Composite particles

Abstract

Provided is as process comprising providing first composite particles, wherein the first composite particles comprise: particulate porous frameworks comprising micropores and optionally mesopores, electroactive material domains located within the pores and optionally on the surface of the particulate porous frameworks; comminuting the first composite particles in the presence of a coating agent, thereby reducing the particle size of the composite particles and forming a coating derived from the coating agent on the composite particles, thereby providing second composite particles; wherein the second composite particles comprise: the coating derived from the coating agent. The process relates to the field of anode materials for lithium-ion batteries

Description

[0001] Composite Particles

[0002] Introduction

[0003] This invention relates to composite particles for use as electroactive materials in metal-ion batteries, such as lithium-ion batteries, and processes for preparing such composite particles.

[0004] Background

[0005] Lithium-ion batteries (LIBs) comprise in general an anode, a cathode and a lithium-containing electrolyte. The anode generally comprises a metal current collector provided with a layer of an electroactive material, defined herein as a material which is capable of inserting and releasing lithium ions during the charging and discharging of a battery. When a LIB is charged, lithium ions are transported from the cathode via the electrolyte to the anode and are inserted into the electroactive material of the anode as intercalated lithium atoms. The terms “cathode” and “anode” are therefore used herein in the sense that the battery is placed across a load, such that the anode is the negative electrode. The term “battery” is used herein to refer both to devices containing a single cell, e.g. a Li-ion or Na-ion cell, and to devices containing multiple connected cells.

[0006] Conventional LIBs use graphite as the anode electroactive material. Graphite anodes can accommodate a maximum of one lithium atom for every six carbon atoms resulting in a maximum theoretical specific capacity of 372 mAh / g in a lithium-ion battery, with a practical capacity that is somewhat lower (ca. 340 to 360 mAh / g). Silicon is a promising alternative to graphite because of its very high capacity for lithium (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al. in Adv. Mater. 1998, 10, No. 10). Silicon has a theoretical maximum specific capacity of about 3,600 mAh / g in a lithium-ion battery (based on LhsSi-t). However, such a high ratio of intercalated lithium to silicon results in expansion of the silicon material by up to 400% of its original volume. Repeated charging and discharging cycles result in significant mechanical stress on the silicon material leading to fracturing and structural failure. Furthermore, the charging of anodes in LIBs results in the formation of a solid electrolyte interphase (SEI) layer. This SEI layer is an ion-conductive yet insulating layer that is formed by the reductive decomposition of electrolytes on exposed electrode surfaces during the initial charge. In a graphite anode, this SEI layer is relatively stable during subsequent charge / discharge cycles. However, the expansion and contraction of a silicon anode results in fracturing and delamination of the SEI layer and the exposure of fresh silicon surface, resulting in further electrolyte decomposition, increased thickness of the SEI layer and irreversible consumption of lithium. These failure mechanisms collectively result in an unacceptable loss of electrochemical capacity over successive charging and discharging cycles. One approach to addressing these problems is the development of a class of composite particles having structure in which electroactive materials such as silicon are deposited into the pore network of highly porous particles, e.g. a porous carbon scaffold, having a carefully controlled pore size distribution. For example, W02020 / 095067, W02020 / 128495, and WO2022 / 029422 report that the improved electrochemical performance of the composite particles can be attributed to the way in which the electroactive materials form small domains with dimensions of the order of a few nanometres or less within the pore network of the porous particles. By controlling the loading of silicon within the porous particles such that only part of the pore volume is occupied by silicon in the uncharged state, the unoccupied pore volume of the porous particles can accommodate a substantial amount of silicon expansion internally. Furthermore, only a small area of the electroactive material surface is accessible to electrolyte and so SEI formation is substantially prevented.

[0007] Although composite particles of the type discussed above have been found to provide excellent performance, there remains room for improvement, for example, to allow the formation of higher density electrodes. Improvements can also be made to the utility of the composite particles for solid-state batteries (SSBs). In the context of this application, the term solid-state battery or SSB encompasses semi-solid batteries and all-solid batteries, but preferably refers to all-solid batteries. The difference in the interface between a liquid electrolyte and the composite particles and a solid electrolyte and the composite particles means that composite particles optimised for one application may not be optimised for the other. For instance, a lower particle size is believed to be advantageous for SSBs but not for liquid electrolyte designs. Similarly, processes optimised for preparing composite particles for liquid electrolyte designs may not be optimised for preparing composite particles for SSBs. Simply choosing a lower particle size for the porous carbon scaffold prior to deposition may result in undesired agglomeration. Simply milling larger composite particles to smaller composite particles may fracture the silicon domains deposited within the scaffold, exposing fresh surfaces which may display undesirable reactivity.

[0008] Coatings are widely used to modify the properties of electroactive materials for LIBs. However, the application of a coating leads to increased manufacturing complexity. Coatings can be difficult to apply to small particles. Coating larger particles then milling them may adversely affect the coating.

[0009] WO2013 / 192205, WO2014 / 143213, WO2017 / 040299, and WO2023 / 215232 disclose the synthesis of composite particles, that coatings can be applied, and that particle size can be reduced after synthesis using milling techniques. US2021 / 0175498 discloses milling porous silicon particles, which are different to the silicon / carbon composite particles described above. US8,753,525B2 discloses milling a carbon-coated zeolite intermediary to remove at least a portion of a surface layer. WO2013 / 120011 discloses that traditional milling of activated carbon materials yields powders having a distribution of particle sizes and a wide and random range of structures (i.e. non-spherical particle shapes). These characteristics limit the ability of activated carbon powders to be densely packed, thus limiting the volumetric capacitance that can be achieved by the same.

[0010] The present invention deals with the issues in the state of the art discussed above.

[0011] Summary of the invention

[0012] In a first aspect, the invention provides a process comprising providing first composite particles, wherein the first composite particles comprise: particulate porous frameworks comprising micropores and optionally mesopores, electroactive material domains located within the pores and optionally on the surface of the particulate porous frameworks; comminuting the first composite particles in the presence of a coating agent, thereby reducing the particle size of the composite particles and forming a coating derived from the coating agent on the composite particles, thereby providing second composite particles; wherein the second composite particles comprise: the coating derived from the coating agent.

[0013] In a second aspect, the invention provides a process comprising providing first composite particles, wherein the first composite particles comprise: particulate porous frameworks comprising micropores and optionally mesopores, electroactive material domains located within the pores and optionally on the surface of the particulate porous frameworks; comminuting the first composite particles in an inert environment thereby reducing the particle size of the composite particles and forming intermediate composite particles; contacting the intermediate composite particles with a coating agent thereby forming a coating derived from the coating agent on the intermediate composite particles, thereby providing second composite particles; wherein the intermediate composite particles are maintained in an inert environment until the coating derived from the coating agent is formed; wherein the second composite particles comprise: the coating derived from the coating agent. Thus, the processes reduce the size of composite particles and form a coating on the particles. The processes are an efficient and convenient way of preparing composite particles with a targeted particle size distribution and a functional coating, avoiding the disadvantages associated with working with precursors having small particle size and in post-synthesis size-reduction of composite particles. Moreover, due to the simultaneous size reduction and coating formation in the first aspect, and due to the maintenance of the inert environment from size reduction to coating in the second aspect, an advantageous interface between the composite particles and the coating is achieved.

[0014] The processes allow the use of a starting material having a larger particle size distribution than is typically used in an anode formulation, which leads to manufacturing advantages. In particular, the first composite particles used in the invention are commonly made by a chemical vapour infiltration (CVI) process. Operating CVI processes using porous frameworks having larger particle size distributions leads to reduced particle cohesion, improved mixing efficiency, and improved safety. Comminuting the resulting first composite particles enables targeting any particle size distribution for use in any anode design independently of the most practical size for the CVI process. Moreover, the first composite particles for use in the invention are typically in the form of silicon domains deposited in the micropores of frameworks such as activated carbon. Composite particles of this sort are believed to have a fractal nature whereby their advantageous nanostructure is preserved even through comminution to a lower particle size. This nanostructure is difficult to obtain, but these difficulties can be mitigated by using larger frameworks during CVI, which is enabled by the invention.

[0015] Comminuting the first composite particles generates fresh surfaces of electroactive material which, with appropriate control of processing conditions, can act as tethering points for new surface functionality and coatings. However, the fresh surfaces may also be prone to undesired side reactions. These include adventitious oxidation processes, e.g. the rapid growth of thick SiC>2 layers, which can contribute to increased irreversible capacity loss in battery anode applications. However, the formation of a controlled thickness of such compounds, in addition to extra functionality or coating chemistry introduced, enables improvements in chemical and electrochemical stability in the end application. To this end, the comminution occurs in the presence of a coating agent or under an inert environment which is maintained until contacting with a coating agent, thus allowing the achievement of application-specific goals of targeted particle size and surface coating functionality. For example, when the electroactive material is silicon the fresh surfaces, having no prior exposure to moisture or atmospheric oxygen, contain a combination of hydride termination and silicon “dangling” bonds. In the absence of an inert environment oxygen tends to saturate these sites resulting in and growth of a thick oxide layer. This tendency increases as the particle size is reduced. The reactions of the fresh surfaces can be controlled by choice of the comminuting solvent (if used) and coating agent to target desired end goals. In one use-case it may be desired that the coating is chemically bound to the surface of the comminuted second composite particles. Here, the coating may be water soluble and capable of binding via Si-OH functionality through siloxane bridging or hydrogen bonding, so inclusion of water to enable hydroxylation of the fresh silicon surface along with solubilisation of the coating agent in water is desired. An example of such a coating agent would be PAA crosslinked with PVA or PEG. The coating derived from the coating agent is then a PAA-PVA or PAA-PEG crosslinked hydrogel. In another use-case, minimisation of surface oxide formation is desired, which may be achieved using an inert solvent like I PA, which is capable of binding to reactive sites on fresh surfaces whilst simultaneously being sterically hindered, allowing for substitution by a subsequently applied coating agent such as PVP. The resulting second composite particles then have a predefined target particle size coupled with a PVP-based coating. In this way, the second composite particles can be prepared having surface chemistry and particle size distribution tailored towards specific electrode applications, for example, aqueous processing, stability in liquid electrolyte, or solid state / gel-solid electrolyte applications.

[0016] Detailed description of the invention

[0017] The invention includes a step of comminuting the first composite particles, thereby reducing their particle size. The comminuting can be performed using different types of comminuting device such as wet mills, ball mills, jet mills, high-shear stirrers, and mechanofusion devices. The comminuting is preferably performed in by wet milling, i.e. in the presence of a solvent, but can also be performed by dry milling.

[0018] The comminuting step can result in the formation of fresh surfaces of the electroactive material domains which may be reactive. For example, when the electroactive material is silicon, the fresh surfaces may be of silicon it its zero oxidation state, which are highly susceptible to oxidation. In the first aspect, the presence of the coating agent when comminuting advantageously results in simultaneous particle size reduction and formation of the coating, which results in an advantageous interface between the electroactive material and coating. In this way, the fresh surfaces may be passivated, reducing their susceptibility to oxidation, e.g. by forming an artificial SEI layer. The comminuting in the second aspect is performed in an inert environment which is maintained until the coating is formed. In this way, undesired reactions with the fresh surfaces such as the formation of SiO2 are minimised before the fresh surfaces are contacted with the coating agent, again forming an advantageous interface between the electroactive material and the coating. The comminuting in the first aspect may also be performed in an inert environment.

[0019] Typically, an inert environment comprises an atmosphere comprising less than 1.0 vol%, preferably less than 0.5 vol%, most preferably less than 0.1 vol% oxygen gas; and less than 1.0 vol%, preferably less than 0.5 vol%, most preferably less than 0.1 vol% water vapour. An inert environment may be readily achieved using nitrogen or a noble gas such as helium or argon at purities of 99.99 vol% and above, which are widely available. For example, the chamber of the comminuting device may be flushed with nitrogen or noble gas during the comminuting step. A vacuum could also be used to achieve an inert environment, e.g. at pressures less than 100 mPa.

[0020] For dry milling, comminuting in an inert environment typically comprises comminuting under an atmosphere of nitrogen or noble gas. For wet milling, comminuting in an inert environment comprises comminuting in an inert solvent under an inert atmosphere. In this way, gaseous oxidising species which could become dissolved in the solvent are avoided.

[0021] In the second aspect, contacting the intermediate composite particles with a coating agent may take place in the same device or in a different device as the device for comminuting the first composite particles. For example, a coating agent may be added to a slurry of intermediate composite particles in a solvent resulting from wet milling. When the same device is used for contacting with the coating agent, the same inert environment for the comminuting step may be maintained from comminuting to coating, providing a convenient way of avoiding oxidation before the coating is formed. Alternatively, a different inert environment may be used. When a different device is used, the intermediate composite particles must be maintained in an inert environment during the transfer to the different device. The different device may be a spray drying device. Thus, the second aspect may comprise transferring the intermediate composite particles to a spray drying device, and spray drying the intermediate composite particles with a coating agent in an inert environment. For example, the second aspect may comprise wet-milling the first composite particles, adding a coating agent to the resulting slurry of intermediate composite particles, and spray drying the slurry of intermediate composite particles and coating agent in an inert environment to remove the solvent and obtain the second composite particles, typically in a deagglomerated form.

[0022] Further ways of contacting the intermediate composite particles with a coating agent include vapour deposition methods such as chemical vapour deposition (CVD), atomic layer deposition (ALD), and physical vapour deposition (PVD); wet chemical methods such as electrodeposition; layer-by-layer coating such as multi-layer coating; and reactive polymerisation. Vapour deposition is preferred, typically CVD using a carbon-containing gas as the coating agent. The carbon- containing gas is preferably a hydrocarbon, such as methane, ethane, acetylene, or ethylene.

[0023] For example, first composite particles may be milled to ~2-2.5 pm using a ball mill with isopropyl alcohol (I PA) as the solvent and under inert (e.g. nitrogen) atmosphere. Once the desired particle size is achieved, the solvent can be evaporated while maintaining the inert atmosphere. The resulting powder can then be transferred to a rotary furnace under inert atmosphere. The furnace can then be heated to an appropriate temperature for CVD, e.g. 400-540°C, and then an inert gas comprising a carbon-containing coating agent, e.g. an acetylene I nitrogen mix, flowed through the furnace, thereby forming a carbon coating derived from the coating agent by CVD.

[0024] The comminuting is most preferably performed by wet milling a slurry of the first composite particles in a solvent, as this leads to various advantages in combination with the first composite particles to be milled. In particular, wet milling leads to improved safety over dry milling, as dry milling could in principle lead to self-ignition of the first composite particles caused by exposure of more reactive surfaces as the particle size reduces. Moreover, the particle size of the composite particles is more controllable under wet milling conditions than under dry. The composite particles are readily recirculated through the milling chamber during wet milling whereas there may be just a single pass if using common dry milling techniques such as jet mills. A further advantage is that surface oxidation of the composite particles can be minimised when using wet milling. The solvent, in particular for the second aspect, may be degassed prior to use to remove dissolved oxygen. Thus, the solvent preferably has an oxygen concentration of less than 1.0 wt%, most preferably less than 0.1 wt%. For example, an inert gas such as argon may be passed through the solvent before its use.

[0025] The solvent for the comminuting may be aqueous or non-aqueous. For the first aspect, the solvent is ideally chosen to allow for dispersion of the coating agent. Suitable solvents include water (e.g. deionised water), hydrocarbons (e.g. selected from toluene, xylenes, n-hexane, n-heptane, n- octane, decane, dodecane, and petroleum ether), ethers (e.g. selected from tetrahydrofuran, 2-Methyltetrahydrofuran, and glymes such as diglyme, and triglyme), ketones (e.g. selected from acetone and methylethylketone), alcohols (e.g. selected from isopropyl alcohol, n-butyl alcohol, and tert-amyl alcohol), halogenated solvents (e.g. selected from 1,2-dichloroethane, 1,1 ,1- trichloroethane), acetonitrile, dimethylformamide (DMF), dimethylsulfoxide (DMSO), and mixtures thereof. Esters (e.g. butyl butyrate) can also be used as the solvent for the first aspect. Preferred solvents for the first aspect include water (preferably deionised water), alcohols, and ketones. Water and isopropyl alcohol are particularly preferred solvents for the first aspect, and water is the most preferred for the first aspect.

[0026] When wet milling in the second aspect, the solvent is inert. For example, the solvent for the comminuting in the second aspect may be selected from benzene, toluene, dimethyl formamide, alcohols (e.g. isopropyl alcohol, n-butyl alcohol, and tert-amyl alcohol), dimethyl carbonate, ketones (e.g. methyl ethyl ketone and aceteone), ethers (e.g. tetrahydrofuran, 2-methyltetrahydrofuran, and glymes such as diglyme and triglyme), and N-methylpyrrolidone; preferably benzene, toluene, dimethyl formamide, isopropyl alcohol, dimethyl carbonate, methyl ethyl ketone, tetrahydrofuran, 2-methyltetrahydrofuran, diglyme, triglyme, and N-methylpyrrolidone. Esters (e.g. butyl butyrate) can also be used as the solvent for the comminuting in the second aspect. The inert solvent typically comprises less than 10 wt.% water, preferably less than 1 wt.% water, most preferably less than 0.1 wt% water, and in particular may be a dry solvent. An inert solvent may also be used in the comminuting step of the first aspect.

[0027] When water is the solvent, the pH during the comminution is preferably neutral or acidic (e.g. no more than pH 7) as this may aid the interaction between the composite particles and the coating agent. The pH during the comminution may be adjusted by adding a pH adjusting agent. Optionally, the pH is about 7 during the comminution step. Maintaining the pH at about 7 does not exclude a prior or subsequent comminuting step at an alternative pH. Optionally, the pH is maintained at about 7 for at least 5 minutes, or at least 20 minutes, or at least 1 hour.

[0028] A neat liquid coating agent may be used, i.e. in the absence of a solvent. Thus, comminuting in the first aspect may be performed by wet milling a slurry of the first composite particles in a neat liquid coating agent. The second aspect may comprise contacting the intermediate composite particles with a neat liquid coating agent. The neat liquid coating agent may be degassed prior to use. Preferably the neat liquid coating agent has an oxygen concentration of less than 1.0 wt% most preferably less than 0.1 wt%. The neat liquid coating agent would normally be selected from agents which are liquid at 25°C and atmospheric pressure.

[0029] The coating agent may be dispersed in the solvent at a concentration of less than 30 wt%, or less than 15 wt%, or less than 10 wt%, or less than 5 wt%, relative to the weight of solvent and coating agent.

[0030] The incipient wetness technique may be used to introduce a coating agent dissolved in a solvent, or a neat liquid coating agent, into the pores of the first composite particles and / or the intermediate composite particles. This facilitates the penetration of the coating agent into the pore structure of the composite particles. The amount of liquid used is minimised, improving efficiency.

[0031] The first composite particle may be comminuted for at least 5 minutes, or at least 20 minutes, or at least 1 hour.

[0032] The process may comprise comminuting the first composite particles in the presence of the coating agent for a first period of time, then introducing additional coating agent and comminuting in the presence of the additional coating agent for a second period of time. Optionally, the first period of time is at least 5 minutes, or at least 20 minutes, or at least 1 hour; and / or the second period of time is at least 5 minutes, or at least 20 minutes, or at least 1 hour.

[0033] The process may comprise comprising comminuting the first composite particles in the absence of a coating agent for a period of time, then comminuting the first composite particles in the presence of the coating agent; optionally the period of time is at least 5 minutes, or at least 20 minutes, or at least 1 hour, or at least 2 hours.

[0034] The comminuting can be performed by dry milling, e.g. by dry milling the first composite particles in the presence of a solid coating agent. Among the dry mills, jet mills are preferred because of capability to grind to lower sizes. Jet mills use a high-speed jet of compressed air or inert gas to impact particles with each other. Jet mills can be used with starting material with a size up to about 1 mm and are known to readily achieve sizes of the order of 1 pm with relatively little energy input.

[0035] There are different types of jet mills, e.g. rotational types (cyclic motion) and fluidised opposed-jet types. In the rotational type, particles are accelerated by using tangential gas force from the walls. The fluidised opposing-jet works by multiples of jet separated at equal angles from each other and works on colliding particles on collision trajectory towards each other. Fluidised opposing-jet type mills are more suitable when a higher capacity is desired. The grinding action in both types of mills is achieved by collision of particles with each other rather than with a hard target. This specific mode of action results in a comminuted product with narrow particle size distribution which is beneficial for incorporation into a metal-ion battery electrode.

[0036] Either a rotational jet mill (e.g. a spiral jet mill) or fluidised opposed jet-mill design can be used with a diameter up to several meters, with grinding gas pressure between 50 and 1000 kPa, and a maximum starting particle size of 1 mm. The grinding gas is either an inert gas such as nitrogen or argon, or a mixture of these with a low partial pressure of air, water or oxygen. The comminuting most preferably does not involve spray drying, as this does not allow for controlled particle size reduction.

[0037] In the second aspect, the intermediate composite particles may be subjected to intervening processes before they are contacted with the coating agent, provided that any intervening processes are performed in an inert environment. For example, the intermediate composite particles may be isolated, e.g. by filtration and / or evaporation if they were comminuted by wet milling. The intermediate composite particles may be classified according to size, e.g. by sieving or centrifugation. The intermediate composite particles may be subjected to a heat treatment, e.g. to an annealing step.

[0038] The second composite particles comprise a coating derived from the coating agent. It will be understood that “derived from” encompasses the coating agent becoming physically adhered to the composite particles without chemical modification, e.g. by intermolecular forces such as hydrogen bonding; and a chemical reaction taking place between the composite particles and the coating agent to form the coating, e.g. chemically bonding the coating agent or a reaction product thereof to the composite particles.

[0039] A variety of different coating agents may be used depending on the desired properties and end-use for the second composite particles. By appropriate choice of the coating agent, the coating can provide one or more of the following advantages:

[0040] (i) Surface conductivity. A coating can improve the ionic and / or electronic conductivity at the surface of the composite particles, thereby improving the interface between the composite particles and the electrolyte. A conductive coating can also minimise the loss of contact of electroactive material with the rest of electrode during expansion and contraction. In this way, more of the electroactive material is utilised during operation.

[0041] (ii) Mechanical strength. A coating can improve the ability of the composite particles with withstand stress, both during lithiation / delithiation and during cell manufacture. This is particularly advantageous for SSBs, where electrodes comprising composite particles are typically constrained at high pressure.

[0042] (iii) Passivation. The comminuting step can result in the formation of fresh surfaces of the electroactive material domains which may be reactive, e.g. resulting in hydrogen gas generation. In the first aspect, the presence of the coating agent when comminuting advantageously results in simultaneous particle size reduction and formation of the coating, which may passivate the fresh surfaces reducing their susceptibility to oxidation, e.g. by forming an artificial SEI layer. In the second aspect, any fresh surfaces formed are maintained in an inert environment before the coating is formed, so undesired reactions with the fresh surfaces are minimised before they are passivated by the coating.

[0043] (iv) Surface interactions. A coating can modify how the composite particles interact with other components, e.g. by modifying the hydrophobicity of the surface. This can aid the dispersion of composite particles in slurries for fabrication of electrodes.

[0044] The coating agent may be selected from polymers, pitches, metal phosphate precursors, metal oxide precursors, salts of lithium and a fatty acid, inorganic lithium compounds, and mixtures thereof.

[0045] Polymer coating agents are preferred. The polymer coating agent may be selected from poly-alkylene-oxides (e.g. polyethylene oxide (PEO), polypropylene oxide (PPO)); halogenated polymers (e.g. polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co- hexafluoropropylene (PVDF-HFP), polyvinylidene chloride (PVDC)); poly-alkyl-acrylates and their acid derivatives (e.g. polymethyl methacrylate (PMMA), polyacrylic acid (PAA));

[0046] Li and / or Na salts of polymeric carboxylic acids (e.g. lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA)); carbon-based polymers comprising nitrogen functionality (e.g. polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyethylamine (PEI), polyvinylamine (PVAm), polyallylamine (PAAm), polydially dimethyl-ammonium chloride (PDDA), polyaniline (PANI), polypyrrole (PPy)); polyimides or polyamide-imides which are preferably unsaturated such as poly(4,4'- oxydiphenylene-pyromellitimide); conductive polymers comprising unsaturated carbon atoms such as aromatic groups and preferably heteroatoms such as N, S, P, and B (e.g. polythiophene (PT), poly(hydroxymethyl 3, 4- ethylene dioxythiophene) (HMEDOT), poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS)); siloxanes and polysiloxanes (e.g. 1 ,1 ,3,3-tetramethyldisiloxane, polydimethylsiloxane (PDMS), polyboronsiloxane (PBS)); silanes which are liquid at 25°C and atmospheric pressure; polyalcohols, polyethers, and polycarbonates (e.g. polyethylene carbonate (PEC), polypropylene carbonate (PPC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethylene glycol octophenyl ether (PEGPE), polyethylene glycol methacrylate (PEGMA), poly(bisphenol A carbonate)); polyether-thioureas (e.g. polyether-thioureas crosslinked with PAA); biopolymers (e.g. lignin, chitosan, shellac, gum resins, gum arabic, elemi resin, gellan gum, alginate, and Li and Na salts thereof; preferably lignin, chitosan, alginate, and Li and Na salts thereof); polyacetylene; amines with two or more amino groups (e.g. 1 ,3-diaminopropane, 1 ,4-diaminobutane, 1 ,5-diaminopentane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine); and mixtures thereof.

[0047] The polymer coating agents may be doped to improve their electronic conductivity. For example, polyacetylene can be doped by p-type dopants including Br2, I2, CI2, and / or ASF2, preferably I2; or by n-type dopants including lithium, sodium, and / or potassium.

[0048] Silanes which are liquid at 25°C and atmospheric pressure may be selected from alkoxysilanes (e.g. methyltrimethoxysilane, ethyltrimethoxysilane, iso-butyltrimethoxysilane, tetraethoxysilane (TEOS), and 1 ,2-dimethoxy-1 ,1 ,2,2-tetramethyldisilane), aminosilanes (e.g. (3-aminopropyl)- triethoxysilane (APTES), (3-aminopropyl)-diethoxy-methylsilane (APDEMS), (3-aminopropyl)- dimethyl-ethoxysilane (APDMES), (3-aminopropyl)-trimethoxysilane (APTMS), bis-gamma- trimethoxysilylpropyl amine, aminoneohexyltrimethoxysilane, aminoneohexyldimethoxysilane, aminoneohexylmethoxysilane, aminoundecyltriethoxysilane, amino-2-(dimethylethoxysilyl)propane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylsilanol), glycidoxysilanes (e.g. (3-glycidoxypropyl)-dimethyl- ethoxysilane (GPMES)), and mercaptosilanes (e.g. (3-mercaptopropyl)-tromethoxysilane (MPTMS), and (3-mercaptopropyl)-methyl-dimethoxysilane (MPDMS)). Atmospheric pressure is 101 ,325 Pa.

[0049] Preferably, the polymer coating agent is selected from poly-alkylene-oxides; poly-alkyl-acrylates and their acid derivatives; Li and / or Na salts of polymeric carboxylic acids; carbon-based polymers comprising nitrogen functionality; conductive polymers comprising unsaturated carbon atoms such as aromatic groups and preferably heteroatoms such as N, S, P, and B; polyalcohols, polyethers, and polycarbonates; and mixtures thereof.

[0050] The polymer may be combined with a plasticiser, which may be selected from nitriles such as succinonitrile (SN) or adiponitrile (AN), adipates, orthophthalates, teraphthalates, trimellitic acid, sebacates, and mixtures thereof; preferably SN, AN, and mixtures thereof. For example, PEO may be combined with SN.

[0051] Polymer coating agents typically provide passivation of the second composite particles. Preferred polymer coating agents for providing passivation are chitosan (including Li and Na salts thereof), alginate (including Li and Na salts thereof), PVP, PAA (including Li and Na salts thereof), PVA, and mixtures thereof; most preferably PVP, PAA (including Li and Na salts thereof) combined with PVA, and mixtures thereof. Lithium stearate and pitch are also preferred coating agents for providing passivation.

[0052] Polymer coating agents can be chosen to target further desired properties in the second composite particles including electronic conductivity, ionic conductivity, and mechanical strength. In this way, polymer coating agents provide advantages (i), (ii), and (iii) above. For example, ionic conductivity may be provided by polyethylene carbonate (PEC), polypropylene carbonate (PPC), polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), polyethylene glycol (PEG), polyethylene glycol octophenyl ether (PEGPE), polyallylamine (PAAm), polydially dimethyl-ammonium chloride (PDDA), polycarbonate, and mixtures thereof. Preferred polymer coating agents for providing ionic conductivity are PEGPE, PEG, PAN, PPO, PEC, PPC, PEO, PEO combined with SN, and mixtures thereof; most preferably PEC, PPC, PEO combined with SN, and mixtures thereof. Lithium phosphate precursors are also preferred coating agents for providing ionic conductivity.

[0053] Electronic conductivity may be provided by polyvinylidene chloride (PVDC), polyacetylene, polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), poly(hydroxymethyl 3, 4-ethylene dioxythiophene) (HMEDOT), poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), and mixtures thereof. Preferred polymer coating agents for providing electronic conductivity are PANI, polyacetylene, PPy, PEDOT: PSS, PEDOT, and mixtures thereof; most preferably PEDOT: PSS, PEDOT, and mixtures thereof. Pitch and zinc oxide precursors are also preferred coating agents for providing electronic conductivity.

[0054] Mechanical strength may be provided by polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), polyboronsiloxane (PBS), polyether-thioureas, polyimides or polyamide-imides, and mixtures thereof; preferably PDMS, PMMA, polyimides or polyamide-imides; most preferably polyimides or polyamide-imides. Modified surface interactions may be provided by siloxanes, polysiloxanes, and silanes which are liquid at 25°C and atmospheric pressure, polyamines (e.g. PEI, PVAm, and PAAm), and amines with two or more amino groups.

[0055] Preferred polymer coating agents are chitosan (including Li and Na salts thereof), alginate (including Li and Na salts thereof), PVP, PAA (including Li and Na salts thereof), PVA, PEGPE, PEG, PAN, PPG, PEC, PPC, PEO, PEO combined with SN, PANI, polyacetylene, PPy, PEDOT:PSS, PEDOT, PDMS, PMMA, polyimides or polyamide-imides, and mixtures thereof. Most preferred polymer coating agents are PVP, PAA (including Li and Na salts thereof) combined with PVA and / or PEG, PEC, PPC, PEO combined with SN, PEDOT:PSS, PEDOT, and mixtures thereof. A particularly preferred polymer coating agent is PAA (including Li and Na salts thereof) combined with PVA and / or PEG.

[0056] The coating agent may be a pitch. Pitch is a mixture of aromatic hydrocarbons of different molecular weights. The pitch may be selected from coal tar pitch, petroleum pitch, mesophase pitch, wood tar pitch, isotropic pitch, bitumen, and mixtures thereof. Pitch as a coating agent provides passivation and electronic conductivity.

[0057] The coating agent may be a metal phosphate precursor, such as a metal source and a phosphate source. The metal may be selected from lithium, aluminium, iron, and nickel, and mixtures thereof; most preferably lithium. The metal source is typically a metal salt or hydroxide. Lithium sources may be selected from lithium nitrate, lithium hydroxide, lithium acetate, and mixtures thereof. The phosphate source may be selected from ammonium dihydrogen phosphate, phosphoric acid, and mixtures thereof. For example, a lithium phosphate precursor may be lithium nitrate and ammonium dihydrogen phosphate; or lithium acetate and phosphoric acid; or lithium nitrate and phosphoric acid optionally with citric acid. During the comminuting step, the metal source and the phosphate source react in-situ to form a metal phosphate coating on the second composite particles, most preferably a lithium phosphate coating. The metal phosphate coating provides ionic conductivity and passivation.

[0058] The coating agent may be a metal oxide precursor, such as a zinc, titanium, aluminium, zirconium, or lithium oxide precursor. The metal oxide precursor may be a salt of the metal, for example a halide or chloride such as zinc chloride. The metal oxide may comprise more than one metal, for example lithium aluminate. The metal oxide precursor forms a metal oxide coating which can provide surface conductivity, mechanical strength, and / or passivation. For example, titanium oxide, zirconium oxide, and aluminium oxide provide passivation. Titanium oxide and zinc oxide provide electronic conductivity. Zinc oxide is a particularly preferred metal oxide as it undergoes lithiation during cycling forming a Zn / Li2O material, which is electrically and ionically conductive.

[0059] The coating agent may be a salt of lithium and a fatty acid, which is typically known as “lithium soap”. Examples include lithium stearate, lithium oleate, and lithium palmitate. Salts of lithium and a fatty acid typically have low melting points (below about 250°C) and thus soften during the comminuting step. In this way, they can enter the pores of the composite particles, coat the electroactive material domains, and create an artificial SEI layer, providing passivation. Moreover, the salt is flexible and will structurally support the composite particles, providing mechanical strength.

[0060] The coating agent may be an inorganic lithium compound, such as an organolithium reagent (e.g. n-butyl lithium), lithium carbonate, lithium fluoride, or a lithium silicate (e.g. lithium polysilicate (Li2SisOi 1), lithium metasilicate (I^SiC ), and / or lithium orthosilicate (I^SiC )). These coating agents provide ionic conductivity.

[0061] In a particularly preferred implementation of the invention, comminuting the first composite particles exposes fresh surfaces of the electroactive material domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces. Passivation reduces the susceptibility of the fresh surfaces to oxidation. In this way, the formation of lithium silicates on cell formation is reduced, improving silicon utilisation. The coating agent for this implementation may be selected from polymers, pitch, metal phosphate precursors (e.g. lithium phosphate precursors), metal oxide precursors (e.g. titanium oxide, zirconium oxide, and aluminium oxide), and salts of lithium and a fatty acid; preferably from polymers.

[0062] In the first aspect, the comminuting takes place in the presence of the coating agent, so the coating passivates fresh surfaces at the same time as they are formed. In the second aspect, the comminuting takes place in an inert environment and the intermediate composite particles are maintained in an inert environment until the coating is formed, so undesired reactions with the fresh surfaces are minimised before the fresh surfaces are passivated by the coating.

[0063] Passivation typically results in reduced hydrogen generation by the second composite particles, in particular when the electroactive material is silicon. Thus, the processes of the invention may provide second composite particles which display reduced hydrogen generation compared to composite particles provided by the same process but omitting the coating agent. Hydrogen generation may be measured according to the following protocol:

[0064] Samples are assessed for their hydrogen activity by storing 0.5 g of the composite particles in 10 g of deionised water in a 20 mL vial with an injectable vial cap for 7 days (168 hours) at 25 °C. The vials are stored upside down except during gas chromatography measurements. Gas chromatography measurements were performed with a Perkin Elmer Clarus GC with an HTA headspace platform. The detector used was a pulsed discharge detector with helium as the ion source. The carrier gas used was Grade 6.0 (99.9999%) gas (O2 <0.01 ppm, H2O <0.02 ppm, THC <0.1 ppm, CO + CO2 <0.1 ppm, N2<1 ppm, CFC <0.001 ppm). The column used for gas chromatography was a CP-Molsieve 5 (7536 fused silica; 25 m; 0.32 mm; 30 pm). The headspace is sampled by first extracting and reintroducing 2.5 mL of gas into the vial 5 times over, to ensure good mixing of the gas in the headspace. Then 1 mL of gas is extracted and injected into the GC unit at 20 mL / min. The injection port temperature is set at 150 °C, the detector temperature is set at 150 °C, the column oven temperature is set at 40°C. The carrier gas pressure is 82.74 kPa (12 psi).

[0065] The response on the detector of the GC unit is calibrated against commercial calibration standard gases to determine the response in ppm. This is then converted to moles of hydrogen gas (H2) under the conversion of 22.4 litres per mole, and the known volume of gas.

[0066] The vials of composite plus water were continuously stored in a controlled environment at 25 °C. Vial caps were carefully crimped and checked as secure to avoid gas leakage. When they were not being measured or prepared for measurement, the vials were stored upside down, to isolate the vial cap from the gas-phase and further prevent potential hydrogen gas loss due to leakage. After a measurement, the vials were left to sit for at least 1 minute prior to re-capping and turning upside for storage, to allow any hydrogen gas to escape (this avoids double-counting for cumulative total.) Each data point in the examples was measured with 2 or 3 repeats, and the numbers given are the average of the repeated measurements. Measurements are taken after 1 day (24 hours), 2 days (48 hours), 3 days (72 hours) and 7 days (168 hours). The values for the 2-day hydrogen activity, 3-day hydrogen activity, and 7-day hydrogen activity are defined herein as the cumulative total of the measurements up to and including the specified day. The result may be normalised to 1 g of silicon. Accordingly, the processes of the invention may provide second composite particles which display reduced 7-day hydrogen activity compared to composite particles provided by the same process but omitting the coating agent. 7-day hydrogen activity is defined as the cumulative hydrogen generation over 7 days in pmol per gram of silicon that is observed when 0.5 g of composite particles are stored in 10 g of deionised water for 7 days (168 hours) at 25 °C. The reduction in 7-day hydrogen activity may be at least a 50% reduction, at least a 60% reduction, or at least a 75% reduction.

[0067] The second composite particles preferably have a 7-day hydrogen activity in water of less than 40 pmol per gram of silicon, or less than 35 pmol per gram of silicon, or less than 30 pmol per gram of silicon, or less than 25 pmol per gram of silicon, or less than 20 pmol per gram of silicon, or less than 15 pmol per gram of silicon, or less than 12 pmol per gram of silicon, or less than 10 pmol per gram of silicon.

[0068] In accordance with conventional IIIPAC terminology, the term “micropore” is used herein to refer to pores of less than 2 nm in diameter, the term “mesopore” is used herein to refer to pores of 2-50 nm in diameter, and the term “macropore” is used to refer to pores of greater than 50 nm diameter. As used herein, P1 is the total volume of micropores and mesopores expressed in cm3 / g. P2 is the volume of macropores between 50-100 nm. Pore volume measured above 100 nm is assumed for the purposes of the invention to be inter-particle porosity and is disregarded.

[0069] The total volume of micropores and mesopores and the pore size distribution of micropores, mesopores, and macropores including the P1 and PDnpore diameter parameters defined herein, are determined using nitrogen gas adsorption at 77 K. Micropores and mesopores are determined down to a relative pressure p / p0of 10-7using quenched solid density functional theory (QSDFT). The measurement is preferably made in accordance with standard methodology as set out in ISO 15901-2:2022. Macropore volume in the range 50-100 nm - denoted P2 are determined using nitrogen gas adsorption where relative pressure down to 10'4P / Po is sufficient. References herein to P2 shall be understood as meaning pore volumes as measured by nitrogen gas adsorption at 77 K by the Barrett-Joyner-Halenda (BJH) method in accordance with standard methodology, preferably as set out in ISO 15901-2:2022. A subtraction of the value of pore volume as determined by BJH at 50 nm from the pore volume at 100 nm width gives the value denoted P2. Nitrogen gas adsorption is a technique that characterises the porosity and pore diameter distributions of a material by allowing a gas to condense in the pores of a solid. As pressure increases, the gas condenses first in the pores of smallest diameter and the pressure is increased until a saturation point is reached at which all of the pores are filled with liquid. The nitrogen gas pressure is then reduced incrementally, to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms, and the hysteresis between them, allows the pore volume and pore size distribution to be determined. Suitable instruments for the measurement of pore volume and pore size distributions by nitrogen gas adsorption include the ASAP 2020 Plus porosity analyzer, which are available from Micromeritics Instrument Corporation, USA, and the Autosorb IQ porosity analyzers, which are available from Quantachrome Instruments.

[0070] In the absence of any indication to the contrary, the pore structure of the composite particles (e.g. P1, P2, PDnpore diameter, etc.) is defined by the pore structure of the particulate porous frameworks taken in isolation, i.e. as measured in the absence of any electroactive material (or any other material) occupying the pores of the particulate porous frameworks.

[0071] Nitrogen gas adsorption is effective for the measurement of pore volume and pore size distributions for pores having a diameter up to 100 nm but is less reliable for pores of much larger diameter. For the purposes of the present invention, nitrogen adsorption is therefore used to determine pore volumes and pore size distributions only for pores having a diameter up to and including 100 nm (i.e. only for micropores, mesopores, and smaller macropores). PDnvalues are likewise determined relative to the total volume of micropores and mesopores only.

[0072] In the case that the particulate porous frameworks of the first composite particles comprise macropores, the volume of pores having diameter in the range from greater than 50 nm and up to 100 nm is preferably no more than 0.3 cm3 / g, or no more than 0.2 cm3 / g, or no more than 0.1 cm3 / g, or no more than 0.05 cm3 / g. A small fraction of macropores may be useful to facilitate electrolyte access into the pore network, but the advantages of the invention are obtained substantially by accommodating electroactive material in micropores and optionally mesopores.

[0073] It will be appreciated that intrusion techniques such as gas adsorption are effective only to determine the pore volume of pores that are accessible to nitrogen or to mercury from the exterior of the particulate porous frameworks. Porosity values specified herein shall be understood as referring to the volume of open pores, i.e. pores that are accessible to a fluid from the exterior of the particulate porous frameworks. Fully enclosed pores which cannot be identified by nitrogen adsorption shall not be taken into account herein when determining porosity values. Likewise, any pore volume located in pores that are so small as to be below the limit of detection by nitrogen adsorption is not taken into account. The pore structure of the particulate porous frameworks may include a monomodal, bimodal or multimodal pore size distribution. As used herein, the term “pore size distribution” relates to the distribution of pore size relative to the cumulative total internal pore volume of the particulate porous frameworks. A bimodal or multimodal pore size distribution is preferred since close proximity between micropores and pores of larger diameter provides the advantage of efficient ionic transport through the porous network to the electroactive material.

[0074] The general term “PDnpore diameter” refers herein to the volume-based nth percentile pore diameter, based on the total volume of micropores and mesopores. For instance, the term “PD5o pore diameter” as used herein refers to the pore diameter below which 50% of the total micropore and mesopore volume is found. For the avoidance of doubt, any macropore volume (pore diameter greater than 50 nm) is not taken into account for the purpose of determining PDnvalues.

[0075] The pore structure of the particulate porous frameworks of the first composite particles has been determined by the inventors on the basis that depositing electroactive materials such as silicon in porous frameworks may be efficiently performed by a chemical vapour infiltration process (CVI). This is a variant of chemical vapour deposition (CVD) where the decomposition surface is within a pore inside a porous framework. For decomposition of a silicon precursor into silicon to occur, the precursor must be able to enter the pore of the framework and travel to a suitable decomposition site. Desirable frameworks generally comprise a three-dimensionally interconnected open pore network comprising micropores and optionally mesopores and optionally a minor volume of macropores.

[0076] Particulate porous frameworks may be characterised by P1 , the total volume of micropores and mesopores (i.e. the total pore volume in the pore diameter range from 0 to 50 nm). Typically, the particulate porous frameworks of the first composite particles include both micropores and mesopores. However, it is not excluded that particulate porous frameworks may be used which include micropores and no mesopores. P1 of the particulate porous frameworks of the first composite particles is preferably least 0.35, or at least 0.4, or at least 0.5, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8. The use of higher porosity particles may be advantageous since it allows a larger amount of electroactive material to be accommodated within the pore volume.

[0077] Preferably, the particulate porous frameworks of the first composite particles comprise mesopores, most preferably wherein the mesopores form at least 40%, or at least 45%, or at least 50%, or at least 55% of the total volume of the micropores and mesopores of the particulate porous frameworks.

[0078] The internal pore volume of the particulate porous frameworks is suitably capped at a value at which increasing fragility of the framework’s structure outweighs the advantage of increased pore volume accommodating a larger amount of electroactive material. P1 of the particulate porous frameworks of the first composite particles may be no more than 2.5, or no more than 2.0, or no more than 1.8, or no more than 1.7, or no more than 1.6, or no more than 1.55, or no more than 1.5, or no more than 1.45, or no more than 1.4, or no more than 1.35, or no more than 1.3, or no more than 1.25, or no more than 1.2, or no more than 1.1.

[0079] Preferably P1 of the particulate porous frameworks of the first composite particles is in the range from 0.4 to 2.2, or from 0.5 to 1.8, or most preferably from 0.6 to 1.6.

[0080] The micropore volume of the particulate porous frameworks of the first composite particles is preferably at least 0.3 cm3 / g, or at least 0.4 cm3 / g, or at least 0.5 cm3 / g, or at least 0.6 cm3 / g.

[0081] The particulate porous frameworks of the first composite particles may have a modal pore diameter of micropores and mesopores of >0.50 nm preferably >0.60 nm.

[0082] In the case that the particulate porous frameworks of the first composite particles comprise macropores, the volume of pores in the range of greater than 50 nm and up to 100 nm may be referred to as P2 cm3 / g and is measured by the BJH method. The volume of macropores (and therefore the value of P2) is preferably small as compared to the volume of micropores and mesopores (and therefore the value of P1). While a small fraction of macropores may be useful to facilitate electrolyte access into the pore network, the advantages of the invention are obtained substantially by accommodating electroactive material in micropores and smaller mesopores.

[0083] Thus, P2 of the particulate porous frameworks of the first composite particles preferably has a value of <0.2xP1 , or <0.1 xP1 , or <0.05xP1, or <0.02xP1, or <0.01xP1 , or <0.005xP1.

[0084] P2 of the particulate porous frameworks of the first composite particles may be <15%, <10%, <8%, or <5% of the total volume of micropores, mesopores, and pores having a diameter in the range of greater than 50 nm and up to 100 nm.

[0085] Optionally, P1 + P2 of the particulate porous frameworks of the first composite particles is no more than 2.5 cm3 / g. The particulate porous frameworks of the first composite particles preferably have a PDgo pore diameter of no more than 25 nm, or 1-20 nm, or 1.5-10 nm, or 2-9 nm. The particulate porous frameworks of the first composite particles preferably have a PD50 pore diameter of no more than 4 nm, or no more than 3 nm, or 1-2.5 nm.

[0086] VP07 is the volume of pores in the particulate porous frameworks of the first composite particles with a pore diameter of 0.7 nm or less expressed as a percentage of P1. VP07 is preferably in the range of 5.1-40%, or 5.5-35%, or 7-30%, or 10-27%, or most preferably 15-25%.

[0087] VP07 is expressed relative to the total volume of micropores and mesopores in the particulate porous frameworks. However, for some uses, it is advantageous to specify a minimum absolute value of the volume of pores with a pore diameter of 0.7 nm or less. Thus, the volume of pores in the particulate porous frameworks with a pore diameter of 0.7 nm or less may be at least 0.05 cm3 / g, preferably 0.08-0.5 cm3 / g, most preferably 0.1-0.3 cm3 / g; when measured by nitrogen adsorption.

[0088] VP1 , VP2, and VP5 are the volume of pores in the particulate porous frameworks of the first composite particles with a pore diameter of 1.0 nm or less, 2.0 nm or less, and 5.0 nm or less, respectively, expressed as a percentage of P1 . VP1 , VP2, and VP5 are measured by nitrogen gas adsorption. Preferably, VP1 is at least 1.5xVP07, or at least 2xVP07. Preferably, VP2 is at least 2.5xVP07, or at least 3xVP07, or at least 4xVP07. Preferably, VP5 is at least 55%, or at least 60%, or at least 70%, or at least 80% or at least 90%, or at least 92%, or at least 93%.

[0089] Preferably, VP2 is at least 20%. For some uses, VP2 is at least 40%, at least 50%, at least 55%, or at least 60%, or at least 70%, or at least 80%, or at least 85%, i.e. the micropores form the majority of the volume of micropores and mesopores. Alternatively, VP2 is less than 50%, or no more than 45%, or no more than 40%, i.e. the mesopores form the majority of the volume of micropores and mesopores.

[0090] VP2 may be less than 99%, or less than 98%, or less than 95%, or preferably less than 90%, for example 40-90%.

[0091] VP2 may be in the range of 45-98%, or 45-90%, or 45-85%, or 45-80%, or 45-78%, or 45-75%, or 45-70%, or 45-60%, or 50-98%, or 50-90%, or 50-85%, or 50-80%, or 50-78%, or 50-75%, or 50- 70%, or 55-98%, or 55-90%, or 55-85%, or 55-80%, or 55-78%, or 55-75%, or 55-70%, or 55-69%. The pore volume at larger pore sizes may be controlled to further refine the properties of the frameworks and resulting composite particles. VP20 and VP10 are defined as the volume of pores in the particulate porous frameworks of the first composite particles with a pore diameter of 20.0 nm or less or 10.0 nm or less, respectively, expressed as a percentage of P1. VP10 and VP20 are measured by nitrogen gas adsorption. VP20 may be at least 80%, or at least 90%, or at least 95%, or at least 97%, or at least 98%. VP10 may be at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97%.

[0092] VP20-VP5 represents the pore volume in the particulate porous frameworks with a pore diameter of more than 5.0 nm up to and including 20.0 nm, expressed as a percentage of P1. VP20-VP5 may be less than 20%, less than 15%, preferably less than 12%, preferably less than 10%, or more preferably less than 9%. Optionally, VP20-VP5 is at least 0.5%, or at least 1%, or at least 2%. VP20-VP5 may be 0.5-20%, 0.5-15%, or 1-12%, or 2-10%, or 2-9%, or 3-9%.

[0093] VP20-VP2 may preferably be no more than 55%, or no more than 50%, or no more than 45%.

[0094] The first composite particles typically have a D50 particle diameter of at least 5.5 pm. Optionally, the D50 particle diameter of the first composite particles may be at least 10, 15, 20, 35, or 40 pm. It is an advantage of the invention that the first composite particles may be chosen to have a large particle size, preferably a D50 particle diameter of at least 35 pm or 40-200 pm, or most preferably 50-150 pm, and then comminuted to a smaller particle size for use in battery electrodes. Using larger first composite particles means that they may be prepared from larger particulate porous frameworks, which leads to a number of advantages. The first composite particles are typically prepared by CVI, which for smaller particles may produce unwanted exothermicity. Larger particles can lead to more efficient gas-solid mixing during CVI. Larger particles are easier to handle and tend to result in less agglomeration. Larger particles are often cheaper to procure.

[0095] In further detail, the handling and processing for the manufacturing of micron-sized powder material can be challenging in practice. Particles with sizes below 30 pm are considered as very cohesive independent of the density (Geldart D, Powder technology, Volume 7, Issue5, 1973, pages 285-292). Particles with high cohesiveness present a series of processing disadvantages such as, agglomeration and clogging of equipment and piping, difficulty to be conveyed or to be transported pneumatically or transferred between different process units, lack of fluidisation or difficulty to be agitated. The latter is paramount to provide a good mixing both between the particles themselves as well as with a silicon-containing gas during CVI in order to provide a homogeneous Si / C composite material with the right physical and electrochemical properties. Current reactors for the silicon deposition stage need a highly sophisticated design to improve the mixing or aeration and avoid dead zones during the deposition stage as well as minimising difficulties with powder transfer to and from secondary process units. Moreover, it is believed that if particulate porous carbon frameworks to be infiltrated are small (e.g. D50 <7 pm), and the targeted silicon loading via the CVI process is high (e.g. >60%), then the chances of an undesirable exothermic side reaction resulting in the creation of silicon carbide increase.

[0096] The use of higher particles sizes reduces cohesiveness and the particles become more aeratable. Other advantages are reducing the risks of clogging, easing powder material handling, conveying and transferring, reducing the degree of agglomeration in the reactor or deposition chamber during the CVI stage, allowing for a better aeration of the porous particles, better gas-solid mixing and minimising the formation of dead zones leading to a Si / C composite with a higher degree of homogeneity and hence, improved physical and electrochemical properties.

[0097] Providing the first composite particles is preferably performed in a different apparatus to comminuting the first composite particles. This is because apparatuses optimised for performing CVI processes are typically not suitable for comminuting the resulting first composite particles. Accordingly, providing the first composite particles may be performed in a reactor vessel suitable for CVI, e.g. suitable for use at pressures of 20-2000 kPa, and comminuting the first composite particles then performed in a comminuting device e.g. selected from wet mills, ball mills, jet mills, high-shear stirrers, and mechanofusion devices.

[0098] The D10 particle diameter of the first composite particles is preferably at least 0.5 pm, or at least 0.8 pm, or at least 1 pm, or at least 1 .5 pm, or at least 2 pm. By maintaining the D10 particle diameter at 0.5 pm or more, the potential for undesirable agglomeration of sub- micron sized particles is reduced, and improved dispersibility of the composite particles formed.

[0099] The Di particle diameter of the first composite particles is preferably at least 0.5 pm, or at least 1 pm, or at least 1.5 pm, or at least 2 pm, or at least 2.5 pm, or at least 3 pm. By controlling the Di particle diameter, the presence of particle fines at very small particle diameters is reduced, thus reducing the deleterious effects of high cohesiveness and surface area associated with very small particles.

[0100] The Do particle diameter of the first composite particles is preferably at least 0.3 pm, or at least 0.5 pm, or at least 1 pm. The Dgo particle diameter of the first composite particles is preferably no more than 250 pm, or no more than 200 pm, or no more than 150 pm, or no more than 100 pm. The Dgs particle diameter of the first composite particles is preferably no more than 300 pm, or no more than 250 pm, or no more than 200 pm, or no more than 150 pm, or no more than 15 pm. The D o particle diameter of the first composite particles is preferably no more than 300 pm.

[0101] 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, wherein the particle volume is understood to include the volume of any intra- particle pores. The terms “Dn” and “Dnparticle diameter” as used herein refer to the volume-based median particle diameter, i.e. the diameter below which n% by volume of the particle population is found.

[0102] Particle diameters and particle size distributions can be determined by standard laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that a particle will scatter light at an angle that varies depending on the size the particle and a collection of particles will produce a pattern of scattered light defined by intensity and angle that can be correlated to a particle size distribution. A number of laser diffraction instruments are commercially available for the rapid and reliable determination of particle size distributions. Unless stated otherwise, particle size distribution measurements as specified or reported herein are as measured by the conventional Malvern Mastersizer™ 3000 particle size analyzer from Malvern Instruments™. The Malvern Mastersizer™ 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing the particles of interest suspended in an aqueous solution. Light rays which strike the particles are scattered through angles which are inversely proportional to the particle size and a photodetector array measures the intensity of light at several predetermined angles and the measured intensities at different angles are processed by a computer using standard theoretical principles to determine the particle size distribution. Laser diffraction values as reported herein are obtained using a wet dispersion of the particles in 2- propanol with a 5 vol% addition of the surfactant SPAN™-40 (sorbitan monopalmitate). The particle refractive index is taken to be 2.68 for particulate porous frameworks and 3.50 for composite particles and the dispersant index is taken to be 1.378. Particle size distributions are calculated using the Mie scattering model.

[0103] In general, the second composite particles have a D50 particle diameter of no more than 10 pm, or no more than 8 pm, or no more than 5.0 pm, or no more than 4.5 pm. The D50 particle diameter of the second composite particles may be at least 0.25 pm, at least 0.5 pm, or at least 0.75 pm, or at least 1.0 pm. Thus, the second composite particles may have a D50 particle diameter of 0.25-10 m, or 0.5-8 pm, or 0.75-5.0 pm, or 1.0-4.5 pm. Preferably, the second composite particles have a D50 particle diameter of 0.25-10 pm, more preferably 0.5-10 pm. Composite particles having particle size distributions within these ranges are believed to be advantageous for use in high density electrodes and / or SSBs. For example, SSBs are often formulated using solid electrolyte particles with a D50 particle diameter of less than about 1 pm. Composite particles having sizes within these ranges aid the interface between the electroactive material and the electrolyte particles.

[0104] The particle size of the intermediate composite particles may be defined by any of the particle size parameters defined herein for the second composite particles.

[0105] A target particle size distribution for the intermediate and second composite particles may be obtained by controlling the comminuting process. For example, the comminuting time, environment (e.g. wet or dry), and equipment (e.g. the size of grinding balls when ball milling) can be varied as known in the art. The second and intermediate composite particles may also be classified according to size.

[0106] The ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles may be no more than 0.9, or no more than 0.75, or no more than 0.5, or no more than 0.3; and optionally at least 0.005, or at least 0.008, or at least 0.01 , or at least 0.1. Thus, the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles may be 0.9-0.005, or 0.75-0.008, or 0.5-0.01 , or 0.3-0.1. Preferably, the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is 0.5-0.005.

[0107] The D10 particle diameter of the second composite particles is preferably at least 0.1 pm, or at least 0.2 pm, or at least 0.4 pm, or at least 0.6 pm, or at least 0.8 pm. By maintaining the D10 particle diameter at 0.1 pm or more, the potential for undesirable agglomeration of sub- micron sized particles is reduced, and improved dispersibility of the composite particles formed.

[0108] The Di particle diameter of the second composite particles is preferably at least 0.05 pm, or at least 0.1 pm, or at least 0.2 pm, or at least 0.4 pm, or at least 0.6 pm. By controlling the Di particle diameter, the presence of particle fines at very small particle diameters is reduced, thus reducing the deleterious effects of high cohesiveness and surface area associated with very small particles. The Do particle diameter of the second composite particles is preferably at least 0.025 pm, or at least 0.05 pm, or at least 0.1 pm, or at least 0.2 pm.

[0109] The Dgo particle diameter of the second composite particles is preferably no more than 35 pm, or no more than 20 pm, or no more than 15 pm, or no more than 10 pm.

[0110] The D98particle diameter of the second composite particles is preferably no more than 40 pm, or no more than 25 pm, or no more than 20 pm, or no more than 15 pm. By controlling the D98particle diameter, the presence of even a small number of over-sized particles remaining within the composite particle population is reduced, thus reducing the deleterious effects relating to packing efficiency and creating inhomogeneities in electrode layers associated with over-sized particles.

[0111] The D100 particle diameter of the second composite particles is preferably no more than 40 pm.

[0112] The second composite particles may have an average sphericity of no more than 0.95, or no more than 0.9, or no more than 0.8. Optionally, they have an average sphericity of at least 0.55 or at least 0.6.

[0113] It is possible to obtain highly accurate two-dimensional projections of micron scale particles by scanning electron microscopy (SEM) or by dynamic image analysis, in which a digital camera is used to record the shadow projected by a particle. The term “sphericity” as used herein shall be understood as the ratio of the area of the particle projection (obtained from such imaging techniques) to the area of a circle, wherein the particle projection and circle have identical circumference. Thus, for an individual particle, the sphericity S may be defined as: wherein Amis the measured area of the particle projection and Cmis the measured circumference of the particle projection. The average sphericity Savof a population of particles as used herein is defined as: wherein n represents the number of particles in the population. The average sphericity for a population of particles is preferably calculated from the two-dimensional projections of at least 50 particles. The second composite particles preferably have a narrow size distribution span. For instance, the particle size distribution span (defined as (Dgo-Dio) / D5o) 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. By maintaining a narrow size distribution span, efficient packing of the particles into dense powder beds is more readily achievable. The particle size distribution span (D98-DI) / DSO is preferably less than 2. Maintaining a tight distribution between the D98and Di particle diameters is believed to aid the deposition of the electroactive material when preparing the composite particles by ensuring homogenous distribution of the frameworks in the reactor vessels typically used during manufacture.

[0114] The process may comprise performing a first iteration of the process to form a first batch of second composite particles, and performing a second iteration of the process to form a second batch of second composite particles, wherein the Dso particle diameter of the second batch of second composite particles is lower than the Dso particle diameter of the first batch of second composite particles, and mixing the first batch and the second batch. The ratio of the Dso particle diameter of the second batch of second composite particles to the Dso particle diameter of the first batch of second composite particles is preferably no more than 0.75, or no more than 0.5, or no more than 0.35. Most preferably, the Dso particle diameter of the first batch of second composite particles is 5.0-10 pm and the Dso particle diameter of the second batch of second composite particles is 0.5-4.5 pm. In this way, the mixture of the first and second batches will have a multi-modal particle size distribution, which facilities packing of the composite particles when incorporated into an electrode. The process may comprise a third and optional further iterations of the process to form third and optional further batches of second composite particles having lower Dso particle diameters than the first and second batches, and mixing the first, second, third, and optional further batches.

[0115] Optionally, the different iterations of the process may be performed using different comminuting devices, to facilitate the formation of batches of second composite particles having different particle size distributions.

[0116] Advantageously, the first composite particles for the first, second, and possible further iterations may be the same. In this way, the same feedstock particles can be converted into second composite particles having different particle size distributions, simplifying manufacture.

[0117] Alternatively, the first composite particles for the first, second, and possible further iterations may be different. Thus, the process may comprise performing a first iteration of the process to form a first batch of second composite particles, and performing a second iteration of the process to form a second batch of second composite particles, wherein the composition of the first composite particles of the first iteration is different to the composition of the first composite particles of the second iteration, and mixing the first batch and the second batch. In this way, a mixture of second composite particles having different compositions may readily be prepared. For example, the ratio of the electroactive material content of the first composite particles of the first iteration to the electroactive material content of the first composite particles of the second iteration may be no more than 0.95, or no more than 0.9, or no more than 0.75, or no more than 0.5; and optionally at least 0.1.

[0118] The coating agent in the first, second, and possible further iterations may be the same or different.

[0119] Optionally, the first iteration is according to the process of the first aspect and the second iteration is according to the process of the second aspect, or the first iteration is according to the process of the second aspect and the second iteration is according to the process of the first aspect.

[0120] The second composite particles preferably have a BET surface area of no more than 500 m2 / g, or no more than 300 m2 / g, or no more than 250 m2 / g, or no more than 200 m2 / g, or no more than 150 m2 / g, or no more than 100 m2 / g, or no more than 80 m2 / g, or more preferably no more than 60 m2 / g, or no more than 50 m2 / g, or no more than 40 m2 / g, or no more than 30 m2 / g, or no more than 25 m2 / g, or no more than 20 m2 / g, or no more than 15 m2 / g, or no more than 10 m2 / g, or no more than 5 m2 / g. In general, a low BET surface area is preferred to minimize the formation of solid electrolyte interphase (SEI) layers at the surface of the composite particles during the first chargedischarge cycle of an anode. However, a BET surface area which is excessively low results in unacceptably low charging rate and capacity due to the inaccessibility of the bulk of the electroactive material to metal ions in the surrounding electrolyte. The BET surface area is preferably at least 0.1 m2 / g, or at least 1 m2 / g, or at least 2 m2 / g. For instance, the BET surface area of the composite particles may be in the range from 0.1 to 100 m2 / g, or from 0.1 to 80 m2 / g, or from 0.5 to 60 m2 / g, or from 0.5 to 40 m2 / g, or from 1 to 30 m2 / g, or from 1 to 25 m2 / g, or from 1 to 20 m2 / g, or from 1 to 15 m2 / g, or from 2 to 10 m2 / g.

[0121] The term “BET surface area” as used herein should be taken to refer to the surface area per unit mass calculated from a measurement of the physical adsorption of gas molecules on a solid surface, using the Brunauer-Emmett-Teller theory, in accordance with ISO 9277:2022. The second composite particles may be subjected to subsequent processing steps. An inert environment may be maintained after the coating has been formed during these subsequent steps. For example, the second composite particles may be isolated, e.g. by filtration and / or evaporation of solvent if present. Excess coating agent may be removed by washing and / or evaporation. Alternatively, a slurry of second composite particles and a solvent resulting from the processes of the invention may be used directly in downstream process, e.g. in manufacturing an electrode comprising the second composite particles.

[0122] The second composite particles may be classified according to size, e.g. by sieving or centrifugation. Preferably, the second composite particles are subjected to a deagglomeration process, such as spray-drying or high-pressure homogenisation.

[0123] The second composite particles may be subjected to a heat treatment, e.g. to an annealing step. This may serve to cure the coating, e.g. introducing cross-links between polymer chains when a polymer coating agent is used, thereby improving the adhesion between the coating and composite particles. Thus, the coating derived from the coating agent may comprise a cross-linked polymer. A heat treatment at higher temperature, e.g. 400 to 900 °C in an inert atmosphere, can be used to convert a carbon-based coating into a pyrolyzed carbon coating.

[0124] The second composite particles may be subjected to a further coating step such as a carbon coating step, e.g. using CVD.

[0125] The particulate porous frameworks of the first composite particles preferably comprise a conductive material. The use of conductive particulate porous frameworks is advantageous as they form a conductive framework within the composite particles which facilitates the flow of electrons between lithium atoms / ions inserted into the electroactive material and a current collector.

[0126] The particulate porous frameworks of the first composite particles preferably have a BET surface area of at least 750 m2 / g, more preferably at least 1 ,000 m2 / g, or at least 1 ,250 m2 / g, or at least 1 ,500 m2 / g. Preferably, the BET surface area of the particulate porous frameworks of the first composite particles is no more than 4,000 m2 / g, or no more than 3,500 m2 / g, or no more than 3,250 m2 / g, or no more than 3,000 m2 / g or no more than 2,500 m2 / g, or no more than 2,000 m2 / g. For example, the particulate porous frameworks may have a BET surface area in the range from 100 m2 / g 10 to 4,000 m2 / g, or from 500 m2 / g to 4,000 m2 / g, or from 750 m2 / g to 3,500 m2 / g, or from 1 ,000 m2 / g to 3,250 m2 / g, or from 1 ,000 m2 / g to 3,000 m2 / g, or from 1 ,000 m2 / g to 2,500 m2 / g, or from 1 ,000 m2 / g to 2,000 m2 / g. A preferred type of particulate porous frameworks of the first composite particles comprises or consist of a conductive carbon material, referred to herein as conductive particulate porous carbon frameworks.

[0127] The particulate porous frameworks of the first composite particles preferably comprise at least 80 wt% carbon, more preferably at least 85 wt% carbon, more preferably at least 90 wt% carbon, more preferably at least 95 wt% carbon, and optionally at least 98wt% or at least 99 wt% carbon. The carbon may be crystalline carbon or amorphous carbon, or a mixture of amorphous and crystalline carbon. The porous carbon particles may be either hard carbon particles or soft carbon particles.

[0128] As used herein, the term “hard carbon” refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2hybridised state (trigonal bonds) in nanoscale polyaromatic domains. The polyaromatic domains are cross-linked with a chemical bond, e.g. a C-O-C bond. Due to the chemical cross-linking between the polyaromatic domains, hard carbons cannot be converted to graphite at high temperatures. Hard carbons have graphite-like character as evidenced by the large G-band (-1600 cm'1) in the Raman spectrum. However, the carbon is not fully graphitic as evidenced by the significant D-band (-1350 cm'1) in the Raman spectrum.

[0129] As used herein, the term “soft carbon” also refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2hybridised state (trigonal bonds) in polyaromatic domains having dimensions in the range from 5 to 200 nm. In contrast to hard carbons, the polyaromatic domains in soft carbons are associated by intermolecular forces but are not cross-linked with a chemical bond. This means that they will graphitise at high temperature. The porous carbon particle frameworks of the first composite particles preferably comprise at least 50% sp2hybridised carbon as measured by XPS. For example, the particulate porous carbon frameworks of the first composite particles may suitably comprise from 50% to 98% sp2hybridised carbon, from 55% to 95% sp2hybridised carbon, from 60% to 90% sp2hybridised carbon, or from 70% to 85% sp2hybridised carbon.

[0130] When the particulate porous frameworks of the first composite particles are particulate porous carbon frameworks, the particulate porous carbon frameworks may have a ratio of the relative intensity of D and G peaks (ID / IG) of <2.0 or <1.8 as measured by Raman spectroscopy. Alternatively, or in addition, ID / IG of the particulate porous carbon frameworks of the first composite particles may be >0.6, or > 0.8, or >1 or >1.05. For example, ID / IG of the particulate porous carbon frameworks of the first composite particles may be in the range of 0.6-1 .8, or 1.0-1.6. The particulate porous frameworks of the first composite particles may be provided by synthesising the frameworks or by obtaining the frameworks from a supplier.

[0131] Most preferably, the particulate porous frameworks of the first composite particles are particulate porous carbon frameworks. The particulate porous carbon frameworks of the first composite particles used in the invention are most preferably a form of activated carbon. The term “activated carbon” refers to a carbonaceous material that has been physically or chemically processed to increase its porosity and surface area. Chemical activation or physical activation (e.g. high temperature steam or CO2) mechanisms are among common methods used in the production of activated carbons. A suitable activation process comprises contacting pyrolyzed carbon with one or more of oxygen, steam, CO, and CO2 at a temperature in the range from 300 to 1500°C, 600 to 1200°C, or 600 to 1000°C.

[0132] Alternatively, frameworks with tailored pore structures can be obtained using template assisted carbonization using zeolites, using known methods. In another approach, frameworks with tailored pore structures can be obtained by carbonizing metal organic frameworks, such as zinc imidazolate frameworks, and washing the carbonized material to remove residual metal.

[0133] Mesopores can also be obtained by known templating processes, using extractable pore formers such as MgO and other colloidal or polymer templates which can be removed by thermal or chemical means post pyrolysis or activation.

[0134] A variety of different particulate porous carbon frameworks are available in the art depending on the starting material and the conditions of the pyrolysis process. Particulate porous carbon frameworks of various different specifications are available from commercial suppliers.

[0135] A variety of different carbonaceous materials and mixtures thereof may be used to prepare suitable particulate porous carbon frameworks via pyrolysis. Preferably, a plant source is used. Examples of plant sources include the husks and shells of seeds, nuts and fruits (also including drupes, kernels and pits). Examples of these plant sources include the shells and husks of coconuts (including coir), groundnuts, walnuts, apricots, almonds, palm seeds, peaches, olives, hazelnuts, bamboos, softwoods, hardwoods, and tree barks (e.g. softwood trees including pine, spruce, larch and poplar, and hardwood trees including oak). A preferred plant source is coconut shells. Fossil carbon sources such as coal may be used. Examples of resins and polymeric materials as carbonaceous materials include phenolic resins, novolac resins, pitch, melamines, polyacrylates, polystyrenes, polyvinylalcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers comprising monomer units of acrylates, styrenes, a-olefins, vinyl pyrrolidone and other ethylenically unsaturated monomers.

[0136] The carbonaceous material, e.g. the plant source, preferably has an elemental composition including at least 40 wt% carbon, at least 3 wt% hydrogen and at least 30 wt% oxygen. Trace amounts of nitrogen, sulphur and chlorine may also be present. More preferably, the carbonaceous material has an elemental composition including around 50 wt% carbon, 5 wt% hydrogen and 40 wt% oxygen with lesser amounts of nitrogen, sulphur and chlorine being present.

[0137] The particulate porous carbon frameworks are typically obtained from the carbonaceous material in a process comprising two steps. Firstly, the carbonaceous material is pyrolyzed by heating in an inert atmosphere. An inert atmosphere may be an atmosphere of nitrogen, CO2, a noble gas, and mixtures thereof. Pyrolysis is usually carried out at a temperature of about 400 to 900 °C, or about 500 to 700 °C, or about 550 to 700 °C so that dehydration and devolatilization of the carbon occur. Preferably, the temperature does not exceed about 700 °C. Optionally, the carbonaceous material is pre-treated to remove impurities prior to heating. Optionally, the carbonaceous material is purified and / or washed and dried prior to heating. Optionally, the carbonaceous material is sieved and crushed or milled to obtain uniform sized particles prior to heating. Optionally the carbonaceous material is pelletized before heating.

[0138] Secondly, the pyrolyzed material is activated by heating in a flow of one or more of oxygen, steam, CO, and CO2at a temperature between 600 °C and 1200 °C. This allows a chemical reaction between the carbon and the flowing gas to take place at the internal surface of the carbon, removing carbon from the pore walls and thereby increasing the pore volume. This gaseous activation process, also known as a physical activation process, allows the pore size to be readily altered producing activated carbons with the desired porosity. Preferably, the pyrolyzed material is activated with steam.

[0139] The physical activation may suitably be performed in a rotary furnace, a fixed bed reactor or a fluidized bed reactor. Optionally, additional washing, cleaning or purifying steps may be performed after the activation. Optionally the pyrolyzation and activation steps may be combined into a continuous process. Optionally, the activated material is comminuted (e.g. milled) and / or sieved after the activation step to obtain particles of the desired size.

[0140] The burn-off of the pyrolyzed material during activation is preferably at least 15%, or at least 30%, or at least 40%. The burn-off is preferably no more than 80%, or no more than 75%, or no more than 70%. The burn-off is the mass fraction of the pyrolyzed material that is removed during the physical activation step, as a percentage of the material mass before physical activation is commenced.

[0141] In chemical activation methods the carbonaceous material is impregnated with a chemical activation agent (such as NaOH, KOH, K2CO3, H3PO4, CaCl2, ZnCl2, and mixtures thereof, etc.). The carbonaceous material is typically impregnated prior to pyrolysis and the pyrolysis step takes place simultaneously with the activation, though the carbonaceous material may be carbonized prior to chemical impregnation. Pyrolysis for chemical activation may take place at 250-1000 °C or 500-950 °C. If the porous carbon is formed using chemical activation processes, then, instead of pores being created by removal of carbon, the activation mechanism works by expanding existing pores or pushing apart graphene sheets (exfoliation) which is not conducive to maintaining a high proportion of micro-pore spaces accessible via narrow channels / openings. This is thought to cause relatively poorer electrochemical performance of composite materials prepared from chemically activated porous carbon materials. Thus, preferably the particulate porous carbon frameworks of the first composite particles are prepared by physical activation.

[0142] Additional information on the synthesis of activated carbon with target pore structures may be found at Porous Carbons: Syntheses and Applications (Kang, Feiyu; Inagaki, Michio; Itoi, Hiroyuki; Elsevier; ISBN 978-0-12-822115-0).

[0143] Alternatives to particulate porous carbon frameworks include particulate porous frameworks formed of titanium nitride, titanium carbide, silicon carbide, boron carbide, nickel oxide, silicon oxide, silicon dioxide, aluminium oxide, silicon-aluminium ternary oxides, magnesium oxide, lead oxide, zirconium oxide, silicon nitride, titanium silicon nitride, nickel nitride, molybdenum nitride, titanium oxynitride, silicon oxycarbide, boron nitride, or vanadium nitride. Preferred alternatives to particulate porous carbon frameworks are particulate porous frameworks formed of titanium nitride, silicon oxycarbide, or boron nitride.

[0144] In a particular example, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores; and silicon domains located within the pores of the particulate porous carbon frameworks; wherein:

[0145] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g, wherein P1 is at least 0.35; and VP07 is the volume of pores in the particulate porous carbon frameworks with a pore diameter of 0.7 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-40%; the micropore volume of the particulate porous carbon frameworks is at least 0.3 cm3 / g; wherein P1, VP07, and the micropore volume are measured by nitrogen gas adsorption.

[0146] In another particular example, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores; and silicon domains located within the pores of the particulate porous carbon frameworks; wherein:

[0147] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g, wherein P1 is at least 0.35; and

[0148] VP07 and VP2 are respectively the volume of pores in the particulate porous carbon frameworks with a pore diameter of 0.7 nm or less and 2.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35% and VP2 is at least 2.5xVP07; the micropore volume of the particulate porous frameworks is at least 0.3 cm3 / g; wherein P1, VP07, VP2, and the micropore volume are measured by nitrogen gas adsorption.

[0149] In another particular example, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores; and silicon domains located within the pores of the particulate porous carbon frameworks; wherein:

[0150] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g, wherein P1 is at least 0.35; and

[0151] VP07, VP2, VP5, and VP20 are respectively the volume of pores in the particulate porous carbon frameworks with a pore diameter of 0.7 nm or less, 2.0 nm or less, 5.0 nm or less, and 20.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35%, VP2 is in the range of 40-90%, and VP20-VP5 is less than 20%; wherein P1, VP07, VP2, VP5, and VP20 are measured by nitrogen gas adsorption.

[0152] The electroactive material is suitably selected from silicon, tin, germanium, aluminium, and mixtures and alloys thereof. A particularly preferred electroactive material is silicon. The electroactive material may optionally comprise a minor amount of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, or nitrogen. Preferably, the dopants are present in a total amount of no more than 2 wt% based on the total amount of the electroactive material (e.g. silicon) and the dopant(s).

[0153] The particulate porous frameworks provide a framework for the electroactive material domains. The term “electroactive material domain” refers to a body of electroactive material, typically in elemental form, having maximum dimensions that are determined by the dimensions of the pores of the particulate porous frameworks in which they are located. The electroactive material domains are typically located in the micropores and optional mesopores of the particulate porous frameworks. Thus, due to the size of the micropores and mesopores, the electroactive domains may therefore be described as nanoscale electroactive domains, wherein the term “nanoscale” is understood to refer generally to dimensions less than 100 nm although, due to the dimensions of micropores and mesopores, the electroactive domains typically have maximum dimensions in any direction of less than 50 nm, and usually significantly less than 50 nm. A domain may for example take the form of a regular or irregular particle or a bounded layer or region of coating.

[0154] The first composite particles may have a range of different electroactive material contents, typically at least 30 wt%, or at least 40 wt%, or at least 45 wt%, or at least 50 wt%, or at least 55 wt%, or at least 60 wt% electroactive material. Optionally, the first composite particles comprise less than 80 wt% electroactive material. Preferably the first composite particles comprise at least 55 wt% or more preferably at least 60 wt% electroactive material. Most preferably the electroactive material is silicon, and the percentages in this paragraph refer to the wt% of silicon, e.g. the first composite particles comprise at least 50 wt%, or at least 55 wt%, or at least 60 wt% silicon.

[0155] The amount of electroactive material in the first composite particles may be selected such that at least 20% and up to 90% of the internal pore volume of the particulate porous frameworks is occupied by the electroactive material following step (b). For example, the electroactive material may occupy from 20% to 80%, or from 25% to 75%, or from 30% to 70%, or from 35 to 65%, or from 40 to 60%, or from 45% to 55% of the internal pore volume of the particulate porous frameworks. Within these preferred ranges, the remaining pore volume of the particulate porous frameworks is effective to accommodate expansion of the electroactive material during charging and discharging, without a large excess pore volume which does not contribute to the volumetric capacity of the composite particles. However, the amount of electroactive material is also not so high as to impede effective lithiation due to inadequate metal-ion diffusion rates or due to inadequate expansion volume resulting in mechanical resistance to lithiation. When the electroactive material is silicon, the amount of silicon in the first composite particles can be related to the available pore volume in the particulate porous frameworks by the requirement that the mass ratio of silicon to the particulate porous frameworks is in the range from [0.5* P1 to 1.9xP1] : 1, wherein P1 is as defined above (e.g. if the particulate porous frameworks have a total volume of micropores and mesopores of 1.2 cm3 / g, then P1 = 1.2). This relationship takes into account the density of silicon and the pore volume of the particulate porous frameworks to define a weight ratio of silicon at which the pore volume is around 20% to 82% occupied. Preferably, the weight ratio of silicon to the particulate porous frameworks is in the range from [0.6xP1 to 1.8xP1] : 1 or from [0.7xP1 to 1.7xP1] : 1, or from [0.8xP1 to 1.6xP1] : 1.

[0156] The electroactive material (e.g. silicon) contents given herein for the first composite particles may also be used to define the second composite particles, since the mass of the coating derived from the coating agent is typically relatively low compared to the mass of the composite particles on which the coating is formed.

[0157] An advantage of the invention is that undesired oxidation of the electroactive material is minimised. Accordingly, optionally the ratio of the amount of oxygen to the amount of silicon in the second composite particles (O / Si) is <0.15, preferably <0.10, most preferably <0.08 based on the wt% of silicon and oxygen in the second composite particles. The amount of oxygen in the second composite particles may be <6 wt%, preferably <5.5 wt%, most preferably <5.1 wt%.

[0158] The amount of silicon or other electroactive material in the composite particles can be determined by elemental analysis. Electroactive material content is preferably determined by ICP-OES (Inductively coupled plasma-optical emission spectrometry). A number of ICP-OES instruments are commercially available, such as the iCAP® 7000 series of ICP-OES analysers available from ThermoFisher Scientific. The carbon content of the composite particles and of the particulate porous frameworks alone (as well as the hydrogen, nitrogen and oxygen content if required) are preferably determined by IR absorption. A suitable instrument for determining carbon, hydrogen, nitrogen and oxygen content is the TruSpec® Micro elemental analyser available from Leco Corporation.

[0159] Providing the first composite particles preferably comprises the steps of (a) providing the particulate porous frameworks defined herein; and (b) depositing electroactive material domains in the pores of the particulate porous frameworks. Step (b) typically comprises contacting the particulate porous frameworks with an electroactive material precursor at a temperature effective to cause deposition of electroactive material domains in the pores of the particulate porous frameworks. The precursor is most preferably gaseous because such precursors may be conveniently used in CVI processes.

[0160] The particle size of the particulate porous frameworks used to make the first composite particles may be defined using the particle size parameters of the first composite particles defined herein. Preferably, the particulate porous frameworks have a D5o particle diameter of at least 35 pm, or 40-200 pm, or most preferably 50-150 pm.

[0161] Suitable silicon precursors include silane (SiH4), disilane (Si2H6), trisilane (SisH8), tetrasilane (Si4Hio), pentasilane (SisHi2), hexasilane (SieHi4), methylsilane (CHsSiHs), dimethylsilane ((CHs)2SiH2), trimethylsilane ((CHshSiH), tetramethylsilane ((CHs)4Si), or chlorosilanes such as trichlorosilane (HSiC ) or dichlorosilane (H2SiCI2) or chlorosilane (HsSiCI), or methylchlorosilanes such as methyltrichlorosilane (CHsSiC ) or dimethyldichlorosilane ((CH3)2SiCI2). Preferably the silicon precursor is selected from silane (Si H4), disilane (Si2He), trisilane (SisHs), tetrasilane (Si4H ). A particularly preferred silicon precursor is silane (SiH4).

[0162] Suitable germanium precursors include germane (GeH4), hexamethyldigermanium ((CH3)sGeGe(CH3)3), tetramethylgermanium ((CHs)4Ge), tributylgermanium hydride ([CH3(CH2)3]sGeH), triethylgermanium hydride (^Hs GeH), and triphenylgermanium hydride ((CeHshGeH). A preferred germanium precursor is germane.

[0163] Suitable tin precursors include bis[bis(trimethylsilyl)amino]tin(l I) ([[(CH3)sSi]2N]2Sn), tetraallyltin ((H2C=CHCH2)4Sn), tetrakis(diethylamido)tin(IV) ([(C2Hs)2N]4Sn), tetrakis(dimethylamido)tin(IV) ([(CH3)2N]4Sn), tetramethyltin (Sn(CH3)4), tetravinyltin (Sn(CH=CH2)4), tin(ll) acetylacetonate (CioHi404Sn), trimethyl(phenylethynyl)tin (C6H5C=CSn(CH3)3), and trimethyl(phenyl)tin (C6H5Sn(CH3)3)- A preferred tin precursor is tetramethyltin.

[0164] Suitable aluminium precursors include aluminium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) (AI(OCC(CH3)3CHCOC(CH3)3)3), trimethylaluminium ((CH3)3AI), and tris(dimethylamido)aluminium(lll) (AI(N(CHs)2)3). A preferred aluminium precursor is trimethylaluminium.

[0165] Step (b) is suitably performed via chemical vapor infiltration (CVI) of a gaseous electroactive material precursor into the pore structure of the particulate porous frameworks. As used herein, CVI refers to processes in which a gaseous precursor is thermally decomposed on a surface to form electroactive material, typically in its elemental form, at the surface and gaseous by-products. In the case that the precursor is a chlorinated compound, such as a chlorosilane, the precursor is used in admixture with hydrogen gas, preferably in at least a 1:1 atomic ratio of hydrogen to chlorine.

[0166] Optionally, the precursor is free of chlorine. Free of chlorine means that the precursor contains less than 1 wt%, preferably less than 0.1wt%, preferably less than 0.01 wt% of chlorine-containing compounds.

[0167] The gaseous electroactive material precursor may be used either in pure form (or substantially pure form) or as a diluted mixture with an inert carrier gas, such as nitrogen or argon. Preferably step (b) comprises contacting the particulate porous frameworks with a gas comprising at least 30 vol%, or at least 40 vol%, or at least 50 vol%, or at least 60 vol%, or at least 70 vol%, or at least 80 vol%, or at least 90 vol%, or at least 95 vol%, or at least 97 vol%, or at least 99 vol% of the gaseous electroactive material precursor based on the total volume of the gas.

[0168] The presence of oxygen in step (b) should be avoided to prevent undesired oxidation of the deposited electroactive material, in accordance with conventional procedures for working in an inert atmosphere. Preferably, the oxygen content is less than 0.01 vol%, more preferably less than 0.001 vol% based on the total volume of gas used in step (b).

[0169] The temperature in step (b) is preferably in the range from 180 to 520 °C, or from 340 to 500 °C, or from 350 to 480 °C, or from 350 to 450 °C, or from 350 to 420 °C, or from 350 to less than 400 °C, or from 355 to 395 °C, or from 360 to 390 °C, or from 360 to 385 °C, or from 360 to 380 °C.

[0170] The pressure in step (b) may be in the range from 1 to 5000 kPa, or from 20 to 500 kPa, or from 40 to 200 kPa, or from 50 to 150 kPa, or from 60 to 120 kPa, or from 80 to 100 kPa. The pressure in at step (b) may be maintained at no more than 200 kPa, or at no more than 150 kPa, or at no more than 120 kPa, or at no more than 110 kPa, or at no more than 100 kPa, or at no more than 90 kPa, or at no more than 80 kPa. References to the pressure in any step of the claimed process refer to the absolute pressure in the reaction zone, which may comprise any suitable form of reactor vessel. For example, preferably the pressure in step (b) is in the range of 200-2000 kPa.

[0171] The deposition of electroactive materials by CVI results in the elimination of by-products, particularly by-product gases such as hydrogen. Step (b) preferably further comprises the separation of by-products from the particles formed in step (b). Separation of by-products may be effected by flushing the reactor with an inert gas and / or by evacuating the reactor by reducing the pressure. For example, the separation of by-products from the particles formed in step (b) may be effected by evacuating the reactor to a pressure of less than 100 kPa, or less than 80 kPa, or less than 60 kPa, or less than 40 kPa, or less than 20 kPa, or less than 10 kPa, or less than 5 kPa, or less than 2 kPa, or less than 1 kPa. Evacuating the reactor to low pressure may be effective not only to remove by-products in the gas phase, but also to desorb any by-products that may be adsorbed onto the surfaces of the deposited electroactive material.

[0172] Electroactive material such as silicon deposited by CVI or other vapour deposition methods into particulate porous frameworks is typically amorphous. Accordingly, the electroactive material of the first composite particles is typically amorphous, as can be observed via XRD. The process for making the second composite particles typically does not result in the crystallisation of the electroactive material. Accordingly, the electroactive material of the second composite particles is typically amorphous. When the electroactive material is silicon, amorphous character can be observed when a CuKa XRD pattern of the composite particles does not exhibit a peak attributed to the Si( 111) plane which satisfies Bragg’s law.

[0173] The nitrogen accessible pore volume of the first composite particles and / or second composite particles may be less than 0.05XP1 , wherein P1 is the total volume of micropores and mesopores in the particulate porous frameworks expressed in cm3 / g prior to deposition of electroactive material within the pores of the particulate porous frameworks. In absolute terms, the total volume of micropores and mesopores in the composite particles after deposition of electroactive material is preferably less than 0.03 cm3 / g or less than 0.01 cm3 / g.

[0174] Composite particles can be characterised by their performance under thermogravimetric analysis (TGA) in air. This method of analysis relies on the principle that a weight gain is observed when electroactive materials are oxidised in air and at elevated temperature.

[0175] As defined herein, “surface silicon” is calculated from the initial mass increase in the TGA trace from a minimum between 150 °C and 500 °C to the maximum mass measured in the temperature range between 300 °C and 680 °C, wherein the TGA is carried out in air with a temperature ramp rate of 10 °C / min. This mass increase is assumed to result from the oxidation of surface silicon and therefore allows the percentage of surface silicon as a proportion of the total amount of silicon to be determined according to the following formula:

[0176] Y = 1 .875 X [(Mmax - Mmin) / Mf] x 1Q0% Wherein Y is the percentage of surface silicon as a proportion of the total silicon in the sample, Mmax is the maximum mass of the sample measured in the temperature range between 550 °C to 650 °C, Mmin is the minimum mass of the sample above 150 °C and below 500 °C, and Mf is the mass of the sample at completion of oxidation at 1400 °C. For completeness, it will be understood that 1 .875 is the molar mass ratio of SiC>2 to O2 (i.e. the mass ratio of SiC>2 formed to the mass increase due to the addition of oxygen). Typically, the TGA analysis is carried out using a sample size of 10 mg ±2 mg.

[0177] Optionally at least 20 wt%, or at least 22 wt%, or at least 25 wt%, or at least 30 wt%, or at least 35 wt % of the silicon of the first composite particles is surface silicon as determined by thermogravimetric analysis (TGA).

[0178] In a particular example of the first or second aspects, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores, silicon domains located within the pores and optionally on the surface of the particulate porous frameworks, and

[0179] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g as measured by nitrogen gas adsorption, wherein P1 is at least 0.35; the comminuting is performed by wet milling; comminuting the first composite particles exposes fresh surfaces of the silicon domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces; the coating agent is selected from polymer coating agents, salts of lithium and a fatty acid, pitch, and mixtures thereof; the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is no more than 0.75; the second composite particles comprise: the coating derived from the coating agent.

[0180] In another particular example of the first or second aspects, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores, silicon domains located within the pores and optionally on the surface of the particulate porous frameworks, a D50 particle diameter of at least 10 pm, and P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g as measured by nitrogen gas adsorption, wherein P1 is 0.35-2.5; the comminuting is performed by wet milling; comminuting the first composite particles exposes fresh surfaces of the silicon domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces; the coating agent is selected from poly-alkylene-oxides; poly-alkyl-acrylates and their acid derivatives; Li and / or Na salts of polymeric carboxylic acids; carbon-based polymers comprising nitrogen functionality; conductive polymers comprising unsaturated carbon atoms such as aromatic groups and preferably heteroatoms such as N, S, P, and B; polyalcohols, polyethers, and polycarbonates; and mixtures thereof; salts of lithium and a fatty acid; pitch; and mixtures thereof; the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is no more than 0.75; the second composite particles comprise: the coating derived from the coating agent, and a BET surface area of no more than 100 m2 / g.

[0181] In another particular example of the first or second aspects, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores, silicon domains located within the pores and optionally on the surface of the particulate porous frameworks, a D50 particle diameter of at least 10 pm, and

[0182] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g as measured by nitrogen gas adsorption, wherein P1 is 0.35-2.5; the comminuting is performed by wet milling; comminuting the first composite particles exposes fresh surfaces of the silicon domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces; the coating agent is selected from chitosan (including Li and Na salts thereof), alginate (including Li and Na salts thereof), PVP, PAA (including Li and Na salts thereof), PVA, PEGPE, PEG, PAN, PPG, PEC, PPC, PEG, PEG combined with SN, PANI, polyacetylene, PPy, PEDOT:PSS, PEDOT, PDMS, PMMA, polyimides or polyamide-imides, and mixtures thereof; the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is 0.75-0.005; the second composite particles comprise: the coating derived from the coating agent, and a BET surface area of no more than 100 m2 / g.

[0183] In another particular example of the first or second aspects, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores, silicon domains located within the pores and optionally on the surface of the particulate porous frameworks, a D5O particle diameter of at least 30 pm, and

[0184] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g as measured by nitrogen gas adsorption, wherein P1 is 0.35-2.5; the comminuting is performed by wet milling; comminuting the first composite particles exposes fresh surfaces of the silicon domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces; the coating agent is selected from PVP, PAA (including Li and Na salts thereof) combined with PVA and / or PEG, PEC, PPC, PEG combined with SN, PEDOT:PSS, PEDOT, and mixtures thereof; the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is 0.5-0.005; the second composite particles comprise: the coating derived from the coating agent, a BET surface area of no more than 50 m2 / g, and at least 50 wt% silicon.

[0185] In another particular example of the first or second aspects, the first composite particles comprise: particulate porous carbon frameworks comprising micropores and optionally mesopores, silicon domains located within the pores and optionally on the surface of the particulate porous frameworks, a D50 particle diameter of 50-150 pm,

[0186] P1 is the total volume of micropores and mesopores in the particulate porous carbon frameworks expressed in cm3 / g, wherein P1 is 0.35-2.5;

[0187] VP07, VP2, VP5, and VP20 are respectively the volume of pores in the particulate porous carbon frameworks with a pore diameter of 0.7 nm or less, 2.0 nm or less, 5.0 nm or less, and 20.0 nm or less expressed as a percentage of P1 , wherein VP07 is in the range of 5.1-35%, VP2 is in the range of 40-90%, and VP20-VP5 is less than 20%, wherein P1 , VP07, VP2, VP5, and VP20 are measured by nitrogen gas adsorption; the comminuting is performed by wet milling; comminuting the first composite particles exposes fresh surfaces of the silicon domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces; the coating agent is selected from PVP, PAA (including Li and Na salts thereof), PVA, PEG, and mixtures thereof; the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is 0.5-0.005; the second composite particles comprise: a D50 particle diameter of 0.5-10 pm; the coating derived from the coating agent, a BET surface area of no more than 50 m2 / g, and at least 50 wt% silicon.

[0188] A particular example of the second aspect is a process comprising providing first composite particles by depositing silicon domains in the pores of particulate carbon porous frameworks via CVI of a gaseous silicon precursor into the pore structure of the particulate porous carbon frameworks; wherein the particulate porous carbon frameworks comprise micropores and optionally mesopores and a total volume of micropores and mesopores as measured by nitrogen gas adsorption of 0.35-2.5 cm3 / g; comminuting the first composite particles in an inert environment thereby reducing the particle size of the composite particles and forming intermediate composite particles; contacting the intermediate composite particles with a coating agent by CVD using a carbon- containing gas, thereby forming a carbon coating derived from the carbon-containing gas on the intermediate composite particles, thereby providing second composite particles; wherein the intermediate composite particles are maintained in an inert environment until the coating derived from the carbon-containing gas is formed; wherein the first composite particles have a D50 particle diameter of at least 10 pm and the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is no more than 0.75; wherein the second composite particles comprise: the coating derived from the coating agent, and a BET surface area of no more than 100 m2 / g.

[0189] The invention includes composite particles obtainable by the processes disclosed herein. As such particles made by the first aspect have been made by a process involving simultaneous particle size reduction and coating, these particles may be distinguished from particles prepared by other processes, such as separate particle size reduction and coating steps. In particular, in the first aspect any fresh surfaces are formed in the presence of the coating agent, thereby providing a unique interface between the composite particles and the coating derived from the coating agent, which can be confirmed by analytical techniques. For instance, separate comminution and coating processes will typically result in the existence of an oxide passivation layer on the electroactive material between the coating and the composite particles. Thus, the oxygen content, e.g. as determined by IR absorption, is informative on how the particles were prepared. Moreover, XPS may be used to confirm the presence of characteristic bonds formed between the coating and the composite, e.g. the coating and the electroactive material, due to the simultaneous particle size reduction and coating. Similarly, the composite particles made by the second aspect have been comminuted in an inert environment which is maintained until the coating derived from the coating agent is formed, again providing a different interface between the composite particles and coating as compared to particles made by alternative methods.

[0190] The second composite particles may be incorporated into a composition comprising at least one other component selected from: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material. This composition is useful as an electrode composition, and thus may be used to form the active layer of an electrode.

[0191] The composition may be a hybrid electrode composition which comprises the second composite particles and at least one additional particulate electroactive material. Examples of additional particulate electroactive materials include graphite, hard carbon, silicon, tin, germanium, aluminium and lead. The at least one additional particulate electroactive material is preferably selected from graphite and hard carbon, and most preferably the at least one additional particulate electroactive material is graphite.

[0192] In the case of a hybrid electrode composition, the composition preferably comprises from 3 to 60 wt%, or from 3 to 50 wt%, or from 5 to 50 wt%, or from 10 to 50 wt%, or from 15 to 50 wt%, of the second composite particles, based on the total dry weight of the composition. The at least one additional particulate electroactive material is suitably present in an amount of from 20 to 95 wt%, or from 25 to 90 wt%, or from 30 to 75 wt%, based on the total dry weight of the composition.

[0193] The at least one additional particulate electroactive material preferably has a D50 particle diameter in the range from 10 to 50 pm, preferably from 10 to 40 pm, more preferably from 10 to 30 pm and most preferably from 10 to 25 pm, for example from 15 to 25 pm. The D particle diameter of the at least one additional particulate electroactive material is preferably at least 5 pm, more preferably at least 6 pm, more preferably at least 7 pm, more preferably at least 8 pm, more preferably at least 9 pm, and still more preferably at least 10 pm.

[0194] The Dgo particle diameter of the at least one additional particulate electroactive material is preferably up to 100 pm, more preferably up to 80 pm, more preferably up to 60 pm, more preferably up to 50 pm, and most preferably up to 40 pm.

[0195] The at least one additional particulate electroactive material is preferably selected from carbon- comprising particles, graphite particles and / or hard carbon particles, wherein the graphite and hard carbon particles have a D50 particle diameter in the range from 10 to 50 pm. Still more preferably, the at least one additional particulate electroactive material is selected from graphite particles, wherein the graphite particles have a D50 particle diameter in the range from 10 to 50 pm.

[0196] The composition may also be a non-hybrid (or “high loading”) electrode composition which is substantially free of additional particulate electroactive materials. In this context, the term “substantially free of additional particulate electroactive materials” should be interpreted as meaning that the composition comprises less than 15 wt%, preferably less than 10 wt%, preferably less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, more preferably less than 0.5 wt% of any additional electroactive materials (i.e. additional materials which are capable of inserting and releasing metal ions during the charging and discharging of a battery), based on the total dry weight of the composition.

[0197] A “high-loading” electrode composition of this type preferably comprises at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt% of the second composite particles, based on the total dry weight of the composition.

[0198] The composition may optionally comprise a binder. A binder functions to adhere the composition to a current collector and to maintain the integrity of the composition. Examples of binders include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and alkali metal salts thereof, modified polyacrylic acid (mPAA) and alkali metal salts thereof, carboxymethylcellulose (CMC), modified carboxymethylcellulose (mCMC), sodium carboxymethylcellulose (Na-CMC), polyvinylalcohol (PVA), alginates and alkali metal salts thereof, styrene-butadiene rubber (SBR) and polyimide. The composition may comprise a mixture of binders. Preferably, the binder comprises polymers selected from polyacrylic acid (PAA) and alkali metal salts thereof, and modified polyacrylic acid (mPAA) and alkali metal salts thereof, SBR and CMC. The binder may suitably be present in an amount of from 0.5 to 20 wt%, preferably 1 to 15 wt%, preferably 2 to 10 wt% and most preferably 5 to 10 wt%, based on the total dry weight of the composition.

[0199] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as cross-linking accelerators, coupling agents and / or adhesive accelerators.

[0200] The composition may optionally comprise one or more conductive additives. Preferred conductive additives are non-electroactive materials that are included so as to improve electrical conductivity between the electroactive components of the composition and between the electroactive components of the composition and a current collector. The conductive additives may be selected from carbon black, carbon fibers, carbon nanotubes, graphene, acetylene black, ketjen black, metal fibers, metal powders and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes.

[0201] The one or more conductive additives may suitably be present in a total amount of from 0.5 to 20 wt%, preferably 1 to 15 wt%, preferably 2 to 10 wt% and most preferably 5 to 10 wt%, based on the total dry weight of the composition.

[0202] The invention also provides a process for forming an electrode comprising the second composite particles, which typically comprises depositing the second composite particles onto a current collector. Electrodes obtainable from this process are provided. For example, the composition used to prepare the electrode may be in the form of a composition comprising the second composite particles at least one other component defined above.

[0203] As used herein, the term current collector refers to any conductive substrate that can carry a current to and from the electroactive particles in the composition. Examples of materials that can be used as the current collector include copper, aluminium, stainless steel, nickel, titanium and sintered carbon. Copper is a preferred material. The current collector is typically in the form of a foil or mesh having a thickness of between 3 to 500 pm. The second composite particles may be applied to one or both surfaces of the current collector to a thickness which is preferably in the range from 10 pm to 1 mm, for example from 20 to 500 pm, or from 50 to 200 pm. The electrode may be fabricated by combining the second composite particles with a solvent and optionally one or more viscosity modifying additives to form a slurry. The slurry is then cast onto the surface of a current collector and the solvent is removed, thereby forming an electrode layer on the surface of the current collector. Further steps, such as heat treatment to cure any binders and / or calendaring of the electrode layer may be carried out as appropriate. The electrode layer suitably has a thickness in the range from 20 pm to 2 mm, preferably 20 pm to 1 mm, preferably 20 pm to 500 pm, preferably 20 pm to 200 pm, preferably 20 pm to 100 pm, preferably 20 pm to 50 pm.

[0204] Alternatively, the slurry may be formed into a freestanding film or mat comprising the second composite particles of the invention, for instance by casting the slurry onto a suitable casting template, removing the solvent and then removing the casting template. The resulting film or mat is in the form of a cohesive, freestanding mass that may then be bonded to a current collector by known methods.

[0205] The electrode may be used as the anode of a metal-ion battery. Thus, the present invention provides a process for preparing rechargeable metal-ion battery comprising the electrode as the anode. Metal-ion batteries obtainable from this process are provided. Typically, the rechargeable metal-ion battery is a lithium-ion battery, for example a solid-state lithium-ion battery or an all-solid state lithium-ion battery.

[0206] The cathode of the rechargeable metal-ion battery typically comprises a current collector and a cathode active material capable of releasing and reabsorbing metal ions. The cathode active material is preferably a metal oxide-based composite. Examples of suitable cathode active materials include LiCoC>2, LiCo0.99AI0.01O2, LiNiC>2, LiMnO2, LiCo0.5Ni0.5O2, LiCo0.7Ni0.3O2, LiCo0.8Ni0.2O2, LiCo0.82Ni0.i8O2, LiCo0.8Ni0.15AI0.05O2, LiNi0.4Co0.3Mn0.3O2 and LiNi0.33Co0.33Mn0.34O2. The cathode current collector is generally of a thickness of between 3 to 500 pm. Sulfur-based cathode active materials may also be utilised. Examples of materials that can be used as the cathode current collector include aluminium, stainless steel, nickel, titanium and sintered carbon.

[0207] Suitable electrolytes for rechargeable metal-ion batteries include a non-aqueous electrolyte containing a lithium salt, and may include, without limitation, non-aqueous electrolytic solutions, organic solid electrolytes, and inorganic solid electrolytes. Examples of non-aqueous electrolyte solutions that can be used include non-protic organic solvents such as propylene carbonate, ethylene carbonate, butylene carbonates, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, 1 ,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfoxide, 1 ,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triesters, trimethoxymethane, sulfolane, methyl sulfolane and 1 ,3-dimethyl-2- imidazolidinone.

[0208] Solid electrolytes may be used with the second composite particles. Examples of organic solid electrolytes include polyethylene derivatives, polyethyleneoxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfide, polyvinylalcohols, polyvinylidine fluoride and polymers containing ionic dissociation groups.

[0209] Examples of inorganic solid electrolytes include nitrides, halides and sulfides of lithium salts such as LisNl2, LisN, Lil, LiSiC , Li2SiSs, Li4SiC>4, LiOH and U3PO4.

[0210] The lithium salt is suitably soluble in the chosen solvent or mixture of solvents. Examples of suitable lithium salts include LiCI, LiBr, Lil, LiCIC , LiBF4, LiBC^s, LiPFe, UCF3SO3, LiAsFe, LiSbF6, LiAICI4, CH3SO3U and CF3SO3LL

[0211] Where the electrolyte is a non-aqueous organic solution, the rechargeable metal-ion battery is preferably provided with a separator interposed between the anode and the cathode. The separator is typically formed of an insulating material having high ion permeability and high mechanical strength. The separator typically has a pore diameter of between 0.01 and 100 pm and a thickness of between 5 and 300 pm. Examples of suitable electrode separators include a micro- porous polyethylene film. The separator may be replaced by a polymer electrolyte material and in such cases the polymer electrolyte material is present within both the composite anode layer and the composite cathode layer. The polymer electrolyte material can be a solid polymer electrolyte or a gel-type polymer electrolyte.

[0212] It will be understood that, unless clearly incompatible, the steps may be performed in any order, with or without other intervening steps. The description above of the particulate porous frameworks, electroactive material precursors, composite particles, electrodes, batteries etc. applies equally to these items provided as products per se or when used as part of a process.

[0213] Example 1

[0214] Example 1 relates to the first aspect. Polymer solutions were prepared by dissolving polymer coating agent (PEG : PAA in a 30 : 70 ratio by mass) in I PA at varying concentrations. A feedstock of Si / C composite particles having a D50 of 14 pm was prepared by CVI of silane into activated carbon as the particulate porous frameworks. The activated carbon had a volume of micropores and mesopores (P1 as defined herein) of 1.6 cm3 / g and a microporosity of 74% (relative to the volume of micropores and mesopores).

[0215] The composite particles were dispersed in I PA. The composite particle dispersion was mixed with the polymer solution to form a slurry. The slurry was introduced into an Eiger bead mill (2 mm YSZ beads / 3500 rpm) and milled to a target D5o of 2-2.5 pm. The atmosphere in the milling chamber was kept as ambient, with an air headspace. Once the desired particle size was reached, the slurry was extracted from the mill and spray dried at 125°C under inert gas (nitrogen) atmosphere to remove the solvent. The resulting extracted powder was then dried in an oven under vacuum at 125 °C overnight before final recovery of milled and polymer coated composite particles (second composite particles). Crosslinks in the polymer coating are believed to be formed during the spray drying and oven drying conditions.

[0216] Comparative composite particles were made using an equivalent process using the same feedstock of Si / C composite particles but without dissolving polymer coating agent in I PA.

[0217] The composite particles were characterised for their silicon content (via TGA), oxygen content (via elemental analysis), surface area (via the BET method), and particle size distribution (via laser diffraction), and silicon utilisation. Half-cells were made using either the milled and polymer coated composite particles or the comparative composite particles as the active anode material. The electrode composition by dry mass was -65:25:10 composite particles : carbon additives : binder. The performance of these cells was measured. The results are shown Table 1 .

[0218] The silicon utilisation allows the coating process to be assessed independently of cell formulation, anode design, and fabrication aspects. It is calculated by the following equation: mAh

[0219] Half cell lithiation capacity (

[0220] Si utilisation % = g

[0221] ( Si wt% x 3600 mAh / g)

[0222] Where “Half-cell lithiation capacity (mAh / g)” is defined as the maximum lithium storage capacity on a mass basis of the second composite particles on initial lithium-ion insertion (i.e. the lithiation capacity per unit mass of the second composite particles on first charge). This gravimetric capacity measurement can be performed by assembling an electrode containing the second composite particles, a suitable binder and a conductive additive (collectively defined above). A constant current - constant voltage lithiation and de-lithiation cycle against a lithium metal counter electrode (the half-cell) is applied, in order to determine the capacity of the second composite particles as known in the art (C / 10 at constant current until the lower cut-off potential of 10 mV is reached; then until C / 40 at constant voltage for lithiation only; discharge of the half-cell is performed at C / 10 to 1.5V; potential window is between 10mV to 1.5V lower and upper cut-off voltage respectively; lithiation capacity is calculated from the first cycle lithiation; de-lithiation capacity is calculated from the first cycle de-lithiation). A higher silicon utilisation is advantageous. 100% defines full utilisation of the silicon available in the composite particles. Less than 100% demonstrates that some of the measured silicon mass is sequestered by irreversible chemical bond formation and cannot be utilised in the reversible electrochemical alloying reaction. This is typically due to formation of silicon-oxygen bonds as SiC>2 which results in irreversible electrochemical reaction summarised below:

[0223] This demonstrates that around half of the silicon sequestered as Si-0 bonding in SiO2 is lost irreversibly as lithium silicates and cannot contribute to the useful capacity of the electrochemical cell. This process typically occurs when the silicon is exposed to oxidising environments. NB: the equation for silicon utilisation assumes that silicon is solely responsible for the measured half-cell lithiation capacity, but since this assumption is not always accurate values of above 100% are possible (e.g. as the carbon framework can provide some capacity). Nevertheless, the silicon utilisation allows for direct comparison between composite particles made from the same or similar carbon frameworks

[0224] The characterisation showed similar silicon content for Samples 2-5. Samples 3-5 was found to have a small increase in oxygen content compared to Sample 2, believed to be due to the oxygen atoms present in the coating agent (PEG and PAA). Sample 2 was found to have a higher surface area than the unmilled Sample 1 due to the smaller particle size. Samples 3-5 showed a reduced surface area compared to Sample 2 due to the polymer coating. The D50 of Samples 3-5 was -50% higher than for Sample 2, believed to be due to the thickness of the polymer coating and / or increased agglomeration due to the coating

[0225] Notably, Samples 3-5 were found to provide cells with higher capacities and higher silicon utilisations than comparative Sample 2. This is believed to be due to the milling in the presence of the coating agent, which minimises the oxidation of fresh silicon surfaces formed during milling, thereby reducing capacity loss, and moreover forming an artificial SEI layer which reduces the first- cycle loss.

[0226] able 1: Description and characterisation of composite particles of Example 1 (nm = not measured)

[0227] Example 2

[0228] Example 2 relates to the second aspect. Inside an argon-filled glovebox, a feedstock of 12g Si / C composite particles is weighed along with 100g of zirconia ball milling media (7mm YSZ beads) and sealed inside a milling jar, to ensure that an inert atmosphere is maintained during the milling process. Two different Si / C feedstocks were used in separate experiments: a first feedstock made from CVI of silane into activated carbon having a volume of micropores and mesopores of 1.6 cm3 / g and a microporosity of 74% relative to the volume of micropores and mesopores (the same feedstock as for Example 1), and second feedstock made from CVI of silane into activated carbon having a volume of micropores and mesopores of 0.7 cm3 / g and a microporosity of 48% relative to the volume of micropores and mesopores.

[0229] The sealed milling jar is then removed from the glovebox and loaded into a ball mill. This is then milled at 300rpm for 3 minutes followed by a 2-minute break, then repeating for a total milling time of 5 hours. After milling, the milling jar was returned to the glovebox to be opened. The milled composite particles (intermediate composite particles) were then recovered and sieved to remove the balls. Half of this material was removed from the glove box to passivate via air, i.e. to produce a comparative sample.

[0230] The remaining half was loaded into a crucible and inserted into a sealable furnace tube. The furnace tube contains a valve on the inlet and outlet to ensure the interior remained free from air. A face plate was then sealed to the furnace tube via a nickel gasket. This allowed for the sample to be removed from the glovebox and maintained in an inert environment as it is placed into a coating furnace. Once placed in the furnace, the lines were purged with nitrogen before opening the inlet valve. Once purged the inlet valve was opened and a constant flow of nitrogen was supplied to keep the sample in an inert environment.

[0231] The furnace was then heated to 520°C at 6.5°C / min under nitrogen at 0.5L / min. Once the target temperature was reached, carbon coating was performed by introducing a flow of acetylene (0.35L / min) to the nitrogen flow (0.79 L / min). The reagents were flown for 90 minutes, thereby coating the milled composite particles, after which the reactor was purged again with nitrogen before cooling down. Once cool, a mix of nitrogen (0.5L / min) and air (0.5L / min) was passed through the furnace to ensure the material was sufficiently passivated and safe to remove from the furnace and the carbon coated composite was recovered (second composite particles).

[0232] The same carbon coating procedure was performed on the comparative other half of the milled composite particles which had been exposed to air before the coating. The composite particles were characterised in the same way as Example 1. The results are shown Table 2. The characterisation showed that each composite prepared according to the second aspect (Samples 7 and 9) had an advantageously lower oxygen content, higher capacity, and higher silicon utilisation than the respective comparative composite prepared from the same feedstock (Samples 6 and 8, respectively). These advantages are believed to be due to the maintenance of the inert environment in Samples 7 and 9 from milling to coating, whereas Samples 6 and 8 were exposed to air between milling and coating. Maintaining the inert environment minimises the oxidation of fresh silicon surfaces formed during milling, thereby reducing capacity loss, and moreover forming an artificial SEI layer which reduces the first-cycle loss.

[0233] able 2: Description and characterisation of composite particles of Example 2

Claims

Claims1. A process comprising providing first composite particles, wherein the first composite particles comprise: particulate porous frameworks comprising micropores and optionally mesopores, electroactive material domains located within the pores and optionally on the surface of the particulate porous frameworks; comminuting the first composite particles in the presence of a coating agent, thereby reducing the particle size of the composite particles and forming a coating derived from the coating agent on the composite particles, thereby providing second composite particles; wherein the second composite particles comprise: the coating derived from the coating agent.

2. A process comprising providing first composite particles, wherein the first composite particles comprise: particulate porous frameworks comprising micropores and optionally mesopores, electroactive material domains located within the pores and optionally on the surface of the particulate porous frameworks; comminuting the first composite particles in an inert environment thereby reducing the particle size of the composite particles and forming intermediate composite particles; contacting the intermediate composite particles with a coating agent thereby forming a coating derived from the coating agent on the intermediate composite particles, thereby providing second composite particles; wherein the intermediate composite particles are maintained in an inert environment until the coating derived from the coating agent is formed; wherein the second composite particles comprise: the coating derived from the coating agent.

3. The process of any preceding claim, wherein the first composite particles have a D50 particle diameter of at least 5.5 pm, or at least 10 pm, or at least 15 pm, or at least 20 pm, or at least 35 pm, or at least 40 pm.

4. The process of any preceding claim, wherein the micropores and mesopores of the particulate porous frameworks of the first composite particles have a total pore volume as measured by nitrogen gas adsorption of P1 cm3 / g, wherein P1 is:(i) at least 0.35; and / or(ii) no more than 2.5; or(iii) 0.4-2.2; or(iv) 0.5-1.8; or(v) 0.6-1.6.

5. The process of claim 4, wherein VP07 is the volume of pores in the particulate porous frameworks of the first composite particles with a pore diameter of 0.7 nm or less expressed as a percentage of P1 as measured by nitrogen gas adsorption, wherein VP07 is in the range of 5.1- 40%, or 5.5-35%, or 7-30%, or 10-27%, or 15-25%.

6. The process of claim 4 or 5, wherein VP20 and VP5 are the volume of pores in the particulate porous frameworks with a pore diameter of 20.0 nm or less and 5.0 nm or less, respectively, expressed as a percentage of P1 as measured by nitrogen gas adsorption, wherein VP20-VP5 is less than 20%, or less than 15%, or less than 12%, or less than 10%, or less than 9%, and optionally at least 0.5%, or at least 1%, or at least 2%.

7. The process of any preceding claim, wherein the particulate porous frameworks of the first composite particles comprise mesopores, optionally wherein the mesopores form at least 40%, or at least 45%, or at least 50%, or at least 55% of the total volume of the micropores and mesopores of the particulate porous frameworks, as measured by nitrogen gas adsorption.

8. The process of any preceding claim, wherein comminuting the first composite particles exposes fresh surfaces of the electroactive material domains of the first composite particles and the coating derived from the coating agent passivates the fresh surfaces.

9. The process of any preceding claim, wherein providing the first composite particles is performed in a different apparatus to comminuting the first composite particles; optionally wherein providing the first composite particles is performed in a reactor vessel suitable for chemical vapour infiltration (CVI) and comminuting the first composite particles is performed in a comminuting device.

10. The process of any preceding claim, wherein the comminuting is performed in a comminuting device selected from wet mills, ball mills, jet mills, high-shear stirrers, and mechanofusion devices.

11. The process of any preceding claim, wherein the comminuting is performed by wet milling the first composite particles in the presence of a solvent.

12. The process of claim 11 when dependent on claim 1, wherein the solvent is selected from:(i) water (e.g. deionised water), hydrocarbons (e.g. selected from toluene, xylenes, n-hexane, n- heptane, n-octane, decane, dodecane, and petroleum ether), ethers (e.g. selected from tetrahydrofuran, 2-methyltetrahydrofuran, and glymes such as diglyme, and triglyme), ketones (e.g. selected from acetone and methylethylketone), alcohols (e.g. selected from isopropyl alcohol, n-butyl alcohol, and tert-amyl alcohol), halogenated solvents (e.g. selected from 1,2- dichloroethane, 1 ,1 ,1 -trichloroethane), acetonitrile, dimethylformamide (DMF), dimethylsulfoxide (DMSO), esters (e.g. butyl butyrate), and mixtures thereof; or(ii) water, alcohols, ketones, and mixtures thereof; or(iii) water or isopropyl alcohol.

13. The process of any preceding claim dependent on claim 1, wherein the comminuting is performed by wet milling wherein the solvent is water, and the pH during the comminuting is no more than 7, or is about 7.

14. The process of claim 11, wherein the solvent is selected from benzene, toluene, dimethyl formamide, alcohols (e.g. isopropyl alcohol, n-butyl alcohol, and tert-amyl alcohol), dimethyl carbonate, ketones (e.g. methyl ethyl ketone and acetone), ethers (e.g. tetrahydrofuran, 2-methyltetrahydrofuran, and glymes such as diglyme and triglyme), and N-methylpyrrolidone; or is selected from benzene, toluene, dimethyl formamide, isopropyl alcohol, dimethyl carbonate, methyl ethyl ketone, tetrahydrofuran, 2-methyltetrahydrofuran, diglyme, triglyme, and N-methylpyrrolidone.

15. The process of any one of claims 11-14, wherein the solvent is degassed; optionally wherein the solvent has an oxygen concentration of less than 1.0 wt% or less than 0.1 wt%.

16. The process of claim 1 or of any of claims 3-10 when dependent on claim 1, wherein the comminuting is performed by wet milling a slurry of the first composite particles in a neat liquid coating agent.

17. The process of claim 2 or of any preceding claim dependent on claim 2, comprising contacting the intermediate composite particles with a neat liquid coating agent.

18. The process of claim 1 or of any preceding claim dependent on claim 1 , wherein the comminuting is performed in an inert environment.

19. The process of claim 2, or of any preceding claim dependent on claim 2, or of claim 18, wherein the inert environment comprises an atmosphere comprising:less than 1.0 vol%, or less than 0.5 vol%, or less than 0.1 vol% oxygen gas; and less than 1.0 vol%, or less than 0.5 vol%, or less than 0.1 vol% water vapour.

20. The process of any preceding claim, wherein the ratio of the D50 particle diameter of the second composite particles to the D50 particle diameter of the first composite particles is no more than 0.9, or no more than 0.75, or no more than 0.5, or no more than 0.3; and optionally at least 0.005, or at least 0.008, or at least 0.01 , or at least 0.1 .

21. The process of any preceding claim, wherein the second composite particles have a D50 particle diameter of no more than 10 pm, or 0.25-10 pm, or 0.5-10 pm, or 0.5-8 pm, or 0.75-5.0 pm, or 1.0-4.5 pm.

22. The process of any preceding claim, comprising performing a first iteration of the process to form a first batch of second composite particles, and performing a second iteration of the process to form a second batch of second composite particles, wherein the D50 particle diameter of the second batch of second composite particles is lower than the D50 particle diameter of the first batch of second composite particles, and mixing the first batch and the second batch.

23. The process of claim 22, wherein the ratio of the D50 particle diameter of the second batch of second composite particles to the D50 particle diameter of the first batch of second composite particles is no more than 0.75, or no more than 0.5, or no more than 0.35.

24. The process of claim 22 or claim 23, wherein the D50 particle diameter of the first batch of second composite particles is 5.0-10 pm and the D50 particle diameter of the second batch of second composite particles is 0.5-4.5 pm.

25. The process of any preceding claim, comprising performing a first iteration of the process to form a first batch of second composite particles, and performing a second iteration of the process to form a second batch of second composite particles, wherein the composition of the first composite particles of the first iteration is different to the composition of the first composite particles of the second iteration, and mixing the first batch and the second batch.

26. The process of claim 25, wherein the ratio of the electroactive material content of the first composite particles of the first iteration to the electroactive material content of the first composite particles of the second iteration is no more than 0.95, or no more than 0.9, or no more than 0.75, or no more than 0.5.

27. The process of any of claims 22-26, wherein the first iteration is according to the process of claim 1 and the second iteration is according to the process of claim 2, or wherein the first iteration is according to the process of claim 2 and the second iteration is according to the process of claim 1.

28. The process of any preceding claim, wherein the coating agent is selected from polymers, pitches, metal phosphate precursors, metal oxide precursors, salts of lithium and a fatty acid, inorganic lithium compounds, and mixtures thereof.

29. The process of any preceding claim, wherein the coating agent is a polymer, optionally wherein:(i) the coating agent is selected from poly-alkylene-oxides (e.g. polyethylene oxide (PEO), polypropylene oxide (PPO)); halogenated polymers (e.g. polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co- hexafluoropropylene (PVDF-HFP), polyvinylidene chloride (PVDC)); poly-alkyl-acrylates and their acid derivatives (e.g. polymethyl methacrylate (PMMA), polyacrylic acid (PAA));Li and / or Na salts of polymeric carboxylic acids (e.g. lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA)); carbon-based polymers comprising nitrogen functionality (e.g. polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyethylamine (PEI), polyvinylamine (PVAm), polyallylamine (PAAm), polydially dimethyl-ammonium chloride (PDDA), polyaniline (PANI), polypyrrole (PPy)); polyimides or polyamide-imides which are preferably unsaturated such as poly(4,4'- oxydiphenylene-pyromellitimide); conductive polymers comprising unsaturated carbon atoms such as aromatic groups and preferably heteroatoms such as N, S, P, and B (e.g. polythiophene (PT), poly(hydroxymethyl 3, 4- ethylene dioxythiophene) (HMEDOT), poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS)); siloxanes and polysiloxanes (e.g. 1 ,1 ,3,3-tetramethyldisiloxane, polydimethylsiloxane (PDMS), polyboronsiloxane (PBS)); silanes which are liquid at 25°C and atmospheric pressure; polyalcohols, polyethers, and polycarbonates (e.g. polyethylene carbonate (PEC), polypropylene carbonate (PPC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethylene glycol octophenyl ether (PEGPE), polyethylene glycol methacrylate (PEGMA), poly(bisphenol A carbonate));polyether-thioureas (e.g. polyether-thioureas crosslinked with PAA); biopolymers (e.g. lignin, chitosan, shellac, gum resins, gum arabic, elemi resin, gellan gum, alginate, and Li and Na salts thereof; or lignin, chitosan, alginate, and Li and Na salts thereof); polyacetylene; amines with two or more amino groups (e.g. 1,3-diaminopropane, 1,4-diaminobutane, 1 ,5-diaminopentane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine); and mixtures thereof; or(ii) the coating agent is selected from poly-alkylene-oxides; poly-alkyl-acrylates and their acid derivatives; Li and / or Na salts of polymeric carboxylic acids; carbon-based polymers comprising nitrogen functionality polymers; conductive polymers comprising unsaturated carbon atoms such as aromatic groups and preferably heteroatoms such as N, S, P, and B; polyalcohols, polyethers, and polycarbonates; and mixtures thereof.

30. The process of any preceding claim, wherein the coating agent is selected from:(i) chitosan (including Li and Na salts thereof), alginate (including Li and Na salts thereof), PVP, PAA (including Li and Na salts thereof), PVA, PEGPE, PEG, PAN, PPG, PEC, PPC, PEO, PEO combined with SN, PANI, polyacetylene, PPy, PEDOT:PSS, PEDOT, PDMS, PMMA, polyimides or polyamide-imides, and mixtures thereof; or(ii) PVP, PAA (including Li and Na salts thereof) combined with PVA and / or PEG, PEC, PPC, PEO combined with SN, PEDOT: PSS, PEDOT, and mixtures thereof; or(iii) PAA (including Li and Na salts thereof) combined with PVA and / or PEG.

31. The process of claim 29 or claim 30, wherein the polymer is combined with a plasticiser; optionally wherein the plasticiser is selected from nitriles such as succinonitrile (SN) or adiponitrile (AN), adipates, orthophthalates, teraphthalates, trimellitic acid, sebacates, and mixtures thereof.

32. The process of any preceding claim, wherein the coating agent is a pitch; optionally wherein the coating agent is selected from coal tar pitch, petroleum pitch, mesophase pitch, wood tar pitch, isotropic pitch, bitumen, and mixtures thereof.

33. The process of any preceding claim, wherein the coating agent is a metal phosphate precursor; optionally a combination of a metal source and a phosphate source; optionally wherein the metal is selected from lithium, aluminium, iron, and nickel, and mixtures thereof.

34. The process of any preceding claim, wherein the coating agent is a metal oxide precursor; optionally wherein:(i) the metal is selected from zinc, titanium, aluminium, zirconium, lithium, and mixtures thereof; or is zinc; and / or(ii) the metal oxide precursor is a metal salt, or a metal halide, or zinc chloride.

35. The process of any preceding claim, wherein the coating agent is a salt of lithium and a fatty acid; optionally lithium stearate, lithium oleate, lithium palmitate, and mixtures thereof.

36. The process of any preceding claim, wherein the coating agent is an inorganic lithium compound; optionally selected from an organolithium reagent such as n-butyl lithium, lithium carbonate, lithium fluoride, or a lithium silicate such as lithium polysilicate (LizSisOn), lithium metasilicate (U2SiO3), and lithium orthosilicate (Li4SiC>4), and mixtures thereof.

37. The process of any preceding claim, wherein the electroactive material of the second composite particles is amorphous.

38. The process of any preceding claim, wherein the electroactive material is selected from silicon, tin, germanium, aluminium, and mixtures and alloys thereof; or wherein the electroactive material is silicon.

39. The process of any preceding claim, wherein the particulate porous frameworks of the first composite particles are particulate porous carbon frameworks.

40. The process of any preceding claim, wherein providing the first composite particles comprises depositing electroactive material domains in the pores of particulate porous frameworks via chemical vapor infiltration (CVI) of a gaseous electroactive material precursor into the pore structure of the particulate porous frameworks.

41. The process of claim 2 or any preceding claim dependent on claim 2, wherein contacting the intermediate composite particles with a coating agent takes place in the same device as comminuting the first composite particles.

42. The process of claim 2 or any of claims 3-40 dependent on claim 2, wherein contacting the intermediate composite particles with a coating agent takes place in a different device than comminuting the first composite particles, optionally wherein contacting the intermediate compositeparticles with the coating agent is achieved by spray drying; vapour deposition methods such as chemical vapour deposition (CVD), atomic layer deposition (ALD), and physical vapour deposition (PVD); wet chemical methods such as electrodeposition; layer-by-layer coating such as multi-layer coating; or by reactive polymerisation; optionally wherein contacting the intermediate composite particles with the coating agent is achieved by CVD using a carbon-containing gas as the coating agent.

43. The process of any preceding claim, wherein the ratio of the amount of oxygen to the amount of silicon in the second composite particles (O / Si) is <0.15, or <0.10, or <0.08 based on the wt% of silicon and oxygen in the second composite particles.

44. The process of any preceding claim, wherein the amount of oxygen in the second composite particles is <6 wt%, or <5.5 wt%, or <5.1 wt%.

45. The process of any preceding claim, comprising isolating the second composite particles.

46. The process of any preceding claim, comprising forming an electrode comprising the second composite particles.

47. The process of claim 46, comprising forming a metal-ion battery comprising the electrode as an anode, optionally wherein the metal-ion battery is lithium-ion battery, or a solid-state lithium-ion battery, or an all-solid-state lithium-ion battery.

48. Composite particles formed by the process of any of claims 1-45.

49. An electrode formed by the process of claim 46.

50. A metal-ion battery formed by the process of claim 47.

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