A method for repairing failed lithium iron phosphate in situ

Abstract

The application provides a method for repairing failed lithium iron phosphate in situ, comprising: separating positive electrode black powder from a positive electrode sheet of a waste lithium iron phosphate battery; obtaining a lithium vacancy rate, a Li-Fe anti-site defect value and a ratio of Fe 3+ / Fe 2+ in a lithium iron phosphate crystal lattice to be repaired in the positive electrode black powder, and evaluating the failure degree of the lithium iron phosphate to be repaired; according to the element content in the positive electrode black powder and the failure degree of the lithium iron phosphate to be repaired, selectively supplementing a lithium source and / or a carbon source, and then heat treating to achieve adaptive repair and regeneration. The method for repairing failed lithium iron phosphate in situ provided by the application realizes lithium vacancy supplement, Fe 3+ reduction, carbon coating layer reconstruction and precise material supplement control, so that the repaired lithium iron phosphate material is pure in phase, controllable in crystal lattice defect, and the first coulomb efficiency, cycle stability and rate performance all reach or are close to the level of commercial lithium iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of regeneration technology for failed lithium iron phosphate, and specifically to a method for in-situ repair of failed lithium iron phosphate. Background Technology

[0002] The exponential surge in demand for clean energy has driven the large-scale deployment of lithium-ion batteries. Among them, lithium iron phosphate (LFP) batteries have become the mainstream battery for electric vehicles and large-scale energy storage systems due to their excellent thermal stability, long cycle life, and low cost. At the same time, LFP batteries are also entering the stage of large-scale retirement. How to efficiently, economically, and greenly regenerate and repair waste LFP cathode materials has become a key technical issue for the sustainable development of the new energy industry chain.

[0003] Currently, lithium iron phosphate (LFP) recycling technologies mainly include wet leaching and resynthesis, pyrometallurgy, and solid-phase lithium replenishment for direct repair. Among these, the solid-phase lithium replenishment method is simple, does not damage the crystal structure of the cathode material, and is suitable for industrial scale-up. Patent CN115621592A discloses a pyrometallurgical repair and regeneration method for waste LFP powder doped with titanium dioxide, which achieves material regeneration by removing impurities, defluorinating, ball milling and doping, and sintering the waste LFP electrode sheets. Patent CN121491123A proposes to synergistically regenerate waste LFP cathode materials by mixing and calcining waste phase change thermal storage materials and lithium salts. However, these methods face challenges in addressing LFP materials with different levels of failure, particularly in terms of lithium vacancy rate and Fe content. 3+ / Fe 2+ Significant differences exist in the valence ratio and the degree of damage to the carbon coating layer. Using uniform feed ratios and calcination conditions makes precise repair difficult, leading to poor batch-to-batch consistency in the repaired products. Secondly, the separated lithium iron phosphate materials typically contain small amounts of Li- and carbon-containing substances, such as carbonate compounds from the electrolyte, LiPF6, and acetylene black. These substances are usually removed as impurities, which not only wastes raw materials but also increases the cost of subsequent repair agents.

[0004] Therefore, developing a precise and low-cost repair method for LFP materials that can maximize the use of raw materials and adapt to different failure levels is of great practical significance and technical value. Summary of the Invention

[0005] The purpose of this invention is to make full use of the internal materials of the battery and establish a multi-dimensional failure assessment system to carry out repair treatments that match different levels, avoid waste of materials, over-repair or under-repair, and improve the batch consistency and electrochemical performance of the repaired materials.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for in-situ repair of failed lithium iron phosphate, comprising: Positive electrode black powder was separated from the positive electrode sheets of waste lithium iron phosphate batteries; Obtain the lithium vacancy rate, Li-Fe antisite defect value, and Fe content in the lithium iron phosphate lattice to be repaired in the cathode black powder. 3+ / Fe 2+ The proportion of lithium iron phosphate to be repaired is used to assess the degree of failure. Based on the elemental content in the cathode black powder, Li source and / or carbon source are selectively supplemented, followed by heat treatment to achieve adaptive repair and regeneration.

[0007] Furthermore, the method involves obtaining the lithium vacancy rate, Li-Fe antisite defect value, and Fe content in the lithium iron phosphate lattice to be repaired within the cathode black powder. 3+ / Fe 2+ The proportion is used to obtain the degree of failure of the lithium iron phosphate to be repaired, including, XRD detection and data refinement calculations were used to obtain the lithium vacancy rate and Li-Fe antisite defect value in the lithium iron phosphate lattice to be repaired. This was combined with XPS detection to obtain the Fe... 3+ / Fe 2+ Peak area ratio is used to comprehensively assess the degree of failure of the lithium iron phosphate lithium to be repaired. Mild failure: Lithium vacancy rate ≤10%, Li Fe inversion defects ≤2.0%, Fe 3+ / Fe 2+ Peak area ratio ≤ 1; Moderate failure: Lithium vacancy rate 10%-20%, Li Fe antisite defects 2.0%-4.0%, Fe 3+ / Fe 2+ Peak area ratio 1-3; Severe failure: Lithium vacancy rate >20%, Li Fe reverse defect >4.0%, Fe 3+ / Fe 2+ Peak area ratio > 3.

[0008] Furthermore, the selective replenishment of Li and / or carbon sources into the cathode black powder based on the elemental content in the cathode black powder and the degree of failure of the lithium iron phosphate to be repaired includes, The content of lithium, carbon, and iron in the cathode black powder was detected by ICP. Mild failure: Selectively supplement the carbon source into the positive electrode black powder, and adjust the total mass ratio of carbon elements to 8%-12%; Moderate failure: Supplement the cathode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 13%-17%; Severe failure: Supplement the positive electrode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 18%-22%.

[0009] Further, the heat treatment includes, Under a protective atmosphere, the temperature is increased to 700-800℃ at a heating rate of 3-8℃ / min and held for 1-5 hours, then naturally cooled to room temperature.

[0010] Furthermore, the positive electrode black powder includes not only the lithium iron phosphate to be repaired, but also binder, conductive agent, graphite, aluminum, copper, electrolyte, lithium salt and organic impurities, wherein the aluminum content is ≤0.05%.

[0011] Furthermore, the Li source is selected from lithium salts in the cathode black powder; The carbon source is selected from at least one of the binder, conductive agent, graphite, electrolyte, and organic impurities in the cathode black powder.

[0012] Furthermore, the separation is carried out using mechanical crushing and screening.

[0013] Furthermore, after being separated, the positive electrode black powder is dried to remove surface adsorbed water.

[0014] The present invention also provides a lithium iron phosphate, which is obtained by the above-described method for in-situ repair of failed lithium iron phosphate.

[0015] The present invention also provides a lithium battery, wherein the positive electrode material includes the aforementioned lithium iron phosphate.

[0016] Compared with the prior art, the beneficial effects of the present invention include: The in-situ repair method for failed lithium iron phosphate of the present invention utilizes the lithium vacancy rate, Li-Fe antisite defect value, and Fe in the lithium iron phosphate lattice to be repaired. 3+ / Fe 2+ The proportion of the material is used to assess the degree of failure, and the assessment results are more consistent with the actual deterioration state of the material, providing a reliable basis for precise repair. According to the degree of failure, Li source and / or carbon source are selectively supplemented, followed by heat treatment to achieve adaptive repair and regeneration, avoid over-repair or under-repair, and improve the batch consistency and electrochemical performance of the repaired material.

[0017] The in-situ repair method for failed lithium iron phosphate of the present invention involves lithium vacancy replenishment and Fe... 3+ Reduction, carbon coating reconstruction, and precise feeding control ensure that the repaired lithium iron phosphate material has a pure phase and controllable lattice defects. For the first time, the coulombic efficiency, cycle stability, and rate performance all reach or approach the level of commercial lithium iron phosphate.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0020] Figure 1 This is a flowchart of a method for in-situ repair of failed lithium iron phosphate according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] The design concept of this invention is to address the shortcomings of existing "one-size-fits-all" repair strategies that are difficult to adapt to the actual degradation state of materials. This invention establishes a system based on XRD refinement (lithium vacancy rate, Li-Fe antisite defects) and XPS detection (Fe 3+ / Fe 2+A two-dimensional failure assessment system based on peak area ratio (PAR) categorizes failed lithium iron phosphate (LiFePO4) into three levels: light, medium, and heavy. Differentiated external feed amounts are then matched to each level to avoid over- or under-repair, improving batch consistency and electrochemical performance of the repaired materials. This is achieved through lithium vacancy replenishment and Fe... 3+ Reduction, carbon coating reconstruction, and precise feeding control ensure that the repaired lithium iron phosphate material has a pure phase and controllable lattice defects. For the first time, the coulombic efficiency, cycle stability, and rate performance all reach or approach the level of commercial lithium iron phosphate.

[0025] Accordingly, the present invention provides a method for in-situ repair of failed lithium iron phosphate, comprising, Positive electrode black powder was separated from the positive electrode sheets of waste lithium iron phosphate batteries; Obtain the lithium vacancy rate, Li-Fe antisite defect value, and Fe content in the lithium iron phosphate lattice to be repaired in the cathode black powder. 3+ / Fe 2+ The proportion of lithium iron phosphate to be repaired is used to assess the degree of failure. Based on the elemental content in the cathode black powder and the degree of failure of the lithium iron phosphate to be repaired, Li source and / or carbon source are selectively added to the cathode black powder, followed by heat treatment to achieve adaptive repair and regeneration.

[0026] In some preferred embodiments, the step of obtaining the lithium vacancy rate, Li-Fe antisite defect value, and Fe in the lithium iron phosphate lattice to be repaired in the cathode black powder is... 3+ / Fe 2+ The proportion is used to obtain the degree of failure of the lithium iron phosphate to be repaired, including, XRD measurements and data refinement calculations were used to obtain the lithium vacancy rate and Li-Fe antisite defect values ​​in the lithium iron phosphate lattice to be repaired. These were combined with XPS detection to obtain Fe... 3+ / Fe 2+ Peak area ratio is used to comprehensively assess the degree of failure of the lithium iron phosphate lithium to be repaired. Mild failure: Lithium vacancy rate ≤10%, Li Fe inversion defects ≤2.0%, Fe 3+ / Fe 2+ Peak area ratio ≤ 1; Moderate failure: Lithium vacancy rate 10%-20%, Li Fe antisite defects 2.0%-4.0%, Fe 3+ / Fe 2+ Peak area ratio 1-3; Severe failure: Lithium vacancy rate >20%, Li Fe reverse defect >4.0%, Fe 3+ / Fe 2+ Peak area ratio > 3.

[0027] In some preferred embodiments, the selective replenishment of Li and / or carbon sources based on the elemental content in the cathode black powder and the degree of failure of the lithium iron phosphate to be repaired includes, The content of lithium, carbon, and iron in the cathode black powder was detected by ICP. Mild failure: Selectively supplement the positive electrode powder with a carbon source, adjusting the total mass ratio of carbon elements to 8%-12%; preferably, adjusting the total mass ratio of carbon elements to 11%-12%. Moderate failure: Supplement the cathode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 13%-17%; Severe failure: Supplement the positive electrode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 18%-22%.

[0028] In some preferred embodiments, the heat treatment includes, Under a protective atmosphere, the temperature is increased to 700-800℃ at a heating rate of 3-8℃ / min and held for 1-5 hours, then naturally cooled to room temperature.

[0029] In addition to the lithium iron phosphate to be repaired, the cathode black powder also includes binder, conductive agent, graphite, aluminum, copper, electrolyte, lithium salt and organic impurities, wherein the aluminum content is ≤0.05%.

[0030] In conventional cathode material regeneration, lithium salts and carbon-containing substances in the cathode black powder are often removed as impurities. This not only increases the number of processing steps but also wastes raw materials and adds to the cost of subsequent remediation agents. However, the lithium salts and carbon-containing substances in the cathode black powder can serve as endogenous Li and carbon sources.

[0031] In some preferred embodiments, lithium salts and organic matter in the cathode black powder serve as endogenous Li and carbon sources for the regeneration of the lithium iron phosphate to be repaired; lithium salts and organic matter separated from the previous or same batch of cathode black powder can also be added as exogenous Li and carbon sources. Therefore, the Li source is selected from lithium salts in the cathode black powder; the carbon source is selected from at least one of binders, conductive agents, graphite, electrolytes, and organic impurities in the cathode black powder. Of course, the types and sources of lithium and carbon sources are not strictly limited. For example, the lithium source may not be lithium salts in the cathode black powder, but may be at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium oxide, etc. The carbon source may also be at least one of glucose, sucrose, citric acid, etc.

[0032] In some preferred embodiments, the separation is performed using mechanical crushing and screening.

[0033] In some preferred embodiments, the positive electrode black powder is dried after being separated to remove surface adsorbed water.

[0034] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0035] Example 1 A method for in-situ repair of failed lithium iron phosphate, such as Figure 1 As shown, it includes the following steps: (1) The retired lithium iron phosphate battery positive electrode sheet is crushed and screened, and then placed in an 85°C constant temperature oven to dry for 12 hours to remove surface adsorbed water and obtain positive electrode black powder. The positive electrode black powder includes spent lithium iron phosphate, binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, of which the content of Al is 0.048%.

[0036] (2) ICP analysis of the cathode black powder showed that the molar ratio of Li, Fe, and P was 1.06:1:1.06, and the mass fraction of C was 8.2%. XRD analysis of the cathode black powder showed that the lithium vacancy rate was 8.8%, and the Li content was 8.2%. The Fe antisite defect was 1.5%; the cathode black powder was subjected to XPS analysis, and the Fe... 3+ / Fe 2+ The peak area ratio is 0.92. It is judged as a slight failure.

[0037] (3) Add glucose to the positive electrode black powder to adjust the total mass ratio of carbon elements to 11.5%. Then transfer it to an argon atmosphere muffle furnace, heat it to 750℃ at a heating rate of 5℃ / min and keep it at that temperature for 3 hours. After naturally cooling to room temperature, grind it and pass it through a 200-mesh sieve to obtain the repaired lithium iron phosphate.

[0038] Example 2 A method for in-situ repair of failed lithium iron phosphate batteries includes the following steps: (1) The retired lithium iron phosphate battery positive electrode sheet is crushed and screened, and then placed in an 85°C constant temperature oven to dry for 12 hours to remove surface adsorbed water and obtain positive electrode black powder. The positive electrode black powder includes spent lithium iron phosphate, binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, of which the content of Al is 0.046%.

[0039] (2) ICP analysis of the cathode black powder showed that the molar ratio of Li, Fe, and P was 0.92:1:1.04, and the mass fraction of C was 7.5%. XRD analysis of the cathode black powder showed that the lithium vacancy rate was 19.45%, and the Li content was 7.5%. The Fe antisite defect rate was 3.1%; XPS analysis of the cathode black powder revealed Fe... 3+ / Fe 2+ The peak area ratio is 1.42. It is judged as a moderate failure.

[0040] (3) Lithium carbonate and glucose were added to lithium iron phosphate to adjust the molar ratio of Li to Fe to 1.05:1 and the total mass percentage of carbon to 14.2%. Then the mixture was transferred to an argon atmosphere muffle furnace and heated to 730°C at a heating rate of 5°C / min and held for 3 hours. After cooling to room temperature, the mixture was ground and passed through a 200-mesh sieve to obtain the repaired lithium iron phosphate.

[0041] Example 3 A method for in-situ repair of failed lithium iron phosphate batteries includes the following steps: (1) The retired lithium iron phosphate battery positive electrode sheet is crushed and screened, and then placed in an 85°C constant temperature oven to dry for 12 hours to remove surface adsorbed water and obtain positive electrode black powder. The positive electrode black powder includes spent lithium iron phosphate, binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, of which the content of Al is 0.041%.

[0042] (2) ICP analysis of the cathode black powder showed that the molar ratio of Li, Fe, and P was 0.53:1:1.05, and the mass fraction of C was 8.8%. XRD analysis of the cathode black powder showed that the lithium vacancy rate was 51.5%, and the Li content was 8.8%. The Fe antisite defect rate was 4.1%; XPS analysis of the cathode black powder revealed Fe... 3+ / Fe 2+ The peak area ratio is 4.8. It is judged to be a severe failure.

[0043] (3) Lithium carbonate and glucose were added to lithium iron phosphate to adjust the molar ratio of Li to Fe to 1.05:1 and the total mass percentage of carbon to 20.2%. Then the mixture was transferred to an argon atmosphere muffle furnace and heated to 750°C at a heating rate of 5°C / min and held for 3 hours. After cooling to room temperature, the mixture was ground and passed through a 200-mesh sieve to obtain the repaired lithium iron phosphate.

[0044] Example 4 A method for in-situ repair of failed lithium iron phosphate batteries includes the following steps: (1) The retired lithium iron phosphate battery positive electrode sheet is crushed and screened, and then placed in an 85°C constant temperature oven to dry for 12 hours to remove surface adsorbed water and obtain positive electrode black powder. The positive electrode black powder includes spent lithium iron phosphate, binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, of which the content of Al is 0.041%.

[0045] (2) ICP analysis of the cathode black powder showed that the molar ratio of Li, Fe, and P was 1.07:1:1.05, and the mass fraction of carbon was 8.5%. XRD analysis of the cathode black powder showed that the lithium vacancy rate was 7.7%, and the Li content was 8.5%. The Fe antisite defect was 1.3%; the cathode black powder was analyzed by XPS, and the Fe... 3+ / Fe 2+ The peak area ratio is 0.73. It is judged as a slight failure.

[0046] (3) After grinding the positive electrode black powder evenly, it is directly transferred to an argon atmosphere muffle furnace, heated to 750°C at a heating rate of 5°C / min and kept at that temperature for 3 hours. After naturally cooling to room temperature, it is ground and passed through a 200-mesh sieve to obtain the repaired lithium iron phosphate.

[0047] Comparative Example 1 A method for in-situ repair of failed lithium iron phosphate batteries includes the following steps: (1) The retired lithium iron phosphate battery positive electrode sheet is crushed and screened, and then placed in an 85°C constant temperature oven to dry for 12 hours to remove surface adsorbed water and obtain positive electrode black powder. The positive electrode black powder includes spent lithium iron phosphate, binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, of which the content of Al is 0.049%.

[0048] (2) The positive electrode black powder is soaked and cleaned in NMP solution to remove residual binder, electrolyte, lithium salt, organic matter and other impurities. Then it is placed in an 85℃ constant temperature oven for 12 hours to obtain the impurity-removed positive electrode black powder.

[0049] (3) ICP analysis of the purified cathode black powder showed that the molar ratio of Li, Fe, and P was 0.91:1:1.01, and the mass fraction of C was 3.2%. XRD analysis of the purified cathode black powder showed that the lithium vacancy rate was 8.7%, and the Li content was 3.2%. The Fe reverse defect was 1.4%; after impurity removal, the cathode black powder was analyzed by XPS, and the Fe... 3+ / Fe 2+ The peak area ratio is 0.89. It is judged as a slight failure.

[0050] (3) After grinding the impurity-removed positive electrode black powder evenly, it is directly transferred to an argon atmosphere muffle furnace, heated to 750°C at a heating rate of 5°C / min and held for 3 hours. After naturally cooling to room temperature, it is ground and passed through a 200-mesh sieve to obtain the repaired lithium iron phosphate.

[0051] Test case The lithium vacancy rate, antisite defects, and Fe content of the lithium iron phosphate materials repaired in Examples 1-3 were also tested using XRD and XPS. 3+ / Fe 2+ The peak area ratios are shown in Table 1.

[0052] Table 1

[0053] As can be seen from the results in Table 1, the lithium vacancy rate of the lithium iron phosphate materials obtained in Examples 1-4 was significantly reduced by the repair method of the present invention, and the antisite defects and Fe were also significantly reduced. 3+ / Fe 2+ The peak area ratio also decreased. However, in Comparative Example 1, after the impurity removal step, the lithium salt and carbon-containing substances in the cathode black powder were removed, and heat treatment without an external Li source and carbon source resulted in limited repair of lithium iron phosphate. These results indicate that retaining the lithium salt and carbon-containing substances in the cathode black powder can serve as an endogenous lithium source, and the carbon-containing substances can serve as a carbon source and reducing agent, thus enabling the repair of lithium iron phosphate during heat treatment. The lithium iron phosphate to be repaired in Examples 1 and 4 were both mildly failed. In Example 1, by introducing an additional exogenous carbon source, the repairability of the lithium iron phosphate material was further improved.

[0054] The lithium iron phosphate materials repaired in Examples 1-4 and Comparative Example 1 were used as positive electrode active materials. They were mixed with binder and conductive agent at a mass ratio of 8:1:1, ball-milled until uniform, and then uniformly coated onto aluminum foil. After drying in a vacuum oven, the mixture was punched to obtain lithium iron phosphate positive electrode sheets. In a vacuum glove box, a clean battery negative electrode shell was placed stably on the work surface. A spring sheet and a metal pad were placed in sequence, and the lithium sheet was used as the counter electrode. Then, an appropriate amount of 1 mol / L LiPF6 electrolyte was evenly dropped onto the surface of the lithium sheet to ensure that the electrolyte fully wetted the surface of the lithium sheet. Next, a Celgard 2500 separator was laid flat to ensure that the separator completely covered the lithium sheet without any misalignment or wrinkles. A small amount of electrolyte was dropped again to wet the separator and eliminate air bubbles between the separator and the electrode. Then, the prepared lithium iron phosphate positive electrode sheet was placed directly opposite the center of the separator to ensure that the positive electrode sheet, separator, and lithium sheet were completely aligned without misalignment or overlap. Finally, the battery positive electrode shell was covered to complete the initial assembly. The assembled battery is transferred into a button cell packaging machine. A suitable pressure and holding time are set for constant pressure packaging to ensure that the battery is tightly sealed, leak-free, and the casing is not deformed. After packaging, the battery is removed and allowed to stand for a period of time for activation. Then, its electrochemical performance is systematically tested and evaluated. The test results are shown in Table 2.

[0055] Table 2

[0056] As can be seen from the results in Table 2, Examples 1-4 achieved lithium vacancy filling and Fe 3+ Reduction, carbon coating reconstruction, and precise feeding control enable the repaired lithium iron phosphate material to achieve or approach the level of commercial lithium iron phosphate in terms of initial coulombic efficiency, cycle stability, and rate performance.

[0057] In summary, the present invention has the following advantages: 1. The black powder separation process is simple and the utilization rate of native elements is high: the cathode black powder is separated only by mechanical and physical means, without introducing pyrolysis, organic solvents and other treatments. While removing Al impurities, the cathode material and the original components of the battery are retained to the maximum extent, and the resource utilization rate is significantly improved.

[0058] 2. High efficiency in utilizing endogenous impurities and significantly reducing repair costs: The residual LiPF6 in the black powder is fully utilized as an endogenous lithium source, and PVDF, carbon from carbonate electrolyte pyrolysis, and acetylene black are used as carbon sources and reducing agents to achieve "waste treatment with waste". The amount of external materials input is significantly reduced, and the repair cost is reduced by more than 30%, resulting in outstanding industrial economics.

[0059] 3. Precise and multi-dimensional failure assessment system: Combining XRD refinement (lattice atom occupancy dimension) and XPS detection (surface valence state dimension) to assess the failure degree of lithium iron phosphate, it breaks through the limitations of single detection and the assessment results are more in line with the actual deterioration state of the material, providing a reliable basis for accurate repair.

[0060] 4. Graded and precise control for stable and controllable repair results: Differentiated external feed amount, calcination temperature and holding time are matched for lithium iron phosphate with different failure levels of light, medium and heavy, avoiding the problem of over-repair of light materials and incomplete repair of heavy materials; the repaired material has a pure phase, controllable lattice defects and excellent batch consistency.

[0061] 5. Short process flow, green and low consumption, no secondary pollution: The entire repair process only requires crushing, screening, drying and single-step calcination, without the need for acid and alkali reagents and complex pretreatment; the process has low energy consumption, is easy to operate, is compatible with existing battery regeneration production lines, has low difficulty in industrial scale-up, has no risk of secondary pollution, and is in line with the green and circular development direction of new energy materials.

[0062] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for in-situ repair of failed lithium iron phosphate, characterized in that, include, Positive electrode black powder was separated from the positive electrode sheets of waste lithium iron phosphate batteries; Obtain the lithium vacancy rate, Li-Fe antisite defect value, and Fe content in the lithium iron phosphate lattice to be repaired in the cathode black powder. 3+ / Fe 2+ The proportion of lithium iron phosphate to be repaired is used to assess the degree of failure. Based on the elemental content in the cathode black powder and the degree of failure of the lithium iron phosphate to be repaired, Li source and / or carbon source are selectively added to the cathode black powder, followed by heat treatment to achieve adaptive repair and regeneration.

2. The method for in-situ repair of failed lithium iron phosphate according to claim 1, characterized in that, The method involves obtaining the lithium vacancy rate, Li-Fe antisite defect value, and Fe content in the lithium iron phosphate lattice to be repaired in the cathode black powder. 3+ / Fe 2+ The proportion is used to obtain the degree of failure of the lithium iron phosphate to be repaired, including, XRD measurements and data refinement calculations were used to obtain the lithium vacancy rate and Li-Fe antisite defect values ​​in the lithium iron phosphate lattice to be repaired. These were combined with XPS detection to obtain Fe... 3+ / Fe 2+ Peak area ratio is used to comprehensively assess the degree of failure of the lithium iron phosphate lithium to be repaired. Mild failure: Lithium vacancy rate ≤10%, Li Fe inversion defects ≤2.0%, Fe 3+ / Fe 2+ Peak area ratio ≤ 1; Moderate failure: Lithium vacancy rate 10%-20%, Li Fe antisite defects 2.0%-4.0%, Fe 3+ / Fe 2+ Peak area ratio 1-3; Severe failure: Lithium vacancy rate >20%, Li Fe reverse defect >4.0%, Fe 3+ / Fe 2+ Peak area ratio > 3.

3. The method for in-situ repair of failed lithium iron phosphate according to claim 2, characterized in that, The method of selectively supplementing the cathode black powder with Li and / or carbon sources based on the elemental content in the cathode black powder and the degree of failure of the lithium iron phosphate to be repaired includes: The content of lithium, carbon, and iron in the cathode black powder was detected by ICP. Mild failure: Selectively supplement the carbon source into the positive electrode black powder, and adjust the total mass ratio of carbon elements to 8%-12%; Moderate failure: Supplement the cathode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 13%-17%; Severe failure: Supplement the positive electrode black powder with Li and carbon sources, adjust the molar ratio of Li to Fe to 1.03-1.07:1, and the total mass percentage of carbon to 18%-22%.

4. The method for in-situ repair of failed lithium iron phosphate according to claim 3, characterized in that, The heat treatment includes, Under a protective atmosphere, the temperature is increased to 700-800℃ at a heating rate of 3-8℃ / min and held for 1-5 hours, then naturally cooled to room temperature.

5. The method for in-situ repair of failed lithium iron phosphate according to claim 1, characterized in that, In addition to the lithium iron phosphate to be repaired, the cathode black powder also includes binder, conductive agent, aluminum, electrolyte, lithium salt and organic impurities, wherein the aluminum content is ≤0.05%.

6. The method for in-situ repair of failed lithium iron phosphate according to claim 5, characterized in that, The Li source is selected from lithium salts in cathode black powder; The carbon source is selected from at least one of the binder, conductive agent, electrolyte, and organic impurities in the cathode black powder.

7. The method for in-situ repair of failed lithium iron phosphate according to claim 1, characterized in that, The separation is achieved through mechanical crushing and screening.

8. The method for in-situ repair of failed lithium iron phosphate according to claim 1, characterized in that, After being separated, the positive electrode black powder is dried to remove surface adsorbed water.

9. A lithium iron phosphate, characterized in that, The method described in claims 1-8 for in-situ repair of failed lithium iron phosphate is used.

10. A lithium battery, characterized in that, Its cathode material includes lithium iron phosphate as described in claim 9.

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