Method for recovering lithium source and iron source from positive plate of lithium iron phosphate battery

Abstract

The invention discloses a method for recovering a lithium source and an iron source in a lithium iron phosphate battery positive plate, which comprises the following steps of: cutting a dried positive plate material into pieces, putting into a tubular furnace, calcining at high temperature, crushing, sieving and separating aluminum foil pieces to obtain lithium iron phosphate positive fine powder; the method comprises the following steps: mixing the lithium iron phosphate positive electrode fine powder with an acidic ingredient, separating and deslagging to obtain a filtrate, dropwise adding an H2O2 solution, adding a NaOH solution to generate a precipitate, and carrying out suction filtration to obtain a residue Fe (OH) 3 colloid and a filtrate Li (OH) solution; and further treating the separated slag by dissolving with dilute sulfuric acid, dropwise adding an ammonium phosphate solution into the generated ferric sulfate salt solution, and adding ammonia water NH3.H2O to adjust the pH value to be 2-3 to form ferric phosphate precipitate, thereby obtaining ferric phosphate powder. And introducing CO2 gas into the filtrate for 2 hours to form white emulsion, thereby obtaining the lithium carbonate. Recycling of the lithium source and the iron source of the waste lithium iron phosphate battery has important significance and wide prospects in the aspects of environmental protection, economy and resource sustainability.

Description

Technical Field

[0001] The present invention belongs to the technical field of mineral processing and metallurgy, and particularly relates to a method for sustainable recovery of lithium source and iron source from waste lithium iron phosphate batteries. Background Art

[0002] According to statistics, the retirement volume of power batteries in China reached 20.2 GWh in 2024, and the proportion of lithium iron phosphate batteries was about 74.6%. The actual recovered amount of waste lithium iron phosphate battery materials in China is expected to be 300,000 tons. It is expected that by 2030, the retirement volume of lithium iron phosphate batteries will account for 60% of all retired batteries. Therefore, the sustainable recovery of waste lithium iron phosphate batteries has broad application prospects.

[0003] During the charge-discharge cycle process, lithium ions in the lithium iron phosphate (LiFePO4) cathode material will continuously intercalate and deintercalate, resulting in irreversible loss of some lithium ions. For example, lithium ions react with solvent molecules in the electrolyte to form lithium salts, or stable lithium compounds are formed on the surface of the cathode material, which can no longer participate in the normal charge-discharge reaction, thus causing a decrease in battery capacity. In addition, the crystal structure of lithium iron phosphate may undergo irreversible phase transformation during long-term charge-discharge processes, changing from the olivine structure to other structures, resulting in blocked diffusion channels for lithium ions, decreased intercalation and deintercalation capabilities, and affecting the battery capacity. During the use of the battery, iron elements in the cathode material will also dissolve into the electrolyte. With the loss of iron ions, the content of active substances in the cathode material decreases, leading to battery capacity attenuation.

[0004] Waste lithium iron phosphate batteries contain valuable metal elements such as lithium, iron, and phosphorus. If not properly treated, these elements may cause serious environmental pollution. Heavy metals in the battery and organic solvents in the electrolyte may seep into the soil and water bodies, endangering the ecological environment and human health. Through effective recovery technologies, these pollution problems can be avoided, and at the same time, the pressure on the exploitation of natural resources can be reduced.

[0005] Lithium and iron are important strategic resources, especially lithium, which is widely used in fields such as batteries, ceramics, and glass. With the rapid development of the new energy vehicle market, the demand for lithium iron phosphate batteries has increased significantly, and the supply pressure of lithium resources has also increased accordingly. By recovering lithium and iron from waste lithium iron phosphate batteries, the problem of resource shortage can be alleviated, and the production cost can be reduced. In addition, the recovered metal elements can be reused to produce new batteries or other products, realizing the recycling of resources and bringing considerable economic benefits to enterprises.

[0006] At present, the recycling technology of waste lithium iron phosphate batteries has made significant progress. Through crushing and sorting technology, high-purity black powder can be obtained, and the recovery rate of electrode powder, copper foil, aluminum foil and other components can reach more than 98%. More advanced recycling methods, such as charged crushing under anaerobic and closed conditions, low-temperature volatilization, wind separation, high-temperature pyrolysis, etc., can achieve full component recovery of waste lithium batteries, with high resource utilization and high product purity. The application of these technologies depends on the purification process of iron and lithium sources in waste lithium iron phosphate batteries. Once a breakthrough is made, the process flow will be greatly shortened, which is very suitable for large-scale recycling and treatment.

[0007] Recycling lithium and iron from used lithium iron phosphate batteries can reduce my country's external dependence on these resources and enhance its independent resource security capabilities. This is of great significance for ensuring the security of national strategic resources and promoting the sustainable development of the new energy industry.

[0008] In summary, the recycling of lithium and iron sources from waste lithium iron phosphate batteries not only has significant environmental significance, but also brings considerable economic benefits and plays an important role in resource sustainability. With the continuous advancement of technology and the gradual maturity of the market, the recycling and reuse of lithium iron phosphate batteries will usher in a broader development prospect and lay a solid foundation for the green future of the new energy industry.

[0009] In the traditional solid phase method of lithium iron phosphate batteries, the combination of lithium carbonate and iron phosphate is widely used because of its economy and ease of operation. Therefore, we use sustainable recycling technology to reuse the iron source in the waste lithium iron phosphate batteries in the form of iron phosphate, and at the same time recycle the lithium source in the battery in the form of lithium carbonate. Compared with traditional mining and smelting methods, the wet chemical method combined with the solid phase chemical synthesis method to recover the iron and lithium sources in the waste lithium iron phosphate positive electrode sheets can significantly reduce energy consumption. For example, the traditional lithium extraction method requires a lot of energy to mine and smelt lithium ore, while recycling the lithium in the waste lithium iron phosphate positive electrode sheets can greatly reduce the energy consumption in this process.

[0010] The main chemical reaction equations involved in each step of the process are:

[0011] The chemical reaction formulas involved in step 2 are:

[0012] LiFePO4+Na2S2O8→FePO4+Li2SO4+Na2SO4

[0013] The chemical reaction formulas involved in step 5 are:

[0014] Fe3(PO4)2+H2O2+H3PO4→3FePO4+2H2O

[0015] FePO4 + 3NaOH → Fe(OH)3↓ + Na3PO4

[0016] Li2SO4 + 2NaOH → 2LiOH + Na2SO4

[0017] The chemical reaction equations involved in Step Six are as follows:

[0018] 2Fe(OH)3 + 3H2SO4 → Fe2(SO4)3 + 6H2O

[0019] Fe2(SO4)3 + 2(NH4)3PO4 → 2FePO4↓ + 3(NH4)2SO4

[0020] The chemical reaction equations involved in Step Seven are as follows:

[0021] 2LiOH + CO2 → Li2CO3↓ + H2O

[0022] In summary, the present invention provides a method that uses waste lithium iron phosphate cathode sheets as raw materials. Through the wet chemical method, elements such as lithium, iron, and phosphorus in the waste lithium iron phosphate cathode sheets can be dissolved out, and then useful materials such as lithium iron phosphate can be re-synthesized through the solid-phase chemical synthesis method, realizing the recycling of resources. This process can effectively alleviate the shortage of resource supply such as lithium and iron. Especially for lithium resources, their demand in the battery industry is huge. Recycling and utilization can reduce the dependence on primary lithium ore and lower the raw material procurement cost. In addition, if waste lithium iron phosphate cathode sheets are discarded randomly, they will cause serious environmental pollution. Through recycling and treatment, these waste materials can be transformed into useful resources, reducing environmental pollution.

[0023] By recycling the iron source and lithium source in waste lithium iron phosphate cathode sheets, a more stable and lower-cost raw material supply can be provided for battery manufacturers, promoting the sustainable development of the battery industry, highly conforming to the national environmental protection policies and sustainable development strategies, and creating more economic and environmental benefits for society. Summary of the Invention

[0024] The present invention adopts a process flow of wet chemistry + solid-phase chemical synthesis to recover the iron source and lithium source from waste lithium iron phosphate batteries. A method for continuously recovering the lithium source and iron source from waste lithium iron phosphate batteries, characterized by including the following steps:

[0025] Step One: Crush the waste lithium iron phosphate battery under anaerobic and airtight conditions, remove the outer shell, then strip the positive and negative electrode sheets and the separator in the battery, and place the stripped positive electrode sheet in an oven at 60 - 65°C for drying for 48 - 72 hours to remove the low-temperature volatile organic solvents in the battery;

[0026] Step 2: To further remove the carbon materials and organic solvents in the cathode material, the dried cathode sheet is cut into pieces and placed in a tube furnace, and calcined at a high temperature of 500 - 510 °C for 2 - 3 h in an argon atmosphere. The heating rate is 5 - 8 °C / min. Then, it is crushed at a speed of 25000 r / min for 30 min using a household small crusher, and the aluminum foil is separated by sieving (above 200 mesh) to obtain the lithium iron phosphate cathode fine powder;

[0027] Step 3: Take a certain amount (5 g) of the lithium iron phosphate cathode fine powder and mix it evenly with the acidic ingredients in different mass ratios, and then place it in a muffle furnace and calcine at 700 - 900 °C with a heating rate of 5 - 8 °C / min for 5 - 6 h;

[0028] Step 4: Add 100 mL of deionized water to the calcined product after taking it out, soak it for 30 min, ultrasonicate for 2 h, heat and stir in a water bath at 80 - 85 °C for 30 min, and then filter it while it is hot for multiple times to separate the residue and obtain the filtrate;

[0029] Step 5: Under the condition of heating and stirring at 80 - 85 °C, use a pipette to drop 5 drops of H2O2 solution (0.3 - 0.5% mass concentration) into the filtrate, aiming to deeply oxidize the Fe in the filtrate, continue stirring for 10 min, and then gradually add 8 - 10 mol / L NaOH solution to adjust the pH = 6 - 7. Reddish-brown flocculent precipitates are formed and filtered for multiple times; 2+ Step 6: Further process the filter residue separated in Step 5. Under the condition of heating and stirring at 80 - 85 °C, dissolve the filter residue with 20 mL of 8 - 10% mass concentration of dilute sulfuric acid to form a ferric sulfate solution, and then slowly drop 50 mL of 0.5 - 1.0 mol / L ammonium phosphate ((NH4)3PO4) solution while continuously stirring, and adjust the pH = 2 - 3 by adding 8 - 10 mol / L ammonia water (NH3·H2O) to facilitate the formation of iron phosphate precipitate. Filter for multiple times, wash, dry at 60 - 65 °C for 3 - 4 h, grind, and then calcine in a muffle furnace at 500 - 550 °C for 3 - 4 h to obtain the iron source iron phosphate;

[0030] Step 7: Further process the filtrate separated in Step 5. Pass CO2 gas into it at a flow rate of 20 - 25 mL / min for 1 - 2 h to form a white emulsion, filter for multiple times, wash for multiple times, dry in an oven at 60 - 65 °C for 24 - 48 h to obtain a white precipitate, grind, and then calcine in a muffle furnace at 500 - 700 °C for 3 - 4 h to obtain the recycled lithium carbonate cathode powder.

[0031] Step 8: Further process the filtrate separated in Step 5. Pass CO2 gas into it at a flow rate of 20 - 25 mL / min for 1 - 2 h to form a white emulsion, filter for multiple times, wash for multiple times, dry in an oven at 60 - 65 °C for 24 - 48 h to obtain a white precipitate, grind, and then calcine in a muffle furnace at 500 - 700 °C for 3 - 4 h to obtain the recycled lithium carbonate cathode powder.

[0032] The specific content is as follows: Sodium persulfate is used as the acidic ingredient. By changing the types of acidic ingredients (sodium persulfate, sodium bisulfate, or ammonium sulfate), the acidic ratios (1:1, 1:2, 1:3, and 1:4), and the calcination temperatures (700 °C, 800 °C, and 900 °C), iron phosphate and lithium carbonate are obtained respectively. The effect of this process is measured based on the recovery rates of iron phosphate and lithium carbonate, as well as the purities of iron phosphate and lithium carbonate. Preferably, sodium persulfate is used as the acidic ingredient, the mass ratio of lithium iron phosphate to sodium persulfate is 1:2, the calcination temperature is 900 °C, and the recovery rates of the finally obtained iron phosphate and lithium carbonate can reach 95.3% and 94.2% respectively, and the purities of iron phosphate and lithium carbonate can reach 98.53% and 99.68% respectively, meeting the purity standards of battery-grade lithium carbonate (according to the national standard GB / T 11075-2013 "Lithium Carbonate" and the industry standard YS / T 582-2023 "Battery-grade Lithium Carbonate", the purity requirement for battery-grade lithium carbonate is that the lithium carbonate content is not less than 99.5%) and battery-grade iron phosphate standards (according to the industry standard HG / T 4701-2021 "Iron Phosphate for Batteries", the purity requirement for battery-grade iron phosphate should be not less than 98.5%).

[0033] The object of the present invention can be achieved by the following technical solutions:

[0034] A method for sustainable recovery of lithium source and iron source from waste lithium iron phosphate batteries, comprising the following steps:

[0035] Step 1, pretreatment of waste lithium iron phosphate batteries, the steps are as follows:

[0036] First, the waste lithium iron phosphate batteries are crushed under anaerobic and airtight conditions to remove the outer shell, and then the positive and negative electrode plates and the separator in the battery are peeled off. The peeled positive electrode plate is placed in an oven at 60 - 65 °C and dried for 48 - 72 h to remove the low-temperature volatile organic solvents in the battery;

[0037] Step 2, calcination of the lithium iron phosphate positive electrode plate in an inert gas, the steps are as follows:

[0038] To further remove the organic solvents in the positive electrode material, the dried positive electrode plate is cut into pieces and placed in a tube furnace, and calcined at a high temperature of 500 - 510 °C for 2 - 3 h in an argon atmosphere, with a heating rate of 5 - 8 °C / min. Then, it is crushed at a speed of 25000 r / min for 30 min using a household small crusher, and the aluminum foil is separated by sieving (more than 200 meshes) to obtain the lithium iron phosphate positive electrode fine powder;

[0039] Step 3, mixed calcination of the lithium iron phosphate positive electrode fine powder and the acidic ingredient, the steps are as follows:

[0040] Take a certain amount (5 g) of lithium iron phosphate cathode fine powder and mix it evenly with the acidic ingredient in different mass ratios, and then place it in a muffle furnace and calcine it at 700 - 900 °C with a heating rate of 5 - 8 °C / min for 5 - 6 h;

[0041] Step 4, mixing and calcining the lithium iron phosphate cathode fine powder and the acidic ingredient, the steps are as follows:

[0042] Add 100 mL of deionized water to the calcined product after taking it out, soak it for 30 min in sequence, ultrasonicate for 2 h, heat and stir in a water bath at 80 - 85 °C for 30 min, and then perform multiple hot filtration while it is hot to separate the residue and obtain the filtrate;

[0043] Step 5, iron precipitation, the steps are as follows:

[0044] Under the condition of heating and stirring at 80 - 85 °C, use a pipette to drop 5 drops of H2O2 solution (0.3 - 0.5% mass concentration) into the filtrate, the purpose is to deeply oxidize the Fe in the filtrate 2+ Get deep oxidation, continue to stir for 10 min, and then gradually add 8 - 10 mol / L NaOH solution to adjust the pH = 6 - 7, and reddish-brown flocculent precipitation will form, and perform multiple filtration;

[0045] Step 6, preparation of iron phosphate, the steps include:

[0046] 1) Further process the filter residue separated in step 5 as follows: under the condition of heating and stirring at 80 - 85 °C, dissolve the filter residue with 20 mL of 8 - 10% mass concentration of dilute sulfuric acid to generate a ferric sulfate salt solution, and then slowly drop 50 mL of 0.5 - 1.0 mol / L ammonium phosphate (NH4)3PO4 solution;

[0047] 2) Adjust the pH = 2 - 3 to the above solution by adding ammonia water (NH3·H2O) with a molar concentration of 8 - 10 mol / L to facilitate the formation of iron phosphate precipitation, perform multiple filtration, washing, dry at 60 - 65 °C for 3 - 4 h, grind, and then calcine at 500 - 550 °C in a muffle furnace for 3 - 4 h to obtain iron phosphate;

[0048] Step 7, preparation of lithium carbonate, the steps include:

[0049] 1) Further process the filtrate separated in step 5 as follows: pass CO2 gas into it at a flow rate of 20 - 25 mL / min for 1 - 2 h to form a white emulsion, perform multiple filtration, multiple washing, and dry in an oven at 60 - 65 °C for 24 - 48 h to obtain a white precipitate;

[0050] 2) Grind and then calcine at 500 - 700 °C in a muffle furnace for 3 - 4 h to obtain the recycled lithium carbonate cathode powder.

[0051] The described lithium iron phosphate battery comes from an electric vehicle repair shop in Xixia District, Yinchuan City. According to ICP-OES detection, the mass fractions of various elements in the positive electrode sheet of the lithium iron phosphate battery are as follows: the Li content is 5.161 wt.%; the Fe content is 33.849 wt.%; the P content is 20.248 wt.%; the F content is 4.202 wt.%; the Na content is 0.070 wt.%; the Al content is 0.016 wt.%; the Si content is 0.057 wt.%; the S content is 0.107 wt.%; the Ca content is 0.041 wt.%; the Ti content is 0.221 wt.%; the Mn content is 0.014 wt.%; the Ni content is 0.007 wt.%; the As content is 0.001 wt.%; the Rb content is 0.004 wt.%; the Zr content is 0.016 wt.%; the Pb content is 0.015 wt.%. The carbon content measured by thermogravimetric analysis is about 34.431 wt.%, so the other undetected components account for about 1.570 wt.% (the other components include one or more of K, Cr, Y, Mo, Cu, Nd, Co, Nb, Bi, Au, Se, Ge, Br).

[0052] The described waste lithium iron phosphate battery is calcined in an argon atmosphere at 500 °C in a tubular furnace, and the mass fractions of various elements in the fine powder of the positive electrode of the lithium iron phosphate battery obtained by grinding are as follows: the Li content is 4.588 wt.%; the Fe content is 23.021 wt.%; the P content is 0.3123 wt.%; the Li content is 5.088 wt.%; the Fe content is 33.721 wt.%; the P content is 19.3123 wt.%; the F content is 1.7166 wt.%; the Na content is 0.0506 wt.%; the Al content is 0.016 wt.%; the Si content is 0.056 wt.%; the S content is 0.041 wt.%; the Ca content is 0.040 wt.%; the Ti content is 0.191 wt.%; the Mn content is 0.011 wt.%; the Ni content is 0.006 wt.%; the As content is 0.001 wt.%; the Rb content is 0.003 wt.%; the Zr content is 0.015 wt.%; the Pb content is 0.015 wt.%. The carbon content measured by thermogravimetric analysis is about 34.273 wt.%, and the other undetected components account for about 5.4435 wt.% (the other components include one or more of K, Cr, Y, Mo, Cu, Nd, Co, Nb, Bi, Au, Se, Ge, Br).

[0053] Further, 5.0 g of the lithium iron phosphate positive electrode powder in step three is weighed.

[0054] Further, the weight ratios of the lithium iron phosphate positive electrode powder to the acidic ingredients in step three are 1:1, 1:2, 1:3, and 1:4 respectively.

[0055] Furthermore, the lithium iron phosphate positive electrode sheet in step three is mixed with the acidic ingredients and then placed in a muffle furnace for calcination at 700° C., 800° C. and 900° C. for 5-6 hours.

[0056] Furthermore, in the step three, the acidic ingredient is one or more of sodium persulfate, sodium bisulfate or ammonium sulfate.

[0057] Furthermore, the "multiple filtrations" in steps 3 to 7 refer to filtration with deionized water at least twice, with the amount of water used each time being 950-1050 mL.

[0058] Furthermore, in the step three, the mass ratio of the lithium iron phosphate positive electrode fine powder and the acidic ingredients uniformly mixed is 1.0:(1.0-4.0), and after calcination at 900°C in a muffle furnace, the lithium iron phosphate reacts with sodium persulfate to generate iron phosphate and lithium sulfate.

[0059] Furthermore, in step 5, hydrogen peroxide is used to oxidize the Fe 2+ Get deep oxidation, adjust pH=6-7, add NaOH to form iron hydroxide

[0060] Shen

[0061] The precipitate and the unreacted lithium sulfate solution are separated by suction filtration.

[0062] Furthermore, in the step 5, NaOH solution is added dropwise to the lithium sulfate filtrate, and lithium sulfate reacts with NaOH to form LiOH.

[0063] Furthermore, in the step 6, the iron hydroxide precipitate separated by suction filtration is dissolved in the filter residue with dilute sulfuric acid to generate iron sulfate;

[0064] Furthermore, in step 6, in order to convert sulfate into phosphate, iron sulfate is first precipitated with ammonium phosphate, and the pH is adjusted to 2-3 with ammonia water to form iron phosphate precipitation;

[0065] Furthermore, in step seven, lithium hydroxide is ultimately converted into lithium carbonate, and CO2 gas needs to be introduced into the lithium hydroxide solution for 1-2 hours. When the white emulsion is no longer generated, the introduction of CO2 is stopped to prevent excess CO2 from causing the production of lithium bicarbonate byproducts.

[0066] Applying the technical solution of the present invention, first, the waste lithium iron phosphate battery is crushed under anaerobic and airtight conditions. The stripped positive electrode sheet is dried and then calcined inertly to burn off the residual moisture, carbon materials, and organic solvents. After mixing with acidic ingredients, it is placed in a muffle furnace for secondary calcination to transform the solid solution phase in the positive electrode material into a fusible salt phase, such as iron phosphate and lithium carbonate, so as to effectively separate the two, which is beneficial to the subsequent purification process. Iron precipitation is achieved through the "acid dissolution + deep oxidation" process, and then iron hydroxide is transformed into iron phosphate. In addition, the "CO2" lithium precipitation process is used for lithium hydroxide to generate lithium carbonate, thus achieving a high degree of separation of the iron source and the lithium source. Finally, the test effect of this process is measured by the dual indicators of "the recovery rates of iron phosphate and lithium carbonate" and "the product purities of iron phosphate and lithium carbonate". Among them, the "product purity of iron phosphate" refers to the chemical composition analysis result of the iron phosphate product (the mass ratio obtained from the X-ray fluorescence spectrometry analysis result, wt.%). According to the industry standard HG / T 4701-2021 "Iron Phosphate for Batteries" (the purity requirement for battery-grade iron phosphate should not be less than 98.5%), it is used to test whether the iron phosphate extracted by this process meets the standard. At the same time, according to the industry standard YS / T 582-2023 "Battery-Grade Lithium Carbonate" (the purity requirement for battery-grade lithium carbonate is that the lithium carbonate content is not less than 99.5%), it is also used to test whether the lithium carbonate extracted by this process meets the standard. The process flow of lithium and iron extraction from waste lithium iron phosphate batteries of the present invention is simple and convenient to operate. Finally, the recovery rates of iron phosphate and lithium carbonate can reach 95.3% and 94.2% respectively, and the purities of iron phosphate and lithium carbonate can reach 98.53% and 99.68% respectively.

[0067] The technology of the present invention for continuously recycling iron sources and lithium sources from waste lithium iron phosphate batteries can greatly reduce waste pollution. By disassembling and processing them through safe recycling technologies, it can effectively avoid the environmental damage caused by these harmful substances. Iron and lithium are key raw materials for lithium iron phosphate batteries. Recycling these resources can reduce the dependence on natural mineral resources and reduce the ecological damage during the mining process. Large-scale recycling of waste batteries can reduce carbon emissions during the production process. The recycled iron sources and lithium sources can be reused as raw materials for battery production, reducing the dependence on imported raw materials, thereby reducing production costs. The development of the waste battery recycling industry will attract social attention to resource recycling and environmental protection, improve the public's environmental awareness, and promote the formation of a green development concept throughout society.

[0068] The large-scale implementation of the technology for continuously recycling iron sources and lithium sources from waste lithium iron phosphate batteries has significant environmental, economic, and social benefits, and is of great significance for promoting resource recycling, the development of the new energy industry, and achieving sustainable development goals.

[0069] The beneficial effects of the present invention:

[0070] 1. By crushing waste lithium iron phosphate batteries under anaerobic and airtight conditions, the risk of explosion is reduced.

[0071] 2. The lithium iron phosphate cathode sheets are calcined at high temperature in an inert atmosphere. On the one hand, the residual carbon is removed. On the other hand, part of the organic electrolyte solution and binder in the lithium iron phosphate cathode sheets are removed. At the same time, the olivine structure of lithium iron phosphate is also destroyed, making the insoluble phase easy to transform into a soluble phase.

[0072] 3. Since the iron in lithium iron phosphate (LiFePO4) is divalent (Fe 2+ ). The iron ions (Fe 2+ ) of lithium iron phosphate with an olivine structure are located at the center of the crystal lattice and form an FeO6 octahedral structure with oxygen atoms. This structure gives lithium iron phosphate good thermal stability and electrochemical performance. Sodium persulfate, a strong oxidant, is used to mix and calcine with the lithium iron phosphate cathode material. The purpose is to destroy the olivine structure of lithium iron phosphate and at the same time convert ferrous ions (Fe 2+ ) into ferric ions (Fe 3+ ). High-temperature calcination dissolves the hard and insoluble mineral phase to facilitate the dissolution of iron ions and lithium ions.

[0073] 4. The "hydrogen peroxide" process is used to deeply oxidize the ferrous ions Fe 2+ in the lithium iron phosphate soaking solution, and the separation of iron ions and lithium ions is greatly improved by the subsequent "alkaline precipitation" method.

[0074] 5. Dilute sulfuric acid is used to slag the iron hydroxide Fe(OH)3 precipitate, avoiding the use of hydrochloric acid or nitric acid to reduce the generation of impurity ions.

[0075] 6. Ammonium phosphate ((NH4)3PO4) is used to chemically react with iron hydroxide to generate iron phosphate. The by-product ammonia water generated in this reaction process can be further treated and recycled, reducing environmental pollution. Compared with the traditional strong acid iron process, the reaction of ammonium phosphate with iron hydroxide does not introduce other metal cation impurities and acid radical impurities, reducing the subsequent purification and treatment steps and reducing the environmental protection pressure.

[0076] 7. CO2 gas is used to react with lithium hydroxide to generate lithium carbonate. The main by-product generated in this reaction process is water, which is environmentally friendly. At the same time, the utilization of carbon dioxide helps to reduce greenhouse gas emissions, meeting environmental protection requirements. By using carbon dioxide to react with lithium hydroxide, lithium carbonate products with good crystallinity and uniform particle size distribution can be obtained, which is beneficial to improving the electrochemical performance of the final product.

[0077] 8. Using ammonia water as a pH regulator, fewer by-products are generated during the reaction process, and ammonia gas is volatile, reducing environmental pollution. At the same time, the use of ammonia water can reduce the use of other strong alkalis (such as sodium hydroxide), further reducing the impact on the environment. The slow addition of ammonia water and the precise control of pH contribute to the formation of uniform iron phosphate particles, improving the crystallinity and particle size distribution uniformity of the product, and high-purity iron phosphate can be prepared.

[0078] 9. The prepared iron phosphate and lithium carbonate are subjected to high-temperature solid-phase synthesis of lithium iron phosphate at 700 - 800 °C in a nitrogen atmosphere to achieve the resource recovery and utilization of waste. Description of the Drawings

[0079] Figure 1 It is a process flow chart for extracting iron source and lithium source from waste lithium iron phosphate batteries.

[0080] Figure 2 It is an X-ray diffraction (XRD) pattern of lithium carbonate (extracted according to Example 1) and commercial lithium carbonate prepared from waste lithium iron phosphate batteries.

[0081] Figure 3 It is an X-ray diffraction (XRD) pattern of iron phosphate (extracted according to Example 1) and commercial iron phosphate prepared from waste lithium iron phosphate batteries. Detailed Embodiments

[0082] It should be noted that, without conflict, the embodiments, features in the embodiments, and comparative examples in this application can be combined with each other. The present invention will be described in detail below with reference to the drawings and examples.

[0083] The present invention will be further described below with reference to the drawings.

[0084] Figure 1 It is a process flow chart for extracting iron source and lithium source from waste lithium iron phosphate batteries, corresponding to Example 1 - 1.

[0085] Among them, the acidic ingredient is one or more of sodium persulfate, sodium bisulfate, or ammonium sulfate.

[0086] Figure 2 It is an X-ray diffraction (XRD) pattern of lithium carbonate (extracted according to Example 1) and commercial lithium carbonate prepared from waste lithium iron phosphate batteries. From the XRD diffraction peaks, the crystal structure of the prepared lithium carbonate highly matches the diffraction peaks of lithium carbonate. It highly conforms to the XRD standard card (PDF#72 - 1216) and has crystal planes such as 110, 200, 111, 202, 002, 112, 020, 311, 021, 311, and 204 in the 2θ range of 15 - 80°.

[0087] Figure 3XRD patterns of the iron phosphate (extracted according to Example 1) prepared from waste lithium iron phosphate batteries and commercial iron phosphate. From the XRD diffraction peaks, the crystal structure of the prepared iron phosphate highly matches the diffraction peaks of iron phosphate, well conforming to the XRD standard card (PDF#70-1793) and having crystal planes such as 100, 012, 110, 104, 112, 200, 114, 024, 212, and 124 within the 2θ range of 15-80°.

[0088] As described in the background art of the present invention, in the prior art, there are problems in the processes of extracting iron sources and lithium sources from waste lithium iron phosphate batteries, such as large carbon emissions, serious environmental pollution, imprecise process flow parameters, difficult process control, and high production costs. The present invention discloses a process for the sustainable recovery of iron sources and lithium sources from waste lithium iron phosphate batteries. The method mainly includes key steps such as "sodium persulfate high-temperature activation", "hydrogen peroxide deep oxidation", "alkali precipitation", "acid dissolution", "iron precipitation", and "CO2 carbonization". First, the waste lithium iron phosphate battery is crushed under anaerobic and airtight conditions to remove the outer shell, and then the positive and negative electrode plates and the separator in the battery are peeled off. The peeled positive electrode plate is placed in an oven and dried for 48 h. After the dried positive electrode plate is cut into pieces, it is placed in a tube furnace and calcined at 500 °C for 2 h in an argon atmosphere, and then aluminum foil is separated by crushing and sieving to obtain fine lithium iron phosphate positive electrode powder. A certain amount of the fine lithium iron phosphate positive electrode powder is uniformly mixed with acidic ingredients in different mass ratios, and then calcined in a muffle furnace at 700-900 °C for 5 h. 100 mL of deionized water is added to the calcined product after taking it out, soaked, ultrasonicated, and heated and stirred in a water bath in sequence, and then filtered hot for multiple times to separate the residue and obtain the filtrate. 5 drops of hydrogen peroxide solution (0.3-0.5% mass concentration) are dropped into the filtrate with a pipette under heating and stirring, and stirring is continued for 10 min. Then, 8-10 mol / L NaOH solution is added dropwise to adjust the pH to 6-7, and reddish-brown flocculent precipitates are formed, and filtration is carried out for multiple times. The filter residue separated in step five is further processed as follows: the filter residue is dissolved in 20 mL of 8-10% mass concentration of dilute sulfuric acid under heating and stirring conditions to form a ferric sulfate salt solution, and then 50 mL of 0.5-1.0 mol / L ammonium phosphate solution is slowly dropped in while continuously stirring, and the pH is adjusted to 2-3 by adding 8-10 mol / L ammonia water to facilitate the formation of iron phosphate precipitate. Filtration, washing, drying, and grinding are carried out for multiple times, and then calcined in a muffle furnace at 500-550 °C for 3-4 h to obtain the iron source iron phosphate. The filtrate separated in step five is further processed as follows: CO2 gas is introduced into it at a flow rate of 20-25 mL / min for 1-2 h to form a white emulsion, and filtration and washing are carried out for multiple times. After drying in an oven for 24 h, a white precipitate is obtained, and after grinding, it is calcined in a muffle furnace at 700 °C for 3-4 h to obtain the recovered lithium carbonate positive electrode powder.

[0089] The used lithium iron phosphate batteries described in the following examples and comparative examples are from an electric vehicle repair shop in Yinchuan City. According to ICP-OES and XRF detections, the mass fractions of each element in the positive electrode sheet of the lithium iron phosphate battery are as follows: the Li content is 5.161 wt.%; the Fe content is 33.849 wt.%; the P content is 20.248 wt.%; the F content is 4.202 wt.%; the Na content is 0.070 wt.%; the Al content is 0.016 wt.%; the Si content is 0.057 wt.%; the S content is 0.107 wt.%; the Ca content is 0.041 wt.%; the Ti content is 0.221 wt.%; the Mn content is 0.014 wt.%; the Ni content is 0.007 wt.%; the As content is 0.001 wt.%; the Rb content is 0.004 wt.%; the Zr content is 0.016 wt.%; the Pb content is 0.015 wt.%. The carbon content measured by thermogravimetric analysis is about 34.431 wt.%, and the others are undetected components (the other components include one or more of K, Cr, Y, Mo, Cu, Nd, Co, Nb, Bi, Au, Se, Ge, Br).

[0090] The positive electrode sheet of the used lithium iron phosphate battery described in Step 2 of Example 1 was calcined in an argon atmosphere at 500 °C in a tube furnace and ground to obtain fine powder of the positive electrode of the lithium iron phosphate battery. According to ICP-OES and XRF detections, the mass fractions of each element in the fine powder of the positive electrode of the lithium iron phosphate battery are as follows: the Li content is 5.088 wt.%; the Fe content is 33.721 wt.%; the P content is 19.3123 wt.%; the F content is 1.7166 wt.%; the Na content is 0.0506 wt.%; the Al content is 0.016 wt.%; the Si content is 0.056 wt.%; the S content is 0.041 wt.%; the Ca content is 0.040 wt.%; the Ti content is 0.191 wt.%; the Mn content is 0.011 wt.%; the Ni content is 0.006 wt.%; the As content is 0.001 wt.%; the Rb content is 0.003 wt.%; the Zr content is 0.015 wt.%; the Pb content is 0.015 wt.%. The carbon content measured by thermogravimetric analysis is about 34.273 wt.%. The others are undetected components (the other components include one or more of K, Cr, Y, Mo, Cu, Nd, Co, Nb, Bi, Au, Se, Ge, Br).

[0091] Example 1:

[0092] A method for sustainable recovery of lithium source and iron source from used lithium iron phosphate batteries, comprising the following steps:

[0093] Step 1: Crush the waste lithium iron phosphate battery under anaerobic and airtight conditions, remove the outer shell, then strip the positive and negative electrode plates and the separator in the battery, and place the stripped positive electrode plate in an oven at 60 - 65°C for 48 hours to remove the low-temperature volatile organic solvents in the battery;

[0094] Step 2: To further remove the carbon materials and organic solvents in the positive electrode material, cut the dried positive electrode plate into pieces (5mm × 5mm), place them in a tube furnace, and calcine at 500°C for 2 hours in an argon atmosphere. The heating rate from room temperature to 500°C is 5°C / min, and then crush them at a speed of 25000 r / min for 30 minutes using a household small crusher (solid material crusher), and separate the aluminum foil by sieving (200-mesh sieve) to obtain the fine lithium iron phosphate positive electrode powder passing through the sieve;

[0095] Step 3: Take a certain amount (5g) of the fine lithium iron phosphate positive electrode powder and mix it evenly with sodium persulfate at a mass ratio of 1:2, then place it in a muffle furnace and heat it to 900°C at a heating rate of 5°C / min for roasting for 5 hours;

[0096] Step 4: Add 100 mL of deionized water to the roasted product after taking it out, soak it for 30 minutes, ultrasonicate for 2 hours, heat and stir in a water bath at 80°C for 30 minutes, and then filter it with water while it is hot 3 times (each time the water consumption is 1000 mL) to separate the residue and obtain the filtrate;

[0097] Step 5: Under the condition of heating and stirring at 80°C, use a pipette to drop 1 ml of H2O2 solution (0.3% mass concentration) into the filtrate to deeply oxidize the Fe in the filtrate, continue to stir for 10 minutes, then gradually add 8 mol / L NaOH solution to adjust the pH = 6.5, and reddish-brown flocculent precipitate will form. Filter it with water 3 times (each time the water consumption is 1000 mL) to obtain the filter residue and the filtrate; 2+ Step 6: Further process the filter residue separated in Step 5. Under the condition of heating and stirring at 80°C, dissolve the filter residue with 20 mL of 8% mass concentration dilute sulfuric acid to form a ferric sulfate salt solution, then slowly drop 50 mL of 0.5 mol / L ammonium phosphate ((NH4)3PO4) solution while constantly stirring, and adjust the pH = 2.5 by adding 8 mol / L ammonia water to facilitate the formation of iron phosphate precipitate. Filter it with water 3 times (each time the water consumption is 1000 mL) for washing, dry the solid at 60°C for 3 hours, grind it, and then calcine it in a muffle furnace at 500°C for 3 hours to obtain iron source iron phosphate, named FePO4-1;

[0098]

[0099] ​Step 7: Further process the filtrate mixture separated in Step 5 by introducing CO2 gas into it at a flow rate of 20 mL / min for 1 h to form a white emulsion. Filter and wash it repeatedly (filter with water and ethanol successively 3 times each, with the amount of water or ethanol being 1000 mL each time), dry it in an oven at 60 °C for 24 h to obtain a white precipitate, grind it, and then calcine it in a muffle furnace at 700 °C for 3 h to obtain the recycled lithium carbonate cathode powder, named Li2CO3-1.

[0100] Example 2:

[0101] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in Step 3 of Example 1, the mass ratio of lithium iron phosphate cathode fine powder to sodium persulfate for uniform blending is changed from 1:2 to 1:1, and other steps remain unchanged (the remaining process and conditions are the same as those in Example 1). Finally, iron phosphate and lithium carbonate are obtained, named FePO4-2 and Li2CO3-2 respectively.

[0102] Example 3:

[0103] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in Step 3 of Example 1, the mass ratio of lithium iron phosphate cathode fine powder to sodium persulfate for uniform blending is changed from 1:2 to 1:3, and other steps remain unchanged (the remaining process and conditions are the same as those in Example 1). Finally, iron phosphate and lithium carbonate are obtained, named FePO4-3 and Li2CO3-3 respectively.

[0104] Example 4:

[0105] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in Step 3 of Example 1, the mass ratio of lithium iron phosphate cathode fine powder to sodium persulfate for uniform blending is changed from 1:2 to 1:4, and other steps remain unchanged (the remaining process and conditions are the same as those in Example 1). Finally, iron phosphate and lithium carbonate are obtained, named FePO4-4 and Li2CO3-4 respectively.

[0106] Comparative Example 1:

[0107] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in Step 3 of Example 1, "sodium persulfate" is changed to "sodium bisulfate", and other steps remain unchanged (the remaining process and conditions are the same as those in Example 1). Finally, iron phosphate and lithium carbonate are obtained, named FePO4-5 and Li2CO3-5 respectively.

[0108] Comparative Example 2:

[0109] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in step 3 of Example 1, "sodium persulfate" is changed to "ammonium sulfate", and the other steps remain unchanged (the remaining processes and conditions are the same as those in Example 1). Finally, iron phosphate and lithium carbonate are obtained, named FePO4-6 and Li2CO3-6 respectively.

[0110] Comparative Example 3:

[0111] The process and conditions are the same as those in Example 1. The difference from Example 1 is that in step 3 of Example 1, "Take a certain amount (5 g) of lithium iron phosphate cathode fine powder and uniformly mix it with the acidic ingredients in different mass ratios, then place it in a muffle furnace and heat it to 900 °C at a heating rate of 5 °C / min for roasting for 5 h" is changed to "Take a certain amount (5 g) of lithium iron phosphate cathode fine powder and uniformly mix it with the acidic ingredients in different mass ratios, then place it in a muffle furnace and heat it to 800 °C at a heating rate of 5 °C / min for roasting for 5 h" to obtain the recycled lithium carbonate cathode powder, named Li2CO3-7.

[0112] Comparative Example 4:

[0113] Specifically, the difference from Example 1 is that in step 3 of Example 1, "Take a certain amount (5 g) of lithium iron phosphate cathode fine powder and uniformly mix it with the acidic ingredients in different mass ratios, then place it in a muffle furnace and heat it to 900 °C at a heating rate of 5 °C / min for roasting for 5 h" is changed to "Take a certain amount (5 g) of lithium iron phosphate cathode fine powder and uniformly mix it with the acidic ingredients in different mass ratios, then place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min for roasting for 5 h" to obtain the recycled lithium carbonate cathode powder, named Li2CO3-8.

[0114] Examples 1-4 and Comparative Examples 1-4 are compared.

[0115] Recovery rate (R Fe ) calculation formula:

[0116]

[0117] The iron content determination of the iron phosphate in the present invention can be based on the data of X-ray fluorescence spectrometry (XRF).

[0118] Specifically refer to the iron phosphate industry standard (HG / T 4701-2021).

[0119] Recovery rate (R Li ) calculation formula:

[0120]

[0121] The lithium content determination of lithium carbonate in the present invention can be based on the data analyzed by an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0122] Specifically, refer to the lithium carbonate industry standard (YS / T 582-2023).

[0123] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0124] The metal composition table of the waste lithium iron phosphate battery is shown in Table 1 (the data is from X-ray fluorescence spectroscopy (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES)) and thermogravimetric analyzer (TG), which is used as the initial data of the metals and carbon materials contained in the waste lithium iron phosphate battery before extracting the iron source.

[0125] Table 2 shows the test schemes of four embodiments and four comparative examples of the present invention.

[0126] Table 3 shows the recovery rates of iron phosphate (R Fe ) and lithium carbonate (R Li ). According to the industry standard HG / T 4701-2021 "Iron Phosphate for Batteries" of iron phosphate (the purity requirement for battery-grade iron phosphate should not be less than 98.5%) and the industry standard YS / T 582-2023 "Lithium Carbonate for Batteries" of lithium carbonate (the purity requirement for battery-grade lithium carbonate is that the lithium carbonate content is not less than 99.5%), the process for extracting lithium and iron from waste lithium iron phosphate batteries in the present invention is simple and convenient to operate. Finally, the recovery rates of iron phosphate and lithium carbonate can reach 95.3% and 94.2% respectively, and the purities of iron phosphate and lithium carbonate can reach 98.53% and 99.68% respectively.

[0127] Table 1 Chemical composition table of the waste lithium iron phosphate battery in the embodiment (wt.%)

[0128] Component Li Fe P F Na Al Si S Mass fraction / % 5.161 33.849 20.248 4.202 0.070 0.016 0.057 0.107 Component Ca Ti Mn Ni As Rb Zr Pb Mass fraction / % 0.041 0.221 0.014 0.007 0.001 0.004 0.016 0.015

[0129] Table 2 Test schemes of four embodiments and four comparative examples

[0130] Condition Acidic ingredient <![CDATA[m 磷酸铁锂正极细粉 : m 酸性配料 > Roasting temperature / °C Example 1 Sodium persulfate 1:2 900 Example 2 Sodium persulfate 1:1 900 Example 3 Sodium persulfate 1:3 900 Example 4 Sodium persulfate 1:4 900 Comparative example 1 Sodium bisulfate 1:2 900 Comparative example 2 Ammonium sulfate 1:2 900 Comparative example 3 Sodium persulfate 1:2 800 Comparative example 4 Sodium persulfate 1:2 700

[0131] Table 3 Recovery rate (%) record table of iron phosphate and lithium carbonate

[0132]

[0133] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Example 1 is simple and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate can reach 98.53% and 99.68% respectively.

[0134] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Example 2 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 97.62% and 96.67% respectively.

[0135] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Example 3 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 96.57% and 94.23% respectively.

[0136] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Example 4 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 96.44% and 93.29% respectively.

[0137] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Comparative Example 1 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 78.27% and 70.34% respectively.

[0138] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Comparative Example 2 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 78.22% and 71.54% respectively.

[0139] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Comparative Example 3 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 88.20% and 90.86% respectively.

[0140] The process for extracting lithium and iron from waste lithium iron phosphate batteries by the method of Comparative Example 4 is simple in process flow and convenient to operate. Finally, the purities of iron phosphate and lithium carbonate obtained can reach 86.29% and 88.58% respectively.

[0141] The present invention discloses a method for extracting iron source and lithium source from waste lithium iron phosphate batteries. First, to remove the carbon materials and organic solvents in the positive electrode material, the dried positive electrode material is cut into pieces and placed in a tube furnace, and high-temperature calcination is carried out in an argon atmosphere. Then, it is pulverized at a speed of 25000 r / min for 30 min by a household small crusher, and the aluminum foil is separated by sieving (more than 200 meshes) to obtain lithium iron phosphate positive electrode fine powder. A certain amount of lithium iron phosphate positive electrode fine powder is uniformly mixed with different masses of acidic ingredients, and then calcined in a muffle furnace at 900 °C for 5 h. Deionized water is added to the calcined product taken out for soaking, ultrasonic treatment for 2 h, water bath heating and stirring, and then hot filtration is carried out while it is hot to separate the residue to obtain the filtrate. H2O2 solution (0.3% mass concentration) is dropped into the filtrate with a pipette to make the Fe in the filtrate 2+It is deeply oxidized, and then NaOH solution is added drop by drop to adjust the pH to 6-7. A reddish-brown flocculent precipitate is formed. The residue obtained by suction filtration is Fe(OH)3 colloid, and the filtrate obtained is Li(OH) solution. The separated residue is further treated as follows: Under heating and stirring at 80 °C, Fe(OH)3 is dissolved in 20 mL of dilute sulfuric acid with a mass concentration of 8%. Then, 50 mL of 0.5 mol / L ammonium phosphate solution is slowly added dropwise to the resulting ferric sulfate solution, and the pH is adjusted to 2-3 by adding 8 mol / L ammonia water to form ferric phosphate precipitate. After suction filtration, washing, drying and grinding in sequence, and finally calcined in a muffle furnace at 500 °C for 3 h, ferric phosphate powder is obtained. The separated filtrate is further treated as follows: CO2 gas is continuously introduced into it at a flow rate of 20 mL / min for 1 h to form a white emulsion. After suction filtration, washing, drying and grinding, it is calcined in a muffle furnace at 700 °C for 3 h to obtain lithium carbonate powder.

[0142] The process for extracting iron and lithium from waste lithium iron phosphate batteries in the present invention has a simple process flow and convenient operation, and can realize the sustainable recycling of a large amount of solid waste - waste lithium iron phosphate batteries, reducing the environmental pollution caused by waste batteries. Since waste lithium iron phosphate batteries contain various harmful substances such as electrolytes and heavy metals, if not properly treated, these harmful substances may seep into the soil and water sources, causing serious pollution. Through high-value recycling, the damage of these harmful substances to the environment can be effectively avoided. More importantly, through sustainable recycling, the utilization efficiency of resources can be improved, and the sustainable utilization of resources can be promoted. The development of the waste battery recycling industry will arouse the society's attention to resource recycling and environmental protection, improve the public's environmental awareness, promote the formation of a green development concept in the whole society, provide strong support for the development of the new energy industry, and promote energy transformation and sustainable development.

Claims

1. A method for recovering lithium source and iron source in a cathode sheet of a lithium iron phosphate battery, characterized in that, It includes the following steps: 1), Cut the dried positive electrode sheet into pieces ((2 - 8) mm × (2 - 8) mm, preferably (4 - 6) mm × (4 - 6) mm), place them in a tube furnace, and calcine at a high temperature of 500 - 510 °C for 2 - 3 h in a nitrogen and / or argon atmosphere. Then, use a solid material crusher to crush at a speed of 20000 - 30000 r / min for 20 - 40 min, and sieve (150 - 200 mesh) to separate the aluminum foil, obtaining lithium iron phosphate positive electrode fine powder passing through the sieve; 2), Take 5 g of lithium iron phosphate positive electrode fine powder and mix it evenly with the acidic ingredient in different mass ratios, and then place it in a muffle furnace and roast at 700 - 900 °C for 5 - 6 h; The weight ratio of the lithium iron phosphate positive electrode fine powder to the acidic ingredient is preferably 1:(1.0 - 4.0); The acidic ingredient is sodium persulfate; 3), Add 60 - 150 mL of water to the roasted product after taking it out, soak for 15 - 40 min, ultrasonicate for 1 - 3 h, heat and stir in a water bath at 80 - 85 °C for 20 - 40 min, and then perform solid-liquid separation while it is hot to separate the residue and obtain the filtrate; 4), Add 0.8 - 2 mL of H2O2 solution (0.3 - 0.5% mass concentration) to the filtrate under the condition of heating and stirring at 80 - 85 °C. The purpose is to deeply oxidize the Fe in the filtrate 2+ to obtain deep oxidation. Continue stirring for 5 - 20 min, then add 8 - 10 mol / L NaOH solution to adjust the pH = 6 - 7. Precipitation occurs, and solid-liquid separation is carried out; 5), Further process the filter residue separated in step 4) as follows: dissolve the filter residue with 15 - 30 mL of 8 - 10% mass concentration dilute sulfuric acid under the condition of heating and stirring at 80 - 85 °C to generate an iron sulfate salt solution, then slowly drop 40 - 60 mL of 0.5 - 1.0 mol / L ammonium phosphate ((NH4)3PO4) solution while constantly stirring, and adjust the pH = 2 - 3 by adding 8 - 10 mol / L ammonia water (NH3·H2O) to facilitate the formation of iron phosphate precipitate. Perform solid-liquid separation, wash the solid, dry at 60 - 65 °C for 3 - 4 h, grind, and then calcine in a muffle furnace at 500 - 550 °C for 3 - 4 h to obtain iron source iron phosphate; 6), Further process the filtrate separated in step 4) as follows: Pass CO2 gas into it at a flow rate of 20 - 25 mL / min for 1 - 2 h to form a white emulsion. Perform solid-liquid separation, wash the solid, dry in an oven at 60 - 65 °C for 24 - 48 h to obtain a white precipitate, grind, and then calcine in a muffle furnace at 500 - 700 °C for 3 - 4 h to obtain the recycled lithium carbonate positive electrode powder.

2. The method according to claim 1, wherein: The lithium iron phosphate battery is a used lithium iron phosphate battery; Among them, the lithium source mainly refers to lithium carbonate, and the iron source mainly refers to iron phosphate; The process for obtaining the positive electrode sheet is as follows: Disassemble the used lithium iron phosphate battery under anaerobic and airtight conditions, remove the outer shell, then peel the positive and negative electrode sheets and the separator in the battery, and place the peeled positive electrode sheet in an oven and dry at 60 - 65 °C for 48 - 72 h to remove the low-temperature volatile organic solvents in the battery.

3. The method according to claim 1, wherein: In step 2), the weight ratio of the lithium iron phosphate positive electrode fine powder to the acidic ingredient is preferably 1:(1.5 - 2.5) (the preferred range is 1:(1.95 - 2.15)).

4. The method according to claim 1, wherein: In the said step 3) to step 5), the "solid-liquid separation" refers to "multiple suction filtrations", specifically, suction filtration is carried out at least 2 times with water, and the water consumption each time is 950 - 1050 mL; In the said step 6), the "solid-liquid separation" refers to "multiple suction filtrations", which means suction filtration is carried out at least 2 times with water and ethanol respectively in sequence, and the water or ethanol consumption each time is 950 - 1050 mL.

5. The method according to claim 1, wherein In the said step 4), the mass concentration of the H2O2 solution is 0.3 - 0.5%; The preparation method of the 0.3 - 0.5% H2O2 solution is: take the H2O2 solution with a mass concentration of 3%, and dilute it 6 - 10 times with deionized water; In the said step 4), the molar concentration of the NaOH solution is 8 - 10 mol / L; The preparation method of the 8 - 10 mol / L NaOH solution is: it is necessary to weigh 400 g of solid NaOH, add deionized water and make the volume up to 1000 - 1250 mL.

6. The method according to claim 1, characterized in that In the said step 5), the mass concentration of the dilute sulfuric acid solution is 8 - 10%; The preparation method of the 8 - 10% mass concentration dilute sulfuric acid solution is: weigh 30 mL of water, add 8 - 10 mL of concentrated sulfuric acid with a glass rod for drainage, stir and then add water to dilute to 100 mL; In the said step 5), the molar concentration of the ammonium phosphate solution is 0.5 - 1.0 mol / L; The preparation method of the 0.5 - 1.0 mol / L molar concentration dilute sulfuric acid solution is: weigh 3.725 - 7.450 g of ammonium phosphate (NH4)3PO4 solid, add appropriate amount of deionized water to dissolve it, and make the volume up to 50 mL; In the said step 5), the molar concentration of the ammonia water solution is 8 - 10 mol / L; The preparation method of the 8 - 10 mol / L concentration NH3·H2O solution is: measure 300 - 375 mL of ammonia water with a mass concentration of 25 - 28%, and dilute it with deionized water to 500 mL.

7. The method according to claim 1, wherein In the said step 6), the white precipitate obtained by suction filtration needs to be dried, then passed through a sieve with 150 - 200 meshes or more, collect the components passing through the sieve, and then place them in a muffle furnace for calcination.

8. The method according to claim 1, wherein In the said step 1), the dried positive electrode sheet is preferably calcined at a constant temperature of 500 - 505 °C in an argon atmosphere in a tubular furnace, and the calcination duration is preferably 2.0 - 2.5 h; In the said step 2), the positive electrode fine powder after admixing with sodium persulfate is preferably calcined at a constant temperature of 850 - 900 °C in a muffle furnace, and the calcination duration is preferably 5.0 - 5.5 h; In the said step 5), for the iron phosphate precipitate, after drying, the preferred temperature for placing it in a muffle furnace for calcination is 500 - 550 °C, and the calcination duration is preferably 3.0 - 3.5 h; In the said step 6), the flow rate of introducing CO2 into the filtrate is preferably 20 - 22 mL / min, and the introduction duration is preferably 1.0 - 1.5 h; In the said step 6), the calcination temperature of the white powder after drying and grinding placed in a muffle furnace is preferably 500 - 550 °C, and the calcination duration is preferably 3.0 - 3.5 h.

9. The method according to claim 1, wherein in the step 4), the reddish-brown flocculent precipitate is mainly iron hydroxide formed after the oxidation of ferrous ions and the reaction with sodium hydroxide to remove iron; in the step 5), the drying temperature of the iron phosphate precipitate in the oven is 60-65 °C, and the drying time is 3.0-4.0 h.

10. The method according to claim 1, wherein in the steps 1), 2), 5) and 6), the heating rate of the muffle furnace or tube furnace to reach the calcination temperature is 5.0-8.0 °C / min.

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