Method for manufacturing silicon-carbon composite materials

Abstract

The present invention provides a method for producing a silicon-carbon composite material, which is simple, low-cost, and can accommodate expansion of production scale, and a method for producing electrodes for lithium-ion batteries. [Solution] A method for producing a silicon-carbon composite material includes the steps of: a) introducing at least flakes of a carbon-based material and, optionally, a catalyst into a reactor chamber; b) introducing at least a precursor compound of a silicon nanostructure into the reactor chamber; c) reducing the oxygen molecular weight in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering a first silicon-carbon composite material; and f) obtaining a second silicon-carbon composite material by spheroidizing the product obtained in step (e).

Description

[Technical field]

[0001] The present invention relates to a method for producing a silicon-carbon composite material containing carbon-based materials and silicon nanostructures. The present invention further relates to a method for producing an electrode for a lithium-ion battery. [Background technology]

[0002] Increasing the energy density of lithium-ion batteries (LIBs) compared to conventional ones is important to meet the demands of electric vehicles and advanced electronics. Silicon has an extremely high theoretical capacity and is therefore considered one of the most promising anode materials for realizing high-energy LIBs, replacing conventional graphite anodes. However, the large volume change that occurs during lithium insertion / extraction has been a major obstacle to practical use.

[0003] These large volume changes during electrochemical cycling lead to repeated cracking and shattering of silicon, which causes the silicon electrode to collapse, break, and become electrically insulated. Repeated cracking and shattering also leads to the continuous destruction of the solid electrolyte interface (SEI) layer and the proliferation of new interfaces, resulting in rapid consumption of electrolyte and Li-ions. Therefore, the use of pure silicon anodes suffers from extremely rapid capacity loss and poor Coulombic efficiency (CE) as a result of the intense volume changes and instability of the SEI film.

[0004] To significantly improve the cycle life of LIBs, advanced material design strategies such as unique nanostructures (e.g., nanowires, nanotubes, core / shell, yolk-shell, nanoporous, etc.) and the formation of composites with carbon, conductive polymers, etc. have been adopted as academic approaches. However, the volumetric energy density and areal mass loading on the electrode of these materials are generally too low for industrial practical use. Commercial goals for realizing high-performance anodes to replace existing commercial graphite materials in the near future include specific capacities of 500mAh / g-1000mAh / g with a capacity retention of 80% after 500-1000 cycles, with an initial CE of more than 90% and an average CE of more than 99.8%. Thus, the pressed density is approximately 1.65g / cm 3 and the electrode bulge is preferably limited to about 10%.

[0005] In recent years, the combination of silicon and graphite has emerged as the most practical anode material for high-energy LIBs. Graphite is a commercially available anode material with low cost, high CE, excellent cycle life, good mechanical flexibility, small volume change, and high electrical conductivity. The addition of silicon to graphite can suppress the volume change and increase the electrical conductivity while increasing the specific capacitance, areal capacitance, and volumetric capacitance. In addition, the combination of silicon and graphite can use the same commercial production line, achieving high productivity with minimal investment. Therefore, the combination makes it possible to combine two different types of anodes at the material level into a single composite material, avoiding the disadvantages of both while retaining their advantages, ensuring success in the anode market.

[0006] There are two main types of silicon-graphite composites: those in which graphite particles are coated with silicon (nanoparticles, nanowires, etc.) (i.e., primary particles) (Non-Patent Documents 1, 2), and those in which silicon is embedded in a graphite matrix (i.e., secondary particles). The former are less relevant to the problem, since they share the same drawbacks as nanosilicon (e.g., large surface area, unstable SEI, low ICE and subsequent CE, low composite density, etc.). The latter are much more relevant, since they are particles with similar characteristics to graphite microparticles (small surface area, stable SEI, high ICE and subsequent CE, high tapped and pressed density, etc.).

[0007] There are various synthetic methods for designing silicon-graphite composites in which silicon is embedded in graphite materials. For example, Sui et al. (Non-Patent Document 3) used a multi-step process consisting mainly of dry / wet ball milling, spray drying, and carbonization to form Si-graphite composites in which silicon is present in the graphite particles, but the authors used a large amount of carbonaceous material, which has good cycling stability but is disadvantageous for initial CE. Liu et al. (Non-Patent Document 4) designed a Si-graphite composite in which nanosilicon is encapsulated within a conductive graphite flake / amorphous carbon framework, but this method consists of five synthetic steps, requires inert conditions and rare and expensive reagents, and the final composite was confirmed to have low ICE (47-68%) and retained CE of less than 99%. Wang et al. (Non-Patent Document 5) reported a silicon / carbon / natural graphite composite prepared by granulating natural graphite and silicon / poly(acrylonitrile-co-divinylbenzene) microspheres by spray drying and subsequent pyrolysis. Silicon nanoparticles are incorporated into crosslinked poly(acrylonitrile-co-divinylbenzene) microspheres by fine suspension polymerization. The composite has an initial coulombic efficiency of 78% and a capacity retention of 88% after 100 cycles when used as an anode against metallic Li. This composite could not be used in commercial batteries for technical and economic reasons.

[0008] The strength of each of the above approaches lies in engineering micrometer-sized hierarchical structures and appropriate morphologies with appropriate manipulation of the distribution of components, conductive networks, sizes, voids, and shells. Although these structures may exhibit competitive performance in terms of energy density, the first three examples are not translatable to industrial-scale production of silicon-graphite composites in the battery industry.

[0009] Over the past two decades, there have been several efforts to find a more industrial method for producing silicon-graphite composites in the form of fine secondary particles. In 2006, Uono et al. (Non-Patent Document 6) reported a "surface-coated" composite of silicon, carbon (pitch), and graphite, prepared by a grinding process and heat treatment. They concluded that a small particle size of Si (100 nm) and a large particle size of graphite (30 μm) are beneficial to reduce the surface area of ​​the composite and thus the irreversible specific capacity. The main steps of this method are simply mixing silicon powder, pitch coke powder, and graphite powder, and forming several types of micrometer secondary particles through several mixing steps. However, this method requires the use of ethanol as an organic solvent in all cases. Another disadvantage is that the majority of silicon nanoparticles are located on the surface of the graphite / carbon / silicon composite, limiting the cyclability of the composite after synthesis.

[0010] In 2008, Lee et al. (Non-Patent Document 7) designed spherical nanostructured silicon / graphite / carbon composites by pelletizing a mixture of nanosilicon / graphite / petroleum pitch powders, followed by heat treatment at 1000°C under argon atmosphere. The resulting composite spheres consist of nanosized silicon and flaked graphite embedded in a carbon matrix formed by pyrolysis of petroleum pitch, with the flaked graphite sheets aligned parallel to each other in a concentric fashion. The composite exhibits a reversible capacity of 700mAh / g and good initial CE (86%). The main drawbacks of this method are the application of solvent-based processing, the large number of steps, and the poor cyclability of the final composite.

[0011] In 2010, Jo et al. (Non-Patent Document 8) compared two types of (Si-graphite-pitch) composites. In one case (Type A), the silicon particles are on the surface of the graphite, and in the other case (Type B), the silicon particles are embedded in the graphite / carbon matrix. While the cycle CE is the same for both, it is observed that the charge capacity (657 mAh / g) and discharge capacity (568 mAh / g) of Type B are higher than Type A. Although the method is solvent-free and simple, the final composite shows a heterogeneous distribution of silicon nanoparticles inside the secondary particles (large agglomerates of 500-1000 nm), resulting in poor cycleability.

[0012] Thus, although there have been efforts to use industrial techniques to produce silicon-graphite composites as anode materials for Li-ion batteries, the methods that have emerged have been too expensive for large-scale production.One of the main problems is the difficulty of dispersing silicon homogeneously in graphite without the use of solvents.

[0013] Patent Documents 1 and 2 disclose a method for producing an electrode active material, which comprises the steps of forming a silicon-containing coating layer on a plate-shaped graphite material, and grinding or polishing the plate-shaped silicon-coated graphite with a mechanical device to reconstruct the silicon coating layer deposited on the outside of the plate-shaped graphite material so that it moves to the inside of the final graphite material. This method uses graphite sheets with an extremely small grain size of about 4 μm, but one drawback is that this method does not allow for satisfactory control of the porosity and required cyclability of the final silicon-graphite material. Furthermore, it is difficult to obtain a nanosilicon layer deposited on an extremely fine graphite powder, especially on a large (industrial) scale, and therefore the amount of silicon embedded inside the graphite is limited. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent Publication No. 10-2020-0095017 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 013499 [Non-Patent Document]

[0015] [Non-Patent Document 1] M. Holzapfel, H. Buqa, F. Krumeich, P. Novak, F.-M. Petrat, C. Veit Chemical Vapor Deposited Silicon / Graphite Compound Material as Negative Electrode for Lithium-Ion Batteries, Electrochemical and Solid-State Letters, 2005, 8(10), A516-A520. [Non-Patent Document 2] Bei Liu, Peng Huang, Zhiyong Xie, Qizhong Huang Large-Scale Production of a Silicon Nanowire / Graphite Composites Anode via the CVD Method for High-Performance Lithium-Ion Batteries, Energy & Fuels 2021, 35, 2758‐2765. [Non-Patent Document 3] Sui D, Xie Y, Zhao W, et al. A high‐performance ternary Si composite anode material with crystal graphite core and amorphous carbon shell. J Power Sources. 2018, 384, 328‐333. [Non-Patent Document 4] Liu W, Zhong Y, Yang S, et al. Electrospray synthesis of nano‐Si encapsulated in graphite / carbon microplates as robust anodes for high performance lithium‐ion batteries. Sustain Energy Fuels. 2018; 2(3), 679‐687.

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

[0016] The battery industry still needs simple, low-cost, and easily scalable manufacturing methods that can be used to integrate silicon and graphite into a single system / composite to obtain desired design criteria such as uniform dispersion of silicon, controlled porosity to accommodate silicon expansion during material cycling, low surface area, and acceptable anode packed density. [Means for solving the problem]

[0017] To achieve the above objectives, the present invention provides a simple method that can be easily scaled up. This method allows the design of special secondary particles from flakes of carbon-based material and silicon nanostructure materials in just two steps: deposition of nanosilicon on the carbon-based material surface by chemical vapor deposition (CVD) and spheroidization of the resulting composite material. The method according to the present invention allows the end product of silicon-carbon-based material to be obtained with well-controlled properties due to the selection of specific materials, specifically carbon-based materials, and / or the presence of catalysts.

[0018] In a first aspect of the invention, there is provided a method for producing a carbon-silicon composite material, the method comprising the steps of: a) introducing at least flakes of a carbon-based material and, optionally, a catalyst into a reactor chamber; b) introducing at least silicon nanostructure precursor compounds into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering the first silicon-carbon composite material; f) subjecting the product obtained in step (e) to spheronization to obtain a second silicon-carbon composite material; The method comprises:

[0019] In a first aspect, the method according to the invention comprises the steps of: a) introducing at least flakes of carbon-based material having a D50 particle size between 25 μm and 500 μm into a reactor chamber; b) introducing at least silicon nanostructure precursor compounds into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering the first silicon-carbon composite material; f) subjecting the product obtained in step (e) to spheronization to obtain a second silicon-carbon composite material; This is a method for providing the above.

[0020] In a second aspect, the method according to the invention comprises the steps of: a) introducing at least flakes of a carbon-based material and a catalyst into a reactor chamber; b) introducing at least silicon nanostructure precursor compounds into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering the first silicon-carbon composite material; f) subjecting the product obtained in step (e) to spheronization to obtain a second silicon-carbon composite material; This is a method for providing the above.

[0021] In a third aspect, the method according to the invention comprises the steps of: a) introducing at least flakes of carbon-based material having a D50 particle size between 25 μm and 500 μm and a catalyst into a reactor chamber; b) introducing at least silicon nanostructure precursor compounds into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering the first silicon-carbon composite material; f) subjecting the product obtained in step (e) to spheronization to obtain a second silicon-carbon composite material; This is a method for providing the above.

[0022] In a preferred embodiment of any aspect of the present invention, the average percentage of the surface of the carbon-based material in the first silicon-carbon composite material that is covered with silicon nanostructures is 50% or more, preferably 70% or more, and more preferably 80% or more.

[0023] In a preferred embodiment of any aspect of the invention, the average percentage of the outer surface of the second silicon-carbon composite material that is covered by silicon nanostructures is 20% or less, preferably 10% or less, and more preferably 5% or less.

[0024] In a first example of any embodiment of the present invention, steps (a)-(e) are carried out in a tumbler type reactor powered by a rotating and / or mixing mechanism. In a second example of any embodiment of the present invention, steps (a)-(e) are carried out in a fixed bed reactor. In a third example of any embodiment of the present invention, steps (a)-(e) are carried out in a vertical fluidized bed reactor.

[0025] In a preferred embodiment of any aspect of the invention, the spheronization step (f) comprises at least one step selected from grinding, milling, compacting, densifying, pressing, compressing, folding, rolling, rolling, crushing, coarsening, pulverizing, applying centrifugal force, or a combination of one or more of these steps.

[0026] In a preferred embodiment of any aspect of the invention, at least a portion of the second silicon-carbon composite material is in the form of micrometric particles having a D50 of 5-50 μm.

[0027] In a preferred embodiment of any aspect of the present invention, the micrometric particles of the second silicon-carbon composite material are potato-shaped.

[0028] In a preferred embodiment of any aspect of the invention, the micrometer particles of the second silicon-carbon composite material are 20 μm to 40 μm in diameter. 2 / g or less, preferably 10m 2 / g or less, more preferably 5m 2 / g or less.

[0029] In a preferred embodiment of the first and / or third aspect of the present invention, the second silicon-carbon composite material has an internal porosity of 5% to 25%.

[0030] In a preferred embodiment of any aspect of the invention, the carbon-based material is selected from graphite, graphene, and carbon. Preferably, the carbon-based material is graphite. Advantageously, said graphite is natural graphite or artificial graphite.

[0031] In a preferred embodiment of any aspect of the invention, the precursor compound of the silicon particles is a silane compound or a mixture of silane compounds, preferably diphenylsilane.

[0032] When a catalyst is used, it is preferred to select said catalyst from the group consisting of metals, metal oxides and metal halides. Preferably, the catalyst is selected from the group consisting of gold (Au), tin (Sn), tin dioxide (SnO 2 ), Tin Halides (SnX 2 ) and mixtures thereof.

[0033] According to said first aspect of the invention, said silicon nanostructures are advantageously in the form of nanoparticles, preferably with a particle size in the range 1 nm to 250 nm.

[0034] According to the second and / or third aspect of the invention, the silicon nanostructures are advantageously in the form of nanowires or nanofibers, preferably nanowires with a diameter in the range of 1 nm to 250 nm. In a preferred embodiment of any aspect of the invention, the method according to the invention further comprises, after step (f), coating an outer surface of the second material with a second carbon material different from the flakes of carbon-based material.

[0035] Another aspect of the present invention is a method for producing an electrode having a current collector, the method comprising the steps of: (i) preparing, as an electrode active material, a carbon-silicon composite material according to any embodiment of the method described above or in the detailed description below; and (ii) coating at least one surface of the current collector with a composition comprising the electrode active material.

[0036] Yet another aspect of the present invention is a method for producing an energy storage element, such as a lithium secondary battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, wherein at least one of the electrodes, preferably the negative electrode, is obtained by the method for producing a carbon-silicon composite material as described above and in more detail below.

[0037] The present invention provides the following advantages over prior art methods for producing negative electrode materials: It is a simple, easily scalable, environmentally friendly, and inexpensive manufacturing method. the second silicon-carbon composite has excellent particle morphology, controlled internal porosity, and low surface area; silicon is uniformly dispersed in the silicon-carbon composite; Depositing silicon nanostructures on a surface of a carbon-based material by chemical vapor deposition (CVD) can improve the processability of the first silicon-carbon-based material; The second silicon-carbon composite material has a much higher coulombic efficiency (CE), which improves cyclability. The overall method is based on micro-particle processing by attaching silicon nanostructures to the carbon-based materials, thus minimizing concerns associated with nanostructured materials. [Brief description of the drawings]

[0038] [Figure 1] 1 is a low-magnification scanning electron microscope (SEM) photograph of silicon nanowire (SiNW) / BNB-90 composite material M1 (Example 1). [Diagram 2] 1 is a high-magnification scanning electron microscope photograph of the BNB-90 / SiNW composite material M1 (Example 1). [Diagram 3] FIG. 1 is an inset showing the average SiNW particle size distribution of the BNB-90 / SiNW composite material M1 (Example 1) (horizontal axis: particle size range (nm), vertical axis: arbitrary unit). [Figure 4] 1 is a scanning electron microscope photograph of composite material M2 (Example 2). [Diagram 5] 17 is a scanning electron micrograph of M17-graphite / SiNW composite material M3 (Example 3). [Figure 6] 17 is an inset chart showing the average particle size distribution of SiNWs in graphite / SiNW composite material M3 (Example 3) (horizontal axis: particle size range (nm), vertical axis: arbitrary units). [Figure 7] 1 is a scanning electron microscope photograph of composite material M4 (Example 4). [Figure 8]FIG. 1 shows typical potential profiles for materials M1 (black) and M2 (grey) (the dashed oval indicates the typical response of the Si material). [Figure 9] FIG. 1 shows typical potential profiles for materials M3 (black) and M4 (grey) (the dashed oval indicates the typical response of the Si material). [Figure 10] FIG. 2 shows the reversible capacity of materials M1 (black) and M2 (grey) (two batteries are presented for each material). [Figure 11] FIG. 1 shows the reversible capacity of materials M3 (black) and M4 (grey) (two batteries are presented for each material). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The phrase "consisting essentially of" one or more features means that the method or material of the invention may contain other components / ingredients or steps in addition to the components / ingredients or steps specified, which do not significantly affect the characteristics or features of the invention.

[0040] The term "X to Y" is inclusive unless otherwise noted. This term means that the range includes values ​​X and Y, as well as all values ​​between X and Y.

[0041] The present invention relates first to a method for making a silicon-carbon composite material containing silicon nanostructure material and a carbon-based material, the silicon-carbon composite material being suitable for use as an anode active material in lithium ion batteries.

[0042] The term "composite material" refers to a material that is made up of at least two constituent materials that have significantly different physical and / or chemical properties.

[0043] The term "nanostructured material" within the meaning of the present invention is to be understood as meaning a material consisting of individual particles, possibly in the form of aggregates or agglomerates, in which at least 5% by weight, preferably at least 10% by weight, of the particles, based on the total weight of the material, have one or more of their external dimensions in the range from 1 nm to 500 nm, preferably from 1 to 100 nm.

[0044] The external dimensions of the particles can be measured by any known method, such as by analysis of images obtained by scanning electron microscopy (SEM) of the composite material according to the invention.

[0045] In particular, the present invention relates to a method for producing a silicon-carbon composite material, the method comprising: a) introducing at least flakes of a carbon-based material and, optionally, a catalyst into a reactor chamber; b) introducing at least silicon nanostructure precursors into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering a first silicon-carbon composite material having silicon nanostructures disposed on the flakes of carbon-based material; f) subjecting the product obtained in step e) to spheronization to obtain a second silicon-carbon composite material in which at least a portion of the silicon nanostructure is embedded in the carbon-based material; This is a method for providing the above.

[0046] In one embodiment, in step a) of the method according to the invention, at least some of the flakes of carbon-based material, preferably all of them, have a D50 particle size of between 25 μm and 500 μm.

[0047] In one embodiment, in step a) of the method according to the invention, a catalyst is introduced into the reactor chamber.

[0048] In a third embodiment, which is a combination of the above two embodiments, in step a) of the method according to the invention, at least some, preferably all, of the flakes of carbon-based material have a D50 particle size between 25 μm and 500 μm and a catalyst is introduced into the reactor chamber.

[0049] The three embodiments of the present invention differ only in step a) of the method of the present invention. In the following disclosure, steps b) to f) and other possible steps are described, but these apply to all three embodiments.

[0050] For purposes of the present invention, the carbon-based material, catalyst, and silicon nanostructure precursors are referred to below as "starting materials," and the first and second silicon-carbon composites are referred to below as "resulting composites." The first silicon-carbon composite is referred to below as the "silicon-carbon intermediate composite" or "first particle," and the second silicon-carbon composite is referred to below as the "silicon-carbon final composite" or "second particle." The first silicon-carbon composite and the second silicon-carbon composite share certain properties. These properties are referred to below as properties of the resulting composites.

[0051] A second aspect of the present invention is a method for producing an electrode active material comprising the silicon-carbon final composite material obtained by the method according to the present invention, and further a method for producing an energy storage element comprising the electrode active material.

[0052] Starting Materials Carbon-based materials In the method according to the invention, flakes of a carbon-based material are used as starting material. Unless otherwise stated, the preferred embodiments described below for carbon-based materials apply to all aspects of the invention.

[0053] As used herein, the term "carbon-based material" refers to a material that contains 50% or more by weight, preferably 70% or more by weight, more preferably 80% by weight carbon, even more preferably 90% by weight, and most preferably 100% by weight carbon.

[0054] In the present invention, carbon-based materials are used as supports for growing / depositing silicon nanostructures.

[0055] The term "flake" in the sense of the present invention is to be understood as meaning a thin piece of carbon-based material in the form of a thin layer or scale, having a thickness of a few nanometers to a few micrometers and two main faces of approximately the same size.

[0056] The flakes of carbon-based material may be used as a mixture with different shapes of carbon-based material, e.g. platelets, needles, ribbons, tubes, continuous fibers, chopped fibers, etc. Preferably, the flakes of carbon-based material represent at least 50% by weight, advantageously at least 70% by weight, more preferably at least 90% by weight, better still at least 95% by weight, very preferably at least 99% by weight of the carbon-based material used in the method according to the invention. Preferably, the carbon-based material consists essentially of flakes of carbon-based material, more preferably it consists only of flakes of carbon-based material.

[0057] The carbon-based material may be any material selected from the group consisting of graphite, graphene, and carbon. More specifically, the carbon-based material may be selected from, for example, natural graphite, artificial graphite, hard carbon, soft carbon, graphene, or a mixture of two or more thereof.

[0058] In a preferred embodiment, the carbon-based material is selected from graphene, synthetic graphite and natural graphite. Preferably, the carbon-based material is selected from natural graphite and synthetic graphite.

[0059] Natural graphite is derived from naturally occurring graphitic materials and occurs as graphite clay, flake graphite, or flake graphite. Artificial graphite is a manufactured product formed by high temperature processing of amorphous carbon materials, such as the graphitization of petroleum coke or coal tar pitch.

[0060] Preferably, based on the total weight of the carbon-based material, 75% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, even more preferably 95% by weight or more, advantageously 99% by weight or more of the carbon-based material consists of natural graphite and artificial graphite.

[0061] Preferably, the carbon-based material consists essentially of natural graphite or artificial graphite, and more preferably consists solely of natural graphite or artificial graphite.

[0062] The purity of the carbon-based material (preferably graphite) is advantageously 95%, preferably 98% or more, more preferably 99% or more, and can be measured by comprehensive tests such as chemical analysis by ICP-OES or equivalent for measuring trace metal elements, XRD, Raman spectroscopy and high precision gravimetry for estimating the ordering / disordering and composition ratio of the graphite.

[0063] Preferably, the thickness of the carbon-based material flakes is from 100 nm to 50 μm, more preferably from 200 nm to 20 μm, and even more preferably from 500 nm to 10 μm.

[0064] Preferably, the flakes of the carbon-based material are in the form of plates with an aspect ratio of average length to thickness of 2-2000, preferably 2-500, more preferably 2-100, and even more preferably 2-50.

[0065] The tap density of the carbon-based material is advantageously between 0.01 and 2 g / cm 3 , preferably 0.02 to 1 g / cm 3, more preferably 0.03 to 0.5 g / cm 3 It is.

[0066] In one embodiment particularly suited to the second aspect of the invention, the flakes of carbon-based material advantageously have a D50 particle size of between 1 μm and 800 μm, preferably between 1 μm and 500 μm, more preferably between 10 and 100 μm.

[0067] In the first and third aspects of the invention, the flakes of carbon-based material have a D50 particle size in the range of 25 μm to 500 μm, preferably 30 μm to 500 μm, more preferably 30 μm to 100 μm, most preferably 35 μm to 50 μm. Preferably, in the first and third aspects of the invention, the flakes of carbon-based material with a D50 particle size in the range of 25 μm to 500 μm account for 50% or more by weight, advantageously 70% or more by weight, more preferably 90% or more by weight, better still 95% or more by weight, very preferably 99% or more by weight of the carbon-based material used in the first and third aspects of the method according to the invention.

[0068] Applicants have found that by using relatively large flakes of carbon-based material, particularly graphite, in these manners, the internal porosity of the material can be better controlled, resulting in an optimal amount of silicon nanostructures embedded within the carbon-based material.

[0069] Measuring the D50 particle size of the flakes can be done by techniques known to those skilled in the art, such as, for example, laser diffraction methods or the use of standard sieves.

[0070] ·catalyst In the process according to the invention, optionally, at least one catalyst is introduced into the reactor chamber. The following features, in particular those defined as preferred, are relevant for the process according to the invention when said catalyst is present, in particular in the case of the second and third aspects.

[0071] The function of the catalyst is to form growth sites on the surface of the carbon-based material. Preferably, the catalyst is selected from metals, bimetallic compounds, metal oxides, metal halides, metal nitrides, metal salts, metal sulfides and organometallic compounds.

[0072] Metal catalysts include gold (Au), cobalt (Co), nickel (Ni), bismuth (Bi), tin (Sn), iron (Fe), indium (In), aluminum (Al), manganese (Mn), iridium (Ir), silver (Ag), copper (Cu), calcium (Ca), and mixtures thereof.

[0073] Bimetallic compounds include manganese platinum (MnPt 3 ) and iron platinum (FePt). Metal sulfides include tin sulfide (SnS). Metal oxides include ferric oxide (Fe 2 O 3 ) and tin oxide (SnO 2-x ) (wherein 0≦x<2). Metal halides include tin halides (SnX 2 ) (wherein X is a halide ion selected from the group consisting of F, Cl, Br and I).

[0074] More preferably, the catalyst is selected from metals, metal oxides and metal halides. Preferably, the catalyst is gold (Au), tin (Sn), tin dioxide (SnO 2 ), Tin Halides (SnX 2 ) and mixtures thereof.

[0075] In a first preferred embodiment of the present invention, the catalyst is gold (Au). For example, gold nanoparticles that can be used in the method according to the present invention are disclosed in M. Brust et al., J. Chemical Society, Chemical Communications, 7(7):801-802, 1994.

[0076] In a second preferred embodiment, the catalyst is tin(II) chloride (SnCl 2 ).

[0077] The catalyst is preferably in the form of particles, more preferably in the form of nanoparticles. The longest dimension of the catalyst nanoparticles is preferably in the range of 1 nm to 100 nm, more preferably 1 nm to 50 nm, and even more preferably 5 nm to 30 nm.

[0078] Advantageously, the catalyst nanoparticles are spherical. In one preferred embodiment, the catalyst is in the form of nanometric spherical particles with a particle size ranging from 1 to 30 nm, preferably from 5 nm to 30 nm.

[0079] The catalyst and the carbon-based material are used in a mass ratio of catalyst / carbon-based material in the range of preferably 0.01 to 1, more preferably 0.02 to 0.5, and further preferably 0.05 to 0.15.

[0080] The catalyst and carbon-based material may or may not be in contact prior to being introduced into the reactor chamber.

[0081] In a preferred embodiment, the carbon-based material and the catalyst are associated with each other prior to being introduced into the reactor. For purposes of the present invention, the term "associated" is intended to mean that the carbon-based material and the catalyst have previously undergone a mixing step that results in the attachment or deposition of at least a portion of the catalyst onto at least a portion of the surface of the carbon-based material.

[0082] By associating a catalyst with a carbon-based material, multiple particle growth sites can be formed on the surface of the carbon-based material.

[0083] Advantageously, the carbon-based material carries catalyst particles on its surface, in one preferred embodiment, the catalyst nanoparticles are preferably uniformly distributed on the surface of the flakes of carbon-based material.

[0084] SnX 2 In the case of the method using the catalyst, SnX 2 (Preferably SnCl 2 The combination of SnCl and carbon-based materials is simple and reliable. 2 Like other tin halides, SnCl is an extremely stable product, making it easier to process than other catalysts. 2 As with other tin halides, the process requires only solid-phase mixing with the carbon-based material. In contrast, when using gold nanoparticles, the preparation of the solid / liquid phase is followed by evaporation of the solvent.

[0085] SnX 2 (Preferably SnCl 2 The cellulose, cellulose ether, and carbon-based material can be combined in any industrial mixing equipment known to those skilled in the art, such as ball mills, attrition mills, hammer mills, high energy mills, pin mills, turbo mills, fine cutting mills, impact mills, fluidized bed mills, conical screw mills, rotor mills, stirred bead mills, jet mills, etc. This process does not take more than 30 minutes and can be carried out without solvent or with any solvent, from aqueous to organic.

[0086] ●Silicon nanostructure precursor In the method according to the invention, at least one precursor compound of silicon nanostructures is introduced into the reactor chamber. The term "precursor compound of silicon nanostructures" refers to a compound capable of forming a silicon nanostructure material by carrying out the method according to the invention, in particular a compound capable of forming a silicon nanostructure material under the conditions of the CVD process.

[0087] The compound may be introduced into the reactor chamber as a liquid or as a gas. If the compound is introduced into the reactor chamber as a liquid, the temperature and pressure within the reactor chamber are controlled to convert the compound into a gaseous state within the reactor chamber. The silicon nanostructure precursor compound, when in a gaseous state, is referred to as a "reactive silicon-containing gas species."

[0088] For example, if the silicon nanostructure precursor compound is a liquid, such as diphenylsilane, then by reaching the appropriate temperature / pressure parameters in the reactor, the liquid precursor will vaporize into a gaseous species.

[0089] The precursor compounds for silicon nanostructures can be introduced into the reactor either as a mixture with a carrier gas or as the precursor gas alone.

[0090] When the precursor compound is in the form of a reactive silicon-containing gaseous species, the precursor compound can be introduced into the reactor chamber in a mixture with a carrier gas (forming a reactive silicon-containing gas mixture). For example, SiH, which is a gas at ambient temperature / pressure, 4 may be introduced directly into the reactor chamber, either alone or in a mixture with a carrier gas. 2 SiH 2 Liquid precursor compounds such as dimethylformamide, dimethyl ether, diethyl ether, dimethyl ...

[0091] "Carrier gas" refers to a gas selected from a reducing gas, an inert gas, or a mixture thereof. Preferably, the reducing gas is hydrogen gas (H 2 ). Preferably, the inert gas is argon (Ar), nitrogen gas (N 2 ), helium (He), or a mixture thereof.

[0092] In a preferred embodiment, the silicon-containing gas mixture is composed of at least 1% by volume of silicon-containing gas species, preferably at least 10% by volume, more preferably at least 50% by volume, and even more preferably 100% by volume. The ratio of silicon-containing gas species to carrier gas may be adjusted to different levels in different steps of the method.

[0093] Preferably, the precursor compound for silicon nanostructures, i.e., the "reactive silicon-containing gas species," is a silane compound or mixture of silane compounds.

[0094] For purposes of the present invention, the term "silane compound" refers to a compound of formula (I): 1 -(SiR 2 R 3 ) n -R 4 (I) (wherein n is an integer from 1 to 10, and R 1 , R 2 , R 3 and R 4 are each independently selected from hydrogen, a C1 to C15 alkyl group, a C6 to C12 aryl group, a C7 to C20 aralkyl group, and chloride.

[0095] Preferably, in this embodiment, the silicon-containing gas species is represented by the formula (I), where n is an integer from 1 to 5, and R 1 , R 2 , R 3 and R 4 are each independently selected from hydrogen, a C1-C3 alkyl group, phenyl and chloride.

[0096] More preferably, n is an integer from 1 to 3, and R 1 , R 2 , R 3 and R 4 are independently selected from hydrogen, methyl, phenyl and chloride.

[0097] Preferably, in this embodiment, the precursor compounds of silicon nanostructures are selected from silane, disilane, trisilane, chlorosilane, dichlorosilane, trichlorosilane, dichlorodimethylsilane, phenylsilane, diphenylsilane, triphenylsilane or mixtures thereof.

[0098] In a preferred embodiment, the precursor compound for silicon nanostructures is silane (SiH 4 ) or diphenylsilane (Si(C 6 H 5 ) 2 H 2 The morphology and physical state of the silicon nanostructure precursor compounds are selected depending on the type of reactor and other parameters of the method.

[0099] In a most preferred embodiment, the precursor compound for silicon nanostructures is diphenylsilane, Si(C 6 H 5 ) 2 H 2 In fact, the presence of phenyl groups in diphenylsilane can provide a source of amorphous carbon inside the second silicon-carbon composite, significantly improving the electrical conductivity of the composite during cycling.

[0100] Doping materials In one embodiment, in the method according to the invention, at least one doping material is introduced into the reactor.

[0101] The term "doping material" in the sense of the present invention is understood to mean a material capable of modifying the electrical conductivity of silicon. A doping material in the sense of the present invention is, for example, a material rich in phosphorus, boron or nitrogen atoms.

[0102] Preferably, in this embodiment, the doping material is introduced into the reactor chamber via a precursor selected from diphenylphosphine, triphenylborane, diphenylamine and triphenylamine. In a first example, this introduction is carried out before the growth of silicon nanostructures is started. For example, the doping material may be introduced into the reactor chamber after step (b) and before step (c).

[0103] In another example, a precursor of the doping material is introduced as a gas simultaneously with (or, in some cases, as part of) the reactive silicon-containing gas mixture.

[0104] Preferably, the molar ratio of the doping material to the precursor compound of the silicon nanostructure is 10 -4 mol% to 10mol%, more preferably 10 -2 mol% to 1mol%.

[0105] (Method of manufacturing carbon-silicon composite materials) The method according to the present invention comprises the steps of: a) introducing at least flakes of a carbon-based material and, optionally, a catalyst into a reactor chamber; b) introducing at least silicon nanostructure precursors into the reactor chamber; c) reducing the molecular weight of oxygen in the reactor chamber; d) performing a heat treatment at a temperature in the range of 200°C to 900°C; e) recovering a first silicon-carbon composite material having silicon nanostructures disposed on the flakes of carbon-based material; f) subjecting the product obtained in step e) to spheronization to obtain a second silicon-carbon composite material in which at least a portion of the silicon nanostructures are embedded in the carbon-based material; This is a method for providing the above.

[0106] Specifically, step a) can be carried out according to any of the first, second and third aspects described above and in the Examples section.

[0107] [Process (a)~(e)] The order of steps (a) to (d) may be exact or may be different, depending essentially on the characteristics of the reactor in which the method is carried out, the method of reducing the molecular weight of oxygen, and also on the state (liquid or gas) in which the precursor compound of the silicon nanostructures is introduced into the reactor.

[0108] Method parameters The method according to the invention comprises step (a) of introducing a carbon-based material, and optionally a catalyst, into a reactor chamber.

[0109] In one preferred embodiment, the method according to the invention comprises a pretreatment step in which the carbon-based material is associated with the catalyst: in this embodiment, the catalyst and flakes of the carbon-based material are mixed together before being introduced into the reactor.

[0110] Preferably, the filling rate of the mixture of the carbon-based material and the catalyst is 10% by volume to 60% by volume, more preferably 20% by volume to 50% by volume, and even more preferably 30% by volume to 50% by volume, based on the volume of the reactor chamber.

[0111] Step (c), which consists of reducing the molecular weight of oxygen in the reactor chamber, can be carried out by various methods. The molecular weight of oxygen in the reactor chamber is reduced by evacuating the reactor, preferably at 10 -1 bar(10 -2 The oxygen concentration in the reactor chamber can be reduced by bringing the pressure to below 100 MPa. Alternatively, the oxygen concentration in the reactor chamber can be reduced by flushing the reactor chamber with an inert gas.

[0112] In the context of the present invention, the expression "flushing the reactor chamber with an inert gas" means injecting a flow of inert gas into the reactor chamber, thereby replacing the gas present in the reactor with the injected inert gas.

[0113] Preferably, the inert gas is nitrogen gas (N2 ), argon (Ar), and mixtures thereof.

[0114] When the reactor is a closed type reactor, the reactor chamber is preferably flushed with an inert gas at least two times, more preferably at least three times.

[0115] If the reactor is an open reactor, an inert gas may be passed through the reactor chamber during all or part of the process.

[0116] Preferably, at the end of step (c), the molecular weight of oxygen in the reactor chamber is less than 1% by volume relative to the total volume of the reactor chamber.

[0117] Preferably, the heat treatment is carried out at a temperature in the range of 200 to 900°C, preferably 300 to 700°C, more preferably 300 to 600°C.

[0118] Preferably, the heat treatment is carried out at low pressure, atmospheric pressure or at a pressure in the range of 0.11 to 30 MPa (although the pressure parameters are influenced by the type of reactor chosen and whether the reactor is open or closed).

[0119] In the process according to the invention, the heat treatment may cause an increase in pressure inside the reactor, which depends on the heat treatment applied and does not necessarily need to be controlled or monitored.

[0120] The heat treatment is preferably applied for 1 minute to 5 hours, preferably 10 minutes to 2 hours, more preferably 30 minutes to 60 minutes.

[0121] In one embodiment variant, the method according to the invention comprises, between steps (d) and (e), a post-treatment step for converting the organic matter into a carbon material. If this step is carried out, it consists essentially of a heat treatment. Advantageously, this step is carried out under an inert atmosphere, for example N 2 , Ar, Ar / H 2The reaction is carried out in a carrier gas atmosphere, such as a mixture of the above, at a temperature in the range of 500°C to 700°C, preferably 550°C to 650°C, and advantageously around 600°C.

[0122] In one variant, the method according to the invention comprises an additional step (e') of washing the first silicon-carbon composite material obtained at the end of step (e).

[0123] The first silicon-carbon composite material obtained at the end of step (e) may be washed with an organic solvent, preferably selected from chloroform, ethanol, toluene, acetone, dichloromethane, petroleum ether and mixtures thereof.

[0124] Alternatively, in a preferred embodiment, the first silicon-carbon composite material obtained at the end of step (e) is washed with an acid solution.

[0125] In this variant, preferably the method further comprises, after step (e'), the auxiliary step of drying the washed composite material.

[0126] Drying is carried out, for example, by placing the first silicon-carbon composite material in an oven, preferably at a temperature of 40° C. or higher, more preferably at a temperature of 60° C. or higher. The drying step is preferably carried out for 15 minutes to 12 hours, more preferably 2 hours to 10 hours, and even more preferably 5 hours to 10 hours.

[0127] Reactor In a first example, the process according to the invention is carried out in a fixed bed reactor. In a second example, the method according to the invention is carried out in the cylindrical chamber of a tumbler reactor equipped with a rotating and / or mixing mechanism. In a third example, the process according to the invention is carried out in a (vertical) fluidized bed reactor.

[0128] In a first embodiment, the reactor is closed during the process. In a second embodiment, the reactor is open during the process.

[0129] By open reactor is meant a reactor which remains open to the gas flow during the process, in particular during the heat treatment step, whereas by closed reactor is meant a reactor which is closed to the gas flow after the gas species are introduced into the reactor at the beginning of the process, during the heat treatment step.

[0130] [First example] In a first example, the process according to the invention is carried out in a fixed bed reactor. Reactor Features The fixed bed reactor may be an open or closed type reactor.

[0131] A reactor which can be used to carry out the process according to the invention is disclosed, for example, in WO 2019 / 020938, in which the reactor is used in the "closed reactor" mode.

[0132] In an alternative embodiment, an open fixed bed reactor is used to carry out the process according to the invention, for example the cylindrical chamber of a tumbler reactor used in stationary mode (without rotation or mixing).

[0133] Parameters In this first example, if the reactor is of the closed type, the oxygen molecular weight in the reactor chamber is preferably 10 -1 bar(10 -2 This can be reduced by reducing the pressure to below 100 MPa.

[0134] Alternatively, the molecular weight of oxygen in the reactor chamber may be reduced by flushing the reactor chamber with an inert gas.

[0135] Preferably, the inert gas is nitrogen gas (N 2In the case of a closed reactor, the reactor chamber is preferably flushed with an inert gas at least twice, more preferably at least three times. In the case of an open reactor, an inert gas may be passed through the reactor chamber during all or part of the process.

[0136] Preferably, at the end of step (c), the molecular weight of oxygen in the reactor chamber is less than 1% by volume relative to the total volume of the reactor chamber.

[0137] In a first embodiment of this example, when the reactor is of the closed type, the precursor compounds of the silicon nanostructures are generally introduced into the reactor as liquids.

[0138] In a first embodiment of this example, when the reactor is of a closed type, the carbon-based material, the catalyst, and the precursor compounds of the silicon nanostructures can be introduced into the reactor in the form of a mixture.

[0139] In a first embodiment of this example, when the reactor is closed, it is preferred that the reactor has at least two input zones: a first zone capable of receiving the precursor compound of the silicon nanostructures, and a second zone capable of receiving the carbon-based material and the catalyst.

[0140] In a first embodiment, the first and second input zones are located at the same height within the reactor chamber.

[0141] In one preferred embodiment, the second input zone is higher than the first input zone.

[0142] In a second embodiment of this example, when the reactor is open, the precursor compound of the silicon nanostructure is generally introduced into the reactor as a gas, in a mixture with an inert gas, referred to as a "reactive silicon-containing gas mixture."

[0143] [Second example] In a second example, the method according to the invention is carried out in the cylindrical chamber of a tumbler reactor equipped with a rotating and / or mixing mechanism.

[0144] Reactor Features The tumbler reactor is composed of at least a tubular chamber that can be filled with a carbon-based material and heated by a furnace. The reactor incorporates a rotation mechanism and / or a mixing mechanism. The reactor can consist of two cylindrical chambers. The longitudinal axis of the cylindrical chambers can be horizontal or inclined to form an angle of up to 20° with the horizontal axis. The reactor further includes a product supply system and a product discharge system, and can produce the first silicon-carbon composite semi-continuously. The tumbler reactor is equipped with a reactor pressure control device, such as a needle valve, a pressure controller, etc.

[0145] A typical mechanical tumbler reactor is a fluidized bed reactor of the Lödige type in which fluidization is produced by the rotation of a horizontal axial helix within a cylindrical chamber.

[0146] Another typical mechanical tumbler reactor comprises a cylindrical rotating chamber that rotates about a longitudinal axis to create fluidization.

[0147] Parameters This example is of great importance for the implementation of the method according to the invention: the fluidization mechanically induced by the reactor is beneficial for bringing the carbon-based material into contact with the silicon, which constitutes the reactive gas species.

[0148] In this example, the silicon nanostructure precursor compounds are preferably introduced into the reactor as gases.

[0149] Each step of the method In this example, the method according to the invention advantageously comprises: (a1) introducing at least a carbon-based material, and optionally a catalyst, into a cylindrical chamber of a reactor; (a2) heating the cylindrical chamber under a carrier gas flow; (a3) rotating the cylindrical chamber and / or starting a mixing mechanism; (b) introducing a reactive silicon-containing gas mixture into the cylindrical chamber; (c) controlling the pressure in the reactor chamber by the flow rate of the mixed gas; (d) subjecting the mixture to a heat treatment in the cylindrical chamber at a temperature in the range of 200° C. to 900° C. under a reactive silicon-containing mixed gas flow while rotating and / or mixing; (e) recovering the resulting product; Equipped with.

[0150] In this example, most steps must be performed in the order shown above, although the rotating and / or mixing of step (a3) ​​may begin before or after step (a1) or step (a2).

[0151] In this example, the heat treatment of step (d) is applied at low pressure (lower than atmospheric pressure), atmospheric pressure or higher than atmospheric pressure.

[0152] Preferably, when the reactor is a tumbler type reactor equipped with a rotating and / or mixing mechanism, the heat treatment in step (d) is applied at a pressure higher than atmospheric pressure.

[0153] [Third example] In a third example, the process according to the invention is carried out in a vertical fluidized bed reactor.

[0154] Reactor Features A vertical fluidized bed reactor generally consists of a vertical cylindrical stainless steel column. At the bottom of the column, there is a perforated steel plate to support the powder and distribute the gas uniformly, and a flange cooled with water to prevent premature decomposition of the silicon nanostructure precursor. At the outlet, a high-performance filtration cartridge allows the particles to be filtered and then collected. The reactor is heated externally by a two-zone electric furnace, and the temperature of its walls is controlled by at least two thermocouples connected to regulators. There are also several thermocouples along the reactor to monitor the axial temperature profile. Pressure sensors allow the pressure in the reactor to be controlled / monitored. Flow meters allow the flow rate of the various gases through the powder in the reactor to be controlled.

[0155] Parameters In a vertical fluidized bed reactor, the process according to the invention can be carried out at atmospheric pressure or at pressures slightly above atmospheric pressure. 5 A pressure of 100 Pa or more is suitable. Preferably, the applied temperature is in the range of 300°C to 600°C.

[0156] In this example, the precursor compounds for the silicon nanostructures are preferably introduced into the reactor as gases. In this example, the catalyst and carbon-based material must be in powder form.

[0157] Each step of the method (a) At least a carbon-based material, and optionally a catalyst, are introduced into a cylindrical chamber. (c) Seal test: perform a seal test on the reactor using nitrogen (1 slm). If the pressure is stable after 1 minute, the seal test is passed. (c') Fluidization of the catalyst and carbon-based material: The fluidization is performed using a neutral gas, the flow rate of which is increased periodically until it is equal to the desired flow rate, for example, by 0.5 slm every 2 minutes until it is equal to the desired flow rate. (d) Application of heat treatment: Next, the heating system of the furnace and the cooling system of the flange at the bottom of the bed are started. (b) After the fluidized bed has reached isothermal stability, reactive gases are introduced into the chamber. (e) Recovery of the product: After the reaction is completed, the reactor is cooled and the resulting product is recovered. For example, the reactor is cooled to 150°C or less and the product is recovered.

[0158] Most of the steps need to be performed in this order. Such a method is disclosed, for example, in WO 2011 / 137446.

[0159] [Process (f)] In the method according to the invention, the silicon-carbon intermediate composite material obtained at the end of steps (a) to (e) is subjected to at least a spheroidizing step (f).

[0160] The spheroidization step (f) of the method according to the invention aims to modify the shape and microstructure and, as a consequence, the physico-chemical properties of the first silicon-carbon composite material.

[0161] In the context of the present invention, the terms "spheroidization" and "rounding" as used herein refer to a shape modification and / or surface treatment process that involves applying at least one mechanical stress to a first silicon-carbon composite material in the form of flakes, resulting in a round-shaped material with a higher density than the first silicon-carbon composite material. This process results in smaller particles of silicon-carbon based composite material. The raw flakes are folded and / or consolidated and / or rolled and / or rolled multiple times to form spherical or potato-shaped particles.

[0162] In the context of the present invention, the terms "spheronization" and "rounding" are used synonymously.

[0163] Advantageously, spheronization comprises at least one step selected from grinding, milling, compacting, densifying, compressing, pressing, folding, rolling, rolling, crushing, granulating, pulverizing, centrifuging, or a combination of one or more of these processes.

[0164] Each step, or a combination of one or more of these steps, may be performed by the same spheronization means or by different means.

[0165] The spheronization means can be selected, for example, from: mortar and pestle; compression machines, e.g., calenders, presses, etc.; mills, such as impact mills, rotary impact mills, vortex mills, vibratory mills, ball mills, stirred ball mills, planetary mills, jet mills, opposite jet mills, fluidized bed jet mills, centrifugal mills, ultra-centrifugal mills, pin mills, hammer mills, rolling mills, classifying mills, downstream classifying mills; and combinations of these and any other comminuting equipment known to the skilled person.

[0166] In one preferred embodiment, the spheronizing means is a mortar and pestle. In another preferred embodiment, the spheronizing means is an opposite jet mill. In another preferred embodiment, the spheronizing means is a rotary impact mill. In another preferred embodiment, the spheronization means is a classifying mill or a downstream classifying mill. In another embodiment, the spheronizing means is an ultracentrifugal mill.

[0167] In another embodiment, the spheronizing means is a ball mill. In this embodiment, the grinding balls can be selected from zirconia grinding balls, steel balls, agate grinding balls, alumina grinding balls, silicon nitride grinding balls, or a combination of these balls. Advantageously, the diameter of the grinding balls is between 5 and 20 mm. Advantageously, the ratio between the volume of the silicon-carbon intermediate composite material, the volume of the grinding balls, and the volume of the space inside the ball mill is 1:1:1 (although the respective values ​​of said ratios may vary by ±20%).

[0168] When the spheronization means is selected from a mill, the mill may be a batch mill or a continuous mill. Within the meaning of the present invention, a "batch mill" is understood to mean a mill that receives and discharges partial amounts of a first silicon-carbon based composite material to be spheroidized, and this process is then repeated as necessary.

[0169] In the sense of the present invention, a "continuous mill" is understood to mean a mill that receives a continuous flow of the first silicon-carbon based composite material to be spheroidized and is therefore capable of operating continuously.

[0170] Advantageously, the spheronization process is carried out in a dry environment, i.e. without the use of solvents.

[0171] The spheronization step (f) of the method according to the invention can be carried out at room temperature or at an elevated temperature, for example, spheronization can be carried out at a temperature between 20°C and 80°C.

[0172] Advantageously, the spheronization or rounding step is carried out for a period of time such that the resulting silicon-carbon based composite material consists essentially of round particles.

[0173] The spheronization or rounding step is carried out for a time such that the tap density of the resulting silicon-carbon based composite material is advantageously at least two times, preferably at least five times, the density of the first silicon-carbon based composite material.

[0174] The spheroidizing or rounding step is carried out over a period of time such that the specific surface area of ​​the resulting silicon-carbon based composite material is advantageously at most 1 / 2, preferably at most 1 / 4, of the specific surface area of ​​the first silicon-carbon based composite material.

[0175] A person skilled in the art can obtain a silicon-carbon based composite material with the desired properties by adjusting the spheroidization process time and parameters of the spheroidization means, such as the rotation speed of the grinder, the force of the compressor, and the temperature.

[0176] [Additional process] In one embodiment, the method further comprises the step (g) of coating at least a portion of the outer surface of the second silicon-carbon composite material with a second carbon material different from the flakes of carbon-based material.

[0177] Advantageously, the second carbon material is chosen from carbon black, acetylene black, graphite, graphene, carbon fibres, carbon nanofibres, carbon nanotubes and mixtures thereof.

[0178] The weight ratio of the coating of the second carbon material to the total weight of the silicon-graphite composite material after coating is advantageously less than or equal to 20% by weight, preferably less than or equal to 15% by weight, more preferably less than or equal to 10% by weight.

[0179] The coating with the second carbon material can be achieved by any method known to those skilled in the art, such as, for example, decomposition of a carbon precursor (acetylene, pitch, sucrose, CMC, etc.), CVD, heat treatment, etc.

[0180] (Materials Obtained) Silicon-carbon intermediate composite material Steps (a) to (d) of the method according to the present invention result in a first silicon-carbon composite material, ie a silicon-carbon intermediate composite material.

[0181] Each embodiment in the following description of the silicon-carbon intermediate composite material applies to every aspect of the invention unless otherwise specified.

[0182] This first silicon-carbon based material comprises, and preferably consists essentially of, a carbon-based material (particularly a carbon-based material in the form of flakes) and silicon nanostructures, the silicon nanostructures resulting from chemical vapor decomposition (growth) of precursor compounds of the silicon nanostructures on the flakes of the carbon-based material.

[0183] The silicon content of the silicon-carbon intermediate composite material is advantageously greater than or equal to 5% by weight, preferably greater than or equal to 20% by weight, based on the total weight of the first silicon-carbon composite material. The silicon content is advantageously between 5% and 70% by weight, preferably between 20% and 50% by weight, based on the total weight of the first silicon-carbon composite material.

[0184] Additionally, the silicon-carbon intermediate composite material may contain traces of catalyst or residues of catalytic decomposition.

[0185] For example, when a catalyst is used according to the second and third aspects of the invention, it is particularly preferred that the catalyst is a metal halide, in particular SnCl 2 In the case where the metal halide is selected from tin halides such as tin halide, the silicon-carbon intermediate composite may contain residual metal halides, particularly tin halides, which can be partially removed by acid treatment of the silicon-carbon intermediate composite.

[0186] Additionally, the silicon-carbon intermediate composite may contain metal particles resulting from the decomposition of the catalyst during the reaction.

[0187] In addition, the catalyst is a metal halide, particularly SnCl 2 In the case where the tin halide is a tin halide such as tin halide, the silicon-carbon intermediate composite material may contain trace amounts of the halide.

[0188] The amount of catalyst or catalytic decomposition residue is preferably 10% by weight or less, more preferably 5% by weight or less, based on the total weight of the silicon-carbon intermediate composite material.

[0189] The flakes of the silicon-carbon composite material preferably have an aspect ratio of average length to thickness of 2-2000, preferably 2-500, more preferably 2-100, and even more preferably 2-50.

[0190] The tap density of the silicon-carbon intermediate composite material is advantageously between 0.01 and 2 g / cm 3 , preferably 0.02 to 1 g / cm 3 , more preferably 0.03 to 0.5 g / cm 3 It is.

[0191] In one preferred embodiment of the present invention, the silicon-carbon intermediate composite material is obtained in the form of flakes decorated with silicon nanostructures.

[0192] Preferably, the particle size of the flakes after decoration with silicon nanostructures is the same as the particle size of the starting carbon-based material flakes.

[0193] The silicon nanostructures obtained by chemical vapor decomposition (growth) of the precursor compounds may be in any form obtainable from this process, in particular in the form of wires, worms, rods, filaments, sheets or spheres.

[0194] In the first aspect of the invention, the silicon nanostructures are preferably in the form of nanoparticles. The term "nanoparticles" in the sense of the present invention is to be understood as meaning spherical, ellipsoidal or plate-like bodies with a particle size of the nanometer order, including, but not limited to, nanospheres, nanosheets, etc.

[0195] Preferably, the silicon nanoparticles have an average particle size in the range of 1 nm to 250 nm, more preferably in the range of 10 nm to 200 nm, even more preferably in the range of 30 nm to 180 nm. In the second and third aspects of the invention, particularly when a catalyst is used in step a) of the method according to the invention, the silicon nanostructures are in the form of nanowires.

[0196] The term "nanowire" in the sense of the present invention is to be understood as meaning an elongated object similar in shape to a wire and having a diameter in the order of nanometers, including, but not limited to, for example, nanowires, nanoworms, nanorods, nanofibers, nanofilaments, etc.

[0197] The average diameter of the silicon nanowires is preferably in the range of 1 nm to 250 nm, more preferably in the range of 10 nm to 200 nm, and further preferably in the range of 30 nm to 180 nm.

[0198] Preferably, the average length of the silicon nanowires is in the range of 50 nm to 500 nm.

[0199] Characterization of silicon nanostructures can be performed by several techniques well known to those skilled in the art, such as, for example, analysis of images obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM) of one or more samples of the resulting carbon-silicon composite.

[0200] Nanoworms are a particular preferred class of nanowires characterized by an aspect ratio (ratio of average length to average diameter) in the low range among nanowires, i.e., an L / D ratio of 10 or less, more preferably 5 or less, advantageously 2 or less.

[0201] Preferably, in the silicon-carbon intermediate composite, the silicon nanostructures are uniformly distributed over the surface of the flakes of carbon-based material, where "uniformly distributed" means that the silicon nanostructures are distributed evenly over the surface of the flakes of carbon-based material without certain areas being more dense than others, i.e. without certain areas having a higher silicon content.

[0202] The average percentage of the surface of the carbon-based material of the silicon-carbon intermediate composite that is covered with silicon nanostructures is advantageously greater than or equal to 50%, preferably greater than or equal to 70%, more preferably greater than or equal to 80%.

[0203] In one embodiment, the silicon nanostructures form a layer on the surface of the carbon-based material having a thickness of less than 500 nm, preferably less than 200 nm, more preferably less than 100 nm.

[0204] The silicon nanostructure forms a layer on the surface of the carbon-based material, advantageously with a thickness of 5 nm to 500 nm, preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm.

[0205] ● Silicon-carbon final composite material After step (f) of the method according to the invention, a second silicon-carbon composite material is obtained, ie the final silicon-carbon composite material.

[0206] Each embodiment in the following description of the silicon-carbon final composite material applies to every aspect of the invention unless otherwise specified.

[0207] This second silicon-carbon based composite material contains, and preferably consists essentially of, a carbon-based material and silicon nanostructures, and the final silicon-carbon composite material may contain trace amounts of catalyst or catalyst decomposition residues.

[0208] In a preferred embodiment, the composition of the final silicon-carbon composite material obtained through step (f) is substantially the same as the composition of the intermediate silicon-carbon composite material obtained through step (e) above.

[0209] The silicon content of the silicon-carbon final composite is advantageously greater than or equal to 5% by weight, preferably greater than or equal to 20% by weight, based on the total weight of the silicon-carbon final composite. The silicon content is advantageously between 5% and 70% by weight, preferably between 20% and 50% by weight, based on the total weight of the silicon-carbon final composite.

[0210] Preferably, at least a portion of the final silicon-carbon composite material according to the invention is of micrometer size.

[0211] Preferably, at least a portion of the silicon-carbon final composite is in the form of micrometric particles, more preferably at least 70%, preferably at least 80%, even more preferably at least 90% of the silicon-carbon final composite is in the form of micrometric particles.

[0212] The spheronization step (f) of the method according to the invention results in micrometric particles of silicon-carbon composite material with a rounded shape, essentially without corners or sharp edges. In particular, the micrometric particles may be ellipsoidal and / or rod-like and / or potato-like.

[0213] Advantageously, the micrometric particles of the silicon-carbon final composite material are in a form other than flakes, preferably less than 10% of the micrometric particles in the silicon-carbon final composite material are in the form of flakes, preferably less than 5%.

[0214] Advantageously, the micrometric particles of the silicon-carbon final composite material are potato-shaped.

[0215] The term "potato-shaped" generally refers to particles having an irregular shape, elongated three-dimensional shape with rounded corners, and a length to diameter ratio of 5:1 to 1:1, preferably 3:1 to 1:1, and more preferably 2:1 to 1:1.

[0216] In the final silicon-carbon composite material, advantageously more than 80%, preferably more than 90%, more preferably more than 95% and advantageously 100% of the micrometric particles are potato-shaped.

[0217] Advantageously, the micrometer particles of the final silicon-carbon composite material have a narrow particle size distribution. The skilled person can narrow the particle size distribution by adjusting the parameters of the spheronization step (f) of the method according to the invention, such as the rotation speed of the mill and / or the duration of the spheronization step and / or the characteristics of the spheronization means (such as the diameter of the grinding balls when using a ball mill). Alternatively, a sieving step can be carried out after step f) to select micrometer particles of a given size.

[0218] "Particle size distribution" or "particle size dispersion" refers to the relative abundance (typically relative mass) of particles of the final silicon-carbon composite material according to their particle size.

[0219] In a preferred embodiment, the D50 of the micrometer particles of the silicon-carbon final composite material is between 5 μm and 50 μm, preferably between 10 μm and 30 μm, more preferably between 15 μm and 25 μm.

[0220] "D50", also called "median particle size" or "median particle size", is the particle size in microns below which half of the population of particles fall and the other half above. For example, if a sample has a D50 of 5 μm, that means 50% of the particles are larger than 5 μm and 50% of the particles are smaller than 5 μm.

[0221] Particle size, particle shape and particle size distribution can be measured by any method known to the skilled artisan, such as, for example, scanning electron microscopy (SEM) and / or focused ion beam (FIB) tomography and / or dynamic light scattering (DLS) and / or scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM / EDS) and / or laser diffraction.

[0222] The micrometer particles of the final silicon-carbon composite material are advantageously 20 mm or less. 2 / g or less, preferably 10m 2 / g or less, more preferably 5m 2 / g or less.

[0223] "Specific surface area" refers to the total surface area per unit mass of the particles of the final silicon-carbon composite. The specific surface area of ​​the final composite can be measured by several techniques well known to those skilled in the art, such as the Brunauer-Emmett-Teller (BET) adsorption method.

[0224] Advantageously, the micrometer particles of the silicon-carbon final composite material have a density of 0.05 to 2 g / cm 3 , preferably 0.2 to 1.5 g / cm 3 , more preferably 0.35 to 1 g / cm 3 The tap density is

[0225] In one embodiment, particularly in one embodiment of the second aspect of the invention, the micrometric particles of the silicon-carbon final composite advantageously have an internal porosity of between 10% and 60%, more preferably between 15% and 50%, more preferably between 20% and 40%.

[0226] In a preferred embodiment of the first and third aspects of the present invention, the micrometric particles of the silicon-carbon final composite material have an internal porosity of between 5% and 25%.

[0227] "Internal porosity" refers to the percentage of the total volume of a micrometer particle that is occupied by pores or empty space. The internal porosity of a composite material can be measured by any method known to those skilled in the art, such as mercury intrusion porosimetry, density measurements, etc.

[0228] Advantageously, in all aspects of the invention, the micrometric particles of the final silicon-carbon composite material have closed pores.

[0229] By "closed pores" it is meant that the pores of the micrometer particles are not interconnected.

[0230] The second silicon-carbon composite material differs from the intermediate material in the arrangement of the carbon-based material and the silicon material. The spheroidization step (f) of the method according to the invention results in micrometer particles with a different microstructure from the first silicon-carbon composite material obtained through step (e). In particular, before the spheroidization step (f), the silicon nanostructures are arranged on the surface of the flakes of the carbon-based material, whereas after spheroidization, the micrometer particles obtained have at least a part of the silicon nanostructures embedded in the carbon-based material.

[0231] In the context of the present invention, the term "microstructure" is intended to mean how the components of a composite are arranged relative to one another, in particular the silicon nanostructures and the carbon-based material. The microstructure of a composite can be characterized, for example, by scanning electron microscopy (SEM) and / or transmission electron microscopy (TEM) and / or energy dispersive spectroscopy (EDS) and / or X-ray diffraction (XRD) and / or Raman spectroscopy.

[0232] In the context of the present invention, the term "embedded" is intended to mean that the silicon nanostructures are embedded in the surrounding carbon-based material matrix, in particular between the folds of the carbon material created during the spheroidization process.

[0233] In all aspects of the invention, advantageously at least 70% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, of the silicon nanostructures are embedded in the carbon-based material, based on the total weight of the silicon nanostructures in the second silicon-carbon based composite material.

[0234] Based on the total weight of the silicon nanostructures in the second silicon-carbon based composite material, preferably 70% by weight to 99% by weight, preferably 80% by weight to 90% by weight, of the silicon nanostructures are embedded in the carbon based material.

[0235] The average percentage of the outer surface of the carbon-based material particles in the silicon-carbon-based final composite material that is covered with silicon nanostructures is preferably 0% to 20%, preferably 0% to 10%, and more preferably 0% to 5%.

[0236] The applicants have found that such a high percentage of silicon nanostructures embedded in the carbon-based material can be obtained in particular by using large particle size carbon-based flakes, in particular flakes having a D50 particle size of 25 μm to 500 μm, preferably 30 μm to 500 μm, more preferably 30 μm to 100 μm, and most preferably 35 μm to 50 μm.

[0237] The silicon nanostructures form a layer of material within the carbon-based material, advantageously having a thickness of between 5 nm and 500 nm, preferably between 10 nm and 200 nm, more preferably between 20 nm and 100 nm.

[0238] (Use of carbon-silicon composite materials) The silicon-carbon composite material of the present invention can be used as an anode active material and in the manufacture of lithium ion batteries.

[0239] The final silicon-carbon composite material obtained by the method according to the invention can be used as such or after further processing as a silicon-carbon composite anode material in lithium ion batteries.

[0240] The present invention further relates to a method for producing an electrode comprising a current collector, the method comprising the steps of: (i) preparing a carbon-silicon composite material as an electrode active material according to the method described above; (ii) coating at least one surface of a current collector with a composition containing the electrode active material; Equipped with.

[0241] An electrode having a current collector can be manufactured by a manufacturing method classically used in the art. For example, the negative electrode active material made of the carbon-silicon composite material of the present invention may be mixed with a binder, a solvent, and a conductive agent. If necessary, a dispersant may be added. The mixture is stirred to prepare a slurry. Next, a current collector is coated with the slurry and pressed to produce a negative electrode.

[0242] As the binder in the present invention, various binder polymers such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate can be used.

[0243] This electrode can be used in the manufacture of a lithium secondary battery, as commonly used in the art, with a separator and an electrolyte disposed between a positive electrode and a negative electrode.

[0244] Specifically, the present invention provides a method for producing an energy storage element, such as a lithium secondary battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, the negative electrode being obtained by the aforementioned method for producing electrodes. EXAMPLES

[0245] In the following examples, contents and percentages are by weight unless otherwise specified.

[0246] material Reactor (fixed bed): Stainless steel reactor (internal volume = 1 L, diameter = 100 mm, height = 125 mm); Ball mill equipment: Model PM100 available from Retsch; Centrifugal mill equipment: Model ZM200 available from Recce, Silicon nanostructure precursor: diphenylsilane (Si(C)) commercially available from Sigma-Aldrich. 6 H5 ) 2 H 2 ) (CAS number: 775-12-2), Catalyst: SnCl, commercially available from Strem Chemicals 2 , Graphite flakes: BNB90 graphite (SSA=21.18m) commercially available from Imerys. 2 / g, D50=43 μm), M17 graphite (SSA=24.48 m) available from Nouveau Monde Graphite 2 / g, D50=16μm), Conductive filler: graphite powder available from Imerys under the trade name C-NERGY® Actilion GHDR-15-4; Conductive additive: carbon black available from Imerys under the trade designation Timcal C-NERGY C65 (CAS number: 1333-86-4); Binder: sodium carboxymethylcellulose (Na-CMC) (CAS number: 9004-32-4) available from Alfa-Aesar, styrene butadiene rubber (SBR) (CAS number: 9003-55-8) available from MTI, Electrolyte: A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume 1:1) containing lithium hexafluorophosphate (LiPF 6 ) (1M) and containing fluoroethylene carbonate (FEC) (10% by weight) and vinylene carbonate (additive) (2% by weight), commercially available from Solvionic.

[0247] Example 1: Batch synthesis of BNB-90 graphite / silicon nanowire material (M1) a) BNB-90 Graphite / SnCl 2 Material preparation 30g BNB-90 with 5g SnCl 2The BNB-90-SnCl was then placed in a steel vessel of the ball mill PM100. Then, 50 10 mm stainless steel balls were placed in the vessel, and the vessel was then tightly closed. 2 The materials are mixed at 400 rpm for 10 minutes and 30 seconds.

[0248] The balls were removed through a sieve and the BNB-90 graphite / SnCl 2 is easily retrieved.

[0249] b) Silicon Nanowire (SiNW) Growth The BNB-90 graphite / SnCl obtained at the end of step a) 2 The material is placed in a glass cup in a fixed bed reactor. Then, 250 mL of diphenylsilane (Ph 2 SiH 2, ) is poured into the bottom of the reactor.

[0250] After sealing the reactor, a gas line and a heating element are connected to the reactor. The reactor is then evacuated and filled with N 2 The reactor is purged several times with a vacuum to remove air / moisture contaminants. The reactor is then heated by an electrical resistor in contact with the outer surface of the reactor. The heating cycle is as follows: increase in temperature from 20°C to 430°C over 90 minutes, maintain at 430°C for 60 minutes, turn off the heating, and then reduce the reactor temperature to 50°C over 60 minutes with water cooling. Finally, the reactor is opened and the resulting material is collected.

[0251] c) Post-processing of BNB-90 graphite / silicon composite Ph 2 SiH 2 The organic matter produced by the decomposition of is carbonized by heat treatment. The composite material obtained at the end of step b) is placed in a crucible and then loaded into a horizontal quartz tube furnace. Argon gas (Ar) and hydrogen gas (H 2) gas lines are connected, which are continuously flowed through the material in a controlled amount with a ratio of 97.5:2.5 (v / v). The heat treatment is carried out at a temperature of 600°C with a heating rate of 6°C / min for 2 hours, and then cooled naturally. Finally, the heating furnace is opened to recover the composite material M1.

[0252] 1 and 2 show a composite material M1 consisting of SiNWs 101,201 with an average size (diameter) of 66 nm (see inset chart in FIG. 3 showing the size distribution of the SiNWs), BNB-90 graphite 102,202 and tin particles 203.

[0253] (Example 2: Molding of composite material M1 (M2)) a) Crushing 10 g of composite material M1 was put into the ultracentrifugal mill ZM200. The material was ground at 6000 rpm and instantly collected in a cassette pan. Finally, the powder was sieved to 250 μm.

[0254] b) Compaction Next, the crushed material is mixed with approximately 7.5t / cm 2 The pellets were collected and finely ground in a mortar. The powder was finally collected and sieved through a 400 μm sieve to obtain composite material M2.

[0255] c) Description of Figure 4 Figure 4 shows the composite material M2 consisting of SiNWs 301 and BNB-90 graphite 302. Compared to the observation of M1, SiNWs 301 are hardly found on the surface of BNB-90 graphite 302. This indicates that the probability that SiNWs are present in the core of the composite material between the graphite flakes is very high. This molding process results in the formation of particles with an average diameter of 15 μm, as indicated by the black dashed line 303.

[0256] Example 3: Batch synthesis of M17 graphite / silicon composite (M3) a) M17 Graphite / SnCl 2 Material preparation 30g M17 graphite with 5g SnCl 2 The M17 graphite / SnCl is then placed in a stainless steel container of a ball mill PM100. Next, 50 10 mm stainless steel balls are placed in the container, and the container is then tightly closed. 2 The materials are mixed at 400 rpm for 10 minutes and 30 seconds. The balls were removed through a sieve and M17 graphite / SnCl 2 Easily recover materials.

[0257] b) Silicon nanowire growth The growth substrate / pre-catalyst material obtained at the end of step a) is placed in a glass cup in a fixed-bed reactor. Then, 250 mL of diphenylsilane (Ph 2 SiH 2, ) is poured into the bottom of the reactor.

[0258] After sealing the reactor, connect the gas line and the heating element to the reactor. The reactor is then evacuated and filled with N 2 The reactor is purged several times with a vacuum to remove air / moisture contaminants. The reactor is then heated by an electrical resistance in contact with the outer surface of the reactor. The heating cycle is as follows: increase in temperature from 20°C to 430°C in 90 minutes, maintain at 430°C for 60 minutes, turn off the heating, and then reduce the temperature of the reactor to 50°C in 60 minutes with water cooling. Finally, the reactor is opened and the resulting material is collected.

[0259] c) Post-processing of growth substrate / silicon composite Ph 2 SiH 2 The organic matter produced by the decomposition of is carbonized by heat treatment.

[0260] The composite material obtained at the end of step b) is placed in a crucible and then in a horizontal tube furnace made of quartz. Argon (Ar) and hydrogen gas (H 2) gas lines are connected to the material, which are continuously flowed through the material in a controlled amount with a ratio of 97.5:2.5 (v / v). The heat treatment is carried out for 2 hours at a temperature of 600°C with a rate of 6°C / min, and then cooled naturally. Finally, the furnace is opened to recover the composite material M3.

[0261] FIG. 5 shows a composite material M3 having SiNWs 401 with an average size (diameter) of 77 nm (see inset chart in FIG. 6 showing the size distribution of SiNWs) on M17 graphite 402.

[0262] (Example 4: Molding of composite material M3 (M4)) a) Crushing 10g of composite material M3 was put into the ultracentrifugal mill ZM200. The material was ground at 6000 rpm and instantly collected in a cassette pan. Finally, the powder was sieved to 250 μm.

[0263] b) Compaction Next, the crushed material is mixed with approximately 7t / cm 2 The mixture was calendered at 100° C. The pellets were collected and finely ground in a mortar. The powder was finally collected to obtain composite material M4.

[0264] c) Description of Figure 7 Figure 7 shows composite material M4 consisting of SiNWs 501 and M17 graphite 502. Compared to the observation results of M3, SiNWs 501 are rarely found on the surface of M17 graphite 502. This indicates that the probability that SiNWs are present in the core of the composite material between the graphite flakes is very high. This molding process results in the formation of secondary particles with an average particle size of 15 μm, as indicated by the black dashed line 503.

[0265] (Example 5: Preparation of electrodes for lithium batteries) The electrochemical properties of each material were evaluated by fabricating coin batteries using any of the materials M1, M2, M3, and M4 (presented as Example 1, Example 2, Example 3, and Example 4, respectively) as the negative electrode active material.

[0266] a) Mixing with conductive filler The resulting composite material was mixed with graphite powder using yttria-stabilized zirconia (YSZ) grinding balls in an IKA Ultra-Turrax disperser with a dispersion tube ST-20. The composite material and the graphite were charged into the disperser in a weight ratio of 38:62. YSZ balls (12 g) with a diameter of 3 mm were used at a rotation speed of 7.5 for 10 minutes. Finally, the mixed material was collected for further processing or characterization.

[0267] b) 2. Preparation of Coin Cells The synthesized materials and graphite powder (Actilion GHDR-15-4 from Imerys) were mixed in a ratio of approximately 38:62 as described above to form the electrode active material. The weight ratio of active material:C65:binder was 95:1:4. Carbon black (1 wt%) was added to each system as a conductive additive, and a solution of sodium carboxymethylcellulose (Na-CMC) (2 wt%) and styrene butadiene rubber (SBR) (2 wt%) were used as the binder. Pure water was used as the solvent. Water was added to achieve a viscosity that allowed electrode processing (dry content: approximately 40 wt%). The materials were wet mixed for 30 min at rpm=5. Each electrode ink was cast on 20 μm copper foil using a doctor blade. After partial air drying, the electrodes were further dried in an oven at 65 °C for 1 h. The electrodes were then cut into 14 mm diameter disks and approximately 0.6 t / cm 2 The mixture was calendered at 400° C., weighed, and finally dried overnight in vacuum at 110° C.

[0268] Half coin cells (Kanematsu KGK Corporation: Stainless Steel 316L) using metallic Li as counter and reference electrodes were fabricated in an Ar glove box using a layer of Whatman glass fiber, a layer of Celgard 2325 separator, and the electrode to be evaluated. The electrode and separator materials were impregnated with an electrolyte purchased from Solvionic Corporation. The composition of the electrolyte was LiPF in EC:DEC (v / v=1 / 1) with 10 wt% FEC (fluoroethylene carbonate) and 2 wt% VC (vinylene carbonate). 6 (1M) was dissolved in the battery. The battery was then sealed with an automatic press, removed from the glove box, and measured with a charge-discharge evaluation device. Seven formation cycles were performed before the normal charge-discharge cycle at 1C rate. The formation cycle consisted of two cycles of C / 7 and five cycles of C / 5, with constant current / constant voltage discharge (lithium insertion) and constant current charge (lithium desorption). Then, 22 cycles of charge-discharge cycles at 1C were performed without changing the contents.

[0269] c) Electrochemical performance measurements The performance of the batteries is measured by constant current charge-discharge cycling using a Biologic BCS-805 charge-discharge measurement system capable of eight different configurations, each with two different electrodes.

[0270] 1. Potential Profile Figures 8 and 9 show the potential profiles obtained for the batteries C1, C2, C3 and C4 (materials M1, M2, M3 and M4), respectively, recorded during the second cycle of C / 7 (second formation cycle). The potential profiles obtained for the batteries from the composites M1, M2, M3 and M4 show that all composites are electrically and electrochemically active due to the additive electrochemical activity of the graphite and silicon materials. The response from the graphite is only measured below 0.3 V during lithium insertion (discharge) and lithium desorption (charge). The lithium desorption (charge) profile shows that the electrochemical activity of Si is spread over the range of 0.1 to 0.8 V. The reaction mechanism of the Si and Li ions is such that after lithium insertion, the cubic Li ions are formed. 15 S 4 The final formation of the phases M1, M2, M3, and M4 is accompanied by a distinct characteristic bend / plateau at around 0.45 V during charging (lithiation). Such plateaus are evident upon material shaping from M1 to M2 and from M3 to M4, demonstrating that material shaping does not hinder or reduce the electrochemical activity of the Si nanomaterials.

[0271] 2.Reversible capacity Figures 10 and 11 show the reversible capacities recorded during 1C charge-discharge cycling for batteries C1, C2, C3 and C4 (materials M1, M2, M3 and M4). The cycle life curves are very similar in shape and slope, which shows that molding the materials does not adversely affect their performance. The CR value, which is the ratio of the capacity of cycle n divided by the capacity of cycle n-1, derived from these curves, further confirms that the molding step f) does not reduce the durability of the materials.

[0272] 3. Initial reversible capacity (ICE), coulombic efficiency (CE) and capacity retention (CR) values The potential profiles of the batteries C1, C2, C3, and C4 made from materials M1, M2, M3, and M4, respectively, were obtained by measuring the potential of the batteries as a function of capacity during C / 7 charge-discharge cycling and subsequent C / 5 and 1C charge-discharge cycling. Table 1 shows the initial reversible capacity and coulombic efficiency derived from the first C / 7 cycle measurements, as well as the CE and CR values ​​obtained during 1C charge-discharge cycling.

[0273] [Table 1]

[0274] The initial capacity of the battery C2 made from composite M2 (847 mA.h / g) is higher than that of the battery C1 made from composite M1 (799 mA.h / g). Thus, the amount of active silicon in composite M2 is slightly higher than that of M1. This may be due to the better physical contact between the Si and graphite materials in M2 than in M1. Furthermore, comparing C1 and C2, it can be seen that the average coulombic efficiencies for cycles 10 and 20 (99.21 / 99.18%, 99.50 / 99.51%, respectively) are increased by about 0.3%, and the average capacity retentions for cycles 10 and 20 are almost the same at about 99.9% (99.92 / 99.87%, 99.88 / 99.91%, respectively). In summary, the CE results show that the molding process of composite M1 to form composite M2 improves the surface protection and stability of silicon by intercalating silicon between the graphite flakes, while the CR results show that the mechanical durability of the silicon nanostructured material can be maintained even after multiple charge-discharge cycles.

[0275] The initial capacity of the battery C4 made from composite M4 (805 mA.h / g) is higher than that of the battery C3 made from composite M3 (761 mA.h / g). Thus, the amount of active silicon in composite M4 is slightly higher than that of M3. This may be due to the better physical contact between the Si and graphite materials in M4 than in M3. Furthermore, comparing C3 and C4, it can be seen that the average coulombic efficiencies at 10 and 20 cycles (99.20 / 99.22%, 99.47 / 99.47%, respectively) are increased by about 0.25%, and the capacity retention at 20 cycles (99.77 / 99.78, 99.76 / 99.83, respectively) is slightly improved. In summary, the above results indicate that the molding process of composite M3 to form composite M4 improves the surface protection and stability of Si by inserting it between the graphite flakes, and the CR results show that the mechanical durability of the silicon nano-object material is maintained even after multiple charge-discharge cycles.

[0276] Also, in full cells with limited Li capacity cathodes (e.g., NMC622, etc.), the cycle life of full cell batteries with formed materials M2 and M4 is better than that of batteries based on unformed materials because the increased CE reduces Li consumption.

[0277] The CE of the anode material is an important parameter for enabling long-term cyclability of lithium-ion batteries. n Using the formula, CE = capacity retention (where n is the number of cycles and CE describes the coulomb loss of the anode alone), if a cathode with CE = 99% is installed in a full cell using a cathode material with limited capacity (e.g., NMC622, etc.), the loss of the anode is assumed to be 37% after 100 cycles. Similarly, a better anode with CE of 99.5% would have a capacity retention of about 60% after 50 cycles in a full cell, and if the CE of the anode is further increased to 99.9%, the capacity retention in a full cell is estimated to be 90%. Therefore, it is essential to design anode materials with good CE. [Explanation of symbols]

[0278] 101,201,301,401 SiNW 102, 202, 302 BNB-90 Graphite 203 Tin particles 303 Composite material particles

Claims

1. 1. A method for producing a silicon-carbon composite material, comprising: (a) introducing at least flakes of a carbon-based material, and optionally a catalyst, into a reactor chamber; (b) introducing at least silicon nanostructure precursor compounds into the reactor chamber; (c) reducing the molecular weight of oxygen in the reactor chamber; (d) heat treating at a temperature in the range of 200°C to 900°C; (e) recovering the first silicon-carbon composite material; (f) spheronizing the product obtained in step (e) to obtain a second silicon-carbon composite material; A method comprising:

2. 10. The method of claim 1, wherein the carbon-based material flakes have a D50 particle size of 25 μm to 500 μm.

3. The method of claim 2 , wherein the second silicon-carbon composite material has an internal porosity of 5% to 25%.

4. 4. The method of claim 1, wherein the silicon nanostructures are in the form of nanoparticles.

5. The method of claim 4, wherein the nanoparticles have a particle size in the range of 1 nm to 250 nm.

6. 10. The method of claim 1, wherein in step (a) a catalyst selected from metals, metal oxides, and metal halides is introduced into the reactor chamber.

7. 7. The method of claim 6, wherein the catalyst is selected from the group consisting of gold (Au), tin (Sn), tin dioxide (SnO ２ ), tin halide (SnX ２ ) and mixtures thereof.

8. 8. The method of claim 6 or 7, wherein the silicon nanostructures are in the form of nanowires or nanofibers.

9. 2. The method of claim 1, wherein the average percentage of the surface of the carbon-based material covered with silicon nanostructures in the first silicon-carbon composite material is 50% or more.

10. 10. The method of claim 1, wherein the average percentage of the outer surface of the second silicon-carbon composite material that is covered with silicon nanostructures is 20% or less.

11. 10. The method of claim 1, wherein steps (a) through (e) are carried out in a fixed bed reactor.

12. 10. The method of claim 1, wherein the spheronizing step (f) comprises at least one step selected from crushing, grinding, compacting, densifying, pressing, compressing, folding, rolling, rolling, crushing, coarsening, pulverizing, applying centrifugal force, or a combination of one or more of these processes.

13. 10. The method of claim 1, wherein at least a portion of the second silicon-carbon composite material is in the form of micrometer particles having a D50 of 5 to 50 μm.

14. 14. The method of claim 13, wherein the micrometer particles of the second silicon-carbon composite material have a potato-like shape.

15. 15. The method of claim 13 or 14, wherein the micrometer particles are 20 m ２ / g or less specific surface area.

16. The method of claim 1 , wherein the carbon-based material is selected from graphite, graphene, and carbon.

17. 10. The method of claim 1, wherein the precursor compound of the silicon particles is a silane compound or a mixture of silane compounds.

18. 10. The method of claim 1, further comprising, after step (f), coating an outer surface of the second material with a second carbon-based material different from the carbon-based material flakes; A method comprising:

19. 1. A method for manufacturing an electrode having a current collector, comprising: (i) preparing a carbon-silicon composite material according to the method of claim 1 as an electrode active material; (ii) coating at least one surface of the current collector with a composition containing the electrode active material; A method comprising:

20. 20. A method for producing an energy storage element comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein at least one of the electrodes is obtained by the method of claim 19.

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