Regeneration and repair method of waste lithium iron phosphate material, lithium iron phosphate material and application of lithium iron phosphate material

Abstract

The invention relates to the technical field of lithium iron phosphate material regeneration, and particularly discloses a waste lithium iron phosphate material regeneration and repair method, a lithium iron phosphate material and application of the lithium iron phosphate material, and the waste lithium iron phosphate material regeneration and repair method comprises the following steps: discharging a decommissioned lithium iron phosphate battery, crushing and disassembling to obtain a waste positive plate; obtaining waste lithium iron phosphate powder from the waste positive plate; adding a lithium salt and a reducing substance into the waste lithium iron phosphate powder, and carrying out ball milling; and drying the ball-milled material, and carrying out ventilation annealing in a magnetic field to obtain the regenerated lithium iron phosphate active material. According to the invention, under the condition of introducing a magnetic field, structure repair and lithium supplement can be directly carried out on the lithium iron phosphate cathode material under relatively low energy input, so that the recyclable battery-grade regenerated lithium iron phosphate cathode material can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate material regeneration, and in particular to a method for regenerating and repairing waste lithium iron phosphate material, a lithium iron phosphate material and applications thereof. Background Art

[0002] Currently, new energy sources are developing rapidly, particularly lithium-ion batteries (LIBs), which have achieved successful commercialization. LIBs are now widely used in a variety of consumer electronics, new energy transportation equipment, and large-scale energy storage power stations. As the installed capacity of LIB systems increases, the number of LIBs in use is also increasing. Considering the average effective life and calendar life of power batteries, the world is gradually approaching a peak in the retirement of spent lithium-ion batteries (SLIBs). SLIBs are known to be highly polluting and highly valuable for recycling, especially for large power batteries, which contain high levels of heavy metals, electrolytes, solvents, and various organic auxiliary materials. Improper disposal of SLIBs can lead to severe contamination of soil and water resources, resulting in significant waste. Recycling the cathode active materials from SLIBs for direct regeneration is one of the most promising solutions, especially for lithium iron phosphate batteries, which account for the majority of the installed base.

[0003] Because lithium iron phosphate batteries contain a single type of valuable elements in their positive electrode active materials but in low content, traditional pyrometallurgical or hydrometallurgical processes have low recycling profits, high energy consumption, and secondary pollution such as acid, alkali, or greenhouse gas emissions. Direct repair and recycling of waste lithium iron phosphate positive electrode materials can avoid complex secondary processing steps such as crushing, retain their original structure, and directly repair and replenish the separated lithium iron phosphate waste powder. This method maximizes the original value of the lithium iron phosphate waste powder, is simple to operate, and the regenerated product can be directly reused, making it suitable for large-scale recycling and reuse. The current direct repair and regeneration route for waste lithium iron phosphate generally involves high-temperature calcination of waste lithium iron phosphate + lithium salt + reducing agent. This method still has the disadvantage of high energy consumption. It is crucial to further reduce energy consumption and achieve rapid structural recovery under low-energy conditions. Summary of the Invention

[0004] Based on this, in view of the shortcomings of existing methods for recycling waste positive electrode materials, such as high energy consumption and low efficiency of the pyrometallurgical process, difficulty in treating waste liquid from the wet process, and serious pollution, especially for the problem of insufficient profit in extracting valuable elements from lithium iron phosphate positive electrode waste with a huge market share through metallurgical processes, the present invention is necessary to provide a method for regenerating and repairing waste lithium iron phosphate materials, lithium iron phosphate materials and their applications.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for regenerating and repairing waste lithium iron phosphate materials, which comprises the following steps: After discharging, crushing and disassembling the retired lithium iron phosphate battery, the waste positive electrode sheet is obtained; Obtaining waste lithium iron phosphate powder from the waste positive electrode sheet; adding lithium salt and reducing substance to the waste lithium iron phosphate powder, and ball milling; The ball-milled material is dried and annealed under a magnetic field to obtain a regenerated lithium iron phosphate active material.

[0006] Under the condition of introducing a magnetic field, the present invention can directly carry out structural repair and lithium replenishment at a relatively low energy input, thereby obtaining a recyclable battery-grade regenerated lithium iron phosphate positive electrode material.

[0007] As a further improvement of the above solution of the present invention, the intensity of the magnetic field is 0.4-1.0 T; and the ventilation annealing is performed by introducing nitrogen or helium at 300-400° C. for 1-3 hours.

[0008] As a further improvement of the above solution of the present invention, the rotation speed of the ball mill is 200-400 r / min, and the ball milling time is 2-4 h.

[0009] As a further improvement of the above solution of the present invention, the drying temperature is 60-100°C.

[0010] As a further improvement of the above solution of the present invention, the discharge is carried out in a NaCl solution with a concentration of 10% and a discharge time of 24 hours.

[0011] As a further improvement of the above-mentioned solution of the present invention, the method for obtaining waste lithium iron phosphate powder from the waste positive electrode sheet is: placing the waste positive electrode sheet in an organic solvent, ultrasonically oscillating, and drying to obtain the waste lithium iron phosphate powder.

[0012] As a further improvement of the above solution of the present invention, the organic solvent is at least one of dimethyl carbonate, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; the ultrasonic vibration time is 30-60 minutes, and the drying is carried out at 60-100°C for 8-12 hours.

[0013] As a further improvement of the above-mentioned scheme of the present invention, the waste lithium iron phosphate powder is detected by inductively coupled plasma mass spectrometry to obtain the amount of lithium element deficiency, and the amount of lithium salt added is determined based on the amount of lithium element deficiency; the lithium salt is at least one of lithium hydroxide, lithium acetate, and lithium carbonate; the reducing substance is one of citric acid, glucose, glycerol, and glutamic acid, and the amount of the reducing substance accounts for 5-10wt% of the mass of the waste lithium iron phosphate powder.

[0014] The present invention also provides a lithium iron phosphate material, which is prepared by the above-mentioned method for regenerating and repairing waste lithium iron phosphate materials.

[0015] The present invention also provides a use of the lithium iron phosphate material as described above in a lithium iron phosphate battery.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention performs annealing under a magnetic field, and only uses the missing amount of lithium salt in the waste powder structure and some low-cost reducing substances. It is possible to directly supplement the missing lithium ions in the lithium iron phosphate waste powder structure and repair the lithium iron anti-site defects and degenerate phases at a relatively low temperature and a short insulation time, so that the lithium iron phosphate waste powder can be regenerated into fresh battery-grade lithium iron phosphate positive electrode material; the regenerated lithium iron phosphate has excellent electrochemical properties and can be used for large-scale recycling and reuse of retired lithium iron phosphate positive electrode materials of lithium ion batteries.

[0017] The present invention, at a relatively low temperature and a short holding time, applies an external magnetic field, which acts in conjunction with a reducing environment to rapidly promote the conversion of high-spin iron that has migrated to the lithium site and been oxidized in the crystal structure of waste lithium iron phosphate to a low-spin state, reducing the superexchange effect of iron in the anti-site, thereby driving the repair of lithium-iron anti-site defects in the crystal structure of waste lithium iron phosphate and the regeneration of degraded FePO4 phases by lithium replenishment, thereby achieving lithium replenishment and structural repair under low energy consumption conditions. The process is simple, safe and pollution-free, easy to mass-produce and promote, and the required energy consumption is low-cost, and the recovered product has high added value. The process method of the present invention can solve the main challenge of expanding the direct recovery of retired lithium iron phosphate lithium-ion batteries in an eco-friendly and economical manner, making it suitable for further industry adoption.

[0018] The present invention effectively solves the problem that the traditional metallurgical method of extracting valuable metal elements is not suitable for the recycling of waste lithium iron phosphate. It repairs the composition and structure of the waste lithium iron phosphate while retaining its original crystal structure, maximizes its intrinsic value, and directly regenerates it into fresh battery-grade lithium iron phosphate positive electrode material, reducing tedious secondary processing and re-preparation processes, greatly improving recycling profits, and is pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The XRD patterns of the lithium iron phosphate material before and after repair in Example 1; Figure 2 This is a graph showing the cycling performance of the lithium iron phosphate material at 0.5C before and after repair in Example 1. DETAILED DESCRIPTION

[0020] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0021] Example 1 This embodiment provides a method for regenerating and repairing waste lithium iron phosphate materials, which includes the following steps: The retired lithium iron phosphate battery was placed in a 10% NaCl solution and discharged for 24 hours. After full discharge, it was manually crushed and disassembled to obtain the spent lithium iron phosphate positive electrode sheet with an aluminum foil substrate; The waste lithium iron phosphate positive electrode sheet is placed in dimethyl carbonate and ultrasonically vibrated for 30 minutes to obtain the stripped waste lithium iron phosphate powder from which the electrolyte salt is removed; According to inductively coupled plasma mass spectrometry, the lithium element deficiency ratio of the waste lithium iron phosphate powder in this embodiment is 20%. Take 10g of waste lithium iron phosphate powder (about 0.063mol) and mix it with 0.013mol of lithium hydroxide and 1g of citric acid. After adding 25ml of deionized water and 25ml of ethanol, transfer it to a ball mill and set the speed to 200r / min for 2 hours. The fully ground material was dried in an 80°C oven for 12 hours; then the dried material was placed in a tubular furnace and annealed at 400°C for 2 hours under an external magnetic field of 0.7T and a nitrogen protective atmosphere to finally obtain a repaired and regenerated lithium iron phosphate positive electrode material.

[0022] Figure 1 The XRD diagrams of the lithium iron phosphate material before and after repair in this embodiment show that there are a large number of degraded irreversible FePO4 phases in the waste lithium iron phosphate structure. The process of this embodiment provides an external driving force through a magnetic field, and uses lithium salts in combination with reducing substances such as citric acid to work together to reduce the trivalent iron in the structure to divalent iron, and supplement the missing lithium ions, repair the missing components and defects in the crystal structure, and convert the degraded FePO4 phase back into the electrochemically active LiFePO4 phase, thereby regenerating the waste lithium iron phosphate into a fresh battery-grade lithium iron phosphate positive electrode material.

[0023] Example 2 The difference between this embodiment and embodiment 1 is that the strength of the externally applied magnetic field is 0.4T.

[0024] Example 3 The difference between this embodiment and embodiment 1 is that the strength of the externally applied magnetic field is 1.0T.

[0025] Comparative Example 1 This comparative example proposes a method for regenerating and repairing waste lithium iron phosphate materials, which includes the following steps: The retired lithium iron phosphate battery was placed in a 10% NaCl solution and discharged for 24 hours. After full discharge, it was manually crushed and disassembled to obtain the spent lithium iron phosphate positive electrode sheet with an aluminum foil substrate; The waste lithium iron phosphate positive electrode sheet is placed in dimethyl carbonate and ultrasonically vibrated for 30 minutes to obtain the stripped waste lithium iron phosphate powder from which the electrolyte salt is removed; According to inductively coupled plasma mass spectrometry, the lithium deficiency ratio of the waste lithium iron phosphate powder in this embodiment is 20%. 10g of waste lithium iron phosphate powder (about 0.063mol) (lithium deficiency ratio 20%) was mixed with 0.013mol of lithium hydroxide and 1g of citric acid. After adding 25ml of deionized water and 25ml of ethanol, the mixture was transferred to a ball mill and ball milled at a speed of 200r / min for 2 hours. The fully ground material was dried in an 80°C oven for 12 hours; the dried material was then placed in a tubular furnace and annealed at 400°C for 2 hours under a nitrogen protective atmosphere to finally obtain a repaired and regenerated lithium iron phosphate positive electrode material.

[0026] Comparative Example 2 The difference between this comparative example and comparative example 1 is that the annealing in this comparative example is performed at 700° C. for 6 hours.

[0027] Test Case (1) The waste lithium iron phosphate powder and the lithium iron phosphate material regenerated by magnetic field-induced low-energy repair in Example 1 were used as positive electrode active materials, respectively, and mixed with acetylene black conductive agent and polyvinylidene fluoride binder in a mass ratio of 9:0.5:0.5 in N-methylpyrrolidone solvent to prepare a new slurry. The prepared slurry was evenly coated on aluminum foil and dried in a vacuum drying oven at 80°C to obtain a new mass loading of 3-5 mg cm −2 The positive electrode was a lithium metal sheet as the negative electrode; a Celgard 2400 single-layer polypropylene (PP) membrane was used as the separator; and an ester electrolyte consisting of 1.0 M LiPF6 dissolved in a 1:1:1 volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) was used. CR2032 coin cells were reassembled in a glove box. The electrochemical performance of the resulting coin cells was compared after 60 cycles at 0.5C. The results are shown in Figure 2. Figure 2 As shown. Figure 2It can be observed that even under low energy input conditions, the regenerated lithium iron phosphate not only has its active lithium replenished in terms of composition, which greatly improves its specific capacity compared to the waste lithium iron phosphate; and because the crystal structure is well repaired, the cycle stability is also greatly improved, reaching the electrochemical performance level of fresh battery-grade lithium iron phosphate positive electrode materials.

[0028] (2) The repaired and regenerated lithium iron phosphate positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-2 were used to prepare lithium iron phosphate batteries. The method was as follows: the repaired and regenerated lithium iron phosphate obtained in Examples 1-3 and Comparative Examples 1-2 were used as positive electrode active materials, respectively, mixed with acetylene black conductive agent and polyvinylidene fluoride binder in a mass ratio of 9:0.5:0.5 in N-methylpyrrolidone solvent to prepare a slurry; the prepared slurry was evenly scraped onto aluminum foil, and dried in a vacuum drying oven at 80°C to prepare a slurry with a mass loading of 3-5 mg cm −2 The positive electrode was a lithium metal sheet as the negative electrode; a Celgard 2400 single-layer polypropylene (PP) membrane was used as the separator; and the ester electrolyte consisted of 1.0 M LiPF₆ dissolved in a 1:1:1 volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC). CR2032 coin cells were reassembled in a glove box. The resulting batteries were subjected to performance testing at 0.5C for 60 cycles. The results are shown in Table 1.

[0029] Table 1 Performance test results

[0030] According to the results in Table 1, we can see that: The conventional regeneration route for waste lithium iron phosphate, that is, the long-term solid-phase sintering of lithium salt + reducing agent at high temperature in Comparative Example 2 to repair defects and degraded phases in the waste lithium iron phosphate structure, although the regenerated lithium iron phosphate electrode exhibits electrochemical properties comparable to those of fresh lithium iron phosphate positive electrode materials, the energy consumption during the regeneration process is very high, which greatly increases the regeneration cost and is not conducive to large-scale promotion.

[0031] When the annealing conditions in Comparative Example 1 were reduced from 700°C for 6 hours to 400°C for 2 hours, it can be seen that due to the low efficiency of repairing the structural defects of the waste lithium iron phosphate, the specific capacity and capacity retention rate of the regenerated lithium iron phosphate were far lower than the commercial level.

[0032] In Examples 1-3, an external magnetic field (magnetic field strength 0.4-1.0 T) was applied during the annealing process. It can be seen that the efficiency of structural defect repair was greatly improved due to the application of the external magnetic field. Even under the same low-energy annealing conditions as in Comparative Example 1 (keeping at 400°C for 2 hours), the regenerated lithium iron phosphate could exhibit electrochemical properties comparable to those of commercial lithium iron phosphate. In Example 1, the best effect was achieved when an external magnetic field strength of approximately 0.7 T was applied (a magnetic field strength that can be obtained by some common permanent magnets, such as aluminum nickel cobalt magnets), which greatly reduced the energy consumption of the regeneration process.

[0033] The present invention provides a process for magnetic field-induced low-energy repair and regeneration of waste lithium iron phosphate positive electrode materials, which can restore the electrical performance of waste lithium iron phosphate under conditions of relatively low energy input.

[0034] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for regenerating and repairing waste lithium iron phosphate materials, characterized in that: It includes the following steps: After discharging, crushing and disassembling the retired lithium iron phosphate battery, the waste positive electrode sheet is obtained; Obtaining waste lithium iron phosphate powder from the waste positive electrode sheet; adding lithium salt and reducing substance to the waste lithium iron phosphate powder, and ball milling; The ball-milled material is dried and annealed under a magnetic field to obtain a regenerated lithium iron phosphate active material.

2. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The intensity of the magnetic field is 0.4-1.0 T; the ventilation annealing is performed by introducing nitrogen or helium at 300-400° C. for 1-3 hours.

3. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The ball milling speed is 200-400 r / min, and the ball milling time is 2-4 h.

4. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The drying temperature is 60-100°C.

5. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The discharge is carried out in a NaCl solution with a concentration of 10% and a discharge time of 24 hours.

6. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The method for obtaining waste lithium iron phosphate powder from the waste positive electrode sheet is as follows: placing the waste positive electrode sheet in an organic solvent, ultrasonically oscillating, and drying to obtain the waste lithium iron phosphate powder.

7. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 6, characterized in that: The organic solvent is at least one of dimethyl carbonate, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; the ultrasonic vibration time is 30-60 minutes, and the drying is performed at 60-100° C. for 8-12 hours.

8. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that: The waste lithium iron phosphate powder is tested by inductively coupled plasma mass spectrometry to obtain the amount of lithium element deficiency, and the amount of lithium salt added is determined based on the amount of lithium element deficiency; the lithium salt is at least one of lithium hydroxide, lithium acetate, and lithium carbonate; the reducing substance is one of citric acid, glucose, glycerol, and glutamic acid, and the amount of the reducing substance used accounts for 5-10wt% of the mass of the waste lithium iron phosphate powder.

9. A lithium iron phosphate material, characterized in that: The waste lithium iron phosphate material is prepared by the regeneration and repair method of waste lithium iron phosphate material according to any one of claims 1 to 8.

10. Use of the lithium iron phosphate material according to claim 9 in a lithium iron phosphate battery.

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