Carbon-silicon composites and methods of producing same

Abstract

Disclosed herein is a method for producing a carbon-silicon composite. The method comprises providing a reaction mixture comprising a carbon-silica-based precursor and an aluminum reducing agent; heating the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature at which a reaction causing the silica to be reduced is initiated; controlling the reaction conditions, thereby preventing the reaction mixture from reaching a temperature at which thermal runaway may occur; and separating the resulting carbon-silicon composite material.

Description

Technical Field

[0001] The present invention relates to a method for producing a carbon-silicon composite material, specifically a method for producing carbon-silicon nanoparticles for use in batteries. Background Art

[0002] Recently, there has been a significant interest in mesoporous (or nanoporous) silicon for Li-ion energy storage systems. Using silicon powder with an appropriate ultrafine morphology as an anode material in a Li-ion battery (LIB) can significantly increase the battery capacity. However, using silicon as an anode material may cause an excessive volume increase during the lithiation of the silicon-based anode. To minimize the resulting impact on the battery structure and integrity, many strategies centered around using a carbon-silicon composite material as the anode material have been proposed. In such strategies, silicon nanoparticles (Si-NP) are typically combined with carbon, aiming to improve or accommodate the volume change during the lithiation / delithiation cycle and provide enhanced electrical conductivity. Generally, such carbon-silicon composite materials are prepared by pyrolysis, mixing, and / or grinding of carbon and Si-NP. However, such methods are limited, including higher costs due to additional steps required to introduce carbon, and the inability to control the structure of the carbon-silicon composite material. Producing Si-NP through conventional routes such as grinding, magnesium reduction, laser ablation, etc. also has problems of high quality and / or cost. Therefore, there is a need for a novel and more affordable method for producing carbon-silicon composite materials that can be used in Li-ion batteries and other applications. Summary of the Invention

[0003] In a first aspect, the present invention provides a method for producing a carbon-silicon composite material. The method comprises:

[0004] providing a reaction mixture comprising a carbon-silica-based precursor and an aluminum reducing agent;

[0005] heating the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature that initiates a reaction to reduce the silica;

[0006] controlling the reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway may occur; and

[0007] separating the resulting carbon-silicon composite material.

[0008] The present invention provides an improvement to the method disclosed in International Patent Application No. PCT / AU2021 / 050400, as the method enables the production of carbon-silicon composites starting from a carbon-silica-based precursor. The method disclosed in PCT / AU2021 / 050400 provides for the reduction of silica and metal oxides, but it was expected that the presence of carbon in the reaction mixture would prevent or at least significantly impede the reduction reaction. It was expected that the presence of carbon would reduce the contact surface area between reducible silica and reduced aluminum, thus hindering the reaction and making it difficult, if not impossible, to achieve any significant degree of reduction. However, the inventors have surprisingly and unexpectedly found that this is not the case. The inventors have found that the beneficial effects of these methods can still be achieved despite the presence of a significant amount of (non-reducible) carbon in the reaction mixture. Accordingly, the present invention can be used to produce carbon-silicon composites having a nano-morphology and structure suitable for use in Li-ion batteries, which cannot be obtained using conventional aluminothermic reduction techniques (and indeed, other manufacturing techniques). The content of PCT / AU2021 / 050400 is incorporated herein by reference in its entirety.

[0009] The present invention provides a method for producing carbon-silicon composites at low temperature by directly in-situ generating silicon nanoparticles starting from a silica-carbon-based precursor. As will be described below, the by-products can include aluminum chloride oxide, which is easier to separate than the conventional metal-oxide by-products typically produced by metal-thermic reactions. Accordingly, the present invention enables the direct production of a pure carbon-silicon composite substantially free of metal oxides, and the yield can be up to more than 99%.

[0010] The low-temperature aluminothermic reduction of silica (and other silicon oxides) is attractive because it enables reduction using solid-state aluminum reactants, has less energy consumption, and has the potential to produce reaction products having nano-morphologies and structures that are not typically obtainable using conventional aluminothermic reduction. Additionally, many aluminum reducing agents (e.g., Al powder) are safe, low-cost, and readily available, making these materials attractive from a techno-economic perspective.

[0011] Further, the low-temperature reduction of C-SiO2 will allow for the production of all-carbon or graphite-silicon composites, silicon-impregnated carbon materials, C-silicon nanoparticles, or microporous C-silicon starting from silica precursors having a morphology that is highly suitable for applications related to Li-ion energy storage systems, such as those described above.

[0012] Accordingly, at least in the preferred embodiments, the present invention can significantly reduce the complexity and steps required to produce C-Si composites; C-Si is directly produced at low temperatures, allowing for the production of C-Si composite powders with improved engineering properties, as well as new products with unique properties imparted by the precursor materials and production techniques. Additionally, in addition to providing a mechanism for controlling the properties of the carbon-silicon product, the methods disclosed herein also reduce production costs. In addition to the steps required to combine carbon and silicon to produce the composite material, the temperatures reached in conventional thermite reactions and the complexity of CVD systems also preclude such advantages.

[0013] In some embodiments, the carbon-silica-based precursor may be provided in one or more of the following forms: a carbon-silica composite, a mixture of carbon powder and silica-based powder, carbon-coated silica powder, a carbon cage encapsulating silica-based precursor particles, carbon nanotubes, or thin graphite flakes or graphene blended or coated onto the particles with silica particles, a reducible carbon-silicon-oxygen-based powder, a porous carbon-based structure impregnated with silica, a carbon-based powder impregnated with silica, a graphite powder impregnated with silica, a charcoal powder impregnated with silica, pyrolyzed rice husk, a powder of natural graphite containing silica, or a mixture thereof.

[0014] The inventors have realized that the presence of silicon nanoparticles or sub-nanoparticles embedded within the graphite used in LIBs can be advantageous as it increases the electrode capacity; in LIBs, the loading capacity of silicon is 10 times that of carbon. The inventors have found that by directly reducing carbon-silica precursor chemicals with appropriate structures and morphologies, carbon-silicon composites such as silicon-impregnated graphite, as well as silicon nanoparticles or silicon nanostructures coated or encapsulated within graphene / graphite materials, can be produced.

[0015] Furthermore, natural graphite is a key component for manufacturing anodes of lithium-ion batteries (LIBs). This material is mined in multiple countries around the world and then processed to remove impurities and increase the carbon content to approximately 99% before being used as an anode for LIBs. Purification can involve crushing and grinding, froth flotation, acid leaching using sulfuric or hydrochloric acid, and heat treatment, and these processes are generally able to increase the purity to around 95%. For some grades, increasing the purity above 95% is highly demanding and may require the use of highly corrosive chemicals such as HF in order to remove residual silica and magnesia. HF is very dangerous and extreme measures are required to control OH&S aspects and potential environmental impacts. Therefore, a novel and affordable method is needed to remove residual impurities from graphite materials and / or convert said impurities into a form suitable and / or compatible for use in Li-ion batteries.

[0016] The present inventors have realized that for natural graphite, if the silica present in the material can be converted to silicon, the final purified product can have a higher value. As outlined elsewhere, when added to the graphite of a Li-ion battery anode, silicon nanoparticles provide a significant capacity enhancement. Therefore, it would be highly advantageous to convert the silica impurities in natural graphite to silicon and use the resulting material as an anode material rather than removing the silica through hazardous chemical processing. Additionally, it is possible to reduce and / or remove other impurities present, such as magnesium oxide, iron oxide, and other metal-based impurities, while converting the silica to silicon.

[0017] In some embodiments, the carbon-silica-based precursor can be provided in the form of a powder, flake, fiber, or microparticle.

[0018] In some embodiments, the method can further comprise pyrolyzing a mixture of a silica-containing substance and a carbon-based compound to produce the carbon-silica-based precursor. The carbon-based compound can be selected, for example, from the group consisting of one or more of the following: organic compounds, polymers, carbohydrates, saccharide compounds, glucose, sucrose, biomass, and hydrocarbons. In some embodiments, the carbon-based compound can be applied to the silica-containing substance by physical deposition (e.g., physical vapor deposition), chemical deposition (e.g., chemical vapor deposition), wet processing, or any other means that results in the formation of a powder containing silica with a carbon-based compound.

[0019] In some embodiments, the method can further comprise impregnating a carbon-based material with a liquid precursor containing silicon and then treating the resulting material to produce a carbon-silica-based precursor in the form of a graphite-silica powder. The liquid precursor containing silicon can be selected, for example, from one or more of the following: silicic acid, sodium silicate, and silanolates. In some embodiments, the carbon-based material is selected from one or more of the following: graphite, synthetic graphite, natural graphite, activated carbon, graphene, carbon nanotubes, graphite-mineral mixtures, charcoal powder, pyrolyzed rice husk, carbonized materials produced by pyrolyzing organic materials, graphite or carbonized materials produced by reacting organic materials with acids, and anode-grade graphite powder.

[0020] In some embodiments, the silica in the carbon-silica-based precursor can be provided in the form of a powder, discrete microparticles, microparticles impregnated within a carbon structure, or in other morphologies containing silica.

[0021] In some embodiments, the silica in the carbon-silica based precursor can be provided in one or more of the following forms: silica nanopowder, fumed silica, precipitated silica, silica fume, silica fiber, silicate, borosilicate, soda glass, silica-based minerals such as halloysite and kaolinite, synthetic mica, mica, and crystalline silica.

[0022] In some embodiments, the particle size of the silica in the carbon-silica based precursor can be less than 100 μm, preferably less than 10 μm, more preferably less than 5 μm, and still more preferably less than 500 nm. In some embodiments, the particle size of the silica in the carbon-silica based precursor can even be less than 100 nm.

[0023] In some embodiments, the solid aluminum chloride can be provided in the form of a powder or fine grains of aluminum chloride with a particle size less than 5 mm. In some embodiments, the aluminum chloride can be included in the reaction mixture.

[0024] In some embodiments, during heating, the gaseous aluminum chloride can be made to flow above or through the reaction mixture.

[0025] In some embodiments, the amount of aluminum chloride provided can be between about 1 wt% and about 500 wt% of the weight of the carbon-silica based precursor. The amount of aluminum chloride provided can be, for example, between about 10 wt% and about 300 wt% of the weight of the carbon-silica based precursor, between about 50 wt% and about 300 wt%, between about 100 wt% and about 200 wt%, between about 100 wt% and about 500 wt%, or between about 100 wt% and about 150 wt%.

[0026] In some embodiments, the aluminum reducing agent can be aluminum or an aluminum alloy.

[0027] In some embodiments, the aluminum reducing agent can be provided in the form of a powder or flakes with a particle size less than about 50 µm in at least one dimension (e.g., less than about 40 µm, less than about 30 µm, or less than about 20 µm). However, in alternative embodiments, the particle size can be up to 100 μm or even up to 500 μm.

[0028] In some embodiments, the amount of the aluminum reducing agent in the reaction mixture is between 1% and 1000% of the weight of the silica in the carbon-silica-based precursor, and preferably between 5 wt% and 500 wt% of the weight of the silica in the carbon-silica-based precursor.

[0029] In some embodiments, the temperature to which the reaction mixture is heated can be below 800 °C, preferably below 600 °C or preferably below 550 °C.

[0030] In some embodiments, the reaction mixture can be heated in a non-reactive atmosphere and preferably in an inert atmosphere (i.e., an atmosphere that is inert to the reactants, which can include a CO2 or N2 atmosphere).

[0031] In some embodiments, the reaction mixture can be heated at a pressure between about 0.8 atmospheres and 1.2 atmospheres, preferably at atmospheric pressure. Reactions carried out at atmospheric pressure or near atmospheric pressure require less complex equipment, which is safer and generally less expensive to operate.

[0032] In some embodiments, the reaction conditions can be controlled by one or more of the following: gradually feeding one or both of the carbon-silica-based precursor and the aluminum reducing agent into the reaction mixture as the reaction mixture is heated; externally cooling the reaction mixture; cooling the reaction mixture with an excess of solid aluminum chloride; and adding a heat load regulator to the reaction mixture. For example, gradually introducing the reactants (specifically Al and AlCl3) into the reaction mixture prevents thermal runaway due to the limited and controllable availability of the reactants at any given time.

[0033] In some embodiments, alloy additives and metal-based catalysts can be included in the reaction mixture. For example, in some embodiments, compounds based on one or more of Li, B, Na, Mg, Al, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Hf, Ta, W, Re, Os, Pt, Au, and Bi can be included in the reaction mixture. In some of such embodiments, the metal-based catalyst or additive can be used to induce the formation of a carbon-silicon composite material in the form of carbon-silicon nanowires. For example, the use of metal-based catalysts such as Ag, AgCl, Zn, and ZnCl2 enables the formation of carbon-silicon nanowires.

[0034] In some embodiments, the carbon-silicon composite may comprise silicon nanoparticles encapsulated within a carbon-based structure. In such embodiments, the method may further comprise processing the carbon-silica-based precursor to control the volume of void space within the carbon-based structure. In some of such embodiments, the carbon-based structure may be a carbon-based shell. In some of such embodiments, the core may comprise void space that occupies from 0.5% to 75% (such as 0.5% to 50%) of the total volume of the core.

[0035] In some embodiments, the implementation of the method may result in the carbon-silicon composite comprising residual aluminum between 0.01 wt% and 70 wt%. The inventors believe that the composite comprising residual aluminum is a unique feature of the present invention and may endow the composite with useful functions. For example, the presence of residual aluminum oxide may help improve the performance of the material as an anode of a Li-ion battery. In addition, since the solubility of aluminum in metallic silicon is negligible, the presence of residual metallic aluminum does not impede the ability of silicon to store lithium, while increasing the conductivity of the anode.

[0036] In some embodiments, the implementation of the method may result in the carbon-silicon composite comprising a silicon compound having an average composition corresponding to SiOx, where x is between 0 and 1.9.

[0037] In a second aspect, the present invention provides carbon-coated silicon nanoparticles produced by the method according to the first aspect, wherein the silicon nanoparticles are in the form of microparticles having an irregular shape and an average particle size between 10 nm and 500 nm, and comprise aluminum between 0.01 wt% and 70 wt%.

[0038] In a third aspect, the present invention provides a carbon-silicon composite produced by the method according to the first aspect, wherein the composite comprises particles having a silicon-containing core and a coating, the thickness of the coating being between 1 nm and 300 nm and containing at least 50 wt% silicon.

[0039] In a fourth aspect, the present invention provides a carbon-silicon composite produced by the method according to the first aspect, wherein the composite is in the form of a core-shell structure, wherein the core comprises void space that occupies from 0.5% to 75% (such as 0.5% to 50%) of the total volume of the core and a silicon-based material having a metallic silicon content of less than 99 wt%; and the shell comprises a porous or non-porous carbon coating having a thickness between 0.01 nm and 1 μm.

[0040] In a fifth aspect, the present invention provides a method for reducing silica in a silica-based precursor. The method comprises:

[0041] Coat a silica-based powder with carbon to produce a carbon-coated silica-based precursor;

[0042] Provide a reaction mixture comprising the carbon-coated silica-based precursor and an aluminum reducing agent;

[0043] Heat the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature that initiates a reaction to reduce the silica;

[0044] Control the reaction conditions so as to prevent the reaction mixture from reaching a temperature at which thermal runaway may occur; and

[0045] Separate the reaction product including the reduced silica.

[0046] Specific embodiments of the method of the fifth aspect will be described below. In a first embodiment, the method comprises:

[0047] Mix a carbon-based liquid-soluble compound with a solvent and a silica-based precursor; and

[0048] Evaporate the solvent to produce a silica-based precursor coated with a carbon-based compound;

[0049] Pyrolyze the silica-based precursor coated with the carbon-based compound to produce a carbon-coated silica-based precursor;

[0050] Heat a reaction mixture comprising the carbon-coated silica-based precursor and an aluminum reducing agent to a temperature that initiates a reaction to reduce the SiO2 in the presence of gaseous aluminum chloride at substantially atmospheric pressure;

[0051] Control the reaction conditions so as to prevent the reaction mixture from exceeding a temperature of about 650 °C; and

[0052] Separate the reaction product including silicon.

[0053] In a second embodiment, the method comprises:

[0054] Form a reaction mixture of carbon, a silica-based powder, an aluminum reducing agent, and a metal catalyst, wherein the weight of the catalyst is between 5% and 50% of the weight of the silica, and wherein the catalyst induces the formation of silicon nanowires;

[0055] Heat the reaction mixture in the presence of gaseous aluminum chloride at atmospheric pressure to a temperature that initiates a reaction to reduce the SiO2;

[0056] Control the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650 °C; and

[0057] Separate the reaction product comprising carbon-silicon nanowires.

[0058] The second embodiment may further comprise impregnating a carbon-based material with a silicon-containing liquid precursor and then treating the resulting material to produce the silica-based powder in the form of a graphite-silica-based powder.

[0059] In a sixth aspect, the present invention provides a method for producing a carbon-silicon composite material. The method comprises:

[0060] Providing natural graphite powder containing 0.1% to 20% by weight of silica; and

[0061] Mixing and heating the powder with a reducing agent containing aluminum in the presence of solid and / or gaseous aluminum chloride, thereby reducing at least a portion of the silica to silicon and producing a carbon-silicon composite powder, as well as by-products comprising Al2O3 and / or AlOCl; and

[0062] Optionally separating the carbon-silicon composite from the by-products.

[0063] In a seventh aspect, the present invention provides a carbon-silicon composite material produced by the method according to any one of the first, fifth, and sixth aspects.

[0064] In an eighth aspect, the present invention provides a silicon-impregnated carbon-based composite material produced by the method according to any one of the first, fifth, and sixth aspects, wherein the carbon-based material in the carbon-silica-based precursor is graphite, pyrolytic biocarbon, or activated carbon.

[0065] In a ninth aspect, the present invention provides a natural graphite-silicon composite material produced by the method according to the first or sixth aspect, wherein the silica impurities in the natural graphite are partially or fully converted to silicon to produce a compound of the natural graphite-Si composite material, wherein the content of silicon is between 0.5 wt% and 25 wt%.

[0066] In a tenth aspect, the present invention provides a carbon-silicon composite material produced by the method according to any one of the first, fifth, and sixth aspects, wherein the silica in the pyrolytic carbon-silica precursor compound is reduced to silicon; the content of silicon is between 1 wt% and 25 wt%.

[0067] In an eleventh aspect, the present invention provides a carbon-silicon composite material composed of carbon, silicon, and aluminum.

[0068] In a twelfth aspect, the present invention provides a carbon-silicon composite material produced solely from rice husks or natural graphite.

[0069] In some embodiments of the eleventh and twelfth aspects, the carbon-silicon composite material is produced using the method of the present invention.

[0070] Also disclosed herein is a method for producing a carbon-silicon composite material. The method comprises:

[0071] - providing a mixture of a silica-based powder and a carbon-based material; the mixture may be in the form of a blended mixture of a silica-based powder and a carbon-based powder, or in the form of a powder of a carbon-coated silica precursor or a powder of a silica-impregnated carbon-based material, or in the form of a powder of natural graphite containing silica-based impurities; and

[0072] - reacting the mixture with an aluminum-based reducing agent comprising aluminum powder and aluminum chloride at a temperature between 300 °C and 650 °C; the aluminum chloride being in solid or gaseous form; and

[0073] - the reaction step resulting in the formation of a powder mixture of a reduced silica-carbon product and an aluminum-based by-product; the product containing carbon and a silicon compound SiO x , where x is between 0 and 1.9; and

[0074] - separating the reaction product;

[0075] - The carbon-based material may be in any form of a phase, including graphite, synthetic graphite, natural graphite, activated carbon, graphene, carbon nanotubes, charcoal, graphite-mineral mixtures, carbon-based minerals, graphite materials produced by pyrolysis of organic materials, graphite materials produced by reacting organic materials with acids, anode-grade graphite powder, charcoal powder, powder of pyrolyzed rice husks, or synthetic graphite. The carbon-based material may be in the form of flakes, spherical powders, porous graphite powders, graphene, carbon nanotubes, carbon nanostructures, and it may be coated or uncoated; and

[0076] - The carbon-based material may be in the form of a coating on the silica-based precursor particles, a carbon cage encapsulating the silica-based precursor particles, thin graphite flakes or graphene blended with or coated onto the particles. Additionally, the carbon-based material may be in the form of a porous structure with silica or a silicon-oxygen-based compound impregnated in the pores of the carbon-based material, or simply in the form of a powder mixed with the silica-based precursor.

[0077] Also disclosed herein is a method for producing a carbon-silicon composite material. The method comprises:

[0078] - Providing reactant powder, the reactant powder comprising a silica-based compound and a carbon / graphite-based compound; and

[0079] - Mixing, heating and reacting the reactant powder with an aluminum-based reducing agent comprising aluminum and aluminum chloride to reduce at least a portion of the silica to silicon; and

[0080] - Separating the silicon-carbon product.

[0081] Also disclosed herein is a method for producing a carbon-silicon composite material. The method comprises:

[0082] - Providing a first reaction mixture, the first reaction mixture comprising a silica-based powder mixed with or coated with a carbon-based compound; and

[0083] - Processing the reaction mixture to convert the carbon-based compound into a stable carbon-based material; and

[0084] - Mixing, heating and reacting the resulting mixture of carbon-based material-silica-based powder with an aluminum-based reducing agent comprising aluminum and aluminum chloride to reduce at least a portion of the silica to silicon; and

[0085] - Separating the silicon-carbon product.

[0086] In some embodiments, the silica-based powder is coated with a carbon-based compound.

[0087] In some embodiments, before reducing the silica to silicon, the coated powder is first processed to produce a stable carbon-based coating around the silica-based powder. Examples of suitable ways include coating with a polymer or other organic compound and then appropriately carbonizing, or other coating techniques such as chemical vapor deposition and physical vapor deposition.

[0088] In some embodiments, the silica-based powder is coated with a compound based on an organic material, and the compound can be pyrolyzed to produce an intermediate product of a carbon-coated silica-based powder. Examples of suitable organic compounds include sugars and glucose.

[0089] In some embodiments, the silica-based powder is coated with glucose, and then the glucose is pyrolyzed to produce an intermediate product of a carbon-coated silica-based powder.

[0090] In some embodiments, an organic compound such as a carbohydrate or saccharide compound is first used to coat a silica-based powder in a suitable manner. Then the coated powder is pyrolyzed to produce an intermediate product of a carbon-coated silica-based powder.

[0091] In some embodiments, the carbon coating over the SiO2-based precursor powder is discontinuous.

[0092] In some embodiments, the carbon coating over the Si-based particulate product is discontinuous.

[0093] In some embodiments, the carbon coating over the SiO2-based precursor powder is porous.

[0094] In some embodiments, the carbon coating over the Si-based particulate product is porous.

[0095] In some embodiments, a soluble silicon-based compound is impregnated into graphite powder and then processed to convert it into silica, producing an intermediate precursor in the form of silica-impregnated graphite powder. Then, the intermediate precursor is reacted with aluminum-aluminum chloride to produce an intermediate product in the form of silicon-impregnated graphite powder and an aluminum-based byproduct. Then the intermediate product is processed to remove the byproduct.

[0096] In an example of this embodiment, the soluble silicon-based compound is sodium silicate. The sodium silicate is first dissolved in water and then mixed with preferably porous graphite powder. Then an acidic reagent such as HCl is added to convert the silicate to aluminum hydroxide. Then the resulting mixture is calcined to convert the hydroxide to an oxide, and the resulting powder is thoroughly washed to remove the NaCl produced by the neutralization process. The remaining intermediate precursor powder consists of graphite powder and silica particles deposited on all available surfaces including the pores and outer surface of the graphite powder. Then, the intermediate precursor is reacted with aluminum-aluminum chloride to produce an intermediate product in the form of silicon-impregnated graphite powder and an aluminum-based byproduct. Then the intermediate product is processed to remove the byproduct.

[0097] In other embodiments, an intermediate precursor powder of silica-impregnated porous carbon can be produced by first impregnating an organic material with silica and then pyrolyzing / carbonizing to produce graphite powder impregnated with silica.

[0098] In some embodiments, the aluminum chloride can be provided in the form of solid aluminum chloride. The aluminum chloride can be provided in the form of a powder or fine grains with a particle size less than 5 mm. In some embodiments, the aluminum chloride powder can be included in the reaction mixture (e.g., premixed with the aluminum reducing agent). Here, the sublimation of AlCl3(s) helps to remove energy from the reactants and counteracts the effect of the exothermic energy generated by the reaction of Al - AlCl3 with SiO2.

[0099] In some embodiments, the aluminum chloride can be provided in the form of gaseous aluminum chloride. For example, the gaseous aluminum chloride can be made to flow above the heated reaction mixture.

[0100] In some embodiments, the temperature to which the reaction mixture is heated (i.e., to initiate the reduction reaction) can be below 800 °C, preferably below 600 °C or preferably between 200 °C and 600 °C. As described herein, a lower reaction temperature is preferred because the reaction product is not molten (and thus easier to purify) and can maintain the morphology of the reagents.

[0101] In some embodiments, the product further reacts with a reagent to reduce the volume of Si encapsulated with a carbon shell. Examples of suitable reagents include acids.

[0102] In some embodiments, the intermediate carbon - silica precursor reacts with a reagent to reduce the amount of Si encapsulated with a carbon shell or pores, and create voids in the shell or pores to allow the formation of aluminum oxychloride by - products, and then allow space for the final product of carbon - encapsulated silicon to expand during the lithiation of silicon.

[0103] In some embodiments, the silica - based precursor can include a metal additive, and then the product can include elemental metals, metal sub - oxides, alloys including metals, compounds including metals, metal - containing composites, or mixtures thereof.

[0104] In some embodiments, the reaction product can contain the product produced by reducing the precursor and one or more by - products of aluminum chloride, aluminum oxychloride, and aluminum oxide. In some embodiments, the reaction product can be further processed to separate the by - products from the product produced by reducing the precursor. In some embodiments, the by - product can include aluminum oxychloride, and the aluminum oxychloride can be separated from the reduced metal oxide by washing the reaction product in an aqueous medium.

[0105] In some embodiments, any gaseous aluminum chloride that is not consumed during the reaction can be condensed for beneficial reuse, such as for recycling back into the reaction mixture.

[0106] In some embodiments, heating the reaction mixture involves multiple heating steps and the formation of intermediate substances. Such embodiments will be described in further detail below.

[0107] In one embodiment of the method of the first aspect of the present invention, the silica-based precursor is SiO2, and the SiO2 is first processed to produce a C-SiO2 precursor powder. The aluminum reducing agent is aluminum or an aluminum alloy in the form of a solid powder. The reaction mixture is heated to an initiation temperature between about 200°C and 600°C (preferably between 300°C and 550°C), and the reaction conditions are controlled to maintain the temperature below about 650°C. The reaction product of such a method can be a composite material of carbon and silicon or a mixture of silicon and SiO2 with a particle size less than 500 nm. In some embodiments, the particles can be in the form of agglomerates with a size of up to 10 μm or more. In some other embodiments, the reaction product can include a mixture of silicon and Al2O3.

[0108] Also disclosed herein is a carbon-coated silicon powder produced according to the method described in the foregoing paragraph, wherein the silicon powder is in the form of fine particles having an irregular shape and an average particle size between 1 nm and 500 nm; and the composition includes Al in a level between 0.01 wt% and 70 wt%.

[0109] Also disclosed herein is a carbon-silicon composite powder having fine particles composed of carbon cages, the carbon cages having cavities containing silicon-based particles and void spaces, wherein the volume ratio of the voids to the silicon-based material can be between 1% and 80%. The carbon cages are composed of a graphite carbon material made of graphite, graphene, or a related composition and can be porous. The thickness of the cage walls can be between 0.01 nm and 10 μm, and preferably between 0.1 nm and 100 nm, and more preferably between 0.1 nm and 10 nm. The particle size of the C-Si fine particles produced according to this aspect can be between 1 nm and 50 μm. For this aspect, the method includes the steps of producing a carbon-coated silica precursor, then etching a portion of the coated silica, and reacting the resulting material according to any of the embodiments.

[0110] Also disclosed herein is a method for reducing SiO2 in a SiO2-containing precursor. The method comprises:

[0111] - providing a reaction mixture comprising a carbon-coated precursor containing SiO2 and an aluminum reducing agent; and

[0112] - At atmospheric pressure, in the presence of gaseous aluminum chloride, heat the reaction mixture to a temperature that initiates a reaction to reduce the SiO2; and

[0113] - Control the reaction conditions such that the temperature of the reaction mixture does not exceed about 650 °C; and

[0114] - Separate the reaction product comprising silicon.

[0115] Also disclosed herein is a carbon-silicon composite powder, which consists of a mixture of graphene or graphite powder and silicon nanoparticles, wherein the powder is produced by reducing carbon-coated silica powder with Al-AlCl3.

[0116] Also disclosed herein is a method for producing a carbon-silicon composite, wherein a mixture of silica and a carbon-based precursor is first reduced with an acid to produce a silica-carbon mixture, and then the mixture is reduced to Si-C using Al-AlCl3.

[0117] Also disclosed herein is a product in the form of graphite powder impregnated with silicon. The silicon may be in the form of nanoparticles or nanowires.

[0118] In one embodiment for producing graphite powder impregnated with silicon nanowires, the method comprises the main step of depositing a metal-based catalyst within the pores of graphite particles, and then adding a silica-based precursor and processing the resulting material according to any of the foregoing or upcoming embodiments or aspects.

[0119] Considering the similarity between aluminothermic and magnesiothermic processes, the inventors believe that the teachings of the present invention will also be applicable to a reducing agent using Mg - aluminum chloride, wherein a magnesium reducing agent is used instead of an aluminum reducing agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] The features, embodiments, and advantages of the present invention will become apparent from the following description of its embodiments, with reference to the accompanying drawings by way of example only, wherein:

[0121] Figure 1 A process schematic diagram of an exemplary embodiment showing the steps for reducing a C - SiO2-based precursor with Al in the presence of gaseous AlCl3 is shown.

[0122] Figure 2 A TEM micrograph of C - Si powder obtained using PVP coating is shown.

[0123] Figure 3 An XRD trace of C-coated Si powder in Example 10 is shown.

[0124] Figure 3 Shows the XRD trace of a pure Si sample obtained without a carbon coating in Example 10. Detailed Description

[0125] Here, unless otherwise clearly stated:

[0126] - The terms "aluminum reducing agent", "reducing Al agent", "reducing Al alloy", and "reducing Al powder" are used interchangeably and refer to powders of pure Al and Al-based alloys.

[0127] - "Based on" materials, such as base metals or alloys based on Al as a reducing agent, refer to materials containing at least 10% and preferably at least 50% of the specified component.

[0128] - The term "aluminum chloride" refers to chlorides of Al such as AlCl3 and Al2Cl6. In use, the term "aluminum chloride" or "aluminum chloride" or "AlCl3" includes any anhydrous metal chloride based on Al-Cl in both gaseous and solid forms.

[0129] - In use, the term "AlCl3(g)" refers to any aluminum chloride in gaseous or vapor form.

[0130] - In use, the term "AlCl3(s)" refers to any aluminum chloride in solid powder form.

[0131] - The term "AlOCl / Al2O3" means AlOCl and / or Al2O3.

[0132] - The terms "AlOCl" and "chloroaluminum oxide" are used interchangeably, and

[0133] - The terms "silicon oxide", "silicon dioxide", and "SiO2" refer to silicon oxide in both amorphous and crystalline forms.

[0134] - The terms "C-based coating", "carbon-based coating" are used to describe carbon-based coating compounds. "C-coated" and "carbon coating" are used to describe coatings based on pure carbon or stable carbon compounds.

[0135] Disclosed herein is a method for forming a carbon-coated silicon-based powder or a carbon-encapsulated silicon-based powder by reacting a powder mixture comprising a carbon-coated reducible precursor SiO2-based precursor and a reducing Al alloy (e.g., Al powder) in the presence of aluminum chloride to reduce the silicon dioxide partially or completely to silicon. The aluminum chloride is in the form of a solid powder or a gaseous / vapor form. In some embodiments, the aluminum chloride can be in the form of a liquid eutectic phase.

[0136] The reduction reaction between silica in the precursor and the reducing reactants Al and AlCl3 is exothermic, and the method includes procedures for controlling the reduction reaction and regulating the reaction rate to prevent thermal runaway and the accompanying reaction products.

[0137] The product of the method is a carbon- and Si-based powder, and the by-products can include aluminum chloride and chloroaluminum hydroxide and / or alumina. The chloroaluminum hydroxide / alumina by-products are discharged together with the product and can be a component of the powder product, or it can be separated by appropriate means. The chloroaluminum hydroxide by-products can be separated from base metals (such as Si powder) by washing in a suitable solvent (e.g., H2O or diluted HCl (H2O-HCl)).

[0138] The example form of the method of the present invention aims to significantly reduce the complexity and the number of steps, as well as the temperature required by conventional reduction techniques and other existing processes that require high temperature or high pressure. This is in addition to providing a way to control the volume of the void space within the carbon shell of the Si microparticles. The example form of the method of the present invention aims to provide powders of metal compounds with improved engineering properties and new products with unique properties inherited from the starting precursor oxides.

[0139] The present invention encompasses multiple aspects, and its specific forms and embodiments will be described below.

[0140] According to a first example, there is provided a method for directly producing a silicon-carbon composite by reducing a carbon-silica-based precursor chemical with a reducing agent based on Al in solid form and aluminum chloride in solid or gaseous / vapor form, preferably at atmospheric pressure, at a temperature below 800 °C, preferably below 600 °C, more preferably between 100 °C and 600 °C, still more preferably between 200 °C and 600 °C, still more preferably between 200 °C and 600 °C, and yet still more preferably between 200 °C and 550 °C, wherein the method includes:

[0141] - generating C-SiO2 by any available means, including blending C- and silica-based powders, impregnating carbon-based powders with silica, coating SiO2-based powders with an organic coating and then converting to carbon, or generating a porous graphite structure impregnated with silica; and

[0142] - mixing, heating and reacting a reactant mixture containing C-SiO2- and Al-based powders in the presence of solid or gaseous aluminum chloride; and

[0143] - the product of the method contains base metal-based compounds; and the by-products include AlOCl and / or Al2O3; and wherein

[0144] - The product of the method is optionally processed to remove by-products.

[0145] Examples of products include Si-impregnated graphite powder, C-coated metal silicon nanoparticles, C-Si-Ag nanoparticles, C-coated SiO2 particles coated with metal silicon, C-coated compositions corresponding to silicon monoxide (SiO or SiO x ), or mixtures thereof. Other examples include C shells encapsulating Si nanoparticles and C shells encapsulating porous Si microparticles.

[0146] According to a second example, there is provided a method for directly producing silicon-based microparticles encapsulated within a carbon / graphite structure, coating, or shell by reducing a carbon-coated solid precursor chemical based on base SiO2 with a reducing agent based on Al in solid form and aluminum chloride in solid or gaseous / vapor form, preferably at atmospheric pressure, at a temperature below 800 °C, preferably below 600 °C, more preferably between 100 °C and 600 °C, still more preferably between 200 °C and 600 °C, still more preferably between 200 °C and 600 °C, and yet still more preferably between 200 °C and 550 °C, wherein the method comprises:

[0147] - Coating a SiO2-based powder with a carbon-based compound and processing to produce a carbon / graphite coating C-SiO2 on the SiO2-based particles; and

[0148] - Optionally removing, etching, or dissolving part of the coated / encapsulated silica particles; and

[0149] - Mixing, heating, and reacting the resulting C-SiO2 powder with Al in the presence of solid or gaseous aluminum chloride; and

[0150] - The product of the method contains base metal-based compounds; and the by-products include AlOCl and / or Al2O3; and wherein

[0151] - The product of the method is optionally processed to remove by-products.

[0152] Examples of products include C-coated metal silicon nanoparticles, C-Si-Ag nanoparticles, C-coated SiO2 particles coated with metal silicon, C-coated compositions corresponding to silicon monoxide (SiO or SiO x ), or mixtures thereof. Other examples include C shells encapsulating Si nanoparticles and C shells encapsulating porous Si microparticles.

[0153] Gaseous aluminum chloride by-products can be continuously removed, and solid by-products such as aluminum oxide and / or aluminum oxychloride can be discharged together with the product and subsequently separated by appropriate post-processing methods.

[0154] According to a third example, a method for producing a C-Si-based metal system is provided, in which a precursor containing C-SiO2 and a metal additive reacts with Al powder in the presence of gaseous aluminum chloride AlCl3(g) at a temperature between 200 °C and 800 °C, preferably at a temperature between 200 °C and 800 °C, more preferably at a temperature between 200 °C and 600 °C to produce a product containing a metal alloy and a compound of a base metal, and a by-product containing aluminum oxychloride and / or aluminum oxide.

[0155] According to a fourth example, a method for producing carbon-encapsulated silicon nanoparticles is provided, in which a precursor containing C-coated SiO2 powder reacts with Al and gaseous aluminum chloride:

[0156] - at a pressure below 1.2 bar, and preferably at atmospheric pressure;

[0157] - and at a temperature below 600 °C, and preferably at a temperature between 200 °C and 600 °C;

[0158] to form a product containing carbon-encapsulated silicon nanoparticles and a solid by-product containing aluminum oxychloride (AlOCl). The silicon nanoparticles can be crystalline, amorphous, or a mixture thereof. Alloy additives can be included by appropriate addition to the silica-based precursor. The excess aluminum chloride is recycled by the method, and other solid by-products are discharged together with the powder product and subsequently separated from the silicon powder by appropriate post-processing methods; AlOCl and any residual Al can be removed by washing in a suitable solvent such as H2O and diluted HCl (H2O-HCl) that can dissolve AlOCl. Residual unreacted precursor can form part of the final product, or alternatively it can be removed using other suitable methods. The C-encapsulated silicon nanoparticles can be in various forms, including porous framework form, nanostructured particulate form, hollow spheres, nanoparticles, nanorods, or nanowires.

[0159] According to a fifth example, a method for producing a carbon-silicon nanowire composite is provided, in which a precursor containing C-SiO2 powder mixed with a metal catalyst precursor reacts with Al and gaseous aluminum chloride:

[0160] - at a pressure below 1.2 bar, and preferably at atmospheric pressure;

[0161] - and at a temperature below 600 °C, and preferably at a temperature between 200 °C and 600 °C;

[0162] to form a product comprising carbon-silicon nanowires and a solid by-product comprising aluminum oxychloride (AlOCl). The silicon nanoparticles can be crystalline, amorphous, or a mixture thereof. The catalyst precursor can be included by appropriate addition to a silica-based precursor of pure metal powder, metal chloride, metal oxide, or a mixture thereof. Suitable catalysts include powders based on transition metals including Ag, Cu, Zn, Au, and Al. The excess aluminum chloride is recycled by the process, and the other solid by-products are discharged together with the powder product and can subsequently be separated from the silicon powder by appropriate post-processing; the AlOCl and any residual Al can be removed by washing in a suitable solvent such as H2O and diluted HCl (H2O-HCl) that can dissolve AlOCl. The residual unreacted precursor can form part of the final product or alternatively it can be removed using other suitable means. The C-silicon nanowires can include other forms of Si, including porous framework form, nanostructured particulate form, hollow spheres, nanoparticles, or nanorods.

[0163] It is known that silica can react with molten Al at a temperature between 700 °C and 1200 °C, typically with a self-propagating reaction / thermal runaway and resulting in the formation of a molten mixture comprising Al2O3, where the removal of Al2O3 is difficult. For the present disclosure, AlCl3 in solid form or gaseous form is added to the SiO2-Al mixture and reacted at atmospheric pressure to reduce the threshold reaction temperature below 600 °C and provide control over the reaction mechanism, which can advantageously enable the formation of specific products including reduced silica.

[0164] Furthermore, the by-product is a solid AlOCl powder, which can be separated from the reaction product by washing and filtration (e.g., in H2O or diluted HCl), as opposed to the Al2O3 by-product which is difficult to remove. Additionally, since the reaction of the method according to the present invention does not involve liquid metal and there is no overheating, many base metals may retain the morphological characteristics from the starting SiO2 precursor (e.g., Si nanopowder from SiO2 nanopowder). Overall, the result includes a significant improvement in product quality, where the processing conditions typically required are greatly simplified.

[0165] It is well known that under high pressure conditions suitable for forming liquid AlCl3 and at temperatures up to 250 °C, SiO2 can react with Al in molten AlCl3 to produce a mixture of Si - SiO2. However, this method has many significant problems, including the need for high pressure to produce molten AlCl3. Further, despite long reaction times (> 10 hours), the maximum reported yield is 75%. The present inventors have found that using gaseous AlCl3 allows the reduction of SiO2 to Si at atmospheric pressure and at temperatures between 200 °C and 600 °C, with yields of up to 99% in a short time. Under the reaction conditions of the present invention, liquid AlCl3 is not present at all.

[0166] The example form of the method provides enhanced product technology with advantages over the prior art, as it is capable of reducing processing temperature and time, and expanding the range of materials that can be produced. The exemplary form of the method of the present invention differs from the prior art carbothermal reduction and metal reduction processes in several other major aspects:

[0167] 1 - The novel method allows the direct production of Si - impregnated carbon - based materials, natural graphite - Si composites, rice - husk - derived carbon - Si composites, or C - coated or carbon - encapsulated Si particles; and

[0168] 2 - The method reduces the threshold reaction temperature and allows the synthesis of compositions and morphologies (e.g., nanoparticle morphology, complex compositions) that are generally not obtainable under the conditions prevalent in carbothermal reduction and metallothermal reduction processes; and

[0169] 3 - The method is carried out under relatively mild atmospheric pressure and relatively low temperature conditions; and

[0170] 4 - The process requires low energy input and does not produce or produces minimal waste; and

[0171] 5 - Al is an attractive reducing agent because it is readily available and inexpensive, and its compounds are valuable industrial chemicals, and there are no significant handling difficulties (e.g., AlCl3); and

[0172] 6 - The process allows control of the void space within the encapsulated shell.

[0173] Detailed Description of the Invention

[0174] As described above, in its preferred embodiment, the present invention provides a low - temperature method for directly producing C - Si - based metal compositions.

[0175] The present disclosure relates to a method for reducing a solid precursor comprising silicon and carbon with a reducing Al alloy in powder form and aluminum chloride in a reaction vessel at a temperature below 800 °C, and preferably below 600 °C, and more preferably between 180 °C and 600 °C, and still more preferably between 400 °C and 600 °C, and most preferably between 200 °C and 600 °C, wherein the method comprises:

[0176] Step 1: Producing a carbon - SiO2 powder; this step can be carried out by any means capable of producing such a composition, including:

[0177] Impregnating graphite powder with silica; or

[0178] Producing a graphite powder - silica composite; or

[0179] Coating a SiO2 - based precursor with a C - based compound and processing to carbonize the coating, and producing a carbon - coated C - SiO2 on SiO2 - based particles;

[0180] And

[0181] Step 2: Mixing, heating, and reacting a reactant mixture comprising a C - SiO2 - based powder with a reducing Al alloy in the presence of aluminum chloride;

[0182] - wherein the aluminum chloride is in gaseous or solid form; and the amount is between 1 wt% and 500 wt% of the weight of the precursor silica; and the product of the method comprises a silicon - based compound; and the by - products include aluminum chloride and aluminum oxychloride and / or alumina; and

[0183] - wherein the reaction between silica and the Al reducing agent is exothermic; and

[0184] - wherein the pressure in the reaction vessel is maintained below the threshold pressure required to produce molten AlCl3; and

[0185] - wherein one or more of the C - SiO2 - based solid precursor powder, reducing Al alloy powder, and aluminum chloride are gradually fed into the reaction vessel; and

[0186] Step 3: Processing the product at the end of Step 2 to remove the by - products and obtaining a final product in the form of a C - Si - based powder.

[0187] Step 4: Optionally reacting the powder with a reagent to remove a portion of the Si - based particles encapsulated within the carbon shell.

[0188] Compared with existing silicon dioxide reduction technologies, according to the following overall reaction, the method of the present invention enables the reaction between SiO2, Al, and AlCl3 to occur at about atmospheric pressure in the range of 200 - 600 °C:

[0189] C - SiO2 + 1.333Al + 0.666AlCl3(g) C - Si + 2AlOCl, at 500 °C, ∆G = -164.6 kJ / mol (R1)

[0190] As outlined herein, the product can be in various forms, including silicon - impregnated carbon, graphite - silicon composites, carbon - coated silicon particles, and carbon - shell - silicon core - shells. For all products, the present invention offers several advantages. For example, in the case of the core - shell structure, there can be significant voids within the carbon shell to allow silicon to expand during lithiation; the starting volume of 1 mole of SiO2 is 23 ml, and the volume of the resulting Si is 12 ml. Assuming that all the carbon - encapsulating shells remain intact, the vacant space within the C shell is about 47.8%, and this space can be used as a buffer for the expansion of Si during the lithiation process. Additionally, a portion of the encapsulated SiO2 particles can be removed prior to reduction to create more vacant space within the carbon - encapsulating shell and avoid shell rupture due to the formation of Si and AlOCl according to reaction R1 during the reaction.

[0191] By controlling the etching of Si within the C shell, the amount of vacant space within the C shell can be further increased. The procedures for increasing the volume of the vacant space include reacting the C - Si composite with liquid chemicals capable of reacting with Si. The resulting Si compound is dissolved and separated from the C - Si product. Examples include using strong acids such as concentrated acids and other suitable chemicals capable of reacting controllably with Si.

[0192] Processing according to this scheme is carried out in an open reaction vessel under 1 atmosphere of an inert gas (e.g., Ar, N2, or CO2). The present inventors have conducted extensive tests to identify the potential reaction mechanisms within the SiO2 - Al - AlCl3(g) system. The results show that for fine precursor chemicals such as fumed silica and fine Al powder, yields of up to 99% can be obtained within a short processing time of less than 1 hour.

[0193] The method of the present invention requires that AlCl3 be in the gas phase without forming a molten AlCl3 phase. Without wishing to be bound by theory, the high yields observed in the tests of the present inventors appear to be due to gas-solid reactions involving gaseous AlCl3 and gaseous Al-Cl species. The presence of a liquid AlCl3 phase can reduce the reaction efficiency because it is limited by the ability of molten AlCl3 to diffuse through the solid particles to the unreacted SiO2 particles and / or particle nuclei. Attempts to use liquid eutectic AlCl3-NaCl as a source of AlCl3 to reduce SiO2 produced much lower yields than those observed with gaseous AlCl3.

[0194] For all aspects and embodiments of the method, the AlCl3 in the reaction vessel or reacting with the other reactant SiO2-Al must not be in a molten state produced by an increase in pressure, where the vessel is closed and heated to induce melting of the AlCl3. For all aspects and embodiments, it is preferred that the reaction in SiO2-Al-AlCl3 according to the present disclosure be carried out in a vessel open to atmospheric pressure and no pressure can be established in the vessel.

[0195] Precursor Chemicals and Products

[0196] As previously mentioned, since AlCl3 reacts with the carbon-SiO2 reactant and aluminum at a temperature below the melting point of aluminum, directly producing carbon-silicon composite materials such as C-encapsulated Si nanoparticles, the present invention has key effects and advantages. The discussions throughout the present disclosure regarding the reactions and mechanisms that promote the role of AlCl3 are only intended to emphasize the various physical mechanisms involved and to outline aspects of the technology. This discussion is not intended to be comprehensive and / or to limit the present invention to any theory or mechanism of action.

[0197] Suitable precursors include amorphous SiO2 powder, quartz powder, silica nanopowder, porous SiO2 powder, precipitates, fumed silica, glass powder, glass flakes, borosilicate glass, natural mica, silica fume, silica minerals, halloysite, kaolinite, synthetic mica, silica-impregnated carbon, silica-impregnated graphite, charcoal impregnated with silica, natural graphite containing silica, pyrolyzed rice husk, or any other composition based on SiO2.

[0198] Suitable precursors for the carbon component of the precursor chemicals include graphite powder, activated carbon, biomass, charcoal, carbon-containing organic compounds, polymers, and carbohydrates. Examples of preferred precursors include graphite powder, porous graphite powder, polyvinylpyrrolidone (PVP), and sugar compounds such as sucrose and glucose-based compounds.

[0199] Depending on the properties of the desired final product, the particle size of the precursor can range from a few nanometers to a few millimeters. However, a small particle size of less than 50 μm is preferred. Nanopowders with a particle size less than 1 μm and less than 100 nm can be used, and generally they produce a more efficient reaction and a better final product. For example, silica nanopowder or fumed silica is a preferred starting precursor for obtaining silicon nanoparticles.

[0200] For Si, the inventors have found that amorphous silica is more suitable for the reaction scheme of the present invention because it is more reactive and can be obtained in a finer form than quartz. Therefore, the Si in the starting SiO2 precursor is preferably amorphous or porous with a large surface area.

[0201] The amount of SiO2 reduced during processing can range from 0.1% to 100% of its starting weight. The remaining unreacted oxide and reducing agent are discharged as part of the product and can be separated in a post-processing step if desired.

[0202] The amount of aluminum reducing agent (such as a reducing Al alloy) used depends on the starting precursor material and the desired composition of the final product, and can be lower or higher than the stoichiometric amount required to reduce all reducible starting precursor chemicals. In some embodiments, the amount of aluminum reducing agent in the reaction mixture can range from 1 wt% to 1000 wt%, from 5 wt% to 500 wt%, and more preferably from 10 wt% to 200 wt%, and still more preferably from 50 wt% to 200 wt% based on the weight of silica in the carbon-silica-based precursor.

[0203] Preferably, Al is in the form of powder or flakes with a particle size less than 50 μm in at least one dimension. More preferably, Al has a particle size between 1 μm and 50 μm in at least one dimension.

[0204] In some embodiments, the amount of AlCl3 used can range from 1 wt% to 500 wt%, preferably from 1 wt% to 200 wt%, and more preferably from 10 wt% to 200 wt%, and still more preferably from 50 wt% to 200 wt% based on the weight of the carbon-silica-based precursor.

[0205] The weight ratio of silica, reducing Al alloy, and AlCl3 can be determined by a combination of various factors, including the desired composition of the final product and the stoichiometric requirements of the reaction within the Si-O-Al-Cl system.

[0206] For embodiments using solid aluminum chloride, the starting solid AlCl3 is preferably in the form of a powder or fine grains with a particle size less than 5 mm. More preferably, the starting solid AlCl3(s) is in the form of a powder with a particle size less than 200 μm, and more preferably less than 100 μm.

[0207] The processing is generally carried out under a protective gas, preferably at atmospheric pressure, in an open reaction vessel. An excess of aluminum chloride can be used, and the AlCl3(g) escaping or diffusing from the reaction vessel can be condensed during processing and returned to the reaction vessel, or collected in a dedicated container for subsequent use or recycling. For the processing according to R1, the excess gaseous aluminum escaping from the reaction vessel can be condensed and returned to the initial stage of reaction R1 for processing, and then condensed and collected in a dedicated container for subsequent use in the final stage of the reaction.

[0208] The excess aluminum chloride in solid form can be fed into the reaction zone together with other reactants, and then at least a part of the excess AlCl3 can sublime and contribute to cooling the reactants. In addition to the latent heat required to heat AlCl3 to the reactant temperature, the heat of sublimation of AlCl3(s) provides an effective way to cool the reactants and control the reaction temperature.

[0209] The excess solid AlCl(s) can be fed together with other reactants and used to control the temperature of the reactants by absorbing heat due to sublimation. The resulting heated AlCl3 vapor is collected from the reaction zone, cooled and then fed directly into a container, or collected and recycled. The amount of AlCl3(s) fed into the reactor is controlled to maintain stable thermal processing conditions.

[0210] The method can be operated in batch mode, semi - continuous mode or fully continuous mode, and AlCl3 can be fed into the reaction zone / vessel as a solid powder, which can react with other precursors at low temperature or sublime into gaseous AlCl3(g) during processing. Alternatively, AlCl3 can also be fed into the reaction zone / vessel alone or preferably as a reaction stream (e.g., fluidized bed, packed bed, moving bed, rotary kiln or continuously moving in a tubular reactor in a gaseous AlCl3 atmosphere) through the reactants or as an additional gas stream in the reactant atmosphere.

[0211] Any residues including aluminum chloride or oxychloride, Al2O3, unreacted oxides and sub - oxides, other residual chlorides, and unreacted Al can be removed from the product in post - processing steps using suitable methods including washing, chemical dissolution, and vacuum sublimation.

[0212] For example, AlOCl can be removed by washing in diluted HCl. If Al2O3 forms and is present in the product, it may remain in the final product either as an independent component in the composite or as part of a compound / particle, where the alumina undergoes physical or chemical reactions with the substances generated by the reduction reaction.

[0213] The processing temperature is typically above 200 °C, and generally the product is substantially free of aluminum chloride, and any aluminum chloride residue is due to contamination during discharge and / or handling. Preferably, the product of the method contains less than 5 wt% and preferably less than 1 wt% of residual solid AlCl3(s) impurities.

[0214] Those of ordinary skill in the art of the present invention will understand that the final product may contain Al in the form of residual Al impurities or metal aluminides at a level between 0.01% and 70 weight (wt)%, and if desired, the Al can be partially or completely removed by various means, including washing in chemicals such as diluted NaOH or diluted HCl.

[0215] In embodiments where the precursor material includes reactive additives (such as alloy additives), the final product may include compounds containing the reactive additives. For example, for additives of carbon, boron, oxygen, and nitrogen, the product may contain carbides, borides, oxides, and nitrides, respectively. Preferred embodiment

[0216] As discussed, the reaction in C - SiO2 - Al - AlCl3 can result in a significant exothermic energy release, capable of raising the reactant temperature to over 1500 °C and then hindering the quality of the product; for example, increasing the reactant temperature above 700 °C can trigger an uncontrollable direct reaction between SiO2 and Al, resulting in the formation of a non - uniform composition containing Al2O3. The present invention advantageously overcomes these problems in the prior art and includes procedures for controlling the exotherm generation and maintaining the temperature at a level suitable for producing a material with uniform and acceptable properties. The reaction rate within the SiO2 - Al - AlCl3(g) system is controlled by a combination of mechanisms including a controlled feed rate of the reactants, mixing with the pre - processed product, and external heat management.

[0217] Preferably, the method is carried out with a gradual feed of at least Al and / or AlCl3 such that the exothermic energy release is moderated, thereby allowing efficient heat management of the reactants; for all exemplary aspects, forms, and embodiments, the method includes means for managing the exotherm generation and maintaining the reactant and reactor temperatures at a safe level.

[0218] In a preferred embodiment, the method includes:

[0219] - Prepare a powder comprising a carbon-based precursor and an SiO2-based precursor, or a powder comprising a C-SiO2-based precursor; and

[0220] - Optionally process the prepared powder to carbonize the carbon-based precursor and produce a stable powder based on carbon-C-SiO2; and

[0221] - Optionally load all or part of the C-SiO2 powder and gradually feed the remaining reactants comprising a reduced Al alloy and AlCl3(s) and / or AlCl3(g) into a reaction vessel, the temperature T1 of which is set to be higher than a certain threshold reaction temperature lower than 800 °C and preferably lower than 650 °C; and

[0222] - Mix and react the reactants in the presence of aluminum chloride to produce a C-Si-based product, mixed with by-products AlOCl or Al2O3; and

[0223] - Wherein T1 is lower than 600 °C, and preferably between 180 °C and 600 °C, and more preferably between 160 °C and 600 °C, and still more preferably between 200 °C and 600 °C, and still more preferably between 200 °C and 600 °C; and

[0224] - Wherein the vessel contains a certain amount of processed reactants; and

[0225] - Wherein AlCl3 is in solid form or gaseous form; and when aluminum chloride is provided in solid form, it can be provided as a premixed mixture with solid Al powder; and

[0226] - Optionally separate the by-products and produce a base-metal-based final product.

[0227] In a preferred embodiment, a precursor C-SiO2 powder stream and a stream consisting of a mixture of Al-AlCl3 powders are gradually fed into a reaction vessel preheated to a temperature between 200 °C and 600 °C, and preferably between 200 °C and 600 °C. Processing is carried out at atmospheric pressure under a non-reactive protective gas in the vessel. For this embodiment, the reaction product is a mixture of Si powder and AlOCl. The product mixture is washed in diluted HCl to separate the metallic Si powder. In one form of this embodiment, the precursor SiO2 powder is silica nanopowder, and the product is nanopowder of Si. In another form, the precursor SiO2 powder is fumed silica powder, and the product is nanopowder of Si. In other forms, the precursor SiO2 powder is fumed silica. In a preferred form of this embodiment, the precursor C-SiO2 powder is pre-loaded into the reaction vessel, and then the mixture of Al-AlCl3 powders is gradually fed into the reaction vessel.

[0228] Figure 1 is a schematic diagram showing the processing steps of a preferred embodiment for the reduction of a SiO2 precursor with Al-AlCl3. For this embodiment, a SiO2-based precursor powder (101) is mixed with a C-based compound (102). If required, the resulting powder is carbonized / pyrolyzed according to the precursor (103) to produce a C-SiO2-based powder (104); C-SiO2. The C-SiO2 precursor powder (104) is then fed into the reactor vessel (105) in one batch or stepwise. The Al powder (106) and the AlCl3 powder (107) are pre-mixed (108), and then gradually fed into the reactor vessel (105) equipped with a mixer (not shown) and set at a processing temperature T1 above the threshold reaction temperature required for the reduction of SiO2. Alloying additives (not shown) can be fed separately or together with other precursors depending on the reactivity and compatibility at level (105) or elsewhere such as (101), (102), (103), (104) or (108).

[0229] The reactants in (105) are continuously mixed or reacted for a residence time t1 under static conditions, such that a solid product is formed comprising a metal-based Si compound and a solid AlOCl by-product. The solid AlCl3 (as part of the mixture Al-AlCl3) fed into the reactor vessel in solid form sublimes to form gaseous AlCl3, and a portion thereof reacts with Al and SiO2 in the reactor to form AlOCl. Another portion of the gaseous AlCl3 escapes or diffuses out of (105) and is condensed and collected in a dedicated vessel (109). Part or all of the aluminum chloride can be recycled through (110). All processing steps are preferably carried out under an inert gas (e.g., Ar) or an incompletely reactive gas (e.g., CO2, N2...) (111). At the outlet of the by-product collection step, the gas is purified in a scrubber (112) before being discharged to the atmosphere or recycled.

[0230] The solid reaction product comprising Si powder and AlOCl by-product, and any other solid residues (if applicable) (e.g., Al2O3, additive precursors...) are discharged through (113). The reaction product (113) is then optionally post-processed (114) as needed to separate the metal product from the unwanted residual precursors (e.g., Al and unreacted SiO2) and by-products, thereby producing the final product (115). The waste from the separation step (114) is processed and stored separately (116).

[0231] The reaction vessel (105) can be a holding reactor vessel equipped with a mixer and operating in batch mode, semi-batch mode or continuous mode. Examples of suitable vessels include conical reactors, auger-based reactors, rotary kilns, fluidized beds and packed bed reactors.

[0232] In one embodiment, a mixture of a SiO2-based precursor and Al is fed into the reaction vessel (105) at a temperature of up to 650 °C in an atmosphere comprising gaseous AlCl3 to induce a reduction reaction, such that a powder product based on one or more of the base metals is formed.

[0233] The SiO2-based precursor can be loaded into the reaction vessel partially or fully first and heated to the reaction temperature. Then, according to any of the embodiments described previously or forthcoming, the other reactants are fed into the reaction vessel.

[0234] The amount of AlCl3 provided for reaction with the SiO2 - Al mixture can be adjusted to suit the processing requirements and control the reaction rate and reaction kinetics. In some embodiments, aluminum chloride is passed over the SiO2 - based precursor / Al mixture as a gas stream, as pure gaseous AlCl3, or as a carrier gas / AlCl3 mixture (e.g., N2 / AlCl3 or Ar / AlCl3). In one embodiment, aluminum chloride passes through the metal oxide / Al mixture in accordance with the configuration in a fluidized bed system.

[0235] In another embodiment for producing a carbon - silicon - based composite material, a method for producing Si - based powder is provided, wherein:

[0236] - The composition of the SiO2 - based precursor can be any of the following: a multi - component powder containing SiO2, pure SiO2, precipitated silica powder, SiO2 nanopowder, fumed silica, silica fume, amorphous silica, quartz powder, glass powder, glass flakes, borosilicate glass powder or flakes, mica, synthetic mica, or any other SiO2 - based composition; alternatively, the SiO2 - based precursor can be in the form of a soluble silicon - based compound that is impregnated into graphite powder and then converted to SiO2; and

[0237] - Step 1: The particle size of the SiO2 - based precursor powder in at least one dimension ranges from a few nanometers to several hundred μm; and

[0238] - An intermediate powder containing a carbon precursor and a SiO2 - based precursor is prepared using the SiO2 - based precursor powder. The resulting intermediate powder can be carbonized or pyrolyzed to produce a C - SiO2 powder; and

[0239] - The C - SiO2 powder reacts with Al and AlCl3 (solid state and / or gaseous state) to produce a powder product; and

[0240] - The by - product is AlOCl, and the product is a mixture of a silicon - based powder, solid state AlOCl, and residual Al; and

[0241] - The product from step 1 can be in the form of a carbon - silicon composite material; the silicon can be in the form of silicon powder, silicon nanopowder with a particle size less than 1 μm, pure silicon material, silicon monoxide - based SiO or SiO xin the form of any one or a mixture thereof of powders of silicon-based powders having an oxygen content between 0.01 wt% and 50 wt%, where x is between 0.2 and 1.8, and the carbon-silicon composite material can be in the form of silicon-coated microparticles, all Si-C composite materials, Si-impregnated graphite, natural graphite-Si, biomass-derived carbon-silicon composite materials, or any other form containing carbon and silicon; and

[0242] - Step 2: Processing the product from Step 1 to remove the AlOCl by-product and / or residual Al, thereby producing the final Si-based product.

[0243] In a preferred embodiment, AlCl3 is fed into the reaction vessel as solid powder AlCl3(s) and gaseous AlCl3(g). The solid AlCl3(s) powder is fed into the reaction vessel together with other reactants, and the gaseous AlCl3(g) can be fed anywhere but preferably from the bottom into the vessel and directed upward through the reactants, for example, in a conical reactor vessel, fluidized bed, or packed bed arrangement. When the reactants sublime, the solid AlCl3(s) helps to cool the reactants, and some of it is present in the reaction vessel, while the gaseous AlCl3(g) is mainly used to maximize the reaction rate within the reactants.

[0244] In one embodiment for producing a silicon-carbon material, a method for producing a Si-based powder is provided, wherein:

[0245] - A mixture of silica and a carbon-based precursor suitable for reacting with an acid is provided; examples of the carbon-based precursor include sucrose, and examples of the acid include sulfuric acid,

[0246] - Reacting the mixture of silica and the carbon-based precursor to produce a silica-carbon mixture,

[0247] - Optionally further pyrolyzing the silica-C mixture to react any residual carbon-based precursor,

[0248] - Reacting the resulting silica-C mixture to produce a Si-C-based material according to any embodiment of any of the foregoing or upcoming embodiments.

[0249] In one embodiment for producing a silicon-carbon material, a method for producing a Si-based powder is provided, wherein:

[0250] - A silicon-containing liquid precursor suitable for producing silica is provided; examples include silicic acid, sodium silicate, and silanolates,

[0251] - Mixing graphite powder with the liquid precursor, and then reacting and / or calcining the liquid precursor to produce a graphite-SiO2 mixture,

[0252] - React a mixture of silica and a carbon-based precursor to produce a silica-C mixture,

[0253] - Optionally further pyrolyze the silica-C mixture to react any remaining carbon-based precursor,

[0254] - React the resulting silica-C mixture to produce a Si-C-based material according to any of the foregoing or upcoming embodiments.

[0255] In one embodiment for producing a carbon material impregnated with silicon, a method for producing a Si-based powder is provided, wherein:

[0256] - Provide a silicon-containing liquid precursor suitable for producing silica; examples include silicic acid, sodium silicate, and silanolates,

[0257] - Impregnate a carbon-based material with the liquid precursor, and then react and / or calcine the liquid precursor to produce a graphite-SiO2 powder,

[0258] - React the resulting mixture of the carbon-based material-silica to produce a Si-C-based material according to any of the foregoing or upcoming embodiments.

[0259] - The carbon-based material can be graphite, synthetic graphite, natural graphite, activated carbon, charcoal, graphite or carbonized material produced by pyrolysis of organic materials such as pyrolyzed rice husks, graphite material produced by reacting an organic material with an acid, or anode-grade graphite powder. The form of the graphite material, which can be in the form of flakes or spherical powder, and which can be coated or uncoated.

[0260] In one form of this embodiment, the liquid precursor is prepared by dissolving silica in a NaOH solution to produce a sodium silicate solution. In another form, the liquid precursor is prepared from sodium silicate. In either form, the method can include the following steps:

[0261] - Mix or impregnate the carbon-based material with the silicate; and

[0262] - React the liquid precursor with an acid (e.g., HCl) to convert the silicate production to Si(OH)4 or SiO2; and

[0263] - Remove the by-products produced from the last reaction step; and

[0264] - React the resulting carbon-based material and silicon-oxygen mixture with Al-aluminum chloride to obtain any of the foregoing or following embodiments.

[0265] In one embodiment, the precursor material consists of a silica mixture based on a carbonaceous material - a silica mixture composed of natural graphite - silica minerals, and then the precursor material reacts with Al - aluminum chloride to obtain any of the foregoing or following embodiments.

[0266] In one embodiment, the precursor material consists of a silica mixture based on a carbonaceous material - a silica mixture composed of charcoal - silica, and then the precursor material reacts with Al - aluminum chloride to obtain any of the foregoing or following embodiments. In one form of this embodiment, the charcoal is first impregnated with a silica-coated precursor and then converted to silica, and then the resulting material is reacted with Al - AlCl3 according to any of the foregoing or upcoming embodiments.

[0267] In one embodiment for producing a carbon - silicon composite material, the method comprises:

[0268] - providing a first natural graphite powder containing between 0.1% and 20% by weight of silica; and

[0269] - mixing, heating, and reacting the first powder with a reducing agent comprising aluminum and aluminum chloride to reduce at least a portion of the silica to silicon and produce a carbon - silicon powder and by-products Al2O3 or AlOCl; and

[0270] - optionally separating the carbon - silicon composite material from the by-products.

[0271] In one embodiment for producing a carbon - silicon composite material, wherein the natural graphite powder contains other impurities, and the method includes the steps of reacting the impurities with an aluminum - aluminum chloride-based reducing agent and then dissolving the resulting impurity-based substance and separating it from the carbon - silicon product.

[0272] In one embodiment, the precursor material consists of a silica mixture based on a carbonaceous material - a silica mixture composed of charcoal - silica, and then the precursor material reacts with Al - aluminum chloride to obtain any of the foregoing or following embodiments. In one form of this embodiment, the charcoal is first impregnated with a silica-coated precursor and then converted to silica, and then the resulting material is reacted with Al - AlCl3 according to any of the foregoing or upcoming embodiments.

[0273] In one embodiment for producing a carbon - silicon composite material, the method comprises:

[0274] - preparing a liquid solution containing a dissolved silica precursor; and

[0275] - providing graphite powder of charcoal and activated carbon material; and

[0276] - Mix the solution with graphite powder; and

[0277] - Convert the silica precursor to silica; and

[0278] - React the resulting carbon-silica material with Al-AlCl3 to produce a C-Si composite; and

[0279] - Separate the carbon-silicon composite from the by-products.

[0280] In one form of this embodiment, the method comprises:

[0281] - Prepare a liquid solution of sodium silicate and water; and

[0282] - Provide charcoal powder; and

[0283] - Mix the sodium silicate solution with the charcoal powder; and

[0284] - Add an appropriate amount of diluted HCl to convert the sodium silicate to silicon hydroxide; and

[0285] - React the resulting carbon-silica material with Al-AlCl3 to produce a C-Si composite; and

[0286] - Filter the solid particulate powder; and

[0287] - Heat the solid particulate powder to convert the silicon hydroxide to silica; and

[0288] - React the resulting carbon-silica material with Al-AlCl3 to produce a C-Si composite; and

[0289] - Separate the carbon-silicon composite from the by-products.

[0290] In one form of this embodiment, the heating is carried out at a temperature below 650 °C.

[0291] In all embodiments, the processing is carried out at a pressure below 1.2 atmospheres.

[0292] In one embodiment where carbon-coated silica powder is provided, the method may include the main steps of dissolving and / or etching a portion of the silica to create pores around the silica particles and thus produce Si-NPs encapsulated within a carbon cage having sufficient voids to allow for the volume increase of the Si-NPs during lithiation.

[0293] In an embodiment of the partial reduction of a SiO2-based precursor and the production of a Si-coated substrate, the SiO2-based precursor is reacted with a substoichiometric amount of Al in the presence of gaseous AlCl3. The product then takes the form of a SiO2-based substrate coated with Si. The SiO2 precursor can be in the form of fine particles such as powders, flakes or fibres. The metal coating on the surface of the fine particles can be continuous or discontinuous and can cover the whole or part of the surface of the fine particles. When the fine particles are in the form of flakes, the coating can be reflective and the fine particles can then be used in applications such as pigments. In other embodiments, the coated fine particles can be further reacted with other precursor chemicals, where metallic Si acts as a reducing agent.

[0294] In some embodiments, metal-based additives can be included in the reaction mixture to affect the properties of the final product. For example, additives based on one or more of Li, B, Na, Mg, Al, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Hf, Ta, W, Re, Os, Pt, Au and Bi can be included in the reaction mixture to include metal impurities in the resulting C-Si product. In some other embodiments, the metal-based additives are suitable for inducing the formation of a carbon-silicon composite in the form of carbon-silicon nanowires as a catalyst.

[0295] For example, an AgCl additive can be included in the precursor chemicals and the final product is a SiO2 substrate coated with Si-Ag or Ag, depending on the amounts of Al and AgCl used and the properties required of the final product.

[0296] The precursor can also include glass powder or glass flakes, fumed silica, silica fume, silica nanopowder, glass bubbles, and the product includes metallic silicon or metal silicide. In one form of this embodiment, the precursor oxide is in the form of flakes and the product is a powder with a flake-like morphology. In another form, the precursor powder includes fibres and the product is a powder with a fibre-like morphology.

[0297] The solid reactants including SiO2 and reduced Al alloy can be continuously mixed, for example, to maximise the contact between the solid reactants and improve the reaction yield.

[0298] In one embodiment, where the by-product is AlOCl, the AlOCl is separated from the metal powder product by washing in a solvent suitable for dissolving AlOCl and then separating the solid powder product.

[0299] The mixing and stirring of the reactants helps to increase the contact between the various components of the mixture, and optimize the product and maximize the reaction yield. Stirring helps to bring the reducible precursor chemicals and unsaturated substances generated during processing into contact with the reducing agent, and then those substances can react or disproportionate, and thus helps to improve the quality of the product. In a preferred embodiment, the process conditions are arranged to maximize the reaction between SiO2 and Al - AlCl3 through efficient mixing of the reactants.

[0300] The pressure in the reaction vessel must be below 1.5 atm, and preferably below 1.2 atm, and more preferably the vessel is maintained under a protective gas at a pressure of about 1 atm and in open communication with the external environment at 1 atm.

[0301] The precursor chemicals can be arranged in two or more material streams, which are fed into the reaction vessel together or independently and react to produce a powder product. In one variant of this form, the reactants can be processed at multiple temperatures for different processing times to optimize the processing conditions and produce a material with desired properties.

[0302] For example, in one embodiment, the reactants can be introduced through several material streams, including a stream containing a mixture of a reducing alloy and aluminum chloride. In one form of this embodiment, the mixture is produced by co - grinding.

[0303] The process can be carried out in an inert gas, or in a non - reactive gas, or in a mixture of a non - reactive gas and a reactive gas; examples of sufficient gases include Ar, N2 or CO2. In one embodiment, the gas stream consists of a mixture of Ar and a reactive component such as NH3.

[0304] In one embodiment, the method comprises an additional step in which the product obtained at the end of the process is reacted with an additional gaseous reactant at a temperature between 25°C and 850°C. The gaseous reactants include gases containing reactive elements such as oxygen, nitrogen, boron and carbon. For example, the product can be heated in a CH4 stream to produce a Si - C - based compound.

[0305] In one embodiment, a carbon - shell silicon - core product is provided, which consists of:

[0306] - A porous carbon cage with a wall thickness between 0.01 nm and 1 μm; and

[0307] - A cavity containing a silicon - based material with at least 50% metallic silicon and vacant space; and

[0308] - The volume ratio of the void space to Si is between 10% and 75% (e.g., between 10% and 50%).

[0309] - The average diameter of the initial silica powder is between 20 nm and 20 μm.

[0310] Examples of such core - shell structures can be produced by any of the foregoing or upcoming embodiments. For example, to produce a core - shell structure starting from 20 nm silica precursor powder and PVP precursor for carbon, the following steps are carried out:

[0311] - The average diameter of the silica powder is 20 nm. The nominal density of silica is 2.62 g / ml. The PVP composition is (C6H9NO) n , with a nominal carbon content of 65 wt%.

[0312] - The silica powder is coated with PVP. The amount of PVP used corresponds to between 0.1 wt% and 100 wt% relative to the weight of silica. Then the PVP - coated silica is pyrolyzed to produce a carbon coating between 0.065 wt% and 65 wt% relative to silica.

[0313] - Then the carbon - coated silica is reduced with Al - AlCl3 at 450°C, where the silica is reduced to silicon. The ratio of carbon to silicon is between 0.1 wt% and 130 wt%.

[0314] - When the silica is completely reduced to silicon, its volume decreases by 49%, such that a shell is formed with a core consisting of 50% Si and 50% voids.

[0315] The present invention extends to materials made using the described method in all its embodiments and forms, without being limited by the examples provided herein in an illustrative manner. Materials produced by the preferred forms of the present invention described herein can have unique properties not obtainable using prior art methods. Specific example properties can include the ability to produce products with nanostructures having large areas and compositions, which are generally not achievable by conventional techniques.

[0316] An example of a material with unique properties obtained using current technology is silicon nanoparticles containing a metal additive for Li - ion batteries. Such materials are characterized by a large surface area and excellent electrical conductivity due to the addition of base metal additives.

[0317] The silicon nanoparticles produced according to the present invention include crystalline silicon and amorphous silicon, including products containing various ratios of crystalline and amorphous phases.

[0318] The silicon nanoparticles produced by the method according to the invention have an irregular specific shape, a particle size in the range of 10 nm to 500 nm, and contain Al at levels of 0.01 wt% and 70 wt%. Other variants of the product include silicon nanoparticles with Ag, Cu, and / or tin at levels between 0.1 wt% and 50 wt%.

[0319] The following are examples of preparing various product compounds according to embodiments of the invention.

[0320] Example 1: C-Si Nanocrystals Starting from Fumed Silica

[0321] React vapor-phase silicon dioxide (SiO2) with Al under Ar - AlCl3 at 1 atm at a temperature of 550 °C. Al and AlCl3 are premixed together. Over a 15-minute period, SiO2 and Al - AlCl3 are fed into the reactor as two separate streams. The temperature of the reactants is continuously monitored, and only a moderate temperature increase is detected. The material obtained at the end of the test has a dark brown color, a yield > 97%; some material is lost during processing and handling. XRD analysis of the material thus produced shows that the gas consists of AlOCl, Si, and carbon; only lines corresponding to crystalline silicon are observed, and the measured XRD pattern indicates that the material does not contain Al2O3. In addition, the broad and shallow feature corresponding to C seems to indicate the presence of carbon.

[0322] TEM analysis of the produced powder shows that the particle size distribution is between 20 nm and 100 nm. SEM analysis confirms the presence of agglomerates with a broad particle size distribution between 50 nm and 200 nm, and this has been observed to be caused by the washing process. If pure H2O without HCl is used, the Si microparticles remain suspended in water indefinitely, and the particle size distribution is in the range of 10 - 100 nm.

[0323] Example 2: C-Si Nanocrystals Starting from C-SiO2 Nanopowder

[0324] Mix 100 g of SiO2 nanopowder (70 nm) with 100 ml of distilled water and 1 g of sugar. Stir the mixture continuously for 10 minutes to ensure complete homogenization, and then heat until all the water has evaporated. Then pyrolyze the resulting sugar - SiO2 powder under nitrogen at 525 °C.

[0325] React the resulting C - SiO2 with Al and AlCl3 under argon at 1 atm at a temperature below 525 °C. The excess AlCl3 is collected in a dedicated container for subsequent use. Over 30 minutes, the materials are gradually fed into the reactor as two separate streams; one SiO2 stream and one Al - AlCl3 mixture stream.

[0326] The material is brown - the collected amount is 290 g. The material is discharged and washed in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of crystalline silicon, and the material is substantially free of Al2O3.

[0327] Example 3: C-Si Starting from Quartz Powder

[0328] 51 g of C - quartz powder (0.5 - 10 μm) is processed with 32 g of Al under argon - AlCl3 at 1 atm at a temperature of 550 °C. The excess AlCl3 is collected in a dedicated container for subsequent use.

[0329] The material is discharged and washed in diluted HCl. The XRD pattern of the product shows that the quartz powder is only partially reduced. All the lines in the figure can be indexed to the known XRD spectra of quartz and silicon.

[0330] Example 4: C-Si Starting from Silica Fume

[0331] A mixture of C - SiO2 derived from silica fume and about 5% carbon is processed under argon - AlCl3 at 1 atm at 525 °C. The C coating is produced in a manner similar to Example 1.

[0332] Analysis of the product shows that Si and C are as expected.

[0333] Example 5: SiO2 Coated with C-Si

[0334] 82 g of SiO2 nanopowder (20 nm) is mixed with 100 ml of distilled water and 1 g of sucrose. The mixture is continuously stirred for 10 minutes to ensure its complete homogeneity, and then heated until all the water has evaporated. The resulting sucrose - coated powder is then pyrolyzed under nitrogen.

[0335] The resulting C - SiO2 nanopowder is processed with Al powder (4 μm) under argon - AlCl3 at 1 atm at a maximum temperature of 500 °C. The SiO2 is partially reduced, and the product consists of SiO2 - Si - C. The amount of the collected material is about 167 g.

[0336] The material is discharged and washed in diluted HCl. The XRD pattern of the product shows crystalline silicon and a broad peak at about 22 degrees corresponding to amorphous silica.

[0337] Example 6: Glass Flakes Coated with C-Silicon

[0338] Mix 200 g of borosilicate glass flakes (-60 μm in diameter and 1 μm thick) with 100 ml of distilled water and 1 g of sucrose. Stir the mixture continuously for 10 minutes to ensure its complete homogenization, and then heat until all the water has evaporated. Then pyrolyze the resulting sugar-coated powder under nitrogen.

[0339] Process the resulting powder with Al - AlCl3 (12.5 g Al) under Ar at 550 °C. Then discharge the product and wash it in H2O.

[0340] The material is golden in color and consists of borosilicate flakes coated with Si. XRD analysis shows a shallow Si peak.

[0341] Example 7: C-Si Starting from C-SiO2 Nanopowder

[0342] First, pyrolyze 25 g of SiO2 nanopowder (70 nm) coated with 2% polyvinylpyrrolidone (PVP) under Ar at 500 °C to produce a SiO2 - C composition. Mix the SiO2 - C with a mixture of 6 g of Al powder (4 μm) and 30 g of AlCl3(s).

[0343] React the resulting C - SiO2 - Al - AlCl3 under Ar at 1 atm at 550 °C. Collect the excess AlCl3 in a dedicated container for subsequent use. Feed the material into the reactor gradually as two separate streams within 10 minutes.

[0344] The material is light gray - brown - the collected amount is 72 g. Discharge the material and wash it in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows that the C - Si product is in the form of Si aggregates with a carbon coating as a rough surface around individual particles. Additionally, the analysis shows that the Si nanoparticles are mainly nanocrystalline but contain a portion of the amorphous phase. TEM - EDS micrographs showing the C and C - Si morphologies of the powder are presented in Figure 2 presented in

[0345] Example 8: C-Si Starting from C-SiO2 Nanopowder

[0346] Step 1: Mix the nanopowder (20 nm) with distilled water and PVP. Stir the mixture to ensure its complete homogenization, and then heat until all the water has evaporated. Then pyrolyze the resulting PVP - coated powder under Ar at 550 °C.

[0347] Step 2: Repeat Step 1 three times.

[0348] Step 3: Mix SiO2-C with Al powder (4 μm) and AlCl3(s). React the resulting C-SiO2-Al-AlCl3 under argon at 1 atm at 550 °C. Collect the excess AlCl3 in a dedicated container for subsequent use. Feed the materials gradually into the reactor as two separate streams over 10 minutes.

[0349] Discharge the materials and wash them in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows a complex structure where Si aggregates and microparticles are encapsulated within a porous carbon coating.

[0350] Example 9: C-Si Starting from C-SiO2 Nanopowder

[0351] Mix SiO2 nanopowder (20 nm) with distilled water and PVP. Then heat the mixture until all the water has evaporated. Then pyrolyze the resulting PVP-coated powder under argon at 550 °C.

[0352] Mix SiO2-C with Al powder and AlCl3(s), and react the resulting C-SiO2-Al-AlCl3 under argon at 1 atm. Collect the excess AlCl3 in a dedicated container for subsequent use. Feed the materials gradually into the reactor as two separate streams.

[0353] Discharge the materials and wash them in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows Si aggregates and microparticles encapsulated within a porous carbon coating.

[0354] Example 10: C-Si Nanoparticles Starting from C-SiO2 Nanoparticles

[0355] Step 1: Dissolve a certain amount of PVP in water. Then, add SiO2 powder and mix well.

[0356] Evaporate the water and pyrolyze the remaining solid PVP-coated silica under argon at 500 °C to produce a SiO2-C composition.

[0357] Step 3: Mix SiO2-C with Al powder and AlCl3(s).

[0358] React the resulting C-SiO2-Al-AlCl3 under argon at 550 °C. Collect the excess AlCl3 in a dedicated container for subsequent use. Feed the materials gradually into the reactor as two separate streams over 10 minutes.

[0359] The material is light grayish brown. The material is discharged and washed in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon, but has very broad peaks. The XRD is shown in Figure 3 . The calculation of the particle size based on the FWHM shows that the particle size is less than 7 nm. For reference, in Figure 4 , the XRD trace of a pure Si sample obtained without a carbon coating is presented. The small particle size obtained is due to the carbon coating preventing the agglomeration and sintering of individual Si nanoparticles. The TEM of the powder shows that the C-Si product is in the form of Si aggregates, where there is a carbon coating as a rough surface around individual microparticles. The TEM analysis shows the presence of a significant amorphous part.

[0360] Example 11: C-Si Nanoparticles Starting from C-SiO2 Nanoparticles

[0361] Step 1: Dissolve PVP in water. Then, add SiO2 nanopowder (70 nm) and mix well.

[0362] Step 2: Evaporate the water and pyrolyze the remaining solid PVP-coated silica to produce a SiO2-C composition.

[0363] Step 3: Mix SiO2-C with Al powder and AlCl3(s).

[0364] React the resulting C-SiO2-Al-AlCl3 under argon. Collect the excess AlCl3 in a dedicated container for subsequent use. Gradually feed the material into the reactor as two separate streams within 10 minutes.

[0365] The material is light grayish brown. The material is discharged and washed in diluted HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon, but has very broad peaks. The TEM of the powder shows that the C-Si product is in the form of Si aggregates, where there is a carbon coating as a rough surface around individual microparticles. The TEM analysis shows the presence of an amorphous part.

[0366] Example 12: C-Si Starting from C-SiO2 Precipitated Silica

[0367] First, pyrolyze SiO2 powder (precipitated silica) coated with 2% polyvinylpyrrolidone (PVP) to produce a SiO2-C composition. Mix SiO2-C with Al powder and AlCl3(s).

[0368] React the resulting C-SiO2-Al-AlCl3 under argon at 1 atm at 475 °C. Collect the excess AlCl3 in a dedicated container for subsequent use.

[0369] The material is light grayish brown. The material is discharged and washed. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows that the C-Si product is in the form of Si aggregates with a carbon coating as a rough surface around individual particles.

[0370] Example 13: C-Si Starting from C-SiO2 Halloysite

[0371] First, SiO2 powder (halloysite) coated with 1% polyvinylpyrrolidone (PVP) is pyrolyzed at 550 °C under argon to produce a SiO2-C composition. The SiO2-C is mixed with Al powder and AlCl3(s).

[0372] The resulting C-SiO2-Al-AlCl3 is reacted at 550 °C under argon. The excess AlCl3 is collected in a special container for subsequent use.

[0373] The material is discharged and washed. The XRD pattern of the washed product matches the known XRD spectra of silicon and Al2O3. The Al2O3 is most likely due to the presence of oxides in the halloysite composition.

[0374] Example 14: C-Si Starting from C-SiO2 Halloysite

[0375] SiO2 powder (halloysite) is washed with sulfuric acid to dealuminate the material and increase the SiO2 concentration in the powder. Then the powder is coated with 2% polyvinylpyrrolidone (PVP) and pyrolyzed at 525 °C under argon to produce a SiO2-C composition. The SiO2-C is mixed with 6 g of Al powder and AlCl3(s).

[0376] The resulting C-SiO2-Al-AlCl3 is reacted at 525 °C under 1 atm of argon. The excess AlCl3 is collected in a special container for subsequent use.

[0377] The material is discharged and washed. The XRD pattern of the washed product matches the known XRD spectrum of silicon.

[0378] Example 15: Si-Impregnated Graphite Powder

[0379] Sodium silicate powder is dissolved in water. Porous graphite powder is added to the solution. Then HCl is added to the solution. Then the mixture is heated at 300 degrees. The dried mixture is washed several times in water to remove the unwanted NaCl. Then the resulting graphite-SiO2 powder is reacted with Al-AlCl3. The product is washed to remove the AlOCl by-product. The resulting material consists of graphite impregnated with Si-NP.

[0380] Example 16: Si-Impregnated Graphite Powder

[0381] Dissolve sodium silicate in water. Add porous graphite powder to the solution and stir for 2 hours. Then add HCl to the solution. Then calcine the mixture at 300 degrees. Wash the dried mixture to remove the NaCl by-product.

[0382] Add a diluted sodium hydroxide solution, and heat and stir the mixture to dissolve a part of SiO2 and create voids around the silica particles. Filter and wash the material, and then dry it.

[0383] Then react the resulting graphite-SiO2 powder with Al-AlCl3. Wash the product to remove the AlOCl by-product. The resulting material consists of graphite impregnated with Si-NP.

[0384] Example 17: Si-Impregnated Graphite Powder Produced from Sucrose

[0385] Dissolve precipitated silica and sucrose in water and stir until completely homogeneous. Then heat the solution until the water has completely evaporated.

[0386] Add H2SO4 to the material and convert the sucrose to porous carbon. The precipitated silica particles are encapsulated within the pores of the resulting carbonized material.

[0387] As previously described, then react the material with Al-AlCl3, and the final product is in the form of Si-impregnated porous graphite powder.

[0388] Example 18: Si-Impregnated Graphite Powder Produced from Sucrose

[0389] Dissolve precipitated silica and sucrose in water and stir until completely homogeneous. Then heat the solution until the water has completely evaporated.

[0390] Add H2SO4 to the material and convert the sucrose to porous carbon. The precipitated silica particles are encapsulated within the resulting graphite pores.

[0391] Add a diluted sodium hydroxide solution, and heat the mixture to dissolve a part of SiO2 and create voids around the silica particles. Filter and wash the material, and then dry it.

[0392] As previously described, then react the resulting material with Al-AlCl3, and the final product is in the form of Si-impregnated porous graphite powder.

[0393] Example 19: Graphite-Si Composite Material from Natural Graphite

[0394] Natural graphite powder with a nominal composition containing 7% silica, 2% magnesia, and 3.2% alumina is mixed with Al powder and AlCl3. The mixture is then processed at 550 °C. The powder is washed with diluted HCl and then filtered and dried. XRD analysis of the powder shows that the silica has been reduced to silicon, with all lines corresponding to silicon present in the XRD pattern. No evidence of Mg compounds was observed in the final product, indicating that MgO has been converted to MgCl2 and removed during the washing step.

[0395] Example 20: Graphite-Si Composite Material Using Charcoal

[0396] Sodium silicate is dissolved in water. Charcoal powder is then added and stirred with the solution for 2 hours. Diluted HCl is added to the solution. The mixture is then filtered and dried, and the resulting powder is heated at 500 °C to form a charcoal-silica mixture.

[0397] Example 21: C-Si Composite Material Starting from Graphite and Precipitated Silica

[0398] Precipitated silica is mixed with 300 g of graphite powder (C-SiO2 powder), loaded into a reactor, and heated to 550 °C.

[0399] A mixture of Al - AlCl3 is gradually fed into a reaction vessel containing C-SiO2 powder. The excess AlCl3 is collected in a dedicated container for subsequent use. The amount of the collected material is 605 g. The material is discharged and washed in diluted HCl.

[0400] Example 22: C-Si Composite Material Starting from Rice Husk

[0401] Dried pyrolyzed rice husk powder is loaded into a reactor and heated to 550 °C.

[0402] Al powder is mixed with AlCl3, and the mixture is gradually fed into a reaction vessel containing C-SiO2 powder. The material is discharged and washed in excess diluted HCl to remove AlOCl and residual Al powder. The XRD material shows a pattern consistent with Si and C, with no other compounds.

[0403] The resulting mixture is processed at a temperature between 475 °C and 550 °C. The product is discharged and washed with diluted HCl, then filtered and dried. XRD analysis of the powder shows that the silica has been reduced to silicon.

[0404] Those skilled in the art of the present invention should understand that many modifications can be made without departing from the spirit and scope of the present invention. For example, the inventors contemplate that it may be possible to use Mg instead of Al as a reducing agent without significantly deviating from the core of the present invention. For example, if Mg is used instead of Al, the by-products may include a mixture of MgAl2Cl8 and AlOCl, both of which are soluble in diluted HCl and should therefore be separable from the base metal products. This means that such modifications are within the scope of the present invention.

[0405] It should be understood that any prior art publication cited herein does not constitute an admission that such publication forms part of the common general knowledge in the art.

[0406] In the following claims and the foregoing description of the present invention, unless the context requires otherwise by reason of express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the stated features but not to exclude the presence or addition of further features in various embodiments of the present invention.

Claims

1. A method for producing a carbon-silicon composite material, the method comprising: providing a reaction mixture comprising a carbon-silica-based precursor and an aluminum reducing agent; heating the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature that initiates a reaction that reduces the silica; controlling the reaction conditions such that the reaction mixture is prevented from reaching a temperature at which thermal runaway may occur; and separating the resulting carbon-silicon composite material.

2. The method according to claim 1, wherein the carbon-silica-based precursor is provided in the form of one or more of the following: a carbon-silica composite material, a mixture of carbon powder and silica-based powder, carbon-coated silica powder, a carbon cage encapsulating silica-based precursor microparticles, carbon nanotubes, or thin graphite flakes or graphene blended with or coated onto the microparticles, reducible carbon-silicon-oxygen-based powder, a porous carbon-based structure impregnated with silica, silica-impregnated carbon-based powder, silica-impregnated graphite powder, silica-impregnated charcoal powder, pyrolyzed rice husk, a powder of natural graphite containing silica, or a mixture thereof.

3. The method according to claim 1 or claim 2, wherein the carbon-silica-based precursor is provided in the form of powder, flakes, fibers, or microparticles.

4. The method according to any one of claims 1 to 3, further comprising pyrolyzing a mixture of a silica-containing substance and a carbon-based compound to produce the carbon-silica-based precursor.

5. The method according to claim 4, wherein the carbon-based compound is selected from the group consisting of one or more of the following: organic compounds, polymers, carbohydrates, saccharide compounds, glucose, sucrose, biomass, and hydrocarbons.

6. The method according to claim 4 or claim 5, wherein the carbon-based compound is applied to the silica-containing substance by physical deposition, chemical deposition, or wet processing.

7. The method according to any one of claims 1 to 3, further comprising impregnating a carbon-based material with a silicon-containing liquid precursor and then treating the resulting material to produce a carbon-silica-based precursor in the form of graphite-silica powder.

8. The method according to claim 7, wherein the silicon-containing liquid precursor is selected from one or more of the following: silicic acid, sodium silicate, and silanolates.

9. The method according to claim 7 or claim 8, wherein the carbon-based material is selected from one or more of the following: graphite, synthetic graphite, natural graphite, activated carbon, graphene, carbon nanotubes, graphite-mineral mixtures, charcoal powder, pyrolyzed rice husk, carbonized materials produced by pyrolyzing organic materials, graphite or carbonized materials produced by reacting organic materials with acids, and anode-grade graphite powder.

10. The method according to any one of claims 1 to 9, wherein the silica in the carbon-silica based precursor is provided in the form of powder, discrete particles, particles impregnated within a carbon structure, or in other forms containing silica.

11. The method according to any one of claims 1 to 10, wherein the silica in the carbon-silica based precursor is provided in one or more of the following forms: silica nano-powder, fumed silica, precipitated silica, silica fume, silica fiber, silicate, borosilicate, soda glass, silica-based mineral, synthetic mica, mica, and crystalline silica.

12. The method according to any one of claims 1 to 11, wherein the particle size of the silica in the carbon-silica based precursor is less than 100 μm, preferably less than 10 μm, more preferably less than 5 μm, and still more preferably less than 500 nm.

13. The method according to any one of claims 1 to 12, wherein the solid aluminum chloride is provided in the form of powder or fine grains of aluminum chloride with a particle size less than 5 mm.

14. The method according to any one of claims 1 to 13, wherein the aluminum chloride is included in the reaction mixture.

15. The method according to any one of claims 1 to 14, wherein during heating, the gaseous aluminum chloride is made to flow above or through the reaction mixture.

16. The method according to any one of claims 1 to 15, wherein the amount of aluminum chloride provided is between 1 wt% and 500 wt% of the weight of the carbon-silica based precursor.

17. The method according to any one of claims 1 to 16, wherein the aluminum reducing agent is aluminum or an aluminum alloy.

18. The method according to any one of claims 1 to 17, wherein the aluminum reducing agent is provided in the form of powder or flakes with a particle size less than about 50 µm in at least one dimension.

19. The method according to any one of claims 1 to 18, wherein the amount of the aluminum reducing agent in the reaction mixture is between 1% and 1000% of the weight of the silica in the carbon-silica based precursor, and preferably between 5 wt% and 500 wt% of the weight of the silica in the carbon-silica based precursor.

20. The method according to any one of claims 1 to 19, wherein the temperature to which the reaction mixture is heated is lower than 800 °C, preferably lower than 600 °C or preferably lower than 550 °C.

21. The method according to any one of claims 1 to 20, wherein the reaction mixture is heated in a non-reactive atmosphere, and preferably in an inert atmosphere.

22. The method according to any one of claims 1 to 21, wherein the reaction mixture is heated at a pressure between about 0.8 atmospheres and 1.2 atmospheres, preferably at atmospheric pressure.

23. The method according to any one of claims 1 to 22, wherein the reaction conditions are controlled by one or more of the following: gradually feeding one or both of the carbon-silica-based precursor and the aluminum reducing agent into the reaction mixture as the reaction mixture is heated; externally cooling the reaction mixture; cooling the reaction mixture with an excess of solid aluminum chloride; and adding a heat load regulator to the reaction mixture.

24. The method according to any one of claims 1 to 23, wherein a metal-based catalyst is included in the reaction mixture.

25. The method according to any one of claims 1 to 24, wherein an additive based on one or more of Li, B, Na, Mg, Al, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Hf, Ta, W, Re, Os, Pt, Au, and Bi is included in the reaction mixture.

26. The method according to claim 24 or claim 25, wherein the metal-based catalyst or additive is adapted to induce the formation of a carbon-silicon composite material in the form of carbon-silicon nanowires.

27. The method according to any one of claims 1 to 23, wherein the carbon-silicon composite material comprises silicon nanoparticles encapsulated within a carbon-based structure.

28. The method according to claim 27, which further comprises processing the carbon-silica-based precursor to control the volume of the vacant space within the carbon-based structure.

29. The method according to claim 27 or claim 28, wherein the carbon-based structure is a carbon-based shell.

30. The method according to claim 29, wherein the core comprises a vacant space accounting for 0.5% to 75% of the total volume of the core.

31. The method according to any one of claims 1 to 30, wherein the carbon-silicon composite material comprises residual aluminum between 0.01 wt% and 70 wt%.

32. The method according to any one of claims 1 to 31, wherein the carbon-silicon composite material includes a silicon compound having an average composition corresponding to SiOx, where x is between 0 and 1.

9.

33. Carbon-coated silicon nanoparticles produced by the method according to claim 1, wherein the silicon nanoparticles are in the form of microparticles having an irregular shape and an average particle size between 10 nm and 500 nm, and include aluminum between 0.01 wt% and 70 wt%.

34. A carbon-silicon composite material produced by the method according to claim 1, wherein the composite material comprises particles having a silicon-containing core and a coating, the thickness of the coating being between 1 nm and 300 nm and containing at least 50 wt% silicon.

35. A carbon-silicon composite material produced by the method according to claim 1, wherein the composite material is in the form of a core-shell structure, wherein: The core contains void space that accounts for 0.5% to 75% of the total volume of the core and a silicon-based material with a metallic silicon content of less than 99 wt%; and The shell contains a porous or non-porous carbon coating with a thickness between 0.01 nm and 1 μm.

36. A method for reducing silicon dioxide in a silica-based precursor, the method comprising: Coating a silica-based powder with carbon to produce a carbon-coated silica-based precursor; Providing a reaction mixture that includes the carbon-coated silica-based precursor and an aluminum reducing agent; Heating the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature that initiates a reaction in which the silicon dioxide is reduced; Controlling the reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway may occur; and Separating the reaction product that includes reduced silicon dioxide.

37. The method according to claim 1, the method comprising: Mixing a carbon-based liquid-soluble compound with a solvent and a silica-based precursor; and Evaporating the solvent to produce a silica-based precursor coated with a carbon-based compound; Pyrolyzing the silica-based precursor coated with the carbon-based compound to produce a carbon-coated silica-based precursor; Heating a reaction mixture that includes the carbon-coated silica-based precursor and an aluminum reducing agent to a temperature that initiates a reaction in which the SiO2 is reduced in the presence of gaseous aluminum chloride at substantially atmospheric pressure; Controlling the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650 °C; and Separating the reaction product that includes silicon.

38. The method according to claim 38, which is used to produce a carbon-silicon composite material in the form of carbon-silicon nanowires, the method comprising: Forming a reaction mixture of carbon, a silica-based powder, an aluminum reducing agent, and a metal catalyst, wherein the weight of the catalyst is between 5% and 50% of the weight of the silica, and wherein the catalyst induces the formation of silicon nanowires; Heating the reaction mixture to a temperature that initiates a reaction in which the SiO2 is reduced in the presence of gaseous aluminum chloride at atmospheric pressure; Controlling the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650 °C; and Separating the reaction product that includes carbon-silicon nanowires.

39. The method according to claim 38, which further comprises: Impregnating a carbon-based material with a liquid precursor containing silicon and then treating the resulting material to produce the silica-based powder in the form of a graphite-silica-based powder.

40. A method for producing a carbon-silicon composite material, the method comprising: Providing natural graphite powder that contains 0.1% to 20% silica by weight; and In the presence of solid and / or gaseous aluminum chloride, the powder is mixed with a reducing agent containing aluminum and heated, whereby at least a part of the silica is reduced to silicon, and a carbon-silicon composite powder is produced, as well as a by-product containing Al2O3 and / or AlOCl; and Optionally, the carbon-silicon composite is separated from the by-product.

41. A carbon-silicon composite produced by the method according to any one of claims 1 to 32 and 36 to 40.

42. A silicon-impregnated carbon-based composite produced by the method according to any one of claims 1 to 32 and 36 to 40, wherein the carbon-based material in the carbon-silica precursor is graphite, pyrolytic biomaterial or activated carbon.

43. A natural graphite-silicon composite produced by the method according to claim 1 or claim 40, wherein the silica impurities in natural graphite are partially or completely converted to silicon to produce a compound of natural graphite-Si composite, wherein the content of the silicon is between 0.5 wt% and 25 wt%.

44. A carbon-silicon composite produced by the method according to any one of claims 1 to 32 and 36 to 40, wherein the silica in the pyrolytic carbon-silica precursor compound is reduced to silicon; the content of the silicon is between 1 wt% and 25 wt%.

45. A carbon-silicon composite composed of carbon, silicon and aluminum.

46. A carbon-silicon composite produced only from rice husks.

47. The carbon-silicon composite according to claim 45 or claim 46, which is produced according to claim 1.

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