High-performance silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a high-performance silicon-carbon negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion battery materials, the high-performance silicon-carbon negative electrode material comprises a porous carbon material, the surface of the porous carbon material is successively deposited with a carbon nanotube network and nano silicon, the porous carbon material on which the carbon nanotube network and the nano silicon are deposited is also provided with a secondary outer layer carbon shell and an outer layer carbon shell from inside to outside; according to the invention, double optimization of the silicon-carbon negative electrode material is realized through a unique structural design: (1) the volume expansion effect of nano silicon is relieved through cooperation of the carbon nanotube network and the multi-layer carbon shell; and (2) the migration rate of lithium ions is accelerated by the carbon nanotubes and the multi-layer carbon coated structure, and the prepared silicon-carbon negative electrode material has excellent cycling stability and rate capability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a high-performance silicon-carbon anode material and its preparation method. Background Technology

[0002] As a core energy storage device in the new energy field, the performance improvement of lithium-ion batteries is crucial for the development of industries such as electric vehicles and energy storage systems. Currently, graphite remains the dominant anode material for lithium-ion batteries, but its theoretical specific capacity of 372 mAh / g is approaching its performance limit, making it difficult to meet the high energy density requirements of new energy vehicles and large-scale energy storage systems. Against this backdrop, silicon-based anode materials have become an ideal next-generation lithium-ion battery anode material due to their advantages such as high specific capacity, abundant sources, and environmental friendliness. However, the volume expansion of silicon-based anode materials during charging and discharging, reaching up to 380%, can cause problems such as particle pulverization and repeated rupture of the SEI film, severely impairing their cycle life and safety.

[0003] To overcome the aforementioned technical problems, silicon-carbon composite technology has become the mainstream solution. However, existing silicon-carbon composite technologies still have the following issues. For example, when physical mixing of nano-silicon and carbon matrix is ​​carried out by mechanical mixing, due to the lack of interfacial chemical bonding, silicon particles are prone to agglomeration and peeling off from the carbon layer, resulting in poor cycle performance. Therefore, developing a high-performance silicon-carbon anode material with excellent cycle stability is a technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a high-performance silicon-carbon anode material and its preparation method, so as to solve the problem of poor cycle stability of silicon-carbon anode materials in the prior art.

[0005] The objective of this invention can be achieved through the following technical solutions: A high-performance silicon-carbon anode material includes a porous carbon material, on the surface of which carbon nanotube networks and nano-silicon are deposited sequentially. The outer surface of the porous carbon material with deposited carbon nanotube networks and nano-silicon is further provided with a sub-outer carbon shell and an outer carbon shell from the inside to the outside.

[0006] The preparation method of the above-mentioned high-performance silicon-carbon anode material includes the following steps: S1. Pre-carbonize the resin material to obtain resin carbon material, mix the resin carbon material with an activator and heat to obtain porous carbon material; S2. The porous carbon material is activated with steam and then washed to obtain the macroporous carbon material. S3. After washing the macroporous carbon material, immerse it in the impregnation solution to obtain the active macroporous carbon material. S4. Place the active macroporous carbon material in a vapor deposition apparatus, introduce a carbon source and protective gas to grow carbon nanotubes, and obtain carbon nanotube-porous activated carbon. S5. The purified carbon nanotube-porous activated carbon is placed in a vapor deposition device, and silane and protective gas are introduced to deposit nano-silicon to obtain a primary silicon-carbon composite material. S6. Place the primary silicon-carbon composite material in a vapor deposition device, introduce a carbon source and protective gas to perform a primary carbon coating, and obtain a secondary silicon-carbon composite material. S7. The secondary silicon-carbon composite material is placed in a vapor deposition apparatus, and a carbon source and protective gas are introduced to perform secondary carbon coating. After coating, the material is graded and demagnetized to obtain a high-performance silicon-carbon anode material.

[0007] Furthermore, in S1, the resin material is any one or both of natural resin and synthetic resin.

[0008] Furthermore, the natural resin is at least one of rosin and amber shellac.

[0009] Furthermore, the synthetic resin is any one or two of thermoplastic resin and thermosetting resin, wherein the thermoplastic resin is at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene and polypropylene, and the thermosetting resin is at least one of phenolic resin and epoxy resin.

[0010] Furthermore, in S1, the pre-carbonization conditions are: a pre-carbonization temperature of 400-1000℃ and a pre-carbonization time of 0.5-6h.

[0011] Further, in S1, the mass ratio of the resin carbon material to the activator is 1:(1-5).

[0012] Further, in S1, the mixing of the resin carbon material with the activator includes the following steps: The resin-based carbon material and the activator are mixed in a VC mixer or a 3D mixer. The VC mixer has a speed of 500-3000 r / min and a mixing time of 0.5h-4h. The 3D mixer has a speed of 200-2000 r / min and a mixing time of 1h-5h.

[0013] Furthermore, in S1, the heating conditions are: under a protective gas, the heating temperature is 650℃-950℃, and the heating time is 0.5-6h, preferably 800℃ for 3h.

[0014] Further, in S1, the activator is at least one selected from KOH, NaOH, KCO3, FeCl3, H3PO4, ZnCl2, K2SO4, LiKNaCO3, and LiMgAl(CO3)3.

[0015] Furthermore, in S1, the specific surface area of ​​the porous carbon material is 1500-2200 m². 2 / g, pore volume is 0.5-1.2 m³ 2 / g, with pores distributed in the 0.5-2nm range accounting for ≥70%.

[0016] Further, in S1, the porous carbon material is classified into D10 with a particle size of 3-4µm, D50 with a particle size of 6.5-8.5µm, and D90 with a particle size of 11-13µm.

[0017] Further, in S2, the activation conditions are: activation temperature of 700℃-1500℃, activation time of 5-6h, and flow rate ratio of water vapor to nitrogen of 1:(1-5).

[0018] Further, in S2, the washing includes the following steps: immersing the product activated by water vapor in a 2 mol / L HCl solution and stirring for 6 h, then removing it and washing it with deionized water until the washing solution is neutral, and drying it at 80°C for 12 h.

[0019] Furthermore, in S2, the macroporous carbon material has a specific surface area of ​​1500-2500 m². 2 / g, pore volume is 0.8-1.5m³ 2 / g, with pores distributed in the 50-100nm range accounting for ≥70%.

[0020] Further, in S3, the washing includes the following steps: placing the macroporous carbon material sequentially into acetone, ethanol, and deionized water and sonicating for 10-15 minutes.

[0021] Further, in S3, the soaking includes the following steps: immersing the washed macroporous carbon material in the impregnation solution, drawing a vacuum, soaking under negative pressure (-101.1KPa) for 1-8 hours, and drying the soaked product at 80°C for 2-24 hours.

[0022] Further, in S3, the impregnation solution is prepared by dissolving ferric nitrate and cobalt nitrate in anhydrous ethanol at a molar ratio of 1:1, and the total concentration of ferric ions and cobalt ions is 0.05 mol / L.

[0023] Furthermore, in S3, the ratio of the macroporous carbon material to the impregnation solution is (1-10) kg: (5-200) L.

[0024] Furthermore, in S4, the conditions for growing carbon nanotubes are: growth temperature of 700-1500℃, heating rate of 1-20℃ / min, and growth time of 4-10h.

[0025] Further, in S5, the purification includes the following steps: immersing carbon nanotube-porous activated carbon in a 3 mol / L HCl solution and sonicating for 1.5 h; after sonication, filtering to remove residual catalyst ions; washing with deionized water and drying at 80 °C for 12 h.

[0026] Furthermore, in S5, the conditions for depositing nano-silicon are: a deposition temperature of 400-700℃, a heating rate of 1-20℃ / min, and a deposition time of 1-8h.

[0027] Furthermore, in S6, the conditions for the first carbon coating are: coating temperature of 500-1000℃, heating rate of 1-20℃ / min, and coating time of 1-6h.

[0028] Furthermore, the conditions for the secondary carbon coating are: coating temperature of 500-900℃, heating rate of 1-20℃ / min, and coating time of 1-6h.

[0029] Furthermore, in S4, S6, and S7, the carbon source is any one or more of methane, methane homologues, acetylene, acetylene homologues, benzene, and homologues.

[0030] Furthermore, in S4, S6 and S7, the ratio of the carbon source to the protective gas flow rate is 1:(1-5).

[0031] Furthermore, in S4, S6, and S7, the total gas flow rate of the carbon source and the protective gas is 5-45 L / min.

[0032] Furthermore, in S5, the ratio of the flow rate of the silane to the flow rate of the protective gas is 1:(1-5).

[0033] Furthermore, in S5, the total gas flow rate of the silane and the protective gas is 5-45 L / min.

[0034] Furthermore, the protective gas is any one of helium, argon, and nitrogen.

[0035] The beneficial effects of this invention are: 1. This invention designs and synthesizes a high-performance silicon-carbon composite material containing a carbon nanotube network. Because the carbon nanotube network can fix the silicon nanoparticles through physical binding and chemical bonding, the silicon nanoparticles can be uniformly distributed in the three-dimensional network space within the pores. The unsaturated filling of the silicon nanoparticles in the design provides a buffer space for the volume expansion during the charge and discharge process, which significantly improves the cycling stability of the material. In addition, the carbon nanotube network further increases the silicon-carbon contact area, improves the electronic conductivity of the material, and enables the synthesized material to have excellent rate performance.

[0036] 2. This invention designs and synthesizes a high-performance silicon-carbon composite material containing carbon nanotubes and a multi-layer carbon coating structure. Because this material has multi-level lithium-ion transport channels, it can further accelerate the migration rate of lithium ions, thereby significantly improving the cycling stability and rate performance of the material.

[0037] 3. This invention successfully prepared porous carbon materials with stable macroporous structures by combining pore-forming with activating agents with steam activation. Compared with traditional pore-expanding processes using activating agents, the steam activation method effectively avoids pore collapse and structural instability caused by excessive use of activating agents, while significantly reducing production costs and environmental pressure. On this basis, iron / cobalt ions are innovatively used to construct ionic active sites, realizing the in-situ controllable growth of carbon nanotubes in porous carbon materials. Finally, a unique unsaturated filling structure is obtained in which nano-silicon particles are surrounded by a carbon nanotube network in carbon channels. This structure provides a buffer space for the volume expansion of silicon particles and constructs a highly efficient conductive network, enabling the material to have both excellent cycle stability and rate performance. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the silicon-carbon anode material of the present invention.

[0039] Figure 2 The graph shows a comparison of the cycle performance of silicon-carbon anode materials in Example 2 and Comparative Examples 1-5.

[0040] Figure 3 This is a comparison chart of the rate performance of silicon-carbon anode materials in Example 2 and Comparative Examples 1-5. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0043] Example 1

[0044] A high-performance silicon-carbon anode material includes a porous carbon material on which carbon nanotube networks and nano-silicon are sequentially deposited. The outer surface of the porous carbon material with deposited carbon nanotube networks and nano-silicon further comprises a sub-outer carbon shell and an outer carbon shell, arranged from the inside out. The structure is as follows: Figure 1 As shown.

[0045] The preparation method of the above-mentioned high-performance silicon-carbon anode material includes the following steps: S1. 10 kg of phenolic resin (purchased from Shenzhen Yoshida Chemical Co., Ltd., model 2123) was placed in a rotary kiln and kept at 600℃ for 2 hours under nitrogen protection to obtain blocky resin carbon material. The blocky resin carbon material was coarsely crushed by a jaw crusher and then pulverized and classified by an air jet mill. The powder particles with a particle size of D50 were collected and passed through a 1650-mesh sieve to obtain resin carbon material. 6 kg of resin carbon material and 18 kg of KOH were placed in a VC mixer and mixed for 2.5 hours to obtain mixture A. Mixture A was placed in a rotary kiln and kept at 800℃ for 1.5 hours under nitrogen protection to obtain porous carbon material. The rotation speed of the VC mixer was 1800 r / min, and the specific surface area of ​​the porous carbon material was 1800 m². 2 / g, pore volume is 0.78m³ 2 / g, with 90% of the pores distributed in the 0.5-2nm range; S2. 2 kg of porous carbon material was placed in a rotary kiln, and steam was introduced to activate the porous carbon material. Under nitrogen protection, the temperature was increased to 900℃ at 2℃ / min for 3 hours. The activated product was then immersed in a 2 mol / L HCl solution and stirred for 6 hours. It was then removed and washed with deionized water until the washing solution was neutral. The product was dried at 80℃ for 12 hours to obtain macroporous carbon material. The steam flow rate was 3.3 L / min, the nitrogen flow rate was 6.7 L / min, and the specific surface area of ​​the macroporous carbon material was 2300 m². 2 / g, pore volume is 1.2 m 2 / g, with 85% of the pores distributed in the 50-100nm range; S3. Place 2 kg of macroporous carbon material into acetone, ethanol, and deionized water in sequence and sonicate for 12 min. After filtration, place the solid product into 10 L of impregnation solution, apply vacuum, and soak under negative pressure (-101.1 kPa) for 6 h. After soaking, dry the product at 80 °C for 12 h to obtain active macroporous carbon material. The impregnation solution is prepared by dissolving ferric nitrate and cobalt nitrate in ethanol at a 1:1 molar ratio, and the total concentration of ferric ions and cobalt ions is 0.05 mol / L. S4. Place 2 kg of activated macroporous carbon material in a vapor deposition apparatus, introduce methane and nitrogen, and keep it at 1200℃ for 4 h. After keeping it at 1200℃, the product is washed with 3 mol / L HCl and deionized water until neutral, and then dried to obtain carbon nanotube-porous activated carbon. The methane flow rate is 2.5 L / min, the argon flow rate is 7.5 L / min, and the heating rate is 5℃ / min. S5. Place 2 kg of carbon nanotubes-porous activated carbon in a vapor deposition apparatus, introduce silane and nitrogen, and keep at 540℃ for 6 h to obtain a primary silicon-carbon composite material, wherein the silane flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 5℃ / min. S6. Place 2 kg of primary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene and nitrogen gas, and keep at 580℃ for 1.5 h to obtain secondary silicon-carbon composite material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min. S7. Place 2 kg of secondary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene, and keep at 580℃ for 2 h. After coating, perform grading and demagnetization to obtain high-performance silicon-carbon anode material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min.

[0046] Example 2

[0047] A high-performance silicon-carbon anode material includes a porous carbon material on which carbon nanotube networks and nano-silicon are sequentially deposited. The outer surface of the porous carbon material with deposited carbon nanotube networks and nano-silicon further comprises a sub-outer carbon shell and an outer carbon shell, arranged from the inside out. The structure is as follows: Figure 1 As shown.

[0048] The preparation method of the above-mentioned high-performance silicon-carbon anode material includes the following steps: S1. 10 kg of phenolic resin (purchased from Shenzhen Yoshida Chemical Co., Ltd., model 2123) was placed in a rotary kiln and kept at 600℃ for 2 hours under nitrogen protection to obtain blocky resin carbon material. The blocky resin carbon material was coarsely crushed by a jaw crusher and then pulverized and classified by an air jet mill. Powdered particles with a particle size of approximately 8 µm (D50) were collected to obtain resin carbon material. 5 kg of resin carbon material and 7.5 kg of KOH were placed in a VC mixer and mixed for 2.5 hours to obtain mixture A. Mixture A was placed in a rotary kiln and kept at 800℃ for 1.5 hours under nitrogen protection to obtain porous carbon material. The rotation speed of the VC mixer was 1800 r / min, and the specific surface area of ​​the porous carbon material was 2000 m². 2 / g, pore volume is 0.90m³ 2 / g, with 95% of the pores distributed in the 0.5-2nm range; S2. 2 kg of porous carbon material was placed in a rotary kiln, and steam was introduced to activate the porous carbon material. Under nitrogen protection, the temperature was increased to 900℃ at 2℃ / min for 3 hours. The activated product was then immersed in a 2 mol / L HCl solution and stirred for 6 hours. It was then removed and washed with deionized water until the washing solution was neutral. The product was dried at 80℃ for 12 hours to obtain macroporous carbon material. The steam flow rate was 3.3 L / min, the nitrogen flow rate was 6.7 L / min, and the specific surface area of ​​the macroporous carbon material was 2400 m². 2 / g, pore volume is 1.3m³ 2 / g, with 90% of the pores distributed in the 50-100nm range; S3. Place 2 kg of macroporous carbon material into acetone, ethanol, and deionized water in sequence and sonicate for 12 min. After filtration, place the solid product into 10 L of impregnation solution, apply vacuum, and soak under negative pressure (-101.1 kPa) for 6 h. After soaking, dry the product at 80 °C for 12 h to obtain active macroporous carbon material. The impregnation solution is prepared by dissolving ferric nitrate and cobalt nitrate in ethanol at a 1:1 molar ratio, and the total concentration of ferric ions and cobalt ions is 0.05 mol / L. S4. Place 2 kg of activated macroporous carbon material in a vapor deposition apparatus, introduce methane and nitrogen, and keep it at 1200℃ for 4 h. After keeping it at 1200℃, the product is washed with 3 mol / HCl acid and deionized water until neutral, and then dried to obtain carbon nanotube-porous activated carbon. The methane flow rate is 2.5 L / min, the argon flow rate is 7.5 L / min, and the heating rate is 5℃ / min. S5. Place 2 kg of carbon nanotubes-porous activated carbon in a vapor deposition apparatus, introduce silane and nitrogen, and keep at 540℃ for 6 h to obtain a primary silicon-carbon composite material, wherein the silane flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 5℃ / min. S6. Place 2 kg of primary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene and nitrogen gas, and keep at 580℃ for 1.5 h to obtain secondary silicon-carbon composite material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min. S7. Place 2 kg of secondary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene, and keep at 580℃ for 2 h. After coating, perform grading and demagnetization to obtain high-performance silicon-carbon anode material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min.

[0049] Example 3

[0050] A high-performance silicon-carbon anode material includes a porous carbon material on which carbon nanotube networks and nano-silicon are sequentially deposited. The outer surface of the porous carbon material with deposited carbon nanotube networks and nano-silicon further comprises a sub-outer carbon shell and an outer carbon shell, arranged from the inside out. The structure is as follows: Figure 1 As shown.

[0051] The preparation method of the above-mentioned high-performance silicon-carbon anode material includes the following steps: S1. 10 kg of phenolic resin (purchased from Shenzhen Yoshida Chemical Co., Ltd., model 2123) was placed in a rotary kiln and kept at 600℃ for 2 hours under nitrogen protection to obtain blocky resin carbon material. The blocky resin carbon material was coarsely crushed by a jaw crusher and then pulverized and classified by an air jet mill. Powdered particles with a particle size of approximately 8 µm (D50) were collected to obtain resin carbon material. 8 kg of resin carbon material and 8 kg of KOH were placed in a VC mixer and mixed for 2.5 hours to obtain mixture A. Mixture A was placed in a rotary kiln and kept at 800℃ for 1.5 hours under nitrogen protection to obtain porous carbon material. The rotation speed of the VC mixer was 1800 r / min, and the specific surface area of ​​the porous carbon material was 1600 m². 2 / g, pore volume is 0.67m³ 2 / g, with 80% of the pores distributed in the 0.5-2nm range; S2. 2 kg of porous carbon material was placed in a rotary kiln, and steam was introduced to activate the porous carbon material. Under nitrogen protection, the temperature was increased to 900℃ at 2℃ / min for 3 hours. The activated product was then immersed in a 2 mol / L HCl solution and stirred for 6 hours. It was then removed and washed with deionized water until the washing solution was neutral. The product was dried at 80℃ for 12 hours to obtain macroporous carbon material. The steam flow rate was 3.3 L / min, the nitrogen flow rate was 6.7 L / min, and the specific surface area of ​​the macroporous carbon material was 1850 m². 2 / g, pore volume is 0.96m³ 2 / g, with 72% of the pores distributed in the 50-100nm range; S3. Place 2 kg of macroporous carbon material into acetone, ethanol, and deionized water in sequence and sonicate for 12 min. After filtration, place the solid product into 10 L of impregnation solution, apply vacuum, and soak under negative pressure (-101.1 kPa) for 6 h. After soaking, dry the product at 80 °C for 12 h to obtain active macroporous carbon material. The impregnation solution is prepared by dissolving ferric nitrate and cobalt nitrate in ethanol at a 1:1 molar ratio, and the total concentration of ferric ions and cobalt ions is 0.05 mol / L. S4. Place 2 kg of activated macroporous carbon material in a vapor deposition apparatus, introduce methane and nitrogen, and keep it at 1200℃ for 4 h. After keeping it at 1200℃, the product is washed with 3 mol / L HCl and deionized water until neutral, and then dried to obtain carbon nanotube-porous activated carbon. The methane flow rate is 2.5 L / min, the argon flow rate is 7.5 L / min, and the heating rate is 5℃ / min. S5. Place 2 kg of carbon nanotubes-porous activated carbon in a vapor deposition apparatus, introduce silane and nitrogen, and keep at 540℃ for 6 h to obtain a primary silicon-carbon composite material, wherein the silane flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 5℃ / min. S6. Place 2 kg of primary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene and nitrogen gas, and keep at 580℃ for 1.5 h to obtain secondary silicon-carbon composite material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min. S7. Place 2 kg of secondary silicon-carbon composite material in a vapor deposition apparatus, introduce acetylene, and keep at 580℃ for 2 h. After coating, perform grading and demagnetization to obtain high-performance silicon-carbon anode material, wherein the acetylene flow rate is 3 L / min, the nitrogen flow rate is 15 L / min, and the heating rate is 2℃ / min.

[0052] Example 4

[0053] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that "holding at 1200℃ for 4 hours" in S4 of Example 1 was modified to "holding at 1000℃ for 4 hours".

[0054] Example 5

[0055] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that "holding at 1200℃ for 4h" in S4 of Example 1 was modified to "holding at 1400℃ for 4h".

[0056] Example 6

[0057] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that "holding at 540℃ for 6 hours" in S5 of Example 1 was modified to "holding at 520℃ for 6 hours".

[0058] Example 7

[0059] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that "holding at 540℃ for 6 hours" in S5 of Example 1 was modified to "holding at 560℃ for 6 hours".

[0060] Example 8

[0061] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that the "holding temperature at 580℃ for 1.5h" in S6 of Example 1 was modified to "holding temperature at 600℃ for 1.5h".

[0062] Example 9

[0063] A high-performance silicon-carbon anode material was prepared according to the method of Example 1, except that the "holding temperature at 580℃ for 1.5h" in S6 of Example 1 was modified to "holding temperature at 620℃ for 1.5h".

[0064] Comparative Example 1

[0065] A high-performance silicon-carbon anode material was prepared according to the method of Example 2, except that steps S6 and S7 in Example 2 were omitted, and the primary silicon-carbon composite material obtained in S5 was directly graded and demagnetized to obtain the silicon-carbon anode material.

[0066] Comparative Example 2

[0067] A high-performance silicon-carbon anode material was prepared according to the method of Example 2, except that step S7 in Example 2 was omitted, and the secondary silicon-carbon composite material obtained in S6 was directly graded and demagnetized to obtain the silicon-carbon anode material.

[0068] Comparative Example 3

[0069] A high-performance silicon-carbon anode material was prepared according to the method of Example 2, except that step S4 in Example 2 was omitted, and the active macroporous carbon material obtained in S3 was used directly to replace the carbon nanotube-porous activated carbon for steps S5-S7.

[0070] Comparative Example 4

[0071] A high-performance silicon-carbon anode material was prepared according to the method of Example 2, except that step S2 in Example 2 was omitted, and the porous carbon material obtained in S1 was used directly to replace the macroporous carbon material for steps S3-S7.

[0072] Comparative Example 5

[0073] A high-performance silicon-carbon anode material was prepared according to the method of Example 2, except that step S3 in Example 2 was omitted, and the macroporous carbon material obtained in S2 was used directly to replace the active macroporous carbon material for steps S4-S7.

[0074] The silicon-carbon anode materials prepared in Examples 1-9 and Comparative Examples 1-5 were mixed with graphite at a weight ratio of 1:4. Subsequently, anode sheets were prepared by homogenization, coating, and other processes according to a mass ratio of active material: binder: dispersant: conductive agent = 93:4:1.5:1.5. The silicon-carbon anode was then matched with an NCM811 ternary cathode to assemble a 4.5Ah lithium-ion pouch battery, and the following electrical performance tests were performed: Capacity tests were conducted on the above batteries at 25°C, including the cycle performance and rate performance of the silicon-carbon anode material assembled batteries of Example 2 and Comparative Examples 1-5; the cycle performance test results are as follows: Figure 2 As shown, the rate performance test results are as follows: Figure 3 As shown, the initial coulombic efficiency (FE) and capacity retention after 800 cycles at 1C and 100 cycles at 4C were calculated for each group of batteries. The battery data shown are the average of at least 5 battery test results, and the test results are shown in Table 1: Table 1

[0075] As shown in Table 1, the silicon-carbon anode material prepared by this invention exhibits excellent electrochemical performance. Specifically, the initial coulombic efficiency exceeds 85.8%, the capacity retention after 800 cycles at 1C exceeds 86.4%, and the capacity retention after 100 cycles at 4C exceeds 61.7%. Example 2 demonstrates particularly outstanding performance: the initial coulombic efficiency reaches 93.4%, the capacity retention after 800 cycles at 1C is 92.8%, and the capacity retention after 100 cycles at 4C is 82.4%.

[0076] Depend on Figure 2 It can be seen that the capacity of all batteries decreases with increasing cycle number, but the capacity decay of Comparative Examples 1-5 is significantly faster than that of Example 2, with Comparative Example 3 showing a significant capacity decrease within 200 cycles; Figure 3 It can be seen that the discharge capacity retention rate first decreases and then rebounds with the increase of the number of cycles and eventually tends to stabilize. However, after 10-20 cycles, the capacity retention rate of Comparative Examples 1-5 decreased significantly more than that of Example 2, and the attenuation of Comparative Example 3 was particularly prominent.

[0077] In contrast, comparing Comparative Example 1 and Example 2, it can be seen that if the initial carbon coating and secondary carbon coating steps are omitted, the large specific surface area of ​​the prepared material will result in the formation of more SEI films on the surface, leading to significant irreversible lithium loss and a decrease in the initial coulombic efficiency. Comparing Comparative Example 1 and Comparative Example 2, it can be seen that the specific surface area of ​​the material decreases after the initial carbon coating, and the initial coulombic efficiency of the material is improved. Comparing the cycling performance of Example 2 with Comparative Examples 1 and 2, it can be seen that the rate performance and cycling stability of the material are improved after two carbon coatings. This is attributed to the relatively stable double-layer carbon shell structure, which alleviates the volume expansion effect of the internal silicon, improves the capacity decay, and provides better conductivity from the outer carbon shell. Combining Comparative Example 5 and Example 2, it can be seen that if the step of constructing active ion sites on the porous carbon material is omitted, and only high-temperature treatment with methane is performed, methane cannot selectively grow on the active sites and may partially deposit on the material surface, failing to construct a three-dimensional conductive network. This significantly reduces the material's cycle stability and rate performance. Similarly, combining Comparative Example 3 and Example 2, it can be seen that if the high-temperature treatment with methane is omitted after constructing active ion sites on the porous carbon material, a three-dimensional conductive carbon nanotube network structure still cannot be constructed, resulting in reduced cycle stability and rate performance. Combining Comparative Example 4 and Example 2, it can be seen that without steam activation and pore expansion, the pores are mostly micropores, lacking space to accommodate the growth of carbon nanotubes, thus failing to construct an ideal carbon nanotube network. In this case, when nano-silicon fills the micropores, there is insufficient unsaturated space to buffer the volume expansion of silicon, resulting in reduced cycle stability and rate performance. These results indicate that introducing a carbon nanotube network and a multilayer carbon coating structure into silicon-carbon composite materials can effectively improve the cycle stability and rate performance of silicon-carbon anode materials.

[0078] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0079] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A high-performance silicon-carbon anode material, characterized in that, The material includes porous carbon materials, on which carbon nanotube networks and nano-silicon are deposited sequentially. The outer surface of the porous carbon material with deposited carbon nanotube networks and nano-silicon is further provided with a sub-outer carbon shell and an outer carbon shell from the inside to the outside.

2. A method for preparing a high-performance silicon-carbon anode material, characterized in that, The method for preparing the high-performance silicon-carbon anode material as described in claim 1 comprises the following steps: S1. Pre-carbonize the resin material to obtain resin carbon material, mix the resin carbon material with an activator and heat to obtain porous carbon material; S2. The porous carbon material is activated with steam and then washed to obtain the macroporous carbon material. S3. After washing the macroporous carbon material, immerse it in the impregnation solution to obtain the active macroporous carbon material. S4. Place the active macroporous carbon material in a vapor deposition apparatus, introduce a carbon source and protective gas to grow carbon nanotubes, and obtain carbon nanotube-porous activated carbon. S5. The purified carbon nanotube-porous activated carbon is placed in a vapor deposition device, and silane and protective gas are introduced to deposit nano-silicon to obtain a primary silicon-carbon composite material. S6. Place the primary silicon-carbon composite material in a vapor deposition device, introduce a carbon source and protective gas to perform a primary carbon coating, and obtain a secondary silicon-carbon composite material. S7. The secondary silicon-carbon composite material is placed in a vapor deposition apparatus, and a carbon source and protective gas are introduced to perform secondary carbon coating. After coating, the material is graded and demagnetized to obtain a high-performance silicon-carbon anode material.

3. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S1, the mass ratio of the resin carbon material to the activator is 1:(1-5).

4. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S1, the activator is KOH, NaOH, KCO3, FeCl3, H3PO4, ZnCl2, or K2SO4. 4、 At least one of LiKNaCO3 and LiMgAl(CO3)3.

5. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S3, the impregnation solution is prepared by dissolving ferric nitrate and cobalt nitrate in anhydrous ethanol at a molar ratio of 1:1, and the total concentration of ferric ions and cobalt ions is 0.05 mol / L.

6. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S3, the ratio of the macroporous carbon material to the impregnation solution is (1-10) kg: (5-200) L.

7. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S4, the conditions for growing carbon nanotubes are: growth temperature of 700-1500℃, heating rate of 1-20℃ / min, and growth time of 4-10h.

8. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S5, the conditions for depositing nano-silicon are: deposition temperature of 400-700℃, heating rate of 1-20℃ / min, and deposition time of 1-8h.

9. The method for preparing the high-performance silicon-carbon anode material according to claim 2, characterized in that, In S6, the conditions for the first carbon coating are: coating temperature of 500-1000℃, heating rate of 1-20℃ / min, and coating time of 1-6h.

10. The method for preparing high-performance silicon-carbon anode material according to claim 2, wherein in S7, the following is characterized: The conditions for the secondary carbon coating are: coating temperature of 500-900℃, heating rate of 1-20℃ / min, and coating time of 1-6h.

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