High-performance resource utilization method of photovoltaic waste

Abstract

The invention discloses a high-performance resource utilization method of photovoltaic waste, and the method comprises the steps of silicon raw material treatment, silicon block crushing and impurity removal, battery graphite treatment, silicon ink compounding, battery production from waste and performance detection. The low-cost and high-performance negative electrode material is realized by utilizing the high energy density of silicon and the excellent conductivity of graphite, and the photovoltaic waste is recycled to prepare the silicon negative electrode, so that the problem of treatment of the photovoltaic waste is solved, high-value utilization of the waste is also realized, the problem of treatment of waste silicon powder in the photovoltaic industry is effectively solved, and the production cost is reduced. And the binding force between the silicon nano-particles and the carbon layer is enhanced, the volume expansion of silicon is inhibited, electron transfer is promoted, uniform mixing of silicon and graphite is promoted, the conductivity is enhanced, and the electrochemical stability of the silicon nano-particles serving as the negative electrode of the lithium battery is improved.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic waste utilization, and in particular to a high-performance resource utilization method for photovoltaic waste. Background Art

[0002] Photovoltaic, or photovoltaic power generation system, is a power generation system that uses the photovoltaic effect of semiconductor materials to convert solar radiation energy into electrical energy. The energy of the photovoltaic power generation system comes from inexhaustible solar energy and is a clean, safe and renewable energy source. The photovoltaic power generation process does not pollute the environment or damage the ecology.

[0003] Photovoltaic power generation systems are divided into independent photovoltaic systems and grid-connected photovoltaic systems. Photovoltaic power generation systems are composed of solar cell arrays, battery packs, charge and discharge controllers, inverters, AC distribution cabinets, solar tracking control systems and other equipment. The photovoltaic industry has developed rapidly in the past decade, and the installed capacity has continued to expand. In the process of manufacturing silicon-based solar panels, diamond wire cutting of silicon ingots produces a large amount of silicon cutting waste, accounting for about 40% of the raw materials. The amount of silicon cutting waste is large. At present, the waste silicon powder produced by diamond wire cutting is usually sold to alloy companies or steel mills at a low price. As one of the raw materials for preparing alloys, it has low added value, low economic and environmental benefits, and the problem of handling waste silicon powder in the photovoltaic industry has become particularly urgent. Summary of the invention

[0004] The purpose of the present invention is to provide a high-performance resource utilization method for photovoltaic waste, so as to solve the problem raised in the above background technology that in the process of manufacturing silicon-based solar panels, diamond wire cutting of silicon ingots produces a large amount of silicon cutting waste, accounting for about 40% of the raw materials. The amount of silicon cutting waste is large. At present, the waste silicon powder generated by diamond wire cutting is usually sold to alloy companies or steel mills at a low price. As one of the raw materials for preparing alloys, it has low added value, low economic and environmental benefits, and the problem of handling waste silicon powder in the photovoltaic industry has become a particularly urgent problem.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-performance resource utilization method for photovoltaic waste, the method comprising the following steps:

[0006] S1. Silicon raw material processing: Refine and purify photovoltaic silicon cutting waste, and the silicon raw material processing includes the following steps:

[0007] Step 1, silicon block crushing and impurity removal: The silicon raw material is crushed by a jaw crusher, and the silicon block is initially crushed to the millimeter level, and then the waste silicon powder is ball-milled by wet ball milling using ethanol medium to obtain waste silicon powder that meets the requirements, and then the waste silicon powder is pickled and impurities are removed, SiO2 is removed by hydrofluoric acid, and Fe and Al metal impurities are effectively removed by hydrochloric acid. The pickling order is HCl to remove metal first, and then HF to remove SiO2, and purified silicon powder is obtained after impurities are removed;

[0008] Step 2, nano-ball milling: finely grinding the silicon powder after impurities removal by a ball mill, specifically, adding 0.5% polyvinyl pyrrolidone as a dispersant by wet ball milling, and obtaining nano-silicon powder after ball milling;

[0009] Step 3, surface modification: The nano-silicon powder obtained in the above step is modified with KH550, and the silane coupling agent is used to improve its dispersibility, so that the silicon surface is amino-modified, and the subsequent interface bonding effect with graphite is improved by modifying the surface of the silicon powder;

[0010] S2. Battery graphite processing: Dismantle discarded lithium batteries and extract the remaining graphite materials for use, including the following steps:

[0011] Step 1: Battery treatment: Place the waste lithium battery in a 2 mol / L NaCl solution for discharge, then split the discharged waste lithium battery, cut the waste negative electrode coating into small pieces of 1×1 square centimeter, mix and stir the cut solid with a water solvent, dry and filter the obtained graphite, and sieve it with 200 mesh to obtain preliminary graphite;

[0012] Step 2: Graphite treatment: calcining the obtained graphite powder at 700°C to decompose the binder in the battery, then treating the graphite powder with acid to dissolve the residual metal, and finally reducing the graphite with microwave at 1000W×30s to restore the conductivity, completing the expansion treatment of the graphite, and finally obtaining the waste lithium battery graphite powder;

[0013] S3, silicon-graphite compounding: the silicon powder obtained in step S1 and step S2 is mixed with graphite powder. If the graphite powder of the discarded battery is insufficient, commercial graphite powder that meets the particle size requirements can be added to obtain silicon-graphite active material used as a negative electrode material for the battery. The specific compounding process is as follows:

[0014] Step 1: Solution mixing: The obtained silicon powder and graphite powder are mixed in a ratio of 1:1, and a binder, a pore-forming agent and a solvent are added and stirred to make the mixture uniform to obtain a slurry.

[0015] Step 2, freeze drying: Use a vacuum freeze dryer to perform freeze drying operations, pour the mixed slurry into a mold, freeze for 12 hours to form a solid, and then transfer to a vacuum drying oven to dry for 24 hours to form a porous precursor, and obtain a dried mixed powder.

[0016] Step 3, mechanical ball milling: the mixed powder is ball milled by a ball mill, and the obtained mixed material is placed in a tube furnace and calcined at 800° C. for 2 h at a temperature increase of 5° C. per minute under a nitrogen atmosphere to finally obtain a silicon-carbon active material powder;

[0017] S4, making batteries from waste materials: the carbon-silicon mixed active material is mixed with the conductive agent and the adhesive in a ratio of 3:1:1 and deionized water is added for grinding to obtain an active material slurry, the obtained slurry is coated on a copper foil through a 100um coater and dried, the electrode sheets are cut into pieces, and the pieces are assembled in an argon atmosphere in a glove box to obtain a complete half-cell;

[0018] S5. Performance testing: Conduct electrochemical performance testing on batteries using silicon ink active materials as negative electrode materials, and perform testing at a current intensity of 500mAg-1;

[0019] By introducing graphite and forming silicon-carbon material through ball milling, the conductivity of silicon is enhanced, while the expansion of silicon is alleviated. Nano-sized Si particles are easy to agglomerate and have limited energy density. The use of wet chemical ball milling combined with freeze drying improves the dispersibility of silicon particles, strengthens the binding force between silicon nano-silicon particles and carbon layers, inhibits the volume expansion of silicon, and promotes electron transfer.

[0020] Preferably, in the crushing and impurity removal of silicon blocks in step S1, the particle size of the silicon material is 1-2 mm by jaw crushing, and the wet ball milling uses ethanol as a medium, and the silicon material is ball milled to a particle size of 1-5 μm.

[0021] Preferably, the nano-ball milling in step S1 is performed at 800 rpm for 8 hours to obtain nano-silicon powder with a particle size of 50-100 nm.

[0022] Preferably, in the surface modification in step S1, 0.5 ml of KH550 is dissolved in 50 ml of ethanol and ultrasonically dispersed for 1 hour to aminize the silicon surface.

[0023] Preferably, during the battery treatment in step S2, the cut solid and the aqueous solvent are stirred at 60° C. for 50 seconds at a solid-to-liquid ratio of 1:5.

[0024] Preferably, in the graphite treatment of step S2, concentrated H2SO4 / H3PO3 mixed acid is used to dissolve the binder, KMnO4 is slowly added, and the temperature is controlled to be <20°C for dissolution treatment.

[0025] Preferably, during freeze drying in step S3, the slurry is frozen at -20°C for 12 hours to form a solid, and then transferred to a vacuum drying oven and dried at -50°C, 10Pa for 24 hours to form a porous precursor.

[0026] Preferably, during the mechanical ball milling in step S3, the mixed powder is placed in a ball mill and ball milled for 2 hours at 750 r / min and a ball-to-material ratio of 30:1. During the drying in step S4, the coated copper foil is placed in an oven and dried at 60-80° C. for 8-12 hours. The stirring time during the solution mixing in step S3 is 30-45 minutes.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The high energy density of silicon and the excellent electrical conductivity of graphite are used to realize low-cost and high-performance negative electrode materials, and photovoltaic waste is recycled to prepare silicon negative electrodes, which not only solves the problem of photovoltaic waste treatment, but also realizes high-value utilization of waste, effectively solves the problem of waste silicon powder treatment in the photovoltaic industry, thereby bringing good economic and environmental benefits. In addition, the present invention introduces graphite and forms silicon-carbon materials through ball milling to enhance the electrical conductivity of silicon, while relieving silicon expansion. Nano-sized Si particles are easy to agglomerate and have limited energy density. Wet chemical ball milling combined with freeze drying is used to improve the dispersibility of silicon particles, strengthen the binding force between silicon nano-silicon particles and carbon layers, inhibit the volume expansion of silicon, promote electron transfer, promote uniform mixing of silicon and graphite, enhance electrical conductivity, and improve its electrochemical stability as a negative electrode of a lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 This is a particle size analysis diagram of the photovoltaic waste silicon powder prepared in the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] See also Figure 1-2 ,

[0033] Example 1

[0034] The present invention provides a high-performance resource utilization method for photovoltaic waste, the method comprising the following steps:

[0035] S1. Silicon raw material processing: The photovoltaic silicon cutting waste is refined and purified, and the silicon raw material processing includes the following steps:

[0036] Step 1, silicon block crushing and impurity removal: The silicon raw material is crushed by a jaw crusher, and the silicon block is initially crushed to the millimeter level, and then the waste silicon powder is ball-milled by wet ball milling using ethanol medium to obtain waste silicon powder that meets the requirements, and then the waste silicon powder is pickled and impurities are removed, SiO2 is removed by hydrofluoric acid, and Fe and Al metal impurities are effectively removed by hydrochloric acid. The pickling order is HCl to remove metal first, and then HF to remove SiO2, and purified silicon powder is obtained after impurities are removed;

[0037] In this embodiment, the waste silicon powder is mainly composed of Si, C, O and Fe elements, and the impurities therein mainly come from residual organic matter, fallen diamond particles and trace stainless steel debris produced by metal wire wear. Since the metal impurities in Si are physical doping, the interface resistance between the particles will increase, so acid leaching is required for impurity removal before preparing the negative electrode of the lithium battery;

[0038] Step 2, nano-ball milling: finely grinding the silicon powder after impurities removal by a ball mill, specifically, adding 0.5% polyvinyl pyrrolidone as a dispersant by wet ball milling, and obtaining nano-silicon powder after ball milling;

[0039] Step 3, surface modification: The nano-silicon powder obtained in the above step is modified with KH550, and the silane coupling agent is used to improve its dispersibility, so that the silicon surface is amino-modified, and the subsequent interface bonding effect with graphite is improved by modifying the surface of the silicon powder;

[0040] S2. Battery graphite processing: Dismantle discarded lithium batteries and extract the remaining graphite materials for use, including the following steps:

[0041] Step 1: Battery treatment: Place the waste lithium battery in a 2 mol / L NaCl solution for discharge, then split the discharged waste lithium battery, cut the waste negative electrode coating into small pieces of 1×1 square centimeter, mix and stir the cut solid with a water solvent, dry and filter the obtained graphite, and sieve it with 200 mesh to obtain preliminary graphite;

[0042] Step 2: Graphite treatment: calcining the obtained graphite powder at 700°C to decompose the binder in the battery, then treating the graphite powder with acid to dissolve the residual metal, and finally reducing the graphite with microwave at 1000W×30s to restore the conductivity, completing the expansion treatment of the graphite, and finally obtaining the waste lithium battery graphite powder;

[0043] S3, silicon-graphite compounding: the silicon powder obtained in step S1 and step S2 is mixed with graphite powder. If the graphite powder of the discarded battery is insufficient, commercial graphite powder that meets the particle size requirements can be added to obtain silicon-graphite active material used as a negative electrode material for the battery. The specific compounding process is as follows:

[0044] Step 1: Solution mixing: The obtained silicon powder and graphite powder are mixed in a ratio of 1:1, and a binder, a pore-forming agent and a solvent are added and stirred to make the mixture uniform to obtain a slurry.

[0045] Step 2, freeze drying: Use a vacuum freeze dryer to perform freeze drying operations, pour the mixed slurry into a mold, freeze for 12 hours to form a solid, and then transfer to a vacuum drying oven to dry for 24 hours to form a porous precursor, and obtain a dried mixed powder.

[0046] Step 3, mechanical ball milling: the mixed powder is ball milled by a ball mill, and the obtained mixed material is placed in a tube furnace and calcined at 800° C. for 2 h at a temperature increase of 5° C. per minute under a nitrogen atmosphere to finally obtain a silicon-carbon active material powder;

[0047] In this embodiment, the capacity of the silicon negative electrode material is higher than that of commercial graphite, and photovoltaic waste is selected to prepare the negative electrode material for lithium batteries to achieve high-price resource recovery. However, silicon as the negative electrode of lithium batteries will produce volume expansion problems during the charging and discharging process. By introducing graphite, the graphite and photovoltaic silicon cutting waste are ball-milled and mixed. By introducing graphite, the ball milling forms a silicon-carbon material, which enhances the conductivity of silicon and alleviates the expansion of silicon. Nano-sized Si particles are easy to agglomerate and have limited energy density. Wet chemical ball milling combined with freeze drying improves the dispersibility of silicon particles, strengthens the binding force between silicon nano-silicon particles and carbon layers, inhibits the volume expansion of silicon, promotes electron transfer, promotes uniform mixing of silicon and graphite, and enhances conductivity.

[0048] S4, making batteries from waste materials: the carbon-silicon mixed active material is mixed with the conductive agent and the adhesive in a ratio of 3:1:1 and deionized water is added for grinding to obtain an active material slurry, the obtained slurry is coated on a copper foil through a 100um coater and dried, the electrode sheets are cut into pieces, and the pieces are assembled in an argon atmosphere in a glove box to obtain a complete half-cell;

[0049] S5. Performance testing: Conduct electrochemical performance testing on batteries using silicon ink active materials as negative electrode materials, and perform testing at a current intensity of 500mAg-1.

[0050] In step S1, the silicon block is crushed and impurities are removed by jaw crushing so that the particle size of the silicon material is 1 mm, and the wet ball milling uses ethanol as a medium, and the silicon material is ball milled to a particle size of 2 μm. In step S1, the nano-ball milling is performed at 800 rpm for 8 hours to obtain nano-silicon powder with a particle size of 50 nm. In step S1, the surface modification is performed by dissolving 0.5 ml of KH550 in 50 ml of ethanol and ultrasonically dispersing for 1 hour to amino the silicon surface.

[0051] During the battery treatment in step S2, the cut solid and water solvent are stirred at 60°C for 50s at a solid-liquid ratio of 1:5. In the graphite treatment of step S2, concentrated H2SO4 / H3PO3 mixed acid is used to dissolve the binder, KMnO4 is slowly added, and the temperature is controlled at <20°C for dissolution treatment.

[0052] During freeze drying in step S3, the slurry is frozen at -20°C for 12 hours to form a solid, and then transferred to a vacuum drying oven and dried at -50°C, 10Pa for 24 hours to form a porous precursor. During mechanical ball milling in step S3, the mixed powder is placed in a ball mill at 750r / min and a ball-to-material ratio of 30:1 for 2 hours. During drying in step S4, the coated copper foil is placed in an oven at 60°C for 8 hours. The stirring time during solution mixing in step S3 is 30 minutes.

[0053] Example 2

[0054] The present invention provides a high-performance resource utilization method for photovoltaic waste, the method comprising the following steps:

[0055] S1. Silicon raw material processing: The photovoltaic silicon cutting waste is refined and purified, and the silicon raw material processing includes the following steps:

[0056] Step 1, silicon block crushing and impurity removal: The silicon raw material is crushed by a jaw crusher, and the silicon block is initially crushed to the millimeter level, and then the waste silicon powder is ball-milled by wet ball milling using ethanol medium to obtain waste silicon powder that meets the requirements, and then the waste silicon powder is pickled and impurities are removed, SiO2 is removed by hydrofluoric acid, and Fe and Al metal impurities are effectively removed by hydrochloric acid. The pickling order is HCl to remove metal first, and then HF to remove SiO2, and purified silicon powder is obtained after impurities are removed;

[0057] In this embodiment, the waste silicon powder is mainly composed of Si, C, O and Fe elements, and the impurities therein mainly come from residual organic matter, fallen diamond particles and trace stainless steel debris produced by metal wire wear. Since the metal impurities in Si are physical doping, the interface resistance between the particles will increase, so acid leaching is required for impurity removal before preparing the negative electrode of the lithium battery;

[0058] Step 2, nano-ball milling: finely grinding the silicon powder after impurities removal by a ball mill, specifically, adding 0.5% polyvinyl pyrrolidone as a dispersant by wet ball milling, and obtaining nano-silicon powder after ball milling;

[0059] Step 3, surface modification: The nano-silicon powder obtained in the above step is modified with KH550, and the silane coupling agent is used to improve its dispersibility, so that the silicon surface is amino-modified, and the subsequent interface bonding effect with graphite is improved by modifying the surface of the silicon powder;

[0060] S2. Battery graphite processing: Dismantle discarded lithium batteries and extract the remaining graphite materials for use, including the following steps:

[0061] Step 1: Battery treatment: Place the waste lithium battery in a 2 mol / L NaCl solution for discharge, then split the discharged waste lithium battery, cut the waste negative electrode coating into small pieces of 1×1 square centimeter, mix and stir the cut solid with a water solvent, dry and filter the obtained graphite, and sieve it with 200 mesh to obtain preliminary graphite;

[0062] Step 2: Graphite treatment: calcining the obtained graphite powder at 700°C to decompose the binder in the battery, then treating the graphite powder with acid to dissolve the residual metal, and finally reducing the graphite with microwave at 1000W×30s to restore the conductivity, completing the expansion treatment of the graphite, and finally obtaining the waste lithium battery graphite powder;

[0063] S3, silicon-graphite compounding: the silicon powder obtained in step S1 and step S2 is mixed with graphite powder. If the graphite powder of the discarded battery is insufficient, commercial graphite powder that meets the particle size requirements can be added to obtain silicon-graphite active material used as a negative electrode material for the battery. The specific compounding process is as follows:

[0064] Step 1: Solution mixing: The obtained silicon powder and graphite powder are mixed in a ratio of 1:1, and a binder, a pore-forming agent and a solvent are added and stirred to make the mixture uniform to obtain a slurry.

[0065] Step 2, freeze drying: Use a vacuum freeze dryer to perform freeze drying operations, pour the mixed slurry into a mold, freeze for 12 hours to form a solid, and then transfer to a vacuum drying oven to dry for 24 hours to form a porous precursor, and obtain a dried mixed powder.

[0066] Step 3, mechanical ball milling: the mixed powder is ball milled by a ball mill, and the obtained mixed material is placed in a tube furnace and calcined at 800° C. for 2 h at a temperature increase of 5° C. per minute under a nitrogen atmosphere to finally obtain a silicon-carbon active material powder;

[0067] In this embodiment, the capacity of silicon negative electrode material is higher than that of commercial graphite. Photovoltaic waste is selected to prepare lithium battery negative electrode material to achieve high-price resource recycling. However, silicon as a negative electrode of lithium battery will produce volume expansion problem during the charging and discharging process. By introducing graphite, graphite and photovoltaic silicon cutting waste are ball-milled and mixed;

[0068] S4, making batteries from waste materials: the carbon-silicon mixed active material is mixed with the conductive agent and the adhesive in a ratio of 3:1:1 and deionized water is added for grinding to obtain an active material slurry, the obtained slurry is coated on a copper foil through a 100um coater and dried, the electrode sheets are cut into pieces, and the pieces are assembled in an argon atmosphere in a glove box to obtain a complete half-cell;

[0069] S5. Performance testing: Conduct electrochemical performance testing on batteries using silicon ink active materials as negative electrode materials, and perform testing at a current intensity of 500mAg-1;

[0070] In this embodiment, graphite is introduced and ball milled to form silicon-carbon material, thereby enhancing the conductivity of silicon and alleviating the expansion of silicon. Nano-sized Si particles are easy to agglomerate and have limited energy density. Wet chemical ball milling combined with freeze drying is used to improve the dispersibility of silicon particles, strengthen the binding force between silicon nano-particles and carbon layers, inhibit the volume expansion of silicon, promote electron transfer, promote uniform mixing of silicon and graphite, and enhance conductivity.

[0071] In step S1, the silicon block is crushed and impurities are removed by jaw crushing so that the particle size of the silicon material is 2 mm, and the wet ball milling uses ethanol as a medium, and the silicon material is ball milled to a particle size of 4 μm. In step S1, the nano-ball milling is performed at 800 rpm for 8 hours to obtain nano-silicon powder with a particle size of 100 nm. In step S1, the surface modification is performed by dissolving 0.5 ml of KH550 in 50 ml of ethanol and ultrasonically dispersing for 1 hour to amino the silicon surface.

[0072] During the battery treatment in step S2, the cut solid and water solvent are stirred at 60°C for 50s at a solid-liquid ratio of 1:5. In the graphite treatment of step S2, concentrated H2SO4 / H3PO3 mixed acid is used to dissolve the binder, KMnO4 is slowly added, and the temperature is controlled at <20°C for dissolution treatment.

[0073] During freeze drying in step S3, the slurry is frozen at -20°C for 12 hours to form a solid, and then transferred to a vacuum drying oven and dried at -50°C, 10Pa for 24 hours to form a porous precursor. During mechanical ball milling in step S3, the mixed powder is placed in a ball milling jar at 750r / min and a ball-to-material ratio of 30:1 for 2 hours. During drying in step S4, the coated copper foil is placed in an oven at 80°C for 12 hours. During the mixing of the solutions in step S3, the stirring time is 45 minutes.

[0074] Example 3

[0075] A high-performance resource utilization method for photovoltaic waste, the method comprising the following steps:

[0076] S1. Silicon raw material processing: The photovoltaic silicon cutting waste is refined and purified, and the silicon raw material processing includes the following steps:

[0077] Step 1, silicon block crushing and impurity removal: The silicon raw material is crushed by a jaw crusher, and the silicon block is initially crushed to the millimeter level, and then the waste silicon powder is ball-milled by wet ball milling using ethanol medium to obtain waste silicon powder that meets the requirements, and then the waste silicon powder is pickled and impurities are removed, SiO2 is removed by hydrofluoric acid, and Fe and Al metal impurities are effectively removed by hydrochloric acid. The pickling order is HCl to remove metal first, and then HF to remove SiO2, and purified silicon powder is obtained after impurities are removed;

[0078] In this embodiment, a mixed solution of HCl and HF is used in the impurity removal process to remove impurities (Fe, SiO2, etc.) in photovoltaic silicon materials. By studying and analyzing the chemical composition, appearance, and physical and chemical properties of photovoltaic silicon waste, a wet chemical method is used as a method for purifying polysilicon waste. Hydrochloric acid and hydrofluoric acid are selected as leaching agents. Hydrofluoric acid is used to open the oxide layer coated on the surface, and hydrochloric acid is used to remove impurities such as iron and lead. By using an orthogonal experiment based on five factors and four levels, the optimal leaching purification conditions are determined from the different influencing factors of reaction time, reaction temperature, acid concentration, and liquid-solid ratio in the reaction process, and the optimal purification conditions are obtained;

[0079] Step 2, nano-ball milling: finely grinding the silicon powder after impurities removal by a ball mill, specifically, adding 0.5% polyvinyl pyrrolidone as a dispersant by wet ball milling, and obtaining nano-silicon powder after ball milling;

[0080] Step 3, surface modification: The nano-silicon powder obtained in the above step is modified with KH550, and the silane coupling agent is used to improve its dispersibility, so that the silicon surface is amino-modified, and the subsequent interface bonding effect with graphite is improved by modifying the surface of the silicon powder;

[0081] S2. Battery graphite processing: Dismantle discarded lithium batteries and extract the remaining graphite materials for use, including the following steps:

[0082] Step 1: Battery treatment: Place the waste lithium battery in a 2 mol / L NaCl solution for discharge, then split the discharged waste lithium battery, cut the waste negative electrode coating into small pieces of 1×1 square centimeter, mix and stir the cut solid with a water solvent, dry and filter the obtained graphite, and sieve it with 200 mesh to obtain preliminary graphite;

[0083] Step 2: Graphite treatment: calcining the obtained graphite powder at 700°C to decompose the binder in the battery, then treating the graphite powder with acid to dissolve the residual metal, and finally reducing the graphite with microwave at 1000W×30s to restore the conductivity, completing the expansion treatment of the graphite, and finally obtaining the waste lithium battery graphite powder;

[0084] S3, silicon-graphite compounding: the silicon powder obtained in step S1 and step S2 is mixed with graphite powder. If the graphite powder of the discarded battery is insufficient, commercial graphite powder that meets the particle size requirements can be added to obtain silicon-graphite active material used as a negative electrode material for the battery. The specific compounding process is as follows:

[0085] Step 1: Solution mixing: The obtained silicon powder and graphite powder are mixed in a ratio of 1:1, and a binder, a pore-forming agent and a solvent are added and stirred to make the mixture uniform to obtain a slurry.

[0086] Step 2, freeze drying: Use a vacuum freeze dryer to perform freeze drying operations, pour the mixed slurry into a mold, freeze for 12 hours to form a solid, and then transfer to a vacuum drying oven to dry for 24 hours to form a porous precursor, and obtain a dried mixed powder.

[0087] Step 3, mechanical ball milling: the mixed powder is ball milled by a ball mill, and the obtained mixed material is placed in a tube furnace and calcined at 800° C. for 2 h at a temperature increase of 5° C. per minute under a nitrogen atmosphere to finally obtain a silicon-carbon active material powder;

[0088] S4, making batteries from waste materials: the carbon-silicon mixed active material is mixed with the conductive agent and the adhesive in a ratio of 3:1:1 and deionized water is added for grinding to obtain an active material slurry, the obtained slurry is coated on a copper foil through a 100um coater and dried, the electrode sheets are cut into pieces, and the pieces are assembled in an argon atmosphere in a glove box to obtain a complete half-cell;

[0089] S5. Performance testing: Conduct electrochemical performance testing on batteries using silicon ink active materials as negative electrode materials, and perform testing at a current intensity of 500mAg-1.

[0090] Preferably, in the crushing and impurity removal of silicon blocks in step S1, the particle size of the silicon material is 1 mm by jaw crushing, and the wet ball milling uses ethanol as a medium, and the silicon material is ball milled to a particle size of 3 μm. In step S1, the nano-ball milling is performed at 800 rpm for 8 hours to obtain nano-silicon powder with a particle size of 50-100 nm.

[0091] Preferably, in step S1, the surface modification is performed by dissolving 0.5 ml of KH550 in 50 ml of ethanol and ultrasonically dispersing for 1 hour to aminize the silicon surface.

[0092] Preferably, during the battery treatment in step S2, the cut solid and the aqueous solvent are stirred at 60°C for 50s at a solid-liquid ratio of 1:5. In the graphite treatment of step S2, the binder is dissolved using concentrated H2SO4 / H3PO3 mixed acid, KMnO4 is slowly added, and the temperature is controlled at <20°C for dissolution treatment.

[0093] Preferably, during freeze drying in step S3, the slurry is frozen at -20°C for 12 hours to form a solid, and then transferred to a vacuum drying oven and dried at -50°C, 10Pa for 24 hours to form a porous precursor. During mechanical ball milling in step S3, the mixed powder is placed in a ball milling jar and ball milled for 2 hours at 750r / min and a ball-to-material ratio of 30:1. During drying in step S4, the coated copper foil is placed in an oven and dried at 70°C for 10 hours. The stirring time during solution mixing in step S3 is 40 minutes.

[0094] When used specifically, the present invention provides a high-performance resource utilization method for photovoltaic waste, which effectively recycles photovoltaic waste for high-value resource recovery, prepares silicon negative electrode materials for lithium battery negative electrodes, and utilizes the high energy density of silicon and the excellent electrical conductivity of graphite to achieve low-cost and high-performance negative electrode materials. Photovoltaic waste is recycled to prepare silicon negative electrodes, which not only solves the problem of photovoltaic waste treatment, but also achieves high-value utilization of waste. In addition, the present invention introduces graphite and forms silicon-carbon materials through ball milling to enhance the electrical conductivity of silicon, while alleviating the expansion of silicon. Nano-sized Si particles are easy to agglomerate and have limited energy density. Wet chemical ball milling combined with freeze drying is used to improve the dispersibility of silicon particles, strengthen the binding force between silicon nano-silicon particles and carbon layers, inhibit the volume expansion of silicon, promote electron transfer, promote uniform mixing of silicon and graphite, enhance electrical conductivity, and improve its electrochemical stability as a lithium battery negative electrode.

[0095] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-performance resource utilization method for photovoltaic waste, characterized in that: The method comprises the following steps: S1. Silicon raw material processing: Refine and purify photovoltaic silicon cutting waste, and the silicon raw material processing includes the following steps: Step 1, silicon block crushing and impurity removal: The silicon raw material is crushed by a jaw crusher, and the silicon block is initially crushed to the millimeter level, and then the waste silicon powder is ball-milled by wet ball milling using ethanol medium to obtain waste silicon powder that meets the requirements, and then the waste silicon powder is pickled and impurities are removed, SiO2 is removed by hydrofluoric acid, and Fe and Al metal impurities are effectively removed by hydrochloric acid. The pickling order is HCl to remove metal first, and then HF to remove SiO2, and purified silicon powder is obtained after impurities are removed; Step 2, nano-ball milling: finely grinding the silicon powder after impurities removal by a ball mill, specifically, adding 0.5% polyvinyl pyrrolidone as a dispersant by wet ball milling, and obtaining nano-silicon powder after ball milling; Step 3, surface modification: The nano-silicon powder obtained in the above step is modified with KH550, and the silane coupling agent is used to improve its dispersibility, so that the silicon surface is amino-modified, and the subsequent interface bonding effect with graphite is improved by modifying the surface of the silicon powder; S2. Battery graphite processing: Dismantle discarded lithium batteries and extract the remaining graphite materials for use, including the following steps: Step 1: Battery treatment: Place the waste lithium battery in a 2 mol / L NaCl solution for discharge, then split the discharged waste lithium battery, cut the waste negative electrode coating into small pieces of 1×1 square centimeter, mix and stir the cut solid with a water solvent, dry and filter the obtained graphite, and sieve it with 200 mesh to obtain preliminary graphite; Step 2: Graphite treatment: calcining the obtained graphite powder at 700°C to decompose the binder in the battery, then treating the graphite powder with acid to dissolve the residual metal, and finally reducing the graphite with microwave at 1000W×30s to restore the conductivity, completing the expansion treatment of the graphite, and finally obtaining the waste lithium battery graphite powder; S3, silicon-graphite compounding: the silicon powder obtained in step S1 and step S2 is mixed with graphite powder. If the graphite powder of the discarded battery is insufficient, commercial graphite powder that meets the particle size requirements can be added to obtain silicon-graphite active material used as a negative electrode material for the battery. The specific compounding process is as follows: Step 1: Solution mixing: The obtained silicon powder and graphite powder are mixed in a ratio of 1:1, and a binder, a pore-forming agent and a solvent are added and stirred to make the mixture uniform to obtain a slurry. Step 2, freeze drying: Use a vacuum freeze dryer to perform freeze drying operations, pour the mixed slurry into a mold, freeze for 12 hours to form a solid, and then transfer to a vacuum drying oven to dry for 24 hours to form a porous precursor, and obtain a dried mixed powder. Step 3, mechanical ball milling: the mixed powder is ball milled by a ball mill, and the obtained mixed material is placed in a tube furnace and calcined at 800° C. for 2 h at a temperature increase of 5° C. per minute under a nitrogen atmosphere to finally obtain a silicon-carbon active material powder; S4, making batteries from waste materials: the carbon-silicon mixed active material is mixed with the conductive agent and the adhesive in a ratio of 3:1:1 and deionized water is added for grinding to obtain an active material slurry, the obtained slurry is coated on a copper foil through a 100um coater and dried, the electrode sheets are cut into pieces, and the pieces are assembled in an argon atmosphere in a glove box to obtain a complete half-cell; S5. Performance testing: Conduct electrochemical performance testing on batteries using silicon ink active materials as negative electrode materials, and perform testing at a current intensity of 500mAg-1.

2. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: In the step S1, the silicon block is crushed and impurities are removed by jaw crushing so that the particle size of the silicon material is 1-2 mm, and the wet ball milling uses ethanol as a medium, and the silicon material is ball milled to a particle size of 1-5 μm.

3. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: In the step S1, the nano-silicon powder is ball-milled at 800 rpm for 8 hours to obtain nano-silicon powder with a particle size of 50-100 nm.

4. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: In the surface modification in step S1, 0.5 ml of KH550 is dissolved in 50 ml of ethanol and ultrasonically dispersed for 1 hour to aminize the silicon surface.

5. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: During the battery treatment in step S2, the cut solid and aqueous solvent are stirred at 60° C. for 50 seconds at a solid-to-liquid ratio of 1:

5.

6. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: In the graphite treatment of step S2, concentrated H2SO4 / H3PO3 mixed acid is used to dissolve the binder, KMnO4 is slowly added, and the temperature is controlled to be less than 20°C for dissolution treatment.

7. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: During freeze drying in step S3, the slurry is frozen at -20°C for 12 hours to form a solid, and then transferred to a vacuum drying oven and dried at -50°C, 10Pa for 24 hours to form a porous precursor.

8. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: During the mechanical ball milling in step S3, the mixed powder is placed in a ball milling jar and ball milled for 2 hours at 750 r / min and a ball-to-material ratio of 30:

1.

9. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: During the drying in step S4, the coated copper foil is placed in an oven at 60-80° C. for drying for 8-12 hours.

10. The high-performance resource utilization method of photovoltaic waste according to claim 1, characterized in that: The stirring time during the solution mixing in step S3 is 30-45 minutes.

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