A method for recycling and processing waste lithium iron phosphate cathode sheets

Abstract

This invention discloses a method for recycling and processing waste lithium iron phosphate (LFP) cathode sheets, comprising: crushing and sieving the cathode sheets of waste LFP batteries to obtain LFP cathode powder; selectively dissolving aluminum using a prepared eutectic solvent, washing the resulting solid phase to obtain the LFP cathode powder required for regeneration, and electrolytically depositing the leachate to obtain metallic aluminum and electrolyte. This invention utilizes the selective dissolution property of the prepared eutectic solvent on aluminum, achieving the effect of removing aluminum without altering the LFP phase through wet leaching, thus enabling the waste LFP cathode powder to undergo further regeneration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste lithium ion battery recycling, and particularly relates to a recycling treatment method for waste lithium iron phosphate positive plate. BACKGROUND

[0002] Lithium iron phosphate (LFP) type batteries are widely used in electric vehicles and hybrid electric vehicle industries due to their stable cycle performance, low price, high safety, good thermal stability and environmental compatibility. In recent years, with the rapid development of new energy vehicles and energy storage industries, the market demand for lithium iron phosphate is increasing year by year. Its production capacity increased from 181,200 tons in 2018 to 898,000 tons in 2021, and it is expected to become the main player in the market in the next few years. However, the scrap amount of lithium iron phosphate (LFP) type batteries also increases with the sudden increase in production. In order to alleviate the pollution of scrap batteries to the environment and the sustainable use of resources, finding an efficient method for recycling waste lithium iron phosphate type batteries has become a hot research topic. The recycling of waste lithium iron phosphate type batteries mainly aims at the recycling of lithium and iron elements (such as CN114988382A, CN114229812A). The recycling method is mainly divided into pyrometallurgy and hydrometallurgy. The temperature required by pyrometallurgy (such as CN113430322A) is generally above 1200℃, which has high energy consumption and causes serious pollution. The product obtained is generally a metal oxide, which needs further treatment. Moreover, if the impurity aluminum content in the waste material is too high, the operation safety hazard is large. Hydrometallurgy is the common method used by most enterprises to recycle batteries, that is, through leaching-precipitation / extraction method, etc. to obtain lithium carbonate / lithium hydroxide / dihydrogen phosphate / lithium phosphate / iron phosphate / iron hydroxide products (such as CN115149140A, CN114772565A, CN114249313A, CN115109936A, CN108218690A). The leaching solution can be selected from sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, etc. However, the acid leaching process faces the problems of large acid consumption, difficult wastewater treatment, and poor metal separation effect caused by complete leaching of metals.

[0003] To optimize the cumbersome process flow, high investment costs, and emissions of waste gas, wastewater, and solid waste in traditional metallurgical processes, direct remediation and regeneration technology has emerged. This technology allows for the adjustment of the lithium iron phosphate (LFP)-carbon ratio, employing methods such as high-energy ball milling followed by atmospheric calcination or microwave roasting to obtain remediated LFP cathode powder. This technology enables a closed-loop process from "retired battery - waste battery cathode material - battery active material - battery," avoiding the use of multiple reagents and the tedious steps of multi-element separation, purification, and recycling. For example, the published patent CN112142029A describes how, by adding a certain amount of lithium and carbon sources and then calcining under an inert atmosphere, remediated carbon-coated LFP cathode material is obtained, which can be directly used as a new battery cathode material. However, this patent does not mention the removal of aluminum impurities, and many other repair and regeneration technologies also fail to address the issue of aluminum presence. Furthermore, the lithium iron phosphate cathode powder required for repair has very high quality requirements, with an aluminum content below 0.02%. Large-scale crushing and screening of waste lithium iron phosphate cathode materials makes it difficult to achieve the quality needed for direct repair. While patent CN114212765A proposes using alkali dissolution followed by CO2 to remove aluminum, this process is cumbersome and costly. Additionally, during alkali dissolution, excessively high local concentrations of alkali can corrode the lithium iron phosphate structure, causing lithium iron phosphate loss and hindering its regeneration and repair. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides a method for recycling and processing waste lithium iron phosphate cathode sheets.

[0005] This invention is achieved through the following technical solution.

[0006] A method for recycling and processing waste lithium iron phosphate cathode sheets includes:

[0007] (1) Crushing and screening of positive electrode sheets: The positive electrode sheets of waste lithium iron phosphate batteries are put into a crusher for coarse crushing to obtain fragments of 2-6cm. The fragments are then finely crushed in a crusher to obtain powder material. 1-100μm lithium iron phosphate positive electrode powder and aluminum foil are separated by a 200-mesh sieve.

[0008] (2) Preparation of eutectic solvent: choline chloride and oxalic acid were dried at 50-80℃ for 20-30h, then mixed in a molar ratio of 1:1-1:3 and placed in an Erlenmeyer flask. The mixture was then magnetically stirred at 70-100℃ for 3-6h, and vacuum dried at 50-80℃ and sealed to obtain the eutectic solvent.

[0009] (3) Selective leaching of Al: The lithium iron phosphate cathode powder obtained in step (1) is dissolved in the eutectic solvent obtained in step (2) for leaching to selectively dissolve Al. The leachate and solid phase are obtained by solid-liquid separation. The leaching temperature is 80-120℃, the liquid-solid ratio is 5-8:1 (the liquid-solid ratio refers to the ratio of eutectic solvent (unit L) to lithium iron phosphate cathode powder (unit kg), the stirring speed is 200-500 r / min, and the stirring time is 0.5-2 h.

[0010] The reaction between Al and the eutectic solvent in lithium iron phosphate cathode powder is as follows:

[0011] 2Al + 3(C2O4) 2- +6H + →Al2(C2O4)3 + 3H2↑

[0012] Al2(C2O4)3+3(C2O4) 2- +6H + →2Al 3+ +6HC2O4 -

[0013] Al 3+ +4Cl - →[AlCl4] -

[0014] Choline chloride is used to broaden the electrochemical window.

[0015] (4) Electrolytic recovery of metal Al: The leachate obtained in step (3) is electrolytically deposited to obtain metal aluminum and electrolyte, wherein the electrolyte is returned to step (3) to selectively leach aluminum from lithium iron phosphate powder;

[0016] The electrolytic deposition process involves adding the leachate to a 250 mL plexiglass electrolytic cell, using a DC regulated power supply, and employing a stainless steel sheet (3 cm²) as the electrode. 2 ) is the cathode, graphite sheet (3cm) 2 The cathode is the anode (where an oxidation reaction occurs, oxidizing oxalic acid to CO2). The distance between the anode and cathode is 1.0–2.0 cm, the cell voltage is 2.1–2.5 V, the electrolysis temperature is 80–120 °C, and metallic aluminum is obtained after electrolytic deposition for 1–2 hours. The cathode reaction is: Al… 3+ +3e - →Al;

[0017] (5) Recovery of lithium iron phosphate powder: The solid phase obtained in step (3) is washed 2-5 times with distilled water and anhydrous ethanol, dried, repaired and regenerated to obtain lithium iron phosphate cathode powder.

[0018] The beneficial technical effects of this invention are as follows: This invention utilizes the selective solubility of aluminum in the prepared eutectic solvent, and achieves the effect of removing aluminum without changing the lithium iron phosphate phase through wet leaching. This allows waste lithium iron phosphate cathode powder to be repaired and regenerated to obtain lithium iron phosphate cathode powder, while simultaneously achieving the separation and recovery of lithium iron phosphate cathode powder and aluminum.

[0019] (1) The present invention uses a low eutectic solvent to selectively leach aluminum. The reagent preparation is simple, the process is short, and there is no need for cumbersome purification. The aluminum content in lithium iron phosphate cathode powder can be reduced to the industrial requirement (Al: 0.02%) or below.

[0020] (2) This invention not only has a good aluminum removal effect, but also can efficiently recover metallic aluminum, and does not damage the phase structure of lithium iron phosphate cathode powder after aluminum removal.

[0021] (3) The waste liquid of the present invention can be reused, and its aluminum removal effect can still meet the requirements of lithium iron phosphate cathode powder required for repair and regeneration.

[0022] (4) The present invention is applicable not only to lithium iron phosphate cathode powder with low carbon and aluminum impurity content, but also to lithium iron phosphate battery black powder with high carbon and aluminum content obtained by direct crushing and screening of waste lithium iron phosphate batteries, and has strong versatility. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention.

[0024] Figure 2 The image shows the XRD pattern of the lithium iron phosphate cathode powder prepared in this invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] The positive electrode sheets of waste lithium iron phosphate batteries are crushed and sieved to obtain positive electrode powder with a particle size of 1-100μm. The contents of each component are shown in the table below:

[0027] Element Al Li Fe P C Content / % 2.06 4.13 32.14 18.13 2.89

[0028] Example 1

[0029] Choline chloride and oxalic acid were dried separately at 60℃ for 24 hours, then mixed at a molar ratio of 1:1 and placed in an Erlenmeyer flask. The mixture was heated at 95℃ and magnetically stirred for 4 hours until a colorless, transparent eutectic solvent was formed. The mixture was then vacuum dried and sealed at 50℃. 50g of waste lithium iron phosphate battery cathode powder was added to a beaker, followed by 250mL of the eutectic solvent. The mixture was heated to 95℃ with a stirring speed of 250r / min. After leaching for 1 hour, the mixture was filtered to obtain leaching residue (solid phase) and leachate. The leachate was placed in a 250mL electrolytic cell powered by a DC regulated power supply, using the leachate as the electrolyte. A 3cm stainless steel sheet was used. 2 ) is the cathode, graphite sheet (3cm) 2 The anode was set at 1.5 cm, the cell voltage was 2.3 V, and the electrolysis temperature was 95 °C. Aluminum was enriched by electrodeposition, and the aluminum recovery rate reached 90% after 1 hour of electrolytic deposition. Finally, the leaching residue was washed three times each with distilled water and anhydrous ethanol, and the aluminum content in the resulting lithium iron phosphate cathode powder after drying was 0.02%.

[0030] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0031] Element Al Li Fe P C Content / % 0.02 4.01 31.78 17.92 2.9

[0032] Example 2

[0033] Choline chloride and oxalic acid were dried separately at 70℃ for 28 hours, then mixed at a molar ratio of 1:2 and placed in an Erlenmeyer flask. The mixture was heated at 85℃ and magnetically stirred for 3 hours until a colorless, transparent eutectic solvent was formed. The solvent was then vacuum dried and sealed at 70℃. 50g of waste lithium iron phosphate battery cathode powder was added to a beaker, followed by 300mL of the eutectic solvent. The mixture was heated to 85℃ and stirred at 400r / min for 1.5 hours. After leaching, the residue and leachate were obtained by filtration. The leachate was placed in a 250mL electrolytic cell powered by a DC regulated power supply, using the leachate as the electrolyte. A 3cm stainless steel sheet was used. 2 ) is the cathode, graphite sheet (3cm) 2 The anode was set as 1.5 cm, the cell voltage was 2.5 V, and the electrolysis temperature was 115 °C. Aluminum was enriched by electrodeposition, and the aluminum recovery rate reached 95% after 2 hours of electrolytic deposition. Finally, the leaching residue was washed four times each with distilled water and anhydrous ethanol. The resulting solid phase after drying matched the physical characteristics of lithium iron phosphate, with fewer impurity peaks. Figure 2 As shown, the structure of lithium iron phosphate was not destroyed after the material was leached with a eutectic solvent to remove aluminum. In addition, the aluminum content in the lithium iron phosphate cathode powder was reduced to 0.01%.

[0034] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0035] Element Al Li Fe P C Content / % 0.01 4.11 32.02 17.89 2.89

[0036] Example 3

[0037] The waste electrolyte from aluminum electrolysis in Case 2 was used to re-dissolve the waste lithium iron phosphate battery cathode powder.

[0038] Choline chloride and oxalic acid were dried separately at 80°C for 21 hours, then mixed at a molar ratio of 1:3 and placed in an Erlenmeyer flask. The mixture was heated at a constant temperature (75°C) and magnetically stirred for 6 hours until a colorless, transparent, eutectic solvent was formed. The mixture was then vacuum dried at 80°C and sealed.

[0039] 50g of waste lithium iron phosphate battery cathode powder was added to a beaker, along with 350mL of eutectic solvent. Then, the waste electrolyte from Example 2 was added and heated to 120℃. The stirring speed was 450r / min. After leaching for 1 hour, the residue and leachate were obtained by filtration. The leachate was placed in a 250mL electrolytic cell, powered by a DC regulated power supply, using the leachate as the electrolyte. Low-carbon steel sheets (3cm) were used. 2 ) is the cathode, graphite sheet (3cm) 2 The anode was set at 1.5 cm, the cell voltage was 2.5 V, and the electrolysis temperature was 95 °C. Aluminum was enriched by electrodeposition. After 1.5 h of electrolytic deposition, the aluminum recovery rate reached 92%. Finally, the leaching residue was washed 5 times each with distilled water and anhydrous ethanol. After drying, the aluminum content in the obtained lithium iron phosphate cathode powder was 0.015%.

[0040] The component contents of lithium iron phosphate cathode powder after aluminum removal by re-leaching of waste electrolyte are shown in the table below:

[0041] Element Al Li Fe P C Content / % 0.015 4.01 31.89 18.15 2.89

[0042] Example 4

[0043] Choline chloride and oxalic acid were dried separately at 50℃ for 26 hours, then mixed at a molar ratio of 1:2 and placed in an Erlenmeyer flask. The mixture was heated at 90℃ and magnetically stirred for 5 hours until a colorless, transparent eutectic solvent was formed. The mixture was then vacuum dried and sealed at 60℃. 50g of waste lithium iron phosphate battery cathode powder was added to a beaker, followed by 400mL of the eutectic solvent. The mixture was heated to 110℃ and stirred at 350r / min for 1.8 hours. After leaching, the residue and leachate were obtained by filtration. The leachate was placed in a 250mL electrolytic cell powered by a DC regulated power supply, using the leachate as the electrolyte. A 3cm stainless steel sheet was used. 2 ) is the cathode, graphite sheet (3cm) 2The electrode was used as the anode, with an electrode spacing of 1.8 cm, a cell voltage of 2.4 V, and an electrolysis temperature of 110 °C. Aluminum was enriched by electrodeposition, and after 1.2 h of electrolytic deposition, the aluminum recovery rate reached 95%. Finally, the leaching residue was washed four times each with distilled water and anhydrous ethanol. The solid phase obtained after drying matched the physical characteristics of lithium iron phosphate, and there were fewer impurity peaks, indicating that the structure of lithium iron phosphate was not destroyed after aluminum removal by leaching with a eutectic solvent. In addition, the aluminum content in the lithium iron phosphate cathode powder was reduced to 0.01%.

[0044] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0045] Element Al Li Fe P C Content / % 0.01 4.05 31.65 17.96 2.89

[0046] Example 5

[0047] Choline chloride and oxalic acid were dried separately at 80℃ for 30 hours, then mixed at a molar ratio of 1:2.5 and placed in an Erlenmeyer flask. The mixture was heated at 80℃ and magnetically stirred for 5.5 hours until a colorless, transparent eutectic solvent was formed. The solvent was then vacuum dried and sealed at 75℃. 50g of waste lithium iron phosphate battery cathode powder was added to a beaker, followed by 400mL of the eutectic solvent. The mixture was heated to 80℃ with a stirring speed of 220r / min. After leaching for 2 hours, the residue and leachate were obtained by filtration. The leachate was placed in a 250mL electrolytic cell powered by a DC regulated power supply, using the leachate as the electrolyte. A 3cm stainless steel sheet was used. 2 ) is the cathode, graphite sheet (3cm) 2 The anode was set at 2.0 cm, the cell voltage at 2.1 V, and the electrolysis temperature at 120 °C. Aluminum was enriched by electrodeposition, and the aluminum recovery rate reached 95% after 1.8 h of electrolytic deposition. Finally, the leaching residue was washed four times each with distilled water and anhydrous ethanol. The solid phase obtained after drying matched the physical characteristics of lithium iron phosphate, and there were fewer impurity peaks, indicating that the structure of lithium iron phosphate was not destroyed after aluminum removal by leaching with a eutectic solvent. In addition, the aluminum content in the lithium iron phosphate cathode powder was reduced to 0.01%.

[0048] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0049] Element Al Li Fe P C Content / % 0.01 4.10 32.10 18.09 2.89

[0050] Comparative Example 1

[0051] Choline chloride was dried at 60℃ for 24 hours and sealed. 50g of waste lithium iron phosphate battery positive electrode powder was added to a beaker, followed by 250mL of choline chloride. The temperature was raised to 95℃, and the stirring speed was 250r / min. After leaching for 1 hour, the mixture was filtered to obtain leaching residue (solid phase) and leachate. The leachate was placed in a 250mL electrolytic cell, powered by a DC regulated power supply, using the leachate as the electrolyte. A 3cm stainless steel sheet was used. 2) is the cathode, graphite sheet (3cm) 2 The anode was set at 1.5 cm, the cell voltage was 2.3 V, and the electrolysis temperature was 95 °C. Aluminum was enriched by electrodeposition, and the aluminum recovery rate reached 70% after 1 hour of electrolytic deposition. Finally, the leaching residue was washed three times each with distilled water and anhydrous ethanol, and the aluminum content in the resulting lithium iron phosphate cathode powder after drying was 0.05%.

[0052] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0053] Element Al Li Fe P C Content / % 0.15 3.98 31.18 17.62 2.9

[0054] Choline chloride alone is not very effective at removing aluminum; the aluminum content is still 0.15% after removal.

[0055] Comparative Example 2

[0056] Prepare a 10% oxalic acid solution using water. Add 50g of waste lithium iron phosphate battery positive electrode powder to a beaker, then add 250mL of the 10% oxalic acid solution. Heat to 95℃, stirring at 250r / min, and leach for 1 hour. Filter to obtain leaching residue (solid phase) and leachate. Place the leachate in a 250mL electrolytic cell, powered by a DC regulated power supply, using the leachate as the electrolyte. Use a 3cm stainless steel sheet. 2 ) is the cathode, graphite sheet (3cm) 2 The anode was set at 1.5 cm, the cell voltage was 2.3 V, and the electrolysis temperature was 95 °C. Aluminum was enriched by electrodeposition. After 1 hour of electrolytic deposition, the aluminum recovery rate was 0%. Finally, the leaching residue was washed three times each with distilled water and anhydrous ethanol. After drying, the aluminum content in the obtained lithium iron phosphate cathode powder was 0.35%.

[0057] The component contents of the lithium iron phosphate cathode powder after aluminum removal by eutectic solvent leaching are shown in the table below:

[0058] Element Al Li Fe P C Content / % Element Li Fe Content / % Element Li Fe Content / % 0.35 3.68 30.18 16.62 2.9

[0059] Oxalic acid solution alone is not effective at removing aluminum, and lithium iron phosphate structure is severely damaged. Furthermore, the dissolved aluminum solution cannot be electrodeposited to recover aluminum.

[0060] The above description is merely a preferred embodiment of the present invention and is not limited to the invention. It should be noted that those skilled in the art can make other equivalent improvements based on the technical teachings provided by the present invention, all of which can achieve the purpose of the present invention and should be considered within the scope of protection of the present invention.

Claims

1. A method for recycling spent lithium iron phosphate positive electrode sheet, characterized by, The method comprises the following steps: (1) crushing and screening waste lithium iron phosphate positive electrode sheet to obtain lithium iron phosphate positive electrode powder; (2) mixing choline chloride and oxalic acid in a molar ratio of 1:1-1:3 and performing a heating reaction, wherein the heating reaction temperature is 70-100 DEG C, the reaction time is 3-6 h, and a eutectic solvent is obtained; (3) leaching the lithium iron phosphate positive electrode powder in the eutectic solvent, and performing solid-liquid separation to obtain leaching solution and solid phase, wherein the leaching temperature is 80-120 DEG C, and the liquid-solid ratio is (5-8) L:1 kg; (4) electrolytic deposition of the leaching solution obtained in step (3) to obtain aluminum; (5) washing, drying, and repairing and regenerating the solid phase obtained in step (3) to obtain lithium iron phosphate positive electrode powder.

2. The method of claim 1, wherein the method is characterized by: The lithium iron phosphate positive electrode powder obtained in step (1) has a particle size of 1-100 mu m.

3. The method of claim 1, wherein the method is characterized by: In step (2), the choline chloride and oxalic acid are dried at 50-80 DEG C for 20-30 h before the heating reaction.

4. The method of claim 1, wherein the method is characterized by: In step (2), the choline chloride and oxalic acid are vacuum dried and sealed at 50-80 DEG C after the heating reaction to obtain the eutectic solvent.

5. The method of claim 1, wherein the method is characterized by: In step (3), the stirring speed is 200-500 r / min, and the stirring time is 0.5-2 h.

6. The method of claim 1, wherein the method is characterized by: In step (4), the leaching solution is introduced into an electrolytic tank as electrolyte, a direct current stabilized power supply is used, a stainless steel sheet is used as the cathode, and a graphite sheet is used as the anode.

7. The method according to claim 6, wherein the method is characterized by, The inter-electrode distance of the cathode and the anode is 1.0-2.0 cm, and the tank voltage is 2.1-2.5 V.

8. The method of claim 1, wherein the method is characterized by: The electrolysis temperature is 80-120 DEG C, and the electrolysis time is 1-2 h. 9.The method of claim 1, wherein the method further comprises: removing the binder from the waste lithium iron phosphate cathode sheet. In step (5), distilled water and anhydrous ethanol are used as the washing agent.

10. The method of claim 9, wherein the method further comprises the step of: The solid phase is washed with distilled water and anhydrous ethanol for 2-5 times. ​

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