Method for regenerating lithium iron phosphate in electrode material

Abstract

The invention discloses a method for regenerating lithium iron phosphate in an electrode material. The method comprises the following steps: adding electrode material powder containing lithium iron phosphate, a photocatalyst and glacial acetic acid into water, and uniformly mixing to obtain a first reaction solution; introducing oxygen into the first reaction solution to obtain a second reaction solution; illuminating the second reaction liquid to perform a photocatalytic reaction to obtain a third reaction liquid; filtering and separating the third reaction liquid into filtrate and filter residues, drying the filter residues to obtain iron phosphate, adding a saturated sodium carbonate aqueous solution into the filtrate, heating and reacting, filtering, and taking precipitate to obtain lithium carbonate; and mixing the iron phosphate and the lithium carbonate, and calcining to obtain regenerated lithium iron phosphate. According to the method, the lithium iron phosphate battery is recycled by utilizing a photocatalytic means with mild reaction conditions, the operation process is simple, and the pollution of the generated wastewater is reduced. According to the method, the leaching rates of lithium and iron can reach 94.81% and 2.9%, efficient recovery of lithium carbonate and iron phosphate is achieved, and then the recovery efficiency of lithium iron phosphate is improved.

Description

Technical Field

[0001] The invention relates to a lithium iron phosphate regeneration method, in particular to a lithium iron phosphate regeneration method in waste lithium iron phosphate battery electrode materials. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, fast charge and discharge speed, long cycle life, and stable high and low temperature performance, and have become the core component of the energy supply system of electric vehicles. The life cycle of LIB batteries is only 3-6 years. Recovering valuable metal elements from retired LIB batteries is of great significance for reducing production costs and reducing resource consumption.

[0003] According to the composition of the positive electrode, LIBs mainly include lithium iron phosphate (LFP) batteries, lithium cobalt oxide (LCO) batteries, lithium manganese oxide (LMO), lithium nickel cobalt manganese oxide (NCM) batteries, and lithium nickel cobalt aluminum oxide (NCA) batteries. At present, LFP and NCM batteries are the two mainstream products in the global electric vehicle industry. However, high-value elements such as Co and Ni have better recycling prospects in the market. For LFP batteries, the main metals recovered are Li and Fe, which are lower in value than Co, Ni, and Mn. In addition, due to the oxygen affinity of lithium, high-temperature metallurgical technology may cause lithium to slag, or volatilize and cause losses due to its high reactivity and hydrogen atomic mass. Lithium ions in the solution will hydrolyze during the hydrometallurgical process, so the recovery rate of lithium needs to be improved. For these reasons, it is urgent to study the key difficulties in the resource utilization of retired LFP batteries to recover lithium metal and regenerate them. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for regenerating lithium iron phosphate in an electrode material to solve the problem of how to recycle and regenerate lithium iron phosphate.

[0005] Technical solution: The method for regenerating lithium iron phosphate in an electrode material described in the present invention comprises the following steps:

[0006] (1) adding lithium iron phosphate-containing electrode material powder, a photocatalyst and glacial acetic acid into water and mixing them to obtain a first reaction solution;

[0007] (2) introducing oxygen into the first reaction liquid to obtain a second reaction liquid;

[0008] (3) irradiating the second reaction liquid with light to perform a photocatalytic reaction to obtain a third reaction liquid;

[0009] (4) filtering the third reaction liquid to separate into a filtrate and a filter residue, drying the filter residue to obtain iron phosphate, adding a saturated sodium carbonate aqueous solution to the filtrate, heating the reaction, and filtering the precipitate to obtain lithium carbonate;

[0010] (5) Mixing the iron phosphate and lithium carbonate described in step (4) and calcining them to obtain regenerated lithium iron phosphate.

[0011] Preferably, in step (1), the photocatalyst is phosphotungstic acid.

[0012] The present invention effectively improves the leaching rate of lithium and iron in the positive electrode material by selecting an appropriate photocatalyst (phosphotungstic acid) for photocatalytic reaction, and supplemented with an appropriate leaching agent (glacial acetic acid) and an oxidant (oxygen). In the chemical reaction process, phosphotungstic acid (molecular formula H3(PW 12 O 40 )) has good oxidizability. Tungsten element can change from +6 valence to +5 valence, and phosphotungstic acid can change from +5 valence to +6 valence through O2 and light. Lithium iron phosphate cannot be converted into iron phosphate by itself, so it is oxidized and reduced through phosphotungstic acid. For example, transition metals such as manganese +7 valence, chromium +6 valence and tungsten +6 valence can oxidize lithium iron phosphate with their high valence states. Therefore, with the assistance of phosphotungstic acid, lithium iron phosphate is oxidized into iron phosphate. At the same time, through the oxidation of phosphotungstic acid and with the assistance of glacial acetic acid acid, lithium iron phosphate will become FePO4 (Fe is +3 valence) and CH3COOLi. Adding an appropriate amount of phosphotungstic acid, under the conditions of excess O2 and light, it will circulate into +6 valence phosphotungstic acid. During the light process, O2 may combine with water to provide a better leaching environment.

[0013] Preferably, in step (1), the electrode material powder containing lithium iron phosphate is prepared as follows:

[0014] The waste lithium iron phosphate batteries after discharge treatment are disassembled, the disassembled positive electrode sheets containing lithium iron phosphate are dried and then calcined at low temperature, and the materials peeled off from the current collector are ground to obtain the electrode material powder containing lithium iron phosphate.

[0015] Preferably, the low-temperature calcination condition is calcination at 500-600° C. for 1-2 h.

[0016] Preferably, in step (1), the material-liquid ratio of the electrode material powder containing lithium iron phosphate, the photocatalyst, glacial acetic acid and water is 10-100 g: 0.1-10 mg: 1-100 mg: 30-80 mL.

[0017] Preferably, in step (2), the method of introducing oxygen is: introducing oxygen into the first reaction liquid at a gas flow rate of 0.1-10 L / min.

[0018] Preferably, in step (3), the photocatalytic reaction method is to treat the second reaction liquid with light for 0.5-8h under stirring.

[0019] Preferably, in step (4), the volume ratio of the filtrate to the saturated sodium carbonate aqueous solution is 10:1-30; the heating reaction method is: heating to 90-100°C for 1-4h until a white precipitate is generated.

[0020] Preferably, in step (5), iron phosphate and lithium carbonate are mixed in a molar ratio of iron element to lithium element of 1:1.03-1.07.

[0021] Preferably, in step (5), the calcination conditions are calcination at 650-750° C. for 1-5 h in air atmosphere.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0023] The present invention avoids the use of strong acid and strong alkali in the recycling process, utilizes photocatalytic means with mild reaction conditions to recycle lithium iron phosphate batteries, has a simple operation process, and reduces the pollution of the generated wastewater. The present invention effectively improves the leaching rate of lithium and iron in waste positive electrode materials, and the leaching rate of lithium and iron can reach 94.81% and 2.9%, respectively, realizes the efficient recovery of lithium carbonate and iron phosphate, and further improves the recovery efficiency of lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD spectrum of the waste positive electrode sheet containing lithium iron phosphate before low-temperature calcination;

[0025] Figure 2 is the XRD spectrum of the electrode material powder containing lithium iron phosphate in Example 1;

[0026] Figure 3 The XRD spectrum of the iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0028] Example 1: A method for regenerating lithium iron phosphate in an electrode material, comprising the following steps;

[0029] (1) The waste lithium iron phosphate battery is discharged by a blue battery system until the voltage is displayed as 0V, and then the battery is disassembled, the disassembled positive electrode sheet containing lithium iron phosphate is dried, calcined at 550°C for 1.5h, and the material peeled off from the current collector is ground to obtain an electrode material powder containing lithium iron phosphate, such as Figure 2 shown.

[0030] (2) adding 70 g of lithium iron phosphate-containing electrode material powder, 5 mg of phosphotungstic acid and 50 mg of glacial acetic acid to 60 mL of deionized water and mixing to obtain a first reaction solution;

[0031] (3) introducing oxygen into the first reaction liquid at a gas flow rate of 4 L / min to obtain a second reaction liquid;

[0032] (4) treating the second reaction solution with visible light for 4 h under stirring at 700 rpm to obtain a third reaction solution;

[0033] (5) The third reaction liquid was filtered to separate into a filtrate and a filter residue, the filter residue was washed with deionized water for 3 times, and then placed in a vacuum oven at 80° C. and dried for 12 h to obtain iron phosphate, such as Figure 3 As shown; add saturated sodium carbonate aqueous solution to the filtrate at a volume ratio of 1:2, heat to 95°C and react for 2.5 hours until a white precipitate is generated, filter the precipitate with a vacuum filtration device while it is hot, wash the precipitate with deionized water for 3 times, and dry it in a vacuum oven at 80°C to constant weight to obtain lithium carbonate;

[0034] (6) The iron phosphate and lithium carbonate described in step (5) are mixed in a molar ratio of iron to lithium of 1:1.05, and then calcined at 700° C. for 3 h in an air atmosphere to obtain regenerated lithium iron phosphate.

[0035] Embodiment 2: A method for regenerating lithium iron phosphate in an electrode material, comprising the following steps;

[0036] (1) The waste lithium iron phosphate battery is discharged by a blue battery system until the voltage is displayed as 0 V, and then the battery is disassembled, the disassembled positive electrode sheet containing lithium iron phosphate is dried, calcined at 500° C. for 2 h, and the material peeled off from the current collector is ground to obtain an electrode material powder containing lithium iron phosphate.

[0037] (2) adding 10 g of lithium iron phosphate-containing electrode material powder, 0.1 mg of phosphotungstic acid and 1 mg of glacial acetic acid to 30 mL of deionized water and mixing to obtain a first reaction solution;

[0038] (3) introducing oxygen into the first reaction liquid at a gas flow rate of 1 L / min to obtain a second reaction liquid;

[0039] (4) treating the second reaction liquid with visible light for 0.5 h under stirring at 500 rpm to obtain a third reaction liquid;

[0040] (5) filtering the third reaction liquid to separate into a filtrate and a filter residue, washing the filter residue with deionized water three times, and then drying it in a vacuum oven at 80° C. for 12 h to obtain iron phosphate; adding a saturated sodium carbonate aqueous solution to the filtrate at a volume ratio of 10:1 between the filtrate and the saturated sodium carbonate aqueous solution, heating to 90° C. for reaction for 4 h until a white precipitate is generated, filtering the precipitate with a vacuum filtration device while it is hot, washing the precipitate with deionized water three times, and drying it in a vacuum oven at 80° C. to constant weight to obtain lithium carbonate;

[0041] (6) The iron phosphate and lithium carbonate described in step (5) are mixed in a molar ratio of iron to lithium of 1:1.03, and then calcined at 650° C. for 5 h in an air atmosphere to obtain regenerated lithium iron phosphate.

[0042] Embodiment 3: A method for regenerating lithium iron phosphate in an electrode material, comprising the following steps;

[0043] (1) The waste lithium iron phosphate battery is discharged by a blue battery system until the voltage is displayed as 0 V, and then the battery is disassembled, the disassembled positive electrode sheet containing lithium iron phosphate is dried, calcined at 600° C. for 1 h, and the material peeled off from the current collector is ground to obtain an electrode material powder containing lithium iron phosphate.

[0044] (2) adding 100 g of electrode material powder containing lithium iron phosphate, 10 mg of phosphotungstic acid and 100 mg of glacial acetic acid into 80 mL of deionized water and mixing to obtain a first reaction solution;

[0045] (3) introducing oxygen into the first reaction liquid at a gas flow rate of 10 L / min to obtain a second reaction liquid;

[0046] (4) treating the second reaction solution with visible light for 8 h under stirring at 600 rpm to obtain a third reaction solution;

[0047] (5) filtering the third reaction liquid to separate into a filtrate and a filter residue, washing the filter residue with deionized water three times, and then drying it in a vacuum oven at 80° C. for 12 h to obtain iron phosphate; adding a saturated sodium carbonate aqueous solution to the filtrate at a volume ratio of 1:3 between the filtrate and the saturated sodium carbonate aqueous solution, heating to 100° C. for reaction for 1 h until a white precipitate is generated, filtering the precipitate with a vacuum filtration device while it is hot, washing the precipitate with deionized water three times, and drying it in a vacuum oven at 80° C. to constant weight to obtain lithium carbonate;

[0048] (6) The iron phosphate and lithium carbonate described in step (5) are mixed in a molar ratio of iron to lithium of 1:1.07, and then calcined at 750° C. for 1 h in an air atmosphere to obtain regenerated lithium iron phosphate.

[0049] Comparative Example 1: The rest is the same as Example 1, except that:

[0050] The phosphotungstic acid in step (2) is replaced by phosphomolybdic acid as the photocatalyst.

[0051] Comparative Example 2: The rest is the same as Example 1, except that:

[0052] The phosphotungstic acid in step (2) is replaced by titanium dioxide as the photocatalyst.

[0053] Comparative Example 3: The rest is the same as Example 1, except that:

[0054] The phosphotungstic acid in step (2) is replaced by the MOF-based catalyst UIO-66-NH2 material.

[0055] Comparative Example 4: The rest is the same as Example 1, except that:

[0056] In step (3), oxygen is not introduced, but hydrogen peroxide is added instead, and the molar ratio of hydrogen peroxide to phosphotungstic acid is 5:1.

[0057] Comparative Example 5: The rest is the same as Example 1, except that:

[0058] The oxygen in step (3) was replaced with nitrogen.

[0059] Comparative Example 6: The rest is the same as Example 1, except that:

[0060] The glacial acetic acid in step (2) is replaced with concentrated sulfuric acid.

[0061] Comparative Example 7: The rest is the same as Example 1, except that:

[0062] The glacial acetic acid in step (2) was replaced by oxalic acid.

[0063] The contents of lithium and iron in the filtrate of Examples 1-3 and Comparative Examples 1-7 were determined by ICP-OES, and then the leaching rates of lithium and iron and the recovery rate of lithium iron phosphate were calculated. The results are as follows:

[0064] Table 1 Effect of different recovery and regeneration systems on leaching rate and recovery rate

[0065]

[0066]

[0067] In the results of Table 1, the leaching rates of lithium and iron elements and the recovery rate of lithium iron phosphate in Comparative Examples 1-7 are significantly lower than those in Example 1. Comparative Examples 1-3 show that existing photocatalysts such as titanium dioxide and phosphomolybdic acid are not suitable for the recovery and regeneration system in the present invention. Only phosphotungstic acid as a photocatalyst can greatly improve the leaching rate of lithium and iron elements and the recovery rate of lithium iron phosphate in the present invention. Comparative Examples 4-5 show that the catalytic effect of phosphotungstic acid depends on the presence of an oxidant, but when the oxidizing property of the oxidant is too strong, the reducibility of phosphotungstic acid is inhibited, that is, the tungsten element in the +6 valence state is prevented from reducing the iron element in the lithium iron phosphate, which will greatly reduce the leaching rate and recovery rate of lithium iron. Comparative Examples 6-7 show that when the leaching agent is replaced with a more acidic acid, the leaching rate and recovery rate of lithium iron are reduced. Although strong acids have better solubility for metal elements, the lower pH conditions provided by strong acids have an inhibitory effect on photocatalysis.

Claims

1. A method for regenerating lithium iron phosphate in an electrode material, characterized in that: The steps include: (1) adding lithium iron phosphate-containing electrode material powder, a photocatalyst and glacial acetic acid into water and mixing them to obtain a first reaction solution; (2) introducing oxygen into the first reaction liquid to obtain a second reaction liquid; (3) irradiating the second reaction liquid with light to perform a photocatalytic reaction to obtain a third reaction liquid; (4) filtering the third reaction liquid to separate into a filtrate and a filter residue, drying the filter residue to obtain iron phosphate, adding a saturated sodium carbonate aqueous solution to the filtrate, heating the reaction, and filtering the precipitate to obtain lithium carbonate; (5) Mixing the iron phosphate and lithium carbonate described in step (4) and calcining them to obtain regenerated lithium iron phosphate.

2. The method for regenerating lithium iron phosphate in the electrode material according to claim 1, characterized in that: In step (1), the photocatalyst is phosphotungstic acid.

3. The method for regenerating lithium iron phosphate in the electrode material according to claim 1, characterized in that: In step (1), the electrode material powder containing lithium iron phosphate is prepared as follows: The waste lithium iron phosphate batteries after discharge treatment are disassembled, the disassembled positive electrode sheets containing lithium iron phosphate are dried and then calcined at low temperature, and the materials peeled off from the current collector are ground to obtain the electrode material powder containing lithium iron phosphate.

4. The method for regenerating lithium iron phosphate in the electrode material according to claim 3, characterized in that: The low temperature calcination condition is calcination at 500-600° C. for 1-2 hours.

5. The method for regenerating lithium iron phosphate in the electrode material according to claim 1, characterized in that: In step (1), the material-liquid ratio of the electrode material powder containing lithium iron phosphate, the photocatalyst, glacial acetic acid and water is 10-100 g: 0.1-10 mg: 1-100 mg: 30-80 mL.

6. The method for regenerating lithium iron phosphate in the electrode material according to claim 1, characterized in that: In step (2), the method of introducing oxygen is: introducing oxygen into the first reaction liquid at a gas flow rate of 0.1-10 L / min.

7. The method for regenerating lithium iron phosphate in electrode material according to claim 1, characterized in that: In step (3), the photocatalytic reaction method is to treat the second reaction liquid with light for 0.5-8h under stirring.

8. The method for regenerating lithium iron phosphate in electrode material according to claim 1, characterized in that: In step (4), the volume ratio of the filtrate to the saturated sodium carbonate aqueous solution is 10:1-30; the heating reaction method is: heating to 90-100°C for 1-4h until a white precipitate is generated.

9. The method for regenerating lithium iron phosphate in electrode material according to claim 1, characterized in that: In step (5), iron phosphate and lithium carbonate are mixed according to a molar ratio of iron element to lithium element of 1:1.03-1.

07.

10. The method for regenerating lithium iron phosphate in electrode material according to claim 1, characterized in that: In step (5), the calcination conditions are 650-750° C. for 1-5 hours in an air atmosphere.

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