Electroactive materials for metal-ion batteries

Abstract

Provided is a process for preparing composite particles for use as an electroactive material for a metal-ion battery, the process comprising the steps of: (a) providing porous particle frameworks comprising micropores and / or mesopores and optionally a polyvalent metal; (b) optionally impregnating the porous particle frameworks with a polyvalent metal; (c) depositing elemental silicon and / or elemental germanium in the pores of the porous particle frameworks; wherein either the porous particle frameworks in step (a) comprise the polyvalent metal, step (b) is performed, or both; thereby providing impregnated porous particle frameworks comprising the polyvalent metal and the silicon and / or germanium; and (d) contacting the impregnated porous particle frameworks with a monovalent metal while applying an electric potential effective to cause the formation of an intermetallic phase which comprises the polyvalent metal, silicon and / or germanium, and the monovalent metal; thereby providing the composite particles.

Description

[0001] Electroactive materials for metal-ion batteries

[0002] Introduction

[0003] This invention relates to composite particles for use as anode electroactive materials in metal-ion batteries, such as lithium-ion batteries, and processes for making the same. The invention also relates to intermediate particles useful for making the composite particles.

[0004] Background

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

[0006] Conventional LIBs use graphite as the anode electroactive material. Graphite anodes can accommodate a maximum of one lithium atom for every six carbon atoms resulting in a maximum theoretical specific capacity of 372 mAh / g in a lithium-ion battery, with a practical capacity that is somewhat lower (ca. 340 to 360 mAh / g). Silicon is a promising alternative to graphite because of its very high capacity for lithium (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al. in Adv. Mater. 1998, 10, No. 10). Silicon has a theoretical maximum specific capacity of about 3,600 mAh / g in a lithium-ion battery (based on LhsSi-j). However, such a high ratio of intercalated lithium to silicon results in expansion of the silicon material by up to 400% of its original volume. Repeated charging and discharging cycles result in significant mechanical stress on the silicon material leading to fracturing and structural failure. Furthermore, the charging of anodes in LIBs results in the formation of a solid electrolyte interphase (SEI) layer. This SEI layer is an ion-conductive yet insulating layer that is formed by the reductive decomposition of electrolytes on exposed electrode surfaces during the initial charge. In a graphite anode, this SEI layer is relatively stable during subsequent charge / discharge cycles. However, the expansion and contraction of a silicon anode results in fracturing and delamination of the SEI layer and the exposure of fresh silicon surface, resulting in further electrolyte decomposition, increased thickness of the SEI layer and irreversible consumption of lithium. Moreover, lithium silicide, particularly in its higher lithiated state Li isSi4, is thermodynamically metastable meaning that contact with electrolyte results in further reactions. These failure mechanisms collectively result in an unacceptable loss of electrochemical capacity over successive charging and discharging cycles.

[0007] One approach that has been taken to addressing these problems is to use Si-based alloy anodes where the alloy is prepared before it is lithiated in the anode, including so-called Si / Li-active systems (Si-Mg, Si-Ge, and Si-Zn) and Si / Li-inactive systems (Si-Fe, Si— Ni, Si— Ti, and Si-Cu) (Feng et al., Int. J. Mineral Metall. Mater, 28(10) (2021), 1549-1564). Other studies alloys include Si-AI-Fe (Urnirov et al.* ACS Appl. Mater. Interfaces 2020, 12, 17406-17414). Alloy negative electrodes are reviewed by Obrovac, Chem. Rev. 2014, 114, 23, 11444-11502.

[0008] Another approach is to add polyvalent metal salts (Mg2+, Zn2+, Al3+, Ca2+) to the electrolyte such that alloying occurs when lithium is inserted into silicon (Li et al., Chem. Mater. 2021 , 33, 13, 4960- 4970; Li et a!., ACS Appl. Energy Mater. 2020, 3, 12, 11534-11539; Han et a!., ACS Appl. Mater. Interfaces 2019, 11, 33, 29780-29790). Consequently, relatively more stable Li-M-Si ternary alloys with less chemical reactivity are said to form in situ in a battery. In one study based on single crystals made ex situ, Li is-xAlxSi4 was said to be thermodynamically stable, in contrast to the metastability of LiisSi4 noted above (Zeilinger et al., Chem. Mater. 2013, 25, 20, 4113-4121).

[0009] An approach previously 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, WO 2020 / 095067, WO 2020 / 128495, and WO 2022 / 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 delithiated without excessive structural stress. As a result, the electroactive materials exhibit good reversible capacity retention over multiple charge-discharge cycles. Moreover, 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, porous carbon materials used to make the composite particles naturally contain impurities, typically considered to be undesirable, which are dependent on the feedstock and processing conditions. Accordingly, carbonaceous feedstocks are typically treated and / or processing conditions adjusted to reduce the level of impurities, which increases manufacturing complexity and costs. For example, W02020 / 056368 proposes to obtain high purity biomass- derived porous carbon using a combination of chemical purification (e.g. treatment in acids) and thermal purification (e.g. heat-treatment at temperatures from around 800-2000 °C causing evaporation of impurities). W02013 / 120011 proposes to pyrolyze specially prepared polymer gel particles to form porous carbon with low impurity levels.

[0010] There remains a need in the art for further improvements to electroactive composite particles of the type described above to provide improvements in electrochemical performance and longevity of the materials over multiple charge discharge cycles, and to widen the scope of porous materials which are suitable for use in manufacturing such particles.

[0011] Summary of the invention

[0012] In first aspect, the invention provides a process for preparing composite particles for use as an electroactive material for a metal-ion battery, the process comprising the steps of:

[0013] (a) providing porous particle frameworks comprising micropores and / or mesopores and optionally a polyvalent metal;

[0014] (b) optionally impregnating the porous particle frameworks with a polyvalent metal;

[0015] (c) depositing elemental silicon and / or elemental germanium in the pores of the porous particle frameworks; wherein either the porous particle frameworks in step (a) comprise the polyvalent metal, step (b) is performed, or both; thereby providing impregnated porous particle frameworks comprising the polyvalent metal and the silicon and / or germanium; and

[0016] (d) contacting the impregnated porous particle frameworks with a monovalent metal while applying an electric potential effective to cause the formation of an intermetallic phase which comprises the polyvalent metal, silicon and / or germanium, and the monovalent metal; thereby providing the composite particles.

[0017] In a second aspect, the invention provides composite particles for use as an electroactive material for a metal-ion battery, the composite particles comprising: a porous particle framework comprising micropores and / or mesopores; and an intermetallic phase comprising a polyvalent metal, silicon and / or germanium, and a monovalent metal.

[0018] The intermetallic phase is believed to be more stable than the binary silicon and / or germanium alloys formed when typical composite particles are lithiated in a battery, e.g. Li isSi4, resulting in fewer reactions with both liquid and solid electrolytes. Moreover, in typical composite particles the silicon may be terminated with hydride groups, resulting in generation of hydrogen during formation cycles. In the invention, the presence of the polyvalent metal is believed to advantageously alter the termination chemistry of the silicon and / or germanium deposited in step (c), resulting in fewer hydride groups and a material less prone to oxidation. A further advantage is that the invention encompasses the use of many sources of porous particle frameworks, such as activated carbons, without the need for the additional processing steps used to remove polyvalent metals which were typically seen as undesirable impurities. Instead, the inventors have realised that the presence of the polyvalent metal is advantageous when implemented in the invention, as it facilitates the formation of the intermetallic phase.

[0019] Yet further advantage is that the electric potential in step (d) which forms the intermetallic phase can readily be applied without modification of existing battery manufacturing processes. For example, it can be applied during electrochemical pre-lithiation of anodes or during battery formation cycling, meaning that the advantages of the invention can be provided as a “drop-in” solution to existing manufacturing lines.

[0020] The invention also provides an electrode comprising the composite particles and an electrochemical cell such as a rechargeable metal-ion battery comprising the electrode, e.g. as an anode. Processes for preparing the electrode and electrochemical cell are also provided.

[0021] In a third aspect, the invention provides a process for making impregnated porous particle frameworks, the process comprising following the process of the first aspect but omitting step (d).

[0022] In a fourth aspect, the invention provides impregnated porous particle frameworks comprising micropores and / or mesopores, a polyvalent metal, and elemental silicon and / or elemental germanium in the pores.

[0023] The impregnated porous particles represent a convenient intermediate material for manufacturing composite particles having the advantages provided by the first and second aspects. Moreover, they may be used as a “drop-in” solution to existing manufacturing lines, since these typically utilise application of an electric potential during battery formation cycling or during electrochemical pre-lithiation of anodes, thereby forming the desired intermetallic phase. Thus, the invention also provides an electrode comprising the impregnated porous particle frameworks and an electrochemical cell such as a rechargeable metal-ion battery comprising the electrode, e.g. as an anode. Processes for preparing the electrode and electrochemical cell are also provided.

[0024] Although the invention is implemented with silicon and / or germanium, e.g. in step (c), most preferably the invention is implemented with silicon. Moreover, although the invention is implemented with monovalent metals such as those from group 1, preferably the monovalent metal is Li or Na, i.e. the invention is implemented in the context of Li- or Na-ion batteries. Most preferably, the monovalent metal is Li.

[0025] Detailed description of the invention

[0026] It will be understood that the steps of the processes herein are labelled for ease of reference. Unless clearly incompatible the steps may be performed in any order, with or without other intervening steps. The description below of the porous particle frameworks, impregnated porous particle frameworks, composite particles, electrodes, cells etc. applies equally to these items provided as products per se or when used as part of a process.

[0027] Step (a) includes providing porous particle frameworks comprising micropores and / or mesopores and optionally a polyvalent metal. Providing the porous particle frameworks includes synthesising the frameworks and obtaining the frameworks from a supplier.

[0028] The porous particle frameworks provide a framework for the silicon and / or germanium, which is typically deposited in the form of a plurality of electroactive material domains. The term “electroactive material domain” refers to a body of electroactive material, e.g. elemental silicon, having maximum dimensions that are determined by the dimensions of the micropores and / or mesopores of the porous particle frameworks in which they are located. 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 material 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. The porous particle frameworks generally comprise a three-dimensionally interconnected open pore network comprising micropores and / or 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.

[0029] References herein to the volume of micropores, mesopores, and macropores in the porous particle frameworks, and also any references to the distribution of pore volume within the porous particle frameworks, relate to the internal pore volume of the porous particle frameworks used as the starting material in step (a) of the claimed process, i.e. prior to deposition of electroactive material into the pore volume in step (c).

[0030] The porous particle frameworks may be characterised by 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 porous particle frameworks include both micropores and mesopores. However, it is not excluded that porous particle frameworks may be used which include micropores and no mesopores, or mesopores and no micropores.

[0031] The total volume of micropores and mesopores in the porous particle frameworks is preferably at least 0.4 cm3 / g, or at least 0.5 cm3 / g, or at least 0.6 cm3 / g, or at least 0.65 cm3 / g, or at least 0.7 cm3 / g, or at least 0.75 cm3 / g, or at least 0.8 cm3 / g. 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.

[0032] The internal pore volume of the porous particle 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. Preferably, the total volume of micropores and mesopores in the porous particle frameworks is no more than 1.8 cm3 / g, or no more than 1.7 cm3 / g, or no more than 1.6 cm3 / g, or no more than 1.55 cm3 / g, or no more than 1.5 cm3 / g, or no more than 1.45 cm3 / g, or no more than 1.4 cm3 / g, or no more than 1.35 cm3 / g, or no more than 1.3 cm3 / g, or no more than 1.25 cm3 / g, or no more than 1.2 cm3 / g, or no more than 1.1 cm3 / g.

[0033] Preferably the total volume of micropores and mesopores in the porous particle frameworks is in the range from 0.4 to 1.8 cm3 / g, or from 0.4 to 1.7 cm3 / g, or from 0.5 to 1.6 cm3 / g, or from 0.5 to 1 .55 cm3 / g, or from 0.6 to 1.5 cm3 / g, or from 0.6 to 1 .45 cm3 / g, or from 0.65 to 1 .4 cm3 / g, or from 0.65 to 1 .35 cm3 / g, or from 0.7 to 1 .3 cm3 / g, or from 0.7 to 1 .25 cm3 / g, or from 0.75 to 1.2 cm3 / g, or from 0.75 to 1.1 cm3 / g, or from 0.8 to 1.2 cm3 / g, or from 0.8 to 1.1 cm3 / g.

[0034] The general term “PDnpore diameter” refers herein to the volume-based nth percentile pore diameter, based on the total volume of micropores and mesopores. For instance, the term “PD5o pore diameter” as used herein refers to the pore diameter below which 50% of the total micropore and mesopore volume is found. For the avoidance of doubt, any macropore volume (pore diameter greater than 50 nm) is not taken into account for the purpose of determining PDnvalues.

[0035] The PDgo pore diameter of the porous particle frameworks is preferably no more than 50 nm, or no more than 30 nm, or no more than 12 nm, or no more than 10 nm, or no more than 8 nm, or no more than 6 nm, or no more than 5 nm. Preferably, the PDgo pore diameter of the porous particle frameworks is at least 3 nm, or at least 4 nm, or at least 5 nm, or at least 6 nm. For example, the PDgo pore diameter of the porous particle frameworks is preferably in the range from 3 to 20 nm, or from 4 to 15 nm, or from 5 to 10 nm, or from 6 to 8 nm.

[0036] The PDso pore diameter of the porous particle frameworks is preferably no more than 30 nm, or no more than 15 nm, or no more than 6 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3 nm, or no more than 2.5 nm, or no more than 2 nm, or no more than 1.9 nm, or no more than 1 .8 nm, or no more than 1.7 nm, or no more than 1.6 nm.

[0037] The micropore volume fraction is at least 0.3, or at least 0.4, or at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6, and / or no more than 0.95, or no more than 0.9, or no more than 0.85, or no more than 0.8, based on the total volume of micropores and mesopores in the porous particle frameworks. When step (b) is performed, most preferably the micropore volume fraction is no more than 0.95 based on the total volume of micropores and mesopores in the porous particle frameworks. In this way, the mesopore volume is greater than 0.05, which provides for sufficient volume of larger pores to facilitate impregnating the porous particle frameworks with the polyvalent metal.

[0038] P1is the total volume of micropores and mesopores in the porous particle frameworks expressed in cm3 / g. VP07 is the volume of pores in the porous particle frameworks with a pore diameter of 0.7 nm or less expressed as a percentage of P1. VP07 is preferably in the range of 5.1-40%, or 5.5-35%, or 7-30%, or 10-27%, or most preferably 15-25%. VP07 is expressed relative to the total volume of micropores and mesopores in the porous particle frameworks. However, for some uses, it is advantageous to specify a minimum absolute value of the volume of pores with a pore diameter of 0.7 nm or less. Thus, the volume of pores in the porous particle frameworks with a pore diameter of 0.7 nm or less may be at least 0.05 cm3 / g, preferably 0.08-0.5 cm3 / g, most preferably 0.1-0.3 cm3 / g; when measured by nitrogen adsorption.

[0039] VP1 , VP2, and VP5 are the volume of pores in the porous particle frameworks with a pore diameter of 1.0 nm or less, 2.0 nm or less, and 5.0 nm or less, respectively, expressed as a percentage of P1. VP1, VP2, and VP5 are measured by nitrogen gas adsorption. Preferably, VP1 is at least 1.5xVP07, or at least 2xVP07. Preferably, VP2 is at least 2.5xVP07, or at least 3xVP07, or at least 4xVP07. Preferably, VP5 is at least 55%, or at least 60%, or at least 70%, or at least 80% or at least 90%, or at least 92%, or at least 93%.

[0040] Preferably, VP2 is at least 20%. For some uses, VP2 is at least 40%, at least 50%, at least 55%, or at least 60%, or at least 70%, or at least 80%, or at least 85%, i.e. the micropores form the majority of the volume of micropores and mesopores. Alternatively, VP2 is less than 50%, or no more than 45%, or no more than 40%, i.e. the mesopores form the majority of the volume of micropores and mesopores.

[0041] VP2 may be less than 99%, or less than 98%, or less than 95%, or preferably less than 90%, for example 40-90%.

[0042] VP2 may be in the range of 45-98%, or 45-90%, or 45-85%, or 45-80%, or 45-78%, or 45-75%, or 45-70%, or 45-60%, or 50-98%, or 50-90%, or 50-85%, or 50-80%, or 50-78%, or 50-75%, or 50- 70%, or 55-98%, or 55-90%, or 55-85%, or 55-80%, or 55-78%, or 55-75%, or 55-70%, or 55-69%.

[0043] The pore volume at larger pore sizes may be controlled to further refine the properties of the frameworks and resulting composite particles. VP20 and VP10 are defined as the volume of pores in the porous particle frameworks with a pore diameter of 20.0 nm or less or 10.0 nm or less, respectively, expressed as a percentage of P1. VP10 and VP20 are measured by nitrogen gas adsorption. VP20 may be at least 80%, or at least 90%, or at least 95%, or at least 97%, or at least 98%. VP10 may be at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97%.

[0044] VP20-VP5 represents the pore volume in the porous particle frameworks with a pore diameter of more than 5.0 nm up to and including 20.0 nm, expressed as a percentage of P1. VP20-VP5 may be less than 20%, less than 15%, preferably less than 12%, preferably less than 10%, or more preferably less than 9%. Optionally, VP20-VP5 is at least 0.5%, or at least 1%, or at least 2%. VP20-VP5 may be 0.5-20%, 0.5-15%, or 1-12%, or 2-10%, or 2-9%, or 3-9%.

[0045] VP20-VP2 may be at least 45%, or at least 50%, or at least 55%.

[0046] The pore size distribution of the porous particle frameworks may be monomodal, bimodal or multimodal. 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 porous particle frameworks. A bimodal or multimodal pore size distribution may be 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.

[0047] The total volume of micropores and mesopores and the pore size distribution of micropores and mesopores are determined using nitrogen gas adsorption at 77 K down to a relative pressure p / po of 10'6using quenched solid density functional theory (QSDFT), preferably in accordance with standard methodology as set out in ISO 15901-2 and ISO 15901-3, most preferably ISO 15901-2:2022. Nitrogen gas adsorption is a technique that characterises the porosity and pore diameter distributions of a material by allowing a gas to condense in the pores of a solid. As pressure increases, the gas condenses first in the pores of smallest diameter and the pressure is increased until a saturation point is reached at which all of the pores are filled with liquid. The nitrogen gas pressure is then reduced incrementally, to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms, and the hysteresis between them, allows the pore volume and pore size distribution to be determined. Suitable instruments for the measurement of pore volume and pore size distributions by nitrogen gas adsorption include the TriStar II and TriStar II Plus porosity analyzers, which are available from Micromeritics Instrument Corporation, USA, and the Autosorb IQ porosity analyzers, which are available from Quantachrome Instruments.

[0048] Nitrogen gas adsorption is effective for the measurement of pore volume and pore size distributions for pores having a diameter up to 50 nm, but is less reliable for pores of much larger diameter. For the purposes of the present invention, nitrogen adsorption is therefore used to determine pore volumes and pore size distributions only for pores having a diameter up to and including 50 nm (i.e. only for micropores and mesopores). PD50 values are likewise determined relative to the total volume of micropores and mesopores only. In view of the limitations of available analytical techniques it is not possible to measure pore volumes and pore size distributions across the entire range of micropores, mesopores and macropores using a single technique. In the case that the porous particle frameworks comprise macropores, the volume of pores having diameter in the range from greater than 50 nm and up to 100 nm may be measured by mercury porosimetry and is preferably no more than 0.3 cm3 / g, or no more than 0.2 cm3 / g, or no more than 0.1 cm3 / g, or no more than 0.05 cm3 / g. A small fraction of macropores may be useful to facilitate electrolyte access into the pore network, and when step (b) is performed to facilitate the impregnation of the porous particle frameworks with the polyvalent metal, but the advantages of the invention are obtained substantially by accommodating electroactive material in micropores and smaller mesopores.

[0049] Any pore volume measured by mercury porosimetry at pore sizes of 50 nm or below is disregarded (as set out above, nitrogen adsorption is used to characterize the mesopores and micropores). Pore volume measured by mercury porosimetry above 100 nm is assumed for the purposes of the invention to be inter-particle porosity and is also disregarded.

[0050] Mercury porosimetry is a technique that characterizes the porosity and pore diameter distributions of a material by applying varying levels of pressure to a sample of the material immersed in mercury. The pressure required to intrude mercury into the pores of the sample is inversely proportional to the size of the pores. Values obtained by mercury porosimetry as reported herein are obtained in accordance with ASTM UOP578-11 , with the surface tension y taken to be 480 mN / m and the contact angle (p taken to be 140° for mercury at room temperature. The density of mercury is taken to be 13.5462 g / cm3at room temperature. A number of high precision mercury porosimetry instruments are commercially available, such as the AutoPore IV series of automated mercury porosimeters available from Micromeritics Instrument Corporation, USA. For a complete review of mercury porosimetry reference may be made to P.A. Webb and C. Orr in “Analytical Methods in Fine Particle Technology, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0051] It will be appreciated that intrusion techniques such as gas adsorption and mercury porosimetry are effective only to determine the pore volume of pores that are accessible to nitrogen or to mercury from the exterior of the porous particle 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 porous particle frameworks. Fully enclosed pores which cannot be identified by nitrogen adsorption or mercury porosimetry shall not be taken into account herein when determining porosity values. Likewise, any pore volume located in pores that are so small as to be below the limit of detection by nitrogen adsorption is not taken into account.

[0052] 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 “D5o” and “D5o particle diameter” as used herein refer to the volume-based median particle diameter, i.e. the diameter below which 50% by volume of the particle population is found. The terms “D ” and “Dw particle diameter” as used herein refer to the 10th percentile volume-based median particle diameter, i.e. the diameter below which 10% by volume of the particle population is found. The terms “Dgo” and “Dgo particle diameter” as used herein refer to the 90th percentile volume-based median particle diameter, i.e. the diameter below which 90% by volume of the particle population is found.

[0053] Particle diameters and particle size distributions can be determined by standard laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that a particle will scatter light at an angle that varies depending on the size the particle and a collection of particles will produce a pattern of scattered light defined by intensity and angle that can be correlated to a particle size distribution. A number of laser diffraction instruments are commercially available for the rapid and reliable determination of particle size distributions. Unless stated otherwise, particle size distribution measurements as specified or reported herein are as measured by the conventional Malvern Mastersizer™ 3000 particle size analyzer from Malvern Instruments™. The Malvern Mastersizer™ 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing the particles of interest suspended in an aqueous solution. Light rays which strike the particles are scattered through angles which are inversely proportional to the particle size and a photodetector array measures the intensity of light at several predetermined angles and the measured intensities at different angles are processed by a computer using standard theoretical principles to determine the particle size distribution. Laser diffraction values as reported herein are obtained using a wet dispersion of the particles in 2- propanol with a 5 vol% addition of the surfactant SPAN™-40 (sorbitan monopalmitate). The particle refractive index is taken to be 2.68 for porous particle 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.

[0054] In general, the porous particle frameworks have a D50 particle diameter in the range from 1 to 30 pm. Optionally, the D50 particle diameter of the porous particle frameworks 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 m. Optionally the D50 particle diameter of the porous particle frameworks may be no more than 25 pm, or no more than 20 pm, or no more than 18 pm, or no more than 15 pm, or no more than 12 pm, or no more than 10 pm, or no more than 8 pm.

[0055] The D10 particle diameter of the porous particle frameworks is preferably at least 0.5 pm, or at least 0.8 pm, or at least 1 pm, or at least 1 .5 pm, or at least 2 pm. By maintaining the D10 particle diameter at 0.5 pm or more, the potential for undesirable agglomeration of sub- micron sized particles is reduced, and improved dispersibility of the composite particles formed.

[0056] The D90 particle diameter of the porous particle frameworks 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.

[0057] The porous particle frameworks preferably have a narrow size distribution span. For instance, the particle size distribution span (defined as (Dgo-Dio) / D5o) is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, efficient packing of the particles into dense powder beds is more readily achievable.

[0058] The porous particle frameworks 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 porous particle frameworks 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.

[0059] It is possible to obtain highly accurate two-dimensional projections of micron scale particles by scanning electron microscopy (SEM) or by dynamic image analysis, in which a digital camera is used to record the shadow projected by a particle. The term “sphericity” as used herein shall be understood as the ratio of the area of the particle projection (obtained from such imaging techniques) to the area of a circle, wherein the particle projection and circle have identical circumference. Thus, for an individual particle, the sphericity S may be defined as: wherein Amis the measured area of the particle projection and Cmis the measured circumference of the particle projection. The average sphericity Savof a population of particles as used herein is defined as: wherein n represents the number of particles in the population. The average sphericity for a population of particles is preferably calculated from the two-dimensional projections of at least 50 particles.

[0060] The porous particle frameworks preferably have a BET surface area of at least 100 m2 / g, or at least 500 m2 / g, or at least 750 m2 / g, or at least 1 ,000 m2 / g, or at least 1 ,250 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 methods, e.g. ISO 9277:2022. Preferably, the BET surface area of the porous particle 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 porous particle frameworks may have a BET surface area in the range from 100 m2 / g 10 to 4,000 m2 / g, or from 500 m2 / g to 4,000 m2 / g, or from 750 m2 / g to 3,500 m2 / g, or from 1 ,000 m2 / g to 3,250 m2 / g, or from 1 ,000 m2 / g to 3,000 m2 / g, or from 1 ,000 m2 / g to 2,500 m2 / g, or from 1 ,000 m2 / g to 2,000 m2 / g.

[0061] The porous particle frameworks preferably have a particle density of at least 0.35 and preferably less than 3 g / cm3, more preferably less than 2 g / cm3, more preferably less than 1.5 g / cm3, most preferably from 0.35 to 1 .2 g / cm3. As used herein, the term “particle density” refers to “apparent particle density” as measured by mercury porosimetry (i.e. the mass of a particle divided by the particle volume wherein the particle volume is taken to be the sum of the volume of solid material and any closed or blind pores (a “blind pore” is pore that is too small to be measured by mercury porosimetry). Preferably, the porous particle frameworks have particle density of at least 0.4 g / cm3, or at least 0.45 g / cm3, or at least 0.5 g / cm3, or at least 0.55 g / cm3, or at least 0.6 g / cm3, or at least 0.65 g / cm3, or at least 0.7 g / cm3. Preferably, the porous particle frameworks have particle density of no more than 1.15 g / cm3, or no more than 1.1 g / cm3, or no more than 1.05 g / cm3, or no more than 1 g / cm3, or no more than 0.95 g / cm3, or no more than 0.9 g / cm3.

[0062] Preferably the porous particle frameworks have: (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.4 to 1.8 cm3 / g;

[0063] (ii) a PD50 pore diameter of no more than 30 nm, and preferably a PD90 pore diameter of no more than 50 nm; and

[0064] (iii) a D50 particle diameter in the range from 1 to 30 pm.

[0065] More preferably the porous particle frameworks have:

[0066] (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.5 to 1.6 cm3 / g;

[0067] (ii) a PD50 pore diameter of no more than 15 nm, and preferably a PD90 pore diameter of no more than 30 nm; and

[0068] (iii) a D50 particle diameter in the range from 1 to 25 pm.

[0069] More preferably the porous particle frameworks have:

[0070] (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.6 to 1.5 cm3 / g;

[0071] (ii) a PD50 pore diameter of no more than 6 nm, and preferably a PD90 pore diameter of no more than 12 nm; and

[0072] (iii) a D50 particle diameter in the range from 1.5 to 20 pm.

[0073] More preferably the porous particle frameworks have:

[0074] (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.65 to 1 .4 cm3 / g;

[0075] (ii) a PD50 pore diameter of no more than 2.5 nm, and preferably a PD90pore diameter of no more than 10 nm; and

[0076] (iii) a D50 particle diameter in the range from 1.5 to 18 pm.

[0077] More preferably the porous particle frameworks have:

[0078] (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.7 to 1.3 cm3 / g;

[0079] (ii) a PD50 pore diameter of no more than 4 nm, and preferably a PD90 pore diameter of no more than 8 nm; and

[0080] (iii) a D50 particle diameter in the range from 2 to 15 pm.

[0081] More preferably the porous particle frameworks have: (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.75 to 1.2 cm3 / g;

[0082] (ii) a PD50 pore diameter of no more than 3 nm, and preferably a PD90 pore diameter of no more than 6 nm; and

[0083] (iii) a D50 particle diameter in the range from 2 to 12 pm.

[0084] More preferably the porous particle frameworks have:

[0085] (i) a total pore volume of micropores and mesopores as measured by nitrogen gas adsorption in the range from 0.8 to 1.2 cm3 / g;

[0086] (ii) a PD50 pore diameter of no more than 2 nm, and preferably a PD90 pore diameter of no more than 5 nm; and

[0087] (iii) a D50 particle diameter in the range from 2.5 to 10 pm.

[0088] In a particular example, the porous particle frameworks are porous carbon particle frameworks comprising micropores and optionally mesopores, wherein:

[0089] P1is the total volume of micropores and mesopores in the porous carbon particle frameworks expressed in cm3 / g, wherein P1is at least 0.35 and optionally less than 2.5; and

[0090] VP07 and VP2 are respectively the volume of pores in the porous carbon particle frameworks with a pore diameter of 0.7 nm or less and 2.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35% and VP2 is at least 2.5xVP07; the micropore volume of the porous carbon particle frameworks is at least 0.3 cm3 / g; wherein P1, VP07, VP2, and the micropore volume are measured by nitrogen gas adsorption.

[0091] In another particular example, the porous particle frameworks are porous carbon particle frameworks comprising micropores and optionally mesopores wherein:

[0092] P1is the total volume of micropores and mesopores in the porous carbon particle frameworks expressed in cm3 / g, wherein P1is at least 0.35 and optionally less than 2.5; and

[0093] VP07, VP2, VP5, and VP20 are respectively the volume of pores in the porous carbon particle frameworks with a pore diameter of 0.7 nm or less, 2.0 nm or less, 5.0 nm or less, and 20.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35%, VP2 is in the range of 40-90%, and VP20-VP5 is less than 20%; optionally the micropore volume of the porous carbon particle frameworks is at least 0.3 cm3 / g; wherein P1, VP07, VP2, VP5, VP20, and the micropore volume are measured by nitrogen gas adsorption. The porous particle frameworks preferably comprise a conductive material. The use of conductive porous particle frameworks is advantageous as they form a conductive framework within the composite particles which facilitates the flow of electrons between lithium atoms / ions inserted into the electroactive material and a current collector.

[0094] A preferred type of porous particle frameworks are particles comprising or consisting of a carbon material, more preferably a conductive carbon material, referred to herein as porous carbon particle frameworks, more preferably conductive porous carbon particle frameworks.

[0095] The porous carbon particle frameworks preferably comprise at least 80 wt% carbon, more preferably at least 85 wt% carbon, more preferably at least 90 wt% carbon, more preferably at least 95 wt% carbon, and optionally at least 98wt% or at least 99 wt% carbon. The carbon may be crystalline carbon or amorphous carbon, or a mixture of amorphous and crystalline carbon. The porous carbon particles may be either hard carbon particles or soft carbon particles.

[0096] As used herein, the term “hard carbon” refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2hybridised state (trigonal bonds) in nanoscale polyaromatic domains. The polyaromatic domains are cross-linked with a chemical bond, e.g. a C-O-C bond. Due to the chemical cross-linking between the polyaromatic domains, hard carbons cannot be converted to graphite at high temperatures. Hard carbons have graphite-like character as evidenced by the large G-band (-1600 cm-1) in the Raman spectrum. However, the carbon is not fully graphitic as evidenced by the significant D-band (-1350 cm-1) in the Raman spectrum.

[0097] As used herein, the term “soft carbon” also refers to a disordered carbon matrix in which carbon atoms are found predominantly in the sp2hybridised state (trigonal bonds) in polyaromatic domains having dimensions in the range from 5 to 200 nm. In contrast to hard carbons, the polyaromatic domains in soft carbons are associated by intermolecular forces but are not cross-linked with a chemical bond. This means that they will graphitise at high temperature. The porous carbon particle frameworks preferably comprise at least 50% sp2hybridised carbon as measured by XPS. For example, the porous carbon particle frameworks may suitably comprise from 50% to 98% sp2hybridised carbon, from 55% to 95% sp2hybridised carbon, from 60% to 90% sp2hybridised carbon, or from 70% to 85% sp2hybridised carbon.

[0098] Porous carbon particle frameworks used in the invention are most preferably a form of activated carbon. The term “activated carbon” refers to a carbonaceous material that has been physically or chemically processed to increase its porosity and surface area. Chemical activation or physical activation (e.g. high temperature steam or CO2) mechanisms are among common methods used in the production of activated carbons. A suitable activation process comprises contacting pyrolyzed carbon with one or more of oxygen, steam, CO, and CO2 at a temperature in the range from 300 to 1500°C, 600 to 1200°C, or 600 to 1000°C.

[0099] 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.

[0100] A variety of different porous carbon particle frameworks are available in the art depending on the starting material and the conditions of the pyrolysis process. Porous carbon particle frameworks of various different specifications are available from commercial suppliers.

[0101] A variety of different carbonaceous materials may be used to prepare suitable porous carbon particle 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.

[0102] 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.

[0103] The porous carbon particle 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.

[0104] 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.

[0105] 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.

[0106] The burn-off of the pyrolyzed material during activation is preferably 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.

[0107] In chemical activation methods the carbonaceous material is impregnated with a chemical activation agent (such as NaOH, KOH, K2CO3, H3PO4, CaCl2, ZnCl2, and mixtures thereof, etc.). The carbonaceous material is typically impregnated prior to pyrolysis and the pyrolysis step takes place simultaneously with the activation, though the carbonaceous material may be carbonized prior to chemical impregnation. Pyrolysis for chemical activation may take place at 250-1000 °C or 500-950 °C. If the porous carbon is formed using chemical activation processes, then, in addition to pore generation by pyrolysis of carbon, the activation mechanism works by expanding existing pores or pushing apart graphene sheets (exfoliation) which is not conducive to maintaining a high proportion of micro-pore spaces accessible via narrow channels / openings. This is thought to cause relatively poorer electrochemical performance of composite materials prepared from chemically activated porous carbon materials. Thus, preferably the particulate porous carbon frameworks are prepared by physical activation. It has been found that a carbonaceous material may be impregnated with a polyvalent metal which acts as a catalyst, lowering costs by allowing the activation process to take place at a lower temperature and / or for a shorter period of time. Typically, the residual polyvalent metal from such a process would be washed out, adding manufacturing complexity and mitigating the cost advantages. However, in the invention such a washing step is not required because the residual polyvalent metal may act to form the intermetallic phase in step (d). Accordingly, step (a) may comprise impregnating a carbonaceous material with a polyvalent metal, activating the impregnated carbonaceous material to form porous carbon particle frameworks comprising micropores and / or mesopores and the polyvalent metal; wherein step (a) most preferably does not comprise a washing step after activating the impregnated carbonaceous material. The impregnating is preferably achieved using a salt or complex of the polyvalent metal, preferably a salt. The salt or complex of the polyvalent metal may be dissolved in a pore former such as ethylene glycol. The polyvalent metal may be selected from group 2 metals, transition metals, and mixtures thereof; preferably calcium, magnesium, nickel, molybdenum, copper, and mixtures thereof; most preferably from calcium. For example, impregnating may be achieved using calcium acetate. The activating may comprise heating in a flow of one or more of oxygen, nitrogen, steam, CO, and CO2at a temperature between 500 °C and 1200 °C.

[0108] An example of a typical activated carbon synthesis is as below:

[0109] Synthetic activated carbons are prepared from a mixture of Novolak resin and 11% of hexamethylenetetramine powder, Bakelite PF 6705 FP, purchased from Hexion GmbH. This starting material is cross-linked at 150 °C for 1 h and the solid blocks of cross-linked material are hammered to 2-3 cm pieces before grinding them to -100 pm particles. This cured resin powder is then pyrolyzed at 800 °C for 10 min under a nitrogen flow of 1 L / min. The carbon yield obtained from this precursor is 57-59%. After carbonization, the carbon is ball milled to particle size of 3-4 pm and the carbon material obtained has a total pore volume of 0.25-0.3 cm3 / g, including 0.20- 0.22 cm3 / g of microporosity and a surface area of 650-700 m2 / g. This carbon is then activated in either steam or CO2 to achieve a desirable pore volume. Typical activation temperature used for CO2 activation to achieve 0.8-0.9 cm3 / g total pore volume, is 950-980 °C with dwell time of 5-8h depending on the amount of carbon being activated, CO2 flow rate, and the type of furnace being used. The temperature used for steam activation is lower than CO2, typically 850 °C, as steam is more reactive. The dwell time at the activation temperature for steam is typically 6-9h depending on the type and amount of charcoal being activated, steam flow rate, and the type of furnace being used. An example of activated carbon made using steam activation is as follows:

[0110] To make steam activated synthetic scaffold with a total pore volume of 0.79 cm3 / g, steam is introduced via a humidifier consisting of nitrogen atomizer (3 bar injection pressure) through 1 mm orifice positioned at right angles to a 1 mm orifice which adds water dropwise to an atomization chamber where the high pressure nitrogen stream induces atomization via impingement of the high pressure gas on the water droplet. Heated tapes are used on the inlet and outlet to prevent adventitious steam condensation. Carbonised phenolic resin is ball-milled in a planetary ball mill to D5O = 3 pm (60 g loading, 105, 10 mm balls, 300 RPM, 20 min interval). Subsequently, 15 g of milled carbonised phenolic resin is loaded into a short alumina crucible, the material is spread evenly along the crucible. Steam activation takes place in a tube furnace with the crucible placed in the middle of the heating zone. The furnace is purged with N2 at 0.8 L / min for 10-30 minutes. A ramp rate of 8.7 °C / min with a set-point of 850 °C is used. Once the temperature has reached 840 °C, water is injected into an atomisation nozzle at a rate of 0.25 mL / min (water injection volume), temperature is held stable once 850 °C is reached. Dwell for 345 min. When dwell has completed, steam flow is set to zero and heating tape is turned off.

[0111] Alternatives to carbon-based particle frameworks include porous particle frameworks comprising 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 of titanium nitride, silicon oxycarbide or boron nitride.

[0112] The porous particle frameworks optionally comprise a polyvalent metal. As noted above, polyvalent metals have often been considered an undesirable impurity in porous carbon frameworks when used in LIBs. Porous carbon frameworks are thus typically subjected to additional processes to remove or minimise the amount of polyvalent metal, before they are used in LIB manufacture. One commonly used process is washing, which can be performed using acidic, basic, or neutral liquids. Other processes include gas purification, which includes reaction with chlorine gas to remove volatile polyvalent metals as metal chlorides. An advantage of the invention is that such additional processes may not be needed, as the polyvalent metal impurity facilitates the formation of the desired intermetallic phase, reducing manufacturing complexity. Accordingly, the porous particle frameworks in step (a) may be those which have not been subjected to processing intended to remove impurities naturally present in the feedstock material used to synthesise the porous particle frameworks. For example, the porous particle frameworks in step (a) may be those which have not been subjected to a washing step intended to remove impurities naturally present in the feedstock material used to synthesise the porous particle frameworks.

[0113] The feedstock used to make the porous particle frameworks affects the type and level of impurities. One economical feedstock is biomass. However, biomass feedstocks in particular contain impurities such as Ca and Mg, and so are typically washed to remove such impurities. The invention allows for the utilisation of biomass feedstocks without the need for such additional processing. Therefore, preferably the porous particle frameworks in step (a) are derived from biomass, most preferably without a washing step intended to remove impurities.

[0114] The porous particle frameworks may comprise Ca, Mg, and S each at a concentration of 50-5,000 ppm relative to the mass of the porous particle frameworks. These are impurities typically present when biomass feedstocks are used.

[0115] The porous particle frameworks may comprise 100-10,000 ppm, 250-8,000 ppm, or 500-5,000 ppm Ca relative to the mass of the porous particle frameworks.

[0116] The porous particle frameworks may comprise at least one transition metal and Al each at a concentration of 50-1 ,000 ppm relative to the mass of the porous particle frameworks. These are impurities typically present when synthetic polymer feedstocks are used.

[0117] P may also be present in the porous particle frameworks, typically derived from chemical activation of feedstocks, e.g. when HsPO s used as the activating agent. For example, the porous particle frameworks may comprise 200-25,000 ppm P, 500-20,000 ppm P, or 1 ,000-16,000 ppm P relative to the mass of the porous particle frameworks.

[0118] In a particular example, the porous particle frameworks are porous carbon particle frameworks comprising:

[0119] 100-10,000 ppm, 250-8,000 ppm, or 500-5,000 ppm Ca relative to the mass of the porous carbon particle frameworks; and

[0120] 200-25,000 ppm, 500-20,000 ppm, or 1 ,000-16,000 ppm P relative to the mass of the porous carbon particle frameworks; preferably comprising 500-5,000 ppm Ca and 1,000-16,000 ppm P relative to the mass of the porous carbon particle frameworks. Such frameworks may be provided as part of step (a) of the process by using H3PO4 to activate a carbonaceous material preferably derived from biomass, wherein step (a) preferably does not comprise a washing step after activation of the carbonaceous material.

[0121] One way of providing porous particle frameworks which comprise a desired polyvalent metal is to introduce the polyvalent metal into the feedstock used to make the frameworks, prior to activation. A polymeric feedstock such as lignin, e.g. Kraft lignin obtained from a wood pulping process, may be dissolved in a suitable solvent with an aqueous solution of a desired polyvalent metal precursor. Non-aqueous systems can be used, such as the dissolution of phenolic resin in an organic solvent such as isopropyl alcohol or acetone with a suitable polyvalent metal precursor. The aqueous or non-aqueous solution could also contain an activating agent, in the case of subsequent chemical activation. The aqueous or non-aqueous solution could also contain a suitable crosslinking agent such as hexamine. The solution is mixed until all components are dissolved. The solvent can then be driven off by thermal evaporation and / or vacuum drying (e.g. in the case of water, excess can be evaporated at 80 °C followed by vacuum drying at 100 °C to remove the residual water). The polymer can then be further crosslinked in a separate step at elevated temperature if required.

[0122] The dried polymer / polyvalent metal precursor mixture can be heated to induce a thermal crosslinking process. The material can subsequently be carbonised and activated according to the usual methods known in the art, e.g. as described above.

[0123] A desired polyvalent metal may be introduced into a carbonised feedstock, prior to activation. A carbonised feedstock material may be ground in the presence of a polyvalent metal precursor. Alternatively, the feedstock may be bathed in a solution of a polyvalent metal precursor followed by removal of the solvent. The mixture is then further heated to drive off remaining volatiles in an inert atmosphere, e.g. at 500 °C in N2. The mixture can then be heated in inert atmosphere to the activation temperature and the atmosphere switched to a different one, e.g. CO2 / N2 at 900 °C, for a suitable period, e.g. 3 hours, if physical activation is desired. The subsequent activated carbon mat then be subjected to post treatment such as jet milling to reduce the particle size or washing to remove excess metallic compound as desired.

[0124] Optional step (b) includes impregnating the porous particle frameworks with a polyvalent metal. Step (b) is performed when the porous particle frameworks in step (a) do not contain a suitable amount or type of polyvalent metal to cause the formation of the intermetallic phase in step (d). Thus, the invention allows the use of a wide variety of porous particulate frameworks with or without a polyvalent metal. Step (b) is typically performed below 1000 °C. Step (b) is typically performed under inert atmosphere, optionally under an atmosphere of nitrogen, CO2, a noble gas, and mixtures thereof.

[0125] When step (b) is performed, it may be performed before or after step (c).

[0126] Step (b) typically comprises impregnating the porous particle frameworks with a polyvalent metal precursor, such as a salt or complex of the polyvalent metal. The polyvalent metal precursor may be selected from oxides, carbonates, nitrates, hydroxides, hydrides, sulphates, carboxylates, halides, oxalates, bisoxalatoborates, bis(trifluoromethanesulfonyl)imides, citrates, phosphates, complexes comprising EDTA, complexes comprising rotaxanes, and mixtures thereof. Step (b) may be achieved by a number of standard techniques known in the art, including wet impregnation, spray drying, rotary evaporation, milling, powder mixing, melt infiltration. Other ways of achieving step (b) are envisaged, such as the use of CVD and / or CVI. The polyvalent metal precursor may be selected from acetates.

[0127] For example, the porous particle frameworks, e.g. activated carbon from a physical or chemical activation process, may be impregnated with a polyvalent metal by exposure of the carbon to a solution of a polyvalent metal precursor such as a chloride or nitrate for a predefined period, such as 24 hrs, to allow wet impregnation of the carbon with the precursor. Excess solution is filtered off and then the resulting wet cake is dried off at 70-80 °C overnight. The resulting solid is then placed in a suitable reactor such as a tube furnace, that can then be heated to a high temperature (such as 750°C) to allow decomposition of the precursor under an inert atmosphere. The material is then recovered and stored in a sealed container, drying oven or dessicator.

[0128] In another example, porous particle frameworks may be milled in a solvent to a desired size in the presence of a polyvalent metal precursor in solution then recovered by spray drying the resulting suspension at a temperature higher than the boiling point of the solvent, such as to transfer the polyvalent metal precursor to the pores of the frameworks. The frameworks with impregnated polyvalent metal can then be heat treated as above to liberate the desired dopant form.

[0129] In another example, the incipient wetness technique may be used to load the porous particle frameworks with a polyvalent metal precursor. A predefined quantity of polyvalent metal precursor is dissolved in a predetermined amount of solvent, determined by the porous volume of the frameworks. Excess solvent is removed by heating and subsequently volatile species are removed using calcination under N2 atmosphere. The resulting impregnated frameworks powders are recovered as described above. Step (c) includes depositing elemental silicon and / or elemental germanium in the pores of the porous particle frameworks. Step (c) typically comprises contacting the porous particle frameworks with a silicon-containing precursor and / or a germanium-containing precursor, most preferably a silicon-containing precursor, at a temperature effective to cause deposition of elemental silicon and / or elemental germanium, most preferably elemental silicon, in the pores of the porous particle frameworks.

[0130] Step (c) is suitably performed via chemical vapor infiltration (CVI) of a gaseous silicon- and / or germanium-containing precursor into the pore structure of the porous particle frameworks. As used herein, CVI refers to processes in which a gaseous precursor is thermally decomposed on a surface to form elemental silicon and / or germanium at the surface and gaseous by-products.

[0131] Suitable gaseous silicon-containing precursors include silane (SiH4), disilane (Si2He), trisilane (SisHs), tetrasilane (Si4H ), pentasilane (SisHi2), hexasilane (SieH^), methylsilane (CHsSiHs), dimethylsilane ((CHs Sib^), or chlorosilanes such as trichlorosilane (HSiCh) or dichlorosilane (H2SiCl2) or chlorosilane (HsSiCI), or methylchlorosilanes such as methyltrichlorosilane (CHsSiC ) or dimethyldichlorosilane ((CHs^SiCfe). Preferably the silicon-containing precursor is selected from the group consisting of silane (Si H4), disilane (Si2He), trisilane (SisHs), tetrasilane (Si4H ). A particularly preferred precursor of silicon is silane.

[0132] Suitable gaseous germanium-containing precursors include germane (GeH4), hexamethyldigermanium ((CH3)sGeGe(CHs)3), tetramethylgermanium ((CHs^Ge), tributylgermanium hydride ([CH3(CH2)s]3GeH), triethylgermanium hydride ((C2H5)sGeH), and triphenylgermanium hydride ((CsHs GeH). Preferably the germanium-containing precursor is germane.

[0133] 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.

[0134] 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 precursors in step (c) may be used either in pure form (or substantially pure form) or as a diluted mixture with an inert carrier gas, such as nitrogen or argon. Preferably step (c) comprises contacting the porous particle 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 precursor based on the total volume of the gas.

[0135] The presence of oxygen in step (c) should be avoided to prevent undesired oxidation of the deposited electroactive material, in accordance with conventional procedures for working in an inert atmosphere. Preferably, the oxygen content is less than 0.01 vol%, more preferably less than 0.001 vol% based on the total volume of gas used in step (c).

[0136] The temperature in step (c) is preferably in the range from 180 to 520 °C, or from 340 to 500 °C, or from 350 to 480 °C, or from 350 to 450 °C, or from 350 to 420 °C, or from 350 to less than 400 °C, or from 355 to 395 °C, or from 360 to 390 °C, or from 360 to 385 °C, or from 360 to 380 °C.

[0137] The pressure in step (c) is preferably in the range from 1 to 5000 kPa, more preferably 200-2000 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. Preferably, the pressure in at step (b) is 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.

[0138] The deposition of electroactive materials by CVI results in the elimination of by-products, particularly by-product gases such as hydrogen. Step (c) preferably further comprises the separation of by-products from the particles formed in step (c). 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 (c) 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 silicon and / or germanium. Either the porous particle frameworks in step (a) comprise the polyvalent metal, step (b) is performed, or both. Accordingly, the impregnated porous particle frameworks comprise the polyvalent metal from step (a) (e.g. as a naturally present impurity), comprise the polyvalent metal added in step (b), or both. More than one polyvalent metal may be present.

[0139] It will be understood that when step (c) is depositing elemental silicon, the polyvalent metal comprises a polyvalent metal which is not silicon. When step (c) is depositing elemental germanium, the polyvalent metal comprises a polyvalent metal which is not germanium.

[0140] For the avoidance of doubt, the term “polyvalent metal” includes elements which may be classified in some literature as “metalloids”, e.g. B, Si, Ge, As, Sb. In the invention, the polyvalent metal may be defined as selected from the metals and metalloids of periods 1-5 of groups 2-14, As, Sb, and mixtures thereof. The polyvalent metal is may be selected from the metals and metalloids of periods 1-5 of group 2, B, periods 4 and 5 of groups 3-14, and mixtures thereof; preferably Mg, Ca, Sn, B, Ge, Zn, Zr, and mixtures thereof; most preferably Ca, Mg, B, Sn, and mixtures thereof.

[0141] The polyvalent metal may be selected from the metals and metalloids of periods 1-5 of group 2, periods 4 and 5 of groups 3-14, Al, Sb, and mixtures thereof; or Mg, Ca, Sn, Ge, Zn, Al, Sb, and mixtures thereof.

[0142] Mg and / or Ca are particularly preferred as the polyvalent metal. For reference, phase diagrams for binary Mg-Si and Ca-Si alloys may be found at Seth et al., RSC Adv., 2020, 10, 37327-37345 and Okamoto, Journal of Phase Equilibria and Diffusion Vol. 28 No. 42007.

[0143] Steps (a), (b), and (c) result in the formation of impregnated porous particle frameworks comprising the polyvalent metal and the silicon and / or germanium. The silicon and / or germanium is preferably in the form of nanoscale electroactive domains as described above. The particle size distribution of the porous particle frameworks in step (a) is assumed to be unchanged by the processes which form the impregnated porous particle frameworks. Accordingly, the particle size distribution parameters defined for the porous particle frameworks may also be used to define the impregnated porous particle frameworks (e.g. D50 etc.).

[0144] In the absence of any indication to the contrary, the pore structure of the impregnated porous particle frameworks (e.g. pore volume, PDnpore diameter, etc.) is defined by pore structure of the porous particle frameworks taken in isolation, i.e. as measured in the absence of any electroactive material (or any other material) occupying the pores of the porous particle frameworks. Therefore, the pore structure parameters defined for the porous particle frameworks in step (a) may also be used to define the impregnated porous particle frameworks.

[0145] The polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% and optionally >0.001 at.%, or 0.1-25 at.%, or 1-20 at.%, relative to the combined amount of polyvalent metal and silicon and / or germanium in the impregnated porous particle frameworks. When step (c) is depositing silicon, the amount of the polyvalent metal may be expressed relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks, using the same atomic percentages. For example, when step (c) is depositing silicon, the polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% and optionally >0.001 at.%, or 0.1-25 at.%, or 1-20 at.%, relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks. When step (c) is depositing silicon and germanium, the amount of the polyvalent metal may be expressed relative to the combined amount of polyvalent metal and silicon and germanium in the impregnated porous particle frameworks, using the same atomic percentages.

[0146] Expressed a different way, the polyvalent metal may be present in the impregnated porous particle frameworks at a concentration of >5 ppm, >50 ppm, >500 ppm, >1 ,100 ppm, >11,000 ppm and optionally <200,000 ppm or <100,000 ppm or <50,000 ppm, relative to the mass of the impregnated porous particle frameworks.

[0147] The impregnated porous particle frameworks preferably comprise at least one of: Mg at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Mg and silicon in the impregnated porous particle frameworks;

[0148] Ca at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Ca and silicon in the impregnated porous particle frameworks;

[0149] Sn at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sn and silicon in the impregnated porous particle frameworks;

[0150] Ge at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20at% relative to the combined amount of Ge and silicon in the impregnated porous particle frameworks; Zn at a concentration of >0.001, >0.01, >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Zn and silicon in the impregnated porous particle frameworks;

[0151] Al at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Al and silicon in the impregnated porous particle frameworks; and

[0152] Sb at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sb and silicon in the impregnated porous particle frameworks; wherein polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks. In this way, an advantageous amount of the intermetallic phase may be formed during step (d). Most preferably, the impregnated porous particle frameworks comprise Mg and / or Ca in the concentration ranges provided above.

[0153] The presence of some polyvalent metals, although suitable for forming the intermetallic phase described herein, may be undesirable for other reasons depending on the desired end-use of the composite particles. For example, some battery manufacturers may wish to minimise the concentration of certain elements to avoid deleterious side-reactions with other battery components. Accordingly, in some instances the impregnated porous particles may comprise at least one of, and optionally all of:

[0154] Fe at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Fe and silicon in the impregnated porous particle frameworks;

[0155] Co at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Co and silicon in the impregnated porous particle frameworks;

[0156] Cu at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Cu and silicon in the impregnated porous particle frameworks;

[0157] Ni at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Ni and silicon in the impregnated porous particle frameworks; and

[0158] Mn at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Mn and silicon in the impregnated porous particle frameworks.

[0159] For example, the impregnated porous particle frameworks may comprise one or both of:

[0160] Mg at a concentration of >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Mg and silicon in the impregnated porous particle frameworks; and Ca at a concentration of >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Ca and silicon in the impregnated porous particle frameworks; and at least one of, and optionally all of:

[0161] Fe at a concentration of <0.01 or <0.001 at% relative to the combined amount of Fe and silicon in the impregnated porous particle frameworks;

[0162] Co at a concentration of <0.01 or <0.001 at% relative to the combined amount of Co and silicon in the impregnated porous particle frameworks;

[0163] Cu at a concentration of <0.01 or <0.001 at% relative to the combined amount of Cu and silicon in the impregnated porous particle frameworks;

[0164] Ni at a concentration of <0.01 or <0.001 at% relative to the combined amount of Ni and silicon in the impregnated porous particle frameworks; and

[0165] Mn at a concentration of <0.01 or <0.001 at% relative to the combined amount of Mn and silicon in the impregnated porous particle frameworks; wherein polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks.

[0166] For example, the impregnated porous particle frameworks may comprise one or both of:

[0167] Mg at a concentration of 0.1-25 at% relative to the combined amount of Mg and silicon in the impregnated porous particle frameworks; and

[0168] Ca at a concentration of 0.1-25 at% relative to the combined amount of Ca and silicon in the impregnated porous particle frameworks; and at least one of, and optionally all of:

[0169] Fe at a concentration of <0.001 at% relative to the combined amount of Fe and silicon in the impregnated porous particle frameworks;

[0170] Co at a concentration of <0.001 at% relative to the combined amount of Co and silicon in the impregnated porous particle frameworks;

[0171] Cu at a concentration of <0.001 at% relative to the combined amount of Cu and silicon in the impregnated porous particle frameworks;

[0172] Ni at a concentration of <0.001 at% relative to the combined amount of Ni and silicon in the impregnated porous particle frameworks; and

[0173] Mn at a concentration of <0.001 at% relative to the combined amount of Mn and silicon in the impregnated porous particle frameworks; wherein polyvalent metal is present in the impregnated porous particle frameworks at a concentration of <30 at.% relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks. A range of different silicon and / or germanium loadings in the impregnated porous particle frameworks may be obtained. The impregnated porous particle frameworks preferably comprise at least 26 wt% silicon and / or germanium, or at least 28 wt% silicon and / or germanium, or at least 30 wt% silicon and / or germanium, or at least 32 wt% silicon and / or germanium, or at least 34 wt% silicon and / or germanium, or at least 36 wt% silicon and / or germanium, or at least 38 wt% silicon and / or germanium, or at least 40 wt% silicon and / or germanium, or at least 42 wt% silicon and / or germanium, or at least 44 wt% silicon and / or germanium. Most preferably, the impregnated porous particle frameworks comprise elemental silicon and these amounts refer to the amount of silicon.

[0174] The amount of elemental silicon and / or elemental germanium in the impregnated composite particles is preferably selected such that at least 20% and up to 90% of the internal pore volume of the porous particle frameworks is occupied by the elemental silicon and / or elemental germanium following step (c). For example, the elemental silicon and / or elemental germanium 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 porous particle frameworks. Most preferably, the impregnated porous particle frameworks comprise elemental silicon and these amounts refer to the amount of silicon. Within these preferred ranges, the remaining pore volume of the porous particle 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 particulate particles. However, the amount of electroactive material is also not so high as to impede effective lithiation due to inadequate metal-ion diffusion rates or due to inadequate expansion volume resulting in mechanical resistance to lithiation.

[0175] In the case that the impregnated porous particle frameworks comprise elemental silicon, the amount of silicon in the impregnated porous particle frameworks can be related to the available pore volume in the porous particle frameworks by the requirement that the mass ratio of silicon to the porous particle frameworks is in the range from [0.5* P1to 1.9xP1] : 1, wherein P1is a dimensionless quantity having the magnitude of the total pore volume of micropores and mesopores in the porous particle frameworks, as expressed in cm3 / g (e.g. if the porous particle 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 porous particle 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 deposited in step (c) to the porous particle frameworks is in the range from [0.6* P1to 1.8xP1] : 1 or from [0.7xP1to 1.7xP1] : 1, or from [0.8xpi to 1.6xpi] : 1. The amount of silicon in the impregnated porous particle frameworks can be determined by elemental analysis. Preferably, elemental analysis is used to determine the elemental composition of the porous particle frameworks, the impregnated porous particle frameworks, and the composite particles.

[0176] Silicon and polyvalent metal 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 impregnated porous particle frameworks and of the porous particle 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.

[0177] Preferably at least 90 wt%, more preferably at least 95 wt%, even more preferably at least 98 wt% of the elemental silicon and / or elemental germanium material in the impregnated porous particle frameworks is located within the internal pore volume of the porous particles such that there is no or very little electroactive material located on the external surfaces of the impregnated porous particle frameworks. As discussed above, deposition of electroactive material in a CVI process occurs at the surfaces of the porous particles. In view of the very high internal surface area of the porous particles, the reaction kinetics of the CVI process ensure that deposition of the electroactive material occurs almost entirely within the pores of the porous particles.

[0178] The internal deposition of the electroactive material is further improved by the requirement that the pressure in step (c) is maintained at less than 200 kPa, or within the more preferred pressure ranges discussed above.

[0179] Impregnated porous particle frameworks obtained by the process of the invention 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.

[0180] It is known in general terms that atoms at the surface of a material have different set of bonding interactions to atoms in the bulk of the material, and this difference is usually described in terms of the surface energy of the material. In the case of silicon that has been deposited by chemical vapor infiltration (CVI), the free valencies of silicon atoms at the surface generally carry hydride groups. If this hydride-terminated silicon surface is accessible to air, it reacts with oxygen to form a native oxide surface. However, surfaces that are not accessible to air remain in the hydride- terminated form.

[0181] 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:

[0182] Y = 1.875 X [(Mmax - Mmin) I Mf] x100%

[0183] 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.

[0184] 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 20 wt% of the total amount of silicon in the impregnated porous particle frameworks. Preferably at least 22 wt%, or at least 25 wt%, or at least 30 wt%, or at least 35 wt%, or at least 40 wt%, or at least 45 wt% of the silicon of the impregnated porous particle frameworks is surface silicon as determined by thermogravimetric analysis (TGA).

[0185] The fact that a significant proportion of hydride-terminated surface silicon is measurable in the particulate material even after passivation in air indicates that the composite particles contain internal silicon surfaces that are inaccessible to air. This indicates that the internal pore spaces of the porous carbon framework are first lined with silicon before being capped to form an internal void space with the hydride-terminated silicon surfaces oriented into the closed internal void space. This in turn indicates that the silicon domains have a characteristic length scale that is much smaller that the pores themselves. As the internal voids are inaccessible to electrolyte, the silicon surfaces are protected from SEI formation, thereby minimising irreversible lithium loss during the first charge cycle. Additional exposure of the electroactive material in subsequent charge-discharge cycles is also substantially prevented such that SEI formation is not a significant failure mechanism leading to capacity loss. Simultaneously, this silicon is constrained hydrostatically during lithiation enabling utilization of the voids during lithiation induced expansion.

[0186] In addition to the surface silicon content, the impregnated porous particle frameworks 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:

[0187] Z = 1.875 x [(Mf- M8OO) I Mf] X 100%

[0188] 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.

[0189] 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.

[0190] 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.

[0191] The impregnated porous particle frameworks 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. More preferably, no more than 100 m2 / g, or no more than 80 m2 / g, or no more than 60 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 in order 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 2 to 20 m2 / g.

[0192] The process may comprise, before step (d), an annealing step of annealing the impregnated porous particle frameworks at elevated temperature under an inert or reducing atmosphere.

[0193] The annealing step is associated with a number of interrelated thermally-induced processes that stabilize the silicon and / or germanium and prolong the cycle-life of the composite particles in LIBs. These processes include elimination of hydrogen from terminal Si-H and / or Ge-H bonds, volumetric contraction of Si and / or Ge domains resulting in the reopening of some pore space, and the promotion of covalent bonds between silicon and the internal surfaces of the porous particle frameworks (e.g. Si-C bonds in the case that the porous particle framework is a porous carbon particle framework).

[0194] For example, the temperature of the annealing step may be at least 450 °C, or at least 500 °C, or at least 510 °C, or at least 520 °C, or at least 540 °C, or at least 560 °C, or at least 580°C, or at least 600°C, or at least 610 °C, or at least 620 °C, or at least 630 °C, or at least 640 °C, or at least 650 °C. Preferably, the temperature of the annealing step is no more than 900 °C, or no more than 850 °C, or no more than 800 °C, or no more than 750 °C, or no more than 700 °C, or no more than 680 °C, or no more than 660 °C, or no more than 650 °C.

[0195] The temperature of the annealing step may be in the range from 200 °C to 1000 °C, 400 °C to 900 °C, or from 500 °C to 900 °C, or from 600 °C to 900 °C. The temperature of the annealing step may be in the range from 500 °C to 800 °C, or from 510 °C to 800 °C, or from 520 °C to 750 °C, or from 540 °C to 700 °C, or from 560 °C to 680 °C, or from 580 °C to 660 °C, or from 600 °C to 650 The temperature of the temperature of the annealing step may be greater than the temperature in step (c). Preferably, the temperature of the annealing step is at least 20 °C, or at least 40 °C, or at least 60 °C, or at least 80 °C, or at least 100 °C, or at least 120 °C, or at least 140 °C, or at least 150 °C greater than the temperature in step (c).

[0196] The duration of the annealing step is preferably at least 1 minute, or at least 2 minutes, or at least 5 minutes, or at least 10 minutes, or at least 15 minutes, or at least 20 minutes, or at least 30 minutes, or at least 45 minutes, or at least 1 hour, or at least 2 hours. Preferably, the duration of the annealing step is no more than 72 hours, or no more than 48 hours, or no more than 24 hours, or no more than 12 hours, or no more than 6 hours, or no more than 5 hours, or no more than 4 hours, or no more than 3 hours.

[0197] The duration of the annealing step may be in the range from 1 minute to 72 hours, or from 2 minutes to 48 hours, or from 5 minutes to 24 hours, or from 10 minutes to 12 hours, or from 15 minutes to 6 hours, or from 20 minutes to 5 hours, or from 30 minutes to 4 hours, or from 1 hour to 4 hours, or from 1 hour to 3 hours.

[0198] The annealing step is carried out under an inert or reducing atmosphere. Preferably, the atmosphere is selected from a nitrogen atmosphere, or an atmosphere comprising hydrogen, or a noble gas atmosphere, or mixtures thereof.

[0199] Preferably, the annealing step is carried out at a temperature in the range in the range from 400 °C to 900 °C and for a period of from 1 minute to 72 hours. Or at a temperature in the range in the range from 500 °C to 900 °C and for a period of from 30 minutes to 4 hours. Or at a temperature in the range in the range from 600 °C to 900 °C for a period of from 1 hour to 4 hours.

[0200] The ratio of BET surface area of the particles formed after the annealing step to BET surface area of the impregnated porous particle frameworks may be at least 1.1:1, or at least 1.2:1, or at least 1.3:1, or at least 1.4:1 , or at least 1.5:1 , or at least 2:1, or at least 3:1, or at least 4:1, or at least 5:1.

[0201] The ratio of BET surface area of the particles formed after the annealing step to BET surface area of the impregnated porous particle frameworks may be no more than 15:1 , or no more than 14:1 , or no more than 13: 1 , or no more than 12:1. The ratio of total pore volume of micropores and mesopores as measured by gas adsorption of the particles formed after the annealing step to total pore volume of micropores and mesopores as measured by gas adsorption of the impregnated porous particle frameworks may be at least 2:1 , or at least 3:1 , or at least 4:1 , or at least 5:1 , or at least 6:1 , or at least 7:1, or at least 8:1.

[0202] The ratio of total pore volume of micropores and mesopores as measured by gas adsorption of the particles formed after the annealing step to total pore volume of micropores and mesopores as measured by gas adsorption of the impregnated porous particle frameworks may be no more than 20:1, or no more than 19:1, or no more than 18:1 , or no more than 17:1 , or no more than 16:1, or no more than 15:1.

[0203] The ratio of total hydrogen content of the particles formed after the annealing step to total hydrogen content of the impregnated porous particle frameworks may be no more than 0.8:1, or no more than 0.7:1, or no more than 0.6: 1 , or no more than 0.5: 1.

[0204] The ratio of total hydrogen content of the particles formed after the annealing step to total hydrogen content of the impregnated porous particle frameworks may be at least 0.1 :1 , or at least 0.2:1, or at least 0.3:1.

[0205] The process may comprise, before step (d), a passivating step of contacting the impregnated porous particle frameworks with a passivating agent.

[0206] As defined herein, a passivating agent is a compound or mixture of compounds which is able to react with the surface of the silicon and / or germanium deposited in step (c) 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.

[0207] Preferably, the passivating step is carried out after the annealing step. As discussed above, one effect of the annealing step is to reopen pore spaces that were previously obstructed or capped by silicon nanostructures, such that the pore spaces are accessible to passivating gases, thus allowing for a more extensive passivation of the silicon surfaces and the elimination of hydrogen- terminated silicon surfaces.

[0208] A preferred type of passivation layer is a native oxide layer. A native oxide layer may be formed, for example, by exposing the silicon and / or germanium 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. 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 impregnated porous particles to a temperature below 300 °C, preferably below 200 °C, optionally below 100 °C, prior to contacting with the oxygen-containing gas.

[0209] The passivating agent may be liquid water or a gas comprising water vapour. The passivating step may comprise contacting the impregnated porous particle frameworks with liquid water or a gas comprising water vapour at a temperature of at least 30 °C and optionally less than 400°C or less than 300°C.

[0210] The passivating step preferably comprises a first step of contacting the impregnated porous particle frameworks with an oxygen-containing gas at a temperature less than 300 °C and a second step of contacting the frameworks resulting from the first step with liquid water or a gas comprising water vapour at a temperature of at least 30 °C and optionally less than 400°C or preferably less than 300°C.

[0211] Another type of passivation layer is a nitride layer that is formed, for example, by exposing the silicon and / or germanium 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 and / or germanium 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 Si Nx, 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 and / or germanium 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 and / or germanium 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.

[0212] Other suitable passivating agents 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:

[0213] (i) R1-CH=CH-R1;

[0214] (ii) R1-C=C-R1; and

[0215] (iii) O=CR1R1; wherein each R1independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having from 1 to 20 carbon atoms, or wherein two R1groups form an unsubstituted or substituted ring structure comprising from 3 to 8 carbon atoms in the ring.

[0216] Particularly preferred passivating agents include one or more compounds of the formulae:

[0217] (i) CH2=CH-R1; and

[0218] (ii) HC=C-R1; wherein R1is as defined above. Preferably, R1is unsubstituted.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] Suitable passivating agents in this category include compounds of the formula

[0223] (iv) HX-R2, and

[0224] (v) HX-C(O)-R1, wherein X represents O, S, NR1or PR1; each R1is independently as defined above; and R2represents an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having from 1 to 20 carbon atoms, or R1and R2together form an unsubstituted or substituted ring structure comprising from 3 to 8 carbon atoms in the ring.

[0225] Preferably X represents O or NH.

[0226] Preferably R2represents 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.

[0227] Contacting the impregnated porous particle frameworks 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.

[0228] The process may further comprise, before step (d), a depositing step of depositing a lithium-ion permeable material into the pores and / or onto the outer surface of the impregnated porous particle frameworks. In this way, the intermetallic phase will be formed in step (d) within a shell of the lithium-ion permeable material, thus protecting the intermetallic phase from subsequent dissolution in an electrolyte. This minimises the risk of lithium plating and dendrite formation. Preferably, the lithium-ion permeable material is a pyrolytic carbon material and the depositing step comprises combining the impregnated porous particle frameworks 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 impregnated porous particle frameworks. In the case that the annealing step is included in the process, the depositing step may optionally be performed before or after the annealing step. If the passivating step is performed, most preferably the depositing step is performed after the passivating step.

[0229] The pyrolytic carbon precursor is preferably a hydrocarbon. Suitable hydrocarbons include polycyclic hydrocarbons comprising from 10 to 25 carbon atoms and optionally from 1 to 3 heteroatoms, optionally wherein the polyaromatic hydrocarbon is selected from naphthalene, substituted naphthalenes such as di-hydroxynaphthalene, anthracene, tetracene, pentacene, fluorene, acenapthene, phenanthrene, fluoranthrene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone and alkyl-substituted derivatives thereof. Suitable pyrolytic carbon precursors also include bicyclic monoterpenoids, optionally wherein the bicyclic monoterpenoid is selected from camphor, borneol, eucalyptol, camphene, careen, sabinene, thujene and pinene. Further suitable pyrolytic carbon precursors include C2-C10 hydrocarbons, optionally wherein the hydrocarbons are selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, and arenes, for example methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, a-terpinene and acetylene. Other suitable pyrolytic carbon precursors include phthalocyanine, sucrose, starches, graphene oxide, reduced graphene oxide, pyrenes, perhydropyrene, triphenylene, tetracene, benzopyrene, perylenes, coronene, and chrysene. A preferred carbon precursor is acetylene.

[0230] 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.

[0231] 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.

[0232] 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 impregnated porous particle frameworks are not exposed to another passivating agent prior to contact with styrene. In this case, passivation and deposition of the conductive carbon material in steps may be carried out simultaneously, for example at a temperature in the range of from 300-700 °C. Alternatively, passivation and deposition of the conductive carbon material may be carried out sequentially, with the same material as the passivating agent and the pyrolytic carbon precursor, but wherein the depositing step is carried out at a higher temperature than, and following, the passivating step. For example, passivation may be carried out at a temperature in the range of from 25 °C to less than 300 °C, and deposition of pyrolytic carbon may be carried out at a temperature in the range from 300-700 °C. These two steps may suitably be carried out sequentially by increasing the temperature while maintaining contact with the compound that functions as both a passivating agent and the pyrolytic carbon precursor. At lower temperatures (e.g. in the range of 25 °C to <300 °C) passivation will be the primary process. As the temperature is increased (e.g. to 300-700 °C) the deposition of pyrolytic carbon will ensue.

[0233] Step (d) involves contacting the impregnated porous particle frameworks with a monovalent metal. The monovalent metal is typically selected from Li, Na, K, Rb, and mixtures thereof. Preferably, the monovalent metal is Li or Na, as these metals are routinely used as charge-carriers in lithium-ion and sodium-ion batteries. Most preferably, the monovalent metal is Li. However, as noted above, the impregnated porous particles are themselves a convenient intermediate material for manufacturing composite particles for metal-ion batteries. Thus, step (d) may be omitted and the impregnated porous particles may be provided for subsequent downstream use.

[0234] Preferably, step (d) comprises contacting the impregnated porous particle frameworks with an electrolyte comprising the monovalent metal. A suitable electrolyte is a non-aqueous electrolyte containing a monovalent metal, e.g. in the form of a lithium salt, and may include, without limitation, non-aqueous electrolytic solutions, organic solid electrolytes, and inorganic solid electrolytes. Examples of non-aqueous electrolyte solutions that can be used include non-protic organic solvents such as propylene carbonate, ethylene carbonate, butylene carbonates, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, 1 ,2-dimethoxyethane, 2- methyltetrahydrofuran, dimethylsulfoxide, 1 ,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triesters, trimethoxymethane, sulfolane, methyl sulfolane and 1 ,3-dimethyl-2-imidazolidinone.

[0235] 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.

[0236] Examples of inorganic solid electrolytes include nitrides, halides and sulfides of lithium salts such as LisNl2, LisN, Lil, LiSiC , Li2SiSs, Li4SiC>4, LiOH and U3PO4.

[0237] The lithium salt is suitably soluble in the chosen solvent or mixture of solvents. Examples of suitable lithium salts include LiCI, LiOH, LiBr, Lil, LiCICU, LiBF4, UBC4O8, LiPFe, UCF3SO3, LiAsFe, LiSbFe, LiAICU, CH3SO3U and CF3SO3LL Equivalent sodium salts may be used.

[0238] In another approach, step (d) may comprise chemically introducing the monovalent metal. Thus, step (d) may comprise contacting the impregnated porous particle frameworks with a monovalent metal precursor. The monovalent metal precursor may be a salt, complex, or organic compound of the monovalent metal. For example, the monovalent metal precursor may be selected from oxides, carbonates, nitrates, hydroxides, hydrides, sulphates, carboxylates, halides, oxalates, bisoxalatoborates, bis(trifluoromethanesulfonyl)imides, citrates, phosphates, complexes comprising EDTA, complexes comprising rotaxanes, organolithium compounds, and mixtures thereof. For example, step (d) may comprise contacting the impregnated porous particle frameworks with an organolithium compound such as butyl lithium, preferably ‘Bu Li, or with LiAIH4. The monovalent metal precursor may be selected from acetates.

[0239] Step (d) involves applying an electric potential. When an appropriate electric potential is applied to electroactive material such as silicon in the presence of a monovalent metal such as Li, an insertion or lithiation reaction occurs resulting in the formation of an intermetallic phase comprising Si and Li, sometimes known as a zintl phase. LiisSi4 (LisjsSi) is formed at maximum levels of Li insertion. In an electrochemical cell a reverse potential is applied to cause delithiation, e.g. forming Lis.75-xSi. Reversing the potential again allows for the cell to be charged and discharged.

[0240] In the invention, due to the presence of the polyvalent metal, applying the electric potential results in the formation of an intermetallic phase comprising silicon and / or germanium, the monovalent metal, and the polyvalent metal. The intermetallic phase is thought to be formed following a coinsertion reaction of e.g. Li and Mg into Si. Ion exchange reactions may also occur to form the intermetallic phase, e.g. ion exchange of Mg with fully or overlithiated binary domains (Li3.75+xSi). For example, when the polyvalent metal is Mg, a Li3.55Mgo.1Si phase may be formed. Reversing the potential in a cell causes delithiation, e.g. forming Li3.55-xMgo.1Si, and the cell may be charged and discharged accordingly. The intermetallic phase is believed to be more stable than the binary silicon and / or germanium alloys formed when typical composite particles are lithiated in a battery, resulting in fewer reactions with both liquid and solid electrolytes.

[0241] It is particularly preferred that step (d) is achieved as part of a battery formation cycle. As is widely known, once a battery is assembled but before it is suitable to be used, it is subjected to at least one controlled charge / discharge cycle, known as the formation cycle. A number of reactions take place during the formation cycle, typically between the electrolyte and the anode (forming the anode solid electrolyte interface SEI), between the electrolyte and the cathode (forming the cathode electrolyte interface CEI), and between the charge-carrier (e.g. Li or Na) and the electroactive materials. Since a formation cycle is already implemented in battery manufacture, implementing step (d) as part of this cycle is advantageous because it minimises modifications required of battery manufacturing processes. Contacting the impregnated porous particle frameworks with a monovalent metal is achieved during a formation cycle via monovalent metal present in the electrolyte, e.g. a Li-containing electrolyte, and / or monovalent metal present in the positive electrode, e.g. a Li-containing cathode (or Na-equivalents when the invention is implemented in the context of Na-ion batteries). Applying the electric potential effective to cause the formation of the intermetallic phase is also achieved during a formation cycle. Thus, the impregnated porous particle frameworks can be used as a “drop-in” solution in place of existing composite particles, before the existing formation cycle is performed, forming the desired intermetallic phase as part of the existing process.

[0242] Accordingly, the process of the first aspect of the invention preferably includes, before step (d), a step of forming an electrochemical cell such as a rechargeable metal-ion battery comprising an anode comprising the impregnated porous particle frameworks, a cathode, and an electrolyte between the anode and cathode; where the cathode and / or the electrolyte comprises the monovalent metal. Step (d) is then achieved as part of a formation cycle of the electrochemical cell.

[0243] Another advantageous process for achieving step (d), where the impregnated porous particles may be used as a drop-in solution, is when electrodes are pre-lithiated before they are incorporated into Li-ion batteries (or pre-sodiated, before they are incorporated into Na-ion batteries). An electrode is typically in the form of a composition comprising an active material deposited on a current collector, such as copper or aluminium foil. Electrodes may be pre-lithiated to compensate in advance for lithium which will be lost during initial cycling, e.g. formation cycling. Pre-lithiation may be achieved by electrochemical methods, and the electric potential applied during these methods may be utilised as the electric potential in step (d). For example, one electrochemical process is when an electrode is placed in an electrolytic bath of a Li-containing electrolyte. This process may be implemented in a roll-to-roll process wherein an electrode layer is passed through the electrolyte bath. Other electrochemical processes include when a cell is formed comprising the electrode, an electrolyte, and a Li-containing counter electrode such as a metallic Li foil, and the cell polarised. Direct contact methods are also envisaged where a metallic Li foil is placed in direct contact with the electrode, and polarised. Since each of these pre-lithiation processes includes contacting the electrode with lithium and applying an electric potential, step (d) may be implemented as part of each of these processes, thus working the invention without the requirement for additional manufacturing steps. Equivalents to each of these processes for pre- sodiation may be used when the invention is applied in the context of Na-ion batteries.

[0244] A specific example of a pre-lithiation process is where an electrode composition comprising a silicon-containing electroactive material is coated onto one or both sides of a current collector, e.g. copper foil, to form an electrode. The electrode is mounted on a frame between carbon counter electrodes with a 2 cm spacing. The system is bathed in a non-aqueous solvent such as gammabutyrolactone contain 0.5 M lithium salt such as LiCI, and typically held at room temperature (25 °C). CO2 may be bubbled through the system. A reducing current density of 0.9 mA / cm2is applied for 150 seconds with a cell-voltage of 6V, followed by a rest period of 30 seconds at 0V. Four such cycles are carried out, followed by a forward / reverse cycle where the rest period is substituted by a current reversal (oxidation) step with a current density of 1.0 mAh / cm2for 30 seconds. The forward / reverse pulsing is repeated until a desired lithium dosage to the electrode composition is achieved.

[0245] Accordingly, the process of the first aspect of the invention preferably includes, before step (d), a step of forming an electrode comprising the impregnated porous particles deposited on a current collector. Step (d) is preferably achieved as part of an electrochemical pre-lithiation or pre- sodiation step of the electrode. The electrode is then typically used as an anode for a lithium-ion or sodium-ion battery. In general, the electric potential used in formation cycling and pre-lithiation described above will be effective to cause the formation of the intermetallic phase. Effective conditions include a constant current I constant voltage cycle at C / n, wherein n>5, with a lower cut-off of voltage of >10 mV.

[0246] It is envisaged that step (d) may also be performed separately from a formation cycle or a pre- lithiation step. For example, the impregnated porous particles may be deposited onto an electrode, step (d) performed, and the resulting composite particles recovered from the electrode for use in downstream processes.

[0247] Step (d) results in the formation of an intermetallic phase which comprises the polyvalent metal, silicon and / or germanium, and the monovalent metal. It will be understood that the polyvalent metal is present in addition to the silicon and / or germanium. When the intermetallic phase comprises silicon, it comprises a polyvalent metal which is not silicon. When the intermetallic phase comprises germanium, it comprises a polyvalent metal which is not germanium.

[0248] The intermetallic phase is preferably an alloy of the polyvalent metal, silicon and / or germanium, and the monovalent metal. Further elements may be incorporated into the intermetallic phase, including H, Li, Na, K, Rb, N, P, S, and mixtures thereof; or H, N, P, S, and mixtures thereof; or H, P, and mixtures thereof. These further elements may be present in the porous particle frameworks and may be incorporated into the intermetallic phase when it is formed during step (d). Moreover, H may be introduced during step (c) as the deposition of elemental silicon and / or elemental germanium often results in the formation of hydride-terminated surfaces (e.g. Si-H).

[0249] The presence of the intermetallic phase can be verified by a variety of standard techniques. These include ion etching with scanning spreading resistance microscopy (SSRM), raman spectroscopy, XPS, HAADF-TEM, TEM-EDS, and solid-state NMR (e.g.7Li and / or29Si NMR); preferably XPS and solid-state NMR.

[0250] Mg is a particularly preferred polyvalent metal. It is relatively small. Mg2+cations have an ionic radius comparable Li+cations. Accordingly, the use of Mg as the polyvalent metal is believed to favour a uniform reaction throughout the bulk of the elemental silicon and / or germanium of the impregnated porous particle frameworks, thus forming a uniform intermetallic phase.

[0251] Ca is another particularly preferred polyvalent metal. Ca2+cations have a larger ionic radius than Mg2+and Li+. Therefore, it is believed to favour a reaction at the surface of the elemental silicon and / or germanium of the impregnated porous particle frameworks, thus forming a surface-enriched layer of intermetallic phase.

[0252] The intermetallic phase forms from the polyvalent metal and the elemental silicon and / or elemental germanium present in the impregnated porous particle frameworks, and the monovalent metal present in step (d). The intermetallic phase is itself an electroactive material, so the invention encompasses processes where all the elemental silicon and / or elemental germanium in the impregnated porous particle frameworks is consumed to form the intermetallic phase. However, although the resulting composite particles may have excellent lifetime, this comes with a penalty in capacity as the intermetallic phase has reduced capacity compared to the parent electroactive material, e.g. elemental silicon. Therefore, most preferably, the composite particles comprise elemental silicon and / or elemental germanium and the intermetallic phase. This may be achieved by controlling the amount of polyvalent metal in the impregnated porous particles such that formation of the intermetallic phase cannot consume all of the silicon and / or germanium. Here, the intermetallic phase may be intimately bonded to the elemental silicon and / or elemental germanium.

[0253] Since elemental silicon and / or elemental germanium is deposited the pores of the porous particle frameworks, typically the intermetallic phase will be present in the pores of the composite particles. However, as discussed below, the elemental silicon and / or elemental germanium may be further deposited on the outer surface of the porous particle frameworks, such that the intermetallic phase may be present on the outer surface of the composite particles.

[0254] Step (d) results in the formation of composite particles comprising a porous particle framework comprising micropores and / or mesopores; and an intermetallic phase comprising a polyvalent metal, silicon and / or germanium, and a monovalent metal. The particle size distribution of the porous particle frameworks in step (a) is assumed to be unchanged by the processes which form the composite particles. Accordingly, the particle size distribution parameters defined for the porous particle frameworks in step (a) may also be used to define the composite particles (e.g. D50 etc.).

[0255] In the absence of any indication to the contrary, the pore structure of the composite particles (e.g. pore volume, PDnpore diameter, etc.) is defined by pore structure of the porous particle frameworks taken in isolation, i.e. as measured in the absence of any electroactive material (or any other material) occupying the pores of the porous particle frameworks. Therefore, the pore structure parameters defined for the porous particle frameworks in step (a) may also be used to define the impregnated porous particle frameworks. It is believed that the polyvalent metal in the impregnated porous particle frameworks is retained in the composite particles following the formation of the intermetallic phase. Thus, the elemental composition of the composite particles may be defined using the same values given herein for the impregnated porous particle frameworks. For example, the amount of the polyvalent metal in the composite particles may be expressed relative to the combined amount of polyvalent metal and silicon in the composite particles using the same values given herein relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks.

[0256] Similarly, the silicon and / or germanium loadings in the composite particles may be defined using the same values given herein for the impregnated porous particle frameworks.

[0257] The elemental silicon and / or elemental germanium is deposited in the pores of the porous particle frameworks, i.e. within the micropores and / or mesopores, because this favours the formation of small domains with dimensions of the order of a few nanometres or less. The small domains are thought be able to lithiate and delithiate without excessive structural stress. Moreover, the unoccupied pore volume of the porous particle framework is able to accommodate a substantial amount of electroactive material expansion internally. In general, it has been considered undesirable to deposit electroactive material on the outer surface of porous particle frameworks, as here the formation of small domains is less favoured. Instead, larger bulky or course domains are favoured, which are thought to underdo more structural stress during lithiation and delithiation. However, this places limitations on the amount of electroactive material which can be deposited in the frameworks. At higher loadings of electroactive material deposition on the outer surface becomes increasingly favoured (“overfilling”). The invention provides a way to alleviate this problem, minimising the deleterious effect of bulky outer surface domains of electroactive material, thus allowing for higher loadings while maintain lifetime.

[0258] In particular, when the elemental silicon and / or elemental germanium is also deposited on the outer surface of the porous particle frameworks, the presence of the polyvalent metal results in the formation of the intermetallic phase on the outer surface of the frameworks, thereby reducing the instability of the bulky outer surface domains of silicon and / or germanium. This provides a way to improve the lifetime of “overfilled” composite particles while maintaining the advantage of the higher capacity provided by the higher loading of electroactive material. Further advantages are that the intermetallic phase on the outer surface of the frameworks provides a convenient alternative to carbon coatings typically used to reduce outer surface reactivity. The outer surface intermetallic phase may also serve to reduce the surface area, reducing the level of side-reactions with the electrolyte and other electrode components.

[0259] Accordingly, the process of the first aspect may be implemented in such a way that step (c) further comprises depositing elemental silicon and / or elemental germanium on the outer surface of the porous particle frameworks; and the intermetallic phase in step (d) is formed on the outer surface of the porous particle frameworks. This may be achieved when the porous particle frameworks in step (a) comprise the polyvalent metal at their outer surface. This may also be achieved when step (b) is performed to impregnate the outer surface of the porous particle frameworks with the polyvalent metal. Preferably, when step (b) is performed in this way, a polyvalent metal precursor is deposited on the outer surface of the porous particle frameworks, and the annealing step is performed. The annealing step causes the reduction of the polyvalent metal precursor, which favours the formation of the intermetallic phase in step (d).

[0260] Preferably, when the process of the first aspect is implemented in such a way that step (c) further comprises depositing elemental silicon and / or elemental germanium on the outer surface of the porous particle frameworks; and the intermetallic phase in step (d) is formed on the outer surface of the porous particle frameworks, the porous particle frameworks are porous carbon particle frameworks where the micropore volume fraction is at least 0.5, or at least 0.55, or at least 0.6, based on the total volume of micropores and mesopores in the porous particle frameworks. More preferably, the porous particle frameworks are porous carbon particle frameworks comprising micropores and optionally mesopores wherein:

[0261] P1is the total volume of micropores and mesopores in the porous carbon particle frameworks expressed in cm3 / g, wherein P1is at least 0.35 and optionally less than 2.5; and

[0262] VP07, VP2, VP5, and VP20 are respectively the volume of pores in the porous carbon particle frameworks with a pore diameter of 0.7 nm or less, 2.0 nm or less, 5.0 nm or less, and 20.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35%, VP2 is in the range of 40-90%, and VP20-VP5 is less than 20%; optionally the micropore volume of the porous carbon particle frameworks is at least 0.3 cm3 / g; wherein P1, VP07, VP2, VP5, VP20, and the micropore volume are measured by nitrogen gas adsorption.

[0263] The process of the first aspect may be performed according to the following variants: In order: step (a), optional step (b), step (c), the passivating step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d).

[0264] In order: step (a), step (c), optional step (b), the passivating step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d).

[0265] In order: step (a), optional step (b), step (c), the annealing step, the passivating step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d).

[0266] In order: step (a), optional step (b), step (c), the passivating step, the annealing step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d).

[0267] In order: step (a), step (c) further comprising depositing elemental silicon and / or elemental germanium on the outer surface of the porous particle frameworks, optional step (b), the passivating step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d) where the intermetallic phase is formed on the outer surface of the porous particle frameworks.

[0268] In order: step (a), step (c) further comprising depositing elemental silicon and / or elemental germanium on the outer surface of the porous particle frameworks, optional step (b), the annealing step, the passivating step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d) where the intermetallic phase is formed on the outer surface of the porous particle frameworks.

[0269] In order: step (a), optional step (b), step (c), the passivating step, the depositing step, the annealing step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d).

[0270] In order: step (a), optional step (b), step (c), the passivating step, the annealing step, the depositing step, forming an electrode comprising the impregnated porous particles, optionally forming an electrochemical cell comprising the electrode, step (d). The impregnated porous particle frameworks or the composite particles (e.g. if recovered after step (d) and not already part of an electrode) may be incorporated into a composition comprising at least one other component. In particular, there is provided a composition comprising the impregnated porous particle frameworks or the 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.

[0271] The composition may be a hybrid electrode composition which comprises the impregnated porous particle frameworks or 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.

[0272] 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 impregnated porous particle frameworks or 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.

[0273] The at least one additional particulate electroactive material preferably has a D50 particle diameter in the range from 10 to 50 pm, preferably from 10 to 40 pm, more preferably from 10 to 30 pm and most preferably from 10 to 25 pm, for example from 15 to 25 pm.

[0274] The D10 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.

[0275] 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.

[0276] 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.

[0277] 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.

[0278] 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 impregnated porous particle frameworks or the composite particles, based on the total dry weight of the composition.

[0279] 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.

[0280] 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.

[0281] 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.

[0282] 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.

[0283] 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.

[0284] The invention also provides an electrode comprising the impregnated porous particle frameworks or the composite particles and a current collector, wherein the impregnated porous particle frameworks or 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 impregnated porous particle frameworks or the composite particles at least one other component defined above.

[0285] 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 impregnated porous particle frameworks or 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.

[0286] The electrode may be fabricated by combining the impregnated porous particle frameworks or 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.

[0287] The electrode may be used as the anode of a metal-ion battery. Thus, the present invention provides a rechargeable metal-ion battery comprising the electrode as the anode. The metal ions are preferably lithium ions. More preferably, the rechargeable metal-ion battery is a lithium-ion battery.

[0288] The cathode of the rechargeable metal-ion battery typically comprises a current collector and a cathode active material capable of releasing and reabsorbing metal ions. The cathode active material is preferably a metal oxide-based composite. Examples of suitable cathode active materials include LiCoC>2, LiCo0.99AI0.01O2, LiNiC>2, LiMnO2, LiCo0.5Ni0.5O2, LiCo0.7Ni0.3O2, LiCo0.8Ni0.2O2, LiCo0.82Ni0.i8O2, LiCo0.8Ni0.15AI0.05O2, LiNi0.4Co0.3Mn0.3O2 and LiNi0.33Co0.33Mn0.34O2. The cathode current collector is generally of a thickness of between 3 to 500 pm. Examples of materials that can be used as the cathode current collector include aluminium, stainless steel, nickel, titanium and sintered carbon.

[0289] Suitable electrolytes for rechargeable metal-ion batteries have been described above in connection with the step of contacting the impregnated porous particle frameworks with an electrolyte comprising the monovalent metal.

[0290] 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.

Claims

Claims1. A process for preparing composite particles for use as an electroactive material for a metal-ion battery, the process comprising the steps of:(a) providing porous particle frameworks comprising micropores and / or mesopores and optionally a polyvalent metal;(b) optionally impregnating the porous particle frameworks with a polyvalent metal;(c) depositing elemental silicon and / or elemental germanium in the pores of the porous particle frameworks; wherein either the porous particle frameworks in step (a) comprise the polyvalent metal, step (b) is performed, or both; thereby providing impregnated porous particle frameworks comprising the polyvalent metal and the silicon and / or germanium; and(d) contacting the impregnated porous particle frameworks with a monovalent metal while applying an electric potential effective to cause the formation of an intermetallic phase which comprises the polyvalent metal, silicon and / or germanium, and the monovalent metal; thereby providing the composite particles.

2. The process of claim 1 , wherein step (b) is performed before step (c).

3. The process of claim 1 , wherein step (b) is performed after step (c).

4. The process of any preceding claim, wherein step (c) is depositing elemental silicon in the pores of the porous particle frameworks.

5. The process of any preceding claim, wherein the polyvalent metal is selected from: the metals and metalloids of periods 1-5 of groups 2-14, As, Sb, and mixtures thereof; or the metals and metalloids of periods 1-5 of group 2, B, periods 4 and 5 of groups 3-14, and mixtures thereof; orMg, Ca, B, Sn, Ge, Zn, Zr, and mixtures thereof; orMg, Ca, B, Sn, and mixtures thereof; or Mg, Ca, and mixtures thereof.

6. The process of any preceding claim, wherein the polyvalent metal is Mg.

7. The process of any preceding claim, wherein the polyvalent metal is Ca.

8. The process of any preceding claim, any preceding claim, wherein the intermetallic phase further comprises:H, Li, Na, K, Rb, N, P, S, and mixtures thereof; orH, N, P, S, and mixtures thereof; orH, P, and mixtures thereof.

9. The process of any preceding claim, wherein step (b) comprises impregnating the porous particle frameworks with a polyvalent metal precursor; optionally wherein the polyvalent metal precursor is a salt or complex of the polyvalent metal; optionally wherein the polyvalent metal precursor is selected from oxides, carbonates, acetates, nitrates, hydroxides, hydrides, sulphates, carboxylates, halides, oxalates, bisoxalatoborates, bis(trifluoromethanesulfonyl)imides, citrates, phosphates, complexes comprising EDTA, complexes comprising rotaxanes, and mixtures thereof.

10. The process of any preceding claim, wherein the polyvalent metal is present in the impregnated porous particle frameworks at a concentration of >5 ppm, >50 ppm, >500 ppm, >1 ,100 ppm, >11,000 ppm and optionally <200,000 ppm or <100,000 ppm or <50,000 ppm, relative to the mass of the impregnated porous particle frameworks.

11. The process of any preceding claim, wherein the polyvalent metal is present in the impregnated porous particle frameworks at a concentration of <30 at.% and optionally >0.001 at%, or 0.1-25 at.%, or 1-20 at.%, relative to the combined amount of polyvalent metal and silicon and / or germanium in the impregnated porous particle frameworks.

12. The process of any preceding claim, wherein step (c) is depositing elemental silicon in the pores of the porous particle frameworks, and the polyvalent metal is present in the impregnated porous particle frameworks at a concentration of no more than 30 at.% and optionally >0.001 at%, or 0.1-25 at.%, or 1-20 at.%, relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks.

13. The process of any preceding claim, wherein the impregnated porous particle frameworks comprise at least one of:Mg at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Mg and silicon in the impregnated porous particle frameworks;Ca at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Ca and silicon in the impregnated porous particle frameworks;Sn at a concentration of >0.001, >0.01, >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sn and silicon in the impregnated porous particle frameworks;Ge at a concentration of >0.001, >0.01, >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20at% relative to the combined amount of Ge and silicon in the impregnated porous particle frameworks;Zn at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Zn and silicon in the impregnated porous particle frameworks;Al at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Al and silicon in the impregnated porous particle frameworks; andSb at a concentration of >0.001, >0.01, >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sb and silicon in the impregnated porous particle frameworks; wherein polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% relative to the combined amount of polyvalent metal and silicon in the impregnated porous particle frameworks.

14. The process of any preceding claim, wherein the impregnated porous particles comprise at least one of, and optionally all of:Fe at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Fe and silicon in the impregnated porous particle frameworks;Co at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Co and silicon in the impregnated porous particle frameworks;Cu at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Cu and silicon in the impregnated porous particle frameworks;Ni at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Ni and silicon in the impregnated porous particle frameworks; andMn at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Mn and silicon in the impregnated porous particle frameworks.

15. The process of any preceding claim wherein step (b) comprises wet impregnation, spray drying, rotary evaporation, milling, powder mixing, or melt infiltration.

16. The process of any preceding claim, wherein step (b) is performed below 1000 °C.

17. The process of any preceding claim, wherein step (b) is performed under inert atmosphere; optionally under an atmosphere of nitrogen, CO2, a noble gas, and mixtures thereof.

18. The process of any preceding claim, wherein step (c) comprises contacting the porous particle frameworks with a silicon-containing precursor at a temperature effective to cause deposition of elemental silicon in the pores of the porous particles.

19. The process of claim 18, wherein the silicon-containing precursor is a gaseous silicon-containing precursor; optionally wherein the gaseous silicon-containing precursor is selected from silane (SiH4), disilane (Si2He), trisilane (SisHs), tetrasilane (Si4H ), methylsilane (CHsSiHs), pentasilane (SisHi2), hexasilane (SieH^), dimethylsilane ((CHs)2SiH2), and chlorosilanes such as trichlorosilane (HSiC ) or dichlorosilane (H2SiCh) or chlorosilane (HsSiCI), or methylchlorosilanes such as methyltrichlorosilane (CHsSiC ) or dimethyldichlorosilane ((CHs SiCh).

20. The process of any preceding claim, wherein step (c) comprises contacting the porous particle 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 a silicon- containing precursor based on the total volume of the gas.

21. The process of preceding claim, wherein the temperature in step (c) is in the range of 180 to 520 °C , or 340-500 °C, or 350-480 °C, or 350-450 °C, or 350-420 °C, or 350- 400 °C, or 355-395 °C, or 360-390 °C, or 360-385 °C, or 360-380 °C.

22. The process of any preceding claim, wherein the pressure in step (c) is in the range of 1-5000 kPa, or 200-2000 kPa, or 20-500 kPa, or 40-200 kPa, or 50-150 kPa, or 60- 120 kPa, or 80-100 kPa.

23. The process of any preceding claim, wherein the composite particles comprise elemental silicon and / or elemental germanium and the intermetallic phase; optionally wherein the composite particles comprise elemental silicon and / or elemental germanium in the pores of the porous particle frameworks and the intermetallic phase in the pores of the porous particle frameworks.

24. The process of claim 23, wherein the intermetallic phase is intimately bonded to the elemental silicon and / or elemental germanium.

25. The process of any preceding claim, wherein: step (c) comprises depositing elemental silicon and / or elemental germanium on the outer surface of the porous particle frameworks; and the intermetallic phase in step (d) is formed on the outer surface of the porous particle frameworks.

26. The process of any preceding claim, wherein step (c) comprises depositing nanoscale elemental silicon domains in the pores of the porous particle frameworks.

27. The process of any preceding claim, comprising, before step (d), a passivating step of contacting the impregnated porous particle frameworks with a passivating agent.

28. The process of 27, wherein the passivating step comprises a first step of contacting the impregnated porous particle frameworks with an oxygen-containing gas at a temperature less than 300 °C and a second step of contacting the frameworks resulting from the first step with liquid water or a gas comprising water vapour at a temperature of at least 30 °C and optionally less than 400°C or less than 300°C.

29. The process of 27, wherein the passivating agent is selected from an oxygencontaining gas, ammonia, a gas comprising ammonia and oxygen, and phosphine.

30. The process of claim 27, wherein the passivating agent is selected is selected from:R1-CH=CH-R1,R1-C=C-R1,O=CR1R1,O=CR1R2,HX-R2, andHX-C(O)-R1, wherein X represents O, S, NR1or PR1; and wherein each R1independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1-20 carbon atoms, or wherein two R1groups form an unsubstituted or substituted ring structure comprising 3-8 carbon atoms in the ring; wherein R2represents an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1-20 carbon atoms, or wherein R1and R2together form an unsubstituted or substituted ring structure comprising 3-8 carbon atoms in the ring.

31. The process of any preceding claim, comprising, before step (d), an annealing step of annealing the impregnated porous particle frameworks at elevated temperature under an inert or reducing atmosphere.

32. The process of claim 31 , wherein the elevated temperature is at least 200 °C, 300-800°C, 400-700°C, and / or below 1000 °C.

33. The process of claim 31 or 32, wherein the inert or reducing atmosphere is a nitrogen atmosphere, or an atmosphere comprising hydrogen, or a noble gas atmosphere, or mixtures thereof.

34. The process of any of claims 31-33, wherein the annealing step is performed for at least one minute, 10 minutes - 10 hours, 30 minutes - 5 hours, and / or for less than 72 hours.

35. The process of claims 27 and 31 , wherein the passivating step is before the annealing step.

36. The process of claims 27 and 31, wherein the annealing step is before the passivating step.

37. The process of any preceding claim, wherein the monovalent metal: is selected from Li, Na, K, Rb, and mixtures thereof; or is selected from Li, Na, and mixtures thereof; or is Li.

38. The process of any preceding claim, comprising, before step (d), a step of depositing a lithium-ion permeable material into the pores and / or onto the outer surface of the impregnated porous particle frameworks.

39. The process of any preceding claim, comprising, before step (d), a step of combining the impregnated porous particle frameworks 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 impregnated porous particle frameworks.

40. The process of any preceding claim, comprising, before step (d), a step of forming an electrode comprising the impregnated porous particle frameworks.

41. The process of claim 40, wherein step (d) is achieved as part of an electrochemical pre-lithiation or pre-sodiation step of the electrode.

42. The process of any preceding claim, wherein step (d) comprises contacting the impregnated porous particle frameworks with a monovalent metal precursor; optionally wherein the monovalent metal precursor is a salt, complex, or organic compound of the monovalent metal; optionally wherein the monovalent metal precursor is selected from oxides, carbonates, acetates, nitrates, hydroxides, hydrides, sulphates, carboxylates, halides, oxalates, bisoxalatoborates, bis(trifluoromethanesulfonyl)imides, citrates, phosphates, complexes comprising EDTA, complexes comprising rotaxanes, organolithium compounds, and mixtures thereof.

43. The process of any preceding claim, wherein step (d) comprises contacting the impregnated porous particle frameworks with an electrolyte comprising the monovalent metal.

44. The process of any preceding claim, comprising, before step (d), a step of forming an electrochemical cell comprising an anode comprising the impregnated porous particle frameworks, a cathode, and an electrolyte between the anode and cathode; where the cathode and / or the electrolyte comprises the monovalent metal; optionally wherein the electrochemical cell is a rechargeable metal-ion battery.

45. The process of claim 44, wherein step (d) is achieved as part of a formation cycle of the electrochemical cell.

46. The process of any of claims 43-45, wherein the electrolyte comprises a polyvalent metal; optionally the same polyvalent metal as the polyvalent metal in step (a) and / or (b) or a different polyvalent metal than the polyvalent metal in steps (a) and (b).

47. The process of any preceding claim, wherein the electric potential in step (d) comprises a constant current I constant voltage cycle at C / n, wherein n>5, with a lower cut-off of voltage of >10 mV.

48. The process of any preceding claim, wherein the porous particle frameworks in step (a) are porous carbon particle frameworks; optionally comprising at least 80 wt% carbon, or at least 85 wt% carbon, or at least 90 wt% carbon, or at least 95 wt% carbon.

49. The process of any preceding claim, wherein the porous particle frameworks in step (a) are porous carbon particle frameworks comprising:100-10,000 ppm, 250-8,000 ppm, or 500-5,000 ppm Ca relative to the mass of the porous carbon particle frameworks; and200-25,000 ppm, 500-20,000 ppm, or 1,000-16,000 ppm P relative to the mass of the porous carbon particle frameworks.

50. The process of any preceding claim, wherein the porous particle frameworks in step (a) are porous carbon particle frameworks comprising micropores and optionally mesopores wherein:P1is the total volume of micropores and mesopores in the porous carbon particle frameworks expressed in cm3 / g, wherein P1is at least 0.35 and optionally less than 2.5; andVP07, VP2, VP5, and VP20 are respectively the volume of pores in the porous carbon particle frameworks with a pore diameter of 0.7 nm or less, 2.0 nm or less, 5.0 nm or less, and 20.0 nm or less expressed as a percentage of P1, wherein VP07 is in the range of 5.1-35%, VP2 is in the range of 40-90%, and VP20-VP5 is less than 20%; optionally the micropore volume of the porous carbon particle frameworks is at least 0.3 cm3 / g; wherein P1, VP07, VP2, VP5, VP20, and the micropore volume are measured by nitrogen gas adsorption.

51. The process of any preceding claim, wherein the porous particle frameworks in step (a) have not been subjected to processing intended to remove impurities naturally present in the feedstock material used to synthesise the porous particle frameworks.

52. The process of any preceding claim, wherein the porous particle frameworks in step (a) have not been subjected to a washing step intended to remove impurities naturally present in the feedstock material used to synthesise the porous particle frameworks.

53. The process of any preceding claim, wherein the porous particle frameworks in step (a) are derived from biomass.

54. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a total volume of micropores and mesopores as measured by gas adsorption of from 0.4-1.8 cm3 / g, or 0.6-1.4 cm3 / g, or 0.75-1.1 cm3 / g.

55. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a PD90pore diameter of no more than 50 nm and / or a PD5o pore diameter of no more than 30 nm.

56. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a micropore volume fraction of at least 0.45 and / or no more than 0.95, based on the total volume of micropores and mesopores.

57. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a bimodal or multimodal pore size distribution.

58. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a BET surface area from 1200-3000 m2 / g.

59. The process of any preceding claim, wherein the porous particle frameworks in step (a) have a D5o particle diameter of 1-30 pm, or 1-20 pm, or 2-8 pm.

60. The process of any preceding claim, wherein the impregnated porous particle frameworks comprise from 30-70 wt% silicon, 35-65 wt% silicon, or 40-60 wt% silicon.

61. The process of any preceding claim, wherein at least 20 wt%, at least 30 wt%, or at least 40 wt% of the silicon of the impregnated porous particle frameworks is surface silicon as determined by thermogravimetric analysis (TGA).

62. The process of any preceding claim, wherein no more than 6 wt%, or no more than 5 wt%, or no more than 4 wt%, or no more than 3.5 wt%, or no more than 3 wt%, or no more than 2.5 wt%, or no more than 2 wt%, or no more than 1.5 wt% of the silicon of the impregnated porous particle frameworks is coarse bulk silicon as determined by thermogravimetric analysis (TGA).

63. Composite particles obtainable by the method of any preceding claim.

64. Composite particles for use as an electroactive material for a metal-ion battery, the composite particles comprising: a porous particle framework comprising micropores and / or mesopores; and an intermetallic phase comprising a polyvalent metal, silicon and / or germanium, and a monovalent metal.

65. The composite particles of claim 64, wherein the intermetallic phase is in the pores of the porous particle framework.

66. The composite particles of claim 64 or 65, wherein the intermetallic phase is on the outer surface of the porous particle framework.

67. The composite particles of any of claims 64-66, comprising elemental silicon and / or elemental germanium deposited in the pores of the porous particle framework; optionally wherein the intermetallic phase is intimately bonded to the elemental silicon and / or elemental germanium in the pores of the porous particle framework.

68. The composite particles of any of claims 64-67, comprising elemental silicon and / or elemental germanium deposited on the outer surface of the porous particle framework; optionally wherein the intermetallic phase is intimately bonded to the elemental silicon and / or elemental germanium on the outer surface of the porous particle framework.

69. The composite particles of any of claims 64-68, wherein the composite particles comprise at least one of:Mg at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Mg and silicon in the composite particles;Ca at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Ca and silicon in the composite particles;Sn at a concentration of >0.001, >0.01, >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sn and silicon in the composite particles;Ge at a concentration of >0.001, >0.01, >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20at% relative to the combined amount of Ge and silicon in the composite particles;Zn at a concentration of >0.001 , >0.01 , >0.1 , or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Zn and silicon in the composite particles;Al at a concentration of >0.001 , >0.01 , >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Al and silicon in the composite particles; andSb at a concentration of >0.001, >0.01, >0.1, or >1 at% and optionally <30 at%, <25 at%, or <20 at% relative to the combined amount of Sb and silicon in the composite particles;wherein polyvalent metal is preferably present in the impregnated porous particle frameworks at a concentration of <30 at.% relative to the combined amount of polyvalent metal and silicon in the composite particles.

70. The composite particles of any of claims 64-69, wherein the composite particles comprise at least one of, and optionally all of:Fe at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Fe and silicon in the composite particles;Co at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Co and silicon in the composite particles;Cu at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Cu and silicon in the composite particles;Ni at a concentration of <0.5, <0.1 , <0.01 , or <0.001 at% relative to the combined amount of Ni and silicon in the composite particles; andMn at a concentration of <0.5, <0.1, <0.01, or <0.001 at% relative to the combined amount of Mn and silicon in the composite particles.

71. An electrode comprising the composite particles of any of claims 64-70.

72. A rechargeable metal-ion battery comprising the electrode of claim 71 , wherein the electrode is the anode.

73. A method of making impregnated porous particle frameworks, the method comprising following the method of any of claims 1-62 but omitting step (d).

74. Impregnated porous particle frameworks obtainable by the method of claim 73.

75. Impregnated porous particle frameworks comprising micropores and / or mesopores, a polyvalent metal, and elemental silicon and / or elemental germanium in the pores.

Images