Composite particles

Abstract

A process for manufacturing composite particles for use as electroactive materials in metal-ion batteries comprises preparing porous particulate frameworks with micropores and optional mesopores, sele

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 LhsSi^. 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 partially infiltrating the frameworks with a blocking agent or precursor thereof in order to block 2 some of the pores thereby rendering them inaccessible to an electroactive precursor gas, and then depositing electroactive material in the accessible pores of the particulate porous frameworks (i.e. pores which are accessible to said electroactive precursor gas). Thus, in a first aspect 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 containing micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks (referred to herein as P1 (initial)) is at least 0.35 g / cm3; (b) partially infiltrating said pores of the initial particulate porous frameworks with a solution comprising a blocking agent and a solvent; (c) removing the solvent to deposit the blocking agent in said pores of the initial particulate porous frameworks such that some of said pores are inaccessible to an electroactive material precursor gas and some of said pores are accessible to an electroactive material precursor gas, thereby providing partially infiltrated particulate porous frameworks comprising the blocking agent in said pores, wherein: (i) P1 of the partially infiltrated particulate porous frameworks (referred to herein as P1 (blocked)) is lower than P1 (initial) and is at least 0.10 g / cm3; and (ii) wherein said blocking agent is deposited such that the blocked volume Vb, expressed as a volumetric ratio to P1 (initial), is in the range of 5 to 60% wherein Vb is defined as: VB = fP1 (initial) - P1 (blocked) - Vol x 100 P1 (initial) wherein: Vo is the occupied volume Vo of said blocked pores which is occupied by the blocking agent, and is calculated as Mb / Pb, where Mb is the mass of the blocking agent in said partially infiltrated particulate porous frameworks and Pb is the density of the blocking agent; and [P1 (initial) - P1 (blocked) - Vo] represents the volume of blocked pores which is not occupied by the blocking agent but which is inaccessible to said electroactive material precursor gas and inaccessible to nitrogen gas in the measurement of P1 by nitrogen gas absorption; and (d) contacting the partially infiltrated particulate porous frameworks with an electroactive material precursor gas at a temperature effective to cause deposition of electroactive material domains in the accessible pores of the 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. 3 In a second aspect 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 containing micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks (referred to herein as P1 (initial)) is at least 0.35 g / cm3; (b) partially infiltrating said pores of the initial particulate porous frameworks with a solution comprising one or more blocking agent precursor(s) and a solvent; (c) reacting said blocking agent precursor(s) to form blocking agent by providing sufficient energy for said reaction and removing said solvent thereby depositing blocking agent in said pores of the initial particulate porous frameworks such that some of said pores are inaccessible to an electroactive material precursor gas and some of said pores are accessible to an electroactive material precursor gas, to provide partially infiltrated particulate porous frameworks comprising blocking agent in said pores, wherein: (i) P1 of the partially infiltrated particulate porous frameworks (referred to herein as P1 (blocked)) is lower than P1 (initial) and is at least 0.10 g / cm3; and (ii) wherein said blocking agent is deposited such that the blocked volume Vb, expressed as a volumetric ratio to P1 (initial), is in the range of 5 to 60% wherein Vb is defined as: VB = FP1 (initial) - P1 (blocked) - Vol x 100 P1 (initial) wherein: Vo is the occupied volume Vo of said blocked pores which is occupied by the blocking agent, and is calculated as Mb / Pb, where Mb is the mass of the blocking agent in said partially infiltrated particulate porous frameworks and Pb is the density of the blocking agent; and [P1 (initial) - P1 (blocked) - Vo] represents the volume of blocked pores which is not occupied by the blocking agent but which is inaccessible to said electroactive material precursor gas and inaccessible to nitrogen gas in the measurement of P1 by nitrogen gas absorption; and (d) contacting the partially infiltrated particulate porous frameworks with an electroactive material precursor gas at a temperature effective to cause deposition of electroactive material domains in the accessible pores of the 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. In the first and second aspects of the invention, micropores and / or mesopores (where present) of the initial particulate porous framework are infiltrated in step (b). In step (c), blocking agent is deposited within this micro-porous and / or meso-porous structure (where present) such that at least some of the initial total volume of the micro / meso-porous structure becomes inaccessible to an electroactive material precursor gas. Blocking may occur predominantly in micropores relative to mesopores, or it may occur predominantly in mesopores relative to micropores, or blocking may occur in substantially similar amounts in micropores and mesopores. In a preferred embodiment, blocking occurs predominantly in micropores relative to mesopores (where present). Thus, it is preferred that blocking agent is deposited such that some of the micropores, and optionally some of the meso-pores (where present), becomes inaccessible to an electroactive material precursor gas. In the processes of the invention, the blocking agent locates within the porous frameworks, and during subsequent deposition of the electroactive material, the blocking agent prevents the electroactive material (or its precursor) from accessing some of the pores. 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. Such modifications provide greater mitigation for the expansion of the electroactive material during charging and discharging. It is the inventors’ understanding that such blocked pores, i.e. pores which contain no electroactive material (e.g. silicon), contribute to the mitigation of cycling-associated expansion, during which individual domains of the electroactive material undergo alloying / de-alloying with the metal ion of the rechargeable battery (i.e. during lithiation and delithiation in respect of LIBs, or during sodiation and desodiation in respect of SIBs). It is the inventors’ understanding that the particulate porous frameworks (particularly carbonaceous frameworks) deform into the void spaces of the blocked pores to accommodate this expansion, which complements the expansion of the electroactive material domains themselves into the void space immediately around said domains. 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, the deposition of blocking agents comprising lithium 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, the deposition of blocking agents comprising sodium 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 processes of the invention, electrodes comprising the composite particles, and rechargeable metal-ion batteries comprising the electrodes. 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 IIIPAC terminology, the term “micropore” is used herein to refer to pores of less than 2 nm in diameter, the term “mesopore” is used herein to refer to pores of 2-50 nm in diameter, and the term “macropore” is used to refer to pores of greater than 50 nm diameter. As used herein, 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 initial particulate porous frameworks without blocking agent within the pores (referred to herein as P1 (initial)) and is measured for partially infiltrated particulate porous frameworks comprising blocking agent within the pores (referred to herein as P1 (blocked)). It will 6 be appreciated that P1 for a framework comprising blocking agent will be lower than P1 for an otherwise identical framework without blocking agent, since the accessible volume is lower when blocking agent is present in the pores. The blocking of some of the pores 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, VP07, 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 parameter before infiltration of the blocking agent or precursor thereof, and “(blocked)” refers to the value for the parameter after the blocking agent has been deposited. The total volume of micropores and mesopores and the pore size distribution of micropores, mesopores and macropores, including the P1, P2, VP07, VP1, VP2, VP5, VP10, VP20, and PDn pore diameter parameters defined herein, are determined using nitrogen gas adsorption at 77 K. Micropores and mesopores are determined down to a relative pressure p / po of 10'7 using quenched solid density functional theory (QSDFT). The measurement is made in accordance with ISO 15901-2:2022. Macropore volume in the range of from greater than 50 nm to 100 nm (referred to herein as P2) are determined using nitrogen gas adsorption where relative pressure down to 10’ 4 P / Po is sufficient. References herein to P2 shall be understood as meaning pore volumes as measured by nitrogen gas adsorption at 77 K by the Barrett-Joyner-Halenda (BJH) method in accordance with standard methodology, preferably as set out in ISO 15901-2:2022. A subtraction of the value of pore volume as determined by BJH at 50 nm from the pore volume at 100 nm width gives the value denoted P2. Pore volume measured method above 100 nm is assumed for the purposes of the invention to be inter-particle porosity and is disregarded. 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). It will be appreciated that intrusion techniques such as gas adsorption are effective only to determine the pore volume of pores that are accessible to nitrogen from the exterior of the particulate porous frameworks. Porosity values specified herein shall be understood as referring to the volume of open pores, i.e. pores that are accessible to a fluid from the exterior of the particulate porous frameworks. Fully enclosed pores which cannot be identified by nitrogen adsorption shall not be taken into account herein when determining porosity values. Likewise, any pore volume located in pores that are so small as to be below the limit of detection by nitrogen adsorption is not taken into account. The pore structure of the particulate porous frameworks may include a monomodal, bimodal or multimodal pore size distribution. As used herein, the term “pore size distribution” relates to the distribution of pore size relative to the cumulative total internal pore volume of the particulate porous frameworks. A bimodal or multimodal pore size distribution is preferred since close proximity between micropores and pores of larger diameter provides the advantage of efficient ionic transport through the porous network to the electroactive material. 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 or no more than 1.50, or no more than 1.40 Preferably P1 (initial) of the particulate porous frameworks is in the range from 0.40 to 2.20, or from 0.40 to 1.80, or from 0.50 to 1.60, or most preferably from 0.60 to 1.50. Preferably, P1 (blocked) is no more than 97%, or no more than 95% of P1 (initial) and more preferably no more than 90% of P1 (initial). P1 (blocked) is preferably at least 30%, more preferably at least 50% of P1 (initial), and preferably is in the range of from 30% to 97%, preferably 50 to 95% of P1 (initial). P1 (blocked) of the partially infiltrated porous frameworks is preferably 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 0.65 or at least 0.70. P1 (blocked) of the partially infiltrated porous frameworks is preferably no more than 2.20, or 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 or no more than 1.00. Preferably, P1 (blocked) is in the range of 0.10 to 2.00, preferably 0.50 to 2.00 cm3 / g, preferably 0.60 to 1.60 cm3 / g, or in the range of 0.65 to 1.10 cm3 / g, or 0.65-1.00 cm3 / g. The value P1 (blocked) of the partially infiltrated porous frameworks is typically lower than P1 (initial) by at least 0.05 cm3 / g, preferably by at least 0.1 cm3 / g, preferably by at least 0.20 cm3 / g, preferably by at least 0.30 cm3 / g, preferably by at least 0.40 cm3 / g. In the process of the present invention, the pore volume of the pores in the partially infiltrated particulate porous frameworks is less than the pore volume of pores in the initial particulate porous frameworks. Preferably, the pore volume of the pores in the partially infiltrated porous frameworks is no more than 90%, no more than 80%, and preferably in the range of 30% to 90%, more preferably 50-80%, more preferably 50-75% of the pore volume of pores in the initial particulate porous framework. Typically, the pore volume of the pores in the partially infiltrated porous frameworks is lower than the pore volume of pores in the initial particulate porous framework by an amount in the range of from about 0.05 to about 0.3 cm3 / g, preferably from about 0.1 to about 0.25 cm3 / g. The partially infiltrated particulate porous frameworks preferably exhibit both micropores and mesopores. In the process of the present invention, the pore volume of the micropores in the partially infiltrated particulate porous frameworks is preferably less than the pore volume of micropores in the initial particulate porous frameworks. Preferably, the pore volume of the micropores in the partially infiltrated porous frameworks is no more than 90%, no more than 80%, and preferably in the range of 30% to 90%, more preferably 50-80%, more preferably 50-75% of the pore volume of micropores in the initial particulate porous framework. Typically, the pore volume of the micropores in the partially infiltrated porous frameworks is lower than the pore volume of micropores in the initial particulate porous framework by an amount in the range of from about 0.05 to about 0.30 cm3 / g, preferably from about 0.10 to about 0.25 cm3 / g. Preferably the micropore volume in the partially infiltrated particulate porous framework is from about 0.10 to about 1.00 cm3 / g, preferably from about 0.20 to about 0.70 cm3 / g, preferably from about 0.30 to about 0.55 cm3 / g. Preferably, in the process of the present invention, the pore volume of the mesopores in the partially infiltrated particulate porous frameworks is less than the pore volume of mesopores in the initial particulate porous frameworks. Typically, the pore volume of the mesopores in the partially infiltrated porous frameworks is lower than the pore volume of mesopores in the initial particulate porous framework by an amount in the range of from about zero to about 0.25 cm3 / g, preferably from about 0.02 to about 0.20 cm3 / g. Preferably the mesopore volume in the partially infiltrated particulate porous framework is from about 0.05 to about 1.00 cm3 / g, preferably from about 0.10 to about 0.80 cm3 / g, preferably from about 0.10 to about 0.50 cm3 / g. Preferably, in the partially infiltrated particulate porous frameworks of the present invention, the micropore volume is greater than the mesopore volume. However, in one embodiment of the present invention, the mesopore volume may be greater than the micropore volume. As used herein, VP07, VP1, VP2, VP5, VP10 and VP20 are the volume of pores in the particulate porous frameworks with a pore diameter of less than 0.7 nm, 1.0 nm, less than 2.0 nm, less than 5.0 nm, less than 10 nm, and less than 20 nm respectively, expressed as a percentage of P1. VP07, VP1, VP2, VP5, VP10 and VP20 are measured as described herein. Thus, as used herein, VPx(initial) is the value VPx of the initial particulate porous framework where x is 07, 1, 2, 5, 10 or 20. Similarly, VPx(blocked) is VPx of the partially infiltrated porous framework where x is 07, 1,2, 5, 10 or 20. It will be appreciated that VP2 is the micropore volume expressed as a percentage of P1. 10 Preferably, VP2(blocked) is at least 20%. In a preferred embodiment, VP2(blocked) 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(blocked) may be at least 60%, or at least 70%, or at least 80%. Alternatively, VP2(blocked) 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(blocked) is suitably less than 90%. Preferably, VP2(blocked) is in the range of 30-90%, 30-80%, 30-75% or 40-75%, or 50-75%. Preferably, VP2(initial) is in the range of 30-90%, 30-80%, 30-75% or 40-75%, or 50-75%. Preferably VP07(blocked) is at least 5%. In a preferred embodiment, VP07(blocked) is at least 7%, or at least 8%. Preferably VP07(blocked) is in the range of 5.5-35%, or 7-30%. Preferably, VP2(blocked) is at least 2.5xVP07(blocked), or at least 3xVP07(blocked), or at least 4xVP07(blocked). Preferably VP5(blocked) is at least 55%, or at least 60%, or at least 70%, or at least 80%, or at least 85%, or at least 90%. 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(blocked) is preferably at least 80%, or at least 90%, or at least 95%, or at least 97%. VPIO(blocked) may be at least 70%, or at least 80%, or at least 90%, or at least 95%. 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., It is preferable to control V20-VP5 for the infiltration methods of the present invention and keep the value of this parameter relatively small. VP20(blocked)-VP5(blocked) is preferably less than 30%, or preferably less than 25%, or preferably less than 11 20%, less than 15%, preferably less than 12%. More preferably VP20(blocked)-VP5(blocked) is less than 10%, or less than 9%. Optionally, VP20(blocked)-VP5(blocked) is at least 2%. VP20(blocked)-VP5(blocked) may be 2-30%, 3-20%, or 3-15%, or 3-12%, or 3-9%. It has been found that particulate porous frameworks having values of VP20(blocked)-VP5(blocked) within these ranges provide a further improvement in average surface silicon. The VP20-VP5 parameter in the partially infiltrated particulate porous frameworks may be higher or lower than the initial VP20-VP5 parameter in the initial particulate porous frameworks. If VP20-VP5 is initially relatively large, then the partial infiltration process of the present invention preferably reduces the value of this parameter, and so in one embodiment VP20(blocked)-VP5(blocked) is less than VP20(initial)-VP5(initial). However, if the value of the parameter is initially low then in the partial infiltration process of the invention the value may or may not decrease but will remain low in the partially infiltrated frameworks, and so in an alternative embodiment VP20(blocked)-VP5(blocked) may be no more than VP20(initial)-VP5(initial). 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 term PDn(blocked) is the value PDn of the partially infiltrated particulate porous framework. The partially infiltrated particulate porous frameworks preferably have a PDgo(blocked) pore diameter of no more than 20 nm, preferably no more than 15 nm or no more than 10 nm, and is preferably in the range of 2-20 nm, 2-15 nm, 2-10 nm or 2.5-8 nm. The partially infiltrated particulate porous frameworks preferably have a PDso(blocked) pore diameter of no more than 6 nm, no more than 5 nm, no more than 4 nm, no more than 3 nm, no more than 2 nm or no more than 1.5 nm. Preferably PDso(blocked) is at least 0.5 nm, at least 0.75 nm or at least 0.9 nm. Thus, PDso(blocked) may be 0.5-5 nm, or 0.5-3 nm, or 0.5-2 nm, or 0.75-2 nm, or 0.9-2 nm. In the case that the particulate porous frameworks comprise macropores, 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). The P2 value of the initial particulate porous frameworks (i.e. P2(initial)) is preferably no more than 0.3 cm3 / g, preferably no more than 0.2 cm3 / g, preferably no more than 0.1 cm3 / g, preferably no more than 0.05 cm3 / g. While a small fraction of macropores may be useful to facilitate electrolyte access into the pore network, the 12 advantages of the invention are obtained substantially by accommodating electroactive material in micropores and / or mesopores, particularly micropores and / or smaller mesopores. Thus, P2 of the blocked particulate porous frameworks (i.e. P2(blocked)) preferably has a value of <0.2xP1 (blocked), or <0.1*P1 (blocked), or <0.05xP1 (blocked), or <0.02xP1 (blocked), or <0.01 xpi(blocked), or <0.005xP1 (blocked). P2(blocked) 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. The skeletal density of the initial particulate porous frameworks (SD(initial)) is preferably at least 1.3 g / cm3, preferably 1.5 to 4.0 g / cm3, preferably 1.5 to 3.0 g / cm3, preferably 1.5 to 2.5 g / cm3. Skeletal density is measured by helium pycnometry. The measurement method is conducted in accordance with ISO-12154-2014 at ambient temperature, preferably wherein the pycnometer has configuration 1 specified in the ISO test, preferably wherein the pycnometer is an ACCUPYC II 1340, preferably wherein the initial sample mass is about 1.0 g. The skeletal density for the particulate porous material is calculated on the basis of a volume measurement which is the sum of the solid particle volume and the void volume of pores which is inaccessible to helium gas. It will therefore be appreciated that the volume measured by helium pycnometry excludes open pore volume and inter-particle volume, which are accessible to helium gas. The skeletal density of the partially infiltrated particulate porous frameworks (SD(blocked)) may be higher or lower than the skeletal density of the initial particulate porous frameworks (SD(initial)), depending on the relative densities of the porous particulate frameworks and the blocking agent, on the amount of infiltrated blocking agent, and on the size of the void volume in blocked pores (which may in turn depend, inter alia, on the pore profile of the framework and the process conditions used to infiltrate it with blocking agent). Thus, SD(blocked) may be higher than SD(initial) for some or all loadings of blocking agents which have a significantly higher density than the porous particulate frameworks. For instance, for carbonaceous frameworks (and taking the density of carbon to be 2.20 g / cm3), the skeletal density of the framework when partially infiltrated by lithium oxide (density of 2.01 g / cm3) will be less than that of the framework when partially infiltrated by lithium niobate (density of 4.65 g / cm3), for the same loading and distribution of blocking agent. Thus, SD(blocked) / SD(initial) may be 0.80-1.25, preferably 0.80-1.10, and is preferably 0.80-0.99. In general, the composite particles have a Dso particle diameter of no more than 30 pm. Optionally, the Dso 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, 13 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 Dw 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 Dw 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 (D9o-Dw) / Dso) is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, efficient packing of the particles into dense powder beds is more readily achievable. The particle size distribution span (D98-Di) / Dso is preferably less 14 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 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 ■ 7T ■ Am (Cm)2 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: 1V f4 ■ 7r ■ Ami 71 4—I (Cm) 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 partially infiltrated 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 partially infiltrated 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 partially infiltrated particulate porous frameworks have a BET surface area of from 750 to 2,500 m2 / g, more preferably from 1,000 to 2,500 m2 / g. The BET surface area of the partially infiltrated particulate porous frameworks is typically no less than 60%, and typically no more than 95%, 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 skeletal density of at least 0.35 and preferably less than 3.0 g / cm3, more preferably less than 2.5 g / cm3. Preferably, the composite particles have a skeletal density of at least 0.40 g / cm3, or at least 0.50 g / cm3, or at least 0.60 g / cm3, or at least 0.70 g / cm3, or at least 1.00 g / cm3, or at least 1.50 g / cm3. For composite particles having a carbonaceous framework, the skeletal density is preferably less than 2.3 g / cm3, more preferably less than 2.2 g / cm3, more preferably less than 2.1 g / cm3, more preferably less than 2.0 g / cm3, more preferably less than 2.0 g / cm3, more preferably less than 1.90 g / cm3, optionally less than 1.80 g / cm3, or less than 1.75 g / cm3. As used herein, the term “skeletal density” is the density by helium pycnometry, 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 blocked pores (i.e. pores that are too small to be measured by helium pycnometry). Skeletal density is measured in accordance with ISO-12154-2014 as described hereinabove. 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 18 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 templated 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 CO2at a temperature between 600 °C and 1200 °C. This allows a chemical reaction between the carbon and the flowing gas to take place at the internal surface of the carbon, removing carbon from the pore walls and thereby increasing the pore volume. This gaseous activation process, also known as a physical activation process, allows the pore size to be readily altered producing activated carbons with the desired porosity. Preferably, the pyrolyzed material is activated with steam. 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, ZnCh, 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 partial infiltration of the blocking agent or precursor thereof according to steps (b) and (c) 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 the present invention blocking agent is retained in the porous framework, 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 CO2at 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) according to the first and second aspects of the present invention described herein. 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). 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. The process of the present invention in either the first or second aspects, preferably comprises an additional step prior to step (b), in which a vacuum is applied to the initial particulate porous frameworks to remove any internal gases. The vacuum is typically applied at a temperature above room temperature (typically above 100 °C, and typically at a temperature in the range of about 100 °C to about 160 °C, typically about 150°C), for a period of time of 30 minutes to 24 hours, typically at least 1 hour, preferably 6 to 24 hours, preferably 18-24 hours. In steps (b) and (c) of each of the first and second aspects of the invention, the blocking agent is deposited in the mouth of pores to generate: a volume (Vo) which is occupied by the blocking agent; and (ii) a blocked void volume within the blocked pores which is not occupied by the blocking agent but which is inaccessible to the electroactive material precursor gas and inaccessible to nitrogen gas in the measurement of P1 by nitrogen gas absorption. The occupied volume (Vo) of said blocked pores is calculated as Mb / Pb, wherein: Mb is the mass of the blocking agent in said partially infiltrated particulate porous frameworks and this is measured by thermogravimetric analysis (TGA). Preferably the TGA measurement is made using the following temperature program: initial isotherm segment step at 25 °C for 10 minutes; dynamic segment step of 25°C to 1400°C @ 10°C / min ramp rate; cooling dynamic segment step of 1400°C to 25°C @ 30°C / min cooling ramp rate. Preferably compressed air is supplied at a flow of 100 mL / min. Preferably the TGA measurement is conducted using a Mettler-Toledo Thermal Analysis System TGA / DSC 3+ instrument. The ash content (%) may be calculated as m(f) / m(i) x 100, where m(f) is the final mass of the sample (this residual mass is the mass of the blocking agent in the frameworks) and m(i) is the initial mass of the sample. Pb is the density of the blocking agent, which is preferably in the range of from greater than 1.0 to 8.0 g / cm3, preferably from 1.5 to 8.0 g / cm3, preferably from 1.5 to 5.0 g / cm3, preferably from 1.5 to 3.0 g / cm3, preferably from 1.5 to 2.6 g / cm3, and values can be found in standard reference texts or from the commercial supplier of the blocking agent and so typically does not need to be re-measured. A table of density values for suitable materials is provided in the examples section hereinbelow. Preferably, density is measured by helium pycnometry in accordance with ISO-12154-2014 as described hereinabove. The mass (Mb) of the blocking agent in said partially infiltrated particulate porous frameworks is preferably in the range of from about 5 to about 50 wt%, preferably about 5 to about 35 wt%, preferably about 5 to about 25 wt%, preferably about 5 to about 15 wt%, by total weight of the partially infiltrated particulate porous frameworks. The blocked void volume is represented by [P1 (initial) - P1 (blocked) - Vo]). In the present invention, the blocked void volume is expressed as a volumetric ratio to P1 (initial), which is referred to herein as the “blocked volume” (Vb) and expressed as a percentage. Preferably, Vb is at least 5%. Preferably Vb is no more than 60%, preferably no more than 50%, preferably no more than 40%, preferably no more than 30%, preferably no more than 25%. Preferably Vb is in the range of 5 to 60%, preferably 5-50%, preferably 5-40%, preferably 5-30%, preferably 5-25%. In the process according to the invention, the blocking agent is preferably selected from the following non-limiting species: metal or non-metal oxides (including mixed oxides), nitrides, carbides, oxynitrides and oxycarbides; metals; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids. Preferably said blocking agent is selected from metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids. In a preferred embodiment, the blocking agent is not a metal or metallic alloy (i.e. a metallic element which is in the form of elemental metal or has a zero oxidation state). Preferably the blocking agent comprises lithium or sodium, preferably lithium. The blocking agent preferably comprises lithium in the case of LIBs. The blocking agent preferably comprises sodium in the case of SIBs. Preferably the blocking agent is selected from a metal-containing compound, and preferably wherein the metal is lithium or sodium, preferably lithium. The blocking agent preferably comprises lithium in the case of LIBs. The blocking agent preferably comprises sodium in the case of SIBs. Suitable metal oxides include lithium oxide, aluminium oxide, tin oxide and transition metal oxides, particularly nickel oxide, zinc oxide, copper oxide, molybdenum oxide, cobalt oxide, manganese oxide, niobium oxide, iron oxide, titanium oxide and tungsten oxide. 24 Suitable non-metal oxides include silicon dioxide. Said mixed oxides may be mixed metal oxides or mixed metal / non-metal oxides. Suitable mixed metal oxides include titanates, tungstates, zirconates, nickelates and niobates, particularly lithium titanate, lithium tungstate, lithium zirconate, lanthanum nickelate, lithium lanthanum zirconate (LLZO) and lithium lanthanum titanate (LLTO). In a preferred embodiment, the mixed metal oxide is a lithium-containing mixed metal oxide, particularly lithium-containing titanates, tungstates, zirconates, nickelates and niobates, particularly lithium titanate, lithium tungstate, lithium zirconate, lithium lanthanum zirconate (LLZO) and lithium lanthanum titanate (LLTO). Lithium tungstate and niobate are preferred embodiments. Such lithium-containing compounds are particularly preferred for LIBs. The sodium-containing analogues of the compounds mentioned in this paragraph are preferred for SIBs. Suitable mixed metal / non-metal oxides include borates, phosphates and carbonates, particularly wherein said oxide comprises lithium. Suitable compounds include lithium borate, lithium phosphate and lithium carbonate, and mixed metal / non-metal oxides in which lithium is present with another metal, such as lithium aluminium phosphate. Lithium borate is a preferred embodiment. Such lithium-containing compounds are particularly preferred for LIBs. The sodium-containing analogues of the compounds mentioned in this paragraph are preferred for SIBs. Suitable nitrides are preferably selected from boron nitride, carbon nitride (particularly graphitic carbon nitride) and transition metal nitrides, particularly titanium nitride, vanadium nitride, chromium nitride and nickel nitride. Suitable nitrides include mixed nitrides such as titanium silicon nitride. Suitable carbides include titanium carbide, silicon carbide and niobium carbide. Mixed carbides may also be used. Suitable oxycarbides include silicon oxycarbide. Suitable oxynitrides include titanium oxynitride. Suitable metals include tin and copper. Suitable sulphides include lithium sulphide. Suitable ionic liquids include imidazolium-based and alkylammonium-based ionic liquids. Suitable metal organic frameworks (MOFs) include transition metal formates, zeolitic imidazolate frameworks and metal trimesates. These compounds are typically synthesised via solvothermal methods. Suitable covalent organic frameworks (COFs) include phenazine functionalised frameworks such as DAPH-TFP-COF and frameworks containing tertiary amines such as TPPDA-PI-COF. Other preferred functionalities include quinoxalines, imines, triazines, quinones, tetraone, sulphides and polysulphides; particularly preferred embodiments include functionalities such as truxenone and EDOT, due to the low reduction potential versus Li / Li+. In a preferred embodiment, said blocking agent is selected from lithium borate, lithium niobate, lithium tungstate. Such lithium-containing compounds are particularly preferred for LIBs. The sodium-containing analogues of the compounds mentioned in this paragraph are preferred for SIBs. In a preferred embodiment of the second aspect of the invention, said blocking agent is (i) lithium borate or (ii) lithium niobate, preferably wherein said blocking agent precursors are selected from (i) lithium hydroxide and boric acid, and (ii) lithium chloride and niobium ethoxide, respectively. Such lithium-containing compounds are particularly preferred for LIBs. The sodium-containing analogues of the compounds mentioned in this paragraph are preferred for SIBs. In the second aspect of the invention, step (b) comprises the provision of one or more precursor(s) of the blocking agents described hereinabove. Preferably at least two blocking agent precursors are provided in solution in step (b). The nature and identity of the blocking agent precursor(s) are determined by the nature and identity of the blocking agents described hereinabove. The formation of the blocking agent from said precursor(s) may be achieved via any conventional reaction pathway or mechanism known in the art. Reactions to form the blocking agent from the blocking agent precursor may involve, for instance, pyrolysis / pyrolytic decomposition, calcination, condensation or crystallisation. In a preferred embodiment, two or more precursors react together within the particulate porous frameworks to form said blocking agent. For instance, lithium hydroxide reacts with boric acid to form a lithium borate blocking agent, or lithium chloride reacts with niobium ethoxide to form lithium niobate blocking agent. Such lithium-containing compounds are particularly preferred for LIBs. The sodium-containing analogues of the compounds mentioned in this paragraph are preferred for SIBs. In an alternative embodiment, a single blocking agent precursor is provided in step (b), which reacts with the gas present in the atmosphere under which the step is performed, or with the scaffold (particularly where the scaffold is a carbonaceous scaffold, for instance to generate a carbide). In a further alternative embodiment, a solution comprising a single blocking agent precursor is partially infiltrated into the porous frameworks in step (b). The precursor decomposes in step (c) to form the blocking agent, optionally with removal of by-product(s) if necessary. For instance, a soluble precursor may be converted by a calcination process into an insoluble oxide. In the second aspect of the process, two or more of the afore-mentioned reaction pathways may occur, simultaneously or sequentially, during the performance of step (c) to form blocking agent. In the first and second aspects of the invention defined hereinabove, the blocking agent or precursor(s) thereof is / are provided in step (b) the form of a solution. The solvent may be selected from any solvent suitable for dissolving the blocking agent or the blocking agent precursor(s). For instance, the solvent may be selected from water, 2-methoxyethanol, methanol, ethanol, isopropyl alcohol (IPA), acetone, tetrahydrofuran (THF), dimethylsulfoxide (DMSO), dimethylformamide (DMF), dichloromethane, triethylene glycol (TEG), polyethylene glycols (PEGs) (typically PEGs having a number average molecular weight of no more than about 1000, for instance PEG400), glycerin, toluene, benzene, xylenes, and combinations thereof. Typically, the solvent comprises at least one polar solvent, and may be a polar solvent in a mixture with a second solvent, such as the solvents listed hereinabove, wherein the second solvent may be a polar or non-polar solvent. Typically, non-polar or aprotic hydrocarbon solvents (such as the ones listed hereinabove) are normally used in combination with polar solvents (such as the ones listed hereinabove). It will be appreciated that the choice of solvent or solvent combination is determined primarily by the nature of the blocking agent or blocking agent precursor(s), in order to maximise solubility thereof. The solution provided in step (b) is preferably an aqueous solution. As is known in the art, pH adjustment can be used to improve solubility. In a preferred embodiment, the solvent in step (b) of the first and second aspects of the invention provides useful surface wetting effects. Infiltration by the solution provided in step (b) is facilitated when the solvent is able to wet the surface of the porous particulate framework. Once the surface has been wetted then capillary effects (i.e. the balance of surface tension and viscosity operating within pores) may play a role in the location of blocking agent deposition. In particular, the surface wetting effects derived from the solution containing said blocking agent or blocking agent precursors mean that the narrower the mouth of the pore, the less likely it is that the solution will enter the pore in step (b), which is particularly relevant for micropores having a size of less than 0.7 nm. For pores having relatively narrower pore mouths, the pore mouth may become blocked when the blocking agent is deposited in subsequent step (c). For pores having relatively wider pore mouths (particularly the larger mesopores), surface wetting effects do not prevent entry of the solution into the pore, which instead becomes coated on the interior surfaces within the pore. During subsequent deposition of the electroactive material, the blocked pores prevent access of the electroactive material (or its precursor), and so no electroactive material domains are deposited in those blocked pores. As noted above, the inventors have observed that such pore-blocking provides greater mitigation for the expansion of the electroactive material during charging and discharging. Surface wetting effects are characterized herein via the contact angle of the solvent. Preferred solvents have a contact angle of no more than 140°, preferably no more than 120°, preferably no more than 90°. Contact angle is preferably measured as the dynamic contact angle using ISO-19403-6:2024, preferably using an optical tensiometer (for instance the Theta Flex instrument from Biolin Scientific). In the first and second aspects of the invention, step (b) preferably comprises stirring the initial particulate porous frameworks with the solution of blocking agent or blocking agent precursor(s) 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. The initial particulate porous frameworks may be stirred with said solution 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 said solution for a duration of from 10 minutes to 5 hr, or from 30 minutes to 2 hr, or from 1 hr to 2 hr. In the first and second aspects of the invention, in step (b) the initial particulate porous frameworks may be stirred with the solution of blocking agent or blocking agent precursor(s) at any suitable temperature. In particular, this step is suitably conducted at a temperature at which the blocking agent or blocking agent precursor(s) are soluble in the solvent. Room temperature may be used if the blocking agent or blocking agent precursor(s) are sufficiently soluble at that temperature. It will be appreciated that, in respect of the second aspect of the invention, step (b) is preferably conducted at a temperature high enough to dissolve said blocking agent precursor(s) but below the point at which reaction of the blocking agent precursor(s) occurs. In the first aspect of the invention, the removal of solvent and deposition of the blocking agent in step (c) may be conducted using any suitable process conventional in the art for solvent removal from a solution and deposition of the solute contained therein. Suitable processes include increasing temperature and / or reducing pressure, and typically the process comprises increasing temperature. Preferably, solvent removal is effected by heating. Said heating step is preferably conducted at a temperature above the boiling point of the solvent but below the temperature at which the particulate porous frameworks and / or blocking agent reacts with the atmosphere under which step (c) is conducted. In the first aspect of the invention, step (c) may be conducted under an oxygen-containing atmosphere (such as air), or under an inert or substantially oxygen-free atmosphere such as a noble gas atmosphere such as a helium or argon atmosphere, or in a nitrogen atmosphere, or mixtures thereof. An inert or substantially oxygen-free atmosphere is preferably defined herein as an atmosphere having an oxygen content of less than 0.01 vol%, more preferably less than 0.001 vol% based on the total volume of gas used. Preferably, step (c) of the first aspect of the invention is conducted under an oxygen-containing atmosphere, preferably air. The appropriate atmosphere is suitably determined by the temperature at which the solvent removal step is conducted, and thus depends on the identity of the solvent. The appropriate atmosphere for step (c) also depends on the identity of the particulate porous frameworks, such that the atmosphere is typically selected to avoid reaction between the atmosphere and the frameworks. The solvents used in the first aspect of the invention typically have a boiling point such that step (c) is conducted at temperatures well below those at which the atmosphere reacts with the particulate porous frameworks, and hence step (c) of the first aspect of the invention is typically conducted under an oxygen-containing atmosphere, preferably air. Thus, 29 for an oxygen-containing atmosphere and carbon-containing particulate porous frameworks, step (c) of the first aspect of the invention is preferably conducted below about 540°C (preferably below about 500°C, preferably below about 450°C, preferably below about 400°C) in order to avoid reaction between oxygen and the carbon-containing frameworks. However, where the removal of solvent requires higher temperatures, then an inert or substantially oxygen-free atmosphere is preferably used. Similarly, the appropriate atmosphere may also depend on the identity of the blocking agent, such that the atmosphere is preferably selected to avoid reaction between the atmosphere and the blocking agent at the temperature of the solvent removal step. Examples of the deposition of blocking agent by removal of the solvent according to step (c) of the first aspect of the invention include the deposition of lithium borate or lithium tungstate from aqueous solution. As the water is driven off (preferably by heating), the lithium borate or lithium tungstate recrystallizes, thereby blocking some of the pores. In the second aspect of the invention, the reaction of the blocking agent precursor(s) to form a blocking agent is effected by providing sufficient energy for the reaction to occur. The energy may be any suitable source of energy, and is preferably selected from thermal energy, microwave energy and infrared energy, and is preferably thermal energy. In the second aspect of the invention, the removal of the solvent may be effected before said reaction or after said reaction or contemporaneously with said reaction, or a combination thereof. The removal of the solvent may facilitate said reaction; for instance solvent removal may drive the reaction towards the desired blocking agent product. In a preferred embodiment solvent is removed contemporaneously with said reaction. For instance, in the reaction of lithium hydroxide with boric acid to make lithium borate and water, the removal of water facilitates the reaction and forces condensation of the desired lithium borate blocking agent. In the second aspect of the invention, the removal of solvent may be conducted as described hereinabove for step (c) of the first aspect of the invention. The removal of solvent may be effected at least partially by the provision of energy for the reaction of said blocking agent precursor(s) to form blocking agent, for instance where solvent removal and said reaction are effected at least partially contemporaneously. Preferably, the removal of solvent is conducted by heating. In the second aspect of the invention, the provision of energy to react the blocking agent precursor(s) in step (c) is preferably conducted by heating. Said heating step comprises 30 maintaining the reaction mixture at a temperature in the range of from about 100°C to about 600°C, preferably from about 200°C to about 500°C, preferably below about 450 °C, for a period of time tR. Said period of time tR is typically at least 10 minutes and typically no more than 5 hours, typically no more than 2 hours. In the second aspect of the invention, step (c) may be conducted under an oxygen-containing atmosphere (such as air), or under an inert or substantially oxygen-free atmosphere such as a noble gas atmosphere such as a helium or argon atmosphere, or in a nitrogen atmosphere, or mixtures thereof. The appropriate atmosphere is suitably determined by the identity of the blocking agent precursor(s) and the temperature at which the reaction is conducted. The appropriate atmosphere for step (c) also depends on the identity of the particulate porous frameworks, such that the atmosphere is preferably selected to avoid reaction between the atmosphere and the frameworks at the temperature used to react the blocking agent precursor(s). Thus, for carbon-containing particulate porous frameworks, step (c) of the second aspect of the invention may be conducted under an oxygen-containing atmosphere (preferably air) where the reaction temperature to form said blocking agent from said blocking agent precursor(s) is conducted below about 500°C (preferably below about 450°C, preferably below about 400°C). The reactions to form blocking agent from blocking agent precursor(s) in the second aspect of the invention are typically conducted at temperatures below those at which the atmosphere reacts with the particulate porous frameworks, and hence step (c) of the second aspect of the invention is typically conducted under an oxygen-containing atmosphere, preferably air. However, where the reaction requires higher temperatures, then an inert or substantially oxygen-free atmosphere is preferably used. In the second aspect of the invention, the atmosphere may also be selected in order to avoid reactions between the atmosphere and the blocking agent precursor(s) at the temperature of reaction of said precursor(s) to form the blocking agent. Alternatively, the atmosphere may be selected in order to promote reaction between the atmosphere and the blocking agent precursor(s). In the second aspect of the invention, step (c) requires the reaction of blocking agent precursor(s) to form the blocking agent in situ. The formation of blocking agent may be contemporaneous with the removal of solvent, as discussed hereinabove. The formation of blocking agent may also occur in solution and be deposited within the particulate porous frameworks upon solvent removal. Alternatively, the blocking agent, once formed, may start to precipitate out of solution under the conditions utilised for the reaction, depending on the relative solubility of the blocking agent and its 31 precursor(s), and become deposited within the frameworks as the reaction proceeds. In a further embodiment, the blocking agent partially precipitates from solution as the reaction proceeds, becoming deposited within the frameworks, with the remainder of the blocking agent becoming deposited within the frameworks upon solvent removal. In a further embodiment of the second aspect of the invention, the solvent is removed before the reaction in the solid state of said precursor(s) to form the blocking agent. It will be appreciated that a combination of the aforementioned mechanisms may operate for a given blocking agent, depending on the solvent and reaction conditions. In the first or second aspects of the invention (and particularly in the second aspect of the invention), the process preferably comprises an annealing step after step (c) and before step (d). The annealing step is conducted in order to promote crystallisation of the blocking agent which has been deposited in the particulate porous frameworks, and to promote an advantageous or desirable morphology. An annealing step is therefore suitably conducted under conditions which order the crystal structure of the blocking agent, and such conditions will vary depending on the identity of the blocking agent. An annealing step preferably comprises maintaining the partially 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, for a period of time U. Preferably said period of time U is greater than 15 minutes, and preferably no more than 5 hours, and is preferably from about 30 minutes to about 2 hours. An annealing step is preferably conducted in an inert or substantially oxygen-free atmosphere, as described above, in order to avoid reaction between the atmosphere and the particular porous frameworks. After annealing, said blocking agent should be retained in the composite particle in the chemical form in which it was deposited, namely as metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metals; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); or ionic liquids, and preferably as metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids. Thus, where the blocking agent comprises a metallic element, the metal-containing blocking agent should be present in the composite particle after the annealing step in a form which is not elemental metal or metallic alloy (or otherwise 32 wherein the metal is in a zero oxidation state). Nevertheless, it is conceivable that the annealing step may result in a small amount of chemical reaction within some regions of deposited blocking agent. However, the purpose of the annealing step is crystallisation of the blocking agent, as described above, i.e. the annealing step should be conducted under conditions which order the crystal structure of the blocking agent and which minimise or avoid conversion of the blocking agent to other chemical species, and such conditions will vary depending on the identity of the blocking agent. This is typically achieved by controlling the temperature to keep it under desired thresholds relevant to the chemical identity of the blocking agent, and also taking into account the chemical identity of the porous particulate frameworks, as well as by appropriate selection of the atmosphere under which the annealing step is performed. In particular, where the blocking agent is a metal-containing blocking agent (including oxides, nitrides, carbides, oxynitrides, oxycarbides, sulphides or MOFs), it is preferred that the annealing step is conducted under conditions which minimise or avoid reduction of the blocking agent into elemental metal (or metal in zero oxidation state). While it is conceivable that a small amount of chemical conversion of the blocking agent may occur during the annealing step (for instance reduction of a small portion of the blocking agent into elemental metal), it is preferred that the conditions of the annealing step are selected such that at least 90%, preferably at least 95%, preferably at least 97.5%, preferably at least 99% of the blocking agent is retained in the composite particle in the chemical form in which it was deposited, as described above. Optionally, after step (c) and prior to step (d), and where a substantially oxygen-free atmosphere has been used in step (c) or said optional annealing step, the process of the invention comprises an incremental exchange of the substantially oxygen-free atmosphere 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). In step (d) of the process according to the invention, electroactive material domains are deposited in the pores of the partially infiltrated 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 33 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 partially infiltrated 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 partially infiltrated 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 (d) 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 partially infiltrated particulate porous frameworks. The electroactive material precursor of step (d) is preferably gaseous. Gaseous precursors are conveniently used in CVI processes. Suitable silicon precursors include silane (SiH4), disilane (SiaHe), trisilane (SisHs), tetrasilane (Si4Hw), methylsilane (CHaSiHa), dimethylsilane ((CHa)2SiH2), trimethylsilane ((CHa)aSiH), tetramethylsilane ((CHa)4Si), or chlorosilanes such as trichlorosilane (HSiCh) or dichlorosilane (HaSiCh) or chlorosilane (HaSiCI), or methylchlorosilanes such as methyltrichlorosilane (CHaSiCla) or dimethyldichlorosilane ((CHa^SiCh). Preferably the silicon precursor is selected from silane (SiH4), disilane (SiaHe), trisilane (SiaHs), tetrasilane (Si4Hw). A particularly preferred silicon precursor is silane (SiH4). Suitable germanium precursors include germane (GeH4), hexamethyldigermanium ((CH3)aGeGe(CHa)3), tetramethylgermanium ((CH3)4Ge), tributylgermanium hydride ([CH3(CH2)3]3GeH), triethylgermanium hydride ((C2Hs)3GeH), and triphenylgermanium hydride ((CeHshGeH). A preferred germanium precursor is germane. Suitable tin precursors include bis[bis(trimethylsilyl)amino]tin(ll) ([[(CH3)3Si]2N]2Sn), tetraallyltin ((H2C=CHCH2)4Sn), tetrakis(diethylamido)tin(IV) ([(C2Hs)2N]4Sn), tetrakis(dimethylamido)tin(IV) ([(CH3)2N]4Sn), tetramethyltin (Sn(CH3)4), tetravinyltin (Sn(CH=CH2)4), tin(ll) acetylacetonate (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 (d) is preferably performed via chemical vapor infiltration (CVI) of a gaseous electroactive material precursor into the pore structure of the partially infiltrated 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 (d) comprises contacting the partially infiltrated 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 (d) should be avoided to prevent undesired oxidation of the deposited electroactive material, in accordance with conventional procedures for working in an 35 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 (d). The temperature in step (d) 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 (d) 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 (d) 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 (d) 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 (d) preferably further comprises the separation of by-products from the particles formed in step (d). 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 (d) 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 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 presence of the blocking agent prevents the gaseous electroactive material precursor from accessing some of the pores. Since the blocked pores 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. In the process of the present invention, after deposition of electroactive material in step (d), said blocking agent is preferably retained in the composite particle in the chemical form in which it was deposited, namely as metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metals; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); or ionic liquids, and preferably as preferably as metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids. Where the blocking agent comprises a metallic element, after deposition of electroactive material in step (d), the metal-containing blocking agent is preferably present in the composite particle in a form which is not elemental metal or metallic alloy (or otherwise in a zero oxidation state). Thus, where the blocking agent is a metal-containing blocking agent (e.g. oxides, nitrides, carbides, oxynitrides, oxycarbides, sulphides or MOFs), it is preferred that the deposition of electroactive material is conducted without reduction of the blocking agent into elemental metal. Where appropriate, avoiding such reduction may be achieved by controlling the temperature profile of step (d), and preferably step (d) is performed at a temperature of no more than 500°C, preferably no more than 450°C, preferably no more than 400°C, as described hereinabove. However, it will be appreciated by the skilled person that in respect of the classes of blocking agents described herein such a reduction reaction is typically energetically unfeasible (in terms of the Gibbs free energy change (AG) of the reaction at a given temperature). Thus, it will be appreciated, for instance, that the reduction of blocking agents such as lithium oxide or lithium carbonate into lithium metal during the deposition of electroactive material in step (d) is not feasible, particularly at the process conditions relevant for step (d), due to the highly negative △G(formation) of such blocking agents. 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 partially infiltrated particulate porous frameworks is occupied by the electroactive material following step (d). For example, the 37 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 partially infiltrated 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 partially infiltrated particulate porous frameworks by the requirement that the mass ratio of silicon to the partially infiltrated particulate porous frameworks is in the range from [0.5xP1 to 1.9xP1]: 1, wherein P1 here is Pl(blocked) and is as defined above (e.g. if the partially infiltrated 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 partially infiltrated 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 partially infiltrated 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 (blocked). 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 partially infiltrated particulate porous frameworks such that there is no or very little electroactive 38 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 partially infiltrated particulate porous frameworks. In view of the very high internal surface area of the partially infiltrated 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 partially infiltrated particulate porous frameworks. The nitrogen-accessible pore volume of the composite particles may be less than 0.05xP1 (blocked), wherein P1 (blocked) is the total volume of micropores and mesopores in the partially infiltrated particulate porous frameworks expressed in cm3 / g prior to deposition of electroactive material within the pores of the partially infiltrated 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 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) I Mf] x100% 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 SiO2 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 - M8oo) I Mf] x100% wherein Z is the percentage of unoxidized silicon at 800 °C, Msoo 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 SiO2. 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. In more detail, thermogravimetric analysis of the composite particles is preferably conducted in air using the following temperature program: initial isotherm segment step at 25°C for 10 minutes; dynamic segment step of 25°C to 1100°C @ 10°C / min ramp rate; cooling dynamic segment step of 1100°C to 25°C @ 30°C / min cooling ramp rate. Preferably compressed air is supplied at a flow of 100 mL / min. Preferably the TGA measurement is made using a Mettler-Toledo Thermal Analysis System TGA / DSC 3+ instrument. TGA may additionally be used to identify reaction products formed in the step (c) of the process, by conducting TGA analysis of the partially infiltrated particulate porous frameworks comprising blocking agent. 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 herein. The partially infiltrated 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 partially infiltrated particulate porous frameworks comprising blocking agents suitable for use as an electroactive material for a metal-ion battery, comprising the steps (a) to (c) as defined in the first or second aspects of the invention hereinabove. In this further aspect of the invention, it will be appreciated that steps (a) to (c) 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 partially infiltrated particulate porous frameworks resulting from the process comprising steps (a)-(c). In this aspect of the invention, said partially infiltrated 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 partially infiltrated 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 (d). 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 (d) 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 a metal species of the blocking agent present in the composite particles and which was introduced earlier in 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 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, a metal species of the blocking agent present in the composite particles 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 (d), 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 solid electrolyte interphase (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 45 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 46 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 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 Dso 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 D50 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 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 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 LiCoCb, LiCo0.99AI0.01O2, LiNiO2, LiMnO2, LiCo0.5Ni0.5O2, LiCo0.7Ni0.3O2, LiCo0.8Ni0.2O2, LiCo0.82Ni0.i8O2, LiCo0.8Ni0.15AI0.05O2, LiNi0.4Co0.3Mn0.3O2 and LiNi0.33Co0.33Mn0.34O2. The cathode current collector is generally of a thickness of between 3 to 500 pm. 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, 50 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, LisN, Lil, LiSiO4, Li2SiSs, Li4SiO4, LiOH and U3PO4. The lithium salt is suitably soluble in the chosen solvent or mixture of solvents. Examples of suitable lithium salts include LiCI, LiBr, Lil, UCIO4, UBF4, LiBC4Os, LiPFe, LiCFsSOs, LiAsFe, LiSbF6, LiAICk, CH3SO3Li and CF3SO3U. 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 In the following examples, the initial particulate porous framework is an activated carbon. Example 1 This example is a process according to the second aspect of the invention. Lithium borate (LB) precursor is generated in situ according to the following reaction: 2LiOH.H2O + 4B(OH)3 Li2B4O7 + 9H2O. The initial particulate porous frameworks (BET surface area of 2406 m2 / g) are pretreated by applying a vacuum at 150 °C for 18 hours in order to remove any internal gases therefrom. The mass of the initial particulate porous frameworks is 5.0 g. The total pore volume of the micropores and mesopores of the initial particulate porous frameworks (i.e. P1 (initial), measured as described herein) is 1.2 cm3 / g. Molar amounts of lithium hydroxide and boric acid as blocking agent precursors are added to a defined volume of water and heated at 90°C until dissolved, to form an aqueous solution. The volume of water is calculated from the P1 (initial) (i.e. if P1 (initial) is 1 cm3 / g then 1 cm3 of water would be used per 1 g of initial particulate porous frameworks). In this example, the volume of water used is 6 mL. The particulate porous frameworks are added to the solution and then stirred and heated under an air atmosphere at a rate of 5°C / min to a temperature of 400°C, with a dwell time at 400°C of 30 minutes. The air atmosphere ensures sufficient oxygen is present to provide stoichiometric Li2B4O7 blocking agent. The reaction to form the blocking agent proceeds as the temperature increases and as the water is removed, which forces polycondensation to form stoichiometric Li2B4O7 blocking agent in situ. The air atmosphere is replaced with a nitrogen atmosphere and the frameworks heated at a rate of 10°C / min to a temperature of 900°C, with a dwell time at 900°C of 1 hour, in order to further crystallise the lithium borate, thereby providing partially infiltrated particulate porous frameworks comprising Li2B4O7 blocking agent within the pores. In this example, partially infiltrated porous particulate frameworks were prepared at three different loadings of lithium borate (LB), to provide Examples 1A, 1B and 1C. X-ray diffraction analyses confirmed the presence of crystalline phase Li2B4O7 blocking agent within the porous particulate frameworks. The amount of lithium borate in the partially infiltrated particulate porous frameworks was determined using thermogravimetric analysis (TGA) in air of a sample (approx. 6mg). 52 Example 2 This example is a process according to the second aspect of the invention. Experiments similar to those of Example 1 were conducted, except that a different initial particulate porous framework was used. Table 1 below gives the pore characteristics, skeletal density and blocked volume Vb (defined and measured as described herein) of the initial and partially infiltrated porous carbon frameworks in these Examples. The BET surface area of the partially infiltrated porous particulate frameworks of Example 1B was 1816 m2 / g. Each of Examples 1 and 2 show that increasing the amount of lithium borate deposited in the pores of the frameworks generally increases the total void volume within blocked pores which is inaccessible to nitrogen gas in the measurement of total pore volume by N2 gas absorption. The void volume within these blocked pores remains un-filled following silicon deposition in subsequent processing. With regard to the skeletal density, this parameter measures the solid particle volume (i.e. the solid material consisting of the initial particulate porous frameworks and the deposited lithium borate) plus the void volume within the blocked pores which is inaccessible to the helium gas used in the pycnometry measurement. The skeletal density values measured in these examples do not follow clear trends because of competing effects: while generating void volumes within blocked pores which are inaccessible in the measurement method would be expected to reduce the skeletal density, the introduction of relatively dense lithium borate will increase the skeletal density. The characterising information which the skeletal density conveys becomes apparent when the skeletal density values are compared with the calculated values of “predicted density” which are presented in Table 1 for the partially infiltrated frameworks. The predicted density is calculated using the density of the blocking agent (as discussed hereinabove), the density of the initial frameworks (measured by He-pycnometry by the method discussed hereinabove) and the measured values of the masses thereof. If no pores were being enclosed, the values of skeletal density would increase in the same way as predicted density as increasing amounts of lithium borate are incorporated into the frameworks. However, in each of the examples of the invention, the values of skeletal density are lower than the values of predicted density, thereby demonstrating the presence of helium-inaccessible void volume within blocked pores. IP0087GB / P086974GB Table 1 Skeletal Density Predicted Density if no blocked volume Pl VP2 Micro Vol Meso Vol Blocked Volume VB wt% LB VP07 VP5 VP10 VP20 VP20-VP5 Example g / cm3 g / cm3 cm3 / g {% of Pl) cm3 / g cm3 / g (% of Pl) % {% of Pl) (% of Pl) {% of Pl) {% of Pl) {% of Pl) 1 (Initial) 2.31 2.31 1.20 54.7 0.65 0.54 0.00 0 7.7 90.6 95.8 97.8 7.2 1A 2.23 2.315 0.99 51.6 0.51 0.48 15.22 6 7.5 91.4 96.0 97.5 6.1 IB 2.19 2.318 0.91 50.4 0.46 0.45 20.91 9 8.4 91.2 96.7 98.7 7.5 IC 2.21 2.329 0.84 51.2 0.43 0.41 22.76 21 8.9 92.3 97.0 98.6 6.3 2 (Initial) 2.29 2.29 0.70 69.6 0.49 0.21 0.00 0 23.0 94.3 96.6 98.0 3.7 2A 2.15 2.297 0.67 69.5 0.46 0.20 1.39 6 24.0 90.2 95.6 97.7 7.5 2B 2.09 2.302 0.60 64.8 0.39 0.21 8.97 11 23.1 89.6 95.3 97.7 8.1 2C 2.10 2.313 0.50 68.7 0.35 0.16 17.70 21 24.8 92.0 95.7 97.8 5.8 2D 2.00 2.326 0.45 67.9 0.30 0.14 16.94 33 22.2 91.3 95.7 98.1 6.8 54 Example 3 This example is a process according to the first aspect of the invention. A known amount of lithium borate is dissolved in a defined volume of water to provide a lithium borate solution. The volume of water is calculated as described for Example 1. The initial particulate porous frameworks are pretreated in the same way as Example 1 and then added to the lithium borate solution. After stirring, the water is removed to recrystallise the lithium borate and deposit the lithium borate blocking agent within the pores, thereby providing partially infiltrated particulate porous frameworks comprising the blocking agent within the pores. Example 4 This example is a process according to the first aspect of the invention. A known amount of lithium tungstate is dissolved in a defined volume of water to provide a lithium tungstate solution. The volume of water is calculated in the same way as Example 1. The initial particulate porous frameworks are pretreated in the same way as Example 1, and then added to the solution. Subsequent removal of the water recrystallises the lithium tungstate and deposits it as a blocking agent in the pores, thereby providing partially infiltrated particulate porous frameworks comprising the blocking agent within the pores. Example 5 This example is a process according to the second aspect of the invention. Molar amounts of lithium chloride and niobium ethoxide are added to a defined volume of dry methoxyethanol to provide a solution. The volume of methoxyethanol is calculated in the same way as Example 1, and the initial particulate porous frameworks are pretreated in the same way as Example 1. The frameworks are added to the solution and stirred. The methoxy ethanol is subsequently removed and the temperature ramped to 400 °C under air, as described for Example 1, which forces polycondensation to form stoichiometric LiNbOs. To further order the blocking agent species, the air atmosphere is replaced with a nitrogen atmosphere and the frameworks heated at a rate of 10°C / min to a temperature of 900°C, with a dwell time at 900°C of 1 hour. Examples - composite particles Silicon-carbon composite particles are then prepared by CVI from each of the partially infiltrated particulate porous frameworks produced in the Examples described above. Thus, about 1.8 g of the partially infiltrated particulate porous frameworks are placed on a stainless-steel plate at a constant thickness of 1 mm along its length. The plate is then placed inside a stainless-steel tube of outer diameter 60 mm with gas inlet and outlet lines located in the hot zone of a retort furnace. 55 The furnace tube is purged with nitrogen gas for 30 minutes at room temperature, then the sample temperature is increased to between 450 and 475 °C. The nitrogen gas flow-rate is adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube and is maintained at that rate for 30 minutes. Then, the gas supply is switched from nitrogen to a mixture of silane (SiH4) in 5 nitrogen at 1.25 vol% concentration. Dosing of silane is performed over a period of up to 5 hours with a reactor pressure maintained at 101.3 kPa (1 atm). After dosing has finished the gas flow rate is kept constant whilst the silane is purged from the furnace using nitrogen. The furnace is purged for 30 minutes under nitrogen before being cooled down to room temperature over several hours. The atmosphere is then switched over to air gradually over a period of two hours by switching the 10 gas flow from nitrogen to air from a compressed air supply. Examples - suitable blocking agents and the density values thereof Table 2 provides examples of blocking agents which may be utilised in the present invention. 15 Table 2 Material Type Density, g / cm3 titanium carbide Carbide 4.93 silicon carbide Carbide 3.21 niobium carbide Carbide 7.6 Metal Organic Frameworks MOF 1.5-3.5 titanium nitride Nitride 5.22 titanium silicon nitride Nitride n / m nickel nitride Nitride 2.05 vanadium nitride Nitride 6.13 boron nitride Nitride 2.1 chromium nitride Nitride 5.9 Graphitic carbon nitride Nitride n / m lithium oxide Oxide 2.01 nickel oxide Oxide 4.84 zinc oxide Oxide 5.61 molybdenum oxide Oxide 4.69 cobalt oxide Oxide 6.44 manganese oxide Oxide 5.43 niobium oxide Oxide 4.47 iron oxide Oxide 5.24 titanium oxide Oxide 4.26 tungsten oxide Oxide 7.16 tin oxide Oxide 6.95 aluminium oxide Oxide 4 silicon dioxide Oxide 4.29 lithium titanate Oxide 3.43 lithium tungstate Oxide 4.56 lithium zirconate Oxide n / m lithium niobate Oxide 4.65 lanthanum nickelate Oxide n / m lithium lanthanum zirconate Oxide 5.5 lithium lanthanum titanate Oxide 5 lithium borate Oxide 2.4 lithium carbonate Oxide 2.11 lithium phosphate phosphate 2.54 lithium aluminium phosphate phosphate 3.56 Silicon oxycarbide Oxycarbide n / m titanium oxynitride Oxynitride n / m Lithium sulphide Sulphide 1.66 Covalent organic frameworks COF 0.5-2.2 Imidazolium based ionic liquids Ionic liquid n / m Alkylammonium based ionic liquids Ionic liquid n / m n / m = not measured

Claims

1. A process for manufacturing composite particles for use as an electroactive material for a metalion battery, comprising the steps of:(a) providing initial particulate porous frameworks containing micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks (referred to herein as P1 (initial)) is at least 0.35 g / cm3;(b) partially infiltrating said pores of the initial particulate porous frameworks with a solution comprising a blocking agent and a solvent;(c) removing the solvent to deposit said blocking agent in said pores of the initial particulate porous frameworks such that some of said pores are inaccessible to an electroactive material precursor gas and some of said pores are accessible to an electroactive material precursor gas, thereby providing partially infiltrated particulate porous frameworks comprising said blocking agent in said pores, wherein:(i) P1 of the partially infiltrated particulate porous frameworks (referred to herein as P1 (blocked)) is lower than P1 (initial) and is at least 0.10 g / cm3, and(ii) wherein said blocking agent is deposited such that the blocked volume Vb, expressed as a volumetric ratio to P1 (initial), is in the range of 5 to 60% wherein Vb is defined as:VB = [P1 (initial) - P1 (blocked) - Vo] x 100P1 (initial) wherein:Vo is the occupied volume Vo of said blocked pores which is occupied by the blocking agent, and is calculated as Mb / Pb, where Mb is the mass of the blocking agent in said partially infiltrated particulate porous frameworks and Pb is the density of the blocking agent; and [P1 (initial) - P1 (blocked) - Vo] represents the volume of blocked pores which is not occupied by the blocking agent but which is inaccessible to said electroactive material precursor gas and inaccessible to nitrogen gas in the measurement of P1 by nitrogen gas absorption; and (d) contacting the partially infiltrated particulate porous frameworks comprising said blocking agent in the pores with an electroactive material precursor gas at a temperature effective to cause deposition of electroactive material domains in the accessible pores of the 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 for manufacturing composite particles for use as an electroactive material for a metalion battery, comprising the steps of:(a) providing initial particulate porous frameworks containing micropores and optionally mesopores, wherein P1 of the initial particulate porous frameworks (referred to herein as P1 (initial)) is at least 0.35 g / cm3;(b) partially infiltrating said pores of the initial particulate porous frameworks with a solution comprising blocking agent precursor(s) and a solvent;(c) reacting said blocking agent precursor(s) to form blocking agent by providing sufficient energy for said reaction and removing said solvent, thereby depositing blocking agent in said pores of the initial particulate porous frameworks such that some of said pores are inaccessible to an electroactive material precursor gas and some of said pores are accessible to an electroactive material precursor gas, to provide partially infiltrated particulate porous frameworks comprising blocking agent in said pores, wherein:(i) P1 of the partially infiltrated particulate porous frameworks (referred to herein as P1 (blocked)) is lower than P1 (initial) and is at least 0.10 g / cm3, and(ii) wherein said blocking agent is deposited such that the blocked volume Vb, expressed as a volumetric ratio to P1 (initial), is in the range of 5 to 60% wherein Vb is defined as:VB = [P1 (initial) - P1 (blocked) - Vo] x 100P1 (initial) wherein:Vo is the occupied volume Vo of said blocked pores which is occupied by the blocking agent, and is calculated as Mb / Pb, where Mb is the mass of the blocking agent in said partially infiltrated particulate porous frameworks and Pb is the density of the blocking agent; and [P1 (initial) - P1 (blocked) - Vo] represents the volume of blocked pores which is not occupied by the blocking agent but which is inaccessible to said electroactive material precursor gas and inaccessible to nitrogen gas in the measurement of P1 by nitrogen gas absorption; and (d) contacting the partially infiltrated particulate porous frameworks comprising said blocking agent in the pores with an electroactive material precursor gas at a temperature effective to cause deposition of electroactive material domains in the accessible pores of the 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 adsorption3. A process according to claim 1 wherein the removal of solvent is conducted by increasing temperature and / or reducing pressure, and preferably by heating, preferably at a temperature above 59the boiling point of the solvent but below the temperature at which the particulate porous frameworks and / or blocking agent react with the atmosphere under which step (c) is conducted.

4. A process according to claim 1 or 3 wherein step (c) is be conducted under an atmosphere which avoids reaction between the atmosphere and the frameworks, preferably wherein the atmosphere is an oxygen-containing atmosphere, preferably air, preferably wherein step (c) is conducted below about 500°C, preferably below about 450°C, preferably below about 400°C.

5. A process according to claim 2, wherein two or more, preferably two, blocking agent precursors are provided in solution in step (b).

6. A process according to claim 2 or 5, wherein the energy provided in step (c) is thermal energy or microwave energy, and is preferably thermal energy, preferably wherein the reaction between the blocking agent precursors is initiated by the provision of sufficient energy by heating said frameworks.

7. A process according to claim 2, 5 or 6 wherein the removal of the solvent may be effected before said reaction or after said reaction or contemporaneously with said reaction, or a combination thereof, and preferably wherein the removal of the solvent facilitates said reaction by driving the reaction towards formation of the blocking agent.

8. A process according to any of claims 2 or 5-7 wherein the removal of the solvent is conducted by increasing temperature and / or reducing pressure, and preferably by heating, preferably at a temperature above the boiling point of the solvent but below the temperature at which the particulate porous frameworks react with the atmosphere under which step (c) is conducted, and / or optionally below the temperature at which the blocking agent precursor(s) react with the atmosphere under which step (c) is conducted.

9. A process according to any of claims 2 or 5-8 wherein the removal of solvent is effected at least partially by the provision of energy for the reaction of said blocking agent precursor(s) to form blocking agent where solvent removal and said reaction are effected at least partially contemporaneously.

10. A process according to any of claims 2 or 5-9 wherein the provision of energy to react the blocking agent precursor(s) in step (c) is conducted by heating, preferably by maintaining the reaction mixture 60at a temperature in the range of from about 100°C to about 600°C, preferably from about 200°C to about 500°C, preferably below about 450 °C, for a period of time tR which is preferably from 10 minutes to 5 hours, preferably no more than 2 hours.

11. A process according to any of claims 2 or 5-10 wherein step (c) is conducted under an atmosphere which avoids reaction between the atmosphere and the frameworks at the temperature used to react the blocking agent precursor(s).

12. A process according to any of claims 2 or 5-11 wherein step (c) is conducted under an atmosphere which avoids reaction between the atmosphere and the blocking agent precursor(s) at the temperature used to react the blocking agent precursor(s).

13. A process according to any of claims 2 or 5-12 wherein step (c) is conducted under an oxygencontaining atmosphere, preferably air, particularly wherein said frameworks are carbon-containing particulate porous frameworks and where the reaction temperature to form said blocking agent from said blocking agent precursor(s) is conducted below about 500°C.

14. A process according to any of claims 2 or 5-12 wherein step (c) is conducted under an inert or substantially oxygen-free atmosphere such as a noble gas atmosphere such as a helium or argon atmosphere, or in a nitrogen atmosphere, or mixtures thereof, particularly where the reaction temperature to form said blocking agent from said blocking agent precursor(s) is conducted above about 500°C.

15. A process according to any preceding claim wherein the process comprises an annealing step after step (c) and before step (d), which comprises maintaining the partially 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, for a period of time U which is preferably from 15 minutes to no more than 5 hours, preferably when said annealing step is conducted in an inert or substantially oxygen-free atmosphere.

16. The process of any preceding claim, wherein a vacuum is applied to the initial particulate porous frameworks prior to the infiltration step (b), preferably at a temperature above 100 °C, preferably fora period of from 30 minutes to 24 hours, preferably 6 to 24 hours, preferably 18 to 24 hours, to remove any internal gases.

17. The process of any preceding claim wherein step (b) comprises stirring the initial particulate porous frameworks with the solution of blocking agent or blocking agent precursor(s) for a duration of from 10 minutes to 5 hr.

18. The process of any preceding claim wherein step (b) comprises stirring the initial particulate porous frameworks with the solution of blocking agent or blocking agent precursor(s) at a temperature at which the blocking agent or blocking agent precursor(s) are soluble in the solvent.

19. A process according to any preceding claim, wherein said blocking agent is selected from metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metals; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids, preferably wherein said blocking agent is selected from metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); and ionic liquids, or wherein said blocking agent is other than a metal.

20. A process according to any preceding claim wherein, after said deposition of electroactive material in step (d), said blocking agent is retained in the composite particle in the form of metal or non-metal oxides, nitrides, carbides, oxynitrides and oxycarbides; metal sulphides; metal organic frameworks (MOFs); covalent organic frameworks (COFs); or ionic liquids, and preferably in the form in which it was deposited in step (c).

21. A process according to any preceding claim, wherein said blocking agent is selected from: lithium oxide; aluminium oxide; tin oxide; transition metal oxides (preferably nickel oxide, zinc oxide, copper oxide, molybdenum oxide, cobalt oxide, manganese oxide, niobium oxide, iron oxide, titanium oxide and tungsten oxide); silicon dioxide; mixed metal oxides selected from titanates, tungstates, zirconates, nickelates and niobates (preferably lithium titanate, lithium tungstate, lithium zirconate, lanthanum nickelate, lithium lanthanum zirconate (LLZO) and lithium lanthanum titanate (LLTO)); mixed metal / non-metal oxides selected from borates, phosphates and carbonates (preferably lithium borate, lithium phosphate, lithium carbonate and lithium aluminium phosphate); boron nitride; carbon nitride; transition metal nitrides (preferably titanium nitride, vanadium nitride, chromium nitride and nickel nitride); titanium silicon nitride; titanium carbide; silicon carbide; silicon oxycarbide; titaniumoxynitride; tin; copper; lithium sulphide; imidazolium-based ionic liquids; and alkylammonium-based ionic liquids.

22. A process according to any preceding claim wherein said blocking agent comprises lithium.

23. A process according to any preceding claim wherein said blocking agent is selected from lithium borate, lithium niobate, lithium tungstate.

24. A process according to claim 2 or any of claims 5-20 when dependent on claim 2, wherein said blocking agent is (i) lithium borate or (ii) lithium niobate, preferably wherein said blocking agent precursors are selected from (i) lithium hydroxide and boric acid, and (ii) lithium chloride and niobium ethoxide, respectively.

25. A process according to any preceding claim wherein the blocking agent comprises a metallic element and wherein, after said deposition of electroactive material in step (d), said metal-containing blocking agent is present in the composite particle in a form other than elemental metal.

26. A process according to any preceding claim, wherein the solvent is selected from water, methoxyethanol, methanol, ethanol, isopropyl alcohol, acetone, tetrahydrofuran, dichloromethane, triethylene glycol, polyethylene glycols, glycerin, toluene, benzene, xylenes, and combinations thereof, preferably wherein the solvent comprises at least one polar solvent.

27. A process according to any preceding claim wherein the surface tension of the solvent is in the range of 20 to 75 dynes / cm, preferably from 40 to 75 dynes / cm, at 25°C.

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

29. A process according to any preceding claim, wherein said initial particulate porous frameworks are particulate porous carbon frameworks, or are formed of titanium nitride, silicon oxycarbide, orboron nitride, preferably wherein said initial particulate porous frameworks are particulate porous carbon frameworks.

30. 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.

31. 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.

32. The process according to any preceding claim, wherein the electroactive material precursor is a silicon precursor; optionally wherein the silicon precursor is selected from silane (SiH4), disilane (Si2He), trisilane (SisHs), tetrasilane (Si4Hw), methylsilane (CHaSiHa), dimethylsilane ((CHa)2SiH2), trimethylsilane ((CHa)aSiH), tetramethylsilane ((CHa)4Si), and chlorosilanes such as trichlorosilane (HsiCh) or dichlorosilane (H2SiCh) or chlorosilane (HaSiCI), or methylchlorosilanes such as methyltrichlorosilane (CHaSiCh) or dimethyldichlorosilane ((CHa^SiCh); optionally wherein the silicon precursor is silane (SiH4).

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

34. The process of any preceding claim, wherein step (d) is performed at a temperature of no more than 500°C, preferably no more than 450°C, preferably no more than 400°C.

35. The process of any preceding claim wherein blocking agent is deposited such that some of the micropores, and optionally some of the meso-pores (where present), become inaccessible to said electroactive material precursor gas.

36. A process according to any preceding claim, wherein P1 (initial) is no more than 2.50 cm3 / g.

37. A process according to any preceding claim, wherein P1 (blocked) is no more than 2.20 cm3 / g.

38. A process according to any preceding claim, wherein P1 (blocked) is in the range of 0.40-2.00 cm3 / g, preferably in the range of 0.50-2.00 cm3 / g, or in the range of 0.60-1.60 cm3 / g, or in the range of 0.65-1.10 cm3 / g, or in the range of 0.65-1.00 cm3 / g.

39. A process according to any preceding claim wherein P1 (blocked) lower than P1 (initial) by at least 0.05 cm3 / g, preferably by at least 0.1 cm3 / g, preferably by at least 0.2 cm3 / g, preferably by at least 0.3 cm3 / g, preferably by at least 0.4 cm3 / g; and / or wherein P1 (blocked) is no more than 97%, preferably no more than 95%, preferably no more than 90%, and preferably in the range of 30-97%, preferably 50-95% of P1 (initial).

40. A process according to any preceding claim wherein the pore volume of the micropores in the partially infiltrated particulate porous frameworks is lower than the pore volume of micropores in the initial particulate porous framework by 0.05-0.3 cm3 / g, preferably by 0.1-0.25 cm3 / g; and / or wherein the pore volume of the micropores in the partially infiltrated porous frameworks is no more than 90%, no more than 80%, and preferably in the range of 50-75% of the pore volume of micropores in the initial particulate porous framework.

41. A process according to any preceding claim wherein VP2(blocked) is in the range of 30-90%, wherein VP2(blocked) is defined as the volume of pores in the partially infiltrated particulate porous frameworks with a pore diameter of less than 2.0 nm expressed as a percentage of P1.

42. A process according to any preceding claim wherein VP07(blocked) is in the range of 5.5-35%, wherein VP07(blocked) is defined as the volume of pores in the partially infiltrated particulate porous frameworks with a pore diameter of less than 0.7 nm expressed as a percentage of P1.

43. A process according to any preceding claim wherein VP2(blocked) is at least 2.5xVP07(blocked).

44. A process according to any preceding claim wherein VP5(blocked) is at least 55%, wherein VP5(blocked) is defined as the volume of pores in the partially infiltrated particulate porous frameworks with a pore diameter of less than 5.0 nm expressed as a percentage of P1.

45. A process according to any preceding claim wherein VP20(blocked) is at least 80%, or at least 90%, or at least 95%, or at least 97% and / or wherein VPIO(blocked) is at least 70%, or at least 80%, or at least 90%, or at least 95%, wherein VP20 and VP10 are defined as the volume of pores in the 65particulate 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.

46. A process according to any preceding claim wherein VP20(blocked)-VP5(blocked) is no more than VP20(initial)-VP5(initial).

47. A process according to any preceding claim wherein the PDgo(blocked) pore diameter, defined as the volume-based 90th percentile pore diameter based on the total volume of micropores and mesopores, is no more than 20 nm, preferably no more than 15 nm or no more than 10 nm, and is preferably in the range of 2-20 nm, or 2-15 nm, or 2-10 nm, or 2.5-8 nm.

48. A process according to any preceding claim wherein the PDso(blocked) pore diameter, defined as the volume-based 50th percentile pore diameter based on the total volume of micropores and mesopores, is no more than 6 nm, preferably no more than 5 nm or no more than 4 nm or no more than 3 nm or no more than 2 nm or no more than 1.5 nm, and is preferably at least 0.5 nm or at least 0.75 nm or at least 0.9 nm, and is preferably in the range of 0.5-5 nm, 0.5-3 nm, 0.5-2 nm, 0.75-2 nm or 0.9-2 nm.

49. 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.

50. A process according to any preceding claim wherein said partially infiltrated particulate porous frameworks have a BET surface area of 750-3000 m2 / g, preferably 1000-2500 m2 / g.

51. A process according to any preceding claim wherein the BET surface area of the partially infiltrated particulate porous frameworks have is no more than 95% of the BET surface area of the initial particulate porous frameworks, and preferably in the range of 60-90%.

52. A process according to any preceding claim wherein Vb is in the range of 5-50%, preferably 5-40%, preferably 5-30%, preferably 5-25%.

53. A process according to any preceding claim wherein the mass (Mb) of the blocking agent in said partially infiltrated particulate porous frameworks is in the range of from about 5 to about 50 wt%, preferably from 5 to 35 wt%, preferably 5 to 25 wt%, preferably about 5 to 15 wt%, by total weight of the partially infiltrated particulate porous frameworks.6654. A process according to any preceding claim wherein the density of the blocking agent is in the range of from greater than 1.0 to 8.0 g / cm3, preferably from to 5.0 g / cm3, preferably from 1.5 to 3.0 g / cm3, preferably from 1.5 to 2.6 g / cm3.

55. A process according to any preceding claim wherein the skeletal density of the initial particulate porous frameworks (SD(initial)) is at least 1.3 g / cm3, preferably 1.5 to 4.0 g / cm3, preferably 1.5 to 3.0 g / cm3, preferably 1.5 to 2.5 g / cm3, wherein skeletal density is measured by helium pycnometry.

56. A process according to any preceding claim wherein the skeletal density of the partially infiltrated particulate porous frameworks (SD(blocked)) is less than the skeletal density of the initial particulate porous frameworks (SD(initial)), preferably wherein SD(blocked) / SD(initial) is 0.80-1.25, preferably 0.80-1.10, and is preferably 0.80-0.99, wherein skeletal density is measured by helium pycnometry.

57. A process according to any preceding claim where the skeletal density of the composite particles is in the range of 0.35 to 3.0 g / cm3, preferably 0.70 to 2.5 g / cm3, and wherein the composite particles have a carbonaceous framework the skeletal density is preferably less than 2.3 g / cm3, more preferably less than 2.0 g / cm3, more preferably less than 1.90 g / cm3, more preferably less than 1.80 g / cm3, more preferably less than 1.75 g / cm3 , wherein skeletal density is measured by helium pycnometry.

58. Composite particles as prepared by the process of any of claims 1-57, or a material comprising said composite particles.

59. An electrode comprising the composite particles prepared by the process of any of claims 1-57.

60. A rechargeable metal-ion battery comprising the electrode of claim 59.s