A method for coupling regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries

Abstract

The invention discloses a method for coupling regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries. The method comprises the following steps: pyrolyzing the positive and negative plates of the waste lithium iron phosphate batteries, and then recovering the lithium iron phosphate active materials by magnetic separation or flotation separation; mixing the lithium iron phosphate active materials with a lithium source, a trivalent iron compound, and an organic carbon source, and ball milling them to obtain a mixture. The mixture is roasted under a protective atmosphere to obtain regenerated and repaired lithium iron phosphate. The method couples the negative electrode with the positive active materials for regeneration and repair during the regeneration and repair of the positive electrode materials of waste lithium iron phosphate batteries, and obtains a lithium iron phosphate positive electrode material with good electrochemical performance. Compared with the existing regeneration and repair, the method omits the complicated impurity removal process, has a lower cost, and provides the possibility for large-scale industrial regeneration and repair of waste lithium iron phosphate active materials.

Description

Technical Field

[0001] The present invention relates to a method for regenerating and repairing positive electrode active materials in waste lithium iron phosphate batteries, and in particular to a method for coupled regeneration and repairing of positive and negative electrode active materials in waste lithium iron phosphate batteries, belonging to the field of secondary resource recovery and utilization. Background Art

[0002] Since waste lithium batteries contain toxic and harmful electrolytes and heavy metal elements, if they are not properly handled, they will cause serious harm to the environment and human health. On the other hand, waste lithium batteries contain valuable metals such as copper, aluminum, iron, lithium, etc., which are an indispensable secondary resource. Therefore, the recycling and utilization of waste lithium batteries has become one of the key issues of recent research.

[0003] The recycling and utilization of waste lithium-ion batteries can be divided into battery collection, pretreatment, active material separation, valuable component extraction and positive electrode active material regeneration and repair. Since the positive electrode active material is the most valuable substance in waste lithium batteries, the regeneration and repair of the positive electrode active material has become one of the most important links in the recycling and utilization of waste lithium batteries. At present, the main methods for the regeneration and repair of positive electrode active materials are hydrometallurgy and pyrometallurgy. Hydrometallurgy uses strong acid or organic acid to leach the valuable components in the positive electrode active material into the solution, and then removes impurities, precipitates and purifies the solution in steps, and finally obtains the precursor and then supplements the corresponding missing metal elements for regeneration and repair. Pyrometallurgy uses a high-temperature furnace to smelt the valuable components in the waste lithium batteries at high temperature, obtains a metal mixture after removing organic impurities, and then uses acid leaching to purify the metal material, and finally obtains the precursor for regeneration and repair. Chinese patent CN114566727A discloses that waste lithium iron phosphate battery materials are placed in the air for burning, and after removing other organic impurities such as carbon, lithium source, iron source, phosphorus source, carbon source, aluminum source and activator are added for ball milling, and then the lithium iron phosphate positive electrode active material is regenerated and repaired. This process is relatively complicated, and the process parameters in this process are difficult to control, and it is difficult to use in industrial production. Chinese patent CN110828887A discloses that a certain amount of phosphorus source, lithium source and iron source are added to the lithium iron phosphate positive electrode active material obtained by manual sorting, and then sintered and regenerated and repaired. Manual disassembly in this process is difficult to achieve in industrial production, so this process is only suitable for small-scale lithium battery recycling. Although many scholars have conducted extensive research on the regeneration and repair of waste lithium iron phosphate batteries, there are still disadvantages such as long regeneration and repair process and high cost. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for coupled regeneration and repair of positive and negative active materials in waste lithium-ion batteries. The method can turn the positive and negative electrode materials in waste lithium iron phosphate batteries into treasures, and obtain lithium iron phosphate positive electrode materials with good electrochemical properties through coupled regeneration of the two. Compared with the existing regeneration and repair process, this method omits the complex and expensive impurity removal process, and has a low cost, which provides the possibility for large-scale industrial regeneration and repair of waste lithium iron phosphate active materials.

[0005] In order to achieve the above technical objectives, the present invention provides a method for coupled regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries. The method comprises the following steps: pyrolyzing the positive and negative electrodes of the waste lithium iron phosphate batteries, and then recovering the lithium iron phosphate active materials by magnetic separation or flotation separation; mixing the lithium iron phosphate active materials with raw materials including a lithium source, a trivalent iron compound and an organic carbon source, and ball milling them to obtain a mixture, which is then calcined under a protective atmosphere.

[0006] The technical solution of the present invention first pyrolyzes the pole pieces (including positive pole pieces and negative pole pieces) of waste lithium iron phosphate batteries to allow the active materials on the positive and negative poles to fall off better. After the active materials are collected, flotation separation or magnetic separation is used to separate the positive electrode active materials and the negative electrode active materials. The main component of the positive electrode active material is lithium iron phosphate, and it also contains graphite carbon and a small amount of amorphous carbon material and a binder. After analysis, it can be seen that the main component of the obtained lithium iron phosphate active material is lithium iron phosphate with an incomplete crystal structure, and the other components are organic matter, amorphous carbon and negative electrode graphite carbon adhering to the surface of the positive electrode active material during the recovery process. Based on the composition characteristics of the recovered lithium iron phosphate active material, the technical solution of the present invention adds an appropriate amount of trivalent iron compound as an oxidant to adjust the carbon content of the regenerated and repaired positive electrode material, and a small amount of unoxidized negative electrode graphite carbon can be used as a conductive agent in the regenerated and repaired lithium iron phosphate material to increase the conductivity of the regenerated and repaired lithium iron phosphate material. At the same time, by introducing an appropriate amount of lithium source and organic carbon source to regenerate and repair the lithium iron phosphate with incomplete crystal structure, the conductivity and specific capacity of the repaired and regenerated positive electrode active material are greatly improved.

[0007] The technical solution of the present invention is key to the regeneration and repair process of the failed lithium iron phosphate in the waste lithium iron phosphate battery, which is reflected in the coupling effect between the externally added organic carbon source and the small amount of organic carbon source remaining in the recovered lithium iron phosphate active material, the negative electrode graphite carbon source, the externally added trivalent iron compound, and the trivalent iron on the surface of the recovered positive electrode active material. The coupling effect is mainly reflected in that in the regeneration and repair process, in the initial stage of temperature rise and roasting (less than 300°C), the organic carbon source in the mixed raw material will flow under the action of heat, and can be better dispersed or coated on the surface of the trivalent iron compound and the failed lithium iron phosphate. As the temperature further increases (300-400°C), the organic carbon source begins to pyrolyze to produce gas and amorphous carbon. At this time, the trivalent iron compound, which is oxidizing, begins to oxidize part of the carbon at the final regeneration and repair temperature (600-800°C). The trivalent iron compound oxidizes the excess pyrolytic carbon and negative electrode graphite, and the amorphous carbon coated on the surface of the lithium iron phosphate is further carbonized to form a conductive layer with high stability. At the same time, the lithium source enters to supplement the missing lithium in the waste lithium iron phosphate, and reacts with the iron introduced by the trivalent iron compound to form new lithium iron phosphate. Therefore, the regenerated and repaired lithium iron phosphate finally obtained has both pyrolytic carbon as the coated carbon and negative electrode graphite as the conductive "bridge", and the carbon content is also controlled within a reasonable range. The technical solution of the present invention effectively solves the technical problem that the negative electrode active material, organic matter and pyrolytic carbon will inevitably be incorporated into the positive electrode active material during the recycling of waste lithium iron phosphate batteries, resulting in separation difficulties. The negative electrode graphite remaining in the lithium iron phosphate positive electrode material is cleverly used as a conductive bridge after regeneration and repair. At the same time, a high-valent iron compound is added to adjust the carbon content in the lithium iron phosphate after regeneration and repair, so that the negative electrode active material and the positive electrode active material can be coupled under certain conditions to be regenerated and repaired to become lithium iron phosphate with excellent electrochemical performance, providing an economical and simple recycling method for efficient, green and low-cost industrial recycling of lithium iron phosphate.

[0008] As a preferred solution, the pyrolysis conditions are: nitrogen atmosphere, temperature of 500-600° C., and time of 1-3 h.

[0009] As a preferred solution, the impurity mass percentage content of graphite carbon and amorphous carbon contained in the lithium iron phosphate active material is 5-50%, the less the impurity carbon content, the better the consistency of the positive electrode active material after regeneration and repair, and the more the impurity carbon content, the worse the consistency of the positive electrode active material after regeneration and repair. The impurity mass percentage content of graphite and carbon contained in the lithium iron phosphate active material is further preferably 15-35%.

[0010] As a preferred solution, the molar ratio of carbon to iron in the mixture is 0.9:1-4:1, the molar ratio of organic carbon to inorganic carbon is 0.1:1-10:1, and the molar ratio of lithium to iron is 0.9:1-1.1:1. As a more preferred solution, the molar ratio of carbon to iron in the mixture is 1.5:1-2.5:1, the molar ratio of organic carbon to inorganic carbon is 0.8:1-2:1, and the molar ratio of lithium to iron is 0.95:1-1.05:1. C, Fe and Li in the mixture need to be controlled within an appropriate range to ensure the best repair effect, and sometimes phosphate can be appropriately supplemented as needed.

[0011] As a preferred solution, 0.1-5% by mass of V2O5 is added to the mixture. To ensure the regeneration coupling repair effect, an appropriate amount of transition metal vanadium oxide can be added to the mixture to dope the lithium iron phosphate positive electrode active material produced during the regeneration repair process with transition metals to improve the electrochemical properties of the lithium iron phosphate positive electrode active material after regeneration repair.

[0012] As a preferred solution, the calcination conditions are: a heating rate of 1 to 30°C / min, a temperature of 550 to 900°C, and a time of 8 to 24 hours. Further preferred calcination conditions are: a heating rate of 5 to 20°C / min, a temperature of 600 to 800°C, and a time of 9 to 12 hours. If the temperature is too low, it is not conducive to the lithium replenishment process of regeneration and repair and the crystallization process of the repaired lithium iron phosphate material; if the temperature is too high, the crystallized lithium iron phosphate will sinter together to form a lithium iron phosphate material with larger particles, which is not conducive to the improvement of electrochemical performance. Calcination is carried out in an inert gas atmosphere (such as argon and / or nitrogen), and cannot be carried out in a reducing atmosphere (such as an atmosphere containing hydrogen and / or carbon monoxide).

[0013] The positive electrode sheet and the negative electrode sheet of the waste lithium iron phosphate battery used in the present invention are obtained by conventional physical methods in the prior art: specifically, the waste lithium iron phosphate battery is crushed, and the electrolyte contained in the crushed waste lithium battery is removed, and then the heavy metal shell and the light diaphragm-like material are selected by physical sorting.

[0014] As a preferred solution, the organic carbon source includes at least one of glucose, sucrose, benzene, and esters; benzenes are mainly small organic molecules containing benzene rings, such as toluene, xylene, benzoic acid, etc., and lipids are mainly small organic molecules containing ester groups, such as ethyl acetate, etc. The preferred organic carbon source can generate a coated carbon layer on the surface of the lithium iron phosphate material during the roasting process.

[0015] As a preferred solution, the trivalent iron compound includes at least one of Fe2O3, FePO4, and Fe3O4. Preferably, the trivalent iron compound acts as an oxidant, mainly oxidizing carbon, and acts as an iron source, mainly reacting with a lithium source and phosphate to form a new lithium iron phosphate active material.

[0016] As a preferred solution, the lithium source includes at least one of LiH2PO4, Li2CO3, and LiOH.

[0017] The lithium iron phosphate positive electrode active material recovered by the present invention is deactivated lithium iron phosphate containing a relatively high carbon content (the carbon comes from the amorphous carbon produced during the pyrolysis process and the graphite carbon of the negative electrode). The content of copper, aluminum and other metals in the pole powder obtained by catalytic pyrolysis is very low and can be almost ignored. Generally speaking, it is difficult to efficiently and thoroughly separate the negative electrode graphite carbon from the lithium iron phosphate positive electrode active material due to the existing conventional separation means. The technical solution of the present invention has lower requirements for the separation means of the lithium iron phosphate positive electrode active material, and the graphite carbon and organic carbon remaining in the deactivated lithium iron phosphate positive electrode active material can be fully utilized. The lithium iron phosphate active material with excellent electrochemical performance can be obtained by coupling the regeneration and repair technology.

[0018] In the lithium iron phosphate positive and negative active material coupled regeneration and repair technology of the present invention, the carbon content in the regeneration and repair raw material can be as high as 50%, and the carbon can be the carbon contained in organic matter, the pyrolytic carbon produced during the pyrolysis process, and the negative electrode graphite carbon.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1) The present invention repairs the positive electrode active material of waste lithium iron phosphate batteries, avoids the complicated carbon impurity removal process, reduces secondary pollution in the recycling process, reduces the recycling process flow, and reduces the recycling cost.

[0021] 2) In the process of regenerating and repairing waste lithium iron phosphate batteries, the present invention utilizes positive electrode materials, negative electrode materials, organic carbon sources and iron oxide sources for coupled regeneration and repair, thereby obtaining lithium iron phosphate positive electrode materials with good electrochemical properties, so that the negative electrode materials and positive electrode materials in the waste lithium batteries can be turned into treasures and recycled.

[0022] 3) The regeneration and repair method of the present invention is simple, has low energy consumption, and the obtained positive electrode active material has excellent electrochemical properties and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a cycle performance diagram of lithium iron phosphate after coupled regeneration repair in Example 1;

[0024] Figure 1Figure a is the charge and discharge cycle diagram of a half-battery composed of lithium iron phosphate positive electrode active material after coupled regeneration and repair. Figure 1 b and c are the charge-discharge cycle diagrams of the half-cell composed of the regenerated and repaired lithium iron phosphate positive electrode active material at different discharge rates; Figure 1 Figure a shows that the discharge capacity of lithium iron phosphate after regeneration and repair at 0.2C is 161.37mAh / g, and the discharge specific capacity after 100 cycles is 157.89mAh / g, with a capacity retention rate of 97.29%. After coupled regeneration and repair, its cycle performance and specific capacity can approach or reach the standards of new lithium iron phosphate positive electrode active materials; Figure 1 Figures b and c show that the discharge capacity of the regenerated and repaired lithium iron phosphate is 160.51 mAh / g at 0.5C, 142.75 mAh / g at 2C, and 122.36 mAh / g at 5C, and the regenerated and repaired lithium iron phosphate material has a stable and long charge and discharge platform. Figure 2 This is a diagram of the electrochemical performance of lithium iron phosphate after coupled regeneration repair in Example 1;

[0025] Figure 2 Figures a to c are the cyclic voltammetry test results, EIS test results and EIS low-frequency region fitting results of waste lithium iron phosphate materials. Figure 2 The a in the figure shows that the waste iron phosphate has a stable redox peak, indicating that its cycle performance is good. The EIS test and the EIS low-frequency region fitting show that the electron transfer rate in the half-battery made of waste lithium iron phosphate active material is 2.79*10 -12 cm 2 S -1 ; This shows that the waste lithium iron phosphate positive electrode active material has good electrochemical performance, which is mainly because the waste lithium iron phosphate active material contains a large amount of carbon, which improves the electrochemical performance of the positive electrode active material; Figure 2 d~f are the cyclic voltammetry test results, EIS test results and EIS low-frequency region fitting results of the regenerated and repaired lithium iron phosphate material. Figure 2 The middle d shows that the regenerated and repaired iron phosphate has a stable redox peak, indicating that its cycle performance is good. The EIS test and EIS low-frequency region fitting show that the electron transfer rate in the half-cell made of the regenerated and repaired lithium iron phosphate active material is 5.55*10 -13 cm 2 S -1 ; It shows that the regenerated and repaired lithium iron phosphate positive electrode active material has good electrochemical properties.

[0026] Figure 3 The electron microscope and transmission electron microscope results of lithium iron phosphate after coupled regeneration repair in Example 1; Figure 3Figures a to c are the TEM test results of lithium iron phosphate active material after regeneration and repair. Figure 3 Figure d in the middle is the SEM test result of the positive electrode active material after regeneration and repair; Figure 3 Figures a to c show that the carbon coating on the surface of the regenerated and repaired lithium iron phosphate positive electrode active material is very uniform, and the regenerated and repaired lithium iron phosphate is completely crystallized, and the crystal structure information such as the interplanar spacing is not much different from that of the standard lithium iron phosphate; Figure 3 In figure d, we can see that the regenerated and repaired lithium iron phosphate contains a part of rod-shaped graphite. This part of the material is the graphite or organic carbon in the regenerated and repaired raw materials. The rod-shaped material can act as a bridge to increase the electrochemical properties of the regenerated and repaired lithium iron phosphate.

[0027] Figure 4 The XRD patterns of the positive electrode active material before and after the coupled regeneration repair in Example 1; Figure 4 This is the XRD diagram of the positive electrode active material before and after regeneration and repair. It can be seen from the figure that the crystal structure of the waste lithium iron phosphate positive electrode active material has been destroyed during long-term use, and the intensity and position of its various diffraction peaks have changed greatly compared with standard lithium iron phosphate. It can be seen from the figure that the crystal structure of the waste lithium iron phosphate positive electrode active material has been well repaired after coupled regeneration and repair, indicating that the regeneration and repair method proposed in the present invention can well repair the crystal defects of the waste lithium iron phosphate positive electrode active material. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0029] Example 1

[0030] In this embodiment, the method for repairing the positive and negative electrodes of waste lithium-ion batteries is as follows:

[0031] 1) The used lithium-ion batteries are crushed with electricity.

[0032] 2) Treat the electrolyte in the crushed waste lithium iron phosphate batteries, and use physical separation to select the diaphragm, shell and other materials therein after the treatment.

[0033] 3) The obtained waste lithium battery positive and negative electrode sheets are pyrolyzed (N2 atmosphere, 550°C, 2h), and a mixture of positive and negative electrode active materials with very little metal content is obtained after pyrolysis.

[0034] 4) A waste lithium iron phosphate positive electrode active material with a lithium iron phosphate content of about 85% was obtained by flotation. After detection and analysis, it was found that the main impurities in the waste lithium iron phosphate positive electrode active material were negative electrode graphite carbon, a small amount of carbon produced during the pyrolysis process, and a very small amount of fluorine-containing compounds.

[0035] 5) By adding appropriate amounts of Li2CO3, FePO4, C6H 12 O6, V2O5 make the molar ratio of elements in the mixed material after addition satisfy: Li:Fe=1:1; C:Fe=2:1; the molar ratio of organic carbon to inorganic carbon is 1:1; V2O5 accounts for 1% of the total material.

[0036] 6) The mixed materials were ball-milled in anhydrous ethanol solution at a speed of 700 rpm for 6 h, and then dried in a vacuum drying oven.

[0037] 7) The dried regenerated repair material is placed in a tubular furnace, high-purity argon is introduced, the temperature is raised to 650°C at a heating rate of 10°C / min, and calcined at 650°C for 11 hours to obtain the regenerated and repaired lithium iron phosphate positive electrode active material. The carbon content in the repaired lithium iron phosphate is 3.12%, which is similar to the carbon content of commercial lithium iron phosphate. The first discharge capacity at 0.2C is 161.37mAh / g, the discharge capacity after 100 cycles is 157.89 mAh / g, and the capacity retention rate is 97.29%. After coupled regeneration and repair, its cycle performance and specific capacity can approach or reach the standards of new lithium iron phosphate positive electrode active materials. The discharge capacity at 0.5C is 160.51mAh / g, the discharge capacity at 2C is 142.75mAh / g, and the discharge capacity at 5C is 122.36mAh / g ( Figure 1 ), which are almost the same as the new lithium iron phosphate positive electrode active material.

[0038] The electron transfer rate in the half-cell made of the positive electrode active material after coupling regeneration and repair is 5.55*10 -13 cm 2 S -1 The new standard of lithium iron phosphate positive electrode active material is achieved, and the particle surface morphology and crystal structure are well repaired ( Figures 2 to 4 ). And the incompletely oxidized graphite acts as a bridge in the regenerated and repaired lithium iron phosphate active material ( Figure 3 (d)

[0039] Example 2 (Comparative Example)

[0040] In this embodiment, the steps of coupling repair of the positive electrode active material are as follows:

[0041] The waste lithium-ion batteries are pretreated, and the pretreatment process is consistent with steps 1) to 3) in Example 1.

[0042] 4) The active material is separated by flotation to obtain positive electrode lithium iron phosphate powder containing about 30% negative electrode graphite.

[0043] 5) By adding appropriate amounts of Li2CO3, FePO4, and V2O5 (without adding an organic carbon source), the molar ratio of the elements in the mixed material after addition satisfies: Li:Fe=1:1; C:Fe=2:1; V2O5 accounts for 0.1% of the total material.

[0044] 6) The mixed materials were ball-milled in anhydrous ethanol solution at a speed of 700 rpm for 7 h, and then dried in a vacuum drying oven.

[0045] 7) The dried regenerated repair material is placed in a tubular furnace, high-purity argon is introduced, the temperature is raised to 650°C at a heating rate of 10°C / min, and calcined at 650°C for 12 hours to obtain the regenerated and repaired lithium iron phosphate positive electrode active material. The first discharge capacity of the repaired lithium iron phosphate at 0.1C is 70.30mAh / g, the discharge specific capacity after 100 cycles is 40.17mAh / g, and the capacity retention rate is 57.14%. After coupled regeneration and repair without the participation of organic carbon source, its cycle performance and specific capacity can be greatly different from those of the new lithium iron phosphate positive electrode active material. Therefore, the organic carbon source is a substance that must be added in the present invention.

[0046] Example 3 (Comparative Example)

[0047] In this embodiment, the steps of coupling repair of the positive electrode active material are as follows:

[0048] The waste lithium-ion batteries are pretreated, and the pretreatment process is consistent with steps 1) to 3) in Example 1.

[0049] 4) The active material is separated by flotation to obtain positive electrode lithium iron phosphate powder containing about 20% negative electrode graphite.

[0050] 5) By adding appropriate amount of Li2CO3, C6H 12 O6, V2O5 (without adding iron source) make the molar ratio of elements in the mixed material satisfy: Li:Fe=1:1; V2O5 accounts for 0.1% of the total material.

[0051] 6) The mixed materials were ball-milled in anhydrous ethanol solution at a speed of 700 rpm for 7 h, and then dried in a vacuum drying oven.

[0052] 7) The dried regenerated repair material is placed in a tubular furnace, high-purity argon is introduced, the temperature is raised to 650°C at a heating rate of 10°C / min, and calcined at 650°C for 12 hours to obtain the regenerated and repaired lithium iron phosphate positive electrode active material. The first discharge capacity of the repaired lithium iron phosphate at 0.1C is 71.32mAh / g, the discharge specific capacity after 100 cycles is 69.53mAh / g, and the capacity retention rate is 97.49%. In the coupled regeneration and repair experiment without the participation of trivalent iron, since the carbon content of the regenerated and repaired material cannot be regulated, its specific capacity is greatly affected and is very different from the new lithium iron phosphate positive electrode active material. Therefore, the trivalent iron source is a means of regulating the carbon content of the product required for the present invention.

[0053] Example 4

[0054] In this embodiment, the steps of coupling repair of the positive electrode active material are as follows:

[0055] The waste lithium-ion batteries are pretreated, and the pretreatment process is consistent with steps 1) to 3) in Example 1.

[0056] 4) The active material is separated by magnetic separation to obtain positive electrode lithium iron phosphate powder containing about 20% negative electrode graphite.

[0057] 5) By adding appropriate amounts of LiH2PO4, Fe2O3, C6H 12 O6, V2O5 make the molar ratio of elements in the mixed material after addition satisfy: Li:Fe=1.01:1; C:Fe=1.5:1; Fe:P=1:1; the molar ratio of organic carbon to inorganic carbon is 1.02:1; V2O5 accounts for 2% of the total material.

[0058] 6) The mixed materials were ball-milled in anhydrous ethanol solution at a speed of 700 rpm for 7 h, and then dried in a vacuum drying oven.

[0059] 7) The dried regenerated repair material is placed in a tubular furnace, high-purity argon is introduced, and the temperature is raised to 700°C at a heating rate of 20°C / min. The material is calcined at 700°C for 12 hours to obtain the regenerated and repaired lithium iron phosphate positive electrode active material. The first discharge capacity of the repaired lithium iron phosphate at 0.2C is 160.30mAh / g, and the discharge capacity after 100 cycles is 156.12mAh / g, with a capacity retention rate of 97.39%. After coupled regeneration and repair, its cycle performance and specific capacity can approach or reach the standards of new lithium iron phosphate positive electrode active materials. The discharge capacity at 0.5C is 159.71mAh / g, the discharge capacity at 2C is 141.23mAh / g, and the discharge capacity at 5C is 121.65mAh / g, which are almost the same as the new lithium iron phosphate positive electrode active material.

[0060] The electron transfer rate in the half-cell made of the positive electrode active material after coupling regeneration and repair is 6.31*10 -13 cm 2 S -1 It meets the new standards for lithium iron phosphate positive electrode active materials, and its surface particles and crystal structure have been well repaired.

[0061] Example 5

[0062] In this embodiment, the steps of coupling repair of the positive electrode active material are as follows:

[0063] The waste lithium-ion batteries are pretreated, and the pretreatment process is consistent with steps 1) to 3) in Example 1.

[0064] 4) The active material is separated by magnetic separation to obtain positive electrode lithium iron phosphate powder containing about 20% negative electrode graphite.

[0065] 5) By adding appropriate amounts of LiH2PO4, Fe2O3, polyvinyl alcohol, and V2O5, the molar ratio of the elements in the mixed material after addition is satisfied: Li:Fe=1.01:1; C:Fe=1.5:1; Fe:P=1:1; the molar ratio of organic carbon to inorganic carbon is 1.02:1; and V2O5 accounts for 1% of the total material.

[0066] 6) The mixed materials were ball-milled in anhydrous ethanol solution at a speed of 700 rpm for 7 h, and then dried in a vacuum drying oven.

[0067] 7) The dried regenerated repair material is placed in a tubular furnace, high-purity argon is introduced, and the temperature is raised to 650°C at a heating rate of 30°C / min. The material is calcined at 650°C for 12 hours to obtain the regenerated and repaired lithium iron phosphate positive electrode active material. The first discharge capacity of the repaired lithium iron phosphate at 0.2C is 159.15mAh / g, and the discharge capacity after 100 cycles is 156.12mAh / g, with a capacity retention rate of 98.06%. After coupled regeneration and repair, its cycle performance and specific capacity can approach or reach the standards of new lithium iron phosphate positive electrode active materials. The discharge capacity at 0.5C is 158.34mAh / g, the discharge capacity at 2C is 139.41mAh / g, and the discharge capacity at 5C is 122.12mAh / g, which are almost the same as the new lithium iron phosphate positive electrode active material.

[0068] The electron transfer rate in the half-cell made of the positive electrode active material after coupling regeneration and repair is 5.86*10 -13 cm 2 S -1It meets the new standards for lithium iron phosphate positive electrode active materials, and its surface particles and crystal structure have been well repaired.

[0069] The above-mentioned specific implementation modes are preferred examples of the present invention. Although they are relatively detailed, they cannot limit the claims of the present invention. Any changes, modifications, substitutions, combinations, and simplifications made using the technical contents disclosed by the present invention should be equivalent embodiments and do not deviate from the technical features of the present invention. They still belong to the scope of the technical features of the present invention and should be included in the protection scope of the present invention.

Claims

1. A method for coupling regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries, characterized in that: After pyrolyzing the positive and negative electrodes of the waste lithium iron phosphate battery, recovering the lithium iron phosphate active material by magnetic separation or flotation separation; mixing the lithium iron phosphate active material with raw materials including a lithium source, a trivalent iron compound and an organic carbon source and ball milling to obtain a mixture, and calcining the mixture under a protective atmosphere to obtain; The molar ratio of carbon to iron in the mixture is 0.9:1~4:1, the molar ratio of organic carbon to inorganic carbon is 0.1:1~10:1, and the molar ratio of lithium to iron is 0.9:1~1.1:1; the mass percentage content of graphite carbon and amorphous carbon impurities contained in the lithium iron phosphate active material is 5~50%; 0.1~5% of V2O5 is added to the mixture; the calcination conditions are: a heating rate of 1~30℃ / min, a temperature of 550~900℃, and a time of 8~24 hours.

2. The method for coupled regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries according to claim 1, characterized in that: The pyrolysis conditions are as follows: the pyrolysis atmosphere is nitrogen, the temperature is 500-600° C., and the time is 1-3 hours.

3. The method for coupled regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries according to claim 1, characterized in that: The organic carbon source includes at least one of glucose, sucrose, benzene, and esters; The trivalent iron compound includes at least one of Fe2O3, FePO4, and Fe3O4; The lithium source includes at least one of LiH2PO4, Li2CO3, and LiOH.

4. The method for coupled regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries according to claim 1, characterized in that: The molar ratio of carbon to iron in the mixture is 1.5:1-2.5:1, the molar ratio of organic carbon to inorganic carbon is 0.8:1-2:1, and the molar ratio of lithium to iron is 0.95:1-1.05:

1.

5. The method for coupled regeneration and repair of positive and negative active materials of waste lithium iron phosphate batteries according to claim 1, characterized in that: The calcination conditions are: a heating rate of 5-20°C / min, a temperature of 600-800°C, and a calcination time of 9-12 hours.

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