Silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a silicon-carbon negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion battery negative electrode materials. Phenolic resin embedded with PAA-Li is used as a carbon precursor, and the prepared porous carbon material is subjected to high-temperature nitrogen doping, silicon deposition in pores, gas-phase carbon coating and composite carbon source pyrolytic carbon coating, so that the obtained silicon-carbon negative electrode material has high capacity, high first efficiency, excellent rate capability and long cycle performance.

Description

Technical Field

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

[0002] Currently, the application scenarios for lithium-ion batteries are gradually increasing, and high energy density and long cycle life are being demanded for them. One key means to improve energy density is to increase the specific capacity of the anode, making silicon anodes with high specific capacity a focus of attention. However, during charging and discharging, the lithium insertion / extraction reaction of silicon is accompanied by a large volume change (>300%), causing damage to the material structure and mechanical pulverization. This leads to separation between electrode material particles and between the electrode material and the current collector, resulting in loss of electrical contact, rapid capacity decay, and deterioration of cycle performance. Furthermore, due to the severe volume effect, the SEI film on the silicon surface is in a dynamic process of destruction and reconstruction, resulting in numerous side reactions with the cell and continuous lithium-ion consumption, further affecting cycle performance. To improve the expansion problem of silicon anode materials, one research direction is to develop silicon-carbon anode materials. Silicon-carbon materials possess advantages such as low expansion and good cycling performance. Currently, silicon-carbon materials are mainly prepared by depositing nano-silicon within the pores of a porous carbon matrix. The porous structure in the porous carbon matrix inhibits silicon growth, forming amorphous / microcrystalline nano-silicon, which exhibits excellent cycling performance. However, the high proportion of micropores in the porous carbon matrix increases side reactions and affects the material's first-efficiency performance. Furthermore, lithium-ion transport requires multiple crossings through the porous carbon-silicon interface, which also affects the material's rate performance. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a silicon-carbon anode material and its preparation method, and the obtained silicon-carbon anode material has the characteristics of high initial efficiency, high rate performance and long cycle performance.

[0004] The present invention proposes a method for preparing a silicon-carbon anode material, comprising the following steps:

[0005] S1. Mix lithium polyacrylate solution with aldehyde compound solution to obtain a mixture; mix phenol compound with the mixture and carry out polycondensation reaction under the action of alkaline catalyst; crush the obtained solid to a particle size D50 of 1~4μm to obtain carbon precursor A.

[0006] S2. The carbon precursor A is heated and carbonized in the presence of an alkaline activator, and then activated and expanded by carbon dioxide or water vapor under heat preservation. The obtained product is acid washed to obtain porous carbon material B.

[0007] S3. The porous carbon material B is calcined at 1000~2000℃ for 3~5h in a mixed atmosphere of ammonia and protective gas to obtain nitrogen-doped porous carbon material C.

[0008] S4. The nitrogen-doped porous carbon material C is subjected to vapor-phase silicon deposition and vapor-phase carbon coating in sequence to obtain product D;

[0009] S5. The product D and the mixed carbon source are stirred evenly in a protective atmosphere at 300~350℃, and then calcined in a protective atmosphere at 600~900℃ for 4~6h to obtain a silicon-carbon anode material with a particle size D50 of 8~12μm; the mixed carbon source is composed of pitch, graphene and carbon nanotubes in a mass ratio of 20:0.5~2:0.5~2.

[0010] Currently, the porous carbon matrix used in silicon-carbon materials is typically a porous carbon material with a particle size D50 of 7-10 μm. Lithium-ion transport requires multiple passages through the porous carbon-silicon interface, affecting rate performance. Alternatively, small-particle porous carbon materials with a D50 of 1-5 μm can be used, but their large specific surface area affects cycle performance. This invention mixes PAA-Li with an aldehyde compound solution, then performs a condensation reaction with a phenolic compound to generate a phenolic resin embedded in PAA-Li. The phenolic resin is then crushed and used as a carbon precursor. It is first carbonized in the presence of an alkaline activator, then activated with carbon dioxide or water vapor, and acid-washed to obtain a porous carbon material. This material is then subjected to high-temperature nitrogen doping. The resulting nitrogen-doped porous carbon material is then deposited with nano-silicon within its pores, followed by vapor-phase carbon coating. Finally, it is mixed with a composite carbon source of pitch, graphene, and carbon nanotubes and calcined. The carbon source is pyrolyzed in situ during coating and granulation, ultimately yielding a silicon-carbon anode material. This invention uses PAA-Li-embedded phenolic resin as a carbon precursor. PAA-Li has a long-chain molecular structure, which, after high-temperature carbonization and activation, can form highly conductive carbon fibers, thereby forming a conductive network in the porous carbon matrix, improving the conductivity of the porous carbon matrix. Simultaneously, it can form a "reinforced concrete" structure, further increasing the strength of the porous carbon matrix, suppressing volume expansion during silicon lithium insertion / extraction, and reducing cell expansion. By controlling the particle size of the carbon precursor to 1~4μm, small-particle-size silicon-carbon materials can be formed, shortening the lithium-ion transport particle size. Furthermore, subsequent granulation gives the material a low specific surface area, reducing side reactions with the electrolyte and improving first-efficiency and cycle performance. Pore expansion using water vapor or carbon dioxide reduces the proportion of micropores and reduces... The invention addresses lithium intercalation side reactions in porous carbon materials, improving initial efficiency. Nitrogen doping at 1000-2000℃ enhances conductivity and improves structural order, reducing defects, increasing strength, suppressing silicon-carbon expansion and cracking / pulverization, and controlling SEI film thickening during cycling, thus improving cycle performance. Finally, a composite carbon source of pitch, graphene, and carbon nanotubes is used for pyrolytic carbon coating. Pitch, a soft carbon material, forms a highly ordered coating layer after carbonization. Graphene, with its layered six-membered ring structure, reduces side reactions with the electrolyte and SEI film thickening during cycling. Carbon nanotubes act as connectors, reinforcing the structural strength of the coating layer, further improving cycle performance. In summary, the silicon-carbon anode material of this invention exhibits high capacity, high initial efficiency, excellent rate performance, and long cycle life.

[0011] Preferably, in S1, the mass ratio of lithium polyacrylate to aldehyde compound is 1:35~80.

[0012] In this invention, no particular limitation is placed on the aldehyde compounds; commonly used aldehyde compounds in the field of phenolic resin synthesis are acceptable. Preferably, the aldehyde compound is selected from at least one of paraformaldehyde, formaldehyde, acetaldehyde, furfural, and salicylaldehyde.

[0013] Preferably, the solid content of the lithium polyacrylate solution is 0.5% to 5%, and the mass fraction of the aldehyde compound solution is 32% to 38%.

[0014] Preferably, the lithium polyacrylate solution is prepared by adding lithium polyacrylate (PAA-Li) powder to an aqueous ethanol solution; preferably, the aqueous ethanol solution has a mass fraction of 75%.

[0015] Preferably, in S1, the mass ratio of the phenolic compound to the mixture is 1:5~8.

[0016] In this invention, no particular limitation is placed on the phenolic compounds; commonly used phenolic compounds in the field of phenolic resin synthesis are acceptable. Preferably, the phenolic compound is selected from at least one of o-cresol, p-cresol, o-cresol, 3,5-xylenol, resorcinol, and bisphenol A.

[0017] In step S1, the conventional method involves mixing phenolic compounds with a mixture and carrying out a polycondensation reaction under the action of an alkaline catalyst. Taking bisphenol A as an example, the specific steps are as follows: heating bisphenol A until it melts, then adding it to the mixture while stirring, heating to 180-200°C, adding an alkaline catalyst solution dropwise until a solid appears, and continuing stirring until it is completely solidified to obtain solid B. The type of alkaline catalyst is conventionally chosen, such as sodium carbonate.

[0018] In step S2, the process parameters for heating and carbonization in the presence of an alkaline activator are conventionally selected and can be adjusted according to actual needs. Preferably, in step S2, the heating and carbonization temperature is 700~900℃ and the time is 1~5h.

[0019] Preferably, in step S2, the mass ratio of the carbon precursor A to the alkali activator is 1:1 to 4. By controlling the mass ratio of the carbon precursor A to the alkali activator, the pore structure of the porous carbon material can be optimized, which is beneficial to further improve the silane deposition efficiency and increase the capacity; wherein, the alkali activator is a conventional choice, for example, it can be selected from at least one of sodium hydroxide and potassium hydroxide.

[0020] Preferably, in S2, the heating carbonization is carried out in a protective gas atmosphere, wherein the protective gas is selected from at least one of nitrogen, argon, and helium.

[0021] In S2, the specific steps and process conditions for carbon dioxide or water vapor activation and pore expansion are conventionally selected and can be adjusted according to actual needs. Preferably, in S2, the specific steps for carbon dioxide or water vapor activation and pore expansion include: introducing carbon dioxide or water vapor at 700~900℃ for 1~3 hours.

[0022] Preferably, in S2, the protective gas is selected from at least one of nitrogen, argon, and helium.

[0023] Preferably, the nitrogen-doped porous carbon material C has a pore size of 1.5~2 nm and a specific surface area of ​​1600~2200 m². 2 / g, with a pore volume of 0.8~1.1cc / g. By controlling the pore size, pore volume, and specific surface area of ​​nitrogen-doped porous carbon material C, the material can have an excellent pore structure, making it more suitable for nano-silicon deposition, thereby further improving the capacity.

[0024] In step S2, the purpose of acid washing is to remove the alkaline activator from the surface or pores of the porous carbon material. The type, concentration, and washing time of the acid used can be adjusted according to actual needs, and this invention does not impose any particular limitation on this. Preferably, the specific steps of acid washing are: stirring and washing in a 0.2~1mol / L hydrochloric acid solution for 1~5 hours; preferably, the mass ratio of the product to the hydrochloric acid solution is 1:1~3; before acid washing, the product may also be washed with water to remove the alkaline activator; after acid washing, the product may also be dried and washed with distilled water until the pH is ≤8 to further remove residual alkaline activator.

[0025] Preferably, in step S3, the volume ratio of the protective gas to ammonia is 2 to 10:1, and the protective gas is selected from at least one of nitrogen, argon, and helium. By controlling the volume ratio of ammonia to the protective gas, the nitrogen doping in the porous carbon material can be made more uniform, further improving the material's conductivity and subsequent silane deposition effect, and increasing the material's capacity.

[0026] In S4, the specific steps and process conditions for vapor phase silicon deposition are conventionally selected and can be adjusted according to actual needs. Preferably, in S4, the specific steps for vapor phase silicon deposition include: holding at 400~700℃ for 2~6 hours in a mixed atmosphere of silicon source gas and protective gas.

[0027] Preferably, in step S4, the volume ratio of the silicon source gas to the protective gas is 3-8:1, and the protective gas is selected from at least one of nitrogen, argon, and helium. By controlling the volume ratio of the silicon source gas to the protective gas in step S4, silane can be deposited more uniformly, which is beneficial for further increasing capacity, alleviating expansion, and improving cycle performance. Preferably, in step S4, the silicon source gas is at least one of silane, disilane, and propane.

[0028] In S4, the specific steps and process conditions for gas-phase carbon coating are conventionally selected and can be adjusted according to actual needs. Preferably, in S4, the specific method for gas-phase carbon coating includes: holding at 500~750℃ for 2~7h in a mixed atmosphere of carbon source gas and protective gas.

[0029] Preferably, the volume ratio of the carbon source gas to the protective gas is 2:1 to 1:3, and the protective gas is selected from at least one of nitrogen, argon, and helium. By controlling the volume ratio of the carbon source gas to the protective gas in S4, the carbon coating can be more uniform, better protecting the nano-silicon from oxidation, thereby improving the electrochemical performance of the material.

[0030] Preferably, in step S5, the mass ratio of product D to the mixed carbon source is 20:1 to 10:1. By controlling the mass ratio of product D to the mixed carbon source, the appropriate particle size and specific surface area of ​​the obtained silicon-carbon anode material can be controlled, thereby reducing the reaction with the electrolyte and improving cycle performance.

[0031] Preferably, in S5, the protective gas is selected from at least one of nitrogen, argon, and helium.

[0032] Preferably, the softening point of the asphalt is 230~290℃.

[0033] One method for preparing the mixed carbon source is, for example, to heat and melt asphalt under a protective gas atmosphere, then add graphene and carbon nanotubes and stir until homogeneous; the protective gas is selected from at least one of nitrogen, argon and helium.

[0034] The present invention also proposes a silicon-carbon anode material, which is prepared by the aforementioned preparation method.

[0035] The present invention also proposes a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode comprises a negative electrode active material, wherein the negative electrode active material comprises the silicon-carbon negative electrode material.

[0036] The beneficial effects of this invention are as follows:

[0037] This invention involves mixing PAA-Li with formaldehyde solution, then reacting it with bisphenol A via a condensation reaction to generate a phenolic resin embedded in PAA-Li. The phenolic resin is then crushed and used as a carbon precursor. It is first carbonized in the presence of an alkaline activator, then activated with carbon dioxide or water vapor and acid-washed to obtain a porous carbon material. This material is then subjected to high-temperature nitrogen doping. The resulting nitrogen-doped porous carbon material is then subjected to in-pore deposition of nano-silicon, followed by gas-phase carbon coating. Finally, it is mixed with a composite carbon source of asphalt, graphene, and carbon nanotubes and calcined. The carbon source is pyrolyzed in situ during coating and granulation, ultimately yielding a silicon-carbon anode material. By using PAA-Li-embedded phenolic resin as a carbon precursor, a "reinforced concrete" structure can be formed, increasing the strength of the porous carbon matrix, suppressing volume expansion during silicon lithium insertion / extraction, thereby improving cycle performance, and forming a conductive network to enhance conductivity. By controlling the particle size of the carbon precursor to 1~4μm, the core of the material has a small particle size of 1~4μm, which can shorten the lithium-ion transport particle size, ensuring the power performance of the material. Furthermore, granulation gives the material a low specific surface area, reducing side reactions with the electrolyte and improving first-efficiency and cycle performance. The silicon-carbon anode material obtained by this invention has high capacity, high first-efficiency, excellent rate performance, and long cycle performance, exhibiting excellent overall performance. Attached Figure Description

[0038] Figure 1 The XRD test results are for the silicon-carbon anode material prepared in Example 2 of this invention.

[0039] Figure 2 The results are from the full-cell cycle test of the silicon-carbon anode material prepared in Example 2 of this invention. Detailed Implementation

[0040] The technical solution of the present invention will now be described in detail through specific embodiments.

[0041] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods.

[0042] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.

[0043] Example 1

[0044] A silicon-carbon anode material, the preparation method of which is as follows:

[0045] S1. Lithium polyacrylate powder is added to an aqueous ethanol solution with a mass fraction of 75% to obtain a lithium polyacrylate solution with a solid content of 0.5%; the lithium polyacrylate solution is mixed with a formaldehyde solution with a mass fraction of 36% to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:35.

[0046] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 180°C, and a 0.5 mol / L sodium carbonate solution was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 4 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:5.

[0047] S2. Carbon precursor A and potassium hydroxide are mixed at a mass ratio of 1:1. The mixture is first calcined at 700℃ for 1 hour in a nitrogen atmosphere, and then activated by steam for 1 hour under heat preservation. The product is washed with water and then added to a 0.2 mol / L hydrochloric acid solution for stirring and washing for 1 hour. After drying, it is washed with distilled water until pH ≤ 8 to obtain porous carbon material B. The mass ratio of product to hydrochloric acid solution is 1:2.

[0048] S3. Porous carbon material B is calcined at 1000℃ for 3 hours in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C is 1.5 nm, and the specific surface area is 1600 m². 2 / g, with a pore volume of 0.8cc / g; the volume ratio of nitrogen to ammonia is 10:1;

[0049] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 400℃ for 2 hours. Then, the introduction of the silane and nitrogen gas mixture is stopped, and a mixture of acetylene and nitrogen gas is introduced instead. The mixture is kept at 500℃ for 2 hours to obtain product D. The volume ratio of silane to nitrogen gas is 8:1, and the volume ratio of acetylene to nitrogen gas is 2:1.

[0050] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 300°C, and then calcined in an argon atmosphere at 600°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 12 μm; wherein the mixed carbon source is composed of pitch (softening point 260°C), graphene and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 20:1.

[0051] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1605 mAh / g, the initial efficiency was 81.6%, and the capacity retention rate was 81.1% after 50 cycles.

[0052] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 18:82 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC at a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 86.5%, and the capacity retention rate was 85.5% after 650 cycles of the full cell.

[0053] Example 2

[0054] A silicon-carbon anode material, the preparation method of which is as follows:

[0055] S1. Add lithium polyacrylate powder to a 75% (w / w) aqueous ethanol solution to obtain a 1% (w / w) lithium polyacrylate solution; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:50.

[0056] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 190°C, and a sodium carbonate solution with a concentration of 0.5 mol / L was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 3 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:6.

[0057] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:2, calcined at 750°C for 1 hour in an argon atmosphere, and then activated by steam for 2 hours under heat preservation. The product is washed with water, then added to a 0.5 mol / L hydrochloric acid solution and stirred and washed for 2 hours. After drying, it is washed with distilled water until pH ≤ 8 to obtain porous carbon material B; wherein the mass ratio of product to hydrochloric acid solution is 1:2.

[0058] S3. Porous carbon material B was calcined at 1200℃ for 3.5 h in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C was 1.65 nm, and the specific surface area was 1700 m². 2 / g, with a pore volume of 0.83cc / g; the volume ratio of nitrogen to ammonia is 8:1;

[0059] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 530℃ for 3 hours. Then, the introduction of the silane and nitrogen gas mixture is stopped, and a mixture of acetylene and nitrogen gas is introduced instead. The mixture is kept at 550℃ for 2 hours to obtain product D. The volume ratio of silane to nitrogen gas is 7:1, and the volume ratio of acetylene to nitrogen gas is 1:1.

[0060] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 300°C, and then calcined in an argon atmosphere at 700°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 11 μm; wherein the mixed carbon source is composed of pitch (softening point 260°C), graphene and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 10:1.

[0061] The silicon-carbon anode material obtained above was subjected to XRD testing, and the test results are as follows: Figure 1 As shown. By Figure 1 It is evident that silicon material is in an amorphous state, exhibits low expansion stress during cycling, and thus possesses good cycling performance.

[0062] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1680 mAh / g, the initial efficiency was 82.9%, and the capacity retention rate was 83.8% after 50 cycles.

[0063] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 18:82 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained through processes including slurry preparation, coating, rolling, slitting, and die-cutting. These electrodes were then stacked, had tabs soldered, top-side sealed, and baked. An electrolyte (composed of LiFSI, LiPF6, and an organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and the organic solvent consisting of EMC and FEC at a volume ratio of 80:20) was then injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room-temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 87.5%, and after 790 cycles, the capacity retention rate was 89.5%. The cycle test results are as follows: Figure 2 As shown.

[0064] Example 3

[0065] A silicon-carbon anode material, the preparation method of which is as follows:

[0066] S1. Add lithium polyacrylate powder to a 75% (w / w) aqueous ethanol solution to obtain a lithium polyacrylate solution with a solid content of 2%; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:60.

[0067] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 195°C, and a 0.5 mol / L sodium carbonate solution was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 3.5 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:7.

[0068] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:2.5, and then calcined at 800°C for 3 hours in a nitrogen atmosphere. Then, it is activated by passing water vapor through the mixture for 2 hours under heat preservation. After washing the product with water, it is added to a 0.5 mol / L hydrochloric acid solution and stirred and washed for 3.5 hours. After drying, it is washed with distilled water until pH≤8 to obtain porous carbon material B, wherein the mass ratio of the product to the hydrochloric acid solution is 1:2.

[0069] S3. Porous carbon material B was calcined at 1500℃ for 3.5 h in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C was 1.73 nm, and the specific surface area was 1900 m². 2 / g, with a pore volume of 0.88cc / g; the volume ratio of nitrogen to ammonia is 7:1;

[0070] S4. Place nitrogen-doped porous carbon material C in a fluidized bed, introduce a mixed gas of silane and nitrogen, and keep it at 550℃ for 3 hours. Then stop introducing the mixed gas of silane and nitrogen, and replace it with a mixed gas of acetylene and nitrogen. Keep it at 600℃ for 2 hours to obtain product D.

[0071] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 300°C, and then calcined in an argon atmosphere at 700°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 10 μm. The mixed carbon source is composed of pitch (softening point 260°C), graphene, and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 13:1.

[0072] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1696 mAh / g, the initial efficiency was 82.1%, and the capacity retention rate was 83.2% after 50 cycles.

[0073] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 5:95 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC at a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 86.5%, and the capacity retention rate was 84.7% after 647 cycles of the full cell.

[0074] Example 4

[0075] A silicon-carbon anode material, the preparation method of which is as follows:

[0076] S1. Add lithium polyacrylate powder to a 75% (w / w) aqueous ethanol solution to obtain a lithium polyacrylate solution with a solid content of 4%; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:65.

[0077] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 195°C, and a 0.5 mol / L sodium carbonate solution was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 2 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:7.

[0078] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:3, and then calcined at 850°C for 4 hours in an argon atmosphere. Then, it is activated by passing steam through the mixture for 2 hours under heat preservation. After washing the product with water, it is added to a 0.85 mol / L hydrochloric acid solution and stirred and washed for 4 hours. After drying, it is washed with distilled water until the pH is ≤8 to obtain porous carbon material B. The mass ratio of the product to the hydrochloric acid solution is 1:3.

[0079] S3. Porous carbon material B was calcined at 1500℃ for 3.5 h in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C was 1.75 nm, and the specific surface area was 2000 m². 2 / g, pore volume is 0.92cc / g; the volume ratio of nitrogen to ammonia is 5:1;

[0080] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 600℃ for 4 hours. Then, the introduction of the silane and nitrogen gas mixture is stopped, and a mixture of acetylene and nitrogen gas is introduced instead. The mixture is kept at 650℃ for 5 hours to obtain product D. The volume ratio of silane to nitrogen gas is 5:1, and the volume ratio of acetylene to nitrogen gas is 1:2.

[0081] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 320°C, and then calcined in an argon atmosphere at 800°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 9 μm. The mixed carbon source is composed of pitch (softening point 260°C), graphene, and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 11:1.

[0082] The high-efficiency silicon suboxide and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the negative electrode was 1600 mAh / g, the initial efficiency was 82.8%, and the capacity retention rate was 84.9% after 50 cycles.

[0083] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 5:95 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC in a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 87.4%, and the capacity retention rate was 94.1% after 450 cycles of the full cell.

[0084] Example 5

[0085] A silicon-carbon anode material, the preparation method of which is as follows:

[0086] S1. Add lithium polyacrylate powder to a 75% (w / w) ethanol aqueous solution to obtain a lithium polyacrylate solution with a solid content of 5%; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:80.

[0087] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 200°C, and a 0.5 mol / L sodium carbonate solution was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 1 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:5.

[0088] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:1, and then calcined at 700°C for 1 hour in a nitrogen atmosphere. Then, water vapor is introduced for activation at the heat for 1 hour. The product is washed with water and then added to a 1 mol / L hydrochloric acid solution for stirring and washing for 5 hours. After drying, it is washed with distilled water until pH ≤ 8 to obtain porous carbon material B, wherein the mass ratio of the product to the hydrochloric acid solution is 1:5.

[0089] S3. Porous carbon material B is calcined at 2000℃ for 5 hours in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C is 2 nm, and the specific surface area is 2200 m². 2 / g, pore volume is 1.1cc / g; the volume ratio of nitrogen to ammonia is 2:1.

[0090] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 700℃ for 6 hours. Then, the introduction of the silane and nitrogen gas mixture is stopped, and a mixture of acetylene and nitrogen gas is introduced instead. The mixture is kept at 750℃ for 7 hours to obtain product D. The volume ratio of silane to nitrogen gas is 3:1, and the volume ratio of acetylene to nitrogen gas is 1:2.

[0091] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 350°C, and then calcined in an argon atmosphere at 900°C for 6 hours to obtain a silicon-carbon anode material with a D50 of 8 μm. The mixed carbon source is composed of pitch (softening point 260°C), graphene, and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 10:1.

[0092] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1580 mAh / g, the initial efficiency was 82.0%, and the capacity retention rate was 83.1% after 50 cycles.

[0093] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 5:95 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte was injected (the electrolyte is composed of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), and an organic solvent, wherein the concentration of LiFSI is 1.25M, the concentration of LiPF6 is 0.05M, and the organic solvent is composed of ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC) at a volume ratio of 80:20). A 7Ah soft-pack battery was assembled. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 87.2%, and the capacity retention rate was 92.5% after 450 cycles of the full battery.

[0094] Comparative Example 1

[0095] A porous carbon matrix (Solide GAC-21H) with a D50 of 8 μm was placed in a fluidized bed, and a mixture of silane and nitrogen gas was introduced. The mixture was kept at 530 °C for 3 h. Then, the introduction of the silane and nitrogen gas mixture was stopped, and a mixture of acetylene and nitrogen gas was introduced instead. The mixture was kept at 550 °C for 2 h to obtain a silicon-carbon anode material. The volume ratio of silane to nitrogen gas was 7:1, and the volume ratio of acetylene to nitrogen gas was 1:1.

[0096] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1580 mAh / g, the initial efficiency was 82.0%, and the capacity retention rate was 51.1% after 50 cycles.

[0097] Comparative Example 2

[0098] A silicon-carbon anode material, the preparation method of which is as follows:

[0099] S1. Bisphenol A is heated to 170℃ to melt it, and then added to a 36% formaldehyde solution with stirring. The mixture is heated to 190℃, and a 0.5 mol / L sodium carbonate solution is added dropwise until a solid appears. Stirring is continued until it is completely solidified to obtain a solid. The solid is then crushed to a particle size D50 of 3 μm to obtain carbon precursor A. The mass ratio of bisphenol A to formaldehyde solution is 1:6.

[0100] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:2, and then calcined at 750°C for 1 hour in an argon atmosphere. Then, it is activated by passing water vapor through the mixture for 2 hours under heat preservation. After washing the product with water, it is added to a 0.5 mol / L hydrochloric acid solution and stirred and washed for 2 hours. After drying, it is washed with distilled water until the pH is ≤8 to obtain porous carbon material B, wherein the mass ratio of the product to the hydrochloric acid solution is 1:2.

[0101] S3. Porous carbon material B was calcined at 1200℃ for 3.5 h in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C was 1.65 nm, and the specific surface area was 1700 m². 2 / g, with a pore volume of 0.83cc / g; the volume ratio of nitrogen to ammonia is 8:1;

[0102] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 530℃ for 3 hours. Then, the introduction of the silane and nitrogen gas mixture is stopped, and a mixture of acetylene and nitrogen gas is introduced instead. The mixture is kept at 550℃ for 2 hours to obtain product D. The volume ratio of silane to nitrogen gas is 7:1, and the volume ratio of acetylene to nitrogen gas is 1:1.

[0103] S5. The product D and the mixed carbon source are stirred evenly in an argon atmosphere at 300°C, and then calcined in an argon atmosphere at 700°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 11 μm; wherein the mixed carbon source is composed of pitch (softening point 260°C), graphene and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product D to the mixed carbon source is 10:1.

[0104] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1629 mAh / g, the initial efficiency was 81.8%, and the capacity retention rate was 70.1% after 50 cycles.

[0105] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 18:82 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC at a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 86.0%, and the capacity retention rate was 80.5% after 790 cycles of the full cell.

[0106] Comparative Example 3

[0107] A silicon-carbon anode material, the preparation method of which is as follows:

[0108] S1. Add lithium polyacrylate powder to a 75% (w / w) aqueous ethanol solution to obtain a 1% (w / w) lithium polyacrylate solution; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:50.

[0109] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 190°C, and a sodium carbonate solution with a concentration of 0.5 mol / L was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 3 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:6.

[0110] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:2, and then calcined at 750°C for 1 hour in an argon atmosphere. After activation by introducing steam at the same temperature for 2 hours, the resulting product is washed with water and then added to a 0.5 mol / L hydrochloric acid solution for stirring and washing for 2 hours. After drying, it is washed with distilled water until the pH is ≤8 to obtain porous carbon material B. The average pore size of porous carbon material B is 1.65 nm, and the specific surface area is 1700 m². 2 / g, with a pore volume of 0.83cc / g; the mass ratio of the product to the hydrochloric acid solution is 1:2;

[0111] S3. Porous carbon material B is placed in a fluidized bed, and a mixture of silane and nitrogen is introduced. The mixture is kept at 530℃ for 3 hours. Then, the mixture of silane and nitrogen is stopped, and a mixture of acetylene and nitrogen is introduced instead. The mixture is kept at 550℃ for 2 hours to obtain product C. The volume ratio of silane to nitrogen is 7:1, and the volume ratio of acetylene to nitrogen is 1:1.

[0112] S5. The product C and the mixed carbon source are stirred evenly in an argon atmosphere at 300°C, and then calcined in an argon atmosphere at 700°C for 4 hours to obtain a silicon-carbon anode material with a D50 of 11 μm; wherein the mixed carbon source is composed of pitch (softening point 260°C), graphene and carbon nanotubes in a mass ratio of 20:1:1, and the mass ratio of product C to the mixed carbon source is 10:1.

[0113] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode was 1630 mAh / g, the initial efficiency was 82.0%, and the capacity retention rate was 82.8% after 50 cycles.

[0114] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 18:82 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC at a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 85.6%, and the capacity retention rate was 79.1% after 790 cycles of the full cell.

[0115] Comparative Example 4

[0116] A silicon-carbon anode material, the preparation method of which is as follows:

[0117] S1. Add lithium polyacrylate powder to a 75% (w / w) aqueous ethanol solution to obtain a 1% (w / w) lithium polyacrylate solution; mix the lithium polyacrylate solution with a 36% (w / w) formaldehyde solution to obtain a mixed solution; wherein the mass ratio of lithium polyacrylate to formaldehyde is 1:50.

[0118] Bisphenol A was heated to 170°C to melt it, and then added to the mixture with stirring. The mixture was heated to 190°C, and a sodium carbonate solution with a concentration of 0.5 mol / L was added dropwise until a solid appeared. Stirring was continued until it was completely solidified to obtain a solid. The solid was crushed to a particle size D50 of 3 μm to obtain carbon precursor A. The mass ratio of bisphenol A to the mixture was 1:6.

[0119] S2. The carbon precursor A is mixed with potassium hydroxide at a mass ratio of 1:2, and then calcined at 750°C for 1 hour in an argon atmosphere. Then, it is activated by passing water vapor through the mixture for 2 hours under heat preservation. The resulting product is washed with water, then added to a 0.5 mol / L hydrochloric acid solution and stirred and washed for 2 hours. After drying, it is washed with distilled water until the pH is ≤8 to obtain porous carbon material B. The mass ratio of the product to the hydrochloric acid solution is 1:2.

[0120] S3. Porous carbon material B was calcined at 1200℃ for 3.5 h in a mixed atmosphere of ammonia and nitrogen to obtain nitrogen-doped porous carbon material C. The average pore size of nitrogen-doped porous carbon material C was 1.65 nm, and the specific surface area was 1700 m². 2 / g, with a pore volume of 0.83cc / g; the volume ratio of nitrogen to ammonia is 8:1;

[0121] S4. Nitrogen-doped porous carbon material C is placed in a fluidized bed, and a mixture of silane and nitrogen gas is introduced. The mixture is kept at 530℃ for 3 hours. Then, the mixture of silane and nitrogen gas is stopped and replaced with a mixture of acetylene and nitrogen gas. The mixture is kept at 550℃ for 2 hours to obtain a silicon-carbon anode material with a D50 of 3.1 μm. The volume ratio of silane to nitrogen gas is 7:1, and the volume ratio of acetylene to nitrogen gas is 1:1.

[0122] The silicon-carbon material and lithium metal obtained above were used to assemble a half-cell, and the electrochemical performance was tested at rates of 0.1C (initial) + 0.5C (cycle). The charge and discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the negative electrode was 1550 mAh / g, the initial efficiency was 68.1%, and the capacity retention rate was 71.1% after 50 cycles.

[0123] The silicon-carbon anode material obtained above was mixed with graphite at a mass ratio of 18:82 to form the anode active material, and NCM622 was used as the cathode active material. The anode and cathode electrodes were obtained by slurry mixing, coating, rolling, slitting, and die cutting. After stacking, tab welding, top and side sealing, and baking, an electrolyte (composed of LiFSI, LiPF6, and organic solvent, with LiFSI concentration of 1.25M, LiPF6 concentration of 0.05M, and organic solvent composed of EMC and FEC at a volume ratio of 80:20) was injected to assemble a 7Ah soft-pack battery. After formation and capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The test results showed that the initial efficiency of the cell was 78.0%, and the capacity retention rate was 78.5% after 790 cycles of the full cell.

[0124] The test results above show that the silicon-carbon anode material of the present invention, prepared by using PAA-Li-embedded phenolic resin as a carbon precursor, undergoes high-temperature nitrogen doping, in-pore silicon deposition, vapor-phase carbon coating, and composite carbon source pyrolysis carbon coating. The resulting silicon-carbon anode material exhibits high capacity, high initial efficiency, and excellent rate performance and long cycle life. In contrast, Comparative Example 1, which uses a conventional 6-10 μm porous carbon matrix and conventional silicon deposition and carbon coating methods to prepare the silicon-carbon anode material, suffers from the drawback of lithium-ion transport requiring multiple passages through the porous carbon-silicon interface, affecting… The problems include rate performance issues and poor long-cycle performance. Compared with Comparative Examples 2 to 4, Comparative Example 2 did not dope PAA-Li during the preparation of the carbon precursor, which could not effectively suppress silicon volume expansion and resulted in significantly worse cycle performance. Comparative Example 3 lacked nitrogen doping treatment by high-temperature calcination in an ammonia-containing atmosphere, which could not improve the structural order of the porous carbon material and also could not effectively suppress silicon-carbon expansion. Comparative Example 4 did not mix with a mixed carbon source and calcinate to achieve in-situ granulation, which could not reduce the specific surface area of ​​the material. The prepared material had a large specific surface area, resulting in low initial efficiency and poor cycle performance.

[0125] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: S1. Mix lithium polyacrylate solution with aldehyde compound solution to obtain a mixture; mix phenol compound with the mixture and carry out polycondensation reaction under the action of alkaline catalyst; crush the obtained solid to a particle size D50 of 1~4μm to obtain carbon precursor A. S2. The carbon precursor A is heated and carbonized in the presence of an alkaline activator, and then activated and expanded by carbon dioxide or water vapor under heat preservation. The obtained product is acid washed to obtain porous carbon material B. S3. The porous carbon material B is calcined at 1000~2000℃ for 3~5h in a mixed atmosphere of ammonia and protective gas to obtain nitrogen-doped porous carbon material C. S4. The nitrogen-doped porous carbon material C is subjected to vapor-phase silicon deposition and vapor-phase carbon coating in sequence to obtain product D; S5. The product D and the mixed carbon source are stirred evenly in a protective atmosphere at 300~350℃, and then calcined in a protective atmosphere at 600~900℃ for 4~6h to obtain a silicon-carbon anode material with a particle size D50 of 8~12μm; the mixed carbon source is composed of pitch, graphene and carbon nanotubes in a mass ratio of 20:0.5~2:0.5~2.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S1, the mass ratio of lithium polyacrylate to aldehyde compound is 1:35~80; the aldehyde compound is selected from at least one of paraformaldehyde, formaldehyde, acetaldehyde, furfural, and salicylaldehyde.

3. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S1, the mass ratio of the phenolic compound to the mixture is 1:5~8; the phenolic compound is selected from at least one of o-cresol, p-cresol, o-cresol, 3,5-xylenol, resorcinol, and bisphenol A.

4. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S2, the heating carbonization temperature is 700~900℃ and the time is 1~5h; the mass ratio of the carbon precursor A to the alkali activator is 1:1~4; the heating carbonization is carried out in a protective gas atmosphere, and the protective gas is selected from at least one of nitrogen, argon and helium.

5. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The nitrogen-doped porous carbon material C has a pore size of 1.5~2 nm and a specific surface area of ​​1600~2200 m². 2 / g, with a pore volume of 0.8~1.1cc / g.

6. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S3, the volume ratio of the protective gas to ammonia is 2 to 10:1; the protective gas is selected from at least one of nitrogen, argon, and helium.

7. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S4, the specific method for vapor phase silicon deposition includes: holding at 400~700℃ for 2~6h in a mixed atmosphere of silicon source gas and protective gas; the volume ratio of silicon source gas to protective gas is 3~8:1, and the protective gas is selected from at least one of nitrogen, argon and helium.

8. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S4, the specific method for gaseous carbon coating includes: holding the gas at 500~750℃ for 2~7h in a mixed atmosphere of carbon source gas and protective gas; the volume ratio of the carbon source gas to the protective gas is 2:1~1:3, and the protective gas is selected from at least one of nitrogen, argon and helium.

9. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In S5, the mass ratio of product D to mixed carbon source is 20:1 to 10:1; the protective gas is selected from at least one of nitrogen, argon, and helium.

10. A silicon-carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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