Silicon-based negative electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a silicon-based negative electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion battery negative electrode materials, the silicon-based negative electrode material comprises silicon-carbon flat particles, the height-length ratio of the silicon-carbon flat particles is less than or equal to 0.44, and the silicon-based negative electrode material can be prepared by extruding and crushing through a specific grinding tool. The flattened sheet structure of the silicon-based negative electrode material can more effectively release expansion stress to the external space of the particles instead of internal accumulation, so that the risks of crushing of the particles and collapse of the electrode structure are greatly reduced, meanwhile, the lithium ion transmission path can be shortened, and the silicon-based negative electrode is endowed with better dynamic performance.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion battery anode materials, and in particular to a silicon-based anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Silicon-based materials are considered core candidates for next-generation high-energy-density lithium-ion battery anodes due to their extremely high theoretical specific capacity (approximately 4200 mAh / g). However, the massive volume expansion (>300%) of silicon-based materials during charging and discharging, leading to structural pulverization, continuous growth of the solid electrolyte interphase (SEI) film, and overall electrode collapse, severely restricts their practical application and commercialization.

[0003] To address these challenges, existing technologies primarily focus on strategies such as "nano-sizing," "porousization," and "carbon composites." For example, silicon is fabricated into nanowires, nanospheres, or nanoporous structures to shorten ion diffusion paths and accommodate some strain, or it is composited with carbon materials to utilize carbon's buffering and conductivity properties to improve stability. However, the high specific surface area of ​​nanomaterials exacerbates side reactions, leading to lower initial efficiency and electrolyte consumption. Furthermore, many nano- or porous structures still exhibit near-isotropic morphologies macroscopically, meaning that the expansion stress generated during cycling cannot be effectively guided and will accumulate within the particles or at interfaces, resulting in performance degradation.

[0004] Therefore, how to shift from "passively accommodating strain" to "actively managing stress" in materials design has become the key to technological breakthroughs. Precisely controlling the physical morphology to prepare silicon-based particles with low aspect ratios and specific anisotropic structures is a highly promising solution.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] One of the objectives of this invention is to provide a silicon-based anode material. The flattened "sheet" structure can more effectively release expansion stress to the external space of the particles, rather than accumulating it inside. This greatly reduces the risk of particle self-crushing and electrode structure collapse, and can also shorten the lithium-ion transport path, giving the silicon-based anode better kinetic performance.

[0007] The second objective of this invention is to provide a method for preparing silicon-based anode materials, which can be prepared by extrusion crushing using a mold. The process path is simpler and more direct, has higher compatibility with existing equipment, is conducive to large-scale production, and has low cost.

[0008] The third objective of this invention is to provide a lithium-ion battery that helps reduce electrode polarization, improve rate performance, and enable the battery to have better fast charging potential.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In one aspect, a silicon-based anode material includes flat silicon-carbon particles; The maximum projected length of the silicon-carbon flat particles is line segment A1B1, and there is at least one direction perpendicular to line segment A1B1, in which the maximum thickness of the particles is line segment A2B2. The length a of line segment A1B1 satisfies 1μm≤a≤50μm; The length c of line segment A2B2 satisfies c / a≤0.44.

[0010] Furthermore, the silicon-carbon flat particles have at least one direction perpendicular to line segments A1B1 and A2B2, and the maximum thickness of the particles in this direction is line segment A3B3. The length b of line segment A3B3 satisfies 0.4 < b / a ≤ 1.

[0011] Furthermore, the maximum cross-sectional area S1 of the silicon-carbon flat particles parallel to line segments A1B1 and A3B3 satisfies πa 2 / 25μm 2 ≤S1≤πa 2 / 4μm 2 ; Preferably, the maximum cross-sectional area S2 of the silicon-carbon flat particles parallel to line segments A1B1 and A2B2 satisfies 0 < S2 ≤ 0.44a. 2 μm 2 .

[0012] Furthermore, a carbon-based coating layer exists within the pores and / or on the surface of the silicon-carbon flat particles; Preferably, the carbon-based coating layer includes at least one of acetylene-based hard carbon film, polyimide film, oxygen-nitrogen carbon film, aromatic carbon film, and standard nitrogen-doped carbon film.

[0013] Furthermore, the silicon-carbon flat particles contain 20%-80% silicon by mass, 15%-80% total carbon by mass, and 0.5%-5% total oxygen, nitrogen, and hydrogen by mass.

[0014] Furthermore, the specific surface area of ​​the silicon-carbon flat particles is 0.1 m². 2 / g-5m 2 / g, powder resistivity 3Ω cm-30Ω cm; Preferably, the porous carbon flat particles in the silicon-carbon flat particles have a pore volume of 0.4 cm³. 3 / g-1.5cm 3 / g; Preferably, the specific surface area of ​​the porous carbon flat particles is 700 m². 2 / g-2200m 2 / g; Preferably, the porous carbon flat particles have a Dv50 particle size of 1μm-50μm and a powder resistivity of 0.1Ω. cm-2Ω cm.

[0015] In a second aspect, a method for preparing the silicon-based anode material according to any one of the above claims includes the following steps: The silicon-based anode material is obtained by depositing silicon on porous flat carbon particles and coating them with a carbon-based film.

[0016] Furthermore, the method for preparing the porous carbon flat particles includes the following steps: Porous carbon is mixed with a lubricant and then extruded and crushed through a rectangular inner-cut mold, followed by heat treatment to obtain the porous carbon flat particles. Preferably, the length of the inner incision of the rectangular inner-cut abrasive is 0.4aμm-aμm, and the width of the inner incision is 0-0.44aμm; Preferably, the temperature of the heat treatment is 600℃-1200℃.

[0017] Furthermore, the silicon deposition temperature is 300℃-700℃; Preferably, the carbon-based film coating temperature is 200℃-600℃.

[0018] Thirdly, a lithium-ion battery, wherein the active material used in the negative electrode of the lithium-ion battery includes the silicon-based negative electrode material described in any of the above-mentioned embodiments.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: The silicon-based anode material provided by this invention is a flat silicon-carbon particle. On the one hand, it can improve structural stability: the unique thin sheet structure (height-to-length ratio ≤ 0.44) directs the huge expansion stress generated by silicon during charging and discharging to the free space outside the particle for release, rather than accumulating inside. This greatly reduces the risk of particle pulverization and electrode structure collapse from a mechanical perspective. On the other hand, it can optimize electrode dynamics: the flattened shape significantly shortens the transport path of lithium ions inside the solid particle, which helps to reduce electrode polarization, improve rate performance, and enable the battery to have better fast charging potential.

[0020] The method for preparing silicon-based anode materials provided by this invention can be based on mold extrusion and crushing, which is a mechanical processing method. Compared with resin structure design that requires complex chemical processes (such as template method and etching method), the process path of the method of this invention is simpler and more direct, has higher compatibility with existing equipment, is conducive to large-scale production, and has low cost.

[0021] The lithium-ion battery provided by this invention helps to reduce electrode polarization, improve rate performance, and give the battery better fast charging potential. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of a silicon-based anode material provided in one embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] According to a first aspect of the present invention, a silicon-based anode material is provided, see... Figure 1 This includes flat silicon-carbon particles; The maximum projected length of the flat silicon-carbon particle is line segment A1B1, and there is at least one direction perpendicular to line segment A1B1, in which the maximum thickness of the particle is line segment A2B2. The length 'a' of line segment A1B1 satisfies 1μm≤a≤50μm; The length c of line segment A2B2 satisfies c / a≤0.44.

[0026] The silicon-based anode material of this invention is a low aspect ratio flat silicon-carbon particle. The particle morphology can be regular or irregular. The unique thin-plate structure (height-to-length ratio ≤ 0.44) of the flat silicon-carbon particle can guide the huge expansion stress generated by silicon during charging and discharging to the free space outside the particle for release, rather than accumulating inside. This greatly reduces the risk of particle pulverization and electrode structure collapse. At the same time, the flattened morphology of the silicon-carbon material significantly shortens the transport path of lithium ions inside the solid particle, which helps to reduce electrode polarization, improve rate performance, and enable the battery to have better fast charging potential.

[0027] In this invention, the silicon-carbon flat particles have at least one direction perpendicular to line segments A1B1 and A2B2, and the maximum thickness of the particles in this direction is line segment A3B3. The length b of line segment A3B3 satisfies 0.4 < b / a ≤ 1.

[0028] In a preferred embodiment, the maximum cross-sectional area S1 of the silicon-carbon flattened particles parallel to line segments A1B1 and A3B3 can satisfy πa. 2 / 25μm 2 ≤S1≤πa 2 / 4μm 2 .

[0029] In a preferred embodiment, the maximum cross-sectional area S2 of the silicon-carbon flat particles parallel to line segments A1B1 and A2B2 can satisfy 0 < S2 ≤ 0.44a. 2 μm 2 .

[0030] In a preferred embodiment, a carbon-based coating layer may be present in the pores and / or on the surface of the silicon-carbon flat particles; wherein the carbon-based coating layer includes, but is not limited to, at least one of acetylene-based hard carbon film, polyimide film, oxygen-containing nitrogen carbon film, aromatic carbon film, and standard nitrogen-doped carbon film.

[0031] In this invention, the silicon mass percentage in the silicon-carbon flat particles can be 20%-80%, with typical but non-limiting mass percentages being 20%, 30%, 40%, 50%, 60%, 70%, and 80%; the total carbon mass percentage can be 15%-80%, with typical but non-limiting mass percentages being 15%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%; and the total oxygen, nitrogen, and hydrogen mass percentage can be 0.5%-5%, with typical but non-limiting mass percentages being 0.5%, 1%, 2%, 3%, 4%, and 5%.

[0032] In a preferred embodiment, the specific surface area of ​​the silicon-carbon flat particles can be 0.1 m². 2 / g-5m 2 / g, powder resistivity 3Ω cm-30Ω cm.

[0033] In a preferred embodiment, the silicon-carbon flat particles are used as a precursor, and the pore volume of the porous carbon flat particles can be 0.4 cm³. 3 / g-1.5cm 3 / g, the specific surface area of ​​porous flat carbon particles can be 700m². 2 / g-2200m 2 / g.

[0034] In a preferred embodiment, the Dv50 particle size of the porous carbon flat particles can be 1μm-50μm, and the powder resistivity can be 0.1Ω. cm-2Ω cm.

[0035] According to a second aspect of the present invention, a method for preparing the silicon-based anode material according to any one of the above claims is provided, comprising the following steps: Silicon-based anode materials are obtained by depositing silicon on porous flat carbon particles and coating them with carbon-based films.

[0036] The method for preparing silicon-based anode materials provided by this invention can be based on mold extrusion and crushing, which is a mechanical processing method. Compared with resin structure design that requires complex chemical processes (such as template method and etching method), the process path of the method of this invention is simpler and more direct, has higher compatibility with existing equipment, is conducive to large-scale production, and has low cost.

[0037] In a preferred embodiment, the method for preparing porous carbon flat particles includes the following steps: Porous carbon is mixed with a lubricant and then extruded and crushed through a rectangular incision die, followed by heat treatment to obtain flat porous carbon particles.

[0038] A typical preparation method for a silicon-based anode material includes the following steps: Step S1 (Mold Extrusion Crushing): After adding an appropriate amount of lubricant to commercial porous carbon and mixing it, the mixture is transferred to the extrusion chamber. A rectangular inner-cut mold of a specific size is loaded at the extruder outlet, and porous carbon of varying lengths is obtained by extrusion crushing. Step S2 (Airflow crushing and sieving): The material is crushed by an airflow mill until the particle size meets the requirements, then sieved and the material remaining on the sieve is collected. Step S3 (Heat Treatment): Place the sieve residue in a protective atmosphere and anneal at high temperature to remove the lubricant, thereby obtaining porous carbon flat particles; Step S4 (Chemical Vapor Deposition): Porous carbon flat particles are sequentially introduced into a silicon source and a carbon source under an inert atmosphere to perform silicon deposition and carbon-based film coating, resulting in silicon-carbon flat particles, which are the desired silicon-based anode materials.

[0039] In a preferred embodiment, the length of the inner slit of the rectangular inner slit mold can be 0.4aμm-aμm, and the width of the inner slit can be 0-0.44aμm.

[0040] In this invention, the mesh of the filter bag used for sieving can be circular with a diameter of 0.4 μm. The heat treatment temperature can be 600℃-1200℃, with typical but non-limiting temperatures such as 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, and 1200℃.

[0041] In a preferred embodiment, the silicon deposition temperature can be 300°C-700°C, with typical but non-limiting temperatures such as 300°C, 400°C, 500°C, 600°C, and 700°C being more conducive to improving the silicon deposition effect.

[0042] In a preferred embodiment, the coating temperature of the carbon-based film can be 200°C-600°C, with typical but non-limiting temperatures such as 200°C, 300°C, 400°C, 500°C, and 600°C being more conducive to improving the coating effect of the carbon-based film.

[0043] According to a third aspect of the present invention, a lithium-ion battery is provided, wherein the active material used in the negative electrode of the lithium-ion battery comprises the silicon-based negative electrode material described in any one of the preceding claims.

[0044] The lithium-ion battery provided by this invention helps to reduce electrode polarization, improve rate performance, and give the battery better fast charging potential.

[0045] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0046] Example 1 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular inner-cut abrasive tool with a length of 7.5μm and a width of 3μm was selected, using a hole volume of 0.85cm. 3 / g of commercial porous carbon, the porous carbon and liquid paraffin are mixed and stirred for 30 minutes at a mass ratio of 1:0.02, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 10μm. The material is then sieved through a cloth bag with a pore size of 4μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 0.85 cm⁻¹. 3 / g、1652m 2 / g, Dv50 particle size 10.5μm and 0.4Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 7 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.3 for coating for 4 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​1.3 m². 2 / g, powder resistivity is 12Ω cm, silicon accounts for 55% of the mass, carbon accounts for 44% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0047] Example 2 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular internal cutting mold with a length of 7.5μm and a width of 3μm was selected, using a hole volume of 0.9cm. 3 / g of commercial porous carbon, the porous carbon and liquid paraffin are mixed and stirred for 30 minutes at a mass ratio of 1:0.02, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 11μm. The material is then sieved through a cloth bag with a pore size of 4μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 0.9 cm⁻¹. 3 / g、1781m 2 / g, Dv50 particle size 12μm and 0.6Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 10 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.5 for coating for 4 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​1.2 m². 2 / g, powder resistivity 15Ω cm, silicon accounts for 60% of the mass, carbon accounts for 39% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0048] Example 3 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular internal cutting mold with a length of 8.3 μm and a width of 3 μm was selected, using a hole volume of 0.93 cm. 3 / g of commercial porous carbon, the porous carbon and rapeseed oil are mixed and stirred at a mass ratio of 1:0.05 for 30 minutes, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 10μm. The material is then sieved through a cloth bag with a pore size of 3μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 0.95 cm⁻¹. 3 / g、1849m 2 / g, Dv50 particle size 10.2μm and 0.7Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 490°C for 20 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.4 for coating for 4 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​1.02 m². 2 / g, powder resistivity is 19Ω cm, silicon accounts for 65% of the mass, carbon accounts for 34% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0049] Example 4 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular internal cutting mold with a length of 8μm and a width of 3.3μm was selected, using a hole volume of 1.07cm. 3 / g of commercial porous carbon, the porous carbon and soybean oil are mixed and stirred at a mass ratio of 1:0.03 for 30 minutes, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 9.4μm. It is then sieved through a filter bag with a pore size of 4μm, and the material remaining on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 1.07 cm⁻¹. 3 / g、1891m 2 / g, Dv50 particle size 9.8μm and 0.78Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 7 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.5 for coating for 4 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​0.98 m². 2 / g, powder resistivity is 23Ω cm, silicon accounts for 70% of the mass, carbon accounts for 28% of the mass, and oxygen, nitrogen and hydrogen account for 2% of the mass.

[0050] Example 5 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular inner-cut abrasive tool with a length of 10μm and a width of 5μm was selected, using a hole volume of 1.25cm. 3 / g of commercial porous carbon, the porous carbon and liquid paraffin are mixed and stirred for 30 minutes at a mass ratio of 1:0.08, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 11μm. The material is then sieved through a cloth bag with a pore size of 5μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 3 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 0.85 cm⁻¹. 3 / g、1652m 2 / g, Dv50 particle size 11.3μm and 0.4Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 22 hours, followed by cooling to 400°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.5 for coating for 7 hours, resulting in silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​0.78 m². 2 / g, powder resistivity 26Ω cm, silicon accounts for 75% of the mass, carbon accounts for 24% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0051] Example 6 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular internal cutting mold with a length of 12μm and a width of 4.3μm was selected, using a hole volume of 1.34cm. 3 / g of commercial porous carbon, the porous carbon and liquid paraffin are mixed and stirred at a mass ratio of 1:0.02 for 60 minutes, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 12μm. The material is then sieved through a cloth bag with a pore size of 4μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 1.34 cm⁻¹. 3 / g、2088m 2 / g, Dv50 particle size 12.4μm and 0.5Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 25 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.6 for coating for 10 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​1.3 μm². 2 / g, powder resistivity 28Ω cm, silicon accounts for 80% of the mass, carbon accounts for 19% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0052] Example 7 A method for preparing a silicon-based anode material includes the following steps: First, a rectangular internal cutting mold with a length of 7.5μm and a width of 3μm was selected, using a hole volume of 0.45cm. 3 / g of commercial porous carbon, the porous carbon and liquid paraffin are mixed and stirred for 30 minutes at a mass ratio of 1:0.02, and then transferred to an extrusion chamber. A rectangular inner-cut mold is fitted onto the chamber opening, and porous carbon of different lengths is obtained by extrusion and crushing. Then, the porous carbon is subjected to airflow crushing until the Dv50 particle size reaches 9μm. The material is then sieved through a filter bag with a pore size of 4μm and the material on the sieve is collected. Subsequently, the sieved material was placed in a protective atmosphere and annealed at 800°C for 2 hours to obtain porous flat carbon particles with a pore volume, specific surface area, particle size, and powder resistivity of 0.45 cm⁻¹. 3 / g、1215m 2 / g, Dv50 particle size 9.2μm and 0.2Ω cm; Finally, the porous carbon flat particles were placed in a deposition furnace, and nitrogen and silane were introduced into the furnace at a volume ratio of 2:0.8. Deposition was carried out at 500°C for 7 hours, followed by cooling to 420°C. Nitrogen and acetylene were then introduced at a volume ratio of 1:0.5 for coating for 4 hours, yielding silicon-carbon flat particles, which are the desired silicon-based anode material with a specific surface area of ​​1.6 m². 2 / g, powder resistivity 10Ω cm, silicon accounts for 25% of the mass, carbon accounts for 74% of the mass, and oxygen, nitrogen and hydrogen account for 1% of the mass.

[0053] Comparative Example 1 The only difference between this comparative example and Example 1 is that the porous carbon used is commercially available perfect spheres, replacing the porous carbon flat particles. The two have different specific surface areas and particle size Dv50. The pore volume, silicon content, carbon content, and oxygen, nitrogen, and hydrogen content of the porous carbon are basically the same as those in Example 1; The remaining steps are the same as in Example 1, and a silicon-based anode material, which is spherical silicon-carbon, is obtained.

[0054] Comparative Example 2 The only difference between this comparative example and Example 1 is that the porous carbon used is commercially available spheres, replacing the porous carbon flat particles. The two have different specific surface areas and particle size Dv50. The pore volume, silicon content, carbon content, and oxygen, nitrogen, and hydrogen content of the porous carbon are basically the same as those in Example 1; The remaining steps are the same as in Example 1, and a silicon-based anode material, which is a spherical silicon-carbon, is obtained.

[0055] Comparative Example 3 The only difference between this comparative example and Example 1 is that the porous carbon used is commercial block instead of porous carbon flat particles, and the two have different specific surface areas and particle size Dv50. The pore volume, silicon content, carbon content, and oxygen, nitrogen, and hydrogen content of the porous carbon are basically the same as those in Example 1; The remaining steps are the same as in Example 1, and a silicon-based anode material, which is bulk silicon-carbon, is obtained.

[0056] Test case The parameters a, c / a, b / a, S1, and S2 of the silicon-based anode material were determined by scanning electron microscopy combined with image simulation (the parameters were the average of 10 particles with a particle size of Dv50), and the parameters are shown in Table 1.

[0057] A negative electrode sheet was prepared using silicon-based negative electrode material as the negative electrode active material; Negative electrode composition: 95% active material, 2% SBR binder, 2.8% conductive agent SP, and 0.2% SWCNT; CR2032 coin cells were fabricated using conventional methods with negative electrode sheets, and the electrical performance of the cells was tested. (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (the volume ratio of EC to DEC is 1:1), wherein the concentration of LiPF6 is 1 mol / L. The battery was charged and discharged using the LAND battery testing system; (2) 1C lithium intercalation rate: After the CR2032 coin cell is left to stand for 6 hours, it is discharged at 0.1C to 0.005V, and then discharged at a constant voltage of 0.005V until the current is zero. The capacity is recorded as C1. After standing for 5 minutes, it is charged at 0.1C to 1.5V, and then charged at a constant voltage of 1.5V until the current is zero. The capacity is recorded as C2. Then it is discharged at 1C to 0.005V, and the capacity is recorded as C3. Then it is charged at 1C to 1.5V, and the capacity is recorded as C4. 1C lithium intercalation rate = C4 / C2 × 100%; (3) Electrode expansion rate: After the CR2032 type button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C, and then discharged to 0.005V at 0.01C; then the button cell was disassembled in the glove box, the electrode was cleaned with DMC and the thickness of the electrode was measured; the expansion rate was calculated as: (thickness of electrode in the first fully charged state - thickness of fresh electrode) / thickness of fresh electrode × 100%; (4) Capacity retention rate test: After standing for 5 minutes, repeat the above charge and discharge steps twice; then discharge to 0.005V at 0.5C; after standing for 5 minutes, charge to 1.5V at 0.5C constant current, cycle 50 times; calculate the capacity retention rate by the charge specific capacity of the 50th cycle / the charge capacity of the 1st cycle × 100%. The test results are shown in Table 1.

[0058] As can be seen from the data in Table 1, compared with the silicon-based anode materials of Comparative Examples 1-3, the silicon-based anode materials of Examples 1-7 of the present invention are flat silicon-carbon particles with a height-to-length ratio ≤0.44. This allows the expansion stress to be released to the external space of the particles instead of accumulating inside, and also shortens the lithium-ion transport path. Therefore, they have better rate capability, volume expansion and cycle performance.

[0059] Table 1

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based anode material, characterized in that, Including flat silicon-carbon particles; The maximum projected length of the silicon-carbon flat particles is line segment A1B1, and there is at least one direction perpendicular to line segment A1B1, in which the maximum thickness of the particles is line segment A2B2. The length a of line segment A1B1 satisfies 1μm≤a≤50μm; The length c of line segment A2B2 satisfies c / a≤0.

44.

2. The silicon-based anode material according to claim 1, characterized in that, The silicon-carbon flat particles have at least one direction perpendicular to line segments A1B1 and A2B2, and the maximum thickness of the particles in this direction is line segment A3B3. The length b of line segment A3B3 satisfies 0.4 < b / a ≤ 1.

3. The silicon-based anode material according to claim 1, characterized in that, The maximum cross-sectional area S1 of the silicon-carbon flat particles, parallel to line segments A1B1 and A3B3, satisfies πa. 2 / 25μm 2 ≤S1≤πa 2 / 4μm 2 ; Preferably, the maximum cross-sectional area S2 of the silicon-carbon flat particles parallel to line segments A1B1 and A2B2 satisfies 0 < S2 ≤ 0.44a. 2 μm 2 .

4. The silicon-based anode material according to any one of claims 1-3, characterized in that, The silicon-carbon flat particles have a carbon-based coating layer inside the pores and / or on the surface. Preferably, the carbon-based coating layer includes at least one of acetylene-based hard carbon film, polyimide film, oxygen-nitrogen carbon film, aromatic carbon film, and standard nitrogen-doped carbon film.

5. The silicon-based anode material according to claim 4, characterized in that, The silicon-carbon flat particles contain 20%-80% silicon by mass, 15%-80% total carbon by mass, and 0.5%-5% total oxygen, nitrogen, and hydrogen by mass.

6. The silicon-based anode material according to claim 4, characterized in that, The specific surface area of ​​the silicon-carbon flat particles is 0.1 m². 2 / g-5m 2 / g, powder resistivity 3Ω cm-30Ω cm; Preferably, the porous carbon flat particles in the silicon-carbon flat particles have a pore volume of 0.4 cm³. 3 / g-1.5cm 3 / g; Preferably, the specific surface area of ​​the porous carbon flat particles is 700 m². 2 / g-2200m 2 / g; Preferably, the porous carbon flat particles have a Dv50 particle size of 1μm-50μm and a powder resistivity of 0.1Ω. cm-2Ω cm.

7. A method for preparing the silicon-based anode material according to any one of claims 1-6, characterized in that, Includes the following steps: The silicon-based anode material is obtained by depositing silicon on porous flat carbon particles and coating them with a carbon-based film.

8. The preparation method according to claim 7, characterized in that, The method for preparing the porous carbon flat particles includes the following steps: Porous carbon is mixed with a lubricant and then extruded and crushed through a rectangular inner-cut mold, followed by heat treatment to obtain the porous carbon flat particles. Preferably, the length of the inner incision of the rectangular inner-cut abrasive is 0.4aμm-aμm, and the width of the inner incision is 0-0.44aμm; Preferably, the temperature of the heat treatment is 600℃-1200℃.

9. The preparation method according to claim 7, characterized in that, The silicon deposition temperature is 300℃-700℃; Preferably, the carbon-based film coating temperature is 200℃-600℃.

10. A lithium-ion battery, characterized in that, The active material used in the negative electrode of the lithium-ion battery includes the silicon-based negative electrode material as described in any one of claims 1-6.

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