A method for repairing and regenerating waste lithium iron phosphate positive electrode material

Abstract

The present invention belongs to the technical field of battery material recycling and regeneration. More specifically, it relates to a method for repairing and regenerating discarded lithium iron phosphate positive electrode materials. The specific regeneration method of the present invention includes the following steps: battery disassembly: disassembling the lithium-ion battery and obtaining the positive electrode sheet, the negative electrode sheet and the diaphragm; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate; positive electrode sheet treatment: separating and removing the positive electrode current collector to obtain the positive electrode active material coating; negative electrode sheet and diaphragm treatment: soaking the negative electrode sheet and the diaphragm in citric acid solution, heating and impregnating to obtain an impregnation solution; positive electrode active material regeneration: mixing the positive electrode active material coating and the impregnation solution, heating and ultrasonically treating, and then freeze-grinding, thawing, and performing 5-10 freeze-grinding-thawing cycles, drying, removing moisture, and then calcining at high temperature to complete the repair and regeneration of the discarded lithium iron phosphate positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material recycling and regeneration, and more specifically, relates to a method for repairing and regenerating waste lithium iron phosphate positive electrode materials. Background Art

[0002] As a key member of the lithium-ion battery family, lithium iron phosphate (LFP) batteries offer advantages such as structural stability, long cycle life, low cost, and superior thermal safety. They are widely used in portable electronic devices, new energy vehicles, energy storage base stations, and other fields. In recent years, with the continued expansion of the electric vehicle and energy storage markets, the high prices of transition metals (such as Ni, Co, and Mn), the widespread adoption of blade batteries, and the price-performance advantages highlighted by fiscal subsidies, LFP battery production and market share have experienced explosive growth. LFP batteries typically have a service life of 7-8 years. Upon reaching this end of life, due to structural failure, LFP batteries are withdrawn from use, resulting in the formation of retired LFP battery materials. Left untreated, these materials not only harm the ecological environment but also waste and deplete non-renewable resources such as lithium, iron, and phosphorus.

[0003] The regeneration of retired lithium iron phosphate (LiFePO4) materials involves a series of reconstruction processes that replenish missing elements and repair structural defects to restore electrochemical activity. Regenerating spent LiFePO4 batteries not only mitigates the environmental hazards associated with their storage as waste but also extends the lifespan of the cathode material, making it a key step in the recycling of non-renewable, rare, and valuable resources. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: for existing retired lithium iron phosphate batteries, the positive electrode active materials therein need to be recovered and regenerated. However, the conventional method requires additional lithium source to be added during the recycling and regeneration process, which will cause the process to be uncontrollable and cause material waste. A method for repairing and regenerating discarded lithium iron phosphate positive electrode materials is provided.

[0005] The purpose of the present invention is to provide a method for repairing and regenerating waste lithium iron phosphate positive electrode materials.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] A method for repairing and regenerating waste lithium iron phosphate positive electrode materials, the specific regeneration method comprising the following steps:

[0008] Battery disassembly:

[0009] Disassemble the lithium-ion battery and obtain the positive electrode sheet, negative electrode sheet and separator;

[0010] The positive electrode plate includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0011] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0012] Positive electrode processing:

[0013] Separating and removing the positive electrode current collector to obtain a positive electrode active material coating;

[0014] Negative electrode and diaphragm processing:

[0015] The negative electrode sheet and the separator are soaked in a citric acid solution, and then heated and immersed to obtain an impregnation solution;

[0016] Regeneration of positive electrode active materials:

[0017] After mixing the positive electrode active material coating and the impregnation solution, the mixture is subjected to ultrasonic treatment by heating, and then subjected to freeze grinding. After thawing, the freeze grinding-thawing cycle is repeated 5-10 times, and the mixture is dried to remove moisture, and then subjected to high temperature calcination to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material;

[0018] During the freeze-grinding process, as water diffuses and penetrates into the pores of the coating, the water condenses to form ice crystals during the freezing process. The ice crystals shatter under the shear pressure of grinding, thereby further widening the pores. After thawing, it is conducive to the further diffusion and penetration of the impregnation liquid into the pores, thereby avoiding the problem of poor diffusion of the impregnation liquid caused by local pore blockage.

[0019] Beneficial effects of the above technical solution:

[0020] The above technical solution is to disassemble the lithium-ion battery to obtain the positive electrode sheet, negative electrode sheet and separator of the corresponding lithium-ion battery. During the battery cycle, some lithium ions are embedded in the negative electrode, and are not completely discharged due to polarization and other reasons during the discharge process, or an SEI film is formed on the surface of the negative electrode, and "dead lithium" is formed on the surface of the negative electrode sheet due to abnormal conditions. The loss of these parts of lithium ions leads to the lack of lithium ions when the positive electrode active material is directly regenerated; and it is difficult to effectively control the addition of an external lithium source. If too little is added, the supplementary effect is limited. If too much is added, the lithium source is seriously wasted. Based on this, the present invention directly performs targeted recycling and regeneration of the above-mentioned various materials derived from the same lithium-ion battery.

[0021] Specifically, citric acid solution is used for immersion. During this process, the residual lithium ions in the negative electrode plate and the diaphragm are dissolved and enter the impregnation solution. Subsequently, during the heating and ultrasonic treatment process, the impregnation solution gradually diffuses and penetrates into the positive electrode active material coating. Since there are more carboxyl functional groups in the molecular structure of citric acid, it can be gradually adsorbed and fixed in the pores of the positive electrode active material coating during the penetration process. Moreover, the present invention directly uses the positive electrode active material coating as the treatment raw material rather than the positive electrode active material. This is because there are rich pore structures in the positive electrode plate coating. These structures themselves are channels for the diffusion and penetration of the electrolyte in each lithium-ion battery. In the above treatment process, the impregnation solution can diffuse and penetrate. Since the channel itself is a conventional diffusion channel for lithium ions along with the electrolyte, the impregnation solution will actually diffuse and penetrate along the channel, thereby achieving a quantitative repair effect close to the in situ.

[0022] Furthermore, the negative electrode plate and separator processing further includes:

[0023] A citric acid solution with a concentration of 1.6-1.8 mol / L is used as the acid solution, the total mass of the negative electrode plate and the separator is used as the solid mass, and the acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 8.5-9.0:1. The mixture is heated and impregnated at a temperature of 90-95°C for 60-80 minutes, filtered, and the filtrate is collected to obtain an impregnation solution.

[0024] Furthermore, the negative electrode plate and separator processing further includes:

[0025] The impregnation solution is concentrated under reduced pressure until the impregnation solution is concentrated to 0.3-0.4 times of its original volume to obtain a concentrated impregnation solution.

[0026] The inventors have discovered that if the impregnation solution is further concentrated, the lithium ion concentration in the impregnation solution can be increased, thereby reducing the uncontrollable loss of lithium ions during the diffusion process.

[0027] Furthermore, the positive electrode active material regeneration further comprises:

[0028] After mixing the positive electrode active material coating and the concentrated impregnation liquid, the mixture is heated and ultrasonically treated for 30-50 minutes at a temperature of 80-90°C and an ultrasonic frequency of 180-200kHz. The mixture is then continuously frozen to a solid state at a temperature of -18--30°C, and then ground with insulation for 10-15 minutes. After natural thawing, the mixture is subjected to 5-10 cycles of freeze-grinding and thawing, dried to remove moisture, and then calcined at high temperature to complete the repair and regeneration of the discarded lithium iron phosphate positive electrode material.

[0029] Furthermore, the high temperature calcination includes:

[0030] In a mixed gas atmosphere of water vapor and carbon dioxide, heat to 350-380°C at a rate of 3-5°C / min, keep warm and calcine for 2-4 hours, then continue heating to 500-520°C at a rate of 0.8-1.5°C / min, keep warm and calcine for 2-4 hours, and then cool to room temperature.

[0031] Furthermore, in the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.0-2.8:1.

[0032] During the high-temperature calcination process, water vapor and carbon dioxide gas are used as a protective atmosphere to first calcine at a lower temperature, and then the temperature is further increased to calcine at a higher temperature, so that the diffusion process of lithium ions is carried out in stages, avoiding a one-time rapid increase in temperature to a higher temperature that may cause the repair of lithium ions to fail.

[0033] Furthermore, the positive electrode plate processing further includes:

[0034] Soak the positive electrode sheet in water for more than 30 minutes, then heat it to 120-150°C, and then immerse the heated positive electrode sheet in ice water at a temperature of 1-4°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0036] Unless otherwise specified, the reagents and materials used in the following examples were commercially available. Example 1

[0037] Battery disassembly:

[0038] Using retired lithium iron phosphate batteries as the test object, after discharging to a cut-off voltage of 2.5V, the battery was left to rest for 20 minutes. The lithium-ion battery was then disassembled, the battery casing was separated and removed, and the positive electrode sheet, negative electrode sheet, and separator were obtained.

[0039] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0040] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0041] Positive electrode processing:

[0042] The positive electrode sheet was soaked in water at room temperature for 30 minutes, then heated to 120°C, and then immersed in ice water at 1°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating; the positive electrode current collector was then separated and removed, and the positive electrode active material coating remaining on the surface of the positive electrode current collector was brushed off with a brush. The remaining material with the positive electrode active material coating was directly concentrated and then dried to obtain the positive electrode active material coating;

[0043] Negative electrode and diaphragm processing:

[0044] A citric acid solution with a concentration of 1.6 mol / L is used as the acid solution, and the total mass of the negative electrode plate and the separator is used as the solid mass. The acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 8.5:1. The mixture is heated and impregnated at 90°C for 60 minutes, filtered, and the filtrate is collected to obtain an impregnation solution.

[0045] The impregnation solution is concentrated under reduced pressure until the impregnation solution is concentrated to 0.3 times of its original volume to obtain a concentrated impregnation solution;

[0046] Regeneration of positive electrode active materials:

[0047] After the positive electrode active material coating and the concentrated impregnation solution obtained above are completely mixed, they are heated and ultrasonically treated at a temperature of 80°C and an ultrasonic frequency of 180kHz for 30 minutes, and then continuously frozen to a solid state at a temperature of -18°C, and then ground for 10 minutes. After natural thawing, the freeze-grinding-thawing cycle is repeated 5 times, and then dried to remove moisture. Then, the mixture is heated to 350°C at a rate of 3°C / min in an atmosphere of a mixed gas of water vapor and carbon dioxide, and calcined at this temperature for 2 hours. Then, the mixture is heated to 500°C at a rate of 0.8°C / min, and calcined at this temperature for 2 hours. Then, the mixture is cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material.

[0048] In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.0:1. Example 2

[0049] Battery disassembly:

[0050] Using retired lithium iron phosphate batteries as the test object, after discharging to a cut-off voltage of 2.5V, the battery was left to stand for 20 minutes. The lithium-ion battery was then disassembled, the battery casing was separated and removed, and the positive electrode sheet, negative electrode sheet, and separator were obtained.

[0051] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0052] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0053] Positive electrode processing:

[0054] The positive electrode sheet was soaked in water at room temperature for 35 minutes, then heated to 130°C, and then immersed in ice water at 2°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating; the positive electrode current collector was then separated and removed, and the positive electrode active material coating remaining on the surface of the positive electrode current collector was brushed off with a brush. The remaining material with the positive electrode active material coating was directly concentrated and then dried to obtain the positive electrode active material coating;

[0055] Negative electrode and diaphragm processing:

[0056] A citric acid solution with a concentration of 1.7 mol / L is used as the acid solution, and the total mass of the negative electrode plate and the separator is used as the solid mass. The acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 8.8:1. The mixture is heated and impregnated at a temperature of 92°C for 70 minutes, filtered, and the filtrate is collected to obtain an impregnation solution.

[0057] Concentrating the impregnation solution under reduced pressure until the impregnation solution is concentrated to 0.35 times its original volume to obtain a concentrated impregnation solution;

[0058] Regeneration of positive electrode active materials:

[0059] After the positive electrode active material coating and the concentrated impregnation solution obtained above are completely mixed, they are heated and ultrasonically treated at a temperature of 85°C and an ultrasonic frequency of 190kHz for 40 minutes, and then continuously frozen to a solid state at a temperature of -20°C, and then ground at this temperature for 12 minutes. After natural thawing, the freeze-grinding-thawing cycle is repeated 8 times, and then dried to remove moisture. Then, the mixture is heated to 360°C at a rate of 4°C / min in an atmosphere of a mixed gas of water vapor and carbon dioxide, and calcined at this temperature for 3 hours. Then, the mixture is heated to 510°C at a rate of 1.2°C / min, and calcined at this temperature for 3 hours. Then, the mixture is cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material.

[0060] In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.5:1. Example 3

[0061] Battery disassembly:

[0062] Using retired lithium iron phosphate batteries as the test object, after discharging to a cut-off voltage of 2.5V, the battery was left to stand for 20 minutes. The lithium-ion battery was then disassembled, the battery casing was separated and removed, and the positive electrode sheet, negative electrode sheet, and separator were obtained.

[0063] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0064] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0065] Positive electrode processing:

[0066] The positive electrode sheet was soaked in water at room temperature for 40 minutes, then heated to 150°C, and then immersed in ice water at 4°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating; the positive electrode current collector was then separated and removed, and the positive electrode active material coating remaining on the surface of the positive electrode current collector was brushed off with a brush. The remaining material with the positive electrode active material coating was directly concentrated and then dried to obtain the positive electrode active material coating;

[0067] Negative electrode and diaphragm processing:

[0068] A citric acid solution with a concentration of 1.8 mol / L is used as the acid solution, and the total mass of the negative electrode plate and the separator is used as the solid mass. The acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 9.0:1. The mixture is heated and impregnated at a temperature of 95°C for 80 minutes, filtered, and the filtrate is collected to obtain an impregnation solution.

[0069] Concentrating the impregnation solution under reduced pressure until the impregnation solution is concentrated to 0.4 times its original volume to obtain a concentrated impregnation solution;

[0070] Regeneration of positive electrode active materials:

[0071] After the positive electrode active material coating and the concentrated impregnation solution obtained above are completely mixed, they are heated and ultrasonically treated at a temperature of 90°C and an ultrasonic frequency of 200kHz for 50 minutes, and then continuously frozen to a solid state at a temperature of -30°C, and then ground for 15 minutes. After natural thawing, the freeze-grinding-thawing cycle is repeated 10 times, and then dried to remove moisture. Then, the mixture is heated to 380°C at a rate of 5°C / min in a mixed gas atmosphere of water vapor and carbon dioxide, and calcined at this temperature for 4 hours. Then, the mixture is heated to 520°C at a rate of 1.5°C / min, and calcined at this temperature for 4 hours, and then cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material;

[0072] In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.8:1. Example 4

[0073] Compared with Example 1, this embodiment has the following differences:

[0074] The high temperature calcination is:

[0075] In a mixed gas atmosphere of water vapor and carbon dioxide, the temperature was raised to 500°C at a rate of 3°C / min, kept at this temperature for 2 hours, and then cooled to room temperature; the other conditions remained unchanged. Example 5

[0076] Compared with Example 1, this embodiment has the following differences:

[0077] The high temperature calcination is:

[0078] In a mixed gas atmosphere of water vapor and carbon dioxide, the temperature was raised to 380°C at a rate of 3°C / min, kept at this temperature for 2 hours, and then cooled to room temperature; the other conditions remained unchanged. Example 6

[0079] Compared with Example 1, this embodiment has the following differences:

[0080] The impregnation solution is not concentrated but used directly, that is, it is directly mixed with the positive electrode active material coating;

[0081] The rest of the conditions remain unchanged.

[0082] Comparative Example 1

[0083] Battery disassembly:

[0084] Using retired lithium iron phosphate batteries as the test object, after discharging to a cut-off voltage of 2.5V, the battery was left to stand for 20 minutes. The lithium-ion battery was then disassembled, the battery casing was separated and removed, and the positive electrode sheet, negative electrode sheet, and separator were obtained.

[0085] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0086] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0087] Positive electrode processing:

[0088] The positive electrode sheet was soaked in water at room temperature for 30 minutes, then heated to 120°C, and then immersed in ice water at 1°C for 20 minutes to separate the positive electrode collector and the positive electrode active material coating; the positive electrode collector was then separated and removed, and the positive electrode active material coating remaining on the surface of the positive electrode collector was brushed off with a brush. The remaining material with the positive electrode active material coating was directly concentrated and dried to obtain the positive electrode active material coating; and then the positive electrode active material coating was calcined at 650°C in a nitrogen atmosphere for 3 hours to remove the binder to obtain the positive electrode active material powder;

[0089] Negative electrode and diaphragm processing:

[0090] A citric acid solution with a concentration of 1.6 mol / L is used as the acid solution, and the total mass of the negative electrode plate and the separator is used as the solid mass. The acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 8.5:1. The mixture is heated and impregnated at 90°C for 60 minutes, filtered, and the filtrate is collected to obtain an impregnation solution.

[0091] Concentrating the impregnation solution under reduced pressure until the impregnation solution is concentrated to 0.3 times its original volume to obtain a concentrated impregnation solution;

[0092] Regeneration of positive electrode active materials:

[0093] The positive electrode active material powder obtained above and the concentrated impregnation solution were mixed, and then subjected to heating and ultrasonic treatment at a temperature of 80°C and an ultrasonic frequency of 180kHz for 30 minutes. After being continuously frozen to a solid state at a temperature of -18°C, the mixture was kept warm and ground for 10 minutes. After natural thawing, the mixture was subjected to a freeze-grinding-thawing cycle 5 times, dried to remove moisture, and then heated to 350°C at a rate of 3°C / min in a mixed gas atmosphere of water vapor and carbon dioxide. After being kept warm and calcined for 2 hours, the mixture was further heated to 500°C at a rate of 0.8°C / min, and after being kept warm and calcined for 2 hours, it was cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material.

[0094] In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.0:1.

[0095] Comparative Example 2

[0096] Battery disassembly:

[0097] Using retired lithium iron phosphate batteries as the test object, after discharging to a cut-off voltage of 2.5V, the battery was left to rest for 20 minutes. The lithium-ion battery was then disassembled, the battery casing was separated and removed, and the positive electrode sheet, negative electrode sheet, and separator were obtained.

[0098] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector;

[0099] The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate;

[0100] Positive electrode processing:

[0101] The positive electrode sheet was soaked in water at room temperature for 30 minutes, then heated to 120°C, and then immersed in ice water at 1°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating; the positive electrode current collector was then separated and removed, and the positive electrode active material coating remaining on the surface of the positive electrode current collector was brushed off with a brush. The remaining material with the positive electrode active material coating was directly concentrated and then dried to obtain the positive electrode active material coating;

[0102] Regeneration of positive electrode active materials:

[0103] 0.1 mol / L lithium citrate solution was used as the immersion solution;

[0104] The positive electrode active material coating and the impregnation solution obtained above were mixed in a mass ratio of 1:10, and then heated and ultrasonically treated for 30 minutes at a temperature of 80°C and an ultrasonic frequency of 180kHz. After being continuously frozen to a solid state at a temperature of -18°C, the mixture was kept warm and ground for 10 minutes. After natural thawing, the mixture was frozen, ground and thawed 5 times, dried to remove moisture, and then heated to 350°C at a rate of 3°C / min in a mixed gas atmosphere of water vapor and carbon dioxide. After being kept warm and calcined for 2 hours, the mixture was continued to be heated to 500°C at a rate of 0.8°C / min, and after being kept warm and calcined for 2 hours, it was cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material.

[0105] In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.0:1.

[0106] The performance of the lithium iron phosphate cathode materials recovered and regenerated in the above examples and comparative examples was tested. The specific test methods and test results are as follows:

[0107] The lithium iron phosphate positive electrode material, the binder PVDF, and the conductive agent acetylene black are mixed in a mass ratio of 80:10:10. Specifically, the binder PVDF and the solvent NMP are first mixed and stirred thoroughly to obtain a glue solution, and then the acetylene black and the positive electrode material are added. After stirring evenly, the mixture is coated on the surface of the aluminum foil. The coated positive electrode sheet is dried and then cut.

[0108] Assemble the positive electrode shell, positive electrode sheet, electrolyte, diaphragm, electrolyte, lithium sheet, gasket, spring, and negative electrode shell in the order of CR2032 button battery in a vacuum glove box, and finally press it with a sealing machine, let it stand for 24 hours, and test its electrochemical performance;

[0109] Among them, the diaphragm is Celgard2400 polypropylene microporous diaphragm, the lithium salt in the electrolyte is lithium hexafluorophosphate (concentration is 1 mol / L), and the solvent is a mixture of EC:DMC:DEC=1:1:1.

[0110] The assembled buckle battery was subjected to cross-current charge and discharge using a Blue Electric test system (CT2001A) with a voltage window of 2.4-4.6V at a constant temperature of 25°C. The capacity retention rate after 200 cycles at 0.2C and the discharge specific capacity at 0.2C were measured. Detailed test results are shown in Table 1.

[0111] Table 1: Product performance test results

[0112] ;

[0113] It can be seen from the test results in Table 1 that the positive electrode material recycled and regenerated by the method of the present invention is comparable to the material regenerated by directly using a lithium source as a lithium supplement.

[0114] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for repairing and regenerating waste lithium iron phosphate positive electrode materials, characterized in that: The specific regeneration method includes the following steps: Battery disassembly: Disassemble the lithium-ion battery and obtain the positive electrode sheet, negative electrode sheet and separator; The positive electrode plate includes a positive electrode current collector and a positive electrode active material coating covering the surface of the positive electrode current collector; The positive electrode active material coating includes a positive electrode active material, and the positive electrode active material is lithium iron phosphate; Positive electrode processing: Soak the positive electrode sheet in water for more than 30 minutes, then heat it to 120-150°C, and then immerse the heated positive electrode sheet in ice water at a temperature of 1-4°C for 20 minutes to separate the positive electrode current collector and the positive electrode active material coating. Then separate and remove the positive electrode current collector, and use a brush to brush off the positive electrode active material coating remaining on the surface of the positive electrode current collector. The remaining material with the positive electrode active material coating is directly concentrated and then dried to obtain the positive electrode active material coating; Negative electrode and diaphragm processing: A citric acid solution with a concentration of 1.6-1.8 mol / L is used as the acid solution, and the total mass of the negative electrode plate and the separator is used as the solid mass. The acid solution, the negative electrode plate and the separator are mixed according to a mass ratio of the acid solution mass to the solid mass of 8.5-9.0:

1. The mixture is heated and impregnated at a temperature of 90-95° C. for 60-80 minutes, filtered, and the filtrate is collected to obtain an impregnation solution; the impregnation solution is concentrated under reduced pressure until the impregnation solution is concentrated to 0.3-0.4 times its original volume to obtain a concentrated impregnation solution; Regeneration of positive electrode active materials: After the positive electrode active material coating and the concentrated impregnation solution are mixed, they are heated and ultrasonically treated, and then freeze-ground. After thawing, the freeze-ground-thaw cycle is repeated 5-10 times, and then dried to remove moisture. Subsequently, the mixture is heated to 350-380°C at a rate of 3-5°C / min in an atmosphere of a mixed gas of water vapor and carbon dioxide, kept warm and calcined for 2-4 hours, and then continued to be heated to 500-520°C at a rate of 0.8-1.5°C / min. After being kept warm and calcined for 2-4 hours, it is cooled to room temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material.

2. The method for repairing and regenerating waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The positive electrode active material regeneration further comprises: After mixing the positive electrode active material coating and the concentrated impregnation liquid, the mixture is heated and ultrasonically treated for 30-50 minutes at a temperature of 80-90°C and an ultrasonic frequency of 180-200kHz. The mixture is then continuously frozen to a solid state at a temperature of -18--30°C, and then ground with insulation for 10-15 minutes. After natural thawing, the mixture is subjected to 5-10 cycles of freeze-grinding and thawing, dried to remove moisture, and then calcined at high temperature to complete the repair and regeneration of the discarded lithium iron phosphate positive electrode material.

3. The method for repairing and regenerating waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the mixed gas, the volume ratio of water vapor to carbon dioxide is 2.0-2.8:1.