Regenerated lithium iron phosphate positive electrode sheet and lithium iron phosphate battery

Abstract

The present application provides a regenerated lithium iron phosphate positive electrode sheet, comprising: 70-90% of a recycled spent lithium iron phosphate positive electrode material, 3-15% of a lithium replenishment additive, 3-10% of a fast ion conductor, and 3-5% of a binder, wherein the recycled spent lithium iron phosphate positive electrode material is obtained by discharging retired power batteries until the voltage thereof drops to 0.5 V or below, using a physical method to disassemble and separate positive electrode sheets, pulverizing the positive electrode sheets and then adding same to a NaOH solution having a pH of 10-14, and then performing stirring, centrifugation, water washing, and drying. The present application further provides a lithium iron phosphate battery, which is a repaired and regenerated lithium iron phosphate battery prepared by using the regenerated lithium iron phosphate positive electrode sheet to pre-form a lithium iron phosphate battery, and then performing a pre-cycling repair treatment. The present application solves the problem of recycling lithium iron phosphate positive electrode materials from power batteries, reliably ensures the electrochemical performance of the lithium iron phosphate batteries while reducing the manufacturing costs thereof, and thus can meet the requirements of commercial energy storage lithium batteries.

Description

A regenerated lithium iron phosphate positive electrode and a lithium iron phosphate battery Technical Field

[0001] This invention relates to the field of waste power battery recycling technology, specifically to a repaired and regenerated lithium iron phosphate positive electrode sheet and a lithium iron phosphate battery prepared from the positive electrode sheet. Background Technology

[0002] With the increasing popularity of electric vehicles, the number of retired power batteries is also increasing year by year. Power batteries are rich in rare metals and toxic chemicals, which can cause serious harm to the environment and human health if not scientifically treated and recycled. At the same time, scientific recycling and reuse can improve resource utilization and economic benefits.

[0003] Currently, lithium iron phosphate (LiFePO4) batteries account for more than one-third of the lithium battery market. LiFePO4 cathode material, in particular, boasts advantages such as good safety performance, fast charging speed, and long service life. As the most widely installed cathode material for power batteries, it now faces a huge amount of waste awaiting recycling. Traditional wet and pyrometallurgical recycling methods require numerous process steps and consume a large amount of energy. Furthermore, elements such as Fe and P have low recycling value, and these methods generate significant amounts of waste, leading to environmental pollution. Technical issues

[0004] Existing technologies for recycling and regenerating waste lithium iron phosphate cathode materials suffer from problems such as long cycles, high costs, environmental pollution, and difficulty in meeting electrochemical performance requirements. Technical solutions

[0005] This application first provides a recycled lithium iron phosphate positive electrode sheet, comprising the following raw materials by weight percentage:

[0006] The recycled waste lithium iron phosphate cathode material comprises 70-90%, lithium replenishing additives 3-15%, fast ion conductors 3-10%, and binders 3-5%. The recycled waste lithium iron phosphate cathode material is obtained by discharging retired power batteries until the voltage drops below 0.5V, then physically crushing the disassembled and separated cathode sheets, adding them to a NaOH solution with a pH of 10-14, stirring, centrifuging, washing with water, and drying.

[0007] This application also provides a lithium iron phosphate battery, which is prepared by using the above-mentioned regenerated lithium iron phosphate positive electrode sheet to prefabricate the lithium iron phosphate battery, and then performing a pre-cycle repair treatment to obtain a repaired and regenerated lithium iron phosphate battery. Beneficial effects

[0008] The recycled lithium iron phosphate cathode sheet provided in this application uses recycled waste lithium iron phosphate cathode material as raw material, mixes it with lithium replenishing additives and fast ion conductors, and binds them together with a binder. Utilizing the high ionic conductivity and high-speed transport performance of the selected fast ion conductors, lithium ions in the waste lithium iron phosphate and lithium replenishing additives can migrate rapidly during charging and discharging, transforming LiFePO4 from a lithium-depleted state to a lithium-saturated state. This completes the repair and regeneration of the waste lithium iron phosphate cathode material, yielding cathode material that can be directly used to prepare lithium iron phosphate batteries. The entire process generates no wastewater, reducing environmental pollution and improving the environmental friendliness of the recycling process, meeting the current societal demand for efficient and environmentally friendly recycling technologies.

[0009] Lithium iron phosphate batteries made using the regenerated lithium iron phosphate cathode sheet repaired in this application, after pre-cycle repair treatment, have a capacity of over 2000mAh. After 1000 charge-discharge cycle tests, the capacity retention rate is over 89%.

[0010] This application solves the problem of recycling lithium iron phosphate cathode materials in power batteries, improves resource utilization, reduces the manufacturing cost of lithium iron phosphate batteries, and ensures the total capacity, energy density and cycle life of lithium batteries, reliably guaranteeing the electrochemical performance of lithium iron phosphate batteries and meeting the requirements of commercial energy storage lithium batteries. The best embodiment of the present invention

[0011] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0012] This application first provides a recycled lithium iron phosphate positive electrode sheet, comprising the following raw materials by weight percentage:

[0013] The recycled waste lithium iron phosphate cathode material comprises 70-90%, lithium supplementation additives 3-15%, fast ion conductors 3-10%, and binders 3-5%.

[0014] The recycled waste lithium iron phosphate cathode material mentioned above is obtained by first discharging retired lithium iron phosphate power batteries until the voltage drops below 0.5V, then separating the cathode sheets using physical methods, crushing them to obtain cathode black powder, and then adding it to a NaOH solution with a pH of 10-14 for stirring, centrifugation, washing with water, and drying.

[0015] The specific steps are as follows:

[0016] (1) Discharge treatment of waste lithium iron phosphate batteries can be carried out by the “Green and Environmentally Friendly Safe Discharge Method for Waste Lithium-ion Batteries” provided by the applicant’s patent CN202210429654.0. Through vibration and gradual pressure linkage, the waste lithium iron phosphate batteries are tightly connected with the discharge particles to ensure that the waste lithium batteries are discharged evenly and completely. Alternatively, the waste lithium iron phosphate batteries can be soaked in a 5wt% to 20wt% NaCl solution to completely discharge the waste lithium iron phosphate batteries until the voltage drops below 0.5V. This ensures the safety of recycling and processing waste lithium iron phosphate batteries while ensuring the recovery of lithium elements in the lithium iron phosphate cathode material.

[0017] (2) The discharged waste lithium iron phosphate batteries are disassembled and separated into a mixture of materials with diaphragms and positive and negative electrodes by mechanical crushing, magnetic separation and screening.

[0018] (3) The positive electrode sheet can be separated from the mixture by using the "flexible and precise separation method and system for positive and negative electrode materials of waste lithium battery" provided by the applicant's patent CN202110279054.6;

[0019] (4) The positive electrode sheet is pulverized by ball mill to obtain positive electrode black powder (Dmax≤38μm). Then, the positive electrode black powder is added to NaOH solution with pH 10-14 and heated to 80℃-100℃. The mixture is stirred and reacted for 30-60 minutes. The solid and liquid components are then separated by centrifugation. The solid components are then washed with deionized water to remove Al impurities. Finally, the mixture is dried in a drying oven at 90℃-120℃ to obtain the recycled waste lithium iron phosphate positive electrode material.

[0020] The chemical formula for waste lithium iron phosphate cathode materials is: Li 1-x FePO4, where 0.6 ≤ x < 1.0.

[0021] Among the above raw materials, the chemical formula of the lithium supplement additive is Li2MO2, where M is at least one of Ni, Mn, Cu, Fe, Cr, Zn, Al, and Mo. These materials are lithium-rich materials with extremely low reversible capacity and can be completely decomposed to provide sufficient active lithium ions.

[0022] Among the above raw materials, the fast ion conductors are LiAlTiPO4 (LATP) and Li7La3Zr2O. 12 (LLZO), Li3BO3, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) or Li 1.5 Al 0.5 Ge 1.5At least one of (PO4)3 (LAGP). These fast ion conductor materials are used to mix with recycled waste lithium iron phosphate cathode materials and lithium replenishment additives, acting between particles such as cathode materials and lithium replenishment additives. They have low requirements for particle size and have lower ion conductivity activation energy and higher conductivity. Since the lithium battery preparation process and pre-cycling process involve high temperatures, the conductivity changes of these materials are relatively less affected by temperature, and they can maintain electrochemical stability during the preparation process.

[0023] Among the above raw materials, the binder is at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyimide (PI), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyurethane (PUR), and sodium carboxymethyl cellulose (CMC).

[0024] The recycled lithium iron phosphate cathode sheet provided in this application mixes recycled waste lithium iron phosphate cathode material with a certain amount of lithium-rich material and fast ion conductor. Through the combined action of lithium-rich material and fast ion conductor, the defect of lacking active lithium ions in waste lithium iron phosphate battery cathode material can be solved. In subsequent lithium battery manufacturing, additional lithium ions are stored in the negative electrode. At the same time, in the pre-cycle discharge process of subsequent lithium battery manufacturing, the low ionic conductivity activation energy and high conductivity of fast ion conductor can be used to promote the rapid migration and insertion of lithium ions from waste lithium iron phosphate and lithium replenishment additives into the lithium vacancies of LiFePO4 at the positive electrode during charging and discharging. This transforms LiFePO4 from a lithium-deficient state to a lithium-filled state, completing the repair and regeneration of waste lithium iron phosphate. In the process of making the cathode sheet, the waste lithium iron phosphate cathode material is mixed with lithium-rich material and fast ion conductor through thorough stirring and slurry preparation. This ensures that the surface of lithium iron phosphate particles is in close contact with the fast ion conductor material, which can effectively improve the conductivity and rate performance of lithium-ion batteries.

[0025] This application also provides a lithium iron phosphate battery, the preparation of which includes the above-mentioned recycled lithium iron phosphate positive electrode sheet, and also includes a graphite negative electrode sheet, electrolyte, separator, etc., specifically including the following steps:

[0026] (1) Preparation of positive electrode sheet:

[0027] The raw materials of the above-mentioned recycled lithium iron phosphate cathode sheet are mixed in the following weight percentages: 70-90% recycled waste lithium iron phosphate cathode material, 3-15% lithium replenishing additive, 3-10% fast ion conductor, and 3-5% binder. Then, an appropriate amount of solvent, such as N-methylpyrrolidone (NMP), is added to dissolve and swell the waste lithium iron phosphate cathode material, lithium replenishing additive, fast ion conductor, and binder, so that the various components are fully contacted and evenly distributed. The overall solid content is 70-80%. The mixture is stirred into a homogeneous cathode slurry under the action of a vacuum mixer.

[0028] The positive electrode slurry is coated onto one surface of the positive electrode current collector using a coating machine and dried at 100–120°C. The same coating process is then repeated on the other surface of the positive electrode current collector to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and welding of electrode tabs, a positive electrode sheet of the specified specifications is obtained.

[0029] (2) Preparation of negative electrode sheet:

[0030] Natural graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a specific ratio, and deionized water was added and stirred until homogeneous to obtain a negative electrode slurry. This slurry was then coated onto both surfaces of the negative electrode current collector and dried to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After cold pressing, cutting, and welding of tabs, a negative electrode sheet of the specified specifications was obtained. The preparation of the negative electrode sheet utilizes existing technology and will not be described in detail here.

[0031] (3) Lithium battery manufacturing:

[0032] The positive electrode, separator, and negative electrode are wound together to obtain the battery cell; the battery cell is placed in a steel shell, electrolyte is injected, and it is then packaged to obtain a prefabricated lithium iron phosphate battery.

[0033] (4) Pre-circulation repair treatment:

[0034] The pre-fabricated lithium iron phosphate battery was charged to 3.65V using a constant current of 2A at a temperature range of 50–80℃, then charged to 2.0V using a constant voltage of A / 2, and after a period of rest, discharged to 2.0V using a constant current of A, where 0.01C ≤ A ≤ 0.05C. This charge-discharge process was repeated three times to obtain a commercially available lithium iron phosphate battery.

[0035] The lithium iron phosphate cathode sheets repaired and regenerated in this application were used to fabricate lithium iron phosphate batteries. After pre-cycle repair treatment, the batteries were tested at a 0.1C rate, showing a capacity exceeding 2000mAh. After 1000 charge-discharge cycles, the capacity retention rate was above 89%. This approach reduces the manufacturing cost of lithium iron phosphate batteries while ensuring the total capacity, energy density, and cycle life of the lithium batteries, reliably guaranteeing their electrochemical performance and meeting the requirements for commercial energy storage lithium batteries. Embodiments of the present invention

[0036] The following are specific embodiments of the preparation of lithium iron phosphate batteries using repaired and regenerated lithium iron phosphate cathode sheets in this application.

[0037] Example 1:

[0038] I. Disposal of used lithium iron phosphate batteries:

[0039] (1) Soak the retired lithium iron phosphate batteries in 10% NaCl solution for 5 hours to completely discharge the waste lithium iron phosphate batteries until the voltage drops below 0.5V;

[0040] (2) The mixture with diaphragm and positive and negative electrode plates is disassembled and separated by mechanical crushing, magnetic separation and screening methods;

[0041] (3) The positive electrode sheet is separated from the mixed material using the "flexible and precise separation method and system for positive and negative electrode materials of waste lithium battery" provided by CN202110279054.6;

[0042] (4) The positive electrode sheet was further pulverized using a ball mill to obtain positive electrode black powder (Dmax < 35 μm), which was then placed in a NaOH solution with pH 13 and heated to 80°C. The mixture was stirred and reacted for 30 min, followed by centrifugation to separate the solid and liquid components. The solid components were then washed with deionized water to remove Al impurities, and finally dried in a forced-air oven at 100°C to obtain waste lithium iron phosphate positive electrode material Li. 0.88 FePO4.

[0043] II. Preparation of positive electrode sheet:

[0044] Li 0.88 FePO4, Li2NiO2, LATP, and PVDF were fed in a mass ratio of 86:5:5:4. An appropriate amount of N-methylpyrrolidone (NMP) was added to achieve a total solid content of 70%. The mixture was stirred in a vacuum mixer until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0045] III. Negative Electrode Preparation:

[0046] Natural graphite, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:2:3, with deionized water added as a solvent. The mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 40%. This slurry was coated onto one surface of a 6 μm thick copper foil and dried at 105°C to obtain a 75 μm thick single-sided negative electrode sheet. The above steps were repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing, cutting, and tab bonding, a negative electrode sheet with dimensions of 64 mm × 872 mm was obtained for later use.

[0047] IV. Lithium-ion battery manufacturing:

[0048] The positive electrode, separator, and negative electrode are rolled up in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting battery cell is then placed in a steel casing and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a cylindrical lithium-ion battery.

[0049] Cylindrical lithium-ion batteries were charged to 3.65V at a constant current of 0.04C, then fully charged at 0.01C at a constant voltage of 3.65V. After resting for 10 minutes, they were discharged to 2.0V at a constant current of 0.02C. This process was repeated three times at 60℃ to obtain regenerated lithium iron phosphate batteries. Finally, the battery capacity and cycle performance were tested at a rate of 0.1C.

[0050] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Example 1 has a capacity of 2330mAh, and the battery capacity retention rate after 1000T cycles is 97.6%, which shows good electrochemical performance.

[0051] Example 2:

[0052] I. Disposal of used lithium iron phosphate batteries:

[0053] (1) Soak the retired lithium iron phosphate batteries in 15% NaCl solution for 5 hours to completely discharge the waste lithium iron phosphate batteries until the voltage drops below 0.5V;

[0054] (2) The mixture with diaphragm and positive and negative electrode plates is disassembled and separated by mechanical crushing, magnetic separation and screening methods;

[0055] (3) The positive electrode sheet is separated from the mixed material using the "flexible and precise separation method and system for positive and negative electrode materials of waste lithium battery" provided by CN202110279054.6;

[0056] (4) The positive electrode sheet was further pulverized using a ball mill to obtain positive electrode black powder (Dmax < 38 μm), which was then placed in a NaOH solution with pH 10 and heated to 100°C. The mixture was stirred and reacted for 60 min, followed by centrifugation to separate the solid and liquid components. The solid components were then washed with deionized water and finally dried in a forced-air oven at 100°C to obtain waste lithium iron phosphate positive electrode material Li. 0.92 FePO4.

[0057] II. Preparation of positive electrode sheet:

[0058] Li 0.92FePO4, Li2NiO2, LATP, and PVDF were fed in a mass ratio of 90:3:3:4. An appropriate amount of N-methylpyrrolidone (NMP) was added to achieve a total solid content of 70%. The mixture was stirred in a vacuum mixer until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0059] III. Negative Electrode Preparation:

[0060] Same as Example 1.

[0061] IV. Lithium-ion battery manufacturing:

[0062] The positive electrode, separator, and negative electrode are rolled up in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting battery cell is then placed in a steel casing and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a cylindrical lithium-ion battery.

[0063] Cylindrical lithium-ion batteries were charged to 3.65V at a constant current of 0.06C, then fully charged at 0.015C under a constant voltage of 3.65V. After resting for 10 minutes, they were discharged to 2.0V at a constant current of 0.03C. This process was repeated three times under a pre-cycle charge-discharge environment at 60℃ to obtain regenerated lithium iron phosphate batteries. Finally, the battery capacity and cycle performance were tested at a rate of 0.1C.

[0064] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Example 2 has different mass ratios of waste lithium iron phosphate cathode material, lithium replenishment additives, fast ion conductors, and additives in its cathode sheet. The pre-cycle repair process parameters are also different from those in Example 1. The prepared lithium iron phosphate battery has a capacity of 2219mAh, and the battery capacity retention rate after 1000T cycles is 94.5%, still exhibiting good electrochemical performance.

[0065] Example 3:

[0066] I. Disposal of used lithium iron phosphate batteries:

[0067] Same as Example 2.

[0068] II. Preparation of positive electrode sheet:

[0069] Li 0.92FePO4, Li2CuO2, LAGP, and PVDF were fed in a mass ratio of 90:3:3:4. An appropriate amount of N-methylpyrrolidone (NMP) was added to achieve a total solid content of 70%. The mixture was stirred in a vacuum mixer until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0070] III. Negative Electrode Preparation:

[0071] Same as Example 1 and Example 2.

[0072] IV. Lithium-ion battery manufacturing:

[0073] Same as Example 2.

[0074] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Example 3 uses different raw materials for lithium replenishment additives and fast ion conductors than that in Example 2, but the pre-cycle repair process parameters are the same as those in Example 2. The capacity is 2252mAh, and the battery capacity retention rate after 1000T cycles is 93.3%, which shows better electrochemical performance.

[0075] Example 4:

[0076] I. Disposal of used lithium iron phosphate batteries:

[0077] (1) The waste lithium iron phosphate batteries were discharged until the voltage dropped to below 0.5V using the “Green and Environmentally Friendly Safe Discharge Method for Waste Lithium-ion Batteries” provided by CN202210429654.0;

[0078] (2) The mixture with diaphragm and positive and negative electrode plates is disassembled and separated by mechanical crushing, magnetic separation and screening methods;

[0079] (3) The positive electrode sheet is separated from the mixed material using the "flexible and precise separation method and system for positive and negative electrode materials of waste lithium battery" provided by CN202110279054.6;

[0080] (4) The positive electrode sheet was further pulverized to obtain positive electrode black powder, which was placed in a NaOH solution with pH 14 and heated to 90°C. The mixture was stirred and reacted for 45 min, followed by centrifugation to separate the solid and liquid components. The solid components were then washed with deionized water and finally dried in a forced-air oven at 120°C to obtain waste lithium iron phosphate positive electrode material Li. 0.78 FePO4.

[0081] II. Preparation of positive electrode sheet:

[0082] Li 0.78 FePO4, Li2CuO2, LLZO, and PAN were fed in a mass ratio of 80:9:7:4. An appropriate amount of N-methylpyrrolidone (NMP) was added to achieve a total solid content of 70%. The mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0083] III. Negative Electrode Preparation:

[0084] Same as Example 1, Example 2 and Example 3.

[0085] IV. Lithium-ion battery manufacturing:

[0086] The positive electrode, separator, and negative electrode are rolled up in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting battery cell is then placed in a steel casing and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a cylindrical lithium-ion battery.

[0087] Cylindrical lithium-ion batteries were charged to 3.65V at a constant current of 0.02C, then fully charged at 0.005C under a constant voltage of 3.65V. After resting for 10 minutes, they were discharged to 2.0V under a constant current of 0.01C. This process was repeated three times at 80℃ to obtain regenerated lithium iron phosphate batteries. Finally, the battery capacity and cycle performance were tested at a rate of 0.1C.

[0088] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Example 4 differs from that in Examples 1, 2 and 3 in the selection of fast ion conductors and binders, as well as the pre-cycle repair process parameters. The battery has a capacity of 2286mAh and a capacity retention rate of 89.4% after 1000T cycles, exhibiting better electrochemical performance.

[0089] Example 5:

[0090] I. Disposal of used lithium iron phosphate batteries:

[0091] Same as Example 1.

[0092] II. Preparation of positive electrode sheet:

[0093] Same as Example 1.

[0094] III. Negative Electrode Preparation:

[0095] Same as Example 1.

[0096] IV. Lithium-ion battery manufacturing:

[0097] The positive electrode, separator, and negative electrode are rolled up in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting battery cell is then placed in a steel casing and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a cylindrical lithium-ion battery.

[0098] Cylindrical lithium-ion batteries were charged to 3.65V at a constant current of 0.1C, then fully charged at 0.025C at a constant voltage of 3.65V. After resting for 10 minutes, they were discharged to 2.0V at a constant current of 0.05C. This process was repeated three times at 50℃ to obtain regenerated lithium iron phosphate batteries. Finally, the battery capacity and cycle performance were tested at a rate of 0.1C.

[0099] The test results are shown in Table 1. As can be seen from Table 1, the pre-cycle repair process parameters of the lithium iron phosphate battery prepared in Example 5 are different from those in Examples 1-4. The capacity of the prepared lithium iron phosphate battery is 2198mAh, and the capacity retention rate after 1000T cycles is 93.2%, which still has good electrochemical performance.

[0100] Comparative Example 1:

[0101] I. Disposal of used lithium iron phosphate batteries:

[0102] Same as Example 1.

[0103] II. Preparation of positive electrode sheet:

[0104] Li 0.88 FePO4, Li2NiO2, and PVDF were fed in a mass ratio of 88.5:7.5:4. An appropriate amount of N-methylpyrrolidone (NMP) was added to achieve a total solid content of 70%. The mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0105] III. Negative Electrode Preparation:

[0106] Same as Example 1.

[0107] IV. Lithium-ion battery manufacturing:

[0108] Same as Example 1.

[0109] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Comparative Example 1 lacked the incorporation of fast ion conductors in its positive electrode preparation. The resulting lithium iron phosphate battery had a capacity of 1866 mAh, and its capacity retention rate after 1000T cycles was only 45.4%. Compared with Example 1, its electrochemical performance was significantly reduced and completely failed to meet the application requirements of lithium iron phosphate batteries.

[0110] Comparative Example 2:

[0111] I. Disposal of used lithium iron phosphate batteries:

[0112] Same as Example 1.

[0113] II. Preparation of positive electrode sheet:

[0114] Li 0.88 FePO4, LTP, and PVDF were fed in a mass ratio of 88.5:7.5:4, with an appropriate amount of N-methylpyrrolidone (NMP) added to achieve a total solid content of 70%. The mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. This slurry was then coated onto one surface of a 10μm thick aluminum foil using a coating machine and dried at 120℃ to obtain a single-sided 90μm thick positive electrode sheet. The same coating process was then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and tab bonding, a positive electrode sheet with dimensions of 62mm × 864mm was obtained.

[0115] III. Negative Electrode Preparation:

[0116] Same as Example 1.

[0117] IV. Lithium-ion battery manufacturing:

[0118] Same as Example 1.

[0119] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Comparative Example 2, for which no lithium-replenishing additive was added during the preparation of the positive electrode, had a capacity of 1560 mAh, and the capacity retention rate after 1000T cycles was 21.2%. Similarly, compared with Example 1, its electrochemical performance was significantly reduced, completely failing to meet the application requirements of lithium iron phosphate batteries.

[0120] Comparative Example 3:

[0121] I. Disposal of used lithium iron phosphate batteries:

[0122] Same as Example 1.

[0123] II. Preparation of positive electrode sheet:

[0124] Same as Example 1.

[0125] III. Negative Electrode Preparation:

[0126] Same as Example 1.

[0127] IV. Lithium-ion battery manufacturing:

[0128] The positive electrode, separator, and negative electrode are rolled up in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting battery cell is then placed in a steel casing and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a cylindrical lithium-ion battery.

[0129] Cylindrical lithium-ion batteries were charged to 3.65V at a constant current of 0.2C, then fully charged at 0.05C under a constant voltage of 3.65V. After resting for 10 minutes, they were discharged to 2.0V under a constant current of 0.1C. This process was repeated three times at 25℃ to obtain regenerated lithium iron phosphate batteries. Finally, the battery capacity and cycle performance were tested at a rate of 0.1C.

[0130] The test results are shown in Table 1. As can be seen from Table 1, the 18650 lithium iron phosphate battery prepared in Comparative Example 3 had higher charge / discharge current parameters and a lower ambient temperature during the pre-cycle procedure compared to the parameters set in this application. The resulting lithium iron phosphate battery had a capacity of 1933 mAh, and its capacity retention rate after 1000T cycles was 77.5%. Compared to Example 1, its electrochemical performance was significantly reduced, making it difficult to meet the application requirements of lithium iron phosphate batteries.

[0131]

[0132] The above embodiments shown in this application are only part of the preferred embodiments of this application and should not be construed as limiting this application. Any modifications, equivalent substitutions and improvements made by those skilled in the art without departing from the spirit of this application shall be within the protection scope of this application.

Claims

1. A regenerated lithium iron phosphate positive electrode, characterized in that, The raw materials include the following weight percentages: The recycled waste lithium iron phosphate cathode material comprises 70-90%, lithium supplementation additives 3-15%, fast ion conductors 3-10%, and binders 3-5%.

2. The regenerated lithium iron phosphate positive electrode sheet as described in claim 1, characterized in that, The recycled waste lithium iron phosphate cathode material is obtained by discharging retired power batteries until the voltage drops below 0.5V, then physically crushing the disassembled and separated cathode sheets, adding them to a NaOH solution with a pH of 10-14, stirring, centrifuging, washing with water, and drying.

3. The regenerated lithium iron phosphate positive electrode sheet as described in claim 2, characterized in that, The aforementioned waste lithium iron phosphate cathode material is obtained by dismantling retired lithium iron phosphate power batteries sequentially using mechanical crushing, magnetic separation, and sieving methods to separate a mixture containing a separator, positive electrode sheet, and negative electrode sheet. The positive electrode sheet is then separated from the mixture and pulverized to obtain positive electrode black powder. The positive electrode black powder is added to a NaOH solution with a pH of 10-14 and heated to 80℃-100℃, stirred for 30-60 minutes, and the solid and liquid components are separated by centrifugation. The solid components are then washed with deionized water and dried in a drying oven at 90℃-120℃ to obtain the recycled waste lithium iron phosphate cathode material.

4. A regenerated lithium iron phosphate positive electrode sheet as described in any one of claims 1-3, characterized in that, The chemical formula of the lithium supplement additive is Li2MO2, where M is at least one of Ni, Mn, Cu, Fe, Cr, Zn, Al, and Mo.

5. A regenerated lithium iron phosphate positive electrode sheet as described in any one of claims 1-3, characterized in that, The fast ion conductor is LiAlTiPO4 or Li7La3Zr2O 12 Li3BO3, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Or Li 1.5 Al 0.5 Ge 1.5 At least one of (PO4)3.

6. A regenerated lithium iron phosphate positive electrode sheet as described in claim 4, characterized in that, The fast ion conductor is LiAlTiPO4 or Li7La3Zr2O 12 Li3BO3, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Or Li 1.5 Al 0.5 Ge 1.5 At least one of (PO4)3.

7. A regenerated lithium iron phosphate positive electrode sheet as described in any one of claims 1-3, characterized in that, The adhesive is at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyimide, polyacrylonitrile, polyvinyl alcohol, polyurethane, or sodium carboxymethyl cellulose.

8. A lithium iron phosphate battery, characterized in that, A lithium iron phosphate battery is prepared by using a pre-fabricated lithium iron phosphate positive electrode sheet as described in any one of claims 1-7, followed by a pre-cycle repair treatment.

9. The lithium iron phosphate battery as described in claim 8, characterized in that, The pre-cycle repair process is as follows: Under a temperature environment of 50-80℃, the prefabricated lithium iron phosphate battery is charged to 3.65V using a constant current of 2A, then charged with a constant voltage of A / 2, and after standing for a period of time, discharged to 2.0V using a constant current of A. The above charging and discharging process is repeated three times, wherein 0.01C≤A≤0.05C.

10. The lithium iron phosphate battery as described in claim 9, characterized in that, The preparation steps include the following: (1) Preparation of positive electrode sheet: The raw materials of the regenerated lithium iron phosphate cathode sheet according to any one of claims 1-7 are mixed in weight percentage, and then an appropriate amount of solvent is added and stirred evenly to obtain a cathode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector and dried to obtain a regenerated lithium iron phosphate positive electrode sheet with a positive electrode material layer on both sides. After cold pressing, cutting and welding of electrode tabs, a regenerated lithium iron phosphate positive electrode sheet of a set specification is obtained. (2) Preparation of negative electrode sheet: Natural graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a certain proportion, and deionized water was added and stirred evenly to obtain the negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector and dried to obtain a negative electrode sheet with a negative electrode material layer on both sides. After cold pressing, cutting and welding of electrode tabs, a negative electrode sheet of the specified specifications is obtained. (3) Prefabrication of lithium iron phosphate batteries: A battery cell is obtained by winding the positive electrode, the separator, and the negative electrode. The battery cell is placed in a steel shell, electrolyte is injected, and then it is sealed to obtain a prefabricated lithium iron phosphate battery. (4) Pre-circulation repair treatment: By subjecting the prefabricated lithium iron phosphate battery to three charge-discharge cycles, a repaired and regenerated lithium iron phosphate battery with a capacity retention rate of over 89% is obtained.

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