Method for synchronously realizing selective extraction of lithium and direct regeneration of iron phosphate

Abstract

The invention relates to the technical field of recovery and regeneration of waste lithium ion battery materials, in particular to a method for synchronously realizing selective extraction of lithium and direct regeneration of iron phosphate. The method comprises the following steps: providing positive electrode powder of the waste lithium iron phosphate battery; a hydrogen bond donor and a hydrogen bond acceptor are mixed, heated and stirred to obtain the eutectic solvent, the hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid and citric acid, and the hydrogen bond acceptor is ethylene glycol; adding water into the deep-eutectic solvent for dilution, then adding the positive electrode powder and an oxidizing agent, heating and stirring, and filtering to obtain a lithium-containing leaching solution and leaching residues; carrying out concentration treatment and impurity removal treatment on the lithium-containing leachate, and then adding a saturated sodium carbonate solution to carry out lithium precipitation reaction to obtain lithium carbonate; and calcining the leaching residues to obtain iron phosphate. According to the method, the specific eutectic solvent is adopted to treat the positive electrode powder of the waste lithium iron phosphate battery, and selective extraction of lithium and direct regeneration of iron phosphate can be synchronously realized under mild conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and regeneration of waste lithium-ion battery materials, and particularly relates to a method for synchronously realizing selective lithium extraction and direct regeneration of iron phosphate. Background Art

[0002] With the rapid development of the new energy vehicle industry, the large-scale recycling of waste lithium-ion batteries has become the focus of global attention. Lithium iron phosphate batteries occupy the mainstream market share due to their high safety, long cycle life and other advantages. However, the efficient recycling of lithium elements in their cathode materials and the resource utilization of the iron phosphate framework structure still face technical bottlenecks. In traditional recycling processes, the hydrometallurgical method mostly uses strong acid (such as sulfuric acid, hydrochloric acid) systems to leach metal ions, which has problems such as acid mist volatilization and equipment corrosion, and additional reducing agents (such as hydrogen peroxide, sodium sulfite) need to be added to destroy the olivine structure of lithium iron phosphate, resulting in complex process flows and high waste liquid treatment costs. Although the pyrometallurgical method can achieve large-scale treatment, high-temperature calcination is likely to cause phase transformation and inactivation of iron phosphate, making it difficult to be directly reused as a precursor, and the economy is limited.

[0003] In recent years, deep eutectic solvents (DES) have been tried for battery recycling due to their low toxicity, strong designability and other characteristics. Although the deep eutectic solvents used in the existing technology can selectively extract lithium, they damage the iron phosphate framework structure, and the reaction requires high temperature (>80 °C) or long-time stirring, with high energy consumption. In addition, the separation of lithium from iron and phosphorus in traditional processes mostly relies on multi-stage extraction or precipitation, with cumbersome steps and high metal loss rates. Therefore, there is still a need to develop a new type of recycling technology that is green and efficient and can synchronously realize selective lithium extraction and direct regeneration of iron phosphate. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a method for synchronously realizing selective lithium extraction and direct regeneration of iron phosphate, aiming to solve the problem that the existing methods cannot synchronously realize selective lithium extraction and direct regeneration of iron phosphate.

[0005] The technical solution of the present invention is as follows: The present invention provides a method for synchronously realizing selective lithium extraction and direct regeneration of iron phosphate, which includes: Step S1: Provide the cathode powder of waste lithium iron phosphate batteries; Step S2: Mix and heat and stir a hydrogen bond donor and a hydrogen bond acceptor to obtain a deep eutectic solvent, where the hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid, and the hydrogen bond acceptor is ethylene glycol; Step S3: Dilute the eutectic solvent obtained in Step S2 with water to obtain a diluted eutectic solvent, then add the positive electrode powder material and the oxidant in Step S1, heat and stir, and filter to obtain a lithium-containing leaching solution and leaching residues; Step S4: Concentrate and purify the lithium-containing leaching solution obtained in Step S3, and then add a saturated sodium carbonate solution for lithium precipitation reaction to obtain lithium carbonate; Step S5: Calcinate the leaching residues obtained in Step S3 to obtain iron phosphate.

[0006] Optionally, in Step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5 - 1.2.

[0007] Optionally, in Step S2, the heating temperature for the mixed heating and stirring is 25°C - 80°C, and the heating time is 30 min - 60 min.

[0008] Optionally, in Step S3, the mass fraction of the diluted eutectic solvent is 1 wt% - 20 wt%; the mass ratio of the positive electrode powder material to the diluted eutectic solvent is 1:5 - 20; the oxidant is 10 wt% - 30 wt% hydrogen peroxide, and the addition amount of the hydrogen peroxide is 5 vol% - 15 vol%.

[0009] Optionally, in Step S3, the heating temperature for the heating and stirring is 60°C - 90°C, and the heating time is 60 min - 120 min.

[0010] Optionally, in Step S4, the concentration treatment specifically includes: concentrating the lithium-containing leaching solution obtained in Step S3 to a concentration of 18 g / L - 30 g / L; The impurity removal treatment specifically includes: adjusting the pH value to 10 - 12 with a 5 wt% - 10 wt% sodium hydroxide solution for impurity removal.

[0011] Optionally, in Step S4, the mass fraction of the saturated sodium carbonate solution is 25 wt% - 30 wt%, and the addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium-containing leaching solution is 0.6 - 0.75:1; The reaction temperature for the lithium precipitation reaction is 90°C - 95°C, and the reaction time is 1 h - 3 h.

[0012] Optionally, in Step S5, the calcination temperature is 600°C - 800°C, the calcination time is 3 h - 6 h, and the calcination atmosphere is air.

[0013] Optionally, after Step S5, there is also Step S6: Mix and ball-mill the lithium carbonate obtained in Step S4 and the iron phosphate obtained in Step S5 with a carbon source, and calcine to obtain lithium iron phosphate.

[0014] Optionally, in the step S6, the molar ratio of the lithium carbonate to the iron phosphate is 0.5-0.6:1.

[0015] Optionally, the carbon source is glucose, and the addition amount of the glucose is 10wt%-15wt% of the mass of the iron phosphate.

[0016] Optionally, in the step S6, the calcination temperature is 350°C-800°C, the calcination time is 8h-12h, and the calcination atmosphere is argon.

[0017] Beneficial effects: (1) The method provided by the present invention can synchronously achieve selective lithium extraction and direct regeneration of iron phosphate, and then battery-grade lithium carbonate and battery-grade lithium iron phosphate can be obtained, forming a "leaching-regeneration" closed-loop recovery path. And the method of the present invention has the advantages of environmental friendliness, low cost, high-efficiency separation of lithium and iron, high added value of products, etc., and has good application prospects. (2) The present invention uses a specific deep eutectic solvent to treat the cathode powder of waste lithium iron phosphate batteries, and selective lithium extraction can be achieved under mild conditions, while keeping the skeleton of iron phosphate intact. The leaching residue can be directly reused as the precursor of iron phosphate, that is, high-value-added iron phosphate can be obtained synchronously during the selective lithium extraction process, eliminating the iron reduction-reoxidation steps in the traditional process and simplifying the recovery process. (3) The present invention uses a specific deep eutectic solvent as the leaching medium. The solvent has good biodegradability, is environmentally friendly, avoids the emission of harmful gases in the traditional strong acid system, and does not require a high-pressure environment during the reaction, with low energy consumption. It is compatible with existing hydrometallurgy equipment and can be rapidly promoted industrially without modifying the production line. Description of the Drawings

[0018] Figure 1 It is a flowchart of a method for synchronously achieving selective lithium extraction and direct regeneration of iron phosphate provided by the present invention.

[0019] Figure 2 It is an XRD pattern of the iron phosphate obtained in step (5) of Examples 1-3. Detailed Embodiments

[0020] The present invention provides a method for synchronously achieving selective lithium extraction and direct regeneration of iron phosphate. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] As Figure 1 shown, the embodiment of the present invention provides a method for synchronously achieving selective lithium extraction and direct regeneration of iron phosphate, which includes: Step S1: Provide the positive electrode powder of waste lithium iron phosphate batteries. Step S2: Mix and heat-stir a hydrogen bond donor and a hydrogen bond acceptor to obtain a deep eutectic solvent. The hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid, and the hydrogen bond acceptor is ethylene glycol. Step S3: Dilute the deep eutectic solvent obtained in Step S2 with water to obtain a diluted deep eutectic solvent, then add the positive electrode powder and an oxidant in Step S1, heat and stir, and filter to obtain a lithium-containing leaching solution and leaching residues. Step S4: Concentrate and purify the lithium-containing leaching solution obtained in Step S3, and then add a saturated sodium carbonate solution to carry out a lithium precipitation reaction to obtain lithium carbonate. Step S5: Calcinate the leaching residues obtained in Step S3 to obtain iron phosphate.

[0022] In the embodiments of the present invention, by using a specific deep eutectic solvent as the leaching medium, treating the positive electrode powder of waste lithium iron phosphate batteries with the specific deep eutectic solvent, the obtained lithium-containing leaching solution is concentrated and purified and then undergoes a lithium precipitation reaction with a saturated sodium carbonate solution to obtain battery-grade lithium carbonate; at the same time, the obtained leaching residues maintain the integrity of the iron phosphate skeleton and can be directly recycled as the iron phosphate precursor, and high-value-added iron phosphate can be obtained through calcination, that is, selective extraction of lithium in the positive electrode material of waste lithium iron phosphate batteries and direct regeneration of iron phosphate are realized under mild conditions. The method provided by the embodiments of the present invention has the advantages of simplified process, environmental friendliness, low cost, efficient separation of lithium and iron, high product added value, etc., and has good application prospects.

[0023] In some embodiments, Step S1 specifically includes: S11: Completely discharge the waste lithium iron phosphate batteries and then disassemble them, and obtain the positive electrode plates after drying and cooling. S12: Immerse the positive electrode plates in pure water at 25°C to 60°C for peeling to obtain the positive electrode material and aluminum foil; the positive electrode material is dried, crushed, and screened to obtain the positive electrode powder.

[0024] In some embodiments, in Step S2, the hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid, and the hydrogen bond acceptor is ethylene glycol. The deep eutectic solvent obtained by mixing the hydrogen bond donor and the hydrogen bond acceptor avoids the iron-containing acidic waste liquid or HF hazardous gas generated by traditional acid leaching, and has the advantages of high biodegradation rate and environmental friendliness. Among them, the phosphate groups or carboxylic acid groups of multi-dentate ligands such as phytic acid and citric acid can preferentially form stable coordination with Li + through the lone pair electrons of oxygen atoms, while iron (Fe 3+ / Fe 2+)(Due to the relatively large ionic radius and the difference in electron configuration, FePO4 precipitation is more likely to occur at a specific pH, thus achieving the selective leaching of lithium. The Li in the leaching solution + can undergo a lithium precipitation reaction through evaporation and concentration to obtain lithium carbonate. Additionally, by adjusting the ratio of hydrogen bond donors such as formic acid / phytic acid, the pH value of the solvent system (1.5 - 3.5) can be precisely controlled. Within this range, the Li - O bond in LiFePO4 breaks, while the Fe - PO4 lattice remains stable, avoiding the massive dissolution of iron. Moreover, the hydrogen bond donors (such as citric acid, formic acid, etc.) in the deep eutectic solvent can inhibit the co - precipitation of impurity ions (Al 3+ 、Cu 2+ ), simplifying the subsequent purification steps.

[0025] In some embodiments, in step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5 - 1.2, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc., and preferably 1:0.8 - 1.0. The deep eutectic solvent obtained within this molar ratio range has low viscosity, good stability, and can be recycled multiple times.

[0026] In some embodiments, in step S2, the heating temperature for the mixed heating and stirring is 25°C - 80°C (for example, it can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.), and the heating time is 30 min - 60 min (for example, it can be 30 min, 40 min, 50 min, 60 min, etc.).

[0027] In some embodiments, in step S3, the mass fraction of the diluted deep eutectic solvent is 1 wt% - 20 wt% (for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%). Diluting the deep eutectic solvent obtained in step S2 can regulate the viscosity of the deep eutectic solvent and save costs.

[0028] In some embodiments, in step S3, the mass ratio of the positive electrode powder material to the diluted deep eutectic solvent is 1:5 - 20 (for example, it can be 1:5, 1:10, 1:15, 1:20, etc.). Within this mass ratio range, the lithium ion leaching rate can reach 99%, and the iron leaching rate is less than 1%, achieving the selective leaching of lithium ions.

[0029] In some embodiments, in step S3, the oxidant is hydrogen peroxide at 10 wt% - 30 wt% (for example, it can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.), and the addition amount of hydrogen peroxide is 5 vol% - 15 vol% (for example, it can be 5 vol%, 6 vol%, 7 vol%, 8 vol%, 9 vol%, 10 vol%, 11 vol%, 12 vol%, 13 vol%, 14 vol%, 15 vol%). The role of the hydrogen peroxide oxidant is to regulate the pH value, oxidize divalent iron in lithium iron phosphate to trivalent iron, and combine with phosphate radicals to form iron phosphate precipitate.

[0030] In some embodiments, in step S3, the heating temperature for the heating and stirring is 60°C - 90°C (for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.), and the heating time is 60 min - 120 min (for example, it can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc.). Under the conditions of this heating and stirring, the leaching effect of valuable metals is better.

[0031] In some embodiments, step S3 specifically includes: Dilute the eutectic solvent obtained in step S2 with water to a mass fraction of 1 wt% - 20 wt%, then add the positive electrode powder material in step S1 and 10 wt% - 30 wt% hydrogen peroxide. The mass ratio of the positive electrode powder material to the diluted eutectic solvent is 1:5 - 20, the addition amount of hydrogen peroxide is 5 vol% - 15 vol%, heat and stir at 60°C - 90°C for 60 min - 120 min, and after filtration, a lithium-containing leaching solution and leaching residue are obtained.

[0032] In some embodiments, in step S4, the concentration treatment specifically includes: concentrating the lithium-containing leaching solution obtained in step S3 to a concentration of 18 g / L - 30 g / L; the impurity removal treatment specifically includes: using 5 wt% - 10 wt% sodium hydroxide to adjust the pH value to 10 - 12 for impurity removal. The purpose of the concentration treatment is to enable the lithium ions to undergo a lithium precipitation reaction. The lithium ion concentration in the leaching solution is too low to undergo a lithium precipitation reaction with saturated sodium carbonate solution. The purpose of the impurity removal treatment is to remove trace impurity ions such as aluminum ions and copper ions that may exist in the leaching solution to ensure high-purity lithium carbonate is obtained.

[0033] In some embodiments, in step S4, the mass fraction of the saturated sodium carbonate solution is 25 wt% to 30 wt% (for example, it can be 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, etc.). The saturated sodium carbonate solution can react with lithium ions in the lithium-containing leachate to precipitate lithium carbonate, thereby obtaining battery-grade lithium carbonate.

[0034] In some embodiments, in step S4, the addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate is 0.6 to 0.75:1.

[0035] In some embodiments, in step S4, the reaction temperature of the lithium precipitation reaction is 90°C to 95°C (such as 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, etc.), and the reaction time is 1 h to 3 h (for example, 1 h, 2 h, 3 h, etc.). Under the conditions of this lithium precipitation reaction, lithium carbonate with a high recovery rate can be obtained.

[0036] In some embodiments, step S4 specifically includes: Concentrate the lithium-containing leachate obtained in step S3 to a concentration of 18 g / L to 30 g / L, then adjust the pH value to 10 to 12 with a 5 wt% to 10 wt% sodium hydroxide solution for impurity removal, and then add a 25 wt% to 30 wt% saturated sodium carbonate solution for lithium precipitation reaction. The reaction temperature is 90°C to 95°C, and the reaction time is 1 h to 3 h to obtain lithium carbonate.

[0037] In some embodiments, step S5 specifically includes: calcining the leaching residue obtained in step S3 at 600°C to 800°C for 3 h to 6 h to obtain iron phosphate.

[0038] In this embodiment, the purpose of calcining is to burn off the residual carbon in the leaching residue to obtain pure iron phosphate.

[0039] In some embodiments, in step S5, the calcination temperature is 600°C to 800°C (for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, etc.), the calcination time is 3 h to 6 h (for example, it can be 3 h, 4 h, 5 h, 6 h, etc.), and the calcination atmosphere is air.

[0040] In some embodiments, after step S5, there is further step S6: mixing and ball-milling the lithium carbonate obtained in step S4 and the iron phosphate obtained in step S5 with a carbon source, and calcining to obtain lithium iron phosphate.

[0041] In some embodiments, step S6 specifically includes: mixing and ball-milling the lithium carbonate obtained in step S4 and the iron phosphate obtained in step S5 with a carbon source, and calcining at 350°C to 800°C for 8h to 12h to obtain lithium iron phosphate.

[0042] In this embodiment, ball-milling makes the materials mix more evenly, and calcination enables lithium carbonate, iron phosphate, and the carbon source to obtain lithium iron phosphate at high temperature.

[0043] In some embodiments, in step S6, the molar ratio of the lithium carbonate to the iron phosphate is 0.5 to 0.6:1.

[0044] In some embodiments, in step S6, the carbon source is glucose, and the addition amount of the glucose is 10wt% to 15wt% of the mass of the iron phosphate.

[0045] In some embodiments, in step S6, the calcination temperature is 350°C to 800°C (for example, it can be 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc.), the calcination time is 8h to 12h (for example, it can be 8h, 9h, 10h, 11h, 12h, etc.), and the calcination atmosphere is argon.

[0046] The present invention will be further described below through specific examples.

[0047] Example 1 This example provides a method for synchronously realizing selective lithium extraction and direct regeneration of iron phosphate, including the following steps: (1) After completely discharging the used lithium iron phosphate battery, disassemble it, and obtain the positive electrode sheet after drying and cooling; soak the positive electrode sheet in pure water at 60°C for 2 minutes for peeling to obtain the positive electrode material and aluminum foil; dry the positive electrode material at 80°C, crush it with a crusher after drying, and then screen it with a 200-mesh sieve to obtain 200-mesh positive electrode powder.

[0048] (2) Mix formic acid and ethylene glycol in a molar ratio of 1:1, and heat and stir at 60°C for 30 minutes to obtain a eutectic solvent.

[0049] (3) Dilute the eutectic solvent obtained in step (2) with water to a mass fraction of 3wt%, add the 200-mesh positive electrode powder in step (1) to the diluted eutectic solvent, where the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:10, and then add 6vol% of hydrogen peroxide with a mass fraction of 30wt% for oxidation, heat and stir at 60°C for 120 minutes, and filter to obtain a lithium-containing leachate and leaching residue.

[0050] (4) Concentrate the lithium-containing leaching solution obtained in step (3) to a concentration of 20 g / L, then adjust the pH value to 12 with 10 wt% sodium hydroxide solution for impurity removal, and then add 25 wt% saturated sodium carbonate solution for lithium precipitation reaction. The addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium-containing leaching solution is 0.6:1. The lithium precipitation reaction temperature is 90 °C, and the lithium precipitation reaction time is 2 h to obtain lithium carbonate.

[0051] (5) Calcinate the leaching residue obtained in step (3) in air at 700 °C for 4 h to obtain iron phosphate.

[0052] (6) Mix and ball-mill the lithium carbonate obtained in step (4) and the iron phosphate obtained in step (5) with glucose. The molar ratio of the added lithium carbonate to iron phosphate is 0.52:1, and the addition amount of glucose is 15 wt% of the mass of the iron phosphate. Under an argon atmosphere, calcine at 450 °C for 4 h and then at 800 °C for 10 h to obtain lithium iron phosphate.

[0053] Element content test: 1. Conduct inductively coupled plasma (ICP) test on the metal content in the positive electrode powder obtained in step (1) above. The results are shown in Table 1.

[0054] Table 1

[0055] 2. Conduct ICP test on the metal content in the lithium-containing leaching solution obtained in step (3) above, and calculate the leaching rates of lithium and iron respectively. The calculation method of the leaching rate is: , where i represents the element, m i is the content of element "i" in the waste lithium iron phosphate powder, C i and V i are the concentration and volume of element "i" in the leaching solution respectively. The results are shown in Table 2.

[0056] Table 2

[0057] 3. Conduct ICP test on the metal content in the iron phosphate obtained in step (5) above. The results are shown in Table 3.

[0058] Table 3

[0059] According to the results in Tables 1 - 3, the Li leaching rate in the lithium - containing leaching solution obtained in step (3) of Example 1 reached 99.33%, and the Fe leaching rate was only 0.03%. It can be seen that the deep eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reached 36.353 wt%, the P content reached 20.932 wt%, and the iron - phosphorus ratio (Fe:P) was 0.96, meeting the standards of battery - grade iron phosphate. This shows that through the method of the present invention, the selective extraction of lithium and the direct regeneration of iron phosphate can be achieved simultaneously, and then battery - grade lithium carbonate and battery - grade lithium iron phosphate can be obtained, realizing the green regeneration of the cathode material in waste lithium iron phosphate batteries.

[0060] Example 2 This example provides a method for simultaneously achieving the selective extraction of lithium and the direct regeneration of iron phosphate, including the following steps: (1) After completely discharging the waste lithium iron phosphate battery, disassemble it. After drying and cooling, obtain the positive electrode sheet; soak the positive electrode sheet in pure water at 60 °C for 2 min for peeling to obtain the cathode material and aluminum foil; dry the cathode material at 80 °C, crush it with a crusher after drying, and then screen it with a 200 - mesh sieve to obtain 200 - mesh positive electrode powder.

[0061] (2) Mix acetic acid and ethylene glycol in a molar ratio of 1:1, heat and stir at 60 °C for 30 min to obtain a deep eutectic solvent.

[0062] (3) Dilute the deep eutectic solvent obtained in step (2) with water to a mass fraction of 6 wt%. Add the 200 - mesh positive electrode powder in step (1) into the diluted deep eutectic solvent, where the mass ratio of the positive electrode powder to the diluted deep eutectic solvent is 1:15. Then add 8 vol% of hydrogen peroxide with a mass fraction of 30 wt% for oxidation, heat and stir at 60 °C for 120 min, and filter to obtain a lithium - containing leaching solution and leaching residue.

[0063] (4) Concentrate the lithium - containing leaching solution obtained in step (3) to a concentration of 20 g / L, then use a 10 wt% sodium hydroxide solution to adjust the pH value to 12 for impurity removal, and then add a 25 wt% saturated sodium carbonate solution for lithium precipitation reaction. The addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium - containing leaching solution is 0.6:1. The lithium precipitation reaction temperature is 90 °C, and the lithium precipitation reaction time is 3 h to obtain lithium carbonate.

[0064] (5) Calcinate the leaching residue obtained in step (3) in air at 700 °C for 4 h to obtain iron phosphate.

[0065] (6) Mix and ball-mill the lithium carbonate obtained in step (4) with the iron phosphate obtained in step (5) and glucose. The molar ratio of the added lithium carbonate to iron phosphate is 0.52:1, and the addition amount of glucose is 15 wt% of the mass of the iron phosphate. Calcinate at 450 °C for 4 h under an argon atmosphere and then at 800 °C for 10 h to obtain lithium iron phosphate.

[0066] Element content test: 1. Conduct an inductively coupled plasma (ICP) test on the metal content in the positive electrode powder obtained in step (1) above. The results are shown in Table 4.

[0067] Table 4

[0068] 2. Conduct an ICP test on the metal content in the lithium-containing leaching solution obtained in step (3) above, and calculate the leaching rates of lithium and iron respectively. The calculation method of the leaching rate is the same as that in Example 1. The results are shown in Table 5.

[0069] Table 5

[0070] 3. Conduct an ICP test on the metal content in the iron phosphate obtained in step (5) above. The results are shown in Table 6.

[0071] Table 6

[0072] According to the results in Tables 4 - 6, it shows that the Li leaching rate in the lithium-containing leaching solution obtained in step (3) of Example 2 reaches 99.10%, and the Fe leaching rate is only 0.06%. It can be seen that the deep eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reaches 36.612 wt%, the P content reaches 20.881 wt%, and the iron-phosphorus ratio (Fe:P) is 0.97, meeting the standard of battery-grade iron phosphate. This indicates that through the method of the present invention, the selective extraction of lithium and the direct regeneration of iron phosphate can be achieved simultaneously, and then battery-grade lithium carbonate and battery-grade lithium iron phosphate can be obtained, realizing the green regeneration of the positive electrode material in waste lithium iron phosphate batteries.

[0073] Example 3 This example provides a method for simultaneously realizing the selective extraction of lithium and the direct regeneration of iron phosphate, including the following steps: (1)Completely discharge the used lithium iron phosphate battery and then disassemble it. After drying and cooling, obtain the positive electrode sheet. Immerse the positive electrode sheet in pure water at 60 °C for 2 min for peeling to obtain the positive electrode material and aluminum foil. Dry the positive electrode material at 80 °C, crush it with a crusher after drying, and then screen it with a 200-mesh sieve to obtain 200-mesh positive electrode powder.

[0074] (2)Mix propionic acid and ethylene glycol in a molar ratio of 2:1, heat and stir at 60 °C for 30 min to obtain a deep eutectic solvent.

[0075] (3)Dilute the deep eutectic solvent obtained in step (2) with water to a mass fraction of 15 wt%. Add the 200-mesh positive electrode powder in step (1) to the diluted deep eutectic solvent, where the mass ratio of the positive electrode powder to the diluted deep eutectic solvent is 1:15. Then add 10 vol% of hydrogen peroxide with a mass fraction of 30 wt% for oxidation, heat and stir at 60 °C for 120 min, and filter to obtain a lithium-containing leachate and leaching residue.

[0076] (4)Concentrate the lithium-containing leachate obtained in step (3) to a concentration of 20 g / L, then use a 10 wt% sodium hydroxide solution to adjust the pH value to 12 for impurity removal, and then add a 25 wt% saturated sodium carbonate solution for lithium precipitation reaction. The addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate is 0.6:1. The lithium precipitation reaction temperature is 90 °C, and the lithium precipitation reaction time is 3 h to obtain lithium carbonate.

[0077] (5)Calcine the leaching residue obtained in step (3) in air at 700 °C for 4 h to obtain iron phosphate.

[0078] (6)Mix the lithium carbonate obtained in step (4) and the iron phosphate obtained in step (5) with glucose and ball mill them. The molar ratio of the added lithium carbonate to iron phosphate is 0.52:1, and the addition amount of glucose is 15 wt% of the mass of the iron phosphate. Under an argon atmosphere, calcine at 450 °C for 4 h and then at 800 °C for 10 h to obtain lithium iron phosphate.

[0079] Element content test: 1. Conduct an inductively coupled plasma (ICP) test on the metal content in the positive electrode powder obtained in step (1) above. The results are shown in Table 7.

[0080] Table 7

[0081] 2. Conduct ICP tests on the metal content in the lithium-containing leaching solution obtained in step (3) above, and calculate the leaching rates of lithium and iron respectively. The calculation method of the leaching rate is the same as that in Example 1. The results are shown in Table 8.

[0082] Table 8

[0083] 3. Conduct ICP tests on the metal content in the iron phosphate obtained in step (5) above. The results are shown in Table 9.

[0084] Table 9

[0085] According to the results in Tables 7 - 9, the Li leaching rate in the lithium-containing leaching solution obtained in step (3) of Example 3 reaches 98.5%, and the Fe leaching rate is only 0.05%. It can be seen that the deep eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reaches 36.714 wt%, the P content reaches 20.615 wt%, and the iron to phosphorus ratio (Fe:P) is 0.98, meeting the standards of battery-grade iron phosphate. This shows that through the method of the present invention, the selective extraction of lithium and the direct regeneration of iron phosphate can be achieved simultaneously, and then battery-grade lithium carbonate and battery-grade lithium iron phosphate can be obtained, realizing the green regeneration of the cathode material in waste lithium iron phosphate batteries.

[0086] In addition, X-ray diffraction (XRD) tests were conducted on the iron phosphate obtained in step (5) of Examples 1 - 3. Figure 2 It is the XRD pattern of the iron phosphate obtained in step (5) of Examples 1 - 3. According to this figure, the XRD characteristic peaks of the iron phosphate prepared in Examples 1 - 3 can correspond one by one to the standard card peaks of iron phosphate, and no other impurity peaks appear, indicating that the prepared iron phosphate has high crystallinity and stable quality, meeting the crystal structure requirements for the expected preparation of iron phosphate.

[0087] Comparative Example 1 This comparative example provides a method for leaching the cathode powder of waste lithium iron phosphate batteries, including the following steps: (1) The cathode powder used is the 200-mesh cathode powder obtained in step (1) of Example 1.

[0088] (2) Mix oxalic acid and choline chloride in a molar ratio of 2:1, heat and stir at 80°C for 30 min to obtain a deep eutectic solvent.

[0089] (3) Add the 200-mesh positive electrode powder in step (1) to the deep eutectic solvent, where the mass ratio of the positive electrode powder to the deep eutectic solvent is 1:10. Heat and stir at 80 °C for 120 min, and after filtration, a lithium-containing leaching solution and leaching residue are obtained.

[0090] Element content test: Perform ICP test on the metal content in the lithium-containing leaching solution obtained in step (3) above, and calculate the leaching rates of lithium and iron respectively. The calculation method of the leaching rate is the same as that in Example 1. The results are shown in Table 10.

[0091] Table 10

[0092] According to the results in Table 10, it shows that the Li leaching rate in the lithium-containing leaching solution obtained in step (3) of Comparative Example 1 reaches 95.83%, and the Fe leaching rate is also as high as 88.56%. It can be seen that iron and lithium are leached simultaneously, and lithium cannot be selectively leached preferentially. The obtained leaching residue cannot be directly calcined to obtain iron phosphate, and the selective extraction of lithium and the direct regeneration of iron phosphate cannot be achieved synchronously.

[0093] Comparative Example 2 This comparative example provides a method for leaching the positive electrode powder of waste lithium iron phosphate batteries, including the following steps: (1) The positive electrode powder used is the 200-mesh positive electrode powder obtained in step (1) of Example 1.

[0094] (2) Mix lactic acid and ethylene glycol in a molar ratio of 1:1, and heat and stir at 80 °C for 30 min to obtain a deep eutectic solvent.

[0095] (3) Add the 200-mesh positive electrode powder in step (1) to the deep eutectic solvent, where the mass ratio of the positive electrode powder to the deep eutectic solvent is 1:10. Heat and stir at 80 °C for 120 min, and after filtration, a lithium-containing leaching solution and leaching residue are obtained.

[0096] Element content test: Perform ICP test on the metal content in the lithium-containing leaching solution obtained in step (3) above, and calculate the leaching rates of lithium and iron respectively. The calculation method of the leaching rate is the same as that in Example 1. The results are shown in Table 11.

[0097] Table 11

[0098] The results according to Table 11 show that the Li leaching rate in the lithium-containing leaching solution obtained in step (3) of Comparative Example 2 reaches 97.64%, and the Fe leaching rate is also as high as 92.15%. It can be seen that iron and lithium are leached efficiently at the same time, and lithium cannot be preferentially selectively leached. The obtained leaching residue cannot directly obtain iron phosphate through calcination, and the selective extraction of lithium and the direct regeneration of iron phosphate cannot be achieved simultaneously.

[0099] In summary, by using a specific eutectic solvent as the leaching medium, the present invention can achieve the selective extraction of lithium and the direct regeneration of iron phosphate in the cathode material of waste lithium iron phosphate batteries under mild conditions. Furthermore, it can also prepare a cathode material of lithium iron phosphate at the battery grade, realizing the green regeneration of the cathode material in waste lithium iron phosphate batteries.

[0100] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate, characterized in that, Including: Step S1: Provide the positive electrode powder of waste lithium iron phosphate batteries; Step S2: Mix and heat-stir a hydrogen bond donor and a hydrogen bond acceptor to obtain a deep eutectic solvent. The hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid, and the hydrogen bond acceptor is ethylene glycol; Step S3: Dilute the deep eutectic solvent obtained in Step S2 with water to obtain a diluted deep eutectic solvent, then add the positive electrode powder and an oxidant in Step S1, heat and stir, and obtain a lithium-containing leaching solution and leaching residue after filtration; Step S4: Concentrate and purify the lithium-containing leaching solution obtained in Step S3, and then add a saturated sodium carbonate solution to carry out a lithium precipitation reaction to obtain lithium carbonate; Step S5: Calcinate the leaching residue obtained in Step S3 to obtain iron phosphate.

2. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, wherein In Step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5 - 1.

2.

3. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In Step S2, the heating temperature for the mixing and heating-stirring is 25°C - 80°C, and the heating time is 30 min - 60 min.

4. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, wherein In Step S3, the mass fraction of the diluted deep eutectic solvent is 1 wt% - 20 wt%; the mass ratio of the positive electrode powder to the diluted deep eutectic solvent is 1:5 - 20; the oxidant is 10 wt% - 30 wt% hydrogen peroxide, and the addition amount of the hydrogen peroxide is 5 vol% - 15 vol%.

5. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, wherein In Step S3, the heating temperature for the heating and stirring is 60°C - 90°C, and the heating time is 60 min - 120 min.

6. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In Step S4, the concentration treatment specifically includes: Concentrating the lithium-containing leaching solution obtained in Step S3 to a concentration of 18 g / L - 30 g / L; The impurity removal treatment specifically includes: Adjusting the pH value to 10 - 12 with a 5 wt% - 10 wt% sodium hydroxide solution for impurity removal.

7. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In Step S4, the mass fraction of the saturated sodium carbonate solution is 25 wt% - 30 wt%, and the addition amount of the saturated sodium carbonate solution satisfies that the molar ratio of carbonate ions to lithium ions in the lithium-containing leaching solution is 0.6 - 0.75:1; The reaction temperature of the lithium precipitation reaction is 90°C - 95°C, and the reaction time is 1 h - 3 h.

8. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, wherein, In Step S5, the calcination temperature is 600°C - 800°C, the calcination time is 3 h - 6 h, and the calcination atmosphere is air.

9. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 1, wherein After Step S5, there is also a step: Mix and ball-mill the lithium carbonate obtained in Step S4 and the iron phosphate obtained in Step S5 with a carbon source, and obtain lithium iron phosphate after calcination.

10. The method for synchronously realizing lithium selective extraction and direct regeneration of iron phosphate according to claim 9, wherein The molar ratio of the lithium carbonate to the iron phosphate is 0.5 - 0.6:1; The carbon source is glucose, and the addition amount of the glucose is 10 wt% - 15 wt% of the mass of the iron phosphate; The calcination temperature is 350°C - 800°C, the calcination time is 8 h - 12 h, and the calcination atmosphere is argon.

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