Electroactive materials for metal ion batteries

Abstract

The present invention relates to a particulate material comprising a plurality of composite particles wherein the composite particles comprise: (a) a porous carbon backbone comprising micropores and / or mesopores having a total volume of at least 0.7 cm3 / g wherein at least half of the micropores / mesopores are in the form of pores having a diameter of no more than 5 nm; and (b) silicon within the micropores and / or mesopores of the porous carbon backbone in a defined amount relative to the volume of the micropores and / or mesopores.

Description

[0001] This application is a divisional application of the application with the invention name "Electroactive Materials for Metal Ion Batteries", PCT international application date of November 8, 2019, PCT international application number of PCT / GB2019 / 053176, and Chinese national application number of 201980079287.2. Technical Field

[0002] The present invention generally relates to electroactive materials suitable for use in the electrodes of rechargeable metal ion batteries, and more particularly to particulate materials having a high electrochemical capacity suitable for use as anode active materials in rechargeable metal ion batteries. Background Art

[0003] Rechargeable metal ion batteries are widely used in portable electronic devices such as mobile phones and laptop computers, and are increasingly being applied to electric vehicles or hybrid vehicles. Rechargeable metal ion batteries generally include an anode layer, a cathode layer, an electrolyte for transporting metal ions between the anode layer and the cathode layer, and an electrically insulating porous separator disposed between the anode and the cathode. The cathode generally includes a metal current collector having a metal oxide-based composite material layer containing metal particles, and the anode generally includes a metal current collector having an electroactive material layer, the electroactive material being defined herein as a material capable of intercalating and releasing metal ions during charging and discharging of the battery. For the sake of clarity, the terms "cathode" and "anode" are used herein in the following sense: the battery is connected to a load such that the cathode is the positive electrode and the anode is the negative electrode. When a metal ion battery is charged, metal ions are transported from the cathode layer containing metal ions through the electrolyte to the anode and intercalate into the anode material. The term "battery" is used herein to refer to both a device containing a single anode and a single cathode and a device containing multiple anodes and / or multiple cathodes.

[0004] Of interest is to increase the weight capacity and / or volume capacity of rechargeable metal ion batteries. The use of lithium ion batteries has provided substantial improvements compared to other battery technologies, but there is still room for further development. To date, commercial lithium ion batteries are largely limited by the use of graphite as the anode active material. When a graphite anode is charged, lithium intercalates between the graphite layers to form a material having the empirical formula Li x C6 (where x is greater than 0 and less than or equal to 1). Thus, the maximum theoretical capacity of graphite in a lithium ion battery is 372 mAh / g, and the actual capacity is slightly lower (about 340 to 360 mAh / g). Other materials such as silicon, tin, and germanium can intercalate lithium at significantly higher capacities compared to graphite, but have not yet found widespread commercial use due to difficulty in maintaining sufficient capacity during multiple charge / discharge cycles.

[0005] In particular, silicon is considered a promising graphite alternative for manufacturing rechargeable metal-ion batteries with high weight and volume capacities 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, issue 10). At room temperature, the theoretical maximum specific capacity of silicon in a lithium-ion battery is approximately 3,600 mAh / g (based on Li 15 Si4). However, the use of silicon as an anode material is complicated by large volume changes during charging and discharging.

[0006] Lithium insertion into bulk silicon causes a substantial increase in the volume of the silicon material, up to 400% of its original volume when the silicon is lithiated to its maximum capacity, and repeated charge-discharge cycles induce significant mechanical stress in the silicon material, leading to fracture and delamination of the silicon anode material. The volume shrinkage of silicon particles during delithiation can result in a loss of electrical contact between the anode material and the current collector. Another difficulty is that the solid electrolyte interface (SEI) layer formed on the silicon surface does not have sufficient mechanical tolerance to accommodate the expansion and contraction of silicon. As a result, the newly exposed silicon surface causes further electrolyte decomposition and an increase in the SEI layer thickness as well as irreversible lithium consumption. These degradation mechanisms together lead to unacceptable electrochemical capacity loss during consecutive charge and discharge cycles.

[0007] A variety of methods have been proposed to overcome the problems associated with the volume changes observed during charging of silicon-containing anodes. The most common approach to address the irreversible capacity loss of silicon anodes is to use some form of finely structured silicon as the electroactive material. It has been reported that compared to silicon particles in the micron size range, finely structured silicon such as silicon films and silicon nanoparticles with cross-sections below approximately 150 nm are more tolerant of volume changes during charging and discharging. However, neither of them is particularly suitable for commercial-scale applications in their unmodified form; nanosized particles are difficult to prepare and handle, and silicon films do not provide sufficient bulk capacity. For example, nanosized particles tend to form aggregates, making it difficult to obtain a usable particle dispersion within the anode material matrix. Additionally, the formation of aggregates of nanosized particles results in unacceptable capacity loss during repeated charge-discharge cycles.

[0008] Ohara et al. (Journal of Power Sources 136 (2004) 303-306) have described depositing silicon as a thin film onto a nickel foil current collector and using this structure as an anode for a lithium ion battery. Although this method gives good capacity retention, the thin film structure does not give an available amount of capacity per unit area and, when the film thickness is increased, eliminates any improvement.

[0009] WO 2007 / 083155 discloses that improved capacity retention can be obtained by using silicon particles having a high aspect ratio (i.e., the ratio of the maximum dimension to the minimum dimension of the particles).

[0010] It is also generally known that an electroactive material such as silicon can be deposited within the pores of a porous support material such as an activated carbon material. These composite materials provide some of the beneficial charge-discharge properties of nanosized silicon particles while avoiding the handling difficulties of nanoparticles. For example, Guo et al. (Journal of Materials Chemistry A, 2013, pages 14075-14079) disclose a silicon-carbon composite material in which a porous carbon substrate provides a conductive backbone and silicon nanoparticles are deposited within the uniformly distributed pore structure of the substrate. SEI formation during the initial charge cycle is limited by the remaining pore volume such that the remaining silicon is not exposed to the electrolyte during subsequent charge cycles. The composite material is known to have improved capacity retention during multiple charge cycles, but the initial capacity (in mAh / g) of the composite material is significantly lower than that of silicon nanoparticles.

[0011] JP2003100284 discloses an active material comprising a carbon-based scaffold having small pores branching from some larger pores. The electroactive material (such as silicon) is optionally located on the walls of both the large and small pores and on the outer surface of the carbon-based scaffold.

[0012] Despite efforts made to date, there is a continuing need to improve the electrochemical storage capacity of lithium ion batteries. In particular, there is still a need to identify alternative silicon-based materials that provide the benefits of a high lithiation capacity of silicon and that have sufficient capacity retention and structural stability for use in commercially viable rechargeable batteries. SUMMARY OF THE INVENTION

[0013] The present invention is based on the observation that the performance of a composite material comprising a porous carbon backbone and silicon as an electroactive material located within the porous carbon backbone can be optimized by using a porous carbon backbone having a specific pore structure and a controlled ratio of silicon to available pore volume.

[0014] In a first aspect, the present invention provides a particulate material comprising a plurality of composite particles, wherein the composite particles comprise:

[0015] (A) A porous carbon framework including micropores and / or mesopores,

[0016] wherein the total pore volume of the micropores and mesopores measured by gas adsorption is P 1 cm 3 / g, where P 1 has a value of at least 0.7,

[0017] wherein the PD 50 pore diameter measured by gas adsorption does not exceed 5 nm; and

[0018] (B) A plurality of elemental nanosized silicon domains located within the micropores and / or mesopores of the porous carbon framework;

[0019] wherein the weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.3×P 1 :1.

[0020] Accordingly, the present invention relates to a particulate material, wherein the porous carbon framework has a relatively high total volume of micropores and mesopores, and wherein pores with a diameter not exceeding 5 nm account for at least 50% of the total pore volume. For the avoidance of doubt, as used herein, P 1 refers to the pore volume of the porous carbon framework when measured separately, i.e., the pore volume of the porous carbon framework in the absence of silicon or any other material occupying the pores of the porous carbon framework.

[0021] Elemental silicon is located in the micropores and / or mesopores in the form of a plurality of nanosized silicon domains. As used herein, the term "nanosized silicon domain" refers to a nanosized silicon body located within the pores of the porous carbon framework. At least a portion of the nanosized silicon domains occupy at least a portion of the mesopores and / or micropores with a diameter less than the PD 50 pore diameter and thus have a size not exceeding 5 nm. The weight ratio of silicon to the porous carbon framework is associated with the total micropore / mesopore volume by the ratio [0.5×P 1 to 1.3×P 1 :1. By defining the weight ratio of silicon based on the value of P 1 , the volume occupancy percentage of silicon in the pore volume is controlled within a specific range. In other words, when the weight ratio of silicon to the porous carbon framework is in the range of [0.5×P 1 to 1.3×P 1 :1, the volume of silicon in the composite particles corresponds to approximately 20% - 55% of the total micropore / mesopore volume of the porous carbon framework.

[0022] Accordingly, the present invention generally relates to a particulate material in which silicon partially occupies the pores of a highly porous carbon skeleton, where the pore volume is mostly in the form of small mesopores and / or micropores. It has been found that this particle architecture provides an electroactive material that has high weight and volume capacities after lithiation and exhibits a unique ability to accommodate silicon expansion, and thus has a high reversible capacity retention during multiple charge-discharge cycles.

[0023] It has been found that the extraordinary reversible capacity retention of the particulate material of the present invention is a function of the high porosity of the porous carbon skeleton, the high proportion of small mesopores and / or micropores in the porous carbon skeleton, and the controlled loading of silicon in the composite material relative to the total mesopore / micropore volume.

[0024] Without being bound by theory, it is believed that having nanoscale silicon domains located within small mesopores and / or micropores first provides a fine silicon structure that is capable of lithiation and delithiation without excessive structural stress. It is believed that these very fine silicon domains have lower resistance to elastic deformation and higher fracture resistance compared to larger silicon structures. Secondly, by controlling the loading of silicon within the porous carbon skeleton such that only a portion of the pore volume is occupied by silicon in the uncharged state, the unoccupied pore volume of the porous carbon skeleton can internally accommodate a significant amount of silicon expansion. More specifically, it is believed that a highly microporous carbon skeleton has a reduced fracture rate due to the ability of its thin pore walls to elastically deform, and the tensile fracture strength of the skeleton is very high.

[0025] Accordingly, the low resistance of silicon to elastic deformation acts in concert with the high relative modulus of carbon to drive silicon expansion into the pore volume of the porous carbon skeleton. Although further lithiation of silicon results in some external expansion of the entire composite particle, the amount of external expansion is limited due to the internal accommodation of silicon expansion. In terms of the particle expanding outwards, the fine pore structure of the porous carbon skeleton can deform without breaking. By carefully controlling the amount of internal versus external expansion, the strain on the porous carbon skeleton and the silicon domains is limited to a level that is tolerated after a large number of charge-discharge cycles without causing significant capacity loss. The high total porosity of the porous carbon skeleton not only provides a high silicon volume loading but also ensures that the porous carbon skeleton has sufficient elasticity to withstand the repeated volume changes during multiple charge-discharge cycles.

[0026] Another factor in the extraordinary performance of the particulate materials of the present invention is the minimization of SEI formation. As described above, by positioning the nano-sized silicon domains within small mesopores and / or micropores, only a small surface area of silicon is electrolyte-accessible, thus limiting SEI formation. To a large extent, additional exposure of silicon during subsequent charge-discharge cycles is prevented, such that SEI formation is not a significant degradation mechanism that can lead to capacity loss. This stands in stark contrast to the excessive and unconstrained SEI formation characteristic of materials such as those disclosed by Guo (see above). Another benefit of minimizing the exposed silicon surface is the reduction of silicon surface oxidation.

[0027] Due to the unique particle architecture of the particulate materials of the present invention, the silicon in the composite particles has electrochemical properties comparable to those of fine silicon nanoparticles, without suffering from the drawbacks of excessive SEI formation and poor dispersibility, such drawbacks which render discrete silicon nanoparticles unsuitable as electrode materials for commercial use.

[0028] The porous carbon framework suitably comprises a three-dimensional interconnected open pore network, the three-dimensional interconnected open pore network comprising a combination of micropores and / or mesopores and optionally a small volume of macropores. According to conventional IUPAC terminology, the term "micropore" is used herein to refer to pores with a diameter less than 2 nm, the term "mesopore" is used herein to refer to pores with a diameter of 2 - 50 nm, and the term "macropore" is used to refer to pores with a diameter greater than 50 nm.

[0029] The volumes of micropores, mesopores, and macropores in the porous carbon framework mentioned herein, and any mention of the pore volume distribution within the porous carbon framework, refer to the internal pore volume of the porous carbon framework alone (i.e., in the absence of any silicon or other material occupying some or all of the pore volume).

[0030] The porous carbon framework is characterized by a high pore volume in the form of micropores and / or mesopores. The total volume of micropores and mesopores (i.e., the total pore volume in the range of 0 to 50 nm) is referred to herein as P 1 cm 3 / g, where P 1 represents a dimensionless natural number with a value of at least 0.7. The value of P 1 is also used to relate the available pore volume in the porous carbon framework and the weight ratio of silicon to the porous carbon framework as described above.

[0031] More preferably, the value of P 1 is at least 0.75, or at least 0.8, or at least 0.85. Optionally, P 1The value can be at least 0.9, or at least 0.95, or at least 1, such as at least 1.05, at least 1.1, at least 1.15, or at least 1.2. It is advantageous to use a high-porosity carbon skeleton because it enables a greater amount of silicon to be accommodated within the pore structure, and it has been found that a high-porosity carbon skeleton in which the pore volume is mainly in the form of micropores and / or smaller mesopores has sufficient strength to accommodate the volume expansion of silicon without fracturing or otherwise degrading the porous carbon skeleton.

[0032] The internal pore volume of the porous carbon skeleton is suitably limited to a value at which the increased brittleness of the porous carbon skeleton outweighs the advantage of the increased pore volume for accommodating a greater amount of silicon. Generally, P 1 The value can be no more than 2.5. However, more preferably, P 1 The value can be no more than 2.2, or no more than 2, or no more than 1.8, or no more than 1.6, or no more than 1.5, or no more than 1.4, or no more than 1.3, or no more than 1.2, or no more than 1.1, or no more than 1.0, or no more than 0.9. More preferably, P 1 The value is no more than 1.2, or no more than 1.1, or no more than 1.0, or no more than 0.9.

[0033] According to the present invention, P 1The value can be, for example, in the range of 0.8 to 2.2, or in the range of 0.85 to 2.2, or in the range of 0.9 to 2.2, or in the range of 0.95 to 2.2, or in the range of 1 to 2.2, or in the range of 1.05 to 2.2, or in the range of 1.1 to 2.2, or in the range of 0.8 to 2, or in the range of 0.85 to 2, or in the range of 0.9 to 2, or in the range of 0.95 to 2, or in the range of 1 to 2, or in the range of 1.05 to 2, or in the range of 1.1 to 2, or in the range of 0.8 to 1.9, or in the range of 0.85 to 1.9, or in the range of 0.9 to 1.9, or in the range of 0.95 to 1.9, or in the range of 1 to 1.9, or in the range of 1.05 to 1.9, or in the range of 1.1 to 1.9, or in the range of 0.8 to 1.8, or in the range of 0.85 to 1.8, or in the range of 0.9 to 1.8, or in the range of 0.95 to 1.8, or in the range of 1 to 1.8, or in the range of 1.05 to 1.8, or in the range of 1.1 to 1.8, or in the range of 0.8 to 1.7, or in the range of 0.85 to 1.7, or in the range of 0.9 to 1.7, or in the range of 0.95 to 1.7, or in the range of 1 to 1.7, or in the range of 1.05 to 1.7, or in the range of 1.1 to 1.7, or in the range of 0.8 to 1.6, or in the range of 0.85 to 1.6, or in the range of 0.9 to 1.6, or in the range of 0.95 to 1.6, or in the range of 1 to 1.6, or in the range of 1.05 to 1.6, or in the range of 1.1 to 1.6.

[0034] Preferably, the value of P1 can be, for example, in the range of 0.7 to 1.5, or in the range of 0.75 to 1.4, or in the range of 0.7 to 1.3, or in the range of 0.75 to 1.3, or in the range of 0.7 to 1.2, or in the range of 0.75 to 1.2, or in the range of 0.7 to 1, or in the range of 0.75 to 1, or in the range of 0.7 to 0.9, or in the range of 0.75 to 0.9.

[0035] PD of the porous carbon framework 50 The pore diameter is less than 5 nm. As used herein, the term "PD 50 pore diameter" refers to the volume median pore diameter based on the total volume of micropores and mesopores (i.e., the pore diameter at which 50% of the measured total micropore and mesopore volume (represented by P 1 is lower than a certain pore diameter). Thus, according to the present invention, at least 50% of the total volume of micropores and mesopores is in the form of pores with a diameter less than 5 nm.

[0036] As used herein, the general term "PDn "Pore diameter" refers to the pore diameter at the nth percentile of the volume based on the total volume of micropores and mesopores. For example, as used herein, the term "D" 90 "Pore diameter" refers to the pore diameter at which 90% of the measured total micropore and mesopore volume (represented by P 1 is lower than a certain pore diameter.

[0037] To avoid ambiguity, for determining the PD n value, any macropore volume (pore diameter greater than 50 nm) is not considered.

[0038] According to the present invention, the PD 50 pore diameter of the porous carbon framework is preferably not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm. Preferably, the PD 50 pore diameter of the porous carbon framework is at least 0.8 nm, or at least 1 nm, or at least 1.2 nm. Thus, it is particularly preferred that more than 50% of the total micropore and mesopore volume is in the form of micropores.

[0039] More preferably, at least 60% of the total micropore and mesopore volume of the porous carbon framework is in the form of pores with a diameter not exceeding 5 nm. Thus, the PD 60 pore diameter of the porous carbon framework is preferably 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.

[0040] More preferably, at least 70% of the total micropore and mesopore volume of the porous carbon framework is in the form of pores with a diameter not exceeding 5 nm. Thus, the PD 70 pore diameter of the porous carbon framework is preferably 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.

[0041] More preferably, at least 80% of the total micropore and mesopore volume of the porous carbon framework is in the form of pores with a diameter not exceeding 5 nm. Thus, the PD 80 pore diameter of the porous carbon framework is preferably 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.

[0042] The volume of the larger mesopores in the porous carbon framework is preferably limited such that the PD 90 pore diameter does not exceed 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.

[0043] Preferably, the PD 95The pore diameter does not exceed 20 nm, or does not exceed 15 nm, or does not exceed 12 nm, or does not exceed 10 nm.

[0044] According to the present invention, the porous carbon framework may be one in which PD 50 does not exceed 5 nm and PD 90 does not exceed 20 nm, or one in which PD 50 does not exceed 4 nm and PD 90 does not exceed 15 nm, or one in which PD 50 does not exceed 3 nm and PD 90 does not exceed 12 nm, or one in which PD 50 does not exceed 3 nm and PD 90 does not exceed 10 nm, or one in which PD 50 does not exceed 2.5 nm and PD 90 does not exceed 10 nm, or one in which PD 50 does not exceed 2 nm and PD 90 does not exceed 8 nm, or one in which PD 50 does not exceed 2 nm and PD 90 does not exceed 6 nm, or one in which PD 50 does not exceed 1.5 nm and PD 90 does not exceed 6 nm.

[0045] More preferably, the porous carbon framework may be one in which PD 50 is from 1 to 5 nm and PD 90 is from 3 to 20 nm, or one in which PD 50 is from 1 to 4 nm and PD 90 is from 3 to 15 nm, or one in which PD 50 is from 1 to 3 nm and PD 90 is from 3 to 12 nm, or one in which PD 50 is from 1 to 3 nm and PD 90 is from 3 to 10 nm, or one in which PD 50 is from 1 to 2.5 nm and PD 90 is from 3 to 10 nm, or one in which PD 50 is from 1 to 2 nm and PD 90 is from 3 to 8 nm, or one in which PD 50 is from 1 to 2 nm and PD 90 is from 3 to 6 nm, or one in which PD 50 is from 1 to 2 nm and PD 90 is from 3 to 6 nm.

[0046] A small fraction of pores with diameters in the larger mesopore range can advantageously facilitate electrolyte access to silicon. Thus, pores with diameters in the range of 10 to 50 nm (i.e., larger mesopores) can optionally constitute at least 1%, at least 2%, at least 5% or at least 10% of the total micropore and mesopore volume of the porous carbon framework.

[0047] The volume ratio of micropores to mesopores in the porous carbon framework can be substantially in the range of 100:0 to 0:100. Preferably, the volume ratio of micropores to mesopores is 90:10 to 55:45, or 90:10 to 60:40, or 85:15 to 65:35.

[0048] The pore size distribution of the porous carbon framework can be unimodal, bimodal or multimodal. As used herein, the term "pore size distribution" relates to the distribution of the pore sizes of the porous carbon framework relative to the cumulative total internal pore volume. A bimodal or multimodal pore size distribution can be preferred because the close proximity between pores with a maximum diameter of 5 nm and pores with larger diameters provides the advantage of efficient ion transport from the porous network to silicon. Thus, the particulate material has high ionic diffusivity and thus improved rate performance.

[0049] Optionally, the porous carbon framework has a bimodal or multimodal pore size distribution, the bimodal or multimodal pore size distribution including at least one peak at less than 2 nm and at least one peak in the range of 5 to 50 nm, preferably the local minimum in the pore size distribution is in the range of 5 to 20 nm. More preferably, the porous carbon framework has a bimodal or multimodal pore size distribution, the bimodal or multimodal pore size distribution including at least one peak at less than 2 nm and at least one peak in the range of 10 to 40 nm, preferably the local minimum in the pore size distribution is in the range of 5 to 15 nm.

[0050] Suitably, the bimodal or multimodal pore size distribution includes a peak pore size in the micropore range and a peak pore size in the mesopore size range, which differ from each other by a factor of 5 to 20, more preferably by approximately a factor of 10. For example, the porous carbon framework can have a bimodal pore size distribution that includes a peak at a pore size of 2 nm and a peak at a pore size of 20 nm.

[0051] According to the methods described in ISO 15901-2 and ISO 15901-3, nitrogen adsorption is used at 77 K, down to 10 -6The relative pressure p / p0 is used to determine the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores using quenched solid density functional theory (QSDFT). Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of materials by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure is increased until the saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually decreased to allow the liquid to evaporate 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 the pore volume and pore size distribution by nitrogen adsorption include the TriStarII and TriStar IIPlus porosimeters (which are available from Micromeritics Instrument Corporation in the United States), and the Autosorb IQ porosimeter (which is available from Quantachrome Instruments).

[0052] Nitrogen adsorption is effective for measuring the pore volume and pore size distribution of pores with a maximum diameter of 50 nm, but is less reliable for pores with much larger diameters. For the purposes of the present invention, therefore, nitrogen adsorption is used only for pores with a maximum diameter of 50 nm (including 50 nm) to determine the pore volume and pore size distribution. As described above, P is determined by considering only pores with a maximum diameter of 50 nm (including 50 nm), i.e., only micropores and mesopores 1 values, and PD is likewise determined relative to the total volume of only micropores and mesopores n values.

[0053] Given the limitations of available analytical techniques, it is not possible to measure the pore volume and pore size distribution over the entire range of micropores, mesopores, and macropores using a single technique. In the case where the porous carbon framework includes macropores, the volume of pores in the range greater than 50 nm to a maximum of 100 nm is considered herein to have a P 2 cm 3 / g value and is measured by mercury intrusion porosimetry. As described above, the P 2 value relates to the pore volume of the porous carbon framework when measured separately, i.e., the pore volume of the porous carbon framework in the absence of silicon or any other material occupying the pores of the porous carbon framework.

[0054] To avoid doubt, the P 2 value only considers pores with a diameter from greater than 50 nm to a maximum of 100 nm (including 100 nm), i.e., it only includes the volume of macropores with a maximum diameter of 100 nm. To determine the P 2Values, without considering any pore volume of pore sizes below 50 nm measured by mercury intrusion porosimetry (as described above, nitrogen adsorption is used to characterize mesopores and micropores). For the purposes of the present invention, the pore volume in the case of above 100 nm measured by mercury intrusion porosimetry is assumed to be the interparticle porosity and is also not considered when determining the P 2 value.

[0055] Mercury intrusion porosimetry is a technique for characterizing the porosity and pore size distribution of a material by applying different 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 intrusion 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 is 140°. The density of mercury at room temperature is 13.5462 g / cm 3 . A variety of high-precision mercury intrusion porosimetry instruments are commercially available, such as the automated mercury porosimeter of the AutoPore IV series, which can be obtained from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury intrusion porosimetry, reference can be made to P.A. Webb and C. Orr, "Analytical Methods in Fine Particle Technology", 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0056] Compared with the volume of micropores and mesopores (and thus the P 1 value), the volume of macropores (and thus the P 2 value) is preferably smaller. 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 silicon in micropores and smaller mesopores.

[0057] Therefore, according to the present invention, the total volume of macropores in the porous carbon framework measured by mercury intrusion porosimetry is P 2 cm 3 / g, where the P 2 value is preferably not more than 0.2 × P 1 , or not more than 0.1 × P 1 , or not more than 0.05 × P 1 , or not more than 0.02 × P 1 , or not more than 0.01 × P 1 , or not more than 0.005 × P 1 .

[0058] In a preferred embodiment, P 2 has a value not exceeding 0.3, or not exceeding 0.25, or not exceeding 0.20, or not exceeding 0.15, or not exceeding 0.1, or not exceeding 0.05. As discussed above for the larger mesopores, a small pore volume fraction within the macropore range can advantageously facilitate electrolyte access to the silicon.

[0059] The open pore network optionally includes a hierarchical pore structure, i.e., a pore structure in which there is a degree of pore size sorting, where the smaller pores branch from the larger pores.

[0060] It should be understood that intrusion techniques such as gas adsorption and mercury porosimetry are only effective for determining the pore volume of pores accessible from the outside of the porous carbon framework by nitrogen or mercury. The porosity values (P 1 and P 2 ) as specified herein should be understood to refer to the volume of open pores (pores accessible from the outside of the porous carbon framework by fluid). In this document, when specifying porosity values, completely encapsulated pores that cannot be identified by nitrogen adsorption or mercury porosimetry should not be considered. Similarly, for determining the value of P 1 , any pore volume located in pores that are too small to be detected by nitrogen adsorption is also not considered.

[0061] The porous carbon framework can include crystalline carbon or amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The porous carbon framework can be a hard carbon or a soft carbon framework and can suitably be obtained by known procedures involving polymer pyrolysis.

[0062] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which carbon atoms are found mainly in the sp 2 hybridization state (triple bond) in nano-scale polyaromatic domains. The polyaromatic domains are crosslinked by chemical bonds such as C-O-C bonds. Due to the chemical crosslinking between the polyaromatic domains, hard carbon cannot be converted to graphite at high temperatures. Hard carbon has graphite-like properties, as evidenced by a large G band (~1600 cm -1 ) in the Raman spectrum. However, this carbon is not completely graphitic, as evidenced by an obvious D band (~1350 cm -1 ) in the Raman spectrum.

[0063] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are found mainly in polyaromatic domains with sizes in the range of 5 - 200 nm in the sp 2 hybridization state (triple 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 framework preferably contains at least 50% of sp 2Hybrid carbon (measured by XPS). For example, the porous carbon framework may suitably comprise 50% to 98% sp 2 hybrid carbon, 55% to 95% sp 2 hybrid carbon, 60% to 90% sp 2 hybrid carbon, or 70% to 85% sp 2 hybrid carbon.

[0064] A variety of different materials can be used to prepare a suitable porous carbon framework. Examples of organic materials that can be used include: plant biomass, which includes lignocellulosic materials such as coconut shells, rice husks, wood, etc., and fossil carbon sources such as coal. Examples of polymeric materials that form a porous carbon framework upon pyrolysis include: phenolic resins, novolac resins, pitch, melamine, polyacrylates, polystyrene, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers containing monomer units of acrylate, styrene, α-olefins, vinylpyrrolidone, and other ethylenically unsaturated monomers. Depending on the raw materials and conditions of the pyrolysis process, various different hard carbon materials can be obtained in the art.

[0065] The porous carbon framework can be subjected to a chemical or gas activation process to increase the volume of mesopores and micropores. Suitable activation processes include contacting the pyrolytic carbon with one or more of oxygen, steam, CO, CO2, and KOH at a temperature in the range of 600 to 1000 °C.

[0066] Mesopores can also be obtained by known templating processes using removable pore formers such as MgO and other colloidal or polymeric templates (which can be removed by thermal or chemical means after pyrolysis or activation).

[0067] The BET surface area of the porous carbon framework is preferably at least 750 m 2 / g, or at least 1,000 m 2 / g, or at least 1,250 m 2 / g, or at least 1,500 m 2 / g. As used herein, the term "BET surface area" shall be considered to refer to the surface area per unit mass calculated from the measurement results of the physical adsorption of gas molecules on the solid surface according to ISO 9277 using the Brunauer–Emmett–Teller principle. Preferably, the BET surface area of the conductive porous particle framework does not exceed 4,000 m 2 / g, or does not exceed 3,500 m 2 / g, or does not exceed 3,250 m 2 / g, or does not exceed 3,000 m 2 / g.

[0068] The amount of silicon in the composite particles of the present invention is preferably selected such that no more than about 55% of the internal pore volume of the porous carbon framework is occupied by silicon (in the uncharged state). Preferably, silicon occupies from about 25% to about 45% of the internal pore volume of the porous carbon framework, more preferably from about 25% to 40% of the internal pore volume of the porous carbon framework. Within these preferred ranges, the pore volume of the porous carbon framework effectively accommodates the expansion of silicon during charging and discharging, but avoids an excessive pore volume that is detrimental to the volumetric capacity of the particulate material. However, the amount of silicon is not so high as to impede effective lithiation due to insufficient metal ion diffusion rate or insufficient expansion volume resulting in mechanical resistance to lithiation.

[0069] By requiring the weight ratio of silicon to the porous carbon framework to be in the range of [0.5×P 1 to 1.3×P 1 :1, the amount of silicon in the porous carbon framework can be correlated with the available pore volume. This relationship takes into account the density of silicon and the pore volume of the porous carbon framework to define a weight ratio of silicon at which the occupied pore volume is approximately 20% to 55%.

[0070] Preferably, the weight ratio of silicon to the porous carbon framework is in the range of [0.55×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1×P 1 :1, or in the range of [0.6×P 1 to 0.95×P 1 :1, or in the range of [0.6×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.85×P 1 :1, or in the range of [0.65×P 1 to 0.8×P 1 :1, or in the range of [0.7×P 1 to 0.8×P 1 :1.

[0071] In some cases, the composite particles can include pores in which the enclosed void space is capped with silicon, thus preventing electrolyte from entering the void space.

[0072] Preferably, at least 90 wt%, more preferably at least 95 wt%, and even more preferably at least 98 wt% of the silicon mass in the composite particles is located within the internal pore volume of the porous carbon framework, such that no or very little silicon is present on the outer surface of the composite particles.

[0073] The particulate materials of the present invention may further be characterized by their performance in air under thermogravimetric analysis (TGA). Preferably, when the particulate materials are analyzed by TGA in air at a heating rate of 10 °C / min, no more than 10%, more preferably no more than 5%, and even more preferably no more than 2% of the silicon content in the particulate materials is oxidized at 800 °C.

[0074] The determination of the amount of unoxidized silicon is obtained from the characteristic TGA traces of these materials. The mass increase at approximately 300 - 500 °C corresponds to the initial oxidation of silicon to SiO2, followed by a mass loss at approximately 500 - 600 °C when carbon is oxidized to CO2 gas. Above approximately 600 °C, there is a further mass increase corresponding to the continued conversion of silicon to SiO2, increasing to an asymptote above 1000 °C as the oxidation of silicon is completed.

[0075] For the purposes of this analysis, it is assumed that any mass increase above 800 °C corresponds to the oxidation of silicon to SiO2, and the total mass at the completion of oxidation is SiO2. This enables the determination of the percentage of silicon unoxidized at 800 °C (as a proportion of the total silicon content) according to the following equation:

[0076] Z = 1.875 × [(M f - M 800 ) / M f × 100%

[0077] where Z is the percentage of silicon unoxidized at 800 °C, M f is the mass of the sample at the completion of oxidation, and M 800 is the mass of the sample at 800 °C.

[0078] Without being bound by theory, it is understood that the temperature at which silicon is oxidized under TGA roughly corresponds to the length scale of the oxide coating on the silicon, as oxygen atoms diffuse through the oxide layer and are thermally activated. The size and location of the silicon nanostructures limit the length scale of the oxide coating thickness. Thus, it is understood that silicon deposited in micropores and mesopores will oxidize at a lower temperature compared to silicon deposits on the particle surface, as there will necessarily be a thinner oxide coating on these structures. Therefore, the preferred materials according to the present invention exhibit substantially complete oxidation of silicon at low temperatures, which is consistent with the small length scale of the silicon nanostructures located in micropores and smaller mesopores. For the purposes of the present invention, the oxidation of silicon at 800 °C is assumed to be silicon on the outer surface of the porous carbon framework.

[0079] The silicon is preferably amorphous silicon. Amorphous silicon is considered to have better properties as the electroactive material. The morphology of the silicon can be determined by known procedures using X-ray diffraction (XRD).

[0080] Preferably, the volume of micropores and mesopores in the composite particles (i.e., in the presence of silicon) measured by nitrogen adsorption does not exceed 0.15x P 1 , or does not exceed 0.10x P 1 , or does not exceed 0.05x P 1 , or does not exceed 0.02x P 1 .

[0081] The weight ratio of silicon to the porous carbon framework can be determined by elemental analysis. Elemental analysis is used to determine the weight percentages of both silicon and carbon in the composite particles. Optionally, the amounts of hydrogen, nitrogen, and oxygen can also be determined by elemental analysis. Preferably, the weight percentage of carbon (and optionally hydrogen, nitrogen, and oxygen) in the separate porous carbon framework is also determined using elemental analysis. Determining the weight percentage of carbon in the separate porous carbon framework takes into account the possibility that the porous carbon framework contains a small amount of heteroatoms within its molecular framework. The two measurements carried out together enable the reliable determination of the weight percentage of silicon relative to the entire porous carbon framework.

[0082] The silicon content is preferably determined by ICP-OES (inductively coupled plasma - optical emission spectrometry). A variety of ICP-OES instruments are commercially available, such as the 7000 series of ICP-OES analyzers (available from ThermoFisher Scientific). The carbon content (and if necessary, the hydrogen content, nitrogen content, and oxygen content) of the composite particles and the separate porous carbon framework is preferably determined by IR absorption. A suitable instrument for determining the carbon content, hydrogen content, nitrogen content, and oxygen content is the Micro elemental analyzer (available from Leco Corporation).

[0083] The composite particles preferably have a low total oxygen content. Oxygen can be present in the composite particles, for example, as part of the porous carbon framework or as an oxide layer on any exposed silicon surface. Preferably, the total oxygen content of the composite particles is less than 15 wt%, more preferably less than 10 wt%, more preferably less than 5 wt%, for example less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%.

[0084] The silicon can optionally contain a small amount of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, nitrogen, or germanium. Preferably, the dopant is present in a total amount not exceeding 2 wt% based on the total amount of silicon and one or more dopants.

[0085] To avoid ambiguity, as used herein, the term "particle size" refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, where the particle volume is understood to include the volume of any pores within the particle. As used herein, the terms "D 50 " and "D 50 particle size" refer to the volume median diameter, i.e., the diameter at which 50% of the volume of the particle population is measured to be below a certain diameter. As used herein, the terms "D 10 " and "D 10 particle size" refer to the 10th percentile volume median diameter, i.e., the diameter at which 10% of the volume of the particle population is measured to be below a certain diameter. As used herein, the terms "D 90 " and "D 90 particle size" refer to the 90th percentile volume median diameter, i.e., the diameter at which 90% of the volume of the particle population is measured to be below a certain diameter.

[0086] The term "D n " used herein to define the particle size distribution should be distinguished from the term "PD n " used herein to define the pore size distribution as described above.

[0087] Particle size and particle size distribution can be determined by conventional laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that particles will scatter light at an angle that varies according to the size of the particle, and multiple particles will produce a scattering light pattern defined by the intensity and angle that can be correlated with the particle size distribution. A variety of commercially available laser diffraction instruments are available for the rapid and reliable determination of particle size distribution. Unless otherwise specified, the particle size distribution measurements specified or reported herein are made using a conventional Malvern Mastersizer TM 3000 particle size analyzer from Malvern Instruments. The Malvern Mastersizer TM 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing the particles of interest suspended in an aqueous solution. The light scattered by the particles strikes at an angle inversely proportional to the particle size, and a photodetector array measures the intensity of the light at multiple predetermined angles, and the intensities measured at different angles are processed by computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values reported herein are obtained using a wet dispersion of the particles in distilled water. The particle refractive index is 3.50, and the dispersant index is 1.330. The Mie scattering model is used to calculate the particle size distribution.

[0088] The D of the composite particles 50The particle size can be in the range of 0.5 to 50 μm. Optionally, D 50 The particle size can be at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm. Optionally, D 50 The particle size can be not more than 40 μm, or not more than 30 μm, or not more than 25 μm, or not more than 20 μm, or not more than 15 μm.

[0089] For example, the D of the composite particles 50 The particle size can be in the range of 1 to 25 μm, or 1 to 20 μm, or 2 to 20 μm, or 2 to 15 μm or 3 to 15 μm. Particles within these size ranges and having the porosity and pore size distribution described herein are ideally suitable for the anode of a metal ion battery due to their dispersibility in the slurry, their structural robustness, their capacity retention with repeated charge-discharge cycles, and their suitability for forming a dense electrode layer with a uniform thickness in the conventional range of 20 to 50 μm.

[0090] The D of the composite particles 10 The particle size is preferably at least 0.2 μm, or at least 0.5 μm, or at least 0.8 μm, or at least 1 μm, or at least 1.5 μm, or at least 2 μm. By keeping the D 10 particle size above 0.2 μm, the possibility of agglomeration of unwanted submicron-sized particles is reduced, resulting in improved dispersion of the particulate material and improved capacity retention.

[0091] The D of the composite particles 90 The particle size is preferably not more than 80 μm, or not more than 60 μm, or not more than 40 μm, or not more than 30 μm, or not more than 25 μm, or not more than 20 μm. The presence of very large particles results in non-uniform formation of fillers in the electrode active layer, thereby disrupting the formation of a dense electrode layer, especially an electrode layer with a thickness in the range of 20 to 50 μm. Therefore, preferably, the D 90 particle size is not more than 40 μm, and more preferably even smaller.

[0092] The composite particles preferably have a narrow span of size distribution. For example, the span of the particle size distribution (defined as (D 90 - D 10 ) / D 50 ) is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow span of size distribution, efficient filling of the particles into the dense electrode layer can be more easily achieved.

[0093] The shape of the composite particles can be spheroid-like. Spheroid-like particles as defined herein can include both spherical particles and ellipsoidal particles, and the shape of the composite particles of the present invention can be suitably defined with reference to the sphericity and aspect ratio of the particles of the present invention. It has been found that spheroid-like particles are particularly well-suited for dispersions in slurries without forming aggregates. Additionally, it has surprisingly been found that when compared to irregularly shaped porous particles and porous particle fragments, the use of porous spheroid-like particles provides a further improvement in strength.

[0094] The sphericity of an object is conventionally defined as the ratio of the surface area of a sphere to the surface area of the object, where the object and the sphere have the same volume. However, it is actually difficult to measure the surface area and volume of individual particles on the micron scale. However, highly accurate two-dimensional projections of micron-scale particles can be obtained by scanning electron microscopy (SEM) and by dynamic image analysis, where a digital camera is used to record the shadow projected by the particles. As used herein, the term "sphericity" should be understood as the ratio of the area of the particle projection to the area of a circle, where the particle projection and the circle have the same perimeter. Thus, for an individual particle, the sphericity S can be defined as:

[0095]

[0096] where A m is the measured area of the particle projection, and C m is the measured perimeter of the particle projection. As used herein, the average sphericity S av of multiple particles is defined as:

[0097]

[0098] where n represents the number of particles in the population.

[0099] As used herein, the term "spheroid-like" applied to the composite particles of the present invention should be understood to mean a material having an average sphericity of at least 0.70. Preferably, the average sphericity of the porous spheroid-like particles of the present invention is at least 0.85, more preferably at least 0.90, more preferably at least 0.92, more preferably at least 0.93, more preferably at least 0.94, more preferably at least 0.95. Optionally, the average sphericity of the porous spheroid-like particles can be at least 0.96, or at least 0.97, or at least 0.98, or at least 0.99.

[0100] It is to be understood that in the case of any particle that is not a perfect sphere, the perimeter and area of the two-dimensional particle projection will depend on the orientation of the particle. However, the influence of particle orientation can be offset by reporting the sphericity and aspect ratio as averages obtained from multiple particles with random orientations. A variety of SEM and dynamic image analysis instruments are commercially available, enabling the rapid and reliable determination of the sphericity and aspect ratio of particulate materials. Unless otherwise stated, the sphericity values as specified or reported herein are measured by a CamSizer XT particle analyzer from Retsch Technology GmbH. The CamSizer XT is a dynamic image analysis instrument that can obtain highly accurate distributions of the size and shape of particulate materials with a sample volume from 100 mg to 100 g, enabling the direct calculation of properties such as average sphericity and aspect ratio through this instrument.

[0101] The BET surface area of the composite particles of the present invention is preferably not more than 300 m 2 / g, or not more than 250 m 2 / g, or not more than 200 m 2 / g, or not more than 150 m 2 / g, or not more than 100 m 2 / g, or not more than 80 m 2 / g, or not more than 60 m 2 / g, or not more than 40 m 2 / g, or not more than 30 m 2 / g, or not more than 25 m 2 / g, or not more than 20 m 2 / g, or not more than 15 m 2 / g, or not more than 10 m 2 / g. Generally, a low BET surface area is preferred to minimize the formation of the solid electrolyte interface (SEI) layer at the surface of the composite particles during the first charge-discharge cycle of the anode containing the particulate material of the present invention. However, an overly low BET surface area results in unacceptably low charge rates and capacities due to the inaccessibility of the bulk electroactive material to metal ions in the surrounding electrolyte. For example, the BET surface area is preferably at least 0.1 m 2 / g, or at least 1 m 2 / g, or at least 2 m 2 / g, or at least 5 m 2 / g. For example, the BET surface area can be in the range of 1 m 2 / g to 25 m 2 / g, more preferably in the range of 2 to 15 m 2 / g.

[0102] The charge specific capacity of the particulate material of the present invention upon first lithiation is from 1200 to 2340 mAh / g. Preferably, the charge specific capacity of the particulate material of the present invention upon first lithiation is at least 1400 mAh / g.

[0103] 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 a porous carbon framework. As used herein, CVI refers to a process in which a gaseous silicon-containing gas is thermally decomposed on a surface to form elemental silicon and gaseous by-products at the surface.

[0104] Suitable gaseous silicon-containing precursors include silane (SiH4), silane derivatives (e.g., disilane, trisilane, and tetrasilane), and trichlorosilane (SiHCl3). The silicon-containing precursor can be used in pure form or more commonly as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the silicon-containing precursor can be used in an amount in the range of 0.5 - 20 vol%, or 1 - 10 vol%, or 1 - 5 vol% based on the total volume of the silicon-containing precursor and the inert carrier. The CVI process is suitably carried out at a low silicon precursor partial pressure at a total pressure of 101.3 kPa (i.e., 1 atm), with the remaining partial pressure made up to atmospheric pressure using an inert fill gas such as hydrogen, nitrogen, or argon. A deposition temperature in the range of 400 - 700 °C is used, such as 400 - 550 °C, or 400 - 500 °C, or 400 - 450 °C or 450 - 500 °C. The CVI process can be suitably carried out in a fixed bed reactor, a fluidized bed reactor (including a spouted bed reactor), or a rotary kiln.

[0105] As an example of the fixed bed reactor method, 1.8 g of particulate porous framework is placed on a stainless steel plate along its length at a constant thickness of 1 mm. The plate is then placed into a 60 mm outer diameter stainless steel tube having gas inlet and outlet lines located in the hot zone of a retort furnace. The furnace tube is purged with nitrogen at room temperature for 30 minutes, and then the sample temperature is raised to 450 - 500 °C. The nitrogen flow rate is adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube, and the nitrogen flow rate is maintained at this rate for 30 minutes. Then, the gas supply is switched from nitrogen to a mixture of silane at a concentration of 1.25 vol% in nitrogen. The feed of silane is carried out over a 5-hour period with the reactor pressure maintained at 101.3 kPa (1 atm). After the feed is completed, the gas flow rate is kept constant while purging the silane from the furnace using nitrogen. The furnace is purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. Then the atmosphere is gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air from a compressed air supply.

[0106] The particulate material of the present invention may optionally comprise a conductive carbon coating. Suitably, the conductive carbon coating can be obtained by chemical vapor deposition (CVD). CVD is a well-known method in the art and involves pyrolyzing a volatile carbon-containing gas (such as ethylene) onto the surface of the particulate material. Alternatively, the carbon coating can be formed by depositing a solution of a carbon-containing compound onto the surface of the particulate material followed by pyrolysis. The conductive carbon coating has sufficient permeability to allow lithium to access the interior of the composite particles without excessive resistance, thus not reducing the rate performance of the composite particles. For example, the thickness of the carbon coating can suitably be in the range of 2 to 30 nm. Optionally, the carbon coating can be porous and / or can only partially cover the surface of the composite particles.

[0107] The carbon coating has the following advantages: it further reduces the BET surface area of the particulate material by smoothing any surface defects and filling any remaining surface micropores, thereby further reducing the first cycle loss. Additionally, the carbon coating improves the conductivity of the surface of the composite particles, thus reducing the need for conductive additives in the electrode composition and also creating an optimal surface for forming a stable SEI layer, resulting in improved capacity retention upon cycling.

[0108] According to a first aspect of the present invention, there is also provided a particulate material according to aspects 1-1 to 1-24 below.

[0109] Aspect 1-1: The particulate material according to the first aspect of the present invention, wherein:

[0110] (i) P 1 is in the range of 0.7 - 1.4;

[0111] (ii) PD 50 has a pore diameter in the range of 0.8 to 4 nm;

[0112] (iii) D of the porous carbon framework 50 has a particle size in the range of 1 to 18 μm;

[0113] Aspect 1-2: The particulate material according to the first aspect of the present invention, wherein:

[0114] (i) P 1 is in the range of 0.7 - 1.4;

[0115] (ii) PD 50 has a pore diameter in the range of 0.8 to 4 nm;

[0116] (iii) D of the porous carbon framework 50 has a particle size in the range of 1 to 12 μm;

[0117] Aspects 1 - 3: The particulate material according to the first aspect of the present invention, wherein:

[0118] (i) P 1 is in the range of 0.7 - 1.4;

[0119] (ii) PD 50 has a pore diameter in the range of 0.8 to 4 nm;

[0120] (iii) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0121] Aspects 1 - 4: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 1.4;

[0122] (ii) PD 50 has a pore diameter in the range of 0.8 to 4 nm;

[0123] (iii) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0124] Aspects 1 - 5: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 1.1;

[0125] (ii) PD 50 has a pore diameter in the range of 1 to 2.5 nm;

[0126] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0127] Aspects 1 - 6: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 1.1;

[0128] (ii) PD 50 has a pore diameter in the range of 1 to 2.5 nm;

[0129] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm;

[0130] Aspects 1 - 7: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 1.1;

[0131] (ii) PD 50 has a pore diameter in the range of 1 to 2.5 nm;

[0132] (iii) D of the porous carbon framework 50 has a particle size in the range of 2 to 8 μm;

[0133] Aspect 1-8: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 1.1;

[0134] (ii) PD 50 has a pore diameter in the range of 1 to 2.5 nm;

[0135] (iii) D of the porous carbon framework 50 has a particle size in the range of 3 to 6 μm;

[0136] Aspect 1-9: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 0.9;

[0137] (ii) PD 50 has a pore diameter in the range of 1.2 to 2 nm;

[0138] (iii) D of the porous carbon framework 50 has a particle size in the range of 1 to 18 μm;

[0139] Aspect 1-10: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 0.9;

[0140] (ii) PD 50 has a pore diameter in the range of 1.2 to 2 nm;

[0141] (iii) D of the porous carbon framework 50 has a particle size in the range of 1 to 12 μm;

[0142] Aspect 1-11: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 - 0.9;

[0143] (ii) PD 50 has a pore diameter in the range of 1.2 to 2 nm;

[0144] (iii) D of the porous carbon framework 50 has a particle size in the range of 2 to 8 μm;

[0145] Aspect 1-12: The particulate material according to the first aspect of the present invention, wherein:

[0146] (i) P 1 is in the range of 0.7 - 0.9;

[0147] (ii) PD 50 The pore diameter is in the range of 1.2 to 2 nm;

[0148] (iii) D of the porous carbon framework 50 The particle size is in the range of 3 to 6 μm;

[0149] Aspect 1-13: The particulate material according to the first aspect of the present invention, wherein:

[0150] (i) P 1 Is in the range of 0.7 - 1.4;

[0151] (ii) PD 50 The pore diameter is in the range of 0.8 to 4 nm;

[0152] (iii) D of the porous carbon framework 50 The particle size is in the range of 1 to 18 μm;

[0153] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.1×P 1 :1.

[0154] Aspect 1-14: The particulate material according to the first aspect of the present invention, wherein:

[0155] (i) P 1 Is in the range of 0.7 - 1.4;

[0156] (ii) PD 50 The pore diameter is in the range of 0.8 to 4 nm;

[0157] (iii) D of the porous carbon framework 50 The particle size is in the range of 1 to 12 μm;

[0158] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.1×P 1 :1.

[0159] Aspect 1-15: The particulate material according to the first aspect of the present invention, wherein:

[0160] (i) P 1 Is in the range of 0.7 - 1.4;

[0161] (ii) PD 50 The pore diameter is in the range of 0.8 to 4 nm;

[0162] (iii) D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm;

[0163] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.1×P 1 :1.

[0164] Aspect 1-16: The particulate material according to the first aspect of the present invention, wherein:

[0165] (i) P 1 is in the range of 0.7-1.4;

[0166] (ii) PD 50 The pore diameter is in the range of 0.8 to 4 nm;

[0167] (iii) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0168] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.1×P 1 :1.

[0169] Aspect 1-17: The particulate material according to the first aspect of the present invention, wherein:

[0170] (i) P 1 is in the range of 0.7-1.1;

[0171] (ii) PD 50 The pore diameter is in the range of 1 to 2.5 nm;

[0172] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0173] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.6×P 1 to 0.9×P 1 :1.

[0174] Aspect 1-18: The particulate material according to the first aspect of the present invention, wherein:

[0175] (i) P 1 is in the range of 0.7-1.1;

[0176] (ii) PD 50 The pore diameter is in the range of 1 to 2.5 nm;

[0177] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm;

[0178] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.6×P 1 to 0.9×P 1 :1.

[0179] Aspect 1-19: The particulate material according to the first aspect of the present invention, wherein:

[0180] (i) P 1 is in the range of 0.7 - 1.1;

[0181] (ii) PD 50 The pore diameter is in the range of 1 to 2.5 nm;

[0182] (iii) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0183] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.6×P 1 to 0.9×P 1 :1.

[0184] Aspect 1-20: The particulate material according to the first aspect of the present invention, wherein:

[0185] (i) P 1 is in the range of 0.7 - 1.1;

[0186] (ii) PD 50 The pore diameter is in the range of 1 to 2.5 nm;

[0187] (iii) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0188] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.6×P 1 to 0.9×P 1 :1.

[0189] Aspect 1-21: The particulate material according to the first aspect of the present invention, wherein:

[0190] (i) P 1 is in the range of 0.7 - 0.9;

[0191] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.5 nm;

[0192] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0193] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.7×P 1 to 0.8×P 1 :1.

[0194] Aspect 1-22: The particulate material according to the first aspect of the present invention, wherein:

[0195] (i) P 1 is in the range of 0.7 - 0.9;

[0196] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.5 nm;

[0197] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm;

[0198] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.7×P 1 to 0.8×P 1 :1.

[0199] Aspect 1-23: The particulate material according to the first aspect of the present invention, wherein:

[0200] (i) P 1 is in the range of 0.7 - 0.9;

[0201] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.5 nm;

[0202] (iii) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0203] (iv) The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.7×P 1 to 0.8×P 1 :1.

[0204] Aspect 1-24: The particulate material according to the first aspect of the present invention, wherein:

[0205] (i) P 1 is in the range of 0.7 - 0.9;

[0206] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.5 nm;

[0207] (iii) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0208] (iv) The weight ratio of silicon in the composite particles to the porous carbon framework is in the range of [0.7×P 1 to 0.8×P 1 :1.

[0209] According to the present invention, it should be understood that the preferred / optional features disclosed herein related to the first aspect of the present invention within the scope of the above aspects 1-1 to 1-24 are also considered to be the preferred / optional features of aspects 1-1 to 1-24. Similarly, any features of the dependent claims within the scope of the above aspects 1-1 to 1-24 should also be construed as if those claims also depend on aspects 1-1 to 1-24.

[0210] In a second aspect of the present invention, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component. The particulate material for preparing the composition of the second aspect of the present invention may have any of the features described as preferred or optional with respect to the first aspect of the present invention, and may be the particulate material according to any one of aspects 1-1 to 1-24. Specifically, the particulate material of the first aspect of the present invention can be used as a component of the electrode composition.

[0211] Accordingly, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component selected from the following: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material. The composition of the present invention can be used as an electrode composition and can therefore be used to form the active layer of an electrode.

[0212] The electrode composition can be a hybrid electrode composition comprising the particulate material according to the first aspect of the present invention and at least one additional particulate electroactive material. Examples of the additional particulate electroactive material include graphite, hard carbon, silicon, germanium, gallium, 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.

[0213] The D 50 particle size of the at least one additional particulate electroactive material is preferably in the range of 10 to 50 μm, preferably 10 to 40 μm, more preferably 10 to 30 μm, and most preferably 10 to 25 μm, such as 15 to 25 μm.

[0214] The D 10 particle size of the at least one additional particulate electroactive material 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.

[0215] The D 90The particle size is preferably not more than 100 μm, more preferably not more than 80 μm, still more preferably not more than 60 μm, yet more preferably not more than 50 μm, and most preferably not more than 40 μm.

[0216] In a preferred embodiment, the at least one additional particulate electroactive material is selected from particles containing carbon, graphite particles, and / or hard carbon particles, wherein the D of the graphite particles and the hard carbon particles 50 The particle size ranges from 10 to 50 μm. Still more preferably, the at least one additional particulate electroactive material is selected from graphite particles, wherein the D of the graphite particles 50 The particle size ranges from 10 to 50 μm.

[0217] The particulate material of the present invention preferably accounts for 0.5 to 80% by weight of the total dry weight of the electroactive materials in the electrode composition (i.e., the total dry weight of the particulate material of the present invention and the at least one additional particulate electroactive material). More preferably, the particulate material of the present invention accounts for 2 to 70% by weight of the total dry weight of the electroactive materials in the electrode composition, still more preferably 4 to 60% by weight, yet more preferably 5 to 50% by weight.

[0218] The electrode composition may optionally contain a binder. The binder serves to adhere the electrode composition to the current collector and maintain the integrity of the electrode composition. Examples of binders that can be used according to the present invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginates and their alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The electrode composition may contain a mixture of multiple binders. Preferably, the binder includes polymers 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.

[0219] The binder may suitably be present in an amount of 0.5 to 20% by weight, preferably 1 to 15% by weight, and most preferably 2 to 10% by weight based on the total dry weight of the electrode composition.

[0220] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as crosslinking promoters, coupling agents, and / or tackifiers.

[0221] The electrode composition may optionally comprise one or more conductive additives. Preferred conductive additives are non-electroactive materials, which are included to improve the conductivity between the electroactive components of the electrode composition and between the electroactive components of the electrode composition and the current collector. The conductive additives may suitably 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.

[0222] One or more conductive additives may suitably be present in a total amount of from 0.5 to 20% by weight, preferably from 1 to 15% by weight, and most preferably from 2 to 10% by weight, based on the total dry weight of the electrode composition.

[0223] In a third aspect, the present invention provides an electrode comprising the particulate material as defined in the first aspect of the present invention in electrical contact with a current collector. The particulate material for preparing the electrode of the third aspect of the present invention may have any of the features described as preferred or optional with respect to the first aspect of the present invention, and may be the particulate material according to any one of aspects 1-1 to 1-24.

[0224] As used herein, the term current collector refers to any conductive substrate capable of carrying current to and from the electroactive particles in the electrode composition. Examples of materials that may be used as the current collector include copper, aluminum, stainless steel, nickel, titanium, and sintered carbon. Copper is the preferred material. The current collector is generally in the form of a foil or mesh having a thickness of from 3 to 500 μm. The particulate material of the present invention may be applied to one or both surfaces of the current collector to a thickness preferably in the range of from 10 μm to 1 mm, such as from 20 to 500 μm, or from 50 to 200 μm.

[0225] Preferably, the electrode comprises the electrode composition as defined in the second aspect of the present invention in electrical contact with a current collector. The electrode composition may have any of the features described as preferred or optional with respect to the second aspect of the present invention.

[0226] The electrode of the third aspect of the present invention may suitably be prepared by combining the particulate material of the present invention (optionally in the form of the electrode composition of the present invention) with a solvent and optionally one or more viscosity modifying additives to form a slurry. The slurry is then cast onto the surface of the current collector, and the solvent is removed to form an electrode layer on the surface of the current collector. Additional steps may be carried out as appropriate, such as heat treatment for curing any binder and / or calendering of the electrode layer. The thickness of the electrode layer is suitably in the range of from 20 μm to 2 mm, preferably from 20 μm to 1 mm, preferably from 20 μm to 500 μm, preferably from 20 μm to 200 μm, preferably from 20 μm to 100 μm, preferably from 20 μm to 50 μm.

[0227] Alternatively, the slurry can be formed into a free-standing film or mat containing the particulate material of the present invention, for example, by casting the slurry onto a suitable casting template, removing the solvent and then removing the casting template. The resulting film or mat is in the form of a sticky free-standing object, which can then be combined with a current collector by known methods.

[0228] The electrode of the third aspect of the present invention can be used as the anode of a metal ion battery. Thus, in a fourth aspect, the present invention provides a rechargeable metal ion battery comprising: an anode comprising the electrode as described above; a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions; and an electrolyte between the anode and the cathode. The particulate material for preparing the battery of the fourth aspect of the present invention can have any of the features described as preferred or optional with respect to the first aspect of the present invention, and can be a particulate material according to any one of aspects 1-1 to 1-24.

[0229] 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 reabsorbing lithium ions.

[0230] The cathode active material is preferably a metal oxide-based composite material. Examples of suitable cathode active materials include LiCoO2, LiCo 0.99 Al 0.01 O2, LiNiO2, LiMnO2, LiCo 0.5 Ni 0.5 O2, LiCo 0.7 Ni 0.3 O2, LiCo 0.8 Ni 0.2 O2, LiCo 0.82 Ni 0.18 O2, LiCo 0.8 Ni 0.15 Al 0.05 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2 and LiNi 0.33 Co 0.33 Mn 0.34 O2. The cathode current collector typically 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.

[0231] The electrolyte is suitably a non-aqueous electrolyte containing a metal salt (such as a lithium salt), and may include but is not limited to non-aqueous electrolytic solutions, 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, triphosphate ester, trimethoxymethane, sulfolane, methylsulfolane, and 1,3-dimethyl-2-imidazolidinone.

[0232] Examples of organic solid electrolytes include polyethylene derivatives, poly(ethylene oxide) derivatives, poly(propylene oxide) derivatives, phosphate esters polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociating groups.

[0233] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts (such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4).

[0234] The lithium salt is suitably soluble in the selected solvent or solvent mixture. Examples of suitable lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, LiBC4O8, LiPF6, LiCF3SO3, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and CF3SO3Li.

[0235] 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 generally formed of an insulating material having high ion permeability and high mechanical strength. The separator generally has a pore size of 0.01 to 100 μm and a thickness of 5 to 300 μm. Examples of suitable electrode separators include microporous polyethylene membranes.

[0236] The separator can be replaced with 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 can be a solid polymer electrolyte or a gel-type polymer electrolyte.

[0237] In a fifth aspect, the present invention provides the use of the particulate material as defined in the first aspect of the present invention as an anode active material. Preferably, the particulate material is in the form of an electrode composition as defined in the second aspect of the present invention, and most preferably, the electrode composition comprises one or more additional particulate electroactive materials as defined above. The particulate material used according to the fifth aspect of the present invention may have any of the features described as preferred or optional with respect to the first aspect of the present invention, and may be a particulate material according to any one of aspects 1-1 to 1-24. BRIEF DESCRIPTION OF THE DRAWINGS

[0238] Figure 1 The capacity retention of the battery in the examples is shown. DETAILED DESCRIPTION

[0239] Example:

[0240] Carbon framework particles having the following properties were used to prepare the particulate composites in Table 1:

[0241] · 1860 m 2 / g BET surface area

[0242] · 0.88 cm 3 / g P 1 pore volume

[0243] · 54% micropore fraction (micropore volume / (micropore + mesopore volume)

[0244] · 1.4 nm PD 50 ; 5.1 nm PD 90 0.60 nm PD 10 0.87 nm PD 30 and 2.79 nm PD 75

[0245] · 3.12 μm particle size D 50 at 1.31 μm D 10 to 11.1 μm D 90 in the range

[0246] Si-C composite material:

[0247] The Si-C composite material prepared by the method described in this article has the properties given in Table 1 below. The silicon-carbon composite material is synthesized in a vertical bubbling fluidized bed reactor including a stainless steel cylindrical container with an inner diameter of 83 mm. 250 g of carbon skeleton particle powder having the properties given above is placed in the reactor. An inert gas (nitrogen) at a low flow rate is injected into the reactor to remove any oxygen. Then the reactor is heated to a reaction temperature of 400 to 500 °C, and silane gas diluted in nitrogen at 4% v / v is supplied to the bottom of the reactor at a flow rate sufficient to sulfide the carbon skeleton particles for a duration sufficient to deposit the target mass of silicon.

[0248] Table 1

[0249]

[0250] Preparation of the electrode

[0251] The following method is used to prepare an anode and a test cell containing the particulate Si-C composite material of Table 1:

[0252] A test button cell is prepared using the negative electrode containing the silicon-based material prepared as described above. A dispersion of Carbon Super P (conductive carbon) in a CMC binder is mixed in a Thinky TM mixer. The silicon-based material is added to the mixture and mixed in a Thinky TM mixer for 30 min. Then an SBR binder is added to provide a CMC:SBR ratio of 1:1, resulting in a slurry with a weight ratio of silicon-based material:CMC / SBR:conductive carbon of 70%:16%:14%. The slurry is mixed in a Thinky TM mixer for another 30 min, then coated on a 10-μm-thick copper substrate (current collector) and dried at 50 °C for 10 minutes, and then dried at 110 °C for 12 hours, thereby forming an electrode including an active layer on the copper substrate.

[0253] Battery fabrication and cycling

[0254] Manufacture of the full cell

[0255] A full button cell is prepared using a circular negative electrode with a radius of 0.8 cm cut from the above electrode, a porous polyethylene separator, and a nickel manganese cobalt (NMC532) positive electrode. The positive and negative electrodes are designed to form a balanced pair such that the design capacity ratio of the electrodes is approximately 0.9. Then, before sealing, an electrolyte is added to the cell, the electrolyte containing 1 M LiPF6 in a 7:3 solution of EMC / FEC (ethyl methyl carbonate / fluoroethylene carbonate) containing 3 wt% ethylene carbonate.

[0256] For each composite material, three button cells were fabricated.

[0257] The full button cells were cycled as follows: a constant current was applied at a rate of C / 25 to lithiate the anode, with a cut-off voltage of 4.3 V. When the cut-off was reached, a constant voltage of 4.3 V was applied until a cut-off current of C / 100 was reached. The cell was then allowed to rest in the lithiated state for 10 minutes. The anode was then delithiated at a constant current of C / 25, with a cut-off voltage of 2.75 V. The cell was then allowed to rest for 10 minutes. After this initial cycle, a constant current of C / 2 was applied to lithiate the anode, with a cut-off voltage of 4.3 V, then a constant voltage of 4.3 V was applied, with a cut-off current of C / 40 and a rest time of 5 minutes. The anode was then delithiated at a constant current of C / 2, with a cut-off of 2.75 V. This process was then repeated for the desired number of cycles.

[0258] The charge (lithiation) and discharge (delithiation) capacities per unit mass of the silicon-carbon composite material were calculated for each cycle, and the capacity retention values for each discharge capacity were calculated as a percentage of the discharge capacity of the second cycle. The first cycle loss (FCL) was (1 – (first delithiation capacity / first lithiation capacity)) x 100%. The average key values for the three button cells of each material were listed in the following table, and the capacity retention of all six cells was plotted in Figure 1 ...

[0259] As demonstrated by Table 2 below and Figure 1 ... the cells fabricated with Material Sample A had very consistent cycling performance and a higher capacity retention compared to the cells fabricated with Material Sample B, whose performance also had variability.

[0260] Table 2

[0261]

Claims

1. A particulate material comprising a plurality of composite particles, wherein the composite particles comprise: (a) a porous carbon framework comprising micropores and / or mesopores, wherein the total pore volume of the micropores and / or mesopores measured by gas adsorption is P 1 cm 3 / g, where P 1 represents a natural number with a value of at least 0.7, and where the PD 50 pore diameter measured by gas adsorption does not exceed 5 nm; and (b) a plurality of elemental nanosized silicon domains located within the micropores and / or mesopores of the porous carbon framework; where the weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.3×P 1 :

1.

2. The particulate material according to claim 1, wherein the value of P 1 is at least 0.75, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95, or at least 1, or at least 1.05, or at least 1.

1.

3. The particulate material according to claim 1 or claim 2, wherein the value of P 1 does not exceed 2.2, or does not exceed 2, or does not exceed 1.8, or does not exceed 1.6, or does not exceed 1.5, or does not exceed 1.4, or does not exceed 1.3, or does not exceed 1.2, or does not exceed 1.1, or does not exceed 1.0, or does not exceed 0.

9.

4. The particulate material according to any one of the preceding claims, wherein the PD 50 pore diameter of the porous carbon framework does not exceed 4 nm, or does not exceed 3 nm, or does not exceed 2.5 nm, or does not exceed 2 nm, or does not exceed 1.5 nm, or does not exceed 1 nm.

5. The particulate material according to any one of the preceding claims, wherein the PD 60 pore diameter of the porous carbon framework does not exceed 5 nm, or does not exceed 4 nm, or does not exceed 3 nm, or does not exceed 2.5 nm, or does not exceed 2 nm, or does not exceed 1.5 nm.

6. The particulate material according to any one of the preceding claims, wherein the PD 70 pore diameter of the porous carbon framework does not exceed 5 nm, or does not exceed 4 nm, or does not exceed 3 nm, or does not exceed 2.5 nm, or does not exceed 2 nm.

7. A composition comprising the particulate material defined in any one of claims 1 - 6 and at least one other component.

8. An electrode, comprising the particulate material defined in any one of claims 1-6 in electrical contact with a current collector.

9. A rechargeable metal ion battery, comprising: (i) An anode, wherein the anode comprises the electrode described in claim 8; (ii) A cathode, the cathode containing a cathode active material capable of releasing and reabsorbing metal ions; and (iii) An electrolyte between the anode and the cathode.

10. Use of the particulate material defined in any one of claims 1-6 as an anode active material.

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