Silicon-containing composite material and method of manufacturing the same

Abstract

The present invention relates to a silicon-containing composite material comprising a plurality of silicon nanoparticles disposed within a carbon matrix and an amorphous carbon shell surrounding the silicon nanoparticles and the carbon matrix, wherein the amorphous carbon shell has a thickness of approximately 10 nm to 5000 nm.

Description

[Technical Field]

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

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

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

[0004] Currently, silicon / graphite composites are considered promising materials for lithium-ion anodes. However, silicon / graphite composites suffer from a number of well-known and understood drawbacks. These drawbacks include high expansion rates of up to 400% and poor cycle life. Commercial applications of silicon / graphite composites require that at least these issues be addressed.

[0005] The irreversible capacity loss of silicon-containing anodes, as currently known and understood, is currently being addressed by using nanostructured silicon particles as the electroactive material. Silicon nanoparticles and nanostructured silicon have been reported to be more resistant to capacity changes during charging and discharging than microscale particles (X.H. Liu et al., “Size-Dependent Fracture of Silicon Nanoparticles During Lithiation,” ACS Nano, 2012, 6(2), 1522–1531). However, nanoscale particles are known to be difficult to prepare and handle, and are therefore considered unsuitable for commercial-scale applications. In addition to issues related to silicon particle size, the nature of the silicon surface also plays an important role in the formation of the solid electrolyte interphase (SEI) and electronic conductivity. Because the SEI on the silicon surface is not stable and constantly consumes lithium, surface modification is necessary to avoid or at least reduce the silicon's exposure to the electrolyte. Furthermore, silicon is not considered a particularly good conductive material.

[0006] A core-shell structured graphite / silicon / pyrolyzed carbon (Gr / Si@C) composite has been fabricated using a process involving mechanical milling, spray drying, and the use of pitch (Li et al., “Scalable synthesis of a novel structured graphite / silicon / pyrolyzed carbon composite as anode material for high-performance lithium-ion batteries”, Journal of Alloys and Compounds 688 (2016) 1072-1079). This prior art process demonstrates a potentially relatively scalable and cost-effective method. Because silicon and graphite are coated with carbon, cyclability is significantly improved compared to many prior art methods. However, the low first-cycle efficiency of 77.9% with a capacity of 637.7 mAh / g is far from the level required by the battery industry.

[0007] International Patent Application PCT / GB2018 / 051689 (WO 2018 / 229515) describes the production of silicon nanoparticles by ball milling silicon particles in a solvent. A pyrolytic "amorphous" carbon precursor containing at least one oxygen or nitrogen atom is added to the silicon nanoparticles and 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. Due to the large amount of amorphous carbon used in this prior art process, significant first cycle loss (FCL) and expansion remain substantial issues. It is believed that amorphous carbon contributes to the majority of the unacceptable FCL and expansion. Additionally, as Si@C expands, the amorphous carbon's inelasticity weakens the bond between silicon and carbon.

[0008] By electrolessly plating a thick layer of nickel onto micron-sized silicon particles, graphene-caged silicon structures were formed, achieving outstanding cell performance, 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, Article No. 15029 (2016)).

[0009] Silicon nanoparticles coated with few layers of graphene have also been described as being formed by chemical vapor deposition (CVD) (Son et al., “Silicon carbide-free graphene growth on silicon for lithium-ion batteries with high volumetric energy density,” Nature Communications, Vol. 6, Article No. 7393 (2015)). Again, these coated silicon nanoparticles are said to offer exceptional cell performance, including high capacity, low expansion, long cycle life, and low FCL. However, the process for forming these graphene-coated materials is known to be expensive and cannot be scaled up to the levels required for commercial applications.

[0010] A more cost-effective method for coating silicon with a few layers of graphene is described in WO 2015 / 073674, where a graphite-silicon mixture is bead-milled to coat the silicon with graphene. However, this method does not produce the required performance. For example, the capacity drops significantly (>45%) within the first 200 cycles.

[0011] U.S. Patent Application Publication No. 2016 / 064731 (Jung Sung-Ho et al.) describes the production of a carbon-silicon composite material by preparing a silicon-carbon-polymer matrix, which is then heat-treated to carbonize the matrix. The carbonized matrix is ​​then pulverized, mixed with a carbon source, and carbonized to produce the carbon-silicon composite material of the invention. This carbon-silicon composite material is used as an anode slurry for secondary batteries.

[0012] US Patent Application Publication No. 2018 / 097229 (Jo Sungnim et al.) describes a densitometric method using a densitometrically controlled densitometer. 3and forming a plurality of the primary particles, a second carbonaceous material, and a foaming agent to form porous silicon-carbon secondary particles, which 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. The composite material includes a plurality of silicon nanoparticles coated with graphite particles, few-layer graphene particles, graphite nanoparticles, a carbon matrix, and an amorphous carbon shell, wherein the silicon nanoparticles coated with graphite particles, the few-layer graphene particles, and the graphite nanoparticles are each held within the carbon matrix. A method for producing the composite material is also described, which includes the steps of: (i) subjecting silicon particles to a size reduction step together with graphite particles in a solvent, optionally in the presence of a polymer, to produce graphite particle-coated silicon nanoparticles, few-layer graphene particles, and graphite nanoparticles; (ii) processing the product of step (i) with or without a binder to produce a composite material; (iii) heat-treating the composite of step (ii) to produce a composite material comprising a plurality of graphite particle-coated silicon nanoparticles, few-layer graphene particles, graphite nanoparticles, and a carbon matrix, each particle held within the carbon matrix; (iv) coating the composite material of step (iii) with a binder; and (v) heat treating the composite material of step (iv) to produce a shell comprising amorphous carbon. Equipped with.

[0014] After the heat treatment in step (iii), the surface area (BET) of the composite is approximately 70–120 m 2 / g, but after the heat treatment in step (v), the BET of the material is about 10-30 m 2 / g range, which is relatively high.

[0015] Additionally, applicant's previously described compositions and processes utilize a non-aqueous solvent, for example, the solvent may be provided in the form of isopropyl alcohol (IPA). However, it is understood that IPA is expensive and toxic, and it would be advantageous to provide compositions and processes that do not require the use of IPA.

[0016] As mentioned herein, a particular problem with silicon-containing anode materials is their expansion. This expansion can lead to the crushing of composite particles, resulting in physical contact and loss of active material. Furthermore, expansion can lead to an unstable SEI layer, resulting in the continuous loss of lithium. To overcome these issues, two approaches are typically used. First, silicon nanoparticles are used, as nanosized materials are more resistant to expansion and crushing. Second, carbon layers are coated on the silicon surface. These treatments can significantly improve the performance of silicon anodes. However, silicon anodes are still insufficient for practical use. Conventional carbon layers formed on silicon surfaces are thought to lack elasticity and uniformity, resulting in insufficient stability of the SEI layer. Therefore, silicon anodes with conformal graphene cages (Li et al., supra) or sliding graphene layers (Son et al., supra) offer relatively good cell performance. However, the manufacturing methods for these graphene coatings are expensive.

[0017] Therefore, the present applicants proposed a composite material and process described in International Patent Application PCT / IB2020 / 056050 (WO 2020 / 261194) to reduce net expansion from silicon composite particles (secondary particles), whereby particles with engineered porosity were engineered to buffer expansion from individual silicon particles within the secondary particles. However, it was found that the porosity of silicon composite particles may not be effectively utilized because silicon expansion tends to occur outward rather than effectively utilizing the internal voids. Therefore, it would be advantageous to provide a composition and process that results in a shell of sufficient thickness and / or hardness for the Si@C material that limits outward expansion during lithiation. Summary of the Invention

[0018] The composite materials and methods of the present invention have as one of their objects to substantially overcome, or at least provide a useful alternative to, one or more of the above-mentioned problems associated with prior art processes.

[0019] The foregoing discussion of the background art is intended only to facilitate an understanding of the present invention, and is not intended as an admission that any of the material referred to is or was part of the common general knowledge at the priority date of this application.

[0020] Throughout this specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising" will be understood to mean the inclusion of a stated integer or group of integers but not the exclusion of other integers or groups of integers.

[0021] Throughout this specification and claims, unless the context requires otherwise, references to "grinding" or "milling" are understood to include the references "ball milling" and "bead milling," and references to "bead milling" or "ball milling" are understood to include the reference "milling." Similarly, unless the context requires otherwise, references to "grinding," "ball milling," and / or "bead milling" are understood to include references to "grinding," and references to "grinding" are understood to include references to "grinding," "bead milling," and / or "ball milling" as the context requires.

[0022] The term "relative" or "relatively" when used in reference to a feature of the present invention is intended to indicate a comparison with, and a typical characterization of, that feature in the prior art, unless the context clearly indicates or requires otherwise.

[0023] It should be understood that the ranges provided herein include the stated range and any value or subrange within the stated range. For example, a range of about 1 μm (micrometer) to about 2 μm, or a range of about 1 μm to about 2 μm, should be interpreted to include not only the explicitly stated limits 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 includes subranges such as about 1.1 μm to about 1.9 μm, about 1.25 μm to about 1.75 μm, etc. Furthermore, when "about" and / or "substantially" are used to describe a value, they are meant to encompass slight variations (up to ±10%) from the stated value.

[0024] DISCLOSURE OF THE INVENTION In accordance with the present invention, there is provided a silicon-containing composite material comprising a plurality of silicon nanoparticles disposed within a carbon matrix and an amorphous carbon outer shell surrounding the silicon nanoparticles and the carbon matrix, wherein the amorphous carbon outer shell has a thickness of about 10 nm to 5000 nm.

[0025] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0026] In one form of the invention, silicon material is milled to provide silicon nanoparticles, preferably in a non-aqueous solvent to avoid the production of SiO and other relatively hazardous by-products such as SiH and H.

[0027] In one aspect of the invention, the carbon matrix has a density of less than about 1.5 g / cc. In one aspect of the invention, the carbon matrix has a porosity of greater than about 65%. In one aspect of the invention, the carbon matrix has a porosity of greater than about 10 m 2 / g~about 500m 2 / g surface area (BET).

[0028] Preferably, the carbon matrix is (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has one or more of the following.

[0029] The carbon matrix is ​​preferably 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.

[0030] Preferably, the carbon matrix comprises, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0031] The silicon nanoparticles are preferably encapsulated by one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0032] The amorphous carbon shell, in a preferred form, has a density greater than about 1.5 g / cc. Preferably, the silicon-containing composite has a surface area (BET) of about 10 m 2 / g, e.g., about 5m 2 / g.

[0033] In one form, the amorphous carbon shell further comprises an additional material from the group of titanium, aluminum, zirconium, niobium, and selenium, or oxides thereof.

[0034] Preferably, the composite material has elastic properties imparted by the presence of one or more of graphite particles, graphene, few layer graphene, and graphite nanoparticles, which may be provided within the amorphous carbon matrix.

[0035] In accordance with the present invention, there is further provided an anode composite comprising the composite material described hereinabove.

[0036] There is further provided in accordance with the present invention a method of making a composite material, the method comprising: (i) passing silicon nanoparticles, a binder, and one or more carbon sources through a first aggregation step to form a first composite in which the silicon nanoparticles are encapsulated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers, and the coated silicon nanoparticles are held in a carbon matrix; (ii) treating the first composite of step (i) and the binder in a coating step to produce a composite having an organic-containing shell; (iii) heat treating the composite and shell of step (ii) to convert the organic material in the shell to carbon to produce a composite comprising a plurality of encapsulated silicon nanoparticles in a carbon matrix and provided with an amorphous carbon shell, wherein the amorphous carbon outer shell has a thickness of about 10 nm to 5000 nm.

[0037] In one form of the invention, an additional heat treatment step is provided to convert the binder used in the first aggregation step to carbon, which forms part of the carbon matrix of the first composite.

[0038] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0039] In one embodiment of the present invention, to provide the silicon nanoparticles of step (i), the first step is to mill the silicon material, preferably in a non-aqueous solvent to avoid the production of SiO2 and other relatively dangerous by-products, such as SiH4 and H2.

[0040] More preferably, the first size reduction step is a milling step. More preferably, the milling step is carried out in one or more bead mills.

[0041] In one aspect of the invention, the carbon matrix has a density of less than about 1.5 g / cc. In one aspect of the invention, the carbon matrix has a porosity of greater than about 65%. In one aspect of the invention, the carbon matrix has a porosity of greater than about 10 m 2 / g~about 500m 2 / g surface area (BET).

[0042] Preferably, the carbon matrix is (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has one or more of the following.

[0043] The carbon matrix is ​​preferably 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.

[0044] More preferably, the carbon matrix comprises, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0045] In one aspect of the invention, the amorphous carbon shell has a density greater than about 1.5 g / cc. In one aspect of the invention, the amorphous carbon shell has a density greater than about 45 m 2 / g, e.g., less than 10m 2 / g or less surface area (BET).

[0046] Preferably, the amorphous carbon shell comprises: (i) a density greater than about 1.5 g / cc; and / or (ii) Approximately 45m 2 / g, e.g., less than 10m 2 / g surface area (BET) It has.

[0047] In one form, the amorphous carbon shell further comprises an additional material from the group of titanium, aluminum, zirconium, niobium, and selenium, or oxides thereof.

[0048] In a further aspect of the invention, the composite material of step (iii) is subjected to a further heat treatment step, whereby its surface area is increased to 5 m 2 / g.

[0049] Preferably, prior to the further heat treatment step, the composite material of step (iii) is loaded with a hydrocarbon, which may be provided in the form of, for example, 1-5 wt % dihydroxynaphthalene.

[0050] In one aspect of the invention, at least the heat treatment in step (iii) and the further heat treatment utilize an aqueous solvent.

[0051] Preferably, the heat treatment and further heat treatment of step (iii) each involve dissolving dihydroxynaphthalene in water.

[0052] More preferably, dihydroxynaphthalene is dissolved in water at about 70°C or higher.

[0053] Preferably, the heat treatment, additional heat treatment and further heat treatment of step (iii) are each provided in the form of pyrolysis.

[0054] More preferably, the heat treatment converts any binder present to amorphous carbon.

[0055] Preferably, the graphite particles in the milling step (i) are provided in the form of pre-exfoliated graphite particles.

[0056] In one form of the invention, the milling step of step (i) produces graphene attached to the silicon nanoparticles.

[0057] The heat treatment in step (iii) is preferably 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.

[0058] An additional heat treatment, which converts the binder employed in the first aggregation step into carbon and forms part of the carbon matrix of the first composite, is carried out at a temperature in the range of about 500°C to 700°C.

[0059] Preferably, the further heat treatment step is carried out at a temperature in the range of about 800°C to 1000°C, for example in the range of about 850°C to 950°C.

[0060] Preferably, the agglomeration step comprises spray drying.

[0061] In accordance with the present invention, there is still further provided a method for producing an anode composite, the method comprising: (i) passing silicon nanoparticles, a binder, and one or more carbon sources through a first aggregation step to form a first composite in which the silicon nanoparticles are encapsulated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers, with the coated silicon nanoparticles held in a carbon matrix; (ii) treating the first composite of step (i) and the binder in a coating step to produce a composite having an organic-containing shell; (iii) heat treating the composite and shell of step (ii) to convert the organic material in the shell to carbon, thereby producing an anode composite comprising a plurality of encapsulated silicon nanoparticles in a carbon matrix and provided with an amorphous carbon shell, wherein the amorphous carbon outer shell has a thickness of about 10 nm to 5000 nm.

[0062] In one form of the invention, an additional heat treatment step is provided to convert the binder employed in the first aggregation step to carbon, which forms part of the carbon matrix of the first composite.

[0063] Preferably, the silicon nanoparticles are provided in a size range of about 20 nm to 300 nm.

[0064] In one embodiment of the present invention, to provide the silicon nanoparticles of step (i), the first step is to mill the silicon material, preferably in a non-aqueous solvent to avoid the production of SiO2 and other relatively dangerous by-products, such as SiH4 and H2.

[0065] More preferably, the first grinding step is a milling step. More preferably, the milling step is carried out in one or more bead mills.

[0066] In one aspect of the invention, the carbon matrix has a density of less than about 1.5 g / cc. In one aspect of the invention, the carbon matrix has a porosity of greater than about 65%. In one aspect of the invention, the carbon matrix has a porosity of greater than about 10 m 2 / g~about 500m 2 / g surface area (BET).

[0067] Preferably, the carbon matrix is (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has one or more of the following.

[0068] The carbon matrix is ​​preferably 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.

[0069] More preferably, the carbon matrix comprises, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0070] In one aspect of the invention, the amorphous carbon shell has a density greater than about 1.5 g / cc. In one aspect of the invention, the amorphous carbon shell has a density greater than about 45 m 2 / g, e.g., less than 10m 2 / g or less surface area (BET).

[0071] Preferably, the amorphous carbon shell comprises: (i) a density greater than about 1.5 g / cc; and / or (ii) Approximately 45m 2 / g, e.g., less than 10m 2 / g surface area (BET) It has.

[0072] In one form, the amorphous carbon shell further comprises an additional material from the group of titanium, aluminum, zirconium, niobium, and selenium, or oxides thereof.

[0073] In a further aspect of the invention, the negative electrode composite of step (iii) is subjected to a further heat treatment step, whereby its surface area is increased to 5 m 2 / g.

[0074] Preferably, prior to the further heat treatment step, the negative electrode composite of step (iii) is subjected to a hydrocarbon, which may be provided, for example, in the form of 1-5 wt % dihydroxynaphthalene.

[0075] In one aspect of the invention, at least the heat treatment in step (iii) and the further heat treatment utilize an aqueous solvent.

[0076] Preferably, the heat treatment and further heat treatment of step (iii) each involve dissolving dihydroxynaphthalene in water.

[0077] More preferably, the dihydroxynaphthalene is soluble in water at about 70°C or above.

[0078] Preferably, the heat treatment, additional heat treatment and further heat treatment of step (iii) are each provided in the form of pyrolysis.

[0079] More preferably, the heat treatment converts any binder present to amorphous carbon.

[0080] Preferably, the graphite particles in the milling step (i) are provided in the form of pre-exfoliated graphite particles.

[0081] In one form of the invention, the milling step of step (i) produces graphene attached to the silicon nanoparticles.

[0082] The heat treatment in step (iii) is preferably 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.

[0083] An additional heat treatment, which converts the binder employed in the first aggregation step into carbon and forms part of the carbon matrix of the first composite, is carried out at a temperature in the range of about 500°C to 700°C.

[0084] Preferably, the further heat treatment step is carried out at a temperature in the range of about 800°C to 1000°C, for example in the range of about 850°C to 950°C.

[0085] Preferably, the agglomeration step comprises spray drying.

[0086] The present invention will now be described, by way of example only, with reference to an embodiment thereof and the accompanying drawings, in which: [Brief explanation of the drawings]

[0087] [Figure 1] 1 is a schematic diagram of a method for producing a composite material according to the present invention. [Figure 2] 1 is a graph of full cell data from testing of graphite and silicon-containing materials, one of which, "Coating 2," is in accordance with a composite of the present invention. [Figure 3] 1 is a graph of specific capacity and capacity retention versus cycle number in a full cell test of a coin cell battery with an electrode density of 1.3 g / cm. "Coating 2" of "G2," one of the silicon-containing materials, is in accordance with the composite material of the present invention. [Figure 4] 1 is a graph of specific capacity and capacity retention versus cycle number for a composite material according to the present invention in a single-layer pouch cell with an electrode density of 1.3 g / cm 3 . [Figure 5] 1 is a graph of specific capacity and capacity retention versus cycle number for a composite material according to the present invention in a single-layer pouch cell with an electrode density of 1.5 g / cm, showing further improvement in performance. DETAILED DESCRIPTION OF THE INVENTION

[0088] The present invention provides a silicon-containing composite material comprising a plurality of silicon nanoparticles disposed within a carbon matrix and an amorphous carbon outer shell surrounding the silicon nanoparticles and the carbon matrix, wherein the thickness of the amorphous carbon outer shell is about 10 nm to 5000 nm.

[0089] The silicon nanoparticles are preferably provided in a size range of about 20 nm to 300 nm. In one embodiment of the present invention, the silicon material is milled to provide the silicon nanoparticles, for example, the silicon material is milled in a non-aqueous solvent to avoid the production of SiO2 and other relatively dangerous by-products, such as SiH4 and H2.

[0090] The carbon matrix, in a preferred embodiment, comprises: (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has.

[0091] Unless otherwise specified, references herein to surface area and surface area measurements are references to specific surface area calculated using Brunauer-Emmett-Teller analysis, which may be referred to as "BET." A common device known in the art for measuring surface area (BET) is the Surface Area Analyzer or BET Analyzer.

[0092] Throughout this specification and claims, unless the context dictates otherwise, "density" is understood to refer to the mass of many particles of a substance divided by the volume they occupy. Density should be understood to include the spaces (pores) between the particles. Methods for measuring density are well known in the art. A common instrument known in the art for measuring density is a densitometer.

[0093] Throughout this specification and claims, unless the context dictates otherwise, "porosity" is understood to refer to the ratio of void volume to total volume. Methods for measuring porosity are well known in the art. One technique for measuring porosity is porosimetry. A common device known in the art for measuring porosity is the mercury porosimeter.

[0094] In one embodiment, the carbon matrix includes, in addition to silicon nanoparticles, 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 amorphous and crystalline carbon matrices. The silicon nanoparticles are encapsulated by one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0095] The amorphous carbon shell, in a preferred form, has a density greater than about 1.5 g / cc. The surface area (BET) of the silicon-containing composite is greater than about 10 m. 2 / g, e.g., about 5m 2 / g.

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

[0097] The composite material ideally has elastic properties imparted by the presence of one or more of graphite particles, graphene, few layer graphene and graphite nanoparticles which may be provided within an amorphous carbon matrix.

[0098] The present invention further provides a negative electrode composite comprising the composite material described herein.

[0099] The present invention further provides a method of making a composite material, the method comprising: (i) passing silicon nanoparticles, a binder, and one or more carbon sources through a first agglomeration step, such as a spray drying step, to form a first composite in which the silicon nanoparticles are encapsulated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers, and the coated silicon nanoparticles are held in a carbon matrix; (ii) treating the first composite of step (i) and the binder in a coating step, e.g., a spray drying step, to produce a composite having an organic-containing shell; (iii) heat treating the composite and shell of step (ii) to convert the organic material in the shell to carbon to produce a composite comprising a plurality of encapsulated silicon nanoparticles in a carbon matrix and provided with an amorphous carbon shell, wherein the amorphous carbon outer shell has a thickness of about 10 nm to 5000 nm.

[0100] Throughout this specification and claims, the term "encapsulation" in this context is understood to refer to at least a portion of the silicon nanoparticles of the present disclosure being partially coated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers. Encapsulation of the silicon particles can be achieved, for example, by passing silicon nanoparticles, a binder, and one or more carbon sources including one or more of graphite, graphene, carbon nanotubes, and carbon fibers through a first aggregation step, such as a spray-drying step, in which a first composite is formed in which the silicon nanoparticles are encapsulated by one or more of graphite, graphene, carbon nanotubes, and carbon fibers.

[0101] In one form of the invention, an additional heat treatment step is provided to convert the binder used in the first aggregation step to carbon, which forms part of the carbon matrix of the first composite.

[0102] The silicon nanoparticles are preferably provided in a size range between about 20 nm and 300 nm.

[0103] In one form of the invention, to provide the silicon nanoparticles of step (i), in a first step the silicon material is milled, for example, the silicon nanoparticles are milled in a non-aqueous solvent so as to avoid the production of SiO2 and other relatively hazardous by-products, such as SiH4 and H2.

[0104] The first step of grinding is, for example, a milling step, which can be carried out in one or more bead mills.

[0105] The carbon matrix, in a preferred embodiment, comprises: (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has.

[0106] In one form, 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.

[0107] The carbon matrix can include, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0108] The amorphous carbon shell, in one form, (i) a density greater than about 1.5 g / cc; and / or (ii) Approximately 45m 2 / g, e.g., less than 10m 2 / g surface area (BET) It has.

[0109] In one form, the amorphous carbon shell further comprises an additional material from the group of titanium, aluminum, zirconium, niobium, and selenium, or oxides thereof.

[0110] In a further aspect of the invention, the composite material of step (iii) is subjected to a further heat treatment step, whereby its surface area is increased to 5 m 2 / g.

[0111] Prior to the further heat treatment step, the composite material of step (iii) is subjected to a hydrocarbon, which may be provided, for example, in the form of 1-5 wt% dihydroxynaphthalene (DHN).

[0112] In one aspect of the invention, at least the heat treatment of step (iii) and the further heat treatment utilize an aqueous solvent, wherein the heat treatment of step (iii) and the further heat treatment each comprise dissolving dihydroxynaphthalene in water, for example, the dihydroxynaphthalene is dissolved in water at a temperature greater than about 70°C.

[0113] The heat treatment, additional heat treatment and further heat treatment of step (iii) may each be provided in the form of pyrolysis, which heat treatment converts any binder present into amorphous carbon.

[0114] The graphite particles of milling step (i) are in one form provided as pre-exfoliated graphite particles.

[0115] In one form of the invention, the milling step of step (i) produces graphene attached to the silicon nanoparticles.

[0116] 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.

[0117] An additional heat treatment, which converts the binder employed in the first aggregation step into carbon and forms part of the carbon matrix of the first composite, is carried out at a temperature in the range of about 500°C to 700°C.

[0118] The further heat treatment step is carried out at a temperature in the range of about 800°C to 1100°C, for example in the range of about 850°C to 950°C.

[0119] The present invention further provides a method for producing a negative electrode composite, the method comprising: (i) passing silicon nanoparticles, a binder, and one or more carbon sources through a first agglomeration step, such as a spray drying step, to form a first composite in which the silicon nanoparticles are encapsulated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers, and the coated silicon nanoparticles are held in a carbon matrix; (ii) treating the first composite of step (i) and the binder in a coating step, e.g., a spray drying step, to produce a composite having an organic-containing shell; (iii) heat treating the composite and shell of step (ii) to convert the organic material in the shell to carbon, thereby producing an anode composite comprising a plurality of encapsulated silicon nanoparticles in a carbon matrix and provided with an amorphous carbon shell, wherein the amorphous carbon outer shell has a thickness of about 10 nm to 5000 nm.

[0120] In one form of the invention, an additional heat treatment step is provided to convert the binder employed in the first aggregation step to carbon, which forms part of the carbon matrix of the first composite.

[0121] The silicon nanoparticles can be provided in a size range of about 20 nm to 300 nm. In one embodiment of the present invention, to provide the silicon nanoparticles in step (i), the silicon material is milled, for example, in a non-aqueous solvent to avoid the production of SiO2 and other relatively hazardous by-products, such as SiH4 and H2.

[0122] In one form, the first step, milling, is a grinding step, for example, performed in one or more bead mills.

[0123] The carbon matrix, in one form, (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m 2 / g~500m 2 / g surface area (BET) It has.

[0124] The carbon matrix may be provided in the form of an amorphous carbon matrix, a crystalline carbon matrix, or a combination of both amorphous and crystalline carbon matrices. The carbon matrix may include, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

[0125] The amorphous carbon shell, in one form, (i) a density greater than about 1.5 g / cc; and / or (ii) Approximately 45m 2 / g, e.g., less than 10m 2 / g surface area (BET) It has.

[0126] In one form, the amorphous carbon shell further comprises an additional material from the group of titanium, aluminum, zirconium, niobium, and selenium, or oxides thereof.

[0127] In a further aspect of the invention, the negative electrode composite of step (iii) is subjected to a further heat treatment step, whereby its surface area is increased to 5 m 2 / g。 Prior to the further heat treatment step, the negative electrode composite of step (iii) is in one form subjected to a hydrocarbon, which can be provided, for example, in the form of 1 to 5 wt % dihydroxynaphthalene.

[0128] In one embodiment of the present invention, an aqueous solvent is used in at least the heat treatment in step (iii) and the further heat treatment. Preferably, the heat treatment in step (iii) and the further heat treatment are each performed by dissolving dihydroxynaphthalene in water, for example, dihydroxynaphthalene can be dissolved in water at a temperature higher than about 70°C.

[0129] The heat treatment, additional heat treatment and further heat treatment of step (iii), each of which may be provided in the form of, for example, pyrolysis, preferably converts any binder present into amorphous carbon.

[0130] 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.

[0131] An additional heat treatment, which converts the binder employed in the first aggregation step into carbon and forms part of the carbon matrix of the first composite, is carried out at a temperature in the range of about 500°C to 700°C.

[0132] The further heat treatment step is carried out at a temperature in the range of about 800°C to 1000°C, for example in the range of about 850°C to 950°C.

[0133] FIG. 1 illustrates a process 10 according to a first embodiment of the present invention for producing a composite material 12. In a first step, a mixture 14 of silicon nanoparticles 16, a binder, such as 1,5-dihydroxynaphthalene (DHN), and one or more of graphite, graphene, carbon nanotubes, and carbon fibers 18 is subjected to a first aggregation 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 the graphite, graphene, carbon nanotubes, and carbon fibers 18, resulting in coated silicon nanoparticles 24 held in a carbon matrix 26. The binder employed in the aggregation step 20 may be provided in the form of a carbon source (free of Cl, Br, and / or S), such as pitch, glucose, sucrose, and phenol-formaldehyde resin.

[0134] The silicon nanoparticles 16 are provided in a size range of approximately 20 nm to 300 nm.

[0135] First composite 22 may then be subjected to a heat treatment step 28 (referred to elsewhere herein as an additional heat treatment step, as it is not described as being present in all embodiments of the present invention), e.g., pyrolysis at a temperature in the range of about 500°C to 700°C, which converts the binder employed in aggregation step 20 fully or partially to carbon, providing heat-treated first composite 30. If the binder used in aggregation 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, described below as resulting from the heat treatment step of the intermediate composite).

[0136] The first composite, whether it is first composite 22 (not heat treated) or first composite 30 (heat treated), may conveniently be referred to as a Si@C composite or material.

[0137] In what is referred to elsewhere herein as the second step, the first composite 22 or 30 is subjected to a coating step 32 with a binder, such as 1,5-dihydroxynaphthalene (DHN), which produces an intermediate composite 34 having an organic shell 36 formed about the first composite 30. Because the first composite 22 or 30 has a relatively large surface area (as described below), its coverage with the organic shell 36 is easily achieved by a simple mixing / spray-drying agglomeration technique.

[0138] In what is referred to elsewhere herein as the third step, intermediate composite 34 is then subjected to a heat treatment step 38, e.g., pyrolysis at a temperature range of about 700°C to 1100°C, which completely converts the 1,5-dihydroxynaphthalene (DHN) binder employed in coating step 32 to amorphous carbon, thereby providing composite material 12. Composite material 12 consists of a plurality of silicon nanoparticles 24 encapsulated in a carbon matrix 26, surrounded by a heat-treated amorphous carbon shell 40.

[0139] The amorphous carbon shell 40 has a density greater than about 1 g / cc and / or a viscosity greater than about 45 m 2 / g, e.g., less than 10m 2 The composite material of the present invention has a surface area of ​​less than 1 / g. The composite material may have one or more additives of 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 contemplated that the composite material of the present invention may include the deposition of additional thin films on the shell 40. For example, an alumina layer of less than about 100 nm may be deposited thereon by atomic layer deposition.

[0140] The thick shell 40 is understood by applicants to reduce or prevent outward expansion of the composite material 12 during lithiation.

[0141] The binder employed in the first aggregation step 20 and the coating step 32 may be the same, however, the inventors have found that it is preferable for the carbon from the binder employed in the coating step 32 to be denser after heat treatment than the carbon obtained from the binder employed in the first aggregation step 20.

[0142] Composite material 12 may conveniently be referred to as a Si@C1@C2 composite or material.

[0143] In one form of the invention, silicon material is milled to provide silicon nanoparticles 16. For example, the silicon material is milled in a non-aqueous solvent such as IPA to avoid the production of SiO and other relatively hazardous by-products, such as SiH and H. Milling can be performed as a grinding step, for example, in one or more bead mills.

[0144] The carbon matrix 26 of the first composite 28 or 30 has a density of less than about 1.5 g / cc, a porosity of greater than about 65%, and a surface area of ​​less than about 10 m 2 / g~500m 2 / g, e.g., about 40 m 2 / g~50m 2 / g. The high porosity is understood to be brought about by the presence of one or more of graphite, graphene, carbon nanotubes, and carbon fibers. The high surface area is understood to be a result of the particular carbon source utilized and / or the relatively low temperature pyrolysis employed.

[0145] Although not shown in FIG. 1, in one embodiment of the present invention, a further heat treatment step, e.g., pyrolysis, at a temperature in the range of about 800° C. to 1000° C., e.g., about 850° C. to 950° C., is applied to the composite material 12, thereby increasing its surface area to 10 m 2 / g or less, e.g., 5m 2 / g or less. Prior to the further heat treatment step, a hydrocarbon is added to the composite material 12, for example, the hydrocarbon being provided in the form of, for example, 1-5 wt % 1,5-dihydroxynaphthalene (DHN). This addition, for example, of DHN, and the further heat treatment step, results in a further composite or material that may conveniently be referred to as Si@C1@C2@C3.

[0146] An additional screening step (also not shown) may be applied to either the intermediate composite 34 or the composite material 12, or both, to aid in homogenizing the materials and reducing the surface area.

[0147] As described herein above, an aqueous solvent is utilized in at least the heat treatment of step (iii) and the further heat treatment, each of which preferably involves dissolving the dihydroxynaphthalene in water, for example at a temperature above about 70°C.

[0148] The process of the present invention can be better understood by reference to the following non-limiting examples. [Example]

[0149] Example 1 Targa exfoliated graphite The applicants have developed a unique exfoliated graphite (which the applicants refer to as Talga HSA) for multiple applications, which is described in detail in International Patent Application PCT / GB2018 / 052095 (WO 019 / 020999), the entire contents of which are incorporated herein by reference.

[0150] The applicant's HSA has enlarged gaps between the graphene layers in the graphite, which makes it easier for the graphene layers to peel off from the HSA compared to regular graphite, and makes it easier to produce few-layer graphene (FLG) during bead milling.

[0151] Full-cell data for graphite and silicon-containing materials The results of the full-cell tests are shown in Figures 2, 3, 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 of both Si@C and Si@C1@C2 is approximately 60%. The weight ratio is C=2C1=2C2, derived from the thermal decomposition of 1,5-dihydroxynaphthalene.

[0152] All full-cell tests were performed using the same protocol: charge cycles 1 and 2 to 4.2 V at C / 10 and then maintain 4.2 V until C / 100; discharge cycles 1 and 2 to 3.0 V at C / 10 and then maintain 4.2 V until C / 10; discharge cycles 1 and 2 to 3.0 V at C / 10 and then maintain 4.2 V until C / 10; discharge cycles 2 and 3.0 V at C / 2. The cathode used was NMC111. N / P = 1.05-1.10.

[0153] Coin Cell Test When an additional coating is applied to Si@C (Si@C-G2), the full cell life at 80% capacity retention increases from 150 to 300 cycles. Si@C-G1: One coating. Si@C-G2: Two coatings. The test was performed with an electrode density of 1.3 g / cm. 3 The test was performed on a coin cell battery. The conditions were as follows: First cycle: Charge at C / 10 to 4.2 V, cutoff current at C / 100; discharge at C / 10 until the voltage reached 3.0 V. Other cycles: Charge at C / 2 to 4.2 V, cutoff current at C / 10; discharge at C / 2 until the voltage reached 3.0 V. Cathode: NMC111, N / P = 1.03-1.1.

[0154] Pouch Cell Test When further coating is applied to Si@C, the full cell cycle life at 80% capacity retention is 1.3g / cm 3 The test was performed on a single-layer pouch cell for 500 cycles. The conditions were as follows: First cycle: Charge at C / 10 to 4.2 V, cutoff current at C / 100; discharge at C / 10 until the voltage reached 3.0 V. Other cycles: Charge at C / 2 to 4.2 V, cutoff current at C / 10; discharge at C / 2 until the voltage reached 3.0 V. Cathode: NMC111. N / P = 1.03-1.1.

[0155] Further improvements (binder, calendaring, composite material, etc.) were made to the second-coated Si@C to achieve an electrode density of 1.5 g / cm 3 A full cell life of 500 cycles with 80% capacity retention was achieved for a monolayer pouch cell. The conditions were as follows: First cycle: Charge at C / 10 to 4.2V, cutoff current at C / 100; discharge at C / 10 until the voltage reached 3.0V. Other cycles: Charge at C / 2 to 4.2V, cutoff current at C / 10; discharge at C / 2 until the voltage reached 3.0V. Cathode: NMC111. N / P = 1.03-1.1. This data meets the customer's basic requirements and the current market Si performance.

[0156] Example 2 Testing performed in accordance with the method of the present invention provides the following details regarding the pyrolysis temperatures employed in the additional heat treatment (referred to in this example as "first pyrolysis" to indicate that this is the first pyrolysis step employed in the method performed in this example) and the heat treatment (referred to in this example as "second pyrolysis" to indicate that this is the second pyrolysis step employed in the method performed in this example). The surface area (BET, m) after the additional heat treatment (first pyrolysis) and the heat treatment (second pyrolysis) 2 / g) are shown in Table 1 below: [Table 1]

[0157] Using Sample 3 (the lowest surface area / BET sample from Table 1) as the starting material, the surface area results after further heat treatment (denoted in this example as "Third Pyrolysis" to indicate that this was the third pyrolysis step employed in the method carried out in this example) are shown in Table 2 below: [Table 2]

[0158] Surface area: 40m 2 / g~50m 2 If the surface area (BET) of the final product (Si@C1@C2@C3) after further thermal treatment (third pyrolysis) can be controlled between 0.1 and 0.2 m / g, the surface area (BET) of the final product (Si@C1@C2@C3) after further thermal treatment (third pyrolysis) can be controlled between 0.1 and 0.2 m / g. 2 It has been determined by the applicant that the solubility can be as low as 45m / g. 2 The surface area / BET results after further heat treatment (third pyrolysis) using a starting material with a surface area (BET) of 1000 / g are shown in Table 3 below: [Table 3]

[0159] It is envisioned that the spray dryers described herein may be advantageously replaced by, for example, an erupted fluidized bed system and / or spray pyrolysis without departing from the scope of the present invention.

[0160] As can be seen with reference to the above description, the composite materials and methods of manufacture of the present invention offer one or more advantages when compared to the prior art, including the use of at least a shell of a thickness understood to reduce or prevent outward expansion during lithiation. The mechanical stability of this shell may be potentially complemented by the incorporation of materials containing titanium, aluminum, zirconium, niobium, selenium, and / or tin, while providing an internal carbon matrix with a relatively high porosity, thereby accommodating the expansion that occurs within the composite.

[0161] Such modifications and variations as would be apparent to one skilled in the art are within the scope of the present invention.

Claims

1. 1. A silicon-containing composite material comprising: a plurality of silicon nanoparticles disposed within a carbon matrix; and an amorphous carbon shell surrounding the silicon nanoparticles and the carbon matrix, wherein the amorphous carbon shell has a thickness of about 10 nm to 5000 nm.

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

3. (i) the silicon nanoparticles are provided by milling silicon material; or (ii) The silicon nanoparticles are SiO ２ and optionally SiH ４ and H ２ The silicon material is milled in a non-aqueous solvent to avoid the generation of relatively dangerous by-products such as The silicon-containing composite material according to claim 1 or 2.

4. The carbon matrix is (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m ２ / g to 500m ２ / g surface area (BET) The silicon-containing composite material according to any one of claims 1 to 3, comprising:

5. 5. The silicon-containing composite material of claim 1, wherein the carbon matrix comprises, in addition to silicon nanoparticles, one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers.

6. 6. The silicon-containing composite material according to any one of claims 1 to 5, 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. 7. The silicon-containing composite material of 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. 8. The silicon-containing composite material of any one of claims 5 to 7, wherein the composite material has elastic properties imparted by the presence of one or more of graphite, graphene, graphite nanoplates, carbon nanotubes, and carbon fibers disposed within the amorphous carbon matrix.

9. The silicon-containing composite material of any one of claims 1 to 8, wherein the amorphous carbon shell has a density greater than about 1.5 g / cc.

10. The surface area (BET) of the silicon-containing composite material is (i) Approximately 10m ２ / g or less; or (ii) Approximately 5m ２ / g or less The silicon-containing composite material according to any one of claims 1 to 9, wherein

11. 11. The silicon-containing composite material of any one of claims 1 to 10, wherein the amorphous carbon shell further comprises an additional material from the group comprising titanium, aluminum, zirconium, niobium and selenium, or oxides thereof.

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

13. (i) passing silicon nanoparticles, a binder, and one or more carbon sources through a first aggregation step to form a first composite in which the silicon nanoparticles are encapsulated with one or more of graphite, graphene, carbon nanotubes, and carbon fibers, with the coated silicon nanoparticles being held in a carbon matrix; (ii) treating the first composite of step (i) and the binder in a coating step to produce a composite having an organic-containing shell; (iii) heat treating the composite and shell of step (ii) to convert the organic material in the shell to carbon to produce a composite material comprising a plurality of encapsulated silicon nanoparticles in a carbon matrix and provided with an amorphous carbon shell; Equipped with The method for producing a composite material, wherein the amorphous carbon shell has a thickness of about 10 nm to 5000 nm.

14. 14. The method of claim 13, wherein an additional heat treatment step is provided to convert the binder employed in the first aggregation step to carbon and form part of the carbon matrix of the first composite.

15. 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. (i) in a first step, grinding a silicon material to provide silicon nanoparticles in step (i); or (ii) SiO ２ and other relatively dangerous by-products, such as SiH ４ and H ２ In a first step, the silicon material is milled in a non-aqueous solvent to provide silicon nanoparticles in step (i), so as to avoid the formation of The method according to any one of claims 13 to 15.

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

18. The carbon matrix is (i) a density of less than about 1.5 g / cc; (ii) a porosity greater than about 65%; and / or (iii) Approximately 10m ２ / g to 500m ２ / g surface area (BET) The method according to any one of claims 13 to 17, comprising:

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

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

22. The method of any one of claims 13 to 21, wherein the amorphous carbon shell further comprises an additional material from the group consisting of titanium, aluminum, zirconium, niobium and selenium, or oxides thereof.

23. The composite material of step (iii) is subjected to a further heat treatment step, whereby its surface area is increased to 5 m ２ The method according to any one of claims 13 to 22, wherein the solubility of hydroxyl group in the hydroxyl group is reduced to less than 1 / g.

24. 24. The method of claim 23, wherein the composite material of step (iii) is subjected to a hydrocarbon prior to the further heat treatment step.

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

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

27. The heat treatment of step (iii) and the further heat treatment each comprise: (i) dissolving 1,5-dihydroxynaphthalene in water; or (ii) dissolving 1,5-dihydroxynaphthalene in water at about 70°C or higher 27. The method of any one of claims 23 to 26, comprising:

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

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

30. 30. The method of any one of claims 14 to 29, wherein an additional heat treatment to convert the binder employed in the first aggregation step to carbon and form part of the carbon matrix of the first composite is carried out at a temperature in the range of about 500°C to 700°C.

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

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

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

Images