Silicon-containing composite material and production method thereof

Abstract

The present invention relates to a silicon-containing composite comprising a plurality of silicon nanoparticles located within a carbon matrix, and an amorphous carbon shell provided around the silicon nanoparticles and the carbon matrix, where the amorphous carbon shell has a thickness of about 10 nm to 5000 nm.

Description

Technical Field

[0001] This invention relates to silicon-containing composite materials. More particularly, the composite materials of this invention are intended for use as anode materials in lithium-ion batteries.

[0002] In a highly preferred form, the invention also relates to an anode composite comprising a silicon-containing composite material.

[0003] The present invention further relates to a method for producing silicon-containing composite materials. Background Technology

[0004] Currently, silicon / graphite composites are understood to show some promise as lithium-ion anode materials. However, there are many well-known and understood drawbacks associated with silicon / graphite composites. These drawbacks include high expansion levels of up to 400% and poor cycle life. Any commercial application of silicon / graphite composites requires addressing at least these issues.

[0005] The known and understood irreversible capacity loss of silicon-containing anodes is currently being addressed by using nanostructured silicon particles as electroactive materials. Silicon nanoparticles and nanostructured silicon have been reported to be more tolerant of volume changes during charging and discharging compared to micron-sized particles (XH Liu et al., “Size-Dependent Fracture of Silicon Nanoparticles During Lithiation”, ACS Nano, 2012, 6(2), 1522-1531). However, nanoscale particles are not considered suitable for commercial-scale applications due to their known difficulty in fabrication and handling. In addition to issues related to silicon particle size, the properties of the silicon surface also play a crucial role in the formation of the solid electrolyte interphase (SEI) and electronic conductivity. The SEI on the silicon surface is unstable and continuously consumes lithium, necessitating surface modification to avoid or at least reduce silicon exposure to the electrolyte. Furthermore, silicon is not considered a particularly good conductive material.

[0006] Core-shell structured graphite / silicon@pyrolysed carbon (Gr / Si@C) composites have been fabricated, including mechanical milling, spray drying, and the use of pitch (Li et al., “Scalable synthesis of a novel structured graphite / silicon / pyrolysed carbon composite as anode material for high-performance lithium-ion batteries”, Journal of Alloys and Compounds 688(2016)1072-1079). This prior art process appears to be a relatively scalable and cost-effective method. Cycling performance is significantly improved compared to many existing technologies due to the presence of carbon coatings of graphite and silicon. However, the low initial cycle efficiency of 77.9% at a capacity of 637.7 mAh / g is far below the levels required by the battery industry.

[0007] International patent application PCT / GB2018 / 051689 (WO 2018 / 229515) first describes the production of silicon nanoparticles by ball milling silicon microparticles in a solvent. A pyrolytic 'amorphous' carbon precursor containing at least one oxygen or nitrogen atom is added to silicon nanoparticles and a solvent. The solvent is removed, and the remaining silicon nanoparticles are coated with a thick layer of the pyrolytic carbon precursor. These coated silicon nanoparticles are then pyrolyzed to form composite particles containing multiple silicon nanoparticles dispersed in a conductive pyrolytic carbon matrix. In this prior art process, significant first cycle loss (FCL) and expansion remain substantial problems due to the use of a large amount of amorphous carbon. It is believed that amorphous carbon contributes a large proportion of the experienced expansion and unacceptable FCL. Furthermore, once Si@C expands, the bond between silicon and carbon weakens because amorphous carbon is inelastic.

[0008] A graphene cage-like silicon structure was formed by using an unplated thick nickel layer on micrometer-sized silicon particles, and outstanding battery performance was achieved, including high capacity, small expansion, long cycle life and low FCL (Li et al., “Growth of conformal graphene cages on micrometer-sized silicon particles as stable battery anodes”, Nature Energy, Vol. 1, No. 15029 (2016)).

[0009] Few-layer graphene-coated silicon nanoparticles have also been described as being formed via chemical vapor deposition (CVD) (Son et al., “Silicon carbide–free graphene growth on silicon for lithium-ion battery with high volumetric energy density”, Nature Communications, Vol. 6, Article 7393 (2015)). Similarly, these coated silicon nanoparticles are said to offer excellent battery performance, including high capacity, low expansion, long cycle life, and low free-closing capacity (FCL). However, the processes for forming these graphene-coated materials are known to be expensive and non-scalable, particularly not to the level required for commercial applications.

[0010] A more cost-effective method for coating few-layer graphene onto silicon is described in patent publication WO 2015 / 073674 A1, which coats silicon with graphene by bead milling a mixture of graphite and silicon. However, this method does not produce products with the desired properties. For example, there is a significant capacity drop (>45%) in the first 200 cycles.

[0011] US 2016 / 064731 (Jung Sung-Ho et al.) describes the manufacture of a carbon-silicon composite, in which a silicon-carbon-polymer matrix is ​​prepared and subsequently heat-treated to carbonize the matrix. The carbonized matrix is ​​pulverized and mixed with a carbon feedstock, and then carbonized to produce the carbon-silicon composite of the invention. This carbon-silicon composite is used as an anode slurry to provide the anode for a secondary battery.

[0012] US 2018 / 097229 (Jo Sungnim et al.) describes the fabrication of a negative electrode active material comprising forming silicon-carbon primary particles with an apparent density of about 2 g / cm³ or greater, heat-treating multiple primary particles, a second carbonaceous material, and a foaming agent to form porous silicon-carbon secondary particles. These secondary particles may or may not have an additional coating layer.

[0013] The applicant's international patent application PCT / IB2020 / 056050 (WO 2020 / 261194) (the entire contents of which are incorporated herein by reference) describes a silicon- and graphite-containing composite material comprising a plurality of silicon nanoparticles coated with graphite particles, few-layer graphene particles, graphite nanoparticles, a carbon matrix, and an amorphous carbon shell, wherein each of the graphite-coated silicon nanoparticles, few-layer graphene particles, and graphite nanoparticles is retained within the carbon matrix. A method for producing the composite material is also described, comprising the following steps:

[0014] (i) Optionally, in the presence of a polymer, silicon particles and graphite particles are subjected to a size reduction step in a solvent to produce graphite-coated silicon nanoparticles, few-layer graphene particles and graphite nanoparticles.

[0015] (ii) Process the product of step (i) with or without a binder to produce a composite;

[0016] (iii) The composite of heat treatment step (ii) thereby producing a composite material comprising a plurality of graphite-coated silicon nanoparticles, few-layer graphene particles, graphite nanoparticles and a carbon matrix, wherein each of the particles is contained within the carbon matrix.

[0017] (iv) Coating the composite material from step (iii) with an adhesive; and

[0018] (v) The composite material of the heat treatment step (iv) thereby producing a shell containing amorphous carbon.

[0019] After the heat treatment in step (iii), the surface area (BET) of the composite material is described as being approximately 70-120 m². 2 Within the range of / g, and after the heat treatment in step (v), the BET of the material is said to be in the range of approximately 10-30m. 2 This is relatively high within the range of / g.

[0020] The compositions and processes previously described by the applicant also utilize non-aqueous solvents, such as isopropanol (IPA). However, it should be understood that IPA is expensive and toxic, and providing compositions and processes that do not require the use of IPA would be considered advantageous.

[0021] As noted above, a specific problem with silicon-based anode materials is their expansion. Expansion leads to the pulverization of composite particles and the loss of physical contact and active material. Furthermore, expansion results in an unstable SEI layer, which can lead to continuous lithium loss. Two methods are typically used to overcome these problems. First, silicon nanoparticles are used as nanoscale materials with improved tolerance to expansion and pulverization. Second, a carbon layer is coated onto the silicon surface. These treatments can significantly improve silicon anode performance. However, silicon-based anodes are still not good enough for practical use. The SEI layer is believed to remain unstable because conventional carbon layers on silicon surfaces are inelastic and non-uniform. Therefore, silicon anodes with conformal graphene cages (Li et al., ibid.) or with sliding graphene layers (Son et al., ibid.) offer relatively superior battery performance. However, the methods used to manufacture these graphene coatings are expensive.

[0022] Therefore, the applicant has filed the composite and process described in International Patent Application PCT / IB2020 / 056050 (WO 2020 / 261194) for reducing net expansion from silicon composite particles (secondary particles), wherein particles with designed-manufactured porosity are designed to buffer the expansion from individual silicon particles within the secondary particles. However, it has been found in some cases that the porosity of the silicon composite particles cannot be effectively utilized because silicon expansion tends to occur in the outward direction rather than effectively utilizing the internal empty space. Therefore, compositions and processes that provide a sufficiently thick and / or hard shell on the Si@C material (which limits outward expansion during lithiation) are considered advantageous. Summary of the Invention

[0023] One object of the composite materials and methods of the present invention is to substantially overcome one or more of the aforementioned problems associated with existing technology processes, or at least to provide useful alternatives to them.

[0024] The foregoing discussion of the background art is intended only to facilitate understanding of the invention. This discussion is not an affirmation or acknowledgment that any material mentioned was part of common general knowledge at the priority date of this application.

[0025] Throughout the specification and claims, unless the context otherwise requires, the word “comprise” or variations such as “comprises” or “comprising” shall be understood to imply inclusion of integers or groups of integers, but not to exclude any other integers or groups of integers.

[0026] Throughout the specification and claims, unless the context otherwise requires, references to “grind” or “mill” shall be construed as including references to “ball milling” and “bead milling,” and references to “bead milling” or “ball milling” shall be construed as including references to “grind.” Similarly, unless the context otherwise requires, references to “grind,” “ball milling,” and / or “bead milling” shall be construed as including references to “crush,” and references to “crush” shall be construed as including references to “grind,” “bead milling,” and / or “ball milling,” as the context requires.

[0027] The terms “relative” or “relatively” used with respect to features of the present invention are intended to indicate a comparison with the feature in the prior art and the typical characteristics of the feature in the prior art, unless the context clearly indicates or requires otherwise.

[0028] It should be understood that the ranges provided herein include the specified range and any values ​​or subranges within the specified range. For example, a range from about 1 micrometer (μm) to about 2 μm, or about 1 μm to 2 μm, should be interpreted as including not only the explicitly listed boundaries between about 1 μm and about 2 μm, but also individual values ​​such as about 1.2 μm, about 1.5 μm, about 1.8 μm, etc., and subranges such as from about 1.1 μm to about 1.9 μm, from about 1.25 μm to about 1.75 μm, etc. Furthermore, when “about” and / or “substantially” are used to describe values, they mean including minute variations (at most + / - 10%) from the specified value.

[0029] According to the present invention, a silicon-containing composite material is provided, comprising a plurality of silicon nanoparticles located within a carbon matrix, and an amorphous carbon shell surrounding the silicon nanoparticles and the carbon matrix, wherein the thickness of the amorphous carbon shell is from about 10 nm to 5000 nm.

[0030] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0031] In one form of the invention, silicon material is milled to provide silicon nanoparticles. Preferably, the silicon material is milled in a non-aqueous solvent to avoid the formation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2.

[0032] In one embodiment of the invention, the density of the carbon matrix is ​​less than about 1.5 g / cc. In one embodiment of the invention, the carbon matrix has a porosity greater than about 65%. In one embodiment of the invention, the carbon matrix has a porosity of about 10 m... 2 / g to 500m 2 / g surface area (BET).

[0033] Preferably, the carbon matrix has one or more of the following:

[0034] (i) A density lower than approximately 1.5 g / cc;

[0035] (ii) Porosity greater than approximately 65%; and / or

[0036] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0037] The carbon matrix is ​​preferably provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both.

[0038] Preferably, in addition to silicon nanoparticles, the carbon matrix also includes one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0039] The silicon nanoparticles are preferably encapsulated by one or more of graphite, graphene, graphite nanoplates, carbon nanotubes and carbon fibers.

[0040] In a preferred embodiment, the amorphous carbon shell has a density greater than about 1.5 g / cc. Preferably, the surface area (BET) of the silicon-containing composite material is less than about 10 m². 2 / g, for example, less than about 5m 2 / g.

[0041] In one form, the amorphous carbon shell further comprises additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0042] Preferably, the composite material has an elastic property level conferred by the presence of one or more of graphite particles, graphene, few-layer graphene, and graphite nanoparticles that can be provided within an amorphous carbon matrix.

[0043] According to the present invention, an anode compound comprising the composite material as described above is also provided.

[0044] According to the present invention, a method for producing composite materials is also provided, the method comprising the following steps:

[0045] (i) passing silicon nanoparticles, a binder and one or more carbon sources through a first aggregation step to form a first composite, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes and carbon fibers, and the encapsulated silicon nanoparticles are retained in a carbon matrix.

[0046] (ii) In the coating step, the first composite and adhesive from step (i) are processed to produce a composite having a shell containing organic matter; and

[0047] (iii) The composite and shell of step (ii) are heat-treated, thereby converting the organic material in the shell into carbon, resulting in a composite material containing multiple encapsulated silicon nanoparticles in a carbon matrix and providing an amorphous carbon shell around them, wherein the thickness of the amorphous carbon shell is about 10 nm to 5000 nm.

[0048] In one embodiment of the invention, an additional heat treatment step is provided, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0049] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0050] In one form of the invention, the silicon material is milled in an initial step to provide the silicon nanoparticles of step (i). Preferably, the silicon material is milled in a non-aqueous solvent to avoid the formation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2.

[0051] More preferably, the initial size reduction step is a crushing step. Even more preferably, the crushing step is carried out in one or more bead mills.

[0052] In one embodiment of the invention, the density of the carbon matrix is ​​less than about 1.5 g / cc. In one embodiment of the invention, the carbon matrix has a porosity greater than about 65%. In one embodiment of the invention, the carbon matrix has a porosity of about 10 m... 2 / g to 500m 2 / g surface area (BET).

[0053] Preferably, the carbon matrix has one or more of the following:

[0054] (i) Density below approximately 1.5 g / cc;

[0055] (ii) Porosity greater than approximately 65%; and / or

[0056] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0057] The carbon matrix is ​​preferably provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both.

[0058] More preferably, in addition to silicon nanoparticles, the carbon matrix also includes one or more of graphite, graphene, graphite nanoplates, carbon nanotubes and carbon fibers.

[0059] In one embodiment of the invention, the amorphous carbon shell has a density greater than about 1.5 g / cc. In another embodiment of the invention, the amorphous carbon shell has a density less than about 45 m³. 2 / g, for example, less than 10m 2 / g surface area (BET).

[0060] Preferably, the amorphous carbon shell has:

[0061] (i) a density greater than about 1.5 g / cc; and / or

[0062] (ii) Less than approximately 45m 2 / g, for example, less than 10m 2 / g surface area (BET).

[0063] In one form, the amorphous carbon shell further comprises additional materials selected from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0064] In another form of the invention, a further heat treatment step is applied to the composite material of step (iii), thereby reducing its surface area to less than 5 m². 2 / g.

[0065] Preferably, prior to the further heat treatment step, the composite material of step (iii) has a hydrocarbon applied thereto. This hydrocarbon may be provided in the form of dihydroxynaphthalene, for example, at 1 to 5% by weight.

[0066] In one form of the invention, an aqueous solvent is used in at least step (iii) of the heat treatment and in further heat treatments.

[0067] Preferably, the heat treatment in step (iii) and the further heat treatment each comprise dissolving dihydroxynaphthalene in water.

[0068] Preferably, the dihydroxynaphthalene is dissolved in water at a temperature greater than about 70°C.

[0069] Preferably, the heat treatment in step (iii), the additional heat treatment, and the further heat treatment are each provided in the form of pyrolysis.

[0070] Preferably, the heat treatment converts any existing binder into amorphous carbon.

[0071] Preferably, the graphite particles from the grinding step (i) are provided in the form of pre-exfoliated graphite particles.

[0072] In one form of the invention, the grinding process in step (i) produces graphene attached to silicon nanoparticles.

[0073] The heat treatment in step (iii) is preferably carried out in the range of about 700°C to 1100°C, for example, in the range of about 850°C to 1000°C.

[0074] Further heat treatment is performed at a temperature in the range of approximately 500°C to 700°C, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0075] Preferably, the further heat treatment step is carried out at a temperature in the range of about 800°C to 1000°C, for example, about 850°C to 950°C.

[0076] Preferably, the agglomeration step includes spray drying.

[0077] According to the present invention, a method for producing an anode compound is further provided, the method comprising the following steps:

[0078] (i) passing silicon nanoparticles, a binder and one or more carbon sources through a first aggregation step to form a first composite, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes and carbon fibers, and the encapsulated silicon nanoparticles are retained in a carbon matrix.

[0079] (ii) In the coating step, the first composite and adhesive from step (i) are processed to produce a composite having a shell containing organic matter; and

[0080] (iii) The composite and shell of step (ii) are heat-treated, thereby converting the organic material in the shell into carbon, thereby producing an anode composite containing multiple encapsulated silicon nanoparticles in a carbon matrix and providing an amorphous carbon shell around them, wherein the thickness of the amorphous carbon shell is about 10 nm to 5000 nm.

[0081] In one embodiment of the invention, an additional heat treatment step is provided, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0082] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0083] In one form of the invention, the silicon material is milled in an initial step to provide the silicon nanoparticles of step (i). Preferably, the silicon material is milled in a non-aqueous solvent to avoid the formation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2.

[0084] Preferably, the initial grinding step is a crushing step. Even more preferably, the crushing step is carried out in one or more bead mills.

[0085] In one embodiment of the invention, the density of the carbon matrix is ​​less than about 1.5 g / cc. In one embodiment of the invention, the carbon matrix has a porosity greater than about 65%. In one embodiment of the invention, the carbon matrix has a porosity of about 10 m... 2 / g to 500m 2 / g surface area (BET).

[0086] Preferably, the carbon matrix has one or more of the following:

[0087] (i) A density lower than approximately 1.5 g / cc;

[0088] (ii) Porosity greater than approximately 65%; and / or

[0089] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0090] The carbon matrix is ​​preferably provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both.

[0091] Preferably, in addition to silicon nanoparticles, the carbon matrix also includes one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0092] In one embodiment of the invention, the amorphous carbon shell has a density greater than about 1.5 g / cc. In another embodiment of the invention, the amorphous carbon shell has a density less than about 45 m³. 2 / g, for example, less than 10m 2 / g surface area (BET).

[0093] Preferably, the amorphous carbon shell has:

[0094] (i) a density greater than about 1.5 g / cc; and / or

[0095] (ii) Less than approximately 45m 2 / g, for example, less than 10m 2 / g surface area (BET).

[0096] In one form, the amorphous carbon shell further comprises additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0097] In another embodiment of the invention, a further heat treatment step is applied to the anolyte of step (iii), thereby reducing its surface area to less than 5 m². 2 / g.

[0098] Preferably, prior to the further heat treatment step, the anolyte complex of step (iii) has a hydrocarbon applied thereto. This hydrocarbon may be provided in the form of dihydroxynaphthalene, for example, at 1 to 5% by weight.

[0099] In one form of the invention, an aqueous solvent is used in at least step (iii) of the heat treatment and in further heat treatments.

[0100] Preferably, the heat treatment in step (iii) and the further heat treatment each comprise dissolving dihydroxynaphthalene in water.

[0101] Preferably, the dihydroxynaphthalene is dissolved in water at a temperature greater than about 70°C.

[0102] Preferably, the heat treatment in step (iii), the additional heat treatment, and the further heat treatment are each provided in the form of pyrolysis.

[0103] Preferably, the heat treatment converts any existing binder into amorphous carbon.

[0104] Preferably, the graphite particles from the grinding step (i) are provided in the form of pre-exfoliated graphite particles.

[0105] In one form of the invention, the grinding process in step (i) produces graphene attached to silicon nanoparticles.

[0106] The heat treatment in step (iii) is preferably carried out in the range of about 700°C to 1100°C, for example, in the range of about 850°C to 1000°C.

[0107] Further heat treatment is performed at a temperature in the range of approximately 500°C to 700°C, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0108] Preferably, the further heat treatment step is carried out at a temperature in the range of about 800°C to 1000°C, for example, about 850°C to 950°C.

[0109] Preferably, the agglomeration step includes spray drying. Attached Figure Description

[0110] The invention will now be described by way of example only, with reference to one embodiment and the accompanying drawings, wherein:

[0111] Figure 1 This is a schematic diagram of a method for producing the composite material according to the present invention;

[0112] Figure 2 This is a diagram of full-cell data from tests of graphite and silicon-containing materials, one of which, “coating 2”, is a composite according to the present invention;

[0113] Figure 3 The electrode density is 1.3 g / cm³. 3 The graph shows the specific capacity and capacity retention relative to cycle number of a full cell test in a button cell, again containing one of the silicon materials, “G2”, “coating 2”, which is a composite according to the invention;

[0114] Figure 4 This is at an electrode density of 1.3 g / cm³. 3 A graph illustrating the specific capacity and capacity retention relative to cycle number of the composite material according to the present invention in a single-layer pouch cell; and

[0115] Figure 5 Again, at an electrode density of 1.5 g / cm³ 3In a single-layer pouch cell, the graphs of the specific capacity and capacity retention relative to cycle number of the composite material according to the invention demonstrate further performance improvements. Detailed Implementation

[0116] The present invention provides a silicon-containing composite material comprising a plurality of silicon nanoparticles located within a carbon matrix, and an amorphous carbon shell surrounding the silicon nanoparticles and the carbon matrix, wherein the thickness of the amorphous carbon shell is from about 10 nm to 5000 nm.

[0117] Silicon nanoparticles are preferably provided in a size range of about 20 nm to 300 nm. In one form of the invention, silicon material is ground to provide silicon nanoparticles, for example, by grinding the silicon material in a non-aqueous solvent to avoid the generation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2.

[0118] The carbon matrix, in its preferred form, has:

[0119] (i) A density lower than approximately 1.5 g / cc;

[0120] (ii) Porosity greater than approximately 65%; and / or

[0121] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0122] Unless otherwise stated, the surface area and surface area measurement mentioned herein refer to the specific surface area calculated using Brunauer-Emmett-Teller analysis and may be referred to as "BET". Common instruments known in the art for measuring surface area (BET) are surface area analyzers or BET analyzers.

[0123] Throughout this specification and claims, unless the context otherwise requires, “density” will be understood as the mass of a plurality of particles of a substance divided by the volume they occupy. Density should be understood to include the space (pores) between the particles. Methods for determining density are well known in the art. A common instrument known in the art for measuring density is a hydrometer.

[0124] Throughout this specification and claims, unless the context otherwise requires, "porosity" will be understood as the fraction of pore volume relative to the total volume. Methods for determining porosity are well known in the art. An exemplary technique for determining porosity is the porosimetry method. A commonly used instrument known in the art for measuring porosity is the mercury porosimeter.

[0125] In one form, in addition to silicon nanoparticles, the carbon matrix also comprises one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers. The carbon matrix is ​​provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both. The silicon nanoparticles are encapsulated by one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0126] In the preferred form, the amorphous carbon shell has a density greater than about 1.5 g / cc. The surface area (BET) of the silicon-containing composite material is less than about 10 m². 2 / g, for example, less than about 5m 2 / g.

[0127] In one form, the amorphous carbon shell further comprises additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0128] The composite material ideally possesses the level of elastic properties conferred by the presence of one or more of graphite particles, graphene, few-layer graphene, and graphite nanoparticles that can be provided within an amorphous carbon matrix.

[0129] The present invention also provides an anode compound comprising the composite material described above.

[0130] The present invention further provides a method for producing composite materials, the method comprising the following steps:

[0131] (i) Silicon nanoparticles, a binder and one or more carbon sources are passed through a first agglomeration step, such as a spray drying step, to form a first composite in the first agglomeration step, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes and carbon fibers, and the encapsulated silicon nanoparticles are retained in a carbon matrix.

[0132] (ii) Processing the first composite and adhesive from step (i) in a coating step (e.g., a spray drying step) to produce a composite having a shell containing organic matter; and

[0133] (iii) The composite and shell of step (ii) are heat-treated, thereby converting the organic material in the shell into carbon, resulting in a composite material containing multiple encapsulated silicon nanoparticles in a carbon matrix and providing an amorphous carbon shell around them, wherein the thickness of the amorphous carbon shell is about 10 nm to 5000 nm.

[0134] Throughout this specification and claims, the term "encapsulation" should be understood to mean that at least some portions of the silicon nanoparticles of this disclosure are encapsulated by one or more of graphite, graphene, carbon nanotubes, and carbon fibers. Encapsulation of the silicon particles can be achieved, for example, by subjecting the silicon nanoparticles, a binder, and one or more carbon sources comprising one or more of graphite, graphene, carbon nanotubes, and carbon fibers to a first agglomeration step (e.g., a spray drying step), in which a first composite is formed, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes, and carbon fibers.

[0135] In one embodiment of the invention, an additional heat treatment step is provided, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0136] Silicon nanoparticles are preferably supplied in a size range of about 20 nm to 300 nm.

[0137] In one form of the invention, the silicon material is milled in an initial step to provide the silicon nanoparticles of step (i), for example, by milling the silicon nanoparticles in a non-aqueous solvent to avoid the generation of SiO2 and other relatively dangerous byproducts, such as SiH4 and H2.

[0138] The initial grinding step is, for example, a crushing step. The crushing step can be carried out in one or more bead mills.

[0139] The carbon matrix, in its preferred form, has:

[0140] (i) A density lower than approximately 1.5 g / cc;

[0141] (ii) Porosity greater than approximately 65%; and / or

[0142] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0143] In one form, the carbon matrix is ​​provided as an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both.

[0144] In addition to silicon nanoparticles, the carbon matrix can also include one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0145] In one form, the amorphous carbon shell has:

[0146] (i) a density greater than about 1.5 g / cc; and / or

[0147] (ii) Less than approximately 45m 2 / g, for example, less than 10m 2 / g surface area (BET).

[0148] In one form, the amorphous carbon shell further comprises additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0149] In another form of the invention, a further heat treatment step is applied to the composite material of step (iii), thereby reducing its surface area to less than 5 m². 2 / g.

[0150] Prior to the further heat treatment step, the composite material of step (iii) has a hydrocarbon applied thereto. This hydrocarbon may be provided in the form of dihydroxynaphthalene (DHN), for example, at 1 to 5% by weight.

[0151] In one form of the invention, an aqueous solvent is used in at least step (iii) and in the further heat treatment. Step (iii) and the further heat treatment each comprise dissolving dihydroxynaphthalene in water, for example, at a temperature greater than about 70°C.

[0152] The heat treatment in step (iii), additional heat treatment and further heat treatment can each be provided in the form of pyrolysis, and the heat treatment will convert any existing binder into amorphous carbon.

[0153] The graphite particles from grinding step (i) are provided in one form as pre-exfoliated graphite particles.

[0154] In one form of the invention, the grinding process in step (i) produces graphene attached to silicon nanoparticles.

[0155] The heat treatment in step (iii) is carried out at a temperature in the range of about 700°C to 1100°C, for example, in the range of about 850°C to 1000°C.

[0156] Further heat treatment is performed at a temperature in the range of approximately 500°C to 700°C, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0157] Further heat treatment steps are carried out at temperatures in the range of about 800°C to 1100°C, for example, between about 850°C and 950°C.

[0158] The present invention further provides a method for preparing an anode composite, the method comprising the following steps:

[0159] (i) Silicon nanoparticles, a binder and one or more carbon sources are passed through a first agglomeration step, such as a spray drying step, to form a first composite in the first agglomeration step, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes and carbon fibers, and the encapsulated silicon nanoparticles are retained in a carbon matrix.

[0160] (ii) Processing the first composite and adhesive from step (i) in a coating step (e.g., a spray drying step) to produce a composite having a shell containing organic matter; and

[0161] (iii) The composite and shell of step (ii) are heat-treated, thereby converting the organic material in the shell into carbon, thereby producing an anode composite containing multiple encapsulated silicon nanoparticles in a carbon matrix and providing an amorphous carbon shell around them, wherein the thickness of the amorphous carbon shell is about 10 nm to 5000 nm.

[0162] In one embodiment of the invention, an additional heat treatment step is provided, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0163] Silicon nanoparticles can be provided in a size range of about 20 nm to 300 nm. In one form of the invention, silicon material is milled to provide the silicon nanoparticles of step (i), for example, by milling the silicon material in a non-aqueous solvent to avoid the generation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2.

[0164] In one form, the initial grinding step is a crushing step, and is carried out, for example, in one or more bead mills.

[0165] Carbon matrix has, in one form:

[0166] (i) A density lower than approximately 1.5 g / cc;

[0167] (ii) Porosity greater than approximately 65%; and / or

[0168] (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

[0169] The carbon matrix is ​​provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both. In addition to silicon nanoparticles, the carbon matrix also includes one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0170] In one form, the amorphous carbon shell has:

[0171] (i) a density greater than about 1.5 g / cc; and / or

[0172] (ii) Less than approximately 45m 2 / g, for example, less than 10m 2 / g surface area (BET).

[0173] In one form, the amorphous carbon shell further comprises additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

[0174] In another embodiment of the invention, a further heat treatment step is applied to the anolyte of step (iii), thereby reducing its surface area to less than 5 m². 2 / g. Prior to further heat treatment steps, in one form, the anolyte complex of step (iii) has a hydrocarbon applied thereto. This hydrocarbon may be provided in the form of dihydroxynaphthalene, for example, at 1 to 5% by weight.

[0175] In one form of the invention, an aqueous solvent is used in at least step (iii) and in the further heat treatment. Step (iii) and the further heat treatment each preferably involve dissolving dihydroxynaphthalene in water, for example, at a temperature greater than about 70°C.

[0176] The heat treatment in step (iii), the additional heat treatment, and the further heat treatment are each provided, for example, in the form of pyrolysis. The heat treatment preferably converts any existing binder into amorphous carbon.

[0177] In a preferred embodiment, the heat treatment in step (iii) is carried out at a temperature in the range of about 700°C to 1100°C, for example, in the range of about 850°C to 1000°C.

[0178] Further heat treatment is performed at a temperature in the range of approximately 500°C to 700°C, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

[0179] Further heat treatment steps are carried out at temperatures in the range of about 800°C to 1000°C, for example, between about 850°C and 950°C.

[0180] exist Figure 1The diagram illustrates a process 10 according to a first embodiment of the invention, used to produce a composite material 12. In a first step, a mixture 14 of silicon nanoparticles 16, a binder (e.g., 1,5-dihydroxynaphthalene (DHN)), and one or more of graphite, graphene, carbon nanotubes, and carbon fibers 18 is subjected to a first agglomeration step 20, such as spray drying, to form a first composite 22. In the first composite 22, the silicon nanoparticles 16 are encapsulated by one or more of graphite, graphene, carbon nanotubes, and carbon fibers 18, and the resulting encapsulated silicon nanoparticles 24 are retained within a carbon matrix 26. The binder used in the agglomeration step 20 may also be provided in the form of a carbon source (free of Cl, Br, and / or S), such as pitch, glucose, sucrose, and phenolic resins.

[0181] Silicon nanoparticles 16 are available in a size range of approximately 20 nm to 300 nm.

[0182] The first composite 22 can then be subjected to a heat treatment step 28 (referred to herein as an additional heat treatment step, as it is not described as present in all embodiments of the invention), for example, pyrolysis at a temperature in the range of about 500°C to 700°C, through which the binder used in the agglomeration step 20 is completely or partially converted into carbon, thereby providing a heat-treated first composite 30. Where the binder used in the agglomeration step 20 is also a carbon source, the first composite preferably comprises low-density carbon after pyrolysis (e.g., a density lower than that of the amorphous carbon shell produced by the heat treatment step of the intermediate composite described below).

[0183] The first composite, whether it is the first composite 22 (untreated) or the first composite 30 (treated), can be conveniently referred to as a Si@C composite or material.

[0184] In what is referred to elsewhere herein as the second step, the first composite 22 or 30 undergoes an encapsulation step 32 with an adhesive (e.g., 1,5-dihydroxynaphthalene (DHN)) to produce an intermediate composite 34 having an organic shell 36 formed around the first composite 30. Because the first composite 22 or 30 has a relatively large surface area (as indicated below), encapsulation with the organic shell 36 can be readily achieved using a simple mixing / spray-drying agglomeration technique.

[0185] In what is referred to elsewhere in this document as the third step, the intermediate composite 34 is then subjected to a heat treatment step 38, for example, pyrolysis in a temperature range of about 700°C to 1100°C, through which the 1,5-dihydroxynaphthalene (DHN) binder employed in the coating step 32 is completely converted into amorphous carbon, thereby providing composite material 12. Composite material 12 contains a plurality of encapsulated silicon nanoparticles 24 in a carbon matrix 26, around which a heat-treated amorphous carbon shell 40 is now provided.

[0186] The amorphous carbon shell 40 has a density greater than about 1 g / cc and / or a surface area less than about 45 m². 2 / g, for example, less than 10m 2 / g. Add titanium, aluminum, zirconium, niobium, selenium, tin, compounds containing one or more of these elements, and / or oxides of these elements such as TiO2, Al2O3, or SnO. It is envisioned that the composite material of the present invention may contain additional thin film deposits surrounding the shell 40. For example, an alumina layer of less than about 100 nm can be deposited thereon by atomic layer deposition.

[0187] The applicant understands that the thick shell 40 reduces or prevents the outward expansion of the composite material 12 during lithiation.

[0188] The adhesive used in the first agglomeration step 20 and the coating step 32 can be the same, although the inventors have noted that it is preferred that, after heat treatment, the carbon from the adhesive used in the coating step 32 is denser than the carbon obtained from the adhesive used in the first agglomeration step 20.

[0189] Composite material 12 can be conveniently referred to as Si@C1@C2 composite or material.

[0190] In one form of the invention, the silicon material is ground to provide silicon nanoparticles 16. For example, the silicon material is ground in a non-aqueous solvent, such as IPA, to avoid the formation of SiO2 and other relatively hazardous byproducts, such as SiH4 and H2. Grinding can be performed as a crushing step and, for example, in one or more bead mills.

[0191] The first composite material 28 or 30 has a carbon matrix 26 with a density of less than about 1.5 g / cc, a porosity of more than about 65%, and a surface area (BET) of about 10 m². 2 / g to 500m 2 Between / g, for example, at about 40m 2 / g to 50m 2Between / g. High porosity should be understood as being provided by the presence of one or more of graphite, graphene, carbon nanotubes, and carbon fibers. High surface area is understood as a result of the specific carbon source utilized and / or the relatively low temperature pyrolysis employed.

[0192] Although not in Figure 1 As shown, but in one form of the invention, the composite material 12 is subjected to a further heat treatment step, such as pyrolysis, at a temperature in the range of about 800°C to 1000°C, for example about 850°C to 950°C, thereby reducing its surface area to less than 10 m². 2 / g, for example, equal to or less than 5m 2 / g. Prior to further heat treatment steps, composite material 12 has a hydrocarbon applied thereto, for example, provided in the form of 1,5-dihydroxynaphthalene (DHN), for example, at 1 to 5% by weight. Such application of DHN and further heat treatment steps, for example, provide a further composite or material that can be conveniently referred to as Si@C1@C2@C3.

[0193] Additional sieving steps (also not shown) may be applied to either or both of the intermediate composite 34 or the composite material 12 to assist in material homogenization and reduction of surface area.

[0194] As described above, an aqueous solvent is used in at least step (iii) and in the further heat treatments. Each of step (iii) and the further heat treatments preferably involves dissolving dihydroxynaphthalene in water, for example, at a temperature greater than about 70°C.

[0195] The method of the present invention can be better understood by referring to the following non-limiting examples.

[0196] Example 1

[0197] Talga strips graphite

[0198] The applicant has developed a unique exfoliated graphite (the applicant calls it Talga HSA) for a variety of applications, described in detail in International Patent Application PCT / GB2018 / 052095 (WO 019 / 020999), the entire contents of which are incorporated herein by reference.

[0199] The applicant's HSA has widened the gaps between the graphene layers in the graphite. Therefore, compared to typical or 'normal' graphite, the graphene layers will be more easily peeled off from the HSA and few-layer graphene (FLG) will be produced during bead milling.

[0200] Full cell data from graphite and silicon-containing materials

[0201] The results of the full battery test are shown in Figure 2 , 3 In coatings 4 and 5, all coatings are based on the same weight ratio of active material:CMC:SBR:carbon additive = 94:2:2:2. For "Graphite", the active material is natural graphite. For "Coating 1", the active material is a mixture of 5% Si@C and 95% natural graphite. For "Coating 2", the active material is a mixture of 5% Si@C1@C2 and 95% natural graphite. The silicon content in both Si@C and Si@C1@C2 is approximately 60%. C = 2C1 = 2C2 by weight and is derived from the pyrolysis of 1,5-dihydroxynaphthalene.

[0202] All full-cell tests were performed using the same procedure: Charging: Cycles 1 and 2: C / 10 to 4.2 V, then held at 4.2 mV until C / 100. Other cycles: C / 2 to 4.2 V, then held at 4.2 V until C / 10. Discharging: Cycles 1 and 2: C / 10 to 3.0 V; other cycles: C2 to 3.0 V. Cathode from NMC 111. N / P = 1.05–1.10.

[0203] Button battery test

[0204] With additional coatings on Si@C (Si@C-G2), the full-cell cycle life at 80% capacity retention increased from 150 cycles to 300 cycles. Si@C-G1: One-layer coating. Si@C-G2: Two-layer coating. At a concentration of 1.3 g / cm³... 3 The electrode density was tested in coin cells. First cycle: C / 10 charging to 4.2 V, cutoff current C / 100; C / 10 discharging to 3.0 V. Other cycles: C / 2 charging to 4.2 V, cutoff current C / 10; C / 2 discharging to 3.0 V. Cathode: NMC111. N / P = 1.03-1.1.

[0205] Soft-pack battery testing

[0206] With additional coatings on Si@C, the electrode density is 1.3 g / cm³. 3 In this single-layer pouch cell, the full-cell cycle life is increased to 500 cycles with 80% capacity retention. First cycle: C / 10 charging to 4.2 V, cutoff current C / 100; C / 10 discharging to 3.0 V. Other cycles: C / 2 charging to 4.2 V, cutoff current C / 10; C / 2 discharging to 3.0 V. Cathode: NMC111. N / P = 1.03-1.1.

[0207] By further modifying the second-coated Si@C (i.e., binder, calendering, composite), an electrode density of 1.5 g / cm³ was achieved. 3 In a single-layer pouch cell, a full-cell cycle life of 500 cycles is achieved with 80% capacity retention. First cycle: C / 10 charging to 4.2 V, cutoff current C / 100; C / 10 discharging to 3.0 V. Subsequent cycles: C / 2 charging to 4.2 V, cutoff current C / 10; C / 2 discharging to 3.0 V. Cathode: NMC111. N / P = 1.03-1.1. This data meets the customer's basic requirements and current market Si performance.

[0208] Example 2

[0209] The tests performed according to the method of the invention provide the following details regarding the pyrolysis temperatures used in the additional heat treatment (described in this embodiment as "first pyrolysis" to specify it as the first pyrolysis step employed in the method performed in this embodiment) and the heat treatment (described in this embodiment as "second pyrolysis" to specify it as the second pyrolysis step employed in the method performed in this embodiment). The surface area (BET, m²) after the additional heat treatment (first pyrolysis) and the heat treatment (second pyrolysis) 2 The results for / g) are listed in Table 1 below:

[0210] Table 1

[0211]

[0212] The surface area results after further heat treatment using Sample 3 (from the lowest surface area / BET sample in Table 1) as the starting material (described in this embodiment as "third pyrolysis" to specify that it is the third pyrolysis step used in the method performed in this embodiment) are shown in Table 2 below:

[0213] Table 2

[0214]

[0215] The applicant determined that if the surface area could be controlled within 40m² 2 / g to 50m 2 Between / g, the surface area (BET) of the final product (Si@C1@C2@C3) after further heat treatment (3rd pyrolysis) can be as low as 3m. 2 / g. When using a surface area (BET) of 45m² 2 The surface area / BET results after further heat treatment (3rd pyrolysis) of the starting material at / g are shown in Table 3 below:

[0216] Table 3

[0217]

[0218] It is envisioned that, without departing from the scope of the invention, the above-described spray dryer can be advantageously replaced by at least one of, for example, a jet fluidized bed system or a spray pyrolysis system.

[0219] As can be seen from the above description, compared with the prior art, the composite material and its production method of the present invention provide one or more advantages, including the use of at least one shell of thickness understood to reduce or prevent outward expansion during lithiation, the mechanical stability of which is potentially supplemented by the incorporation of materials containing titanium, aluminum, zirconium, niobium, selenium and / or tin, while also providing an internal carbon matrix with relatively high porosity that can thus accommodate expansion occurring inside the composite material.

[0220] Modifications and variations that are obvious to those skilled in the art are considered to fall within the scope of this invention.

Claims

1. A silicon-containing composite material comprising a plurality of silicon nanoparticles located within a carbon matrix, and an amorphous carbon shell provided surrounding the silicon nanoparticles and the carbon matrix, wherein the thickness of the amorphous carbon shell is from about 10 nm to 5000 nm.

2. The composite material of claim 1, wherein the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

3. The composite material according to claim 1 or 2, wherein: (i) grinding silicon material to provide silicon nanoparticles; or (ii) Grinding silicon materials in a non-aqueous solvent to provide silicon nanoparticles, thereby avoiding the generation of SiO2 and optional other relatively dangerous byproducts such as SiH4 and H2.

4. The composite material according to any one of the preceding claims, wherein the carbon matrix comprises: (i) A density lower than approximately 1.5 g / cc; (ii) Porosity greater than approximately 65%; and / or (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

5. The composite material according to any one of the preceding claims, wherein, in addition to silicon nanoparticles, the carbon matrix further comprises one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

6. The composite material according to any one of the preceding claims, wherein the carbon matrix is ​​provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both an amorphous carbon matrix and a crystalline carbon matrix.

7. The composite material according to claim 5 or 6, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, graphite nanoplates, carbon nanotubes and carbon fibers.

8. The composite material according to any one of claims 5 to 7, wherein the composite material has an elastic property level conferred by the presence of one or more of graphite, graphene, graphite nanoplates, carbon nanotubes and carbon fibers provided within an amorphous carbon matrix.

9. The composite material according to any one of the preceding claims, wherein the amorphous carbon shell has a density greater than about 1.5 g / cc.

10. The composite material according to any one of the preceding claims, wherein the surface area (BET) of the silicon-containing composite material is: (i) Less than approximately 10m 2 / g; (ii) Less than approximately 5m 2 / g.

11. The composite material according to any one of the preceding claims, wherein, The amorphous carbon shell also contains additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

12. An anode compound comprising the composite material according to any one of claims 1 to 11.

13. A method for producing composite materials, comprising the following method steps: (i) Passing silicon nanoparticles, a binder and one or more carbon sources through a first aggregation step to form a first composite, wherein the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes and carbon fibers, and the encapsulated silicon nanoparticles are retained in a carbon matrix. (ii) In the coating step, the first composite and adhesive from step (i) are processed to produce a composite having a shell containing organic matter; and (iii) The composite and shell of step (ii) are heat-treated, thereby converting the organic material in the shell into carbon, thereby producing a composite material containing multiple encapsulated silicon nanoparticles in a carbon matrix and providing an amorphous carbon shell around them, wherein the thickness of the amorphous carbon shell is about 10 nm to 5000 nm.

14. The method of claim 13, wherein, An additional heat treatment step is provided, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

15. The method of claim 13 or 14, wherein the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

16. The method according to any one of claims 13 to 15, wherein: (i) Grinding the silicon material in the initial step to provide the silicon nanoparticles of step (i); or (ii) Grind the silicon material in the initial step to provide the silicon nanoparticles of step (i) in a non-aqueous solvent to avoid the generation of SiO2 and other relatively dangerous byproducts such as SiH4 and H2.

17. The method of claim 16, wherein the initial grinding step is a crushing step, optionally carried out in one or more bead mills.

18. The method according to any one of claims 13 to 17, wherein the carbon matrix comprises: (i) A density lower than approximately 1.5 g / cc; (ii) Porosity greater than approximately 65%; and / or (iii) Approximately 10m 2 / g to 500m 2 / g surface area (BET).

19. The method according to any one of claims 13 to 18, wherein the carbon matrix is ​​provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both an amorphous carbon matrix and a crystalline carbon matrix.

20. The method according to any one of claims 13 to 19, wherein, in addition to silicon nanoparticles, the carbon matrix further comprises one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

21. The method according to any one of claims 13 to 20, wherein the amorphous carbon shell has: (i) a density greater than about 1.5 g / cc; and / or (ii) Less than approximately 45m 2 / g, for example, less than 10m 2 / g surface area (BET).

22. The method according to any one of claims 13 to 21, wherein, The amorphous carbon shell also contains additional materials from the group consisting of titanium, aluminum, zirconium, niobium, and selenium or their oxides.

23. The method according to any one of claims 13 to 22, wherein the composite material of step (iii) is subjected to a further heat treatment step, thereby reducing its surface area to less than 5 m². 2 / g.

24. The method of claim 23, wherein the composite material of step (iii) has hydrocarbons applied thereto prior to the further heat treatment step.

25. The method of claim 24, wherein the hydrocarbon is provided in the form of 1,5-dihydroxynaphthalene, optionally in 1 to 5% by weight.

26. The method according to any one of claims 23 to 25, wherein an aqueous solvent is used in at least the heat treatment in step (iii) and in the further heat treatment.

27. The method according to any one of claims 23 to 26, wherein the heat treatment in step (iii) and the further heat treatment each comprise: (i) Dissolve 1,5-dihydroxynaphthalene in water; or (ii) Dissolve 1,5-dihydroxynaphthalene in water at a temperature greater than about 70°C.

28. The method according to any one of claims 23 to 27, wherein the heat treatment in step (iii), the additional heat treatment and the further heat treatment are each provided in the form of pyrolysis, optionally converting any existing binder into amorphous carbon.

29. The method according to any one of claims 13 to 28, wherein the heat treatment in step (iii) is carried out at a temperature within the range of: (i) Approximately 700°C to 1100°C; or (ii) Approximately 850°C to 1000°C.

30. The method according to any one of claims 14 to 29, wherein, Further heat treatment is performed at a temperature in the range of about 500°C to 700°C, through which the binder used in the first agglomeration step is converted into carbon and partially forms the carbon matrix of the first composite.

31. The method according to any one of claims 24 to 30, wherein the further heat treatment step is carried out at a temperature within the following range: (i) Approximately 800°C to 1000°C; or (ii) Approximately 850°C to 950°C.

32. The method according to any one of claims 13 to 31, wherein the agglomeration step or each agglomeration step comprises spray drying.

33. A method for producing an anode compound, the method comprising the method steps of any one of claims 13 to 32.

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