Biomass-based silicon-carbon negative electrode material and preparation method thereof

Abstract

The application discloses a biomass-based silicon-carbon negative electrode material and a preparation method thereof, and comprises the following steps: S1, placing porous biomass carbon powder in a reaction furnace, and introducing a silicon source gas and an inert gas to perform high-temperature calcination at 450 DEG C to 700 DEG C for 2 to 8 hours to obtain silicon-carbon powder; S2, mixing the silicon-carbon powder with a phenolic resin precursor solution, and then performing heating and stirring polymerization, and then performing solid-liquid separation, and then sintering the obtained solid material at 600 DEG C to 800 DEG C under an inert atmosphere for 4 to 6 hours, so that the silicon-carbon negative electrode material is obtained. The silicon-carbon negative electrode material disclosed by the application takes biomass as a raw material, has low cost, and has excellent specific capacity and cycle stability.

Description

Technical Field

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

[0002] Currently, with the increasing popularity of electric vehicles, the demand for high-energy-density lithium-ion batteries is growing. Silicon materials are highly anticipated due to their high theoretical capacity (>4000mAh / g) and low lithium intercalation potential (<0.4V). During lithium intercalation and deintercalation, silicon materials undergo a volume change exceeding 400%, causing them to pulverize and detach, forming a large amount of SEI film. Therefore, the cycle stability of silicon anodes is poor. Amorphous silicon obtained through silane deposition has a smaller volume change compared to crystalline silicon, which is more conducive to electrochemical performance. However, most carbon matrices used for silane deposition on the market are porous carbon materials prepared from organic polymers. The preparation method of porous carbon obtained in this way is complex and costly, hindering the widespread application of silicon-carbon materials. Moreover, current silicon-carbon materials are generally synthesized using high-temperature methods, resulting in larger silicon grains, which is detrimental to battery cycle performance. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a biomass-based silicon-carbon anode material and its preparation method.

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

[0005] S1. The porous biomass carbon powder is placed in a reactor, and silicon source gas is introduced under an inert atmosphere. The mixture is then calcined at 450℃~700℃ for 2~8h to obtain silicon carbon powder.

[0006] The method for preparing the porous biochar powder includes: heating the biomass raw material in an oxidant solution under acidic conditions to obtain a biomass precursor; mixing and ball-milling the biomass precursor with an activator, and then calcining it at a high temperature of 700℃~900℃ for 1~8h under an inert atmosphere to obtain the product.

[0007] S2. The silicon carbon powder is mixed with the phenolic resin precursor solution and then heated and stirred to polymerize. Then, the solid and liquid are separated, and the resulting solid material is sintered at 600℃~800℃ for 4~6h under an inert atmosphere to obtain the final product.

[0008] In the preparation method of biomass-based silicon-carbon anode material proposed in this invention, the biomass is first boiled in an oxidizing solution under acidic conditions to selectively remove lignin and hemicellulose components from the biomass raw material. This process increases the specific surface area of ​​the raw material and makes the biomass skeleton clearer, which is beneficial for further activation and subsequent carbon skeleton establishment.

[0009] Subsequently, the raw materials are activated by carbonization using alkali or salt activators. During this step, the alkali / salt reacts with the carbon matrix to create pores and generates a large amount of gas, which facilitates the increase of pore size. Simultaneously, metal ions enter the carbon matrix, expanding the interlayer spacing of the carbon crystals, which is beneficial for the entry of the activator and the reaction. After calcination, washing, and drying, a porous carbon matrix with a large specific surface area and abundant pores is obtained. Biomass carbon materials treated in this way have an increased specific surface area and more surface functional groups, which is conducive to the wetting of the activator and further etching of the carbon material. This makes the pore-forming process more complete and uniform, resulting in porous carbon with a larger pore volume, narrower pore size range, and more uniform pore distribution. This type of porous carbon is easily decomposed by silane gas during deposition, resulting in a material with uniformly distributed nano-silicon in the carbon matrix, which helps to mitigate the volume expansion of the material during charging and discharging.

[0010] Subsequently, a large amount of nano-silicon was deposited on a porous carbon matrix by cracking using silicon source gas. Due to the rich specific surface area and pore size confinement effect of porous carbon, it is equivalent to putting these nano-silicon in cages, which restricts the growth of nano-silicon crystals, thus forming nano-silicon with smaller grains, and obtaining silicon-carbon material in which nano-silicon is confined between the porous carbon framework and uniformly distributed.

[0011] Finally, phenolic resin is used to carbon-coat the silicon-carbon material, modifying the porous surface, reducing the specific surface area, improving the electrical conductivity, protecting the internal nanostructure, reducing contact with the electrolyte, improving processing performance, and enhancing the slurry stability of the material.

[0012] Preferably, in the method for preparing porous biochar powder, the preparation step of the biomass precursor is as follows: heating the oxidant solution to a certain temperature, then adding biomass raw materials, then adding acetic acid dropwise, and continuing the heating treatment to obtain the biomass precursor.

[0013] Preferably, the oxidant solution is heated to 60–100°C.

[0014] Preferably, the volume of acetic acid added is 1% to 3% of the volume of the oxidant solution.

[0015] Preferably, in the method for preparing porous biochar powder, the mass ratio of biomass raw material to oxidant is 200-500:100-500; the concentration of the oxidant solution is 10-200 g / L. By controlling the amount and concentration of oxidant used in the selective oxidation pretreatment of biomass in the method for preparing porous biochar powder, it is beneficial to fully activate the carbon skeleton and further improve the uniformity of porous carbon pore size, thereby more effectively improving the recycling performance of silicon-carbon materials.

[0016] Preferably, the biomass raw material is at least one of coconut shell, peanut shell, wheat straw, rice husk, rice straw, reed leaves, and corn leaves.

[0017] Preferably, the oxidant is at least one selected from hydrogen peroxide, perchloric acid, sodium chlorate, and sodium hypochlorite.

[0018] Preferably, the solvent of the oxidant solution is water.

[0019] Preferably, in the method for preparing porous biomass char powder, the heating treatment under acidic conditions is carried out at a temperature of 60–100°C for 8–12 hours. By controlling the conditions for selective oxidation pretreatment of biomass in the preparation method of porous biomass char powder, it is beneficial to fully activate the carbon skeleton and further improve the uniformity of porous carbon pore size, thereby more effectively improving the recycling performance of silicon-carbon materials.

[0020] In the preparation of biomass precursors, after heat treatment, conventional follow-up processing steps such as cooling, washing, and drying are also included.

[0021] Preferably, in the method for preparing porous biomass char powder, the mass ratio of biomass precursor to activator is 1:1 to 1:6. By controlling the mass ratio of biomass precursor to activator, the degree of reaction between the carbon skeleton and the activator can be controlled, resulting in porous carbon with different specific surface areas and pore volumes, thus affecting the amount of silicon deposition and achieving the purpose of regulating the capacity and first coulombic efficiency of silicon-carbon materials.

[0022] Preferably, the activator is at least one selected from potassium hydroxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and zinc chloride.

[0023] In the preparation method of porous biochar powder, after high-temperature calcination, conventional subsequent processing steps such as acid washing, water washing, and drying are also included.

[0024] Preferably, in S1, the silicon source gas is at least one of silicon tetrafluoride, silicon tetrachloride, trichlorosilane, dichlorosilane, and ethylsilane.

[0025] In this invention, an inert atmosphere refers to an atmosphere formed by an inert gas, which is a non-reactive gas that does not participate in the reaction, preferably nitrogen, argon, or a combination thereof.

[0026] Preferably, in step S2, the heating and stirring polymerization conditions are: stirring polymerization at 60℃~100℃ for 8~12h. By controlling the reaction conditions of heating and stirring polymerization in step S2, a denser and more complete silicon carbide material surface coating layer can be obtained, further improving the material's electrical conductivity and cycle stability.

[0027] Preferably, the phenolic resin precursor solution is obtained by dissolving phenols and aldehydes in a mixed solvent of an aqueous acid solution and ethanol; the phenols are at least one selected from phenol, resorcinol, m-cresol, and xylenol; the aldehydes are at least one selected from formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde; the molar ratio of the phenols to the aldehydes is 1:2 to 2:1; the volume ratio of the aqueous acid solution to ethanol is 1:3 to 3:1; the aqueous acid solution is an aqueous solution of at least one selected from hydrochloric acid, oxalic acid, phosphoric acid, and sulfuric acid, with a concentration of 0.5 mol / L to 3 mol / L.

[0028] Preferably, the specific surface area of ​​the porous biochar powder is 1000 cm². 2 / g~3500cm 2 / g. Controlling the specific surface area of ​​porous biochar powder within a suitable range provides a volume space that is more suitable for the deposition of nano-silicon and provides sufficient volume expansion space for silicon during charge-discharge cycles, which is beneficial for further improving the cycling performance of the material.

[0029] A biomass-based silicon-carbon anode material is prepared by the method described above.

[0030] Preferably, in the biomass-based silicon-carbon anode material, silicon accounts for 30% to 60% of the total mass of the material. By controlling the silicon content, i.e., the silicon-to-carbon ratio, in the biomass-based silicon-carbon anode material, silicon-carbon materials suitable for different specific surface areas and pore volumes can be obtained, thereby achieving the purpose of adjusting and controlling the capacity and initial coulombic efficiency of the silicon-carbon material.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention uses biomass carbon as a porous carbon raw material, which is activated after selective oxidation treatment to obtain carbon materials with rich pore sizes. The specific surface area of ​​the carbon materials can reach 1000 cm². 2 / g~3500cm 2 The silicon-carbon anode is obtained by depositing silicon nanoparticles within a porous carbon matrix, forming a uniformly distributed silicon-carbon material, and then carbonizing it with phenolic resin. This method yields a silicon-carbon anode material with low cost, uniform silicon distribution within the carbon matrix without silicon crystal formation, and excellent specific capacity and cycle stability, achieving a capacity of 1400 mAh / g to 1600 mAh / g at 0.8V. Attached Figure Description

[0033] Figure 1 This is a SEM image of the biomass-based silicon-carbon anode material prepared in Example 2 of the present invention.

[0034] Figure 2 The image shows the XRD pattern of the biomass-based silicon-carbon anode material prepared in Example 2 of this invention. Detailed Implementation

[0035] The technical solution of the present invention will now be described in detail through specific embodiments.

[0036] Example 1

[0037] Preparation of biomass-based silicon-carbon anode materials:

[0038] S1. The porous biochar powder is placed in a rotary kiln and purged with argon gas for 1 hour. Then, the temperature is increased to 600°C at a heating rate of 2°C / min. Ethylsilane is introduced and kept at the temperature for 6 hours. After cooling, silicon carbon powder is obtained.

[0039] The preparation method of porous biomass char powder is as follows: 500g of sodium hypochlorite is dissolved in 3L of water and heated to 100℃. 500g of wheat straw is added, and then 50mL of acetic acid is added dropwise. The mixture is heated at 100℃ for 12h. After cooling, it is washed with water and dried to obtain a biomass precursor. Potassium hydroxide and potassium carbonate are mixed in a mass ratio of 1:1 to obtain an activator. 1500g of the activator is mixed with 300g of the biomass precursor and ground for 10h. The mixture is then transferred to an argon atmosphere and calcined at 900℃ for 8h. After washing with hydrochloric acid, water, and drying, a specific surface area of ​​3000cm² is obtained. 2 / g~3300cm 2 / g porous biochar powder;

[0040] S2. After mixing silicon carbon powder with phenolic resin precursor solution, stir and polymerize at 80°C for 12 hours, collect the precipitate, transfer it to a tube furnace and calcine at 800°C for 4 hours under argon conditions to obtain biomass-based silicon carbon anode material.

[0041] The phenolic resin precursor solution is obtained by dissolving phenol and formaldehyde in a mixed solvent at a molar ratio of 6:7. The mixed solvent is composed of a 1M hydrochloric acid aqueous solution and ethanol at a volume ratio of 1:1.

[0042] In the biomass-based silicon-carbon anode material obtained above, silicon accounts for 60% of the total mass of the material.

[0043] The obtained biomass-based 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 voltage ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1750.2 mAh / g, with an initial efficiency of 83.0%.

[0044] The obtained biomass-based silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 85.5%, and the capacity retention rate was 87.3% after 600 cycles of the full battery.

[0045] Example 2

[0046] Preparation of biomass-based silicon-carbon anode materials:

[0047] S1. The porous biochar powder is placed in a rotary kiln and purged with argon gas for 1 hour. Then, the temperature is increased to 550°C at a heating rate of 5°C / min. Silicate is introduced and kept at the temperature for 4 hours. After cooling, silicon carbon powder is obtained.

[0048] The preparation method of porous biomass char powder is as follows: 200g of hydrogen peroxide is dissolved in 2L of water and heated to 100℃. 100g of rice husks are added, and then 20mL of acetic acid is added dropwise. The mixture is heated at 100℃ for 12h. After cooling, it is washed with water and dried to obtain a biomass precursor. 100g of sodium hydroxide and 50g of the biomass precursor are mixed and ground for 10h. The mixture is then transferred to an argon atmosphere and calcined at 700℃ for 4h. After washing with hydrochloric acid, water, and drying, a specific surface area of ​​2000cm² is obtained. 2 / g~2500cm 2 / g porous biochar powder;

[0049] S2. After mixing silicon carbon powder with phenolic resin precursor solution, stir and polymerize at 80°C for 12 hours, collect the precipitate, transfer it to a tube furnace and calcine at 700°C for 4 hours under argon conditions to obtain biomass-based silicon carbon anode material.

[0050] The phenolic resin precursor solution is obtained by dissolving resorcinol and acetaldehyde in a 1:1 molar ratio in a mixed solvent, which consists of a 2M oxalic acid aqueous solution and ethanol in a 1:2 volume ratio.

[0051] In the biomass-based silicon-carbon anode material obtained above, silicon accounts for 53% of the total mass of the material.

[0052] The obtained biomass-based 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 sheet could reach 1625.6 mAh / g, with an initial efficiency of 81.9%.

[0053] The obtained biomass-based silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 84.9%, and the capacity retention rate was 92.1% after 500 cycles of the entire battery.

[0054] Example 3

[0055] Preparation of biomass-based silicon-carbon anode materials:

[0056] S1. The porous biochar powder is placed in a rotary kiln and purged with argon gas for 1 hour. Then, the temperature is increased to 500°C at a heating rate of 3°C / min. Tetrafluorosilane is introduced and kept at this temperature for 3 hours. After cooling, silicon carbon powder is obtained.

[0057] The preparation method of porous biochar powder is as follows: 200g of sodium chlorate is dissolved in 3L of water and heated to 100℃. 200g of corn leaves are added, and then 30mL of acetic acid is added dropwise. The mixture is heated at 100℃ for 12h. After cooling, it is washed with water and dried to obtain a biomass precursor. 100g of potassium hydroxide is mixed with 100g of the biomass precursor and ground for 10h. The mixture is then transferred to an argon atmosphere and calcined at 800℃ for 4h. After washing with hydrochloric acid, water, and drying, a specific surface area of ​​1500cm² is obtained. 2 / g~1700cm 2 / g porous biochar powder;

[0058] S2. After mixing silicon carbon powder with phenolic resin precursor solution, stir and polymerize at 60°C for 12 hours, collect the precipitate, transfer it to a tube furnace and calcine at 800°C for 4 hours under argon conditions to obtain biomass-based silicon carbon anode material.

[0059] The phenolic resin precursor solution is obtained by dissolving m-cresol and formaldehyde in a mixed solvent at a molar ratio of 1:2. The mixed solvent consists of a 2M aqueous solution of phosphoric acid and ethanol at a volume ratio of 1:2.

[0060] In the biomass-based silicon-carbon anode material obtained above, silicon accounts for 47% of the total mass of the material.

[0061] The obtained biomass-based 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 voltage ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1613.9 mAh / g, with an initial efficiency of 80.2%.

[0062] The obtained biomass-based silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 84.2%, and the capacity retention rate was 89.2% after 500 cycles of the full battery.

[0063] Comparative Example 1

[0064] Preparation of silicon-carbon anode materials:

[0065] S1. Commercially available porous carbon powder (specific surface area 2053 cm²) 2 / g) was placed in a rotary furnace, argon gas was introduced for purging for 1 hour, and then the temperature was increased to 550°C at a heating rate of 5°C / min. Siloam was introduced and kept at the temperature for 4 hours. After cooling, silicon carbon powder was obtained.

[0066] S2. After mixing silicon carbon powder with phenolic resin precursor solution, stir and polymerize at 80°C for 12 hours, collect the precipitate, transfer it to a tube furnace and calcine at 700°C for 4 hours under argon conditions to obtain biomass-based silicon carbon anode material.

[0067] The phenolic resin precursor solution is obtained by dissolving resorcinol and acetaldehyde in a 1:1 molar ratio in a mixed solvent, which consists of a 2M oxalic acid aqueous solution and ethanol in a 1:2 volume ratio.

[0068] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rate was 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage was 0.005–0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1590.1 mAh / g, and the initial efficiency was 79.8%. Therefore, compared with Example 2, Comparative Example 1 shows that the half-cell composed of silicon-carbon material obtained by silane deposition using porous biomass carbon prepared in Example 2 as the matrix has higher capacity and initial efficiency. This is because the porous biomass carbon material obtained in this invention has a narrower pore size range, which is more conducive to silicon deposition, resulting in a higher silicon deposition amount. Furthermore, the nano-silicon integrates better with the carbon matrix, which is beneficial for performance.

[0069] The obtained silicon-carbon anode material was uniformly mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the cathode, a 7Ah soft-pack battery was assembled through processes including slurry preparation, coating, rolling, slitting, die-cutting, stacking, tab welding, top-side sealing, baking, and electrolyte injection. After capacity testing, a room-temperature cycle test was conducted at a 1C / 1C current density. The initial cell efficiency was 83.1%, and after 500 cycles, the capacity retention was 86.5%. Therefore, compared to Example 2, the silicon-carbon material obtained by silane deposition using biomass carbon as the matrix in Example 2 has a higher initial cell efficiency and better full-cell cycle performance. This is because the porous biomass carbon material obtained in this invention has a more uniform pore distribution, resulting in a more uniform distribution of nano-silicon in the carbon matrix. This is more conducive to mitigating volume expansion during silicon lithium intercalation, thus leading to better cycle performance.

[0070] Comparative Example 2

[0071] Preparation of biomass-based silicon-carbon anode materials:

[0072] S1. The porous biochar powder is placed in a rotary kiln and purged with argon gas for 1 hour. Then, the temperature is increased to 550°C at a heating rate of 5°C / min. Siloam is introduced and kept at the temperature for 4 hours. After cooling, silicon-carbon material is obtained.

[0073] The preparation method of porous biomass char powder is as follows: 100g of sodium hydroxide and 50g of rice husk are mixed and ground for 10 hours, then transferred to an argon atmosphere and calcined at 700℃ for 4 hours. The powder is then washed with hydrochloric acid, water, and dried to obtain a specific surface area of ​​1200 cm². 2 / g~1500cm 2 / g porous biochar powder;

[0074] S2. After mixing silicon carbon material with phenolic resin precursor solution, stir and polymerize at 80°C for 12 hours, collect the precipitate, transfer it to a tube furnace and calcine at 700°C for 4 hours under argon conditions to obtain biomass-based silicon carbon anode material.

[0075] The phenolic resin precursor solution is obtained by dissolving resorcinol and acetaldehyde in a 1:1 molar ratio in a mixed solvent, which consists of a 2M oxalic acid aqueous solution and ethanol in a 1:2 volume ratio.

[0076] The obtained biomass-based silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rate was 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage was 0.005–0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1537.5 mAh / g, and the initial efficiency was 79.2%. Therefore, compared with Example 2, Comparative Example 2 shows that the half-cell composed of silicon-carbon material obtained by selectively oxidizing and activating biomass in Example 2 as a matrix and then depositing it with silane has higher capacity and initial efficiency. This is because the porous biomass carbon prepared by selectively oxidizing and activating biomass in this invention has a larger specific surface area and a narrower pore size range, which is more conducive to performance.

[0077] The obtained biomass-based silicon-carbon anode material was uniformly mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled through processes including slurry preparation, coating, rolling, slitting, die-cutting, stacking, tab welding, top-side sealing, baking, and electrolyte injection. After capacity testing, a room-temperature cycle test was conducted at a 1C / 1C current density. The initial cell efficiency was 82.8%, and after 500 cycles, the capacity retention was 87.5%. Therefore, compared to Example 2, Comparative Example 2, using the porous biomass carbon prepared by selective oxidation and activation treatment of biomass in Example 2 as the matrix for silane deposition, resulted in a higher initial cell efficiency and better full-cell cycle performance. This is because the porous biomass carbon material obtained in this invention has a larger specific surface area and a more uniform pore distribution. Therefore, the nano-silicon in the silicon-carbon material obtained in this invention is more uniformly distributed in the carbon matrix, which is more conducive to mitigating volume expansion during silicon lithium intercalation, thus resulting in better cycle performance.

[0078] Comparative Example 3

[0079] Preparation of biomass-based silicon-carbon anode materials:

[0080] Porous biomass carbon powder was placed in a rotary furnace and purged with argon gas for 1 hour. Then, the temperature was increased to 550°C at a heating rate of 5°C / min. Siloam was introduced and kept at this temperature for 4 hours. After cooling, silicon-carbon anode material was obtained.

[0081] The preparation method of porous biomass char powder is as follows: 200g of hydrogen peroxide is dissolved in 2L of water and heated to 100℃. 100g of rice husks are added, and then 20mL of acetic acid is added dropwise. The mixture is heated at 100℃ for 12h. After cooling, it is washed with water and dried to obtain a biomass precursor. 100g of sodium hydroxide and 50g of the biomass precursor are mixed and ground for 10h. The mixture is then transferred to an argon atmosphere and calcined at 700℃ for 4h. After washing with hydrochloric acid, water, and drying, a specific surface area of ​​2000cm² is obtained. 2 / g~2500cm 2 / g porous biochar powder.

[0082] The obtained biomass-based silicon-carbon anode material and lithium metal were used to compose a half-cell for electrochemical performance testing. The test rate was 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage was 0.005–0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1613.5 mAh / g, and the initial efficiency was 77.6%. Therefore, compared with Example 2, Comparative Example 3 shows that the half-cell composed of silicon-carbon material coated with phenolic resin carbon in Example 2 has higher capacity and initial efficiency. This is because coating with phenolic resin carbon can modify the porous surface, reduce side reactions, and improve conductivity.

[0083] The obtained biomass-based silicon-carbon anode material was uniformly mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled through processes including slurry preparation, coating, rolling, slitting, die-cutting, stacking, tab welding, top-side sealing, baking, and electrolyte injection. After capacity testing, a room-temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 81.7%, and after 500 cycles, the capacity retention rate was 82.3%. Therefore, compared to Example 2, Comparative Example 3, using the silicon-carbon material coated with phenolic resin carbon in Example 2, exhibits higher initial efficiency and better full-cell cycle performance. This is because coating with phenolic resin carbon can modify the porous surface, improve conductivity, protect the internal nanostructure, and reduce contact with the electrolyte.

[0084] 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 biomass-based silicon-carbon anode material, characterized in that, Includes the following steps: S1. The porous biomass carbon powder is placed in a reactor, and silicon source gas is introduced under an inert atmosphere. The mixture is then calcined at 450℃~700℃ for 2~8 hours to obtain silicon carbon powder. The method for preparing the porous biochar powder includes: heating the biomass raw material in an oxidant solution at 60-100°C for 8-12 hours under acidic conditions to obtain a biomass precursor; The biomass precursor is mixed with an activator and ball-milled, then calcined at 700℃~900℃ for 1~8h under an inert atmosphere to obtain the product; the oxidant is at least one of hydrogen peroxide, perchloric acid, sodium chlorate, and sodium hypochlorite; the activator is at least one of potassium hydroxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and zinc chloride. S2. The silicon carbon powder is mixed with the phenolic resin precursor solution and then heated and stirred to polymerize. Then, the solid and liquid are separated, and the resulting solid material is sintered at 600℃~800℃ for 4~6 hours under an inert atmosphere to obtain the final product.

2. The method for preparing biomass-based silicon-carbon anode material according to claim 1, characterized in that, In the method for preparing porous biochar powder, the mass ratio of biomass raw material to oxidant is 200~500:100~500; the concentration of the oxidant solution is 10~200g / L.

3. The method for preparing biomass-based silicon-carbon anode material according to claim 1, characterized in that, In the method for preparing porous biochar powder, the mass ratio of biomass precursor to activator is 1:1 to 1:

6.

4. The method for preparing biomass-based silicon-carbon anode material according to claim 1, characterized in that, In S2, the heating and stirring polymerization conditions are: stirring polymerization at 60℃~100℃ for 8~12h.

5. The method for preparing biomass-based silicon-carbon anode material according to claim 1, characterized in that, The specific surface area of ​​the porous biomass char powder is 1000 cm². 2 / g~3500cm 2 / g.

6. A biomass-based silicon-carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

7. The biomass-based silicon-carbon anode material according to claim 6, characterized in that, In the biomass-based silicon-carbon anode material, silicon accounts for 30% to 60% of the total mass of the material.

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