Electroactive materials for metal ion batteries

Abstract

The present invention relates to a particulate material consisting of a plurality of composite particles wherein the composite particles comprise: (a) a porous carbon skeleton comprising micropores and / or mesopores having a total volume of at least 0.6 cm3 / g wherein at least half of the micropores / mesopores are in the form of pores having a diameter of not more than 2 nm; and (b) an electroactive material located within the micropores and / or mesopores of the porous carbon backbone. The D90 particle size of the composite particle is not more than 10nm.

Description

[0001] This application is a divisional application of the application with the invention title "Electroactive materials for metal ion batteries", PCT international application date of November 8, 2019, PCT international application number of PCT / GB2019 / 053175, and Chinese national application number of 201980079208.8. 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 high mechanical strength and 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. A rechargeable metal ion battery generally includes 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 avoidance of doubt, 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 both to a device containing a single anode and a single cathode and to 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 been widely commercially adopted 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, No. 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 successive 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 with silicon particles in the micron size range, finely structured silicon such as silicon films and silicon nanoparticles with a cross-section 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 the anode of 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 size to the minimum size 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 the 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 framework and silicon nanoparticles are deposited in a 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 materials are known to have improved capacity retention during multiple charge cycles, but the initial capacity (in mAh / g) of the composite materials is significantly lower than the initial capacity of the silicon nanoparticles.

[0011] JP2003100284 discloses an active material comprising a carbon-based support 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 support.

[0012] Despite the efforts made to date, there is a continuing need to improve the electrochemical storage capacity of lithium ion batteries. Specifically, composite materials that rely on a porous support material having an electroactive material deposited within its pore structure generally have a structural strength that is insufficient for commercial use. Conventional electrode fabrication processes generally rely on rolling the electrode material onto a current collector to densify the electrode layer and to optimize the space utilization within the battery design. Highly porous materials are prone to fracture during electrode fabrication, resulting in impaired electrochemical performance. Summary of the Invention

[0013] The present invention is based on the observation that the mechanical properties of composite particles comprising a porous carbon skeleton and an electroactive material located within the porous carbon skeleton can be optimized by using a porous carbon skeleton having a specific pore structure and a simultaneously carefully controlled pore size distribution.

[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 comprising 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 0.6,

[0017] wherein the PD 50 pore diameter measured by gas adsorption does not exceed 2 nm; and

[0018] (b) an electroactive material located within the micropores and / or mesopores of the porous carbon framework;

[0019] wherein the D 90 particle size of the composite particles does not exceed 10 μm.

[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, wherein pores having a diameter not exceeding 2 nm account for at least 50% of the total pore volume, and a particle size distribution that is strongly skewed towards particles having a diameter not exceeding 10 μm. For the avoidance of doubt, the pore volume of the porous carbon framework referred to herein (in the absence of any contrary indication) relates to the pore volume of the porous carbon framework alone, i.e., the pore volume of the porous carbon framework measured in the absence of any electroactive material (or any other material) occupying the pores of the porous carbon framework.

[0021] It has been found that the combination of small particle size and a highly differentiated pore volume provides an electroactive material with high resistance to mechanical degradation during electrode manufacture. The highly refined pore structure of the porous carbon framework results in very fine pore walls, and without being bound by theory, it is believed that these very fine pore walls are capable of elastic deformation to reduce the fracture rate, such that the fracture resistance of the framework under compressive stress is very high. The controlled pore size distribution additionally contributes to particle strength, as well as achieving improved close packing of the composite particles in the electrode active layer, thereby reducing the need for excessive calendering pressure.

[0022] Another benefit of the particulate material of the present invention is that the highly microporous carbon framework has a high tensile fracture strength, and thus can accommodate at least a portion of the expansion of the electroactive material within the pore volume without fracture. Although complete lithiation of the electroactive material may result in some external expansion of the entire composite particle, the amount of external expansion is limited due to the accommodation of the expansion internally. In terms of the outward expansion of the material, the highly microporous carbon framework is capable of deforming without fracture. The high total porosity of the porous carbon framework not only provides a high volume loading of the electroactive material, but also ensures that the porous carbon framework has sufficient elasticity to withstand repeated volume changes during multiple charge-discharge cycles.

[0023] The highly microporous carbon framework provides the following additional benefits: The electroactive material is located within the microporous network in the form of small domains having dimensions of about a few nanometers or less. These fine electroactive structures have lower resistance to elastic deformation and higher resistance to fracture compared to larger electroactive structures, and thus can be lithiated and delithiated without excessive structural stress. Therefore, the high microporosity of the porous carbon framework not only provides improved mechanical strength of the particles, but also ensures that the electroactive material has sufficient elasticity to withstand repeated volume changes during multiple charge-discharge cycles without significant capacity loss.

[0024] Another factor in the exceptional performance of the particulate material of the present invention is the minimization of SEI formation. As described above, by locating the electroactive material within small mesopores and / or micropores, only a small surface area of the electroactive material is accessible to the electrolyte, thus limiting SEI formation. The additional exposure of the electroactive material during subsequent charge-discharge cycles is largely prevented, such that SEI formation is not a significant degradation mechanism that can lead to capacity loss. This is in stark contrast to the excessive and unconstrained SEI formation characteristic of materials such as those disclosed by Guo (see above).

[0025] The porous carbon framework suitably comprises a 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 having a diameter of less than 2 nm, the term "mesopore" is used herein to refer to pores having a diameter of 2 to 50 nm, and the term "macropore" is used to refer to pores having a diameter greater than 50 nm.

[0026] The volumes of micropores, mesopores, and macropores in the porous carbon framework mentioned herein, as well as any reference to the distribution of pore volume within the porous carbon framework, refer to the internal pore volume of the porous carbon framework alone (i.e., in the absence of any electroactive material or other material occupying some or all of the pore volume).

[0027] The porous carbon framework is characterized by a high pore volume in the form of micropores and / or mesopores. The total volume of the micropores and mesopores (i.e., the total pore volume in the range from 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 0.6. More preferably, P 1 has a value of at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85. Optionally, P 1 can have a value of at least 0.9, or at least 0.95, or at least 1, or at least 1.05, or at least 1.1, or at least 1.15, or at least 1.2.

[0028] The use of the highly porous carbon framework is advantageous because it enables a larger amount of electroactive material to be accommodated within the pore structure, while dividing the pore volume into fine mesopores and micropores ensures that the composite particles have sufficient tolerance to the compressive stress used in the conventional electrode manufacturing process.

[0029] The internal pore volume of the porous carbon framework is suitably limited to a value at which the increased brittleness of the porous carbon framework exceeds the advantage of the increased pore volume for accommodating a larger amount of electroactive material. Generally, P 1 can have a value not exceeding 2.5. However, more preferably, P 1 can have a value not exceeding 2.4, or not exceeding 2.2, or not exceeding 2, or not exceeding 1.8, or not exceeding 1.6, or not exceeding 1.5, or not exceeding 1.4, or not exceeding 1.3, or not exceeding 1.2, or not exceeding 1.1, or not exceeding 1.0, or not exceeding 0.9. More preferably, P 1 has a value not exceeding 1.2, or not exceeding 1.1, or not exceeding 1.0, or not exceeding 0.9.

[0030] 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.

[0031] Preferably, the value of P1 can be, for example, in the range of 0.6 to 1.4, or in the range of 0.65 to 1.4, or in the range of 0.7 to 1.4, 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.

[0032] PD of the porous carbon framework 50 The pore size does not exceed 2 nm. As used herein, the term "PD 50 pore size" refers to the volume median pore size based on the total volume of micropores and mesopores (i.e., the pore size at which 50% of the measured total micropore and mesopore volume (represented by P 1 is lower than a certain pore size). 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 not exceeding 2 nm.

[0033] As used herein, the general term "PD n 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 when 90% of the measured total micropore and mesopore volume (represented by P 1 ) is lower than a certain pore diameter.

[0034] To avoid ambiguity, for determining the PD n value, any macropore volume (pore diameter greater than 50 nm) is not considered.

[0035] According to the present invention, the PD 50 pore diameter of the porous carbon framework is preferably not more than 1.8 nm, or not more than 1.6 nm, or not more than 1.4 nm, or not more than 1.2 nm, or not more than 1 nm. Preferably, the PD 80 pore diameter of the porous carbon framework is at least 0.8 nm, or at least 1 nm, or at least 1.2 nm.

[0036] 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 3 nm. Therefore, the PD 60 pore diameter of the porous carbon framework is preferably not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm, or not more than 1.8 nm, or not more than 1.6 nm, or not more than 1.4 nm, or not more than 1.2 nm.

[0037] 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 3.5 nm. Therefore, the PD 70 pore diameter of the porous carbon framework is preferably not more than 3.5 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2.2 nm, or not more than 2 nm, or not more than 2.5 nm, or not more than 2 nm, or not more than 1.8 nm, or not more than 1.6 nm, or not more than 1.4 nm.

[0038] 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. Therefore, the PD 80 pore diameter of the porous carbon framework is preferably not more than 5 nm, or not more than 4.5 nm, or not more than 4 nm, or not more than 3.5 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2.2 nm, or not more than 2 nm, or not more than 1.8 nm, or not more than 1.6 nm.

[0039] The volume of the larger mesopores in the porous carbon framework is preferably limited so that the PD 90The pore size does not exceed 10 nm, or does not exceed 8 nm, or does not exceed 6 nm, or does not exceed 5 nm, or does not exceed 4 nm, or does not exceed 3 nm, or does not exceed 2.5 nm, or does not exceed 2 nm.

[0040] Preferably, PD 95 The pore size does not exceed 15 nm, or does not exceed 12 nm, or does not exceed 10 nm.

[0041] According to the present invention, the porous carbon framework can be one in which PD 50 does not exceed 2 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 1.8 nm and PD 90 does not exceed 8 nm, or one in which PD 50 does not exceed 1.8 nm and PD 90 does not exceed 6 nm, or one in which PD 50 does not exceed 1.6 nm and PD 90 does not exceed 6 nm, or one in which PD 50 does not exceed 1.2 nm and PD 90 does not exceed 5 nm, or one in which PD 50 does not exceed 1 nm and PD 90 does not exceed 4 nm, or one in which PD 50 does not exceed 1 nm and PD 90 does not exceed 3 nm, or one in which PD 50 does not exceed 1 nm and PD 90 does not exceed 2.5 nm, or one in which PD 50 does not exceed 1 nm and PD 90 does not exceed 2 nm.

[0042] More preferably, the porous carbon framework can be one in which PD 50 is 1 to 2 nm and PD 90 is 3 to 10 nm, or one in which PD 50 is 1 to 2 nm and PD 90 is 3 to 8 nm, or one in which PD 50 is 1 to 2 nm and PD 90 is 3 to 6 nm, or one in which PD50 is from 1 to 1.8 nm and PD 90 is a porous carbon framework from 3 to 8 nm, or in which PD 50 is from 1 to 1.8 nm and PD 90 is a porous carbon framework from 3 to 6 nm, or in which PD 50 is from 1 to 1.6 nm and PD 90 is a porous carbon framework from 3 to 6 nm.

[0043] A small fraction of pores within the larger mesopore range can advantageously facilitate electrolyte access to the electroactive material. Thus, pores within the range of 5 to 50 nm in diameter (i.e., the 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.

[0044] The volume ratio of micropores to mesopores in the porous carbon framework can essentially be in the range of 100:0 to 50:50. 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.

[0045] 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 a larger diameter provides the advantage of efficient ion transport from the porous network to the electroactive material. Thus, the particulate material has high ionic diffusivity and thus improved rate performance.

[0046] 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 2.5 to 20 nm, preferably with a local minimum in the pore size distribution in the range of 2 to 50 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 2.5 to 15 nm, preferably with a local minimum in the pore size distribution in the range of 2 to 5 nm.

[0047] Suitably, the bimodal or multimodal pore size distribution includes a peak pore size within the micropore range and a peak pore size within 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 including a peak at a pore size of 1.2 nm and a peak at a pore size of 12 nm.

[0048] Using the methods described in ISO 15901-2 and ISO 15901-3, nitrogen adsorption was carried out at 77 K down to a relative pressure p / p0 of 10 -6 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. Then the nitrogen pressure is gradually reduced 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 TriStar II and TriStar IIPlus porosimeters (which are available from Micromeritics Instrument Corporation in the United States), and Autosorb IQ porosimeter (which is available from Quantachrome Instruments).

[0049] 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 value, and PD is similarly determined relative to the total volume of only micropores and mesopores n value.

[0050] Due to 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 individual porous carbon framework (i.e., the pore volume of the porous carbon framework in the absence of any electroactive material or other material that occupies some or all of the pore volume).

[0051] To avoid doubt, P 2The value only considers pores with diameters ranging 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 P 2 value, any pore volume of pore sizes below 50 nm measured by mercury intrusion porosimetry is not considered (as described above, nitrogen adsorption is instead 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 P 2 value.

[0052] 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.

[0053] Compared with the volume of micropores and mesopores, the volume of macropores is preferably small. 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 basically obtained by mainly accommodating the pore volume in micropores and smaller mesopores.

[0054] 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 value of P 2 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 exceeding 0.005×P 1 .

[0055] In a preferred embodiment, the value of P 2 does not exceed 0.3, or does not exceed 0.25, or does not exceed 0.20, or does not exceed 0.15, or does not exceed 0.1, or does not exceed 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 electroactive material.

[0056] The open pore network optionally includes a hierarchical pore structure, i.e., a pore structure in which there is a degree of pore size ordering, where the smaller pores branch from the larger pores.

[0057] 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 in pores that are too small to be detected by nitrogen adsorption is also not considered.

[0058] As used herein, the term "particle size" refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, where the particle volume should be understood to include the volume of any intra-particle pores. As used herein, the terms "D 50 " and "D 50 particle size" refer to the volume median diameter, i.e., the diameter at which 50% of the volume of the particle population is 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.

[0059] The term "D n " used herein to define the particle size distribution should be distinguished from the term "PD n " used herein above to define the pore size distribution.

[0060] The 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 particles, and multiple particles will produce a scattered light pattern defined by the intensity and angle that can be correlated with the particle size distribution. A variety of laser diffraction instruments are commercially available for the rapid and reliable determination of particle size distribution. Unless otherwise stated, 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 hitting the particles is 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.

[0061] The D 90 particle size of the composite particles is preferably not more than 9.5 μm, or not more than 9 μm, or not more than 8.5 μm, or not more than 8 μm, or not more than 7.5 μm, or not more than 7 μm, or not more than 6.5 μm, or not more than 6 μm, or not more than 5.5 μm, or not more than 5 μm, or not more than 4.5 μm, or not more than 4 μm.

[0062] The D 50 particle size of the composite particles can be in the range of 0.5 to 7 μm. Optionally, the D 50 particle size of the composite particles can be at least 1 μm, or at least 1.5 μm, or at least 2 μm, or at least 2.5 μm, or at least 3 μm.

[0063] Optionally, the D 50 particle size of the composite particles can be not more than 6.5 μm, or not more than 6 μm, or not more than 5.5 μm, or not more than 5 μm, or not more than 4.5 μm, or not more than 4 μm, or not more than 3.5 μm.

[0064] For example, the D 50The particle size can be in the range of 1 to 6.5 μm, or 1.5 to 6 μm, or 2 to 5.5 μm, or 2.5 to 5 μm or 3 to 4.5 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 a slurry, their structural robustness, their capacity retention with repeated charge-discharge cycles, and their suitability for forming a dense electrode layer of uniform thickness without structural degradation.

[0065] 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 likelihood of agglomeration of unwanted submicron-sized particles is reduced, resulting in improved particulate material dispersibility and improved capacity retention.

[0066] The D of the composite particles 99 The particle size is preferably not more than 25 μm, or not more than 20 μm, or not more than 18 μm, or not more than 15 μm, or not more than 12 μm, or not more than 10 μm, or not more than 9 μm, or not more than 8 μm, or not more than 7 μm, or not more than 6 μm, or not more than 5 μm.

[0067] The particle size preferably has a positive skew in the volume-based distribution, i.e., the volume-based distribution is asymmetric with a longer tail on the right hand side. A positive skew in the volume-based particle size distribution is advantageous because it provides a denser electrode due to a higher natural packing factor than if all particles were the same size, thereby reducing the need for calendering or other physical densification processes.

[0068] The composite particles preferably have a narrow size distribution span. For example, the size distribution span (defined as (D 90 - D 10 ) / D 50 ) is preferably not more than 8, and can optionally be 5 or less, or 4 or less, or 3 or less. Preferably, the size distribution span is at least 1, and can optionally be at least 1.5, or at least 2.

[0069] The shape of the composite particles is preferably quasi-spherical. Quasi-spherical 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 quasi-spherical 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 quasi-spherical particles provides a further improvement in strength.

[0070] 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 practically 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 particle. 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:

[0071]

[0072] 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:

[0073]

[0074] where n represents the number of particles in the population.

[0075] As used herein, the term "quasi-spherical" 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. The average sphericity of the porous particles of the present invention is preferably at least 0.85, or at least 0.90, or at least 0.92, or at least 0.93, or at least 0.94, or at least 0.95. Optionally, the average sphericity of the porous quasi-spherical particles can be at least 0.96, or at least 0.97, or at least 0.98, or at least 0.99.

[0076] Preferably, the sphericity within these preferred ranges is combined with a positive skewness in the volume-based particle size distribution to obtain the best packing of the particles into the dense electrode layer while reducing the need for physical densification (e.g., by rolling).

[0077] It is to be understood that in the case of any particles that are not perfectly spherical, the perimeter and area of the two-dimensional particle projection will depend on the orientation of the particles. However, the influence of particle orientation can be offset by reporting the sphericity and aspect ratio as averages obtained from a plurality of 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 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 of 100 mg to 100 g, enabling the direct calculation of properties such as average sphericity and aspect ratio through this instrument.

[0078] The porous carbon framework can include crystalline carbon, amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The porous carbon framework can be a hard carbon or soft carbon framework and can suitably be obtained by known procedures involving polymer pyrolysis.

[0079] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which carbon atoms are predominantly found in sp 2 hybridization state (triple bond) polyaromatic domains at the nanoscale. The polyaromatic domains are crosslinked using 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 characteristics, which are evidenced by a large G band (~1600 cm-1) in the Raman spectrum. However, this carbon is not completely graphitic, which is evidenced by an obvious D band (~1350 cm-1) in the Raman spectrum.

[0080] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are predominantly found in sp 2 hybridization state (triple bond) polyaromatic domains with sizes in the range of 5 to 200 nm. Compared with hard carbon, the polyaromatic domains in soft carbon are associated by intermolecular forces rather than crosslinked using chemical bonds. This means that they will be graphitized at high temperatures. The porous carbon framework preferably contains at least 50% sp 2 hybrid carbon (measured by XPS). For example, the porous carbon framework can suitably contain 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.

[0081] 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.

[0082] 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.

[0083] 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).

[0084] 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" should be considered to refer to the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on the solid surface 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. In some cases, the particulate material of the present invention may include pores in which the completely enclosed void space is capped with an electroactive material, thus preventing the electrolyte from entering the void space.

[0085] The electroactive material is suitably selected from silicon, tin, germanium, and aluminum and mixtures thereof. The preferred electroactive material is silicon. The electroactive material may optionally contain a small amount of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, or nitrogen. Preferably, the dopant is present in a total amount of no more than 2 wt% based on the total amount of the electroactive material (e.g., silicon) and one or more dopants.

[0086] The amount of the electroactive material 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 the electroactive material (in the uncharged state). This is referred to herein as the "filling factor" of the electroactive material within the porous carbon framework. Preferably, the electroactive material 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 the electroactive material during charging and discharging, but avoids an excessive pore volume that is not conducive to the volumetric capacity of the particulate material. However, the amount of the electroactive material 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.

[0087] The weight ratio of the electroactive material to the porous carbon framework can be determined by elemental analysis. Elemental analysis is used to determine the weight percentages of both the electroactive material 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 taken together enable the reliable determination of the weight percentage of the electroactive material relative to the entire porous carbon framework.

[0088] Preferably, the weight percentage of the electroactive material (such as silicon, germanium, tin, and aluminum) is 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). Preferably, 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 determined by IR absorption. A suitable instrument for determining the carbon content, hydrogen content, nitrogen content, and oxygen content is a Micro elemental analyzer (available from Leco Corporation).

[0089] The weight ratio of the electroactive material to the porous carbon framework is a function of the available pore volume, the desired packing factor, and the density of the electroactive material.

[0090] In the case where the electroactive material is silicon, the weight ratio of silicon to the porous carbon framework is preferably [0.5×P 1 to 1.7×P 1 :1, where P 1 represents the value of the total micropore / mesopore volume measured in cm 3 / g. 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 1.7×P 1 :1, the volume of silicon in the composite particles is equivalent to approximately 20% to 55% of the total micropore / mesopore volume of the porous carbon framework.

[0091] Optionally, the weight ratio of silicon to the porous carbon framework can be in the range of [0.5×P 1 to 1.3×P 1 :1. More 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.

[0092] Optionally, the weight ratio of silicon to the porous carbon framework can be in the range of [1×P 1 to 1.7×P 1 :1. More preferably, the weight ratio of silicon to the porous carbon framework is in the range of [1.1×P1 to 1.7×P 1 :1, or within the range of [1.1×P 1 to 1.65×P 1 :1, or within the range of [1.1×P 1 to 1.6×P 1 :1, or within the range of [1.15×P 1 to 1.6×P 1 :1, or within the range of [1.15×P 1 to 1.55×P 1 :1, or within the range of [1.15×P 1 to 1.5×P 1 :1, or within the range of [1.2×P 1 to 1.5×P 1 :1, or within the range of [1.25×P 1 to 1.5×P 1 :1, or within the range of [1.3×P 1 to 1.5×P 1 :1.

[0093] Preferably at least 90 wt%, more preferably at least 95 wt%, even more preferably at least 98 wt% of the electroactive material in the composite particles is located within the internal pore volume of the porous carbon framework such that no or very little electroactive material is located on the outer surface of the composite particles.

[0094] 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%, even more preferably no more than 2% of the silicon content in the particulate materials is oxidized at 800 °C.

[0095] The determination of the amount of unoxidized silicon is obtained from the characteristic TGA traces of these materials. The mass increase at about 300 - 500 °C corresponds to the initial oxidation of silicon to SiO2, followed by a mass loss at about 500 - 600 °C when carbon is oxidized to CO2 gas. Above about 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 silicon oxidation is completed.

[0096] 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 end of oxidation is SiO2. This enables the determination of the percentage of silicon unoxidized at 800 °C (as a proportion of the total silicon) according to the following formula:

[0097] Z = 1.875 × [(M f - M 800 ) / M f × 100%

[0098] where Z is the percentage of silicon that is not oxidized at 800 °C, M f is the mass of the sample at the end of oxidation, and M 800 is the mass of the sample at 800 °C.

[0099] Without being bound by theory, it should be understood that the temperature at which silicon is oxidized under TGA roughly corresponds to the length scale of the oxide coating on the silicon, because 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 should be understood that silicon deposited in micropores and mesopores will oxidize at a lower temperature compared to silicon deposits on the particle surface, because there will necessarily be a thinner oxide coating on these structures. Thus, 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.

[0100] The silicon is preferably amorphous silicon. It is believed that amorphous silicon has better performance as an electroactive material. The morphology of the silicon can be determined using X-ray diffraction (XRD) by known procedures.

[0101] Preferably, the volume of micropores and mesopores in the composite particles measured by nitrogen adsorption (i.e., in the presence of the electroactive material) does not exceed 0.15xP 1 , or does not exceed 0.10xP 1 , or does not exceed 0.05xP 1 , or does not exceed 0.02xP 1 .

[0102] 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 electroactive material 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%, such as less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%.

[0103] The BET surface area of the particulate material of the present invention preferably does not exceed 300 m 2 / g, or does not exceed 250 m 2 / g, or does not exceed 200 m 2 / g, or does not exceed 150 m 2 / g, or not exceeding 100 m 2 / g, or not exceeding 80 m 2 / g, or not exceeding 60 m 2 / g, or not exceeding 40 m 2 / g, or not exceeding 30 m 2 / g, or not exceeding 25 m 2 / g, or not exceeding 20 m 2 / g, or not exceeding 15 m 2 / g, or not exceeding 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.

[0104] The particulate material of the present invention has a first lithiation charge specific capacity of 1200 to 2340 mAh / g. Preferably, the particulate material of the present invention has a first lithiation charge specific capacity of at least 1400 mAh / g.

[0105] 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.

[0106] 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 to 20% by volume, or 1 to 10% by volume, or 1 to 5% by volume based on the total volume of the silicon-containing precursor and the inert carrier. The CVI process is suitably carried out at a low partial pressure of the silicon precursor at a total pressure of 101.3 kPa (i.e., 1 atm), and the remaining partial pressure is made up to atmospheric pressure using an inert fill gas such as hydrogen, nitrogen, or argon. A deposition temperature in the range of 400 to 700 °C is used, such as 400 to 550 °C, or 400 to 500 °C, or 400 to 450 °C or 450 to 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.

[0107] As an example of the fixed bed reactor method, 1.8 g of particulate porous scaffold is placed on a stainless steel plate along its length with a constant thickness of 1 mm. Then the plate is 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 to 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% by volume in nitrogen. The feeding of silane is carried out over a 5-hour period with the reactor pressure maintained at 101.3 kPa (1 atm). After the feeding is completed, the gas flow rate is kept constant while purging the silane from the furnace with 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.

[0108] The particulate material of the present invention may optionally contain a conductive carbon coating. Suitably, the conductive carbon coating can be obtained by chemical vapor deposition (CVD) method. CVD is a well-known method in the art and involves thermally decomposing a volatile carbon-containing gas (e.g., ethylene) onto the surface of the particulate material. Alternatively, a carbon coating can be formed by depositing a solution of a carbon-containing compound onto the surface of the particulate material and then pyrolyzing it. 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.

[0109] 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, thereby 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 during cycling.

[0110] According to a first aspect of the present invention, there is also provided a particulate material according to aspects 1-1 to 1-16 below.

[0111] Aspect 1-1: The particulate material according to the first aspect of the present invention, wherein:

[0112] (i) P 1 is in the range of 0.6 to 1.4;

[0113] (ii) PD 50 has a pore diameter in the range of 0.8 to 2 nm;

[0114] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm. Aspect 1-2: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.6 to 1.4;

[0115] (ii) PD 50 has a pore diameter in the range of 0.8 to 2 nm;

[0116] (iii) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm. Aspect 1-3: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.6 to 1.4;

[0117] (ii) PD 50 has a pore diameter in the range of 0.8 to 2 nm;

[0118] (iii) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm. Aspect 1-4: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.6 to 1.4;

[0119] (ii) PD 50 has a pore diameter in the range of 0.8 to 2 nm;

[0120] (iii) The D 50The particle size is in the range of 3 to 6 μm. 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 to 1.2;

[0121] (ii) PD 50 The pore diameter is in the range of 1 to 2 nm;

[0122] (iii) The D of the porous carbon framework 50 The particle size is in the range of 1 to 18 μm. 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 to 1.2;

[0123] (ii) PD 50 The pore diameter is in the range of 1 to 2 nm;

[0124] (iii) The D of the porous carbon framework 50 The particle size is in the range of 1 to 12 μm. 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 to 1.2;

[0125] (ii) PD 50 The pore diameter is in the range of 1 to 2 nm;

[0126] (iii) The D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm. Aspects 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 to 1.2;

[0127] (ii) PD 50 The pore diameter is in the range of 1 to 2 nm;

[0128] (iii) The D of the porous carbon framework 50 The particle size is in the range of 3 to 6 μm. Aspects 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 to 1;

[0129] (ii) PD 50 The pore diameter is in the range of 1.2 to 2 nm;

[0130] (iii) The D of the porous carbon framework 50 The particle size is in the range of 1 to 18 μm. Aspects 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 to 1;

[0131] (ii) PD50 The pore diameter is in the range of 1.2 to 2 nm;

[0132] (iii) D of the porous carbon framework 50 The particle size is in the range of 1 to 12 μm. Aspects 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 to 1;

[0133] (ii) PD 50 The pore diameter is in the range of 1.2 to 2 nm;

[0134] (iii) D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm. Aspects 1-12: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 to 1;

[0135] (ii) PD 50 The pore diameter is in the range of 1.2 to 2 nm;

[0136] (iii) D of the porous carbon framework 50 The particle size is in the range of 3 to 6 μm. Aspects 1-13: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 to 1;

[0137] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.8 nm;

[0138] (iii) D of the porous carbon framework 50 The particle size is in the range of 1 to 18 μm. Aspects 1-14: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 to 1;

[0139] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.8 nm;

[0140] (iii) D of the porous carbon framework 50 The particle size is in the range of 1 to 12 μm;

[0141] Aspects 1-15: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 to 1;

[0142] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.8 nm;

[0143] (iii) D of the porous carbon framework50 The particle size is in the range of 2 to 8 μm;

[0144] Aspects 1-16: The particulate material according to the first aspect of the present invention, wherein: (i) P 1 is in the range of 0.7 to 1;

[0145] (ii) PD 50 The pore diameter is in the range of 1.2 to 1.8 nm;

[0146] (iii) D of the porous carbon framework 50 The particle size is in the range of 3 to 6 μm;

[0147] 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 1-16 are also considered to be the preferred / optional features of aspects 1-1 to 1-16. Similarly, any features of the dependent claims within the scope of the above aspects 1-1 to 1-16 should also be construed as if those claims also depend on aspects 1-1 to 1-16.

[0148] 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 1-16. Specifically, the particulate material of the first aspect of the present invention can be used as a component of the electrode composition.

[0149] 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.

[0150] The electrode composition may optionally 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.

[0151] The particulate material of the present invention can account for 0.5 to 99.5% by weight of the total dry weight of the electrode composition (i.e., the total dry weight of the particulate material of the present invention and any additional particulate electroactive material, binder, and / or conductive additive). More preferably, the electrode composition comprises a high loading of the particulate material of the present invention. For example, the particulate material of the present invention can preferably account for at least 50% by weight, or at least 55% by weight, or at least 60% by weight, or at least 65% by weight, or at least 70% by weight, or at least 75% by weight, or at least 80% by weight, or at least 85% by weight, or at least 90% by weight or at least 95% by weight of the total dry weight of the electrode composition.

[0152] The electrode composition can optionally comprise 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), alginate and its alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The electrode composition can comprise a mixture of multiple binders. Preferably, the binder comprises 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.

[0153] The binder can 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.

[0154] The binder can 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.

[0155] The electrode composition can optionally comprise 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 electrode composition and between the electroactive components of the electrode composition and the current collector. The conductive additives can 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.

[0156] One or more conductive additives can suitably be present in a total 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.

[0157] In a third aspect, the present invention provides an electrode comprising particulate material as defined in the first aspect of the present invention in electrical contact with a current collector. The particulate material for use in 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 particulate material according to any one of aspects 1-1 to 1-16.

[0158] 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 can be used as current collectors 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 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, such as 20 to 500 μm, or 50 to 200 μm.

[0159] Preferably, the electrode comprises an 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.

[0160] The electrode of the third aspect of the present invention can 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, thereby forming an electrode layer on the surface of the current collector. Additional steps may be carried out as appropriate, such as heat treatment to cure 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.

[0161] Alternatively, the slurry can be formed into a free-standing film or mat comprising the particulate material of the present invention, for example, by casting the slurry onto a suitable casting template, removing the solvent and then removing the casting template. The resulting film or mat is in the form of a sticky free-standing body which can then be bonded to the current collector by known methods.

[0162] 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, which includes: an anode comprising the electrode as described above; a cathode containing 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 1-16.

[0163] 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.

[0164] 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.

[0165] The electrolyte is suitably a non-aqueous electrolyte containing a metal salt (such as a lithium salt), and can 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, trimethoxymethane, sulfolane, methylsulfolane, and 1,3-dimethyl-2-imidazolidinone.

[0166] 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 dissociative groups.

[0167] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts (such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4).

[0168] 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.

[0169] 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 diameter of 0.01 to 100 μm and a thickness of 5 to 300 μm. Examples of suitable electrode separators include microporous polyethylene membranes.

[0170] 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.

[0171] In a fifth aspect, the present invention provides the use of the particulate material 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 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 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 1-16. BRIEF DESCRIPTION OF THE DRAWINGS

[0172] Figure 1 Shows the capacity retention of the battery in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0173] Example

[0174] Example 1

[0175] Porous carbon framework particles (activated carbon particles) having the properties listed in Table 1 are provided.

[0176] Table 1

[0177]

[0178] *Volume fraction of micropores based on the total volume of micropores and mesopores

[0179] Silicon-carbon composite particles are prepared by depositing silicon in the pores of the porous carbon framework particles of Table 1 at 475 °C in a fixed-bed reactor using silane gas as described herein.

[0180] Example 2 - Compression test

[0181] By using a high-precision micro-compression testing machine (Shimadzu TM Model MCT-510), a compression test was performed on single particles under the conditions of a flat indenter with a diameter of 50 μm, a test force of 9.8 to 4903 mN, and a loading rate of 7.75 mN·s- 1 to analyze the resistance of the particulate material of the present invention to mechanical degradation.

[0182] Particles of different sizes were selected from different composite particle samples (samples A1 to A4 were obtained from framework A, and samples B1 and C1 were obtained from frameworks B and C, respectively). For each target particle size, at least 5 particles with sizes close to the target size were analyzed. The particle size was measured by the specimen size measurement function of Model MCT-510, which uses the average of the geometric mean diameter and length of the specimen using the top image (obtained by optical microscope). Each particle was fastened between the flat indenter and the lower pressure plate, and then a test force of 9.8 to 4900 mN was applied to the specimen and increased at the said loading rate. A sudden increase in displacement indicates fracture in the particle. The force applied at the first fracture event is considered the particle crushing force. The crushing pressure is calculated by dividing the applied crushing force by the area of the particle projected onto the indenter plane. The average crushing pressure of multiple specimens of different sizes of each composite material is considered the final crushing pressure. The results are shown in Table 2.

[0183] Table 2

[0184]

[0185] It is to be understood that the crushing pressure of individual particles has a wide variation because of unpredictable differences between individual particles (e.g., the presence of defects, the shape of the particles in the case of particle-indenter contact). To compensate for this inherent variability, the applicant also calculated for P 1The average crush pressure obtained for a wide variety of different particles having a micropore fraction of 0.69 to 1.21, a micropore fraction of 0.54 to 0.78, and a silicon weight % of 45% to 59%. The summary results from multiple experiments with particle sizes of approximately 3 μm, 5 μm, 8 μm, 12 μm, and 15 μm are provided in Table 3 and clearly demonstrate the relationship between the particle size distribution and robustness of the composite particles. Tables 2 and 3 demonstrate that the particles of the present invention having a particle size of 8 μm or less (measured by a micro compression tester as described herein) have a crush pressure averaged over 5 particles of at least 250 MPa.

[0186] Table 3

[0187]

[0188] Example 3 - Electrochemical Tests

[0189] with a mixture comprising a 90 The negative electrode of silicon-carbon particles with particle size above and below 10 μm was used to prepare the test button cells. The dispersion of Carbon Super P (conductive carbon) in CMC binder was prepared in Thinky TM The silicon-carbon particle material is added to the conductive dispersion and mixed in a Thinky TM The mixture was mixed in a mixer for 30 min. SBR binder was then added to provide a CMC:SBR ratio of 1:1 to obtain a slurry with a weight ratio of granular silicon-carbon: CMC / SBR binder: conductive carbon of 70:16:14. The slurry was placed in a Thinky TM The mixture was mixed in a mixer for another 30 minutes, and then coated on a 10 μm thick copper substrate (current collector) and dried at 50° C. for 10 minutes, and then dried at 120-180° C. for 12 hours, thereby forming an electrode including an active layer on a copper substrate.

[0190] Full Cell Fabrication

[0191] A full button cell was prepared using a circular negative electrode with a radius of 0.8 cm cut from this electrode with a porous polyethylene separator and a nickel manganese cobalt (NMC532) positive electrode. The positive and negative electrodes were designed to form a balanced pair so that the designed capacity ratio of the electrodes was about 0.9 (positive electrode: negative electrode). The electrolyte was then added to the cell before sealing, the electrolyte comprising 1M LiPF6 in a 7:3 solution of EMC / FEC (ethyl methyl carbonate / fluoroethylene carbonate) containing 3 wt% ethylene carbonate.

[0192] The full coin 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. Then the cell was allowed to rest in the lithiated state for 10 minutes. Then the anode was delithiated at a constant current of C / 25, with a cut-off voltage of 2.75 V. Then the cell was 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. Then the anode was delithiated at a constant current of C / 2, with a cut-off of 2.75 V. Then this process was repeated for the desired number of cycles. Figure 1 The discharge capacities in mAh / g (per gram of silicon-carbon composite particles) of three test cells are plotted.

[0193] All three silicon-carbon materials used in the negative electrode have similar silicon weight percentages and thus similar initial discharge capacities. When analyzed by TGA as described herein, each material also has an unoxidized silicon content of less than 10% at 800 °C. Samples X and Y have D 90 particle sizes (and D 50 particle sizes of 3.2 μm and 4.1 μm, respectively), and exhibit good capacity retention within the scope of the present invention. Sample Z has a D 50 particle size of 6.5 μm and a D 90 particle size outside the scope of the present invention, and exhibits an increased rate of capacity loss. Without being bound by theory, these results are observed to be consistent with the hypothesis that the small size and high microporosity of the particles of the present invention can better accommodate the stress caused by silicon expansion during multiple cycles, as well as the compressive stress demonstrated above.

Claims

1. A particulate material comprising a plurality of composite particles, wherein said composite particles comprise: (a) a porous carbon framework comprising micropores and / or mesopores, wherein the total pore volume of said micropores and mesopores measured by gas adsorption is P 1 cm 3 / g, where P 1 represents a natural number having a value of at least 0.6, wherein the PD 50 pore diameter measured by gas adsorption does not exceed 2 nm; and (b) an electroactive material located within the micropores and / or mesopores of said porous carbon framework; wherein the D 90 particle size of said composite particles does not exceed 10 μm.

2. The particulate material according to claim 1, wherein said porous carbon framework comprises macropores having a diameter in the range of greater than 50 nm to 100 nm, and the total volume of said macropores measured by mercury intrusion is P 2 cm 3 / g, where P 2 does not exceed 0.2×P 1 , or does not exceed 0.1×P 1 , or does not exceed 0.05×P 1 , or does not exceed 0.02×P 1 , or does not exceed 0.01×P 1 , or does not exceed 0.005×P 1 .

3. The particulate material according to claim 1, wherein at least a portion of said micropores and / or mesopores comprises void spaces completely encapsulated by said electroactive material.

4. The particulate material according to claim 1, wherein the D 90 particle size of said composite particles does not exceed 9.5 μm, or does not exceed 9 μm, or does not exceed 8.5 μm, or does not exceed 8 μm, or does not exceed 7.5 μm, or does not exceed 7 μm, or does not exceed 6.5 μm, or does not exceed 6 μm, or does not exceed 5.5 μm, or does not exceed 5 μm, or does not exceed 4.5 μm, or does not exceed 4 μm.

5. The particulate material according to claim 1, wherein the D 50 particle size of said composite particles is in the range of 0.5 to 7 μm.

6. The particulate material according to claim 5, wherein the D 50 particle size of said composite particles is 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.

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

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

9. A rechargeable metal ion battery, the 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 to 6 as an anode active material.

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