Silicon negative electrode composite material, preparation method thereof and lithium ion battery

Abstract

This invention belongs to the technical field of lithium-ion batteries, and discloses a silicon anode composite material, its preparation method, and a lithium-ion battery. The preparation method provided by this invention employs an extraction process combining alkaline extraction and acid precipitation to treat fly ash, resulting in the extraction of silicon dioxide in gel form. Subsequently, a treatment process combining magnesothermic reduction, a first hydrofluoric acid treatment, PEG modification, and a second hydrofluoric acid treatment is used to obtain a nano-silicon material with ideal morphology, surface functional group composition, and crystal lattice structure. Finally, the nano-silicon material undergoes silver deposition, resin coating, and carbonization to achieve Ag modification and hard carbon coating, resulting in an ideal SiO2-Ag-carbon gradient interface structure within the composite material. This yields a silicon anode composite material with excellent conductivity, cycle stability, initial coulombic efficiency, and rate performance, showing promising application prospects.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion batteries, and particularly relates to a silicon anode composite material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the continued growth in demand for lithium-ion batteries, the need for high-energy-density lithium-ion batteries is increasing daily. However, the theoretical specific capacity of graphite, currently the mainstream anode material, is only 372 mAh·g. -1 However, this is no longer sufficient to meet the demand for high specific energy. Among many anode materials such as silicon-based, transition metal oxide, and tin-based materials, silicon has a theoretical specific capacity as high as 4200 mAh·g. -1 Li can be formed 4.4 Silicon alloys have an energy density more than 11 times that of graphite and a discharge potential as low as about 0.5V, making silicon a promising candidate for the next generation of anode materials.

[0003] Despite the significant advantages of silicon anode materials, their commercialization remains hampered, primarily due to two critical drawbacks. First, during charge and discharge, silicon undergoes rapid volume expansion, exceeding 300%, leading to electrode pulverization and detachment from the current collector, resulting in rapid capacity decay. Second, silicon, being a semiconductor material, exhibits extremely poor conductivity, resulting in low specific capacity and poor capacity retention under high-rate charge and discharge conditions. Therefore, resolving the current challenges of silicon anode materials has become crucial for developing next-generation high-energy-density battery anode materials.

[0004] Carbon coating technology is an effective means to alleviate the volume expansion of silicon-based anodes, but carbon materials have limited effect on improving conductivity. Meanwhile, silicon dioxide materials are generally prepared using precursors, and the preparation process usually generates waste, resulting in poor environmental friendliness, high cost, and difficulty in large-scale production. Furthermore, the preparation cost of nanoscale silicon materials is high; processing silicon materials from larger sizes to the nanoscale increases the cost by at least 100%, and the preparation process is also more complex.

[0005] Therefore, finding a safe, reliable, low-cost, and environmentally friendly silicon-containing raw material, and using it as a raw material to prepare silicon materials with both low volume expansion and excellent electrical properties, is of great significance for the research and development of next-generation high-energy-density battery anode materials. Summary of the Invention

[0006] The primary objective of this invention is to address the problems of high preparation cost, poor environmental friendliness, and contradictions in the low volume expansion and excellent electrical properties of existing silicon-based anode materials, and to provide a method for preparing silicon anode composite materials.

[0007] The second objective of this invention is to provide a silicon anode composite material.

[0008] A third objective of this invention is to provide a lithium-ion battery.

[0009] Specifically, the preparation method of the silicon anode composite material provided by the present invention includes: S1, preparation of silicon dioxide: taking fly ash for alkaline extraction and acid precipitation treatment to obtain the silicon dioxide; S2, preparation of nano-silicon material: taking the silicon dioxide for magnesium thermal reduction treatment, first hydrofluoric acid treatment, PEG modification treatment and second hydrofluoric acid treatment to obtain the nano-silicon material; S3, preparation of silver-modified silicon particle composite material: taking the nano-silicon material for silver deposition treatment to obtain the silver-modified silicon particle composite material; S4, preparation of silicon anode composite material: taking the silver-modified silicon particle composite material for resin coating treatment and carbonization treatment to obtain the silicon anode composite material; in step S2, the PEG modification treatment includes: taking the solid product obtained by the first hydrofluoric acid treatment and mixing it evenly with polyethylene glycol melt, ultrasonically treating it at a frequency of 30Hz~45Hz for 1h~2h, and calcining it at 700℃~800℃ for 3h~5h to complete the PEG modification treatment.

[0010] Furthermore, the fly ash comprises 50% (w / w) to 60% (w / w) of SiO2 and 30% (w / w) to 45% (w / w) of Al2O3.

[0011] Further, in step S2, the PEG modification treatment includes one or more of the following technical features: (1) the mass ratio of the solid product obtained by the first hydrofluoric acid treatment to the polyethylene glycol melt is 1:(4~6); (2) the preparation of the polyethylene glycol melt includes: taking polyethylene glycol, heating it to 100℃~110℃ and stirring it continuously for 1.5h~3h to obtain the polyethylene glycol melt; (3) the weight average molecular weight of polyethylene glycol in the polyethylene glycol melt is 3000~8000.

[0012] Further, in step S1, the alkaline extraction treatment includes: mixing the fly ash with an alkaline solution and stirring at 90℃~95℃ for 3h~6h to complete the alkaline extraction treatment.

[0013] Further, in step S1, the alkaline extraction treatment includes one or more of the following technical features: (1) the alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution; (2) the concentration of alkali in the alkaline solution is 2M~4M; (3) the addition ratio of fly ash to alkaline solution is (500~1000)g:1L.

[0014] Further, in step S1, the acid precipitation treatment includes: adjusting the pH of the liquid product obtained by the alkaline extraction treatment to 6.8~7 using acid solution I, and letting it stand for 18h~24h to complete the acid precipitation treatment.

[0015] Further, in step S1, the acid precipitation treatment includes one or more of the following technical features: (1) the acid solution I includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution I is 0.5M~1.5M.

[0016] Further, step S1 includes a first purification treatment performed before alkaline extraction. The first purification treatment includes: mixing the fly ash with water and soaking it in hot water at 80℃~100℃ for 2~3 hours; mixing acid solution II with the fly ash that has been soaked in hot water and performing a first acid leaching treatment at 90℃~95℃ for 3~6 hours to complete the first purification treatment.

[0017] Further, in step S1, the first purification process includes one or more of the following technical features: (1) the acid solution II includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution II is 0.5M~1.5M; (3) the addition ratio of fly ash and acid solution is (80~150)g:1L.

[0018] Further, step S1 includes a second purification process after acid precipitation treatment. The second purification process includes: mixing acid solution III and the solid product obtained by acid precipitation treatment, and performing a second acid leaching treatment at 90℃~95℃ for 3h~5h to complete the second purification process.

[0019] Further, in step S1, the second purification process includes one or more of the following technical features: (1) the acid solution III includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution III is 0.5M~1.5M; (3) the addition ratio of the solid product obtained by the acid precipitation treatment to the acid solution is (400~600)g:1L.

[0020] Further, in step S2, the magnesium thermal reduction treatment includes: mixing the silicon dioxide, magnesium powder and sodium chloride, gradually heating to 600℃~800℃ in an inert atmosphere at a heating rate of 2℃ / min~5℃ / min, and then holding at that temperature for 3h~8h to complete the magnesium thermal reduction treatment.

[0021] Further, in step S2, the mass ratio of silicon dioxide, magnesium powder and sodium chloride is 1:(0.7~1.5):(2~3).

[0022] Further, in step S2, the first hydrofluoric acid treatment includes: mixing the solid product obtained by the magnesium thermal reduction treatment with acid solution IV, and performing a third acid leaching treatment at 60℃~85℃ for 2h~4h; mixing the solid product obtained by the third acid leaching treatment with HF solution I, and performing stirring treatment for 2h~4h to complete the first hydrofluoric acid treatment.

[0023] Further, in step S2, the first hydrofluoric acid treatment includes one or more of the following technical features: (1) the acid solution IV includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution IV is 1.5M~2M; (3) the molar ratio of silicon added in the solid product obtained by acid and magnesium thermal reduction treatment in the acid solution IV is 1:(1.5~2); (4) the concentration of HF solution I is 0.05M~0.15M; (5) the addition ratio of the solid product obtained by the third acid leaching treatment to HF solution I is (100~300)g:1L.

[0024] Further, in step S2, the second hydrofluoric acid treatment includes: taking water, HF solution II and anhydrous ethanol, mixing them, adding the solid product obtained by the PEG modification treatment, and stirring for 5 min to 8 min to complete the second hydrofluoric acid treatment.

[0025] Further, in step S2, the second hydrofluoric acid treatment includes one or more of the following technical features: (1) the concentration of HF solution II is 35% (w / v) to 45% (w / v); (2) the volume ratio of water, HF solution II and anhydrous ethanol is (6~7):1:(1.5~2.5); (3) the concentration of the solid product obtained by the PEG modification treatment is 25 g / L to 35 g / L.

[0026] Further, in step S3, the silver deposition process includes: mixing the nano-silicon material and silver nitrate solution, adding HF solution III, and stirring for 5 min to 10 min to complete the silver deposition process.

[0027] Further, in step S3, the silver deposition treatment includes one or more of the following technical features: (1) the concentration of silver nitrate is 2mM~4mM; (2) the concentration of the added nano-silicon material is 13g / L~18g / L; (3) the concentration of HF solution III is 35%(w / v)~45%(w / v).

[0028] Further, in step S4, the resin coating treatment includes: taking the silver-modified silicon particle composite material, resin and volatile solvent, mixing them evenly, and stirring at 50℃~55℃ until the volatile solvent is completely evaporated, thus completing the resin coating treatment.

[0029] Further, in step S4, the resin coating treatment includes one or more of the following technical features: (1) the resin includes a thermosetting resin; (2) the volatile solvent includes one or more of methanol, ethanol and acetone; (3) the mass ratio of the silver-modified silicon particle composite material to the resin is (13~17):1.

[0030] Further, in step S4, the resin includes one or more of phenolic resin, polyimide resin, polyacrylonitrile resin, pitch-based resin, and lignin-based resin.

[0031] Furthermore, in step S4, the carbonization treatment is carried out at a temperature of 700℃~900℃ for 3h~4h.

[0032] The silicon anode composite material provided by the present invention is prepared by the above-described method for preparing silicon anode composite materials.

[0033] The lithium-ion battery provided by the present invention includes the above-mentioned silicon anode composite material.

[0034] Beneficial effects: In the preparation method provided by this invention, fly ash, a low-cost silicon source, is used as the raw material for extracting silicon dioxide. First, the fly ash is treated with an extraction process combining alkaline extraction and acid precipitation, so that silicon dioxide is extracted in gel form. Then, a treatment process combining magnesothermic reduction treatment, first hydrofluoric acid treatment, PEG modification treatment, and second hydrofluoric acid treatment is used to convert silicon dioxide into silicon and gradually optimize the particle size, morphology, surface functional group composition, and crystal structure of silicon particles, thereby obtaining a nano-silicon material with ideal morphology, surface functional group composition, and crystal structure. Finally, the nano-silicon material is subjected to silver deposition treatment, resin coating treatment, and carbonization treatment to achieve Ag modification and hard carbon coating of the nano-silicon material, constructing an ideal SiO2-Ag-carbon gradient interface structure inside the material, thereby obtaining a silicon anode composite material with excellent conductivity, cycle stability, first coulombic efficiency, and rate performance, which has very promising application prospects. Attached Figure Description

[0035] Figure 1 This is a SEM image of the silicon anode composite material provided in Example 1 of the present invention. Detailed Implementation

[0036] Based on the need to address the problems of high production costs, decreased cycle stability due to volume expansion during charge and discharge, and unsatisfactory conductivity in existing silicon anode materials, the inventors of this invention chose fly ash as the silicon source and used Ag modification and hard carbon coating as modification strategies to improve the cycle stability and conductivity of the material. However, the inventors found in experiments that, compared with pure silicon sources such as TEOS and high-purity sodium silicate, the high-purity nano-silicon material obtained by multiple purification and extraction processes from fly ash is affected by factors such as the impurity composition, microstructure, and surface properties of fly ash itself. Compared with single modification, simultaneous Ag modification and hard carbon coating actually degrades the material performance. Conventional silicon extraction and nano-silicon material preparation methods cannot be well matched with the Ag modification and hard carbon coating modification process using fly ash as the silicon source.

[0037] Through further in-depth research and extensive experimentation, the inventors creatively discovered that by employing an extraction process combining alkaline extraction and acid precipitation, coupled with a nano-silicon preparation process combining magnesiothermal reduction treatment, a first hydrofluoric acid treatment, PEG modification treatment, and a second hydrofluoric acid treatment, the nano-silicon material extracted from fly ash can be well adapted to the requirements of Ag modification and hard carbon coating for nanoparticle morphology, surface functional group composition, and lattice structure. The Ag modification and hard carbon coating at this stage can construct an ideal SiO2-Ag-carbon gradient interface structure within the material, which can alleviate the volume expansion problem of silicon-based anode materials while improving the electrical performance of the material. Ultimately, a silicon-based anode material with excellent conductivity, cycle stability, initial coulombic efficiency, and rate performance is prepared, which is of great significance for the development of high-energy-density lithium-ion batteries. Based on this, the technical solution of this invention is obtained.

[0038] The preparation method of the silicon anode composite material provided by this invention specifically includes: S1, preparation of silicon dioxide: taking fly ash and performing alkaline extraction treatment and acid precipitation treatment to obtain the silicon dioxide; S2, preparation of nano-silicon material: taking the silicon dioxide and performing magnesium thermal reduction treatment, first hydrofluoric acid treatment, PEG modification treatment and second hydrofluoric acid treatment to obtain the nano-silicon material; S3, preparation of silver-modified silicon particle composite material: taking the nano-silicon material and performing silver deposition treatment to obtain the silver-modified silicon particle composite material; S4, preparation of silicon anode composite material: taking the silver-modified silicon particle composite material and performing resin coating treatment and carbonization treatment to obtain the silicon anode composite material.

[0039] In this invention, fly ash refers to fine particulate solid waste collected from flue gas during the high-temperature combustion of pulverized coal. Specifically, fly ash includes 50% (w / w) to 60% (w / w) of SiO2 and 30% (w / w) to 45% (w / w) of Al2O3.

[0040] In this invention, in step S1, the alkaline extraction treatment refers to the process of using strong alkaline substances such as sodium hydroxide and potassium hydroxide to dissolve SiO2 in fly ash, so that silicon dissolves in water in the form of metasilicate, thereby achieving effective separation of silicon from impurities such as alumina, ferric oxide, calcium oxide, and sulfur in fly ash. The specific reaction that occurs in this process is shown in formula (1).

[0041] Equation (1) In this invention, step S1, the alkali extraction treatment specifically includes: mixing the fly ash with an alkaline solution and stirring at 90℃~95℃ for 3h~6h to complete the alkali extraction treatment. More specifically, the stirring temperature can be 90℃, 91℃, 92.5℃, 94℃, 95℃ or any value between them, and the time can be 3h, 4h, 5h, 6h or any value between them.

[0042] In some specific embodiments, the alkaline solution in the alkaline extraction process includes, but is not limited to, sodium hydroxide solution and / or potassium hydroxide solution.

[0043] In some specific embodiments, the concentration of alkali in the alkali solution during the alkali extraction process is preferably 2M to 4M, specifically 2M, 2.1M, 2.4M, 2.7M, 2.9M, 3M, 3.2M, 3.5M, 3.8M, 4M or any value between them.

[0044] In some specific embodiments, the preferred ratio of fly ash to alkaline solution in the alkaline extraction treatment is (500~1000) g:1L, specifically 500g:1L, 600g:1L, 700g:1L, 800g:1L, 900g:1L, 1000g:1L or any value between them.

[0045] In this invention, step S1 preferably includes a first purification treatment performed before alkaline extraction. The first purification treatment achieves pre-activation of fly ash and effective removal of impurities such as aluminum, iron, and calcium, thereby improving the efficiency of subsequent alkaline extraction.

[0046] In this invention, step S1, the first purification treatment specifically includes: mixing the fly ash with water and soaking it in hot water at 80℃~100℃ for 2~3 hours; mixing acid solution II with the fly ash that has undergone the hot water soaking treatment, and performing a first acid leaching treatment at 90℃~95℃ for 3 hours~6 hours to complete the first purification treatment. More specifically, the temperature of the hot water soaking treatment can be 80℃, 83℃, 85℃, 90℃, 95℃, 100℃ or any value between them, and the time can be 2 hours, 2.2 hours, 2.4 hours, 2.8 hours, 3 hours or any value between them. The temperature of the first acid leaching treatment can be 90℃, 91℃, 92℃, 93℃, 94℃, 95℃ or any value between them, and the time can be 2 hours, 2.3 hours, 2.5 hours, 3 hours or any value between them.

[0047] In this invention, step S1, the first purification treatment preferably includes a drying treatment of the solid product obtained from the first acid leaching treatment. The drying conditions include a temperature preferably of 100℃~120℃, specifically 100℃, 105℃, 110℃, 115℃, 120℃ or any value between them; and a time preferably of 12h~18h, specifically 12h, 13h, 14h, 15h, 17h, 18h or any value between them.

[0048] In some specific embodiments, specific examples of the acid solution II in the first purification process include, but are not limited to, one or more of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution.

[0049] In some specific embodiments, during the first purification process, the concentration of acid in acid solution II is preferably 0.5M to 1.5M, specifically 0.5M, 0.7M, 0.9M, 1M, 1.2M, 1.5M or any value between them.

[0050] In some specific embodiments, the preferred addition ratio of fly ash to acid solution in the first purification process is (80~150) g:1L, specifically 80g:1L, 85g:1L, 90g:1L, 100g:1L, 110g:1L, 125g:1L, 140g:1L, 150g:1L or any value between them.

[0051] In this invention, in step S1, the acid precipitation treatment refers to the process of reacting strong acidic substances such as hydrochloric acid, sulfuric acid, and nitric acid with metasilicate to precipitate silicon in the form of hydrated silicon dioxide from the solution to obtain silicon dioxide gel. The specific reactions that occur in this process are shown in formulas (2) to (7).

[0052] Equation (2) Equation (3) Equation (4) Equation (5) Equation (6) Equation (7) In this invention, step S1 specifically includes: adjusting the pH of the liquid product obtained by the alkaline extraction treatment to 6.8-7 using acid solution I, and letting it stand for 18-24 hours to complete the acid precipitation treatment.

[0053] In some specific embodiments, the acid solution I in the acid precipitation treatment includes, but is not limited to, one or more of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution.

[0054] In some specific embodiments, in the acid precipitation treatment, the concentration of acid in the acid solution I is preferably 0.5M to 1.5M, specifically 0.5M, 0.8M, 1M, 1.1M, 1.3M, 1.5M or any value between them.

[0055] In this invention, step S1 preferably includes a drying process on the solid product obtained by the acid precipitation treatment. The drying conditions include a temperature preferably of 100℃~120℃, specifically 100℃, 105℃, 110℃, 115℃, 120℃ or any value between them; and a time preferably of 12h~18h, specifically 12h, 13h, 14h, 15h, 17h, 18h or any value between them.

[0056] In this invention, step S1 preferably includes a second purification process performed after the acid precipitation treatment. The second purification process further removes impurities from the solid product (with or without drying) obtained by the acid precipitation treatment, thereby improving the purity of the obtained silica.

[0057] In this invention, step S2, the second purification process specifically includes: mixing acid solution III and the solid product obtained by acid precipitation, and performing a second acid leaching treatment at 90℃~95℃ for 3h~5h to complete the second purification process. More specifically, the temperature of the second acid leaching treatment can be 90℃, 92℃, 94℃, 95℃ or any value between them, and the time can be 3h, 3.5h, 4h, 4.5h, 5h or any value between them.

[0058] In some specific embodiments, the acid solution III in the second purification process includes, but is not limited to, one or more of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution.

[0059] In some specific embodiments, in the second purification process, the concentration of acid in acid solution III is preferably 0.5M to 1.5M, specifically 0.5M, 0.8M, 1M, 1.2M, 1.5M or any value between them.

[0060] In some specific embodiments, in the second purification process, the addition ratio of the solid product obtained by the acid precipitation treatment to the acid solution is preferably (400~600) g:1L, specifically it can be 400g:1L, 420g:1L, 450g:1L, 500g:1L, 550g:1L, 600g:1L or any value between them.

[0061] In this invention, step S1, the second purification process preferably includes drying the solid product obtained from the second acid leaching treatment. The drying conditions include a temperature preferably of 100℃~120℃, specifically 100℃, 105℃, 110℃, 115℃, 120℃, or any value between them; and a time preferably of 12h~18h, specifically 12h, 13h, 14h, 15h, 17h, 18h, or any value between them.

[0062] In this invention, in step S2, the magnesium thermal reduction treatment refers to the process of reducing silicon dioxide to silicon with magnesium as a reducing agent to obtain silicon material with low porosity. The specific reaction that occurs in this process is shown in formula (8).

[0063] Equation (8) In this invention, step S2, the magnesian thermal reduction treatment specifically includes: mixing the silicon dioxide, magnesium powder, and sodium chloride, and gradually heating the mixture to 600℃~800℃ in an inert atmosphere at a heating rate of 2℃ / min~5℃ / min, followed by holding at that temperature for 3h~8h to complete the magnesian thermal reduction treatment. More specifically, the heating rate can be 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 5℃ / min, or any value between them; the holding temperature can be 600℃, 620℃, 650℃, 700℃, 750℃, 800℃, or any value between them; and the holding time can be 3h, 4h, 5h, 6h, 7h, 8h, or any value between them.

[0064] In some specific embodiments, in the magnesothermic reduction treatment, the preferred mass ratio of silicon dioxide, magnesium powder and sodium chloride is 1:(0.7~1.5):(2~3), specifically 1:0.7:2, 1:0.9:2.5, 1:1.5:3 or any value between them.

[0065] In this invention, in step S2, the first hydrofluoric acid treatment refers to first using strong acidic substances such as hydrochloric acid, nitric acid, and sulfuric acid to remove magnesium oxide and unreacted magnesium from the solid product obtained by magnesium thermal reduction treatment, and then using hydrofluoric acid to remove silicon dioxide, thereby purifying the solid product obtained by magnesium thermal reduction treatment.

[0066] In this invention, step S2, the first hydrofluoric acid treatment specifically includes: mixing the solid product obtained from the magnesium thermal reduction treatment with acid solution IV, and performing a third acid leaching treatment at 60℃~85℃ for 2h~4h; then mixing the solid product obtained from the third acid leaching treatment with HF solution I and stirring for 2h~4h to complete the first hydrofluoric acid treatment. More specifically, the temperature of the third acid leaching treatment can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or any value between them, and the time can be 2h, 2.3h, 2.5h, 2.8h, 3h, 3.5h, 4h or any value between them. The stirring time can be 2h, 2.3h, 2.5h, 2.8h, 3h, 3.5h, 4h or any value between them.

[0067] In some specific embodiments, the first hydrofluoric acid treatment, specifically examples of the acid solution IV include, but are not limited to, one or more of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution.

[0068] In some specific embodiments, during the first hydrofluoric acid treatment, the concentration of acid in the acid solution IV is preferably 1.5M to 2M, specifically 1.5M, 1.6M, 1.8M, 2M or any value between them.

[0069] In some specific embodiments, the preferred molar ratio of silicon added to the solid product obtained by acid and magnesium thermal reduction treatment in acid solution IV is 1:(1.5~2), specifically it can be 1:1.5, 1:1.7, 1:1.9, 1:2 or any value between them.

[0070] In some specific embodiments, the concentration of the HF solution I is preferably 0.05M to 0.15M, specifically 0.05M, 0.08M, 0.1M, 0.12M, 0.15M or any value between them.

[0071] In some specific embodiments, the addition ratio of the solid product obtained by the third acid leaching treatment to HF solution I is preferably (100~300) g:1L, specifically it can be 100g:1L, 150g:1L, 200g:1L, 250g:1L, 300g:1L or any value between them.

[0072] In this invention, step S2 preferably includes washing and drying the solid product obtained from the first hydrofluoric acid treatment. Specifically, the washing process involves washing the solid product obtained from the first hydrofluoric acid treatment with distilled water until it reaches neutrality. The drying conditions include a temperature preferably between 100°C and 120°C, specifically 100°C, 105°C, 110°C, 115°C, 120°C, or any value between them; and a time preferably between 3 hours and 5 hours, specifically 3 hours, 3.5 hours, 3.8 hours, 4 hours, 4.5 hours, 5 hours, or any value between them.

[0073] In this invention, step S2, the PEG modification treatment refers to the process of using PEG as a modifier, and simultaneously employing ultrasonic treatment and calcination treatment to achieve the modification of silicon particles by crushing, adjusting the microstructure, optimizing the crystal structure, and optimizing the surface functional groups.

[0074] In this invention, step S2, the PEG modification treatment specifically includes: uniformly mixing the solid product obtained from the first hydrofluoric acid treatment with molten polyethylene glycol, ultrasonically treating it at a frequency of 30Hz~45Hz for 1h~2h, and calcining it at 700℃~800℃ for 3h~5h to complete the PEG modification treatment. More specifically, the frequency of the ultrasonic treatment can be 30Hz, 32Hz, 35Hz, 38Hz, 40Hz, 42Hz, 45Hz or any value between them, and the time can be 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h or any value between them. The temperature of the calcination treatment can be 700℃, 715℃, 720℃, 750℃, 780℃, 800℃ or any value between them, and the time can be 3h, 3.5h, 4h, 4.5h, 5h or any value between them.

[0075] In some specific embodiments, the mass ratio of the solid product obtained from the first hydrofluoric acid treatment to the polyethylene glycol melt in the PEG modification treatment is preferably 1:(4~6), specifically 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or any value between them.

[0076] In some specific embodiments, the preparation of the polyethylene glycol melt in the PEG modification treatment preferably includes: heating polyethylene glycol to 100°C~110°C and stirring continuously for 1.5h~3h to obtain the polyethylene glycol melt.

[0077] In some specific embodiments, during the PEG modification treatment, the weight-average molecular weight of polyethylene glycol in the polyethylene glycol melt is preferably 3000~8000, specifically 3000, 3200, 3500, 4000, 4500, 5000, 7000, 8000 or any value between them.

[0078] In this invention, step S2, the second hydrofluoric acid treatment refers to the process of effectively removing the oxide layer on the surface of silicon particles by using the solution environment provided by water, HF and ethanol, thereby purifying and activating the surface of silicon particles.

[0079] In this invention, step S2 specifically includes: taking water, HF solution II and anhydrous ethanol, mixing them, adding the solid product obtained by the PEG modification treatment, and stirring for 5 min to 8 min to complete the second hydrofluoric acid treatment.

[0080] In some specific embodiments, in the second hydrofluoric acid treatment, the concentration of the HF solution II is preferably 35% (w / v) to 45% (w / v), specifically 35% (w / v), 36% (w / v), 38% (w / v), 40% (w / v), 42% (w / v), 45% (w / v) or any value between them.

[0081] In some specific embodiments, in the second hydrofluoric acid treatment, the preferred volume ratio of water, HF solution II and anhydrous ethanol is (6~7):1:(1.5~2.5), specifically 6:1:1.5, 6.5:1:1.8, 7:1:2, 7:1:2.5 or any value between them.

[0082] In some specific embodiments, the concentration of the solid product obtained by the PEG modification treatment in the second hydrofluoric acid treatment is preferably 25 g / L to 35 g / L, specifically 25 g / L, 28 g / L, 30 g / L, 33 g / L, 35 g / L or any value between them.

[0083] In this invention, step S2, the second hydrofluoric acid treatment preferably includes a drying process on the resulting solid product. The drying conditions include a temperature preferably of 50°C to 55°C, specifically 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, or any value between them; and a time preferably of 5 hours to 8 hours, specifically 5 hours, 5.2 hours, 5.5 hours, 6 hours, 7 hours, 8 hours, or any value between them.

[0084] In this invention, the silver deposition treatment in step S3 refers to the Ag modification process of reducing silver ions and depositing them on the surface of nano-silicon particles.

[0085] In this invention, step S3 specifically includes: mixing the nano-silicon material and silver nitrate solution, adding HF solution III, and stirring for 5 to 10 minutes to complete the silver deposition process. More specifically, the stirring time can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or any value between them.

[0086] In some specific embodiments, the concentration of silver nitrate in the silver deposition treatment is preferably 2mM to 4mM, specifically 2mM, 2.5mM, 3mM, 3.5mM, 4mM or any value between them.

[0087] In some specific embodiments, the concentration of the added nano-silicon material in the silver deposition process is preferably 13 g / L to 18 g / L, specifically 13 g / L, 15 g / L, 17 g / L, 18 g / L or any value between them.

[0088] In some specific embodiments, the concentration of the HF solution III in the silver deposition process is preferably 35% (w / v) to 45% (w / v), specifically 35% (w / v), 38% (w / v), 40% (w / v), 42% (w / v), 45% (w / v) or any value between them.

[0089] In this invention, step S3, the silver deposition treatment preferably includes a drying process on the obtained silver-modified silicon particle composite material. The drying conditions include a temperature preferably of 50°C to 55°C, specifically 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, or any value between them; and a time preferably of 5 hours to 8 hours, specifically 5 hours, 5.2 hours, 5.5 hours, 6 hours, 7 hours, 8 hours, or any value between them.

[0090] In this invention, step S4, the resin coating treatment refers to the process of coating the surface of silver-modified silicon particles with resin in the presence of a volatile solvent.

[0091] In this invention, step S4, the resin coating treatment specifically includes: taking the silver-modified silicon particle composite material, resin, and volatile solvent, mixing them evenly, and stirring at 50℃~55℃ until the volatile solvent is completely evaporated, thus completing the resin coating treatment. More specifically, the temperature for stirring can be 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, or any value between them.

[0092] In some specific embodiments, the resin coating treatment specifically includes thermosetting resins, and specific examples of thermosetting resins include, but are not limited to, one or more of phenolic resins, polyimide resins, polyacrylonitrile resins, pitch-based resins, and lignin-based resins.

[0093] In some specific embodiments, examples of the volatile solvent in the resin coating treatment include, but are not limited to, one or more of methanol, ethanol, and acetone.

[0094] In some specific embodiments, in the resin coating treatment, the preferred mass ratio of the silver-modified silicon particle composite material to the resin is (13~17):1, specifically it can be 13:1, 14:1, 15:1, 16:1, 17:1 or any value between them.

[0095] In this invention, step S4, the carbonization treatment refers to the process of converting the resin layer coating the surface of silver-modified silicon particles into a hard carbon layer under high temperature conditions. More specifically, the conditions for the carbonization treatment include a temperature preferably of 700℃~900℃, specifically 700℃, 750℃, 780℃, 800℃, 850℃, 900℃ or any value between them; and a time preferably of 3h~4h, specifically 3h, 3.2h, 3.5h, 3.8h, 4h or any value between them.

[0096] The present invention also provides a silicon anode composite material, which is prepared by the above-described method for preparing silicon anode composite materials.

[0097] The present invention also provides a lithium-ion battery comprising the above-mentioned silicon anode composite material.

[0098] The embodiments of the present invention are described in detail below. These embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0099] Example 1 This embodiment illustrates a method for preparing a silicon anode composite material, specifically including the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0100] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0101] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0102] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0103] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0104] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0105] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0106] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt. Then, according to the mass ratio of 1:5, take solid product 4 and polyethylene glycol melt and mix them. Stir for 20 minutes, then use 35Hz frequency for ultrasonic treatment for 1.5 hours, and calcine at 750°C for 3 hours to complete the PEG modification treatment and obtain solid product 5.

[0107] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0108] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0109] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and phenolic resin (M) at a mass ratio of 15:1, take silver-modified silicon particle composite material and phenolic resin (M) w Mix approximately 300~2000 g of the resin evenly, then add an appropriate amount of anhydrous ethanol and stir at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0110] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0111] The silicon anode composite material provided in this embodiment was imaged using a scanning electron microscope (SEM, Quanta 200FEG), and the results are as follows. Figure 1 As shown. By Figure 1 The results show that silver nanoparticles are effectively attached to the surface of the nano-silicon material.

[0112] Example 2 This embodiment illustrates a method for preparing a silicon anode composite material, specifically including the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 90°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0113] The fly ash contains 55% (w / w) SiO2 and 41% (w / w) Al2O3.

[0114] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0115] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0116] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. After the second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour), the solution is allowed to stand and cool to room temperature. After filtration and washing the residue with distilled water until neutral, it is dried at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0117] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0118] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the acid purification treatment is completed. The solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 200g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0119] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:4.5 and mix and stir for 20 minutes. Then, use 40Hz frequency for ultrasonic treatment for 2 hours and calcine at 750°C for 3 hours to complete PEG modification treatment and obtain solid product 5.

[0120] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0121] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 18 g / L. Then, add a 40% (w / v) HF solution at a volume ratio of 1:25 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0122] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and polyimide resin (M) at a mass ratio of 17:1, take silver-modified silicon particle composite material and polyimide resin (M) w Approximately 5×10 4 ~2×10 5 Mix thoroughly, then add an appropriate amount of anhydrous ethanol, and stir at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0123] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0124] Example 3 This embodiment illustrates a method for preparing a silicon anode composite material, specifically including the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0125] The fly ash contains 47% (w / w) SiO2 and 38% (w / w) Al2O3.

[0126] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0127] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0128] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. After the second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour), the solution is allowed to stand and cool to room temperature. After filtration and washing the residue with distilled water until neutral, it is dried at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0129] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0130] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into 1.6M nitric acid. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 250g:1L, take 0.1M HF solution and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0131] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:5.5 and stir for 20 minutes. Then, use 35Hz frequency for ultrasonic treatment for 1 hour and calcine at 750°C for 3 hours to complete PEG modification treatment and obtain solid product 5.

[0132] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0133] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add a 40% (w / v) HF solution at a volume ratio of 1:15 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0134] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the mass ratio of 13:1, take silver modified silicon particle composite material and lignin-based resin (Mw is about 1000~5000) and mix them evenly. Then add an appropriate amount of anhydrous ethanol and stir at 50°C for 6 hours until all the anhydrous ethanol evaporates to complete the resin coating treatment and obtain solid product 6.

[0135] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0136] Example 4 This embodiment illustrates a method for preparing a silicon anode composite material, specifically including the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0137] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0138] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0139] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0140] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. After the second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour), the solution is allowed to stand and cool to room temperature. After filtration and washing the residue with distilled water until neutral, it is dried at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0141] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1.5:2 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700°C at a heating rate of 3°C / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0142] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into sulfuric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0143] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:5 and stir for 20 minutes. Then, use 45Hz frequency for ultrasonic treatment for 2 hours and calcine at 750°C for 3 hours to complete PEG modification treatment and obtain solid product 5.

[0144] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0145] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0146] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and phenolic resin (M) at a mass ratio of 15:1, take silver-modified silicon particle composite material and phenolic resin (M) w The mixture is approximately 300~2000 (same as in Example 1). After mixing evenly, an appropriate amount of anhydrous ethanol is added, and the mixture is stirred at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0147] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0148] The specific conditions used in each step of Examples 1 to 4 are shown in Table 1.

[0149] Table 1.

[0150] Comparative Example 1 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials. The difference is that the PEG modification treatment in "Preparation of Nano-Silicon Materials in Step S2" does not introduce calcination, and "Preparation of Silver-Modified Silicon Particle Composite Materials (Si / Ag) in Step S3" and "Preparation of Silver-Modified Silicon Particle Composite Materials (Si / Ag@HC) in Step S4" are not performed. Other conditions remain the same, and the specific steps are as follows: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0151] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0152] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0153] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0154] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0155] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0156] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0157] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:5 and stir for 20 minutes. Then use 35Hz frequency to perform ultrasonic treatment for 1.5 hours to complete PEG modification treatment and obtain solid product 5.

[0158] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue. Dry it under vacuum at 50°C for 6 h to obtain nano-silicon material, that is, silicon anode composite material.

[0159] Comparative Example 2 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that "S3, preparation of silver-modified silicon particle composite material (Si / Ag)" and "S4, preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC)" are not performed. All other conditions remain the same, and the specific steps include: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0160] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0161] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0162] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0163] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0164] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0165] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0166] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt. Then, according to the mass ratio of 1:5, take solid product 4 and polyethylene glycol melt and mix them. Stir for 20 minutes, then use 35Hz frequency for ultrasonic treatment for 1.5 hours, and calcine at 750°C for 3 hours to complete the PEG modification treatment and obtain solid product 5.

[0167] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue. Dry it under vacuum at 50°C for 6 h to obtain nano-silicon material, that is, silicon anode composite material.

[0168] Comparative Example 3 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that "step S3, preparation of silver-modified silicon particle composite material (Si / Ag)" is not performed, while other conditions remain the same. Specifically, it includes the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0169] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0170] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0171] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0172] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0173] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0174] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0175] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt. Then, according to the mass ratio of 1:5, take solid product 4 and polyethylene glycol melt and mix them. Stir for 20 minutes, then use 35Hz frequency for ultrasonic treatment for 1.5 hours, and calcine at 750°C for 3 hours to complete the PEG modification treatment and obtain solid product 5.

[0176] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0177] Preparation of S3, hard carbon-coated silicon particle composite material (Si@HC) (1) Take nano-silicon material and phenolic resin (M) according to the addition amount of 15:1 by mass. w The mixture is approximately 300~2000 (same as in Example 1). After mixing evenly, an appropriate amount of anhydrous ethanol is added, and the mixture is stirred at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0178] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain hard carbon coated silicon particle composite material (Si@HC), which is also silicon anode composite material.

[0179] Comparative Example 4 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that it does not perform "step S4, preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC)". Specifically, this includes the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0180] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0181] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0182] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0183] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0184] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0185] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0186] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt. Then, according to the mass ratio of 1:5, take solid product 4 and polyethylene glycol melt and mix them. Stir for 20 minutes, then use 35Hz frequency for ultrasonic treatment for 1.5 hours, and calcine at 750°C for 3 hours to complete the PEG modification treatment and obtain solid product 5.

[0187] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0188] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 minutes to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 hours to obtain the silver-modified silicon particle composite material (Si / Ag), which is also the silicon anode composite material.

[0189] Comparative Example 5 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that PEG modification is not performed in "Step S2, Preparation of Nano-Silicon Materials", while other conditions remain the same. Specifically, it includes the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0190] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0191] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0192] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0193] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0194] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0195] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0196] (3) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 4 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0197] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0198] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver modified silicon particle composite material and phenolic resin (Mw is about 300~2000, the same as in Example 1) at a mass ratio of 15:1, mix them evenly, then add an appropriate amount of anhydrous ethanol, stir at 50°C for 6 hours until all the anhydrous ethanol evaporates, and complete the resin coating treatment to obtain solid product 6.

[0199] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0200] Comparative Example 6 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, the difference being that the PEG modification treatment in "Step S2, Preparation of Nano-Silicon Materials" does not involve calcination, while other conditions remain the same, specifically including the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0201] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0202] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0203] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0204] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). Let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0205] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0206] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0207] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:5 and stir for 20 minutes. Then use 35Hz frequency to perform ultrasonic treatment for 1.5 hours to complete PEG modification treatment and obtain solid product 5.

[0208] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0209] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0210] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and phenolic resin (M) at a mass ratio of 15:1, take silver-modified silicon particle composite material and phenolic resin (M) w The mixture is approximately 300~2000 (same as in Example 1). After mixing evenly, an appropriate amount of anhydrous ethanol is added, and the mixture is stirred at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0211] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0212] Comparative Example 7 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that the ultrasonic treatment is not introduced in "Step S2, Preparation of Nano-Silicon Materials", while other conditions remain the same. Specifically, it includes the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0213] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0214] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0215] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0216] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0217] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0218] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0219] (3) Heat PEG6000 to 100°C and stir continuously for 2 hours to obtain polyethylene glycol melt; then add solid product 4 and polyethylene glycol melt at a mass ratio of 1:5 and stir for 20 minutes. Then calcine at 750°C for 3 hours to complete PEG modification treatment and obtain solid product 5.

[0220] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0221] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0222] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and phenolic resin (M) at a mass ratio of 15:1, take silver-modified silicon particle composite material and phenolic resin (M) w The mixture is approximately 300~2000 (same as in Example 1). After mixing evenly, an appropriate amount of anhydrous ethanol is added, and the mixture is stirred at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0223] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0224] Comparative Example 8 This comparative example uses the method provided in Example 1 to prepare silicon anode composite materials, except that in "Step S2, Preparation of Nano-Silicon Materials", PVA modification treatment is used instead of PEG modification treatment, while other conditions remain the same. Specifically, it includes the following steps: Preparation of S1 and silicon dioxide: (1) Take fly ash and soak it in hot water at 80°C for 2 hours. Then, according to the solid-liquid ratio of 100g:1L, take 1M hydrochloric acid and mix it evenly with the fly ash soaked in hot water. Perform the first acid leaching treatment at 90°C for 4 hours. After filtration and washing the residue with hot distilled water until neutral, dry it at 100°C for 12 hours to complete the first purification treatment and obtain solid product 1.

[0225] The fly ash contains 56% (w / w) SiO2 and 35% (w / w) Al2O3.

[0226] (2) According to the solid-liquid ratio of 600g:1L, take solid product 1 and sodium hydroxide solution with a concentration of 3M and mix them evenly. Stir at 90℃ and 150rpm for 4h to complete the alkaline extraction treatment. Filter and collect the filtrate to obtain liquid product 1.

[0227] (3) The pH of liquid product 1 was adjusted to 7 with 1M hydrochloric acid, and the mixture was allowed to stand at room temperature for 24 hours to complete the acid precipitation treatment. After filtration and washing the residue three times with hot distilled water, the solid product 2 was dried at 100℃ for 16 hours to obtain solid product 2.

[0228] (4) According to the solid-liquid ratio of 500g:1L, take 1M hydrochloric acid and solid product 2 and mix them evenly. Then, perform a second acid leaching treatment at 90℃ for 4h (stirring 6 times per hour). After that, let the solution stand and cool to room temperature, filter and wash the residue with distilled water until neutral, and then dry at 100℃ for 4h to complete the second purification treatment and obtain silicon dioxide.

[0229] S2, Preparation of nano-silicon materials (1) Add silicon dioxide, magnesium powder and sodium chloride in a mass ratio of 1:1:2.5 and mix them evenly. In an argon atmosphere, gradually heat the mixture to 700℃ at a heating rate of 3℃ / min and keep it at that temperature for 6 hours to complete the magnesium thermal reduction treatment. Then slowly cool it to room temperature to obtain solid product 3.

[0230] (2) According to the addition amount of hydrochloric acid and silicon with a molar ratio of 1:1.5, take solid product 3 and slowly add it into hydrochloric acid with a concentration of 1.6M. After the third acid leaching treatment at 70℃ for 3h, the solution is allowed to stand and cool to room temperature, and the residue is collected by filtration. According to the addition amount of solid-liquid ratio of 150g:1L, take HF solution with a concentration of 0.1M and mix it evenly with the residue. Stir at 25℃ for 3h to complete the first hydrofluoric acid treatment. Filter and wash the residue with distilled water until neutral. Dry at 100℃ for 4h to obtain solid product 4.

[0231] (3) According to the addition amount of PVA (M) at a material-to-liquid ratio of 200g:1L, take... w =13000~23000, Merck, catalog number 363170) and deionized water were mixed and heated to 100°C, and stirred continuously for 2 hours to obtain a PVA solution; then, according to the addition amount of solid product 4 and PVA in a mass ratio of 1:5, solid product 4 and PVA solution were mixed and stirred for 20 minutes, then sonicated at a frequency of 35 Hz for 1.5 hours, and calcined at 750°C for 3 hours to complete the PVA modification treatment and obtain solid product 5.

[0232] (4) According to the volume ratio of 7:1:2, take ultrapure water, HF solution with a concentration of 40% (w / v) and anhydrous ethanol and mix them evenly. Then, add solid product 5 slowly according to the final concentration of 30 g / L. Stir at 25°C for 6 min to complete the second hydrofluoric acid treatment. Filter 5 times to collect the residue and vacuum dry at 50°C for 6 h to obtain nano-silicon material.

[0233] Preparation of S3, silver-modified silicon particle composite material (Si / Ag) Add the nano-silicon material slowly to a 3mM silver nitrate solution at a final concentration of 15 g / L. Then, add 40% (w / v) HF solution at a volume ratio of 1:20 (silver nitrate solution to HF solution). Stir for 8 min to complete the silver deposition process. Filter five times to collect the residue and vacuum dry at 50℃ for 6 h to obtain the silver-modified silicon particle composite material (Si / Ag).

[0234] S4. Preparation of hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC) (1) According to the addition amount of silver-modified silicon particle composite material and phenolic resin (M) at a mass ratio of 15:1, take silver-modified silicon particle composite material and phenolic resin (M) w The mixture is approximately 300~2000 (same as in Example 1). After mixing evenly, an appropriate amount of anhydrous ethanol is added, and the mixture is stirred at 50°C for 6 hours until all the anhydrous ethanol evaporates, thus completing the resin coating process and obtaining solid product 6.

[0235] (2) Take solid product 6 and calcine it at 800℃ for 4 hours to complete the carbonization treatment and obtain a hard carbon-coated silver-modified silicon particle composite material (Si / Ag@HC), which is also a silicon anode composite material.

[0236] Test case This test example illustrates the relevant performance of the silicon anode composite material provided in the above embodiments, with comparative examples 1-8 serving as controls. The specific tests include: 1. Resistivity: The resistivity of the silicon anode composite material was tested using a powder resistivity meter under a pressure of 20 MPa. The results are shown in Table 2.

[0237] 2. Particle size: The particle size of the silicon anode composite material was tested using a BT-9300H laser particle size analyzer, and the results are shown in Table 2.

[0238] 3. Specific surface area: using Brunauer... Emmet The specific surface area of ​​the silicon anode composite material was tested using the Teller (BET) method, and the results are shown in Table 2.

[0239] 4. Electrical performance: (1) Take silicon anode composite material, sodium alginate, carbon black and appropriate amount of deionized water in a mass ratio of 70:15:15 to form a uniform slurry, coat it evenly on copper foil to form an active material layer with a thickness of 150μm, dry it at 120℃ for 12h, and then cut it into a circular piece with a diameter of 14mm to obtain the electrode to be tested. (2) Using the electrode to be tested as the working electrode, lithium metal as the counter electrode, polyethylene film as the separator, and LiPF6 EC / DMC / DEC organic solution as the electrolyte, the CR2032 button-type half cell was assembled in a glove box filled with argon gas. (3) The Blue Electric test system was used to test the 0.1C first charge and discharge performance of CR2032 button half-cell and the capacity retention rate after 200 cycles at 0.5C under the voltage window of 5mV~1.5V. The results are shown in Table 2.

[0240] Table 2.

[0241] Compared to Comparative Examples 1-8, the silicon anode composite materials provided in Examples 1-4 of this invention have lower resistivity, smaller particle size, and higher specific surface area. The CR2032 button-type half-cell prepared from this silver-modified silicon particle composite material as the active material exhibits superior electrochemical performance, with higher 0.1C discharge specific capacity and first charge-discharge efficiency. It also has higher discharge capacity at 0.5C rate and higher capacity retention after 200 cycles. This silver-modified silicon particle composite material can well meet the application requirements of high-capacity, long-cycle, and high-rate lithium-ion anodes and has excellent application prospects.

[0242] It is worth noting that, based on the performance test data of Comparative Example 1 and Comparative Example 2, it can be seen that the calcination process introduced during PEG modification causes a metallothermal reaction between silicon dioxide and magnesium, which can effectively reduce the particle size of silicon particles, optimize the particle pore structure, and improve electrical performance.

[0243] The performance test data of Comparative Examples 3 to 5 show that, compared with the silicon anode composite materials obtained by only hard carbon coating (Comparative Example 3) or Ag modification (Comparative Example 4), the performance of the silicon anode composite material obtained by simultaneously performing hard carbon coating and Ag modification (Comparative Example 5) is significantly reduced. This indicates that the modification effects of hard carbon coating and Ag modification on silicon anode materials are not simply linearly additive. Ag modification may break the integrity and continuity of hard carbon coating, and may also introduce multiple heterogeneous interfaces, thereby aggravating interfacial side reactions, or leading to a decrease in structural stability. The negative effects caused by these modifications may offset or even exceed the performance gains brought by a single modification, ultimately leading to a significant deterioration in the performance of the silicon anode composite material.

[0244] Comparison of performance test data from Comparative Examples 5-8 and Example 1 shows that the preparation method provided by this invention introduces PEG modification treatment during the preparation of nano-silicon materials. Ultrasonic treatment is then performed in the presence of PEG, and ultrasonic treatment and high-temperature calcination are used to optimize particle breakage, surface functional groups, pore structure, and lattice structure. This results in the preparation of a nano-silicon material with ideal morphology, surface functional group composition, and lattice structure. This effectively solves the problems of uneven surface energy, severe agglomeration, impurity fluctuations, weak interfacial bonding, and easy delamination and collapse in nano-silicon materials prepared from fly ash as raw material during Ag modification and hard carbon coating. This constructs an ideal SiO2-Ag-carbon gradient interface structure, achieving an organic combination of Ag modification and hard carbon coating. While alleviating the volume expansion problem of silicon-based anode materials, it significantly improves the material's conductivity, cycle stability, first coulombic efficiency, and rate performance, ultimately obtaining a low-cost, high-performance silicon-based anode material with excellent application prospects.

[0245] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a silicon anode composite material, characterized in that, The preparation method includes: S1. Preparation of silicon dioxide: fly ash is subjected to alkaline extraction and acid precipitation to obtain the silicon dioxide; S2. Preparation of nano-silicon materials: The silicon dioxide is subjected to magnesium thermal reduction treatment, first hydrofluoric acid treatment, PEG modification treatment and second hydrofluoric acid treatment to obtain the nano-silicon materials. S3. Preparation of silver-modified silicon particle composite material: The nano-silicon material is subjected to silver deposition treatment to obtain the silver-modified silicon particle composite material; S4. Preparation of silicon anode composite material: The silver-modified silicon particle composite material is subjected to resin coating and carbonization treatment to obtain the silicon anode composite material; In step S2, the PEG modification treatment includes: taking the solid product obtained from the first hydrofluoric acid treatment and mixing it evenly with polyethylene glycol melt, ultrasonically treating it at a frequency of 30Hz~45Hz for 1h~2h, and calcining it at 700℃~800℃ for 3h~5h to complete the PEG modification treatment.

2. The method for preparing the silicon anode composite material according to claim 1, characterized in that, The fly ash comprises 50% (w / w) to 60% (w / w) of SiO2 and 30% (w / w) to 45% (w / w) of Al2O3.

3. The method for preparing the silicon anode composite material according to claim 1, characterized in that, In step S2, the PEG modification treatment includes one or more of the following technical features: (1) The mass ratio of the solid product obtained by the first hydrofluoric acid treatment to the polyethylene glycol melt is 1:(4~6); (2) The preparation of the polyethylene glycol melt includes: heating polyethylene glycol to 100℃~110℃ and stirring continuously for 1.5h~3h to obtain the polyethylene glycol melt; (3) The weight average molecular weight of polyethylene glycol in the polyethylene glycol melt is 3000~8000.

4. The method for preparing the silicon anode composite material according to claim 1, characterized in that, In step S1, the alkaline extraction treatment includes: mixing the fly ash with an alkaline solution and stirring at 90℃~95℃ for 3h~6h to complete the alkaline extraction treatment; Optionally, the alkaline extraction treatment includes one or more of the following technical features: (1) the alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution; (2) the concentration of alkali in the alkaline solution is 2M~4M; (3) the addition ratio of fly ash to alkaline solution is (500~1000)g:1L; Optionally, the acid precipitation treatment includes: adjusting the pH of the liquid product obtained by the alkaline extraction treatment to 6.8-7 using acid solution I, and letting it stand for 18-24 hours to complete the acid precipitation treatment; Optionally, the acid precipitation treatment includes one or more of the following technical features: (1) the acid solution I includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution I is 0.5M~1.5M.

5. The method for preparing the silicon anode composite material according to claim 1, characterized in that, Step S1 includes a first purification process performed before alkaline extraction. The first purification process includes: mixing the fly ash with water and soaking it in hot water at 80℃~100℃ for 2~3 hours; mixing acid solution II with the fly ash that has been soaked in hot water and performing a first acid leaching treatment at 90℃~95℃ for 3~6 hours to complete the first purification process. Optionally, the first purification process includes one or more of the following technical features: (1) the acid solution II includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution II is 0.5M~1.5M; (3) the addition ratio of fly ash and acid solution is (80~150)g:1L; Optionally, a second purification process is included after the acid precipitation treatment, the second purification treatment comprising: mixing acid solution III and the solid product obtained by acid precipitation treatment, and performing a second acid leaching treatment at 90℃~95℃ for 3h~5h to complete the second purification treatment; Optionally, the second purification process includes one or more of the following technical features: (1) the acid solution III includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution III is 0.5M~1.5M; (3) the addition ratio of the solid product obtained by the acid precipitation treatment to the acid solution is (400~600)g:1L.

6. The method for preparing the silicon anode composite material according to claim 1, characterized in that, In step S2, the magnesium thermal reduction treatment includes: mixing the silicon dioxide, magnesium powder and sodium chloride, gradually heating to 600℃~800℃ in an inert atmosphere at a heating rate of 2℃ / min~5℃ / min, and then holding at that temperature for 3h~8h to complete the magnesium thermal reduction treatment; Optionally, the mass ratio of silicon dioxide, magnesium powder and sodium chloride is 1:(0.7~1.5):(2~3); Optionally, the first hydrofluoric acid treatment includes: mixing the solid product obtained by the magnesium thermal reduction treatment with acid solution IV, and performing a third acid leaching treatment at 60℃~85℃ for 2h~4h; mixing the solid product obtained by the third acid leaching treatment with HF solution I, and performing a stirring treatment for 2h~4h to complete the first hydrofluoric acid treatment. Optionally, the first hydrofluoric acid treatment includes one or more of the following technical features: (1) the acid solution IV includes one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; (2) the concentration of acid in the acid solution IV is 1.5M~2M; (3) the molar ratio of silicon added in the solid product obtained by the acid and magnesium thermal reduction treatment in the acid solution IV is 1:(1.5~2); (4) the concentration of HF solution I is 0.05M~0.15M; (5) the addition ratio of the solid product obtained by the third acid leaching treatment to HF solution I is (100~300)g:1L; Optionally, the second hydrofluoric acid treatment includes: taking water, HF solution II and anhydrous ethanol, mixing them, adding the solid product obtained by the PEG modification treatment, and stirring for 5 min to 8 min to complete the second hydrofluoric acid treatment; Optionally, the second hydrofluoric acid treatment includes one or more of the following technical features: (1) the concentration of HF solution II is 35% (w / v) to 45% (w / v); (2) the volume ratio of water, HF solution II and anhydrous ethanol is (6~7):1:(1.5~2.5); (3) the concentration of the solid product obtained by the PEG modification treatment is 25 g / L to 35 g / L.

7. The method for preparing the silicon anode composite material according to claim 1, characterized in that, In step S3, the silver deposition process includes: mixing the nano-silicon material and silver nitrate solution, adding HF solution III, and stirring for 5 min to 10 min to complete the silver deposition process; Optionally, the silver deposition treatment includes one or more of the following technical features: (1) the concentration of silver nitrate is 2mM to 4mM; (2) the concentration of the added nano-silicon material is 13g / L to 18g / L; (3) the concentration of HF solution III is 35% (w / v) to 45% (w / v).

8. The method for preparing the silicon anode composite material according to claim 1, characterized in that, In step S4, the resin coating process includes: taking the silver-modified silicon particle composite material, resin and volatile solvent, mixing them evenly, and stirring them at 50℃~55℃ until the volatile solvent is completely evaporated, thus completing the resin coating process; Optionally, the resin coating treatment includes one or more of the following technical features: (1) the resin includes a thermosetting resin; (2) the volatile solvent includes one or more of methanol, ethanol and acetone; (3) the mass ratio of the silver-modified silicon particle composite material to the resin is (13~17):

1. Optionally, the resin includes one or more of phenolic resin, polyimide resin, polyacrylonitrile resin, pitch-based resin, and lignin-based resin; Optionally, the carbonization treatment is carried out at a temperature of 700℃ to 900℃ for a time of 3h to 4h.

9. A silicon anode composite material, characterized in that, The silicon anode composite material is prepared by the method for preparing silicon anode composite material according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the silicon anode composite material as described in claim 9.

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