Method for synchronously reducing-doping-carbon-coating regenerated waste LiFePO4, positive electrode sheet and battery

Abstract

The application discloses a method for synchronously reducing-doping-carbon-coating regenerated waste LiFePO4, 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 a waste lithium iron phosphate battery, separating out a positive material, and obtaining waste LiFePO4 powder after drying, ball milling and sintering; S2, ball milling and mixing the waste LiFePO4 powder, a lithium source and an organic aluminum hypophosphite compound to prepare a mixture; and S3, sintering the mixture in an inert atmosphere, and obtaining the positive material of the regenerated waste LiFePO4 after cooling. The method provided by the application can solve the problems of complex process, uneven element supplement, poor material conductivity and poor recovery of electrochemical performance of the existing regeneration technology, realize the synchronous reduction, Al 3+ doping, lattice doping, phosphorus element supplement and surface carbon coating, and significantly improve the comprehensive performance of the regenerated material. 3+ doping, lattice doping, phosphorus element supplement and surface carbon coating, and significantly improve the comprehensive performance of the regenerated material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a method for synchronously reducing-doping-carbon-coating regenerated waste LiFePO4, a positive plate and a battery technical field. BACKGROUND

[0002] With the rapid development of new energy automobile industry, a large number of lithium iron phosphate (LiFePO4) power batteries are entering the large-scale retirement period. In the face of huge environmental and resource pressure, efficient recycling and utilization of waste lithium iron phosphate positive material has become an urgent need of the industry. At present, the mainstream recycling method such as hydrometallurgy (using acid, alkali, oxidizing agent and other reagents to selectively leach valuable elements) can realize the separation and recovery of lithium, iron, phosphorus and other elements, but its process is long, energy consumption is high, wastewater treatment cost is large, and the final product is lithium carbonate, iron phosphate and other basic chemical raw materials, which need to go through a complex resynthesis process to be used in battery manufacturing again. The economic efficiency and atomic utilization efficiency need to be improved. In comparison, the direct regeneration method can directly restore the electrochemical performance by repairing the damaged material structure, has the advantages of short process, low cost and small pollution, and becomes a more promising recycling strategy. However, the existing direct regeneration technology generally focuses on supplementing the lost lithium element in the cycle process, but ignores the simultaneous loss of phosphorus element, resulting in unbalanced stoichiometric ratio of regenerated material; at the same time, the problems of Fe 3+ insulating phase, carbon coating layer degradation and conductivity decline existing in the long-term cycle of the material are also not solved, which seriously restricts the performance recovery effect and practical application potential of the regenerated material. SUMMARY

[0003] Therefore, the present application provides a method for synchronously reducing-doping-carbon-coating regenerated waste LiFePO4, a positive plate and a battery, aiming at solving the problems of complex process flow, unbalanced element supplement, low intrinsic conductivity of material and limited regeneration effect in the prior art.

[0004] To achieve the above-mentioned purpose, in a first aspect, the present application provides a method for synchronously reducing-doping-carbon-coating regenerated waste LiFePO4, comprising the following steps:

[0005] S1, discharging and disassembling the waste lithium iron phosphate battery, separating out the positive material, and obtaining waste LiFePO4 powder after drying, ball milling and sintering;

[0006] S2, ball milling the waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound to prepare a mixture;

[0007] S3, sintering the mixture under inert atmosphere, and obtaining the positive material of regenerated waste LiFePO4 after cooling.

[0008] The application solves the problems of complex regeneration technology process, uneven element supplement, poor material conductivity and poor electrochemical performance recovery, realizes Fe 3+ reduction, Al 3+ The synergistic effect of lattice doping, phosphorus element supplement and surface carbon coating significantly improves the comprehensive performance of the regenerated material. The reaction mechanism is that: the organic aluminum hypophosphite salt compound releases a phosphorus-based intermediate with reducing property during thermal decomposition. The intermediate acts as a reducing agent to reduce Fe 3+ into electrochemically active Fe 2+ , thereby eliminating the adverse effects of insulating phase materials such as FePO4 on material performance. The reason is that after the battery undergoes long-term cycling, irreversible phase transition occurs, i.e. lithium ions are removed from the LiFePO4 lattice, causing the crystal structure to change to the lithium-deficient FePO4 phase, which has extremely low electronic conductivity and lithium ion diffusion capacity, severely hindering charge transport and causing capacity decay. The strong reducing atmosphere generated by the decomposition of the organic aluminum hypophosphite salt in the application can reduce the electrochemically inert FePO4 phase and convert it into the electrochemically active LiFePO4 phase with a lithium source, thereby repairing the material structure and restoring its capacity. At the same time, Al 3+ ions generated by the decomposition of the organic aluminum hypophosphite salt compound dope into the LiFePO4 lattice, widening the lithium ion migration channel and improving the intrinsic electronic conductivity and structural stability. At the same time, the decomposition of the compound can supplement the phosphorus element lost due to long-term cycling and repair the crystal structure defects. In addition, its incomplete carbonization forms a uniform nanometer carbon coating layer on the surface of the particles, enhancing interface electron conduction and inhibiting electrolyte side reactions.

[0009] In some embodiments of the application, the organic aluminum hypophosphite salt compound in step S2 includes at least one of aluminum methyl hypophosphite, aluminum-amino acid hypophosphite complex, aluminum diethyl hypophosphite and aluminum-diphenyl phosphite. The above-mentioned specific types of organic aluminum hypophosphite salt compounds act as reducing agents, doping sources, phosphorus supplements and carbon sources during heat treatment, and the multi-effect synergistic effect simplifies the process and reduces the cost.

[0010] In some embodiments of the application, the atomic ratio of Li:Fe:P in the mixture in step S2 is (1.05-1.10):1:1. Based on the above-mentioned suitable atomic ratio range, the regenerated material forms a complete olivine structure and sufficient lithium-extractable sites, and the theoretical capacity and electrochemical performance of the material are restored.

[0011] In some embodiments of the present application, the ball milling in step S1 comprises the following parameters: using anhydrous ethanol as dispersant, ball-to-material ratio of 10:1-20:1, ball milling speed of 300-600 r / min, and ball milling time of 2-4 hours. Based on the above ball milling parameter range, the raw materials are fully refined and uniformly mixed, providing a basis for subsequent uniform sintering reaction and structure reconstruction.

[0012] In some embodiments of the present application, the sintering in step S1 is performed at a temperature of 450-600℃ for 2-4 hours. Based on the above pre-treatment sintering temperature and time range, the residual binder and conductive carbon are effectively removed, the material surface is purified, and the crystal structure is preliminarily repaired, which is beneficial to the subsequent main regeneration process.

[0013] In some embodiments of the present application, the inert atmosphere in step S3 comprises one of argon, nitrogen or helium atmosphere. By using the above-mentioned types of inert atmosphere, the material is prevented from being oxidized during high-temperature sintering, and the reduction, doping and carbon coating reactions proceed smoothly.

[0014] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained.

[0015] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained.

[0016] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained.

[0017] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained.

[0018] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0019] The technical solutions in the embodiments of the present application or the prior art will be described below more clearly with the help of the accompanying drawings needed in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by one of ordinary skill in the art without any creative effort based on the structures shown in the accompanying drawings.

[0020] Figure 1 A scanning electron microscope (SEM) image of the regenerated lithium iron phosphate material prepared for the embodiment 1 of the present application;

[0021] Figure 2 A scanning electron microscope (SEM) image of the regenerated lithium iron phosphate material prepared for the embodiment 2 of the present application;

[0022] Figure 3 A first circle charge-discharge curve graph of the regenerated lithium iron phosphate material prepared for the embodiment 1 at 0.1C rate;

[0023] Figure 4 A first circle charge-discharge curve graph of the regenerated lithium iron phosphate material prepared for the embodiment 2 at 0.1C rate;

[0024] Figure 5 A long cycle performance graph of the regenerated lithium iron phosphate material prepared for the embodiment 2 at 1C rate;

[0025] Figure 6 A long cycle performance graph of the regenerated lithium iron phosphate material prepared for the embodiment 2 at 10C high rate.

[0026] The implementation, functional features and advantages of the present application will be further described with reference to the accompanying drawings in combination with the embodiments. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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:

[0031] 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.

[0032] S2. The waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound are ball-milled and mixed to obtain a mixture.

[0033] S3. The mixture is sintered under an inert atmosphere and cooled to obtain the cathode material of recycled waste LiFePO4.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In some embodiments of the present application, the ball milling in step S1 includes the following parameters: anhydrous ethanol as dispersant, ball-to-material ratio of 10:1-20:1, ball milling speed of 300-600 r / min, and ball milling time of 2-4 hours. For example, 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., the ball milling time can be 2 hours, 3 hours, 4 hours, etc., or within the range formed by any two of the above values. Based on the above ball milling parameter range, the raw materials are fully refined and uniformly mixed, providing a basis for subsequent uniform sintering reaction and structure reconstruction.

[0038] In some embodiments of the present application, the sintering in step S1 is performed at a temperature of 450-600℃ for 2-4 hours. For example, 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 formed by any two of the above values. Based on the above pre-treatment sintering temperature and time range, the residual binder and conductive carbon are effectively removed, the material surface is purified, and the crystal structure is preliminarily repaired, which is beneficial to the subsequent main regeneration process.

[0039] In some embodiments of the present application, the inert atmosphere in step S3 includes one of argon, nitrogen or helium atmosphere. By using the above inert atmosphere, the material is prevented from being oxidized during high-temperature sintering, and the reduction, doping and carbon coating reactions proceed smoothly.

[0040] In some embodiments of the present application, the sintering in step S3 is performed at a temperature of 700-900℃ for 7-11 hours. For example, 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 formed by any two of the above values. Based on the above high-temperature sintering parameters, the reduction, doping, lattice repair and carbon layer generation processes are fully completed, and finally a high-performance regenerated positive electrode material is obtained.

[0041] In some embodiments of the present application, the temperature is raised to the sintering temperature at a rate of 5-10℃ / min in step S3. For example, the temperature rising rate can be 5℃ / min, 7.5℃ / min, 10℃ / min, etc., or within the range formed by any two of the above values. Based on the above temperature rising rate range, the reactants are uniformly heated, avoiding local overheating or insufficient reaction, and the consistency and quality stability of the product are guaranteed.

[0042] In a second aspect, the present application provides a regenerated LiFePO4 cathode material, which is prepared by any one of the methods in the first aspect. By adopting the technical scheme, the present application obtains a cathode material with accurate element measurement ratio, complete crystal structure, high electronic and ionic conductivity, and the electrochemical performance and cycle stability of the regenerated material are effectively improved.

[0043] In a third aspect, the present application provides a lithium ion battery cathode sheet, which comprises the regenerated LiFePO4 cathode material in the second aspect. By adopting the technical scheme, the present application forms a good conductive network for the cathode sheet and maintains the structural stability, and the capacity performance and long cycle life of the battery are correspondingly improved.

[0044] In a fourth aspect, the present application provides a lithium ion battery, which comprises the lithium ion battery cathode sheet in the third aspect. By adopting the technical scheme, the present application presents high energy density, excellent cycle performance and safety for the battery, and achieves high-value recycling of waste lithium iron phosphate batteries.

[0045] The technical scheme of the present application will be further described in detail in combination with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present application, and are not used to limit the present application.

[0046] Unless otherwise specified, all raw materials in the present application are commercially available.

[0047] The following are specific embodiments of the present application:

[0048] Example 1, preparation of regenerated lithium iron phosphate (LiFePO4) cathode material;

[0049] (S1), pretreatment of waste LFP cathode material:

[0050] (S1.1), the waste lithium iron phosphate soft package battery is completely discharged, and the cathode sheet is obtained by disassembling in an argon glove box with H2O<0.01ppm and O2<0.01ppm.

[0051] (S1.2), the cathode sheet is soaked in deionized water at 25℃ for 1.5 minutes to separate the cathode material from the aluminum foil.

[0052] (S1.3), the separated cathode material is placed in a 90℃ vacuum drying box for 12 hours. Then, the dried material is placed in a planetary ball mill, zirconium oxide balls are added as dispersants with a ball-to-material ratio of 15:1, and the ball milling is carried out at a speed of 450r / min for 3 hours. After ball milling, the slurry is dried at 90℃ to obtain the pretreated waste LiFePO4 powder.

[0053] (S2), component preparation and mixing:

[0054] (S2.1), element analysis of the pretreated waste LiFePO4 powder was performed by ICP-OES, and lithium carbonate (Li2CO3) and reducing agent aluminum methyl hypophosphite (C2H9AIO8P2) were added to make the atomic ratio of Li:Fe:P in the mixture 1.05:1:1 according to the analysis results. The mixture was placed in a planetary ball mill, zirconium oxide grinding balls were added as dispersants, the ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the mixture was ball-milled for 8 hours to ensure uniform mixing.

[0055] (S3), sintering regeneration:

[0056] (S3.1), the ball-milled mixture was sieved through a 300-mesh sieve to separate the grinding balls, and then dried in a vacuum drying oven at 70℃ for 12 hours. The completely dried mixed powder was placed in an alumina porcelain boat and compacted, and then transferred to a tube furnace. High-purity argon was introduced into the furnace as a protective atmosphere, the temperature was raised to 800℃ at a rate of 7.5℃ / min, and sintering was carried out at this temperature for 7 hours. After sintering, the sample was cooled to room temperature with the furnace, and the argon atmosphere was maintained throughout the process.

[0057] (S3.2), the sintered block material was ground using an agate mortar and sieved through a 300-mesh sieve, and finally the regenerated lithium iron phosphate (LiFePO4) positive electrode material was obtained, denoted as sample LFP-800℃-7h.

[0058] Example 2

[0059] The present embodiment provides a method for preparing a regenerated lithium iron phosphate (LiFePO4) positive electrode material, which specifically comprises the following steps:

[0060] (S1), pretreatment of waste LFP positive electrode material:

[0061] (S1.1), the waste lithium iron phosphate soft-pack battery was completely discharged, and the positive electrode sheet was obtained by disassembling in an argon glove box with H2O<0.01ppm and O2<0.01ppm.

[0062] (S1.2), the positive electrode sheet was soaked in deionized water at 25℃ for 1.5 minutes to separate the positive electrode material from the aluminum foil.

[0063] (S1.3), the separated positive electrode material was dried in a vacuum drying oven at 90℃ for 12 hours. Subsequently, the dried material was placed in a planetary ball mill, zirconium oxide grinding balls were added as dispersants, the ball-to-material ratio was 15:1, the rotation speed was 450 r / min, and the mixture was ball-milled for 3 hours. After ball-milling, the slurry was dried at 90℃ to obtain the pretreated waste LiFePO4 powder.

[0064] (S2) Component preparation and mixing:

[0065] (S2.1) Element analysis of the pretreated powder was performed by ICP-OES, and lithium carbonate (Li2CO3) and reducing agent aluminum diethylphosphinate (C6H 18 AlO6P3) were added to make the atomic ratio of Li:Fe:P in the mixture 1.05:1:1.

[0066] (S2.2) The mixture was placed in a planetary ball mill, zirconium oxide balls were added as dispersants at a ball-to-material ratio of 20:1, and ball milling was performed at a speed of 450 r / min for 12 hours to ensure uniform mixing.

[0067] (S3) Sintering and regeneration:

[0068] (S3.1) The milled mixture was sieved through a 300-mesh sieve to separate the balls, and then dried in a vacuum drying oven at 70°C for 12 hours. The completely dried mixed powder was placed in an alumina porcelain boat and compacted, 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 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, and the argon atmosphere was maintained throughout the process.

[0069] (S3.2) The sintered block material was ground using an agate mortar and passed through a 300-mesh sieve to obtain the regenerated lithium iron phosphate (LiFePO4) positive electrode material, denoted as sample LFP-850℃-7h.

[0070] Example 3

[0071] The difference between this example and Example 2 is that in the preparation of the regenerated lithium iron phosphate (LiFePO4) positive electrode material, the atomic ratio of Li:Fe:P in the mixture in step (S2.1) is 1.08:1:1. The rest is consistent with Example 2.

[0072] Example 4

[0073] The difference between this example and Example 2 is that in the preparation of the regenerated lithium iron phosphate (LiFePO4) positive electrode material, the atomic ratio of Li:Fe:P in the mixture in step (S2.1) is 1.10:1:1. The rest is consistent with Example 2.

[0074] Comparative Example 1

[0075] The difference between the present comparative example and Example 1 is that the waste LiFePO4 powder after pretreatment but without additional addition and regeneration sintering in Example 1 (step S1.3) is taken as sample D-LFP1.

[0076] Comparative Example 2

[0077] The difference between the present comparative example and Example 1 is that only lithium carbonate (Li2CO3) is supplemented as the lithium source in step (S2.1) (the addition amount of Li2CO3 is consistent with that in step (S2.1)), without adding any organic aluminum hypophosphite salt compound, followed by regeneration sintering, and the obtained sample is recorded as D-LFP2.

[0078] Experimental detection:

[0079] The regenerated materials prepared in Examples 1 to 4 and the samples D-LFP1 and D-LFP2 of Comparative Examples 1 to 2 are subjected to electrochemical performance test.

[0080] The test method is as follows: the active material, conductive agent Super P and binder PVDF are mixed at a mass ratio of 8:1:1 to prepare slurry, which is uniformly coated on an aluminum foil current collector, and then dried, rolled, punched to prepare a positive electrode sheet.

[0081] A CR2032 button cell is assembled in an argon glove box (H2O<0.01ppm, O2<0.01ppm) with lithium metal as the counter electrode, polypropylene as the separator and lithium hexafluorophosphate as the electrolyte.

[0082] Test method:

[0083] (1) First circle charge-discharge performance (0.1C rate): after the battery is assembled, it is left for 12h, first charged at 0.1C (e.g. LFP theoretical capacity 150mAh g -1 ) to 4V, then converted to constant voltage charging, current <0.05C. After charging, it is left for 2min, and discharged at 0.1C to 2V.

[0084] (2) Long cycle performance (1C rate): after the first circle activation is completed, it is left for 10min, first charged at 1C (e.g. LFP theoretical capacity 150mAh g -1 ) to 4V, then converted to constant voltage charging, current <0.05C. After charging, it is left for 2min, and discharged at 1C to 2V.

[0085] (3) High rate performance (10C rate): after the first circle activation is completed, it is left for 10min, first charged at 10C (e.g. LFP theoretical capacity 150mAh g -1charged to 4 V, then constant voltage charged, current <0.05C. After the end of the charge, 10 min, 10C constant current discharge to 2 V.

[0086] The results of the experiment are shown in Table 1.

[0087] Table 1

[0088]

[0089] Result analysis: (1) Material morphology and structure characterization: as shown in Figure 1 (LFP-800℃-7h) and Figure 2 (LFP-850℃-7h), the scanning electron microscope (SEM) images of the regenerated materials show that the material particle morphology is regular, and the surface is covered with a uniform thin carbon layer (about 3-5 nm), which effectively suppresses the pulverization of the particles and the electrolyte side reaction in the cycle process. The XRD pattern shows that the diffraction peak of the regenerated material is completely matched with the standard LiFePO4 PDF card, and no FePO4 or other impurity phase is detected.

[0090] (2) First charge-discharge performance (0.1C rate): as shown in Figure 3 and Figure 4 , the regenerated LFP samples all show flat charge-discharge platforms, indicating that the FePO4 insulating phase is successfully reduced and the normal electrochemical behavior is restored. Among them, the LFP-850℃-7h sample shows the highest initial specific discharge capacity, which can reach more than 155 mAh / g (see the attached Figure 4 850℃ 7h curve for details), close to the theoretical capacity, and the coulombic efficiency is more than 95%.

[0091] (3) Long cycle performance (1C rate): as shown in Figure 5 , the LFP-850℃-7h sample has a capacity retention rate of more than 91% after 500 cycles at 1C rate (see the attached Figure 5 cycle capacity decay curve for details), showing excellent cycle stability. This is due to the enhanced intrinsic structural stability of Al 3+ doping and the maintained good conductive network of the uniform carbon coating layer. The LFP-800℃-7h sample also shows good cycle performance, with a capacity retention rate of about 86% after 500 cycles.

[0092] (4) High rate performance (10C rate): as shown in Figure 6 , the LFP-850℃-7h sample can still release a capacity of about 100 mAh / g at 10C high rate, and the capacity retention rate is more than 80% after 550 cycles, indicating that the material has excellent rate performance and sustained cycle ability. The performance is due to the Al 3+The doping widens the lithium ion migration channel, and the surface carbon coating layer significantly improves the electrode electronic conductivity, which together guarantees the fast charging and discharging capacity of the material under high rate condition.

[0093] In summary, the synchronous reduction-doping-carbon coating synergistic regeneration method can effectively restore and improve the electrochemical performance of the waste LiFePO4 cathode material.

[0094] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the patent protection scope of the present application.

Claims

1. A method for synchronously reducing-doping-carbon-coated regenerated waste LiFePO4, characterized in that, The method comprises the following steps: S1, discharging, disassembling the waste lithium iron phosphate battery, separating out the positive electrode material, drying, ball milling, sintering to obtain waste LiFePO4 powder; S2, ball milling the waste LiFePO4 powder, lithium source and organic aluminum hypophosphite compound to obtain a mixture; wherein the organic aluminum hypophosphite compound includes at least one of aluminum methyl hypophosphite, aluminum-amino acid hypophosphite complex, aluminum diethyl hypophosphite, and aluminum-diphenyl hypophosphite; S3, sintering the mixture under an inert atmosphere to obtain the regenerated waste LiFePO4 positive electrode material.

2. The method for synchronous deactivation-doping-carbon-coating regeneration of waste LiFePO4 according to claim 1, characterized in that, In step S2, the atomic ratio of Li:Fe:P in the mixture is (1.05-1.10):1:

1.

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

4. The method of claim 1, wherein the method is characterized by, In step S1, the sintering temperature is 450-600℃, and the sintering time is 2-4 hours.

5. The method of claim 1, wherein the method is characterized by, In step S3, the inert atmosphere includes one of argon, nitrogen or helium atmosphere.

6. The method of claim 1, wherein the method is characterized by, In step S3, the sintering temperature is 700-900℃, and the sintering time is 7-11 hours.

7. The method of claim 6, wherein the method is characterized by, In step S3, the sintering temperature is 700-900℃, and the sintering time is 7-11 hours.

8. A regenerated LiFePO4 cathode material, characterized in that, In step S3, the sintering temperature is 700-900℃, and the sintering time is 7-11 hours.

9. A lithium-ion battery cathode sheet, characterized by, The method for synchronously reducing-doping-carbon-coated regenerated waste LiFePO4 according to any one of claims 1-7.

10. A lithium-ion battery, characterized by, The regenerated LiFePO4 positive electrode material according to claim 8. The lithium ion battery positive electrode sheet according to claim 9.

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