Novel composites for anode electrodes

Abstract

A novel composite is described for use in an anode electrode of a battery. The novel composite comprises a silicon-based nanostructure attached to a carbon-based substrate with a polymer disposed thereon, the polymer comprising monomer units formed from styrene and allyl alcohol. The composite allows the preparation of an anode electrode with a low ratio of inactive material to active material and improved processability by both wet and dry anode coating techniques. Anode electrodes comprising the composite have improved uniformity and tend to better accommodate volume changes during cycling.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 293,442, filed December 23, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] The technology described herein relates to composites for use in anode electrodes of batteries, as well as anode electrodes and batteries (e.g., lithium ion batteries) comprising the composites, and methods for preparing the same. In particular, the technology described herein relates to composites comprising silicon-based nanostructures attached to a carbon-based substrate, such as a carbon-based powder. [Background technology]

[0003] There has been a great deal of effort focused on reducing the cost and increasing the performance of energy storage devices, and the goal towards widespread adoption of electric vehicles (EVs) has been a major motivator for this effort. Strategies ranging from adopting new anode active materials (e.g., silicon-carbon anode materials) to improve performance, to applying new cell manufacturing methods (e.g., dry electrode coating or prelithiation) to reduce cost, have been explored by many, with most being forced by difficult trade-offs to combine new materials and large-scale production methods while simultaneously reducing cost, with uncertain results.

[0004] The manufacture of high energy density anode electrodes for EV cells requires mixing active materials, such as silicon and graphite, with inactive materials, such as binders and conductive additives. Since the inactive materials do not contribute to reversible lithium and electron storage in the anode, there is a trend to reduce the mass ratio of inactive materials to active materials in order to increase the energy density of EV cells while reducing the total mass. Furthermore, the incorporation of more silicon, which has a higher specific capacity and a slightly higher voltage plateau than graphite, into the anode typically allows the anode electrode to be thinner and charge faster. However, the volume change associated with the alloying of lithium ions with silicon (up to 300%) is much larger than the volume change associated with the intercalation of lithium ions into graphite (typically less than 10%). This creates a significant problem in the selection of a polymer binder that can maintain the mechanical and electrical integrity of the anode layer and adhesion to the current collector foil, while safely allowing higher silicon anode content while reducing manufacturing costs.

[0005] Some of the major binders that are accepted for use in aqueous electrode fabrication for silicon-based anode electrodes are carboxymethyl cellulose (CMC) and polyacrylic acid (PAA). These binders are soluble in water and provide high mechanical stiffness and hardness. However, CMC and PAA used as the sole binders require high binder content (e.g., around 8 wt %) in the silicon-graphite anode electrode layer, which can increase the stiffness and hardness of the anode and have negative effects on the electrode winding process and other important production processes.

[0006] Another strategy used today is to use styrene butadiene rubber (SBR) as a binder to improve flexibility, bond strength, adhesion and cohesion, however, SBR is difficult to disperse uniformly in the electrode slurry and can adversely affect electrode performance.

[0007] In other cases, efforts to develop silicon as a usable anode material for lithium-ion batteries have typically been directed to one of the following approaches: (a) mixing small amounts of silicon oxide additives (e.g., SiOx, where x is close to a value of 1) with graphite particles, and / or (b) embedding silicon particles in a carbon shell that includes amorphous carbon, hard carbon, and / or pyrolytic polymer. In both approaches, the anode is formed by mixing the anode active material with a polymer binder to produce a slurry, which is then used to form an anode layer on a copper current collector foil. However, these approaches exhibit several drawbacks. For example, the strategy according to approach (a) is technically complex and relatively costly, meaning that it is limited to formulations that contain only small amounts of silicon, resulting in anodes that exhibit first cycle efficiencies of less than 90%, and therefore require costly cathode materials to compensate. The strategy according to approach (b) requires a silicon precursor to form the silicon particles and a carbon precursor to form the shell. The cost of producing these carbon shells is prohibitive due to the low conversion rate of the silicon precursor to reversible silicon capacity in the anode. Furthermore, the new materials and particles involved in these two-approach strategies can have a significant effect on the rheology of the anode slurry, which in turn can impair the uniformity of the anode coating, the uniformity of the silicon distribution within the anode layer, and the adhesion of the anode layer to the current collector foil. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 10,243,207 [Patent Document 2] U.S. Patent No. 9,812,699 [Patent Document 3] U.S. Patent No. 5,677,082 [Patent Document 4] U.S. Patent No. 6,303,266 [Patent Document 5] U.S. Patent No. 6,479,030 Summary of the Invention [Means for solving the problem]

[0009] Aspects of the present disclosure are directed to improved silicon-based anode materials that have a low ratio of inactive material to active material, provide improved processability, increase the uniformity of the slurry and silicon distribution in the anode layer, can facilitate the prelithiation process, and / or are suitable for large-scale production at competitive costs using current and future cell production facilities.

[0010] According to a first aspect, there is provided a composite comprising a plurality of silicon-based nanostructures attached to a carbon-based substrate, the plurality of silicon-based nanostructures and the carbon-based substrate having a polymer disposed thereon, the polymer comprising monomer units formed from styrene and allyl alcohol.

[0011] According to a second aspect, there is provided a method for preparing a composite, the method comprising: mixing a plurality of silicon-based nanostructures attached to a carbon-based substrate with a solution of a polymer comprising monomer units formed from styrene and allyl alcohol to form a mixture; and drying the mixture.

[0012] According to a third aspect there is provided a conjugate obtained, directly obtained or obtainable by the method of the second aspect.

[0013] According to a fourth aspect, there is provided an anode electrode comprising a first anode layer, the first anode layer comprising a binder and a composite as described herein.

[0014] According to a fifth aspect, there is provided a method for preparing an anode electrode, the method comprising mixing a composite as described herein with a binder and applying an anode layer of the mixture resulting from the mixing step.

[0015] According to a sixth aspect, there is provided an anode electrode obtained, directly obtained or obtained by the method of the fifth aspect.

[0016] According to a seventh aspect, there is provided a battery comprising the composite and / or anode electrode described herein.

[0017] To describe the above-listed disclosure and how its advantages and features can be obtained, a more particular description of the above principles will be given by reference to the specific examples illustrated in the accompanying drawings. These drawings merely depict exemplary aspects of the disclosure and therefore should not be construed as limiting its scope. These principles will be described and explained with further specificity and detail through the use of the following figures. [Brief description of the drawings]

[0018] [Figure 1A] FIG. 2 shows an SEM (scanning electron microscope) image showing silicon-based nanowires attached to the surface of a particle of uncoated natural graphite (uncoated natural graphite) for use in a composite according to an embodiment of the present invention. [Figure 1B] 1 shows an SEM image of a portion of a particle of uncoated natural graphite for use in a composite according to an embodiment of the present invention, the particle being cut using FIB (focused ion beam) cutting to reveal the inner wall surfaces of the pores in the graphite particle and the silicon-based nanowires deposited thereon. [Figure 1C] 1C is an SEM image showing a portion of a particle of uncoated natural graphite for use in a composite according to an embodiment of the present invention (1C is an enlarged view of the rectangular portion of 1B). The particle has been cut using FIB (focused ion beam) cutting to reveal the inner wall surfaces of the pores in the graphite particle and the silicon-based nanowires deposited thereon. [Figure 2A] FIG. 1 is a flow diagram illustrating a method for preparing a complex in accordance with an embodiment of the present invention. [Figure 2B] FIG. 1 is a flow diagram illustrating a method for preparing a complex in accordance with an embodiment of the present invention. [Diagram 3] FIG. 2 is a flow diagram illustrating a method for preparing an anode electrode in accordance with an embodiment of the present invention. [Figure 4] 1 is a graph showing curves illustrating the performance of a half cell in accordance with an embodiment of the present invention. [Diagram 5] 1 is a graph showing curves illustrating the cycling performance of an anode in a full cell in accordance with an embodiment of the present invention. [Figure 6] 6A-6C are graphs illustrating curves showing half cells in accordance with an embodiment of the present invention, and are detailed views of a portion of the curve shown in FIG. [Figure 7A] FIG. 1 shows a TEM image of silicon nanowires and graphite particles coated with a uniform PSAA carbonized layer in accordance with an embodiment of the present invention. [Figure 7B] FIG. 1 shows a TEM image of silicon nanowires and graphite particles coated with a uniform PSAA carbonized layer in accordance with an embodiment of the present invention. [Figure 8] 1 is a graph illustrating cycling performance between a baseline battery cell and a battery cell in accordance with an embodiment of the present invention using a first cycling protocol. [Figure 9] 1 is a graph illustrating cycling performance between a baseline battery cell and a battery cell in accordance with an embodiment of the present invention using a second cycling protocol different from the first. [Figure 10] FIG. 1 shows the specifications, first charge capacity and first discharge capacity of four sets of electrochemical cells containing anode material composites with different SiNW-carbon and PSAA combinations. [Figure 11] 1 is a graph showing the discharge specific capacity over hundreds of cycles for two types of electrochemical cells: the first type includes an anode composite prepared using a single surface treatment, and the second type includes an anode composite prepared using a dual surface treatment. [Figure 12]1 is a graph showing % capacity retention over hundreds of cycles for two types of electrochemical cells: the first type includes anode composites prepared using a single surface treatment, and the second type includes anode composites prepared using a dual surface treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] definition As used herein, a "nanostructure" is a structure having at least one region or characteristic dimension having a dimension less than about 500 nm, e.g., less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm. Typically, the region or characteristic dimension is along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, nanofibers, nanoparticles, and the like. Nanostructures may be, for example, substantially crystalline, substantially monocrystalline, polycrystalline, amorphous, or combinations thereof. In certain embodiments, each of the three dimensions of the nanostructure has a dimension less than about 500 nm, e.g., less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm.

[0020] As used herein, "aspect ratio" refers to the length of a first axis of a nanostructure divided by the average of the lengths of the second and third axes of the nanostructure, where the second and third axes are the two axes whose lengths are closest to being equal. For example, the aspect ratio of a perfect rod would be the length of its long axis divided by the diameter of the cross section perpendicular to the long axis.

[0021] As used herein, the "diameter" of a nanostructure refers to the diameter of a cross section perpendicular to a first axis of the nanostructure, the first axis having the greatest length difference relative to the second and third axes (the second and third axes being the two axes that are closest to being equally long). The first axis is not necessarily the longest axis of the nanostructure, e.g., in the case of a disk-shaped nanostructure, the cross section is a substantially circular cross section perpendicular to the short longitudinal axis of the disk. If the cross section is not circular, the diameter is the average of the longer and shorter axes of the cross section. In the case of elongated or high aspect ratio nanostructures, e.g., nanowires, the diameter is measured between the two ends of a cross section perpendicular to the longest axis of the nanowire. In the case of spherical nanostructures, the diameter is measured from one side through the center of the sphere to the other.

[0022] As used herein, the term "crystalline" or "substantially crystalline" when used in reference to nanostructures refers to the fact that the nanostructures typically exhibit long-range order across one or more dimensions of the structure. One of skill in the art will appreciate that the term "long-range order" depends on the absolute size of a particular nanostructure, since order for a single crystal cannot extend beyond the boundaries of the crystal. In this case, "long-range order" refers to substantial order across at least most of the dimensions of the nanostructure. In some examples, the nanostructures may have an oxide or other coating, or may be comprised of a core and at least one shell. In such examples, it is understood that the oxide, shell, or other coating need not exhibit such order (e.g., may be amorphous, polycrystalline, or otherwise). In such examples, the phrases "crystalline," "substantially crystalline," "substantially monocrystalline," or "monocrystalline" refer to the central core of the nanostructure (excluding any coating layers or shells). The terms "crystalline" or "substantially crystalline," as used herein, are also intended to encompass structures that contain various defects, stacking disorders, atomic substitutions, and the like, so long as the structures exhibit substantial long-range order (e.g., order over at least about 80% of the length of at least one axis of the nanostructure or its core). In addition, it is understood that the interface between the core and the exterior of the nanostructure, or between the core and an adjacent shell, or between a shell and a second adjacent shell, may contain non-crystalline regions or even be amorphous. This does not prevent the nanostructure from being crystalline or substantially crystalline as defined herein.

[0023] As used herein, the term "monocrystalline" when used in reference to a nanostructure indicates that the nanostructure is substantially crystalline and comprises substantially a single crystal. When used in reference to a nanostructure heterostructure comprising a core and one or more shells, "monocrystalline" indicates that the core is substantially crystalline and comprises substantially a single crystal.

[0024] As used herein, a "nanoparticle" is a nanostructure having each dimension (e.g., each of the three dimensions of the nanostructure) less than about 500 nm, e.g., less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm. Nanoparticles may be of any shape, including, for example, nanocrystals, substantially spherical particles (having an aspect ratio of about 0.8 to about 1.2), and irregularly shaped particles. Nanoparticles may optionally have an aspect ratio of less than about 1.5. Nanoparticles may be amorphous, crystalline, monocrystalline, partially crystalline, polycrystalline, or otherwise. Nanoparticles may be substantially uniform in material properties, or in certain embodiments, may be heterogeneous (e.g., heterostructures). Nanoparticles may be made from essentially any convenient material, for example, nanoparticles may include "pure" materials, substantially pure materials, doped materials, and the like.

[0025] A "nanowire" is a nanostructure with one major axis that is longer than the other two major axes. As a result, nanowires have an aspect ratio greater than 1, and the nanowires of the present invention typically have an aspect ratio greater than about 1.5, or greater than about 2. Short nanowires, sometimes called nanorods, typically have an aspect ratio between about 1.5 and about 10. Longer nanowires have an aspect ratio greater than about 10, greater than about 20, greater than about 50, or greater than about 100, or even greater than about 10,000. The diameter of a nanowire is typically less than about 500 nm, preferably less than about 200 nm, more preferably less than about 150 nm, and most preferably less than about 100 nm, about 50 nm, or about 25 nm, or even less than about 10 nm or about 5 nm. Nanowires may be substantially uniform in material properties, or in certain embodiments may be non-uniform (e.g., nanowire heterostructures). Nanowires can be made from essentially any convenient material. Nanowires can include "pure" materials, substantially pure materials, doped materials, and the like, and can include insulators, conductors, and semiconductors. Nanowires are typically substantially crystalline and / or substantially monocrystalline, but may be, for example, polycrystalline or amorphous. In some examples, nanowires can have an oxide or other coating, or can include a core and at least one shell. In such examples, it is understood that the oxide, shell, or other coating need not exhibit such order (e.g., may be amorphous, polycrystalline, or otherwise). Nanowires can have an inconstant diameter, or a substantially uniform diameter, i.e., a diameter that exhibits a variance of less than about 20% (e.g., less than about 10%, or less than about 5%, or less than about 1%) over the area of ​​greatest variation and over a linear dimension of at least 5 nm (e.g., at least 10 nm, at least 20 nm, or at least 50 nm). Typically, the diameter is evaluated away from the ends of the nanowire (eg, over the central 20%, 40%, 50% or 80% of the nanowire).A nanowire may be straight over the entire length of its long axis, or over a portion thereof, or may be curved or bent, for example. In certain embodiments, a nanowire, or a portion thereof, may exhibit two- or three-dimensional quantum confinement. Nanowires, in some embodiments, may explicitly exclude carbon nanotubes, and in certain embodiments, exclude "whiskers" or "nanowhiskers," particularly whiskers having a diameter of more than 100 nm or more than about 200 nm.

[0026] As used herein, "silicon-based," when used with respect to nanostructures, indicates that the nanostructures comprise at least about 50% silicon by weight. Suitably, silicon-based nanostructures comprise at least about 60% silicon by weight, at least about 70% silicon by weight, at least about 80% silicon by weight, at least about 90% silicon by weight, at least about 95% silicon by weight, or about 100% silicon by weight, including 100% silicon.

[0027] As used herein, "carbon-based substrate" refers to a porous substrate comprising at least about 50% by weight carbon. Suitably, the carbon-based substrate comprises at least about 60% by weight carbon, at least about 70% by weight carbon, at least about 80% by weight carbon, at least about 90% by weight carbon, at least about 95% by weight carbon, or about 100% by weight carbon, including 100% carbon. The carbon-based substrate may be in the form of a sheet or discrete particles, and may be a cross-linked structure. The carbon-based substrate specifically excludes metallic materials, such as steel, including stainless steel. Typically, the carbon-based substrate is a graphite powder (e.g., artificial graphite powder or natural graphite powder). The graphite powder may be coated (e.g., carbon coated) or uncoated. The carbon-based substrate particles may be of essentially any desired shape, such as spherical or substantially spherical, elongated, elliptical / oval, and / or plate-like (e.g., plate, flake, or sheet). Similarly, the carbon-based substrate (e.g., graphite particles) can be of essentially any size and porosity. Typically, the carbon-based substrate (e.g., graphite particles) has a D of between about 0.5 μm and about 50 μm. 50 D 50 is understood to refer to the median particle diameter corresponding to the 50th percentile of the cumulative undersize distribution. The measurement method used is laser diffraction according to ISO standard number 13320. Thus, for example, if the carbon-based substrate is a graphite powder, a D of 0.5 μm to 50 μm is used. 50 means that a graphite powder sample has a D of 0.5 μm or more and 50 μm or less when measured by laser diffraction in accordance with ISO #13320. 50It is understood that this means having a D of between about 0.5 μm and about 2 μm, between about 2 μm and about 10 μm, between about 2 μm and about 5 μm, between about 5 μm and about 50 μm, between about 10 μm and about 30 μm, between about 10 μm and about 20 μm, between about 15 μm and about 25 μm, between about 15 μm and about 20 μm, or about 20 μm. This measurement is commonly used in the specifications of commercially available carbon-based substrates (e.g., graphite powder) used by lithium ion battery manufacturers and is therefore well understood by those skilled in the art. Alternatively, the carbon-based substrate may have a D of between about 0.5 μm and about 2 μm, between about 2 μm and about 10 μm, between about 2 μm and about 5 μm, between about 5 μm and about 50 μm, between about 10 μm and about 30 μm, between about 10 μm and about 20 μm, between about 15 μm and about 25 μm, between about 15 μm and about 20 μm, or about 20 μm. 50 The graphite powder (e.g., coated or uncoated, natural or artificial graphite powder) may include particles with a plurality of pores disposed therein and a surface area including the inner wall surfaces of the openings that define the plurality of pores. As is known to those skilled in the art, the porosity of graphite particles can be estimated from various types of measurements, such as gas absorption surface area according to "BET" or "SSA" standards, direct FIB SEM imaging, and mercury porosimetry. A standard definition of porosity is "the percentage of the total volume of the material that is occupied by pores", as found in ASTM Standard C709, which has definitions of the term for manufactured carbon and graphite. When calculating the apparent density of a material, the pore volume is included in the calculation. This results in a porosity of 1.6 g / cm. 3 ~1.90g / cm 3 The typical apparent density of synthetic graphite was obtained, 2.26 g / cm 3 (The specific capacity of graphite is the reciprocal of the specific density.) The difference between the apparent density (particle mass divided by particle volume including pore volume) and the theoretical density (mass per unit volume without pores) is a measure of the total pore volume per unit mass. Porosity can then be defined as the fraction of pore volume per unit mass divided by the sum of the specific capacity and the pore volume per unit mass. A typical apparent (bulk) density of natural graphite for anode applications is 1.2 g / cm, where the porosity of natural graphite is in the range of about 5% to about 50%. 3 ~2.14g / cm 3 is within the range.

[0028] The term "about," as used herein, indicates that the value of a given quantity may vary by ±10% of that value, or optionally, in some cases, by ±5% of that value, or in some embodiments, by ±1% of the stated value.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The following definitions supplement those in the art and are directed to this application and should not be attributed to any related or unrelated cases, such as commonly owned patents or applications. Although any methods and materials similar or equivalent to those described herein can be used in practice, certain materials and methods are described herein. Thus, the terminology used herein is only for the purpose of describing specific embodiments and is not intended to be limiting.

[0030] Throughout the description and claims of this specification, when subject matter is described herein using the term "comprise" (or "comprises" or "comprising"), it is contemplated that the same subject matter is instead described using the term "consist of" (or "consists of" or "consisting of") or "consist essentially of" (or "consists essentially of" or "consisting essentially of").

[0031] Throughout this specification and the claims, the singular encompasses the plural unless the context requires otherwise. In particular, where the indefinite article is used, the specification is to be understood as contemplating plural as well as singular, unless the context requires otherwise.

[0032] It is to be understood that features (and their relative suitability) described in conjunction with a particular aspect, embodiment or example may be applied to any other aspect, embodiment or example described herein, unless incompatible. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) and / or all of the steps of any disclosed method or process may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. The invention is not limited to the details of any of the specific embodiments recited herein. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) or any novel one, or any novel combination of the steps of any disclosed method or process.

[0033] Unless otherwise specified, when the quantity or concentration of a particular component in a given product is identified as a percentage by mass (% by mass, wt%) or % w / w), the percentage by mass refers to the percentage by mass of the component relative to the total mass of the entire product. It will be understood by one of ordinary skill in the art that the sum of the mass percentages of all components of a product totals 100% by mass. However, when components are not all listed (e.g., when a product is said to "comprise" one or more particular components), unspecified components can optionally and in some cases make up the remaining mass percentage up to 100% by mass.

[0034] Unless otherwise specified, when a range is provided, the value can be any value or range of values ​​within that range.

[0035] Conjugates and their preparation In one aspect, an embodiment provides a composite comprising a plurality of silicon-based nanostructures attached to a carbon-based substrate, the plurality of silicon-based nanostructures and the carbon-based substrate having a polymer disposed thereon, the polymer comprising monomer units formed from styrene and allyl alcohol.

[0036] After rigorous research, the inventors have surprisingly found that the application of a polymer containing monomer moieties (monomer-derived units) formed from styrene and allyl alcohol to silicon-based nanostructures attached to a carbon-based substrate greatly enhances the dispersion and binding capabilities of the resulting composite, which can be directly and inexpensively processed with other active and inactive materials (e.g., binders, conductive additives, etc.) to form a highly uniform anode material. In particular, the inventors have determined that the characteristics of the polymer disposed on the silicon-based nanostructures and carbon-based substrate create favorable binding interactions with materials commonly used as binders in the preparation of battery anode materials. This improved interaction between the anode slurry components allows the preparation of anode materials using both wet and dry processing methods that have a high ratio of active material to inactive material and also have the ability to provide a longer cycle life, i.e., a higher anode reversible capacity over more charge / discharge cycles, even when the charge or discharge involves a higher current. Furthermore, polymers containing monomer moieties (monomer-derived units) formed from styrene and allyl alcohol can form more stable interfaces between silicon-based nanostructures and semi-solid / solid-state electrolytes and exhibit improved ability to withstand volume changes that occur in silicon-based nanostructures during charge / discharge cycling. As a result, batteries incorporating the composites described herein provide improved electrical properties (e.g., specific capacity, and / or initial coulombic efficiency (ICE), and / or capacity retention over many charge / discharge cycles, even at high C-rates).

[0037] The composite is suitable for use in an anode electrode, particularly an anode electrode of a lithium ion battery.

[0038] For polymers disposed on a plurality of silicon-based nanostructures and carbon-based substrates, a monomer unit formed from styrene is understood to refer to a repeat unit whose repeats form a polystyrene chain (ignoring the end groups). Similarly, a monomer unit formed from allyl alcohol (i.e., prop-2-en-1-ol) is understood to refer to a repeat unit whose repeats form a poly(allyl alcohol) chain (ignoring the end groups). The monomer units formed from styrene and allyl alcohol are depicted below:

[0039] [ka]

[0040] Without wishing to be bound by theory, the inventors hypothesize that the structure and / or properties of the polymer comprising monomer units formed from styrene and allyl alcohol promote improved interaction with other anode slurry components, which in turn improves the dispersion ability of silicon-based nanostructures attached to the carbon-based substrate, making the anode material more uniform. In particular, the functional groups / structural motifs present on the polymer are free to participate in intermolecular interactions with functional groups / structural motifs that may be present on the binder contained in the slurry. As an example, the hydroxyl groups of the polymer can participate in hydrogen bonding with groups present on the binder (e.g., hydroxyl groups present on carboxymethyl cellulose), and / or the phenyl groups of the polymer can participate in pi-pi stacking with groups present on the binder (e.g., phenyl groups present on styrene-butadiene rubber). The improved dispersion capability of silicon-based nanostructures attached to carbon-based substrates is particularly important when preparing anodic materials by dry coating methods, for example, when a solid mixture of silicon-based nanostructures attached to a carbon-based substrate is dispersed in a thermoplastic polymer binder (e.g., polytetrafluoroethylene) under solvent-free conditions and then laminated as a film onto a current collector.

[0041] The polymer comprising monomer units formed from styrene and allyl alcohol may form a coating (e.g., a partial or complete coating) on ​​the silicon based nanostructures and the carbon based substrate. Preferably, the polymer is substantially uniformly disposed (e.g., coated) on the silicon based nanostructures and the carbon based substrate.

[0042] Polymers containing monomer units formed from styrene and allyl alcohol preferably have a softening point below 200°C. Such polymers typically exhibit better compatibility with binders used in anode slurries. More preferably, the polymer has a softening point between 50°C and 100°C. Most preferably, the polymer has a softening point between 60°C and 90°C.

[0043] The polymer containing monomer units formed from styrene and allyl alcohol had a molecular weight of 800 gmol as determined by gas permeation chromatography (GPC). -1 ~5000gmol -1 Molecular weight (M n ). Preferably, the polymer has a molecular weight of 1000 gmol -1 ~3000gmol -1 Molecular weight (M n Most preferably, the polymer has a molecular weight of 1200 gmol -1 ~2000gmol -1 Molecular weight (M n ).

[0044] Polymers containing monomer units formed from styrene and allyl alcohol are preferably soluble in alcohol solvents, especially ethanol. Polymers that exhibit these solubility characteristics facilitate drying of the resulting composite. In contrast to the use of water-soluble polymers, solutions of polymers that are soluble in, for example, ethanol can be dried directly at lower temperatures without leaving any solvent residues on the silicon-based nanostructures that may adversely affect battery performance. More preferably, the polymer is insoluble in water. The polymer may be insoluble in carbonate-based electrolytes, such as those used in the preparation of lithium-ion batteries. Preferably, ethanol may be recovered and reused during the drying process, thereby reducing costs and waste.

[0045] A polymer comprising monomer units formed from styrene and allyl alcohol may comprise at least 20 mol % (e.g., 20 mol % to 50 mol %) of monomer units formed from allyl alcohol. Preferably, the polymer comprises 25 mol % to 45 mol % of monomer units formed from allyl alcohol. Most preferably, the polymer comprises 30 mol % to 36 mol % of monomer units formed from allyl alcohol. In addition, the polymer may comprise at least 50 mol % of monomer units formed from styrene.

[0046] In certain embodiments, the polymer comprising monomer units formed from styrene and allyl alcohol is poly(styrene-co-allyl alcohol) (PSAA). The polymer may have any of the properties described above. PSAA is an inexpensive, environmentally friendly, non-toxic polymer that is readily soluble in ethanol.

[0047] The composite may contain 0.1% to 10% by weight of a polymer containing monomer units formed from styrene and allyl alcohol (e.g., PSAA).Suitably, the composite contains 0.5% to 5% by weight (e.g., 0.7% to 2% by weight) of the polymer.

[0048] The silicon-based nanostructures are attached to the carbon-based substrate and are in electrical relationship with each other. Typically, the silicon-based nanostructures are attached to the outer surface of the carbon-based substrate. However, if the carbon-based substrate is porous (e.g., porous graphite powder), the silicon-based nanostructures may be attached to both the inner surface (the surface defining the pores) and the outer surface of the carbon-based substrate. This can be achieved by several methods known in the art. For example, silicon-based nanostructures (e.g., silicon nanowires) can be grown from catalyst particles deposited on the carbon-based substrate (e.g., graphite particles) by vapor-liquid-solid (VLS) or vapor-solid-solid (VSS) chemical vapor deposition. Alternatively, silicon-based nanostructures (e.g., silicon nanowires) can be electrochemically deposited on the carbon-based substrate (e.g., graphite particles). See U.S. Pat. Nos. 10,243,207 and 9,812,699, which are incorporated herein by reference in their entirety. In some embodiments, the silicon-based nanostructures are mechanically attached to the carbon-based substrate. In some embodiments, the silicon-based nanostructures are attached to the carbon-based substrate and are in electrical relationship with each other without the need for the use of a conductive polymer to achieve mechanical and electrical connection. In some embodiments, the electrical relationship is via a low electrical impedance pathway during cycling.

[0049] In certain embodiments, the silicon-based nanostructure is preferably a silicon-based nanowire, e.g., a silicon nanowire. The dimensions of the silicon-based nanostructure (e.g., silicon nanowire) have been previously described herein. Preferably, the silicon-based nanowire (e.g., silicon nanowire) has a diameter in the range of 10 nm to 200 nm. The silicon-based nanostructure may comprise a monocrystalline core and a shell layer, where the shell layer comprises amorphous silicon, polycrystalline silicon, or a combination thereof.

[0050] The carbon-based substrate is provided as a plurality of particles, with the silicon-based nanostructures attached to (e.g., on) the surface of the particles. Some particles may have more silicon-based nanostructures attached than others. The carbon-based substrate may be selected from graphite powder (e.g., artificial graphite powder or natural graphite powder), which may be coated (e.g., carbon coated) or uncoated, mesocarbon microbead powder (also referred to as "MCMB" in industrial applications), or combinations thereof. Most preferably, the carbon-based substrate is graphite powder. The dimensions of the carbon-based substrate are described hereinbefore. Preferably, the carbon-based substrate (e.g., graphite powder) has a D in the range of about 5 μm to about 50 μm, as measured by standard industry practices and equipment. 50 Preferably, the carbon-based substrate (e.g., graphite powder) has a porosity in the range of about 10% to 30%, as measured by methods known in the art as described above. In the examples provided herein, Brunauer-Emmett-Teller (BET) measurements and direct FIB SEM imaging were used to measure the porosity and visualize the nanowires and PSAA coating as shown in the figures.

[0051] The plurality of silicon-based nanostructures (e.g., silicon nanowires) and the carbon-based substrate (e.g., graphite powder) may together comprise 90% or more by mass of the composite. Preferably, the plurality of silicon-based nanostructures and the carbon-based substrate may together comprise 95% or more by mass of the composite.

[0052] In an embodiment, the silicon-based nanostructure is a silicon nanowire having a diameter in the range of 10 nm to 200 nm. Preferably, the silicon nanowire and the carbon-based powder account for 90% or more by mass of the composite.

[0053] The plurality of silicon-based nanostructures (e.g., silicon nanowires) attached to the carbon-based substrate (e.g., graphite powder) may comprise 1% to 40% silicon by weight. Preferably, the plurality of silicon-based nanostructures attached to the carbon-based substrate comprise 2.5% to 25% silicon by weight. Most preferably, the plurality of silicon-based nanostructures attached to the carbon-based substrate comprise 5% to 15% silicon by weight (e.g., 8% to 11% silicon by weight).

[0054] In an embodiment, the silicon-based nanostructures are silicon nanowires having diameters in the range of 10 nm to 200 nm, and the carbon-based substrates are silicon nanowires having diameters in the range of 5 μm to 50 μm. 50 Preferably, the silicon-based nanowires attached to the graphite powder contain 1% to 40% by weight (eg, 5% to 15% by weight) of silicon.

[0055] In an embodiment, the composite comprises 90% by weight or more of a plurality of silicon-based nanostructures (e.g., silicon nanowires) and a carbon-based substrate (e.g., graphite powder), and 0.1% to 10% by weight of a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA). Suitably, the composite comprises 95% by weight or more of a plurality of silicon-based nanostructures and a carbon-based substrate, and 0.5% to 5% by weight (e.g., 0.7% to 2% by weight) of a polymer comprising monomer units formed from styrene and allyl alcohol. Silicon may comprise 2% to 40% by weight (e.g., 5% to 15% by weight) of the plurality of silicon-based nanostructures attached to the carbon-based substrate.

[0056] In certain embodiments, a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA) can be provided as an outer coating layer (partial or complete) on the plurality of silicon-based nanostructures and the carbon-based substrate. In such embodiments, the plurality of silicon-based nanostructures and the carbon-based substrate can further comprise a conductive carbon coating provided as an inner coating layer. The inner coating layer is located between the plurality of silicon-based nanostructures and the carbon-based substrate and the outer coating layer. The conductive carbon coating can be formed by carbonizing (e.g., at a temperature between 200° C. and 750° C.) a polymeric coating pre-disposed on the silicon-based nanostructures and the carbon-based substrate, and the polymeric coating can be a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA).

[0057] In some embodiments, the composite comprises a population of silicon based nanostructures and carbon based substrate having a polymer comprising monomer units formed from styrene and allyl alcohol disposed directly on the silicon based nanostructures and carbon based substrate, and a population of silicon based nanostructures and carbon based substrate having a polymer comprising monomer units formed from styrene and allyl alcohol disposed indirectly on the silicon based nanostructures and carbon based substrate through an intervening conductive carbon coating.

[0058] The composite may further comprise a conductive additive. Conductive additives useful in preparing battery anode materials are well known to those skilled in the art and include carbon black particles, carbon nanofibers, carbon nanotubes, graphite particles, graphene particles, mesocarbon microbead particles, and combinations of two or more thereof. As used herein, "carbon black" refers to a material produced by the incomplete combustion of petroleum products. Carbon black is a form of amorphous carbon that has an extremely high surface area to volume ratio. "Graphene" refers to a single atomic layer of carbon formed as a sheet and can be prepared as graphene powder. See U.S. Patent Nos. 5,677,082, 6,303,266, and 6,479,030, the disclosures of each of which are incorporated herein by reference in their entirety. A particularly suitable conductive additive is carbon black. When present, the conductive additive can be disposed on or dispersed throughout the polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA). In some embodiments, the use of a conductive carbon coating formed from carbonized PSAA may eliminate the need for additional conductive additives.

[0059] The composite is preferably provided as a plurality of particles. The exact form of the composite depends on the nature of the silicon-based nanostructure and the carbon-based substrate. For example, the composite can be provided as a powder (e.g., a free-flowing powder). The presence of a polymer comprising monomer units formed from styrene and allyl alcohol on the outer surface of the silicon-based nanostructure and the carbon-based substrate results in little, if any, aggregation between individual composite particles at room temperature or at a temperature below the softening point of the polymer.

[0060] In a second aspect, embodiments provide a method for preparing a composite, which method is illustrated, for example, in Figure 2A. As shown in Figure 2A, the method (100) includes mixing (104) a plurality of silicon-based nanostructures attached to a carbon-based substrate with a solution of a polymer including monomer units formed from styrene and allyl alcohol to form a mixture, and drying (108) the mixture.

[0061] It will be appreciated that features of the second aspect described hereinbefore with respect to the first aspect may have any of the definitions set forth above.

[0062] Silicon-based nanostructures attached to a carbon-based substrate can be prepared by growing silicon-based nanostructures (e.g., silicon nanowires) from catalyst particles deposited on the surface of the carbon-based substrate by VLS or VSS chemical vapor deposition. In some embodiments, the carbon-based substrate is a graphite powder (e.g., natural graphite powder or artificial graphite powder) including a plurality of graphite particles, each of which has a plurality of pores, and the silicon-based nanostructures (e.g., silicon nanowires) are grown from catalyst particles (e.g., catalyst nanoparticles including copper, copper compounds, and / or copper alloys) deposited on the outer and inner surfaces (i.e., the surfaces defining the pores) of the graphite particles by VLS or VSS chemical vapor deposition, thereby obtaining silicon-based nanostructures attached to the outer and inner surfaces of the graphite particles. 1A-1C show SEM images of uncoated natural graphite particles comprising silicon-based nanowires attached to the surfaces of the graphite particles, including silicon nanowires attached to the interior surfaces of the graphite particles (i.e., the surfaces defining the pores).

[0063] The solution of the polymer (e.g., PSAA) may include the polymer and ethanol. In contrast to the use of water-soluble polymers, polymers that are soluble in ethanol can be directly dried at low temperature and / or subatmospheric pressure without leaving any solvent residue on the silicon-based nanostructures that may adversely affect the battery performance. The ethanol removed during drying can be recovered and reused in the process. Preferably, the solution contains less than 5% water by weight. More preferably, the solution is water-free.

[0064] The solution of the polymer may contain 0.05% to 10% by weight of the polymer (eg, 0.05% to 10% by weight of the polymer in ethanol), preferably 0.1% to 3% by weight of the polymer.

[0065] The drying step may be carried out at ambient or reduced pressure (e.g. under vacuum) and at a temperature in the range of 20° C. to 150° C. Suitably, the drying step is carried out at a temperature of 30° C. to 130° C. Step (b) may be carried out under an inert gas (e.g. nitrogen).

[0066] In another aspect, embodiments provide a method for preparing a composite, for example as depicted in Figure 2B. As shown in Figure 2B, the method (process) (150) includes mixing (154) a plurality of silicon-based nanostructures attached to a carbon-based substrate with a solution of a polymer including monomer units formed from styrene and allyl alcohol to form a mixture, and drying (158) the mixture.

[0067] In an embodiment, the plurality of silicon based nanostructures and the carbon based substrate have a conductive carbon coating disposed thereon. The coating may be partial or complete. The conductive carbon coating may be formed by carbonizing (162) a polymeric coating pre-disposed on the plurality of silicon based nanostructures and the carbon based substrate, as shown in FIG. 2B. The polymeric coating may include monomer units formed from styrene and allyl alcohol (e.g., PSAA). The polymeric coating may be pre-disposed on the plurality of silicon based nanostructures and the carbon based substrate by mixing the plurality of silicon based nanostructures and the carbon based substrate with a solution of polymeric material (e.g., a solution of PSAA in ethanol, e.g., a 5-10 wt. % solution of PSAA in ethanol). The polymeric material pre-disposed on the plurality of silicon-based nanostructures and the carbon-based substrate is then carbonized by heating the plurality of silicon-based nanostructures and the carbon-based substrate, optionally in an inert atmosphere (e.g., under nitrogen), to a temperature of 200° C. to 750° C. (e.g., 500° C. to 750° C.) such that, in some embodiments, the composite obtained by drying can include a PSAA disposed on the carbonized PSAA coating layer provided on the silicon-based nanostructures and the carbon-based substrate.

[0068] The composite obtained by drying is preferably a powder (e.g., a free-flowing powder). By using a polymer containing monomer units formed from styrene and allyl alcohol (especially PSAA), little to no aggregation occurs between the composite particles.

[0069] As shown in FIG. 2B, the method (150) may further include mixing (166) the carbon-coated Si-based nanostructures attached to the carbon-based substrate with a solution of a polymer comprising monomer units formed from styrene and allyl alcohol, and drying (170) the mixture to obtain a composite comprising the polymer coating disposed on the carbon-coated Si-based nanostructures attached to the carbon-based substrate.

[0070] In a third aspect, embodiments provide a conjugate obtained, directly obtained or obtainable by the method of the second aspect.

[0071] Anode Electrode and Its Preparation In a fourth aspect, an embodiment provides an anode electrode comprising a first anode layer, the first anode layer comprising a binder and a composite as described herein.

[0072] Anode electrodes comprising a polymer comprising a monomer moiety formed from styrene and allyl alcohol disposed on a silicon-based nanostructure attached to a carbon-based substrate as described herein have advantageous properties previously discussed herein, including improved uniformity, ease of processing by wet or dry electrode coating methods, improved ability to accommodate volume changes, and excellent adhesion to other anode components, including the current collector and any additional anode layers. Thus, batteries incorporating the anode electrodes of the present invention provide improved electrical performance (e.g., specific capacity and / or initial coulombic efficiency (ICE)).

[0073] It will be appreciated that features of the fourth aspect described herein above in relation to the first, second or third aspects may have any of the definitions set forth above.

[0074] The first anode layer preferably comprises a binder and the composite of the first aspect in an intimate and substantially uniform mixture. Any suitable binder may be used in the first anode layer. Preferably, the binder is selected from the group consisting of styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly(vinylidene fluoride) (PVDF), poly(acrylic acid) (PAA), poly(acrylonitrile) (PAN), poly(acrylamide-co-diallyldimethylammonium) (PAADAA), poly(tetrafluoroethylene) (PTFE), and combinations of two or more thereof. In a particular embodiment, the binder is a mixture of styrene butadiene rubber and carboxymethyl cellulose. For example, the binder can be a mixture of styrene butadiene rubber and carboxymethyl cellulose, including 30% to 70% by weight of styrene butadiene rubber and 30% to 70% by weight of carboxymethyl cellulose, more preferably 40% to 60% by weight of styrene butadiene rubber and 40% to 60% by weight of carboxymethyl cellulose. In another embodiment, the binder is poly(tetrafluoroethylene), which is particularly useful when the first anode layer is prepared by a dry coating method.

[0075] The first anode layer may additionally include a conductive additive, preferably in an amount of 0.2% to 5% by weight. Suitable conductive additives are described herein above. A particularly suitable conductive additive is carbon black. The conductive additive may be dispersed throughout the binder, and / or the composite, binder and conductive additive may form an intimate and substantially uniform mixture within the first anode layer. A polymer including monomer units formed from styrene and allyl alcohol (e.g., PSAA) may be disposed on the conductive additive.

[0076] The first anode layer preferably comprises 90% by weight or more of the composite. As previously described herein, the plurality of silicon-based nanostructures attached to the carbon-based substrate present in the composite may comprise 1% to 40% by weight silicon. As also previously described herein, the composite may comprise 0.1% to 10% by weight of a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA).

[0077] The presence of a polymer comprising monomer units formed from styrene and allyl alcohol in the composite of the first embodiment allows the preparation of an anode electrode having a reduced amount of binder, the anode electrode having a low ratio of inactive material to active material. For example, the first anode layer may comprise 0.5% to 10% by weight of binder. Preferably, the first anode layer comprises 1% to 6% by weight of binder.

[0078] The first anode layer may include 0.5% to 10% by weight of the binder and 90% to 99.5% by weight of the composite. Preferably, the first anode layer includes 1% to 6% by weight of the binder and 94% to 99% by weight of the composite. In the composite, the plurality of silicon-based nanostructures attached to the carbon-based substrate may include 1% to 40% by weight of silicon. The composite may include 0.1% to 10% by weight of a polymer including monomer units formed from styrene and allyl alcohol (e.g., PSAA).

[0079] In some embodiments, the first anode layer comprises 0.5% to 10% by weight of a binder and 90% to 99.5% by weight of a composite, the composite comprising 0.1% to 10% by weight (e.g., 0.5% to 5% by weight) of a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA). Preferably, the binder is a mixture of styrene butadiene rubber and carboxymethyl cellulose (e.g., 30% to 70% by weight of styrene butadiene rubber and 30% to 70% by weight of carboxymethyl cellulose). The first anode layer may further comprise 0.2% to 5% by weight of a conductive additive (e.g., carbon black).

[0080] In some embodiments, the first anode layer may include 1% to 6% by weight of a binder and 94% to 99% by weight of a composite, and the composite may include 0.1% to 10% by weight (e.g., 0.5% to 3% by weight) of a polymer including monomer units formed from styrene and allyl alcohol (e.g., PSAA). Preferably, the binder is a mixture of carboxymethyl cellulose and styrene butadiene rubber (e.g., 40% to 60% by weight of styrene butadiene rubber and 40% to 60% by weight of carboxymethyl cellulose). The first anode layer may further include 0.2% to 5% by weight of a conductive additive (e.g., carbon black).

[0081] The anode electrode may be a single layer anode electrode, such that the first anode layer is a single anode layer.

[0082] Alternatively, the anode electrode may be a multi-layer anode electrode, such that the anode electrode includes one or more additional anode layers. Each additional anode layer may independently include an active material and a binder, preferably in an intimate and substantially uniform mixture. Any one or more of the aforementioned binders may be used. The active material may be selected from the group consisting of graphite powder, a plurality of silicon-based nanostructures attached to a carbon-based substrate, the composite of the first aspect, and combinations of two or more thereof. Each additional anode layer may optionally include one or more conductive additives as described herein. A multi-layer anode electrode may be described as a stack of anode layers (e.g., a first anode layer, and one or more additional anode layers). In a multi-layer anode, one or more of the anode layers may include a different carbon-based substrate and a different amount of silicon-based nanostructures attached to the carbon-based substrate. Each of the layers may also include a D 50 Each of the layers may comprise a different carbon-based substrate. Each of the layers may also have a different porosity. A polymer containing monomer units formed from styrene and allyl alcohol (e.g., PSAA) may be applied to the silicon-based nanostructures and the carbon-based substrate in all layers or in only some layers.

[0083] The anode electrode may further include a current collector. Any suitable current collector may be used in the anode electrode of the present invention. Preferably, the current collector is copper foil or carbon-coated copper foil.

[0084] The first anode layer, and any additional anode layers, are intended to be in electrical communication with the current collector, such that electrical current can flow from the electrolyte to the current collector, which may form part of the anode electrode.

[0085] In certain embodiments, the first anode layer includes a first surface configured to be in contact with (or in contact with) a current collector and a second surface in contact with one or more additional anode layers. The second surface of the first anode layer may include metallic lithium disposed thereon. The metallic lithium may be selected from lithium metal foil, stabilized lithium metal powder, and combinations thereof.

[0086] In other embodiments, the anode electrode includes one or more additional anode layers described herein disposed between the first anode layer and the current collector.

[0087] The first anode layer and any additional anode layers may be substantially free (e.g., completely free) of solvent residues and / or each may be provided as a free-standing film. Such anode layers may be formed, for example, by dry coating methods (e.g., extrusion and / or calendaring). In an embodiment, the anode electrode is a multi-layer anode electrode, and all anode layers are substantially free (e.g., completely free) of solvent residues (e.g., formed by dry coating methods).

[0088] The polymer (e.g., PSAA) containing monomer units formed from styrene and allyl alcohol present in the composite exhibits favorable interactions with binders (e.g., poly(tetrafluoroethylene)) typically used in forming the anode layer by dry coating methods. At room temperature, the composite containing the polymer (e.g., PSAA) is typically provided as a powder with little to no particle agglomeration. The composite (e.g., composite powder) can be mixed directly with the binder to provide an intimate and substantially uniform powder with little to no agglomeration. Moderate increases in temperature (e.g., from 50° C. to 200° C., or from 60° C. to 180° C.) soften the polymer (e.g., PSAA) of the composite and promote adhesion to the binder particles, allowing the dried anode layer to be formed (e.g., extruded and / or calendered) into a film, e.g., a free-standing film.

[0089] In an embodiment, the binder of the first anode layer is poly(tetrafluoroethylene), and the first anode layer is substantially free (e.g., completely free) of solvent residues. The anode electrode may be a single layer anode electrode. Alternatively, the anode electrode may be a multi-layer anode electrode, in which one or more additional anode layers also comprise poly(tetrafluoroethylene) as a binder. The multi-layer anode electrode may be one in which all anode layers are substantially free (e.g., completely free) of solvent residues.

[0090] The first anode layer, and any additional anode layers, have a capacitance of 1 g cm -3 ~1.7g cm -3 Preferably, the first anode layer, and any additional anode layers, have a density of 1.3 g cm -3 ~1.5g cm -3 The density may be

[0091] In a fifth aspect, embodiments provide a method (200) for preparing an anode electrode, as shown in Figure 3. The method of Figure 3 includes mixing (204) a composite described herein with a binder to form a mixture, and applying (208) a layer of the mixture.

[0092] It is understood that the features of the fifth aspect described herein above in relation to the first, second, third or fourth aspects may have any of the definitions set out above. For example, it is understood that the conjugate of the fifth aspect may first be prepared by the process outlined in the second aspect.

[0093] The components mixed during the mixing step may further include a conductive additive. Suitable conductive additives are described herein above. A particularly suitable conductive additive is carbon black. A polymer including monomer units formed from styrene and allyl alcohol (e.g., PSAA) may be disposed on the conductive additive. The amount of conductive additive may be 0.2% to 5% by weight, based on the weight of the composite and (dry) binder.

[0094] The applied layer is configured to be in contact with a current collector. For example, applying a layer of the mixture may include applying a layer of the mixture in electrical communication with a current collector.

[0095] In certain embodiments, the mixture is provided as a wet slurry and the method further comprises drying the applied layer. For example, the binder may be provided as a solution (e.g., an aqueous solution). The dried layer may then be calendered onto the current collector.

[0096] In other embodiments, the mixture is provided as a solid. In such embodiments, the step of applying the layer may include forming (e.g., by extrusion and / or calendering) a layer (e.g., a film) of the solid mixture. Prior to forming, the solid mixture may be heated to a temperature of 50° C. to 200° C. (e.g., 60° C. to 180° C.), which may promote adhesion of the composite and binder, thereby resulting in a more uniform layer. The formed (e.g., extruded and / or calendered) layer may optionally be a free-standing film, possibly free of solvent residues. The formed (e.g., extruded and / or calendered) layer (e.g., a free-standing film) may then be laminated onto a current collector.

[0097] The step of applying a layer of the mixture may include applying a layer of the mixture onto a current collector. The anode electrode may be a single layer anode electrode, such that the applied layer is a single anode layer. Alternatively, the anode electrode may be a multi-layer anode electrode, such that the method further includes applying one or more additional anode layers over the applied layer, the one or more additional anode layers independently comprising an active material and a binder. The application of the one or more additional anode layers over the layer may be described as forming a stack of anode layers.

[0098] In an additional aspect, an embodiment provides a method for preparing an anode electrode, the method comprising: mixing a plurality of silicon-based nanostructures attached to a carbon-based substrate, a polymer comprising monomer units formed from styrene and allyl alcohol, and a binder to form a mixture; and applying a layer of the mixture.

[0099] It will be understood that the features of this additional aspect described herein above in relation to the first, second, third, fourth or fifth aspects may have any of the definitions set forth above.

[0100] In a sixth aspect, embodiments provide an anode electrode obtained, directly obtained, or obtained by the method for preparing an anode electrode as described hereinbefore.

[0101] battery In a seventh aspect, embodiments provide a battery comprising the composite and / or anode electrode described herein.

[0102] Batteries whose anodes include a polymer comprising a monomeric portion formed from styrene and allyl alcohol disposed on silicon-based nanostructures attached to a carbon-based substrate have the advantageous properties discussed herein above, including improved anode uniformity, improved ability to accommodate volumetric changes, and superior integrity of the anode components. Thus, the batteries described herein provide improved electrical performance (e.g., specific capacity and / or initial coulombic efficiency (ICE)).

[0103] Most preferably, the battery is a lithium ion battery.

[0104] Numbered Description The following numbered statements 1-64 are not claims but rather describe certain aspects and embodiments. 1. A composite comprising a plurality of silicon-based nanostructures attached to a carbon-based substrate, the plurality of silicon-based nanostructures and the carbon-based substrate having a polymer disposed thereon, the polymer comprising monomer units formed from styrene and allyl alcohol. 2. The composite of statement 1, wherein the polymer has a softening point of less than 200°C. 3. A conjugate of statement 1 or 2, wherein the polymer is insoluble in water. 4. The conjugate of statements 1, 2 or 3, wherein the polymer is soluble in alcohol (e.g., ethanol). 5. The conjugate of any one of the preceding statements wherein the polymer is poly(styrene-co-allyl alcohol). 6. The conjugate of any one of the preceding statements, wherein the polymer comprises at least 25 mol % of monomer units formed from allyl alcohol. 7. A composite of any one of the preceding claims comprising 0.1% to 10% by weight of a polymer. 8. A composite of any one of the preceding claims comprising 0.5% to 5% by weight of a polymer. 9. The composite of any one of the preceding statements, wherein the plurality of silicon-based nanostructures are silicon nanowires, silicon nanoparticles, or a combination thereof. 10. The composite of any one of the preceding descriptions, wherein the plurality of silicon-based nanostructures are silicon nanowires. 11. The complex of statement 10, wherein the silicon nanowire has a diameter in the range of 10 nm to 200 nm. 12. The composite of any one of the preceding statements, wherein the plurality of silicon-based nanostructures comprises a monocrystalline core and a shell layer, the shell layer comprising amorphous silicon, polycrystalline silicon, or a combination thereof. 13. The composite of any one of the preceding statements comprising 90% by weight or more of silicon-based nanostructures attached to the carbon-based substrate. The composite of any one of the preceding statements comprising 14.95% by weight or more of silicon-based nanostructures attached to the carbon-based substrate. 15. The composite of any one of the preceding statements, wherein the carbon-based substrate is a carbon-based powder. 16. Carbon powder has a diameter of 5μm to 50μm. 50 A complex of description 15 having: 17. The composite of any one of the preceding statements, wherein the carbon-based substrate is selected from the group consisting of graphite powder, mesocarbon microbead powder, or combinations thereof. 18. The composite of any one of the preceding statements, wherein the carbon-based substrate is graphite powder. 19. The composite of any one of the preceding statements, wherein the carbon-based substrate is a graphite powder, the graphite powder comprising a plurality of graphite particles, each particle having a plurality of pores disposed therein, and the silicon-based nanostructures are attached to surfaces defining said pores. 20. The composite of any one of the preceding claims, wherein the carbon-based substrate is a graphite powder comprising uncoated natural graphite particles. 21. The composite of any one of the preceding statements, wherein the plurality of silicon-based nanostructures attached to the carbon-based substrate comprises 1% to 40% silicon by weight. 22. A composite of any one of the preceding statements, wherein the plurality of silicon-based nanostructures attached to the carbon-based substrate comprises 2.5% to 25% silicon by weight (e.g., 5% to 15% silicon by weight). 23. The composite of any one of the preceding statements, wherein the plurality of silicon-based nanostructures and the carbon-based substrate further comprises a conductive carbon coating (e.g., carbonized PSAA), and a polymer comprising monomer units formed from styrene and allyl alcohol (e.g., PSAA) is disposed on the conductive carbon coating. 24. The composite of statement 23, wherein a conductive carbon coating (e.g., carbonized PSAA) is provided as an inner coating layer over the plurality of silicon-based nanostructures and the carbon-based substrate, and a polymer (e.g., PSAA) comprising monomer units formed from styrene and allyl alcohol is provided as an outer coating layer over the plurality of silicon-based nanostructures and the carbon-based substrate. 25. A method for preparing a complex, comprising: mixing a plurality of silicon-based nanostructures attached to a carbon-based substrate with a solution of a polymer including monomer units formed from styrene and allyl alcohol to form a mixture; drying the mixture; and A method comprising: 26. The method of statement 25, wherein the solution of the polymer comprises a polymer and an alcohol solvent (e.g., ethanol). 27. The method of statement 25 or 26, wherein the solution of the polymer does not contain water. 28. The method of statements 25, 26, or 27, wherein the solution comprises 0.05% to 10% by weight of the polymer. 29. The method of any one of statements 25-28, wherein the solution comprises 0.1% to 3% by weight of the polymer (e.g., 0.5% to 1.5% by weight). 30. The method of any one of statements 25-29, wherein the drying step is carried out at ambient pressure or reduced pressure (e.g., under vacuum) and at a temperature between 20°C and 150°C. 31. The method of any one of statements 25-30, wherein the drying step is optionally carried out under an inert gas (e.g., nitrogen) at a temperature between 30°C and 130°C. 32. The method of any one of statements 25-31, wherein the plurality of silicon-based nanostructures attached to the carbon-based substrate comprises a conductive carbon coating. 33. The method of statement 32, wherein the conductive carbon coating is formed by carbonizing a polymeric coating pre-disposed on the silicon-based nanostructures and carbon-based substrate. 34. The method of statement 33, wherein the polymeric coating predisposed on the silicon-based nanostructures and carbon-based substrate is a polymer comprising monomer units formed from styrene and allyl alcohol. 35. The method of statements 33 or 34, wherein the step of carbonizing the polymeric coating pre-disposed on the silicon-based nanostructures and the carbon-based substrate comprises heating the silicon-based nanostructures and the carbon-based substrate with the polymeric coating pre-disposed thereon at a temperature between 200°C and 750°C (e.g., between 500°C and 750°C), optionally in an inert atmosphere (e.g., under nitrogen). 36. An anode electrode comprising a first anode layer, the first anode layer comprising a binder and the composite of any one of statements 1-24. 37. The anode electrode of statement 36, wherein the binder is selected from the group consisting of styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly(vinylidene fluoride) (PVDF), poly(acrylic acid) (PAA), poly(acrylonitrile) (PAN), poly(acrylamide-co-diallyldimethylammonium) (PAADAA), poly(tetrafluoroethylene) (PTFE), and combinations of two or more thereof. 38. The anode electrode of statement 36 or 37, wherein the binder is a mixture of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC). 39. The anode electrode of statement 38, wherein the binder comprises 30% to 70% by weight of butadiene rubber (SBR) and 30% to 70% by weight of carboxymethyl cellulose (CMC). 40. The anode electrode of statement 36 or 37, wherein the binder is poly(tetrafluoroethylene) (PTFE). 41. The anode electrode of any one of statements 36-40, wherein the first anode layer includes 0.5% to 10% by weight of a binder. 42. The anode electrode of any one of statements 36-41, wherein the first anode layer includes 1% by weight to 6% by weight of a binder. 43. The anode electrode of any one of statements 36-42, wherein the first anode layer comprises 90% or more by weight of the composite. 44. The anode electrode of any one of statements 36-43, wherein the first anode layer further comprises a conductive additive. 45. The anode electrode of statement 44, wherein the first anode layer includes 0.2% to 5% by weight of a conductive additive. 46. ​​The anode electrode of statement 44 or 45, wherein the conductive additive is selected from the group consisting of carbon black particles, carbon nanofibers, carbon nanotubes, and combinations of two or more thereof. 47. The anode electrode of any one of statements 36-46, further comprising a current collector. 48. The anode electrode of statement 47, wherein the current collector is copper foil or carbon-coated copper foil. 49. The anode electrode of any one of statements 36-48, further comprising one or more additional anode layers, each additional anode layer independently comprising an active material and a binder. 50. The anode electrode of statement 49, wherein the first anode layer includes a first surface configured to be in contact with (or in contact with) a current collector, and a second surface in contact with one or more additional anode layers. 51. The anode electrode of statement 50, wherein the second surface of the first anode layer includes metallic lithium disposed thereon. 52. The anode electrode of statement 51, wherein the metallic lithium is selected from lithium metal foil, stabilized lithium metal powder, and combinations thereof. 53. The anode electrode of any one of statements 49-52, wherein the active material is selected from the group consisting of graphite powder, a plurality of silicon-based nanostructures attached to a carbon-based substrate, a composite of any one of statements 1-24, and combinations of two or more thereof. 54. The anode electrode of statement 53, wherein at least one of the one or more additional anode layers further comprises a conductive additive, the conductive additive being selected from the group consisting of carbon black particles, carbon nanofibers, carbon nanotubes, and combinations of two or more thereof. 55. A method for preparing an anode electrode, comprising: 25. The composite of any one of statements 1 to 24, and a binder to form a mixture; applying a layer of the mixture; A method comprising: 56. The method of statement 55, wherein the layer is configured to be in contact with a current collector. 57. The method of statement 55 or 56, wherein the mixture is provided as a wet slurry and the method further comprises the step of drying the layer. 58. The method of statement 55 or 56, wherein the mixture is provided as a solid and the applying step includes forming a layer of the solid mixture. 59. The method of any one of statements 55-58, wherein the applying step includes applying a layer of the mixture onto a current collector. 60. The method of statement 59, further comprising applying one or more additional anode layers over the layer, the one or more additional anode layers each independently comprising an active material and a binder. 61. The method of statement 60, wherein the active material is selected from the group consisting of graphite powder, a plurality of silicon-based nanostructures attached to a carbon-based substrate, a composite of any one of statements 1-24, and combinations of two or more thereof. 62. The method of statement 61, wherein at least one of the one or more additional anode layers further comprises a conductive additive, the conductive additive being selected from the group consisting of carbon black particles, carbon nanofibers, carbon nanotubes, and combinations of two or more thereof. 63. A battery comprising the composite of any one of statements 1 to 24 and / or the anode electrode of any one of statements 36 to 54. 64. A battery of statement 63 that is a lithium ion battery. EXAMPLES

[0105] One or more embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings. FIG. 4 shows the performance of half cells 1-3 described in Example 2. FIG. 5 shows the cycling performance of the three anodes described in Example 2. FIG. 6 shows the performance of half cells 1-3 described in Example 2. 7A and 7B show high magnification SEM images of the SiNW-carbon powder after PSAA carbonization in Example 3, showing that a thin coating layer is present on both the silicon and graphite surfaces. FIG. 8 shows the performance of two NCA pouch cells described in Example 4. FIG. 9 shows the performance of two NCA pouch cells described in Example 5. FIG. 10 shows the specifications, first charge capacity and first discharge capacity of four sets of electrochemical cells containing anode material composites with different SiNW-carbon and PSAA combinations. FIG. 11 shows the discharge specific capacity over hundreds of cycles for two types of electrochemical cells, the first type including anode composites prepared using a single surface treatment and the second type including anode composites prepared using a dual surface treatment. FIG. 12 shows the % capacity retention over hundreds of cycles for two types of electrochemical cells, the first type including anode composites prepared using a single surface treatment and the second type including anode composites prepared using a dual surface treatment.

[0106] Example 1 Preparation of complexes The following drugs were combined: 1 kg of silicon nanowires with a mass percentage of Si equal to 9.7% (hereafter referred to as SiNW-carbon powder) mechanically and conductively attached to graphite particles. The silicon nanowires have a diameter in the range of 20 nm to 100 nm (measured using FESEM) and the graphite particles have a diameter of D 50 = 14 microns of commercially available natural graphite. Silicon nanowires were grown on the graphite particles using decomposition of a silane gas precursor with a copper (I) oxide nanoparticle catalyst disposed on the graphite particles in a CVD reactor as described in U.S. Patent No. 10,243,207, which is incorporated herein by reference in its entirety. 20.2 g of a 50% by weight solution of PSAA in EtOH (calculated PSAA polymer content of 10.1 g), obtained from Sigma-Aldrich, with a molecular weight of M n is about 1600. 1000g ethanol.

[0107] The complex was prepared as follows. a) In a 5 liter stainless steel container, 1000 g of ethanol was mixed with 20.2 g of a 50 wt % PSAA solution in ethanol by propelling for 5 minutes to yield 1020.2 g of a diluted PSAA solution containing approximately 10.1 g of PSAA polymer. b) In a 5 liter container, 1 kg of SiNW-carbon powder was immersed in the PSAA solution and mixed for 30 minutes to obtain a mixture comprising SiNW-carbon powder with PSAA polymer uniformly disposed thereon. c) The mixture in the 5 liter container was placed in an oven under nitrogen for drying at a temperature between 40° C. and 120° C. for approximately 2 hours to obtain 1010.1 g of dry composite particles. The PSAA coated SiNW-carbon powder was formed into a powder of discrete particles without any milling or sieving.

[0108] Example 2 Half-cell study Three types of half-cells were prepared according to the following general protocol. a) In a planetary kneader vessel, 6.12 g of a 1.5 wt. % CMC stock solution (in DI water) was slowly added to 3.97 g of DI (deionized) water, then mixed at 600 rpm for 15 minutes. The resulting mixture was kept at 30°C. b) 5.94 g of SiNW-carbon powder (with or without PSAA placed thereon) was gradually added to the mixture obtained from step a) and the resulting mixture was mixed in a planetary kneader vessel (non-bubbling kneader, NBK-1) at 400 rpm for 15 min. c) 0.23 g of a 40% by weight SBR suspension was added to the mixture obtained from step b) The resulting mixture was then mixed at 400 rpm for 15 minutes. d) The slurry from step c) was placed in a 40°C bath for 2 minutes and then mixed again to achieve a slurry temperature of 30°C. e) The slurry from step d) was then used to coat an anode electrode on a copper foil using a doctor blade. The electrode was then dried at 90° C. for 60 minutes. f) After 60 minutes at room temperature, the electrode obtained from step e) is then heated at 1–1.65 g cm -3 Calendered to a density of 1.4 g cm -3 was used as an example.

[0109] Half-cell 1 was used to establish baseline performance for an anode with 96 wt% SiNW-carbon powder (no PSAA) containing 1.5 wt% CMC, 1.5 wt% SBR, 1 wt% Super P® (carbon black) conductive additive, and 9.7 wt% Si. Lithium foil was used as the counter electrode. As shown in FIG. 4 and Table 1 (below), the initial specific capacity observed upon delithiation was 629.03 mAh / g and the initial coulombic efficiency (ICE) observed was 90.00%.

[0110] Half-cell 2: An aqueous slurry was prepared by mixing 95.54 wt% SiNW-carbon powder (9.7 wt% Si), 1.5 wt% CMC, 1.5 wt% SBR, 1 wt% Super P® (carbon black) conductive additive, and 1 wt% PSAA (from a 50 wt% solution of PSAA in EtOH). This slurry was used to coat an anode electrode on a copper foil. When 1 wt% PSAA was added to a slurry containing 1.5 wt% CMC, 1.5 wt% SBR, and 1 wt% Super P, and 95.54 wt% SiNW-carbon powder (9.7 wt% Si), the resulting anode exhibited an initial specific capacity upon delithiation of 633.08 mAh / g and an initial coulombic efficiency (ICE) of 90.13%, as shown in FIG. 4 and Table 1 (below). The results show that the incorporation of PSAA into the anode results in high delithiation capacity and high ICE relative to the baseline anode half-cell 1.

[0111] Half-cell 3: Following the deposition method outlined in Example 1, a slurry was prepared by mixing 96 wt% SiNW-carbon powder (9.7 wt% Si) pretreated with 1 wt% PSAA, 1.5 wt% CMC, 1.5 wt% SBR, and 1 wt% Super P® (carbon black) conductive additive. This slurry was used to coat an anode electrode on copper foil. When using 1 wt% PSAA pretreated SiNW-carbon powder, the resulting anode shows a further increased initial specific capacity upon delithiation of 634.89 mAh / g and a further improved ICE of 90.92%, as shown in FIG. 4 and Table 1 (below). This result demonstrates that the presence of PSAA on the SiNW-carbon powder can result in favorable interactions with the CMC / SBR binder. These interactions make the anode more uniform and provide better access for lithium ions to the active materials (SiNWs and graphite), which results in improved specific capacity and ICE.

[0112] The performance of these three anode half-cells is summarized in Table 1 and illustrated in FIG.

[0113] [Table 1]

[0114] As shown in Figure 4 and Table 1, the application of PSAA increases the ICE by nearly 1%. Depending on the N / P ratio of the anode and cathode specific capacity (i.e., N / P=1.05), the approximately 1% higher anode ICE results in approximately 1% savings in cathode material, which is up to 5 times more expensive than graphite material, providing significant savings to EV cell fabricators.

[0115] The same slurry composition was used to prepare three anodes, which were then used in NCA pouch cells. The NCA material was purchased from BASF. The N / P ratio was 1.05. After the preparation process was completed with the consequent charge / discharge at C / 20 between 4.2V and 2.5V for one cycle, C / 10 between 4.2V and 3V for one cycle, and C / 5, respectively, the three cells were cycled at C / 3 charge and C / 2 discharge between 4.2V and 3V, as shown in FIG. 5. The cycling performance was measured and compared, as outlined in FIG. 5.

[0116] The cycling performance is established with a baseline anode using 1.5 wt% CMC / 1.5 wt% SBR, 1 wt% Super P, and SiNW-carbon powder (9.7 wt% Si). As shown in FIG. 5, when 1 wt% PSAA was added to the slurry, the resulting anode showed some improvement in NCA full cell cycling performance compared to the baseline NCA cell. Further improvement was achieved using an anode containing 1 wt% PSAA pretreated SiNW-carbon powder, as shown in FIG. 5. The results demonstrate that PSAA pretreated SiNW-carbon powder can significantly improve the performance of SiNW-carbon anode full cells, especially in anodes using low CMC / SBR binder content.

[0117] Example 3 A study on carbonization of PSAA The following drugs were combined: 1 kg of silicon nanowires with a mass percentage of Si equal to 9.7% (hereinafter also referred to as SiNW-carbon powder) mechanically and conductively attached to graphite particles. The silicon nanowires have a diameter in the range of 20 nm to 100 nm (measured using FESEM) and the graphite particles have a diameter of D 50= 14 microns of commercially available natural graphite. The silicon nanowires were grown on the graphite particles using decomposition of a silane gas precursor with a copper (I) oxide nanoparticle catalyst disposed on the graphite particles in a CVD reactor as described in U.S. Patent No. 10,243,207, the entirety of which is incorporated herein by reference. 160.0 g of a 50% by weight solution of PSAA in EtOH (calculated to contain 80.0 g of PSAA polymer), obtained from Sigma-Aldrich, with a molecular weight of M n is about 1600. 1000g ethanol.

[0118] The complex was prepared as follows. a) In a 5 liter stainless steel container, 1000 g of ethanol was mixed with 160.0 g of a 50 wt % PSAA solution in ethanol by propelling for 5 minutes to yield 560.0 g of a diluted PSAA solution containing 80.0 g of PSAA polymer. b) In a 5 liter container, 1 kg of SiNW-carbon powder was immersed in the PSAA solution and mixed for 30 minutes to obtain a mixture comprising SiNW-carbon powder with PSAA polymer uniformly disposed thereon. c) The mixture in the 5 liter container was placed in an oven under nitrogen for drying at a temperature between 40° C. and 120° C. for approximately 2 hours to obtain 1080.0 g of dry composite particles. The PSAA coated SiNW-carbon powder was formed into a powder of discrete particles without any milling or sieving.

[0119] This PSAA on SiNW-carbon powder can be carbonized at 700° C. for 1 hour under nitrogen gas.

[0120] For comparison, amorphous carbon coatings on the same SiNW-carbon powders were prepared using acetylene / nitrogen (1:1) gas at 700° C. for 1 h.

[0121] Three types of half-cells were prepared according to the following general protocol. a) In a planetary kneader vessel, 6.12 g of a 1.5 wt. % CMC stock solution (in DI water) was slowly added to 3.97 g of DI (deionized) water and then mixed at 600 rpm for 15 minutes. The resulting mixture was kept at 30°C. b) 5.94 g of SiNW-carbon powder (with or without PSAA placed thereon) was gradually added to the mixture obtained from step a) and the resulting mixture was mixed in a planetary kneader vessel (non-bubbling kneader, NBK-1) at 400 rpm for 15 min. c) 0.23 g of a 40% by weight SBR suspension was added to the mixture obtained from step b) The resulting mixture was then mixed at 400 rpm for 15 minutes. d) The slurry from step c) was placed in a 40°C bath for 2 minutes and then mixed again to achieve a slurry temperature of 30°C. e) The slurry from step d) was then used to coat an anode electrode on a copper foil using a doctor blade. The electrode was then dried at 90° C. for 60 minutes. f) After 60 minutes at room temperature, the electrode obtained from step e) is then heated at 1–1.65 g cm -3 Calendered to a density of 1.4 g cm -3 was used as an example.

[0122] Half-cell 1 was used to establish baseline performance for an anode with 97 wt% SiNW-carbon powder (no PSAA) containing 1.5 wt% CMC, 1.5 wt% SBR, and 9.7 wt% Si. Lithium foil was used as the counter electrode. The initial specific capacity observed upon delithiation was 648.27 mAh / g. The initial coulombic efficiency (ICE) observed was 92.41%.

[0123] Half-cell 2: An aqueous slurry was prepared by mixing 97 wt% SiNW-carbon powder with an amorphous carbon coating (9.7 wt% Si), 1.5 wt% CMC, and 1.5 wt% SBR. This slurry was used to coat an anode electrode on a copper foil. The resulting anode exhibited an initial specific capacity upon delithiation of 632.46 mAh / g and an initial coulombic efficiency (ICE) of 91.78%, indicating that the amorphous carbon-coated SiNW-carbon powder anode had a slightly lower delithiation capacity and therefore a lower ICE than the uncoated SiNW-carbon powder anode in half-cell 1.

[0124] Half-cell 3: A slurry was prepared by mixing 97 wt% PSAA pretreated SiNW-carbon powder (9.7 wt% Si) and carbonized at 700 °C under nitrogen. The binder was 1.5 wt% CMC and 1.5 wt% SBR. This slurry was used to coat an anode electrode on a copper foil. The resulting anode showed an initial specific capacity upon delithiation of 638.69 mAh / g and an ICE of 91.89%. The lithiation is comparable to that of an amorphous carbon coated SiNW-carbon powder anode derived from acetylene decomposition in a CVD process. However, the delithiation was better than that of the amorphous carbon coated SiNW-carbon powder anode, resulting in a higher ICE.

[0125] In FIG. 6, the x-axis is volume % normalized by the full lithiation capacity, and illustrates the lithiation curves for the three half-cells of Example 3. As shown in FIG. 6, the lithiation curves for the carbonized PSAA are similar to those for the amorphous carbon coating obtained by pyrolysis of acetylene on SiNW-carbon powder. As shown in FIG. 6A, the carbonized PSAA-coated SiNW-carbon anode and the amorphous carbon-coated SiNW-carbon anode have similarly enhanced lithiation with respect to the uncoated SiNW-carbon anode due to the carbonized layer. As shown in FIG. 6B, the delithiation for the carbonized PSAA-coated SiNW-carbon anode occurs at a lower potential than the amorphous carbon-coated SiNW-carbon anode and the uncoated SiNW-carbon anode. As shown in FIG. 6C, the carbonized PSAA-coated SiNW-carbon anode maintains good initial coulombic efficiency. As shown in Figure 6 , the PSAA-derived carbon coating was more uniform, easier to apply with less waste, and promoted the delithiation of SiNWs compared to the more traditional method of pyrolysis of acetylene gas.

[0126] Example 4 Cyclic operation of a full electrochemical cell (single-sided NCA cathode + single-layer SiNW-carbon powder anode without or with PSAA single surface treatment) The following drugs were prepared: 0.0973 kg of silicon nanowires with a mass % of Si equal to 9.73% in 1 kg of Si-C composite mechanically and conductively attached to uncoated natural graphite particles (hereafter referred to as SiNW-carbon powder in the examples). The silicon nanowires have a diameter in the range of 20 nm to 100 nm (measured using FESEM) and the graphite particles have a diameter of D 50 = 14 microns of commercially available uncoated natural graphite. Silicon nanowires were grown on the graphite particles using decomposition of silane gas precursors from copper(I) oxide nanoparticle catalysts disposed on the graphite particles in a CVD reactor as described in U.S. Patent No. 10,243,207, which is incorporated herein by reference in its entirety. 1000 g of a 11.111 wt% solution of PSAA in EtOH (calculated PSAA polymer content of 111.11 g), obtained from Sigma-Aldrich, with a molecular weight Mn of approximately 1600. 888.89g of ethanol

[0127] The following mixtures were prepared: a) In a 5-liter stainless steel container, 888.89 g of ethanol was mixed with 111.11 g of a 11.111 wt % PSAA solution in ethanol for 5 minutes by impeller stirring to yield 1000 g of diluted PSAA solution containing 111.11 g of PSAA polymer. b) In a 5-liter container, 1 kg of SiNW-carbon powder was immersed in the PSAA solution and mixed for 30 minutes to obtain a mixture comprising SiNW-carbon powder with PSAA polymer uniformly disposed thereon. c) The mixture in the 5-liter container was placed in an oven under nitrogen for at least 2 hours for drying at a temperature between 40° C. and 120° C. to obtain 1111.11 g of dried composite particles with 10% PSAA in the composite. The PSAA coated SiNW-carbon powder was formed into a powder of discrete particles without any milling or sieving.

[0128] It should be noted that the PSAA content on the surface prior to carbonization can be from 1% to 80% by weight, or from 5% to 30% by weight. In this example, 10% by weight of PSAA was used.

[0129] The carbonization process can be carried out in a reactor under an inert gas environment (e.g., N at 1.0 LPM per kg of SiNW-carbon powder with 10% PSAA while the reactor temperature is ramped to 700° C.). 2 Then, the temperature was kept at 700° C. for 1 hour to complete the carbonization of the PSAA, and then N 2The reactor is cooled to a temperature below 300°C by continuing to flow, and the treated SiNW-carbon powder is then removed from the reactor. The carbonization temperature can be in the range of 450°C to 900°C. The carbonization time can be from 30 minutes to 5 hours. 2 The flow rate can vary from 0.1 LPM / kg SiNW-carbon powder to 5 LPM / kg SiNW-carbon powder. 2 The purpose of the flow is air / O 2 and to remove decomposition gases from the reactor, and to prevent the carbonized surface coating from being oxidized.

[0130] Since PSAA can be easily and uniformly coated on the SiNW-carbon powder surface, i.e., on both the graphite and Si nanowire surfaces, the carbonized surface coating is also uniform; for example, a uniform 1.9 nm coating layer can be observed on both the Si nanowire surface and the graphite surface in the TEM images of Figures 7A and 7B, where the Si nanowire has a diameter of 20.7 nm after carbonization treatment.

[0131] Two sets of NCA pouch cells were prepared, one with PSAA carbonization treatment and the second without. a) 100 g of a 4 wt% CMC stock solution (in DI water) was placed in a planetary kneader vessel. The vessel was kept at 30°C. b) 46 g of SiNW-carbon powder (with carbonized PSAA on top for the set with PSAA carbonization treatment and without PSAA for the set without treatment) was gradually added to the mixture obtained from step a) and the resulting mixture was mixed in a planetary kneader vessel (non-bubbling kneader, NBK-1) at 400 rpm for 15 min. c) The slurry from step b) was placed in a 40°C bath for 2 minutes and then mixed again to achieve a slurry temperature of 30°C. d) The slurry from step c) was then used to coat anode electrodes on copper foil using a doctor blade, one with PSAA carbonization treatment and the second without treatment for each of the two NCA cells, and the electrodes were then dried at 90° C. for 60 minutes. e) After 60 min at room temperature, the electrode obtained from step d) was then cooled to 1.4 g cm -3 The material was calendered to a density of 1 g cm -3 to 1.65 g cm -3 (Densities between 0.01 and 0.15 can be used).

[0132] Two sets of electrochemical cells were constructed by pairing the NCA cathode with a SiNW-carbon powder anode electrode that was coated with 92 wt.% SiNW-carbon powder containing 8 wt.% CMC and 9.73 wt.% Si. The first set contained SiNW-carbon powder with carbonized PSAA, and the second set contained SiNW-carbon powder without any PSAA coating.

[0133] The cycling performance of the two sets of electrochemical cells was compared over 500 cycles using different cycling protocols, as shown in Figures 8 and 9.

[0134] The electrochemical cells were subjected to a simple formation protocol with a charge current of C / 20 between OCV and 4.25V and a discharge current of C / 20 between 4.25V and 2.5V. No prelithiation of the electrodes was performed. The cells were characterized at C / 10 for one cycle and at C / 5 for another cycle. The cells were then cycled at C / 3 for charge and C / 3 for discharge for 500 cycles (first cycling protocol) as shown in FIG. 8. The cell using the untreated anode showed 71% capacity retention at the 500th cycle. The cell using the treated anode showed better cycling with 74% capacity retention at the 500th cycle. The treatment improved the capacity retention during cycling and resulted in slower capacity fade. In FIG. 9 (second cycling protocol), the cells were cycled at C / 3 charge and C / 2 discharge. After every 100 cycles, the capacity was checked using the cell at C / 10, resulting in a capacity spike, indicating that the Si nanowires remained electrochemically active and full capacity was realized at C / 10. The capacity checks at two C / 10 cycles activated the Li-ion diffusion channels, and thus the capacity spike was followed by a slow decay. As a result, the cell with the untreated anode showed 70.5% capacity retention at the 500th cycle. The cell with the treated anode showed better cycling behavior, with 75.5% capacity retention at the 500th cycle. This once again demonstrates that the carbonized PSAA surface treatment improved cycling behavior and slowed capacity fade.

[0135] Example 5 Cycling operation of a full electrochemical cell (single-sided NCA cathode + single-layer SiNW-carbon powder anode with single and double PSAA surface treatments) Silicon nanowires with a Si mass percentage equal to 9.73%, mechanically and conductively attached to commercial uncoated natural graphite particles, were first uniformly coated using 5-20% PSAA (e.g., 20% PSAA) according to the process described in Example 4, and then carbonized at temperatures up to 700°C. After the carbonization process, a second surface coating was uniformly applied on the carbonized SiNW-carbon powder by using 0.1-5% PSAA (double surface treatment). In this example, 0.3% PSAA by mass was used. The second PSAA coating was applied following the same procedure as described in the previous example and was not carbonized.

[0136] Four sets of electrochemical cells (full cells with SiNW-carbon powder anode and NCA cathode) were prepared to evaluate and compare the full cell performance for different types of anode materials and PSAA coating combinations. 1) An electrochemical cell (without surface treatment) using an anode with 8 wt.% CMC and 92 wt.% SiNW-carbon powder with Si wt.% equal to 9.7%. 2) Electrochemical cell (single surface treatment) with an anode made of 8 wt% CMC and 92 wt% SiNW-carbon powder with Si wt% equal to 9.7%, uniformly coated with a coating layer of 5-20% PSAA (e.g. 20% PSAA) and carbonized at temperatures up to 700 °C. 3) Electrochemical cell (single surface treatment) with an anode made of only 5 wt% CMC, 5 wt% C65 carbon black conductive additive (IMERYS Graphite & Carbon) and 90 wt% SiNW-carbon powder with Si wt% equal to 9.7%, uniformly coated with a coating layer of 5-20% PSAA (e.g. 20% PSAA) and carbonized at temperatures up to 700°C. 4) Electrochemical cell using an anode with only 5 wt% CMC, 5 wt% C65 carbon black conductive additive (IMERYS Graphite & Carbon), 90 wt% SiNW-carbon powder with Si wt% equal to 9.7%, uniformly coated with a first coating layer with 5-20% PSAA (e.g. 20% PSAA) and carbonized at a temperature up to 700°C, then uniformly coated with a second coating layer with 0.1-5% PSAA (e.g. 0.3 wt%) and not carbonized (dual surface treatment).

[0137] A summary of the four sets of electrochemical cells outlining the type of anode material used in each set, and the initial cell performance is shown in FIG.

[0138] The electrochemical cells were subjected to a simple formation process at C / 20 for charging between 4.25V from OCV and C / 20 for discharging between 4.25V and 2.5V. No prelithiation was performed on the anode and cathode. The cells were characterized at C / 10 for one cycle and C / 5 for another. The cells were cycled at C / 3 for charging and C / 3 for discharging for 500 cycles. Figures 11 and 12 contain two charts comparing the discharge specific capacity and capacity retention between the third type of electrochemical cell (single surface treatment with carbonized surface, 5% CMC) and the fourth electrochemical cell (dual surface treatment with 0.3% PSAA coated on carbonized surface, 5% CMC) described in the previous paragraph.

[0139] The cycling performance was compared over 500 cycles using different cycling protocols. The charts in Figures 11 and 12 show the discharge specific capacity and % capacity retention over 500 cycles for the electrochemical cells with a single surface treatment and the electrochemical cells with a dual surface treatment.

[0140] It can be inferred from the chart that the electrochemical cell with dual surface treatment exhibits more stable cycling performance compared to the electrochemical cell with single surface treatment. As shown in the chart, a reversible capacity of 400 mAh / g is reached after 200 cycles for the cell with single surface treatment and after 400 cycles for the cell with dual surface treatment.

[0141] The dual surface treatment allows for the use of less polymer binder (e.g., only 5% CMC) and improves the stability of cell performance. Without wishing to be bound by theory, the inventors hypothesize that the dual surface treatment reduces the surface area and stabilizes the interface between the material and the electrolyte.

[0142] These novel PSAA surface coatings according to embodiments of the present invention can be applied to silicon nanowires, graphite particles, or other types of particles (e.g., carbon, metal, or oxides or alloys thereof). These coatings contribute to uniform surfaces of the silicon nanowires and graphite particles. Greater surface uniformity improves SEI formation and contributes to better stability and cycling performance. PSAA coatings according to embodiments of the present invention are inexpensive and provide a convenient way to apply uniform surface treatments to SiNW-carbon powder materials without using additional milling processes to break up the powder. The PSAA surface coatings uniformly applied to both silicon nanowires and graphite particles can optionally be carbonized according to embodiments of the present invention to create a uniform carbon coating layer on the silicon nanowires and graphite particles, which can reduce the need for conductive additives and enhance the interaction (affinity) with various binder polymers in the electrodes.

[0143] While specific embodiments of the present invention have been described herein for purposes of reference and description, various modifications will become apparent to those skilled in the art that do not depart from the scope of the invention as defined in the appended claims.

[0144] The description of the embodiments of the present disclosure is not intended to be exhaustive or to limit the present disclosure to the precise form disclosed. As will be recognized by those skilled in the relevant art, the specific embodiments and examples of the present disclosure are described herein for illustrative purposes, and various equivalent modifications are possible within the scope of the present disclosure. For example, while method steps or functions are presented in a given order, in alternative embodiments, functions may be performed in a different order, or functions may be performed substantially simultaneously. The teachings of the disclosure provided herein can be applied to other procedures or methods, as appropriate. The various embodiments described herein can be combined with each other to provide further embodiments. Aspects of the present disclosure can be modified, if necessary, to employ the compositions, functions and concepts referenced above, and applications to provide yet further embodiments of the present disclosure. These and other changes can be made to the present disclosure in light of the detailed description. All such modifications are intended to be within the scope of the appended claims.

[0145] Specific elements of any of the foregoing embodiments may be combined with or substituted for elements in other embodiments. Additionally, although advantages associated with certain embodiments of the present disclosure have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments necessarily need to exhibit such advantages to be within the scope of the present disclosure.

Claims

1. 1. A composite comprising a plurality of silicon-based nanostructures attached to a carbon-based substrate, wherein the plurality of silicon-based nanostructures and the carbon-based substrate have a polymer disposed thereon, the polymer comprising monomer units formed from styrene and allyl alcohol.

2. 10. The composite of claim 1, wherein the polymer has a softening point of less than 200°C.

3. 10. The composite of claim 1, wherein the polymer is insoluble in water.

4. 10. The composite of claim 1, wherein the polymer is soluble in alcohol.

5. 10. The composite of claim 1, wherein the polymer is poly(styrene-co-allyl alcohol).

6. 10. The composite of claim 1, wherein the polymer comprises at least 25 mol% of monomer units formed from allyl alcohol.

7. 10. The composite of claim 1 comprising 0.5% to 5% by weight of the polymer.

8. 10. The composite of claim 1, wherein the plurality of silicon-based nanostructures are silicon nanowires.

9. 9. The composite of claim 8, wherein the silicon nanowires have a diameter in the range of 10 nm to 200 nm.

10. 10. The composite of claim 1, wherein the plurality of silicon-based nanostructures comprises a monocrystalline core and a shell layer, wherein the shell layer comprises amorphous silicon, polycrystalline silicon, or a combination thereof.

11. The composite of claim 1, comprising 95% or more by mass of silicon-based nanostructures attached to a carbon-based substrate.

12. The composite of claim 1 , wherein the carbon-based substrate is a carbon-based powder.

13. The carbon powder has a D of 5 μm to 50 μm. ５０ 13. The complex of claim 12, having the formula:

14. 10. The composite of claim 1, wherein the carbon-based substrate is graphite powder.

15. 10. The composite of claim 1, wherein the carbon-based substrate is graphite powder, the graphite powder comprising a plurality of graphite particles, each particle having a plurality of pores disposed therein, and wherein silicon-based nanostructures are attached to surfaces defining the pores.

16. 10. The composite of claim 1, wherein the plurality of silicon-based nanostructures attached to the carbon-based substrate comprises 2.5% to 25% silicon by weight.

17. 10. The composite of claim 1, wherein the plurality of silicon-based nanostructures and the carbon-based substrate further comprise a conductive carbon coating, and wherein a polymer comprising monomer units formed from styrene and allyl alcohol is disposed on the conductive carbon coating.

18. 20. The composite of claim 17, wherein the conductive carbon coating is provided as an inner coating layer on the plurality of silicon-based nanostructures and the carbon-based substrate, and the polymer comprising monomer units formed from styrene and allyl alcohol is provided as an outer coating layer on the plurality of silicon-based nanostructures and the carbon-based substrate.

19. A battery comprising the composite of any one of claims 1 to 18.

20. 20. The battery of claim 19, which is a lithium ion battery.

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