A method for remediating retired lithium iron phosphate batteries

Abstract

This invention provides a method for repairing retired lithium iron phosphate batteries, comprising the following steps: measuring the voltage of the retired lithium iron phosphate batteries; grouping the batteries according to voltage, then disassembling the batteries by group to separate the positive electrode sheet, obtaining positive electrode powder; and repairing the positive electrode powder from different groups separately. This method for repairing retired lithium iron phosphate batteries overcomes the interference caused by the presence of lithium fluoride in the positive electrode powder during ICP analysis of the positive electrode powder in existing technologies, thus avoiding defects such as insufficient or excessive lithium replenishment and improving the performance of lithium iron phosphate repair.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling, and in particular relates to a method for repairing retired lithium iron phosphate batteries. Background Technology

[0002] Currently, the main methods for recycling the cathode material from retired lithium iron phosphate batteries or the cathode scraps from the lithium iron phosphate battery production process include wet recycling and high-temperature solid-phase repair / regeneration. Among them, wet recycling mainly uses a sulfuric acid system to dissolve the cathode sheet to recover lithium salts, which has disadvantages such as complex processes and long production cycles.

[0003] In high-temperature solid-state remediation / regeneration technology, the recovery of cathode powder is crucial, and the main methods include mechanical crushing recovery, organic solvent dissolution, and heating separation. ICP testing is then used to determine the molar ratio of lithium, iron, and phosphorus in the recovered cathode powder. The molar ratio is then adjusted to a range such as 1.02:1:1 by adding lithium, iron, and phosphorus sources. Finally, high-temperature solid-state remediation is performed [Yang Shenglong, Liu Kui. Regeneration of Waste Lithium Iron Phosphate Cathode Materials [C] / / The 4th National Conference on New Energy and Chemical New Materials and the National Symposium on Energy Conversion and Storage Materials, 2019].

[0004] Due to limitations in the recycling process, the positive electrode powder cannot completely eliminate the impact of lithium fluoride generated by electrolyte decomposition. This portion of lithium will appear in the lithium element test results during ICP detection, making it impossible to distinguish whether it is lithium from lithium iron phosphate or lithium fluoride. However, lithium fluoride cannot be fully utilized through high-temperature solid-phase repair / regeneration technology, as it is an inactive lithium, which adversely affects the subsequent high-temperature repair process and the performance of repaired lithium iron phosphate. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for repairing retired lithium iron phosphate batteries. By measuring the voltage of retired lithium iron phosphate batteries, the cathode powder is classified and repaired. Unlike existing methods, this method does not require elemental analysis of the cathode powder, thus avoiding interference from lithium fluoride on the content of elements such as lithium and improving the performance of lithium iron phosphate repair.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for rehabilitating retired lithium iron phosphate batteries includes the following steps:

[0008] (1) Measure the voltage of retired lithium iron phosphate batteries;

[0009] (2) Group the batteries in step (1) according to voltage, and then disassemble them according to group to separate the positive electrode sheet and obtain positive electrode powder;

[0010] (3) Repair the different groups of positive electrode powder in step (2) to obtain repaired lithium iron phosphate.

[0011] The principle of the repair method in this invention is as follows: the voltage of a battery is mainly determined by the types of positive and negative electrode materials. Based on this, the voltage of retired lithium iron phosphate batteries is first measured, then they are grouped and disassembled to obtain positive electrode powder at different voltages. Finally, repair is performed. Repair methods include, but are not limited to, high-temperature solid-state repair by supplementing lithium sources or direct high-temperature heating repair. Other methods that can restore the active lithium content in the positive electrode powder can also be used. The repair method in this invention controls the type of positive electrode powder from the source, overcoming the interference of inactive lithium such as lithium fluoride when using ICP testing to test the elemental content in the positive electrode powder, avoiding defects such as insufficient or excessive lithium supplementation, and improving the performance of lithium iron phosphate repair.

[0012] In this invention, the method for separating the positive electrode in step (2) is not specifically limited. Any method commonly used by those skilled in the art is applicable to this invention.

[0013] In this invention, the method for obtaining positive electrode powder in step (2) is not specifically limited. It can be to crush the positive electrode sheet and sieve it to obtain positive electrode powder, or to heat-treat the positive electrode sheet to obtain positive electrode powder. Any method commonly used by those skilled in the art is applicable to this invention. For example, it can be the following method: discharge the battery, disassemble the battery case, separate the positive electrode sheet, separator and negative electrode sheet, dry the positive electrode sheet, crush and sort it to obtain positive electrode powder.

[0014] Furthermore, in step (2), the batteries are grouped according to the voltage gradient based on the measured voltage, and the type of positive electrode powder is determined based on the group. Then, the repair is carried out. This can improve the repair efficiency while ensuring the repair performance. The voltage gradient of the batteries in the same group can be 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1V, etc. If the voltage gradient is set too large, the difference between the positive electrode powders will be large, which is not conducive to repair. If the voltage gradient is set too small, the production efficiency will be low, which is not conducive to industrialization and promotion.

[0015] Furthermore, in step (2), the batteries are grouped according to a voltage gradient of 0.5V based on the measured voltage. Grouping the batteries according to a 0.5V voltage gradient helps to balance the differences between cathode powders and production efficiency.

[0016] Furthermore, in step (2), the batteries are divided into groups A, B, C, D, E, and F according to their voltage, where the voltage of group A is V. A , 0≤V A ≤0.5V, Group B voltage is V B 0.5V < V B ≤1V, the voltage of group C is V C1V < V C ≤1.5V, the voltage of group D is V D 1.5V < V D ≤2V, the voltage of group E is V E 2V < V E ≤3V, the voltage of group F is V F V F >3V.

[0017] Furthermore, the specific operation method for repairing the cathode powder in step (3) includes: mixing the cathode powder with the lithium source, first heating it to 350-450℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, or 450℃, and holding it at that temperature for 1-3 hours, for example, 1 hour, 1.2 hours, 1.5 hours, or 1.8 hours. 2h, 2.3h, 2.5h, 2.7h, 3h, then raise the temperature to 680-780℃, for example, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, and hold for 1-5h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h.

[0018] Preferably, the specific operation method for replenishing lithium to the positive electrode powder in step (3) includes: mixing the positive electrode powder with the lithium source, first heating to 380-430℃ and holding for 1.5-2.5h, then heating to 700-730℃ and holding for 2-3h.

[0019] Furthermore, the repair of the positive electrode powder in step (3) is carried out under the protection of an inert gas, which can be nitrogen, argon, helium, etc.

[0020] Further, the lithium source includes one or more combinations of lithium carbonate, lithium hydroxide, lithium acetate, or lithium oxalate; preferably, the lithium source is lithium hydroxide and / or lithium oxalate.

[0021] Furthermore, the amount of lithium source used is 0.5%-10% of the weight of the cathode powder; for example, it can be 0.5%, 0.7%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 7%, 9% and 10%, etc.

[0022] Preferably, the amount of lithium source used is 2%-6% of the weight of the cathode powder; more preferably, the amount of lithium source used is 3%-5% of the weight of the cathode powder. The amount of lithium source used can be determined by experimentation using methods such as the controlled variable method to find the optimal amount of lithium replenishment.

[0023] As a further preferred technical solution of the present invention, the method includes the following steps:

[0024] (1) Measure the voltage of retired lithium iron phosphate batteries and group them according to the voltage gradient of 0.5V;

[0025] (2) Disassemble the grouped batteries, separate the positive electrode sheet, and obtain positive electrode powder;

[0026] (3) The cathode powder obtained from different groups is mixed with a lithium source. Under an inert atmosphere, the temperature is first raised to 380-430℃ and kept for 1.5-2.5h, then raised to 700-730℃ and kept for 2-3h to obtain repaired lithium iron phosphate.

[0027] The lithium source includes lithium hydroxide and / or lithium oxalate, and the amount used is 3%-5% of the weight of the cathode powder.

[0028] Compared with existing technologies, the remediation method for decommissioned lithium iron phosphate described in this invention has the following advantages:

[0029] (1) The repair method described in this invention classifies the positive electrode powder from the source by measuring the voltage of retired lithium iron phosphate batteries, and then seeks the appropriate amount of lithium replenishment by means of controlled variable method, which overcomes the interference caused by the presence of lithium fluoride formed by electrolyte decomposition in the positive electrode powder during ICP testing in the prior art, avoids defects such as insufficient or excessive lithium replenishment, and improves the performance of repairing lithium iron phosphate.

[0030] (2) The repair method described in this invention does not require elemental analysis of the positive electrode powder, which reduces the limitations of the testing equipment, especially for manufacturers or research institutions that do not have ICP testers, shortens the testing cycle, improves production efficiency, and is conducive to promoting industrialization. Detailed Implementation

[0031] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0032] The present invention will be described in detail below with reference to the embodiments.

[0033] Example 1

[0034] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0035] (1) Select a 0.02V battery pack, disassemble the battery case, separate the positive electrode plate, dry the positive electrode plate directly, cut it into small pieces of 3*3cm, crush it, pass it through a 200-mesh sieve, and the material that passes through the sieve is the positive electrode powder;

[0036] (2) Under nitrogen protection, the temperature is first raised to 350℃ and held for 1 hour, then raised to 750℃ and held for 1 hour, and then cooled naturally to 20℃ to obtain repaired lithium iron phosphate.

[0037] The discharge specific capacity of lithium iron phosphate at 0.1C was 146.6 mAh / g, and the discharge specific capacity after 100 cycles was 144.5 mAh / g.

[0038] During the discharge process of a lithium iron phosphate battery, lithium ions are extracted from the graphite negative electrode, enter the electrolyte, pass through the separator, migrate to the surface of the lithium iron phosphate crystal through the electrolyte, and then re-embed into the lithium iron phosphate lattice. As a result, the battery voltage decreases and the lithium ion content in the positive electrode increases. Therefore, in this embodiment, the positive electrode powder can achieve good repair results by directly performing high-temperature solid-phase repair without adding a lithium source.

[0039] Example 2

[0040] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0041] (1) Select a 0.02V battery pack, disassemble the battery case, separate the positive electrode plate, dry the positive electrode plate directly, cut it into small pieces of 3*3cm, crush it, pass it through a 200-mesh sieve, and the material that passes through the sieve is the positive electrode powder;

[0042] (2) Weigh out lithium carbonate and dry mix it with the cathode powder. The mass of lithium carbonate is 0.5% of the mass of the cathode powder. Then, under nitrogen protection, heat it to 350℃ and keep it at that temperature for 1 hour. Then heat it to 750℃ and keep it at that temperature for 1 hour. Then cool it down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0043] The specific discharge capacity of lithium iron phosphate at 0.1C was 147.1 mAh / g, and the specific discharge capacity after 100 cycles was 146.3 mAh / g.

[0044] Example 3

[0045] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0046] (1) Select a 1.7V battery pack, disassemble the battery case, separate the positive electrode plate, clean the positive electrode plate with DMC, dry it, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0047] (2) Weigh out lithium carbonate and dry mix it with the cathode powder. The mass of lithium carbonate is 3% of the mass of the cathode powder. Then, under nitrogen protection, heat it to 360℃ and keep it at that temperature for 2 hours. Then heat it to 730℃ and keep it at that temperature for 1 hour. Then cool it down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0048] The specific discharge capacity of the restored lithium iron phosphate at 0.1C was 154.9 mAh / g, and the specific discharge capacity after 100 cycles was 152.7 mAh / g.

[0049] Example 4

[0050] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0051] (1) Select a 0.9V battery pack, disassemble the battery case, separate the positive electrode plate, clean the positive electrode plate with DMC, dry it, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0052] (2) Weigh out lithium carbonate and wet mix it with positive electrode powder. The mass of lithium carbonate is 2% of the mass of positive electrode powder. Then, under nitrogen protection, first heat up to 380℃ and keep it at that temperature for 2 hours, then continue to heat up to 730℃ and keep it at that temperature for 2 hours, and then cool down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0053] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 155.6 mAh / g, and the discharge specific capacity after 100 cycles was 154.3 mAh / g.

[0054] Example 5

[0055] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0056] (1) Select a 2.3V battery pack, disassemble the battery case, separate the positive electrode plate, clean the positive electrode plate with DMC, dry it, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0057] (2) Weigh out lithium hydroxide monohydrate and wet mix it with the positive electrode powder. The mass of lithium hydroxide monohydrate is 8% of the mass of the positive electrode powder. Then, under nitrogen protection, first heat up to 350℃ and keep it at that temperature for 1 hour, then continue to heat up to 750℃ and keep it at that temperature for 1 hour, and then cool down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0058] The discharge specific capacity of lithium iron phosphate at 0.1C was 146.0 mAh / g, and the discharge specific capacity after 100 cycles was 144.8 mAh / g.

[0059] Example 6

[0060] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0061] (1) Select a 1.2V battery pack, disassemble the battery case, separate the positive electrode plate, clean the positive electrode plate with DMC, dry it, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0062] (2) Weigh out lithium hydroxide monohydrate and wet mix it with the positive electrode powder. The mass of lithium hydroxide monohydrate is 3% of the mass of the positive electrode powder. Then, under nitrogen protection, first heat up to 350℃ and keep it at that temperature for 1 hour, then continue to heat up to 750℃ and keep it at that temperature for 1 hour, and then cool down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0063] The specific discharge capacity of lithium iron phosphate at 0.1C was 145.3 mAh / g, and the specific discharge capacity after 100 cycles was 142.9 mAh / g.

[0064] Example 7

[0065] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0066] (1) Select a 3.2V battery pack, disassemble the battery case, separate the positive electrode plate, clean the positive electrode plate with DMC, dry it, cut the positive electrode plate into small pieces of 3*3cm, crush it, pass it through a 200-mesh sieve, and the material that passes through the sieve is positive electrode powder.

[0067] (2) Weigh out lithium carbonate and wet mix it with positive electrode powder. The mass of lithium carbonate is 10% of the mass of positive electrode powder. Then, under nitrogen protection, first heat up to 350℃ and keep it at that temperature for 1 hour, then continue to heat up to 750℃ and keep it at that temperature for 1 hour, and then cool down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0068] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 155.6 mAh / g, and the discharge specific capacity after 100 cycles was 153.8 mAh / g.

[0069] Example 8

[0070] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0071] (1) Select 100 battery packs with a voltage range of 2.5-3V for disassembly, separate the positive electrode sheets, dry them directly, crush the positive electrode sheets, sieve them, take the sieve material and mix them evenly to obtain positive electrode powder;

[0072] (2) Weigh out lithium hydroxide monohydrate and wet mix it with positive electrode powder. The mass of lithium hydroxide monohydrate is 6% of the mass of positive electrode powder. A mixture of water and ethanol is used as a medium. Then dry it and heat it to 750°C under argon protection for 1 hour. Then cool it down naturally to 20°C to obtain repaired lithium iron phosphate.

[0073] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 145.2 mAh / g, and the discharge specific capacity after 100 cycles was 142.5 mAh / g.

[0074] Example 9

[0075] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0076] (1) Select 100 battery packs with a voltage range of 0-0.5V for disassembly, separate the positive electrode sheet, clean the positive electrode sheet with DMC, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0077] (2) Weigh out lithium acetate and dry mix it with the positive electrode powder. The mass of lithium acetate is 2.5% of the mass of the positive electrode powder. Then, under nitrogen protection, heat it to 400℃ and keep it at that temperature for 2.5 hours. Then heat it to 700℃ and keep it at that temperature for 3 hours. Then cool it down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0078] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 153.6 mAh / g, and the discharge specific capacity after 100 cycles was 150.5 mAh / g.

[0079] Example 10

[0080] This embodiment provides a method for remediating decommissioned lithium iron phosphate batteries, including the following steps:

[0081] (1) Select 100 battery packs with a voltage range of 0.5-1V for disassembly, separate the positive electrode sheet, clean the positive electrode sheet with DMC, cut it into small pieces of 3*3cm, crush it, and pass it through a 200-mesh sieve. The material that passes through the sieve is the positive electrode powder.

[0082] (2) Weigh out lithium acetate and dry mix it with the positive electrode powder. The mass of lithium oxalate is 3.5% of the mass of the positive electrode powder. Then, under nitrogen protection, first heat up to 450℃ and keep it at that temperature for 1.5h, then continue to heat up to 720℃ and keep it at that temperature for 2.5h, and then cool down naturally to 20℃ to obtain repaired lithium iron phosphate.

[0083] The specific discharge capacity of lithium iron phosphate at 0.1C was 148.6 mAh / g, and the specific discharge capacity after 100 cycles was 145.8 mAh / g.

[0084] Example 11

[0085] Compared with Example 4, the only difference is that the mass of lithium carbonate is 3% of the mass of the cathode powder, and all other operations are the same as in Example 4.

[0086] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 158.3 mAh / g, and the discharge specific capacity after 100 cycles was 156.8 mAh / g.

[0087] Example 12

[0088] Compared with Example 6, the only difference is that the mass of lithium hydroxide monohydrate is 1% of the mass of the cathode powder, and all other operations are the same as in Example 6.

[0089] The discharge specific capacity of lithium iron phosphate at 0.1C was 138.3 mAh / g, and the discharge specific capacity after 100 cycles was 134.2 mAh / g.

[0090] Example 13

[0091] Compared with Example 6, the only difference is that the mass of lithium hydroxide monohydrate is 2% of the mass of the cathode powder; all other operations are the same as in Example 6.

[0092] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 142.5 mAh / g, and the discharge specific capacity after 100 cycles was 141.3 mAh / g.

[0093] Example 14

[0094] Compared with Example 6, the only difference is that the mass of lithium hydroxide monohydrate is 4% of the mass of the cathode powder, and all other operations are the same as in Example 6.

[0095] The specific discharge capacity of the restored lithium iron phosphate at 0.1C was 152.9 mAh / g, and the specific discharge capacity after 100 cycles was 151.4 mAh / g.

[0096] Comparing the test results of Examples 6 and 12-14, it can be seen that the electrical performance of the repaired lithium iron phosphate is improved with the increase of lithium replenishment. This is because the cathode powder is effectively repaired with the increase of lithium source usage. Based on this principle, in order to balance repair cost and repair performance, the preferred lithium source usage at this voltage is 2%-4% of the cathode powder mass.

[0097] Comparative Example 1

[0098] This comparative example provides a method for repairing retired lithium iron phosphate batteries, which employs existing technologies and specifically includes the following steps:

[0099] (1) Using existing technology, the content of lithium, iron and phosphorus in the positive electrode powder was tested. The molar ratio of lithium, iron and phosphorus was adjusted to 1.02:1:1 by adding lithium carbonate, ferrous oxalate and diammonium hydrogen phosphate, and ball milling for 5 hours.

[0100] (2) Sintering at 750°C for 8 hours in an argon atmosphere yielded repaired lithium iron phosphate.

[0101] The discharge specific capacity of lithium iron phosphate at 0.1C was 130mAh / g, and after 100 cycles, the discharge specific capacity was 110mAh / g.

[0102] Comparative Example 2

[0103] Compared with Example 2, the only difference is that the content of lithium, iron and phosphorus in the positive electrode powder was tested, and the molar ratio of lithium, iron and phosphorus was adjusted to 1.06:1:1 by adding lithium carbonate, ferrous oxalate and diammonium hydrogen phosphate. All other conditions were the same as in Example 2.

[0104] The repaired lithium iron phosphate showed a discharge specific capacity of 127.2 mAh / g at 0.1C, and a discharge specific capacity of 114.3 mAh / g after 100 cycles.

[0105] Comparative Example 3

[0106] Compared with Example 3, the only difference is that ICP testing was used to test the lithium, iron and phosphorus content in the cathode powder, and the molar ratio of lithium, iron and phosphorus was adjusted to 1.02:1:1 by adding lithium carbonate, ferrous oxalate and diammonium hydrogen phosphate. All other conditions were the same as in Example 3.

[0107] The discharge specific capacity of the restored lithium iron phosphate at 0.1C was 130.1 mAh / g, and the discharge specific capacity after 100 cycles was 126.2 mAh / g.

[0108] Comparative Example 4

[0109] Compared with Example 4, the only difference is that the content of lithium, iron and phosphorus in the positive electrode powder was tested, and the molar ratio of lithium, iron and phosphorus was adjusted to 1.02:1:1 by adding lithium carbonate, ferrous oxalate and diammonium hydrogen phosphate. All other conditions were the same as in Example 4.

[0110] The discharge specific capacity of lithium iron phosphate at 0.1C was 117.5 mAh / g, and the discharge specific capacity after 100 cycles was 103.3 mAh / g.

[0111] Comparative Example 5

[0112] Compared with Example 8, the only difference is that the content of lithium, iron and phosphorus in the positive electrode powder was tested, and the molar ratio of lithium, iron and phosphorus was adjusted to 1.02:1:1 by adding lithium carbonate, ferrous oxalate and diammonium hydrogen phosphate. All other conditions were the same as in Example 8.

[0113] The specific discharge capacity of the restored lithium iron phosphate at 0.1C was 124.5 mAh / g, and the specific discharge capacity after 100 cycles was 116.2 mAh / g.

[0114] Comparing the test results of Example 2 with Comparative Example 2, Example 3 with Comparative Example 3, Example 4 with Comparative Example 4, and Example 8 with Comparative Example 5, it can be seen that the repair effect of the repair method in this invention is significantly better than that of the prior art. This is because although the prior art can repair retired lithium iron phosphate by adjusting the lithium, iron, and phosphorus content through elemental analysis, the elemental detection results are affected by the interference of inactive lithium in the cathode powder. The repaired lithium iron phosphate obtained based on the detection results usually cannot achieve the expected repair effect, which is not conducive to improving the performance of repaired lithium iron phosphate. However, the repair method in this invention can accurately reflect the content of active components of effective elements in the cathode by measuring the battery voltage, avoiding the interference of inactive components. Therefore, the repaired lithium iron phosphate obtained by repairing based on voltage measurement results in this invention has better electrochemical performance.

[0115] Comparing the test results of Examples 3, 4, 6, and 11, it can be seen that when the positive electrode powder of batteries within a certain voltage difference range is repaired using the same or similar amount of lithium source, the repaired lithium iron phosphate has similar electrochemical performance. This is because the positive electrode sheets of batteries within a certain voltage difference range have similar active lithium content. Based on this principle, after mixing the positive electrode sheets of batteries within a certain voltage difference range, the same amount of lithium source is used for repair, which can greatly improve the repair efficiency and reduce the repair cost while ensuring that the repaired lithium iron phosphate performance meets the repair requirements.

[0116] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for remediating retired lithium iron phosphate batteries, characterized in that, Includes the following steps: (1) Measure the voltage of retired lithium iron phosphate batteries; (2) Group the batteries in step (1) according to voltage, and then disassemble them according to group to separate the positive electrode sheet and obtain positive electrode powder; (3) Repair the different groups of positive electrode powder in step (2) to obtain repaired lithium iron phosphate; In step (2), the batteries are divided into groups A, B, C, D, E, and F according to the measured voltage and voltage gradient. The voltage of group A is V. A , 0≤V A ≤0.5V, Group B is V B 0.5V < V B ≤1V, the voltage of group C is V C 1V < V C ≤1.5V, the voltage of group D is V D 1.5V < V D ≤2V, the voltage of group E is V E 2V < V E ≤3V, the voltage of group F is V F V F >3V.

2. The repair method according to claim 1, characterized in that, The repair of the positive electrode powder in step (3) is carried out under the protection of inert gas.

3. The repair method according to claim 1, characterized in that, The specific operation method for repairing the positive electrode powder in step (3) includes: mixing the positive electrode powder with the lithium source, first heating to 350-450℃ and holding for 1-3 hours, then heating to 680-780℃ and holding for 1-5 hours.

4. The repair method according to claim 3, characterized in that, The lithium source includes one or more combinations of lithium carbonate, lithium hydroxide, lithium acetate, or lithium oxalate.

5. The repair method according to claim 3, characterized in that, The amount of lithium source used is 0.5%-10% of the weight of the cathode powder.

6. The repair method according to claim 1, characterized in that, The method includes the following steps: (1) Measure the voltage of retired lithium iron phosphate batteries and group them according to the voltage gradient of 0.5V; (2) Disassemble the grouped batteries, separate the positive electrode sheet, and obtain positive electrode powder; (3) The cathode powder obtained from different groups is mixed with a lithium source. Under an inert atmosphere, the temperature is first raised to 380-430℃ and kept for 1.5-2.5h, then raised to 700-730℃ and kept for 2-3h to obtain repaired lithium iron phosphate. The lithium source includes lithium hydroxide and / or lithium oxalate, and the amount used is 3%-5% of the weight of the cathode powder.