Method for preparing lithium manganese iron phosphate from waste lithium iron phosphate

Abstract

The present application relates to the technical field of battery material recycling, and particularly relates to a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate. The method comprises the following steps: determining the content of iron, phosphorus and lithium in waste lithium iron phosphate positive electrode powder; determining the adding amount of lithium source, manganese source, phosphorus source and carbon source to be supplemented; mixing the waste lithium iron phosphate positive electrode powder, the lithium source, the manganese source, the phosphorus source and the carbon source and dissolving them in water to form a mixed solution; heating and stirring the mixed solution at 80-100 DEG C for 5-8h, and then performing drying and grinding treatment to prepare lithium manganese iron phosphate precursor powder; and finally sintering the lithium manganese iron phosphate precursor powder. The present application breaks through the limitation of traditional direct repair technology which can only restore the original performance of the material, and realizes the direct upgrading and reconstruction from low energy density lithium iron phosphate to high energy density and high value-added lithium manganese iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of battery material recycling technology, and in particular to a method for regenerating waste lithium iron phosphate to prepare lithium manganese iron phosphate. Background Technology

[0002] Lithium-ion batteries, as a novel electrochemical energy storage system, have been widely used in new energy vehicles and mobile electronic devices. Among various battery types, lithium iron phosphate (LFP) batteries have steadily increased their market share due to their advantages such as high safety, low cost, excellent cycle stability, and long cycle life. However, the lifespan of LFP batteries is typically 5-8 years. The increasing number of used LFP batteries not only brings serious environmental problems and safety hazards but also results in a huge waste of resources. Therefore, how to efficiently recycle and reuse these retired battery materials has become a crucial issue in the current lithium-ion battery industry chain.

[0003] Traditional methods for recycling spent lithium iron phosphate (LFP) include pyrometallurgy, hydrometallurgy, and direct remediation. Pyrometallurgy enriches metal elements through high-temperature calcination. This process is extremely energy-intensive and emits large amounts of harmful gases, causing environmental pollution. Hydrometallurgy uses strong acids and alkalis to leach the material, followed by extraction, precipitation, and separation to extract valuable metal elements. This method consumes large amounts of chemicals and generates difficult-to-treat waste liquids and residues, easily causing secondary pollution. Direct remediation restores the electrochemical performance of spent materials to usable levels by replenishing lost lithium elements and repairing structural defects, thus enabling direct reuse. This method is low-carbon, efficient, economical, and does not damage the main crystal structure of the cathode material. However, current research mainly focuses on restoring the original structure and capacity of the material, without considering further optimization of electrochemical performance. Therefore, exploring how to fully utilize the degradation characteristics of spent LFP while simultaneously repairing the crystal structure and improving capacity is of significant research value.

[0004] Compared to ternary lithium batteries, lithium iron phosphate (LFP) batteries have a relatively low energy density, making it difficult to meet the long-range requirements of end products. Although advancements in packaging technology have narrowed the energy density gap in battery packs, improving the performance of LFP itself is still necessary to further enhance its electrochemical performance. Lithium manganese iron phosphate (LFP) is considered an ideal upgrade to LFP, possessing a similar crystal structure and advantages such as low cost and excellent safety. Furthermore, compared to LFP cathode materials, the addition of manganese increases the charge and discharge voltage, significantly improving energy density. Therefore, if it is possible to directly recycle waste LFP into LFP cathode materials, it will not only enhance the competitiveness of recycled products in the market but also strongly promote the vigorous development of the waste lithium-ion battery recycling industry.

[0005] Current methods for upgrading and regenerating spent lithium iron phosphate (LFP) into lithium manganese iron phosphate (LMP) have certain drawbacks and limitations. For example, they require complete dissolution of the waste in the leachate, which consumes a significant amount of time and generates substantial wastewater. These methods are not only complex and environmentally damaging but also highly dependent on precursors. Therefore, developing a green and efficient process for directly regenerating spent LFP into LMP materials is crucial. This process would not only be simpler, have lower energy consumption and production costs, but also significantly improve the material's energy density, making it of significant value for industrialization. Summary of the Invention

[0006] This invention provides a method for regenerating waste lithium iron phosphate to prepare lithium manganese iron phosphate, which solves the shortcomings of existing technologies such as complex processes, high energy consumption, and easy generation of secondary pollution in traditional recycling methods, as well as the fact that existing direct repair technologies can only achieve performance restoration but cannot improve the energy density of materials. This invention achieves the green and efficient upgrading and regeneration of low-value-added waste lithium iron phosphate into lithium manganese iron phosphate with higher energy density and excellent electrochemical performance, while simplifying the recycling process, reducing costs and minimizing environmental impact.

[0007] This invention provides a method for regenerating waste lithium iron phosphate to prepare lithium manganese iron phosphate, comprising the following steps: Step S1: Determine the content of iron, phosphorus and lithium in waste lithium iron phosphate cathode powder; Step S2: Based on the measurement results in Step S1 and the composition of the target lithium manganese iron phosphate, determine the amount of lithium source, manganese source, phosphorus source and carbon source to be added so that; Step S3: Mix the waste lithium iron phosphate cathode powder, and the lithium source, manganese source, phosphorus source and carbon source added in the amounts determined in step S2, and dissolve them in water to form a mixed solution; heat and stir the mixed solution at 80-100℃ for 5-8 hours, and then dry and grind it to obtain lithium manganese iron phosphate precursor powder; Step S4: Sinter the obtained lithium manganese iron phosphate precursor powder to obtain lithium manganese iron phosphate cathode material.

[0008] In this invention, ICP-OES is used to determine the content of iron, phosphorus and lithium in waste lithium iron phosphate cathode powder.

[0009] The method for regenerating waste lithium iron phosphate (LFP) into lithium manganese iron phosphate (LMFP) provided by this invention first involves quantitative composition analysis of the waste LFP powder, then targeted supplementation with lithium, phosphorus, and manganese (a key element for performance upgrade), followed by adding the raw materials to water and heating and stirring at a specific temperature and time. Finally, solid-state sintering is used to repair the crystal structure and achieve in-situ doping of manganese while preserving the original material framework. This method avoids the complex and highly polluting process of traditional hydrometallurgy, which requires complete acid dissolution of waste materials, and surpasses direct remediation technologies. It not only achieves high-value conversion of waste materials (from LFP to LMFP) and significantly improves the energy density of the recycled cathode material, but also simplifies the entire process, reduces costs, and is environmentally friendly.

[0010] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, the molar amounts of each element in the supplemented system satisfy the following relationship: with the molar amount of phosphorus as 1 unit, the molar amount of lithium is 1.0-1.08, the molar amount of iron is 0.2-0.99, the molar amount of manganese is 0.01-0.8, and the sum of the molar amounts of iron and manganese is 1; the molar ratio of the amount of carbon source added to the target lithium manganese iron phosphate is (1-4):1.

[0011] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, the molar amount of phosphorus is 1 unit, the molar amount of lithium is 1.0-1.05, the molar amount of iron is 0.5-0.7, the molar amount of manganese is 0.3-0.5, and the sum of the molar amounts of iron and manganese is 1.

[0012] The above ratio ensures that manganese is effectively doped to improve the voltage platform and energy density, while maintaining a stable olivine crystal structure. This avoids lattice distortion or impurity phases caused by excessive manganese content, thus ensuring that the final product has high purity and excellent electrochemical stability.

[0013] According to the method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to the present invention, the molar ratio of the amount of carbon source added to the target lithium manganese iron phosphate is (2-3):1, preferably 2:1.

[0014] This invention limits the molar ratio of added carbon source to a specific range to ensure that a conductive carbon coating layer of moderate thickness and uniform distribution can be formed during subsequent sintering. This high-quality carbon layer can significantly improve the inherent defect of low electronic conductivity of lithium manganese iron phosphate material, thereby greatly improving the rate performance and cycle stability of the material, and ensuring that the recycled material still exhibits excellent electrochemical performance even under high rate charge and discharge.

[0015] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, the lithium source is one or more of lithium hydroxide, lithium acetate, lithium carbonate and lithium oxalate; the manganese source is one or more of manganese acetate, manganese phosphate, manganese carbonate and manganese hydroxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid; and the carbon source is one or more of citric acid, glucose and sucrose.

[0016] The raw materials selected in this invention all have good water solubility or dispersibility, and the cost is relatively controllable. This ensures that during the liquid phase mixing process in step S3, the supplemented elements can be uniformly distributed around the waste lithium iron phosphate particles in the form of ions or small molecules, which is beneficial for the subsequent formation of a uniform precursor and the realization of in-situ uniform doping.

[0017] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, step S3 includes the following steps: mixing the waste lithium iron phosphate cathode powder and the lithium source, manganese source, phosphorus source and carbon source added in amounts determined according to step S2 and dissolving them in water to form a mixed solution; heating and stirring the mixed solution, followed by drying and grinding to obtain lithium manganese iron phosphate precursor powder.

[0018] This invention achieves uniform microscale composite formation of supplementary elements and waste powder particles through wet mixing and heating / stirring. The heating process promotes the adhesion and initial reaction of precursor materials on the surface of waste particles, ensuring that the supplementary lithium, manganese, phosphorus, and other elements are uniformly coated on the original LFP particle framework in the form of a coating. This facilitates the in-situ doping of manganese into the crystal lattice during subsequent high-temperature sintering, rather than simple physical mixing.

[0019] According to the method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to the present invention, the mixed solution is heated and stirred at 80-100°C for 5-8 hours.

[0020] This invention optimizes the process efficiency and quality of lithium manganese iron phosphate precursor powder preparation. This temperature range can effectively promote the mixing and uniform coating of various materials, while avoiding rapid evaporation of solvent (water) or side reactions caused by excessively high temperature; sufficient stirring time ensures the adequacy of the coating process.

[0021] According to the method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to the present invention, the drying in step S3 is drying at 100-150℃ for 8-16 hours; the grinding treatment in step S3 is ball milling.

[0022] This invention employs thorough drying within a temperature range of 100-150℃, which efficiently and completely removes the solvent, preventing side reactions caused by residual moisture during subsequent high-temperature sintering, and also prevents premature decomposition of the organic carbon source, thus preserving the uniform coating state of each component. The subsequent grinding process further breaks down the hard agglomerates formed during drying into fine powders with uniform particle size and good dispersibility. These two steps together ensure that the final precursor is a homogeneous, highly active composite powder, which is beneficial for achieving uniform element diffusion and efficient phase transformation during subsequent solid-state sintering.

[0023] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, in step S4, the sintering is carried out under an inert atmosphere at a heating rate of 3-8℃ / min to 650-750℃ for 8-12 hours. The optimized sintering temperature and time curve can provide sufficient driving force for the solid-phase reaction, promote the diffusion of supplementary elements into the LFP lattice, repair structural defects and complete the transformation to LMFP, and finally obtain a recycled cathode material with high crystallinity and excellent electrochemical performance.

[0024] Preferably, the inert atmosphere is any one of argon, nitrogen, or a mixture of hydrogen and argon. An inert atmosphere effectively prevents the oxidation of ferrous iron in the material, ensuring the integrity of the main phase structure.

[0025] According to the method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to the present invention, the waste lithium iron phosphate cathode powder is obtained by discharging, dismantling and separating waste lithium iron phosphate batteries.

[0026] According to the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to the present invention, the specific separation steps are as follows: the positive electrode sheet of the waste lithium iron phosphate battery is cut and then soaked in water to separate the waste lithium iron phosphate positive electrode material from the current collector; the separated waste lithium iron phosphate positive electrode material is dried and ball-milled to obtain waste lithium iron phosphate positive electrode powder.

[0027] This invention provides a mild and environmentally friendly solution for waste lithium iron phosphate cathode powder. It employs water immersion to separate the cathode material from the current collector (such as aluminum foil), avoiding the use of toxic organic solvents such as NMP, thus reducing environmental burden and operational risks. Subsequent drying and ball milling steps effectively remove moisture and refine the particles, increasing their specific surface area and enhancing their activity in subsequent chemical reactions, providing high-quality raw materials for efficient regeneration.

[0028] Preferably, the soaking time is 12-36 hours; the drying temperature is 80-120°C, and the drying time is 12-24 hours; the ball-to-material ratio of the ball milling is (10-30):1, the rotation speed is 250-400 rpm, and the time is 4-10 hours. Sufficient soaking time ensures gentle and effective separation of the positive electrode active material and the current collector in an aqueous medium, avoiding the use of organic solvents; gentle drying conditions thoroughly remove moisture without damaging the original structure of the material; and the optimized ball milling process effectively refines particles and increases the specific surface area, thereby significantly improving the reactivity of the waste powder.

[0029] According to a second aspect of the present invention, the present invention provides a lithium manganese iron phosphate, which is obtained by regeneration using the above-described method; the specific capacity of the lithium manganese iron phosphate cathode material is ≥150 mAh / g, preferably 150 mAh / g-170 mAh / g.

[0030] Compared with existing technologies, the method for preparing lithium manganese iron phosphate from waste lithium iron phosphate provided by the present invention has the following beneficial effects: (1) This invention breaks through the limitation of traditional direct repair technology, which can only restore the original performance. By precisely supplementing the waste lithium iron phosphate with elements such as lithium, manganese, and phosphorus, it realizes the direct upgrading and remanufacturing from low energy density lithium iron phosphate (LFP) to high energy density and high added value lithium manganese iron phosphate (LMFP). The resulting recycled product has a higher voltage platform and significantly improved energy density due to the doping of manganese, making it more competitive in the market.

[0031] (2) This method eliminates the complex strong acid leaching, extraction, and precipitation steps in traditional hydrometallurgy, avoiding the consumption of large amounts of chemical reagents and the generation of acidic waste liquid and residue, thus fundamentally reducing secondary pollution. The entire process is shorter, simpler to operate, and has lower energy consumption and production costs, meeting the requirements of green chemistry and sustainable development.

[0032] (3) This method preserves the original olivine-type crystal framework of waste lithium iron phosphate materials. Based on this, structural repair and element doping are carried out to achieve full recovery and in-situ utilization of elements such as lithium, iron, and phosphorus in waste cathode materials, maximizing the preservation of the value of the original materials and achieving a very high resource recovery rate.

[0033] (4) The regenerated lithium manganese iron phosphate cathode material prepared by this method not only repairs the crystal structure defects and lithium loss caused by cycle decay, but also exhibits excellent rate performance and long cycle stability through uniform carbon coating and stable crystal structure. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a process flow diagram of a method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to Embodiment 1 of the present invention.

[0036] Figure 2 The images show the XRD patterns of recycled lithium manganese iron phosphate in Examples 1-3 and waste lithium iron phosphate and recycled lithium iron phosphate in Comparative Examples 1-2 of the present invention.

[0037] Figure 3 This is a SEM image of waste lithium iron phosphate S-LFP provided in Comparative Example 1 of the present invention.

[0038] Figure 4 This is a SEM image of the regenerated lithium manganese iron phosphate R-LF5M5P provided in Example 1 of the present invention.

[0039] Figure 5 The first two charge-discharge curves of a lithium-ion battery made of S-LFP material at a 0.1C rate.

[0040] Figure 6 The first two charge-discharge curves of a lithium-ion battery made of R-LF5M5P material at a 0.1C rate.

[0041] Figure 7 This is a comparison chart of the rate performance of lithium-ion batteries made from S-LFP in Comparative Example 1 and R-LF5M5P in Example 1 of the present invention.

[0042] Figure 8 This is a comparison chart of the cycle performance of lithium-ion batteries made in Comparative Example 1S-LFP and Example 1R-LF5M5P at 1C rate. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0045] Unless otherwise specified, all test methods are standard and all instrument settings are as recommended by the manufacturer. The specific capacity test method is as follows: the material is assembled into a button cell, and a constant current charge-discharge test is performed using a Blue Charge tester.

[0046] The following examples and comparative examples use waste lithium iron phosphate cathode powder prepared according to the following methods: Shenzhen Xinmao New Energy Technology Co., Ltd. discharges and disassembles spent lithium iron phosphate batteries that have undergone long-term cycle degradation to obtain the positive electrode sheets of the spent lithium iron phosphate batteries. The residual electrolyte on the surface of the positive electrode sheets is washed away with deionized water. After cutting, the sheets are soaked in water for 12-36 hours to separate the spent lithium iron phosphate positive electrode material from the current collector. The separated spent lithium iron phosphate positive electrode material is dried at 80-120℃ for 12-24 hours and then ball-milled at a ball-to-material ratio of (10-30):1 and a rotation speed of 250-400 rpm for 4-10 hours to obtain spent lithium iron phosphate positive electrode powder.

[0047] Example 1 This embodiment provides a method for regenerating lithium iron phosphate from waste lithium iron phosphate to prepare lithium manganese iron phosphate. The lithium source used is lithium hydroxide, the manganese source is manganese acetate, the phosphorus source is ammonium dihydrogen phosphate, and the carbon source is citric acid. The chemical formula of the regenerated lithium manganese iron phosphate cathode material is LiFe. 0.5 Mn 0.5 PO4, abbreviated as R-LF5M5P, such as Figure 1 As shown, the specific steps include the following: S1: Waste lithium iron phosphate (LFP) batteries were discharged and disassembled to obtain the positive electrode sheets. Residual electrolyte on the surface of the positive electrode sheets was washed away with deionized water. After cutting, the sheets were soaked in water for 24 hours to separate the waste LFP positive electrode material from the current collector. The separated waste LFP positive electrode material was dried at 100°C for 24 hours and then ball-milled at a ball-to-material ratio of 20:1 and a rotation speed of 350 rpm for 6 hours to obtain waste LFP positive electrode powder. The iron, phosphorus, and lithium content in the waste LFP positive electrode powder was determined using ICP-OES.

[0048] S2: Based on the measurement results in S1, take 1.5776g of waste lithium iron phosphate cathode powder, and determine to add 0.5035g of lithium source, 2.4509g of manganese source, 1.1503g of phosphorus source and 7.68g of citric acid, so that the molar ratio of lithium, iron, manganese and phosphorus in the supplemented system reaches Li:Fe:Mn:P=1.05:0.5:0.5:1, and the molar ratio of the citric acid content to the target lithium manganese iron phosphate is 2:1.

[0049] S3: Dissolve the waste lithium iron phosphate cathode powder, lithium source, manganese source, phosphorus source and citric acid weighed in S2 into 150mL of deionized water, and then place the suspension in a magnetic stirrer and heat and stir at 90℃ for 5h; after heating and stirring, place the mixed solution in a forced-air drying oven at 120℃ and dry for 12h, and then ball mill to obtain precursor powder.

[0050] S4: The precursor powder was sintered at 700℃ for 10 h under an argon atmosphere with a heating rate of 5℃ / min. After cooling, the regenerated lithium manganese iron phosphate cathode material was obtained. The specific capacity of the lithium manganese iron phosphate cathode material was 164.6 mAh / g.

[0051] Example 2 This embodiment provides a method for regenerating lithium iron phosphate from waste lithium iron phosphate to prepare lithium manganese iron phosphate. The lithium source used is lithium hydroxide, the manganese source is manganese acetate, the phosphorus source is ammonium dihydrogen phosphate, and the carbon source is citric acid. The chemical formula of the regenerated lithium manganese iron phosphate cathode material is LiFe. 0.7 Mn 0.3 PO4, abbreviated as R-LF7M3P, specifically includes the following steps: S1: The preparation method of waste lithium iron phosphate cathode powder is the same as in Example 1. The contents of iron, phosphorus and lithium in the waste lithium iron phosphate cathode powder are determined by ICP-OES.

[0052] S2: Based on the measurement results in S1, take 2.20864g of waste lithium iron phosphate cathode powder, and determine to add 0.369248g of lithium source, 1.47054g of manganese source, 0.69018g of phosphorus source and 7.68g of citric acid, so that the molar ratio of lithium, iron, manganese and phosphorus in the supplemented system reaches Li:Fe:Mn:P=1.05:0.7:0.3:1, and the molar ratio of the citric acid content to the target lithium manganese iron phosphate is 2:1.

[0053] S3: Dissolve the waste lithium iron phosphate cathode powder, lithium source, manganese source, phosphorus source and citric acid weighed in S2 into 150mL of deionized water, and then place the suspension in a magnetic stirrer and heat and stir at 90℃ for 5h; after heating and stirring, place the mixed solution in a forced-air drying oven at 120℃ and dry for 12h, and then ball mill to obtain precursor powder.

[0054] S4: The precursor powder was sintered at 700℃ for 10 h under an argon atmosphere with a heating rate of 5℃ / min. After cooling, the regenerated lithium manganese iron phosphate cathode material was obtained. The specific capacity of the lithium manganese iron phosphate cathode material was 157.4 mAh / g.

[0055] Example 3 This embodiment provides a method for regenerating lithium iron phosphate from waste lithium iron phosphate to prepare lithium manganese iron phosphate. The lithium source used is lithium hydroxide, the manganese source is manganese acetate, the phosphorus source is ammonium dihydrogen phosphate, and the carbon source is citric acid. The chemical formula of the regenerated lithium manganese iron phosphate cathode material is LiFe. 0.3 Mn 0.7 PO4, abbreviated as R-LF3M7P, specifically includes the following steps: S1: The preparation method of waste lithium iron phosphate cathode powder is the same as in Example 1. The contents of iron, phosphorus and lithium in the waste lithium iron phosphate cathode powder are determined by ICP-OES.

[0056] S2: Based on the measurement results in S1, take 0.94656g of waste lithium iron phosphate cathode powder, and determine the addition of 0.6377g of lithium source, 3.43126g of manganese source, 1.6104g of phosphorus source and 7.68g of citric acid, so that the molar ratio of lithium, iron, manganese and phosphorus in the supplemented system reaches Li:Fe:Mn:P=1.05:0.3:0.7:1, and the molar ratio of the citric acid content to the target lithium manganese iron phosphate is 2:1.

[0057] S3: Dissolve the waste lithium iron phosphate cathode powder, lithium source, manganese source, phosphorus source and citric acid weighed in S2 into 150mL of deionized water, and then place the suspension in a magnetic stirrer and heat and stir at 90℃ for 5h; after heating and stirring, place the mixed solution in a forced-air drying oven at 120℃ and dry for 12h, and then ball mill to obtain precursor powder.

[0058] S4: The precursor powder is sintered at 700°C for 10 hours under an argon atmosphere with a heating rate of 5°C / min. After cooling, the regenerated lithium manganese iron phosphate cathode material is obtained.

[0059] Comparative Example 1 This comparative example provides unrepaired retired lithium iron phosphate cathode material, abbreviated as S-LFP, with a specific capacity of 131.8 mAh / g.

[0060] Comparative Example 2 The lithium source used in this comparative example is lithium hydroxide, and the carbon source is citric acid. The chemical formula of the regenerated lithium iron phosphate cathode material is LiFePO4, abbreviated as R-LFP. The specific steps include the following: S1: Waste lithium iron phosphate cathode powder is obtained by discharging, dismantling and separating waste lithium iron phosphate batteries. The content of iron, phosphorus and lithium elements in the waste lithium iron phosphate cathode powder is determined by ICP-OES.

[0061] S2: Based on the measurement results in S1, take 1.5776g of waste lithium iron phosphate cathode powder, and determine to add 0.08392g of lithium source and 7.68g of citric acid, so that the molar ratio of lithium, iron and phosphorus in the supplemented system reaches Li:Fe:P=1.05:1:1, and the molar ratio of the content of citric acid to the target lithium iron phosphate is 2:1.

[0062] S3: Dissolve the waste lithium iron phosphate cathode powder, lithium source and citric acid weighed in S2 into 150mL of deionized water, and then place the suspension in a magnetic stirrer and heat and stir at 90℃ for 5h; after heating and stirring, place the mixed solution in a forced-air drying oven at 120℃ and dry for 12h, and then grind to obtain precursor powder.

[0063] S4: The precursor powder is sintered at 700°C for 10 hours under an argon atmosphere with a heating rate of 5°C / min. After cooling, the regenerated lithium iron phosphate cathode material is obtained.

[0064] Figure 2 XRD patterns of recycled lithium manganese iron phosphate (LFP) in Examples 1-3 and in Comparative Examples 1-2 (waste LFP and recycled LFP) are presented. As shown in the figures, the FePO4 and LiFePO4 phases coexist in S-LFP. After lithium supplementation and citric acid remediation, R-LFP exhibits a single pure phase. Among the three recycled LFP materials with different manganese contents, R-LF7M3P and R-LF5M5P, with lower manganese contents, exhibit good crystallinity and a single pure phase. However, with increasing manganese content, obvious impurity peaks appear in the XRD pattern of R-LF3M7P. This is because the high manganese content doping exceeds the solubility limit of the S-LFP lattice, resulting in large-radius Mn... 2+ Entering the lattice framework of S-LFP will induce lattice distortion and form impurity phases.

[0065] Figure 3 The image shown is a SEM image of waste lithium iron phosphate S-LFP in Comparative Example 1. Figure 4 This is a SEM image of the regenerated lithium manganese iron phosphate R-LF5M5P from Example 1. S-LFP consists of irregular particles containing residual binders and other impurities, as well as some microcracks on the surface. R-LF5M5P particles exhibit a uniform particle size, complete morphology, and a smooth surface.

[0066] Figure 5 and Figure 6The figure shows the charge-discharge curves of lithium-ion batteries made of S-LFP and R-LF5M5P materials for the first two cycles at a 0.1C rate. The S-LFP battery exhibits a discharge specific capacity of 131.8 mAh / g and a coulombic efficiency of 78.1% in the first cycle. The R-LF5M5P battery shows a discharge specific capacity of 164.6 mAh / g and a coulombic efficiency of 96.9%. Furthermore, a manganese charge-discharge plateau is observed at 4.1V, indicating that the increased charge-discharge voltage improves the energy density of the materials.

[0067] Figure 7 The figure shows a comparison of the rate performance of lithium-ion batteries made from S-LFP in Comparative Example 1 and R-LF5M5P in Example 1. As shown in the figure, R-LF5M5P has excellent rate performance at the same rate.

[0068] Figure 8 This is a comparison chart of the cycle performance of lithium-ion batteries made from S-LFP in Comparative Example 1 and R-LF5M5P in Example 1 at 1C rate. As shown in the figure, the discharge specific capacity of S-LFP after 300 cycles at 1C rate is 107 mAh / g, with a capacity retention rate of 87.1%; while the discharge specific capacity of R-LF5M5P obtained from S-LFP as raw material after 300 cycles at 1C rate is 137 mAh / g, with a capacity retention rate of 94.1%.

[0069] The specific capacities of the materials obtained in each embodiment and comparative example are shown in Table 1.

[0070] Table 1 Material Specific capacity S-LFP 131.8mAh / g R-LFP 160.3mAh / g R-LF5M5P 164.6mAh / g R-LF7M3P 157.4mAh / g Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for regenerating lithium iron phosphate waste to prepare lithium manganese iron phosphate, characterized in that, Includes the following steps: Step S1: Determine the content of iron, phosphorus and lithium in waste lithium iron phosphate cathode powder; Step S2: Based on the measurement results in Step S1 and the composition of the target lithium manganese iron phosphate, determine the amount of lithium source, manganese source, phosphorus source and carbon source that need to be added. Step S3: Mix the waste lithium iron phosphate cathode powder, and the lithium source, manganese source, phosphorus source and carbon source added in the amounts determined in step S2, and dissolve them in water to form a mixed solution; The mixed solution was heated and stirred at 80-100℃ for 5-8 hours, followed by drying and grinding to obtain lithium manganese iron phosphate precursor powder; Step S4: Sinter the obtained lithium manganese iron phosphate precursor powder to obtain lithium manganese iron phosphate cathode material.

2. The method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to claim 1, characterized in that, In step S2, the molar amounts of each element in the supplemented system satisfy the following relationship: with the molar amount of phosphorus as 1 unit, the molar amount of lithium is 1.0-1.08, the molar amount of iron is 0.2-0.99, the molar amount of manganese is 0.01-0.8, and the sum of the molar amounts of iron and manganese is 1; the molar ratio of the amount of carbon source added to the target lithium manganese iron phosphate is (1-4):

1.

3. The method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to claim 2, characterized in that, With the molar amount of phosphorus as 1 unit, the molar amount of lithium is 1.0-1.05, the molar amount of iron is 0.5-0.7, the molar amount of manganese is 0.3-0.5, and the sum of the molar amounts of iron and manganese is 1.

4. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to claim 2 or 3, characterized in that, The molar ratio of the added carbon source to the target lithium manganese iron phosphate is (2-3):

1.

5. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to any one of claims 1-4, characterized in that, The lithium source is one or more of lithium hydroxide, lithium acetate, lithium carbonate, and lithium oxalate; the manganese source is one or more of manganese acetate, manganese phosphate, manganese carbonate, and manganese hydroxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; and the carbon source is one or more of citric acid, glucose, and sucrose.

6. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to any one of claims 1-5, characterized in that, The drying in step S3 is performed at 100-150℃ for 8-16 hours; the grinding process in step S3 is ball milling.

7. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to any one of claims 1-6, characterized in that, In step S4, the sintering is carried out under an inert atmosphere at a heating rate of 3-8℃ / min to 650-750℃ for 8-12 hours. Preferably, the inert atmosphere is any one of argon, nitrogen, or a mixture of hydrogen and argon.

8. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate according to any one of claims 1-7, characterized in that, The waste lithium iron phosphate cathode powder is obtained by discharging, dismantling, and separating waste lithium iron phosphate batteries.

9. The method for preparing lithium manganese iron phosphate by regenerating waste lithium iron phosphate according to claim 8, characterized in that, The specific steps of the separation are as follows: the positive electrode sheet of the waste lithium iron phosphate battery is cut and then soaked in water to separate the waste lithium iron phosphate positive electrode material from the current collector. The separated waste lithium iron phosphate positive electrode material is dried and ball-milled to obtain waste lithium iron phosphate positive electrode powder. Preferably, the soaking time is 12-36 hours; the drying temperature is 80-120°C and the drying time is 12-24 hours; the ball-to-material ratio of the ball mill is (10-30):1, the rotation speed is 250-400 rpm, and the time is 4-10 hours.

10. A lithium manganese iron phosphate, characterized in that, The lithium manganese iron phosphate cathode material is obtained by regeneration using the method described in any one of claims 1-9; the specific capacity of the lithium manganese iron phosphate cathode material is ≥150 mAh / g.

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