Lithium iron phosphate material regeneration method, regenerated lithium iron phosphate and regenerated battery

Abstract

The invention discloses a lithium iron phosphate material regeneration method, regenerated lithium iron phosphate and a regenerated battery, and relates to the technical field of lithium iron phosphate treatment. Comprising the following steps: mixing a lithium iron phosphate material to be subjected to impurity removal with an impurity removal solution to obtain a first mixture; the impurity removal solution comprises acid radicals complexed with impurity metal ions; the first mixture reacts at the first temperature, solid and liquid are obtained through solid-liquid separation after the reaction is finished, the solid comprises the lithium iron phosphate material subjected to impurity removal, and the liquid comprises a complex formed by complexing impurity metal ions and acid radicals; and mixing the impurity-removed lithium iron phosphate material with a regeneration solution to obtain a second mixture, and carrying out heat treatment on the second mixture to obtain regenerated lithium iron phosphate. According to the method, the lithium iron phosphate material to be subjected to impurity removal is mixed with the impurity removal solution, acid radicals in the impurity removal solution are complexed with impurity metal ions, further dissolution of impurity metal and oxide thereof is promoted, and separation of the impurity metal and oxide thereof from the lithium iron phosphate material is achieved.

Description

Technical Field

[0001] This application relates to the technical field of lithium iron phosphate processing, specifically to a method for regenerating lithium iron phosphate materials, regenerated lithium iron phosphate, and regenerated batteries. Background Technology

[0002] During the battery recycling process, after physical pretreatment steps such as discharge, disassembly, mechanical crushing, and grinding, the recycled lithium iron phosphate material inevitably contains metallic impurities from battery structural components (such as current collectors and casings), especially aluminum and copper.

[0003] Currently, the existing technology for removing metal impurities such as aluminum and copper from lithium iron phosphate materials generally involves first adding a mixed solution consisting of inorganic acid, metal removal solution (such as polymaleic acid or polyacrylic acid), and water to the impurity-containing lithium iron phosphate material to carry out an aluminum removal reaction; then dissolving the aluminum-removed material in a mixture of inorganic acid and oxidant (such as hydrogen peroxide) to carry out a copper removal reaction.

[0004] However, while removing aluminum and copper, the aforementioned process also converts lithium iron phosphate material into corresponding ions, significantly damaging the structure of the lithium iron phosphate material. Moreover, the process involves numerous steps, resulting in high reagent consumption and wastewater generation, making it difficult to meet the demands for efficient, green, and low-cost resource regeneration. Summary of the Invention

[0005] The first aspect of this application provides a method for regenerating lithium iron phosphate material, the method comprising: The lithium iron phosphate material to be purified is mixed with the purification solution to obtain a first mixture; wherein, the purification solution includes acid radicals that are complexed with impurity metal ions, the acid radicals include at least one of citrate, ethylenediaminetetraacetic acid, tartrate and pyrophosphate, and the impurity metal ions include copper ions and aluminum ions. The first mixture is reacted at a first temperature. After the reaction is completed, solid and liquid are separated to obtain solid and liquid. The solid includes lithium iron phosphate material after impurity removal, and the liquid includes complexes formed by the complexation of impurity metal ions and acid radicals. The purified lithium iron phosphate material is mixed with a regeneration solution to obtain a second mixture. The second mixture is subjected to a first heat treatment. After the first heat treatment, solid-liquid separation is performed to obtain a solid substance. The solid substance is subjected to a second heat treatment to obtain regenerated lithium iron phosphate.

[0006] In some optional embodiments of the first aspect of this application, the total concentration of acid radicals in the impurity removal solution is 0.01 mol / L to 5.0 mol / L.

[0007] In some optional embodiments of the first aspect of this application, the liquid-to-solid ratio between the impurity removal solution and the lithium iron phosphate material to be removed is (3~20):1, in mL / g.

[0008] In some optional embodiments of the first aspect of this application, the first temperature is 30°C to 90°C; The reaction of the first mixture at the first temperature includes: stirring the first mixture at the first temperature for 0.5 h to 5 h.

[0009] In some optional embodiments of the first aspect of this application, the pH of the impurity removal solution is 4 to 10.

[0010] In some optional embodiments of the first aspect of this application, the first heat treatment of the second mixture includes heating the second mixture at 120°C to 500°C for 5 to 15 hours; The second heat treatment of the solid material includes: drying the solid material, and then heating the solid material at 100℃~800℃ for 2h~12h in an inert gas atmosphere.

[0011] In some optional embodiments of the first aspect of this application, the regeneration solution includes a lithium source, a reducing agent and water, and the mass ratio of the lithium source, the reducing agent and the purified lithium iron phosphate material is 1:(1~10):(2~10).

[0012] In some optional embodiments of the first aspect of this application, the liquid-to-solid ratio of the regenerated solution to the purified lithium iron phosphate material is (3~20):1, in mL / g.

[0013] The second aspect of this application provides a regenerated lithium iron phosphate, which is prepared by the above-described lithium iron phosphate material regeneration method.

[0014] A third aspect of this application provides a regenerated battery, including a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode includes the aforementioned regenerated lithium iron phosphate.

[0015] Beneficial effects: The regeneration method provided in the first aspect of this application firstly involves mixing the lithium iron phosphate material to be purified with a purification solution and then heating it. The acid radicals in the purification solution complex with the impurity metal ions, promoting the further dissolution of the impurity metals and their oxides. Ultimately, the impurity metals and their oxides are largely dissolved and separated from the lithium iron phosphate material. No other insoluble impurities are introduced during the purification process, resulting in good purification effect, significantly reducing the loss of lithium, iron, and phosphorus, and minimizing damage to the lithium iron phosphate crystal structure, thus laying a good foundation for subsequent direct regeneration. Moreover, the purification process is simple.

[0016] The lithium iron phosphate material regeneration method provided in the first aspect of this application first removes impurities from the lithium iron phosphate material to be purified, thereby removing impurity metals to obtain purified lithium iron phosphate material, and then directly regenerates the purified lithium iron phosphate material through a hydrothermal method. The regeneration method has a simple process flow.

[0017] The recycled lithium iron phosphate provided in the second aspect of this application has low residual levels of impurity metal elements, with copper residue less than 40 ppm and aluminum residue less than 400 ppm.

[0018] The regenerative battery provided in the third aspect of this application has good electrochemical performance, and its discharge specific capacity at a 0.1C rate can reach more than 155mAh / g. Attached Figure Description

[0019] Figure 1 This is a flowchart of a lithium iron phosphate material regeneration method in one embodiment of this application; Figure 2 This is a charge-discharge curve of the battery composed of recycled lithium iron phosphate obtained in Comparative Example 2 of this application at a rate of 0.1C; Figure 3 This is a charge-discharge curve of the battery composed of recycled lithium iron phosphate obtained in Example 1 of this application at a rate of 0.1C. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In one embodiment, a method for regenerating lithium iron phosphate material is provided, the method comprising: The lithium iron phosphate material to be purified is mixed with the purification solution to obtain a first mixture; wherein, the purification solution includes acid radicals that are complexed with impurity metal ions, the acid radicals include at least one of citrate, ethylenediaminetetraacetic acid, tartrate and pyrophosphate, and the impurity metal ions include copper ions and aluminum ions. The first mixture is reacted at a first temperature. After the reaction is completed, solid and liquid are separated to obtain solid and liquid. The solid includes lithium iron phosphate material after impurity removal, and the liquid includes complexes formed by the complexation of impurity metal ions and acid radicals. The purified lithium iron phosphate material is mixed with a regeneration solution to obtain a second mixture. The second mixture is subjected to a first heat treatment. After the first heat treatment, solid-liquid separation is performed to obtain a solid substance. The solid substance is subjected to a second heat treatment to obtain regenerated lithium iron phosphate.

[0023] In the above scheme, the lithium iron phosphate material to be purified is mixed with a purification solution to obtain a first mixture, which is then heated to undergo a reaction. During the reaction, a small amount of impurity metals and their oxides (such as Cu, Cu₂O, Al) in the first mixture are oxidized into ions by dissolved oxygen. Then, the acid radicals in the purification solution complex with the impurity metal ions to form complexes, reducing the concentration of impurity metal ions in the first mixture. This further promotes the dissolution of the impurity metals, ultimately leading to a significant dissolution of the impurity metals and their oxides, thereby achieving the separation of the impurity metals and their oxides from the lithium iron phosphate material. No other insoluble impurities are introduced during the purification process, resulting in good purification performance, significantly reducing the loss of lithium, iron, and phosphorus, and minimizing damage to the lithium iron phosphate crystal structure.

[0024] Citrate can be derived from citric acid or citrate salts; ethylenediaminetetraacetic acid (EDTA) can be derived from EDTA or EDTA salts; tartrate can be derived from tartaric acid or tartrate salts; and pyrophosphate can be derived from pyrophosphate or pyrophosphate salts.

[0025] The impurity removal solution provided in this embodiment can effectively leach out impurity metals and their oxides, while lithium, iron, and phosphorus exist in solid form, thus achieving the separation of impurity metal elements such as aluminum and copper from lithium iron phosphate. The following uses citrate ion as an example to further illustrate the impurity removal principle in this embodiment.

[0026] Lithium iron phosphate itself has a highly stable crystal structure that is not destroyed in citric acid or its salt solutions. This system can maintain the stability of lithium iron phosphate while efficiently dissolving impurity metals such as aluminum and copper.

[0027] Citric acid or sodium citrate solution includes Cit 3- or HCit 2- The process of leaching out copper impurities is as follows: (1) Dissolution: The O2 dissolved in the impurity-removing solution acts as an oxidizing agent, oxidizing elemental copper or copper oxides on the surface into copper ions. The reaction equation is: 2Cu + 4H + +O2=2Cu 2+ +2H2O; Cu₂O + 4H⁺ + +O2=2Cu 2+ +2H2O.

[0028] In the above reaction, only a small amount of hydrogen ions is needed to initiate the reaction, and subsequent hydrogen ions are replenished by the reaction products (such as Cu).2+ With HCit 2- Complexation release of H + ).

[0029] (2) Complexation: The reaction equation is: Cu 2+ +2Cit 3- =[Cu(Cit)2] 4- ; Cu 2+ +HCit 2- =CuCit - +H + .

[0030] Cu generated by the above oxidation and dissolution 2+ Cit 3- or HCit 2- When Cu in the first mixture undergoes complexation to form a soluble complex, the Cu... 2+ The concentration of copper decreases, which in turn further promotes the reaction of copper dissolution to generate copper ions during the oxidation and dissolution process.

[0031] The process of leaching aluminum impurities in citric acid or sodium citrate solution is as follows: (1) Dissolution: A small amount of hydrogen ions are provided in citric acid or sodium citrate solution, which react with aluminum impurities to form Al. 3+ .

[0032] (2) Complexation: The reaction equation is: Al 3+ +3Cit 3- =[Al(Cit)3] 6- .

[0033] Al 3+ With Cit 3- Formation of a complex [Al(Cit)3] 6- The formation of complexes reduces the Al content in the solution. 3+ The concentration promotes dissolution.

[0034] In some optional embodiments of this application, the total concentration of acid radicals in the impurity removal solution is 0.01 mol / L to 5.0 mol / L.

[0035] This setup ensures that the total concentration of acid radicals in the purification solution remains within the aforementioned range, guaranteeing that impurities such as copper and aluminum are fully complexed and preventing side reactions. If the total acid radical concentration is less than 0.01 mol / L, the reaction is incomplete, resulting in insufficient complexation of impurities such as copper and aluminum, making effective removal difficult. Conversely, if the total acid radical concentration is greater than 5.0 mol / L, side reactions are more likely to occur, potentially damaging the crystal structure of lithium iron phosphate and causing significant unintended leaching of elements such as lithium, iron, and phosphorus.

[0036] In some optional embodiments of this application, the total concentration of acid radicals in the impurity removal solution is 0.1 mol / L to 0.5 mol / L. Further optimization of the total concentration of acid radicals in the impurity removal solution significantly improves the removal rate of impurities such as copper and aluminum, and avoids the large-scale unintended leaching of elements such as lithium, iron, and phosphorus.

[0037] In some optional embodiments of this application, the liquid-to-solid ratio between the impurity removal solution and the lithium iron phosphate material to be removed is (3~20):1, in mL / g.

[0038] In some optional embodiments of this application, the first temperature is 30°C to 90°C. With this setting, as the reaction temperature increases, the kinetic energy of the reactant molecules increases, causing more molecular collisions to exceed the activation energy. This greatly increases the number of effective collisions between reactant molecules, thereby significantly accelerating the complexation reaction rate, promoting the complexation of impurity metals with acid radicals, and further promoting the dissolution of impurity metals.

[0039] In some optional embodiments of this application, the first temperature is 50°C to 90°C. Further optimizing the range of the first temperature significantly improves the removal rate of impurities such as copper and aluminum.

[0040] In some optional embodiments of this application, reacting the first mixture at a first temperature includes: stirring the first mixture at a first temperature for 0.5 h to 5 h.

[0041] In some optional embodiments of this application, the pH of the impurity removal solution is 4 to 10.

[0042] The acid radicals mentioned above exist in different forms under different pH conditions. Taking citrate as an example: at pH < 2.5, citrate exists in the forms of H3Cit and H2Cit. - The citrate ion has low complexing ability; in the pH range of 2.5-4, the citrate ion exists in the form of H2Cit. - HCit 2- The citrate complexation ability is moderate; in the pH range of 4 to 6.5, the citrate exists in the form of HCit. 2- Cit 3- It has a high citrate complexing ability; at pH > 6.5, the citrate ion exists in the form of Citrate. 3- Citrate ions have the highest complexing ability, but if the pH is too high, such as >11, copper and aluminum will precipitate, which is not conducive to the leaching of copper and aluminum. Therefore, the pH of the impurity removal solution should be 4~10 to ensure the complexing ability of the acid ions while avoiding the formation of copper and aluminum precipitates.

[0043] In some optional embodiments of this application, the pH of the impurity removal solution is 6.5~10. Further optimizing the pH range of the impurity removal solution improves the complexing ability of acid radicals and enhances the removal effect of impurities such as copper and aluminum.

[0044] In some optional embodiments of the first aspect of this application, the first heat treatment of the second mixture includes heating the second mixture at 120°C to 500°C for 5 to 15 hours; The second heat treatment of the solid material includes: drying the solid material, and then heating the solid material at 100℃~800℃ for 2h~12h in an inert gas atmosphere.

[0045] In some optional embodiments of this application, the regeneration solution includes a lithium source, a reducing agent and water, and the mass ratio of the lithium source, the reducing agent and the purified lithium iron phosphate material is 1:(1~10):(2~10).

[0046] In some optional embodiments of this application, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium phosphate.

[0047] In some optional embodiments of this application, the reducing agent includes at least one selected from malic acid, malate, oxalic acid, oxalate, ascorbic acid, ascorbate, sulfurous acid, sulfite, tartaric acid, tartrate, citric acid, and citrate.

[0048] In some optional embodiments of this application, the liquid-to-solid ratio of the regenerated solution to the purified lithium iron phosphate material is (3~20):1, in mL / g.

[0049] In another embodiment, a regenerated lithium iron phosphate is provided, which is prepared by the above-described lithium iron phosphate material regeneration method.

[0050] In another embodiment, a regenerated battery is provided, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode comprises the aforementioned regenerated lithium iron phosphate.

[0051] The present application is further illustrated below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials, reagents, materials, and equipment used in this application are all commercially available products conventionally used in the art. The lithium iron phosphate materials to be purified used in all embodiments and comparative examples are from the same batch.

[0052]

Example 1

[0053] S2. Stir the first mixture at a first temperature of 90°C for 1 hour and the stirring speed is 600 rpm. After the reaction is completed, filter the mixture in a Buchner funnel to obtain a solid and an extract. Wash the solid with deionized water and collect the solid in a 110°C oven to dry it. After drying for 3 hours, the purified lithium iron phosphate material is obtained.

[0054] S3. Mix 1.5g of purified lithium iron phosphate material with the regeneration solution to obtain a second mixture. The regeneration solution includes 0.32g of lithium hydroxide, 0.68g of ascorbic acid and 13.5g of deionized water. The liquid-solid ratio of the regeneration solution to the purified lithium iron phosphate material is 9:1 mL / g.

[0055] S4. Heat the second mixture at 180°C for 12 hours. After heating, cool it to room temperature. Filter the second mixture in a Buchner funnel to obtain a solid substance. Rinse the solid substance with deionized water and then dry it in an oven at 110°C.

[0056] S5. Place the dried solid material in a tube furnace and heat it at 700°C for 6 hours in a nitrogen atmosphere. After heating, regenerated lithium iron phosphate is obtained.

[0057]

Example 2

[0058] S2 to S5 are the same as in Example 1.

[0059]

Example 3

[0060] S2 to S5 are the same as in Example 1.

[0061]

Example 4

[0062] S2. Stir the first mixture at a first temperature of 30°C for 1 hour. The stirring speed is 600 rpm. After the reaction is complete, filter the mixture in a Buchner funnel to obtain a solid and an extract. Rinse the filter cake with deionized water. After rinsing, collect the filter cake and dry it in an oven at 110°C. After drying for 3 hours, the purified lithium iron phosphate material is obtained.

[0063] S3 to S5 are the same as in Example 1.

[0064]

Example 5

[0065] S2. Stir the first mixture at a first temperature of 50°C for 1 hour and the stirring speed is 600 rpm. After the reaction is completed, filter the mixture in a Buchner funnel to obtain a solid and an extract. Wash the solid with deionized water and collect the solid in a 110°C oven to dry it. After drying for 3 hours, the purified lithium iron phosphate material is obtained.

[0066] S3 to S5 are the same as in Example 1.

[0067]

Example 6

[0068] S2 to S5 are the same as in Example 1.

[0069]

Example 7

[0070] S2 to S5 are the same as in Example 1.

[0071]

Example 8

[0072] S2 to S5 are the same as in Example 1.

[0073]

Example 9

[0074] S2 to S5 are the same as in Example 1.

[0075]

Example 10

[0076] S2 to S5 are the same as in Example 1.

[0077] Comparative Example 1 The lithium iron phosphate in Comparative Example 1 that needs to be purified is left untreated.

[0078] Comparative Example 2 S1. Mix 1.5g of lithium iron phosphate material to be purified with the regeneration solution to obtain a mixture, wherein the regeneration solution includes 0.32g of lithium hydroxide, 0.68g of ascorbic acid and 13.5g of deionized water, and the liquid-solid ratio of the regeneration solution to the purified lithium iron phosphate material is 9:1mL / g.

[0079] S2. Heat the mixture at 180°C for 12 hours. After heating, cool it to room temperature. Filter the mixture in a Buchner funnel to obtain a solid substance. Rinse the solid substance with deionized water and then dry it in an oven at 110°C.

[0080] S3. Place the dried solid material in a tube furnace and heat it at 700°C for 6 hours in a nitrogen atmosphere. After heating, regenerated lithium iron phosphate is obtained.

[0081] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is the concentration of the citric acid aqueous solution in S1; the remaining steps are the same. Specifically: S1. Mix 20g of lithium iron phosphate material to be purified with the purification solution to obtain a first mixture, wherein the purification solution is a 0.001mol / L citric acid aqueous solution; the pH of the purification solution is 6.5; and the liquid-solid ratio of the purification solution to the lithium iron phosphate material to be purified is 6:1mL / g.

[0082] S2 to S5 are the same as in Example 1.

[0083] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is the concentration of the citric acid aqueous solution in S1; the remaining steps are the same. Specifically: S1. Mix 20g of lithium iron phosphate material to be purified with the purification solution to obtain a first mixture, wherein the purification solution is a 5.50mol / L citric acid aqueous solution; the pH of the purification solution is 6.5; and the liquid-solid ratio of the purification solution to the lithium iron phosphate material to be purified is 6:1mL / g.

[0084] S2 to S5 are the same as in Example 1.

[0085] The reaction conditions of each embodiment and comparative example are summarized in Table 1.

[0086] Table 1 Summary of reaction conditions for each embodiment and comparative example

[0087] [Testing Method] (a) The residual amounts of copper and aluminum in the lithium iron phosphate materials after impurity removal in Examples 1 to 10, as well as Comparative Examples 3 and 4, and the leaching rates of lithium and phosphorus were measured.

[0088] (1) After the lithium iron phosphate material to be purified is mixed with the purification solution and the reaction is completed at the first temperature, solid-liquid separation is performed, and the solid and leachate are collected respectively.

[0089] (2) Take 0.10g of solid, weigh it accurately and place it in a polytetrafluoroethylene digestion vessel. Add nitric acid and hydrogen peroxide solution, and digest it by microwave (program: 120℃ 5min→150℃ 5min→180℃ 30min) until it is completely dissolved. Cool it and make up to 50mL with ultrapure water and shake well.

[0090] The concentrations of copper (Cu) and aluminum (Al) in the solution were determined using ICP-OES, and the residual amounts (ppm) of Cu and Al in the solid were calculated based on the sample weight.

[0091] Cu / Al residue (ppm) = (C × 0.05) / m × 1000. Where m is the mass of the solid sample and C is the concentration of copper or aluminum.

[0092] (3) Take the leachate, dilute it appropriately, and determine the concentrations of lithium (Li) and phosphorus (P) using ICP-OES. Record the total volume of the leachate and calculate the total amount of Li and P leached out. At the same time, take the unpurified lithium iron phosphate material to be purified, and digest and determine it using ICP in the same way to obtain the total content of Li and P.

[0093] The leaching rate is calculated as follows: Leaching rate (%) = (total mass of elements in the leachate / total mass of elements in the raw material) × 100%.

[0094] (ii) The lithium iron phosphate materials to be purified in Comparative Examples 1 and 2 were not mixed with the purification solution for purification. Therefore, the leaching rates of lithium and phosphorus in Comparative Examples 1 and 2 were 0 during the purification process.

[0095] The steps for measuring the residual amounts of copper and aluminum in the lithium iron phosphate materials to be purified in Comparative Example 1 and Comparative Example 2 are as follows: Take 0.10g of the lithium iron phosphate material sample to be purified, weigh it accurately, and place it in a polytetrafluoroethylene digestion vessel. Add nitric acid and hydrogen peroxide solution, and digest it by microwave (program: 120℃ 5min→150℃ 5min→180℃ 30min) until it is completely dissolved. After cooling, make up to 50mL with ultrapure water and shake well.

[0096] The concentrations of copper (Cu) and aluminum (Al) in the solution were determined using ICP-OES, and the residual amounts (ppm) of Cu and Al in the lithium iron phosphate material sample to be purified were calculated based on the sample weight.

[0097] Cu / Al residue (ppm) = (C × 0.05) / m × 1000. Where m is the mass of the lithium iron phosphate material sample to be purified, and C is the concentration of copper or aluminum.

[0098] (iii) The electrochemical performance of the regenerated lithium iron phosphate obtained in Examples 1 to 10 and Comparative Examples 2 to 4, and the untreated lithium iron phosphate material to be purified in Comparative Example 1 were tested.

[0099] The electrochemical performance testing methods are as follows: (1) Lithium iron phosphate, conductive agent acetylene black, and binder PVDF were added to a mixing tank at a mass ratio of 9:0.5:0.5. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred thoroughly in a homogenizer to obtain a uniform and stable positive electrode slurry. The slurry was uniformly coated onto aluminum foil using a coating machine, and then dried in a vacuum drying oven at 100℃ for 2 hours to completely remove the solvent. After drying, the electrode was cut into circular electrode sheets with a diameter of 12 mm using a slicing machine.

[0100] (2) In a glove box under an argon atmosphere, a CR2032 coin cell was assembled using the prepared positive electrode, a lithium metal sheet as the negative electrode, a polypropylene microporous membrane as the separator, and 1 mol / L lithium hexafluorophosphate in EC / DMC (1:1, v / v) solution as the electrolyte. After assembly, the cells were allowed to stand for 12 hours to allow the electrolyte to fully wet the electrodes and the separator.

[0101] (3) Electrochemical performance was tested using the Blue Electric series battery testing system: the first efficiency (i.e., the first coulombic efficiency) was determined by conducting the first charge and discharge test at a current density of 0.1C within a voltage range of 2.5V to 4.0V, and the ratio of the first discharge specific capacity to the first charge specific capacity was calculated as the first efficiency; the constant current charge ratio was obtained by analyzing the proportion of the constant current capacity to the total charge capacity during the first charge process; in the rate performance test, charge and discharge cycles were performed at current densities of 0.1C and 1C respectively, and the corresponding discharge specific capacity was recorded to evaluate the electrochemical activity and stability of the material at low and high rates.

[0102] The results of measuring the residual amounts of copper and aluminum, the leaching rates of lithium and phosphorus, and the electrochemical performance tests are summarized in Table 2.

[0103] Table 2 Summary of test results for each embodiment and comparative example

[0104] Analysis based on Tables 1 and 2: In Comparative Example 1, the lithium iron phosphate material to be purified was not treated. The residual copper content in the lithium iron phosphate material to be purified in Comparative Example 1 was 775.7 ppm, and the residual aluminum content was 2573.9 ppm.

[0105] In Comparative Example 2, the lithium iron phosphate material to be purified was not subjected to purification treatment and was directly regenerated. The residual copper content in the lithium iron phosphate material to be purified in Comparative Example 2 was 775.7 ppm, and the residual aluminum content was 2573.9 ppm.

[0106] As shown in Table 2, the copper and aluminum content in the lithium iron phosphate materials obtained in Examples 1 to 10 after impurity removal is significantly lower than that in Comparative Examples 1 and 2. This indicates that the impurity removal solution used in this application can effectively remove the impurity metals copper and aluminum from the lithium iron phosphate materials.

[0107] The leaching rates of lithium in the leachates obtained in Examples 1 to 10 were 1.31% to 5.16%, and the leaching rates of phosphorus were 0.25% to 1.93%. The content of lithium and phosphorus leached in each example was not high. This indicates that while achieving the leaching of impurities and their separation from lithium iron phosphate materials, each example reduced the damage to the crystal structure of lithium iron phosphate, thus greatly reducing the loss of lithium and phosphorus.

[0108] The difference between Examples 1 to 3, Comparative Example 3, and Comparative Example 4 lies in the concentration of citric acid. The concentrations of citric acid in Examples 1 to 3, Comparative Example 3, and Comparative Example 4 were 0.50 mol / L, 0.10 mol / L, 0.20 mol / L, 0.001 mol / L, and 5.50 mol / L, respectively. Data on copper and aluminum residues obtained from Examples 1 to 3 show that the removal effect of copper gradually increases with increasing citric acid concentration; however, once the citric acid concentration reaches a certain level, the removal effect of aluminum stabilizes. The copper and aluminum residues in Comparative Example 3 are similar to those in Comparative Examples 1 and 2, indicating that when the concentration of citric acid is too low, it cannot effectively perform complexation and thus cannot promote the removal of copper and aluminum. The residual amounts of copper and aluminum, as well as the leaching rates of lithium and phosphorus in Comparative Example 4, were much higher than those in Example 1. This indicates that when citric acid reaches a certain concentration, excessive citric acid will destroy the crystal structure of lithium iron phosphate, leading to the non-selective dissolution of target elements (such as lithium and phosphorus), while failing to effectively inhibit or remove impurity metals such as copper and aluminum.

[0109] The difference between Examples 1, 4 and 5 lies in the first temperature. The first temperatures of Examples 1, 4 and 5 are 90℃, 30℃ and 50℃, respectively. According to the data on the residual copper and aluminum obtained from Examples 1, 4 and 5, as the reaction temperature increases during the impurity removal process, the removal effect of copper and aluminum gradually increases and the impurity removal reaction effect is better.

[0110] The difference between Examples 1, 6 to 10 lies in the type of impurity removal solution. Data on the residual amounts of copper and aluminum obtained from Examples 1, 6 to 10 show that the residual amounts of copper and aluminum obtained from Examples 1, 6 to 10 are significantly reduced, indicating that the different impurity removal solutions can achieve good impurity removal effects.

[0111] The batteries composed of recycled lithium iron phosphate as the cathode material in Examples 1 to 10 exhibited the following measured effects: initial efficiency range of 98.73% to 99.31%, constant current charge ratio range of 99.39% to 99.77%, 0.1C discharge specific capacity range of 159.33 mAh / g to 160.13 mAh / g, and 1C discharge specific capacity range of 140.93 mAh / g to 142.12 mAh / g. The electrochemical performance test data measured in Examples 1 to 10 are all higher than those in Comparative Examples 1 to 3, indicating that effectively reducing the copper and aluminum impurity content in lithium iron phosphate can significantly improve the battery's initial efficiency, constant current charge ratio, and 0.1C / 1C discharge specific capacity.

[0112] Although the residual amounts of copper and aluminum in Comparative Example 4 were similar to those in Example 4, the leaching rates of lithium and phosphorus in Comparative Example 4 were higher than those in Example 4. This indicates that the excessively high concentration of citric acid caused more damage to the lithium iron phosphate lattice structure. The resulting structural damage resulted in Comparative Example 4 having significantly lower first-efficiency, constant current charge ratio, and 0.1C and 1C discharge specific capacities than Example 4.

[0113] Figure 2 This is a charge-discharge curve of the battery composed of recycled lithium iron phosphate obtained in Comparative Example 2 at a 0.1C rate. Figure 3 This is a charge-discharge curve of the battery composed of regenerated lithium iron phosphate obtained in Example 1 at a rate of 0.1C. Figure 2 and Figure 3 The rising curve represents the charging process, and the falling curve represents the discharging process.

[0114] By comparison Figure 2 and Figure 3 It can be seen that the battery discharge capacity measured in Comparative Example 2 was only 129.51 mAh / g, and the voltage plateau was relatively low and unstable. The battery discharge capacity measured in Example 1 was significantly increased to approximately 160.13 mAh / g, and the discharge curve showed a very flat and stable high voltage plateau in most ranges (such as the 0~140 mAh / g range), with the voltage stabilizing at around 3.4V until the end of the discharge period when the voltage rapidly decreased from the plateau period. This indicates that the regenerated lithium iron phosphate obtained in Example 1 has good electrochemical performance.

[0115] It should be noted that, in this document, "comprising," "including," or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0116] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The above descriptions are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A method for regenerating lithium iron phosphate materials, characterized in that, The regeneration method includes: The lithium iron phosphate material to be purified is mixed with a purification solution to obtain a first mixture; wherein, the purification solution includes anions complexed with impurity metal ions, the anions include at least one of citrate, ethylenediaminetetraacetic acid, tartrate and pyrophosphate, and the impurity metal ions include copper ions and aluminum ions. The first mixture is reacted at a first temperature. After the reaction is completed, solid and liquid are separated to obtain a solid and a liquid. The solid includes lithium iron phosphate material after impurity removal, and the liquid includes complexes formed by the impurity metal ions and the acid radicals. The purified lithium iron phosphate material is mixed with a regeneration solution to obtain a second mixture. The second mixture is subjected to a first heat treatment. After the first heat treatment, a solid substance is obtained by solid-liquid separation. The solid substance is subjected to a second heat treatment to obtain regenerated lithium iron phosphate.

2. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The total concentration of the acid radicals in the impurity removal solution is 0.01 mol / L to 5.0 mol / L.

3. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The liquid-to-solid ratio between the impurity removal solution and the lithium iron phosphate material to be impurized is (3~20):1, in mL / g.

4. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The first temperature is 30℃~90℃; The reaction of the first mixture at the first temperature includes: stirring the first mixture at the first temperature for 0.5 h to 5 h.

5. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The pH of the impurity removal solution is 4-10.

6. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The first heat treatment of the second mixture includes heating the second mixture at 120°C to 500°C for 5 hours to 15 hours. The second heat treatment of the solid material includes: drying the solid material, and then heating the solid material at 100℃~800℃ for 2h~12h in an inert gas atmosphere.

7. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The regeneration solution includes a lithium source, a reducing agent and water, and the mass ratio of the lithium source, the reducing agent and the purified lithium iron phosphate material is 1:(1~10):(2~10).

8. The method for regenerating lithium iron phosphate materials as described in claim 1, characterized in that, The liquid-to-solid ratio of the regenerated solution to the purified lithium iron phosphate material is (3~20):1, with units of mL / g.

9. A type of recycled lithium iron phosphate, characterized in that, It is prepared by the lithium iron phosphate material regeneration method according to any one of claims 1 to 8.

10. A regenerable battery, characterized in that, The regenerated battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode includes regenerated lithium iron phosphate as described in claim 9.

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