Method for regenerating waste LiFePO4 through synchronous reduction-doping-carbon coating, positive plate and battery

Abstract

The invention discloses a method for regenerating waste LiFePO4 through synchronous reduction-doping-carbon coating, a positive plate and a battery, and relates to the technical field of battery materials. The method comprises the following steps: S1, discharging and disassembling the waste lithium iron phosphate battery, separating out a positive electrode material, and drying, ball-milling and sintering to obtain waste LiFePO4 powder; s2, carrying out ball-milling mixing on the waste LiFePO4 powder, a lithium source and an organic aluminum hypophosphite salt compound to prepare a mixed material; and S3, sintering the mixed material in an inert atmosphere, and cooling to obtain the regenerated waste LiFePO4 positive electrode material. According to the method provided by the invention, the problems of complex process, uneven element supplement, poor material conductivity and poor electrochemical performance recovery of the existing regeneration technology can be solved, synergistic proceeding of Fe < 3 + > reduction, Al < 3 + > lattice doping, phosphorus element supplement and surface carbon coating is realized, and the comprehensive performance of the regenerated material is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for the simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4, a cathode sheet, and the field of battery technology. Background Technology

[0002] With the rapid development of the new energy vehicle industry, a large number of lithium iron phosphate (LiFePO4) power batteries are entering their large-scale retirement period. Faced with enormous environmental and resource pressures, efficient recycling of spent LiFePO4 cathode materials has become an urgent industry need. Currently, mainstream recycling methods such as hydrometallurgy (using reagents such as acids, alkalis, and oxidants to selectively leach valuable elements) can separate and recover elements such as lithium, iron, and phosphorus, but their processes are lengthy, energy-intensive, and costly in wastewater treatment. Furthermore, the final products are basic chemical raw materials such as lithium carbonate and iron phosphate, which require complex resynthesis processes before they can be reused in battery manufacturing. Therefore, both economic efficiency and atom utilization efficiency need improvement. In contrast, direct regeneration methods can directly restore the electrochemical performance of damaged materials by repairing their structure, offering advantages such as shorter processes, lower costs, and less pollution, making it a more promising recycling strategy. However, existing direct regeneration technologies generally focus on replenishing lithium lost during the cycle, neglecting the simultaneous loss of phosphorus, leading to an imbalance in the stoichiometry of the recycled materials. Simultaneously, the presence of Fe in the materials after long-term cycling... 3+ Problems such as the degradation of the insulating phase and carbon coating layer, as well as the decrease in conductivity, have not been addressed in a coordinated manner, which seriously restricts the performance recovery effect and practical application potential of recycled materials. Summary of the Invention

[0003] In view of this, the present invention provides a method for the simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4, a positive electrode sheet, and a battery, aiming to solve the problems of complex process flow, uneven element replenishment, low intrinsic conductivity of materials, and limited regeneration effect in the prior art.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a method for the simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4, comprising the following steps: S1. Discharge and disassemble the waste lithium iron phosphate battery to separate the positive electrode material, and obtain waste LiFePO4 powder after drying, ball milling and sintering. S2. The waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound are ball-milled and mixed to obtain a mixture. S3. The mixture is sintered under an inert atmosphere and cooled to obtain the cathode material of recycled waste LiFePO4.

[0005] This invention, by employing the above-described technical solution, solves the problems of complex processes, uneven element replenishment, poor material conductivity, and unsatisfactory electrochemical performance recovery in existing regeneration technologies, thereby achieving Fe... 3+ Reduction, Al 3+ The synergistic effect of lattice doping, phosphorus supplementation, and surface carbon coating significantly improves the overall performance of recycled materials. The reaction mechanism lies in the fact that during the thermal decomposition of the organic aluminum hypophosphite compound, a reducing phosphorus-based intermediate is released. This intermediate acts as a reducing agent, reducing Fe... 3+ Efficient reduction to electrochemically active Fe 2+ This invention eliminates the adverse effects of insulating materials like FePO4 on material performance. The reason is that after long-term cycling, an irreversible phase transition occurs, where lithium ions escape from the LiFePO4 lattice, causing the crystal structure to transform into a lithium-deficient FePO4 phase. The FePO4 phase has extremely low electronic conductivity and lithium-ion diffusion capacity, severely hindering charge transport and leading to capacity decay. The strong reducing atmosphere generated by the decomposition of the organic aluminum hypophosphite in this invention can reduce this electrochemically inert FePO4 phase and, combined with a lithium source, transform it into an electrochemically active LiFePO4 phase, thereby repairing the material structure and restoring its capacity. Simultaneously, the Al produced by the decomposition of this organic aluminum hypophosphite compound... 3+ Ion doping into the LiFePO4 lattice broadens the lithium-ion migration channels, improving intrinsic electronic conductivity and structural stability. At the same time, the decomposition of this compound can replenish phosphorus lost due to long-term cycling and repair crystal structure defects. In addition, its incomplete carbonization forms a uniform nano-carbon coating layer on the particle surface, enhancing interfacial electronic conduction and suppressing electrolyte side reactions.

[0006] In some embodiments of the present invention, the organoaluminum hypophosphite compound in step S2 includes at least one of methylaluminum hypophosphite, aluminum-hypophosphoamino acid complex, diethylaluminum hypophosphite, and aluminum-diphenylphosphine. By employing the above-described technical solution, the present invention enables these specific types of organoaluminum hypophosphite compounds to simultaneously function as a reducing agent, dopant source, phosphorus supplement, and carbon source during heat treatment, achieving a synergistic effect that simplifies the process and reduces costs.

[0007] In some embodiments of the present invention, the atomic ratio of Li:Fe:P in the mixture during step S2 is (1.05-1.10):1:1. Based on the above-mentioned suitable atomic ratio range, the recycled material forms a complete olivine structure and sufficient lithium insertion / extraction sites, thus restoring the theoretical capacity and electrochemical performance of the material.

[0008] In some embodiments of the present invention, the ball milling in step S1 includes the following parameters: anhydrous ethanol as the dispersant, a ball-to-material ratio of 10:1-20:1, a ball milling speed of 300-600 r / min, and a ball milling time of 2-4 hours. Based on the above ball milling parameter range, the present invention achieves thorough refinement and uniform mixing of the raw materials, providing a foundation for subsequent uniform sintering reaction and structural reconstruction.

[0009] In some embodiments of the present invention, the sintering temperature in step S1 is 450-600℃, and the time is 2-4 hours. Based on the above-mentioned pretreatment sintering temperature and time range, the present invention effectively removes residual binder and conductive carbon, purifies the material surface, and achieves preliminary repair of the crystal structure, which is beneficial to the subsequent main regeneration process.

[0010] In some embodiments of the present invention, the inert atmosphere in step S3 includes one of argon, nitrogen, or helium. By employing the above-mentioned types of inert atmospheres, the present invention avoids oxidation of the material during high-temperature sintering, and ensures the smooth progress of reduction, doping, and carbon coating reactions.

[0011] In some embodiments of the present invention, the sintering temperature in step S3 is 700-900℃, and the sintering time is 7-11 hours. Based on the above-mentioned high-temperature sintering parameters, the present invention ensures that the reduction, doping, lattice repair, and carbon layer formation processes are fully completed, ultimately yielding a high-performance regenerated cathode material.

[0012] In some embodiments of the present invention, in step S3, the temperature is increased to the sintering temperature at a heating rate of 5-10°C / min. Based on the above heating rate range, the reactants are heated uniformly, avoiding localized overheating or incomplete reaction, thus ensuring the consistency and quality stability of the product.

[0013] Secondly, this invention provides a regenerated LiFePO4 cathode material, prepared by any of the methods described in the first aspect. By employing the above-mentioned technical solutions, this invention obtains a cathode material with accurate elemental stoichiometry, a complete crystal structure, and high electronic and ionic conductivity, effectively improving the electrochemical performance and cycle stability of the regenerated material.

[0014] Thirdly, this invention provides a lithium-ion battery cathode material comprising the recycled LiFePO4 cathode material described in the second aspect. By employing the above technical solution, this invention enables the cathode material to form a good conductive network while maintaining structural stability, thereby improving the battery's capacity and cycle life.

[0015] Fourthly, this invention provides a lithium-ion battery comprising the lithium-ion battery positive electrode sheet of the third aspect. By employing the above-described technical solution, this invention enables the battery to exhibit high energy density, excellent cycle performance, and safety, achieving high-value recycling of spent lithium iron phosphate batteries. Attached Figure Description

[0016] 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 the structures shown in these drawings without creative effort.

[0017] Figure 1 The image shows a scanning electron microscope (SEM) image of the regenerated lithium iron phosphate material prepared in Example 1 of this invention. Figure 2 The image shows a scanning electron microscope (SEM) image of the regenerated lithium iron phosphate material prepared in Example 2 of this invention. Figure 3 The first charge-discharge curve of the recycled lithium iron phosphate material prepared in Example 1 at a rate of 0.1C is shown. Figure 4 The first charge-discharge curve of the recycled lithium iron phosphate material prepared in Example 2 at a rate of 0.1C is shown. Figure 5 The graph shows the long-cycle performance of the recycled lithium iron phosphate material prepared in Example 2 at 1C rate. Figure 6 The graph shows the long-cycle performance of the regenerated lithium iron phosphate material prepared in Example 2 at a high rate of 10C.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. 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.

[0020] With the rapid development of the new energy vehicle industry, a large number of lithium iron phosphate (LiFePO4) power batteries are entering their large-scale retirement period. Faced with enormous environmental and resource pressures, efficient recycling of spent LiFePO4 cathode materials has become an urgent industry need. Currently, mainstream recycling methods such as hydrometallurgy (using reagents such as acids, alkalis, and oxidants to selectively leach valuable elements) can separate and recover elements such as lithium, iron, and phosphorus, but their processes are lengthy, energy-intensive, and costly in wastewater treatment. Furthermore, the final products are basic chemical raw materials such as lithium carbonate and iron phosphate, which require complex resynthesis processes before they can be reused in battery manufacturing. Therefore, both economic efficiency and atom utilization efficiency need improvement. In contrast, direct regeneration methods can directly restore the electrochemical performance of damaged materials by repairing their structure, offering advantages such as shorter processes, lower costs, and less pollution, making it a more promising recycling strategy. However, existing direct regeneration technologies generally focus on replenishing lithium lost during the cycle, neglecting the simultaneous loss of phosphorus, leading to an imbalance in the stoichiometry of the recycled materials. Simultaneously, the presence of Fe in the materials after long-term cycling... 3+ Problems such as the degradation of the insulating phase and carbon coating layer, as well as the decrease in conductivity, have not been addressed in a coordinated manner, which seriously restricts the performance recovery effect and practical application potential of recycled materials.

[0021] In view of this, the present invention provides a method for the simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4, a positive electrode sheet, and a battery, aiming to solve the problems of complex process flow, uneven element replenishment, low intrinsic conductivity of materials, and limited regeneration effect in the prior art.

[0022] To achieve the above objectives, in a first aspect, the present invention provides a method for the simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4, comprising the following steps: S1. Discharge and disassemble the waste lithium iron phosphate battery to separate the positive electrode material, and obtain waste LiFePO4 powder after drying, ball milling and sintering. S2. The waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound are ball-milled and mixed to obtain a mixture. S3. The mixture is sintered under an inert atmosphere and cooled to obtain the cathode material of recycled waste LiFePO4.

[0023] This invention, by employing the above-described technical solution, solves the problems of complex processes, uneven element replenishment, poor material conductivity, and unsatisfactory electrochemical performance recovery in existing regeneration technologies, thereby achieving Fe... 3+ Reduction, Al 3+ The synergistic effect of lattice doping, phosphorus supplementation, and surface carbon coating significantly improves the overall performance of recycled materials. The reaction mechanism lies in the fact that during the thermal decomposition of the organic aluminum hypophosphite compound, a reducing phosphorus-based intermediate is released. This intermediate acts as a reducing agent, reducing Fe...3+ Efficient reduction to electrochemically active Fe 2+ This eliminates the adverse effects of FePO4 and other insulating materials on the material's properties; on the other hand, the Al produced by decomposition... 3+ Ion doping into the LiFePO4 lattice broadens the lithium-ion migration channels, improving intrinsic electronic conductivity and structural stability. At the same time, the decomposition of this compound can replenish phosphorus lost due to long-term cycling and repair crystal structure defects. In addition, its incomplete carbonization forms a uniform nano-carbon coating layer on the particle surface, enhancing interfacial electronic conduction and suppressing electrolyte side reactions.

[0024] In some embodiments of the present invention, the organoaluminum hypophosphite compound in step S2 includes at least one of methylaluminum hypophosphite, aluminum-hypophosphoamino acid complex, diethylaluminum hypophosphite, and aluminum-diphenylphosphine. By employing the above-described technical solution, the present invention enables these specific types of organoaluminum hypophosphite compounds to simultaneously function as a reducing agent, dopant source, phosphorus supplement, and carbon source during heat treatment, achieving a synergistic effect that simplifies the process and reduces costs.

[0025] In some embodiments of the present invention, the atomic ratio of Li:Fe:P in the mixture in step S2 is (1.05-1.10):1:1. As an example, the amount of lithium source added can be 105%, 108%, 110% of the stoichiometric ratio, or within a range consisting of any two of the above values. Based on the above-mentioned suitable atomic ratio range, the present invention enables the recycled material to form a complete olivine structure and sufficient lithium insertion / extraction sites, thus restoring the material's theoretical capacity and electrochemical performance.

[0026] In some embodiments of the present invention, the ball milling in step S1 includes the following parameters: anhydrous ethanol as the dispersant, a ball-to-material ratio of 10:1-20:1, a ball milling speed of 300-600 r / min, and a ball milling time of 2-4 hours. As examples, the ball-to-material ratio can be 10:1, 15:1, 20:1, etc., the ball milling speed can be 300 r / min, 450 r / min, 600 r / min, etc., and the ball milling time can be 2 hours, 3 hours, 4 hours, etc., or within the range of any two of the above values. Based on the above ball milling parameter range, the present invention achieves sufficient refinement and uniform mixing of the raw materials, providing a foundation for subsequent uniform sintering reaction and structural reconstruction.

[0027] In some embodiments of the present invention, the sintering temperature in step S1 is 450-600℃, and the time is 2-4 hours. As examples, the sintering temperature can be 450℃, 525℃, 600℃, etc., and the time can be 2 hours, 3 hours, 4 hours, etc., or within the range of any two of the above values. Based on the above pretreatment sintering temperature and time range, the present invention effectively removes residual binder and conductive carbon, purifies the material surface, and initially repairs the crystal structure, which is beneficial for the subsequent main regeneration process.

[0028] In some embodiments of the present invention, the inert atmosphere in step S3 includes one of argon, nitrogen, or helium. By employing the above-mentioned types of inert atmospheres, the present invention avoids oxidation of the material during high-temperature sintering, and ensures the smooth progress of reduction, doping, and carbon coating reactions.

[0029] In some embodiments of the present invention, the sintering temperature in step S3 is 700-900℃, and the sintering time is 7-11 hours. As examples, the sintering temperature can be 700℃, 800℃, 900℃, etc., and the time can be 7 hours, 9 hours, 11 hours, etc., or within the range of any two of the above values. Based on the above high-temperature sintering parameters, the present invention ensures that the reduction, doping, lattice repair, and carbon layer formation processes are fully completed, ultimately obtaining a high-performance regenerated cathode material.

[0030] In some embodiments of the present invention, in step S3, the temperature is increased to the sintering temperature at a heating rate of 5-10°C / min. As an example, the heating rate can be 5°C / min, 7.5°C / min, 10°C / min, or within a range consisting of any two of the above values. Based on the above heating rate range, the present invention ensures uniform heating of the reactants, avoids localized overheating or incomplete reaction, and guarantees the consistency and quality stability of the product.

[0031] Secondly, this invention provides a regenerated LiFePO4 cathode material, prepared by any one of the methods described in the first aspect. By employing the above technical solutions, this invention obtains a cathode material with accurate elemental stoichiometry, a complete crystal structure, and high electronic and ionic conductivity, effectively improving the electrochemical performance and cycle stability of the regenerated material.

[0032] Thirdly, this invention provides a lithium-ion battery cathode material comprising the recycled LiFePO4 cathode material described in the second aspect. By employing the above technical solution, this invention enables the cathode material to form a good conductive network while maintaining structural stability, thereby improving the battery's capacity and cycle life.

[0033] Fourthly, this invention provides a lithium-ion battery comprising the lithium-ion battery positive electrode sheet of the third aspect. By employing the above-described technical solution, this invention enables the battery to exhibit high energy density, excellent cycle performance, and safety, achieving high-value recycling of spent lithium iron phosphate batteries.

[0034] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0035] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0036] The following are specific embodiments of this application: Example 1: Preparation of regenerated lithium iron phosphate (LiFePO4) cathode material; (S1) Pretreatment of waste LFP cathode materials: (S1.1) The waste lithium iron phosphate soft-pack battery is fully discharged and disassembled in an argon glove box with H2O<0.01ppm and O2<0.01ppm to obtain the positive electrode sheet.

[0037] (S1.2) Soak the positive electrode in deionized water at 25°C for 1.5 minutes to separate the positive electrode material from the aluminum foil.

[0038] (S1.3) The separated positive electrode material was dried in a vacuum drying oven at 90℃ for 12 hours. Then, the dried material was placed in a planetary ball mill, and zirconium oxide grinding balls were added at a ball-to-material ratio of 15:1 using anhydrous ethanol as a dispersant. The milling was carried out at 450 r / min for 3 hours. After milling, the slurry was dried at 90℃ to obtain pretreated waste LiFePO4 powder.

[0039] (S2) Ingredient formulation and mixing: (S2.1) Elemental analysis of the pretreated waste LiFePO4 powder was performed using ICP-OES. Based on the analysis results, lithium carbonate (Li2CO3) and reducing agent aluminum methylphosphite (C2H9AlO8P2) were calculated and added to make the atomic ratio of Li:Fe:P in the mixture 1.05:1:1. The mixture was placed in a planetary ball mill, and anhydrous ethanol was used as the dispersant. Zirconia grinding balls were added at a ball-to-material ratio of 20:1, and the mixture was ball-milled at 400 r / min for 8 hours to ensure uniform mixing.

[0040] (S3), Sintering Regeneration: (S3.1) The ball-milled mixture was passed through a 300-mesh sieve to separate the grinding balls, and then dried in a vacuum drying oven at 70°C for 12 hours. The completely dried mixed powder was compacted in an alumina ceramic boat and then transferred to a tube furnace. High-purity argon was introduced into the furnace as a protective atmosphere, and the temperature was raised to 800°C at a heating rate of 7.5°C / min, and sintered at this temperature for 7 hours. After sintering, the sample was cooled to room temperature with the furnace, maintaining an argon atmosphere throughout the process. (S3.2) The sintered block material was ground using an agate mortar and passed through a 300-mesh sieve to finally obtain the regenerated lithium iron phosphate (LiFePO4) cathode material, denoted as sample LFP-800℃-7h.

[0041] Example 2 This embodiment provides a method for preparing regenerated lithium iron phosphate (LiFePO4) cathode material, specifically including the following steps: (S1) Pretreatment of waste LFP cathode materials: (S1.1) The waste lithium iron phosphate soft-pack battery is fully discharged and disassembled in an argon glove box with H2O<0.01ppm and O2<0.01ppm to obtain the positive electrode sheet.

[0042] (S1.2) Soak the positive electrode in deionized water at 25°C for 1.5 minutes to separate the positive electrode material from the aluminum foil.

[0043] (S1.3) The separated positive electrode material was dried in a vacuum drying oven at 90℃ for 12 hours. Then, the dried material was placed in a planetary ball mill, and zirconium oxide grinding balls were added at a ball-to-material ratio of 15:1 using anhydrous ethanol as a dispersant. The milling was carried out at 450 r / min for 3 hours. After milling, the slurry was dried at 90℃ to obtain pretreated waste LiFePO4 powder.

[0044] (S2) Ingredient formulation and mixing: (S2.1) Elemental analysis of the pretreated powder was performed using ICP-OES. Based on the analysis results, lithium carbonate (Li2CO3) and reducing agent aluminum diethylphosphite (C6H2CO3) were calculated and supplemented. 18 AlO6P3), so that the atomic ratio of Li:Fe:P in the mixture is 1.05:1:1.

[0045] (S2.2) Place the mixture in a planetary ball mill, use anhydrous ethanol as a dispersant, add zirconia grinding balls at a ball-to-material ratio of 20:1, and ball mill at a speed of 450 r / min for 12 hours to ensure uniform mixing.

[0046] (S3) Sintering Regeneration: (S3.1) The ball-milled mixture was passed through a 300-mesh sieve to separate the grinding balls, and then dried in a vacuum drying oven at 70°C for 12 hours. The completely dried mixed powder was compacted in an alumina ceramic boat and then transferred to a tube furnace. High-purity argon was introduced into the furnace as a protective atmosphere, and the temperature was raised to 850°C at a heating rate of 7.5°C / min, and sintered at this temperature for 7 hours. After sintering, the sample was cooled to room temperature with the furnace, maintaining an argon atmosphere throughout the process.

[0047] (S3.2) The sintered block material was ground using an agate mortar and passed through a 300-mesh sieve to finally obtain the regenerated lithium iron phosphate (LiFePO4) cathode material, denoted as sample LFP-850℃-7h.

[0048] Example 3 The difference between this embodiment and Embodiment 2 is that, in this embodiment, the atomic ratio of Li:Fe:P in the mixture during step (S2.1) of preparing the regenerated lithium iron phosphate (LiFePO4) cathode material is 1.08:1:1. The rest remains the same as in Embodiment 2.

[0049] Example 4 The difference between this embodiment and Embodiment 2 is that, in this embodiment, the atomic ratio of Li:Fe:P in the mixture during step (S2.1) of the preparation of the regenerated lithium iron phosphate (LiFePO4) cathode material is 1.10:1:1. The rest remains the same as in Embodiment 2.

[0050] Comparative Example 1 The difference between this comparative example and Example 1 is that the waste LiFePO4 powder that was pretreated in Example 1 but was not supplemented or regenerated and sintered (step S1.3) is taken and denoted as sample D-LFP1.

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (S2.1), only lithium carbonate (Li2CO3) is added as a lithium source (the amount of Li2CO3 added is consistent with the amount of Li2CO3 added in step (S2.1)), without adding any organic aluminum hypophosphite compound, and then regenerated and sintered. The resulting sample is denoted as D-LFP2.

[0052] Experimental testing: Electrochemical performance tests were performed on the recycled materials prepared in Examples 1 to 4 of the present invention and on samples D-LFP1 and D-LFP2 of Comparative Examples 1 to 2.

[0053] The test method is as follows: The active material, conductive agent Super P and binder PVDF are mixed in a mass ratio of 8:1:1 to form a slurry, which is then uniformly coated on an aluminum foil current collector. After drying, rolling and stamping, the positive electrode sheet is formed.

[0054] A CR2032 coin cell was assembled in an argon glove box (H2O<0.01ppm, O2<0.01ppm) using a lithium metal sheet as the counter electrode, a polypropylene membrane as the separator, and lithium hexafluorophosphate as the electrolyte.

[0055] Test method: (1) First charge-discharge performance (0.1C rate): After the battery is assembled, it is left to stand for 12 hours, and then subjected to a constant current of 0.1C (e.g., LFP theoretical capacity 150mAh g). -1 Charge to 4V, then switch to constant voltage charging with a current <0.05C. After charging is complete, let it rest for 2 minutes, then discharge at a constant current of 0.1C to 2V.

[0056] (2) Long cycle performance (1C rate): After the first activation cycle is completed, let it rest for 10 minutes, and then run it at a constant current of 1C (e.g., LFP theoretical capacity 150mAh g). -1 Charge to 4V, then switch to constant voltage charging with a current <0.05C. After charging is complete, let it rest for 2 minutes, then discharge at a constant current of 1C to 2V.

[0057] (3) High rate performance (10C rate): After the first round of activation, let it stand for 10 minutes, then apply a constant current of 10C (e.g., LFP theoretical capacity 150mAh g). -1 Charge to 4V, then switch to constant voltage charging with a current <0.05C. After charging is complete, let it rest for 10 minutes, then discharge at a constant current of 10C to 2V.

[0058] The results of this experiment are shown in Table 1.

[0059] Table 1

[0060] Results analysis: (1) Characterization of material morphology and structure: such as Figure 1 (LFP-800℃-7h) and Figure 2 As shown in the (LFP-850℃-7h) scanning electron microscope (SEM) image, the regenerated material exhibits a regular particle morphology with a uniform thin carbon layer (approximately 3-5 nm) covering the surface, effectively suppressing particle pulverization and electrolyte side reactions during cycling. XRD patterns show that the diffraction peaks of the regenerated material perfectly match the PDF card of standard LiFePO4, and no FePO4 or other impurity phases were detected.

[0061] (2) First-cycle charge / discharge performance (0.1C rate): such as Figure 3and Figure 4 As shown, the regenerated LFP samples all exhibited flat charge-discharge plateaus, indicating that the FePO4 insulating phase was successfully reduced and normal electrochemical behavior was restored. Among them, the LFP sample at -850℃ for 7 hours showed the highest initial discharge specific capacity, exceeding 155 mAh / g (see appendix for details). Figure 4 The 850℃ 7h curve is close to the theoretical capacity, and the coulombic efficiency exceeds 95%.

[0062] (3) Long-cycle performance (1C rate): such as Figure 5 As shown, the LFP-850℃-7h sample, after 500 cycles at 1C, maintained a capacity retention of over 91% (see attached figure for details). Figure 5 The mid-cycle capacity decay curve shows extremely excellent cycling stability. This is due to Al 3+ The doping enhances the intrinsic structural stability, and the uniform carbon coating maintains a good conductive network. The LFP-800℃-7h sample also exhibits good cycling performance, with a capacity retention of approximately 86% after 500 cycles.

[0063] (4) High-rate performance (10C rate): such as Figure 6 As shown, the LFP-850℃-7h sample still releases approximately 100 mAh / g of capacity at a high rate of 10C, and retains over 80% of its capacity after 550 cycles, indicating excellent rate performance and sustained cycling capability. This performance stems from Al 3+ Doping broadens the lithium-ion migration channels, while the surface carbon coating significantly improves the electronic conductivity of the electrode, together ensuring the material's rapid charge and discharge capability under high-rate conditions.

[0064] In summary, the simultaneous reduction-doping-carbon coating synergistic regeneration method provided by this invention can effectively restore and improve the electrochemical performance of waste LiFePO4 cathode materials. Among them, the sample LFP-850℃-7h prepared using the process parameters of sintering at 850℃ for 7 hours (Example 3) exhibits the best overall performance, demonstrating excellent capacity, cycle life, and rate performance.

[0065] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for simultaneously reducing, doping, and carbon-coating waste LiFePO4, characterized in that, The method includes the following steps: S1. Discharge and disassemble the waste lithium iron phosphate battery to separate the positive electrode material, and obtain waste LiFePO4 powder after drying, ball milling and sintering. S2. The waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound are ball-milled and mixed to obtain a mixture. S3. The mixture is sintered under an inert atmosphere and cooled to obtain the cathode material of the recycled waste LiFePO4.

2. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to claim 1, characterized in that, In step S2, the organoaluminum hypophosphite compound includes at least one of methylaluminum hypophosphite, aluminum-hypophosphoamino acid complex, diethylaluminum hypophosphite, and aluminum-diphenylphosphite; and / or, In step S2, the atomic ratio of Li:Fe:P in the mixture is (1.05-1.10):1:

1.

3. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to any one of claims 1 to 2, characterized in that, In step S1, the ball milling includes the following parameters: anhydrous ethanol as the dispersant, a ball-to-material ratio of 10:1 to 20:1, a ball milling speed of 300 to 600 r / min, and a ball milling time of 2 to 4 hours.

4. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to claim 1, characterized in that, In step S1, the sintering temperature is 450-600℃ and the time is 2-4 hours.

5. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to claim 1, characterized in that, In step S3, the inert atmosphere includes one of argon, nitrogen, or helium.

6. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to claim 1, characterized in that, In step S3, the sintering temperature is 700-900℃ and the sintering time is 7-11 hours.

7. The method for simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 according to claim 6, characterized in that, In step S3, the temperature is increased to the sintering temperature at a heating rate of 5-10℃ / min.

8. A recycled LiFePO4 cathode material, characterized in that, It is prepared by the method of simultaneous reduction-doping-carbon coating regeneration of waste LiFePO4 as described in any one of claims 1 to 7.

9. A positive electrode sheet for a lithium-ion battery, characterized in that, It includes the recycled LiFePO4 cathode material as described in claim 8.

10. A lithium-ion battery, characterized in that, It includes the lithium-ion battery positive electrode sheet as described in claim 9.

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