Method for repairing and regenerating spent lithium iron phosphate positive electrode material, and lithium battery

Abstract

The present application provides a method for repairing and regenerating a spent lithium iron phosphate positive electrode material, comprising the steps of: discharging the spent lithium iron phosphate battery, crushing, disassembling, and separating the discharged spent lithium iron phosphate battery to obtain a lithium iron phosphate positive electrode sheet, and then performing thermal treatment in an inert atmosphere to separate the positive electrode sheet from a current collector, so as to obtain spent lithium iron phosphate positive electrode black powder; performing thermal treatment again in a furnace having an oxygen content higher than 50%, and removing impurities to obtain oxidized lithium iron phosphate red powder; after supplementing a lithium source, mixing the oxidized lithium iron phosphate red powder with the lithium source by means of ball milling; and placing the mixture in a reducing atmosphere furnace, introducing an inert gas entraining a carbonizable small molecule organic substance, and performing thermal treatment to obtain a regenerated lithium iron phosphate positive electrode material. A lithium iron phosphate battery is prepared by using the positive electrode material. Because the surfaces of lithium iron phosphate particles are coated with a carbonaceous material, the conductivity and rate performance of the lithium iron phosphate battery can be effectively improved, the gram capacity of lithium iron phosphate therein at 0.1 C reaches 155 mAh / g or more, and after 1000 cycles of charging and discharging, the capacity retention rate is higher than 90%.

Description

A method for repairing and regenerating waste lithium iron phosphate cathode material and a lithium battery Technical Field

[0001] This application relates to the field of waste power battery recycling technology, and in particular to a method for repairing and regenerating waste lithium iron phosphate cathode material and a lithium iron phosphate battery prepared using this method. Background Technology

[0002] With the rapid development of the electric vehicle market, the demand for power batteries is also constantly increasing. As the most widely used positive electrode material for power batteries, lithium iron phosphate (LiFePO4) has advantages such as good safety performance, fast charging speed, and long service life.

[0003] Lithium iron phosphate (LFP) cathode materials are widely used in power batteries due to their high safety, long lifespan, and environmental friendliness. However, with the increasing use of power batteries, a large amount of waste LFP cathode materials will be generated. How to effectively recycle and reuse these waste materials has become an important research topic. Current solutions mainly involve disassembling the battery and separating the positive electrode, negative electrode, and separator. The recycling of LFP cathode materials involves methods such as acid leaching, alkaline leaching, or high-temperature pyrolysis to extract valuable metal elements, which are then used to synthesize new LFP cathode materials. Technical issues

[0004] Existing technologies often require the use of strong acids, strong alkalis, or high temperatures, generating significant amounts of wastewater and exhaust gases. This not only pollutes the environment but also increases recycling costs. Furthermore, these methods often damage the structure of lithium iron phosphate cathode materials, affecting their performance and making them unsuitable for use in power batteries. The diverse sources of recycled lithium batteries can also lead to inconsistent performance of the regenerated lithium iron phosphate cathode materials. In addition, these methods have long processing cycles, are complex, and consume a lot of energy, further limiting their large-scale application. Technical solutions

[0005] This application first provides a method for repairing and regenerating waste lithium iron phosphate cathode materials, including the following steps:

[0006] S1 discharges and then crushes and disassembles the waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode sheets. The obtained positive electrode sheets are then heat-treated in an inert atmosphere to separate the lithium iron phosphate positive electrode sheets from the current collector, resulting in waste lithium iron phosphate positive electrode black powder.

[0007] S2 involves heat-treating the waste lithium iron phosphate cathode black powder again in an environment furnace with an oxygen content higher than 60%, removing impurities while oxidizing the surface of the lithium iron phosphate red powder to obtain oxidized lithium iron phosphate red powder.

[0008] S3 tests the content of P, Fe and Li elements in the lithium iron phosphate red powder obtained in step S2, and adds lithium source appropriately according to the test results. Then, the lithium iron phosphate red powder and lithium source are ball-milled and mixed to obtain a lithium-added lithium iron phosphate mixture.

[0009] S4 places the lithium iron phosphate oxide mixture with lithium replenishment in a reducing atmosphere furnace and passes an inert gas containing carbonizable small molecule organic matter through it. After heat treatment, the lithium iron phosphate oxide mixture is carbonized and reduced in a reducing atmosphere to obtain regenerated lithium iron phosphate cathode material.

[0010] The carbonizable small molecule organic compound is at least one of methanol, ethanol, acetone, formic acid, acetic acid, ethyl acetate, or diethyl ether.

[0011] This application also provides lithium iron phosphate batteries prepared using the above-mentioned repaired and regenerated waste lithium iron phosphate cathode material. Beneficial effects

[0012] The method for repairing and regenerating waste lithium iron phosphate cathode materials provided in this application involves immersing the material in NaCl solution for discharge treatment followed by disassembly. Impurities are removed in an environment with an oxygen content higher than 60%. The lithium source is then replenished based on the tested P, Fe, and Li element content of the lithium iron phosphate red powder. Reduction and carbon coating are achieved by using an inert gas to entrain carbonizable small molecule organic matter for heat treatment. All process steps work together to complete the repair and regeneration of waste lithium iron phosphate, resulting in cathode materials that can be directly used to prepare lithium iron phosphate batteries.

[0013] The method for repairing and regenerating waste lithium iron phosphate cathode materials provided in this application effectively solves the recycling problem of lithium iron phosphate cathode materials in power batteries, improves resource utilization, reduces the environmental pressure of lithium battery production, realizes the direct regeneration of lithium iron phosphate cathode materials, avoids the strong acid, strong alkali or high temperature conditions in traditional recycling methods, has a short process cycle, low energy consumption, does not generate any wastewater, reduces environmental pollution, improves the environmental friendliness of the recycling process, is conducive to large-scale application, is suitable for industrial production, and meets the current social demand for efficient and environmentally friendly recycling technologies.

[0014] The lithium iron phosphate battery provided in this application, prepared using the aforementioned regenerated waste lithium iron phosphate cathode material, effectively improves the conductivity and rate performance of the battery due to the carbonaceous coating on the surface of the regenerated lithium iron phosphate particles. Its 0.1C specific capacity reaches over 155 mAh / g, and after 1000 charge-discharge cycles, the capacity retention rate is no less than 90.0%. This achieves the recycling of lithium-ion battery materials, reducing the manufacturing cost of lithium batteries while reliably ensuring the battery's initial efficiency and high capacity electrochemical performance. This promotes the recycling and application of lithium batteries and has broad market prospects and application value. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the inert gas-assisted carbonizable small molecule organic compound preparation device of this application. The best embodiment of the present invention

[0016] 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.

[0017] The method for repairing and regenerating waste lithium iron phosphate cathode materials provided in this application includes the following steps:

[0018] S1 discharges and then crushes and disassembles the waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode sheets. The obtained positive electrode sheets are then heat-treated in an inert atmosphere to separate the lithium iron phosphate positive electrode sheets from the current collector, resulting in waste lithium iron phosphate positive electrode black powder.

[0019] This step involves discharging the recycled waste lithium iron phosphate batteries. The discharging process involves immersing the waste lithium iron phosphate batteries in a 5wt%–20wt% NaCl solution for 30–240 minutes. Based on the fact that sodium and lithium have the same external electron arrangement and coordination environment, sodium can easily replace the lithium in lithium iron phosphate, allowing all the active lithium ions inside the waste lithium iron phosphate battery to be embedded back into the lithium iron phosphate cathode material, avoiding resource waste. This reduces the amount of additional lithium source required in subsequent processes and allows the waste lithium iron phosphate batteries to be completely discharged to 0V, thus ensuring no safety issues during the dismantling of waste lithium batteries.

[0020] After discharge, the lithium iron phosphate positive electrode sheet, negative electrode sheet, separator and shell are separated by physical methods such as mechanical crushing and dismantling. The obtained positive electrode sheet is then heat-treated in an inert atmosphere at a temperature of 300-600℃ for 30-180 minutes to separate the lithium iron phosphate positive electrode sheet from the current collector, resulting in waste lithium iron phosphate positive electrode black powder.

[0021] Specifically, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0022] S2 involves heat-treating the waste lithium iron phosphate cathode black powder again in an environment furnace with an oxygen content higher than 60%, removing impurities while oxidizing the surface of the lithium iron phosphate red powder to obtain oxidized lithium iron phosphate red powder.

[0023] This step involves re-heat-treating the waste lithium iron phosphate cathode powder in an environment with an oxygen content higher than 60%. The heat treatment temperature is 400℃~800℃, and the time is 60~300min. On the one hand, this removes all inactive impurities such as binders, conductive agents, and electrolyte residues from the waste lithium iron phosphate cathode powder, thereby improving the purity of the final product. On the other hand, it oxidizes the surface of the waste lithium iron phosphate cathode powder, which allows for more thorough contact with the supplemented lithium source in subsequent processes and prepares for the formation of a uniform carbon coating layer during the subsequent vapor deposition process.

[0024] S3 tests the P, Fe, and Li content of the lithium iron phosphate red powder obtained in step S2, and adds lithium source appropriately based on the test results. Then, the lithium iron phosphate red powder and lithium source are ball-milled and mixed to obtain a lithium-replenished lithium iron phosphate mixture.

[0025] Because the recycled lithium-ion batteries come from diverse sources, this step uses ICP testing to determine the P, Fe, and Li content in the lithium iron phosphate (LiFePO4) oxide powder. Based on the test results, the active lithium lost from the recycled LiFePO4 batteries is appropriately replenished to ensure consistent electrochemical performance of the regenerated LiFePO4 cathode material. This ensures that when using the recycled cathode material to prepare lithium-ion batteries, the required total capacity, energy density, and cycle life can be achieved, guaranteeing the electrochemical performance of the prepared lithium-ion batteries.

[0026] The lithium source should be replenished so that the molar ratio of P, Fe, and Li in the lithium iron phosphate red powder satisfies the following relationship: P:Fe:Li = (1±0.01):(1±0.01):(1.05±0.005). The lithium source can be one or more of lithium carbonate, lithium acetate, lithium hydroxide, lithium nitrate, lithium oxide, lithium phosphate, lithium chloride, or lithium fluoride.

[0027] The lithium iron phosphate red powder and the lithium source were ball-milled at 400-1200 rpm for 6-15 hours to reduce the particle size of the mixture of lithium iron phosphate red powder and lithium source, and to ensure that the lithium iron phosphate red powder and lithium source could be mixed more evenly. This is also beneficial for the subsequent carbon coating on the surface of lithium iron phosphate particles. The particle size after grinding meets the following requirements: D50≤2um, (D90-D10) / D50≤2.5.

[0028] S4 places the lithium iron phosphate oxide mixture in a reducing atmosphere furnace and introduces an inert gas containing carbonizable small molecule organic matter. After heat treatment, the lithium iron phosphate oxide mixture undergoes carbon deposition coating and reduction in the reducing atmosphere to obtain regenerated lithium iron phosphate cathode material.

[0029] This step involves carbon deposition and reduction of the lithium iron phosphate (LiFePO4) oxide mixture in a reducing atmosphere. Using a carbon-sourced organic gas, heating and gas flow cause the organic molecules to undergo pyrolysis and redox reactions at high temperatures, resulting in carbonization and the conversion of hydrogen into hydrogen gas (CH4→C+2H2). The gaseous molecules gradually deposit into solid carbon, reducing the LiFePO4 oxide mixture. Carbon atoms gradually deposit on the surface of the LiFePO4 oxide mixture, forming a carbon-coated LiFePO4. This simultaneous in-situ reduction and coating, achieving a dense and uniform carbon coating layer, significantly improves the efficiency of cathode material repair and regeneration, and also enhances the electrochemical performance of the cathode material.

[0030] A specific method for preparing an inert gas carrying carbonizable small-molecule organic matter: An inert gas device (see Figure 1) is installed outside a reducing atmosphere furnace. This device includes a container 1, into which liquid carbonizable small-molecule organic matter (organic solution 4) is placed. Sufficient space is reserved within the container 1 to allow the gas to fully contact and react with the organic solution 4. An inlet pipe 2 and an outlet pipe 3 are located at the upper end of the container 1. The inlet pipe 2 is a long conduit, with one end supplying the inert gas and the other end inserted into the container 1. The inlet of the inlet pipe 2 is positioned near the bottom of the container 1. The inert gas exits from the inlet and enters the bottom of the container 1, mixing with the liquid carbonizable small-molecule organic matter. Because the inert gas enters from the bottom of the container 1, there is sufficient contact area and time between the inert gas and the liquid carbonizable small-molecule organic matter, ensuring that the carbonizable small-molecule organic matter adheres to the inert gas, forming an overflowing gas stream carrying the carbonizable small-molecule organic matter. One end of the outlet pipe 3 is connected to the inner cavity of container 1, and the other end is connected to the inner cavity of the reducing atmosphere furnace. The gas flow carrying carbonizable small molecule organic matter rises and enters the reducing atmosphere furnace through the outlet pipe 3, causing the lithium iron phosphate oxide mixture to be reduced in the reducing atmosphere and form a carbon deposition coating. It should be noted that the above-mentioned specific method for preparing the inert gas carrying carbonizable small molecule organic matter is only one embodiment of this application. Any method that can ensure that the carbonizable small molecule organic matter adheres to the inert gas, forming a gas flow carrying carbonizable small molecule organic matter and exiting it, is within the scope of protection of this application.

[0031] In the above process, the amount of carbonizable small molecule organic matter participating in subsequent reactions can be controlled by adjusting the flow rate of the inert gas. Depending on the type of organic matter, the proportion of carbonizable small molecule organic matter in the mixed gas after passing through container 1 is approximately 0.02% to 0.5%, which means that the amount of carbonizable small molecule organic matter participating in subsequent reactions is approximately 0.02% to 0.5% of the inert gas flow rate.

[0032] The inert gas is one or more of nitrogen, argon, and helium, and the small molecule organic compounds that can be carbonized are at least one of methanol, ethanol, acetone, formic acid, acetic acid, ethyl acetate, and diethyl ether. The pyrolysis and carbonization temperatures of these compounds match the synthesis temperature of lithium iron phosphate, and they are inexpensive, easily volatile, and readily adhere to the inert gas to form a mixed gas flow.

[0033] The inert gas containing carbonizable small-molecule organic matter is heat-treated in a reducing atmosphere furnace at a temperature of 600–900°C for 6–18 hours. Within this temperature range, the carbonization of organic molecules to achieve carbon coating is achieved, and it is also the reaction temperature for the mixture to transform into lithium iron phosphate. Within this time range, the reduction of the lithium iron phosphate mixture and the formation of carbon-coated lithium iron phosphate are guaranteed.

[0034] In the method described in this application, immersion in NaCl solution followed by discharge treatment and then disassembly ensures the recovery of lithium from the lithium iron phosphate cathode material. Impurity removal in an environment with an oxygen content higher than 60% improves the quality of the cathode material and simultaneously oxidizes the surface of the waste lithium iron phosphate cathode black powder, which is beneficial for subsequent carbon deposition and coating reduction. The lithium source is supplemented based on the tested P, Fe, and Li content of the oxidized lithium iron phosphate red powder, solving the defect of inconsistent sources of recycled waste lithium iron phosphate batteries and ensuring the consistency of the electrochemical performance of the regenerated lithium iron phosphate cathode material. Reduction and carbon coating are achieved through heat treatment using an inert gas entrainment of carbonizable small-molecule organic matter, improving both the repair and regeneration efficiency and the electrochemical performance of the cathode material. The above process steps work together to complete the repair and regeneration of waste lithium iron phosphate cathode material, obtaining cathode material that can be directly used to prepare lithium iron phosphate batteries.

[0035] The lithium iron phosphate cathode material repaired and regenerated in this application was used to make lithium iron phosphate batteries (button cells). Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The reversible capacity was above 155mAh / g. After 1000 charge and discharge cycles, the capacity retention rate was above 90%. This effectively ensured the electrochemical performance of lithium-ion batteries while reducing the manufacturing cost of lithium-ion batteries. Embodiments of the present invention

[0036] The method for repairing and regenerating waste lithium iron phosphate cathode materials will be further described in detail below with reference to specific embodiments.

[0037] Example 1:

[0038] S1 involves immersing the waste lithium iron phosphate battery in a 10% NaCl solution for 120 minutes to discharge it, then disassembling and separating it to obtain the positive electrode sheet; the obtained positive electrode sheet is then placed in an N2 atmosphere furnace and sintered at 500°C for 120 minutes to separate the positive electrode sheet from the current collector, thus obtaining waste lithium iron phosphate positive electrode black powder.

[0039] S2: The positive electrode black powder obtained in step S1 is transferred to an oxygen-containing atmosphere furnace, and a gas with an oxygen content of 60% is introduced. After heat treatment at 500°C for 60 minutes, lithium iron phosphate red powder is obtained.

[0040] S3 performed ICP testing on the lithium iron phosphate red powder obtained in step S2, and its Li, Fe, P molar ratio was 0.951:1.004:1.002. Dry grinding was then performed using a planetary ball mill. Lithium iron phosphate red powder and lithium hydroxide were added to the ball mill to achieve a Li, Fe, P molar ratio of 1.052:1.001:1.003 in the lithium-added lithium iron phosphate oxide mixture. The ball milling speed was 600 rpm, and after 9 hours, a lithium-added lithium iron phosphate oxide mixture was obtained. Laser particle size analysis showed that the lithium-added lithium iron phosphate oxide mixture had D10 = 0.76 μm, D50 = 1.82 μm, and D90 = 5.13 μm.

[0041] S4 places the ground lithium iron phosphate oxide mixture in an inert atmosphere furnace. Simultaneously, nitrogen gas is introduced through inlet pipe 2 into a nitrogen-containing container 1 (see Figure 1), located outside the inert atmosphere furnace, containing a methanol solution (organic solution 4). Nitrogen gas enters the bottom of the container 1 through inlet pipe 2 and comes into contact with the methanol solution. The nitrogen gas carrying methanol then enters the inert atmosphere furnace through outlet pipe 3 as a protective atmosphere. The methanol content in this mixed gas is approximately 0.3% of the nitrogen gas flow. The furnace temperature is raised to 750°C and held for 12 hours, allowing the lithium iron phosphate oxide mixture to be reduced in a reducing atmosphere and form a carbon deposition coating. After natural cooling, regenerated lithium iron phosphate cathode material is obtained.

[0042] The recycled lithium iron phosphate cathode material was used to make 2035 coin-type lithium batteries. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and capacity retention after 1000T cycles were recorded. The results showed that the reversible capacity was 157.2 mAh / g and the cycle performance was 94.5%, which fully met the requirements of commercial lithium iron phosphate batteries.

[0043] Comparative Example 1:

[0044] Steps S1 and S2 are the same as in Example 1.

[0045] S3 performs ICP testing on the lithium iron phosphate red powder obtained in step S2, in which the molar ratio of Li, Fe, and P is 0.951:1.004:1.002.

[0046] Dry grinding was performed using a planetary ball mill. Lithium iron phosphate red powder from step S2 was added to the ball mill at 300 rpm for 9 hours to obtain a lithium iron phosphate oxide mixture. Laser particle size analysis showed that the particle sizes of the lithium iron phosphate oxide mixture were D10 = 0.96 μm, D50 = 3.23 μm, and D90 = 13.45 μm.

[0047] Step S4 is the same as in Example 1.

[0048] The lithium iron phosphate cathode material obtained in Comparative Example 1 was used to make a 2035 coin cell lithium battery. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and the capacity retention rate after 1000T cycles were recorded. The results were: reversible capacity of 152.4 mAh / g and cycle performance of 56.6%.

[0049] As can be seen from the comparison, Comparative Example 1 did not supplement the lithium source for lithium iron phosphate red powder, the ball milling speed was lower than the range set in this application, and the particle size after grinding was also higher than the range set in this application. Although the reversible capacity was slightly lower than that of Example 1, the cycle performance was about 38 percentage points lower than that of Example 1.

[0050] Example 2:

[0051] S1 involves immersing the waste lithium iron phosphate battery in a 15% NaCl solution for 150 minutes to discharge it, then disassembling and separating it to obtain the positive electrode sheet; the obtained positive electrode sheet is then placed in an N2 atmosphere furnace and sintered at 600℃ for 120 minutes to separate the positive electrode sheet from the current collector, thus obtaining waste lithium iron phosphate positive electrode black powder.

[0052] S2: The positive electrode black powder obtained in step S1 is transferred to an oxygen-containing atmosphere furnace, and a gas with an oxygen content of 80% is introduced. After heat treatment at 600°C for 150 minutes, lithium iron phosphate red powder is obtained.

[0053] S3 performed ICP testing on the lithium iron phosphate red powder obtained in step S2, and the molar ratio of Li, Fe, and P was 0.837:1.002:1.005.

[0054] Dry grinding was performed using a planetary ball mill. Lithium iron phosphate red powder and lithium carbonate were added to the ball mill to achieve a Li:Fe:P molar ratio of 1.048:1.002:1.002 in the lithium-added lithium iron phosphate oxide mixture. The ball milling speed was 800 rpm, and the mixture was ground for 10 hours to obtain the lithium-added lithium iron phosphate oxide mixture. Laser particle size analysis showed that the lithium-added lithium iron phosphate oxide mixture had D10 = 0.69 μm, D50 = 1.92 μm, and D90 = 5.42 μm.

[0055] S4 places the ground lithium iron phosphate oxide mixture in an inert atmosphere furnace. Simultaneously, nitrogen gas is introduced through inlet pipe 2 into a nitrogen-containing container 1 (see Figure 1), located outside the inert atmosphere furnace, containing a nitrogen gas stream that can carbonize small organic molecules. Container 1 contains an ethanol solution (organic solution 4). Nitrogen gas enters the bottom of the container 1 through inlet pipe 2 and comes into contact with the ethanol solution. The nitrogen gas stream carrying ethanol then enters the inert atmosphere furnace through outlet pipe 3 as a protective atmosphere. The ethanol content in this mixed gas is approximately 0.1% of the nitrogen gas stream. The furnace temperature is raised to 700°C and held for 8 hours, allowing the lithium iron phosphate oxide mixture to be reduced in a reducing atmosphere and form a carbon deposition coating. After natural cooling, regenerated lithium iron phosphate cathode material is obtained.

[0056] The recycled lithium iron phosphate cathode material was used to make 2035 coin-type lithium batteries. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and capacity retention rate after 1000T cycles were recorded. The results showed that the reversible capacity was 156.8mAh / g and the cycle performance was 92.9%, which fully met the requirements of commercial lithium iron phosphate batteries.

[0057] Comparative Example 2:

[0058] Step S1 is the same as step S1 in Example 2.

[0059] In step S2, the cathode black powder obtained in step S1 is transferred to a tube furnace and subjected to heat treatment at 600°C for 150 minutes to obtain lithium iron phosphate red powder.

[0060] Step S3 is the same as step S3 in Example 2.

[0061] S4 places the ground lithium iron phosphate oxide mixture in a nitrogen furnace, heats the furnace to 700°C, holds it at that temperature for 8 hours, and then allows it to cool naturally to obtain the regenerated lithium iron phosphate cathode material.

[0062] The lithium iron phosphate cathode material obtained in Comparative Example 2 was used to make a 2035 coin cell. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and the capacity retention rate after 1000T cycles were recorded. The results were: reversible capacity of 132.5mAh / g and cycle performance of 27.6%.

[0063] Compared with Example 2, Comparative Example 2 did not have an oxygen-containing environment in the heat treatment of step S2. Although a lithium source was added during the grinding in step S3, nitrogen was not used as a protective atmosphere to carry carbonizable small molecule organic matter in step S4. The results showed that the reversible capacity of Comparative Example 2 was much lower than that of Example 2, and the cycle performance was much lower than that of Example 2.

[0064] Example 3:

[0065] S1 involves immersing the waste lithium iron phosphate battery in a 10% NaCl solution for 240 minutes to discharge it, then disassembling and separating it to obtain the positive electrode sheet; the obtained positive electrode sheet is then placed in an N2 atmosphere furnace and sintered at 550°C for 60 minutes to separate the positive electrode sheet from the current collector, thus obtaining waste lithium iron phosphate positive electrode black powder.

[0066] S2. The positive electrode black powder obtained in step S1 is transferred to an oxygen-containing atmosphere furnace, and a gas with an oxygen content of 70% is introduced. After heat treatment at 700°C for 240 minutes, lithium iron phosphate red powder is obtained.

[0067] S3 performed ICP testing on the lithium iron phosphate red powder obtained in step S2, and the molar ratio of Li, Fe, and P was 0.730:0.998:1.004.

[0068] Dry grinding was performed using a planetary ball mill. Lithium iron phosphate red powder and lithium acetate were added to the ball mill to achieve a Li:Fe:P molar ratio of 1.053:1.001:1.005 in the lithium-added lithium iron phosphate oxide mixture. The ball milling speed was 1000 rpm, and the mixture was ground for 15 hours to obtain the lithium-added lithium iron phosphate oxide mixture. Laser particle size analysis showed that the lithium-added lithium iron phosphate oxide mixture had D10 = 0.89 μm, D50 = 1.58 μm, and D90 = 4.77 μm.

[0069] S4 places the ground lithium iron phosphate oxide mixture in an inert atmosphere furnace. Simultaneously, nitrogen gas is introduced through inlet pipe 2 into a nitrogen-containing container 1 (see Figure 1), located outside the inert atmosphere furnace, containing a nitrogen gas stream that can carbonize small organic molecules. Container 1 contains an acetone solution (organic solution 4). Nitrogen gas enters the bottom of the container 1's inner cavity through inlet pipe 2 and comes into contact with the acetone solution. The nitrogen gas stream carrying acetone then enters the inert atmosphere furnace through outlet pipe 3 as a protective atmosphere. The acetone content in this mixed gas is approximately 0.3% of the nitrogen gas stream. The furnace temperature is raised to 700°C and held for 15 hours, allowing the lithium iron phosphate oxide mixture to be reduced in a reducing atmosphere and form a carbon deposition coating. After natural cooling, regenerated lithium iron phosphate cathode material is obtained.

[0070] The recycled lithium iron phosphate cathode material was used to make 2035 coin-type lithium batteries. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and capacity retention rate after 1000T cycles were recorded. The results showed that the reversible capacity was 155.6mAh / g and the cycle performance was 91.8%, which fully met the requirements of commercial lithium iron phosphate batteries.

[0071] Comparative Example 3:

[0072] Steps S1 and S2 are the same as in Example 3.

[0073] S3 performs ICP testing on the lithium iron phosphate red powder obtained in step S2, in which the molar ratio of Li, Fe, and P is 0.951:1.004:1.002.

[0074] A mixture of lithium iron phosphate oxide was obtained by dry grinding using a planetary ball mill at a speed of 1000 rpm for 15 hours. Laser particle size analysis showed that the lithium iron phosphate oxide mixture had D10=0.89 μm, D50=1.58 μm, and D90=4.77 μm.

[0075] S4 places the ground lithium iron phosphate oxide mixture in an inert atmosphere furnace, heats the furnace to 600°C, holds it at that temperature for 18 hours, and then cools it naturally to obtain the regenerated lithium iron phosphate cathode material.

[0076] The lithium iron phosphate cathode material obtained in Comparative Example 3 was used to make a 2035 coin cell lithium battery. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and the capacity retention rate after 1000T cycles were recorded. The results were: reversible capacity of 114.9 mAh / g and cycle performance of 14.5%.

[0077] Compared with Example 3, although Comparative Example 3 was carried out in an atmosphere with an oxygen content of 70% in the heat treatment of step S2, no lithium source was added during the grinding in step S3, and no nitrogen was used as a protective atmosphere to carry carbonizable small molecule organic matter in step S4. The results show that the reversible capacity of Example 3 is much higher than that of Comparative Example 3, and the cycle performance is 6.3 times that of Comparative Example 3.

[0078] Example 4:

[0079] S1 involves immersing the waste lithium iron phosphate battery in a 10% NaCl solution for 90 minutes to discharge it, then disassembling and separating it to obtain the positive electrode sheet; the obtained positive electrode sheet is then placed in an N2 atmosphere furnace and sintered at 600℃ for 60 minutes to separate the positive electrode sheet from the current collector, thus obtaining waste lithium iron phosphate positive electrode black powder.

[0080] In step S2, the positive electrode black powder obtained in step S1 is transferred to an oxygen-containing atmosphere furnace, and a gas with an oxygen content of 90% is introduced. After heat treatment at 400°C for 240 minutes, lithium iron phosphate red powder is obtained.

[0081] S3 performed ICP testing on the lithium iron phosphate red powder obtained in step S2, and the molar ratio of Li, Fe, and P was 0.967:1.002:1.007.

[0082] Dry grinding was performed using a planetary ball mill. Lithium iron phosphate red powder and lithium oxalate were added to the ball mill to achieve a Li:Fe:P molar ratio of 1.056:1.002:1.005 in the lithium-added lithium iron phosphate oxide mixture. The ball milling speed was 400 rpm, and the mixture was ground for 15 hours to obtain the lithium-added lithium iron phosphate oxide mixture. Laser particle size analysis showed that the lithium-added lithium iron phosphate oxide mixture had D10 = 0.38 μm, D50 = 1.42 μm, and D90 = 3.72 μm.

[0083] S4 places the ground lithium iron phosphate oxide mixture in an inert atmosphere furnace. Simultaneously, nitrogen gas is introduced through inlet pipe 2 into a nitrogen-containing container 1 (see Figure 1), located outside the inert atmosphere furnace, which contains a nitrogen gas carrying carbonizable small-molecule organic matter. Container 1 contains an acetic acid solution (organic solution 4). Nitrogen gas enters the bottom of the inner cavity of container 1 through inlet pipe 2 and comes into contact with the acetic acid solution. The nitrogen gas gas carrying acetic acid then enters the inert atmosphere furnace through outlet pipe 3 as a protective atmosphere. The acetic acid content in this mixed gas is approximately 0.1% of the nitrogen gas flow. The furnace temperature is raised to 800°C and held for 8 hours, allowing the lithium iron phosphate oxide mixture to be reduced in a reducing atmosphere and form a carbon deposition coating. After natural cooling, regenerated lithium iron phosphate cathode material is obtained.

[0084] The recycled lithium iron phosphate cathode material was used to make 2035 coin-type lithium batteries. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and capacity retention rate after 1000T cycles were recorded. The results showed that the reversible capacity was 156.5mAh / g and the cycle performance was 93.8%, which fully met the requirements of commercial lithium iron phosphate batteries.

[0085] Comparative Example 4:

[0086] Step S1 is the same as in Example 4.

[0087] In step S2, the cathode black powder obtained in step S1 is transferred to a tube furnace and subjected to heat treatment at 40°C for 240 minutes to obtain lithium iron phosphate red powder.

[0088] S3 performs ICP testing on the lithium iron phosphate red powder obtained in step S2, in which the molar ratio of Li, Fe, and P is 0.967:1.002:1.007.

[0089] A mixture of lithium iron phosphate oxide was obtained by dry grinding using a planetary ball mill at a speed of 400 rpm for 15 hours. Laser particle size analysis showed that the lithium iron phosphate oxide mixture had D10=0.38 μm, D50=1.42 μm, and D90=3.72 μm.

[0090] S4 places the ground lithium iron phosphate oxide mixture in a nitrogen furnace. The nitrogen in the furnace does not carry any organic matter. The furnace is heated to 800°C and held for 8 hours. After natural cooling, the regenerated lithium iron phosphate cathode material is obtained.

[0091] The lithium iron phosphate cathode material obtained in Comparative Example 4 was used to make a 2035 coin cell. Charge and discharge tests were conducted within the cutoff voltage range of 2.0 to 3.75V. The initial reversible capacity and the capacity retention rate after 1000T cycles were recorded. The results were: reversible capacity of 95.5mAh / g and cycle performance of 4.1%.

[0092] The comparison shows that in Comparative Example 4, step S2 had no oxygen-containing environment, step S3 did not add a lithium source, and step S4 did not use an inert gas containing carbonizable small molecule organic matter. The results indicate that the reversible capacity of Comparative Example 4 is much lower than that of Example 4, and its cycle performance is only 1 / 20 of that of Example 4.

[0093] 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 method for repairing and regenerating a waste and old lithium iron phosphate positive electrode material, characterized in that, Includes the following steps: S1 After discharging and processing the waste lithium iron phosphate battery, it is crushed and disassembled to separate the lithium iron phosphate positive electrode sheet. Then, the obtained positive electrode sheet is heat-treated in an inert atmosphere to separate the lithium iron phosphate positive electrode sheet from the current collector, and waste lithium iron phosphate positive electrode black powder is obtained. S2 involves heat-treating the waste lithium iron phosphate cathode black powder again in an environment furnace with an oxygen content higher than 60%, removing impurities while oxidizing the surface of the lithium iron phosphate red powder to obtain oxidized lithium iron phosphate red powder. S3 Test the content of P, Fe and Li elements in the lithium iron phosphate red powder obtained in step S2, and add lithium source appropriately according to the test results. Then, ball mill and mix the lithium iron phosphate red powder and the lithium source to obtain a lithium-added lithium iron phosphate mixture. S4 The lithium iron phosphate oxide mixture is placed in a reducing atmosphere furnace and an inert gas containing carbonizable small molecule organic matter is introduced. After heat treatment, the lithium iron phosphate oxide mixture is carbonized and reduced in a reducing atmosphere to obtain regenerated lithium iron phosphate cathode material. The carbonizable small molecule organic compound is at least one of methanol, ethanol, acetone, formic acid, acetic acid, ethyl acetate, or diethyl ether.

2. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1, characterized in that, In step S1, the discharge treatment involves immersing the waste lithium iron phosphate battery in a 5wt% to 20wt% NaCl solution for 30 to 240 minutes, so that all the active lithium ions inside the waste lithium iron phosphate battery are intercalated back into the lithium iron phosphate cathode material while discharging.

3. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1, characterized in that, In step S1, the inert atmosphere is one or more of nitrogen, argon, and helium, the heat treatment temperature is 300–600°C, and the heat treatment time is 30–180 min.

4. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to any one of claims 1-3, characterized in that, In step S2, the heat treatment temperature for the waste lithium iron phosphate cathode black powder is 400℃~800℃, and the time is 60~300min.

5. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1, characterized in that, In step S3, a lithium source is added so that the molar ratio of P, Fe, and Li elements in the lithium iron phosphate red powder satisfies the following relationship: P:Fe:Li = (1±0.01):(1±0.01):(1.05±0.005).

6. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1 or 5, characterized in that, In step S3, lithium iron phosphate red powder and lithium source are mixed and ball-milled at 400-1200 rpm for 6-15 hours. The particle size of the mixture meets the following requirements: D50≤2um, (D90-D10) / D50≤2.

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7. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1 or 5, characterized in that, In step S3, the lithium source is at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium nitrate, lithium oxide, lithium phosphate, lithium chloride, or lithium fluoride.

8. The method for repairing and regenerating waste and old lithium iron phosphate positive electrode material according to claim 1, characterized in that, In step S4, the inert gas carrying the carbonizable small molecule organic matter is heat-treated in a reducing atmosphere furnace at a temperature of 600–900°C for a holding time of 6–18 hours.

9. A method for repairing and regenerating waste lithium iron phosphate cathode material as described in claim 1 or 8, characterized in that, In step S4, the method for preparing the inert gas carrying the carbonizable small molecule organic matter is as follows: Liquid carbonizable small molecule organic matter is placed in a container. An inlet pipe and an outlet pipe are installed on the container. The inlet pipe is a long conduit, with one end through which inert gas is introduced and the other end inserted into the container. The inlet of the inlet pipe is close to the bottom of the container, allowing the inert gas to fully mix with the carbonizable small molecule organic matter, forming bubbles carrying the carbonizable small molecule organic matter that overflow. One end of the outlet pipe connects to the inner cavity of the container, and the other end connects to a reducing atmosphere furnace. The inert gas carrying the carbonizable small molecule organic matter rises and enters the reducing atmosphere furnace through the outlet pipe.

10. A lithium iron phosphate battery prepared by the method for repairing and regenerating waste lithium iron phosphate cathode material as described in any one of claims 1-9.

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