A green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials

Abstract

The present invention relates to the technical field of lithium-ion battery material recycling, and in particular to a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials. The method comprises the steps of: discharging and disassembling the waste lithium iron phosphate battery to obtain a positive electrode sheet; mixing a hydrogen bond acceptor, a hydrogen bond donor, and water with heating and stirring to obtain a low eutectic solvent, wherein the hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate, or ammonium, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, mono-n-butylamine, N-ethylethylenediamine, 1-propanethiol, and diallyl sulfide; placing the positive electrode sheet in the low eutectic solvent for immersion stripping to obtain a stripped and recycled positive electrode material. The method of the present invention realizes the stripping and recycling of the positive electrode material, and the stripped and recycled positive electrode material has a complete structure, high purity, and exhibits excellent electrochemical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery material recycling, and in particular to a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials. Background Art

[0002] Lithium-ion batteries (Li-ion batteries) are widely used in energy storage and conversion due to their long lifespan, high energy efficiency, and environmental friendliness. However, with a lifespan of approximately 8-10 years, a significant amount of spent Li-ion batteries is generated. Spent Li-ion batteries contain a significant amount of key metals (such as lithium, cobalt, nickel, and manganese), at concentrations far higher than those found in naturally occurring minerals. Therefore, the efficient recycling of these spent Li-ion batteries, particularly their cathode materials, has become a crucial research topic. To this end, various methods are currently being employed to recycle spent cathode materials, including mechanical crushing, pyrometallurgy, and hydrometallurgy. However, these methods suffer from low recovery rates, high energy consumption, and environmental pollution.

[0003] Direct recycling is an emerging recycling method that directly repairs the battery's electrode materials and restores their performance, avoiding complex recycling processes. This method can effectively simplify recycling steps, reduce costs, and reduce environmental pollution. However, due to the strong adhesion between the positive electrode material and the current collector, the direct recycling process is hindered. Therefore, it is necessary to perform pretreatment to separate the positive electrode material and the current collector. Common stripping methods usually include: (1) mechanical stripping, such as grinding, crushing, screening, etc. This method is environmentally friendly and can be used on a large scale, but it will lose a lot of active materials and leave a lot of impurities. (2) High-temperature calcination stripping, treating the positive electrode at high temperature to decompose or inactivate the organic binder, thereby achieving the purpose of separating the positive electrode material and the current collector. This method has the characteristics of short process, high productivity, and mature technology, but it also has the disadvantages of high energy consumption and high emissions, and high-temperature calcination may also destroy the structure of the positive electrode active material. (3) Acid / base treatment stripping, by using strong acid or strong base to dissolve the current collector, the current collector and active material can be quickly separated. However, this process will produce a large amount of hydrogen, the active material will also dissolve into the solution, and will produce waste liquid with high pollution. (4) Organic solvent stripping. Some organic solvents can dissolve PVDF (polyvinylidene fluoride) according to the principle of "like dissolves like", and then strip the positive electrode material and current collector, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAC), which has little effect on the original structure of the active material. However, due to the limited solubility of PVDF in these organic solvents, a large amount of solvent is often required to dissolve it, and these solvents are also highly toxic, so it is difficult to put them into practical use. It can be seen that the above-mentioned traditional stripping methods have problems such as introducing impurities, polluting the environment, destroying the structure or high cost, making it difficult for their practical application to be further developed.

[0004] Deep eutectic solvents (DES), a new type of green stripping solvent, have shown great potential in the field of cathode material recycling in recent years. Typically composed of renewable organic acids and amines, DESs offer advantages such as low energy consumption, low toxicity, biodegradability, and minimal damage to the product, making them significantly advantageous in terms of environmental protection and sustainability. However, DESs also face challenges in cathode material recycling, including technical complexity, high viscosity, regeneration issues, and scalability challenges.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, aiming to solve the problems of complex technology and high viscosity in the existing DES positive electrode material recycling process.

[0007] The technical solutions of the present invention are as follows:

[0008] The present invention provides a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, which comprises the following steps:

[0009] S1. Discharging and disassembling the waste lithium iron phosphate battery to obtain a positive electrode sheet;

[0010] S2. Mixing a hydrogen bond acceptor, a hydrogen bond donor, and water with heating and stirring to obtain a deep eutectic solvent, wherein the hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate, or ammonium, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, mono-n-butylamine, N-ethylethylenediamine, 1-propanethiol, and diallyl sulfide;

[0011] S3, placing the positive electrode sheet in the deep eutectic solvent for immersion and stripping to obtain a positive electrode material that is stripped and recovered.

[0012] Optionally, the hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate or potassium carbonate.

[0013] Optionally, the hydrogen bond acceptor is ammonium sulfate, and the hydrogen bond donor is mono-n-butylamine.

[0014] Optionally, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1-5:1-5, and the mass percentage of water in the deep eutectic solvent is 10 wt%-40 wt%.

[0015] Optionally, in step S2, the hydrogen bond acceptor, the hydrogen bond donor and water are mixed, heated and stirred at a temperature of 10° C. to 150° C., and the stirring time is 5 min to 60 min.

[0016] Optionally, in step S3, the mass ratio of the positive electrode sheet to the deep eutectic solvent is 1:10-50.

[0017] Optionally, in step S3, the positive electrode sheet is placed in the deep eutectic solvent for immersion and peeling at a temperature of 10° C. to 90° C. and a peeling time of 1 min to 60 min.

[0018] Optionally, in step S3, the step of placing the positive electrode sheet in the deep eutectic solvent for immersion and stripping to obtain the stripped and recovered positive electrode material specifically includes:

[0019] The positive electrode sheet is placed in the low eutectic solvent for immersion and stripping, and the stripped and recovered positive electrode material is obtained through screening, washing and drying.

[0020] Beneficial Effects: The present invention provides a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials. This method utilizes a low eutectic solvent composed of a specific hydrogen bond acceptor, a hydrogen bond donor, and water to soak and strip the positive electrode sheets of waste lithium iron phosphate batteries, thereby achieving stripping and recycling of the positive electrode material. The stripped and recycled positive electrode material has a complete structure and high purity, can be directly used as the positive electrode material for lithium iron phosphate batteries, and exhibits excellent electrochemical performance. Furthermore, the method of the present invention has the advantages of simple operation, high stripping efficiency, minimal material damage, no additional waste generation, recyclability, significant economic benefits, and environmental friendliness, thus possessing high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials provided by the present invention.

[0022] Figure 2 These are ICP characterization images of the stripped and recovered positive electrode materials obtained in Example 1, Comparative Example 1 and Comparative Example 2, and the positive electrode sheets of brand new, unused lithium iron phosphate batteries.

[0023] Figure 3 These are XRD characterization diagrams of the stripped and recovered positive electrode materials obtained in Example 1, Comparative Example 1 and Comparative Example 2, as well as the positive electrode sheets of brand new and unused lithium iron phosphate batteries.

[0024] Figure 4 The following are rate performance diagrams of the positive electrode materials recovered by stripping obtained in Example 1, Comparative Example 1 and Comparative Example 2, and the positive electrode sheets of brand new and unused lithium iron phosphate batteries as positive electrodes of button batteries.

[0025] Figure 5 1 is a comparison diagram of the waste lithium iron phosphate positive electrode materials in Example 2 and Comparative Example 4 after immersion and stripping for 20 minutes. DETAILED DESCRIPTION

[0026] The present invention provides a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described below in detail. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0027] like Figure 1 As shown, an embodiment of the present invention provides a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, which includes the following steps:

[0028] S1. Discharging and disassembling the waste lithium iron phosphate battery to obtain a positive electrode sheet;

[0029] S2. Mixing a hydrogen bond acceptor, a hydrogen bond donor, and water with heating and stirring to obtain a deep eutectic solvent, wherein the hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate, or ammonium, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, mono-n-butylamine, N-ethylethylenediamine, 1-propanethiol, and diallyl sulfide;

[0030] S3, placing the positive electrode sheet in the deep eutectic solvent for immersion and stripping to obtain a positive electrode material that is stripped and recovered.

[0031] The present invention provides an environmentally friendly stripping and recycling method for waste lithium iron phosphate battery positive electrode materials. The waste lithium iron phosphate batteries are first discharged and disassembled to obtain positive electrode sheets. A deep eutectic solvent (DES) is then prepared by combining specific hydrogen bond acceptors, hydrogen bond donors, and water. The resulting positive electrode sheets are then immersed in the DES for stripping and recycling, achieving complete stripping of the lithium iron phosphate positive electrode material. The innovation of the present invention lies primarily in the use of a deep eutectic solvent composed of a specific combination of hydrogen bond acceptors, hydrogen bond donors, and water. This process avoids the use of harmful, corrosive chemicals such as strong acids and bases, ensuring the integrity and purity of the recovered positive electrode material. Furthermore, the addition of water controls the viscosity of the deep eutectic solvent and reduces preparation costs, resulting in significant economic advantages. Compared with traditional stripping processes (such as high-temperature calcination and organic solvents), the product obtained by this process exhibits improved structural integrity and sample purity, and exhibits superior electrochemical performance when used directly as a positive electrode material for lithium iron phosphate batteries. In addition, the method of the embodiment of the present invention has the advantages of simple operation, high stripping efficiency, little damage to the material, no additional waste generation, recyclability, significant economic benefits and environmental friendliness, and has high practical value.

[0032] In the embodiment of the present invention, the cathode electrode of the waste lithium iron phosphate battery is soaked and stripped by using a specific combination of deep eutectic solvents, and the hydrogen bond receptor in DES dissociates to produce H + / OH - It also reacts with Al2O3 on the surface of the aluminum foil, thereby destroying the interfacial bonding between the aluminum foil and the positive electrode material. In addition, since DES binds to PVDF via hydrogen bonds, it also inactivates the PVDF on the surface of the positive electrode material. The combined effect of these two effects allows the aluminum foil to be quickly separated from the positive electrode material. Based on the above effects, the use of the specific combination of deep eutectic solvents described in the present invention can simultaneously obtain a high-purity and structurally stable separated lithium iron phosphate layer material and an intact aluminum foil.

[0033] In the embodiments of the present invention, inorganic salts capable of generating sulfate, nitrate, phosphate, carbonate, or ammonium groups are used as hydrogen bond acceptors. These salts possess strong hydrogen bond acceptor capacity and can form stable hydrogen bonds with hydrogen bond donors, effectively lowering the melting point of the deep eutectic solvent, allowing it to form a uniform, transparent liquid at relatively low temperatures, facilitating subsequent stripping operations. Furthermore, these inorganic salts are generally chemically stable, environmentally friendly, and readily available. Urea, thiourea, tetraethylenepentamine, mono-n-butylamine, N-ethylethylenediamine, 1-propanethiol, and diallyl sulfide are used as hydrogen bond donors. The electronegativity difference between the hydrogen bond donor atoms (such as nitrogen, phosphorus, and sulfur) and hydrogen atoms in these materials is significant, enabling the formation of stable hydrogen bonds. Furthermore, these materials are commonly used in various additives, fertilizers, and pharmaceuticals, offering the advantages of low cost and minimal environmental impact. Furthermore, the addition of water helps reduce the viscosity of the DES, thereby enhancing the permeability and fluidity of the deep eutectic solvent, improving the stripping effect, and reducing costs. The hydrogen bond acceptor, hydrogen bond donor, and water are formulated into a deep eutectic solvent, which has advantages such as a stable hydrogen bond structure, a low melting point, and a low viscosity. It can quickly and effectively strip lithium iron phosphate cathode materials, and is also environmentally friendly and low-cost. The deep eutectic solvent of the embodiment of the present invention can effectively achieve the stripping and recovery of lithium iron phosphate cathode materials.

[0034] In some embodiments, the hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate, or potassium carbonate.

[0035] In some embodiments, the hydrogen bond acceptor is ammonium sulfate, potassium carbonate, or tripotassium phosphate, and the hydrogen bond donor is mono-n-butylammonium.

[0036] In some embodiments, the hydrogen bond acceptor is ammonium sulfate and the hydrogen bond donor is mono-n-butylammonium. In this embodiment, the deep eutectic solvent obtained by mixing ammonium sulfate, mono-n-butylammonium, and water with heating and stirring has a fast stripping rate for the cathode material and can produce a structurally intact cathode material.

[0037] In some embodiments, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1-5):(1-5), and the mass percentage of water in the deep eutectic solvent is 10 wt%-40 wt%. Within this mass percentage range, the deep eutectic solvent exhibits low viscosity and fast stripping rate.

[0038] In some embodiments, in step S2, the heating temperature for mixing, heating, and stirring the hydrogen bond acceptor, hydrogen bond donor, and water is 10°C to 150°C (for example, 10°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, etc.), and the stirring time is 5 min to 60 min (for example, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.). Under the above mixing, heating, and stirring conditions, less energy consumption is required, fewer equipment requirements are required, and better operational safety is exhibited.

[0039] In some embodiments, in step S3, the mass ratio of the positive electrode sheet to the deep eutectic solvent is 1:(10-50). Within this mass ratio range, the peeling rate of the aluminum foil and lithium iron phosphate layer of the positive electrode sheet is faster, and a lower mass ratio of the solution helps reduce costs and waste generation.

[0040] In some embodiments, in step S3, the positive electrode sheet is immersed in the deep eutectic solvent for stripping at a temperature of 10°C to 90°C (e.g., 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc.), and the stripping time is 1 min to 60 min (e.g., 1 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.). Under the immersion stripping conditions, the reaction conditions are milder, the required energy cost is lower, and the lower temperature also reduces the risk of high-temperature operation.

[0041] In some embodiments, in step S3, the step of placing the positive electrode sheet in the deep eutectic solvent for immersion and stripping to obtain the stripped and recovered positive electrode material specifically includes:

[0042] The positive electrode sheet is placed in the low eutectic solvent for immersion and stripping, and the stripped and recovered positive electrode material is obtained through screening, washing and drying.

[0043] In some embodiments, in step S1, the steps of discharging and disassembling the waste lithium iron phosphate battery to obtain the positive electrode sheet specifically include:

[0044] The waste lithium iron phosphate batteries were immersed in a 5% to 10% sodium chloride solution for 48 hours to completely discharge them. The batteries were then disassembled to obtain the positive electrode sheets. The sodium chloride solution's conductivity was used to short-circuit the battery's positive and negative electrodes to achieve discharge.

[0045] The present invention will be further described below with reference to specific examples.

[0046] Example 1

[0047] This example explores the structural damage of the positive electrode material caused by the green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials provided by the present invention. In order to avoid the interference of various structural damages that already exist in the waste lithium iron phosphate positive electrode materials, this example selects brand new, unused positive electrode sheets of lithium iron phosphate batteries purchased on the market for demonstration, as follows:

[0048] (1) Ammonium sulfate (hydrogen bond acceptor) and monobutylamine (hydrogen bond donor) in a molar ratio of 2:1 and 40.0 wt% of water in a deep eutectic solvent were mixed and heated and stirred at 25°C for 10 min to obtain a deep eutectic solvent;

[0049] (2) Cut the positive electrode of a new, unused lithium iron phosphate battery into 2 cm 2 The cathode sheet is placed in a deep eutectic solvent at a mass ratio of 1:20 and then immersed in the solvent for 10 minutes at 40°C for stripping, completely separating the aluminum foil from the lithium iron phosphate cathode material. The aluminum foil is then removed and dried, and the remaining mixture is sieved and washed. The sieved material is collected and dried to obtain the stripped and recovered cathode material.

[0050] Comparative Example 1

[0051] High temperature calcination stripping recovery of positive electrode material: the positive electrode sheet of the new and unused lithium iron phosphate battery as in Example 1 was cut into 2 cm 2 The size of the sample was calcined at 550 °C for 3 h with a heating rate of 5 °C / min to obtain aluminum foil and peeled-off recovered positive electrode materials.

[0052] Comparative Example 2

[0053] Organic solvent stripping and recovery of positive electrode materials: Use the same new, unused positive electrode sheet of lithium iron phosphate battery as in Example 1 and cut it into 2 cm 2 The size of the aluminum foil was placed in NMP solution and gently stirred at 100 ° C for 24 hours. After the stripping process, the aluminum foil and the recovered positive electrode material were obtained through screening, washing and drying.

[0054] Performance testing:

[0055] (1) Inductively coupled plasma (ICP) characterization and X-ray diffraction (XRD) characterization were performed on the stripped and recovered positive electrode materials obtained in Example 1, Comparative Example 1 and Comparative Example 2, as well as the positive electrode sheets of new and unused lithium iron phosphate batteries.

[0056] Figure 2 The positive electrode materials recovered from the stripping in Example 1, Comparative Example 1 and Comparative Example 2, and the positive electrode sheets of new and unused lithium iron phosphate batteries (in Figure 2 The ICP characterization graphs of the stripped and recovered cathode materials (marked as original in Figure 1) show that the composition of the stripped and recovered cathode materials obtained in Example 1, Comparative Examples 1, and Comparative Examples 2 is very similar to that of a brand-new, unused cathode sheet for lithium iron phosphate batteries. Furthermore, although the deep eutectic solvent used in Example 1 contains alkaline substances, it does not cause significant leaching of lithium and iron from the cathode material, demonstrating that the deep eutectic solvent used in the present invention has minimal destructive effect on the structure of the stripped and recovered cathode material.

[0057] Figure 3 The positive electrode materials recovered from the stripping in Example 1, Comparative Example 1 and Comparative Example 2, and the positive electrode sheets of new and unused lithium iron phosphate batteries (in Figure 3 The XRD characterization diagram of the cathode material (marked as original brand new in the figure) shows that the cathode material recovered by high-temperature calcination and stripping in Comparative Example 1 has two impurity peaks at about 18.4° and 18.9°, which may be related to the structural transformation of lithium iron phosphate at high temperature, while the cathode materials recovered by stripping in Example 1 and Comparative Example 2 do not have impurity peaks, which shows that the structures of the cathode material recovered by stripping obtained by the method of the present invention and the cathode material recovered by stripping with an organic solvent remain very complete, proving that the method of the present invention can well strip and recover the cathode material.

[0058] (2) The positive electrode materials recovered from the stripping in Example 1, Comparative Example 1 and Comparative Example 2 were used as positive electrode active materials to prepare positive electrode sheets, which were used in button batteries for electrochemical performance testing, as follows:

[0059] Preparation of positive electrode sheets: The binder polyvinylidene fluoride (PVDF) was dissolved in the organic solvent N-methylpyrrolidone (NMP) to prepare a 10 wt% binder solution. The stripped and recovered positive electrode material obtained in Example 1, Comparative Example 1, or Comparative Example 2, the binder solution, and the conductive carbon black were stirred in a stirring degassing machine at a mass ratio of 8:1:1 to obtain a slurry. The slurry was then evenly coated on an aluminum (Al) foil. After the coating process was completed, the aluminum foil was dried in a forced air drying oven at 80°C until the organic solvent was completely evaporated. It was then transferred to a vacuum drying oven and dried at 65°C for 12 hours. The aluminum foil was then punched into positive electrode sheets with a diameter of 13 mm using a manual punch.

[0060] Preparation of button cells: The button cells were assembled in a glove box under an argon atmosphere, with water and oxygen levels maintained below 0.01 ppm. The battery housing was a 2032 button cell model, the separator was a Celgard 2350 composite separator, and the electrolyte was a lithium-ion cathode electrolyte containing 1 M LiPF6. The solvents were ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The positive electrode was the positive electrode obtained in step (1) above, and the negative electrode was a commercial lithium sheet. After assembling the components into a button cell, the button cell was placed on a sealing machine to complete the sealing, ensuring that the electrolyte was completely absorbed by the active material before the electrochemical test was performed.

[0061] In addition, the same method as the above-mentioned method for preparing button batteries is used to prepare button batteries using the positive electrode plates of brand new and unused lithium iron phosphate batteries. The difference is that the positive electrode plates use the positive electrode plates of brand new and unused lithium iron phosphate batteries, and the electrochemical performance of the button batteries is tested.

[0062] The CT3001A battery testing system was used to evaluate the electrochemical performance of the four prepared button cells in the voltage range of 2.5~4.2 V. The rate performance test of the battery was performed by cycling three times at a current of 0.1C for activation, and then continuing the charge and discharge test in the order of 0.5C, 1C, 2C, 5C and 1C, with each rate cycle repeated five times.

[0063] Figure 4 The positive electrode materials recovered from the stripping in Example 1, Comparative Example 1 and Comparative Example 2, and the positive electrode sheets of new and unused lithium iron phosphate batteries (in Figure 4 The figure shows the discharge capacity of the original positive electrode sheet at 0.1C, 0.5C, 1C, 2C and 5C, respectively, as 152.18 mAh·g -1 、144.22 mAh·g -1 、135.49 mAh·g-1 、121.76 mAh·g -1 and 97.65 mAh·g -1 The discharge specific capacities of the recovered cathode material obtained in Example 1 at 0.1C, 0.5C, 1C, 2C, and 5C were 147.80 mAh·g -1 、138.24 mAh·g -1 、129.31 mAh·g -1 、117.95 mAh·g -1 and 96.51 mAh·g -1 At 5C, the discharge capacity of the recovered cathode material obtained in Example 1 is only 1.14 mAh·g lower than that of the original new cathode sheet. -1 , showing excellent rate performance retention. In contrast, the rate performance of the stripped and recovered cathode material obtained in Comparative Example 1 was significantly lower than that of Example 1, and its discharge capacity at 5C was only 77.13 mAh·g -1 , which may be related to the structural transformation mentioned in the above XRD test. Similarly, the stripped and recovered cathode material obtained in Comparative Example 2 had a capacity of 88.48 mAh·g at 5C. -1 The discharge specific capacity is also significantly lower than that of Example 1. This shows that the positive electrode material recovered by the green stripping and recycling method of the present invention shows good electrochemical performance, and its performance is very consistent with that of the original new positive electrode sheet.

[0064] The above results indicate that the composition and structure of the cathode material recovered by the stripping method of the present invention closely resemble those of new, unused cathode materials for lithium iron phosphate batteries, demonstrating excellent structural integrity and high product purity. Furthermore, compared to cathode materials recovered by high-temperature calcination stripping and organic solvent stripping, the recovered cathode material exhibits superior electrochemical performance.

[0065] Example 2

[0066] This embodiment provides a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, which is as follows:

[0067] (1) Soak the waste lithium iron phosphate battery in a sodium chloride solution with a concentration of 11.7% at room temperature and pressure for 48 hours to discharge the residual power of the battery, and then disassemble the battery to obtain the positive electrode of the waste lithium iron phosphate battery;

[0068] (2) ammonium sulfate (hydrogen bond acceptor) and monobutylamine (hydrogen bond donor) in a molar ratio of 2:1 and 40.0 wt% of water in a deep eutectic solvent were mixed and heated and stirred at 25°C for 10 min to obtain a deep eutectic solvent;

[0069] (3) Cut the waste lithium iron phosphate battery positive electrode obtained in step (1) into 2 cm 2 The cathode sheet is placed in a deep eutectic solvent at a mass ratio of 1:20 and then stripped for 20 minutes at 40°C, completely separating the aluminum foil from the cathode material. The aluminum foil is then removed and dried. The remaining mixture is then sieved and washed, and the sieved material is collected and dried to obtain the stripped and recovered cathode material.

[0070] Example 3

[0071] The same method as in Example 2 was used, except that the hydrogen bond acceptor in step (2) of Example 2 was replaced by potassium carbonate, and the soaking and stripping time in step (3) was adjusted to 40 min, to finally obtain a stripped and recovered positive electrode material.

[0072] Example 4

[0073] The same method as in Example 2 was used, except that the hydrogen bond donor in step (2) of Example 2 was replaced with urea, and the soaking and stripping time in step (3) was adjusted to 45 min, to finally obtain a stripped and recovered positive electrode material.

[0074] Example 5

[0075] The same method as in Example 2 was used, except that the mass percentage of water in step (2) of Example 2 was adjusted to 20.0 wt%, and the soaking and stripping time in step (3) was adjusted to 35 min, to finally obtain a stripped and recovered positive electrode material.

[0076] Comparative Example 3

[0077] The method of Comparative Example 3 is the same as that of Example 2, except that the hydrogen bond donor in step (2) of Example 2 is replaced with ethylene glycol, and the soaking and stripping time in step (3) is adjusted to 50 min, and finally a stripped and recovered positive electrode material is obtained.

[0078] Comparative Example 4

[0079] The method of Comparative Example 4 is the same as that of Example 2, except that the hydrogen bond donor in step (2) of Example 2 is replaced by lactic acid.

[0080] Comparing Example 2 with Example 3 and Example 4, although the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the deep eutectic solvent used in all three examples was 2:1, and the amount of water used was the same, Example 2 only required 20 minutes to completely separate the aluminum foil from the cathode material, while Examples 3 and 4 required 40 and 45 minutes, respectively. This indicates that the deep eutectic solvent prepared using ammonium sulfate, mono-n-butylamine, and water in Example 2 has a faster stripping rate for the cathode material.

[0081] Compared with Example 2 and Example 5, although the molar ratio of the hydrogen bond acceptor and the hydrogen bond donor of the deep eutectic solvent used in the two examples is 2:1, the deep eutectic solvent used in Example 2 has a faster stripping rate for the positive electrode material. This is because the viscosity of the deep eutectic solvent in Example 2 is 4.16 cP at 40°C, and the viscosity of the deep eutectic solvent in Example 5 is 4.80 cP at 40°C. When the viscosity of the deep eutectic solvent is large, it is difficult to exert its stripping effect. The higher water content in Example 2 reduces the viscosity of the deep eutectic solvent, and the decrease in viscosity is often conducive to the penetration and flow of the deep eutectic solvent, which accelerates the reaction process and subsequent dynamic separation during the stripping process, thereby improving the stripping effect. In addition, the addition of water can also reduce the preparation cost of the deep eutectic solvent, making it have higher commercial value.

[0082] Comparing Example 2 with Comparative Example 3, although the ratio of hydrogen bond acceptor to hydrogen bond donor in the deep eutectic solvent used was the same, replacing the hydrogen bond donor with ethylene glycol prolonged the time required for complete exfoliation from 20 minutes to 50 minutes. This result fully demonstrates the significant exfoliation performance advantages of the deep eutectic solvent composed of ammonium sulfate, mono-n-butylamine, and water in the present invention.

[0083] in addition, Figure 5 is a comparison diagram of the waste lithium iron phosphate positive electrode material in Example 2 and Comparative Example 4 after immersion and stripping for 20 minutes, wherein Figure 5 Figure a is the experimental result of Example 2. Figure 5 Figure b is the experimental result of Comparative Example 4. It can be clearly seen from the figure that although the waste lithium iron phosphate positive electrode materials in the two examples are completely separated at the same immersion time, the low eutectic solvent after stripping treatment in Example 2 appears transparent white, while the low eutectic solvent after stripping treatment in Comparative Example 4 appears light green. This phenomenon indicates that when the hydrogen bond donor is replaced by lactic acid, there are more Fe 2+ This result fully demonstrates the advantage of the specific combination of deep eutectic solvents used in the present invention in terms of low damage to the cathode material.

[0084] In summary, the green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials provided by the present invention effectively realizes the stripping and recycling of positive electrode materials and aluminum foil. The positive electrode material obtained by stripping and recycling has a complete structure and high purity, can be directly used as the positive electrode material of lithium iron phosphate batteries, and exhibits excellent electrochemical performance. At the same time, the method of the present invention has the advantages of simple operation, high stripping efficiency, minimal damage to the material, no additional waste generation, recyclability, significant economic benefits, and environmental friendliness, and has high practical value.

[0085] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, characterized in that: Including steps: S1. Discharging and disassembling the waste lithium iron phosphate battery to obtain a positive electrode sheet; S2. Mixing a hydrogen bond acceptor, a hydrogen bond donor, and water with heating and stirring to obtain a deep eutectic solvent, wherein the hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate, or potassium carbonate, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, mono-n-butylamine, N-ethylethylenediamine, and 1-propanethiol; S3, placing the positive electrode sheet in the deep eutectic solvent for immersion and stripping to obtain a positive electrode material that is stripped and recovered.

2. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: The hydrogen bond acceptor is ammonium sulfate, and the hydrogen bond donor is mono-n-butylamine.

3. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1-5:1-5, and the mass percentage of water in the deep eutectic solvent is 10 wt %-40 wt %.

4. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: In step S2, the hydrogen bond acceptor, the hydrogen bond donor and water are mixed and heated with stirring at a temperature of 10° C. to 150° C. for a stirring time of 5 min to 60 min.

5. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: In step S3, the mass ratio of the positive electrode sheet to the deep eutectic solvent is 1:10-50.

6. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: In step S3, the positive electrode sheet is placed in the deep eutectic solvent for immersion and peeling at a temperature of 10° C. to 90° C. and a peeling time of 1 min to 60 min.

7. The green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: In step S3, the positive electrode sheet is placed in the deep eutectic solvent for immersion and stripping to obtain the stripped and recovered positive electrode material, which specifically includes: The positive electrode sheet is placed in the low eutectic solvent for immersion and stripping, and the stripped and recovered positive electrode material is obtained through screening, washing and drying.

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