A method for regenerating a lithium iron phosphate material, regenerated lithium iron phosphate, and a secondary battery

Abstract

This application discloses a method for regenerating lithium iron phosphate (LFP) materials, regenerated LFP, and a secondary battery, relating to the technical field of LFP material regeneration. The regeneration method includes the following steps: mixing LFP materials to be replenished with lithium, organic acid, lithium source, and water to obtain a mixture; wherein, the organic acid reacts with the lithium source to generate an organolithium salt, which includes chelating groups that can coordinate with metal ions; filtering the mixture to obtain replenished LFP materials; and heating the replenished LFP materials to obtain regenerated LFP. In this application, the organolithium salt contains chelating groups. Under the action of filtration, lithium ions diffuse to the surface of the LFP materials to be replenished with lithium, and the chelating groups coordinate with the metal ions on the surface of the LFP to form chelates, promoting the lithium replenishment process. The replenished LFP materials are then heat-treated to promote lithium lattice diffusion, thereby improving the quality of the LFP.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium iron phosphate material regeneration, and particularly relates to a lithium iron phosphate material regeneration method, regenerated lithium iron phosphate and a secondary battery. BACKGROUND

[0002] Lithium iron phosphate material is widely used in the new energy field, and waste powder generated in the service failure or production process usually has problems such as lithium loss, which is difficult to be directly reused. In order to realize efficient use of resources, it is urgent to regenerate and repair the lithium iron phosphate waste to restore its electrochemical performance.

[0003] For the regeneration of lithium iron phosphate waste, a method for directly repairing battery-grade lithium iron phosphate by pyroprocessing is disclosed in the prior art, which mainly includes the following steps: high-temperature roasting of lithium iron phosphate waste powder in an air or oxygen atmosphere to obtain calcine; adding lithium source, iron source, phosphorus source, carbon source and activator to the calcine; adding a dispersion medium for high-speed ball milling to realize activation and granulation; removing volatile solvents (such as alcohol) and realizing solvent recovery; high-temperature solid-phase sintering in an inert atmosphere; removing metal impurities through a vibrating screen with a permanent magnet to finally obtain a battery-grade lithium iron phosphate product.

[0004] However, the above-mentioned pyroprocessing regeneration process still has obvious deficiencies: the reaction occurs at the solid-solid interface in the lithium supplementing stage, the mass transfer resistance is large, resulting in uneven mixing of components and incomplete reaction, which needs to rely on long-time high-intensity ball milling to improve uniformity, causing high energy consumption and low efficiency. SUMMARY

[0005] In a first aspect, the present application provides a lithium iron phosphate material regeneration method, which includes the following steps:

[0006] Mixing the lithium iron phosphate material to be supplemented with lithium, an organic acid, a lithium source and water to obtain a mixture; wherein the organic acid reacts with the lithium source to generate an organic lithium salt, and the organic lithium salt includes a chelating group capable of coordinating with metal ions;

[0007] Filtration of the mixture to obtain lithium-supplemented lithium iron phosphate material; and heating treatment of the lithium-supplemented lithium iron phosphate material to obtain regenerated lithium iron phosphate.

[0008] In some optional embodiments of the first aspect of the present application, the filtration of the mixture to obtain the lithium-supplemented lithium iron phosphate material includes:

[0009] S100, filtration of the mixture to obtain a filtrate and a filter cake;

[0010] S200, re-mixing the filtrate and the filter cake and performing filtration again;

[0011] S300, repeating S200 at least once, and the final obtained filter cake is the lithium-supplemented lithium iron phosphate material.

[0012] In some optional embodiments of the first aspect of the present application, the heating treatment of the lithium-supplemented lithium iron phosphate material comprises:

[0013] After the lithium-supplemented lithium iron phosphate material is dried, it is crushed and ground, and then the lithium-supplemented lithium iron phosphate material is heated at 600-700°C for 2-10 hours in an inert gas atmosphere.

[0014] In some optional embodiments of the first aspect of the present application, the organic acid comprises at least one of ascorbic acid, tannic acid, citric acid, and tartaric acid.

[0015] In some optional embodiments of the first aspect of the present application, the concentration of the organic acid in the mixture is 0.3-1 mol / L, and the concentration of the lithium source is 0.3-2 mol / L.

[0016] In some optional embodiments of the first aspect of the present application, the molar ratio of the organic acid to the lithium source is 1:(0.5-3.5).

[0017] In some optional embodiments of the first aspect of the present application, the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be supplemented with lithium in the mixture is (3-20):1, in mL / g.

[0018] In some optional embodiments of the first aspect of the present application, the suction filtration pressure is 0.01-0.1 MPa.

[0019] In some optional embodiments of the first aspect of the present application, before the lithium iron phosphate material to be supplemented with lithium, the organic acid, the lithium source, and the water are mixed, the regeneration method further comprises:

[0020] The lithium iron phosphate waste material is heated at 100-400°C for 2-10 hours, and after the heating is completed, the lithium iron phosphate waste material is crushed and sieved to obtain the lithium iron phosphate material to be supplemented with lithium.

[0021] The second aspect of the present application provides a regenerated lithium iron phosphate, which is prepared by the above-mentioned regeneration method of lithium iron phosphate material.

[0022] The third aspect of the present application provides a secondary battery, which comprises a positive electrode made of the above-mentioned regenerated lithium iron phosphate.

[0023] Advantages:

[0024] In the first aspect of the present application, the lithium-deficient lithium iron phosphate material is mixed with an organic acid, a lithium source and water. The organic acid reacts with the lithium source to form an organic lithium salt, which contains a chelating group. Under the action of suction filtration, lithium ions diffuse to the surface of the lithium-deficient lithium iron phosphate material, and the chelating group coordinates with the metal ions on the surface of the lithium iron phosphate to form a chelate, further promoting the lithium supplement process and achieving efficient lithium supplement. The lithium-supplemented lithium iron phosphate material is then heat-treated to reduce trivalent iron in the lithium iron phosphate material to divalent iron using the carbon in the chelate to repair the structure and promote lithium lattice diffusion, thereby improving the quality of the lithium iron phosphate.

[0025] The Li / Fe molar ratio of the regenerated lithium iron phosphate obtained in the second aspect of the present application is more ideal, and the regenerated lithium iron phosphate has a better balanced chemical composition ratio, which is beneficial to improving the overall electrochemical performance and stability of the material.

[0026] The secondary battery obtained in the third aspect of the present application has a good specific discharge capacity and good electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart of the regeneration of the lithium iron phosphate material in the waste lithium ion battery in an embodiment of the present application;

[0028] Figure 2 is a charge-discharge curve diagram of the regenerated lithium iron phosphate obtained in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0029] The present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0030] In one embodiment, a regeneration method of a lithium iron phosphate material, the regeneration method comprising the following steps:

[0031] The lithium-deficient lithium iron phosphate material, the organic acid, the lithium source and water are mixed to obtain a mixture. The organic acid reacts with the lithium source to form an organic lithium salt, and the organic lithium salt includes a chelating group that can coordinate with metal ions.

[0032] The mixture is suction filtered to obtain a lithium-supplemented lithium iron phosphate material. The lithium-supplemented lithium iron phosphate material is heat-treated to obtain a regenerated lithium iron phosphate.

[0033] In the above scheme, the lithium iron phosphate material to be replenished with lithium is mixed with organic acid, lithium source and water. Under the action of stirring, the organic acid reacts with the lithium source to generate organic lithium salt. The acid radical in the organic lithium salt contains chelating groups. Under the action of filtration, lithium ions in the mixture diffuse to the surface of the lithium iron phosphate to be replenished with lithium, and the chelating groups coordinate with the free iron ions on the surface of lithium iron phosphate to form chelates. This prevents iron ions from depositing on the surface of lithium iron phosphate to form insulating impurity phases (such as iron oxide), thereby ensuring the cleanliness of the lithium iron phosphate surface, which is conducive to the embedding of lithium ions into lithium iron phosphate, further promoting the lithium replenishment process, thereby achieving efficient lithium replenishment.

[0034] The lithium iron phosphate after lithium replenishment is then subjected to heat treatment. The carbon in the chelate reduces the trivalent iron in the lithium iron phosphate material to divalent iron, thereby achieving structural repair and promoting lithium lattice diffusion, thus improving the quality of lithium iron phosphate.

[0035] In some optional embodiments of this application, the mixture is filtered to obtain lithium iron phosphate material after lithium replenishment, including:

[0036] S100. Filter the mixture to obtain filtrate and filter cake;

[0037] S200: Remix the filtrate and filter cake, and filter again.

[0038] S300 is repeated at least once, and the final filter cake is lithium iron phosphate material after lithium replenishment.

[0039] This setup, during lithium replenishment, promotes the chelation of chelating groups with iron ions and the diffusion of lithium ions onto the lithium iron phosphate by repeatedly filtering the mixture. Specifically, repeated filtration, through repeated solid-liquid contact and separation, prolongs the effective interaction time between the chelating groups and free iron ions on the surface, allowing unreacted chelating groups to further penetrate into the micropores or defect regions of the lithium iron phosphate particles, enhancing coordination coverage. Simultaneously, multiple cycles help the system approach adsorption equilibrium, resulting in a more compact and stable chelate structure.

[0040] Moreover, multiple remixing and filtration processes help to homogenize the distribution of lithium ions on the particle surface. In the initial mixing stage, lithium ions are locally enriched on the outer layer of the particles; through filtrate reuse and re-contact, lithium ions can gradually migrate to the low-concentration region during multiple permeation and adsorption processes, forming a more uniform surface lithium adsorption layer. This reduces local concentration polarization of lithium ions and provides a more uniform precursor state for the bulk diffusion of lithium into the lithium iron phosphate lattice during subsequent heat treatment, thereby improving lithium replenishment efficiency and electrochemical consistency of lithium iron phosphate materials.

[0041] In some optional embodiments of this application, the heat treatment of the lithium iron phosphate material after lithium replenishment includes:

[0042] After being dried, the lithium iron phosphate material was pulverized and ground. Then, in an inert gas atmosphere, the lithium iron phosphate material was heated at 600℃~700℃ for 2h~10h.

[0043] With this setup, the lithium iron phosphate material obtained by filtration and lithium replenishment is dried to remove water from the surface and pores of the lithium iron phosphate, preventing water vaporization during subsequent heat treatment and structural damage. After drying, the lithium iron phosphate material is crushed and ground into powder to reduce particle agglomeration and improve the dispersibility and uniformity of the powder. Finally, it is calcined in an inert gas atmosphere to promote the full diffusion of lithium ions and their embedding into the crystal lattice to repair lithium vacancies, and to reduce trivalent iron to divalent iron, thereby improving the performance of the lithium iron phosphate material.

[0044] In some optional embodiments of this application, the organic acid includes at least one selected from ascorbic acid, tannic acid, citric acid, and tartaric acid.

[0045] In some optional embodiments of this application, the lithium source includes lithium hydroxide.

[0046] In this embodiment, all the aforementioned organic acids can react in situ with lithium hydroxide to form organolithium salts, in which the acid radicals contain chelating groups. Specifically, ascorbic acid radicals include enol anions and adjacent hydroxyl groups (or carbonyl oxygen) as chelating groups, which can achieve coordination through their synergy; tannic acid radicals include carboxylate, phenoxy, and polyhydroxyl groups, which can form multidentate coordination structures; citrate radicals include multiple carboxylate radicals and one ortho-hydroxyl group as chelating groups; tartrate radicals include two carboxylate radicals and two ortho-hydroxyl groups as chelating groups. Citrate and tartrate radicals can achieve bidentate or multidentate coordination through the combination of carboxylate radicals and hydroxyl groups. These organic acid radicals can coordinate with iron ions exposed on the surface of lithium iron phosphate due to crystal defects or lithium deficiency, forming stable surface chelates.

[0047] In some optional embodiments of this application, the concentration of the organic acid in the mixture is 0.3 mol / L to 1 mol / L, and the concentration of the lithium source is 0.3 mol / L to 2 mol / L. It should be noted that in this embodiment, the organic acid and lithium source will react; therefore, the concentrations of the organic acid and lithium source here should be the concentrations of the organic acid and lithium source in the mixture before the reaction, i.e., the initial concentrations of the organic acid and lithium source.

[0048] In some optional embodiments of this application, the molar ratio of organic acid to lithium source in the mixture is 1:(0.5~3.5).

[0049] In this embodiment, the concentration of lithium source in the mixture is 0.3 mol / L to 2 mol / L. Within this concentration range, the lithium source can fully compensate for the lithium deficiency in the lithium iron phosphate material during the lithium replenishment process, while avoiding excessive adsorption of lithium leading to a decrease in particle caking performance.

[0050] In this embodiment, the organic acid reacts with the lithium source to generate an organic lithium salt. By reasonably setting the molar ratio range of the organic acid and the lithium source, as well as the concentration of the organic acid, it is possible to avoid the excessive generation of organic acid anions and excessive chelation on the surface of lithium iron phosphate due to excessive organic acid, and also to prevent insufficient chelation due to insufficient organic acid, thereby achieving precise control over the degree of chelation on the surface of lithium iron phosphate.

[0051] In some optional embodiments of this application, the liquid-to-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished in the mixture is (3~20):1, in mL / g.

[0052] In this embodiment, the liquid-to-solid ratio is within the above-mentioned range. This ensures that the organic acid and lithium salt are fully dissolved and effectively diffused to the particle surface, achieving uniform adsorption and coordination. It also avoids difficulties in subsequent processing or waste of resources due to excessive liquid. Furthermore, it ensures that the filter cake retains sufficient internal liquid after each filtration to maintain the effective components (such as organic lithium salts), and that the remixed system has good fluidity, promoting the redistribution and deep penetration of organic lithium salts on the surface of lithium iron phosphate particles. If the liquid-to-solid ratio is too high (>30:1), a large amount of filtrate needs to be processed in subsequent filtration processes, which not only prolongs the operation time but may also cause liquid overflow or incomplete filtration due to filter paper / membrane saturation or the capacity limitation of the filtration system. If the liquid-to-solid ratio is too low (e.g., <3:1), the filter cake becomes too dense and has extremely low liquid content during multiple filtration and remixing processes. It is difficult to form a uniform suspension during remixing, which instead exacerbates mass transfer resistance. Moreover, the small amount of residual liquid is easily completely absorbed during repeated filtration, causing irreversible loss of effective components (such as organic lithium salts) and weakening the cycle enhancement effect.

[0053] In some optional embodiments of this application, the filtration pressure is 0.01 MPa to 0.1 MPa.

[0054] In this embodiment, the filtration pressure is set to the above range. While ensuring a relatively fast solid-liquid separation rate, the filter cake maintains a loose and porous structure, which is beneficial to retain an appropriate amount of internal liquid to support subsequent backmixing reactions and reduce the physical loss of effective components (such as organic lithium salts) during operation, thereby ensuring the effectiveness and process stability of multiple filtration cycles.

[0055] In some optional embodiments of this application, the regeneration method further includes, before mixing the lithium iron phosphate material to be replenished with lithium, organic acid, lithium source, and water:

[0056] The lithium iron phosphate waste is heated at 100℃~400℃ for 2h~10h. After heating, the lithium iron phosphate waste is crushed and sieved to obtain lithium iron phosphate material to be replenished.

[0057] like Figure 1As shown, when the lithium iron phosphate material to be replenished with lithium comes from waste lithium-ion batteries, the waste lithium-ion batteries are fully discharged, disassembled, crushed and sorted. The lithium iron phosphate waste obtained after sorting to remove copper and aluminum impurities contains impurities such as carbon and binders. These impurities need to be removed. Therefore, the lithium iron phosphate waste needs to be heat-treated to decompose the carbon and binders, so as to obtain lithium iron phosphate material to be replenished with lithium with less impurities.

[0058] When the lithium iron phosphate material to be replenished originates from the material synthesis stage, contains a small amount of in-situ coated carbon, and does not contain binders, the lithium iron phosphate material to be replenished does not need to undergo heat treatment and can be directly replenished with lithium.

[0059] In another embodiment, a regenerated lithium iron phosphate is provided, which is prepared by the above-described method for regenerating lithium iron phosphate material.

[0060] In another embodiment, a secondary battery is provided, including a positive electrode made of recycled lithium iron phosphate as described above.

[0061] 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.

[0062] It is worth noting that the following embodiments and comparative examples were tested using lithium iron phosphate waste derived from spent lithium-ion batteries. The same batch of spent lithium-ion batteries was fully discharged, disassembled, crushed, and sorted to obtain the lithium iron phosphate waste used in each embodiment and comparative example.

[0063]

Example 1

[0064] S1: Place the lithium iron phosphate waste in a muffle furnace and keep it at 250°C for 10 hours. After heating, take it out, grind and crush it, and sieve it through a 200-mesh sieve to obtain the lithium iron phosphate material to be replenished with lithium.

[0065] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0066] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0067] S3: After the lithium iron phosphate material is dried, it is crushed and ground, then placed in a crucible and put into a tube furnace. Under an argon atmosphere, the temperature is raised to 700°C at a rate of 5°C / min and held for 2 hours. After the holding period, regenerated lithium iron phosphate is obtained.

[0068]

Example 2

[0069] Example 2 differs from Example 1 in the concentrations of ascorbic acid and lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0070] S1 is the same as in Example 1.

[0071] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.4 mol / L, the concentration of lithium hydroxide is 0.4 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0072] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0073] S3 is the same as in Example 1.

[0074]

Example 3

[0075] Example 3 differs from Example 1 in the concentrations of ascorbic acid and lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0076] S1 is the same as in Example 1.

[0077] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 1.0 mol / L, the concentration of lithium hydroxide is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0078] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0079] S3 is the same as in Example 1.

[0080]

Example 4

[0081] Example 4 differs from Example 1 in that ascorbic acid is replaced with tannic acid; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0082] S1 is the same as in Example 1.

[0083] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tannic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tannic acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0084] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0085] S3 is the same as in Example 1.

[0086]

Example 5

[0087] Example 5 differs from Example 4 in the concentrations of tannic acid and lithium hydroxide; the remaining steps are the same as in Example 4. The specific steps are as follows:

[0088] S1 is the same as in Example 4.

[0089] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tannic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tannic acid is 1.0 mol / L, the concentration of lithium hydroxide is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0090] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0091] S3 is the same as in Example 4.

[0092]

Example 6

[0093] Example 6 differs from Example 1 in that ascorbic acid is replaced with citric acid; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0094] S1 is the same as in Example 1.

[0095] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, citric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of citric acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0096] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0097] S3 is the same as in Example 1.

[0098]

Example 7

[0099] Example 7 differs from Example 6 in the concentrations of citric acid and lithium hydroxide; the remaining steps are the same as in Example 6. The specific steps are as follows:

[0100] S1 is the same as in Example 6.

[0101] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, citric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of citric acid is 1.0 mol / L, the concentration of lithium hydroxide is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0102] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0103] S3 is the same as in Example 6.

[0104]

Example 8

[0105] Example 8 differs from Example 1 in that ascorbic acid is replaced with tartaric acid; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0106] S1 is the same as in Example 1.

[0107] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tartaric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tartaric acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0108] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0109] S3 is the same as in Example 1.

[0110]

Example 9

[0111] Example 9 differs from Example 8 in the concentrations of tartaric acid and lithium hydroxide; the remaining steps are the same as in Example 8. The specific steps are as follows:

[0112] S1 is the same as in Example 8.

[0113] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tartaric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tartaric acid is 1.0 mol / L, the concentration of lithium hydroxide is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0114] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0115] S3 is the same as in Example 8.

[0116]

Example 10

[0117] Example 10 differs from Example 1 in the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0118] S1 is the same as in Example 1.

[0119] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.4 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0120] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0121] S3 is the same as in Example 1.

[0122]

Example 11

[0123] Example 11 differs from Example 1 in the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0124] S1 is the same as in Example 1.

[0125] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.6 mol / L, the concentration of lithium hydroxide is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0126] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0127] S3 is the same as in Example 1.

[0128]

Example 12

[0129] Example 12 differs from Example 1 in the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0130] S1 is the same as in Example 1.

[0131] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.6 mol / L, the concentration of lithium hydroxide is 2.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0132] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0133] S3 is the same as in Example 1.

[0134]

Example 13

[0135] Example 13 differs from Example 1 in the concentrations of ascorbic acid and lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0136] S1 is the same as in Example 1.

[0137] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.3 mol / L, the concentration of lithium hydroxide is 0.3 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0138] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0139] S3 is the same as in Example 1.

[0140]

Example 14

[0141] Example 14 differs from Example 1 in that the heating temperature in step S3 is different; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0142] S1 and S2 are the same as in Example 1.

[0143] S3: After the lithium iron phosphate material is dried, it is crushed and ground, then placed in a crucible and put into a tube furnace. Under an argon atmosphere, the temperature is increased to 600℃ at a heating rate of 5℃ / min and held for 2 hours. After the holding period, regenerated lithium iron phosphate is obtained.

[0144]

Example 15

[0145] Example 15 differs from Example 1 in that the heating temperature in S1 is different; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0146] S1: Place the lithium iron phosphate waste in a muffle furnace and keep it at 400℃ for 10 h. After heating, take it out, grind and crush it, and sieve it through a 200-mesh sieve to obtain the lithium iron phosphate material to be replenished with lithium.

[0147] S2 and S3 are the same as in Example 1.

[0148]

Example 16

[0149] Example 16 differs from Example 1 in that the heating temperature in S1 is different; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0150] S1: Place the lithium iron phosphate waste in a muffle furnace and keep it at 300℃ for 10 h. After heating, take it out, grind and crush it, and sieve it through a 200-mesh sieve to obtain the lithium iron phosphate material to be replenished with lithium.

[0151] S2 and S3 are the same as in Example 1.

[0152] Comparative Example 1

[0153] S1: Place the lithium iron phosphate waste in a muffle furnace and keep it at 250°C for 10 hours. After heating, take it out, grind and crush it, and sieve it through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0154] Comparative Example 2

[0155] Comparative Example 2 differs from Example 1 in that no organic acid is added; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0156] S1 is the same as in Example 1.

[0157] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water and lithium hydroxide, and stir for 10 min until the mixture is homogeneous to obtain a mixture; in the mixture, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g.

[0158] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0159] S3 is the same as in Example 1.

[0160] Comparative Example 3

[0161] The difference between Comparative Example 3 and Example 1 lies in the concentrations of ascorbic acid and lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0162] S1 is the same as in Example 1.

[0163] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 2.0 mol / L, the concentration of lithium hydroxide is 2.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0164] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0165] S3 is the same as in Example 1.

[0166] Comparative Example 4

[0167] The difference between Comparative Example 4 and Example 1 lies in the type and concentration of the organic acid and the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0168] S1 is the same as in Example 1.

[0169] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tannic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tannic acid is 2.0 mol / L, the concentration of lithium hydroxide is 2.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0170] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0171] S3 is the same as in Example 1.

[0172] Comparative Example 5

[0173] The difference between Comparative Example 5 and Example 1 lies in the type and concentration of the organic acid and the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0174] S1 is the same as in Example 1.

[0175] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, citric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of citric acid is 2.0 mol / L, the concentration of lithium hydroxide is 2.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0176] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0177] S3 is the same as in Example 1.

[0178] Comparative Example 6

[0179] The difference between Comparative Example 6 and Example 1 lies in the type and concentration of the organic acid and the concentration of lithium hydroxide; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0180] S1 is the same as in Example 1.

[0181] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, tartaric acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of tartaric acid is 2.0 mol / L, the concentration of lithium hydroxide is 2.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0182] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0183] S3 is the same as in Example 1.

[0184] Comparative Example 7

[0185] The difference between Comparative Example 7 and Example 1 is the type of lithium source; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0186] S1 is the same as in Example 1.

[0187] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium carbonate, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 0.6 mol / L, the concentration of lithium carbonate is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0188] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0189] S3 is the same as in Example 1.

[0190] Comparative Example 8

[0191] The difference between Comparative Example 8 and Example 1 lies in the concentration of ascorbic acid and the type and concentration of the lithium source; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0192] S1 is the same as in Example 1.

[0193] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, ascorbic acid, and lithium carbonate, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of ascorbic acid is 1.0 mol / L, the concentration of lithium carbonate is 1.0 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0194] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0195] S3 is the same as in Example 1.

[0196] Comparative Example 9

[0197] Comparative Example 9 differs from Example 1 in that ascorbic acid is replaced with acetic acid; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0198] S1 is the same as in Example 1.

[0199] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, acetic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of acetic acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0200] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0201] S3 is the same as in Example 1.

[0202] Comparative Example 10

[0203] Comparative Example 10 differs from Example 1 in that ascorbic acid is replaced with formic acid; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0204] S1 is the same as in Example 1.

[0205] S2: Place the lithium iron phosphate material to be replenished with lithium in a 500 mL beaker, add 400 mL of deionized water, formic acid, and lithium hydroxide, and stir for 10 min until homogeneous to obtain a mixture; in the mixture, the concentration of formic acid is 0.6 mol / L, the concentration of lithium hydroxide is 0.6 mol / L, and the liquid-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is 10:1 mL / g;

[0206] The mixture is filtered until the liquid in the mixture is removed. The filtration pressure is 0.05 MPa. After filtration, filtrate and filter cake are obtained. The filtrate and filter cake are mixed again and then filtered a second time. The filtration is repeated 5 to 6 times. The final filter cake is lithium iron phosphate material after lithium replenishment.

[0207] S3 is the same as in Example 1.

[0208] The test conditions for each embodiment and comparative example are summarized in Table 1.

[0209] Table 1 Summary of test conditions for each embodiment and comparative example

[0210]

[0211] [Performance Testing]

[0212] The regenerated lithium iron phosphate obtained in each embodiment and comparative example was subjected to performance testing. The testing methods are as follows:

[0213] (1) Li / Fe molar ratio determination: The regenerated lithium iron phosphate was ground, pulverized, and passed through a 200-mesh standard sieve. Then, it was completely dissolved by acid digestion (nitric acid, hydrochloric acid, hydrofluoric acid, etc.) to obtain a clear test solution. Subsequently, the clear test solution and the standard solution were introduced into the atomizer through a peristaltic pump to form an aerosol, which was then carried into the ICP plasma torch by the carrier gas for testing, thereby determining the molar ratio of Li to Fe in the regenerated lithium iron phosphate.

[0214] (2) Button cell assembly and electrochemical testing:

[0215] Regenerated lithium iron phosphate material, acetylene black conductive agent, and polyvinylidene fluoride (PVDF) were placed in 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 mixing tank was placed in a homogenizer to mix thoroughly, obtaining a positive electrode material slurry. The positive electrode material slurry was uniformly coated onto aluminum foil using a coating machine, and then the aluminum foil was placed in a 100℃ vacuum drying oven for 2 hours to allow the NMP to completely evaporate. The dried electrode was then cut into 12 mm diameter circular pieces using a slicing machine to obtain the positive electrode sheet.

[0216] In an argon-atmospheric glove box, coin cells were assembled in the following order: positive electrode shell, lithium sheet, electrolyte, separator, electrolyte, negative electrode sheet, spring sheet, and gasket. The assembled coin cells were then sealed using a sealing machine and allowed to stand for 12 hours. Following this, the coin cells were subjected to their first constant current charge-discharge test using a Blue Electric testing system at current rates of 0.1C and 1C, and the corresponding discharge specific capacity was recorded.

[0217] The performance test results of each embodiment and comparative example are shown in Table 2.

[0218] Table 2 Summary of performance test data for each embodiment and comparative example

[0219]

[0220] Analysis of Tables 1 and 2 shows that the 0.1C discharge specific capacity of each embodiment ranges from 124.45 mAh / g to 152.59 mAh / g, the 1C discharge specific capacity ranges from 117.34 mAh / g to 142.97 mAh / g, and the Li / Fe molar ratio ranges from 0.95 to 1.15. The comparative example shows a 0.1C discharge specific capacity range of 95.62 mAh / g to 130.62 mAh / g, a 1C discharge specific capacity range of 64.81 mAh / g to 115.27 mAh / g, and a Li / Fe molar ratio range of 0.838 to 1.25. Overall, the embodiments are superior to the comparative example in terms of discharge specific capacity and Li / Fe ratio.

[0221] The regenerated lithium iron phosphate obtained by calcining the lithium iron phosphate waste in Comparative Example 1 without lithium replenishment has a very low Li / Fe molar ratio of only 0.838.

[0222] Compared to Examples 1, 4, 6, and 8, Comparative Example 2 did not add organic acid during the lithium replenishment process, and only used lithium hydroxide as the lithium source. The regenerated lithium iron phosphate obtained in Examples 1, 4, 6, and 8 had a higher Li / Fe molar ratio than Comparative Example 2, and their 0.1C discharge specific capacity and 1C discharge specific capacity were significantly higher than those of Comparative Example 2. This indicates that the chelating groups in the organic acid anions chelate with the iron ions on the surface of lithium iron phosphate, which can promote the lithium replenishment effect and improve the electrochemical performance of the regenerated lithium iron phosphate.

[0223] The concentration ratio of ascorbic acid to lithium hydroxide was the same in Comparative Example 3 and Example 3, the difference being that the concentrations of both ascorbic acid and lithium hydroxide in Comparative Example 3 were twice that of Example 3. The 0.1C and 1C discharge specific capacities measured in Example 3 were significantly higher than those in Comparative Example 3, indicating that excessive organic lithium salts over-chelated on the surface of lithium iron phosphate, reducing the electrochemical performance of the regenerated lithium iron phosphate. The same pattern was observed between Comparative Example 4 and Example 5, Comparative Example 5 and Example 7, and Comparative Example 6 and Example 9.

[0224] Compared with Example 1, Comparative Example 7 replaced lithium hydroxide with lithium carbonate, and compared with Example 3, Comparative Example 8 replaced lithium hydroxide with lithium carbonate. The discharge specific capacity obtained by Comparative Example 7 was significantly lower than that of Example 1, and the discharge specific capacity obtained by Comparative Example 8 was significantly lower than that of Example 3. This is because lithium hydroxide has high solubility in water and can effectively react with organic acids to form organolithium salts; while lithium carbonate has low solubility in water, and its reaction rate with organic acids in the aqueous phase is slow and the conversion rate is low, making it difficult to effectively form high-purity organolithium salts.

[0225] Compared to Example 1, Comparative Examples 9 and 10 used acetic acid and formic acid instead of ascorbic acid, respectively. The Li / Fe molar ratio, 0.1C discharge specific capacity and 1C discharge specific capacity measured in Comparative Examples 9 and 10 were significantly lower than those in Example 1, but similar to those in Comparative Example 1. This indicates that the effect achieved by using acetic acid and formic acid is not as good as that of ascorbic acid.

[0226] It is worth noting that, Figure 2 The image shows the charge-discharge curves of the battery prepared from the recycled lithium iron phosphate obtained in Example 1. Figure 2 The curve showing the voltage increasing with increasing discharge specific capacity represents the charging stage, while the curve showing the voltage decreasing with increasing discharge specific capacity represents the discharging stage. For example... Figure 2 As shown, the plateau voltage of the first and second cycles at 0.1C is stable at around 3.5V, indicating that the regenerated lithium iron phosphate material has good reversibility and structural stability. The capacity at 0.1C is about 152.59mAh / g, at 0.5C it is about 147.23mAh / g, and at 1C it is about 142.97mAh / g, indicating that the regenerated lithium iron phosphate has good rate performance.

[0227] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0228] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for regenerating lithium iron phosphate material, characterized in that, The regeneration method includes the following steps: The lithium iron phosphate material to be replenished with lithium, organic acid, lithium source and water are mixed to obtain a mixture; wherein, the organic acid reacts with the lithium source to generate an organic lithium salt, the organic lithium salt including chelating groups that can coordinate with metal ions; The mixture is filtered to obtain lithium iron phosphate material after lithium replenishment; the lithium iron phosphate material after lithium replenishment is heated to obtain regenerated lithium iron phosphate. The process of filtering the mixture to obtain lithium iron phosphate material after lithium replenishment includes: S100. The mixture is filtered to obtain filtrate and filter cake. S200: Remix the filtrate and the filter cake, and perform vacuum filtration again; S300, repeat S200 at least once, and the final filter cake is the lithium iron phosphate material after lithium replenishment; The filtration pressure is 0.01 MPa to 0.1 MPa. In the mixture, the concentration of the organic acid is 0.6 mol / L to 1 mol / L, and the concentration of the lithium source is 0.6 mol / L to 1 mol / L; The molar ratio of the organic acid to the lithium source is 1:1; The organic acid is selected from one of ascorbic acid, tannic acid, citric acid or tartaric acid; The lithium source is lithium hydroxide.

2. The method for regenerating lithium iron phosphate material as described in claim 1, characterized in that, The heat treatment of the lithium iron phosphate material after lithium replenishment includes: After the lithium-replenished lithium iron phosphate material is dried, it is crushed and ground, and then heated at 600℃~700℃ for 2h~10h in an inert gas atmosphere.

3. The method for regenerating lithium iron phosphate material as described in claim 1, characterized in that, In the mixture, the liquid-to-solid ratio between the liquid phase and the lithium iron phosphate material to be replenished with lithium is (3~20):1, in mL / g.

4. The method for regenerating lithium iron phosphate material as described in claim 1, characterized in that, Before mixing the lithium iron phosphate material to be replenished with lithium, organic acid, lithium source, and water, the regeneration method further includes: The lithium iron phosphate waste is heated at 100℃~400℃ for 2h~10h. After heating, the lithium iron phosphate waste is crushed and sieved to obtain the lithium iron phosphate material to be replenished.

5. A type of recycled lithium iron phosphate, characterized in that, It is prepared by the regeneration method of lithium iron phosphate material as described in any one of claims 1 to 4.

6. A secondary battery, characterized in that, Includes a positive electrode, said positive electrode being made of recycled lithium iron phosphate as described in claim 5.

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