Electroactive material for metal ion batteries

Abstract

To provide particulate electroactive materials having sufficient structural strength alongside increased electrochemical storage capacity and reversible capacity retention that are suitable for use as anode active materials.SOLUTION: This invention relates to particulate electroactive materials consisting of a plurality of composite particles, wherein the composite particles comprise: (a) a porous carbon framework including micropores and mesopores having a total volume of 0.4 cm3 / g to 0.75 cm3 / g, wherein the micropore volume fraction is in the range of 0.5 to 0.85 based on the total volume of micropores and mesopores; and (b) silicon located at least within the micropores of the porous carbon framework in a defined amount relative to the volume of the micropores and mesopores.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention generally relates to an electroactive material suitable for use in electrodes for rechargeable metal ion batteries, and more specifically to a particulate material having a high electrochemical capacity suitable for use as an anode active material in rechargeable metal ion batteries.

Background Art

[0002] Rechargeable metal ion batteries are widely used in portable electronic devices such as mobile phones and laptop computers, and their application in electric vehicles or hybrid vehicles is increasing. A rechargeable metal ion battery generally includes an anode layer, a cathode layer, an electrolyte that transports metal ions between the anode layer and the cathode layer, and an electrically insulating porous separator disposed between the anode and the cathode. The cathode typically includes a metal current collector having a layer of metal ions containing a metal oxide-based composite material, and the anode typically includes, in this specification, a metal current collector having a layer of an electroactive material defined as a material capable of inserting and releasing metal ions during charging and discharging of the battery. To avoid misunderstanding, in this specification, the terms "cathode" and "anode" are used in the sense that when a load is applied to the battery, the cathode becomes the positive electrode and the anode becomes the negative electrode. When the metal ion battery is charged, metal ions are transported from the metal ion-containing cathode layer through the electrolyte to the anode and inserted into the anode material. In this specification, the term "battery" is used to refer to both a device containing a single anode and a single cathode, as well as a device containing a plurality of anodes and / or a plurality of cathodes.

[0003] There is a growing interest in improving the weight capacity and / or volume capacity of rechargeable metal ion batteries. The use of lithium ion batteries has already provided a significant improvement compared to other battery technologies, but there is still room for further development. So far, commercially available lithium ion batteries have been mainly limited to the use of graphite as the anode active material. When the graphite anode is charged, lithium is inserted into the graphite interlayer, and the experimental Lix A material of C6 (where x is greater than 0 and less than or equal to 1) is formed. As a result, graphite has a maximum theoretical capacity of 372 mAh / g in a lithium-ion battery, and the practical capacity is slightly lower than that (about 340 mAh / g to 360 mAh / g). Other materials such as silicon, tin, and germanium can insert lithium with a significantly higher capacity than graphite, but it is difficult to maintain sufficient capacity over multiple charge-discharge cycles, so they are not yet widely used commercially.

[0004] In particular, silicon has been recognized as a promising alternative to graphite in the manufacture of rechargeable metal-ion batteries with high weight and volume capacities because of its very high capacity for lithium (see, for example, Non-Patent Document 1). Silicon has a theoretically maximum specific capacity of about 3600 mAh / g (based on Li 15 Si4) at room temperature in a lithium-ion battery. However, due to the large volume change during charging and discharging, the use of silicon as an anode material is complex.

[0005] When lithium is inserted into bulk silicon, the volume of the silicon material increases significantly, and when the silicon is lithiated to its maximum capacity, it increases to 400% of its original volume. Then, as the charge-discharge cycle is repeated, a large mechanical stress is generated in the silicon material, resulting in the destruction and delamination of the silicon anode material. The volume shrinkage of the silicon particles during delithiation may result in the loss of electrical contact between the anode material and the current collector. What is more difficult is that the solid electrolyte interface (SEI) layer formed on the silicon surface does not have sufficient mechanical durability to adapt to the expansion and contraction of silicon. As a result, the electrolyte is further decomposed by the newly exposed silicon surface, the thickness of the SEI layer increases, and lithium is irreversibly consumed. These defect mechanisms collectively result in unacceptable loss of electrochemical capacity over consecutive charge-discharge cycles.

[0006] Numerous efforts have been proposed to overcome problems associated with the volume changes observed when charging silicon-containing anodes. The most prevalent effort to address the irreversible capacity loss of silicon-containing anodes is to use silicon structured in some form as the electroactive material. Fine silicon structures with a cross-section of less than about 150 nm, such as silicon films and silicon nanoparticles, have been reported to be more durable against volume changes during charge and discharge compared to silicon particles in the micron-size range. However, none of these are particularly suitable for application on a commercial scale without modifying their form. Nanoscale particles are difficult to manufacture and handle, and silicon films do not provide sufficient bulk capacity. For example, nanoscale particles tend to form aggregates, making it difficult to effectively disperse the particles within the anode material matrix. Also, the formation of aggregates of nanoscale particles results in unacceptable capacity loss during repeated charge-discharge cycles.

[0007] Ohara et al. (Non-Patent Document 2) described depositing silicon as a thin film on a nickel foil current collector and using this structure as the anode of a lithium-ion battery. According to this effort, good capacity retention is obtained, but the thin film structure has a capacity per unit area that is not a useful amount, and any improvement is eliminated as the film thickness increases.

[0008] Patent Document 1 discloses that the capacity retention can be improved by using silicon particles with a high aspect ratio, that is, the ratio of the maximum dimension to the minimum dimension of the particles. Due to such particles having a small cross-section, the structural stress applied to the material due to volume changes during charge and discharge is reduced. However, such particles can be difficult and costly to manufacture and can be fragile. Also, having a large surface area can lead to the formation of excessive SEI and can lead to excessive capacity loss during the first charge-discharge cycle.

[0009] It is also generally known that electroactive materials such as silicon can be deposited within the pores of a porous carrier material such as an activated carbon material. These composite materials provide some of the beneficial charge and discharge characteristics of nanoscale silicon particles while avoiding the difficulties of handling nanoparticles. For example, Guo et al. (Non-Patent Document 3) disclose a silicon-carbon composite material that provides a conductive skeleton comprising silicon nanoparticles uniformly distributed and deposited within the pore structure of the substrate. The formation of the SEI in the first charge cycle is limited to the remaining pore volume so that the remaining silicon is not exposed to the electrolyte in subsequent charge cycles. Although this composite material improves the capacity retention rate over multiple charge cycles, it has been shown that the initial capacity of the composite material in mAh / g is significantly lower than the capacity for silicon nanoparticles. For example, Guo et al. (Non-Patent Document 3) disclose a silicon-carbon composite material that provides a conductive skeleton comprising silicon nanoparticles uniformly distributed and deposited within the pore structure of the substrate. The formation of the SEI in the first charge cycle is limited to the remaining pore volume so that the remaining silicon is not exposed to the electrolyte in subsequent charge cycles. Although this composite material improves the capacity retention rate over multiple charge cycles, it has been shown that the initial capacity of the composite material in mAh / g is significantly lower than the capacity for silicon nanoparticles.

[0010] Patent Document 2 discloses an active material including a carbon-based scaffold having small pores branching from a small number of larger pores. The electroactive material (e.g., silicon) is randomly located on the walls of both the large and small pores, as well as on the outer surface of the carbon-based scaffold.

[0011] Silicon suboxide materials (e.g., SiO x (where 0 < x < 2)) have been used in "hybrid" electrodes mainly containing graphite as an active material. However, since SiO x expands during lithiation and there is a relatively large irreversible lithium loss in the first charge cycle, the maximum filling amount of SiO x is typically about 10% by weight based on the total electroactive material in the electrode. When the filling amount of SiO x is larger, it causes excessive electrode expansion and irreversible damage to the electrode. Therefore, there is a need for a high-capacity electrode material that has a lithiation capacity equivalent to that of silicon suboxide, while reducing expansion and reducing the capacity loss in the first charge cycle. This allows a high-capacity material to be used for SiO xIt becomes possible to be used at a higher filling amount.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0014] Desirable expansion characteristics of the electrode material need to be obtained together with other important characteristics. In particular, commercially viable alternative electrode materials need to provide the advantage of high lithiation capacity along with high capacity retention over multiple charge-discharge cycles. Also, it is important that new electroactive materials can be easily substituted for known materials in conventional electrode fabrication processes. These processes typically rely on calendaring the electrode material onto the current collector to densify the electrode layer and improve space utilization within the battery design. Porous materials are prone to damage during electrode fabrication, leading to a decline in electrochemical performance. Therefore, there is a specific requirement that new electrochemical materials need to have sufficient structural strength along with high electrochemical storage capacity and high reversible capacity retention. **Means for Solving the Problems**

[0015] The inventors have found that the mechanical properties of a composite material comprising a porous carbon skeleton and an electroactive material located within the porous carbon skeleton can be improved by using a porous carbon skeleton having a specific pore structure, a carefully controlled pore size distribution, and a controlled filling amount of the electroactive material within the pores of the porous carbon skeleton. The location of the electroactive material within the carbon skeleton also reduces the contact with the electrolyte solvent in the cell, minimizing chemical side reactions that lead to irreversible lithium loss during the first and subsequent charge cycles.

[0016] In a first aspect, the present invention is a particulate material consisting only of a plurality of composite particles, wherein the composite particles are (a) a porous carbon skeleton containing micropores and mesopores, the micropores and the mesopores having a total pore volume measured by gas adsorption of P 1 cm 3 / g, where P 1 represents a natural number having a value of 0.4 to 0.75, and the volume ratio of the micropores to the total volume of the micropores and mesopores being in the range of 0.5 to 0.85, a porous carbon skeleton, and (b) A plurality of nanoscale elemental silicon domains located within the pores of the porous carbon framework, comprising, wherein the weight ratio of silicon to the porous carbon framework in the composite particles is in the range of [0.9×P 1 ~1.9×P 1 :1, to provide a particulate material.

[0017] The present invention relies, in particular, on the use of a porous carbon framework with a relatively low porosity to provide a high-strength framework for accommodating electroactive silicon domains. In particular, when the upper limit of the porosity is 0.75 cm 3 / g, the fracture resistance of the porous carbon framework under compressive stress becomes very high.

[0018] The porous carbon framework includes a three-dimensionally interconnected open pore network including micropores and mesopores. The porous carbon framework can optionally further include a small amount of macropores. According to the conventional IUPAC terminology, in this specification, the term "micropore" is used to refer to pores with a diameter of less than 2 nm, and in this specification, the term "mesopore" is used to refer to pores with a diameter of 2 nm to 50 nm, and the term "macropore" is used to refer to pores with a diameter of more than 50 nm.

[0019] The total volume of micropores and mesopores in the porous carbon framework is 0.4 cm 3 / g to 0.75 cm 3 / g. To avoid misunderstanding, references in this specification to the pore volume of the porous carbon framework (unless otherwise specified) relate to the pore volume of the porous carbon framework measured alone, i.e., in the absence of electroactive material (or other material) occupying the pores of the porous carbon framework.

[0020] In this specification, the total volume of micropores and mesopores (i.e., the total pore volume of pores having a diameter in the range of 0 nm to 50 nm) is referred to as P 1 cm 3 / g, where P 1 represents a dimensionless natural number having a value of 0.4 to 0.75. P1 The value of is used to correlate the effective pore volume in the porous carbon framework with the weight ratio of silicon to the porous carbon framework, as described below.

[0021] Elemental silicon is located within the pore network of the porous carbon framework. Therefore, silicon has the form of a plurality of nanoscale silicon domains. As used herein, the term "nanoscale silicon domain" refers to a nanoscale body of silicon having dimensions determined by the location of silicon within the micropores and / or mesopores of the porous carbon framework.

[0022] The microporous carbon framework provides the advantage that the electroactive material is located within the micropore network in the form of small domains having dimensions on the order of a few nanometers or less. These fine electroactive structures can lithiate and delithiate without excessive structural stress because they have lower resistance to elastic deformation and higher fracture resistance than larger electroactive structures. Therefore, the microporosity of the porous carbon framework not only provides an improvement in the mechanical strength of the particles, but also ensures that the electroactive material itself has sufficient elasticity to withstand repeated volume changes over multiple charge-discharge cycles without significant capacity loss.

[0023] In order to provide a material with sufficiently high weight and volume capacities, it is necessary that the pore volume of the porous carbon framework is small, so that the occupancy of the pore volume by silicon is relatively high. The weight ratio of silicon to the porous carbon framework is related to the total micropore / mesopore volume in a ratio of [0.9×P 1 ~1.9×P 1 :1. By defining the weight ratio of silicon based on the value of P 1 the volume occupancy of the pore volume by silicon is controlled within a specific limit. For reference, when the weight ratio of silicon to the porous carbon framework is [0.9×P 1 ~1.9×P 1 :1, it corresponds to the volume of silicon being approximately 40% - 82% of the total volume of the micropores and mesopores.

[0024] It has been found that the weight ratio of silicon to the required porous carbon skeleton can only be obtained by controlling the pore size distribution of the porous carbon skeleton within specific limits. The high-porosity skeleton developed by the applicant of another application has a highly interconnected pore network that includes multiple paths to the innermost pores, but the low-porosity skeleton has far fewer interconnections within the pore network. In order to preferentially deposit silicon inside the pores rather than on the outer surface of the porous carbon skeleton, since the deposition of silicon into the micropores is kinetically advantageous, it is necessary that the microporosity in the porous carbon skeleton is relatively high. However, if the microporosity is too high, it has been found that silicon deposits substantially on the outer surface of the porous carbon skeleton. This is thought to be because the initial deposits of silicon form obstacles in the pore network. The usefulness of alternative paths through the pore network is a function of the total pore volume. In low-porosity materials, the relative lack of alternative paths through the pore network means that this type of obstacle can make a portion of the pore volume inaccessible to the silicon precursor. Therefore, ensuring the internal deposition of silicon in a low-porosity carbon skeleton has been a particular problem addressed by the inventors. In summary, it has been found that the achievement of an electroactive material having the required properties such as high compressive strength, limited expansion, high electrochemical capacitance, and high capacity retention depends on the combination of the total pore volume, the pore size distribution, and the degree of pore occupancy by silicon. Another factor related to the interconnectivity of the pore network in a low-porosity skeleton is the particle size. Larger particles necessarily have a longer path through the pore network to the innermost pores, so the larger the particles, the more difficult it becomes to obtain the required internal deposition of silicon at the required weight ratio. Therefore, in a preferred embodiment of the present invention, not only the particle size distribution but also the median particle diameter (D

[0025] of the porous carbon skeleton 50) It is also carefully controlled. The control of the particle size distribution not only additionally contributes to the particle strength, but also enables the improvement of the closest packing of the composite particles in the electrode active layer, thereby reducing the need for excessive calendaring pressure.

[0026] The highly microporous carbon backbone of the composite material of the present invention has a high tensile fracture strength, so it can adapt within the pore volume to a fairly large amount of expansion of the electroactive material without breaking. When the electroactive material is fully lithiated, the whole composite material can expand externally to some extent, but the amount of external expansion is limited by the controlled total pore volume and thus the maximum weight ratio of silicon to the porous carbon backbone. This high-strength porous carbon backbone is less likely to elastically deform under stress than a more porous backbone, but by controlling the ratio of silicon to the porous carbon backbone, the expansion stress applied to the porous carbon backbone during maximum lithiation is kept below the level required to cause fracture.

[0027] Another factor in the outstanding performance of the composite material of the present invention is that the formation of the SEI is minimized. Since the electroactive material is located within the pore network, only a small area of the electroactive material surface is accessible to the electrolyte, so the formation of the SEI on the surface of the electroactive material is limited, thereby minimizing the irreversible lithium loss during the first charge cycle. The additional exposure of the electroactive material in subsequent charge-discharge cycles is also substantially prevented so that the formation of the SEI does not become a significant defect mechanism leading to capacity loss. This is clearly in contrast to the excessive SEI formation which is a characteristic of the materials disclosed, for example, by Guo (see above). is clearly in contrast (see above).

[0028] As a result of the unique particle structure of the particulate material of the present invention, the composite particles have electrochemical performance that improves on current SiO x technologies. In particular, the particulate material of the present invention has a higher electrochemical capacity, a smaller overall expansion, and a comparable reversible capacity retention rate than previously achieved, so there is a possibility that a higher filling amount of the high-capacity electroactive material can be achieved.

[0029] Any reference in this specification to the volume of micropores, mesopores, and macropores within the porous carbon framework, and any reference to the pore volume distribution within the porous carbon framework, refers to the internal pore volume of the porous carbon framework alone (i.e., in the absence of an electroactive material or other material that occupies some or all of the pore volume).

[0030] P 1 is preferably at least 0.42, more preferably at least 0.45, more preferably at least 0.47, and more preferably at least 0.5. A higher porosity framework is advantageous because it can accommodate a greater amount of silicon within the pore structure without compromising the resistance of the porous carbon framework to breakage under the compressive stress during electrode manufacture or the expansion stress due to the lithiation of silicon. As described above, the value of P 1 is limited by the value at which the high compressive strength of the particles is maintained. Thus, the value of P 1 can be up to 0.75. However, the value of P 1 can more preferably be up to 0.72, more preferably up to 0.7, more preferably up to 0.67, more preferably up to 0.65, more preferably up to 0.62, and more preferably up to 0.6. P 1 can optionally have a value less than 0.6.

[0031] P 1It can be in the range of 0.42 to 0.75, or in the range of 0.42 to 0.72, or in the range of 0.42 to 0.7, or in the range of 0.42 to 0.67, or in the range of 0.42 to 0.65, or in the range of 0.42 to 0.62, or in the range of 0.42 to 0.6, or in the range less than 0.42 to 0.6, or in the range of 0.45 to 0.75, or in the range of 0.45 to 0.72, or in the range of 0.45 to 0.7, or in the range of 0.45 to 0.67, or in the range of 0.45 to 0.65, or in the range of 0.45 to 0.62, or in the range of 0.45 to 0.6, or in the range less than 0.45 to 0.6, or in the range of 0.47 to 0.75, or in the range of 0.47 to 0.72, or in the range of 0.47 to 0.7, or in the range of 0.47 to 0.67, or in the range of 0.47 to 0.65, or in the range of 0.47 to 0.62, or in the range of 0.47 to 0.6, or in the range less than 0.47 to 0.6, or in the range of 0.5 to 0.75, or in the range of 0.5 to 0.72, or in the range of 0.5 to 0.7, or in the range of 0.5 to 0.67, or in the range of 0.5 to 0.65, or in the range of 0.5 to 0.62, or in the range of 0.5 to 0.6, or in the range less than 0.5 to 0.6.

[0032] As used herein, the "volume ratio of micropores" refers to the ratio of the volume of micropores to the total volume of micropores and mesopores. In other words, the volume ratio of micropores is the volume ratio of pores with a diameter of 2 nm or less to the total volume of pores with a diameter of up to 50 nm. As described above, it is necessary to carefully control the volume ratio of micropores to the total volume of micropores and mesopores to be within the range of 0.5 to 0.85. Preferably, the volume ratio of micropores to the total volume of micropores and mesopores is at least 0.55, or at least 0.56, or at least 0.58, or at least 0.6, or at least 0.62, or at least 0.64, or at least 0.65. Preferably, the volume ratio of micropores to the total volume of micropores and mesopores is at most 0.84, or at most 0.82, or at most 0.8, or at most 0.78, or at most 0.76, or at most 0.75.

[0033] The volume ratio of micropores to the total volume of micropores and mesopores is arbitrary and can be in the range of 0.5 to 0.84, or in the range of 0.5 to 0.82, or in the range of 0.5 to 0.8, or in the range of 0.5 to 0.78, or in the range of 0.5 to 0.76, or in the range of 0.5 to 0.75, or in the range of 0.55 to 0.84, or in the range of 0.55 to 0.82, or in the range of 0.55 to 0.8, or in the range of 0.55 to 0.78, or in the range of 0.55 to 0.76, or in the range of 0.55 to 0.75, or in the range of 0.6 to 0.84, or in the range of 0.6 to 0.82, or in the range of 0.6 to 0.8, or in the range of 0.6 to 0.78, or in the range of 0.6 to 0.76, or in the range of 0.6 to 0.75, or in the range of 0.65 to 0.84, or in the range of 0.65 to 0.82, or in the range of 0.65 to 0.8, or in the range of 0.65 to 0.78, or in the range of 0.65 to 0.76, or in the range of 0.65 to 0.75.

[0034] When the micropore ratio is within these ranges, the silicon nanostructure has dimensions small enough to prevent excessive stress during lithiation and also has pore dimensions large enough to deposit silicon at a high level (e.g., by chemical vapor infiltration) within the pore structure of the porous carbon framework within an acceptable processing time. If the micropore ratio is higher than specified, silicon may form plugs and / or caps during deposition, especially when the deposition rate is faster, resulting in pockets of pore volume that cannot be filled by silicon due to inaccessibility, leading to excessive deposition of silicon on the outer surface of the particles. When the micropore ratio is within these ranges, the silicon nanostructure has dimensions small enough to prevent excessive stress during lithiation and also has pore dimensions large enough to deposit silicon at a high level (e.g., by chemical vapor infiltration) within the pore structure of the porous carbon framework within an acceptable processing time. If the micropore ratio is higher than specified, silicon may form plugs and / or caps during deposition, especially when the deposition rate is faster, resulting in pockets of pore volume that cannot be filled by silicon due to inaccessibility, leading to excessive deposition of silicon on the outer surface of the particles.

[0035] The PD of the porous carbon framework 90 The pore diameter of the porous carbon framework is preferably at most 20 nm, more preferably at most 15 nm, more preferably at most 12 nm, more preferably at most 10 nm, more preferably at most 8 nm, more preferably at most 6 nm, and more preferably at most 5 nm.

[0036] As used herein, "PD" 90The term "pore diameter" refers to the volume-based 90th percentile pore diameter with respect to the total volume of micropores and mesopores. In other words, as used herein, "D 90 The term "pore diameter" means that 90% of the total micropore and mesopore volume represented by P 1 is present at a pore diameter less than that pore diameter). To avoid misunderstanding, any macropore volume (pore diameter greater than 50 nm) is not considered for the purpose of determining the PD 90 value.

[0037] Preferably, the PD 95 pore diameter is at most 20 nm, or at most 15 nm, or at most 12 nm, or at most 10 nm, or at most 8 nm. As used herein, "PD 95 pore diameter" refers to the volume-based 95th percentile pore diameter.

[0038] A low volume fraction of pores having a diameter in the range of larger mesopores can be advantageous for facilitating electrolyte access to silicon. Thus, pores having a diameter in the range of 10 nm to 50 nm (i.e., larger mesopores) can optionally constitute at least 1%, at least 2%, at least 5%, or at least 10% of the total micropore and mesopore volume of the porous carbon skeleton.

[0039] The pore diameter distribution of the porous carbon skeleton is preferably bimodal or multimodal. As used herein, the term "pore diameter distribution" relates to the distribution of pore diameters with respect to the cumulative total internal pore volume of the porous carbon skeleton. A bimodal or multimodal pore diameter distribution may be preferred because the proximity of micropores to pores of larger diameter provides the advantage of efficient ion transport to silicon through the porous network. Thus, the particulate material has high ion diffusivity, improving the rate performance.

[0040] The total volume of micropores and mesopores, as well as the pore size distribution of micropores and mesopores, are determined using the quenched solid density functional theory (QSDFT) with nitrogen gas adsorption at 77K in accordance with the standard methodology defined in ISO 15901-2 and ISO 15901-3. Nitrogen gas adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing the gas inside the pores of the solid. As the pressure is increased, the gas first condenses in the pores with the smallest diameter, and the pressure is increased until the saturation point where all pores are filled with liquid is reached. Then, the nitrogen gas pressure is decreased stepwise to evaporate the liquid from the system. By analyzing the adsorption isotherm and desorption isotherm, as well as the hysteresis between them, the pore volume and pore size distribution can be determined. Suitable devices for measuring the pore volume and pore size distribution by nitrogen gas adsorption include the TriStar II Porosimeter and TriStar II Plus Porosimeter available from Micromeritics Instrument Corporation in the United States.

[0041] Nitrogen gas adsorption is effective for measuring the pore volume and pore size distribution of pores with diameters up to 50 nm, but becomes less reliable for pores with much larger diameters. Therefore, for the purposes of this invention, nitrogen adsorption is used to determine the pore volume and pore size distribution only for pores with diameters up to 50 nm or less. As described above, the value of P is determined considering only pores with diameters up to 50 nm or less (i.e., only micropores and mesopores), and similarly, the values of PD 1 and PD 90 and PD 95 as well as the microporosity are determined with respect to the total volume of only micropores and mesopores.

[0042] In view of the limitations of available analytical techniques, it is not possible to measure the pore volume and pore size distribution over the entire range of micropores, mesopores, and macropores using a single technique. If the porous carbon framework contains macropores, the volume of pores in the range greater than 50 nm and up to a maximum of 100 nm is designated as P 2 cm 3The value of / g is specified and measured by the mercury intrusion method. As described above, P 2 The value of is related to the pore volume of the porous carbon skeleton when measured alone, i.e., when there is no silicon or other material occupying the pores of the porous carbon skeleton.

[0043] To avoid misunderstanding, P 2 The value of only considers pores with a diameter greater than 50 nm and at most 100 nm. That is, P 2 The value of only includes the volume of macropores with a diameter of at most 100 nm. Any pore volume measured by the mercury intrusion method with a pore diameter of 50 nm or less is ignored for the purpose of determining the value of P 2 (as described above, nitrogen adsorption is used to characterize mesopores and micropores). The pore volume measured by the mercury intrusion method above 100 nm is assumed to be the interparticle porosity for the purposes of the present invention and is not considered when determining the value of P 2 .

[0044] The mercury intrusion method is a technique for characterizing the porosity and pore size distribution of a material by applying various levels of pressure to a sample of the material immersed in mercury. The pressure required to penetrate mercury into the pores of the sample is inversely proportional to the pore diameter. The values obtained by the mercury intrusion method reported in this specification were obtained in accordance with ASTM UOP578-11 with a surface tension γ of mercury at room temperature of 480 mN / m and a contact angle φ of 140°. The density of mercury at room temperature is 13.5462 g / cm 3 . Many high-precision mercury intrusion devices are commercially available, such as the AutoPore IV series of automatic mercury intrusion porosimeters available from Micromeritics Instrument Corporation in the United States. For a complete report on the mercury intrusion method, see "Analytical Methods in Fine Particle Technology, 1997, Micromeritics Instrument Corporation" (ISBN 0-9656783-0).

[0045] The volume of the macropores (i.e., the value of P 2 is preferably smaller compared to the volume of the micropores and mesopores (i.e., the value of P 1 ). While some of the macropores may be useful for facilitating the access of electrolytes to the pore network, the advantages of the present invention are substantially obtained by accommodating silicon in the micropores and the smaller mesopores.

[0046] Thus, according to the present invention, the total volume of the macropores in the porous carbon framework is P 2 cm 3 / g as measured by mercury intrusion porosimetry, where P 2 preferably has a value of 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 .

[0047] It will be understood that intrusion techniques such as gas adsorption and mercury intrusion porosimetry are only effective for determining the pore volume of pores accessible to nitrogen or mercury from the outside of the porous carbon framework. The values of the porosity (P 1 and P 2 ) defined herein should be understood to refer to the volume of the open pores, i.e., the pores accessible to fluid from the outside of the porous carbon framework. Completely enclosed pores that cannot be identified by nitrogen adsorption or mercury intrusion porosimetry shall not be considered when defining the porosity values herein. Similarly, any pore volume located within pores smaller than the detection limit by nitrogen adsorption shall not be considered in the determination of the value of P 1 .

[0048] The porous carbon framework can include crystalline carbon, amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The porous carbon framework can be either a hard carbon framework or a soft carbon framework, and preferably can be obtained by known procedures including thermal decomposition of a carbon-containing material including an organic material, a resin, and a polymer. The porous carbon material can also be obtained by other processes, for example, from a carbide-containing precursor.

[0049] The porous carbon framework preferably has an elemental composition containing at least 90 wt% carbon, more preferably at least 95 wt% carbon, and even more preferably at least 98 wt% carbon. The porous carbon framework can 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 by performing conventional elemental analysis in the absence of silicon.

[0050] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which carbon atoms are mainly in an sp 2 hybridized state (triple bond) in nanoscale polycyclic aromatic domains. These polycyclic aromatic domains are crosslinked by chemical bonds, for example, C-O-C bonds.

[0051] Since the polycyclic aromatic domains are chemically crosslinked to each other, hard carbon cannot be converted to graphite at high temperatures. As revealed by the high G band (about 1600 cm -1 ) in the Raman spectrum, hard carbon has properties similar to graphite. However, as revealed by the high D band (about 1350 cm -1 ) in the Raman spectrum, the carbon is not completely like graphite.

[0052] As used herein, the term "soft carbon" also means that carbon atoms are mainly in polycyclic aromatic domains having dimensions in the range of 5 nm to 200 nm and in an sp 2Refers to a disordered carbon matrix in a hybrid state (triple bond). In contrast to hard carbon, the polycyclic aromatic domains in soft carbon are bonded by intermolecular forces rather than cross-linked by chemical bonds. That is, at high temperatures, soft carbon can be graphitized. The porous carbon skeleton preferably contains at least 50% sp 2 hybrid carbon when measured by XPS. For example, the porous carbon skeleton preferably contains 50% - 98% sp 2 hybrid carbon, 55% - 95% sp 2 hybrid carbon, 60% - 90% sp 2 hybrid carbon, or 70% - 85% sp 2 hybrid carbon.

[0053] To produce a suitable porous carbon skeleton, various different materials can be used. Examples of organic materials that can be used include plant biomass containing lignocellulosic materials (such as coconut shells, rice husks, wood, etc.) and fossil carbon sources such as coal. Examples of resins and polymer materials that form a porous carbon skeleton by pyrolysis include phenolic resins, novolac resins, pitch, melamine, polyacrylates, polystyrenes, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and various copolymers containing monomer units of acrylates, styrenes, α-olefins, vinyl pyrrolidone, and other ethylenically unsaturated monomers. Depending on the starting materials and the conditions of the pyrolysis process, various different hard carbon materials are available in the art.

[0054] To increase the volume of mesopores and micropores, a chemical activation process or a gas activation process can be performed on the porous carbon skeleton. Suitable activation processes include contacting the pyrolyzed carbon with one or more of oxygen, steam, CO, CO2, and KOH at a temperature in the range of 600°C to 1000°C.

[0055] Mesopores can be removed by thermal or chemical means after pyrolysis or activation. It can also be obtained by known templating processes using extractable pore-forming agents such as kiru, MgO and other colloidal templates or polymer templates.

[0056] The amount of silicon in the composite particles of the present invention is selected such that silicon occupies at least about 40% and up to about 78% of the internal pore volume of the porous carbon skeleton (in the uncharged state). Silicon preferably occupies from about 50% to about 75% of the internal pore volume of the porous carbon skeleton, more preferably from about 55% to 70% of the internal pore volume of the porous carbon skeleton. Within these preferred ranges, the pore volume of the porous carbon skeleton is effective in accommodating the expansion of silicon during charge and discharge, and an excessive pore volume that does not contribute to the volume capacity of the particulate material is avoided. However, the amount of silicon is also not so much that it hinders effective lithiation due to an insufficient metal ion diffusion rate or an insufficient expansion volume that results in mechanical resistance to lithiation.

[0057] As described above, the amount of silicon in the porous carbon skeleton can be correlated with the effective pore volume by the requirement that the weight ratio of silicon to the porous carbon skeleton is in the range of [0.9×P 1 ~1.9×P 1 :1. In this relationship, considering the density of silicon and the pore volume of the porous carbon skeleton, a weight ratio of silicon is defined such that about 40% to 82% of the pore volume is occupied. Preferably, the weight ratio of silicon to the porous carbon skeleton is in the range of [0.9×P 1 ~1.8×P 1 :1, which indicates that about 40% to 78% of the pore volume is occupied.

[0058] Preferably, the weight ratio of silicon to the porous carbon skeleton is at least 0.95×P 1 、or at least 1×P 1 、or at least 1.05×P 1 、or at least 1.1×P 1 、or at least 1.15×P 1 、or at least 1.2×P1 It is.

[0059] Preferably, the weight ratio of silicon to the porous carbon skeleton is at most 1.85×P 1 or at most 1.8×P 1 or at most 1.75×P 1 or at most 1.7×P 1 or at most 1.65×P 1 or at most 1.6×P 1 It is.

[0060] For example, the weight ratio of silicon to the porous carbon skeleton is in the range of [0.95×P 1 ~1.85×P 1 :1, or in the range of [0.95×P 1 ~1.8×P 1 :1, or in the range of [1×P 1 ~1.8×P 1 :1, or in the range of [1.05×P 1 ~1.75×P 1 :1, or in the range of [1.1×P 1 ~1.7×P 1 :1, or in the range of [1.15×P 1 ~1.7×P 1 :1, or in the range of [1.2×P 1 ~1.65×P 1 :1, or in the range of [1.25×P 1 ~1.65×P 1 :1, or in the range of [1.3×P 1 ~1.6×P 1 :1, or in the range of [1.35×P 1 ~1.6×P 1 :1, or in the range of [1.4×P 1 ~1.55×P 1 :1 and can be set.

[0061] The composite particles preferably contain less than 10% by weight of oxygen, more preferably less than 5% by weight of oxygen, and even more preferably less than 2% by weight of oxygen, based on the total weight of the composite particles. It is preferable that silicon and carbon together constitute at least 90% by weight of the composite particles, and more preferably at least 95% by weight of the composite particles.

[0062] The composite particles can optionally include pores covered with silicon such that the completely enclosed voids are inaccessible to the electrolyte.

[0063] Preferably at least 80 wt%, more preferably at least 85 wt%, more preferably at least 90 wt%, more preferably at least 95 wt%, and still preferably at least 98 wt% of the silicon in the composite particles is located within the internal pore volume of the porous carbon skeleton, such that there is no or little silicon located on the outer surface of the composite particles.

[0064] The particulate material of the present invention can be further characterized by its performance in thermogravimetric analysis (TGA) in air. When the particulate material is analyzed by TGA in air at a heating rate of 10 °C / min, preferably 10% or less, more preferably 5% or less, and more preferably 2% or less of the silicon content of the particulate material is unoxidized at 800 °C.

[0065] The amount of unoxidized silicon is determined by derivation from the TGA trace specific to these materials. The mass increase at about 300 °C to 500 °C corresponds to the initial oxidation of silicon to SiO2, followed by a mass decrease at about 500 °C to 600 °C as the carbon is oxidized to CO2 gas. Above about 600 °C, there is a further mass increase corresponding to the continued conversion of silicon to SiO2, increasing towards an asymptote above 1000 °C as the oxidation of silicon is completed.

[0066] For the purposes of this analysis, any mass increase above 800 °C corresponds to the oxidation of silicon to SiO2, and the total mass at the end of oxidation is assumed to be SiO2. Thus, the proportion of unoxidized silicon at 800 °C can be determined as a proportion of the total amount of silicon according to the following formula: Z = 1.875 × [(M f - M 800 ) / M f × 100% (where Z is the proportion of unoxidized silicon at 800 °C, M f is the mass of the sample at the end of oxidation, M 800 is the mass of the sample at 800 °C).

[0067] Although not bound by theory, since the diffusion of oxygen atoms through the oxide layer is thermally activated, it is understood that the temperature at which silicon is oxidized under TGA generally corresponds to the length scale of the oxide film on silicon. The length scale of the oxide film thickness is limited by the size and location of the silicon nanostructures. Therefore, it is understood that silicon deposited in micropores and smaller mesopores oxidizes at a lower temperature than silicon deposits on the particle surface because the oxide films present on these structures are necessarily thinner. Thus, the preferred materials according to the present invention exhibit substantially complete oxidation of silicon at low temperatures, consistent with the silicon nanostructures located in micropores and smaller mesopores having a small length scale.

[0068] The total volume of micropores and optionally mesopores in the composite particles (i.e., in the presence of silicon), measured by nitrogen gas adsorption, is preferably 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 .

[0069] The weight ratio of silicon to the porous carbon framework can be determined by elemental analysis. Elemental analysis is used to determine the weight percentages of both silicon and carbon in the composite particles. Optionally, the amounts of hydrogen, nitrogen, and oxygen can also be determined by elemental analysis. Preferably, elemental analysis is also used to determine the weight percentage of carbon (and optionally, hydrogen, nitrogen, and oxygen) in the porous carbon framework only. By determining the weight percentage of carbon in the porous carbon framework only, the possibility that this porous carbon framework contains a small amount of heteroatoms within its molecular framework is considered. By performing both measurements together, the weight ratio of silicon to the entire porous carbon framework can be reliably determined.

[0070] The silicon content is preferably determined by ICP-OES (inductively coupled plasma optical emission spectrometry). There are many commercially available ICP-OES analyzers such as the iCAP (trademark) 7000 series from ThermoFisher Scientific. The carbon content (and optionally, the hydrogen, nitrogen, and oxygen contents) in the composite particles and the porous carbon framework only is preferably determined by IR absorption. A suitable device for determining the carbon, hydrogen, nitrogen, and oxygen contents is the TruSpec (trademark) Micro elemental analyzer available from LECO Corporation.

[0071] The composite particles preferably have a low total oxygen content. Oxygen can be present in the composite particles, for example, as part of the porous carbon framework or as an oxide layer on any exposed silicon surface. The total oxygen content of the composite particles is preferably less than 15 wt%, more preferably less than 10 wt%, even more preferably less than 5 wt%, for example, less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%.

[0072] Silicon can optionally contain small amounts of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, nitrogen, or germanium. Preferably, the dopant is present in a total amount of 2 wt% or less based on the total amount of silicon and the dopant(s).

[0073] To avoid misunderstanding, the term "particle size" as used herein refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, where the volume of the particle is understood to include the volume of pores within the particle. As used herein, "D 50 " and "D 50 particle size" refer to the volume-based median particle size, i.e., the diameter below which 50 volume% of the particle population is present. As used herein, "D 10 " and "D 10 particle size" refer to the volume-based 10th percentile median particle size, i.e., the diameter below which 10 volume% of the particle population is present. As used herein, "D 90 " and "D 90 particle size" refer to the volume-based 90th percentile median particle size, i.e., the diameter below which 90 volume% of the particle population is present.

[0074] The term "D n " as used herein to define the particle size distribution should be distinguished from the term "PD n " as used herein to define the pore size distribution, as described above.

[0075] The particle size and particle size distribution can be determined by a conventional laser diffraction method in accordance with ISO 13320:2009. Laser diffraction is based on the principle that particles scatter light at angles that vary according to the size of the particles, and a collection of particles generates a scattered light pattern defined by the intensity and angle that can be correlated to the particle size distribution. To determine the particle size distribution quickly and reliably, many laser diffraction devices are commercially available. Unless otherwise specified, the particle size distribution measurement values defined or reported in this specification are those measured by a conventional Malvern Mastersizer (trademark) 3000 particle size analyzer manufactured by Malvern Instruments. This Malvern Mastersizer (trademark) 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing the target particles suspended in an aqueous solution. The light beam hitting the particles is scattered at an angle inversely proportional to the particle size, and a photodetector array measures the intensity of the light at several predetermined angles. The intensities measured at various angles are processed by a computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values reported in this specification are obtained using a wet dispersion of the particles in distilled water. The refractive index of the particles is 3.50, and the refractive index of the dispersant is 1.330. The particle size distribution is calculated using the Mie scattering model.

[0076] The composite particles can have a D 50 particle size in the range of 1 μm to 30 μm. Optionally, the D 50 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, the D 50 particle size can be at most 20 μm, or at most 18 μm, or at most 16 μm, or at most 14 μm, or at most 12 μm, or at most 10 μm.

[0077] For example, the composite particles can have a D particle size in the range of 1 μm to 20 μm, or 1 μm to 18 μm, or 1 μm to 16 μm, or 2 μm to 16 μm, or 2 μm to 14 μm, or 3 μm to 12 μm, or 4 μm to 10 μm.50 It can have a particle size. Particles within these size ranges and having the porosity and pore size distribution described herein are dispersible in a slurry, have structural robustness, retain capacity over repeated charge-discharge cycles, and are suitable for forming a dense electrode layer having a uniform thickness in the conventional range of 20 μm to 50 μm, and are thus ideally suitable for use in an anode for a metal ion battery.

[0078] The D of the composite particles 10 The particle size is preferably 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. The D 10 By maintaining the particle size at 0.5 μm or more, the possibility of undesirable aggregation of submicron-sized particles is reduced, the dispersibility of the particulate matter is improved, and the capacity retention rate is improved.

[0079] The D of the composite particles 90 The particle size is preferably at most 50 μm, or at most 40 μm, or at most 30 μm, or at most 25 μm, or at most 20 μm. The presence of very large particles leads to non-uniform shaping and filling of the particles in the electrode active layer, thus hindering the formation of a dense electrode layer, particularly an electrode layer having a thickness in the range of 20 μm to 50 μm. Therefore, the D 90 The particle size is preferably at most 40 μm, and more preferably even smaller.

[0080] The composite particles preferably have a narrow particle size distribution span. For example, the particle size distribution span ((D 90 -D 10 ) / D 50 as defined) 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 particle size distribution span, more efficient filling of the particles into a dense electrode layer can be more easily achieved.

[0081] The composite particles can have a spheroidal shape. The spheroidal particles defined herein can include both spherical particles and ellipsoidal particles, and the shape of the composite particles of the present invention can preferably be defined by referring to the sphericity and aspect ratio of the particles of the present invention. It has been found that spheroidal particles are particularly suitable for dispersion in a slurry without forming aggregates. Also, the use of porous spheroidal particles has surprisingly been found to provide a further improvement in strength when compared to porous particles and porous particle fragments of irregular shape.

[0082] The sphericity of an object has conventionally been defined as the ratio of the surface area of a sphere to the surface area of the object, where the object and the sphere have the same volume. However, in practice, it is difficult to measure the surface area and volume of individual particles on the micron scale. However, high-precision two-dimensional projection images of micron-scale particles can be obtained by scanning electron microscopy (SEM) and dynamic image analysis that records the shadow projected by the particles using a digital camera. The term "sphericity" as used herein is understood to be the ratio of the area of the particle projection image to the area of a circle, where the particle projection image and the circle have the same circumference. Thus, for an individual particle, the sphericity S is defined as follows:

Equation

Equation

[0083] In this specification, the term "ellipsoidal of revolution" used in connection with the composite particles of the present invention is understood to refer to a material having an average sphericity of at least 0.70. The porous ellipsoidal particles of the present invention preferably have an average sphericity of at least 0.85, more preferably at least 0.90, more preferably at least 0.92, more preferably at least 0.93, more preferably at least 0.94, more preferably at least 0.95. The porous ellipsoidal particles can optionally have an average sphericity of at least 0.96, or at least 0.97, or at least 0.98, or at least 0.99.

[0084] It will be understood that the circumference and area of the two-dimensional particle projection image depend on the orientation of the particles in the case of any particles that are not perfectly ellipsoidal of revolution. However, the influence of particle orientation can be offset by reporting sphericity and aspect ratio as average values obtained from a plurality of particles having a random orientation. Many SEM devices and dynamic image analysis devices are commercially available, and the sphericity and aspect ratio of particulate matter can be determined quickly and reliably. Unless otherwise specified, the sphericity values defined or reported in this specification are those measured by a CamSizer XT particle analyzer manufactured by Retsch Technology GmbH. This CamSizer XT is a dynamic image analysis device capable of obtaining a high-precision distribution of the size and shape of particulate matter in a sample volume of 100 mg to 100 g, and characteristics such as average sphericity and aspect ratio can be directly calculated by this device.

[0085] The composite particles of the present invention preferably have a maximum of 100 m 2 / g, or a maximum of 80 m 2 / g, or a maximum of 60 m 2 / g, or a maximum of 50 m 2 / g, or a maximum of 40 m 2 / g, or a maximum of 30 m 2 / g, or a maximum of 25 m 2 / g, or a maximum of 20 m 2 / g, or a maximum of 15 m 2 / g, or a maximum of 10 m 2It has a BET surface area of / g. As used herein, the term "BET surface area" should be interpreted to refer to the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules onto the solid surface using the Brunauer-Emmett-Teller theory in accordance with ISO 9277. Usually, during the first charge-discharge cycle of the anode containing the particulate material of the present invention, in order to minimize the formation of the solid electrolyte interface (SEI) layer on the surface of the composite particles, it is preferable that the BET surface area is small. However, if the BET surface area is excessively small, metal ions in the surrounding electrolyte cannot access most of the electroactive material, leading to unacceptable low charge rates and capacity limitations. For example, the BET surface area is preferably at least 0.1 m 2 / g, or at least 1 m 2 / g, or at least 2 m 2 / g, or at least 5 m 2 / g. For example, the BET surface area can be in the range of 1 m 2 / g to 25 m 2 / g, more preferably in the range of 2 m 2 / g to 15 m 2 / g.

[0086] The particulate material of the present invention typically has a specific charge capacity of 1200 mAh / g to 2000 mAh / g during the first lithiation. Preferably, the particulate material of the present invention has a specific charge capacity of at least 1400 mAh / g during the first lithiation.

[0087] The composite particles of the present invention are preferably produced by chemical vapor infiltration (CVI) of a silicon-containing precursor into the pore structure of the porous carbon framework. As used herein, CVI refers to a process in which a gaseous silicon-containing precursor is thermally decomposed on the surface to form elemental silicon and gaseous by-products on the surface. products are formed.

[0088] Suitable gaseous silicon-containing precursors include silane (SiH4), silane derivatives (e.g., disilane, trisilane, and tetrasilane), and trichlorosilane (SiHCl3). The silicon-containing precursor can be used in pure form or, more commonly, as a diluted mixture with an inert carrier gas such as nitrogen or argon. For example, the silicon-containing precursor can be used in an amount in the range of 0.5 vol% to 20 vol%, or 1 vol% to 10 vol%, or 1 vol% to 5 vol% based on the total volume of the silicon-containing precursor and the inert carrier gas. The CVI process is preferably carried out at a total pressure of 101.3 kPa (i.e., 1 atm) with a low partial pressure of the silicon precursor, and the remaining partial pressure is made up to atmospheric pressure using an inert padding gas such as hydrogen, nitrogen, or argon. A deposition temperature in the range of 400 °C to 700 °C, for example, 450 °C to 550 °C, or 450 °C to 500 °C is used. The CVI process can preferably be carried out in a fixed bed reactor, a rotary kiln, or a fluidized bed reactor (including a jet fluidized bed reactor).

[0089] As an example of the fixed bed reactor method, 1.8 g of particulate porous skeleton was placed on a stainless steel plate with a constant thickness of 1 mm along its length. The plate was then placed inside a stainless steel tube with an outer diameter of 60 mm, and the gas inlet line and outlet line were placed in the hot zone of a retort furnace. After purging the furnace tube with nitrogen gas at room temperature for 30 minutes, the sample temperature was raised to 450 °C to 500 °C. The flow rate of nitrogen gas was adjusted so that a gas residence time of at least 90 seconds was ensured inside the furnace tube and maintained at that rate for 30 minutes. Then, the gas supply was switched from nitrogen to a mixture of monosilane in nitrogen with a concentration of 1.25 vol%. The introduction of monosilane was carried out over 5 hours while maintaining the reactor pressure at 101.3 kPa (1 atm). After the introduction was completed, the gas flow rate was kept constant while purging the silane from the furnace using nitrogen. After purging the furnace with nitrogen for 30 minutes, it was cooled to room temperature over several hours. Then, the atmosphere was gradually switched to air over 2 hours by switching the gas flow from nitrogen to air from a compressed air supply.

[0090] The particulate material of the present invention can optionally include a conductive carbon coating. Preferably, the conductive carbon coating can be obtained by chemical vapor deposition (CVD). CVD is a methodology known in the art and involves thermal decomposition of a volatile carbon-containing gas (e.g., ethylene) on the surface of the particulate material. Alternatively, the carbon coating can be formed by depositing a solution of a carbon-containing compound on the surface of the particulate material followed by thermal decomposition. The conductive carbon coating has sufficient permeability for lithium to access the interior of the composite particles without excessive resistance so as not to reduce the rate performance of the composite particles. For example, the thickness of the carbon coating can preferably be in the range of 2 nm to 30 nm. The carbon coating can optionally be porous and / or can cover only partially the surface of the composite particles.

[0091] The carbon coating has the advantage of further reducing the BET surface area of the particulate material by smoothing any surface defects and filling the remaining microporosity of the surface, thereby further reducing the first cycle loss. Also, the carbon coating improves the conductivity of the surface of the composite particles, reduces the need for a conductive additive in the electrode composition, and improves the surface for the formation of a stable SEI layer, improving the capacity retention rate during cycling. by filling, and thereby further reducing the first cycle loss. Also, the carbon coating improves the conductivity of the surface of the composite particles, reduces the need for a conductive additive in the electrode composition, and improves the surface for the formation of a stable SEI layer, improving the capacity retention rate during cycling.

[0092] According to a first aspect of the present invention, particulate materials according to the following aspects 1-1 to 1-25 are further provided.

[0093] Aspect 1-1: (i) The volume ratio of micropores is in the range of 0.55 to 0.85, (ii) The weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9× P 1 ~1.8×P 1 :1, Particulate material according to the first aspect of the present invention.

[0094] Aspect 1-2: (i) P 1is in the range of 0.45 to 0.75, (ii) the volume ratio of the micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0095] Aspect 1-3: (i) P 1 is in the range of 0.45 to 0.75, (ii) the volume ratio of the micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0096] Aspect 1-4: (i) P 1 is in the range of 0.45 to 0.75, (ii) the volume ratio of the micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0097] Aspect 1-5: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume ratio of the micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0098] Aspects 1-6: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume fraction of micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0099] Aspects 1-7: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume fraction of micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0100] Aspects 1-8: (i) P 1 is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0101] Aspects 1-9: (i) P 1 is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1, The particulate material according to the first aspect of the present invention.

[0102] Aspects 1-10: (i) P 1 is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1. The particulate material according to the first aspect of the present invention.

[0103] Aspects 1-11: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) the volume fraction of micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1. The particulate material according to the first aspect of the present invention.

[0104] Aspects 1-12: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) the volume fraction of micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P 1 ~1.6×P 1 :1. The particulate material according to the first aspect of the present invention.

[0105] Aspects 1-13: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) the volume fraction of micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [0.9×P1 ~1.6×P 1 :1 is in the range of The particulate material according to the first aspect of the present invention.

[0106] Aspects 1-14: (i) P 1 is in the range of 0.45 to 0.75, (ii) The volume fraction of micropores is in the range of 0.55 to 0.8, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is [1×P 1 ~1.5×P 1 :1 is in the range of (iv) PD 90 The pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0107] Aspects 1-15: (i) P 1 is in the range of 0.45 to 0.75, (ii) The volume fraction of micropores is in the range of 0.55 to 0.75, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is [1×P 1 ~1.5×P 1 :1 is in the range of (iv) PD 90 The pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0108] Aspects 1-16: (i) P 1 is in the range of 0.45 to 0.75, (ii) The volume fraction of micropores is in the range of 0.6 to 0.75, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is [1×P 1 ~1.5×P 1 :1 is in the range of (iv) PD 90 The pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0109] Aspect 1-17: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume fraction of micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the pore diameter of PD 90 is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0110] Aspect 1-18: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume fraction of micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the pore diameter of PD 90 is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0111] Aspect 1-19: (i) P 1 is in the range of 0.5 to 0.75, (ii) the volume fraction of micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the pore diameter of PD 90 is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0112] Aspect 1-20: (i) P 1is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.55 to 0.8, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0113] Aspect 1-21: (i) P 1 is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.55 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0114] Aspect 1-22: (i) P 1 is in the range of 0.5 to 0.7, (ii) the volume fraction of micropores is in the range of 0.6 to 0.75, (iii) the weight ratio of silicon to the porous carbon skeleton in the composite particles is in the range of [1×P 1 ~1.5×P 1 :1, (iv) the PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0115] Aspect 1-23: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) the volume fraction of micropores is in the range of 0.55 to 0.8, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is in the range of [1×P 1 ~1.5×P 1 :1, (iv) The PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0116] Aspect 1-24: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) The volume ratio of micropores is in the range of 0.55 to 0.75, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is in the range of [1×P 1 ~1.5×P 1 :1, (iv) The PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0117] Aspect 1-25: (i) P 1 is in the range of 0.45 to less than 0.6, (ii) The volume ratio of micropores is in the range of 0.6 to 0.75, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is in the range of [1×P 1 ~1.5×P 1 :1, (iv) The PD 90 pore diameter is at most 10 nm, The particulate material according to the first aspect of the present invention.

[0118] Aspect 1-26: (i) P 1 is in the range of 0.45 to 0.75, (ii) The volume ratio of micropores is in the range of 0.55 to 0.8, (iii) In the composite particles, the weight ratio of silicon to the porous carbon skeleton is in the range of [1×P 1 ~1.8×P 1is in the range of 1, (iv) PD 90 with a maximum pore diameter of 8 nm, The particulate material according to the first aspect of the present invention.

[0119] Aspects 1-27: (i) P 1 is in the range of 0.45 to 0.75, (ii) the volume ratio of micropores is in the range of 0.55 to 0.8, (iii) in the composite particles, the weight ratio of silicon to the porous carbon skeleton is [1×P 1 ~1.8×P 1 :1, (iv) PD 90 with a maximum pore diameter of 6 nm, The particulate material according to the first aspect of the present invention.

[0120] According to the present invention, for the first aspect of the present invention within the scope of Aspects 1-1 to 1-27 described above, the preferred / optional features disclosed herein should be considered to be the preferred / optional features of Aspects 1-1 to 1-27. It should be understood that similarly, any features of the dependent claims within the scope of Aspects 1-1 to 1-27 above should be construed as if those claims were dependent on Aspects 1-1 to 1-27.

[0121] In a second aspect of the present invention, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component. In particular, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component selected from (i) a binder, (ii) a conductive additive, and (iii) an additional particulate electroactive material. The composition according to the second aspect of the present invention is useful as an electrode composition and thus can be used to form an active layer on an electrode.

[0122] ​The particulate material used to make the composition of the second aspect of the present invention can have any of the characteristics described as preferred or optional with respect to the first aspect of the present invention.

[0123] The composition can be a hybrid electrode composition comprising a particulate material according to the first aspect of the present invention and at least one additional particulate electroactive material. Examples of additional particulate electroactive materials 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. The at least one additional particulate electroactive material is most preferably graphite.

[0124] In the case of a hybrid electrode composition, this composition preferably contains the particulate material according to the first aspect of the present invention in an amount of 15% to 60% by weight, or 20% to 50% by weight, or 30% to 50% by weight, based on the total dry weight of the composition.

[0125] The at least one additional particulate electroactive material is preferably present in an amount of 20% to 70% by weight, or 25% to 65% by weight, or 30% to 60% by weight of the at least one additional particulate electroactive material.

[0126] The at least one additional particulate electroactive material preferably has a D 50 particle size in the range of 10 μm to 50 μm, preferably 10 μm to 40 μm, more preferably 10 μm to 30 μm, most preferably 10 μm to 25 μm, for example 15 μm to 25 μm.

[0127] The D 10 particle size of the at least one additional particulate electroactive material is preferably at least 5 μm, more preferably at least 6 μm, more preferably at least 7 μm, more preferably at least 8 μm, more preferably at least 9 μm, still more preferably at least 10 μm.

[0128] D of at least one additional particulate electroactive material 90 The particle size is preferably at most 100 μm, more preferably at most 80 μm, more preferably at most 60 μm, more preferably at most 50 μm, and most preferably at most 40 μm.

[0129] At least one additional particulate electroactive material is preferably selected from carbon-containing particles, graphite particles, and / or hard carbon particles, where the graphite particles and hard carbon particles have a D in the range of 10 μm to 50 μm. 50 More preferably, at least one additional particulate electroactive material is selected from graphite particles, where the graphite particles have a D in the range of 10 μm to 50 μm. 50 Particle size.

[0130] The composition may be a non-hybrid (i.e., "high loading") electrode composition that substantially does not contain additional particulate electroactive material. In this context, the term "substantially does not contain additional particulate electroactive material" means that the composition contains, relative to the total dry weight of the composition, any additional electroactive material (i.e., additional material capable of inserting and releasing metal ions during charging and discharging of the battery) of less than 15 wt%, preferably less than 10 wt%, preferably less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, and more preferably less than 0.5 wt%.

[0131] This type of "high loading" electrode composition contains, relative to the total dry weight of the composition, the particulate material according to the first aspect of the invention, preferably at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt%.

[0132] The composition can optionally contain a binder. The binder functions to adhere the composition to the current collector and maintain the integrity of the composition. Examples of binders that can be used according to the present invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginates and their alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The composition can contain a mixture of binders. Preferably, the binder contains polymers selected from polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, SBR, and CMC.

[0133] The binder can preferably be present in an amount of 0.5 wt% to 20 wt%, preferably 1 wt% to 15 wt%, preferably 2 wt% to 10 wt%, and most preferably 5 wt% to 10 wt% based on the total dry weight of the composition.

[0134] The binder can optionally be present in combination with one or more additives that modify the properties of the binder, such as a crosslinking accelerator, a coupling agent, and / or an adhesion promoter.

[0135] The composition can optionally contain one or more conductive additives. Preferred conductive additives are non-electrically active materials included to improve the conductivity between the electroactive components of the composition and between the electroactive components of the composition and the current collector. The conductive additive can preferably be selected from carbon black, carbon fiber, carbon nanotube, graphene, acetylene black, ketjen black, metal fiber, metal powder, and conductive metal oxide. Preferred conductive additives include carbon black and carbon nanotubes.

[0136] One or more conductive additives can preferably be present in a total amount of from 0.5 wt% to 20 wt%, preferably from 1 wt% to 15 wt%, preferably from 2 wt% to 10 wt%, and most preferably from 5 wt% to 10 wt% based on the total dry weight of the composition.

[0137] In a third aspect, the present invention provides an electrode comprising a particulate material defined with reference to the first aspect of the present invention in electrical contact with a current collector. The particulate material used to fabricate the electrode of the third aspect of the present invention can have any of the features described as preferred or optional with respect to the first aspect of the present invention.

[0138] As used herein, the term current collector refers to any conductive substrate capable of conducting current to or from the electroactive particles in the composition. Examples of materials that can be used as the current collector include copper, aluminum, stainless steel, nickel, titanium, and sintered carbon. Copper is a preferred material. The current collector typically has the form of a foil or mesh having a thickness of from 3 μm to 500 μm. The particulate material of the present invention can be applied to one or both sides of the current collector, preferably in a thickness ranging from 10 μm to 1 mm, for example, from 20 μm to 500 μm, or from 50 μm to 200 μm.

[0139] Preferably, the electrode comprises a composition defined with reference to the second aspect of the present invention in electrical contact with a current collector. The composition can have any of the features described as preferred or optional with respect to the second aspect of the present invention.

[0140] The electrode of the third aspect of the present invention can preferably be produced by forming a slurry by combining the particulate material of the present invention (optionally in the form of the composition of the present invention) with a solvent and optionally one or more viscosity-adjusting additives. Then, the slurry is cast on the surface of the current collector, and by removing the solvent, an electrode layer is formed on the surface of the current collector. Further steps such as heat treatment for curing any binder and / or calendaring treatment of the electrode layer can be appropriately performed. The electrode layer preferably has a thickness 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.

[0141] Alternatively, for example, the slurry can be cast on a suitable casting template, the solvent can be removed, and then the casting template can be removed to form the slurry into a self-supporting film or mat containing the particulate material of the present invention. The obtained film or mat has the form of a self-supporting agglomerate and can then be adhered to the current collector by known methods.

[0142] The electrode of the third aspect of the present invention can be used as the anode of a metal ion battery. Thus, in a fourth aspect, the present invention provides a rechargeable metal ion battery including an anode containing an electrode as described above, a cathode containing a cathode active material capable of releasing and reabsorbing metal ions, and an electrolyte between the anode and the cathode.

[0143] 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 can release and accept lithium ions.

[0144] The cathode active material is preferably a metal oxide-based composite material. Examples of suitable cathode active materials include LiCoO2, LiCo 0.99 Al 0.01 O2, LiNiO2, LiMnO2, LiCo 0.5 Ni0.5 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 is included. The cathode current collector usually has a thickness of 3 μm to 500 μm. Examples of materials that can be used as the cathode current collector include aluminum, stainless steel, nickel, titanium, and sintered carbon.

[0145] The electrolyte is preferably a non-aqueous electrolyte containing a metal salt, such as a lithium salt, and can include a non-aqueous electrolyte solution, a solid electrolyte, and an inorganic solid electrolyte, but is not limited thereto. Examples of non-aqueous electrolyte solutions that can be used include aprotic organic solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydro furan, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triesters, trimethoxymethane, sulfolane, methyl sulfolane, and 1,3-dimethyl-2-imidazolidinone.

[0146] Examples of organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups.

[0147] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4.

[0148] The lithium salt is preferably soluble in the selected solvent or mixture of solvents. Examples of suitable lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, LiBC4O8, LiPF6, LiCF3SO3, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and CF3SO3Li.

[0149] When the electrolyte is a non-aqueous organic solution, the metal ion battery preferably includes a separator inserted between the anode and the cathode. The separator is typically formed of an insulating material having high ion permeability and high mechanical strength. The separator typically has a pore size of 0.01 μm to 100 μm and a thickness of 5 μm to 300 μm. An example of a suitable electrode separator is a microporous polyethylene film.

[0150] The separator can be replaced with a polymer electrolyte material. In such a case, the polymer electrolyte material is present in both the composite anode layer and the composite cathode layer. The polymer electrolyte material can be a solid polymer electrolyte or a gel-type polymer electrolyte.

[0151] In a fifth aspect, the present invention provides the use of the particulate material as an anode active material as defined with reference to the first aspect of the present invention. Preferably, the particulate material has the form of a composition as defined with reference to the second aspect of the present invention, and most preferably the composition contains one or more additional particulate electroactive materials as defined above.

Mode for Carrying Out the Invention

Examples

[0152] The porous carbon skeletons C1 to C5 used in the following examples have the properties shown in Table 1.

[0153]

Table 1

[0154] Example 1 - Preparation of Composite Particles in a Fixed-Bed Reactor 1.8 g of particulate porous skeletons having the properties shown in Table 1 were arranged on a stainless-steel plate at a constant thickness of 1 mm along its length to produce silicon-carbon composite particles. Subsequently, the plate was placed inside a stainless-steel tube with an outer diameter of 60 mm, and the gas inlet line and outlet line were placed in the hot zone of a retort furnace. After purging the furnace tube with nitrogen gas at room temperature for 30 minutes, the sample temperature was raised to 450 °C to 500 °C. The flow rate of nitrogen gas was adjusted so that a gas residence time of at least 90 seconds was ensured inside the furnace tube and maintained at that rate for 30 minutes. Subsequently, the gas supply was switched from nitrogen to a mixture of monosilane in nitrogen with a concentration of 1.25% by volume. The introduction of monosilane was carried out over 5 hours while maintaining the reactor pressure at 101.3 kPa (1 atm). After the introduction was completed, the gas flow rate was kept constant while purging the silane from the furnace using nitrogen. After purging the furnace with nitrogen for 30 minutes, it was cooled to room temperature over several hours. Subsequently, the gas flow was switched from nitrogen to air from a compressed-air supply, gradually switching the atmosphere to air over 2 hours.

[0155] The composite material prepared according to Example 1 has the properties shown in Table 2 below.

[0156]

Table 2

[0157] From the data, it can be seen that in order to enable efficient penetration of silicon into the micropores, the porous carbon skeleton needs to have a carefully controlled pore-size distribution.

[0158] From the TGA analysis of sample S3, it can be seen that when the microporosity is too high, silicon cannot penetrate into the pores of the porous carbon skeleton. Instead, silicon is deposited on the surface of the porous carbon skeleton. This can be seen from the fact that a high level of crude silicon is measured by TGA analysis. This is presumably because the initial silicon deposition rapidly blocks the open pores, inhibiting the access of silane gas to the internal pore space. Therefore, a minimum amount of mesoporosity is required to ensure sufficient transport of silane gas into the micropores. However, from the TGA analysis of sample S4, it can be seen that when the microporosity is too low, an excessive amount of crude silicon is obtained again. It is thought that the volume of the micropores is rapidly exhausted, and larger silicon deposits will be formed both inside the mesopores and on the surface of the porous carbon skeleton.

[0159] In contrast, from the TGA analysis of sample S1, sample S2, sample S5, and sample S6, it can be seen that the content of crude silicon is very small, indicating that all of the silicon essentially exists in the form of fine silicon nanostructures located within the micropores and smaller mesopores. These fine silicon nanostructures have a low resistance to deformation and a higher fracture resistance than coarser silicon structures, making them more suitable for use as electroactive materials in lithium-ion batteries.

[0160] Example 2 - Preparation of Composite Particles in a Rotary Tube Furnace Reactor 5 g of particulate porous skeleton having the characteristics shown in Table 1 was placed in a quartz tube (length 11.4 cm) with a spherical part to fabricate silicon-carbon composite particles. Next, the quartz tube was placed inside a rotary tube furnace reactor equipped with a heating zone of about 15 cm × 20 cm (L × D), and the gas inlet line and outlet line were placed about 29 cm away from the hot zone of the furnace. The quartz tube in the furnace rotated about 315° clockwise and then counterclockwise, thereby continuously moving / rotating the porous carbon. After purging the furnace tube with nitrogen gas at room temperature for 30 minutes, the sample temperature was raised to 450°C - 500°C. The flow rate of nitrogen gas was adjusted so that a gas residence time of at least 90 seconds was ensured inside the furnace tube and maintained at that rate for 30 minutes. Then, the gas supply was switched from nitrogen to a mixture of monosilane in nitrogen at a concentration of 1.25% by volume. The introduction of monosilane was carried out over 5 hours while maintaining the reactor pressure at 101.3 kPa (1 atm). After the introduction was completed, the gas flow rate was kept constant while purging the silane from the furnace using nitrogen. After purging the furnace with nitrogen for 30 minutes, it was cooled to room temperature over several hours. Then, the atmosphere was gradually switched to air over 2 hours by switching the gas flow from nitrogen to air from a compressed air supply. The composite material produced according to Example 2 has the characteristics shown in Table 3 below.

[0161]

[0162]

Table 3

[0163] Example 3 - Fabrication of Electrodes Anodes and test cells incorporating the particulate Si-C composite material of Table 1 were fabricated using the following method.

[0164] ​The test coin cell was fabricated using a negative electrode containing the silicon-based material prepared as described above. A dispersion of Carbon Super P (conductive carbon) and a CMC binder was mixed with a Thinky (trademark) mixer. The silicon-based material was added to this mixture and mixed with the Thinky (trademark) mixer for 30 minutes. Subsequently, an SBR binder was added to make the CMC:SBR ratio 1:1, and a slurry with a weight ratio of silicon-based material:CMC / SBR:conductive carbon of 70%:16%:14% was obtained. The slurry was further mixed with the Thinky (trademark) mixer for 30 minutes, then coated on a copper substrate (current collector) with a thickness of 10 μm, dried at 50 °C for 10 minutes, and then further dried at 110 °C for 12 hours to form an electrode with an active layer on the copper substrate.

[0165] Example 4 - Manufacture and Cycling of Full Cell The full coin cell was fabricated using a porous polyethylene separator and a nickel manganese cobalt (NMC532) positive electrode, together with a circular negative electrode with a radius of 0.8 cm cut from the electrode of Example 3. The positive and negative electrodes were designed to form a well-balanced pair such that the target capacity ratio of these electrodes was approximately 0.9. Subsequently, an electrolyte containing 1 M LiPF6 was added to the cell before sealing in a 7:3 EMC / FEC (ethyl methyl carbonate / fluoroethylene carbonate) solution containing 3 wt% vinylene carbonate.

[0166] Three coin cells were fabricated for each composite material.

[0167] The full coin cell was cycled as follows. A constant current was applied at a rate of C / 25 with a cut-off voltage of 4.3V to lithiate the anode. When the cut-off voltage was reached, a constant voltage of 4.3V was applied until the cut-off current of C / 100 was reached. Then, the cell was rested in the lithiated state for 10 minutes. Next, the anode was delithiated at a constant current of C / 25 with a cut-off voltage of 2.75V. Then, the cell was rested for 10 minutes. After this first cycle, a constant current of C / 2 was applied at a cut-off voltage of 4.3V to lithiate the anode, followed by applying a constant voltage of 4.3V at a cut-off current of C / 40 with a rest time of 5 minutes. Next, the anode was delithiated at a constant current of C / 2 with a cut-off voltage of 2.75V. Then, this was repeated for the desired number of cycles. For each sample, the charge and discharge capacity was tracked up to the 1000th cycle, and the capacity retention rates (CR100, CR300, and CR500) at the 100th and 300th cycles were determined. For S2, CR1000 was also determined. This data is shown in Table 4 together with the initial lithiation capacity, initial delithiation capacity, and first cycle loss (FCL) of each sample.

[0168] The charge (lithiation) capacity and discharge (delithiation) capacity of each cycle were calculated per unit mass of the silicon-carbon composite material, and the capacity retention value was calculated as a percentage of the discharge capacity of the second cycle for each discharge capacity. The first cycle loss (FCL) is (1 - (initial delithiation capacity / initial lithiation capacity)) × 100%. The values averaged over three coin cells for each sample are shown in Table 4.

[0169] From Table 4 below, it can be seen that the cells formed from the materials according to the present invention have high initial capacity, consistent cycle performance, and high capacity retention rate. The S2 material with a lower content of crude silicon (4.8 wt%) shows a higher capacity retention rate at higher cycle numbers than the S7 material with a higher content of crude silicon (10.1 wt%).

[0170]

Table 4

[0171] Example 5 - Manufacture of Half - Cell The half - coin cell was fabricated using a porous polyethylene separator, a lithium foil as the counter - electrode, and a 1:5:14 FEC / EC / EMC (fluoroethylene carbonate / ethylene carbonate / ethyl methyl carbonate, v / v / v) solution containing 3 wt% vinylene carbonate, together with an electrolyte containing 1 M LiPF6, and a circular electrode with a radius of 0.8 cm cut from the electrode of Example 3.

[0172] Using these half - cells, the initial volume energy density (VED1), the first - cycle loss (FCL), and the first - de - lithiation capacity of the active layer were measured. The relevant values are shown in Table 4. The half - cells were tested as follows. A constant current of C / 25 (where "C" represents the specific capacity of the electrode in mAh and "25" refers to 25 hours) was applied at a cut - off voltage of 10 mV to lithiate the electrode containing porous particles. When the cut - off voltage was reached, a constant voltage of 10 mV was applied at a cut - off current of C / 100. Then, the cell was allowed to rest in the lithiated state for 1 hour. Next, at a cut - off voltage of 1 V, the electrode was de - lithiated at a constant current of C / 25, and then the cell was allowed to rest for 1 hour. Then, for the second time, a constant current of C / 25 was applied at a cut - off voltage of 10 mV to lithiate the cell, followed by applying a constant voltage of 10 mV at a cut - off current of C / 100. The values averaged over three cells for each sample are shown in Table 5.

[0173] [Table 5]

Claims

1. A particulate material consisting only of a plurality of composite particles, wherein the composite particles are (a) a porous carbon skeleton containing micropores and mesopores, where The micropores and the mesopores have a total pore volume of P １ cm ３ / g, where P １ represents a dimensionless number having a value of 0.45 to 0.75, where the micropores and the mesopores are measured by nitrogen gas adsorption at 77 K using the quenched solid density functional theory (QSDFT), and the volume ratio of micropores to the total volume of micropores and mesopores is in the range of 0.55 to 0.8, and the PD 90 pore diameter of the porous carbon skeleton is at most 8 nm, a porous carbon skeleton; and (b) a plurality of nanoscale elemental silicon domains located within the pores of the porous carbon skeleton; and In the composite particles, the weight ratio of silicon to the porous carbon skeleton is in the range of [1 × P １ ~1.8 × P １ :1, particulate material; here, the composite particles have a D 90 particle size of at most 20 μm; and when the particulate material is analyzed by TGA at a temperature increase rate of 10 °C / min in air, a Z value of less than 10% where the Z value can be determined according to the following formula: Z = 1.875 × [(M f - M 800 ) / M f ] × 100% (where Z is the proportion of unoxidized silicon at 800 °C, M f is the mass of the sample at the end of oxidation, and M 800 is the mass of the sample at 800 °C).

2. P １ The particulate material according to claim 1, wherein P has a value in the range of 0.45 to 0.7, or in the range of 0.47 to 0.67, or in the range of 0.47 to 0.65, or in the range of 0.5 to 0.62, or in the range of 0.5 to 0.6, or in the range of less than 0.5 to 0.

6.

3. The particulate material according to claim 1 or 2, wherein the volume ratio of the micropores is in the range of 0.6 to 0.8, or in the range of 0.6 to 0.78, or in the range of 0.65 to 0.76, or in the range of 0.65 to 0.

75.

4. The PD of the porous carbon skeleton ９０ The particulate material according to any one of claims 1 to 3, wherein the pore diameter is at most 6 nm or at most 5 nm.

5. The particulate material according to any one of claims 1 to 4, wherein the weight ratio of silicon to carbon is in the range of [1.1 × P 1 to 1.7 × P 1 ]:1, or in the range of [1.2 × P 1 to 1.65 × P 1 ]:1, or in the range of [1.3 × P 1 to 1.6 × P 1 ]:1, or in the range of [1.35 × P 1 to 1.6 × P 1 ]:1, or in the range of [1.4 × P 1 to 1.55 × P 1 ]:

1.

6. The particulate material according to any one of claims 1 to 5, wherein at least 80 wt%, or at least 85 wt%, or at least 90 wt%, or at least 95 wt%, or at least 98 wt% of the silicon in the composite particles is located within the internal pore volume of the porous carbon skeleton.

7. The particulate material according to any one of claims 1 to 6, wherein the Z value is 5% or less, preferably 2% or less.

8. The particulate material according to any one of claims 1 to 7, wherein the composite particles have any of the following: (i) a D 50 particle size in the range of 1 μm to 12 μm; (ii) a D10 particle size of 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; and (iii) a particle size distribution span of 5 or less, or 4 or less, or 3 or less, or 2 or less, or 1.5 or less.

9. The composite particles have a BET surface area of up to 100 m ２ / g, or up to 80 m ２ / g, or up to 60 m ２ / g, or up to 50 m ２ / g, or up to 40 m ２ / g, or up to 30 m ２ / g, or up to 25 m ２ / g, or up to 20 m ２ / g, or up to 15 m ２ / g, or up to 10 m ２ / g, and are the particulate material according to any one of claims 1 to 8.

10. The volume of micropores and mesopores in the composite particles in the presence of silicon, measured by nitrogen gas adsorption, is at most 0.15 × P １ cm3 / g, or at most 0.10 × P １ cm3 / g, or at most 0.05 × P １ cm3 / g, or at most 0.02 × P １ cm3 / g, and the particulate material according to any one of claims 1 to 9

11. A particulate material according to any one of claims 1 to 10, and (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material A composition comprising at least one other component selected from.

12. The particulate material according to any one of claims 1 to 10 is contained in an amount of 15% by weight to 60% by weight, or 20% by weight to 50% by weight, or 30% by weight to 50% by weight based on the total dry weight of the composition, and further comprises at least one additional particulate electroactive material. The composition according to claim 11.

13. The composition according to claim 12, wherein the at least one additional particulate electroactive material is selected from graphite, hard carbon, silicon, tin, germanium, aluminum, and lead.

14. The particulate material according to any one of claims 1 to 10 is contained in an amount of 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 based on the total dry weight of the composition, and substantially does not contain an additional particulate electroactive material. The composition according to claim 11.

15. (i) a binder; and (ii) one or more conductive additives The composition according to any one of claims 11 to 14, comprising at least one of.

16. An electrode comprising the particulate material according to any one of claims 1 to 10 in electrical contact with a current collector.

17. (i) an anode comprising the electrode according to claim 16, (ii) a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions, (iii) an electrolyte between the anode and the cathode, A rechargeable metal ion battery comprising.

Images