Method for recovering aluminum, iron and lithium from waste lithium iron phosphate battery

Abstract

The invention discloses a method for recycling aluminum, iron and lithium from waste lithium iron phosphate batteries, and belongs to the technical field of lithium battery recycling. The method comprises the following steps: firstly, separating a positive electrode material of a waste battery cell, removing a binder through high-temperature treatment, adding the positive electrode material into a NaOH solution and a viscous liquid cosolvent, finally stirring and dissolving, neutralizing and adjusting the pH value through sulfuric acid, and precipitating and recovering aluminum; then sulfuric acid is matched with hydrogen peroxide, residual filter residues are stirred and dissolved, and iron and lithium are precipitated and recycled through multi-step pH value adjustment; the viscous liquid cosolvent disclosed by the invention is prepared from 1-aminoethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imine salt and boric acid powder; the synergism of impurity dispersion and metal dissolution can be enhanced, and the solution viscosity and filtering resistance can be reduced. According to the method, the recovery rate of aluminum, lithium and iron is high, the recovery cost is low, and the economic value is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recycling, and in particular relates to a method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion secondary batteries are widely used in electric vehicles, consumer electronics, and other fields. However, the large amount of waste lithium-ion secondary batteries has led to problems such as resource waste and environmental pollution. The cathode materials of waste lithium-ion secondary batteries contain various valuable metal elements such as aluminum, lithium, and iron. Effectively recycling these metal elements would not only alleviate resource shortages but also reduce environmental impact.

[0003] Currently, methods for recycling spent lithium-ion secondary battery cathode materials have several drawbacks. Some methods have low recovery efficiency and fail to fully extract metal elements; some, such as those in patent applications CN116903003A and CN117013128A, are complex and energy-intensive, leading to increased production costs; and some methods are prone to metal element loss or impurities during the recovery process, impacting the quality of the recycled product. Therefore, there is an urgent need to develop an efficient, environmentally friendly, and economical method for recovering metal elements from spent lithium-ion secondary battery cathode materials. Summary of the Invention

[0004] To address the above-mentioned problems, the present invention provides a method for recovering aluminum, iron, and lithium from waste lithium iron phosphate batteries. The method first separates the positive electrode material from the waste battery core, removes the binder through high-temperature treatment, and then adds it to a NaOH solution and a viscous liquid co-solvent, stirring and dissolving it. The pH is then adjusted by neutralization with sulfuric acid to precipitate and recover the aluminum. Sulfuric acid is then combined with hydrogen peroxide to stir and dissolve the remaining filter residue. The pH is then adjusted in multiple steps to precipitate iron and lithium, respectively, to obtain Fe(OH)3 and Li2CO3 precipitates. The viscous liquid co-solvent of the present invention is prepared from 1-aminoethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt and boric acid powder. The method has high aluminum, lithium, and iron recovery rates, low recovery costs, and high economic value.

[0005] The specific technical solutions of the present invention are as follows: The present invention provides a method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, comprising the following steps: S1. Remove the outer packaging of the waste lithium iron phosphate battery, separate the battery cells, and obtain the positive electrode material; S2, crushing the positive electrode material and then subjecting it to high temperature treatment to decompose the binder; S3. Aluminum recovery: The positive electrode material with the binder removed is placed in an alkaline solution, and a viscous liquid co-solvent is added to dissolve the aluminum foil; the viscous liquid co-solvent is a boric acid functionalized compound containing an ionic liquid structure; After filtration, a filter residue and a filtrate are obtained, an acid solution is added to the filtrate to adjust the pH value of the filtrate, and the precipitate is collected by filtration to complete the recovery of the aluminum element; S4, lithium and iron element recovery: Dissolving the filter residue collected in step S3 with an acid solution and an oxidant to allow iron and lithium to enter the solution; filtering to obtain an iron-lithium solution; adjusting the pH of the iron-lithium solution to 7-8, filtering and separating the precipitate to complete the recovery of the iron element; Then, a carbonate solution is added to the filtrate after separation and precipitation, and the precipitate is collected by filtration to complete the recovery of the lithium element.

[0006] Specifically, in step S2, the high temperature treatment temperature is 300-350° C., and the time is 40-60 minutes.

[0007] As a preferred embodiment, in step S3, the alkali solution is a 5%-10% mass concentration NaOH solution. By weight, the mixture comprises 14-22 parts of the binder-removed positive electrode material, 120-200 parts of the alkali solution, and 1-5 parts of the viscous liquid co-solvent. The mixture is stirred and dissolved at room temperature for 20-30 minutes to fully dissolve the aluminum and form NaAlO2.

[0008] Furthermore, in step S3, the acid solution is a sulfuric acid solution with a mass concentration of 10%-20%, and the pH of the filtrate is adjusted to 9. At this pH, aluminum is precipitated in the form of Al(OH)3, and the precipitated solution is filtered to obtain Al(OH)3 precipitate.

[0009] As a preferred embodiment, the boric acid functionalized compound containing an ionic liquid structure is formed by combining an aqueous solution of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt with boric acid through an amidation reaction.

[0010] Furthermore, the preparation method of the boric acid functionalized compound containing an ionic liquid structure comprises: Prepare 43-86 parts of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt into a 20%-30% mass concentration aqueous solution and fully dissolve it at 40-60°C; Add 6-12 parts of boric acid and react at 60-70°C for 2-6 hours to obtain the product, during which time a NaOH solution with a mass concentration of 5%-10% is used to maintain the pH at 8-9.

[0011] Reaction mechanism: In lithium battery recovery, the anions and cations of the ionic liquid (1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt aqueous solution) interact electrostatically and coordinate with metal ions such as lithium, aluminum, and iron. The trifluoromethanesulfonyl imide group of the anion reacts with Li+ Form a stable ion pair to reduce the crystallization free energy of Li2CO3; the imidazole ring structure of the cation can react with Al 3+ 、Fe 3+ Weak coordination occurs, promoting its dissolution and dispersion in the solution. At the same time, ionic liquids have good solubility for binder decomposition products and carbon impurities, accelerating material separation.

[0012] As a preferred embodiment, in step S4, the acid solution is a sulfuric acid solution with a mass concentration of 10%-20%, and the oxidant is a hydrogen peroxide solution with a mass concentration of 20%-30%; By weight, 12-18 parts of filter residue, 60-100 parts of acid solution, and 50-80 parts of oxidant; The dissolution conditions are stirring at 50-60°C for 90-120 minutes.

[0013] During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, entering the solution in the form of Fe2(SO4)3 and Li2SO4, thereby separating it from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate. The dissolved solution is then filtered to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity filter residue.

[0014] Furthermore, the carbonate solution is a saturated Na2CO3 solution, and the addition amount is 80-100 parts by weight; after adding the carbonate solution, the reaction is carried out at 80-90°C for 90-120 minutes to precipitate lithium as Li2CO3, and the Li2CO3 precipitate is collected by filtration.

[0015] In some embodiments of the present invention, in step S4, when adjusting the pH of the iron-containing lithium solution, a mixed alkaline precipitant of NaOH solution and ammonia water is used to adjust the pH.

[0016] Furthermore, the volume ratio of the NaOH solution to the ammonia water is 2-3:1, wherein the mass concentration of the NaOH solution is 5%-10%, and the mass concentration of the ammonia water is 5%-10%.

[0017] Add 5%-10% NaOH solution and 5%-10% ammonia water to the filtrate to adjust the pH value to 7-8, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration.

[0018] Compared with the prior art, the present invention has the following significant effects: 1. Enhance the synergy between impurity dispersion and metal dissolution: effectively improve the carbon impurity dispersion efficiency and metal ion leaching rate, and significantly improve the stability of the dissolution system.

[0019] 2. Reduce solution viscosity and filtration resistance: effectively inhibit the formation of colloidal substances during the dissolution process, reduce solution viscosity and shorten filtration time.

[0020] 3. Efficient recycling: The present invention can efficiently recover metal elements such as aluminum, lithium, and iron from waste lithium-ion secondary battery positive electrode materials, thereby improving the recycling rate of resources. Among them, the recovery rate of aluminum can reach up to 91.3%, the recovery rate of lithium can reach up to 92.1%, and the recovery rate of iron can reach up to 99.5%.

[0021] 4. Good environmental protection: It reduces the pollution of waste lithium-ion secondary batteries to the environment, and at the same time realizes the recycling of resources, which meets the requirements of sustainable development. DETAILED DESCRIPTION

[0022] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention object, the following is a detailed description in conjunction with examples and comparative examples: Example 1 The preparation method of the viscous liquid cosolvent used in this embodiment is: H1: Dissolve 43 g of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in deionized water to prepare a 20% solution, heat to 40°C and stir until completely dissolved; H2: Slowly add 6 g of boric acid powder and continue stirring at 60 °C for 2 hours. During this time, add 5% NaOH solution to adjust the pH to 8. H3: After the reaction is completed, water is removed by distillation under reduced pressure to obtain a viscous liquid co-solvent containing an ionic liquid structure.

[0023] A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, the operating steps of which are as follows: S1. Cell processing and cathode material acquisition: After removing the outer packaging of the waste lithium-ion secondary battery, take out the cell and separate the cathode material; S2. Crushing the positive electrode sheet and removing the binder: Crushing the positive electrode sheet into small pieces, and then subjecting the crushed pieces to a high-temperature treatment at 300°C for 40 minutes to decompose and remove the binder at high temperature; S3. Aluminum recovery: Aluminum foil dissolution: 14g of the positive electrode material after removing the binder is placed in 120g of a 5% NaOH solution, 1g of a viscous liquid co-solvent is added, and the mixture is stirred and dissolved at room temperature for 20min to fully dissolve the aluminum to form NaAlO2; Neutralization precipitation: Filter the dissolved solution to remove insoluble matter, add 10% sulfuric acid solution to the filtrate for neutralization, adjust the solution pH to 9, and precipitate aluminum in the form of Al(OH)3; Filtration and collection: Filter the precipitated solution to obtain Al(OH)3 precipitate; S4, lithium and iron element recovery: Dissolution of filter residue: 12g of filter residue after removing the aluminum foil is placed in 60g of 10% sulfuric acid solution, and 50g of 20% hydrogen peroxide is added. Stir and dissolve at 50°C for 90min. During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, and enters the solution in the form of Fe2(SO4)3 and Li2SO4, achieving separation from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate; Filtration separation: Filter the dissolved solution to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity residue; Iron precipitation: add 5% NaOH solution and 5% ammonia water to the filtrate to adjust the pH to 7, with the volume ratio of NaOH solution to ammonia water being 2:1, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration; Lithium element precipitation: add 80g of saturated Na2CO3 solution to the residual liquid after separating the Fe(OH)3 precipitate, react at 80℃ for 90min, so that lithium is precipitated as Li2CO3, and collect the Li2CO3 precipitate by filtration.

[0024] Example 2 The preparation method of the viscous liquid cosolvent used in this embodiment is: H1: Dissolve 55g of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in deionized water to prepare a 25% solution, heat to 45°C and stir until completely dissolved; H2: Slowly add 8 g of boric acid powder and continue stirring at 65 °C for 3 hours. During this time, add 6% NaOH solution to adjust the pH to 8. H3: After the reaction is completed, water is removed by distillation under reduced pressure to obtain a viscous liquid co-solvent containing an ionic liquid structure.

[0025] A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, the operating steps of which are as follows: S1. Cell processing and cathode material acquisition: After removing the outer packaging of the waste lithium-ion secondary battery, take out the cell and separate the cathode material; S2. Crushing the positive electrode sheet and removing the binder: Crushing the positive electrode sheet into small pieces, and then subjecting the crushed pieces to a high-temperature treatment at 310°C for 45 minutes to decompose and remove the binder at high temperature; S3. Aluminum recovery: Aluminum foil dissolution: 16g of the positive electrode material after removing the binder is placed in 140g of a 6% NaOH solution, 2g of a viscous liquid co-solvent is added, and the mixture is stirred and dissolved at room temperature for 25min to fully dissolve the aluminum to form NaAlO2; Neutralization precipitation: Filter the dissolved solution to remove insoluble matter, add 15% sulfuric acid solution to the filtrate for neutralization, adjust the solution pH to 9, and precipitate aluminum in the form of Al(OH)3; Filtration and collection: Filter the precipitated solution to obtain Al(OH)3 precipitate; S4, lithium and iron element recovery: Dissolution of filter residue: 14g of filter residue after removing the aluminum foil is placed in 70g of 15% sulfuric acid solution, and 60g of 25% hydrogen peroxide is added. Stir and dissolve at 55°C for 100min. During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, and enters the solution in the form of Fe2(SO4)3 and Li2SO4, achieving separation from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate; Filtration separation: Filter the dissolved solution to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity residue; Iron precipitation: add 6% NaOH solution and 6% ammonia water to the filtrate to adjust the pH to 7, with the volume ratio of NaOH solution to ammonia water being 2:1, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration; Lithium element precipitation: add 85g of saturated Na2CO3 solution to the residual liquid after separating the Fe(OH)3 precipitate, react at 85℃ for 100min, so that lithium is precipitated as Li2CO3, and filter and collect the Li2CO3 precipitate.

[0026] Example 3 The preparation method of the viscous liquid cosolvent used in this embodiment is: H1: Dissolve 80g of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in deionized water to prepare a 25% solution, heat to 55°C and stir until completely dissolved; H2: Slowly add 10 g of boric acid powder and continue stirring at 65 °C for 5 hours. During this time, add 8% NaOH solution dropwise to adjust the pH to 9. H3: After the reaction is completed, water is removed by distillation under reduced pressure to obtain a viscous liquid co-solvent containing an ionic liquid structure.

[0027] A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, the operating steps of which are as follows: S1. Cell processing and cathode material acquisition: After removing the outer packaging of the waste lithium-ion secondary battery, take out the cell and separate the cathode material; S2. Crushing the positive electrode sheet and removing the binder: Crushing the positive electrode sheet into small pieces, and then subjecting the crushed pieces to a high-temperature treatment at 340°C for 55 minutes to decompose and remove the binder at high temperature; S3. Aluminum recovery: Dissolution of aluminum foil: Place 20g of the cathode material after removing the binder into 180g of 8% NaOH solution, add 4g of viscous liquid co-solvent, and stir and dissolve at room temperature for 25min to fully dissolve the aluminum to form NaAlO2; Neutralization precipitation: Filter the dissolved solution to remove insoluble matter, add 15% sulfuric acid solution to the filtrate for neutralization, adjust the solution pH to 9, and precipitate aluminum in the form of Al(OH)3; Filtration and collection: Filter the precipitated solution to obtain Al(OH)3 precipitate; S4, lithium and iron element recovery: Dissolution of filter residue: 16g of filter residue after removing the aluminum foil is placed in 90g of 15% sulfuric acid solution, and 70g of 25% hydrogen peroxide is added. Stir and dissolve at 55°C for 110min. During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, entering the solution in the form of Fe2(SO4)3 and Li2SO4, achieving separation from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate; Filtration separation: Filter the dissolved solution to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity residue; Iron precipitation: add 8% NaOH solution and 8% ammonia water to the filtrate to adjust the pH to 8, with the volume ratio of NaOH solution to ammonia water being 3:1, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration; Lithium element precipitation: Add 95g of saturated Na2CO3 solution to the residual liquid after separating the Fe(OH)3 precipitate, react at 85℃ for 110min, so that lithium is precipitated as Li2CO3, and filter and collect the Li2CO3 precipitate.

[0028] Example 4 The preparation method of the viscous liquid cosolvent used in this embodiment is: H1: Dissolve 86g of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide in deionized water to make a 30% solution, heat to 60°C and stir until completely dissolved; H2: Slowly add 12 g of boric acid powder and continue stirring at 70 °C for 6 h. During this time, add 10% NaOH solution dropwise to adjust the pH to 9. H3: After the reaction is completed, water is removed by distillation under reduced pressure to obtain a viscous liquid co-solvent containing an ionic liquid structure.

[0029] A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, the operating steps of which are as follows: S1. Cell processing and cathode material acquisition: After removing the outer packaging of the waste lithium-ion secondary battery, take out the cell and separate the cathode material; S2. Crushing the positive electrode sheet and removing the binder: Crushing the positive electrode sheet into small pieces, and then subjecting the crushed pieces to a high-temperature treatment at 350°C for 60 minutes to decompose and remove the binder at high temperature; S3. Aluminum recovery: Aluminum foil dissolution: 22g of the positive electrode material after removing the binder is placed in 200g of a 10% NaOH solution, 5g of a viscous liquid co-solvent is added, and the mixture is stirred and dissolved at room temperature for 30min to fully dissolve the aluminum to form NaAlO2; Neutralization precipitation: The dissolved solution is filtered to remove insoluble matter, and a 20% sulfuric acid solution is added to the filtrate for neutralization. The pH value of the solution is adjusted to 9, and aluminum is precipitated in the form of Al(OH)3; Filtration and collection: Filter the precipitated solution to obtain Al(OH)3 precipitate; S4, lithium and iron element recovery: Dissolution of filter residue: 18g of filter residue after removing the aluminum foil is placed in 100g of 20% sulfuric acid solution, and 80g of 30% hydrogen peroxide is added. Stir and dissolve at 60°C for 120min. During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, and enters the solution in the form of Fe2(SO4)3 and Li2SO4, achieving separation from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate; Filtration separation: Filter the dissolved solution to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity residue; Iron precipitation: add 10% NaOH solution and 10% ammonia water to the filtrate to adjust the pH to 8, with the volume ratio of NaOH solution to ammonia water being 3:1, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration; Lithium element precipitation: Add 100g of saturated Na2CO3 solution to the residual liquid after separating the Fe(OH)3 precipitate, react at 90℃ for 120min to precipitate lithium as Li2CO3, and collect the Li2CO3 precipitate by filtration.

[0030] Comparative Example 1 A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, the operating steps of which are as follows: S1. Cell processing and cathode material acquisition: After removing the outer packaging of the waste lithium-ion secondary battery, take out the cell and separate the cathode material; S2. Crushing the positive electrode sheet and removing the binder: Crushing the positive electrode sheet into small pieces, and then subjecting the crushed pieces to a high-temperature treatment at 300°C for 40 minutes to decompose and remove the binder at high temperature; S3. Aluminum recovery: Aluminum foil dissolution: 14g of the positive electrode material after removing the binder was placed in 120g of a 5% NaOH solution and stirred at room temperature for 20min to fully dissolve the aluminum to form NaAlO2. Neutralization precipitation: Filter the dissolved solution to remove insoluble matter, add 10% sulfuric acid solution to the filtrate for neutralization, adjust the solution pH to 9, and precipitate aluminum in the form of Al(OH)3; Filtration and collection: Filter the precipitated solution to obtain Al(OH)3 precipitate; S4, lithium and iron element recovery: Dissolution of filter residue: 12g of filter residue after removing the aluminum foil is placed in 60g of 10% sulfuric acid solution, and 50g of 20% hydrogen peroxide is added. Stir and dissolve at 50°C for 90min. During this process, lithium iron phosphate reacts with sulfuric acid and hydrogen peroxide, and enters the solution in the form of Fe2(SO4)3 and Li2SO4, achieving separation from impurities such as carbon black and carbon coated on the surface of lithium iron phosphate; Filtration separation: Filter the dissolved solution to separate the filtrate containing Fe2(SO4)3 and Li2SO4 and the impurity residue; Iron precipitation: add 5% NaOH solution and 5% ammonia water to the filtrate to adjust the pH to 7, with the volume ratio of NaOH solution to ammonia water being 2:1, so that the iron is precipitated as Fe(OH)3, and the Fe(OH)3 precipitate is separated by filtration; Lithium element precipitation: add 80g of saturated Na2CO3 solution to the residual liquid after separating the Fe(OH)3 precipitate, react at 80℃ for 90min, so that lithium is precipitated as Li2CO3, and collect the Li2CO3 precipitate by filtration.

[0031] Test Example 1 The recovery rates of aluminum, lithium, and iron were determined using inductively coupled plasma atomic emission spectrometry. The results are shown in Table 1.

[0032] Table 1

[0033] The data of the above examples and comparative examples show that, as shown in Table 1, in the recovery rate tests of aluminum, lithium, and iron, the recovery rates of Examples 1-4 of the present invention are significantly higher than those of Comparative Example 1. Specifically, the recovery rate of aluminum in the examples is 90.3%-91.3%, with a maximum of 91.3%; the recovery rate of lithium is 90.9%-92.1%, with a maximum of 92.1%; and the recovery rate of iron is 98.4%-99.5%, with a maximum of 99.5%. In Comparative Example 1, the recovery rates of aluminum, lithium, and iron are only 60.8%, 63.4%, and 76.7%, respectively, which are significantly lower than those of the examples, fully demonstrating the significant advantages of the present invention in the recovery efficiency of aluminum, lithium, and iron.

Claims

1. A method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries, characterized in that: The following steps are involved: S1. Remove the outer packaging of the waste lithium iron phosphate battery, separate the battery cells, and obtain the positive electrode material; S2, crushing the positive electrode material and then subjecting it to high temperature treatment to decompose the binder; S3. Aluminum recovery: The positive electrode material with the binder removed is placed in an alkaline solution, and a viscous liquid co-solvent is added to dissolve the aluminum foil; the viscous liquid co-solvent is a boric acid functionalized compound containing an ionic liquid structure; After filtration, a filter residue and a filtrate are obtained, an acid solution is added to the filtrate to adjust the pH value of the filtrate, and the precipitate is collected by filtration to complete the recovery of the aluminum element; S4, lithium and iron element recovery: Dissolving the filter residue collected in step S3 with acid and an oxidant to allow the iron and lithium to enter the solution; After filtering, an iron- and lithium-containing solution is obtained; the pH of the iron- and lithium-containing solution is adjusted to 7-8, and the iron element is recovered by filtering and separating the precipitate; Then, a carbonate solution is added to the filtrate after separation and precipitation, and the precipitate is collected by filtration to complete the recovery of the lithium element.

2. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S2, the high temperature treatment is performed at a temperature of 300-350° C. for a time of 40-60 minutes.

3. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S3, the alkali solution is a NaOH solution with a mass concentration of 5%-10%. In parts by weight, the positive electrode material from which the binder has been removed, the alkali solution, and the viscous liquid co-solvent are 14-22 parts, 120-200 parts, and 1-5 parts.

4. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1 or 3, characterized in that: In step S3, the acid solution is a sulfuric acid solution with a mass concentration of 10%-20%, and the pH of the filtrate is adjusted to 9.

5. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: The boric acid functionalized compound containing an ionic liquid structure is formed by combining a 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt aqueous solution with boric acid through an amidation reaction.

6. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: The preparation method of the boric acid functionalized compound containing an ionic liquid structure comprises: Prepare 43-86 parts of 1-aminoethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt into a 20%-30% mass concentration aqueous solution and fully dissolve it at 40-60°C; Add 6-12 parts of boric acid and react at 60-70°C for 2-6 hours to obtain the product, during which time a NaOH solution with a mass concentration of 5%-10% is used to maintain the pH at 8-9.

7. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S4, the acid solution is a sulfuric acid solution with a mass concentration of 10%-20%, and the oxidant is a hydrogen peroxide solution with a mass concentration of 20%-30%; By weight, 12-18 parts of filter residue, 60-100 parts of acid solution, and 50-80 parts of oxidant; The dissolution conditions are stirring at 50-60°C for 90-120 minutes.

8. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 7, characterized in that: The carbonate solution is a saturated Na2CO3 solution, and the addition amount is 80-100 parts by weight; After adding the carbonate solution, react at 80-90°C for 90-120 minutes.

9. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: In step S4, when adjusting the pH of the iron-lithium solution, a mixed alkaline precipitant of NaOH solution and ammonia water is used to adjust the pH.

10. The method for recovering aluminum, iron and lithium from waste lithium iron phosphate batteries according to claim 9, characterized in that: The volume ratio of the NaOH solution to the ammonia water is 2-3:1, wherein the mass concentration of the NaOH solution is 5%-10%, and the mass concentration of the ammonia water is 5%-10%.

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