Recycling method of lithium iron phosphate battery electrode material

Abstract

The invention relates to a method for recovering an electrode material of a lithium iron phosphate battery. The method comprises the following steps: 1) crushing, grinding and carrying out anaerobic pyrolysis on the electrode material of a discharged waste lithium ion battery; (2) carrying out aerobic roasting on the black powder obtained in the step (1); 3) putting the aerobic clinker obtained in the step 2) into a leaching tank, and adding concentrated sulfuric acid into the leaching tank at normal temperature; after fully stirring, carrying out solid-liquid separation; first filtrate and first leaching residues are obtained; 4) adjusting the pH value of the first filtrate obtained in the step 3) to 1-3; raising the temperature to 70 to 90 DEG C; after fully stirring, carrying out solid-liquid separation to obtain second filtrate and second leaching residues; and 5) introducing ammonia gas into the second filtrate obtained in the step 4) to precipitate copper ions and aluminum ions, and carrying out solid-liquid separation.According to the method, before leaching, the electrode material is subjected to aerobic roasting to oxidize LiFePO4 into Li3Fe2 (PO4) 3 and Fe2O3 so as to improve the fineness and porosity of the material, and grinding is not needed in subsequent leaching.

Description

Technical Field

[0001] This invention relates to a method for recycling lithium iron phosphate, and more particularly to a method for recycling lithium iron phosphate battery electrode materials. Background Technology

[0002] Since its discovery, lithium iron phosphate (LFP) batteries have dominated the lithium-ion battery market due to their low cost, long cycle life, and good safety performance. Consequently, the number of discarded LFP batteries is enormous. Improper disposal of these batteries can cause serious environmental pollution and resource waste.

[0003] Currently, the recycling of electrode materials for lithium iron phosphate (LFP) lithium-ion batteries generally employs hydrometallurgical recycling, pyrometallurgical recycling, and lithium replenishment regeneration. Among these, hydrometallurgical recycling is gaining increasing attention due to its advantages of high metal recovery rate, low energy consumption, and minimal environmental pollution. However, the leaching residue after hydrometallurgical recycling has low recycling value and is generally stockpiled or landfilled. The main component of leaching residue is iron-phosphorus slag, with a high phosphorus content, which can easily cause serious environmental pollution; therefore, it needs to be treated. Furthermore, traditional hydrometallurgical recycling currently uses high-temperature oxidation roasting, which is costly. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for recycling lithium iron phosphate battery electrode materials with low calcination cost, low requirements for leaching equipment, and harmless treatment of leaching products.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for recycling electrode materials of lithium iron phosphate batteries, comprising the following steps:

[0006] 1) The electrode material of the discharged waste lithium-ion battery is crushed, ground and pyrolyzed in an anaerobic environment to obtain a black powder containing organic binder.

[0007] 2) The black powder obtained in step 1) is subjected to aerobic roasting to obtain aerobic clinker; the temperature of aerobic roasting is between 450-550℃ and the time is between 20-60 minutes.

[0008] 3) Place the aerobic clinker obtained in step 2) into a leaching tank, add concentrated sulfuric acid to the leaching tank at room temperature; after thorough stirring, separate the solid and liquid; and obtain the first filtrate and the first leaching residue.

[0009] 4) Adjust the pH of the first filtrate obtained in step 3) to 1-3; raise the temperature to 70-90℃; after thorough stirring, separate the solid and liquid to obtain the second filtrate and the second leaching residue;

[0010] 5) Ammonia gas is introduced into the second filtrate obtained in step 4) to adjust the pH, so that copper ions and aluminum ions precipitate; solid-liquid separation.

[0011] The preferred method for recycling lithium iron phosphate battery electrode materials described above involves post-processing the second leaching residue obtained in step 4), which includes the following steps:

[0012] 4.1) Add the second leaching residue obtained in step 4) to the sulfuric acid solution and stir until homogeneous; the concentration of the sulfuric acid solution is 1.2 mol / L-1.5 mol / L; after adding the second leaching residue to the sulfuric acid solution, the solid-liquid ratio in the solution is 1:7; the second leaching residue is the solid residue of lithium iron phosphate after lithium extraction;

[0013] 4.2) Add iron powder to the solution from step 4.1); stir thoroughly at 75-100℃, and then separate the solid and liquid phases to obtain the third filtrate and the third leaching residue. The filtrate mainly contains phosphoric acid and ferrous sulfate, which can be separated by organic solvent extraction followed by water reverse extraction; or by heating and evaporation to crystallize.

[0014] The preferred method for recovering lithium iron phosphate battery electrode materials described above involves taking the mixed solution from step 4.1) and analyzing the content of its components, wherein the components include Fe. 3+ According to Fe 3+ The content of iron powder in step 4.2) is 1-1.1.

[0015] In the above-mentioned method for recycling lithium iron phosphate battery electrode materials, preferably, the molar ratio of iron phosphate to sulfuric acid in the leachate in step 4.1) is 1:2-1:3 (1:2.26).

[0016] In the above-mentioned method for recycling lithium iron phosphate battery electrode materials, preferably, the weight concentration of concentrated sulfuric acid in step 3) is between 95% and 98%.

[0017] In the above-mentioned method for recycling lithium iron phosphate battery electrode materials, preferably, the temperature of the anaerobic pyrolysis in step 1) is 400-800℃, and stirring is maintained during the anaerobic pyrolysis.

[0018] In the preferred embodiment of the above-mentioned method for recovering lithium iron phosphate battery electrode materials, the pH value of the filtrate is adjusted by adding water for dilution in step 4).

[0019] Compared with the prior art, the advantages of the present invention are as follows: The recycling method of the present invention has the following advantages: 1. Before leaching, the electrode material is first calcined with oxygen to oxidize LiFePO4 to Li3Fe2(PO4)3 and Fe2O3, thereby improving the fineness and porosity of the material, and grinding is not required in the subsequent leaching.

[0020] 2. Industrial concentrated sulfuric acid can be used as the leaching solution in this invention, which saves costs; this allows for a reduction in leaching temperature while ensuring the leaching rate.

[0021] 3. In this invention, the leaching material with ferric phosphate as the main component is post-treated to reduce the impact on the environment. Detailed Implementation

[0022] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0023] It should be noted that when a component is described as being "fixed to, attached to, connected to or connected to" another component, it can be directly fixed to, attached to, connected to or connected to the other component, or it can be indirectly fixed to, attached to, connected to or connected to the other component through other intermediate connectors.

[0024] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0025] Example 1

[0026] This embodiment provides a method for recycling electrode materials of lithium iron phosphate batteries, including the following steps:

[0027] 1) The electrode materials from discharged waste lithium-ion batteries are crushed, ground, and subjected to anaerobic pyrolysis to obtain a black powder containing organic binders. The anaerobic pyrolysis temperature is maintained at 400-800℃, and stirring is kept during the anaerobic pyrolysis process. The electrode materials mainly include copper foil, aluminum foil, separator, and electrode mixed powder.

[0028] 2) The black powder obtained in step 1) is subjected to aerobic calcination to obtain aerobic clinker; the aerobic calcination temperature is between 450-550℃, and the time is between 20-60 minutes. During aerobic calcination, LiFePO4 is almost completely oxidized to Li3Fe2(PO4)3 and Fe2O3, thereby promoting subsequent leaching. In step 2), the residual organic binders such as PVDF are pyrolyzed during aerobic calcination, thus creating pores. In this embodiment, the aerobic calcination temperature is between 450-550℃, which can ensure the Fe content in LiFePO4 is maintained. 2+ Oxidized into Fe 3+The material does not sinter at calcination temperatures of 450-550℃; and organic binders such as PVDF can be pyrolyzed, thereby generating a large number of nanoscale pores in the material. During aerobic calcination, the graphite in the material undergoes only slight oxidation.

[0029] 3) Place the aerobic clinker obtained in step 2) into a leaching tank, and add concentrated sulfuric acid with a concentration of 95%-98% to the leaching tank at room temperature; after thorough stirring, separate the solid and liquid; and obtain the first filtrate and the first leaching residue. In this embodiment, industrial sulfuric acid is used to save costs.

[0030] 4) Dilute the first filtrate obtained in step 3) with water to adjust the pH value to 1-3; raise the temperature to 70-90℃; after thorough stirring, separate the solid and liquid to obtain the second filtrate and the second leaching residue.

[0031] 5) Ammonia gas is introduced into the second filtrate obtained in step 4) to adjust the pH, so that copper ions and aluminum ions precipitate; solid-liquid separation.

[0032] In step 3) of this embodiment, during leaching, the reaction rate between Fe2O3 and concentrated sulfuric acid in the aerobic roasting product is slow. Specifically, because the leaching in step 3) of this embodiment is carried out at room temperature, the reaction between concentrated sulfuric acid and Fe2O3 is slow. Therefore, most of the Fe2O3 remains in the leaching residue, thereby reducing the amount of sulfuric acid used. Simultaneously, since LiFePO4 is almost completely oxidized to Li3Fe2(PO4)3 after aerobic roasting of the electrode material, there is essentially no Fe in the electrode material after aerobic roasting. 2+ This avoids the Fe... 2+ The oxidation reaction with concentrated sulfuric acid does not produce SO2. After the leaching reaction in step 3), the main components of the first leaching residue are graphite and Fe2O3.

[0033] In this embodiment, the following reactions mainly occur in step 3):

[0034] Li3Fe2(PO4)3 + H2SO4 + 2H2O = Li2SO4 + LiH2PO4 + 2FePO4⋅2H2O;

[0035] CuO + H2SO4 = CuSO4 + H2O;

[0036] Al2O3 + 3H2SO4 = Al2(SO4)3 + 3H2O;

[0037] Fe2O3 + 3H2SO4 = Fe2(SO4)3 + 3H2O.

[0038] In this embodiment, in step 2), increasing the calcination temperature can completely burn off the graphite, but at the graphite combustion temperature, the calcined electrode material will sinter, requiring grinding before the subsequent leaching reaction, which increases the process flow.

[0039] In this embodiment, after adjusting the pH of the second filtrate to 1-3 in step 4), a high-purity FePO4⋅2H2O will be obtained; Li + and Cu 2+ And Al 3+ Remaining in the second filtrate; after ammonia gas is introduced into the second filtrate in step 5), Cu 2+ And Al 3+ It will precipitate out from the second filtrate, Li + They will be left behind, thus completing the separation.

[0040] In this embodiment, the main components of the second leaching residue obtained in step 4) are ferric phosphate and graphite; the second leaching residue obtained in step 4) is then subjected to post-processing, which includes the following steps:

[0041] 4.1) Add the second leaching residue obtained in step 4) to the sulfuric acid solution and stir until homogeneous; the concentration of the sulfuric acid solution is 1.2 mol / L-1.5 mol / L; after adding the leachate to the sulfuric acid solution, the solid-liquid ratio in the solution is 1:7. The molar ratio of ferric phosphate to sulfuric acid in the second leaching residue is 1:2-1:3, with the optimal ratio being 1:1.25.

[0042] 4.2) Add iron powder to the solution from step 4.1); at 75-100℃; after thorough stirring, separate the solid and liquid to obtain the third filtrate and the third leaching residue. The third filtrate mainly contains phosphoric acid and ferrous sulfate, while the third leaching residue mainly contains graphite that was not completely separated in steps 3) and 4).

[0043] In this embodiment, the main reactions occurring during the post-treatment of the second leaching residue are as follows:

[0044] 2FePO4 + 3H2SO4 = 2Fe 3+ +3SO4 2- +2H3PO4;

[0045] 2Fe 3+ +Fe =3Fe 2+ ;

[0046] 2FePO4 + 3H2SO4 + Fe = 2Fe 2+ +3SO4 2- +2H3PO4;

[0047] Fe + H₂SO₄ = Fe2+ +SO4 2- +H2↑ ;

[0048] In this embodiment, during the treatment of ferric phosphate, FePO4 is dissolved in dilute sulfuric acid, and then iron powder is added; Fe 3+ It can be effectively reduced to Fe 2+ This process inhibits the redeposition of FePO4·2H2O, reducing FePO4 to the more soluble Fe2(PO4)3; thus, it reduces the consumption of H2SO4 during leaching. In the treatment of ferric phosphate, adding iron powder halves the leaching time and reduces sulfuric acid consumption by 25% compared to not adding iron powder.

[0049] In this embodiment, the separation of phosphoric acid and ferrous sulfate in the third filtrate can be achieved by concentration and crystallization or extraction.

Claims

1. A method for recycling electrode materials of lithium iron phosphate batteries, characterized in that; Includes the following steps: 1) The electrode material of the discharged waste lithium-ion battery is crushed, ground and pyrolyzed in an anaerobic environment to obtain a black powder containing organic binder. 2) The black powder obtained in step 1) is subjected to aerobic roasting to obtain aerobic clinker; the temperature of aerobic roasting is between 450-550℃ and the time is between 20-60 minutes. 3) Place the aerobic clinker obtained in step 2) into a leaching tank, add concentrated sulfuric acid to the leaching tank at room temperature; after thorough stirring, separate the solid and liquid; and obtain the first filtrate and the first leaching residue. 4) Adjust the pH of the first filtrate obtained in step 3) to 1-3; raise the temperature to 70-90℃; after thorough stirring, separate the solid and liquid to obtain the second filtrate and the second leaching residue; 5) Ammonia gas is introduced into the second filtrate obtained in step 4) to adjust the pH, so that copper ions and aluminum ions precipitate; solid-liquid separation.

2. The method for recycling lithium iron phosphate battery electrode materials according to claim 1, characterized in that; The second leaching residue obtained in step 4) is subjected to post-treatment, which includes the following steps: 4.1) Add the second leaching residue obtained in step 4) to the sulfuric acid solution and stir until homogeneous; the concentration of the sulfuric acid solution is 1.2 mol / L-1.5 mol / L; after adding the second leaching residue to the sulfuric acid solution, the solid-liquid ratio in the solution is 1:7; the second leaching residue is the solid residue of lithium iron phosphate after lithium extraction; 4.2) Add iron powder to the solution from step 4.1); stir thoroughly at 75-100℃, and then separate the solid and liquid to obtain the third filtrate and the third leaching residue. The filtrate mainly contains phosphoric acid and ferrous sulfate, which can be separated by organic solvent extraction followed by water reverse extraction, or by heating and evaporation to crystallize.

3. The method for recycling lithium iron phosphate battery electrode materials according to claim 2, characterized in that; Take the mixed solution from step 4.1) and analyze the content of its components, wherein the components include Fe. 3+ According to Fe 3+ The content of iron powder in step 4.2) is 1-1.

1.

4. The method for recycling lithium iron phosphate battery electrode materials according to claim 2, characterized in that; In step 4.1), the molar ratio of ferric phosphate to sulfuric acid in the leachate is 1:2-1:3 (1:2.26).

5. The method for recycling lithium iron phosphate battery electrode materials according to claim 1, characterized in that: In step 3), the weight concentration of concentrated sulfuric acid is between 95% and 98%.

6. The method for recycling lithium iron phosphate battery electrode materials according to claim 1, characterized in that: In step 1), the temperature of anaerobic pyrolysis is 400-800℃, and stirring is maintained during anaerobic pyrolysis.

7. The method for recycling lithium iron phosphate battery electrode materials according to claim 1, characterized in that: In step 4), the pH value of the filtrate is adjusted by diluting it with water.