A method for repairing waste lithium iron phosphate cathode material and its application, lithium-ion batteries

Abstract

This invention provides a method for repairing waste lithium iron phosphate cathode materials and their applications in lithium-ion batteries. The method for repairing waste lithium iron phosphate cathode materials includes the following steps: adding waste lithium iron phosphate cathode materials, a lithium source, and a reducing agent to water, and carrying out a hydrothermal reaction to obtain repaired lithium iron phosphate cathode materials; wherein the reducing agent is cysteine. This method, using cysteine ​​as a reducing agent, effectively regulates the valence state of iron ions and repairs the crystal structure in waste lithium iron phosphate under all-aqueous conditions and mild conditions. It eliminates the need for high-temperature annealing, simplifies the process, reduces energy consumption, and significantly improves the electrochemical performance of regenerated lithium iron phosphate, showing promising application prospects. Compared with traditional wet and pyrometallurgical recycling processes, this repair method significantly reduces energy consumption and production costs, demonstrating good economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of electrode material recycling technology, and in particular to a method for repairing and applying waste lithium iron phosphate cathode materials, and lithium-ion batteries. Background Technology

[0002] With the rapid development of the electric vehicle and energy storage industries, lithium iron phosphate (LFP) batteries have been widely used due to their high safety, long cycle life, and low cost, and their installed capacity has been increasing year by year. However, the lifespan of lithium-ion power batteries is typically only 5-10 years. As batteries launched in the early stages of the market gradually enter their retirement period, the amount of waste LFP batteries will show a rapid growth trend in the future. If retired batteries cannot be efficiently recycled and reused, it will not only cause serious waste of resources such as lithium, iron, and phosphorus, but may also lead to environmental pollution problems. Therefore, developing green and efficient recycling and regeneration technologies for waste LFP cathode materials is of great significance for achieving the closed-loop development of the lithium-ion battery industry chain.

[0003] Existing research indicates that the capacity decay of lithium iron phosphate (LFP) batteries during long-term cycling is mainly due to lithium loss in the cathode material, increased iron-lithium antisite defects, and localized crystal structure collapse, making it difficult to directly reuse retired cathode materials. Currently, some recycling technologies employ high-temperature pyrolysis to process waste LFP materials, obtaining usable cathode materials through calcination, lithium replenishment, and resynthesis. However, these methods often require complete reconstruction of the material under air or high-temperature conditions, inevitably destroying the original olivine crystal structure and resulting in the loss of the material's intrinsic structural advantages. Furthermore, these methods suffer from high energy consumption, significant residual lithium volatilization, and high economic costs.

[0004] In addition, wet recycling technology is also widely used for the regeneration of waste lithium iron phosphate cathode materials. It typically involves leaching the metal elements from the cathode material with strong acids or alkalis, followed by precipitation, filtration, and hydrothermal or solid-state reactions to resynthesize the lithium iron phosphate cathode material. Although this method can achieve high metal recovery rates, it still has significant shortcomings in practical applications. For example, it requires large amounts of acid and alkali reagents, has a complex process flow, is prone to secondary pollution, and the resulting products often need to undergo a complete synthesis process again, which is not conducive to reducing production costs and achieving large-scale industrial applications.

[0005] Given the shortcomings of existing recycling methods for waste lithium iron phosphate cathode materials, there is an urgent need to develop a regeneration process that can repair material defects and compensate for composition while preserving the original crystal structure as much as possible. Summary of the Invention

[0006] To address the aforementioned technical deficiencies, this invention provides a method for repairing waste lithium iron phosphate cathode materials and its application in lithium-ion batteries. The repair method for waste lithium iron phosphate cathode materials provided by this invention features a simple process flow, enabling lithium replenishment and structural repair to be completed under all-aqueous conditions without the need for high-temperature annealing. Compared to traditional wet and pyrometallurgical recycling processes, it significantly reduces energy consumption and production costs, resulting in good economic and environmental benefits. This invention uses cysteine ​​as a reducing agent to effectively regulate the valence state of iron ions and restore the crystal structure in waste lithium iron phosphate under hydrothermal conditions, avoiding the extensive use of strong reducing agents and organic solvents. This is beneficial for improving the electrochemical performance of regenerated lithium iron phosphate materials. The method is highly safe and suitable for widespread application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for repairing waste lithium iron phosphate cathode materials, comprising the following steps:

[0009] Waste lithium iron phosphate cathode material, lithium source and reducing agent are added to water to carry out hydrothermal reaction to obtain repaired lithium iron phosphate cathode material;

[0010] The reducing agent is cysteine;

[0011] The mass ratio of the waste lithium iron phosphate cathode material to the reducing agent is (0.5~2):(0.03~0.1).

[0012] Preferably, the lithium source includes at least one of lithium acetate, lithium hydroxide, and lithium sulfate.

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 160~220 ℃ for a time of 6~12 h.

[0014] Preferably, in the step of adding waste lithium iron phosphate cathode material, lithium source and reducing agent to water, the mass ratio of waste lithium iron phosphate cathode material, lithium source, reducing agent and water is (0.5~2):(0.1~0.6):(0.03~0.1):(15~60).

[0015] Preferably, the positive electrode sheet of the waste lithium iron phosphate battery is discharged to obtain the positive electrode material; the positive electrode material is then peeled off and cleaned to obtain the waste lithium iron phosphate positive electrode material.

[0016] Preferably, the positive electrode of the waste lithium iron phosphate battery is placed in a sodium chloride aqueous solution for discharge treatment;

[0017] The sodium chloride aqueous solution has a mass fraction of 2-10%, a discharge temperature of 20-30℃, and a discharge time of 24-48h.

[0018] Preferably, the cathode material is subjected to ultrasonic stripping in N,N-dimethylformamide, and then the obtained cathode active material is ultrasonically cleaned with deionized water and ethanol to obtain waste lithium iron phosphate cathode material.

[0019] Preferably, in the step of ultrasonically exfoliating the positive electrode material in N,N-dimethylformamide, the ultrasonic power is 200~600W, the ultrasonic time is 10~60min, and the ultrasonic temperature is 25~35℃.

[0020] The mass-to-volume ratio of the cathode material to N,N-dimethylformamide is (5~15)g:(25~75)mL.

[0021] Secondly, the present invention also provides the application of the repaired lithium iron phosphate cathode material obtained by the repair method described above in the preparation of lithium-ion batteries.

[0022] Thirdly, the present invention also provides a lithium-ion battery, comprising the repaired lithium iron phosphate cathode material obtained by the repair method described above.

[0023] The method for repairing waste lithium iron phosphate cathode materials and its application in lithium-ion batteries of the present invention have the following advantages compared with the prior art:

[0024] The present invention discloses a method for repairing waste lithium iron phosphate cathode materials. Using cysteine ​​as a reducing agent, it achieves effective control of the valence state of iron ions and repair of the crystal structure in waste lithium iron phosphate under all-aqueous system and mild conditions. It eliminates the need for high-temperature annealing, simplifies the process, reduces energy consumption, and can significantly improve the electrochemical performance of regenerated lithium iron phosphate, showing promising application prospects. Compared with traditional wet and pyrometallurgical recycling processes, the repair method of the present invention can significantly reduce energy consumption and production costs, resulting in good economic and environmental benefits. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced 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.

[0026] Figure 1 This is a comparison chart of the specific capacity of the regenerated lithium iron phosphate cathode materials obtained under different mass cysteine ​​conditions in Examples 1 and 2 after being assembled into button batteries under 0.2C conditions.

[0027] Figure 2XRD comparison of the lithium iron phosphate cathode materials obtained from the repair in Example 1 and Comparative Examples 1-3;

[0028] Figure 3 Comparison charts showing the rate performance of button batteries assembled from the repaired lithium iron phosphate cathode materials obtained in Example 1, Comparative Examples 1-3, and the waste lithium iron phosphate cathode materials obtained in step S2 of Example 1.

[0029] Figure 4 The graph shows a comparison of the 100-cycle charge-discharge performance of button batteries assembled from the repaired lithium iron phosphate cathode materials obtained in Example 1, Comparative Examples 1-3, and the waste lithium iron phosphate cathode materials obtained in step S2 of Example 1. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0032] This application provides a method for repairing waste lithium iron phosphate cathode materials, including the following steps:

[0033] Waste lithium iron phosphate cathode material, lithium source and reducing agent are added to water to carry out hydrothermal reaction to obtain repaired lithium iron phosphate cathode material;

[0034] The reducing agent is cysteine;

[0035] The mass ratio of waste lithium iron phosphate cathode material to reducing agent is (0.5~2):(0.03~0.1).

[0036] The present invention relates to a method for repairing waste lithium iron phosphate cathode materials. Using cysteine ​​(i.e., L-cysteine, molecular formula: C3H7NO2S, CAS number: 52-90-4) as a reducing agent, the method effectively regulates the valence state of iron ions and repairs the crystal structure in waste lithium iron phosphate under all-aqueous system and mild conditions. It eliminates the need for high-temperature annealing, simplifies the process, reduces energy consumption, and can significantly improve the electrochemical performance of regenerated lithium iron phosphate, showing promising application prospects.

[0037] Specifically, cysteine ​​can efficiently repair deactivated lithium iron phosphate cathode materials without destroying the original olivine-type crystal framework structure. In hydrothermal systems, cysteine ​​has good solubility in aqueous solutions, and its molecule contains multiple active functional groups such as thiol (-SH), amino (-NH2), and carboxyl (-COOH), which can construct a synergistic environment during the reaction. On the one hand, the carboxyl group provides mild proton exchange conditions, promoting the Li-Li content in the lithium salt. + The dissolution and migration of cysteine ​​helps compensate for lithium vacancies caused by delithiation in the lattice of waste lithium iron phosphate; on the other hand, the thiol group in cysteine ​​has a strong reducing ability, which can dissolve the Fe generated during the delithiation process. 3+ Effectively reduced to Fe 2+ This process repairs the Fe / Li antisite defects and restores the orderliness of the lithium iron phosphate lattice. Simultaneously, amino functional groups can coordinate or hydrogen bond with the cathode material surface, promoting uniform adsorption and reaction during the repair process and facilitating gradual lattice reconstruction. Under hydrothermal conditions, cysteine ​​can also serve as a source of sulfur and nitrogen, achieving mild doping or inducing the formation of a sulfur- and nitrogen-containing carbonaceous coating layer on the lithium iron phosphate surface. This coating layer improves the electron transport properties of the material surface, enhancing the conductivity and structural stability of the electrode material. Through this invention, the particle size distribution and microstructure of the regenerated lithium iron phosphate cathode material can be effectively controlled, resulting in a more uniform chemical composition, a complete crystal structure, and excellent electrochemical performance.

[0038] Furthermore, when the mass ratio of waste lithium iron phosphate cathode material to reducing agent is (0.5~2):(0.03~0.1), the lithium battery assembled from the repaired lithium iron phosphate cathode material has good performance, with a specific capacity of 134~161 mAh / g.

[0039] In some embodiments, the lithium source includes at least one of lithium acetate, lithium hydroxide, and lithium sulfate, preferably lithium acetate.

[0040] In some embodiments, the hydrothermal reaction temperature is 160~220 °C and the time is 6~12 h; preferably, the hydrothermal reaction temperature is 180~200 °C, more preferably 180 °C; the reaction time is 8~10 h, more preferably 10 h; the lattice structure of waste lithium iron phosphate can be repaired without the introduction of reducing gas or any high-temperature annealing treatment during the reaction.

[0041] In some embodiments, in the step of adding waste lithium iron phosphate cathode material, lithium source and reducing agent to water, the mass ratio of waste lithium iron phosphate cathode material, lithium source, reducing agent and water is (0.5~2):(0.1~0.6):(0.03~0.1):(15~60).

[0042] In some embodiments, the amount of waste lithium iron phosphate cathode material used is 0.5~2 g, preferably 0.5 g; the amount of water used is 15~60 mL, preferably 30 mL; the amount of cysteine ​​used is 0.03~0.1 g, preferably 0.06 g; the amount of lithium acetate used is 0.1~0.6 g, preferably 0.3 g; the lithium source and reducing agent are first added to water and stirred to dissolve, and then the waste lithium iron phosphate cathode active material is added and stirred again to improve the uniformity of lithium replenishment and reduction repair.

[0043] In some embodiments, the positive electrode sheet of a waste lithium iron phosphate battery is discharged to obtain a positive electrode material; the positive electrode material is then peeled off and cleaned to obtain a waste lithium iron phosphate positive electrode material.

[0044] In some embodiments, the positive electrode sheet obtained from dismantling waste lithium iron phosphate batteries is placed in a sodium chloride aqueous solution for discharge treatment until the voltage drops below 0V. After discharge, the aluminum foil is peeled off the positive electrode sheet to obtain waste lithium iron phosphate positive electrode material containing a carbon coating layer and binder. The mass fraction of the sodium chloride aqueous solution is 2% to 10%, preferably 5%; the discharge temperature is 20 to 30 °C, preferably 25 °C; and the discharge time is 24 to 48 h, preferably 24 h, to ensure that the battery is fully discharged and to improve the safety of subsequent processing.

[0045] The positive electrode material is stripped and cleaned, specifically including: placing the positive electrode material in N,N-dimethylformamide for ultrasonic stripping treatment; the mass-to-volume ratio of the positive electrode material to N,N-dimethylformamide is (5~15) g:(25~75) mL, preferably 10 g:50 mL; the ultrasonic power is 200~600 W, preferably 500 W; the ultrasonic time is 10~60 min, preferably 30 min; the stripping process temperature is controlled at 25~35 °C, preferably 35 °C; after stripping, the obtained positive electrode active material is ultrasonically cleaned sequentially with deionized water and ethanol to remove residual binder and organic solvent, dried, and sieved to obtain waste lithium iron phosphate positive electrode material; specifically, the drying temperature is 60~100 °C, preferably 70~80 °C, more preferably 80 °C; the drying time is 8~12 h, preferably 10 h; after drying, it is sieved through a ≥100 mesh screen to obtain waste lithium iron phosphate positive electrode material with uniform particle size;

[0046] In some embodiments, waste lithium iron phosphate cathode material, a lithium source, and a reducing agent are added to water for a hydrothermal reaction. After the thermal reaction is complete, the resulting product is naturally cooled to room temperature, washed, filtered, and dried to obtain the structurally repaired lithium iron phosphate cathode material. This repair process is completed in an aqueous system, with a simple process flow, low energy consumption, and environmental friendliness. Cysteine ​​plays a major role in the reduction and repair process, effectively restoring the Fe content in the material. 2+ / Fe 3+ Valence equilibrium and lattice integrity.

[0047] Based on the same inventive concept, the present invention also provides an application of the repaired lithium iron phosphate cathode material obtained by the above-mentioned repair method in the preparation of lithium-ion batteries.

[0048] Based on the same inventive concept, the present invention also provides a lithium-ion battery, including the repaired lithium iron phosphate cathode material obtained by the above-described repair method.

[0049] The following further illustrates the repair method and application of waste lithium iron phosphate cathode materials and lithium-ion batteries according to specific embodiments. This section further explains the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0050] Example 1

[0051] This embodiment provides a method for repairing waste lithium iron phosphate cathode materials, including the following steps:

[0052] S1. Take the positive electrode sheet obtained from the dismantling of retired lithium iron phosphate batteries, place the positive electrode sheet in a 5% sodium chloride aqueous solution, and discharge it (discharge temperature is 25 °C, discharge time is 24 h) until the voltage drops below 0V. After the discharge is completed, peel off the aluminum foil from the positive electrode sheet to obtain waste lithium iron phosphate positive electrode material containing carbon coating and binder.

[0053] S2. The cathode material from S1 is subjected to ultrasonic stripping in N,N-dimethylformamide. The solid-liquid ratio of waste lithium iron phosphate to N,N-dimethylformamide is 10 g:50 mL. The ultrasonic power is 500 W, the ultrasonic time is 30 min, and the temperature is controlled at 35 °C during the stripping process. After stripping, the obtained solid is ultrasonically cleaned twice each with deionized water and ethanol to remove residual binder and organic solvent. Then, it is vacuum dried at 80 °C for 10 h to constant weight and sieved through a 100-mesh stainless steel sieve. The sieve-underfill material is collected as the cathode active material, thus obtaining the waste lithium iron phosphate cathode material.

[0054] S3. Add 0.5 g of the waste lithium iron phosphate cathode material from step S2, 0.3 g of lithium acetate, and 0.06 g of cysteine ​​to the reactor. Add 30 mL of deionized water to the reactor and stir magnetically for 30 min at room temperature (25°C) to ensure that the lithium source and cysteine ​​are fully dispersed and uniformly contacted with the cathode active material. Then, carry out a hydrothermal reaction at 180 °C for 10 h. After the reaction is completed, allow it to cool naturally to room temperature, centrifuge to separate the obtained solid product, and wash it three times with deionized water. Place the washed solid product in a vacuum drying oven and dry it at 80 °C for 10 h to obtain the lithium iron phosphate cathode material after hydrothermal reduction and lithium replenishment with cysteine.

[0055] Example 2

[0056] The method for repairing waste lithium iron phosphate cathode material provided in this embodiment is the same as that in embodiment 1, except that the amount of cysteine ​​added in step S3 is 0.03g, 0.04g, 0.05g, 0.07g, 0.08g, 0.09g, and 0.1g respectively; the other process parameters are the same as those in embodiment 1.

[0057] Comparative Example 1

[0058] The method for repairing waste lithium iron phosphate cathode material provided in this comparative example is the same as that in Example 1, except that the reducing agent used in step S3 is replaced by an equal amount of serine (0.052 g), while the other process parameters are the same as those in Example 1.

[0059] Comparative Example 2

[0060] The method for repairing waste lithium iron phosphate cathode material provided in this comparative example is the same as that in Example 1, except that the reducing agent used in step S3 is replaced by an equal amount of mercaptoethanol (34.7 μL) instead of cysteine. All other process parameters are the same as those in Example 1.

[0061] Comparative Example 3

[0062] The method for repairing waste lithium iron phosphate cathode material provided in this comparative example is the same as that in Example 1, except that the amount of cysteine ​​added in step S3 is 0g (i.e., no reducing agent is added), and the other process parameters are the same as those in Example 1.

[0063] Performance testing

[0064] The repaired lithium iron phosphate cathode materials obtained from different embodiments or comparative examples were assembled into button batteries, and their performance was tested. NMP was used as a solvent to mix the repaired lithium iron phosphate cathode materials from different embodiments or comparative examples with carbon black and PVDF at a mass ratio of 8:1:1 to obtain a cathode slurry. The cathode slurry was coated onto aluminum foil and dried to obtain a cathode sheet. A lithium metal sheet was used as the anode. A PP separator was used. The electrolyte was prepared using 1 mol / L LiPF6 (EC:EMC = 3:7, volume ratio, i.e., ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 3:7 were used as solvents, and lithium hexafluorophosphate (LiPF6) was used as the solute). The cathode sheet, anode, separator, and electrolyte were assembled into a button battery.

[0065] The test voltage range was 2.5V~4.2V. After 10 cycles of activation at 0.2C, the charge / discharge capacity and cycle performance of button batteries assembled from the repaired lithium iron phosphate cathode materials of Examples 1 and Comparative Examples 1-3 were tested at a current density of 1C. The rate performance of the assembled button batteries was tested at current densities of 0.2C, 0.5C, 1C, 2C, and 5C. The performance test results are shown in Table 1. Figures 3-4 As shown.

[0066] Table 1 - Performance of different button cells

[0067]

[0068] Table 1 shows that the electrochemical performance of regenerated lithium iron phosphate cathode materials obtained through hydrothermal remediation under different reducing agent conditions varies significantly. The cysteine ​​system exhibits the best remediation effect, followed by mercaptoethanol and serine, while the system without a reducing agent shows the worst performance. This is because cysteine ​​possesses strong reducing power and multi-functional group synergistic effects under hydrothermal conditions, which is beneficial for promoting Fe... 3+ To Fe 2+Transformation and repair of lattice defects; mercaptoethanol has reducing properties, but has few sites of action and limited repair effect; serine has weak reducing ability and can only play an auxiliary repair role; and without reducing agents, it is difficult to effectively repair structural defects in retired lithium iron phosphate, resulting in poor electrochemical performance.

[0069] The specific capacity comparison charts of the regenerated lithium iron phosphate cathode materials obtained under different mass cysteine ​​conditions in Examples 1 and 2 after being assembled into button batteries are shown below. Figure 1 As shown, Figure 1 The horizontal axis represents the amount of cysteine ​​added.

[0070] from Figure 1 As can be seen, when the amount of cysteine ​​added is 0.06g, the specific capacity of the button battery assembled from the repaired lithium iron phosphate cathode material reaches the maximum value of 161mAh / g under 0.2C conditions.

[0071] Figure 2 XRD comparison of the lithium iron phosphate cathode materials obtained from the repair in Example 1 and Comparative Examples 1-3; Figure 2 In the example, S-LFP represents the XRD of the waste lithium iron phosphate cathode material obtained in step S2 of Example 1, cysteine ​​represents the XRD of the lithium iron phosphate cathode material repaired in Example 1, serine represents the XRD of the lithium iron phosphate cathode material repaired in Comparative Example 1, mercaptoethanol represents the XRD of the lithium iron phosphate cathode material repaired in Comparative Example 2, and no reducing agent represents the XRD of the lithium iron phosphate cathode material repaired in Comparative Example 3.

[0072] Depend on Figure 2 It can be seen that the main diffraction peaks of the cysteine-repaired lithium iron phosphate material are consistent with those of standard LiFePO4, and no obvious impurity phase peaks were observed, indicating that its crystal structure was effectively restored; the serine, mercaptoethanol, and non-reducing agent systems still contain some Fe 3+ Related impurity phases (LiFe) 3+ The presence of FePO4(OH) indicates that lattice defects and delithiation secondary phases in the material were not fully repaired; S-LFP shows numerous FePO4 impurity phase peaks, reflecting severe lattice damage in the decommissioned material. These results suggest that cysteine ​​provides both thiol and amino functional groups, effectively reducing Fe... 3+ It also forms a uniform carbon / nitrogen doped coating layer, thereby achieving high-fidelity repair of the lithium iron phosphate lattice.

[0073] Figure 3 The graph shows a comparison of the rate performance of button batteries assembled from the repaired lithium iron phosphate cathode materials obtained in Example 1, Comparative Examples 1-3, and the waste lithium iron phosphate cathode materials obtained in step S2 of Example 1; wherein, Figure 3S-LFP represents the rate performance of a button battery assembled from the waste lithium iron phosphate cathode material obtained in step S2 of Example 1 (the assembly method is the same as above, except that the repaired lithium iron phosphate cathode material is replaced with the waste lithium iron phosphate cathode material obtained in step S2 of Example 1).

[0074] Cys (cysteine) represents the rate performance of the coin cell assembled from the lithium iron phosphate cathode material repaired in Example 1.

[0075] Ser (serine) represents the rate performance of the button battery assembled from the lithium iron phosphate cathode material repaired in Comparative Example 1; β-ME (mercaptoethanol) represents the rate performance of the button battery assembled from the lithium iron phosphate cathode material repaired in Comparative Example 2; Blank (no reducing agent) represents the rate performance of the button battery assembled from the lithium iron phosphate cathode material repaired in Comparative Example 3.

[0076] Depend on Figure 3 It can be seen that cysteine-repaired lithium iron phosphate exhibits the highest specific capacity and the smallest capacity decrease at all rates, demonstrating excellent rate performance. Serine and mercaptoethanol-repaired materials show improved capacity at low and medium rates, but their specific capacity at high rates is significantly lower than that of the cysteine ​​system, indicating a lack of synergistic repair effect. The sample without reducing agent exhibits the worst rate performance, with the S-LFP material showing the lowest capacity and a significant decrease with increasing rate. These results suggest that the thiol-based reducing effect provided by cysteine, combined with amino-assisted surface coating, synergistically promotes electron / ion transport and improves electrochemical performance at high rates.

[0077] Figure 4 The graph shows a comparison of the 100-cycle charge-discharge performance of button batteries assembled from the repaired lithium iron phosphate cathode materials obtained in Example 1, Comparative Examples 1-3, and the waste lithium iron phosphate cathode materials obtained in step S2 of Example 1; among them, Figure 4 "Waste lithium iron phosphate" represents the cycle performance of a button battery assembled from the waste lithium iron phosphate cathode material obtained in step S2 of Example 1 (the assembly method is the same as above, only the repaired lithium iron phosphate cathode material is replaced with the waste lithium iron phosphate cathode material obtained in step S2 of Example 1); "cysteine" represents the cycle performance of a button battery assembled from the repaired lithium iron phosphate cathode material obtained in Example 1; "serine" represents the cycle performance of a button battery assembled from the repaired lithium iron phosphate cathode material obtained in Comparative Example 1; "mercaptoethanol" represents the cycle performance of a button battery assembled from the repaired lithium iron phosphate cathode material obtained in Comparative Example 2; and "no reducing agent" represents the cycle performance of a button battery assembled from the repaired lithium iron phosphate cathode material obtained in Comparative Example 3.

[0078] Depend on Figure 4The results show that cysteine-repaired lithium iron phosphate maintained a high specific capacity and exhibited the smallest capacity decay after 100 cycles, demonstrating good cycling stability. The serine, mercaptoethanol, and no-reducing-agent systems showed significant capacity decay, with the no-reducing-agent group showing the fastest decline. Waste lithium iron phosphate materials exhibited the worst cycling performance and the largest capacity decay. These results indicate that the cysteine ​​system can effectively repair lattice defects and form a stable surface coating, thereby inhibiting structural degradation during electrochemical cycling and significantly improving the cycling stability of the material.

[0079] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0080] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for repairing waste lithium iron phosphate cathode materials, characterized in that, Includes the following steps: Waste lithium iron phosphate cathode material, lithium source and reducing agent are added to water to carry out hydrothermal reaction to obtain repaired lithium iron phosphate cathode material; The reducing agent is cysteine; The mass ratio of the waste lithium iron phosphate cathode material to the reducing agent is (0.5~2):(0.03~0.1).

2. The method for repairing waste lithium iron phosphate cathode materials as described in claim 1, characterized in that, The lithium source includes at least one of lithium acetate, lithium hydroxide, and lithium sulfate.

3. The method for repairing waste lithium iron phosphate cathode materials as described in claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 160~220 ℃ for a time of 6~12 h.

4. The method for repairing waste lithium iron phosphate cathode materials as described in claim 1, characterized in that, In the step of adding waste lithium iron phosphate cathode material, lithium source and reducing agent to water, the mass ratio of waste lithium iron phosphate cathode material, lithium source, reducing agent and water is (0.5~2):(0.1~0.6):(0.03~0.1):(15~60).

5. The method for repairing waste lithium iron phosphate cathode materials as described in claim 1, characterized in that, The cathode sheet of the waste lithium iron phosphate battery is discharged to obtain the cathode material; the cathode material is then peeled off and cleaned to obtain the waste lithium iron phosphate cathode material.

6. The method for repairing waste lithium iron phosphate cathode materials as described in claim 5, characterized in that, The positive electrode of the waste lithium iron phosphate battery is placed in a sodium chloride aqueous solution for discharge treatment; The sodium chloride aqueous solution has a mass fraction of 2-10%, a discharge temperature of 20-30℃, and a discharge time of 24-48h.

7. The method for repairing waste lithium iron phosphate cathode materials as described in claim 5, characterized in that, The cathode material was subjected to ultrasonic stripping in N,N-dimethylformamide, and then ultrasonically cleaned with deionized water and ethanol to obtain waste lithium iron phosphate cathode material.

8. The method for repairing waste lithium iron phosphate cathode materials as described in claim 5, characterized in that, In the step of ultrasonically exfoliating the positive electrode material in N,N-dimethylformamide, the ultrasonic power is 200~600W, the ultrasonic time is 10~60min, and the ultrasonic temperature is 25~35℃. The mass-to-volume ratio of the cathode material to N,N-dimethylformamide is (5~15)g:(25~75)mL.

9. The application of the repaired lithium iron phosphate cathode material obtained by the repair method according to any one of claims 1 to 8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, characterized in that, This includes the repaired lithium iron phosphate cathode material obtained by the repair method as described in any one of claims 1 to 8.

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