阅读说明：本技术 用于锂离子电池阳极的组成调整的硅涂层 (Silicon coating for composition adjustment of lithium ion battery anodes ) 是由 C·于 王维洁 C·I·斯特凡 J·柏恩斯坦 D·西奥 于 2020-02-21 设计创作，主要内容包括：本文提供了用于锂离子电池电极的纳米结构和制造方法。在一些实施方案中,提供了涂覆有硅基涂层的纳米结构模版。所述硅涂层可以包括非保形的较多孔的富硅SiE-(x)层和在所述非保形的较多孔层上的保形的较致密的SiE-(x)层。在一些实施方案中,使用两种不同的沉积工艺：PECVD层以沉积非保形的富硅SiE-(x)层,和热CVD工艺以沉积保形的层。富硅SiE-(x)材料可防止硅晶畴生长,限制宏观膨胀,增加锂扩散速率并显著提高锂离子电池充电和放电循环期间的电池寿命。(Provided herein are nanostructures and methods of manufacture for electrodes of lithium ion batteries. In some embodiments, there is providedA nanostructured template coated with a silicon-based coating is provided. The silicon coating may comprise non-conformal, more porous silicon-rich SiE x A layer and a conformal denser SiE on the non-conformal more porous layer x And (3) a layer. In some embodiments, two different deposition processes are used: PECVD layer to deposit non-conformal silicon-rich SiE x A layer, and a thermal CVD process to deposit a conformal layer. Silicon-rich SiE x The material can prevent silicon crystalline domain growth, limit macroscopic expansion, increase lithium diffusion rate and significantly improve battery life during charge and discharge cycles of a lithium ion battery.)

1. An anode for a lithium battery, comprising:

a substrate;

an array of nanowires rooted at the substrate, each nanowire having a surface;

a first layer coating most or all of the surface of the nanowire, the layer comprising SiE_xA material; and

a second layer over the first layer, any exposed surfaces of the nanowires, and the substrate, the second layer comprising silicon or SiF_yA material;

wherein x is greater than zero and less than 1;

wherein y is greater than zero and less than 1; and is

Wherein E and F are each independently selected from the group consisting of nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof.

2. The anode of claim 1, wherein x is between 0.01 and 0.5.

3. The anode of claim 1, wherein x is between 0.01 and 0.3.

4. The anode of claim 1, wherein x is between 0.01 and 0.1.

5. The anode of claim 1, wherein the concentration profile of E varies across the thickness of the first layer and/or the concentration profile of F varies across the thickness of the second layer.

6. The anode of claim 1, wherein the density of the second layer is greater than the density of the first layer.

7. The anode of claim 1, wherein the first layer has an average density of less than 2.1g/cm³。

8. The anode of claim 1, whichThe average density of the second layer is more than 2.0g/cm³。

9. The anode of claim 1, wherein the density of the first layer varies throughout the first layer.

10. The anode of claim 1, wherein the density of the second layer varies throughout the second layer.

11. The anode of claim 1, wherein the first layer is non-conformal to the nanowire stencil.

12. The anode of claim 1, wherein the second layer is conformal to the first layer.

13. The anode of claim 1, further comprising a third layer over the second layer, the third layer comprising no silicon.

14. The anode of claim 1, wherein the nanowire stencil comprises silicide nanowires.

15. The anode of claim 1, wherein the thickness of the first layer at its largest diameter is about 5 to 20 microns.

16. The anode of claim 1, wherein the second layer has a thickness of 5 to 500 nanometers.

17. The anode of claim 1, wherein the second layer has a thickness of 5 to 100 nanometers.

18. A lithium battery, comprising:

the anode of claim 1;

a cathode containing lithium;

an electrolyte in ionic communication with both the anode and the cathode.

19. A method of manufacturing an anode for a lithium battery, comprising the steps of:

providing a substrate;

growing nanowires from a substrate, each nanowire having a surface;

depositing a first layer comprising a first silicon-rich SiE using a PECVD method to coat most or all of the surface of the nanowires_x；

Depositing a second layer comprising a second silicon-rich SiE over the first layer, any exposed surfaces of the nanowires, and the substrate using a thermal CVD process_x。

20. The method according to claim 19, wherein the PECVD process is an expanding thermal plasma process.

21. The method of claim 19, wherein the nanowires are silicide nanowires.

22. The method of claim 19, wherein a chamber pressure during the thermal CVD method is less than about 2 torr.

Technical Field

The present invention relates generally to nanostructures, and more particularly to multilayer silicon nanowire structures that can be used in battery anodes.

Much work has been done to find ways to use silicon in lithium battery anodes. Silicon is promising because its lithium capacity is ten times that of the graphite currently used. Unfortunately, however, silicon expands 400% upon absorbing so much lithium, which typically results in silicon breakage and short battery life.

Background

SUMMARY

One aspect of the present disclosure relates to an anode for a lithium battery, comprising: a substrate; an array of nanowires rooted at the substrate, each nanowire having a surface; a first layer coating most or all of the surface of the nanowire, the layer comprising SiE_xA material; and in the first layer, the nanowiresA second layer over any exposed surface and substrate, the second layer comprising silicon or SiF_yA material; wherein x is greater than zero and less than 1; wherein y is greater than zero and less than 1; and wherein E and F are each independently selected from the group consisting of nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof. In some embodiments, wherein x is between 0.01 and 0.5, between 0.01 and 0.3, or between 0.01 and 0.1. In some embodiments, wherein y is between 0.01 and 0.5, between 0.01 and 0.3, or between 0.01 and 0.1. Lower values of x and/or y may be used in some embodiments.

In some embodiments, the concentration profile of E varies across the thickness of the first layer and/or the concentration profile of F varies across the thickness of the second layer. In some embodiments, the density of the second layer is greater than the density of the first layer. In some embodiments, the average density of the first layer is less than 2.1g/cm³. In some embodiments, the average density of the second layer is greater than 2.0g/cm³. In some embodiments, the density of the first layer varies throughout the first layer. In some embodiments, the density of the second layer varies throughout the second layer. In some implementations, the first layer is non-conformal to the nanowire template (template). In some embodiments, the second layer is conformal (conformal) to the first layer. In some embodiments, the anode further comprises a third layer over the second layer, the third layer comprising no silicon. In some embodiments, the nanowire template comprises silicide nanowires. In some embodiments, the thickness of the first layer at its largest diameter is about 5 to 20 microns. In some embodiments, the second layer has a thickness of 5 to 500 nanometers. In some embodiments, the second layer has a thickness of 5 to 100 nanometers.

Another aspect of the present disclosure relates to a lithium battery, including: an anode as described herein; a lithium-containing cathode; and an electrolyte in ionic communication with both the anode and the cathode.

Another aspect of the present disclosure relates to a method of manufacturing an anode for a lithium battery, comprising: providing a substrate; growing nanowires from a substrate, each nanowire having a surface; deposition of a first layer to coat using PECVD methodMost or all of the surface of the nanowire, the first layer comprising a first silicon-rich SiE_x(ii) a Depositing a second layer comprising a second silicon-rich SiE over the first layer, any exposed surfaces of the nanowires, and the substrate using a thermal CVD process_x。

In some embodiments, the PECVD process is an expanding thermal plasma process. In some embodiments, the nanowires are silicide nanowires. In some embodiments, the chamber pressure during the thermal CVD process is less than about 2 torr.

These and other aspects of the disclosure are further described below with reference to the drawings.

Brief Description of Drawings

The foregoing aspects and others will become readily apparent to those skilled in the art from the following description of the illustrative embodiments, when read in connection with the accompanying drawings.

Figure 1 is a schematic illustration of a nanowire on which a layer of silicon-based material has been deposited using PECVD (plasma enhanced chemical vapor deposition).

Figure 2 is a schematic illustration of nanowires on which a first silicon-based material layer has been deposited using PECVD and then a second silicon-based material layer using thermal CVD, in accordance with one embodiment of the present invention.

Figure 3 shows a schematic of a non-conformal silicon coating on a template nanowire.

Fig. 4A is a schematic of a plan view of a partially assembled electrochemical cell (cell) using electrodes described herein, according to certain embodiments.

Fig. 4B is a schematic of a cross-sectional view of an electrode stack of an electrochemical cell using partial assembly of electrodes described herein, according to certain embodiments.

Fig. 5A-5C are schematic diagrams of various views of an electrode wound together with two sheets of separator to form a cell, according to certain embodiments.

Fig. 6A and 6B are schematic diagrams of cross-sectional and perspective views of stacked cells including a plurality of cells, according to certain embodiments.

Fig. 7 is a schematic of a cross-sectional view of a wound cylindrical cell according to certain embodiments.

FIG. 8 is a graph showing the relationship with SiE_xCapacity retention of silicon anodes versus cycle number for anodes.

Detailed Description

Certain embodiments are illustrated in the context of silicon deposition onto silicide nanowires to form anode structures for lithium battery cells. However, the skilled person will readily appreciate that the materials and methods disclosed herein will have application in many other scenarios where it is useful to adjust the deposition to produce a layer or particle with specific properties. For example, various embodiments are described herein with reference to nanowires. However, it should be understood that, unless otherwise indicated, nanowires mentioned herein include other types of nanostructures described in U.S. patent No. US 8,257,866 (incorporated herein by reference), such as nanotubes, nanoparticles, nanospheres, nanorods, nanowhiskers, and the like.

Generally, the term "nanostructure" refers to a structure having at least one dimension less than about 1 micron. In some embodiments, the structure has at least one dimension less than 500 nanometers or 100 nanometers. The dimension may be the diameter of the nanostructure (e.g., silicide-templated nanowire) or the final coated structure. However, any overall dimensions (length and diameter) of the final coated structure need not be on the order of nanometers. For example, the final structure may include a layer having a thickness of about 10 microns at its largest diameter and coated over a template having a diameter of about 100 nanometers and a length of 20 microns. While this overall structure has a maximum diameter of about 10.1 microns and a length of 20 microns, it may be generally referred to as a "nanostructure" due to the size of the template. In a particular embodiment, the term "nanowire" refers to a structure having a nanoscale shell located over an elongated template structure.

In various embodiments, the nanowires (as the particular case of nanostructures) have an aspect ratio of greater than one, at least about two, or at least about four. In various embodiments, the nanowires have an aspect ratio of at least 10, at least 100, or at least 500. The nanowires may be connected to other electrode components (e.g., conductive substrates, other active material structures, or conductive additives). For example, the nanowires may be rooted to the substrate such that one end of the nanowires is in contact with the substrate.

The term "silicon-based material" refers to a material that is silicon alone or silicon-rich SiE_xWherein E is any one or more elements that can form an intermetallic or alloy compound with silicon, such as nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof. Silicon comprises at least 50 atomic percent of the silicon-based material.

More than one element E may be mixed with the silicon. In this case, x is the sum of the values of the elements (e.g., SiE 1)_x1E2_x2(ii) a x ═ x1+ x2, and the like). In various embodiments, the value of x is less than 1, between 0.001 and 0.5, between 0.005 and 0.3; between 0.01 and 0.3; between 0.03 and 3; between 0.01 and 0.1; and between 0.01 and 0.05.

As will be understood below, in some embodiments, the nanostructure includes two different silicon-rich sies_xLayers, wherein E and/or x are the same and/or different for each layer. In this case, the second SiE_xThe material is also alternatively referred to as SiF_y. It will thus be understood that any description herein of E and x may apply to F and y, respectively. For example, F is any one or more elements that can form an intermetallic or alloy compound with silicon, such as nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof, and y can be any value independent of that stated for x, independent of the particular value of x.

In some embodiments, the nanostructures described herein may be fabricated by first growing a nanowire template structure on a substrate. In many embodiments, the nanowire-stencil structure is made of a conductive material. Examples of conductive materials that may be used to form the nanowire-template structure include metals and metal silicides. In some embodiments, the conductive template may include an oxide. And then coating the nanowire template structure with one or more layers of silicon-based electrode active materials. Thermal CVD (chemical vapor deposition), HWCVD (hot wire CVD), PECVD (plasma enhanced chemical vapor deposition) and/or evaporation (with or without thermal or laser assistance) may be used to deposit the silicon-based electrode active material layer.

When a silicon-based electrode active material layer is deposited onto a nanowire template, various deposition processes produce different profiles. For example, thermal CVD produces conformal amorphous silicon-based electrode active material coatings. HWCVD (also known as catalytic CVD) produces a high-density, non-conformal coating of amorphous silicon-based electrode active material that is thicker at or near the nanowire tips and thinner at the nanowire roots near the substrate. PECVD also produces a non-conformal amorphous silicon-based electrode active material coating that is thicker at the nanowire ends and thinner near the nanowire roots of the substrate. PECVD coatings have a low density and many small voids.

Silicon-rich SiE_xIncluding silicon compounds where x is less than 1 or any range contained therein.

In some embodiments of the invention, silicon-rich SiE is deposited using PECVD in a reaction chamber_xAnd depositing onto the nanowire template. Examples of process gases that may be used for such deposition include, but are not limited to, Silane (SiH) diluted with hydrogen or argon and mixed with an elemental E precursor₄). These gases become reactive species and produce silicon-rich SiE on the surface of the nanowire template under AC/DC plasma_xAnd (4) coating. The amount of element E and the value of x can be controlled by adjusting the ratio of the process gases. The reaction chamber temperature may be in the range of 200 ℃ to 600 ℃ or 300 ℃ to 500 ℃. The plasma power may be in the range of 500W-1000W, depending on the chamber size. The pressure in the process chamber may be in the range of 1 to 200 mTorr.

Initially, PECVD may deposit an extremely thin silicon-based electrode active material layer having a thickness of less than 1 micron or between 0.1 and 0.4 microns onto the nanowire template, along all surfaces, including on the substrate and at the root of the nanowires adjacent to the substrate. However, as deposition continues, more and more silicon-based electrode active material accumulates at or near the tips of the nanowires in the nanowire template, thereby shadowing areas of the substrate. The result is that an extremely thin layer of silicon-based electrode active material on the substrate may or may not be continuous, depending on the density and uniformity of the nanowires along the surface of the substrate.

FIG. 1 is a schematic illustration of nanowires on which silicon-rich SiE has been deposited using PECVD_xAnd (3) a layer. The nanowire template 110 is rooted to the substrate 120. Silicon-based electrode active material (SiE)_x) A layer 140 is deposited onto the nanowire template 110. Note that SiE_xThe layer 140 is thickest at or near the tips of the nanowires of the nanowire template 110 and tapers down until there is little or no SiE at the roots of the nanowires_x。SiE_xLayer 140 is a non-conformal coating, i.e., it does not conform to the shape in which it is deposited. FIG. 1 shows that substrate 120 is also substantially free of SiE_xExamples of (3). In some arrangements, there is a thin continuous SiE on the substrate 120_xAnd (3) a layer. In some arrangements, there is a thin discontinuous SiE on the substrate 120_xAnd (3) a layer. In some arrangements, some or all of the nanowire regions (roots of nanowires) adjacent to the substrate have a thin (0.1-0.4 micron) SiE_xAnd (4) coating.

Fig. 2 is a schematic diagram of a nanowire template on which two silicon-based electrode active material layers have been deposited according to an embodiment. Two different deposition methods were used to provide an optimal coating of silicon-based electrode active material. The nanowire template 210 is rooted to a substrate 220. Already utilizing PECVD will contain silicon-rich SiE_xIs deposited onto the nanowire template 210, onto the first silicon-based electrode active material layer 240. First SiE_xLayer 240 has the following profile: thickest at or near the tips of the nanowires of the nanowire template 110 and tapered until there is little or no SiE at the roots of the nanowires_x. In some embodiments, the first silicon layer 240 has a thickness of 0.5 to 50 microns, 0.5 to 20 microns, or 10 to 20 microns at or near the tip of the nanowire. Has been subjected to thermal CVD to contain silicon-rich SiE_xIs deposited onto the nanowire first layer 240, a second silicon-based electrode active material layer 230. (As mentioned above, the kind and/or amount of the element "E" may be the same as or different from those in the first silicon-based electrode active material layer 240; this material may be referred to as silicon-rich SiF)_ySo as to be brought into contact with the silicon-rich SiE in layer 240_xMaterials are distinguished). In some embodiments, the second SiE_xLayer 230 has a thickness of 5 to 500nm,A thickness of 10 to 200nm or 10 to 90 nm. Second SiE_xLayer 230 is a conformal coating, i.e., it conforms to the shape deposited. Second SiE_xThe layer 230 conforms to the surfaces of the first silicon-based electrode active material layer 240, the substrate 220, and any exposed portions of the nanowire stencil 210. Second SiE_xLayer 230 has an approximately uniform thickness. The resulting structure has much more silicon-based electrode active material at or near the tip of the nanowire than at the root end (due to the non-conformal nature of the first silicon-based electrode active material layer 240).

First SiE_xLayer 240 has a surface roughness and porosity. Can be adjusted to have a first SiE_xSecond SiE of smoother surface of layer 240_xThickness of layer 230 to mitigate first SiE_xThe surface roughness of layer 240. Smooth SiE_xThe second layer 230 reduces the total surface area of the coated nanowires. The reduced surface area means that there are fewer surfaces on which an SEI (solid electrolyte interface) layer can be formed when the battery is cycled. Less SEI means less lithium consumption, leaving more lithium available for cycling. In some arrangements, following the first SiE_xThe surface roughness of the layer is increased, adding a second SiE_xThe thickness of layer 230 is useful. In some arrangements, the second SiE_xThe thickness of layer 230 is between 5nm and 500nm, between 10nm and 200nm, or between 10nm and 90 nm.

The structure described herein has many advantages. In some embodiments, SiE near the nanowire tip_xMore material than at the root, but SiE is still present at the root_xA thin layer of material. Having such a thin silicon layer at the roots strengthens the mechanical connection between the nanowires of the nanowire template and the substrate, helping to ensure that the nanowires do not separate from the substrate during cycling.

Another advantage is PECVD SiE_xLayer as good as thermal CVD SiE_xThe layer is dense. SiE fabricated using PECVD_xThe layer may contain a large number of voids and pores. These defects greatly help to provide a space into which the silicon-based electrode active material may expand upon absorption of lithium during charging of the battery cell.

In some clothsIn particular, even small amounts of the additional element E support and buffer the swelling of the silicon-based electrode active material when it absorbs lithium ions, which reduces cracking of the silicon-based electrode active material and improves reversibility and cycle life of the battery cell. Element E also significantly improves lithium ion transport through the silicon-based electrode active material. In some embodiments, element E combines with silicon to create a structure that disperses nanometer-sized silicon domains in a material matrix. Since the silicon grains are physically separated by the structure, the silicon grains or domains retain their nano-scale dimensions over a greater number of cycles. In addition, unlike SiO₂(which upon lithiation reacts with lithium to irreversibly form lithium silicate compounds and lead to extremely high first cycle losses and cell capacity degradation), silicon-rich sies_xThe material does not cause high first cycle loss and cell capacity degradation. In some embodiments, the E level in the silicon rich layer is at least 0.005, 0.01, 0.05, 0.07, 0.1, or 0.15.

In some embodiments, the E level in the silicon rich layer is maintained at a level that allows a sufficient amount of silicon active material to be available. In some embodiments, sies in one or both layers_xE level x in (a) does not exceed 0.3, 0.2, 0.15, 0.1, 0.07, 0.05, 0.03 or 0.01. In some embodiments, only one of the two layers comprises SiE_xA layer and the other layer is pure silicon or comprises another element.

In some embodiments, the first SiE is deposited using PECVD_xThe silicon layer is amorphous and has less than 2.25g/cm³Less than 2.10g/cm³Or less than 1.70g/cm³And may include many small voids. Second SiE deposited using thermal CVD_xThe layer is amorphous and has a thickness of more than 2.0g/cm³Or greater than 2.25g/cm³The average density of (a). In some embodiments, the density of two layers may be described in terms of the difference in density between the layers, rather than their absolute density. In some embodiments, the second SiE_xThe average density of the layer is at least 0.05g/cm greater than the average density of the first layer³At least 0.1g/cm³At least 0.2g/cm³At least 0.3g/cm³. One of ordinary skill in the art will appreciate that the density of the amorphous silicon-based electrode active material is less than the density of the same material having a crystalline or polycrystalline morphology.

According to various embodiments, the nanostructures described herein may be characterized as being in a first SiE_xHaving a second SiE over the layer_xA layer, the second layer having a higher density than the first layer. Such structures may be used to form anodes in lithium battery cells. In some embodiments, the first SiE_xThe layer is amorphous with a low density and may also contain some voids, all of which serve to provide space when the SiE is cycled during a battery cycle_xWhich can expand into the space upon absorption of lithium ions. This is an advantage over crystalline or polycrystalline silicon-based electrode active materials, which have a higher density and may undergo stress cracking when they absorb lithium ions. Furthermore, lithium ions diffuse more readily through amorphous materials than through crystalline or polysilicon-based electrode active materials. Therefore, the density of each layer can be adjusted according to the requirements of silicon cycle capacity, power or cycle magnification and nanowire template density.

In certain embodiments, an anode for a lithium battery cell is formed from a nanowire template structure rooted on a conductive substrate that may serve as a current collector for the anode. Examples of conductive substrates include copper, metal oxide coated copper, stainless steel, titanium, aluminum, nickel, chromium, tungsten, other metals, metal silicides and other conductive metal compounds, carbon fiber, graphite, graphene, carbon mesh, conductive polymers, doped silicon, or combinations thereof, including multilayer structures. The substrate may be formed as a foil, film, mesh, foam, laminate, wire, tube, particle, multilayer structure, or any other suitable configuration. In certain embodiments, the substrate is a metal foil having a thickness between about 1 micron and 50 microns, or more specifically between about 5 microns and 30 microns.

The nanowires may be physically and conductively attached to the substrate. Physical attachment may not be merely a simple mechanical contact, which may result, for example, from coating an adhesive with discrete nanostructures onto a substrate. In some embodiments, the physical attachment is due to the fusion of the nanostructure with the substrate or to the direct deposition of the nanostructure or portions of the nanostructure on the substrate, e.g., using CVD techniques or using vapor-liquid-solid CVD growth. In some embodiments, the physical attachment is due to impact penetration of the nanowires onto the substrate. In various embodiments, the physical attachment includes a metallurgical bond, such as forming an alloy of two bonding materials (e.g., a silicide). In other embodiments, nanowires are grown from the substrate using other nanowire growth techniques that produce structures having similar shapes and dimensions.

In many embodiments, the nanowires of the nanowire template comprise a metal or metal silicide and are electronically conductive. In some embodiments, the nanowires comprise one or more oxides. The conductive stencil may be used to provide an electron transport path from the silicon-based electrode active material to a substrate or current collector. In various embodiments, the nanowires in the nanowire template have a diameter between 10 nanometers and 100 nanometers and a length between 10 micrometers and 100 micrometers. Anodes for lithium battery cells comprising nanowire templates are further described in U.S. patent No. US 7,816,031, which is incorporated herein by reference.

In some embodiments, the silicon-based material nanostructures have substantially circular symmetry. It should be noted that nanowire arrays having substantially circular symmetry include arrays in which asymmetry may be introduced due to the proximity of two nanowires that are sufficiently close that their coatings abut each other.

FIG. 3 shows a schematic cross-sectional view showing two SiEs that have been coated_xNanowire of a layer, said SiE_xThe layers are deposited using different deposition methods, as described herein. The dimensions d1, d2, and h are labeled: d1 is the maximum diameter of the coating, d2 is the bottom diameter of the coating, and h is the height of the coated nanowire. In some embodiments, the non-conformal coating (either a porous non-conformal coating alone, or a porous non-conformal coating conformally coated with a dense coating) is characterized by the following ratio: 1/2 to 1/9 d1/h, 1/400 to 1/70 d2/h, and 50:a d1/d2 ratio of 1 to 1.5: 1. In various embodiments, d1 is between 4 and 15 microns or between 4 and 12 microns; d2 is between 0.2 and 2 microns; and h is between 20 and 50 microns or between 30 and 40 microns.

In one example, nanowires having a diameter of about 10 to 50nm and a length of about 10 to 25 microns are coated with silicon-rich silicon nitride such that after coating the diameter at the root of the nanostructure is 100 to 400nm, the maximum diameter is 2to 20 microns, and the total anode height is 20 to 50 microns.

In some embodiments, a non-conformal layer of silicon-based electrode active material deposited by PECVD may include a hydrogen content of at least 10%. In some embodiments, a conformal layer of silicon-based electrode active material deposited by thermal CVD may include a hydrogen content of no more than 7% or no more than 5%.

In some embodiments, non-conformal sies are deposited by_xLayer (b): evaporation or Physical Vapor Deposition (PVD) or Hot Wire Chemical Vapor Deposition (HWCVD) instead of or in addition to PECVD.

In the PECVD deposition process, plasma may be generated in a chamber in which a substrate is disposed, or may be generated upstream of the chamber and supplied into the chamber. Any type of plasma may be used, including capacitively coupled plasmas, inductively coupled plasmas, and conductively coupled plasmas. Any plasma source may be used, including direct current, alternating current, radio frequency, and microwave sources.

PECVD process conditions may vary depending on the particular process and tool used. A fairly wide temperature range, for example 180 ℃ to 600 ℃, may be used. The pressure of the plasma process is typically low, for example, ranging from 1mTorr to 400Torr, or 10mTorr to 100mTorr, depending on the process.

In some embodiments, the PECVD process used to form the new structures described herein is an expanding thermal plasma chemical vapor deposition (ETP-CVD) process. In such a process, a plasma-generating gas is passed through a direct current arc plasma generator to form a plasma, in an adjoining vacuum chamber with a web (web) comprising a nanowire template or a web thereofIt is a substrate. A silicon-based source gas is injected into the plasma to generate radicals. The plasma is expanded through a diverging nozzle and injected into the vacuum chamber and toward the substrate, forming amorphous SiE on the nanowire template_xThe non-conformal layer of (a). Examples of plasma generating gases include, but are not limited to, argon (Ar) and ammonia (NH)₃) And nitrogen (N)₂). In some embodiments, ionizing argon and NH in the plasma₃/N₂The species collide with silane molecules to form free radical species of silicon source, resulting in SiE_xDeposited on the nanowire template. An example range of voltage and current for the dc plasma source is 60 to 80 volts or 50 to 70 amps.

In some embodiments, Atomic Layer Deposition (ALD) is used in place of or in addition to thermal CVD to deposit a conformal dense silicon layer. Any suitable thermal CVD process may be used, such as low pressure CVD (lpcvd). The temperature can be as high as the thermal budget allows, provided the metal substrate is carefully treated to ensure that no metal silicide forms around the nanowire-substrate interface. In some embodiments, the chamber pressure during the thermal CVD process is kept low, e.g., 100mTorr to 2Torr, to prevent vapor phase reactions and non-conformal deposition. Higher pressures, such as above 2Torr or 500Torr, can result in non-conformal deposition.

Any suitable silicon source in combination with an elemental E source may be used for the non-conformal and conformal SiEs_x. Examples of silicon sources include, but are not limited to, Silane (SiH)₄) Dichlorosilane (H)₂SiCl₂) Monochlorosilane (H)₃SiCl), trichlorosilane (HSiCl)₃) Silicon tetrachloride (SiCl)₄). Examples of nitrogen sources include, but are not limited to, ammonia (NH)₃) And nitrogen (N)₂) To form a silicon-rich silicon nitride layer. Can be prepared from gaseous precursors (CH)₄、GeH₄、B₂H₆Etc.) or vaporized liquid precursor, to introduce other elements into the plasma, as is the case with organometallic precursors.

Additional description of depositing layers of active materials with controlled density can be found in U.S. patent application No. 13/277,821, which is incorporated herein by reference.

Further, in some embodiments, the non-Si dominated layer may be the outermost shell of the nanostructure. Examples of layers include metal oxides such as alumina, titania, cobalt oxide, and zirconia, metal nitrides, and silicon nitride or carbon-based layers. In some embodiments, a thin layer of any of these may be deposited in addition to or in place of the dense Si layer described above.

In some embodiments, SiE_xThe outer layer may be chemically modified by gas or solution phase treatment/exposure at the surface to add or remove elements and produce a 1-10nm thick layer of different chemical composition, such as an oxide or halide.

According to various embodiments, the first SiE_xLayer and second SiE_xThe layers each have a uniform density. In some embodiments, the deposition conditions may be adjusted during deposition to provide a density gradient in one or both layers. For example, one or both layers may become more dense toward the exterior of the layer. In such embodiments, the average density of the layers may be used to characterize the density of the layers.

According to various embodiments, the first SiE_xLayer and second SiE_xThe layers each have a uniform concentration of the E element. SiE_xRelating to the total amount of Si and E in the layer. However, in some embodiments, the deposition conditions may be adjusted during deposition to provide a concentration gradient in one or both layers. In one example, the E concentration of one or both layers may increase toward the outside of the layer. In another example, one or both layers may have a decrease in E concentration towards the outside of the layer. In yet another example, one or both layers may have an E concentration that varies in a manner that not only increases but also decreases throughout the layer. In such embodiments, the average E concentration of the layer may be used to characterize the E concentration of the layer. It can be said that the concentration profile of E varies across the layer thickness. The following concentration profiles were included: the concentration profile comprises one or more flat (uniformly) distributed areas and one or more increased and/or decreased areas.

Assembly

Fig. 4A is a plan view of a partially assembled electrochemical cell using electrodes described herein, according to certain embodiments. The cell has a positive electrode active layer 402 shown covering a majority of a positive current collector 403. The cell also has a negative electrode active layer 404, shown covering a majority of a negative current collector 405. Separator 406 is between positive electrode active layer 402 and negative electrode active layer 404.

In one embodiment, the negative electrode active layer 404 is slightly larger than the positive electrode active layer 402 to ensure that the active material of the negative electrode active layer 404 captures lithium ions released from the positive electrode active layer 402. In one embodiment, the negative electrode active layer 404 extends at least about 0.25 mm to 7 mm beyond the positive electrode active layer 402 in one or more directions. In a more specific embodiment, the negative electrode active layer 404 extends about 1 mm to 2 mm beyond the positive electrode active layer 402 in one or more directions. In certain embodiments, the edge of separator 406 extends beyond at least the outer edge of the negative electrode active layer 404 to provide complete electronic insulation of the negative electrode from other battery components.

Fig. 4B is a cross-sectional view of an electrode stack 400 of a partially assembled electrochemical cell using electrodes described herein, according to certain embodiments. There is a positive electrode current collector 403 having a positive electrode active layer 402a on one side and a positive electrode active layer 402b on the opposite side. There is a negative current collector 405 having a negative electrode active layer 404a on one side and a negative electrode active layer 404b on the opposite side. A separator 406a is present between the positive electrode active layer 402a and the negative electrode active layer 404 a. The separator sheets 406a and 406b serve to maintain mechanical separation between the positive electrode active layer 402a and the negative electrode active layer 404a and serve as a sponge to absorb a liquid electrolyte (not shown) to be added later. The ends of the current collectors 403, 405 that are free of active material may be used to connect to appropriate terminals (not shown) of the cell.

The electrode layers 402a, 404a, current collectors 403, 405, and separator 406a may be considered to collectively form one electrochemical cell unit. The total stack 400 shown in fig. 4B comprises electrode layers 402B, 404B and an additional separator 406B. The current collectors 403, 405 may be shared between adjacent cells. When such a stacked body is repeated, the result is a cell or battery having a larger capacity than a single cell unit.

Another way to manufacture batteries or cells with large capacity is to manufacture one very large cell unit and wind it on itself to manufacture a multiple stack. The cross-sectional schematic in fig. 5A shows how a long and narrow electrode is wound together with two sheets of separator to form a battery or cell, sometimes referred to as a jelly roll 500. The jelly roll is shaped and sized to fit the internal dimensions of a curved, generally cylindrical housing 502. The jelly roll 500 has a positive electrode 506 and a negative electrode 504. The white space between the electrodes is the separator sheet. The jelly roll may be inserted into the housing 502. In some embodiments, the jelly roll 500 may have a mandrel 508 in the center that establishes the initial roll diameter and prevents the inner roll from occupying the central axial region. The mandrel 508 may be made of an electrically conductive material, and in some embodiments, it may be part of a cell terminal. Fig. 5B shows a perspective view of the jelly roll 500 with the positive and negative tabs 512 and 514 protruding from the positive and negative current collectors (not shown), respectively. The tab (tab) may be welded to the current collector.

The length and width of the electrode depend on the overall dimensions of the cell and the thickness of the active layer and current collector. For example, a conventional 18650 type cell having a diameter of 18mm and a length of 85mm may have an electrode that is about 300 to 1000mm long. Shorter electrodes corresponding to lower rate and/or higher capacity applications are thicker and have less wrap-around.

The cylindrical design may be useful for some lithium ion cells, particularly when the electrodes may expand during cycling and thus exert pressure on the casing. It is useful to use a cylindrical casing that is as thin as possible while still being able to maintain sufficient pressure on the cell (with a good safety margin). Prismatic (flat) cells may be similarly wound, but their casings may be flexible, so they can be bent along the longer sides to accommodate internal pressure. Furthermore, the pressure within different portions of the cell may not be the same and corners of the prismatic cell may be left empty. Empty pockets (empty pockets) can be avoided in the lithium ion battery, as the electrodes tend to be pushed unevenly into these pockets during electrode expansion. In addition, electrolyte may accumulate in empty pocket cavities and leave dry regions between the electrodes, thereby negatively affecting lithium ion transport between the electrodes. However, for certain applications, such as those dictated by a rectangular form factor, prismatic cells are suitable. In some embodiments, prismatic cells employ stacks of rectangular electrodes and separator sheets to avoid some of the difficulties encountered with winding prismatic cells.

Fig. 5C shows a top view of the rolled prismatic jelly roll 520. The jelly roll 520 includes a positive electrode 524 and a negative electrode 526. The white space between the electrodes is the separator sheet. The jelly roll 520 is enclosed in a rectangular prismatic case 522. Unlike cylindrical jelly rolls, the winding of prismatic jelly rolls starts with a flat extension in the middle of the jelly roll. In one embodiment, the jelly roll may include a mandrel (not shown) in the middle of the jelly roll around which the electrodes and separator are wound.

Fig. 6A illustrates a cross-section of a stacked cell comprising a plurality of cells (601a, 601b, 601c, 601d, and 601e), each having a positive electrode (e.g., 603a, 603b), a positive current collector (e.g., 602), a negative electrode (e.g., 605a, 605b), a negative current collector (e.g., 604), and a separator (e.g., 606A, 606b) interposed between the electrodes. Each current collector is shared by adjacent cells. Stacked cells can be made in almost any shape, which is particularly suitable for prismatic batteries. Current collector tabs typically extend from the stack and lead to the cell terminals. Fig. 6B shows a perspective view of a stacked cell comprising a plurality of cells.

Once the electrodes are arranged as described above, the cell is filled with electrolyte. The electrolyte in the lithium ion cell may be a liquid, solid or gel. Lithium ion cells with solid electrolytes are referred to as lithium polymer cells.

Typical liquid electrolytes comprise one or more solvents and one or more salts, at least one of which includes lithium. During the first charge cycle (also sometimes referred to as a formation cycle), the organic solvent in the electrolyte may partially decompose on the negative electrode surface to form an SEI layer. The mesophase is typically electrically insulating but ionically conducting, allowing lithium ions to pass through. The intermediate phase also prevents the electrolyte from decomposing in the subsequent charge subcycles.

Some examples of non-aqueous solvents suitable for some lithium ion cells include the following: cyclic carbonates (e.g., Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), and Vinyl Ethylene Carbonate (VEC)), Vinylene Carbonate (VC), lactones (e.g., γ -butyrolactone (GBL), γ -valerolactone (GVL), and α -Angelolactone (AGL)), linear carbonates (e.g., dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC), methylbutyl carbonate (NBC), and dibutyl carbonate (DBC)), ethers (e.g., Tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1, 4-dioxane, 1, 2-Dimethoxyethane (DME), 1, 2-diethoxyethane, and 1, 2-dibutoxyethane), nitriles (e.g., acetonitrile and hexane), linear esters (e.g., methyl propionate, methyl pivalate, butyl pivalate, and octyl pivalate), amides (e.g., dimethylformamide), organophosphates (e.g., trimethyl phosphate and trioctyl phosphate), organic compounds containing S ═ O groups (e.g., dimethyl sulfone and divinyl sulfone), and combinations thereof.

Non-aqueous liquid solvents may be used in combination. Examples of such combinations include the following combinations: cyclic carbonate-linear carbonate, cyclic carbonate-lactone-linear carbonate, cyclic carbonate-linear carbonate-lactone, cyclic carbonate-linear carbonate-ether, and cyclic carbonate-linear ester. In one embodiment, the cyclic carbonate may be combined with a linear ester. In addition, cyclic carbonates may be combined with lactones and linear esters. In particular embodiments, the volume ratio of cyclic carbonate to linear ester is about 1:9 to 10:0, preferably 2:8 to 7: 3.

The salt for the liquid electrolyte may include one or more of: LiPF₆、LiBF₄、LiClO₄、LiAsF₆、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂、LiCF₃SO₃、LiC(CF₃SO₂)₃、LiPF₄(CF₃)₂、LiPF₃(C₂F₅)₃、LiPF₃(CF₃)₃、LiPF₃(iso-C)₃F₇)₃、LiPF₅(iso-C)₃F₇) Lithium salt having a cyclic alkyl group (e.g., (CF)₂)₂(SO₂)_2xLi) and (CF)₂)₃(SO₂)_2xLi) and combinations thereof. Common combinations include LiPF₆And LiBF₄；LiPF₆And LiN (CF)₃SO₂)₂(ii) a And LiBF₄And LiN (CF)₃SO₂)₂。

In one embodiment, the total concentration of salt in the liquid nonaqueous solvent (or solvent combination) is at least about 0.3M; in a more specific embodiment, the salt concentration is at least about 0.7M. The upper concentration limit may be determined by the solubility limit or may be no greater than about 2.5M; in a more specific embodiment, it may be no more than about 1.5M.

The solid electrolyte is typically used without a separator, as it itself acts as a separator. It is electrically insulating, ionically conducting and electrochemically stable. In the solid electrolyte configuration, a lithium-containing salt is utilized, which may be the same as described above with respect to the liquid electrolyte cell, but is not dissolved in the organic solvent, which remains in the solid polymer composite. Examples of the solid polymer electrolyte may be ion-conducting polymers prepared from monomers containing atoms having a lone pair of electrons, which are useful for attachment and movement of lithium ions of electrolyte salts therebetween during conduction, such as polyvinylidene fluoride (PVDF) or copolymers of polyvinylidene chloride or their derivatives, poly (chlorotrifluoroethylene), poly (ethylene-chlorotrifluoroethylene), or poly (ethylene-propylene fluoride), polyethylene oxide (PEO) and oxymethylene linked PEO, PEO-PPO-PEO crosslinked with trifunctional urethane, poly (bis (methoxy-ethoxy-ethoxide)) -phosphazene (MEEP), triol type PEO crosslinked with bifunctional urethane, poly ((oligo) ethylene oxide) methacrylate-co-alkali metal methacrylate, Polyacrylonitrile (PAN), polymethylmethacrylate (PNMA), Polymethacrylonitrile (PMAN), polysiloxanes and their copolymers and derivatives, acrylate-based polymers, other similar solventless polymers, combinations of the above polymers (either condensed or crosslinked to form different polymers), and physical mixtures of any of the foregoing polymers. Other less conductive polymers that can be used in combination with the above polymers to improve the strength of the thin laminate include: polyester (PET), polypropylene (PP), polyethylene naphthalate (PEN), polyvinylidene fluoride (PVDF), Polycarbonate (PC), Polyphenylene Sulfide (PPs), and Polytetrafluoroethylene (PTFE).

Fig. 7 shows a cross-sectional view of a wound cylindrical cell according to an embodiment. The jelly roll contains a spirally wound positive electrode 702, a negative electrode 704, and two sheets of separator 706. The jelly roll is inserted into the cell casing 716 and the cell is sealed using a cover 718 and gasket 720. It should be noted that in certain embodiments, the cells are not sealed until after subsequent operations. In some cases, the cover 718 or the cell housing 716 includes a safety device. For example, if excessive pressure builds in the cell, a safety vent or burst valve may be utilized to open. In certain embodiments, a one-way gas release valve is included to release oxygen released during activation of the positive electrode material. In addition, a Positive Thermal Coefficient (PTC) device may be incorporated into the conductive path of the cover 718 to reduce damage that may result if the cell is subjected to a short circuit. The outer surface of the cover 718 may serve as a positive terminal, and the outer surface of the cell casing 716 may serve as a negative terminal. In an alternative embodiment, the polarity of the battery is reversed and the outer surface of the cover 718 serves as the negative terminal, while the outer surface of the cell casing 716 serves as the positive terminal. Tabs 708 and 710 may be used to establish connections between the positive and negative electrodes and the respective terminals. Appropriate insulating gaskets 714 and 712 may be inserted to prevent the possibility of internal short circuits. For example, Kapton^TMThe film may be used for internal insulation. During manufacture, the cover 718 may be crimped to the cell casing 716 to seal the cells. However, prior to this operation, electrolyte (not shown) is added to fill the porous spaces of the jelly roll.

Rigid housings are typically used for lithium ion cells, while lithium polymer cells can be encased in flexible foil-type (polymer laminate) housings. A variety of materials may be selected for the housing. For lithium ion batteries, Ti-6-4, other Ti alloys, Al alloys, and 300 series stainless steels may be suitable for the positive conductive case portion and end caps, and commercially pure Ti, Ti alloys, Cu, Al alloys, Ni, Pb, and stainless steels may be suitable for the negative conductive case portion and end caps.

In addition to the above-described battery applications, the nanostructures can also be used in fuel cells (e.g., for anodes, cathodes, and electrolytes), heterojunction solar cell active materials, various forms of current collectors, and/or absorption coatings.

Experiment and results

The nanowire template on the metal foil is exposed to silane, argon and ammonia or nitrogen gas in a PECVD plasma chamber, resulting in silicon-rich SiN deposited on the nanowire template_xThe first of the layers. Thermal CVD to first SiN_xDeposition of silicon-rich SiN on the layer_xTo form an anode of a lithium battery cell. In addition to the anode fabricated above, the cell also included a lithium cobalt oxide cathode, a separator, and a lithium battery having LiPF₆A carbonate-based electrolyte of a salt.

FIG. 8 is a graph showing for silicon rich SiN_xA graph of capacity retention versus cell cycle number for both cells and cells with anodes containing only silicon. And both the two battery cells are charged and discharged at C/2 multiplying power. SiN_xSiN of battery core_xThe capacity retention curve drops much slower than a Si cell only. SiN_xThe life cycle of the cell was about 75% longer than that of a Si-only cell. From the group comprising silicon-rich SiEs as described herein_xCycling data for the cells of the anodes indicate: such anodes have an increased cycle life compared to anodes made only of silicon.

The present invention has been described herein in considerable detail in order to provide those skilled in the art with information relevant to the implementation of the novel principles and the construction and use of such specialized components as are required. It is to be understood, however, that the invention may be embodied in different equipment, materials, and devices, and that various modifications, both as to the equipment and operating procedures, may be accomplished without departing from the scope of the invention itself.