A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste

Abstract

This invention relates to a method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, belonging to the field of silicon waste resource recycling technology. The invention involves a two-step metal-assisted chemical etching process using copper salts to uniformly introduce nano- and micro-sized copper particles into the silicon material. The etching product is then controlled-electrode oxidized and pressed into a sheet for sintering to form an electrolytic precursor. The upper and lower surfaces of the electrolytic precursor are then attached to a sheet-like current collector and placed on a hook-shaped cathode current collector for a two-step constant-current molten salt electrolysis. Electrolytic reduction is performed at a relatively low current density to reduce copper oxide and silicon oxide, avoiding side reactions and obtaining the silicon-copper composite nanowire anode material. This silicon-copper composite nanowire anode material not only has a small diameter and a large aspect ratio but also significantly improved conductivity and surface area, which helps to form a stable solid electrolyte film during lithium-ion battery lithium-ion intercalation / deintercalation.

Description

Technical Field

[0001] This invention relates to a method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, belonging to the field of silicon waste resource recycling technology. Background Technology

[0002] With the booming development of the photovoltaic industry, the demand for silicon wafers in solar photovoltaic panels is increasing year by year. However, silicon wafers are obtained by wire cutting of silicon ingots. During the wire cutting process, 30-40% silicon debris (silicon waste) will be generated. Silicon waste has a sheet-like structure, low impurity content, and its surface is very easy to be oxidized to form an oxide layer.

[0003] With the rapid development of the energy storage industry, commercially available graphite-based lithium battery anode materials have low theoretical specific capacity (372 mAh g). -1 The current lithium-ion battery technology is gradually failing to meet people's demands for long battery life and extended battery life. Silicon materials theoretically have a higher specific capacity (4200mAh g). -1 While silicon anodes have low lithium intercalation potentials, during charge and discharge, the volume expansion (approximately 300%) caused by lithium intercalation / deintercalation can easily lead to the breakage and pulverization of active materials, resulting in side reactions and repeated rupture and regeneration of the solid electrolyte membrane, continuously consuming the limited electrolyte in the lithium battery. Furthermore, the poor conductivity of silicon anodes limits the current conduction efficiency of lithium batteries during charge and discharge, reducing the rate performance. Simultaneously, the slow lithium-ion migration rate in lithium batteries using pure silicon anodes increases internal resistance during charge and discharge, affecting charging speed and capacity retention. These issues are the main reasons for the instability of the electrochemical performance of silicon anode materials. Therefore, finding a method to modify the silicon anode structure is crucial.

[0004] In existing technologies, direct molten salt electrolytic reduction of silica is prone to problems such as incomplete electrodeoxidation, impurity generation, and low reduction efficiency. Therefore, to improve electrodeoxidation efficiency, researchers have employed the method of incorporating metal oxides into silica during electrolysis. However, this method results in incomplete structural modification of silicon-metal materials for mass production and the formation of large-particle metal impurities, which can reduce the charge-discharge specific capacity of lithium-ion batteries. Researchers have also used a series of complex reactions to deposit metal oxides onto the silica surface, but this method has a long operational process and is not conducive to industrial-scale production. Furthermore, existing electrolysis equipment typically only operates the precursor along a single transverse or longitudinal direction. As the electrolysis process progresses, the poor conductivity of silicon after silica reduction leads to low current conduction efficiency in the precursor, reducing the driving force for electrolytic reduction and significantly lowering the electrodeoxidation rate. This results in some silica not being completely electrolyzed and easily introduces side reactions, leading to impure electrolysis products. Using molten salt electrolytic silicon with impure electrolysis products as silicon anode material has problems such as poor conductivity, volume expansion during lithium insertion / extraction, and poor electrochemical performance of silicon anode material. Summary of the Invention

[0005] To address the problems of impure silicon produced by molten salt electrolysis and its poor conductivity, volume expansion during lithium insertion / extraction, and overall poor electrochemical performance when used as silicon anode materials, this invention proposes a method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste. This invention employs metal-assisted chemical etching to introduce nano- and micro-structured copper particles into the silicon material. After controlled oxidation, the precursor is subjected to a two-step constant-current electrolysis process along both the axial and radial directions using an improved molten salt electrolysis device. Because the precursor and current collector are in uniform contact, the current density through the precursor is relatively uniform during molten salt electrolysis. Furthermore, constant-current electrolysis allows for precise control of the electrolytic reaction rate, resulting in a more uniform electrodeoxidation reaction and reducing side reactions during electrolysis. During electrolysis, copper oxide and silicon oxide are continuously reduced to copper and silicon. The reduced copper enhances the conductivity of the electrolytic precursor, promotes silicon nucleation, and generates silicon-copper alloy nanowires, thereby improving the lithium-ion transport rate during charging and discharging in lithium-ion batteries. The silicon-copper composite nanowire anode material of this invention can significantly improve the conductivity of silicon anode materials during the lithium-ion battery de-intercalation and de-intercalation process, alleviate its own volume expansion, and fully enhance the electrochemical performance of silicon anodes.

[0006] This invention involves a two-step metal-assisted chemical etching process using copper salts to uniformly introduce nano- and micro-sized copper particles into the silicon material. The etched product is then controlled for oxidation and pressed and sintered to form an electrolytic precursor. The upper and lower surfaces of the electrolytic precursor are then attached to a sheet-like current collector and placed on a hook-shaped cathode current collector for a two-step constant-current molten salt electrolysis. Electrolytic reduction is performed at a relatively low current density to reduce copper oxide and silicon oxide, avoiding side reactions and obtaining a silicon-copper composite nanowire anode material.

[0007] A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0008] (1) Add photovoltaic silicon cutting waste to copper salt solution and mix evenly. Add reducing agent and carry out reduction chemical deposition so that copper ions in copper salt solution are reduced to copper nanoparticles and deposited on the surface of silicon waste.

[0009] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent to perform metal-assisted chemical etching so that the nano-micro copper particles are uniformly introduced into the silicon waste to obtain a nano-micro copper / silicon composite; the etching agent is HF-oxidant-organic solvent;

[0010] (3) The nano-micro copper / silicon composite is placed in an air atmosphere for controlled oxidation treatment to obtain a controlled oxidation product. The controlled oxidation product, binder and pore-forming agent are mixed and pressed into tablets, and sintered under a protective atmosphere to obtain a molten salt electrolysis precursor.

[0011] (4) After the upper and lower surfaces of the molten salt electrolysis precursor are attached to the sheet current collector, it is suspended on the hook-shaped cathode current collector as the cathode. The graphite crucible is used as the anode. The metal halide molten salt is added to the graphite crucible. Under the protective atmosphere, the first constant current molten salt electrolysis reduction and the second constant current molten salt electrolysis reduction are carried out in sequence to obtain the silicon-copper composite nanowire anode material.

[0012] The silicon-copper composite nanowire anode material can be used to prepare lithium-ion battery silicon anode materials. The lithium-ion battery silicon anode material consists of silicon-copper composite nanowire anode material, a conductive agent, and a binder. Based on 100 parts by weight of the lithium-ion battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 60-80 parts, the conductive agent accounts for 10-20 parts, and the binder accounts for 10-20 parts. Preferably, the conductive agent is acetylene black, graphene, conductive carbon black, polyaniline, polypyrrole, or carbon nanotubes; the binder is polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), sodium alginate, polyacrylic acid (PAA), polyethyleneimine (PEI), or polyetheretherketone (PEEK).

[0013] This invention employs molten salt electrolysis to modify the structure of silicon material obtained by two-step copper-assisted chemical etching with controlled oxidation. Ultimately, the sheet-like morphology of silicon waste is successfully modified into a silicon-copper nanowire composite structure, which effectively improves the electrochemical performance of silicon anode materials during the charge-discharge cycle of lithium-ion batteries.

[0014] The beneficial effects of this invention are:

[0015] (1) This invention transforms the sheet-like structure of silicon waste into a silicon-copper composite nanowire structure, without generating by-products. The silicon-copper composite nanowire structure greatly alleviates the problem of self-generated volume expansion of sheet-like silicon waste during charging and discharging, and improves the electrochemical performance of lithium batteries.

[0016] (2) This invention cleverly introduces metallic copper to achieve uniform etching of porous structures on the surface of silicon waste and embed metallic copper inside the silicon waste. After the etched silicon material is controlled to oxidize, copper oxide is uniformly distributed inside the silicon oxide material. During molten salt electrolysis, the copper oxide inside the silicon waste is first reduced to nano-micro structure copper. This part of copper promotes the nucleation of reduced silicon. After reaching a certain precipitation point, silicon-copper alloy nanowires with small diameter and large aspect ratio grow. This helps to form a stable solid electrolyte film layer during the lithium-ion battery de-intercalation process, avoids repeated consumption of lithium ions and improves the conductivity of the lithium-ion battery during the cycle process, thereby improving the rate performance of the lithium battery; it accelerates the migration rate of lithium ions during the de-intercalation process, reduces the charge transfer resistance, thereby extending the life of the lithium battery and enhancing the safety of the use process; at the same time, the generated copper also enhances the conductivity of the electrolytic precursor, ensuring that the precursor is completely electrolyzed during the electrolysis process.

[0017] (3) This invention cleverly utilizes the sheet-like structure of silicon waste to reduce the accumulation of silicon waste and reduce its pollution to the environment. By recycling silicon waste, the demand for new silicon materials can be reduced, resources can be saved, and production costs can be reduced. High-purity silicon-copper alloy nanowires are obtained by constant current electrolysis, which significantly improves the conductivity and surface area of ​​the material and effectively alleviates the volume expansion phenomenon of the material. Moreover, the silicon-copper alloy nanowire preparation process of this invention is short and has low energy consumption, making it easier to achieve continuous, low-cost, large-scale industrial production.

[0018] (4) In the process of molten salt electrolysis, the precursor is placed on a hook-shaped current collector with a sheet-shaped current collector attached. The design of the sheet-shaped current collector can maintain the uniform distribution of current in the electrolytic precursor during the electrolysis process, improve the electrolysis efficiency, and help to form uniform silicon-copper composite nanowires. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of molten salt electrolysis according to the present invention; wherein, 1-anode, 2-stainless steel rod, 3-cathode current collector, 4-molten salt, 5-electrolysis precursor; 6-plate-shaped cathode current collector;

[0020] Figure 2 Here is a SEM image of the powdered waste silicon powder from Example 1;

[0021] Figure 3 This is a schematic diagram of the mechanism of metal-assisted chemical etching in Example 1;

[0022] Figure 4 This is a SEM image of the nano / micro copper / silicon composite obtained by metal-assisted chemical etching in Example 1;

[0023] Figure 5 The image shows the XRD pattern of the controllable oxidation product and the silicon-copper composite nanowire in Example 1.

[0024] Figure 6 Here is a SEM image of the silicon-copper composite nanowires in Example 1;

[0025] Figure 7 Cyclic performance test graphs of the lithium battery anode prepared by the silicon-copper composite nanowire structure in Example 1 and the lithium battery anode in Comparative Example 1. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0027] Overview of the Invention

[0028] A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0029] (1) Add photovoltaic silicon cutting waste to copper salt solution and mix evenly. Add reducing agent and carry out reduction chemical deposition so that copper ions in copper salt solution are reduced to copper nanoparticles and deposited on the surface of silicon waste.

[0030] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent to perform metal-assisted chemical etching so that the nano-micro copper particles are uniformly introduced into the silicon waste to obtain a nano-micro copper / silicon composite; the etching agent is HF-oxidant-organic solvent;

[0031] (3) The nano-micro copper / silicon composite is placed in an air atmosphere for controlled oxidation treatment to obtain a controlled oxidation product. The controlled oxidation product, binder and pore-forming agent are mixed and pressed into tablets, and sintered under a protective atmosphere to obtain a molten salt electrolysis precursor.

[0032] (4) After the upper and lower surfaces of the molten salt electrolysis precursor are attached to the sheet current collector, they are suspended on the hook-shaped cathode current collector as the cathode. The graphite crucible is used as the anode. The metal halide molten salt is added to the graphite crucible. The first constant current molten salt electrolysis reduction and the second constant current molten salt electrolysis reduction are carried out in sequence under a protective atmosphere to obtain the silicon-copper composite nanowire negative electrode material.

[0033] Preferably, the particle size of the photovoltaic silicon cutting waste in step (1) is 0.5 to 10 μm. Controlling the particle size of the photovoltaic silicon cutting waste can increase the specific surface area of ​​the silicon material, which is helpful for the subsequent copper-assisted chemical etching reaction and electrolysis process, and improves the performance of the final product.

[0034] Preferably, the copper salt in step (1) is one or more of Cu(NO3)2, CuCl2, CuSO4, Cu(C2H3O2)2, CuO, Cu(OH)2, CuCO3, Cu(CN)2, and CuF2, and the copper salt solution contains Cu 2+ The concentration is 0.005–1 mol / L; the reducing agent is one or more of HF, sodium borohydride, ascorbic acid, hydrazine, and formaldehyde, and the molar amount of the reducing agent added is Cu. 2+ 1 to 60 times;

[0035] Preferably, in step (2), the oxidant in the etching agent is one or more of H2O2, HClO3, KMnO4, HNO3, Br2, concentrated H2SO4, and C2H4O3, the organic solvent is one or more of acetone, methanol, ethanol, tetrahydrofuran, and benzene, the reducing agent concentration is 0.1–22 mol / L, and the oxidant concentration is 0.1–5 mol / L.

[0036] Preferably, the temperature of the metal-assisted chemical etching step (2) is 15-80°C and the time is 1-400 min;

[0037] Preferably, the controlled oxidation treatment in step (3) is carried out at a temperature of 300–1000°C for 2–10 h; the mass ratio of the controlled oxidation product, binder, and pore-forming agent is 100:20–50:10–50; the pressing pressure is 5–30 MPa, the holding time is 1–10 min; and the sintering temperature is 300–800°C for 2–5 h.

[0038] Preferably, the adhesive in step (3) is one or more of epoxy resin, silicone, starch, chitosan, polyamide, acrylate, phenolic resin, polyimide, polyvinyl alcohol, and polyvinyl butyral; the pore-forming agent is one or more of halogen salt, NH4NO3, (NH4)2SO4, (NH4)2CO3, and NH4HCO3; and the protective atmosphere is nitrogen, argon, or helium.

[0039] Preferably, in step (4), the sheet current collector is platinum, tungsten, molybdenum or zirconium, the hook cathode current collector is a platinum hook, tungsten hook, molybdenum hook or zirconium hook corresponding to the sheet current collector, the metal halide molten salt is NaCl-CaCl2 molten salt, NaCl-KCl-MgCl2 molten salt, CaF2-NaF-MgF2 molten salt, NaCl-CaCl2-LiF molten salt, NaCl-CaCl2-LiCl molten salt, KCl-CaCl2 molten salt, NaCl-KCl molten salt, NaCl-CaCl2-CaF2 molten salt, NaCl molten salt, CaCl2 molten salt, CaCl2-KCl-MgCl2 molten salt, LiF-BeF2 molten salt or NaF-ZrF4 molten salt, and the protective atmosphere is nitrogen, argon or helium;

[0040] Preferably, the temperature of the first constant current molten salt electrolytic reduction in step (4) is 700-1000℃, the current is 0.5-3A, and the time is 1-6h;

[0041] Preferably, the temperature of the second constant current molten salt electrolytic reduction in step (4) is 700-1000℃, the current of the second constant current molten salt electrolytic reduction is 0.3-0.5A lower than the current of the first constant current molten salt electrolytic reduction, and the time is 1-6h.

[0042] In this invention, the cathode system for molten salt electrolysis is improved by adding a sheet-like current collector that maintains good contact with the precursor to the hook-shaped current collector at the cathode. Good contact is ensured between the electrolytic precursor, the hook-shaped cathode current collector, and the sheet-like current collector. During electrolysis in an inert atmosphere, a DC power supply is applied, and some electrons are transferred to the sheet-like cathode current collector, while others are transferred to the hook-shaped cathode current collector. At this point, the precursor surface in contact with the sheet-like current collector receives electrons and begins to reduce. Furthermore, because the electrons transferred through the surface of the hook-shaped cathode current collector contact the center of the precursor, the center of the precursor also begins to undergo radial electrolytic reduction. Subsequently, the electrolytic reduction reaction occurs simultaneously from the center of the precursor in the radial direction and in the axial direction where it contacts the sheet-like current collector. Therefore, electrodeoxidation is thorough and the reduction rate is fast. The current remains constant throughout this process, and the introduction of the sheet-like current collector ensures the uniformity of the current density of the electrolytic precursor during electrolysis, avoiding side reactions and ensuring the introduction of no electrolytic byproducts. Furthermore, in the two-step copper-assisted chemical etching process using controlled oxidation, the theoretical decomposition voltage of copper oxide is lower than that of the silicon waste after controlled oxidation. Therefore, at the start of electrolysis, copper oxide in the precursor first gains electrons and is reduced to copper. The formation of copper increases the conductivity of the precursor. Combined with the excellent electrodeoxidation characteristics of the precursor in both the axial and radial directions, the electrodeoxidation effect of the precursor is more complete, resulting in higher electrolysis efficiency. Meanwhile, oxygen ions released from the precursor readily combine with the molten salt and the anode graphite crucible to generate CO or CO2, which then overflows from the molten salt surface, avoiding the formation of carbonate impurities. After etching and oxidation, copper nanoparticles were successfully introduced into the silicon waste through a two-step copper-assisted chemical etching process. After controlled oxidation, copper and silicon were oxidized separately. At the beginning of electrolysis, the copper oxide inside the pores of the controlled oxidized silicon was first reduced to copper. As electrolysis proceeded, the controlled oxidized silicon gained electrons and was gradually reduced to silicon. At this time, the nano- and micro-sized copper particles promoted the nucleation of reduced silicon inside the silicon oxide. When the reduced silicon reached a certain concentration, it catalyzed the growth of silicon-copper alloy nanowires. Because the copper particles introduced through metal-assisted chemical etching are small in size, silicon-copper alloy nanowires with small diameter and high aspect ratio were grown under the catalysis of copper. This facilitates the formation of a stable solid electrolyte membrane during the lithium-ion battery's lithium insertion and extraction process, effectively alleviates the volume expansion phenomenon of lithium-ion batteries during charging and discharging, and is beneficial to improving the electrochemical performance of lithium-ion batteries.

[0043] Conventional molten salt electrolysis uses SiO2 powder as the electrolysis precursor, and the introduced metal oxides generally adhere to the surface of the SiO2 powder. This makes it easier for oxygen ions released during electrolysis to combine with SiO2 and molten salt to form silicate impurities, resulting in impure electrolysis products and affecting the electrochemical performance of lithium batteries. Compared with conventional SiO2 electrolysis, this invention uses copper salt to etch silicon waste and uniformly introduces metallic copper particles into the silicon material. After the silicon material is etched by copper salt in a controlled manner, the electrolysis device of this invention can simultaneously cause the electrolysis precursor to undergo electro-deoxidation reduction reactions in both radial and axial directions. This helps to accelerate the electro-deoxidation rate, reduce electrolysis time, achieve energy saving, and realize the purpose of mass production of silicon-copper alloy nanowires.

[0044] Example 1: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0045] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 0.5–6 μm) was added to a 0.2 mol / L Cu(NO3)2 solution and mixed thoroughly. A reducing agent (20 mol / L HF solution) was added, and reduction chemical deposition was performed for 60 min. This allowed the copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amount of the reducing agent (HF) added was equal to the Cu(NO3)2 solution. 2+ 20 times;

[0046] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-H2O2-anhydrous ethanol) and perform metal-assisted chemical etching at 25°C for 60 min to uniformly introduce the nano- and micro-sized copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano- and micro-sized copper / silicon composite. The HF concentration in the etching agent is 4.5 mol / L and the H2O2 concentration is 0.5 mol / L.

[0047] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 900℃ for 5h to obtain a controlled oxidation product. The controlled oxidation product, binder (polyvinyl alcohol) and pore-forming agent (ammonium bicarbonate) were mixed and pressed into tablets at a pressure of 15MPa for 3min. Then, it was sintered in an argon atmosphere (argon flow rate 15mL / min) at 600℃ for 3h to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (polyvinyl alcohol) and pore-forming agent (ammonium bicarbonate) was 100:30:30.

[0048] (4) Figure 1As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the molybdenum sheet current collector and suspended on the molybdenum hook cathode current collector (good contact is maintained between the electrolysis precursor, the molybdenum hook current collector, and the molybdenum sheet current collector). Using a graphite crucible as the anode, NaCl-CaCl2 molten salt (molar ratio of NaCl to CaCl2 is 4:6) is added to the graphite crucible. Under an argon atmosphere (argon flow rate of 20 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector extracts [the solution] from the molten salt. The product was naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed for 2 hours with an HCl-HF mixed acid solution (HCl concentration 0.5 mol / L, HF concentration 0.5 mol / L) to obtain the silicon-copper composite nanowire anode material. The first constant-current molten salt electrolytic reduction was carried out at a temperature of 700℃, a current of 1.5A, and a time of 2 hours. The second constant-current molten salt electrolytic reduction was carried out at a temperature of 700℃, a current of 1.1A, and a time of 2 hours.

[0049] The SEM image of the photovoltaic silicon cutting waste in this embodiment is shown below. Figure 2 ,from Figure 2 It is known that photovoltaic silicon cutting waste exists in the form of irregular nano- and micro-scale sheet structures. The distribution between each sheet structure is relatively loose and there are significant gaps. This structure facilitates further etching in the solution.

[0050] The mechanism diagram of copper-assisted chemical etching in this embodiment is shown below. Figure 3 , Figure 3 The left side of the image shows the process of copper deposition on the surface of silicon waste. When the HF solution comes into contact with the silicon waste, it first dissolves the natural oxide layer on the surface, exposing the pure silicon. Finally, the HF solution oxidizes some of the silicon atoms on the surface of the silicon waste into tetravalent silicon ions, releasing electrons. These electrons then react with Cu in the solution. 2+ This process reduces the silicon waste to nano- and micro-sized copper particles, which then adhere to the surface of the silicon waste. Figure 3 The right side of the middle section shows the process of nano- and micro-sized copper particles etching into the interior of silicon waste. Under the catalytic effect of the nano- and micro-sized copper particles, hydrogen peroxide, as an oxidant, accelerates the oxidation reaction, causing silicon dioxide to form rapidly on the surface of the silicon waste. At the same time, due to the presence of HF, the SiO2 generated on the surface of the silicon waste dissolves rapidly in the etchant, thus allowing the nano- and micro-sized copper particles to gradually etch into the interior of the silicon waste.

[0051] The SEM image of the nano-micro copper / silicon composite obtained by copper-assisted chemical etching in this embodiment is shown below. Figure 4 ,from Figure 4 It can be seen that after two-step copper-assisted chemical etching, a uniform porous structure appears on the surface of the silicon waste, indicating that nano- and micro-sized copper particles are uniformly etched into the interior of the silicon waste.

[0052] The XRD pattern of the controllable oxidation products and silicon-copper composite nanowires in this embodiment is shown below. Figure 5 ,from Figure 5 It can be seen that after the silicon waste undergoes two-step copper-assisted chemical etching and high-temperature oxidation pretreatment, the crystalline peak of the silicon waste is transformed into the amorphous peak of silicon oxide, indicating that most of the etched silicon material is oxidized. At the same time, the appearance of the copper oxide crystalline peak also indicates that the copper is successfully oxidized. After the precursor is electrolyzed in two steps with constant current using an improved molten salt electrolysis device, it was found that the amorphous silicon oxide peak disappeared and the crystalline silicon peak reappeared. In addition, the copper oxide peak also disappeared and the copper-silicon alloy peak appeared. No other impurity peaks appeared in this process, indicating that there are few side reactions in this electrolysis method.

[0053] The SEM image of the silicon-copper composite nanowire in this embodiment is shown below. Figure 6 ,contrast Figure 2 and Figure 6 It can be seen that the method in this embodiment successfully converted waste silicon powder with sheet structure into nanowire structure in batches;

[0054] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (conductive carbon black) and binder (sodium alginate). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 60 parts, the conductive agent (conductive carbon black) accounts for 20 parts, and the binder (sodium alginate) accounts for 20 parts.

[0055] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half-cell. Under a charge-discharge current density of 500 mA / g, the cycle performance of the lithium-ion battery silicon anode material is as follows: Figure 7 As shown, the initial discharge specific capacity of the silicon anode material for lithium batteries is 2206.8 mAh / g, the initial coulombic efficiency can reach 85.6%, and the reversible specific capacity after 300 cycles is 930.4 mAh / g.

[0056] Comparative Example 1: Lithium-ion battery silicon anode material was prepared directly from the vacuum-dried photovoltaic silicon cutting waste (particle size 0.5-6 μm) of Example 1: The lithium-ion battery silicon anode material is composed of photovoltaic silicon cutting waste, conductive agent (conductive carbon black) and binder (sodium alginate). Based on 100 parts by weight of the lithium-ion battery silicon anode material, photovoltaic silicon cutting waste accounts for 60 parts, conductive agent (conductive carbon black) accounts for 20 parts, and binder (sodium alginate) accounts for 20 parts.

[0057] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half-cell. Under a charge-discharge current density of 500 mA / g, the cycle performance of the lithium-ion battery silicon anode material is as follows: Figure 7As shown, the initial discharge specific capacity of the comparative lithium battery silicon anode material is 2732.1 mAh / g, the initial coulombic efficiency can reach 75.5%, and the reversible specific capacity after 300 cycles is only 280.1 mAh / g; while the reversible specific capacity of Example 1 after 300 cycles is 650.3 mAh / g higher than that of the comparative example. Therefore, the long-term cycling performance of Example 1 is much greater than that of waste silicon powder (flakes).

[0058] Example 2: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0059] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 1-3 μm) was added to a 0.3 mol / L CuSO4 solution and mixed thoroughly. A reducing agent (a 3 mol / L sodium borohydride solution) was added, and reduction chemical deposition was carried out for 90 min. This allowed the copper ions in the copper salt solution to gain electrons and be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amount of the reducing agent (sodium borohydride) added was equal to the Cu content in the CuSO4 solution. 2+ 25 times;

[0060] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-HNO3-acetone) and perform metal-assisted chemical etching at 30°C for 120 min to uniformly introduce the nano-micro copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano-micro copper / silicon composite. The HF concentration in the etching agent is 5.0 mol / L and the HNO3 concentration is 1.0 mol / L.

[0061] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 800℃ for 6 hours to obtain a controlled oxidation product. The controlled oxidation product, binder (polyvinyl butyral) and pore-forming agent (ammonium chloride) were mixed and pressed into tablets at a pressure of 18MPa for 4 minutes. Then, the tablets were sintered in a nitrogen atmosphere (nitrogen flow rate 20mL / min) at 650℃ for 3.5 hours to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (polyvinyl butyral) and pore-forming agent (ammonium chloride) was 100:35:25.

[0062] (4) Figure 1As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the tungsten sheet current collector and suspended on the tungsten hook cathode current collector (good contact exists between the electrolysis precursor, the tungsten hook current collector, and the tungsten sheet current collector). Using a graphite crucible as the anode, NaCl-KCl-MgCl2 molten salt (molar ratio of NaCl, KCl, and MgCl2 is 5:3:2) is added to the graphite crucible. Under a nitrogen atmosphere (nitrogen flow rate of 25 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector flows from... The material was removed from the molten salt and naturally cooled to room temperature under a nitrogen atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an HCl-HF mixed acid solution (HCl concentration of 1 mol / L and HF concentration of 0.5 mol / L) for 1 hour to obtain the silicon-copper composite nanowire anode material. The first constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 1.8A, and a time of 1.5 hours. The second constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 1.5A, and a time of 2.5 hours.

[0063] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (conductive carbon black) and binder (sodium alginate). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 60 parts, the conductive agent (conductive carbon black) accounts for 20 parts, and the binder (sodium alginate) accounts for 20 parts.

[0064] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2160.5mAh / g, the initial coulombic efficiency can reach 83.60%, and the reversible specific capacity after 300 cycles is 980.6mAh / g.

[0065] Example 3: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0066] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 1-5 μm) was added to a 0.25 mol / L CuCl2 solution and mixed thoroughly. A reducing agent (a 13 mol / L formaldehyde solution) was added, and reduction chemical deposition was carried out for 90 min. This allowed the copper ions in the copper salt solution to gain electrons and be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amount of the reducing agent (formaldehyde solution) added was equal to the CuCl2 solution concentration. 2+ 15 times;

[0067] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-H2O2-anhydrous ethanol) and perform metal-assisted chemical etching at 40°C for 90 min to uniformly introduce the nano-micro copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano-micro copper / silicon composite. The HF concentration in the etching agent is 6 mol / L and the H2O2 concentration is 1.5 mol / L.

[0068] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 850℃ for 5h to obtain a controlled oxidation product. The controlled oxidation product, binder (phenolic resin) and pore-forming agent (ammonium sulfate) were mixed and pressed into tablets at a pressure of 20MPa for 3min. Then, it was sintered in an argon atmosphere (argon flow rate 25mL / min) at 750℃ for 4h to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (phenolic resin) and pore-forming agent (ammonium sulfate) was 100:40:30.

[0069] (4) Figure 1 As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the platinum sheet current collector and suspended on the platinum hook cathode current collector (good contact exists between the electrolysis precursor, the platinum hook current collector, and the platinum sheet current collector). Using a graphite crucible as the anode, NaCl-CaCl2-CaF2 molten salt (molar ratio of NaCl, CaCl2, and CaF2 is 6:3:1) is added to the graphite crucible. Under an argon atmosphere (argon flow rate of 30 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The fluid was removed from the molten salt and naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an HCl-HF mixed acid solution (HCl concentration of 1.5 mol / L and HF concentration of 0.5 mol / L) for 2 hours to obtain the silicon-copper composite nanowire anode material. The first constant current molten salt electrolytic reduction was carried out at a temperature of 850℃, a current of 1.5A, and a time of 2 hours. The second constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 1A, and a time of 2 hours.

[0070] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (graphene) and binder (sodium alginate). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 70 parts, the conductive agent (graphene) accounts for 15 parts, and the binder (sodium alginate) accounts for 15 parts.

[0071] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2463.6mAh / g, the initial coulombic efficiency can reach 84.86%, and the reversible specific capacity after 300 cycles is 1056.3mAh / g.

[0072] Example 4: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0073] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 0.5–7 μm) was added to a 0.4 mol / L Cu(C₂H₃O₂)₂ solution and mixed thoroughly. A reducing agent (10 mol / L hydrazine solution) was added, and reduction chemical deposition was performed for 150 min. This allowed the copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amount of the reducing agent (hydrazine solution) added was equal to the molar amount of Cu in the Cu(C₂H₃O₂)₂ solution. 2+ 30 times;

[0074] (2) Silicon waste with deposited copper nanoparticles was added to an etchant (HF-KMnO4-tetrahydrofuran) and subjected to metal-assisted chemical etching at 50°C for 120 min to uniformly introduce nano- and micro-sized copper particles into the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried to obtain a nano- and micro-sized copper / silicon composite. The etchant contained HF with a concentration of 6.5 mol / L and KMnO4 with a concentration of 2 mol / L.

[0075] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 900℃ for 6 hours to obtain a controlled oxidation product. The controlled oxidation product, binder (chitosan) and pore-forming agent (ammonium nitrate) were mixed and pressed into tablets at a pressure of 23MPa for 5 minutes. Then, the tablets were sintered in a helium atmosphere (helium flow rate 20mL / min) at 700℃ for 3 hours to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (chitosan) and pore-forming agent (ammonium nitrate) was 100:35:30.

[0076] (4) Figure 1As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the zirconium sheet current collector and suspended on the zirconium hook cathode current collector (good contact is maintained between the electrolysis precursor, the zirconium hook current collector, and the zirconium sheet current collector). Using a graphite crucible as the anode, NaCl-CaCl2-LiF molten salt (molar ratio of NaCl, CaCl2, and LiF is 5:4:1) is added to the graphite crucible. Under a helium atmosphere (helium flow rate of 25 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector flows from the molten salt... The product was removed from the electrolyte and naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an H2SO4-HF mixed acid solution (H2SO4 concentration of 1 mol / L and HF concentration of 0.5 mol / L) for 1 h to obtain the silicon-copper composite nanowire anode material. The first constant current molten salt electrolytic reduction was carried out at a temperature of 750℃, a current of 1.6A, and a time of 1.5 h. The second constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 1.2A, and a time of 3 h.

[0077] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (carbon nanotubes) and binder (carboxymethyl cellulose). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 70 parts, the conductive agent (carbon nanotubes) accounts for 15 parts, and the binder (carboxymethyl cellulose) accounts for 15 parts.

[0078] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2362.8mAh / g, the initial coulombic efficiency can reach 82.9%, and the reversible specific capacity after 300 cycles is 920.4mAh / g.

[0079] Example 5: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0080] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 1-8 μm) was added to a 0.5 mol / L Cu(C2H3O2)2 solution and mixed thoroughly. A reducing agent (3 mol / L ascorbic acid solution) was added, and reduction chemical deposition was carried out for 180 min. This allowed the copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amount of the reducing agent (ascorbic acid) added was equal to the amount of Cu in the Cu(C2H3O2)2 solution. 2+ 20 times;

[0081] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-C2H4O3-methanol) and perform metal-assisted chemical etching at 60°C for 90 min to uniformly introduce the nano- and micro-sized copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano- and micro-sized copper / silicon composite. The HF concentration in the etching agent is 7 mol / L and the C2H4O3 concentration is 2.5 mol / L.

[0082] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 950℃ for 4h to obtain a controlled oxidation product. The controlled oxidation product, binder (polyimide) and pore-forming agent (ammonium carbonate) were mixed and pressed into tablets at a pressure of 25MPa for 3min. Then, it was sintered in a nitrogen atmosphere (nitrogen flow rate 25mL / min) at 780℃ for 3.5h to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (polyimide) and pore-forming agent (ammonium carbonate) was 100:28:32.

[0083] (4) Figure 1 As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the tungsten sheet current collector and suspended on the tungsten hook cathode current collector (good contact exists between the electrolysis precursor, the tungsten hook current collector, and the tungsten sheet current collector). Using a graphite crucible as the anode, NaCl-CaCl2-LiCl molten salt (molar ratio of NaCl, CaCl2, and LiCl is 6:3:1) is added to the graphite crucible. Under an argon atmosphere (argon flow rate of 30 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector... The material was removed from the molten salt and naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an HNO3-HF mixed acid solution (HNO3 concentration of 1 mol / L and HF concentration of 0.6 mol / L) for 2 hours to obtain the silicon-copper composite nanowire anode material. The first constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 1.4A, and a time of 2 hours. The second constant current molten salt electrolytic reduction was carried out at a temperature of 850℃, a current of 1.0A, and a time of 2.5 hours.

[0084] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (conductive carbon black) and binder (sodium alginate). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 80 parts, the conductive agent (acetylene black) accounts for 10 parts, and the binder (polyacrylic acid) accounts for 10 parts.

[0085] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2538.7mAh / g, the initial coulombic efficiency can reach 83.5%, and the reversible specific capacity after 300 cycles is 908.8mAh / g.

[0086] Example 6: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows: a 3 mol / L sodium borohydride solution.

[0087] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 0.5–8.5 μm) was added to a 0.6 mol / L CuCl2 solution and mixed thoroughly. A reducing agent (15 mol / L HF solution and 3 mol / L sodium borohydride solution) was added, and reduction chemical deposition was performed for 180 min. This allowed copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amounts of the reducing agent (HF and sodium borohydride) added were respectively the amount of Cu in the CuCl2 solution. 2+ 40 times and 20 times;

[0088] (2) Silicon waste with deposited copper nanoparticles was added to an etchant (HF-HClO3-tetrahydrofuran) and subjected to metal-assisted chemical etching at 70°C for 180 min to uniformly introduce nano- and micro-sized copper particles into the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried to obtain a nano- and micro-sized copper / silicon composite. The etchant contained 7.5 mol / L of HF and 0.5 mol / L of HClO3.

[0089] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 900℃ for 6h to obtain a controlled oxidation product. The controlled oxidation product, binder (acrylate) and pore-forming agent (LiCl) were mixed and pressed into tablets at a pressure of 15MPa for 6min. Then, it was sintered in a nitrogen atmosphere (nitrogen flow rate 35mL / min) at 680℃ for 4h to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (acrylate) and pore-forming agent (LiCl) was 100:30:35.

[0090] (4) Figure 1As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the zirconium sheet current collector and suspended on the zirconium hook cathode current collector (good contact is maintained between the electrolysis precursor, the zirconium hook current collector, and the zirconium sheet current collector). Using a graphite crucible as the anode, KCl-CaCl2 molten salt (KCl to CaCl2 molar ratio of 4:6) is added to the graphite crucible. Under a nitrogen atmosphere (nitrogen flow rate of 40 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector is removed from the molten salt and naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water, and then acid-washed with a mixed acid solution of H2SO4-HCl-HF (H2SO4 concentration of 1 mol / L, HCl concentration of 1 mol / L, and HF concentration of 0.5 mol / L) for 1.5 h to obtain silicon-copper composite nanowire anode material; the first constant current molten salt electrolytic reduction was carried out at a temperature of 850℃, a current of 1.3A, and a time of 2 h; the second constant current molten salt electrolytic reduction was carried out at a temperature of 800℃, a current of 0.9A, and a time of 2.5 h;

[0091] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (polypyrrole) and binder (sodium alginate). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 80 parts, the conductive agent (conductive carbon black) accounts for 10 parts, and the binder (styrene-butadiene rubber) accounts for 10 parts.

[0092] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2386.7mAh / g, the initial coulombic efficiency can reach 84.2%, and the reversible specific capacity after 300 cycles is 890.7mAh / g.

[0093] Example 7: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0094] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 3-9 μm) was added to a 0.7 mol / L CuSO4 solution and mixed thoroughly. Reducing agents (10 mol / L HF solution and 8 mol / L hydrazine solution) were added, and reduction chemical deposition was performed for 240 min. This allowed copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amounts of the reducing agents (HF and hydrazine) added were respectively the Cu ions in the CuSO4 solution. 2+ 50 times and 15 times;

[0095] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-HNO3-methanol) and perform metal-assisted chemical etching at 75°C for 300 min to uniformly introduce the nano- and micro-sized copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano- and micro-sized copper / silicon composite. The HF concentration in the etching agent is 8 mol / L and the HNO3 concentration is 0.5 mol / L.

[0096] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 700℃ for 7h to obtain a controlled oxidation product. The controlled oxidation product, binder (epoxy resin) and pore-forming agent (ammonium chloride) were mixed and pressed into tablets at a pressure of 18MPa for 6min. Then, it was sintered in a helium atmosphere (helium flow rate 25mL / min) at 650℃ for 3h to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (epoxy resin) and pore-forming agent (ammonium chloride) was 100:35:25.

[0097] (4) Figure 1 As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the platinum sheet current collector and then suspended on the platinum hook cathode current collector (the electrolysis precursor, platinum hook current collector, and platinum sheet current collector are in good contact). A graphite crucible is used as the anode, and NaCl-KCl is added.

[0098] Molten salt (NaCl and KCl in a molar ratio of 7:3) was added to a graphite crucible. Under a helium atmosphere (helium flow rate of 30 mL / min), a first constant-current molten salt electrolytic reduction and a second constant-current molten salt electrolytic reduction were performed sequentially. The cathode current collector was removed from the molten salt and allowed to cool naturally to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an HCl-HF mixed acid solution (HCl concentration of 1.5 mol / L and HF concentration of 1 mol / L) for 2.5 h to obtain the silicon-copper composite nanowire anode material. The first constant-current molten salt electrolytic reduction was performed at a temperature of 800℃, a current of 1.7 A, and a time of 1.5 h; the second constant-current molten salt electrolytic reduction was performed at a temperature of 800℃, a current of 1.3 A, and a time of 2 h.

[0099] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (polyaniline) and binder (polyvinylidene fluoride). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 70 parts, the conductive agent (polyaniline) accounts for 15 parts, and the binder (polyvinylidene fluoride) accounts for 15 parts.

[0100] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500 mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2316.4 mAh / g, the initial coulombic efficiency can reach 82.3%, and the reversible specific capacity after 300 cycles is 916.3 mAh / g.

[0101] Example 8: A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, the specific steps of which are as follows:

[0102] (1) Vacuum-dried photovoltaic silicon cutting waste (particle size 0.5–9.5 μm) was added to a 0.8 mol / L Cu(NO3)2 solution and mixed thoroughly. A reducing agent (8 mol / L HF solution and 3 mol / L ascorbic acid solution) was added, and reduction chemical deposition was performed for 300 min. This allowed copper ions in the copper salt solution to be reduced to copper nanoparticles, which were then deposited on the surface of the silicon waste. Solid-liquid separation was performed, and the solid was washed with deionized water and vacuum dried. The molar amounts of the reducing agent (HF and ascorbic acid) added were respectively the amount of Cu in the CuSO4 solution. 2+ 55 times and 10 times;

[0103] (2) Add the silicon waste with deposited copper nanoparticles to the etching agent (HF-H2O2-tetrahydrofuran), and perform metal-assisted chemical etching at 80℃ for 360 min to uniformly introduce the nano-micro copper particles into the silicon waste. Separate the solid and liquid, wash the solid with deionized water, and vacuum dry to obtain the nano-micro copper / silicon composite. The HF concentration in the etching agent is 10 mol / L, and the H2O2 concentration is 1.5 mol / L.

[0104] (3) The nano-micro copper / silicon composite was placed in an air atmosphere and subjected to controlled oxidation treatment at 800℃ for 6 hours to obtain a controlled oxidation product. The controlled oxidation product, binder (acrylate) and pore-forming agent (ammonium sulfate) were mixed and pressed into tablets at a pressure of 20MPa for 3 minutes. Then, the tablets were sintered in an argon atmosphere (argon flow rate 25mL / min) at 600℃ for 4 hours to obtain a circular sheet-like molten salt electrolysis precursor. The mass ratio of the controlled oxidation product, binder (acrylate) and pore-forming agent (ammonium sulfate) was 100:38:30.

[0105] (4) Figure 1As shown, the upper and lower surfaces of the molten salt electrolysis precursor are attached to the molybdenum sheet current collector and suspended on the molybdenum hook cathode current collector (good contact exists between the electrolysis precursor, the molybdenum hook current collector, and the molybdenum sheet current collector). Using a graphite crucible as the anode, a CaCl2-KCl-MgCl2 molten salt (the molar ratio of CaCl2, KCl, and MgCl2 is 5:3:2) is added to the graphite crucible. Under a nitrogen atmosphere (nitrogen flow rate of 35 mL / min), the first and second constant-current molten salt electrolysis reductions are performed sequentially. The cathode current collector... The material was removed from the molten salt and naturally cooled to room temperature under an argon atmosphere. The electrolysis product was washed with deionized water and then acid-washed with an HCl-HF mixed acid solution (HCl concentration of 1 mol / L and HF concentration of 0.5 mol / L) for 2 hours to obtain the silicon-copper composite nanowire anode material. The first constant current molten salt electrolytic reduction was carried out at a temperature of 850℃, a current of 1.5A, and a time of 1.5 hours. The second constant current molten salt electrolytic reduction was carried out at a temperature of 850℃, a current of 1.1A, and a time of 2.5 hours.

[0106] The silicon-copper composite nanowire anode material can be used to prepare lithium battery silicon anode materials: the lithium battery silicon anode material is composed of silicon-copper composite nanowire anode material, conductive agent (graphene) and binder (carboxymethyl cellulose). Based on 100 parts by mass of the lithium battery silicon anode material, the silicon-copper composite nanowire anode material accounts for 70 parts, the conductive agent (graphene) accounts for 15 parts, and the binder (carboxymethyl cellulose) accounts for 15 parts.

[0107] In a glove box, lithium-ion battery silicon anode material and lithium sheet (counter electrode) are assembled into a half cell. Under a current density of 500mA / g, the initial discharge specific capacity of the lithium-ion battery silicon anode material is 2318.4mAh / g, the initial coulombic efficiency can reach 81.4%, and the reversible specific capacity after 300 cycles is 934.6mAh / g.

[0108] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing silicon-copper composite nanowire anode materials using photovoltaic silicon cutting waste, characterized in that, The specific steps are as follows: (1) Add photovoltaic silicon cutting waste to copper salt solution and mix evenly. Add reducing agent and carry out reduction chemical deposition so that copper ions in copper salt solution are reduced to copper nanoparticles and deposited on the surface of silicon waste. (2) Add the silicon waste with deposited copper nanoparticles to the etching agent to perform metal-assisted chemical etching so that the nano-micro copper particles are uniformly introduced into the silicon waste to obtain a nano-micro copper / silicon composite; the etching agent is HF-oxidant-organic solvent; (3) The nano-micro copper / silicon composite is placed in an air atmosphere for controlled oxidation treatment to obtain a controlled oxidation product. The controlled oxidation product, binder and pore-forming agent are mixed and pressed into tablets, and sintered under a protective atmosphere to obtain a molten salt electrolysis precursor. (4) After the upper and lower surfaces of the molten salt electrolysis precursor are attached to the sheet current collector, it is suspended on the hook-shaped cathode current collector as the cathode. The graphite crucible is used as the anode. The metal halide molten salt is added to the graphite crucible. Under the protective atmosphere, the first constant current molten salt electrolysis reduction and the second constant current molten salt electrolysis reduction are carried out in sequence to obtain the silicon-copper composite nanowire anode material.

2. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (1) The particle size of photovoltaic silicon cutting waste is 0.5-10μm.

3. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (1) The copper salt is one or more of Cu(NO3)2, CuCl2, CuSO4, Cu(C2H3O2)2, CuO, Cu(OH)2, CuCO3, Cu(CN)2, and CuF2. The copper salt solution contains Cu... 2+ The concentration is 0.005–1 mol / L; the reducing agent is one or more of HF, sodium borohydride, ascorbic acid, hydrazine, and formaldehyde, and the molar amount of the reducing agent added is Cu. 2+ 1 to 60 times.

4. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: In step (2), the oxidant in the etching agent is one or more of H2O2, HClO3, KMnO4, HNO3, Br2, concentrated H2SO4, and C2H4O3, the organic solvent is one or more of acetone, methanol, ethanol, tetrahydrofuran, and benzene, the reducing agent concentration is 0.1-22 mol / L, and the oxidant concentration is 0.1-5 mol / L.

5. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 4, characterized in that: Step (2) The temperature for metal-assisted chemical etching is 15-80℃ and the time is 1-400 min.

6. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (3) The controlled oxidation treatment temperature is 300-1000℃ and the time is 2-10h; the mass ratio of controlled oxidation product, binder and pore-forming agent is 100:20-50:10-50; the pressing pressure is 5-30MPa and the holding time is 1-10min; the sintering temperature is 300-800℃ and the time is 2-5h.

7. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (3) The binder is one or more of epoxy resin, silicone, starch, chitosan, polyamide, acrylate, phenolic resin, polyimide, polyvinyl alcohol, and polyvinyl butyral; the pore-forming agent is one or more of halogen salt, NH4NO3, (NH4)2SO4, (NH4)2CO3, and NH4HCO3; the protective atmosphere is nitrogen, argon, or helium.

8. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (4) The sheet current collector is made of platinum, tungsten, molybdenum or zirconium, the hook cathode current collector is a platinum hook, tungsten hook, molybdenum hook or zirconium hook corresponding to the sheet current collector, the metal halide molten salt is NaCl-CaCl2 molten salt, NaCl-KCl-MgCl2 molten salt, CaF2-NaF-MgF2 molten salt, NaCl-CaCl2-LiF molten salt, NaCl-CaCl2-LiCl molten salt, KCl-CaCl2 molten salt, NaCl-KCl molten salt, NaCl-CaCl2-CaF2 molten salt, NaCl molten salt, CaCl2 molten salt, CaCl2-KCl-MgCl2 molten salt, LiF-BeF2 molten salt or NaF-ZrF4 molten salt, and the protective atmosphere is nitrogen, argon or helium.

9. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (4) The temperature of the first constant current molten salt electrolytic reduction is 700-1000℃, the current is 0.5-3A, and the time is 1-6h.

10. The method for preparing silicon-copper composite nanowire anode material using photovoltaic silicon cutting waste according to claim 1, characterized in that: Step (4) The temperature of the second constant current molten salt electrolysis reduction is 700-1000℃, the current of the second constant current molten salt electrolysis reduction is 0.3-0.5A lower than the current of the first constant current molten salt electrolysis reduction, and the time is 1-6h.

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