Silicon-carbon negative electrode material, porous carbon and preparation method

Abstract

The invention discloses a silicon-carbon negative electrode material, porous carbon and a preparation method, the porous carbon is prepared by mixing ammonium fluoride and a pre-carbonized material to prepare a premix; and putting the premix in an inert atmosphere, and carrying out pre-activation, drying, carbonization, activation and crushing treatment to obtain the composite material. And uniformly depositing the nano silicon particles into the porous carbon skeleton through a mature CVD (Chemical Vapor Deposition) process to obtain the silicon-carbon composite material. Fluorine and nitrogen co-doping modification can increase the defect degree of a carbon skeleton, efficiently relieve mechanical stress accompanied by lithium storage volume expansion of the silicon negative electrode in a micro scale, provide abundant lithium ion transport and mass transfer channels and enhance the conductivity of porous carbon, and ammonium fluoride is used as a supplementary activator besides water vapor, so that the porosity of the porous carbon is further improved, and the conductivity of the porous carbon is improved. An effective space is provided for uniform deposition of silicon, the fluorine-containing carbon layer can induce formation of a high-stability SEI film rich in LiF on the surface of the nano silicon material, and the interface stability and coulombic efficiency of the silicon negative electrode are further improved.

Description

Technical Field

[0001] The present invention relates to the field of negative electrode materials, and in particular to a silicon-carbon negative electrode material, porous carbon and a preparation method thereof. Background Art

[0002] In recent years, the lithium-ion battery industry has flourished alongside the rapid development of electric vehicles and the energy storage industry. Consequently, market demands for lithium-ion battery performance have increased, posing challenges to existing materials. Currently, graphite remains the mainstream anode material for lithium-ion batteries, but its theoretical specific capacity is only 372 mAh / g, making it difficult to meet the growing demand for high-capacity batteries. Therefore, developing anode materials with higher specific capacities has become a research priority in this field.

[0003] Silicon has attracted widespread attention due to its abundant reserves in the earth's crust and its excellent electrochemical properties. Compared with graphite, silicon has a higher theoretical specific capacity (3725mAh / g), a lower chemical potential, and does not produce lithium dendrites during the charge and discharge process, making it a potential candidate for the next generation of high-performance negative electrode materials. However, silicon-based negative electrode materials also have many challenges, such as its low electrical conductivity as a semiconductor material, and the rupture of the solid electrolyte interface (SEI) film due to volume expansion during lithiation and delithiation, which affects the cycle stability of the battery. Therefore, how to overcome the inherent defects of silicon-based negative electrode materials to improve their practical application performance has become a key issue in current research.

[0004] Silicon-carbon negative electrode materials are usually composed of a composite of nano-silicon particles and a porous carbon matrix, in which the porous carbon matrix plays a key role in optimizing the performance of the material. On the one hand, it can provide abundant lithium storage sites and improve the lithium ion storage capacity of the material; on the other hand, it can effectively buffer the volume expansion of silicon during the charge and discharge process, reduce the damage to the electrode structure, and thus improve the cycle stability and rate performance. At present, the preparation of porous carbon materials mainly depends on the high-temperature activation process of coke and alkaline activators. For example, patent application CN109037679A discloses a method for preparing porous carbon materials based on petroleum coke and its application in silicon-carbon negative electrode materials. The method first uses a ball milling process to fully mix the petroleum coke and the pore-forming agent, and then calcines at high temperature to obtain a porous carbon material. This method can optimize the pore structure of the carbon matrix while maintaining its conductivity, providing a new technical path for improving the performance of silicon-carbon negative electrode materials.

[0005] Patent CN116588933A discloses a method for preparing nano-silicon-carbon materials based on modified activated carbon. The method first introduces carbon dioxide (CO2) at 500-800°C to carbonize the activated carbon to modify its structure and properties, and then introduces the silicon component through nano-deposition technology. The introduction of CO2 plays a role in activating the pores during the carbonization process of the activated carbon, optimizing the pore structure of the material to a certain extent, thereby facilitating the cracking and deposition of silane and improving the loading efficiency of silicon. However, although CO2 treatment can improve the pore characteristics of activated carbon to a certain extent, the effect of improving the dispersibility of porous carbon materials in a fluidized state is not significant, and there are still certain limitations. In addition, although the above method is relatively simple, the prepared porous carbon material still has problems such as small specific surface area and low porosity. This structural characteristic limits the diffusion path of lithium ions to a certain extent, reduces its transmission rate, and thus affects the rate performance of the electrode. At the same time, low porosity makes it difficult to effectively buffer the volume expansion of silicon during charge and discharge, which can easily lead to the aggregation and shedding of silicon particles, thereby weakening the structural stability and cycle life of the silicon-carbon anode material. Therefore, how to optimize the pore structure of porous carbon materials to improve their conductivity and volume buffering capacity remains an important research direction. Summary of the Invention

[0006] In view of this, the present invention addresses the deficiencies in the prior art, and its main purpose is to provide a silicon-carbon negative electrode material, porous carbon and a preparation method, which can effectively solve the problems of the existing negative electrode materials having small specific surface area, low porosity and inability to buffer the volume expansion of the negative electrode during charging and discharging.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing porous carbon comprises the following steps:

[0009] (1) The pre-carbonized material and ammonium fluoride particles are placed in a mortar and ground for 15-30 minutes, with the mass ratio of ammonium fluoride to pre-carbonized material being 1:(1.75-3.25). After mixing evenly, deionized water is added, and the amount of deionized water added is such that the solid content of the premix is 15-30%. The mixture is stirred at room temperature, and the temperature is gradually increased to 50-80° C. and kept stirred for 2-4 hours. Finally, the mixture is dried and cured under vacuum conditions at 80° C. for 12-24 hours until the liquid is completely evaporated to obtain a premix.

[0010] (2) The premix obtained in step (1) was naturally cooled and ground in a mortar for 15-30 minutes to obtain a powder sample;

[0011] (3) placing the powder sample obtained in step (2) in a rotary kiln for carbonization at a temperature of 700-900° C. for 3-5 h to obtain a carbonized sample;

[0012] (4) The carbonized sample obtained in step (3) is heated to 900-950°C, and water vapor is introduced to activate and form pores. The activation time is 3-5 hours to obtain porous carbon.

[0013] As a preferred embodiment, in step (1), the pre-carbonized material is a biomass-based pre-carbonized material or a phenolic resin-based pre-carbonized material. The biomass pre-carbonized material is obtained by acid washing and low-temperature carbonization treatment of at least one material selected from coconut shells, bamboo shells, and straws. The phenolic resin-based pre-carbonized material is obtained by cross-linking phenolic resin and then carbonizing it at a low temperature.

[0014] As a preferred solution, the powder sample in step (3) is first heated to 600°C at a heating rate of 5-10°C / min, then heated to 700-900°C at a heating rate of 2°C / min, and kept warm for 3-5h.

[0015] As a preferred solution, the carbonized sample in step (4) is heated to 900-950°C at a heating rate of 1-2°C / min, and water vapor is introduced to activate and form pores, and the activation time is 3-5 hours.

[0016] As a preferred solution, the water vapor flow rate in step (4) is 1.2-4.3 g / min.

[0017] A porous carbon is prepared by the above-mentioned method for preparing porous carbon.

[0018] A silicon-carbon negative electrode material is obtained by using the porous carbon obtained by the above-mentioned porous carbon preparation method as a raw material, and sequentially performing silane deposition and carbon source gas coating.

[0019] As a preferred embodiment, the method for preparing the silicon-carbon negative electrode material comprises the following steps:

[0020] Porous carbon is added to a fluidized bed reactor, and a silicon source gas is introduced to perform a primary chemical vapor deposition to deposit silicon on the porous carbon. The temperature of the primary chemical vapor deposition is 600-750°C, the primary deposition time is 4-8 hours, and the silicon source gas pressure is 0.1-1MPa to obtain a silicon-carbon composite material. Then, a carbon source gas is introduced to perform a secondary chemical vapor deposition to coat the surface of the silicon-carbon composite material with carbon. The temperature of the secondary chemical vapor deposition is 500-600°C, the secondary deposition time is 2-4 hours, and the pressure is 0.1-0.3MPa to obtain a silicon-carbon negative electrode material.

[0021] As a preferred solution, the silane gas is monosilane gas and / or disilane gas, and the carbon source gas is at least one of methane, ethane, propane, acetylene, ethylene, and propylene.

[0022] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, it can be seen from the above technical solution that:

[0023] Pre-carbonized material is used as raw material, and porous carbon with uniform pore distribution and good porosity is prepared through mixing with ammonium fluoride, grinding, carbonization, physical activation and other processes. It effectively improves the problems of non-concentrated pore distribution and low porosity of traditional porous carbon. At the same time, fluorine and nitrogen co-doping modification can increase the defectivity of the carbon skeleton, effectively alleviate the mechanical stress accompanied by the volume expansion of silicon negative electrode lithium storage at the microscale, provide abundant lithium ion transport and mass transfer channels, enhance the conductivity of porous carbon, and ammonium fluoride as a supplementary activator besides water vapor to further improve the porosity of porous carbon and provide effective space for the uniform deposition of silicon. The fluorine-containing carbon layer can induce the formation of a highly stable SEI film rich in LiF on the surface of the nano-silicon material, further improving the interface stability and Coulomb efficiency of the silicon negative electrode.

[0024] To more clearly illustrate the structural features and effects of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM photo of the porous carbon prepared in Example 1 of the present invention;

[0026] Figure 2 This is a SEM photo of the porous carbon prepared in Example 2 of the present invention;

[0027] Figure 3 This is a SEM photo of the porous carbon prepared in Example 3 of the present invention;

[0028] Figure 4 This is a SEM photo of the porous carbon prepared in Example 1 of the present invention;

[0029] Figure 5 This is a SEM photo of the porous carbon prepared in Example 2 of the present invention;

[0030] Figure 6 This is a SEM photo of the porous carbon prepared in Example 3 of the present invention;

[0031] Figure 7 This is a SEM photo of the first silicon-carbon negative electrode material of the present invention;

[0032] Figure 8 The voltage-specific capacity curve of the first silicon-carbon negative electrode material of the present invention during the first charge and discharge;

[0033] Figure 9 This is a SEM photo of the second silicon-carbon negative electrode material of the present invention;

[0034] Figure 10 This is the voltage-specific capacity curve of the first charge and discharge of the second silicon-carbon negative electrode material of the present invention. DETAILED DESCRIPTION

[0035] The present invention discloses a method for preparing porous carbon, which comprises the following steps:

[0036] (1) Pre-carbonized material and ammonium fluoride particles are placed in a mortar and ground for 15-30 minutes, with the mass ratio of ammonium fluoride to pre-carbonized material being 1:(1.75-3.25). After uniform mixing, deionized water is added, and the amount of deionized water added is such that the solid content of the premix is 15-30%. The mixture is stirred at room temperature, and the temperature is gradually increased to 50-80° C. and kept stirred for 2-4 hours. Finally, the mixture is dried and cured under vacuum conditions at 80° C. for 12-24 hours until all the liquid is evaporated to dryness, thereby obtaining a premix. The pre-carbonized material is a biomass-based pre-carbonized material or a phenolic resin-based pre-carbonized material. The biomass pre-carbonized material is obtained by acid washing and low-temperature carbonization treatment of at least one material selected from coconut shell, bamboo shell, and straw, and the phenolic resin-based pre-carbonized material is obtained by cross-linking phenolic resin and then low-temperature carbonization.

[0037] (2) The premix obtained in step (1) was naturally cooled and ground in a mortar for 15-30 minutes to obtain a powder sample;

[0038] (3) placing the powder sample obtained in step (2) in a rotary furnace for carbonization at a carbonization temperature of 700-900°C for a carbonization time of 3-5h to obtain a carbonized sample; specifically, the powder sample is first heated to 600°C at a heating rate of 5-10°C / min, then heated to 700-900°C at a heating rate of 2°C / min, and kept warm for 3-5h.

[0039] (4) heating the carbonized sample obtained in step (3) to 900-950°C, introducing water vapor to activate and form pores, and the activation time is 3-5 hours to obtain porous carbon; specifically, the carbonized sample is heated to 900-950°C at a heating rate of 1-2°C / min, introducing water vapor to activate and form pores, and the activation time is 3-5 hours, and the water vapor flow rate is 1.2-4.3 g / min.

[0040] A silicon-carbon negative electrode material is obtained by sequentially performing silane deposition and carbon source gas coating using the porous carbon obtained by the aforementioned porous carbon preparation method as a raw material; the preparation method of the silicon-carbon negative electrode material comprises the following steps:

[0041] Porous carbon is added to a fluidized bed reactor, and a silicon source gas is introduced to perform a chemical vapor deposition to deposit silicon on the porous carbon. The temperature of the first chemical vapor deposition is 600-750°C, the first deposition time is 4-8h, and the silicon source gas pressure is 0.1-1MPa to obtain a silicon-carbon composite material. Then, a carbon source gas is introduced to perform a secondary chemical vapor deposition to perform carbon coating on the surface of the silicon-carbon composite material. The temperature of the secondary chemical vapor deposition is 500-600°C, the secondary deposition time is 2-4h, and the pressure is 0.1-0.3MPa to obtain a silicon-carbon negative electrode material. Specifically, the silane gas is monosilane gas and / or disilane gas, and the carbon source gas is at least one of methane, ethane, propane, acetylene, ethylene, and propylene.

[0042] Example 1

[0043] (1) 50 g of coconut shell pre-carbonized material and 15.4 g of ammonium fluoride particles were placed in a mortar and ground for 15 min. After mixing evenly, 152 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 60 ° C and kept stirring for 2 h. Finally, the mixture was dried and cured under vacuum conditions at 80 ° C for 12 h until all the liquid was evaporated to dryness to obtain a premix.

[0044] (2) The premix obtained in step (1) was cooled naturally and ground in a mortar for 15 min to obtain a powder sample.

[0045] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 10°C / min, then heated to 750°C at a heating rate of 2°C / min, and kept warm for 3 h.

[0046] (4) The carbonized sample obtained in step (3) was heated to 900°C at a heating rate of 2°C / min, and water vapor was introduced for activation and pore formation. The activation time was 3 h, and the water vapor flow rate was 1.2 g / min to obtain porous carbon.

[0047] Example 2

[0048] (1) 50 g of coconut shell pre-carbonized material and 20 g of ammonium fluoride particles were placed in a mortar and ground for 20 min. After mixing evenly, 280 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 60 ° C and kept stirring for 3 h. Finally, the mixture was dried and cured under vacuum conditions at 80 ° C for 18 h until all the liquid was evaporated to dryness to obtain a premix.

[0049] (2) The premix obtained in step (1) was cooled naturally, and ground in a mortar for 20 min to obtain a powder sample.

[0050] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 8°C / min, then heated to 800°C at a heating rate of 2°C / min, and kept warm for 4 h.

[0051] (4) The carbonized sample obtained in step (3) was heated to 900°C at a heating rate of 2°C / min, and water vapor was introduced for activation and pore formation. The activation time was 4 h, and the water vapor flow rate was 3.5 g / min to obtain porous carbon.

[0052] Example 3

[0053] (1) 50 g of coconut shell pre-carbonized material and 28.6 g of ammonium fluoride particles were placed in a mortar and ground for 30 min. After mixing evenly, 445 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 80 ° C and kept stirring for 3 h. Finally, the mixture was dried and cured under vacuum conditions at 80 ° C for 24 h until all the liquid was evaporated to dryness to obtain a premix.

[0054] (2) The premix obtained in step (1) was cooled naturally, and ground in a mortar for 30 min to obtain a powder sample.

[0055] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 5°C / min, then heated to 900°C at a heating rate of 2°C / min, and kept warm for 5 h.

[0056] (4) The carbonized sample obtained in step (3) was heated to 950°C at a heating rate of 1°C / min, and water vapor was introduced for activation and pore formation. The activation time was 5 h, and the water vapor flow rate was 4.3 g / min to obtain porous carbon.

[0057] Example 4

[0058] (1) 50 g of pre-carbonized bamboo shell material and 20 g of ammonium fluoride particles were placed in a mortar and ground for 20 min. After mixing evenly, 280 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 60 °C and kept stirring for 3 h. Finally, the mixture was dried and cured under vacuum conditions at 80 °C for 18 h until all the liquid was evaporated to dryness to obtain a premix.

[0059] (2) The premix obtained in step (1) was cooled naturally, and ground in a mortar for 20 min to obtain a powder sample.

[0060] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 8°C / min, then heated to 800°C at a heating rate of 2°C / min, and kept warm for 4 h.

[0061] (4) The carbonized sample obtained in step (3) was heated to 900°C at a heating rate of 2°C / min, and water vapor was introduced for activation and pore formation. The activation time was 4 h, and the water vapor flow rate was 3.5 g / min to obtain porous carbon.

[0062] Example 5

[0063] (1) 50 g of straw pre-carbonized material and 20 g of ammonium fluoride particles were placed in a mortar and ground for 20 min. After mixing evenly, 280 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 60 °C and kept stirring for 3 h. Finally, the mixture was dried and cured under vacuum conditions at 80 °C for 18 h until all the liquid was evaporated to obtain a premix.

[0064] (2) The premix obtained in step (1) was cooled naturally, and ground in a mortar for 20 min to obtain a powder sample.

[0065] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 8°C / min, then heated to 800°C at a heating rate of 2°C / min, and kept warm for 4 h.

[0066] (4) The carbonized sample obtained in step (3) was heated to 900°C at a heating rate of 2°C / min, and water vapor was introduced for activation and pore formation. The activation time was 4 h, and the water vapor flow rate was 3.5 g / min to obtain porous carbon.

[0067] Example 6

[0068] (1) 50 g of phenolic resin pre-carbonized material and 28.6 g of ammonium fluoride particles were placed in a mortar and ground for 30 min. After mixing evenly, 445 ml of deionized water was added and stirred at room temperature. The temperature was gradually increased to 80 ° C and kept stirring for 3 h. Finally, the mixture was dried and cured under vacuum conditions at 80 ° C for 24 h until all the liquid was evaporated to dryness to obtain a premix.

[0069] (2) The premix obtained in step (1) was cooled naturally, and ground in a mortar for 30 min to obtain a powder sample.

[0070] (3) The powder sample obtained in step (2) was placed in a rotary furnace for carbonization, firstly heated to 600°C at a heating rate of 5°C / min, then heated to 900°C at a heating rate of 2°C / min, and kept warm for 5 h.

[0071] (4) The carbonized sample obtained in step (3) was heated to 950°C at a heating rate of 1°C / min, and water vapor was introduced for activation and pore formation. The activation time was 5 h, and the water vapor flow rate was 4.3 g / min to obtain porous carbon.

[0072] The porous carbon prepared in Example 3 was used as a raw material to prepare two silicon-carbon negative electrode materials.

[0073] The preparation method of the first silicon-carbon negative electrode material is as follows:

[0074] Porous carbon is added to a fluidized bed reactor, and monosilane gas is introduced for a primary chemical vapor deposition to deposit silicon on the porous carbon. The gas pressure of monosilane is 0.5 MPa, the temperature of the primary chemical vapor deposition is 650°C, and the deposition time is 4 hours to obtain a silicon-carbon composite material. Then, methane gas is introduced for a secondary chemical vapor deposition to coat the surface of the silicon-carbon composite material with carbon. The temperature of the secondary chemical vapor deposition is 520°C, the deposition time is 2.5 hours, and the gas pressure of methane is 0.15 MPa to obtain a silicon-carbon negative electrode material.

[0075] The preparation method of the second silicon-carbon negative electrode material is as follows:

[0076] Porous carbon is added to a fluidized bed reactor, and monosilane gas is introduced for a primary chemical vapor deposition to deposit silicon on the porous carbon. The gas pressure of monosilane is 0.8 MPa, the temperature of the primary chemical vapor deposition is 700°C, and the deposition time is 6 hours to obtain a silicon-carbon composite material. Then, methane gas is introduced for a secondary chemical vapor deposition to coat the surface of the silicon-carbon composite material with carbon. The temperature of the secondary chemical vapor deposition is 560°C, the deposition time is 3 hours, and the gas pressure of methane is 0.25 MPa to obtain a silicon-carbon negative electrode material.

[0077] right Figures 1-6 Analyze from Figures 1-6 It can be seen that the porous carbon materials prepared in Examples 1-6 are biomass-based porous carbon materials. The biomass-based porous carbon materials exhibit a typical porous structure. The surface is composed of irregular and interconnected honeycomb pores, presenting a highly developed three-dimensional interconnected porous network structure. The pore size distribution range is wide and uneven, ranging from micron to submicron, forming an obvious hierarchical pore system. Moreover, its carbon skeleton is rough and presents an uneven lamellar structure, accompanied by a large number of granular protrusions and cracks, indicating that the material has undergone significant structural reorganization during the pyrolysis process, forming a highly developed multi-level pore system. At the same time, the pore wall thickness of the porous carbon material is uneven, and some areas present thin-walled macropore characteristics. This open pore structure is conducive to improving the specific surface area and mass transfer efficiency of the material. The overall morphology retains some structural characteristics of the resin precursor. This open three-dimensional porous network structure is conducive to material transport and surface reaction, which is a typical feature of biomass carbon materials.

[0078] right Figure 7-10 Analyze from Figure 7-10It can be seen that the silicon-carbon negative electrode material presents a typical binary composite structure under SEM. The carbon matrix forms a continuous three-dimensional porous network with uniform pore size distribution. The pore radius is 0.5-2μm, and the pore wall surface presents a rough nanoscale texture. The silicon phase is evenly dispersed in the carbon matrix in the form of irregular particles. The particle size is 1-3μm, the particle boundaries are clear and tightly bonded to the carbon matrix. No obvious cracks or shedding are observed. The overall structure of the silicon-carbon negative electrode material is complete, and the highly conductive porous network of the carbon skeleton provides good support and conductive paths for the silicon particles. This "silicon particles embedded in a porous carbon matrix" construction method is conducive to alleviating the intrinsic low conductivity of silicon. At the same time, the porous structure reserves a buffer space for possible subsequent volume changes.

[0079] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing porous carbon, characterized in that: The following steps are included: (1) The pre-carbonized material and ammonium fluoride particles are placed in a mortar and ground for 15-30 minutes, with the mass ratio of ammonium fluoride to pre-carbonized material being 1:(1.75-3.25). After mixing evenly, deionized water is added, and the amount of deionized water added is such that the solid content of the premix is 15-30%. The mixture is stirred at room temperature, and the temperature is gradually increased to 50-80° C. and kept stirred for 2-4 hours. Finally, the mixture is dried and cured under vacuum conditions at 80° C. for 12-24 hours until the liquid is completely evaporated to obtain a premix. (2) The premix obtained in step (1) was naturally cooled and ground in a mortar for 15-30 minutes to obtain a powder sample; (3) placing the powder sample obtained in step (2) in a rotary kiln for carbonization at a temperature of 700-900° C. for 3-5 h to obtain a carbonized sample; (4) The carbonized sample obtained in step (3) is heated to 900-950°C, and water vapor is introduced to activate and form pores. The activation time is 3-5 hours to obtain porous carbon.

2. The method for preparing porous carbon according to claim 1, wherein: In the step (1), the pre-carbonized material is a biomass-based pre-carbonized material or a phenolic resin-based pre-carbonized material. The biomass pre-carbonized material is obtained by acid washing and low-temperature carbonization treatment of at least one material selected from coconut shells, bamboo shells, and straws. The phenolic resin-based pre-carbonized material is obtained by cross-linking phenolic resin and then carbonizing it at a low temperature.

3. The method for preparing porous carbon according to claim 1, wherein: The powder sample in step (3) is first heated to 600°C at a heating rate of 5-10°C / min, then heated to 700-900°C at a heating rate of 2°C / min, and kept warm for 3-5h.

4. The method for preparing porous carbon according to claim 1, wherein: The carbonized sample in step (4) is heated to 900-950° C. at a heating rate of 1-2° C. / min, and water vapor is introduced to activate and form pores. The activation time is 3-5 hours.

5. The method for preparing porous carbon according to claim 1, wherein: The water vapor flow rate in step (4) is 1.2-4.3 g / min.

6. A porous carbon, characterized in that: The porous carbon is prepared by the method for preparing the porous carbon according to any one of claims 1 to 5.

7. A silicon-carbon negative electrode material, characterized in that: The porous carbon obtained by the porous carbon preparation method according to claim 6 is used as a raw material, and silane deposition and carbon source gas coating are performed in sequence to obtain the porous carbon.

8. The silicon-carbon negative electrode material according to claim 7, characterized in that: The preparation method of the silicon-carbon negative electrode material comprises the following steps: Porous carbon is added to a fluidized bed reactor, and a silicon source gas is introduced to perform a primary chemical vapor deposition to deposit silicon on the porous carbon. The temperature of the primary chemical vapor deposition is 600-750°C, the primary deposition time is 4-8 hours, and the silicon source gas pressure is 0.1-1MPa to obtain a silicon-carbon composite material. Then, a carbon source gas is introduced to perform a secondary chemical vapor deposition to coat the surface of the silicon-carbon composite material with carbon. The temperature of the secondary chemical vapor deposition is 500-600°C, the secondary deposition time is 2-4 hours, and the pressure is 0.1-0.3MPa to obtain a silicon-carbon negative electrode material.

9. The silicon-carbon negative electrode material according to claim 8, characterized in that: The silane gas is monosilane gas and / or disilane gas, and the carbon source gas is at least one of methane, ethane, propane, acetylene, ethylene, and propylene.

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