Preparation method of surface-modified silicon-based anode material

Abstract

This invention discloses a method for preparing a surface-modified silicon-based anode material, comprising the following steps: preparing a silicon-based matrix material, fluoride coating modification, coupling agent grafting modification, post-treatment, and carbon coating. By using silicon dioxide, silicon, and lithium silicate as the matrix, and then sequentially modifying it with fluoride coating and coupling agent grafting, a rigid-flexible synergistic three-dimensional cross-linked network can be constructed, suppressing the volume expansion of silicon particles. The modified material effectively improves its hydrophilicity and interfacial stability, while simultaneously enhancing interfacial stability and conductivity, ultimately improving the cycle life and rate performance of the silicon-based anode.

Description

Technical Field

[0001] This invention relates to the field of silicon-based anode technology, and in particular to a method for preparing a surface-modified silicon-based anode material. Background Technology

[0002] Silicon-based anode materials have a very high theoretical specific capacity, reaching up to 4200 mAh / g, making them an important research direction for lithium-ion battery anode materials. Current technologies primarily employ ternary silicon-based anode materials with crystalline SiO2, silicon, and lithium silicate as their core components. These ternary silicon-based anode materials utilize the inertial confinement effect of crystalline SiO2 and lithium silicate to effectively suppress the volume expansion of silicon grains and improve battery cycle performance.

[0003] Although the aforementioned ternary silicon-based anode material effectively suppresses the volume expansion of silicon grains, thereby improving the battery's cycle performance, the following technical problems still exist: The surface of the ternary silicon-based anode material is hydrophilic, resulting in poor interfacial compatibility with organic electrolytes. Electrolytes are prone to side reactions on the surface of the ternary silicon-based anode material, forming an unstable solid electrolyte interfacial film, which in turn leads to increased interfacial impedance and decreased battery cycle performance. Furthermore, the lithium-ion transport channels on the surface of the ternary silicon-based anode material are discontinuous, and the ionic conductivity decreases significantly at low temperatures, resulting in poor low-temperature discharge performance and failing to meet the application requirements of wide-temperature-range power batteries. Additionally, the surface of the ternary silicon-based anode material has numerous lattice defects, which easily lead to localized segregation of silicon grains during cycling, further exacerbating battery capacity decay. Therefore, it is necessary to propose a new solution to address these problems. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies of the existing technology, and its main objective is to provide a method for preparing surface-modified silicon-based anode materials. This method can effectively solve the problems of poor interfacial compatibility between existing silicon-based anode materials and electrolytes, easy production of unstable SEI films, resulting in increased interfacial impedance, poor low-temperature discharge performance, and severe battery capacity decay.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a surface-modified silicon-based anode material, comprising the following steps: (1) Preparation of silicon-based matrix material: Mix 1-1.5 kg of silicon dioxide and 120-360 g of lithium source evenly, then transfer to a tube furnace and heat to 700-900 °C under argon atmosphere, keep warm for 2-8 h, then discharge, crush and sieve to obtain silicon-based matrix material; (2) Fluoride coating modification: Dissolve 5-15g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being (1-3):1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:(10-20)mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 80-120℃ for 2-4h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with fluoride coating layer; (3) Coupling agent grafting modification: Dissolve 2-6g of coupling agent in 94-98mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: (15-25)mL, ultrasonically disperse for 20min, and hydrothermally stir at 60-80℃ for 1-3h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; (4) Post-treatment and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 80-90℃ for 10-12h. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is (1-2):1. The material is kept at 750-900℃ for 1-1.5h to obtain the surface-modified silicon-based anode material.

[0006] As a preferred option, in step (1), 1-1.5 kg of silicon dioxide and 120-360 g of lithium source are placed in a ball mill and ball milled for 1.5-3 h at a speed of 600 r / min under an argon atmosphere to achieve uniform mixing and dispersion.

[0007] As a preferred option, in step (1), 1-1.5 kg of silica and 120-360 g of lithium source are dispersed in 15 L of isopropanol to achieve uniform mixing and dispersion.

[0008] As a preferred embodiment, in step (1), the silicon dioxide is either crystalline silicon dioxide or amorphous silicon dioxide, and the lithium source is either lithium hydride, lithium nitride, or lithium phosphate.

[0009] As a preferred embodiment, in step (2), the fluoride is one of lithium fluoride, ammonium fluoride and hydrogen fluoride.

[0010] As a preferred embodiment, in step (3), the coupling agent is one of KH550, KH560 and KH570.

[0011] As a preferred embodiment, in step (4), the carbon source gas is at least one of acetylene and propane.

[0012] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution: By using silica, silicon, and lithium silicate as the matrix, and then successively modifying them with fluoride coating and coupling agent grafting, a rigid-flexible synergistic three-dimensional cross-linked network can be constructed to suppress the volume expansion of silicon particles. The modified material effectively improves its hydrophilicity and interfacial stability, while strengthening interfacial stability and conductivity, ultimately improving the cycle life and rate performance of silicon-based anodes.

[0013] To more clearly illustrate the effects of the present invention, the present invention will be described in detail below with reference to several specific embodiments. Detailed Implementation

[0014] This invention discloses a method for preparing a surface-modified silicon-based anode material, which includes the following steps: (1) Preparation of silicon-based matrix material: Mix 1-1.5 kg of silicon dioxide and 120-360 g of lithium source evenly, then transfer to a tube furnace and heat to 700-900 °C under argon atmosphere, keep warm for 2-8 h, after discharge, crush and sieve to obtain silicon-based matrix material; there are two main ways to mix and disperse silicon dioxide and lithium source. Specifically, place silicon dioxide and lithium source in a ball mill and ball mill at 600 r / min for 1.5-3 h under argon atmosphere to achieve uniform mixing and dispersion, or disperse silicon dioxide and lithium source in 15 L of isopropanol to achieve uniform mixing and dispersion; and the silicon dioxide is one of crystalline silicon dioxide and amorphous silicon dioxide, and the lithium source is one of lithium hydride, lithium nitride and lithium phosphate.

[0015] (2) Fluoride coating modification: Dissolve 5-15g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being (1-3):1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:(10-20)mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 80-120℃ for 2-4h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is one of lithium fluoride, ammonium fluoride and hydrogen fluoride.

[0016] (3) Coupling agent grafting modification: Dissolve 2-6g of coupling agent in 94-98mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: (15-25)mL, ultrasonically disperse for 20min, and hydrothermally stir at 60-80℃ for 1-3h; after filtration, wash 3 times with anhydrous ethanol to obtain a double-modified silicon-based material; the coupling agent is one of KH550, KH560 and KH570.

[0017] (4) Post-treatment and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 80-90℃ for 10-12h. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is (1-2):1. The material is kept at 750-900℃ for 1-1.5h to obtain surface-modified silicon-based anode material. The carbon source gas is at least one of acetylene and propane.

[0018] The following detailed description is provided in conjunction with several specific embodiments and comparative examples. Example 1 (1) Preparation of silicon-based matrix material: 1.5 kg of silicon dioxide and 120 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 900 °C under an argon atmosphere. The temperature is maintained for 2 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are placed in a ball mill and ball milled at a speed of 600 r / min for 1.5 h under an argon atmosphere to achieve uniform mixing and dispersion. The silicon dioxide is crystalline silicon dioxide and the lithium source is lithium hydride. In the silicon-based matrix material, the particle size of silicon dioxide is 30 nm, the particle size of silicon is 6 nm, the particle size of lithium silicate is 15 nm, and the particle size Dv50 of the silicon-based matrix material is 5 μm.

[0019] (2) Fluoride coating modification: Dissolve 10g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 2:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:20mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 100℃ for 3h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is lithium fluoride.

[0020] (3) Coupling agent grafting modification: Dissolve 4g of coupling agent in 96mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 20mL, ultrasonically disperse for 20min, and hydrothermally stir at 70℃ for 2h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH550.

[0021] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 90°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 800°C for 1.5 hours to obtain a surface-modified silicon-based anode material. The carbon source gas is acetylene.

[0022] Example 2 (1) Preparation of silicon-based matrix material: 1.5 kg of silicon dioxide and 200 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 900 °C under an argon atmosphere and kept at that temperature for 3 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are dispersed in 15 L of isopropanol to achieve uniform mixing and dispersion. The silicon dioxide is amorphous silicon dioxide and the lithium source is lithium nitride. In the silicon-based matrix material, the particle size of silicon dioxide is 40 nm, the particle size of silicon is 8 nm, the particle size of lithium silicate is 20 nm, and the particle size Dv50 of the silicon-based matrix material is 8 μm.

[0023] (2) Fluoride coating modification: Dissolve 15g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 3:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:15mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 120℃ for 2h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is ammonium fluoride.

[0024] (3) Coupling agent grafting modification: Dissolve 6g of coupling agent in 94mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 25mL, ultrasonically disperse for 20min, and hydrothermally stir at 80℃ for 1h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH560.

[0025] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 90°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 800°C for 1.5 hours to obtain surface-modified silicon-based anode material. The carbon source gas is propane.

[0026] Example 3 (1) Preparation of silicon-based matrix material: 1 kg of silicon dioxide and 360 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 700 °C under an argon atmosphere. The temperature is maintained for 8 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are placed in a ball mill and ball milled at a speed of 600 r / min for 3 h under an argon atmosphere to achieve uniform mixing and dispersion. The silicon dioxide is amorphous silicon dioxide and the lithium source is lithium phosphate. In the silicon-based matrix material, the particle size of silicon dioxide is 25 nm, the particle size of silicon is 5 nm, the particle size of lithium silicate is 10 nm, and the particle size Dv50 of the silicon-based matrix material is 3 μm.

[0027] (2) Fluoride coating modification: Dissolve 5g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 1:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:10mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 80℃ for 4h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is hydrogen fluoride.

[0028] (3) Coupling agent grafting modification: Dissolve 2g of coupling agent in 98mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 15mL, ultrasonically disperse for 20min, and hydrothermally stir at 60℃ for 3h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH570.

[0029] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 80°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 900°C for 1 hour to obtain a surface-modified silicon-based anode material. The carbon source gas is a mixture of acetylene and propane with a volume ratio of 1:1.

[0030] Example 4 (1) Preparation of silicon-based matrix material: 1.5 kg of silicon dioxide and 120 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 900 °C under an argon atmosphere. The temperature is maintained for 2 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are placed in a ball mill and ball milled at a speed of 600 r / min for 1.5 h under an argon atmosphere to achieve uniform mixing and dispersion. The silicon dioxide is crystalline silicon dioxide and the lithium source is lithium hydride. In the silicon-based matrix material, the particle size of silicon dioxide is 30 nm, the particle size of silicon is 6 nm, the particle size of lithium silicate is 15 nm, and the particle size Dv50 of the silicon-based matrix material is 5 μm.

[0031] (2) Fluoride coating modification: Dissolve 10g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 1:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:18mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 100℃ for 3h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is ammonium fluoride.

[0032] (3) Coupling agent grafting modification: Dissolve 3g of coupling agent in 97mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 25mL, ultrasonically disperse for 20min, and hydrothermally stir at 70℃ for 2h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH550.

[0033] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 90°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1.5:1. The material is kept at 800°C for 1.5 hours to obtain a surface-modified silicon-based anode material. The carbon source gas is acetylene.

[0034] Example 5 (1) Preparation of silicon-based matrix material: 1.5 kg of silicon dioxide and 200 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 900 °C under an argon atmosphere and kept at that temperature for 3 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are dispersed in 15 L of isopropanol to achieve uniform mixing and dispersion. The silicon dioxide is amorphous silicon dioxide and the lithium source is lithium nitride. In the silicon-based matrix material, the particle size of silicon dioxide is 40 nm, the particle size of silicon is 8 nm, the particle size of lithium silicate is 20 nm, and the particle size Dv50 of the silicon-based matrix material is 8 μm.

[0035] (2) Fluoride coating modification: Dissolve 15g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 2:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:20mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 120℃ for 2h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is lithium fluoride.

[0036] (3) Coupling agent grafting modification: Dissolve 6g of coupling agent in 94mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 20mL, ultrasonically disperse for 20min, and hydrothermally stir at 80℃ for 1h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH560.

[0037] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 90°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 780°C for 1.5 hours to obtain surface-modified silicon-based anode material. The carbon source gas is propane.

[0038] Example 6 (1) Preparation of silicon-based matrix material: 1 kg of silicon dioxide and 360 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 700 °C under an argon atmosphere. The temperature is maintained for 8 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are placed in a ball mill and ball milled at a speed of 600 r / min for 3 h under an argon atmosphere to achieve uniform mixing and dispersion. The silicon dioxide is amorphous silicon dioxide and the lithium source is lithium phosphate. In the silicon-based matrix material, the particle size of silicon dioxide is 25 nm, the particle size of silicon is 5 nm, the particle size of lithium silicate is 10 nm, and the particle size Dv50 of the silicon-based matrix material is 3 μm.

[0039] (2) Fluoride coating modification: Dissolve 5g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being 1:1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:10mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 80℃ for 4h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with a fluoride coating layer; the fluoride is hydrogen fluoride.

[0040] (3) Coupling agent grafting modification: Dissolve 5g of coupling agent in 95mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: 20mL, ultrasonically disperse for 20min, and hydrothermally stir at 60℃ for 3h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; the coupling agent is KH570.

[0041] (4) Post-processing and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 80°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 900°C for 1 hour to obtain surface-modified silicon-based anode material. The carbon source gas is a mixture of acetylene and propane with a volume ratio of 2:1.

[0042] Comparative Example 1 (1) Preparation of silicon-based matrix material: 1.5 kg of silicon dioxide and 120 g of lithium source are mixed and dispersed evenly. Then, the mixture is transferred to a tube furnace and heated to 900 °C under an argon atmosphere. The temperature is maintained for 2 h. After discharge, the mixture is crushed and sieved to obtain silicon-based matrix material. Specifically, silicon dioxide and lithium source are placed in a ball mill and ball milled at a speed of 600 r / min for 1.5 h under an argon atmosphere to achieve uniform mixing and dispersion. The silicon dioxide is crystalline silicon dioxide and the lithium source is lithium hydride. In the silicon-based matrix material, the particle size of silicon dioxide is 30 nm, the particle size of silicon is 6 nm, the particle size of lithium silicate is 15 nm, and the particle size Dv50 of the silicon-based matrix material is 5 μm.

[0043] (2) Post-processing and carbon coating: The silicon-based matrix material obtained in step (1) is vacuum dried at 90°C for 12 hours. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is 1:1. The material is kept at 800°C for 1.5 hours to obtain silicon-based anode material. The carbon source gas is acetylene.

[0044] The performance of the anode materials prepared in the above embodiments and comparative examples was tested, and the test results are shown in Table 1.

[0045]

[0046] Table 1 Analyze the above data. The preparation method of this invention employs coupling agent grafting modification, transforming the surface of the silicon-based material from hydrophilic to oleophilic. This reduces the contact angle with the organic electrolyte from 80° to 25°-31°, significantly improving interfacial compatibility and effectively suppressing side reactions between the electrolyte and the material surface. This results in a more stable SEI film, with the interfacial impedance decreasing from 180.6Ω to 50-70Ω. Furthermore, the fluoride coating fills lattice defects on the material surface, further enhancing the constraint on silicon grain volume expansion and simultaneously suppressing silicon grain segregation. After 300 cycles at 1C, the modified material exhibits a capacity retention of ≥90%, far exceeding the 75%-80% of traditional ternary silicon-based materials. Simultaneously, the fluoride coating constructs continuous lithium-ion transport channels, improving the ionic conductivity of the material surface. The modified material maintains high conductivity at -20°C and 0.5C. The rate-reversible capacity retention rate is ≥75%, while the traditional ternary silicon-based material only achieves 50%-60%; furthermore, it undergoes dual surface modification, resulting in better particle dispersion and preventing agglomeration. The compaction density is increased from the traditional 1.3-2.0 g / cm³ to 2.1-0~2.3 g / cm³, which is beneficial for improving the volumetric energy density of the battery.

[0047] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a surface-modified silicon-based anode material, characterized in that: It includes the following steps: (1) Preparation of silicon-based matrix material: Mix 1-1.5 kg of silicon dioxide and 120-360 g of lithium source evenly, then transfer to a tube furnace and heat to 700-900 °C under argon atmosphere, keep warm for 2-8 h, then discharge, crush and sieve to obtain silicon-based matrix material; (2) Fluoride coating modification: Dissolve 5-15g of fluoride in 100mL of alcohol-water mixed solution, with the volume ratio of ethanol to deionized water being (1-3):1, to prepare a fluoride modification solution; take 50g of silicon-based matrix material obtained in step (1) and add it to the fluoride modification solution, with a solid-liquid ratio of 1g:(10-20)mL, ultrasonically disperse for 30min, and perform hydrothermal reaction at 80-120℃ for 2-4h; after filtration, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry at 60℃ for 6h to obtain silicon-based material with fluoride coating layer; (3) Coupling agent grafting modification: Dissolve 2-6g of coupling agent in 94-98mL of anhydrous ethanol to prepare a coupling agent modification solution; add the silicon-based material with fluoride coating obtained in step (2) to the coupling agent modification solution, with a solid-liquid ratio of 1g: (15-25)mL, ultrasonically disperse for 20min, and hydrothermally stir at 60-80℃ for 1-3h; after filtration, wash 3 times with anhydrous ethanol to obtain the double-modified silicon-based material; (4) Post-treatment and carbon coating: The double-modified silicon-based material obtained in step (3) is vacuum dried at 80-90℃ for 10-12h. Then, it is placed in a rotary kiln and argon and carbon source gas are introduced. The volume ratio of argon and carbon source gas is (1-2):

1. The material is kept at 750-900℃ for 1-1.5h to obtain the surface-modified silicon-based anode material.

2. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (1), 1-1.5 kg of silicon dioxide and 120-360 g of lithium source are placed in a ball mill and ball milled for 1.5-3 h at a speed of 600 r / min under an argon atmosphere to achieve uniform mixing and dispersion.

3. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (1), 1-1.5 kg of silica and 120-360 g of lithium source are dispersed in 15 L of isopropanol to achieve uniform mixing and dispersion.

4. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (1), the silicon dioxide is one of crystalline silicon dioxide and amorphous silicon dioxide, and the lithium source is one of lithium hydride, lithium nitride and lithium phosphate.

5. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (2), the fluoride is one of lithium fluoride, ammonium fluoride and hydrogen fluoride.

6. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (3), the coupling agent is one of KH550, KH560 and KH570.

7. The method for preparing the surface-modified silicon-based anode material according to claim 1, characterized in that: In step (4), the carbon source gas is at least one of acetylene and propane.

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