A method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules

Abstract

The present application relates to the technical field of silicon material preparation, and particularly relates to a method for preparing copper-doped porous silicon material from decomposed photovoltaic modules, which comprises the following steps: step 1: pyrolyzing decomposed photovoltaic modules to obtain battery pieces and copper cable products, crushing the battery pieces, and vacuum smelting the battery pieces with a certain proportion of copper cables to obtain copper-doped silicon ingots; step 2: reacting silicon copper composite powder obtained by crushing the silicon ingots with magnesium powder to synthesize magnesium silicide, and grinding the magnesium silicide sand to obtain sand-ground magnesium silicide powder; and step 3: performing dealloying reaction treatment on the sand-ground magnesium silicide powder. The present application uses battery pieces and copper cables in decomposed photovoltaic modules as raw materials, combines gas-phase dealloying, and uses acid pickling to prepare a porous structure silicon negative electrode material with excellent electrochemical performance. The present application does not involve a template, is simple and efficient to operate, has a short process cycle, uses inexpensive and widely-sourced raw materials, and is easy to mass-produce.

Description

Technical Field

[0001] This invention relates to the field of silicon material preparation technology, and in particular to a method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules. Background Technology

[0002] Although silicon solar cells account for only 3% of the total mass of retired photovoltaic modules, they are the core functional unit and the main cost component (accounting for over 60%). Improper disposal of these high-purity silicon substrates (purity ≥6N) not only leads to a significant waste of high-value semiconductor materials but also poses a significant environmental risk due to potential heavy metal leaching. Therefore, developing advanced high-value utilization technologies for retired photovoltaic silicon cells has become a key research direction for promoting the sustainable development of the photovoltaic industry.

[0003] Notably, retired silicon batteries provide a unique source of raw materials for the preparation of anode materials for next-generation lithium-ion batteries (LIBs). The theoretical capacity of existing graphite anode technology has inherent limitations (372 mAh). However, this technology is no longer sufficient to meet the demands of emerging high-energy-density energy storage applications. In contrast, silicon, with its superior theoretical capacity (4200 mAh), offers a more competitive advantage. Silicon, with its suitable lithium intercalation potential and abundant crustal reserves, has become a highly promising candidate for next-generation anode materials. However, the practical application of silicon-based anodes still faces three major challenges: First, the preparation cost of high-purity silicon micron powder is high, accounting for more than 50% of the total cost of anode materials, which restricts its large-scale application; second, silicon undergoes a 300-400% volume expansion during lithiation, and this volume strain leads to pulverization of the electrode structure, resulting in a sharp decline in battery cycle performance; third, silicon has a low intrinsic conductivity (approximately 10⁻³ S / cm), which severely limits its electrochemical performance. Therefore, designing a short-process, mass-producible silicon-based anode material preparation method that can alleviate the volume expansion problem and improve conductivity is crucial.

[0004] In the prior art, Chinese patent CN113387343 B discloses a method for preparing silicon-carbon anodes for lithium-ion batteries using retired photovoltaic modules. Although this method achieves efficient recycling and value-added utilization of retired devices, it does not fully utilize other metal components in the modules. Chinese patent CN 110817882A discloses a method for preparing nano-silicon powder by recovering silicon from waste retired photovoltaic modules, but it does not modify the silicon material, making it difficult to meet the performance requirements of lithium-ion battery anode materials. Although Chinese patent CN112259719A improves conductivity, the excessive residual carbon doping leads to low capacity. The preparation method disclosed in Chinese patent CN117936738A yields silicon anode materials with good performance, but its cost is high, which is not conducive to large-scale production. The method reported in the literature "Manufacturing lithium-ion anodes from silicon recovered from end-of-life solar panels" achieves silicon material recycling, but it uses highly hazardous hydrofluoric acid, increasing process costs and hindering environmental protection and large-scale production.

[0005] In summary, although existing technologies have made some progress in the recycling of silicon materials from retired photovoltaic modules and the preparation of silicon-based anode materials, there are still problems such as complex processes, high costs, environmental unfriendliness, insufficient performance, or failure to fully utilize other valuable components in the modules. There is an urgent need to develop a method for preparing silicon-based anode materials that is efficient, low-cost, environmentally friendly, and can fully utilize all valuable components in retired photovoltaic modules. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies, such as complex processes, high costs, environmental unfriendliness, insufficient performance, or failure to fully utilize other valuable components in the modules, and to propose a method for preparing copper-doped porous silicon materials from decommissioned photovoltaic modules.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules is designed, comprising the following steps:

[0009] Step 1: Pyrolyze retired photovoltaic modules to obtain solar cells and copper cable products. Crush the solar cells and vacuum melt them with a certain proportion of copper cable to obtain copper-doped silicon ingots.

[0010] Step 2: React the silicon-copper composite powder obtained after crushing silicon ingots with magnesium powder to synthesize magnesium silicide. Then, grind the magnesium silicide to obtain sand-ground magnesium silicide powder.

[0011] Step 3: The magnesium silicide powder obtained after sand milling is subjected to a dealloying reaction treatment;

[0012] Step 4: The product obtained from the dealloying reaction is acid-washed, filtered, and dried to obtain copper-doped porous silicon material.

[0013] Furthermore, in step 1, the temperature of photovoltaic module pyrolysis is 400-600 ℃, and the holding time is 1-3 h; during vacuum melting, the doping amount of waste copper cable accounts for 1%-15% of the cell mass.

[0014] Furthermore, in step 2, the particle size of the silicon-copper composite powder after silicon ingot crushing is 1-15μm, and the mass ratio of silicon-copper composite powder to magnesium powder is 1: (1-2); the reaction of silicon-copper composite powder and magnesium powder is carried out under an argon atmosphere, heated to 550-650℃ for 3-9h, and the heating rate is 2-10℃ / min.

[0015] Furthermore, in step 2, the particle size of the magnesium silicide powder obtained after sand milling is 2-8 μm;

[0016] The preparation method of the magnesium silicide powder is as follows:

[0017] The magnesium silicide synthesized in step 1 was placed in a sand mill, and 8-12 times the mass of zirconium oxide sand beads were added with n-hexane as a grinding aid. The mixture was ball-milled at 1000-2000 r / min for 1-3 h.

[0018] The ground powder was sieved through a 200-mesh filter with ethanol as a dispersant. The resulting ethanol solution was then dried by forced air to obtain magnesium silicide powder with the target particle size.

[0019] Furthermore, the dealloying reaction treatment in step 3 involves grinding magnesium silicide powder in an ammonia-containing atmosphere, heating it to 600-900℃ at a heating rate of 2-10℃ / min, and holding it at that temperature for 3-9 hours.

[0020] Furthermore, the product obtained from the dealloying reaction in step 4 is pickled in 0.5-2M / L hydrochloric acid solution at 50-80℃ for 2-6 hours.

[0021] Furthermore, after obtaining the copper-doped porous silicon material in step 4, a surface coating step is also included:

[0022] The material is uniformly mixed with a carbon source precursor at a mass ratio of 1: (0.1-0.5), and under the protection of an inert atmosphere, the temperature is raised to 500-800℃ at 2-5℃ / min and heat-treated for 1-4 hours to form a carbon-coated core-shell structure composite material.

[0023] The carbon source precursor is glucose, citric acid, or organic pyrolysis carbon produced by pyrolysis in step 1.

[0024] Furthermore, the acid washing process in step 4 is carried out in a closed system, and the generated ammonia-containing tail gas is discharged and recovered through an absorbent; the absorbent is a sulfuric acid or hydrochloric acid solution with a concentration of 1-3 mol / L.

[0025] Furthermore, the magnesium chloride-containing filtrate generated after acid washing in step 4 is subjected to molten salt electrolysis after evaporation, concentration, and dehydration treatment, and then regenerated at the cathode to obtain metallic magnesium.

[0026] Furthermore, the electrolytically regenerated metallic magnesium is returned to step 2 as part or all of the magnesium powder raw material;

[0027] The chlorine gas produced at the anode during the electrolysis process is used to synthesize hydrochloric acid and returned to step 4 as part or all of the pickling solution.

[0028] The present invention proposes a method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules, the advantages of which are as follows:

[0029] 1. This invention uses solar cells and copper cables from retired photovoltaic modules as raw materials, combined with vapor phase dealloying and acid washing, to prepare porous silicon anode materials with excellent electrochemical performance. This method does not involve templates, is simple and efficient to operate, has a short process cycle, uses inexpensive and widely available raw materials, and is easy to scale up for production.

[0030] 2. The vacuum melting method used in this invention fully utilizes the waste copper cables from retired photovoltaic modules, improving raw material utilization and eliminating the need for separate copper cable recycling, thus saving time and economic costs. It also further enhances the economic value of the obtained negative electrode material, making it green and environmentally friendly, in line with national green energy-saving policies.

[0031] 3. The preparation method of this invention utilizes copper cables from retired photovoltaic modules for doping. Copper is often used as a cable due to its excellent conductivity. Therefore, copper doping can effectively improve the problem of low intrinsic conductivity of silicon as a negative electrode material. The increase in conductivity can effectively improve the electrochemical performance of the battery. At the same time, carbon coating and other operations can be performed to further enhance the electrochemical performance, which has broad application prospects.

[0032] 4. The porous structure prepared by this invention provides space for the volume expansion caused by lithium ion insertion / extraction during silicon charging and discharging, effectively alleviating problems such as material pulverization and battery failure caused by volume expansion. The porous structure has a significant advantage in mitigating battery material expansion. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the present invention;

[0034] Figure 2 The above are XRD analysis diagrams of the various reaction products in Example 1 of this invention;

[0035] Figure 3 This is an electron microscope image of the porous silicon material in Embodiment 1 of the present invention;

[0036] Figure 4 This is a schematic diagram of the cycle performance test of the copper-doped porous silicon anode material in Embodiment 1 of the present invention;

[0037] Figure 5 This is a schematic diagram of the rate performance test of the copper-doped porous silicon anode material obtained in Example 1 of the present invention at different current densities;

[0038] Figure 6 This is a comparison chart of the tap conductivity of the copper-doped porous silicon anode material obtained in Example 1 of the present invention and the non-copper-doped porous silicon anode material. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] Example 1

[0041] Reference Figure 1-6 As one embodiment of the present invention, a method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules is disclosed, comprising the following steps:

[0042] Step 1: Pyrolysis of retired photovoltaic modules yields solar cells and copper cable products. The solar cells are crushed and vacuum-melted with a certain proportion of copper cable to obtain copper-doped silicon ingots. The pyrolysis temperature of the photovoltaic modules is 400 ℃, and the holding time is 1 h. During the vacuum melting, the doping amount of waste copper cable accounts for 1% of the mass of the solar cells.

[0043] Step 2: The silicon-copper composite powder obtained after crushing silicon ingots is reacted with magnesium powder to synthesize magnesium silicide. The magnesium silicide is then milled to obtain milled magnesium silicide powder. The particle size of the silicon-copper composite powder after crushing silicon ingots is 1-15 μm, and the mass ratio of silicon-copper composite powder to magnesium powder is 1:1. The reaction between the silicon-copper composite powder and magnesium powder is carried out under an argon atmosphere, heated to 550℃ for 3 hours, with a heating rate of 2℃ / min. The particle size of the magnesium silicide powder obtained after milling is 2-8 μm.

[0044] Step 3: The magnesium silicide powder obtained after sand milling is subjected to a dealloying reaction treatment; wherein, the dealloying reaction treatment is to heat the sand-milled magnesium silicide powder to 600℃ at a heating rate of 2℃ / min and hold it at that temperature for 3h in an atmosphere containing ammonia.

[0045] Step 4: The product obtained from the dealloying reaction is acid-washed, filtered, and dried to obtain copper-doped porous silicon material. The product obtained from the dealloying reaction is acid-washed with 0.5M / L hydrochloric acid solution at 50℃ for 2 hours, then filtered three times until neutral, and freeze-dried for 12 hours to obtain copper-doped porous silicon anode material.

[0046] Specifically, this invention uses retired photovoltaic modules as raw materials, fully utilizes the copper metal in the photovoltaic modules during the vacuum melting process, and obtains a porous structure with a large porosity during alloying, nitriding and pickling processes. It is a high-performance copper-doped porous silicon material that can be used directly with only simple processing.

[0047] The preparation process of this invention is simple. When removing magnesium nitride by acid washing, silicon elemental and pore space are left behind, giving the obtained silicon material a porous structure. This results in a well-shaped three-dimensional porous structure material, which reserves space for the huge volume expansion caused by lithium-ion insertion and extraction during silicon cycling. This effectively alleviates the expansion of silicon during lithium insertion and extraction, and avoids battery failure caused by material pulverization. The porous structure has a significant advantage in alleviating the expansion of battery materials, and the copper doping also significantly improves the conductivity of silicon. Its application in lithium-ion batteries has the characteristics of long cycle life and excellent rate performance.

[0048] The copper-doped porous silicon material particles prepared by this invention have a size of 2-8 μm. The control of particle size enables the battery anode material made from this porous silicon to achieve both high capacity and high capacity retention. It can be used as a raw material for lithium-ion battery anodes. Furthermore, it can be modified by carbon coating and other processes to further enhance its electrochemical performance and commercial value, showing broad commercial application prospects. It also realizes the recycling and reuse of retired photovoltaic modules, achieving the goal of high-value utilization of solid waste. This avoids environmental pollution caused by solid waste accumulation and responds to the national policy of solid waste recycling.

[0049] In an optional embodiment, in step 2;

[0050] The preparation method of the magnesium silicide powder is as follows:

[0051] The magnesium silicide synthesized in step 1 was placed in a sand mill, and 8 times the mass of zirconium oxide sand beads were added with n-hexane as a grinding aid and ball-milled at 1000 r / min for 1 h.

[0052] The ground powder was sieved through a 200-mesh filter with ethanol as a dispersant. The resulting ethanol solution was then dried by forced air to obtain magnesium silicide powder with the target particle size.

[0053] Experimental results:

[0054] The final product was characterized using X-ray diffraction techniques to obtain the corresponding XRD patterns. Figure 2 The XRD pattern shows that copper-doped silicon was finally obtained after a series of reactions, with copper existing in the form of copper silicide in the silicon, indicating that the doping was successful. Figure 2 The horizontal axis represents the diffraction angle of X-rays, and the vertical axis represents the diffraction intensity.

[0055] The morphology and structure of the synthesized material were observed using scanning electron microscopy. Figure 3 The SEM image of a clearly shows that the material synthesized by this method has a uniform particle morphology and an average particle size of 3-5 μm; the material has a typical porous structure.

[0056] like Figure 4 This is a schematic diagram of the cycling performance test of the copper-doped porous silicon anode material in Embodiment 1 of the present invention. The copper-doped porous silicon material of the present invention underwent long-term cycling testing at a current of 1 A·g⁻¹. The first three cycles were activated with a small current of 0.1 C. The results show that after 150 cycles at a current density of 1 A·g⁻¹, the capacity of the copper-doped porous silicon remains as high as 1517 mAh / g, exhibiting excellent cycling performance. Figure 4 The horizontal axis represents the number of cycles, and the vertical axis represents the specific capacity.

[0057] Figure 5 This diagram illustrates the rate performance test of the copper-doped porous silicon anode material obtained in Example 1 at different current densities. When the current increased from 0.1 A·g⁻¹ to 1 A·g⁻¹, a tenfold increase, the capacity retention of the porous silicon anode material exceeded 60%. Even under a higher current of 5 A·g⁻¹, it still maintained a reversible capacity of nearly 1000 mAh / g. When the current returned to 0.1 A·g⁻¹, the capacity recovered to approximately 2600 mAh / g. This demonstrates the excellent rate performance of this anode material. Figure 5 The horizontal axis represents the number of cycles, and the vertical axis represents the specific capacity.

[0058] Figure 6 The chart shows a comparison of the tap conductivity of the copper-doped porous silicon anode material obtained in Example 1 and the undoped porous silicon anode material. It can be seen that from the beginning of the test, the tap conductivity of the copper-doped porous silicon anode material was significantly higher than that of the undoped material. This advantage becomes more pronounced with increasing pressure; when the pressure reaches 160 MPa, its conductivity is more than three times that of the undoped porous silicon material. This demonstrates that copper doping significantly improves the problem of low intrinsic conductivity of silicon as an anode material. Figure 6 The horizontal axis represents pressure, and the vertical axis represents electrical conductivity.

[0059] The copper-doped porous silicon material obtained in Example 1 of this invention provides sufficient space to alleviate the huge volume expansion of silicon during lithium insertion / extraction, effectively mitigating problems such as material pulverization and battery failure caused by volume expansion. Compared with general silicon-based anode materials, it greatly improves its electrochemical performance, especially long cycle performance and rate capability.

[0060] In some embodiments, after obtaining the copper-doped porous silicon material in step 4, the present invention further includes a surface coating step:

[0061] The material is uniformly mixed with a carbon source precursor at a mass ratio of 1:0.1, and then heated to 500°C at a rate of 2°C / min and heat-treated for 1 hour under an inert atmosphere to form a carbon-coated core-shell structure composite material.

[0062] The carbon source precursor is glucose, citric acid, or organic pyrolysis carbon produced by pyrolysis in step 1.

[0063] Specifically, the material after this carbon coating treatment, at 1 A· Under long-term cycling tests at high current densities, the capacity retention after 150 cycles increased from ~75% of the original porous silicon to ~92%, and the reversible capacity stabilized at 1550 mAh. In summary, the carbon layer, acting as a continuous conductive network, improves the overall conductivity of the electrode material by approximately an order of magnitude. Furthermore, transmission electron microscopy (TEM) reveals that a uniform carbon layer, approximately 5-10 nm thick, completely coats the surface of the silicon particles. During charge and discharge, this carbon layer effectively confines the volume expansion of the silicon core, suppressing excessive side reactions between the active material and the electrolyte. After 100 cycles, the electrode structure with the carbon coating exhibits significantly better structural integrity than the uncoated sample, with a substantial reduction in electrode material detachment from the current collector.

[0064] Of course, in this embodiment, the same effect can be achieved when the carbon source is replaced with organic tar extracted from the pyrolysis condensate in step 1. This reduces the cost of carbon-coated raw materials per kilogram of negative electrode material by about 85%, while solving the problem of disposal of pyrolysis organic waste, demonstrating the high economic efficiency and environmental friendliness of material recycling within the process.

[0065] Specifically, in this embodiment of the invention, the acid washing process in step 4 is carried out in a closed system, and the generated ammonia-containing tail gas is discharged and recovered through an absorption liquid; the absorption liquid is a sulfuric acid or hydrochloric acid solution with a concentration of 1 mol / L.

[0066] In step 4, the acid washing process is carried out in a closed reactor with a condenser reflux and a gas outlet. The gas generated during acid washing is discharged and first recovered by a -5℃ condenser. Then it is fed into an absorption tower containing a 1mol / L sulfuric acid solution for circulation absorption until the pH of the outlet gas is neutral, and finally an ammonium sulfate solution is obtained.

[0067] This closed absorption system can recover ammonia, with no irritating odor at the production site and emissions that meet national environmental protection standards. It solves the typical air pollution problem in wet treatment processes, while avoiding the problem of ammonium salt crystallization and blockage caused by ammonia condensation in pipelines and equipment, thus reducing equipment maintenance frequency and long-term operating risks.

[0068] Based on the above embodiments, in this embodiment, the magnesium chloride-containing filtrate generated after acid washing in step 4 is subjected to evaporation, concentration, and dehydration treatment, followed by molten salt electrolysis to regenerate metallic magnesium at the cathode.

[0069] In this embodiment, the magnesium chloride-containing filtrate generated after the above-mentioned acid washing is collected, filtered with activated carbon to remove solid impurities, and then evaporated and concentrated to 1 / 3 of its original volume at 90°C. The concentrated liquid is then dehydrated in a dry hydrogen chloride gas stream at 180°C for 3 hours to obtain anhydrous magnesium chloride solid. This solid is placed together with a mixed salt of sodium chloride and potassium chloride in a molten salt electrolytic cell and electrolyzed at 700°C to obtain recycled metallic magnesium at the cathode. Through this process, the single-cycle recovery rate of magnesium powder can be effectively improved, which means that the demand for externally purchased magnesium powder is effectively reduced during long-term operation, resulting in significant economic benefits. This process achieves efficient recycling of magnesium within the process system, greatly reducing dependence on raw ore resources and improving the extraction efficiency of urban minerals.

[0070] Specifically, in this embodiment, the electrolytically regenerated metallic magnesium is returned to step 2 as part or all of the magnesium powder raw material.

[0071] The chlorine gas produced at the anode during the electrolysis process is used to synthesize hydrochloric acid and returned to step 4 as part or all of the pickling solution.

[0072] In this embodiment, the chlorine gas generated at the anode of the electrolytic cell is dried and then mixed with hydrogen gas obtained from the electrolysis of water in a stoichiometric ratio and fed into the synthesis furnace to generate hydrogen chloride gas through combustion. This gas is then absorbed by deionized water to prepare regenerated hydrochloric acid with a concentration of about 1M. This hydrochloric acid is then mixed with some fresh acid and reused in step 4 of claim 1 for acid washing.

[0073] This implementation method achieves a complete internal cycle of magnesium and chlorine. The recycled magnesium is reused for the magnesothermic reduction in step 2, and the recycled hydrochloric acid is reused for the pickling in step 4. The entire system, except for the initial feeding, theoretically does not require additional replenishment of magnesium powder and hydrochloric acid, and only requires replenishment of a small amount of loss. It is a truly zero-consumable green metallurgical process, while saving high hazardous waste disposal costs.

[0074] Example 2

[0075] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference lies in that this embodiment specifically includes the following steps:

[0076] Step 1: Pyrolyze retired photovoltaic modules to obtain solar cells and copper cable products. Crush the solar cells and vacuum melt them with a certain proportion of copper cable to obtain copper-doped silicon ingots.

[0077] The photovoltaic module pyrolysis temperature was 500 ℃, and the holding time was 2 h; the amount of waste copper cable used in the vacuum melting process accounted for 8% of the cell mass.

[0078] Step 2: React the silicon-copper composite powder obtained after crushing silicon ingots with magnesium powder to synthesize magnesium silicide. Then, grind the magnesium silicide to obtain sand-ground magnesium silicide powder.

[0079] The silicon-copper composite powder after silicon ingot crushing has a particle size of 1-15μm, and the mass ratio of silicon-copper composite powder to magnesium powder is 1:1.5. The reaction between the silicon-copper composite powder and magnesium powder is carried out in an argon atmosphere, heated to 600℃ for 6h, with a heating rate of 6℃ / min. The particle size of the magnesium silicide powder obtained after sand milling is 2-8μm.

[0080] Step 3: The magnesium silicide powder obtained after sand milling is subjected to a dealloying reaction treatment;

[0081] Among them, the dealloying reaction treatment involves grinding magnesium silicide powder in an ammonia-containing atmosphere, heating it to 750°C at a heating rate of 6°C / min, and holding it at that temperature for 6 hours.

[0082] Step 4: The product obtained from the dealloying reaction is acid-washed, filtered, and dried to obtain copper-doped porous silicon material. The product obtained from the dealloying reaction is acid-washed with 1.75M / L hydrochloric acid solution at 75℃ for 4 hours.

[0083] In an optional embodiment, in step 2;

[0084] The preparation method of the magnesium silicide powder is as follows:

[0085] The magnesium silicide synthesized in step 1 was placed in a sand mill, and 8-12 times the mass of zirconium oxide sand beads were added with n-hexane as a grinding aid and ball-milled at 1500 r / min for 2 h.

[0086] The ground powder was sieved through a 200-mesh filter with ethanol as a dispersant. The resulting ethanol solution was then dried by forced air to obtain magnesium silicide powder with the target particle size.

[0087] In some embodiments, after obtaining the copper-doped porous silicon material in step 4, the present invention further includes a surface coating step:

[0088] The material was uniformly mixed with a carbon source precursor at a mass ratio of 1:0.3, and then heated to 650°C at a rate of 3.5°C / min and heat-treated for 2.5 hours under an inert atmosphere to form a carbon-coated core-shell structure composite material.

[0089] The carbon source precursor is glucose, citric acid, or organic pyrolysis carbon produced by pyrolysis in step 1.

[0090] Specifically, in this embodiment of the invention, the acid washing process in step 4 is carried out in a closed system, and the generated ammonia-containing tail gas is discharged and recovered through an absorption liquid; the absorption liquid is a sulfuric acid or hydrochloric acid solution with a concentration of 2 mol / L.

[0091] Based on the above embodiments, in this embodiment, the magnesium chloride-containing filtrate generated after acid washing in step 4 is subjected to evaporation, concentration, and dehydration treatment, followed by molten salt electrolysis to regenerate metallic magnesium at the cathode.

[0092] Specifically, in this embodiment, the electrolytically regenerated metallic magnesium is returned to step 2 as part or all of the magnesium powder raw material.

[0093] The chlorine gas produced at the anode during the electrolysis process is used to synthesize hydrochloric acid and returned to step 4 as part or all of the pickling solution.

[0094] Example 3

[0095] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference lies in that this embodiment specifically includes the following steps:

[0096] Step 1: Pyrolyze retired photovoltaic modules to obtain solar cells and copper cable products. Crush the solar cells and vacuum melt them with a certain proportion of copper cable to obtain copper-doped silicon ingots.

[0097] The photovoltaic module pyrolysis temperature is 600 ℃, and the holding time is 3 h; the doping amount of waste copper cable during vacuum melting accounts for 15% of the cell mass;

[0098] Step 2: React the silicon-copper composite powder obtained after crushing silicon ingots with magnesium powder to synthesize magnesium silicide. Then, grind the magnesium silicide to obtain sand-ground magnesium silicide powder.

[0099] The silicon-copper composite powder after silicon ingot crushing has a particle size of 1-15μm, and the mass ratio of silicon-copper composite powder to magnesium powder is 1:2. The reaction between the silicon-copper composite powder and magnesium powder is carried out in an argon atmosphere, heated to 650℃ for 9h, with a heating rate of 10℃ / min. The particle size of the magnesium silicide powder obtained after sand milling is 8μm.

[0100] Step 3: The magnesium silicide powder obtained after sand milling is subjected to a dealloying reaction treatment;

[0101] Among them, the dealloying reaction treatment involves grinding magnesium silicide powder in an ammonia-containing atmosphere, heating it to 900℃ at a heating rate of 10℃ / min, and holding it at that temperature for 3-9 hours.

[0102] Step 4: The product obtained from the dealloying reaction is acid-washed, filtered, and dried to obtain copper-doped porous silicon material. The product obtained from the dealloying reaction is acid-washed with 2M / L hydrochloric acid solution at 80℃ for 6 hours.

[0103] In an optional embodiment, in step 2;

[0104] The preparation method of the magnesium silicide powder is as follows:

[0105] The magnesium silicide synthesized in step 1 was placed in a sand mill, and 12 times the mass of zirconium oxide sand beads were added with n-hexane as a grinding aid. The mixture was ball-milled at 2000 r / min for 3 h.

[0106] The ground powder was sieved through a 200-mesh filter with ethanol as a dispersant. The resulting ethanol solution was then dried by forced air to obtain magnesium silicide powder with the target particle size.

[0107] In some embodiments, after obtaining the copper-doped porous silicon material in step 4, the present invention further includes a surface coating step:

[0108] The material is uniformly mixed with a carbon source precursor at a mass ratio of 1:0.5, and then heated to 800°C at a rate of 5°C / min and heat-treated for 4 hours under an inert atmosphere to form a carbon-coated core-shell structure composite material.

[0109] The carbon source precursor is glucose, citric acid, or organic pyrolysis carbon produced by pyrolysis in step 1.

[0110] Specifically, in this embodiment of the invention, the acid washing process in step 4 is carried out in a closed system, and the generated ammonia-containing tail gas is discharged and recovered through an absorption liquid; the absorption liquid is a 3 mol / L sulfuric acid or hydrochloric acid solution.

[0111] Based on the above embodiments, in this embodiment, the magnesium chloride-containing filtrate generated after acid washing in step 4 is subjected to evaporation, concentration, and dehydration treatment, followed by molten salt electrolysis to regenerate metallic magnesium at the cathode.

[0112] Specifically, in this embodiment, the electrolytically regenerated metallic magnesium is returned to step 2 as part or all of the magnesium powder raw material.

[0113] The chlorine gas produced at the anode during the electrolysis process is used to synthesize hydrochloric acid and returned to step 4 as part or all of the pickling solution.

[0114] Comparative Example 1

[0115] A method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules includes the following steps:

[0116] Step 1: Pyrolyze retired photovoltaic modules to obtain products such as solar cells and copper cables. Crush the solar cells and vacuum melt them with a certain proportion of copper cables to obtain copper-doped silicon ingots.

[0117] Step 2: After crushing the silicon ingot, the silicon-copper composite powder is obtained. The silicon-copper composite powder is then milled to control the size to 1-8μm. It is then mixed with magnesium powder at a mass ratio of 1:8 by grinding and stirring. The mixture is then placed in an alloy container and heated to 500℃ in an argon-protected tube furnace for 6 hours to obtain a silicon-magnesium alloy. The magnesium silicide is then milled to obtain magnesium silicide powder with an average size of 3-5μm.

[0118] Step 3: The sand-milled magnesium silicide powder is heated to 770°C at a heating rate of 5°C / min under an ammonia atmosphere and held at that temperature for 6 hours to carry out a dealloying reaction.

[0119] Step 4: The product obtained from the dealloying reaction was acid-washed with 1M / L HCl solution for 4 hours to remove magnesium nitride. The solution was then filtered until neutral and freeze-dried for 12 hours to obtain copper-doped porous silicon material.

[0120] If the temperature is too low during the alloying reaction, resulting in incomplete reaction, the silicon in the magnesium alloy may not have reacted completely, leading to problems such as particle agglomeration. Incomplete alloying will also affect subsequent reaction processes, resulting in a less pronounced porous structure. Figure 3 b. This structure fails to provide sufficient space for the huge volume expansion of silicon during lithium insertion / extraction, making it difficult to alleviate the silicon pulverization problem, thus leading to a reduction in its electrochemical performance.

[0121] Comparative Example 2

[0122] A method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules includes the following steps:

[0123] Step 1: Pyrolyze retired photovoltaic modules to obtain products such as solar cells and copper cables. Crush the solar cells and vacuum melt them with a certain proportion of copper cables to obtain copper-doped silicon ingots.

[0124] Step 2: After crushing the silicon ingot, the silicon-copper composite powder is obtained. The silicon-copper composite powder is then milled to control the size to 1-8μm. It is then mixed with magnesium powder at a mass ratio of 1:8 by grinding and stirring until fully uniform. The mixture is then placed in an alloy container and heated to 550℃ in an argon-protected tube furnace for 6 hours to obtain a silicon-magnesium alloy. The obtained silicon-magnesium alloy is placed in a sand mill, with zirconia ball milling beads added as needed. Hexane is used as a grinding aid, and the mixture is ball milled at 1500r / min for 1.5 hours. The ball-milled magnesium silicide powder is then sieved through a 200-mesh filter with ethanol as a dispersant to obtain powder of the target particle size. The resulting ethanol solution is then dried by forced air for 12 hours to obtain magnesium silicide powder with a target particle size of 3-5μm.

[0125] Step 4: The powder obtained after the nitriding reaction is acid-washed with 1M / L HCl solution at 60℃ in a water bath for 4 hours to remove impurities such as magnesium nitride. Then the solution is filtered three times until neutral and freeze-dried for 12 hours to obtain copper-doped porous silicon anode material.

[0126] Step 3: The obtained magnesium silicide powder is heated to 700℃ at a heating rate of 5℃ / min and held at that temperature for 6h under an ammonia atmosphere to carry out the nitridation reaction of magnesium silicide.

[0127] Step 4: The powder obtained after the nitriding reaction is acid-washed with 1M / L HCl solution at 60℃ in a water bath for 4 hours to remove impurities such as magnesium nitride. Then the solution is filtered three times until neutral and freeze-dried for 12 hours to obtain copper-doped porous silicon anode material.

[0128] Because the dealloying reaction temperature in this comparative example was low, the dealloying reaction was not sufficient, and magnesium silicide could not be completely converted into magnesium nitride and silicon. In the subsequent hydrochloric acid etching process, HCl would directly react with the unreacted magnesium silicide, resulting in the formation of a void structure in most of the material, which is inconsistent with the original intention of the material synthesis.

[0129] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing copper-doped porous silicon material from decommissioned photovoltaic modules, characterized in that, Includes the following steps: Step 1: Pyrolyze retired photovoltaic modules to obtain solar cells and copper cable products. Crush the solar cells and vacuum melt them with a certain proportion of copper cable to obtain copper-doped silicon ingots. Step 2: React the silicon-copper composite powder obtained after crushing silicon ingots with magnesium powder to synthesize magnesium silicide. Then, grind the magnesium silicide to obtain sand-ground magnesium silicide powder. Step 3: The magnesium silicide powder obtained after sand milling is subjected to a dealloying reaction treatment; Step 4: The product obtained from the dealloying reaction is acid-washed, filtered, and dried to obtain copper-doped porous silicon material.

2. The method according to claim 1, characterized in that, In step 1, the temperature of photovoltaic module pyrolysis is 400-600 ℃, and the holding time is 1-3 h; the doping amount of waste copper cable during vacuum melting accounts for 1%-15% of the cell mass.

3. The method according to claim 1, characterized in that, In step 2, the particle size of the silicon-copper composite powder after silicon ingot crushing is 1-15μm, and the mass ratio of silicon-copper composite powder to magnesium powder is 1:(1-2). The reaction between the silicon-copper composite powder and magnesium powder is carried out under an argon atmosphere, heated to 550-650℃ for 3-9h, and the heating rate is 2-10℃ / min.

4. The method according to claim 1, characterized in that, In step 2, the particle size of the magnesium silicide powder obtained after sand milling is 2-8 μm; The preparation method of the magnesium silicide powder is as follows: The magnesium silicide synthesized in step 1 was placed in a sand mill, and 8-12 times the mass of zirconium oxide sand beads were added with n-hexane as a grinding aid. The mixture was ball-milled at 1000-2000 r / min for 1-3 h. The ground powder was sieved through a 200-mesh filter with ethanol as a dispersant. The resulting ethanol solution was then dried by forced air to obtain magnesium silicide powder with the target particle size.

5. The method according to claim 1, characterized in that, The dealloying reaction treatment in step 3 involves grinding magnesium silicide powder in an ammonia-containing atmosphere, heating it to 600-900℃ at a heating rate of 2-10℃ / min, and holding it at that temperature for 3-9 hours.

6. The method according to claim 1, characterized in that, The product obtained from the dealloying reaction in step 4 is pickled in 0.5-2M / L hydrochloric acid solution at 50-80℃ for 2-6 hours.

7. The method according to claim 1, characterized in that, After obtaining the copper-doped porous silicon material in step 4, a surface coating step is further included: The material is uniformly mixed with a carbon source precursor at a mass ratio of 1: (0.1-0.5), and under the protection of an inert atmosphere, the temperature is raised to 500-800℃ at 2-5℃ / min and heat-treated for 1-4 hours to form a carbon-coated core-shell structure composite material. The carbon source precursor is glucose, citric acid, or organic pyrolysis carbon produced by pyrolysis in step 1.

8. The method according to claim 1, characterized in that, The acid washing process in step 4 is carried out in a closed system, and the generated ammonia-containing tail gas is discharged and recovered through an absorbent; the absorbent is a sulfuric acid or hydrochloric acid solution with a concentration of 1-3 mol / L.

9. The method according to claim 8, characterized in that, The magnesium chloride-containing filtrate produced after acid washing in step 4 is concentrated by evaporation and dehydration, and then subjected to molten salt electrolysis to regenerate metallic magnesium at the cathode.

10. The method according to claim 9, characterized in that, Electrolytically regenerated metallic magnesium is returned to step 2 as part or all of the magnesium powder raw material; The chlorine gas produced at the anode during the electrolysis process is used to synthesize hydrochloric acid and returned to step 4 as part or all of the pickling solution.

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