Method for recovering and regenerating lithium iron phosphate battery positive electrode powder

Abstract

The application provides a method for recovering and regenerating lithium iron phosphate battery positive electrode powder, which comprises the following steps: pretreating the retired lithium iron phosphate battery positive electrode powder, constructing a composite leaching system by using polyhydric alcohol compounds and small-molecule organic acid compounds, and simultaneously realizing efficient leaching of lithium elements and selective precipitation of iron elements; the leaching solution is carbonated and precipitated to recover lithium salt, and after the iron-based precipitate is mixed with the lithium salt, carbon source and dispersant are added, and the regenerated lithium iron phosphate positive electrode material is prepared by staged calcination; the polyhydric alcohol-small-molecule organic acid is used as the core to construct the composite leaching system, and the method is green, environmentally friendly and weakly corrosive, and does not need additional oxidizing agents or reducing agents, so that the element separation process is simplified; the closed-loop recovery of lithium and iron elements is realized, the resource utilization rate is high, the electrochemical performance of the regenerated positive electrode material is excellent; the process operation is mild, the parameters are easy to control, the method is suitable for large-scale industrial production, and the method has good environmental benefits, economic benefits and application prospect.

Description

Technical Field

[0001] This invention relates to the field of electrical component technology, specifically to a method for recycling and regenerating lithium iron phosphate battery cathode powder. Background Technology

[0002] With the rapid popularization of new energy vehicles and energy storage equipment, the use of lithium iron phosphate (LiFePO4) batteries has increased significantly, and retired batteries are also being produced on a large scale. The cathode material of lithium iron phosphate batteries contains valuable elements such as lithium, iron, and phosphorus. If they are not properly recycled, it will not only waste mineral resources, but may also cause environmental problems such as soil and water pollution due to the leakage of hazardous substances, thus hindering the green and sustainable development of the new energy industry.

[0003] Currently, lithium iron phosphate battery cathode powder recycling technologies are mainly divided into three categories: pyrometallurgy, hydrometallurgy, and direct regeneration. Pyrometallurgy separates and recovers valuable elements through high-temperature roasting, but it has drawbacks such as high energy consumption, large equipment investment, easy generation of flue gas pollution, and poor element recovery selectivity. Direct regeneration can preserve the original crystal structure of the cathode material to the greatest extent, but it has extremely high requirements for the purity of retired battery cathode powder, making it difficult to adapt to the low-purity raw materials for large-scale recycling, thus limiting its applicability. Hydrometallurgy, due to its gentle operation, low energy consumption, and high element recovery efficiency, has become the mainstream technology.

[0004] Existing wet leaching systems mostly use strong acids as leaching agents, supplemented by oxidants. Although they can efficiently leach lithium, they suffer from severe equipment corrosion, high acid consumption, and high subsequent wastewater treatment costs. Furthermore, they can easily lead to the simultaneous leaching of elements such as iron and phosphorus, requiring the addition of complex impurity removal reagents to separate lithium from other elements. This process is cumbersome and prone to secondary pollution.

[0005] Green and environmentally friendly composite leaching systems are gradually becoming a research hotspot. Polyol solvents have good solubility and stability, and can form a synergistic leaching system with small molecule organic acids, reducing corrosion to equipment. Furthermore, small molecule organic acids have both leaching and complexing effects, and can selectively bind to metal ions to achieve stepwise element separation. However, existing technologies mostly focus on the general leaching of valuable metals, failing to achieve the simultaneous efficient leaching of lithium and selective precipitation of iron. They also do not involve a closed-loop recycling process for combining precipitated products with lithium salts to prepare recycled cathode materials, thus failing to fully realize efficient resource recycling and exhibiting shortcomings such as incomplete processes and a need to improve resource recovery rates.

[0006] In addition, in existing recycling processes, lithium is mostly recovered and utilized separately in the form of specific salts, while iron is mostly treated as waste residue, failing to achieve the synergistic regeneration of lithium and iron, resulting in low resource utilization. Some processes require the addition of additional oxidants or reducing agents to the leaching system, which increases process costs and operational complexity.

[0007] Therefore, there is an urgent need for a green, efficient, simple process based on polyols and small molecule organic acids to recycle lithium iron phosphate battery cathode powder, which can achieve synergistic regeneration of lithium iron phosphate. Summary of the Invention

[0008] This invention addresses the problems of highly corrosive leaching systems, cumbersome element separation, low resource utilization, and non-closed-loop processes in existing lithium iron phosphate battery cathode powder recycling technologies. It provides a method for recycling and regenerating lithium iron phosphate battery cathode powder by constructing a composite leaching system using polyols and small-molecule organic acids. This achieves efficient lithium leaching and selective iron precipitation. Simultaneously, the precipitated products are calcined with lithium precipitate products to prepare regenerated cathode materials, constructing a closed-loop recycling process of "leaching-separation-regeneration," balancing environmental friendliness and resource utilization efficiency.

[0009] This invention provides a method for recycling and regenerating lithium iron phosphate battery cathode powder, comprising the following steps: S1. Discharge, disassemble and separate retired lithium iron phosphate batteries to obtain positive electrode sheets, remove aluminum foil from the surface of the positive electrode sheets, crush and sieve to obtain lithium iron phosphate positive electrode powder with a particle size of 100~200 mesh, and dry it at 80~120℃ in an inert atmosphere to obtain pretreated positive electrode powder. S2. Polyol compounds and small molecule organic acid compounds are mixed in a molar ratio of 1:5 to 5:1, heated, and stirred at 40 to 80°C for 30 to 60 min to obtain a composite leachate; Polyols are alcohols containing two or more hydroxyl groups in their molecules, and small molecule organic acids are any one of the following: ascorbic acid, citric acid, malic acid, formic acid, acetic acid, propionic acid, butyric acid, and isobutyric acid; S3. The pretreated cathode powder is added to the composite leaching solution at a solid-liquid ratio of 1:20~1:50 g / mL to dissolve lithium and precipitate iron, resulting in lithium leaching solution and iron-based precipitate. The leaching temperature is 70~120℃, the stirring rate is 200~500 r / min, and the leaching time is 4~12 h. After the leaching reaction was completed, solid-liquid separation was performed and the lithium leaching solution and iron-based precipitate were collected separately. S4. Add a carbonation reagent to the lithium element leaching solution, adjust the pH value to 7-9, react for 1-3 h to convert lithium ions into lithium salt precipitate, filter and wash, and then dry at 100-120℃ to obtain lithium salt. The carbonation reagent is one or a mixture of sodium carbonate and sodium bicarbonate; S5. Iron-based precipitate and lithium salt are mixed at a Fe:Li molar ratio of 1:1 to 1:1.1 to obtain a precursor. A carbon source and dispersant are added to the precursor and then ground to obtain a mixed precursor. The mixed precursor is calcined in stages under an inert atmosphere, and then cooled, crushed and sieved to obtain a regenerated lithium iron phosphate cathode material.

[0010] The method for recycling and regenerating lithium iron phosphate battery cathode powder according to the present invention, as a preferred embodiment, in step S1, the retired lithium iron phosphate battery is discharged to 0V, and the aluminum foil on the surface of the cathode sheet is removed by mechanical peeling; the drying time is 2~24 h. In steps S1 and S5, the inert atmosphere is nitrogen or argon.

[0011] In a preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, in step S2, the polyol compound and the small molecule organic acid compound are miscible with a molar ratio of 1:2 to 2:1, and the polyol compound is ethylene glycol or glycerol.

[0012] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, in step S2, the polyol compound is ethylene glycol and the small molecule organic acid compound is propionic acid.

[0013] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, in step S2, the polyol compound is glycerol and the small molecule organic acid compound is citric acid.

[0014] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, during the leaching reaction in step S3, small molecule organic acid compounds provide H⁺, which disrupts the crystal structure of lithium iron phosphate, allowing lithium ions to dissolve from the lithium iron phosphate crystal lattice in the pretreated cathode powder and enter the composite leaching solution. At the same time, the small molecule organic acid compounds inhibit the hydrolysis of lithium ions. Iron elements form a complex with the small molecule organic acid compounds, and after the complex reaches saturation, an iron-based precipitate is obtained.

[0015] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, no oxidizing agent or reducing agent is used during the leaching reaction in step S3.

[0016] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, in step S4, the amount of carbonation reagent added is 1.0 to 1.2 times the amount theoretically required to convert lithium ions into lithium salt precipitation.

[0017] In a preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, in step S5, the carbon source is one or more of sucrose, glucose, and acetylene black, and the amount added is 3% to 8% of the total mass of the precursor. The dispersant is ethanol or ethylene glycol, and the amount added is 5% to 10% of the total mass of the precursor.

[0018] In the preferred embodiment of the method for recycling and regenerating lithium iron phosphate battery cathode powder described in this invention, during the segmented calcination in step S5: the temperature is first raised to 300~400℃ and held for 2~4 h, then raised to 650~850℃ and held for 4~8 h, with a heating rate of 2~5℃ / min, and the calcination atmosphere is nitrogen or argon.

[0019] This invention uses a polyol-small molecule organic acid composite solvent system to leach lithium iron phosphate cathode powder, achieving efficient leaching of lithium and selective precipitation of iron. The precipitated product is then used to calcine lithium salts to prepare regenerated cathode materials.

[0020] This invention provides a method for recycling and regenerating lithium iron phosphate battery cathode powder, comprising five steps: cathode powder pretreatment, preparation of a polyol-small molecule organic acid composite leaching system, lithium leaching and iron precipitation, lithium precipitation recovery, and preparation of regenerated cathode material. First, retired lithium iron phosphate battery cathode powder is pretreated. Then, a composite leaching system is constructed using polyol compounds (alcohols containing two or more hydroxyl groups, such as ethylene glycol and glycerol) and small molecule organic acid compounds (ascorbic acid, citric acid, malic acid, propionic acid, aspartic acid, or salicylic acid) to simultaneously achieve efficient lithium leaching and selective iron precipitation. The leaching solution is carbonated to precipitate and recover lithium salt. After mixing the iron-based precipitate with the lithium salt, a carbon source and dispersant are added, and regenerated lithium iron phosphate cathode material is prepared through staged calcination.

[0021] This invention constructs a composite leaching system with polyols and small molecule organic acids as the core. It is green and environmentally friendly, with low corrosiveness, and requires no additional oxidants or reducing agents, simplifying the element separation process. It realizes closed-loop recovery of lithium and iron elements, with high resource utilization and excellent electrochemical performance of the regenerated cathode material. The process is mild and the parameters are easy to control, making it suitable for large-scale industrial production. It has good environmental benefits, economic benefits and application prospects.

[0022] This invention provides a method for recycling and regenerating lithium iron phosphate battery cathode powder, comprising the following steps: S1. Positive electrode powder pretreatment: Discharge and disassemble retired lithium iron phosphate batteries to obtain positive electrode sheets; remove aluminum foil from the surface of the positive electrode sheets, crush and sieve to obtain lithium iron phosphate positive electrode powder with a particle size of 100~200 mesh, and dry it in an inert atmosphere of nitrogen or argon for later use. The drying temperature is 80~120℃ and the drying time is 24 h. S2. Preparation of composite leaching system: Polyol compounds and small molecule organic acid compounds are mixed in a molar ratio of 1:5 to 5:1, heated to 40 to 80°C, and stirred for 30 to 60 min to obtain a uniform and transparent liquid, which is a new type of green composite solvent. Polyols have good solubility and stability, and can form a synergistic leaching system with small molecule organic acids to reduce equipment corrosion; small molecule organic acids are small molecule organic acids that have both leaching and complexing effects and can selectively bind to metal ions.

[0023] The optimal molar ratio of polyols to small molecule organic acids is 1:2 to 2:1.

[0024] S3. Lithium leaching and iron precipitation: The pretreated cathode powder is added to the composite leaching solution. The solid-liquid ratio of the cathode powder to the composite leaching solution is 1:20~1:50 g / mL. The leaching conditions are controlled for the reaction: the leaching temperature is 70~120℃, with an optimal temperature of 90~110℃; the stirring rate is 200~500 r / min, with an optimal temperature of 300~400 r / min; and the leaching time is 4~12 h, with an optimal temperature of 4~6 h. The leaching solution and iron-based precipitate are collected after solid-liquid separation. At this point, the lithium leaching rate is ≥99%, and the iron precipitation rate is ≥90%. During the reaction, lithium dissolves from the lithium iron phosphate lattice into the leachate, while iron forms a complex with small-molecule organic acids and gradually precipitates out, forming an iron-based precipitate. After the leaching reaction is completed, solid-liquid separation is performed, and the leachate (containing lithium ions) and the iron-based precipitate are collected separately.

[0025] S4. Lithium precipitation recovery: Add carbonation reagent to the leachate, adjust the pH value to 7-9 and react for 1-3 h to convert lithium ions into lithium salt precipitate. After filtration and washing, dry at 100-120℃ to obtain lithium salt. The carbonation reagent is one or a mixture of sodium carbonate and sodium bicarbonate, and the amount added is 1.0 to 1.2 times the theoretically required amount; S5. Preparation of regenerated cathode material: Iron-based precipitate and lithium salt are mixed at a molar ratio of 1:1 to 1:1.1 (calculated as Fe and Li), carbon source and dispersant are added and ground to obtain a precursor. The mixed precursor is calcined in stages under an inert atmosphere, cooled, crushed and sieved to obtain regenerated lithium iron phosphate cathode material. The carbon source is one or more of sucrose, glucose, and acetylene black, and the amount added is 3% to 8% of the total mass of the precursor. The dispersant is ethanol or ethylene glycol, and the amount added is 5% to 10% of the total mass of the precursor. The segmented calcination parameters are as follows: first, heat to 300~400℃ and hold for 2~4 h, then heat to 650~850℃ and hold for 4~8 h, with a heating rate of 2~5℃ / min, and the calcination atmosphere is nitrogen or argon.

[0026] The initial discharge specific capacity of the regenerated lithium iron phosphate cathode material is ≥155 mAh / g, and the capacity retention rate is ≥90% after 100 cycles.

[0027] In this invention, polyol compounds and small-molecule organic acid compounds form a synergistic leaching system. The mechanism of action is as follows: the small-molecule organic acid compounds provide H⁺, which disrupts the crystal structure of lithium iron phosphate, causing Li⁺ to dissolve; at the same time, the functional groups in the small-molecule organic acid form stable complexes with Fe³⁺. As the reaction proceeds, the complexes gradually precipitate after reaching saturation, achieving selective precipitation of Fe. The polyol compounds not only improve the solubility and system stability of the small-molecule organic acid, but also inhibit the hydrolysis of Li⁺, increase the lithium leaching rate, and reduce the corrosiveness of the system to the equipment, avoiding secondary pollution.

[0028] Compared with existing technologies, the leaching system of this invention does not require the addition of additional oxidants or reducing agents. It can simultaneously achieve efficient leaching of lithium and selective precipitation of iron through the synergistic effect of polyol-small molecule organic acid composite solvent, simplifying the element separation process. At the same time, the iron-based precipitation and lithium salt are used in synergy for the preparation of regenerated cathode materials, realizing the closed-loop recovery of lithium and iron elements, greatly improving resource utilization and reducing recycling costs.

[0029] The present invention has the following advantages: (1) The leaching system is green and environmentally friendly: the polyol-small molecule organic acid composite system is used to replace the traditional strong acid leaching agent. It has weak corrosiveness, low equipment requirements, and no need to add additional oxidants or reducing agents. This reduces acid consumption and wastewater treatment costs, avoids secondary pollution, and conforms to the green and environmentally friendly industrial development trend.

[0030] (2) Efficient and simple element separation: Through the synergistic effect of polyols and small molecule organic acids, the efficient leaching of lithium (leaching rate ≥99%) and selective precipitation of iron (precipitation rate ≥90%) are achieved simultaneously. No complicated impurity removal process is required, which simplifies the recycling process and improves production efficiency.

[0031] (3) Closed-loop recycling of resources: The lithium salt obtained by iron-based precipitation and lithium precipitation is used in combination to prepare regenerated lithium iron phosphate cathode materials, realizing the full utilization of lithium, iron and phosphorus elements, avoiding the waste of iron elements, and constructing a closed-loop recycling system of "leaching-separation-regeneration", which significantly improves the resource utilization rate.

[0032] (4) Excellent performance of recycled products: Through the optimization of the segmented calcination process, the recycled lithium iron phosphate cathode material has a complete crystal structure and excellent electrochemical performance. It can be reused in the production of power batteries or energy storage equipment, realizing the recycling of resources and reducing the raw material dependence of the power battery industry.

[0033] (5) Strong process feasibility: The entire process is mild, the parameters are easy to control, the equipment investment is moderate, it is suitable for large-scale industrial production, and has good industrial application prospects and economic benefits. Attached Figure Description

[0034] Figure 1 A flowchart of a method for recycling and regenerating lithium iron phosphate battery cathode powder; Figure 2 Example 1: Schematic diagram of metal leaching and precipitation efficiency for a method of recovering and regenerating lithium iron phosphate battery cathode powder; Figure 3 XRD pattern of lithium iron phosphate cathode material for a method of recycling and regenerating lithium iron phosphate battery cathode powder; Figure 4 This is a schematic diagram of the electrochemical performance of a regenerated lithium iron phosphate battery, which is a method for recycling and regenerating positive electrode powder of a lithium iron phosphate battery. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0036] like Figure 1 As shown, a method for recycling and regenerating lithium iron phosphate battery cathode powder includes the following steps: S1. Positive electrode powder pretreatment: The retired lithium iron phosphate battery is fully discharged (voltage drops to 0V), and the positive electrode sheet is obtained after disassembly; the aluminum foil on the surface of the positive electrode sheet is removed by mechanical peeling, and the remaining positive electrode active material is crushed and passed through a 150-mesh sieve to obtain lithium iron phosphate positive electrode powder; the positive electrode powder is placed in a nitrogen atmosphere and dried at 80°C for 4 hours to remove moisture and impurities, and is ready for use.

[0037] S2. Preparation of composite leaching system: Mix ethylene glycol and propionic acid compound at a molar ratio of 2:1, heat to 50℃, and stir evenly to obtain composite solution.

[0038] S3. Lithium leaching and iron precipitation: Pretreated lithium iron phosphate cathode powder was added to the composite leaching solution at a solid-liquid ratio of 1:30 g / mL. The leaching temperature was controlled at 100℃, the stirring rate at 350 r / min, and the leaching time at 6 h. After the reaction, solid-liquid separation was performed by vacuum filtration, and the leaching solution and iron-based precipitate were collected separately. The lithium leaching rate was 99.5%, and the iron precipitation rate was 93.8%.

[0039] S4. Lithium precipitation recovery: Add sodium carbonate (1.1 times the theoretical amount) to the leachate, adjust the pH of the system to 8, stir the reaction for 2 h to convert lithium ions into lithium salt precipitate; after the reaction is completed, filter, wash 3 times with deionized water, and dry at 110℃ for 3 h to obtain lithium salt product.

[0040] S5. Preparation of regenerated cathode material: Iron-based precipitate and lithium salt are mixed at a molar ratio of Fe:Li = 1:1.05. Sucrose (5% of the total mass of the mixed precursor) and ethanol (8% of the total mass of the mixed precursor) are added and ground for 30 min until homogeneous to obtain a mixed precursor. The mixed precursor is placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 3℃ / min, held for 3 h, then heated to 750℃ and held for 6 h. After cooling, it is pulverized and passed through a 200-mesh sieve to obtain regenerated lithium iron phosphate cathode material.

[0041] The electrochemical performance test results of the recycled lithium iron phosphate cathode material are as follows: Figures 2-4 As shown, Figure 2 As shown, in this embodiment, the lithium leaching rate is 99.5%, and the iron precipitation efficiency is 93.8%; Figure 3 As shown, the regenerated lithium iron phosphate battery has a spectrum similar to that of the standard. Figure 1 This example has been successfully synthesized. Figure 4 The specific capacity of the regenerated lithium iron phosphate battery in this embodiment after 1, 20, 40, 60, 80, and 100 charge-discharge cycles was measured. The initial discharge specific capacity of this embodiment was 165 mAh / g, and the capacity retention rate after 100 cycles was 92.7%. It can be seen that this embodiment has good electrochemical performance, high charge-discharge capacity, and good rate performance, which can meet the requirements of power battery use. Example 2

[0042] like Figure 1 As shown, a method for recycling and regenerating lithium iron phosphate battery cathode powder includes the following steps: S1. Positive electrode powder pretreatment: The retired lithium iron phosphate battery is fully discharged (voltage drops to 0V), and the positive electrode sheet is obtained after disassembly; the aluminum foil on the surface of the positive electrode sheet is removed by chemical stripping (immersion in dilute sulfuric acid), and the remaining positive electrode active material is crushed and passed through a 100-mesh sieve to obtain lithium iron phosphate positive electrode powder; the positive electrode powder is placed in an argon atmosphere and dried at 100℃ for 3 h to remove moisture and impurities, and is ready for use.

[0043] S2. Preparation of composite leaching system: Glycerol and citric acid compound are mixed at a molar ratio of 2:1, heated to 60℃, and stirred evenly to obtain composite solution.

[0044] S3. Lithium leaching and iron precipitation: Pretreated lithium iron phosphate cathode powder was added to the composite leaching solution at a solid-liquid ratio of 1:40 g / mL. The leaching temperature was controlled at 100℃, the stirring rate at 400 r / min, and the leaching time at 6 h. After the reaction, solid-liquid separation was performed by centrifugal filtration, and the leaching solution and iron-based precipitate were collected separately. The lithium leaching rate was 99.1%, and the iron precipitation rate was 92.8%.

[0045] S4. Lithium precipitation recovery: Add sodium bicarbonate (1.2 times the theoretical amount) to the leachate, adjust the pH of the system to 9, stir the reaction for 1.5 h to convert lithium ions into lithium salt precipitate; after the reaction is completed, filter, wash twice with deionized water, and dry at 120℃ for 2 h to obtain lithium salt product.

[0046] S5. Preparation of Regenerated Cathode Material: Iron-based precipitate and lithium salt are mixed at a molar ratio of Fe:Li = 1:1.1. Acetylene black (3% of the total mass of the mixed precursor) and ethylene glycol (5% of the total mass of the mixed precursor) are added and ground for 40 min until homogeneous to obtain a mixed precursor. The mixed precursor is placed in an argon atmosphere and heated to 400℃ at a heating rate of 5℃ / min, held for 2 h, then heated to 800℃ and held for 4 h. After cooling, it is pulverized and passed through a 200-mesh sieve to obtain the regenerated lithium iron phosphate cathode material.

[0047] Electrochemical performance tests were conducted on the regenerated lithium iron phosphate cathode material. The results showed that its initial discharge specific capacity was 161 mAh / g, and its capacity retention rate was 93.8% after 100 cycles, indicating excellent electrochemical performance.

[0048] Comparative Example 1 Citric acid system was used as the leaching agent, and the other steps were exactly the same as in Example 2, as follows: The leaching system had a citric acid concentration of 2 mol / L, and the leaching conditions were the same as in Example 2. The lithium leaching rate was 69.3%, and the iron precipitation rate was 60.5%. The initial discharge specific capacity of the regenerated lithium iron phosphate cathode material was 112 mAh / g, and the capacity retention rate after 100 cycles was 54.1%.

[0049] The results show that the leaching effect of the single small molecule organic acid system is much lower than that of the polyol-small molecule organic acid composite leaching system of the present invention, and the performance of the recycled material is poor. This indicates that the synergistic effect of polyol and small molecule organic acid can significantly improve the lithium leaching rate and iron precipitation rate, and optimize the performance of the recycled material.

[0050] Comparative Example 2 A sulfuric acid-hydrogen peroxide system was used as the leaching agent (sulfuric acid concentration 2 mol / L, hydrogen peroxide added at 5% of the cathode powder mass), and the other steps were exactly the same as in Example 1. The lithium leaching rate was 98.7%, and the iron leaching rate was 99.2%. Additional sodium hydroxide was needed to adjust the pH value for iron ion removal, after which the lithium recovery rate decreased to 95.1%. The results show that while the traditional strong acid system can achieve efficient lithium leaching, it also leaches iron simultaneously, requiring additional impurity removal, making the process cumbersome, and reducing the lithium recovery rate. Furthermore, the system is highly corrosive, resulting in high wastewater treatment costs. Overall, its performance is inferior to the polyol-small molecule organic acid composite leaching system of this invention.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for recycling and regenerating lithium iron phosphate battery cathode powder, characterized in that: Includes the following steps: S1. Discharge, disassemble and separate retired lithium iron phosphate batteries to obtain positive electrode sheets, remove aluminum foil from the surface of the positive electrode sheets, crush and sieve to obtain lithium iron phosphate positive electrode powder with a particle size of 100~200 mesh, and dry it at 80~120℃ under an inert atmosphere to obtain pretreated positive electrode powder. S2. Polyol compounds and small molecule organic acid compounds are mixed in a molar ratio of 1:5 to 5:1, heated, and stirred at 40 to 80°C for 30 to 60 min to obtain a composite leachate; The polyol compounds are alcohols containing two or more hydroxyl groups in their molecules, and the small molecule organic acid compounds are any one of the following: ascorbic acid, citric acid, malic acid, formic acid, acetic acid, propionic acid, butyric acid, and isobutyric acid; S3. The pretreated cathode powder is added to the composite leaching solution at a solid-liquid ratio of 1:20~1:50 g / mL to dissolve lithium and precipitate iron, resulting in lithium leaching solution and iron-based precipitate. The leaching temperature is 70~120℃, the stirring rate is 200~500 r / min, and the leaching time is 4~12 h. After the leaching reaction is completed, solid-liquid separation is performed and the lithium element leaching solution and the iron-based precipitate are collected separately. S4. Add a carbonation reagent to the lithium element leaching solution, adjust the pH value to 7-9 and react for 1-3 h to convert lithium ions into lithium salt precipitate. After filtration and washing, dry at 100-120℃ to obtain lithium salt. The carbonation reagent is one or a mixture of sodium carbonate and sodium bicarbonate; S5. The iron-based precipitate and the lithium salt are mixed at a Fe:Li molar ratio of 1:1 to 1:1.1 to obtain a precursor. A carbon source and a dispersant are added to the precursor and then ground to obtain a mixed precursor. The mixed precursor is calcined in stages under an inert atmosphere, and then cooled, crushed and sieved to obtain a regenerated lithium iron phosphate cathode material.

2. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S1, the retired lithium iron phosphate battery is discharged to 0V, and the aluminum foil on the surface of the positive electrode is removed by mechanical peeling; the drying time is 2~24 h. In steps S1 and S5, the inert atmosphere is nitrogen or argon.

3. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S2, the polyol compound and the small molecule organic acid compound are miscible and have a molar ratio of 1:2 to 2:1, and the polyol compound is ethylene glycol or glycerol.

4. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S2, the polyol compound is ethylene glycol, and the small molecule organic acid compound is propionic acid.

5. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S2, the polyol compound is glycerol, and the small molecule organic acid compound is citric acid.

6. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S3, during the leaching reaction, the small molecule organic acid compound provides H⁺, which disrupts the crystal structure of lithium iron phosphate, allowing lithium ions to dissolve from the lithium iron phosphate crystal structure in the pretreated cathode powder and enter the composite leaching solution. At the same time, the small molecule organic acid compound inhibits the hydrolysis of lithium ions. Iron element forms a complex with the small molecule organic acid compound, and after the complex reaches saturation, it precipitates to obtain the iron-based precipitate.

7. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S3, during the leaching reaction, neither oxidizing nor reducing agents are used.

8. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S4, the amount of the carbonation reagent added is 1.0 to 1.2 times the amount theoretically required to convert lithium ions into lithium salt precipitation.

9. The method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S5, the carbon source is one or more of sucrose, glucose, and acetylene black, and the amount added is 3% to 8% of the total mass of the precursor. The dispersant is ethanol or ethylene glycol, and the amount added is 5% to 10% of the total mass of the precursor.

10. A method for recycling and regenerating lithium iron phosphate battery cathode powder according to claim 1, characterized in that: In step S5, during segmented calcination: first, raise the temperature to 300~400℃ and hold for 2~4 h, then raise the temperature to 650~850℃ and hold for 4~8 h, with a heating rate of 2~5℃ / min, and the calcination atmosphere is nitrogen or argon.

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