Electroactive materials for metal ion batteries

Abstract

The present invention relates to a particulate electroactive material consisting of a plurality of composite particles wherein the composite particles comprise: (a) a porous carbon skeleton comprising micropores and mesopores, the total volume of the micropores and mesopores being 0.5 to 1.5 cm3 / g; and (b) silicon located at least within the micropores of the porous carbon backbone in a defined amount relative to the volume of the micropores and mesopores. At least 20% by weight of the silicon is characterized as surface silicon by thermogravimetric analysis.

Description

[0001] This application is a divisional application of Chinese invention patent application with an international filing date of August 3, 2021, international application number PCT / GB2021 / 052004, Chinese national phase application number 202180018757.1, and invention title "Electroactive Materials for Metal-Ion Batteries". Technical Field

[0002] The present invention generally relates to electroactive materials suitable for use in electrodes of rechargeable metal-ion batteries, and more specifically to particulate materials with high electrochemical capacity suitable for use as anodic active materials in rechargeable metal-ion batteries. Background Technology

[0003] Rechargeable metal-ion batteries are widely used in portable electronic devices, such as mobile phones and laptops, and are increasingly being applied to electric vehicles or hybrid vehicles. Rechargeable metal-ion batteries typically include an anode in the form of a metal current collector having a layer of electroactive material, defined herein as a material capable of inserting and releasing metal ions during battery charging and discharging. The terms "cathode" and "anode" are used herein in the context of connecting the battery to a load such that the anode is the negative electrode. When a metal-ion battery is charged, metal ions are transported from the metal-ion-containing cathode layer to the anode via the electrolyte and inserted into the anode material. The term "battery" herein refers both to a device containing a single anode and a single cathode and to a device containing multiple anodes and / or multiple cathodes.

[0004] Interestingly, improving the gravimetric and / or volumetric capacity of rechargeable metal-ion batteries is crucial. To date, commercial lithium-ion batteries have been largely limited by the use of graphite as the anode active material. When a graphite anode is charged, lithium is intercalated between the graphite layers to form an empirically defined Lia. x Materials with C6 content (where x is greater than 0 and less than or equal to 1) are used. Therefore, the maximum theoretical capacity of graphite in lithium-ion batteries is 372 mAh / g, with a slightly lower actual capacity (approximately 340 to 360 mAh / g). Other materials such as silicon, tin, and germanium can intercalate lithium at significantly higher capacities than graphite, but they have not yet been widely used commercially due to their difficulty in maintaining sufficient capacity during multiple charge / discharge cycles.

[0005] In particular, silicon is considered a promising alternative to graphite for manufacturing rechargeable metal-ion batteries with high gravimetric and volumetric capacity due to its very high lithium capacity (see, for example, Insertion Electrode Materials for rechargeable Lithium Batteries, Winter, M et al., Adv. Mater. 1998, 10, No. 10). At room temperature, the theoretical maximum specific capacity of silicon in lithium-ion batteries is approximately 3,600 mAh / g (based on Li). 15 (Si4). However, when silicon is lithiated to its maximum capacity, lithium insertion into the bulk silicon results in a large volume increase of up to 400% of the original volume of the silicon material. Repeated charge-discharge cycles create significant mechanical stress in the silicon material, leading to breakage and delamination of the silicon anode material. The volume shrinkage of silicon particles during delithiation can lead to loss of electrical contact between the anode material and the current collector. Another challenge is that the solid electrolyte interface (SEI) layer formed on the silicon surface lacks 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 increased SEI layer thickness, as well as irreversible lithium consumption. These destructive mechanisms collectively result in unacceptable electrochemical capacity loss during continuous charge-discharge cycles.

[0006] Several methods have been proposed to overcome the problems associated with the volume changes observed during charging of silicon-containing anodes. Microcrystalline silicon structures with cross-sections below approximately 150 nm, such as silicon films and silicon nanoparticles, have been reported to be more tolerant of volume changes during charging and discharging compared to silicon particles in the micrometer range. However, none of these are suitable for commercial-scale applications in their unrefined form; nanoscale particles are difficult to fabricate and handle, and silicon films do not provide sufficient bulk capacity.

[0007] WO 2007 / 083155 discloses that improved capacity retention can be achieved using silicon particles with a high aspect ratio (i.e., the ratio of the maximum to the minimum particle size). The small cross-section of such particles reduces structural stress on the material due to volume changes during charging and discharging. However, the fabrication of such particles can be difficult and expensive, and they may be brittle. Furthermore, the high surface area can lead to excessive SEI formation, resulting in excessive capacity loss during the first charge-discharge cycle.

[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 nanosized silicon particles while avoiding the handling difficulties of nanoparticles. Guo et al. (Journal of Materials Chemistry A, 2013, pages 14075 - 14079) disclosed a silicon-carbon composite material in which a porous carbon substrate provides a conductive framework and silicon nanoparticles are deposited in a uniformly distributed pore structure of the substrate. It is known that the composite material has improved capacity retention after multiple charge cycles, but the initial capacity (in mAh / g) of the composite material is significantly lower than that of silicon nanoparticles.

[0009] JP 2003100284 discloses an active material comprising a carbon-based support having small pores branching from some larger pores. The electroactive material (such as silicon) is optionally located on the walls of both the large and small pores and on the outer surface of the carbon-based support.

[0010] Low oxide materials of silicon (such as SiO x , where 0 < x < 2) have been used in "hybrid" electrodes that mainly contain graphite as the active material. However, due to the expansion of SiO x upon lithiation and the relatively high irreversible lithium loss during the first charge cycle, the maximum loading of SiO x is generally about 10 wt% of the total electroactive material in the electrode. Therefore, there is a need for high-capacity electrode materials that have a comparable lithiation capacity to silicon oxides but have reduced expansion and reduced capacity loss during the first charge cycle.

[0011] The desirable expansion properties of electrode materials must be achieved together with other important properties. In particular, commercially available alternative electrode materials need to provide the benefits of high lithiation capacity and high capacity retention after a large number of charge-discharge cycles. Additionally, it is important that any new electroactive material should be easily replaceable with known materials in conventional electrode fabrication processes. These processes generally rely on calendaring the electrode material onto a current collector to densify the electrode layer and improve the space utilization within the electrode design. Porous materials are prone to fracture during electrode fabrication, resulting in impaired electrochemical performance. Therefore, it is particularly required that new electrochemical materials should have sufficient structural strength, as well as increased electrochemical storage capacity and reversible capacity retention. Summary of the Invention

[0012] In one embodiment, the present invention provides a particulate material composed of a plurality of composite particles, wherein the composite particles comprise:

[0013] (a) A porous carbon framework comprising micropores and mesopores, wherein the total pore volume of the micropores and mesopores, as measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a number with a value between 0.5 and 1.5, where PD 90 The pore size is at least 3 nm and less than 12 nm; and it is based on P 1 The micropore volume fraction ranged from 0.43 to 0.85.

[0014] and

[0015] (b) A plurality of nanoscale elemental silicon structural domains located within the pores of the porous carbon framework, wherein the particulate material comprises 25% to 65% silicon by weight, and wherein at least 20% by weight of the silicon is surface silicon as determined by thermogravimetric analysis (TGA).

[0016] Preferably, where P 1 The value is at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75.

[0017] Preferably, where P 1 The value shall not exceed 1.4, or 1.3, or 1.2, or 1.1, or 1, or 0.95.

[0018] Preferably, the PD of the porous carbon framework 90 The pore size is no more than 10 nm, or no more than 8 nm, or no more than 6 nm.

[0019] Preferably, the PD of the porous carbon framework 90 The pore size is at least 3.2 nm, or at least 3.5 nm, or at least 3.8 nm, or at least 4 nm.

[0020] Preferably, the PD of the porous carbon framework 75 The pore size is no more than 10 nm, or no more than 8 nm, or no more than 6 nm, or no more than 4 nm.

[0021] Preferably, the PD of the porous carbon framework 50 The pore size is no more than 2 nm, or no more than 1.9 nm, or no more than 1.8 nm, or no more than 1.7 nm, or no more than 1.6 nm.

[0022] Preferably, the PD of the porous carbon framework 50 The pore size is at least 1 nm, or at least 1.1 nm, or at least 1.2 nm.

[0023] Preferably, the PD of the porous carbon framework30 The pore size is not more than 1.6 nm, or not more than 1.5 nm, or not more than 1.4 nm, or not more than 1.3 nm, or not more than 1.2 nm, or not more than 1.1 nm, or not more than 1 nm.

[0024] Preferably, the PD of the porous carbon framework 30 The pore size is at least 0.6 nm or at least 0.7 nm.

[0025] Preferably, the micropore volume fraction of the porous carbon framework is at least 0.45, or at least 0.48, or at least 0.5, or at least 0.52, or at least 0.54, or at least 0.56, or at least 0.58, or at least 0.6, based on the total volume of micropores and mesopores.

[0026] Preferably, the micropore volume fraction of the porous carbon framework is no more than 0.8, or no more than 0.79, or no more than 0.78, or no more than 0.76, or no more than 0.74, or no more than 0.72, or no more than 0.7, based on the total volume of micropores and mesopores.

[0027] Preferably, the total volume of the micropores in the porous carbon framework is at least 0.36 cm³. 3 / g, or at least 0.38cm 3 / g, at least 0.40 cm 3 / g, at least 0.42 cm 3 / g.

[0028] Preferably, the volume fraction of pores with a pore size of less than 5 nm is at least 0.8, or at least 0.82, or at least 0.84, or at least 0.86, or at least 0.88, or at least 0.9.

[0029] Preferably, the volume fraction of pores with a pore size of less than 10 nm is at least 0.9, or at least 0.92, or at least 0.94, or at least 0.96.

[0030] Preferably, the volume fraction of pores with a pore size of less than 20 nm is at least 0.94, or at least 0.96, or at least 0.98.

[0031] Preferably, the porous carbon framework has a bimodal or multimodal pore size distribution.

[0032] Preferably, the total volume of pores with diameters in the range of 50 nm to 100 nm is defined as P. 2 cm 3 / g, where P 2 Not exceeding 0.2×P 1or not exceeding 0.1×P 1 or not exceeding 0.05×P 1 or not exceeding 0.02×P 1 or not exceeding 0.01×P 1 or not exceeding 0.005×P 1 .

[0033] Preferably, the BET surface area of ​​the porous carbon framework is 1200 to 3000 m². 2 / g.

[0034] Preferably, the particulate material comprises at least 26% by weight, or at least 28% by weight, or at least 30% by weight, or at least 32% by weight of silicon, or at least 34% by weight of silicon, or at least 36% by weight of silicon, or at least 38% by weight of silicon, or at least 40% by weight of silicon, or at least 42% by weight of silicon, or at least 44% by weight of silicon.

[0035] Preferably, the particulate material contains no more than 60% by weight of silicon, no more than 58% by weight of silicon, no more than 56% by weight of silicon, no more than 54% by weight of silicon, no more than 52% by weight of silicon, or no more than 50% by weight of silicon.

[0036] Preferably, the porous carbon framework is a steam-activated porous carbon framework.

[0037] Preferably, the porous carbon framework comprises at least 80% by weight of carbon, or at least 90% by weight of carbon, or at least 95% by weight of carbon, or at least 98% by weight of carbon, or at least 99% by weight of carbon.

[0038] Preferably, the weight ratio of silicon to the porous carbon framework is at least 0.50 × P. 1 or at least 0.55×P 1 or at least 0.6×P 1 or at least 0.65×P 1 or at least 0.7×P 1 or at least 0.75×P 1 or at least 0.8×P 1 or at least 0.85×P 1 or at least 0.9×P 1 or at least 0.95×P 1 , or at least 1×P 1 .

[0039] Preferably, the weight ratio of silicon to the porous carbon framework does not exceed 1.9 × P. 1 or not exceeding 1.85×P 1 or not exceeding 1.8 × P 1or not exceeding 1.75×P 1 or not exceeding 1.7 × P 1 or not exceeding 1.65×P 1 or not exceeding 1.6×P 1 or not exceeding 1.55×P 1 or not exceeding 1.5×P 1 .

[0040] Preferably, as determined by thermogravimetric analysis (TGA), at least 22% by weight, or at least 25% by weight, or at least 30% by weight, or at least 35% by weight, or at least 40% by weight, or at least 45% by weight, of silicon is surface silicon.

[0041] Preferably, the silicon is a coarse phase silicon, as determined by thermogravimetric analysis (TGA), comprising no more than 10% by weight, or no more than 8% by weight, or no more than 6% by weight, or no more than 5% by weight, or no more than 4% by weight, or no more than 3% by weight, or no more than 2% by weight, or no more than 1.5% by weight.

[0042] Preferably, at least a portion of the micropores and / or mesopores comprises void spaces completely encapsulated by the silicon.

[0043] Preferably, the D of the composite particles 50 The particle size ranges from 1 to 30 µm.

[0044] Preferably, the D of the composite particles 10 The particle size is at least 0.5 µm, or at least 0.8 µm, or at least 1 µm, or at least 1.5 µm, or at least 2 µm.

[0045] Preferably, the D of the composite particles 90 The particle size is not more than 50 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 15 µm.

[0046] Preferably, the BET surface area of ​​the composite particles does not exceed 100 m². 2 / g, or not exceeding 80 m 2 / g, or not exceeding 60 m 2 / g, or not exceeding 50 mg 2 / g, or not exceeding 40 mg 2 / g, or not exceeding 30 m 2 / g, or not exceeding 25 mg 2 / g, or not exceeding 20 mg 2 / g, or not exceeding 15 m 2 / g, or not exceeding 10 mg2 / g.

[0047] Preferably, the BET surface area of ​​the composite particles is at least 0.1 m². 2 / g, or at least 1 m 2 / g, or at least 2m 2 / g, or at least 5 m 2 / g.

[0048] Preferably, the volume of micropores and mesopores in the composite particles in the presence of silicon, as measured by nitrogen adsorption, does not exceed 0.15 × 10⁻⁶ P. 1 or not exceeding 0.10×P 1 or not exceeding 0.05×P 1 or not exceeding 0.02×P 1 .

[0049] Preferably, the composite particles are obtained by chemical vapor infiltration (CVI) of silicon-containing precursors into the porous structure of a porous carbon framework.

[0050] In another embodiment, the present invention provides a composition comprising the particulate material as defined above and at least one other component.

[0051] Preferably, the composition comprises at least one additional particulate electroactive material.

[0052] Preferably, the composition comprises 20% to 70% by weight, or 25% to 65% by weight, or 30% to 60% by weight of the at least one other particulate electroactive material.

[0053] Preferably, based on the total dry weight of the composition, the composition comprises 15% to 60% by weight, or 20% to 50% by weight, or 30% to 50% by weight of the particulate material defined above.

[0054] Preferably, the at least one additional particulate electroactive material is selected from graphite, hard carbon, silicon, tin, germanium, aluminum, and lead.

[0055] Preferably, the composition is substantially free of additional particulate electroactive materials.

[0056] Preferably, based on the total dry weight of the composition, the composition comprises at least 50% by weight, or at least 60% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight of the particulate material defined above.

[0057] Preferably, the composition comprises an adhesive.

[0058] Preferably, based on the total dry weight of the composition, the composition comprises 0.5% to 20% by weight, or 1% to 15% by weight, or 2% to 10% by weight, or 5% to 10% by weight of the binder.

[0059] Preferably, the composition comprises one or more conductive additives.

[0060] Preferably, based on the total dry weight of the composition, the composition comprises 0.5% to 20% by weight, or 1% to 15% by weight, or 2% to 10% by weight, or 5% to 10% by weight of the one or more conductive additives.

[0061] In another embodiment, the present invention provides an electrode comprising the particulate material defined above in electrical contact with the current collector.

[0062] Preferably, the particulate material is in the form of the composition defined above.

[0063] In another embodiment, the present invention provides a rechargeable metal-ion battery comprising: (i) an anode, wherein the anode comprises the electrodes described above; (ii) a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions; and (iii) an electrolyte between the anode and the cathode.

[0064] In another embodiment, the present invention provides a method for preparing composite particles, the method comprising the following steps:

[0065] (a) Provide a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein: (i) the total pore volume of said micropores and mesopores, measured by gas adsorption, is P. 1 cm 3 / g, where P 1 (ii) PD represents a number with a value between 0.5 and 1.5; 90 The pore size is at least 3 nm and less than 12 nm; and (iii) based on P 1 The micropore volume fraction ranged from 0.43 to 0.85.

[0066] (b) The plurality of porous carbon particles are brought into contact with a gas containing 0.5 vol% to 20 vol% silicon precursor gas at a temperature of 400 to 700 °C to deposit silicon into the pores of the porous carbon particles.

[0067] In another embodiment, the present invention provides a method for preparing composite particles, the method comprising the following steps:

[0068] (a) Provide a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein: (i) the total pore volume of said micropores and mesopores, measured by gas adsorption, is P. 1 cm 3 / g, where P 1 (ii) PD represents a number with a value between 0.5 and 1.5; 90 The pore size is at least 3 nm and less than 12 nm; and (iii) based on P 1 The micropore volume fraction ranged from 0.43 to 0.85.

[0069] (b) The plurality of porous carbon particles are contacted with a gas containing silicon precursor gas at a temperature of 400 to 700 °C to deposit silicon into the pores of the porous carbon particles, wherein the partial pressure of the silicon precursor gas is 0.5 to 20 kPa.

[0070] Preferably, the composite particles are as defined above. Attached Figure Description

[0071] Figure 1 The TGA trace of a particulate material comprising a high surface silicon level and a low bulk coarse silicon level according to the present invention is shown.

[0072] Figure 2 TGA traces of particulate materials containing low surface silicon levels and high bulk coarse silicon levels are shown. Detailed Implementation

[0073] The inventors have determined that the properties of composite materials containing silicon and porous carbon depend on the pore structure of the porous carbon framework, as well as the amount of silicon and its distribution within the porous carbon framework. It has now been further determined that the properties of these composite materials depend on the location of silicon, its characteristic length dimension, and surface functionality.

[0074] Generally, it is known that atoms on a material surface have different bonding and interaction configurations than atoms in the bulk phase of the material, and this difference is usually described by the surface energy of the material. In the case of silicon deposited by chemical vapor infiltration (CVI), the free valences of silicon atoms on the surface are typically occupied by hydride groups. If this hydride-terminated silicon surface is air-accessible, it reacts with oxygen to form a native oxide surface. However, surfaces that are not air-accessible retain the hydride-terminated form.

[0075] It has been found that composite materials with a high proportion of hydride-terminated surface silicon without a native oxide layer improve their performance as electroactive materials. The amount of this hydride-terminated surface silicon can be quantified using thermogravimetric analysis (TGA).

[0076] In a first aspect, the present invention provides a particulate material composed of a plurality of composite particles, wherein the composite particles comprise:

[0077] (a) A porous carbon framework containing micropores and mesopores.

[0078] The total pore volume of the micropores and mesopores, measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a value between 0.5 and 1.5.

[0079] Among them PD 90 The pore size is at least 3 nm and less than 12 nm; and

[0080] Among them, based on P 1 The micropore volume fraction ranged from 0.43 to 0.85; and

[0081] (b) Multiple nanoscale elemental silicon structural domains located within the pores of the porous carbon framework.

[0082] The particulate material contains 25% to 65% silicon, and wherein at least 20% of the silicon is surface silicon, as determined by thermogravimetric analysis (TGA).

[0083] Due to this unique particle structure, composite particles have the ability to improve upon existing SiO₂. x The electrochemical performance of the technology. In particular, the particulate materials of the present invention have greater electrochemical capacity, lower overall expansion and comparable reversible capacity retention, resulting in the possibility of loading higher capacity electroactive materials than previously achieved.

[0084] The composite particles of the present invention have a structure in which multiple elemental nanoscale silicon domains are located within the pore network of a porous carbon framework. As used herein, the term "nanoscale silicon domain" refers to a nanoscale elemental silicon body having a defined maximum size by positioning silicon within the micropores and / or mesopores of a porous carbon framework.

[0085] Microporous carbon frameworks offer the following benefits: electroactive materials reside within a microporous network in the form of small structural domains with dimensions of approximately a few nanometers or less. These fine electroactive structures exhibit lower tolerance to elastic deformation and higher fracture resistance compared to larger electroactive structures, thus enabling lithiation and delithiation without excessive structural stress. Therefore, the microporosity of the porous carbon framework ensures that the electroactive material itself possesses sufficient elasticity to withstand repeated volume changes during multiple charge-discharge cycles without significant capacity loss.

[0086] The particulate material of this invention is characterized by a high content of unoxidized surface silicon, quantified by TGA analysis. This analytical method relies on the principle that a weight increase is observed when silicon is in air and oxidized to silicon dioxide (SiO2) at high temperatures. The mechanism of silicon oxidation is temperature-dependent. Silicon atoms on the surface of silicon nanostructures are oxidized at lower temperatures compared to silicon atoms in the bulk phase of silicon nanostructures (Reference: Bardet et al., Phys. Chem. Chem. Phys. (2016), 18, 18201). TGA analysis enables the quantification of the relative content of surface silicon based on the weight increase observed when silicon is in air and oxidized to silicon dioxide (SiO2) at high temperatures. By plotting the weight increase against temperature, bulk silicon and surface silicon in the sample can be distinguished and quantified.

[0087] Figure 1 The TGA trace of a particulate material comprising a high surface silicon level and a low bulk coarse silicon level according to the present invention is shown.

[0088] Figure 2 TGA traces of particulate materials containing low surface silicon levels and high bulk coarse silicon levels are shown.

[0089] like Figure 1 and 2 As shown, the amount of unoxidized surface silicon was determined from the characteristic TGA traces of these materials. The initial mass loss at approximately 300 °C (in...) Figure 1 and 2 Following the mass decrease shown in (a) to (b), a significant mass increase was observed starting at approximately 400 °C and peaking between 550 °C and 650 °C. Figure 1 and 2 (This is shown as a mass increase from (b) to (c)). Then, a mass decrease was observed when the porous carbon framework was oxidized to CO2 gas (the mass decrease starting from (c)), and then a mass increase corresponding to the continued conversion of silicon to SiO2 was observed again above about 800 °C, increasing asymptotically above 1000 °C as silicon oxidation is complete (the mass increase from (d) to (e)). The temperature at which the weight increase occurs is related to the silicon structure; surface silicon oxidizes at lower temperatures, while bulk silicon oxidizes at higher temperatures. Therefore, the coarser the silicon structural domains, the more oxidation is observed at higher temperatures.

[0090] Any natural oxides that have formed on silicon surfaces exposed to air do not affect TGA analysis, as oxidized silicon does not result in an increase in mass during TGA analysis. Therefore, the more silicon surfaces capable of reacting with air to form natural oxides, the less surface silicon will be observed via TGA. To avoid ambiguity, the calculation of “surface silicon” therefore only considers silicon that is not oxidized at the start of TGA analysis after the material has been passivated with air or other surface passivating agents, as described herein (i.e., the particulate material is not held under any particular inert conditions prior to TGA analysis).

[0091] As defined herein, “surface silicon” is the initial mass increase in a TGA trace measured from a minimum between 150 °C and 500 °C to a maximum mass between 550 °C and 650 °C, wherein the TGA is performed in air at a heating rate of 10 °C / min. This mass increase is considered to be due to the oxidation of the surface silicon, thus allowing the percentage of surface silicon as a proportion of the total silicon to be determined according to the following formula:

[0092] Y = 1.875 × [(M max – M min ) / M f ] ×100%

[0093] Where Y is the percentage of surface silicon, representing the proportion of total silicon in the sample, and M... max The maximum mass of the sample measured within the temperature range of 550 ℃ to 650 ℃. Figure 1 and 2 The mass (c) in M min It is the minimum mass of the sample at temperatures above 150 °C and below 500 °C. Figure 1 and 2 The mass of (b) in M, and M f The mass of the sample when oxidation is completed at 1400 ℃ ( Figure 1 and 2 The mass (e) of the SiO2. For completeness, 1.875 should be understood as the molar mass ratio of SiO2 to O2 (i.e., the mass ratio of the SiO2 formed to the mass increase due to the addition of oxygen). Typically, TGA analysis is performed using a sample amount of 10 mg ± 2 mg.

[0094] It has been found that when the surface silicon content, as determined by the above-mentioned TGA method, is at least 20% by weight of the total silicon content in the material, the reversible capacity retention after multiple charge / discharge cycles is significantly improved. Preferably, as determined by thermogravimetric analysis (TGA), at least 22% by weight, or at least 25% by weight, or at least 30% by weight, or at least 35% by weight, or at least 40% by weight, or at least 45% by weight of silicon is surface silicon.

[0095] Optionally, the amount of surface silicon determined by TGA is at most 80% by weight, or at most 75% by weight, or at most 65% by weight, or at most 60% by weight, or at most 55% by weight of the total silicon in the particulate material. For example, the amount of surface silicon determined by TGA can be from 20% to 80% by weight, or 22% to 75% by weight, or 25% to 70% by weight, or 30% to 65% by weight, or 35% to 60% by weight, or 40% to 55% by weight of the total silicon in the particulate material. The amount of surface silicon determined by TGA can also be in the range of 20% to 55% by weight, or 22% to 60% by weight, or 25% to 65% by weight, or 30% to 70% by weight, or 35% to 75% by weight, or 40% to 80% by weight of the total silicon in the particulate material. Further preferred ranges can be defined by combining the upper and lower limits of any of the foregoing ranges.

[0096] The fact that a significant proportion of hydride-terminated surface silicon can still be measured in particulate materials even after passivation in air indicates that the composite particles contain internal silicon surfaces that are not easily accessible by air. This suggests that the internal pore spaces of the porous carbon framework are first lined with silicon and then capped to form internal void spaces, in which the hydride-terminated silicon surfaces are oriented into the closed internal void spaces. This further indicates that the silicon domains have a characteristic length dimension much smaller than their own pores.

[0097] Because the internal voids are inaccessible to the electrolyte, the silicon surface is protected from SEI formation, thereby minimizing irreversible lithium loss during the first charge cycle. It also largely prevents additional exposure of electroactive materials in subsequent charge-discharge cycles, so that SEI formation is not a significant destructive mechanism leading to capacity loss. Simultaneously, the silicon is hydrostatically confined during lithiation, allowing the voids to be utilized during lithiation-induced expansion.

[0098] Porous carbon frameworks comprise three-dimensionally interconnected open pore networks, including micropores and mesopores. Porous carbon frameworks may optionally also include small-volume macropores. According to standard 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 between 2 and 50 nm, and the term "macropore" is used herein to refer to pores with a diameter greater than 50 nm.

[0099] It has been found that the high surface silicon levels required by this invention can only be obtained when the pore structure of the porous carbon framework is controlled within the specific range defined above. References herein to the volumes of micropores, mesopores, and macropores in the porous carbon framework, and 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 occupying some or all of the pore volume).

[0100] The total volume of micropores and mesopores (i.e., the total pore volume of pores with diameters in the range of 0 to 50 nm) is referred to as P in this paper. 1 cm 3 / g, where P 1 Values ​​are dimensionless numbers ranging from 0.5 to 1.5. To avoid ambiguity, the pore volume of the porous carbon framework mentioned herein (unless otherwise indicated) refers to the pore volume of the porous carbon framework alone, i.e., the pore volume of the porous carbon framework measured in the absence of any electroactive material (or any other material) occupying the pores of the porous carbon framework.

[0101] P 1 The value of P is preferably at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75. A framework with higher porosity is advantageous because it allows for the inclusion of larger amounts of silicon within the porous structure without compressing the porous carbon framework under compressive stress during electrode fabrication or under expansion stress due to silicon lithiation. However, if P... 1 If the level is too high, it becomes impossible to achieve the elevated surface silicon level that is a feature of this invention. Therefore, P 1 The value is preferably 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, or no more than 0.95.

[0102] For example, P 1 It can be in the range of 0.55 to 1.4, or 0.6 to 1.4, or 0.6 to 1.3, or 0.65 to 1.3, or 0.65 to 1.2, or 0.7 to 1.2, or 0.7 to 1.1, or 0.7 to 1, or 0.75 to 0.95.

[0103] Following the standard methods described in ISO 15901-2 and ISO 15901-3, nitrogen adsorption was used to reduce the nitrogen concentration to 10 at 77 K. -6The relative pressure p / p0 is determined using quenched solid density functional theory (QSDFT) to determine the total volume of micropores and mesopores, as well as the pore size distribution of micropores and mesopores. Nitrogen adsorption is a technique that characterizes the porosity and pore size distribution of a material by condensing a gas within 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 point all pores are filled with liquid. The nitrogen pressure is then gradually decreased to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them allows for the determination of pore volume and pore size distribution. Suitable instruments for measuring pore volume and pore size distribution by nitrogen adsorption include the TriStar II and TriStar II Plus porosity analyzers (available from Micromeritics Instrument Corporation, USA) and the Autosorb IQ porosity analyzer (available from Quantachrome Instruments).

[0104] Nitrogen adsorption is effective for measuring pore volume and pore size distribution of pores with a maximum diameter of 50 nm, but it is less reliable for pores with much larger diameters. For the purposes of this invention, nitrogen adsorption is therefore used only for pores with a maximum diameter of 50 nm (including 50 nm) to determine pore volume and pore size distribution. As described above, P 1 The value is determined by considering only pores with a maximum diameter of 50 nm (including 50 nm) (i.e., only micropores and mesopores).

[0105] General term "PD" n In this paper, "pore size" refers to the nth percentile pore size based on the total volume of micropores and mesopores. For example, the term "PD" as used herein. 90 "Aperture" refers to the measured total volume of micropores and mesopores (as measured by P). 1 The aperture is the aperture that is 90% lower than a certain aperture diameter.

[0106] As mentioned above, the PD of porous carbon framework 90 The pore size is at least 3 nm and less than 12 nm. It has been found that if the PD... 90 If the value is too low, it is impossible to deposit silicon into the micropores, and instead, silicon is deposited on the outer surface of the porous carbon framework. However, if the PD value is too low, silicon will deposit on the outer surface of the porous carbon framework. 90 If the value is too high, excessive coarse silica deposits and / or excessive natural oxides will result in low surface silica content.

[0107] PD of porous carbon framework 90 The pore size is preferably no more than 10 nm, or no more than 8 nm, or no more than 6 nm. Preferably, the PD uses a porous carbon framework.90 The pore size is at least 3.2 nm, or at least 3.5 nm, or at least 3.8 nm, or at least 4 nm. For example, PD with a porous carbon framework. 90 The pore size is preferably in the range of 3.5 to 10 nm, or 3.8 to 8 nm, or 4 to 6 nm.

[0108] PD of porous carbon framework 75 The pore size is preferably no more than 10 nm, or no more than 8 nm, or no more than 6 nm, or no more than 4 nm. PD of porous carbon framework 75 The pore size is preferably at least 1 nm.

[0109] PD of porous carbon framework 50 The pore size is preferably no more than 2 nm, or no more than 1.9 nm, or no more than 1.8 nm, or no more than 1.7 nm, or no more than 1.6 nm. Preferably, the PD has a porous carbon framework. 50 The pore size is at least 1 nm, or at least 1.1 nm, or at least 1.2 nm. For example, PD with a porous carbon framework. 50 The pore size is preferably in the range of 1 to 2 nm, or 1 to 1.9 nm, or 1.1 to 1.8 nm, or 1.1 to 1.7 nm, or 1.2 to 1.6 nm.

[0110] PD of porous carbon framework 30 The pore size is preferably no more than 1.6 nm, or no more than 1.5 nm, or no more than 1.4 nm, or no more than 1.3 nm, or no more than 1.2 nm, or no more than 1.1 nm, or no more than 1 nm. Preferably, the PD has a porous carbon framework. 30 The pore size is at least 0.6 nm or at least 0.7 nm.

[0111] PD 90 Aperture and PD 30 The aperture ratio is preferably no more than 14, or no more than 12, or no more than 10, or no more than 8.

[0112] PD 90 Aperture and PD 10 The aperture ratio is preferably no more than 11, or no more than 10, or no more than 9, or no more than 8, or no more than 7.

[0113] As used in this paper, the micropore volume fraction refers to the volume of micropores expressed as a fraction of the total volume of micropores and mesopores, denoted by P. 1In other words, the micropore volume fraction is the volume fraction of pores with a diameter of less than 2 nm relative to the total volume of pores with a diameter of no more than 50 nm. As discussed above, the micropore volume fraction of the porous framework is selected in the range of 0.43 to 0.85 to obtain the desired high level of surface silicon content in the composite particles.

[0114] Preferably, based on the total volume of micropores and mesopores, the micropore volume fraction is at least 0.45, or at least 0.48, or at least 0.5, or at least 0.51, or at least 0.52, or at least 0.54, or at least 0.56, or at least 0.58, or at least 0.6. Preferably, based on the total volume of micropores and mesopores, the micropore volume fraction is no more than 0.8, or no more than 0.79, or no more than 0.78, or no more than 0.76, or no more than 0.74, or no more than 0.72, or no more than 0.7.

[0115] Based on the total volume of micropores and mesopores, the micropore volume fraction can optionally be between 0.45 and 0.85, or 0.5 and 0.8, or 0.45 and 0.78, or 0.48 and 0.8, or 0.48 and 0.78, or 0.48 and 0.76, or 0.5 and 0.8, or 0.5 and 0.78, or 0.5 and 0.76, or 0.5 and 0.74, or 0.5 and 0. The range is 0.72, or 0.5 to 0.7, or 0.51 to 0.76, or 0.52 to 0.74, or 0.53 to 0.74, or 0.54 to 0.72, or 0.6 to less than 0.8, or 0.6 to 0.79, or 0.6 to 0.78, or 0.6 to 0.76, or 0.6 to 0.74, or 0.6 to 0.72, or 0.6 to 0.7.

[0116] The total volume of micropores in the porous carbon framework (measured using nitrogen adsorption at 77 K as described herein) is preferably at least 0.36 cm³. 3 / g, or at least 0.38 cm 3 / g, at least 0.40 cm 3 / g, at least 0.42 cm 3 / g. Because silicon located in micropores has a small length dimension, the higher total micropore volume allows a higher proportion of surface silicon to be contained within the porous carbon framework, thereby allowing for higher gravimetric and volumetric capacities of the composite particles.

[0117] The volume of any pore within the mesoporous range is preferably substantially within the smaller mesoporous range. Therefore, based on the total volume of micropores and mesopores, the volume fraction of pores with a pore size of 5 nm or less is preferably at least 0.8, or at least 0.82, or at least 0.84, or at least 0.86, or at least 0.88, or at least 0.9. Preferably, based on the total volume of micropores and mesopores, the volume fraction of pores with a pore size of 10 nm or less is preferably at least 0.9, or at least 0.92, or at least 0.94, or at least 0.96. Preferably, based on the total volume of micropores and mesopores, the volume fraction of pores with a pore size of 20 nm or less is preferably at least 0.94, or at least 0.96, or at least 0.98.

[0118] A small fraction of pores with diameters in the larger mesopore range can advantageously facilitate electrolyte access to the silicon domain. Therefore, pores with diameters in the range of 10 to 50 nm (i.e., larger mesopores) can optionally account for no more than 2%, 4%, or 6% of the total micropore and mesopore volume of the porous carbon framework.

[0119] The pore size distribution of the porous carbon framework is preferably bimodal or multimodal. As used herein, the term "pore size distribution" refers to the distribution of pore size in the porous carbon framework relative to the cumulative total internal pore volume. A bimodal or multimodal pore size distribution may be preferred because the close proximity between micropores and pores with larger diameters provides the advantage of efficient ion transport from the porous network to silicon. Consequently, the particulate material exhibits high ion diffusivity and thus improved rate performance.

[0120] Due to limitations in available analytical techniques, it is not possible to measure pore volume and pore size distribution across the entire range of micropores, mesopores, and macropores using a single technique. In the case of porous carbon frameworks including macropores, the pore volume in the range of greater than 50 nm to a maximum of 100 nm is considered to have P in this paper. 2 cm 3 The value of / g was determined by mercury porosimetry. As mentioned above, P 2 The value relates to the pore volume of the porous carbon framework when measured alone, that is, 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.

[0121] To avoid ambiguity, P 2 The value only considers pores with diameters ranging from greater than 50 nm to a maximum of 100 nm (inclusive), meaning it only includes the volume of macropores with a maximum diameter of 100 nm. To determine P... 2The value of P is not considered for any pore volume below 50 nm as measured by mercury intrusion porosimetry (as mentioned above, nitrogen adsorption is used to characterize mesopores and micropores). For the purposes of this invention, the pore volume above 100 nm as measured by mercury intrusion porosimetry is assumed to be the interparticle porosity, and the value of P is determined by... 2 The value of is not considered.

[0122] Mercury porosimetry (also known as mercury intrusion porosimetry) is a technique for characterizing the porosity and pore size distribution of a material sample by applying different levels of pressure to the sample immersed in mercury. The pressure required to allow mercury to penetrate the pores of the sample is inversely proportional to the pore size. The values ​​obtained by mercury intrusion porosimetry reported in this paper are based on ASTM UOP578-11, where the surface tension γ is 480 mN / m and the contact angle φ is 140° for mercury at room temperature. o Mercury has a density of 13.5462 g / cm³ at room temperature. 3 A variety of high-precision mercury porosimetry instruments are commercially available, such as the AutoPore IV series automated mercury porosimeter, which is available from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury porosimetry, see PA Webb and C. Orr, “Analytical Methods in Fine Particle Technology,” 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0123] With respect to the volume of micropores and mesopores (and therefore P) 1 Compared to the value of P, the volume of the macropore (and therefore P) 2 The value of is preferably small. Although a small number of macropores can be useful for facilitating the entry of electrolytes into the porous network, the advantages of the present invention are essentially obtained by accommodating silicon in micropores and smaller mesopores.

[0124] Therefore, according to the present invention, the total volume of macropores in the porous carbon framework measured by mercury porosimetry is P. 2 cm 3 / g, where P 2 The preferred value is at most 0.2 × P. 1 or at most 0.1×P 1 Or at most 0.05×P 1 Or at most 0.02×P 1 Or at most 0.01×P 1 Or at most 0.005×P 1 .

[0125] 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 to nitrogen or mercury from the outside of the porous carbon framework. As indicated in this paper, the porosity value (P...) 1 and P 2 Porosity should be understood as referring to the volume of open pores (i.e., pores accessible to the fluid from the outside of the porous carbon framework). In this paper, when specifying porosity values, fully encapsulated pores that cannot be identified by nitrogen adsorption or mercury porosimetry should not be considered. Similarly, for determining P... 1 The value is not considered, nor is the pore volume of any pore located in pores that are as small as below the detection limit of nitrogen adsorption.

[0126] The preferred BET surface area of ​​the porous carbon framework is 1200 to 3000 m². 2 / g. Preferably, the BET surface area of ​​the porous carbon framework is at least 1500 m². 2 / g, or at least 1700 m 2 / g. Preferably, the BET surface area of ​​the porous carbon framework does not exceed 2500 m². 2 / g, or not exceeding 2000 m 2 / g. As used herein, the term “BET surface area” should be understood to refer to the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on a solid surface according to ISO 9277 using the Brunauer–Emmett–Teller principle.

[0127] Porous carbon frameworks can include crystalline carbon or amorphous carbon, or a mixture of amorphous and crystalline carbon. Porous carbon frameworks can be hard or soft carbon frameworks and can be suitably obtained through known procedures involving the pyrolysis of carbon-containing materials, including organic materials, resins, and polymers. Porous carbon materials can also be obtained by other methods, such as from carbide-containing precursors. Highly porous carbon materials are commercially available and are commonly referred to as activated carbon.

[0128] The porous carbon framework preferably has an elemental composition comprising at least 90% by weight of carbon, more preferably at least 95% by weight of carbon, more preferably at least 98% by weight of carbon, or at least 99% by weight of carbon. The porous carbon framework may optionally contain small amounts of other elements, such as oxygen, nitrogen, sulfur, and hydrogen. The elemental composition of the porous carbon framework can be determined using conventional elemental analysis techniques performed in the absence of silicon.

[0129] As used in this article, the term "hard carbon" refers to carbon atoms found to be primarily sp(s) within nanoscale polyaromatic domains. 2 A disordered carbon matrix in a hybrid state (triple bond). Polyaromatic domains are cross-linked using chemical bonds such as COC bonds.

[0130] Due to the chemical crosslinking between polyaromatic domains, hard carbon cannot be converted into graphite at high temperatures. Hard carbon exhibits graphitic properties, as evidenced by its large G band (~1600 cm⁻¹) in Raman spectroscopy. -1 This is evidenced by the fact that the carbon is not entirely graphitic, as evidenced by the distinct D band (~1350 cm⁻¹) in the Raman spectrum. -1 As proven by ).

[0131] As used in this article, the term "soft carbon" also refers to carbon atoms found primarily in polyaromatic domains with dimensions in the 5-200 nm range, where sp atoms are located. 2 Disordered carbon matrices in a hybrid state (triple bond). Compared to hard carbon, the polyaromatic domains in soft carbon are associated through intermolecular forces rather than cross-linked by chemical bonds. This means they will graphitize at high temperatures. Porous carbon frameworks preferably contain at least 50% sp. 2 Hybridized carbon (measured by XPS). For example, porous carbon frameworks can suitably contain 50% to 98% sp. 2 Hybridized carbon, 55% to 95% sp 2 Hybridized carbon, 60% to 90% sp 2 Hybridized carbon, or 70% to 85% sp 2 Hybridized carbon.

[0132] A wide variety of materials can be used to prepare suitable porous carbon frameworks. Examples of usable organic materials include plant biomass, including lignocellulosic materials (such as coconut shells, rice husks, wood, etc.), and fossil carbon sources, such as coal. Examples of resin and polymer materials that form porous carbon frameworks upon pyrolysis include phenolic resins, phenolic varnish resins, bitumen, melamine, polyacrylates, polystyrene, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers containing monomer units of acrylates, styrene, α-olefins, vinylpyrrolidone, and other olefinically unsaturated monomers. Depending on the raw materials and conditions of the pyrolysis process, a wide variety of hard carbon materials are available in the art.

[0133] Porous carbon frameworks can undergo chemical or gas activation processes to increase the volume of mesopores and micropores. Suitable activation processes involve contacting pyrolytic carbon with one or more of oxygen, water vapor, CO, CO2, and KOH at temperatures ranging from 600 to 1000°C. Preferably, the porous carbon framework is a steam-activated porous carbon framework.

[0134] Mesoporous structures can also be obtained through known templated processes using removable pore-forming agents such as MgO and other colloidal or polymeric templates (which can be removed by thermal or chemical means after pyrolysis or activation).

[0135] The elemental composition of the composite particles can be determined by elemental analysis. Elemental analysis is used to determine the weight percentages of both silicon and carbon in the composite particles. Optionally, the amounts of hydrogen, nitrogen, and oxygen can also be determined by elemental analysis. Preferably, elemental analysis is also used to determine the weight percentage of carbon (and optionally hydrogen, nitrogen, and oxygen) in the individual porous carbon framework. Determining the weight percentage of carbon in the individual porous carbon framework takes into account the possibility that the porous carbon framework contains a small number of heteroatoms within its molecular framework. The two measurements performed together allow for a reliable determination of the weight percentage of silicon relative to the entire porous carbon framework.

[0136] Silicon content is preferably determined by ICP-OES (Induced Coupled Plasma-Optical Emission Spectroscopy). A variety of ICP-OES instruments are commercially available, such as the iCAP® 7000 series ICP-OES analyzers (available from Thermo Fisher Scientific). Alternatively, the carbon content (and, if desired, hydrogen, nitrogen, and oxygen content) of the composite particles and individual porous carbon framework can be determined by combustion and infrared (IR) absorption techniques. A suitable instrument for determining carbon, hydrogen, nitrogen, and oxygen content is the TruSpec® Micro elemental analyzer (available from LECO Corporation).

[0137] Elemental analysis revealed that the particulate material of the present invention contains 25% to 65% silicon, preferably 30% to 65% silicon. More preferably, the particulate material of the present invention contains at least 26% by weight, or at least 28% by weight, or at least 30% by weight, or at least 32% by weight, or at least 34% by weight, or at least 36% by weight, or at least 38% by weight, or at least 40% by weight, or at least 42% by weight, or at least 44% by weight silicon. More preferably, the particulate material of the present invention contains no more than 60% by weight, or no more than 58% by weight, or no more than 56% by weight, or no more than 54% by weight, or no more than 52% by weight, or no more than 50% by weight silicon.

[0138] For example, the particulate material of the present invention may contain 26% to 65% by weight, or 28% to 65% by weight, or 30% to 65% by weight, or 32% to 60% by weight, or 34% to 60% by weight, or 36% to 60% by weight, or 38% to 58% by weight, or 40% to 58% by weight, or 42% to 56% by weight, or 44% to 54% by weight of silicon.

[0139] A minimum amount of silicon is required to ensure that particulate materials have sufficient volumetric capacity for commercial use. However, excessive silicon causes silicon to deposit in larger pores and / or on the surface of porous carbon frameworks, resulting in low surface silicon content and poor performance as an electroactive material.

[0140] The amount of silicon in the composite particles of the present invention is selected such that at least about 20% and at most about 78% of the internal pore volume (based on micropores and mesopores) of the porous carbon framework is occupied by silicon (in the uncharged state). Generally, the higher the micropore fraction of the porous carbon framework, the higher the amount of silicon that can be used without reducing the proportion of surface silicon.

[0141] Preferably, silicon occupies about 20% to about 78% of the internal pore volume of the porous carbon framework, for example, about 23% to 75%, or about 26% to 72%, or about 28% to 70%, or about 30% to 70%, or about 35% to 68%, or about 40% to 65%, or about 45% to 60% 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 detrimental to the volumetric capacity of the particulate material. However, the amount of silicon will not be so high as to hinder effective lithiation due to insufficient metal ion diffusion rate or insufficient expansion volume leading to mechanical resistance to lithiation.

[0142] By requiring the weight ratio of silicon to porous carbon framework to be within [0.50×P] 1 Up to 1.9×P 1 Within the range of 1:1, the amount of silicon in the porous carbon framework can be correlated with the available pore volume. This relationship takes into account the density of silicon and the pore volume of the porous carbon framework to define the weight ratio of silicon, and estimates that the occupied pore volume at said weight ratio is approximately 20% to 78%. Preferably, the weight ratio of silicon to the porous carbon framework is within [0.7 × P]. 1 Up to 1.8×P 1 Within the range of 1, this indicates that the occupied pore volume is approximately 30% to 78%.

[0143] Preferably, the weight ratio of silicon to the porous carbon framework is at least 0.50 × P. 1 or at least 0.55×P 1 or at least 0.6×P 1 or at least 0.65×P 1 or at least 0.7×P 1 or at least 0.75×P 1 or at least 0.8×P 1 or at least 0.85×P 1 or at least 0.9×P 1 or at least 0.95×P 1 , or at least 1×P1 Preferably, the weight ratio of silicon to the porous carbon framework does not exceed 1.85 × P. 1 or not exceeding 1.8 × P 1 or not exceeding 1.75×P 1 or not exceeding 1.7 × P 1 or not exceeding 1.65×P 1 or not exceeding 1.6×P 1 or not exceeding 1.55×P 1 or not exceeding 1.5×P 1 .

[0144] The composite particles preferably have a low total oxygen content (determined by elemental analysis). Oxygen may be present in the composite particles, for example, as part of a 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% by weight, more preferably less than 12% by weight, more preferably less than 10% by weight, even more preferably less than 5% by weight, for example less than 4% by weight, or less than 3% by weight, or less than 2% by weight, or less than 1% by weight, or less than 0.5% by weight. Preferably, silicon and carbon together constitute at least 90% by weight of the composite particles, more preferably at least 95% by weight.

[0145] Silicon may optionally contain small amounts of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, nitrogen, or germanium. Preferably, the dopants are present in a total amount not exceeding 2% by weight based on the total amount of silicon and one or more dopants.

[0146] In addition to the surface silicon content, the particulate material of the present invention preferably has a low coarse-phase silicon content, as determined by TGA. Coarse-phase silicon is defined herein as silicon oxidized at temperatures above 800 °C, as determined by TGA, wherein the TGA is performed in air at a heating rate of 10 °C / min. This is in Figure 1 and 2 The mass increase is shown from (d) to (e). Therefore, the coarse phase silicon content is determined according to the following formula:

[0147] Z = 1.875 × [(M f - M 800 ) / M f ] ×100%

[0148] Where Z is the percentage of silicon that was not oxidized at 800 °C, and M... 800 The mass of the sample at 800 °C ( Figure 1 and 2 The mass (d) in M, and M f The mass of ash at the point where oxidation is complete at 1400 ℃ ( Figure 1 and2 The mass (e) in the analysis is assumed to be SiO2 when any mass increase above 800 °C corresponds to the oxidation of silicon to SiO2 and the total mass at which oxidation is complete is SiO2.

[0149] Preferably, the silicon is coarse phase silicon as determined by TGA, not exceeding 10% by weight, or not exceeding 8% by weight, or not exceeding 6% by weight, or not exceeding 5% by weight, or not exceeding 4% by weight, or not exceeding 3% by weight, or not exceeding 2% by weight, or not exceeding 1.5% by weight.

[0150] Preferably, at least 30% by weight of silicon (e.g., 30% to 75% by weight, 30% to 70% by weight, or 30% to 65% by weight) is surface silicon, and no more than 10% by weight of silicon is bulk silicon, wherein both are determined by TGA. More preferably, at least 35% by weight of silicon (e.g., 35% to 70% by weight, 35% to 65% by weight, or 35% to 60% by weight) is surface silicon, and no more than 8% by weight of silicon is bulk silicon, wherein both are determined by TGA. More preferably, at least 40% by weight of silicon (e.g., 40% to 65% by weight, 40% to 60% by weight, or 40% to 55% by weight) is surface silicon, and no more than 5% by weight of silicon is bulk silicon, wherein both are determined by TGA. More preferably, at least 45% by weight of silicon is surface silicon, and no more than 2% by weight of silicon is bulk silicon, wherein both are determined by TGA.

[0151] Preferably, the total volume of micropores and mesopores in the composite particles, as measured by nitrogen adsorption (i.e., in the presence of silicon), is at most 0.15 × P. 1 or at most 0.10×P 1 Or at most 0.05×P 1 Or at most 0.02×P 1 .

[0152] Preferably, the total volume of micropores and mesopores in the composite particles, as measured by nitrogen adsorption, is less than 0.2 cm³. 3 / g, preferably less than 0.15 cm 3 / g, or less than 0.1 cm 3 / g, or less than 0.08 cm 3 / g, or less than 0.06 cm 3 / g, or less than 0.04 cm 3 / g, or less than 0.02 cm 3 / g, or less than 0.015 cm 3 / g, or less than 0.012 cm 3 / g, or less than 0.010cm3 / g, or less than 0.008 cm 3 / g.

[0153] As used herein, the term "particle size" refers to the equivalent sphere diameter (esd), which is the diameter of a sphere with the same volume as a given particle, where particle volume should be understood to include the volume of any internal pores within the particle. As used herein, the term "D"... 50 "and "D 50 "Particle size" refers to the volume median particle size, that is, the diameter at which 50% of the volume of the particle population is measured to be smaller than a certain diameter. As used in this article, the term "D" is similar. 10 "and "D 10 "Particle size" refers to the 10th percentile volume median particle size, that is, the diameter at which 10% of the particle population by volume is measured to be smaller than a certain diameter. As used in this paper, the term "D" is similar. 90 "and "D 90 "Particle size" refers to the 90th percentile volume median particle size, that is, the diameter at which 90% of the volume of the particle population is measured to be smaller than a certain diameter.

[0154] The term "D" used in this document to define particle size distribution should be used in conjunction with the term "D". n "and the term 'PD' used in this document to define aperture distribution as described above" n "Distinguish them."

[0155] Particle size and particle size distribution can be determined using conventional laser diffraction techniques according to ISO 13320:2009. Unless otherwise specified, particle size distribution measurements indicated or reported herein are performed using a conventional Malvern Mastersizer from Malvern Instruments. TM Measured using a 3000 particle size analyzer. Malvern Mastersizer TM The 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing particles of interest suspended in an aqueous solution. Light striking the particles is scattered by an angle inversely proportional to the particle size, and a photodetector array measures the light intensity at multiple predetermined angles. The particle size distribution is determined by computer processing of the intensities measured at different angles using standard theoretical principles. The laser diffraction values ​​reported in this paper use samples with 5 vol% surfactant SPAN added. TM The particles were obtained as a wet dispersion in 2-propanol at -40°C (sorbitan monopalmitate). The refractive index of the porous carbon framework particles was considered to be 2.68, the refractive index of the composite particles was considered to be 3.50, and the refractive index of the dispersant was considered to be 1.378. The particle size distribution was calculated using the Mie scattering model.

[0156] D of composite particles 50 The particle size can range from 1 to 30 µm. Optionally, D 50 The particle size can be at least 1 µm, or at least 2 µm, or at least 3 µm, or at least 4 µm, or at least 5 µm. Optionally, D 50 The particle size may not exceed 20 µm, or 18 µm, or 16 µm, or 14 µm, or 12 µm, or 10 µm, or 8 µm.

[0157] For example, the D of composite particles 50 The particle size can be in the range of 1 to 20 µm, or in the range of 1 to 18 µm, or in the range of 1 to 16 µm, or in the range of 2 to 16 µm, or in the range of 2 to 14 µm, or in the range of 2 to 12 µm, or in the range of 2 to 10 µm, or in the range of 2 to 8 µm. Particles within these size ranges and having the porosity and pore size distribution described herein are ideally suited for the anode of metal-ion batteries due to their dispersibility in slurries, their structural robustness, their capacity retention after repeated charge-discharge cycles, and their suitability for forming dense electrode layers with a uniform thickness in the conventional range of 20 to 50 µm.

[0158] D of composite particles 10 The particle size is preferably at least 0.5 µm, or at least 0.8 µm, or at least 1 µm. This is achieved by using D... 10 By maintaining a particle size above 0.5 µm, the likelihood of agglomeration of undesirable submicron-sized particles is reduced, resulting in improved particulate material dispersibility and improved capacity retention.

[0159] D of composite particles 90 The particle size is preferably no more than 50 µm, or no more than 40 µm, or no more than 30 µm, or no more than 25 µm, or no more than 20 µm, or no more than 15 µm. The presence of very large particles leads to uneven particle formation in the electrode active layer, thereby disrupting the formation of a dense electrode layer, particularly an electrode layer with a thickness in the range of 20 to 50 µm. Therefore, D is preferred. 90 The particle size is at most 40 µm, and more preferably even smaller.

[0160] Composite particles preferably have a narrow size distribution span. For example, the particle size distribution span (defined as (D...) 90 -D 10 ) / D 50The particle size distribution is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, it is easier to effectively fill the particles into the dense electrode layer.

[0161] The composite particles preferably exhibit a positive skew in the volume-based distribution, for example, making the volume-based distribution asymmetric, with a longer tail on the right-hand side. Positive skew in the volume-based particle size distribution is advantageous because it provides a denser electrode due to the naturally higher fill factor compared to when all particles are of the same size, thus reducing the need for rolling or other physical densification processes. Preferably, D 50 The composite particle diameter is smaller than the volume average of the particle size distribution (D[4.3]). Preferably, the skewness of the composite particle size distribution (by Malvern Mastersizer) TM (Measured by a 3000 analyzer) The value should not exceed 5, or 3.

[0162] The average sphericity of the composite particles (as defined herein) may be at least 0.5 or at least 0.55. Preferably, the average sphericity is at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8.

[0163] Highly accurate two-dimensional projections of micrometer-scale particles can be obtained using scanning electron microscopy (SEM) or dynamic image analysis, where a digital camera is used to record the shadows cast by the particles. As used herein, the term "sphericity" should be understood as the ratio of the area of ​​the particle projection (obtained by such imaging techniques) to the area of ​​a circle, wherein the particle projection and the circle have the same circumference. Therefore, for an individual particle, the sphericity S can be defined as:

[0164]

[0165] Where A m It is the measured area of ​​the particle projection, and C m This is the measured perimeter of the particle's projection. For example, the average sphericity S of multiple particles used in this paper... av Defined as:

[0166]

[0167] Where n represents the number of particles in the swarm. The average sphericity of the particle swarm is preferably calculated by a two-dimensional projection of at least 50 particles.

[0168] The BET surface area of ​​the composite particles of the present invention is preferably not more than 200 m². 2 / g. Preferably, the BET surface area of ​​the composite particles does not exceed 150 m². 2 / g, or not exceeding 100 mg 2 / g, or not exceeding 80 m 2 / g, or not exceeding 60 m 2 / g, or not exceeding 50m 2 / g, or not exceeding 40 mg 2 / g, or not exceeding 30 m 2 / g, or not exceeding 25 mg 2 / g, or not exceeding 20 mg 2 / g, or not exceeding 15m 2 / g, or not exceeding 10 mg 2 / g.

[0169] Typically, a low BET surface area is preferred to minimize the formation of a solid electrolyte interface (SEI) layer at the surface of the composite particles during the first charge-discharge cycle of the anode containing the particulate material of the present invention. However, an excessively low BET surface area results in unacceptably low charge rates and capacity limitations due to the inaccessibility of the electroactive material bulk to metal ions in the surrounding electrolyte. For example, a BET surface area of ​​at least 0.1 m² is preferred. 2 / g, or at least 1 m 2 / g, or at least 2m 2 / g, or at least 5 m 2 / g. For example, the surface area of ​​BET can be 1 m². 2 / g to 25 m 2 Within the range of / g, more preferably within 2 to 15 m 2 Within the range of / g.

[0170] The particulate material of the present invention typically has a charge specific capacity of 900 to 2300 mAh / g during initial lithiation. Preferably, the particulate material of the present invention has a charge specific capacity of at least 1200 mAh / g or at least 1400 mAh / g during initial lithiation.

[0171] The particulate material of the present invention may optionally comprise a silicon surface that has been treated with a passivating agent. As discussed in more detail below, a passivating agent is defined herein as a compound capable of modifying the surface of an electroactive material to inhibit or prevent the formation of surface oxides.

[0172] The composite particles of the present invention may optionally include a coating that at least partially or completely covers the outer surface of the particles. The coating is preferably a lithium-ion permeable coating. As used herein, the term "lithium-ion permeable" refers to an ion-conducting material that enables lithium ions to be transported from the exterior of the composite particles to the nanoscale electroactive material structural domains. Preferably, the lithium-ion permeable coating is impermeable to solvents such as liquid electrolytes. Preferably, the lithium-ion permeable filler material is < 0.1 V (vs. Li / Li + It is electrochemically stable.

[0173] Optionally, the coating may include a conductive carbon coating. Suitably, the conductive carbon coating can be obtained by chemical vapor deposition (CVD). CVD is a method well known in the art and involves thermally decomposing a volatile carbon-containing gas (e.g., ethylene) onto the surface of the particulate material. Alternatively, the carbon coating can be formed by depositing a solution of a carbon-containing compound onto the surface of the particulate material followed by pyrolysis. The conductive carbon coating has sufficient permeability to allow lithium to access the interior of the composite particles without excessive resistance, thereby not degrading the rate performance of the composite particles. For example, the thickness of the carbon coating can suitably be in the range of 2 to 30 nm. Optionally, the carbon coating can be porous and / or can only partially cover the surface of the composite particles.

[0174] Alternatively, the coating may comprise a lithium-ion permeable solid electrolyte. Examples of suitable lithium-ion permeable solid electrolytes include: garnet-type solid electrolytes (including “LLZO” electrolytes, such as Li7La3Zr2O). 12 and Li 6.5 La3Ti 0.5 Zr 1.5 O 12 ); Perovskite-type solid electrolytes (including "LLTO" electrolytes, such as Li ); 0.33 La 0.57 TiO3); LISICON-type solid electrolytes, NaSICON-type solid electrolytes (such as Li); 1.3 Al 0.3 Ti 1.7 (PO4)3); Lithium phosphorus oxynitride (LiPON) solid electrolyte; Li3N type solid electrolyte; Lithium phosphate (Li3PO4) solid electrolyte; Lithium titanate (Li4Ti5O) 12 Solid electrolytes; lithium tantalate (LiTaO3) solid electrolytes; sulfide solid electrolytes; silver sulfide germanite solid electrolytes; and anti-perovskite solid electrolytes. Variations (e.g., including dopants) and combinations of these electrolyte types are also included.

[0175] The coating offers the following advantages: it further reduces the BET surface area of ​​the particulate material by smoothing any surface defects and filling any residual surface micropores, thereby further reducing first-cycle loss. The use of conductive coatings, such as carbon coatings, is particularly advantageous because they improve the surface conductivity of the composite particles, improve the rate performance of the particulate material when used as an electroactive material in lithium-ion batteries, and / or reduce the need for conductive additives in the electrode composition, and also create an improved surface for forming a stable SEI layer, resulting in improved capacity retention during cycling. In cases where the composite particles include a coating, the silicon content of the particles (in weight %) is determined based on the weight of the particles including the coating.

[0176] A preferred particulate material according to the present invention is a particulate material wherein P 1 The particulate material contains 38 wt% to 58 wt% silicon in the range of 0.65 to 1.2, with a micropore volume fraction in the range of 0.5 to 0.7, and at least 30 wt% silicon (e.g., 30 wt% to 75 wt%, 30 wt% to 70 wt%, or 30 wt% to 65 wt%) as determined by thermogravimetric analysis (TGA) is surface silicon. Preferably, no more than 10 wt% silicon is coarse-phase silicon as determined by TGA. Any of the features disclosed herein as preferred or optional may also be applicable to this embodiment.

[0177] A more preferred particulate material according to the present invention is a particulate material wherein P 1 The particulate material contains 40 wt% to 58 wt% silicon in the range of 0.7 to 1.1, with a micropore volume fraction in the range of 0.48 to 0.76, and at least 35 wt% silicon (e.g., 35 wt% to 70 wt%, 35 wt% to 65 wt%, or 35 wt% to 60 wt%) as determined by thermogravimetric analysis (TGA) is surface silicon. Preferably, no more than 8 wt% silicon is coarse-phase silicon as determined by TGA. Any of the features disclosed herein as preferred or optional may also be applicable to this embodiment.

[0178] A more preferred particulate material according to the present invention is a particulate material wherein P 1 The particulate material contains 42 wt% to 56 wt% silicon in the range of 0.75 to 1.1, with a micropore volume fraction in the range of 0.5 to 0.74, and at least 40 wt% silicon (e.g., 40 wt% to 65 wt%, 40 wt% to 60 wt%, or 40 wt% to 55 wt%) as determined by thermogravimetric analysis (TGA) is surface silicon. Preferably, no more than 5 wt% silicon is coarse-phase silicon as determined by TGA. Any of the features disclosed herein as preferred or optional may also be applicable to this embodiment.

[0179] A more preferred particulate material according to the present invention is a particulate material wherein P 1 The particulate material contains 44 wt% to 54 wt% silicon in the range of 0.8 to 1, and the micropore volume fraction is in the range of 0.52 to 0.72. As determined by thermogravimetric analysis (TGA), at least 45 wt% of the silicon (e.g., 45 wt% to 65 wt%, 45 wt% to 60 wt%, or 45 wt% to 55 wt%) is surface silicon. Preferably, as determined by TGA, no more than 2 wt% of the silicon is bulk silicon. Any of the features disclosed herein as preferred or optional may also be applicable to this embodiment.

[0180] The composite particles of the present invention are suitably prepared by chemical vapor infiltration (CVI) of silicon-containing precursors into the porous structure of a porous carbon framework. As used herein, CVI refers to the process in which gaseous silicon-containing gas is thermally decomposed on a surface to form elemental silicon and gaseous byproducts at the surface.

[0181] According to a second aspect of the present invention, a method for preparing silicon-containing composite particles is provided, the method comprising the following steps:

[0182] (a) Providing a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein:

[0183] (i) The total pore volume of the micropores and mesopores, as measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents numbers with values ​​between 0.5 and 1.5.

[0184] (ii)PD 90 The pore size is at least 3 nm and less than 12 nm; and

[0185] (iii) Based on P 1 The micropore volume fraction ranged from 0.43 to 0.85.

[0186] (b) The plurality of porous carbon particles are brought into contact with a gas containing 0.5 vol% to 20 vol% silicon precursor gas at a temperature of 400 to 700 °C to deposit silicon into the pores of the porous carbon particles.

[0187] According to a third aspect of the present invention, a method for preparing silicon-containing composite particles is provided, the method comprising the following steps:

[0188] (a) Providing a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein:

[0189] (i) The total pore volume of the micropores and mesopores, as measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a number with a value between 0.5 and 1.5.

[0190] (ii)PD 90 The pore size is at least 3 nm and less than 12 nm; and

[0191] (iii) Based on P 1 The micropore volume fraction ranged from 0.43 to 0.85.

[0192] (b) The plurality of porous carbon particles are contacted with a gas containing silicon precursor gas at a temperature of 400 to 700 °C to deposit silicon into the pores of the porous carbon particles, wherein the partial pressure of the silicon precursor gas is 0.5 to 20 kPa.

[0193] The methods of the second and third aspects of the present invention can be used to prepare the particulate material of the first aspect of the present invention. Unless otherwise specified, the following preferred features are applicable to the second and third aspects.

[0194] Suitable gaseous silicon-containing precursors include silanes (SiH4), silane derivatives (e.g., disilane, propane, and butane), and trichlorosilanes (SiHCl3).

[0195] Optionally, the silicon-containing precursor is chlorine-free. Chlorine-free means that the silicon-containing precursor contains less than 1% by weight, preferably less than 0.1% by weight, and preferably less than 0.01% by weight of a chlorine-containing compound.

[0196] Silicon-containing precursors can be used in pure form, or more commonly as a mixture diluted with an inert carrier gas such as nitrogen or argon.

[0197] Step (b) is suitably performed at a low partial pressure of silicon precursor at a total pressure below 101.3 kPa (i.e. 1 atm), with the remaining partial pressure being made up to atmospheric pressure using an inert filling gas such as hydrogen, nitrogen or argon.

[0198] According to a second aspect of the invention, the silicon-containing precursor is used in an amount of 0.5 vol% to 20 vol%, for example 1 vol% to 15 vol%, or 1 vol% to 10 vol%, or 1 vol% to 5 vol%, preferably at least 3 vol%, based on the total volume of the silicon precursor gas and the inert carrier gas.

[0199] According to a third aspect of the invention, the partial pressure of the silicon precursor gas is 0.5 to 20 kPa, or 1 to 15 kPa, or 1 to 10 kPa, or 1 to 5 kPa. As used herein, the partial pressure of the silicon precursor gas is defined as the total pressure multiplied by the volume fraction of the silicon precursor gas (i.e., assuming ideal gas behavior). If pure silicon precursor gas is used, the partial pressure of the silicon precursor gas is equal to the total pressure. Alternatively, the total pressure may be the sum of the partial pressures of the silicon precursor gas and the inert filling gas, such as nitrogen or argon.

[0200] In step (b), a temperature in the range of 400 to 700 °C is used, preferably 425 to 550 °C, or 425 to 500 °C. Optionally, the porous carbon particles are brought into contact with the silicon precursor gas at an initial temperature below 400 °C, and then the reaction temperature is increased to the range of 400 to 700 °C.

[0201] Step (b) may optionally be carried out using agitation or fluidization of porous carbon particles, which is particularly preferred when the process is carried out on a large scale. Suitable reactor types include rotary kilns or fluidized bed reactors (including spouted bed reactors).

[0202] To obtain the particulate material with high surface silicon content of the present invention, the CVI process must be carefully controlled to ensure that the silicon deposition rate is low relative to the diffusion rate of the silicon precursor gas into the porous carbon framework. Operation within a preferred temperature range of 425 to 500 °C and the use of low-concentration silicon precursor gas also help control the silicon deposition rate, ensuring a low rate of silicon deposition relative to the permeation rate of the silicon precursor. Conditions within the CVI reactor should also be as uniform as possible. Agitation or fluidization of the porous carbon particles ensures uniform permeation of the silicon precursor gas into the particles and ensures that the temperature in the reactor is uniform throughout the particle bed.

[0203] Preferably, step (b) is performed at a pressure below atmospheric pressure. For example, step (b) may be performed at an absolute pressure below 100 kPa, or below 90 kPa, or below 80 kPa, or below 70 kPa, or below 60 kPa. Preferably, step (b) is performed at an absolute pressure of at least 5 kPa, or at least 10 kPa, or at least 15 kPa, or at least 20 kPa, or at least 25 kPa, or at least 30 kPa. For example, step b is preferably performed at an absolute pressure in the range of 10 to 90 kPa, or 20 to 80 kPa, or 20 to 70 kPa, or 30 to 60 kPa.

[0204] It has been found that performing step (b) at a pressure below atmospheric pressure results in a significant improvement in the surface silicon content of the particulate material product.

[0205] Preferred operating conditions for forming a particulate material product containing more than 20% surface silicon in step (b) include using a gas containing 0.5 vol% to 20 vol% silicon precursor gas (preferably silane) at an absolute pressure of 10 to 90 kPa. More preferably, a gas containing 2 vol% to 15 vol% silicon precursor is used at an absolute pressure of 20 to 80 kPa. Even more preferably, a gas containing 5 vol% to 10 vol% silicon precursor is used at an absolute pressure of 30 to 60 kPa. Referring to the accompanying embodiments, operation within these preferred conditions reliably provides particulate materials with a very high surface silicon content of at least 30% or even at least 40%. The careful selection of porous carbon particles described herein, along with the use of controlled CVI conditions, enables the production of particulate materials with very high surface silicon content and low coarse-phase silicon content, indicating that a high proportion of silicon exists in the form of ultrafine silicon nanostructures. Such materials have not been reported in the prior art.

[0206] The surface of the electroactive material deposited via CVI is reactive to oxygen and forms a natural oxide layer upon exposure to atmospheric oxygen. In the case of silicon, an amorphous silicon dioxide film forms immediately upon exposure of the silicon surface to oxygen. The formation of the natural oxide layer is exothermic, thus requiring careful process control to prevent overheating or even combustion of the particulate material during manufacturing or storage. The presence of the natural oxide layer is associated with irreversible capacity loss and shortened cycle life, and may therefore be detrimental to the performance of the electroactive material in lithium-ion batteries. Therefore, the method of the present invention may optionally include an additional step (c): contacting the exposed surface of the deposited silicon with a passivating agent, wherein the silicon is not exposed to oxygen prior to contact with the passivating agent.

[0207] Passivating agents are defined in this paper as compounds that can modify the surface of electroactive materials to inhibit or prevent the formation of surface oxides.

[0208] Suitable passivating agents include compounds containing olefin, alkyne or carbonyl functional groups, more preferably terminal olefin, terminal alkyne or aldehyde groups.

[0209] Preferred passivating agents include one or more compounds having the following formula:

[0210] (i)R-CH=CH-R;

[0211] (ii) RC≡CR; and

[0212] (iii) O=CH-R;

[0213] Wherein R represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, preferably 2 to 10 carbon atoms, or wherein the two R groups in formula (i) form an unsubstituted or substituted hydrocarbon ring structure containing 3 to 8 carbon atoms.

[0214] Particularly preferred passivating agents include one or more compounds having the following formula:

[0215] (i)CH2=CH-R; and

[0216] (ii) HC≡CR;

[0217] Wherein R is as defined above. Preferably, R is unsubstituted.

[0218] Examples of suitable compounds include ethylene, propylene, 1-butene, butadiene, 1-pentene, 1,4-pentadiene, 1-hexene, 1-octene, styrene, divinylbenzene, acetylene, phenylacetylene, norbornene, norbornadiene, and bicyclo[2.2.2]oct-2-ene. Mixtures of different passivating agents may also be used. A preferred passivating agent is ethylene.

[0219] It is believed that the olefin, alkyne, or carbonyl groups of the passivating agent undergo an insertion reaction with MH groups (where M represents an atom of the electroactive material) on the surface of the electroactive material to form a covalently passivated surface resistant to air oxidation. When silicon is the electroactive material, the passivation reaction between the silicon surface and the passivating agent can be understood as a form of hydrosilylation, as illustrated below.

[0220]

[0221] Other suitable passivating agents include compounds containing active hydrogen atoms bonded to oxygen, nitrogen, sulfur, or phosphorus. For example, passivating agents can be alcohols, amines, thiols, or phosphine. The reaction of the group –XH with the hydride group on the surface of the electroactive material is understood to result in the elimination of H2 and the formation of a direct bond between X and the surface of the electroactive material.

[0222] Suitable passivating agents of this type include compounds of the following formula:

[0223] (iv) HX-R,

[0224] Where X represents O, S, NR, or PR, and each R is independently as defined above. The two R groups in formula (iv) may also form substituted or unsubstituted hydrocarbon ring structures containing 3 to 8 carbon atoms. Preferably, X represents O or NH, and R represents optionally substituted aliphatic or aromatic groups having 2 to 10 carbon atoms. Amine groups may also be incorporated into 4-10 member aliphatic or aromatic ring structures, such as those found in pyrrolidine, pyrrole, imidazole, piperazine, indole, or purine.

[0225] When the passivating agent is a carbon-containing compound, the contact between the electroactive material and the passivating agent in step (c) can be performed above or below the pyrolysis temperature of the passivating agent. When the electroactive material is contacted with the passivating agent at a temperature below the pyrolysis temperature of the passivating agent, only a passivation layer is formed on the silicon surface. When the electroactive material is contacted with the passivating agent at a temperature above the pyrolysis temperature of the passivating agent, passivation of the silicon surface occurs simultaneously with the formation of a pyrolytic carbon coating.

[0226] The contact between the electroactive material and the passivating agent in step (c) can be carried out at a temperature ranging from 25 to 700 °C and at a pressure ranging from 100 kPa to 50 MPa. For example, step (c) can suitably be carried out within the preferred temperature and pressure ranges as described herein with respect to step (b).

[0227] Another suitable passivating agent is ammonia. Therefore, step (c) may include contacting the surface of the deposited electroactive material with ammonia at a temperature in the range of 200-700 °C, preferably 400-700 °C. For example, when the passivating agent is ammonia, step (c) may be performed at the same temperature used to deposit the electroactive material in step (b). The temperature is then increased to the range of 500 to 1,000 °C if necessary to form a crystalline nitride surface (e.g., a silicon nitride surface of formula SiNx, where x ≤ 4 / 3). Thus, passivation with ammonia provides an alternative means of limiting the oxidation of the electroactive material. Because stoichiometric silicon nitrides are conductive, this step also results in the formation of a conductive network that allows the electroactive material to charge and discharge more quickly.

[0228] The passivation in step (c) can optionally be carried out in the same reactor as in step (b), for example by stopping the flow of silicon precursor gas to the reactor and starting the flow of passivating agent gas to the reactor. Optionally, the reactor can be flushed with an inert gas prior to step (c).

[0229] The method of the present invention may optionally include an additional step (d): forming a conductive carbon coating on the surface of the composite particles from step (b) or from step (c) (if a passivation step is performed). Step (d) suitably includes contacting the electroactive material with the pyrolytic carbon precursor at a temperature higher than the pyrolysis temperature of the pyrolytic carbon precursor.

[0230] The appropriate conditions for step (d) are discussed in detail in WO 2021 / 048556.

[0231] As an example of the fixed-bed reactor method (experimental scale), 1.8 g of particulate porous carbon skeleton was placed on a stainless steel plate at a constant thickness of 1 mm along its length. The plate was then placed in a 60 mm outer diameter stainless steel tube with gas inlet and outlet lines located in the hot zone of a still furnace. The furnace tube was purged with nitrogen at room temperature for 30 minutes, and then the sample temperature was raised to 450–500 ˚C. The nitrogen flow rate was adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube, and the nitrogen flow rate was maintained at this rate for 30 minutes. The gas supply was then switched from nitrogen to a mixture of silane at a concentration of 1.25 vol% in nitrogen. The silane feed was carried out over a period of 5 hours while the reactor pressure was maintained at 101.3 kPa (1 atm). After the feed was complete, the gas flow rate was kept constant while the silane was purged from the furnace with nitrogen. The furnace was purged with nitrogen for 30 minutes. Optionally, a surface passivation step was then performed by contacting the material with a passivation gas. The furnace was then cooled to room temperature over several hours. The atmosphere was then gradually switched to air over a two-hour period by changing the gas flow from nitrogen to air supplied by compressed air.

[0232] As an example of a fluidized bed reactor method (production scale), 50 g of particulate porous carbon skeleton was placed in a fluidized bed reactor, which was fabricated with a 0.95 cm (3 / 8”) stainless steel inlet, a 60 mm outer diameter (OD) tubular section with a length of 520 mm, and a 100 mm OD stainless steel enlarged head. The reactor was suspended on a frame, and the vertically oriented tubular furnace was arranged such that the hot zone extended from the conical section to the cylindrical section for ¾ of its length (approximately 380 mm). The minimum fluidization rate was determined using cold flow pressure drop testing and nitrogen as the inert gas, with the gas flow rate varying between 1 and 2.5 L / min. Once the minimum fluidization rate was determined, the inert gas flow rate was kept constant above the minimum fluidization rate. The furnace was heated to the desired reaction temperature at a constant inert gas flow rate. The temperature ranged from 435 to 500 °C. After the target temperature stabilizes between ℃, the fluidizing gas is switched from pure nitrogen to 1.25 vol% silane in nitrogen. The reaction progress is monitored by measuring the pressure drop between the top and bottom of the bed and the furnace temperature difference. Throughout the run, the gas flow rate is adjusted to maintain a pressure drop consistent with continuous fluidization and to maintain a minimum temperature difference between the top and bottom of the bed below 40 °C. After 12 hours, the fluidizing gas is switched back to pure nitrogen while maintaining fluidization; this purging lasts for 30 minutes. Optionally, a surface passivation step is then performed by contacting the material with a passivation gas. The furnace is then cooled to ambient temperature over several hours. Upon reaching ambient temperature, the furnace atmosphere is gradually switched to air over several hours.

[0233] As an example of a reduced-pressure fluidized bed reactor method (production scale), 250 g of particulate porous carbon skeleton is placed in a fluidized bed reactor, which is fabricated with multiple nozzles designed for horizontal gas injection at an injection velocity of 0.5–2 m / s into a tubular reactor section with a length of 1100 mm and an outer diameter (OD) of 89 mm, and a stainless steel expander head with an OD of 457 mm. The reactor is suspended on a frame, and the vertically oriented tubular furnace is arranged such that the hot zone extends from the conical section across the entire length of the cylindrical section (approximately 380 mm). The reactor vessel is vibrated at a frequency of 5–140 Hz. The porous carbon particles are fluidized at a pressure (absolute) of 38 kPa using nitrogen as an inert gas at a flow rate of 10 sL / min. The furnace is heated to a temperature of 450 °C at a constant inert gas flow rate. The gas flow was then slowly switched to a mixture of 2 sL / min silane (SiH4) and 9 sL / min nitrogen. The rate of silicon deposition was monitored by measuring the volume percentage of hydrogen in the effluent gas over time. Once approximately 200 g of silicon (approximately 45 wt% Si) had been deposited, the gas flow was switched to a mixture of 0.5 sL / min silane (SiH4) and 9 sL / min nitrogen until approximately 250 g of silicon (approximately 49.5 wt% to 51.5 wt% Si) had been deposited. The fluidizing gas was then switched to pure nitrogen for approximately 30 minutes to purge the reactor while maintaining fluidization. Optionally, a surface passivation step was then performed by contacting the material with a passivation gas. The furnace was then cooled to ambient temperature over several hours. Upon reaching ambient temperature, the furnace atmosphere was gradually switched to air over several hours.

[0234] In a fourth aspect of the invention, a composition comprising a particulate material according to a first aspect of the invention and at least one other component is provided. Specifically, a composition comprising a particulate material according to a first aspect of the invention and at least one other component selected from: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material is provided. The composition according to the fourth aspect of the invention can be used as an electrode composition and therefore can be used to form the active layer of an electrode.

[0235] The particulate material used to prepare the composition of the fourth aspect of the invention may have any of the features described in relation to the first aspect of the invention as preferred or optional.

[0236] The composition may be a hybrid electrode composition comprising a particulate material according to the first aspect of the invention and at least one additional particulate electroactive material. Examples of the additional particulate electroactive material include graphite, hard carbon, silicon, tin, germanium, aluminum, and lead. The at least one additional particulate electroactive material is preferably selected from graphite and hard carbon, and most preferably, the at least one additional particulate electroactive material is graphite.

[0237] In the case of a hybrid electrode composition, based on the total dry weight of the composition, the composition preferably contains 3% to 60% by weight, 3% to 50% by weight, 5% to 50% by weight, or 10% to 50% by weight, or 15% to 50% by weight of particulate material according to the first aspect of the invention.

[0238] At least one additional particulate electroactive material is suitably present in an amount of 20% to 95% by weight, or 25% to 90% by weight, or 30% to 750% by weight.

[0239] At least one other particulate electroactive material D 50 The particle size is preferably in the range of 10 to 50 µm, more preferably in the range of 10 to 40 µm, more preferably in the range of 10 to 30 µm, and most preferably in the range of 10 to 25 µm, for example in the range of 15 to 25 µm.

[0240] At least one other particulate electroactive material D 10 The particle size is preferably at least 5 µm, more preferably at least 6 µm, more preferably at least 7 µm, more preferably at least 8 µm, more preferably at least 9 µm, and still more preferably at least 10 µm.

[0241] At least one other particulate electroactive material D 90 The particle size is preferably up to 100 µm, more preferably up to 80 µm, more preferably up to 60 µm, more preferably up to 50 µm, and most preferably up to 40 µm.

[0242] At least one additional particulate electroactive material is preferably selected from carbon-containing particles, graphite particles, and / or hard carbon particles, wherein the D of the graphite particles and hard carbon particles is... 50 The particle size is in the range of 10 to 50 µm. More preferably, the at least one additional particulate electroactive material is selected from graphite particles, wherein the graphite particles have a D... 50 The particle size ranges from 10 to 50 µm.

[0243] The composition may also be an unmixed (or “high-load”) electrode composition that is substantially free of additional particulate electroactive material. In this case, the term “substantially free of additional particulate electroactive material” should be interpreted as meaning that, based on the total dry weight of the composition, the composition contains less than 15% by weight, preferably less than 10% by weight, preferably less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, and more preferably less than 0.5% by weight of any additional electroactive material (i.e., additional material capable of intercalating and releasing metal ions during battery charging and discharging).

[0244] Based on the total dry weight of the composition, this type of "high-load" electrode composition preferably contains at least 50% by weight, or at least 60% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight of particulate material according to the first aspect of the invention.

[0245] The composition may optionally include an adhesive. The adhesive serves to adhere the composition to the current collector and maintain the integrity of the composition. Examples of adhesives that can be used according to the invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginate and its alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The composition may contain a mixture of various adhesives. Preferably, the adhesive comprises polymers selected from: polyacrylic acid (PAA) and its alkali metal salts, and modified polyacrylic acid (mPAA) and its alkali metal salts, SBR, and CMC.

[0246] The adhesive may suitably be present in an amount of 0.5% to 20% by weight, preferably 1% to 15% by weight, preferably 2% to 10% by weight, and most preferably 5% to 10% by weight, based on the total dry weight of the composition.

[0247] The adhesive may optionally be present in combination with one or more additives that alter the properties of the adhesive, such as crosslinking accelerators, coupling agents, and / or adhesion promoters.

[0248] The composition may optionally include one or more conductive additives. Preferred conductive additives are non-electroactive materials included to improve the conductivity between the electroactive components of the composition and the conductivity between the electroactive components and the current collector. Conductive additives may suitably be selected from carbon black, carbon fibers, carbon nanotubes, graphene, acetylene black, Ketjen black, metal fibers, metal powders, and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes.

[0249] One or more conductive additives may suitably be present in a total amount of 0.5% to 20% by weight, preferably 1% to 15% by weight, preferably 2% to 10% by weight, and most preferably 5% to 10% by weight, based on the total dry weight of the composition.

[0250] In a fifth aspect, the present invention provides an electrode comprising a particulate material defined according to a first aspect of the invention in electrical contact with a current collector. The particulate material used to prepare the electrode of the fifth aspect of the invention may have any of the features described in relation to the first aspect of the invention as preferred or optional.

[0251] As used herein, the term current collector refers to any conductive substrate capable of carrying current to and from electroactive particles in a composition. Examples of materials that can be used as current collectors include copper, aluminum, stainless steel, nickel, titanium, and sintered carbon. Copper is a preferred material. Current collectors are generally in the form of foils or meshes with a thickness of 3 to 500 μm. The particulate material of the present invention can be applied to one or both surfaces of the current collector to achieve a thickness preferably in the range of 10 μm to 1 mm, for example, 20 to 500 μm, or 50 to 200 μm.

[0252] Preferably, the electrode comprises a composition defined according to the fourth aspect of the invention that is in electrical contact with the current collector. The composition may have any of the features described in relation to the fourth aspect of the invention as preferred or optional.

[0253] The electrode of the fifth aspect of the present invention can be suitably prepared by combining the particulate material of the present invention (optionally in the form of a composition of the present invention) with a solvent and optionally one or more viscosity-modifying additives to form a slurry. The slurry is then cast onto the surface of a current collector, and the solvent is removed, thereby forming an electrode layer on the surface of the current collector. Additional steps may be performed as appropriate, such as heat treatment for curing any binder and / or calendering of the electrode layer. The thickness of the electrode layer is suitably in the range of 20 µm to 2 mm, preferably 20 µm to 1 mm, preferably 20 µm to 500 µm, preferably 20 µm to 200 µm, preferably 20 µm to 100 µm, preferably 20 µm to 50 µm.

[0254] Alternatively, the slurry can be formed into a self-standing film or pad containing the particulate material of the present invention, for example, by casting the slurry onto a suitable casting stencil, removing the solvent, and then removing the casting stencil. The resulting film or pad is in the form of a viscous, self-standing object, which can then be bonded to a current collector by known methods.

[0255] The electrode of the fifth aspect of the present invention can be used as the anode of a metal-ion battery. Therefore, in a sixth aspect, the present invention provides a rechargeable metal-ion battery comprising: an anode including the electrode as described above; a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions; and an electrolyte between the anode and the cathode.

[0256] The metal ions are preferably lithium ions. More preferably, the rechargeable metal ion battery of the present invention is a lithium ion battery, and the cathode active material is capable of releasing and accepting lithium ions.

[0257] The cathode active material is preferably a composite material based on metal oxides. Examples of suitable cathode active materials include LiCoO2 and LiCo. 0.99 Al 0.01 O2, LiNiO2, LiMnO2, LiCo 0.5 Ni 0.5 O2, LiCo 0.7 Ni 0.3 O2, LiCo 0.8 Ni 0.2 O2, LiCo 0.82 Ni 0.18 O2, LiCo 0.8 Ni 0.15 Al 0.05 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2 and LiNi 0.33 Co 0.33 Mn 0.34 O2. Cathode current collectors typically have a thickness of 3 to 500 μm. Examples of materials that can be used as cathode current collectors include aluminum, stainless steel, nickel, titanium, and sintered carbon.

[0258] Electrolytes are suitably non-aqueous electrolytes containing metal salts (e.g., lithium salts), and may include, but are not limited to, non-aqueous electrolytes, solid electrolytes, and inorganic solid electrolytes. Examples of non-aqueous electrolyte solutions that can be used include aprotic organic solvents such as propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, and 1,3-dimethyl-2-imidazolium ketone.

[0259] Examples of organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ion-dissociating groups.

[0260] Examples of inorganic solid electrolytes include lithium salt nitrides, halides, and sulfides (such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4).

[0261] Lithium salts are suitably soluble in a solvent or mixture of solvents of choice. Examples of suitable lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, LiBC4O8, LiPF6, LiCF3SO3, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and CF3SO3Li.

[0262] When the electrolyte is a non-aqueous organic solution, the metal-ion battery preferably has a separator between the anode and cathode. The separator is generally formed of an insulating material with high ion permeability and high mechanical strength. The separator typically has a pore size of 0.01 to 100 μm and a thickness of 5 to 300 μm. Examples of suitable electrode separators include microporous polyethylene membranes.

[0263] A polymer electrolyte material can be used instead of the diaphragm, and in this case, the polymer electrolyte material exists within both the composite anode layer and the composite cathode layer. The polymer electrolyte material can be a solid polymer electrolyte or a gel-type polymer electrolyte.

[0264] Example

[0265] The porous carbon frameworks C1 to C13 used in the following examples have the properties listed in Table 1.

[0266]

[0267] Example 1: Preparation of particulate materials in a static furnace

[0268] Silicon-carbon composite particles were prepared by placing 1.8 g of a porous granular framework with the properties listed in Table 1 at a constant thickness of 1 mm along the length of a stainless steel plate. The plate was then placed in a 60 mm outer diameter stainless steel tube with gas inlet and outlet lines located in the hot zone of a still furnace. The furnace tube was purged with nitrogen at room temperature for 30 minutes, and then the sample temperature was raised to 450–475 ˚C. The nitrogen flow rate was adjusted to ensure a gas residence time of at least 90 seconds in the furnace tube, and this rate was maintained for 30 minutes. The gas supply was then switched from nitrogen to a mixture of silane at a concentration of 1.25 vol% in nitrogen. The silane feed was carried out over a period of up to 5 hours while the reactor pressure was maintained at 101.3 kPa (1 atm). After the feed was complete, the gas flow rate was kept constant while the silane was purged from the furnace with nitrogen. The furnace was purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. Then, over a two-hour period, the atmosphere was gradually changed to air by switching the airflow from nitrogen to air supplied by compressed air.

[0269] Example 2: Determination of surface silicon content

[0270] Using the method of Example 1, a series of composite particles with varying amounts of deposited silicon (ranging from 20 wt% to 60 wt%) were prepared using the various carbons mentioned in Table 1. Surface silicon was calculated from the TGA curves of each sample. Table 2 provides the average, maximum, and minimum surface silicon values ​​for the sample groups prepared with various carbons. It can be seen that very small or negligible amounts of surface silicon can be achieved using carbons C1, C10, and C13, while consistently good surface silicon levels are achieved in all samples using carbons C3, C4, C5, C7, C8, and C9. Different surface silicon levels were obtained using other carbons.

[0271] Table 2

[0272]

[0273] *Comparison Samples

[0274] Example 3: Preparation of particulate materials in a fluidized bed reactor

[0275] Silicon-carbon composite particles were prepared in a vertical bubbling fluidized bed reactor, consisting of a stainless steel cylindrical vessel with an inner diameter of 83 mm, operating at atmospheric pressure. 250 g of carbon framework particle powder with properties listed in Table 1 was placed in the reactor. A low-flow-rate inert gas (nitrogen) was injected into the reactor to remove any oxygen. The reactor was then heated to a reaction temperature of 430–500°C, and a 4% v / v silane gas diluted in nitrogen was supplied to the bottom of the reactor at a flow rate sufficient to fluidize the carbon framework particles, for a duration sufficient to deposit the target mass of silicon. The reactor was purged with nitrogen for 30 minutes and then cooled to room temperature over several hours. The atmosphere was then gradually switched to air over a two-hour period by switching the gas flow from nitrogen to air supplied from compressed air.

[0276] The particulate materials S1, S2, and S4 to S8 in Table 3 were prepared using the method described in Example 3.

[0277] Example 4: Preparation of particulate materials under low pressure in a fluidized bed reactor

[0278] Silicon-carbon composite particles were prepared in a vertical bubbling fluidized bed reactor comprising a stainless steel cylindrical container with an inner diameter of 83 mm. 250 g of carbon framework particle powder with properties listed in Table 1 was placed in the reactor. The porous carbon particles were fluidized at a pressure (absolute) of 38 kPa using nitrogen at a flow rate of 10 sL / min (standard liters per minute) as an inert gas. The furnace was heated to 450 °C at a constant inert gas flow rate. The gas flow was then slowly switched to a mixture of silane (SiH4) at a flow rate of 2 sL / min and nitrogen at a flow rate of 9 sL / min. The rate of silicon deposition was monitored by measuring the volume percentage of hydrogen in the effluent gas over time. Once approximately 200 g of silicon (approximately 45 wt% Si) had been deposited, the gas flow was switched to a mixture of silane (SiH4) at a flow rate of 0.5 sL / min and nitrogen at a flow rate of 9 sL / min until approximately 250 g of silicon (approximately 49.5 wt% to 51.5 wt% Si) had been deposited. Then, while maintaining fluidization, the fluidizing gas was switched to pure nitrogen at 10 sL / min for approximately 30 minutes to purge the reactor. The fluidizing gas was then switched to a mixture of ethylene (C₂H₄) at 2 sL / min and nitrogen at 9 sL / min to passivate the silicon surface. The fluidizing gas was then switched back to pure nitrogen at 4 sL / min. The furnace was then cooled to ambient temperature over several hours. Upon reaching ambient temperature, the furnace atmosphere was gradually switched to air over several hours.

[0279] The particulate materials S9 to S11 in Table 3 were prepared using the method of Example 4.

[0280] Example 5: Carbon Coating:

[0281] A large quantity of composite particles prepared using the method of Example 3 were placed into a stainless steel tube loaded into a rotary furnace tube and sealed. The reactor space was purged with nitrogen at 0.2 L / min for 30 minutes. The furnace temperature was raised to 675 °C under a nitrogen flow. A measured quantity of styrene was placed in a Dreschel flask and heated to 75 °C in a water bath. After the furnace temperature stabilized for 10 minutes, styrene was allowed to flow into the reactor tube by bubbling nitrogen at 2 L / min into the Dreschel flask for 90 minutes. The reactor was then purged with nitrogen and cooled to ambient temperature under nitrogen to obtain a carbon-coated material.

[0282] The particulate material S3 in Table 3 was prepared according to the method of Example 3, and then carbon coated using the method of Example 4.

[0283] Example 6: Calculation of surface silicon and bulk silicon:

[0284] The procedure for calculating the surface silicon and bulk silicon of the composite material used in the examples is as follows: 10 mg (±2 mg) of the test sample was loaded into a 70 µL crucible. The sample was loaded into a Mettler Toledo TGA / DSC 3+ instrument, using Ar purge gas, N2 filling gas, and air reaction gas at a rate of 100 mL / min. The TGA furnace chamber was heated from 25°C to 1400°C at a rate of 10°C / min. Data were collected at 1-second intervals. Figure 1 The image shows the TGA plot of the sample from material S1 in Table 3, and... Figure 2 This is a graph of sample S7 from Table 3. The values ​​for bulk silicon and surface silicon were extracted by finding the maximum mass (in mg) measured in the temperature range of 550 °C to 650 °C (labeled c), the final ash mass (labeled e), the minimum mass below 500 °C after loss of volatiles (labeled b), and the mass at 800 °C (labeled d). The values ​​for surface silicon (Y) and bulk coarse silicon (Z) were calculated using the formulas listed above.

[0285] Table 3

[0286]

[0287] *Comparison Samples

[0288] ‡ Carbon coating was performed on sample S3 according to the method in Example 5.

[0289] Comparative samples S7 and S8 demonstrate the importance of careful control and regulation in the FBR reaction. In comparative sample S7, interruption of the fluidizing gas supply caused defluidization of particles in the reactor bed and the formation of superheated regions within the reactor, resulting in reduced silicon permeation and increased silicon deposition on the surface of the porous carbon framework (as indicated by the increased coarse silicon measurements). In comparative example S8, temperature variations in the FBR reaction caused the reaction to proceed partially below 400 °C. While theoretically, silicon deposition into the micropores is considered kinetically favorable at temperatures above 400 °C, and particularly above 425 °C, the lower temperatures resulted in increased silicon deposition on the outer surface of the porous carbon support.

[0290] Samples S9 to S11 demonstrate the effectiveness of step (b) performed at pressures below atmospheric pressure. Samples S1 to S6, after their preparation using the atmospheric pressure CVI process, contain 22% to 40% surface silicon, while samples S9 to S11, prepared at 38 kPa, contain approximately 50% surface silicon.

[0291] Example 7: Preparation of the test battery

[0292] The negative electrode coating (anode) was prepared using the Si-C composite material from Table 3, and tested in an all-button cell. To fabricate the electrode, a dispersion of carbon black in a CMC binder was prepared using Thinky... TM Mixing in a mixer. The Si-C composite material is added to the mixture and then mixed in a thinner. TM Mix in a mixer for 30 minutes. Then add SBR binder to provide a 1:1 CMC:SBR ratio, resulting in a slurry with a Si-C composite:CMC / SBR:carbon black weight ratio of 70%:16%:14%. Place the slurry in a Thinky... TM The mixture was further mixed in the mixer for 30 minutes, then coated onto a 10 μm thick copper substrate (current collector) and dried at 50 °C for 10 minutes, followed by drying at 110 °C for 12 hours, resulting in a coating with a density of 0.7 ± 0.5 g / cm³. 3 The negative electrode.

[0293] A fully button cell was fabricated using a circular negative electrode with a radius of 0.8 cm cut from the negative electrode, along with a porous polyethylene separator and a nickel-manganese-cobalt (NMC532) positive electrode. The positive and negative electrodes were designed to form a balanced pair, resulting in a capacity ratio of 0.9. Before sealing, an electrolyte comprising 1 M LiPF6 in a solution containing 3% by weight of fluoroethylene carbonate, ethylene carbonate, and methyl ethyl carbonate was added to the cell.

[0294] Cycle the coin cell as follows: Apply a constant current at a rate of C / 25 to lithium-ionize the anode, with a cutoff voltage of 4.3 V. When cutoff is reached, apply a constant voltage of 4.3 V until a cutoff current of C / 100 is reached. Then let the battery rest in the lithium-ion state for 10 minutes. Then delithiate the anode at a constant current of C / 25, with a cutoff voltage of 2.75 V. Then let the battery rest for 10 minutes. After this initial cycle, apply a constant current of C / 2 to lithium-ionize the anode, with a cutoff voltage of 4.3 V, then apply a constant voltage of 4.3 V with a cutoff current of C / 40, and let rest for 5 minutes. Then delithiate the anode at a constant current of C / 2, with a cutoff voltage of 2.75 V. Then repeat this process for the required number of cycles. The capacity retention at the 100th cycle (CR100) and the capacity retention at the 500th cycle (CR500) are calculated and given in Table 4 along with the first lithiation capacity, the first delithiation capacity, and the first cycle loss (FCL).

[0295] Calculate the charge (lithiation) and discharge (delithiation) capacity per unit mass of silicon-carbon composite material for each cycle, and calculate the capacity retention value for each discharge capacity as a percentage of the discharge capacity in the second cycle. The first cycle loss (FCL) is (1 – (first delithiation capacity / first lithiation capacity)) × 100%. The values ​​in Table 4 are averages of three coin cells for each material.

[0296] Table 4: Electrochemical Data

[0297]

[0298] *Comparison samples.

Claims

1. A particulate material composed of multiple composite particles, wherein the composite particles comprise: (a) A porous carbon framework containing micropores and mesopores. The total pore volume of the micropores and mesopores, measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a number with a value between 0.5 and 1.

5. Among them PD 90 The pore size is at least 3 nm and less than 12 nm; and Among them, based on P 1 The micropore volume fraction ranged from 0.43 to 0.

85. and (b) Multiple nanoscale elemental silicon structural domains located within the pores of the porous carbon framework. The particulate material contains 25% to 65% silicon, and wherein at least 20% of the silicon is surface silicon, as determined by thermogravimetric analysis (TGA).

2. The particulate material according to claim 1, wherein P 1 The value is at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.

75.

3. The particulate material according to claim 1 or claim 2, wherein P 1 The value shall not exceed 1.4, or 1.3, or 1.2, or 1.1, or 1, or 0.

95.

4. A composition comprising the particulate material as defined in any one of claims 1 to 3 and at least one other component.

5. An electrode comprising particulate material as defined in any one of claims 1 to 3 in electrical contact with a current collector.

6. The electrode according to claim 5, wherein the particulate material is in the form of the composition defined in claim 4.

7. A rechargeable metal-ion battery, the rechargeable metal-ion battery comprising: (i) an anode, wherein the anode comprises the electrode of claim 5 or 6; (ii) A cathode comprising a cathode active material capable of releasing and reabsorbing metal ions; as well as (iii) The electrolyte between the anode and the cathode.

8. A method for preparing composite particles, the method comprising the following steps: (a) Providing a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein: (i) The total pore volume of the micropores and mesopores, as measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a number with a value between 0.5 and 1.5; (ii)PD 90 The pore size is at least 3 nm and less than 12 nm; and (iii) Based on P 1 The micropore volume fraction ranged from 0.43 to 0.

85. (b) The plurality of porous carbon particles are contacted with a gas containing 0.5 vol% to 20 vol% silicon precursor gas at a temperature of 400 to 700°C to deposit silicon into the pores of the porous carbon particles.

9. A method for preparing composite particles, the method comprising the following steps: (a) Providing a plurality of porous carbon particles, said porous carbon particles comprising micropores and / or mesopores, wherein: (i) The total pore volume of the micropores and mesopores, as measured by gas adsorption, is P. 1 cm 3 / g, where P 1 This represents a number with a value between 0.5 and 1.5; (ii)PD 90 The pore size is at least 3 nm and less than 12 nm; and (iii) Based on P 1 The micropore volume fraction ranged from 0.43 to 0.

85. (b) The plurality of porous carbon particles are contacted with a gas containing silicon precursor gas at a temperature of 400 to 700 °C to deposit silicon into the pores of the porous carbon particles, wherein the partial pressure of the silicon precursor gas is 0.5 to 20 kPa.

10. The method according to claim 8 or claim 9, wherein the composite particles are as defined in any one of claims 1 to 3.

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