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; heat treating the particles at a temperature of at least 400 DEG C and in the presence of an inert gas; and contacting the particles with a silicon-containing precursor at a temperature effective to cause deposition of additional silicon domains in the pores of the porous particles.

Description

introduction

[0001] The present invention relates to a method for preparing composite particles comprising silicon deposited into the pores of porous particles. The method of the present invention involves a step of heating the composite particles after the silicon is deposited. The composite particles can be used as electroactive materials in electrodes of rechargeable metal ion batteries. In particular, the method of the present invention enables the preparation of composite particles with high electrochemical capacity, which are suitable for use as anode active materials in rechargeable metal ion batteries. The present invention also relates to novel composite particles prepared by the method of the present invention. Background Art

[0002] Lithium-ion batteries (LIBs) typically include an anode, a cathode, and a lithium-containing electrolyte. The anode typically includes a metal current collector having a layer of an electroactive material, which is defined herein as a material capable of inserting and releasing lithium ions during charging and discharging of the battery. When the LIB is charged, lithium ions are transported from the cathode to the anode via the electrolyte and are inserted into the electroactive material of the anode as inserted lithium atoms. Therefore, the terms "cathode" and "anode" are used herein in the following sense: the battery is placed across the load so that the anode is the negative electrode. The term "battery" is used herein to refer to both a device comprising a single lithium-ion battery cell and a device comprising multiple connected lithium-ion battery cells.

[0003] LIBs were developed in the 1980s and 1990s and have been widely used in portable electronic devices since then. The recent growth of electric or hybrid vehicles has created a large new market for LIBs, and renewable energy has further created demand for grid-connected energy storage that can be at least partially met by LIB farms. Overall, global production of LIBs is expected to grow from approximately 290 GWh in 2018 to more than 2,000 GWh in 2028.

[0004] As total storage capacity grows, there is a strong interest in improving the weight and / or volumetric capacity of rechargeable metal ion batteries so that the same energy storage can be achieved with less battery mass and / or battery volume. Conventional LIBs use graphite as the anode electroactive material. The graphite anode can accommodate up to one lithium atom for every six carbon atoms, resulting in a maximum theoretical specific capacity of lithium ion batteries of 372 mAh / g, while the actual capacity is slightly lower (approximately 340 to 360 mAh / g).

[0005] Silicon is a promising graphite replacement due to its very high lithium capacity (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al., Adv. Mater. 1998, 10, No. 10). 15 Si 4 ) has a theoretical maximum specific capacity of about 3,600 mAh / g. However, such a high ratio of inserted lithium to silicon results in the expansion of silicon materials up to 400% of their original volume. Repeated charge and discharge cycles cause significant mechanical stress to the silicon material, resulting in cracking and structural damage. In addition, the charging of the anode in the LIB leads to the formation of a solid electrolyte interface (SEI) layer. The SEI layer is an ion-conductive but insulating layer that is formed by the reduction decomposition of the electrolyte on the exposed electrode surface during the initial charge. In the graphite anode, the SEI layer is relatively stable during subsequent charge / discharge cycles. However, the expansion and contraction of the silicon anode leads to the rupture and delamination of the SEI layer and the exposure of the fresh silicon surface, resulting in further electrolyte decomposition, increased SEI layer thickness and irreversible lithium consumption. These destruction mechanisms together lead to unacceptable electrochemical capacity loss during continuous charge and discharge cycles.

[0006] The inventors have previously reported the development of a class of electroactive materials with composite structures, in which electroactive materials (such as silicon) are deposited into a pore network of highly porous particles (such as porous carbon materials) with carefully controlled pore size distribution. For example, WO 2020 / 095067 and WO 2020 / 128495 report that the improved electrochemical performance of these materials can be attributed to the way in which the electroactive material forms a small domain of a size of a few nanometers or less in the pore network of the porous particles, so that the porous particles act as a skeleton for the composite particles. The fine electroactive structure is considered to have less resistance to elastic deformation and higher fracture resistance than the larger electroactive structure, so it can be lithiated and delithiated without excessive structural stress. As a result, the electroactive material shows good reversible capacity retention with multiple charge and discharge cycles. Secondly, by controlling the loading amount of silicon in the porous carbon skeleton, only a portion of the pore volume is occupied by silicon in the uncharged state, and the unoccupied pore volume of the porous carbon skeleton can accommodate a significant amount of silicon expansion inside. Excessive expansion is limited by the particle skeleton. Furthermore, only a small area of ​​the electroactive material surface is accessible to the electrolyte, thus substantially preventing SEI formation.

[0007] In WO 2022 / 029422, the applicant reports further advances in which control of the distribution of electroactive silicon within the pore network of the particle skeleton leads to still further improvements in the electrochemical performance of the composite particles. Specifically, the applicant has demonstrated that electrochemical performance is optimized when the length dimensions of individual silicon structures in the composite particles are minimized so that a large proportion of silicon atoms are located in the surface region of the silicon structure, while a relatively small proportion of silicon atoms are located within the bulk / coarse silicon structure. The applicant has identified an optimized pore structure for the porous particle skeleton and a set of conditions for depositing silicon into the porous particle skeleton that allow an increased proportion of this so-called "surface" silicon while also ensuring that a large amount of silicon is incorporated into the composite particles in total to meet the overall volumetric energy density requirements.

[0008] It is challenging to efficiently deposit silicon in porous particles to achieve a commercially attractive balance of silicon content and residual surface area without the accumulation of so-called coarse silicon. This is due to silicon having a large characteristic length size deposited into the mesopores or on the outer surface of the porous particles. In this deposition mechanism, the silicon domain size can grow in an unrestricted manner. Coarse silicon may negatively affect the electrochemical performance of the composite particles.

[0009] It has now been found that additional modification of the composite particle structure after silicon deposition can provide further improvements in the electrochemical properties of the composite particles. 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, wherein the porous particles include micropores and / or mesopores;

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

[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] (d) contacting the particles from step (c) with a silicon-containing precursor at a temperature effective to cause deposition of additional silicon domains in the pores of the porous particles.

[0015] The method of the present invention involves forming a composite particle in step (b) wherein a plurality of silicon domains are deposited in the pore network of the porous particle by thermal decomposition of a suitable precursor compound. The composite particle from step (b) is then heat treated in step (c).

[0016] Without being bound by theory, it is believed that the deposited silicon domains in the porous particles may block the micropores and mesopores, resulting in enclosed voids and preventing further deposition of silicon within the pores. This is believed to reduce the density of silicon in the composite particles and act to form coarse silicon.

[0017] The silicon domains formed by thermal decomposition of the silicon-containing precursor are believed to be in the form of nanoclusters of silicon atoms terminated substantially by silicon-hydrogen bonds (Si-H). The thermal treatment of the particles in step (c) is believed to promote the elimination of hydrogen and the formation of molecular hydrogen (H 2 ). In the case where the silicon domains as a direct result of step (b) do not contain hydrogen atoms, the silicon domains may be reduced prior to step (c). Those skilled in the art are aware of suitable methods for reducing the silicon domains. The heat treatment in step (c) may also result in the elimination of terminal portions other than hydrogen bonded to the silicon surface. The elimination of terminal portions (such as hydrogen) is believed to shrink the silicon domains, exposing additional pores previously occupied by deposited silicon. This increases the pore volume accessible to the deposition of additional silicon, thereby increasing the porosity of the particles.

[0018] The increased porosity of the particles after the heat treatment step is measurable. The porosity can be measured directly, for example, by using nitrogen adsorption at 77 K down to 10 -6 Relative pressure p / p 0 The total volume of micropores and / or mesopores was measured using quenched solid density functional theory (QSDFT). The increase in BET surface area of ​​the treated particles also indicates an increase in the porosity of the particles.

[0019] Increasing the porosity of the particles enables further deposition of silicon. In step (d), the exposed pores are infiltrated by additional silicon. The deposition of silicon domains in mesoporous and / or microporous particles is a kinetically controlled mechanism that is selective for micropores and micromesopores due to the relatively high surface area of ​​micropores and micromesopores. This avoids deposition of silicon outside of micropores and micromesopores, resulting in improved structural control.

[0020] The method of the present invention increases the silicon loading of the composite particles, producing a very dense composite material in which the silicon is preferentially located within the pores of the porous particles, rather than on the particle surface or in large open accessible mesopores. In this way, the structure and characteristic length dimensions of the silicon are better controlled.

[0021] Thus, the present invention can achieve high composite density while maintaining low crude silicon values.

[0022] In a second aspect, the present invention provides a granular material, the granular material consisting of 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) according to the present invention on the total volume of micropores and mesopores of composite particles obtained by chemical vapor infiltration of silicon into the pores of porous particles. DETAILED DESCRIPTION

[0027] The present invention generally relates to a method for preparing composite particles, wherein a plurality of silicon domains are deposited into a pore network of micropores and / or mesoporous porous particles using thermal decomposition of a silicon-containing precursor. The porous particles act as a skeleton for silicon, which is generally deposited in the form of a plurality of silicon domains. As used herein, the term "silicon domain" refers to a body of elemental silicon, the maximum size of which is determined by the location of silicon in the micropores and / or mesopores of the porous particles. The silicon domain can be described as a nanoscale silicon domain, wherein the term "nanoscale" is understood to generally refer to a size less than 100 nm. However, due to the size of the micropores and mesopores, the silicon domain is typically less than 50 nm in any direction, and is typically significantly less than 50 nm. The domain, for example, can take the form of a layer or region of a regular or irregular particle or a bounded coating.

[0028] The porous particles generally include a three-dimensional interconnected open pore network including micropores and / or mesopores and optionally small volumes of macropores. According to conventional IUPAC terminology, the term "micropores" is used herein to refer to pores with a diameter less than 2 nm, the term "mesopores" is used herein to refer to pores with a diameter of 2-50 nm, and the term "macroporous" is used to refer to pores with a diameter greater than 50 nm.

[0029] References herein to the volumes of micropores, mesopores and macropores in porous particles and to the distribution of pore volumes within porous particles relate to the internal pore volume of the porous particles used as the starting material in step (a) of the claimed method (i.e., before depositing silicon into the pore volume in step (b)).

[0030] The porous particles can be characterized by the total volume of micropores and mesopores (i.e., the total pore volume in the pore size range of 0 to 50 nm). Typically, the porous particles contain both micropores and mesopores. However, it is not excluded that porous particles including micropores but not mesopores or porous particles including mesopores but not micropores can be used.

[0031] The quenched solid density functional theory (QSDFT) was used to calculate the quenched solid density functional theory (QSDFT) at 77 K down to 10 -6 Relative pressure p / p 0 Nitrogen adsorption is used to 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 increases until a saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them enables the determination of the pore volume and pore size distribution. Suitable instruments for measuring pore volume and pore size distribution by nitrogen adsorption include TriStar II and TriStar II Plus porosity analyzers (which are available from Micromeritics Instrument Corporation in the United States), and Autosorb IQ porosity analyzer (which is available from Quantachrome Instruments).

[0032] Nitrogen adsorption is effective for measuring pore volume and pore size distribution for pores up to 50 nm in diameter, but is less reliable for pores with much larger diameters. For the purposes of the present invention, therefore, pore volume and pore size distribution are determined using nitrogen adsorption only for pores up to (and including) 50 nm in diameter (i.e., only for micropores and mesopores). 50 The values ​​are likewise determined only relative to the total volume of micropores and mesopores.

[0033] Given the limitations of available analytical techniques, it is not possible to measure pore volume and pore size distribution over the entire range of micropores, mesopores and macropores using a single technique. Where the porous particles include macropores, the volume of pores with diameters in the range of greater than 50 nm to 100 nm can be measured by mercury intrusion porosimetry and preferably not exceeding 0.3 cm 3 / g, or not more than 0.2 cm 3 / g, or not more than 0.1 cm 3 / g, or not more than 0.05 cm 3 / g. Although a small fraction of macropores can be useful for facilitating the entry of electrolyte into the pore network, the advantages of the present invention are substantially obtained by accommodating the electroactive material in the micropores and smaller mesopores. Any pore volume measured by mercury intrusion below 50 nm is ignored (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 is assumed to be interparticle porosity and is also ignored.

[0034] Mercury porosimetry is a technique for characterizing the porosity and pore size distribution of a material by applying varying levels of pressure to a sample of the material immersed in mercury. The pressure required to force mercury into the pores of the sample is inversely proportional to the size of the pores. The values ​​obtained by mercury porosimetry reported herein are obtained according to ASTM UOP578-11, where for mercury at room temperature, the surface tension γ is 480 mN / m and the contact angle φ is 140°. The density of mercury at room temperature is 13.5462 g / cm 3 A variety of high-precision mercury intrusion instruments are commercially available, such as the AutoPore IV series of automated mercury intrusion instruments, which are available from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury intrusion, reference can be made to "Analytical Methods in Fine Particle Technology" by PA Webb and C. Orr, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0035] It should be understood that intrusion techniques such as gas adsorption and mercury intrusion are only valid for determining the pore volume of pores accessible to nitrogen or mercury from the outside of the porous particle. The porosity values ​​specified herein should be understood to refer to the volume of open pores (i.e., pores accessible to the fluid from the outside of the porous particle). In this context, completely enclosed pores that cannot be identified by nitrogen adsorption or mercury intrusion should not be considered when determining porosity values. Likewise, any pore volume located in pores so small as to be below the detection limit of nitrogen adsorption is also not considered.

[0036] The total pore volume of the micropores and mesopores in the porous particles can be at least 0.4 cm 3 The total pore volume of micropores and mesopores in the porous particles can be 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 0.8cm 3 The use of more porous particles can be advantageous because it enables a larger amount of electroactive material to be accommodated within the pore volume.

[0037] The internal pore volume of the porous particles is suitably limited to a value at which the increased fragility of the particle structure outweighs the advantages of increased pore volume for accommodating larger amounts of electroactive material. The total pore volume of micropores and mesopores in the porous particles may not exceed 2 cm 3 / g, or not more than 1.8 cm 3 / g, or not more than 1.7cm 3 / g, or not more than 1.6 cm 3 / g, or not more than 1.55 cm 3 / g, or not more than 1.5 cm 3 / g, or not more than 1.45 cm 3 / g, or not more than 1.4 cm 3 / g, or not more than 1.35 cm 3 / g, or not more than 1.3 cm 3 / g, or not more than 1.25 cm 3 / g, or not more than 1.2 cm 3 / g.

[0038] When measured by gas adsorption, the total pore volume of micropores and mesopores in porous particles can range from 0.4 to 2 cm 3 / g, or 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 range.

[0039] The general term "PD n "Pore size" herein refers to the nth percentile pore size by volume based on the total volume of micropores and mesopores. For example, as used herein, the term "PD 50 The term "pore size" refers to the pore size below which 50% of the total micropore and mesopore volume is located. For the avoidance of doubt, in order to determine the PD n values, without taking into account any macropore volume (pores larger than 50 nm).

[0040] PD of porous particles 90 The pore size may be no greater than 30 nm, or no greater than 25 nm, or no greater than 20 nm, or no greater than 15 nm, or no greater than 12 nm, or no greater than 10 nm, or no greater than 8 nm, or no greater than 6 nm, or no greater than 5 nm.

[0041] PD of porous particles 90 The pore size may be at least 3.2 nm, or at least 3.5 nm, or at least 3.8 nm, or at least 4 nm.

[0042] PD of porous particles 90 The pore size may be in the range of 3.2 to 30 nm, or 3.5 to 25 nm, or 3.8 to 20 nm, or 4 to 8 nm.

[0043] PD of porous particles 50 The pore size may be no more than 20 nm, or no more than 15 nm, or no more than 12 nm, or no more than 10 nm, or no more than 8 nm, or no more than 6 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3 nm, or no more than 2.5 nm, or no more than 2 nm, or no more than 1.5 nm.

[0044] The micropore volume fraction based on the total volume of micropores and mesopores in the porous particle may be at least 0.4, or at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7.

[0045] The total pore volume of the micropores and mesopores in the composite particles formed in the final step (d) may not exceed 0.6 cm 3 / g, or not more than 0.5 cm 3 / g, or not more than 0.4 cm 3 / g, or not more than 0.3 cm 3 / g, or not more than 0.2 cm 3 / g, or not more than 0.1 cm 3 / g.

[0046] The total pore volume of micropores and mesopores in the composite particles formed in the final step (d) may be at least 0.01 cm 3 / g.

[0047] The pore size distribution of the porous particles may be unimodal, bimodal or multimodal. As used herein, the term "pore size distribution" relates to the distribution of pore sizes of the porous particles relative to the cumulative total internal pore volume. Bimodal or multimodal pore size distributions may be preferred because the close proximity between micropores and pores with larger diameters provides the advantage of efficient ion transport from the porous network to the electroactive material.

[0048] 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, wherein the particle volume is understood to include the volume of any pores within the particle. As used herein, the term "D 50 ” and “D 50 "Particle size" refers to the median particle size by volume, that is, the diameter below which 50% of the volume of the particle population is located. As used herein, the term "D 10 ” and “D 10 "D" refers to the 10th percentile median particle size by volume, i.e., the diameter below which 10% of the volume of the particle population is located. As used herein, the term "D 90 ” and “D 90 "Particle size" refers to the 90th percentile median particle size by volume, i.e., the diameter below which 90% of the volume of the particle population lies.

[0049] Particle size and particle size distribution can be determined by standard laser diffraction techniques according to ISO 13320:2009. Laser diffraction relies on the principle that particles will scatter light at an angle that varies depending on the size of the particle, and that a collection of multiple particles will produce a scattered light pattern defined by intensity and angle that can be related to the particle size distribution. A wide variety of laser diffraction instruments are commercially available for rapid and reliable determination of particle size distribution. Unless otherwise stated, particle size distribution measurements indicated or reported herein were obtained by a laser diffraction analyzer from Malvern Instruments. TM The regular Malvern Mastersizer TM Measured by Malvern Mastersizer 3000 particle size analyzer. TMThe 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing particles of interest suspended in an aqueous solution. The light impinging on the particles is scattered through angles inversely proportional to the particle size, and an array of photodetectors measures the intensity of the light at a number of predetermined angles, and the measured intensities at different angles are processed by computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values ​​reported herein were calculated using an aqueous solution with 5% by volume of the surfactant SPAN. TM The particle wet dispersion of 1,4-dihydro- ...

[0050] D of porous particles 50 The particle size may be in the range of 1 to 30 μm. Optionally, the D 50 The particle size may 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 The particle size may be no greater than 25 µm, or no greater than 20 µm, or no greater than 18 µm, or no greater than 15 µm, or no greater than 12 µm, or no greater than 10 µm, or no greater than 8 µm.

[0051] D of porous particles 10 The particle size 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. 10 The particle size is maintained above 0.5 µm, reducing the possibility of undesirable agglomeration of submicron-sized particles and improving the dispersibility of the formed composite particles.

[0052] D of porous particles 90 The particle size is preferably no more than 50 μm, or no more than 40 μm, or no more than 30 μm, or no more than 25 μm, or no more than 20 μm, or no more than 15 μm.

[0053] The porous particles preferably have a narrow size distribution span. For example, the particle size distribution span (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, efficient packing of particles into a dense powder bed can be more easily achieved.

[0054] The D of the composite particles formed in the final step (d) 50 Particle sizes can range from 1 to 30 µm.

[0055] The D of the composite particles formed in the final step (d) 10 The particle size may be 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.

[0056] The D of the composite particles formed in the final step (d) 90 The particle size may be no greater than 50 µm, or no greater than 40 µm, or no greater than 30 µm, or no greater than 25 µm, or no greater than 20 µm, or no greater than 15 µm.

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

[0058]

[0059] Among them A m is the measured area of ​​the particle projection, and C m is the measured circumference of the particle projection. As used herein, the average sphericity S of a plurality of particles av is defined as:

[0060]

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

[0062] The average sphericity (as defined herein) of the porous particles may 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 believed to contribute to uniformity of deposition and at the same time facilitate denser packing in batch pressure reactors and in the final product when incorporated into electrodes.

[0063] The term "BET surface area" as used herein should be taken to mean the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on a solid surface according to ISO 9277 using the Brunauer-Emmett-Teller principle.

[0064] The BET surface area of ​​porous particles can be 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 range.

[0065] The BET surface area of ​​the composite particles formed in step (c) may be at least 30 m greater than the BET surface area of ​​the composite particles formed in step (b). 2 / g, or at least 40 m 2 / g, or at least 50 m 2 / g, or at least 60 m 2 / g, or at least 70 m 2 / g, or at least 80 m 2 / g, or at least 90 m 2 / g, or at least 100 m 2 / g.

[0066] The BET surface area of ​​the composite particles formed in the last step (d) may be in the range of 0.1 to 100 m 2 / g, or 0.1 to 80m 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. Generally, a low BET surface area is preferred to minimize the formation of a solid electrolyte interface (SEI) layer at the surface of the composite particles during the first charge-discharge cycle of the anode. However, too low a BET surface area leads to unacceptably low charge rates and capacities due to the inaccessibility of the bulk of the electroactive material to the metal ions in the surrounding electrolyte.

[0067] As used herein, the term "particle density" refers to the "apparent particle density" measured by mercury porosimetry (i.e., the mass of the particle divided by the particle volume, where the particle volume is considered to be the sum of the volume of the solid material and any closed or blind pores ("blind pores" are pores that are too small to be measured by mercury porosimetry). The particle density of porous particles is preferably at least 0.35 and preferably less than 3 g / cm 3 , more preferably less than 2 g / cm 3 , more preferably less than 1.5 g / cm 3 , most preferably 0.35 to 1.2 g / cm 3 Preferably, the porous particles have a particle density of 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 not more than 1.1 g / cm 3 , or not more than 1.05 g / cm 3 , or not more than 1 g / cm 3 , or not more than 0.95 g / cm 3 , or not more than 0.9 g / cm 3 .

[0068] Porous particles can have:

[0069] (i) 0.4 to 1.8 cm3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0070] (ii) PDs not exceeding 10 nm 50 pore size, and preferably no more than 20 nm PD 90 Aperture; and

[0071] (iii) D in the range of 1 to 30 µm 50 Particle size.

[0072] Porous particles can have:

[0073] (i) 0.5 to 1.6 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0074] (ii) PDs not exceeding 8 nm 50 pore size, and preferably no more than 15 nm PD 90 Aperture; and

[0075] (iii) D in the range of 1 to 25 µm 50 Particle size.

[0076] Porous particles can have:

[0077] (i) 0.6 to 1.5 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0078] (ii) PDs not exceeding 6 nm 50 pore size, and preferably no more than 12 nm PD 90 Aperture; and

[0079] (iii) D in the range of 1.5 to 20 µm 50 Particle size.

[0080] Porous particles can have:

[0081] (i) 0.65 to 1.4 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0082] (ii) PDs not exceeding 2.5 nm 50 pore size, and preferably no more than 10 nm PD 90 Aperture; and

[0083] (iii) D in the range of 1.5 to 18 µm 50 Particle size.

[0084] Porous particles can have:

[0085] (i) 0.7 to 1.3 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0086] (ii) PDs not exceeding 4 nm 50 pore size, and preferably no more than 8 nm PD 90 Aperture; and

[0087] (iii) D in the range of 2 to 15 µm 50 Particle size.

[0088] Porous particles can have:

[0089] (i) 0.75 to 1.2 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0090] (ii) PDs not exceeding 3 nm 50 pore size, and preferably no more than 6 nm PD 90 Aperture; and

[0091] (iii) D in the range of 2 to 12 µm 50 Particle size.

[0092] Porous particles can have:

[0093] (i) 0.8 to 1.2 cm 3 The total pore volume of micropores and mesopores measured by nitrogen adsorption in the range of 1 / g;

[0094] (ii) PDs not exceeding 2 nm 50 pore size, and preferably no more than 5 nm PD 90 Aperture; and

[0095] (iii) D in the range of 2.5 to 10 µm 50 Particle size.

[0096] The porous particles may be conductive porous particles. The porous particles may be conductive porous carbon particles. The use of conductive porous particles is advantageous because the porous particles form a conductive skeleton within the composite particles, which facilitates the flow of electrons between lithium atoms / ions inserted into the electroactive material and the current collector.

[0097] The conductive porous carbon particles may contain at least 80% by weight of carbon, or at least 85% by weight of carbon, or at least 90% by weight of carbon, or at least 95% by weight of carbon. The carbon may be crystalline carbon or amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The conductive porous carbon particles may be hard carbon particles or soft carbon particles.

[0098] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which the carbon atoms are primarily in sp 2 Hybrid state (trigonal bond). The polyaromatic domains are cross-linked using chemical bonds such as C-O-C bonds. Due to the chemical cross-linking between the polyaromatic domains, hard carbon cannot be converted into graphite at high temperatures. Hard carbon has graphite-like properties, which is reflected by the large G band (~1600 cm -1 However, the carbon is not completely graphitic, as evidenced by the distinct D band (~1350 cm -1 )prove.

[0099] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which the carbon atoms are mainly in sp polyaromatic domains with sizes ranging from 5 to 200 nm. 2 Hybridization state (triangular bond). Compared with hard carbon, the polyaromatic domains in soft carbon are associated by intermolecular forces rather than crosslinked 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 may suitably contain 50% to 98% sp 2 Hybridized carbon, 55% to 95% sp 2 Hybridized carbon, 60% to 90% sp 2 Hybridized carbon, or 70% to 85% sp 2 Hybridized carbon.

[0100] 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, including lignocellulosic materials (such as coconut shells, rice husks, wood, etc.), and fossil carbon sources, such as coal. Examples of resins and polymer materials that form porous carbon particles during pyrolysis include: phenolic resins, novolac resins, asphalt, melamine materials, polyacrylate materials, polystyrene materials, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and various copolymers of monomer units comprising acrylic ester monomers, styrene monomers, α-olefins, vinyl pyrrolidone and other ethylenically unsaturated monomers. Various carbon materials are available in the art according to the raw materials and conditions of the pyrolysis process. Porous carbon particles of various specifications can be obtained from commercial suppliers.

[0101] The porous carbon particles can be subjected to chemical or gas activation processes to increase the volume of the mesopores and micropores. Suitable activation processes include: exposing the pyrolyzed carbon to oxygen, water vapor, CO, CO 2 and one or more of KOH at a temperature in the range of 600 to 1000°C.

[0102] Mesopores can also be obtained by known templating processes using removable pore formers such as MgO and other colloidal or polymer templates that can be removed by thermal or chemical means after pyrolysis or activation.

[0103] Alternatives to carbon-based conductive particles include porous particles comprising 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).

[0104] The composite particles of the present invention are suitably prepared by chemical vapor infiltration (CVI) of a silicon-containing precursor into the pore structure of the porous particles. As used herein, CVI refers to a process in which a silicon-containing precursor is thermally decomposed on a surface to form elemental silicon and byproducts at the surface.

[0105] The silicon-containing precursor may be a gaseous silicon-containing precursor. The gaseous silicon-containing precursor in step (b) and / or (d) may be used in pure form (or substantially pure form), or may be used as a diluted mixture with an inert carrier gas such as nitrogen or argon. Based on the total volume of the gas, the gaseous silicon-containing precursor in step (b) and / or (d) may independently comprise 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.

[0106] The silicon-containing precursor in step (b) and / or (d) may be independently selected from the group consisting of: monosilane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), butadienesilane (Si 4 H 10 ), methylsilane, dimethylsilane and chlorosilane, preferably selected from the group consisting of: monosilane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ) and butadienesilane (Si 4 H 10 ). A particularly preferred silicon precursor is monosilane.

[0107] In case the precursor is a chlorinated compound such as chlorosilane, the precursor is preferably used in admixture with hydrogen, preferably in an atomic ratio of hydrogen to chlorine of at least 1:1.

[0108] Optionally, the precursor is free of chlorine. Chlorine-free means that the precursor contains less than 1 wt%, preferably less than 0.1 wt%, preferably less than 0.01 wt% of chlorine-containing compounds.

[0109] According to the conventional procedure of working in an inert atmosphere, the presence of oxygen in steps (b) and (d) should be avoided to prevent undesired oxidation of the deposited silicon. Preferably, the oxygen content is lower than 0.01% by volume, more preferably lower than 0.001% by volume, based on the total volume of the gas used in step (b) or (d).

[0110] Step (b) and / or (d) may be independently carried out at a temperature 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, step (b) and / or (d) are independently carried out at a temperature in the range of 340 to less than 400° C., or 370 to 395° C.

[0111] Steps (b) and / or (d) may be independently carried out at a pressure in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or about 100 kPa.

[0112] The pressures referred to in any step of the claimed process refer to the absolute pressure in the reaction zone which may comprise any suitable form of reaction vessel.

[0113] The deposition of silicon by CVI leads to the elimination of byproducts, particularly byproduct gases such as hydrogen. Step (b) preferably also includes separating the byproducts from the particles formed in step (b). The separation of the byproducts can be achieved by flushing the reactor with an inert gas and / or emptying the reactor by reducing the pressure. For example, the separation of the byproducts from the particles formed in step (b) can be achieved by emptying the reactor to a pressure lower than 100 kPa, or lower than 80 kPa, or lower than 60 kPa, or lower than 40 kPa, or lower than 20 kPa, or lower than 10 kPa, or lower than 5 kPa, or lower than 2 kPa, or lower than 1 kPa. Emptying the reactor to low pressure can not only effectively remove the byproducts in the gas phase, but also effectively desorb any byproducts that may be adsorbed on the surface of the deposited silicon.

[0114] 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) may be at least 1.1:1, or at least 1.2:1, or at least 1.3:1, or at least 1.4:1, or at least 1.5:1, or at least 2:1, or at least 3:1, or at least 4:1, or at least 5:1.

[0115] 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) may be no more than 15:1, or no more than 14:1, or no more than 13:1, or no more than 12:1.

[0116] The ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) when measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) when 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.

[0117] The ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) when measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) when measured by gas adsorption may be no more than 20:1, or no more than 19:1, or no more than 18:1, or no more than 17:1, or no more than 16:1, or no more than 15:1.

[0118] 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 no more than 0.8:1, or no more than 0.7:1, or no more than 0.6:1, or no more than 0.5:1.

[0119] 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.

[0120] The temperature in step (c) may be higher than the temperature in step (b). The temperature in step (c) may be 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).

[0121] The temperature in step (c) may be at least 450°C, or at least 500°C, or at least 510°C, or at least 520°C, or at least 540°C, or at least 560°C, or at least 580°C, or at least 600°C, or at least 610°C, or at least 620°C, or at least 630°C, or at least 640°C, or at least 650°C. Preferably, the temperature 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. The temperature in step (c) may be no more than 900°C, or no more than 850°C, or no more than 800°C, or no more than 750°C, or no more than 700°C, or no more than 680°C, or no more than 660°C, or no more than 650°C. Preferably, the temperature in step (c) is no more than 750°C. More preferably, the temperature in step (c) is no more than 700°C.

[0122] The temperature in step (c) may 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) may 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.

[0123] 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. Preferably, step (c) is carried out for a period of at least 30 minutes. More preferably, step (c) is carried out for a period of at least 1 hour. More preferably, step (c) is carried out for a period of at least 90 minutes. Preferably, the duration of step (c) is no more than 72 hours, or no more than 48 hours, or no more than 24 hours, or no more than 12 hours, or no more than 6 hours, or no more than 5 hours, or no more than 4 hours, or no more than 3 hours. Preferably, step (c) is carried out for a period of no more than 24 hours. More preferably, step (c) is carried out for a period of no more than 12 hours. More preferably, step (c) is carried out for a period of no more than 6 hours.

[0124] 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.

[0125] Step (c) preferably comprises maintaining the particles from step (b) for a period of time t above a lower threshold temperature TL of at least 400° C. More preferably, step (c) comprises maintaining the particles from step (b) for a period of time t between the lower threshold temperature TL and the upper threshold temperature TU.

[0126] The lower threshold temperature TL in step (c) may 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.

[0127] The lower threshold temperature TL and the upper threshold temperature TU may be 400°C and 900°C, or 500°C and 900°C, or 600°C and 900°C, respectively. The lower threshold temperature TL and the upper threshold temperature TU may be 500°C and 800°C, or 510°C and 800°C, or 520°C and 750°C, or 540°C and 700°C, or 560°C and 680°C, or 580°C and 660°C, 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.

[0128] 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 is no more than 72 hours, or no more than 48 hours, or no more than 24 hours, or no more than 12 hours, or no more than 6 hours, or no more than 5 hours, or no more than 4 hours, or no more than 3 hours. More preferably, the time period t is no more than 24 hours. More preferably, the time period t is no more than 12 hours. More preferably, the time period t is no more than 6 hours.

[0129] The time period t 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 time period t is in the range of 30 minutes to 24 hours. More preferably, the time period t is in the range of 1 hour to 12 hours. More preferably, the time period t is in the range of 90 minutes to 6 hours.

[0130] Step (c) is carried out in the presence of an inert gas. An inert gas refers herein to any gas that does not react under the conditions of step (c). Therefore, there is no gas that reacts under the conditions of step (c) during step (c). Preferably, the inert gas is selected from nitrogen and rare gases, particularly argon. Optionally, the inert gas may comprise hydrogen. The inert gas may be selected from the group consisting of nitrogen, argon, helium and a combination 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 a combination thereof.

[0131] Preferably, step (c) is carried out under the following conditions:

[0132] (i) a temperature in the range of 400°C to 900°C;

[0133] (ii) last for a period ranging from 1 minute to 72 hours; and

[0134] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0135] Preferably, step (c) is carried out under the following conditions:

[0136] (i) a temperature in the range of 500°C to 900°C;

[0137] (ii) lasts for a period of 30 minutes to 4 hours; and

[0138] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0139] Preferably, step (c) is carried out under the following conditions:

[0140] (i) a temperature in the range of 600°C to 900°C;

[0141] (ii) a period lasting from 1 hour to 4 hours; and

[0142] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0143] Preferably, step (c) is carried out under the following conditions:

[0144] (i) a temperature in the range of 500°C to 750°C;

[0145] (ii) lasts for a period of 30 minutes to 24 hours; and

[0146] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0147] Preferably, step (c) is carried out under the following conditions:

[0148] (i) a temperature in the range of 500°C to 750°C;

[0149] (ii) lasts for a period of 1 hour to 12 hours; and

[0150] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0151] Preferably, step (c) is carried out under the following conditions:

[0152] (i) a temperature in the range of 500°C to 700°C;

[0153] (ii) lasts for a period of 90 minutes to 6 hours; and

[0154] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0155] Preferably, step (c) is carried out under the following conditions:

[0156] (i) a temperature in the range of 510°C to 750°C;

[0157] (ii) lasts for a period of 30 minutes to 24 hours; and

[0158] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0159] Preferably, step (c) is carried out under the following conditions:

[0160] (i) a temperature in the range of 510°C to 750°C;

[0161] (ii) lasts for a period of 1 hour to 12 hours; and

[0162] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0163] Preferably, step (c) is carried out under the following conditions:

[0164] (i) a temperature in the range of 510°C to 700°C;

[0165] (ii) lasts for a period of 90 minutes to 6 hours; and

[0166] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0167] Preferably, step (c) is carried out under the following conditions:

[0168] (i) a temperature in the range of 520°C to 750°C;

[0169] (ii) lasts for a period of 30 minutes to 24 hours; and

[0170] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0171] Preferably, step (c) is carried out under the following conditions:

[0172] (i) a temperature in the range of 520°C to 750°C;

[0173] (ii) lasts for a period of 1 hour to 12 hours; and

[0174] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0175] Preferably, step (c) is carried out under the following conditions:

[0176] (i) a temperature in the range of 520°C to 700°C;

[0177] (ii) lasts for a period of 90 minutes to 6 hours; and

[0178] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0179] Preferably, step (c) is carried out under the following conditions:

[0180] (i) the lower threshold temperature TL is 500°C and the upper threshold temperature is 750°C;

[0181] (ii) a period of time t lasting from 30 minutes to 24 hours; and

[0182] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0183] Preferably, step (c) is carried out under the following conditions:

[0184] (i) the lower threshold temperature TL is 500°C and the upper threshold temperature is 750°C;

[0185] (ii) a period of time t lasting from 1 hour to 12 hours; and

[0186] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0187] Preferably, step (c) is carried out under the following conditions:

[0188] (i) the lower threshold temperature TL is 500°C and the upper threshold temperature is 700°C;

[0189] (ii) a period of time t lasting from 90 minutes to 6 hours; and

[0190] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0191] Preferably, step (c) is carried out under the following conditions:

[0192] (i) the lower threshold temperature TL is 510°C and the upper threshold temperature is 750°C;

[0193] (ii) a period of time t lasting from 30 minutes to 24 hours; and

[0194] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0195] Preferably, step (c) is carried out under the following conditions:

[0196] (i) the lower threshold temperature TL is 510°C and the upper threshold temperature is 750°C;

[0197] (ii) a period of time t lasting from 1 hour to 12 hours; and

[0198] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0199] Preferably, step (c) is carried out under the following conditions:

[0200] (i) the lower threshold temperature TL is 510°C and the upper threshold temperature is 700°C;

[0201] (ii) a period of time t lasting from 90 minutes to 6 hours; and

[0202] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0203] Preferably, step (c) is carried out under the following conditions:

[0204] (i) the lower threshold temperature TL is 520°C and the upper threshold temperature is 750°C;

[0205] (ii) a period of time t lasting from 30 minutes to 24 hours; and

[0206] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0207] Preferably, step (c) is carried out under the following conditions:

[0208] (i) the lower threshold temperature TL is 520°C and the upper threshold temperature is 750°C;

[0209] (ii) a period of time t lasting from 1 hour to 12 hours; and

[0210] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0211] Preferably, step (c) is carried out under the following conditions:

[0212] (i) the lower threshold temperature TL is 520°C and the upper threshold temperature is 700°C;

[0213] (ii) a period of time t lasting from 90 minutes to 6 hours; and

[0214] (iii) in the presence of an inert gas (optionally comprising hydrogen).

[0215] 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, promote the formation of covalent bonds between silicon and the inner surface of the porous particle skeleton while avoiding the formation of silicon carbide, reduce the surface area of ​​the silicon domains, and / or improve the chemical stability of the silicon domains.

[0216] Steps (b), (c) and (d) 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 to carry out step (c). During the transfer to the second reaction vessel, the particles can be kept at a temperature lower than the temperature in step (b). Preferably, during the transfer to the second reaction vessel, the particles are kept at a temperature of at least 50°C. Afterwards, the particles formed in step (c) can be transferred to the first reaction vessel to carry out step (d). Alternatively, the particles formed in step (c) can be transferred to a third reaction vessel to carry out step (d).

[0217] In one aspect, the present invention provides a method for preparing composite particles, the method comprising the steps of:

[0218] (a) providing a plurality of porous particles, wherein the porous particles include micropores and / or mesopores;

[0219] (b) contacting the porous particle with a silicon-containing precursor at a temperature effective to cause deposition of a plurality of nanoscale silicon domains in the pores of the porous particle;

[0220] (c) maintaining said particles from step (b) above a lower threshold temperature TL of at least 400° C. for a period of time t;

[0221] (d) contacting the particles from step (c) with a silicon-containing precursor at a temperature effective to cause deposition of additional silicon domains in the pores of the porous particles.

[0222] 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.

[0223] Preferably, the lower threshold temperature TL is 500° C., the upper threshold temperature TU is 700° C., and the time period t is 90 minutes to 6 hours.

[0224] The above aspects of the invention may optionally be combined with any other features disclosed herein in relation to the first aspect of the invention.

[0225] Steps (c) and / or (d) may be repeated more than once.

[0226] The composite particles obtained by the process of the invention can be characterized by their performance under thermogravimetric analysis (TGA) in air. This analytical method relies on the principle that a weight increase is observed when an electroactive material is oxidized in air and at elevated temperature.

[0227] As defined herein, "surface silicon" is calculated from the initial mass increase in the TGA trace from the minimum value between 150°C and 500°C to the maximum mass measured in the temperature range of 550°C to 650°C, wherein the TGA is performed in air at a heating rate of 10°C / min. This mass increase is believed to be due to oxidation of the surface silicon and therefore allows the percentage of surface silicon to be determined as a proportion of the total amount of silicon according to the following formula:

[0228] Y = 1.875 × [(M max – M min ) / M f ] ×100%

[0229] where Y is the percentage of surface silicon as a proportion of the total silicon in the sample, M max is the maximum mass of the sample measured in the temperature range of 550℃ to 650℃, M min is the minimum mass of the sample above 150°C and below 500°C, and M fis the mass of the sample at 1400°C when oxidation is complete. For completeness, it should be understood that 1.875 is SiO 2 With O 2 The molar mass ratio (i.e. the SiO 2 Typically, TGA analysis is performed using a sample amount of 10 mg ± 2 mg.

[0230] It has been found that when the surface silicon measured by the above TGA method is at least 20% by weight of the total amount of silicon in the composite particles, the reversible capacity retention after multiple charge / discharge cycles is significantly improved. Preferably, when measured by thermogravimetric analysis (TGA), at least 22% by weight, or at least 25% by weight, at least 30% by weight of silicon, or at least 35% by weight of silicon, or at least 40% by weight of silicon, or at least 45% by weight of silicon is surface silicon.

[0231] As used herein, "coarse bulk silicon" is defined as silicon that undergoes oxidation above 800°C when measured by TGA, wherein TGA is conducted in air at a heating rate of 10°C / min. Thus, the coarse bulk silicon content is determined according to the following formula:

[0232] Z = 1.875 × [(M f -M 800 ) / M f ] ×100%

[0233] 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 ash at 1400°C when oxidation is complete. For the purposes of this analysis, it is assumed that any mass increase above 800°C corresponds to oxidation of silicon to SiO 2 , and the total mass when oxidation is complete is SiO 2 .

[0234] Preferably, no more than 10 wt%, or no more than 8 wt%, or no more than 6 wt%, or no more than 5 wt%, or no more than 4 wt%, or no more than 3 wt%, or no more than 2 wt%, or no more than 1.5 wt% of the silicon in the particles formed in the final step (d) is coarse bulk silicon when measured by TGA.

[0235] Preferably, at least 30 wt% of the silicon is surface silicon and no more than 10 wt% of the silicon is coarse bulk silicon, both of which are determined by TGA. More preferably, at least 35 wt% of the silicon is surface silicon and no more than 8 wt% of the silicon is coarse bulk silicon, both of which are determined by TGA. More preferably, at least 40 wt% of the silicon is surface silicon and no more than 5 wt% of the silicon is coarse bulk silicon, both of which are determined by TGA. More preferably, at least 45 wt% of the silicon is surface silicon and no more than 2 wt% of the silicon is coarse bulk silicon, both of which are determined by TGA. It is believed that the method of the present invention can produce composite particles with a low coarse silicon content. Preferably, no more than 10 wt % of the silicon, or no more than 8 wt % of the silicon, or no more than 6 wt % of the silicon, 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 formed in the final step (d) is coarse bulk silicon when determined by thermogravimetric analysis (TGA).

[0236] The amount of silicon in the composite particles may 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.

[0237] The silicon content is preferably determined by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy). A variety of ICP-OES instruments are commercially available, such as the ICP-OES analyzers of the iCAP® 7000 series (available from ThermoFisherScientific). The carbon content, hydrogen content, nitrogen content and / or oxygen content of the composite particles and / or porous carbon particles are preferably determined by infrared absorption. A suitable instrument for determining carbon content, hydrogen content, nitrogen content and / or oxygen content is the TruSpec® Micro elemental analyzer (available from Leco Corporation).

[0238] A range of different silicon loadings in composite particles can be obtained using the method of the present invention. The particles formed in the final step (d) contain 5 wt % to 85 wt %, or 10 wt % to 85 wt %, or 15 wt % to 85 wt %, or 20 wt % to 80 wt %, or 25 wt % to 80 wt %, or 30 wt % to 75 wt %, or 35 wt % to 75 wt %, or 40 wt % to 70 wt %, or 45 wt % to 65 wt % silicon based on the total mass of the particles.

[0239] The mass ratio of silicon to porous particles is [0.50×P 1 To 1.9×P 1]: 1, the amount of silicon in the composite particles formed in the final step (d) can be related to the available pore volume in the porous particles, where P 1 is a dimensionless number whose value corresponds to the number of micropores and mesopores in a porous particle measured by gas adsorption in cm. 3 / g represents the same total pore volume (for example, if the total volume of micropores and mesopores of a porous particle 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 a weight ratio of silicon at which the occupied pore volume is about 20% to 82%. Preferably, the weight ratio of silicon in the composite particles formed in the last step (d) is [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.

[0240] The amount of silicon in the composite particles is preferably selected so that at least 25% and up to 90% of the internal pore volume of the porous particles is occupied by silicon after the last step (d). For example, silicon may occupy 25% 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 charge and discharge without large excess pore volume that does not contribute to the volume capacity of the granular particles. However, the amount of electroactive material is also not so high that it hinders effective lithiation due to insufficient metal ion diffusion rate or due to insufficient expansion volume that causes mechanical resistance to lithiation.

[0241] At least 85 wt % of the silicon in the particles formed in the last step (d) can be located in the internal pore volume of the porous particles. Optionally, at least 90 wt %, or at least 95 wt %, or at least 98 wt % of the silicon in the particles formed in the last step (d) are located in the internal pore volume of the porous particles. As discussed above, the deposition of silicon in the CVI process occurs on the surface of the porous particles. In view of the very high internal surface area of ​​the porous particles, the reaction kinetics of the CVI process ensure that the deposition of silicon occurs almost completely in the pores of the porous particles. The internal deposition of silicon is further improved by subjecting the particles formed in step (b) to a heat treatment step (c) and subsequently in step (d) the further deposition of silicon.

[0242] The method of the present invention may further comprise the following steps:

[0243] (e) contacting the surface of the particles from the last step (d) with a passivating agent.

[0244] As defined herein, a passivating agent is a compound or mixture of compounds capable of reacting with the surface of the silicon deposited in the last step (d) to form a modified surface. In particular, a passivating agent as defined herein is a material capable of reacting with the surface of silicon to further reduce its surface energy.

[0245] The passivating agent may be selected from: (i) an oxygen-containing gas; (ii) ammonia; (iii) a gas comprising ammonia and oxygen; and (iv) a phosphine.

[0246] The passivating agent may be selected from:

[0247] (i)R 1 -CH=CH-R 1 ;

[0248] (ii) R 1 -C≡CR 1 ;

[0249] (iii) O=CR 1 R 1 ;

[0250] (iv)HX-R 2 ,as well as

[0251] (v)HX-C(O)-R 1 ,

[0252] Where X represents O, S, NR 1 or PR 1 ;and

[0253] Each R 1 independently represent H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or two R 1 The groups form unsubstituted or substituted ring structures containing 3 to 8 carbon atoms in the ring;

[0254] Where 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 they form an unsubstituted or substituted ring structure containing from 3 to 8 carbon atoms in the ring.

[0255] 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. The passivation layer can include a material of the formula SiO xSilicon oxides with 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 bringing the silicon surface into contact with the oxygen-containing gas.

[0256] 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. The passivation layer may comprise silicon nitride of the formula SiN x where 0 < x ≤ 4 / 3. The silicon nitride is preferably amorphous silicon nitride. The nitride layer can be formed by bringing the silicon surface into contact 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.

[0257] Another type of passivation layer is an oxynitride layer formed, for example, by exposing the silicon surface to a passivating agent containing ammonia (or other nitrogen-containing molecules) and oxygen. The passivation layer may comprise silicon oxynitride of the formula SiO x N y where 0 < x < 2, 0 < y < 4 / 3, and 0 < (2x + 3y) ≤ 4). The silicon nitride is preferably amorphous silicon oxynitride.

[0258] Another type of passivation layer is a carbide layer. The passivation layer may comprise 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 bringing the silicon surface into contact 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, for example. At lower temperatures, covalent bonds are formed between the silicon surface and the carbon-containing precursor, which transforms into a crystalline silicon carbide monolayer as the temperature rises. The modified material domain may comprise silicon carbide of the formula SiCx where 0 < x ≤ 1.

[0259] Other suitable passivating agents include: compounds containing olefinic, acetylenic or carbonyl functional groups, more preferably terminal olefins, terminal acetylenes, aldehyde groups or ketone groups.

[0260] Particularly preferred deactivators include one or more compounds having the formula:

[0261] (i)CH 2 =CH-R 1 ;as well as

[0262] (ii) HC≡CR 1 ;

[0263] Where R 1 As defined above. Preferably, R 1 is unsubstituted.

[0264] Examples of suitable deactivators include: ethylene, propylene, 1-butene, butadiene, 1-pentene, 1,4-pentadiene, 1-hexene, 1-octene, styrene, divinylbenzene, acetylene, phenylacetylene, norbornene, norbornadiene and bicyclo[2.2.2]oct-2-ene. Optionally, mixtures of different deactivators can also be used.

[0265] It is believed that passivating agents containing olefins, alkynes or carbonyl groups undergo insertion reactions with Si-H groups on the silicon surface to form a covalently passivated surface that is resistant to air oxidation. Therefore, the passivation reaction between the silicon surface and the passivating agent can be understood as a form of hydrosilylation, as schematically shown below.

[0266]

[0267] Other suitable passivating agents include compounds containing active hydrogen atoms bonded to oxygen, nitrogen, sulfur or phosphorus. For example, the passivating agent may be an alcohol, an amine, a thiol or a phosphine. The reaction of the group -XH with the hydride groups on the silicon surface is understood to result in H 2 elimination of and formation of a direct bond between X and the surface of the electroactive material.

[0268] Suitable deactivators in this class include compounds having the formula:

[0269] (iv)HX-R 2 ,as well as

[0270] (v)HX-C(O)-R 1 ,

[0271] Where X and each R 1 and R 2 Independently as defined above.

[0272] Preferably, X represents O or NH.

[0273] Preferably, R 2represents an optionally substituted aliphatic or aromatic group having 2 to 10 carbon atoms. The amine group may also be incorporated into a 4-10 membered aliphatic or aromatic ring structure, as in pyrrolidine, pyrrole, imidazole, piperazine, indole or purine.

[0274] Another suitable passivating agent is water. For example, the silicon surface can be exposed to water vapor. Alternatively, the particles from step (d) can be immersed in water. Optionally, the passivation using water can be performed after the passivation using one or more of the passivating agents disclosed above.

[0275] Preferably, step (e) is performed using a passivating agent other than air.

[0276] Step (e) may 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 in the range of 100 to 400°C.

[0277] The method of the present invention may further comprise the following steps:

[0278] (f) combining the particles from the last step (d) or step (e) with a pyrolytic carbon precursor; and heating the pyrolytic carbon precursor to a temperature effective to cause deposition of the electrically conductive pyrolytic carbon material into the pores and / or on the outer surfaces of the composite particles.

[0279] Where the method comprises step (e), step (f) may optionally be carried out before or after step (e). In either case, step (f) is carried out after the last step (d).

[0280] 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 wherein the polycyclic hydrocarbon is selected from naphthalene, substituted naphthalene (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 wherein 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 A hydrocarbon, optionally wherein the hydrocarbon is 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-triphenylene, tetracene, benzopyrene, perylene, coronene and chrysene. A preferred carbon precursor is acetylene.

[0281] Temperatures suitable for deposition of the pyrolytic carbon material in step (f) are in the range of 300 to 800°C, or 400 to 700°C. For example, the temperature may be no more than 680°C, or no more than 660°C, or no more than 640°C, or no more than 620°C, or no more than 600°C, or no more than 580°C, or no more than 560°C, or no more than 540°C, or no more than 520°C, or no more than 500°C. The minimum temperature will depend on the type of carbon precursor 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.

[0282] The pyrolytic carbon precursor used in step (c) can be used in pure form or in a diluted mixture with an inert carrier gas such as nitrogen or argon. For example, the pyrolytic carbon precursor can be used in an amount ranging from 0.1% to 100% by volume, or from 0.5% to 20% by volume, or from 1% to 10% by volume, or from 1% to 5% by volume, based on the total volume of the precursor and the inert carrier gas.

[0283] In the case of depositing pyrolytic carbon material in step (f), the same compound may act as both the passivating agent in step (e) and the pyrolytic carbon precursor in step (f). For example, if styrene is selected as the pyrolytic carbon precursor, styrene will also act as a passivating agent if the particles from step (d) are not exposed to other passivating agents before contacting with styrene. In this case, the passivation in the steps and the deposition of the conductive pyrolytic carbon material may be carried out simultaneously, for example at a temperature in the range of 300-700°C. Alternatively, the passivation and the deposition of the conductive pyrolytic carbon material may be carried out sequentially, using the same material as the passivating agent and the pyrolytic carbon precursor, but wherein step (f) is carried out after the passivation in step (e) at a higher temperature than in step (e). For example, the passivation in step (e) may be carried out at a temperature in the range of 25°C to less than 300°C, and the deposition of pyrolytic carbon may be carried out at a temperature in the range of 300-700°C. The two steps may be suitably carried out sequentially by increasing the temperature while maintaining contact with the compound that acts as both the passivating agent and the pyrolytic carbon precursor. At lower temperatures (eg in the range of 25°C to <300°C), passivation will be the predominant process. As the temperature increases (eg to 300-700°C), deposition of pyrolytic carbon will ensue.

[0284] 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 composite particles formed can be present in the reactor in the form of a fixed bed of particles or in the form of a moving or stirred bed of particles.

[0285] In a second aspect, the present invention provides a granular material, the granular material consisting of a plurality of composite particles obtainable by the method of the first aspect.

[0286] In a third aspect of the invention, a composition is provided, comprising the particulate material of the second aspect of the invention and at least one other component. The at least one other component may be one or more of the following: (i) a binder; (ii) a conductive additive; and (iii) another particulate electroactive material. The composition according to the third aspect of the invention may be used as an electrode composition and may therefore be used to form an active layer of an electrode.

[0287] The composition may be a hybrid electrode composition comprising the composite particles and at least one additional particulate electroactive material. Examples of additional particulate electroactive materials include graphite, hard carbon, silicon, tin, germanium, aluminum and lead. The at least one additional particulate electroactive material is preferably selected from graphite and hard carbon, and most preferably, the at least one additional particulate electroactive material is graphite.

[0288] In the case of a hybrid electrode composition, the composition preferably comprises 3 wt % to 60 wt %, or 3 wt % to 50 wt %, or 5 wt % to 50 wt %, or 10 wt % to 50 wt %, or 15 wt % to 50 wt % of the particulate material according to the second aspect of the invention, based on the total dry weight of the composition.

[0289] 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.

[0290] At least one additional particulate electroactive material D 50 The particle size is preferably in the range of 10 to 50 μm, preferably in the range of 10 to 40 μm, more preferably in the range of 10 to 30 μm, and most preferably in the range of 10 to 25 μm, for example in the range of 15 to 25 μm.

[0291] At least one additional particulate electroactive material D 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.

[0292] At least one additional particulate electroactive material D 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.

[0293] The at least one additional particulate electroactive material is preferably selected from carbonaceous particles, graphite particles and / or hard carbon particles, wherein the D of the graphite particles and the hard carbon particles is 50 The particle size is in the range of 10 to 50 μm. Still more preferably, the at least one additional particulate electroactive material is selected from graphite particles, wherein the D 50 The particle size ranges from 10 to 50 µm.

[0294] 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" should be interpreted to mean that 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 materials capable of inserting and releasing metal ions during charge and discharge of the battery), based on the total dry weight of the composition.

[0295] This type of "high loading" electrode composition preferably comprises at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt% of the particulate material according to the second aspect of the invention, based on the total dry weight of the composition.

[0296] The composition may optionally include 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), alginate and its alkali metal salts, styrene-butadiene rubber (SBR) and polyimide. The composition may include a mixture of multiple binders. Preferably, the binder includes a polymer selected from the following: polyacrylic acid (PAA) and its alkali metal salts, and modified polyacrylic acid (mPAA) and its alkali metal salts, SBR and CMC.

[0297] The binder may suitably be present in an amount of 0.5 to 20 wt%, preferably 1 to 15 wt%, preferably 2 to 10 wt% and most preferably 5 to 10 wt% based on the total dry weight of the composition.

[0298] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as crosslinking accelerators, coupling agents and / or adhesion promoters.

[0299] The composition may optionally include 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 the conductivity between the electroactive components of the composition and the current collector. 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.

[0300] One or more conductive additives may suitably be present in a total amount of 0.5 to 20 wt%, preferably 1 to 15 wt%, preferably 2 to 10 wt% and most preferably 5 to 10 wt%, based on the total dry weight of the composition.

[0301] In a fourth aspect, the present invention provides an electrode, the electrode comprising the particulate material according to the second aspect of the present invention or the composition according to the third aspect of the present invention. The particulate material may be in electrical contact with a current collector.

[0302] As used herein, the term current collector refers to any conductive substrate capable of carrying an electric current to or 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 3 to 500 μm. The granular 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 10 μm to 1 mm, for example 20 to 500 μm or 50 to 200 μm.

[0303] The electrode of the fourth aspect of the present invention can be prepared in the following manner: the particulate material of the second aspect of the present invention is combined with a solvent and one or more optional viscosity regulating additives to form a slurry. The slurry is then cast onto the surface of the current collector, and the solvent is removed to form an electrode layer on the surface of the current collector. Additional steps may be performed 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 20 μm to 2 mm, preferably 20 μm to 1 mm, preferably 20 μm to 500 μm, preferably 20 μm to 200 μm, preferably 20 μm to 100 μm, preferably 20 μm to 50 μm.

[0304] Alternatively, the slurry can be formed into a self-supporting 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 self-supporting object that is integrally formed and can then be combined with a current collector by known methods.

[0305] The electrode of the fourth aspect of the invention may be used as an anode of a metal ion battery. Therefore, in a fifth aspect, the invention provides a rechargeable metal ion battery comprising the electrode of the fourth aspect as an anode.

[0306] 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.

[0307] The cathode of a rechargeable metal ion battery generally includes a current collector and a cathode active material capable of releasing and reabsorbing metal ions. The cathode active material is preferably a composite material based on metal oxides. Examples of suitable cathode active materials include LiCoO 2 、LiCo 0.99 Al 0.01 O 2 、LiNiO 2 、LiMnO 2 、LiCo 0.5 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.

[0308] 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.

[0309] 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.

[0310] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts, such as Li 5 NI 2 , Li 3 N, LiI, LiSiO 4 , Li 2 SiS 3 , Li 4 SiO 4 , LiOH and Li 3 PO 4 .

[0311] 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.

[0312] In the case where the electrolyte is a non-aqueous organic solution, the metal ion battery preferably has 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 films.

[0313] The separator may be replaced by a polymer electrolyte material, and in such a case, the polymer electrolyte material is present in both the composite anode layer and the composite cathode layer. The polymer electrolyte material may be a solid polymer electrolyte or a gel-type polymer electrolyte.

[0314] Example

[0315] Example 1

[0316] The silicon-carbon composite material sample A (30 g) was loaded into the furnace tube. The furnace 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).

[0317] The silicon-carbon composite was then annealed at 650° C. for 90 minutes under nitrogen (0.5 L / min). The furnace temperature was then cooled to room temperature under nitrogen (0.5 L / min).

[0318] Subsequently, the annealed material was passivated at room temperature under nitrogen (0.2 L / min) and air (0.3 L / min) flows for 35 minutes, and then under air (0.5 L / min) flow for 90 minutes.

[0319] The obtained powder was characterized and designated as Sample B.

[0320] The characterization of Samples A and B is provided below in Table 1. Sample A is the silicon-carbon composite material used to prepare Sample B.

[0321] Cumulative pore volume of samples A and B (cm 3 / g) Figure 1 Shown in.

[0322] Table 1: Characterization of samples A and B

[0323]

[0324] Example 2

[0325] The silicon-carbon composite material sample C (40 g) was loaded into the 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.

[0326] The nitrogen flow rate was increased to 0.66 L / min, the rotation speed was increased to 50 rpm, and the silicon-carbon composite was annealed for 180 minutes. The furnace was then cooled to room temperature.

[0327] The annealed material was then passivated at room temperature under nitrogen (0.2 L / min) and air (0.3 L / min) flows for 30 minutes, and then under air (0.5 L / min) flow for 30 minutes.

[0328] The obtained powder was characterized and designated as sample D.

[0329] Samples EF were prepared using the method described for Sample D and the conditions listed below in Table 2. Characterization of Samples CF is provided below in Table 3. Sample C is the silicon carbon composite material used to prepare Samples DF.

[0330] Table 2: Annealing conditions of samples DF

[0331]

[0332] Table 3: Characterization of samples CF

[0333]

[0334] As shown in Tables 1 and 3, the hydrogen content decreases due to annealing.

[0335] Adding hydrogen to the annealing atmosphere (as in Sample F) results in increased retention of hydrogen within the structure and, therefore, a surface silicon content more similar to the baseline silicon carbon composite Sample C.

Claims

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

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

4. A method according to any preceding claim, wherein the PD of the porous particles 90 The pore diameter is not more than 30 nm, or not more than 25 nm, or 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.

5. A method according to any preceding claim, wherein the PD of the porous particles 90 The pore size is at least 3.2 nm, or at least 3.5 nm, or at least 3.8 nm, or at least 4 nm.

6. A method according to any preceding claim, wherein the PD of the porous particles 50 The pore diameter is 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, 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 1.5 nm.

7. A method according to any preceding claim, wherein in the porous particles, the volume fraction of micropores based on the total volume of micropores and mesopores 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, or at least 0.65, or at least 0.

7.

8. A method according to any preceding claim, wherein the porous particles have a BET surface area 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 range.

9. A method according to any preceding claim, wherein the porous particles are conductive porous particles, preferably conductive porous carbon particles, more preferably conductive porous carbon particles comprising at least 80 wt% carbon, or at least 85 wt% carbon, or at least 90 wt% carbon, or at least 95 wt% carbon.

10. A method according to any preceding claim, wherein the silicon-containing precursor is a gaseous precursor.

11. The method according to claim 10, wherein steps (b) and / or (d) include: The porous particles are contacted 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.

12. The method according to any preceding claim, wherein the silicon-containing precursor in steps (b) and / or (d) is independently selected from the group consisting of: monosilane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), butadienesilane (Si 4 H 10 ), methylsilane, dimethylsilane and chlorosilane, preferably selected from the group consisting of: monosilane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ) and butadienesilane (Si 4 H 10 ).

13. A method according to any preceding claim, wherein no more than 10 wt% of the silicon, or no more than 8 wt% of the silicon, or no more than 6 wt% of the silicon, 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 particles formed in the final step (d) is coarse bulk silicon when determined by thermogravimetric analysis (TGA).

14. A process according to any preceding claim, wherein steps (b) and / or (d) are independently carried out at a temperature 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 below 400°C, or 355 to 395°C, or 360 to 390°C, or 360 to 385°C, or 360 to 380°C, preferably steps (b) and / or (d) are independently carried out at a temperature in the range of 340 to below 400°C, or 370 to 395°C.

15. A process according to any preceding claim, wherein steps (b) and / or (d) are independently carried out at a pressure in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or about 100 kPa.

16. A method according to any preceding claim, wherein 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) is 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.

17. A method according to any preceding claim, wherein 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) is no more than 15:1, or no more than 14:1, or no more than 13:1, or no more than 12:

1.

18. A method according to any preceding claim, wherein the ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) when measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) when measured by gas adsorption is 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.

19. A method according to any preceding claim, wherein the ratio of the total pore volume of micropores and mesopores of the particles formed in step (c) when measured by gas adsorption to the total pore volume of micropores and mesopores of the particles formed in step (b) when measured by gas adsorption is no more than 20:1, or no more than 19:1, or no more than 18:1, or no more than 17:1, or no more than 16:1, or no more than 15:

1.

20. A method according to any preceding claim, wherein 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) is no more than 0.8:1, or no more than 0.7:1, or no more than 0.6:1, or no more than 0.5:

1.

21. A method according to any preceding claim, wherein 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) is at least 0.1:1, or at least 0.2:1, or at least 0.3:

1.

22. The method according to any preceding claim, wherein the inert gas used in step (c) is selected from the group consisting of nitrogen, argon, helium and combinations thereof.

23. The method of claim 22, wherein the inert gas comprises hydrogen.

24. A process according to any preceding claim, wherein step (c) is carried out in the presence of nitrogen and hydrogen.

25. A process according to any preceding claim, wherein the temperature in step (c) is higher 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 higher than the temperature in step (b).

26. The process according to any preceding claim, 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.

27. The process according to any preceding claim, 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.

28. The method according to any preceding claim, wherein step (c) is performed for a period of 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 performed for a period of at least 30 minutes, more preferably wherein step (c) is performed for a period of at least 1 hour, more preferably wherein step (c) is performed for a period of at least 90 minutes.

29. A method according to any preceding claim, wherein step (c) is performed for a period of 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 performed for a period of no more than 24 hours, more preferably wherein step (c) is performed for a period of no more than 12 hours, more preferably wherein step (c) is performed for a period of no more than 6 hours.

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

31. The method according to claim 30, wherein the lower threshold temperature TL is 500°C, the upper threshold temperature TU is 700°C, and the time period t is 90 minutes to 6 hours.

32. A method according to any preceding claim, wherein steps (c) and / or (d) are repeated more than once.

33. A method according to any preceding claim, wherein the weight ratio of silicon in the particles formed in step (d) 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 corresponds to the number of micropores and mesopores in the porous particle as measured by gas adsorption in cm 3 The total pore volume expressed in g is the same.

34. A method according to any preceding claim, wherein the particles formed in the last step (d) comprise 5 wt% to 85 wt%, or 10 wt% to 85 wt%, or 15 wt% to 85 wt%, or 20 wt% to 80 wt%, or 25 wt% to 80 wt%, or 30 wt% to 75 wt%, or 35 wt% to 75 wt%, or 40 wt% to 70 wt%, or 45 wt% to 65 wt% silicon, based on the total mass of the particles.

35. A method according to any preceding claim, wherein the amount of silicon in the particles formed in the final step (d) occupies at least 25% and at most 90% of the internal pore volume of the porous particles.

36. A method according to any preceding claim, wherein at least 85 wt %, more preferably at least 90 wt %, more preferably at least 95 wt %, more preferably at least 98 wt % of the silicon in the particles formed in the last step (d) is located within the internal pore volume of the porous particles.

37. A process according to any preceding claim, wherein the particles formed in the last step (d) have a BET surface area of ​​from 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 range.

38. A method according to any preceding claim, wherein the total pore volume of micropores and mesopores in the particles formed in the last step (d) does not exceed 0.6 cm 3 / g, or not more than 0.5 cm 3 / g, or not more than 0.4 cm 3 / g, or not more than 0.3 cm 3 / g, or not more than 0.2 cm 3 / g, or not more than 0.1 cm 3 / g.

39. A method according to any preceding claim, wherein the particles formed in the last step (d) have a total pore volume of micropores and mesopores of at least 0.01 cm 3 / g.

40. A method according to any preceding claim, wherein the particles formed in the last step (d) have a D 50 The particle size ranges from 1 to 30 µm.

41. A method according to any preceding claim, wherein the particles formed in the last step (d) have a D 10 The particle size 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.

42. A method according to any preceding claim, wherein the particles formed in the last step (d) have a D 90 Particle size not exceeding 50 µm, or not exceeding 40 µm, or not exceeding 30 µm, or not exceeding 25 µm, or not exceeding 20 µm, or not exceeding 15 µm.

43. A method according to any preceding claim, further comprising: The following steps are involved: (e) contacting the surface of the particles from the last step (d) with a passivating agent.

44. The method of claim 43, wherein the passivating agent is selected from the group consisting of: (i) an oxygen-containing gas; (ii) ammonia; (iii) a gas comprising ammonia and oxygen; (iv) phosphine; and (v) water.

45. The method according to claim 43, wherein the passivating agent is selected from: (i)R 1 -CH=CH-R 1 ; (ii) R 1 -C≡CR 1 4 (iii)O=CR 1 R 1 ; (iv)HX-R 2 ,as well as (v)HX-C(O)-R 1 , Where X represents O, S, NR 1 or PR 1 ;and Each R 1 independently represent H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or two R 1 The groups form unsubstituted or substituted ring structures containing 3 to 8 carbon atoms in the ring; Where 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 they form an unsubstituted or substituted ring structure containing from 3 to 8 carbon atoms in the ring.

46. ​​The method of claim 43, wherein the passivating agent is ethylene.

47. A method according to any preceding claim, further comprising: The following steps are involved: (f) combining the particles from the last step (d) or step (e) with a pyrolytic carbon precursor; and heating the pyrolytic carbon precursor to a temperature effective to cause deposition of the electrically conductive pyrolytic carbon material into the pores and / or on the outer surfaces of the composite particles.

48. A particulate material consisting of a plurality of composite particles obtainable by a method according to any preceding claim.

49. A composition comprising the particulate material of claim 48 and at least one other component.

50. An electrode comprising the particulate material of claim 48 or the composition of claim 49.

51. A rechargeable metal ion battery, comprising the electrode of claim 50.

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