Silicon-carbon composite materials and methods

Abstract

To provide electroactive materials with a conductive carbon coating.SOLUTION: The invention provides methods for providing composite particles with a carbon coating, and core-shell particulate material obtained thereby. The methods comprise subjecting a plurality of precursor composite particles to a heat treatment by contact with a pyrolytic carbon precursor, so that an outer shell of a pyrolytic conductive carbon material is formed on the precursor composite particles, where the heat treatment is carried out at a temperature of 700°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for preparing core-shell composite particles comprising electroactive materials such as carbon and silicon.The present invention also relates to particulate materials comprising silicon and carbon and having a core-shell structure. [Background technology]

[0002] Rechargeable metal-ion batteries are widely used in portable electronic devices such as mobile phones and laptops. Rapid developments in electric and hybrid vehicle technology have also created a large new market for high-performance secondary batteries. Metal-ion battery anodes typically have a metallic current collector provided with a layer of electroactive material (defined here as a material capable of inserting and releasing metal ions during battery charging and discharging). When a metal-ion battery is charged, metal ions are transported from the metal-ion-containing cathode layer through the electrolyte and inserted into the anode material.

[0003] Conventional lithium-ion batteries use graphite as the electroactive material in the anode. When a graphite-containing anode is charged, lithium is intercalated between the graphite layers, according to the empirical formula Li x Materials with C6 (where x is greater than 0 and less than or equal to 1) are formed. This means that in lithium-ion batteries, graphite has a maximum theoretical capacity of 372 mAh / g, but the practical capacity is somewhat lower (about 340 to 360 mAh / g). The development of portable electronic devices and electric vehicles with high energy demands means that there is a need for electroactive materials that offer an improvement over graphite's gravimetric and volumetric capacities.

[0004] Materials such as silicon, tin, and germanium have significantly higher intercalation capacity for lithium atoms than graphite. In particular, silicon, due to its extremely high lithium capacity, has been identified as a promising alternative to graphite for the production of rechargeable metal-ion batteries with high gravimetric and volumetric capacities (see, for example, Winter, M. et al., "Intercalation Electrode Materials for Rechargeable Lithium Batteries," Adv. Mater. 1998, 10, No. 10). Silicon has a theoretical maximum specific capacity of about 3,600 mAh / g at room temperature in lithium-ion batteries (Li 15 (Based on Si4).

[0005] Silicon's high specific capacity is accompanied by large volume changes during charge and discharge. The intercalation of lithium into bulk silicon increases the volume of the silicon material by up to 400% of its original volume. Repeated charge-discharge cycles therefore create significant mechanical stresses on the silicon material, resulting in fracture and delamination of the silicon anode material and deformation of other battery components. Silicon particle shrinkage during delithiation can lead to loss of electrical contact between the anode material and the current collector. Another problem is the formation of a solid-electrolyte interface (SEI) layer on the nascent silicon surface during the initial charge cycle as a result of electrolyte deposition. This SEI layer lacks sufficient mechanical durability to accommodate the silicon's expansion and contraction and delaminates from the silicon surface. The newly exposed silicon surface then leads to further electrolyte decomposition, increasing the SEI layer thickness and resulting in irreversible lithium consumption. These failure mechanisms together result in an unacceptable loss of electrochemical capacity over successive charge and discharge cycles.

[0006] Many approaches have been proposed to overcome the problems associated with the volume changes observed during charging of silicon-containing anodes. One approach is to use some form of microstructured silicon as the electroactive material. Microstructured silicon structures with cross sections less than about 150 nm, such as silicon films and silicon nanoparticles, are more resistant to volume changes during charge and discharge than silicon particles in the micron-size range. However, in their unaltered forms, neither is particularly suitable for commercial-scale applications. Nanoscale particles are difficult to prepare and handle, and silicon films do not offer sufficient bulk capacitance. Additionally, the relatively high surface area of ​​microstructured silicon results in unacceptable capacity loss during the first charge cycle due to excessive SEI formation.

[0007] To address the lack of available silicon-containing electroactive materials, the present inventors have developed a class of composite particles in which silicon is deposited within the pores of a porous conductive material (e.g., a carbon-containing porous material such as activated carbon). The median pore diameter is approximately 5 to 10 nm or less. By carefully controlling the total pore volume, the pore size distribution of the conductive material, and the weight ratio of silicon to the conductive material, it has been determined that it is possible to obtain materials with controlled expansion characteristics, limited SEI formation, and high reversible capacity retention. However, further improvements in the properties of these materials can be obtained by reducing the surface area. Reducing the surface area has several advantages, including further reduction in SEI formation and a reduction in the amount of binder required to form the electrode active layer. Excess binder can contribute to reduced rate performance. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, there is a need for an electroactive material having composite particles of the aforementioned type, while at the same time having a conductive carbon coating that helps reduce the particle surface area, improve the composite's kinetic properties, and provide improved electrical conductivity for the electrode active layer having core-shell particles. However, the aforementioned composite particles are characterized by an extremely fine microstructure, with fine domains of silicon and fine pore walls. The fine microstructure of the composite particles is crucial for their function as electroactive materials in anodes, but is incompatible with conventional techniques for applying conductive carbon coatings. [Means for solving the problem]

[0009] In a first aspect of the present invention, there is provided a method for preparing core-shell composite particles, comprising the steps of: (a) Below: (i) a porous carbon skeleton having micropores and / or mesopores, the total pore volume of the micropores and mesopores being at least 0.4 cm as measured by gas adsorption; 3 / g, and the PD of the porous carbon skeleton 50 a porous carbon skeleton having a pore diameter of 10 nm or less; and (ii) a plurality of nanoscale electroactive material domains arranged with said porous carbon framework; providing a plurality of precursor composite particles comprising: (b) heat-treating the plurality of precursor composite particles by contacting them with a pyrolytic carbon precursor, wherein an outer shell of pyrolytic conductive carbon material is formed on the precursor composite particles, the heat-treating being at a temperature of 700°C or less; A method is provided, comprising:

[0010] Important to the method of the present invention is that the pyrolysis of the pyrolytic carbon precursor is carried out at a temperature of 700°C or less. Conventional processes for forming pyrolytic carbon coatings typically require temperatures exceeding 700°C, e.g., in the range of 800°C to 1200°C. However, it has been found that the fine microstructure of the precursor composite particles is incompatible with such high temperatures and undergoes various thermally induced changes, including heat treatment and crystallization processes. Heat treatment of the particle microstructure can lead to the elimination of void spaces that accommodate the expansion of electroactive materials, such as silicon. Furthermore, because amorphous silicon exhibits good properties as an electroactive material, crystallization of silicon is problematic. Furthermore, excessive temperatures during the formation of the pyrolytic carbon coating can lead to the formation of undesirable compounds, such as silicon carbide and silicon nitride, that have no or low electrochemical activity. Taken together, these processes are detrimental to the properties of the carbon-coated particles as electroactive materials in lithium-ion battery anodes.

[0011] It has surprisingly been found that low temperature carbon coating processes are effective in providing carbon coatings with sufficient graphitic properties to provide the necessary electrical conductivity for the coating, but do not adversely affect the structure underlying the precursor composite particle core. Thus, the method of the present invention provides an effective method for preparing core-shell composite particles with enhanced properties as electroactive materials.

[0012] Another advantage of the method of the present invention is that the surface area and pore volume are each 100 m 2 / g and above 0.1 mL / g of material. In open-void systems, the carbon partially penetrates into the pore structure, allowing conductive tendrils to extend from the pyrolytic carbon coating into the interior of the particle. The coating combined with these conductive tendrils has the effect of shortening the average electron transport length in the core-shell composite particles. Instead, electrons can be transported to or from the current collector through the highly conductive carbon matrix during lithium insertion and desorption.

[0013] The heat treatment temperature in step (b) is preferably less than 700° C. The heat treatment may be carried out at a temperature of, for example, 680° C. or less, 660° C. or less, 650° C. or less, 640° C. or less, 620° C. or less, or 600° C. or less.

[0014] The lower limit of the heat treatment temperature in step (b) is not limited. However, in general, the deposition rate of the carbon coating increases with increasing temperature. The required minimum temperature also depends on the type of carbon precursor used in the deposition step. The heat treatment temperature in step (b) is preferably at least 300°C or higher, for example, at least 500°C or higher, at least 520°C or higher, at least 540°C or higher, at least 560°C or higher, or at least 580°C or higher.

[0015] The carbon precursor may be contacted with the precursor composite particles in one of two ways: 1. Steam system contact, 2 Contact from liquids or solutions.

[0016] Some carbon precursors are suitable for only one of these two contacting methods.

[0017] Certain other carbon precursors are suitable for both contacting methods, depending on the temperature at which the contacting occurs. These carbon precursors may be in liquid form at low temperatures and sublimate into vapor precursors above a set temperature before pyrolyzing at high temperatures. They may be applied as liquids to the precursor composite particles, if desired. Examples of such compounds include camphor, anthracene, pentacene, and metal phthalocene complexes.

[0018] The pyrolytic carbon precursor may be contacted with the precursor composite particles as a vapor, preferably as a hydrocarbon vapor, during the heat treatment step. Suitable hydrocarbons include polycyclic hydrocarbons containing 10 to 25 carbon atoms and, optionally, 1 to 3 heteroatoms, optionally selected from naphthalene, substituted naphthalenes such as dihydroxynaphthalene, anthracene, tetracene, pentacene, fluorene, acenaphthene, phenanthrene, fluorene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone, and alkyl-substituted derivatives thereof. Suitable pyrolytic carbon precursors also include bicyclic monoterpenoids, optionally selected from camphor, borneol, eucalyptol, camphene, carene, sabinene, thujene, and pinene. Suitable pyrolytic carbon precursors also include C1-C 10 or C2~C 10 and optionally, the hydrocarbon is selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, and arenes, such as methane, ethylene, propylene, acetylene, and cyclohexane. Other suitable pyrolytic carbon precursors include phthalocyanine, sucrose, starch, graphene oxide, reduced graphene oxide, pyrene, perhydropyrene, triphenylene, tetracene, benzopyrene, perylene, coronene, and chrysene. Preferably, the carbon precursor comprises acetylene, and more preferably, the carbon precursor is acetylene.

[0019] The hydrocarbon vapor may be contacted with a transition metal catalyst at a temperature of at least 500°C prior to contact with the precursor composite particles. The transition metal catalyst may be selected from nickel, iron, cobalt, copper, and mixtures thereof, most preferably nickel. The transition metal catalyst may be in the form of a mesh, which is disposed in the flow path of the vapor prior to contact with the precursor composite particles.

[0020] Alternatively, the transition metal catalyst may be disposed on the surface of the precursor composite particles. For example, prior to step (b), gaseous nickel carbonyl may be thermally decomposed to deposit nickel on the surface of the precursor composite particles. If necessary, the nickel deposition may be carried out in the same reactor as the heat treatment described above. A suitable temperature for the decomposition of nickel carbonyl is about 220 to 250°C. If necessary, after the deposition of the carbon coating, the nickel may be converted back to nickel carbonyl vapor by contacting the coated particles with carbon monoxide gas, for example, at a temperature of 50 to 60°C. Thus, the nickel carbonyl gas may be recycled.

[0021] Transition metal catalyzed processing offers further improvements in the formation of pyrolytic carbon coatings at low temperatures, and the recovery and recycling of nickel in the form of nickel carbonyl gas makes the process cost-effective.

[0022] Alternatively, the pyrolytic carbon precursor may be contacted with the precursor composite particles in liquid form. In particular, the precursor composite particles may be contacted with a dispersion or solution of the pyrolytic carbon precursor in a solvent, after which the solvent is removed to provide precursor composite particles coated with the pyrolytic carbon precursor prior to heat treatment. Suitable pyrolytic carbon precursors for contacting the precursor composite particles in liquid form include polymers and oligomers containing a carbon-containing backbone, such as polyvinylpyrrolidone (PVP) or copolymers of vinylpyrrolidone with one or more other ethylenically unsaturated monomers.

[0023] Carbon precursor compounds that can be deposited from solution include polydopamine, poly(diallyldimethylammonium chloride) (PDDA), citric acid, mixtures containing citric acid and ethanol, polyacrylonitrile (PAN), PAN derivatives, polymerized polypyrrole (PPy) composites, melamine resins such as melamine-formaldehyde resin, pitch, glucose, sucrose, phenolic resins, polyvinyl alcohol (PVA), polyacrylic acid (PAA), resorcinol-formaldehyde resin, poly(methyl methacrylate) (PMMA), camphor, anthracene, pentacene, and metal phthalocene complexes.

[0024] If desired, a dopant material may be introduced into the carbon coating. The dopant material may be introduced into the coating by incorporating a dopant precursor. Preferably, the dopant is boron or phosphorus. Doping the pyrolytic carbon coating further increases the electrical conductivity of the coating. Incorporation of a dopant material into the carbon coating also preferably dopes the electroactive material domains, further increasing their electrical conductivity.

[0025] When the pyrolytic carbon precursor is provided as a vapor, it may be used in conjunction with a gaseous precursor of the dopant material. When the dopant is boron, suitable gaseous dopant precursors include borane (BH), diborane (BH), triisopropyl borate ([(CH)CHO]B), triphenylborane ((CH)B), and tris(pentafluorophenyl)borane (CF)B, with diborane being preferred. When the dopant is phosphorus, a suitable gaseous dopant precursor is phosphine (PH).

[0026] Alternatively, if the pyrolytic carbon precursor is a volatile liquid, the dopant may be introduced as a volatile liquid. For boron, a preferred dopant precursor is triethylborane. For phosphorus, a preferred dopant precursor is triethylphosphine.

[0027] When the pyrolytic carbon precursor is supplied as a solution or suspension, suitable boron dopant precursors include boric acid (HBO), sodium tetraborate (Na[BO(OH)].8HO, borazine (BHN), and ammonia borane (BHN), with the preferred source being boric acid. When the dopant is phosphorus, suitable precursors include phosphoric acid (HPO), or phosphonates and phosphonic acids.

[0028] Another option when using liquid, solution phase, or suspended pyrolytic carbon precursors is to For example, the dopant may be introduced into the reactor as a gas in an inert gas stream fed to the headspace of the reactor. Suitable gaseous dopant precursors include those previously described.

[0029] The outer shell of the conductive carbon material formed by the method of the present invention preferably has a thickness after pyrolysis of 10 nm or less, 5 nm or less, 4 nm or less, 2 nm or less, or 1 nm or less.

[0030] The outer shell of the conductive carbon material deposited by the method of the present invention may be amorphous, crystalline, or have both amorphous and crystalline domains. Preferably, the carbon coating is amorphous carbon. Preferred types of crystalline carbon coatings are graphite and graphene.

[0031] The porous carbon framework has a three-dimensionally interconnected open pore network, which comprises micropores and / or mesopores, and optionally contains a small amount of macropores. Following conventional IUPAC terminology, the term "macropores" is used herein to refer to pores with a diameter of less than 2 nm, the term "mesopores" is used to refer to pores with a diameter of 2 to 50 nm, and the term "macropores" is used to refer to pores with a diameter of more than 50 nm.

[0032] References to the volumes of micropores, mesopores, and macropores in a porous carbon skeleton, as well as references to the distribution of pore volumes in a porous carbon skeleton, are intended to define the pore structure of the porous carbon skeleton when separation is taken into account. Pore occupation by nanoscale electroactive material domains results in a measurable reduction in pore volume; however, this is not taken into account for purposes of defining the pore structure of the porous carbon skeleton.

[0033] Using the quenched solid density functional theory (QSDFT) according to the standard method specified in ISO15901-2 and ISO15901-3, -6 Nitrogen gas adsorption at a relative pressure of p / p0 (or less) was used to determine the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores. Nitrogen gas adsorption is a technique for characterizing the porosity and pore diameter distribution of a material by condensing a gas into the pores of a solid. As the pressure is increased, the gas condenses first into the smallest diameter pores until a saturation point is reached where all pores are filled with liquid. The nitrogen gas pressure is then gradually reduced, allowing the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them determine the pore volume and pore diameter distribution. Suitable instruments for measuring pore volume and pore diameter distribution by nitrogen gas adsorption include the TriStar II and TriStar II Plus porosity analyzers available from Micromeritics Instruments, Inc., USA, and the Autosorb IQ porosity analyzer available from Quantachrome Instruments, Inc.

[0034] Nitrogen gas adsorption is effective for measuring pore volume and pore size distribution for pores up to 50 nm in diameter, but is unreliable for pores with larger diameters. Therefore, for the purposes of this invention, the nitrogen adsorption method is used to measure pore volume and pore size distribution only for pores with diameters up to 50 nm (i.e., only micropores and mesopores). Similarly, PD 50is defined only for the total volume of micropores and mesopores.

[0035] The porous conductive particles have a thickness of at least 0.4 cm when measured by gas adsorption. 3 The porous carbon skeleton is characterized by the total volume of micropores and mesopores (i.e., the total pore volume in the range of 0 to 50 nm) in sieves per gram. Typically, the porous carbon skeleton contains both micropores and mesopores. However, it is not excluded to use a porous carbon skeleton that contains micropores but no mesopores, or a porous carbon skeleton that contains mesopores but no micropores.

[0036] More preferably, the total volume of the micropores and mesopores in the porous conductive particles is at least 0.45 cm 3 / g, at least 0.5 cm 3 / g, at least 0.55 cm 3 / g, at least 0.6 cm 3 / g, at least 0.65 cm 3 / g, at least 0.7cm 3 / g, at least 0.75 cm 3 / g, at least 0.8 cm 3 / g, at least 0.85 cm 3 / g, at least 0.9 cm 3 / g, at least 0.95 cm 3 / g, or at least 1 cm 3 / g. The use of conductive particles with high porosity is advantageous because it allows a greater amount of silicon to be accommodated within the pore structure.

[0037] The internal pore volume of the porous conductive particles is suitably capped at a value where the increased embrittlement of the porous conductive particles outweighs the benefit of the increased pore volume accommodating a greater amount of silicon. Preferably, the total volume of micropores and mesopores in the porous conductive particles is less than 2.2 cm. 3 / g or less, 2cm 3 / g or less, 1.8cm 3 / g or less, 1.6cm 3 / g or less, 1.5cm 3 / g or less, 1.45cm3 / g or less, 1.4cm 3 / g or less, 1.35cm 3 / g or less, 1.3cm 3 / g or less, 1.25cm 3 / g or less, or 1.2cm 3 / g or less.

[0038] In one example, the total volume of micropores and mesopores in the porous conductive particle is between 0.7 and 2.2 cm 3 / g range, 0.7 to 2 cm 3 / g range, 0.8 to 2 cm 3 / g range, 0.8 to 1.8 cm 3 / g range, 0.9 to 1.8 cm 3 / g range, 0.9 to 1.6 cm 3 / g range, 1 to 1.6 cm 3 / g range, or 1.1 to 1.6 cm 3 / g.

[0039] In another example, the total volume of micropores and mesopores in the porous conductive particle is between 0.4 and 0.75 cm 3 / g, 0.4 to 0.7 cm 3 / g, 0.4 to 0.65 cm 3 / g, 0.45 to 0.75 cm 3 / g, 0.45 to 0.7 cm 3 / g, 0.45 to 0.65 cm 3 / g, or 0.45 to 0.6 cm 3 / g.

[0040] In another example, the total volume of micropores and mesopores in the porous conductive particle is between 0.6 and 2 cm. 3 / g, 0.6 to 1.8 cm 3 / g, 0.7 to 1.8 cm 3 / g, 0.7 to 1.6 cm 3 / g, 0.8 to 1.6 cm 3 / g, 0.8 to 1.5 cm 3 / g, 0.8 to 1.4 cm 3 / g, 0.9 to 1.5 cm 3 / g, 0.9 to 1.4 cm 3 / g, or 1 to 1.4 cm 3 / g.

[0041] The pore size distribution of the porous conductive particles may be monomodal, bimodal, or multimodal. As used herein, the term "pore size distribution" refers to the distribution of pore sizes relative to the cumulative total internal pore volume of the porous conductive particles. Bimodal or multimodal pore size distributions are preferred, as the close proximity between micropores and larger diameter pores provides the advantage of efficient ion transport through the porous network to the nanoscale electroactive material domains.

[0042] Given the limitations of available analytical techniques, it is difficult to measure the pore volume and pore size distribution across the entire range of micropores, mesopores, and macropores using a single technique. When a porous carbon skeleton has macropores, the volume of pores with diameters in the range of greater than 50 nm and less than or equal to 100 nm can be measured by mercury porosimetry, which is preferably performed on a 0.3 cm 3 / g or less, or 0.20cm 3 / g or less, or 0.1cm 3 / g or less, or 0.05cm 3 / g or less. Although a small proportion of macropores is beneficial because it facilitates electrolyte access to the pore network, the advantages of the present invention are achieved by substantially containing the silicon in the micropores and smaller mesopores.

[0043] Pore ​​volumes measured by mercury porosimetry at pore sizes below 50 nm are ignored (as previously mentioned, mesopores and micropores are characterized using nitrogen adsorption techniques). Pore volumes measured by mercury porosimetry above 100 nm are assumed to be interparticle porosity for purposes of this invention and are ignored.

[0044] Mercury porosimetry is a technique for characterizing the porosity and pore diameter distribution of a material by applying various levels of pressure to a sample of the material immersed in mercury. The pressure required to force mercury into the pores of the sample is inversely proportional to the pore size. The values ​​obtained by the mercury porosimetry method described herein were obtained in accordance with ASTM UOP578-11, and the surface tension γ is 480 mN / m and the contact angle φ is 140° for mercury at room temperature. The density of mercury is 13.5462 g / cm at room temperature. 3 Many high-precision mercury porosimeters are commercially available, such as the AutoPore IV series of automated mercury porosimeters available from Micromeritics Instrument Corporation, USA. For a complete review of mercury porosimetry methods, see PA Webb and C. Orr, "Analytical Methods in Fine Particle Technology, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0."

[0045] It is understood that intrusion techniques such as gas adsorption and mercury porosimetry are only effective in determining the pore volume of pores accessible to nitrogen or mercury from the outside of the porous conductive particle. It is understood that the porosity values ​​specified herein represent the volume of open pores, i.e., pores accessible to fluids from the outside of the porous carbon skeleton. In determining the porosity value, pores that are completely surrounded and cannot be identified by nitrogen adsorption or mercury porosimetry are not taken into account. Similarly, any pore volume located in pores so small that they are below the detection limit by nitrogen adsorption is not taken into account.

[0046] The general term "PD" used in this application n "Pore diameter" refers to the pore diameter of n percent by volume, based on the total volume of micropores and mesopores. For example, the term "PD 90 The pore diameter is less than P 1represents the pore diameter at which 90% of the total micropore and mesopore volume is found, and PD 50 The pore diameter is the median pore diameter below which 50% of the total micropore and mesopore volume is found.

[0047] PD of porous carbon frameworks 90 The pore diameter may be 20 nm or less, or 15 nm or less. 90 The pore diameter of the porous carbon skeleton is 12 nm or less, 10 nm or less, 8 nm or less, or 6 nm or less. 90 The pore diameter is at least 3 nm, at least 3.2 nm, at least 3.5 nm, at least 3.8 nm, or at least 4 nm.

[0048] PD of porous carbon frameworks 30 The pore diameter is preferably 1.6 nm or less, 1.5 nm or less, 1.4 nm or less, 1.3 nm or less, 1.2 nm or less, 1.1 nm or less, or 1 nm or less. 30 The pore diameter is preferably at least 0.45 nm, at least 0.5 nm, at least 0.6 nm, or at least 0.7 nm.

[0049] Photodischarge of conductive multiporous particle scaffolds 50 The pore diameter is preferably 8 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2.5 nm or less, 2 nm or less, or 1.5 nm or less. 50 The pore diameter is at least 1 nm, at least 1.1 nm, or at least 1.2 nm. Thus, in the present invention, it is preferred that at least 50% of the total volume of micropores and mesopores within the conductive porous particle framework is in the form of pores with a diameter of less than 8 nm.

[0050] For the avoidance of doubt, macropore volume (pore diameters greater than 50 nm) is defined as PD 50 are not considered for purposes of determining value.

[0051] Typically, the precursor composite particles have a D in the range of 1 to 50 μm. 50 Optionally, the precursor composite particles may have a particle diameter D 50 The particle diameter may be at least 1.5 μm, at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm. If desired, the D of the precursor composite particles 50 The particle diameter may be 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, 15 μm or less, 12 μm or less, 10 μm or less.

[0052] For example, the precursor composite particles may have a D in the range of 1 to 25 μm, 1 to 20 μm, 2 to 25 μm, 2 to 20 μm, 2 to 18 μm, 3 to 20 μm, 3 to 18 μm, 3 to 15 μm, 4 to 18 μm, 4 to 15 μm, 4 to 12 μm, 5 to 15 μm, 5 to 12 μm, or 5 to 10 μm. 50 The precursor composite particles may have particle diameters within these size ranges and have the porosity and pore diameter distributions described herein. Precursor composite particles within these size ranges and having the porosity and pore diameter distributions described herein are ideally suited for preparing composite particles for use in metal-ion battery anodes. These particles provide core-shell composite particles with good dispersibility in slurries, structural robustness, high capacity retention over repeated charge-discharge cycles, and suitability for forming dense electrode layers of uniform thickness in the conventional 20 to 50 μm thickness range.

[0053] For the avoidance of doubt, the term "particle diameter" as used herein refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, and it is understood that particle volume includes the volume of any intra-particle pores. 50 " and "D 50 "Particle diameter" refers to the volume-based median particle diameter, i.e., the diameter below which less than 50% by volume of the particle population is found. 10 " and "D 10 "Particle diameter" refers to the 10 percent volume-based median particle diameter, i.e., the diameter below which less than 10 volume percent of the particle population is found. As used herein, the term "D 90" and "D 90 "Particle diameter" refers to the 90 percent volume-based median particle diameter, i.e., the diameter below which less than 90% by volume of the particle population is found.

[0054] Particle diameter and particle size distribution can be measured by standard laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that particles scatter light at angles that vary depending on the particle size, and that a collection of particles produces a scattered light pattern defined by intensity and angle that correlates to particle size distribution. Many laser diffraction instruments are commercially available for rapid and reliable particle size distribution measurements. Unless otherwise noted, particle size distribution measurements described or reported herein were measured using a conventional Malvern Instruments Malvern Mastersizer™ 3000 particle size analyzer. The Malvern Mastersizer™ 3000 particle size analyzer operates by shining a helium-neon gas laser beam through a transparent cell containing particles of interest suspended in an aqueous solution. The light beam striking the particles is scattered at angles inversely proportional to the particle size, and a photodetector array measures the light intensity at several predetermined angles. The intensities measured at different angles are processed by a computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values ​​reported herein are obtained using a wet dispersion of particles in distilled water. The particle refractive index is 3.50, and a dispersant index of 1.330 is used. The particle size distribution is calculated using the Mie scattering model.

[0055] D of precursor composite particles 10 The particle diameter is preferably at least 0.2 μm, at least 0.5 μm, at least 0.8 μm, at least 1 μm, at least 1.5 μm, or at least 2 μm. 10 Maintaining particle diameters of 0.2 μm or greater reduces the likelihood of undesirable agglomeration of submicron-sized particles, resulting in improved flow behavior and improved dispersibility of the composite particles formed.

[0056] D of precursor composite particles 90 The particle diameter is preferably 40 μm or less, or 30 μm or less, or 25 μm or less, or 20 μm or less. The use of larger precursor composite particles results in non-uniform packing of the core-shell composite particle product in the electrode active layer, thus preventing the formation of a dense electrode layer, particularly an electrode layer having a thickness in the range of 20 to 50 μm.

[0057] The precursor composite particles preferably have a narrow size distribution span. For example, the particle size distribution span (D 90 -D 10 ) / D 50 (defined as) is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. Maintaining a narrow size distribution span facilitates efficient packing of the core-shell composite particle product into a dense electrode layer.

[0058] The porous carbon skeleton preferably comprises at least 80% by weight carbon, more preferably at least 90% by weight carbon, more preferably at least 95% by weight carbon, and optionally at least 98% or at least 99% by weight carbon. The carbon may be crystalline carbon, amorphous carbon, or a mixture of amorphous and crystalline carbon. The porous carbon particles may be either hard or soft carbon particles and may be suitably obtained by known procedures including pyrolysis of polymers. Porous carbon particles of various specifications are available from commercial suppliers.

[0059] The precursor composite particles may have a range of different electroactive material loadings. For example, the amount of electroactive material in the precursor composite particles may be selected so that at least 25% and up to 80% or more of the internal pore volume of the porous carbon skeleton is occupied by the electroactive material. For example, the electroactive material may occupy 25% to 60%, 25% to 55%, 25% to 50%, 25% to 45%, or 25% to 40% of the internal pore volume of the porous carbon skeleton. Within these preferred ranges, the pore volume of the porous carbon skeleton effectively accommodates the expansion of the electroactive material during charge and discharge and avoids excess pore volume that does not contribute to the volumetric capacity of the core-shell composite particles. However, the amount of electroactive material is not so high that inadequate metal ion diffusion rates prevent effective lithiation or inadequate expansion volume creates mechanical resistance to lithiation.

[0060] The electroactive material in the precursor composite particles is preferably selected from silicon, tin, germanium, aluminum and mixtures thereof. A preferred electroactive material is silicon.

[0061] When the electroactive material is silicon, the preferred mass ratio of silicon to porous carbon skeleton is [0.5 × P 1 to 1.3 × P1]:1, where P1 is a dimensionless quantity having the size of the total pore volume of micropores and mesopores in the porous conductive particle, cm 3 / g unit (e.g., porous carbon particles 1.2 cm 3 / g, the total volume of micropores and mesopores is expressed as P1 = 1.2). This equation takes into account the density of silicon and the pore volume of the porous conductive particle, and determines the weight ratio of silicon that will occupy approximately 20% to 55% of the pore volume, assuming that the silicon is completely located within the internal pore volume.

[0062] In practice, it is preferred that at least 90 wt. %, more preferably at least 95 wt. %, and even more preferably at least 98 wt. % of the electroactive material in the precursor composite particles be located within the interior pore volume of the porous carbon skeleton, with very little or no silicon located on the exterior surface of the precursor composite particles. Preparing precursor composite particles by chemical vapor infiltration (CVI) is an effective method for ensuring that only very small amounts of the electroactive material are located on the exterior surface. This is because the kinetics of the CVI process favor the deposition of silicon into small pores, thus resulting in preferential deposition of silicon on the interior surfaces of the porous conductive particles.

[0063] The heat treatment in step (b) may suitably be carried out for a period of 1 to 3 hours.

[0064] Step (a) of providing a plurality of precursor composite particles may include contacting the electroactive material precursor with a plurality of porous carbon particles at a temperature of 200 to 800° C., thereby depositing the electroactive material within the pores of the carbon particles. The electroactive material may be selected from silicon, tin, germanium, aluminum, and mixtures thereof. A preferred electroactive material is silicon.

[0065] Suitable gaseous precursors for silicon deposition include silane (SiH4) and trichlorosilane (SiHCl3). The CVI method is particularly useful for preparing the electroactive materials disclosed herein because it causes minimal damage to the geometry of porous substrates.

[0066] Suitable silicon-containing precursors include silane (SiH), disilane (SiH), trisilane (SiH), tetrasilane (SiH), 10), or chlorosilanes such as trichlorosilane (HSiCl), or methylchlorosilanes such as methyltrichlorosilane (CHSiCl) or dimethyldichlorosilane ((CH)SiCl). Preferably, the silicon-containing precursor is a silane. Suitable tin-containing precursors include bis[bis(trimethylsilyl)amino]tin(II) ([(CHSi]N)Sn), tetraallyltin (((HC=CHCHSn), tetrakis(diethylamido)tin(IV) ([(CHN]Sn), tetrakis(dimethylamido)tin(IV) ([(CHN]Sn), tetramethyltin (Sn(CH)), tetravinyltin (Sn(CH=CH), tin(II) acetylacetonate (C), and the like. 10 H 14 04Sn), trimethyl(phenyl)tin (C6H5C≡CSn(CH3)3), and trimethyl(phenyl)tin (C6H5Sn(CH3)3). Preferably, the tin-containing precursor is tetramethyltin.

[0067] Suitable aluminum-containing precursors include aluminum tris(2,2,6,6-tetramethyl-3,5-heptanedionate) (Al(OCC(CH)CHCOC(CH))), trimethylaluminum ((CH)Al), and tris(dimethylamido)aluminum(III) (Al(N(CH))). Preferably, the aluminum-containing precursor is trimethylaluminum.

[0068] Suitable germanium-containing precursors include germane (GeH), hexamethyldigermanium ((CH)GeGe(CH), tetramethylgermanium ((CH)Ge), tributylgermanium hydride ([CH(CH)]GeH), triethylgermanium hydride ((CH)GeH), and triphenylgermanium hydride ((CH)GeH). Preferably, the germanium-containing precursor is germane.

[0069] The CVI process may also utilize gaseous precursors of the dopant material to deposit the doped electroactive material into the micropores and / or mesopores of the porous carbon skeleton. When the dopant is boron, suitable precursors include borane (BH), diborane (BH), triisopropyl borate ([(CH)CHO]B), triphenylborane ((CH)B), and tris(pentafluorophenyl)borane (CF)B, preferably borane. When the dopant is phosphorus, a suitable precursor is phosphine (PH).

[0070] The precursors may be used in pure form or, more commonly, as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the precursors may be used in an amount ranging from 0.5 to 20 vol%, or 1 to 10 vol%, or 1 to 5 vol%, based on the total volume of the precursor and inert carrier gas. The CVI process is preferably carried out at low partial pressures of the gaseous precursors, with the total pressure being at or near 101.3 kPa (i.e., atmospheric pressure, 1 atm), and the remaining partial pressure being brought to atmospheric pressure using an inert padding gas such as hydrogen, nitrogen, or argon. The presence of oxygen should be minimized according to conventional procedures operating in an inert atmosphere to prevent undesired oxidation of the deposited electroactive material. Preferably, the oxygen content is less than 0.01 vol%, more preferably less than 0.001 vol%, based on the total volume of the gas used in step (b).

[0071] The temperature of the CVI process is suitably selected to pyrolyze the precursor into the electroactive material. The CVI process is suitably carried out at a temperature in the range of 200 to 800°C, 400 to 700°C, 400 to 600°C, 400 to 550°C, 450 to 550°C, or 450 to 500°C. Preferably, the CVI process is carried out at a temperature in the range of 400 to 500°C, preferably 450 to 500°C.

[0072] The surface of electroactive materials deposited by CVI is reactive to oxygen, and when exposed to atmospheric oxygen, a native oxide layer forms. In the case of silicon, an amorphous silicon dioxide film quickly forms when the silicon surface is exposed to oxygen. The formation of the native oxide layer is reactive, and therefore requires careful process control to prevent overheating or combustion of the particulate material during fabrication. The presence of the native oxide layer can lead to irreversible capacity loss and reduced cycle life, and thus be detrimental to the performance of the electroactive material in lithium-ion batteries. Therefore, it is preferable that the electroactive material not be exposed to oxygen prior to deposition of the lithium-ion permeable filler material.

[0073] More preferably, step (b) of the method of the present invention further comprises step (b2) of contacting the surface of the deposited electroactive material with a passivating agent, wherein the electroactive material is not exposed to oxygen prior to contacting with the passivating agent, where a passivating agent is defined as a compound capable of modifying the surface of the electroactive material in such a way as to inhibit or prevent the formation of surface oxides.

[0074] Suitable passivating agents include compounds containing an alkene, alkyne, or carbonyl functionality, more preferably compounds containing a terminal alkene, terminal alkyne, or aldehyde group.

[0075] Suitable passivating agents include one or more of the following chemical formulas: (i) R-CH=CH-R; (ii) RC≡CR; (iii) O=CH-R; wherein R represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having from 1 to 20 carbon atoms, preferably from 2 to 10 carbon atoms, or two R groups in formula (i) form an unsubstituted or substituted hydrocarbyl ring structure containing from 3 to 8 carbon atoms. Particularly preferred passivators include compounds of one or more of the following formulae: (i) CH2=CH-R; (ii) HC≡CR; wherein R is defined as above. Preferably, R is unsubstituted.

[0076] Examples of suitable compounds include ethylene, propylene, 1-butene, butadiene, 1-pentene, 1,4-pentadiene, 1-hexene, 1-octene, styrene, divinylbenzene, acetylene, phenylacetylene, norbornene, norbornadiene, and bicyclo[2.2.2]oct-2-ene. Mixtures of different passivating agents may also be used.

[0077] It is understood that the alkene, alkyne, or carbonyl group of the passivating agent undergoes an insertion reaction with M—H groups (where M represents an atom of the electroactive material) on the surface of the electroactive material to form a covalently passivated surface that is resistant to oxidation by air. When silicon is the electroactive material, the passivation reaction between the silicon surface and the passivating agent may be understood as a form of hydrosilylation, as shown schematically below:

[0078] [ka] Other suitable passivating agents include compounds containing an active hydrogen atom bonded to oxygen, nitrogen, sulfur, or phosphorus. For example, the passivating agent may be an alcohol, amine, thiol, or phosphine. It is understood that the reaction of an -XH group with a hydroxyl group on the surface of the electroactive material results in the elimination of H and the formation of a direct bond between X and the surface of the electroactive material.

[0079] Suitable passivators in this category include compounds of the formula HX-R, where X represents O, S, NR, or PR, and each R is independently defined as above. The two R groups in formula (iv) may form an unsubstituted or substituted hydrocarbyl ring structure containing 3 to 8 carbon atoms. Preferably, X represents O or NH, and optionally, R represents a substituted aliphatic or aromatic group having 2 to 10 carbon atoms. The amine group may also be incorporated into a 4- to 10-membered aliphatic or aromatic ring structure, such as pyrrolidine, pyrrole, imidazole, piperazine, indole, or purine. The contacting step of the electroactive material with the passivator in step (b2) may be carried out at a temperature ranging from 25 to 700°C. For example, step (b2) may be suitably carried out within the suitable temperature ranges of step (b) and / or step (c) described herein. Preferably, step (c) is carried out at the same temperature as step (b2) or at a higher temperature than step (b2). For example, step (b2) may be carried out at a temperature in the range of 25°C to less than 500°C, and step (c) may be carried out at a temperature in the range of 500°C to 700°C.

[0080] After passivation of the surface of the electroactive material, a lithium ion permeable filler material may be deposited in step (c) as described above, and the R group of the passivating agent may be incorporated into the lithium ion permeable filler such that a covalent bond is formed between the lithium ion permeable filler and the surface of the electroactive material via the passivating agent.

[0081] When the lithium ion permeable filler material is a conductive pyrolytic carbon material, the same compound may function as both the passivator and the pyrolytic carbon precursor. For example, if styrene is selected as the pyrolytic carbon precursor, it also functions as the passivator, provided that the electroactive material is not exposed to oxygen before contacting the styrene. Therefore, step (c) may include depositing a conductive pyrolytic carbon material by a CVI process. The pyrolytic carbon precursor is the same as the passivator used in step (b2). In this case, passivation in step (b2) and deposition of the conductive carbon material in step (c) may be performed simultaneously, for example, at a temperature in the range of 500 to 700°C. Alternatively, passivation in step (b2) and deposition of the conductive carbon material in step (c) may be performed sequentially using the same material as the passivator and pyrolytic carbon precursor, provided that step (c) is performed at a higher temperature than step (b2). For example, step (b2) may be carried out at a temperature in the range of 25°C to less than 500°C, and step (c) may be carried out at a temperature in the range of 500°C to 700°C.

[0082] Alternatively, different compounds may be used as the passivation agent in step (b2) and the pyrolytic carbon precursor in step (c). For example, the electroactive material may first be contacted with a passivation agent in step (b2), followed by deposition of the conductive pyrolytic carbon material in step (c), where the pyrolytic carbon precursor used in step (c) is different from the passivation agent used in step (b2). For example, the passivation agent in step (b2) may be styrene, and the pyrolytic carbon precursor in step (c) may be a compound such as cyclohexane. Cyclohexane is a compound that can form a pyrolytic carbon material but cannot passivate the surface of the electroactive material. When the passivation agent and the pyrolytic carbon precursor are different materials, steps (b2) and (c) may be performed at the same temperature, for example, in the range of 500 to 700°C. Alternatively, step (c) may be performed at a higher temperature than step (b2). For example, step (b2) may be carried out at a temperature in the range of 25°C to less than 500°C, and step (c) may be carried out at a temperature in the range of 500°C to 700°C.

[0083] Another suitable passivating agent is ammonia. Step (b2) may therefore comprise contacting the surface of the deposited electroactive material with ammonia at a temperature in the range of 200 to 800°C, preferably in the range of 400 to 700°C. For example, when the passivating agent is ammonia, step (b2) may be carried out at the same temperature as that used in depositing the electroactive material in step (b). Thereafter, if necessary, the temperature may be increased to the range of 500 to 1,000°C to form a crystalline nitride surface (e.g., a nitride of formula SiN x (where x≦4 / 3) is formed. Thus, ammonia passivation provides another means of inhibiting oxidation of the electroactive material. Because substoichiometric silicon nitride is electrically conductive, this step also results in the formation of a conductive network that allows for more rapid charging and discharging of the electroactive material.

[0084] When the electroactive material is silicon, it is preferred that the silicon be amorphous. The amorphous nature of silicon can be measured by X-ray diffraction (XRD), as shown in Figure 3 for Example 4.

[0085] One advantage of the present invention is that the temperature of the carbon coating process can suppress or substantially prevent annealing of the composite particle microstructure. The composite particle microstructure can be evaluated by TGA analysis. This analysis is based on the principle that a weight gain is observed when elemental silicon oxidizes to silicon dioxide (SiO2) in air at high temperatures. The mechanism by which Si oxidizes is temperature dependent. Silicon atoms at the surface of silicon nanostructures oxidize at lower temperatures than silicon atoms in the bulk of the silicon nanostructure (Reference: Bardet et al., Phys. Chem. Chem. Phys. (2016), 18, 18201). TGA analysis can quantify the relative amount of surface silicon based on the weight gain observed when silicon oxidizes to silicon dioxide (SiO2) in air at high temperatures. By plotting the weight gain versus temperature, fine and coarse silicon in a sample can be distinguished and quantified.

[0086] As shown in Figure 1, a determination of the amount of unoxidized surface silicon can be obtained from the characteristic TGA traces of these materials. After an initial mass loss up to approximately 300 °C (shown in Figure 1 as a mass loss from (a) to (b)), a significant mass gain begins to be observed at approximately 400 °C, peaking between 550 and 650 °C (shown in Figure 1 as a mass gain from (b) to (c)). Subsequently, a mass loss is observed as the porous carbon skeleton oxidizes to CO gas (mass loss from (c)). Then, above approximately 800 °C, a mass gain is observed again, corresponding to the continued conversion of silicon to SiO. This increases toward an asymptotic value above 1000 °C (mass gain from (d) to (e)) as the silicon oxidation nears completion. The temperature at which the weight gain occurs is related to the silicon structure; silicon at the surface of the silicon structure is oxidized at lower temperatures, while bulk silicon is oxidized at higher temperatures. Thus, at higher temperatures, the silicon domains become coarser and more oxidation is observed.

[0087] Coarse silicon is defined herein as silicon that oxidizes above 800°C as measured by TGA, where the TGA is performed under air at a temperature ramp rate of 10°C / min. This is shown in Figure 1 as increasing in mass from (d) to (e). The content of coarse bulk silicon is therefore determined according to the following formula: Z = 1.875 × [(M f -M 800 ) / M f ]×100% where Z is the percentage of unoxidized silicon at 800°C and M 800 is the mass of the sample at 800°C (mass (d) in Figure 1), and M fis the mass of ash at the completion of oxidation at 1400°C (mass (e) in Figure 1). In this analysis, any mass increase at temperatures above 800°C corresponds to the oxidation of silicon to SiO2, and it is assumed that the total mass at the completion of oxidation is SiO2. For completeness, it is understood that 1.875 is the molar mass ratio of SiO2 to O2 (i.e., the mass ratio of SiO2 formed to the mass increase due to the addition of oxygen).

[0088] In a second aspect of the present invention, there is provided a particulate material comprising a plurality of core-shell composite particles obtainable by the method described above.

[0089] In a third aspect of the present invention, A particulate material comprising a plurality of core-shell composite particles, The core-shell composite particles are (a) a core, (i) a porous carbon skeleton having micropores and / or mesopores, the micropores and / or mesopores having a size of at least 0.4 cm as measured by gas adsorption; 3 / g of total pore volume, and the PD of said porous carbon skeleton 50 a porous carbon skeleton having a pore diameter of 10 nm or less, preferably 5 nm or less; (ii) a plurality of electroactive material domains disposed within the micropores and / or mesopores of the porous carbon skeleton; and a core having (b) an outer shell of a pyrolytic conductive carbon material surrounding at least a portion of the core; A particulate material is provided having the following structure:

[0090] If desired, the pyrolyzable conductive carbon coating may also infiltrate into the pores of the porous carbon skeleton.

[0091] The core-shell composite particles may have different electroactive material loading ranges. For example, the amount of electroactive material in the precursor composite particles may be selected so that at least 25% and up to 80% or more of the internal pore volume of the porous carbon skeleton is occupied by the electroactive material. For example, the electroactive material may occupy 25% to 60%, 25% to 55%, 25% to 50%, 25% to 45%, or 25% to 40% of the internal pore volume of the porous carbon skeleton. Within these preferred ranges, the pore volume of the porous carbon skeleton effectively accommodates the expansion of the electroactive material during charge and discharge, avoiding excess pore volume that does not contribute to the volumetric capacity of the core-shell composite particles. However, the amount of electroactive material is not so high that inadequate metal ion diffusion rates or inadequate expansion volume create mechanical resistance to lithiation and prevent effective lithiation.

[0092] The electroactive material in the precursor composite particles is preferably selected from silicon, tin, germanium, aluminum and mixtures thereof. A preferred electroactive material is silicon.

[0093] Preferably, the core-shell composite particles are substantially free of silicon carbide. Preferably, the core-shell composite particles are substantially free of silicon nitride. The presence or absence of silicon carbide and silicon nitride can be determined by X-ray diffraction (XRD) analysis. Suitable apparatus and methods for this purpose are well known to those skilled in the art.

[0094] The core-shell composite particles have a D ranging from 1.5 to 60 μm. 50 It is preferred to have a particle diameter.

[0095] If necessary, the D of the core-shell composite particles 50 The particle diameter may be at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm. If desired, the D of the core-shell composite particles 50The particle diameter may be 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, or 15 μm or less.

[0096] For example, core-shell composite particles may have a D in the range of 2 to 50 μm, 2 to 40 μm, 2 to 30 μm, 3 to 30 μm, 3 to 25 μm, 3 to 20 μm, 4 to 25 μm, 4 to 20 μm, 4 to 18 μm, 5 to 20 μm, 5 to 18 μm, 5 to 15 μm. 50 Core-shell composite particles within these size ranges and having the porosity and pore diameter distributions described herein are ideally suited for preparing composite particles for use in metal-ion battery anodes due to their good dispersibility in slurries, structural robustness, high capacity retention over repeated charge-discharge cycles, and suitability for forming uniformly thick, dense electrode layers in the conventional thickness range of 20 to 50 μm.

[0097] The core-shell composite particles are 50m 2 It is preferred that the BET surface area is less than or equal to 30 m / g, preferably less than or equal to 30 m 2 / g or less, more preferably 15m 2 / g or less, or 12m 2 / g or less, or 10m 2 / g or less, or 8m 2 / g or less, or 6m 2 / g or less, or 5m 2 The composite particles have a particle size of at least 0.1 m 2 / g, or at least 0.5m 2 / g, at least 1m 2 / g, or at least 2m 2 / g, or at least 3m 2 / g BET surface area.

[0098] The particulate material of the present invention may have a specific capacity upon lithiation of from 1200 to 2340 mAh / g, measured per gram of particulate material.

[0099] In a fourth aspect of the present invention, there is provided a composition comprising the particulate material of the second or third aspect of the present invention and at least one other component. The at least one other component may suitably be selected from one or more of: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material. The composition of the fourth aspect of the present invention may in particular be used as an active layer in the anode of a metal-ion battery.

[0100] The composition may have from 1 to 95%, or from 2 to 90%, or from 5 to 85%, or from 10 to 80% by weight of the particulate material of the present invention, based on the total dry weight of the composition.

[0101] The binder may be present in an amount of 0.5 to 20 wt %, or 1 to 15 wt %, or 2 to 10 wt %, based on the total dry weight of the electrode composition.

[0102] The one or more conductive additives may be present in a total amount of 0.5 to 20 wt %, or 1 to 15 wt %, or 2 to 10 wt %, based on the total dry weight of the electrode composition.

[0103] The optional at least one additional particulate electroactive material may be selected from graphite, hard carbon, silicon, tin, germanium, gallium, aluminum and lead.

[0104] In a fifth aspect, the present invention provides an electrode having a particulate material according to the second or third aspect of the present invention in electrical contact with a current collector. If desired, the particulate material may be in the form of a composition according to the fourth aspect of the present invention.

[0105] In a sixth aspect, the present invention provides a rechargeable metal-ion battery comprising: (i) an anode, the anode comprising an electrode according to the fifth aspect of the present invention; (ii) a cathode having a cathode active material capable of releasing and resorbing metal ions; (iii) an electrolyte between the anode and the cathode;

[0010] A rechargeable metal-ion battery is provided, having

[0106] In a seventh aspect, the present invention provides the use of a particulate material according to the second or third aspect of the present invention as an anode active material, in which the particulate material may be in the form of a composition of the present invention.

[0107] The present invention will now be described with reference to examples and the accompanying drawings. [Brief explanation of the drawings]

[0108] [Figure 1] FIG. 1 shows a characteristic TGA trace of a particulate material according to the present invention having low levels of coarse silicon. [Figure 2] FIG. 1 shows thermogravimetric analysis (TGA) data for Example 4. [Figure 3] FIG. 1 shows X-ray diffraction (XRD) data for Example 4. [Figure 4] FIG. 10 shows cell data of Example 5. [Figure 5] FIG. 10 is a graph showing the effect of temperature on the coarse silicon content in Example 4. [Figure 6] FIG. 1 shows XRD data of Example 6. [Figure 7] FIG. 10 is a graph showing the effect of temperature on the amount of coarse silicon in Example 7. [Figure 8] Figure 1 shows the effect of temperature on capacity retention over 100 cycles. The numbers for each data point indicate the level of roughened silicon. [Figure 9] Figure 1 shows the effect of temperature on capacity retention at 200 cycles. The numbers for each data point indicate the level of roughened silicon. DETAILED DESCRIPTION OF THE INVENTION

[0109] (example) The porous carbon skeletons C1 to C3 used in the following examples have the characteristics shown in Table 1.

[0110] [Table 1] Example 1: Preparation of particulate material in a fluidized bed reactor Silicon-carbon composite particles were prepared in a vertical bubbling fluidized-bed reactor with a stainless steel cylindrical vessel having an inner diameter of 83 mm. A powder of carbon skeleton particles with the properties listed in Table 1 was placed in the reactor. A slow flow of inert gas (nitrogen) was introduced into the reactor to remove oxygen. The reactor was then heated to a reaction temperature between 430 and 500 °C, and 4% by volume monosilane gas diluted with nitrogen was introduced into the bottom of the reactor at a flow rate sufficient to fluidize the carbon skeleton particles for a period long enough to deposit the desired mass of silicon. The reactor was purged under nitrogen for 30 minutes and then cooled to room temperature over several hours. The atmosphere was then gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air from a compressed air supply.

[0111] (Example 2: Preparation of granular materials in a static furnace) Silicon-carbon composite particles were prepared by placing 1.8 g of a particulate porous scaffold with the properties listed in Table 1 on a stainless steel plate at a uniform thickness of 1 mm along its entire length. The plate was then placed inside a 60 mm outer diameter stainless steel tube with gas inlet and outlet lines located in the hot zone of a retort furnace. After purging the furnace tube with nitrogen gas for 30 minutes at room temperature, the sample temperature was increased from 450 to 475 °C. The nitrogen gas flow rate was adjusted to ensure a gas residence time of at least 90 seconds within the furnace tube and maintained at this flow rate for 30 minutes. The gas supply was then switched from nitrogen to a mixture containing 1.25 vol% monosilane in nitrogen. Dosing of the monosilane was carried out for a period of up to 5 hours. The reactor pressure was maintained at 101.3 kPa (1 atm). After dosing was completed, the gas flow rate was held constant while silane was purged from the furnace with nitrogen. The furnace is purged under nitrogen for 30 minutes, then allowed to cool to room temperature over several hours. The atmosphere is then gradually switched to air over a period of 2 hours by switching the gas flow from nitrogen to air from a compressed air supply.

[0112] (Example 3: Measurement of weight percent of coarse silicon) The procedure used to calculate the coarse silicon for the example composites was as follows: 10-20 mg of the sample to be tested was loaded into a 70 μL crucible. The sample was loaded into a Mettler Toledo TGA / DSC3+ instrument. 100 mL / min of Ar purge gas, N2 padding gas, and air reaction gas were used. The TGA furnace chamber was heated from 25°C to 1400°C at a rate of 10°C / min. Data were collected at 1-second intervals.

[0113] The amount of coarse silicon was determined by determining the final mass of the ash at the end of the TGA test and the mass at 800° C. The formula above is used to calculate the coarse silicon (Z) value.

[0114] Example 4 - Heat Treatment of Uncoated Particles Silicon-carbon composite particles were prepared using 125 g of carbon C1 and the method of Example 1. The silicon-carbon composite particles were separated into five samples. Each sample was then individually jet milled for 25 minutes using a Hosokawa Alpine 50 AS Spiral Jet Mill at a feed gas pressure of 8 bar and a feed rate of 8 rpm. After jet milling and before any heat treatment steps, the resulting volumetric particle size distributions were measured using laser diffraction as previously described, and are shown in Table 2.

[0115] The first sample served as a reference and was not subjected to any additional treatment. The remaining four samples were flushed with argon at a flow rate of 1 L / min for 30 minutes, then ramped at 5°C / min to the corresponding heat treatment temperature of 600°C, 700°C, 800°C, or 900°C, and then held at the heat treatment temperature for 1 hour. The properties of the silicon-carbon composite precursor particles were measured after heat treatment and compared with those of the reference sample.

[0116] (result) The reference sample and the heat-treated samples were subjected to various analyses to compare the effect of each temperature on the material properties.

[0117] Thermogravimetric analysis (TGA) in air (Figure 2) confirmed that samples exposed to heat treatments at 800°C and 900°C suffered from the formation of larger silicon domains via thermal treatment of the fine micropore structure and the coalescence of nanoscale silicon domains within the pore structure. The sample heat-treated at 600°C exhibited a TGA profile nearly identical to that of the reference sample, indicating that the carbon coating process on these silicon-carbon composite precursor particles is highly unlikely to damage the fine micropore structure, which is highly desirable for the use of particulate materials in anodes.

[0118] Figure 5 shows the amount of coarse silicon in each sample, as measured by the method of Example 3. The reference sample is represented as 430, and the other samples are represented by the temperature of the heat treatment step to which they were subjected. Fine silicon is more desirable than coarse silicon in the final product. Figure 5 shows that any treatment steps performed at temperatures above 700°C tend to result in a final particulate product with a higher proportion of coarse silicon compared to products treated (e.g., carbon-coated) at temperatures below 700°C.

[0119] Total pore volume and BET surface area were evaluated using the methods described above.

[0120] [Table 2] These data show that the total pore volume decreases as the treatment temperature increases. The total pore volumes obtained for the 800°C and 900°C samples are reduced to unfavorable levels, which can be explained by the heat treatment of the pores at these high temperatures.

[0121] The total pore volume and BET surface area depend on the particle size of the sample. The increase in the BET surface area and total pore volume of the sample heat treated at 600°C compared to the reference sample is explained by the fact that the sample heat treated at 600°C has a larger particle size than all the other samples because the samples were jet milled individually.

[0122] The chemical composition of the five samples was further analyzed using X-ray diffraction (XRD), and the results are shown in Figure 3.

[0123] Up to 700°C, and especially up to 600°C, the broad peaks characteristic of amorphous silicon are observed. In the 700°C, 800°C, and 900°C samples, a degree of crystalline silicon variation is observed, particularly in the 800°C and 900°C samples.

[0124] Evidence of silicon carbide is also clearly visible in the 900°C sample. The formation of silicon carbide is undesirable in silicon-carbon composite particles because it is not electrochemically active and has poor electrical conductivity. Thus, the formation of this compound reduces the overall effectiveness of the product in conjunction with the anode.

[0125] Additionally, electrodes were tested, each containing one of the test samples of particulate material.

[0126] (Example 5 - Electrochemical Test) Test coin cells were fabricated using a negative electrode containing the composite material prepared as described in Example 4. Carbon Super P (conductive carbon) was dispersed in a CMC binder and mixed in a Thinky™ mixer. The silicon-based material was added to the mixture and mixed in the Thinky™ mixer for 30 minutes. Next, SBR binder was added to achieve a 1:1 CMC:SBR ratio to obtain a slurry with a silicon-based material: CMC / SBR: conductive carbon ratio of 70%:16%:14% by weight. The slurry was further mixed in the Thinky™ mixer for 30 minutes. The resulting mixture was then coated onto a 10 μm-thick copper substrate (current collector) and dried at 50°C for 10 minutes. The resulting mixture was further dried at 110°C for 12 hours to form an electrode with an active layer on the copper substrate.

[0127] A coin half-cell was fabricated using a ring electrode with a radius of 0.8 cm cut from the electrode, a porous polyethylene separator, lithium foil as the counter electrode, and an electrolyte containing 1 M LiPF6 in a 7:3 solution of EC / FEC (ethylene carbonate / fluoroethylene carbonate) containing 3 wt% vinylene carbonate.

[0128] Using these half-cells, the initial volumetric energy density (VED2, mAh / cm 3The volatility, first cycle loss (FCL), and first delithiation capacity (DC1) of the active layer were measured. The half-cells were evaluated by applying a constant current of C / 25 (where "C" represents the specific capacity of the electrode in mAh and "25" represents 25 hours) to lithiate the porous particle-containing electrode at a cutoff voltage of 10 mV. Once the cutoff was reached, a constant voltage of 10 mV was applied. The cutoff current was C / 100. The cell was then rested in the lithiation state for 10 minutes. The electrode was then delithiated at a constant current of C / 25 with a cutoff voltage of 1 V, after which the cell was rested for 10 minutes. The cell was then subjected to a second lithiation at a constant current of C / 25 and a cutoff voltage of 10 mV. A constant voltage of 10 mV was then applied with a cutoff current of C / 100 and rested for 5 minutes.

[0129] The effect of silicon carbide formation on cell performance is shown in Figure 4. The delithiation capacity, measured as described above, is significantly reduced for the 900°C heat-treated samples, indicating the adverse effect of silicon carbide formation on anode performance.

[0130] Figure 4 also shows the thickness change of the electrode coating (excluding the current collector) for electrodes prepared and evaluated using half-cells as described above. In lithium-ion half-cells, the anode was removed after lithiation, delithiation, and the second lithiation cycle, and the thickness change in percent was measured ex situ in the charged state. In other words, the thickness change was measured for the anode in the lithiated state.

[0131] The anode incorporating the particulate material subjected to a 900°C heat treatment showed the greatest increase in thickness, suggesting that a carbon coating process at the same temperature would have an adverse effect on the usefulness of the particulate material in the anode. Typically, the degree of electrode expansion is expected to be positively correlated with the amount of active silicon. However, the opposite was observed for the electrode containing the 900°C sample. While not wishing to be bound by theory, the fact that this electrode exhibited the highest degree of expansion of all samples is believed to indicate that the structural and chemical relationships within the particulate material have deteriorated so severely that particle expansion is no longer controlled. This excessive expansion is expected to lead to isolated particles and poor cycle retention.

[0132] Additional electrode performance data was measured on anodes each incorporating one of the samples. The results of these tests are shown in Table 3 and FIG. 4.

[0133] These data show that both the first lithiation capacity and the first delithiation capacity of the electrode-integrated samples decreased with increasing heat treatment temperature. The percentage of active silicon relative to the total particle mass also decreased with increasing heat treatment temperature. The active silicon content of the composite particles was calculated by dividing the first delithiation capacity of the half-cell (per mAh of composite particles) by the theoretical capacity of silicon (3579 mAh / g), and the result is expressed as a percentage. The first-cycle loss increased with increasing heat treatment temperature, especially for the 900°C-treated sample. The anode thickness increased for all samples after 1.5 cycles. However, the thickness increase was nearly constant for the reference sample, the 600°C-treated sample, and the 700°C-treated sample, whereas the 800°C- and 900°C-treated samples showed a significant increase in electrode thickness. For batteries, it is desirable to maintain the electrode thickness as constant as possible.

[0134] Overall, the anode volumetric capacity was similar for the 600°C treated sample and the reference sample, decreased slightly for the 700°C treated sample, and decreased significantly for the 800°C and 900°C treated samples.

[0135] These tests were performed on half-cells with silicon-carbon composite precursor particles without a carbon coating. However, the results are expected to be reproduced with a carbon coating, suggesting that the high-temperature carbon coating process adversely affects the properties of the carbon-coated particulate silicon-carbon composite product.

[0136] [Table 3-1] (Example 6 - Uncoated sample) Evaluation Procedure Silicon-carbon composite particles were prepared using 125 g of carbon C1 and the method of Example 2. The heat treatment test procedure of Example 4 was repeated, except that there was no jet milling step prior to the heat treatment step and the heat treatment step was carried out in a nitrogen atmosphere instead of an argon atmosphere.

[0137] (result) The heat-treated and reference samples were analyzed using XRD, and the results are shown in Figure 6. The heat treatment temperature for each sample is on the right side of the XRD plot, with the XRD trace for the 600°C sample shown on the front side and the XRD trace for the 900°C sample shown on the back side.

[0138] An important effect observed depending on the heat treatment temperature was the formation of compounds. In particular, non-electroactive compounds such as Si3N4 and SiC were formed in the 800°C and 900°C samples. This is an undesirable result because it reduces the overall capacity of the material, thereby reducing its value as an anode material. Furthermore, SiC is a poor electrical conductor, and its presence in the final product may interfere with the lithiation of silicon within the granular material, making it even more undesirable.

[0139] The absence of silicon nitride formation after heat treatment at temperatures below 700° C. is an important advantage, as it means that the method of the present invention can be carried out in a nitrogen atmosphere instead of an argon atmosphere.

[0140] Similarly, in the 800°C and 900°C samples, crystallization of the silicon was observed, which is undesirable; the preferred form of silicon for these materials is amorphous silicon.

[0141] For the 700 °C sample, a mixture of amorphous and crystalline silicon was observed in the XRD data. At this temperature, a small crystalline silicon peak overlaps a broad amorphous peak. Furthermore, if silicon crystallization occurs, this is thought to be a sign of an increase in the average length scale of silicon domains within the particulate material caused by the heat treatment.

[0142] The deposition of the carbon coating in the method of the present invention takes approximately the same time as the samples were held at their respective temperatures in these tests. By evaluating uncoated particles, the effect of temperature on the microstructure of the composite particles can be more easily observed than when they are coated. It is expected that similar effects will be observed when carbon deposition is performed at the same temperatures.

[0143] Therefore, the method of the present invention, in which carbon deposition is performed at temperatures below 700°C, is expected to avoid or mitigate the detrimental effects observed in this experiment at 800°C and 900°C, thus providing the benefits of the conductive coating and pore capping while preserving the significant microstructure previously developed by the inventors. At temperatures below 600°C, the material properties of the particles are more suitable for use in anodes.

[0144] (Example 7: Carbon coating) A series of composite particle samples were prepared using carbon skeletons C2 and C3 according to the method of Example 1. The precursor particles had the properties listed in Table 3. The amount of coarse silicon was determined using the TGA method described in Example 3. All composite particle samples contained less than 4 wt% coarse silicon.

[0145] [Table 3-2] The composite particulate samples listed in Table 3 were carbon-coated by the following method. Mixed particles (60 g) were placed in a stainless steel tube (57 mm diameter, 500 mm length) packed (sealed) in the heating zone of a rotary furnace. The reactor space was purged with nitrogen at 0.2 L / min for 30 minutes. The furnace temperature was increased to the temperature listed in Table 4 under nitrogen flow. An excess amount of styrene was placed in a Drescher bottle and heated to a maximum of 75°C in a water bath. After allowing the furnace temperature to stabilize for 10 minutes, styrene was flowed into the reactor tube by bubbling nitrogen into the Drescher bottle at 2 L / min (as shown in Table 4) for a maximum of 90 minutes. The reactor was then purged with nitrogen and cooled to ambient temperature under nitrogen to obtain the carbon-coated material.

[0146] The carbon coated particles from Example 7 were analyzed for elemental composition and coarse silicon content, again using the TGA method described in Example 3. The results are shown in Table 4 and FIG. S1(58m 2 / g) and S10 (22m 2 / g), all carbon-coated particles showed a 6 to 12 m2 BET surface areas in the range of / g were obtained.

[0147] [Table 4] *Comparative example The data in Table 4 show that when carbon coating is performed at temperatures below 700°C, the relative increase in coarse silicon is less than 190% in all cases. However, when temperatures exceed 700°C, the amount of coarse silicon increases significantly. This suggests that particles coated at temperatures above 700°C undergo heat treatment of the fine micropore structure and nanoscale silicon domains within the pore structure to form large silicon domains. This therefore supports the hypothesis in Example 4 that the changes in silicon domains observed during heating of uncoated particles are also observed during the carbon coating process.

[0148] (Example 8 - Electrochemical evaluation of coated particles) Negative electrode coatings (anodes) were prepared using the Si-C composites listed in Table 4 and tested in full-coin cells. To fabricate the electrodes, a carbon black dispersion was mixed with a CMC binder in a Thinky™ mixer. The Si-C composite was added to the mixture and mixed in the Thinky™ mixer for 30 minutes. Next, SBR binder was added to achieve a 1:1 CMC:SBR ratio to form a slurry with a weight ratio of 70%:16%:14% Si-C composite:CMC / SBR:carbon black. The slurry was mixed in the Thinky™ mixer for an additional 30 minutes, then coated onto a 10 μm-thick copper substrate (current collector) and dried at 50°C for 10 minutes. It was then further dried at 110°C for 12 hours, resulting in a coating density of 0.7±0.5 g / cm. 3 A negative electrode of 1000 kJ / cm2 was formed.

[0149] A 0.8 cm diameter circular negative electrode cut from the negative electrode was used to fabricate a full coin cell with a porous polyethylene separator and a nickel manganese cobalt oxide (NMC532) positive electrode. The positive and negative electrodes were designed to form a balanced pair, with a positive to negative electrode capacity ratio of 0.9. An electrolyte consisting of 1 M LiPF6 in a solution of fluoroethylene carbonate, ethylene carbonate, and ethyl methyl carbonate containing 3 wt% vinylene carbonate was then added to the cell before sealing.

[0150] The coin cells were cycled as follows: a constant current was applied at a rate of C / 25 to lithiate the anode. The cutoff voltage was 4.3 V. Once the cutoff was reached, a constant voltage of 4.3 V was applied until a cutoff current of C / 100 was reached. The cells were then allowed to rest in the lithiation state for 10 minutes. The anode was then delithiated at a constant current of C / 25 with a cutoff voltage of 2.75 V. The cells were then allowed to rest for 10 minutes. After this first cycle, a constant current of C / 2 was applied to lithiate the anode to a cutoff voltage of 4.3 V, followed by a constant voltage of 4.3 V with a cutoff current of C / 40 with a 5-minute rest period. The anode was then delithiated at a constant current of C / 2 with a cutoff voltage of 2.75 V. This was then repeated for the desired number of cycles. Capacity retention at 100 cycles (CR100) and 200 cycles (CR200) ​​was calculated. This is shown in Table 5 along with the first lithiation capacity, first delithiation capacity, and first cycle loss (FCL).

[0151] The charge (lithiation) and discharge (delithiation) capacities for each cycle are calculated per unit mass of silicon-carbon composite material, and the capacity retention is calculated for each discharge capacity as a percentage of the discharge capacity at the second cycle. The first cycle loss (FCL) is (1 - (1st delithiation capacity / 1st lithiation capacity)) x 100%. The values ​​in Table 5 are averaged across three coin cells of each material.

[0152] The active silicon level is determined from half-cell experiments as described in Example 5.

[0153] The data in Table 5 show that increasing the coarse Si weight percent with increasing carbon coating temperature is reflected in a degradation of electrochemical properties. As the level of coarse silicon increases, the amount of active silicon in the material (determined from half cells) decreases, the initial lithiation and delithiation capacity of the material decreases, and the normalized capacity retention over multiple charge-discharge cycles decreases. Figures 8 and 9 show the normalized capacity retention of these materials.

[0154] [Table 5] *Comparative example **To facilitate comparison between samples with different initial capacities, the capacity retention values ​​in Table 5 have been normalized to 45 wt% active silicon by multiplying the capacity retention percentage by the active Si value and dividing by 45.

Claims

1. 1. A method for preparing core-shell composite particles, comprising: (a) Below: i. A porous carbon skeleton having micropores and / or mesopores, wherein the total pore volume of the micropores and mesopores is at least 0.6 cm as measured by gas adsorption. 3 / g and 1.2cm 3 / g or less, and the PD of the porous carbon skeleton 50 The pore diameter is 2.5 nm or less, and the PD of the porous carbon skeleton is 90 a porous carbon skeleton having a pore diameter of at least 3 nm and no greater than 10 nm; and ii. a plurality of nanoscale electroactive material domains disposed within the porous carbon skeleton, the electroactive material being silicon; providing a plurality of precursor composite particles comprising: (b) heat-treating the plurality of precursor composite particles by contacting them with a pyrolytic carbon precursor, wherein an outer shell of pyrolytic conductive carbon material is formed on the precursor composite particles, the heat-treating being at a temperature of 680°C or less; A method comprising:

2. 10. The method of claim 1, wherein the heat treatment is carried out at 660°C or less, or 650°C or less, or 640°C or less, or 620°C or less, or 600°C or less.

3. 3. The method of claim 1 or claim 2, wherein the heat treatment is carried out at a temperature of at least 500°C, or at least 520°C, or at least 540°C, or at least 560°C, or at least 580°C.

4. 4. The method of claim 1, wherein the pyrolytic carbon precursor is contacted with the composite particles as a vapor.

5. The method of claim 4 , wherein the vapor is a hydrocarbon vapor.

6. 6. The method of claim 5, wherein the hydrocarbon is selected from polycyclic hydrocarbons having from 10 to 25 carbon atoms and optionally from 1 to 3 heteroatoms.

7. 7. The method of claim 6, wherein the polycyclic hydrocarbon is selected from naphthalene, anthracene, tetracene, pentacene, fluorene, acenaphthene, phenanthrene, fluoranthrene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone, and alkyl-substituted derivatives thereof.

8. 6. The method of claim 5, wherein the hydrocarbon is selected from bicyclic monoterpenoids.

9. 9. The method of claim 8, wherein the bicyclic monoterpenoid is selected from camphor, borneol, eucalyptol, camphene, careen, sabinene, thujene, and pinene.

10. The hydrocarbon is C 2 From C 10 and 6. The method of claim 5, wherein the hydrocarbon is selected from an alkane, an alkene, an alkyne, a cycloalkane, a cycloalkene, and an arene.

11. 11. The method of claim 10, wherein the hydrocarbon is selected from methane, ethylene, propylene, and acetylene.

12. 12. The method of claim 4, wherein the pyrolytic carbon precursor vapor is contacted with a transition metal catalyst at a temperature of at least 500°C prior to contacting the composite particles.

13. 13. The method of claim 12, wherein the transition metal catalyst comprises nickel, iron, cobalt, copper, and mixtures thereof.

14. the transition metal catalyst is in the form of a mesh; 14. The method of claim 12 or 13, wherein the mesh is positioned in the flow path of the hydrocarbon vapor before contacting the composite particles.

15. 14. The method of claim 12 or 13, wherein the transition metal catalyst is disposed on the surface of the composite particles.

16. 12. The method of claim 1, wherein, prior to step (b), gaseous nickel carbonyl is thermally decomposed to deposit nickel on the surfaces of the composite particles.

17. 17. The method of claim 16, wherein after step (b), the carbon-coated particulate material is contacted with carbon monoxide gas to form gaseous nickel carbonyl, thereby removing nickel from the carbon-coated composite particles.

18. Step (b) contacting the composite particles with a dispersion or solution of a pyrolytic carbon precursor in a solvent; removing the solvent prior to the heat treatment to provide composite particles coated with the pyrolytic carbon precursor; 4. The method according to claim 1, wherein the

19. 20. The method of claim 18, wherein the pyrolyzable carbon precursor is a polymer or oligomer comprising a carbon-containing backbone.

20. 20. The method of claim 18 or claim 19, wherein the pyrolyzable carbon precursor is polyvinylpyrrolidone (PVP) or a copolymer of vinylpyrrolidone and one or more other ethylenically unsaturated monomers.

21. 21. A method according to any preceding claim, wherein the outer shell of pyrolytic conductive carbon material has a thickness of 10 nm or less, or 5 nm or less, or 4 nm or less, or 2 nm or less, or 1 nm or less.

22. The total pore volume of micropores and mesopores measured by gas adsorption is at least 0.65 cm 3 / g or at least 0.7 cm 3 / g and at least 0.75 cm 3 / g, or at least 0.8 cm 3 / g, or at least 0.85 cm 3 / g or at least 0.9 cm 3 / g or at least 0.95 cm 3 / g or at least 1 cm 3 / g or at least 1.05 cm 3 / g or at least 1.1 cm 3 22. The method of claim 1, wherein the hydroxyl group is 0.15 to 0.25g.

23. PD of the porous carbon skeleton 50 23. The method of any one of claims 1 to 22, wherein the pore diameter is 2 nm or less, or 1.5 nm or less, or 1 nm or less.

24. 24. The method of claim 1, wherein step (a) of providing a plurality of precursor composite particles comprises contacting a plurality of porous carbon particles with a silicon precursor gas at a temperature between 400°C and 650°C, thereby depositing silicon in the pores of the carbon particles.

25. 25. The method of claim 24, wherein the temperature is between 400°C and 500°C.

26. The silicon precursor gas is silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ) tetrasilane (Si 4 H 10 26. The method according to claim 24 or 25, wherein the silane is selected from the group consisting of chlorosilanes, methylchlorosilanes, and preferably silanes.

27. The precursor composite particles have a D of at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm. 50 27. The method of any one of claims 1 to 26, wherein the particle diameter is

28. The precursor composite particles have a D of 50 μm or less, or 40 μm or less, or 30 μm or less, or 25 μm or less, or 20 μm or less, or 15 μm or less, or 12 μm or less, or 10 μm or less. 50 28. The method of any one of claims 1 to 27, wherein the particle diameter is

29. 29. The method of any one of claims 1 to 28, wherein the volumetric fill factor of the electroactive material within the porous carbon skeleton, based on the volume of the micropores and / or mesopores, is 85% or less, or 75% or less, or 65% or less, or 55% or less, or 45% or less.

30. 30. The method of claim 1, wherein the volume filling of the electroactive material within the porous carbon skeleton, based on the volume of the micropores and / or mesopores, is at least 20%, or at least 25%.

31. 31. The method of any one of claims 1 to 30, wherein the porous carbon skeleton comprises at least 80% by weight carbon, or at least 85% by weight carbon, or at least 90% by weight carbon, or at least 95% by weight carbon.

32. 32. The method of any one of claims 1 to 31, wherein the duration of the heat treatment in step (b) is from 1 to 3 hours.

33. The step (a) further comprises: (a2) contacting the surface of the deposited silicon with a passivation agent; and 33. The method of any one of claims 1 to 32, wherein the silicon is not exposed to oxygen prior to contact with the passivating agent.

34. The passivator has the general formula (i) R-CH=CH-R, (ii) R-CH≡CH-R, (iii) O=CH-R and wherein R represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, preferably 2 to 10 carbon atoms, or 34. The method of claim 33, wherein the two R groups in formula (i) form an unsubstituted or substituted hydrocarbyl ring structure having from 3 to 8 carbon atoms.

35. 35. The method of claim 33 or 34, wherein step (b) is carried out at the same temperature as step (a2) or at a higher temperature than step (a2).

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