A method for repairing and regenerating a positive electrode material of a waste lithium iron phosphate battery

Abstract

The application discloses a kind of waste lithium iron phosphate battery positive electrode material's repair regeneration method, comprising the following steps: lithium source, reducing monomer, waste lithium iron phosphate material and solvent are mixed to carry out lithium supplement, then the mixture is sequentially washed and dried to obtain polymer-coated repaired lithium iron phosphate material;Under the protection of inert gas, the repaired lithium iron phosphate material is heated, and the surface polymer of lithium iron phosphate material is carbonized to obtain regenerated lithium iron phosphate material.The method can repair Li + Vacancies and Fe-Li antisite defects are simultaneously repaired, and after repair, the surface layer compound of the material can be converted into carbon, and the carbon structure on the surface of lithium iron phosphate particles can be simultaneously repaired.In addition, the method is simple, safe and low in energy consumption, which can reduce production cost and requirement for equipment, so as to realize large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of waste battery resource recycling technology, specifically relating to a method for repairing and regenerating the cathode material of waste lithium iron phosphate batteries. Background Technology

[0002] With the increasing demand and production of lithium-ion batteries year by year, the number of waste lithium iron phosphate batteries is also increasing dramatically. If these waste lithium iron phosphate batteries are not properly disposed of, they will not only waste resources but also cause significant environmental pollution. Therefore, recycling lithium iron phosphate batteries has enormous economic and social value. Common methods for recycling lithium iron phosphate cathode materials fall into two main categories: wet leaching, which aims to recover precious metals, and remediation and regeneration of the lithium iron phosphate material.

[0003] Wet recycling mainly uses chemical reagents for treatment, based on the idea of ​​material structure destruction and re-extraction. It is characterized by a long recycling process, high energy consumption, high emissions, generation of large amounts of acidic ammonia and alkaline wastewater, and difficulty in controlling costs and emissions. Moreover, compared with lithium cobalt oxide and ternary cathode materials, lithium iron phosphate cathode materials do not contain valuable metals such as cobalt and nickel, so the economics of the recycled products are not high.

[0004] Currently, the main direct regeneration processes for lithium iron phosphate (LFP) include solid-state calcination for lithium replenishment and hydrothermal relithiation. However, in practice, high temperature, high pressure, and long reaction times (typically 24 hours) exacerbate particle agglomeration during regeneration, which subsequently affects the recovery of electrochemical performance. Furthermore, high temperature and high pressure not only increase energy consumption but also place high demands on equipment, limiting large-scale production. On the other hand, the carbon coating on the particle surface is damaged after long-term cycling, leading to a decrease in conductivity in the waste LFP particles. Therefore, in addition to lithium replenishment, direct regeneration technology for LFP should also consider the repair of the carbon structure on the particle surface. Summary of the Invention

[0005] The purpose of this invention is to provide a method for repairing and regenerating waste lithium iron phosphate battery cathode materials. This method can repair and regenerate Li... + The method simultaneously repairs vacancies and Fe-Li antisite defects, and after repair, the surface compounds of the material can be converted into carbon, which can simultaneously repair the carbon structure on the surface of lithium iron phosphate particles. In addition, the method is simple, safe and energy-efficient, which can reduce production costs and equipment requirements, thereby enabling large-scale production.

[0006] To achieve the above objectives, this invention discloses a method for repairing and regenerating waste lithium iron phosphate battery cathode materials, comprising the following steps:

[0007] (1) Lithium source, reducing monomer, waste lithium iron phosphate material and solvent are mixed to replenish lithium, and the reaction is stirred at room temperature. After the reaction product is filtered, the filter residue is washed and dried to obtain polymer-encapsulated repaired lithium iron phosphate material.

[0008] (2) Under the protection of inert gas, the lithium iron phosphate material repaired in step (1) is heated and carbonized to obtain regenerated lithium iron phosphate material.

[0009] Preferably, in step (1), the lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium sulfate, lithium chloride, lithium iodide, lithium formate, and lithium tetraborate.

[0010] Preferably, in step (1), the reducing monomer is a polyphenolic compound, which is one or more of dopamine, tannic acid, catechol, and gallic acid.

[0011] Preferably, in step (1), the solvent is one or more of water, ethanol, methanol, benzene, carbon tetrachloride, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, and N-methyl-2-pyrrolidone.

[0012] Preferably, in step (1), the lithium replenishment reaction takes 3 to 12 hours.

[0013] Preferably, in step (1), the total mass of the lithium source, reducing monomer and waste lithium iron phosphate material to the mass-volume ratio of the solvent is (1.75-4) g: 10 ml.

[0014] Preferably, in step (1), the mass ratio of the lithium source, reducing monomer, and waste lithium iron phosphate material is (0.5-5):(0.5-5):2.

[0015] Preferably, in step (2), the inert gas is nitrogen or argon, the heating temperature is 400-700℃, and the heating time is 1-8h.

[0016] In this invention, the reducing monomer can play a reducing role during the polymerization process. In addition, after the reducing monomer is polymerized, a polymer layer can be formed on the surface of lithium iron phosphate. Heating and carbonizing it into nitrogen-doped carbon can improve the electrochemical performance of the repaired lithium iron phosphate, making it superior to commercially available lithium iron phosphate materials. The addition of lithium salt plays a role in lithium replenishment.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) This invention, by combining waste lithium iron phosphate materials with appropriate lithium sources and reducing monomers, can achieve the Li-reducing process of waste lithium iron phosphate materials without the need for high-temperature and high-pressure environments or special equipment. +This invention simultaneously repairs vacancies and Fe-Li antisite defects; it is energy-efficient, produces low carbon emissions, is safe and controllable, and has low cost; furthermore, it can be carried out in aquatic systems, resulting in less pollution.

[0019] (2) This invention converts the polymer coated on the surface of the repaired lithium iron phosphate material into carbon through a carbonization reaction, thereby improving the electrochemical performance of the repaired lithium iron phosphate, which is of great significance for the restoration of the electrochemical performance of waste lithium iron phosphate materials. Attached Figure Description

[0020] Figure 1 These are high-resolution transmission electron microscopy (TEM) images of lithium iron phosphate materials before and after repair in Embodiment 1 of the present invention.

[0021] Figure 2 The figure shows the electrochemical performance test results of the recycled lithium iron phosphate material prepared in Example 1. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments.

[0023] Example 1

[0024] A method for repairing and regenerating waste lithium iron phosphate battery cathode materials includes the following steps:

[0025] (1) Add 1g lithium chloride, 1g dopamine and 2g waste lithium iron phosphate material to 10ml water, stir and react at room temperature for 6h, filter the reaction product, wash the filter residue with deionized water 5 times, and then put the water-washed filter residue into a forced-air drying oven to dry for 10h to obtain polymer-coated repaired lithium iron phosphate material.

[0026] (2) Under the protection of argon gas, the polymer-encapsulated repaired lithium iron phosphate material is heated and carbonized at 500°C for 5 hours, and the polymer on the surface of the lithium iron phosphate material is carbonized to obtain the regenerated lithium iron phosphate material.

[0027] High-resolution transmission electron microscopy (HRTEM) tests were performed on the lithium iron phosphate material before and after repair in this embodiment. The results are as follows: Figure 1 As shown. Compared to the waste lithium iron phosphate material before repair, the crystal structure of the repaired lithium iron phosphate material in this embodiment is significantly restored, and the surface of the regenerated lithium iron phosphate material is coated with a uniform layer of carbon, indicating that this embodiment successfully repaired the waste lithium iron phosphate material and obtained regenerated lithium iron phosphate material.

[0028] Electrochemical performance tests were performed on the recycled lithium iron phosphate material prepared in this embodiment. The test method was as follows: 2g of the recycled lithium iron phosphate material prepared in Example 1 was weighed and compounded with PVDF (polyvinylidene fluoride) and Super P carbon in a mass ratio of 80:10:10. NMP (N-methylpyrrolidone) was used as a dispersant to prepare the slurry. The slurry was coated onto a flat aluminum foil and dried in a forced-air dryer for 12 hours. After rolling, it was pressed into a 14mm diameter positive electrode sheet. In an inert glove box, a lithium metal sheet was used as the negative electrode material, a Celgard 2400 membrane was used as the separator, and a solution of 1mol / L lithium hexafluorophosphate dissolved in a mixture of EC (ethylene carbonate):DMC (dimethyl carbonate) = 3:7 (volume ratio) was used as the electrolyte to assemble a coin cell. The coin cell test was conducted with the test voltage controlled between 2.5 and 4.2V. The electrochemical performance test results are as follows: Figure 2 As shown, the electrochemical performance of the repaired lithium iron phosphate cathode material of this invention can achieve a discharge capacity of 142 mAh / g at a 1C rate, representing a significant capacity improvement. Furthermore, its cycle performance is superior compared to commercially available lithium iron phosphate materials.

[0029] Example 2

[0030] A method for repairing and regenerating waste lithium iron phosphate battery cathode materials includes the following steps:

[0031] (1) Add 0.5g lithium hydroxide, 1g dopamine and 2g waste lithium iron phosphate material to 20ml water, stir and react at room temperature for 9h, filter the reaction product, wash the filter residue with deionized water 5 times, and then put the water-washed filter residue into a forced-air drying oven to dry for 8h to obtain polymer-coated repaired lithium iron phosphate material.

[0032] (2) Under the protection of argon gas, the polymer-encapsulated repaired lithium iron phosphate material is heated and carbonized at 600°C for 6 hours, and the polymer on the surface of the lithium iron phosphate material is carbonized to obtain the regenerated lithium iron phosphate material.

[0033] High-resolution transmission electron microscopy (HRTEM) tests were performed on the lithium iron phosphate materials before and after the repair in this embodiment. The results showed that, compared with the waste lithium iron phosphate materials before repair, the crystal structure of the repaired lithium iron phosphate materials in this embodiment was significantly restored, and the surface of the regenerated lithium iron phosphate materials was coated with a uniform layer of carbon. This indicates that the waste lithium iron phosphate materials were successfully repaired in this embodiment, and regenerated lithium iron phosphate materials were obtained.

[0034] The electrochemical performance of the regenerated lithium iron phosphate material prepared in this embodiment was tested using the same method as in Example 1. The electrochemical performance test results show that the electrochemical performance of the repaired lithium iron phosphate cathode material of this invention achieves a discharge capacity of 145 mAh / g at a 1C rate, and retains approximately 90% of its discharge specific capacity after 400 cycles. Furthermore, its cycle performance is superior to that of commercially available lithium iron phosphate materials.

[0035] Example 3

[0036] A method for repairing and regenerating waste lithium iron phosphate battery cathode materials includes the following steps:

[0037] (1) Add 0.8g lithium sulfate, 1g catechol and 2g waste lithium iron phosphate material to 20ml ethanol, stir at room temperature for 3h, filter the reaction product, wash the filter residue with deionized water 5 times, and then put the water-washed filter residue into a forced-air drying oven to dry for 8h to obtain polymer-coated repaired lithium iron phosphate material.

[0038] (2) Under the protection of argon gas, the polymer-encapsulated repaired lithium iron phosphate material is heated and carbonized at 400°C for 8 hours. The polymer on the surface of the lithium iron phosphate material is carbonized to obtain the regenerated lithium iron phosphate material.

[0039] High-resolution transmission electron microscopy (HRTEM) tests were performed on the lithium iron phosphate materials before and after the repair in this embodiment. The results showed that, compared with the waste lithium iron phosphate materials before repair, the crystal structure of the repaired lithium iron phosphate materials in this embodiment was significantly restored, and the surface of the regenerated lithium iron phosphate materials was coated with a uniform layer of carbon. This indicates that the waste lithium iron phosphate materials were successfully repaired in this embodiment, and regenerated lithium iron phosphate materials were obtained.

[0040] The electrochemical performance of the regenerated lithium iron phosphate material prepared in this embodiment was tested using the same method as in Example 1. The electrochemical performance test results show that the electrochemical performance of the repaired lithium iron phosphate cathode material of this invention can achieve a discharge capacity of 140 mAh / g at a 1C rate, and retains approximately 92% of its discharge specific capacity after 400 cycles.

[0041] Example 4

[0042] A method for repairing and regenerating waste lithium iron phosphate battery cathode materials includes the following steps:

[0043] (1) Add 0.8g lithium oxalate, 1g tannic acid and 2g waste lithium iron phosphate material to 20ml acetonitrile, stir and react at room temperature for 12h, filter the reaction product, wash the filter residue with deionized water 5 times, and then put the water-washed filter residue into a forced-air drying oven to dry for 8h to obtain polymer-coated repaired lithium iron phosphate material.

[0044] (2) Under the protection of argon gas, the polymer-encapsulated repaired lithium iron phosphate material is heated and carbonized at 700°C for 3 hours. The polymer on the surface of the lithium iron phosphate material is carbonized to obtain the regenerated lithium iron phosphate material.

[0045] High-resolution transmission electron microscopy (HRTEM) tests were performed on the lithium iron phosphate materials before and after the repair in this embodiment. The results showed that, compared with the waste lithium iron phosphate materials before repair, the crystal structure of the repaired lithium iron phosphate materials in this embodiment was significantly restored, and the surface of the regenerated lithium iron phosphate materials was coated with a uniform layer of carbon. This indicates that the waste lithium iron phosphate materials were successfully repaired in this embodiment, and regenerated lithium iron phosphate materials were obtained.

[0046] The electrochemical performance of the regenerated lithium iron phosphate material prepared in this embodiment was tested using the same method as in Example 1. The electrochemical performance test results show that the electrochemical performance of the repaired lithium iron phosphate cathode material of this invention achieves a discharge capacity of 144 mAh / g at a 1C rate, and retains approximately 92% of its discharge specific capacity after 400 cycles.

Claims

1. A method for repairing and regenerating a positive electrode material of a waste lithium iron phosphate battery, characterized in that, The method comprises the following steps: (1) mixing a lithium source, a reducing monomer, a waste lithium iron phosphate material and a solvent to perform lithium supplement, stirring at room temperature, filtering the reaction product, and then washing and drying the obtained filter residue to obtain a polymer-wrapped repaired lithium iron phosphate material; the reducing monomer is a polyphenol compound, and the polyphenol compound is one or more of dopamine, tannic acid, catechol and gallic acid; the mass ratio of the lithium source, the reducing monomer and the waste lithium iron phosphate material is (0.5-5):(0.5-5):2; (2) under the protection of an inert gas, heating and carbonizing the repaired lithium iron phosphate material of step (1) to obtain a regenerated lithium iron phosphate material.

2. The method according to claim 1, wherein the method is characterized by, In step (1), the lithium source is one or more of lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium sulfate, lithium chloride, lithium iodide, lithium formate and lithium tetraborate.

3. The method according to claim 1 or 2, characterized in that, In step (1), the solvent is one or more of water, ethanol, methanol, benzene, carbon tetrachloride, dimethyl sulfoxide, acetonitrile, tetrahydrofuran and N-methyl-2-pyrrolidone.

4. The method according to claim 1 or 2, characterized in that, In step (1), the lithium supplement reaction time is 3-12 h.

5. The method according to claim 1 or 2, characterized in that, In step (1), the mass-volume ratio of the total mass of the lithium source, the reducing monomer and the waste lithium iron phosphate material to the mass of the solvent is (1.75-4) g:10 ml.

6. The method according to claim 1 or 2, characterized in that, In step (2), the inert gas is nitrogen or argon, the heating temperature is 400-700 DEG C, and the heating time is 1-8 h.

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