Method for regenerating and repairing waste lithium iron phosphate material, lithium iron phosphate material and application thereof

Abstract

This invention relates to the field of lithium iron phosphate (LFP) material regeneration technology, specifically disclosing a method for regenerating and repairing waste LFP materials, as well as LFP materials and their applications. The method for regenerating and repairing waste LFP materials includes the following steps: discharging retired LFP batteries, crushing and disassembling them to obtain waste positive electrode sheets; obtaining waste LFP powder from the waste positive electrode sheets; adding lithium salt and reducing agents to the waste LFP powder, and ball milling; drying the ball-milled material, and annealing it under a magnetic field to obtain regenerated LFP active material. This invention, under the condition of introducing a magnetic field, can achieve direct structural repair and lithium replenishment at a relatively low energy input, obtaining recyclable battery-grade regenerated LFP positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate material regeneration technology, and in particular to a method for regenerating and repairing waste lithium iron phosphate materials, as well as lithium iron phosphate materials and their applications. Background Technology

[0002] Currently, new energy is developing rapidly, especially lithium-ion batteries (LIBs), which have been successfully commercialized. LIBs are now maturely applied in various consumer electronics products, new energy transportation equipment, and large-scale energy storage power stations. With the increase in installed capacity of LIB systems, the number of LIBs used is also increasing. Considering the average effective lifespan and calendar lifespan of power batteries, the world is gradually entering a peak period of retirement for spent lithium-ion batteries (SLIBs). As is well known, SLIBs are highly polluting and have high recycling value, especially for large power batteries, which contain high levels of heavy metals, electrolytes, solvents, and various organic auxiliary materials. Improper disposal of SLIBs can severely pollute soil and water resources, while also causing a significant waste of resources. Recycling the positive electrode active material from SLIBs for direct repair and regeneration is one of the most promising solutions, especially for lithium iron phosphate batteries, which account for a large share of the installed market.

[0003] Lithium iron phosphate (LFP) batteries suffer from low profitability and high energy consumption due to the limited variety and abundance of valuable elements in their cathode active materials. Traditional pyrometallurgical or hydrometallurgical recycling processes also generate secondary pollution from acid and alkali emissions or greenhouse gas emissions. Direct repair and recycling of waste LFP cathode materials avoids complex secondary processing steps such as crushing, preserving the original structure. The separated LFP powder undergoes direct structural repair and lithium replenishment, maximizing the original value of the waste LFP powder. The process is simple, and the recycled products can be directly reused, making it suitable for large-scale recycling. Currently, the typical direct repair and regeneration route for waste LFP involves high-temperature calcination of waste LFP + lithium salt + reducing agent. However, this method still suffers from high energy consumption. Therefore, further reducing energy consumption and achieving rapid structural restoration under low-energy conditions is crucial. Summary of the Invention

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

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention first provides a method for regenerating and repairing waste lithium iron phosphate materials, which includes the following steps: After the retired lithium iron phosphate batteries are discharged, they are crushed and disassembled to obtain waste positive electrode sheets. Waste lithium iron phosphate powder was obtained from the waste cathode sheets; Lithium salt and reducing agent are added to the waste lithium iron phosphate powder, and then ball-milled. The ball-milled material is dried and then annealed under a magnetic field to obtain regenerated lithium iron phosphate active material.

[0006] This invention enables direct structural repair and lithium replenishment of lithium iron phosphate cathode materials with low energy input under the condition of introducing a magnetic field, thereby obtaining recyclable battery-grade regenerated lithium iron phosphate cathode materials.

[0007] As a further improvement to the above-mentioned scheme of the present invention, the strength of the magnetic field is 0.4-1.0T; the gas annealing is to introduce nitrogen or helium and anneal at 300-400℃ for 1-3 hours.

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

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

[0010] As a further improvement to the above-described scheme of the present invention, the discharge is carried out in a NaCl solution with a concentration of 10% for a duration of 24 hours.

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

[0012] As a further improvement to the above-mentioned scheme 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 min; and the drying is carried out at 60-100℃ for 8-12 h.

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

[0015] The present invention also provides an application of the lithium iron phosphate material as described above in lithium iron phosphate batteries.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention performs annealing under a magnetic field, using only the missing lithium salt in the waste powder structure and some low-cost reducing materials. It can directly replenish the missing lithium ions in the structure of lithium iron phosphate waste powder and repair lithium iron phosphate reverse site defects and degradation phases at relatively low temperatures and short holding times, thus regenerating lithium iron phosphate waste powder into fresh battery-grade lithium iron phosphate cathode material. The regenerated lithium iron phosphate has excellent electrochemical performance and can be used for large-scale recycling and reuse of retired lithium-ion battery lithium iron phosphate cathode materials.

[0017] This invention, under relatively low temperature and short holding time, utilizes an external magnetic field in conjunction with a reducing environment to rapidly promote the conversion of high-spin iron that has migrated to oxidized lithium sites in the crystal structure of spent lithium iron phosphate (LFP) batteries to a low-spin state. This reduces the superexchange effect of iron at antisite sites, thereby driving the repair of lithium-iron antisite defects in the LFP crystal structure and the regeneration of degraded FePO4 phase through lithium replenishment. This achieves lithium replenishment and structural repair under low energy consumption conditions. The process is simple, safe, pollution-free, and easily scaled up for mass production, with low energy consumption and low cost, and high added value of the recycled products. The process of this invention addresses the main challenges of expanding the direct recycling of retired LFP lithium-ion batteries in an eco-friendly and economical manner, making it suitable for further industry adoption.

[0018] This invention effectively solves the problem that traditional metallurgical methods for extracting valuable metal elements are not suitable for recycling waste lithium iron phosphate. By preserving the original crystal structure of waste lithium iron phosphate, the composition and structure are repaired, maximizing its intrinsic value and directly regenerating it into fresh battery-grade lithium iron phosphate cathode material. This reduces the cumbersome secondary processing and reprocessing steps, greatly increases the profit of recycling, and is pollution-free. Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the lithium iron phosphate material before and after repair in Example 1. Figure 2 The graph shows the cycling performance of lithium iron phosphate material before and after repair in Example 1 at 0.5C. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0021] Example 1 This embodiment proposes a method for regenerating and repairing waste lithium iron phosphate materials, which includes the following steps: Retired lithium iron phosphate batteries were placed in a 10% NaCl solution and discharged for 24 hours. After full discharge, they were manually crushed and disassembled to obtain waste lithium iron phosphate positive electrode sheets with aluminum foil substrates. Waste lithium iron phosphate cathode sheets were placed in dimethyl carbonate and ultrasonically vibrated for 30 minutes to obtain stripped waste lithium iron phosphate powder after removing electrolyte salts. According to inductively coupled plasma mass spectrometry, the lithium content of the waste lithium iron phosphate powder in this embodiment is 20%. 10g of waste lithium iron phosphate powder (about 0.063mol) 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 jar and ball milled at 200 r / min for 2 hours. The thoroughly ground material was dried in an oven at 80°C for 12 hours. Then, the dried material was placed in a tube 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 the repaired and regenerated lithium iron phosphate cathode material.

[0022] Figure 1 The XRD patterns of the lithium iron phosphate material before and after repair in this embodiment show that the waste lithium iron phosphate structure contains a large amount of degraded irreversible FePO4 phase. In this embodiment, the process provides an external driving force through a magnetic field, and uses lithium salt and reducing substances such as citric acid to work together to reduce the trivalent iron in the structure to divalent iron, replenish the missing lithium ions, repair the missing components and defects in the crystal structure, and regenerate the degraded FePO4 phase into the electrochemically active LiFePO4 phase, thereby regenerating the waste lithium iron phosphate into fresh battery-grade lithium iron phosphate cathode material.

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

[0024] Example 3 The difference between this embodiment and Embodiment 1 is that the externally applied magnetic field strength 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: Retired lithium iron phosphate batteries were placed in a 10% NaCl solution and discharged for 24 hours. After full discharge, they were manually crushed and disassembled to obtain waste lithium iron phosphate positive electrode sheets with aluminum foil substrates. Waste lithium iron phosphate cathode sheets were placed in dimethyl carbonate and ultrasonically vibrated for 30 minutes to obtain stripped waste lithium iron phosphate powder after removing electrolyte salts. According to inductively coupled plasma mass spectrometry, the lithium content of the waste lithium iron phosphate powder in this embodiment is 20%. Take 10g of waste lithium iron phosphate powder (about 0.063mol) (with a lithium content of 20%), mix it with 0.013mol of lithium hydroxide and 1g of citric acid, add 25ml of deionized water and 25ml of ethanol, transfer it to a ball mill jar, and ball mill at 200r / min for 2 hours. The thoroughly ground material was dried in an oven at 80°C for 12 hours; then the dried material was placed in a tube furnace and annealed at 400°C for 2 hours under a nitrogen protective atmosphere to finally obtain the repaired and regenerated lithium iron phosphate cathode material.

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

[0027] Test case (1) The waste lithium iron phosphate powder and the magnetic field-induced low-energy regenerated lithium iron phosphate material from Example 1 were used as positive electrode active materials, and were 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 uniformly coated onto aluminum foil and dried in a vacuum drying oven at 80°C to obtain a new material with a mass loading of 3-5 mg cm⁻¹. −2 The positive electrode was a lithium metal sheet, and the negative electrode was a Celgard 2400 single-layer polypropylene (PP) membrane. The electrolyte was a 1.0 M LiPF6 solution in a 1:1:1 volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) mixed organic solvent. The CR2032 type button cell was reassembled in a glove box. The electrochemical performance of the fabricated button cell after 60 cycles at 0.5C was compared, and the results are as follows: Figure 2 As shown. From 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, resulting in a significant improvement in specific capacity compared to waste lithium iron phosphate; but also, due to the intact restoration of the crystal structure, its cycle stability is greatly improved, reaching the electrochemical performance level of fresh battery-grade lithium iron phosphate cathode materials.

[0028] (2) The repaired and regenerated lithium iron phosphate cathode 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 cathode active materials, and were 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 uniformly coated onto aluminum foil and dried in a vacuum drying oven at 80°C to obtain a new slurry with a mass loading of 3-5 mg cm⁻¹. −2 The positive electrode was a lithium metal sheet; the negative electrode was a Celgard 2400 single-layer polypropylene (PP) membrane; the electrolyte was a mixture of 1.0 M LiPF6 dissolved in a 1:1:1 volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) as an ester electrolyte; and the CR2032 button cell was reassembled in a glove box. The performance of each battery was tested: 60 cycles at 0.5C, and the results are shown in Table 1.

[0029] Table 1 Performance Test Results

[0030] According to the results in Table 1: The conventional recycling route for waste lithium iron phosphate, namely the lithium salt + reducing agent solid-state sintering at high temperature for a long time in Comparative Example 2, is used to repair the defects and degraded phases in the structure of waste lithium iron phosphate. Although the recycled lithium iron phosphate electrode exhibits electrochemical performance comparable to that of fresh lithium iron phosphate cathode material, the energy consumption in the recycling process is very high, which greatly increases the recycling cost and is not conducive to large-scale promotion.

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

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

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

[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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 embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should 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 the retired lithium iron phosphate batteries are discharged, they are crushed and disassembled to obtain waste positive electrode sheets. Waste lithium iron phosphate powder was obtained from the waste cathode sheets; Lithium salt and reducing agent are added to the waste lithium iron phosphate powder, and then ball-milled. The ball-milled material is dried and then annealed under a magnetic field: annealing at 300-400℃ for 1-3 hours to obtain 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 strength of the magnetic field is 0.4-1.0T; the gas-purifying annealing is performed by introducing nitrogen or helium.

3. The method for regenerating and repairing waste lithium iron phosphate materials according to claim 1, characterized in that, The ball mill rotates at a speed of 200-400 r / min and the 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℃.

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% for 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: the waste positive electrode sheet is placed in an organic solvent, ultrasonically vibrated, and dried to obtain 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 oscillation time is 30-60 min; and the drying is carried out at 60-100℃ for 8-12 h.

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 analyzed by inductively coupled plasma mass spectrometry to determine the amount of lithium missing. The amount of lithium salt to be added is determined based on the amount of lithium missing. The lithium salt is at least one of lithium hydroxide, lithium acetate, and lithium carbonate. The reducing agent is one of citric acid, glucose, glycerol, and glutamic acid. The amount of the reducing agent is 5-10 wt% of the mass of the waste lithium iron phosphate powder.

9. A lithium iron phosphate material, characterized in that, It is prepared using the method for regenerating and repairing waste lithium iron phosphate materials as described in any one of claims 1-8.

10. The application of the lithium iron phosphate material as described in claim 9 in a lithium iron phosphate battery.

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