Method for recycling lithium iron phosphate battery cathode material

Abstract

A method for recycling lithium iron phosphate battery positive electrode material by combining pyrogenic process and wet process is provided, PVDF is recycled by wet process, the process not only realizes separation of materials from the pole piece, but also recycles PVDF and aluminum foil, and the solvent can also be recycled; by two-stage filtration and adjusting the particle size of the filter screen, the conductive agent in the positive electrode pole piece can be partially recycled; the pyrogenic process not only oxidizes and consumes the amorphous carbon coated on the surface of the material, but also decomposes and oxidizes the lithium iron phosphate, which is convenient for subsequent process recycling; the subsequent process uses suitable solvents for treatment according to the characteristics of the material, simplifies the recycling process, saves the recycling cost, and realizes clean recycling of lithium iron phosphate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a method for recycling and reusing a lithium iron phosphate battery positive electrode material. BACKGROUND

[0002] The new energy vehicle industry in China is developing rapidly, and the demand for power lithium batteries is growing rapidly. Batteries enter the regular replacement stage. A large amount of high-value metals such as lithium, cobalt and nickel can be recycled in power batteries, which can generate great economic benefits after recycling. A large number of waste power lithium batteries are expected to create a huge recycling market. With the growth of new energy vehicle sales, the installed capacity of power batteries is rising, and the problem of waste power batteries has also attracted attention. It is understood that the number of new energy vehicles in China reached 492 million in 2020, and the cumulative retired power batteries amounted to 200 million tons. By 2025, the capacity of waste power batteries that need to be recycled in China is expected to reach 137.4GWh, which is more than 5 times that of 2020. Once the electrode material enters the environment, metal ions, carbon dust, strong alkali and heavy metal ions may cause serious environmental pollution. The disassembly and recycling of waste batteries can effectively reduce the pollution to the ecological environment and have great social benefits.

[0003] With the improvement of industry technology level, lithium iron phosphate has regained the attention of vehicle manufacturers. By July 2021, lithium iron phosphate has successfully reversed the situation by surpassing ternary lithium, and various power battery manufacturers have expanded production capacity and made early layout. The market share of lithium iron phosphate will gradually increase. At the same time, since 2021, the price of battery raw materials has continued to rise, especially the price of lithium carbonate, which has soared from 50,000 yuan / ton to 350,000 yuan / ton at the end of the year. As of February 2022, the average price of lithium carbonate has broken through 450,000 yuan / ton. Recycling lithium iron phosphate batteries will have great economic and social benefits, and is of great significance to energy saving and emission reduction and sustainable development.

[0004] The recycling technology route of lithium batteries is divided into physical, fire and wet methods. Physical recycling has a simple process and low cost, but the recovery rate is low, and impurities are easily introduced to affect the performance of regenerated materials. Fire method may cause organic lithium to overflow with furnace ash, causing resource waste, and harmful gases produced will cause environmental pollution. The wet process is complex and consumes a lot of acid and alkali solution, which poses a great challenge to environmental protection. Specifically:

[0005] Chinese patent application CN201310001972 discloses a method for recovering lithium ions from waste lithium ion batteries by ion exchange resin. The method first takes out the positive electrode sheet of the waste battery, separates the positive electrode material by alkali immersion, obtains a solution by immersion with sulfuric acid and hydrogen peroxide, then removes impurities in the filtrate by adding calcium carbonate or magnesium oxide, and then recovers lithium ions in the solution by ion exchange resin adsorption. The lithium carbonate product is obtained by heating, concentrating, filtering, separating and drying. Although the method has high recovery efficiency and high purity of the recovered product, the process is complex and has three technical problems: (1) the positive electrode current collector is treated by alkali immersion, but the binder PVDF cannot be dissolved, the positive electrode material is difficult to fall off, and part of the positive electrode material is also dissolved by alkali, resulting in high material loss rate; (2) the ion exchange resin is expensive, and it is difficult to effectively separate lithium ions, resulting in high cost of industrialization equipment; (3) other materials and metals in the positive electrode sheet are not recycled, which not only wastes resources but also has a great impact on the environment.

[0006] Chinese patent application CN201210404862 discloses a method for recovering lithium hydroxide from lithium iron phosphate waste. The lithium iron phosphate waste is calcined in a calcining furnace to separate the coated carbon and the positive electrode material. The positive electrode material is dissolved by concentrated sulfuric acid, and Fe, P and Li are separated by adjusting the pH value. Then, lithium hydroxide is obtained by cooling, crystallization and filtration. Although the method is simple, it can only treat lithium iron phosphate waste and does not involve how to treat the positive electrode material from battery recycling. The method separates the elements by adjusting the pH value, and the purity of the separated material is not high, the impurities are relatively high, and the market value of the product is not high.

[0007] Chinese patent application CN201611138818 discloses a method for recovering lithium from lithium iron phosphate waste battery to prepare battery-grade lithium carbonate. The lithium iron phosphate powder is separated from the treated lithium iron phosphate waste battery, and then sintered at high temperature. Inorganic acid is added to obtain a lithium-containing filtrate and acid leaching residue. Inorganic alkali is added to obtain a lithium-containing purified liquid and magnesium hydroxide residue. The battery-grade lithium carbonate is obtained by pressure filtration, washing and drying. The method has the advantages of high lithium recovery rate, environmental friendliness, high product purity, etc. However, it does not involve how to separate lithium iron phosphate from the electrode sheet, and the recovery of metals is high, PVDF and Fe will be treated as waste, which pollutes the environment.

[0008] Chinese patent application CN201710380176 discloses a recycling method of waste lithium iron phosphate battery. The lithium iron phosphate pole piece is washed, high-temperature treated, and pulverized, and then placed in an organic acid solution to dissolve. Effective lithium is extracted by an extraction liquid, and then a sodium carbonate solution is added to obtain lithium carbonate with high purity. The method has a simple process, high recovery rate and high purity of recovered lithium carbonate. However, the process uses a large number of organic solvents and inorganic acids, which has a great risk of environmental pollution. In addition, other materials and metals in the positive pole piece are not effectively recycled and utilized, and the recycling cost is high.

[0009] Therefore, there is an urgent need for a new recycling method of lithium iron phosphate battery positive electrode material to solve the above technical problems. SUMMARY

[0010] To solve the above technical problems, the present application provides a recycling method of lithium iron phosphate battery positive electrode material combining pyrometallurgy and hydrometallurgy. The method has a simple process, less environmental pollution, and high utilization rate of valuable resources.

[0011] Specifically, the present application provides a recycling method of lithium iron phosphate battery positive electrode material, comprising the following steps:

[0012] (1) disassembling and separating the waste lithium iron phosphate battery to obtain the positive pole piece;

[0013] (2) crushing the positive pole piece and mixing it with solvent A, dissolving for a certain time, and then separating the first solid phase and the first mixed liquid after the powder on the positive pole piece falls off. The first solid phase is the separated aluminum foil, which can be directly recycled and utilized;

[0014] (3) standing the first mixed liquid obtained in step (2) to separate layers, and then using a filtering device to sequentially perform first filtering and second filtering to obtain coarse particulate matter, fine particulate matter, and first filtrate;

[0015] (4) placing the first filtrate obtained in step (3) in water to fully separate phases, and then separating the second solid phase and the second liquid phase. The second solid phase is dried and crushed to obtain polyvinylidene fluoride (PVDF) regenerated material. The second liquid phase is subjected to cyclic distillation to remove water, and the remaining liquid phase is collected as regenerated solvent A for recycling;

[0016] (5) drying and crushing the coarse particulate matter obtained in step (3), and then performing high-temperature carbon removal treatment. After the graphite coating layer on the surface of the coarse particulate matter is removed, it is crushed again to obtain a precursor powder;

[0017] (6) drying and crushing the fine particulate matter obtained in step (3) to obtain a conductive agent;

[0018] (7) placing the precursor powder obtained in step (5) in an ammonia water solution, and after sufficient reaction, filtering to obtain a third solid phase and a third filtrate;

[0019] (8) placing the third solid phase obtained in step (7) in a reaction tank, adding a sulfuric acid solution to the reaction tank, and after reaction for a certain time, filtering to obtain a fourth solid phase and a fourth filtrate;

[0020] (9) distilling and concentrating the fourth filtrate obtained in step (8), and cooling and crystallizing to obtain FeSO4·7H2O crystals, which are used as a lithium iron phosphate reaction raw material;

[0021] (10) drying and crushing the fourth solid phase obtained in step (8) to obtain FePO4 powder, which is used as a lithium iron phosphate reaction raw material;

[0022] (11) placing the third filtrate obtained in step (7) in a reactor, slowly adding phosphoric acid while stirring, and stopping adding the phosphoric acid when the pH value of the solution is less than 7, to react to generate lithium phosphate precipitate, filtering to obtain a fifth solid phase and a fifth filtrate;

[0023] (12) distilling and concentrating, cooling and crystallizing, centrifuging and drying the fifth solid phase obtained in step (11) to obtain lithium phosphate finished product;

[0024] (13) distilling and concentrating, cooling and crystallizing the fifth filtrate obtained in step (11) to obtain ammonium phosphate powder, which is used as a lithium iron phosphate reaction raw material.

[0025] In the step (2), the diameter of the crushed positive electrode sheet is 5-10 mm.

[0026] In the step (2), the solvent A is any one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methyl pyrrolidone.

[0027] In the step (2), the dissolving is performed at a temperature of 60-85°C for 5-24 h, and can be assisted by one or both of ultrasonic oscillation or mechanical stirring.

[0028] In the step (3), the static layering is performed at 60-85°C.

[0029] In the step (3), the first filtering and the second filtering are performed under pressure.

[0030] In the step (3), the first filtering uses a screen mesh with a mesh number of 2-100, and the second filtering uses a screen mesh with a mesh number of 200-500.

[0031] In the step (3), the filter equipment with two layers of filter layers arranged from top to bottom is used to realize the first filtration and the second filtration by pressure filtration, and the mesh numbers of the upper and lower filter layers are 20-100 mesh and 200-500 mesh respectively.

[0032] In the step (4), the water includes one or both of distilled water and deionized water.

[0033] In the step (5), the conductive agent includes one or more of Super P, carbon nanotube, conductive carbon black, acetylene black, conductive graphite, carbon fiber and graphene.

[0034] In the step (6), the high-temperature carbon removal treatment temperature is 300-800 DEG C, and the treatment time is 8-24h.

[0035] In the step (6), the high-temperature carbon removal treatment includes loading the fine powder particles obtained after drying and crushing into a ceramic crucible and placing the ceramic crucible into a sintering furnace for high-temperature carbon removal treatment, and fresh air is introduced during the high-temperature carbon removal treatment.

[0036] In the step (6), the re-crushing includes mechanical crushing.

[0037] In the step (7), the mass concentration of the ammonia solution is 30-80%.

[0038] In the step (7), the reaction temperature of the reaction is 50-90 DEG C, and the reaction time is 5-15h.

[0039] In the step (7), one or both of ultrasonic oscillation and mechanical stirring is used for uniform stirring during the reaction.

[0040] In the step (8), the mass concentration of the sulfuric acid solution is 50-95%.

[0041] In the step (8), mechanical stirring is performed during the reaction, and the pH value of the reaction solution is controlled to be 5-7 by adding the sulfuric acid solution.

[0042] In the step (11), the mass concentration of the phosphoric acid is 50-85%.

[0043] Therefore, the present application has the following beneficial technical effects:

[0044] (1) The recycling process of the present application is simple, the chemical reagents used are relatively conventional, the use amount is small, and part of the reagents can be repeatedly used, thereby reducing the pressure on environmental protection;

[0045] (2) The present application fully combines the pyrogenic process and the wet process, separates the materials in the lithium iron phosphate pole piece with relatively large purity by using the characteristics of the materials, simplifies the recovery process, saves the recovery cost, and realizes the clean recovery and utilization of lithium iron phosphate; specifically:

[0046] The PVDF is recovered and reused by the wet process, which not only realizes the separation of the materials from the pole piece, but also recycles and reuses the PVDF and aluminum foil, and the solution can also be recycled and reused;

[0047] By two-stage filtration and adjusting the particle size of the filter screen, the conductive agent in the positive pole piece can be partially recovered;

[0048] The pyrogenic process not only oxidizes and consumes the amorphous carbon coated on the surface of the material, but also decomposes and oxidizes the lithium iron phosphate, which is convenient for subsequent process recovery and utilization;

[0049] The subsequent process uses the characteristics of the materials to select suitable solvents for treatment, simplifies the recovery process, saves the recovery cost, and realizes the clean recovery and utilization of lithium iron phosphate;

[0050] (3) The product of the method has high utilization rate, and the PVDF, conductive agent, Li, Fe and P in the lithium iron phosphate pole piece are fully recovered and utilized, and the recovery method is simple and has high recovery purity;

[0051] (4) The present application can also be used for recovering the lithium iron phosphate positive pole piece discarded by battery enterprises;

[0052] (5) The equipment used in the present application is also relatively simple, and the equipment capacity is also conventional, which effectively reduces the recovery cost.

[0053] Brief description of the drawings

[0054] Figure 1 The process flow chart of the lithium iron phosphate battery positive material recovery and reuse method is described.

[0055] Figure 2 The chemical reactions occurring in the process of the present application are described. DETAILED DESCRIPTION

[0056] The present application will be further described in conjunction with specific examples. However, it should be understood that these examples are only used to illustrate and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or modifications to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the claims of the present application.

[0057] Example 1

[0058] (1) The waste lithium iron phosphate battery is disassembled, the shell is peeled off, the positive plate is separated from the battery, the separated positive plate is crushed, the diameter of the plate is 8 mm, then the crushed plate is dissolved in a mixed solution of N, N-dimethylformamide and N, N-dimethylacetamide, the mass ratio of the two solvents is 1:1, and the plate is dissolved for 20 hours under the action of ultrasonic oscillation and mechanical stirring at 70℃, then the aluminum foil is taken out after the powder on the plate falls off, and the aluminum foil is directly recycled.

[0059] (2) The above-mentioned solution is filtered by using a filtering device, and two layers of filter layers are arranged, the mesh number of the first layer of filter is 100 meshes, and the mesh number of the second layer of filter is 500 meshes; then the filtered solution collected after the second filtration is placed in distilled water to fully separate the phases, and then the solidified substance is collected, dried, crushed, and PVDF regenerated material is obtained; the separated filtered solution is subjected to distillation to remove distilled water, and the remaining solution is collected for recycling; then the solid phase collected in the second layer is dried and crushed to obtain a mixed conductive agent with fine particles.

[0060] (3) The precipitate filtered in the first layer in (2) is dried and crushed to obtain fine powder particles, which are respectively loaded into ceramic mortars and subjected to high-temperature carbon removal treatment in a sintering furnace, and fresh air is introduced, the sintering temperature is 800℃, and the sintering time is 8 hours; after high-temperature sintering, the obtained precursor powder with uniform particles is obtained by mechanical crushing.

[0061] (4) The crushed precursor powder is dissolved in an ammonia water solution with a mass concentration of 50%, and a 100r / min mechanical uniform speed stirring is started to accelerate the dissolution of the powder, the solution temperature is 80℃, and the reaction time is 10 hours; after the solution is fully reacted, the solution is filtered and separated by using a filtering device.

[0062] (5) An 80% sulfuric acid solution is added to a reaction tank containing the above-mentioned filtered solid phase, and a 150r / min mechanical stirring is used to accelerate the solution reaction, the reaction temperature is 50℃, and the pH of the reaction solution is controlled to be 6 by adding sulfuric acid solution during the reaction; then the reaction solution is filtered and separated, the filtered solution is subjected to distillation and concentration, cooling crystallization, to obtain FeSO4.7H2O crystals; the precipitate filtered is dried and crushed to obtain FePO4 powder.

[0063] (6) An 80% phosphoric acid solution is slowly added to the reaction tank of the filtered solution in (4), and fully reacted under the condition of 150r / min uniform stirring, the pH value of the reaction solution is tested, and the addition of phosphoric acid is stopped when the pH value is 7; after full reaction, the solution is filtered by using a filtering device, distilled and concentrated, cooled and crystallized, centrifugally separated, and dried to obtain Li3PO4 finished product; the filtered solution is distilled and concentrated, cooled and crystallized to obtain (NH4)3PO4 powder.

[0064] Example 2

[0065] (1) The waste lithium iron phosphate positive electrode sheet collected by the battery factory is crushed, the diameter of the electrode sheet is 10 mm, then the crushed electrode sheet is dissolved in N-methyl pyrrolidone solution, the dissolution temperature is 50°C, and ultrasonic oscillation and mechanical stirring are carried out, the power of ultrasonic oscillation is 20 kHz, the stirring rate of mechanical stirring is 150 r / min, the dissolution time is 10 h, after the powder on the electrode sheet falls off, the separated aluminum foil is directly recycled.

[0066] (2) The above-mentioned dissolved solution is subjected to pressure filtration by using a filtering device, and two layers of filter layers are set, the mesh number of the first layer of filter screen is 50 meshes, and the mesh number of the second layer of filter screen is 400 meshes; then the filtrate collected after the second layer of filtration is placed in distilled water for sufficient phase separation, and then the solidified substance is collected, dried, crushed, and PVDF regenerated material is obtained; the separated filtrate is subjected to cycle distillation to remove distilled water, and the remaining solution is collected for recycling; then the solid phase collected in the second layer is subjected to drying and crushing treatment, and a conductive agent with uniform particles is obtained.

[0067] (3) The precipitate after the first layer of filtration in (2) is subjected to drying and crushing treatment to obtain fine powder particles, which are then respectively loaded into ceramic mortars and placed in a sintering furnace for high-temperature carbon removal treatment, and sufficient fresh air is introduced, the sintering temperature is 500°C, and the sintering time is 15 h; after high-temperature sintering is completed, the obtained precursor powder with uniform particles is obtained by mechanical crushing.

[0068] (4) The crushed precursor powder is dissolved in an ammonia water solution with a mass concentration of 80%, and a 150 r / min mechanical uniform speed stirring is started to accelerate the dissolution of the powder, the solution temperature is 60°C, and the reaction time is 15 h; after the solution is fully reacted, the solution is filtered and separated by using a filtering device.

[0069] (5) A sulfuric acid solution with a mass concentration of 50% is added to the reaction tank of the filtered solid phase in (4), and a 200 r / min mechanical stirring is used to accelerate the solution reaction, the reaction temperature is 60°C, and the pH of the reaction solution is controlled to be 5.5 by adding sulfuric acid solution during the reaction; then the reaction solution is filtered and separated, the filtered solution is subjected to distillation concentration, cooling crystallization, and FeSO4.7H2O crystals are obtained; the filtered precipitate is dried and crushed to obtain FePO4 powder.

[0070] (6) Slowly add phosphoric acid with a mass concentration of 60% to the reaction tank of the filtrate after filtering (4), and fully react under uniform stirring at 200 r / min. Test the pH value of the reaction solution, and stop adding phosphoric acid when the pH value is 6.5. After full reaction, filter through a filtering device, distill and concentrate, cool and crystallize, centrifugally separate, and dry to obtain Li3PO4 finished product. The filtrate after filtering is distilled and concentrated, cooled and crystallized to obtain (NH4)3PO4 powder.

[0071] Example 3

[0072] (1) After disassembling the waste lithium iron phosphate battery, the outer shell is peeled off, the positive plate is separated from the battery, and then the separated positive plate is pulverized, the diameter of the plate is 5 mm, then the pulverized plate is dissolved in a mixed solution of dimethyl sulfoxide and N-methyl pyrrolidone, the mass ratio of the two solvents is 3:7, and ultrasonic oscillation and mechanical stirring are carried out at 50°C, the power of ultrasonic oscillation is 22 kHz, the stirring rate of mechanical stirring is 200 r / min, the reaction time is 15 h, and after the powder on the plate falls off, the separated aluminum foil is directly recycled.

[0073] (2) The above-mentioned dissolved solution is pressurized and filtered by using a filtering device, and two layers of filter layers are set, the mesh number of the first layer of filter is 20 meshes, and the mesh number of the second layer of filter is 200 meshes; then the filtrate collected after the second layer of filtration is fully separated in distilled water, and then the solidified material is collected, dried, and pulverized to obtain PVDF regenerated material; the separated filtrate is subjected to cycle distillation to remove distilled water, and the remaining solution is collected for recycling; then the solid phase collected in the second layer is dried and pulverized to obtain a mixed conductive agent with fine particles.

[0074] (3) The precipitate collected after the first layer of filtration in (2) is dried and pulverized to obtain fine powder particles, which are respectively loaded into ceramic crucibles and subjected to high-temperature carbon removal treatment in a sintering furnace, and sufficient fresh air is introduced, the sintering temperature is 500°C, and the sintering time is 18 h; after high-temperature sintering, the obtained precursor powder material with uniform particles is obtained by mechanical pulverization.

[0075] (4) The pulverized precursor powder material is dissolved in an ammonia water solution with a mass concentration of 65%, and a mechanical uniform stirring at 180 r / min is started to accelerate the dissolution of the powder, the solution temperature is 75°C, the reaction time is 13 h, and after the solution is fully reacted, the solution is filtered and separated by using a filtering device.

[0076] (5) Add the solution of sulfuric acid with a mass concentration of 68% into the reaction tank of the solid phase after filtration of (4), and use mechanical stirring at 180 r / min to accelerate the solution reaction, the reaction temperature is 60°C, and the pH of the reaction solution is controlled at 6.5 by adding the solution of sulfuric acid during the reaction; then the reaction solution is separated by filtration, the filtered solution is concentrated by distillation, and cooled to crystallize to obtain FeSO4.7H2O crystals; the filtered precipitate is dried and crushed to obtain FePO4 powder.

[0077] (6) Slowly add the solution of phosphoric acid with a mass concentration of 68% into the reaction tank of the filtrate after filtration of (4), and fully react under uniform stirring at 180 r / min, test the pH of the reaction solution, stop adding the solution of phosphoric acid when the pH is 6.5, filter after full reaction, concentrate by distillation, cool to crystallize, centrifugal separation, and dry to obtain Li3PO4 finished product; the filtered filtrate is concentrated by distillation, cooled to crystallize, and dried to obtain (NH4)3PO4 powder.

[0078] Obviously, the above examples are only examples for clearly illustrating, but not limit the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for recycling lithium iron phosphate battery cathode material, comprising the following steps: (1) disassembling and separating the waste lithium iron phosphate battery to obtain a cathode sheet; (2) crushing the cathode sheet, mixing it with a solvent A, dissolving for a certain time, and separating a first solid phase and a first mixed solution after the powder on the cathode sheet falls off, wherein the first solid phase is the separated aluminum foil, and the separated aluminum foil is directly recycled; (3) standing and stratifying the first mixed solution obtained in step (2), and then sequentially performing first filtration and second filtration by using a filtering device to obtain coarse particles, fine particles and a first filtrate; (4) fully separating the first filtrate obtained in step (3) in water, and then separating a second solid phase and a second liquid phase; drying and crushing the second solid phase to obtain polyvinylidene fluoride regenerated material; and removing water from the second liquid phase by cyclic distillation, and collecting the remaining liquid phase as regenerated solvent A for recycling; (5) drying and crushing the coarse particles obtained in step (3), and then performing high-temperature carbon removal treatment, crushing again after the graphite coating layer on the surface of the coarse particles is removed, to obtain a precursor powder; (6) drying and crushing the fine particles obtained in step (3) to obtain a mixed conductive agent; (7) placing the precursor powder obtained in step (5) in an ammonia solution, fully reacting, and then filtering to obtain a third solid phase and a third filtrate; (8) placing the third solid phase obtained in step (7) in a reaction tank, adding a sulfuric acid solution to the reaction tank, and filtering after reacting for a certain time to obtain a fourth solid phase and a fourth filtrate; (9) distilling and concentrating the fourth filtrate obtained in step (8), and cooling and crystallizing to obtain FeSO4·7H2O crystals, which are used as lithium iron phosphate reaction raw materials; (10) drying and crushing the fourth solid phase obtained in step (8) to obtain FePO4 powder, which is used as lithium iron phosphate reaction raw materials; (11) placing the third filtrate obtained in step (7) in a reactor, slowly adding phosphoric acid while stirring, stopping adding phosphoric acid when the pH value of the solution is less than 7, and reacting to generate lithium phosphate precipitate, filtering to obtain a fifth solid phase and a fifth filtrate; (12) distilling and concentrating the fifth solid phase obtained in step (11), cooling and crystallizing, centrifugally separating, and drying to obtain lithium phosphate finished product; (13) distilling and concentrating the fifth filtrate obtained in step (11), cooling and crystallizing to obtain ammonium phosphate powder, which is used as lithium iron phosphate reaction raw materials; In step (2), the solvent A is any one or mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methyl pyrrolidone; In step (3), the first filtration and the second filtration are performed under pressure; the first filtration uses a screen with a mesh size of 20-100, and the second filtration uses a screen with a mesh size of 200-500; In step (8), mechanical stirring is performed while controlling the pH value of the reaction solution to be 5-7 by adding a sulfuric acid solution.

2. The method for recycling lithium iron phosphate battery cathode material according to claim 1, wherein, In the step (3), the first filtration and the second filtration are achieved by using a filter device with two layers of filter layers arranged from top to bottom, and the filtration is achieved by pressure filtration, and the mesh numbers of the upper and lower filter layers are 20-100 mesh and 200-500 mesh respectively.

3. The method of recycling lithium iron phosphate battery cathode material according to claim 1, wherein, In the step (6), the high-temperature decarburization treatment temperature is 300-800℃, and the treatment time is 8-24h.

4. The method of recycling lithium iron phosphate battery cathode material according to claim 1, wherein, In the step (7), the mass concentration of the ammonia solution is 30-80%.

5. The method of recycling lithium iron phosphate battery cathode material according to claim 1, wherein, In the step (8), the mass concentration of the sulfuric acid solution is 50-95%.

6. The method of recycling lithium iron phosphate battery cathode material according to claim 1, wherein, In the step (11), the mass concentration of the phosphoric acid is 50-85%.

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