A highly stable silicon-carbon anode material prepared using photovoltaic silicon waste, its preparation method and application

Abstract

This invention provides a high-stability silicon-carbon anode material prepared from photovoltaic silicon waste, its preparation method, and its application, belonging to the field of lithium-ion battery silicon anode technology. The invention involves adding photovoltaic silicon waste to an acidic system for pre-purification treatment, followed by drying to obtain powdered silicon-based material. The purified silicon-based material is placed in a container, and ethanol is added to disperse it. Magnesium lignosulfonate is then dissolved in a solvent, and a high-efficiency co-solvent is added to accelerate dissolution. The purified silicon waste, magnesium lignosulfonate, carbon-based material, high-efficiency co-solvent, and solvent are mixed uniformly to form a spray-dried precursor solution. The precursor solution is spray-dried and granulated, then annealed at high temperature with a carbon source gas to achieve a high-stability silicon-carbon anode material coated with carbon and magnesium oxide. This invention achieves precise control of the coating layer, improves the initial coulombic efficiency of the anode, suppresses the volume expansion of internal silicon and the generation of hydrofluoric acid during battery charging and discharging, thereby improving the cycle performance of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of silicon anode technology for lithium-ion batteries, and in particular to a highly stable silicon-carbon anode material prepared using photovoltaic crystalline silicon waste, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of electric vehicles, smart electronic devices, and large-scale energy storage systems, the market's performance requirements for lithium-ion batteries have been increasing. Currently, commercially available lithium-ion batteries generally use graphite-based anode materials, but their theoretical specific capacity is only 372 mAh / g, which is insufficient to meet the development needs of high-energy-density batteries. Against this backdrop, silicon-based anode materials have attracted much attention due to their high theoretical specific capacity of 4200 mAh / g and low electrochemical potential, and are considered one of the most promising next-generation anode materials. However, silicon materials face severe challenges in practical applications. The most prominent problem is the approximately 300% volume expansion effect that occurs during charging and discharging. This drastic volume change not only leads to the cracking and pulverization of active material particles but also causes damage to the electrode structure and breakage of the conductive network. More seriously, this continuous expansion and contraction triggers repeated rupture and regeneration of the solid electrolyte interfacial film, continuously consuming electrolyte and active lithium, and causing rapid capacity decay and a significant reduction in cycle life. These problems severely restrict the commercialization process of silicon-based anode materials.

[0003] To address these issues with silicon-based anode materials, researchers have explored various modification strategies. Preparing nano-silicon materials can shorten the lithium-ion diffusion path and alleviate mechanical stress, but the high specific surface area of ​​nanomaterials exacerbates side reactions and incurs high preparation costs. While combining silicon with carbon materials can utilize the conductivity and flexibility of carbon to buffer volume expansion, traditional mechanical mixing methods often struggle to achieve uniform coating, leading to insufficient interfacial stability. Constructing hollow or porous silicon structures can accommodate expansion, but the process is complex and the material's tap density is low. Currently, the most mainstream carbon coating technology, while improving silicon conductivity and reducing its direct contact with the electrolyte, still suffers from limitations such as difficulty in controlling the coating thickness and uniformity, the potential for pores or cracks during pyrolysis, and insufficient interfacial bonding between the coating and silicon. Furthermore, existing processes largely rely on high-purity silicon raw materials, resulting in high costs. Meanwhile, the large amount of silicon waste generated annually by the photovoltaic industry remains unutilized. This waste has micron-sized particles and a purity of over 99%. If it could be converted into high-value-added battery materials, it would simultaneously achieve the dual benefits of resource recycling and cost reduction. Based on this, developing a low-cost silicon-carbon composite material preparation method that can precisely control the carbon coating structure and interface properties, solve problems such as silicon volume expansion, poor conductivity and SEI instability, and achieve large-scale preparation is of great significance for promoting the commercial application of silicon-based anode materials. Summary of the Invention

[0004] The purpose of this invention is to provide a high-stability silicon-carbon anode material prepared using photovoltaic silicon waste, its preparation method, and its application, in order to solve the technical problems of existing lithium-ion battery silicon-carbon anodes, such as the volume expansion effect leading to repeated formation of SEI film, which reduces battery cycle stability and causes serious capacity loss.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste, comprising the following steps: 1) Photovoltaic crystalline silicon waste is added to a treatment solution for purification and dried to obtain silicon-based materials; the silicon-based materials are dispersed in a mixture of ethanol and water and then ultrasonically dispersed to obtain a silicon-based material suspension. 2) Magnesium lignosulfonate and carbon-based materials were dispersed in water, and then a co-solvent was added to obtain a magnesium lignosulfonate suspension; 3) The silicon-based material suspension was mixed in the magnesium lignosulfonate suspension and then subjected to ultrasonic treatment to obtain the composite precursor suspension; 4) The composite precursor suspension was dried and granulated by spray drying to obtain precursor powder; 5) The precursor powder is annealed by introducing carbon source gas in an inert gas atmosphere and then subjected to chemical vapor deposition to obtain a high-stability silicon-carbon anode material.

[0006] Furthermore, in step 1), the treatment solution contains one or more of hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid and hydrogen peroxide, the concentration of the treatment solution is 1~8 mol / L, the liquid-solid ratio of the treatment solution to the photovoltaic silicon waste is 3~10 mL:1 g, and the purification treatment time is 1~8 h.

[0007] Furthermore, in step 1), the ratio of silicon-based material, ethanol, and dispersant is 30-60g:1mL:5-10mL, the power of ultrasonic dispersion is 300-800W, the processing time is 10-30min, and the working mode is ultrasonic for 2s followed by intermittent for 1s.

[0008] Furthermore, in step 2), the co-solvent includes an ethanol-water mixed solvent, an ionic liquid co-solvent, a polyethylene glycol co-solvent, or an alkaline regulator, and the ratio of magnesium lignosulfonate to co-solvent is 30-50:20.

[0009] Furthermore, the carbon-based material comprises one or more of graphene oxide, graphene, soluble sucrose, glucose, chitosan, phenolic resin, pitch, polydopamine, polyethylene glycol, and carbon nanotubes.

[0010] Furthermore, in the composite precursor suspension, by mass fraction, silicon-based materials account for 3-10%, magnesium lignosulfonate accounts for 20-30%, carbon-based materials account for 2-10%, and solvent accounts for 60-75%.

[0011] Furthermore, in step 4), the peristaltic pump speed is 5~30 rpm, the feed rate is 0.1~100 mL / min, the carrier gas is argon, nitrogen, helium or argon-hydrogen, the inlet temperature is 100~180℃, and the outlet temperature is 100~150℃.

[0012] Furthermore, in step 5), the annealing temperature is 500~1000℃, and the heating rate is 5~20℃ / min; the carbon source gas used in chemical vapor deposition is acetylene, ethylene, or carbon dioxide.

[0013] The present invention also provides a highly stable silicon-carbon anode material prepared by the above preparation method.

[0014] This invention also provides the application of the above-mentioned highly stable silicon-carbon anode material in the preparation of lithium-ion battery electrodes.

[0015] The beneficial effects of this invention are: (1) This invention can not only effectively solve the problem of recycling silicon waste from photovoltaic industry cutting and by-products from papermaking process, but also prepare highly stable silicon-based anode materials; (2) This invention designs and utilizes a highly efficient co-solvent system with "directional traction". The co-solvent molecules can preferentially interact with the active functional groups such as sulfonic acid groups and phenolic hydroxyl groups on the magnesium lignosulfonate chain through intermolecular interactions such as hydrogen bonds and van der Waals forces. This process not only significantly improves the dispersibility and migration rate of magnesium lignosulfonate in the solvent, but more importantly, the highly efficient co-solvent system activates these functional groups, achieving the effect of molecular navigation, guiding them to accumulate and oriented towards the surface of silicon particles, laying the kinetic foundation for the formation of a uniform and dense initial coating layer; (3) This invention achieves interface microenvironment reconstruction and in-situ anchoring. This cosolvent system provides a moderately alkaline environment (e.g., by releasing O) (Or it may be an alkaline substance), precisely regulating the microenvironment of the silicon-liquid interface. This alkaline condition induces the deprotonation of silanol groups (-Si-OH) on the surface of photovoltaic-cut silicon waste, generating negatively charged silicon-oxygen anions (-Si-). This significantly increases the surface's negative charge and nucleophilicity. This change allows the positively charged magnesium ions (Mg²⁺) in the activated magnesium lignosulfonate to... 2+ The strong electrostatic attraction and coordination between the lignin sulfonate and the silicon surface is generated in the electronegative region, thus realizing the in-situ chemical anchoring of magnesium lignin sulfonate on the silicon surface. (4) This invention utilizes the synergistic effect and SEI evolution to form a good artificial SEI layer. The uniform pre-coating layer formed in the above process undergoes pyrolysis of magnesium lignosulfonate during subsequent high-temperature annealing in an inert atmosphere. Its carbon skeleton transforms into a conductive carbon layer, while magnesium reacts with the silicon-oxygen layer, generating a dense nano-magnesium oxide (MgO) layer in situ at the silicon-carbon interface. During the first charge-discharge process of the battery, this MgO reacts with fluoride salts (such as LiPF6) in the electrolyte, transforming in situ into an artificial SEI film primarily composed of lithium fluoride (LiF). This artificial SEI film possesses high interfacial energy, high mechanical modulus, and excellent lithium-ion conductivity. Its advantages include: Physical barrier: Effectively suppressing the massive volume expansion during silicon core cycling and preventing the breakage of active particles. Chemical stability: Its stable chemical properties prevent the continuous decomposition of the electrolyte, reducing the consumption of active lithium and electrolyte. Ion conductor: The LiF-rich interfacial phase provides a channel for the rapid transport of Li+, improving rate performance. This in-situ constructed stable artificial SEI layer fundamentally solves the core pain point of traditional silicon-carbon anodes, which suffers from low coulombic efficiency and short cycle life due to repeated SEI film rupture and regeneration.

[0016] (5) This invention proposes for the first time to enrich magnesium lignosulfonate on the silicon surface with a cosolvent and prepare multilayer coated silicon-based anode material by spray granulation and CVD. The magnesium lignosulfonate coating operation is simple and direct. High-temperature annealing realizes the crystal transformation of carbon, thereby improving the capacity of the electrode material, improving the overall structural stability and the first coulombic efficiency, effectively coping with the volume expansion of silicon anode and improving cycle stability. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention; Figure 2 The image shows the XRD pattern of the composite material prepared in Example 1. Figure 3 SEM image of the composite material prepared in Example 2; Figure 4 The image shows a SEM image of the composite material prepared in Example 3.

[0018] Figure 5 The image shows a SEM image of the composite material prepared in Example 4.

[0019] Figure 6 The image shows the battery cycle performance of the composite material prepared in Example 5. Detailed Implementation

[0020] This invention provides a method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste, comprising the following steps: 1) Photovoltaic crystalline silicon waste is added to a treatment solution for purification and dried to obtain silicon-based materials; the silicon-based materials are dispersed in a mixture of ethanol and water and then ultrasonically dispersed to obtain a silicon-based material suspension. 2) Magnesium lignosulfonate and carbon-based materials were dispersed in water, and then a co-solvent was added to obtain a magnesium lignosulfonate suspension; 3) The silicon-based material suspension was mixed in the magnesium lignosulfonate suspension and then subjected to ultrasonic treatment to obtain the composite precursor suspension; 4) The composite precursor suspension was dried and granulated by spray drying to obtain precursor powder; 5) The precursor powder is annealed by introducing carbon source gas in an inert gas atmosphere and then subjected to chemical vapor deposition to obtain a high-stability silicon-carbon anode material.

[0021] In this invention, in step 1), the treatment solution contains one or more of hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, and hydrogen peroxide, preferably hydrofluoric acid, hydrochloric acid, or nitric acid; the concentration of the treatment solution is 1~8 mol / L, preferably 2~6 mol / L, more preferably 3~5 mol / L; the liquid-to-solid ratio of the treatment solution to the photovoltaic silicon waste is 3~10 mL:1 g, preferably 4~9 mL:1 g, more preferably 5~8 mL:1 g; the purification treatment time is 1~8 h, preferably 2~7 h, more preferably 3~6 h.

[0022] In this invention, in step 1), the ratio of silicon-based material, ethanol, and dispersant is 30-60g:1mL:5-10mL, preferably 30-50g:1mL:6-9mL; the power of ultrasonic dispersion is 300-800W, preferably 400-700W, more preferably 500-600W; the processing time is 10-30min, preferably 20min, and the working mode is ultrasonic for 2s followed by intermittent for 1s. The dispersant is ammonia, sodium hydroxide, or polyethylene glycol.

[0023] In this invention, in step 2), the co-solvent comprises an ethanol-water mixed solvent, an ionic liquid co-solvent, a polyethylene glycol co-solvent, or an alkaline regulator, preferably an ionic liquid co-solvent; the ratio of magnesium lignosulfonate to co-solvent is 30-50:20, preferably 30-40:20. The magnesium lignosulfonate of this invention is industrial-grade magnesium lignosulfonate. In step 2), the mixing time is 1-3 hours, preferably 2 hours; the mixing temperature is 20-30°C, preferably 22-28°C.

[0024] In this invention, the carbon-based material comprises one or more of graphene oxide, graphene, soluble sucrose, glucose, chitosan, phenolic resin, asphalt, polydopamine, polyethylene glycol, and carbon nanotubes, preferably graphene oxide, graphene, soluble sucrose, or glucose.

[0025] In this invention, the composite precursor suspension contains, by mass fraction, 3-10% silicon-based material, preferably 4-9%, more preferably 5-8%; 20-30% magnesium lignosulfonate, preferably 22-28%, more preferably 24-26%; 2-10% carbon-based material, preferably 4-9%, more preferably 5-8%; and 60-75% solvent, preferably 65-70%.

[0026] In this invention, in step 4), the spray drying method uses a peristaltic pump with a rotation speed of 5-30 rpm and a feed rate of 0.1-100 mL / min, preferably 1-50 mL / min, and more preferably 20-40 mL / min; the carrier gas is argon, nitrogen, helium, or argon-hydrogen; the inlet temperature is 100-180℃, preferably 120-160℃, and more preferably 140-150℃; and the outlet temperature is 100-150℃, preferably 110-140℃, and more preferably 120-130℃.

[0027] In this invention, in step 5), the annealing temperature is 500~1000℃, preferably 600~900℃, and more preferably 700~800℃; the heating rate is 5~20℃ / min, preferably 8~18℃ / min, and more preferably 10~15℃ / min; the carbon source gas used in chemical vapor deposition is acetylene, ethylene, or carbon dioxide.

[0028] The present invention also provides a highly stable silicon-carbon anode material prepared by the above preparation method.

[0029] This invention also provides the application of the above-mentioned highly stable silicon-carbon anode material in the preparation of lithium-ion battery electrodes.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing highly stable silicon-carbon anodes using photovoltaic crystalline silicon waste (see...) Figure 1 The specific steps are as follows: (1) Photovoltaic crystalline silicon waste (average particle size 220nm) was added to a hydrofluoric acid solution with a concentration of 1mol / L for purification treatment for 1h, and then dried at a temperature of 80℃ to obtain purified silicon-based material; the liquid-solid ratio of hydrofluoric acid solution to photovoltaic crystalline silicon waste mL:g was 3:1; (2) Weigh 30g of silicon-based material according to the mass ratio and disperse it in a measured amount of anhydrous ethanol. Then add 10ml of ammonia water as a dispersant. Then place the mixture in a water bath and use an ultrasonic cleaner at 400W power for 20 minutes (working mode: 2 seconds of ultrasonication, 1 second of intermittent) to obtain a uniformly dispersed and stable silicon-based material suspension.

[0033] (3) Weigh 50g of magnesium lignosulfonate and 20g of glucose according to the mass ratio, dissolve them in the measured amount of deionized water, add ionic liquid co-solvent, and mechanically stir at 300 rpm for 60 minutes at room temperature until completely dissolved to obtain a clear or slightly brown aqueous solution.

[0034] (4) While continuously stirring the silicon-based material suspension at 800 rpm, slowly add the aqueous solution obtained in step (3). After the addition is complete, continue stirring for 30 minutes. Then transfer the mixture to an ice-water bath for external field strengthening (ultrasonic treatment at 200W power for 5 minutes) to finally obtain a homogeneous and stable composite precursor suspension with a solid content of 15% and a pH value of 9.

[0035] (5) The composite precursor suspension obtained in step (4) is dried and granulated using a spray dryer. The process parameters are: nitrogen as the atomization and drying medium, feed rate of 10 mL / min, inlet temperature controlled at 160°C, and outlet temperature controlled at 100°C. The high sphericity precursor powder doped with magnesium lignosulfonate obtained after drying is collected.

[0036] (6) The precursor powder obtained in step (5) is placed in a CVD furnace and heated to 600°C at a rate of 5°C / min under an inert argon atmosphere. It is then held at this temperature for 2 hours and acetylene is introduced for carbon coating. During this process, glucose undergoes a crystal transformation at high temperatures, magnesium lignosulfonate undergoes pyrolysis, and magnesium reacts with oxygen generated during pyrolysis at the interface with silicon to form dense magnesium oxide in situ. After the reaction, the mixture is naturally cooled to room temperature to obtain the final carbon and magnesium oxide-coated high-stability silicon-carbon anode material (see...). Figure 2 ).

[0037] (7) The silicon-carbon anode material obtained in Example 1 was subjected to electrochemical performance testing. The testing method was carried out in Appendix D of the national standard GB / T 38823-2020. The results showed that the initial coulombic efficiency (ICE) of this example was 89%, and the capacity retention rate after 200 cycles was 85% compared with the first discharge.

[0038] Example 2

[0039] A method for preparing highly stable silicon-carbon anodes using photovoltaic crystalline silicon waste (see...) Figure 1 The specific steps are as follows: (1) Photovoltaic crystalline silicon waste (average particle size 500nm) was added to a hydrofluoric acid solution with a concentration of 1mol / L for purification treatment for 2h, and then dried at a temperature of 70℃ to obtain purified silicon-based material; the liquid-solid ratio of hydrofluoric acid solution to photovoltaic crystalline silicon waste mL:g was 5:1; (2) Weigh 60g of silicon-based material according to the mass ratio and disperse it in a measured amount of anhydrous ethanol. Then add 5ml of sodium hydroxide as a dispersant. Then place the mixture in a water bath and use an ultrasonic cleaner at 500W power for 25 minutes (working mode: ultrasonic for 4 seconds, intermittent for 1 second) to obtain a uniformly dispersed and stable silicon-based material suspension.

[0040] (3) Weigh 100g of magnesium lignosulfonate and 40g of chitosan according to the mass ratio, dissolve them in the measured amount of deionized water, add polyethylene glycol as a co-solvent, and mechanically stir at 400 rpm for 120 minutes at room temperature until completely dissolved to obtain a clear or slightly brown aqueous solution.

[0041] (4) While continuously stirring the silicon-based material suspension at 600 rpm, slowly add the aqueous solution obtained in step (3). After the addition is complete, continue stirring for 60 minutes. Then transfer the mixture to an ice-water bath for external field strengthening (ultrasonic treatment at 400W power for 15 minutes) to finally obtain a homogeneous and stable composite precursor suspension with a solid content of 25% and a pH of 9.

[0042] (5) The composite precursor suspension obtained in step (4) is dried and granulated using a spray dryer. The process parameters are: nitrogen as the atomization and drying medium, feed rate of 10 mL / min, inlet temperature controlled at 140°C, and outlet temperature controlled at 100°C. Collect the dried microspherical precursor powder doped with magnesium lignosulfonate (see...). Figure 3 ).

[0043] (6) The precursor powder obtained in step (5) is placed in a CVD furnace and heated to 800°C at a rate of 5°C / min under an inert argon atmosphere. The temperature is then maintained at this level for 3 hours, followed by the introduction of methane for carbon coating. During this process, chitosan undergoes a crystal transformation at high temperatures, magnesium lignosulfonate undergoes pyrolysis, and magnesium reacts with oxygen generated during pyrolysis at the interface with silicon to form dense magnesium oxide in situ. After the reaction, the mixture is naturally cooled to room temperature to obtain the final carbon and magnesium oxide-coated high-stability silicon-carbon anode material.

[0044] (7) The silicon-carbon anode material obtained in Example 2 was subjected to electrochemical performance testing. The testing method was carried out in Appendix D of the national standard GB / T 38823-2020. The results showed that the initial coulombic efficiency (ICE) of this example was 87%, and the capacity retention rate after 200 cycles was 80% compared with the first discharge.

[0045] Example 3

[0046] A method for preparing highly stable silicon-carbon anodes using photovoltaic crystalline silicon waste (see...) Figure 1 The specific steps are as follows: (1) Photovoltaic crystalline silicon waste (average particle size 420nm) was added to a hydrofluoric acid solution with a concentration of 1mol / L for 3h to remove impurities, and then dried at a temperature of 70℃ to obtain purified silicon-based material; the liquid-solid ratio of hydrofluoric acid solution to photovoltaic crystalline silicon waste mL:g was 5:1; (2) Weigh 30g of silicon-based material according to the mass ratio and disperse it in a measured amount of anhydrous ethanol. Then add 10ml of polyethylene glycol as a dispersant. Then place the mixture in a water bath and use an ultrasonic cleaner at 400W power for 30 minutes (working mode: ultrasonic for 2 seconds, intermittent for 1 second) to obtain a uniformly dispersed and stable silicon-based material suspension.

[0047] (3) Weigh 50g of magnesium lignosulfonate and 20g of cellulose according to the mass ratio, dissolve them in the measured amount of deionized water, add ionic liquid co-solvent, and mechanically stir at 400 rpm for 80 minutes at room temperature until completely dissolved to obtain a clear or slightly brown aqueous solution.

[0048] (4) While continuously stirring the silicon-based material suspension at 500 rpm, slowly add the aqueous solution obtained in step (3). After the addition is complete, continue stirring for 60 minutes. Then transfer the mixture to an ice-water bath for external field strengthening (ultrasonic treatment at 200W power for 5 minutes) to finally obtain a homogeneous and stable composite precursor suspension with a solid content of 35% and a pH of 8.5.

[0049] (5) The composite precursor suspension obtained in step (4) is dried and granulated using a spray dryer. The process parameters are: nitrogen as the atomization and drying medium, feed rate of 10 mL / min, inlet temperature controlled at 130°C, and outlet temperature controlled at 100°C. Collect the dried microspherical precursor powder doped with magnesium lignosulfonate (see...). Figure 4 ).

[0050] (6) The precursor powder obtained in step (5) is placed in a CVD furnace and heated to 700°C at a rate of 5°C / min under an inert argon atmosphere. The temperature is then maintained at this level for 4 hours, and carbon dioxide is introduced for carbon coating. During this process, cellulose undergoes a crystal transformation at high temperatures, magnesium lignosulfonate undergoes pyrolysis, and magnesium reacts with oxygen generated during pyrolysis at the interface with silicon to form dense magnesium oxide in situ. After the reaction, the mixture is naturally cooled to room temperature to obtain the final carbon and magnesium oxide-coated high-stability silicon-carbon anode material.

[0051] (7) The silicon-carbon anode material obtained in Example 3 was subjected to electrochemical performance testing. The testing method was carried out in Appendix D of the national standard GB / T 38823-2020. The results showed that the initial coulombic efficiency (ICE) of this example was 90%, and the capacity retention rate after 500 cycles was 80% compared with the first discharge.

[0052] Example 4

[0053] A method for preparing highly stable silicon-carbon anodes using photovoltaic crystalline silicon waste (see...) Figure 1 The specific steps are as follows: (1) Photovoltaic crystalline silicon waste (average particle size 270nm) was added to a hydrofluoric acid solution with a concentration of 1mol / L for 1.5h to remove impurities, and then dried at a temperature of 80℃ to obtain purified silicon-based material; the liquid-solid ratio of hydrofluoric acid solution to photovoltaic crystalline silicon waste mL:g was 4:1; (2) Weigh 30g of silicon-based material according to the mass ratio and disperse it in a measured amount of anhydrous ethanol. Then add 10ml of ammonia water as a dispersant. Then place the mixture in a water bath and use an ultrasonic cleaner at 400W power for 40 minutes (working mode: 2 seconds of ultrasonication, 1 second of intermittent) to obtain a uniformly dispersed and stable silicon-based material suspension.

[0054] (3) Weigh 50g of magnesium lignosulfonate and 20g of soluble sucrose according to the mass ratio, dissolve them in the measured amount of deionized water, add ammonia water as a co-solvent, and mechanically stir at 300 rpm for 60 minutes at room temperature until completely dissolved to obtain a clear or slightly brown aqueous solution.

[0055] (4) While continuously stirring the silicon-based material suspension at 800 rpm, slowly add the aqueous solution obtained in step (3). After the addition is complete, continue stirring for 30 minutes. Then transfer the mixture to an ice-water bath for external field strengthening (ultrasonic treatment at 200W power for 5 minutes) to finally obtain a homogeneous and stable composite precursor suspension with a solid content of 15% and a pH value of 9.5.

[0056] (5) The composite precursor suspension obtained in step (4) is dried and granulated using a spray dryer. The process parameters are: nitrogen as the atomization and drying medium, feed rate of 10 mL / min, inlet temperature controlled at 160°C, and outlet temperature controlled at 100°C. The dried microspherical precursor powder doped with magnesium lignosulfonate is collected, with the morphology as shown in the figure. Figure 4 .

[0057] (6) The precursor powder obtained in step (5) is placed in a CVD furnace and heated to 800°C at a rate of 10°C / min under an inert argon atmosphere. This temperature is maintained for 2 hours, and methane is introduced for carbon coating. Soluble sucrose undergoes a crystal transformation at high temperatures, magnesium lignin sulfonate undergoes pyrolysis, and magnesium reacts with oxygen generated during pyrolysis at the interface with silicon to form dense magnesium oxide in situ. After the reaction, the mixture is naturally cooled to room temperature to obtain the final carbon and magnesium oxide-coated high-stability silicon-carbon anode material (see...). Figure 5 ).

[0058] (7) The silicon-carbon anode material obtained in Example 4 was subjected to electrochemical performance testing. The testing method was carried out in Appendix D of the national standard GB / T 38823-2020. The results showed that the initial coulombic efficiency (ICE) of this example was 91%, and the capacity retention rate after 400 cycles was 81% compared with the first discharge.

[0059] Example 5

[0060] A method for preparing highly stable silicon-carbon anodes using photovoltaic crystalline silicon waste (see...) Figure 1 The specific steps are as follows: (1) Photovoltaic crystalline silicon waste (average particle size 620nm) was added to a hydrofluoric acid solution with a concentration of 1mol / L for 2h to remove impurities, and then dried at 80℃ to obtain purified silicon-based material; the liquid-solid ratio of hydrofluoric acid solution to photovoltaic crystalline silicon waste mL:g was 5:1; (2) Weigh 40g of silicon-based material according to the mass ratio and disperse it in a measured amount of anhydrous ethanol. Then add 10ml of ammonia water as a dispersant. Then place the mixture in a water bath and use an ultrasonic cleaner at 400W power for 15 minutes (working mode: 2 seconds of ultrasonication, 1 second of intermittent) to obtain a uniformly dispersed and stable silicon-based material suspension.

[0061] (3) Weigh 70g of magnesium lignosulfonate and 40g of phenolic resin according to the mass ratio, dissolve them in the measured amount of deionized water, add polyethylene glycol as a co-solvent, and mechanically stir at 400 rpm for 50 minutes at room temperature until completely dissolved to obtain a clear or slightly brown aqueous solution.

[0062] (4) While continuously stirring the silicon-based material suspension at 650 rpm, slowly add the aqueous solution obtained in step (3). After the addition is complete, continue stirring for 45 minutes. Then transfer the mixture to an ice-water bath again and sonicate it at 200W for 8 minutes to finally obtain a homogeneous and stable composite precursor suspension with a solid content of 27% and a pH of 10.

[0063] (5) The composite precursor suspension obtained in step (4) is dried and granulated using a spray dryer. The process parameters are: nitrogen as the atomization and drying medium, feed rate of 10 mL / min, inlet temperature controlled at 140°C, and outlet temperature controlled at 110°C. The dried microspherical precursor powder doped with magnesium lignosulfonate is collected, with the morphology as shown in the figure. Figure 5 .

[0064] (6) The precursor powder obtained in step (5) is placed in a CVD furnace and heated to 660°C at a rate of 4°C / min under an inert argon atmosphere. The temperature is then maintained at this level for 4 hours, followed by the introduction of acetylene for carbon coating. During this process, the phenolic resin undergoes a crystal transformation at high temperatures, and magnesium lignosulfonate undergoes pyrolysis. Magnesium reacts with oxygen generated during pyrolysis at the interface with silicon to form dense magnesium oxide in situ. After the reaction, the mixture is naturally cooled to room temperature to obtain the final carbon and magnesium oxide-coated high-stability silicon-carbon anode material.

[0065] (7) The silicon-carbon anode material obtained in Example 5 was subjected to electrochemical performance testing. The testing method was carried out according to Appendix D of the national standard GB / T 38823-2020. The results showed that the initial coulombic efficiency (ICE) of this example was 90.5%, and the capacity retention rate after 200 cycles was 86% compared with the first discharge. (See...) Figure 6 ).

[0066] As can be seen from the above embodiments, the present invention provides a high-stability silicon-carbon anode material prepared from photovoltaic crystalline silicon waste, its preparation method, and its application. The present invention disperses magnesium lignosulfonate on the surface of photovoltaic crystalline silicon waste by adding a co-solvent, then mixes it with carbon-based materials and spray-dries it to obtain a nanoscale silicon-carbon composite material with high sphericity and high tap density. A high-stability silicon-carbon anode is obtained by forming a carbon coating layer through high-temperature annealing. The present invention can achieve precise control of the coating layer, which not only improves the electronic conductivity, tap density, and first coulombic efficiency of the composite material, but also suppresses the volume expansion of internal silicon and the generation of hydrofluoric acid during battery charging and discharging, thus improving the cycle life of the battery.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste, characterized in that, Includes the following steps: 1) Photovoltaic crystalline silicon waste is added to a treatment solution for purification and dried to obtain silicon-based material; the silicon-based material is dispersed in a mixture of ethanol and dispersant, and then ultrasonically dispersed to obtain a silicon-based material suspension. 2) Magnesium lignosulfonate and carbon-based materials were dispersed in water, and then a co-solvent was added to obtain a magnesium lignosulfonate suspension; 3) The silicon-based material suspension was mixed in the magnesium lignosulfonate suspension and then subjected to ultrasonic treatment to obtain the composite precursor suspension; 4) The composite precursor suspension was dried and granulated by spray drying to obtain precursor powder; 5) The precursor powder was annealed by introducing carbon source gas in an inert gas atmosphere and then subjected to chemical vapor deposition to obtain a high-stability silicon-carbon anode material. In step 1), the dispersant is ammonia or sodium hydroxide; In step 2), the co-solvent includes an ethanol-water mixed solvent, an ionic liquid co-solvent, a polyethylene glycol co-solvent, or an alkaline regulator, and the ratio of magnesium lignosulfonate to co-solvent is 30-50:

20.

2. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 1, characterized in that, In step 1), the treatment solution contains one or more of hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid and hydrogen peroxide, the concentration of the treatment solution is 1~8 mol / L, the liquid-solid ratio of the treatment solution to the photovoltaic silicon waste is 3~10 mL:1 g, and the purification treatment time is 1~8 h.

3. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 1 or 2, characterized in that, In step 1), the ratio of silicon-based material, ethanol and dispersant is 30~60g:1mL:5~10mL, the power of ultrasonic dispersion is 300~800W, the processing time is 10~30min, and the working mode is ultrasonic 2s, intermittent 1s.

4. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 1 or 2, characterized in that, The carbon-based material includes one or more of graphene oxide, graphene, soluble sucrose, glucose, chitosan, phenolic resin, asphalt, polydopamine, polyethylene glycol, and carbon nanotubes.

5. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 4, characterized in that, In the composite precursor suspension, by mass fraction, silicon-based materials account for 3-10%, magnesium lignosulfonate accounts for 20-30%, carbon-based materials account for 2-10%, and solvent accounts for 60-75%.

6. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 1 or 5, characterized in that, In step 4), the spray drying method uses a peristaltic pump with a rotation speed of 5-30 rpm, a feed rate of 0.1-100 mL / min, a carrier gas of argon, nitrogen, helium or argon-hydrogen, an inlet temperature of 100-180℃, and an outlet temperature of 100-150℃.

7. The method for preparing highly stable silicon-carbon anode materials using photovoltaic crystalline silicon waste according to claim 6, characterized in that, In step 5), the annealing temperature is 500~1000℃ and the heating rate is 5~20℃ / min; the carbon source gas used in chemical vapor deposition is acetylene, ethylene or carbon dioxide.

8. The high-stability silicon-carbon anode material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the high-stability silicon-carbon anode material according to claim 8 in the preparation of lithium-ion battery electrodes.

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