Composite Particles

Abstract

A process for manufacturing composite particles for use as an electroactive material for a metal-ion battery includes providing initial particulate porous frameworks having micropores and optionally m

Description

Introduction This invention relates to a process for manufacturing particulate porous frameworks with optimised pore structures, and to the frameworks themselves. The frameworks are particularly suited for preparing composite particles for use as electroactive materials in metal-ion batteries, such as lithium-ion or sodium-ion batteries, particularly lithium-ion batteries. Background Lithium-ion batteries (LIBs) or sodium-ion batteries (SIBs) comprise in general an anode, a cathode and a lithium-containing or sodium-containing electrolyte, respectively. 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. The following description refers primarily to LIBs but the skilled person will appreciate that the operational principles apply equally to SIBs. 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. 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 LiisSi^. 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 1 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 reported by the present inventors is the development of a class of electroactive materials having a composite structure in which electroactive materials such as silicon are deposited into the pore network of highly porous particles, e.g. a porous carbon material, having a carefully controlled pore size distribution. For example, WO2020 / 095067, WO2020 / 128495, and WO2022 / 029422 report that the improved electrochemical performance of these materials 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, which thus function as a framework for the composite particles. The fine electroactive structures are thought to have a lower resistance to elastic deformation and higher fracture resistance than larger electroactive structures, and are therefore able to lithiate and delithiate without excessive structural stress. As a result, the electroactive materials exhibit good reversible capacity retention over multiple charge-discharge cycles. By controlling the loading of silicon within the porous particle framework such that only part of the pore volume is occupied by silicon in the uncharged state, the unoccupied pore volume of the porous particle framework is able to accommodate a substantial amount of silicon expansion internally. Excessive expansion is constrained by the particle framework. Furthermore, only a small area of the electroactive material surface is accessible to electrolyte and so SEI formation is substantially prevented. However, although desirable pore size distribution parameters for the frameworks have previously been reported by the present inventors, there remains a need to further optimise the pore structure of the frameworks to further improve the properties of the composite particles prepared therefrom. In particular, it is an objective of this invention to further optimise the pore structure in order to mitigate the deleterious effects associated with expansion of the deposited electroactive material. The present invention achieves that objective by tailoring the pore structure in the porous framework prior to the deposition of the electroactive material. Summary of the invention The inventors have found that the pore structure of particulate porous frameworks can be tailored by infiltrating the frameworks with a porosity modifier, effecting a reaction involving the porosity 2 modifier and the particulate porous frameworks, washing the frameworks to partially remove the reaction products, and then depositing electroactive material in the pores of the washed particulate porous frameworks. Thus, the invention provides a process for manufacturing composite particles for use as an electroactive material for a metal-ion battery, comprising the steps of: (a) providing initial particulate porous frameworks comprising micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks is greater than a value P1 (initial) which is at least 0.35 cm3 / g; (b) infiltrating the pores of the initial particulate porous frameworks with a porosity modifier comprising Li or Na, thereby providing infiltrated particulate porous frameworks; (c) providing sufficient energy to the infiltrated particulate porous frameworks to cause a reaction involving the porosity modifier and the initial particulate porous frameworks, thereby providing modified particulate porous frameworks comprising reaction products from the reaction within the pores, wherein P1 (modified) of the modified particulate porous frameworks is lower than P1 (initial); (d) washing the modified particulate porous frameworks to partially remove the reaction products from the pores, thereby providing washed particulate porous frameworks comprising residual reaction-products within the pores, wherein P1 (washed) of the washed particulate porous frameworks is higher than P1 (modified); (e) depositing electroactive material domains in the pores of the washed particulate porous frameworks, thereby providing composite particles; wherein P1 (i.e. P1 (initial), P1 (modified) and P1 (washed)) is the total volume of micropores and mesopores in the particulate porous frameworks expressed in cm3 / g as measured by nitrogen gas adsorption. The modification of the pore structure according to the present invention increases the dimensions of some of the existing micropores to provide mesopores. In the process of the invention, larger micropores increase in size and become mesopores. Any mesopores already present in the initial particulate porous framework also appear to increase in size. Smaller micropores appear to be less susceptible to modification. In the process of the invention, the reaction products produced by the reaction locate within the pores, and during subsequent deposition of the electroactive material, these reaction products prevent the electroactive material (or its precursor) from accessing some of the pores, i.e. some of the pores become blocked. The inventors have observed that the extent of blocking is greatest for micropores, particularly smaller micropores. Since the blocked pores are then inaccessible to the electroactive material precursor, no electroactive material domains are deposited in the blocked pores in the subsequent deposition step. The inventors have observed that these modifications provide greater mitigation for the expansion of the electroactive material during charging and discharging. Thus, the process of the invention modifies or tailors the pore structure such that subsequent deposition of electroactive material provides electroactive material domains located advantageously within the pore structure of the frameworks in a way which better accommodates cycling-associated expansion. In addition, for porosity modifiers comprising lithium, the reaction products deposited in the pores advantageously provide a degree of pre-lithiation, improving cell performance through improved ion transport pathways, better coulombic efficiency and capacity retention. Similarly, for porosity modifiers comprising sodium, the reaction products deposited in the pores advantageously provide a degree of pre-sodiation, improving cell performance through improved ion transport pathways, better coulombic efficiency and capacity retention. The present invention also provides composite particles prepared by the process, electrodes comprising the composite particles, and rechargeable metal-ion batteries comprising the electrodes. Figures Figure 1 Figure 1a shows the pore volume of particulate porous frameworks at various stages of the process plotted against pore width. Figure 1b shows the differential pore volume dV / dW of particulate porous frameworks at various stages of the process plotted against pore width. Figure 2 shows thermogravimetric analysis (TGA) plots of particulate porous frameworks at various stages of the process. Detailed description of the invention The following description refers primarily to LIBs but the skilled person will appreciate that the operational principles apply equally to SIBs. The optimisation of the pore structure is of particular utility when the deposition of electroactive materials such as silicon in porous frameworks is 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. In accordance with conventional IUPAC 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, and as will be appreciated by the skilled person, the term “diameter” of said pores is synonymous with the term “width”, and does not signify any particular pore geometry (i.e. spherical or cylindrical). The porosity of the porous framework is characterised by a variable defined herein as P1, which is the total accessible volume of micropores and mesopores expressed in cm3 / g as measured by nitrogen gas adsorption. Herein, P1 is measured for porous frameworks without reaction products within the pores (referred to herein as P1 (initial)), and is also measured for frameworks comprising reaction products within the pores (i.e. P1 (modified) and P1 (washed)). It will be appreciated that P1 for a framework comprising reaction products will be lower than P1 for an otherwise identical framework without reaction products, since the accessible volume is lower when reaction products are present in the pores. However, as detailed herein, the pore structure itself is also modified as a result of the reaction involving the porosity modifier and the porous frameworks. The blocking of some of the pores, particularly the smaller micropores, according to the present invention means that these pores then remain un-filled following silicon deposition, which improves the elastic response of the composite under large strains (e.g. during lithiation and delithiation in respect of LIBs, or during sodiation and desodiation in respect of SIBs), thereby minimising the scale of outward expansion and significantly reducing fracturing of the composite. Herein, each parameter relating to the pore structure of the composite particles (e.g. P1, P2, VP1, VP2, VP5, VP10, VP20, PDn pore diameter, etc.) is further specified according to the stage at which the parameter is measured during the process. Hence, “(initial)” refers to the value for the 5 parameter before infiltration of the porosity modifier; “(modified)” refers to the value for the parameter after the reaction between the infiltrated porosity modifier and the porous framework; and “(washed)” refers to the value for the parameter subsequent to the washing step. The total volume of micropores and mesopores and the pore size distribution of micropores and mesopores, including the P1, VP1, VP2, VP5, VP10, VP20, and PDn pore diameter parameters defined herein, are determined using nitrogen gas adsorption at 77 K down to a relative pressure p / po of 10-7 using quenched solid density functional theory (QSDFT) in accordance with standard methodology, preferably as set out in ISO 15901-2:2022. 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 Autosorb IQ porosity analyzers (available from Quantachrome Instruments, USA). Nitrogen gas adsorption is effective for the measurement of pore volume and pore size distributions for pores having a diameter up to 50 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 50 nm (i.e. only for micropores and mesopores). PDn values are likewise determined relative to the total volume of micropores and mesopores only. In view of the limitations of available analytical techniques it is not possible to measure pore volumes and pore size distributions across the entire range of micropores, mesopores and macropores using a single technique. In the case that the particulate porous frameworks comprise macropores, the volume of pores having diameter in the range from greater than 50 nm and up to 100 nm may be measured by mercury porosimetry and 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 the aforementioned pore modification and blocking of micropores and mesopores. Any pore volume measured by mercury porosimetry at pore sizes of 50 nm or below is disregarded (as set out above, nitrogen adsorption is used to characterize the mesopores and micropores). Pore volume measured by mercury porosimetry above 100 nm is assumed for the purposes of the invention to be inter-particle porosity and is also disregarded. Mercury porosimetry is a technique that characterizes the porosity and pore diameter distributions of a material by applying varying levels of pressure to a sample of the material immersed in mercury. The pressure required to intrude mercury into the pores of the sample is inversely proportional to the size of the pores. Values obtained by mercury porosimetry as reported herein are obtained in accordance with ASTM UOP578-11, with the surface tension y taken to be 480 mN / m and the contact angle (p taken to be 140° for mercury at room temperature. The density of mercury is taken to be 13.5462 g / cm3 at room temperature. A number of high precision mercury porosimetry instruments are commercially available, such as the AutoPore IV series of automated mercury porosimeters available from Micromeritics Instrument Corporation, USA. For a complete review of mercury porosimetry reference may be made to P.A. Webb and C. Orr in “Analytical Methods in Fine Particle Technology, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0. It will be appreciated that intrusion techniques such as gas adsorption and mercury porosimetry 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 or mercury porosimetry 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. The particulate porous frameworks are 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 initial particulate porous frameworks include both micropores and mesopores. However, it is not excluded that initial particulate porous frameworks may be used which include micropores and no mesopores. P1 (initial) of the initial particulate porous frameworks is least 0.35, or preferably at least 0.40, at least 0.50, at least 0.60, at least 0.65, at least 0.70, at least 0.75 or at least 0.80. 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. 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 (initial) of the initial particulate porous frameworks may be no more than 2.50, preferably no more than 2.20, no more than 2.00, no more than 1.80, no more than 1.70, no more than 1.60, no more than 1.55, no more than 1.50, no more than 1.45, no more than 1.40, no more than 1.35, no more than 1.30, no more than 1.25, no more than 1.20 or no more than 1.10. Preferably P1 (initial) of the particulate porous frameworks is in the range from 0.40 to 1.80, or from 0.50 to 1.60, or most preferably from 0.60 to 1.20. Preferably, P1 (modified) is in the range of from 30% to 90% of P1 (initial). Pl(modified) of the modified porous frameworks is preferably at least 0.01, at least 0.05, at least 0.10, at least 0.15, at least 0.20, at least 0.30, at least 0.40, at least 0.50, at least 0.60 or at least 0.70. Preferably, P1 (modified) is at least 0.10. P1 (modified) of the modified porous frameworks is preferably no more than 2.00, or no more than 1.80, no more than 1.60, no more than 1.40, no more than 1.20, no more than 1.00, no more than 0.90, no more than 0.80, no more than 0.70, no more than 0.60, no more than 0.50 or no more than 0.40, or no more than 0.30. Preferably, P1 (modified) is no more than 2.00. Preferably, Pl(modified) is in the range of 0.10 to 2.00. P1 (washed) of the washed porous frameworks is preferably at least 0.45, at least 0.50, at least 0.55, at least 0.60 at least 0.70 or at least 0.80. P1(washed) of the washed porous frameworks is preferably no more than 2.50, preferably no more than 2.00, or no more than 1.80, or no more than 1.70, or no more than 1.60, or no more than 1.55, or no more than 1.50, or no more than 1.45, or no more than 1.40, or no more than 1.35, or no more than 1.30, or no more than 1.25, or no more than 1.20. P1 (washed) of the washed porous frameworks is preferably in the range from 0.45 to 2.00, preferably from 0.50 to 1.50, or from 0.60 to 1.00. P1 (washed) of the washed particulate porous frameworks may be lower than or greater than P1 (initial) of the initial particulate porous framework. Preferably, P1 (washed) is within ±30% of Pl(initial), more preferably within ±20% of Pl(initial), more preferably within ±10% of P1 (initial). The washed particulate porous frameworks preferably exhibit both micropores and mesopores. In the process of the present invention, it is preferred that the pore volume of the mesopores in the washed particulate porous frameworks is greater than the pore volume of mesopores in the modified particulate porous frameworks and is greater than the pore volume of mesopores in the initial particulate porous frameworks. In the process of the present invention, it is preferred that the pore volume of the micropores in the washed particulate porous frameworks is greater than the pore volume of micropores in the modified particulate porous frameworks and is preferably no more than the pore volume of micropores in said initial particulate porous frameworks. As used herein, VP1, VP2, and VP5 are the volume of pores in the particulate porous frameworks with a pore diameter of less than 1.0 nm, less than 2.0 nm, and less than 5.0 nm, respectively, expressed as a percentage of P1. VP1, VP2, and VP5 are measured by nitrogen gas adsorption. VP2 is therefore the micropore volume expressed as a percentage of P1. Preferably, VP2(washed) is at least 20%. In a preferred embodiment, VP2(washed) is at least 30%, preferably at least 40%, preferably at least 50%, and preferably greater than 50%, i.e. wherein the micropores form the majority of the volume of micropores and mesopores, in which case VP2(washed) may be at least 60%, or at least 70%, or at least 80%. Alternatively, VP2(washed) is no more than 50%, or no more than 45%, i.e. the mesopores form the majority of the volume of micropores and mesopores. VP2(washed) is suitably less than 90%. Preferably, VP2(washed) is in the range of 30-90%, 30-80%, 30-75% or 40-75%. The pore volume at larger pore sizes may be controlled to further refine the properties of the frameworks and resulting composite particles. As used herein, VP20 and VP10 are defined as the volume of pores in the particulate porous frameworks with a pore diameter of less than 20.0 nm or less than 10.0 nm, respectively, expressed as a percentage of P1. VP10 and VP20 are measured by nitrogen gas adsorption. VP20(washed) is preferably at least 75%, or at least 80%, or at least 90%, or at least 95%. VPIO(washed) may be at least 65%, or at least 70%, or at least 80%, or at least 90%. VP20-VP5 represents the pore volume in the particulate porous frameworks at any given stage in the process of the invention 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(washed) is preferably less than 30%, or preferably less than 25%, or preferably less than 20%, less than 15%, preferably less than 12%, or preferably less than 10%. Optionally, VP20 VP5(washed) is at least 2%. VP20-VP5(washed) may be 2-30%, 3-20%, or 3-15%, or 3-12%. It has been found that particulate porous frameworks having values of VP20-VP5(washed) within these ranges provide a further improvement in average surface silicon. The general term “PDn pore diameter” refers herein to the volume-based nth percentile pore diameter, based on the total volume of micropores and mesopores. For instance, the term “PDso 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 PDn values. The washed particulate porous frameworks preferably have a PD90(washed) pore diameter of no more than 30 nm, preferably no more than 25 nm or 2-30 nm, or 2-25 nm, or 2-20 nm, or 2-15 nm. The washed particulate porous frameworks preferably have a PD5o(washed) pore diameter of no more than 6 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3 nm, or 1-5 nm. In the case that the particulate porous frameworks 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 10 measured by mercury porosimetry. 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 mesopores, particularly micropores and smaller mesopores. Thus, P2 of the washed particulate porous frameworks preferably has a value of <0.2*P1, or <0.1 xpi, or <0.05xP1, or <0.02xP1, or <0.01 xpi, or <0.005xP1, wherein P1 here is P1 (washed). P2(washed) is preferably <15%, <10%, <8%, or <5% of the total volume of micropores, mesopores, and pores having a diameter in the range of >50-100 nm. In general, the composite particles have a D50 particle diameter of no more than 30 pm. Optionally, the D50 particle diameter of the composite particles may be 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, or at least 4 pm, or at least 5 pm. Optionally the D50 particle diameter of the composite particles may be no more than 25 pm, or no more than 20 pm, or no more than 18 pm, or no more than 15 pm, or no more than 12 pm, or no more than 10 pm, or no more than 8 pm. The D10 particle diameter of the 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. The Di particle diameter of the 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. The Do particle diameter of the composite particles is preferably at least 0.3 pm, or at least 0.5 pm, or at least 1 pm. The D90 particle diameter of the composite particles is preferably no more than 50 pm, or no more than 40 pm, or no more than 30 pm, or no more than 25 pm, or no more than 20 pm, or no more than 15 pm. The D98 particle diameter of the composite particles is preferably no more than 35 pm, or no more than 30 pm, or no more than 25 pm, or no more than 20 pm, or no more than 15 pm. By controlling the D98 particle 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. The Dwo particle diameter of the composite particles is preferably no more than 40 pm. The 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 (Dg8-Di) / Dso is preferably less than 2. Maintaining a tight distribution between the Dgs and 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. Control over the particle size distribution may be achieved by known classification methods, such as dynamic air classification, hydroclassification, or gravity separation. A suitable classifying apparatus is a dynamic air classifier, such as the Alpine TTD Ultra-Fine Air Classifier from Hosokawa Micron Powder Systems. 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 “Dn particle 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. 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 SPANTM-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. The composite particles may have an average sphericity (as defined herein) of more than 0.5. Preferably they have an average sphericity of at least 0.55, 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, or at least 0.85. Preferably, the composite particles have an average sphericity of at least 0.90, or at least 0.92, or at least 0.93, or at least 0.94, or at least 0.95. Spherical particles are believed to aid uniformity of deposition and facilitate denser packing both in the batch pressure reactor and of the final product when incorporated into electrodes. 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: 4■n■Am S= wherein Am is the measured area of the particle projection and Cm is the measured circumference of the particle projection. The average sphericity Sav of a population of particles as used herein is defined as: 1 y [4 ■ 7T ' Am av nLl (Cmy 1=1 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 particle size distribution of the particulate porous frameworks is assumed to be unchanged by the processes which form the composite particles. Accordingly, the particle size distribution parameters defined for the composite particles may also be used to define the particulate porous frameworks (e.g. Dso, sphericity, etc.). The initial particulate porous frameworks 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 1,400 m2 / g, or at least 1,500 m2 / g. 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. Preferably, the BET surface area of the initial particulate porous frameworks 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 initial particulate porous frameworks may have a BET surface area in the range from 500 m2 / g to 4,000 m2 / g, or from 750 m2 / g to 3,500 m2 / g, or from 800 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. Preferably, the initial particulate porous frameworks have a BET surface area of from 1000 to 3000 m2 / g, more preferably from 1400 to 3000 m2 / g. The washed particulate porous frameworks preferably have a BET surface area of at least 750 m2 / g, or at least 800 m2 / g, or at least 1,000 m2 / g, or at least 1,200 m2 / g, or at least 1,250 m2 / g, or at least 1,400 m2 / g, or at least 1,500 m2 / g. The washed particulate porous frameworks may have a BET surface area of 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. Preferably, the washed particulate porous frameworks have a BET surface area of from 800 to 3000 m2 / g, more preferably from 1200 to 3000 m2 / g. The BET surface area of the modified particulate porous frameworks may be less than the initial particulate porous frameworks, and preferably the BET surface area of the washed particulate porous frameworks is greater than the BET surface area of the modified particulate porous frameworks. The BET surface area of the washed particulate porous frameworks is typically no less than 60% of the BET surface area of the initial particulate porous frameworks, and is preferably in the range of 60-90% of the initial particulate porous frameworks. The composite particles preferably have a BET surface area of 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 charge- discharge 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, or at least 5 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. The composite particles preferably have a particle density of at least 0.35 and preferably less than 3 g / cm3, more preferably less than 2 g / cm3, more preferably less than 1.5 g / cm3, most preferably from 0.35 to 1.2 g / cm3. As used herein, the term “particle density” refers to “apparent particle density” as measured by mercury porosimetry (i.e. the mass of a particle divided by the particle volume wherein the particle volume is taken to be the sum of the volume of solid material and any closed or blind pores (a “blind pore” is pore that is too small to be measured by mercury porosimetry). Preferably, the composite particles have particle density of at least 0.4 g / cm3, or at least 0.45 g / cm3, or at least 0.5 g / cm3, or at least 0.55 g / cm3, or at least 0.6 g / cm3, or at least 0.65 15 g / cm3, or at least 0.7 g / cm3. Preferably, the composite particles have particle density of no more than 1.15 g / cm3, or no more than 1.1 g / cm3, or no more than 1.05 g / cm3, or no more than 1 g / cm3, or no more than 0.95 g / cm3, or no more than 0.9 g / cm3. The initial particulate porous frameworks 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 (or between sodium atoms / ions in the case of SIBs) inserted into the electroactive material and a current collector. A preferred type of particulate porous framework comprises or consists of a conductive carbon material, referred to herein as conductive particulate porous carbon frameworks. The initial particulate porous frameworks preferably comprise at least 60 wt% carbon, more preferably at least 70 wt% carbon, more preferably 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 98 wt% 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. As used herein, the term “hard carbon” refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2 hybridised 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. As used herein, the term “soft carbon” also refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2 hybridised 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 initial porous carbon particle frameworks preferably comprise at least 50% sp2 hybridised carbon as measured by XPS. For example, the particulate porous carbon frameworks may suitably comprise from 50% to 98% sp2 hybridised carbon, from 55% to 95% sp2 hybridised carbon, from 60% to 90% sp2 hybridised carbon, or from 70% to 85% sp2 hybridised carbon. When the initial particulate porous frameworks are particulate porous carbon frameworks, the initial 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 initial particulate porous carbon frameworks may be >0.6, or >0.8, or >1 or >1.05. For example, Id / Ig of the initial particulate porous carbon frameworks may be in the range of 0.6-1.8, or 1.0-1.6. The initial particulate porous frameworks may be provided by synthesising the frameworks or by obtaining the frameworks from a commercial supplier thereof. Most preferably, the initial particulate porous frameworks are particulate porous carbon frameworks. The initial particulate porous carbon frameworks used in the invention may be a tern plated carbon or a form of activated carbon, and 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 physical 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. Alternatively, frameworks can be obtained using template-assisted carbonization using zeolites, using known methods. In another approach, frameworks can be obtained by carbonizing metal organic frameworks, such as zinc imidazolate frameworks, and washing the carbonized material to remove residual metal. 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. 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. A variety of different carbonaceous materials may be used to prepare suitable initial 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, and tree barks (e.g. the bark of 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. 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. The initial 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. Secondly, the pyrolyzed material is activated by heating in a flow of one or more of oxygen, steam, CO and CO2 at 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. 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. 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. In chemical activation methods, the carbonaceous material is impregnated with a chemical activation agent (such as NaOH, KOH, K2CO3, H3PO4, CaCh, ZnCt, 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 initial particulate porous carbon frameworks provided to step (a) of the process of the present invention are prepared by physical activation. It will be appreciated that the chemical activation methods described immediately hereinabove are distinct from the infiltration and reaction of a porosity modifier according to steps (b) and (c) followed by partial removal of reaction products according to step (d) of the present invention. Firstly, step (b) of the process of the invention is conducted on a material which is already a particulate porous framework, and specifically one which has a P1 value of at least 0.35. Secondly, in step (d) of the present invention the reaction products are only partially removed, whereas in the chemical activation processes described immediately hereinabove any products resulting from reactions between the chemical activation agents and the carbonaceous material are at least substantially completely removed, and preferably completely removed, typically by one or more washing steps, from the porous framework which results from the activation process. In one embodiment, the process of the present invention includes the manufacture of the initial particulate porous carbon frameworks defined herein, the process comprising activating pyrolyzed carbon by heating in a flow of CO2 at a temperature between 600 °C and 1200 °C, wherein the burn-off of the pyrolyzed carbon is no more than 50wt% or no more than 45wt% and optionally at least 15%. Thus, such manufacture constitutes step (a) in the process for preparing composite particles provided herein, and is followed by steps (b)-(e) of infiltrating with a porosity modifier, providing energy to effect a reaction involving the porosity modifier and the initial particulate porous frameworks, washing the modified particulate porous frameworks, and depositing electroactive material domains in the pores of the washed particulate porous frameworks. 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). An example of a typical activated carbon synthesis is as below: Synthetic activated carbons are prepared from a mixture of Novolak resin and 11% of hexamethylenetetramine powder, Bakelite PF 6705 FP, purchased from Hexion GmbH. This starting material is cross-linked at 150 °C for 1 h and the solid blocks of cross-linked material are hammered to 2-3 cm pieces before grinding them to -100 pm particles. This cured resin powder is then pyrolyzed at 800 °C for 10 min under a nitrogen flow of 1 Umin. The carbon yield obtained from this precursor is 57-59%. After carbonization, the carbon is ball milled to particle size of 3-4 pm and the carbon material obtained has a total pore volume of 0.25-0.3 cm3 / g, including 0.20-0.22 cm3 / g of microporosity and a surface area of 650-700 m2 / g. This carbon is then activated in either steam or CO2 to achieve a desirable pore volume. Typical activation temperature used for CO2 activation to achieve 0.8-0.9 cm3 / g total pore volume, is 950-980 °C with dwell time of 5-8h depending on the amount of carbon being activated, CO2 flow rate, and the type of furnace being used. The temperature used for steam activation is lower than CO2, typically 850 °C, as steam is more reactive. The dwell time at the activation temperature for steam is typically 6-9h depending on the type and amount of charcoal being activated, steam flow rate, and the type of furnace being used. An example of activated carbon made using steam activation is as follows: To make steam activated synthetic scaffold with a total pore volume of 0.79 cm3 / g, steam is introduced via a humidifier consisting of nitrogen atomizer (3 bar injection pressure) through 1 mm orifice positioned at right angles to a 1 mm orifice which adds water dropwise to an atomization chamber where the high pressure nitrogen stream induces atomization via impingement of the high pressure gas on the water droplet. Heated tapes are used on the inlet and outlet to prevent adventitious steam condensation. Carbonised phenolic resin is ball-milled in a planetary ball mill to D50 = 3 pm (60 g loading, 105, 10 mm balls, 300 RPM, 20 min interval). Subsequently, 15 g of milled carbonised phenolic resin is loaded into a short alumina crucible, the material is spread evenly along the crucible. Steam activation takes place in a tube furnace with the crucible placed in the middle of the heating zone. The furnace is purged with N2 at 0.8 L / min for 10-30 minutes. A ramp rate of 8.7 °C / min with a set-point of 850 °C is used. Once the temperature has reached 840 °C, water is injected into an atomisation nozzle at a rate of 0.25 mL / min (water injection volume), temperature is held stable once 850 °C is reached. Dwell for 345 min. When dwell has completed, steam flow is set to zero and heating tape is turned off. When the material is recovered, two fractions are taken from the resulting carbon (one closest to steam, and furthest from steam to assess any differences in total pore volume). As described hereinabove, the initial particulate porous frameworks provided to step (a) of the present invention preferably comprise at least 60 wt% carbon, and are suitably derived from activated carbonaceous materials. However, the initial particulate porous frameworks may also comprise alternatives to particulate porous carbon frameworks, which 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. Such alternative particulate porous frameworks preferably make up less than 60 wt%, preferably less than 50 wt%, preferably less than 40 wt%, preferably less than 30 wt%, preferably less than 20 wt%, preferably less than 15 wt%, preferably less than 10 wt%, preferably less than 5 wt%, or less than 2 wt% or less than 1 wt% of the total weight of the initial particulate porous framework. Preferably, the initial particulate porous framework is derived completely from activated carbonaceous material. In step (b) of the process according to the invention, the porosity modifier infiltrating the pores of the initial particulate porous frameworks may comprise M3PO4, MCI, MOH, MCIO4, M2SO4, MNO3, 21 C2M2O4, M2O2, M2CO3, MOAc, MB(C2O4)2, or mixtures thereof, wherein M = Li or Na, preferably wherein M = Li. Preferably, the porosity modifier comprises LiOH. The porosity modifier may be provided in the form of a solution, preferably an aqueous solution, comprising an Li-containing and / or Na-containing species, preferably the molar concentration of said □-containing and / or Na-containing species is in the range of from 1.0 to 10.0 mol / L, preferably from 2.5 to 7.5, preferably about 5 mol / L. The initial particulate porous frameworks may be stirred with the porosity modifier for a duration of at least 5 minutes, or at least 10 minutes, or at least 20 minutes, or at least 30 minutes, or at least 1 hr. Preferably, the initial particulate porous frameworks is stirred with the porosity modifier for a duration of at least 10 minutes. Preferably, the initial particulate porous frameworks may be stirred with the porosity modifier for a duration of up to about 72 hr, typically up to about 48 hr, typically up to about 24 hr, typically up to about 10 hr, typically up to about 5 hr, typically up to about 2 hr. Preferably, the initial particulate porous frameworks is stirred with the porosity modifier for a duration of from 10 minutes to 5 hr, or from 30 minutes to 2 hr, or from 1 hr to 2 hr. Preferably, the initial particulate porous frameworks may be stirred with the porosity modifier for a duration of from 1 to 2 hr. The initial particulate porous frameworks may be stirred with the porosity modifier at any suitable temperature, preferably at room temperature. The energy provided in step (c) of the process according to the invention may be any suitable source of energy, and is preferably selected from thermal energy, microwave energy and infrared energy, and is preferably thermal energy. The provision of energy to the infiltrated particulate porous frameworks in step (c) is suitably conducted by heating the frameworks. Such a heat treatment preferably comprises a high-temperature hold for a period of time t which comprises maintaining the infiltrated particulate porous frameworks at a temperature of at least 650°C, preferably at least 700 °C, preferably at least 800°C, preferably at least 850°C, preferably at least 900°C. and preferably no more than 1250°C, preferably no more than 1100°C, preferably no more than 1000°C, and preferably in the range of 850 to 950°C, and preferably at about 900°C. The period of time t is typically greater than 10 minutes, and is preferably at least 1 hr, and is preferably from about 3 to about 10 hours, preferably from about 5 to about 7 hours, and is preferably about 6 hours. Prior to the provision of energy to the infiltrated particulate porous frameworks in step (c), particularly wherein step (c) is a heating step comprising a high temperature hold, the infiltrated particulate porous frameworks may first be dried. Any suitable process for removing moisture may be used. For example, the infiltrated particulate porous frameworks may be heated at a low-temperature hold for a period of time at a temperature in the range of from 100°C to 200 °C, preferably at a temperature in the range of from greater than 100°C to 150°C, preferably about 110 °C. This low-temperature hold may be performed for any suitable time period, for example, more than 10 minutes and less than 2 hr, preferably about 1 hr. Step (c) is preferably performed in a substantially oxygen-free atmosphere. Preferably, step (c) is performed in a noble gas atmosphere such as a helium or argon atmosphere, or in a nitrogen atmosphere, or mixtures thereof. Most preferably, step (c) is performed in a nitrogen 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 (c). The atmosphere in step (c) is preferably an inert atmosphere, such that reactions between said atmosphere and the frameworks or the porosity modifier are avoided. In an alternative embodiment, reaction between the porosity modifier and the atmosphere may be desirable, such that in the case of a nitrogen atmosphere for example, nitrides such as lithium or sodium nitride may be formed. Optionally, after step (c) and prior to step (d), the process comprises an incremental exchange of the substantially oxygen-free or inert atmosphere under which step (c) has been conducted, by incrementally increasing the amount of air in said atmosphere. This is suitably achieved by introducing, and then increasing the relative proportion of, air in the nitrogen or noble gas atmosphere under which the frameworks are held, for instance by adjusting the ratio of nitrogen (or noble gas) to air to 75:25, 50:50, 25:75 and finally 0:100, over a period of time (for instance from 0.2 to 1 hour). Thus, this optional step is effectively passivating the modified particulate porous frameworks prior to the washing step. The reaction products resulting from the reaction in step (c) preferably comprise reaction products selected from the metal M, the metal M oxides, the metal M hydroxides, metal M carbonates and metal M nitrides and mixtures thereof, i.e. Li metal or Na metal, oxides of Li or Na, hydroxides of Li or Na, carbonates of Li or Na, nitrides of Li or Na, or lithium-based mixtures thereof (in the case of LIBs) or sodium-based mixtures thereof (in the case of SIBs). Preferably the metal M is lithium, as noted hereinabove. Preferably, the reaction products comprise lithium metal, lithium oxide, lithium carbonate and / or lithium nitride, preferably lithium metal, lithium oxide and / or lithium carbonate, and more preferably comprise lithium metal and / or lithium carbonate. In step (d) of the process according to the invention, the modified particulate porous frameworks are washed to partially remove the reaction products from the pores. Thus, a proportion of the reaction products formed in step (c) remain in the pores after this washing step. Washing the modified particulate porous frameworks in step (d) may comprise washing with a suitable solvent, provided that the solvent does not result in complete removal of reaction products from the modified particulate porous framework. The solvent may comprise water, methanol, ethanol, isopropyl alcohol (IPA), acetone, dichloromethane, toluene, benzenes, xylenes, or mixtures thereof. Typically, the solvent comprises a polar solvent in a mixture with a second solvent, such as the solvents listed hereinabove, wherein the second solvent may also be a polar solvent. Typically, non-polar or aprotic hydrocarbon solvents (such as the ones listed hereinabove) are used only in a mixture with said polar solvents. The solvent may be selected based on the pore profile of the modified particulate porous frameworks and / or on the desired pore characteristics of the composite material. In one preferred embodiment, the solvent comprises water and IPA. The ratio of water to IPA by volume may be about 2-8, about 4-6, or about 5. The washed particulate porous frameworks are suitably collected by filtration from the solvent and further washed with IPA to remove residual water. The washing in step (d) may be performed at any suitable temperature, and is preferably performed at room temperature. The washing in step (d) is suitably performed for a duration of at least 5 minutes, and is preferably performed for a duration of 15-20 minutes. In step (e) of the process according to the invention, electroactive material domains are deposited in the pores of the washed particulate porous frameworks, thereby providing composite particles. The electroactive material is suitably selected from silicon, tin, germanium and 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). The washed 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 washed 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. Step (e) preferably 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 washed particulate porous frameworks. The electroactive material precursor of step (e) is preferably gaseous. Gaesous precursors are conveniently used in CVI processes. Suitable silicon precursors include silane (SiH4), disilane (SizHe), trisilane (SisHg), tetrasilane (Si4Hio), methylsilane (CH3SiH3), dimethylsilane ((CH3)2SiH2), trimethylsilane ((CH3)3SiH), tetramethylsilane ((CH3)4Si), or chlorosilanes such as trichlorosilane (HSiCI3) or dichlorosilane (HzSiCh) or chlorosilane (H3SiCI), or methylchlorosilanes such as methyltrichlorosilane (CH3SiCI3) or dimethyldichlorosilane ((CH^SiCh). Preferably the silicon precursor is selected from silane (SiH4), disilane (SizHe), trisilane (Si3H8), tetrasilane (Si4Hw). A particularly preferred silicon precursor is silane (SiH4). Suitable germanium precursors include germane (GeH4), hexamethyldigermanium ((CH3)3GeGe(CH3)3), tetramethylgermanium ((CH3)4Ge), tributylgermanium hydride ((CH3(CH2)3]3GeH), triethylgermanium hydride ((C2Hs)3GeH), and triphenylgermanium hydride ((CsHshGeH). A preferred germanium precursor is germane. Suitable tin precursors include bis[bis(trimethylsilyl)amino]tin(ll) ([[(CHsJsSikNkSn), 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 (CwHi4O4Sn), trimethyl(phenylethynyl)tin (C6HsC=CSn(CH3)3), and trimethyl(phenyl)tin (CeHsSntCHsh). A preferred tin precursor is tetramethyltin. 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(CH3)2)3). A preferred aluminium precursor is trimethylaluminium. Step (e) is preferably performed via chemical vapor infiltration (CVI) of a gaseous electroactive material precursor into the pore structure of the washed 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. 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. The gaseous electroactive material precursor may be used either in pure form (or substantially pure form) or as a diluted mixture with a carrier gas, such as nitrogen or argon. Preferably step (e) comprises contacting the washed 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. The presence of oxygen in step (e) 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 (e). The temperature in step (e) is preferably in the range 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. The pressure in step (e) 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 (e) 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. In one implementation, the pressure in step (e) is at least 150 kPa, or at least 200 kPa, and optionally no more than 5000 kPa, or no more than 3000 kPa, or no more than 2000 kPa. For example, preferably the pressure in step (e) is in the range of 200-2000 kPa. The deposition of electroactive materials by CVI results in the elimination of by-products, particularly by-product gases such as hydrogen. Step (e) preferably further comprises the separation of by-products from the particles formed in step (e). 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 (e) 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. A range of different electroactive material loadings in the composite particles may be obtained. The composite particles preferably comprise 20-80 wt% electroactive material, or 30-70 wt% electroactive material, or 40-60 wt% electroactive material. The composite particles may comprise at least 26 wt% electroactive material, or at least 28 wt% electroactive material, or at least 30 wt% electroactive material, or at least 32 wt% electroactive material, or at least 34 wt% electroactive 27 material, or at least 36 wt% electroactive material, or at least 38 wt% electroactive material, or at least 40 wt% electroactive material, or at least 42 wt% electroactive material, or at least 44 wt% electroactive material. The reaction products in step (c) prevent the precursor from accessing some of the pores, i.e. some of the pores are blocked. The efficacy of blocking is greatest for smaller micropores. Since the blocked micropores are then inaccessible to the electroactive material precursor, no electroactive material domains will be deposited in these pores, thereby creating space within the composite particles to accommodate expansion of the electroactive material during charging and discharging. The amount of electroactive material in the composite particles is preferably selected such that at least 20% and up to 90% of the internal pore volume of the washed particulate porous frameworks is occupied by the electroactive material following step (e). 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 washed 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 (or sodiation in respect of SIBs) due to inadequate metal-ion diffusion rates or due to inadequate expansion volume resulting in mechanical resistance to lithiation (or sodiation in respect of SIBs). When the electroactive material is silicon, the amount of silicon in the composite particles can be related to the available pore volume in the washed particulate porous frameworks by the requirement that the mass ratio of silicon to the washed particulate porous frameworks is in the range from [0.5*P1 to 1.9*P1]: 1, wherein P1 here is P1 (washed) and is as defined above (e.g. if the washed 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 washed 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 washed 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 wherein P1 here is P1(washed). 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. Preferably at least 70 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or most preferably 98 wt% of the electroactive material in the composite particles is located within the internal pore volume of the washed particulate porous frameworks such that there is no or very little electroactive material located on the external surfaces of the particulate porous frameworks. As discussed above, deposition of electroactive material in a CVI process occurs at the surfaces of the washed particulate porous frameworks. In view of the very high internal surface area of the washed particulate porous frameworks, the reaction kinetics of the CVI process ensure that deposition of the electroactive material occurs almost entirely within the pores of the washed particulate porous frameworks. The nitrogen-accessible pore volume of the composite particles may be less than 0.05*P1(washed), wherein P1(washed) is the total volume of micropores and mesopores in the washed particulate porous frameworks expressed in cm3 / g prior to deposition of electroactive material within the pores of the washed 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. 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 oxidized in air and at elevated temperature. 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 550 °C and 650 °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 29 therefore allows the percentage of surface silicon as a proportion of the total amount of silicon to be determined according to the following formula: Y= 1.875 x [(Mmax ” Mmin) / Mf] X 1 00% 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 SiO2 to O2 (i.e. the mass ratio of S1O2 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. It has been found that reversible capacity retention over multiple charge / discharge cycles is considerably improved when the surface silicon as determined by the TGA method described above is at least 10 wt % of the total amount of silicon in the composite particles. Thus, preferably at least 10 wt%, or at least 15 wt%, or more preferably 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 composite particles is surface silicon as determined by thermogravimetric analysis (TGA). The particulate porous frameworks produced by the process of the present invention facilitate the achievement of advantageous amounts of surface silicon, when the silicon precursor is used to deposit silicon in the frameworks. In addition to the surface silicon content, the composite particles preferably have a low content of coarse bulk silicon as determined by TGA. Coarse bulk silicon is defined herein as silicon which undergoes oxidation above 800 °C as determined by TGA, wherein the TGA is carried out in air with a temperature ramp rate of 10 °C / min. The coarse bulk silicon content is therefore determined according to the following formula: Z = 1.875 x [(Mf - M800) I Mf] x100% Wherein Z is the percentage of unoxidized silicon at 800 °C, M8oo is the mass of the sample at 800 °C, and Mf is the mass of ash at completion of oxidation at 1400 °C. For the purposes of this analysis, it is assumed that any mass increase above 800 °C corresponds to the oxidation of silicon to SiO2 and that the total mass at completion of oxidation is S1O2. 30 Silicon that undergoes oxidation above 800 °C is less desirable. Preferably, no more than 10 wt%, or no more than 8 wt%, or no more than 6 wt%, or no more than 5 wt%, or no more than 4 wt%, or no more than 3 wt%, or no more than 2 wt%, or no more than 1.5 wt% of the silicon is coarse bulk silicon as determined by TGA. Preferably, at least 30 wt% of the silicon is surface silicon and no more than 10 wt% of the silicon is coarse bulk silicon, wherein both are determined by TGA. More preferably, at least 35 wt% of the silicon is surface silicon and no more than 8 wt% of the silicon is coarse bulk silicon, wherein both are determined by TGA. More preferably, at least 40 wt% of the silicon is surface silicon and no more than 5 wt% of the silicon is coarse bulk silicon, wherein both are determined by TGA. More preferably, at least 45 wt% of the silicon is surface silicon and no more than 2 wt% of the silicon is coarse bulk silicon, wherein both are determined by TGA. TGA may additionally be used to identify reaction products formed in the step (c) of the process, by conducting TGA analysis of the modified particulate porous frameworks. When the particulate porous frameworks are particulate porous carbon frameworks, the composite particles 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 composite particles may be >0.6, or >0.8, or >1 or >1.05. For example, Id / Ig of the composite particles may be in the range of 0.6-1.8, or 1.0-1.6. In a further aspect of the invention, there is provided composite particles as prepared by the process described hereinabove. The washed particulate porous frameworks defined herein as part of the process of manufacturing composite particles of the invention may be produced or provided in the absence of electroactive material domains located within the pores. This represents a convenient starting material for the manufacture of the composite particles of the invention. Therefore, in a further aspect of the present invention, there is provided a process for manufacturing washed particulate porous frameworks suitable for use as an electroactive material for a metal-ion battery, comprising the steps of: (a) providing initial particulate porous frameworks comprising micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks is greater than a value P1 (initial) which is at least 0.35; 31 (b) infiltrating the pores of the initial particulate porous frameworks with a porosity modifier comprising Li or Na, thereby providing infiltrated particulate porous frameworks; (c) providing sufficient energy to the infiltrated particulate porous frameworks to cause a reaction involving the porosity modifier and the initial particulate porous frameworks, thereby providing modified particulate porous frameworks comprising reaction products from the reaction within the pores, wherein P1 (modified) of the modified particulate porous frameworks is lower than P1 (initial); (d) washing the modified particulate porous frameworks to partially remove the reaction products from the pores, thereby providing washed particulate porous frameworks comprising residual reaction-products within the pores, wherein P1 (washed) of the washed particulate porous frameworks is higher than P1 (modified); wherein P1 is the total volume of micropores and mesopores in the particulate porous frameworks expressed in cm3 / g as measured by nitrogen gas adsorption. In this further aspect of the invention, it will be appreciated that steps (a) to (d) are the same as the steps described hereinabove in respect of the process for preparing composite particles, and the same preferences apply mutatis mutandis. In a further aspect of the invention, there is provided the washed particulate porous frameworks resulting from the process comprising steps (a)-(d). In this aspect of the invention, said washed particulate porous frameworks may be provided as a kit together with an electroactive material precursor. The components of the kit may be held separately until the electroactive material precursor is used to deposit electroactive material domains in the pores of said washed particulate porous frameworks. The process may, and preferably does, comprise a passivating step of contacting the composite particles with a passivating agent. Said passivating step is conducted after step (e). As defined herein, a passivating agent is a compound or mixture of compounds which is able to react with the surface of the silicon deposited in step (e) to form a modified surface. In particular, a passivating agent as defined herein is a material which is able to react with the surfaces of silicon to further reduce the surface energy thereof. One type of passivation layer is a native oxide layer. A native oxide layer may be formed, for example, by exposing the silicon surface to a passivating agent selected from air or another oxygen containing gas. The passivation layer may comprise a silicon oxide of the formula SiOx, wherein 0 <x <2. The silicon oxide is preferably amorphous silicon oxide. Similarly, a native oxide layer may also be formed on the sodium or lithium metal species which may be present in the composite particles and which were introduced via the porosity modifier in step (b) of the process of the present invention. The formation of a native oxide layer is exothermic and therefore requires careful process control to prevent overheating or even combustion of the particulate material. In the case that the passivating agent is an oxygen-containing gas, the passivating step may comprise cooling the composite particles to a temperature below 300 °C, preferably below 200 °C, optionally below 100 °C, prior to contacting with the oxygen-containing gas. Another type of passivation layer is a nitride layer that is formed, for example, by exposing the silicon surfaces to a passivating agent selected from ammonia or another nitrogen containing molecule. The passivation layer may comprise a silicon nitride of the formula SiNx, wherein 0 <x <4 / 3. The silicon nitride is preferably amorphous silicon nitride. A nitride layer may be formed by contacting the silicon surfaces with ammonia at a temperature in the range from 200-700 °C, preferably from 400-700 °C, more preferably from 400-600 °C. The temperature may then be increased if necessary into the range of 500 to 1,000 °C to form a nitride surface (e.g. a silicon nitride surface of the formula SiNx, wherein x <4 / 3). Nitride passivation may be preferred to oxide passivation. As sub-stoichiometric nitrides (such as SiNx, wherein 0 <x <4 / 3) are conductive, nitride passivation layers may function as a conductive network that allows for faster charging and discharging of the electroactive material. Phosphine may also be used as a passivating agent, as a phosphorus analog of ammonia. Another type of passivation layer is an oxynitride layer that is formed, for example, by exposing the silicon surfaces to a passivating agent comprising ammonia (or another nitrogen containing molecule) and oxygen gas. The passivation layer may comprise a silicon oxynitride of the formula SiOxNy, wherein 0<x<2, 0<y< 4 / 3, and 0 <(2x+3y) <4). The silicon nitride is preferably amorphous silicon oxynitride. Another type of passivation layer is a carbide layer. The passivation layer may comprise a silicon carbide of the formula SiCx, wherein 0 <x <1. The silicon carbide is preferably amorphous silicon carbide. A carbide layer may be formed by contacting the silicon surfaces with a passivating agent 33 selected from carbon containing precursors, e.g. methane or ethylene at elevated temperatures, e.g in the range from 250 to 700 °C. At lower temperatures, covalent bonds are formed between the silicon surfaces and the carbon-containing precursors, which are the converted to a monolayer of crystalline silicon carbide as the temperature is increased. The silicon carbide may have the formula SiCx, wherein 0 <x <1. As described in respect of native oxide layers, sodium or lithium metal species which may be present in the composite particles and which were introduced via the porosity modifier in step (b) of the process of the present invention may also form passivation layers thereon, the passivation layers being selected from phosphide, oxynitride and carbide passivation layers, as described hereinabove for silicon surfaces. Other suitable passivating agents for a silicon surface include compounds comprising an alkene, alkyne or carbonyl functional group, more preferably a terminal alkene, terminal alkyne, aldehyde or ketone group. Preferred passivating agents include one or more compounds of the formulae: (i) R1-CH=CH-R1; (ii) R1-C=C-R1; and (iii) O=CR1R1; wherein each R1 independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having from 1 to 20 carbon atoms, or wherein two R1 groups form an unsubstituted or substituted ring structure comprising from 3 to 8 carbon atoms in the ring. Particularly preferred passivating agents include one or more compounds of the formulae: (i) CH2=CH-R1; and (ii) HC=C-R1; wherein R1 is as defined above. Preferably, R1 is unsubstituted. Examples of suitable passivating agents include ethylene, propylene, 1-butene, butadiene, 1-pentene, 1,4-pentadiene, 1-hexene, 1-octene, styrene, divinylbenzene, acetylene, phenylacetylene, norbornene, norbornadiene and bicyclo[2.2.2]oct-2-ene. Optionally, mixtures of different passivating agents may also be used. It is believed that passivating agents comprising an alkene, alkyne or carbonyl group undergo an insertion reaction with Si-H groups at the silicon surface to form a covalently passivated surface which is resistant to oxidation by air. The passivation reaction between the silicon surface and the passivating agent may therefore be understood as a form of hydrosilylation, as shown schematically below. Other suitable passivating agents include compounds including an active hydrogen atom bonded to oxygen, nitrogen, sulphur or phosphorus. For example, the passivating agent may be an alcohol, amine, thiol or phosphine. Reaction of the group -XH with hydride groups at the silicon surfaces is understood to result in elimination of H2 and the formation of a direct bond between X and the silicon surfaces. Suitable passivating agents in this category include compounds of the formula (iv) HX-R2, and (v) HX-C(O)-R1, wherein X represents O, S, NR1 or PR1; each R1 is independently as defined above; and R2 represents an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having from 1 to 20 carbon atoms, or R1 and R2 together form an unsubstituted or substituted ring structure comprising from 3 to 8 carbon atoms in the ring. Preferably X represents O or NH. Preferably R2 represents an optionally substituted aliphatic or aromatic group having from 2 to 10 carbon atoms. Amine groups may also be incorporated into a 4-10 membered aliphatic or aromatic ring structure, as in pyrrolidine, pyrrole, imidazole, piperazine, indole, or purine. Contacting the composite particles with the passivating agent may be carried out at a temperature in the range of 25 to 500 °C, preferably at a temperature in the range of from 50 to 450 °C, more preferably from 100 to 400 °C. The process may comprise, after step (e), a depositing step of depositing a lithium-ion permeable material (or sodium-ion permeable material in respect of SIBs) into the pores and / or onto the outer surface of the composite particles. The use of lithium-ion filler (or sodium filler in respect of SIBs) reduces SEI formation by reducing the surface area of the composite particles and by preventing contact between the electrolyte and the silicon domains in the particle interior. Preferably, the lithium-ion (or sodium-ion) permeable material is a pyrolytic carbon material and the depositing step comprises combining the composite particles with a pyrolytic carbon precursor; and heating the pyrolytic carbon precursor to a temperature effective to cause the deposition of a conductive pyrolytic carbon material into the pores and / or onto the outer surface of the composite particles. If the passivating step described hereinabove is performed, most preferably the depositing step is performed after the passivating step. The pyrolytic carbon precursor is preferably a hydrocarbon. Suitable hydrocarbons include polycyclic hydrocarbons comprising from 10 to 25 carbon atoms and optionally from 1 to 3 heteroatoms, optionally wherein the polyaromatic hydrocarbon is selected from naphthalene, substituted naphthalenes such as di-hydroxynaphthalene, anthracene, tetracene, pentacene, fluorene, acenapthene, phenanthrene, fluoranthrene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone and alkyl-substituted derivatives thereof. Suitable pyrolytic carbon precursors also include bicyclic monoterpenoids, optionally wherein the bicyclic monoterpenoid is selected from camphor, borneol, eucalyptol, camphene, careen, sabinene, thujene and pinene. Further suitable pyrolytic carbon precursors include C2-C10 hydrocarbons, optionally wherein the hydrocarbons are selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, and arenes, for example methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, a-terpinene and acetylene. Other suitable pyrolytic carbon precursors include phthalocyanine, sucrose, starches, graphene oxide, reduced graphene oxide, pyrenes, perhydropyrene, triphenylene, tetracene, benzopyrene, perylenes, coronene, and chrysene. A preferred carbon precursor is acetylene. A suitable temperature for the deposition of a pyrolytic carbon material in the depositing step is in the range from 300 to 800 °C, or from 400 to 700 °C. For example, the temperature may be no more than 680 °C or no more than 660 °C, or no more than 640 °C or no more than 620 °C, or no more than 600 °C, or no more than 580 °C, or no more than 560 °C, or no more than 540 °C, or no more than 520 °C, or no more than 500 °C. The minimum temperature will depend on the type of carbon precursor that is used. Preferably, the temperature is at least 300 °C, or at least 350 °C, or at least 400 °C, or at least 450 °C, or at least 500 °C. The carbon-containing precursors used in the depositing step may be used in pure form, or as a diluted mixture with an inert carrier gas, such as nitrogen or argon. For instance, the carbon-containing precursor may be used in an amount in the range from 0.1 to 100 vol%, or 0.5 to 20 vol%, or 1 to 10 vol%, or 1 to 5 vol% based on the total volume of the precursor and the inert carrier gas. In the case that a pyrolytic carbon material is deposited, the same compound may function as both a passivating agent in the passivating step and the pyrolytic carbon precursor in the depositing step. For example, if styrene is selected as the pyrolytic carbon precursor, then it will also function as a passivating agent if the composite particles are not exposed to another passivating agent prior to contact with styrene. In this case, passivation and deposition of the conductive carbon material in steps may be carried out simultaneously, for example at a temperature in the range of from 300-700 °C. Alternatively, passivation and deposition of the conductive carbon material may be carried out sequentially, with the same material as the passivating agent and the pyrolytic carbon precursor, but wherein the depositing step is carried out at a higher temperature than, and following, the passivating step. For example, passivation may be carried out at a temperature in the range of from 25 °C to less than 300 °C, and deposition of pyrolytic carbon may be carried out at a temperature in the range from 300-700 °C. These two steps may suitably be carried out sequentially by increasing the temperature while maintaining contact with the compound that functions as both a passivating agent and the pyrolytic carbon precursor. At lower temperatures (e.g. in the range of 25 °C to <300 °C) passivation will be the primary process. As the temperature is increased (e.g. to 300-700 °C) the deposition of pyrolytic carbon will ensue. According to a further aspect of the invention, the composite particles resulting from the process of the invention may be incorporated into a composition comprising at least one other component. In particular, in this further aspect of the invention, there is provided a composition comprising said composite particles and 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. The composition may be a hybrid electrode composition which comprises the composite particles and at least one additional particulate electroactive material. Examples of additional particulate 37 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. 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 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. The at least one additional particulate electroactive material preferably has a D5q 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 Dw 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. The D90 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. 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 D5o particle diameter in the range from 10 to 50 pm. 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 38 of inserting and releasing metal ions during the charging and discharging of a battery), based on the total dry weight of the composition. 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 composite particles, based on the total dry weight of the composition. 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. 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. 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. 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. According to a further aspect of the invention, there is provided an electrode comprising the composite particles. The electrode is typically associated with a current collector, wherein the composite particles are in electrical contact with the current collector. The particulate material used to prepare the electrode may be in the form of a composition comprising the composite particles and at least one other component defined above. 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 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 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. Alternatively, the slurry may be formed into a freestanding film or mat comprising the particulate material 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. The electrode may be used as the anode of a metal-ion battery. Thus, according to a further aspect of the present invention, there is provided a rechargeable metal-ion battery comprising the electrode as the anode. The metal ions may be sodium or lithium ions and are preferably lithium 40 ions. More preferably, the rechargeable metal-ion battery may be a sodium-ion or lithium-ion battery and is preferably a lithium-ion battery (LIB). The following description relates primarily to lithium-containing components for LIBs but the skilled person will appreciate that corresponding sodium-containing materials are available for SIBs. 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 LiCoO2, LiCo0.99AI0.01O2, LiNiO2, LiMnO2, LiCo0.5Ni0.5O2, LiCo0.7Ni0.3O2, LiCo0.3Ni0.2O2, LiCo0.82Ni0.13O2, LiCo0.3Ni0.15AI0.05O2, LiNi0.4Co0.3Mn0.3O2 and LiNi0.33Co0.33Mn0.34O2. The cathode current collector is generally of a thickness of between 3 to 500 pm. Examples of materials that can be used as the cathode current collector include aluminium, stainless steel, nickel, titanium and sintered carbon. 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. 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. Examples of inorganic solid electrolytes include nitrides, halides and sulfides of lithium salts such as U5NI2, Li3N, Lil, LiSiO4, Li2SiS3, Li4SiO4, LiOH and Li3PO4. The lithium salt is suitably soluble in the chosen solvent or mixture of solvents. Examples of suitable lithium salts include LiCI, LiBr, Lil, LiCIO4, LiBF4, LiBC4Os, LiPF6, UCF3SO3, LiAsF6, LiSbF6, LiAICI4, CH3SO3U and CF3SO3Li. 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. It will be understood that the description herein of the particulate porous frameworks, silicon precursors, composite particles, electrodes, batteries etc. applies equally to these items provided as products per se or when used as part of a process. The invention sill now be illustrated by means of the following examples. It will be understood that the examples are for illustrative purposes only and do not limit the invention defined hereinabove. Examples Infiltration and pore modification of particulate porous frameworks In the following examples, the initial particulate porous framework (or “scaffold”) was an activated carbon. The infiltration and pore modification reaction for the carbon scaffolds were carried out as follows. 5g of carbon scaffold is mixed with ~30 mL of 5 mol / L LiOH at room temperature. The mixture is stirred for 1-2 hr and then put into a furnace, under a nitrogen atmosphere at a flow rate of 1L / min, with a prior purge for 30 mins. The furnace conditions were as follows: a flow rate of N2 of 1L / min, temperature ramp rate of 2°C / min to 110 °C, hold for 1 hr to remove moisture, before ramping at 5°C / min to 900 °C, followed by a high-temperature hold at that temperature for a dwell time of 6 hr. As a safety precaution, after the porosity modification reaction, the material is passivated with differing ratios of nitrogen to air before removal from the furnace, 72:25, 50:50, 25:75, and finally 100% air (total flow 1L / min) for 30 mins. Figure 1a shows the cumulative pore volume plotted against pore width, as obtained by N2 adsorption. Figure 1b shows the differential pore volume dV / dW plotted against pore width, as obtained by N2 adsorption. These plots show a bimodal distribution, with the peak at lower pore width falling within the microporous regime, and the peak at higher pore width falling within the mesoporous regime. Each of Figures 1a and 1b plots data for: the initial carbon scaffold (labelled “baseline”); - the modified carbon scaffold from the high-temperature heat treatment performed in a furnace at 900 °C (labelled “900”); - the washed carbon scaffold where the solvent used was IPA and the washing duration was 30 minutes (labelled “900-IPA”); and the washed carbon scaffold where the solvent used was water (labelled “900-water”). The modified carbon shows the lowest cumulative pore volume, showing that the original porosity has been blocked by the reaction products derived from the LiOH porosity modifier, such as Li, U2O and U2CO3. The IPA-washed carbon shows a higher cumulative pore volume than the modified carbon scaffold, and a lower cumulative pore volume than the initial carbon scaffold. The increase is due to the partial removal of soluble reaction products from the carbon scaffolds. The cumulative pore volume for the water washed carbon scaffold is greater than the modified carbon scaffold, and also greater than of the initial carbon scaffold, demonstrating that pore modification has taken place. Water-washing appears to completely remove the reaction products (which is corroborated by TGA analysis as discussed hereinbelow). Thus, it can be inferred that both the total pore volume and the pore size distribution have been modified relative to the initial carbon scaffold. This conclusion is confirmed by Figure 1b, which provides further detail on the nature of the pore modification. Figure 1b shows that relative to the initial carbon scaffold, the water-washed scaffold shows a reduction in the volume and / or number of larger micropores, accompanied by an increase in the volume and / or number of mesopores. The volume and / or number of smaller micropores appears to remain relatively unchanged, suggesting that the LiOH solution cannot access these 43 smaller micropores, and hence that one result of the pore-modification reaction is the blocking of these pores. This is accompanied by a relative increase in the proportion of pore volume contributed by mesopores as noted above. Thus, Figures 1a and 1b demonstrate both the tailoring of the pore structure brought about by the process of the invention, and the blocking of microporosity by reaction products of the process. Table 1 provides the total pore volume (TPV), micropore volume (MPV), MPV / TPV ratio, and the BET surface area, for the carbon scaffold described above at different stages of the process. Pore volumes were obtained by N2 adsorption. TPV in Table 1 is indicative of the parameter P1 described herein. MPV / TPV in Table 2 is indicative of the parameter VP2 described herein. Table 1 Process stage TPV cm3 / g MPV cm3 / g MPV / TPV % BET SA m2 / g Initial 0.76 0.56 74 1673 Modified 0.45 0.25 56 831 IPA-washed 0.59 0.34 58 1115 DI H2O-washed 0.90 0.51 57 1687 TGA analysis of modified particulate porous frameworks Figure 2 shows TGA plots for modified carbon scaffolds (referred to as “900”) and modified carbon scaffolds subsequently washed by water (referred to as “900-water”) or by I PA (referred to as 900-IPA”). It is evident that water-washing completely removes any reaction products. This confirms the conclusion noted above that there is an increase in total pore volume as a result of the pore modification reaction. The IPA-washed scaffold demonstrates clear transitions which can be attributed to the oxidation of carbon, and to the decomposition of lithium carbonate, as highlighted in Figure 2. The plot for the modified carbon scaffold (“900”) shows an initial oxidation peak occurring at about 600°C. The inventors postulate that this may be attributed to the oxidation of metallic lithium. A secondary mass loss is observed at temperatures higher than the lithium carbonate decomposition, which the inventors postulate could be attributed to lithium hydroxide decomposition. The mass drop at 1300°C can be attributed to the boiling point of lithium. Washing of modified particulate porous frameworks The objective of this experiment was to develop a washing method to target a given total pore volume without completely removing all Li-containing reaction products from the modified carbon scaffold. As described above, washing with pure water leaches all Li-containing species from the modified scaffold. The modified carbon scaffold was prepared the conditions described for the examples hereinabove. The experiment used mixtures of water and I PA with varying water: I PA ratios. The water / IPA mixture was stirred together for 5 min. The modified carbon scaffold was added to the mixture and stirred for 15-20 min at room temperature. The washed carbon scaffold was then collected by filtration and additionally washed with IPA to remove any residual water. For the particular carbon scaffold utilised in this study, the inventors observed that the ratio of water to IPA by volume required to attain the target pore volume was about 5. It will be appreciated that different initial carbon scaffolds, different modified carbon scaffolds and different target pore characteristics may require different solvent ratios or different solvent mixtures, and that appropriate identification of a suitable solvent profile can readily be achieved using the protocols and analytical procedures described in the experimental work described hereinabove.

Claims

1. A process for manufacturing composite particles for use as an electroactive material for a metal-ion battery, comprising the steps of:(a) providing initial particulate porous frameworks comprising micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks is greater than a value P1 (initial) which is at least 0.35;(b) infiltrating the pores of the initial particulate porous frameworks with a porosity modifier comprising Li or Na, thereby providing infiltrated particulate porous frameworks;(c) providing sufficient energy to the infiltrated particulate porous frameworks to cause a reaction involving the porosity modifier and the initial particulate porous frameworks, thereby providing modified particulate porous frameworks comprising reaction products from the reaction within the pores, wherein P1 (modified) of the modified particulate porous frameworks is lower than P1 (initial);(d) washing the modified particulate porous frameworks to partially remove the reaction products from the pores, thereby providing washed particulate porous frameworks comprising residual reaction-products within the pores, wherein P1 (washed) of the washed particulate porous frameworks is higher than P1 (modified);(e) depositing electroactive material domains in the pores of the washed particulate porous frameworks, thereby providing composite particles;wherein P1 is the total volume of micropores and mesopores in the particulate porous frameworks expressed in cm3 / g as measured by nitrogen gas adsorption.

2. A process according to claim 1 wherein P1 (initial) is no more than 2.20.

3. A process according to claim 1 or 2 wherein P1 (modified) is in the range of at least 0.10 tono more than 2.00, and / or wherein P1 (modified) is in the range of from 30% to 90% of P1 (initial).

4. A process according to any preceding claim wherein P1 (washed) is in the range of 0.45 to 2.00, preferably in the range of 0.50 to 1.50, or in the range of 0.60 to 1.00.

5. A process according to any preceding claim wherein P1 (washed) of said washed particulate porous frameworks may be lower than or greater than P1 (initial) of said initial particulateporous frameworks, preferably wherein P1 (washed) is within ±20%, preferably within ±10%, of P1 (initial).

6. A process according to any preceding claim wherein said washed particulate porous frameworks exhibit micropores and mesopores, wherein the pore volume of said mesopores in said washed particulate porous frameworks is greater than the pore volume of mesopores in said modified particulate porous frameworks and is greater than the pore volume of mesopores in said initial particulate porous frameworks.

7. A process according to any preceding claim wherein said washed particulate porous frameworks exhibit micropores and mesopores, wherein the pore volume of said micropores in said washed particulate porous frameworks is greater than the pore volume of micropores in said modified particulate porous frameworks and is preferably no more than the pore volume of micropores in said initial particulate porous frameworks.

8. A process according to any preceding claim wherein said washed particulate porous frameworks exhibit micropores and mesopores, wherein the pore volume of said micropores is greater than the pore volume of said mesopores, preferably wherein VP2(washed) is greater than 30% and preferably in the range of 30% to 90%, more preferably 30% to 80%, more preferably 30-75%, more preferably 40-75%.

9. A process according to any preceding claim wherein said initial particulate porous frameworks have a BET surface area of 1000-3000 m2 / g, preferably 1400-3000 m2 / g.

10. A process according to any preceding claim wherein said washed particulate porous frameworks have a BET surface area of 800-3000 m2 / g, preferably 1200-3000 m2 / g.

11. A process according to any preceding claim wherein the BET surface area of said modified particulate porous frameworks is less than said initial particulate porous frameworks, and preferably wherein the BET surface area of said washed particulate porous frameworks is greater than the BET surface area of said modified particulate porous frameworks.

12. A process according to any preceding claim, wherein said initial particulate porous frameworks are particulate porous carbon frameworks.

13. A process according to any preceding claim, wherein the electroactive material is selected from silicon, tin, germanium, aluminium, and mixtures and alloys thereof; preferably wherein the electroactive material is silicon.

14. A process according to any preceding claim wherein said composite particles comprise 20-80 wt% of the electroactive material, or 30-70 wt% of the electroactive material, or 40-60 wt% of the electroactive material.

15. A process according to any preceding claim wherein the porosity modifier infiltrating the pores of the initial particulate porous frameworks in step (b) comprises M3PO4, MCI, MOH, MCIO4, M2SO4, MNO3, C2M2O4, M2O2, M2CO3, MOAc, MB(C2O4)2, or mixtures thereof, wherein M = Li or Na, and preferably wherein M = Li, and preferably wherein the porosity modifier comprises LiOH.

16. A process according to any preceding claim wherein the porosity modifier is a solution, preferably an aqueous solution, comprising an Li-containing or Na-containing species, preferably wherein the molar concentration of said Li-containing or Na-containing species is in the range of from 1.0 to 10.0 mol / L, preferably from 2.5 to 7.5, preferably about 5 mol / L.

17. A process according to any preceding claim wherein the initial particulate porous frameworks are stirred with the porosity modifier, preferably for a duration of at least 10 minutes, and / or preferably wherein the stirring is performed at room temperature.

18. A process according to any preceding claim wherein the energy provided in step (c) is thermal energy or microwave energy, and is preferably thermal energy.

19. A process according to any preceding claim wherein the provision of energy to the infiltrated particulate porous frameworks in step (c) is conducted by heating said frameworks.

20. A process according to claim 19 wherein said heating comprises heating at a high-temperature hold for a period of time t which comprises maintaining the infiltrated particulate porous frameworks at a temperature of at least 650°C, preferably at least 700 °C, preferably at least 800°C, preferably at least 850°C, preferably at least 900°C. and preferably no more than 1250°C, preferably no more than 1100°C, preferably no more than 1000°C, and preferably in the range of 850 to 950°C, and preferably at about 900°C.

21. A process according to claim 20 wherein said period of time t is greater than 10 minutes, preferably at least 1 hr, and is preferably from about 3 to about 10 hours, preferably from about 5 to about 7 hours, and is preferably about 6 hours.

22. A process according to any preceding claim wherein step (c) is performed in a substantially oxygen-free atmosphere, preferably in a helium, argon, or nitrogen atmosphere, most preferably in a nitrogen atmosphere.

23. A process according to any preceding claim, wherein said reaction products resulting from the reaction comprise Li metal or Na metal, oxides of Li or Na, hydroxides of Li or Na, carbonates of Li or Na, nitrides of Li or Na, or lithium-based mixtures or sodium-based mixtures thereof, preferably wherein the reaction products comprise lithium metal, lithium oxide and / or lithium carbonate, preferably wherein the reaction products comprise lithium metal and / or lithium carbonate.

24. A process according to any preceding claim wherein washing the modified particulate porous frameworks in step (d) comprises washing with a solvent, wherein the solvent comprises water, methanol, ethanol, isopropyl alcohol (IPA), acetone, dichloromethane, toluene, benzenes, xylenes, or mixtures thereof.

25. A process according to claim 24, wherein the solvent comprises water and IPA, preferably wherein the ratio of water to IPA by volume is 2-8, more preferably wherein the ratio of water to IPA by volume is about 4-6.

26. A process according to claim 25, wherein the washed particulate porous frameworks are collected by filtration from the solvent and further washed with IPA to remove residual water.

27. A process according to any preceding claim wherein the washing is performed at room temperature.

28. A process according to any preceding claim wherein the washing is performed for a duration of at least 5 minutes, preferably for a duration of 15-20 minutes.

29. A process according to any preceding claim wherein step (e) comprises contacting the particulate porous frameworks with an electroactive material precursor at a temperature effective to 49cause deposition of electroactive material domains in the pores of the washed particulate porous frameworks.

30. The process of claim 29, wherein the electroactive material precursor is gaseous.

31. The process of claim 30, wherein the electroactive material precursor is a silicon precursor;optionally wherein the silicon precursor is selected from silane (SiH4), disilane (Si2He), trisilane (SiaHs), tetrasilane (S14H10), methylsilane (CHaSiHs), dimethylsilane ((CH3)2SiH2), trimethylsilane ((CHshSiH), tetramethylsilane ((CH3)4Si), and chlorosilanes such as trichlorosilane (HSiCh) or dichlorosilane (H2SiCl2) or chlorosilane (H3S1CI), or methylchlorosilanes such as methyltrichlorosilane (CHsSiCh) or dimethyldichlorosilane ((CH3)2SiCl2); optionally wherein the silicon precursor is silane (SiH4).

32. The process of any preceding claim, wherein step (e) is performed at a pressure of at least 150 kPa, or at least 200 kPa, optionally no more than 5,000 kPa.

33. A material comprising composite particles as prepared by the process of any of claims 1-32.

34. An electrode comprising the composite particles prepared by the process of any of claims 1-32.

35. A rechargeable metal-ion battery comprising the electrode of claim 34.Application No: GB2400754.4Examiner: Dr Fiona RogersClaims searched: 1-32Date of search: 20 February 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance A - CN 116598452 A (HANGMEN HECHUANG NEW ENERGY MAT CO LTD) See whole document.Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From HO IM 0004 / 36 01 / 01 / 2006 C01B 0032 / 342 01 / 01 / 2017 C01B 0033 / 027 01 / 01 / 2006 C01B 0033 / 029 01 / 01 / 2006 C01B 0033 / 03 01 / 01 / 2006 C23C 0016 / 24 01 / 01 / 2006 HO IM 0004 / 133 01 / 01 / 2010 HO IM 0004 / 134 01 / 01 / 2010 HO IM 0004 / 1393 01 / 01 / 2010 HO IM 0004 / 1395 01 / 01 / 2010 HO IM 0004 / 38 01 / 01 / 2006 HO IM 0004 / 62 01 / 01 / 2006

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