A method for coating the surface of a silicon-based negative electrode material

Abstract

This invention discloses a method for coating a silicon-based anode material surface. The method utilizes a liquid-phase coating technique to achieve a controllable thickness of an alumina film on the surface of a silicon-based substrate. The thickness of the alumina film is 1-50 nm. The formula for precisely controlling the thickness of the alumina film is as follows: M=S AA *m*d*K / c, M: precursor mass, S AA : Specific surface area of ​​raw material, d: coating thickness, c: molecular weight percentage of aluminum in the precursor, K: coating coefficient, which is related to the precursor and ranges from 1.55 to 2.25. This invention uses a liquid-phase coating method, which features simple equipment, convenient operation, and easy large-scale production. It achieves good versatility and economy. Through dense alumina film coating, excellent interfacial stability can be achieved, effectively suppressing the volume expansion effect of silicon, thereby effectively blocking direct contact between the electrolyte and the silicon substrate, suppressing side reactions, reducing active lithium loss, and improving cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically a method for coating the surface of silicon-based anode materials. Background Technology

[0002] Silicon-based anode materials, with their extremely high theoretical specific capacity (up to 4200 mAh / g), are a core research direction for high-energy-density anode materials in lithium-ion batteries, and are expected to break through the current energy density bottleneck of batteries. However, the practical application of silicon-based anode materials faces two major challenges: First, silicon's intrinsic conductivity is low, which limits the transport efficiency of Li⁺ at high current densities, affecting the battery's rate performance; second, silicon undergoes approximately 300% volume expansion during lithium intercalation, easily leading to electrode structure shattering, repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, ultimately resulting in a sharp decline in material cycle stability and severe capacity decay. To alleviate these problems, the industry often adopts a composite structure design of "silicon-based core + carbon coating layer," using the carbon coating layer to suppress silicon volume expansion, improve conductivity, and stabilize the SEI film. The combination of porous carbon support and carbon coating is one of the mainstream technical approaches. For example, existing solutions load silicon particles into the pores of a porous carbon carrier, and then form a carbon protective layer on the surface of the composite material through a vapor deposition process. Some technologies (such as the solution disclosed in Chinese patent CN120109182A) further optimize the structure through multiple vapor deposition carbon coatings. Essentially, they still belong to silicon-based anode preparation technologies centered around "carbon coating optimization".

[0003] However, the uniformity and adhesion of carbon coatings deposited by vapor deposition are insufficient: the carbon coating is prone to uneven thickness, local defects (such as no coating in "shaded areas" or "thicker on the outside and thinner on the inside" in pores), and microcracks. Moreover, the adhesion between the carbon coating and the silicon substrate is mostly physical, lacking a stable chemical bond. This leads to the coating being prone to cracking and detachment during cycling, making it difficult to effectively suppress volume expansion and stabilize the SEI film, resulting in rapid capacity decay.

[0004] The carbon coating material deposited by vapor deposition exhibits poor structural and interfacial stability: due to uneven coating and weak bonding, the internal stress distribution of the material is uneven, which exacerbates the breakage of silicon particles and the repeated rupture and regeneration of the SEI film, continuously consuming electrolyte and lithium source, resulting in low coulombic efficiency and shortened cycle life. At the same time, coating defects provide channels for electrolyte penetration, triggering continuous side reactions.

[0005] Inadequate utilization of precursors and safety risks: In the vapor deposition process, the carbon source precursor may not decompose completely, leaving behind small-molecule organic matter or heteroatom groups. These residues not only reduce the electrochemical performance of the material, but may also undergo side reactions with the electrolyte during battery operation, or pose safety hazards at high temperatures. Summary of the Invention

[0006] This invention addresses the problems of uneven coating, weak bonding, and complex processes in existing coating technologies by providing a liquid-phase coating method with adjustable coating thickness to prepare silicon-based anode materials coated with alumina thin films. The prepared materials have advantages such as interface stability, long cycle life, low preparation cost, and controllable thickness.

[0007] To address the aforementioned technical problems, this invention provides the following technical solution: a method for coating a silicon-based anode material surface, wherein a controllable-thickness alumina thin film is coated on the surface of a silicon-based substrate material using a liquid-phase coating method. The thickness of the alumina thin film is 1-50 nm, and the calculation formula for precisely controlling the thickness of the alumina thin film is as follows: M=S AA *m*d*K / c M: Precursor mass S AA Specific surface area of ​​raw materials d: Coating thickness c.: Molecular weight percentage of aluminum element in precursor K: Coverage coefficient, which is related to the precursor and ranges from 1.55 to 2.25.

[0008] Preferably, the preparation process of the silicon-based matrix material is as follows: porous carbon material is placed in a fluidized bed chemical vapor deposition reactor, using 5~40 L / min nitrogen as the fluidizing carrier gas, and then heated to 400~800℃, followed by the introduction of 5wt%~30wt% silane gas for a reaction time of 30~200 min; finally, the temperature is raised to 500~900℃, and 2wt%~40wt% acetylene gas is introduced for a reaction time of 30~300 min. After cooling the reaction system to room temperature, the silicon-based matrix material is obtained, and then the surface area of ​​the obtained silicon-based matrix material is analyzed.

[0009] Preferably, the porous carbon material includes at least one of porous artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene; the specific surface area of ​​the porous carbon material is 50~3500 m² / g, the pore volume is 0.2~2.5 cm³ / g, and the particle size D is... 10 =0.6~1.0, D 50 =6~8um, D 90 =18~22um.

[0010] A method for coating the surface of a silicon-based anode material, comprising the following specific steps: S1. Preparation of precursor solution: Dissolve the alumina precursor in a suitable solvent, control the pH at 6.5-8.0, preferably at 6.8-7.5, and keep the solution temperature at 30-60℃ to achieve the pre-preparation of the alumina precursor-coated solution. S2. Based on the formula for calculating the specific surface area and thickness of the silicon-based matrix material, after determining a suitable precursor, the silicon-based matrix material is added to the alumina precursor solution obtained in S1 according to the calculated ratio. The solid content is controlled at 10-30%, the pH is controlled at 5.0-7.0, and the material is thoroughly stirred and dispersed using a dispersion device. Then, the solvent is removed by an evaporation device to achieve material drying. S3. Place the powder obtained in S2 in a heating furnace and heat it under an inert protective gas atmosphere using a heating device. After cooling, the silicon-based anode material coated with alumina is obtained.

[0011] Preferably, the alumina precursor in step S1 is an inorganic aluminum salt or an organoaluminum compound; the inorganic aluminum salt is selected from one or more combinations of aluminum nitrate nonahydrate, aluminum chloride hexahydrate, aluminum sulfate octahydrate, potassium aluminum sulfate dodecahydrate, or aluminum ammonium nitrate nonahydrate; the organoaluminum compound is selected from one or more combinations of aluminum isopropoxide, aluminum acetylacetone, aluminum trisec-butoxy, aluminum triethoxy, or aluminum tributoxy.

[0012] Preferably, the solvent in step S1 is selected from one or more of water, methanol, ethanol, isopropanol, propanol, butanol, ethylene glycol, and ethyl acetate; the pH-adjusting reagent is one or more of acetic acid, oxalic acid, citric acid, gallic acid, salicylic acid, ammonia, sodium citrate, sodium carbonate, and sodium bicarbonate.

[0013] Preferably, the thickness of the alumina film is 2nm, 5nm, 10nm, 30nm, 50nm, or any value within the range of any two of the above values. The alumina film is used to reduce the amount of gas generated by the reaction between the silicon-based anode active material and the electrolyte. Controlling the thickness of the alumina film within the above range is beneficial to maintaining the stability of the material structure of the silicon-based anode material during cycling.

[0014] Furthermore, the thickness of the alumina film can be 1 nm to 20 nm, which is beneficial for the rapid insertion and extraction of lithium ions.

[0015] Preferably, the dispersing equipment in step S2 includes, but is not limited to, a combination of one or more of the following: a homogenizing emulsifier, a high-speed disperser, an ultrasonic disperser, and a three-roll mill; the evaporation equipment includes, but is not limited to, one or more of the following: spray drying, freeze drying, forced-air drying, and supercritical drying.

[0016] Preferably, in step S3, the heating treatment involves raising the temperature to 550℃ to 1000℃ at a rate of 1℃ / min to 20℃ / min for 3 to 12 hours; exemplary values ​​could be 550℃, 600℃, 700℃, 800℃, 850℃, 900℃, 950℃, or 1000℃, but other values ​​within the above range are also possible and are not limited herein. Appropriate heating rates, heating temperatures, and holding times help the alumina coating layer form a certain crystal structure, improve stability, and strengthen the coating layer. The heating equipment includes at least one of a box-type atmosphere furnace, a high-temperature rotary furnace, and a fluidized bed; the inert protective atmosphere includes at least one of nitrogen, argon, helium, carbon dioxide, and hydrogen.

[0017] Preferably, in step S1, the pH is controlled at 6.8-7.5 and the temperature of the solution is controlled at 40-55℃; in step S2, the solid content is controlled at 15-25% and the pH is controlled at 5.5-6.5.

[0018] The following benefits can be achieved by adopting the technical solution of this invention: The liquid-phase coating method used in this invention has the advantages of simple process equipment, convenient operation, and easy large-scale production, and can achieve good universality and economy. Through dense alumina film coating, excellent interface stability can be achieved, effectively suppressing the volume expansion effect of silicon, thereby effectively blocking direct contact between the electrolyte and the silicon substrate, suppressing side reactions, reducing active lithium loss, and improving cycle stability. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the silicon-based material coated with alumina according to the present invention; Figure 2 This is a TEM image of the silicon-based material coated with alumina according to the present invention; Figure 3 is a SEM image of the silicon-based anode material prepared in Example 4 of the present invention; Figure 4 is a test curve of the charge-discharge performance of the silicon-based anode material prepared in Example 4 of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0021] A method for coating the surface of a silicon-based anode material involves selecting aluminum nitrate nonahydrate as an aluminum-containing precursor, with a coating coefficient K=2.0 and a designed coating thickness of 10 nm. 70 g of the silicon-based substrate from Comparative Example 1 and 58.3 g of aluminum nitrate nonahydrate are weighed. The aluminum nitrate nonahydrate is then dissolved in 500 g of water and 247 g of ethanol. Ammonia and acetic acid are added to control the pH at 6.5, and then the silicon-based substrate material is added. The mixture is dispersed using a high-speed disperser for 30 min. After dispersion, the dispersed mixture is dried using a spray granulation device at a temperature <200℃ to obtain a pre-coated precursor. The precursor is transferred to a box-type atmosphere furnace and held at 250℃ for 2 h under a nitrogen (N2) atmosphere. After holding, it is naturally cooled to room temperature to obtain the silicon-based anode material of this invention.

[0022] The silicon-based anode material was prepared using essentially the same method as in Example 1. The difference was that the raw material used was the silicon-based substrate from Comparative Example 2, specifically 99.1 g of aluminum nitrate nonahydrate.

[0023] Aluminum isopropoxide was selected as the aluminum-containing precursor, with a coating coefficient K=1.8 and a designed coating thickness of 5nm. 70g of the silicon-based matrix from Comparative Example 1 and 14.3g of aluminum isopropoxide were weighed. The silicon-based matrix and aluminum isopropoxide were dissolved together in 530g of isopropanol to form a mixed system. The mixed system was dispersed using a homogenizing emulsifier for 30min. After dispersion, the dispersed mixture was dried using a spray dryer to obtain the precursor. The precursor was transferred to a crucible and kept at 500℃ for 2h under a nitrogen (N2) atmosphere. After the heating period, it was naturally cooled to room temperature to obtain the silicon-based anode material of this invention.

[0024] The silicon-based anode material was prepared using essentially the same method as in Example 3. The difference was that the raw material used was the silicon-based substrate from Comparative Example 2, with 24.3 g of aluminum isopropoxide.

[0025] Aluminum chloride isohexahydrate was selected as the aluminum-containing precursor, with a coating coefficient K=2.2 and a designed coating thickness of 3nm. 70g of the silicon-based matrix from Comparative Example 1 and 11.7g of aluminum chloride hexahydrate were weighed. The silicon-based matrix and aluminum chloride hexahydrate were dissolved together in 440g of deionized water to form a mixed system. The mixed system was dispersed using a high-speed disperser for 30min. After dispersion, the mixture was placed in a vacuum drying oven and vacuum dried at 110℃ to obtain the precursor. The precursor was transferred to a crucible and kept at 300℃ for 2h under an argon (Ar2) atmosphere. After the holding time, it was naturally cooled to room temperature to obtain the silicon-based anode material of this invention.

[0026] The silicon-based anode material was prepared using essentially the same method as in Example 5. The difference was that the raw material used was the silicon-based substrate from Comparative Example 2, with 19.9 g of aluminum chloride hexahydrate.

[0027] Aluminum triethoxy was selected as the aluminum-containing precursor, with a coating coefficient K=1.7 and a designed coating thickness of 1 nm. 70 g of the silicon-based matrix from Comparative Example 1 and 4.3 g of aluminum triethoxy were weighed. The silicon-based matrix and aluminum triethoxy were dissolved together in 490 g of methanol to form a mixed system. The mixed system was dispersed using a high-speed disperser for 30 min. After dispersion, the dispersed mixture was dried using a spray granulation device to obtain the precursor. The precursor was transferred to a crucible and kept at 600 °C for 2 h under an argon (Ar2) atmosphere. After the heating period, it was naturally cooled to room temperature to obtain the silicon-based anode material of this invention.

[0028] The silicon-based anode material was prepared using essentially the same method as in Example 7. The difference was that the raw material used was the silicon-based matrix of Comparative Example 2, with 7.4 g of aluminum triethoxy.

[0029] Detailed physicochemical test results of the negative electrode material in this embodiment are shown in Table 1.

[0030] The coin cell performance test results of the negative electrode material in this embodiment are detailed in Table 2.

[0031] SEM testing: The morphological characteristics of the silicon-based anode material were characterized using scanning electron microscopy.

[0032] TEM testing: The structure of the coating layer was observed and the thickness was measured using a transmission electron microscope.

[0033] Specific surface area testing method: Using the ASAP2406 surface area and pore size analyzer from Mic, USA, and combining the law of adsorption amount changing with relative pressure during adsorption, various models can be fitted to calculate the specific surface area.

[0034] Particle size testing: The particle size testing method refers to GB / T 19077-2016. The analyzer used is the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0035] Resistivity testing: A four-probe resistivity meter (probe spacing 1mm, probe pressure 5N) was used. The pressed sample was placed horizontally in the center of the meter's stage, ensuring that the four probes made perpendicular and uniform contact with the sample surface. The test current was set to 1mA, and the resistance value was recorded after the instrument reading stabilized. Three parallel tests were performed, and the average value was taken as the final resistivity result.

[0036] Coating strength test: Take the prepared silicon-based anode material and mix it with 0.5 mol / L sodium hydroxide solution to prepare a suspension with a silicon-based anode material mass ratio of 40%; use a clean and dry 10 mL syringe to draw 6 mL of the above suspension, mark it V1, seal the syringe tip tightly with a stopcock, and then place it in a constant temperature 60℃ oven for 48 h; after cooling to room temperature, record the gas volume in the syringe, mark it V2, and calculate the coating strength Q = (V2 - V1) / V1 * 100%.

[0037] Electrochemical performance testing: The prepared silicon-carbon anode material was used as the active material. It was mixed with an aqueous dispersion of propylene multi-element copolymer binder (PAA, solid content 7.5%) and a conductive agent (Super P) at a mass ratio of 96:3:1. A suitable amount of water was added as a solvent to prepare a slurry with a solid content of 55%. This slurry was coated onto copper foil, vacuum dried, rolled, and cut to obtain the anode sheet. A lithium metal sheet was used as the counter electrode, and a 1 mol / L LiPF6 solution was used as the electrolyte. The solvent was a 1:1:1 volume ratio mixture of EC, DMC, and EMC. A polypropylene microporous membrane was used as the separator. The CR2032 coin cell was assembled in an inert gas-filled glove box. Charge-discharge tests of the coin cells were conducted on the LANHE battery testing system.

[0038] Initial charge-discharge performance test: Under normal temperature conditions, discharge at a constant current of 0.1C until the voltage reaches 0.01V, then discharge at a constant current of 0.02C until the voltage reaches 0.005V, and then charge at a constant current of 0.1C until the voltage reaches 1.5V to obtain the initial reversible specific capacity and initial coulombic efficiency. This cycle is repeated 50 times, and the capacity retention rate after 50 cycles is calculated.

[0039] Expansion rate test method: After one cycle, move the coin cell to the glove box, disassemble it to obtain the negative electrode sheet, place it on a lint-free paper to dry, use a micrometer to measure the thickness of the electrode sheet, take at least three points with similar thickness, the measurement position should be on the coating and at least 1mm away from the edge of the electrode sheet, summarize the data and calculate the expansion rate.

[0040] Analysis of the data in Table 1 shows that, compared to the uncoated sample of Comparative Example 1, the coating strength values ​​of the alumina-coated samples (Examples 1 / 3 / 5 / 7) are lower, and the values ​​decrease with increasing coating thickness. This indicates a reduction in gas production in the alkaline environment, demonstrating that the dense alumina film provides effective protection and effectively isolates the alkaline solution from chemical reactions with silicon. Simultaneously, the specific surface area of ​​the alumina-coated samples is lower, indicating that the alumina film modifies the silicon substrate surface, reducing surface defects. The alumina-coated samples have higher resistivity because alumina is an insulator; therefore, the alumina film should not be too thick, otherwise the material's conductivity will be affected. The particle size of the alumina-coated samples is not significantly affected, indicating that the alumina coating thickness in the examples is at the nanoscale. These conclusions are also consistent with Comparative Example 2 and the examples using it as a raw material.

[0041] Analysis of the data in Table 2 shows that the reversible specific capacity of the alumina-coated film decreased to varying degrees. This is because alumina does not possess lithium storage capacity, therefore the amount of alumina added should not be excessive. The alumina-coated samples exhibited increased first-pass efficiency, indicating that this dense alumina film can effectively reduce side reactions with the electrolyte and the silicon-carbon substrate, thereby reducing Li... + Loss and improved first-time efficiency. High mechanical strength further restrains the expansion of silicon particles, while compensating for the defects and weak bonding of the gas-phase coated carbon layer. The decrease in expansion rate after 1 cycle and the varying degrees of increase in capacity retention after 50 cycles after coating confirm this.

[0042] Porous carbon with a pore volume of 0.85 cm³ / g was added to a fluidized bed reactor, using nitrogen (N₂) as the carrier gas at a flow rate of 18 L / min. The heating system was started, and the temperature inside the fluidized bed was raised to 450°C at a rate of 5°C / min for 60 min. After the holding period, silane gas was introduced into the fluidized bed at a flow rate of 3 L / min for 180 min. After the silane gas was stopped, the temperature inside the fluidized bed was raised to 600°C at a rate of 5°C / min for 40 min. Then, acetylene gas was introduced into the fluidized bed at a flow rate of 5 L / min for 120 min before the introduction was stopped. The carrier gas was continuously introduced, and the material was discharged after the temperature inside the fluidized bed naturally cooled to room temperature to obtain the comparative silicon-based matrix material.

[0043] Silicon-based matrix materials were prepared using essentially the same method as in Comparative Example 1, except that the pore volume of the porous carbon raw material was 1.20 cm³ / g. The fluidized bed temperature was 500°C when silane was introduced and 550°C when acetylene was introduced.

[0044] name Particle size D50 / um Coating strength / % Specific surface area / m2 / g resistivity / Ω·cm Example 1 7.83 3.71 1.94 15.36 Example 2 7.82 3.83 3.16 19.24 Example 3 7.82 5.24 2.23 12.11 Example 4 7.81 5.4 3.55 16.23 Example 5 7.81 6.15 2.57 7.23 Example 6 7.80 6.57 3.98 8.32 Example 7 7.81 6.83 2.86 5.84 Example 8 7.80 7.16 4.47 7.15 Comparative Example 1 7.81 13.52 3.25 5.24 Comparative Example 2 7.80 15.24 5.54 6.48 Table 1. Physicochemical test results of samples from comparative examples. name Reversible specific capacity / mAh / g First-time effect / % 1-ring electrode expansion rate / % Capacity retention rate after 50 laps / % Example 1 1650 92.1 35.6 95.9 Example 2 1631 91.2 42.3 93.5 Example 3 1674 92.3 40.2 96.2 Example 4 1654 91.5 45.2 94.2 Example 5 1706 92.3 42.5 96.4 Example 6 1682 92.0 47.8 94.4 Example 7 1726 92.5 44.3 96.1 Example 8 1697 91.7 50.3 94.1 Comparative Example 1 1743 91.3 59.8 93.5 Comparative Example 2 1715 90.9 62.3 92.2 Table 2. Results of coin cell performance tests for comparative example samples. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for coating the surface of a silicon-based anode material, characterized in that: Alumina thin films with controllable thickness, ranging from 1 to 50 nm, are achieved on the surface of silicon-based substrates using a liquid-phase coating method. The calculation formula for precisely controlling the thickness of the alumina thin film is as follows: M=S AA *m*d*K / c M: Precursor mass S AA Specific surface area of ​​raw materials d: Coating thickness c.: Molecular weight percentage of aluminum element in precursor K: Coverage coefficient, which is related to the precursor and ranges from 1.55 to 2.

25.

2. The method for coating the surface of a silicon-based anode material according to claim 1, characterized in that: The preparation process of the silicon-based matrix material is as follows: porous carbon material is placed in a fluidized bed chemical vapor deposition reactor, using 5~40 L / min nitrogen as the fluidizing carrier gas, and then heated to 400~800℃, followed by the introduction of 5wt%~30wt% silane gas for a reaction time of 30~200 min; finally, it is heated to 500~900℃, followed by the introduction of 2wt%~40wt% acetylene gas for a reaction time of 30~300 min, and the reaction system is cooled to room temperature to obtain the silicon-based matrix material. The surface area of ​​the obtained silicon-based matrix material is then analyzed.

3. The method for coating the surface of a silicon-based anode material according to claim 1, characterized in that: The porous carbon material includes at least one of porous artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene; the specific surface area of ​​the porous carbon material is 50~3500 m² / g, the pore volume is 0.2~2.5 cm³ / g, and the particle size D is... 10 =0.6~1.0, D 50 =6~8um, D 90 =18~22um.

4. The method for coating the surface of a silicon-based anode material according to claim 1, characterized in that: The specific steps are as follows: S1. Preparation of precursor solution: Dissolve the alumina precursor in a suitable solvent, control the pH at 6.5-8.0, preferably at 6.8-7.5, and keep the solution temperature at 30-60℃ to achieve the pre-preparation of the alumina precursor-coated solution. S2. Based on the formula for calculating the specific surface area and thickness of the silicon-based matrix material, after determining a suitable precursor, the silicon-based matrix material is added to the alumina precursor solution obtained in S1 according to the calculated ratio. The solid content is controlled at 10-30%, the pH is controlled at 5.0-7.0, and the material is thoroughly stirred and dispersed using a dispersion device. Then, the solvent is removed by an evaporation device to achieve material drying. S3. Place the powder obtained in S2 in a heating furnace and heat it under an inert protective gas atmosphere using a heating device. After cooling, the silicon-based anode material coated with alumina is obtained.

5. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: In step S1, the alumina precursor is an inorganic aluminum salt or an organoaluminum compound; the inorganic aluminum salt is selected from one or more combinations of aluminum nitrate nonahydrate, aluminum chloride hexahydrate, aluminum sulfate octahydrate, potassium aluminum sulfate dodecahydrate, or aluminum ammonium nitrate nonahydrate; the organoaluminum compound is selected from one or more combinations of aluminum isopropoxide, aluminum acetylacetone, aluminum trisec-butoxy, aluminum triethoxy, or aluminum tributoxy.

6. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: In step S1, the solvent is selected from one or more of the following: water, methanol, ethanol, isopropanol, propanol, butanol, ethylene glycol, and ethyl acetate; the pH-adjusting reagent is one or more of the following: acetic acid, oxalic acid, citric acid, gallic acid, salicylic acid, ammonia, sodium citrate, sodium carbonate, and sodium bicarbonate.

7. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: The thickness of the alumina film is 2nm, 5nm, 10nm, 30nm, 50nm or any value within the range of any two of the above values. The alumina film is used to reduce the amount of gas generated by the reaction between the silicon-based anode active material and the electrolyte. Controlling the thickness of the alumina film within the above range is beneficial to maintaining the stability of the material structure of the silicon-based anode material during cycling.

8. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: The dispersing equipment in step S2 includes, but is not limited to, homogenizing emulsifiers, high-speed dispersers, ultrasonic dispersers, and three-roll mills, or a combination thereof; the evaporation equipment includes, but is not limited to, spray drying, freeze drying, forced-air drying, and supercritical drying, or a combination thereof.

9. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: In step S3, the heating treatment involves raising the temperature to 550℃ to 1000℃ at a rate of 1℃ / min to 20℃ / min for 3h to 12h. Appropriate heating rates, temperatures, and holding times help the alumina coating form a certain crystalline structure, improving stability and strengthening the coating. The heating equipment includes at least one of a box-type atmosphere furnace, a high-temperature rotary furnace, and a fluidized bed. The inert protective atmosphere includes at least one of nitrogen, argon, helium, carbon dioxide, and hydrogen.

10. The method for coating the surface of a silicon-based anode material according to claim 4, characterized in that: In step S1, the pH is controlled at 6.8-7.5 and the solution temperature is controlled at 40-55℃; in step S2, the solid content is controlled at 15-25% and the pH is controlled at 5.5-6.5.

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