阅读说明：本技术 包含硅基主体材料的电极和使用其的电池组电池的制备方法 (Electrode comprising silicon-based host material and method for preparing battery cell using the same ) 是由 N.希门尼斯 M.P.巴洛夫 I.C.哈拉莱 R.克 于 2020-04-29 设计创作，主要内容包括：制备电极的方法,该方法包括用浆料涂覆集电器,以及将涂覆的集电器热解以产生包含硅基主体材料层的电极。浆料可以包含一种或多种溶剂和干部分,所述干部分具有硅颗粒、一种或多种聚合物粘合剂和碳纤维。热解包括在第一温度下加热,并随后在高于第一温度的第二温度下加热。硅颗粒包括单相硅和/或Li<Sub>2</Sub>Si,具有小于10微米的平均粒径,并可以为干部分的70%。聚合物粘合剂可以仅是聚丙烯腈,或任选地包含一种或多种氟化聚合物。碳纤维具有至少约50纳米的平均直径,至少约1微米的平均长度,并可以为干部分的至多15 wt%。(A method of making an electrode, the method comprising coating a current collector with a slurry, and pyrolysing the coated current collector to produce an electrode comprising a silicon-based host material layer. The slurry may comprise one or more solvents anda dry portion having silicon particles, one or more polymeric binders, and carbon fibers. Pyrolysis includes heating at a first temperature and subsequently heating at a second temperature that is higher than the first temperature. The silicon particles comprise single-phase silicon and/or Li 2 Si, having an average particle size of less than 10 microns, and may be 70% of the dry fraction. The polymeric binder may be polyacrylonitrile alone, or optionally comprise one or more fluorinated polymers. The carbon fibers have an average diameter of at least about 50 nanometers, an average length of at least about 1 micron, and may be up to 15 wt% of the dry portion.)

1. A method of preparing an electrode, the method comprising:

coating a current collector with a slurry to form a coated current collector, wherein the slurry comprises:

a dry portion comprising:

the particles of silicon are selected such that,

one or more polymeric binders, and

carbon fiber, and

one or more solvents; and

pyrolyzing the coated current collector to produce an electrode comprising a silicon-based host material layer, wherein pyrolyzing the coated current collector comprises heating at a first temperature and subsequently heating at a second temperature, wherein the second temperature is higher than the first temperature.

2. A method as claimed in any one of the preceding claims wherein the silicon particles comprise single phase silicon and/or Li₂Si and has an average particle size of less than about 10 microns.

3. The method of any of the above claims, wherein the dry portion comprises at least about 70 wt% silicon particles, up to about 10 wt% polymeric binder, and up to about 15 wt% carbon fibers.

4. A method according to any preceding claim, wherein the polymeric binder comprises polyacrylonitrile and/or one or more fluorinated polymers.

5. A method as claimed in any preceding claim, wherein the polymeric binder is composed of polyacrylonitrile.

6. The method of any of the above claims, wherein the carbon fibers have an average diameter of at least about 50 nanometers and an average length of at least about 1 micrometer.

7. The method of any of the above claims, further comprising, after coating and before pyrolyzing, drying the coated current collector.

8. The method of any of the above claims, wherein the first temperature is about 250 ℃ to about 400 ℃ and the second temperature is less than about 750 ℃.

9. The method of any of the preceding claims, wherein the silicon-based host material layer has a thickness of about 20 microns to about 50 microns.

10. The method of any of the above claims, further comprising subsequently assembling a battery cell by placing the electrodes and positive electrode in an electrolyte.

Technical Field

Lithium ion batteries are a type of rechargeable battery in which lithium ions move between a negative electrode (i.e., the anode) and a positive electrode (i.e., the cathode). Liquid, solid and polymer electrolytes can facilitate the movement of lithium ions between the anode and cathode. Lithium ion batteries are becoming increasingly popular in the defense, automotive and aerospace fields due to their high energy density and ability to withstand continuous charge-discharge cycles.

Background

A method of preparing an electrode is provided that may include coating a current collector with a slurry to form a coated current collector, and pyrolyzing the coated current collector to produce an electrode comprising a silicon-based host material layer. The slurry may comprise a dry fraction (dry fraction) and one or more solvents. The dry portion may comprise silicon particles, one or more polymeric binders, and carbon fibers. Pyrolyzing the coated current collector may include heating at a first temperature and then heating at a second temperature, wherein the second temperature is higher than the first temperature. The silicon particles may be single phase silicon and Li₂And (3) Si. The silicon particles may have an average particle size of less than about 10 microns. The dry portion may comprise at least about 70 wt% silicon particles. The polymeric binder may comprise polyacrylonitrile and/or one or more fluorinated polymers. The polymeric binder may be polyacrylonitrile only. The polymeric binder may comprise up to about 10 wt% of the dry portion. The carbon fibers may have an average diameter of at least about 50 nanometers. The carbon fibers may have an average length of at least about 1 micron. The carbon fibers may comprise up to about 15 wt% of the dry portion. The solvent may include N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, propylene carbonate, ethylene carbonate, acetone and/orMethyl ethyl ketone. The method may further comprise, after coating and before pyrolyzing, drying the coated current collector. Drying may be carried out at a temperature of less than about 100 ℃. The first temperature may be about 250 ℃ to about 400 ℃, and the second temperature may be less than about 750 ℃. Pyrolysis can be carried out in an environment substantially free of oxygen-containing gases (oxygenated gases). The silicon-based host material layer may have a thickness of about 20 microns to about 50 microns.

A method of preparing a battery cell is provided and may include coating a current collector with a slurry to form a coated current collector, pyrolyzing the coated current collector to produce an anode comprising a silicon-based host material layer, and then assembling a battery cell by placing the anode and a cathode in an electrolyte. The slurry may comprise a dry portion and one or more solvents. The dry portion may comprise silicon particles, one or more polymeric binders, and carbon fibers, wherein the silicon particles comprise Li₂Si and single phase silicon, wherein the polymeric binder comprises polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene copolymer, and/or perfluoroalkoxyalkane, and wherein the carbon fibers have an average diameter of about 100 nanometers to about 200 nanometers and an average length of about 1 micrometer to about 10 micrometers. Pyrolyzing the coated current collector may include heating at a first temperature of up to about 400 ℃ and subsequently heating at a second temperature of about 450 ℃ to about 750 ℃. The silicon particles may have an average particle size of less than about 10 microns. The dry portion may be at least about 70 wt% silicon particles. The pyrolyzed one or more polymer binders may form a carbon layer around the silicon particles.

Specifically, the present invention relates to the following items.

1. A method of preparing an electrode, the method comprising:

coating a current collector with a slurry to form a coated current collector, wherein the slurry comprises:

a dry portion comprising:

the particles of silicon are selected such that,

one or more polymeric binders, and

carbon fiber, and

one or more solvents; and

pyrolyzing the coated current collector to produce an electrode comprising a silicon-based host material layer, wherein pyrolyzing the coated current collector comprises heating at a first temperature and subsequently heating at a second temperature, wherein the second temperature is higher than the first temperature.

2. The method of item 1, wherein the silicon particles comprise single-phase silicon and Li₂Si。

3. The method of item 1, wherein the silicon particles have an average particle size of less than about 10 microns.

4. The method of item 1, wherein the dry portion comprises at least about 70 wt% silicon particles.

5. The method of item 1, wherein the polymeric binder comprises polyacrylonitrile and/or one or more fluorinated polymers.

6. The method of claim 1, wherein the polymeric binder is comprised of polyacrylonitrile.

7. The method of item 1, wherein the polymeric binder comprises up to about 10 wt% of the dry portion.

8. The method of item 1, wherein the carbon fibers have an average diameter of at least about 50 nanometers.

9. The method of item 1, wherein the carbon fibers have an average length of at least about 1 micron.

10. The method of item 1, wherein the carbon fibers comprise up to about 15 wt% of the dry portion.

11. The method of item 1, wherein the solvent comprises N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, propylene carbonate, ethylene carbonate, acetone and/or methyl ethyl ketone.

12. The method of item 1, further comprising, after coating and before pyrolyzing, drying the coated current collector.

13. The method of item 11, wherein drying is performed at a temperature of less than about 100 ℃.

14. The method of item 1, wherein the first temperature is from about 250 ℃ to about 400 ℃ and the second temperature is less than about 750 ℃.

15. The method of item 13, wherein the pyrolyzing can be carried out in a substantially oxygen-containing gas-free environment.

16. The method of item 1, wherein the silicon-based host material layer has a thickness of about 20 microns to about 50 microns.

17. A method of making a battery cell, the method comprising:

coating a current collector with a slurry to form a coated current collector, wherein the slurry comprises:

a dry portion comprising:

silicon particles, wherein the silicon particles comprise Li₂Si and single-phase silicon, and the silicon,

one or more polymeric binders comprising polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene copolymer and/or perfluoroalkoxy alkanes, and

a carbon fiber, wherein the carbon fiber has an average diameter of about 100 nanometers to about 200 nanometers and an average length of about 1 micron to about 10 microns, and

one or more kinds of solvents are used in the solvent,

pyrolyzing the coated current collector to produce an anode comprising a silicon-based host material layer, wherein pyrolyzing the coated current collector comprises heating at a first temperature of up to about 400 ℃ and subsequently heating at a second temperature of about 450 ℃ to about 750 ℃; and

the battery cell is then assembled by placing the negative and positive electrodes in an electrolyte.

18. The method of item 17, wherein the silicon particles have an average particle size of less than about 10 microns.

19. The method of item 17, wherein the dry portion comprises at least about 70 wt% silicon particles.

20. The method of item 17, wherein the pyrolyzed one or more polymer binders form a carbon layer around the silicon particles.

Other objects, advantages and novel features of the exemplary embodiments will become more apparent from the following detailed description of the exemplary embodiments and the accompanying drawings.

Drawings

Fig. 1 illustrates a lithium battery cell according to one or more embodiments;

FIG. 2 shows a schematic diagram of a hybrid electric vehicle according to one or more embodiments;

fig. 3 illustrates a method for making an electrode and a battery utilizing the same, according to one or more embodiments;

fig. 4 shows a schematic cross-sectional side view of a pyrolytic electrode in accordance with one or more embodiments.

Detailed Description

Embodiments of the present invention are described herein. However, it is to be understood that the disclosed embodiments are merely exemplary and that other embodiments may take different and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As one of ordinary skill in the art will appreciate, various features shown and described with reference to any one of the figures may be combined with features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combination of features shown provides a representative embodiment for a typical application. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or practices.

Provided herein are methods for preparing electrodes and battery cells comprising silicon-based host materials. These methods provide high capacity electrodes with high mechanical strength, minimal irreversible capacity loss during the first formation cycle, and improved capacity retention during long-term cycling.

Fig. 1 shows a lithium battery cell 10 comprising a negative electrode (i.e., anode) 11, a positive electrode (i.e., cathode) 14, an electrolyte 17 operatively disposed between the anode 11 and the cathode 14, and a separator 18. Anode 11, cathode 14, and electrolyte 17 may be enclosed in a container 19, and container 19 may be, for example, a hard (e.g., metal) shell or a soft (e.g., polymer) bag. Anode 11 and cathode 14 are located on opposite sides of separator 18, which separator 18 may comprise a microporous polymer or other suitable material capable of conducting lithium ions and optionally an electrolyte (i.e., a liquid electrolyte). The electrolyte 17 is a liquid electrolyte comprising one or more lithium salts dissolved in a nonaqueous solvent. Anode 11 typically comprises a current collector 12 and a lithium intercalation host material 13 coated thereon. The cathode 14 generally includes a current collector 15 and a lithium-based or chalcogen-based active material 16 coated thereon. For example, as described below, the battery cell 10 may include a chalcogen active material 16 or a lithium metal oxide active material 16, or the like. For example, active material 16 may store lithium ions at a higher potential than intercalation host material 13. The current collectors 12 and 15 associated with the two electrodes are connected by an external circuit that can be interrupted, which allows a current to pass between the electrodes to electrically balance the relative migration of lithium ions. Although fig. 1 schematically illustrates the host material 13 and the active material 16 for clarity, the host material 13 and the active material 16 may include dedicated interfaces between each of the anode 11 and the cathode 14 and the electrolyte 17.

The battery cell 10 may be used in a variety of applications. For example, fig. 2 shows a schematic diagram of a hybrid electric or electric vehicle 1 containing a battery pack 20 and related components. A battery pack (e.g., battery pack 20) may include a plurality of battery cells 10. For example, a plurality of battery cells 10 may be connected in parallel to form a group, and a plurality of groups may be connected in series. Those skilled in the art will understand that any number of battery cell connection configurations are possible with the battery cell architectures disclosed herein, and will further recognize that vehicle applications are not limited to the described vehicle architectures. The battery pack 20 may provide energy to the traction inverter 2, and the traction inverter 2 converts Direct Current (DC) battery voltage to a three-phase Alternating Current (AC) signal, which is used by the drive motor 3 to propel the vehicle 1 via one or more wheels (not shown). The optional engine 5 may be used to drive the generator 4, which in turn may provide energy to charge the battery pack 20 through the inverter 2. In some embodiments, the drive motor 3 and the generator 4 comprise a single device (i.e., a motor/generator). External (e.g., grid) energy may also be used to charge the battery pack 20 through additional circuitry (not shown). For example, the engine 5 may include a gasoline or diesel engine.

The battery cell 10 generally operates by reversibly passing lithium ions between an anode 11 and a cathode 14. Lithium ions move from the cathode 14 to the anode 11 upon charging, and from the anode 11 to the cathode 14 upon discharging. At the beginning of discharge, the anode 11 contains a high concentration of intercalated/alloyed lithium ions while the cathode 14 is relatively depleted, and in this case, the establishment of a closed external circuit between the anode 11 and the cathode 14 results in extraction of the intercalated/alloyed lithium ions from the anode 11. While leaving an intercalation/alloying host at the electrode-electrolyte interface, the extracted lithium atoms are split into lithium ions and electrons. Lithium ions are carried by the ion conducting electrolyte 17 through the pores of the separator 18 from the anode 11 to the cathode 14, while electrons are transported through an external circuit from the anode 11 to the cathode 14 to balance the entire electrochemical cell. This flow of electrons through the external circuit can be harnessed and fed to the load device until the level of intercalated/alloyed lithium in the negative electrode drops below a workable level or the need for power ceases.

The battery cell 10 may be recharged after its available capacity has been partially or fully discharged. To charge or re-power the lithium ion battery cells, an external power source (not shown) is connected to the positive and negative electrodes to drive the reversal of the discharging electrochemical reaction of the cells. That is, during charging, the external power source extracts lithium ions present in the cathode 14 to generate lithium ions and electrons. The lithium ions are carried back through the separator by the electrolyte solution, while the electrons are driven back through the external circuit, both moving toward the anode 11. The lithium ions and electrons eventually recombine at the negative electrode, replenishing it with intercalated/alloyed lithium for future use in discharging the battery cell.

A lithium-ion battery cell 10, or a battery module or pack comprising a plurality of battery cells 10 connected in series and/or parallel, may be used to reversibly provide power and energy to an associated load device. Lithium ion batteries are also used in a variety of consumer electronics devices (e.g., laptops, cameras, and cell/smart phones), military electronics (e.g., radios, mine detectors, and thermal weapons), airplanes and satellites, and the like. Lithium ion batteries, battery modules, and battery packs may be incorporated into vehicles such as Hybrid Electric Vehicles (HEVs), Battery Electric Vehicles (BEVs), plug-in HEVs, or Extended Range Electric Vehicles (EREVs) to generate sufficient power and energy to operate one or more systems of the vehicle. For example, battery cells, battery modules, and battery packs may be used in conjunction with gasoline or diesel internal combustion engines to propel a vehicle (e.g., in a hybrid electric vehicle), or may be used alone to propel a vehicle (e.g., in a battery-powered vehicle).

Returning to fig. 1, the electrolyte 17 conducts lithium ions between the anode 11 and the cathode 14, for example, during charging or discharging of the battery cell 10. The electrolyte 17 includes one or more solvents, and one or more lithium salts dissolved in the one or more solvents. Suitable solvents may include cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate), acyclic carbonates (dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate), aliphatic carboxylic acid esters (methyl formate, methyl acetate, methyl propionate), gamma-lactones (gamma-butyrolactone, gamma-valerolactone), chain structured ethers (1, 3-dimethoxypropane, 1, 2-Dimethoxyethane (DME), 1-2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane), and combinations thereof. A non-limiting list of lithium salts that can be dissolved in the organic solvent to form a non-aqueous liquid electrolyte solution includes LiClO₄、LiAlCl₄、LiI、LiBr、LiSCN、LiBF₄、LiB(C₆H₅)₄LiAsF₆、LiCF₃SO₃、LiN(CF₃SO₂)₂、LiN(FSO₂)₂、LiPF₆And mixtures thereof.

In one embodiment, the microporous polymer membrane 18 may comprise a polyolefin. The polyolefins may be homopolymers (derived from a single monomer component) or heteropolymers (derived from more than one monomer component), and may be linear or branched. If used, derived from two monomeric componentsRaw heteropolymers, the polyolefin may exhibit any copolymer chain arrangement, including block copolymer or random copolymer chain arrangements. This is also the case if the polyolefin is a heteropolymer derived from more than two monomeric components. In one embodiment, the polyolefin may be Polyethylene (PE), polypropylene (PP), or a mixture of PE and PP. The microporous polymer membrane 18 may also comprise other polymers in addition to polyolefins such as, but not limited to, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), and/or polyamide (nylon). The diaphragm 18 may optionally be ceramic coated with a material including ceramic-type alumina (e.g., Al)₂O₃) And lithiated zeolite-type oxides, and the like. The lithiated zeolite-type oxide can improve the safety and cycle life performance of a lithium ion battery, such as battery cell 10. Those skilled in the art will no doubt know and understand the many polymers and commercial products from which the microporous polymer membrane 18 may be made, and the many manufacturing processes that may be used to produce the microporous polymer membrane 18.

The active material 16 may comprise any lithium-based active material sufficient to undergo intercalation and delamination of lithium while functioning as the positive terminal of the battery cell 10. The active material 16 may also include a polymeric binder material to structurally hold the lithium-based active material together. The active material 16 may comprise a lithium transition metal oxide (e.g., a layered lithium transition metal oxide) or a chalcogen material. The cathode current collector 15 may include aluminum or any other suitable conductive material known to those skilled in the art, and may be formed in a foil or mesh shape. The cathode current collector 15 may be treated with (e.g., coated with) a highly conductive material including one or more of conductive carbon black, graphite, carbon nanotubes, carbon nanofibers, graphene, Vapor Grown Carbon Fibers (VGCF), and the like. The same highly conductive material may additionally or alternatively be dispersed in the host material 13.

Lithium transition metal oxides suitable for use as the active material 16 may include spinel lithium manganese oxide (LiMn)₂O₄) Lithium cobalt oxide (LiCoO)₂) Nickel manganese oxide spinel (Li (Ni))_0.5Mn_1.5)O₂) Layered nickel manganese cobalt oxide (having the general formula xLi)₂MnO₃·(1-x)LiMO₂Where M consists of nickel, manganese and/or cobalt in any proportion). A specific example of a layered nickel manganese oxide spinel isxLi₂MnO_3·(1−x)Li(Ni_1/3Mn_1/3Co_1/3)O₂. Other suitable lithium-based active materials include Li (Ni)_1/3Mn_1/3Co_1/3)O₂)、LiNiO₂、Li_x+yMn_2-yO₄（LMO，0<x<1 and 0<y<0.1) or lithium iron polyanionic oxides, e.g. lithium iron phosphate (LiFePO)₄) Or lithium iron fluorophosphate (Li)₂FePO₄F) In that respect Other lithium-based active materials, such as LiNi, may also be used_xM_1-xO₂(M consists of Al, Co and/or Mg in any proportion), LiNi_1-xCo_1-yMn_x+yO₂Or LiMn_{1.5- x}Ni_0.5-yM_x+yO₄(M consists of Al, Ti, Cr and/or Mg in any proportion), stabilized lithium manganese oxide spinel (Li)_xMn_{2- y}M_yO₄Where M is comprised of Al, Ti, Cr and/or Mg in any proportion), lithium nickel cobalt aluminum oxide (e.g., LiNi)_0.8Co_0.15Al_0.05O₂Or NCA), aluminum stabilized lithium manganese oxide spinel (Li)_xMn_2-xAl_yO₄) Lithium vanadium oxide (LiV)₂O₅）、Li₂MSiO₄(M consists of Co, Fe and/or Mn in any proportion) and any other high efficiency nickel manganese cobalt material (HE-NMC, NMC or LiNiMnCoO)₂). By "any ratio" is meant that any element can be present in any amount. Thus, for example, M may be Al, with or without Co and/or Mg, or any other combination of the listed elements. In another example, anionic substitution may be made in the crystal lattice of any example of the lithium transition metal-based active material to stabilize the crystal structure. For example, any O atom may be replaced by a F atomAnd (4) substitution.

For example, the chalcogen-based active material may include one or more sulfur and/or one or more selenium materials. Sulfur materials suitable for use as the active material 16 may include sulfur-carbon composites, S₈、Li₂S₈、Li₂S₆、Li₂S₄、Li₂S₂、Li₂S、SnS₂And combinations thereof. Another example of a sulfur-based active material includes a sulfur-carbon composite. Selenium materials suitable for use as the active material 16 may include elemental selenium, Li₂Se, selenium sulfide alloy, SeS₂、SnSe_xS_y(e.g., SnSe_0.5S_0.5) And combinations thereof. The chalcogen-based active material of the positive electrode 22' may be mixed with a polymeric binder and a conductive filler. Suitable binders include polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), Ethylene Propylene Diene Monomer (EPDM) rubber, carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR), styrene butadiene rubber carboxymethylcellulose (SBR-CMC), polyacrylic acid (PAA), cross-linked polyacrylic polyethylene imine, polyimide, or any other suitable binder material known to those skilled in the art. Other suitable binders include polyvinyl alcohol (PVA), sodium alginate, or other water soluble binders. The polymer binder structurally holds the chalcogen-based active material and the conductive filler together. An example of a conductive filler is a high surface area carbon, such as acetylene black or activated carbon. The conductive filler ensures electron conduction between the positive electrode-side current collector 26 and the chalcogen-based active material. In one example, the positive electrode active material and the polymer binder may be encapsulated with carbon. In one example, the weight ratio of S and/or Se to C in the positive electrode 22' is between 1:9 and 9: 1.

The anode current collector 12 may comprise copper, nickel, a copper-nickel alloy, or any other suitable conductive material known to those skilled in the art. The anode current collector 12 may be treated (e.g., coated) with a highly conductive material including one or more of chromium, conductive carbon black, graphite, carbon nanotubes, carbon nanofibers, graphene, Vapor Grown Carbon Fibers (VGCF), and the like. For example, the current collector surface may be roughened, and/or the current collector may be perforated. Silicon has the highest theoretical known lithium charge capacity, making it one of the most promising negative host materials 13 for rechargeable lithium ion batteries. Accordingly, provided herein are electrodes comprising silicon-based host material 13 and methods of making the electrodes.

Fig. 3 illustrates a method of preparing an electrode (e.g., anode 11) and a battery cell (e.g., battery cell 10) utilizing the electrode. The method 100 comprises: the current collector 12 is coated 101 with the slurry 103 to form a coated current collector 102, and the coated current collector 102 is pyrolyzed 110 to produce an electrode (anode 11) comprising at least one layer of a silicon-based host material 13. As shown in fig. 3, the current collector 12 has one or more faces (e.g., a first current collector face 12A and a second current collector face 12B) to which the slurry 103 may be applied. The method 100 may also include, after coating 101 and before pyrolyzing 110, drying 105 the coated current collector 102. Method 100 may also include subsequently assembling 115 a battery cell (e.g., battery cell 10) by disposing an electrode (e.g., anode 11) and a positive electrode (e.g., cathode 14) in an electrolyte (e.g., electrolyte 17). Assembling 115 the battery cell may also include disposing a separator (e.g., separator 18) between an electrode (e.g., anode 11) and a positive electrode (e.g., cathode 14).

The slurry 103 comprises a dry portion and one or more solvents. The dry portion comprises silicon particles, one or more polymeric binders, and carbon fibers. The amount of solvent used in the slurry is adjusted to obtain a particular slurry viscosity and/or any other physical characteristic suitable for applying the slurry 103 to a current collector. The slurry may comprise a dry portion of about 5wt% to about 50 wt%. For example, in one example, the slurry can comprise about 25 wt% to about 30 wt% of the dry portion and about 70 wt% to about 75 wt% of the solvent. The solvent may include any polar solvent including N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethyl sulfoxide, propylene carbonate, ethylene carbonate, acetone, methyl ethyl ketone, and the like. In some examples, the slurry comprises 100 wt% dry portion without solvent.

The silicon particles may include elemental silicon particles, group V elements of the periodic Table (e.g., P, As, Sb, Bi)) n-type doped silicon particles and/or Li₂And (3) Si particles. The silicon particles may additionally or alternatively comprise SiOx, where typically x ≦ 2. In some embodiments, for some SiO_xParticle, x ≈ 1. For example, x can be from about 0.9 to about 1.1, or from about 0.99 to about 1.01. In the SiOx particle matrix, SiO may also be present₂And/or a Si domain. In some embodiments, the silicon particles may be considered "single phase" and do not include any added conductive carbon (e.g., graphite). In other words, in these embodiments, the carbon present in the host material 13 may consist essentially of carbon contributed by the carbon fibers, carbon nanotubes, carbon present in the current collector, and carbon contributed by the pyrolized polymeric binder.

Using Li₂The Si particles may help prevent the volume expansion of the silicon particles and irreversibly trap lithium from the cathode 14 during the initial cycling of the battery cell 10. In some embodiments, the silicon particles may have an average particle size of less than about 10 microns, from about 50 nanometers to about 10 microns, or from about 3 microns to about 10 microns. In some embodiments, particularly battery cells 10 configured for fast charge, the silicon particles may have an average particle size of from about 1 micron to about 3 microns or from about 0.5 microns to about 1 micron. The dry portion may comprise at least about 70 wt% silicon particles. In some embodiments, the dry portion may comprise about 70 wt% to about 95wt% silicon particles. In some embodiments, the dry portion may comprise about 75 wt% to about 85wt% silicon particles. In the use of Li₂In embodiments of Si particles, the amount of lithium atoms in the dry portion may be substantially equal to the amount of silicon atoms. For example, the silicon particles may comprise from about 45% to about 50% (by count) of the total number of silicon and lithium atoms.

The one or more polymeric binders may comprise Polyacrylonitrile (PAN) and/or one or more fluorinated polymers (e.g., polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), and Perfluoroalkoxyalkane (PFA)). In one embodiment, the polymeric binder may consist of PAN. The polymeric binder may comprise up to about 10 wt%, or from about 5wt% to about 10 wt% of the dry portion. The amount of polymeric binder in the dry portion can be adjusted to achieve the desired cage of the pyrolyzed polymeric binder on the silicon particles, as described below.

The carbon fibers may have an average diameter of at least about 50 nanometers, from about 50 nanometers to 200 nanometers, or from about 100 nanometers to 200 nanometers. The carbon fibers may have an average length of at least about 1 micron, or from about 1 micron to about 20 microns. The carbon fibers provide stiffness and mechanical integrity to the host material 13 while being electrically conductive. The dry portion may optionally further comprise carbon nanotubes. For example, the carbon nanotubes may have an average diameter of about 20 nanometers to about 50 nanometers and an average length of about 1 micron to about 2 microns. Carbon nanotubes are very flexible and provide minimal strength relative to carbon fibers, but increase the electrical connection between individual silicon particles and between the silicon particles and current collector 12. In some embodiments, the weight ratio of carbon fibers to carbon nanotubes may be from about 50:1 to about 4: 1. The carbon fibers (and optionally carbon nanotubes, along with carbon fibers) may constitute up to about 15 wt%, or about 2wt% to about 15 wt% of the dry portion. The upper limit of the amount of carbon fibers (and optionally carbon nanotubes, along with the carbon fibers) may be defined by the amount of polymeric binder needed to maintain the structural integrity of the resulting host material 13.

After coating 101 and before pyrolysis 110, the coated current collector 102 may be dried 105. Drying 105 substantially removes the solvent from the slurry, typically by evaporation, and thus suitable solvents may be considered volatile organic compounds. Drying 105 may be performed at a temperature of less than about 100 ℃ or less than about 200 ℃, and may be performed in an open-air (e.g., non-inert) environment. In some embodiments, drying may be performed at higher temperatures (e.g., up to about 500 ℃) and with significantly shorter drying times relative to lower temperature (e.g., 100 ℃) drying methods. Drying prevents the slurry solvent from introducing oxides during pyrolysis. Pyrolysis 110 is preferably substantially free of oxygen-containing gas (e.g., O)₂、CO、CO₂Etc.) or "inert atmosphere". For example, the inert atmosphere may include N₂Ar and/or He atmosphere, or vacuum.

Pyrolysis 110 may include heating at a first temperature and then heating at a second temperature, where the second temperature is higher than the first temperature. Fig. 4 shows a schematic cross-sectional side view of a pyrolysis 110 electrode (i.e., anode 11). The pyrolysis 110 carbonizes the polymer binder to form a carbon layer 132 around the silicon particles 131 to buffer the expansion of the silicon particles 131 and further anchor the carbon fibers 133 to the silicon particles 131, the current collector 12, and the optional carbon nanotubes 134. Pyrolysis 110 at the first and second temperatures may more suitably convert the polymeric binder into a desired material having desired mechanical and/or electrical properties. For example, the polymeric binder PAN may be substantially converted to a pyridine ring at a first temperature, and the pyridine ring and other remaining polymeric compounds may be dehydrogenated at a second temperature. Dehydrogenation increases the conductivity of the polymer binder.

Too high a pyrolysis temperature may result in a mechanically weak brittle host material 13. Thus, the first temperature may be up to about 400 ℃, or about 250 ℃ to about 400 ℃, and the second temperature may be less than about 750 ℃ and higher than the first temperature, about 450 ℃ to about 750 ℃, about 500 ℃ to about 750 ℃, or about 700 ℃ to about 750 ℃. Pyrolysis 110 at the first temperature may be carried out for about 1 hour, or from about 0.25 hours to about 2 hours. Pyrolysis at the second temperature may be carried out for about 1 hour, or from about 0.25 hours to about 2 hours. The pyrolysis duration may be adjusted for the thickness T of the layer of host material 13, wherein a thinner layer of host material 13 generally requires a shorter pyrolysis duration. In some embodiments, the thickness T of the layer of silicon-based host material 13 is about 20 microns to about 50 microns, or up to about 50 microns.