A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials

Abstract

A method for the synergistic lithium and phosphorus supplementation and targeted regeneration of lithium iron phosphate (LFP) cathode materials is disclosed, involving a regeneration and repair method for retired LFP cathode materials. This method aims to address the technical problems of poor uniformity, poor electrochemical performance, and poor safety associated with existing direct regeneration methods for retired LFP cathode materials. The method comprises: 1. Cathode material stripping and crushing; 2. Preparation of an aqueous repair solution using a reducing agent, lithium salt, and phytic acid; reaction of the degraded LFP black powder in the repair solution; filtration, drying, and segmented sintering to completely reconstruct the material's intact crystal structure and coat it with a highly conductive carbon layer. The regenerated LFP cathode material exhibits a discharge specific capacity of up to 149.7 mAh g⁻¹ at a current density of 1 C. ‑ ¹, and it is cycle-stable, making it suitable for use in the battery industry.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery recycling technology, specifically relating to a method for regenerating and repairing retired lithium iron phosphate (LiFePO4) cathode materials. Background Technology

[0002] With the widespread adoption of electric vehicles, power batteries are entering a period of large-scale retirement. The cathode materials of these batteries contain valuable metals, giving them high recycling value. Lithium iron phosphate (LFP) batteries account for a large proportion of retired batteries due to their safety profile. Currently, the processes for recovering LFP through hydrometallurgy and pyrometallurgy suffer from serious secondary pollution, long processes, high energy consumption, and poor economic efficiency. Direct regeneration and repair technology has emerged as a green and promising alternative. However, existing direct regeneration methods each have limitations: the direct lithium replenishment-calcination method suffers from insufficient solid-phase contact, leading to poor uniformity and electrochemical performance of the recycled materials; while the hydrothermal method, although capable of repair, relies on high-temperature and high-pressure conditions, posing safety risks and hindering large-scale application. Therefore, developing a direct regeneration method that combines green, safe, and efficient characteristics is crucial for achieving high-value recycling of retired LFP cathode materials. Summary of the Invention

[0003] This invention addresses the technical problems of poor uniformity, poor electrochemical performance, and poor safety in existing direct regeneration methods for retired lithium iron phosphate (LFP) cathode materials. It provides a method for synergistic lithium and phosphorus replenishment and targeted repair and regeneration of LFP cathode materials. This method constructs an aqueous repair system composed of phytic acid, a lithium source, and a reducing agent. Utilizing the unique coordination properties of phytic acid, it simultaneously achieves two functions: firstly, it regulates the solvation structure of lithium ions in aqueous solution; secondly, it activates the trivalent iron on the surface of the failed material, thereby significantly reducing the chemical energy barrier for subsequent targeted repair. Based on this, the method can efficiently and uniformly replenish lithium and phosphorus in a water bath environment at normal pressure and low temperature (e.g., 25-80 °C). Subsequently, through precise carbon source composite and segmented sintering processes, the intact crystal structure of the material is completely reconstructed and coated with a highly conductive carbon layer. This method is green and economical throughout the entire process. The regenerated LFP material fully recovers its rate performance and cycle life, surpassing that of commercially available new products, providing a technological path with significant industrial potential for the recycling of retired batteries.

[0004] The method for synergistic lithium and phosphorus supplementation and targeted repair of regenerated lithium iron phosphate cathode materials according to the present invention includes the following steps:

[0005] I. Cathode material stripping and crushing: Disassemble retired lithium iron phosphate batteries to obtain cathode sheets, then soak them in deionized water to separate the cathode material from the current collector, and then dry and crush the cathode material to obtain spent lithium iron phosphate black powder.

[0006] II. Water bath repair: Add reducing agent, lithium salt and phytic acid in a molar ratio of 1:1:(0.01~0.5) to water to prepare a repair solution; then place the failed lithium iron phosphate black powder obtained in step one into the repair solution, heat it in a water bath to 25~80 ℃ and maintain it for 1~6 hours to carry out the reaction. After the reaction is completed, filter and dry to obtain lithium iron phosphate black powder with added lithium and phosphorus.

[0007] 3. Segmented sintering: The lithium iron phosphate black powder with lithium and phosphorus replenishment obtained in step 2, the carbon source, and the lithium source are mixed to obtain a mixed powder; the lithium source is used to compensate for lithium loss at high temperature; the mixed powder is placed in a high-temperature furnace, and under an inert atmosphere, it is first heated to 250~350 ℃ for 1~4 hours for preliminary calcination, and then heated to 600~750 ℃ ​​for 1~5 hours for crystal phase reconstruction and conductive carbon layer repair. After cooling, the lithium iron phosphate cathode material with synergistic lithium and phosphorus replenishment and directional repair and regeneration is obtained.

[0008] Preferably, in step one, the pulverization is performed using a ball mill;

[0009] Preferably, in step one, the ball milling is carried out for 1 to 5 hours under the conditions of a ball-to-material mass ratio of (15~20):1 and a rotation speed of 600~1200 rpm; the particle size D50 of the spent lithium iron phosphate black powder after ball milling reaches 1~10 μm.

[0010] Preferably, in step two, the reducing agent is ascorbic acid, citric acid, or tartaric acid. These reducing agents are organic acids that are stable in water and can reduce ferric iron to ferrous iron.

[0011] Preferably, in step two, the lithium salt is lithium carbonate, lithium hydroxide, lithium chloride, or lithium nitrate.

[0012] Preferably, in step two, the molar ratio of the reducing agent, lithium salt and phytic acid is 1:1:(0.15~0.35).

[0013] Preferably, in step three, the carbon source is glucose, sucrose, or citric acid.

[0014] Preferably, in step three, the lithium source is lithium carbonate, lithium acetate, or lithium hydroxide.

[0015] Preferably, in step three, the inert gas is nitrogen, argon, or a mixture of argon and hydrogen.

[0016] Preferably, in steps one and two, the drying process is carried out at a temperature of 60 ℃ to 100 ℃ for 6 to 14 hours.

[0017] The repair mechanism of this invention relies on a highly efficient synergistic system composed of phytic acid, lithium salt, and a reducing agent. In the liquid-phase repair stage, the reducing agent initiates the reduction reaction, while phytic acid, through molecular coordination, simultaneously regulates the behavior of lithium ions and activates trivalent iron defects on the material surface. This synergistic effect significantly reduces the energy barrier for directional repair, achieving efficient and uniform lithium and phosphorus replenishment at low temperatures. During this process, phytic acid acts as an auxiliary phosphorus source, ensuring that iron species are fully and accurately converted into the lithium iron phosphate phase, reducing the residue of inactive impurities. The subsequent calcination stage focuses on the long-range ordered reconstruction of the material's crystal structure and the formation of a conductive carbon coating layer.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The entire process of this invention involves no strong acids, strong alkalis, or high-temperature smelting, thus avoiding the emission of heavy metals and toxic gases.

[0020] 2. The core repair steps of this invention are carried out in a normal pressure, low temperature water bath environment, completely eliminating the dependence of hydrothermal methods on high-pressure reactors and eliminating the corresponding safety risks. This process is mild and requires minimal equipment, providing a solid foundation for large-scale industrial application.

[0021] 3. By utilizing the unique mechanism of phytic acid in the aqueous phase for repairing depleted lithium iron phosphate, targeted repair and lithium / phosphorus replenishment of the depleted material were achieved. The liquid-phase reaction ensured sufficient contact, overcoming the shortcomings of direct solid-phase calcination methods such as uneven mixing and incomplete repair, thus regenerating a cathode material with a complete crystal structure and a uniform carbon coating. The regenerated lithium iron phosphate cathode material exhibited stable cycle performance, with rate performance superior to commercially available new lithium iron phosphate materials, and a discharge specific capacity as high as 149.7 mAh g⁻¹ at a current density of 1 C. - ¹.

[0022] 4. The introduction of phytic acid not only acts as a dual-effect "catalyst" for structural repair but also serves as a supplementary phosphorus source, ensuring the full conversion and utilization of iron and improving product yield and purity. Simultaneously, phytic acid acts as an antioxidant, protecting the reducing agent. This method directly regenerates high-value-added cathode materials, significantly improving economic benefits compared to traditional recycling methods that produce low-value raw materials. Attached Figure Description

[0023] Figure 1 This is a SEM image of the failed lithium iron phosphate black powder LFP-S from step one in Example 1 and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and directional repair and regeneration.

[0024] Figure 2The XRD patterns are of the failed lithium iron phosphate black powder LFP-S from step one in Example 1 and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and directional repair and regeneration.

[0025] Figure 3 This is an ICP data diagram of the failed lithium iron phosphate black powder LFP-S from step one in Example 1 and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and directional repair and regeneration.

[0026] Figure 4 These are rate performance curves of the failed lithium iron phosphate black powder LFP-S from step one of Example 1, the lithium iron phosphate cathode material LFP-R prepared by synergistic lithium and phosphorus replenishment and directional repair and regeneration in step three, and the commercial lithium iron phosphate cathode material LFP-C.

[0027] Figure 5 The graphs show the cycle performance of the failed lithium iron phosphate black powder LFP-S from step one of Example 1, the lithium iron phosphate cathode material LFP-R prepared by synergistic lithium and phosphorus replenishment and directional repair and regeneration in step three, and the commercial lithium iron phosphate cathode material LFP-C.

[0028] Figure 6 The image shows the ICP data of Li and Fe elements in the lithium iron phosphate cathode material LFP-R prepared by synergistic lithium and phosphorus supplementation and directional repair and regeneration in Example 1 and the lithium iron phosphate cathode material LFP-R' without phytic acid repair in Comparative Example 1.

[0029] Figure 7 These are images of the repair solution and the control repair solution after being left to stand in the air for 15 and 30 days, respectively, in an antioxidant comparison experiment.

[0030] Figure 8 This is a comparison chart of expenditures and revenues between the direct regeneration method of Example 1 and hydrometallurgy and pyrometallurgy. Detailed Implementation

[0031] Example 1: The method for synergistic lithium and phosphorus supplementation and targeted repair of regenerated lithium iron phosphate cathode materials in this example is carried out according to the following steps:

[0032] I. Cathode Material Stripping and Crushing: The cathode sheet was obtained by disassembling the retired lithium iron phosphate battery and then soaked in deionized water. The cathode material and current collector were stirred and separated. The separated cathode material was then dried at 80 ℃ for 8 hours and then placed in a ball mill and ball-milled for 3 hours at a ball-to-material mass ratio of 20:1 and a rotation speed of 1000 rpm to obtain spent lithium iron phosphate black powder, denoted as LFP-S. The particle size of the ball-milled spent lithium iron phosphate black powder is approximately 5 μm.

[0033] II. Water bath remediation: Prepare 50 mL of remediation solution with ascorbic acid concentration of 0.03 mol / L, lithium hydroxide concentration of 0.03 mol / L, and phytic acid concentration of 0.01 mol / L; then place 1 g of the depleted lithium iron phosphate black powder obtained in step one into 50 mL of remediation solution, heat in a water bath to 60 ℃ and maintain for 1 hour to react. After the reaction is completed, filter and dry the solid phase at 80 ℃ for 8 hours to obtain lithium iron phosphate black powder with added lithium and phosphorus.

[0034] III. Segmented Sintering: The lithium iron phosphate black powder with lithium and phosphorus replenishment obtained in step II, glucose, and lithium carbonate are mixed to obtain a mixed powder. The amount of glucose added is 3% of the mass of the lithium iron phosphate black powder with lithium and phosphorus replenishment, and the amount of lithium carbonate added is 3% of the amount of iron in the lithium iron phosphate black powder with lithium and phosphorus replenishment. The addition of lithium carbonate is to compensate for lithium loss at high temperature. The mixed powder is placed in a tube furnace and calcined at 300 ℃ for 2 hours under argon protection for preliminary calcination. Then, the temperature is raised to 650 ℃ for 3 hours for crystal phase reconstruction and conductive carbon layer repair. After natural cooling, the lithium iron phosphate cathode material with synergistic lithium and phosphorus replenishment and directional repair and regeneration is obtained, denoted as LFP-R.

[0035] The SEM images of the failed lithium iron phosphate black powder LFP-S from step one of this embodiment and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and targeted repair are shown below. Figure 1 As shown, from Figure 1 It can be seen that the surface impurities of lithium iron phosphate are reduced after regeneration and repair.

[0036] The XRD spectra of the failed lithium iron phosphate black powder LFP-S from step one of this embodiment and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and targeted repair are shown below. Figure 2 As shown, from Figure 2 It can be seen that the FePO4 impurity phase in the regenerated and repaired lithium iron phosphate cathode material is completely eliminated.

[0037] The ICP data images of Li and Fe elements in the failed lithium iron phosphate black powder LFP-S from step one of this embodiment and the lithium iron phosphate cathode material LFP-R prepared in step three through synergistic lithium and phosphorus replenishment and targeted repair are shown below. Figure 3 As shown, from Figure 3 It can be seen that the Li / Fe molar ratio increased from 0.82 to 1.03 before and after water bath immersion, indicating that the lost lithium in the failed lithium iron phosphate was successfully replenished.

[0038] The failed lithium iron phosphate black powder LFP-S from step one of Example 1, the lithium iron phosphate cathode material LFP-R prepared by synergistic lithium and phosphorus replenishment and directional repair and regeneration in step three, and the commercial lithium iron phosphate cathode material LFP-C were used as cathodes. With lithium metal as the counter electrode, commercial lithium iron phosphate electrolyte was added dropwise to assemble them into coin cells, and electrochemical tests were performed. Figure 4 The graphs show the rate performance curves of LFP-R, LFP-S, and LFP-C. Figure 5 The cycling performance diagrams for LFP-R, LFP-S, and LFP-C are shown below. Figure 4 and Figure 5 It can be seen that at a current density of 1 C, the discharge specific capacity of the lithium iron phosphate cathode material LFP-R, which undergoes synergistic lithium and phosphorus replenishment and targeted regeneration, reaches as high as 149.7 mAh g⁻¹. - ¹, and its cycle stability is comparable to that of commercial materials (LFP-C). More importantly, its rate performance significantly surpasses that of commercial lithium iron phosphate materials, fully demonstrating the effectiveness of the "water bath repair-segmented sintering" synergistic process of this invention.

[0039] Example 2: The method for synergistic lithium and phosphorus supplementation and targeted repair of regenerated lithium iron phosphate cathode materials in this example is carried out according to the following steps:

[0040] I. Cathode Material Stripping and Crushing: The cathode sheet was obtained by disassembling the retired lithium iron phosphate battery and then soaked in deionized water. The cathode material and current collector were stirred and separated. The separated cathode material was then dried at 80 ℃ for 8 hours and then placed in a ball mill and ball-milled for 3 hours at a ball-to-material mass ratio of 20:1 and a rotation speed of 1000 rpm to obtain spent lithium iron phosphate black powder, denoted as LFP-S. The particle size of the ball-milled spent lithium iron phosphate black powder is approximately 5 μm.

[0041] II. Water bath remediation: Prepare 50 mL of remediation solution with ascorbic acid concentration of 0.03 mol / L, lithium hydroxide concentration of 0.03 mol / L, and phytic acid concentration of 0.005 mol / L; then place 1 g of the depleted lithium iron phosphate black powder obtained in step one into 50 mL of remediation solution, heat in a water bath to 60 ℃ and maintain for 1 hour to react. After the reaction is completed, filter and dry the solid at 80 ℃ for 8 hours to obtain lithium iron phosphate black powder with added lithium and phosphorus.

[0042] III. Segmented Sintering: The lithium iron phosphate black powder with lithium and phosphorus replenishment obtained in step II, glucose, and lithium carbonate are mixed to obtain a mixed powder. The amount of glucose added is 3% of the mass of the lithium iron phosphate black powder with lithium and phosphorus replenishment, and the amount of lithium carbonate added is 3% of the amount of iron in the lithium iron phosphate black powder with lithium and phosphorus replenishment. The addition of lithium carbonate is to compensate for lithium loss at high temperature. The mixed powder is placed in a tube furnace and, under argon protection, is first heated to 300 ℃ and calcined for 2 hours for preliminary calcination, and then heated to 700 ℃ and calcined for 3 hours for crystal phase reconstruction. After natural cooling, the lithium iron phosphate cathode material with synergistic lithium and phosphorus replenishment and directional repair and regeneration is obtained, denoted as LFP-R.

[0043] Using the same method as in Example 1, the recycled lithium iron phosphate cathode material prepared in this example was assembled into a coin cell for electrochemical testing. Charge-discharge tests were conducted at a current density of 1 C, and the measured discharge specific capacity of the material was 147.2 mAh g⁻¹. - ¹.

[0044] Comparative Example 1: No phytic acid was added to the remediation solution in this comparative example. The specific method for regenerating lithium iron phosphate cathode material was carried out according to the following steps:

[0045] I. Cathode Material Stripping and Crushing: The cathode sheet was obtained by disassembling the retired lithium iron phosphate battery and then soaked in deionized water. The cathode material and current collector were stirred and separated. The separated cathode material was then dried at 80 ℃ for 8 hours and then placed in a ball mill and ball-milled for 3 hours at a ball-to-material mass ratio of 20:1 and a rotation speed of 1000 rpm to obtain spent lithium iron phosphate black powder, denoted as LFP-S. The particle size of the ball-milled spent lithium iron phosphate black powder is approximately 5 μm.

[0046] II. Water bath repair: Prepare 50 mL of repair solution with a concentration of 0.03 mol / L ascorbic acid and 0.03 mol / L lithium hydroxide; then place 1 g of the failed lithium iron phosphate black powder obtained in step one into 50 mL of repair solution, heat in a water bath to 60 ℃ and maintain for 1 hour to react. After the reaction is completed, filter and dry the solid at 80 ℃ for 8 hours to obtain lithium iron phosphate black powder repaired only by lithium replenishment.

[0047] III. Segmented Sintering: The lithium iron phosphate black powder obtained in step II (repaired only by lithium replenishment), glucose, and lithium carbonate are mixed to obtain a mixed powder. The amount of glucose added is 3% of the mass of the lithium iron phosphate black powder (repaired only by lithium replenishment), and the amount of lithium carbonate added is 3% of the amount of iron in the lithium iron phosphate black powder (repaired only by lithium replenishment). The addition of lithium carbonate is to compensate for lithium loss at high temperature. The mixed powder is placed in a tube furnace and, under argon protection, is first heated to 300 ℃ and calcined for 2 hours for preliminary calcination, and then heated to 650 ℃ and calcined for 3 hours for crystal phase reconstruction. After natural cooling, the repaired and regenerated lithium iron phosphate cathode material, LFP-R', is obtained.

[0048] The ICP data images of P and Fe elements in the lithium iron phosphate cathode material LFP-R prepared in Example 1 with synergistic lithium and phosphorus supplementation and targeted regeneration are shown below, compared with the lithium iron phosphate cathode material LFP-R' without phytic acid regeneration in this comparative example. Figure 6 As shown, from Figure 6 It can be seen that the P / Fe molar ratio increased from 0.96 to 1.01 before and after the addition of phytic acid, proving that phytic acid successfully utilized the iron impurities in the failed material by converting electrochemically inactive impurities such as iron oxide into electrochemically active lithium iron phosphate, thus achieving targeted repair.

[0049] Using the same method as in Example 1, the recycled lithium iron phosphate cathode material LFP-R' prepared in this comparative example was assembled into a coin cell for electrochemical testing. Charge-discharge tests were conducted at a current density of 1 C, and the measured discharge specific capacity of the material was 143.7 mAh g⁻¹. - ¹.

[0050] Comparative Example 2: Excess phytic acid was added to the remediation solution in this comparative example. The specific method for regenerating lithium iron phosphate cathode material was carried out according to the following steps:

[0051] I. Cathode Material Stripping and Crushing: The cathode sheet was obtained by disassembling the retired lithium iron phosphate battery and then soaked in deionized water. The cathode material and current collector were stirred and separated. The separated cathode material was then dried at 80 ℃ for 8 hours and then placed in a ball mill and ball-milled for 3 hours at a ball-to-material mass ratio of 20:1 and a rotation speed of 1000 rpm to obtain spent lithium iron phosphate black powder, denoted as LFP-S. The particle size of the ball-milled spent lithium iron phosphate black powder is approximately 5 μm.

[0052] II. Water bath remediation: Prepare 50 mL of remediation solution with ascorbic acid concentration of 0.03 mol / L, lithium hydroxide concentration of 0.03 mol / L, and phytic acid concentration of 0.03 mol / L; then place 1 g of the depleted lithium iron phosphate black powder obtained in step one into 50 mL of remediation solution, heat in a water bath to 60 ℃ and maintain for 1 hour to carry out the reaction. After the reaction is completed, filter and dry the solid phase at 80 ℃ for 8 hours to obtain lithium iron phosphate black powder with added lithium and phosphorus.

[0053] III. Segmented Sintering: The lithium iron phosphate black powder with lithium and phosphorus replenishment obtained in step II, glucose, and lithium carbonate are mixed to obtain a mixed powder. The amount of glucose added is 3% of the mass of the lithium iron phosphate black powder with lithium and phosphorus replenishment, and the amount of lithium carbonate added is 3% of the amount of iron in the lithium iron phosphate black powder with lithium and phosphorus replenishment. The addition of lithium carbonate is to compensate for lithium loss at high temperature. The mixed powder is placed in a tube furnace and, under argon protection, is first heated to 300 ℃ and calcined for 2 hours for preliminary calcination, and then heated to 650 ℃ and calcined for 3 hours for crystal phase reconstruction. After natural cooling, the repaired and regenerated lithium iron phosphate cathode material is obtained.

[0054] Using the same method as in Example 1, the recycled lithium iron phosphate cathode material prepared in this comparative example was assembled into a coin cell for electrochemical testing. Charge-discharge tests were conducted at a current density of 1 C, and the measured discharge specific capacity of the material was 132.1 mAh g⁻¹. - ¹. The discharge specific capacity of this material is lower than that of the material in Example 1. This is because excessive phytic acid can induce an aggregation effect and introduce a large number of electrochemically inactive impurity phases such as Li3Fe2(PO4)3 and Li3PO4, thereby leading to a decrease in the discharge specific capacity of the material. Therefore, the amount of phytic acid added needs to be precisely controlled.

[0055] The repair solution of this invention incorporates phytic acid. Besides its unique repair mechanism for depleted lithium iron phosphate in the aqueous phase, phytic acid also functions as an antioxidant, effectively protecting the reducing agent ascorbic acid. To verify this effect of phytic acid on the repair solution, an antioxidant comparative experiment was conducted:

[0056] 1. Prepare a repair solution with ascorbic acid (AA) concentration of 0.03 mol / L, lithium hydroxide concentration of 0.03 mol / L, and phytic acid (PA) concentration of 0.01 mol / L; at the same time, prepare a control repair solution with ascorbic acid concentration of 0.03 mol / L and lithium hydroxide concentration of 0.03 mol / L.

[0057] 2. The repair solution and the control repair solution were simultaneously placed in air and allowed to stand. After 15 and 30 days of standing, the solution without phytic acid showed a significantly darker color, indicating severe oxidation of ascorbic acid; while the solution containing phytic acid showed only a slight color change. Figure 7 As shown, a is a photo after 15 days of standing, and b is a photo after 30 days of standing, which proves that phytic acid effectively delays the oxidation process of ascorbic acid.

[0058] The direct regeneration method provided by this invention can efficiently regenerate failed cathode materials into high-value-added lithium iron phosphate products. Taking Example 1 as an example, the expenditure and revenue of the direct regeneration method of this invention are compared with those of hydrometallurgy and pyrometallurgy. Figure 8 As shown, the traditional method produces low-value lithium carbonate and iron phosphate, which require subsequent resynthesis processes. However, the present invention eliminates the resynthesis step and directly produces high-value end products. The method of the present invention can bring significant economic benefits.

Claims

1. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials, characterized in that, This method is performed in the following steps: I. Cathode material stripping and crushing: Disassemble retired lithium iron phosphate batteries to obtain cathode sheets, then soak them in deionized water to separate the cathode material from the current collector, and then dry and crush the cathode material to obtain spent lithium iron phosphate black powder. II. Water bath repair: Add reducing agent, lithium salt and phytic acid in a molar ratio of 1:1:(0.01~0.5) to water to prepare a repair solution; then place the failed lithium iron phosphate black powder obtained in step one into the repair solution, heat it in a water bath to 25~80 ℃ and maintain it for 1~6 hours to carry out the reaction. After the reaction is completed, filter and dry to obtain lithium iron phosphate black powder with added lithium and phosphorus.

3. Segmented sintering: The lithium iron phosphate black powder with lithium and phosphorus replenishment obtained in step 2, carbon source and lithium source are mixed to obtain mixed powder; the mixed powder is placed in a high-temperature furnace, and under an inert atmosphere, it is first heated to 250~350 ℃ for 1~4 hours for preliminary calcination, and then heated to 600~750 ℃ ​​for 1~5 hours for crystal phase reconstruction and conductive carbon layer repair. After cooling, the lithium iron phosphate cathode material with synergistic lithium and phosphorus replenishment and directional repair and regeneration is obtained.

2. The method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1, characterized in that, In step one, the pulverization is carried out using a ball mill.

3. The method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 2, characterized in that, The ball milling is carried out for 1 to 5 hours under the conditions of a ball-to-material mass ratio of (15~20):1 and a rotation speed of 600~1200 rpm.

4. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step two, the reducing agent is ascorbic acid, citric acid, or tartaric acid.

5. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step two, the lithium salt is lithium carbonate, lithium hydroxide, lithium chloride, or lithium nitrate.

6. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step two, the molar ratio of the reducing agent, lithium salt and phytic acid is 1:1:(0.15~0.35).

7. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step three, the carbon source is glucose, sucrose, or citric acid.

8. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step three, the lithium source is lithium carbonate, lithium acetate, or lithium hydroxide.

9. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In step three, the inert gas is nitrogen, argon, or a mixture of argon and hydrogen.

10. A method for synergistic lithium and phosphorus replenishment and targeted repair of regenerated lithium iron phosphate cathode materials according to claim 1 or 2, characterized in that, In steps one and two, the drying process involves drying at a temperature of 60 ℃ to 100 ℃ for 6 to 14 hours.

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