Method for preparing electroactive material for metal ion battery

Abstract

The present disclosure relates to methods for preparing particulate materials with high electrochemical capacity suitable for use as anode active materials in rechargeable metal ion batteries. In one aspect, the disclosure provides a method for preparing a particulate material comprising a plurality of composite particles. The method comprises: providing a particulate porous carbon skeleton comprising micropores and / or mesopores, wherein the porous carbon skeleton has a D50 particle size of at least 20 [mu] m; depositing an electroactive material selected from the group consisting of silicon and alloys thereof into micropores and / or mesopores of the porous carbon backbone using a chemical vapor infiltration process in a fluidized bed reactor to provide intermediate particles; and comminuting the intermediate particles to provide the composite particles.

Description

[0001] This application is a divisional application of a Chinese invention application with an international filing date of December 20, 2019, an international application number of PCT / GB2019 / 053676, an application number for entering the Chinese national phase of 201980092696.6, and an invention title of "Method for preparing electroactive materials for metal ion batteries". Technical Field

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

[0003] Rechargeable metal ion batteries are widely used in portable electronic devices such as mobile phones and laptop computers, and are increasingly applied to electric vehicles or hybrid vehicles. A rechargeable metal ion battery generally includes an anode layer, a cathode layer, an electrolyte for transporting metal ions between the anode layer and the cathode layer, and an electrically insulating porous separator disposed between the anode and the cathode. The cathode generally includes a metal current collector having a metal oxide-based composite material layer containing metal particles, and the anode generally includes a metal current collector having an electroactive material layer, where the electroactive material is defined herein as a material capable of intercalating and releasing metal ions during charging and discharging of the battery. For the sake of clarity, the terms "cathode" and "anode" are used herein in the following sense: the battery is connected across a load such that the cathode is the positive electrode and the anode is the negative electrode. When charging a metal ion battery, 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" herein refers 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 charging a graphite anode, lithium intercalates between the graphite layers to form a material with an empirical formula of Li x C 6 (where x is greater than 0 and less than or equal to 1). Thus, the maximum theoretical capacity of graphite in a lithium ion battery is 372 mAh / g, and the actual capacity is slightly lower (about 340 to 360 mAh / g). Other materials such as silicon, tin, and germanium can intercalate lithium at significantly higher capacities compared to graphite, but have not been widely commercially adopted due to difficulty in maintaining sufficient capacity during multiple charge / discharge cycles.

[0005] In particular, silicon is considered a promising graphite alternative for manufacturing rechargeable metal-ion batteries with high weight and volume capacities due to its very high lithium capacity (see, e.g., 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 Si 4 count). However, the use of silicon as an anode material is complicated due to large volume changes during charging and discharging.

[0006] Lithium insertion into bulk silicon results in a substantial increase in the volume of the silicon material, with the volume of the silicon material increasing by up to 400% of its original volume when 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 silicon particles during delithiation can result in a loss of electrical contact between the anode material and the current collector. Another difficulty is that the solid electrolyte interface (SEI) layer formed on the silicon surface does not have sufficient mechanical tolerance to accommodate the expansion and contraction of silicon. As a result, the newly exposed silicon surface 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 continuous charge and discharge cycles.

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

[0008] It is also generally known that electroactive materials such as silicon can be deposited within the pores of a porous support material such as an activated carbon material. These composite materials provide some beneficial charge-discharge properties of nano-sized silicon particles while avoiding the handling difficulties of nano-particles. For example, Guo et al. (Journal of Materials Chemistry A, 2013, pages 14075-14079) disclose a silicon-carbon composite material in which a porous carbon substrate provides a conductive framework and silicon nanoparticles are deposited in a uniformly distributed pore structure of the substrate. SEI formation during the initial charge cycle is limited by the remaining pore volume, such that the remaining silicon is not exposed to the electrolyte during subsequent charge cycles. It is known that the composite material has 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.

[0009] JP2003100284 discloses an active material that includes a carbon-based support having small pores branching from some larger pores. The electroactive material (such as silicon) is optionally located on the walls of both the large pores and the small pores, as well as on the outer surface of the carbon-based support.

[0010] It has been observed that the performance of a composite material comprising a porous carbon framework and an electroactive material such as silicon located within the porous carbon framework can be optimized by using a porous carbon framework having a specific pore structure and a controlled ratio of electroactive material to available pore volume. It is believed that a low particle size (e.g., D less than 20 μm) is beneficial for the desired end use of these composite materials in metal ion batteries. However, it is difficult to prepare these composite materials in an efficient and consistent manner, especially for large-scale production for commercial use. It is difficult to control the deposition of the electroactive material such that it is deposited in the desired locations within the pores of the porous carbon framework. It is also difficult to control the deposition when preparing a product having the desired low particle size. The present invention aims to solve this problem. 50 ) is beneficial for the desired end use of these composite materials in metal ion batteries. However, it is difficult to prepare these composite materials in an efficient and consistent manner, especially for large-scale production for commercial use. It is difficult to control the deposition of the electroactive material such that it is deposited in the desired locations within the pores of the porous carbon framework. It is also difficult to control the deposition when preparing a product having the desired low particle size. The present invention aims to solve this problem.

[0011] Chemical vapor infiltration (CVI) is a process of infiltrating a porous substrate material with an additional phase using reactive gaseous precursors. The porous substrate is placed on a perforated metal plate, and a mixture of a carrier gas and a gaseous precursor is passed through the porous substrate maintained at a high temperature. The gaseous precursor undergoes a chemical reaction within the porous structure of the substrate material at the high temperature and is deposited on the inner surface of the pore space. The CVI process increases the density of the porous substrate material. CVI is particularly useful because it causes very little damage to the geometry of the porous substrate. Additionally, a high degree of uniformity within the substrate can be achieved by controlling the purity of the reactive gaseous precursor and the pressure and temperature of infiltration.

[0012] It has been determined that chemical vapor infiltration (CVI) can be used to deposit electroactive materials into microporous and / or mesoporous carbon materials having a particle size less than 20 μm to obtain composite materials having desirable electrochemical properties. In the present invention, CVI particularly refers to the process in which a gaseous precursor of an electroactive material such as silicon is thermally decomposed on the surface to deposit the electroactive material in elemental form at the surface and form gaseous by-products, which allows deposition onto the inner surface, particularly the surface of the pore walls.

[0013] Generally, the low diffusivity of the gaseous silicon precursors used in the CVI of silicon compounds into microporous and / or mesoporous systems or other gaseous precursors for other electroactive materials means that a deposition scheme limited by kinetics (surface reaction limited) must be used. However, from a processing perspective, this adds many complexities. A major problem is that in large volume samples and reactor systems for high-throughput / high-volume and continuous processing, it is difficult to ensure the high thermal uniformity and mass transfer uniformity required to maintain a uniform deposition rate with respect to reactor position, process time, and particle pore system position. Therefore, it is difficult to use CVI to deposit electroactive materials into the pores of a porous carbon framework on a commercially available scale. It is believed that there is no general commercial manufacturing route that uses CVI as a deposition technique specifically for powders in the size range less than 20 μm.

[0014] A fluidized bed reactor (FBR) can be used to perform CVI. FBRs have a variety of applications in industry. They provide a very efficient means of gas-solid contact while providing a uniform temperature distribution in the bed. This is mainly achieved by using an air flow to fluidize the particles and by bringing all surfaces into contact with the reactant gas. FBRs address many of the above mass transfer and heat transfer problems. When fluidization is achieved, excellent solid-solid and gas-solid mixing is observed, particularly when compared to alternative powder processing schemes for performing CVI such as fixed beds and rotary furnaces.

[0015] The fluidization behavior of particles is classified into a group according to the size and density of the particles. These groups are called Geldart group A, B, C, and D materials. Group A, B, and D materials can be fluidized with / without bubble and slugging behavior. However, Geldart C includes low-size, low-density materials, and they may be difficult to fluidize due to the cohesion resulting from their small size. Low particle size carbon powders can be considered Geldart group C materials.

[0016] As described in Vahlas et al., Principles and applications of CVD powder technology, Materials Science and Engineering R 53 (2006) 1–72, fluidized bed reactor - chemical vapor deposition (CVD) (including CVI) has been used to deposit a variety of catalytic metals and non - metals on porous and non - porous materials.

[0017] However, carbon powders with a size less than 20 μm tend to form agglomerates when used in a fluidized bed reactor due to the strength of the inter - particle cohesive forces at this length scale. This is a problem because fluidization may occur only as large millimeter - sized agglomerates rather than individual particle fluidization, leading to related problems associated with the mass transfer rate within the agglomerates. Additionally, there may be no fluidization of the carbon powder, and instead, channeling ("rat - holing") occurs because the locally applied shear force exerted by the gas flow is insufficient to break the cohesive forces between the particles (i.e., the gas finds a path around the powder bed rather than passing through the powder bed). For these reasons, fluidized bed reactors have been considered unsuitable for processes involving carbon powders with a size less than 20 μm. SUMMARY OF THE INVENTION

[0018] The present invention uses chemical vapor infiltration into a fluidized porous carbon powder, enabling control of the kinetic and thermodynamic conditions of the infiltration reaction and ensuring that each porous carbon particle experiences a similar chemical and thermal environment. Substantially, the present invention treats individual micron - sized powders as micro - infiltration substrates, reducing the characteristic length scale of precursor diffusion and reaction and facilitating the transition to a continuous process for mass production.

[0019] In a first aspect, the present invention provides a method for preparing a particulate material comprising a plurality of composite particles, the method comprising:

[0020] (a) providing a particulate porous carbon framework comprising micropores and / or mesopores, wherein the D 50 particle size of the porous carbon framework is at least 20 μm;

[0021] (b) depositing an electroactive material selected from silicon, tin, aluminum, germanium, and their alloys into the micropores and / or mesopores of the porous carbon framework in a fluidized bed reactor using chemical vapor infiltration to provide intermediate particles; and

[0022] (c) pulverizing the intermediate particles to provide the composite particles.

[0023] Accordingly, the method of the present invention utilizes the advantages of CVI to deposit electroactive materials into the pores of a porous carbon framework, thereby providing functional nanostructures comprising electroactive materials. The method also utilizes the advantages of performing CVI using FBR. The method also avoids the difficulties of using FBR with low-grit carbon powders, as the method uses a particulate porous carbon framework with a particle size of at least 20 μm as a starting material. The milling step means that the method can be used to provide composite particles with a reduced particle size compared to the starting material, which is considered useful for the desired end use in a metal ion battery. In particular, composite particles in these size ranges are ideally suited for use as the composite film negative electrode (or "anode") in a metal ion battery due to their dispersibility in a slurry, their structural robustness, and their capacity retention over repeated charge-discharge cycles. The thickness of such a composite film is generally less than 100 µm, or less than 50 µm, and smaller particle sizes also help to achieve a denser film with a uniform thickness. Accordingly, the method of the present invention provides an effective method for preparing composite particles suitable for large-scale commercial use. 50 Using CVI in an FBR to prepare intermediate composite particles and then milling the intermediate particles may seem counterintuitive. In particular, the milling step may be considered to damage the functional nanostructures of the intermediate particles obtained from the CVI process, i.e., the electroactive materials deposited within the pores of the carbon framework. However, the inventors have found that milling can be performed without a significant level of damage due to the relative μm-length scale of the fracture compared to the nm-length scale of the functional units of the composite particles. Since the carbon framework includes micropores and / or mesopores, the desired properties are retained in the product upon milling. Detailed Description

[0024] The method of the present invention enables the selection of the properties of the porous carbon framework material to provide a final product with a set of desired properties. For example, since the milling step can be performed without significant damage to the pore structure, selecting a porous carbon framework with a specific pore structure enables the preparation of a product with a specific micropore and / or mesopore structure.

[0025] The electroactive material can be silicon or tin. Preferably, the electroactive material is silicon. The electroactive material can optionally contain a small amount of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, or nitrogen. When silicon is the electroactive material, silicon can also be doped with a small amount of one or more other electroactive materials such as tin, aluminum, and germanium. Preferably, the dopant is present in a total amount of no more than 2 wt% based on the total amount of the electroactive material and one or more dopants.

[0026]

[0027] ​To avoid ambiguity, as used herein, the term "particle size" refers to the equivalent spherical diameter (ESD), i.e., the diameter of a sphere having the same volume as a given particle, where the particle volume is understood to include the volume of any internal pores of 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% by volume of the particle population is below a certain diameter. As used herein, the terms "D 10 " and "D 10 particle size" refer to the 10th percentile volume-based median particle size, i.e., the diameter at which 10% by volume of the particle population is below a certain diameter. As used herein, the terms "D 90 " and "D 90 particle size" refer to the 90th percentile volume-based median particle size, i.e., the diameter at which 90% by volume of the particle population is below a certain diameter.

[0028] The term "D n " used herein to define the particle size distribution should be distinguished from the term "PD n " used herein to define the pore size distribution. As used herein, the general term "PD n pore size" refers to the nth percentile volume-based pore size based on the total volume of micropores and mesopores. For example, as used herein, the term "D 50 pore size" refers to the pore size at which 50% of the total micropore and mesopore volume (denoted by P 1 ) is lower than a certain pore size.

[0029] To avoid ambiguity, for the determination of the PD n value, any macropore volume (pore size greater than 50 nm) is not considered.

[0030] Particle size and particle size distribution can be determined by conventional laser diffraction techniques in accordance with ISO 13320:2009. Laser diffraction relies on the principle that particles will scatter light at an angle that varies according to the size of the particle, and multiple particles will produce a scattered light pattern defined by the intensity and angle that can be correlated with the particle size distribution. A variety of commercially available laser diffraction instruments are available for the rapid and reliable determination of particle size distribution. Unless otherwise stated, the particle size distribution measurements specified or reported herein are made using a conventional Malvern Mastersizer TM 3000 particle size analyzer from Malvern Instruments. Malvern Mastersizer TMThe 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 intensity measured at different angles is processed by computer using standard theoretical principles to determine the particle 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 particle size distribution.

[0031] Porous carbon framework

[0032] D of the porous carbon framework 50 The particle size is at least 20 μm. In this way, the porous carbon framework can be easily used in the FBR. Optionally, the D of the porous carbon framework 50 The particle size ranges from 20 to 1000 μm, 30 to 500 μm, or 60 to 150 μm. Optionally, the D of the porous carbon framework 50 The particle size is at least 30 μm, at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm, or at least 80 μm. Optionally, the D of the porous carbon framework 50 The particle size does not exceed 1000 μm, or does not exceed 500 μm, or does not exceed 250 μm, or does not exceed 150 μm.

[0033] Optionally, the D of the porous carbon framework 10 The particle size is at least 5 μm, at least 15 μm, at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm. By maintaining the D 10 particle size above these values, the presence of a large number of carbon frameworks with small particle sizes that may not be suitable for the FBR is advantageously avoided.

[0034] Optionally, the D of the porous carbon framework 90 The particle size does not exceed 1,500 μm, or does not exceed 1,000 μm, or does not exceed 750 μm, or does not exceed 500 μm, or does not exceed 200 μm. Optionally, the D of the porous carbon framework 98 The particle size does not exceed 1,550 μm, or does not exceed 1,050 μm, or does not exceed 800 μm, or does not exceed 550 μm, or does not exceed 250 μm. By maintaining the D 90 and / or D 98 particle size below these values, the presence of a large number of carbon frameworks with large particle sizes that may not be suitable for CVI is advantageously avoided.

[0035] For example, the porous carbon framework may have a D of at least 15 μm 10 particle size, a D of at least 20 μm 50 particle size, and a D of not more than 200 μm 90 particle size. The porous carbon framework may have a D of at least 5 μm 10 particle size, a D in the range of 20 to 250 μm 50 particle size, a D of not more than 750 μm 90 particle size, and a D of not more than 1,000 μm 98 particle size. The porous carbon framework may have a D of at least 5 μm 10 particle size, a D in the range of 20 to 200 μm 50 particle size, a D of not more than 500 μm 90 particle size, and a D of not more than 800 μm 98 particle size. The porous carbon framework may have a D of at least 40 μm 10 particle size, a D in the range of 60 to 150 μm 50 particle size, and a D of not more than 200 μm 90 particle size, and a D of not more than 250 μm 98 particle size.

[0036] The porous carbon framework preferably has a narrow span of size distribution. For example, the span of 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, a uniform deposition of the electroactive material into the pores of the carbon framework can be achieved more easily.

[0037] The porous carbon framework suitably includes a three-dimensional interconnected open pore network, which includes a combination of micropores and / or mesopores and optionally a small volume of macropores. According to the 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 to 50 nm, and the term "macropore" is used to refer to pores with a diameter greater than 50 nm.

[0038] The volumes of micropores, mesopores, and macropores in the porous carbon framework mentioned herein, as well as any mention of the distribution of pore volume within the porous carbon framework, refer to the internal pore volume of the porous carbon framework alone (i.e., in the absence of any electroactive material or other material that occupies some or all of the pore volume).

[0039] The volume fraction of micropores (based on the total volume of micropores and mesopores) is denoted by the symbol φ ais denoted, and the volume fraction of mesopores (based on the total volume of micropores and mesopores) is denoted by the symbol φ b is denoted, and thus it will be understood that φ a + φ b = 1.

[0040] The pore volume of the porous carbon framework in the form of micropores and / or mesopores is characteristic. The total volume of micropores and mesopores (i.e., the total pore volume in the range from 0 to 50 nm) may be referred to herein as P 1 cm 3 / g, where P 1 denotes a dimensionless natural number. The value of P 1 is also used to relate the available pore volume in the porous carbon framework to the weight ratio of the electroactive material to the porous carbon framework in the final product.

[0041] To avoid doubt, as used herein, P 1 refers to the pore volume of the porous carbon framework when measured separately, i.e., the pore volume of the porous carbon framework in the absence of silicon or any other material occupying the pores of the porous carbon framework. Similarly, the volumes of micropores, mesopores, and macropores in the porous carbon framework mentioned herein and any mention of the distribution of the pore volume within the porous carbon framework refer to the internal pore volume of the porous carbon framework alone (i.e., in the absence of any silicon or other material occupying the pore volume).

[0042] P 1 The value of can be in the range from 0.4 to 2.5. Thus, the pore volume of the porous carbon framework can be at least 0.4 cm 3 / g and at most 2.5 cm 3 / g.

[0043] P 1 The value of can be in the range from 0.4 to 0.6. This corresponds to a low pore volume in the form of micropores and / or mesopores.

[0044] Alternatively, the value of P 1 can be at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95, or at least 1, or at least 1.05, or at least 1.1, or at least 1.2. It is advantageous to use a highly porous carbon framework because it enables a larger 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 the electroactive material without causing the porous carbon framework to break or otherwise deteriorate.

[0045] P 1The value can be no more than 2.5, or no more than 2.2, or no more than 2, or no more than 1.8, or no more than 1.6, or no more than 1.5, or no more than 1.4, or no more than 1.3, or no more than 1.2. The internal pore volume of the porous carbon framework is suitably limited to a value at which the increased brittleness of the porous carbon framework outweighs the advantage of the increased pore volume for accommodating a larger amount of electroactive material.

[0046] P 1 The value can be in the range of 0.4 to 2.5, or in the range of 0.6 to 2.5, or in the range of 0.7 to 2, or in the range of 0.7 to 1.2.

[0047] The volume fraction (φ a ) of the micropores can be at least 0.1, or in the range of 0.1 to 0.9. Preferably, φ a is greater than 0.5, more preferably greater than 0.6, more preferably greater than 0.7, more preferably greater than 0.8.

[0048] A small fraction of pores with diameters in the larger mesopore range can advantageously facilitate the approach of the electrolyte to the electroactive material in the final product. Thus, pores with diameters in the range of 10 to 50 nm (i.e., larger mesopores) can optionally account for at least 1%, at least 2%, at least 5% or at least 10% of the total micropore and mesopore volume of the porous carbon framework.

[0049] 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 larger diameters provides the advantage of efficient ion transport from the porous network to the electroactive material. Thus, the composite particles prepared from the porous carbon framework have high ion diffusivity and thus improved rate performance.

[0050] Suitably, the bimodal or multimodal pore size distribution includes a peak pore size in the micropore range and a peak pore size in the mesopore size range, which differ from each other by a factor of 5 to 20, more preferably by 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. The porous carbon framework can have a bimodal pore size distribution that includes a peak at a pore size of 2 nm and a peak at a pore size of 20 nm. The porous carbon framework can have a bimodal pore size distribution that includes a peak at a pore size of 1.2 nm and a peak at a pore size of 12 nm.

[0051] The standard method described in ISO 15901-2 and ISO 15901-3 was used to perform nitrogen adsorption at 77 K down to 10 -6 Relative pressure p / p 0 , using quenched solid density functional theory (QSDFT) to determine the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores. Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases until a saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them enables the determination of pore volume and pore size distribution. Suitable instruments for measuring pore volume and pore size distribution by nitrogen adsorption include TriStar II and TriStar II Plus porosity analyzers (which are available from Micromeritics Instrument Corporation in the United States), and Autosorb IQ porosity analyzer (which is available from Quantachrome Instruments).

[0052] Nitrogen adsorption is effective for measuring the pore volume and pore size distribution of pores with a diameter of up to 50 nm, but is less reliable for pores with much larger diameters. For the purposes of the present invention, therefore, only pores with a diameter of up to 50 nm (including 50 nm) are used to determine the pore volume and pore size distribution using nitrogen adsorption. As described above, P is determined by considering only pores with a diameter of up to 50 nm (including 50 nm) (i.e., only micropores and mesopores). 1 The value of PD is also determined relative to the total volume of micropores and mesopores alone. n and φ a ,φ b ,φ 20 ,φ 10 and φ 5 (discussed below).

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

[0054] To avoid ambiguity, P 2 The value only considers pores with diameters from greater than 50 nm to a maximum of 100 nm (including 100 nm), i.e., it only includes the volume of macropores with a maximum diameter of 100 nm. To determine P 2 The value, any pore volume of pore sizes below 50 nm measured by mercury intrusion porosimetry is not considered. For the purposes of the present invention, the pore volume in the case of above 100 nm measured by mercury intrusion porosimetry is assumed to be the interparticle porosity and is also not considered when determining P 2 The value. As described above, nitrogen adsorption is used to characterize mesopores and micropores.

[0055] 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 a sample of the material immersed in mercury. The pressure required to force mercury into the pores of the sample is inversely proportional to the size of the pores. The values obtained by mercury intrusion porosimetry reported herein are obtained according to ASTM UOP578-11, where for mercury at room temperature, the surface tension γ is 480 mN / m and the contact angle φ is 140°. The density of mercury at room temperature is 13.5462 g / cm 3 . A variety of high-precision mercury intrusion porosimetry instruments are commercially available, such as the automated mercury porosimeter of the AutoPore IV series, which can be obtained from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury intrusion porosimetry, reference can be made to P.A. Webb and C. Orr, "Analytical Methods in Fine Particle Technology", 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0056] Compared with the volume of micropores and mesopores (and thus the value of P 1 ), the volume of macropores (and thus the value of P 2 ) is preferably smaller. Although a small fraction of macropores can be useful for facilitating the entry of electrolyte into the pore network, the advantages of the present invention are essentially obtained by accommodating silicon in micropores and smaller mesopores.

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

[0058] In a preferred embodiment, P 2 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 promote the proximity of the electrolyte to the electroactive material in the final product.

[0059] 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 sorting, where the smaller pores branch from the larger pores.

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

[0061] The porous carbon framework can include crystalline carbon, amorphous carbon, or a mixture of amorphous 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.

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

[0063] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are found mainly in polyaromatic domains with sizes in the range of 5 - 200 nm and in the sp 2 hybridization state (triple bond). Compared to hard carbon, the polyaromatic domains in soft carbon are associated by intermolecular forces rather than cross-linked using chemical bonds. This means that they will graphitize at high temperatures. The porous carbon framework preferably contains at least 50% sp 2 hybrid carbon (measured by XPS). For example, the porous carbon framework may suitably contain 50% to 98% sp 2 hybrid carbon, 55% to 95% sp 2 hybrid carbon, 60% to 90% sp 2 hybrid carbon, or 70% to 85% sp 2 hybrid carbon.

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

[0065] The porous carbon framework can be subjected to a chemical or gas activation process to increase the volume of mesopores and micropores. Suitable activation processes include contacting the pyrolytic carbon with one or more of oxygen, steam, CO, CO 2 and KOH at a temperature in the range of 600 to 1000 °C.

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

[0067] The BET surface area of the porous carbon framework is preferably at least 750 m 2 / g, or at least 1,000 m 2 / g, or at least 1,250 m 2 / g, or at least 1,500 m 2 / g. As used herein, the term "BET surface area" shall be considered to refer to the surface area per unit mass calculated from the measurement 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 skeleton does not exceed 4,000 m 2 / g, or does not exceed 3,500 m 2 / g, or does not exceed 3,250 m 2 / g, or does not exceed 3,000 m 2 / g.

[0068] As discussed above, the inventors have recognized that since the carbon skeleton includes micropores and / or mesopores, the desired properties are retained in the product upon comminution. Thus, the present invention can enable: by controlling the pore structure of the porous carbon skeleton, the desired properties of the composite particle product can be targeted. Some types of porous carbon skeletons are discussed below and can be used in the present invention to provide some types of composite particle products. It is to be understood that the characteristics of the types of porous carbon skeletons discussed below should be considered in combination with the characteristics of the porous carbon skeletons discussed above such as particle size.

[0069] Porous carbon skeleton 1

[0070] Porous carbon skeleton 1 is characterized by a P 1 value of at least 0.5 and a PD 50 pore diameter not exceeding 5 nm.

[0071] Preferably, the P 1 value is at least 0.75, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95, or at least 1, such as at least 1.05, or at least 1.1, or at least 1.15, or at least 1.2.

[0072] The P 1 value can be at most 2.5. Preferably, the P 1 value can not exceed 2.2, or not exceed 2, or not exceed 1.8, or not exceed 1.6, or not exceed 1.5, or not exceed 1.4, or not exceed 1.3, or not exceed 1.2, or not exceed 1.1, or not exceed 1.0, or not exceed 0.9. More preferably, the P 1 value does not exceed 1.2, or not exceed 1.1, or not exceed 1.0, or not exceed 0.9.

[0073] Preferably, the P 1The value can be, for example, in the range of 0.7 to 1.5, or in the range of 0.75 to 1.4, or in the range of 0.7 to 1.3, or in the range of 0.75 to 1.3, or in the range of 0.7 to 1.2, or in the range of 0.75 to 1.2, or in the range of 0.7 to 1, or in the range of 0.75 to 1, or in the range of 0.7 to 0.9, or in the range of 0.75 to 0.9.

[0074] PD of the porous carbon framework 1 50 The pore diameter is preferably not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm. Preferably, the PD of the porous carbon framework 50 The pore diameter is at least 0.8 nm, or at least 1 nm, or at least 1.2 nm. Therefore, it is particularly preferred that more than 50% of the total micropore and mesopore volume is in the form of micropores.

[0075] More preferably, at least 80% of the total micropore and mesopore volume of the porous carbon framework 1 is in the form of pores with a diameter not exceeding 5 nm. Therefore, the PD of the porous carbon framework 1 80 The pore diameter is preferably not more than 5 nm, or not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm.

[0076] The volume of the larger mesopores in the porous carbon framework 1 is preferably limited so that the PD 90 The pore diameter does not exceed 20 nm, or not more than 15 nm, or not more than 12 nm, or not more than 10 nm, or not more than 8 nm, or not more than 6 nm, or not more than 5 nm, or not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm.

[0077] Preferably, the PD 95 The pore diameter does not exceed 20 nm, or not more than 15 nm, or not more than 12 nm, or not more than 10 nm.

[0078] Porous carbon framework 2

[0079] Porous carbon framework 2 is characterized by a P value of at least 0.6 1 and a micropore volume fraction φ in the range of 0.1 to 0.9 a .

[0080] Porous carbon framework 2 is further characterized by a pore volume that is substantially biased 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 φ 20 and the symbol φ10 and φ 5 are respectively used to define the corresponding volume fractions of pores with diameters not exceeding 10 nm and not exceeding 5 nm.

[0081] Preferably, P 1 has a value of at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95, or at least 1. Optionally, P 1 can be at least 1.05, or at least 1.1, or at least 1.15, or at least 1.2. P 1 has a value that can be at most 2.2. More preferably, P 1 has a value not exceeding 2.2, or not exceeding 1.8, or not exceeding 1.6, or not exceeding 1.5, or not exceeding 1.4, or not exceeding 1.3, or not exceeding 1.2.

[0082] Preferably, P 1 has a value that 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.

[0083] φ a has a value that is preferably in the range of 0.15 to 0.85, more preferably in the range of 0.2 to 0.8. In some embodiments, φ a is preferably in the range of 0.45 to 0.85, or in the range of 0.5 to 0.8, or in the range of 0.6 to 0.8, thereby particularly taking advantage of the high capacity retention rate of the very fine electroactive material nanostructures located within the micropores. In other cases, φ a is preferably in the range of 0.2 to 0.5, or in the range of 0.3 to 0.5, thereby particularly taking advantage of the high opportunity for electroactive material loading.

[0084] Preferably, φ 20 is at least 0.8, more preferably at least 0.85, even more preferably at least 0.9.

[0085] Preferably, based on the total volume of micropores and mesopores, φ 10 is at least 0.75, or at least 0.8, or at least 0.85. Preferably, based on the total volume of micropores and mesopores, φ 5 is at least 0.75, or at least 0.8, or at least 0.85. Thus, at least 75% of the total micropore and mesopore volume of the porous carbon framework is preferably in the form of pores with a diameter of no more than 10 nm and more preferably no more than 5 nm.

[0086] Porous carbon framework 3

[0087] The porous carbon framework 3 is characterized by a P 1 value of at least 0.6 and a PD 50 pore diameter of no more than 2 nm.

[0088] Preferably, the P 1 value is at least 0.75, or at least 0.8, or at least 0.85. Optionally, the P 1 can be at least 0.9, or at least 0.95, or at least 1, or at least 1.05, or at least 1.1, or at least 1.15, or at least 1.2. Generally, the P 1 value can be no more than 2.5. More preferably, the P 1 value is no more than 2.4, or no more than 2.2, or no more than 2, or no more than 1.8, or no more than 1.6, or no more than 1.5, or no more than 1.4, or no more than 1.3, or no more than 1.2, or no more than 1.1, or no more than 1.0, or no more than 0.9.

[0089] Preferably, the P 1 value can be, for example, in the range of 0.6 to 1.4, or in the range of 0.65 to 1.4, or in the range of 0.7 to 1.4, or in the range of 0.75 to 1.4, or in the range of 0.7 to 1.3, or in the range of 0.75 to 1.3, or in the range of 0.7 to 1.2, or in the range of 0.75 to 1.2, or in the range of 0.7 to 1, or in the range of 0.75 to 1, or in the range of 0.7 to 0.9, or in the range of 0.75 to 0.9.

[0090] The PD 50 pore diameter of the porous carbon framework 3 is preferably no more than 1.8 nm, or no more than 1.6 nm, or no more than 1.4 nm, or no more than 1.2 nm, or no more than 1 nm.

[0091] Preferably, at least 80% of the total micropore and mesopore volume of the porous carbon framework 3 is in the form of pores with a diameter of no more than 5 nm. Thus, the PD 80The pore diameter is preferably not more than 5 nm, or not more than 4.5 nm, or not more than 4 nm, or not more than 3.5 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2.2 nm, or not more than 2 nm, or not more than 1.8 nm, or not more than 1.6 nm.

[0092] PD 90 The pore diameter is preferably not more than 10 nm, not more than 8 nm, or not more than 6 nm, or not more than 5 nm, or not more than 4nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm.

[0093] Preferably, PD 95 The pore diameter is not more than 15 nm, or not more than 12 nm, or not more than 10 nm.

[0094] CVI / FBR

[0095] A laboratory-scale FBR can be used to contact a porous carbon framework with a gas mixture of a gaseous precursor containing an electroactive material (such as silane) to deposit the electroactive material into the micropores and / or mesopores of the framework via CVI. Nitrogen can be used as the inert fluidizing gas, but other inert gases such as argon, hydrogen or helium can also be used. It will be understood that in the method of the present invention, the porous carbon framework is fluidized in the FBR.

[0096] The method of the present invention uses CVI of a gaseous precursor of an electroactive material into the pore structure of a porous carbon framework. Preferably, the gaseous precursor is a silicon-containing gas.

[0097] Suitable silicon-containing precursors include silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), tetrasilane (Si 4 H 10 ), or chlorosilane such as trichlorosilane (HSiCl 3 ), or methylchlorosilane such as methyltrichlorosilane (CH 3 SiCl 3 ), or dimethyldichlorosilane ((CH 3 ) 2 SiCl 2 ). Preferably, the silicon-containing precursor is silane.

[0098] The CVI process can also employ a gaseous precursor of a dopant material to deposit a doped electroactive material into the micropores and / or mesopores of a porous carbon framework. When the dopant is boron, suitable precursors include borane (BH 3) Triisopropyl borate ([(CH 3 ) 2 CHO] 3 B), triphenyl borane ((C 6 H 5 ) 3 B) and tris(pentafluorophenyl)borane (C 6 F 5 ) 3 B, preferably borane. When the dopant is phosphorus, a suitable precursor is phosphine (PH 3 ).

[0099] The precursor can be used in pure form or more usually as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the precursor can be used in an amount in the range of 0.5 to 20% by volume, or 1 to 10% by volume or 1 to 5% by volume based on the total volume of the precursor and the inert carrier gas. The CVI process is suitably carried out at a low partial pressure of the gaseous precursor and the total pressure is below atmospheric pressure (101.3 kPa) (e.g., between 50 and 101.3 kPa), and the remaining partial pressure is made up to atmospheric pressure using an inert fill gas such as hydrogen, nitrogen or argon.

[0100] The temperature of the CVI process is selected to pyrolyze the precursor into the electroactive material. The CVI process is suitably carried out at a temperature in the range of 200 to 1,250 °C, or in the range of 400 to 700 °C, or in the range of 400 to 600 °C, or in the range of 400 to 550 °C, or in the range of 450 to 550 °C, or in the range of 450 to 500 °C. Preferably, the CVI process is carried out at a temperature in the range of 400 to 500 °C, preferably 400 to 450 °C or 450 to 500 °C. The CVI process is preferably carried out above the minimum fluidization velocity (Umf) of the particulate material. Preferably, the superficial velocity is higher than the minimum fluidization velocity (Umf) of the particulate material. The minimum fluidization velocity (Umf) is generally a measured quantity and its value varies according to particle size, particle density and gas viscosity. The minimum fluidization velocity defines the flow rate of the gas that must be supplied to the reaction vessel to achieve the velocity at which the particles are lifted to a "fluid-like" state. The flow rate of the CVI process is suitably selected to provide good solid-solid and solid-gas mixing and minimal particle entrainment from the reactor. The CVI process is suitably carried out in the range of 1 to 20 times the minimum fluidization velocity (Umf).

[0101] Without wishing to be bound by theory, it is believed that when the particle size of the porous carbon framework is controlled in the manner discussed above, the infiltration of the electroactive material is kinetically controlled. It is believed that the kinetic control of infiltration will result in composite particles in which the electroactive material is uniformly distributed. After depositing a certain amount of electroactive material, this may lead to the closure of pores throughout the framework volume. Controlling the particle size of the porous carbon framework has the following advantages: achieving high infiltration efficiency in the temperature and concentration ranges used for the CVI process; while also making the framework suitable for fluidization in the traditional sense (such as Geldert Group A).

[0102] Grinding

[0103] The method of the present invention includes the step of grinding intermediate particles to provide the composite particles. The grinding step results in a particle size of the composite particles that is lower than the particle size of the particulate porous carbon framework. One benefit of the present invention is that the grinding step enables the use of CVI in an FBR as a process suitable for large-scale commercial use, while providing a final product with a low particle size suitable for metal ion batteries.

[0104] During the CVI process in the FBR, there may be some agglomerates of the porous carbon framework. Therefore, the particle size of the intermediate particles can be higher than the particle size of the porous carbon framework.

[0105] Grinding can be carried out by different types of grinding devices such as mills such as wet mills, ball mills, jet mills, high-shear stirring, ultrasound, etc. Preferably, due to the reactivity of the intermediate particles, grinding is carried out immediately in a dry mill after infiltration is completed, because the electroactive material deposited by the CVI process may be reactive. For example, silicon deposited from silane contains a large number of Si-H bonds. These bonds are reactive towards organic molecules and water. Therefore, the presence of oxygen or organic solvents may lead to an exothermic reaction, which results in the destruction and / or degradation of the Si / C composite material to an amount lower than that required for commercial metal ion battery materials.

[0106] In a dry mill, a jet mill is preferred due to its ability to grind to a lower size. A jet mill uses the high-speed jet of compressed air or an inert gas to make the particles collide with each other. A jet mill can be used for feedstock with a size of up to about 1 mm, and it is known to easily achieve a size in the 1 μm range with less energy input.

[0107] There are different types of jet mills, such as rotary (periodic motion) and fluidized opposed jet types. In the rotary type, particles are accelerated by using the tangential gas force of the wall. The fluidized opposed jet acts through multiple jets separated from each other at equal angles and acts on colliding particles whose collision trajectories are towards each other. When higher capacity is required, the fluidized opposed jet type mill is more suitable. The grinding action in both types of mills is achieved by the collision of particles with each other rather than with a hard target. This specific mode of action results in a comminuted product with a narrow particle size distribution, which is beneficial for incorporation into metal ion battery electrodes. Therefore, when using an inert grinding gas with a controlled composition (limited oxygen and water content), the comminuted product has high purity.

[0108] Rotary jet mills (such as spiral jet mills) or fluidized opposed jet mill designs can be used in diameters ranging from 0.04 m up to several meters, where the grinding gas pressure is 50 to 1000 kPa and the maximum starting particle size is 1 mm. The grinding gas is an inert gas such as nitrogen or argon, or a mixture of them with low partial pressures of air, water, or oxygen.

[0109] The comminuted particles can optionally be classified according to size, for example by centrifugation or by sieving.

[0110] The intermediate particles can be passivated before the comminution step. That is, the particle surface can be treated to reduce its chemical reactivity, preferably minimizing or preventing any further oxidation of the particle surface in subsequent process steps or handling. For example, the intermediate particles can be passivated in an environment with a low oxygen concentration, such as an environment with an oxygen concentration below 10 vol% oxygen. The intermediate particles can be passivated using an inert gas such as nitrogen. A low oxygen concentration gas mixture can also be used. Passivating the intermediate particles has the advantage of suppressing unwanted further reactions of the intermediate particles. For example, passivating the intermediate particles can remove reactive Si-H bonds. This helps to maintain the structure of the electroactive material deposited in the pores of the porous carbon framework from the CVI process, which is advantageous when the composite particles are used in metal ion batteries. The comminution step can also be carried out in an environment with a low oxygen concentration, such as in an inert gas or a low oxygen concentration gas mixture. Conveniently, the comminution step can be carried out in the same atmosphere as the optional passivation step.

[0111] The intermediate particles can be cooled before the comminution step, optionally in combination with the passivation step. Cooling can be to below 100 °C, or below 50 °C, or to ambient temperature. Cooling the intermediate particles has the advantage of facilitating the transfer of the intermediate particles to the comminution device.

[0112] The method of the present invention can be a continuous process or a batch process. In a continuous process, the passivation and cooling steps need to be carried out in a container separate from the FBR. The container separate from the FBR can be a comminution device.

[0113] Composite particle product

[0114] One advantage of the present invention is that the properties of the composite particle product can be controlled by selecting the properties of the porous carbon framework starting material. This is achieved for the following reasons: The inventors have found that due to the relative μm-length scale of the fracture compared to the nm-length scale of the functional units of the composite particles, comminution can be carried out without a significant level of damage. In other words, the comminution step provides the desired particle size of the composite particle product while maintaining the ideal nanostructure obtained by depositing the electroactive material into the porous carbon framework including micropores and / or mesopores using CVI. For example, both the intermediate particles and the composite particles can include a plurality of nanosized domains of electroactive material in elemental form located within the micropores and / or mesopores of the porous carbon framework. As used herein, the term "nanosized domain" refers to a nanosized body of electroactive material located within the pores of the porous carbon framework. The maximum size of the nanosized silicon domain is defined by the pore diameter of the pore in which the silicon is located.

[0115] Generally speaking, the composite particles are particulate materials in which the nanosized domains of the electroactive material occupy the pore volume of the porous carbon framework, where the pore volume includes micropores and / or mesopores. It has been found that this particle structure 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.

[0116] Without being bound by theory, it is believed that having the nanosized electroactive domains located within the micropores and / or mesopores first provides a fine electroactive structure that is capable of lithiation and delithiation without excessive structural stress. It is believed that these very fine electroactive domains have a lower tolerance to elastic deformation and a higher fracture tolerance compared to larger electroactive structures. By ensuring that a higher proportion of the pore volume is occupied by the electroactive material, the composite particles can have a high capacity. In addition, by having the nanosized electroactive domains located within the micropores and / or mesopores, only a small area of the electroactive surface is accessible to the electrolyte, thus limiting SEI formation.

[0117] In some cases, the composite particles prepared by the present invention can include pores in which the completely enclosed void space is capped by the electroactive material, thereby preventing the electrolyte from entering the void space.

[0118] The particle size of the composite particles can be targeted by controlling the comminution step and optionally the step of classifying the particles according to size, thereby providing the particle size distribution required for the end use.

[0119] Due to the comminution of the intermediate particles in step (c), the D 50 particle size of the composite particles is smaller than the D 50 particle size of the porous carbon framework. Therefore, the D 50 particle size of the composite particles obtained in step (c) can be, for example, at most 50 μm, as long as the D 50 particle size of the porous carbon framework is still larger. For example, the D 50 particle size of the composite particles can be not more than 40 µm, or not more than 30 µm, or not more than 25 µm.

[0120] Preferably, the D 50 particle size of the composite particles can be not more than 20 μm. For example, the D 50 particle size of the composite particles can be not more than 15 µm, or not more than 12 µm, or not more than 10 µm, or not more than 9 µm, or not more than 8 µm, or not more than 7 µm, or not more than 6.5 µm, or not more than 6 µm, or not more than 5.5 µm, or not more than 5 µm, or not more than 4.5 µm, or not more than 4 µm, or not more than 3.5 µm.

[0121] The D 50 particle size of the composite particles can be at least 1 µm, or at least 2 µm, or at least 3 µm, or at least 4 µm, or at least 5 µm.

[0122] Preferably, the D 50 particle size of the composite particles is in the range of 0.5 to 20 μm, or in the range of 0.5 to 15 μm, or in the range of 0.5 to 12 μm, or in the range of 0.5 to 10 μm, or in the range of 0.5 to 8 μm, or in the range of 0.5 to 9 μm, or in the range of 0.5 to 7 μm. Composite particles within these size ranges and having the porosity and pore size distribution described herein are ideally suitable for use as anodes in metal ion batteries due to their dispersibility in slurries, their structural robustness, their capacity retention over repeated charge-discharge cycles, and their suitability for forming a dense electrode layer with a uniform thickness in the conventional range of 20 to 50 µm.

[0123] The D 10 particle size of the composite particles can be 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.

[0124] The D 90The particle size may not exceed 40 µm, or may not exceed 30 µm, or may not exceed 20 µm, or may not exceed 15 µm, or may not exceed 10 µm, or may not exceed 8 µm, or may not exceed 6 µm.

[0125] Preferably, the D of the porous carbon framework in step (a) 50 The particle size is at least 30 μm, and the D of the composite particles obtained in step (c) 50 The particle size does not exceed 20 μm. More preferably, the D of the porous carbon framework in step (a) 50 The particle size is at least 40 μm, and the D of the composite particles obtained in step (c) 50 The particle size does not exceed 20 μm. More preferably, the D of the porous carbon framework in step (a) 50 The particle size is at least 50 μm, and the D of the composite particles obtained in step (c) 50 The particle size does not exceed 20 μm.

[0126] Preferably, the BET surface area of the composite material of the present invention does not exceed 300 m 2 / g, or does not exceed 250 m 2 / g, or does not exceed 200 m 2 / g, or does not exceed 150 m 2 / g, or does not exceed 100 m 2 / g, or does not exceed 80 m 2 / g, or does not exceed 60 m 2 / g, or does not exceed 40 m 2 / g, or does not exceed 30 m 2 / g, or does not exceed 25 m 2 / g, or does not exceed 20 m 2 / g, or does not exceed 15 m 2 / g, or does not exceed 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 between 1 m 2 / g and 25 m 2in the range of 2 to 15 m / g, more preferably in the range of 2 to 15 m / g. 2 / g.

[0127] Preferably, at least 90 wt%, more preferably at least 95 wt%, more preferably at least 98 wt%, more preferably at least 99 wt% of the electroactive mass in the composite particles is located within the internal pore volume of the porous carbon framework, such that no or very little electroactive material is present on the outer surface of the composite particles.

[0128] Preferably, the volume of micropores and mesopores in the composite particles (i.e., in the presence of the electroactive material) measured by nitrogen adsorption does not exceed 0.15×P 1 , or does not exceed 0.10×P 1 , or does not exceed 0.05×P 1 , or does not exceed 0.02×P 1 .

[0129] The weight ratio of the electroactive material such as silicon to the porous carbon framework in the composite particles can be determined by elemental analysis. Elemental analysis is used to determine the weight percentages of both the electroactive material and carbon in the composite particles. Optionally, the amounts of hydrogen, nitrogen, and oxygen can also be determined by elemental analysis. Preferably, elemental analysis is also used to determine the weight percentage of carbon (and optionally hydrogen, nitrogen, and oxygen) in the separate porous carbon framework. Determining the weight percentage of carbon in the porous carbon framework itself takes into account the possibility that the porous carbon framework contains a small amount of heteroatoms within its molecular framework. The two measurements carried out together enable the reliable determination of the weight percentage of silicon relative to the entire porous carbon framework.

[0130] Preferably, the content of the electroactive material (e.g., silicon) is determined by ICP - OES (Inductively Coupled Plasma - Optical Emission Spectrometry). A variety of ICP - OES instruments are commercially available, such as the iCAP® 7000 series ICP - OES analyzers (obtainable from ThermoFisher Scientific). Preferably, the carbon content (and if necessary, the hydrogen content, nitrogen content, and oxygen content) of the composite particles and the porous carbon framework itself is determined by IR absorption. A suitable instrument for determining the carbon content, hydrogen content, nitrogen content, and oxygen content is the TruSpec® Micro elemental analyzer (obtainable from Leco Corporation).

[0131] Suitably, when the electroactive material is silicon, the composite particles contain 30 wt% to 80 wt% of silicon, preferably 45 wt% to 65 wt% of silicon.

[0132] The composite particles preferably have a low total oxygen content. Oxygen may 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%, still more preferably less than 5 wt%, such as less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%.

[0133] When the electroactive material is silicon, the weight ratio of silicon to the porous carbon framework in the composite particles is preferably in the range of [0.5×P 1 to 2.2×P 1 :1. 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 pore volume occupied by silicon is approximately 20% to 95% by volume.

[0134] The composite particles generally have a charge specific capacity of 1200 to 2340 mAh / g during the first lithiation. Preferably, the composite particles have a charge specific capacity of at least 1400 mAh / g during the first lithiation.

[0135] As discussed above, some types of porous carbon frameworks are targeted for some types of composite particle products. It will be understood that the pore structure of the porous carbon framework, such as micropores and / or mesopores, will be retained in the composite particle product. Some types of composite particle products are discussed below. It will be understood that the characteristics of the types of composite particles discussed below should be considered in combination with the characteristics of the composite particles discussed above, such as particle size.

[0136] Composite Particle 1

[0137] Composite Particle 1 prepared by the method of the present invention comprises:

[0138] (a) a porous carbon framework comprising micropores and / or mesopores,

[0139] wherein the total pore volume of the micropores and / or mesopores measured by gas adsorption is P 1 cm 3 / g, where P 1 represents a natural number with a value of at least 0.7, and

[0140] where the PD 50 pore diameter measured by gas adsorption does not exceed 5 nm; and

[0141] (b) a plurality of elemental nanosized silicon domains located within the micropores and / or mesopores of the porous carbon framework;

[0142] where the weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.5×P 1 to 1.3×P 1in the range of [0.55×P

[0143] The porous carbon framework 1 can be used as a raw material to prepare the composite particle 1. Therefore, the pore structure of the porous carbon framework 1 can exist in the composite particle 1.

[0144] Preferably, the weight ratio of silicon to carbon is in the range of [0.55×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1×P 1 :1, or in the range of [0.6×P 1 to 0.95×P 1 :1, or in the range of [0.6×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.85×P 1 :1, or in the range of [0.65×P 1 to 0.8×P 1 :1, or in the range of [0.7×P 1 to 0.8×P 1 :1.

[0145] Preferably, silicon occupies about 25% to about 45%, more preferably about 25% to 40% of the internal pore volume of the porous carbon framework. Within these preferred ranges, the pore volume of the porous carbon framework effectively accommodates the expansion of silicon during charging and discharging, but avoids excessive pore volume, which is not conducive to the volume capacity of the particulate material. However, due to insufficient metal ion diffusion rate or insufficient expansion volume resulting in mechanical resistance to lithiation, the amount of silicon is not so high as to hinder effective lithiation.

[0146] The D 50 particle size of the composite particle 1 can be in the range of 0.5 to 50 µm. Optionally, the D 50 particle size can not exceed 20 µm.

[0147] For example, the D 50 particle size of the composite particle 1 can be in the range of 1 to 25 µm, or in the range of 1 to 20 µm, or in the range of 2 to 20 µm, or in the range of 2 to 15 µm, or in the range of 3 to 15 µm.

[0148] Composite particle 2

[0149] The composite particle 2 prepared by the method of the present invention comprises:

[0150] (a) A porous carbon framework including micropores and mesopores, wherein

[0151] (i) The total pore volume of the micropores and mesopores measured by gas adsorption is P 1 cm 3 / g, where the value of P 1 is at least 0.6,

[0152] (ii) Based on the total volume of the micropores and mesopores, the volume fraction (φ a ) of the micropores is in the range of 0.1 to 0.9;

[0153] (iii) Based on the total volume of the micropores and mesopores, the volume fraction (φ 20 ) of the pores with a pore diameter not exceeding 20 nm is at least 0.75, and

[0154] (iv) The D 50 particle size of the porous carbon framework is less than 20 µm;

[0155] (b) A plurality of nano-sized elemental silicon domains located in the micropores and / or mesopores of the porous carbon framework;

[0156] where the weight ratio of silicon to the porous carbon framework in the composite particle is in the range of [1×P 1 to 2.2×P 1 :1.

[0157] The porous carbon framework 2 can be used as a raw material to prepare the composite particle 2. Therefore, the pore structure of the porous carbon framework 2 can exist in the composite particle 2.

[0158] The composite particle 2 is particularly suitable for a "hybrid" electrode comprising a combination of graphite and the composite particle.

[0159] The weight ratio of silicon to the porous carbon framework in the composite particle is in the range of [1×P 1 to 2.2×P 1 :1. Considering that the silicon density is about 2.3 g / cm 3 , the weight ratio of [1×P 1 :1 corresponds to an occupancy of approximately 43% v / v of the pores of the porous carbon framework by silicon. The upper ratio limit of [2.2×P 1 :1 corresponds to an occupancy of approximately 95% v / v of the pores of the porous carbon framework by silicon.

[0160] Preferably, the weight ratio of silicon to the porous carbon framework is at least 1.1×P 1 , more preferably at least 1.15×P 1 , more preferably at least 1.2×P 1 , more preferably at least 1.25×P 1 , more preferably at least 1.3×P 1 , more preferably at least 1.35×P 1 , more preferably at least 1.4×P 1 .

[0161] In the case where the porous carbon framework includes a relatively high ratio of mesopores to micropores (e.g., in the case where φ a is 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 carbon can also be higher, for example, at least 1.45×P 1 , more preferably at least 1.5×P 1 , more preferably at least 1.55×P 1 , more preferably at least 1.6×P 1 , more preferably at least 1.65×P 1 , more preferably at least 1.5×P 1 .

[0162] In a further preferred embodiment, the minimum weight ratio of silicon to the porous carbon framework is at least the value given by [φ b +0.75]×P 1 , or at least the value given by [φ b +0.8]×P 1 , or at least the value given by [φ b +0.9]×P 1 , or at least the value given by [φ b +1]×P 1 , or at least the value given by [φ b +1.1]×P 1 . Thus, in the case where the mesopore fraction (φ b ) has a higher value, the amount of silicon in the composite particles 2 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 composite particles 2. 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.

[0163] In a further embodiment, the maximum weight ratio of silicon to the porous carbon framework does not exceed the value given by [φ b +1.6]×P 1The value given, more preferably not exceeding the value given by [φ b +1.5]×P 1 The relationship between the mesopore fraction and the maximum weight ratio of the porous carbon framework ensures that the porous carbon framework with a higher micropore fraction is not overly filled with silicon.

[0164] The D 50 particle size of composite particle 2 can be in the range of 0.5 to 20 µm. Preferably, the D 50 particle size of composite particle 2 does not exceed 12 µm, or does not exceed 10 µm, or does not exceed 8 µm.

[0165] For example, the D 50 particle size of composite particle 2 can be in the range of 1 to 12 µm, or 1 to 10 µm, or 2 to 10 µm, or 3 to 8 µm.

[0166] The D 10 particle size of composite particle 2 is preferably at least 0.5 µm.

[0167] The D 90 particle size of composite particle 2 is preferably not more than 12 µm, or not more than 10 µm.

[0168] Composite particle 3

[0169] The composite particle 3 prepared by the method of the present invention comprises:

[0170] (a) A porous carbon framework including micropores and / or mesopores,

[0171] wherein the total pore volume of the micropores and mesopores measured by gas adsorption is at least 0.7 cm 3 / g,

[0172] wherein the PD 50 pore diameter measured by gas adsorption does not exceed 2 nm; and

[0173] (b) An electroactive material located in the micropores and / or mesopores of the porous carbon framework;

[0174] wherein the D 90 particle size of the composite particle does not exceed 10 µm.

[0175] The porous carbon framework 3 can be used as a raw material to prepare the composite particle 3. Therefore, the pore structure of the porous carbon framework 3 can exist in the composite particle 3.

[0176] Composite particle 3 relates to a particulate material in which the porous carbon framework has a relatively high total volume of micropores and mesopores, where pores with a diameter of no more than 2 nm account for at least 50% of the total pore volume. This pore structure can be derived from the porous carbon framework 3. Composite particle 3 has a particle size distribution that strongly favors particles with a diameter of no more than 10 µm. It has been found that the combination of small particle size and a highly differentiated pore volume provides an electroactive material with high resistance to mechanical degradation during electrode fabrication.

[0177] The D of composite particle 3 90 The particle diameter is preferably no more than 9.5 µm, or no more than 9 µm, or no more than 8.5 µm, or no more than 8 µm, or no more than 7.5 µm, or no more than 7 µm, or no more than 6.5 µm, or no more than 6 µm, or no more than 5.5 µm, or no more than 5 µm, or no more than 4.5 µm, or no more than 4 µm.

[0178] The D of composite particle 3 50 The particle diameter is preferably in the range of 0.5 to 7 µm. Optionally, D 50 The particle diameter can be at least 1 µm, or at least 1.5 µm, or at least 2 µm, or at least 2.5 µm, or at least 3 µm.

[0179] Optionally, D 50 The particle diameter can be no more than 6.5 µm, or no more than 6 µm, or no more than 5.5 µm, or no more than 5 µm, or no more than 4.5 µm, or no more than 4 µm, or no more than 3.5 µm.

[0180] For example, the D of composite particle 3 50 The particle diameter can be in the range of 1 to 6.5 µm, or in the range of 1.5 to 6 µm, or in the range of 2 to 5.5 µm, or in the range of 2.5 to 5 µm, or in the range of 3 to 4.5 µm.

[0181] The D of composite particle 3 10 The particle diameter is preferably at least 0.5 µm.

[0182] The D of composite particle 3 99 The particle diameter is preferably no more than 25 µm.

[0183] The amount of electroactive material in composite particle 3 is preferably selected such that no more than about 55% of the internal pore volume of the porous carbon framework is occupied by the electroactive material (in the uncharged state). Preferably, the electroactive material occupies about 25% to about 45% of the internal pore volume of the porous carbon framework, more preferably about 25% to 40% of the internal pore volume of the porous carbon framework.

[0184] When the electroactive material is silicon, the weight ratio of silicon to the porous carbon framework is preferably [0.5×P 1 to 1.3×P 1 :1. More preferably, the weight ratio of silicon to carbon is in the range of [0.55×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1.1×P 1 :1, or in the range of [0.6×P 1 to 1×P 1 :1, or in the range of [0.6×P 1 to 0.95×P 1 :1, or in the range of [0.6×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.9×P 1 :1, or in the range of [0.65×P 1 to 0.85×P 1 :1, or in the range of [0.65×P 1 to 0.8×P 1 :1, or in the range of [0.7×P 1 to 0.8×P 1 :1.

[0185] Carbon coating

[0186] The method of the present invention may optionally include an additional step of depositing a conductive coating / preferably a carbon-based coating on the composite particles. Suitably, the conductive carbon-based 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-based 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 coating (such as a carbon-based coating) has sufficient permeability to allow lithium to access the interior of the composite particles without excessive resistance, thus not reducing the rate performance of the composite particles. For example, the thickness of the conductive coating can suitably be in the range of 2 to 30 nm. Optionally, the conductive coating can be porous and / or can only partially cover the surface of the composite particles.

[0187] The conductive coating has the following advantages: it further reduces the BET surface area of the composite particles by smoothing any surface defects and by filling any remaining surface micropores, thereby further reducing the first cycle loss. Additionally, the conductive coating improves the electronic 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 upon cycling.

[0188] Preferably, the BET surface area of the composite particles after deposition of the conductive coating is less than 50, less than 30, less than 20, more preferably less than 10, or less than 5 m 2 / g.

[0189] End use of the product

[0190] The method of the present invention may optionally include an additional step of forming an electrode composition comprising composite particles (optionally wherein the composite particles have been coated with a conductive carbon coating). The electrode composition may comprise at least one other component selected from the following: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material.

[0191] The method of the present invention may optionally include an additional step of forming a slurry comprising composite particles (optionally wherein the composite particles have been coated with a conductive carbon coating) and a solvent.

[0192] Product defined by the method

[0193] The present invention also provides a particulate material comprising composite particles obtainable by the method of the present invention. The nanostructure of the electroactive material deposited by the CVI process of the present invention is different from the nanostructure of electroactive materials deposited by other means. Additionally, since the composite particles are obtained from the CVI process and a subsequent comminution process, they can be distinguished from particles of similar size prepared without the subsequent comminution step. For example, the comminution step produces fracture surfaces that can be observed by microscopy. Thus, composite particles obtainable by the method of the present invention can be distinguished from composite particles obtained by other means.

[0194] Examples

[0195] A silicon-carbon composite material was synthesized in a vertical bubbling fluidized bed reactor including a stainless steel cylindrical container with an inner diameter of 83 mm. 126 g of a material with a BET surface area of 1777 m 2 / g, a total pore volume of 0.78 cm 3 / g, PD 10 = 0.97 nm, PD 50 = 1.15 nm, PD90 = 2.23 nm and φ a A pre - mixed mixture of porous carbon particles with a particle size of = 2.23 nm and φ = 61%. An inert gas (nitrogen) at a low flow rate is injected into the reactor to remove any oxygen. Then the reactor is heated to a reaction temperature of 420 to 440 °C, and 1.25 % v / v of silane gas diluted in nitrogen is supplied to the bottom of the reactor at a flow rate sufficient to fluidize the carbon skeleton particles for a time of 32.3 hours (Sample 1) or 37 hours (Sample 2). Once the reaction time is completed, the reactor atmosphere is switched to pure nitrogen while maintaining fluidization, and this purge lasts for 30 minutes. Thereafter, the furnace is cooled to ambient temperature within a few hours. When ambient temperature is reached, the furnace atmosphere is gradually switched to air over a period of several hours.

[0196] The product is added to the feed tray of an MC DecJet® 30 mill and ground in an inert atmosphere. The ring pressure is set to 650 kPa and the Venturi pressure is set to 700 kPa. The product is micronized and then collected in a suitable container. The material properties of these two composites are given in Table 1.

[0197] Table 1

[0198]

[0199] Preparation of the negative electrode

[0200] Negative electrode coatings (anodes) are prepared from the respective materials of Samples 1 and 2. A dispersion of carbon black SuperP ® (conductive carbon) in a CMC binder is mixed in a Thinky TM mixer. The Si - C composite material is added to the mixture and mixed in a Thinky TM mixer for 30 min. Then SBR binder is 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 is remixed in a Thinky TM mixer for another 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.

[0201] Battery fabrication and cycling

[0202] Full - cell fabrication

[0203] A full button cell was prepared using a circular negative electrode with a radius of 0.8 cm cut from the coatings (as described above) made from Samples 1 and 2, 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 containing 1 M LiPF 6 in a 7:3 solution of EMC / FEC (ethyl methyl carbonate / fluoroethylene carbonate) containing 3 wt% ethylene carbonate was added to the cell.

[0204] The 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.

[0205] The charge (lithiation) and discharge (delithiation) capacities per unit mass of the silicon-carbon composite material for each cycle were calculated, 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 - (the first delithiation capacity / the first lithiation capacity)) × 100%. The key values were the averages of 3 button cells for each material and are listed in Table 2.

[0206] Table 2

[0207]

[0208] The present invention includes but is not limited to the following embodiments:

[0209] 1. A method for preparing composite particles, the method comprising:

[0210] (a) providing a particulate porous carbon framework comprising micropores and / or mesopores, wherein the D 50 particle size of the porous carbon framework is at least 20 μm;

[0211] (b) depositing an electroactive material selected from silicon, tin, aluminum, germanium, and their alloys into the micropores and / or mesopores of the porous carbon framework using chemical vapor infiltration in a fluidized bed reactor to provide intermediate particles; and

[0212] (c) pulverizing the intermediate particles to provide the composite particles.

[0213] 2. The method according to embodiment 1 further comprises transferring the intermediate particles to a comminution device before step (c).

[0214] 3. The method of embodiment 1 or embodiment 2, wherein the electroactive material is silicon.

[0215] 4. The method according to any preceding embodiment, wherein the intermediate particles and the composite particles comprise a plurality of nano-sized domains of the electroactive material in elemental form located within the micropores and / or mesopores of the porous carbon framework.

[0216] 5. A method according to any of the preceding embodiments, wherein the chemical vapor infiltration method is carried out at a temperature in the range of 200 to 1,250°C, or 400 to 700°C, or 450 to 550°C, or 450 to 500°C.

[0217] 6. The method according to any preceding embodiment, further comprising a step of cooling the intermediate particles before comminuting the intermediate particles, optionally wherein the cooling is to a temperature below 100 °C or below 50 °C, or to ambient temperature.

[0218] 7. The method according to any preceding embodiment, further comprising the step of passivating the intermediate particles before comminuting the intermediate particles, optionally wherein the passivation is performed in an inert gas or in an environment with an oxygen concentration of less than 10% by volume of oxygen.

[0219] 8. The method according to any preceding embodiment, wherein the comminution device is a jet mill.

[0220] 9. The method according to any preceding embodiment, wherein the step of comminuting the intermediate particles is performed in an inert gas or in an environment with an oxygen concentration lower than 10% by volume of oxygen.

[0221] 10. The method according to any preceding embodiment, wherein the method is a continuous process, or wherein the method is a batch process.

[0222] 11. The method according to any of the preceding embodiments, wherein the total pore volume of micropores and / or mesopores of the porous carbon skeleton measured by gas adsorption is P 1 cm 3 / g, where P 1The value is at least 0.4, or at least 0.5, or at least 0.6, 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, or at least 1.05, or at least 1.1, or at least 1.2.

[0223] 12. The method according to any one of the preceding embodiments, wherein the total pore volume of the micropores and / or mesopores of the porous carbon framework measured by gas adsorption is P 1 cm 3 / g, wherein P 1 The value does not exceed 2.5, or does not exceed 2.2, or does not exceed 2, or does not exceed 1.8, or does not exceed 1.6, or does not exceed 1.5, or does not exceed 1.4, or does not exceed 1.3.

[0224] 13. The method according to embodiment 12, wherein the total pore volume of the micropores and / or mesopores of the porous carbon framework measured by gas adsorption is P 1 cm 3 / g, wherein P 1 The value is in the range of 0.4 to 2.5, or in the range of 0.6 to 2.5, or in the range of 0.7 to 2, or in the range of 0.7 to 1.2.

[0225] 14. The method according to any one of the preceding embodiments, wherein the D 50 particle size of the porous carbon framework is in the range of 60 to 150 μm.

[0226] 15. The method according to any one of the preceding embodiments, wherein the D 50 particle size of the porous carbon framework is at least 30μm, or at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm, or at least 80 μm.

[0227] 16. The method according to any one of the preceding embodiments, wherein the D 50 particle size of the porous carbon framework does not exceed 1000 μm, or does not exceed 500 μm, or does not exceed 250 μm, or does not exceed 150 μm.

[0228] 17. The method according to any one of the preceding embodiments, wherein the D 10 particle size of the porous carbon framework is at least 5μm, or at least 15 μm, or at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm.

[0229] 18. The method according to any one of the preceding embodiments, wherein the D 90The particle size is not more than 1,500 μm, or not more than 1,000 μm, or not more than 750 μm, or not more than 500 μm, or not more than 200 μm.

[0230] 19. The method according to any one of the preceding embodiments, wherein the D of the porous carbon framework 98 The particle size is not more than 1,550 μm, or not more than 1,050 μm, or not more than 800 μm, or not more than 550 μm, or not more than 250 μm.

[0231] 20. The method according to any one of the preceding embodiments, wherein the BET surface area of the porous carbon framework is 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.

[0232] 21. The method according to any one of the preceding embodiments, wherein the BET surface area of the porous carbon 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.

[0233] 22. The method according to embodiment 21, wherein the BET surface area of the porous carbon framework is 1,500 to 3,000 m 2 / g.

[0234] 23. The method according to any one of the preceding embodiments, wherein the PD of the porous carbon framework measured by gas adsorption 50 The pore size is not more than 5 nm, or not more than 4 nm, or not more than 3 nm, or not more than 2.5 nm, or not more than 2 nm, or not more than 1.5 nm, or not more than 1 nm.

[0235] 24. The method according to any one of the preceding embodiments, wherein the D of the composite particles 50 The particle size is in the range of 0.5 to 20 µm.

[0236] 25. The method according to embodiment 24, wherein the D of the composite particles 50 The particle size is at least 1 µm, or at least 2 µm, or at least 3 µm, or at least 4 µm, or at least 5 µm.

[0237] 26. The method according to embodiment 24 or embodiment 25, wherein the D 50 particle size of the composite particles is not more than 20 μm, or not more than 15 µm, or not more than 12 µm, or not more than 10 µm, or not more than 9 µm, or not more than 8 µm, or not more than 7 µm, or not more than 6.5 µm, or not more than 6 µm, or not more than 5.5 µm, or not more than 5 µm, or not more than 4.5 µm, or not more than 4 µm, or not more than 3.5 µm.

[0238] 27. The method according to any one of the preceding embodiments, wherein the D 10 particle size of the composite particles is 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.

[0239] 28. The method according to any one of the preceding embodiments, wherein the D 90 particle size of the composite particles is not more than 80 µm, or not more than 60 µm, or not more than 40 µm, or not more than 30 µm, or not more than 25 µm, or not more than 20 µm, or not more than 10 μm.

[0240] 29. The method according to any one of the preceding embodiments, wherein the span of the particle size distribution of the composite particles is not more than 5, or not more than 4, or not more than 3, or not more than 2, or not more than 1.5.

[0241] 30. The method according to any one of the preceding embodiments, wherein the electroactive material is silicon, and the pore volume of the composite particles is expressed as P 1 cm 3 / g, and for the composite particles, the weight ratio of silicon in the composite particles to the porous carbon framework is in the range of [0.5×P 1 to 2.2×P 1 :1, or in the range of [1×P 1 to 2.2×P 1 :1, or in the range of [0.5×P 1 to 1.3×P 1 :1.

[0242] 31. The method according to any one of the preceding embodiments, wherein the electroactive material is silicon, and the composite particles contain 30 wt% to 80 wt% of silicon, or 45 wt% to 65 wt% of silicon.

[0243] 32. The method according to any one of the foregoing embodiments, wherein the composite particles comprise no more than 15% by weight of oxygen, or no more than 10% by weight of oxygen.

[0244] 33. A particulate material comprising composite particles obtainable by the method according to any one of the foregoing embodiments.

Claims

1. A method for preparing composite particles, the method comprising: (a) Provide a particulate porous carbon framework comprising micropores and / or mesopores, wherein the D of the porous carbon framework 50 particle size is at least 20 μm; (b) in a fluidized bed reactor, depositing an electroactive material selected from silicon, tin, aluminum, germanium, and their alloys into the micropores and / or mesopores of the porous carbon framework using chemical vapor infiltration to provide intermediate particles; and (c) pulverizing the intermediate particles to provide the composite particles.

2. The method according to any one of the preceding claims, wherein the method is a continuous process, or wherein the method is a batch process.

3. The method according to any one of the preceding claims, wherein the total pore volume of micropores and / or mesopores of the porous carbon framework measured by gas adsorption is P 1 cm 3 / g, where the value of P 1 is at least 0.4, or at least 0.5, or at least 0.6, 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, or at least 1.05, or at least 1.1, or at least 1.

2.

4. The method according to any one of the preceding claims, wherein the total pore volume of the micropores and / or mesopores of the porous carbon framework measured by gas adsorption is P 1 cm 3 / g, where the value of P 1 does not exceed 2.5, or does not exceed 2.2, or does not exceed 2, or does not exceed 1.8, or does not exceed 1.6, or does not exceed 1.5, or does not exceed 1.4, or does not exceed 1.

3.

5. The method according to claim 4, wherein the total pore volume of micropores and / or mesopores of the porous carbon framework measured by gas adsorption is P 1 cm 3 / g, where P 1 has a value in the range of 0.4 to 2.5, or in the range of 0.6 to 2.5, or in the range of 0.7 to 2, or in the range of 0.7 to 1.

2.

6. The method according to any one of the preceding claims, wherein the D 50 particle size of the porous carbon framework is in the range of 60 to 150 μm.

7. The method according to any one of the preceding claims, wherein the D 50 particle size of the porous carbon framework is at least 30 μm, or at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm, or at least 80 μm.

8. The method according to any one of the preceding claims, wherein the D 50 particle size of the porous carbon framework is not more than 1000 μm, or not more than 500 μm, or not more than 250 μm, or not more than 150 μm.

9. The method according to any one of the preceding claims, wherein the D 10 particle size of the porous carbon framework is at least 5 μm, or at least 15 μm, or at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm.

10. A particulate material comprising composite particles obtainable by the method according to any one of the preceding claims.

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