A high-capacity silicon-carbon negative electrode material and its preparation process

Abstract

This application relates to the field of lithium battery negative electrode materials, and specifically discloses a high-capacity silicon-carbon negative electrode material and its preparation process. The preparation process includes: preparing a total pore volume of 1.0-1.3cm 3 / g, and a compressive strength of 20-40 MPa; using a fluidized bed chemical vapor deposition process, silicon nanoparticles are deposited within the pores and on the surface of the porous carbon matrix to obtain a silicon-carbon core material; acetylene is then used as a carbon source to deposit a thin carbon layer on the surface of the silicon-carbon core material; and a rotary kiln is used for secondary carbon coating to form a silicon-carbon negative electrode material. The silicon-carbon negative electrode material prepared using this process not only improves the mechanical stability and cyclic stability of the material; at the same time, the porous activated carbon with a large pore volume provides ample deposition space for silicon nanoparticles, effectively improving the reversible capacity and significantly suppressing the volume expansion of silicon during the cycle.

Description

Technical Field

[0001] The present application relates to the field of lithium battery negative electrode materials, and more specifically, to a high-capacity silicon-carbon negative electrode material and a preparation process thereof. Background Art

[0002] As an important component of modern energy storage technology, lithium-ion batteries have developed rapidly in recent years. Especially in the fields of new energy vehicles and portable electronic devices, their high energy density and long cycle life make them the mainstream choice. As a key component of lithium-ion batteries, negative electrode materials directly affect the overall performance of the battery. At present, silicon-based negative electrode materials have attracted much attention because their theoretical specific capacity is much higher than that of traditional graphite materials, and have become one of the research hotspots. However, in practical applications, silicon-based negative electrode materials still face many challenges, especially the cracking problem caused by volume expansion during the cycle and the need to increase reversible capacity. These problems have put higher requirements on the research and development of silicon-based negative electrode materials.

[0003] To address the volume expansion of silicon-based anode materials during cycling, currently used techniques include: nanosizing silicon particles to reduce the impact of volume changes; combining silicon and carbon materials in a composite material format to improve overall stability; and surface coating the silicon material to enhance its mechanical properties. Furthermore, optimizing the preparation process, such as chemical vapor deposition or sol-gel methods, can improve the material's interface characteristics and conductivity.

[0004] However, although these methods have alleviated the volume expansion problem of silicon-based negative electrode materials to a certain extent, the reversible capacity of silicon-based negative electrode materials still needs to be improved. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a high-capacity silicon-carbon negative electrode material and a preparation process thereof.

[0006] This application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a process for preparing a high-capacity silicon-carbon negative electrode material, which comprises:

[0008] (1) Prepare a total pore volume of 1.0-1.3 cm 3 / g, biomass activated carbon with a compressive strength of 20-40 MPa;

[0009] (2) placing the biomass activated carbon into a fluidized bed, using a fluidized bed chemical vapor deposition process, using silane as a silicon source, depositing silicon nanoparticles in the pores and on the surface of the biomass activated carbon to obtain a silicon-carbon core material; then using acetylene as a carbon source, depositing a thin carbon layer on the surface of the silicon-carbon core material;

[0010] (3) The silicon-carbon core material with a thin carbon layer is extracted from the fluidized bed, and acetylene is used as the carbon source and a rotary kiln is used for secondary carbon coating to form a silicon-carbon negative electrode material.

[0011] By adopting the above technical solution, the high-capacity silicon-carbon negative electrode material prepared has significantly improved reversible capacity and cycle stability. The specific effects are as follows: By preparing biomass activated carbon with a total pore volume of 1.0-1.3cm³ / g and a compressive strength greater than 20Mpa, the problem of high pore volume and mechanical strength being difficult to balance is effectively solved, thereby improving the overall stability and capacity of the material. Silicon nanoparticles are deposited in the pores and on the surface of the porous carbon matrix using a fluidized bed chemical vapor deposition process, which can effectively inhibit the volume expansion of silicon during the charge and discharge cycle, reduce the generation of cracks, and thus significantly improve the cycle stability of the material. The sequential deposition of a thin carbon layer and secondary carbon coating on the surface of the silicon-carbon core material further enhances the conductivity and structural stability of the material, while reducing the direct contact between silicon and the electrolyte, thereby improving the cycle life and overall performance of the material.

[0012] Furthermore, in a preferred embodiment, the specific surface area of the biomass activated carbon is ≥ 2150m 2 / g, the micropore volume accounts for more than 62%, and the mesopore volume accounts for less than 38%.

[0013] Preferably, in a preferred embodiment, the specific surface area of the biomass activated carbon is ≥ 2350m 2 / g, the micropore volume accounts for more than 80%, and the mesopore volume accounts for less than 20%.

[0014] By adopting the above technical solutions, the multi-level pore structure design effectively improves the material's silicon loading capacity while ensuring rapid lithium ion transport, thereby significantly increasing the reversible capacity of the silicon-carbon anode material. In addition, the optimized pore structure enhances the material's mechanical stability, helping to alleviate the volume expansion problem of silicon during cycling.

[0015] Furthermore, in a preferred embodiment, the method for preparing the biomass activated carbon comprises:

[0016] Select hard-shelled plant raw materials and pre-treat them to obtain biomass raw materials;

[0017] The biomass raw material is heat-treated in a carbonization furnace for 1.5-2.5 hours to obtain a carbonized material;

[0018] The carbonized material is mixed with an inorganic base at an alkali-carbon ratio of 1.5-2.5:1, the mixture is placed in an activation furnace, and activated at 800-850° C. for 0.8-2 hours to obtain an activated material;

[0019] The activated material is crushed, acid-washed, filtered, and air-flow-pulverized to obtain biomass activated carbon.

[0020] By adopting the above technical solution, a biomass activated carbon that can simultaneously take into account mechanical strength and high pore volume properties is prepared. Specifically, the process is as follows: hard-shelled plant raw materials are selected and pretreated. Due to their high fiber content, they help to obtain activated carbon materials with high pore volume; the biomass raw materials are heat-treated in a carbonization furnace to obtain carbonized material. This process helps to form a stable carbon skeleton structure and improve the mechanical strength of the material; the carbonized material is mixed with an inorganic base and then activated in an activation furnace. By controlling the alkali-carbon ratio and activation temperature, porous carbon with high pore volume and suitable pore size distribution is obtained; and post-processing steps are used to further optimize the pore structure and surface properties of the porous carbon.

[0021] Furthermore, in a preferred embodiment, before the mixed material is put into the activation furnace for activation, the process further comprises:

[0022] The mixed material is heat-treated at 450-550° C. for 1.5-2.5 hours for curing; and then heat-treated at 800-850° C. for 0.8-1.2 hours for activation.

[0023] By adopting the above technical solution, the mixture is first heat-treated at 450-550°C to achieve solidification, which effectively enhances the mechanical strength of the biomass activated carbon and prevents structural collapse during the subsequent activation process, thereby ensuring the material's high pore volume characteristics. Subsequently, a short-term activation at 800-850°C can further increase the material's porosity and specific surface area without destroying the solidified structure, providing ample space for silicon deposition, effectively improving the reversible capacity of the negative electrode material and suppressing the adverse effects of volume expansion.

[0024] Furthermore, in a preferred embodiment, after the carbonized material is mixed with an inorganic base to obtain a mixed material, the method further comprises: adding 8-15 vol% ethanol solution to the mixed material as a dispersant.

[0025] By adopting the above technical solution, the addition of the dispersant allows the inorganic base and the carbonized material to be mixed more fully, thereby forming a more uniform pore structure in the subsequent activation process.

[0026] Furthermore, in a preferred embodiment, when preparing the carbonized material, the heat treatment process is a programmed temperature process, comprising:

[0027] The carbonization furnace is heated to 200°C at 4-6°C / min and kept warm for 20-40 minutes; then heated to 400°C at 4-6°C / min and kept warm for 20-40 minutes; finally heated to 600-650°C at 4-6°C / min and kept warm for 2 hours.

[0028] By employing this technical solution, the programmed temperature process effectively controls the pyrolysis reaction of the biomass feedstock, ensuring the structural stability and pore uniformity of the carbonized material. Specifically, the staged heating and holding treatments help gradually remove volatiles from the biomass feedstock while preventing excessive decomposition or coking of the feedstock at high temperatures, thereby producing biomass activated carbon with a high pore volume and excellent mechanical strength.

[0029] Furthermore, in a preferred embodiment, in step (2), the flow ratio of silane to carrier gas is 1:7-8, the temperature is 440-460°C, and the treatment time is 7-8h; the flow ratio of acetylene to carrier gas is 1:6-7, the coating temperature is 580-600°C, and the coating time is 5-6h.

[0030] By adopting the above technical solution, by controlling the flow ratio of silane to carrier gas, temperature and treatment time, the deposition amount and distribution uniformity of silicon nanoparticles can be accurately adjusted, so that the silicon content is stabilized in the range of 40-50wt%, avoiding the phenomenon of particle agglomeration and cracking, and ensuring the structural stability and electrochemical performance of the material. At the same time, a thin carbon layer (specific surface area of 30-50m2) can be formed on the surface of the silicon-carbon core material obtained in step (2) very conveniently using a fluidized bed. 2 / g), thereby isolating the active sites on the silicon surface from being oxidized.

[0031] Furthermore, in a preferred embodiment, in step (3), the flow ratio of acetylene to carrier gas is 1:2-3, the coating temperature is 560-580°C, and the coating time is 4-6h.

[0032] By adopting the above technical solution, by controlling the flow ratio of acetylene to carrier gas, temperature and processing time, a dense and uniform carbon layer (specific surface area ≤ 5m2) is coated on the surface of the thin carbon layer using rotary kiln chemical vapor deposition technology. 2 / g), and finally formed a gradient double-layer carbon protective layer with a dense outer layer and a loose inner layer, which further suppressed the volume effect and reduced the interface side reaction.

[0033] In a second aspect, the present application provides a high-capacity silicon-carbon negative electrode material prepared by the above-mentioned preparation process, wherein the reversible capacity of the silicon-carbon negative electrode material is ≥2000mAh / g.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. By using biomass activated carbon with a total pore volume of 1.0-1.3 cm³ / g and a compressive strength greater than 20 MPa as the matrix, the mechanical stability and cyclic stability of the material are improved. At the same time, the porous activated carbon with large pore volume provides ample deposition space for silicon nanoparticles, effectively improving the reversible capacity of the material and significantly suppressing the volume expansion of silicon during the cycle.

[0036] 2. Silicon nanoparticles are deposited within the pores and on the surface of the porous carbon matrix using a fluidized bed chemical vapor deposition process. A double carbon coating process forms a protective layer, effectively alleviating the cracking problem of the single-layer carbon coating. The thin inner carbon layer prevents oxidation of the silicon-carbon material in the inner core during fluidized bed transfer. The outer carbon coating enhances the isolation effect of the electrolyte, further enhancing the material's conductivity and structural stability. It also reduces direct contact between silicon and the electrolyte, improving the material's cycle life and overall performance.

[0037] 3. In a preferred embodiment, by optimizing the preparation process of biomass activated carbon, and on the premise that the mechanical strength of the activated carbon can meet the requirements of the fluidized bed process and the overall mechanical stability of the material, the multi-level pore structure design is used to increase the proportion of micropore volume to more than 60%, further enhancing the loading capacity of silicon nanoparticles, effectively suppressing the negative impact of volume expansion, and improving the reversible capacity of the material. DETAILED DESCRIPTION

[0038] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0039] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0040] For ease of recording, the following rules are used to name the prepared samples:

[0041] D2-Ⅰ 1 / 1 II 1 / 1 -(tn)-Tm

[0042] Wherein: D2 refers to the raw material being coconut shell; I refers to the activator being KOH, II refers to the activator being NaOH, and the subscript refers to the alkali-carbon ratio; t refers to the curing temperature, n refers to the curing time; T refers to the activation temperature, and m refers to the activation time.

[0043] Preparation Example 1

[0044] This preparation example provides a method for preparing biomass activated carbon, including:

[0045] Coconut shells were used as raw materials, acid-washed and washed to neutrality, dried and heat-treated at 300°C for 1h for pre-oxidation, and then air-flow crushed to D50=150μm to obtain biomass raw materials;

[0046] The biomass raw materials were put into a rotary kiln for heat treatment. The temperature of the rotary kiln was raised to 200°C at a rate of 5°C / min and kept warm for 30 minutes; then the temperature was raised to 400°C at a rate of 5°C / min and kept warm for 30 minutes; finally, the temperature was raised to 650°C at a rate of 5°C / min and kept warm for 2 hours. The whole process was protected by nitrogen (flow rate of 40L / min) and the rotation speed was 25Hz to obtain carbonized material.

[0047] The carbonized material was mixed with the inorganic base KOH at an alkali-carbon ratio of 2: 1. During the mixing process, the inorganic base was added to the carbonized material in three batches, with each batch being mixed for 20 minutes to obtain a mixed material.

[0048] The mixed material was placed in a tubular activation furnace and heat treated at 800°C for 60 minutes to obtain an activated material;

[0049] The activated material was crushed, soaked in acid solution (0.5M HCl) overnight, washed with water to neutralize, dried, and air flow crushed to D50 = 15μm to obtain biomass activated carbon, which was recorded as D2-Ⅰ 2 / 1 -800-60.

[0050] Preparation Example 2

[0051] The difference between this preparation example and preparation example 1 is that the inorganic bases are KOH and NaOH, the alkali-carbon ratio is KOH:NaOH:carbonized material = 1:1.5:1; the activation temperature is 850°C and the treatment time is 60 min. The obtained activated carbon is designated as D2-I 1 / 1 Ⅱ 1.5 / 1 -850-60.

[0052] Preparation Example 3

[0053] The difference between this preparation example and preparation example 1 is that the mixing step (1) is: the inorganic base is KOH and NaOH, and the alkali-carbon ratio is KOH:NaOH:carbonized material = 1:1.5:1. The activation temperature is 800℃ and the treatment time is 60min. The obtained activated carbon is recorded as D2-Ⅰ 1 / 1 Ⅱ 1.5 / 1 -800-60.

[0054] Preparation Example 4

[0055] The difference between this preparation example and Preparation Example 1 is that the inorganic base is KOH, and the alkali-carbon ratio is KOH:carbonized material = 2.5:1. The activation step is as follows: the mixed material is placed in a tubular activation furnace and heat-treated at 500°C for 2 hours to solidify; then heat-treated at 800°C for 50 minutes to activate. The resulting activated carbon is designated D2-I 2.5 / 1 -500-120-800-50.

[0056] Preparation Example 5

[0057] The difference between this preparation example and Preparation Example 1 is that the inorganic base is KOH, the alkali-carbon ratio is KOH:carbonized material = 2.5:1, and a 10 vol% ethanol solution is added as a dispersant (the mass ratio of dispersant to carbonized material is 0.05:1). The activation step is as follows: the mixed material is placed in a tubular activation furnace and heat treated at 500°C for 2 hours for curing; then heat treated at 800°C for 50 minutes for activation. The resulting activated carbon is designated D2-I. 2.5 / 1、0.05 / 1 -500-120-800-50.

[0058] Preparation Example 6

[0059] The difference between this preparation example and Preparation Example 1 is that the inorganic base is KOH, and the alkali-carbon ratio is KOH:carbonized material = 2.5:1. The activation step is as follows: the mixed material is placed in a tubular activation furnace and heat-treated at 500°C for 2 hours to solidify; then heat-treated at 800°C for 50 minutes to activate. The resulting activated carbon is designated D2-I 2.5 / 1 -500-120-800-50.

[0060] Comparative Preparation Example 1

[0061] The difference between this preparation example and preparation example 1 is that the inorganic base is KOH, the alkali-carbon ratio is KOH: carbonized material = 1.5:1, and the activation step is: activation temperature is 850, and treatment time is 90 minutes. The obtained activated carbon is recorded as D2-I 1.5 / 1 -850-90.

[0062] Comparative Preparation Example 2

[0063] The difference between this preparation example and preparation example 1 is that the inorganic base is KOH and NaOH, the alkali carbon ratio is KOH:NaOH:carbonized material = 1:1:1.5, and the activation step is: activation temperature is 800, and treatment time is 60min. The obtained activated carbon is recorded as D2-I 1 / 1.5 Ⅱ 1 / 1.5 -800-60.

[0064] Comparative Preparation Example 3

[0065] The difference between this preparation example and preparation example 1 is that the inorganic base is KOH and NaOH, the alkali carbon ratio is KOH:NaOH:carbonized material = 1:1.5:1, and the activation step is: activation temperature is 750, and treatment time is 90min. The obtained activated carbon is recorded as D2-I 1 / 1 Ⅱ 1.5 / 1 -750-90.

[0066] Comparative Preparation Example 4

[0067] The difference between this preparation example and Preparation Example 1 is that the inorganic base is KOH, and the alkali-carbon ratio is KOH:carbonized material = 1.5:1. The activation step is as follows: the mixed material is placed in a tubular activation furnace and heat-treated at 500°C for 60 minutes for curing; then heat-treated at 850°C for 50 minutes for activation. The resulting activated carbon is designated D2-I 1.5 / 1 -500-60-850-50.

[0068] Comparative Preparation Example 5

[0069] The difference between this preparation example and Preparation Example 1 is that the inorganic base is KOH, and the alkali-carbon ratio is KOH:carbonized material = 1.8:1. The activation steps are as follows: the mixed material is placed in a tubular activation furnace and heat treated at 750°C for 40 minutes; then heat treated at 850°C for 50 minutes to activate. The resulting activated carbon is designated D2-I 1.8 / 1 -750-40-850-50.

[0070] The performance index of the activated carbon sample provided in the above preparation example was tested and compared with commercially available activated carbon. The specific testing method is as follows:

[0071] Specific surface area: physical adsorption and desorption test (BET)

[0072] Pore volume: physical adsorption-desorption test (BET)

[0073] Average pore size: physical adsorption-desorption test (BET)

[0074] Mechanical strength: particle crusher.

[0075] The results are shown in Table 1:

[0076] Table 1.

[0077]

[0078] As can be seen from Table 1, in the preparation process of biomass activated carbon, the alkali-carbon ratio, curing temperature / time parameters, and activation temperature / time parameters will affect the pore volume and mechanical strength of biomass activated carbon. When the alkali-carbon ratio is 2-2.5:1, curing can be omitted and the activation process can be carried out directly. And when the inorganic base is KOH and NaOH (the ratio of the two is 1:1.5), the pore volume of the activated carbon obtained is the largest (1.3 cm 3 / g), while still maintaining a mechanical strength of 23 MPa, achieving optimal pore volume / strength parameters (see Preparation Example 2). When the alkali-to-carbon ratio is 1.5-1.8:1, activated carbon with optimal pore volume / strength parameters must be cured at a specific temperature and for a certain period of time (see Preparation Example 6 and Comparative Examples 1, 4, and 5). Furthermore, even with the same carbon-to-carbon ratio, the curing temperature and time parameters can further affect the properties of the activated carbon.

[0079] Example 1

[0080] This embodiment provides a high-capacity silicon-carbon negative electrode material, and the preparation method thereof includes:

[0081] The biomass activated carbon (D2-Ⅰ 2 / 1 -800-1) as a matrix;

[0082] A chemical vapor deposition process was carried out using a vertical fluidized bed with a diameter of Φ500 mm and a height-to-diameter ratio of 1:4. Silane was used as the silicon source, nitrogen was used as the carrier gas, the flow ratio was 1:7, the temperature was controlled at 450°C, and the air intake time was 7 hours to obtain a silicon-carbon core material.

[0083] The chemical vapor deposition process was continued in the vertical fluidized bed, with acetylene as the carbon source and nitrogen as the carrier gas, the flow ratio was 1:6, the temperature was controlled at 590 ° C, the coating time was 5 h, and the coating was cooled at a rate of 8 ° C / min under nitrogen protection to form a thin carbon layer (specific surface area of 41 m 2 / g);

[0084] The silicon-carbon core material with a thin carbon layer was guided out of the fluidized bed and placed in a rotary furnace. Acetylene was used as the carbon source and nitrogen was used as the carrier gas with a volume ratio of 1:2.5. The temperature was controlled at 570°C and the coating time was 5 h. Carbon coating was performed again on the surface of the thin carbon layer and cooled at a rate of 8°C / min under nitrogen protection to obtain a silicon-carbon composite negative electrode material (specific surface area of 3.2 m 2 / g).

[0085] Examples 2-6

[0086] The difference between this group of embodiments and embodiment 1 is that:

[0087] The biomass activated carbon provided in Preparation Example 2-6 was used as the matrix.

[0088] Comparative Examples 1-5

[0089] The difference between this comparative example and Example 1 is that:

[0090] The activated carbon provided in Comparative Preparation Examples 1-5 was used as the matrix.

[0091] Comparative Example 6

[0092] The difference between this comparative example and Example 1 is that only a vertical fluidized bed is used for primary carbon coating, and no secondary carbon coating is performed. The specific parameters are:

[0093] In a vertical fluidized bed, acetylene was used as the carbon source, nitrogen was used as the carrier gas, the flow ratio was 1:6, the temperature was controlled at 590°C, the coating time was 10h, and the cooling rate was 8°C / min.

[0094] Comparative Example 7

[0095] The difference between this comparative example and Example 1 is that during the preparation of the silicon-carbon core material, silane is used as the silicon source, nitrogen is used as the carrier gas, the flow ratio is 1:4, the temperature is controlled at 450° C., and the air intake time is 8 hours.

[0096] The various performance parameters of the silicon-carbon negative electrode materials obtained in the above examples and comparative examples were measured, and commercially available activated carbon was used as a control. The measurement method is as follows:

[0097] Reversible capacity: The battery test system is charged and discharged cycled to calculate the amount of lithium embedded per unit mass of material.

[0098] Initial efficiency: The battery test system is charged and discharged for the first time, and the ratio of discharge capacity to charge capacity is calculated.

[0099] The results are shown in Table 2:

[0100] Table 2.

[0101]

[0102] As shown in Table 2, the reversible capacity of the silicon-carbon anode materials provided by Examples 1-6 is significantly higher than that of commercially available activated carbon and Comparative Examples 1-5. This is primarily because the substrates of Examples 1-6 are biomass activated carbons with larger pore volumes, providing more space for silicon deposition. Furthermore, this ensures a relatively high initial efficiency.

[0103] Compared with Comparative Examples 6 and 7, Example 1 shows that the flow rate ratio in the secondary coating and silicon-carbon deposition process is helpful to improve the reversible capacity of the silicon-carbon negative electrode material.

[0104] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A process for preparing a high-capacity silicon-carbon negative electrode material, characterized in that: It includes: (1) Preparation of total pore volume of 1.0-1.3cm 3 / g, biomass activated carbon with a compressive strength of 20-40Mpa; (2) placing the biomass activated carbon into a fluidized bed, using a fluidized bed chemical vapor deposition process, using silane as a silicon source, depositing silicon nanoparticles in the pores and on the surface of the biomass activated carbon to obtain a silicon-carbon core material; then using acetylene as a carbon source, depositing a thin carbon layer on the surface of the silicon-carbon core material; (3) The silicon-carbon core material with a thin carbon layer is guided out of the fluidized bed, and acetylene is used as a carbon source, and a rotary kiln is used for secondary carbon coating to form a silicon-carbon negative electrode material; The preparation method of the biomass activated carbon comprises: Select hard-shelled plant raw materials and pre-treat them to obtain biomass raw materials; The biomass raw material is heat-treated in a carbonization furnace for 1.5-2.5 hours to obtain a carbonized material; the heat treatment process is a programmed temperature process, comprising: heating the carbonization furnace to 200° C. at a rate of 4-6° C. / min, holding the temperature for 20-40 minutes; then heating the carbonization furnace to 380-420° C. at a rate of 4-6° C. / min, holding the temperature for 20-40 minutes; and finally heating the carbonization furnace to 600-650° C. at a rate of 4-6° C. / min, holding the temperature for 1.5-2.5 hours; The carbonized material is mixed with an inorganic base at an alkali-carbon ratio of 1.5-2.5:1, the mixture is placed in an activation furnace, heat-treated at 450-550° C. for 1.5-2.5 hours for curing, and then activated at 800-850° C. for 0.8-2 hours to obtain an activated material; The activated material is crushed, acid-washed, filtered, and air-flow-pulverized to obtain biomass activated carbon.

2. The preparation process of the high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The specific surface area of the biomass activated carbon is ≥2150m 2 / g, the micropore volume accounts for more than 62%, and the mesopore volume accounts for less than 38%.

3. The preparation process of the high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: After the carbonized material is mixed with an inorganic base to obtain a mixed material, the method further comprises: adding 8-15 vol% ethanol solution as a dispersant into the mixed material.

4. The process for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, wherein: In the step (2), the flow ratio of silane to carrier gas is 1:7-8, the temperature is 440-460°C, and the treatment time is 7-8h; the flow ratio of acetylene to carrier gas is 1:6-7, the coating temperature is 580-600°C, and the coating time is 5-6h.

5. The process for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, wherein: In the step (3), the flow ratio of acetylene to carrier gas is 1:2-3, the coating temperature is 560-580° C., and the coating time is 4-6 hours.

6. A high-capacity silicon-carbon negative electrode material prepared by the preparation process according to any one of claims 1 to 5, characterized in that: The reversible capacity of the silicon-carbon negative electrode material is ≥2000 mAh / g.

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