A method for removing PVDF and aluminum from lithium iron phosphate cathode materials

Abstract

This disclosure proposes a method for removing PVDF and aluminum from lithium iron phosphate cathode materials, comprising the following steps: S1: mixing and ball milling lithium iron phosphate powder, a first ionic liquid, and ethanol to separate the solid and liquid phases, thereby obtaining PVDF-free lithium iron phosphate powder; S2: mixing and heating the ethanol, a second ionic liquid, and the PVDF-free lithium iron phosphate powder obtained in step S1 to separate the ethanol and aluminum alkoxide, thereby obtaining PVDF-free and aluminum-free lithium iron phosphate powder; wherein, in steps S1 and S2, the first ionic liquid and the second ionic liquid are independently selected from fluorine-containing ionic liquids.

Description

Technical Field

[0001] This disclosure belongs to the field of lithium-ion battery technology, specifically relating to a method for removing PVDF and aluminum from lithium iron phosphate cathode materials. Background Technology

[0002] Lithium-ion batteries are widely used in pure / hybrid electric vehicles and various electronic devices due to their advantages such as high operating voltage, long cycle life, and no memory effect. Among them, lithium iron phosphate (LFP) batteries, as a simple and safe power source, have high cycle performance and do not contain precious metals, holding a large market share in power batteries, and their demand is experiencing explosive growth in new energy, base station energy storage, and other fields. However, the lifespan of lithium-ion batteries is generally 5-7 years, resulting in a large amount of waste LFP batteries in the coming years. On the one hand, waste batteries contain many valuable components, such as iron, copper, aluminum, lithium, and phosphorus; recycling these valuable components can prevent the waste of these resources. On the other hand, the organic electrolyte in the batteries can cause serious pollution to water and soil. Therefore, the recycling of waste LFP batteries is imperative.

[0003] LFP battery recycling methods are generally classified into three categories: direct regeneration, pyrometallurgy, and hydrometallurgy. Compared to pyrometallurgy and hydrometallurgy, direct regeneration has the advantages of a shorter and more efficient recycling process. As a short and efficient process, direct regeneration can be used to recover remaining waste, but it faces difficulties when processing materials with high impurity content, materials from different sources, or materials of different types.

[0004] Removing PVDF from spent lithium iron phosphate (LFP) cathode materials typically relies on high-temperature pyrolysis to convert it into hydrogen fluoride and fluorocarbons. However, during this process, the generated hydrogen fluoride corrodes the LFP material, forming lithium fluoride, which degrades the material's performance. Furthermore, lithium fluoride is extremely difficult to remove as an impurity. On the other hand, alkaline solutions are commonly used to remove aluminum impurities from spent LFP cathode materials, but this method inevitably introduces sodium impurities and also causes some damage to the LFP material. Therefore, there is a significant challenge in efficiently removing PVDF and aluminum impurities from spent LFP materials while maintaining the structural integrity of the LFP. Summary of the Invention

[0005] This disclosure aims to at least solve one of the technical problems existing in the prior art. To this end, this disclosure proposes a method for removing PVDF and aluminum from lithium iron phosphate cathode materials.

[0006] According to the first aspect of this disclosure, a method for removing PVDF and aluminum from lithium iron phosphate cathode materials is proposed, comprising the following steps:

[0007] S1: Lithium iron phosphate powder, first ionic liquid and ethanol are mixed and ball-milled, and solid-liquid separation is performed to obtain lithium iron phosphate powder without PVDF;

[0008] S2: Mix the alcohol, the second ionic liquid and the PVDF-free lithium iron phosphate powder obtained in step S1, and heat to separate the alcohol and aluminum alkoxide to obtain PVDF-free and aluminum-free lithium iron phosphate powder.

[0009] In steps S1 and S2, the first ionic liquid and the second ionic liquid are independently selected from fluorine-containing ionic liquids.

[0010] In some embodiments, in step S1, the lithium iron phosphate powder is obtained by discharging, dismantling and crushing waste lithium iron phosphate batteries.

[0011] In some embodiments, in steps S1 and S2, the ionic liquid is at least one of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (CAS: 174899-82-2), 1-ethyl-3-methylimidazolium tetrafluoroborate (CAS: 143314-16-3), 1-ethyl-3-methylimidazolium hexafluorophosphate (CAS: 155371-19-0), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (CAS: 235789-75-0), 1-ethyl-3-methylimidazolium trifluoroacetate (CAS: 174899-65-1), or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (CAS: 145022-44-2).

[0012] In some embodiments, in step S1, the mass of the ionic liquid is 5-20% of the mass of the lithium iron phosphate powder.

[0013] In some embodiments, in step S1, the liquid-to-solid ratio of the ethanol to the lithium iron phosphate powder is 2-5 mL / g.

[0014] In some embodiments, the process parameters of the ball mill in step S1 are: ball-to-material ratio of (4-10):1; rotation speed of 300-400 rpm; and time of 120-480 min.

[0015] In some embodiments, step S1, the solid-liquid separation includes: washing the ball-milled mixture, separating the washing liquid, and obtaining lithium iron phosphate powder free of PVDF. The washing liquid may be the same as the alcohol added during ball milling.

[0016] In some embodiments, in step S1, the lithium iron phosphate powder excluding PVDF is further dried; the drying temperature is 50-80°C and the time is 4-24 hours.

[0017] In some embodiments, in step S1, the liquid phase after solid-liquid separation is subjected to rotary evaporation, and after further solid-liquid separation, ionic liquid and PVDF are obtained. Ethanol can be recovered by rotary evaporation of the filtrate obtained after washing the lithium iron phosphate mixture with ethanol and then performing solid-liquid separation.

[0018] In some embodiments, the rotary evaporation temperature is 50–80°C; the vacuum degree is approximately -0.1 MPa.

[0019] In some embodiments, in step S2, the alcohol is at least one of n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, or tert-butanol.

[0020] In some embodiments, in step S2, the liquid-to-solid ratio of the alcohol to the lithium iron phosphate mixture is 5–10 mL / g.

[0021] In some embodiments, in step S2, the mass of the second ionic liquid is 5 to 20% of the mass of the lithium iron phosphate mixture.

[0022] In some embodiments, step S2, the heating separation of the alcohol and aluminum alkoxide, includes: first heating to generate the aluminum alkoxide, then heating a second time to sequentially separate the alcohol and aluminum alkoxide. Under heating conditions, an ionic liquid acts as a catalyst to react aluminum and alcohol to convert them into aluminum alkoxide.

[0023] In some embodiments, in step S2, the temperature of the first heating is 80–120°C; the heating time is 60–180 min; the temperature of the second heating is 80–180°C; and the heating time is 60–120 min. The second heating can evaporate the aluminum alkoxide, thereby removing aluminum impurities from lithium iron phosphate.

[0024] According to a second aspect of this disclosure, a method for recycling lithium-ion batteries is proposed, including the steps of the method for removing PVDF and aluminum from lithium iron phosphate cathode materials as described in the first aspect of this disclosure.

[0025] According to a third aspect of this disclosure, the method for removing PVDF and aluminum from lithium iron phosphate cathode materials as described in the first aspect of this disclosure is proposed for use in lithium-ion battery recycling.

[0026] According to one embodiment of this disclosure, at least the following beneficial effects are achieved:

[0027] (1) This disclosure involves adding a fluorine-containing ionic liquid to lithium iron phosphate material and reacting it with PVDF at a certain temperature to form hydrogen bonds, thereby removing PVDF from the lithium iron phosphate powder. Simultaneously, the fluorine-containing ionic liquid can also act as a catalyst to catalyze the reaction of aluminum and alcohol, converting aluminum impurities into aluminum alkoxides, which are then removed from the lithium iron phosphate. This method is simple to operate, removing PVDF and aluminum impurities from the lithium iron phosphate cathode material in two steps. Furthermore, the removal of PVDF and aluminum ensures that the structure of the lithium iron phosphate is not damaged and that no impurities are introduced.

[0028] (2) This disclosure enables PVDF to be separated from lithium iron phosphate cathode material by forming hydrogen bonds with ionic liquid, and the hydrogen bonds are easily broken under heating conditions, which allows ionic liquid and PVDF to be recycled and reused.

[0029] (3) This disclosure effectively catalyzes the reaction between aluminum and alcohol by forming hydrogen bonds between ionic liquid and alcohol, so that aluminum impurities are converted into aluminum alkoxides for removal, and the alcohol used can also be recycled, thus forming an economical, green and environmentally friendly closed-loop recycling route.

[0030] (4) Since the process for regenerating lithium iron phosphate by removing PVDF and aluminum impurities is simple and easy to operate, it can be applied on a large scale in industry. Attached Figure Description

[0031] The present disclosure will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0032] Figure 1 This is a flowchart of the process for regenerating lithium iron phosphate from lithium iron phosphate cathode material in Embodiment 1 of this disclosure, after removing PVDF and aluminum impurities. Detailed Implementation

[0033] The following will describe the concept and technical effects of this disclosure clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this disclosure.

[0034] Example 1

[0035] A method for removing PVDF and aluminum from lithium iron phosphate cathode materials, such as... Figure 1 As shown, it includes the following steps:

[0036] (1) Waste lithium iron phosphate batteries are discharged, disassembled and crushed to obtain waste lithium iron phosphate cathode materials.

[0037] (2) The lithium iron phosphate powder obtained in step 1, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide with a mass of 5 wt% of lithium iron phosphate powder, and ethanol (liquid-solid ratio = 2 mL / g) were put into a ball mill jar. Zirconium balls with a ball-to-material ratio of 4:1 were added into the ball mill jar, and the mixture was placed on a planetary ball mill and ball-milled at 400 rpm for 120 min to obtain a lithium iron phosphate mixture.

[0038] (3) Wash the lithium iron phosphate mixture obtained in step 2 with ethanol at a mass ratio of 5 times that of lithium iron phosphate and then filter it. Repeat this process 3 times.

[0039] (4) Place the filter residue obtained in step 3 into an oven and dry it at 50°C for 24 hours to obtain lithium iron phosphate powder regenerated without PVDF.

[0040] (5) The filtrate obtained in step 3 was rotary evaporated at 50°C to recover ethanol under a vacuum of -0.1 MPa to obtain a mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and PVDF.

[0041] (6) The mixture obtained in step 5 is filtered to recover 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and PVDF.

[0042] (7) The lithium iron phosphate powder obtained in step 4 (excluding PVDF), isopropanol (liquid-solid ratio = 5 mL / g), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (5 wt% of lithium iron phosphate powder) as catalyst were added to a flask and heated in an oil bath at 85°C under reflux for 1 h to convert aluminum to aluminum isopropoxide as completely as possible.

[0043] (8) After aluminum is converted into aluminum isopropoxide, continue heating at 90°C for 30 min to evaporate and recover the isopropanol solvent. Increase the temperature to 140°C and heat for 50 min to evaporate the aluminum isopropoxide to obtain a mixture of lithium iron phosphate powder and ionic liquid with PVDF and aluminum removed.

[0044] (9) The mixture obtained in step 8 was filtered to obtain purified lithium iron phosphate powder and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was recovered.

[0045] A method for recycling lithium-ion batteries includes the steps of the above-mentioned method for removing PVDF and aluminum from lithium iron phosphate cathode materials.

[0046] Example 2

[0047] A method for removing PVDF and aluminum from lithium iron phosphate cathode materials includes the following steps:

[0048] (1) Waste lithium iron phosphate batteries are discharged, disassembled and crushed to obtain waste lithium iron phosphate cathode materials.

[0049] (2) The lithium iron phosphate powder obtained in step 1, 1-ethyl-3-methylimidazolium tetrafluoroborate (10 wt% of lithium iron phosphate powder), and ethanol (liquid-solid ratio = 4 mL / g) were placed into a ball mill jar. Zirconium balls with a ball-to-material ratio of 6:1 were added into the ball mill jar, and the mixture was placed on a planetary ball mill and milled at 400 rpm for 240 min to obtain a lithium iron phosphate mixture.

[0050] (3) Wash the lithium iron phosphate mixture obtained in step 2 with ethanol at a mass ratio of 5 times that of lithium iron phosphate and then filter it. Repeat this process 3 times.

[0051] (4) Place the filter residue obtained in step 3 into an oven and dry it at 60°C for 12 hours to obtain lithium iron phosphate powder regenerated without PVDF.

[0052] (5) The filtrate obtained in step 3 was rotary evaporated at 70°C under a vacuum of -0.1 MPa to recover ethanol and obtain a mixture of 1-ethyl-3-methylimidazolium tetrafluoroborate and PVDF.

[0053] (6) The mixture obtained in step 5 is filtered to recover 1-ethyl-3-methylimidazolium tetrafluoroborate and PVDF.

[0054] (7) The lithium iron phosphate powder obtained in step 4 (excluding PVDF), tert-butanol (liquid-solid ratio = 8 mL / g), and 1-ethyl-3-methylimidazolium tetrafluoroborate (10 wt% of lithium iron phosphate powder) as catalyst were added to a flask and heated in an oil bath at 85°C under reflux for 2 hours to convert aluminum to aluminum tert-butoxide as completely as possible.

[0055] (8) After aluminum is converted into aluminum tert-butoxide, continue heating at 85°C for 30 min to evaporate and recover the tert-butanol solvent. Then raise the temperature to 160°C and heat for 60 min to evaporate the aluminum tert-butoxide to obtain lithium iron phosphate powder with PVDF and aluminum removed.

[0056] (9) The mixture obtained in step 8 is filtered to obtain purified lithium iron phosphate powder and 1-ethyl-3-methylimidazolium tetrafluoroborate is recovered.

[0057] A method for recycling lithium-ion batteries includes the steps of the above-mentioned method for removing PVDF and aluminum from lithium iron phosphate cathode materials.

[0058] Example 3

[0059] A method for removing PVDF and aluminum from lithium iron phosphate cathode materials includes the following steps:

[0060] (1) Waste lithium iron phosphate batteries are discharged, disassembled and crushed to obtain waste lithium iron phosphate cathode materials.

[0061] (2) The lithium iron phosphate powder obtained in step 1, 1-ethyl-3-methylimidazolium hexafluorophosphate with a mass of 15wt% of lithium iron phosphate powder, and ethanol (liquid-solid ratio = 5mL / g) were put into a ball mill jar. Zirconium balls with a ball-to-material ratio of 10:1 were added into the ball mill jar, and the mixture was placed on a planetary ball mill and milled at 400rpm for 480min to obtain a lithium iron phosphate mixture.

[0062] (3) Wash the lithium iron phosphate mixture obtained in step 2 with ethanol at a mass ratio of 5 times that of lithium iron phosphate and then filter it. Repeat this process 3 times.

[0063] (4) Place the filter residue obtained in step 3 into an oven and dry it at 80°C for 4 hours to obtain lithium iron phosphate powder regenerated without PVDF.

[0064] (5) The filtrate obtained in step 3 was rotary evaporated at 80°C and under a vacuum of -0.1 MPa to recover ethanol, resulting in a mixture of 1-ethyl-3-methylimidazolium hexafluorophosphate and PVDF.

[0065] (6) The mixture obtained in step 5 is filtered to recover 1-ethyl-3-methylimidazolium hexafluorophosphate and PVDF.

[0066] (7) The lithium iron phosphate powder obtained in step 4 (excluding PVDF), n-propanol (liquid-solid ratio = 10 mL / g), and 1-ethyl-3-methylimidazolium hexafluorophosphate (15 wt% of lithium iron phosphate powder) as catalyst were added to a flask and heated in an oil bath at 100°C under reflux for 3 h to convert aluminum to aluminum n-propoxide as completely as possible.

[0067] (8) After aluminum is converted into aluminum propoxide, continue heating at 100°C for 40 minutes to distill off and recover the propanol. Then raise the temperature to 170°C and heat for 40 minutes to distill off the aluminum propoxide and obtain lithium iron phosphate powder with PVDF and aluminum removed.

[0068] (9) The mixture obtained in step 8 is filtered to obtain purified lithium iron phosphate powder and 1-ethyl-3-methylimidazolium hexafluorophosphate is recovered.

[0069] A method for recycling lithium-ion batteries includes the steps of the above-mentioned method for removing PVDF and aluminum from lithium iron phosphate cathode materials.

[0070] Comparative Example 1

[0071] The only difference from Example 1 is that 2 wt% of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is added in step 2.

[0072] Comparative Example 2

[0073] The only difference from Example 1 is that in step 7, the liquid-to-solid ratio of isopropanol to lithium iron phosphate powder excluding PVDF is 3 mL / g.

[0074] Comparative Example 3

[0075] The only difference from Example 1 is that the ionic liquid in steps 2 and 7 is replaced with 1-ethyl-3-methylimidazolium chloride.

[0076] Test case

[0077] Table 1 shows the test data for Fe, Li, and Al contents (specific data obtained by ICP-AES equipment), P content (specific data obtained by titration), and F content (specific data obtained by potentiometric method) of the lithium iron phosphate products prepared from waste lithium iron phosphate materials, Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3. As can be seen from Table 1, the Fe, P, and Li contents in the lithium iron phosphate prepared in the examples are normal, while the F and Al contents are effectively reduced, meeting the industrial production standards for lithium iron phosphate batteries. Specifically, the Al content in the lithium iron phosphate prepared in Example 1 decreased from 2.1% to 0.04%, and the F content decreased from 0.2% to 0.002%. Compared to Example 1, Comparative Example 1 added less 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide in step 2, and the resulting lithium iron phosphate powder still contained a relatively high amount of PVDF residue, with an F content of 0.12%. Compared to Example 1, Comparative Example 2 added less isopropanol in step 7, and the resulting lithium iron phosphate powder still contained a relatively high amount of Al residue, with an Al content of 1.3%. Compared to Example 1, Comparative Example 3 used a fluorine-free ionic liquid, and the resulting lithium iron phosphate powder did not show a significant decrease in F and Al content, with an F content of 0.2% and an Al content of 2.08%.

[0078] Table 1. Element Content Test Data

[0079]

[0080]

[0081] Electrochemical performance:

[0082] Table 2 shows the electrochemical performance of lithium iron phosphate batteries prepared using Examples 1, 2, and 3 and the raw materials. Specific data were obtained through testing using equipment such as an electrochemical workstation. As shown in Table 2, the electrochemical performance of the lithium iron phosphate products obtained in the examples, excluding those with PVDF remediation and regeneration, is improved compared to the raw materials. Specifically, Example 1 achieves a charging capacity of 158.6 mAh / g and a discharging capacity of 152.6 mAh / g, with a calculated first charge / discharge efficiency of 96.2% (discharge capacity / charging capacity).

[0083] Table 2 Electrochemical Test Data

[0084] Electrochemical performance Charging capacity (mAh / g) Discharge capacity (mAh / g) raw material 145.9 138.7 Example 1 158.6 152.6 Example 2 159.9 150.1 Example 3 159.7 150.5 Comparative Example 1 156.3 147.7 Comparative Example 2 152.9 145.3 Comparative Example 3 146.0 138.1

Claims

1. A method for removing PVDF and aluminum from lithium iron phosphate cathode materials, characterized in that, Includes the following steps: S1: Lithium iron phosphate powder, first ionic liquid and ethanol are mixed and ball-milled, and solid-liquid separation is performed to obtain lithium iron phosphate powder without PVDF; S2: Mix and heat the alcohol, the second ionic liquid and the PVDF-free lithium iron phosphate powder obtained in step S1 to separate the alcohol and aluminum alkoxide, and obtain PVDF-free and aluminum-free lithium iron phosphate powder. In steps S1 and S2, the first ionic liquid and the second ionic liquid are independently selected from at least one of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium trifluoroacetate, or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. In step S2, the liquid-to-solid ratio of the alcohol to the PVDF-free lithium iron phosphate powder is 5-10 mL / g; the mass of the second ionic liquid is 5-20% of the mass of the PVDF-free lithium iron phosphate powder; the heating separation of alcohol and aluminum alkoxide includes: first heating to generate aluminum alkoxide, then heating a second time to separate alcohol and aluminum alkoxide sequentially.

2. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S1, the lithium iron phosphate powder is obtained by discharging, dismantling and crushing waste lithium iron phosphate batteries.

3. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S1, the mass of the first ionic liquid is 5-20% of the mass of the lithium iron phosphate powder.

4. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1 or 3, characterized in that, In step S1, the liquid-to-solid ratio of the ethanol to the lithium iron phosphate powder is 2~5 mL / g.

5. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S1, the process parameters for ball milling are: ball-to-material ratio of (4~10):1; rotation speed of 300~400 rpm; and time of 120~480 min.

6. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S1, the solid-liquid separation includes: washing the ball-milled mixture, separating the washing liquid, and obtaining lithium iron phosphate powder free of PVDF.

7. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1 or 6, characterized in that, In step S1, the liquid phase after solid-liquid separation is subjected to rotary evaporation, and after solid-liquid separation again, ionic liquid and PVDF are obtained.

8. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S2, the alcohol is at least one of n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, or tert-butanol.

9. The method for removing PVDF and aluminum from lithium iron phosphate cathode materials according to claim 1, characterized in that, The temperature of the first heating is 80~120℃; the time of the first heating is 60~180min; the temperature of the second heating is 80~180℃; the time of the second heating is 60~120min.

10. A method for recycling lithium-ion batteries, comprising the steps of the method for removing PVDF and aluminum from lithium iron phosphate cathode materials as described in any one of claims 1-9.

11. The application of the method for removing PVDF and aluminum from lithium iron phosphate cathode material according to any one of claims 1-9 in lithium-ion battery recycling.

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