Method for degrading positive electrode side reaction product after high-temperature discharge of lithium iron phosphate cell

Abstract

The invention provides a method for degrading a positive electrode side reaction product after high-temperature discharge of a lithium iron phosphate cell, which comprises the following steps: calcining a lithium iron phosphate pole piece obtained by precise disassembly at low temperature to remove electrolyte and adhesive in the lithium iron phosphate pole piece, then crushing and screening to realize powder separation, soaking and washing the powder, and then carrying out medium-temperature purification and high-temperature shaping, thereby obtaining the positive electrode side reaction product after high-temperature discharge of the lithium iron phosphate cell. According to the method, residual byproducts react with carbon dioxide through medium-temperature purification, corroded surfaces of particles can be repaired through high-temperature shaping, degradation of positive electrode side reaction products after high-temperature discharge of the lithium iron phosphate cell is completed, lithium iron phosphate powder with extremely low content of side reaction products to be supplemented with lithium is obtained, and subsequent repair and regeneration of the lithium iron phosphate powder are guaranteed. Through a series of processes, the degradation of the side reaction product of the positive electrode after the lithium iron phosphate cell is discharged at high temperature is realized, the lithium supplement effect hindering regeneration and repair due to the existence of the side reaction product is improved, and a solution is provided for the regeneration and repair engineering of the decommissioned lithium iron phosphate material after the subsequent large-scale high-temperature discharge.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion waste battery recycling, regeneration and repair technology, and in particular to a method for degrading positive electrode by-reaction products after high-temperature discharge of lithium iron phosphate cells. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in automotive power batteries, energy storage systems, as well as in power tools, electric bicycles, electric motorcycles, military equipment, aerospace, 3C products, and many other fields, in very large quantities. However, as the lifespan of lithium-ion batteries approaches its end, a large number of retired and scrapped batteries will be generated.

[0003] Currently, dry physical recycling methods are becoming increasingly mainstream. Their green, environmentally friendly, low-energy, and rapid regeneration and repair methods offer high economic benefits, especially in the regeneration and repair of waste lithium iron phosphate (LFP) electrode sheets on conventional industrial sites. However, currently, liquid-filled LFP cells account for over 90% of all waste LFP cells, making the regeneration and repair of failed LFP electrode sheets essential.

[0004] A significant portion of retired and scrapped lithium iron phosphate (LFP) battery cells have been discharged under high-temperature conditions. At these temperatures, the electrolyte decomposes, and impurities in the active materials react with the electrolyte to form byproducts. These byproducts negatively impact the repair process during subsequent lithium replenishment and regeneration. The byproducts generated during discharges at temperatures between 45 and 80°C are particularly numerous and complex, primarily consisting of various lithium salts and inorganic substances. These byproducts bind tightly to the degraded LFP active materials. If these byproducts are not removed, the lithium and carbon sources cannot make proper contact with the degraded LFP materials during regeneration, thus affecting the lithium replenishment effect of the solid-phase reaction. Therefore, it is urgent to address the problem of byproducts generated during high-temperature discharge of LFP battery cells affecting subsequent lithium replenishment and regeneration.

[0005] In view of this, it is necessary to design an improved method for degrading the positive electrode side reaction products of lithium iron phosphate cells after high-temperature discharge in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge. Through precise disassembly, low-temperature calcination, coarse crushing and sieving, soaking and washing, medium-temperature purification and high-temperature shaping, the method achieves the degradation of the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, and avoids the impact of by-products on the regeneration and repair of lithium iron phosphate.

[0007] To achieve the above-mentioned objective, this invention provides a method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, comprising the following steps:

[0008] S1. The failed lithium iron phosphate battery cell after high-temperature discharge is precisely disassembled into lithium iron phosphate positive electrode sheet, graphite negative electrode sheet and other auxiliary materials.

[0009] S2. The lithium iron phosphate cathode sheet obtained in step S1 is subjected to low-temperature calcination to remove the electrolyte and adhesive.

[0010] S3. The lithium iron phosphate cathode sheet processed in step S2 is crushed and sieved to separate the powder, and the powder is soaked and washed multiple times and then dried.

[0011] S4. The lithium iron phosphate particles dried in step S3 are purified at medium temperature under a carbon dioxide atmosphere.

[0012] S5. The lithium iron phosphate particles purified by temperature in step S4 are subjected to high-temperature shaping to complete the degradation of the positive electrode side reaction products after high-temperature discharge of the lithium iron phosphate battery cell and repair the corroded surface of the particles.

[0013] As a further improvement of the present invention, in step S2, the temperature of the low-temperature calcination is 120-450°C, the time is 0.5-6 hours, and the calcination atmosphere is an oxygen-free atmosphere.

[0014] As a further improvement of the present invention, in step S4, the temperature of the medium-temperature purification is 450-650°C and the time is 6-12 hours.

[0015] As a further improvement of the present invention, in step S5, the temperature of the high-temperature shaping is not lower than 650°C, the time is 4 to 6 hours, and the atmosphere of the high-temperature shaping is an inert gas atmosphere or a vacuum environment.

[0016] As a further improvement of the present invention, the low-temperature calcination is carried out in a kiln, the medium-temperature purification is carried out in a rotary kiln, and the high-temperature shaping is carried out in a roller kiln.

[0017] As a further improvement of the present invention, in step S3, the soaking and washing use the same solvent, which is one or a mixture of deionized water and ethanol, and the soaking time is not less than 30 minutes; the drying method is one or more of vacuum drying, inert atmosphere drying, freeze drying, etc.

[0018] As a further improvement of the present invention, in step S1, the atmosphere for precise disassembly is an inert gas atmosphere or a vacuum environment.

[0019] As a further improvement of the present invention, in step S3, the coarse crusher used for crushing includes one or more of the following: impact mill, disc mill, cage pin mill, air jet mill, ball mill, sand mill, grinding mill, etc.; during screening, the screen mesh number used is 80 to 200 mesh, and the screening form includes one or more of the following: linear screen, drum screen, gyratory screen, ultrasonic vibrating screen, etc.; after screening, the lighter by-reaction products with different densities from lithium iron phosphate powder are removed by cyclone classification and pulse dust removal.

[0020] As a further improvement of the present invention, the soaking method is one or more of stirring and ultrasonication, and the washing method is one or more of vacuum filtration and centrifugation.

[0021] As a further improvement of the present invention, the kiln includes one or more of roller kilns, rotary kilns, tunnel kilns, and pusher kilns.

[0022] The beneficial effects of this invention are:

[0023] 1. The method of degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge of the present invention firstly involves precise disassembly in an inert gas or vacuum environment to prevent the electrolyte on the disassembled lithium iron phosphate electrode from further producing other by-reaction substances. The lithium iron phosphate electrode is then calcined at low temperature to remove the electrolyte and adhesive in the lithium iron phosphate electrode. Next, it is crushed and sieved to separate the powder. The lithium iron phosphate powder is then soaked and washed to remove some of the water-soluble by-reaction products present. Finally, it undergoes medium-temperature purification and high-temperature shaping. The medium-temperature purification allows the residual by-products to react with carbon dioxide to achieve purification. The high-temperature shaping repairs the corroded surface of the particles, making their morphology more regular. This completes the degradation of the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, resulting in lithium iron phosphate powder with very low content of by-reaction products to be replenished, ensuring the subsequent repair and regeneration of lithium iron phosphate powder.

[0024] 2. This invention degrades most of the by-reaction products of lithium iron phosphate battery cells after high-temperature discharge by soaking, washing and three-stage calcination treatment, thereby improving the lithium replenishment effect that hinders regeneration and repair due to the presence of by-reaction products after high-temperature discharge. This allows lithium iron phosphate materials disassembled after high-temperature discharge to be regenerated and repaired for lithium replenishment, providing a solution for the engineering of regeneration and repair of retired lithium iron phosphate materials after large-scale high-temperature discharge. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of the method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to the present invention.

[0026] Figure 2 The image shows SEM images of lithium iron phosphate powder before and after degradation of by-reaction products in Example 1 of this invention.

[0027] Figure 3 This is a graph showing the specific capacity of lithium iron phosphate for subsequent lithium replenishment at different processes in Embodiment 1 of the present invention.

[0028] Figure 4 The specific capacity charge-discharge curve of the lithium iron phosphate material obtained in Example 2 of this invention is shown. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0031] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] Please see Figure 1 As shown, a method for degrading positive electrode byproducts of lithium iron phosphate battery cells after high-temperature discharge includes the following steps:

[0033] S1. The failed lithium iron phosphate battery cell after high-temperature discharge is precisely disassembled into lithium iron phosphate positive electrode sheet, graphite negative electrode sheet and other auxiliary materials.

[0034] S2. The lithium iron phosphate cathode sheet obtained in step S1 is subjected to low-temperature calcination to remove the electrolyte and adhesive. The low-temperature calcination temperature is 120-450℃, the time is 0.5-6h, and the calcination atmosphere is an oxygen-free atmosphere to ensure that the relevant solvents and some low-boiling-point side reaction products (mainly organic solvents) can be removed.

[0035] S3. The lithium iron phosphate cathode sheet processed in step S2 is crushed and sieved to separate the powder, and the powder is soaked and washed multiple times and then dried.

[0036] S4. The lithium iron phosphate particles dried in step S3 are purified at medium temperature under a carbon dioxide atmosphere. The temperature of medium temperature purification is 450-650℃ and the time is 6-12h.

[0037] S5. The lithium iron phosphate particles purified by temperature in step S4 are subjected to high-temperature shaping to complete the degradation of the positive electrode side reaction products after high-temperature discharge of the lithium iron phosphate battery cell and repair the corroded surface of the particles; wherein, the high-temperature shaping temperature is not lower than 650℃, the time is 4 to 6 hours, and the high-temperature shaping atmosphere is an inert gas atmosphere or a vacuum environment.

[0038] Specifically, this method first involves precise disassembly under an inert gas or vacuum environment to prevent the electrolyte on the disassembled lithium iron phosphate electrode from further producing other by-reaction substances. The lithium iron phosphate electrode is then calcined at low temperature to remove the electrolyte and adhesive. Next, it is crushed and sieved to separate the powder. The lithium iron phosphate powder is then soaked and washed to remove some of the water-soluble by-reaction products. Finally, it undergoes medium-temperature purification and high-temperature shaping. Medium-temperature purification allows residual by-products to react with carbon dioxide, achieving purification. High-temperature shaping repairs the corroded surface of the particles, making their morphology more regular and completing the degradation of by-reaction products of the positive electrode after high-temperature discharge of the lithium iron phosphate battery cell. This results in lithium iron phosphate powder with very low content of by-reaction products to be replenished, ensuring the subsequent repair and regeneration of lithium iron phosphate powder.

[0039] Specifically, low-temperature calcination is carried out in a kiln, including one or more types such as roller kilns, rotary kilns, tunnel kilns, and pusher kilns. Medium-temperature purification is carried out in a rotary kiln with a frequency controlled between 6 and 25 Hz, and high-temperature shaping is carried out in a roller kiln. Thus, this invention utilizes existing kilns for the three-stage calcination process, saving on the recycling costs of lithium iron phosphate batteries and facilitating industrial application.

[0040] In step S3, soaking and washing use the same solvent, which is one or more of deionized water and ethanol. The soaking time is no less than 30 minutes, and the soaking method is one or more of stirring and ultrasonication. The washing method is one or more of suction filtration and centrifugation. The drying method is one or more of vacuum drying, inert atmosphere drying, and freeze drying. The crushing uses one or more of the following coarse crushers: impact mill, disc mill, cage pin mill, air jet mill, ball mill, sand mill, and grinding mill. During sieving, the screen mesh size is 80-200 mesh, and the sieving form includes one or more of the following: linear screen, drum screen, gyratory screen, and ultrasonic vibrating screen. After sieving, lighter by-reaction products with different densities from lithium iron phosphate powder are removed by cyclone classification and pulse dust removal.

[0041] In some specific embodiments, the coarse crusher includes a coarse crusher body, a cyclone classifier and collection box, a pulse dust collector and an induced draft fan, and its main function is to remove fine carbon powder and some by-reaction products.

[0042] In step S1, the atmosphere for precise disassembly is an inert gas atmosphere or a vacuum environment. The disassembly method includes automatic disassembly of the equipment or manual disassembly using a glove box. The inert gas is specifically one or more mixed gases such as nitrogen, argon, and helium. This avoids the lithium hexafluorophosphate (LiPF6) containing electrolyte in the lithium iron phosphate electrode from easily decomposing upon contact with oxygen in the air after disassembly, which would further generate other side reaction substances.

[0043] This invention degrades most of the by-reaction products of lithium iron phosphate (LFP) battery cells after high-temperature discharge by soaking, washing, and three-stage calcination. From precise disassembly to medium-temperature purification, LFP does not come into contact with oxygen. It can only come into contact with air after high-temperature shaping, ensuring no secondary generation of by-reaction products. This improves the lithium replenishment effect that is hindered by by-reaction products after high-temperature discharge, allowing LFP materials disassembled after high-temperature discharge to be regenerated and repaired. This provides a solution for the engineering of regeneration and repair of large quantities of retired LFP materials after high-temperature discharge.

[0044] Example 1

[0045] This embodiment provides a method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, including the following steps:

[0046] S1. Select high-temperature discharged cells from retired cells and manually disassemble them into lithium iron phosphate positive electrode sheets, graphite negative electrode sheets, and other auxiliary materials. The manual disassembly is carried out in a glove box with a nitrogen atmosphere to ensure that the lithium iron phosphate electrode sheets and lithium iron phosphate positive electrode sheets are the raw materials for subsequent regeneration, repair, and processing into products and are sealed and stored.

[0047] S2. The lithium iron phosphate cathode sheet obtained in step S1 is calcined in a roller kiln at 200°C for 6 hours. The calcination atmosphere is an oxygen-free atmosphere to ensure that the relevant solvents and some low-boiling-point side reaction products can be removed, mainly organic solvents.

[0048] S3. The lithium iron phosphate electrode sheets after low-temperature treatment are crushed and sieved. The electrode sheets are processed by air jet mill to obtain initial crushed material, which is then screened through an 80-mesh drum screen and a 160-mesh linear screen to achieve powder separation. At the same time, lighter by-reaction products with different densities from lithium iron phosphate powder are removed by cyclone classification and pulse dust removal.

[0049] After sieving, the exhausted lithium iron phosphate powder was soaked in ethanol solution and sonicated for 1 hour. Then it was washed three times by centrifugation with ethanol solution and then dried under vacuum at 120°C to ensure that most of the remaining by-reaction products were gradually washed away.

[0050] S4. The lithium iron phosphate particles dried in step S3 are calcined at 650℃ for 12 hours in a rotary kiln for medium-temperature purification under a carbon dioxide atmosphere and a rotary kiln rotation frequency of 10 Hz. By constantly stirring in the rotary kiln, the residual by-reaction products are ensured to react completely with carbon dioxide at medium temperature, especially carbonate compounds, thus achieving purification.

[0051] S5. The lithium iron phosphate particles purified in step S4 are calcined at 700°C for 4 hours in a roller kiln under a nitrogen atmosphere to perform high-temperature shaping, thereby repairing the surface defects of the lithium iron phosphate particles, making the morphology more regular, and completing the degradation of the positive electrode side reaction products after high-temperature discharge of the lithium iron phosphate battery cell, finally obtaining lithium iron phosphate powder with less side reaction product content to be replenished.

[0052] Please see Figure 2 The image shows SEM images of lithium iron phosphate powder before and after degradation of by-reaction products in Example 1. As can be seen from the image, before degradation using this method, lithium iron phosphate contained a large amount of impurities and by-reaction products, and these by-reaction products were tightly bound to the active material of lithium iron phosphate, affecting the subsequent repair and regeneration of lithium iron phosphate. After degradation using this method, the by-reaction products were significantly reduced, indicating that this method has a good degradation effect and is beneficial to the repair and regeneration of lithium iron phosphate cathode materials.

[0053] Please see Figure 3 The figure shows the specific capacity of lithium iron phosphate for subsequent lithium replenishment at different stages of Example 1. As can be seen from the figure, the better the lithium replenishment effect of lithium iron phosphate is obtained as each stage of this application is performed sequentially, the fewer the degradation byproducts are, verifying that the scheme of this embodiment successfully degrades the positive electrode byproducts after high-temperature discharge of the lithium iron phosphate cell.

[0054] Example 2

[0055] This embodiment provides a method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, including the following steps:

[0056] S1. Select high-temperature discharged cells from retired cells and precisely disassemble them into lithium iron phosphate positive electrode sheets, graphite negative electrode sheets and other auxiliary materials using automated disassembly equipment. Mechanical disassembly is carried out automatically by a complete disassembly box. Nitrogen atmosphere is used to protect the lithium iron phosphate electrode sheets. The lithium iron phosphate positive electrode sheets are used as raw materials for subsequent regeneration, repair and processing into products and are sealed and stored.

[0057] S2. The lithium iron phosphate cathode sheet obtained in step S1 is calcined in a box furnace for 0.5 h under a nitrogen atmosphere, and then calcined in a roller kiln at 400 °C for 3 h to ensure that the relevant solvents and some low-boiling-point side reaction products can be removed, mainly organic solvents.

[0058] S3. The lithium iron phosphate electrode sheets after low-temperature treatment are crushed and sieved. The electrode sheets are processed by an impact mill to obtain initial crushed material, which is then sieved through an 80-mesh ultrasonic vibrating screen and a 120-mesh linear screen to separate the powder. At the same time, lighter by-reaction products with different densities from lithium iron phosphate powder are removed by cyclone classification and pulse dust removal.

[0059] After sieving, the exhausted lithium iron phosphate powder was soaked in ethanol solution and sonicated for 2 hours. Then it was washed three times by centrifugation with a mixture of deionized water and ethanol. Finally, it was freeze-dried under vacuum to ensure that most of the remaining by-reaction products were gradually washed away.

[0060] S4. The lithium iron phosphate particles dried in step S3 are calcined at 500℃ for 12 hours in a rotary kiln for medium-temperature purification under a carbon dioxide atmosphere and a rotary kiln rotation frequency of 25Hz. By constantly stirring in the rotary kiln, the residual by-reaction products are ensured to react completely with carbon dioxide at medium temperature, especially carbonate compounds, thus achieving purification.

[0061] S5. The lithium iron phosphate particles purified in step S4 are calcined at 750°C for 1 hour in a roller kiln under an argon atmosphere to perform high-temperature shaping, thereby repairing surface defects of the lithium iron phosphate particles, making their morphology more regular, and completing the degradation of positive electrode side reaction products after high-temperature discharge of lithium iron phosphate cells, finally obtaining lithium iron phosphate powder with less content of side reaction products to be replenished.

[0062] Please see Figure 4 The figure shows the specific capacity charge-discharge curve of the lithium iron phosphate material obtained in Example 2. As can be seen from the figure, the high-temperature discharge lithium iron phosphate cell cathode material that cannot be replenished with lithium was processed using the method of Example 2 to achieve a specific capacity of 152 mAh / g, indicating that most of the byproducts in the lithium iron phosphate cell cathode material were degraded and removed.

[0063] Comparative Example 1

[0064] Comparative Example 1 provides a method for degrading positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, comprising the following steps:

[0065] S1. Select high-temperature discharged cells from retired cells, disassemble the lithium iron phosphate electrode sheets directly in the air, and dry them by blowing air at 100°C for 2 hours to obtain dry lithium iron phosphate electrode sheets.

[0066] S2. The lithium iron phosphate electrode sheet obtained in step S1 is heated in a box furnace at 550°C in a nitrogen atmosphere for 2 hours, and then manually de-powdered to obtain lithium iron phosphate powder.

[0067] Comparative Example 2

[0068] Comparative Example 2 provides a method for degrading positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, comprising the following steps:

[0069] S1. Select high-temperature discharged cells from retired cells, disassemble the lithium iron phosphate electrode sheets directly in the air, and dry them by blowing air at 100°C for 2 hours to obtain dry lithium iron phosphate electrode sheets.

[0070] S2. The lithium iron phosphate electrode sheet obtained in step S1 is directly crushed by a pulverizer and then sieved to obtain lithium iron phosphate powder.

[0071] The lithium iron phosphate powders obtained in Examples 1-2 and Comparative Examples 1-2 were subjected to lithium replenishment and their specific capacity was tested. The results are shown in the table below.

[0072] Table 1. Specific capacity of lithium iron phosphate powder after lithium replenishment in Examples 1-2 and Comparative Examples 1-2

[0073] Capacity after lithium replenishment (mAh / g) Example 1 148 Example 2 152 Comparative Example 1 57.5 Comparative Example 2 23.4

[0074] As shown in Table 1, the lithium iron phosphate powder obtained in Examples 1 and 2 using the scheme of this application has a specific capacity of approximately 150 mAh / g after lithium replenishment. This indicates that the degradation effect of the positive electrode by-reaction products after high-temperature discharge of the lithium iron phosphate battery cell is good, avoiding their impact on the active material of lithium iron phosphate. However, the lithium iron phosphate powder obtained by Comparative Example 1, which only underwent one medium-temperature calcination, still contained a large number of by-reaction products, affecting the lithium replenishment effect and resulting in a lower specific capacity after lithium replenishment. In Comparative Example 2, only the positive electrode material of the lithium iron phosphate battery cell was dried and powdered, resulting in a higher content of impurities and by-reaction products, leading to a poor lithium replenishment effect and the lowest specific capacity after lithium replenishment.

[0075] In summary, this invention provides a method for degrading the positive electrode by-reaction products of lithium iron phosphate (LFP) battery cells after high-temperature discharge. First, precise disassembly is performed in an inert gas or vacuum environment to prevent the electrolyte on the disassembled LFP electrode from further producing other by-reaction substances. The LFP electrode is then subjected to low-temperature calcination to remove the electrolyte and adhesive. Next, it is crushed and sieved to separate the powder. The LFP powder is then soaked and washed to remove some of the water-soluble by-reaction products. Finally, it undergoes medium-temperature purification and high-temperature shaping. Medium-temperature purification allows residual by-products to react with carbon dioxide, achieving purification. High-temperature shaping repairs the corroded surface of the particles, making their morphology more regular. This process completes the degradation of the positive electrode by-reaction products after high-temperature discharge of the LFP battery cell, resulting in LFP powder with extremely low by-reaction product content, ensuring the subsequent repair and regeneration of the LFP powder. This invention utilizes a process involving precise disassembly, low-temperature calcination, coarse crushing and sieving, soaking and washing, medium-temperature purification, and high-temperature shaping to degrade the positive electrode byproducts of lithium iron phosphate cells after high-temperature discharge. This improves the lithium replenishment effect that hinders regeneration and repair due to the presence of byproducts after high-temperature discharge, enabling the regeneration and repair of lithium iron phosphate materials after high-temperature discharge disassembly. This provides a solution for the subsequent engineering of regeneration and repair of large quantities of retired lithium iron phosphate materials after high-temperature discharge.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for degrading positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge, characterized in that, Includes the following steps: S1. The failed lithium iron phosphate battery cell after high-temperature discharge is precisely disassembled into lithium iron phosphate positive electrode sheet, graphite negative electrode sheet and other auxiliary materials. S2. The lithium iron phosphate cathode sheet obtained in step S1 is subjected to low-temperature calcination to remove the electrolyte and adhesive. S3. The lithium iron phosphate cathode sheet processed in step S2 is crushed and sieved to separate the powder, and the powder is soaked and washed multiple times and then dried. S4. The lithium iron phosphate particles dried in step S3 are purified at medium temperature under a carbon dioxide atmosphere. S5. The lithium iron phosphate particles purified by temperature in step S4 are subjected to high-temperature shaping to complete the degradation of the positive electrode side reaction products after high-temperature discharge of the lithium iron phosphate battery cell and repair the corroded surface of the particles.

2. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S2, the low-temperature calcination temperature is 120-450℃, the time is 0.5-6h, and the calcination atmosphere is an oxygen-free atmosphere.

3. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S4, the temperature for the intermediate-temperature purification is 450–650°C, and the time is 6–12 hours.

4. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S5, the temperature of the high-temperature shaping is not lower than 650°C, the time is 4 to 6 hours, and the atmosphere of the high-temperature shaping is an inert gas atmosphere or a vacuum environment.

5. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, The low-temperature calcination is carried out in a kiln, the medium-temperature purification is carried out in a rotary kiln, and the high-temperature shaping is carried out in a roller kiln.

6. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S3, the soaking and washing use the same solvent, which is one or a mixture of deionized water and ethanol, and the soaking time is not less than 30 minutes; the drying method is one or more of vacuum drying, inert atmosphere drying, freeze drying, etc.

7. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S1, the atmosphere for precise disassembly is an inert gas atmosphere or a vacuum environment.

8. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 1, characterized in that, In step S3, the crushing process uses one or more of the following coarse crushers: impact mill, disc mill, cage pin mill, air jet mill, ball mill, sand mill, and grinding mill. During screening, the screen mesh size is 80 to 200 mesh, and the screening method includes one or more of the following: linear screen, drum screen, gyratory screen, and ultrasonic vibrating screen. After screening, lighter by-reaction products with different densities from lithium iron phosphate powder are removed by cyclone classification and pulse dust removal.

9. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 6, characterized in that, The soaking method is one or more of stirring and ultrasonication, and the washing method is one or more of vacuum filtration and centrifugation.

10. The method for degrading the positive electrode by-reaction products of lithium iron phosphate battery cells after high-temperature discharge according to claim 5, characterized in that, The kiln includes one or more of the following: roller kiln, rotary kiln, tunnel kiln, and pusher kiln.

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