Retired lithium iron phosphate battery electrochemical leaching method and preparation method of positive electrode material

Abstract

This invention belongs to the field of resource recycling technology for lithium iron phosphate battery cathode materials, specifically involving an electrochemical leaching method for retired lithium iron phosphate batteries and a method for preparing cathode materials. The method includes the following steps: 1) pretreatment; 2) cathode material treatment; 3) electrochemical selective leaching; 4) leaching product recovery to obtain solid iron phosphate and lithium carbonate products. This invention uses electrochemical technology to recover cathode materials from retired lithium iron phosphate batteries, achieving a lithium ion leaching rate of over 99% and an iron ion leaching rate controlled below 1%. It can recover high-purity lithium carbonate and iron phosphate. When the recovered lithium carbonate and iron phosphate are applied to reassembled button batteries, the first-cycle capacity can reach 149.2 mAh g. ‑1 .

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology for lithium iron phosphate battery cathode materials, specifically relating to an electrochemical leaching method for retired lithium iron phosphate batteries and a method for preparing cathode materials. Background Technology

[0002] Driven by the continued electrification of the automotive industry, lithium-ion batteries (LIBs), compared to other power batteries, possess advantages such as high voltage, high energy density, fast charge and discharge rates, long cycle life without memory effect, and stable high and low temperature performance, thus becoming the mainstay of electric vehicles, with transaction volumes reaching millions. With its high safety, excellent cycle life, and significant cost advantages, lithium iron phosphate (LFP) batteries have become one of the mainstream choices in energy storage systems and power batteries since their industrial application. Currently, all pure electric buses use LFP batteries, and in the early stages of the industry, LFP power batteries were the mainstream supporting battery system. Therefore, the peak period for the retirement of LFP batteries will arrive first. With the continued increase in market demand for LFP batteries, expanding their recycling scale will not only create significant economic benefits but is also a key measure to ensure the security of national strategic resources. The industry predicts that the market size for the recycling of retired LFP batteries will surge from 120 GWh in 2020 to 1500 GWh in 2030. In the face of the upcoming recycling boom, developing an environmentally friendly, efficient, and high-value-added selective lithium extraction technology and promoting its industrial application has become an urgent need for industrial development.

[0003] Currently, the disposal of spent lithium iron phosphate batteries mainly follows two technical approaches: one is to separate and recover elements such as lithium, iron, and phosphorus in compound form; the other is to directly regenerate the material by supplementing missing elements and repairing the crystal structure. Currently developed recycling and reuse methods mainly include cascade utilization, pretreatment, direct regeneration, pyrometallurgical processes, and hydrometallurgical processes. Among these, the hydrometallurgical process is the mainstream application in the industry due to its high metal recovery rate. In practice, to achieve the best economic benefits and recycling effect, multiple technologies are usually used in combination. Its core lies in using chemical reagents such as acids, alkalis, or oxidants to break down the material structure, leaching valuable metals such as lithium, iron, and phosphorus into a solution, and then separating and purifying them through precipitation, extraction, and other methods. This process has advantages such as low energy consumption, relatively simple equipment, and high product purity. Current research mainly focuses on optimizing the leaching and separation stages: a typical process is to first obtain a metal-enriched leachate through acid leaching, and then use solvent extraction or chemical precipitation to achieve comprehensive metal recovery. Depending on the leaching reagent, wet leaching processes can be mainly divided into two categories: inorganic acid leaching and organic acid leaching. Although inorganic acid leaching is widely used in the wet recycling of lithium iron phosphate batteries, its disadvantages are also quite prominent: the process consumes a lot of acid and generates a large amount of acidic wastewater that requires subsequent treatment, significantly increasing environmental and operating costs. A more critical issue is that conventional inorganic acid leaching has poor selectivity, making it difficult to efficiently separate the target metal. While organic acid leaching has the advantage of a mild reaction, its application is limited by cost, environmental protection, and technology: organic acids are expensive; the process easily generates difficult-to-treat organic wastewater; and the metal complexes formed are highly dependent on efficient separation technologies (such as targeted extraction or precipitation), increasing the process difficulty.

[0004] Electrochemical methods, as an emerging branch of hydrometallurgy, are receiving increasing attention due to their environmental friendliness and high selectivity. This process is based on the principle of electrolysis: during electrolysis, oxidation occurs at the anode and reduction occurs at the cathode. Electrons act as clean "oxidation-reduction agents," directly providing the necessary oxidation-reduction capacity, thereby achieving efficient leaching of valuable metals from waste cathode materials. Traditional selective leaching processes often use chemical oxidants such as hydrogen peroxide, but these are chemically unstable and pose high risks during storage and transportation. Other oxidants often generate large amounts of high-salinity wastewater after use, increasing subsequent treatment costs and environmental burden. Therefore, this study proposes combining electrolysis technology with lithium-ion battery recycling processes. Based on the principle of selective leaching, a controllable oxidation-reduction potential is directly provided using an electric field, with electrons acting as a green oxidant. No external chemical oxidizing reagents are required, and the electrolyte can be recycled after separation from lithium, thus achieving a highly efficient and clean leaching process. This is the core innovation of this patent research. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an electrochemical leaching method for retired lithium iron phosphate batteries and a method for preparing cathode materials.

[0006] The technical solution provided by this invention is as follows: An electrochemical leaching method for retired lithium iron phosphate batteries includes the following steps: 1) Pretreatment: The retired lithium iron phosphate batteries are discharged and disassembled in sequence. Specifically, the retired lithium iron phosphate batteries are soaked in a 10 wt% NaCl solution for 24 hours. After complete discharge, they are manually disassembled to obtain the metal casing, separator, and positive and negative electrode plates. The purpose of discharge is to completely release the residual charge in the retired lithium iron phosphate batteries. If they are disassembled directly without discharge, the high temperature sparks generated by the short circuit (up to 2500°C) can easily cause a fire or even an explosion. The positive electrode plate is obtained. 2) Cathode material processing: The aluminum foil current collector in the cathode sheet obtained in step 1) is separated from the lithium iron phosphate by water separation method to obtain flake lithium iron phosphate; after coarse grinding in a mortar, it is placed in a ball mill for fine grinding, and then the ball milled material is calcined at high temperature in a tube furnace under a protective atmosphere to obtain calcined powder. 3) Electrochemical selective leaching: The calcined powder obtained in step 2) is added to an acidic sodium sulfate solution and stirred and mixed evenly at room temperature. Ruthenium-iridium-titanium electrodes are used as the cathode and anode, and electrochemical leaching is carried out by external direct current to obtain the leachate. 4) Leaching product recovery: After the electrochemical leaching is completed, the leachate obtained in step 3) is filtered to recover the filter residue, and iron phosphate solid and lithium-rich filtrate are obtained; sodium carbonate is added to the lithium-rich filtrate to precipitate lithium ions and obtain lithium carbonate product.

[0007] In the above technical solution: 1) Lithium iron phosphate (LFP) in the cathode material can be oxidized to FePO4 at a positive potential. The lithium ions of LFP are selectively released into the electrolyte and separated from the insoluble FePO4. 2) The leached ferrous iron is reduced to elemental iron by utilizing the reduction effect of the cathode, and the ferrous ions in the solution are separated by the electrodeposition process to achieve selective recovery.

[0008] Specifically: In step 1), the retired lithium iron phosphate battery refers to a retired lithium iron phosphate power battery.

[0009] The water separation method utilizes the residual electrolyte LiPF6 between the current collector aluminum foil and the active material. LiPF6 reacts with water to generate HF, which further corrodes the current collector aluminum foil, thereby achieving electrode separation.

[0010] Specifically, in step 2): a planetary ball mill is used for ball milling at a speed of 250-350 r / min for 160-200 min. The protective gas for roasting is nitrogen, the roasting temperature is 400-500℃, and the roasting time is 100-140 min. After the ball milling roasting process, the waste lithium iron phosphate particles can be made more uniform and the binders between the particles can be removed, which is beneficial to the next leaching process.

[0011] Specifically, in step 3): The solid-liquid ratio of the calcined powder to the sodium sulfate solution is 8-12 g / L; The concentration of the sodium sulfate solution is 0.04-0.06 mol / L; The pH value of acidic sodium sulfate solution is 1-2; The external DC power supply voltage is 4.1-4.5V; The temperature for the electrochemical reaction is 65-75℃; The electrochemical reaction takes 160-200 minutes.

[0012] In the above technical solution, the ruthenium-iridium-titanium electrode used is typically used in the chlor-alkali industry. It is resistant to acid corrosion. Furthermore, in this invention, the electrode has a high oxygen evolution and hydrogen evolution potential, which can suppress the occurrence of side reactions at both the anode and cathode. It also has good durability and can be used for long-term cyclic applications.

[0013] Specifically, in step 4): the leachate is concentrated by rotary evaporation at 60-70°C, hydrogen peroxide solution is added after concentration, and sodium hydroxide solution is added to adjust the pH to 4-6. The reaction is carried out at 60-70°C for 0.5-1.5 h. After the reaction is complete, the mixture is filtered to obtain solid iron phosphate and lithium-rich filtrate.

[0014] Specifically, in step 4): Li is added to the lithium-rich filtrate in a molar ratio of... + CO3 2- Solid sodium carbonate is added in a ratio of 2:(1.0-1.2). The dissolution of solid sodium carbonate in water is exothermic. The reaction is carried out for 1-3 hours. The mixture is then filtered while hot and washed twice with boiling water. Since lithium carbonate has lower solubility at higher temperatures, while sodium carbonate has higher solubility at higher temperatures, this method can yield a lithium carbonate product with higher purity.

[0015] This invention also provides a method for preparing a cathode material, comprising the following steps: 1) The lithium carbonate product is obtained by using the method described above; 2) The lithium carbonate product and FePO4 composite material are mixed in a molar ratio of Li:Fe:P=(1-1.1):1:1 to prepare recycled lithium iron phosphate; 3) The regenerated lithium iron phosphate, Ketjen black and PVDF are mixed in a mass ratio of (7.5-8.5):1:1, and then a positive electrode slurry mixture is prepared. Finally, the positive electrode slurry is used as a coating liquid to prepare the positive electrode material with aluminum foil.

[0016] Specifically, in step 2): the lithium carbonate product and FePO4 are thoroughly ground in a mortar, and 4-6 wt% of glucose is added as a reducing agent; then the ground material is reduced and sintered in an argon atmosphere to obtain regenerated lithium iron phosphate; wherein the reduction and sintering temperature is 680-720℃, and the reduction and sintering time is 1-3 h.

[0017] Specifically, in step 3): the regenerated lithium iron phosphate, Ketjen black and PVDF are thoroughly ground and then stirred in N-methylpyrrolidone for 20-28 hours to prepare a positive electrode slurry mixture; after stirring, the slurry is coated on aluminum foil, vacuum dried at 110-130°C for 10-14 hours, and then pressed with a tablet press to obtain the positive electrode material.

[0018] This invention utilizes electrochemical technology to recover cathode materials from retired lithium iron phosphate batteries. The lithium-ion leaching rate reaches over 99%, while the iron-ion leaching rate is controlled to within 1%. High-purity lithium carbonate and iron phosphate can be recovered. When the recovered lithium carbonate and iron phosphate are used in reassembled button batteries, the initial charge capacity can reach 149.2 mAh g. -1 .

[0019] This invention also provides a method for preparing a lithium iron phosphate battery, comprising the following steps: 1) The cathode material was prepared using the method described above; 2) The cathode material obtained in step 1) is used as a novel cathode material to prepare lithium iron phosphate batteries.

[0020] The beneficial effects of this invention are as follows: 1) This invention utilizes electrochemical direct oxidation to achieve green, efficient, and highly selective leaching. The leaching rate of lithium is >99%, and the leaching rate of iron is <1%.

[0021] 2) Compared with the electrodialysis method, it reduces the use of membranes and the high-temperature treatment of molten salt, simplifies the LFP cathode material recycling process, and solves the problem of large waste generation in traditional methods.

[0022] 3) The recovered products can be used as precursors for LFP synthesis, realizing the recycling and regeneration of LFP. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of the present invention; Figure 2This is a schematic diagram of the present invention and the result of achieving selective leaching; Figure 3 The images show X-ray diffraction patterns of lithium iron phosphate before and after recycling, a scanning electron microscope image of the recycled lithium iron phosphate, cathode products, and precipitated products. Figure 4 The cycling performance, coulombic efficiency, and impedance curves of the regenerated lithium iron phosphate cathode material of this invention at a 1C rate are shown. Detailed Implementation

[0024] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0025] Unless otherwise specified, the test methods used in the embodiments are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0026] Kojic Black was purchased from Suzhou Desai New Energy Materials.

[0027] Example 1 1) Pretreatment: The retired lithium iron phosphate batteries are discharged sequentially to obtain the positive and negative electrode plates and the separator; 2) Cathode material processing: The cathode sheet obtained in step 1) is separated by water to obtain sheet-shaped lithium iron phosphate cathode material. Then, the sheet-shaped lithium iron phosphate is first ground in a mortar and then ball-milled in a ball mill. The resulting ball milled material is then calcined at high temperature under a protective gas to obtain calcined powder. 3) Electrochemical selective leaching: The pretreated black powder was placed in a 250ml beaker, and sodium sulfate solution with a certain pH was added according to the solid-liquid ratio. The mixture was stirred and mixed evenly at room temperature. A 3*3*1mm ruthenium-iridium-titanium electrode plate was used as the anode and cathode, and different voltages were applied for 3 hours. After that, the mixture was filtered to obtain filtrate and filter residue. The filtrate was subjected to ICP test and the filter residue was characterized by XRD. The optimal leaching conditions for selective leaching of lithium ions were determined by exploring different conditions such as temperature, pH, voltage, solid-liquid ratio, and time. 4) Leachate product recovery: The leachate was concentrated by rotary evaporation at 65°C. After concentration, a small amount of hydrogen peroxide was added to ensure that the leachate contained only ferric iron. Sodium hydroxide solution was then added in small amounts several times to adjust the pH to 5. The reaction was carried out at 65°C for 1 hour. The solution changed from clear to turbid, and a yellowish-white precipitate formed. Trace amounts of iron in the solution were removed by ferric phosphate. The solution was then separated by suction filtration to obtain a colorless and transparent filtrate. The product was then processed according to the Li:CO3 ratio. 2− Solid sodium carbonate was added in a ratio of 2:1.1 and reacted for 2 hours. The mixture was then filtered while hot to obtain a pure white solid. 5) Regeneration of Lithium Iron Phosphate: The leached lithium carbonate and FePO4 were thoroughly ground in a mortar at a molar ratio of Li:Fe:P = 1.05:1:1. 5 wt% glucose was added as a reducing agent and mixed thoroughly. The ground material was then reduced and sintered in an argon atmosphere to obtain regenerated lithium iron phosphate, named R-LFP. The sintering temperature was 700 °C and the sintering time was 2 h. R-LFP was then thoroughly ground with Ketjen Black and PVDF (mass ratio 8:1:1) and stirred in N-methylpyrrolidone (NMP) for 24 h to prepare a positive electrode slurry mixture. After stirring, the slurry was manually coated onto aluminum foil using a scraper and vacuum dried at 120 °C for 12 h. It was then pressed into 12 mm diameter circular positive electrode sheets using a tablet press, and finally assembled into 2016-type button batteries in a glove box. (See flowchart below.) Figure 1 .

[0028] In this embodiment of the invention, lithium iron phosphate in the cathode material can be oxidized to iron phosphate at a positive potential. The lithium ions of lithium iron phosphate are selectively released into the electrolyte, achieving highly selective leaching. At the same time, the collected iron phosphate and the precipitated lithium carbonate can be reused, realizing the reuse of the cathode material.

[0029] like Figure 2 As shown, this invention utilizes an electrochemical method to selectively leach lithium ions from spent lithium iron phosphate batteries.

[0030] like Figure 3 As shown, the LiFePO4 phase (PDF card NO. 40-1499) corresponding to lithium iron phosphate before recycling is clearly distinguishable from the FePO4 phase (PDF card NO. 34-0134) corresponding to lithium iron phosphate after recycling, with clear peak shapes, indicating that the recycled product is mainly FePO4. Meanwhile, most of the leached ferrous ions are enriched at the cathode under the action of an electric field and separated by reduction at the cathode, with the attached product corresponding to the Fe phase (PDF card NO. 06-0696). Morphological analysis of the regenerated lithium iron phosphate shows that the particle size is relatively uniform and corresponds to the corresponding elements.

[0031] like Figure 4 As shown, the regenerated lithium iron phosphate cathode material obtained by this invention has a first-cycle discharge specific capacity of 149.2 mAh g at a 1C rate. -1 It still maintains 145.3 mAh g after 250 cycles. -1 The discharge specific capacity of the recycled lithium iron phosphate material is significantly lower than that of the waste lithium iron phosphate material, indicating that the material has superior reversible capacity.

[0032] Example 2 Referring to Example 1, the difference lies in replacing the working electrode with a platinum sheet electrode. Under these conditions, the lithium leaching rate can reach over 99%, but the iron leaching rate exceeds 10%, making selective separation of lithium and iron impossible. When the resulting leaching products are assembled into a 2016-type button cell, its first-cycle specific capacity is only 90.2 mAh·g. -1 The performance is poor. If this cathode material is used in power batteries, the low initial capacity usually indicates unstable material structure and severe side reactions, leading to rapid capacity decay in subsequent cycles. Power batteries typically require a capacity retention rate of no less than 80% after thousands of cycles, while this material may fail within tens or hundreds of cycles. Furthermore, residual iron elements, primarily Fe, will... 2+ / Fe 3+ Iron dendrites exist on the surface of the positive electrode or in the electrolyte and are prone to redox shuttle or reduction deposition on the negative electrode, which can pierce the separator and cause micro-short circuits, leading to increased battery self-discharge, abnormal temperature rise, and even thermal runaway in severe cases.

[0033] Example 3 Referring to Example 1, the difference lies in replacing sulfuric acid with hydrochloric acid and changing the electrolyte from sodium sulfate to sodium chloride. Under these conditions, the lithium leaching rate can reach over 97%, while the iron leaching rate is less than 3%. The resulting leaching products were assembled into a 2016-type button battery, with an initial discharge specific capacity of 130.2 mAh·g. -1 The performance of this cathode material is lower than that of the recycled material in Example 1. If this cathode material is used in a power battery, the residual iron impurities and chloride ions result in poor conductivity and lithium-ion diffusion coefficient, leading to voltage plateau collapse and significant capacity reduction during high-rate discharge. Electric vehicles typically require acceleration and fast charging capabilities at 3-5C or even higher rates, which this material cannot meet. Furthermore, if the hydrochloric acid and sodium chloride used in the preparation process are not thoroughly washed, residual chloride ions will corrode the aluminum current collector and battery casing, especially under high temperature or high voltage conditions, easily generating AlCl3, causing increased contact resistance, tab breakage, and even electrolyte decomposition and gas generation, leading to battery bulging and failure.

[0034] Comparative Example 1 Referring to Example 1, the difference lies in replacing the ruthenium-iridium-titanium electrode with a ruthenium-titanium electrode. Under these conditions, the lithium leaching rate can reach over 98%, while the iron leaching rate is less than 1%. The resulting leaching products were assembled into a 2016-type button battery, with an initial discharge specific capacity of 142.3 mAh·g. -1The ruthenium-iridium-titanium electrode exhibits better battery performance. However, compared to the ruthenium-iridium-titanium electrode used in Example 1, the ruthenium-titanium electrode is mainly used in the chlor-alkali industry, where RuO2 has good selectivity for the chlorine precipitation reaction. The addition of iridium can significantly improve the catalytic activity and corrosion resistance of the electrode, while inhibiting the oxidation of the titanium substrate, thereby extending the electrode life. Considering the lithium iron leaching rate and the performance of the assembled button battery, the ruthenium-iridium-titanium electrode has the following advantages over the ruthenium-titanium electrode: 1. Higher catalytic activity: The addition of iridium significantly improves the catalytic performance of the electrode, making its electrochemical reaction efficiency higher in a strong acid environment.

[0035] 2. Stronger corrosion resistance Ruthenium-iridium-titanium electrodes exhibit superior corrosion resistance in strong acid media, but they are mainly suitable for the chlor-alkali industry and lack stability in long-term operation under strong acid systems.

[0036] 3. Inhibits oxidation of titanium substrate and extends electrode life. Iridium can effectively inhibit the oxidation process of titanium substrates, reduce electrode wear, and thus significantly extend the service life of electrodes.

[0037] 4. More suitable for large-scale industrial reuse Combining the above characteristics of high catalytic activity, strong corrosion resistance, and long lifespan, ruthenium-iridium-titanium electrodes can meet the requirements of repeated use in industrial production, reducing long-term operating costs. 5. Higher purity of leaching products Ruthenium-titanium electrodes exhibit weaker corrosion resistance than ruthenium-iridium-titanium electrodes in strong acid environments. Long-term electrolysis may lead to anodic dissolution, releasing trace amounts of Ru ions into the leachate. These ions may remain in subsequent cathode preparation and, during battery cycling, reduce to form metal dendrites at the anode, piercing the separator and causing micro-short circuits. They can also catalyze electrolyte decomposition, generating gas and causing battery bulging. Ruthenium-titanium electrodes have a shorter lifespan (titanium substrates are easily oxidized), and during industrial reuse, the electrode active area and catalytic efficiency gradually decrease, resulting in significant fluctuations in the purity, particle size, and impurity content of different batches of leachate products. Although the initial cost of ruthenium-titanium electrodes may be lower than that of ruthenium-iridium-titanium electrodes, their short lifespan, frequent replacement, and poor product performance necessitate additional design compensation for the battery system (such as increased cooling and rate limiting), potentially increasing the overall cost.

[0038] Given that this reaction is carried out in a strong acid environment and needs to be reused on a large scale in the industry, and that the leaching products are to be used in power batteries, the leaching rate, purity of the leaching products and electrochemical performance of the recycled products need to be considered. If ruthenium titanium electrodes are used forcibly, problems such as short range, slow charging, short lifespan and great safety hazards will be faced. Therefore, ruthenium iridium titanium electrodes are preferred in this system.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for electrochemical leaching of decommissioned lithium iron phosphate batteries, characterized in that, Includes the following steps: 1) Pretreatment: The retired lithium iron phosphate batteries are discharged and disassembled in sequence to obtain the positive electrode sheet; 2) Cathode material processing: The aluminum foil current collector in the cathode sheet obtained in step 1) is separated from the lithium iron phosphate by water separation method to obtain sheet-like lithium iron phosphate; after coarse grinding in a mortar, it is placed in a ball mill for fine grinding, and then the ball milled material is calcined at high temperature in a tube furnace under a protective atmosphere to obtain calcined powder. 3) Electrochemical selective leaching: The calcined powder obtained in step 2) is added to an acidic sodium sulfate solution and stirred and mixed evenly at room temperature. Ruthenium-iridium-titanium electrodes are used as the cathode and anode, and electrochemical leaching is carried out by external direct current to obtain the leachate. 4) Leaching product recovery: After the electrochemical leaching is completed, the leachate obtained in step 3) is filtered to recover the filter residue, and iron phosphate solid and lithium-rich filtrate are obtained; sodium carbonate is added to the lithium-rich filtrate to precipitate lithium ions and obtain lithium carbonate product.

2. The electrochemical leaching method for decommissioned lithium iron phosphate batteries according to claim 1, characterized in that: In step 1), the retired lithium iron phosphate battery refers to a retired lithium iron phosphate power battery.

3. The electrochemical leaching method for decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, In step 2): Use a planetary ball mill for ball milling at a speed of 250-350 r / min for a time of 160-200 min. Use nitrogen as the protective gas for calcination at a temperature of 400-500℃ for a time of 100-140 min.

4. The electrochemical leaching method for decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, In step 3): The solid-liquid ratio of the calcined powder to the sodium sulfate solution is 8-12 g / L; The concentration of the sodium sulfate solution is 0.04-0.06 mol / L; The pH value of acidic sodium sulfate solution is 1-2; The external DC power supply voltage is 4.1-4.5V; The temperature for electrochemical leaching is 65-75℃; The electrochemical leaching time is 160-200 min.

5. The electrochemical leaching method for decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, In step 4): the leachate is concentrated by rotary evaporation at 60-70°C. After concentration, 3-5 drops of 25-35wt% hydrogen peroxide solution are added, and then 0.09-0.11M sodium hydroxide solution is added to adjust the pH to 4-6. The reaction is carried out at 60-70°C for 0.5-1.5 h. After the reaction is complete, the mixture is filtered to obtain solid iron phosphate and lithium-rich filtrate.

6. The electrochemical leaching method for decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, In step 4): Li is added to the lithium-rich filtrate in a molar ratio of... + CO3 2- Solid sodium carbonate was added in a ratio of 2:(1.0-1.2), and the reaction was carried out for 1-3 hours. The mixture was then filtered while hot to obtain the lithium carbonate product.

7. A method for preparing a positive electrode material, characterized in that, Includes the following steps: 1) A lithium carbonate product is obtained by means of any one of claims 1 to 6; 2) The lithium carbonate product is mixed with FePO4 in a molar ratio of Li:Fe:P = (1-1.1):1:1 to prepare recycled lithium iron phosphate; 3) The regenerated lithium iron phosphate, Ketjen black and PVDF are mixed in a mass ratio of (7.5-8.5):1:1 to prepare a positive electrode slurry mixture. Finally, the positive electrode slurry mixture is used as a coating liquid to prepare a positive electrode material on an aluminum foil.

8. The method for preparing the cathode material according to claim 7, characterized in that, In step 2): the composite material of lithium carbonate and FePO4 is thoroughly ground in a mortar, and 4-6 wt% of glucose is added as a reducing agent. Then the ground material is reduced and sintered in an argon atmosphere to obtain regenerated lithium iron phosphate. The reduction and sintering temperature is 680-720℃, and the reduction and sintering time is 1-3 h.

9. The method for preparing the cathode material according to claim 7, characterized in that, In step 3): After thoroughly grinding the regenerated lithium iron phosphate, Ketjen black and PVDF, stir in N-methylpyrrolidone for 20-28 hours to prepare a positive electrode slurry mixture; after stirring, coat the positive electrode slurry mixture onto aluminum foil, vacuum dry at 110-130℃ for 10-14 hours, and then press it with a tablet press to obtain the positive electrode material.

10. A method for preparing a lithium iron phosphate battery, characterized in that, Includes the following steps: 1) A cathode material is prepared by the preparation method according to any one of claims 7 to 9; 2) The cathode material obtained in step 1) is used as a novel cathode material to prepare lithium iron phosphate batteries.

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