Method for preparing porous silicon-based negative electrode material by utilizing silicon-aluminum-copper waste synergistic phosphorus-strontium ultra-fining

Abstract

The invention belongs to the technical field of lithium ion battery silicon-based negative electrode material preparation and solid waste recycling, and discloses a method for preparing a porous silicon-based negative electrode material through cooperation of silicon-aluminum-copper waste and phosphorus-strontium ultra-refining. Pretreated battery recycled waste aluminum, high-purity silicon powder, industrial waste copper and alloy raw materials are mixed and smelted to prepare a continuous aluminum-silicon alloy thin strip, the thin strip is crushed to 0.5-10 mm, and the porous silicon-based negative electrode material can be obtained through the steps of hydrochloric acid leaching, oxalic acid deep treatment, gradient solvent replacement and the like in sequence. The invention innovatively provides a core thought of solid waste synergy-multi-component synergy modification-multi-phase synergy etching: diamond wire cutting silicon waste (DSSW), industrial waste aluminum and waste copper are taken as raw materials, phosphorus (P), strontium (Sr) and other optional modification elements are introduced, and the submicron porous silicon-based negative electrode material is prepared by adopting an aluminum-silicon-copper alloy method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery silicon-based negative electrode material preparation and solid waste resource utilization, and more particularly to a method for preparing submicron porous silicon-based negative electrode material by taking diamond wire cutting silicon waste (DSSW) and industrial waste aluminum and waste copper as raw materials, through aluminum-silicon-copper alloy method and combining phosphorus and strontium multi-component collaborative modification technology. BACKGROUND

[0002] Silicon (Si) is considered as one of the most potential anode materials for the next generation of high energy density lithium ion batteries due to its extremely high theoretical specific capacity (about 4200 mAh / g) and abundant reserves. However, it faces core challenges in practical application: up to 300%~400% volume change when lithium ions are inserted / extracted, leading to electrode material structure breakage, solid electrolyte interface (SEI) film continuous thickening and active material shedding, thus causing capacity rapid decay and cycle life shortening. To solve the above problems, current research focuses on nano-structuring, compounding and poration strategies. Among them, the porous silicon structure can effectively accommodate volume expansion, shorten the lithium ion diffusion path, and maintain structural integrity, which is one of the important directions to break through the application bottleneck of silicon anode.

[0003] Under the promotion of the "double carbon" goal, China's photovoltaic industry has been developing at a high speed. A large amount of diamond wire cutting silicon waste (DSSW) is produced in the process of silicon wafer diamond wire cutting, which contains about 35%~40% high-purity silicon (purity usually >99.5%), but most of it has not been recycled and utilized at high value. On the other hand, the explosive growth of the new energy vehicle industry has produced a large amount of retired lithium battery structural parts and electrode materials containing aluminum and copper. Traditional recycling strategies often focus on purifying DSSW for photovoltaic-grade silicon or simply remelting waste aluminum / waste copper for regeneration, without being able to synergistically convert the two types of solid waste and directly use them for green preparation of high-end battery materials.

[0004] Therefore, a new method is developed to economically and efficiently prepare high-performance silicon-based negative electrode material with submicron porous structure by taking diamond wire cutting silicon waste and industrial waste aluminum and waste copper as core raw materials, through multi-component alloy design, controllable solidification and selective etching technology, which not only can greatly reduce the raw material cost of the negative electrode material (expected to reduce more than 90%), perfectly fit the national strategy of circular economy and resource regeneration, but also provides a new technical path to solve the volume expansion problem of silicon-based negative electrode, which has great economic, environmental and social benefits. SUMMARY

[0005] Therefore, the present application provides a method for preparing porous silicon-based negative electrode material by synergistically phosphorus and strontium superfine of silicon aluminum copper waste.

[0006] Porous silicon has become one of the ideal material systems to solve the problem of volume expansion of silicon negative electrode due to its unique three-dimensional interconnected pore structure and high specific surface area. The pores can provide buffer space for volume change, enhance structural stability, and facilitate electrolyte infiltration and rapid ion transport.

[0007] Based on this, the application innovatively proposes the core idea of "solid waste coordination-multi-component coordination modification-multi-phase coordination etching": taking diamond wire cutting silicon waste (DSSW) and industrial waste aluminum and waste copper as raw materials, introducing phosphorus (P), strontium (Sr) and other optional modification elements, and using aluminum-silicon-copper alloy method to prepare sub-micron porous silicon-based negative electrode material.

[0008] The application is realized by the following key technologies:

[0009] The industrial waste aluminum and the silicon waste form a low melting point eutectic system (Al-Si eutectic point 577 DEG C), which greatly reduces the energy consumption; the industrial waste copper introduces the easily etched CuAl2 phase, which provides a fast channel for high-efficiency and environmentally friendly acid immersion.

[0010] The "phosphorus-strontium" modification technology is innovatively used: phosphorus (P) is used as a nucleating agent to refine primary silicon, strontium (Sr) is used as a modifier to refine eutectic silicon, and both of them realize the synchronous ultra-fining of silicon phase, which fundamentally improves the mechanical properties and electrochemical uniformity of the material.

[0011] The process integrates the closed-loop process of "pretreatment → multi-component smelting → ultra-fast condensation → crushing → staged acid leaching (hydrochloric acid to remove aluminum / copper + oxalic acid to complex residual aluminum) → gradient solvent displacement → vacuum drying" to realize the efficient dissolution and recovery of waste aluminum and waste copper, and the high-fidelity formation of porous silicon structure.

[0012] The application converts photovoltaic silicon solid waste and battery recycling metal waste into high-value battery materials, not only reduces the cost of silicon-based negative electrode raw materials to the level of ten thousand yuan / ton (more than 90% reduction compared with commercial nano-silicon), greatly reduces the carbon emissions of the production process, but also realizes the transformation of solid waste into treasure, and has significant economic and ecological benefits.

[0013] In order to achieve the above purpose, the application provides a method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and phosphorus-strontium ultra-fining, which comprises the following steps:

[0014] (1) Pretreatment: The battery recycling scrap aluminum is calcined to remove surface oil; the industrial scrap copper is calcined to remove surface organic matter and insulating paint film, and then soaked in hydrochloric acid solution to completely remove copper oxides; the silicon scrap is etched in a mixed acid solution to remove the SiO2 layer; all the pretreated materials are washed with deionized water until neutral, and then washed alternately with deionized water and ethanol, and then vacuum dried to obtain high-purity silicon powder, the surface hydroxyl group is replaced by a hydrophobic H-terminated surface, and then dried at a temperature of 80°C and a vacuum degree of ≤-0.095 MPa for 12 hours, and high-purity nitrogen (N2) can be filled to create a protective atmosphere to prevent oxidation of the material and ensure complete drying;

[0015] The purpose of using ethanol for washing is to prevent the powder from agglomerating during the drying stage.

[0016] (2) Mixed melting: The pretreated battery recycling scrap aluminum, high-purity silicon powder, industrial scrap copper, and alloy raw materials are mixed uniformly, the surface of the melt is covered with a covering agent to isolate air, and an electromagnetic induction heating device is used to completely melt into a melt under an argon atmosphere, and the melt is kept at 850-950°C for 5-30 min to obtain a uniform silicon-aluminum-copper melt, which is completely melted and homogenized in composition, and finally solidified to obtain a multi-phase structure containing primary silicon, α-Al dendrites, Al-Si eutectic, and CuAl2 intermetallic compounds;

[0017] In the above operation: the addition of copper can refine the grains and synergistically enhance the effect with phosphorus. In addition, the copper phase is easier to remove with mild acid solution, reducing the use of HF and being more environmentally friendly and safe.

[0018] Melting under an argon (Ar) atmosphere is strictly prohibited, as silicon will volatilize extremely severely under vacuum at high temperatures.

[0019] In the Al-Si-Cu ternary system, copper mainly forms intermetallic compound CuAl2 (θ phase). The melting point of CuAl2 is about 591°C, but its complete dissolution in the alloy melt requires a higher temperature.

[0020] If the temperature is too low (such as 720°C), the CuAl2 phase may not be completely dissolved, resulting in uneven composition in the melt, and the CuAl2 phase is coarse and unevenly distributed after solidification, which will seriously affect the uniformity of subsequent acid leaching for pore formation.

[0021] The more alloying elements, the higher the requirement for the fluidity of the melt to ensure sufficient diffusion of each component and prevent composition segregation. Higher temperature (850°C) can significantly reduce the viscosity of the melt and improve the fluidity, making the distribution of elements such as Cu, P, and Si more uniform. This is a prerequisite for obtaining a fine and uniform microstructure.

[0022] (3) Controllable solidification: The uniform Al-Si-Cu melt is cast through a 1mm wide nozzle slit onto a rotating copper roller with a high cooling rate of 10 5 ~10 7 K / s. The melt spreads on the roller surface to form a stable melt pool. The melt at the bottom of the melt pool is cooled rapidly to form a continuous Al-Si-Cu alloy thin strip with a thickness of 280μm.

[0023] (4) Breaking: The Al-Si-Cu alloy thin strip is broken into 0.5-10mm pieces, and the fine powder is removed by sieving to obtain Al-Si alloy thin strip pieces.

[0024] (5) Hydrochloric acid leaching (to remove main Al and CuAl2): The Al-Si-Cu alloy thin strip pieces are added to hydrochloric acid in a covered reaction tank, and stirred to react. After the reaction, the filter cake 1 is obtained by filtration, and is ready for use.

[0025] The hydrochloric acid leaching step is aimed at efficiently removing the main Al phase and CuAl2 intermetallic compound in the alloy.

[0026] (6) Oxalic acid deep treatment (complexing and removing residual Al): The filter cake 1 is added to a 5wt% oxalic acid aqueous solution, and stirred to react under constant temperature. After the reaction, the filter cake 2 is obtained by filtration, and is ready for use.

[0027] The oxalic acid deep treatment step is aimed at complexing and removing residual Al and preventing its redeposition.

[0028] The above oxalic acid aqueous solution can optionally add 1-3wt% citric acid as a complexing enhancer, and can also add corrosion inhibitors such as benzotriazole (BTA) or thiourea.

[0029] (7) Gradient solvent replacement: To ensure that the porous silicon nanostructure is not damaged by capillary force during drying, strict gradient solvent replacement is carried out. The specific steps are as follows: first, primary dehydration with ethanol, the filter cake 2 is added to anhydrous ethanol at a solid-liquid ratio of 1:5g / mL, and is stirred for 5min before filtration. This process is repeated twice to replace most of the water; then anhydrous ethanol is replaced by tert-butyl alcohol for stirring and filtration, and the low surface tension (only 1 / 3 of water) is used to completely replace the residual ethanol and water, which fundamentally eliminates the risk of structure collapse caused by capillary force during drying.

[0030] (8) Vacuum drying: After filtration, the material is transferred to a vacuum drying oven and dried at 80℃ and a vacuum degree of ≤-0.095MPa for 12h. High-purity nitrogen can be filled several times during the process to maintain a protective atmosphere, prevent oxidation of the material, and ensure heat conduction to promote complete drying. The porous silicon-based negative electrode material is obtained.

[0031] Preferably, in step (1), the mixed acid solution is a mixture of 2.5wt% HF and 3wt% CH3COOH (acetic acid buffer), with a total acid concentration of 5.5wt%, and the solid-liquid ratio of the silicon waste to the mixed acid solution is 1:3 g / mL, and the etching is carried out at 30°C for 30 min.

[0032] Preferably, in step (2), the alloy raw material is an alloy containing phosphorus and strontium; and the covering agent is a mixed salt of NaCl-KCl.

[0033] In the above operation: P is effective for primary silicon, and Sr is effective for eutectic silicon, and the target is to solve the problem of synchronous refinement of the two.

[0034] Preferably, the pre-processed battery recycling waste aluminum, industrial waste copper, high-purity silicon powder and alloy raw material are mixed according to the atomic percentage of Al:Si:Cu:P:Sr being (40-80 at%):(20-30 at%):(5-15 at%):(1-5 at%):(0.05 at%-0.5 at%).

[0035] Preferably, the alloy raw material further contains one or more auxiliary elements selected from the group consisting of Ca, Sn, Ge, rare earth elements, high-melting-point metal elements and non-metallic elements.

[0036] Among them, the rare earth elements are selected from one or more of Nd, Sm, Gd, Ce, La, Y; the high-melting-point metal elements are selected from one or more of Ti, Zr, V, Nb, Cr; and the non-metallic elements are selected from one or more of B, C, N.

[0037] Preferably, in step (5), the preparation process of the hydrochloric acid is as follows: 100 mL of concentrated hydrochloric acid is slowly added to 900 mL of deionized water and stirred to mix, to prepare a 10vol% hydrochloric acid aqueous solution, and 0.05vol% Triton X-100 is added as a wetting agent and mixed; the solid-liquid ratio of the silicon-aluminum-copper alloy thin strip fragments to the hydrochloric acid is 1:15 g / mL; and the reaction is carried out at a constant temperature of (60±2) °C under mechanical stirring at 300 rpm for 4 h.

[0038] In the above operation: moderate heating can accelerate the reaction process, and a sealed container can prevent volatilization and maintain a moderate internal pressure to promote the reaction to proceed fully.

[0039] Preferably, in step (5), the reaction endpoint is determined by the rate of hydrogen gas bubble generation - a large number of hydrogen gas bubbles are generated at the beginning, and the rate decreases to less than 10% of the initial rate at the end, indicating completion. After the reaction is completed, immediately perform suction filtration separation and discard the filtrate.

[0040] The operation of the filtration separation is: repeating the "water dispersion-stirring-filtration" step 3-4 times with 60°C deionized water, washing the filter cake until the filtrate is neutral, using 0.1M AgNO3 solution to detect the last washing filtrate until the filtrate remains clear after dropping into the AgNO3 solution, without white AgCl precipitate, indicating that the chloride ion has been completely washed out.

[0041] In the above operation: the reaction of hydrochloric acid and aluminum is very violent itself, and the chemical driving force provided is already large enough. At a suitable temperature (60°C) and mechanical stirring (300 rpm), the reaction can be efficiently and sufficiently carried out. The ultrasonic is unnecessary in this step. Between the transition from "hydrochloric acid leaching" to "oxalic acid deep treatment", a thorough intermediate washing must be carried out. This step is crucial and directly determines the effect of the subsequent oxalic acid treatment and the purity of the final product. A large amount of Cl - ions in the hydrochloric acid waste liquid will form complexes with some metal impurities if they are brought into the oxalic acid step, interfering with the reaction of oxalic acid with the target aluminum and affecting the purity of the final product. Using hot water: can significantly improve the solubility of ionic impurities (such as AlCl3) in water, and wash them out of the pores, with a much higher washing efficiency than cold water. Repeating the "water dispersion-stirring-filtration" step 3-4 times. Use 0.1M AgNO3 solution to detect the last washing filtrate. If the filtrate becomes turbid (white AgCl precipitate is generated), it means that there is still Cl - residual, and washing should continue. If the filtrate is clear and unchanged, it means that the Cl - has been basically washed out, and the next step of oxalic acid treatment can be carried out.

[0042] Preferably, in step (6), the operation of stirring reaction under constant temperature conditions is: stirring at 200 rpm for 6h under constant temperature conditions of (80±2)℃, which can significantly enhance the complexing ability of oxalic acid; to improve the reaction efficiency, 40kHz / 100W low-frequency ultrasound can be applied to assist the reaction to promote the reaction in the deep grain boundaries. The end of the reaction is determined by the light transmittance of the solution. When the light transmittance is not less than 90% measured at 600nm wavelength using a UV spectrophotometer, it indicates that the residual colloidal aluminum salt has been completely removed.

[0043] Preferably, in step (6), the operation of the filtration separation is: repeating the "water dispersion-stirring-filtration" step 3-4 times with 80°C hot deionized water, washing the filter cake until the filtrate is neutral, using 0.1M CaCl2 solution to detect the filtrate until no white precipitate is generated, ensuring that the oxalate ion is completely removed.

[0044] In the above operation: the oxalic acid deep treatment reaction is mild, mainly complexation reaction, and the rate is slow, and the aluminum surface has a dense Al2O3 passivation film. The high pressure microjet generated by ultrasonic cavitation can instantly break the film and accelerate the reaction initiation. Oxalic acid and citric acid form a synergistic complex effect, can form a more stable multi-complex with Al 3+ , further reduce the free Al 3+ concentration in the solution, prevent its redeposition, and have better deep purification effect. The corrosion inhibitor can preferentially adsorb on the surface of silicon to form an extremely thin protective film, extremely slightly inhibit the potential chemical corrosion of oxalic acid on the silicon skeleton, and better protect the nano structure of silicon while deep removing aluminum.

[0045] Through the above technical solution, compared with the prior art, the beneficial effects obtained by the application are:

[0046] 1. The application innovatively uses diamond wire cutting silicon waste (DSSW) and industrial waste aluminum and industrial waste copper to prepare sub-micron porous silicon-based negative electrode materials by an aluminum-silicon-copper alloy method. The core lies in: first, the inherent aluminum element in the raw material forms an Al-Si eutectic (eutectic temperature 577 DEG C), which significantly reduces the melting point of silicon; second, industrial waste copper is innovatively introduced, and a low-potential CuAl2 intermetallic compound phase is formed, which provides a fast channel for subsequent mild acid leaching selective aluminum removal; third, Fe, Mg and other elements in industrial waste aluminum and waste copper and Fe, B, P and other elements in silicon waste have "impurity complementary effect", and in-situ generate FeSi2, B2Fe, AlP and other easily soluble intermetallic compounds during eutectic process. These compounds act as heterogeneous nucleation cores to significantly refine alloy grains. More importantly, by actively adding P and Sr elements, "Sr-P synergistic modification" is realized, in which P acts as a nucleating agent to refine primary silicon, and Sr acts as a modifier to refine eutectic silicon, and the two synergistically act to realize synchronous ultra-fining of primary silicon and eutectic silicon, successfully converting impurities and added elements into "in-situ grain synergistic refinement" advantage. The process shows excellent removal effect on impurity elements, and can reduce the content of B, P and other impurities to a very low level. The obtained porous silicon precursor can meet the requirements of battery-grade materials. The prepared porous silicon negative electrode material has significant advantages in first coulombic efficiency, cycle stability and volume expansion control, and the performance is better than that of mainstream commercial nano-silicon negative electrode. The process can greatly reduce the cost of raw materials, and significantly reduce the carbon footprint of the production process, and has significant environmental and economic benefits.

[0047] 2. Based on the original "multi-phase synergistic regulation" alloy design, combined with ultrafast cooling planar flow casting technology, sub-micron porous silicon with micro-nano dual-scale pore structure can be successfully prepared. The material presents a continuous three-dimensional interconnected macroporous framework, and the framework is filled with abundant mesoporous structure. The material shows high specific surface area and high pore volume characteristics, and has typical type IV adsorption-desorption curve. Its reversible specific capacity is significantly higher than that of traditional graphite negative electrode, and the volume expansion rate during the first lithium intercalation process is effectively inhibited, which greatly improves the cycle stability, and simultaneously realizes high specific capacity and low volume expansion rate.

[0048] 3. The present application constructs a waste liquid / solvent closed-loop regeneration system, leading to green manufacturing. The hydrochloric acid leaching solution has improved reaction efficiency due to the presence of CuAl2 phase, and the treated waste liquid can be used to recover high-value-added by-products; the organic solvent can be efficiently reused through a recycling process. The carbon footprint of this process is significantly lower than that of traditional preparation methods, realizing the leap from "waste regeneration" to "zero waste manufacturing".

[0049] 4. The present application uses ultrasonic-assisted fractional acid leaching process to achieve deep removal of grain boundary residual metal in aluminum-silicon alloy. This process can reduce the residual aluminum and copper content in the final product to a low level, which helps to obtain more open, uniform and complete porous silicon pore structure, and improve the specific surface area of the material. When this material is used as the negative electrode of lithium ion battery, it shows high initial coulombic efficiency, which fully proves the great advantages of this process in improving the purity, pore structure and comprehensive performance of the material.

[0050] 5. Further, in order to enhance certain specific properties of the alloy, such as further improve the electrical conductivity, strength or improve the melt flowability, in some optional embodiments of the present application, the alloy can further comprise auxiliary elements selected from the following group: Ca, Sn, Ge, rare earth elements (such as Nd, Sm, Gd, Ce, La, Y), high melting point metal elements (such as Ti, Zr, V, Nb, Cr) and non-metallic elements (such as B, C, N). In particular, by adding high melting point metal elements and non-metallic elements in combination, nanoscale high hardness and high conductivity ceramic phases (such as TiC, VB2, ZrN, etc.) can be generated in situ in the alloy. These dispersed ceramic phases can further strengthen the porous silicon framework and improve its structural stability and electrical conductivity. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0052] Example 1: Intra-group variable design (alloy composition)

[0053] (1) Pretreatment:

[0054] The battery recycling scrap aluminum was calcined at 300°C for 1 h to remove surface oil stains; the industrial scrap copper was calcined at 400°C for 1.5 h to remove surface organic matter and insulating paint film, and then was immersed in a 15 vol% hydrochloric acid solution at 55°C for 20 min to completely remove copper oxides; the diamond wire cutting silicon waste was placed in a polytetrafluoroethylene beaker containing a 2.5 wt% HF + 3 wt% CH3COOH (acetic acid buffer) mixed acid solution to etch the SiO2 layer (total acid concentration: 5.5 wt%, solid-liquid ratio: 1:3, temperature: 30°C, time: 30 min). All pretreated materials were washed with deionized water to neutral, and then were washed with deionized water and anhydrous ethanol alternately for three times, the surface hydroxyl groups were converted to hydrophobic H-Terminated terminal groups by solvent replacement, and finally were dried at 80°C under a vacuum of ≤-0.095 MPa for 12 hours, and high-purity nitrogen (N2) was filled to maintain a protective atmosphere to prevent surface re-oxidation.

[0055] (2) Mixed smelting:

[0056] Aluminum (Al), silicon (Si), copper (Cu), and aluminum phosphorus (Al-P) intermediate alloys were configured according to the following five groups of mixtures in terms of Al:Si:Cu:P atomic percentage:

[0057] Example 1A: Al:Si:Cu:P = 74 at%:20 at%:5 at%:1 at% (low Cu low P reference group);

[0058] Example 1B: Al:Si:Cu:P = 60 at%:30 at%:5 at%:5 at% (low Cu high P group);

[0059] Example 1C: Al:Si:Cu:P = 62 at%:20 at%:15 at%:3 at% (high Cu medium P group);

[0060] Example 1D: Al:Si:Cu:P = 63 at%:25 at%:10 at%:2 at% (optimized balance group);

[0061] Example 1E: Al:Si:Cu:P = 51 at%:30 at%:15 at%:4 at% (high Cu high Si high P group).

[0062] The five groups of powders were mixed uniformly and placed in a quartz crucible, and the surface of the melt was covered with a mixture of NaCl-KCl salt to isolate the air. The melt was completely melted into a melt by an electromagnetic induction heating device under an argon (Ar) atmosphere, and then was kept at a temperature in the range of 850-950 °C for 5-30 min to completely melt and homogenize the composition, and finally solidified to obtain a multi-phase structure containing primary silicon, a-Al dendrites, Al-Si eutectic, and CuAl2 intermetallic compounds.

[0063] Note: The addition of copper can refine the grains and synergistically enhance the effect with phosphorus. In addition, the copper phase is easier to remove with mild acid, reducing the use of HF and being more environmentally friendly and safe.

[0064] (3) Controllable solidification:

[0065] The five groups of uniform aluminum-silicon-copper melts were respectively flowed through a 1 mm wide nozzle slit onto a high-speed rotating 10 m / s and well heat-conducting metal cooling copper roller by a planar flow casting cooling device. The melt was spread on the outer circumferential surface of the cooling roller to form a stable melt pool, and the melt at the bottom of the melt pool was rapidly cooled at a high rate to form a continuous aluminum-silicon-copper alloy thin strip with a thickness of 280 μm after contacting the roller surface. 5

[0066] (4) Breaking:

[0067] The five groups of precursor samples were respectively pretreated, and the precursor aluminum-silicon alloy thin strips were broken into 0.5-10 mm fragments, and <100 μm fine powder was removed by sieving.

[0068] (5) Hydrochloric acid leaching (remove main body Al & CuAl2):

[0069] The specific operation process of the five groups of samples is as follows: first, prepare 10 vol% hydrochloric acid aqueous solution, slowly add 100 mL concentrated hydrochloric acid into 900 mL deionized water and stir to mix uniformly. Then, according to the solid-liquid ratio of 1:15, the alloy powder is added into the acid solution (for example, 10 g powder corresponds to 150 mL acid solution), and placed in a covered reaction tank. The reaction is carried out at a constant temperature of (60±2) °C and 300 rpm mechanical stirring for 4 hours. The reaction endpoint is judged by the gas bubble generation rate - initially a large amount of hydrogen gas bubbles are generated, and at the end the rate is reduced to less than 10% of the initial rate. Immediately after the reaction is completed, the filter separation is carried out, and the filtrate is discarded. The steps of "dispersion-stirring-filtration" are repeated 3-4 times with 60 °C hot deionized water, and the filter cake is washed until the filtrate is neutral (pH=7). The last washing filtrate is detected with 0.1 M AgNO3 (silver nitrate) solution until the filtrate remains clear after dropping into the AgNO3 solution, without white AgCl precipitate being generated, indicating that the chloride ions have been completely washed out.

[0070] (6) Oxalic acid deep treatment (complexing and removing residual aluminum):​

[0071] The following operations were performed on the five groups of samples: 5wt% oxalic acid aqueous solution was used as the reaction medium, and the specific preparation method was to dissolve 50g of oxalic acid crystals in 950mL of hot deionized water at about 60°C and stir until completely dissolved. The reaction was carried out at a solid-liquid ratio of 1:10 (for example: take the washed filter cake and add 100mL of oxalic acid solution), and stirred at 200rpm under constant temperature conditions of (80±2) °C for 6 hours. This high temperature condition can significantly enhance the complexing ability of oxalic acid; in order to improve the reaction efficiency, 40kHz / 100W low frequency ultrasound can be applied to promote the reaction in the deep grain boundary. The reaction endpoint was determined by the transmittance of the solution. When the transmittance was not less than 90% at 600nm wavelength measured by ultraviolet spectrophotometer, it indicated that the residual colloidal aluminum salt had been completely removed. After the reaction was completed, the filter cake was separated by suction filtration, and the "water dispersion-stirring-suction filtration" steps were repeated 3-4 times with 80°C hot deionized water. The filter cake was washed until the filtrate was neutral (pH=7). The filtrate was detected with 0.1M CaCl2 solution until no white precipitate (calcium oxalate) was produced, ensuring that the oxalate ion (C2O4 2- ) was completely removed.

[0072] (7) Gradient solvent replacement:

[0073] In order to ensure that the porous silicon nanostructure is not damaged by capillary force during the drying process, gradient solvent replacement was strictly performed on the five groups of samples. The specific steps are as follows: first, primary dehydration with ethanol, the filter cake after acid immersion was transferred to a beaker, anhydrous ethanol was added according to a solid-liquid ratio of 1:5, and after stirring for 5 minutes, suction filtration was performed. This process was repeated twice to replace most of the water; then, t-butanol final replacement, in the third replacement operation, t-butanol (t-Butanol) was used according to the same solid-liquid ratio of 1:5 for stirring and suction filtration. Its extremely low surface tension (only 1 / 3 of water) completely replaced the residual ethanol and water, fundamentally eliminating the risk of structure collapse caused by capillary force during the drying process.

[0074] (8) Vacuum drying:

[0075] The five groups of materials after t-butanol replacement were placed in a vacuum drying oven at a temperature of 80°C and a vacuum degree of ≤-0.095MPa for 12 hours. High-purity nitrogen (N2) was filled several times during the process to maintain a protective atmosphere, prevent material oxidation, and ensure heat conduction to promote complete drying.

[0076] Comparative Example 1: No additional P addition

[0077] The difference from Example 1 is only in step (2) of mixing and melting:

[0078] Aluminum (Al), Silicon (Si), Copper (Cu) are configured in atomic percentage Al:Si:Cu = 65 at%:25 at%:10 at%, uniformly mixed and placed into a quartz crucible, the surface of the melt is covered with a covering agent NaCl-KCl mixed salt to isolate air. It is completely melted into a melt under an argon (Ar) atmosphere by using an electromagnetic induction heating device, then kept at 850°C for 5-30 min, so that it is completely melted and composition homogenized, and finally solidified to obtain a multi-phase structure containing primary silicon, alpha-Al dendrites, Al-Si eutectic and CuAl2 intermetallic compounds.

[0079] Note: Proportion based on Example 1D, but replace the share of P with Al, become Al:Si:Cu = 65:25:10 at%, and no Al-P intermediate alloy is added.

[0080] Comparative Example 2: Modification with Strontium (Sr) alone

[0081] Purpose: Based on Comparative Example 1, but adding Sr, to prove that using Sr alone cannot solve the problem of primary silicon coarsening.

[0082] The difference from Comparative Example 1 is only in step (2) mixing and melting:

[0083] Aluminum (Al), Silicon (Si), Copper (Cu) and Aluminum Strontium (Al-10Sr) intermediate alloy are configured in atomic percentage Al:Si:Cu:Sr = 74 at%:20 at%:5 at%:1 at%, uniformly mixed and placed into a quartz crucible, the surface of the melt is covered with a covering agent NaCl-KCl mixed salt to isolate air. It is completely melted into a melt under an argon (Ar) atmosphere by using an electromagnetic induction heating device, then kept at 850-950°C for 5-30 min, so that it is completely melted and composition homogenized, and finally solidified to obtain a multi-phase structure containing primary silicon, alpha-Al dendrites, Al-Si eutectic and CuAl2 intermetallic compounds.

[0084] Note: No Al-P intermediate alloy is added, only relying on the trace amount of phosphorus inherent in the raw materials.

[0085] Example 2: Strontium-Phosphorus (Sr-P) synergistic modification optimization group (Sr content gradient experiment)

[0086] Note: On the basis of the preferred best formula (such as 1D), a second variable Sr is introduced to show the surpassing effect of the "P+Sr" synergistic effect.

[0087] The difference from Example 1D is only in step (2) mixing and melting:

[0088] Aluminum (Al), Silicon (Si), Copper (Cu), Aluminum Phosphorus (Al-P) master alloy, Aluminum Strontium (Al-Sr) master alloy are configured in the following three groups of mixtures according to the atomic percentage of Al:Si:Cu:P:Sr:

[0089] Example 2A: Al:Si:Cu:P:Sr = 62.95at%:25at%:10at%:2at%:0.05at% (low Sr group);

[0090] Example 2B: Al:Si:Cu:P:Sr = 62.8at%:25at%:10at%:2at%:0.2at% (medium Sr group);

[0091] Example 2C: Al:Si:Cu:P:Sr = 62.5at%:25at%:10at%:2at%:0.5at% (high Sr group).

[0092] The three groups of powders are uniformly mixed and placed in a quartz crucible, and the surface of the melt is covered with a covering agent NaCl-KCl mixed salt to isolate air. The complete melting into a melt is carried out using an electromagnetic induction heating device under an argon (Ar) atmosphere, and then the temperature is kept at 850°C for 5-30 min to completely melt and homogenize the composition, and finally solidification to obtain a multi-phase structure containing primary silicon, a-Al dendrites, Al-Si eutectic and CuAl2 intermetallic compounds.

[0093] Note: On the basis of Example 1D, an Al-Sr master alloy is additionally added, and the addition amount of Sr is usually 0.02-0.1wt% (about 0.02-0.1at%), and 0.2at% is selected here as an effective and common dosage range. The 0.2at% of Sr is deducted from the share of Al, so that Al is adjusted from 63at% to 62.8at%. The proportions of other elements remain unchanged.

[0094] Example 3: Slow solidification control group

[0095] The difference from Example 2 is only in step (2) mixing and melting:

[0096] Aluminum (Al), Silicon (Si), Copper (Cu), Aluminum Phosphorus (Al-P) master alloy, Aluminum Strontium (Al-Sr) master alloy are configured in the following three groups of mixtures according to the atomic percentage of Al:Si:Cu:P:Sr Al:Si:Cu:P:Sr = 62.95at%:25at%:10at%:2at%:0.2at% (medium Sr group);

[0097] and step (3) controllable solidification:

[0098] No planar flow casting cooling device was used. Instead, the melt was poured into a low carbon steel mold preheated to 200 °C (mold cavity size: 100 mm long x 50 mm wide x 5 mm thick). The melt was cooled statically in the steel mold to room temperature at a cooling rate of about 50-100 K / s, resulting in an alloy ingot with a thickness of about 5 mm.

[0099] Note: This cooling rate is 3 orders of magnitude lower than the cooling rate of the example (~1 x 10 5 K / s), providing sufficient time for the full growth of the crystal structure.

[0100] Comparative Example 3: No Copper (Cu) Group

[0101] The difference from Example 2 is only in step (2) mixed melting:

[0102] Aluminum (Al), silicon (Si), aluminum phosphorus (Al-P) intermediate alloy, aluminum strontium (Al-Sr) intermediate alloy were configured according to the atomic percentage of Al:Si:P:Sr Al:Si:P:Sr = 70.3 at%:27.5 at%:2 at%:0.2 at%.

[0103] Comparative Example 4: Ordinary water washing process

[0104] Note: The traditional and simple post-processing method of using deionized water for washing and drying in a normal pressure oven will cause irreversible collapse and contamination of the porous silicon nanostructure, thereby seriously deteriorating its electrochemical performance as a battery anode material. This contrasts with the key and advanced nature of the "organic solvent replacement-vacuum drying" or "tert-butyl alcohol replacement-supercritical drying" process in the present invention.

[0105] The difference from Example 2 is only in step (2) mixed melting:

[0106] Aluminum (Al), silicon (Si), copper (Cu), aluminum phosphorus (Al-P) intermediate alloy, aluminum strontium (Al-Sr) intermediate alloy were configured according to the atomic percentage of Al:Si:Cu:P:Sr Al:Si:Cu:P:Sr = 62.95 at%:25 at%:10 at%:2 at%:0.2 at% (Sr group).

[0107] And without step (7) gradient solvent replacement.

[0108] Note: This step only uses water for washing, without solvent replacement using ethanol or tert-butyl alcohol.

[0109] The porous silicon materials prepared in the examples and comparative examples were systematically tested and characterized for performance:

[0110] Material structure characterization: X-ray diffraction (XRD) was used to analyze the phase composition; scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) were used to observe the microstructure of the hierarchical pores; nitrogen adsorption-desorption test (BET) was used to determine the specific surface area, pore volume and pore size distribution; X-ray photoelectron spectroscopy (XPS) was used to analyze the surface elemental composition and chemical state to verify the residual metal content.

[0111] Electrochemical performance test: The material was assembled into a CR2032 type button half-cell, and constant current charge-discharge test was carried out using a blue electric test system to evaluate its specific capacity, first coulombic efficiency and long cycle stability; cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests were carried out by electrochemical workstation to explore the lithium intercalation and deintercalation mechanism and interface impedance; lithium ion diffusion coefficient was calculated by using constant current intermittent titration technique (GITT) to analyze the reaction kinetics characteristics.

[0112] Mechanism in-depth analysis: Raman spectroscopy was used to analyze the crystal structure of the material; battery capacitance dual-mode energy storage analysis was used to quantify the contribution ratio of surface capacitance effect and diffusion control during charge and discharge process, and to reveal the high-performance dynamics source in depth.

[0113] Extended explanation:

[0114] It should be particularly noted that the above examples are only the preferred specific implementation modes for illustrating the core idea of the present application, but the protection scope of the present application is by no means limited to the specific components and proportions listed above. Those skilled in the art should fully understand that various adjustments, modifications and modifications can be made to the alloy system without departing from the design principle of the present application, i.e. "realizing silicon phase synchronous refinement and constructing easy-etching multi-phase structure through multi-group element collaborative design", and these changes should be considered as falling within the protection scope of the present application.

[0115] The adjustments and modifications include but are not limited to:

[0116] Introducing second phase strengthening particles: In order to further improve the mechanical strength and electronic conductivity of the porous silicon skeleton, the following element combination which can generate in-situ nanoscale high hardness and high conductivity ceramic phase can be introduced into the Al-Si-Cu-P-Sr basic system:

[0117] Adding 0.1-1 at% of active metal elements such as Ti, Zr, V, Nb, Cr, Mo and W, and 0.1-1 at% of non-metallic elements such as C, B and N.

[0118] During the smelting process, the aforementioned elements can react to generate dispersed nano-ceramic particles such as TiC, ZrC, VB2, NbC, CrB2, Mo2B, and WN. These particles not only pin grain boundaries and further refine the grains, but also remain in the porous silicon framework after subsequent acid leaching, playing a dual role as a reinforcing body and a conductive network, significantly improving the cycle stability and rate performance of the electrode material.

[0119] Example formulation: Based on Example 2B (Al:Si:Cu:P:Sr = 62.8:25:10:2:0.2), add an additional 0.5 at% Ti and 0.5 at% C.

[0120] Introducing rare earth elements for deep purification and microalloying: To deeply purify the melt, improve melt flowability, and achieve unique grain boundary segregation strengthening, the following elements can be added:

[0121] Add 0.01-0.5 at% of rare earth elements, including but not limited to La, Ce, Pr, Nd, Sm, Gd, Y and their mixed rare earths (such as MM-mixed metals, Ce-rich rare earths).

[0122] Rare earth elements preferentially react with harmful impurities such as oxygen, sulfur, and hydrogen in the melt to form high-melting-point compounds that float to the slag, thus playing a refining and purifying role. At the same time, trace amounts of rare earth elements adsorbed at grain boundaries or phase boundaries can effectively reduce interfacial energy, inhibit grain growth, and may alter the growth morphology of eutectic silicon.

[0123] Example formulation: Based on Example 1D, add 0.1 at% Ce.

[0124] Utilizing other low-melting-point metallic elements to adjust microstructure and properties: The following elements can be introduced to adjust the solidification range of an alloy, improve processability, or introduce other functional properties:

[0125] Add 0.1-5 at% of low-melting-point metal elements such as Sn, Ge, Ga, and In.

[0126] These elements are soluble in the silicon or aluminum phase, altering their electronic structure or chemical activity, which may help to form a more uniform corrosion or regulate the surface chemical state of porous silicon during acid leaching.

[0127] Synergistic effect of compatibility with background impurity elements: A major advantage of this invention lies in its high tolerance and conversion of inherent impurity elements in industrial waste. Therefore, the alloy system naturally contains and is compatible with the following elements:

[0128] Fe (≤0.5at%), Mg (≤0.3at%), Zn (≤0.3at%), Mn (≤0.2at%), Ni (≤0.1at%), etc.

[0129] These elements can form phases such as Al5FeSi, Mg2Si, AlSiMn, etc. Through the ultrafast cooling process of the present application, these phases can be controlled at the nanometer or sub-micron scale, whose presence does not necessarily impair the performance, and even in the subsequent acid leaching can be preferentially dissolved over silicon phases, helping to form a more abundant multi-level pore structure.

[0130] Other modifying elements: In addition, elements such as Li, Ag, etc. can be used to fine-tune the electrode potential of the alloy; Ca can be used to assist modification; Cr can be used to enhance corrosion resistance (but the amount needs to be controlled to avoid excessive impact on acid leaching). The addition of these elements is within the scope of consideration of the present application.

[0131] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a porous silicon-based anode material by using silicon-aluminum-copper waste and synergizing with strontium phosphate superfine, characterized in that, The method comprises the following steps: (1) Pretreatment: roasting battery recycling waste aluminum to remove surface oil stains; roasting industrial waste copper to remove surface organic matter and insulating paint film, and then soaking in hydrochloric acid solution; etching silicon waste in mixed acid solution; washing all pretreated materials with deionized water to neutral, and then washing with deionized water and ethanol alternately, and then vacuum drying to obtain high-purity silicon powder for standby; (2) Mixed smelting: mixing the pretreated battery recycling waste aluminum, industrial waste copper, high-purity silicon powder and alloy raw materials uniformly, completely covering with covering agent, completely melting into melt under argon atmosphere by electromagnetic induction heating device, and then keeping at 850-950℃ for 5-30 min to obtain uniform silicon aluminum copper melt; (3) Controllable solidification: preparing the uniform aluminum silicon melt into continuous silicon aluminum copper alloy thin strip by using plane flow casting cooling device; (4) Crushing: crushing the silicon aluminum copper alloy thin strip to 0.5-10 mm, removing fine powder by sieving, and obtaining aluminum silicon alloy thin strip fragments; (5) Hydrochloric acid leaching: adding the silicon aluminum copper alloy thin strip fragments into hydrochloric acid, stirring and reacting in a covered reaction tank, immediately performing suction filtration separation after the reaction is completed, and obtaining filter cake 1 for standby; (6) Oxalic acid deep treatment: adding the filter cake 1 into 5wt% oxalic acid aqueous solution, stirring and reacting under constant temperature condition, performing suction filtration separation after the reaction is completed, and obtaining filter cake 2 for standby; (7) Gradient solvent replacement: firstly performing primary dehydration with ethanol, adding the filter cake 2 into anhydrous ethanol, stirring and then performing suction filtration, and repeating the process twice; then replacing the anhydrous ethanol with tert-butyl alcohol for stirring and suction filtration; (8) Vacuum drying: drying in a vacuum drying box after suction filtration, and filling high-purity nitrogen several times to maintain protective atmosphere during the process, so that the porous silicon-based negative electrode material is obtained.

2. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (1), the mixed acid solution is a mixed solution of 2.5wt% HF and 3wt% CH3COOH, the total acid concentration is 5.5wt%, the solid-liquid ratio of silicon waste to mixed acid solution is 1:3g / mL, and the etching is 30℃ etching for 30 min.

3. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (2), the alloy raw material is an alloy containing phosphorus and strontium; and the covering agent is NaCl-KCl mixed salt.

4. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 3, characterized in that, The pretreated battery recycling waste aluminum, industrial waste copper, high-purity silicon powder and alloy raw material are mixed according to the atomic percentage of Al:Si:Cu:P:Sr being (40-80at%):(20-30at%):(5-15at%):(1-5at%):(0.05at%-0.5at%).

5. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 3, characterized in that, On the basis of the alloy raw material, the auxiliary elements are also contained, which are selected from one or more of Ca, Sn, Ge, rare earth elements, high-melting-point metal elements and non-metallic elements; wherein the rare earth elements are selected from one or more of Nd, Sm, Gd, Ce, La and Y; the high-melting-point metal elements are selected from one or more of Ti, Zr, V, Nb and Cr; and the non-metallic elements are selected from one or more of B, C and N.

6. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (3), the solidification process of the plane flow casting cooling device is: The uniform aluminum-silicon melt is flowed through a 1mm wide nozzle slit to a metal cooling copper roller rotating at a high speed of 10-50m / s and having good heat conductivity, the melt spreads on the outer circumferential surface of the cooling roller at a cooling rate of about 10 5 -10 7 K / s to form a stable melt pool, the melt at the bottom of the melt pool is rapidly cooled at a high rate after contacting the roller surface to form a continuous aluminum-silicon alloy thin strip with a thickness of 280μm.

7. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (5), the preparation of hydrochloric acid is as follows: 100 mL of concentrated hydrochloric acid is slowly added to 900 mL of deionized water and stirred to mix, 10 vol% hydrochloric acid aqueous solution is prepared, and 0.05 vol% Triton X-100 is added as a wetting agent and mixed; the solid-liquid ratio of the silicon-aluminum-copper alloy ribbon fragments to hydrochloric acid is 1:15 g / mL; the reaction is carried out at a constant temperature of (60±2) °C under mechanical stirring at 300 rpm for 4 h.

8. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (5), the operation of separating by suction filtration is as follows: the "water dispersion-stirring-suction filtration" step is repeated 3-4 times with 60 °C deionized water, the filter cake is washed until the filtrate is neutral, the last washing filtrate is detected with 0.1 M AgNO3 solution until the filtrate remains clear after being dropped into the AgNO3 solution, and no white AgCl precipitate is generated.

9. The method for preparing porous silicon-based negative electrode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (6), the operation of stirring reaction under constant temperature conditions is as follows: the reaction is stirred at a constant temperature of (80±2) °C under a stirring speed of 200 rpm for 6 h, and 40 kHz / 100 W low-frequency ultrasound is applied to assist the reaction.

10. The method for preparing porous silicon-based anode material by using silicon-aluminum-copper waste and cooperatively superfine strontium phosphate according to claim 1, characterized in that, In step (6), the operation of separating by suction filtration is as follows: the "water dispersion-stirring-suction filtration" step is repeated 3-4 times with 80 °C hot deionized water, the filter cake is washed until the filtrate is neutral, the filtrate is detected with 0.1 M CaCl2 solution until no white precipitate is generated, and it is ensured that the oxalate ions are completely removed.