Method and reactor for synchronously separating and regenerating positive electrode and negative electrode of waste lithium iron phosphate battery

Abstract

The invention relates to a waste lithium iron phosphate battery positive and negative electrode synchronous separation and regeneration method and a reactor, and the regeneration method comprises the following steps: respectively placing a positive plate and a negative plate of a waste lithium iron phosphate battery into a reaction container, adding a reducing agent with a pH value of 8-12 into the reaction container, and supplementing a mixed aqueous solution of a lithium salt so as to respectively react with the positive plate and the negative plate, the two reaction containers are communicated, and a filter is arranged at the communication part; and after the reaction is finished, filtering and drying the product to obtain a copper foil, an aluminum foil and repaired graphite and lithium iron phosphate. According to the invention, simultaneous separation and regeneration of the waste positive electrode and the waste negative electrode can be realized, and additional conditions such as high temperature and high pressure are not needed, so that the environmental influence and the cost involved in the recovery process are greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery recycling and reuse, and specifically to a method and reactor for synchronous separation and regeneration of the positive and negative electrodes of used lithium iron phosphate batteries. Background Art

[0002] Lithium iron phosphate (LiFePO 4 , LFP) batteries are widely used in the fields of energy storage and new energy vehicles. In recent years, with the proposal of the "dual carbon" goal, the production of lithium iron phosphate batteries has been continuously climbing. However, the limited service life inevitably leads to a continuous increase in the number of scrapped batteries. An efficient and environmentally friendly method for recycling used batteries is of great significance for environmental protection and resource conservation.

[0003] Lithium iron phosphate batteries generally include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, electrode tabs, and outer packaging materials. Before recycling, the batteries need to be pretreated, such as through processes like discharging, disassembling, crushing, and screening. The purpose of pretreatment is to screen valuable components and serve the subsequent material recycling process. For example, the recycling method for crushing and disassembling lithium-ion batteries proposed in CN105811040A is simple to operate. However, during the crushing process, the electrode materials are crushed synchronously with the copper and aluminum foils, and the resulting electrode materials contain a large amount of metal impurities, making it difficult to purify the electrode materials in the subsequent process. Moreover, it is difficult to separate the lithium iron phosphate positive electrode material and the graphite negative electrode material for recycling. Among the negative electrode materials, graphite and copper foil are usually water-based binders with weak binding forces, and effective separation can be achieved through direct water washing. However, among the positive electrode materials, active materials usually use organic binders such as polyvinylidene fluoride (PVDF), with relatively tight binding. Organic solvent methods, heat treatment, etc. are often used to achieve their effective peeling. For example, CN106129513A proposes a method of dissolving the binder with an organic solvent to separate the positive electrode material and the aluminum foil, which can avoid the introduction of metal impurities in the positive electrode material. However, the organic solvents used in this method are expensive and most are toxic, posing certain hazards to the environment and the human body. Secondly, although the heat treatment method is simple to operate, it has high energy consumption and toxic gases are easily generated during the high-temperature calcination of PVDF, which is not conducive to environmental protection and sustainable development.

[0004] On the other hand, the failure mechanism of used lithium iron phosphate mainly stems from the vacancy defects of Li, forming anti-site defects of Fe, resulting in the attenuation of battery performance, but the morphology and bulk crystal structure still remain intact. Secondly, the formation of Li vacancies is mainly due to the consumption of active Li during the long-term electrochemical cycling process. Li + Li + is not only consumed during the formation and thickening of the solid electrolyte interface (SEI) on the surface of the negative electrode graphite particles, but also due to the increase in polarization, Li +It is also trapped in the structure of graphite. Currently, the direct repair and regeneration strategy, without the need for leaching or smelting processes, is an emerging and effective closed-loop recycling method aimed at restoring components and repairing structural defects without damaging the lithium iron phosphate structure, thereby maintaining the highest added value and ensuring the maximum sustainability of waste cathode materials. For example, CN115259130B proposes a regeneration method for repairing lithium iron phosphate recycling materials by high-temperature roasting. The waste lithium iron phosphate, lithium source, and organic solvent are mixed, and ammonium ferric citrate is added for iron supplementation treatment to obtain a mixed slurry. The mixed slurry is subjected to primary and secondary calcination to obtain a carbon-coated lithium iron phosphate regenerated material. However, it is still limited by lithium iron phosphate with different lithium deficiencies, and the electrochemical performance consistency of the repaired lithium iron phosphate is poor. The liquid phase method does not require precise positioning of the lithium source ratio. For example, patent CN111547697A proposes a hydrothermal repair method for waste lithium iron phosphate. The waste lithium iron phosphate, lithium source solution, and reducing agent are mixed in a reaction kettle and reacted at 100 - 200 °C for 2 - 10 h, which can be fully carried out in an aqueous solution. However, the liquid phase reaction has a high temperature and requires high-pressure reaction equipment, especially the lack of utilization of the residual lithium embedded in the negative electrode. Summary of the Invention

[0005] The present invention aims to provide a method and reactor for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries, realizing the simultaneous separation and regeneration of waste positive and negative electrodes without additional high-temperature, high-pressure, etc. conditions, thereby greatly reducing the environmental impact and cost involved in the recycling process.

[0006] To solve the above technical problems, the specific solution adopted by the present invention is as follows: A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries. The positive electrode sheet and the negative electrode sheet of the waste lithium iron phosphate battery are respectively placed into reaction vessels. A mixed aqueous solution of a reducing agent with a pH of 8 - 12 and a supplementary lithium salt is added to the reaction vessels to react with the positive electrode sheet and the negative electrode sheet respectively. The two reaction vessels are connected and a filter is provided at the connection; after the reaction ends, the product is filtered and dried to obtain copper foil, aluminum foil, and repaired graphite and lithium iron phosphate.

[0007] Preferably, it includes the following steps:

[0008] 1). Discharge and disassemble the waste lithium iron phosphate battery to obtain the positive electrode sheet and the negative electrode sheet;

[0009] 2). Cut the positive electrode sheet and the negative electrode sheet obtained in step 1) to a size of 1 cm × 1 cm - 10 cm × 10 cm;

[0010] 3). Respectively place the positive electrode sheet and the negative electrode sheet obtained in step 2) into reaction vessels that are connected and have a filter provided at the connection, and add the above-mentioned mixed aqueous solution to the reaction vessels for reaction respectively; after the reaction ends, filter and dry the reaction product to obtain copper foil, aluminum foil, and repaired graphite and lithium iron phosphate.

[0011] Preferably, after step 3), the prepared graphite and lithium iron phosphate are ground respectively to obtain graphite powder and lithium iron phosphate powder, and the graphite powder and lithium iron phosphate powder are calcined respectively under the protection of inert gas to obtain regenerated graphite and regenerated lithium iron phosphate.

[0012] Preferably, the calcination temperature is 200 - 700 °C, and the heating rate is 1 - 10 °C / min -1 , and the calcination time is 1 - 6 h.

[0013] Preferably, the supplementary lithium salt in step 3) is one or a combination of lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, and lithium acetate, and the concentration is 0.1 - 10 mol / L -1 ; the reducing agent is one or a combination of sodium nitrite, potassium sodium tartrate, sodium sulfite, reducing sugar, hydrogen peroxide, and sodium phosphite, and the concentration is 0.1 - 10 mol / L -1 .

[0014] Preferably, in step 3), one or more acids among hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and acetic acid, and one or more bases among sodium hydroxide and potassium hydroxide are used for pH adjustment, and the concentrations of the acid and the base are both 0.1 - 5 mol / L -1 .

[0015] Preferably, the reaction temperature in step 3) is 20 - 90 °C, the reaction time is 0.5 - 8 h, and the solid-liquid ratio of the total amount of the positive electrode sheet and the negative electrode sheet to the mixed aqueous solution is 5 - 150 g / L -1 .

[0016] A reactor for synchronous separation and regeneration of the positive and negative electrodes of a waste lithium iron phosphate battery, comprising monomer containers for the reactions of the positive electrode sheet and the negative electrode sheet respectively, and a communication pipeline connected between the monomer containers, and a filtering material is provided in the communication pipeline.

[0017] Preferably, the filtering material is one of sponge, glass sand core, and filter membrane, and the pore diameter of the filtering material is 10 - 1000 μm.

[0018] Preferably, filter meshes for supporting the positive electrode sheet or the negative electrode sheet are respectively provided in the monomer containers, and the communication pipeline is located below the filter meshes. Beneficial effects

[0019] The present invention extracts residual lithium in the graphite anode by a direct water washing method, realizes the separation of graphite from the copper foil and the removal of residual lithium in the graphite, and obtains a weakly alkaline lithium-rich solution; due to the lower reduction potential of the reducing agent in the alkaline solution, waste lithium iron phosphate is mixed with the lithium-rich and weakly alkaline solution to realize the lithium supplementation and repair of the failed lithium iron phosphate. The hydroxide ions consumed in the lithiation process avoid the further corrosion of the aluminum foil while separating the aluminum foil; the delithiated graphite and lithium-supplemented lithium iron phosphate after filtration are calcined briefly to complete the whole regeneration. Therefore, by directly treating water, the residual lithium ions in the anode can be reintroduced into the cathode in the form of liquid-phase lithiation repair, realizing the simultaneous separation and regeneration of the waste cathode and anode without additional high temperature, high pressure and other conditions, greatly reducing the environmental impact and cost involved in the recycling process. Specifically:

[0020] The present invention directly extracts the residual lithium in the waste graphite by a water washing method, and at the same time strips the graphite from the copper foil, avoiding a large amount of waste water generated by acidic chemicals such as hydrochloric acid and sulfuric acid involved in the extraction of residual lithium from the graphite anode. In addition, there is no need to sinter the water-washed graphite at an ultra-high temperature (>1000 °C), effectively reducing the recycling cost, and it can be reused as a lithium-ion anode.

[0021] The weakly alkaline lithium-rich solution extracted from the anode graphite of the present invention can be directly used for the stripping and repair of the waste lithium iron phosphate cathode material. The alkaline aqueous solution can effectively reduce the reduction potential of the reducing agent, realizing liquid-phase lithium supplementation under conditions below the boiling point of the solution and normal pressure. The OH- consumed in the lithiation process can also prevent the further corrosion of the separated aluminum foil.

[0022] The present invention realizes the synchronous separation and regeneration of the positive and negative electrodes of waste lithium-ion batteries, recovers the lost lithium in the lithium-ion battery, is used for the co-regeneration of waste cathodes and anodes, and reacts at low temperature (<100 °C) and normal pressure (1 atm) to directly obtain the separated copper foil, aluminum foil, repaired anode graphite and cathode lithium iron phosphate, with low energy consumption and short time, and can achieve better economic and environmental benefits.

[0023] In addition, in the process of delithiation and regeneration of the anode graphite and lithium supplementation and repair of the cathode lithium iron phosphate in the present invention, due to the reactivity of the residual lithium in the process of delithiation and regeneration of the anode graphite with water, the residual lithium can be extracted by a direct water washing method, and the process of forming a weakly alkaline lithium-rich solution is continuous. Therefore, the weak alkalinity of the solution can be continuously maintained, so that the residual alkali on the surface of the weakly alkaline solution and the waste lithium iron phosphate cathode material can promote the separation of the cathode active material and the aluminum foil. At the same time, the OH- consumed in the lithium supplementation process can prevent the further corrosion of the Al current collector after separation. Therefore, the present invention only needs to adjust the pH of the solution by acid-base at the beginning of the reaction, and the negative electrode reaction maintains the weakly alkaline solution after the reaction starts, achieving the complementary effect of the positive and negative electrode reactions.

[0024] Since aluminum is an amphoteric metal and can dissolve in acid or alkali solutions, while the electrode material usually does not react with alkali, the lithium iron phosphate cathode material of the aluminum foil is peeled off by the alkali leaching method in the present invention. After the lithium-ion battery undergoes multiple cycles, residual alkali will form on the surface of the waste cathode material, and the lithium iron phosphate active material and the aluminum foil can be separated by reacting it with pure water. Secondly, taking sodium sulfite as a reducing agent as an example, during the lithium supplementation process, OH in water will be consumed - , which can avoid the further corrosion of the aluminum foil by the alkalinity of the solution after the separation of the lithium iron phosphate active material and the aluminum foil. The reaction formula is FePO 4 +Li + +OH - +1 / 2SO 3 2- =LiFePO 4 +1 / 2SO 4 2- +1 / 2H 2 O. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic flow chart of a method for synchronously separating and regenerating the positive and negative electrodes of a waste lithium iron phosphate battery according to the present invention;

[0026] Figure 2 is a schematic structural diagram of a reactor for synchronously separating and regenerating the positive and negative electrodes of a waste lithium iron phosphate battery according to the present invention;

[0027] Figure 3 is an XRD diagram comparing the recovered copper foil with the commercial copper foil in Example 1 of the present invention;

[0028] Figure 4 is an XRD diagram comparing the recovered aluminum foil with the commercial aluminum foil in Example 1 of the present invention;

[0029] Figure 5 is an XRD diagram of waste graphite, liquid-phase delithiated graphite, and calcined graphite in Example 1 of the present invention;

[0030] Figure 6 is an XRD diagram of waste lithium iron phosphate, liquid-phase lithium-supplemented lithium iron phosphate, and calcined lithium iron phosphate in Example 1 of the present invention;

[0031] Figure 7 is a comparison diagram of the cycling performance of waste graphite and calcined regenerated graphite in Example 2 of the present invention;

[0032] Figure 8 is a comparison diagram of the cycling performance of waste lithium iron phosphate and calcined regenerated lithium iron phosphate in Example 2 of the present invention.

[0033] In the figure, the markings are: 1, monomer container; 2, filter screen; 3, connecting pipeline; 4, filtering material. Detailed implementation mode

[0034] The present invention provides a method and a reactor for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries, realizing the synchronous separation and co-regeneration of the positive and negative electrodes. Based on the failure process of waste lithium iron phosphate, the formation of SEI on the surface of the negative electrode graphite consumes a large amount of Li + , and with the increase of polarization, Li + remains in the bulk structure of graphite, and removing the residual lithium is crucial for regenerating the waste negative electrode. Through quantitative analysis, it is found that the residual lithium in waste graphite shows reactivity to water, and the residual lithium can be extracted by direct water washing method to obtain a weakly alkaline lithium-rich solution. Then, based on the dominant region in the E-pH diagram, the alkaline solution can effectively reduce the reduction potential of the reducing agent. Under the conditions of temperature below the boiling point of the solution and normal pressure, combined with the above-mentioned alkaline lithium-rich solution, the pH and Li + concentration can be precisely controlled to realize the liquid-phase lithium supplementation and repair of waste lithium iron phosphate. At the same time, the weakly alkaline aqueous solution and the residual alkali on the surface of the waste lithium iron phosphate battery positive electrode material promote the separation of the positive electrode active material and the aluminum foil.

[0035] As Figure 1 and Figure 2 shown, the reactor for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries includes two identical monomer containers 1 distributed at intervals. A filter screen 2 is provided in the middle of each of the two monomer containers 1. The filter screen 2 is used to support the positive electrode sheet and the negative electrode sheet to separate graphite and copper foil, or separate lithium iron phosphate and aluminum foil after the reaction. The positions of the two monomer containers 1 below the filter screen 2 are connected by a connecting pipeline 3, so that the lithium separated from the graphite can enter the lithium iron phosphate through the connecting pipeline 3 for regeneration. To avoid the mixing of graphite and lithium iron phosphate generated by the reaction, a filtering material 4 is also provided in the connecting pipeline 3. The filtering material 4 is one of sponge, glass sand core and filter membrane, and the pore diameter of the filtering material 4 is 10-1000 μm.

[0036] Based on the above reactor, a method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries of the present invention is illustrated by the following 3 examples:

[0037] Example 1

[0038] Including the following steps:

[0039] 1) Discharge and disassemble the waste lithium iron phosphate battery, and separate the separator, positive electrode sheet and negative electrode sheet.

[0040] 2) Weigh the required cut positive and negative electrode sheets and place them on the filter screen 2 of the two monomer containers 1 respectively. A 100 μm glass sand core is used as the filtering material 4 in the connecting pipeline 3; a mixed aqueous solution is introduced into the monomer container 1 for reaction. The solid-liquid ratio of graphite to the mixed aqueous solution is 10 gL -1, the solid-liquid ratio of lithium iron phosphate to the mixed aqueous solution is 5 g / L -1 . The mixed aqueous solution contains a reducing agent and a supplementary lithium salt. The reducing agent is sodium sulfite with a concentration of 0.5 mol / L -1 , and the supplementary lithium salt is lithium hydroxide with a lithium ion concentration of 0.25 mol / L in the solution -1 . The initial pH value of the whole solution is measured by a pH meter and adjusted to 9.5 with acid or base. The temperature of the reaction system is 70 °C and the time is 1 h. After the reaction, the lithium-depleted graphite in the liquid phase at the bottom of the tank, the lithium-supplemented lithium iron phosphate in the liquid phase, the copper foil and aluminum foil on the filter screen 2 are collected and dried respectively. The repaired graphite and lithium iron phosphate powder are ball-milled at a speed of 300 rpm for 1 h respectively, and then graphite and lithium iron phosphate with uniform particle distribution can be obtained;

[0041] 4) Place the repaired graphite and lithium iron phosphate powder under an argon atmosphere and heat them to 700 °C at a rate of 2 °C / min -1 for 3 h to obtain regenerated graphite and lithium iron phosphate, and test their electrochemical properties respectively.

[0042] Figure 3 、 4 are the XRD patterns of the recycled copper foil and aluminum foil compared with the commercial copper foil and aluminum foil respectively. The characteristic diffraction peaks of the separated copper foil and aluminum foil are completely consistent with those of the commercial copper foil and aluminum foil, and there are no impurity peaks.

[0043] Figure 5 is the XRD pattern of waste graphite, lithium-depleted graphite in the liquid phase and calcined graphite. The peak shapes of the repaired and calcined regenerated graphite are sharp, and the intensity of the characteristic diffraction peak at (002) is relatively strong.

[0044] Figure 6 is the XRD pattern of waste lithium iron phosphate, lithium-supplemented lithium iron phosphate in the liquid phase and calcined lithium iron phosphate. The diffraction peaks of the iron phosphate phase in the repaired and calcined regenerated lithium iron phosphate have disappeared, and there are no other impurity peaks.

[0045] Example 2

[0046] 1) The waste lithium iron phosphate is discharged and disassembled by the battery, and the separator, the positive electrode plate and the negative electrode plate are separated.

[0047] 2) Weigh the required cut positive and negative electrode plates and place them on the filter screen 2 respectively. The glass sand core with a pore size of 500 μm is used at the connection. The solid-liquid ratio of graphite to the solution is 20 g / L -1 , and the solid-liquid ratio of lithium iron phosphate to the solution is 10 g / L -1 . The reducing agent used is potassium sodium tartrate with a concentration of 1 mol / L -1 , and the supplementary lithium salt is lithium acetate with a lithium ion concentration of 0.5 mol / L in the solution -1The initial pH value of the whole solution, measured by a pH meter, was adjusted to 9.5 with acid or base. The temperature of the reaction system was 80 °C and the time was 1 h. After the reaction, the lithium-depleted graphite in the liquid phase at the bottom of the tank, the lithium-complemented lithium iron phosphate in the liquid phase, the copper foil and aluminum foil on the filter screen 2 were collected and dried respectively. The repaired graphite and lithium iron phosphate powders were ball-milled at a speed of 300 rpm for 1 h respectively, and then graphite and lithium iron phosphate with uniform particle distribution could be obtained.

[0048] 3) The repaired graphite and lithium iron phosphate powders were respectively placed under an argon atmosphere and heated to 650 °C at a rate of 2 °C / min -1 and calcined for 4 h to obtain regenerated graphite and lithium iron phosphate, and their electrochemical properties were tested respectively.

[0049] Figure 7 Figure 1 is a comparison chart of the cycling performance of waste graphite and regenerated graphite after calcination. The charge specific capacity of the regenerated graphite after calcination at a rate of 0.5C for 300 cycles is 341.7 mAh / g -1 which is significantly higher than 327.3 mAh / g of the waste graphite -1 .

[0050] Figure 8 Figure 2 is a comparison chart of the cycling performance of waste lithium iron phosphate and regenerated lithium iron phosphate after calcination. It can be seen from the figure that the discharge specific capacity of the regenerated lithium iron phosphate after calcination at a rate of 1C for 500 cycles is 142.4 mAh / g -1 and the capacity retention rate is 99%, which is significantly higher than 106.0 mAh / g of the waste lithium iron phosphate -1 with a capacity retention rate of 91%.

[0051] Example 3

[0052] 1) The waste lithium iron phosphate battery was discharged and disassembled, and the separator, positive electrode sheet and negative electrode sheet were separated.

[0053] 2) Weighed the required cut positive and negative electrode sheets and placed them on the filter screen 2 respectively. A 50-μm glass sand core was used at the connection. The solid-liquid ratio of graphite to the solution was 20 g / L -1 and the solid-liquid ratio of lithium iron phosphate to the solution was 1 g / L -1 . The reducing agent used was glucose with a concentration of 2 mol / L -1 , and the lithium salt supplement was lithium hydroxide. The lithium ion concentration in the solution was 1 mol / L -1 . The initial pH value of the whole solution was measured by a pH meter and adjusted to 10 with acid or base. The temperature of the reaction system was 70 °C and the time was 1 h. After the reaction, the lithium-depleted graphite in the liquid phase at the bottom of the tank, the lithium-complemented lithium iron phosphate in the liquid phase, the copper foil and aluminum foil on the filter screen 2 were collected and dried respectively. The repaired graphite and lithium iron phosphate powders were ball-milled at a speed of 300 rpm for 1 h respectively, and then graphite and lithium iron phosphate with uniform particle distribution could be obtained.

[0054] 3) Place the repaired graphite and lithium iron phosphate powder under a nitrogen atmosphere and heat them at a rate of 5 °C / min -1 to 650 °C and calcine for 5 h to obtain regenerated graphite and lithium iron phosphate.

Claims

1. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries, characterized in that: The positive electrode sheet and the negative electrode sheet of the waste lithium iron phosphate battery are placed in reaction containers respectively, and a mixed aqueous solution of a reducing agent with a pH of 8-12 and a supplementary lithium salt is added to the reaction container to react with the positive electrode sheet and the negative electrode sheet respectively, and the two reaction containers are connected and a filter is set at the connection point; after the reaction is completed, the product is filtered and dried to obtain copper foil, aluminum foil and repaired graphite and lithium iron phosphate.

2. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 1, characterized in that: The following steps are involved: 1) Discharging and disassembling the waste lithium iron phosphate battery to obtain the positive electrode sheet and the negative electrode sheet; 2) The positive electrode sheet and the negative electrode sheet obtained in step 1) are cut into a size of 1cm×1cm-10cm×10cm; 3) The positive electrode sheet and the negative electrode sheet obtained in step 2) are respectively placed in a reaction container connected and provided with a filter at the connection point, and the mixed aqueous solution is respectively added to the reaction container for reaction; after the reaction is completed, the reaction product is filtered and dried to obtain copper foil, aluminum foil and repaired graphite and lithium iron phosphate.

3. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 2, characterized in that: After step 3), the prepared graphite and lithium iron phosphate are ground to obtain graphite powder and lithium iron phosphate powder respectively, and the graphite powder and lithium iron phosphate powder are calcined under the protection of inert gas to obtain regenerated graphite and regenerated lithium iron phosphate.

4. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 3, characterized in that: The calcination temperature is 200-700℃, and the heating rate is 1-10℃min -1 , the calcination time is 1-6h.

5. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 2, characterized in that: The supplementary lithium salt in step 3) is a combination of one or more of lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate and lithium acetate, with a concentration of 0.1-10 molL -1 The reducing agent is a combination of one or more of sodium nitrite, potassium sodium tartrate, sodium sulfite, reducing sugar, hydrogen peroxide and sodium phosphite, with a concentration of 0.1-10 molL -1 .

6. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 2, characterized in that: In step 3), pH is adjusted by using one or more acids selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and acetic acid, and one or more bases selected from sodium hydroxide and potassium hydroxide, wherein the concentrations of the acid and base are both 0.1-5 mol / L -1 .

7. A method for synchronously separating and regenerating the positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 2, characterized in that: The reaction temperature in step 3) is 20-90°C, the reaction time is 0.5-8h, and the solid-liquid ratio of the total amount of the positive electrode sheet and the negative electrode sheet to the mixed aqueous solution is 5-150g / L -1 .

8. A reactor for synchronous separation and regeneration of positive and negative electrodes of waste lithium iron phosphate batteries, characterized in that: It comprises monomer containers for respectively providing reactions for the positive electrode sheet and the negative electrode sheet and a connecting pipeline connected between the monomer containers, wherein a filter material is arranged in the connecting pipeline.

9. A reactor for synchronous separation and regeneration of positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 1, characterized in that: The filter material is one of a sponge, a glass sand core and a filter membrane, and the pore size of the filter material is 10-1000 μm.

10. A reactor for synchronous separation and regeneration of positive and negative electrodes of waste lithium iron phosphate batteries as claimed in claim 1, characterized in that: A filter screen supporting the positive electrode sheet or the negative electrode sheet is respectively arranged in the monomer container, and the connecting pipeline is located below the filter screen.

Images