Silicon-carbon negative electrode material derived from polyazoles framework and preparation method thereof

Abstract

This invention discloses a silicon-carbon anode material derived from a polyazole framework and its preparation method. The material uses a zinc-based polyazole metal-organic framework synthesized from a zinc source, 5-methyltetrazazole, and boric acid in DMF as a precursor. After silicon coating, magnesothermic reduction, and purification, a composite material is obtained consisting of a boron-nitrogen co-doped porous carbon framework and uniformly distributed nano-silicon. This invention achieves boron and nitrogen co-doping of the carbon framework through precise control of the precursor ratio, effectively improving the conductivity and structural stability of the material. The obtained silicon-carbon anode material has a conductivity of 0.5 A g. ‑1 Under the given current density conditions, after 100 cycles, the battery's specific capacity is 823 mAh / g. This indicates that the material can significantly alleviate the volume expansion effect of silicon, exhibiting high specific capacity, excellent rate performance, and cycle life, and has broad application prospects in the field of lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of new energy and energy storage materials technology, specifically relating to silicon-carbon anode materials derived from polyazole frameworks, and also to a method for preparing silicon-carbon anode materials derived from polyazole frameworks. Background Technology

[0002] With the increasing global demand for clean energy and the growing concern over fossil fuel depletion, the development of efficient energy storage technologies has become paramount. While renewable energy sources such as solar and wind power are increasingly accounting for a larger share of the energy mix, their intermittent and unstable nature necessitates the use of high-performance electrochemical energy storage systems. Lithium-ion batteries, with their high energy density and long cycle life, have secured a core position in portable electronic devices, new energy vehicles, and large-scale energy storage. However, as driving range and energy storage scale expand, the energy density of commercial lithium-ion batteries is gradually approaching its theoretical limit. The theoretical specific capacity of mainstream graphite anodes is only 372 mAh / g, insufficient to meet the urgent needs of future high-energy-density energy storage systems. Therefore, developing novel anode materials with higher capacity has become a research focus.

[0003] Among numerous candidate materials, silicon anode materials are considered one of the most promising next-generation anode materials due to their ultra-high theoretical specific capacity (approximately 4200 mAh / g), suitable lithium intercalation potential, and abundant reserves. However, silicon faces severe challenges in practical applications: during lithium-ion insertion and extraction, silicon undergoes massive volume expansion and contraction, with a change rate exceeding 300%. This drastic volume effect leads to electrode material pulverization, failure of electrical contact between the active material and the current collector, and repeated rupture and regeneration of the solid electrolyte interface film, continuously consuming the electrolyte. Ultimately, this results in a sharp decline in battery capacity and a severely shortened cycle life, significantly hindering the commercialization of silicon anodes. To overcome these problems, researchers have proposed various modification strategies, among which silicon-carbon composites have proven to be one of the most effective methods. Carbon materials possess excellent conductivity and mechanical flexibility, providing a conductive network and a support framework to buffer volume expansion for silicon, and can also form a protective layer on the surface of silicon particles to stabilize the SEI film. Therefore, constructing a silicon / carbon composite structure with excellent structural stability and conductivity is key to realizing the application of silicon anodes.

[0004] In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their unique structural advantages. MOFs are crystalline porous materials formed by the self-assembly of metal ions and organic ligands through coordination bonds, possessing extremely high specific surface area, abundant pore structure, tunable pore size, and diverse composition. These characteristics make them ideal precursors or templates for preparing porous carbon materials. High-temperature pyrolysis of MOFs can yield porous carbon frameworks doped with heteroatoms, which not only inherit the high specific surface area and abundant pores of MOFs but also introduce more active sites through heteroatomation, significantly improving the conductivity and electrochemical activity of carbon materials. Based on the above analysis, this invention proposes a method using a zinc-, boron-, and nitrogen-containing polyazole metal-organic framework synthesized in a specific molar ratio as a precursor, and preparing a low-silicon-content silicon-carbon composite anode material through in-situ coating of silica and magnesothermic reduction technology. This material uniformly loads nano-silicon into a boron- and nitrogen-doped porous carbon framework, synergistically leveraging the high capacity of silicon and the structural stability of the carbon framework, effectively suppressing silicon volume expansion, and simultaneously improving electrode conductivity and rate performance, ultimately obtaining a structurally stable silicon-carbon anode material with excellent electrochemical performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing silicon-carbon anode materials derived from polyazole frameworks, so as to solve the problem of silicon volume expansion and improve the conductivity of the electrode.

[0006] Another objective of this invention is to develop silicon-carbon anode materials derived from polyazole frameworks.

[0007] The first technical solution adopted in this invention is a method for preparing silicon-carbon anode materials derived from polyazole frameworks, and the specific operation steps are as follows:

[0008] Step 1: Dissolve zinc source, 5-methyltetrazole and boric acid in N,N-dimethylformamide (DMF), cool it to room temperature, transfer the mixed solution to a reaction vessel, and solvothermically react in an oven. After the reaction is complete, cool it naturally to room temperature, collect the solid product by centrifugation or filtration, wash it three times each with DMF and anhydrous methanol, and finally vacuum dry it to obtain MOF precursor powder A containing zinc, boron and nitrogen. Step 2: Precursor powder A is uniformly dispersed in a mixed solution of deionized water and ethanol by ultrasonication. Then, the surfactant cetyltrimethylammonium bromide (CTAB) and the silicon source are added sequentially. The mixture is stirred at room temperature. After the reaction is complete, the precipitate is collected by centrifugation, washed with ethanol, and dried to obtain silicon-coated MOF composite material B. Step 3: Mix composite material B with magnesium powder and sodium chloride at a certain mass ratio and grind thoroughly until uniform. Place the mixture in a corundum boat and heat it to 600-700℃ at a heating rate of 1-5℃ / min under a N2 atmosphere, hold for 6 hours, and then allow it to cool naturally to room temperature to obtain crude product C. Step 4: The crude product C is soaked and washed several times with dilute hydrochloric acid solution to remove unreacted magnesium powder, magnesium oxide, sodium chloride, and reduced and volatilized zinc impurities. Then it is washed with deionized water until neutral, and finally vacuum dried at 60-80℃ to obtain the purified silicon / carbon composite powder D.

[0009] Step 5: Mix silicon / carbon composite powder D with conductive agent carbon black and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, grind thoroughly, add an appropriate amount of solvent N-methylpyrrolidone (NMP), and continue grinding until a uniform and fluid slurry E is formed. Step 6: Ultrasonically clean and dry the current collector copper foil with ethanol. Apply the slurry E prepared in Step 5 evenly onto the copper foil using a scraper, then place it in a forced-air drying oven at 60-100°C to remove the solvent, forming a silicon-carbon anode material. Step 7: Cut the dried silicon-carbon anode material into circular electrode sheets with a diameter of 14 mm using a tablet press, and then dry them thoroughly in a vacuum drying oven at 60°C to obtain anode sheet M.

[0010] Step 8: Move the negative electrode M into a glove box filled with argon gas, and assemble it with the lithium metal sheet (counter electrode), electrolyte, separator, etc. in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet, negative electrode shell to form a CR2032 button cell for subsequent electrochemical performance testing.

[0011] The invention is further characterized in that, Step 1: The zinc source is zinc nitrate hexahydrate, and the organic solvent is N,N-dimethylformamide.

[0012] In step 1, the temperature of the solvothermal reaction can be selected within the range of 100~140°C, the reaction time is 24~48 hours, the washing solvent is DMF and anhydrous methanol, the vacuum drying temperature is 60~80°C, and the drying time is 6~12 hours. In step 2, the volume ratio of ethanol to water is 1:1, the ultrasonic time is 30-60 minutes, the stirring time is 2-6 hours, and the drying temperature is 60-80°C. o C, drying time is 6~12 hours.

[0013] In step 3, the mass ratio of composite material B to magnesium powder and sodium chloride is 1:1:1.

[0014] In step 4, the molar concentration of the dilute hydrochloric acid used is 1.0 mol / L.

[0015] In step 5, the mass ratio of the purified silicon / carbon composite powder D to carbon black and polyvinylidene fluoride (PVDF) is 8:1:1.

[0016] In steps 6 and 7, the drying temperature after coating and the pre-drying temperature of the copper foil are both 60~100℃. o C.

[0017] In step 7, the temperature for vacuum drying of the electrode sheet is 60°C. o C.

[0018] The synthesis principle of the key steps in this invention: (i) Synthesis of MOF precursors: forming a highly ordered crystalline framework structure. The introduction of boron can achieve in-situ boron doping of the carbon framework during subsequent carbonization, forming a B / N co-doping system together with nitrogen in the framework, synergistically improving the electronic conductivity and electrochemical activity of carbon materials.

[0019] (II) Construction and Reduction of Core-Shell Structure: A silica layer was uniformly coated onto the surface of MOF particles using a solution-phase method. Subsequently, the silica layer was reduced in situ to elemental silicon via a magnesothermic reduction reaction. Due to the controllable and low silicon loading, the generated nano-silicon particles not only coated the surface of the carbon material but also partially penetrated into the pores of the carbon framework. This structure utilizes the mechanical buffering effect of porous carbon to effectively suppress the volume expansion of silicon during cycling.

[0020] (III) Formation of porous carbon framework: During the high-temperature process of magnesothermic reduction, the organic ligands in MOF are carbonized to form a porous carbon framework. At the same time, elemental zinc is reduced and volatilized at high temperature (or removed by subsequent acid washing), which further increases the porosity of the carbon material and provides a channel for the rapid transport of lithium ions.

[0021] The second technical solution adopted in this invention is: a silicon-carbon anode material derived from a polyazole framework prepared by the above preparation method.

[0022] The beneficial effects of this invention are: (1) By using the precise ratio of 0.5 mmol zinc nitrate hexahydrate: 0.5 mmol 5-methyltetrazazole: 0.5 mmol boric acid, a Zn-based polyazole MOF precursor with a well-defined composition and uniform structure was synthesized, laying a solid foundation for the subsequent derivation of high-performance B and N co-doped porous carbon.

[0023] (2) In the prepared silicon / carbon composite material, nano-silicon is uniformly distributed inside and outside the porous carbon framework co-doped with B and N. This structure can not only give full play to the high capacity of silicon, but also utilize the conductivity and buffering effect of the carbon framework, which significantly improves the cycling stability and rate performance of the electrode.

[0024] (3) Thanks to the above-mentioned structural and compositional advantages, this material can be used as a negative electrode for lithium batteries. During cycling, it can effectively suppress the volume expansion of silicon and exhibit high specific capacity, excellent rate performance and long cycle life. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method for preparing silicon-carbon anode material according to the present invention; Figure 2 This is the electrochemical impedance spectroscopy (EIS) spectrum of the silicon-carbon anode material prepared in this invention; Figure 3 This is a graph showing the cycling performance of the silicon-carbon anode material of this invention at a current density of 500 mA / g. Figure 4 This is a charge-discharge curve of the silicon-carbon anode material of the present invention during the first cycle. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0027] Example 1: Step 1: 0.5 mmol (0.1487 g) zinc nitrate hexahydrate, 0.5 mmol (0.0425 g) 5-methyltetrazole, and 0.5 mmol (0.0309 g) boric acid were dissolved in 20 mL DMF, transferred to a 50 mL reaction vessel, and solvothermically reacted in a 120°C oven for 48 hours. After natural cooling, the precipitate was collected by centrifugation, washed three times each with DMF and methanol, and vacuum dried at 60°C for 12 hours to obtain MOF precursor powder A. Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 80 mL ethanol and 80 mL deionized water. Sonicate for 40 minutes. Add 0.1 g of CTAB, stir for 30 minutes, then slowly add 0.3 mL of TEOS. Continue stirring at room temperature for 4 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 60°C for 8 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.3 g of magnesium powder, and 0.3 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 650°C at a rate of 2°C / min under nitrogen protection, hold it at that temperature for 6 hours, and then allow it to cool naturally to room temperature to obtain crude product C. Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and dried under vacuum at 60°C for 8 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E.

[0028] Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution for 30 minutes, and then dry it in a 60°C forced-air drying oven.

[0029] Step 7: Using a scraper, select a certain thickness of the slurry E obtained in Step 5 and scrape it onto the copper foil. Then place it at 60°C. o Dry in a forced-air drying oven.

[0030] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0031] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in an argon-filled glove box in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet and negative electrode shell, for subsequent performance testing.

[0032] Example 2: Step 1: Weigh 0.5 mmol (0.1198 g) zinc chloride, 0.5 mmol (0.0425 g) 5-methyltetrazole, and 0.5 mmol (0.0309 g) boric acid, dissolve them in 20 mL DMF, transfer to a 50 mL reaction vessel, and solvothermally react in an oven at 140°C for 36 hours. After natural cooling, collect the precipitate by centrifugation, wash three times each with DMF and methanol, and vacuum dry at 70°C for 10 hours to obtain MOF precursor powder A; Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 60 mL ethanol and 60 mL deionized water. Sonicate for 50 minutes. Add 0.1 g of CTAB, stir for 30 minutes, then slowly add 0.5 mL of TEOS. Continue stirring at room temperature for 5 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 70°C for 10 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.3 g of magnesium powder, and 0.3 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 600°C at 3°C / min under nitrogen protection, hold it at that temperature for 8 hours, and then allow it to cool naturally to room temperature to obtain crude product C; Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and vacuum dried at 70°C for 6 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E.

[0033] Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution for 30 minutes, then place it at 65°C. oC. Drying in a forced-air drying oven.

[0034] Step 7: Using a scraper, apply the slurry E obtained in Step 5 to a certain thickness onto the copper foil, and then place it at 70°C. o Dry in a forced-air drying oven.

[0035] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0036] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in a glove box filled with argon (Ar) in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet, and negative electrode shell, for subsequent performance testing.

[0037] Example 3: Step 1: Weigh 0.5 mmol (0.1096 g) zinc acetate, 0.5 mmol (0.0425 g) 5-methyltetrazole, and 0.5 mmol (0.0309 g) boric acid, dissolve them in 25 mL DMF, transfer to a 50 mL reaction vessel, and solvothermally react in an oven at 110°C for 48 hours. After natural cooling, collect the precipitate by centrifugation, wash three times each with DMF and methanol, and vacuum dry at 80°C for 6 hours to obtain MOF precursor powder A; Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 70 mL ethanol and 70 mL deionized water. Sonicate for 30 minutes. Add 0.1 g of CTAB and stir for 30 minutes. Then slowly add 0.4 mL of TEOS and continue stirring at room temperature for 3 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 80°C for 6 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.3 g of magnesium powder, and 0.3 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 680°C at a rate of 2°C / min under nitrogen protection, hold it at that temperature for 5 hours, and then allow it to cool naturally to room temperature to obtain crude product C. Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and dried under vacuum at 60°C for 8 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E.

[0038] Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution, and then place it at 80°C. oC. Drying in a forced-air drying oven.

[0039] Step 7: Using a scraper, select a certain thickness of the slurry E obtained in Step 5 and scrape it onto the copper foil. Then place it at 80°C. o Dry in a forced-air drying oven.

[0040] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0041] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in an argon-filled glove box in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet and negative electrode shell, for subsequent performance testing.

[0042] Example 4: Step 1: Weigh 0.5 mmol (0.1435 g) zinc sulfate, 0.5 mmol (0.0425 g) 5-methyltetrazolium and 0.5 mmol (0.0309 g) boric acid, dissolve them in 20 mL DMF, transfer to a 50 mL reaction vessel, and solvothermally react in a 120°C oven for 42 hours. After natural cooling, collect the precipitate by centrifugation, wash three times each with DMF and methanol, and vacuum dry at 60°C for 12 hours to obtain MOF precursor powder A; Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 80 mL ethanol and 80 mL deionized water. Sonicate for 60 minutes. Add 0.1 g of CTAB, stir for 30 minutes, then slowly add 0.6 mL of TEOS. Continue stirring at room temperature for 6 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 60°C for 12 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.3 g of magnesium powder, and 0.3 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 620°C at a rate of 2°C / min under nitrogen protection, hold it at that temperature for 7 hours, and then allow it to cool naturally to room temperature to obtain crude product C; Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and vacuum dried at 60°C for 10 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E; Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution for 30 minutes, then place it at 90°C. o C. Drying in a forced-air drying oven.

[0043] Step 7: Using a scraper, select a certain thickness of the slurry E obtained in Step 5 and scrape it onto the copper foil. Then place it at 90°C. o Dry in a forced-air drying oven.

[0044] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0045] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in a glove box filled with argon (Ar) in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet, and negative electrode shell, for subsequent performance testing.

[0046] Example 5 Step 1: 0.5 mmol (0.1487 g) zinc nitrate hexahydrate, 0.5 mmol (0.0425 g) 5-methyltetrazole, and 0.5 mmol (0.0309 g) boric acid were dissolved in 20 mL DMF, transferred to a 50 mL reaction vessel, and solvothermically reacted in a 100°C oven for 36 hours. After natural cooling, the precipitate was collected by centrifugation, washed three times each with DMF and methanol, and vacuum dried at 60°C for 12 hours to obtain MOF precursor powder A. Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 80 mL ethanol and 80 mL deionized water. Sonicate for 40 minutes. Add 0.1 g of CTAB, stir for 30 minutes, then slowly add 0.3 mL of TEOS. Continue stirring at room temperature for 4 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 60°C for 8 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.25 g of magnesium powder, and 0.3 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 700°C at 3°C / min under nitrogen protection, hold it at that temperature for 5 hours, and then allow it to cool naturally to room temperature to obtain crude product C; Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and dried under vacuum at 60°C for 8 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E.

[0047] Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution for 30 minutes, and then dry it in a 60°C forced-air drying oven.

[0048] Step 7: Using a scraper, select a certain thickness of the slurry E obtained in Step 5 and scrape it onto the copper foil. Then place it at 60°C. o Dry in a forced-air drying oven.

[0049] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0050] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in an argon-filled glove box in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet and negative electrode shell, for subsequent performance testing.

[0051] Example 6 Step 1: Weigh 0.5 mmol (0.1435 g) zinc sulfate, 0.5 mmol (0.0425 g) 5-methyltetrazolium and 0.5 mmol (0.0309 g) boric acid, dissolve them in 20 mL DMF, transfer to a 50 mL reaction vessel, and solvothermally react in a 130°C oven for 40 hours. After natural cooling, collect the precipitate by centrifugation, wash three times each with DMF and methanol, and vacuum dry at 60°C for 12 hours to obtain MOF precursor powder A; Step 2: Weigh 0.3 g of powder A and ultrasonically disperse it in a mixture of 80 mL ethanol and 80 mL deionized water. Sonicate for 60 minutes. Add 0.1 g of CTAB, stir for 30 minutes, then slowly add 0.6 mL of TEOS. Continue stirring at room temperature for 6 hours. Collect the precipitate by centrifugation, wash with ethanol, and dry at 60°C for 12 hours to obtain silica-coated MOF composite material B. Step 3: Weigh 0.3 g of composite material B, 0.3 g of magnesium powder, and 0.25 g of sodium chloride, and grind and mix them evenly. Place the mixture in a corundum boat, heat it to 630°C at a rate of 4°C / min under nitrogen protection, hold it at that temperature for 7 hours, and then allow it to cool naturally to room temperature to obtain crude product C. Step 4: The crude product C was soaked and washed three times with 1.0 mol / L dilute hydrochloric acid, then washed with deionized water until neutral, and vacuum dried at 60°C for 10 hours to obtain silicon / carbon composite powder D. Step 5: Weigh 0.16 g of powder D, 0.02 g of carbon black and 0.02 g of PVDF, grind and mix them, add an appropriate amount of NMP, and continue grinding to form a uniform slurry E; Step 6: Sonicate a copper foil of a certain thickness in an ethanol solution for 30 minutes, then place it at 90°C. o C. Drying in a forced-air drying oven.

[0052] Step 7: Using a scraper, select a certain thickness of the slurry E obtained in Step 5 and scrape it onto the copper foil. Then place it at 90°C. o Dry in a forced-air drying oven.

[0053] Step 8: Press the prepared electrode into a circular electrode sheet with a diameter of 14 mm using a pressing machine, and place it at 60°C. o C is dried in a vacuum drying oven to form the negative electrode M.

[0054] Step 9: Assemble the negative electrode M and the positive electrode lithium sheet into a button cell in a glove box filled with argon (Ar) in the following order: positive electrode shell, negative electrode sheet, electrolyte, separator, lithium sheet, gasket, spring sheet, and negative electrode shell, for subsequent performance testing.

[0055] like Figure 1 The flowchart shown below illustrates the preparation method of silicon-carbon anode material according to the present invention, demonstrating the entire process from MOF precursor synthesis to battery assembly.

[0056] like Figure 2 This is the electrochemical impedance spectroscopy (EIS) of the silicon-carbon anode material of this invention. The impedance curve consists of a semicircle in the high-frequency region and a sloping line in the low-frequency region: the diameter of the semicircle corresponds to the charge transfer resistance (Rct), and the sloping line reflects the lithium-ion diffusion behavior. The test results show that the semicircle diameter is smaller in the high-frequency region, indicating that the material has a lower charge transfer resistance, which is attributed to the improved electronic conductivity of the boron and nitrogen co-doped carbon framework; the sloping line is steeper in the low-frequency region, indicating low ion diffusion resistance and fast lithium-ion transport speed.

[0057] like Figure 3 This diagram shows the cycling performance of the silicon-carbon anode material of this invention at a current density of 0.5 A / g. The initial specific capacity is 1370 mAh / g. After 100 cycles, the electrode still maintains a specific capacity of 823 mAh / g, indicating that the MOF-derived porous carbon framework effectively suppresses the volume expansion effect of silicon during charge and discharge, preventing pulverization and detachment of the electrode material. The boron and nitrogen co-doped carbon framework not only provides an excellent conductive network but also acts as a mechanical buffer, stabilizing the electrode structure.

[0058] like Figure 4 This is a charge-discharge curve of the silicon-carbon anode material of the present invention during the first cycle, illustrating that the polyazole framework-derived silicon-carbon anode material has high specific capacity and good electrochemical reversibility.

Claims

1. A method for preparing polyazole framework-derived silicon-carbon anode materials, characterized in that, A polyazole metal-organic framework precursor was synthesized and then coated with silicon to obtain a MOF composite material. The MOF composite material was then mixed with magnesium powder and sodium chloride and heat-treated. Finally, it was acid-washed and water-washed to remove impurities to obtain a silicon / carbon composite material. The silicon / carbon composite material, conductive agent, and binder were mixed, and a solvent was added to form a slurry. The slurry was coated on a current collector and dried to obtain a silicon-carbon anode material.

2. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 1, characterized in that, The specific operating steps are as follows: Step 1: Dissolve zinc source, 5-methyltetrazole and boric acid in N,N-dimethylformamide in a molar ratio of 1:1:1 and carry out a solvothermal reaction. After post-treatment, MOF precursor powder A is obtained. Step 2: Disperse the MOF precursor powder A obtained in Step 1 in an alcohol-water mixture, add a silicon source and a surfactant to carry out a coating reaction, and obtain MOF composite material B; Step 3: The composite material B obtained in Step 2 is mixed with magnesium powder and sodium chloride, and heat-treated at 600~700°C under an inert atmosphere to obtain crude product C; Step 4: The crude product C obtained in Step 3 is subjected to acid washing and water washing to remove impurities, 60 o C is dried to obtain silicon / carbon composite powder D; Step 5: Mix the silicon / carbon composite material powder D obtained in step 4 with a conductive agent and a binder, add a solvent to make a slurry, coat it onto the current collector, and dry it to obtain the silicon-carbon anode material.

3. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 2, characterized in that, The zinc source in step 1 is zinc nitrate hexahydrate, the organic solvent is N,N-dimethylformamide, and the temperature of the solvothermal reaction is 100~140°C, and the time is 24~48 hours.

4. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 2, characterized in that, The silicon source in step 2 is tetraethyl orthosilicate, the surfactant is hexadecyltrimethylammonium bromide, and the volume ratio of ethanol to water in the alcohol-water mixture is 1:

1.

5. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 2, characterized in that, In step 3, the mass ratio of composite material B, magnesium powder, and sodium chloride is 1:0.5~1.5:0.5~1.

5. The heating rate of the heat treatment is 1~5°C / min, the holding temperature is 600~700°C, and the holding time is 4~8 hours.

6. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 2, characterized in that, The concentration of the dilute hydrochloric acid used for pickling in step 4 is 1.0 mol / L.

7. The method for preparing the polyazole framework-derived silicon-carbon anode material according to claim 2, characterized in that, In step 5, the mass ratio of silicon / carbon composite powder D, conductive agent, and binder is 7~9 : 0.5~2 : 0.5~2. The conductive agent is carbon black, the binder is polyvinylidene fluoride, and the solvent is N-methylpyrrolidone. The drying temperature after coating is 60~100°C.

8. A silicon-carbon anode material derived from a polyazole framework, characterized in that, The silicon-carbon anode material derived from the polyazole framework as described in any one of claims 1-7 was prepared.

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