Method for producing electroactive composite particles

Abstract

The invention relates to a method for preparing composite particles. The method comprises the following steps: providing a plurality of porous particles, wherein the porous particles comprise micropores and / or mesopores; contacting the porous particle with a silicon-containing precursor at a temperature effective to cause deposition of a plurality of silicon domains in pores of the porous particle; and heat treating the particles at a temperature of at least 400 DEG C and in the presence of an inert gas.

Description

[0001] Introduction

[0002] The present invention relates to a method for preparing composite particles comprising an electroactive material deposited into pores of a porous particle skeleton. The method of the present invention particularly relates to a step of thermally post-treating the composite particles to improve the electrochemical performance when the composite particles are used as an anode active material in a rechargeable lithium-ion battery. Background Art

[0003] Lithium-ion batteries (LIBs) generally comprise an anode, a cathode, and a lithium-containing electrolyte. The anode typically comprises a metal current collector provided with a layer of electroactive material, which is defined herein as a material capable of intercalating and releasing lithium ions during charging and discharging of the battery. When an LIB is charged, lithium ions are transported from the cathode to the anode via the electrolyte and are intercalated into the electroactive material of the anode as intercalated lithium atoms. Thus, the terms "cathode" and "anode" are used herein in the sense that the battery is connected to a load such that the anode is the negative electrode. The term "battery" is used herein both to refer to a device comprising a single lithium-ion battery cell and to refer to a device comprising a plurality of interconnected lithium-ion battery cells.

[0004] LIBs were developed in the 1980s and 1990s and have since been widely used in portable electronic devices. The recent development of electric or hybrid vehicles has created a large new market for LIBs, and renewable energy has further created a need for grid-connected energy storage, which the LIB market can at least partially meet. Overall, the global production of LIBs is expected to grow from approximately 290 GWh in 2018 to more than 2,000 GWh in 2028.

[0005] While the total storage capacity is increasing, there is a strong interest in improving the weight and / or volume capacity of rechargeable metal-ion batteries such that the same energy storage is achieved with less battery mass and / or less battery volume. Conventional LIBs use graphite as the anode electroactive material. Graphite anodes can accommodate at most one lithium atom per six carbon atoms, resulting in a maximum theoretical specific capacity of 372 mAh / g for lithium-ion batteries, while the actual capacity is slightly lower (about 340 to 360 mAh / g).

[0006] Silicon has emerged as a promising alternative to graphite due to its very high lithium capacity (see, e.g., Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al., Adv. Mater. 1998, 10, No. 10). Silicon in lithium-ion batteries (based on Li15 Si 4 ) has a theoretical maximum specific capacity of about 3,600 mAh / g. However, such a high ratio of lithium insertion to silicon results in a swelling of the silicon material up to 400% of its original volume. Repeated charge and discharge cycles impose significant mechanical stress on the silicon material, leading to cracking and structural failure. In addition, charging of the anode in a LIB results in the formation of a solid electrolyte interface (SEI) layer. This SEI layer is an ion-conductive but insulating layer that is formed by the reductive decomposition of the electrolyte on the exposed electrode surface during the initial charge. In a graphite anode, this SEI layer is relatively stable during subsequent charge / discharge cycles. However, the swelling and shrinking of a silicon anode result in cracking and delamination of the SEI layer and exposure of fresh silicon surfaces, leading to further electrolyte decomposition, an increase in the SEI layer thickness, and irreversible lithium consumption. These degradation mechanisms together result in unacceptable electrochemical capacity loss during successive charge and discharge cycles.

[0007] The present inventors previously reported the development of a class of electroactive materials having a composite structure in which an electroactive material (such as silicon) is deposited into the pore network of highly porous particles (such as porous carbon materials) having a carefully controlled pore size distribution. For example, WO 2020 / 095067 and WO 2020 / 128495 reported that the improved electrochemical performance of these materials can be attributed to the way in which the electroactive material forms small domains on the order of a few nanometers or less in size within the pore network of the porous particles, such that the porous particles act as a skeleton for the composite particles. The fine electroactive structures are thought to have lower resistance to elastic deformation and higher fracture resistance compared to larger electroactive structures and thus be able to lithiate and delithiate without excessive structural stress. As a result, the electroactive material exhibits good reversible capacity retention with multiple charge and discharge cycles. Second, by controlling the loading of silicon within the porous carbon skeleton such that only a portion of the pore volume is occupied by silicon in the uncharged state, the unoccupied pore volume of the porous carbon skeleton can internally accommodate a significant amount of silicon swelling. Excessive swelling is restricted by the particle skeleton. In addition, only small areas of the electroactive material surface are accessible to the electrolyte, thus substantially preventing SEI formation.

[0008] In WO 2022 / 029422, the applicant reported further progress, where control of the distribution of electroactive silicon within the pore network of the particle framework led to a further improvement in the electrochemical performance of the composite particles. Specifically, the applicant has demonstrated that when the length dimension of the individual silicon structures in the composite particles is minimized such that a large proportion of the silicon atoms are located in the surface region of the silicon structures while a relatively small proportion of the silicon atoms are located inside the bulk / crude silicon structures, the electrochemical performance is optimized. The applicant has determined an optimized pore structure of the porous particle framework and a set of conditions for depositing silicon onto the porous particle framework, which can increase the proportion of this so-called "surface silicon" while also ensuring that a large total amount of silicon is incorporated into the composite particles to meet the overall volumetric energy density requirements.

[0009] There is still a need in the art for further improvement of electroactive composite particles of the above type to provide improved electrochemical performance and lifespan of the material during multiple charge-discharge cycles. Summary of the Invention

[0010] In a first aspect, the present invention provides a method for preparing composite particles, the method comprising the following steps:

[0011] (a) providing a plurality of porous particles, the porous particles comprising micropores and / or mesopores;

[0012] (b) contacting the porous particles with a silicon-containing precursor at a temperature effective to cause deposition of a plurality of nano-sized silicon domains in the pores of the porous particles;

[0013] (c) heat-treating the particles from step (b) at a temperature of at least 400 °C and in the presence of an inert gas.

[0014] Thus, the present invention generally relates to a method for preparing composite particles, wherein a plurality of nano-sized silicon domains are deposited into the pore network of microporous and / or mesoporous porous particles by thermal decomposition of a silicon-containing precursor material. Thus, the composite particles prepared according to the method of the present invention comprise: a first component in the form of a porous particle framework, the porous particle framework being derived from the porous particles provided in step (a), and a second component in the form of a plurality of nano-sized silicon domains, the plurality of nano-sized silicon domains being deposited in the pore structure of the porous particle framework in step (b). As used herein, the term "nano-sized silicon domain" refers to a nano-sized elemental silicon body having a defined maximum size by positioning silicon within the micropores and / or mesopores of the porous particles.

[0015] The method of the present invention is further developed on the basis of the applicant's previous disclosures by adding a heat treatment step in the method for forming silicon-containing composite particles, said silicon-containing composite particles comprising a plurality of silicon domains in the pores of microporous and / or mesoporous particles.

[0016] The deposition of silicon nano-sized domains in mesoporous and / or microporous particles is kinetically controlled such that thermal deposition preferentially occurs at the inner pore surface of the porous particles. The inventors have determined that the nano-sized silicon domains formed in this way are thermodynamically unstable / metastable due to a series of unbalanced bonding interactions of silicon atoms in the surface region of the nano-sized silicon domains. The heat treatment of the particles in step (c) of the method of the present invention is associated with a plurality of interrelated heat-induced processes that stabilize the silicon material and extend the cycle life of the composite particles in a LIB.

[0017] The nano-sized silicon domains formed by the thermal decomposition of a silicon precursor are believed to be in the form of nano-clusters of silicon atoms terminated substantially by silicon-hydrogen bonds (Si-H). The surface of these nano-clusters is highly reactive, especially due to the elimination of hydrogen and the resulting instability of silicon atoms with free valences. The heat treatment of the particles in step (c) is believed to promote the elimination of hydrogen and the solid-state rearrangement of silicon atoms, thereby reducing the density of unstable and reactive Si-H bonds and promoting the formation of more thermodynamically stable Si-Si bonds.

[0018] The rearrangement of silicon atoms also contributes to the volume shrinkage of the silicon domains. As a result, the pore space that was previously blocked or capped by the silicon nanostructures reopens, allowing passivation gases and other functional gases to enter the remaining pore volume. The increased entry of passivation gases into the remaining pore space enables a more extensive passivation of the silicon surface, while the elimination of hydrogen from the silicon nanostructures in the previously inaccessible pore space reduces hydrogen evolution during charging and discharging.

[0019] Similar to the formation of Si-Si bonds, the heat treatment in step (c) is also believed to promote the formation of covalent bonds (e.g., Si-C bonds in the case where the porous particle framework is a porous carbon particle framework) between the silicon and the inner surface of the porous particle framework. These bonding interactions between the nano-sized silicon domains and the porous particle framework are believed to improve the mechanical stabilizing effect of silicon during charging and discharging, especially by improving the constraint of the porous particle framework on the excessive expansion of silicon.

[0020] Other effects of the heat treatment in step (c) are believed to include: a reduction in the surface area of the nano-sized silicon domains (which reduces the reactivity of silicon with the electrolyte and thus reduces the formation of the SEI layer), and the elimination of surface contaminants.

[0021] All of these factors are found to contribute to the improved stability of the electroactive material during charging and discharging, and thus contribute to the improved cycle life of a lithium-ion battery comprising the particulate material as an anode active material.

[0022] In a second aspect, the present invention provides a particulate material comprising a plurality of composite particles obtainable by the method of the first aspect.

[0023] In a third aspect, the present invention provides a composition comprising the particulate material of the second aspect and at least one other component.

[0024] In a fourth aspect, the present invention provides an electrode comprising the particulate material of the second aspect or the composition of the third aspect.

[0025] In a fifth aspect, the present invention provides a rechargeable metal ion battery comprising the electrode of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a graph showing the effect of the heat treatment of step (c) on the total micropore and mesopore volume of composite particles obtained by chemical vapor infiltration of silicon into the pores of porous particles.

[0027] Figure 2 is a graph showing the effect of the heat treatment of step (c) and the passivation of step (d) on the total micropore and mesopore volume of composite particles obtained by chemical vapor infiltration of silicon into the pores of porous particles. DETAILED DESCRIPTION

[0028] The method of the first aspect of the present invention comprises the following steps:

[0029] (a) providing a plurality of porous particles comprising micropores and / or mesopores;

[0030] (b) contacting the porous particles with a silicon-containing precursor at a temperature effective to cause deposition of a plurality of nanosized silicon domains in the pores of the porous particles;

[0031] (c) heat-treating the particles from step (b) at a temperature of at least 400 °C and in the presence of an inert gas.

[0032] The porous particles serve as a framework for the electroactive material, which is generally deposited in the form of a plurality of electroactive material domains. The term "electroactive material domain" refers to a body of electroactive material having a maximum size determined by the size of the micropores and / or mesopores of the porous particles in which they are located, such as elemental silicon. Thus, the electroactive domains can be described as nanosized electroactive domains, where the term "nanosized" is understood to generally refer to a size less than 100 nm. However, due to the size of the micropores and mesopores, the maximum size of the electroactive material domains in any direction is less than 50 nm and is typically significantly less than 50 nm. The domains can, for example, take the form of regular or irregular particles or bounded layers or regions of a coating.

[0033] The porous particles generally comprise a three-dimensional interconnected open pore network, which includes micropores and / or mesopores and optionally a minor volume of macropores. According to conventional IUPAC terminology, the term "micropore" is used herein to refer to pores with a diameter less than 2 nm, the term "mesopore" is used herein to refer to pores with a diameter of 2 - 50 nm, and the term "macropore" is used to refer to pores with a diameter greater than 50 nm.

[0034] As used herein, the volume of micropores, mesopores, and macropores in the porous particles and any reference to the distribution of pore volume within the porous particles relate to the internal pore volume of the porous particles, which are used as starting materials in step (a) of the claimed method (i.e., before depositing the electroactive material into the pore volume in step (b)).

[0035] The porous particles can be characterized 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 particles contain both micropores and mesopores. However, it is not excluded that porous particles including only micropores without mesopores or including only mesopores without micropores can be used.

[0036] The total volume of micropores and mesopores in the porous particles is preferably at least 0.4 cm 3 / g, or at least 0.5 cm 3 / g, or at least 0.6 cm 3 / g, or at least 0.65 cm 3 / g, or at least 0.7 cm 3 / g, or at least 0.75 cm 3 / g, or at least 0.8 cm 3 / g. The use of particles with a higher porosity can be advantageous as it enables a greater amount of electroactive material to be accommodated within the pore volume.

[0037] The internal pore volume of the porous particles is suitably limited to such a value that, in this case, the increased brittleness of the particle structure exceeds the advantage of the increased pore volume for accommodating a larger amount of electroactive material. Preferably, the total volume of micropores and mesopores in the porous particles does not exceed 1.8 cm 3 / g, or does not exceed 1.7 cm 3 / g, or does not exceed 1.6 cm 3 / g, or does not exceed 1.55 cm 3 / g, or does not exceed 1.5 cm 3 / g, or does not exceed 1.45 cm 3 / g, or does not exceed 1.4 cm 3 / g, or does not exceed 1.35 cm 3 / g, or does not exceed 1.3 cm 3 / g, or does not exceed 1.25 cm 3 / g, or does not exceed 1.2 cm 3 / g, or does not exceed 1.1 cm 3 / g.

[0038] Preferably, the total volume of micropores and mesopores in the porous particles is in the range of 0.4 to 1.8 cm 3 / g, or 0.4 to 1.7 cm 3 / g, or 0.5 to 1.6 cm 3 / g, or 0.5 to 1.55 cm 3 / g, or 0.6 to 1.5 cm 3 / g, or 0.6 to 1.45 cm 3 / g, or 0.65 to 1.4 cm 3 / g, or 0.65 to 1.35 cm 3 / g, or 0.7 to 1.3 cm 3 / g, or 0.7 to 1.25 cm 3 / g, or 0.75 to 1.2 cm 3 / g, or 0.75 to 1.1 cm 3 / g, or 0.8 to 1.2 cm 3 / g, or 0.8 to 1.1 cm 3 / g.

[0039] The general term "PD n pore diameter" herein refers to the pore diameter at the nth percentile of the volume based on the total volume of micropores and mesopores. For example, the term "PD 50 pore diameter" as used herein refers to the pore diameter at which 50% of the measured total micropore and mesopore volume is lower than a certain pore diameter. To avoid ambiguity, for determining PD nValue, without considering any macropore volume (pore diameter greater than 50 nm).

[0040] PD of the porous particles 90 The pore diameter is preferably not more than 20 nm, or not more than 15 nm, or not more than 12 nm, or not more than 10 nm, or not more than 8 nm, or not more than 6 nm, or not more than 5 nm. Preferably, the PD of the porous particles 90 The pore diameter is at least 3 nm, or at least 4 nm, or at least 5 nm, or at least 6 nm. For example, the PD of the porous particles 90 The pore diameter is preferably in the range of 3 to 20 nm, or 4 to 15 nm, or 5 to 10 nm, or 6 to 8 nm.

[0041] PD of the porous particles 50 The pore diameter is preferably not more than 10 nm, or not more than 8 nm, or not more than 6 nm, or not more than 5 nm, or not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm, or not more than 1.9 nm, or not more than 1.8 nm, or not more than 1.7 nm, or not more than 1.6 nm.

[0042] Based on the total volume of micropores and mesopores in the porous particles, the micropore volume fraction is at least 0.4, or at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6.

[0043] The pore size distribution of the porous particles can be unimodal, bimodal or multimodal. As used herein, the term "pore size distribution" relates to the distribution of the pore sizes of the porous particles relative to the cumulative total internal pore volume. A bimodal or multimodal pore size distribution can be preferred because the close proximity between the micropores and the pores with larger diameters provides the advantage of efficient ion transport from the porous network to the electroactive material.

[0044] According to the standard methods described in ISO 15901-2 and ISO 15901-3, using the quenched solid density functional theory (QSDFT), nitrogen adsorption is used at 77 K, down to 10 -6 of the relative pressure p / p 0To determine the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores. Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure is increased until a saturation point is reached, at which all pores are filled with liquid. Then the nitrogen pressure is gradually decreased to allow the liquid to evaporate from the system. The analysis of the adsorption and desorption isotherms and the hysteresis between them enables the determination of the pore volume and the pore size distribution. Suitable instruments for measuring the pore volume and pore size distribution by nitrogen adsorption include the TriStar II and TriStar II Plus porosimeters (which are available from Micromeritics Instrument Corporation in the United States), and the Autosorb IQ porosimeter (which is available from Quantachrome Instruments).

[0045] Nitrogen adsorption is effective for measuring the pore volume and pore size distribution of pores with a maximum diameter of 50 nm, but is less reliable for pores with much larger diameters. For the purposes of the present invention, therefore, nitrogen adsorption is used only for pores with a maximum diameter of 50 nm (including 50 nm) (i.e., only for micropores and mesopores) to determine the pore volume and pore size distribution. The PD 50 value is also determined only with respect to the total volume of micropores and mesopores.

[0046] Given the limitations of available analytical techniques, it is not possible to measure the pore volume and pore size distribution over the entire range of micropores, mesopores, and macropores using a single technique. In the case where the porous particles include macropores, the volume of pores in the range of greater than 50 nm to 100 nm in diameter can be measured by mercury intrusion porosimetry, and preferably does not exceed 0.3 cm 3 / g, or does not exceed 0.2 cm 3 / g, or does not exceed 0.1 cm 3 / g, or does not exceed 0.05 cm 3 / g. Although a small fraction of the macropores can be useful for facilitating the entry of electrolyte into the pore network, the advantages of the present invention are obtained substantially by accommodating the electroactive material in the micropores and the smaller mesopores.

[0047] Any pore volume of pore sizes below 50 nm measured by mercury intrusion porosimetry is not considered (as described above, nitrogen adsorption is used to characterize mesopores and micropores). For the purposes of the present invention, the pore volume above 100 nm measured by mercury intrusion porosimetry is assumed to be the interparticle porosity and is ignored.

[0048] Mercury intrusion porosimetry is a technique for characterizing the porosity and pore size distribution of a material sample by applying different levels of pressure to the sample immersed in mercury. The pressure required to make mercury intrude into the pores of the sample is inversely proportional to the size of the pores. The values obtained by mercury intrusion porosimetry reported in this article are obtained according to ASTM UOP578-11, where for mercury at room temperature, the surface tension γ is taken as 480 mN / m, and the contact angle φ is taken as 140°. The density of mercury at room temperature is taken as 13.5462 g / cm 3 . A variety of high-precision mercury intrusion porosimetry instruments are commercially available, such as the automated mercury porosimeter of the AutoPore IV series, which can be obtained from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury intrusion porosimetry, reference can be made to "Analytical Methods in Fine Particle Technology" by P.A. Webb and C. Orr, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0049] It should be understood that intrusion techniques such as gas adsorption and mercury intrusion porosimetry are only effective for determining the pore volume of pores accessible from the outside of the porous particles by nitrogen or mercury. The porosity values specified in this article should be understood to refer to the volume of open pores (i.e., pores accessible from the outside of the porous particles by fluid). In this article, when determining the porosity value, completely encapsulated pores that cannot be identified by nitrogen adsorption or mercury intrusion porosimetry should not be considered. Similarly, any pore volume located in pores smaller than the detection limit of nitrogen adsorption is not considered.

[0050] As used herein, the term "particle size" refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, where the particle volume should be understood to include the volume of any intra-particle pores. As used herein, the terms "D 50 " and "D 50 particle size" refer to the volume median diameter, i.e., the diameter at which 50% of the volume of the particle population is below a certain diameter. As used herein, the terms "D 10 " and "D 10 particle size" refer to the 10th percentile volume median diameter, i.e., the diameter at which 10% of the volume of the particle population is below a certain diameter. As used herein, the terms "D 90 " and "D 90 particle size" refer to the 90th percentile volume median diameter, i.e., the diameter at which 90% of the volume of the particle population is below a certain diameter.

[0051] The particle size and size distribution can be determined by standard laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that particles will scatter light at an angle that varies according to the size of the particle, and a collection of multiple particles will produce a scattered light pattern defined by the intensity and angle that can be correlated to the size distribution. There are many commercially available laser diffraction instruments for the rapid and reliable determination of size distribution. Unless otherwise stated, the size distribution measurements specified or reported herein are by a conventional Malvern Mastersizer TM from Malvern Instruments TM Model 3000 particle size analyzer. The Malvern Mastersizer TM Model 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. The light impinging on the particles is scattered at an angle inversely proportional to the particle size, and a photodetector array measures the intensity of the light at multiple predetermined angles, and the intensities measured at different angles are processed by a computer using standard theoretical principles to determine the size distribution. The laser diffraction values reported herein were obtained using a wet dispersion of particles in 2-propanol with 5 volume % surfactant SPAN TM -40 (sorbitan monopalmitate). The particle refractive index of the porous particles is considered to be 2.68, and the particle refractive index of the composite particles is considered to be 3.50, and the refractive index of the dispersant is considered to be 1.378. The Mie scattering model is used to calculate the size distribution.

[0052] Generally, the D 50 particle size of the porous particles is in the range of 1 to 30 µm. Optionally, the D 50 particle size of the porous particles can be at least 1 µm, or at least 1.5 µm, or at least 2 µm, or at least 2.5 µm, or at least 3 µm, or at least 4 µm, or at least 5 µm. Optionally, the D 50 particle size of the porous particles can be not more than 25 µm, or not more than 20 µm, or not more than 18 µm, or not more than 15 µm, or not more than 12 µm, or not more than 10 µm, or not more than 8 µm.

[0053] The D 10 particle size of the porous particles is preferably at least 0.5 µm, or at least 0.8 µm, or at least 1 µm, or at least 1.5 µm, or at least 2 µm. By maintaining the D 10 particle size above 0.5 µm, the likelihood of agglomeration of unwanted submicron-sized particles is reduced, and the dispersibility of the composite particles formed is improved.

[0054] D of the porous particles 90 The particle size is preferably not more than 50 µm, or not more than 40 µm, or not more than 30 µm, or not more than 25 µm, or not more than 20 µm, or not more than 15 µm.

[0055] The porous particles preferably have a narrow size distribution span. For example, the span of the particle size distribution (defined as (D 90 - D 10 ) / D 50 ) 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, it is possible to more easily achieve efficient filling of the particles into a dense powder bed.

[0056] The average sphericity (as defined herein) of the porous particles can exceed 0.5. Preferably, their average sphericity is 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 average sphericity of the porous particles is 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 considered to contribute to the uniformity of deposition and at the same time are beneficial for denser filling in a batch pressure reactor and in the final product when incorporated into an electrode.

[0057] Highly accurate two-dimensional projections of micron-scale particles can be obtained by scanning electron microscopy (SEM) or by dynamic image analysis, where a digital camera is used to record the shadow of the particle projection. As used herein, the term "sphericity" should be understood as the ratio of the area of the particle projection (obtained by such imaging techniques) to the area of a circle, where the particle projection and the circle have the same perimeter. Thus, for an individual particle, the sphericity S can be defined as:

[0058]

[0059] where A m is the measured area of the particle projection, and C m is the measured perimeter of the particle projection. The average sphericity S av of multiple particles as used herein is defined as:

[0060]

[0061] where n represents the number of particles in the population. The average sphericity of the particle population is preferably calculated from the two-dimensional projections of at least 50 particles.

[0062] The BET surface area of the porous particles is preferably at least 100 m 2 / g, or at least 500 m 2 / g, or at least 750 m 2 / g, or at least 1,000 m 2 / g, or at least 1,250 m 2 / g, or at least 1,500 m 2 / g. As used herein, the term "BET surface area" shall be considered to refer to the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on the solid surface using the Brunauer - Emmett - Teller principle in accordance with ISO 9277. Preferably, the BET surface area of the porous particles does not exceed 4,000 m 2 / g, or does not exceed 3,500 m 2 / g, or does not exceed 3,250 m 2 / g, or does not exceed 3,000 m 2 / g, or does not exceed 2,500 m 2 / g, or does not exceed 2,000 m 2 / g. For example, the BET surface area of the porous particles can be in the range of 100 m 2 / g to 4,000 m 2 / g, or 500 m 2 / g to 4,000 m 2 / g, or 750 m 2 / g to 3,500 m 2 / g, or 1,000 m 2 / g to 3,250 m 2 / g, or 1,000 m 2 / g to 3,000 m 2 / g, or 1,000 m 2 / g to 2,500 m 2 / g, or 1,000 m 2 / g to 2,000 m 2 / g.

[0063] The particle density of the porous particles is preferably at least 0.35 and preferably less than 3 g / cm 3 , more preferably less than 2 g / cm 3 , still more preferably less than 1.5 g / cm 3 , and most preferably from 0.35 to 1.2 g / cm 3As used herein, the term "particle density" refers to the "apparent particle density" measured by mercury intrusion porosimetry (i.e., the mass of the particles divided by the particle volume, where the particle volume is considered the sum of the volume of the solid material and any closed or blind pores (a "blind pore" is a pore that is too small to be measured by mercury intrusion porosimetry). Preferably, the particle density of the porous particles is at least 0.4 g / cm 3 , or at least 0.45 g / cm 3 , or at least 0.5 g / cm 3 , or at least 0.55 g / cm 3 , or at least 0.6 g / cm 3 , or at least 0.65 g / cm 3 , or at least 0.7 g / cm 3 . Preferably, the particle density of the porous particles does not exceed 1.15 g / cm 3 , or does not exceed 1.1 g / cm 3 , or does not exceed 1.05 g / cm 3 , or does not exceed 1 g / cm 3 , or does not exceed 0.95 g / cm 3 , or does not exceed 0.9 g / cm 3 .

[0064] Preferably, the porous particles have:

[0065] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.4 to 1.8 cm 3 / g;

[0066] (ii) a PD 50 pore diameter not exceeding 10 nm, and preferably a PD 90 pore diameter not exceeding 20 nm; and

[0067] (iii) a D 50 particle size in the range of 1 to 30 µm.

[0068] More preferably, the porous particles have:

[0069] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.5 to 1.6 cm 3 / g;

[0070] (ii) a PD 50 pore diameter not exceeding 8 nm, and preferably a PD 90 pore diameter not exceeding 15 nm; and

[0071] (iii) a D 50 particle size in the range of 1 to 25 µm.

[0072] More preferably, the porous particles have:

[0073] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.6 to 1.5 cm 3 / g;

[0074] (ii) a PD 50 pore diameter not exceeding 6 nm, and preferably a PD 90 pore diameter not exceeding 12 nm; and

[0075] (iii) a D 50 particle size in the range of 1.5 to 20 µm.

[0076] More preferably, the porous particles have:

[0077] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.65 to 1.4 cm 3 / g;

[0078] (ii) a PD 50 pore diameter not exceeding 2.5 nm, and preferably a PD 90 pore diameter not exceeding 10 nm; and

[0079] (iii) a D 50 particle size in the range of 1.5 to 18 µm.

[0080] More preferably, the porous particles have:

[0081] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.7 to 1.3 cm 3 / g;

[0082] (ii) a PD 50 pore diameter not exceeding 4 nm, and preferably a PD 90 pore diameter not exceeding 8 nm; and

[0083] (iii) a D 50 particle size in the range of 2 to 15 µm.

[0084] More preferably, the porous particles have:

[0085] (i) a total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.75 to 1.2 cm 3 / g;

[0086] (ii) a PD 50 pore diameter not exceeding 3 nm, and preferably a PD 90Pore size; and

[0087] (iii) D in the range of 2 to 12 µm 50 Particle size.

[0088] More preferably, the porous particles have:

[0089] (i) The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 0.8 to 1.2 cm 3 / g;

[0090] (ii) A PD pore size not exceeding 2 nm, and preferably a PD pore size not exceeding 5 nm 50 ; and 90 (iii) D in the range of 2.5 to 10 µm

[0091] Particle size. 50

[0092] The porous particles preferably contain a conductive material. The use of conductive porous particles is advantageous because the porous particles form a conductive skeleton within the composite particles, which facilitates the electron flow between the lithium atoms / ions embedded in the electroactive material and the current collector.

[0093] A preferred conductive porous particle is a particle containing or consisting of a conductive carbon material, which is herein referred to as a conductive porous carbon particle.

[0094] The conductive porous carbon particles preferably contain at least 80 wt% carbon, more preferably at least 85 wt% carbon, more preferably at least 90 wt% carbon, more preferably at least 95 wt% carbon, and optionally at least 98 wt% or at least 99 wt% carbon. The carbon can be crystalline carbon, amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The porous carbon particles can be hard carbon particles or soft carbon particles.

[0095] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which the carbon atoms are found mainly in the sp 2 hybridized state (trigonal bond) in nano-sized polyaromatic domains. The polyaromatic domains are crosslinked by chemical bonds such as C-O-C bonds. Due to the chemical crosslinking between the polyaromatic domains, hard carbon cannot be converted to graphite at high temperatures. Hard carbon has graphite-like properties, which are evidenced by a large G band (~1600 cm -1 ) in the Raman spectrum. However, the carbon is not completely graphitic, which is evidenced by an obvious D band (~1350 cm -1 ) in the Raman spectrum.

[0096] ​As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which the carbon atoms are found predominantly in sp 2 hybridized states (triple bonds) in polyaromatic domains in the size range of 5 to 200 nm. Compared to hard carbon, the polyaromatic domains in soft carbon are associated by intermolecular forces rather than cross-linked by chemical bonds. This means that they will graphitize at high temperatures. The porous carbon particles preferably contain at least 50% sp 2 hybridized carbon (measured by XPS). For example, the porous carbon particles can suitably contain from 50% to 98% sp 2 hybridized carbon, from 55% to 95% sp 2 hybridized carbon, from 60% to 90% sp 2 hybridized carbon, or from 70% to 85% sp 2 hybridized carbon.

[0097] Suitable porous carbon particles can be prepared by pyrolysis using a variety of different materials. Examples of organic materials that can be used include: plant biomass, which includes lignocellulosic materials (such as coconut shells, rice husks, wood, etc.), and fossil carbon sources such as coal. Examples of resin and polymer materials that form porous carbon particles upon pyrolysis include: phenolic resins, novolac resins, pitch, melamine-based materials, polyacrylate-based materials, polystyrene-based materials, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers containing monomer units of acrylate monomers, styrene monomers, α-olefins, vinylpyrrolidone, and other ethylenically unsaturated monomers. Depending on the raw materials and conditions of the pyrolysis process, a variety of different carbon materials can be obtained in the art. Porous carbon particles of various different specifications are available from commercial suppliers.

[0098] The porous carbon particles can be subjected to a chemical or gas activation process to increase the volume of mesopores and micropores. Suitable activation processes include: contacting the pyrolytic carbon with one or more of oxygen, steam, CO, CO 2 and KOH at a temperature in the range of 600 to 1000 °C.

[0099] Mesopores can also be obtained by a known templating method process using removable pore formers such as MgO and other colloidal or polymeric templates (which can be removed by thermal or chemical means after pyrolysis or activation).

[0100] Alternatives to the carbon-based conductive particles include porous particles containing: titanium nitride (TiN), titanium carbide (TiC), silicon carbide (SiC), nickel oxide (NiOx), titanium silicon nitride (TiSiN), nickel nitride (Ni 3 N), molybdenum nitride (MoN), titanium oxynitride (TiO x N 1-x) Silicon oxycarbide (SiOC), boron nitride (BN), or vanadium nitride (VN). Preferably, the porous particles comprise titanium nitride (TiN), silicon oxycarbide (SiOC), or boron nitride (BN).

[0101] The composite particles of the present invention are suitably prepared by chemical vapor infiltration (CVI) of a gaseous silicon-containing precursor into the pore structure of the porous particles. As used herein, CVI refers to a process in which a gaseous silicon-containing precursor is thermally decomposed on the surface to form elemental silicon and gaseous by-products at the surface.

[0102] Suitable gaseous silicon-containing precursors include: silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), tetrasilane (Si 4 H 10 ), methylsilane (CH 3 SiH 3 ), dimethylsilane ((CH 3 ) 2 SiH 2 ), or chlorosilane such as trichlorosilane (HSiCl 3 ), or methylchlorosilane such as methyltrichlorosilane (CH 3 SiCl 3 ), or dimethyldichlorosilane ((CH 3 ) 2 SiCl 2 ). Preferably, the silicon-containing precursor is selected from the group consisting of silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), tetrasilane (Si 4 H 10 ). A particularly preferred precursor of silicon is silane.

[0103] In the case where the precursor is a chlorinated compound such as chlorosilane, the precursor is used in admixture with hydrogen, preferably in an atomic ratio of hydrogen to chlorine of at least 1:1.

[0104] Optionally, the precursor is chlorine-free. Chlorine-free means that the precursor contains less than 1% by weight, preferably less than 0.1% by weight, preferably less than 0.01% by weight of chlorine-containing compounds.

[0105] The gaseous silicon-containing precursor in step (b) can be used in pure form (or substantially pure form), or as a mixture diluted with an inert carrier such as nitrogen or argon. Preferably, step (b) includes: contacting the porous particles with a gas comprising at least 30% by volume, or at least 40% by volume, or at least 50% by volume, or at least 60% by volume, or at least 70% by volume, or at least 80% by volume, or at least 90% by volume, or at least 95% by volume, or at least 97% by volume, or at least 99% by volume of the silicon-containing precursor based on the total volume of the gas.

[0106] In accordance with conventional procedures for working in an inert atmosphere, the presence of oxygen in step (b) should be avoided to prevent inappropriate oxidation of the deposited electroactive material. Preferably, based on the total volume of the gas used in step (b), the oxygen content is less than 0.01% by volume, more preferably less than 0.001% by volume.

[0107] The temperature in step (b) is preferably in the range of 340 to 500 °C, or 350 to 480 °C, or 350 to 450 °C, or 350 to 420 °C, or 350 to less than 400 °C, or 355 to 395 °C, or 360 to 390 °C, or 360 to 385 °C, or 360 to 380 °C. More preferably, the temperature in step (b) is in the range of 340 to less than 400 °C, or 370 to 395 °C.

[0108] The pressure in step (b) is preferably in the range of 1 to 5000 kPa, or 20 to 500 kPa, or 40 to 200 kPa, or 50 to 150 kPa, or 60 to 120 kPa, or 80 to 100 kPa. Preferably, the pressure in step (b) is maintained not to exceed 200 kPa, or not to exceed 150 kPa, or not to exceed 120 kPa, or not to exceed 110 kPa, or not to exceed 100 kPa, or not to exceed 90 kPa, or not to exceed 80 kPa.

[0109] The pressure mentioned in any step of the claimed method refers to the absolute pressure in the reaction zone, which may include any suitable form of reaction vessel.

[0110] Deposition of electroactive materials by CVI results in the elimination of by-products, in particular by-product gases such as hydrogen. Step (b) preferably further includes separating the by-products from the particles formed in step (b). The separation of the by-products can be achieved by flushing the reactor with an inert gas and / or by evacuating the reactor by reducing the pressure. For example, the separation of the by-products from the particles formed in step (b) can be achieved by evacuating the reactor to a pressure below 100 kPa, or below 80 kPa, or below 60 kPa, or below 40 kPa, or below 20 kPa, or below 10 kPa, or below 5 kPa, or below 2 kPa, or below 1 kPa. Evacuating the reactor to a low pressure can not only effectively remove the by-products in the gas phase, but also effectively desorb any by-products that may be adsorbed on the surface of the deposited silicon.

[0111] The temperature in step (c) can be higher than the temperature in step (b). Preferably, the temperature in step (c) 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 higher than the temperature in step (b).

[0112] For example, the temperature in step (c) can 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 in step (c) is at least 500 °C. More preferably, the temperature in step (c) is at least 510 °C. More preferably, the temperature in step (c) is at least 520 °C. Preferably, the temperature in step (c) does not exceed 900 °C, or does not exceed 850 °C, or does not exceed 800 °C, or does not exceed 750 °C, or does not exceed 700 °C, or does not exceed 680 °C, or does not exceed 660 °C, or does not exceed 650 °C. More preferably, the temperature in step (c) does not exceed 750 °C. More preferably, the temperature in step (c) does not exceed 700 °C.

[0113] The temperature in step (c) can be in the range of 400 °C to 900 °C, or 500 °C to 900 °C, or 600 °C to 900 °C. The temperature in step (c) can be in the range of 500 °C to 800 °C, or 510 °C to 800 °C, or 520 °C to 750 °C, or 540 °C to 700 °C, or 560 °C to 680 °C, or 580 °C to 660 °C, or 600 °C to 650 °C. Preferably, the temperature in step (c) is in the range of 500 °C to 750 °C. More preferably, the temperature in step (c) is in the range of 510 °C to 750 °C. More preferably, the temperature in step (c) is in the range of 520 °C to 700 °C.

[0114] The duration of step (c) 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. More preferably, the duration of step (c) is at least 30 minutes. More preferably, the duration of step (c) is at least 1 hour. More preferably, the duration of step (c) is at least 90 minutes. Preferably, the duration of step (c) does not exceed 72 hours, or does not exceed 48 hours, or does not exceed 24 hours, or does not exceed 12 hours, or does not exceed 6 hours, or does not exceed 5 hours, or does not exceed 4 hours, or does not exceed 3 hours. More preferably, the duration of step (c) does not exceed 24 hours. More preferably, the duration of step (c) does not exceed 12 hours. More preferably, the duration of step (c) does not exceed 6 hours.

[0115] The duration of step (c) can be in the range of 1 minute to 72 hours, or 2 minutes to 48 hours, or 5 minutes to 24 hours, or 10 minutes to 12 hours, or 15 minutes to 6 hours, or 20 minutes to 5 hours, or 30 minutes to 4 hours, or 1 hour to 4 hours, or 1 hour to 3 hours. Preferably, the duration of step (c) is in the range of 30 minutes to 24 hours. More preferably, the duration of step (c) is in the range of 1 hour to 12 hours. More preferably, the duration of step (c) is in the range of 90 minutes to 6 hours.

[0116] Step (c) preferably includes holding the particles from step (b) above a lower threshold temperature TL of at least 400 °C for a period of time t. More preferably, step (c) includes holding the particles from step (b) between the lower threshold temperature TL and the upper threshold temperature TU for a period of time t.

[0117] The lower threshold temperature TL in step (c) can be 450 °C, or 500 °C, or 510 °C, or 520 °C, or 540 °C, or 560 °C, or 580 °C, or 600 °C, or 610 °C, or 620 °C, or 630 °C, or 640 °C, or 650 °C. Preferably, the lower threshold temperature TL in step (c) is 500 °C. More preferably, the lower threshold temperature TL in step (c) is 510 °C. More preferably, the lower threshold temperature TL in step (c) is 520 °C. Preferably, the upper threshold temperature TU in step (c) is 900 °C, or 850 °C, or 800 °C, or 750 °C, or 700 °C, or 695 °C, or 680 °C, or 660 °C, or 650 °C. More preferably, the upper threshold temperature TU in step (c) is 750 °C. More preferably, the upper threshold temperature TU in step (c) is 700 °C.

[0118] The lower threshold temperature TL and the upper threshold temperature TU can be 400 °C and 900 °C respectively, or 500 °C and 900 °C respectively, or 600 °C and 900 °C respectively. The lower threshold temperature TL and the upper threshold temperature TU can be 500 °C and 800 °C respectively, or 510 °C and 800 °C respectively, or 520 °C and 750 °C respectively, or 540 °C and 700 °C respectively, or 560 °C and 680 °C respectively, or 580 °C and 660 °C respectively, or 600 °C and 650 °C respectively. Preferably, the lower threshold temperature TL and the upper threshold temperature TU are 500 °C and 750 °C respectively. More preferably, the lower threshold temperature TL and the upper threshold temperature TU are 510 °C and 750 °C respectively. More preferably, the lower threshold temperature TL and the upper threshold temperature TU are 520 °C and 700 °C respectively.

[0119] The time period t 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. More preferably, the time period t is at least 30 minutes. More preferably, the time period t is at least 1 hour. More preferably, the time period t is at least 90 minutes. Preferably, the time period t does not exceed 72 hours, or does not exceed 48 hours, or does not exceed 24 hours, or does not exceed 12 hours, or does not exceed 6 hours, or does not exceed 5 hours, or does not exceed 4 hours, or does not exceed 3 hours. More preferably, the time period t does not exceed 24 hours. More preferably, the time period t does not exceed 12 hours. More preferably, the time period t does not exceed 6 hours.

[0120] The said time period t may be in the range of 1 minute to 72 hours, or 2 minutes to 48 hours, or 5 minutes to 24 hours, or 10 minutes to 12 hours, or 15 minutes to 6 hours, or 20 minutes to 5 hours, or 30 minutes to 4 hours, or 1 hour to 4 hours, or 1 hour to 3 hours. Preferably, the time period t is in the range of 30 minutes to 24 hours. More preferably, the said time period t is in the range of 1 hour to 12 hours. Even more preferably, the said time period t is in the range of 90 minutes to 6 hours.

[0121] Step (c) is carried out in the presence of an inert gas. An inert gas herein refers to any gas that does not react under the conditions of step (c). Thus, there is no gas that reacts under the conditions of step (c) during step (c). Preferably, the inert gas is selected from nitrogen and noble gases, especially argon. Optionally, the inert gas may contain hydrogen. The inert gas may be selected from the group consisting of nitrogen, argon, helium, and combinations thereof. Step (c) may be carried out in the presence of hydrogen and a gas selected from the group consisting of nitrogen, argon, helium, and combinations thereof.

[0122] Preferably, step (c) is carried out under the following conditions:

[0123] (i) A temperature in the range of 400 °C to 900 °C;

[0124] (ii) A time duration of 1 minute to 72 hours; and

[0125] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0126] Preferably, step (c) is carried out under the following conditions:

[0127] (i) A temperature in the range of 500 °C to 900 °C;

[0128] (ii) A time duration of 30 minutes to 4 hours; and

[0129] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0130] Preferably, step (c) is carried out under the following conditions:

[0131] (i) A temperature in the range of 600 °C to 900 °C;

[0132] (ii) A time duration of 1 hour to 4 hours; and

[0133] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0134] Preferably, step (c) is carried out under the following conditions:

[0135] (i) A temperature in the range of 500 °C to 750 °C;

[0136] (ii) A time duration of 30 minutes to 24 hours; and

[0137] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0138] Preferably, step (c) is carried out under the following conditions:

[0139] (i) A temperature in the range of 500 °C to 750 °C;

[0140] (ii) A time duration of 1 hour to 12 hours; and

[0141] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0142] Preferably, step (c) is carried out under the following conditions:

[0143] (i) A temperature in the range of 500 °C to 700 °C;

[0144] (ii) A time duration of 90 minutes to 6 hours; and

[0145] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0146] Preferably, step (c) is carried out under the following conditions:

[0147] (i) A temperature in the range of 510 °C to 750 °C;

[0148] (ii) A time duration of 30 minutes to 24 hours; and

[0149] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0150] Preferably, step (c) is carried out under the following conditions:

[0151] (i) A temperature in the range of 510 °C to 750 °C;

[0152] (ii) A time duration of 1 hour to 12 hours; and

[0153] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0154] Preferably, step (c) is carried out under the following conditions:

[0155] (i) A temperature in the range of 510 °C to 700 °C;

[0156] (ii) A time duration of 90 minutes to 6 hours; and

[0157] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0158] Preferably, step (c) is carried out under the following conditions:

[0159] (i) A temperature in the range of 520 °C to 750 °C;

[0160] (ii) A time duration of 30 minutes to 24 hours; and

[0161] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0162] Preferably, step (c) is carried out under the following conditions:

[0163] (i) A temperature in the range of 520 °C to 750 °C;

[0164] (ii) A time duration of 1 hour to 12 hours; and

[0165] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0166] Preferably, step (c) is carried out under the following conditions:

[0167] (i) A temperature in the range of 520 °C to 700 °C;

[0168] (ii) A time duration of 90 minutes to 6 hours; and

[0169] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0170] Preferably, step (c) is carried out under the following conditions:

[0171] (i) The lower threshold temperature TL is 500 °C and the upper threshold temperature is 750 °C;

[0172] (ii) A time period t of 30 minutes to 24 hours; and

[0173] (iii) In the presence of an inert gas (optionally containing hydrogen).

[0174] Preferably, step (c) is carried out under the following conditions:

[0175] (i) The lower threshold temperature TL is 500 °C and the upper threshold temperature is 750 °C;

[0176] (ii) A time period t of 1 hour to 12 hours; and

[0177] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0178] Preferably, step (c) is carried out under the following conditions:

[0179] (i) The lower threshold temperature TL is 500 °C and the upper threshold temperature is 700 °C;

[0180] (ii) A time period t of 90 minutes to 6 hours; and

[0181] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0182] Preferably, step (c) is carried out under the following conditions:

[0183] (i) The lower threshold temperature TL is 510 °C and the upper threshold temperature is 750 °C;

[0184] (ii) A time period t of 30 minutes to 24 hours; and

[0185] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0186] Preferably, step (c) is carried out under the following conditions:

[0187] (i) The lower threshold temperature TL is 510 °C and the upper threshold temperature is 750 °C;

[0188] (ii) A time period t of 1 hour to 12 hours; and

[0189] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0190] Preferably, step (c) is carried out under the following conditions:

[0191] (i) The lower threshold temperature TL is 510 °C and the upper threshold temperature is 700 °C;

[0192] (ii) A time period t of 90 minutes to 6 hours; and

[0193] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0194] Preferably, step (c) is carried out under the following conditions:

[0195] (i) The lower threshold temperature TL is 520 °C and the upper threshold temperature is 750 °C;

[0196] (ii) A time period t of 30 minutes to 24 hours; and

[0197] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0198] Preferably, step (c) is carried out under the following conditions:

[0199] (i) The lower threshold temperature TL is 520 °C and the upper threshold temperature is 750 °C;

[0200] (ii) A time period t of from 1 hour to 12 hours; and

[0201] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0202] Preferably, step (c) is carried out under the following conditions:

[0203] (i) The lower threshold temperature TL is 520 °C and the upper threshold temperature is 700 °C;

[0204] (ii) A time period t of from 90 minutes to 6 hours; and

[0205] (iii) in the presence of an inert gas (optionally containing hydrogen).

[0206] Step (c) preferably comprises heat-treating the particles from step (b) at a temperature of at least 400 °C and in the presence of an inert gas to promote the formation of Si-Si bonds in the silicon domains, to promote the formation of covalent bonds between the silicon and the inner surface of the porous particle skeleton while avoiding the formation of silicon carbide, to reduce the surface area of the silicon domains, and / or to improve the chemical stability of the silicon domains.

[0207] Steps (b) and (c) can be carried out in the same reaction vessel. Alternatively, step (b) can be carried out in a first reaction vessel, and then the particles formed in step (b) can be transferred to a second reaction vessel for step (c). During the transfer to the second reaction vessel, the particles can be maintained at a temperature lower than the temperature in step (b). Preferably, during the transfer to the second reaction vessel, the particles are maintained at a temperature of at least 50 °C.

[0208] In one aspect, the present invention provides a method for preparing composite particles, the method comprising the following steps:

[0209] (a) Providing a plurality of porous particles comprising micropores and / or mesopores;

[0210] (b) Contacting the porous particles with a silicon-containing precursor at a temperature effective to cause the deposition of a plurality of nanosized silicon domains in the pores of the porous particles;

[0211] (c) Maintain the particles from step (b) at a lower threshold temperature TL of at least 400 °C for a period of time t.

[0212] Preferably, step (c) includes maintaining the particles from step (b) between a lower threshold temperature TL and an upper threshold temperature TU for a period of time t.

[0213] Preferably, the lower threshold temperature TL is 500 °C, the upper threshold temperature TU is 700 °C, and the period of time t is from 90 minutes to 6 hours.

[0214] The above aspect of the present invention may optionally be combined with any other features disclosed herein regarding the first aspect of the present invention.

[0215] The method of the present invention optionally further comprises the following steps:

[0216] (d) Contact the surface of the particles from step (c) with a passivating agent, or prior to step (c), contact the particles from step (b) with a passivating agent.

[0217] As defined herein, a passivating agent is a compound or mixture of compounds capable of reacting with the surface of the silicon deposited in step (b) to form a modified surface. In particular, as defined herein, a passivating agent is a material capable of reacting with the surface of silicon to further reduce its surface energy.

[0218] Preferably, step (d) is carried out after step (c). As discussed above, one function of step (c) is to reopen the pore space that was previously blocked or capped by the silicon nanostructures, making the pore space accessible to the passivating gas, thereby allowing for more extensive passivation of the silicon surface and the elimination of the hydrogen-terminated silicon surface.

[0219] One type of passivation layer is a native oxide layer. The native oxide layer can be formed, for example, by exposing the silicon surface to a passivating agent selected from air or other oxygen-containing gases. This passivation layer may contain silicon oxide of the formula SiO x where 0 < x ≤ 2. The silicon oxide is preferably amorphous silicon oxide. The formation of the native oxide layer is exothermic, so careful process control is required to prevent overheating or even combustion of the particulate material. In the case where the passivating agent is an oxygen-containing gas, step (c) may include: cooling the material formed in step (b) to a temperature below 300 °C, preferably below 200 °C, optionally below 100 °C, before contacting the silicon surface with the oxygen-containing gas.

[0220] Another type of passivation layer is a nitride layer formed, for example, by exposing the silicon surface to a passivating agent selected from ammonia or other nitrogen-containing molecules. This passivation layer may contain silicon nitride of the formula SiN xa silicon nitride where 0 < x ≤ 4 / 3. The silicon nitride is preferably amorphous silicon nitride. The nitride layer can be formed by contacting the silicon surface with ammonia at a temperature in the range of 200 to 700 °C, preferably 400 to 700 °C, more preferably 400 to 600 °C. Then, the temperature can be raised to the range of 500 to 1,000 °C if necessary to form a nitride surface (e.g., a silicon nitride surface of the formula SiNx where x ≤ 4 / 3). Nitride passivation can be superior to oxide passivation. Because sub-stoichiometric nitrides (such as SiN x , where 0 < x ≤ 4 / 3) are conductive, the nitride passivation layer can act as a conductive network that allows for faster charging and discharging of electroactive materials. As a phosphorus analogue of ammonia, phosphine can also be used as a passivating agent.

[0221] Another type of passivation layer is, for example, an oxynitride layer formed by exposing the silicon surface to a passivating agent containing ammonia (or other nitrogen-containing molecules) and oxygen. The passivation layer can contain an oxynitride of the formula SiO x N y , where 0 < x < 2, 0 < y < 4 / 3, and 0 < (2x + 3y) ≤ 4). The silicon oxynitride is preferably amorphous silicon oxynitride.

[0222] Another type of passivation layer is a carbide layer. The passivation layer can contain silicon carbide of the formula SiC x , where 0 < x ≤ 1. The silicon carbide is preferably amorphous silicon carbide. The carbide layer can be formed by contacting the silicon surface with a passivating agent selected from carbon-containing precursors (such as methane or ethylene) at a high temperature in the range of 250 to 700 °C. At lower temperatures, covalent bonds are formed between the silicon surface and the carbon-containing precursor, and the carbon-containing precursor is converted into a crystalline silicon carbide monolayer as the temperature increases. The silicon carbide can have the formula SiCx, where 0 < x ≤ 1.

[0223] Other suitable passivating agents include: compounds containing olefin, alkyne or carbonyl functional groups, more preferably terminal olefins, terminal alkynes, aldehyde groups or ketone groups.

[0224] Preferred passivating agents include one or more compounds having the following formula:

[0225] (i) R 1 -CH=CH-R 1 ;

[0226] (ii) R 1 -C≡C-R 1 ; and

[0227] (iii) O=CR 1 R 1 ;

[0228] Each R 1 independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or two R 1 groups form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring.

[0229] Particularly preferred passivating agents include one or more compounds having the following formula:

[0230] (i) CH 2 =CH-R 1 ; and

[0231] (ii) HC≡C-R 1 ;

[0232] wherein R 1 is as defined above. Preferably, R 1 is unsubstituted.

[0233] 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, a mixture of different passivating agents can also be used.

[0234] It is believed that passivating agents containing olefinic, acetylenic, or carbonyl groups undergo an insertion reaction with Si-H groups on the silicon surface to form a covalently passivated surface that is resistant to air oxidation. Thus, the passivation reaction between the silicon surface and the passivating agent can be understood as a form of hydrosilylation, as schematically shown below.

[0235]

[0236] Other suitable passivating agents include compounds containing active hydrogen atoms bonded to oxygen, nitrogen, sulfur, or phosphorus. For example, the passivating agent can be an alcohol, an amine, a thiol, or a phosphine. The reaction of the group -XH with the hydride group on the silicon surface is understood to result in the elimination of H 2 and the formation of a direct bond between X and the silicon surface.

[0237] Suitable passivating agents in this category include compounds having the following formula:

[0238] (iv) HX-R 2 , and

[0239] (v) HX-C(O)-R 1 ,

[0240] wherein X represents O, S, NR 1 or PR1 ; each R 1 is independently as defined above; and R 2 represents an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or R 1 and R 2 together form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring.

[0241] Preferably, X represents O or NH.

[0242] Preferably, R 2 represents an optionally substituted aliphatic or aromatic group having 2 to 10 carbon atoms. An amino group can also be incorporated into a 4- to 10-membered aliphatic or aromatic ring structure, such as in pyrrolidine, pyrrole, imidazole, piperazine, indole or purine.

[0243] Another suitable passivating agent is water. For example, the silicon surface can be exposed to water vapor. Alternatively, the particles from step (c) can be immersed in water. Optionally, passivation with water can be carried out after passivation with one or more of the passivating agents disclosed above.

[0244] Preferably, step (d) is carried out using a passivating agent other than air.

[0245] The contact of the electroactive material with the passivating agent in step (d) can be carried out at a temperature in the range of 25 to 500 °C, preferably in the range of 50 to 450 °C, more preferably 100 to 400 °C.

[0246] The method of the present invention optionally further comprises the following step:

[0247] (e) depositing a lithium-ion permeable material into the pores and / or outer surface of the composite particles from step (c) or step (d).

[0248] Preferably, the lithium-ion permeable material is a pyrolytic carbon material, and step (e) comprises: combining the particles from step (c) or step (d) with a pyrolytic carbon precursor; and heating the pyrolytic carbon precursor to a temperature effective to cause deposition of a conductive pyrolytic carbon material into the pores and / or outer surface of the composite particles. In the case where step (d) is included in the method, step (e) can optionally be carried out before or after step (d). In each case, step (e) is carried out after step (c).

[0249] The pyrolytic carbon precursor is preferably a hydrocarbon. Suitable hydrocarbons include polycyclic hydrocarbons containing 10 to 25 carbon atoms and optionally 1 to 3 heteroatoms, optionally where the polycyclic hydrocarbons are selected from naphthalene, substituted naphthalenes (such as dihydroxynaphthalene), anthracene, tetracene, pentacene, fluorene, acenapthene, phenanthrene, fluoranthene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone, and their alkyl-substituted derivatives. Suitable pyrolytic carbon precursors also include bicyclic monoterpenes, optionally where the bicyclic monoterpenes are selected from camphor, borneol, eucalyptol, camphene, careen, sabinene, limonene, and pinene. Other suitable pyrolytic carbon precursors include C 2 -C 10 hydrocarbons, optionally where the hydrocarbons are selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, and aromatic hydrocarbons, such as methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, α-terpinene, and acetylene. Other suitable pyrolytic carbon precursors include phthalocyanine, sucrose, starch, graphene oxide, reduced graphene oxide, pyrene, perhydropyrene, 9,10-benzophenanthrene, tetracene, benzopyrene, perylene, coronene, and chrysene. A preferred carbon precursor is acetylene.

[0250] The temperature suitable for the deposition of the pyrolytic carbon material in step (e) is in the range of 300 to 800 °C, or 400 to 700 °C. For example, the temperature can be not more than 680 °C, or not more than 660 °C, or not more than 640 °C, or not more than 620 °C, or not more than 600 °C, or not more than 580 °C, or not more than 560 °C, or not more than 540 °C, or not more than 520 °C, or not more than 500 °C. The minimum temperature will depend on the type of carbon precursor 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.

[0251] The carbon precursor used in step (e) can be used in pure form or as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the usage amount of the carbon precursor can be in the range of 0.1 vol% to 100 vol%, or 0.5 vol% to 20 vol%, or 1 vol% to 10 vol%, or 1 vol% to 5 vol% based on the total volume of the precursor and the inert carrier gas.

[0252] In the case of depositing a pyrolytic carbon material in step (e), the same compound can serve as both the passivating agent in step (d) and the pyrolytic carbon precursor in step (e). For example, if styrene is selected as the pyrolytic carbon precursor, styrene will also serve as a passivating agent in the case where the particles from step (b) are not exposed to other passivating agents before contacting styrene. In this case, passivation and deposition of the conductive carbon material in some steps can be carried out simultaneously, for example, at a temperature in the range of 300 to 700 °C. Alternatively, passivation and deposition of the conductive carbon material can be carried out sequentially, using the same material as the passivating agent and the pyrolytic carbon precursor, but where step (e) is carried out at a temperature higher than the passivation in step (d) after the passivation in step (d). For example, the passivation in step (d) can be carried out at a temperature in the range of 25 °C to less than 300 °C, while the deposition of pyrolytic carbon can be carried out at a temperature in the range of 300 to 700 °C. These two steps can be suitably carried out sequentially by raising the temperature while maintaining contact with the compound that serves as both the passivating agent and the pyrolytic carbon precursor. At a lower temperature (e.g., in the range of 25 °C to <300 °C), passivation will be the main process. As the temperature rises (e.g., rises to 300 to 700 °C), deposition of pyrolytic carbon will then occur.

[0253] A series of different silicon loadings in the composite particles can be obtained using the method of the present invention. The composite particles obtained according to the method of the present invention preferably contain at least 26 wt% of silicon, or at least 28 wt% of silicon, or at least 30 wt% of silicon, or at least 32 wt% of silicon, or at least 34 wt% of silicon, or at least 36 wt% of silicon, or at least 38 wt% of silicon, or at least 40 wt% of silicon, or at least 42 wt% of silicon, or at least 44 wt% of silicon.

[0254] The amount of the electroactive material (e.g., silicon) in the composite particles is preferably selected such that at least 20% to 90% of the internal pore volume of the porous particles is occupied by the electroactive material after step (c). For example, the electroactive material can occupy 20% to 80%, or 25% to 75%, or 30% to 70%, or 35% to 65%, or 40% to 60%, or 45% to 55% of the internal pore volume of the porous particles. Within these preferred ranges, the remaining pore volume of the porous particles effectively accommodates the expansion of the electroactive material during charging and discharging, without a large excess pore volume, which is not conducive to the volumetric capacity of the particulate particles. However, the amount of the electroactive material is not so high as to hinder effective lithiation due to insufficient metal ion diffusion rate or due to insufficient expansion volume resulting in mechanical resistance to lithiation.

[0255] In the case where the electroactive material is silicon, by requiring the mass ratio of silicon to the porous particles to be in the range of [0.5×P 1 to 1.9×P 1In the range of [0,1], the amount of silicon in the composite particles can be correlated with the available pore volume in the porous particles, where P 1 is a dimensionless quantity having a magnitude of the total pore volume (expressed in cm 3 / g) of the micropores and mesopores in the porous particles (for example, if the total volume of the micropores and mesopores in the porous particles is 1.2 cm 3 / g, then P 1 = 1.2). This relationship takes into account the density of silicon and the pore volume of the porous particles to define the weight ratio of silicon at which the occupied pore volume is approximately 20% to 82%. Preferably, the weight ratio of the silicon deposited in step (b) to the porous particles is in the range of [0.6×P 1 to 1.8×P 1 :1, or [0.7×P 1 to 1.7×P 1 :1, or [0.8×P 1 to 1.6×P 1 :1.

[0256] The amount of silicon in the composite particles can be determined by elemental analysis. Preferably, elemental analysis is used to determine the elemental composition of the individual porous particles and the composition of the composite particles.

[0257] Preferably, the silicon content is determined by ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry). A variety of ICP-OES instruments are commercially available, such as the iCAP® 7000 series ICP-OES analyzer (available from ThermoFisher Scientific). Preferably, the carbon content (and if necessary, the hydrogen content, nitrogen content, and oxygen content) of the composite particles and the porous carbon particles themselves is determined by IR absorption. A suitable instrument for determining the carbon content, hydrogen content, nitrogen content, and oxygen content is the TruSpec® Micro elemental analyzer (available from Leco Corporation).

[0258] Preferably, at least 90 wt%, more preferably at least 95 wt%, and even more preferably at least 98 wt% of the electroactive material in the composite particles is located within the internal pore volume of the porous particles, such that no or very little electroactive material is located on the outer surface of the composite particles. As discussed above, the deposition of the electroactive material during the CVI process occurs on the surface of the porous particles. Given the very high internal surface area of the porous particles, the reaction kinetics of the CVI process ensure that the deposition of the electroactive material occurs almost entirely within the pores of the porous particles. The internal deposition of the electroactive material is further improved by requiring that the pressure in step (b) be maintained below 200 kPa or within the more preferred pressure range discussed above.

[0259] The characteristics of the composite particles obtained by the method of the present invention can lie in their performance under thermogravimetric analysis (TGA) in air. This analysis method relies on the following principle: an increase in weight is observed when the electroactive material is oxidized in air and at elevated temperature.

[0260] As defined herein, "surface silicon" is calculated from the initial mass increment in the TGA trace from the minimum mass between 150 °C and 500 °C to the maximum mass measured in the temperature range of 550 °C to 650 °C, where the TGA is carried out in air at a heating rate of 10 °C / min. This mass increment is considered to be due to the oxidation of surface silicon, thus enabling the percentage of surface silicon to be determined as a proportion of the total silicon according to the following formula:

[0261] Y = 1.875 × [(M max - M min ) / M f × 100%

[0262] where Y is the percentage of surface silicon (proportion of the total silicon in the sample), M max is the maximum mass of the sample measured in the temperature range of 550 °C to 650 °C, M min is the minimum mass of the sample above 150 °C and below 500 °C, and M f is the mass of the sample at the completion of oxidation at 1400 °C. For completeness, it should be understood that 1.875 is the molar mass ratio of SiO 2 to O 2 (i.e., the mass ratio of the formed SiO 2 to the mass increment due to the addition of oxygen). Typically, the TGA analysis is carried out using a sample amount of 10 mg ± 2 mg.

[0263] It has been found that when the surface silicon determined by the above TGA method is at least 20 wt% of the total amount of silicon in the material, the reversible capacity retention rate after multiple charge / discharge cycles is significantly improved. Preferably, by thermogravimetric analysis (TGA) determination, at least 22 wt%, or at least 25 wt%, at least 30 wt% of silicon, or at least 35 wt% of silicon, or at least 40 wt% of silicon, or at least 45 wt% of silicon is surface silicon.

[0264] In addition to the surface silicon content, the silicon-containing composite particles obtained by the method of the present invention preferably have a low content of bulk-phase silicon as determined by TGA. Bulk-phase silicon is defined herein as the silicon that is oxidized at a temperature above 800 °C as determined by TGA, where the TGA is carried out in air at a heating rate of 10 °C / min. Thus, the bulk-phase silicon content is determined according to the following formula:

[0265] Z = 1.875 × [(M f - M 800 ) / M f × 100%

[0266] where Z is the percentage of silicon that is not oxidized at 800 °C, M 800 is the mass of the sample at 800 °C, and M f is the mass of the ash at the end 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 SiO 2 , and the total mass at the end of oxidation is SiO 2 .

[0267] Silicon oxidized above 800 °C is less desirable. Preferably, by TGA measurement, 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 bulk-phase silicon.

[0268] Preferably, at least 30 wt% of the silicon is surface silicon and no more than 10 wt% of the silicon is bulk-phase silicon, both 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 bulk-phase silicon, both 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 bulk-phase silicon, both 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 bulk-phase silicon, both determined by TGA.

[0269] The BET surface area of the composite particles obtained by the method according to the invention is preferably no more than 300 m 2 / g, or no more than 250 m 2 / g, or no more than 200 m 2 / g, or no more than 150 m 2 / g. More preferably, no more than 100 m 2 / g, or no more than 80 m 2 / g, or no more than 60 m 2 / g, or no more than 40 m 2 / g, or no more than 30 m 2 / g, or no more than 25 m 2 / g, or no more than 20 m 2 / g, or no more than 15 m 2 / g, or no more than 10 m 2 / g, or no more than 5 m2 / g. Generally, a low BET surface area is preferred to minimize the formation of the solid electrolyte interface (SEI) layer at the surface of the composite particles during the first charge-discharge cycle of the anode. However, an overly low BET surface area results in unacceptably low charge rates and capacities 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 m 2 / g, or at least 1 m 2 / g, or at least 2 m 2 / g, or at least 5 m 2 / g. For example, the BET surface area of the composite particles can be in the range of 0.1 to 100 m 2 / g, or 0.1 to 80 m 2 / g, or 0.5 to 60 m 2 / g, or 0.5 to 40 m 2 / g, or 1 to 30 m 2 / g, or 1 to 25 m 2 / g, or 2 to 20 m 2 / g.

[0270] The ratio of the BET surface area of the particles formed in step (c) to the BET surface area of the particles formed in step (b) can 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.

[0271] The ratio of the BET surface area of the particles formed in step (c) to the BET surface area of the particles formed in step (b) can be not more than 15:1, or not more than 14:1, or not more than 13:1, or not more than 12:1.

[0272] The ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) measured by gas adsorption can 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.

[0273] The ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) measured by gas adsorption can be not more than 20:1, or not more than 19:1, or not more than 18:1, or not more than 17:1, or not more than 16:1, or not more than 15:1.

[0274] The ratio of the total hydrogen content of the particles formed in step (c) to the total hydrogen content of the particles formed in step (b) may be not more than 0.8:1, or not more than 0.7:1, or not more than 0.6:1, or not more than 0.5:1.

[0275] The ratio of the total hydrogen content of the particles formed in step (c) to the total hydrogen content of the particles formed in step (b) may be at least 0.1:1, or at least 0.2:1, or at least 0.3:1.

[0276] The reaction process can be carried out using any reactor capable of bringing solids and gases into contact at high temperatures. The porous particles and the formed composite particles can exist in the reactor in the form of a fixed bed of particles or in the form of a moving or stirred bed of particles.

[0277] In a second aspect, the present invention provides a composite particle obtainable by the method according to the first aspect of the present invention.

[0278] In a third aspect of the present invention, there is provided a composition comprising the composite particle according to the second aspect of the present invention and at least one other component. In particular, there is provided a composition comprising the composite particle according to the second aspect of the present invention and at least one other component selected from: (i) a binder; (ii) a conductive additive; and (iii) a further particulate electroactive material. The composition according to the third aspect of the present invention can be used as an electrode composition and can thus be used to form an active layer of an electrode.

[0279] The composition can be a mixed-type electrode composition comprising the composite particle and at least one further particulate electroactive material. Examples of the further particulate electroactive material include graphite, hard carbon, silicon, tin, germanium, aluminum, and lead. The at least one further particulate electroactive material is preferably selected from graphite and hard carbon, and most preferably, the at least one further particulate electroactive material is graphite.

[0280] In the case of the mixed-type electrode composition, the composition preferably comprises from 3 wt% to 60 wt%, or from 3 wt% to 50 wt%, or from 5 wt% to 50 wt%, or from 10 wt% to 50 wt%, or from 15 wt% to 50 wt% of the composite particle according to the second aspect of the present invention, based on the total dry weight of the composition.

[0281] The at least one further particulate electroactive material is suitably present in an amount of from 20 wt% to 95 wt%, or from 25 wt% to 90 wt%, or from 30 wt% to 75 wt% of the at least one further particulate electroactive material.

[0282] The D of the at least one further particulate electroactive material 50The particle size is preferably in the range of 10 to 50 µm, preferably 10 to 40 µm, more preferably 10 to 30 µm, and most preferably 10 to 25 µm, for example in the range of 15 to 25 µm.

[0283] D of at least one additional particulate electroactive material 10 The particle size is preferably at least 5 µm, more preferably at least 6 µm, more preferably at least 7 µm, more preferably at least 8 µm, more preferably at least 9 µm, and still more preferably at least 10 µm.

[0284] D of at least one additional particulate electroactive material 90 The particle size is preferably at most 100 µm, more preferably at most 80 µm, more preferably at most 60 µm, more preferably at most 50 µm, and most preferably at most 40 µm.

[0285] At least one additional particulate electroactive material is preferably selected from carbon-containing particles, graphite particles and / or hard carbon particles, wherein the D of the graphite particles and the hard carbon particles 50 The particle size is in the range of 10 to 50 µm. Still more preferably, at least one additional particulate electroactive material is selected from graphite particles, wherein the D of the graphite particles 50 The particle size is in the range of 10 to 50 µm.

[0286] The composition may also be a non-mixed (or "high loading") electrode composition that is substantially free of additional particulate electroactive materials. In this case, the term "substantially free of additional particulate electroactive materials" shall be construed to mean that, based on the total dry weight of the composition, the composition contains 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 material (i.e., additional material capable of intercalating and releasing metal ions during charging and discharging of the battery).

[0287] Based on the total dry weight of the composition, this type of "high loading" electrode composition preferably contains at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt% of the composite particles according to the second aspect of the present invention.

[0288] The composition may optionally contain a binder. The binder serves to adhere the composition to the current collector and maintain the integrity of the composition. Examples of binders that can be used according to the present invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginates and their alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The composition may contain a mixture of multiple binders. Preferably, the binder includes a polymer selected from the following: polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, SBR, and CMC.

[0289] The binder may suitably be present in an amount of 0.5 wt% to 20 wt%, preferably 1 wt% to 15 wt%, preferably 2 wt% to 10 wt%, and most preferably 5 wt% to 10 wt% based on the total dry weight of the composition.

[0290] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as crosslinking promoters, coupling agents, and / or adhesion promoters.

[0291] The composition may optionally contain one or more conductive additives. Preferred conductive additives are non-electroactive materials that are included to improve the conductivity between the electroactive components of the composition and between the electroactive components of the composition and the current collector. The conductive additives may be selected from carbon black, carbon fiber, carbon nanotubes, graphene, acetylene black, Ketjen black, metal fibers, metal powders, and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes.

[0292] One or more conductive additives may suitably be present in a total amount of 0.5 wt% to 20 wt%, preferably 1 wt% to 15 wt%, preferably 2 wt% to 10 wt%, and most preferably 5 wt% to 10 wt% based on the total dry weight of the composition.

[0293] In a fourth aspect, the present invention provides an electrode comprising the composite particles according to the second aspect of the present invention and a current collector, wherein the composite particles are in electrical contact with the current collector. The particulate material for preparing the electrode according to the fourth aspect of the present invention may be in the form of the composition according to the third aspect of the present invention.

[0294] As used herein, the term current collector refers to any conductive substrate that is capable of carrying an electric current to the electroactive particles in the composition and of carrying an electric current away from the electroactive particles in the composition. Examples of materials that can be used as current collectors include copper, aluminum, 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 from 3 to 500 μm. The particulate material of the present invention can be applied to one or both surfaces of the current collector to a thickness preferably in the range of from 10 μm to 1 mm, such as from 20 to 500 μm, or from 50 to 200 μm.

[0295] The electrode of the fourth aspect of the present invention can be prepared by combining the particulate material of the present invention with a solvent and optionally one or more viscosity-modifying additives to form a slurry. The slurry is then cast onto the surface of the current collector and the solvent is removed, thereby forming an electrode layer on the surface of the current collector. Additional steps can be carried out as appropriate, such as heat treatment for curing any binder and / or calendering of the electrode layer. The thickness of the electrode layer is suitably in the range of from 20 µm to 2 mm, preferably from 20 µm to 1 mm, preferably from 20 µm to 500 µm, preferably from 20 µm to 200 µm, preferably from 20 µm to 100 µm, preferably from 20 µm to 50 µm.

[0296] Alternatively, the slurry can be formed into a free-standing film or mat comprising the particulate material of the present invention, for example, 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 sticky free-standing object that can then be bonded to the current collector by known methods.

[0297] The electrode of the fourth aspect of the present invention can be used as the anode of a metal ion battery. Thus, in a fifth aspect, the present invention provides a rechargeable metal ion battery comprising the electrode of the fourth aspect as the anode.

[0298] The metal ion is preferably a lithium ion. More preferably, the rechargeable metal ion battery of the present invention is a lithium ion battery and the cathode active material is capable of releasing and accepting lithium ions.

[0299] The cathode of a rechargeable metal ion battery generally 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 material. Examples of suitable cathode active materials include LiCoO 2 、LiCo 0.99 Al 0.01 O 2 、LiNiO 2 、LiMnO 2 、LiCo0.5 Ni 0.5 O 2 、LiCo 0.7 Ni 0.3 O 2 、LiCo 0.8 Ni 0.2 O 2 、LiCo 0.82 Ni 0.18 O 2 、LiCo 0.8 Ni 0.15 Al 0.05 O 2 、LiNi 0.4 Co 0.3 Mn 0.3 O 2 and LiNi 0.33 Co 0.33 Mn 0.34 O 2 The cathode current collector generally has a thickness of 3 to 500 μm. Examples of materials that can be used as the cathode current collector include aluminum, stainless steel, nickel, titanium, and sintered carbon.

[0300] Suitable electrolytes are non-aqueous electrolytes containing metal salts (e.g., lithium salts), and may include, but are not limited to, non-aqueous electrolytes, solid electrolytes, and inorganic solid electrolytes. Examples of non-aqueous electrolyte solutions that can be used include: aprotic organic solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triesters of phosphate, trimethoxymethane, sulfolane, methyl sulfolane, and 1,3-dimethyl-2-imidazolidinone.

[0301] Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ion dissociative groups.

[0302] Examples of inorganic solid electrolytes include lithium salts of nitrides, halides, and sulfides, such as Li 5 NI 2 , Li 3 N, LiI, LiSiO 4 , Li 2 SiS 3 , Li 4 SiO 4 , LiOH and Li 3 PO4 .

[0303] The lithium salt is suitably soluble in the selected solvent or solvent mixture. Examples of suitable lithium salts include LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiBC 4 O 8 , LiPF 6 , LiCF 3 SO 3 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li and CF 3 SO 3 Li.

[0304] In the case where the electrolyte is a non-aqueous organic solution, the metal ion battery is preferably provided with a separator 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 size of 0.01 to 100 μm and a thickness of 5 to 300 μm. Examples of suitable electrode separators include microporous polyethylene membranes.

[0305] The separator can be replaced with a polymer electrolyte material, and in such a case, the polymer electrolyte material is present within the composite anode layer and both of them.

[0306] Examples

[0307] Example 1

[0308] Load the silicon-carbon composite material sample A (30 g) into the furnace tube. Seal the furnace tube and then purge it with nitrogen (0.3 L / min) for 30 minutes. Heat the furnace tube to the target temperature (650 °C) in 97 minutes under nitrogen (0.3 L / min).

[0309] Then anneal the silicon-carbon composite material at 650 °C for 180 minutes under nitrogen (0.5 L / min). Then cool the furnace temperature to room temperature under nitrogen (0.5 L / min).

[0310] After that, passivate the annealed material with 100% acetylene gas (0.75 L / min) for 60 minutes. Then cool the furnace to room temperature under the flow of acetylene (0.16 L / min) and nitrogen (0.35 L / min).

[0311] Then the final passivation step was carried out at room temperature for 35 minutes under a flow of nitrogen (0.2 L / min) and air (0.3 L / min), and then for 90 minutes under a flow of air (0.5 L / min).

[0312] The resulting powder was characterized as Sample B.

[0313] Sample C was prepared using the method described for Sample B and the conditions listed in Table 1 below. The characterization of Samples A - C is provided in Table 2 below. Sample A is the silicon - carbon composite material used to prepare Samples B - C.

[0314] The cumulative pore volumes of Samples A and C are shown in Figure 1 .

[0315] Table 1: Annealing conditions for Samples B and C

[0316]

[0317] Table 2: Characterization of Samples A - C

[0318]

[0319] Example 2

[0320] A silicon - carbon composite material sample D (40 g) was loaded into a rotary kiln tube. The rotary kiln tube was sealed and then purged with nitrogen (0.3 L / min) for 30 minutes. The furnace tube was heated to the target temperature (520 °C) in 80 minutes under nitrogen (0.3 L / min) and stabilized for 10 minutes.

[0321] The nitrogen flow rate was increased to 0.66 L / min, the rotation speed was increased to 50 rpm, and the silicon - carbon composite material was annealed for 180 minutes. Then the furnace was cooled to room temperature.

[0322] Then the annealed material was passivated at room temperature for 30 minutes under a flow of nitrogen (0.2 L / min) and air (0.3 L / min), and then for 30 minutes under a flow of air (0.5 L / min).

[0323] The resulting powder was characterized as Sample E.

[0324] Sample F - G was prepared using the method described for Sample E and the conditions listed in Table 3 below. The characterization of Samples D - G is provided in Table 4 below. Sample D is the silicon - carbon composite material used to prepare Samples E - G.

[0325] Table 3: Annealing conditions for Samples E - G

[0326]

[0327] Table 4: Characterization of Samples D - G

[0328]

[0329] As shown in Tables 2 and 4, the hydrogen content decreases due to annealing.

[0330] Adding hydrogen to the annealing atmosphere (as in Sample G) results in increased retention of hydrogen within the structure, and thus, the surface silicon content is more similar to that of the baseline silicon carbide composite sample D.

[0331] Example 3

[0332] Load silicon carbide composite sample A (30 g) into a furnace tube. Seal the furnace tube and then purge with nitrogen (0.3 L / min) for 30 minutes. Heat the furnace tube to the target temperature (600 °C) in 97 minutes under nitrogen (0.3 L / min).

[0333] Then anneal the silicon carbide composite at 600 °C for 30 minutes under nitrogen (0.5 L / min). Then cool the furnace temperature to 400 °C.

[0334] After that, passivate the annealed material with 100% ethylene gas (0.75 L / min) for 60 minutes. Then cool the furnace to room temperature under a flow of ethylene (0.16 L / min) and nitrogen (0.35 L / min).

[0335] Then the final passivation step is carried out at room temperature under a flow of nitrogen (0.2 L / min) and air (0.3 L / min) for 35 minutes, and then under a flow of air (0.5 L / min) for 90 minutes.

[0336] Screen the resulting black - gray powder through a 53 - micron sieve and perform characterization as Sample H.

[0337] Prepare Samples I - K using the method described for Sample H and the conditions listed in Table 5 below. The characterization of Samples H - K is provided in Table 6 below. Sample A is the silicon carbide composite used to prepare Samples H - K.

[0338] Table 5: Annealing and Passivation Conditions for Samples H - K

[0339]

[0340] Table 6: Characterization of Samples H - K

[0341]

[0342] The BET surface area and LECO - H% of Samples A, H, I, C, and K decreased (relative to Sample A) inFigure 2 This is shown in Figure 2 . Heat treatment increases the pore volume accessible to gases because of the volume shrinkage of silicon due to hydrogen desorption (LECO-H% of samples H, I, C, and K decreases relative to sample A).

[0343] Example 4

[0344] A silicon-carbon composite material sample L (31 g) was charged into a rotary kiln tube. The rotary kiln tube was sealed and then purged with nitrogen (0.3 L / min) for 30 minutes. The furnace tube was heated to the target temperature (650 °C) in 97 minutes under nitrogen (0.3 L / min) and stabilized for 10 minutes. The silicon-carbon composite material was annealed for 180 minutes.

[0345] Then the furnace was cooled to 520 °C, and the annealed material was contacted with a mixture of acetylene (0.35 L / min) and nitrogen (0.79 L / min) for 90 minutes and then only with nitrogen (0.5 L / min) for 10 minutes to form a carbon coating. Then the material was cooled to room temperature.

[0346] Then the carbon-coated material was passivated for 30 minutes at room temperature under a flow of nitrogen (0.2 L / min) and air (0.3 L / min), and then passivated for 30 minutes under a flow of air (0.5 L / min).

[0347] The resulting powder was characterized as sample M.

[0348] Sample N was prepared using a procedure similar to that of sample M, except that the annealed material was carbon-coated at 650 °C.

[0349] Sample O was prepared using a procedure similar to that of sample M, except that sample A was used as the raw material.

[0350] Table 6: Annealing and carbon coating conditions for samples M - O

[0351]

[0352] Table 7: Characterization of samples L - O

[0353]

[0354] As shown in Table 7, the combination of both annealing and carbon coating achieved a significant reduction in surface area and hydrogen content.

[0355] Reference Example 5

[0356] Load 30 g of silicon-carbon composite material sample A into a furnace tube. Seal the furnace tube and then purge it with nitrogen (0.3 L / min) for 30 minutes. Heat the furnace tube to the target temperature (650 °C) in 97 minutes under nitrogen (0.3 L / min) and keep it stable for 10 minutes.

[0357] After that, bring the composite material into contact with a mixture of acetylene (0.35 L / min) and nitrogen (0.75 L / min) for 90 minutes, and then only with nitrogen (0.5 L / min) for 15 minutes to form a carbon coating. Then cool the material to room temperature.

[0358] Then passivate the carbon-coated material at room temperature under a nitrogen (0.2 L / min) and air (0.3 L / min) flow for 30 minutes, and then passivate it under an air (0.5 L / min) flow for 30 minutes to obtain sample P.

[0359] Table 8: Characterization of sample P

[0360]

[0361] As shown in Table 8, carbon coating using acetylene without a separate annealing step results in a reduced surface area and also causes significant structural deterioration, and the surface silicon content in sample P is significantly lower compared to sample O.

[0362] Example 6 - Battery testing

[0363] Manufacture an electrode by adding silicon-carbon composite particles to a dispersion of carbon black in a CMC binder in a Thinky TM mixer. Add an SBR binder to provide a CMC:SBR ratio of 1:1, obtaining a slurry with a weight ratio of Si-C composite material: CMC / SBR: carbon black of 70%:16%:14%. Cast the slurry onto a 10 μm thick copper substrate (current collector) and dry it at 50 °C for 10 minutes, and then dry it at 110 °C for 12 hours to form a negative electrode with a coating density of 1.5 - 2.0 ± 0.5 g / cm 3 of.

[0364] Use this electrode as the negative electrode and a nickel-manganese-cobalt (NMC532) electrode as the positive electrode to manufacture a full pouch single-layer battery, where based on their respective areal capacities (in mAh / cm 2For the pouch cell, the electrodes were balanced to a cathode-to-anode ratio of 0.9. The pouch cell also includes a porous polyethylene separator, and the electrolyte was added to the cell before sealing the cell. The electrolyte contains 1 M LiPF6 in a 1:5:14 (v / v / v) FEC:EC:EMC (fluoroethylene carbonate / ethylene carbonate / ethylene methyl carbonate) containing 3 wt% VC (vinylene carbonate). 6 .

[0365] The pouch single cells were soaked overnight. For the first formation cycle, the cells were charged at a constant current applied at a rate of C / 25 with a cut-off voltage of 4.3 V. When the cut-off voltage was reached, a constant voltage of 4.3 V was applied until a cut-off current of C / 100 was reached. The cells were allowed to rest for 10 minutes and then discharged at a constant current of C / 25 with a cut-off voltage of 2.75 V. Then the cells were allowed to rest for 10 minutes to complete formation.

[0366] After this formation cycle, the cells were degassed and then reconnected for cycling tests. Cycling was performed at 45 °C under stressed conditions. A 1C current was used, corresponding to the discharge capacity after formation. The cells were charged at a constant current applied at a rate of C / 2 with a cut-off voltage of 4.3 V. When the cut-off voltage was reached, a constant voltage of 4.3 V was applied until a cut-off current of C / 40 was reached, followed by a 5-minute rest period. Then the cells were discharged at a constant current of C / 2 with a cut-off voltage of 2.75 V and a rest period of 5 minutes. This charge-discharge procedure was repeated to determine the number of cycles before the cell reached an 80% capacity retention rate, i.e., before the discharge capacity of the cell decreased to 0.8×(the first discharge capacity after the formation cycle).

[0367] The charge (lithiation) capacity and discharge (delithiation) capacity per unit mass of the silicon-carbon composite material for each cycle were calculated. The results are shown in Table 9.

[0368] Table 9: Cell cycling at 45 °C

[0369]

[0370] As shown in Table 9, cell cycling under stressed conditions (45 °C) shows a significant effect of the annealing process described herein on the cycle life of the electroactive material. The unannealed samples (A, L) showed a significantly faster loss of reversible capacity compared to the annealed sample O (relative to A) and M and N (both relative to L).

Claims

1. A method for preparing composite particles, the method comprising the following steps: (a) providing a plurality of porous particles comprising micropores and / or mesopores; (b) contacting the porous particles with a silicon-containing precursor at a temperature effective to cause deposition of a plurality of silicon domains in the pores of the porous particles; (c) heat-treating the particles from step (b) at a temperature of at least 400 °C and in the presence of an inert gas.

2. The method according to claim 1, wherein the total pore volume of micropores and mesopores in the porous particles measured by gas adsorption is at least 0.4 cm 3 / g, or at least 0.5 cm 3 / g, or at least 0.6 cm 3 / g, or at least 0.65 cm 3 / g, or at least 0.7 cm 3 / g, or at least 0.75 cm 3 / g, or at least 0.8 cm 3 / g.

3. The method according to claim 1 or claim 2, wherein the total pore volume of micropores and mesopores in the porous particles measured by gas adsorption does not exceed 1.8 cm 3 / g, or does not exceed 1.7 cm 3 / g, or does not exceed 1.6 cm 3 / g, or does not exceed 1.55 cm 3 / g, or does not exceed 1.5 cm 3 / g, or does not exceed 1.45 cm 3 / g, or does not exceed 1.4 cm 3 / g, or does not exceed 1.35 cm 3 / g, or does not exceed 1.3 cm 3 / g, or does not exceed 1.25 cm 3 / g, or does not exceed 1.2 cm 3 / g, or does not exceed 1.1 cm 3 / g.

4. The method according to any one of the preceding claims, wherein the PD 90 pore diameter of the porous particles does not exceed 20 nm, or does not exceed 15 nm, or does not exceed 12 nm, or does not exceed 10 nm, or does not exceed 8 nm, or does not exceed 6 nm, or does not exceed 5 nm.

5. The method according to any one of the preceding claims, wherein the PD of the porous particles 90 has a pore diameter of at least 3 nm, or at least 4 nm, or at least 5 nm, or at least 6 nm.

6. The method according to any one of the preceding claims, wherein the PD 50 pore diameter of the porous particles does not exceed 10 nm, or does not exceed 8 nm, or does not exceed 6 nm, or does not exceed 5 nm, or does not exceed 4 nm, or does not exceed 3 nm, or does not exceed 2.5 nm, or does not exceed 2 nm, or does not exceed 1.9 nm, or does not exceed 1.8 nm, or does not exceed 1.7 nm, or does not exceed 1.6 nm.

7. The method according to any one of the preceding claims, wherein based on the total volume of micropores and mesopores in the porous particles, the micropore volume fraction is at least 0.4, or at least 0.45, or at least 0.5, or at least 0.55, or at least 0.

6.

8. The method according to any one of the preceding claims, wherein the D 50 particle size of the composite particles is in the range of 1 to 30 µm.

9. The method according to any one of the preceding claims, wherein the D 10 particle size of the composite particles is at least 0.5 µm, or at least 0.8 µm, or at least 1 µm, or at least 1.5 µm, or at least 2 µm.

10. The method according to any one of the preceding claims, wherein the D 90 particle size of the composite particles does not exceed 50 µm, or does not exceed 40 µm, or does not exceed 30 µm, or does not exceed 25 µm, or does not exceed 20 µm, or does not exceed 15 µm.

11. The method according to any one of the preceding claims, wherein the BET surface area of the porous particles is in the range of 100 m 2 / g to 4,000 m 2 / g, or 500 m 2 / g to 4,000 m 2 / g, or 750 m 2 / g to 3,500 m 2 / g, or 1,000 m 2 / g to 3,250 m 2 / g, or 1,000 m 2 / g to 3,000 m 2 / g, or 1,000 m 2 / g to 2,500 m 2 / g, or 1,000 m 2 / g to 2,000 m 2 / g.

12. The method according to any one of the preceding claims, wherein the porous particles are conductive porous particles, preferably conductive porous carbon particles, more preferably conductive porous carbon particles comprising at least 80 wt%, or at least 85 wt%, or at least 90 wt%, or at least 95 wt% carbon.

13. The method according to any one of the preceding claims, wherein the silicon-containing precursor is a gaseous precursor.

14. The method according to any one of the preceding claims, wherein the silicon-containing precursor is selected from silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), tetrasilane (Si 4 H 10 ), methylsilane, dimethylsilane, and chlorosilane, preferably wherein the silicon-containing precursor is selected from the group consisting of: silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), tetrasilane (Si 4 H 10 ).

15. The method according to claim 13 or claim 14, wherein step (b) comprises: contacting the porous particles 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 silicon-containing precursor based on the total volume of the gas.

16. The method according to any one of the preceding claims, wherein the temperature in step (b) is in the range of 340 to 500 °C, or 350 to 480 °C, or 350 to 450 °C, or 350 to 420 °C, or 350 to less than 400 °C, or 355 to 395 °C, or 360 to 390 °C, or 360 to 385 °C, or 360 to 380 °C, preferably wherein the temperature in step (b) is in the range of 340 to less than 400 °C, or 370 to 395 °C.

17. The method according to any one of the preceding claims, wherein the pressure in step (b) is in the range of 1 to 5000 kPa, or 20 to 500 kPa, or 40 to 200 kPa, or 50 to 150 kPa, or 60 to 120 kPa, or 80 to 100 kPa.

18. The method according to any one of the preceding claims, wherein the temperature in step (c) is greater than the temperature in step (b), optionally wherein the temperature in step (c) 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 (b).

19. The method according to any one of the preceding claims, wherein the temperature in step (c) is 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 wherein the temperature in step (c) is at least 500 °C, more preferably wherein the temperature in step (c) is at least 510 °C, more preferably wherein the temperature in step (c) is at least 520 °C.

20. The method according to any one of the preceding claims, wherein the temperature in step (c) does not exceed 900 °C, or does not exceed 850 °C, or does not exceed 800 °C, or does not exceed 750 °C, or does not exceed 700 °C, or does not exceed 680 °C, or does not exceed 660 °C, or does not exceed 650 °C, preferably wherein the temperature in step (c) does not exceed 750 °C, more preferably wherein the temperature in step (c) does not exceed 700 °C.

21. The method according to any one of the preceding claims, wherein step (c) is carried out for 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 wherein step (c) is carried out for at least 30 minutes, more preferably wherein step (c) is carried out for at least 1 hour, more preferably wherein step (c) is carried out for at least 90 minutes.

22. The method according to any one of the preceding claims, wherein step (c) is carried out for 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, preferably wherein step (c) is carried out for no more than 24 hours, more preferably wherein step (c) is carried out for no more than 12 hours, more preferably wherein step (c) is carried out for no more than 6 hours.

23. The method according to any one of the preceding claims, wherein step (c) comprises maintaining the particles from step (b) above a lower threshold temperature TL of at least 400 °C for a period of time t, preferably step (c) comprises maintaining the particles from step (b) between a lower threshold temperature TL and an upper threshold temperature TU for a period of time t.

24. The method according to claim 23, wherein the lower threshold temperature TL is 500 °C, the upper threshold temperature TU is 700 °C, and the period of time t is from 90 minutes to 6 hours.

25. The method according to any one of the preceding claims, the method further comprises the following steps: (d) contacting the surface of the particles from step (c) with a passivating agent, or before step (c), contacting the particles from step (b) with a passivating agent.

26. The method according to claim 25, wherein the passivating agent is selected from: (i) an oxygen-containing gas; (ii) ammonia; (iii) a gas containing ammonia and oxygen; (iv) phosphine; and (v) water.

27. The method according to claim 25, wherein the passivating agent is selected from: (i)R 1 -CH=CH-R 1 ; (ii)R 1 -C≡C-R 1 ; (iii)O=CR 1 R 1 ; (iv) HX-R 2 and (v) HX-C(O)-R 1 , wherein X represents O, S, NR 1 or PR 1 ; and Each R 1 independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or two R 1 groups together form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring; wherein R 2 represents an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or wherein R 1 and R 2 together form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring.

28. The method according to any one of the preceding claims, the method further comprises the steps of: (e) depositing a lithium-ion permeable material into the pores and / or outer surface of the composite particles from step (c) or step (d).

29. The method according to claim 28, wherein the lithium-ion permeable material is a pyrolytic carbon material, and wherein step (e) comprises: combining the particles from step (c) or step (d) with a pyrolytic carbon precursor; and heating the pyrolytic carbon precursor to a temperature effective to cause deposition of a conductive pyrolytic carbon material into the pores and / or outer surface of the composite particles, optionally wherein step (e) is carried out before step (d).

30. The method according to any one of the preceding claims, wherein the composite particles comprise at least 26 wt%, or at least 28 wt%, or at least 30 wt%, or at least 32 wt%, or at least 34 wt%, or at least 36 wt%, or at least 38 wt%, or at least 40 wt%, or at least 42 wt%, or at least 44 wt% of silicon.

31. The method according to any one of the preceding claims, wherein the weight ratio of the silicon deposited in step (b) to the porous particles is in the range of [0.50×P 1 to 1.9×P 1 :1, or [0.6×P 1 to 1.8×P 1 :1, or [0.7×P 1 to 1.7×P 1 :1, or [0.8×P 1 to 1.6×P 1 :1, where P 1 is a dimensionless number whose value is the same as the total pore volume in cm 3 / g of the micropores and mesopores in the porous particles measured by gas adsorption.

32. The method according to any one of the preceding claims, wherein, as determined by thermogravimetric analysis (TGA), at least 20 wt%, or 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 in the composite particles is surface silicon.

33. The method according to any one of the preceding claims, wherein, as determined by thermogravimetric analysis (TGA), 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 in the composite particles is bulk-phase silicon.

34. A particulate material, the particulate material being composed of a plurality of composite particles obtainable by the method according to any one of the preceding claims.

35. A composition, the composition comprising the particulate material according to claim 34 and at least one other component.

36. An electrode, the electrode comprising the particulate material according to claim 34 or the composition according to claim 35.

37. A rechargeable metal ion battery, the rechargeable metal ion battery comprising the electrode according to claim 36.

Images