Method for recycling waste lithium iron phosphate positive electrode material

Abstract

The application provides a recycling method of waste lithium iron phosphate positive electrode material, comprising the following steps: mixing an organic acid solution and a waste lithium iron phosphate mixture, and reacting to obtain a solution containing lithium ions and FePO4 filter residue; washing and drying the FePO4 filter residue to obtain C / FePO4 powder; adding the C / FePO4 powder into a Na2S2O3 aqueous solution to obtain a suspension; stirring, washing and drying the suspension to obtain C / NaFePO4 powder; removing impurities from the solution containing lithium ions and evaporating and concentrating, then adding a sodium phosphate solution, washing, filtering and separating to obtain lithium phosphate. The method has the advantages of simple operation, low cost, less pollution, low energy consumption and high economic benefits. In the whole recycling process, the waste lithium iron phosphate is fully recycled, the recycling process is simple, only a small amount of reagent and room temperature are needed to complete the lithium removal, and finally the synthesized sodium iron phosphate maintains the excellent morphology and microstructure characteristics of the original lithium iron phosphate, and exhibits high rate performance.

Description

TECHNICAL FIELD

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

[0002] With the increasing promotion of LiFePO4 batteries in the electric vehicle industry, the recycling of waste LiFePO4 batteries is imminent. However, since the LiFePO4 battery does not contain any noble metal, it makes it less attractive to the battery recycling industry. Adopting a reasonable recycling method can effectively alleviate the environmental pollution and resource waste problems caused by waste lithium iron phosphate batteries, and at the same time, it can turn waste into treasure, which is conducive to realizing the full life cycle of LiFePO4 batteries. The recycling process of waste lithium iron phosphate currently includes LiFePO4 material repair and regeneration and element selective recycling. LiFePO4 material repair and regeneration involves a complex high-energy process, which needs to be supplemented with lithium, and before adding Li2CO3 in the dry high-temperature process, the molar ratio of Li / Fe needs to be accurately measured. There are problems such as large energy consumption, multiple waste liquid generation, etc. in the regeneration process. Element selective recycling mainly recycles lithium resources, phosphorus and iron resources through wet treatment. The existing technology mainly uses acid solutions such as phosphoric acid and sulfuric acid to dissolve lithium iron phosphate, and recovers valuable metals lithium, iron and phosphorus through certain means. In the actual recycling process, the technical cost is high, the process is complicated, the production efficiency is low, the effective leaching of metal elements cannot be realized at room temperature, and due to the large use of chemical reagents, improper handling can easily cause pollution.

[0003] Therefore, in view of the technical problems such as complicated process, inability to effectively leach metal elements at room temperature, generation of a large amount of chemical reagents, and high cost in the actual recycling process of lithium iron phosphate, it is necessary to develop a recycling method of waste lithium iron phosphate positive electrode material. SUMMARY

[0004] The application provides a recycling method of waste lithium iron phosphate positive electrode material to solve the above technical problems.

[0005] One technical solution of the application is to provide a recycling method of waste lithium iron phosphate positive electrode material, comprising the following steps:

[0006] (1) reacting an organic acid solution and a waste lithium iron phosphate mixed solution, and obtaining a solution containing lithium ions and FePO4 filter residue after filtration;

[0007] (2) washing and drying the FePO4 filter residue to obtain C / FePO4 powder, adding the C / FePO4 powder to a Na2S2O3 aqueous solution to obtain a suspension, stirring, washing, and drying the suspension to obtain C / NaFePO4 powder;

[0008] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then a sodium phosphate solution is added, washed, filtered, and separated to obtain lithium phosphate.

[0009] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the molar ratio of the organic acid solution to the waste lithium iron phosphate in step (1) is 1-3:3-1, and the reaction time is 10-30 h.

[0010] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the organic acid solution in step (1) is any one or more of peroxoacetic acid, acetic acid, formic acid, and oxalic acid; the volume concentration of the organic acid solution is 10%-15%, and the dropping speed of the organic acid solution is 1.8-2.5 mL / min.

[0011] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the preparation method of the waste lithium iron phosphate mixed solution in step (1) is: dissolving the waste lithium iron phosphate in deionized water, stirring for 5-10 min, and the concentration of the waste lithium iron phosphate mixed solution is 0.2-0.6 mol / L.

[0012] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the washing in step (2) is washing with deionized water for three times; the drying is drying at 200-300°C under N2 atmosphere for 6-8 h, and the stirring is magnetic stirring at 60-80°C for 24-30 h.

[0013] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the concentration of the Na2S2O3 aqueous solution in step (2) is 0.2-0.4 M, and the molar ratio of FePO4 to Na2S2O3 is 0.8-1.3:1.5-2.5.

[0014] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the concentration of the sodium phosphate solution in step (3) is 0.8-1.0 M.

[0015] As a preferred solution of the recycling method of the waste lithium iron phosphate positive electrode material, the molar ratio of Li + in the solution containing lithium ions to PO4 3- in the sodium phosphate solution in step (3) is 1-2:1.

[0016] As a preferred scheme of the method for recycling waste lithium iron phosphate positive electrode material, the sodium phosphate solution in step (3) is added to the concentrated solution containing lithium ions in three times.

[0017] As a preferred scheme of the method for recycling waste lithium iron phosphate positive electrode material, the reaction temperature of the sodium phosphate solution in step (3) added to the concentrated solution containing lithium ions is 60-90 DEG C, and the temperature of the washing and filtering is 75-90 DEG C.

[0018] Compared with the prior art, the method for recycling waste lithium iron phosphate positive electrode material has the advantages that:

[0019] 1. The waste LiFePO4 battery is chemically oxidized to form iron lithium mineral NaFePO4 for home energy storage application, which provides a new idea for the battery recycling industry and provides a second life for the waste LiFePO4 battery.

[0020] 2. In the process of recycling waste lithium iron phosphate material, only a simple peroxoacetic acid solvent is used, which can be directly dissolved in deionized water, and the reaction can be directly carried out in air without inert atmosphere protection, which has the advantages of simple recycling method, low cost, less environmental pollution, good energy saving effect and high economic benefit.

[0021] 3. The synthesis of iron phosphate in the salinization process adopts an environmentally friendly process, without adding dangerous chemicals and organic solvents, which greatly reduces environmental pollution.

[0022] 4. When recycling lithium, lithium phosphate is precipitated in the lithium-containing solution by adding phosphate, which has a higher lithium content than traditional methods of synthesizing lithium carbonate to recycle lithium resources, and is more difficult to dissolve than lithium carbonate, which can make the lithium recycling process more effective.

[0023] 5. The method has the characteristics of high selectivity in recycling waste lithium iron phosphate positive electrode material, and the main components can be separated by chemical method, and the materials obtained after separation can be regenerated and synthesized into NaFePO4 and lithium phosphate by using an environmentally friendly process, realizing the full recycling and regeneration of lithium, iron and phosphorus in lithium iron phosphate, and having high industrial production value. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with specific embodiments.

[0025] First, the term "one embodiment" or "an embodiment" as may appear in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments.

[0026] The application discloses a novel recycling method of waste lithium iron phosphate positive electrode material, and specific operation steps comprise:

[0027] (1) the waste lithium iron phosphate is dissolved in 500-800 mL of deionized water, and stirred for 5-10 min to obtain a waste lithium iron phosphate mixed solution, in order to control the flow rate and prevent excessive oxidation, 0.15-0.35 mol of an organic acid solution is added into the 0.2-0.6 mol / L waste lithium iron phosphate mixed solution at a speed of 1.8-2.5 mL / min for chemical oxidation decomposition for 10-30 h, and a solution containing lithium ions and FePO4 filter residue are obtained after filtration, wherein the organic acid solution comprises any one or more of peracetic acid, acetic acid, formic acid and oxalic acid, and the volume concentration is 10%-15%.

[0028] (2) the FePO4 filter residue is washed with deionized water for three times, dried at 200-300 DEG C under N2 atmosphere for 6-8 h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added into a 0.2-0.4 M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 0.8-1.3:1.5-2.5, and finally the obtained suspension is magnetically stirred at 60-80 DEG C for 24-30 h, and C / NaFePO4 powder is obtained after washing and drying.

[0029] (3) the solution containing lithium ions is impurity-removed and evaporated and concentrated, then a 0.8-1.0 M sodium phosphate solution is added, the concentration of Li + in the solution containing lithium ions is 0.1-0.2 M, and the concentration of PO4 3-The molar ratio is 1-2:1. The sodium phosphate solution is added to the concentrated lithium-ion-containing solution in three equal portions. Adding the sodium phosphate solution in stages ensures a high Li concentration in the initial stage, effectively inhibiting the hydrolysis of Na3PO4 and ensuring that all added Na3PO4 participates in the Li precipitation reaction. This significantly improves precipitation efficiency and lithium phosphate recovery. The higher the Li concentration, the higher the Li precipitation efficiency. The reaction temperature is 60-90℃ because the precipitation rate of Li3PO4 is slow at low temperatures, and the rate increases with higher temperatures. As the temperature rises, the sedimentation rate increases in the later stages, but the growth rate is not significant. After the reaction is complete, the lithium phosphate is obtained by washing and filtering at 75-90℃. This temperature is chosen because the byproduct Na2HPO4 is readily soluble in water, and its solubility increases with temperature. Increasing the filtration temperature helps improve the purity of lithium phosphate.

[0030] For detailed implementation methods and related comparisons, please refer to the following examples:

[0031] Example 1

[0032] The present invention discloses a novel method for recycling and reusing waste lithium iron phosphate cathode material, comprising the following steps:

[0033] (1) Dissolve 0.2 mol of waste lithium iron phosphate in 500 mL of deionized water and stir for 10 min. Then, slowly add 0.3 mol of 12% peracetic acid solution dropwise to the above solution at a rate of 2 mL / min, and chemically oxidize and decompose for 24 h. After filtration, a solution containing lithium ions and FePO4 residue are obtained;

[0034] (2) After washing the FePO4 filter residue three times with deionized water, it was dried at 250℃ under N2 atmosphere for 6h to remove excess water and obtain C / FePO4 powder. Then, the C / FePO4 powder was added to a 0.3M Na2S2O3 aqueous solution with a molar ratio of FePO4 to Na2S2O3 of 1:2.5. Finally, the resulting suspension was magnetically stirred at 60℃ for 24h, washed and dried to obtain C / NaFePO4 powder.

[0035] (3) The lithium-ion-containing solution was purified and concentrated by evaporation. Then, a 1M sodium phosphate solution was added to the concentrated lithium-ion-containing solution in three portions at 80°C. The lithium-ion-containing solution contained Li... + PO4 in sodium phosphate solution 3- The molar ratio was 1:1. After the reaction was completed, the mixture was washed and filtered at 90°C, and then dried to obtain lithium phosphate.

[0036] Example 2

[0037] A novel recycling method of waste lithium iron phosphate positive electrode material, comprising the steps of:

[0038] (1) 0.2 mol of waste lithium iron phosphate is dissolved in 500 mL of deionized water and stirred for 10 min. Then 0.2 mol of peracetic acid solution with a volume concentration of 12% is slowly added to the above solution at a rate of 2 mL / min, and chemical oxidation decomposition is carried out for 24 h. After filtration, a solution containing lithium ions and FePO4 filter residue are obtained;

[0039] (2) The FePO4 filter residue is washed with deionized water three times, then dried at 250°C under N2 atmosphere for 6 h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added to a 0.3 M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 1:2, and finally the obtained suspension is magnetically stirred at 60°C for 24 h, and C / NaFePO4 powder is obtained after washing and drying.

[0040] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then 0.9 M sodium phosphate solution is added to the concentrated solution containing lithium ions in three portions at 80°C, the molar ratio of Li + in the solution containing lithium ions to PO4 3- in the sodium phosphate solution is 1:1, after the reaction is completed, washing and filtration are carried out at 90°C, and lithium phosphate is obtained after drying.

[0041] Example 3

[0042] A novel recycling method of waste lithium iron phosphate positive electrode material, comprising the steps of:

[0043] (1) 0.2 mol of waste lithium iron phosphate is dissolved in 500 mL of deionized water and stirred for 10 min. Then 0.2 mol of peracetic acid solution with a volume concentration of 15% is slowly added to the above solution at a rate of 2 mL / min, and chemical oxidation decomposition is carried out for 24 h. After filtration, a solution containing lithium ions and FePO4 filter residue are obtained;

[0044] (2) The FePO4 filter residue is washed with deionized water three times, then dried at 250°C under N2 atmosphere for 6 h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added to a 0.3 M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 1:1.5, and finally the obtained suspension is magnetically stirred at 60°C for 24 h, and C / NaFePO4 powder is obtained after washing and drying.

[0045] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then 0.8M sodium phosphate solution is added into the concentrated solution containing lithium ions in three times at 90°C, the molar ratio of Li + and PO4 3- in the solution containing lithium ions to PO4 in the sodium phosphate solution is 1.5:1, after the reaction is completed, washing and filtration are carried out at 80°C, and lithium phosphate is obtained after drying.

[0046] Example 4

[0047] The method for recycling and reusing a new type of waste lithium iron phosphate positive electrode material comprises the steps of:

[0048] (1) 0.3 mol of waste lithium iron phosphate is dissolved in 500 mL of deionized water and stirred for 10 min. Then 0.2 mol of peroxyacetic acid solution with a volume concentration of 15% is slowly added into the above solution at a rate of 2.5 mL / min, and chemical oxidation decomposition is carried out for 24 h. After filtration, a solution containing lithium ions and FePO4 filter residue are obtained;

[0049] (2) The FePO4 filter residue is washed with deionized water for three times, then dried at 200°C under N2 atmosphere for 6 h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added into 0.3M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 1:1.5, finally the obtained suspension is stirred at 80°C for 24 h under magnetic stirring, and C / NaFePO4 powder is obtained after washing and drying.

[0050] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then 0.8M sodium phosphate solution is added into the concentrated solution containing lithium ions in three times at 90°C, the molar ratio of Li + and PO4 3- in the solution containing lithium ions to PO4 in the sodium phosphate solution is 1.5:1, after the reaction is completed, washing and filtration are carried out at 80°C, and lithium phosphate is obtained after drying.

[0051] Example 5

[0052] The method for recycling and reusing a new type of waste lithium iron phosphate positive electrode material comprises the steps of:

[0053] (1) 0.3 mol of waste lithium iron phosphate is dissolved in 700 mL of deionized water and stirred for 10 min. Then 0.2 mol of peroxyacetic acid solution with a volume concentration of 15% is slowly added into the above solution at a rate of 2.5 mL / min, and chemical oxidation decomposition is carried out for 24 h. After filtration, a solution containing lithium ions and FePO4 filter residue are obtained;

[0054] (2) The FePO4 filter residue is washed with deionized water three times, then dried at 280°C under N2 atmosphere for 8h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added to a 0.3M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 1:1.5, finally the obtained suspension is stirred at 80°C under magnetic stirring for 24h, after washing and drying, C / NaFePO4 powder is obtained.

[0055] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then 0.8M sodium phosphate solution is added to the concentrated solution containing lithium ions three times at 90°C, the molar ratio of Li + in the solution containing lithium ions to PO4 3- in the sodium phosphate solution is 2:1, after the reaction, washing and filtering are carried out at 60°C, and after drying, lithium phosphate is obtained.

[0056] Example 6

[0057] The novel recycling method of waste lithium iron phosphate positive electrode material according to the present application comprises the following steps:

[0058] (1) 0.3mol of waste lithium iron phosphate is dissolved in 700mL of deionized water, and stirred for 10min. Then 0.2mol of 15% peroxoacetic acid solution is slowly added to the above solution at a rate of 2.5mL / min, and chemical oxidation decomposition is carried out for 24h. After filtering, a solution containing lithium ions and FePO4 filter residue are obtained;

[0059] (2) The FePO4 filter residue is washed with deionized water three times, then dried at 280°C under N2 atmosphere for 8h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder is added to a 0.4M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 is 1:1.5, finally the obtained suspension is stirred at 80°C under magnetic stirring for 24h, after washing and drying, C / NaFePO4 powder is obtained.

[0060] (3) The solution containing lithium ions is impurity-removed and concentrated by evaporation, then 1M sodium phosphate solution is added to the concentrated solution containing lithium ions three times at 90°C, the molar ratio of Li + in the solution containing lithium ions to PO4 3- in the sodium phosphate solution is 1:1, after the reaction, washing and filtering are carried out at 75°C, and after drying, lithium phosphate is obtained.

[0061] Comparative Example 1

[0062] (1) 0.2 mol of waste lithium iron phosphate was dissolved in 500 mL of deionized water and stirred for 10 min. Then 0.3 mol of 12% peroxoacetic acid solution was slowly added to the above solution at a rate of 2 mL / min, and chemical oxidation decomposition was carried out for 24 h. After filtration, a solution containing lithium ions and FePO4 filter residue were obtained;

[0063] (2) The FePO4 filter residue was washed with deionized water three times, then dried at 250°C under N2 atmosphere for 6 h to remove excess water to obtain C / FePO4 powder, then the C / FePO4 powder was added to a 0.3 M Na2S2O3 aqueous solution, the molar ratio of FePO4 to Na2S2O3 was 1:2.5, and finally the obtained suspension was stirred at 60°C for 24 h. After washing and drying, C / NaFePO4 powder was obtained.

[0064] (3) The solution containing lithium ions was purified and concentrated by evaporation, then 1 M sodium phosphate solution was added to the concentrated solution containing lithium ions at 80°C, the molar ratio of Li + in the solution containing lithium ions to PO4 3- in the sodium phosphate solution was 1:1. After the reaction was completed, washing and filtration were carried out at 90°C, and lithium phosphate was obtained after drying.

[0065] Comparative Example 2

[0066] The title is: A method for recycling and preparing battery-grade iron phosphate from waste lithium iron phosphate; Application No. 202210925323.6.

[0067] Comparative Example 3

[0068] The title is: A method for recycling and preparing battery-grade iron phosphate from waste lithium iron phosphate; Application No. 202211519104.4.

[0069] Comparative Example 4

[0070] The title is: A method for recycling and preparing battery-grade iron phosphate from waste lithium iron phosphate; Application No. 202310285978.6.

[0071] The obtained C / NaFePO4 positive electrode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was coated on an aluminum foil, dried, punched and pressed to form a positive electrode material sheet. A metal sodium sheet was used as the negative electrode, Grade GF / D was used as the separator, and 1 mol / L NaPF6 was used as the electrolyte. After assembling the battery in an argon atmosphere vacuum glove box, constant current charge and discharge tests were carried out at 25°C, the voltage range was 1.5-4.0 V, and the charge and discharge were carried out at 0.1C and 0.5C current rates, respectively, to evaluate the rate performance of the material. The test results are shown in Table 1.

[0072]

[0073]

[0074] Table 1

[0075] From Table 1, it can be seen that the first discharge specific capacity at 0.1C and 0.5C rate and the 0.1C coulombic efficiency of Examples 1-6 are all greater than those of Comparative Examples 1-4, indicating that the C / NaFePO4 cathode material obtained by the recycling method of the waste lithium iron phosphate cathode material has excellent rate performance.

[0076] The lithium phosphate precipitate obtained in the examples and comparative examples was dried, weighed, and the purity was determined, and the lithium recovery rate in the waste lithium iron phosphate cathode material was calculated, and the results are shown in Table 2.

[0077] Sample Purity of lithium phosphate (%) Lithium recovery rate (%) Example 1 98.6 96.1 Example 2 96.2 94.6 Example 3 95.5 93.2 Example 4 97.2 94.8 Example 5 96.4 93.9 Example 6 95.2 93.7 Comparative Example 1 86.8 85.1

[0078] Table 2

[0079] From Table 2, it can be seen that the purity and recovery rate of lithium phosphate obtained in Examples 1-6 are all greater than those of Comparative Example 1, indicating that the stepwise addition of sodium phosphate can ensure that the solution is in a high Li concentration state in the early stage, effectively inhibit the hydrolysis of Na3PO4, and make the added Na3PO4 all participate in the Li precipitation reaction, significantly improve the precipitation efficiency and the recovery rate of lithium phosphate. The lithium phosphate material obtained by the recycling method of the waste lithium iron phosphate cathode material provided by the application has excellent precipitation efficiency, and the lithium recovery rate is high, which significantly reduces the loss of lithium in the recycling process.

[0080] The lithium extraction process of the examples and comparative examples was compared, and the results are shown in Table 3.

[0081]

[0082]

[0083] Table 3

[0084] From Table 3, it can be seen that the lithium extraction process of the product can be completed at room temperature, while the reactions of Comparative Examples 2, 3 and 4 all require heating, and the lithium extraction step of Comparative Example 4 also needs to be carried out in an inert atmosphere, indicating that the recycling method of the waste lithium iron phosphate cathode material provided by the application has good energy-saving effect and high economic benefit, which is beneficial to reduce the material recycling cost. Comparative Examples 2, 3 and 4 require more reagents, so the cost of recycling the waste lithium iron phosphate material by using the application can be reduced by 50-75%, and has good environmental protection.

[0085] In summary, the method for recycling and reusing waste lithium iron phosphate positive electrode material provided by the application realizes high-efficiency separation of different substances in the waste lithium iron phosphate battery material by high-selectivity leaching of lithium ions at room temperature through low-cost organic acid, preserves the chemical properties of the surface of the lithium iron phosphate while recycling lithium ions, and synthesizes a polyanionic sodium iron sulfate positive electrode material for sodium ion batteries by using an environmentally friendly process. The method is simple to operate, has the advantages of low cost, less pollution, low energy consumption, and high economic benefits, and the like. In the entire recycling process, the waste lithium iron phosphate is fully recycled, the recycling process is simple, and only a small amount of reagent and room temperature are required to complete the delithiation, and finally the synthesized sodium iron phosphate retains the excellent morphology and microstructure characteristics of the original lithium iron phosphate, and exhibits high rate performance.

[0086] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for recycling waste lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: (1) mixing an organic acid solution and a waste lithium iron phosphate solution to obtain a solution containing lithium ions and FePO4 residue, wherein the molar ratio of the organic acid solution to the waste lithium iron phosphate is 1-3:3-1, the reaction time is 10-30 h, the organic acid solution is any one or more of peroxyacetic acid, acetic acid, formic acid and oxalic acid, the volume concentration of the organic acid solution is 10%-15%, and the dropping speed of the organic acid solution is 1.8-2.5 mL / min; (2) washing and drying the FePO4 residue to obtain C / FePO4 powder, adding the C / FePO4 powder into a Na2S2O3 aqueous solution to obtain a suspension, stirring, washing and drying the suspension to obtain C / NaFePO4 powder; (3) removing impurities from the solution containing lithium ions and evaporating and concentrating the solution, then adding a sodium phosphate solution to the concentrated solution, washing and filtering to obtain lithium phosphate.

2. The method of recycling a spent lithium iron phosphate cathode material of claim 1, wherein, In step (1), the waste lithium iron phosphate solution is prepared by dissolving the waste lithium iron phosphate in deionized water and stirring for 5-10 min, and the concentration of the waste lithium iron phosphate solution is 0.2-0.6 mol / L.

3. The method of recycling spent lithium iron phosphate cathode material according to claim 1, characterized in that: In step (2), the washing is performed by washing with deionized water three times, the drying is performed at 200-300 ℃ under N2 atmosphere for 6-8 h, and the stirring is performed at 60-80 ℃ for 24-30 h.

4. The method of recycling spent lithium iron phosphate cathode material according to claim 1, characterized in that: In step (2), the concentration of the Na2S2O3 aqueous solution is 0.2-0.4 M, and the molar ratio of FePO4 to Na2S2O3 is 0.8-1.3:1.5-2.

5.

5. The method of recycling spent lithium iron phosphate cathode material according to claim 1, characterized in that: In step (3), the concentration of the sodium phosphate solution is 0.8-1.0 M.

6. The method of recycling spent lithium iron phosphate cathode material according to claim 1, wherein: The molar ratio of Li in the solution containing lithium ions in step (3) to PO4 in the sodium phosphate solution + is 1-2:

1. 3- is 1-2:

1.

7. The method of recycling spent lithium iron phosphate cathode material according to claim 1, wherein: In step (3), the reaction temperature for adding the sodium phosphate solution into the concentrated solution containing lithium ions is 60-90 ℃, and the temperature for washing and filtering is 75-90 ℃.

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