Composite material containing a void portion, as well as its preparation and its use

Abstract

Composite materials for use in an electrical energy storage system (e.g., a high-capacity battery) and a method for preparing the same are provided herein. The composite materials of the present disclosure include silicon particles and a three-dimensional carbon network. The composite materials further include voids between the outer surface of each silicon particle and the three-dimensional carbon network. The voids advantageously provide space to accommodate the volume change of the silicon particles during charging and discharging of the electrical energy storage system.

Description

Technical Field

[0001] Cross - reference to related applications This application claims the priority and benefit of U.S. Provisional Application No. 63 / 390,838, filed on July 20, 2022, the entire content of which is incorporated herein by reference.

[0002] The present disclosure generally relates to composite materials including voids for use in electrical energy storage systems (e.g., high - capacity batteries), and methods for preparing the same. More specifically, the present invention relates to materials and methods for manufacturing composite materials including silicon particles and a three - dimensional carbon network, where the voids (e.g., pores) are present between the outer surface of the silicon particles and the three - dimensional carbon network.

Background Art

[0003] High - capacity battery materials, such as lithium - ion batteries (LIBs), represent the most attractive energy storage systems and are playing an increasingly important role in modern society. They already dominate the market for portable electronic devices such as mobile phones, laptops, and digital cameras. They are also regarded as the power sources to be selected for electric vehicles and stationary energy storage. However, even the current state - of - the - art technologies cannot meet the continuously increasing needs for electric vehicles and large - scale energy storage.

[0004]

[0005] Silicon is one of the most promising anode materials for lithium - ion batteries because it has the highest known theoretical capacity and is abundantly present in the earth's crust. It has been revealed that the theoretical weight capacity of silicon is as high as about 4200 mAh / g, compared to only 372 mAh / g for graphite. Therefore, silicon (Si) active material is regarded as a promising candidate for the next - generation anode of lithium - ion batteries (LIBs).Unfortunately, it is known that silicon exhibits a significant "breathing effect" during the insertion / extraction of lithium in a continuous charge-discharge process. This "breathing effect" causes significant structural degradation, leading to a decrease in specific capacity and an increase in battery impedance. That is, the volume of Si expands to approximately 400% of its original size during lithiation (insertion of lithium ions into silicon), and then may decrease to various sizes during delithiation (extraction of lithium ions from silicon). The significant volume change causes substantial problems in maintaining the form of the Si electrode during cycling.

[0006] In each cycle, expansion causes stress and strain in the silicon, leading to cracking and breakage. The process by which silicon breaks is known as pulverization. Due to pulverization, the electrical insulation of silicon fragments causes loss of contact with adjacent fragments. In addition, the space created by the extrusion of the surrounding conductive material away from the active material by expansion also causes loss of contact, resulting in a lower conductivity. Without a strong electrical contact with the current collector, the silicon fragments either do not lithiate or cannot contribute to the capacity of the battery. This behavior leads to a decrease in capacity stability and rapid capacity degradation with each cycle. The decrease in capacity during charge and discharge cycles is called fading or continuous capacity loss and is generally irreversible.

[0007] The particle size of silicon particles can affect the rate of battery performance degradation. Although not bound by theory, silicon particles in the nanometer size range have excellent ability to adapt to the volume change of Si because of their large specific surface area and high average binding energy per atom at the surface. Therefore, these materials can minimize the stress on them due to volume change, avoid cracking or pulverization of their structure, reduce irreversible capacity, and improve cycle stability.

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

[0009] Therefore, there is a need for improved methods to control, select, modify, or enhance the surface properties and morphology of electroactive materials, such as silicon. SUMMARY OF THE INVENTION

[0010] For example, to remove or mitigate at least one drawback of previous methods and materials for improving the performance (e.g., cycle stability, battery life) of high-capacity batteries such as lithium-ion batteries, the present technology provides a composite material comprising voids (e.g., pores). The composite material provided herein further comprises silicon particles and a three-dimensional carbon network, wherein the voids are present between the outer surface of the silicon particles and the three-dimensional carbon network.

[0011] In one aspect, the plurality of voids of the present technology provide several advantages, such as providing space for accommodating the volume expansion of silicon particles during the charging process and stabilizing the composite material. Without wishing to be bound by theory, accommodation of the volume expansion of silicon particles may slow the fragmentation of silicon particles due to continuous charge and discharge battery cycles.

[0012] The presence of voids secures space for the silicon particles during volume expansion, relieves the mechanical compression of the three-dimensional carbon network (also referred to as a porous network or a porous network composite material), as a result, the structural integrity is significantly improved, and thus, Si can be prevented from being directly exposed to the electrolyte.

[0013] Voids that sufficiently accommodate the volume expansion of silicon particles provide free space for accommodating the volume expansion.

[0014] In one aspect, the voids between the outer surface of the silicon particles and the three-dimensional carbon network can provide good dispersion and aggregation resistance of the silicon particles.

[0015] In one aspect, the materials provided by the present disclosure can advantageously prevent or reduce rapid capacity fading of large-capacity batteries (e.g., within at least 10 cycles).

[0016] The composite material of the present technology can improve the performance of a lithium-ion battery as compared to a lithium-ion battery having an electrode that does not have the composite material of the present disclosure (e.g., a composite material without voids).

[0017] Provided herein is a composite material comprising voids, further comprising silicon particles having a diameter of less than about 1000 nm, and a three-dimensional carbon network, wherein the voids are present between the outer surface of the silicon particles and the three-dimensional carbon network. That is, the voids surround or encircle the silicon particles and provide a separation or space for accommodating the "breathing" of silicon. In some embodiments, the silicon particles have a diameter of less than about 300 nm.

[0018] Provided herein is a composite material comprising voids, further comprising silicon particles having a diameter in the range of about 50 nm to about 1000 nm, about 300 nm to about 1000 nm, and a three-dimensional carbon network, wherein the voids are present between the outer surface of the silicon particles and the three-dimensional carbon network.

[0019] In some embodiments, the volume of the void portion is 1% to 80%, 1% to 70%, 1% to 60%, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, 3% to 80%, 3% to 60%, 3% to 40%, 3% to 40%, 3% to 30%, 3% to 20%, 3% to 10%, 3% to 20%, 3% to 50%, 3% to 100%, 3% to 200%, 3% to 250%, 5% to 50%, 5% to 40%, 5% to 20%, 5% to 15%, 10% to 20%, 20% to 40%, 20% to 50%, 20% to 60%, 20% to 80%, 20% to 100%, 50% to 100%, 20% to 120%, 20% to 140%, 20% to 160%, 20% to 180%, 20% to 200%, 20% to 250%, 50% to 200%, 80% to 200%, 100% to 200%, 50% to 250% of the volume of the silicon particles. The present technology provides the advantage of designing void portions whose volume can be controlled. In some embodiments, the volume of the voids is controlled by providing a sacrificial layer of a known thickness around the silicon particles. In some embodiments, the void portion is designed by controlling the number and / or distribution of the silicon particles having the sacrificial layer.

[0020] In some embodiments, the three-dimensional carbon network includes a polyimide-derived carbon aerogel. In some embodiments, the three-dimensional carbon network includes a carbon aerogel, a carbon xerogel, a carbon ambigel, a carbon aerogel-xerogel hybrid material, a carbon aerogel-ambigel hybrid material, a carbon aerogel-ambigel-xerogel hybrid material, or a combination thereof. In some embodiments, the three-dimensional carbon network is in the form of beads. In some embodiments, the beads are substantially spherical and have a diameter of about 100 nm to about 4 mm, or about 5 μm to about 4 mm.

[0021] In some embodiments, the silicon particles are dispersed within a three-dimensional carbon network. In some embodiments, the silicon particles are heterogeneously dispersed throughout the three-dimensional carbon network. In some embodiments, about 10 wt% to about 20 wt%, about 10 wt% to about 30 wt%, about 10 wt% to about 60 wt%, about 20 wt% to about 50 wt% of the dispersed silicon particles are in an aggregated state. In some embodiments, less than about 20 wt% of the dispersed silicon particles are in an aggregated state.

[0022] In some embodiments, the carbon network is one carbon network. In some embodiments, the pore structure of the three-dimensional carbon network includes those with a pore size of about 150 nm or less at the maximum peak of the distribution. In some embodiments, the three-dimensional carbon network has a total bead-level pore volume of at least 0.3 cc / g. In some embodiments, the three-dimensional carbon network has a total bead-level porosity of about 10% to about 90%. In some embodiments, the three-dimensional carbon network has a porosity of less than about 90%.

[0023] In some embodiments, the composite material has a capacity of about 500 mAh / g to about 3000 mAh / g. In some embodiments, the three-dimensional carbon network has a conductivity of at least about 1 S / cm.

[0024] In one aspect, an energy storage system comprising a composite material according to the present technology is provided herein. In some embodiments, the energy storage system is a battery. In one embodiment, the battery is a rechargeable battery. In another embodiment, the rechargeable battery is a Li-ion battery.

[0025] In another aspect, a rechargeable battery comprising a composite material according to the present technology is provided herein.

[0026] In one aspect, a method for preparing a composite material is provided herein, the method comprising: a. providing silicon particles; b. oxidizing the surface of the silicon particles to obtain hydroxyl groups on the surface of the silicon particles; c. forming a sacrificial layer on at least a portion of the surface of the silicon particles; d. providing a sol-gel solution, the sol-gel solution comprising a polar solvent and a precursor of a porous network; e. treating the silicon particles in the presence of the sol-gel solution to obtain precursor beads comprising silicon particles dispersed within the precursor beads, the precursor beads optionally being able to contain pores or optionally not containing pores; and f. pyrolyzing the precursor beads comprising silicon particles dispersed throughout the precursor beads to obtain a porous network composite material, the porous network composite material comprising voids. In some embodiments, the three-dimensional network is a porous network. In some embodiments, the silicon particles have a diameter of less than 1000 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.

[0027] In some embodiments, the sacrificial layer is formed from a material selected from polymethyl methacrylate (PMMA), polyvinyl pyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethyleneimine (PEI), polyurethane, poly(3,4-ethylenedioxythiophene) (PEDOT), polyvinyl butyral, polyethylene oxide copolymer, polypropylene oxide copolymer, polycarbonate (PC), polyvinyl chloride (PVC), polycaprolactone, polyvinylidene fluoride, polystyrene, or combinations thereof.

[0028] In some embodiments, the sacrificial layer has a thickness of about 100 nm or less, or a thickness of about 100 nm to about 60 nm, or a thickness of about 60 nm to 0.3 nm. In some embodiments, the sacrificial layer has a thickness in the range of about 20% to about 0.01% of the diameter of the silicon particles.

[0029] In some embodiments, the sacrificial layer has a carbonization yield of less than about 20 wt%. In some embodiments, the chemical decomposition temperature of the sacrificial material layer is in the range of about 130 °C to about 850 °C.

[0030] In some embodiments, the sacrificial layer is uniform over at least a portion of the surface of the silicon particles. In some embodiments, the sacrificial layer is continuous over 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 9% of the surface of the silicon particles.

[0031] In some embodiments, the composite material is in a monolithic form, a thin sheet form, or a particulate form.

[0032] In some embodiments, the method further includes a step of subcritical drying or supercritical drying after treatment of the silicon particles in the presence of a sol-gel solution and before pyrolysis of the precursor beads containing the silicon particles.

[0033] In some embodiments, the porous network includes an aerogel, a xerogel, an ambigel, an aerogel-xerogel hybrid material, an aerogel-ambigel hybrid material, an aerogel-ambigel-xerogel hybrid material, or a combination thereof. In some embodiments, the porous network includes a polyimide derivative. In some embodiments, the porous network is in the form of beads.

[0034] In some embodiments, the porous network has a carbonization yield of greater than about 30 wt%.

[0035] In some embodiments, the pyrolysis of the precursor beads carbonizes the sacrificial layer. In some embodiments, the sacrificial layer has a carbonization yield of less than about 20 wt%.

[0036] In one aspect, a method of preparing a composite material is provided herein, the method comprising: a. providing silicon particles; b. forming a sacrificial layer on at least a portion of the surface of the silicon particles; d. incorporating the silicon particles into a three-dimensional network; and e. treating the three-dimensional network to obtain a composite material comprising voids surrounding the silicon particles. In some embodiments, the three-dimensional network is a porous three-dimensional network.

[0037] In some embodiments, at least a portion of the surface of the silicon particles is at least 70%, at least 90%, or at least 95% of the surface of the silicon particles.

[0038] In some embodiments, the three-dimensional network comprises an organic material. In some embodiments, treating the three-dimensional network comprises heating the three-dimensional network to the carbonization temperature of the sacrificial layer. In some embodiments, treating the three-dimensional network comprises pyrolyzing the three-dimensional network. In some embodiments, the three-dimensional network has a carbonization yield of greater than about 30 wt%. In some embodiments, the pyrolysis of the three-dimensional network carbonizes the sacrificial layer. In some embodiments, the sacrificial layer has a carbonization yield of less than about 20 wt%.

[0039] A composite material comprising voids surrounding silicon particles is provided herein, the composite material obtainable by any one of the methods described according to the present technology.

[0040] In another aspect, a method of improving the performance of an energy storage system is provided herein. The method comprises incorporating a composite material according to the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] This technology will be more fully understood from the following detailed description in conjunction with the accompanying drawings.

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Figure 1B

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DETAILED DESCRIPTION OF THE INVENTION

[0042] Silicon (Si) is regarded as a promising alternative LIB anode material. This is because during the alloying process, Li7Si3, Li 12 Si7, Li 13 Si4, Li 15 Si4, and Li 22 Si5 silicon-lithium alloys are formed, among which, Li 15 Si4 has a capacity of 3579 mAh g -1 (2194 Ah L -1 ) at room temperature, which is the highest theoretical capacity known for anode materials. Therefore, it is desirable to incorporate silicon into the anode as much as possible.

[0043] Meanwhile, the average voltage platform of Si(Li / Li + at 0.4 V) is higher than that of the graphite electrode (Li / Li + at 0.125 V), which enables avoiding lithium surface coating 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. In addition, Si has the advantages of being abundant in the earth's crust and inexpensive, which further promotes the industrial interest in using silicon in batteries.

[0044] Despite these advantages, when used as an electrode material, silicon still has significant drawbacks. The main problem regarding the use of Si in LIBs is the huge volume expansion during lithiation. Si electrodes can expand up to 400%, which is much larger than 10% of graphite electrodes. First, Si particles are gradually pulverized by repeated volume changes, losing electrical contact between the active component and other components including conductive carbon and binder, which results in a rapid decrease in capacity and a rapid decline in cycle performance. Second, the volume change also gradually detaches the active material from the current collector, resulting in the loss of electrical contact between the active material and the current collector and electrode capacity reduction after the first cycle. Moreover, the solid electrolyte interphase (SEI) layer continuously fractures and reforms due to the volume expansion / shrinkage behavior of the Si electrode during cycling, and as a result, new Si surfaces are continuously exposed to the electrolyte. As a result, electrolyte degradation continuously occurs on the newly lithiated Si surface, which is highly reducing, leading to irreversible capacity loss in each cycle and ultimately exhausting the cell's life. Both mechanical failure and electrolyte degradation can potentially cause the Si electrode to very rapidly lose its electrochemical activity during the cycling process.

[0045] The composite materials provided herein remove or mitigate at least some of the drawbacks of Si when used as an electrode material. Without wishing to be bound by theory, generally, the composite materials provided herein may be adapted to the volume change of the active Si material during battery operation. Generally, the composite materials of the present technology include accommodating or designed voids that adapt to the volume change of the silicon particles incorporated within the composite material.

[0046] In the following description, since Li-ion technology is currently widespread and popular, several examples are provided in the context of Li-ion batteries. However, such examples are provided merely to aid in the understanding and illustration of basic technologies, and these technologies may equally apply to various other metal-ion batteries, such as those using Li + 、Na + 、Mg 2+ 、Ca 2+ and Al 3+ It should be understood that they may also apply equally to various other metal-ion batteries, such as those using other metal ions such as Li, Na, Mg, Ca, and Al, as well as other metal-ion batteries. The composite materials of the present disclosure can be used, for example, in other battery chemistries (e.g., reversible redox reactions) where the active particles undergo significant volume changes during their operation, including batteries containing aqueous electrolytes.

[0047] Definitions The articles "a" and "an" are used herein to refer to one or more than one (i.e., at least one) of the grammatical objects of the article.

[0048] Within the scope of the context of the present disclosure, the term "about" is used throughout this specification to describe and account for small variations. For example, the term "about" may refer to ±10% or less, ±5% or less, for example, ±2% or less, ±1% or less, ±0.5% or less, ±0.2% or less, ±0.1% or less, or ±0.05% or less. All numerical values in this specification are modified by the term "about" whether explicitly indicated or not. Values modified by the term "about" of course include the specific value. For example, "about 5.0" should include 5.0.

[0049] Within the scope of the present disclosure, the terms "aerogel" or "aerogel material" refer to a solid object that contains a framework of interconnected solids, regardless of shape or size, along with a corresponding network of interconnected pores integrated within the framework, and contains a gas such as air as a dispersed interstitial medium. As such, aerogels such as the carbon aerogels of the present application are non-fluid colloidal or polymer networks that are unrestricted and expanded throughout their entire volume by a gas. Aerogels, such as carbon aerogels, are generally prepared by removing the solvent from a gel (a solid network containing a solvent) in such a manner that the shrinkage of the gel is minimized or does not occur at all by removing all swelling factors from the corresponding wet gel by virtue of its capillary force in the pore walls, that is, without substantial volume reduction or network compression. Methods of solvent removal include, but are not limited to, supercritical drying (or drying using a supercritical fluid such that the low surface tension of the supercritical fluid exchanges with the transient solvent within the gel), solvent exchange with a supercritical fluid, subsequent solvent exchange with a fluid that transitions to the supercritical state, subcritical fluid drying or near-critical fluid drying, and sublimation of the frozen solvent in a freeze-drying process. See, for example, PCT Patent Application Publication No. WO2016127084A1.

[0050] Aerogels such as carbon aerogels contain a highly porous network of micro, meso, and macro-sized pores and generally have aerogels: (a) an average pore diameter in the range of about 2 nm to about 100 nm; (b) a total bead-level porosity of at least 60% or more, and (c) about 100 m 2 / g or more, for example, a specific surface area of about 100 to about 1000 m 2 / g as determined by nitrogen adsorption analysis, and are characterized by physical and structural properties (in accordance with nitrogen porosity measurement tests and helium pycnometry).

[0051] Accordingly, the aerogel materials of the present disclosure include any aerogel or other unrestricted cell compound that meets the defining elements described in the preceding paragraphs.

[0052] As used herein, the terms "xerogel" and "ambigel" refer to gels containing an unrestricted non-fluid colloidal or polymer network formed by removing all swelling factors from the corresponding wet gel without precautions taken to avoid substantial volume reduction or compression, such as under ambient pressure drying. In contrast to aerogels, for example, carbon aerogels, xerogels such as carbon xerogel generally contain a compact structure. Xerogels experience substantial volume reduction during ambient pressure drying and may have a smaller surface area, such as 0 to 100 m 2 / g, or about 0 to about 20 m 2 / g, as measured by nitrogen adsorption analysis.

[0053] Within the context of the present disclosure, the term "continuous" refers to a layer without gaps, holes, or any discontinuities. For example, a continuous layer that does not contain two (or more) component materials physically separated (or spaced apart) within the layer.

[0054] As used herein, the term "uniform" refers to a variation in the thickness of a material (e.g., a coating of the present disclosure) of less than about 10%, less than about 5%, or less than about 1%.

[0055] Within the context of the present disclosure, the term "capacity" refers to the amount of specific energy or charge that a battery can store. Capacity is specifically measured as the discharge current that a battery can deliver over time per unit mass. This is typically provided as ampere-hours or milliampere-hours per gram of total active material mass (Ah / g or mAh / g). For example, a battery with a capacity of 1 Ah can supply a current of 1 ampere for 1 hour, or 0.5 ampere for 2 hours, etc. Thus, 1 ampere-hour (Ah) is equal to 3,600 coulombs of 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 (especially the anode) can be determined, for example, by applying a constant constant-current load to a fully charged cell until the voltage of the cell reaches the end-of-discharge voltage value, multiplying the constant current by the time until the end-of-discharge voltage is reached to obtain the discharge capacity, and dividing the discharge capacity by the weight or volume of the electrode material, but is not limited thereto and can be determined by methods known in the art. Within the context of the present disclosure, measured values of capacity are obtained according to this method unless otherwise specified. Unless otherwise specified, capacity is reported for the 10th cycle of the battery.

[0056] As used herein, the term "electrode" refers to "cathode" or "anode". As used herein, the term "positive electrode" is used in the same sense as "cathode". Similarly, the term "negative electrode" is used in the same sense as "anode".

[0057] Within the context of the present disclosure, the term "dispersion" refers to the state of dispersion in which a substance (dispersed phase) is distributed in units dispersed throughout another substance (continuous phase or medium). Generally, the dispersed phase does not substantially agglomerate but rather exists at intervals within another substance. Dispersion includes the aggregation or contact of a small number of particles (e.g., less than 2, 3, 4, 5), but the particles generally exist uniformly spaced throughout another substance.

[0058] Within the context of the present disclosure, the term "framework" or "framework structure" refers to a network of interconnected oligomers, polymers, or colloidal particles that form the solid structure of a gel or aerogel. The polymers or particles that make up the framework structure typically have a diameter of about 100 angstroms. However, the framework structures of the present disclosure can also include networks of interconnected oligomers, polymers, or colloidal particles of all diameter sizes that form a solid structure within the gel or aerogel.

[0059] As used herein, the term "particle size D50" refers to the size at which 50% of the volume is cumulative, which is the particle size at the 50% point on the cumulative curve when the particle size distribution is obtained on a volume basis and the cumulative curve is drawn such that the total volume is 100% (i.e., the diameter of the particles at the 50th percentile (median) of the volume of the particles).

[0060] Composite material In one aspect, the composite materials provided herein offer a high lithium storage capacity with improved cyclability.

[0061] Figures 1A and 1B show exemplary composite materials of the present disclosure. Referring to Figures 1A and 1B, in one aspect, a composite material 100 including voids 120 (e.g., void 120) is provided herein. The composite materials of the present disclosure include silicon particles 110 having a diameter of less than about 300 nm and a three-dimensional carbon network 130. The silicon particles are typically provided from the same source and have known desired particle sizes, shapes, porosities, and other material attributes that are substantially similar. In some examples, the silicon particles have a diameter of less than 1000 nm, less than 800 nm, less than 500 nm, less than 300 nm, less than 250 nm, less than 200 nm, less than 150 nm, or less than 100 nm. In some embodiments, the three-dimensional carbon network is a carbon aerogel or a carbon xerogel. The voids shown in Figures 1A and 1B exist between the outer surface of the silicon particles and the three-dimensional carbon network. That is, the voids surround or envelop at least a portion of the silicon particles and, as a result, can accommodate volume changes of the silicon particles.

[0062] Within the scope of the context of the present disclosure, the terms "void" or "voids" used throughout this specification refer to "empty" space, i.e., space not utilized by either silicon or the three-dimensional carbon network.

[0063] In some embodiments, the volume of the voids is about 1% to about 20%, about 3% to about 15%, about 5% to about 15%, about 3% to about 10%, or about 5% to about 10% of the volume of the silicon particles. In the effort to design the voids of the present disclosure, a sacrificial layer is first formed on at least a portion of the outer surface of the silicon particles. The sacrificial layer of the present technology provides the advantage of designing voids whose volume can be controlled. That is, the voids between the outer surface of the silicon particles and the three-dimensional carbon network can be created by partially or completely removing the sacrificial layer. By adjusting the thickness of the sacrificial layer of the present technology, the volume of the voids can be controlled.

[0064] In another embodiment, the volume of the voids can be adjusted by controlling the amount of sacrificial layer that is removed (e.g., decomposed) when exposed to an external stimulus / factor. Without wishing to be bound by theory, as the amount of sacrificial layer removed increases, the volume of the voids increases.

[0065] In some embodiments, the volume of the voids is adjusted or controlled by controlling the distribution of silicon particles. In certain embodiments, the volume of the voids is adjusted or controlled by engineering the number or volume fraction of silicon particles (e.g., volume fraction of particles, volume fraction of sacrificial layer content) within the composite material.

[0066] Generally, silicon is at least partially contained within the pores of the porous network. That is, silicon is disposed within the framework of the porous network. Silicon receives lithium ions during charging and releases lithium ions during discharging. In certain embodiments, the porous network forms an interconnected structure around the silicon, which is connected to the porous network at multiple locations. In some embodiments, the three-dimensional network is a porous network.

[0067] Measurement of Composite Material Properties The composite material can be characterized by properties such as pore volume, porosity, surface area, and pore size distribution. These properties and related terms are defined hereinbelow, along with methods for measuring and / or calculating such properties.

[0068] Within the context of the present disclosure, the term "pore volume" refers to the total volume of pores within a sample of a porous material. The pore volume is measured, in particular, as the volume of voids within the porous material when the voids are measurable and / or accessible by another material, such as an electrochemically active species, e.g., silicon particles. This is typically recorded as cubic centimeters per gram (cm 3 / g or cc / g).

[0069] Within the context of the present disclosure, the term "porosity" when used with respect to the polymer networks or composite materials disclosed herein refers to the volume ratio of pores that do not contain another material (e.g., electrochemically active species such as silicon particles) bound to the pore walls. For purposes of explanation and illustration, within the scope of a particular implementation of a silicon-doped polymer network, such as an aerogel, as the primary anode material in a LIB, it should be noted that porosity refers to the voids after inclusion of the silicon particles. As such, the porosity can be, for example, about 10% to 70% before the anode is in the lithiated state (accommodating ion transport and silicon expansion), and about 1% to 50% after the anode is in the lithiated state. It should be noted that pore volume and porosity are different measures of the same property of the pore structure, i.e., the "empty space" within the pore structure. For example, when silicon is used as an electrochemically active species contained within the pores of a polymer network (e.g., a composite material as described herein), pore volume and porosity refer to the "empty" space, i.e., the space not utilized by silicon or carbon.

[0070] 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 the sample volume of a porous material. A narrower pore size distribution refers to a relatively large proportion of pores within a narrow range of pore sizes, and thus optimizes the amount of pores that can surround electrochemically active species and maximizes the use of pore volume. Conversely, a wider pore size distribution refers to a relatively small proportion of pores within a narrow range of pore sizes. As such, pore size distribution is typically measured as a function of pore volume and recorded as the unit size of the full width at half maximum of the main peak within a pore size distribution chart.

[0071] Within the context of the present disclosure, the term "pore size at the maximum peak of the distribution" refers to the value at the recognizable peak on the graph exemplifying the pore size distribution. The pore size at the maximum peak of the distribution is specifically measured as the pore size at which the largest proportion of pores is formed. This is typically recorded in terms of pore size per any unit length, for example, in micrometers or nanometers (nm).

[0072] Within the context of the present disclosure, the term "BET surface area" has its ordinary meaning referring to the Brunauer - Emmett - Teller method for determining surface area by N2 adsorption measurement. The BET surface area, expressed in m 2 / g, is a measure of the total surface area of the porous material per unit mass. Unless otherwise specified, "surface area" refers to the BET surface area. Instead of the BET surface area, for example, the geometric outer surface area of polyimide or carbon beads can be calculated based on the diameter of the beads. Generally, such geometric outer surface area of the beads of the present disclosure is in the range of about 3 to about 700 μm 2 in range.

[0073] As used herein, the term "particle size D50" refers to the cumulative 50% size based on volume, which is the particle size at the 50% point on the cumulative curve (i.e., the diameter of the particle at the 50th percentile (median) of the volume of the particles) when the particle size distribution is obtained on a volume basis and the cumulative curve is drawn such that the total volume is 100%.

[0074] Within the context of the present disclosure, the term "density" refers to a measure 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 density or skeletal density of the material, as well as the bulk density of the material or composition. Density is typically reported in g / cm 3 , g / cc, or g / mL.

[0075] The composite material properties can be determined using mercury intrusion porosimetry and helium pycnometry experiments. Mercury intrusion porosimetry can be used to determine the porosity, pore size distribution, and pore volume with respect to solid particles. During normal mercury intrusion porosimetry, a pressure chamber is used to press mercury into the voids within the porous substrate. As pressure is applied, mercury first fills the larger pores. As the pressure increases, mercury can enter smaller pores. Mercury pycnometry can access and measure pores larger than approximately 3 nm. Mercury intrusion porosimetry can be used to measure the bulk density, skeletal density, and porosity. By varying the test parameters (e.g., pressure range), pores of different sizes can be excluded. The lower pore size limit for mercury intrusion porosimetry is approximately 3 nm.

[0076] Helium pycnometry measures the volume of the pores in a solid material using helium gas. During helium pycnometry, the sample is sealed within a partition and helium gas is added into that partition. The helium gas penetrates deeply into the small pores within the material. After the system has equilibrated, the skeletal density of the solid material can be determined using the change in pressure. Helium pycnometry can access and measure pores larger than approximately 0.3 nm, e.g., pores sized from approximately 3 nm to approximately 300 nm.

[0077] The "Hg skeletal density" (g / cm 3 ) is measured by dividing the mass (g) of the composite material particles by the volume (cm 3 ) of the particles. At this time, the volume is measured by controlling (e.g., by pressure) the mercury access to the pores of the particles larger than 3 nm during the measurement. This volume does not include the volume of the mercury-accessible pores of the composite material larger than 3 nm. Instead, the volume only includes the volume of the "skeleton" of the composite material particles. The volume of pores less than 3 nm is considered part of the skeleton and is included in the calculation of the skeletal density.

[0078] The "Hg bulk density" is the mass (g) of the composite material particles divided by the volume (cm 3) is measured by dividing. At this time, the volume is measured by controlling (e.g., by pressure) so that mercury does not access the pores of the particles during measurement. This volume includes the pore volume of the composite material including those greater than 3 nm and less than 3 nm.

[0079] The "He skeletal density" is obtained by dividing the mass (g) of the composite material particles by the volume of the particles (cm 3 ) is measured by dividing. At this time, the volume is measured by controlling (e.g., by pressure) so that helium accesses the pores of the particles greater than 0.3 nm during measurement. This volume does not include the volume of the helium-accessible pores of the composite material greater than 0.3 nm. Instead, the volume includes only the volume of the "skeleton" of the composite material particles. The volume of pores less than 0.3 nm is regarded as part of the skeleton and is included in the calculation of the skeletal density.

[0080] The composite material may also include pores that are not accessible to either helium or mercury during the helium or mercury specific gravity measurement test. For example, a part of the pores formed by removing sacrificial particles may be enclosed in a three-dimensional network and thus not accessible to either the helium or mercury specific gravity measurement. These non-accessible pores are usually very small in the composite materials disclosed herein. The non-accessible pores are treated as part of the volume of the skeleton without significant variation.

[0081] Various physical properties can be calculated according to the following formula using the mercury (Hg) intrusion skeletal density measurement value (Hg skeletal density) measured by mercury porosimetry, the mercury intrusion volume density (Hg volume density) measured by mercury porosimetry, and the helium (He) skeletal density (He skeletal density) tested by He porosimetry.

Equation

[0082] "Total bead-level porosity" (%) refers to the ratio of the volume of pores within the composite material particles to the volume of the composite material particles. The total bead-level porosity is calculated by Equation (1). The total bead-level porosity includes pores larger than 0.3 nm accessible by helium and mercury.

[0083] "Total pore volume" (cm 3 / g) refers to the total pore volume per unit weight of the composite material particles. The total pore volume is calculated by Equation (2). The total pore volume includes pores larger than 0.3 nm accessible by helium and mercury.

[0084] "Micropore volume" (cm 3 / g) refers to the micropore volume per unit weight of the composite material particles. The micropore volume of the composite material (cm 3 / g) is the difference between the reciprocal (cm 3 / g) of the mercury skeletal density (g / cm 3 ) and the reciprocal (cm 3 / g) of the helium skeletal density (g / cm 3 ). The micropore volume includes pores larger than 0.3 nm and less than 3 nm. Micropores are accessible by helium but not by mercury.

[0085] "Micropore volume percentage" (%) refers to the volume ratio of the volume of micropores to the total pore volume. The micropore volume percentage is calculated by Equation (4).

[0086] "Mesopore volume percentage" (%) refers to the volume ratio of the mesopore volume to the total pore volume. Mesopores refer to pores of about 3 nm to about 50 nm that are accessible by mercury. Pores less than 3 nm are not accessible by mercury. The mesopore volume percentage can be directly measured by using mercury porosimetry and excluding pores larger than 50 nm. The mesopore volume percentage can also be obtained by subtracting the micropore volume percentage (calculated by Equation (4)) and the macropore volume percentage (measured by mercury porosimetry) from the total pore volume percentage (100%).

[0087] "Macropore volume percentage" (%) refers to the volume ratio of the macropore volume to the total pore volume. Macropores are pores larger than about 50 nm that are accessible by mercury. The macropore volume percentage can be directly measured by using mercury porosimetry and excluding pores smaller than 50 nm. The macropore volume percentage can also be obtained by subtracting the micropore volume percentage (calculated by Equation (4)) and the mesopore volume percentage (measured by mercury porosimetry) from the total pore volume percentage (100%).

[0088] Composite material properties Total porosity The composite materials described herein generally include micropores (less than 3 nm), mesopores (3 nm to 50 nm), and macropores (greater than 50 nm). The composite materials described herein include a three-dimensional carbon network having a significant amount of macropores. In some embodiments, the total level of porosity (total bead level 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 embodiments, the total level of porosity of the three-dimensional carbon network is 25% - 35%, 30% - 40%, 35% - 45%, 40% - 50%, 55% - 65%, or 60% - 70%.

[0089] Total pore volume In some embodiments, the aerogel materials or compositions of the present disclosure (without incorporation of electrochemically active species, such as 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 the range between any two of these values. In other embodiments, the aerogel materials or compositions of the present disclosure (with incorporation of electrochemically active species, such as 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 the range between any two of these values. In further embodiments, the total pore volume of the composite material is about 0.1 cm 3 / g to about 1.5 cm 3 / g, about 0.1 cm 3 / g to about 1.0 cm 3 / g, about 0.1 cm 3 / g to about 0.5 cm 3 / g, about 0.1 cm 3 / g to about 0.4 cm 3 / g, about 0.4 cm 3 / g to about 1.0 cm 3 / g, or about 0.9 cm 3 / g to about 1.4 cm 3 / g.

[0090] Pore size distribution In certain embodiments, the aerogel materials or compositions of the present disclosure have a relatively narrow pore size distribution (full width at half maximum) of about 150 nm or less, 100 nm or less, 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 the range between any two of these values.

[0091] Macropores, mesopores, and micropores In some embodiments, the macropores constitute a volume fraction of more than about 5%, more than about 10%, more than about 20%, more than about 30%, more than about 40%, more than about 50%, more than about 60%, more than about 70%, more than about 80% of the total pore volume of the three-dimensional carbon network. In some embodiments, the macropores constitute a volume fraction of 45% - 55%, 55% - 65%, 65% - 75%, or 70% - 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 embodiments, 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 embodiments, the mesopores constitute a volume fraction of 10% - 20%, 5% - 10%, or 1% - 5% of the total pore volume of the three-dimensional carbon network.

[0092] The composite materials described herein contain a higher percentage of micropores compared to mesopores. In some embodiments, 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 embodiments, the micropores constitute a volume fraction of about 10% - about 50%, about 10% - about 45%, about 10% - about 40%, about 10% - about 35%, about 10% - about 30%, about 10% - about 25%, about 10% - about 20%, about 10% - about 15%, about 15% - about 25%, about 25% - about 35%, about 35% - about 45%, or about 45% - about 55% of the total pore volume of the three-dimensional carbon network.

[0093] Skeletal density In some embodiments, the composite material has a skeletal density of from about 1.0 g / mL to about 2.5 g / mL, from about 1.5 g / mL to about 2.5 g / mL, from about 1.0 g / mL to about 2.0 g / mL, or from 1.0 g / mL to about 1.5 g / mL, as measured using helium pycnometry. In some embodiments, the composite material has a skeletal density of from about 0.5 g / mL to about 2.5 g / mL, from about 1.5 g / mL to about 2.5 g / mL, from about 1.5 g / mL to about 2.0 g / mL, from about 0.5 g / mL to about 2.0 g / mL, from about 0.5 g / mL to about 1.5 g / mL, or from about 0.5 g / mL to about 1.0 g / mL, as measured using mercury intrusion. In some embodiments, the composite material has a bulk density of from about 0.5 g / mL to about 2.5 g / mL, from about 0.5 g / mL to about 2.0 g / mL, from about 0.5 g / mL to about 1.5 g / mL, or from about 0.5 g / mL to about 1.0 g / mL, as measured using mercury pycnometry.

[0094] In some embodiments, the composite materials of the present disclosure include low bulk density materials such as carbon aerogels. In some embodiments, the low bulk density material includes a skeletal framework comprising nanofibers, the skeletal framework forming a pore structure including an array of interconnected pores. In some embodiments, such materials can have a fibrillar morphology. In some embodiments, the composite material is a carbon aerogel, a carbon xerogel, a carbon cryogel, or a carbon ambigel, or a combination thereof. In some embodiments, the composite material is an aerogel. In contrast to aerogels, xerogels such as silica xerogel generally include a compact structure. Xerogels experience a substantial volume reduction during ambient pressure drying and, when measured by nitrogen adsorption analysis, have a surface area of from 0 to 100 m 2 / g, or from about 0 to about 20 m 2It may have a small surface area, such as / g. In addition, xerogel has a fibrillar form compressed to a high density as compared to aerogel. Within the scope of the context of the present disclosure, the term "fibrillar form" refers to the structural form of a nanoporous material (e.g., carbon aerogel) including struts, rods, fibers, or filaments. Structurally, some embodiments of the carbon network have a fibrillar form with strut sizes that result in, among other properties, the narrow pore size distribution, porosity, and extended connectivity described above. In any embodiment, the fibrillar form of the carbon network may include an average strut width of about 2 to 10 nm, or more specifically about 2 to 5 nm.

[0095] Within the scope of the context of the present disclosure, the term "strut width" refers to the average diameter of the nanoscale struts, nanorods, nanofibers, or nanofilaments that form a material having a fibrillar form. This is typically recorded in any unit of length, e.g., micrometers or nm. The strut width can be determined by methods known in the art including, but not limited to, scanning electron microscope image analysis. Within the scope of the context of the present disclosure, measurements of strut width are obtained according to this method unless otherwise specified. In certain embodiments, the 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 the range between any two of these values. An exemplary range of strut width is about 2 to 5 nm. Such smaller strut widths allow for a greater amount of struts to be present within the network and thus come into contact with electrochemically active species, thereby allowing for a greater amount of electrochemically active species to be present within the composite. This results in an increase in conductivity and mechanical strength.

[0096] Method for preparing a composite material Referring to FIG. 2, a method 200 for manufacturing a composite material includes five steps (210, 220, 230, 240, 250). First, as shown in step 210, silicon particles are provided. Generally, the silicon particles need to be homogeneous. That is, the silicon particles are typically provided from the same source and have a known desired particle size, shape, porosity, and other substantially similar material properties. After obtaining the silicon particles, method 200 includes oxidizing the surface of the particles (i.e., step 220) to obtain hydroxyl functional groups on the surface of the particles. Oxidation of the surface of the silicon particles is necessary for further functionalization of the surface of a particular source of Si particles. Oxidation of the surface of the silicon particles can result in complete or partial oxidation of the Si-H groups on the surface. That is, all or a certain percentage of the Si-H groups on the surface of the silicon particles are converted to Si-O groups or Si-OH groups after the oxidation process. The silicon particles can be oxidized in a single step or multiple steps (multiple possible). Oxidation can be thermal (e.g., at high temperature in air), chemical (e.g., acids and / or oxidants), electrochemical, or a combination thereof. As shown in step 230, the third step is to form a sacrificial layer on at least a portion of the surface of the silicon particles. Forming a sacrificial layer on the surface of the silicon particles is performed before introducing the silicon particles into a sol-gel solution containing a precursor of a porous three-dimensional network. The characteristics of the sacrificial layer formed in the third step (e.g., thickness, type of material) can affect the dispersion of the silicon particles in the sol-gel solution introduced in the fourth step 240. The sacrificial layer can be made of a polymer, metal, natural and synthetic organics, salts, ceramic compounds, or a combination thereof. After forming the sacrificial layer, as shown in step 240, a sol-gel solution containing a polar solvent and a precursor of a porous network is provided. The silicon particles are dispersed in the sol-gel solution homogeneously or heterogeneously, preferably homogeneously. The precursor of the porous network can be a precursor of an aerogel.After providing a sol-gel solution to silicon particles having a sacrificial layer, as shown in 250, the silicon particles having a sacrificial layer are processed in the presence of the sol-gel solution to obtain precursor beads containing silicon particles dispersed within the precursor beads. The processing may include gelling the sol-gel solution to form the precursor beads. Method 200 further includes a step of subcritical drying or supercritical drying after the processing of the silicon particles in the presence of the sol-gel solution. For example, the drying step may result in the formation of an aerogel material, such as an aerogel, xerogel, ambigel, or a combination thereof. In a final step 260, the precursor beads containing silicon particles dispersed throughout the precursor beads are pyrolyzed to obtain a composite material 100 containing voids. During pyrolysis, a three-dimensional carbon network is formed from the porous network.

[0097] In one embodiment, the amount of sacrificial material removed depends on the duration of the heat treatment, such as pyrolysis, applied to the precursor beads containing the silicon particles.

[0098] In some embodiments, the sacrificial layer is formed from a material selected from polymethyl methacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide copolymer, polypropylene oxide copolymer, polycarbonate (PC), polyvinyl chloride (PVC), polycaprolactone, polyvinylidene fluoride, polystyrene, or a combination thereof. In some embodiments, the sacrificial layer has a thickness of about 100 nm or less, or a thickness in the range of about 100 nm to about 60 nm, or about 60 nm to 0.3 nm. In some embodiments, the sacrificial layer has a thickness in the range of about 20% to about 0.01% of the diameter of the silicon particles.

[0099] In some embodiments, the sacrificial layer has a char yield of less than about 20 wt%. In some embodiments, the chemical decomposition temperature of the sacrificial material layer is in the range of about 130 °C to about 850 °C.

[0100] Within the scope of the context of the present disclosure, the terms "pyrolyze" or "pyrolysis" or "carbonize" refer to the decomposition or conversion of an organic compound or composition by heat into pure or substantially pure carbon. In each example, the term "carbonization yield" refers to the percentage ratio of the weight of the carbon obtained to the weight of the organic compound or composition from which the carbon is produced.

[0101] In some embodiments, the sacrificial layer is uniform over at least a portion of the surface of the silicon particles. In some embodiments, the sacrificial layer is continuous over 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%, at least 90%, or at least 95% of the surface of the silicon particles.

[0102] Referring to FIG. 3, a method 300 showing the manufacture of a composite material includes six steps (310, 320, 330, 340, 350, 360). In this method 300, the sacrificial layer is formed during or after the provision of the sol-gel solution. First, as shown in step 310, silicon particles are provided. Generally, the silicon particles need to be homogeneous. 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 obtaining the silicon particles, method 300 includes oxidizing the surface of the particles (i.e., step 320) to obtain hydroxyl functional groups on the surface of the particles. Oxidation of the surface of the silicon particles can result in complete or partial oxidation of the Si-H groups on the surface. That is, all or a certain percentage of the Si-H groups on the surface of the silicon particles are converted to Si-O groups or Si-OH groups after the oxidation process. The silicon particles can be oxidized in a single step or multiple steps (multiple possible). Oxidation can be thermal (e.g., at high temperature in air), chemical (e.g., acids and / or oxidants), electrochemical, or a combination thereof. The third step 330 requires silicon particles having hydroxyl functional groups on their surface to react covalently with at least one functional silane group. Bonding of the silane group to the surface can facilitate further modification of the silicon particle surface. In addition, the silane groups present on the surface of the silicon particles can assist in the dispersion of the silicon particles, which is important for further steps. After bonding at least one functional silane group to the surface of the silicon particles, as shown in step 340, a sol-gel solution containing a polar solvent and a precursor of a porous three-dimensional network is provided. The silicon particles are dispersed homogeneously or heterogeneously, preferably homogeneously, in the sol-gel solution. The precursor of the porous three-dimensional network can be a precursor of an aerogel. As shown in step 350, the fifth step is to form a sacrificial layer on at least a portion of the surface of the silicon particles. Forming the sacrificial layer on the surface of the silicon particles is performed within the sol-gel solution containing the precursor of the porous three-dimensional network.The properties of the sacrificial layer (e.g., thickness, material type) formed in step 350 can affect the dispersion of silicon particles in the composite material formed in step 360. The sacrificial layer can be made of polymers, metals, natural and synthetic organics, salts, ceramic compounds, or combinations thereof. After the formation of the sacrificial layer, as shown in step 360, the silicon particles having the sacrificial layer are treated in the presence of a sol-gel solution to obtain a composite material. The treatment can include gelling the sol-gel solution to form a precursor three-dimensional network. Method 300 further includes a step of subcritical drying or supercritical drying after the treatment of the silicon particles in the presence of the sol-gel solution. For example, the drying step can result in the formation of an aerogel.

[0103] The step 350 of forming the sacrificial layer in method 300 includes: i. fusing a polymer initiator to the surface of the silicon particles to react with monomers; and ii. polymerizing the monomers on the surface of the silicon particles to form the sacrificial layer.

[0104] Figures 4A and 4B show an exemplary route for preparing silicon particles having a sacrificial layer. The process of forming the sacrificial layer mainly includes three steps (410, 420, 430). In the first step 410, silicon particles 401 having hydroxyl functional groups on their surface react covalently with functional silane groups. In this example, 3-aminopropyltriethoxysilane (APTES) 402 is used as the functional silane group. The hydroxyl groups react with the silane groups in a polar solvent (e.g., ethanol 403) as shown in step 410. The reaction is carried out at a high temperature, e.g., a temperature higher than 25°C. After covalently bonding APTES onto the surface of the silicon particles to form silicon particles 404 containing -NH2 groups on their surface, a polymer initiator (e.g., azobis(4-cyanovaleric acid) (ACPA) 405) is fused onto the surface of the silicon particles for further reaction with monomers. In step 420, the fusion of the polymer initiator onto the surface of the silicon particles is carried out in a polar solvent (e.g., ethanol 403). The selected polar solvent needs to be suitable for dissolving each component, e.g., the polymer initiator of the reaction. The third step 430 results in the formation of silicon particles 110 having a sacrificial layer. In step 430, the monomer initiator on the surface of the silicon particles 406 undergoes a polymerization reaction with a monomer, e.g., methyl methacrylate 407. The monomer selected for the polymerization reaction depends on the type of sacrificial layer desired on the surface. As shown in step 430, the polymerization reaction can be carried out in a polar solvent (e.g., water 404). The polymerization reaction is carried out at a temperature higher than 25°C.

[0105] An exemplary route for the preparation of silicon particles having a sacrificial layer as shown in FIGS. 4A and 4B can also be applied to Method 300. In Method 300, a first step 410 in which silicon particles 401 having hydroxyl functional groups on their surfaces react covalently with a functional silane group, for example, aminopropyltriethoxysilane (APTES) 402, is performed before providing the sol-gel solution. The second step 420 and the third step 430 are performed in the sol-gel solution during or after the step 340 of providing the sol-gel solution. That is, steps 420 and 430 are performed in a sol-gel solution containing a precursor of a three-dimensional network.

[0106] In some embodiments, the polymeric initiator includes azobis(4-cyanovaleric acid) (ACPA), 2,2'-azobis(2-amidinopropane) hydrochloride (V50), ammonium persulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride (VA044), and ammonium persulfate / sodium metabisulfite. In some embodiments, the polymeric initiator includes azobis(4-cyanovaleric acid) (ACPA).

[0107] The step of covalently reacting hydroxyl groups on the surface of the silicon particles includes the use of at least one functional group selected from 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), and N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES) or combinations thereof.

[0108] In some embodiments, the method of preparing the composite material further includes a step of dispersing silicon particles in the sol-gel solution before the step of forming the sacrificial layer. In some embodiments, the method of preparing the composite material further includes a step of dispersing silicon particles in the sol-gel solution after the step of forming the sacrificial layer. In some embodiments, the method of preparing the composite material further includes a step of dispersing silicon particles in the sol-gel solution before and after the step of forming the sacrificial layer.

[0109] In some embodiments, the method of preparing the composite material further includes a step of treating the composite material to substantially remove the sacrificial layer, for example, a step of pyrolyzing the precursor beads. In one embodiment, treating the composite material to substantially remove the sacrificial layer includes heating the composite material to the chemical decomposition temperature of the sacrificial layer. In some embodiments, the chemical decomposition temperature of the sacrificial material layer ranges from about 130°C to about 850°C. In certain embodiments, treating the composite material to partially or completely remove the sacrificial layer provides voids around the silicon particles.

[0110] In some embodiments, the method of preparing the composite material further includes a step of subcritical drying or supercritical drying after treating the silicon particles in the presence of the sol-gel solution. In some embodiments, after treating the silicon particles in the presence of the sol-gel solution, a step of subcritical drying or supercritical drying. In some embodiments, the step of subcritical drying or supercritical drying results in the formation of an aerogel material, such as xerogel, aerogel, etc.

[0111] Oxidizing the surface of the plurality of silicon particles may include an acid treatment step. In some embodiments, the acid treatment step includes the use of sulfochromic acid or H2O2 (hydrogen peroxide). In some examples, the acid treatment step includes subjecting the plurality of silicon particles to ultrasonic treatment for a period of time, such as at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes, or at least 60 minutes. Oxidizing the surface of the plurality of silicon particles may include a pyrolysis step at a temperature of about 300, about 400, or about 500 to about 600, about 650, about 700, about 800, about 850, 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 conversion of an organic compound or composition to pure or substantially pure carbon caused by heat. Oxidizing the surface of the plurality of silicon particles may result in a decrease in the number of Si-H bonds on the surface of the silicon particles.

[0112] In some embodiments, the method of preparing the composite material of the present disclosure further includes a step of removing a subcritical or supercritical solvent (before or after the pyrolysis step), such as drying, after treating the plurality of silicon particles in the presence of a sol-gel solution. Methods of solvent removal include, but are not limited to, supercritical drying (or drying using a supercritical fluid such that the low surface tension of the supercritical fluid exchanges with the transient solvent in the gel), solvent exchange with a supercritical fluid, followed by solvent exchange with a fluid that transitions to the supercritical state, subcritical fluid drying or near-critical fluid drying, and sublimation of the frozen solvent in a freeze-drying process. See, for example, PCT Patent Application Publication No. WO2016127084A1.

[0113] The composite material may be in a variety of different physical forms. In some embodiments, the composite material may take a monolithic form. As used herein, the term "monolithic" refers to a material in which most (by weight) of the low-density skeletal framework contained in the composite material is in the form of a single continuous self-supporting object. With respect to aerogel materials, monolithic aerogel materials include aerogel materials that are initially formed to have a definite shape but can then crack, fracture, or split into non-self-repeating objects. For example, an irregular mass may be considered monolithic. Monolithic aerogels may take the form of a self-standing structure, or a fiber-reinforced material, or an interconnected foam.

[0114] In other embodiments, the composite material may be in a particulate form, such as beads, or particles, for example, resulting from the grinding of a monolithic material. As used herein, the term "beads" means generally to include separate small units or portions having a spherical shape. In some embodiments, the composite material beads are substantially spherical.

[0115] The particulate composite material 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., length, width, or height). The particle size can vary depending on the physical form, the preparation method, and any subsequent physical processes. In some embodiments, the particulate composite material can have a particle size in the range of about 1 micrometer to about 1 millimeter. For example, the particulate composite material 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 a particle size in the range between any two of these values.

[0116] In some embodiments, the composite material has a particle size D90 value of 40 micrometers or less. 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 the range of about 5 micrometers to about 20 micrometers.

[0117] The density of the composite material can vary. In some embodiments, the composite material has a tapped density in the range of about 0.15 g / cm 3 ~ about 1.2 g / cm 3 of the range.

[0118] The surface area of the composite material can vary. For example, the surface area can be up to about 100 m 2 / g, or can be greater than 100 m 2 / g. In some embodiments, the composite material has a surface area in the range of about 1 m 2 / g to about 400 m 2 / g, such as, for example, about 1, about 10, or about 50 to about 100, about 200, about 300, or about 400 m 2 / g.

[0119] In some embodiments, the composite material comprises silicon in an amount by weight of about 20% to about 85%, such as, for example, 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% of the total weight of the composite material, or 85% by weight of silicon.

[0120] The composite material can 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 a material in which most (by weight) of the low-density skeletal framework contained within the composite material is in the form of a single continuous self-supporting object. With respect to aerogel materials, monolithic aerogel materials include aerogel materials that are initially formed to have a defined shape but can then crack, fracture, or split into non-self-repeating objects. For example, an irregular lump may be considered a monolith. Monolithic aerogels can take the form of self-standing structures, or materials reinforced with fibers, or interconnected interpenetrating foams.

[0121] In other embodiments, the composite material can be in particulate form, such as beads, or particles, for example, resulting from the grinding of a monolithic material. As used herein, the term "beads" is meant to generally encompass separate small units or portions having a spherical shape. In some embodiments, the carbon-silicon composite beads are substantially spherical.

[0122] The capacity of the composite material can 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 a specific capacity in the range between any two of these values.

[0123] The conductivity of the anode material can vary. Within the context of the present disclosure, the term "conductivity" refers to a measure of the ability of a material to conduct an electric current, or to allow the flow of electrons to pass through or within it. Conductivity is specifically measured as the electrical conductivity / susceptance / admittance of the material per unit size of the material. This is typically recorded as S / m (Siemens / meter) or S / cm (Siemens / centimeter). The conductivity or resistivity of a material can be determined by methods known in the art, such as, 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, the measured value of conductivity is obtained in accordance with the ASTM F84-resistivity (R) measurement value obtained by measuring the voltage (V) divided by the current (I), unless otherwise specified. In certain embodiments, the anode material of the present disclosure has a 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 a conductivity in the range between any two of these values.

[0124] Three-dimensional carbon network The three-dimensional carbon network of the present disclosure includes a carbon-based network selected from carbon aerogels, carbon xerogels, carbon ambigels, carbon aerogel-xerogel hybrid materials, carbon aerogel-ambigel hybrid materials, carbon aerogel-ambigel-xerogel hybrid materials, or combinations thereof.

[0125] The aerogels used in the present disclosure can be carbonized to obtain a three-dimensional carbon network, such as the carbon-based aerogels of the present technology. Carbonization may be carried out by pyrolysis at a high temperature in an inert atmosphere. The carbonized form of the aerogel used in the present disclosure may have a nitrogen content of 0 to 20%. A typical pyrolysis temperature range is 500°C to 2000°C. The temperature may be raised to reduce the nitrogen content of the resulting carbon aerogel. Pyrolysis is typically carried out in an inert atmosphere (i.e., nitrogen, helium, neon, argon, or some combination).

[0126] In some embodiments, the three-dimensional carbon network includes a polyimide-derived carbon aerogel. In some embodiments, to obtain a polyimide-derived carbon aerogel by carbonizing a polyimide aerogel, the dried polyimide aerogel is exposed to a processing temperature of 400°C or higher, 600°C or higher, 800°C or higher, 1000°C or higher, 1200°C or higher, 1400°C or higher, 1600°C or higher, 1800°C or higher, 2000°C or higher, 2200°C or higher, 2400°C or higher, 2600°C or higher, 2800°C or higher, or in a range between any two of these values.

[0127] This disclosure includes the formation and use of three-dimensional carbon networks, such as carbon aerogels, as electrode materials within energy storage devices, e.g., as a primary anode material within a LIB. The pores of the porous network are designed, configured, and constructed to accommodate silicon or other metalloid or metal particles and the expansion of such particles upon lithiation within a LIB. Alternatively, the pores of the porous network may be filled with sulfides, hydrides, any suitable polymer, or other additives, in which case there are benefits such as contacting the additives with a conductive material to obtain a more effective electrode.

[0128] To further expand exemplary applications within a LIB, when a carbon-based aerogel material as in the examples of this disclosure is used as a primary electrode material, e.g., an anode material, the carbon aerogel porous core has a narrow pore size distribution and provides a high conductivity, high mechanical strength, and a morphological and sufficient pore volume (at the final density) to accommodate a high weight percentage of silicon particles and their expansion.

[0129] In some examples, the surface of the three-dimensional carbon network may be modified via chemical, physical, or mechanical means to improve performance by electrochemically active species contained within the pores of the porous network.

[0130] Furthermore, it is contemplated herein that a three-dimensional carbon network and particularly carbon aerogels can take the form of a monolithic structure. When essentially monolithic, the carbon aerogel obviates the need for any binder. In other words, the anode can be binderless. As used herein, the term "monolithic" refers to an aerogel material in which most (by weight) of the aerogel contained within the aerogel material or composition is in the form of a single continuous interconnected aerogel nanostructure. Monolithic carbon aerogel materials include carbon aerogel materials that are initially formed to have a single interconnected gel or aerogel nanostructure but can subsequently crack, fracture, or split into non-single aerogel nanostructures. Monolithic aerogels can take the form of a self-standing structure or a reinforcing (fiber or foam) material. By comparison, using silicon lithiation as an example, silicon incorporated within a monolithic aerogel can be utilized more effectively against the theoretical capacity as compared to the same amount of silicon incorporated within a slurry using conventional processes.

[0131] Monolithic aerogel materials, e.g., monolithic carbon aerogels, are distinguished from particulate aerogel materials. The term "particulate aerogel material" refers to an aerogel material in which most (by weight) of the aerogel contained within the aerogel material is in the form of microparticles, particles, granules, beads, or powders, which can be combined together (i.e., via a binder such as a polymer binder) or compressed together but lack an interconnected aerogel nanostructure between the individual particles. Collectively, this form of aerogel material is said to have a powder or particulate form (as opposed to a monolithic form). It should be noted that, despite the individual particles of a powder having a single structure, the individual particles are not considered monoliths herein. Incorporating an aerogel powder into an electrochemical cell can typically involve the preparation of a paste or slurry from the powder, casting and drying onto a substrate, and optionally calendaring.

[0132] Particulate aerogel materials, such as carbon aerogel beads, have certain advantages. For example, the particulate material can be used as a direct alternative to other materials, such as graphite, in LIB anodes and anode manufacturing processes. The particulate material can also result in improved lithium ion diffusion rates due to shorter diffusion paths within the particulate material. The particulate material can also enable electrodes with increased packing density, for example, by adjusting the particle size and packing arrangement. The particulate material can also improve access to silicon due to the interparticle and intraparticle porosity.

[0133] Carbon aerogels can be formed from inorganic materials, organic materials, or mixtures thereof. Carbon aerogels can be formed from inorganic aerogels, organic aerogels, or mixtures thereof. Inorganic aerogels, organic aerogels, or mixtures thereof can be carbonized to obtain a three-dimensional carbon network, such as the porous carbon aerogels of the present disclosure. Aerogels can be formed of inorganic materials, organic materials, or mixtures thereof. For example, when formed of organic materials such as phenol, resorcinol formaldehyde (RF), phloroglucinol - furfuraldehyde (PF), polyacrylonitrile (PAN), polyimide (PI), polyurethane (PU), polyurea (PUA), polyamine (PA), polybutadiene, polydicyclopentadiene, and their precursors or polymer derivatives, the organic aerogels can be carbonized (e.g., by pyrolysis) to form carbon aerogels that can have different or overlapping properties (e.g., pore volume, pore size distribution, morphology, etc.) depending on the precursor materials and methodologies used.

[0134] Inorganic aerogel Inorganic aerogels are generally formed from metal oxide or metal alkoxide materials. The metal oxide or metal alkoxide materials can 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, etc. Inorganic silica aerogels have conventionally been made via hydrolysis and condensation of silica-based alkoxides (e.g., tetraethoxysilane) or via gelation of silicic acid or water glass. Other related inorganic precursor materials for silica-based aerogel synthesis include metal silicates such as sodium silicate or potassium silicate, alkoxysilanes, partially hydrolyzed alkoxysilanes, tetraethoxysilane (TEOS), partially hydrolyzed TEOS, condensation polymers of TEOS, tetramethoxysilane (TMOS), partially hydrolyzed TMOS, condensation polymers of TMOS, tetra-n-propoxysilane, partially hydrolyzed and / or condensation polymers of tetra-n-propoxysilane, polysilicate, partially hydrolyzed polysilicate, monomeric alkylalkoxysilane, bis-trialkoxyalkyl or arylsilane, polyhedral silsesquioxane, or combinations thereof, but are not limited thereto.

[0135] In certain embodiments of the present disclosure, pre-hydrolyzed TEOS such as Silbond® H-5 (SBH5, Evonik Corp), which is hydrolyzed at a water / silica ratio of about 1.9 to 2, may be commercially available or may be further hydrolyzed prior to being incorporated into the gelation process. Partially hydrolyzed TEOS or TMOS, such as polysilicate (Silbond® 40) or polymethylsilicate, may also be commercially available or may be further hydrolyzed prior to incorporation into the gelation process.

[0136] Inorganic aerogels can also include a gel precursor containing at least one hydrophobic group, such as an alkyl metal alkoxide, a cycloalkyl metal alkoxide, and an aryl metal alkoxide, which can impart or improve specific properties of the gel, such as stability and hydrophobicity. Specifically, inorganic silica aerogels can include hydrophobic precursors such as alkylsilanes or arylsilanes. A hydrophobic gel precursor may be used as the main precursor material to form the framework of the gel material. However, hydrophobic gel precursors are more commonly used as co-precursors in combination with simple metal alkoxides for the formation of amalgam aerogels. Examples of hydrophobic inorganic precursor materials for silica-based aerogel synthesis include, but are not limited to, trimethylmethoxysilane (TMS), dimethyldimethoxysilane (DMS), methyltrimethoxysilane (MTMS), trimethylethoxysilane, dimethyldiethoxysilane (DMDS), methyltriethoxysilane (MTES), ethyltriethoxysilane (ETES), diethyldiethoxysilane, dimethyldiethoxysilane (DMDES), ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane (PhTES), hexamethyldisilazane, and hexaethyldisilazane. Any derivative of any of the above precursors may be used, specifically, specific polymers of other chemical groups may be added to or cross-linked with one or more of the above precursors.

[0137] Organic aerogel Organic aerogels are generally formed from carbon-based polymer precursors. Such polymer materials include, but are not limited to, resorcinol formaldehyde (RF), polyimide, polyacrylate, polymethyl methacrylate, acrylate oligomer, polyoxyalkylene, polyurethane, polyphenol, polybutadiene, trialkoxysilyl-terminated polydimethylsiloxane, polystyrene, polyacrylonitrile, polyfurfural, melamine-formaldehyde, cresol formaldehyde, phenol-furfural, polyether, polyol, polyisocyanate, polyhydroxybenzene, polyvinyl alcohol dialdehyde, polycyanurate, polyacrylamide, various epoxies, agar, agarose, chitosan, and combinations thereof. As an example, organic RF aerogels are typically made from the sol-gel polymerization of resorcinol or melamine and formaldehyde under alkaline conditions.

[0138] In certain embodiments, the aerogels of the present disclosure comprise polyamic acid, polyimide, or a combination thereof, or are carbon aerogels obtained from (i.e., derived from) polyamic acid or polyimide by carbonization. In certain embodiments, the aerogels comprise polyamic acid, polyimide, or a combination thereof, or are obtained by thermal decomposition of polyamic acid, polyimide, or a combination thereof. In some embodiments, the polyamic acid or polyimide is prepared in an aqueous solution (i.e., via an aqueous sol-gel process). References herein to an aqueous solution or an aqueous sol-gel process mean that the solution or aqueous sol-gel process is substantially free of any organic solvents. The term "substantially free of" as used herein in the context of organic solvents means that no organic solvents are intentionally added and that no organic solvents in excess of trace amounts are present. For example, in certain embodiments, the aqueous solution may be characterized as having less than 1 volume % of an organic solvent, or less than 0.1 volume %, or less than 0.01 volume %, or 0 volume % of an organic solvent.

[0139] The use of an aqueous sol-gel process has the advantage of providing rapid gelation, for example, to create a process that can be adapted to continuous process configurations in order to prepare polyimide beads. The aqueous sol-gel process for preparing polyamic acid and polyimide gel materials is economically preferable over conventional methods for such materials (e.g., expensive organic solvents are avoided and disposal costs are minimized), and is "green" (i.e., environmentally beneficial because potentially toxic organic solvents are avoided and the production of toxic by-products is minimized or eliminated), and is advantageous in potentially reducing the overall number of operations required to be carried out to provide a carbon or polyamic acid / polyimide gel material. As disclosed in International Patent Application Publication No. WO2022 / 125835 and International Patent Application PCT / US2023 / 016821, each of which is hereby incorporated by reference in its entirety, polyamic acid and polyimide gels can be prepared in water in monolithic or bead form, the gels can be converted to aerogels having nanostructures with properties similar to those of aerogels prepared by conventional organic solvent-based processes, and the aerogels are optionally pyrolyzed to form the corresponding carbon aerogels.

[0140] In some embodiments, the aerogel of the present disclosure is a polyamic acid aerogel in monolithic or bead form, where the polyamic acid is prepared by acidification of an aqueous solution of the 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 a non-nucleophilic amine base). In other embodiments, the polyamic acid is prepared in situ under aqueous conditions, whereby a polyamic acid salt solution is directly formed. In some embodiments, the polyamic acid is any commercially available polyamic acid. In other embodiments, the polyamic acid is pre-formed ( "pre-formed") and isolated, for example, by reaction of a diamine and a tetracarboxylic dianhydride in an organic solvent according to conventional synthetic methods. In some embodiments, an aqueous solution of the polyamic acid salt is prepared in situ, for example, by reaction of a diamine and a tetracarboxylic dianhydride in the presence of a non-nucleophilic amine, whereby an aqueous solution of the ammonium salt of the polyamic acid is obtained. Suitable methods for preparing polyamic acid aerogels under such aqueous conditions are described in WO2022 / 125835 and PCT / US2023 / 016821 (incorporated by reference above).

[0141] In some embodiments, the aerogel of the present disclosure is a polyimide aerogel in monolithic or bead form, where the polyimide is prepared by thermal or chemical imidization of the polyamic acid in aqueous solution. Suitable methods for forming monoliths and beads under such aqueous conditions (e.g., utilizing droplet or emulsion-based processes) are described in WO2022 / 125835 and PCT / US2023 / 016821 (incorporated by reference above).

[0142] Organic / inorganic hybrid aerogel Organic / inorganic hybrid aerogels are mainly composed of (organically modified silica ("ormosil")) aerogels. These ormosil materials contain organic components covalently bonded to the silica network. Ormosil is typically formed by the hydrolysis and condensation of an organically modified silane, R-Si(OX)3, and a conventional alkoxide precursor, Y(OX)4. In these formulas, X can represent, for example, CH3, C2H5, C3H7, C4H9, Y can represent, for example, Si, Ti, Zr, or Al, and R can be any organic fragment such as methyl, ethyl, propyl, butyl, isopropyl, methacrylate, acrylate, vinyl, epoxide, etc. Also, the organic components in the ormosil aerogel may be dispersed throughout the silica network or chemically bonded to the silica network.

[0143] In certain embodiments, the aerogels of the present disclosure are preferably inorganic silica aerogels mainly formed from a pre-polymerized silica precursor as an oligomer, or hydrolyzed silicate esters formed from silicon alkoxides in an alcohol solvent. In certain embodiments, such pre-polymerized silica precursors or hydrolyzed silicate esters can be formed in situ from other precursors or silicate esters, such as alkoxysilanes or water glass. However, the present disclosure may generally be practiced using any other aerogel compositions known to those skilled in the art and is not limited to any one precursor material or an amalgam mixture of precursor materials.

[0144] Silicon particles Silicon generally exists in the composite material as silicon particles. Within the scope of the context of this disclosure, the term "silicon particles" refers to silicon or silicon-based materials having a range of particle sizes. The particle size of silicon in the composite material can vary. The silicon particles of this disclosure can be nanoparticles, for example, particles having two or three dimensions in the range of about 1 nm to about 150 nm. The silicon particles of this disclosure can be microparticles, for example, micron-sized particles having the diameter of a substantially spherical particle in the range of the maximum dimension, for example, about 150 nm to about 10 micrometers or more. For example, the silicon particles of this disclosure can have the diameter of a substantially spherical particle in the range of the maximum dimension, for example, about 10 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 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 the range between any two of these values.

[0145] In some embodiments, the silicon particles can be monodisperse or substantially monodisperse. In other embodiments, the silicon particles can have a particle size distribution. Within the scope of the context of this disclosure, the dimensions of the silicon particles are provided based on the median of the particle size distribution, that is, D50. In some embodiments, the silicon in the composite material has an average particle size of about 1 μm or less.

[0146] The silicon particles of this disclosure can be silicon wires, crystalline silicon, amorphous silicon, silicon alloys, silicon oxides (SiOx), and any combination of these. Particles, such as particles of an electroactive material such as silicon particles, can have various shapes with respect to the embodiments disclosed herein. In some embodiments, the silicon particles disclosed herein can be substantially spherical. In other embodiments, the particles of the electroactive material can be substantially planar, cubic, oval, elliptical, disc-shaped, or donut-shaped.

[0147] In one example, prior to the formation of the sacrificial layer, the surface of silicon particles (e.g., silicon nanoparticles) can be modified by functional groups, thereby helping to disperse the silicon particles in the precursor beads. In another example, the formation of the sacrificial layer can further help to disperse the silicon particles in the precursor beads. In one example, the precursor beads can be a sol-gel, an aerogel, a xerogel, a foam structure, etc. In some embodiments, the precursor beads are carbonized to obtain the three-dimensional carbon network of the present disclosure according to a plurality of embodiments disclosed herein.

[0148] For example, the functional groups can be fused to the surface of the silicon particles by covalent bonds. Prior to functionalization, the surface of the silicon particles contains silane groups such as silicon hydride and / or silicon oxide groups. In some embodiments, at least a portion of the silane and silicon oxide groups can be present in combination with the bonding functional groups after functionalization of the surface of the silicon particles. For example, the silicon particle surface can contain silane groups and covalently bonded functional groups, silicon oxide groups and covalently bonded functional groups, or both silane and silicon oxide groups and covalently bonded functional groups. The presence of functional groups on the surface of the silicon particles can be detected by various techniques, e.g., by infrared spectroscopy.

[0149] The surface of the silicon particles can be functionalized with hydrophilic groups to assist in the improvement of dispersion within the porous network. Without being bound by theory, functionalization with hydroxide groups results in improved covalent bonding between the surface groups of the silicon particles and the porous network. As a result, the functionalized silicon particles can be uniformly dispersed within the porous network. For example, hydrophilic hydroxide groups can be fused to the surface of the particles by unsaturated glycols to improve the hydrophilicity of the silicon particle surface. By improving the hydrophilicity of the silicon particles, the particles become and remain more uniformly dispersed within the network and can maintain a uniformly dispersed state within the network in any additional processing (e.g., pyrolysis). In one example, functionalization via glycol can improve the dispersion of silicon particles within polyimide sol-gel and / or aerogel or carbon aerogel. In particular, any suitable glycol including, but not limited to, ethylene glycol methyl ether methacrylate, poly(ethylene glycol) methyl ether methacrylate can be used.

[0150] In some embodiments, the individual silicon particles are heterogeneously dispersed throughout the three-dimensional carbon network. In some embodiments, the individual silicon particles are homogeneously dispersed throughout the three-dimensional carbon network. The expression "homogeneously dispersed" refers to the distribution of Si particles throughout the three-dimensional carbon network without significant variation in local concentration across the accessible network surface.

[0151] In some embodiments, about 30 wt% to about 70 wt%, about 20 wt% to about 50 wt% of the dispersed individual silicon particles within the plurality of silicon particles are in an aggregated state. In some embodiments, 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 are in an aggregated state. In some embodiments, the homogeneously distributed Si particles can refer to the distribution of a 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 in an aggregated state within the plurality of silicon particles.

[0152] sacrificial layer In an exemplary embodiment, the composite material can include a sacrificial material or a layer of a sacrificial material. Within the scope of the context of the present disclosure, the terms "sacrificial material" or "sacrificial layer" refer 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 be decomposed when exposed to high temperature or high stress and / or continuous stress. In some embodiments, the sacrificial material layer can be disposed on an outer surface, e.g., an outer surface of a core portion of a multi-layer material, or an outer surface, e.g., an outer surface of a multi-layer material.

[0153] The sacrificial layer can be selected from the group consisting of siloxane, polyolefin, polyurethane, phenolic resin, melamine, cellulose acetate, and polystyrene. In some cases, the material layer is in the form of a foam. In some embodiments, the sacrificial material can be worn away by being exposed to mechanical (such as periodic) loads. In some embodiments, the sacrificial layer decomposes after being exposed to a single mechanical, chemical, and / or thermal event.

[0154] In some embodiments, the onset temperature of chemical decomposition of the sacrificial material layer ranges from about 100°C to about 700°C, from about 100°C to about 500°C, from about 200°C to about 400°C.

[0155] The polymer for use in the sacrificial layer can be selected from a variety of thermoplastic resins, mixtures of thermoplastic resins, or thermosetting resins. Examples of thermoplastic resins that can be used include polyacetal, polyacrylic resin, styrene acrylonitrile, polyolefin, acrylonitrile-butadiene-styrene, polycarbonate, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polyamide, for example, but not limited to, nylon 6, nylon 6,6, nylon 6,10, nylon 6,12, nylon 11 or nylon 12, polyamideimide, polyarylate, polyurethane, ethylene propylene rubber (EPR), polyarylsulfone, polyethersulfone, polyphenylene sulfide, polyvinyl chloride, polysulfone, polyetherimide, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyether ketone, polyether ether ketone, polyether ketone ketone, etc., or combinations including at least one of the aforementioned thermoplastic resins.

[0156] Examples of mixtures 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 alloy, polyethylene terephthalate / polybutylene terephthalate, styrene-maleic anhydride / acrylonitrile-butadiene-styrene, polyether ether ketone / polyethersulfone, styrene-butadiene rubber, polyethylene / nylon, polyethylene / polyacetal, ethylene propylene rubber (EPR), etc., or combinations including at least one of the aforementioned mixtures.

[0157] Examples of polymer thermosetting resins that can be used for the sacrificial layer include polyurethane, epoxy, phenolic resin, polyester, polyamide, silicone, etc., or combinations containing at least one of the aforementioned thermosetting resins. Mixtures of thermosetting resins as well as mixtures of thermoplastic resins and thermosetting resins can be used.

[0158] Lithium-ion battery A basic embodiment of a lithium-ion battery includes a cathode, an anode that is electrically connected to the cathode, an electrolyte disposed between the anode and the cathode, and a separator similarly disposed between the anode and the cathode.

[0159] The electrolyte is an ion-conductive material and may contain a solvent, an ionic liquid, a metal salt, ions such as metal ions or inorganic ions, a polymer, a ceramic, and other components. The electrolyte may be an organic solid or an inorganic solid or a liquid, such as a solvent containing a dissolved salt (e.g., a non-aqueous solvent). Examples of non-aqueous electrolytes include organic solvents such as cyclic carbonates, linear carbonates, fluorinated carbonates, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and mixtures thereof. Examples of salts that can be contained in the electrolyte include lithium salts such as LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y-1(SO2), (where x and y are natural numbers), LiCl, LiI, and mixtures thereof. In some embodiments, the liquid molecules include an electrolyte solvent (electrolyte). The electrolyte solvent of the present disclosure can be selected from any of the aforementioned suitable electrolytes. In particular, 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 combinations thereof.

[0160] The separator is typically a thin, porous or semi-permeable insulating film having high ion permeability. The separator can be made of a polymer such as an olefin-based polymer (e.g., polyethylene, polypropylene, and / or polyvinylidene fluoride). When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte can also act as a separator.

[0161] The anode is composed of an active anode material that participates in the electrochemical reaction during the operation of the battery. Examples of anode active materials include elemental materials such as lithium, alloys containing Si and Sn or other lithium compounds, and intercalation host materials such as graphite. By way of example only, the anode active material may include lithium, its alloys, or metals and / or semimetals that can be alloyed with its oxides. Metals and semimetals that can be alloyed with lithium include Si, Sn, Al, Ge, Pb, Bi, and Sb. For example, oxides of metals / semimetals alloyable with lithium are lithium titanate, vanadium oxide, lithium vanadium oxide, SnO2, or SiO x (0 < x < 2) may also be possible.

[0162] The cathode consists of an active cathode material that participates in the electrochemical reaction during the operation of the battery. The active cathode material may be a lithium composite oxide and may include layered materials such as LiCoO2, olivine-type materials such as LiFePO4, spinel-type materials such as LiMn2O4, and similar materials. Spinel-type materials include those having a structure similar to natural spinal LiMn2O4. This contains a small amount of nickel cations in addition to lithium cations and optionally also contains anions other than manganate. By way of example, such materials have the formula LiNi (0.5-x) Mn 1.5 M x O4 (0 ≤ x ≤ 0.2, M is Mg, Zn, Co, Cu, Fe, Ti, Zr, Ru, or Cr).

[0163] Within the scope of 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., a LIB) can support before its capacity drops below about 80% of its original rated capacity. Cycle life can be affected by various factors, such as the mechanical strength of the underlying substrate (e.g., carbon aerogel) and the maintenance of the interconnectivity of the aerogel. Note that these factors, which actually remain relatively invariant over time, are a surprising aspect of certain examples of the present disclosure. Cycle life can be determined by methods known in the art, including, but not limited to, a cycle test in which a battery cell is subjected to repeated charge / discharge cycles at a predetermined current rate and operating voltage. Within the scope of the context of the present disclosure, measured values of cycle life are obtained according to this method unless otherwise specified. An energy storage device such as a battery or its electrodes 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 within a range between any two of these values.

[0164] The present disclosure includes an electrical energy storage device having at least one anode including a composite material of the present technology as described herein, at least one cathode, and an electrolyte having lithium ions. The electrical energy storage device may have an initial cycle efficiency (i.e., the Coulombic efficiency of the cell from the first charge and discharge) of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, any intervening value (e.g., 65%), or a range between any two of these values (e.g., in the range of about 30% to about 50%). As previously described herein, the 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.

[0165] According to different embodiments, the composite material of the present disclosure can be applied to both the positive and negative electrodes of an electrochemical energy storage device or to an individual electrode (either the positive or negative electrode). In various embodiments, the cathode, anode, or solid electrolyte material is coated with the composite material of the present technology.

Examples

[0166] The following examples are included to demonstrate preferred embodiments of the present technology. However, those skilled in the art will understand that, in view of the present disclosure, many changes can be made in the specific embodiments disclosed, and still obtain similar or analogous results without departing from the spirit and scope of the present technology.

[0167] 1.1 Oxidation of Silicon Particles Commercially available silicon particles may or may not include oxidized (partially or fully) silicon particles. Thus, depending on the surface functional groups of the silicon particles provided by the commercial supplier, the oxidation process provided herein is optional.

[0168] Silicon particles (available from Evonik; 10 - 100 g, 100 - 3000 nm) were heated at a temperature range of 400 - 800 °C for 1 - 5 hours under moisture, or dispersed in 10 - 1000 mL of 0.1 - 5 M sulfochromic acid or 10 - 1000 mL of 1 - 10 M H2O2 (hydrogen peroxide). For Si dispersion, while stirring at a constant rate, it was heated to 50 - 120 °C for 1 - 10 hours 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 hours of stirring of the solution, the solution was cooled to room temperature and centrifuged to obtain oxidized silicon particles. The obtained silicon particles were washed 3 - 5 times with water having a volume of 100 - 3000 mL to remove residual acid and dried for 3 - 10 hours under ambient conditions. The decrease in band intensity at 2105 and 1993 cm -1 and the increase in band intensity at 1052 cm -1 As demonstrated by, the surface oxidation was confirmed by IR spectrum (Figure 5). The oxidation by heating the dry powder can also be confirmed by the mass increase after treatment.

[0169] 1.2 Synthesis of Si particles coated with sacrificial layer The acidified silicon particles (10 grams) were dispersed in 50 mL of ethanol. To prevent aggregation of the silicon particles, the dispersion was sonicated for 30 minutes. Next, 1 gram of AEAPTMS was added to the dispersion, and the dispersion was stirred for 240 minutes while controlling the dispersion temperature at 70 °C on a hot plate. After cooling the dispersion to room temperature, 0.5 gram of the initiator 4,4′-azobis(4-cyanovaleric acid) was added to the dispersion, and it was stirred for an additional 240 minutes. Next, the dispersion was allowed to stand overnight to precipitate the silicon particles, after which the clear solvent on the surface was poured out, and the remaining silicon slurry was dispersed in 67 mL of water by stirring at 600 RPM for 5 minutes. The monomer methyl methacrylate (25.3 grams) was added to the dispersion, and it was stirred on a hot plate at 500 RPM for 60 minutes while controlling the dispersion temperature at 80 °C. Next, the stirring speed was decreased to 300 RPM, and after 60 minutes, it was increased to 500 RPM. After the dispersion was stirred for an additional 180 minutes, 2.6 grams of the polymer modifier methacrylic acid (hydroxyethyl) was added to the dispersion. The dispersion temperature was changed to 70 °C and stirred overnight. The synthesis of silicon particles with a sacrificial polymer coating was carried out the next morning. As shown in Figure 5, when the silicon particles coated with PPMA were analyzed by IR, no characteristic peak of the Si-H bond was observed between 1950 and 2200 cm -1 and a good coating of the silicon surface by the PMMA layer was revealed.

[0170] 1.3 Synthesis of composite Si / C material containing voids In a typical synthesis, 12.7 g of p-phenylenediamine (PDA) was added to 313 g of water in a beaker and stirred for 30 minutes until all of the PDA had dissolved. Next, 28.5 g of triethylamine was added to the solution and stirred for 10 minutes. Thereafter, 25.5 g of benzene-1,2,4,5-tetracarboxylic dianhydride was added to the above solution and stirred for 4 hours. Next, Si particles modified with 1.5 - 25 g of PMMA were added to the above solution and stirred for 10 minutes. Next, acetic anhydride (51.4 g) was poured into the above suspension, stirred for 50 seconds, and then the suspension was poured while mixing at 3600 rpm into 1200 mL of mineral spirit containing a surfactant. Next, the resulting emulsion was aged overnight and then filtered. After the filtration was completed, the obtained material was rinsed several times with ethanol and dried in an oven at 700 °C. Although the present disclosure has been particularly illustrated and described with reference to its exemplary embodiments, as will be understood by those skilled in the art, various changes in form and detail may be made therein without departing from the scope of the technology encompassed by the appended claims.

[0171] Although the present disclosure has been particularly illustrated and described with reference to its exemplary embodiments, as will be understood by those skilled in the art, various changes in form and detail may be made therein without departing from the scope of the technology encompassed by the appended claims.

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