Carbon-silicon composite material and method for producing same

Abstract

Disclosed herein is a method for producing a carbon-silicon composite material, comprising providing a reaction mixture containing a carbon-silica precursor and an aluminum reductant, heating the reaction mixture in the presence of solid or gaseous aluminum chloride or a mixture thereof to a temperature at which a reaction resulting in the reduction of silica is initiated, controlling the reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway could occur, and isolating the produced carbon-silicon composite material.

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbon-silicon composite materials, and in particular to a method for producing carbon-silicon nanoparticles for use in batteries. [Background technology]

[0002] Microporous (or nanoporous) silicon for applications related to lithium-ion energy storage systems has attracted considerable interest in recent years. The use of silicon powder with an appropriate ultrafine morphology as an anode material for lithium-ion batteries (LIBs) can significantly increase battery capacity. However, using silicon as an anode material can result in excessive volume expansion during lithiation of silicon-based anodes. To minimize the resulting impact on battery structure and integrity, many strategies have been proposed focusing on the use of carbon-silicon composites for use as anode materials. In such strategies, silicon nanoparticles (Si-NPs) are typically combined with carbon to improve or tailor the volume change during lithiation / delithiation cycles and provide increased electrical conduction. Typically, such carbon-silicon composites are prepared through pyrolysis, mixing, and / or milling of carbon and Si-NPs. However, such approaches suffer from limitations, including higher costs incurred due to the additional steps required to introduce carbon and an inability to control the structure of the carbon-silicon composite. There are also questionable quality and / or high costs associated with producing Si-NPs via conventional routes such as milling, magnesium reduction, and laser ablation. Therefore, new and more affordable approaches are needed to produce carbon-silicon composites that can be used in lithium-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 comprising: providing a reaction mixture comprising a carbon-silica based precursor and an aluminum reductant; heating the reaction mixture in the presence of solid or gaseous aluminum chloride, or a mixture thereof, to a temperature at which a reaction is initiated resulting in the reduction of silica; Controlling the reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway could occur; and isolating the produced carbon-silicon composite material.

[0004] The present invention offers an improvement over the methods disclosed in International Patent Application No. PCT / AU2021 / 050400 in that it enables the production of carbon-silicon composite materials starting from carbon-silica-based precursors. While the methods disclosed in PCT / AU2021 / 050400 provide for the reduction of silica and metal oxides, it was expected that the presence of carbon in the reaction mixture would inhibit, or at least substantially hinder, the reduction reaction. It was expected that the presence of carbon would reduce the contact area between the reducible silica and the reducing aluminum, thus hindering the reaction and making it difficult (if not impossible) to obtain any significant degree of reduction. However, the inventors have surprisingly and unexpectedly discovered that this is not the case. The inventors have discovered that the beneficial effects of these methods can still be achieved despite the presence of significant amounts of (non-reducible) carbon in the reaction mixture. Thus, the present invention can be used to produce carbon-silicon composite materials with nanomorphologies and structures compatible with use in lithium-ion batteries, but which cannot be obtained using conventional aluminothermic reduction techniques (and indeed other manufacturing techniques). The contents of PCT / AU2021 / 050400 are incorporated herein by reference in their entirety.

[0005] The present invention provides a method for the low-temperature production of carbon-silicon composite materials through the direct in-situ production of silicon nanoparticles starting from silica-carbon-based precursors. As explained below, by-products can include aluminum oxychloride, which is more easily separable than in traditional metallothermal reactions, which typically result in metal oxide by-products. Thus, the present invention enables the direct production of pure carbon-silicon composite materials, substantially free of metal oxides, with yields that can exceed 99%.

[0006] Low-temperature aluminothermic reduction of silica (and other silicon oxides) is attractive because it allows reduction using solid aluminum reactants, consumes little energy, and has the potential to produce reaction products with nanomorphologies and structures that are typically not obtainable using conventional aluminothermic reduction. Furthermore, many aluminum reductants (e.g., Al powder) are safe, low-cost, and readily available, making this material attractive from a techno-economic standpoint.

[0007] Furthermore, low-temperature reduction of C-SiO2 allows the production of full carbon or graphite-silicon composites, silicon-impregnated carbon materials, C-silicon nanoparticles, or microporous C-silicon starting from silica precursors with morphologies well suited for use in applications related to lithium-ion energy storage systems, as discussed above.

[0008] Thus, in at least preferred embodiments, the present invention achieves a significant reduction in the complexity and steps required to produce C-Si composites, where C-Si is produced directly at low temperatures, enabling 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. The approach disclosed herein also reduces production costs, in addition to providing a mechanism for controlling the properties of carbon-silicon products. The temperatures reached in conventional metallothermal reactions and the complexity of CVD systems, along with the steps required to combine carbon with silicon to produce composites, preclude such advantages.

[0009] 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, a carbon-coated silica powder, a carbon cage encapsulating silica-based precursor particulates, a carbon nanotube, or a thin graphitic sheet or graphene blended with or coated on a silica particulate, a reducible carbon-silicon-oxygen based powder, a silica-impregnated porous carbon-based structure, a silica-impregnated carbon-based powder, a silica-impregnated graphite powder, a silica-impregnated charcoal powder, pyrolyzed rice husks, a powder of natural graphite containing silica, or a mixture thereof.

[0010] The present inventors have recognized that the presence of silicon nanoparticles or subnanoparticles embedded within graphite used in LIBs can be advantageous because it increases the electrode capacity; silicon has the ability to carry 10 times more power than carbon in LIBs. The present inventors have discovered that it is possible to produce carbon-silicon composite materials, such as silicon-impregnated graphite and silicon nanoparticles or nanostructures coated or encapsulated in graphene / graphitic materials, through the direct reduction of carbon-silica precursor chemicals with the appropriate structure and morphology.

[0011] Furthermore, natural graphite is an important raw material for manufacturing anodes for lithium-ion batteries (LIBs). This material is mined in many countries around the world and then processed to remove impurities and increase the carbon content to approximately 99% before use as anodes for LIBs. Refining can include crushing and grinding, froth flotation, acid leaching using sulfuric or hydrochloric acid, and heat treatment; these processes typically improve purity to approximately 95%. For some grades, purity improvements beyond 95% may be required, necessitating the use of very aggressive chemicals, such as HF, to remove residual silicon oxide and magnesium oxide. HF is highly hazardous, requiring extreme measures to contain OH&S aspects and potential environmental impacts. Therefore, new, affordable approaches are needed to generate and / or convert residual impurities from graphite materials into forms suitable and / or compatible for use in lithium-ion batteries.

[0012] The present inventors have recognized that for natural graphite, if the silica present in the material can be converted to silicon, the final refined product can be made even more valuable. As outlined elsewhere, silicon nanoparticles provide significant capacity enhancement when added to graphite in lithium battery anodes. Therefore, rather than removing the silica through harmful chemical processes, it would be highly advantageous to convert the silica impurities in natural graphite to silicon and use the resulting material as an anode material. Furthermore, while converting silica to silicon, it may be possible to reduce and / or remove other impurities present, such as magnesium oxide, iron oxide, and other metallic impurities.

[0013] In some embodiments, the carbon-silica based precursor may be provided in the form of a powder, flakes, fibers, or particulates.

[0014] In some embodiments, the method can further include pyrolyzing the mixture of silica-containing material and a carbon-based compound to produce a carbon-silica-based precursor. The carbon-based compound can be, for example, selected from the group consisting of one or more of the following: organic compounds, polymers, carbohydrates, sugars, glucose, sucrose, biomass, and hydrocarbons. The carbon-based compound, in some embodiments, can be applied to the silica-containing material 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 silica-containing powder together with the carbon-based compound.

[0015] In some embodiments, the method may further include impregnating the 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 a graphite-silica powder. The silicon-containing liquid precursor may be selected from, for example, one or more of silicic acid, sodium silicate, and silicon alkoxide. In some embodiments, the carbon-based material may be selected from one or more of graphite, synthetic graphite, natural graphite, activated carbon, graphene, carbon nanotubes, graphite-mineral mixtures, charcoal powder, pyrolyzed rice husks, carbonized materials produced from the pyrolysis of organic materials, graphitic or carbonized materials produced by reacting organic materials with acid, and anode-grade graphite powder.

[0016] In some embodiments, the silica in the carbon-silica based precursor can be provided in the form of a powder, free-standing particles, particles impregnated within a carbon structure, or other morphologies that include silica.

[0017] In some embodiments, the silica in the carbon-silica-based precursor may be provided as one or more of silica nanopowder, fumed silica, precipitated silica, silica fume, silica fiber, silicates, borosilicates, soda glass, silica-based minerals such as halloysite and kaolinite, synthetic mica, mica, and crystalline silica.

[0018] In some embodiments, the silica in the carbon-silica based precursor may have a particle size of less than 100 micrometers, preferably less than 10 micrometers, more preferably less than 5 micrometers, and even more preferably less than 500 nm. In some embodiments, the silica in the carbon-silica based precursor may even have a particle size of less than 100 nm.

[0019] In some embodiments, the solid aluminum chloride may be provided in the form of aluminum chloride powder or granules having a particle size of less than 5 mm. In some embodiments, the aluminum chloride may be included in the reaction mixture.

[0020] In some embodiments, gaseous aluminum chloride may be caused to flow over or through the reaction mixture during heating.

[0021] In some embodiments, the amount of aluminum chloride provided can be about 1 wt % to about 500 wt % of the weight of the carbon-silica precursor, for example, about 10 wt % to about 300 wt %, about 50 wt % to about 300 wt %, about 100 wt % to about 200 wt %, about 100 wt % to about 500 wt %, or about 100 wt % to about 150 wt % of the weight of the carbon-silica precursor.

[0022] In some embodiments, the aluminum reductant can be aluminum or an aluminum alloy.

[0023] In some embodiments, the aluminum reductant may be provided in the form of a powder or flake having a particle size in at least one dimension of less than about 50 μm (e.g., less than about 40 μm, less than about 30 μm, or less than about 20 μm), although in alternative embodiments the particle size may be up to 100 micrometers, or even up to 500 micrometers.

[0024] In some embodiments, the amount of aluminum reductant in the reaction mixture can be from 1% to 1000% by weight of the silica in the carbon-silica based precursor, preferably from 5% to 500% by weight of the silica in the carbon-silica based precursor.

[0025] In some embodiments, the temperature to which the reaction mixture is heated can be less than 800°C, preferably less than 600°C, or preferably less than 550°C.

[0026] In some embodiments, the reaction mixture may be heated in a non-reactive atmosphere, preferably an inert atmosphere (i.e., an atmosphere that is inert to the reactants, which may include a CO2 or N2 atmosphere).

[0027] In some embodiments, the reaction mixture can be heated at a pressure of about 0.8 to 1.2 atmospheres, preferably at atmospheric pressure. Reactions carried out at or near atmospheric pressure require less sophisticated equipment, are safer, and are generally cheaper to carry out.

[0028] In some embodiments, the reaction conditions can be controlled by one or more of the following: gradually feeding additional one or both of the carbon-silica-based precursor and the aluminum reductant into the reaction mixture as it is heated, externally cooling the reaction mixture, quenching the reaction mixture with excess solid aluminum chloride, and adding a thermal load mitigator to the reaction mixture. The gradual introduction of reactants into the reaction mixture (particularly Al and AlCl) prevents thermal runaway due to, for example, limited and controllable availability of reactants at any given time.

[0029] In some embodiments, alloying additives and metal-based catalysts may 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, Pg, Ag, Sn, Sb, Hf, Ta, W, Re, Os, Pt, Au, and Bi may be included in the reaction mixture. In some such embodiments, the metal-based catalyst or additive may act to induce the formation of carbon-silicon composites in the form of carbon-silicon nanowires. For example, the use of metal-based catalysts such as Ag, AgCl, Zn, and ZnCl2 results in the formation of carbon-silicon nanowires.

[0030] In some embodiments, the carbon-silicon composite material can include silicon nanoparticles encapsulated within a carbon-based structure. In such embodiments, the method can further include processing the carbon-silica-based precursor to control the volume of void space within the carbon-based structure. In some such embodiments, the carbon-based structure can be a carbon-based shell. In some such embodiments, the core can include void space of 0.5% to 75% (e.g., 0.5% to 50%) of the total volume of the core.

[0031] In some embodiments, performance of the present method can result in carbon-silicon composite materials containing 0.01 wt. % to 70 wt. % residual aluminum. The inventors believe that composite materials containing residual aluminum are a unique feature of the present invention and likely confer useful functionality to the composite material. For example, the presence of residual aluminum oxide can help improve the material's performance as an anode in lithium-ion batteries. Furthermore, because the solubility of aluminum in metallic silicon is negligible, the presence of residual metallic aluminum does not interfere with the silicon's ability to store lithium and may increase the conductivity of the anode.

[0032] In some embodiments, performance of this method can result in carbon-silicon composite materials comprising silicon compounds having an average composition corresponding to SiOx, where x is between 0 and 1.9.

[0033] In a second aspect, the present invention provides carbon-coated silicon nanoparticles produced according to the method of the first aspect, the silicon nanoparticles being in the form of fine particles having an irregular shape and an average particle size of from 10 nm to 500 nm, and comprising from 0.01% to 70% by weight of aluminium.

[0034] In a third aspect, the present invention provides a carbon-silicon composite material produced according to the method of the first aspect, the composite material comprising particles having a silicon-containing core and a coating having a thickness of from 1 nm to 300 nm and containing at least 50% silicon by weight.

[0035] In a fourth aspect, the present invention provides a carbon-silicon composite material produced according to the method of the first aspect, the composite material being in the form of a core-shell structure, the core comprising a silicon-based material having a metallic silicon content of less than 99 wt.% and 0.5% to 75% (e.g., 0.5% to 50%) of the total volume of the core being void space, and the shell comprising a porous or non-porous carbon coating having a thickness of 0.01 nm to 1 micrometer.

[0036] In a fifth aspect, the present invention provides a method for reducing silica in a silica-based precursor, the method comprising: coating a silica-based powder with carbon to form a carbon-coated silica-based precursor; providing a reaction mixture comprising a carbon-coated silica-based precursor and an aluminum reductant; heating the reaction mixture in the presence of solid or gaseous aluminum chloride, or a mixture thereof, to a temperature at which a reaction is initiated resulting in the reduction of silica; Controlling the reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway could occur; and isolating the reaction product comprising the reduced silica.

[0037] Specific embodiments of the method of the fifth aspect are described below. In a first embodiment, the method comprises: mixing a liquid soluble carbon-based compound with a solvent and a silica-based precursor; evaporating the solvent to produce a silica-based precursor coated with a carbon-based compound; pyrolyzing the carbon-based compound-coated silica-based precursor to produce a carbon-coated silica-based precursor; heating a reaction mixture comprising a carbon-coated silica-based precursor and an aluminum reductant at substantially atmospheric pressure and in the presence of gaseous aluminum chloride to a temperature at which a reaction resulting in the reduction of SiO2 is initiated; controlling the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650°C; and isolating the silicon-containing reaction product.

[0038] In a second embodiment, the method comprises: forming a reaction mixture of carbon, a silica-based powder, an aluminum reductant, and a metal catalyst, the weight of the catalyst being 5% to 50% of the weight of the silica, the catalyst inducing the formation of silicon nanowires; heating the reaction mixture at atmospheric pressure and in the presence of gaseous aluminum chloride to a temperature at which a reaction is initiated resulting in the reduction of SiO2; controlling the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650°C; and isolating the reaction product comprising the carbon-silicon nanowires.

[0039] The second embodiment may further include impregnating the carbon-based material with a liquid precursor comprising silicon and then processing the resulting material to produce a silica-based powder in the form of a graphite-silica-based powder.

[0040] In a sixth aspect, the present invention provides a method for producing a carbon-silicon composite material, the method comprising: Providing a powder of natural graphite containing 0.1% by weight to 20% by weight of silica; mixing the powder with a reducing agent comprising aluminum in the presence of solid and / or gaseous aluminum chloride and heating, whereby at least a portion of the silica is reduced to silicon and a carbon-silicon composite powder is produced, along with by-products comprising Al2O3 and / or AlOCl; Optionally, separating the carbon-silicon composite material from the by-products.

[0041] In a seventh aspect, the present invention provides a carbon-silicon composite material produced according to the method of any of the first, fifth and sixth aspects.

[0042] In an eighth aspect, the present invention provides a silicon-impregnated carbon-based composite material produced according to the method of any of the first, fifth, and sixth aspects, wherein the carbon-based material in the carbon-silica-based precursor is graphite, pyrolyzed biomaterial, or activated carbon.

[0043] In a ninth aspect, the present invention provides a natural graphite-silicon composite material produced according to the method of the first or sixth aspects, wherein silica impurities in the natural graphite are partially or fully converted to silicon to produce a compound of natural graphite-Si composite material, and the silicon content is between 0.5% and 25% by weight.

[0044] In a tenth aspect, the present invention provides a carbon-silicon composite material produced according to the method of any of the first, fifth, and sixth aspects, wherein the silica in the pyrolyzed carbon-silica precursor compound is reduced to silicon, and the silicon content is between 1% and 25% by weight.

[0045] In an eleventh aspect, the present invention provides a carbon-silicon composite material consisting of carbon, silicon, and aluminum.

[0046] In a twelfth aspect, the present invention provides a carbon-silicon composite material made exclusively from rice husk or natural graphite.

[0047] In some embodiments of the eleventh and twelfth aspects, a carbon-silicon composite material is produced using the method of the present invention.

[0048] Also disclosed herein is a method for producing a carbon-silicon composite material, the method comprising: - providing a mixture of a silica-based powder and a carbon-based material, the mixture being in the form of a blended mixture of a silica-based powder and a carbon-based powder, or a powder of a carbon-coated silica precursor, or a powder of a silica-impregnated carbon-based material, or a powder of natural graphite containing silica-based impurities; reacting the mixture with an aluminum-based reductant, including aluminum powder and aluminum chloride, at a temperature of 300°C to 650°C, wherein the aluminum chloride is in the form of a solid or gaseous form; The reaction step results in the formation of a powder mixture of reduced silica-carbon product and aluminum-based by-products, the product being the carbon and silicon compound SiO x and x is 0 to 1.9; - separating the reaction products, The carbon-based material can be in any form or phase, including graphite, synthetic graphite, natural graphite, activated carbon, graphene, carbon nanotubes, charcoal, graphite-mineral mixtures, carbon-based minerals, graphitic materials produced from the pyrolysis of organic materials, graphitic materials produced by reacting organic materials with acids, anode-grade graphite powder, charcoal powder, pyrolyzed rice husk powder, or synthetic graphite. The carbon-based material can be in the form of flakes, spherical powders, porous graphite powders, graphene, carbon nanotubes, carbon nanostructures, which may be coated or uncoated. The carbon-based material can be in the form of a coating on the silica-based precursor microparticles, a carbon cage encapsulating the silica-based precursor microparticles, thin graphitic sheets or graphene blended with or coated on the silica microparticles, a porous structure in which silica or silicon-oxygen compounds are impregnated into the pores of the carbon-based material, or simply in the form of a powder mixed with the silica-based precursor.

[0049] Also disclosed herein is a method for producing a carbon-silicon composite material, the method comprising: providing a reactant powder comprising a silica-based compound and a carbon / graphite-based compound; - mixing, heating and reacting the reactant powder with an aluminum-based reductant comprising aluminum and aluminum chloride to reduce at least a portion of the silica to silicon; and separating the silicon-carbon product.

[0050] Also disclosed herein is a method for producing a carbon-silicon composite material, the method comprising: providing a first reaction mixture comprising a silica-based powder mixed or coated with a carbon-based compound; treating the reaction mixture to convert the carbon-based compounds into stable carbon-based materials; - mixing the resulting carbonaceous material-silica-based powder mixture with an aluminum-based reductant containing aluminum and aluminum chloride, heating and reacting to reduce at least a portion of the silica to silicon; and separating the silicon-carbon product.

[0051] In some embodiments, the silica-based powder is coated with a carbon-based compound.

[0052] In some embodiments, the coated powder is first treated to produce a stable carbon-based coating around the silica-based powder before proceeding to reduce the silica to silicon. Examples of suitable means include coating with a polymer or other organic compound, followed by suitable carbonization or other coating techniques such as chemical vapor deposition and physical vapor deposition.

[0053] In some embodiments, the silica-based powder is coated with a compound based on an organic material that can be pyrolyzed to produce the intermediate product of the carbon-coated silica-based powder. Examples of suitable organic compounds include sugar and glucose.

[0054] In some embodiments, the silica-based powder is coated with glucose, which is then pyrolyzed to produce the intermediate product of a carbon-coated silica-based powder.

[0055] In some embodiments, the silica-based powder is first coated using a suitable means with an organic compound such as a carbohydrate or sugar, and the coated powder is then pyrolyzed to produce the intermediate product of a carbon-coated silica-based powder.

[0056] In some embodiments, the carbon coating on the SiO2-based precursor powder is discontinuous.

[0057] In some embodiments, the carbon coating on the Si-based particle product is discontinuous.

[0058] In some embodiments, the carbon coating on the SiO2-based precursor powder is porous.

[0059] In some embodiments, the carbon coating on the Si-based particle product is porous.

[0060] In some embodiments, a soluble silicon-based compound is impregnated into graphite powder, which is then treated to convert it to silica, to obtain an intermediate precursor in the form of a silica-impregnated graphite powder. The intermediate precursor is then reacted with aluminum-aluminum chloride to produce an intermediate product in the form of a silicon-impregnated graphite powder and an aluminum-based by-product. The intermediate product is then treated to remove the by-product.

[0061] In one example of this embodiment, the soluble silicon-based compound is sodium silicate. First, the sodium silicate is dissolved in water and then mixed with graphite powder, which is preferably porous. An acidic reagent, such as HCl, is then added to convert the silicate to aluminum hydroxide. The resulting mixture is then calcined to convert the hydroxide to oxide, and the resulting powder is thoroughly washed to remove NaCl resulting from the neutralization process. The remaining intermediate precursor powder consists of graphite powder with silica particles deposited on all available surfaces, including the pores and outer surfaces of the graphite powder. The intermediate precursor is then reacted with aluminum-aluminum chloride to produce an intermediate product in the form of silicon-impregnated graphite powder and aluminum-based by-products. The intermediate product is then treated to remove the by-products.

[0062] In other embodiments, an intermediate precursor powder of silica-impregnated porous carbon can be produced by first impregnating an organic material with silica, followed by pyrolysis / carbonization to produce a silica-impregnated graphitic powder.

[0063] In some embodiments, the aluminum chloride may be provided in the form of solid aluminum chloride. The aluminum chloride may be provided in the form of a powder or granules having a particle size of less than 5 mm. In some embodiments, aluminum chloride powder may be included in the reaction mixture (e.g., premixed with the aluminum reductant), where AlCl sublimes to remove energy from the reactants and help offset the effect of the exothermic energy generated by the reaction of Al-AlCl with SiO.

[0064] In some embodiments, the aluminum chloride may be provided in the form of gaseous aluminum chloride, which may be, for example, caused to flow over the heated reaction mixture.

[0065] In some embodiments, the temperature to which the reaction mixture is heated (i.e., to initiate the reduction reaction) can be less than 800° C., preferably less than 600° C., preferably between 200° C. and 600° C. As described herein, lower reaction temperatures are preferred because the reaction products do not melt (and are therefore more easily purified) and the morphology of the reagents can be preserved.

[0066] In some embodiments, the product is further reacted with a reagent to reduce the volume of Si encapsulated in the carbon shell. Examples of suitable reagents include acids.

[0067] In some embodiments, the intermediate carbon-silica precursor is reacted with a reagent to reduce the amount of Si encapsulated in the carbon shell or pores, creating voids in the shell or pores to allow for the formation of aluminum oxychloride by-products, which then allow space for the final carbon-encapsulated silicon product to expand during silicon lithiation.

[0068] In some embodiments, the silica-based precursor may include a metal additive, and the product may then include an elemental metal, a metal suboxide, an alloy including a metal, a compound including a metal, a composite including a metal, or a composite including a metal or mixtures thereof.

[0069] In some embodiments, the reaction products can include products resulting from reducing the precursor and one or more by-products of aluminum chloride, aluminum oxychloride, and aluminum oxide. In some embodiments, the reaction products can be further processed to separate the by-products from the product resulting from reducing the precursor. In some embodiments, the by-products can include aluminum oxychloride, which can be separated from the reduced metal oxide by washing the reaction products with an aqueous medium.

[0070] In some embodiments, any gaseous aluminum chloride that is not consumed during the reaction can be condensed for beneficial reuse, such as recycling to the reaction mixture.

[0071] In some embodiments, heating the reaction mixture includes multiple heating steps and the formation of intermediate species, such embodiments will be described in more detail below.

[0072] In one embodiment of the method of the first aspect of the present invention, the silica-based precursor is SiO, which is first processed to produce a C-SiO precursor powder; the aluminum reductant is aluminum or an aluminum alloy in solid powder form; and the reaction mixture is heated to an initial temperature of about 200°C to 600°C (preferably 300°C to 550°C) and the reaction conditions are controlled to maintain a temperature below about 650°C. The reaction product of such a method can be a carbon and silicon composite or a mixture of silicon and SiO, having a particle size of less than 500 nm. In some embodiments, the particles can be in the form of agglomerates having a diameter of up to greater than 10 micrometers. In some other embodiments, the reaction product can include a mixture of silicon and AlO.

[0073] Also disclosed herein is a carbon-coated silicon powder produced according to the method described in the preceding paragraph, the silicon powder being in the form of particulates having irregular shapes and an average particle size of 1 nm to 500 nm, and a composition comprising Al at a level of 0.01 wt% to 70 wt%.

[0074] Also disclosed herein is a carbon-silicon composite powder having particulates composed of silicon-based particles and carbon cages with cavities containing void spaces, where the volume ratio of voids to silicon-based material can be 1% to 80%. The carbon cages can be composed of graphitic carbon materials made from graphite, graphene, or related compositions, and can be porous. The cage wall thickness can be 0.01 nm to 10 micrometers, preferably 0.1 nm to 100 nm, and more preferably 0.1 nm to 10 nm. The particle size of the C—Si particulates produced according to this aspect can be 1 nm to 50 micrometers. For this aspect, the method includes 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.

[0075] Also disclosed herein is a method for reducing SiO in a SiO-containing precursor, the method comprising: providing a reaction mixture comprising a carbon-coated precursor containing SiO and an aluminum reductant; - heating the reaction mixture at atmospheric pressure in the presence of gaseous aluminum chloride to a temperature at which the reaction leading to the reduction of SiO2 begins; - controlling the reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650°C; - isolating the silicon-containing reaction product.

[0076] Also disclosed herein is a carbon-silicon composite powder consisting of a mixture of graphene or graphitic powder and silicon nanoparticles, produced by reducing carbon-coated silica powder with Al-AlCl.

[0077] Also disclosed herein is a method for producing carbon-silicon composite materials, in which a mixture of silica and a carbon-based precursor is first reduced with an acid to produce a silica-carbon mixture, which is then reduced to Si-C using Al-AlCl.

[0078] Also disclosed herein is a product in the form of graphite powder impregnated with silicon, which may be in the form of nanoparticles or nanowires.

[0079] In one embodiment for the production of graphite powder impregnated with silicon nanowires, the method comprises the main steps of depositing a metal-based catalyst within the pores of graphite particles, followed by adding a silica-based precursor and processing the resulting material according to any of the preceding or subsequent embodiments or aspects.

[0080] Given the similarities between the aluminothermal and magnesiumothermal processes, the inventors believe that the teachings of the present invention will also be applicable to reductants using magnesium-aluminum chloride, where a magnesium reductant is used instead of an aluminum reductant. [Brief explanation of the drawings]

[0081] Features, embodiments and advantages of the present invention will become apparent, by way of example only, from the following description of embodiments thereof, with reference to the accompanying drawings, in which:

[0082] [Figure 1] FIG. 1 shows a process schematic of one exemplary embodiment showing steps for reducing a C—SiO 2 -based precursor with Al in the presence of gaseous AlCl 3 . [Figure 2] TEM micrographs of C-Si powder obtained using PVP coating. [Figure 3] 1 shows the XRD trace for the C-coated Si powder of Example 10. [Figure 3] 1 shows an XRD trace for a pure Si sample obtained without a carbon coating in Example 10. DETAILED DESCRIPTION OF THE INVENTION

[0083] In this specification, unless expressly stated otherwise: The terms "aluminum reducer", "reduced Al agent", "reduced Al alloy" and "reduced Al powder" are used interchangeably and refer to powders of pure Al and alloys based on Al; - References to a material "based on", e.g., a base metal or alloy based on Al as the reducing agent, refer to a material that contains at least 10%, preferably at least 50%, of the named component; - the term "aluminum chloride" refers to chlorides of Al, such as AlCl3 and Al2Cl6. When used, the terms "aluminum chloride" or "aluminum chloride", or "AlCl3" include reference to any anhydrous metal chloride based on Al-Cl, in both gaseous and solid form; - When used, the term "AlCl3(g)" refers to any aluminum chloride in gaseous or vapor form; - When used, the term "AlCl3(s)" refers to any aluminum chloride in solid powder form; the term "AlOCl / Al2O3" means AlOCl and / or Al2O3, - the terms "AlOCl" and "aluminum oxychloride" are used interchangeably; The terms "silicon oxide," "silica," and "SiO2" refer to both amorphous and crystalline forms of silicon oxide. The terms "C-based coating" and "carbon-based coating" are used to describe coating compounds based on carbon. "C-coated" and "carbon-coated" are used to describe coatings based on pure carbon or stable carbon compounds.

[0084] Disclosed herein is a method for forming a carbon-coated or carbon-encapsulated silicon-based powder by reacting a powder mixture containing a carbon-coated reducible precursor SiO-based precursor and a reduced Al alloy (e.g., Al powder) in the presence of aluminum chloride to partially or completely reduce silica to silicon. The aluminum chloride is in the form of a solid powder or a gas / vapor. In some embodiments, the aluminum chloride can be in the form of a liquid eutectic phase.

[0085] The reduction reaction between the silica in the precursor and the reduction reactants Al and AlCl is exothermic, and the method includes procedures to control the reduction reaction and moderate the reaction rate to prevent thermal runaway and additional reaction products.

[0086] The product of this process is a carbon and Si-based powder, and the by-products may include aluminum chloride and aluminum oxychloride, and / or aluminum oxide. The aluminum oxychloride / aluminum oxide by-products are discharged with the product and may be components of the powder product, or they can be separated by suitable means. The aluminum oxychloride by-products can be separated from the base metal (e.g., Si powder) by washing in a suitable solvent (e.g., HO or dilute HCl (HO-HCl)).

[0087] Exemplary embodiments of the method of the present invention aim to achieve a significant reduction in the complexity and number of steps, as well as a significant reduction in the temperatures required by conventional reduction techniques and other existing processes that require high temperatures or pressures. This is in addition to providing a means for controlling the volume of void space within the carbon that encapsulates the Si particulates. Exemplary embodiments of the method of the present invention aim to provide powders of metal compounds with improved engineering properties, and new products with unique properties inherited from the starting precursor oxides.

[0088] The present invention includes several aspects, specific forms, and embodiments described below.

[0089] According to a first example, there is provided a method for the direct production of silicon-carbon composite materials through the reduction of carbon-silica based precursor chemicals with Al in solid form and a reducing agent based on aluminum chloride in solid or gas / vapor form, preferably at atmospheric pressure and at temperatures below 800°C, preferably below 600°C, more preferably between 100°C and 600°C, even more preferably between 200°C and 600°C, even more preferably between 200°C and 600°C, even more preferably between 200°C and 550°C, the method comprising: - making C-SiO2 by any available means, including blending powders based on C-based and silica, impregnating a carbon-based powder with silica, coating an SiO2-based powder with an organic coating and then converting it to carbon, or making a porous graphitic structure impregnated with silica; - mixing, heating and reacting a reaction mixture comprising C-SiO2 and Al-based powder in the presence of solid or gaseous aluminum chloride, the products of the process comprise compounds based on base metals and by-products comprise AlOCl and / or Al2O3; The product of the process is optionally treated to remove by-products.

[0090] Examples of products include Si-impregnated graphite powder, C-coated metal silicon nanoparticles, C-Si-Ag nanoparticles, metal silicon-coated carbon-coated SiO2 particles, silicon monoxide (SiO or SiO x ), or mixtures thereof. Other examples include C-shells encapsulating Si-nanoparticles and C-shells encapsulating porous Si microparticles.

[0091] According to a second example, there is provided a method for the direct production of silicon-based microparticles encapsulated in a carbon / graphitic structure, coating or shell, carried out 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 gas / vapor form, preferably at atmospheric pressure, at a temperature below 800°C, preferably below 600°C, more preferably at a temperature between 100°C and 600°C, even more preferably at a temperature between 200°C and 600°C, even more preferably at a temperature between 200°C and 600°C, even more preferably at a temperature between 200°C and 550°C, the method comprising: - coating and treating the SiO2-based powder with a carbon-based compound to produce a carbon / graphite coating on the SiO2-based particles, C-SiO2; - optionally removing, etching or dissolving a portion of the coated / encapsulated silica particles; - mixing, heating and reacting the obtained C-SiO2 powder with Al in the presence of solid or gaseous aluminum chloride; the products of the process comprise compounds based on base metals and by-products comprise AlOCl and / or Al2O3; The product of the process is optionally treated to remove by-products.

[0092] Examples of products include C-coated metal silicon nanoparticles, C-Si-Ag nanoparticles, metal silicon coated carbon-coated SiO2 particles, silicon monoxide (SiO or SiO x ), or mixtures thereof. Other examples include C-shells encapsulating Si-nanoparticles and C-shells encapsulating porous Si microparticles.

[0093] The gaseous aluminum chloride by-product may be continuously removed, and the solid by-products, such as aluminum oxide and / or aluminum oxychloride, may be discharged with the product and then separated by appropriate post-treatment means.

[0094] According to a third example, there is provided a method for producing a C-Si based metal system, wherein a precursor comprising C-SiO2 and a metal additive is reacted with Al powder in the presence of gaseous aluminum chloride AlCl3(g) at a temperature between 200°C and 800°C, preferably between 200°C and 800°C, more preferably between 200°C and 600°C, to produce a product comprising a metal alloy and a compound of a base metal, and a by-product comprising aluminum oxychloride and / or aluminum oxide.

[0095] According to a fourth example, a method for producing carbon-encapsulated silicon nanoparticles is provided, in which a precursor comprising C-coated SiO2 powder is reacted with Al and gaseous aluminum chloride. at a pressure below -1.2 bar, preferably at atmospheric pressure, The reaction is carried out at a temperature below -600°C, preferably at a temperature between 200°C and 600°C, A product is formed containing carbon-encapsulated silicon nanoparticles and solid by-products including aluminum oxychloride (AlOCl). The silicon nanoparticles can be crystalline, amorphous, or a mixture thereof. Alloying additives can be included through suitable addition to the silica-based precursor. Excess aluminum chloride is recycled through the process, and other solid by-products are discharged with the powder product, which can then be separated from the silicon powder by appropriate post-processing means. AlOCl and any residual Al can be removed by washing in a suitable solvent capable of dissolving AlOCl, such as HO and diluted HCl (HO-HCl). Residual unreacted precursor can form part of the final product, or alternatively, they can be removed using other suitable means. The carbon-encapsulated silicon nanoparticles can be in a variety of morphologies, including porous frameworks, nanostructured particulates, hollow spheres, nanoparticles, nanorods, or nanowires.

[0096] According to a fifth embodiment, a method for producing a carbon-silicon nanowire composite is provided, comprising: mixing a precursor comprising C—SiO powder mixed with a metal catalyst precursor with Al and gaseous aluminum chloride; at a pressure below -1.2 bar, preferably at atmospheric pressure, The reaction is carried out at a temperature below -600°C, preferably at a temperature between 200°C and 600°C, A product containing carbon-silicon nanowires and a solid by-product containing aluminum oxychloride (AlOCl) are formed. The silicon nanoparticles can be crystalline, amorphous, or a mixture thereof. A catalyst precursor may be included through the appropriate addition of pure metal powders, metal chlorides, metal oxides, or mixtures thereof to the silica-based precursor. Suitable catalysts include transition metal-based powders, including Ag, Cu, Zn, Au, and Al. Excess aluminum chloride is recycled throughout the process, and other solid by-products are discharged with the powder product, which can then be separated from the silicon powder by appropriate post-processing means. AlOCl and any residual Al can be removed by washing in a suitable solvent capable of dissolving AlOCl, such as HO and diluted HCl (HO-HCl). Residual unreacted precursors can form part of the final product, or alternatively, they can be removed using other suitable means. C-silicon nanowires can contain other forms of Si, including porous skeletal forms, nanostructured particulate forms, hollow spheres, nanoparticles, or nanorods.

[0097] Silica can react with molten Al at temperatures between 700°C and 1200°C, usually with a self-propagating reaction / thermal runaway, resulting in the formation of a molten mixture containing Al2O3, which is known to be difficult to remove. In the present disclosure, AlCl3, in solid or gaseous form, is added to the SiO2-Al mixture and reacted at atmospheric pressure, reducing the threshold reaction temperature below 600°C and providing control over the reaction mechanism, which can advantageously lead to the formation of specific products, including reduced silica.

[0098] Furthermore, the by-product is a solid AlOCl powder that can be separated from the reaction product by washing and filtering (e.g., with HO or dilute HCl), as opposed to the Al2O3 by-product, which is difficult to remove. Also, because the reaction according to this method does not involve liquid metals and excessive heating, it is possible for many base metals to preserve morphological features from the starting SiO2 precursor (e.g., Si nanopowder from SiO2 nanopowder). Overall, the results include significant improvements to product quality, accompanied by a significant simplification of processing conditions typically required.

[0099] It is known that SiO2 can react with Al in molten AlCl3 to produce a Si-SiO2 mixture under high-pressure conditions suitable for the formation of liquid AlCl3 and at temperatures up to 250°C. However, this method suffers from a number of significant problems, including the need for high pressure to produce molten AlCl3. Furthermore, despite long reaction times (>10 hours), the maximum reported yield is 75%. The inventors have discovered that by using gaseous AlCl3, the reduction of SiO2 to Si can be carried out at temperatures between 200°C and 600°C and atmospheric pressure, with yields up to 99% over short periods of time. Liquid AlCl3 simply cannot exist under the reaction conditions of the present invention.

[0100] Exemplary embodiments of the present method provide an enhanced product technology that has advantages over the prior art due to the ability to reduce processing temperatures and times and expand the range of materials that can be produced. Exemplary embodiments of the present approach differ from prior art carbothermal and metallothermal processes in several other key aspects. 1- The novel method allows the direct production of Si-impregnated carbon-based materials, natural graphite-silicon composites, rice husk-based derived carbon-silicon composites, or C-coated or C-encapsulated Si particles. 2- The method reduces the threshold reaction temperature, allowing the synthesis of compositions and morphologies that are not normally obtainable under carbothermal and metallothermal processes (e.g., nanoparticle morphologies, complex compositions). 3- The process is carried out under relatively mild conditions at atmospheric pressure and relatively low temperatures. 4- The process requires low energy input and generates no or minimal waste. 5-Al is an attractive reducing agent because it is readily available and low cost, and the compound is a valuable industrial chemical and does not present significant handling difficulties (e.g., AlCl). 6- The process allows control over the void space within the encapsulated shell.

[0101] Detailed Description of the Invention As noted above, in a preferred embodiment, the present invention provides a low temperature method for the direct production of C-Si based metal compositions.

[0102] Disclosed herein is a method for reducing a solid precursor comprising silicon and carbon using a reduced Al alloy in powder form and aluminum chloride in a reaction vessel at a temperature below 800°C, preferably below 600°C, more preferably between 180°C and 600°C, even more preferably between 400°C and 600°C, and most preferably between 200°C and 600°C, the method comprising: Step 1: Fabricating carbon-SiO2 powder, which can be done via any means capable of producing such a composition, including: Impregnating graphite powder with silica, or Fabricating a graphite powder-silica composite; or The first step is to coat a SiO2-based precursor with a C-based compound and then treat it to carbonize the coating, producing a carbon coating on the SiO2-based particles, C-SiO2. Step 2: Mixing the reaction mixture containing the C-SiO2-based powder with the reduced Al alloy in the presence of aluminum chloride, heating and reacting; aluminum chloride is in gaseous or solid form and is present in an amount of 1% to 500% by weight of the precursor silica, the product of the process comprises silicon-based compounds, and by-products comprise aluminum chloride and aluminum oxychloride, and / or aluminum oxide; The reaction between silica and the reducing Al agent is exothermic, - the pressure in the reaction vessel is kept below the threshold pressure required to produce molten AlCl3; One or more of the —C—SiO 2 based solid precursor powder, the reduced Al alloy powder, and aluminum chloride are gradually fed into a reaction vessel. Step 3: At the end of step 2, the product is treated to remove by-products and obtain the final product in the form of a powder based on C-Si. Step 4: Optionally, react the powder with a reagent to remove some of the Si-based particles encapsulated within the carbon casing.

[0103] In contrast to existing techniques for the reduction of silicon oxide, the present method allows the reaction between SiO2, Al, and AlCl3 to occur at near atmospheric pressure in the range of 200-600 °C, according to the overall reaction: C-SiO2 + 1.333Al + 0.666AlCl3(g) → C-Si + 2AlOCl, ΔG = -164.6 kJ / mol at 500°C (R1)

[0104] As outlined herein, the products can be in various forms, including silicon-impregnated carbon, graphite-silicon composites, carbon-coated silicon particles, and carbon-shell-silicon core-shell structures. For all products, the present invention offers several advantages. For example, in the case of the core-shell structure, significant voids exist within the carbon shell to allow for silicon expansion during lithiation; the starting volume of 1 mole of SiO2 is 23 mL, and the resulting volume of Si is 12 mL. Assuming all carbon-encapsulated shells remain intact, the free space within the C shell is approximately 47.8%, which can be used as a buffer for Si expansion during the lithiation process. Furthermore, a portion of the encapsulated SiO2 particles can be removed prior to reduction, according to reaction R1, to create more free space within the encapsulating carbon shell and avoid shell collapse during the reaction due to the formation of Si and AlOCl.

[0105] The amount of void space within the C-shell can be further increased through controlled etching of Si within the C-shell. Procedures for increasing the volume of void space include reacting the C-Si composite with a liquid chemical 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 controllably reacting with Si.

[0106] The process according to this scheme is carried out in an open reactor vessel under 1 atmosphere of inert gas (e.g., Ar, N2, or CO2). Extensive testing has been carried out by the inventors to identify 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 in short processing times of less than 1 hour.

[0107] The method of the present invention requires that AlCl3 be in the gas phase and that a molten AlCl3 phase not form. While not wishing to be bound by theory, the high yields observed in our tests appear to be due to a gas-solid reaction involving gaseous AlCl3 and gaseous Al-Cl species. The presence of a liquid AlCl3 phase may reduce the efficiency of the reaction because it becomes limited by the ability of molten AlCl3 to diffuse through the solid particles to reach unreacted SiO2 particles and / or particle cores. Attempts to use liquid eutectic AlCl3-NaCl as a source of AlCl3 for the reduction of SiO2 have resulted in much lower yields than those observed with gaseous AlCl3.

[0108] For all aspects and embodiments of the present method, the AlCl in the reaction vessel or reacting with the other reactant SiO-Al must not be in a molten state due to pressure buildup, and the vessel is sealed and heated to induce melting of the AlCl. For all aspects and embodiments, the reaction in SiO-Al-AlCl according to the present disclosure is preferably carried out in a vessel open to atmospheric pressure, with no ability to build pressure within the vessel.

[0109] Precursor Chemicals and Products As previously mentioned, the primary effects and advantages of the present invention arise due to AlCl reacting with the carbon-SiO reactant and aluminum at temperatures below the melting point of aluminum, resulting in the direct production of carbon-silicon composite materials, such as C-encapsulated Si nanoparticles. Discussions throughout this disclosure that refer to the reactions and mechanisms driving the role of AlCl are intended only to highlight 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.

[0110] Suitable precursors include amorphous SiO2 powder, quartz powder, silica nanopowder, porous silica powder, precipitates, fumed silica, glass powder, glass flake, borosilicate glass, natural mica, silica fume, silica minerals, halloysite, kaolinite, synthetic mica, silica impregnated carbon, silica impregnated graphite, silica impregnated charcoal, natural graphite containing silica, pyrolyzed rice husk, or any other composition based on SiO2.

[0111] 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 sugars such as sucrose and glucose-based compounds.

[0112] The particle size of the precursor can range from a few nanometers to several millimeters, depending on the desired properties of the final product. However, small particle sizes of less than 50 micrometers are preferred. Nanopowders with particle sizes of less than 1 micrometer and less than 100 nm can be used and typically result in more efficient reactions and better final products. For example, silica nanopowder or fumed silica is preferred as a starting precursor for obtaining silicon nanoparticles.

[0113] Regarding Si, we have found that amorphous silica is more suitable for this reaction scheme because it is more reactive and can be obtained in a finer form than quartz. Therefore, it is preferred that the Si in the starting SiO precursor be amorphous or porous with a large surface area.

[0114] The amount of SiO2 reduced during processing can be 0.1% to 100% of their 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.

[0115] The amount of aluminum reductant (e.g., reduced Al alloy) used depends on the starting precursor material and the desired composition of the final product and may be less than or greater than the stoichiometric amount required to reduce all reducible starting precursor chemicals. In some embodiments, the amount of aluminum reductant in the reaction mixture may be from 1 wt. % to 1000 wt. %, from 5 wt. % to 500 wt. %, more preferably from 10 wt. % to 200 wt. %, and even more preferably from 50 wt. % to 200 wt. % of the weight of silica in the carbon-silica precursor.

[0116] Preferably, the Al is in the form of a powder or flakes having a particle size of less than 50 micrometers in at least one dimension, and more preferably, the Al has a particle size of between 1 micrometer and 50 micrometers in at least one dimension.

[0117] The amount of AlCl used can be, in some embodiments, from 1 wt. % to 500 wt. % of the weight of the carbon-silica precursor, preferably from 1 wt. % to 200 wt. %, more preferably from 10 wt. % to 200 wt. %, and even more preferably from 50 wt. % to 200 wt. %.

[0118] The weight ratios of silica, reduced Al alloy, and AlCl3 may be determined by a combination of factors, including the required composition of the final product and the stoichiometric requirements of the reactions within the Si-O-Al-Cl system.

[0119] For embodiments using solid aluminum chloride, the starting solid AlCl is preferably in the form of a powder or granules having a particle size of less than 5 mm. More preferably, the starting solid AlCl(s) is in the form of a powder having a particle size of less than 200 micrometers, more preferably less than 100 micrometers.

[0120] The treatment is typically carried out in an open reaction vessel under a protective gas, preferably at atmospheric pressure. An excess amount of aluminum chloride may be used, and AlCl(g) escaping or diffusing from the reaction vessel may be condensed during treatment and returned to the reaction vessel or collected in a dedicated vessel for later use or recycling. For treatment according to R1, excess gaseous aluminum escaping from the reaction vessel may be condensed and returned to treatment in the early stages of reaction R1, and then condensed and collected in a dedicated vessel for later use in the final stage of the reaction.

[0121] An excess of aluminum chloride in solid form can be fed to the reaction zone along with the other reactants, and then at least a portion of the excess AlCl can be sublimated to help cool the reactants. The heat of sublimation of AlCl, in addition to the latent heat taken up to heat the AlCl to the reactant temperature, provides an effective means for cooling the reactants and controlling the reaction temperature.

[0122] Excess solid AlCl(s) can be fed along with the other reactants and used to control the temperature of the reactants through absorbing heat from sublimation. The resulting heated AlCl vapor is collected away from the reaction zone, cooled, and then either fed directly back to the vessel or collected and recycled. The amount of AlCl(s) fed to the reactor is controlled to maintain stable heat treatment conditions.

[0123] The process can be operated in batch, semi-continuous, or fully continuous modes, and AlCl may be supplied to the reaction zone / vessel as a solid powder that can react with other precursors at low temperature or that can sublimate to gaseous AlCl(g) during processing. Alternatively, AlCl may also be supplied to the reaction zone / vessel alone, or preferably as an additional gas stream through the reactants (e.g., a continuously moving reactant stream in a fluidized bed, packed bed, moving bed, rotary kiln, or tubular reactor in a gaseous AlCl atmosphere) or in the reactant atmosphere.

[0124] Any residues, including aluminum chloride or oxychlorides, Al2O3, unreacted oxides and suboxides, other residual chlorides, and also unreacted Al, can be removed from the product in post-processing steps using appropriate means, including washing, chemical dissolution, and vacuum sublimation.

[0125] For example, AlOCl can be removed by washing in dilute HCl. If Al2O3 is formed and present in the product, it may remain part of the final product either as an independent component, such as in a composite, or as part of a compound / particulate where the aluminum oxide reacts physically or chemically with species resulting from the reduction reaction.

[0126] Processing temperatures are typically above 200°C and the product is usually substantially free of aluminum chloride, any aluminum chloride residues will result from contamination during discharge and / or handling. Preferably, the product of the process contains less than 5 wt. % residual solid AlCl(s) impurity, preferably less than 1 wt. %.

[0127] Those skilled in the art of the present invention will appreciate that the final product may contain Al in the form of residual Al impurities or metal aluminides at levels of 0.01% to 70% by weight, and that, if desired, the Al can be partially or completely removed by a variety of means, including washing with chemicals such as dilute NaOH or dilute HCl.

[0128] In embodiments where the precursor material includes a reactive additive (e.g., an alloying additive), the final product can include a compound containing the reactive additive. For example, for carbon, boron, oxygen, and nitrogen additives, the product can include carbides, borides, oxides, and nitrides, respectively.

[0129] Preferred Embodiments As discussed, reactions in C-SiO2-Al-AlCl3 result in significant exothermic energy release capable of raising reactant temperatures to over 1500°C, which can then compromise product quality; for example, increasing reactant temperatures above 700°C can cause uncontrolled direct reaction between SiO2 and Al, leading to the formation of heterogeneous compositions containing Al2O3. The present invention advantageously overcomes these problems in the art and includes procedures for controlling exothermic generation and maintaining temperatures at levels suitable for producing materials with uniform and acceptable properties. Reaction rates within the SiO2-Al-AlCl3(g) system are controlled through a combination of mechanisms, including controlled feed rates for reactants, mixing with pretreated products, and external heat management.

[0130] The method is preferably carried out with a gradual supply of at least Al and / or AlCl so that exothermic energy release is mitigated and efficient thermal management of the reactants is possible, and for all exemplary aspects and embodiments, the method includes means for managing exothermic heat generation and maintaining reactant and reactor temperatures at safe levels.

[0131] In a preferred embodiment, the method comprises: - preparing a powder containing a carbon-based precursor and a SiO2-based precursor or a powder containing a C-SiO2-based precursor; - optionally treating the prepared powder to carbonize the carbon-based precursor to produce a stable powder based on carbon-C-SiO2; - optionally filling all or part of the C-SiO2 powder and gradually feeding the reduced Al alloy and the remaining reactants comprising AlCl3(s) and / or AlCl3(g) into a reaction vessel set at a temperature T1 above a certain threshold reaction temperature below 800°C, preferably below 650°C; - mixing and reacting the reactants in the presence of aluminum chloride, mixed with a by-product of AlOCl or Al2O3, leading to a C-Si based product, -T1 is a temperature of less than 600°C, preferably 180°C to 600°C, more preferably 160°C to 600°C, even more preferably 200°C to 600°C, and even more preferably 200°C to 600°C; the vessel contains the amount of reactant to be treated; -AlCl3 is in solid or gaseous form, and if aluminum chloride is provided as a solid, it may be provided with solid Al powder as a premixed mixture; Optionally, separating the by-products and producing a final product based on the base metals.

[0132] In one preferred embodiment, a stream of precursor C-SiO2 powder and a stream consisting of a mixture of Al-AlCl3 powder are gradually fed into a preheated reaction vessel at a temperature between 200°C and 600°C, preferably between 200°C and 600°C. The process is carried out at atmospheric pressure under a non-reactive protective gas in the vessel. In this embodiment, the reaction product is a mixture of Si powder and AlOCl. The product mixture is washed in dilute HCl to separate the metallic Si powder. In one version of this embodiment, the precursor SiO2 powder is a silica nanopowder and the product is a Si nanopowder. In another version, the precursor SiO2 powder is a fumed silica powder and the product is a Si nanopowder. In another version, the precursor SiO2 powder is fumed silica. In one preferred version of this embodiment, the precursor C-SiO2 powder is pre-loaded into the reaction vessel, and then the Al-AlCl3 powder mixture is gradually fed into the reaction vessel.

[0133] FIG. 1 is a schematic diagram illustrating the process steps for one preferred embodiment for reducing a SiO precursor with Al—AlCl. In this embodiment, a SiO-based precursor powder (101) is mixed with a C-based compound (102). The resulting powder is optionally carbonized / pyrolyzed, depending on the precursor (103), to produce a C—SiO-based powder (104); C—SiO. The C—SiO precursor powder (104) is then fed into a reaction vessel (105) either in a single batch or incrementally. Al powder (106) and AlCl powder (107) are premixed (108) and then gradually fed into the reaction vessel (105) equipped with a mixer (not shown) and set to a process temperature T1, which is higher than the threshold reaction temperature required to reduce SiO. Alloying additives (not shown) may be supplied separately or with other precursors depending on their reactivity and compatibility at level (105) or elsewhere such as (101), (102), (103), (104), or (108).

[0134] The reactants in (105) are continuously mixed or reacted under quiescent conditions for a certain residence time t1, resulting in the formation of solid products, including metal-Si-based compounds and solid AlOCl by-products. Solid AlCl, supplied in solid form to the reaction vessel (as part of the Al-AlCl mixture), sublimes to form gaseous AlCl, a portion of which reacts with Al and SiO in the reactor to form AlOCl. Another portion of the gaseous AlCl escapes or diffuses out of (105), is condensed, and collected in a dedicated container (109). Some 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 a partially reactive gas (e.g., CO, N, etc.) (111). At the outlet of the by-product collection step, the gas is scrubbed in a scrubber (112) before being vented to the atmosphere or recycled.

[0135] The solid reaction product, including Si powder and AlOCl by-product, and any other solid residues, if applicable (e.g., AlO, additive precursors, etc.), is discharged through (113). The reaction product (113) is then optionally post-processed (114) as needed to separate the metal product from undesired residual precursors (e.g., Al and unreacted SiO) and by-products, leading to the final product (115). Waste from the separation step (114) is separately processed and stored (116).

[0136] The reactor vessel (105) can hold a reactor equipped with a mixer and can be operated in batch, semi-batch, or continuous mode. Examples of suitable vessels include conical reactors, spiral reactors, rotary kilns, fluidized bed reactors, and packed bed reactors.

[0137] In one embodiment, a mixture of SiO2-based precursor and Al is fed to a reaction vessel (105) in an atmosphere containing gaseous AlCl3 at a temperature of up to 650°C to induce a reduction reaction, resulting in the formation of a powder product based on one or more of the base metals.

[0138] The SiO2-based precursor may be first partially or completely charged into the reaction vessel and heated to the reaction temperature, and then other reactants are fed into the reaction vessel according to any of the previous or future embodiments.

[0139] The amount of AlCl provided to react with the SiO-Al mixture can be adjusted to meet process requirements and control reaction rate and kinetics. In some embodiments, aluminum chloride is passed over the SiO-based precursor / Al mixture as a gas stream, as pure AlCl gas, or as a carrier gas / AlCl mixture (e.g., N / AlCl, or Ar / AlCl). In one embodiment, aluminum chloride is passed over the metal oxide / Al mixture according to the configuration in a fluidized bed system.

[0140] In another embodiment for the production of carbon-silicon based composite materials, a method for producing a Si-based powder is provided, comprising: The composition of the SiO2-based precursor can be either SiO2, pure SiO2, precipitated silica powder, SiO2 nanopowder, fumed silica, silica fume, amorphous silica, quartz powder, glass powder, glass flake, borosilicate glass powder or flake, mica, synthetic mica, or a multi-component powder including any other composition based on SiO2; 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; Step 1: the precursor silica-based powder has a particle size ranging from a few nanometers to a few hundred micrometers in at least one dimension; - Using the SiO2-based precursor powder, an intermediate powder containing a carbon precursor and a SiO2-based precursor is prepared, which can be carbonized or pyrolyzed to produce a C-SiO2 powder; - reacting the C-SiO2-powder with Al and AlCl3 (solid and / or gas) to produce a powder product; the by-product is AlOCl and the product is a mixture of silicon-based powder with solid AlOCl and residual Al; The product from step 1 may be in the form of a carbon-silicon composite material, wherein the silicon is silicon powder, silicon nanopowder with a particle size of less than 1 micrometer, pure silicon material, silicon monoxide SiO or SiO x (where x is 0.2 to 1.8), silicon-based powders having an oxygen content of 0.01 to 50 wt %, or mixtures thereof; and the carbon silicon composite may be in the form of silicon-coated particulate, full Si-C composite, Si-impregnated graphite, natural graphite-Si, biomass-derived carbon-silicon composite, or any other form containing carbon and silicon. Step 2: The product from step 1 is treated to remove AlOCl by-products and / or residual Al to produce a Si-based final product.

[0141] In a preferred embodiment, AlCl is supplied to the reaction vessel as solid powder AlCl(s) and gaseous AlCl(g). The solid AlCl(s) powder is supplied to the reaction vessel along with the other reactants, and the gaseous AlCl(g) can be supplied to the vessel anywhere, but preferably from the bottom, directed upward through the reactants, for example, according to a conical reaction vessel, fluidized bed, or packed bed configuration. The solid AlCl(s) helps cool the reactants as they sublimate, and some of it remains in the reaction vessel, but the gaseous AlCl(g) is primarily intended to maximize the reaction rate within the reactants.

[0142] In one embodiment for the production of silicon carbon materials, a method for producing a Si-based powder is provided, comprising: a mixture of silica and a carbon-based precursor is provided that is suitable for reacting with an acid, an example of the carbon-based precursor being sucrose and an example of the acid being sulfuric acid; - reacting a mixture of silica and a carbonaceous precursor to form a silica-carbon mixture; - optionally further pyrolyzing the silica-C mixture to react any residual carbonaceous precursors; - Reacting the resulting silica-C mixture to produce a Si-C based material according to any of the preceding or future embodiments.

[0143] In one embodiment for the production of silicon carbon materials, a method for producing a Si-based powder is provided, comprising: - a silicon-containing liquid precursor suitable for producing silica is provided, examples of which include silicic acid, sodium silicate, and silicon alkoxides; - mixing graphite powder with a liquid precursor, and then reacting and / or calcining the liquid precursor to produce a graphite-SiO2 mixture; - reacting a mixture of silica and a carbonaceous precursor to form a silica-C mixture; - optionally further pyrolyzing the silica-C mixture to react any residual carbonaceous precursors; - Reacting the resulting silica-C mixture to produce a Si-C based material according to any of the preceding or future embodiments.

[0144] In one embodiment for the production of silicon-impregnated carbon materials, a method for producing a Si-based powder is provided, comprising: - a silicon-containing liquid precursor suitable for producing silica is provided, examples of which include silicic acid, sodium silicate, and silicon alkoxides; - impregnating a carbon-based material with a liquid precursor and then reacting and / or calcining the liquid precursor to produce a graphite-SiO2 powder; reacting the resulting carbon-based material-silica mixture to produce a Si—C-based material according to any of the preceding or future embodiments. The carbon-based material may be graphite, synthetic graphite, natural graphite, activated carbon, charcoal, or graphitic or carbonized materials produced from the pyrolysis of organic materials, such as pyrolyzed rice husks, graphitic materials produced by reacting organic materials with acids, or anode-grade graphite powder. In the form of graphitic materials, they may be in the form of flakes or spherical powders, which may be coated or uncoated.

[0145] 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 comprises the following steps: - mixing or impregnating a carbon-based material with a silicate; - reacting the liquid precursor with an acid (e.g., HCl) to convert the silicate to Si(OH) or SiO; - removing by-products resulting from the last reaction step; reacting the resulting carbon-based material and silicon-oxygen mixture with Al-aluminum chloride according to any of the preceding or subsequent embodiments.

[0146] In one embodiment, the precursor material comprises a carbon-based material, i.e., a silica mixture consisting of natural graphite-silica minerals, which is then reacted with Al-aluminum chloride according to any of the preceding or subsequent embodiments.

[0147] In one embodiment, the precursor material comprises a carbonaceous material, i.e., a silica mixture consisting of charcoal and silica, which is then reacted with Al-aluminum chloride according to any of the preceding or subsequent embodiments. In one form of this embodiment, charcoal is first impregnated with a silica coating precursor that is then converted to silica, and the resulting material is then reacted with Al-AlCl according to any of the preceding or subsequent embodiments.

[0148] In one embodiment for producing a carbon-silicon composite material, the method comprises: providing a first powder of natural graphite containing silica at a level of between 0.1% and 20% by weight; - 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 with a by-product of Al2O3 or AlOCl; - optionally separating the carbon-silicon composite material from the by-products.

[0149] In one embodiment for producing a carbon-silicon composite material, the natural graphite powder contains other impurities, and the method includes reacting the impurities with an aluminum-aluminum chloride based reducing agent, and then dissolving and separating the resulting impurity-based species from the carbon-silicon product.

[0150] In one embodiment, the precursor material comprises a carbonaceous material, i.e., a silica mixture consisting of charcoal and silica, which is then reacted with Al-aluminum chloride according to any of the preceding or subsequent embodiments. In one form of this embodiment, charcoal is first impregnated with a silica coating precursor that is then converted to silica, and the resulting material is then reacted with Al-AlCl according to any of the preceding or subsequent embodiments.

[0151] In one embodiment for producing a carbon-silicon composite material, the method comprises: - preparing a liquid solution containing a dissolved silica precursor; providing graphitic powders of charcoal and activated carbon materials; - mixing graphite powder into the solution; - converting a silica precursor into silica; reacting the resulting carbon-silica material with Al—AlCl3 to produce a C—Si composite material; - separating the carbon-silicon composite material from the by-products.

[0152] In one form of this embodiment, the method comprises: - preparing a liquid solution of sodium silicate and water; providing charcoal powder; - mixing charcoal powder into a sodium silicate solution; - adding an appropriate amount of diluted HCl to convert the sodium silicate to silicon hydroxide; reacting the resulting carbon-silica material with Al—AlCl3 to produce a C—Si composite material; filtering the solid particulate powder; - heating the solid particulate powder to convert the silica hydroxide to silica; reacting the resulting carbon-silica material with Al—AlCl3 to produce a C—Si composite material; - separating the carbon-silicon composite material from the by-products.

[0153] In one form of this embodiment, the heating is at a temperature below 650°C.

[0154] In all embodiments, the treatment is carried out at a pressure of less than 1.2 atmospheres.

[0155] In one embodiment where a carbon-coated silica powder is provided, the method can include the main step of dissolving and / or etching a portion of the silica to create pores around the silica particulates, thus producing Si-NPs encapsulated within carbon cages with sufficient voids within the cage to allow for a volumetric expansion of the Si-NPs during lithiation.

[0156] In an embodiment for partially reducing a SiO-based precursor to produce a Si-coated substrate, the SiO-based precursor is reacted with a substoichiometric amount of Al in the presence of gaseous AlCl. The product is then in the form of a Si-coated SiO-based substrate. The SiO precursor can be in the form of particulates, such as powder, flakes, or fibers. The metal coating on the particulate surface can be continuous or patchy and can cover all or part of the particulate surface. When the particulates are in the form of flakes, the coating can be reflective, allowing the particulates to be used in applications such as pigments. In other embodiments, the coated particulates can be further reacted with other precursor chemicals in which metallic Si acts as a reducing agent.

[0157] 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, Pg, 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 additive is adapted as a catalyst to induce the formation of carbon-silicon composites in the form of carbon-silicon nanowires.

[0158] For example, AgCl additives may be included in the precursor chemicals, and the final product will be a Si-Ag or Ag coated SiO2 substrate, depending on the amounts of Al and AgCl used and the desired properties of the final product.

[0159] The precursor may also include glass powder or glass flake, fumed silica, silica fume, silica nanopowder, glass bubbles, and the product may include metal 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 flake-like morphology. In another form, the precursor powder includes fibers, and the product is a powder with fiber-like morphology.

[0160] The solid reactants, including SiO2 and reduced Al alloy, can be mixed, for example, continuously to maximize contact between the solid reactants and improve the reaction yield.

[0161] In one embodiment where the by-product is AlOCl, the AlOCl is separated from the metal powder product by washing in a suitable solvent to dissolve the AlOCl, followed by separation of the solid powder product.

[0162] Mixing and agitating the reactants can help increase contact between the various components of the mixture, optimizing the product and maximizing the reaction yield. Agitation helps to contact the reducible precursor chemicals and unsaturated species generated during processing with the reducing agent, which then reacts or disproportionates, thus improving product quality. In a preferred embodiment, process conditions are adjusted to maximize the reaction between SiO2 and Al-AlCl3 through efficient mixing of the reactants.

[0163] The pressure within the reaction vessel should be less than 1.5 atmospheres, preferably less than 1.2 atmospheres, and more preferably the vessel is kept under protective gas at a pressure of about 1 atmosphere and in open communication with the external environment at 1 atmosphere.

[0164] The precursor chemicals can be configured into two or more streams of material that are fed together or independently into the reaction vessel and react to produce the powder product. In one variation of this configuration, the reactants can be processed at multiple temperatures for various processing times to optimize processing conditions and produce materials with desired properties.

[0165] In one embodiment, for example, the reactants may be introduced through several material streams, including a stream containing a mixture of reduced alloy and aluminum chloride, which in one form of this embodiment is produced by co-grinding.

[0166] The process can be carried out in an inert or non-reactive gas, or a mixture of non-reactive and reactive gases, examples of suitable 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.

[0167] In one embodiment, the method includes the additional step of reacting the product obtained at the end of the process with additional gaseous reactants 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 flow of CH4 to produce Si-C based compounds.

[0168] In one embodiment, a carbon shell-silicon core product is provided, the product comprising: a porous carbon cage having a wall thickness of 0.01 nm to 1 micrometer; a cavity containing at least 50% silicon metal and a silicon-based material with open space, The volume ratio of the empty space to the -Si is 10% to 75% (for example, 10% to 50%). The starting silica powder has an average diameter of 20 nm to 20 micrometers.

[0169] This core-shell structure example can be produced by any of the previous or future embodiments. For example, to produce a core-shell structure starting from a 20 nm silica precursor powder and a PVP precursor for carbon, the following steps are performed: The average diameter of the silica powder is 20 nm. The nominal density of the silica is 2.62 g / mL. The PVP composition has a nominal carbon content of 65 wt% (C6H9NO) n is. The silica powder is coated with PVP. The amount of PVP used corresponds to 0.1% to 100% by weight relative to the weight of the silica. The PVP-coated silica is then pyrolyzed, resulting in a carbon coating of 0.065% to 65% by weight relative to the silica. The carbon-coated silica is then reduced with Al-AlCl3 at 450°C to reduce the silica to silicon, with a carbon to silicon ratio of 0.1% to 130% by weight. When silica is completely reduced to silicon, its volume decreases by 49% and a shell is formed with a core consisting of 50% Si and 50% voids.

[0170] The present invention extends to materials made using the present methods in all its embodiments and forms, without being limited by the examples provided herein for illustrative purposes. Materials produced by preferred forms of the invention described herein may have unique properties that may not be obtainable using prior art methods. Specific exemplary properties may include nanostructured products with large areas and the ability to produce compositions that are generally unattainable using conventional techniques.

[0171] One example of a material with unique properties obtainable using current technology is silicon nanoparticles with metal additives for use in lithium-ion batteries. Such materials are characterized by a large surface area and excellent electrical conductivity resulting from the addition of base metal additives.

[0172] Silicon nanoparticles produced in accordance with the present invention include crystalline and amorphous silicon, including products containing varying ratios of crystalline and amorphous phases.

[0173] The silicon nanoparticles produced according to this method have irregular, specific shapes with particle sizes ranging from 10 nm to 500 nm and contain Al levels of 0.01% and 70% by weight. Other variations of this product include silicon nanoparticles with Ag, Cu, and / or tin levels of 0.1% to 50% by weight.

[0174] Below are examples of the preparation of various product compounds according to one embodiment of the present invention.

[0175] Example 1: C-Si nanocrystals starting from fumed silica Fumed silica (SiO2) was reacted with Al under Ar-AlCl3 at 1 atmosphere pressure at 550°C. Al and AlCl3 were premixed together. SiO2 and Al-AlCl3 were fed into the reactor as two separate streams over a 15-minute period. The temperature of the reactants was continuously monitored, and only a moderate temperature increase was detected. The material obtained at the end of the test had a deep brown color with a yield of over 97%; some material was lost during processing and handling. XRD analysis of the as-produced materials showed that they consisted of AlOCl, Si, and carbon. Only lines corresponding to crystalline silicon could be observed, and the measured XRD pattern suggested that the material was free of Al2O3. Additionally, a broad, shallow feature corresponding to C appears to indicate the presence of carbon.

[0176] TEM analysis of the as-produced powder suggests a particle size distribution 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, which are observed to result from the washing process. When pure H2O is used without HCl, the Si particles remain suspended in water indefinitely, with a particle size distribution in the 10-100 nm range.

[0177] Example 2: C-Si nanocrystals starting from C-SiO2 nanopowder 100g of SiO2 nanopowder (70nm) is mixed with 100mL of distilled water and 1g of sugar. The mixture is stirred continuously for 10 minutes to ensure homogeneity and heated until all the water has evaporated. The resulting sugar-SiO2 powder is then pyrolyzed at 525°C under nitrogen.

[0178] The resulting C-SiO2 is reacted with Al and AlCl3 at <525°C under 1 atmosphere of argon. Excess AlCl3 is collected in a dedicated container for later use. This material is gradually fed into the reactor as two separate streams over 30 minutes: one SiO2 stream and one Al-AlCl3 mixture stream.

[0179] The recovered amount of brown material was 290 g. The material was drained and washed in dilute HCl. The XRD pattern of the washed product matched the known XRD spectrum of crystalline silicon, and the material was substantially free of Al2O3.

[0180] Example 3: C-Si starting from quartz powder 51 g of C-quartz powder (0.5-10 micrometers) was treated with 32 g of Al under argon-AlCl3 at 1 atmosphere and a temperature of 550 °C. Excess AlCl3 was collected in a dedicated container for later use.

[0181] The material was drained and washed in dilute HCl. The XRD pattern of the product shows that the quartz powder was only partially reduced. All lines in the pattern can be indexed to known XRD spectra of quartz and silicon.

[0182] Example 4: C-Si starting from SiO2 fume A mixture of C-SiO2 derived from silica fume with approximately 5% carbon was treated under argon-AlCl3 at 1 atmosphere and 525°C. The C coating was produced in a similar manner to Example 1.

[0183] Analysis of the product shows Si and C, as expected.

[0184] Example 5: C-Si coated SiO Mix 82 g of SiO2 nanopowder (20 nm) with 100 mL of distilled water and 1 g of sucrose. Stir the mixture continuously for 10 minutes to ensure it is homogeneous, then heat until all the water has evaporated. The resulting sucrose-coated powder is then pyrolyzed under nitrogen.

[0185] The resulting C-SiO2 nanopowder was treated with Al powder (4 micrometers) under argon-AlCl3 at 1 atmosphere and a maximum temperature of 500 °C. The SiO2 was partially reduced and the product consisted of SiO2-Si-C. The amount of collected material was approximately 167 g.

[0186] The material was drained and washed in dilute HCl. The XRD pattern of the product shows crystalline silicon and a broad peak at about 22 degrees corresponding to amorphous silica.

[0187] Example 6: C - Silicon Coated Glass Flakes 200 g of borosilicate glass flakes (approximately 60 micrometers in diameter and 1 micrometer thick) were mixed with 100 mL of distilled water and 1 g of sucrose. The mixture was continuously stirred for 10 minutes to ensure homogeneity, and then heated until all the water had evaporated. The resulting sugar-coated powder was then pyrolyzed under nitrogen.

[0188] The obtained powder was treated with Al-AlCl (12.5 g Al) under Ar at 550° C. The product was then discharged and washed in H2O.

[0189] The material has a golden color and consists of Si-coated borosilicate flakes. XRD analysis shows a shallow Si peak.

[0190] Example 7: C-Si starting from C-SiO2 nanopowder 25 g of SiO2 nanopowder (70 nm) coated with 2% polyvinylpyrrolidone (PVP) is first pyrolyzed under argon at 500 °C to obtain the SiO2-C composition. The SiO2-C is mixed with 6 g of a mixture of Al powder (4 micrometers) and 30 g of AlCl3(s).

[0191] The resulting C-SiO2-Al-AlCl3 was reacted under argon at 1 atmosphere and 550 °C. Excess AlCl3 was collected in a dedicated vessel for later use. The material was fed gradually into the reactor in two separate streams over a 10 minute period.

[0192] The material has a light brown color, and the recovered amount is 72 g. The material was drained and washed in dilute HCl. The XRD pattern of the washed product is consistent with 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 the individual particles. This analysis also suggests that the Si nanoparticles are primarily nanocrystalline but contain some amorphous phase. TEM-EDS micrographs of the powders showing the morphology of C and C-Si are shown in Figure 2.

[0193] Example 8: C-Si starting from C-SiO2 nanopowder Step 1: Nanopowder (20 nm) is mixed with distilled water and PVP. The mixture is stirred to ensure homogeneity and heated until all the water has evaporated. The resulting PVP-coated powder is then pyrolyzed at 550°C under argon.

[0194] Step 2: Repeat step 1 three times.

[0195] Step 3: SiO2-C is mixed with Al powder (4 micrometers) and AlCl3(s). The resulting C-SiO2-Al-AlCl3 is reacted under argon at 1 atmosphere and 550 °C. Excess AlCl3 is collected in a dedicated container for later use. The materials were fed gradually into the reactor as two separate streams over a 10 minute period.

[0196] The material was drained and washed in dilute HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows a complex structure with Si aggregates and fine particles caged within the porous carbon coating.

[0197] Example 9: C-Si starting from C-SiO2 nanopowder SiO2 nanopowder (20 nm) is mixed with distilled water and PVP. The mixture is then heated until all the water has evaporated. The resulting PVP-coated powder is then pyrolyzed at 550°C under argon.

[0198] SiO2-C was mixed with Al powder and AlCl3(s), and the resulting C-SiO2-Al-AlCl3 was reacted under argon at 1 atmosphere. Excess AlCl3 was collected in a dedicated container for later use. This material was gradually fed into the reactor as two separate streams.

[0199] The material was drained and washed in dilute HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon. TEM of the powder shows that Si aggregates and fine particles are caged within the porous carbon coating.

[0200] Example 10: C-Si nanoparticles starting from C-SiO nanoparticles Step 1: Dissolve a certain amount of PVP in water. Then add SiO2 powder and mix thoroughly.

[0201] Step 2: The water is evaporated and the remaining solid PVP-coated silica is pyrolyzed at 500°C under argon to obtain the SiO2-C composition.

[0202] Step 3: Mix Al powder and AlCl(s) into SiO2-C.

[0203] The resulting C-SiO2-Al-AlCl3 was reacted under argon at 550 °C. Excess AlCl3 was collected in a dedicated container for later use. The material was fed gradually into the reactor in two separate streams over a 10 min period.

[0204] The material has a light gray-brown color. The material was drained and washed in dilute 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. Particle size calculations based on FWHM suggest a particle size of less than 7 nm. For reference, Figure 4 presents an XRD trace for a pure Si sample obtained without a carbon coating. The small particle size obtained is due to the carbon coating preventing agglomeration and sintering of the individual Si nanoparticles. TEM of the powder shows that the C-Si product is in the form of Si aggregates with the carbon coating as a rough surface around the individual particles. TEM analysis suggests the presence of significant amorphous fractions.

[0205] Example 11: C-Si nanoparticles starting from C-SiO nanoparticles Step 1: Dissolve PVP in water. Then add SiO2 nanopowder (70 nm) and mix thoroughly.

[0206] Step 2: Evaporate the water and pyrolyze the remaining solid PVP-coated silica to obtain the SiO2-C composition.

[0207] Step 3: Mix Al powder and AlCl(s) into SiO2-C.

[0208] The resulting C-SiO2-Al-AlCl3 was reacted under argon. Excess AlCl3 was collected in a dedicated container for later use. The materials were fed gradually into the reactor in two separate streams over a 10-minute period.

[0209] The material has a light gray-brown color. The material was drained and washed in dilute HCl. The XRD pattern of the washed product matches the known XRD spectrum of silicon, but with very broad peaks. 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 the individual particles. TEM analysis suggests the presence of amorphous fragments.

[0210] Example 12: C-Si starting from C-SiO precipitated silica SiO2 powder (precipitated silica) coated with 2% polyvinylpyrrolidone (PVP) is first pyrolyzed to obtain a SiO2-C composition, which is then mixed with Al powder and AlCl3(s).

[0211] The resulting C-SiO2-Al-AlCl3 is reacted under argon at 1 atmosphere and 475°C, with the excess AlCl3 collected in a dedicated container for later use.

[0212] The material has a light gray-brown color. The material was drained 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 the individual particles.

[0213] Example 13: C-Si starting from C-SiO halloysite Powdered SiO2 (halloysite) is coated with 1% polyvinylpyrrolidone (PVP) and first pyrolyzed at 550 °C under argon to obtain a SiO2-C composition, which is then mixed with Al powder and AlCl3(s).

[0214] The resulting C-SiO2-Al-AlCl3 is reacted under argon at 550° C. The excess AlCl3 is collected in a dedicated container for later use.

[0215] The material was drained and washed. The XRD pattern of the washed product matches known XRD spectra for silicon and Al2O3. The Al2O3 is most likely due to the presence of oxides in the halloysite composition.

[0216] Example 14: C-Si starting from C-SiO halloysite SiO2 powder (halloysite) is washed with sulfuric acid to dealuminate the material and increase the SiO2 concentration in the powder. The powder is then coated with 2% polyvinylpyrrolidone (PVP) and pyrolyzed at 525°C under argon to obtain the SiO2-C composition. 6g of Al powder and AlCl3(s) are mixed with this SiO2-C.

[0217] The resulting C-SiO2-Al-AlCl3 is reacted under argon at 1 atmosphere and 525°C, with the excess AlCl3 collected in a dedicated container for later use.

[0218] The material was drained and washed, and the XRD pattern of the washed product matches the known XRD spectrum of silicon.

[0219] Example 15: Si-impregnated graphite powder Sodium silicate powder is dissolved in water. Porous graphite powder is added to the solution. HCl is then added to the solution. The mixture is then heated to 300°C. The dried mixture is washed multiple times with water to remove the unwanted NaCl. The resulting graphite-SiO2 powder is then reacted with Al-AlCl3. The product is washed to remove the AlOCl by-product. The resulting material consists of graphite impregnated with Si-NPs.

[0220] Example 16: Si-impregnated graphite powder Sodium silicate is dissolved in water. Porous graphite powder is added to the solution and stirred for 2 hours. HCl is then added to the solution. The mixture is then calcined at 300°C. The dried mixture is washed to remove the NaCl by-product.

[0221] A dilute solution of sodium hydroxide is added and the mixture is heated and stirred to dissolve some of the SiO2 and create voids around the silica particles. The material is filtered, washed, and then dried.

[0222] The resulting graphite-SiO powder is then reacted with Al-AlCl. The product is washed to remove the AlOCl by-product. The resulting material consists of graphite impregnated with Si-NPs.

[0223] Example 17: Si-impregnated graphite powder produced from sucrose The precipitated silica and sucrose are dissolved in water and stirred until well homogenized, and the solution is then heated until the water has completely evaporated.

[0224] H2SO4 is added to the material to convert the sucrose into porous carbon. Precipitated silica particles become encapsulated within the pores of the resulting carbonized material.

[0225] The material is then reacted with Al-AlCl3 as previously described, with the final product being in the form of a Si-impregnated porous graphite powder.

[0226] Example 18: Si-impregnated graphite powder produced from sucrose The precipitated silica and sucrose are dissolved in water and stirred until well homogenized, and the solution is then heated until the water has completely evaporated.

[0227] H2SO4 is added to the material to convert the sucrose into porous carbon. Precipitated silica particles become encapsulated in the resulting graphitic pores.

[0228] A dilute solution of sodium hydroxide is added and the mixture is heated to dissolve some of the SiO2 and create voids around the silica particles. The material is filtered, washed, and then dried.

[0229] The resulting material is then reacted with Al-AlCl3 as previously described, with the final product being in the form of a Si-impregnated porous graphite powder.

[0230] Example 19: Graphite-Si composite from natural graphite Natural graphite powder with a nominal composition containing 7% silica, 2% magnesium oxide, and 3.2% aluminum oxide is mixed with Al powder and AlCl3. This mixture is then treated at 550°C. The powder is washed with dilute HCl, then filtered and dried. XRD analysis of the powder shows that the silica has been reduced to silicon, and all lines correspond to silicon present in the XRD pattern. No evidence of Mg compounds is found in the final product, suggesting that MgO has been converted to MgCl2 and removed during the washing step.

[0231] Example 20: Graphite-Si composite using charcoal Sodium silicate is dissolved in water. Charcoal powder is then added and the solution is stirred for 2 hours. Dilute HCl is added to the solution. The mixture is then filtered and dried, and the resulting powder is heated to 500°C to form a charcoal-silica mixture.

[0232] Example 21: C-Si composites starting from graphite and precipitated silica The precipitated silica is mixed with 300 g of graphite powder (C-SiO2 powder), and the mixture is placed in a reactor and heated to 550°C.

[0233] The Al-AlCl3 mixture is slowly fed into a reaction vessel containing C-SiO2 powder. Excess AlCl3 is collected in a dedicated vessel for later use. The amount of recovered material is 605 g. The material is drained and washed in diluted HCl.

[0234] Example 22: C-Si composites starting from rice husks The dried and pyrolyzed rice husk powder is placed in a reactor and heated to 550°C.

[0235] Al powder was mixed with AlCl3 and this mixture was slowly fed into a reaction vessel containing C-SiO2 powder. The material was discharged and washed with excess dilute HCl to remove AlOCl and residual Al powder. XRD of the material showed a pattern consistent with Si and C phases, with no other compounds present.

[0236] The resulting mixture is treated at a temperature of 475°C to 550°C. The product is discharged, washed with dilute HCl, then filtered and dried. XRD analysis of the powder shows that the silica has been reduced to silicon.

[0237] Those skilled in the art will understand that many modifications can be made without departing from the spirit and scope of the present invention. For example, the inventors anticipate that it will be possible to use Mg instead of Al as the reducing agent without significantly departing from the core of the present invention. For example, if Mg is used instead of Al, the by-products may include a mixture of MgAlCl and AlOCl, both of which are soluble in dilute HCl and should therefore be separable from the base metal product. Such modifications are intended to be within the scope of the present invention.

[0238] It is to be understood that any prior art publication mentioned herein is not an admission that such publication forms part of the common general knowledge in the art.

[0239] In the following claims and the preceding description of the invention, unless the context requires otherwise by reason of the language of expression or necessary implication, the term "comprise" or variations such as "comprises" or "comprising" are used in the inclusive sense, i.e., to specify the presence of stated features, but do not preclude the presence or addition of further features in various embodiments of the invention.

Claims

1. 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 reductant; heating the reaction mixture in the presence of solid or gaseous aluminum chloride, or a mixture thereof, to a temperature at which a reaction is initiated resulting in the reduction of silica; controlling reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway may occur; and isolating the carbon-silicon composite material produced.

2. 10. The method of claim 1, wherein the carbon-silica based precursor is provided in one or more of the following forms: a carbon-silica composite, a mixture of carbon powder and a silica-based powder, a carbon-coated silica powder, carbon cages encapsulating silica-based precursor particulates, carbon nanotubes or thin graphitic sheets or graphene blended with or coated on silica particulates, a reducible carbon-silicon-oxygen based powder, a porous carbon-based structure impregnated with silica, a silica-impregnated carbon-based powder, a silica-impregnated graphite powder, a silica-impregnated charcoal powder, pyrolyzed rice husks, a powder of natural graphite containing silica, or a mixture thereof.

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

4. 4. The method of claim 1, further comprising pyrolyzing a mixture of a silica-containing material and a carbon-based compound to produce the carbon-silica-based precursor.

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

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

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

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

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

10. 10. The method of any one of claims 1 to 9, wherein the silica in the carbon-silica precursor is provided in the form of a powder, isolated particles, particles impregnated within a carbon structure, or other morphology that includes silica.

11. 11. The method of any one of claims 1 to 10, wherein the silica in the carbon-silica based precursor is provided as one or more of silica nanopowder, fumed silica, precipitated silica, silica fume, silica fiber, silicates, borosilicates, soda glass, silica-based minerals, synthetic mica, mica, and crystalline silica.

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

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

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

15. 15. A process according to any one of claims 1 to 14, wherein the gaseous aluminium chloride is caused to flow over or through the reaction mixture during heating.

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

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

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

19. 19. The method of any one of claims 1 to 18, wherein the amount of the aluminum reductant in the reaction mixture is from 1% to 1000% by weight of silica in the carbon-silica based precursor, preferably from 5% to 500% by weight of silica in the carbon-silica based precursor.

20. A method according to any one of the preceding claims, wherein the temperature to which the reaction mixture is heated is below 800°C, preferably below 600°C, or preferably below 550°C.

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

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

23. 23. The method of any one of claims 1 to 22, wherein the reaction conditions are controlled by one or more of the following: gradually feeding additional one or both of the carbon-silica based precursor and the aluminum reductant 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 mitigating agent to the reaction mixture.

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

25. 25. The method of 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, Pg, Ag, Sn, Sb, Hf, Ta, W, Re, Os, Pt, Au, and Bi is included in the reaction mixture.

26. 26. The method of claim 24 or 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 of any one of claims 1 to 23, wherein the carbon-silicon composite material comprises silicon nanoparticles encapsulated within a carbon-based structure.

28. 28. The method of claim 27, further comprising treating the carbon-silica based precursor to control the volume of void space within the carbon-based structure.

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

30. 30. The method of claim 29, wherein the core comprises void space of 0.5% to 75% of the total volume of the core.

31. A method according to any preceding claim, wherein the carbon-silicon composite material comprises from 0.01% to 70% by weight of residual aluminium.

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

9.

33. 10. Carbon-coated silicon nanoparticles produced according to the method of claim 1, wherein the silicon nanoparticles are in the form of fine particles having irregular shapes and an average particle size of 10 nm to 500 nm, and contain 0.01% to 70% by weight of aluminum.

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

35. 10. A carbon-silicon composite material produced according to the method of claim 1, wherein the composite material is in the form of a core-shell structure; the core comprises a silicon-based material having a void space of 0.5% to 75% of the total volume of the core and a metallic silicon content of less than 99% by weight; A carbon-silicon composite material, wherein the shell comprises a porous or non-porous carbon coating having a thickness of 0.01 nm to 1 micrometer.

36. 1. A method for reducing silica in a silica-based precursor, the method comprising: coating a silica-based powder with carbon to form a carbon-coated silica-based precursor; providing a reaction mixture comprising the carbon-coated silica-based precursor and an aluminum reductant; heating the reaction mixture in the presence of solid or gaseous aluminum chloride, or a mixture thereof, to a temperature at which a reaction is initiated resulting in the reduction of silica; controlling reaction conditions to prevent the reaction mixture from reaching a temperature at which thermal runaway may occur; and isolating the reaction product comprising reduced silica.

37. mixing a liquid soluble carbon-based compound with a solvent and a silica-based precursor; evaporating the solvent to produce a silica-based precursor coated with a carbon-based compound; pyrolyzing the silica-based precursor coated with a carbon-based compound to produce a carbon-coated silica-based precursor; A reaction mixture comprising the carbon-coated silica-based precursor and an aluminum reductant is subjected to a SiO 2 reaction at substantially atmospheric pressure in the presence of gaseous aluminum chloride. ２ heating to a temperature at which a reaction is initiated resulting in the reduction of controlling reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650°C; and isolating the silicon-containing reaction product.

38. 10. The method of claim 1 for producing a carbon-silicon composite material in the form of carbon-silicon nanowires, said method comprising: forming a reaction mixture of carbon, a silica-based powder, an aluminum reductant, and a metal catalyst, the weight of the catalyst being 5% to 50% of the weight of the silica, the catalyst inducing the formation of silicon nanowires; The reaction mixture is heated at atmospheric pressure in the presence of gaseous aluminum chloride to form the SiO ２ heating to a temperature at which a reaction is initiated resulting in the reduction of controlling reaction conditions to prevent the reaction mixture from exceeding a temperature of about 650°C; and isolating the reaction product comprising the carbon-silicon nanowires.

39. 39. The method of claim 38, further comprising impregnating a carbon-based material with a liquid precursor comprising silicon and then processing the resulting material to produce said silica-based powder in the form of a graphite-silica-based powder.

40. 1. A method for producing a carbon-silicon composite material, the method comprising: providing a powder of natural graphite containing 0.1% to 20% by weight of silica; The powder is mixed with an aluminum-containing reducing agent in the presence of solid and / or gaseous aluminum chloride and heated, whereby at least a portion of the silica is reduced to silicon, and the carbon-silicon composite powder is formed. ２ O ３ and / or with by-products including AlOCl; and optionally separating said carbon-silicon composite material from said by-products.

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

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

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

44. 41. A carbon-silicon composite material produced according to the method of any one of claims 1 to 32 and 36 to 40, wherein silica in the pyrolyzed carbon-silica precursor compound is reduced to silicon, and the silicon content is from 1% to 25% by weight.

45. A carbon-silicon composite material consisting of carbon, silicon, and aluminum.

46. A carbon-silicon composite material made solely from rice husks.

47. 47. The carbon-silicon composite material of claim 45 or 46 produced according to claim 1.

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