Efficient regeneration method of waste lithium iron phosphate battery positive electrode material

Abstract

The invention belongs to the technical field of lithium iron phosphate batteries, and particularly relates to an efficient regeneration method of a waste lithium iron phosphate battery positive electrode material, which comprises the following steps: S1, waste material pretreatment: removing an aluminum foil current collector of a positive electrode plate of a retired power battery, collecting lithium iron phosphate powder, and carrying out ball milling and drying treatment to obtain waste LFP powder; s2, preparation of a lithium supplementing solution: mixing caffeic acid with LiOHH2O to prepare a liquid-phase lithium supplementing solution; s3, liquid-phase lithium supplementing and repairing: adding the SLFP into the lithium supplementing solution, stirring and reacting at a preset temperature, and washing and drying to obtain LFP powder for lithium supplementing and repairing; and S4, heat treatment and carbon coating: mixing the LLFP with glucose, carrying out heating heat treatment in an inert protective atmosphere, and naturally cooling to obtain regenerated lithium iron phosphate powder. And a solution with performance advantages and economical efficiency is provided for recycling of the waste lithium iron phosphate battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery technology, and particularly relates to an efficient method for regenerating waste lithium iron phosphate battery cathode materials. Background Technology

[0002] With the widespread use of lithium-ion batteries, the recycling and reuse of waste batteries has become an urgent problem to be solved. Lithium iron phosphate (LiFePO4) batteries have been widely used in electric vehicles and energy storage devices due to their high stability and safety.

[0003] However, after prolonged use, lithium iron phosphate batteries experience a significant performance degradation due to lithium loss and the conversion of lithium iron phosphate. Existing regeneration methods mostly rely on high-temperature reduction or direct high-temperature recycling, but these methods typically require the removal of impurities from the battery, making the process complex and costly.

[0004] In the prior art, patent CN202010825386.5 provides a method for repairing and regenerating the cathode material of waste lithium iron phosphate batteries. This method involves obtaining retired lithium iron phosphate powder through refined disassembly, and then processing it at 700~900℃. Carbon removal is achieved by calcination under oxygen partial pressure conditions, followed by ball milling of lithium source (lithium carbonate, etc.) and carbon source (sucrose or glucose), and finally calcination at 650~800℃ in an inert atmosphere. However, this method requires multiple high-temperature treatments, has high energy consumption and a complex process, and does not consider side reactions such as iron leaching.

[0005] Patent CN202110939900.2 discloses a method for regenerating the positive electrode waste of discarded lithium iron phosphate batteries. It uses a multi-component lithium-replenishing modifier containing lithium carbonate, starch, silver nitrate, titanium sulfate, and carbon nanotubes, combined with a microwave high-temperature hydrothermal reaction at 300~400W and 175~215℃ and a calcination process at 600~800℃. However, the preparation steps of the lithium-replenishing modifier are complicated, the microwave hydrothermal reaction requires special high-temperature and high-pressure equipment, the cost is high, and it cannot simultaneously improve the lithium-ion diffusion efficiency.

[0006] Patent CN202310867048.1 proposes to regenerate lithium carboxymethyl cellulose. The process involves pre-treating the waste lithium iron phosphate powder by washing it with acetonitrile and calcining it at 500°C for 3 hours. After testing the lithium deficiency by ICP-OES, the powder is mixed with lithium carboxymethyl cellulose and calcined at 600~700°C in an Ar / H2 atmosphere for 10~15 hours. However, this method requires prior detection of lithium deficiency, is cumbersome, has a long high-temperature calcination time, consumes a lot of energy, and lacks a side reaction inhibition mechanism.

[0007] Therefore, developing an efficient and low-cost method for regenerating lithium iron phosphate has become a technical challenge in the current battery recycling field. Summary of the Invention

[0008] The purpose of this invention is to provide an efficient method for regenerating waste lithium iron phosphate battery cathode materials to solve the above-mentioned problems.

[0009] To achieve the above objectives, the present invention provides the following solution: An efficient method for regenerating waste lithium iron phosphate battery cathode materials includes: S1. Waste material pretreatment: Remove the aluminum foil current collector from the positive electrode sheet of the retired power battery, collect the lithium iron phosphate powder and ball mill and dry it to obtain waste LFP powder; S2. Preparation of lithium supplementation solution: Caffeic acid and... Mix at a molar ratio of 1:0.9-1.1 to prepare a liquid-phase lithium replenishment solution; S3. Liquid phase lithium replenishment and repair: SLFP is added to the lithium replenishment solution in step S2, and the mixture is stirred and reacted at a preset temperature. After washing and drying, lithium-repaired LFP powder is obtained. S4. Heat treatment and carbon coating: LLFP and glucose are mixed at a mass ratio of 10:0.8-1.2, and heat-treated under an inert protective atmosphere. After natural cooling, regenerated lithium iron phosphate powder is obtained.

[0010] Preferably, in step S1, the ball-to-material ratio of the ball mill is 10:1, the ball milling speed is 300 r / min, and the ball milling time is 2 hours.

[0011] Preferably, in step S1, the drying is vacuum drying, the drying temperature is 60°C, and the drying time is 12 hours.

[0012] Preferably, in step S2, the concentration of the liquid phase lithium replenishment solution is 0.05–0.2 mol / L.

[0013] Preferably, in step S3, the preset temperature is 60°C and the stirring reaction time is 6 hours.

[0014] Preferably, in step S4, the inert protective atmosphere is a mixture of Ar and H2.

[0015] Preferably, the volume ratio of Ar to H2 in the mixed atmosphere of Ar and H2 is 95:5.

[0016] Preferably, in step S4, the heating rate is 5℃ / min, the heat treatment temperature is 700℃, and the holding time is 2 hours.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This technical solution significantly improves the electrochemical performance of waste lithium iron phosphate cathode materials by combining the synergistic effect of caffeic acid and LiOH with glucose carbon coating.

[0018] The regenerated lithium iron phosphate powder exhibits a significantly improved specific capacity in the first cycle compared to waste materials, with greatly optimized cycle stability and a markedly reduced capacity decay rate. The material consistently delivers high capacity at various rates, maintaining excellent capacity stability even at high rates, effectively addressing the performance degradation issue of traditional recycled materials at high rates. The synergistic effect of caffeic acid and LiOH inhibits side reactions such as iron dissolution and repairs crystal structure defects, while glucose-carbon coating further enhances conductivity. These three factors collectively ensure the overall performance of the recycled material.

[0019] Meanwhile, the process does not require high-temperature reduction treatment, avoiding related side reactions, and does not require complex impurity removal steps. It achieves efficient regeneration while reducing costs, providing a solution that combines performance advantages and economic efficiency for the recycling and reuse of waste lithium iron phosphate batteries. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 The graph shows the specific capacity of six samples at different rates (0.1C, 0.2C, 0.5C, 1C, 2C, 5C) as a function of the number of cycles: lithium supplementation with LiOH only (Comparative Example A), acid substitution (replaced with citric acid - Comparative Example B, oxalic acid - Comparative Example D, benzoic acid - Comparative Example F), lithium supplementation in liquid phase missing (Comparative Example C), and caffeic acid + LiOH liquid phase lithium supplementation + glucose + 700° CAr / H2 (Example 1 of the present invention). Figure 2 This is a comparison chart of the capacity retention rates of the above six groups of materials (including Comparative Example A, Comparative Example B, Comparative Example C, Comparative Example D, Comparative Example F, and Example 1) after 150 cycles. Figure 3 A comparison chart of the cycling performance of recycled lithium iron phosphate material (r-lfp) and waste lithium iron phosphate material (s-lfp) at a rate of 0.1C. Figure 4 This is a schematic diagram of the chemical reaction mechanism of caffeic acid. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1 This embodiment provides an efficient regeneration method for waste lithium iron phosphate battery cathode materials, specifically including: S1. Waste material pretreatment: Take the positive electrode sheet of retired power battery, remove the aluminum foil current collector and collect lithium iron phosphate powder. The powder is ball-milled (ball-to-material ratio 10:1, rotation speed 300r / min, grinding time 2 hours). After ball milling, it is dried in a vacuum environment at 60℃ for 12 hours to obtain waste LFP powder (SLFP). S2. Preparation of caffeic acid-LiOH lithium supplementation solution: Weigh caffeic acid and LiOH... H2O, control the molar ratio of the two to be 1:1, prepare a 0.1 mol / L caffeic acid-LiOH mixed solution, and stir thoroughly until completely dissolved; S3. Lithium replenishment and repair: Take a certain amount of SLFP (added according to the ratio of 1g SLFP: 20mL caffeic acid-LiOH mixed solution) and add it to the above caffeic acid-LiOH mixed solution. Stir continuously at 60℃ for 6 hours. After the reaction is completed, wash and dry to obtain lithium replenishment and repair LFP powder (LLFP). S4. Heat treatment and carbon coating: LLFP and glucose are mixed uniformly at a mass ratio of 10:1, placed in a tube furnace, and an Ar / H2 (volume ratio 95:5) protective atmosphere is introduced. The temperature is raised to 700℃ at a heating rate of 5℃ / min and held for 2 hours. After natural cooling, regenerated lithium iron phosphate powder (r-lfp) is obtained.

[0024] Example 2 This embodiment provides a method for regenerating waste lithium iron phosphate battery cathode material, which differs from Embodiment 1 only in that the concentration of the caffeic acid-LiOH mixed solution in step S2 is 0.05 mol / L.

[0025] Example 3 This embodiment provides a method for regenerating waste lithium iron phosphate battery cathode material, which differs from Embodiment 1 only in that the concentration of the caffeic acid-LiOH mixed solution in step S2 is 0.15 mol / L.

[0026] Example 4 This embodiment provides a method for regenerating waste lithium iron phosphate battery cathode material, which differs from Embodiment 1 only in that the concentration of the caffeic acid-LiOH mixed solution in step S2 is 0.2 mol / L.

[0027] Comparative Example A This comparative example provides a method for regenerating waste lithium iron phosphate battery cathode material. The only difference from Example 1 is that only LiOH is used when preparing the lithium replenishment solution, without adding caffeic acid, and the subsequent steps of mixing with glucose and heat treatment at 700°C under Ar / H2 atmosphere for carbon coating are omitted. The remaining pretreatment (ball milling, drying) and lithium replenishment reaction conditions (60°C, 6 hours) are the same as in Example 1.

[0028] Comparative Example B This comparative example provides a method for regenerating waste lithium iron phosphate battery cathode material. The only difference from Example 1 is that, in the lithium replenishment solution preparation stage, citric acid is used instead of caffeic acid and LiOH. The mixed solution was prepared by molar ratio of H2O 1:1, and the remaining steps and parameters were the same as in Example 1.

[0029] Comparative Example C This comparative example provides a method for regenerating waste lithium iron phosphate battery cathode material. The only difference from Example 1 is that the caffeic acid-LiOH liquid phase lithium replenishment step is omitted, and the pretreated SLFP is directly mixed with glucose at a mass ratio of 10:1. The subsequent tube furnace heat treatment conditions (Ar / H2 atmosphere, heating to 700℃ at 5℃ / min and holding for 2 hours) are the same as in Example 1.

[0030] Comparative Example D This comparative example provides a method for regenerating waste lithium iron phosphate battery cathode material. The only difference from Example 1 is that, in the lithium replenishment solution preparation stage, oxalic acid is used instead of caffeic acid and LiOH. The mixed solution was prepared by molar ratio of H2O 1:1, and the remaining steps and parameters were the same as in Example 1.

[0031] Comparative Example F This comparative example provides a method for regenerating waste lithium iron phosphate battery cathode material. The only difference from Example 1 is that, in the lithium replenishment solution preparation stage, benzoic acid is used instead of caffeic acid and LiOH. The mixed solution was prepared by molar ratio of H2O 1:1, and the remaining steps and parameters were the same as in Example 1.

[0032] Experimental Example 1 This experimental example aims to verify the superior rate performance of the "caffeic acid + LiOH liquid-phase lithium supplementation + glucose + 700℃ Ar / H2" scheme compared to the schemes involving only LiOH lithium supplementation, acid substitution (i.e., substitution with citric acid in comparative example B, oxalic acid in comparative example D, and benzoic acid in comparative example F), and liquid-phase lithium supplementation, specifically including: Experimental preparation: 1. Test samples: Sample from Example 1, and samples from Comparative Examples A, B, C, D, and F; 2. Test conditions: Coin cell (CR2032, positive electrode: test sample + PVDF binder + Super P conductive agent, mass ratio 8:1:1; negative electrode: lithium metal sheet; separator: Celgard2400; electrolyte: 1 mol / L LiPF6-EC / DMC / EMC (1:1:1, volume ratio)), charge / discharge cutoff voltage 2.0 V–4.2 V. Test rates were 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C respectively; ambient temperature was 25±1 ℃, relative humidity was 30±5%RH; 5 cycles were performed at each rate (30 cycles in total), and the discharge specific capacity at the last cycle of each rate was recorded for rate performance comparison.

[0033] Experimental steps: S1. Assemble button half-cells in an argon glove box. Assemble 3 cells in parallel for each sample group and let stand for 12 hours for later use. S2. Place the assembled battery in the charge-discharge tester and perform constant current charge-discharge cycle tests at various rates according to the above test conditions. S3. Record the discharge specific capacity of each sample per cycle and plot the discharge specific capacity-cycle count curve.

[0034] The test results are as follows Figure 1 As shown: The sample in Example 1 exhibited slow capacity decay during cycling at discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, demonstrating excellent rate capability. In contrast: Comparative Example C has the lowest capacity at all rates, indicating that structural defects in the material are difficult to repair when lithium is added in the liquid phase, and its high-rate performance is significantly limited. Comparative Example A showed a more significant capacity decrease at high rates such as 1C, 2C and 5C, indicating that when only LiOH is used for lithium supplementation and there is a lack of caffeic acid synergy and subsequent carbon coating, lithium diffusion and structural stability are insufficient. The high-rate capacity of Comparative Example B (acid replaced with citric acid) was better than that of Comparative Example A, but still lower than that of this scheme; Comparative Example D (acid replaced with oxalic acid) has inferior capacity and stability at high rates compared to this scheme, and its overall performance is between that of citric acid replacement and lithium supplementation with only LiOH. Although the comparative example F (acid replaced with benzoic acid) can still output a certain capacity at low rates, its capacity retention and recovery capabilities at high rates are lower than those of this scheme.

[0035] Experimental results show that the rate performance of the present invention is significantly better than that of the comparative examples. The combined effect of the synergistic lithium supplementation of caffeic acid and LiOH and the carbon coating of glucose effectively promotes lithium diffusion, inhibits side reactions and improves conductivity, enabling the material to maintain stable capacity output at high rates.

[0036] Experimental Example 2 This experimental example aims to verify the cycling stability advantages of the proposed solution compared to solutions involving only LiOH lithium replenishment, acid replacement, or lithium replenishment in a liquid-deficient phase. Specifically, it includes: Experimental preparation: 1. Test samples: Consistent with the samples of Example 1 in Test Example 1, and Comparative Examples A, B, C, D, and F; 2. Test conditions: The parameters of the button cell half-cell are the same as those in Test Example 1. The charge / discharge rate is 1C, the charge / discharge cut-off voltage is 2.0 V–4.2 V, the test environment temperature is 25±1 ℃, the relative humidity is 30±5%RH, the number of cycles is 100, and the capacity retention rate is calculated based on the discharge specific capacity of the first cycle.

[0037] Experimental steps: S1. Assemble button half-cells according to the assembly process and parameters of Experiment Example 1. Assemble 3 cells in parallel for each sample group and let stand for 12 hours for later use. S2. Place the battery in the charge-discharge tester and perform 100 constant current charge-discharge cycle tests under the above test conditions. S3. Record the discharge specific capacity of each sample group per cycle, calculate the capacity retention rate after 100 cycles, and draw a capacity retention rate comparison chart.

[0038] The test results are as follows Figure 2 As shown: After 100 cycles, the sample in Example 1 maintained 97% capacity retention, with a discharge specific capacity of 142 mAh / g in the first cycle and 140 mAh / g after 100 cycles, exhibiting a capacity retention of approximately 97% and minimal capacity decay. In comparison: In Comparative Example A, the capacity gradually decreased during the cycle, with a capacity retention rate of approximately 89% after 100 cycles. Comparative Example C has a lower overall capacity level than this scheme and exhibits some capacity decay, with a capacity retention rate of approximately 90%. Comparative Example B (citric acid) exhibited the most severe capacity decay, with a discharge specific capacity of less than 50% of that of the first cycle after 100 cycles, and a capacity retention rate of approximately 48%. The cycling stability and capacity of Comparative Example D (oxalic acid) remained lower than those of this scheme, indicating that oxalic acid replacement is difficult to achieve the effects of synergistic lithium replenishment and suppression of side reactions at the same time. The comparative example, F (benzoic acid), also exhibited more significant capacity decay during cycling than this scheme, indicating that benzoic acid replacement cannot provide the antioxidant and Li-promoting effects of caffeic acid. + Synergistic effects in diffusion.

[0039] Experimental results show that this scheme, through the synergistic lithium replenishment and repair of the crystal structure by caffeic acid and LiOH and the inhibition of iron dissolution, combined with glucose carbon coating to improve structural stability, can effectively reduce side reactions and structural degradation during cycling, thus exhibiting significantly better cycling stability than the comparative examples.

[0040] Acid substitution analysis: The experimental results of Examples 1 and 2 show that different organic acids have significant differences in their effects on the lithium replenishment system and the performance of the regenerated lithium iron phosphate material. For example, Comparative Example D (oxalic acid replacing caffeic acid) and Comparative Example F (benzoic acid replacing caffeic acid) are significantly inferior to the scheme of this invention in terms of rate performance and cycle stability. The main reasons for this can be analyzed from the following mechanistic perspectives: First, both oxalic acid and benzoic acid are carboxylic acids. In lithium replenishment solutions, they preferentially undergo acid-base neutralization reactions with LiOH to generate the corresponding lithium salts and consume the LiOH in the system, thereby reducing the effective LiO2 content as a high-efficiency lithium source. + Activity. Among them, oxalic acid is a dicarboxylic acid, which has a stronger ability to consume LiOH. Under the same molar conditions, it will further weaken the driving force of the lithium replenishment reaction, resulting in an insufficient and uneven lithium replenishment process.

[0041] Secondly, oxalate It possesses strong bidentate coordination and complexing capabilities, and readily combines with lithium iron phosphate materials. Complexation occurs, promoting the migration of iron species from the crystal lattice or particle surface into the solution, increasing the risk of iron dissolution and disrupting the crystal structure integrity of lithium iron phosphate. Furthermore, oxalate or hydrogen oxalate salts may form a coating layer or localized deposition on the particle surface during the reaction and subsequent processing, correspondingly increasing lithium-ion transport impedance and further hindering the improvement of rate performance and cycle stability.

[0042] Furthermore, benzoic acid contains only a single carboxyl group in its molecular structure and lacks a polyphenolic hydroxyl structure. Therefore, after neutralization with LiOH to form lithium benzoate, it cannot be effectively stabilized and regulated through coordination. It also lacks the ability to scavenge free radicals and resist oxidation, making it difficult to inhibit the effects of charging, discharging, and regeneration. Towards The oxidation and transformation of benzoic acid leads to an increase in side reactions and a decrease in structural stability after replacing caffeic acid with benzoic acid, resulting in accelerated capacity decay of the material under high-rate and long-cycle conditions.

[0043] In contrast, caffeic acid molecules are rich in active phenolic hydroxyl structures, which can react with [the rest of the text] without significantly consuming lithium. It forms coordination interactions, enhancing the stability and diffusion capacity of lithium ions in the lithium replenishment system; simultaneously, its antioxidant properties effectively scavenge active free radicals in the reaction system, inhibiting Fe-related side reactions and iron dissolution. These synergistic effects result in the caffeic acid-LiOH system being significantly superior to the oxalic acid and benzoic acid replacement systems in terms of lithium replenishment uniformity, structural repair, and cycle stability.

[0044] In summary, oxalic acid and benzoic acid are difficult to achieve efficient lithium replenishment and structural stabilization repair of waste lithium iron phosphate materials due to their insufficient acid-base neutralization consumption of lithium source and inadequate complexation or inhibition effects. However, the caffeic acid-LiOH synergistic system adopted in this invention can simultaneously take into account lithium source efficiency, structural protection and electrochemical stability, thus exhibiting significantly better comprehensive performance than each comparative example.

[0045] Experimental Example 3 This experimental example aims to verify the remediation effect of the method of the present invention on waste lithium iron phosphate (S-LFP) materials, and to compare the electrochemical performance of the materials before and after remediation, specifically including: Experimental preparation: 1. Test samples: waste material samples (s-lfp, sourced from retired lithium iron phosphate power batteries, with a service life of 5 years, prepared according to the invention's pretreatment steps, without lithium replenishment or carbon coating), and recycled material samples (r-lfp, prepared according to the complete steps of Example 1). 2. Test conditions: The parameters of the button cell were the same as those in Test Example 1, with a charge / discharge rate of 0.1C, a charge / discharge cutoff voltage of 2.0V-4.2V, a temperature of 25±1℃, a relative humidity of 30±5%RH, a cycle count of 150, and a positive electrode sample loading mass of 2.2mg / cm².

[0046] Experimental steps: S1. Prepare s-lfp and r-lfp positive electrode sheets respectively according to the positive electrode sheet preparation method of Experimental Example 1; S2. Assemble button half-cells in an argon glove box. Assemble 3 cells in parallel for each sample group and let stand for 12 hours for later use. S3. Place the battery in the charge-discharge tester and perform 150 constant current charge-discharge cycles at a 0.1C rate, recording the discharge specific capacity for each cycle. S4. Plot the discharge specific capacity-cycle count curves of s-lfp and r-lfp, and calculate the capacity retention rate of both after 150 cycles.

[0047] The test results are as follows Figure 3 As shown: The s-lfp sample had a discharge specific capacity of about 70 mAh / g in the first cycle, and the discharge specific capacity dropped to about 55 mAh / g after 150 cycles, with a low overall capacity retention rate and poor cycle stability. The r-lfp sample provided in Example 1 of this invention had a discharge specific capacity of about 150 mAh / g in the first cycle, and the discharge specific capacity remained at about 140 mAh / g after 150 cycles, with a capacity retention rate of 93%.

[0048] Experimental results show that the method of the present invention can effectively repair the electrochemical performance of waste lithium iron phosphate materials. Through the synergistic effect of liquid-phase lithium replenishment to compensate for lithium loss, caffeic acid to inhibit side reactions, and glucose carbon coating to improve conductivity, the specific capacity of the recycled materials is greatly improved and the cycle stability is significantly enhanced.

[0049] The following will combine Figure 4 The mechanism of action of caffeic acid is explained in detail, focusing on the synergistic effect between caffeic acid and LiOH. The caffeic acid molecule contains a highly reactive phenolic hydroxyl group (–OH), which can dissociate with LiOH to produce lithium ions. A coordination reaction occurs, forming a structurally stable caffeic acid-Li coordination complex. The chemical reaction formula is as follows: Caffeic acid (C7H6O4) + Li + → Caffeic acid-Li coordination complex Specifically, caffeic acid reacts with lithium ions through the oxygen atom in its phenolic hydroxyl group. The formation of stable coordination bonds not only effectively enhances the stability of lithium ions in the reaction system, preventing them from agglomerating or being lost prematurely, but also significantly promotes the diffusion rate of lithium ions into the waste lithium iron phosphate (LiFePO4) material, providing a key guarantee for the uniformity and sufficiency of the subsequent lithium replenishment process.

[0050] The phenolic hydroxyl groups in caffeic acid also possess strong antioxidant activity, a property that enables them to react with hydroxyl radicals generated in the reaction system and during battery charging and discharging. When active substances react, the corresponding antioxidant reaction formula is: Caffeic acid (C7H6O4)+ OH → Oxidized caffeic acid Through this reaction, caffeic acid can effectively consume free radicals in the system, reducing unnecessary redox side reactions initiated by free radicals, thereby maintaining the stability of the reaction system. More importantly, this antioxidant property can specifically inhibit oxidation in lithium iron phosphate materials. The oxidation transformation occurs during the charge-discharge cycle of a lithium battery. Easily oxidized by hydroxyl radicals It dissolves into the electrolyte, and the reaction formula is:

[0051] The reducing properties of caffeic acid can neutralize this oxidation reaction and prevent it. Towards The conversion effectively inhibits the dissolution of iron ions, thus ensuring the integrity of the crystal structure of lithium iron phosphate materials.

[0052] LiOH serves as a highly efficient lithium source in this invention, as it can dissociate into sufficient lithium ions in solution. These lithium ions can react with the lithium-replenishing portions of waste lithium iron phosphate materials that have lost lithium due to long-term use, and the corresponding chemical reaction formula is:

[0053] This reaction directly targets the core cause of lithium iron phosphate material failure. By providing lithium ions through LiOH, it replenishes the missing lithium element in the material, quickly repairs the crystal structure defects caused by lithium loss, and lays the foundation for the recovery of the material's electrochemical performance.

[0054] Glucose (C6H) 12 O6) In the subsequent heat treatment process of this invention (Ar / H2 (95:5) protective atmosphere, 700℃ for 2 hours), a pyrolysis reaction will occur, and its chemical reaction formula is as follows: C6H 12 O6→C (carbon coating) + CO2 + H2O The carbon elements generated after glucose pyrolysis form a uniform carbon coating layer on the surface of the repaired lithium iron phosphate particles. This carbon coating layer can significantly improve the electronic conductivity of the material, solve the inherent problem of poor conductivity of lithium iron phosphate material itself, and thus provide strong support for further optimization of the material's rate performance and cycle stability.

[0055] In summary, caffeic acid and LiOH form a highly efficient synergistic effect in the regeneration process of this invention, and the comprehensive reaction formula is as follows: LiFePO4 + caffeic acid + LiOH → Repair of the LiFePO4 + caffeic acid-Li complex In this synergistic system, LiOH plays a core role as the lithium source, providing sufficient lithium ions to compensate for lithium loss in waste lithium iron phosphate materials. Caffeic acid exerts a synergistic effect through two aspects: firstly, by coordinating with lithium ions, it accelerates the diffusion of lithium ions, ensuring a uniform and sufficient lithium replenishment process; secondly, by inhibiting iron dissolution and various side reactions through its antioxidant / reduction activity, it ensures the stability of the material's crystal structure. The synergistic effect of the two allows lithium ions to be replenished more efficiently into the material and remain stable. Combined with the improved conductivity brought about by glucose carbon coating, the electrochemical performance of waste lithium iron phosphate materials is ultimately fully restored and significantly improved.

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A highly efficient method for regenerating waste lithium iron phosphate battery cathode material, characterized in that, include: S1. Waste material pretreatment: Remove the aluminum foil current collector from the positive electrode sheet of the retired power battery, collect the lithium iron phosphate powder and ball mill and dry it to obtain waste LFP powder; S2. Preparation of lithium supplementation solution: Caffeic acid and... Mix at a molar ratio of 1:0.9-1.1 to prepare a liquid-phase lithium replenishment solution; S3. Liquid phase lithium replenishment and repair: SLFP is added to the lithium replenishment solution in step S2, and the mixture is stirred and reacted at a preset temperature. After washing and drying, lithium-repaired LFP powder is obtained. S4. Heat treatment and carbon coating: LLFP and glucose are mixed at a mass ratio of 10:0.8-1.2, and heat-treated under an inert protective atmosphere. After natural cooling, regenerated lithium iron phosphate powder is obtained.

2. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S1, the ball-to-material ratio of the ball mill is 10:1, the ball mill speed is 300 r / min, and the ball milling time is 2 hours.

3. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S1, the drying is vacuum drying, the drying temperature is 60℃, and the drying time is 12 hours.

4. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S2, the concentration of the liquid-phase lithium replenishment solution is 0.05–0.2 mol / L.

5. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S3, the preset temperature is 60℃ and the stirring reaction time is 6 hours.

6. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S4, the inert protective atmosphere is a mixture of Ar and H2.

7. A method for efficient regeneration of waste lithium iron phosphate battery cathode material according to claim 6, characterized in that: In the mixed atmosphere of Ar and H2, the volume ratio of Ar to H2 is 95:

5.

8. The efficient regeneration method for waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step S4, the heating rate is 5℃ / min, the heat treatment temperature is 700℃, and the holding time is 2 hours.

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