A method for recycling waste lithium-ion batteries

Abstract

The present invention belongs to the technical field of recycling and regeneration of waste lithium-ion batteries, and particularly relates to a method for recycling and reusing waste lithium-ion batteries. The recycling and reusing method of the present invention comprises the following steps: separating the positive electrode sheet and the negative copper foil from the waste lithium-ion battery; immersing the positive electrode sheet in a liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and calcining the separated positive electrode material to obtain a positive electrode active material; using the positive electrode active material as a raw material, preparing a regenerated positive electrode sheet after regeneration, and then assembling to prepare a regenerated lithium-ion battery; or using the negative copper foil, the positive electrode active material and a liquid second Ga-based alloy as raw materials to prepare a high-entropy alloy nanoparticle catalyst. There is no aluminum residue in the positive electrode active material separated by the present invention, and the separation method has minimal influence on the positive electrode material itself, and can well maintain its structural integrity.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling and regeneration of waste lithium - ion batteries, and particularly relates to a method for recycling and reusing waste lithium - ion batteries. Background Art

[0002] At present, the recycling and reusing of waste lithium - ion batteries have become a key area of resource recycling and environmental protection. Among them, waste lithium - ion batteries contain abundant high - value metals such as lithium, cobalt, and nickel. The recycling of these metals not only helps to alleviate the problem of resource shortage but also reduces the potential harm to the environment. In addition, the positive electrode sheets and negative copper foils of waste lithium - ion batteries are also important recyclable materials. The positive electrode sheet contains aluminum foil and positive electrode materials. Among them, as the carrier of high - value metal resources, the efficient separation and recycling of positive electrode materials are the key links in resource recycling.

[0003] At present, the separation methods for aluminum foil and positive electrode active materials mainly include heat treatment method, organic solvent dissolution method, and chemical corrosion method of aluminum foil with mineral acid. Among them, the heat treatment method reduces the adhesion force between active material particles by decomposing the binder at high temperature, thereby weakening the adhesion force between the active material layer and the aluminum foil to achieve the separation of the positive electrode active material and the aluminum foil. The organic solvent dissolution method uses an organic solvent with good solubility to treat the positive electrode sheet, causing the positive electrode active material to fall off from the aluminum foil. The chemical corrosion method of aluminum foil with mineral acid uses mineral acid to dissolve the aluminum foil to achieve the rapid separation of the aluminum foil and the active material.

[0004] However, the above - mentioned separation methods inevitably introduce aluminum residues in the separated positive electrode active materials, which not only increases the difficulty of subsequent recycling processes but also limits the application scope of the positive electrode active materials in waste lithium - ion batteries.

[0005] In addition, the existing technologies mainly focus on the recycling of single metals in waste lithium - ion batteries, making it difficult to fully utilize the potential value of positive electrode active materials and limiting the application of positive electrode active materials in waste lithium - ion batteries. Summary of the Invention

[0006] In order to solve the above - mentioned technical problems, the present invention provides a method for recycling and reusing waste lithium - ion batteries.

[0007] The present invention realizes the rapid, pollution - free, and low - energy - consumption separation of aluminum foil and positive electrode active material layer through the characteristics that the first Ga - based alloy can remain liquid at room temperature and the high wettability of the first Ga - based alloy to aluminum foil; based on the separated positive electrode active material, combined with the negative copper foil and the second Ga - based alloy, a synthesis method of high - entropy alloy nanoparticles catalyst is developed, which solves the problem of aluminum residues in the separated positive electrode active materials in the prior art and expands the application of positive electrode active materials.

[0008] The first object of the present invention is to provide a method for recycling waste lithium-ion batteries, comprising the following steps:

[0009] Separate the positive electrode plate and the negative copper foil from the waste lithium-ion battery.

[0010] Immerse the separated positive electrode plate into a liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and calcine the separated positive electrode material to obtain a positive electrode active material; the liquid first Ga-based alloy is a GaSn alloy; the mass percentage of Ga contained in the liquid first Ga-based alloy is 85% - 90%.

[0011] Using the positive electrode active material as a raw material, prepare a recycled positive electrode plate after regeneration, and then assemble it to prepare a recycled lithium-ion battery.

[0012] Alternatively, using the negative copper foil, the positive electrode active material and a liquid second Ga-based alloy as raw materials, prepare a high-entropy alloy nanoparticle catalyst; the liquid second Ga-based alloy is a GaIn alloy.

[0013] It should be noted that in order to prevent the waste lithium-ion battery from short-circuiting or self-igniting during the treatment process, the present invention uses brine immersion to discharge the waste lithium-ion battery until the voltage drops to 0V; then manually disassemble the battery package to take out the positive electrode plate and the negative copper foil.

[0014] It should also be noted that the first Ga-based alloy is a eutectic alloy that is liquid at room temperature and has excellent metal wettability and high activity. When the first Ga-based alloy contacts the aluminum foil in the positive electrode plate, the flowable first Ga-based alloy can quickly spread on the surface of the aluminum foil and penetrate into the microcracks, destroying the original aluminum oxide protective layer on the surface of the aluminum foil. At the same time, due to the high wettability of Ga atoms in the first Ga-based alloy to the aluminum foil, the Ga atoms can directly contact the aluminum foil matrix. The Ga atoms preferentially diffuse along the grain boundaries of the aluminum foil, weakening the grain boundaries, resulting in the fracture and disintegration of the aluminum foil structure; after the grains of the aluminum foil are eroded by the Ga atoms and gradually dissolved, the surface of the aluminum foil becomes powdery or porous, obtaining the positive electrode active material, realizing the rapid separation of the aluminum foil from the positive electrode active material.

[0015] Preferably, the mass percentage of Ga contained in the liquid first Ga-based alloy is 85% - 90%; more preferably, the mass percentage of Ga contained in the liquid first Ga-based alloy is 87.5%, because when there is too much or too little Ga, Ga or other metals in the first Ga-based alloy will precipitate at room temperature, causing waste.

[0016] Preferably, the GaSn alloy is prepared by the following method: mixing Ga and Sn and heating under vacuum conditions to obtain the GaSn alloy; the heating temperature is 300 °C, which can make Ga form a liquid state and synthesize the GaSn alloy with Sn.

[0017] To ensure complete reaction after the aluminum foil in the positive electrode sheet contacts the GaSn alloy, preferably, the immersion time is 30 min to 35 min.

[0018] Preferably, the calcination temperature during the separation of the positive electrode active material is 600 °C, and the time is 4 h to 6 h, so as to ensure complete reaction and removal of graphite and binder in the positive electrode material.

[0019] The present invention uses a negative electrode copper foil, a positive electrode active material, and a liquid second Ga-based alloy as raw materials to prepare a high-entropy alloy nanoparticle catalyst. The high-entropy alloy nanoparticle catalyst has a relatively high specific surface area and unique catalytic activity, thus playing an important role in the fields of organic liquid flow battery catalysis and nitrate reduction catalysis. Through this recycling method, the positive electrode material and negative electrode copper foil of waste batteries can be recycled, which not only reduces the environmental burden of electronic waste but also provides a new way for the green synthesis of catalysts.

[0020] Preferably, the specific method for preparing the high-entropy alloy nanoparticle catalyst is as follows:

[0021] Dissolve the separated negative electrode copper foil and the liquid second Ga-based alloy in a solvent, perform fragmentation to obtain a nanoparticle solution; mix the nanoparticle solution and the positive electrode active material evenly to obtain a precursor solution; place the precursor solution on a carbon paper and perform pulsed heating under a vacuum environment to obtain the high-entropy alloy nanoparticle catalyst.

[0022] It should be noted that the liquid second Ga-based alloy is a GaIn alloy. The Ga atoms in the GaIn alloy have a relatively negative mixing enthalpy with the Cu atoms in the copper foil, the Co atoms and Fe atoms in the positive electrode active material, which makes the atoms tend to be affinity; at the same time, the liquid GaIn alloy has high diffusivity and can quickly react with other metal atoms; and at high temperatures, this diffusion effect will accelerate the mixing of metal atoms, creating conditions for the formation of high-entropy alloys.

[0023] Preferably, the GaIn alloy is prepared by the following method: mixing Ga and In and heating under vacuum conditions to obtain the GaIn alloy.

[0024] Preferably, the mass percentage of Ga contained in the GaIn alloy is 70% to 80%; more preferably, the mass percentage of Ga contained in the GaIn alloy is 75%, because when there is too much or too little Ga, Ga or In will precipitate at room temperature, causing waste.

[0025] Preferably, the heating temperature for preparing the GaIn alloy is 300 °C so that Ga is in a liquid state to synthesize the GaIn alloy with In.

[0026] Preferably, the positive electrode active material is a mixture of LiCoO2 positive electrode active material and LiFePO4 positive electrode active material.

[0027] Preferably, the mass ratio of the liquid second Ga-based alloy to the negative electrode copper foil is 2:1; the mass of the positive electrode active material is 6 times the mass of the liquid second Ga-based alloy; the mass ratio of the LiCoO2 positive electrode active material to the LiFePO4 positive electrode active material is 1:1.

[0028] Preferably, the LiCoO2 positive electrode active material is prepared by the following method: separating the positive electrode plate from the waste LiCoO2 lithium-ion battery, then immersing it in the liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and calcining the separated positive electrode material to obtain the LiCoO2 positive electrode active material.

[0029] Preferably, the LiFePO4 positive electrode active material is prepared by the following method: separating the positive electrode plate from the waste LiFePO4 lithium-ion battery, then immersing it in the liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and calcining the separated positive electrode material to obtain the LiFePO4 positive electrode active material.

[0030] Preferably, the conditions for pulse heating are: at 1500 °C, pulse heating for 200 ms, adding 5 to 10 times, with an interval of 1000 ms each time.

[0031] The present invention uses the positive electrode active material as a raw material, regenerates and prepares a regenerated positive electrode plate, and then assembles it to prepare a regenerated lithium-ion battery to realize the reuse of the positive electrode active material.

[0032] Preferably, the specific method for preparing the regenerated lithium-ion battery is:

[0033] Adding lithium carbonate to the positive electrode active material and calcining to obtain a regenerated positive electrode material; using the regenerated positive electrode material as the positive electrode active substance to prepare a regenerated positive electrode plate; assembling the negative electrode plate, the separator material, the electrolyte and the regenerated positive electrode plate in sequence to obtain a regenerated lithium-ion battery.

[0034] Preferably, the regenerated positive electrode plate is prepared by the following method:

[0035] S1. Add lithium carbonate to the positive electrode active material and calcine it at 800 °C for 12 h to realize the regeneration of the electrode material and obtain the regenerated electrode material; wherein, the molar amount of lithium carbonate is 10% of the molar amount of the positive electrode active material.

[0036] S2. Mix the regenerated electrode material, conductive carbon black and polyvinylidene fluoride to obtain an active slurry; wherein, the mass ratio of the regenerated electrode material, conductive carbon black and polyvinylidene fluoride is 8:1:1.

[0037] S3. Coating the active slurry on the current collector, after drying, to form an active material layer on the current collector and obtain a regenerated positive electrode plate.

[0038] It should be noted that adding lithium carbonate to the positive electrode active material, by heating, enables the de-lithiated metal oxide in the positive electrode active material to react with lithium carbonate, restoring the original composition and performance of the positive electrode active material. In addition, under the action of high temperature, some harmful substances such as electrolyte residues and impurities are decomposed or volatilized; at the same time, high temperature can also promote the reconstruction of the crystal structure of the positive electrode active material, making it more orderly, thereby improving the electrochemical performance of the regenerated lithium-ion battery.

[0039] Preferably, the current collector is aluminum foil.

[0040] Preferably, the drying temperature is 60 °C and the drying time is 6 h.

[0041] Preferably, the negative electrode plate is a lithium sheet.

[0042] Preferably, the solute in the electrolyte is 1 mol / L lithium hexafluorophosphate; the solvents in the electrolyte are dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the volume ratio is 1:1:1.

[0043] Compared with the prior art, the present invention has the following technical effects:

[0044] 1. The present invention separates the positive electrode plate and the negative copper foil from the waste lithium-ion battery; by utilizing the property that the first Ga-based alloy can remain liquid at room temperature and the high wettability of the first Ga-based alloy to aluminum foil, the rapid, pollution-free and low-energy consumption separation of the aluminum foil and the positive electrode active material layer is realized. At the same time, the mass percentage of Ga contained in the liquid first Ga-based alloy is 85% - 90%, avoiding the precipitation of Ga at room temperature and affecting the effective separation of the aluminum foil and the positive electrode active material layer. There is no aluminum residue in the separated positive electrode active material, and the separation method has a minimal impact on the positive electrode material itself and can well maintain its structural integrity.

[0045] 2. The positive electrode active material separated by the present invention can be used to prepare recycled lithium-ion batteries. In addition, the positive electrode active material can be combined with the negative electrode copper foil and the second Ga-based alloy to prepare a high-entropy alloy nanoparticle catalyst, broadening the applications of the positive electrode sheet and the negative electrode copper foil in waste lithium-ion batteries.

[0046] 3. The separation method of the present invention can achieve the reusable of the liquid first Ga-based alloy. Specifically, water is added to the liquid first Ga-based alloy after the reaction. Aluminum in the liquid first Ga-based alloy reacts rapidly with water to form alumina solids, separating the liquid first Ga-based alloy and achieving the reusable of the liquid first Ga-based alloy.

[0047] 4. The high-entropy alloy nanoparticle catalyst prepared by the present invention undergoes the reduction reaction of NO3 - , and the Faraday efficiency of catalytic nitrate reduction reaches 92.1% at a potential of -1.4V. At the same time, the high-entropy alloy nanoparticle catalyst prepared by the present invention has good chemical stability and anti-degradability. The present invention realizes the efficient utilization of resources by recycling waste lithium-ion battery materials. Description of the Drawings

[0048] Figure 1 Shows the change in the Al content in the GaSn alloy during the separation of the positive electrode material in Example 1.

[0049] Figure 2 Shows the separation time and separation efficiency of the recycled GaSn alloy separated from the positive electrode sheet.

[0050] Figure 3 Shows the inductively coupled plasma test mass spectrum of the GaSn alloy.

[0051] Figure 4 Shows the inductively coupled plasma test mass spectrum of the recycled GaSn alloy in Example 1.

[0052] Figure 5 Shows the X-ray diffraction patterns of the lithium-ion batteries prepared in Example 1 and Comparative Example 3.

[0053] Figure 6 Shows the X-ray diffraction pattern of the LiFePO4 positive electrode active material separated in Comparative Example 1.

[0054] Figure 7 Shows the X-ray diffraction pattern of the LiCoO2 positive electrode active material separated in Comparative Example 2.

[0055] Figure 8 Shows the comparison chart of the long cycle performance of the lithium-ion batteries prepared in Example 1 and Comparative Example 3.

[0056] Figure 9Rate tests of the lithium-ion batteries prepared in Example 1 and Comparative Example 3.

[0057] Figure 10 Linear sweep voltammetry curve of nitrate reduction for the high-entropy alloy nanoparticle catalyst prepared in Example 1.

[0058] Figure 11 Faradaic efficiency of nitrate reduction catalyzed by the high-entropy alloy nanoparticle catalyst prepared in Example 1 at different potentials.

[0059] Figure 12 Cyclic voltammetry stability of the high-entropy alloy nanoparticle catalyst prepared in Example 1 for the reaction of anthraquinone-2,7-disulfonic acid disodium for 100 cycles compared with the original carbon paper. Detailed implementation manners

[0060] As described in the background art, the separation methods of the aluminum foil and the positive electrode active material layer mainly include a heat treatment method, an organic solvent dissolution method, and a chemical corrosion method of the aluminum foil with mineral acid. The heat treatment method reduces the adhesion force between the active material particles by thermally decomposing the binder at high temperature, thereby weakening the adhesion between the active material layer and the aluminum foil and realizing the separation of the positive electrode active material and the aluminum foil. The organic solvent dissolution method is to treat the positive electrode sheet with an organic solvent having good solubility to make the positive electrode active material fall off from the aluminum foil; wherein, the organic solvents include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. The chemical corrosion method of the aluminum foil with mineral acid is to dissolve the aluminum foil with mineral acid to realize the rapid separation of the aluminum foil and the active material.

[0061] Although the heat treatment method is simple to operate, its energy consumption is high, and harmful gases such as hydrogen fluoride, phosphorus oxides, and other toxic compounds will be released. At the same time, a large amount of aluminum residue will be introduced into the recovered active material. The organic solvents in the organic solvent dissolution method include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. These organic solvents can effectively dissolve the commonly used polyvinylidene fluoride binder in the positive electrode sheet. However, due to the limited solubility of polyvinylidene fluoride in these solvents, usually 5wt% - 10wt%, there is still aluminum residue in the active material. During the chemical corrosion process of the aluminum foil with mineral acid, since the mineral acid will also react with the positive electrode active material, it is necessary to control the concentration and dosage of the mineral acid to avoid the corrosion of the positive electrode active material; at the same time, the mineral acid cannot react completely with the aluminum foil, resulting in the presence of aluminum residue in the positive electrode active material.

[0062] The above separation methods will inevitably introduce aluminum residue into the separated positive electrode active material, which will increase the difficulty of the subsequent recovery process.

[0063] The present invention develops a separation method of embrittling aluminum foil and cathode active material based on a liquid-phase first Ga-based alloy. By corroding the aluminum foil and the aluminum oxide protective layer on its surface with Ga atoms in the first Ga-based alloy, rapid, pollution-free and low-energy consumption peeling of the aluminum foil and the cathode active material layer in waste lithium-ion batteries is achieved, and there is no aluminum residue in the separated cathode active material.

[0064] The present invention relates to a cathode active material separated by the separation method of the above-mentioned waste lithium-ion battery; preferably, the cathode active material is a LiCoO₂ cathode active material, a LiFePO₄ cathode active material, a LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O₂ cathode active material or a Li₂Mn₂O₄ cathode active material.

[0065] Based on the cathode active material, the present invention combines a negative copper foil, a cathode active material and a liquid-phase second Ga-based alloy, and proposes a synthesis method of a high-entropy alloy nanoparticle catalyst, aiming to realize the efficient utilization of resources by recycling waste lithium-ion battery materials.

[0066] The high-entropy alloy nanoparticle catalyst has a relatively high specific surface area and unique catalytic activity, and thus plays an important role in the fields of organic liquid flow battery catalysis and nitrate reduction catalysis. Through this method of the present invention, waste battery materials can be recycled, which not only reduces the environmental burden of electronic waste, but also provides a new way for the green synthesis of catalysts.

[0067] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described below with specific embodiments.

[0068] In the description of the present invention, unless otherwise specified, the reagents used are commercially available, and the methods used are conventional techniques in the art.

[0069] Example 1

[0070] This example provides a method for recycling waste lithium-ion batteries.

[0071] Separate the cathode active material:

[0072] S1. Put the waste NMC333 ternary lithium-ion battery into a 500 mL NaCl solution containing 5 wt% and soak it for 24 h to fully discharge it; then manually disassemble the discharged lithium-ion battery to obtain a cathode strip, and place it in a fume hood to dry for later use.

[0073] S2. Under vacuum conditions, mix Ga and Sn according to a mass ratio of 87.5:12.5, and heat and stir at 300 °C for 24 h to obtain a GaSn alloy.

[0074] S3. Cut the positive electrode strip into positive electrode sheets of 1 cm × 1 cm, and immerse them in 10 mL of GaSn alloy for 30 min to obtain a mixture.

[0075] S4. Separate the positive electrode material from the mixture by suction filtration to obtain the positive electrode material; among them, the filter membrane used for suction filtration is a nylon filter membrane with a pore size of 20 μm.

[0076] S5. Add 20 ml of water to the separated mixture and react for 10 min, then centrifuge at a speed of 8000 rpm for 5 min using a centrifuge, and collect the filtrate as the recycled GaSn alloy.

[0077] S6. Place the positive electrode material in a muffle furnace and calcine it at 600 °C for 5 h to obtain the positive electrode active material, and the positive electrode active material is LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2.

[0078] Preparation of recycled lithium-ion batteries:

[0079] S1. Add lithium carbonate to the positive electrode active material and calcine it at 800 °C for 12 h to regenerate the electrode material and obtain the recycled electrode material; among them, the molar amount of lithium carbonate is 10% of the molar amount of the positive electrode active material.

[0080] S2. Add the recycled electrode material, conductive carbon black, and polyvinylidene fluoride to a mortar in a mass ratio of 8:1:1, and grind and mix them until they are viscous to obtain the active slurry.

[0081] S3. Coat the active slurry on the aluminum foil with a thickness of 10 μm, and dry it in a vacuum oven at 60 °C for 6 h to obtain the positive electrode sheet.

[0082] S4. In a glove box where the oxygen and water content are both lower than 0.1 ppm, assemble a lithium sheet as the negative electrode sheet, a separator material, an electrolyte of model LB-002, a positive electrode sheet, and a CR2032 battery case in sequence to prepare a recycled lithium-ion battery, denoted as the recycled NMC battery.

[0083] Preparation of high-entropy alloy nanoparticle catalysts:

[0084] S1. Immerse the used NMC333 ternary lithium-ion battery in 500 mL of NaCl solution containing 5 wt% for 24 h to fully discharge it; then manually disassemble the discharged lithium-ion battery to obtain the negative electrode copper foil, and place it in a fume hood to dry for later use.

[0085] S2. Under vacuum conditions, Ga, In and the negative copper foil are mixed at a mass ratio of 75:25:50, and heated and stirred at 300 °C for 24 h to obtain a GaInCu alloy.

[0086] S3. Add 10 ml of ethanol to the GaInCu alloy, and use a cell disruptor to set it to 300 W and break it for 3 h to obtain a GaInCu nanoparticle solution.

[0087] S4. The LiFePO4 cathode active material separated in Comparative Example 1 and the LiCoO2 cathode active material separated in Comparative Example 2 are successively added to the nanoparticle solution and ultrasonicated for 5 min; among them, the mass of the LiCoO2 cathode active material is three times the total mass of Ga and In, and the mass of the LiFePO4 cathode active material is three times the total mass of Ga and In, to obtain a precursor solution.

[0088] S5. Drop the precursor solution onto a 3 cm × 1 cm carbon paper, and under a vacuum environment, pulse heat it at 1500 °C, each heating for 200 ms, with an interval of 1000 ms each time, and heat it 5 times to obtain a high-entropy alloy nanoparticle catalyst, denoted as GaInCuFeCo.

[0089] Comparative Example 1

[0090] This example provides a method for separating the cathode active material of waste lithium-ion batteries.

[0091] S1. Put the waste LFP18650 lithium-ion battery into a 500 mL NaCl solution containing 5 wt% and soak it for 24 h to fully discharge it; then manually disassemble the discharged lithium-ion battery to obtain a cathode strip, and place it in a fume hood to dry for later use.

[0092] S2. Under vacuum conditions, Ga and Sn are mixed at a mass ratio of 87.5:12.5, and heated and stirred at 300 °C for 24 h to obtain a GaSn alloy.

[0093] S3. Cut the cathode strip into a 1 cm × 1 cm cathode electrode sheet, and immerse it in 10 mL of the GaSn alloy for 30 min to obtain a mixture.

[0094] S4. Separate the cathode material from the mixture by suction filtration to obtain the cathode material; among them, the filter membrane used for suction filtration is a nylon filter membrane, and the pore size of the filter membrane is 20 μm.

[0095] S5. Add 20 ml of water to the separated mixture and react for 10 min, then centrifuge it at a speed of 8000 rpm for 5 min, and collect the filtrate as the recovered GaSn alloy.

[0096] S6. Place the positive electrode material in a muffle furnace and calcine it at 600 °C for 5 h to obtain the LiFePO4 positive electrode active material.

[0097] Comparative Example 2

[0098] This comparative example provides a method for separating the positive electrode active material of waste lithium-ion batteries.

[0099] S1. Place the waste R747 lithium-ion battery in a 500 mL NaCl solution containing 5 wt% and soak it for 24 h to fully discharge it; then manually disassemble the discharged lithium-ion battery to obtain the positive electrode strip, and place it in a fume hood to dry for later use.

[0100] S2. Under vacuum conditions, mix Ga and Sn in a mass ratio of 87.5:12.5, and heat and stir at 300 °C for 24 h to obtain the GaSn alloy.

[0101] S3. Cut the positive electrode strip into positive electrode plates of 1 cm × 1 cm, and immerse them in 10 mL of the GaSn alloy for 30 min to obtain a mixture.

[0102] S4. Separate the positive electrode material from the mixture by suction filtration to obtain the positive electrode material; among them, the filter membrane used for suction filtration is a nylon filter membrane with a pore size of 20 μm.

[0103] S5. Add 20 ml of water to the separated mixture and react for 10 min, then centrifuge at a speed of 8000 rpm for 5 min using a centrifuge, and collect the filtrate as the recycled GaSn alloy.

[0104] S6. Place the positive electrode material in a muffle furnace and calcine it at 600 °C for 5 h to obtain the LiCoO2 positive electrode active material.

[0105] Comparative Example 3

[0106] This comparative example provides a method for preparing a lithium-ion battery.

[0107] S1. Add the positive electrode active material, conductive carbon black, and polyvinylidene fluoride prepared in Example 1 to a mortar in a mass ratio of 8:1:1, and grind and mix them until they are viscous to obtain the active slurry.

[0108] S2. Coat the active slurry on the aluminum foil with a thickness of 10 μm, and dry it in a vacuum oven at 60 °C for 6 h to obtain the positive electrode plate.

[0109] S3. In a glove box where the oxygen and water content are both less than 0.1 ppm, assemble the lithium sheet as the negative electrode plate, the separator material, the electrolyte of model LB-002, and the CR2032 battery case in sequence to prepare a lithium-ion battery, denoted as the NMC battery.

[0110] Experimental test

[0111] 1. Separation test

[0112] Water is added to the reacted GaSn alloy in the present invention to react, and the recycled GaSn alloy is obtained; the recycled GaSn alloy is separated for the first time to obtain the reacted GaSn alloy, which is denoted as the first cycle. Repeat five times, and record the separation time and separation efficiency under each cycle respectively.

[0113] As Figure 1 shown, the positive electrode plate is immersed in the GaSn alloy for reaction, and the reaction is almost complete in 30 min. Therefore, in order to ensure the complete reaction of the aluminum foil in the positive electrode plate with the GaSn alloy, preferably, the immersion time is greater than 30 min, and more preferably, the immersion time is 30 min to 35 min.

[0114] As Figure 2 shown, the recycled GaSn alloy can react with the aluminum foil in the positive electrode plate multiple times and separate the positive electrode active material; and the separation time under each cycle is stable at 30 min, and the separation efficiency is always stable above 99%. This shows that through the liquid GaSn alloy, the present invention can achieve the rapid, pollution-free and low-energy consumption separation of the aluminum foil and the positive electrode active material layer. And the recyclability of the liquid GaSn alloy is realized.

[0115] 2. Inductively coupled plasma test

[0116] As Figure 3 shown, the GaSn alloy shows Ga element, Sn element and Al element. The content of Ga element is 87.50293 wt%, the content of Sn element is 12.4517 wt%, and the content of Al element is 9.43376E -4 wt%.

[0117] As Figure 4 shown, the recycled GaSn alloy shows Ga element, Sn element and Al element; the content of Ga element is 87.5372 wt%, and the content of Sn element is 12.4604 wt%.

[0118] Compared with Figure 3 , the elemental composition of the recycled GaSn alloy is basically the same as that of the GaSn alloy before reaction, and the contents of Ga element and Sn element are also the same. This shows that after the reaction separation of the GaSn alloy and the positive electrode material, the Ga element and Sn element in the GaSn alloy are not lost during the reaction separation, and the obtained positive electrode active material does not dissolve either, and there is no Al residue in the recycled GaSn alloy.

[0119] 3. X-ray diffraction analysis

[0120] As shown Figure 5 in FIG. 3, by comparing the diffraction peaks of the X-ray diffraction patterns of the NMC battery prepared in Comparative Example 3 and the recycled NMC battery prepared in Example 1, after repair with lithium carbonate, the impurity peaks of the recycled lithium-ion battery disappeared and the signal of the diffraction peaks increased; the lattice defects in the NMC battery were repaired, the crystallinity was significantly improved, and it was consistent with the standard pattern. This shows that the NMC battery can be repaired by lithium carbonate to obtain a recycled lithium-ion battery. At the same time, there is no diffraction peak of aluminum atoms in the diffraction peaks of the recycled lithium-ion battery, indicating that there is no aluminum residue in the positive electrode active material separated in the present invention.

[0121] As shown Figure 6 in FIG. 4, the characteristic peaks of the X-ray diffraction pattern match the standard card, proving that the separated positive electrode active material is LiFePO4.

[0122] As shown Figure 7 in FIG. 5, the characteristic peaks of the X-ray diffraction pattern match the standard card, proving that the separated positive electrode active material is LiCoO2.

[0123] 4. Electrochemical tests.

[0124] The present invention uses a Neware battery tester to conduct electrochemical tests, and evaluates the cycle stability, rate performance, and efficiency change of the battery through the analysis of charge-discharge curves to evaluate the performance of the battery.

[0125] In the cyclic charge-discharge test, the battery was subjected to 100 cycles of constant current and constant voltage charging and constant current discharging tests at a rate of 0.2C. In the rate test, the battery was tested at charge-discharge rates of 0.1C, 0.2C, 0.5C, 1C, and 2C respectively, and the specific capacity indexes of the battery at different rates were recorded. All tests were carried out at room temperature.

[0126] As shown Figure 8 in FIG. 6, compared with the NMC battery prepared without repair with lithium carbonate, the recycled NMC battery after repair with lithium carbonate can still maintain a specific capacity of 140 mAh / g after 100 charge-discharge cycles.

[0127] As shown Figure 9 in FIG. 7, compared with the NMC battery, the recycled NMC battery also shows excellent rate performance at different rates, proving the successful recycling of waste lithium-ion batteries.

[0128] 5. Catalytic tests.

[0129] The present invention uses an electrolytic cell and a three - electrode system to measure the linear sweep voltammetry curve of the reaction; among them, the working electrode is the carbon paper where the catalytic product is located, cut into 1 cm×1 cm, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum mesh electrode. When measuring the linear sweep voltammetry, K2SO4 electrolytes with a concentration of 0.5 M, and mixed electrolytes of KNO3 with a concentration of 0.1 M and K2SO4 with a concentration of 0.5 M are respectively selected for comparative tests. The current response is recorded in the range of 0 V to - 1.7 V at a scanning rate of 10 mV / s to analyze the initial potential of nitrate reduction and the catalytic activity.

[0130] As Figure 10 shown, after adding KNO3, an obvious change in current density occurs in the linear sweep voltammetry, indicating that the reduction reaction of NO3 - has occurred on the high - entropy alloy nanoparticle catalyst prepared by the present invention.

[0131] The determination of the Faraday efficiency usually adopts the potentiostatic electrolysis method. A 0.5 M K2SO4 electrolyte, or a mixed electrolyte of 0.5 M K2SO4 and 0.1 M KNO3 is selected, and electrolysis is carried out at - 1.2 V, - 1.3 V, - 1.4 V, - 1.5 V, - 1.6 V and - 1.7 V for 1 h respectively. The Faraday efficiency is calculated by the indophenol blue ultraviolet colorimetric method. For the indophenol blue ultraviolet colorimetric method, 5 ml of the reaction solution is diluted 100 times to ensure that the absorption wavelength meets the range, and then 2 ml of 1 M sodium hydroxide solution containing 5 wt% salicylic acid and 5 wt% sodium citrate, 1 ml of 0.05 M sodium hypochlorite solution and 0.2 ml of 1 wt% nitroferrous disulfonate dihydrate solution are added in sequence. After standing for 2 h, the ammonium ion concentration is measured at a wavelength of 660 nm using a UV - Vis spectrophotometer, and the Faraday efficiency is calculated through the ammonium ion concentration.

[0132] As Figure 11 shown, the Faraday efficiency of the high - entropy alloy nanoparticle catalyst prepared in Example 1 for catalytic nitrate reduction reaches 92.1% at a potential of - 1.4 V.

[0133] The same electrodes are used for the high - entropy alloy nanoparticle catalyst to catalyze sodium anthraquinone - 2,7 - disulfonate, and the electrolyte is 10 mM sodium anthraquinone - 2,7 - disulfonate, 0.1 M H2SO4 and 1 M NH4CL for testing. It is cycled 100 times in the range of 0.1 V to - 0.6 V at a scanning rate of 10 mV / s and the current response is recorded to explore the stability of catalyzing sodium anthraquinone - 2,7 - disulfonate.

[0134] As Figure 12As shown, the high-entropy alloy nanoparticle catalyst prepared in Example 1 catalyzes sodium anthraquinone-2,7-disulfonate, and the current density increases significantly, especially at the positions of the oxidation peak and the reduction peak. The high-entropy alloy nanoparticle catalyst improves the redox reaction rate of sodium anthraquinone-2,7-disulfonate, showing high catalytic activity; at the same time, the curve shape under the condition of the high-entropy alloy nanoparticle catalyst remains symmetric and regular after 100 cycles.

[0135] This shows that the high-entropy alloy nanoparticle catalyst prepared by the present invention itself has good chemical stability and anti-degradability.

[0136] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the adopted step methods are the same as those in the examples, in order to prevent repetition, the present invention describes the preferred examples. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept, and these changes and modifications all fall within the scope of the present invention.

[0137] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of the equivalent technology of the present invention, the present invention also intends to include these changes and deformations.

Claims

1. A method for recycling waste lithium-ion batteries, characterized in that: The following steps are involved: Separate the positive electrode sheet and negative electrode copper foil from waste lithium-ion batteries; The separated positive electrode sheet is immersed in a liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and the separated positive electrode material is calcined to obtain a positive electrode active material; the liquid first Ga-based alloy is a GaSn alloy; the mass percentage of Ga contained in the liquid first Ga-based alloy is 85% to 90%; Using the positive electrode active material as raw material, regenerating to prepare a regenerated positive electrode sheet, and then assembling to prepare a regenerated lithium-ion battery; Alternatively, a high entropy alloy nanoparticle catalyst is prepared using negative electrode copper foil, positive electrode active material and a liquid second Ga-based alloy as raw materials; the liquid second Ga-based alloy is a GaIn alloy.

2. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The specific method for preparing a regenerated lithium-ion battery is: The positive electrode active material is mixed with lithium carbonate and calcined to obtain a regenerated positive electrode material; the regenerated positive electrode material is used as the positive electrode active material to prepare a regenerated positive electrode plate; the negative electrode plate, the diaphragm material, the electrolyte and the regenerated positive electrode plate are assembled in sequence to obtain a regenerated lithium-ion battery.

3. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The specific method for preparing high entropy alloy nanoparticle catalyst is: The negative electrode copper foil and the liquid second Ga-based alloy are dissolved in a solvent and crushed to obtain a nanoparticle solution; the nanoparticle solution is evenly mixed with the positive electrode active material to obtain a precursor solution; the precursor solution is placed on carbon paper and pulse-heated in a vacuum environment to obtain a high entropy alloy nanoparticle catalyst; The positive electrode active material is a mixture of LiCoO2 positive electrode active material and LiFePO4 positive electrode active material.

4. The method for recycling waste lithium-ion batteries according to claim 3, characterized in that: The LiCoO2 positive electrode active material is prepared by the following method: Separating a positive electrode sheet from a waste LiCoO2 lithium-ion battery, and then immersing the sheet in a liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and calcining the separated positive electrode material to obtain a LiCoO2 positive electrode active material; The LiFePO4 positive electrode active material is prepared by the following method: The positive electrode sheet is separated from the waste LiFePO4 lithium-ion battery, and then immersed in a liquid first Ga-based alloy to separate the aluminum foil from the positive electrode material, and the separated positive electrode material is calcined to obtain the LiFePO4 positive electrode active material.

5. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The GaSn alloy is prepared by the following method: Ga and Sn are used as raw materials, Ga and Sn are mixed, and then heated under vacuum conditions to obtain a GaSn alloy; the heating temperature is 300°C.

6. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The calcination temperature is 600° C. and the calcination time is 4 h to 6 h.

7. The method for recycling waste lithium-ion batteries according to claim 3, characterized in that: The mass ratio of the liquid second Ga-based alloy to the negative electrode copper foil is 2:1; The mass ratio of the LiCoO2 positive electrode active material to the LiFePO4 positive electrode active material is 1:1; The mass of the positive electrode active material is 6 times the mass of the liquid second Ga-based alloy.

8. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The mass percentage of Ga contained in the GaIn alloy is 70% to 80%.

9. The method for recycling waste lithium-ion batteries according to claim 1, characterized in that: The regenerated positive electrode plate is prepared by the following method: The positive electrode active material is mixed with lithium carbonate, and then calcined at 800°C for 12 hours to achieve the regeneration of the electrode material to obtain a regenerated electrode material; the regenerated electrode material, conductive carbon black and polyvinylidene fluoride are mixed to obtain an active slurry; wherein the mass ratio of the regenerated electrode material, conductive carbon black and polyvinylidene fluoride is 8:1:1; The active slurry is coated on a current collector and dried to form an active material layer on the current collector to obtain a regenerated positive electrode sheet.

10. The method for recycling waste lithium-ion batteries according to claim 9, characterized in that: The molar amount of lithium carbonate is 10% of the molar amount of the positive electrode active material.

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