Silicon-carbon composite material and preparation method thereof

Abstract

The present invention relates to the field of lithium-ion battery negative electrodes, and discloses a silicon-carbon composite material coated with a carbon aerogel material and a preparation method thereof. The silicon-carbon composite material comprises nano-silicon particles and a porous carbon layer. In the present invention, the natural polymer material carrageenan is dissolved in water, and after adding nano-silicon particles, a gel colloidal structure with uniformly dispersed nano-silicon particles is formed at room temperature. Subsequently, a flexible carbon aerogel-coated silicon negative electrode material is prepared through carbon fiber wrapping formed by in-situ carbonization of cellulose esters, low surface tension solvent replacement, and high-temperature carbonization processes. The material of the present invention has high porosity and self-supporting properties, which significantly improves the performance of the material compared to similar materials.

Description

Technical field:

[0001] The present invention relates to the related field of lithium ion battery negative electrode materials, and specifically provides a method for preparing a novel silicon-carbon negative electrode material using natural polymers. Background technology:

[0002] As various small electronic devices, power tools, and large electric vehicles continue to dominate the market, the demand for high-energy-density energy storage materials continues to increase. After decades of development, lithium-ion batteries have become ubiquitous in modern life. Due to the short cycle life and low safety factor of batteries using lithium as the negative electrode, traditional lithium-ion batteries typically use inexpensive graphite materials as the negative electrode. However, due to the inherent limitations of graphite materials, the theoretical capacity of 370 mAh / g has gradually fallen behind the needs of the times. Consequently, silicon-carbon composites have emerged. Silicon, as the active material, has a theoretical capacity of up to 4200 mAh / g. During cycling, silicon and lithium form a silicon-lithium alloy. The drastic volume change and silicon's inherent poor conductivity lead to a series of problems such as low actual capacity, poor cycle life, and low initial efficiency. From the perspective of material synthesis and preparation, silicon-carbon composites also face complex processes and high costs, further limiting their industrial development. Furthermore, the complex process from electrode material to electrode preparation, coupled with the introduction of large amounts of binders and conductive agents, further reduces the energy density of the finished battery. Some patents describe the use of nitrogen-containing porous carbon materials prepared through a sol-gel process as active material carriers. However, the gel becomes brittle during drying, resulting in the final product remaining as a powder, which cannot avoid a series of problems in subsequent electrode preparation. Therefore, the preparation of a silicon-carbon composite material with a three-dimensional structure that can be directly used as a negative electrode material has become a current research focus. Summary of the invention:

[0003] The present invention aims to provide a method for preparing a silicon-carbon composite material, resulting in a three-dimensional structure that maintains excellent flexibility and self-support. This composite material can be easily cut and used as a negative electrode material, reducing the complexity of the application process. Using this material as a negative electrode material for lithium batteries can improve the battery's initial coulombic efficiency, specific capacity, and cycle life.

[0004] In order to achieve the above object of the invention, the technical solution of the present invention is as follows:

[0005] A silicon-carbon composite material is characterized in that it is silicon particles wrapped in carbon aerogel, including nano silicon particles and a porous carbon layer, wherein the silicon content is 5wt% to 35wt% and the rest is carbon.

[0006] A method for preparing a silicon-carbon composite material comprises the following steps:

[0007] (1) dissolving carrageenan in water at 60-120° C. and adding a certain amount of alkali metal salt to obtain a carrageenan / alkali metal salt mixed sol;

[0008] (2) adding nano-silicon material and cellulose lipids to the carrageenan solution, and then continuously stirring to form a uniformly dispersed slurry;

[0009] (3) cooling the slurry obtained in step 2) to room temperature to obtain a colloid;

[0010] (4) placing the colloid obtained in step 3) in a low surface tension solvent so that the water solvent in the colloid is replaced by the solvent, and replacing the solvent multiple times so that the colloid is completely filled;

[0011] (5) drying the colloid obtained in step 4) to obtain a precursor material;

[0012] (6) The precursor material obtained in step 4) is subjected to high-temperature treatment under a protective atmosphere. The obtained product is preferably immersed in dilute hydrochloric acid after etching, washed with water and then dried to obtain a silicon-carbon composite material.

[0013] The preparation method of the present invention forms a gel network formed by natural polymers in a water solvent system, which maintains a network structure after high-temperature carbonization, forming a carbon network with good electronic conductivity and ion conductivity, thereby improving its actual specific capacity. At the same time, by adding cellulose esters and treating the surface tension during the drying process, the influence of nano-silicon particles in the raw materials on the gel morphology is reduced, so that the material maintains good flexibility and self-supporting properties, thereby simplifying the battery process in subsequent applications; the specific surface area of ​​the material is further increased through acid etching after sintering, effectively alleviating the volume expansion of the silicon negative electrode and the problem of capacity attenuation.

[0014] In the method of the present invention, the carrageenan in step 1) is any one of κ-type and λ-type carrageenan, and the concentration of the carrageenan in the sol is 1 wt% to 5 wt%. The alkali metal salt is one of sodium chloride, potassium chloride, sodium hydroxide, and potassium hydroxide, and the concentration of the alkali metal salt in the sol is 0.2 wt% to 0.8 wt%.

[0015] In the method of the present invention, the nano-silicon material in step 2) is one or more of elemental nano-silicon, silicon oxide, and diatomaceous earth. The average particle size D50 is ≈20-200nm, and the amount of nano-silicon added is such that the silicon content in the prepared silicon-carbon composite material is 5wt% to 35wt%. The type of the cellulose lipid is one or more of cellulose acetate, cellulose acetate-propionate, cellulose acetate-butyrate, and cellulose propionate, and the amount added is 1wt% to 10wt% of the amount of the nano-silicon material. The addition of cellulose ester can coat the gel skeleton, which can maintain the skeleton structure to avoid collapse during the drying process, and on the other hand, form a carbon fiber-coated surface morphology in a step in the subsequent carbonization process, forming an efficient ion channel.

[0016] In the method of the present invention, in step 3), the slurry can be cooled in a mold to obtain a colloid with a certain shape. The shape of the colloid can be selected from a corresponding mold according to application requirements.

[0017] In the method of the present invention, the low surface tension solvent in step 4) is one or more of methanol, ethanol, isopropanol, and acetone, preferably anhydrous ethanol. The replacement time is 3-15 hours, the number of replacements is 3-5 times, and the amount used each time is 2-5 times the volume of the colloid. Repeated replacement can reduce the surface tension of the colloid, which helps the colloid maintain its flexibility and three-dimensional structure during the drying process.

[0018] In the method of the present invention, the drying method in step 5) is one of atmospheric pressure drying, supercritical drying, freeze drying, and critical drying. The solvent content of the gel after drying is between 0.5-1 wt%, preferably freeze drying, and the drying time is 12-48 hours.

[0019] In the method of the present invention, the high temperature treatment conditions in step 6) are 500-1000° C., the time is 1-6 hours, and the protective atmosphere is nitrogen atmosphere or argon atmosphere.

[0020] The concentration of the dilute hydrochloric acid in step 6) is 0.5-2 M, and the immersion time is 10 min-2 h. Acid etching can further increase the specific surface area of ​​the material and alleviate the problem of volume expansion.

[0021] The silicon-carbon composite material obtained by the method of the present invention comprises silicon particles encapsulated in carbon aerogel, with a silicon content of 5% to 35%. It is flexible and self-supporting, comprising nano-silicon particles and a porous carbon layer. Its flexibility and self-supporting properties are achieved through a sol-gel process, carbon fiber support using a cellulose ester template, and treatment with a low-surface-tension solvent.

[0022] The silicon-carbon composite material prepared by the present invention can be directly used as a negative electrode material for lithium batteries without the need to mix with a binder and a conductive agent before coating on a current collector.

[0023] The positive effects of the present invention are:

[0024] The present invention prepares a self-supporting silicon-carbon negative electrode material by using the natural and inexpensive polymer material carrageenan. The porous structure of the carbon gel network can effectively alleviate the volume expansion of the silicon-carbon negative electrode during the charge and discharge process, buffer its structural stress, and form an electron conduction channel, thereby improving the battery's initial coulombic efficiency, specific capacity, and cycle life. At the same time, the surface of the colloidal skeleton is modified by wrapping it with cellulose lipids to form sites that are easy for lithium ions to attach, forming efficient ion channels and effectively improving electrochemical performance. In addition, the cellulose coating support and the low surface tension treatment of the colloid synergistically maintain its macroscopic three-dimensional morphology, making the electrode material self-supporting to a certain extent and directly applicable to batteries, thereby avoiding the reduction of energy density in the electrode preparation process. Description of the drawings:

[0025] Figure 1 is the XRD pattern of the material obtained in Example 1;

[0026] Figure 2 This is a graph showing the discharge capacity of a lithium-ion button cell prepared from the material obtained in Example 1 during cyclic use at 100 mA / g.

[0027] Figure 3 is an optical image of the material obtained in Example 1. Specific implementation method:

[0028] The present invention provides a method for preparing a novel silicon-carbon anode material using natural polymers. To clearly illustrate the technical solutions and advantages of the present invention, the following examples further illustrate the invention using specific embodiments. The capacity retention rate is calculated by multiplying the initial discharge capacity by the coulombic efficiency to obtain the initial charge capacity. The capacity retention rate is calculated as the charge capacity after cycling divided by the initial charge capacity.

[0029] Example 1

[0030] 1) Add 3 g of κ-carrageenan to 97 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.2 g of NaCl and stir until it is completely dissolved to form a viscous sol.

[0031] 2) While maintaining heating and stirring, slowly add 0.3 g of nano-silicon material (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) and 30 mg of cellulose acetate-butyrate to the sol, then continue stirring to form a uniformly dispersed slurry;

[0032] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid;

[0033] 4) placing the colloid obtained in step 3) in a large container, adding an ethanol solution three times the volume of the colloid, and letting it stand for 10 hours. Then, replacing the ethanol solution, and letting it stand again. This process is repeated five times to replace the water solvent in the colloid with ethanol;

[0034] 5) Freezing the colloid obtained in step 4) with liquid nitrogen, subliming the solvent in a freeze dryer, and thoroughly drying for 48 hours to obtain a precursor material;

[0035] 6) The precursor material was placed in a tube furnace and treated at 600°C for 5 hours under nitrogen protection. The resulting product was immersed in 0.5M dilute hydrochloric acid for 10 minutes, then repeatedly washed with deionized water, filtered, and dried at normal pressure for 12 hours to obtain a new silicon-carbon composite material. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace to be 75%, and the specific surface area was measured by BET (nitrogen isothermal adsorption and desorption test) to be 104m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0036] 7) To test the performance of the present invention in a lithium-ion battery, the above-mentioned material was cut into 12 mm diameter discs. A button cell was assembled in an argon-filled glove box with a separator, electrolyte, and a CR2032 button cell case using metallic lithium as the counter electrode. The electrolyte was prepared by preparing a mixed solvent of 4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC) in a volume ratio of 1:2:7, and dissolving the electrolyte salt lithium hexafluorophosphate at a ratio of 1.2 mol / kg.

[0037] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material demonstrated an initial discharge capacity of 2135.15 mAh / g at a current density of 100 mA / g, with an initial coulombic efficiency of 87.52%. After 50 cycles, the charge capacity reached 1728.60 mAh / g, with a capacity retention rate of 92.51%.

[0038] Example 2

[0039] 1) Add 1 g of κ-carrageenan to 99 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.5 g of NaCl and stir until it is completely dissolved to form a viscous sol.

[0040] 2) While maintaining heating and stirring, slowly add 0.1 g of nano-silicon material (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) and 10 mg of cellulose acetate to the sol, then continue stirring to form a uniformly dispersed slurry;

[0041] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid with the same shape as the mold used;

[0042] 4) placing the colloid obtained in step 3) in a large volume container, adding an ethanol solution twice the volume of the colloid, and letting it stand for 10 hours. Then, replacing the ethanol solution, and letting it stand again. This process is repeated three times to replace the water solvent in the colloid with ethanol;

[0043] 5) drying the colloid obtained in step 4) in a supercritical carbon dioxide drying vessel at 40° C. and 10 MPa, maintaining the temperature for 4 hours, and then slowly releasing the pressure and cooling to room temperature to obtain a precursor material;

[0044] 6) The precursor material was placed in a tube furnace and treated at 700°C for 2 hours under nitrogen protection. The resulting product was immersed in 0.5M dilute hydrochloric acid for 30 minutes, then repeatedly washed with deionized water, filtered, and dried again at normal pressure for 12 hours to obtain a new silicon-carbon composite material. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace to be 75%, and the specific surface area was measured by BET (nitrogen isothermal adsorption and desorption test) to be 121m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0045] 7) To test the performance of the present invention in lithium-ion batteries, the above materials were cut into 12 mm diameter discs, and button batteries were prepared using metallic lithium as the counter electrode. The preparation method was similar to that in Example 1.

[0046] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material exhibited an initial specific capacity of 1986.24 mAh / g at a current density of 100 mA / g, with a Coulombic efficiency of 86.98%. After 50 cycles, the specific capacity was 1607.39 mAh / g, with a capacity retention rate of 93.04%.

[0047] Example 3

[0048] 1) Add 1 g of κ-carrageenan to 99 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.8 g of KCl and stir until completely dissolved to form a viscous sol.

[0049] 2) While maintaining heating and stirring, slowly add 0.1 g of nanosilicon (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) and 6 mg of cellulose acetate to the sol, then continue stirring to form a uniformly dispersed slurry;

[0050] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid with the same shape as the mold used;

[0051] 4) placing the colloid obtained in step 3) in a large container, adding an ethanol solution five times the volume of the colloid, and letting it stand for 3 hours. Then, replacing the ethanol solution, and letting it stand again. This process is repeated five times to replace the water solvent in the colloid with ethanol;

[0052] 5) drying the colloid obtained in step 4) in a supercritical carbon dioxide drying vessel at 40° C. and 15 MPa, maintaining the temperature for 4 hours, and then slowly releasing the pressure and cooling to room temperature to obtain a precursor material;

[0053] 6) The precursor material was placed in a tube furnace and treated at 900°C for 3 hours under nitrogen protection. The resulting product was immersed in 1M dilute hydrochloric acid for 30 minutes, then repeatedly washed with deionized water, filtered, and dried at normal pressure for 12 hours to obtain a new silicon-carbon composite material. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace to be 67%, and the specific surface area was measured by BET (nitrogen isothermal adsorption and desorption test) to be 95m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0054] 7) To test the performance of the present invention in lithium-ion batteries, the above materials were cut into 12 mm diameter discs, and button batteries were prepared using metallic lithium as the counter electrode. The preparation method was similar to that in Example 1.

[0055] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material exhibited an initial discharge capacity of 1524.64 mAh / g at a current density of 100 mA / g, with a Coulombic efficiency of 80.57%. After 50 cycles, the charge capacity reached 1051.51 mAh / g, with a capacity retention rate of 85.60%.

[0056] Example 4

[0057] 1) Add 2 g of κ-carrageenan to 98 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.5 g of NaOH and stir until completely dissolved to form a viscous sol.

[0058] 2) While maintaining heating and stirring, slowly add 0.3 g of nanosilicon (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) and 3 mg of cellulose acetate-propionate to the sol, then continue stirring to form a uniformly dispersed slurry;

[0059] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid with the same shape as the mold used;

[0060] 4) placing the colloid obtained in step 3) in a large container, adding an ethanol solution three times the volume of the colloid, and letting it stand for 15 hours. Then, replacing the ethanol solution, and letting it stand again, repeat this process five times to replace the water solvent in the colloid with ethanol;

[0061] 5) placing the colloid obtained in step 4) in a fume hood and drying it naturally at room temperature and pressure for 48 hours to obtain a precursor material;

[0062] 6) The precursor material was placed in a tube furnace and treated at 700°C for 4 hours under nitrogen protection. The resulting product was immersed in 0.5M dilute hydrochloric acid for 1 hour, then repeatedly washed with deionized water, filtered, and dried at normal pressure for 12 hours to obtain a new silicon-carbon composite material. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace to be 71%, and the specific surface area was measured by BET (nitrogen isothermal adsorption and desorption test) to be 104m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0063] 7) To test the performance of the present invention in lithium-ion batteries, the above materials were cut into 12 mm diameter discs, and button batteries were prepared using metallic lithium as the counter electrode. The preparation method was similar to that in Example 1.

[0064] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material exhibited an initial discharge capacity of 1987.35 mAh / g at a current density of 100 mA / g, with a Coulombic efficiency of 69.42%. After 50 cycles, the charge capacity reached 1288.01 mAh / g, with a capacity retention rate of 93.36%.

[0065] Example 5

[0066] 1) Add 5 g of κ-carrageenan to 95 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.3 g of NaOH and stir until completely dissolved to form a viscous sol.

[0067] 2) While maintaining heating and stirring, slowly add 0.4 g of nanosilicon (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) and 10 mg of cellulose acetate-butyrate to the sol, then continue stirring to form a uniformly dispersed slurry;

[0068] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid with the same shape as the mold used;

[0069] 4) placing the colloid obtained in step 3) in a large volume container, adding an ethanol solution twice the volume of the colloid, and letting it stand for 10 hours. Then, replacing the ethanol solution, and letting it stand again. This process is repeated five times to replace the water solvent in the colloid with ethanol;

[0070] 5) Freezing the colloid obtained in step 4) with liquid nitrogen, subliming the solvent in a freeze dryer, and thoroughly drying for 12 hours to obtain a precursor material;

[0071] 6) The precursor material was placed in a tube furnace and treated at 600°C for 5 hours under nitrogen protection. The resulting product was immersed in 0.5M dilute hydrochloric acid for 10 minutes, then repeatedly washed with deionized water, filtered, and dried at normal pressure for 12 hours to obtain a new silicon-carbon composite material. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace to be 85%, and the specific surface area was measured by BET (nitrogen isothermal adsorption and desorption test) to be 129m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0072] 7) To test the performance of the present invention in lithium-ion batteries, the above materials were cut into 12 mm diameter discs, and button batteries were prepared using metallic lithium as the counter electrode. The preparation method was similar to that in Example 1.

[0073] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material exhibited an initial discharge capacity of 1864.54 mAh / g at a current density of 100 mA / g, with a Coulombic efficiency of 70.04%. After 50 cycles, the charge capacity reached 1135.50 mAh / g, with a capacity retention rate of 86.95%.

[0074] Comparative Example 1

[0075] 1) Add 3 g of κ-carrageenan to 97 ml of deionized water, heat to 80°C, and stir until the carrageenan dissolves. Then, add 0.2 g of NaCl and stir until it is completely dissolved to form a viscous sol.

[0076] 2) While maintaining heating and stirring, slowly add 0.3 g of nano-silicon material (Shanghai Shuitian Material Technology Co., Ltd., 30 nm) to the sol, then continue stirring to form a uniformly dispersed slurry;

[0077] 3) Stop stirring and heating the slurry and wait for it to cool to room temperature to obtain a colloid;

[0078] 4) freezing the colloid obtained in step 3) with liquid nitrogen, subliming the solvent in a freeze dryer, and thoroughly drying for 48 hours to obtain a precursor material;

[0079] 5) The precursor material was placed in a tube furnace and treated at 600°C for 5 hours under nitrogen protection. The resulting product was immersed in 0.5M dilute hydrochloric acid for 10 minutes, then repeatedly washed with deionized water, filtered, dried at normal pressure for 12 hours, and ground to obtain a new silicon-carbon composite material in the form of a powder. The carbon content was measured by ignition loss at 800°C for 2 hours in a muffle furnace, and the specific surface area was measured to be 95m 2 / g, the desorption temperature was 200℃, and the desorption time was 2h.

[0080] 6) To test the performance of the present invention in a lithium-ion battery, the above-mentioned material was mixed with a binder and a conductive agent, ground, and then coated on the surface of a copper foil. After drying, it was cut into 12 mm disc electrodes. Metallic lithium was used as the counter electrode. A button battery was assembled with a separator, electrolyte, and a CR2032 button battery shell in an argon-filled glove box.

[0081] The preparation method of the disc electrode is as follows: after mixing the silicon-carbon composite material, La133 binder and Super P conductive agent in a ratio of 8:1:1, diluting it with deionized water to a slurry with a solid content of 50% and stirring it evenly, the slurry is then coated on the surface of the copper foil, dried for 12 hours, and then cut to obtain the disc electrode.

[0082] The electrolyte solution was prepared by preparing a mixed solvent of 4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:2:7, and dissolving the electrolyte salt lithium hexafluorophosphate at a ratio of 1.2 mol / kg.

[0083] Constant current charge and discharge tests were conducted using Xinwei battery testing equipment within a voltage range of 0.1-1.5 V. The material exhibited an initial discharge capacity of 1925.45 mAh / g at a current density of 100 mA / g, with an initial coulombic efficiency of 68.87%. After 50 cycles, the charge capacity reached 829.45 mAh / g, with a capacity retention of 62.55%.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: (1) dissolving carrageenan in water at 60-120° C. and adding an alkali metal salt to obtain a carrageenan / alkali metal salt mixed sol; (2) adding nano-silicon material and cellulose lipids to the carrageenan solution, and then continuously stirring to form a uniformly dispersed slurry; (3) cooling the slurry obtained in step (2) to room temperature to obtain a colloid; (4) placing the colloid obtained in step (3) in a low surface tension solvent so that the water solvent in the colloid is replaced by the solvent, and replacing the solvent multiple times so that the colloid is completely filled; (5) drying the colloid obtained in step (4) to obtain a precursor material; (6) subjecting the precursor material obtained in step (4) to high-temperature treatment under a protective atmosphere, and the resulting product is acid-etched, washed with water, and then dried to obtain a silicon-carbon composite material; The carbon-silicon composite material is silicon particles wrapped in carbon aerogel, including nano-silicon particles and porous carbon layers, wherein the silicon content is 5wt% to 35wt% and the rest is carbon.

2. The preparation method according to claim 1, wherein: The carrageenan in step (1) is any one of κ-type and λ-type carrageenan, and the concentration of carrageenan in the sol is 1 wt% to 5 wt%.

3. The preparation method according to claim 1 or 2, characterized in that: The alkali metal salt is one of sodium chloride, potassium chloride, sodium hydroxide and potassium hydroxide, and the concentration of the alkali metal salt in the sol is 0.2wt%-0.8wt%.

4. The preparation method according to claim 1, wherein: The nano-silicon material in step (2) is one of elemental nano-silicon, silicon oxide, and diatomaceous earth; the average particle size D50 is 20-200nm, and the amount of nano-silicon added is such that the silicon content in the prepared silicon-carbon composite material is 5wt% to 35wt%.

5. The preparation method according to claim 1 or 4, characterized in that: The cellulose lipids are one or more of cellulose acetate, cellulose acetate-propionate, cellulose acetate-butyrate, and cellulose propionate, and the added amount is 1 wt% to 10 wt% of the amount of the nano-silicon material.

6. The preparation method according to claim 1, wherein: The low surface tension solvent in step (4) is one or more of methanol, ethanol, isopropanol, and acetone. The replacement time is 3h-15h, the number of replacements is 3-5 times, and the amount used each time is 2-5 times the volume of the colloid.

7. The preparation method according to claim 1, wherein: The drying method in step (5) is one of normal pressure drying, supercritical drying, freeze drying and critical drying, and the content of the gel solvent after drying is between 0.01% and 1%.

8. The preparation method according to claim 7, characterized in that: The drying method in step (5) is freeze drying, and the drying time is 12h-48h.

9. The preparation method according to claim 1, wherein: The high temperature treatment conditions in step (6) are 500-1000° C., the time is 1-6 h, and the protective atmosphere is nitrogen atmosphere or argon atmosphere.

10. The preparation method according to claim 1 or 9, characterized in that: The acid etching in step (6) is to immerse the obtained product in dilute hydrochloric acid.

11. The preparation method according to claim 10, characterized in that: The concentration of the dilute hydrochloric acid in step (6) is 0.5-2M, and the soaking time is 10min-2h.

12. Use of the silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 11 as a negative electrode for a lithium-ion battery.

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