Method for producing carbon-silicon composite powder and carbon-silicon composite powder

Abstract

The present disclosure relates to a method for producing a carbon-silicon composite powder, the method comprising: providing a carbon-containing precursor that is lignin; providing at least one silicon-containing active material; melt-mixing at least the carbon-containing precursor and the silicon-containing active material to obtain a molten mixture; providing the molten mixture in a non-fibrous form; cooling the molten mixture to provide an isotropic intermediate composite material; subjecting the isotropic intermediate composite material to a heat treatment, the heat treatment comprising a carbonization step to provide a carbon-silicon composite material; and pulverizing the carbon-silicon composite material to provide the carbon-silicon composite powder. The present disclosure also relates to a carbon-silicon composite powder obtained by the method, a negative electrode for a non-aqueous secondary battery, such as a lithium-ion battery, comprising the silicon carbide composite powder, and the use of the silicon carbide composite powder in a negative electrode of a non-aqueous secondary battery.

Description

[Technical Field]

[0001] This disclosure relates to a method for producing a carbon-silicon composite powder and the carbon-silicon composite powder obtained by the method. This disclosure also relates to a negative electrode for a non-aqueous secondary battery, such as a lithium-ion battery, that includes the carbon-silicon composite powder obtained by the method as an active material. This disclosure also relates to the use of the carbon-silicon composite powder obtained by the method as an active material in a negative electrode of a non-aqueous secondary battery, such as a lithium-ion battery. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, are electric batteries that can be repeatedly charged and discharged, i.e., rechargeable batteries. For example, lithium-ion batteries are commonly used in portable electronic devices and electric vehicles today. Lithium-ion batteries have high energy density, high operating voltage, low self-discharge, and low maintenance requirements.

[0003] In lithium-ion batteries, lithium ions flow from the negative electrode through the electrolyte to the positive electrode during discharge and back during charging. Today, lithium compounds, especially lithium metal oxides, are typically used as the positive electrode material, and carbonaceous materials are typically used as the negative electrode material.

[0004] Graphite (natural or synthetic) is used as the anode material in most lithium-ion batteries today. Graphite has a resistance of 50-300 mV vs. Li / Li. + It offers a theoretical capacity of 372 mAh / g (corresponding to LiC6 stoichiometry) at a low potential, which translates into high energy density at the cell level. Furthermore, it offers stable charge / discharge performance, typically over 1,000 to several thousand cycles.

[0005] Alternatives to graphite are amorphous carbon materials such as hard carbon (refractory amorphous carbon) and soft carbon (easily graphitizable amorphous carbon), which lack graphitic long-range order. Amorphous carbon can be used as the sole active electrode material or in a mixture with graphite (and / or other active materials).

[0006] Amorphous carbon can be derived from lignin, an aromatic polymer that is the primary component of wood, for example, and one of the most abundant carbon sources on Earth. In recent years, the development and commercialization of techniques to extract lignin in a highly purified, solid, and particulate form from pulp production processes has attracted significant attention as a renewable alternative to the primarily aromatic chemical precursors currently supplied by the petrochemical industry. Lignin-derived amorphous carbon is typically non-graphitizable, i.e., hard carbon.

[0007] Hard carbons typically exhibit very good charge-discharge rate performance (higher than graphite) at both room and low temperatures, which is desirable for high-power systems, fast-charging devices, and low-temperature applications. Electrochemical charging and discharging of hard carbons occurs between approximately 1.3 V vs. Li / Li+ and <0 V vs. Li / Li+, and when the electrode potential is plotted across capacity, it contains a steadily sloping potential region above approximately 0.1 V vs. Li / Li+ and an extended potential plateau below this value. The average electrode potential is higher than that of graphite. Due to their lower geometric density and higher average electrode potential, they provide a lower usable energy density at the cell level than graphite.

[0008] What graphite and amorphous carbon have in common is that they undergo small volume changes during charging (Li insertion) and discharging (Li de-insertion) (about 10% by volume of graphite), which provides good mechanical stability of the electrode material and the electrode and helps maintain good cycling stability.

[0009] Both graphite and amorphous carbon operate in a potential range outside the thermodynamic stability window of the electrolyte. During the first charge, the electrolyte decomposes, and some of the decomposition products form a protective layer on the electrode surface, the so-called "solid electrolyte interface" (SEI). The formation of the SEI irreversibly consumes charge, mostly during the first charge, resulting in irreversible capacity loss over the first few cycles and a decrease in the initial coulombic efficiency (ICE, or first cycle charge-discharge efficiency). Once the SEI is fully formed, electrolyte decomposition ceases and reversible cycling becomes possible.

[0010] Due to the small volume change during cycling between graphite and amorphous carbon, the mechanical strain of the SEI is small, the SEI once fully formed remains more or less stable, and the irreversible capacity loss due to SEI formation (then) drops to zero.

[0011] Yet another alternative anode material is silicon. Elemental Si has a capacity of 3579 mAh / g (corresponding to the reaction: 4 Si + 15 Li + +15 e - ←→Li 15 They offer ultra-high theoretical capacities of Si4 and practical capacities approaching this value. However, the use of pure Si is hindered by the enormous volume changes that occur during charge and discharge, which are in the range of 260% by volume, and typically result in mechanical strain and electrode cracking and collapse. This causes irreversible capacity loss (due to loss of cyclable Si), reduces coulombic efficiency (first and subsequent cycles), and shortens cycle life. This problem can be partially alleviated by using special binders (such as carboxymethyl cellulose derivatives or polyacrylates) that form strong covalent bonds to Si (and, after cracking, Si fragments).

[0012] Like graphite and amorphous carbon, Si operates outside the electrolyte's stability window, forming an SEI, leading to irreversible capacity loss and reduced initial coulombic efficiency. However, due to the enormous volume change during charge and discharge, the SEI, once fully formed, is not stable but can be damaged and must be repaired in subsequent cycles. This repair leads to additional irreversible capacity loss and reduced coulombic efficiency, even in cycles following the first. It has been shown that this situation can be partially alleviated by using special electrolytes and electrolyte additives, such as fluoroethylene carbonate (FEC), which produce an SEI specifically adapted to Si electrodes.

[0013] Some degree of stabilization of the Si electrode can be achieved by using Si-rich compounds instead of pure elemental Si. Si-rich compounds are silicon suboxides (SiO, where 0≦x≦2). x ), Si alloys (e.g., SiFe x , SiFe x Al y , or SiFe x C y ), and other Si-rich compounds. An example is silicon suboxide, SiO x SiO x Various models have been proposed to describe the structure of SiO x is described as a mixture of Si and SiO2 interdispersed on the nanometer scale.

[0014] SiO x It is proposed that the reaction occurs in two steps. For simplicity, consider the case where x=1: the first SiO is 4 SiO + 4 Li + +4 e - → Li4SiO4 + 3 Si, resulting in an irreversible capacity loss of 608 mAh / g. In the second step, and during all subsequent charge-discharge cycles, the released Si reacts irreversibly according to the reaction: 4 Si + 15 Li + +15 e - ←→Li 15The reaction follows the reaction of Si4, resulting in a reversible capacity of 1710 mAh / g. The theoretical initial coulombic efficiency is therefore 73.8%, which is lower than that of elemental Si (theoretical initial coulombic efficiency is 100%). However, compared to pure elemental Si, the Li incorporation and therefore SiO x The volume change of SiO is significantly smaller, thus improving cycle stability. x Similar considerations regarding apply to other Si compounds where the reacting Si is diluted within a stabilizing matrix.

[0015] A common route to harnessing the high capacity of Si or Si-rich compounds (generically referred to herein as silicon-containing active materials or SiX) without unduly sacrificing cycling stability is to add small amounts of SiX to graphite electrodes. For example, every 1 wt. % of elemental Si added to graphite increases the reversible capacity by approximately 10%. Thus, the addition of Si or Si-rich compounds can be used to increase the reversible capacity of amorphous carbon.

[0016] Commercially available composites of carbon and SiX, such as graphite and SiX composites, are today typically produced by a process that includes any one of the following steps: Mixing of graphite and SiX prior to electrode preparation, e.g. using high energy mixing or milling techniques Coating of graphite with a thin layer of silicon-containing active material, e.g., by chemical vapor deposition (CVD), to obtain a graphite / SiX core / shell material Coating of SiX particles with a thin carbon layer, e.g., by wet chemical methods, to obtain SiX / carbon core / shell materials - Blending graphite and SiX when preparing electrodes

[0017] The SiX component in the above method may be surface pre-oxidized or carbon coated to enhance its stability. Additionally, composites of carbon and SiX materials may be additionally carbon coated to enhance their stability.

[0018] When utilized as a secondary battery electrode material, the graphite / carbon and SiX composite is typically provided in powder form and mixed with a binder to form the electrode.

[0019] US 2014 / 0287315A1 describes a method for producing a Si / C composite, the method including providing a silicon-containing active material, providing lignin, contacting the active material with a C precursor containing lignin, and carbonizing the active material by converting the lignin to carbon in an inert gas atmosphere at a temperature of at least 400° C. The silicon-based active material can be ground with the lignin or physically mixed with the lignin.

[0020] However, in graphite / carbon and SiX composites obtained by methods such as milling or coating, the individual components are typically adjacent to each other (SiX next to graphite / carbon) or overlapping each other (SiX on the surface of graphite / carbon or graphite / carbon on the surface of SiX). Therefore, while maintaining good and uniform dispersion of Si, the SiX loading is limited. Furthermore, unless the SiX or graphite / carbon and SiX composite is carbon-coated, the SiX will come into direct contact with the binder and electrolyte of the secondary battery in which the composite is used as the negative electrode active material, causing all the problems with cycle stability and coulombic efficiency mentioned above. This requires special binders and electrolytes.

[0021] Therefore, there is still room for improvement in the manufacturing method of carbon-silicon composite powder. Summary of the Invention

[0022] It is an object of the present invention to provide an improved method for producing carbon-silicon composite powders which allows for the use of renewable carbon sources, which eliminates or mitigates at least some of the disadvantages of prior art methods, and which provides improved carbon-silicon composite powders suitable for use as active materials in negative electrodes of secondary batteries, such as lithium-ion batteries.

[0023] The above objectives, as well as other objectives which will be realized by those skilled in the art in light of the present disclosure, are accomplished by various aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0024] According to a first aspect presented herein, there is provided a method for producing a carbon-silicon composite powder, the method comprising: providing a carbon-containing precursor, the carbon-containing precursor being lignin; providing at least one silicon-containing active material; - melt-mixing at least two components into a molten mixture, the carbon-containing precursor constituting one component and each silicon-containing active material constituting one component, the melt-mixing being carried out at a temperature of 120-250°C; providing the molten mixture in a non-fibrous form and cooling the molten mixture in the non-fibrous form to provide an isotropic intermediate composite material; - subjecting the isotropic intermediate composite material to a heat treatment, the heat treatment including a carbonization step to provide a carbon-silicon composite material; and - pulverizing the carbon-silicon composite to provide the carbon-silicon composite powder; Includes.

[0025] The present invention is based on the surprising realization that high loadings of silicon-containing active material and good or high dispersion of the silicon-containing active material may be obtained by melt-mixing (i.e., using combined mechanical and thermal energy) lignin (a carbon-containing precursor) and at least one silicon-containing active material at temperatures between 120 and 250°C to provide a molten mixture. The melt-mixing method of the first aspect allows for the incorporation of the silicon-containing active material while the carbon of the carbon-containing precursor is still plastic or liquid (and before it has been converted to hard carbon). Therefore, the silicon-containing active material can be well- or highly finely and uniformly dispersed both within and on the carbon (rather than just adjacent to or on top of the carbon as in prior art methods). This allows for high loadings of silicon-containing active material to be obtained while maintaining good or high dispersion of the silicon-containing active material.

[0026] Furthermore, the good or highly uniform dispersion of the silicon-containing active material both within the carbon and on its surface means that the majority of the silicon-containing active material is surrounded by carbon and therefore not in direct contact with the electrolyte when used as an active material in a secondary battery, such as a lithium-ion battery. This alleviates problems associated with prior art materials, such as electrolyte reduction at the surface of the silicon-containing active material and the instability of the SEI that forms on the silicon-containing active material. Furthermore, when used as an active material in a secondary battery, such as a lithium-ion battery, the silicon-containing active material expands and contracts during electrochemical charging and discharging, causing mechanical strain on the material. The surrounding carbon matrix helps stabilize the expanding silicon-containing active material.

[0027] Furthermore, an isotropic carbon-silicon composite powder can be obtained by providing a non-fibrous molten mixture, cooling the non-fibrous molten mixture to provide an isotropic intermediate composite, subjecting the isotropic intermediate composite to a heat treatment including a carbonization step to provide a carbon-silicon composite (which is therefore isotropic), and pulverizing the carbon-silicon composite. Using an isotropic carbon-silicon composite powder as the active material in the negative electrode of a secondary battery, such as a lithium-ion battery, is advantageous because the isotropy means that the properties of the active material, and therefore the electrode, can be more uniform than when an anisotropic material is used. For example, using an isotropic carbon-silicon composite as the active material in the negative electrode of a secondary battery instead of an anisotropic material results in more uniform electrode volume changes during charging and discharging.

[0028] Thus, by using the method according to the first aspect of the present invention, improved carbon-silicon composite powders can be obtained, which have high loadings of silicon-containing active material, high or good dispersion, and are isotropic, which imply advantages when used as the active material in the negative electrodes of secondary batteries, such as lithium-ion batteries. Furthermore, because lignin is used as the carbon-containing precursor, a renewable carbon source can be utilized.

[0029] The term "carbon-silicon composite," as in phrases such as "carbon-silicon composite material" and "carbon-silicon composite powder," as used herein refers to a composite comprising carbon and one or more silicon-containing active materials, e.g., a composite comprising carbon and elemental silicon, a composite comprising carbon and one or more silicon-rich compounds, or a composite comprising carbon, elemental silicon, and one or more silicon-rich compounds.

[0030] As used herein, the term "carbon-containing precursor" refers to a carbon precursor material used as a carbon source for the carbon matrix material of the carbon-silicon composite materials of the present disclosure. According to the present disclosure, the carbon-containing precursor is lignin.

[0031] The term "lignin" as used herein refers to any kind of lignin that can be used as a carbon source for producing carbonized carbon-silicon composites, i.e., conductive carbon-silicon composites. Examples of lignin include, but are not limited to, lignin obtained from plant materials, such as wood, for example, softwood lignin, hardwood lignin, and lignin derived from cyclic plants. Lignin can also be chemically synthesized.

[0032] Preferably, the lignin is purified or isolated before use in the methods of the present disclosure. Lignin may be isolated from black liquor and, optionally, further purified before use in the methods of the present disclosure. Purification is typically such that the lignin is at least 90%, preferably at least 95%, pure. Thus, lignin used in accordance with the methods of the present disclosure preferably contains less than 10%, more preferably less than 5%, of impurities such as cellulose, ash, and / or moisture.

[0033] Preferably, the carbon-containing precursor contains less than 1% ash, more preferably less than 0.5% ash.

[0034] Lignin can be obtained by different fractionation methods such as the organosolv method or the kraft method. For example, lignin can be obtained by using the method disclosed in WO2006031175 or the method called LignoBoost method.

[0035] Preferably, the carbon-containing precursor used in the method of the first aspect of the present disclosure is kraft lignin, i.e., lignin obtained by the kraft process. Preferably, the kraft lignin is obtained from hardwood or softwood, most preferably from softwood.

[0036] Preferably, the carbon-containing precursor utilized in the method of the first aspect is a dry material. Preferably, the carbon-containing precursor contains less than 5% moisture. The carbon-containing precursor utilized in the method of the first aspect may be provided in particulate form, such as a powder, preferably having an average particle size of 0.1 μm to 3 mm.

[0037] As used herein, the term "silicon-containing active material" (SiX) refers to a silicon-containing material that can be used as a (battery) capacity enhancing material for carbon-silicon composites and thus can be used to make carbonized carbon-silicon composites, i.e., conductive carbon-silicon composites.

[0038] As used herein, the term "silicon-containing active material" (SiX) encompasses both pure elemental Si and Si-rich compounds. Si-rich compounds include silicon suboxide (SiO, where 0≦x≦2). x ), Si alloys (e.g., SiFe x , SiFe x Al y , or SiFe x C y ), and other Si-rich compounds. x Various models have been proposed to describe the structure of SiO x is described as a mixture of Si and SiO2 interdispersed on the nanometer scale. The silicon-containing active material (SiX) may be provided in crystalline or amorphous form and may further be surface pre-oxidized or carbon-coated to enhance stability.

[0039] Thus, in some embodiments, each silicon-containing active material utilized in the first aspect of the method is selected from the group of elemental silicon, silicon suboxide, silicon-metal alloy, or silicon-metal carbon alloy. Silicon suboxide is SiO, where 0≦x≦2. x The silicon-metal alloy may be, for example, SiFe x or SiFe x Al yThe silicon-metal carbon alloy may be any suitable silicon-metal alloy, such as SiFe x C y may be.

[0040] In some embodiments, one silicon-containing active material is utilized, i.e., the step of providing at least one silicon-containing active material includes providing one silicon-containing active material. In some of these embodiments, the silicon-containing active material is elemental silicon. In some of these embodiments, the silicon-containing active material is silicon suboxide (SiO), where 0≦x≦2. x In some of these embodiments, the silicon-containing active material is, for example, SiFe x or SiFe x Al y In some of these embodiments, the silicon-containing active material is a silicon-metal alloy, such as, for example, SiFe x C y and other silicon-metal carbon alloys.

[0041] In some embodiments, two or more silicon-containing active materials are utilized, i.e., the step of providing at least one silicon-containing active material includes providing two, three, four, or more silicon-containing active materials. Each silicon-containing active material then constitutes a component melt-mixed in the melt-mixing step. Each silicon-containing active material can then be selected from the silicon-containing active materials described above. In one example, elemental silicon and silicon suboxide are provided as the silicon-containing active materials. In another example, two different silicon suboxides are provided as the silicon-containing active materials. In a further example, uncoated elemental silicon and coated elemental silicon are provided as the silicon-containing active materials. In yet a further example, carbon-coated elemental silicon and silicon suboxide are provided as the silicon-containing active materials.

[0042] The silicon-containing active material is preferably provided in particulate form, preferably micro- or nano-sized. By "micro-sized particulate form" herein, it is meant that the silicon-containing active material is in particulate form, with an average particle size in the micrometer range, for example, 1 to 50 μm. By "nano-sized particulate form" herein, it is meant that the silicon-containing active material is in particulate form, with an average particle size in the nanometer range, for example, 1 to 999 nm.

[0043] Typically, the average particle size of the silicon-containing active material in particulate form can be from 5 nm to 5 μm.

[0044] The silicon-containing active material in particulate form may be at least partially oxidized or carbon-coated prior to melt mixing, i.e., addition to the carbon-containing precursor, and may be provided in crystalline or amorphous form.

[0045] In some embodiments, the carbon-containing precursor is mixed with 0.5 to 30 wt%, or 1 to 15 wt%, or 2 to 10 wt% of at least one silicon-containing active material in the melt-mixing step. Thus, in these embodiments, a total of 0.5 to 30 wt%, or 1 to 15 wt%, or 2 to 10 wt% of the silicon-containing active material is mixed with the carbon-containing precursor in the melt-mixing step.

[0046] As described above, the melt-mixing step of the method of the first embodiment includes melt-mixing at least two components into a molten mixture, with the carbon-containing precursor constituting one component and each silicon-containing active material constituting one component. Thus, the melt-mixing step may include melt-mixing only the carbon-containing precursor and the silicon-containing active material. Alternatively, however, the melt-mixing step may include melt-mixing the carbon-containing precursor, the silicon-containing active material, and one or more additional components. The additional components may be, for example, one or more dispersing additives. The melt-mixing step does not utilize a solvent.

[0047] In some embodiments, the method according to the first aspect further comprises providing at least one dispersing additive, and the components melt-mixed in the melt-mixing step comprise at least one dispersing additive. Thus, in these embodiments, the melt-mixing step comprises melt-mixing at least a carbon-containing precursor, a silicon-containing active material, and at least one dispersing additive.

[0048] The dispersion additive may be selected from the group consisting of monoethers, polyethers, monoalcohols, polyalcohols, amines, polyamines, carbonates, polycarbonates, monoesters, polyesters, and polyether fatty acid esters. For example, the dispersion additive may be selected from the group consisting of polyethylene oxide (PEO) and branched polyether fatty acid esters (such as TWEEN, e.g., TWEEN 80).

[0049] In some embodiments, one dispersing additive is provided and melt mixed with the other components in a melt-mixing process, and the dispersing additive is PEO. In some embodiments, one dispersing additive is provided and melt mixed with the other components in a melt-mixing process, and the dispersing additive is a branched polyether fatty acid ester (such as TWEEN, e.g., TWEEN 80).

[0050] In some embodiments, the carbon-containing precursor is mixed with 0.5 to 30 wt%, or 1 to 15 wt%, or 2 to 10 wt% of at least one silicon-containing active material and 0.5 to 10 wt%, or 1 to 7 wt% of at least one dispersing additive in the melt-mixing step. Thus, in these embodiments, a total of 0.5 to 30 wt%, or 1 to 15 wt%, or 2 to 10 wt% of the silicon-containing active material and a total of 0.5 to 10 wt%, or 1 to 7 wt% of the dispersing additive are mixed with the carbon-containing precursor in the melt-mixing step. However, the amount of dispersing additive will depend on the type of dispersing additive utilized.

[0051] As mentioned above, the melt-mixing step of the method of the first embodiment is carried out at a temperature of 120 to 250° C., for example, 150 to 200° C. Preferably, the melt-mixing is carried out for 1 to 60 minutes, for example, 1 to 30 minutes or 1 to 25 minutes.

[0052] As mentioned above, melt-mixing lignin (a carbon-containing precursor) with a silicon-containing active material at temperatures between 120 and 250°C can result in high loadings of silicon-containing active material and good or high dispersion of the silicon-containing active material. The melt-mixing method of the first embodiment allows the incorporation of the silicon-containing active material while the carbon of the carbon-containing precursor is still plastic or liquid (and before it is converted to hard carbon). Therefore, the silicon-containing active material can be dispersed both finely and uniformly within the carbon and on its surface (rather than just adjacent to or on top of the carbon as in prior art methods). Therefore, the method of the first embodiment results in the carbon of the carbon-containing precursor containing both embedded silicon-containing active material and silicon-containing active material covering a certain percentage of the surface.

[0053] It has been unexpectedly found that by including at least one dispersing additive as described above in the melt-mixing of the method of the first embodiment, the dispersion degree of the silicon-containing active material in the carbon of the carbon-containing precursor can be further improved.Therefore, the uniform dispersion of the silicon-containing active material can be further improved, and an isotropic carbon-silicon composite powder can be obtained, which means advantages when used as the negative electrode active material of secondary batteries such as lithium-ion batteries.

[0054] Furthermore, depending on the choice of dispersing additive(s), the use of dispersing additive(s) can mean, among other things, that the melt viscosity can be kept low and the melt can be kept stable, thus improving processability. For example, the dispersing additives PEO and TWEEN, such as TWEEN 80, provide further such properties that are advantageous for processability.

[0055] The melt-mixing step of the method of the first aspect also allows for the incorporation of additional composite components in addition to the silicon-containing active material. Thus, in some embodiments, one or more additional composite components constitute one or more components melt-mixed in the melt-mixing step, i.e., one or more additional composite components are melt-mixed with the carbon-containing precursor and the silicon-containing active material and any other components, such as dispersion additives, in the melt-mixing step. For example, the additional composite components may be graphite particles, carbon particles, Sn or Sn compounds, converted oxide MO, or the like. X or sulfide MS X (M is a metal that can react reversibly with Li), and may be any other material that reacts with Li and contributes to the Li storage capacity of the carbon-silicon composite, or that does not react with Li and helps to stabilize other components of the carbon-silicon composite.

[0056] Thus, in some embodiments, the method further comprises providing graphite and / or carbon particles, and the components melt-mixed in the melt-mixing step comprise graphite and / or carbon particles.

[0057] The melt-mixing step of the method of the first embodiment can be carried out by any suitable device. The melt-mixing step can be carried out, for example, by kneading, compounding, or extrusion. Thus, the melt-mixing step can be carried out, for example, in a kneader, compounder, or extruder. Melt-mixing essentially means that the molten material of the produced melt mixture is isotropic.

[0058] After the melt-mixing in the method of the first embodiment, as described above, the melt-mix is ​​provided in a non-fibrous form and cooled in a non-fibrous form to provide an isotropic intermediate composite material. Preferably, the melt-mix is ​​cooled to room temperature, for example, room temperature. Thus, after the melt-mixing and cooling are completed, an isotropic intermediate composite material is provided.

[0059] After melt mixing is complete, the molten mixture can be provided in a non-fibrous form inside or outside the melt mixing device and cooled in a non-fibrous form to provide an isotropic intermediate composite material. For example, the molten mixture can be provided as a mass or lump inside or outside the melt mixing device, where the mass or lump is not fibrous and is cooled in a non-fibrous form to provide a mass or lump of an isotropic intermediate composite material. Thus, for example, if an extruder is used as the melt mixing device, the molten mixture can be extruded in a non-fibrous form to produce an isotropic material, and the extruded molten mixture can be cooled to room temperature in a non-fibrous form to provide an isotropic intermediate composite material. In another example, a kneader can be used as the melt mixing device, whereby the molten mixture can be provided in a mass or lump inside the kneader after melt mixing is complete and is cooled to room temperature to provide an isotropic intermediate composite material.

[0060] By providing the molten mixture in a non-fibrous form after completion of the melt mixing and cooling the molten mixture in a non-fibrous form, the isotropic characteristics of the molten material of the molten mixture are maintained, i.e., the intermediate composite material produced is isotropic.

[0061] As used herein, the term "non-fibrous" refers to a form that does not have the shape of a fiber, thread, yarn, filament, strand, or any other elongated form.

[0062] The term "isotropic," as used herein with respect to material specifications, such as in phrases such as "isotropic intermediate composite" and "isotropic carbon-silicon composite," indicates that the material has isotropic characteristics, i.e., at least essentially uniformity in all directions, at least at the microscopic level (i.e., on the micrometer scale). "At least essentially uniformity in all directions" means that there is at least essentially uniform structure (crystallographic order on the atomic scale), texture (arrangement of pores within particles made up of crystallites), and morphology (external shape of particles, which may be made up of crystallites and pores) of the C / Si composite particles or intermediate C / Si composite particles in all directions, and no preferred morphological and structural orientation of the SiX within the carbon matrix.

[0063] In some embodiments, the method of the first aspect further comprises premixing at least two components prior to the melt-mixing step. Thus, the premixing step premixes at least two of the components to be melt-mixed in the melt-mixing step. Additional components can then be added in the melt-mixing step.

[0064] In embodiments that include a premixing step, the carbon-containing precursor and at least one silicon-containing active material may be premixed in the premixing step. In embodiments that include the use of two or more silicon-containing active materials, one or more silicon-containing active materials may be premixed with the carbon-containing precursor, and one or more additional silicon-containing active materials may be added in the melt-mixing step. When one or more dispersing additives are melt-mixed with the carbon-containing precursor and the silicon-containing active material, the one or more dispersing additives may also be included in the premixing step, for example, premixed with the carbon-containing precursor and the silicon-containing active material and / or added in the melt-mixing step. In one alternative, one or more dispersing additives may be premixed with the carbon-containing precursor while the silicon-containing active material is being added in the melt-mixing step. In another alternative, one or more dispersing additives may be premixed with the silicon-containing active material while the carbon-containing precursor is being added in the melt-mixing step.

[0065] For example, premixing can be performed by dry mixing (i.e., without solvent), dry milling, wet milling, melt mixing, solution mixing, spray coating, spray drying, and / or dispersion mixing. Preferably, premixing is performed by dry mixing. Premixing can be performed in one or more substeps.

[0066] As mentioned above, the resulting isotropic intermediate composite material is subjected to a heat treatment, which includes a carbonization step (ie, a carbonization step) to provide a carbon-silicon composite material.

[0067] The carbonization step is performed to increase the carbon content of the composite material and may be performed at a carbonization temperature ranging from 700 to 1300°C, preferably 900 to 1200°C. The carbonization step may include a temperature gradient from a starting temperature, such as room temperature, to a target carbonization temperature ranging from 700 to 1300°C, preferably 900 to 1200°C. The residence time at the target carbonization temperature may be 1 to 180 minutes, preferably 1 to 120 minutes, and most preferably 30 to 90 minutes. For example, the heating rate in a batch process may be 1 to 100°C / min. When the batch process is performed in a continuous mode, the heating rate may be even higher than approaching a flash injection hot zone. Alternatively, the carbonization may be performed in one or more temperature sub-steps using various heating rates and intermediate temperatures before reaching the target carbonization temperature ranging from 700 to 1300°C, preferably 900 to 1200°C.

[0068] Carbonization is carried out in an inert gas, such as nitrogen or argon, or an inert gas mixture, at ambient pressure or elevated or reduced pressure. Alternatively, carbonization is carried out under reduced pressure. Carbonization can be carried out in a batch or continuous mode. Any suitable reactor can be utilized for the carbonization process.

[0069] In some embodiments, the heat treatment of the method of the first aspect comprises a carbonization step.

[0070] In some embodiments, the heat treatment of the method of the first aspect includes the carbonization step described above and one or more additional initial heating steps prior to the carbonization step. Each initial heating step is performed to pre-carbonize the composite material, particularly to remove volatile substances, and can be performed batchwise or continuously. Each initial heating step can be performed at a temperature ranging from 250 to 700°C, preferably 400 to 600°C. Each initial heating step can include a temperature gradient from a starting temperature, such as room temperature, to a target initial heating temperature ranging from 250 to 700°C, preferably 400 to 600°C. The duration (dwell time) at the target initial heating temperature can be 1 to 180 minutes, preferably 3 to 120 minutes. For example, the heating rate of the temperature gradient can be 1 to 100°C / min. Alternatively, the initial heating of each initial heating step can be performed in one or more temperature sub-steps using various heating rates and intermediate temperatures to reach the target initial heating temperature ranging from 250 to 700°C, preferably 400 to 600°C. Further alternatively, when two or more initial heating steps are included, one or more of the initial heating steps can include a temperature ramp to a target initial heating temperature as described above, and the one or more initial heating steps can include one or more temperature sub-steps as described above. The initial heating can be carried out in the same type of reactor and inert gas or inert gas mixture, or under reduced pressure, as described above for carbonization.

[0071] As described above, the carbon-silicon composite material obtained by the heat treatment carbonization of the method of the first embodiment is pulverized to obtain a carbon-silicon composite powder. Pulverization can be carried out by any suitable method, for example, using a cutting mill, a blade mixer, a ball mill, a hammer mill, and / or a jet mill. Optionally, fine / coarse particle selection by classification and / or sieving may be carried out after pulverization.

[0072] The milling of the carbon-silicon composite material and optional fine / coarse particle selection can be carried out to obtain a carbon-silicon composite powder comprising powder particles having an average particle size of 5 to 25 μm, as measured, for example, by laser diffraction.

[0073] The method of the first embodiment may include one or more additional grinding or pulverizing steps in addition to the step of pulverizing the carbon-silicon composite material. As noted above, the heat treatment may also include one or more initial heating steps in addition to the carbonization step. The method of the first embodiment may include one or more additional grinding or pulverizing steps after the one or more initial heating steps but before the carbonization step, or may include one or more additional grinding or pulverizing steps between any initial heating steps.

[0074] In some embodiments, the method of the first aspect includes grinding or pulverizing the isotropic intermediate composite material prior to heat treatment. Thus, in these embodiments, the isotropic intermediate composite material is in pulverized or milled form when heat treatment is initiated.

[0075] In some embodiments, the heat treatment of the method of the first aspect includes at least one initial heating step and a carbonization step, with a crushing or pulverizing step being performed between the initial heating step and the carbonization step. Thus, carbonization of the intermediate carbon-silicon composite material pre-carbonized in powder or crushed form is then carried out. Thus, in these embodiments, the carbon-silicon composite material is in powder or crushed form after the heat treatment is completed, and is then subjected to a further pulverizing step (i.e., the pulverizing step described above) to provide a carbon-silicon composite powder. Optionally, these embodiments may also include a step of crushing or pulverizing the isotropic intermediate composite material prior to the heat treatment. The isotropic intermediate composite material is then in powder or crushed form when the heat treatment begins.

[0076] Optionally, fine / coarse particle selection by classification and / or sieving may be carried out after any grinding or comminution step.

[0077] The silicon carbon composite powder obtained by the process of pulverizing the silicon carbon composite can be subjected to further processing such as, for example, carbon coating by chemical vapor deposition (CVD), pitch coating, thermal and / or chemical refining, heat treatment, particle size adjustment, and blending with other electrode materials, for example, to further improve its electrochemical performance.

[0078] In some embodiments, the carbon-silicon composite powder comprises powder particles and the method of the first aspect further comprises carbon coating the carbon-silicon composite powder particles, preferably by chemical vapor deposition.

[0079] According to a second aspect presented herein, there is provided a carbon-silicon composite powder obtainable by the method according to the first aspect. The carbon-silicon composite powder according to the second aspect may be further defined as described above with reference to the first aspect.

[0080] The carbon-silicon composite powder obtained by the method according to the first aspect is preferably used as an active material in the negative electrode of a non-aqueous secondary battery, such as a lithium-ion battery. When used to manufacture such a negative electrode, any suitable method for forming such a negative electrode can be utilized. In forming the negative electrode, the carbon-silicon composite powder may be processed with additional components. Such additional components may include, for example, one or more binders for forming the carbon-silicon composite powder into an electrode, conductive materials such as carbon black, carbon nanotubes, or metal powder, and / or additional Li-storage materials such as graphite or lithium. For example, the binder may be selected from, but is not limited to, poly(vinylidene fluoride), poly(tetrafluoroethylene), carboxymethyl cellulose, natural butadiene rubber, synthetic butadiene rubber, polyacrylate, poly(acrylic acid), alginate, etc., or combinations thereof. Optionally, a solvent, such as 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water, or acetone, is utilized during processing.

[0081] According to a third aspect presented herein, there is provided an anode for a non-aqueous secondary battery, such as a lithium-ion battery, comprising as an active material a carbon-silicon composite powder obtainable by the method according to the first aspect. The carbon-silicon composite powder of the anode according to the third aspect may be further defined as described above with reference to the first aspect.

[0082] According to a fourth aspect exemplified herein, there is provided the use of a carbon-silicon composite powder obtainable by the method according to the first aspect as an active material in the negative electrode of a non-aqueous secondary battery, such as a lithium-ion battery. The carbon-silicon composite powder of the fourth aspect may be further defined as described above with reference to the first aspect.

[0083] Secondary batteries, such as lithium-ion batteries, are electric batteries that can be repeatedly charged and discharged, i.e., rechargeable batteries. For example, lithium-ion batteries are commonly used in portable electronic devices and electric vehicles today. Lithium-ion batteries have high energy density, high operating voltage, low self-discharge, and low maintenance requirements. [Brief explanation of the drawings]

[0084] [Figure 1a-b] 1A and 1B are SEM (1a) and SEM-EDX (1b, carbon only) images of HC / Si composite powder obtained by initial ball milling of lignin and silicon as described in Example 2. [Figure 1c] FIG. 1c is an SEM-EDX (1c, silicon only) image of HC / Si composite powder obtained by initial ball milling of lignin and silicon as described in Example 2. [Figure 2a] 2a is an SEM (2b) image of HC / Si composite powder with less than 13 wt. % Si obtained by melt mixing without dispersing additives, as described in Example 3. [Figure 2b-c]2b, SEM-EDX (2c, silicon only) images of HC / Si composite powders with less than 13 wt. % Si obtained by melt mixing without dispersing additives, as described in Example 3. [Figure 3a-b] 10 is an SEM image of HC / Si composite powder with less than 13 wt % Si obtained by melt mixing with PEO (a dispersion additive) as described in Example 4. [Figure 3c-d] 3c, SEM-EDX (3d, silicon only) images of HC / Si composite powders with less than 13 wt. % Si obtained by melt mixing with PEO (a dispersion additive) as described in Example 4. [Figure 3e-f] Cross-sectional SEM (3e) and SEM-EDX (3f, carbon only) images of HC / Si composite powder with less than 13 wt % Si obtained by melt-mixing with PEO (dispersion additive) as described in Example 4. The oval structures / particles on the left are not part of the HC / Si sample but are artifacts from the sample preparation, i.e., epoxy resin used to mount the cross-sectional HC / Si sample. [Figure 3g] Figure 10 is a cross-sectional SEM-EDX (3 g, silicon only) image of HC / Si composite powder with less than 13 wt% Si obtained by melt mixing with PEO (a dispersion additive) as described in Example 4. The oval structures / particles on the left are not part of the HC / Si sample, but are artifacts from the sample preparation, i.e., epoxy resin used to mount the cross-sectional HC / Si sample. [Figure 4a] 10 is an SEM image of a pre-carbonized intermediate C / Si composite powder obtained by melt mixing with TWEEN 80 (a dispersing additive) as described in Example 7. [Figure 4b-c] 4a and 4b are SEM-EDX (4b, carbon only) and (4c, silicon only) images of pre-carbonized intermediate C / Si composite powders obtained by melt-mixing with TWEEN 80 (dispersion additive), respectively, as described in Example 7. [Figure 5a-b]SEM (5a) and SEM-EDX (5b, carbon only) images of pre-carbonized intermediate C / Si composite powder obtained by melt mixing with TWEEN 80 (dispersion additive), respectively, as described in Example 8. [Figure 5c] FIG. 5C is a SEM-EDX (5c, silicon only) image of a pre-carbonized intermediate C / Si composite powder obtained by melt mixing with TWEEN 80 (dispersion additive) as described in Example 8. [Figure 6] FIG. 10 shows the electrochemical behavior of HC / Si composite powders obtained by melt mixing, as described in Example 9. [Example]

[0085] Example 1: Pure hard carbon (HC) (comparative example) Softwood kraft lignin was heat treated in N2 at 500°C under flowing N2 using a heating rate of 10°C / min and a residence time of 1 hour at 500°C (initial heating). After cooling to room temperature, the resulting cake was crushed. The crushed material was heat treated under N2 at 1000°C using a heating rate of 10°C / min and a residence time of 1 hour at 1000°C (carbonization). After cooling, the carbonized material was crushed and classified using a laboratory fluidized-bed opposed jet mill and a single-wheel classifier to obtain a carbon powder with an average particle size of 10 μm as measured by laser diffraction.

[0086] Example 2: HC / Si composite powder obtained by ball milling (comparative example) Softwood kraft lignin was mixed with Si particles (primary particle size 200 nm) using a laboratory mixer. The mixture was then transferred to a ball mill and milled at 20 Hz for 3 minutes. The resulting lignin / Si mixture was then heat-treated, milled, and classified in the same manner as the material in Example 1 to obtain HC / Si composite powder with an average particle size of 10 μm. Figures 1a-c show SEM (1a) and SEM-EDX (1b, carbon only) and (1c, silicon only) images of the resulting HC / Si composite powder.

[0087] Example 3: HC / Si composite powder with less than 13 wt% Si obtained by melt mixing without dispersing additives Softwood kraft lignin was premixed (dry mixed) with 5 wt% Si particles (primary particle size 200 nm) using a laboratory mixer. The mixture was then melt-mixed for 20 minutes using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160 °C. After cooling to room temperature, the kneader produced a mass of molten mixture (i.e., an isotropic intermediate composite). The material was then ground using a cutting mill (equipped with a 0.5 mm cutoff sieve). The resulting lignin / Si mixture was then heat-treated, ground, and classified according to Example 1 to obtain an HC / Si composite powder with less than 13 wt% Si and an average particle size of 10 μm. Figures 2a-c show SEM (2a) and SEM-EDX (2b, carbon only), (2c, silicon only) images of the resulting HC / Si composite powder, respectively. As is evident from the SEM image (2a), a high silicon loading and a high degree of silicon dispersion are obtained.

[0088] Example 4: HC / Si composite powder with less than 13 wt% Si obtained by melt mixing with PEO Using a laboratory mixer, softwood kraft lignin was premixed (dry mixed) with 5 wt. % Si particles (primary particle size 200 nm) and 5 wt. % PEO (Mw = 1500 g / mol). The mixture was then melt-mixed for 20 minutes using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160 °C. After cooling to room temperature, the kneader produced a mass of molten mixture (i.e., an isotropic intermediate composite). The material was then ground using a cutting mill (equipped with a 0.5 mm coarse cutoff sieve). The resulting lignin / Si mixture was then heat-treated, ground, and classified in the same manner as the material in Example 1 to produce a HC / Si composite powder with less than 13 wt. % Si and an average particle size of 10 μm. Figures 3a-3g show SEM (3a-3b) and SEM-EDX (3c, carbon only) (3d, silicon only) images of the resulting HC / Si composite powder, as well as cross-sectional SEM (3e) and SEM-EDX (3f, carbon only) (3g, silicon only) images of the resulting HC / Si composite powder. Note that the oval structures / particles on the left side of Figures 3e-3g are not part of the HC / Si sample but are artifacts from the sample preparation, i.e., the epoxy resin used to mount the cross-sectional HC / Si sample. It is clear from both SEM and SEM-EDX that a high loading of silicon is obtained in the matrix, with the silicon being very uniformly distributed on the surface and in the interior, as seen in the cross-sectional photographs. It is also clear from the SEM images in Figures 3a-3g that the use of a dispersing additive (PEO) results in further improvement of the silicon dispersion in the carbon matrix, when compared to the SEM images in Figures 2a-2c.

[0089] Example 5: HC / Si composite powder with 2.0 wt% Si obtained by melt mixing with PEO Using a laboratory mixer, softwood kraft lignin was premixed (dry mixed) with 0.9 wt. % Si particles (primary particle size 200 nm) and 5 wt. % PEO (Mw = 1500 g / mol). The mixture was then melt-mixed for 20 minutes using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160 °C. After cooling to room temperature, the kneader produced a mass of molten mixture (i.e., an isotropic intermediate composite). The material was then ground using a cutting mill (equipped with a 0.5 mm cutoff sieve). The resulting lignin / Si mixture was then heat-treated, ground, and classified according to Example 1 to produce an HC / Si composite powder with 2.0 wt. % Si and an average particle size of 10 μm.

[0090] Example 6: HC / Si composite powder with 4.8 wt% Si obtained by melt mixing with PEO Using a laboratory mixer, softwood kraft lignin was premixed (dry mixed) with 2.0 wt. % Si particles (primary particle size 200 nm) and 5 wt. % PEO (Mw = 1500 g / mol). The mixture was then melt-mixed for 20 minutes using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160 °C. After cooling to room temperature, the kneader produced a mass of molten mixture (i.e., an isotropic intermediate composite). The material was then ground using a cutting mill (equipped with a 0.5 mm cutoff sieve). The resulting lignin / Si mixture was then heat-treated, ground, and classified according to Example 1 to produce an HC / Si composite powder with 4.8 wt. % Si and an average particle size of 10 μm.

[0091] Example 7: Pre-carbonized intermediate C / Si composite powder obtained by melt mixing with TWEEN In a laboratory mixer, softwood kraft lignin was premixed (dry mixed) with 5 wt. % Si particles (primary particle size 200 nm). The mixture was then melt-mixed for 20 minutes using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160°C, and 5 wt. % TWEEN 80 was added immediately after heating in the kneader. After cooling to room temperature, a mass of molten mixture (i.e., an isotropic intermediate composite) was obtained in the kneader. The material was then ground using a cutting mill (equipped with a 0.5 mm coarse cutoff sieve). The resulting lignin / Si mixture was then heat-treated by initial heating (but without carbonization) according to Example 1, and ground and classified according to Example 1 to obtain a pre-carbonized intermediate C / Si composite powder with an average particle size of 10 μm. Figures 4a-c show SEM (4a) and SEM-EDX (4b, carbon only) and (4c, silicon only) images of the resulting pre-carbonized intermediate C / Si composite powder, respectively. The highly uniform distribution of Si is evident from both SEM and SEM-EDX.

[0092] Example 8: Pre-carbonized intermediate C / Si composite powder obtained by melt mixing with TWEEN Softwood kraft lignin (90 g) was dispersed in water (1 L) and TWEEN 80 (5 g) was added while mixing for 5 minutes at room temperature using an Ultraturrax mixer. In the next step, nanosilicon (200 nm) was added, and mixing continued for another 5 minutes at room temperature. The mixture was then filtered and dried in vacuum at 80 °C (10 mbar). The sample was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with a Banbury rotor) at a set temperature of 160 °C for 20 minutes and further processed as described in Example 7. Figures 5a-5c show SEM (5a) and SEM-EDX (5b, carbon only) and SEM-EDX (5c, silicon only) images of the resulting pre-carbonized intermediate C / Si composite powder, respectively. A highly uniform distribution of Si is evident from both SEM and SEM-EDX.

[0093] Example 9: Electrochemical behavior of HC / Si composite powders obtained by melt mixing Electrodes were prepared from the HC / Si composite powder of Example 6 or from the pure HC of Example 1 and electrochemically characterized as follows: 82 wt% HC / Si or HC was mixed with 8 wt% poly(vinylidene fluoride) binder dissolved in 1-methyl-2-pyrrolidone, coated onto Cu foil via doctor blade method, and dried. Experimental three-electrode cells were constructed from the HC / Si or HC electrode, Li metal counter electrode, and Li metal reference electrode using a glass fiber separator and 1M LiPF6 dissolved in ethylene carbonate:dimethyl carbonate (1:1 by weight) as the electrolyte. Constant-current charging and discharging of the cells was performed between 5 mV vs. Li / Li+ and 1.5 V vs. Li / Li+ using a specific current of 74.4 mA / g(AM), where g(AM) represents grams of active material in the electrode. Figure 6 compares the discharge potential curves of the HC / Si and pure HC materials. The addition of Si increased the capacity by approximately 120 mAh / g. The presence of Si and its influence on the charge-discharge regime were investigated using a 0.1 V vs. Li / Li + Due to the extension of the potential plateau below 0.4-0.5 V vs. Li / Li + This is evident by the appearance of a second potential plateau.

[0094] In view of the above detailed description of the invention, other modifications and variations will be apparent to those skilled in the art, and it is evident, however, that such other modifications and variations can be made without departing from the spirit and scope of the invention.

Claims

1. 1. A method for producing a carbon-silicon composite powder, comprising: - providing lignin, - providing at least one silicon-containing active material; - melt mixing at least two components into a molten mixture, wherein the lignin constitutes one component and each silicon-containing active material constitutes one component, and wherein the melt mixing is carried out at a temperature between 120 and 250°C; providing a non-fibrous molten mixture and cooling the non-fibrous molten mixture to provide an isotropic intermediate composite material; - subjecting the isotropic intermediate composite material to a heat treatment, the heat treatment including a carbonization step to provide a carbon-silicon composite material, the heat treatment further including one or more initial heating steps prior to the carbonization step, each initial heating step being carried out at a temperature between 250 and 700°C; and - pulverizing said carbon-silicon composite to provide said carbon-silicon composite powder; A method comprising:

2. The method described in claim 1, wherein the lignin is kraft lignin.

3. 3. The method of claim 1 or 2, wherein the lignin is provided in particulate form, preferably with an average particle size of between 0.1 μm and 3 mm.

4. The method according to any one of claims 1 to 3, wherein the silicon-containing active material is selected from the group consisting of elemental silicon, silicon suboxide, silicon-metal alloy or silicon-metal carbon alloy.

5. The method according to any one of claims 1 to 4, wherein the silicon-containing active material is preferably provided in the form of micro- or nano-sized particles.

6. The method of claim 1, wherein the lignin is mixed with 0.5 to 30 wt. % of the at least one silicon-containing active material in a melt-mixing step.

7. 7. The method of any one of claims 1 to 6, further comprising the step of providing at least one dispersing additive, wherein the components melt-mixed in the melt-mixing step comprise said at least one dispersing additive.

8. 8. The method of claim 7, wherein the dispersant additive is selected from the group of monoethers, polyethers, monoalcohols, polyalcohols, amines, polyamines, carbonates, polycarbonates, monoesters, polyesters, and polyether fatty acid esters.

9. 9. The method of claim 8, wherein the dispersing additive is selected from the group of polyethylene oxide and branched polyether fatty acid esters.

10. A method described in any one of claims 7 to 9, wherein the lignin is mixed with 0.5 to 30 wt% of the at least one silicon-containing active material and 0.5 to 10 wt% of the at least one dispersing additive in a melt-mixing process.

11. 11. The method of any one of claims 1 to 10, further comprising the step of providing graphite and / or carbon particles, wherein the components melt-mixed in the melt-mixing step comprise said graphite and / or carbon particles.

12. The method according to any one of claims 1 to 11, wherein the melt mixing is carried out by kneading, compounding or extruding.

13. The method of claim 1, further comprising premixing at least two of the components to be melt-mixed prior to the melt-mixing step.

14. 14. The method of claim 13, wherein the premixing is carried out by dry mixing, dry milling, wet milling, melt mixing, solution mixing, spray coating, spray drying and / or dispersion mixing.

15. A method according to any one of the preceding claims, wherein the carbonization is carried out at a temperature of from 700 to 1300°C.

16. 16. The method of any one of claims 1 to 15, further comprising a pulverizing step after the one or more initial heating steps and before the carbonizing step.

17. The method of any one of claims 1 to 16, further comprising the step of grinding or pulverizing the isotropic intermediate composite material prior to said heat treatment.

18. The method of any one of claims 1 to 17, wherein the carbon-silicon composite powder comprises powder particles having an average particle size of 5 to 25 μm.

19. 19. The method of any one of claims 1 to 18, wherein the carbon-silicon composite powder comprises powder particles, and further comprising the step of carbon coating the carbon-silicon composite powder particles, preferably by chemical vapor deposition.

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