WO2024020393A1

WO2024020393A1 - Silicon nanoparticles comprising a sacrifical layer, composite materials including them, preparation and uses thereof

Info

Publication number: WO2024020393A1
Application number: PCT/US2023/070422
Authority: WO
Inventors: Zhifei Li; Wei Xie
Original assignee: Aspen Aerogels, Inc.
Priority date: 2022-07-20
Filing date: 2023-07-18
Publication date: 2024-01-25

Abstract

Provided herein are composite materials for use in an electrical energy storage system (e.g., a high-capacity battery) and methods for preparing the same. The composite materials of the present disclosure include silicon particles having a sacrificial layer on at least a portion of a surface of the silicon particles and a three-dimensional network. The sacrificial layer of the present disclosure is between the surface of the silicon particles and a portion of the three-dimensional network.

Description

SILICON NANOPARTICLES COMPRISING A SACRIFICAL LAYER, COMPOSITE

MATERIALS INCLUDING THEM, PREPARATION AND USES THEREOF

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/390,832, filed July 20, 2022, which is herein incorporated by reference in its entirety.

FIELD OF THE TECHNOLOGY

[0002] The present disclosure relates generally to the silicon particles comprising a sacrificial layer formed on at least a portion of a surface of the silicon particles, composite materials containing said silicon particles, and methods for preparing the same. More specifically, it relates to materials and methods for producing composite materials including a three-dimensional network and the silicon particles comprising a sacrificial layer for use in an electrical energy storage system such as high-capacity batteries.

BACKGROUND

[0003] High-capacity battery materials e.g., lithium-ion batteries (LIBs) have become an indispensable power source for many emerging applications, such as electric vehicles, portable electronic products, and large-scale energy storage systems, because of their high energy density, good rate capability, and long cycle life. However, present LIB technology is reaching its theoretical limit in energy density, and thus is not suitable to meet the rapid growth of energy demand for high performance electronic devices. As one of the most important indicators of battery performance, energy density is mainly determined by the specific capacities and working potentials of electrode materials.

[0004] Silicon has attracted considerable attention because of its highest theoretical specific capacity (about 4200 mAh/g), which is ten times higher than that of conventional carbon anodes (372 mAh/g) and satisfactory potentials for lithium insertion and extraction and satisfactory potentials for lithium insertion and extraction (<0.5 V versus Li/Li⁺). [0005] Unfortunately, practical application of Si anodes is currently hampered by multiple challenges. The primary one is its huge volume change (approximately 400% of its original size) upon full lithiation and the resultant expansion/shrinkage stress during lithiation (the insertion of lithium-ions into silicon)/delithiation (the extraction of lithium-ions from silicon). The significant volume change poses a real challenge for Si electrodes to retain its morphology over cycling.

[0006] With each cycle, the expansion produces stress and strain on the silicon, causing cracks and breakage. The process of the silicon breaking down is known as pulverization. Due to this pulverization, electrical isolation of silicon fragments causes a loss in contact with neighboring fragments. In addition, the space created from the expansion pushes surrounding conducting material away from the active material. And also causes a loss of contact, resulting in low electrical conductivity. Without strong electrical contact with the current collector, the silicon fragments are not lithiated or able to contribute to the battery’s capacity. This behavior yields low- capacity stability and rapid capacity degradation over a number of cycles. The decrease in capacity during charging and discharging cycles is referred to as fading or continuous capacity decrease and is generally irreversible.

[0007] The particle size of the silicon particles can play a role in how quickly the battery performance declines. Without being bound by theory, nanometer-sized silicon particles have better capability in accommodating the volume change of Si due to their larger specific surface area and higher average binding energy per atom at the surface. These materials can thus minimize the stress on them over volume change and avoid cracking or pulverization of their structures and reduce irreversible capacity and enhance cycling stability.

[0008] Furthermore, the chemical properties, surface properties and morphology of silicon particles can affect the mechanical stability, agglomeration, processing, and electrochemical properties of the silicon particles.

SUMMARY

[0009] To tackle the aforementioned problems, embodiments disclosed herein provide silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles and composite materials including them.

[0010] One object of the present disclosure is to provide improved battery components (e.g., anode materials) including the composite materials of the present technology, improved batteries made therefrom, and methods of making and using the same. However, it is contemplated that the present disclosure may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed subject matter should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.

[0011] In one aspect, the present technology relates to preparing silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles. That is, a sacrificial layer is formed on at least a portion the exterior of the silicon particles. Sacrificial layer of the present technology can be removed before or after the fabrication of components (e.g., battery components) made with materials which incorporate the silicon particles of the present technology. The sacrificial layer can be removed, for example, by mechanical, thermal, chemical and/or electromagnetic changes experienced by the sacrificial layer.

[0012] The composite materials of the present technology can improve the performance of high-capacity batteries, relative to high-capacity batteries having electrodes which do not possess the composite material of the present disclosure. For example, the materials provided in the present disclosure may advantageously prevent or mitigate rapid capacity fading (e.g., within at least 10 cycles) of high-capacity batteries e.g., lithium-ion batteries.

[0013] In one aspect provided herein is a composite material comprising: the silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles; and a three- dimensional network, wherein the silicon particles are within the three-dimensional network and the sacrificial layer is between the surface of the silicon particles and a portion of the three- dimensional network. In some embodiments, the silicon particles have a diameter of less than 1000 nm, less than 500 nm, less than 300 nm, less than 200 nm, or less than 150 nm. In some embodiments, the silicon particles have a diameter in the range of about 300 nm to about 1000 nm. In some embodiments, the silicon particles have a diameter of less than 300 nm.

[0014] The use of the sacrificial layer of the present technology in high-capacity batteries such as Li-ion batteries provides several advantages, including reducing stress exerted on a composite material upon Si expansion/contraction during charging and discharging processes compared to the stress exerted by Si particles that do not have a sacrificial layer. While not wishing to be bound by theory, it is believed that this stress relief can improve performance of high-capacity batteries, such as, e.g., Lithium-ion batteries (e.g., cycling stability, battery lifetime).

[0015] In one aspect, the sacrificial layer may be covalently bonded with the three-dimensional network providing improved dispersion properties (e.g., homogenous distribution of silicon particles within the network) to the silicon particles compared to the silicon particles without a sacrificial layer. Without wishing to be bound by theory, better distribution of the silicon particles within the three-dimensional network may reduce the stress exerted on the three-dimensional network in which the silicon particles are dispersed compared to the stress exerted by silicon particles which do not have a sacrificial layer. Inhibition or mitigation of the stress generated by the swelling of the silicon particles may improve the battery performance.

[0016] In some embodiments, the silicon particles are dispersed throughout the three- dimensional network. In some embodiments, the silicon particles are dispersed heterogeneously throughout the three-dimensional network. In some embodiments, the silicon particles are dispersed homogeneously throughout the three-dimensional network. In some embodiments, about 20 wt% to about 50 wt% of the dispersed silicon particles are in an agglomerated state. In one embodiment, less than about 20 wt% of the dispersed silicon particles are in an agglomerated state. [0017] In some embodiments, the sacrificial layer is formed from a material selected from polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polypropylene oxide (PEO), polypropylene oxide (PPO), polyethyleneimine (PEI), polyurethane, poly(3,4-ethylenedioxythiophene) (PEDOT), polyvinylbutyral, polyethylene oxide copolymer, polypropylene oxide copolymer, polycarbonate (PC), polyvinylchloride (PVC), polycaprolactone, polyvinylidene fluoride, polystyrene or combination thereof.

[0018] In some embodiments, the sacrificial layer has a thickness of less than or equal to about 700 nm, a thickness of less than or equal to about 500 nm, or a thickness between about 100 nm and about 600 nm, or a thickness of about 600 nm to 3000 nm. In some embodiments, the sacrificial layer has a thickness in the range of about 300% to about 1% of the diameter of the silicon particles. In some embodiments, the sacrificial layer has a thickness in the range of about 300% to about 100 % of the diameter of the silicon particles. In some embodiments, the sacrificial layer has a thickness in the range of about 80% to about 0.01%, about 70% to about 0.1%, about 65% to about 20%, about 65% to about 50%, about 65% to about 55% of the diameter of the silicon particles. In some embodiments, the sacrificial layer has a thickness in the range of about 60% of the diameter of the silicon particles.

[0019] In one aspect, the sacrificial layer of the present technology provides the advantage of designing in void spaces the size of which can be controlled. That is, the size of the void space between the surface of the silicon particles and the three-dimensional network created by removal of the sacrificial layer can be tailored by adjusting the thickness of the sacrificial layer provided herein.

[0020] In some embodiments, the sacrificial layer has a carbonization yield of less than about 20 wt%. In some embodiments, the temperature of chemical decomposition of the sacrificial material layer is in the range of about 130°C to about 800°C.

[0021] In some embodiments, the sacrificial layer is uniform on at least a portion of the surface of the silicon particles. In some embodiments, the sacrificial layer is continuous on at least a portion of the surface of the silicon particles. In some embodiments, at least a portion of the surface of the silicon particles is at least 70% of the surface of the silicon particles, at least 90% of the surface of the silicon particles, or at least 95% of the surface of the silicon particles.

[0022] In some embodiments, the composite material is in monolithic form, in the form of thin sheets, or in particulate form.

[0023] In some embodiments, the three-dimensional network comprises an aerogel, a xerogel, an ambigel, an aerogel-xerogel hybrid material, an aerogel-ambigel hybrid material, an aerogel- ambigel-xerogel hybrid material, or combinations thereof.

[0024] In some embodiments, the three-dimensional network is in the form of a bead. In one or more embodiments, the bead is substantially spherical, having a diameter from about 100 nm to about 4 mm, or from about 5 pm to about 4 mm.

[0025] In some embodiments, the three-dimensional network has a low bulk density, wherein the low bulk density is in the range of about 0.25 g/cc to about 1.0 g/cc.

[0026] In some embodiments, the three-dimensional network comprises a skeletal framework comprising nanofibers, wherein the skeletal framework comprising an array of interconnected pores.

[0027] In some embodiments, the three-dimensional network is a porous three-dimensional network. In some embodiments, the three-dimensional network has a pore volume of at least 0.3 cc/g.

[0028] In some embodiments, the three-dimensional network has a porosity between about 10% and about 90% of volume of the core. In some embodiments, a pore structure of the three- dimensional network includes a pore size at max peak from distribution of about 150 nm or less. In some embodiments, a pore structure of the three-dimensional network includes a pore size at max peak from distribution of about 100 nm or less.

[0029] In some embodiments, the three-dimensional network comprises an organic material or is derived from an organic material. In some embodiments, the three-dimensional network comprises a polyimide or is derived from a polyimide. In some embodiments, the three- dimensional network comprises a carbon aerogel obtained from pyrolysis of an organic material. In some embodiments, the three-dimensional network comprises a carbon aerogel obtained from pyrolysis of a polyimide gel material.

[0030] In some embodiments, the three-dimensional network comprises from about 20% to about 95% by weight of the composite, based on the total weight of the composite material.

[0031] In some embodiments, a volume of the silicon particles comprises between 35 % to 60 % of a volume of the three-dimensional network. In some embodiments, the silicon particles are present at least partially within the pore structure of the three-dimensional network.

[0032] Provided herein is an energy storage system e.g., a battery comprising the composite material of the present disclosure. In some embodiments, the battery is a rechargeable battery e.g., a Li-ion battery.

[0033] Also provided herein is a rechargeable battery comprising the composite material of the present disclosure.

[0034] In one aspect, provided herein is a method of preparing a composite material. The method includes: a. providing silicon particles; b. oxidizing a surface of the silicon particles to obtain hydroxyl functional groups on the surface; c. forming a sacrificial layer onto at least a portion of a surface of the silicon particles; d. providing a sol-gel solution, the sol-gel solution comprising a polar solvent and a precursor of a three-dimensional network; and e. processing the silicon particles in the presence of the sol-gel solution to yield the composite material. In some embodiments, the step of forming the sacrificial layer comprises: i. covalently reacting hydroxyl functional groups on the surface of the silicon particles with at least one functional silane group; ii. grafting a polymer initiator on the surface of the silicon particles to react with a monomer; and iii. polymerizing the monomer on the surface of the silicon particles to form the sacrificial layer. In some embodiments, silicon particles have diameter of less than 1000 nm, less than 900 nm, less than 800 nm, less than 700 nm, less than 600 nm, less than 500 nm, less than 400 nm, less than 300 nm. [0035] In one aspect, provided herein is a method of preparing a composite material. The method includes: a. providing silicon particles having a diameter of less than 1000 nm; b. oxidizing a surface of the silicon particles to obtain hydroxyl functional groups on the surface; c. forming a sacrificial layer onto at least a portion of a surface of the silicon particles; d. providing a sol-gel solution, the sol-gel solution comprising a polar solvent and a precursor of a three-dimensional network; and e. processing the silicon particles in the presence of the sol-gel solution to yield the composite material. In some embodiments, the step of forming the sacrificial layer comprises: i. covalently reacting hydroxyl functional groups on the surface of the silicon particles with at least one functional silane group; ii. grafting a polymer initiator on the surface of the silicon particles to react with a monomer; and iii. polymerizing the monomer on the surface of the silicon particles to form the sacrificial layer.

[0036] In another aspect, a method of preparing a composite material is provided. The method comprises: a. providing silicon particles; b. oxidizing a surface of the silicon particles to obtain hydroxyl functional groups on the surface; c. covalently reacting hydroxyl functional groups on the surface of the silicon particles with at least one functional silane group; d. providing a sol-gel solution, the sol-gel solution comprising a polar solvent and a precursor of a three-dimensional network; e. forming a sacrificial layer onto at least a portion of a surface of the silicon particles; and e. processing the precursor of the three-dimensional network to yield the composite material. In some embodiments, the step of forming the sacrificial layer comprises: i. grafting a polymer initiator on the surface of the silicon particles to react with a monomer; and ii. polymerizing the monomer on the surface of the silicon particles to form the sacrificial layer.

[0037] In some embodiments, the method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution prior to the step of forming the sacrificial layer. In some embodiments, the method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution after the step of forming the sacrificial layer. In some embodiments, the method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution prior to and after the step of forming the sacrificial layer.

[0038] In some embodiments, the method of preparing a composite material further comprises processing the composite material to substantially remove the sacrificial layer. In one embodiment, the processing the composite material to substantially remove the sacrificial layer includes heating the composite material to a chemical decomposition temperature of the sacrificial layer. In some embodiments, the chemical decomposition temperature of the sacrificial material layer is in the range of about 130°C to about 800°C. In certain embodiments, processing the composite material to substantially remove the sacrificial layer provides a void volume around the silicon particles.

[0039] In some embodiments, the method of preparing a composite material further comprises a step of subcritical or supercritical drying after processing the silicon particles in the presence of the sol-gel solution.

[0040] In some embodiments, the sacrificial layer has a thickness in the range of about 80% to about 0.01% of the diameter of the silicon particles (i.e., the diameter of the silicon particles prior to the formation of the sacrificial layer). In some embodiments, the sacrificial layer has a carbonization yield of less than about 20 wt%.

[0041] In one aspect, provided herein is a composite material prepared by the method of any one of the embodiments disclosed herein.

[0042] In one aspect, the present technology provides silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles. In some embodiments, the silicon particles comprising sacrificial layer are dispersed throughout a carbon-based three-dimensional network. In some embodiments, the sacrificial layer is selected from polymers that have low pyrolysis yield (e.g., less than 30%, less than 25%, less than 20%, less than 10% or less than 5%). [0043] In another aspect, provided herein is a method of improving the performance of an energy storage system, the method comprising incorporating the composite material according to multiple aspects and embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The technology will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings.

[0045] FIGS. 1A and IB are schematic representations of materials according to the present disclosure. FIG. 1A is a schematic representation of the silicon particles of the present disclosure comprising a sacrificial layer. FIG. IB is a schematic representation of a composite material including a plurality of silicon particles having a sacrificial layer according to an embodiment of the present disclosure. [0046] FIG. 2 is a flow diagram illustrating a method of preparing the composite materials of the present disclosure according to an embodiment of the present disclosure.

[0047] FIG. 3 is a flow diagram illustrating a method of preparing the composite materials of the present disclosure according to an embodiment of the present disclosure.

[0048] FIGS. 4A and 4B are exemplary preparation schemes for forming a sacrificial layer on at least a portion of a surface of the silicon particles Si particles of the present disclosure.

[0049] FIG. 5 is a series of overlayed infrared (IR) spectra of pristine, oxidized, and surface modified Si particles.

DETAILED DESCRIPTION

[0050] Silicon (Si) is considered to be a promising alternative lithium-ion battery (LIB) anode material. It forms LiySis, Li 12S17, Li 13S U, Li 15SL, and Li22Sis silicon-lithium alloys during the alloying process, among which LiisSi4 has a capacity of 3579 mAh g^-1 (2194 Ah L^-1) at room temperature, which is the highest theoretical capacity known for the anode material. Therefore, incorporating as much silicon as possible within the anode is desirable.

[0051] At the same time, the average voltage platform of Si (0.4 V vs. Li/Li⁺) is higher than that of the graphite electrode (0.125 V vs. Li/Li⁺), which makes it possible to avoid lithium plating and dendritic lithium formation on the anode material surface during the lithiation process. As a result, the safety performance of the battery can be significantly improved. Also, Si has the advantages of abundant reserves in the earth's crust and low price, which fosters further the industrial interest to utilize silicon in batteries.

[0052] Despite these advantages, silicon still has severe shortcomings when used as an electrode material. The core problem for the utilization of Si in a LIB is its vast volume expansion during lithiation. Si electrode can expand by up to 400%, which is much more than the 10% for a graphite electrode. First, Si particles are gradually pulverized due to the repeated volume change and lose electrical contact between the active and other components, including conductive carbon and binder, which causes the capacity to decrease sharply and the cycle performance to decline rapidly. Secondly, the volume change also gradually causes active material to peel off the current collector, resulting in an electrical contact loss between the active material and the current collector, and the electrode capacity reduction after the initial cycle. Besides, the solid electrolyte interphase (SEI) layer is fractured and reformed continuously due to the volume expansion/contraction behavior of the Si electrode during cycling, resulting in the continuous exposure of fresh Si surface to the electrolyte. As a result, electrolyte degradation takes place continually on the highly reducing fresh lithiated Si surface, thus leading to an irreversible capacity loss at each cycle and eventual cell death. Both the mechanical failure and the electrolyte degradation can make the Si electrode lose its electrochemical activity very rapidly in the cycling process.

[0053] The composite materials provided herein obviate or mitigate at least one disadvantage of Si when used as an electrode material. Without wishing to be bound by theory, in general, the composite particles provided herein may be able to accommodate changes in volume of the active Si material during battery operation. Specifically, composite materials of the present technology incorporate a sacrificial layer surrounding the silicon. Prior to or during use of the composite materials in accordance with the present technology, the sacrificial layer is removed providing a void space that can accommodate the expansion and contraction of the silicon.

[0054] In the description below, several examples are provided in the context of Li-ion batteries because of the current prevalence and popularity of Li-ion technology. However, it will be appreciated that such examples are provided merely to aid in the understanding and illustration of the underlying techniques, and that these techniques may be similarly applied to various other metal-ion batteries, such as Li⁺, Na⁺, Mg²⁺, Ca²⁺, and Al³⁺, and other metal-ion batteries. The composite material of the present disclosure can be used in other battery chemistries where active particles undergo significant volume changes during their operation (e.g., reversible reductionoxidation reactions), including, for example, aqueous electrolyte-containing batteries.

[0055] In some embodiments, the composite material of the present technology features a matrix material formed of a polymer (and in some cases the polymer is in the form of an aerogel, xerogel, or foam). Within the matrix, a plurality of silicon particles including a sacrificial layer are provided. The sacrificial layer can be formed on the particles prior to their incorporation within the composite materials. In some embodiments, the sacrificial layer is formed on the silicon particles during their incorporation within a matrix material (e.g., reaction between precursor(s) forming matrix and an surface oxidized silicon particle. In any embodiment, the sacrificial layer surrounding or partially surrounding the silicon particle is removed to create a void space that can absorb the stress/strain of expansion/contraction of silicon during use (e.g., lithiation cycling) Definitions [0056] The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0057] Within the context of the present disclosure, the term "about" used throughout this specification is used to describe and account for small fluctuations. For example, the term "about" can refer to less than or equal to ±10%, or less than or equal to ±5%, such as less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.2%, less than or equal to ±0.1% or less than or equal to ±0.05%. All numeric values herein are modified by the term "about," whether or not explicitly indicated. A value modified by the term "about" of course includes the specific value. For instance, "about 5.0" must include 5.0.

[0058] Within the context of the present disclosure, the term "aerogel" or "aerogel material" refers to a solid object, irrespective of shape or size, comprising a framework of interconnected solid structures, with a corresponding network of interconnected pores integrated within the framework, and containing gases such as air as a dispersed interstitial medium. As such, aerogels are open non-fluid colloidal or polymer networks that are expanded throughout their whole volume by a gas. Aerogels are generally prepared by removing the solvent from a gel (a solid network that contains a solvent) in a manner such that minimal or no contraction of the gel can be brought by capillary forces at its pore walls, in other words, by the removal of all swelling agents from a corresponding wet-gel without substantial volume reduction or network compaction. Methods of solvent removal include, but are not limited to, supercritical drying (or drying using supercritical fluids, such that the low surface tension of the supercritical fluid exchanges with the transient solvent within the gel), exchange of solvent with supercritical fluid, exchange of solvent with fluid that is subsequently transformed to the supercritical state, sub- or near-critical fluid drying, and sublimating a frozen solvent in a freeze-drying process. See for example, PCT Patent Application Publication No. WO2016127084A1.

[0059] Aerogels include a highly porous network of micro-, meso-, and macro-sized pores, and are generally characterized by the following physical and structural properties (according to nitrogen porosimetry testing and helium pycnometry) attributable to aerogels: (a) an average pore diameter ranging from about 2 nm to about 100 nm; (b) a porosity of at least 60% or more, and (c) a specific surface area of about 100 m²/g or more, such as from about 100 to about 1000 m²/g by nitrogen sorption analysis. [0060] Aerogel materials of the present disclosure thus include any aerogels or other open- celled compounds, which satisfy the defining elements set forth in previous paragraphs.

[0061] As used herein, the terms "xerogel" and "ambigel" refer to gels comprising an open, non-fluid colloidal or polymer network that is formed by the removal of all swelling agents from a corresponding wet-gel without any precautions taken to avoid substantial volume reduction or compaction, such as under ambient pressure drying. In contrast to an aerogel, a xerogel, such as a silica xerogel, generally comprises a compact structure. Xerogels experience substantial volume reduction during ambient pressure drying, and can have lower surface areas compared to aerogels, such as 0-100 m²/g, or from about 0 to about 20 m²/g as measured by nitrogen sorption analysis.

[0062] Within the context of the present disclosure, the term "continuous" refers to a layer free of gaps, holes, or any discontinuities. For example, a continuous layer that does not include two (or more) component materials physically separated (or spaced apart) within this layer.

[0063] As used herein, the term "uniform" refers to a variation in the thickness of a material (e.g., the coating of the present disclosure of less than about 10%, less than about 5%, or less than about 1%).

[0064] Within the context of the present disclosure, the term "capacity" refers to the amount of specific energy or charge that a battery is able to store. Capacity is specifically measured as the discharge current that the battery can deliver over time, per unit mass. It is typically provided as Ampere-hours or milliAmpere-hours per gram (Ah/g or mAh/g) of total active material mass. For example, a battery with 1 Ah capacity can supply a current of one ampere for one hour or 0.5 amps for two hours, etc. Therefore, 1 Ampere-hour (Ah) is the equivalent of 3,600 coulombs of electrical charge. Similarly, the term "milliampere-hour (mAh)" also refers to a unit of the storage capacity of a battery and is 1/1 ,000 of an Ampere-hour. The capacity of a battery (and an anode in particular) may be determined by methods known in the art, for example including, but not limited to: applying a fixed constant current load to a fully charged cell until the cell’s voltage reaches the end of discharge voltage value; the time to reach end of discharge voltage multiplied by the constant current is the discharge capacity; by dividing the discharge capacity by the weight of electrode material or volume. Within the context of the present disclosure, measurements of capacity are acquired according to this method, unless otherwise stated. Unless otherwise noted, capacity is reported at cycle 10 of the battery. [0065] As used herein, the term "electrode" refers to a "cathode" or an "anode." As used herein, the term "positive electrode" is used interchangeably with cathode. Likewise, the term "negative electrode" is used interchangeably with anode.

[0066] Within the context of the present disclosure, the term "pyrolyze" or "pyrolysis" or "carbonization" refers to the decomposition or transformation of an organic compound or composition to pure or substantially pure carbon caused by heat. In the examples, the term "carbonization yield" refers to a percentage ratio of the weight of the resultant carbon to the weight of the organic compound or composition from which the carbon are produced. In some embodiments, porous gel materials (e.g., carbon aerogels) may be described as "derived from" or "obtained from" an organic material, meaning that the organic material has been subjected to one or more processes to create porosity (e.g., creatin of an aerogel), to convert the organic material substantially to carbon (e.g., pyrolysis), or both.

The Composite Material

[0067] Referring to FIG. 1A and FIG. IB, in one aspect provided herein is a composite material 100 comprising: silicon particles 110 comprising a sacrificial layer 120 on at least a portion of a surface of the silicon particles; and three-dimensional network 130, wherein the silicon particles are within the three-dimensional network 130 and the sacrificial layer 120 is between the surface of the silicon particles and a portion of the three-dimensional network. In some embodiments, the silicon particles have a diameter of less than lOOOnm, less than 500 nm, less than 300 nm, less than 200 nm, or less than 150 nm.

[0068] The sacrificial layer 120 of the present technology can be partially or completely removed by mechanical, thermal, chemical and/or electromagnetic forces and/agents applied to the sacrificial layer. The way that the sacrificial material is removed depends primarily on the type of the sacrificial material is used. For example, synthetic and natural organics when used as a sacrificial layer can be partially or completely removed through pyrolysis by applying long thermal treatments at temperatures between 130 and 850°C. Sacrificial layer of the present technology may be partially or completely removed during charging and discharging battery cycles due to continuous mechanical and/or temperature and/or chemical changes experienced by the sacrificial layer. Partial or complete removal of the sacrificial layer during battery cyclic processes may generate void spaces between the surface of the silicon particles and the three-dimensional network. Without wishing to be bound by theory, the generated void spaces may allow accommodating volume changes of Si particles upon lithiation process.

[0069] In one aspect, the sacrificial layer of the present technology provides the advantage of designing in void spaces the size of which can be adjusted. That is, the size of the void space between the surface of the silicon particles and the three-dimensional network created by removal of the sacrificial layer can be tailored by changing the thickness of the sacrificial layer provided herein.

[0070] In another aspect, the sacrificial layer of the present technology may aid relieving stress between the surface of the Si particles and the surface of the three-dimensional network upon Si expansion/contraction during charging and discharging processes, whereby improving performance of high-capacity batteries, such as, e.g., lithium-ion batteries (e.g., cycling stability, battery lifetime).

[0071] In one aspect, the sacrificial layer may be covalently bonded with the three-dimensional network providing improved dispersion properties (e.g., homogenous distribution of silicon particles within the network) to the silicon particles compared to the silicon particles without a sacrificial layer. Without wishing to be bound by theory, better distribution of the silicon particles within the three-dimensional network may alleviate the stress created on the composite material due to swelling of the silicon particles during charging and discharging processes.

[0072] In one aspect, the present technology relates to preparing silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles. That is, a sacrificial layer is formed on at least a portion the exterior of the silicon particles. Sacrificial layer of the present technology can be removed before or after the fabrication of the battery components, for example by mechanical, thermal, chemical and/or electromagnetic changes experienced by the sacrificial layer.

[0073] In some embodiments, the sacrificial layer is formed on the silicon particles prior to their incorporation into a matrix material forming a portion or a phase of the composite material. In other embodiments, the sacrificial layer is formed during the incorporation or processing of the composite material. For example, the sacrificial layer can form by a reaction, such as a covalent reaction between precursors used to build the matrix material surrounding silicon particles (e.g., silicon particles with a surface layer containing an oxide). [0074] Within the context of the present disclosure, the term "dispersion" refers to a dispersion in which one substance, which is the dispersed phase, is distributed in discrete units throughout the second substance (continuous phase or medium). In general, the dispersed phase is not substantially agglomerated, but rather spaced within the second substance. While dispersion includes the gathering or touching of a few particles (e.g., two, three, four, less than five), the particles are generally spaced evenly throughout the second substance, such as that shown in FIG. IB.

[0075] Generally, the silicon is contained at least partially within the pores of the three- dimensional network, i.e., the silicon is disposed within the framework of the three-dimensional network. The silicon accepts lithium ions during charge and releases lithium ions during discharge. In certain embodiments, the three-dimensional network forms interconnected structures around the silicon, which is connected to the three-dimensional network at a plurality of points.

Measurement of Composite Material Properties

[0076] The composite materials can be characterized by properties such as pore volume, porosity, surface area, and pore size distribution. These properties and associated terms are defined herein below, along with methods of measuring and/or calculating such properties.

[0077] Within the context of the present disclosure, the term "pore volume" refers to the total volume of pores within a sample of porous material. Pore volume is specifically measured as the volume of void space within the porous material, where that void space may be measurable and/or may be accessible by another material, for example an electrochemically active species such as silicon particles. It is typically recorded as cubic centimeters per gram (cm³/g or cc/g).

[0078] Within the context of the present disclosure, the term "porosity" when used with respect to the polymeric network or the composite materials disclosed herein, refers to a volumetric ratio of pores that does not contain another material (e.g., an electrochemically active species such as silicon particles) bonded to the walls of the pores. For clarification and illustration purposes, it should be noted that within the specific implementation of silicon-doped polymeric network e.g., an aerogel as the primary anodic material in a LIB, porosity refers to the void space after inclusion of silicon particles. As such, porosity may be, for example, about 10%-70% when the anode is in a pre-lithiated state (to accommodate for ion transport and silicon expansion) and about 1 %-50% when the anode is in a post-lithiated state. It should be noted that pore volume and porosity are different measures for the same property of the pore structure, namely the "empty space" within the pore structure. For example, when silicon is used as the electrochemically active species contained within the pores of the polymeric network (e.g., a composite material as described herein), pore volume and porosity refer to the space that is "empty", namely the space not utilized by the silicon or the carbon.

[0079] Within the context of the present disclosure, the term "pore size distribution" refers to the statistical distribution or relative amount of each pore size within a sample volume of a porous material. A narrower pore size distribution refers to a relatively large proportion of pores at a narrow range of pore sizes, thus optimizing the amount of pores that can surround the electrochemically active species and maximizing use of the pore volume. Conversely, a broader pore size distribution refers to relatively small proportion of pores at a narrow range of pore sizes. As such, pore size distribution is typically measured as a function of pore volume and recorded as a unit size of a full width at half max of a predominant peak in a pore size distribution chart.

[0080] Within the context of the present disclosure, the term "pore size at max peak from distribution" refers to the value at the discernible peak on a graph illustrating pore size distribution. Pore size at max peak from distribution is specifically measured as the pore size at which the greatest percentage of pores is formed. It is typically recorded as any unit length of pore size, for example micrometers or nanometers (nm).

[0081] Within the context of the present disclosure, the term "BET surface area" has its usual meaning of referring to the Brunauer-Emmett-Teller method for determining surface area by N2 adsorption measurements. The BET surface area, expressed in m²/g, is a measure of the total surface area of a porous material per unit of mass. Unless otherwise stated, "surface area" refers to BET surface area. As an alternative to BET surface area, a geometric outer surface area of e.g., a polyimide or carbon bead may be calculated based on the diameter of the bead. Generally, such geometric outer surface areas for beads of the present disclosure are within a range from about 3 to about 700 m².

[0082] As used herein, the term "particle size D50" which is a volume-based accumulative 50% size which is a particle size at a point of 50% on an accumulative curve (i.e., a diameter of a particle in the 50th percentile (median) of the volumes of particles) when the accumulative curve is drawn so that a particle size distribution is obtained on the volume basis and the whole volume is 100%.

[0083] Within the context of the present disclosure, the term "density" refers to a measurement of the mass per unit volume of a material (e.g., a composite material as described herein). The term "density" generally refers to the true or skeletal density of a material, as well as to the bulk density of a material or composition. Density is typically reported as g/cm³, g/cc, or g/mL.

[0084] The composite material properties can be determined using mercury intrusion porosity and helium pycnometry experiments. Mercury intrusion porosity can be used to determine porosity, pore size distribution and pore volume to solid particles. During a typical mercury intrusion porosity, a pressurized chamber is used to force mercury into the voids in a porous substrate. As pressure is applied, mercury fills the larger pores first. As the pressure increases, the mercury can enter into smaller pores. The mercury pycnometry can access and measure pores greater than about 3 nm. Mercury intrusion porosity can be used measure bulk density, skeletal density and porosity. By varying testing parameters (e.g., the pressure range), pores with different sizes can be excluded. The lower pore size limit if mercury intrusion porosity is about 3 nm.

[0085] Helium pycnometry uses helium gas to measure the volume of pores of a solid material. During helium pycnometry, a sample is sealed in a compartment and helium gas is added to the compartment. The helium gas penetrates into small pores in the material. After the system has equilibrated, the change in pressure can be used to determine the skeletal density of the solid material. The helium pycnometry can access and measure pores greater than about 0.3 nm, for example, pores sizing from about 3 nm to about 300 nm.

[0086] The "Hg skeletal density" (g/cm³) is measured by dividing the mass (g) of the composite material particles by the volume (cm³) of the particles, where the volume is measured by controlling (e.g., by pressure) the mercury access to pores of the particles greater than 3nm during the measurement. This volume does not include the volume of the mercury accessible pores of the composite materials greater than 3 nm. Instead, the volume only includes the volume of the "skeleton" of the composite material particles. The volume of the pores less than 3 nm is considered as part of the skeleton and included in the skeletal density calculation.

[0087] The "Hg bulk density" is measured by dividing the mass (g) of the composite material particles by the volume (cm³) of the particles, where the volume is measured by controlling (e.g., by pressure) the mercury not to access pores of the particles during the measurement. This volume includes the volume of the pores of the composite materials, including pores greater than 3 nm and less than 3 nm.

[0088] The "He skeletal density" is measured by dividing the mass (g) of the composite material particles by the volume (cm³) of the particles, where the volume is measured by controlling (e.g., by pressure) the helium to access pores of the particles greater than 0.3 nm during the measurement. This volume does not include the volume of the helium accessible pores of the composite materials greater than 0.3 nm. Instead, the volume only includes the volume of the "skeleton" of the composite material particles. The volume of the pores less than 0.3 nm is considered as part of the skeleton and included in the skeletal density calculation.

[0089] The composite material may also include pores not accessible to either helium nor mercury during the helium pycnometry or mercury pycnometry tests. For example, some of pores formed by removing sacrificial particles may be enclosed in the three-dimensional network and therefore accessible to neither helium pycnometry nor the mercury pycnometry. These non- accessible pores are usually a very small amount in the composite materials disclosed herein. The non-accessible pores are treated as part of the volume of the skeleton without introducing significant variations.

[0090] Various physical properties can be calculated according to the formulas below using mercury (Hg) intrusion skeletal density measurements (Hg skeletal density) measured by mercury pycnometry, mercury intrusion bulk density (Hg bulk density) measured by mercury pycnometry, and helium (He) skeletal density (He skeletal density) tested by He pycnometry.

Total beads level porosity (%) = {(l - - - — ) / 1 } * 100 (I)

‘ ^J He skeletal density ’ ^v

... . . . Total beads level porosity ...

1 otal p

¹ ore volume - (2)

100

1 1

Micropore volume (cm³/g) = - _: - — (3)

Hg skeletal density He skeletal density

Micropore volume percentage (%, vs total pore volume)

= micropore volume /total pore volume (4) Mesopore volume percentage (%, vs total pore volume) can be obtained through the mercury intrusion by excluding all the pores > 50 nm

Macropore volume percentage (%, vs total pore volume)

= 1 - micropore volume percentage - mesopore volume percentage (5)

[0091] The "total beads level porosity" (%) refers to the ratio of the volume of the pores in the composite material particles to the volume of the composite material particles. The total beads level porosity is calculated by equation (1). The total beads level porosity includes pores of greater than 0.3 nm that can be accessed by helium and mercury.

[0092] The "total pore volume" (cm³/g) refers to the total pore volume of unit weight of the composite material particles. The total pore volume is calculated by equation (2). The total pore volume includes pores greater than 0.3 nm that can be accessed by helium and mercury.

[0093] The "micropore volume" (cm³/g) refers to the micropore volume of unit weight of the composite material particles. The micropore volume (cm³/g) of the composite material is the difference between of the reciprocal (cm³/g) of the mercury skeletal density (g/cm³) and the reciprocal (cm³/g) of the helium skeletal density (g/cm³) according to equation (3). The micropore volume includes pores greater than 0.3 nm but less than 3 nm. The micropores are accessible by helium but not accessible by mercury.

[0094] The "micropore volume percentage" (%) refers to the volumetric ratio between the volume of the micropore to the total pore volume. The micropore volume percentage is calculated by equation (4).

[0095] The "mesopore volume percentage" (%) refers to the volumetric ratio between the volume of the mesopores to the total pore volume. Mesopores refers to pores between about 3nm to about 50nm that are accessible by mercury. Pores below 3 nm are not accessible by mercury. Mesopore volume percentage can be directly measured using mercury pycnometry by excluding pores greater than 50 nm. The mesopore volume percentage can also be obtained by subtracting micropore volume percentage (calculated in equation (4)) and macropore volume percentage (measured by mercury pycnometry) from total pore volume percentage (100%).

[0096] The "macropore volume percentage" (%) refers to the volumetric ratio between the volume of the macropores to the total pore volume. Macropores are greater than about 50 nm that are accessible by mercury. Macropore volume percentage can be directly measured using mercury pycnometry by excluding pores smaller than 50 nm. The macropore volume percentage can also be obtained by subtracting micropore volume percentage (calculated in equation (4)) and mesopore volume percentage (measured by mercury pycnometry) from total pore volume percentage (100%).

Composite Material Properties

Total porosity

[0097] Composite materials described herein generally include micropores (< 3 nm), mesopores (3 nm - 50 nm), and macropores (> 50 nm). The composite materials described herein include a three-dimensional carbon network having a substantial amount of macropores. In some aspects, the total level of porosity of the three-dimensional carbon network is greater than 10%, greater than 20%, greater than 30%, greater than 40%, greater than 50%, greater than 60%, or greater than 70%. In some aspects, the total level of porosity of the three-dimensional carbon network is 25% to 35%, 30% to 40%, 35% to 45%, 40% to 50%, 55% to 65%, or 60% to 70%.

[0098] In certain embodiments, aerogel materials or composite materials of the present disclosure have a total bead level porosity of about 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or in a range between any two of these values.

Total pore volume

[0099] In some aspects, aerogel materials or compositions of the present disclosure (without incorporation of electrochemically active species, e.g., silicon) have a relatively large total pore volume of about 1 cc/g or more, 1.5 cc/g or more, 2 cc/g or more, 2.5 cc/g or more, 3 cc/g or more, 3.5 cc/g or more, 4 cc/g or more, or in a range between any two of these values. In other embodiments, aerogel materials or compositions of the present disclosure (with incorporation of electrochemically active species, e.g., silicon) have a total pore volume of about 0.3 cc/g or more, 0.6 cc/g or more, 0.9 cc/g or more, 1.2 cc/g or more, 1.5 cc/g or more, 1.8 cc/g or more, 2.1 cc/g or more, 2.4 cc/g or more, 2.7 cc/g or more, 3.0 cc/g or more, 3.3 cc/g or more, 3.6 cc/g or more, or in a range between any two of these values. In further aspects, the total pore volume of the composite material (with incorporation of electrochemically active species, e.g., silicon) is from about 0.1 cm³/g to about 1.5 cm³/g, about 0.1 cm³/g to about 1.0 cm³/g, about 0.1 cm³/g to about 0.5 cm³/g, about 0.1 cm³/g to about 0.4 cm³/g, about 0.4 cm³/g to about 1.0 cm³/g, or about 0.9 cm³/g to about 1.4 cm³/g.

Pore size distribution

[00100] In certain embodiments, aerogel materials or compositions of the present disclosure have a pore size at max peak from distribution of about 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 10 nm or less, 5 nm or less, 2 nm or less, or in a range between any two of these values.

[00101] In certain embodiments, aerogel materials or compositions of the present disclosure have a relatively narrow pore size distribution (full width at half max) of about 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, or in a range between any two of these values.

Macropores, mesopores, and micropores

[00102] In some aspects, the macropores constitute a volume fraction of greater than about 5%, greater than about 10%, greater than about 20%, greater than about 30%, greater than about 40%, greater than about 50%, greater than about 60%, greater than about 70%, or greater than about 80% of the total pore volume of the three-dimensional carbon network. In some aspects, the macropores constitute a volume fraction of 45% to 55%, 55% to 65%, 65% to 75%, or 70% to 80% of the total pore volume of the three-dimensional carbon network. The composite materials described herein generally have a low volume fraction of mesopores. In some aspects, the mesopores constitute a volume fraction of less than 20%, less than 10%, less than 5%, less than 2%, or less than 1% of the total pore volume of the three-dimensional carbon network. In some aspects, the mesopores constitute a volume fraction of 10% to 20%, 5% to 10%, or 1% to 5% of the total pore volume of the three-dimensional carbon network.

[00103] The composite materials described herein include a higher percentage of micropores compared to mesopores. In some aspects, the micropores constitute a volume fraction of less than 80%, less than 70%, less than 65%, less than 55%, less than 50%, less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, or less than 10% of the total pore volume of the three-dimensional carbon network. In some aspects, the micropores constitute a volume fraction of about 10% to about 50%, about 10% to about 45%, about 10% to about 40%, about 10% to about 35%; about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, about 10% to about 15%, about 15% to about 25%, about 25% to about 35%, about 35% to about 45%, or about 45% to about 55% of the total pore volume of the three- dimensional carbon network.

Skeletal density

[00104] In some aspects, the composite materials have a skeletal density, measured using helium pycnometry, of about 1.0 g/mL to about 2.5 g/mL, about 1.5 g/mL to about 2.5 g/mL, about 1.0 g/mL to about 2.0 g/mL, or 1.0 g/mL to about 1.5 g/mL. In some aspects, the composite materials have a skeletal density, measured using mercury intrusion, of about 0.5 g/mL to about 2.5 g/mL, about 1.5 g/mL to about 2.5 g/mL, about 1.5 g/mL to about 2.0 g/mL, about 0.5 g/mL to about 2.0 g/mL, about 0.5 g/mL to about 1.5 g/mL, or about 0.5 g/mL to about 1.0 g/mL. In some aspects, the composite materials have a bulk density, measured using mercury pycnometry, of 0.5 g/mL to about 2.5 g/mL, of 0.5 g/mL to about 2.0 g/mL, about 0.5 g/mL to about 1.5 g/mL, or about 0.5 g/mL to about 1.0 g/mL.

[00105] Preferably, aerogel materials or composite materials of the present disclosure have a tap density of about 1.50 g/cc or less, about 1.40 g/cc or less, about 1.30 g/cc or less, about 1.20 g/cc or less, about 1.10 g/cc or less, about 1.00 g/cc or less, about 0.90 g/cc or less, about 0.80 g/cc or less, about 0.70 g/cc or less, about 0.60 g/cc or less, about 0.50 g/cc or less, about 0.40 g/cc or less, about 0.30 g/cc or less, about 0.20 g/cc or less, about 0.10 g/cc or less, or in a range between any two of these values, for example between about 0.15 g/cc and 1.5 g/cc or more particularly 0.50 g/cc and 1.30 g/cc.

[00106] In some embodiments, the composite material of the present disclosure comprises a low bulk density material. In some embodiments, the low bulk density material comprises a skeletal framework comprising nanofibers, the skeletal framework forming a pore structure comprising an array of interconnected pores. In some embodiments, such materials may have a fibrillar morphology. In some embodiments, the composite material is an aerogel, a xerogel, a cryogel, or an ambigel, or combination thereof. In some embodiments, the composite material is an aerogel. [00107] Structurally, some embodiments of the carbonized network have a fibrillar morphology with a strut size that produces the aforementioned narrow pore size distribution, porosity, and enhanced connectedness, among other properties. In any embodiment, the fibrillar morphology of the carbon material can include an average strut width of about 2-10 nm, or even more specifically about 2-5 nm. Within the context of the present disclosure, the term "strut width" refers to the average diameter of nanostruts, nanorods, nanofibers, or nanofilaments that form a material having a fibrillar morphology. It is typically recorded as any unit length, for example micrometers or nm. The strut width may be determined by methods known in the art, for example including, but not limited to, scanning electron microscopy image analysis. Within the context of the present disclosure, measurements of strut width are acquired according to this method, unless otherwise stated. In certain embodiments, materials or compositions of the present disclosure have a strut width of about 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, or in a range between any two of these values. An exemplary range of strut widths is about 2-5 nm. Smaller strut widths, such as these, permit a greater amount of struts to be present within the network and thus contact the electrochemically active species, in turn allowing more of the electrochemically active species to be present within the composite. This increases electrical conductivity and mechanical strength.

Method of preparing a composite material

[00108] Referring to FIG. 2 and FIG. 3, in one aspect, the present technology provides useful pathways for creating a composite material comprising silicon particles with a sacrificial layer and a three-dimensional network.

[00109] The present technology provides methods of forming a composite material including a sacrificial layer. In method 200 shown in FIG. 2, illustrated is a method that includes forming the sacrificial layer prior to the incorporation of the silicon particles within a network (e.g., a sol-gel solution comprising a precursor of the three-dimensional network). In other embodiments, such as a method 300 shown in FIG. 3, the sacrificial layer is formed during or after providing the solgel solution.

[00110] Referring to FIG. 2, method 200 illustrates the manufacture of a composite material including five steps (210, 220, 230, 240, 250). First, as shown in step 210, silicon particles are provided. In general, the silicon particles should be homogenous. That is, the silicon particles are typically provided from the same source and have a known, desired particle size, shape, porosity and other material attributes that are substantially similar. After procuring the silicon particles, the method 200 includes oxidizing a surface of the particles to obtain hydroxyl functional groups on the surface (i.e., step 220). Oxidation of the surfaces of silicon particles for certain type of Si sources is typically necessary for further functionalization of the surfaces. Oxidizing the surface of silicon particles may lead to complete or partial oxidation of surface Si-H groups. That is, all or certain percentage of Si-H groups on the surface of the silicon particles are converted to Si-OH groups after the oxidation process. The silicon particles may be oxidized in a single or multiple step(s). The oxidation can be thermal (e.g., at elevated temperatures under air), chemical (e.g., acid and/or oxidizing agent), electrochemical or combinations thereof. As shown in step 230, the third step is to form a sacrificial layer onto at least a portion of a surface of the silicon particles. The formation of sacrificial layer on the surface of the silicon particles is performed before introducing the silicon particles into a sol-gel solution comprising a precursor of three-dimensional network. The properties of the sacrificial layer (e.g., thickness, the type of the material, surface functionalities) formed in the third step can affect the dispersion of the silicon particles in the solgel solution which is introduced in the fourth step 240. The sacrificial layer can be made of polymers, metals, natural and synthetic organics, salts, ceramic compounds or combination thereof. After formation of the sacrificial layer, a sol-gel solution comprising a polar solvent and a precursor of the three-dimensional network is provided as shown in step 240. The silicon particles are dispersed in the sol-gel solution homogeneously or heterogeneously, preferably homogenously. A precursor of the three-dimensional network may be a precursor of an aerogel or xerogel. After providing sol-gel solution to the silicon particles with sacrificial layer, the silicon particles with the sacrificial layer is processed in the presence of the sol-gel solution to yield the composite material as shown in 250. Processing can include gelation of the sol-gel solution to form the three-dimensional network. The method 200 further comprises step of subcritical or supercritical drying after processing the silicon particles in the presence of the sol-gel solution. For example, the drying step can lead to the formation of an aerogel.

[00111] Referring to FIG. 3, method 300 illustrates the manufacture of a composite material including six steps (310, 320, 330, 340, 350, 360). In this method 300, the sacrificial layer is formed during or after providing the sol-gel solution. First, as shown in step 310, silicon particles are provided. In general, the silicon particles should be homogenous. That is, the silicon particles are typically provided from the same source and have a known, desired particle size, shape, porosity and other material attributes that are substantially similar. After procuring the silicon particles, the method 300 includes oxidizing a surface of the particles to obtain hydroxyl functional groups on the surface (i.e., step 320). Oxidizing the surface of silicon particles may lead to complete or partial oxidation of surface Si-H groups. That is, all or certain percentage of Si-H groups on the surface of the silicon particles are converted to Si-OH groups after oxidation process. The silicon particles may be oxidized in a single or multiple step(s). The oxidation can be thermal (e.g., at elevated temperatures under air), chemical (e.g., acid and/or oxidizing agent), electrochemical or combinations thereof. The third step 330 requires the silicon particles having hydroxyl functional groups on the surface thereof to covalently react with at least one functional silane group. Attachment of silane groups to the surface can pave the way for further modification of the silicon particles’ surfaces. In addition, silane groups present on the surface of the silicon particles can aid the dispersion of the silicon particles which is crucial for further steps. After attaching at least one functional silane group on the surface of silicon particles, a sol-gel solution comprising a polar solvent and a precursor of the three-dimensional network is provided as shown in step 340. The silicon particles are dispersed in the sol-gel solution homogeneously or heterogeneously, preferably homogenously. A precursor of the three-dimensional network may be a precursor of an aerogel. As shown in step 350, the fifth step is to form a sacrificial layer onto at least a portion of a surface of the silicon particles. The formation of sacrificial layer on the surface of the silicon particles is performed within the sol-gel solution comprising a precursor of three- dimensional network. The properties of the sacrificial layer (e.g., thickness, the type of the material) formed in the step 350 can affect the dispersion of the silicon particles in the composite material which is formed in the last step 360. The sacrificial layer can be made of polymers, metals, natural and synthetic organics, salts, ceramic compounds or combination thereof. After formation of the sacrificial layer, the silicon particles with the sacrificial layer are processed in the presence of the sol-gel solution to yield the composite material as shown in step 360. Processing can include gelation of the sol-gel solution to form the three-dimensional network. The method 300 further comprises step of subcritical or supercritical drying after processing the silicon particles in the presence of the sol-gel solution. For example, the drying step can lead to the formation of an aerogel. [00112] The step 350 of forming the sacrificial layer in method 300 comprises: i. grafting a polymer initiator on the surface of the silicon particles to react with a monomer; ii. polymerizing the monomer on the surface of the silicon particles to form the sacrificial layer.

[00113] FIGS. 4A and 4B show an exemplary route for preparation of silicon particles with a sacrificial layer. The process of forming the sacrificial layer mainly comprises three steps (410, 420, 430). In the first step 410, the silicon particles 401 having hydroxyl functional groups on the surface thereof covalently reacts with a functional silane group. In this example, 3- aminopropyltriethoxy silane (APTES) 402 is used as the functional silane group. Hydroxyl groups react with the silane groups in a polar solvent (e.g., ethanol 403) as shown in step 410. The reaction takes place at elevated temperatures e.g., a temperature higher than 25°C. After covalently attaching the APTES on the surface of the silicon particles to form silicon particles 404 comprising -NH2 groups on the surface, a polymer initiator (e.g., azobis(4-cyanovaleric acid); ACPA; 405) is grafted on the surface of the silicon particles for further reaction with a monomer. The step 420 grafting a polymer initiator on the surface of the silicon particles takes place in a polar solvent (e.g., ethanol 403). The selected polar solvent should be suitable for dissolving each component, e.g., the polymer initiator of the reaction. The third step 430 leads to formation of the silicon particles 110 with the sacrificial layer. In step 430, the monomer initiators on the surface the silicon particles 406 undergo a polymerization reaction with a monomer e.g., methyl methacrylate 407. The monomer chosen for the polymerization reaction depends on the type of the sacrificial layer that is desired on the surface. As shown in step 430, the polymerization reaction can take place in a polar solvent (e.g., water 404). The polymerization reaction takes place at a temperature higher than 25 °C.

[00114] The exemplary route for preparation of the silicon particles with the sacrificial layer as shown in FIG. 4A and 4B can also be applied to the method 300. In method 300, the first step 410 wherein the silicon particles 401 having hydroxyl functional groups on the surface thereof covalently reacts with a functional silane group e.g., aminopropyltriethoxysilane (APTES) 402, takes place prior to providing a sol-gel solution. The second 420 and third steps 430 are performed within the sol-gel solution during or after the step 340 of providing the sol-gel solution. That is, the steps 420 and 430 are performed within the sol-gel solution comprising the precursor of the three-dimensional network. [00115] In some embodiments, the polymer initiator comprises azobis(4-cyanovaleric acid) (ACPA), 2,2'-azobis(2-amidinopropane) hydrochloride (V50), ammonium persulfate, 2,2'-azobis (N,N'-dimethylene isobutyramidine) dihydrochloride (VA044), and ammonium persulfate/sodium metabisulfite. In some embodiments, the polymer initiator comprises azobis(4-cyanovaleric acid) (ACPA).

[00116] The step of covalently reacting hydroxyl functional groups on the surface of the silicon particles with at least one functional silane group includes the use of silanes selected from 3- aminopropyltriethoxy silane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2- aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), and N-(2-aminoethyl)-3- aminopropyltrimethoxy silane (AEAPTMS), and N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES), or combination thereof.

[00117] In some embodiments, method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution prior to the step of forming the sacrificial layer. In some embodiments, the method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution after the step of forming the sacrificial layer. In some embodiments, the method of preparing a composite material further comprises a step of dispersing the silicon particles in the sol-gel solution prior and after the step of forming the sacrificial layer.

[00118] In some embodiments, the method of preparing a composite material further comprises processing the composite material to substantially remove the sacrificial layer. In one embodiment, the processing the composite material to substantially remove the sacrificial layer includes heating the composite material to a chemical decomposition temperature of the sacrificial layer. In some embodiments, the chemical decomposition temperature of the sacrificial material layer is in the range of about 200°C to about 800°C. In certain embodiments, processing the composite material to substantially remove the sacrificial layer provides a void volume around the silicon particles.

[00119] In some embodiments, the method of preparing a composite material further comprises step of subcritical or supercritical drying after processing the silicon particles in the presence of the sol-gel solution. In some embodiments, a step of subcritical or supercritical drying after processing the silicon particles in the presence of the sol-gel solution.

[00120] Oxidizing a surface of the plurality of the silicon particles may comprise an acid treatment step. In some embodiments, the acid treatment step comprises the use of sulphochromic acid and/or H2O2 (hydrogen peroxide). In some examples, the acid treatment step comprises a step of sonicating the plurality of the silicon particles for a certain period of time, e.g., at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes, or at least 60 minutes. Oxidizing a surface of the plurality of the silicon particles may comprise a step of pyrolysis at a temperature about at 300, about 400, or about 500, to about 600, about 650, about 700, about 800, or about 900°C. In some embodiments, the temperature is about 650°C. As used herein, the term "pyrolyze" or "pyrolysis" refers to the decomposition or transformation of an organic compound or composition to pure or substantially pure carbon caused by heat. Oxidizing a surface of the plurality of the silicon particles may lead to decrease in the number of Si-H bonds on the surface of the silicon particles.

[00121] In some embodiments, the method of preparing a composite material of the present disclosure further comprises a step of subcritical or supercritical solvent removal, e.g., drying, after processing the plurality of silicon particles in the presence of the sol-gel solution. Methods of solvent removal include, but are not limited to, supercritical drying (or drying using supercritical fluids, such that the low surface tension of the supercritical fluid exchanges with the transient solvent within the gel), exchange of solvent with supercritical fluid, exchange of solvent with fluid that is subsequently transformed to the supercritical state, sub- or near-critical fluid drying, and sublimating a frozen solvent in a freeze-drying process. See for example, PCT Patent Application Publication No. WO2016127084A1.

[00122] The amount of silicon present in the composite material varies according to the density of the low bulk density carbon material, with lower densities resulting in higher weight percent incorporation of silicon. In some embodiments, the composite material comprises silicon in an amount by weight from about 20% to about 85%, such as from about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, or about 50%, to about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, or about 85% silicon by weight, based on the total weight of the composite material. In some embodiments, the composite material comprises silicon in an amount by weight from about 30% to about 35% by weight, based on the total weight of the composite material.

[00123] The composite material may be in a variety of different physical forms. In some embodiments, the composite material can take the form of a monolith. As used herein, the term "monolith" refers to materials in which a majority (by weight) of the low-density skeletal framework included in the composite material is in the form of a unitary, continuous, self- supporting object. With reference to aerogel materials, monolithic aerogel materials include aerogel materials which are initially formed to have a well-defined shape, but which can be subsequently cracked, fractured or segmented into non-self-repeating objects. For example, irregular chunks may be considered as monoliths. Monolithic aerogels may take the form of a freestanding structure, or a reinforced material with fibers or an interpenetrating foam.

[00124] In other embodiments, the composite material may be in particulate form, for example as beads or as particles from, e.g., crushing a monolithic material. As used herein, the term "beads" is meant to include discrete small units or pieces having a generally spherical shape. In some embodiments, the composite material beads are substantially spherical.

[00125] The composite material in particulate form can have various particle sizes. In the case of spherical particles (e.g., beads), the particle size is the diameter of the particle. In the case of irregular particles, the term particle size refers to the maximum dimension (e.g., a length, width, or height). The particle size may vary depending on the physical form, preparation method, and any subsequent physical steps performed. In some embodiments, the composite material in particulate form can have a particle size from about 1 micrometer to about 1 millimeter. For example, the composite material in particulate form can have a particle size of about 1 micrometer, about 2 micrometers, about 3 micrometers, about 4 micrometers, about 5 micrometers, about 6 micrometers, about 7 micrometers, about 8 micrometers, about 9 micrometers, about 10 micrometers, about 15 micrometers, about 20 micrometers, about 25 micrometers, about 30 micrometers, about 35 micrometers, about 40 micrometers, about 45 micrometers, about 50 micrometers, about 60 micrometers, about 70 micrometers, about 80 micrometers, about 90 micrometers, about 100 micrometers, about 200 micrometers, about 300 micrometers, about 400 micrometers, about 500 micrometers, about 600 micrometers, about 700 micrometers, about 800 micrometers, about 900 micrometers, about 1 millimeter, or in a range between any two of these values.

[00126] In some embodiments, the composite material has a particle size D90 value of less than or equal to 40 micrometers. In some embodiments, the composite material has a particle size D10 value of at least 1 micrometer. In some embodiments, the composite material has a particle size D50 in a range from about 5 micrometers to about 20 micrometers. [00127] The density of the composite material may vary. In some embodiments, the composite material has a tap density in a range from about 0.15 g/cm³ to about 1.2 g/cm³.

[00128] The surface area of the composite material may vary. For example, the surface area may be up to about 100 m²/g, or may be greater than 100 m²/g. In some embodiments, the composite material has a surface area in a range from about 1 m²/g to about 400 m²/g, such as from about 1, about 10, or about 50, to about 100, about 200, about 300, or about 400 m²/g.

[00129] In some embodiments, the composite material comprises silicon in an amount by weight from about 20 to about 85%, such as from about 20, about 25, about 30, about 35, about 40, about 45, or about 50, to about 55, about 60, about 65, about 70, about 75, about 80, or about 85% silicon by weight, based on the total weight of the composite material.

[00130] The composite material may be in a variety of different physical forms. In some embodiments, the composite material can take the form of a monolith. As used herein, the term "monolith" refers to materials in which a majority (by weight) of the low-density skeletal framework included in the composite material is in the form of a unitary, continuous, self- supporting object. With reference to aerogel materials, monolithic aerogel materials include aerogel materials which are initially formed to have a well-defined shape, but which can be subsequently cracked, fractured or segmented into non-self-repeating objects. For example, irregular chunks may be considered as monoliths. Monolithic aerogels may take the form of a freestanding structure, or a reinforced material with fibers or an interpenetrating foam.

[00131] In other embodiments, the composite material may be in particulate form, for example as beads or as particles from, e.g., crushing a monolithic material. As used herein, the term "beads" is meant to include discrete small units or pieces having a generally spherical shape. In some embodiments, the carbon-silicon composite beads are substantially spherical.

[00132] The capacity of the composite material may vary. In some embodiments, the composite material has a specific capacity of at least about 400 mAh/g. In some embodiments, the composite material has a specific capacity of about 400, about 500, about 600, about 700, about 800, about 900, about 1000, or about 1100 mAh/g. In some embodiments, the composite material has a specific capacity of 1200 mAh/g or more, 1400 mAh/g or more, 1600 mAh/g or more, 1800 mAh/g or more, 2000 mAh/g or more, 2400 mAh/g or more, 2800 mAh/g or more, 3200 mAh/g or more, or in a range between any two of these values. [00133] The electrical conductivity of the anode material may vary. Within the context of the present disclosure, the term "electrical conductivity" refers to a measurement of the ability of a material to conduct an electric current or other allow the flow of electrons therethrough or therein. Electrical conductivity is specifically measured as the electric conductance/susceptance/admittance of a material per unit size of the material. It is typically recorded as S/m (Siemens/meter) or S/cm (Siemens/centimeter). The electrical conductivity or resistivity of a material may be determined by methods known in the art, for example including, but not limited to: In-line Four Point Resistivity (using the Dual Configuration test method of ASTM F84-99). Within the context of the present disclosure, measurements of electrical conductivity are acquired according to ASTM F84 - resistivity (R) measurements obtained by measuring voltage (V) divided by current (I), unless otherwise stated. In certain embodiments, anode materials of the present disclosure have an electrical conductivity of about 10 S/cm or more, 20 S/cm or more, 30 S/cm or more, 40 S/cm or more, 50 S/cm or more, 60 S/cm or more, 70 S/cm or more, 80 S/cm or more, or in a range between any two of these values.

The Porous Three-Dimension Network

[00134] In some embodiments, the porous polymer network is a sol-gel solution. In one or more embodiments, the sol-gel solution comprises an aerogel precursor, a xerogel precursor, an ambigel precursor, an aerogel-xerogel hybrid material precursor, an aerogel-ambigel hybrid material precursor, an aerogel-ambigel-xerogel hybrid material precursor, or combinations thereof.

[00135] In some embodiments, the porous polymer network is a three-dimensional network. In some embodiments, the polymer network is a porous polymer network, e.g., a porous three- dimensional network.

[00136] In some embodiments, the porous polymer network comprises an aerogel, a xerogel, an ambigel, an aerogel-xerogel hybrid material, an aerogel-ambigel hybrid material, an aerogel- ambigel-xerogel hybrid material, or combinations thereof.

[00137] Aerogel materials of the present disclosure can include any aerogels or other open- celled compounds, which satisfy the defining elements set forth in previous paragraphs, including compounds, which can be otherwise categorized as xerogels, cryogels, ambigels, microporous materials, and the like. [00138] To further expand on the exemplary application within LIBs, when aerogel material is used as the primary electrode material e.g., anodic material as in examples of this present disclosure, the porous core of the aerogel has a narrow pore size distribution, and provides for high electrical conductivity, high mechanical strength, and a morphology and sufficient pore volume (at a final density) to accommodate a high percentage by weight of silicon particles and expansion thereof.

[00139] In some examples, the surface of the three-dimensional network may be modified via chemical, physical, or mechanical methods in order to enhance performance with electrochemically active species contained within the pores of the three-dimensional network.

[00140] Furthermore, it is contemplated herein that the three-dimensional network, and specifically aerogels, can take the form of monolithic structures. When monolithic in nature, the carbon aerogel eliminates the need for any binders; in other words, the anode can be binder-less. As used herein, the term "monolithic" refers to aerogel materials in which a majority (by weight) of the aerogel included in the aerogel material or composition is in the form of a unitary, continuous, interconnected aerogel nanostructure. Monolithic aerogel materials include aerogel materials which are initially formed to have a unitary interconnected gel or aerogel nanostructure, but which can be subsequently cracked, fractured or segmented into non-unitary aerogel nanostructures. Monolithic aerogels may take the form of a freestanding structure or a reinforced (fiber or foam) material. In comparison, using silicon lithiation as an example, silicon incorporated into a monolithic aerogel can be utilized more effectively relative to theoretical capacity, as compared to the same amount of silicon incorporated into a slurry using conventional processes.

[00141] Monolithic aerogel materials are differentiated from particulate aerogel materials. The term "particulate aerogel material" refers to aerogel materials in which a majority (by weight) of the aerogel included in the aerogel material is in the form of particulates, particles, granules, beads, or powders, which can be combined together (i.e., via a binder, such as a polymer binder) or compressed together but which lack an interconnected aerogel nanostructure between individual particles. Collectively, aerogel materials of this form will be referred to as having a powder or particulate form (as opposed to a monolithic form). It should be noted that despite an individual particle of a powder having a unitary structure, the individual particle is not considered herein as a monolith. Integration of aerogel powder into an electrochemical cell typically preparation of a paste or slurry from the powder, casting and drying onto a substrate, and may optionally include calendaring.

[00142] Particulate aerogel materials, e.g., aerogel beads, provide certain advantages. For example, particulate materials can be used as a direct replacement for other materials such as graphite in LIB anodes and anode manufacturing processes. Particulate materials can also provide improved lithium-ion diffusion rates due to shorter diffusion paths within the particulate material. Particulate materials can also allow for electrodes with enhanced packing densities, e.g., by tuning the particle size and packing arrangement. Particulate materials can also provide improved access to silicon due to inter-particle and intra-particle porosity.

[00143] Aerogels can be formed of inorganic materials, organic materials, or mixtures thereof. When formed of organic materials such as, for example, phenols, resorcinol-formaldehyde (RF), phloroglucinol-furfuraldehyde (PF), polyacrylonitrile (PAN), polyimide (PI), polyurethane (PU), polyurea (PUA), polyamine (PA), polybutadiene, polydicyclopentadiene, and precursors or polymeric derivatives thereof, the organic aerogel may be carbonized (e.g., by pyrolysis) to form a carbon aerogel, which can have properties (e.g. , pore volume, pore size distribution, morphology, etc.) that differ or overlap from each other, depending on the precursor materials and methodologies used.

[00144] In some embodiments, the three-dimensional network comprises an organic material or is derived from an organic material, meaning the three-dimensional network may be a wet-gel or an aerogel comprising an organic material as described herein, or may be a carbon aerogel obtained or derived from an organic material as described herein (i.e., by pyrolysis of an organic material under conditions suitable to convert at least a portion of the organic material to carbon).

Inorganic aerogels

[00145] Inorganic aerogels are generally formed from metal oxide or metal alkoxide materials. The metal oxide or metal alkoxide materials may be based on oxides or alkoxides of any metal that can form oxides. Such metals include, but are not limited to silicon, aluminum, titanium, zirconium, hafnium, yttrium, vanadium, cerium, and the like. Inorganic silica aerogels are traditionally made via the hydrolysis and condensation of silica-based alkoxides (such as tetraethoxylsilane), or via gelation of silicic acid or water glass. Other relevant inorganic precursor materials for silica based aerogel synthesis include, but are not limited to metal silicates such as sodium silicate or potassium silicate, alkoxysilanes, partially hydrolyzed alkoxysilanes, tetraethoxylsilane (TEOS), partially hydrolyzed TEOS, condensed polymers of TEOS, tetramethoxylsilane (TMOS), partially hydrolyzed TMOS, condensed polymers of TMOS, tetra- n-propoxysilane, partially hydrolyzed and/or condensed polymers of tetra-n-propoxysilane, poly ethylsilicates, partially hydrolyzed polyethysilicates, monomeric alkylalkoxy silanes, bis- trialkoxy alkyl or aryl silanes, polyhedral silsesquioxanes, or combinations thereof.

[00146] In certain embodiments of the present disclosure, pre -hydrolyzed TEOS, such as Silbond® H-5 (SBH5, Evonik Corp), which is hydrolyzed with a water/silica ratio of about 1.9-2, may be used as commercially available or may be further hydrolyzed prior to incorporation into the gelling process. Partially hydrolyzed TEOS or TMOS, such as polyethysilicate (Silbond® 40) or polymethylsilicate may also be used as commercially available or may be further hydrolyzed prior to incorporation into the gelling process.

[00147] Inorganic aerogels can also include gel precursors comprising at least one hydrophobic group, such as alkyl metal alkoxides, cycloalkyl metal alkoxides, and aryl metal alkoxides, which can impart or improve certain properties in the gel such as stability and hydrophobicity. Inorganic silica aerogels can specifically include hydrophobic precursors such as alkylsilanes or arylsilanes. Hydrophobic gel precursors may be used as primary precursor materials to form the framework of a gel material. However, hydrophobic gel precursors are more commonly used as co-precursors in combination with simple metal alkoxides in the formation of amalgam aerogels. Hydrophobic inorganic precursor materials for silica based aerogel synthesis include, but are not limited to trimethyl methoxysilane (TMS), dimethyl dimethoxysilane (DMS), methyl trimethoxy silane (MTMS), trimethyl ethoxysilane, dimethyl diethoxysilane (DMDS), methyl triethoxy silane (MTES), ethyl triethoxysilane (ETES), diethyl diethoxysilane, dimethyl diethoxy silane (DMDES), ethyl triethoxysilane, propyl trimethoxysilane, propyl triethoxysilane, phenyl trimethoxysilane, phenyl triethoxy silane (PhTES), hexamethyldisilazane and hexaethyldisilazane, and the like. Any derivatives of any of the above precursors may be used and specifically certain polymeric of other chemical groups may be added or cross-linked to one or more of the above precursors.

[00148] Aerogels may also be treated to impart or improve hydrophobicity. Hydrophobic treatment can be applied to a sol-gel solution, a wet-gel prior to liquid extraction, or to an aerogel subsequent to liquid extraction. Hydrophobic treatment is especially common in the production of metal oxide aerogels, such as silica aerogels. An example of a hydrophobic treatment of a gel is discussed below in greater detail, specifically in the context of treating a silica wet-gel. However, the specific examples and illustrations provided herein are not intended to limit the scope of the present disclosure to any specific type of hydrophobic treatment procedure or aerogel substrate. The present disclosure can include any gel or aerogel known to those in the art, as well as associated methods of hydrophobic treatment of the aerogels, in either wet-gel form or dried aerogel form.

[00149] Hydrophobic treatment is carried out by reacting a hydroxy moiety on a gel, such as a silanol group (Si-OH) present on a framework of a silica gel, with a functional group of a hydrophobizing agent. The resulting reaction converts the silanol group and the hydrophobizing agent into a hydrophobic group on the framework of the silica gel. The hydrophobizing agent compound can react with hydroxyl groups on the gel according to the following reaction: RNMX4- N (hydrophobizing agent) + MOH (silanol) MOMRN (hydrophobic group) + HX. Hydrophobic treatment can take place both on the outer macro-surface of a silica gel, as well as on the inner- pore surfaces within the porous network of a gel.

[00150] A gel can be immersed in a mixture of a hydrophobizing agent and an optional hydrophobic-treatment solvent in which the hydrophobizing agent is soluble, and which is also miscible with the gel solvent in the wet-gel. A wide range of hydrophobic-treatment solvents can be used, including solvents such as methanol, ethanol, isopropanol, xylene, toluene, benzene, dimethylformamide, and hexane. Hydrophobizing agents in liquid or gaseous form may also be directly contacted with the gel to impart hydrophobicity.

[00151] The hydrophobic treatment process can include mixing or agitation to help the hydrophobizing agent to permeate the wet-gel. The hydrophobic treatment process can also include varying other conditions such as temperature and pH to further enhance and optimize the treatment reactions. After the reaction is completed, the wet-gel is washed to remove unreacted compounds and reaction by-products.

[00152] Hydrophobizing agents for hydrophobic treatment of an aerogel are generally compounds of the formula: RNMX4-N; where M is the metal; R is a hydrophobic group such as CH3, CH2CH3, CeHe, or similar hydrophobic alkyl, cycloalkyl, or aryl moieties; and X is a halogen, usually Cl. Specific examples of hydrophobizing agents include, but are not limited to trimethylchloro silane (TMCS), triethylchloro silane (TECS), triphenylchlorosilane (TPCS), dimethylchlorosilane (DMCS), dimethyldichlorosilane (DMDCS), and the like. Hydrophobizing agents can also be of the formula: Y(RsM)2; where M is a metal; Y is bridging group such as NH or 0; and R is a hydrophobic group such as CH3, CH2CH3, CeHe, or similar hydrophobic alkyl, cycloalkyl, or aryl moieites. Specific examples of such hydrophobizing agents include, but are not limited to, hexamethyldisilazane [HMDZ] and hexamethyldisiloxane [HMDSO]. Hydrophobizing agents can further include compounds of the formula: RNMV4-N, wherein V is a reactive or leaving group other than a halogen. Specific examples of such hydrophobizing agents include, but are not limited to, vinyltriethoxysilane and vinyltrimethoxysilane.

[00153] Hydrophobic treatments of the present disclosure may also be performed during the removal, exchange or drying of liquid in the gel. In a specific embodiment, the hydrophobic treatment may be performed in supercritical fluid environment (such as, but not limited to supercritical carbon dioxide) and may be combined with the drying or extraction step.

Organic aerogels

[00154] Organic aerogels are generally formed from carbon-based polymeric precursors. Such polymeric materials include, but are not limited to resorcinol formaldehydes (RF), polyimide, polyacrylate, polymethyl methacrylate, acrylate oligomers, polyoxyalkylene, polyurethane, polyphenol, polybutadiene, trialkoxysilyl-terminated polydimethylsiloxane, polystyrene, polyacrylonitrile, polyfurfural, melamine-formaldehyde, cresol formaldehyde, phenol-furfural, polyether, polyol, polyisocyanate, polyhydroxybenze, polyvinyl alcohol dialdehyde, polycyanurates, polyacrylamides, various epoxies, agar, agarose, chitosan, and combinations thereof. As one example, organic RF aerogels are typically made from the sol-gel polymerization of resorcinol or melamine with formaldehyde under alkaline conditions.

[00155] In certain embodiments, aerogels of the present disclosure comprise a polyamic acid, a polyimide, or combination thereof, or are carbon aerogels obtained (i.e., derived) from a polyamic acid or polyimide by carbonization. In particular embodiments, the aerogel comprises a polyamic acid, a polyimide, or combination thereof, or is obtained by pyrolysis of a polyamic acid, a polyimide, or combination thereof. In some embodiments, the polyamic acid or polyimide is prepared in an aqueous solution (i.e., via an aqueous sol-gel process). Reference herein to an aqueous solution or aqueous sol-gel process means that the solution or aqueous sol-gel process is substantially free of any organic solvent. The term "substantially free" as used herein in the context of organic solvents means that no organic solvent has been intentionally added, and no organic solvent is present beyond trace amounts. For example, in certain embodiments, an aqueous solution can be characterized as having less than 1% by volume of organic solvent, or less than 0.1%, or less than 0.01%, or even 0% by volume of organic solvent.

[00156] Utilization of an aqueous sol-gel process is advantageous in providing rapid gelation, making the process amenable to configuration in a continuous process, for example, for preparing polyimide beads. Aqueous sol-gel processes for preparing polyamic acid and polyimide gel materials are economically preferable to conventional methods of such materials (e.g., expensive organic solvents are avoided, and disposal costs are minimized) and "green"(i.e., beneficial from an environmental standpoint, as potentially toxic organic solvents are avoided and production of toxic byproducts is minimized or eliminated), and are advantageous in potentially reducing the overall number of operations which must be performed to provide carbon or polyamic acid/polyimide gel materials. As disclosed in International Patent Application Publication No. WO2022/125835, and International Patent Application PCT/US2023/016821, each of which is incorporated by reference herein in their entirety, polyamic acid and polyimide gels can be prepared in water, in monolithic or bead form, the gels may be converted to aerogels, which possess nanostructures with similar properties to aerogels prepared by a conventional organic solvent-based process, and the aerogels optionally pyrolyzed to form a corresponding carbon aerogel.

[00157] In some embodiments, the aerogel of the present disclosure is a polyamic acid aerogel, in monolithic or bead form, wherein the polyamic acid is prepared by acidification of an aqueous solution of a polyamic acid. In some embodiments, the polyamic acid is dissolved in water in the presence of a base (e.g., an alkali metal hydroxide or non-nucleophilic amine base). In other embodiments, the polyamic acid is prepared in situ under aqueous conditions, directly forming the polyamic acid salt solution. In some embodiments, the polyamic acid is any commercially available polyamic acid. In other embodiments, the polyamic acid has been previously formed ("pre-formed") and isolated, e.g., prepared by reaction of a diamine and a tetracarboxylic dianhydride in an organic solvent according to conventional synthetic methods. In some embodiments, the aqueous solution of a polyamic acid salt is prepared in situ by e.g., reaction of a diamine and a tetracarboxylic acid dianhydride in the presence of a non-nucleophilic amine, providing an aqueous solution of the polyamic acid ammonium salt. Suitable methods for preparing polyamic acid aerogels under such aqueous conditions are disclosed in WO2022/125835 and PCT/US2023/016821, previously incorporated by reference.

[00158] In some embodiments, the aerogel of the present disclosure is a polyimide aerogel, in monolithic or bead form, wherein the polyimide is prepared by thermal or chemical imidization of a polyamic acid in aqueous solution. Suitable methods of forming monoliths and beads (e.g., utilizing droplet or emulsion-based processes) under such aqueous conditions are disclosed in WO2022/125835 and PCT/US2023/016821, previously incorporated by reference.

Organic/inorganic hybrid aerogels

[00159] Organic/inorganic hybrid aerogels are mainly comprised of (organically modified silica ("ormosil") aerogels. These ormosil materials include organic components that are covalently bonded to a silica network. Ormosils are typically formed through the hydrolysis and condensation of organically modified silanes, R-Si(OX)3, with traditional alkoxide precursors, Y(OX)4. In these formulas, X may represent, for example, CH3, C2H5, C3H7, C4H9; Y may represent, for example, Si, Ti, Zr, or Al; and R may be any organic fragment such as methyl, ethyl, propyl, butyl, isopropyl, methacrylate, acrylate, vinyl, epoxide, and the like. The organic components in ormosil aerogel may also be dispersed throughout or chemically bonded to the silica network.

[00160] In certain embodiments, aerogels of the present disclosure are inorganic silica aerogels formed primarily from prepolymerized silica precursors preferably as oligomers, or hydrolyzed silicate esters formed from silicon alkoxides in an alcohol solvent. In certain embodiments, such prepolymerized silica precursors or hydrolyzed silicate esters may be formed in situ from other precurosrs or silicate esters such as alkoxy silanes or water glass. However, the disclosure as a whole may be practiced with any other aerogel compositions known to those in the art and is not limited to any one precursor material or amalgam mixture of precursor materials.

Silicon Particles

[00161] The silicon is generally present in the composite material as silicon particles. Within the context of the present disclosure, the term "silicon particles" refers to silicon or silicon-based materials with a range of particle sizes. The particle size of the silicon in the composite material may vary. Silicon particles of the present disclosure can be nanoparticles, e.g., particles with two or three dimensions in the range of about 1 nm to about 150 nm. Silicon particles of the present disclosure can be fine particles, e.g., micron-sized particles with a maximum dimension, e.g., a diameter for a substantially spherical particle, in the range of about 150 nm to about 10 micrometers or larger. The silicon particles may have two-dimensional plate shapes. The thicknesses of the two-dimensional plate shapes may range from about 20 nm to about 200 nm. The lengths of the two-dimensional plate shapes may range from about 20 nm to about 3 pm. For example, silicon particles of the present disclosure can have a maximum dimension, e.g., a diameter for a substantially spherical particle, of about 10 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120nm, 130 nm, 140 nm, 150 nm, 180 nm, 200 nm, 500 nm, 1 micrometer, 1.5 micrometers, 2 micrometers, 3 micrometers, 5 micrometers, 10 micrometers, 20 micrometers, 40 micrometers, 50 micrometers, 100 micrometers, or in a range between any two of these values.

[00162] In some embodiments, the silicon particles can be monodispersed or substantially monodispersed. In other embodiments, the silicon particles can have a particle size distribution. Within the context of the present disclosure, the dimensions of silicon particles are provided based upon the median of the particle size distribution, i.e., the D50. In some embodiments, the silicon in the composite material has an average particle size of about 1 pm or less.

[00163] Silicon particles of the present disclosure can be silicon wires, crystalline silicon, amorphous silicon, silicon alloys, silicon oxides (SiOx), and any combinations thereof. The particles, e.g., particles of electroactive materials such as silicon particles, can have various shapes to embodiments disclosed herein. In some embodiments, silicon particles disclosed herein can be substantially spherical. In other embodiments, particles of electroactive materials can be substantially planar, cubic, obolid, elliptical, disk-shaped, or toroidal.

[00164] In an example, prior to formation of a sacrificial layer, the silicon particle (e.g., silicon nanoparticle) surface can be modified with functional groups that can aid in dispersing the silicon particles in a three-dimensional network. In another example, formation of the sacrificial layer may can further aid in dispersing the silicon particles in a three-dimensional network. In an example, the three-dimensional network can be a sol-gel, aerogel, xerogel, foam structure, among others.

[00165] For example, functional groups can be grafted onto the surface of the silicon particles by covalent bonds. Before functionalization, the surface of the silicon particles includes silane groups, such as silicon hydride, and/or silicon oxide groups. In some embodiments, at least a portion of those silane and silicon oxide groups can be present in combination with the bonded functional groups after functionalization of the surface of the silicon particle, e.g., the silicon particle surface can include silane groups and the covalently attached functional groups, silicon oxide groups and the covalently attached functional groups, or both silane and silicon oxide groups and the covalently attached functional groups. The presence of the functional groups on the surface of the silicon particles can be detected by various techniques, for example, by infrared spectroscopy.

[00166] In one example, the functional groups can be silane groups selected from 3- aminopropyltriethoxy silane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2- aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), and N-(2-aminoethyl)-3- aminopropyltrimethoxy silane (AEAPTMS), and N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES), or combination thereof. FIGS. 4A and 4B illustrate the preparation scheme for silicon nanoparticles functionalized with APTES prior to formation of a sacrificial layer (e.g., prior to grafting a polymer initiator). Oxidized Si particles are functionalized with 3- aminopropyltriethoxy silane in ethanol with a heat treatment to obtain APTES functionalized Si particles according to the multiple an embodiment of the present disclosure.

[00167] The surface of the silicon particles can be functionalized with hydrophilic groups to aid in improved dispersion within the porous polymer network. Without being bound by theory, the functionalization with hydroxide groups creates increased covalent bonding between the surface groups on the silicon particles and the porous polymer network. As a result, the functionalized silicon particles can be uniformly dispersed within the porous polymer network. For example, hydrophilic hydroxide groups can be grafted to the surface of the particles by unsaturated glycol to increase the hydrophilicity of silicon particle surfaces. Increasing the hydrophilicity of the silicon particles allows for the particles to be and remain more uniformly dispersed in the polymer network and remain uniformly dispersed in the network in any additional processing (e.g., pyrolysis). In an example, functionalization via glycol can improve the dispersion of silicon particles within a polyimide sol-gel and/or aerogel. Any suitable glycol can be used including, but not limited to, ethylene glycol methyl ether methacrylate, polyethylene glycol methyl ether methacrylate, among others.

[00168] In some embodiments, the individual silicon particles comprising a sacrificial layer are dispersed heterogeneously throughout the porous polymer network. In some embodiments, the individual silicon particles comprising a sacrificial layer are dispersed homogenously throughout the porous polymer network. The expression "homogenously dispersed" refers to a distribution of the Si particles throughout the porous polymer network without large variations in the local concentration across the accessible network surface.

[00169] In some embodiments, about 30 wt% to 70 wt % of the dispersed individual silicon particles within the plurality of silicon particles are in an agglomerated state. In certain embodiments, about 20 wt% to about 50 wt% of the dispersed individual silicon particles within the plurality of silicon particles are in an agglomerated state. In some embodiments, less than about 30 wt% (e.g., less than about 20 wt%, less than about 10 wt%, about 5 wt%) of the dispersed individual silicon particles within the plurality of silicon particles are in an agglomerated state. In some embodiments, homogenously distributed Si particles may refer to a distribution of the plurality of Si particles throughout the porous polymer network having less than about 30 wt%, less than about 20 wt%, less than about 10 wt% of the dispersed individual silicon particles within the plurality of silicon particles in an agglomerated state.

Sacrificial Layer

[00170] In exemplary embodiments, the composite material can include a sacrificial material or layers of sacrificial material. Within the context of the present disclosure, the term "sacrificial material" or "sacrificial layer" refers to a material or layer that is intended to be sacrificed or at least partially removed in response to mechanical, thermal, chemical and/or electromagnetic conditions experienced by the layer. For example, the sacrificial material or sacrificial layer can decompose when exposed the high temperatures or high and/or continuous stress. In some embodiments, a sacrificial material layer can be disposed on an exterior surface, e.g., an outer surface of the core portion of the multilayer material or an exterior surface, e.g., an outer surface of the multilayer material.

[00171] The sacrificial layer can be selected from the group consisting of siloxanes, polyolefins, polyurethanes, phenolics, melamine, cellulose acetate, and polystyrene. In some cases, material layer is in the form of foam. In some embodiments, the sacrificial material can be worn away due to exposure to mechanical (such as cyclical) loads. In some embodiments, sacrificial layer decomposes after exposure to a singular mechanical, chemical and/or thermal event.

[00172] In some embodiments, the onset temperature of chemical decomposition of the sacrificial material layer is in the range of about 130°C to about 400°C. [00173] Polymers for use in the sacrificial layer can be selected from a wide variety of thermoplastic resins, blends of thermoplastic resins, or thermosetting resins. Examples of thermoplastic resins that can be used include polyacetals, polyacrylics, styrene acrylonitrile, polyolefins, acrylonitrile-butadiene-styrene, polycarbonates, polystyrenes, polyethylene terephthalates, polybutylene terephthalates, polyamides such as, but not limited to Nylon 6, Nylon 6,6, Nylon 6,10, Nylon 6,12, Nylon 11 or Nylon 12, polyamideimides, polyarylates, polyurethanes, ethylene propylene rubbers (EPR), poly arylsulfones, polyethersulfones, polyphenylene sulfides, polyvinyl chlorides, polysulfones, polyetherimides, polytetrafluoroethylenes, fluorinated ethylene propylenes, polychlorotrifluoroethylenes, polyvinylidene fluorides, polyvinyl fluorides, polyether ketones, polyether ether ketones, polyether ketone ketones, and the like, or a combination comprising at least one of the foregoing thermoplastic resins.

[00174] Examples of blends of thermoplastic resins that can be used in the sacrificial layer include acrylonitrile-butadiene-styrene/nylon, polycarbonate/acrylonitrile-butadiene-styrene, acrylonitrile butadiene styrene/polyvinyl chloride, polyphenylene ether/polystyrene, polyphenylene ether/nylon, polysulfone/acrylonitrile-butadiene-styrene, polycarbonate/thermoplastic urethane, polycarbonate/polyethylene terephthalate, polycarbonate/polybutylene terephthalate, thermoplastic elastomer alloys, polyethylene terephthalate/polybutylene terephthalate, styrene-maleic anhydride/acrylonitrile-butadiene- styrene, polyether ether ketone/polyether sulfone, styrene-butadiene rubber, polyethylene/nylon, polyethylene/polyacetal, ethylene propylene rubber (EPR), and the like, or a combination comprising at least one of the foregoing blends.

[00175] Examples of polymeric thermosetting resins that can be used in the sacrificial layer include polyurethanes, epoxies, phenolics, polyesters, polyamides, silicones, and the like, or a combination comprising at least one of the foregoing thermosetting resins. Blends of thermosetting resins as well as blends of thermoplastic resins with thermosetting resins can be used.

Lithium-ion Batteries

[00176] A basic embodiment of a lithium-ion battery includes: a cathode; an anode in electrical communication with the cathode; an electrolyte disposed between the anode and the cathode; and a separator also disposed between the anode and the cathode. [00177] The electrolytes are ionically conductive materials and may include solvents, ionic liquids, metal salts, ions such as metal ions or inorganic ions, polymers, ceramics, and other components. An electrolyte may be an organic or inorganic solid or a liquid, such as a solvent (e.g., a non-aqueous solvent) containing dissolved salts. Non-aqueous electrolytes can include organic solvents, such as, cyclic carbonates, linear carbonates, fluorinated carbonates, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, y-butyrolactone, dioxolane, 4 methyldioxolane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxy ethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and mixtures thereof. Example salts that may be included in electrolytes include lithium salts, such as LiPFr,. LiBF4, LiSbFe, LiAsFe, LiC10₄, LiCFaSCh, Li(CF3SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃, LiA10₂, LiAlCl₄, LiN(C_xF_2x+iSO₂)(C_yF_2y-iSO₂), (where x and y are natural numbers), LiCl, Lil, and mixtures thereof. In some embodiments, the liquid molecules comprise an electrolyte solvent (an electrolyte). The electrolyte solvent of the present disclosure can be selected from any of the suitable electrolyte described above. Particularly, the electrolyte is selected from ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), fluorinated ether (F-EPE), 1,3-dioxolane (DOL), dimethoxyethane (DME), or combination thereof.

[00178] The separators are typically thin, porous or semi-permeable, insulating films with high ion permeabilities. The separators can be composed of polymers, such as olefin-based polymers (e.g., polyethylene, polypropylene, and/or polyvinylidene fluoride). If a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte may also act as the separator.

[00179] The anodes are composed of an active anode material that takes part in an electrochemical reaction during the operation of the battery. Example anode active materials include elemental materials, such as lithium; alloys including alloys of Si and Sn, or other lithium compounds; and intercalation host materials, such as graphite. By way of illustration only, the anode active material may include a metal and/or a metalloid alloyable with lithium, an alloy thereof, or an oxide thereof. Metals and metalloids that can be alloyed with lithium include Si, Sn, Al, Ge, Pb, Bi, and Sb. For example, an oxide of the metal/metalloid alloyable with lithium may be lithium titanate, vanadium oxide, lithium vanadium oxide, SnO₂, or SiO_x (0<x<2).

[00180] The cathodes are composed of an active cathode material that takes part in an electrochemical reaction during the operation of the battery. The active cathode materials may be lithium composite oxides and include layered-type materials, such as LiCoCh; olivine-type materials, such as LiFcPC ; spinel-type materials, such as LiMniO4; and similar materials. The spinel-type materials include those with a structure similar to natural spinal LiMniCU, that include a small amount nickel cation in addition to the lithium cation and that, optionally, also include an anion other than manganate. By way of illustration, such materials include those having the formula LiNi(o.5-x)Mm.5M_x04, where 0<x<0.2 and M is Mg, Zn, Co, Cu, Fe, Ti, Zr, Ru, or Cr.

[00181] Within the context of the present disclosure, the term "cycle life" refers to the number of complete charge/discharge cycles that an anode or a battery (e.g., LIB) is able to support before its capacity falls under about 80% of its original rated capacity. Cycle life may be affected by a variety of factors, for example mechanical strength of the underlying substrate (e.g., carbon aerogel) and maintenance of interconnectivity of the aerogel. It is noted that these factors actually remaining relatively unchanged over time is a surprising aspect of certain examples of the present disclosure. Cycle life may be determined by methods known in the art, for example including, but not limited to, cycle testing, where battery cells are subject to repeated charge/discharge cycles at predetermined current rates and operating voltage. Within the context of the present disclosure, measurements of cycle life are acquired according to this method, unless otherwise stated. Energy storage devices, such as batteries, or electrode thereof, can have a cycle life of about 25 cycles or more, 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, 300 cycles or more, 500 cycles or more, 1000 cycles or more, or in a range between any two of these values. [00182] The present disclosure includes an electrical energy storage device with at least one anode comprising the composite material of present technology as described herein, at least one cathode, and an electrolyte with lithium ions. The electrical energy storage device can have a first cycle efficiency (i.e., a cell’s coulombic efficiency from the first charge and discharge) of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, any intervening value (e.g., 65%) or in a range between any two of these values (e.g., ranges from about 30% to about 50%). As previously described herein, reversible capacity can be at least 150 mAh/g. The at least one cathode can be selected from the group consisting of conversion cathodes such as lithium sulfide and lithium air, and intercalation cathodes such as phosphates and transition metal oxides.

[00183] According to different embodiments, the composite materials of the present disclosure may be applied to both the positive electrode and the negative electrode of electrochemical energy storage devices, or to the electrodes individually (either the positive electrode or the negative electrode). In various embodiments, a cathode, anode, or solid-state electrolyte material is coated with the composite materials of the present technology.

EXAMPLES

[00184] The following examples are included to demonstrate preferred embodiments of the technology. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the technology.

1.1 Oxidation of Silicon Particles

[00185] Commercially available silicon particles may or may not include oxidized (partially or completely) silicon particles. Therefore, depending on the surface functionalities of silicon particles provided by commercial providers, the oxidation step provided herein is optional.

[00186] Silicon particles (Available from Evonik; 10-100 g of 100-3000 nm) were either heated in the temperature range of 400-800°C under moisture for 1-5 hours or dispersed in 10-1000 mL of 0.1-5M sulphochromic acid or 10-1000 mL of 1-10M H2O2 (hydrogen peroxide). For the Si dispersion, it was heated to 50-120°C for 1-10 hour under constant stirring in order to obtain hydroxyl functional groups (or silanol groups) on the surface of the silicon particles. In principle, other oxidizing agents can also be used for this purpose. After 1-10 hour of stirring the solution, the solution was cooled to room temperature and centrifuged to obtain oxidized silicon particles. The obtained silicon particles were washed with a 100-3000 mL volume of water 3-5 times to remove any residual acid and dried under ambient conditions for 3- 10 hours. The surface oxidation was confirmed by IR spectrum (FIG. 5) as evidenced by the reduced intensity of band at 2105 and 1993 cm'¹ and the increase of band intensity at 1052 cm'¹. The oxidation by heating dry powder can also be confirmed by the mass increase after the treatment.

1.2 Synthesis of Si particles with a sacrificial layer

[00187] Oxidized silicon particles (10 grams) were dispersed in 50 mL of ethanol. The dispersion was sonicated for 30 minutes to prevent agglomeration of the silicon particles. Then, 1 gram of AEAPTMS was added to the dispersion and stirred for 240 minutes on a hot plate with dispersion temperature controlled at 70°C. After the dispersion cooled down to room temperature, 0.5 gram of initiator 4,4'-azobis(4-cyanovaleric acid) was added to the dispersion which was stirred for another 240 minutes. The dispersion was then left still overnight to let silicon particles precipitate, after which the top clear solvent was poured out and left silicon slurry was dispersed in 67 mL of water by stirring at 600 RPM for 5 minutes. Monomeric methyl methacrylate (25.3 grams) was added to the dispersion and was stirred on a hot plate at 500 RPM with the dispersion temperature controlled at 80°C for 60 minutes. The stirring speed was then lowered to 300 RPM for 60 minutes before it was raised to 500 RPM. The dispersion was stirred for another 180 minutes before 2.6 gram of polymer modifier (hydroxyethyl)methacrylate was added to the dispersion. The dispersion temperature was changed to 70°C and stirred overnight. The synthesis of silicon particles with sacrificial polymer coating was done by the next morning. The PPMA coated silicon particles were analyzed by IR as shown in FIG.5 and the characteristic peaks of Si-H bond between 1950 and 2200 cm'¹ were found missing, indicating a good coverage of silicon surface by the PMMA layer.

1.3 Synthesis of composite materials including Si particles with a sacrificial layer

[00188] In a typical synthesis, 12.7 g of p-phenylenediamine (PDA) was added to 313 g water in a beaker and stirred for 30 min until all the PDA was dissolved. Then 28.5 g of triethylamine was added to the solution and stirred for 10 min. After that, 25.5 g of benzene- 1,2, 4,5- tetracarboxylic anhydride was added to the above solution and stirred for 4 h. Then, 1.5 to 25 g PMMA modified Si particles are added to the above solution and stirred for 10 min. Acetic anhydride (51.4 g) was then poured into the above suspension and stirred for 50 s before pouring the suspension into 1200 mL mineral spirits with surfactant under mixing at 3600 rpm. The obtained emulsion was then aged overnight before running the filtration. After finishing filtration, the obtained material was rinsed with ethanol several times and dried in the oven at 700°C.

[00189] While this disclosure has been particularly shown and described with reference to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the technology encompassed by the appended claims.

Claims

What is claimed is:

1. A composite material comprising: a. silicon particles having a diameter of less than 1000 nm, the silicon particles comprising a sacrificial layer on at least a portion of a surface of the silicon particles; and b. a three-dimensional network, wherein the silicon particles are within the three- dimensional network and the sacrificial layer is between the surface of the silicon particles and a portion of the three-dimensional network.

2. The composite material of claim 1, wherein the silicon particles are dispersed throughout the three-dimensional network.

3. The composite material of claim 2, wherein the silicon particles are dispersed heterogeneously throughout the three-dimensional network.

4. The composite material according to claim 2 or 3, wherein about 20 wt% to about 50 wt% of the dispersed silicon particles are in an agglomerated state.

5. The composite material according to claim 2 or 3, wherein less than about 20 wt% of the dispersed silicon particles are in an agglomerated state.

6. The composite material of claim 1, wherein the sacrificial layer is formed from a material selected from polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polypropylene oxide (PEO), polyethyleneimine (PEI), polyurethane, poly(3,4-ethylenedioxythiophene, PEDOT), polyvinylbutyral, polypropylene oxide (PPO), polyethylene oxide copolymer, polypropylene oxide copolymer, polycarbonate (PC), polyvinylchloride (PVC), polycaprolactone, polyvinylidene fluoride, polystyrene or combination thereof. The composite material of claim 1, wherein the sacrificial layer has a thickness of less than or equal to about 100 nm, or a thickness between about 100 nm and about 600 nm, or a thickness of about 600 nm to 3000 nm. The composite material of claim 1, wherein the sacrificial layer has a thickness in the range of about 300% to about 1% of the diameter of the silicon particle. The composite material according to any one of claims 1-8, wherein the sacrificial layer has a carbonization yield of less than about 20 wt%. The composite material according to any one of claims 1-9, wherein the temperature of chemical decomposition of the sacrificial material layer is in the range of about 130°C to about 800°C. The composite material of claim 1, wherein the sacrificial layer is uniform on at least a portion of the surface of the silicon particles. The composite material of claim 1, wherein the sacrificial layer is continuous on at least a portion of the surface of the silicon particles. The composite material of claim 1, wherein at least a portion of the surface of the silicon particles is at least 70 % of the surface of the silicon particles, at least 90 % of the surface of the silicon particles, or at least 95 % of the surface of the silicon particles. The composite material according to any one of claims 1-13, wherein the composite material is in monolithic form, in the form of thin sheets, or in particulate form. The composite material of claim 1, wherein the three-dimensional network comprises an aerogel, a xerogel, an ambigel, an aerogel-xerogel hybrid material, an aerogel-ambigel hybrid material, an aerogel-ambigel-xerogel hybrid material, or combinations thereof. The composite material of claim 1, wherein the three-dimensional network comprises an organic material or is derived from an organic material. The composite material of claim 1, wherein the three-dimensional network is in the form of a bead. The composite material of claim 17, wherein the bead is substantially spherical, having a diameter from about 100 nm to about 4 mm, or from about 5 pm to about 4 mm The composite material of claim 1, wherein the three-dimensional network has a low bulk density, wherein the low bulk density is in a range of about 0.25 g/cc to about 1.0 g/cc. The composite material of claim 1, wherein the three-dimensional network comprises a skeletal framework comprising nanofibers, the skeletal framework comprising an array of interconnected pores. The composite material according to any one of claims 1-20, wherein the three-dimensional network comprises a polyimide or is derived from a polyimide. . The composite material of claim 21, wherein the three-dimensional network has a pore volume of at least 0.3 cc/g. The composite material of claim 21, wherein the three-dimensional network has a porosity between about 10% and about 90% of a volume of the three-dimensional network. The composite material of claim 21, wherein a pore structure of the three-dimensional network includes a pore size at max peak from distribution of about 150 nm or less. The composite material of claim 21, wherein a pore structure of the three-dimensional network includes a pore size at max peak from distribution of about 100 nm or less. The composite material according to any one of claims 1-25, wherein the three-dimensional network comprises from about 20% to about 65% by weight of the silicon particles, based on the total weight of the composite material. The composite material according to any one of claims 1-26, wherein a volume of the silicon particles comprises between 35% to 60% of a volume of the three-dimensional network. The composite material according to any one of claims 1-27, wherein the silicon particles are present at least partially within the pore structure of the three-dimensional network. The composite material according to any one of claims 1-28, wherein the silicon particles are dispersed heterogeneously throughout the three-dimensional network. The composite material according to any one of claims 1-29, wherein about 20 wt% to about 50 wt% of the dispersed silicon particles are in an agglomerated state. The composite material according to any one of claims 1-29, wherein less than about 20 wt% of the dispersed silicon particles are in an agglomerated state. An energy storage system comprising the composite material of any one of claims 1-31. The energy storage system of claim 32, wherein the energy storage system is a battery. The energy storage system of claim 33, wherein the battery is a rechargeable battery. The energy storage system of claim 34, wherein the rechargeable battery is a Li-ion battery. A rechargeable battery comprising the composite material of any one of claims 1-31. A method of preparing a composite material, the method comprising: a. providing silicon particles having a diameter of less than 1000 nm; b. oxidizing a surface of the silicon particles to obtain hydroxyl functional groups on the surface; c. forming a sacrificial layer onto at least a portion of a surface of the silicon particles; d. providing a sol-gel solution, the sol-gel solution comprising a polar solvent and a precursor of a three-dimensional network; and e. processing the silicon particles in the presence of the sol-gel solution to yield the composite material.

38. The method of claim 37, wherein the step of forming the sacrificial layer comprises: i. covalently reacting hydroxyl functional groups on the surface of the silicon particles with at least one functional silane group; ii. grafting a polymer initiator on the surface of the silicon particles to react with a monomer; and iii. polymerizing the monomer on the surface of the silicon particles to form the sacrificial layer.

39. The method of claim 37, further comprising a step of dispersing the silicon particles in the solgel solution prior to the step of forming the sacrificial layer.

40. The method of claim 37, further comprising a step of dispersing the silicon particles in the solgel solution after the step of forming the sacrificial layer.