Electroactive materials for metal ion batteries

Abstract

The present invention generally relates to electroactive materials for metal ion batteries. Specifically, 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 mesopores having a total pore volume of at least 0.6 cm3 / g wherein the volume fraction of micropores is in the range of 0.1 to 0.9 and the volume fraction of pores having a pore size of not more than 20 nm is at least 0.75, the D50 particle size of the porous carbon skeleton is less than 20 m; (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 an application with the invention name "Electroactive Materials for Metal Ion Batteries", having a PCT international filing date of December 19, 2019, a PCT international application number of PCT / GB2019 / 053640, and a Chinese national application number of 201980088762.2. Technical Field

[0002] The present invention generally relates to electroactive materials suitable for use in electrodes of rechargeable metal ion batteries, and more particularly to particulate materials having high electrochemical capacity suitable for use as anode active materials in rechargeable metal ion batteries. The particulate electroactive materials of the present invention have particular utility in hybrid anodes comprising more than two different electroactive materials. 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 typically 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 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 compound with the empirical formula Li xMaterials of 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 with significantly higher capacities compared to graphite, but have not yet been widely commercially applied due to the 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 due to the large volume changes during charging and discharging.

[0006] The intercalation of lithium into bulk silicon causes a significant 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 cause significant mechanical stress in the silicon material, leading to fracture and delamination of the silicon anode material. The volume shrinkage of the silicon particles during de-lithiation 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 leads to further electrolyte decomposition and an increase in the SEI layer thickness as well as irreversible lithium consumption. These degradation mechanisms together result in unacceptable electrochemical capacity loss during consecutive charge and discharge cycles.

[0007] A variety of methods have been proposed to overcome 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 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 dispersion of particles 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 achieved good capacity retention, the thin film structure did not give a usable amount of capacity per unit area, and any improvement was eliminated when the film thickness was increased.

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

[0010] It is also generally known that an electroactive material such as silicon can be deposited within the pores of a porous carrier 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) disclosed a silicon-carbon composite material in which a porous carbon substrate provides a conductive framework 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 including a carbon-based scaffold having small pores branching from some larger pores. An electroactive material (such as silicon) is optionally located on the walls of both the large pores and the small pores, and on the outer surface of the carbon-based scaffold.

[0012] Despite efforts made so far, there is a continuing need to improve the electrochemical storage capacity of lithium-ion batteries. Although a long-term goal is to develop electrodes containing a high proportion of silicon as an electroactive material, another goal of battery manufacturers is to determine ways to use a small amount of silicon to supplement the capacity of graphite anodes. Thus, the current focus is on obtaining a gradual improvement to existing metal-ion battery technology by using "hybrid" electrodes that incorporate a combination of graphite and Si-based electroactive materials rather than a wholesale transition from graphite anodes to silicon anodes.

[0013] The use of hybrid electrodes presents its own challenges. Any additional electroactive material must be provided in a form compatible with the form of graphite particles used in metal-ion batteries. For example, the additional electroactive material must be dispersible throughout the graphite particle matrix, and the particles of the additional electroactive material must have sufficient structural integrity to withstand mixing with the graphite particles and subsequent electrode layer formation (e.g., by steps such as compression, drying, and calendaring).

[0014] In addition, when developing hybrid anodes, the differences in the metallization properties of graphite and other electroactive materials must be considered. For example, in the lithiation of a silicon-graphite hybrid anode in which graphite accounts for at least 50 wt% of the electroactive material, the silicon needs to be lithiated to its maximum capacity to obtain the capacity benefit from all electroactive materials. While in a non-hybrid silicon electrode, the silicon material is typically restricted to about 25 to 60% of its maximum weight capacity during charge and discharge to avoid imposing excessive mechanical stress on the silicon material and causing a reduction in the overall volumetric capacity of the battery, this option is not available for hybrid electrodes. Thus, the silicon material must be able to withstand very high levels of mechanical stress during repeated charge and discharge cycles. SUMMARY OF THE INVENTION

[0015] Accordingly, there is a need in the art for silicon-containing electroactive materials that combine high lithiation capacity with sufficient capacity retention and structural stability during multiple charge-discharge cycles. In particular, materials for supplementing conventional electroactive materials such as graphite will need to maintain capacity and structural stability when repeatedly lithiated to their maximum capacity. The present invention solves this problem by providing particulate materials comprising a porous carbon backbone and a plurality of nano-sized elemental silicon domains located within the pores of the porous carbon backbone. The pore structure of the porous carbon backbone and the ratio of silicon to the available pore volume of the porous carbon backbone are carefully controlled separately to obtain optimal performance, particularly under the stringent criteria required for hybrid electrodes.

[0016] In a first aspect, the present invention provides a particulate material comprising a plurality of composite particles, wherein said composite particles comprise:

[0017] (a) a porous carbon framework comprising micropores and mesopores, wherein

[0018] (i) the total pore volume of said micropores and mesopores measured by gas adsorption is P1 cm 3 / g, where the value of P1 is at least 0.6,

[0019] (ii) based on the total volume of the micropores and mesopores, the volume fraction of the micropores is in the range of 0.1 to 0.9

[0020] range;

[0021] (iii) based on the total volume of the micropores and mesopores, the volume fraction of pores with a pore diameter not exceeding 20 nm ([[]] ) is at least 0.75, and

[0022] (iv) the D 50 particle size of said porous carbon framework is less than 20 μm;

[0023] (b) a plurality of nanosized domains of elemental silicon located within the micropores and / or mesopores of said porous carbon framework;

[0024] where the weight ratio of silicon to said porous carbon framework in said composite particles is in the range of [1×P1 to 2.2×P1]:1.

[0025] Thus, the present invention relates to a particulate material, wherein the porous carbon framework comprises both micropores and mesopores, and the minimum total volume of said micropores and mesopores is at least 0.6 cm 3 / g. The total volume of the micropores and mesopores is denoted herein as P1 cm 3 / g. P1 itself is a dimensionless quantity having a value of at least 0.6, and said value is also used to relate the available pore volume to the weight ratio of silicon in the particulate material.

[0026] 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.

[0027] The pore volume is distributed between the micropores and mesopores such that, based on the total volume of the micropores and mesopores, the volume fraction of the micropores is in the range of 0.1 to 0.9. The volume fraction of the micropores (based on the total volume of the micropores and mesopores) is denoted herein by the symbol and the volume fraction of the mesopores (based on the total volume of the micropores and mesopores) is denoted by the symbol is denoted and will thus be understood

[0028] The porous carbon framework is also defined by a pore volume that is generally skewed towards smaller pores, such that at least 75% of the total micropore and mesopore volume is in the form of pores with a diameter not exceeding 20 nm. The volume fraction of pores with a diameter not exceeding 20 nm (based on the total volume of micropores and mesopores) is denoted herein by the symbol and the symbols and are used to define the respective volume fractions of pores with a diameter not exceeding 10 nm and not exceeding 5 nm, respectively.

[0029] In addition, the porous carbon framework is defined by a D 50 particle size of less than 20 μm.

[0030] To avoid ambiguity, as used herein, P1 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. Similarly, when referring to the volume of micropores, mesopores, and macropores in the porous carbon framework and any mention of the distribution of pore volume within the porous carbon framework, it refers to the internal pore volume of the porous carbon framework alone (i.e., in the absence of any silicon or other material occupying the pore volume).

[0031] The weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [1×P1 to 2.2×P1]:1. Thus, the weight ratio of silicon to the porous carbon framework is proportional to the available pore volume in the porous carbon framework, such that considering a silicon density of approximately 2.3 g / cm 3 , a weight ratio of [1×P1]:1 corresponds to approximately 43% v / v of the pores of the porous carbon framework being occupied by silicon. The upper ratio limit of [2.2×P1]:1 corresponds to approximately 95% v / v of the pores of the porous carbon framework being occupied by silicon. Typically, these ratios are calculated based on pure carbon and pure silicon.

[0032] Elemental silicon is located in the micropores and / or mesopores in the form of multiple nano-sized silicon domains. As used herein, the term "nano-sized silicon domain" refers to nano-sized silicon bodies located within the pores of the porous carbon framework. The maximum size of the nano-sized silicon domain is defined by the pore diameter of the pore in which the silicon is located.

[0033] Thus, the present invention generally relates to a particulate material in which nano-sized silicon domains occupy a majority of the pore volume of the porous carbon framework, where the pore volume is distributed between small mesopores (diameter not exceeding 20 nm) and micropores. It has been found that this particle configuration provides an electroactive material having a very high weight and volume capacity after lithiation, as well as a high reversible capacity retention rate during multiple charge-discharge cycles.

[0034] Without being bound by theory, it is believed that having nano-sized silicon domains located within small mesopores and / or micropores provides, in the first place, 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. By ensuring that a relatively high proportion of the pore volume is occupied by silicon, the particulate material of the present invention has a high capacity. In addition, by having nano-sized silicon domains located within small mesopores and / or micropores as described above, only a small surface area of the silicon is electrolyte-accessible, thus limiting SEI formation.

[0035] The inventors have found that the dual objective of obtaining a high capacity and a high reversible capacity retention depends on careful control of the pore size distribution. Although it may be expected that very fine silicon structures within micropores are most effective for reversible lithiation, it has been found that a porous carbon framework with an excessive micropore fraction can accommodate less than the optimal amount of silicon, resulting in a lower volumetric capacity of the material. Without being bound by theory, it is believed that deposition of silicon into a very highly microporous carbon framework results in the formation of silicon structures (such as caps or walls) that block access to the unoccupied pore volume, thus limiting the achievable silicon loading.

[0036] However, if silicon is deposited into a carbon framework with a very high degree of mesoporosity, the silicon nanostructures are inappropriately large and the carbon wall thickness increases. As a result, although a higher volumetric capacity can be achieved, both the silicon nanostructures and the porous carbon framework undergo excessive structural strain during lithiation, particularly when lithiated to maximum capacity, and the same is true in a hybrid anode that also contains graphite as an electroactive material. This excessive structural strain can lead to rupture of the silicon nanostructures and the porous carbon framework. Then, additional exposure of the silicon to the electrolyte from the ruptured surfaces during subsequent charge-discharge cycles means that SEI formation can become a significant failure mechanism leading to capacity loss. By controlling the relative volume fractions of micropores and mesopores and by ensuring that the mesopore volume is largely confined to pores smaller than 20 nm, the particulate material of the present invention avoids these failure mechanisms and maintains a high reversible capacity over multiple charge-discharge cycles while also accommodating a relatively large proportion of silicon within the pore volume of the porous carbon framework. This stands in sharp contrast to the characteristics of materials such as those disclosed by Guo (see above), namely excessive and unconstrained SEI formation.

[0037] Although lithiation of silicon may cause a certain degree of external expansion of the entire composite material, careful control of the micropore and mesopore volume fractions and the size distribution of the mesopore volume fraction towards smaller pore sizes ensures that the particulate material can deform reversibly without rupture over multiple charge-discharge cycles. Thus, the stress on the carbon framework and the silicon material is controlled at a level acceptable for a large number of charge-discharge cycles without significant capacity loss.

[0038] Due to the unique particle structure of the composite material of the present invention, the silicon in the particulate material of the present invention has electrochemical properties comparable to those of fine silicon nanoparticles without suffering from the drawbacks of excessive SEI formation and poor dispersibility, such drawbacks that make discrete silicon nanoparticles not commercially viable as electrode materials. The relatively high volume content of silicon in the particulate material makes it particularly suitable as a component for a hybrid anode.

[0039] 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. 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 from 0 to 50 nm) is herein referred to as P1 cm 3 / g, where P1 represents a dimensionless natural number having a value of at least 0.6. As described above, the value of P1 is also used to correlate the available pore volume in the porous carbon framework with the weight ratio of silicon to porous carbon framework as described above.

[0040] Preferably, the value of P1 is at least 0.65, or at least 0.7, or 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. More preferably, the value of P1 is at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85. Optionally, the total volume of micropores and mesopores can be greater than 1 cm 3 / g, for example, P1 can be at least 1.05, or at least 1.1, or at least 1.15, or at least 1.2.

[0041] It is advantageous to use a highly porous carbon framework as it enables a greater amount of silicon to be accommodated within the pore structure, and it has been found that a highly porous carbon framework in which the pore volume is mainly in the form of micropores and smaller mesopores has sufficient strength to accommodate the volume expansion of silicon without fracturing or otherwise degrading the porous carbon framework.

[0042] The internal pore volume of the porous carbon framework is limited to a value at which the increased brittleness of the porous carbon framework outweighs the advantage of the increased pore volume for accommodating a greater amount of silicon. Generally, the value of P1 may not exceed 2.2. However, preferably, the value of P1 may not exceed 2, or may not exceed 1.8, or may not exceed 1.6, or may not exceed 1.5, or may not exceed 1.4, or may not exceed 1.3, or may not exceed 1.2, or may not exceed 1.1, or may not exceed 1.0, or may not exceed 0.9. More preferably, the value of P1 does not exceed 1.2, or does not exceed 1.1, or does not exceed 1.0, or does not exceed 0.9.

[0043] According to the present invention, the value of P1 can be, for example, in the range of 0.6 to 2 (i.e., the total volume of micropores and mesopores is 0.6 to 2 cm 3 / g). For example, P1 can be in the range of 0.6 to 1.8, or in the range of 0.65 to 1.8, or in the range of 0.7 to 1.8, or in the range of 0.75 to 1.8, 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 0.65 to 1.7, or in the range of 0.7 to 1.7, or in the range of 0.75 to 1.7, 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 0.7 to 1.6, or in the range of 0.75 to 1.6, 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 0.75 to 1.5, or in the range of 0.8 to 1.5, or in the range of 0.85 to 1.5, or in the range of 0.9 to 1.5, or in the range of 0.95 to 1.5, or in the range of 1 to 1.5, or in the range of 0.8 to 1.4, or in the range of 0.85 to 1.4, or in the range of 0.9 to 1.4, or in the range of 0.95 to 1.4, or in the range of 1 to 1.4.

[0044] 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 0.6 to 1.3, or in the range of 0.65 to 1.3, 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 0.6 to 1.2, or in the range of 0.65 to 1.2, 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 0.6 to 1, or in the range of 0.65 to 1, or in the range of 0.7 to 1, or in the range of 0.75 to 1, or in the range of 0.6 to 0.9, or in the range of 0.65 to 0.9, or in the range of 0.7 to 0.9, or in the range of 0.75 to 0.9.

[0045] The volume fraction of micropores is preferably in the range of 0.15 to 0.85, more preferably in the range of 0.2 to 0.8.

[0046] Preferably, In the range of 0.45 to 0.85, more preferably in the range of 0.5 to 0.8, more preferably in the range of 0.5 to 0.75, more preferably in the range of 0.5 to 0.7, in order to particularly utilize the high capacity retention rate of the very fine silicon nanostructures located within the micropores. For example, it can be in the range of 0.55 to 0.8, or in the range of 0.6 to 0.8, or in the range of 0.6 to 0.75.

[0047] Alternatively, it can be in the range of 0.2 to 0.5, more preferably in the range of 0.3 to 0.5, in order to particularly utilize the opportunity of high silicon loading.

[0048] As discussed above, the pore volume is substantially biased towards the smaller pores, such that at least 75% of the total micropore and mesopore volume of the porous carbon framework is in the form of pores with a diameter not exceeding 20 nm. More preferably, it is at least 0.8, more preferably at least 0.85, more preferably at least 0.9.

[0049] Preferably, based on the total volume of the micropores and mesopores, it is at least 0.70, or at least 0.75, or at least 0.8, or at least 0.85. More preferably, based on the total volume of the micropores and mesopores, it is at least 0.75, or at least 0.8, or at least 0.85. Thus, in a preferred embodiment, at least 75% of the total micropore and mesopore volume of the porous carbon framework is in the form of pores with a diameter not exceeding 10 nm and more preferably not exceeding 5 nm.

[0050] A small fraction of pores in the larger mesopore range can advantageously facilitate the access of the electrolyte to the silicon domains. Thus, pores in the range of 10 to 50 nm (i.e., larger mesopores) can optionally account for no more than 1%, or no more than 2%, or no more than 5%, or no more than 10% of the total micropore and mesopore volume of the porous carbon framework.

[0051] The volume ratio of micropores to mesopores in the porous carbon framework can basically be 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.

[0052] 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 the smallest pores and the pores with a larger diameter provides the advantage of efficient ion transport from the porous network to silicon. Thus, the particulate material has high ion diffusivity and thus improved rate performance.

[0053] 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 about 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 1.5 nm and a peak at a pore size of 15 nm.

[0054] According to the methods described in ISO 15901-2 and ISO 15901-3, the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores are determined using nitrogen adsorption at 77 K down to a relative pressure p / p0 of 10 -6 using quenched solid density functional theory (QSDFT). Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure is increased until the saturation point is reached, at which point all pores are filled with liquid. Then the nitrogen pressure is 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 TriStar II and TriStar II Plus porosimeters (which are available from Micromeritics Instrument Corporation, USA), and Autosorb IQ porosimeter (which is available from Quantachrome Instruments).

[0055] 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, the value of P1 is determined by considering only pores with a maximum diameter of 50 nm (including 50 nm), i.e., only micropores and mesopores, and is likewise determined relative to the total volume of only micropores and mesopores and value.

[0056] Due to limitations of available analytical techniques, it is not possible to measure pore volume and pore size distribution over the entire range of micropores, mesopores, and macropores using a single technique. In the case where the porous carbon framework includes macropores, the volume of pores in the range greater than 50 nm up to a maximum of 100 nm is herein considered to have a value of P2 cm 3 / g and is measured by mercury intrusion porosimetry. As described above, the value of P2 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.

[0057] To avoid ambiguity, the value of P2 only considers pores with diameters from greater than 50 nm up 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 value of P2, any pore volume of pore sizes below 50 nm measured by mercury intrusion porosimetry is not considered (as described above, nitrogen adsorption is used to characterize mesopores and micropores). For the purposes of the present invention, the pore volume in the case of pore sizes above 100 nm measured by mercury intrusion porosimetry is assumed to be the interparticle porosity and is also not considered when determining the value of P2.

[0058] Mercury intrusion porosimetry is a technique for characterizing the porosity and pore size distribution of a material sample by applying different levels of pressure to the sample immersed in mercury. The pressure required to 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 porosimeters of the AutoPore IV series, which are available from Micromeritics Instrument Corporation of 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.

[0059] Compared with the volume of the micropores and mesopores (and thus the value of P1), the volume of the macropores (and thus the value of P2) is preferably smaller. Although a small fraction of the macropores can be useful for facilitating the entry of electrolyte into the pore network, the advantages of the present invention are essentially obtained by accommodating silicon in the micropores and smaller mesopores.

[0060] Thus, according to the present invention, the total volume of the macropores in the porous carbon framework measured by mercury intrusion is P2 cm 3 / g, where the value of P2 is preferably not more than 0.2×P1, or not more than 0.1×P1, or not more than 0.05×P1, or not more than 0.02×P1, or not more than 0.01×P1, or not more than 0.005×P1.

[0061] In a preferred embodiment, the value of P2 is not more than 0.3, or not more than 0.25, or not more than 0.20, or not more than 0.15, or not more than 0.1, or not more than 0.05. As discussed above for the larger mesopores, a small pore volume fraction in the macropore range can advantageously facilitate the approach of the electrolyte to the silicon.

[0062] The open pore network optionally includes a hierarchical pore structure, i.e., a pore structure in which there is a certain degree of pore size ordering, where the smaller pores branch from the larger pores.

[0063] It should be understood that intrusion techniques such as gas adsorption and mercury intrusion are only effective for determining the pore volume of the pores accessible from the outside of the porous carbon framework by nitrogen or mercury. The porosity values (P1 and P2) as specified herein should be understood to refer to the volume of the open pores (pores accessible from the outside of the porous carbon framework by fluid). In this document, when specifying the porosity value, fully encapsulated pores that cannot be identified by nitrogen adsorption or mercury intrusion should not be considered. Similarly, for determining the value of P1, any pore volume in pores that are too small to be detected by nitrogen adsorption is not considered.

[0064] 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 soft carbon framework and can suitably be obtained by known procedures involving the pyrolysis of polymers or organic substances.

[0065] 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 of the physical adsorption of gas molecules on the surface of a solid 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.

[0066] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which carbon atoms are predominantly found in the sp 2 hybridized state (triple bond) in polyaromatic structural domains at the nanoscale. The polyaromatic structural domains are crosslinked by chemical bonds such as C–O–C bonds. Due to the chemical crosslinking between the polyaromatic structural domains, hard carbon cannot be converted to graphite at high temperatures. Hard carbon has graphite-like characteristics, as evidenced by a large G band (~1600 cm -1 ) in the Raman spectrum. However, the carbon is not completely graphitic, as evidenced by a distinct D band (~1350 cm -1 ) in the Raman spectrum.

[0067] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are predominantly found in polyaromatic structural domains with sizes in the range of 5 to 200 nm in the sp 2 hybridized state (triple bond). Compared with hard carbon, the polyaromatic structural 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% sp 2 hybridized carbon (measured by XPS). For example, the porous carbon framework can suitably contain 50% to 98% sp 2 hybridized carbon, 55% to 95% sp 2 hybridized carbon, 60% to 90% sp 2 hybridized carbon, or 70% to 85% sp 2 hybridized carbon.

[0068] 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, a variety of different hard carbon materials can be obtained in the art.

[0069] 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.

[0070] 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).

[0071] The D 50 particle size of the porous carbon framework can be in the range of 0.5 to 20 μm. Preferably, the D 50 particle size is at least 1 μm, more preferably at least 2 μm, such as at least 3 μm, or at least 4 μm, or at least 5 μm. Preferably, the D 50 particle size of the particulate material does not exceed 18 μm, more preferably does not exceed 16 μm, more preferably does not exceed 14 μm, more preferably does not exceed 12 μm, more preferably does not exceed 10 μm, such as does not exceed 9 μm, or does not exceed 8 μm. More preferably, the D 50 particle size preferably does not exceed 10 μm, or does not exceed 9 μm, or does not exceed 8 μm, or does not exceed 7 μm, or does not exceed 6 μm, or does not exceed 5 μm.

[0072] For example, the D 50 particle size of the porous carbon framework can be in the range of 1 to 12 μm, or in the range of 1 to 10 μm, or in the range of 2 to 10 μm, or in the range of 2 to 8 μm, or in the range of 2 to 6 μm, or in the range of 3 to 10 μm, or in the range of 3 to 8 μm, or in the range of 3 to 7 μm, or in the range of 3 to 6 μm, or in the range of 3 to 5 μm.

[0073] By requiring the weight ratio of silicon to the porous carbon framework in the composite particles to be in the range of [1×P1 to 2.2×P1]:1, the amount of silicon in the porous carbon framework is associated 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 the weight ratio of silicon, at which the internal pore volume (P1 cm 3 / g) of the porous carbon framework is occupied by silicon by approximately 43% to 95% v / v (in the uncharged state).

[0074] Preferably, the weight ratio of silicon to the porous carbon framework is at least 1.1×P1, more preferably at least 1.15×P1, more preferably at least 1.2×P1, more preferably at least 1.25×P1, more preferably at least 1.3×P1, more preferably at least 1.35×P1, more preferably at least 1.4×P1.

[0075] In the case where the porous carbon framework includes a relatively high ratio of mesopores to micropores (e.g., in the range of 0.2 to 0.5 or in the range of 0.3 to 0.5), the weight ratio of silicon to the porous carbon framework can still be higher, such as at least 1.45×P1, more preferably at least 1.5×P1, more preferably at least 1.55×P1, more preferably at least 1.6×P1, more preferably at least 1.65×P1, more preferably at least 1.7×P1.

[0076] By requiring the weight ratio of silicon to the porous carbon framework in the composite particles to be at least 1×P1, the minimum weight ratio of silicon to the porous carbon framework is associated with the mesopore fraction and the total pore volume. More preferably, the weight ratio of silicon to the porous carbon framework has at least the value given by , more preferably at least the value given by , more preferably at least the value given by , more preferably at least the value given by , more preferably at least the value given by (provided that the value is at least 1×P1). Thus, in the case where the mesopore fraction has a higher value, the minimum amount of silicon in the composite particles is also higher. This relationship between the mesopore fraction and the minimum weight ratio of silicon to the porous carbon framework ensures that the porous carbon framework with a higher mesopore fraction is more occupied by silicon, thereby optimizing the volume capacity of the particulate material. Ensuring that the porous carbon framework with a higher mesopore fraction has a higher minimum silicon loading also reduces the possibility that the larger micropores will be partially occupied by silicon, thereby reducing the silicon surface area exposed to the electrolyte and thus limiting the formation of undesirable SEI.

[0077] Also, by requiring the weight ratio of silicon to the porous carbon framework in the composite particles not to exceed the value given by 1.9×P1, the maximum weight ratio of silicon to the porous carbon framework is associated with the mesopore fraction is associated with the total pore volume. More preferably, the weight ratio of silicon to the porous carbon framework does not exceed the value given by and more preferably does not exceed the value given by (provided that the value does not exceed 1.9×P1). The relationship between the mesopore fraction and the maximum weight ratio of the porous carbon framework ensures that a porous carbon framework with a higher micropore fraction is not overly filled with silicon. As described above, in the case where the porous carbon framework is more highly microporous due to the possibility of forming walls or caps that enclose the occupied pore volume, it may be more difficult to achieve a very high ratio of silicon. Additionally, in the case where the porous carbon framework is more highly microporous, the diffusion of lithium through the very fine silicon structure becomes rate-limiting, which reduces the rate capability of the particulate material. Therefore, controlling the upper limit of the silicon ratio ensures the extent to which the electrolyte enters the internal pore volume of the porous carbon framework, which promotes the transport of lithium ions into the silicon domains.

[0078] Preferably, the silicon mass in the composite particles is substantially or completely located within the pores of the porous carbon framework in the form of the above-described nanoscale silicon domains. For example, it is preferred that at least 90 wt%, more preferably at least 95 wt%, more preferably at least 98 wt%, more preferably at least 99 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 located on the outer surface of the composite particles.

[0079] The particulate materials of the present invention may further be characterized by their thermogravimetric analysis (TGA) properties in air. Preferably, the particulate materials contain no more than 10% unoxidized silicon at 800 °C, as determined by TGA in air at a heating rate of 10 °C / min. More preferably, the particulate materials contain no more than 5% or no more than 2% unoxidized silicon at 800 °C, as determined by TGA in air at a heating rate of 10 °C / min.

[0080] 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. At temperatures 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.

[0081] 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 unoxidized silicon at 800 °C (as a proportion of the total silicon amount) according to the following formula:

[0082] Z = 1.875×[(M f - M800 ) / M f ×100%

[0083] 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.

[0084] Without being bound by theory, it is to 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. Accordingly, it is to be understood that silicon deposited in micropores and mesopores will oxidize at lower temperatures compared to silicon deposits on the surface of the particles, because there will necessarily be a thinner oxide coating on these structures. Accordingly, 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. This is also referred to herein as "coarse silicon".

[0085] The silicon is preferably amorphous silicon. It is believed that amorphous silicon has better properties as an electroactive material. The morphology of the silicon can be determined using X-ray diffraction (XRD) by known procedures.

[0086] 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 P1, or does not exceed 0.10x P1, or does not exceed 0.05x P1, or does not exceed 0.02x P1.

[0087] 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 taken together enable the reliable determination of the weight percentage of silicon relative to the entire porous carbon framework.

[0088] 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 ICP-OES analyzers of the 7000 series (available from Thermo Fisher Scientific). The carbon content (and, if desired, hydrogen content, nitrogen content, and oxygen content) of the composite particles and the individual porous carbon frameworks is preferably determined by IR absorption. Suitable instruments for determining carbon content, hydrogen content, nitrogen content, and oxygen content are Micro elemental analyzers (available from Leco Corporation).

[0089] 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%, such as less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%.

[0090] Silicon can optionally contain small amounts of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, nitrogen, or germanium. Preferably, the dopants are present in a total amount of no more than 2 wt% based on the total amount of silicon and one or more dopants.

[0091] For the avoidance of doubt, 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 pores within the particle. As used herein, the terms "D 50 " and "D 50 particle size" refer to the volume-based median particle size, i.e., the diameter at which 50% of the measured particle population has a volume less than a certain diameter. As used herein, the terms "D 10 " and "D 10 particle size" refer to the 10th percentile volume-based median particle size, i.e., the diameter at which 10% of the measured particle population has a volume less than a certain diameter. As used herein, the terms "D 90 " and "D 90 particle size" refer to the 90th percentile volume-based median particle size, i.e., the diameter at which 90% of the measured particle population has a volume less than a certain diameter.

[0092] The particle size and 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 size distribution. A variety of laser diffraction instruments are commercially available for the rapid and reliable determination of size distribution. Unless otherwise stated, the 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 that strikes the particles is scattered at an angle inversely proportional to the particle size, and a photodetector array measures the intensity of the light at multiple predetermined angles, and the intensities measured at different angles are processed by computer using standard theoretical principles to determine the size distribution. The laser diffraction values reported herein were obtained using a wet dispersion of the particles in distilled water. The particle refractive index was 3.50 and the dispersant index was 1.330. The Mie scattering model was used to calculate the size distribution.

[0093] The D 50 particle size of the composite particles can range from 0.5 to 20 μm. Preferably, the D 50 particle size is at least 1 μm, more preferably at least 2 μm, such as at least 3 μm, or at least 4 μm, or at least 5 μm. Preferably, the D 50 particle size of the particulate material does not exceed 18 μm, more preferably does not exceed 16 μm, more preferably does not exceed 14 μm, more preferably does not exceed 12 μm, more preferably does not exceed 10 μm, such as does not exceed 9 μm, or does not exceed 8 μm.

[0094] For example, the D 50 particle size of the composite particles can range from 1 to 12 μm, or 1 to 10 μm, or 2 to 10 μm, or 3 to 10 μm or 3 to 8 μm. Particles within these size ranges and having the porosity and pore size distribution described herein are ideally suited for use as hybrid anodes in metal ion batteries due to their dispersibility in slurries, their structural robustness, their capacity retention with repeated charge-discharge cycles, and their ability to occupy the interstitial space between conventional graphite particles used in the electrodes of metal ion batteries.

[0095] The D 10The 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 D 10 the particle size above 0.2 μm, the possibility of agglomeration of undesired sub-micron-sized particles is reduced, resulting in improved dispersibility of the particulate material and improved capacity retention.

[0096] The D 90 particle size of the composite particles is preferably not more than 40 μm, or not more than 30 μm, or not more than 20 μm, or not more than 15 μm, or not more than 12 μm, or not more than 10 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, particularly an electrode layer within the conventional thickness range of 20 to 50 μm. Therefore, preferably, the D 90 particle size is not more than 20 μm, and even more preferably even smaller.

[0097] 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.

[0098] The shape of the composite particles can be 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 appropriately 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, unexpectedly, it has 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.

[0099] 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 at 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:

[0100]

[0101] where A m is the area of the measured particle projection, and C m is the perimeter of the measured particle projection. The average sphericity S of multiple particles as used herein av is defined as:

[0102]

[0103] where n represents the number of particles in the population.

[0104] As used herein, the term "near-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. Preferably, the average sphericity of the porous near-spherical 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, preferably at least 0.94, more preferably at least 0.95. Optionally, the average sphericity of the porous near-spherical particles can be at least 0.96, or at least 0.97, or at least 0.98, or at least 0.99.

[0105] It is to be understood that in the case of any particles that are not perfectly near-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 multiple particles having 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 size and shape distributions 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 by the instrument.

[0106] The BET surface area of the composite particles is preferably 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 of the 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.

[0107] 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.

[0108] 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.

[0109] 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 partial pressure of the silicon precursor 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, for example 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.

[0110] A particular advantage of the present invention is that the porous carbon framework has a very high ratio of internal surface area to external surface area due to the very low pore size. As a result, it is kinetically favorable for silicon to deposit on the inner surface of the porous carbon framework. Thus, a very high proportion of the silicon in the composite particles of the present invention is in the form of nano-sized elemental silicon domains within the micropores and / or mesopores of the porous carbon framework (e.g., as described above, at least 90 wt%, more preferably at least 95 wt%, more preferably at least 98 wt%, more preferably at least 99 wt% of the silicon mass in the composite particles).

[0111] In contrast, the formation of silicon deposits on the outer surface of the porous carbon framework proceeds at a significantly lower rate, such that the composite particles generally contain a very small amount of external silicon on the outer surface of the porous carbon framework. Without being bound by theory, it is believed that the larger size of the silicon on the outer surface of the porous carbon framework means that the external silicon (referred to herein as "coarse silicon") is less able to cycle reversibly and results in a proportionally larger amount of silicon oxide and SEI formation, such that composite particles with a large amount of external silicon will have a poor capacity retention rate after multiple charge and discharge cycles.

[0112] 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 thermally decomposing 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, thereby 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.

[0113] The carbon coating has the following advantages: it further reduces the BET surface area of the particulate material by smoothing any surface defects and by 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.

[0114] According to a first aspect of the present invention, there is also provided a particulate material according to aspects 1-1 to 1-41 below. Aspect 1-1: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.7 - 1.4;

[0115] (ii) in the range of 0.5 to 0.8;

[0116] (iii) is at least 0.8;

[0117] (iv) D of the porous carbon framework 50 The particle size 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) P1 is in the range of 0.7 - 1.4;

[0118] (ii) is in the range of 0.5 to 0.8;

[0119] (iii) is at least 0.8;

[0120] (iv) D of the porous carbon framework 50 The particle size 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) P1 is in the range of 0.7 - 1.4;

[0121] (ii) is in the range of 0.5 to 0.8;

[0122] (iii) is at least 0.8;

[0123] (iv) D of the porous carbon framework 50 The particle size 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) P1 is in the range of 0.7 - 1.4;

[0124] (ii) is in the range of 0.5 to 0.8;

[0125] (iii) is at least 0.8;

[0126] (iv) D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm. Aspect 1-5: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.7 - 1.4;

[0127] (ii) is in the range of 0.5 to 0.8;

[0128] (iii) is at least 0.75;

[0129] (iv) D of the porous carbon framework 50The particle size is in the range of 2 to 8 μm. Aspects 1-6: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.8 - 1.2;

[0130] (ii) is in the range of 0.6 to 0.8;

[0131] (iii) is at least 0.8;

[0132] (iv) The D of the porous carbon framework 50 The particle size is in the range of 1 to 18 μm. Aspects 1-7: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.8 - 1.2;

[0133] (ii) is in the range of 0.6 to 0.8;

[0134] (iii) is at least 0.8;

[0135] (iv) The D of the porous carbon framework 50 The particle size is in the range of 1 to 12 μm. Aspects 1-8: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.8 - 1.2;

[0136] (ii) is in the range of 0.6 to 0.8;

[0137] (iii) is at least 0.8;

[0138] (iv) The D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm. Aspects 1-9: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.8 - 1.2;

[0139] (ii) is in the range of 0.6 to 0.8;

[0140] (iii) is at least 0.8;

[0141] (iv) The D of the porous carbon framework 50 The particle size is in the range of 2 to 8 μm. Aspects 1-10: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.8 - 1.2;

[0142] (ii) is in the range of 0.6 to 0.8;

[0143] (iii) is at least 0.75;

[0144] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm. Aspects 1-11: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.7 - 0.9;

[0145] (ii) is in the range of 0.6 to 0.8;

[0146] (iii) is at least 0.75;

[0147] (iv) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm. Aspects 1-12: The particulate material according to the first aspect of the present invention, wherein: (i) P1 is in the range of 0.7 - 1.4;

[0148] (ii) is in the range of 0.5 to 0.8;

[0149] (iii) is at least 0.8;

[0150] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0151] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0152] Aspects 1-13: The particulate material according to the first aspect of the present invention, wherein:

[0153] (i) P1 is in the range of 0.7 - 1.4;

[0154] (ii) is in the range of 0.5 to 0.8;

[0155] (iii) is at least 0.8;

[0156] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm;

[0157] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0158] Aspect 1-14: The particulate material according to the first aspect of the present invention, wherein:

[0159] (i) P1 is in the range of 0.7 - 1.4;

[0160] (ii) is in the range of 0.5 to 0.8;

[0161] (iii) is at least 0.8;

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

[0163] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0164] Aspect 1-15: The particulate material according to the first aspect of the present invention, wherein:

[0165] (i) P1 is in the range of 0.7 - 1.4;

[0166] (ii) is in the range of 0.5 to 0.8;

[0167] (iii) is at least 0.8;

[0168] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0169] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0170] Aspect 1-16: The particulate material according to the first aspect of the present invention, wherein:

[0171] (i) P1 is in the range of 0.7 - 1.4;

[0172] (ii) is in the range of 0.5 to 0.8;

[0173] (iii) is at least 0.75;

[0174] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0175] (v) The weight ratio of silicon to the porous carbon framework is at least by the given value, and preferably not exceeding the value given by the given value.

[0176] Aspect 1-17: The particulate material according to the first aspect of the present invention, wherein:

[0177] (i) P1 is in the range of 0.7 - 0.9;

[0178] (ii) is in the range of 0.6 to 0.8;

[0179] (iii) is at least 0.75;

[0180] (iv) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0181] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by the given value, and preferably not exceeding the value given by the given value.

[0182] Aspect 1-18: The particulate material according to the first aspect of the present invention, wherein:

[0183] (i) P1 is in the range of 0.8 - 1.2;

[0184] (ii) is in the range of 0.6 to 0.8;

[0185] (iii) is at least 0.8;

[0186] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0187] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by the given value, and preferably not exceeding the value given by the given value.

[0188] Aspect 1-19: The particulate material according to the first aspect of the present invention, wherein:

[0189] (i) P1 is in the range of 0.8 - 1.2;

[0190] (ii) is in the range of 0.6 to 0.8;

[0191] (iii) is at least 0.8;

[0192] (iv) The D50 The particle size is in the range of 1 to 12 μm;

[0193] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0194] Aspect 1-20: The particulate material according to the first aspect of the present invention, wherein:

[0195] (i) P1 is in the range of 0.8 - 1.2;

[0196] (ii) is in the range of 0.6 to 0.8;

[0197] (iii) is at least 0.8;

[0198] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0199] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0200] Aspect 1-21: The particulate material according to the first aspect of the present invention, wherein:

[0201] (i) P1 is in the range of 0.8 - 1.2;

[0202] (ii) is in the range of 0.6 to 0.8;

[0203] (iii) is at least 0.8;

[0204] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0205] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0206] Aspect 1-22: The particulate material according to the first aspect of the present invention, wherein:

[0207] (i) P1 is in the range of 0.8 - 1.2;

[0208] (ii) is in the range of 0.6 to 0.8;

[0209] (iii) is at least 0.75;

[0210] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0211] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0212] Aspect 1 - 23: The particulate material according to the first aspect of the present invention, wherein:

[0213] (i) P1 is in the range of 0.7 - 0.9;

[0214] (ii) is in the range of 0.6 to 0.8;

[0215] (iii) is at least 0.75;

[0216] (iv) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0217] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0218] Aspect 1 - 24: The particulate material according to the first aspect of the present invention, wherein:

[0219] (i) P1 is in the range of 0.8 - 1.2;

[0220] (ii) is in the range of 0.6 to 0.8;

[0221] (iii) is at least 0.8;

[0222] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0223] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by .

[0224] Aspect 1 - 25: The particulate material according to the first aspect of the present invention, wherein:

[0225] (i) P1 is in the range of 0.8 - 1.2;

[0226] (ii) in the range of 0.6 to 0.8;

[0227] (iii) is at least 0.8;

[0228] (iv) The D of the porous carbon framework 50 particle size is in the range of 1 to 12 μm;

[0229] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given value.

[0230] Aspect 1-26: The particulate material according to the first aspect of the present invention, wherein:

[0231] (i) P1 is in the range of 0.8 - 1.2;

[0232] (ii) in the range of 0.6 to 0.8;

[0233] (iii) is at least 0.8;

[0234] (iv) The D of the porous carbon framework 50 particle size is in the range of 2 to 8 μm;

[0235] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given value.

[0236] Aspect 1-27: The particulate material according to the first aspect of the present invention, wherein:

[0237] (i) P1 is in the range of 0.8 - 1.2;

[0238] (ii) in the range of 0.6 to 0.8;

[0239] (iii) is at least 0.8;

[0240] (iv) The D of the porous carbon framework 50 particle size is in the range of 2 to 8 μm;

[0241] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given value.

[0242] Aspect 1-28: The particulate material according to the first aspect of the present invention, wherein:

[0243] (i) P1 is in the range of 0.8 - 1.2;

[0244] (ii) is in the range of 0.6 to 0.8;

[0245] (iii) is at least 0.75;

[0246] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0247] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0248] Aspect 1-29: The particulate material according to the first aspect of the present invention, wherein:

[0249] (i) P1 is in the range of 0.7 - 0.9;

[0250] (ii) is in the range of 0.6 to 0.8;

[0251] (iii) is at least 0.75;

[0252] (iv) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0253] (v) The weight ratio of silicon to the porous carbon framework is at least the value given by and preferably does not exceed the value given by given.

[0254] Aspect 1-30: The particulate material according to the first aspect of the present invention, wherein:

[0255] (i) P1 is in the range of 0.7 - 1.4;

[0256] (ii) is in the range of 0.5 to 0.8;

[0257] (iii) is at least 0.8;

[0258] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0259] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.8 × P1]:1.

[0260] Aspect 1-31: The particulate material according to the first aspect of the present invention, wherein:

[0261] (i) P1 is in the range of 0.7 - 1.4;

[0262] (ii) is in the range of 0.5 to 0.8;

[0263] (iii) is at least 0.8;

[0264] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 12 μm;

[0265] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.8 × P1]:1.

[0266] Aspect 1-32: The particulate material according to the first aspect of the present invention, wherein:

[0267] (i) P1 is in the range of 0.7 - 1.4;

[0268] (ii) is in the range of 0.5 to 0.8;

[0269] (iii) is at least 0.8;

[0270] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0271] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.8 × P1]:1.

[0272] Aspect 1-33: The particulate material according to the first aspect of the present invention, wherein:

[0273] (i) P1 is in the range of 0.7 - 1.4;

[0274] (ii) is in the range of 0.5 to 0.8;

[0275] (iii) is at least 0.8;

[0276] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0277] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.8×P1]:1. Aspect 1-34: The particulate material according to the first aspect of the present invention, wherein:

[0278] (i) P1 is in the range of 0.7 - 1.4;

[0279] (ii) is in the range of 0.5 to 0.8;

[0280] (iii) is at least 0.75;

[0281] (iv) The D 50 particle size of the porous carbon framework is in the range of 2 to 8 μm;

[0282] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.8×P1]:1. Aspect 1-35: The particulate material according to the first aspect of the present invention, wherein:

[0283] (i) P1 is in the range of 0.7 - 0.9;

[0284] (ii) is in the range of 0.6 to 0.8;

[0285] (iii) is at least 0.75;

[0286] (iv) The D 50 particle size of the porous carbon framework is in the range of 3 to 6 μm;

[0287] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.8×P1]:1. Aspect 1-36: The particulate material according to the first aspect of the present invention, wherein:

[0288] (i) P1 is in the range of 0.8 - 1.2;

[0289] (ii) is in the range of 0.6 to 0.8;

[0290] (iii) is at least 0.8;

[0291] (iv) The D 50 particle size of the porous carbon framework is in the range of 1 to 18 μm;

[0292] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.6×P1]:1. Aspect 1-37: The particulate material according to the first aspect of the present invention, wherein:

[0293] (i) P1 is in the range of 0.8 - 1.2;

[0294] (ii) is in the range of 0.6 to 0.8;

[0295] (iii) is at least 0.8;

[0296] (iv) The D of the porous carbon framework 50 particle size is in the range of 1 to 12 μm;

[0297] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.6 × P1]:1. Aspect 1 - 38: The particulate material according to the first aspect of the present invention, wherein:

[0298] (i) P1 is in the range of 0.8 - 1.2;

[0299] (ii) is in the range of 0.6 to 0.8;

[0300] (iii) is at least 0.8;

[0301] (iv) The D of the porous carbon framework 50 particle size is in the range of 2 to 8 μm;

[0302] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.6 × P1]:1.

[0303] Aspect 1 - 39: The particulate material according to the first aspect of the present invention, wherein:

[0304] (i) P1 is in the range of 0.8 - 1.2;

[0305] (ii) is in the range of 0.6 to 0.8;

[0306] (iii) is at least 0.8;

[0307] (iv) The D of the porous carbon framework 50 particle size is in the range of 2 to 8 μm;

[0308] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2 × P1 to 1.6 × P1]:1.

[0309] Aspect 1 - 40: The particulate material according to the first aspect of the present invention, wherein:

[0310] (i) P1 is in the range of 0.8 - 1.2;

[0311] (ii) in the range of 0.6 to 0.8;

[0312] (iii) is at least 0.75;

[0313] (iv) D of the porous carbon framework 50 particle size is in the range of 2 to 8 μm;

[0314] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.6×P1]:1.

[0315] Aspect 1-41: The particulate material according to the first aspect of the present invention, wherein:

[0316] (i) P1 is in the range of 0.7 - 0.9;

[0317] (ii) is in the range of 0.6 to 0.8;

[0318] (iii) is at least 0.75;

[0319] (iv) D of the porous carbon framework 50 particle size is in the range of 3 to 6 μm;

[0320] (v) The weight ratio of silicon to the porous carbon framework is in the range of [1.2×P1 to 1.6×P1]:1.

[0321] 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 1-41 are also considered to be the preferred / optional features of aspects 1-1 to 1-41. Similarly, any features of the dependent claims within the scope of the above aspects 1-1 to 1-41 should also be construed as if those claims also depend on aspects 1-1 to 1-41.

[0322] 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. Preferably, the composition according to the second aspect of the present invention can be used to form an active layer of an electrode. Such a composition may be referred to herein as an "electrode composition". The particulate material used to prepare the composition of the second aspect of the present invention may have any one 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 1-41.

[0323] Accordingly, there is provided a composition comprising a 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.

[0324] The composition is preferably a mixed-type electrode composition comprising a particulate material according to the first aspect of the present invention and at least one additional particulate electroactive material.

[0325] The lithiation specific capacity of the at least one additional particulate electroactive material is preferably in the range of 100 to 600 mAh / g or 200 to 500 mAh / g. Examples of the additional particulate electroactive material include graphite, hard carbon, silicon, tin, 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.

[0326] 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 in the range of 10 to 40 μm, more preferably in the range of 10 to 30 μm, and most preferably in the range of 10 to 25 μm, such as in the range of 15 to 25 μm.

[0327] 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.

[0328] The D 90 particle size of the at least one additional particulate electroactive material is preferably not more than 100 μm, more preferably not more than 80 μm, more preferably not more than 60 μm, more preferably not more than 50 μm, and most preferably not more than 40 μm.

[0329] In a preferred embodiment, the at least one additional particulate electroactive material is selected from graphite and hard carbon particles, and the D 50 particle size of the graphite and hard carbon particles is in the range of 10 to 50 μm. Still more preferably, the at least one additional particulate electroactive material is selected from graphite particles, and the D 50 particle size of the graphite particles is in the range of 10 to 50 μm.

[0330] The at least one additional particulate electroactive material is preferably in the form of spheroidal particles having an average sphericity of at least 0.70, preferably 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, and most preferably at least 0.95.

[0331] The average aspect ratio of at least one additional particulate electroactive material is preferably less than 3:1, preferably not exceeding 2.5:1, more preferably not exceeding 2:1, more preferably not exceeding 1.8:1, more preferably not exceeding 1.6:1, more preferably not exceeding 1.4:1, and most preferably not exceeding 1.2:1.

[0332] The particulate material of the present invention can account for 0.5 to 80% by weight of the total dry weight of the electroactive material in the composition. For example, the particulate material of the present invention can account for 2 to 70% by weight, or 4 to 60% by weight, or 5 to 50% by weight of the total dry weight of the electroactive material in the composition.

[0333] In the case where the composition is a mixed electrode composition comprising at least one additional particulate electroactive material as described above, the electrode composition preferably comprises 1 to 20% by weight, or 2 to 15% by weight, or 2 to 10% by weight, or 2 to 5% by weight of the particulate material of the present invention based on the total dry weight of the composition.

[0334] Furthermore, in the case where the composition is a mixed electrode composition, the electrode composition preferably comprises 10 to 98% by weight, or 15 to 97% by weight, or 20 to 97% by weight, or 25 to 97% by weight of at least one additional particulate electroactive material based on the total dry weight of the composition.

[0335] The ratio of at least one additional particulate electroactive material to the particulate material of the present invention is suitably in the range of 50:50 to 99:1 by weight, more preferably in the range of 60:40 to 98:2 by weight, more preferably in the range of 70:30 to 97:3 by weight, more preferably in the range of 80:20 to 96:4 by weight, and most preferably in the range of 85:15 to 95:5 by weight.

[0336] At least one additional particulate electroactive material and the particulate material of the present invention preferably together account for at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, and most preferably at least 80% by weight of the total weight of the composition, such as at least 85% by weight, at least 90% by weight or at least 95% by weight.

[0337] The composition may optionally comprise a binder. The binder serves to adhere the composition to the current collector and maintain the integrity of the composition. Examples of binders that can be used according to the present invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginates and their alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The composition may 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.

[0338] 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 composition.

[0339] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as crosslinking promoters, coupling agents, and / or adhesion promoters.

[0340] The composition may 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 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.

[0341] One or more conductive additives may 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.

[0342] 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 1-41.

[0343] As used herein, the term current collector refers to any conductive substrate capable of carrying current to and from the electroactive particles in an 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 from 10 μm to 1 mm, such as from 20 to 500 μm, or from 50 to 200 μm.

[0344] Preferably, the electrode comprises an electrode composition as defined in the second aspect of the present invention in electrical contact with the current collector. The electrode composition can have any of the features described as preferred or optional in the second aspect of the present invention.

[0345] 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 to form an electrode layer on the surface of the current collector. Additional steps can 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 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.

[0346] 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.

[0347] 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 an 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 in the first aspect of the present invention and can be a particulate material according to any one of aspects 1-1 to 1-41.

[0348] 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.

[0349] 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.

[0350] 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, trimethoxymethane, sulfolane, methylsulfolane, and 1,3-dimethyl-2-imidazolidinone.

[0351] Examples of organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate esters polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups.

[0352] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts (such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4).

[0353] 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.

[0354] 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.

[0355] 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.

[0356] 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 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 1-41. Description of the Drawings

[0357] Figure 1 Illustrates the capacity retention rate of the battery in the examples during multiple cycles. Detailed Description

[0358] Example

[0359] The porous carbon skeletons C1 to C3 used in the following examples have the properties listed in Table 1.

[0360] Table 1

[0361]

[0362] Example 1 - Preparation of Composite Particles in a Fixed Bed Reactor

[0363] Silicon-carbon composite particles were prepared by placing 1.8 g of a particulate porous backbone having the properties listed in Table 1 on a stainless steel plate at a constant thickness of 1 mm along the length of the stainless steel plate. The plate was then placed into a 60 mm outside diameter stainless steel tube located in the hot zone of a retort furnace, which stainless steel tube had gas inlet and outlet lines. The furnace tube was purged with nitrogen at room temperature for 30 minutes, and then the sample temperature was raised to 450 - 500 °C. The nitrogen flow rate was adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube, and the nitrogen flow rate was maintained at that rate for 30 minutes. Then, the gas supply was switched from nitrogen to a mixture of silane in nitrogen (the concentration of silane being 1.25 vol%). The feeding of silane was carried out over a 5-hour period with the reactor pressure maintained at 101.3 kPa (1 atm). After the feeding was completed, the gas flow rate was kept constant while purging the silane from the furnace with nitrogen. The furnace was purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. Then the atmosphere was gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air from a compressed air supply.

[0364] The composite material prepared according to Example 1 has the properties listed in Table 2 below.

[0365] Example 2 - Preparation of Composite Particles in a Fluidized Bed Reactor

[0366] Silicon-carbon composite particles were prepared in a vertical bubbling fluidized bed reactor including a stainless steel cylindrical container with an 83 mm inner diameter. 250 g of carbon backbone particle powder having the properties listed in Table 1 were placed in the reactor. A low flow rate of an inert gas (nitrogen) was injected into the reactor to remove all oxygen. Then the reactor was heated to a reaction temperature of 400 to 500 °C, and a 4% v / v silane gas diluted with nitrogen was supplied to the bottom of the reactor at a flow rate sufficient to sulfide the carbon backbone particles for a duration sufficient to deposit the target mass of silicon. The reactor was purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. Then the atmosphere was gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air from a compressed air supply.

[0367] The composite material prepared according to Example 2 has the properties listed in Table 2 below.

[0368] Example 3 - Preparation of Composite Particles in a Rotary Tube Furnace Reactor

[0369] Silicon-carbon composite particles were prepared by placing 5 g of a particulate porous framework having the properties listed in Table 1 into a quartz tube having a bubble-shaped portion (11.4 cm in length). The quartz tube was then placed inside a rotary reactor tube furnace having a heating zone of approximately 15 x 20 cm (L x D), and gas inlet and outlet lines located approximately 29 cm from the hot zone of the furnace. The quartz tube inside the furnace was rotated clockwise by approximately 315°, and then counterclockwise, thereby continuously moving / rotating the porous carbon. The furnace tube was purged with nitrogen at room temperature for 30 minutes, and then the sample temperature was raised to 450 - 500 °C. The nitrogen flow rate was adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube, and the nitrogen flow rate was maintained at this rate for 30 minutes. Then, the gas supply was switched from nitrogen to a mixture of silane in nitrogen at a concentration of 1.25 vol%. The feeding of silane was carried out over a period of 5 hours while maintaining the reactor pressure at 101.3 kPa (1 atm). After the feeding was completed, the gas flow rate was kept constant while purging the silane from the furnace with nitrogen. The furnace was purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. Then, the atmosphere was gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air from a compressed air supply.

[0370] The composite material prepared according to Example 3 has the properties listed in Table 2 below.

[0371]

[0372] Example 4 - Preparation of Electrodes

[0373] A negative electrode coating (anode) was prepared from the materials of the samples and comparative samples given in Table 1 using the following method.

[0374] A test button cell was prepared using the negative electrode containing the silicon-based composite material prepared as described above. A dispersion of carbon black (conductive carbon) in a CMC binder was mixed in a Thinky TM mixer. The Si-C composite material was added to the mixture and mixed in a Thinky TM mixer for 30 min. Then, an SBR binder was added to provide a CMC:SBR ratio of 1:1, resulting in a slurry with a weight ratio of Si-C composite material:CMC / SBR:carbon black of 70%:16%:14%. The slurry was remixed in a Thinky TM mixer for 30 min, then coated onto a 10-μm-thick copper substrate (current collector) and dried at 50 °C for 10 minutes, and then further dried at 110 °C for 12 hours, thereby forming the negative electrode.

[0375] Example 5 - Manufacture of a Full Cell

[0376] A full button cell was prepared using a circular negative electrode with a radius of 0.8 cm cut from the electrode of Example 4, a porous polyethylene separator, and a nickel manganese cobalt (NMC532) positive electrode. The positive and negative electrodes were designed to form a balanced pair such that the capacity ratio of the positive electrode to the negative electrode was 0.9. Then, before sealing, an electrolyte was added to the cell, which contained 1 M LiPF6 in a 7:3 solution of EMC / FEC (ethyl methyl carbonate / fluoroethylene carbonate) containing 3 wt% ethylene carbonate.

[0377] The full button cell was 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 stand 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 stand 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 standing 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 required number of cycles. 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 rate value of each discharge capacity was 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)) × 100%. The values in Table 3 are the averages of 3 button cells for each sample. Figure 1 The capacity retention rate during multiple cycles is also illustrated in

[0378] Calculate the charge (lithiation) and discharge (delithiation) capacities per unit mass of the silicon-carbon composite material for each cycle, and calculate the capacity retention rate value of each discharge capacity as a percentage of the discharge capacity of the second cycle. The first cycle loss (FCL) is (1 – (first delithiation capacity / first lithiation capacity)) × 100%. The values in Table 3 are the averages of 3 button cells for each sample.

[0379] Table 3

[0380]

Claims

1. A particulate material comprising a plurality of composite particles, wherein the composite particles comprise: (a) a porous carbon framework comprising micropores and mesopores, wherein (i) the total pore volume of the micropores and mesopores measured by gas adsorption is P1 cm 3 / g, where P1 represents a natural number with a value of at least 0.6, (ii) based on the total volume of the micropores and mesopores, the volume fraction of the micropores is in the range of 0.1 to 0.9; (iii) based on the total volume of the micropores and mesopores, the volume fraction of pores with a pore diameter not exceeding 20 nm is at least 0.75, and (iv) the D 50 particle size of the porous carbon framework is less than 20 μm; (b) a plurality of nano-sized elemental silicon domains located within the micropores and / or mesopores of the porous carbon framework; wherein the weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [1×P1 to 2.2×P1]:

1.

2. The particulate material according to claim 1, wherein the porous carbon framework has a unimodal pore size distribution.

3. The particulate material according to claim 1, wherein the porous carbon framework has a bimodal or multimodal pore size distribution.

4. The particulate material according to any one of the preceding claims, wherein the porous carbon framework comprises macropores with a diameter in the range of greater than 50 nm to 100 nm, and the total volume of the macropores measured by mercury intrusion porosimetry is P2 cm 3 / g, where P2 does not exceed 0.2×P1, or does not exceed 0.1×P1, or does not exceed 0.05×P1, or does not exceed 0.02×P1, or does not exceed 0.01×P1, or does not exceed 0.005×P1.

5. The particulate material according to any one of the preceding claims, wherein the D 50 particle size of the composite particles is at least 0.5 μm, at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm.

6. The particulate material according to any one of the preceding claims, wherein the D 50 particle size of the composite particles does not exceed 18 μm, or does not exceed 16 μm, or does not exceed 14 μm, or does not exceed 12 μm, or does not exceed 10 μm, or does not exceed 9 μm, or does not exceed 8 μm, or does not exceed 7 μm, or does not exceed 6 μm, or does not exceed 5 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 as claimed in claim 8; (ii) A cathode, the cathode comprising 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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