Method for recycling and regenerating lithium iron phosphate battery material by liquid phase

Abstract

The invention belongs to the technical field of secondary battery materials. More specifically, the invention relates to a method for recycling and regenerating a lithium iron phosphate battery material by adopting a liquid phase. The method comprises the following steps: stripping a surface active material layer of a positive pole piece to obtain a positive active material layer, mixing the positive active material layer with NMP, and carrying out microwave ultrasonic heating reaction to obtain a positive active material; mixing the positive active material with the mixed acid solution, adding hydrogen peroxide, heating and carrying out an acid leaching reaction, filtering and collecting a leaching solution; adjusting the pH value of the leachate to 3.5, filtering, removing precipitates, supplementing a lithium source, adjusting the molar ratio of Li to Fe to P to 1.05: 1: 1, adjusting the pH value to 9.0, reacting at the temperature of 50-60 DEG C, heating to 80 DEG C, standing, aging, filtering and drying to obtain a dried precursor; and calcining the dried precursor in a reducing atmosphere, cooling, and discharging to obtain the regenerated lithium iron phosphate material.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery materials. More specifically, it relates to a method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery. Background Art

[0002] Recycling and regenerating the cathode material of lithium iron phosphate batteries by the liquid phase method is an efficient, environmentally friendly and economical way, which is mainly achieved through steps such as dissolution, separation, purification and regeneration. For example, acid leaching is one of the commonly used methods. First, mild organic acids such as citric acid and oxalic acid, or low-concentration inorganic acids such as sulfuric acid or hydrochloric acid are used to avoid iron dissolution or phosphorus loss caused by strong acid solutions. On this basis, a reducing agent is added to reduce the possible trivalent iron ions to divalent ferrous ions; during this process, the acid leaching effect also needs to be ensured by controlling the temperature and acid concentration; subsequently, by adjusting the pH, ferrous ions and phosphate ions are retained in the solution, while impurities such as chloride ions form precipitates, and finally, ferrous ions are precipitated in the form of Fe3(PO4)2 by the precipitation method to achieve the separation of Li⁺ and Fe²⁺; subsequently, it is mixed with a lithium source and then calcined in an inert atmosphere to obtain the recycled lithium iron phosphate cathode material.

[0003] Based on the above description, it can be known that the traditional recycling and regeneration processes are complex, and a large amount of auxiliaries, especially acidic solutions, are consumed during the process, bringing great pressure to the environment. Therefore, how to develop a recycling and regeneration method with a simpler process and environmental friendliness is still one of the technical problems faced by those skilled in the art. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: when recovering and regenerating the cathode material from lithium iron phosphate batteries by the acid leaching method, using strong acid solutions for treatment is likely to bring great pressure to the environment, while using organic acids for treatment results in low acid leaching efficiency. Based on the above problems, the present invention provides a method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery.

[0005] The purpose of the present invention is to provide a method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery.

[0006] The above object of the present invention is achieved by the following technical solutions: A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery, the specific method comprising the following steps: Disassembling the lithium iron phosphate battery and recovering the cathode plate; Peeling off the surface active material layer of the cathode plate to obtain the cathode active material layer, then mixing it with NMP at a mass ratio of 1:8 - 10, heating and reacting by microwave ultrasonic, and then filtering, washing and drying to obtain the cathode active material; By using NMP as a solvent, it can quickly and uniformly penetrate into the internal pores under the action of ultrasonic waves, effectively swelling and dissolving the binder. Synchronously combined with microwave heating, the microwave can directly act on the carbon-based conductive agent in the positive active material layer. Thanks to the uniform distribution of the conductive agent itself, it is conducive to the rapid and uniform transfer of heat inside, accelerating the swelling and dissolving effect of NMP on the binder; Mix the positive active material and the mixed acid solution at a mass ratio of 1:8.5 - 9.0, add hydrogen peroxide accounting for 10 - 12% of the mass of the mixed acid solution, heat and carry out an acid leaching reaction at a temperature of 50 - 90 °C for 2 - 3 h, then filter and collect the leaching solution; Among them, the mixed acid solution is prepared by compounding a malic acid solution with a concentration of 1.8 - 2.2 mol / L and a citric acid solution with a concentration of 1.5 - 2.0 mol / L according to a mass ratio of 1:1; The above technical solution first uses the combination of malic acid and citric acid to replace the traditional sulfuric acid or a single citric acid system to achieve an efficient and environmentally friendly leaching process; specifically, malic acid can ionize to generate hydrogen ions at a lower temperature, thereby realizing the dissolution of ferrous ions, and after dissolution, form a complex with medium stability with ferrous ions, thereby promoting the dissolution of Fe, but can avoid excessive binding; while citric acid can preferentially and firmly complex the iron ions in the system, avoiding the formation of precipitates coating the surface of the cathode material, thus affecting the mass transfer process of the acid leaching process and the acid leaching efficiency. At the same time, citric acid can also react with hydrogen peroxide to generate active hydroxyl radicals, destroying the passivation layer on the surface of lithium iron phosphate and accelerating the leaching efficiency; Since organic acid cooperation is used to replace sulfuric acid, its final wastewater can be biodegradable, ensuring environmental protection; Adjust the pH of the leaching solution to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, and then adjust the pH to 9.0. After reacting at a temperature of 50 - 60 °C, raise the temperature to 80 °C, stand and age for 4 h, then filter and dry to obtain a dry precursor; Calcine the dry precursor in a reducing atmosphere at a temperature of 650 - 670 °C for 6 - 8 h, then cool and discharge to obtain the regenerated lithium iron phosphate material.

[0007] The above technical solution adjusts the pH to 3.5, so that ferric ions in the system precipitate out in the form of a precipitate, and then are removed by filtration. After supplementing the lithium source and achieving the corresponding ratio, adjust the pH to 9.0, and start to form a precursor precipitate. During the aging process, the crystallinity of the precursor is further improved. Finally, through the calcination in a reducing atmosphere, the regeneration of the lithium iron phosphate material is achieved.

[0008] Furthermore, the microwave ultrasonic heating reaction includes: Under the conditions of microwave power of 300 - 320 W and ultrasonic frequency of 80 - 100 kHz, perform microwave ultrasonic reaction for 2 - 2.5 h.

[0009] Furthermore, the specific method further includes: Add anhydrous ethanol with the same volume as the leaching solution to the leaching solution, then adjust the pH to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, react under the condition of temperature of 50 - 60 °C, then raise the temperature to 80 °C, stand for aging for 4 h, transfer to a high-pressure reactor, under the condition of temperature of 180 - 190 °C, perform high-temperature reaction for  8 - 10 h, then cool, discharge, filter, and dry to obtain a dry precursor.

[0010] The beneficial effects of the above technical solution are: By further adding anhydrous ethanol to the leaching solution in the above technical solution, as a polar solvent, ethanol can improve the wetting of the system for lithium iron phosphate materials and accelerate the interfacial reaction; in addition, it can balance the oxidation effect of hydrogen peroxide and prevent ferrous ions from being over-oxidized to ferric ions.

[0011] Furthermore, the specific method further includes: Add anhydrous ethanol with the same volume as the leaching solution to the leaching solution, then adjust the pH to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, react under the condition of temperature of 50 - 60 °C, add a dopamine solution with 6 - 8% of the mass of the leaching solution, then raise the temperature to 80 °C, stand for aging for 4 h, then transfer to a high-pressure reactor, under the condition of temperature of 180 - 190 °C, perform high-temperature reaction for 8 - 10 h, then cool, discharge, filter, and dry to obtain a dry precursor; Among them, the concentration of the dopamine solution is 8 - 10 g / L.

[0012] The beneficial effects of the above technical solution are: In the above technical solution, by further introducing dopamine into the system, and utilizing the oxidative polymerization of dopamine on the surface of the precursor at a pH of 9.0 to form a polymer coating layer containing carbon and nitrogen elements, this coating layer can be transformed into an SP2 hybrid carbon coating layer under the subsequent calcination temperature conditions, and its electrical conductivity is more excellent than that of the traditional sucrose carbon coating layer; in addition, the presence of nitrogen elements can form pyridine nitrogen in the coating layer after calcination, further promoting electron transfer; moreover, the functional groups in dopamine can form coordination bonds with ferrous ions or phosphate ions, inhibiting the agglomeration of precursor particles and improving the uniformity of precursor particles; and the selection of the addition timing of dopamine can partially embed into the lattice of the precursor during the aging process to form nitrogen doping, improving the intrinsic conductivity of the material.

[0013] Furthermore, the specific method further includes: The dried precursor is heated and raised to 650 - 670 °C at a rate of 0.8 - 1.5 °C / min in a reducing atmosphere, calcined for 6 - 8 h while maintaining the temperature, and then cooled to room temperature with the furnace, and the product is taken out to obtain the regenerated lithium iron phosphate material.

[0014] Furthermore, the reducing atmosphere is composed of nitrogen and hydrogen mixed in a volume ratio of 9 - 9.5:1.

[0015] Furthermore, the specific method further includes: The cathode active material and the mixed acid solution are mixed at a mass ratio of 1:8.5 - 9.0, and 10 - 12% of hydrogen peroxide based on the mass of the mixed acid solution is added. First, at a temperature of 50 - 60 °C and a stirring speed of 200 - 220 r / min, the acid leaching reaction is carried out for 1 - 1.5 h by heating, and then at a temperature of 80 - 90 °C and a stirring speed of 150 - 180 r / min, the acid leaching reaction is continued for 1 - 1.5 h by heating. Subsequently, filtration is carried out to collect the leachate.

[0016] The beneficial effects of the above technical solution are as follows: By further controlling the acid leaching process and carrying out distributed acid leaching reactions at two-stage reaction temperature steps, in the temperature range of 50 - 60 °C, it is the process dominated by the dissolution of malic acid, while in the temperature range of 80 - 90 °C, it is the process dominated by the deep complexation of citric acid; by controlling the temperature, the functions of both are fully exerted to improve the acid leaching effect.

[0017] Furthermore, the mass fraction of the hydrogen peroxide is 28 - 32%. Specific Embodiments

[0018] The following specific examples are used to further illustrate the present invention, but the examples do not impose any form of limitation on the present invention. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0019] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available. Example 1

[0020] The lithium iron phosphate battery was disassembled, and the positive electrode sheet was recovered: Specifically, by separating and removing the electrolyte, negative electrode sheet and separator, the positive electrode sheet was retained, and the positive electrode sheet was soaked and washed with DMC to remove the residual electrolyte such as lithium salt on the surface or in the pores of the positive electrode sheet. When washing again, DMC can be continuously soaked for 8 h; The positive electrode sheet was soaked in N-methylpyrrolidone (NMP), and under the conditions of a temperature of 60 °C and an ultrasonic frequency of 180 kHz, after ultrasonic stripping for 1 h, the positive electrode current collector was separated and removed, and the positive electrode active material layer was collected; Subsequently, it was mixed with NMP at a mass ratio of 1:8, and under the conditions of a microwave power of 300 W and an ultrasonic frequency of 80 kHz, microwave ultrasonic reaction was carried out for 2 h, and then through filtration, washing and drying, the positive electrode active material was obtained; The positive electrode active material and the mixed acid solution were mixed at a mass ratio of 1:8.5, and 10% hydrogen peroxide based on the mass of the mixed acid solution was added. First, under the conditions of a temperature of 50 °C and a stirring speed of 200 r / min, heating and acid leaching reaction was carried out for 1 h, and then under the conditions of a temperature of 80 °C and a stirring speed of 150 r / min, the heating and acid leaching reaction was continued for 1 h. Subsequently, filtration was carried out to collect the leaching solution; The mass fraction of the hydrogen peroxide is 28%; Among them, the mixed acid solution is prepared by compounding a malic acid solution with a concentration of 1.8 mol / L and a citric acid solution with a concentration of 1.5 mol / L according to a mass ratio of 1:1; An equal volume of absolute ethanol was added to the leaching solution, and then the pH was adjusted to 3.5. After filtration, the precipitate was removed. Subsequently, lithium hydroxide was used as the lithium source to supplement the lithium source, and the molar ratio of Li:Fe:P was adjusted to 1.05:1:1. Then the pH was adjusted to 9.0. Under the conditions of a temperature of 50 °C and a stirring speed of 200 r / min, after reacting for 30 min, a dopamine solution with 6% of the mass of the leaching solution was added. Subsequently, the temperature was raised to 80 °C, and stirring and mixing were continued for 10 min. Then, it was left to age for 4 h, and then transferred to a high-pressure reactor. Under the conditions of a temperature of 180 °C and a stirring speed of 400 r / min, after high-temperature reaction for 8 h, it was cooled, discharged, filtered, and dried to obtain a dried precursor; Among them, the concentration of the dopamine solution is 8 g / L; The dried precursor was heated and raised to 650 °C at a rate of 0.8 °C / min in a reducing atmosphere, and after holding and calcining for 6 h, it was cooled to room temperature with the furnace, and discharged to obtain the regenerated lithium iron phosphate material; The reducing atmosphere is composed of nitrogen and hydrogen mixed according to a volume ratio of 9:1. Example 2

[0021] The lithium iron phosphate battery is disassembled, and the positive electrode plate is recovered: Specifically, by separating and removing the electrolyte, negative electrode plate and separator, the positive electrode plate is retained, and the positive electrode plate is soaked and cleaned with DMC to remove the electrolyte such as lithium salt remaining on the surface or in the pores of the positive electrode plate. When cleaning again, DMC can be continuously soaked for 8 h; The positive electrode plate is soaked in N-methylpyrrolidone (NMP), and under the conditions of a temperature of 60 °C and an ultrasonic frequency of 180 kHz, after ultrasonic stripping for 1 h, the positive electrode current collector is separated and removed, and the positive electrode active material layer is collected; Subsequently, it is mixed with NMP at a mass ratio of 1:9, and under the conditions of a microwave power of 310 W and an ultrasonic frequency of 90 kHz, a microwave ultrasonic reaction is carried out for 2.2 h, and then through filtration, washing and drying, the positive electrode active material is obtained; The positive electrode active material and the mixed acid solution are mixed at a mass ratio of 1:8.8, and hydrogen peroxide accounting for 11% of the mass of the mixed acid solution is added. First, under the conditions of a temperature of 55 °C and a stirring speed of 210 r / min, the acid leaching reaction is carried out for 1.2 h by heating, and then under the conditions of a temperature of 86 °C and a stirring speed of 160 r / min, the acid leaching reaction is continued for 1.2 h by heating. Subsequently, filtration is carried out to collect the leaching solution; The mass fraction of the hydrogen peroxide is 30%; Among them, the mixed acid solution is prepared by compounding a malic acid solution with a concentration of 2.0 mol / L and a citric acid solution with a concentration of 1.8 mol / L according to a mass ratio of 1:1; An equal volume of absolute ethanol is added to the leaching solution, and then the pH is adjusted to 3.5, and filtration is carried out to remove the precipitate. Subsequently, lithium hydroxide is used as the lithium source to supplement the lithium source, and the molar ratio of Li:Fe:P is adjusted to 1.05:1:1. Then the pH is adjusted to 9.0, and under the conditions of a temperature of 56 °C and a stirring speed of 200 r / min, after reacting for 30 min, a dopamine solution accounting for 7% of the mass of the leaching solution is added. Subsequently, the temperature is raised to 80 °C, and stirring and mixing are continued for 10 min, and then static aging is carried out for 4 h. Then it is transferred to a high-pressure reactor, and under the conditions of a temperature of 186 °C and a stirring speed of 400 r / min, after a high-temperature reaction for 9 h, it is cooled, discharged, filtered, and dried to obtain a dry precursor; Among them, the concentration of the dopamine solution is 9 g / L; The dry precursor is heated and raised to 660 °C at a rate of 1.2 °C / min in a reducing atmosphere, calcined at a constant temperature for 7 h, and then cooled to room temperature with the furnace, and discharged to obtain the regenerated lithium iron phosphate material; The reducing atmosphere is composed of nitrogen and hydrogen mixed according to a volume ratio of 9.2:1. Example 3

[0022] Disassembly of lithium iron phosphate battery and recovery of positive electrode sheet: Specifically, by separating and removing the electrolyte, negative electrode sheet and separator, retaining the positive electrode sheet, and soaking and cleaning the positive electrode sheet with DMC to remove electrolytes such as lithium salts remaining on the surface or in the pores of the positive electrode sheet. When cleaning again, DMC can be continuously soaked for 8 h; Soak the positive electrode sheet in N-methylpyrrolidone (NMP), under the conditions of a temperature of 60 °C and an ultrasonic frequency of 180 kHz, after ultrasonic stripping for 1 h, separate and remove the positive electrode current collector, and collect the positive electrode active material layer; Subsequently, mix it with NMP at a mass ratio of 1:10, under the conditions of a microwave power of 320 W and an ultrasonic frequency of 100 kHz, carry out microwave ultrasonic reaction for 2.5 h, and then through filtration, washing and drying, obtain the positive electrode active material; Mix the positive electrode active material and the mixed acid solution at a mass ratio of 1:9.0, and add hydrogen peroxide accounting for 12% of the mass of the mixed acid solution. First, under the conditions of a temperature of 60 °C and a stirring speed of 220 r / min, heat and carry out acid leaching reaction for 1.5 h, and then under the conditions of a temperature of 90 °C and a stirring speed of 180 r / min, continue to heat and carry out acid leaching reaction for 1.5 h. Subsequently, filter and collect the leaching solution; The mass fraction of the hydrogen peroxide is 32%; Among them, the mixed acid solution is prepared by compounding a malic acid solution with a concentration of 2.2 mol / L and a citric acid solution with a concentration of 2.0 mol / L according to a mass ratio of 1:1; Add anhydrous ethanol with the same volume as the leaching solution to the leaching solution, then adjust the pH to 3.5, filter to remove the precipitate, then use lithium hydroxide as the lithium source to supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, under the conditions of a temperature of 60 °C and a stirring speed of 200 r / min, react for 30 min, add a dopamine solution accounting for 8% of the mass of the leaching solution, then raise the temperature to 80 °C, continue to stir and mix for 10 min, then stand for aging for 4 h, and then transfer it to a high-pressure reactor, under the conditions of a temperature of 190 °C and a stirring speed of 400 r / min, carry out high-temperature reaction for 10 h, then cool, discharge, filter, and dry to obtain a dry precursor; Among them, the concentration of the dopamine solution is 10 g / L; Heat and raise the temperature of the dry precursor to 670 °C at a rate of 1.5 °C / min in a reducing atmosphere, keep it for calcination for 8 h, then cool it to room temperature with the furnace, discharge, and obtain the regenerated lithium iron phosphate material; The reducing atmosphere is composed of nitrogen and hydrogen mixed according to a volume ratio of 9.5:1. Example 4

[0023] The difference between this embodiment and embodiment 1 is that an equal mass of sucrose solution with a mass fraction of 10% is used to replace the dopamine solution, and other conditions remain unchanged. Example 5

[0024] Compared with Example 1, this embodiment differs in that no anhydrous ethanol is added, and other conditions remain unchanged. Example 6

[0025] Compared with Example 1, this embodiment has the following differences: The positive electrode active material and the mixed acid solution were mixed in a mass ratio of 1:8.5, and hydrogen peroxide with a mass ratio of 10% of the mixed acid solution was added. The mixture was heated at a temperature of 50°C and a stirring speed of 200 r / min for acid leaching reaction for 2 hours, and then filtered to collect the leachate. The rest of the conditions remain unchanged. Example 7

[0026] Compared with Example 1, this embodiment has the following differences: The positive electrode active material and the mixed acid solution were mixed in a mass ratio of 1:8.5, and hydrogen peroxide with a mass ratio of 10% of the mixed acid solution was added. The mixture was heated and acid-leached for 2 hours at a temperature of 80°C and a stirring speed of 150 r / min, and then filtered to collect the leachate. The rest of the conditions remain unchanged.

[0027] Comparative Example 1 Compared with Example 1, this comparative example has the following differences: No malic acid solution was added, only citric acid solution was added, and the other conditions remained unchanged.

[0028] Comparative Example 2 Compared with Example 1, this comparative example has the following differences: No citric acid solution was added, only malic acid solution was added, and the other conditions remained unchanged.

[0029] The performance evaluation tests were conducted on the products obtained in the examples and comparative examples. The specific evaluation methods and test results are as follows: The lithium iron phosphate positive electrode material, the binder PVDF, and the conductive agent acetylene black are mixed in a mass ratio of 90:5:5. Specifically, the binder PVDF and the solvent NMP are first mixed and stirred to obtain a glue solution, and then the acetylene black and the positive electrode material are added. After stirring evenly, the glue solution is coated on the surface of the aluminum foil. The coated positive electrode sheet is dried and cut. The compaction density on the surface of the aluminum foil is controlled to be 2.75g / cm 3 , thickness is 80μm; Assemble the CR2032 button battery in the glove box in the order of the positive electrode case, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, gasket, spring piece, and negative electrode case. Finally, press it with a sealing machine, let it stand for 24 hours, and test its electrochemical performance; Among them, the separator is a Celgard 2400 polypropylene microporous separator. In the electrolyte, the lithium salt is lithium hexafluorophosphate (concentration: 1 mol / L), and the solvent is a mixture of EC:DMC:DEC = 1:1:1.

[0030] Use a BlueTEC test system (CT2001A) to perform constant current charge and discharge on the assembled button battery. The voltage window is 2.4 - 4.6 V. Under the condition of constant temperature at 25°C, conduct the test. Respectively, obtain the capacity retention rate 1 after 200 cycles at 0.2 C, and the capacity retention rate 2 corresponding to 200 cycles at 0.6 C. The detailed test results are shown in Table 1; Table 1: Test Results of Product Performance

[0031] It can be seen from the test results in Table 1 that the product obtained by the present invention has excellent cycle performance, and moreover, with the increase of the charging rate, the decline of the cycle performance of the product is relatively not obvious.

[0032] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for recycling lithium iron phosphate battery materials by liquid-phase recovery, characterized in that, The specific method includes the following steps: Disassemble the lithium iron phosphate battery and recycle to obtain the positive electrode plate. Peel off the surface active material layer of the positive electrode plate to obtain the positive electrode active material layer. Then, mix it with NMP at a mass ratio of 1:8 - 10, heat it by microwave ultrasonic reaction, filter, wash, and dry to obtain the positive electrode active material. Mix the positive electrode active material and the mixed acid solution at a mass ratio of 1:8.5 - 9.0, add hydrogen peroxide accounting for 10 - 12% of the mass of the mixed acid solution, and carry out an acid leaching reaction by heating at 50 - 90 °C for 2 - 3 h, then filter and collect the leaching solution. Among them, the mixed acid solution is prepared by compounding a malic acid solution with a concentration of 1.8 - 2.2 mol / L and a citric acid solution with a concentration of 1.5 - 2.0 mol / L according to a mass ratio of 1:

1. Adjust the pH of the leaching solution to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, react at 50 - 60 °C, then raise the temperature to 80 °C, stand for aging for 4 h, filter, and dry to obtain the dried precursor. Calcine the dried precursor in a reducing atmosphere at 650 - 670 °C for 6 - 8 h, then cool and discharge to obtain the regenerated lithium iron phosphate material.

2. The method for recycling and regenerating lithium iron phosphate battery materials by liquid phase according to claim 1, characterized in that, The microwave ultrasonic heating reaction includes: Under the conditions of a microwave power of 300 - 320 W and an ultrasonic frequency of 80 - 100 kHz, carry out a microwave ultrasonic reaction for 2 - 2.5 h.

3. A method for recycling and regenerating lithium iron phosphate battery materials using liquid phase recovery, as claimed in claim 1, characterized in that, The specific method further includes: Add anhydrous ethanol with the same volume as the leaching solution to the leaching solution, then adjust the pH to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, react at 50 - 60 °C, then raise the temperature to 80 °C, stand for aging for 4 h, transfer to a high-pressure reactor, carry out a high-temperature reaction at 180 - 190 °C for 8 - 10 h, then cool, discharge, filter, and dry to obtain the dried precursor.

4. A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery, according to any one of claims 1-3, characterized in that, The specific method further includes: Add anhydrous ethanol with the same volume as the leaching solution to the leaching solution, then adjust the pH to 3.5, filter to remove the precipitate, then supplement the lithium source, adjust the molar ratio of Li:Fe:P to 1.05:1:1, then adjust the pH to 9.0, react at 50 - 60 °C, add a dopamine solution accounting for 6 - 8% of the mass of the leaching solution, then raise the temperature to 80 °C, stand for aging for 4 h, transfer to a high-pressure reactor, carry out a high-temperature reaction at 180 - 190 °C for 8 - 10 h, then cool, discharge, filter, and dry to obtain the dried precursor. Among them, the concentration of the dopamine solution is 8 - 10 g / L.

5. A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery, according to any one of claims 1 to 3, characterized in that The specific method further includes: Heat the dried precursor in a reducing atmosphere at a rate of 0.8 - 1.5 °C / min to 650 - 670 °C, keep it for calcination for 6 - 8 h, then cool to room temperature with the furnace and discharge to obtain the regenerated lithium iron phosphate material.

6. A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery according to claim 5, characterized in that, The reducing atmosphere is composed of nitrogen and hydrogen mixed according to a volume ratio of 9 - 9.5:

1.

7. A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery according to claim 1, characterized in that, The specific method further includes: Mix the positive electrode active material and the mixed acid solution at a mass ratio of 1:8.5 - 9.0, and add hydrogen peroxide accounting for 10 - 12% of the mass of the mixed acid solution. First, carry out an acid leaching reaction by heating at a temperature of 50 - 60 °C and a stirring speed of 200 - 220 r / min for 1 - 1.5 h, and then continue the acid leaching reaction by heating at a temperature of 80 - 90 °C and a stirring speed of 150 - 180 r / min for 1 - 1.5 h. Subsequently, filter and collect the leachate.

8. A method for recycling and regenerating lithium iron phosphate battery materials by liquid phase recovery, according to claim 1, characterized in that The mass fraction of the hydrogen peroxide is 28 - 32%.

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