltages of the anode are plotted against cycle number when the battery reaches its cutoff voltage upon charging or discharging.

As illustrated in fig. 67, in cells with L FP or NCA cathodes, the terminal voltages on the anode steadily increased over cycling, as they did on the cathodes, but the anode paired with NCA exhibited a voltage window of about 0.45 volts, the anode paired with L FP exhibited a 0.55 volt window, furthermore, the anode paired with NCA operated at a window that was on average about 0.1 volts lower than the window of the anode paired with L FP.

These results show that the silicon nanostructures paired with NCA are delithiated to a lesser extent, and thus less cracking occurs as a result of silicon shrinkage.

In view of these results, and the higher energy density of the NCA, several NCA cathodes were selected for additional studies.

Example 14

Scaled-up production of 1/3AAA full cells containing several silicon nanostructured anodes

Several industrial prototypes of full cells (cylindrical 1/3AAA cells) were prepared and subjected to 500 cycles. Several exemplary batteries are depicted in fig. 68.

As illustrated in fig. 69, while one of the three cells tested performed poor from the beginning, each of the other two cells was cycled 600 cycles and exhibited less than 50% loss of capacitance after 500 cycles of C/20 rate cycling, with an initial capacitance of about 3 milliamp-hours per square centimeter and 1200 milliamp-hours per gram of silicon.

The cell performance (calculated and tested) on cycling is summarized in table 11 below, and compared to a corresponding cell that differed only in the presence of a commercial graphite anode.

Table 11: performance parameters of 1/3AAA batteries with SiNS anodes or commercial graphite anodes

As shown in table 11, the calculated energy density of the battery was about 30% higher than the calculated commercial battery (of the same size) with a graphite anode.

Although the experimentally determined energy density is reduced by 6% due to stability problems (30% irreversible capacity), it is believed that this can be overcome by optimization.

In a full cell, the silicon electrical capacity of 3000 milliamp-hours per gram of silicon is not achieved because the voltage window and the cell capacity are limited by the cathode.

Cycling the cathode at higher voltages (to obtain deeper lithiation of the silicon) will result in faster degradation of the cell.

The cathode capacitance is determined by its maximum thickness, which is diffusion limited.

A second batch of anodes was assembled which was then used to assemble eleven 1/3AAA batteries, nine of which were tested under the same test conditions as the first batch (C/20 and C/60), and two of which were cycled at C/3 over a voltage range of 2.9 to 4 volts.

As shown in fig. 70 and 71, the stability of the cells of the number (second lot) at C/6 and C/20 is inferior to the stability of the cells of the first lot, although the initial capacity of the cells is higher: about 4 milliamps per square centimeter and 1800 milliamp-hours per gram of silicon.

The several experiments described use a C/3 rate as a baseline rate discharge capability test and provide exciting results.

As shown in fig. 71, the several cells still exhibited the same degradation rate as observed at C/6 (fig. 70) when the current density was doubled from C/6 to C/3, and the voltage range was widened by 0.1 volts.

These results show that the higher degradation rate in the second batch may be due to inaccurate balancing of the several cells or mechanical damage suffered by the several anodes upon assembly, which reduces the amount of active silicon available.

Example 15

Carbon coating layer modified silicon nano structure anode

The effect of several silicon nanostructured carbon coatings was further investigated. The coating of silicon nanostructures is thus effected outside the coating of the (opposite) side of the anode having a current collector, also at the side of the anode facing the cathode. Such a coating is therefore referred to herein as a "double" coating.

Single-walled carbon nanotubes are selected for their higher conductivity and lower weight percentage. The active material loading was 2.4 mg silicon/cm, tested under standard conditions.

As shown in fig. 72, double coating with single-walled carbon nanotubes did not significantly affect the cycling stability of the several anodes; double-coated with single-walled carbon nanotubes followed by thermal cracking at 750 ℃ for 1 hour in an argon-hydrogen atmosphere resulted in improved stability relative to the uncoated control.

As shown in fig. 73A and 73B, the silicon nanostructures were coated with a network of SWCNTs, showing that SWCNTs formed a conductive network around the silicon nanostructures.

Furthermore, as shown in fig. 73B, the several silicon nanostructures exhibited structural stability upon thermal cracking.

Without being bound by any particular theory, it is hypothesized that the thermal cracking forms stronger chemical bonds between the silicon or silicon oxide and the SWCNTs.

Taken together, the above results show that the infusion of several carbon nanotubes leads to percolation of the carbon and increases the conductivity of the anode. The expected result of the increase in conductivity is an increase in the energy capacity of the anode and a reduction in the degradation rate upon cycling. The reduction in degradation may be due to the silicon being grafted by the carbon nanotube network, thus reducing damage associated with volume changes; and/or due to an increase in the rate of capacity retention by reducing a loss of electrical conductivity between the plurality of silicon nanostructures (e.g., between the plurality of nanostructures and the network).

Since one goal of the carbon nanotube coating was to coat several commercial-sized electrodes, several samples were immersed in several different solvents, in several diluted nanotube suspensions of several different concentrations, water and water/ethanol (1:1) were tested as solvents in view of the importance of the suspensions ability to spread the carbon nanotubes and wet the silicon, in both cases, commercial TUBA LL suspension with 0.2% SWCNTs was diluted 6-fold with water or water/ethanol.

As shown in fig. 74, the water/ethanol suspension resulted in better cycle performance in half cells with a conventional 1-sided coating, while the samples coated with aqueous suspension collapsed after no more than 50 cycles.

As further shown therein, the advantage of the carbon nanotube coating is that the SEI precipitation at low current density is not mitigated by the carbon nanotube coating, which is reduced after 0.1 milliamp cycle to cycles 101-103.

Without being bound by any particular theory, it is believed that the SEI formed at low current density separates the silicon from the carbon nanotubes, thus offsetting the effect of the carbon nanotubes.

Full cells are also assembled using anodes coated with a carbon nanotube suspension as a stabilizer. The anodes are either artificially coated on both sides, coated and thermally cracked at 750 ℃, or immersed in a dilute suspension (once in an aqueous suspension and once in water/ethanol).

As shown in fig. 75, the best performance in several full cells relative to the results in half cells described above is due to coating the anodes on both sides without further treatment (neglecting capacitance peaks due to equipment problems), in the half cells results the thermal cracking of the anodes improved the performance, and the dilution of the nanotube suspension with ethanol improved the performance.

Taken together, these results show that coating the silicon nanostructures with carbon, such as carbon nanotubes, on the side of the anode facing the cathode can (e.g., separate from the enhancement of current collection achieved by carbon discussed above) enhance the performance of a battery comprising silicon nanostructure anodes.

Example 16

Mechanical properties of silicon nanostructured anodes

In the production of cylindrical lithium ion batteries, the several anodes are typically rolled into small diameters (about 2 mm) and stretched by the roll-to-roll production process. The ability to withstand such mechanical stress while preserving performance was therefore evaluated. Furthermore, it may be desirable to define the several mechanical properties of the anode in the acceptance test plan.

Several tests were used to evaluate the several mechanical properties as follows:

and (3) curling test: to examine the tolerance of the anode layers (stainless steel and silicon nanostructures) when rolled to several different diameters; the appearance of cracks and peeling on the surface of an electrode subjected to tensile stress was evaluated;

and (3) tensile test: to evaluate the ability to support a load (tensile strength-the maximum amount of pressure before failure, yield strength-the pressure at which plastic deformation begins); the specimen was grasped in a tensile tester and loaded with uniaxial pressure until failure;

peeling test: tape was used to evaluate the tearing of several silicon nanostructures from the stainless steel.

The tensile test was performed using a device (depicted in fig. 76) capable of testing in situ in an environmental scanning electron microscope (eSEM).

As shown in fig. 77 and in table 12 below, hydrofluoric acid treatment enhanced the ductility (higher degree of deformation at a given degree of pressure, and failure occurred at a higher degree of deformation) of the several stainless steel samples; and the deposition of several silicon nanostructures increases the brittleness.

Table 12 yield strength, tensile strength and elongation of 4 batches of several 316L Stainless Steel (SS) web samples coated on the web with or without hydrofluoric acid treatment and from silicon nanostructures (SiNS) at different loading values after hydrofluoric acid treatment.

As further shown in table 12, the number of samples with the highest silicon loading (lots 1 and 4) had the highest young's modulus and the number of samples with the lowest silicon loading (lot 3) had the lowest young's modulus, showing that silicon loading is related to young's modulus (and thus also stiffness). A similar relationship is exhibited between silicon loading and yield and tensile strength.

A comparison of the above results with the values reported in the 316L stainless steel literature (485 MPa ultimate tensile strength, 170MPa yield strength (0.2%)), shows that the mesh described herein is significantly more elastic and weaker as would be expected when comparing the mesh to bulk materials.

As shown in fig. 78A and 78B, when the steel fibers in a sample from one batch (fig. 78A, batch 1) broke, the silicon and silicide layers were not separated from the fibers, showing good adhesion consistent with the higher ultimate tensile strength shown in fig. 77; while in a sample from the other batch (fig. 78B, batch 2), the silicon and silicide layers were separated from the steel fibers at break, but remained intact, showing poor adhesion, higher ductility (the steel fibers were stretched thin under the silicon shell) and lower mechanical strength, also consistent with the results shown in fig. 77.

As shown in fig. 79A, there are two different levels of silicide (an inner layer and an intermediate layer) between the plurality of stainless steel fibers and the plurality of silicon nanostructures ("level 3"), as revealed by a lift-off test.

As shown in fig. 79B, the inner layer ("layer 1") is silicide-poor and the intermediate layer ("layer 2") is silicide-rich as determined by energy dispersive X-ray spectroscopy.

Several anode layers (several silicon nanostructures on stainless steel mesh) were rolled into several cylinders of different diameters and examined by scanning electron microscopy. The correlation between the number of defects (e.g., cracks and/or peelings) and diameters observed is determined.

Several crimped and uncrimped anodes were electrochemically characterized with respect to lithium in order to evaluate the effect of crimping on anode performance. Several anodes from 3 batches were compared.

As shown in fig. 80A-80D, lot 1 (as discussed above, e.g., with respect to fig. 80A-80B) exhibited good adhesion of silicon to several steel fibers, and also exhibited the lowest capacitance reduction after crimping. As further demonstrated therein, batch 2, which exhibited the highest capacitance reduction (and poor silicon adhesion) after curling, also exhibited a reduction in the standard deviation thereafter; while batches 1 and 3 exhibited an increase in standard deviation.

These results show that the strong silicon attachment is associated with resistance to curling.

Example 17

Combination of silicon nanostructures and solid electrolyte

To develop a Solid Polymer Electrolyte (SPE), a mixture of polyethylene oxide (PEO) and polyethylene glycol (PEG) was combined with a lithium salt (L iTFSI) and ceramic fillers, which were used to enhance the ionic conductivity of the SPE (L iTFSI).

A mixture of PEO (n ═ 20) and PEG (n ═ 2000) was dissolved in acetonitrile in a glove box for 12 hours. The ceramic filler (Al)₂O₃Powder, (volume to volume ratio)) and the salt (L iTFSI, mole ratio to PEO 1:20) were then added, and the mixture was mixed for an additional 12 hours a portion of the prepared solution was molded in a teflon template and dried to be used as a separator membrane a number of anodes with 2 mg of silicon per square centimeter were then coated with 70 microliters of the mixture and dried a number of anodes and a number of separator membranes were dried in the glove box, followed by overnight at 65 degrees in vacuo.

FIGS. 81A and 81B show anodes each coated with an SPE with (FIG. 81B) or without (FIG. 81A) alumina. The corners of the anode were exposed for comparison.

As shown in fig. 81A and 81B, several silicon nanostructures were not visible in the SPE-coated portion, showing the thorough coating of the SPE.

Similarly, no more than 1% by weight of silicon was detected by EDX-ray spectroscopy, further confirming complete coverage of the SPE.

A plurality of cells are constructed with the plurality of coated anodes, the plurality of prepared separation films, and a plurality of lithium electrodes without any liquid electrolyte. The several cells are then cycled at 110 degrees. The first cycle of an exemplary battery with SPE is presented in fig. 82.

A second SPE uses fumed silica (0.04% volume to volume) instead of Al₂O₃Thus, it is constructed. Several cells were prepared using this SPE, and several cycles were described above.

As shown in fig. 83, the alumina-containing SPEs and the silica-containing SPEs each exhibited sufficient ionic conductivity to allow the SiNS to be lithiated and delithiated.

To improve performance, several different lithium salts (e.g., L iFSi), several different ceramic fillers, and several different PEO: PEG ratios were tested using a process such as that described above.

A flexible microbattery is then constructed using an anode (as described herein) containing silicon nanostructures, an SPE (as described herein) and a layer of cathode active material (e.g., L FP).

While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present application. If paragraph headings are used, they should not be considered as necessarily limiting.

While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present application. If paragraph headings are used, they should not be considered as necessarily limiting.