Method for recycling stripping waste positive plate current collector and positive material by using NMP

Abstract

This invention discloses a method for cyclically separating waste positive electrode current collectors and positive electrode materials using NMP, comprising the following steps: adding the positive electrode sheet to an NMP solution, stirring, and sieving to obtain a positive electrode cleaning filtrate and aluminum foil; adding a flocculant to the positive electrode cleaning filtrate, stirring, and allowing it to stand for solid-liquid separation to obtain crude NMP solution and positive electrode material powder; adding a dehydrating agent to the crude NMP solution, filtering to remove solids to obtain a recovered NMP solution, which is then recycled for the separation of the positive electrode current collector and positive electrode material. This method reuses the NMP solution repeatedly, thus reducing costs and solving the problem of high costs associated with organic solvents. Furthermore, by introducing non-solvent water into the system, the thermodynamic stability of the system is altered, increasing the solubility of PVDF and accelerating the dissolution rate.

Description

Technical Field

[0001] This invention belongs to the field of electrode material recycling technology, specifically relating to a method for cyclically stripping current collectors and cathode materials from waste cathode sheets using NMP. Background Technology

[0002] In recent years, the new energy electric vehicle industry has developed rapidly under the impetus of national policies. Sales of new energy electric vehicles reached 370,000 units in 2015, and are projected to reach approximately 1.06 million units in 2020, and 1.6 million units in 2022. However, as power batteries reach the end of their lifespan, a large number of waste batteries will be generated. These waste batteries contain various rare and precious metals, and finding a low-cost and effective method for recycling them will achieve significant social and economic benefits.

[0003] The adhesive used in the positive electrode of a battery is mainly polyvinylidene fluoride (PVDF). PVDF, as a battery adhesive, possesses good mechanical strength, chemical stability, electrochemical stability, thermal stability, and good affinity for the electrolyte. Conventional methods for removing adhesives involve high-temperature incineration under nitrogen protection. This method is not only energy-intensive and has a low recovery rate, but also causes significant environmental pollution.

[0004] Polyvinylidene fluoride (PVDF), as a stable adhesive, is insoluble in most solvents, only in a few solvents including N-methylpyrrolidone (NMP). Through the combined effects of mechanical and cavitation processes in the equipment, the current collector and cathode material of waste cathode sheets can be separated. However, the NMP solvent used is expensive, and without proper treatment, it can cause environmental pollution. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP. This method can repeatedly recycle and reuse NMP, reducing the cost of solvent use while reducing wastewater discharge to the environment.

[0006] According to one aspect of the present invention, a method for cyclically stripping current collectors and cathode materials from waste cathode plates using NMP is provided, comprising the following steps:

[0007] S1: Add the positive electrode sheet to the NMP solution, stir, and sieve to obtain the positive electrode cleaning filtrate and aluminum foil;

[0008] S2: Add flocculant to the positive electrode cleaning filtrate obtained in step S1, stir, let stand, and then separate the solid and liquid to obtain NMP crude liquid and positive electrode material powder.

[0009] S3: Add a dehydrating agent to the crude NMP solution obtained in step S2, filter to remove solids and obtain NMP recovery solution. The NMP recovery solution is used for the separation of positive electrode current collector and positive electrode material in steps S1-S2.

[0010] In some embodiments of the present invention, in step S1, the positive electrode sheet is obtained by the following steps: the recycled waste positive electrode sheet is shredded by a biaxial shredder to obtain a positive electrode sheet with an area of ​​(2cm*2cm)-(5cm*5cm) and an irregular thickness of the original thickness.

[0011] In some embodiments of the present invention, in step S1, the concentration of the NMP solution is 95wt%-99wt%, and the solid-liquid ratio of the positive electrode to the NMP solution is 1g:(2-100)mL.

[0012] In some preferred embodiments of the present invention, in step S1, the NMP solution is prepared by the following steps: taking an NMP solution with a concentration of ≥99.9% and adding deionized water to prepare an NMP solution with a concentration of 95wt%-99wt%.

[0013] In some preferred embodiments of the present invention, in step S1, the NMP solution concentration is approximately 95 wt%.

[0014] In some embodiments of the present invention, in step S1, the stirring is also accompanied by heating, the heating temperature is 60-90°C, and the heating time is 60-120 min.

[0015] In some embodiments of the present invention, in step S1, the stirring is also accompanied by ultrasound, the frequency of which is 30-60 kHz and the duration of which is 60-120 min.

[0016] In some preferred embodiments of the present invention, in step S1, the stirring is also accompanied by ultrasound, the frequency of which is about 40 kHz and the duration of which is about 60 min.

[0017] In some embodiments of the present invention, in step S1, the mesh size of the sieve is 30-100 mesh.

[0018] In some preferred embodiments of the present invention, in step S1, the mesh size of the sieve is 40 mesh.

[0019] In some more preferred embodiments of the present invention, in step S1, the material is further washed with water after sieving.

[0020] In some embodiments of the present invention, in step S2, the flocculant includes a flocculant solution and a coagulant aid, wherein the flocculant solution is at least one of a polyacrylamide solution and a ferrous sulfate solution.

[0021] In some preferred embodiments of the present invention, the concentration of the flocculant solution is 0.5 wt% to 5.0 wt%.

[0022] In some preferred embodiments of the present invention, the coagulant is at least one of diatomaceous earth, activated carbon, and graphite.

[0023] In some more preferred embodiments of the present invention, in step S2, the amount of flocculant used is 8%-12% of the mass of the positive electrode cleaning filtrate, wherein the ratio of the flocculant solvent to the coagulant is (10:0)-(3:7).

[0024] In some preferred embodiments of the present invention, in step S2, the amount of flocculant used is approximately 10% of the mass of the positive electrode cleaning filtrate.

[0025] In some embodiments of the present invention, in step S3, the dehydrating agent is at least one of calcium chloride and magnesium chloride.

[0026] In some embodiments of the present invention, in step S3, water is added to make the concentration of the NMP recovery solution 95wt%-97wt%.

[0027] In some preferred embodiments of the present invention, in step S3, water is added to make the concentration of the NMP recovery solution approximately 95 wt%.

[0028] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved:

[0029] 1. This invention introduces non-solvent water into the system, which changes the thermodynamic stability of the system, increases the solubility of PVDF and accelerates the dissolution rate; on the other hand, through heating, stirring and ultrasonication, the PVDF of the positive electrode sheet dissolves in NMP, thereby realizing the dispersion and subsequent recovery of the black powder of the positive electrode sheet.

[0030] 2. The flocculants used in this invention include flocculant solutions and coagulant aids. When polyacrylamide is used as a flocculant solution, its long-chain molecular structure and the presence of a large number of active groups (amide groups, carboxyl groups, etc.) promote the sedimentation of particles in the system under the combined action of flocculation bridging and chemical adsorption, which is beneficial for filtration. When diatomaceous earth is used as a coagulant aid, it not only effectively improves the flocculation effect, but also improves the recovery rate of NMP after flocculation, so as to facilitate subsequent recycling.

[0031] 3. The flocculants and dehydrating agents used in this invention are common reagents, and the operation is simple and easy to implement. They can be dried and recycled, and the recovery rate is higher than that of dry incineration.

[0032] 4. Since NMP will undergo hydrolysis, adding a dehydrating agent to the crude NMP solution can quickly remove water from the system and prevent NMP from hydrolyzing and reducing the subsequent recovery rate.

[0033] 5. Because N-methylpyrrolidone can be repeatedly recycled and reused, the cost of this invention is relatively low, thus solving the problem of high cost of organic solvents. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0035] Figure 1 This is a schematic diagram of the process flow of Embodiment 1 of the present invention. Detailed Implementation

[0036] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for cyclically stripping current collectors and cathode materials from waste cathode plates using NMP, such as... Figure 1 As shown, it includes the following steps:

[0039] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 95% mass fraction NMP solution.

[0040] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 70°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonic waves at a frequency of 40kHz. The reaction time is 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0041] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0042] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker, and add polyacrylamide aqueous solution and diatomaceous earth to it at 7% and 3% of the mass of the positive electrode cleaning filtrate, respectively. Stir to obtain a mixed solution and let it stand for 1 hour.

[0043] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder.

[0044] (6) Add calcium chloride particles with a relative mass fraction of 30% to the NMP crude solution filtered in step (5). After dehydration by the dehydrating agent, the concentration of the NMP crude solution returns to ≥95%. After filtering to remove the solid dehydrating agent, add deionized water to adjust the concentration of the NMP crude solution to about 95%. This concentration is measured by a handheld NMP concentration meter.

[0045] (7) Repeat steps (2)(3)(4)(5)(6) to achieve the cyclic separation of positive electrode black powder and current collector. The NMP recovery rate of this method is greater than or equal to 99%.

[0046] Example 2

[0047] A method for cyclically stripping current collectors and cathode materials from waste cathode plates using NMP includes the following steps:

[0048] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 95% mass fraction NMP solution.

[0049] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 70°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonic waves at a frequency of 40kHz. The reaction time is 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0050] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0051] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker, and add ferrous sulfate aqueous solution and activated carbon to it at 7% and 3% of the mass of the positive electrode cleaning filtrate, respectively. Stir to obtain a mixed solution and let it stand for 1 hour.

[0052] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder.

[0053] (6) Add calcium chloride particles with a relative mass fraction of 30% to the NMP crude solution filtered in step (5). After dehydration by the dehydrating agent, the concentration of the NMP crude solution returns to ≥95%. After filtering to remove the solid dehydrating agent, add deionized water to adjust the concentration of the NMP crude solution to about 95%. This concentration is measured by a handheld NMP concentration meter.

[0054] (7) Repeat steps (2)(3)(4)(5)(6) to achieve the cyclic separation of positive electrode black powder and current collector. The NMP recovery rate of this method is greater than or equal to 97%.

[0055] Example 3

[0056] A method for cyclically stripping current collectors and cathode materials from waste cathode plates using NMP includes the following steps:

[0057] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 95% mass fraction NMP solution.

[0058] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 70°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonic waves at a frequency of 40kHz. The reaction time is 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0059] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0060] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker, and add polyacrylamide aqueous solution and graphite respectively at 7% and 3% of the mass of the positive electrode cleaning filtrate. Stir to obtain a mixed solution and let it stand for 1 hour.

[0061] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder.

[0062] (6) Add calcium chloride particles with a relative mass fraction of 30% to the NMP crude solution filtered in step (5). After dehydration by the dehydrating agent, the concentration of the NMP crude solution returns to ≥95%. After filtering to remove the solid dehydrating agent, add deionized water to adjust the concentration of the NMP crude solution to about 95%. This concentration is measured by a handheld NMP concentration meter.

[0063] (7) Repeat steps (2)(3)(4)(5)(6) to achieve the cyclic separation of positive electrode black powder and current collector. The NMP recovery rate of this method is greater than or equal to 98%.

[0064] Comparative Example 1

[0065] A method for cyclically stripping current collectors and cathode materials from waste cathode plates using NMP, the main difference from Example 1 is that a 90% mass fraction NMP solution is prepared in step (1), and includes the following steps:

[0066] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 90% mass fraction NMP solution.

[0067] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 80°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonic waves at a frequency of 40kHz. The reaction time is 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0068] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0069] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker, and add polyacrylamide aqueous solution and diatomaceous earth to it at 7% and 3% of the mass of the positive electrode cleaning filtrate, respectively. Stir to obtain a mixed solution and let it stand for 1 hour.

[0070] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder.

[0071] (6) Add calcium chloride particles with a relative mass fraction of 30% to the NMP crude solution filtered in step (5). After dehydration by the dehydrating agent, the concentration of the NMP crude solution returns to ≥95%. After filtering to remove the solid dehydrating agent, add deionized water to adjust the concentration of the NMP crude solution to about 95%. This concentration is measured by a handheld NMP concentration meter.

[0072] (7) The NMP recovery rate of this method is greater than or equal to 97%.

[0073] Comparative Example 2

[0074] A method for cyclically stripping waste positive electrode current collectors and positive electrode materials using NMP, the main difference from Example 1 is that no flocculant is added in step (4), and includes the following steps:

[0075] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 95% mass fraction NMP solution.

[0076] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 70°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonic waves at a frequency of 40kHz. The reaction time is 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0077] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0078] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker and let it stand for 1 hour;

[0079] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder. The colloidal substances in the system are easy to clog the filter paper, which greatly increases the filtration time.

[0080] (6) Add calcium chloride particles with a relative mass fraction of 30% to the NMP crude solution filtered in step (5). After dehydration by the dehydrating agent, the concentration of the NMP crude solution returns to ≥95%. After filtering to remove the solid dehydrating agent, add deionized water to adjust the NMP crude solution concentration to about 95%. This concentration is measured by a handheld NMP concentration meter.

[0081] (7) The NMP recovery rate of this method is greater than or equal to 90%.

[0082] Comparative Example 3

[0083] A method for cyclically stripping waste positive electrode current collectors and positive electrode materials using NMP, the main difference from Example 1 is that step (6) of adding a dehydrating agent is omitted, and the method includes the following steps:

[0084] (1) Shred the recycled waste positive electrode sheet using a biaxial shredder to obtain a positive electrode sheet with an area of ​​2cm*2cm and an irregular thickness of the original thickness; take N-methylpyrrolidone solution with a concentration of ≥99.9%, add deionized water, and prepare a 95% mass fraction NMP solution.

[0085] (2) Place the positive electrode sheet and the prepared NMP solution into a beaker at a solid-liquid ratio of 1g:10mL. Place the beaker under a paddle stirrer and in an ultrasonic water bath. Heat to 70°C, turn on the stirrer and adjust the stirring speed to 350rpm. Turn on the ultrasonication for 40kHz and for 1h until the black powder of the positive electrode sheet is completely dispersed, and obtain the positive electrode cleaning solution and the current collector aluminum foil.

[0086] (3) Pass the mixture of positive electrode cleaning solution and current collector aluminum foil through a 40-mesh sieve. The material on the sieve is then rinsed with water to obtain clean aluminum foil, and the material under the sieve is the positive electrode cleaning filtrate.

[0087] (4) Place the positive electrode cleaning filtrate obtained in step (3) into a beaker, and add polyacrylamide aqueous solution and diatomaceous earth to it at 7% and 3% of the mass of the positive electrode cleaning filtrate, respectively. Stir to obtain a mixed solution and let it stand for 1 hour.

[0088] (5) After standing, filter the mixed solution to separate the solid and liquid. The filtrate is crude NMP solution and the filter residue is positive electrode material powder.

[0089] (6) The positive electrode and the crude NMP solution obtained in step (5) were placed in a beaker at a solid-liquid ratio of 1g:10mL, heated to 70℃, stirred and sonicated for 1h, and the cleaning effect was compared. See Table 2.

[0090] Test case

[0091] 1. Polyvinylidene fluoride (PVDF) is insoluble in most solvents, but only soluble in a few limited solvents such as N-methylpyrrolidone (NMP). 2g of PVDF powder was weighed and dissolved in 100g of NMP solutions with different mass fractions. The dissolution phenomenon was observed and the viscosity was measured. The results are shown in Table 1.

[0092] Table 1 PVDF Solubility Test

[0093]

[0094] Experimental results show that when the NMP concentration is <95%, the solubility of PVDF decreases, and when the NMP concentration is ≤90%, PVDF is insoluble. When the NMP concentration is ≥95%, the solubility of PVDF is good, and the dissolution rate increases with decreasing mass fraction. This invention introduces non-solvent water into a system with an NMP concentration ≥95%, altering the system's thermodynamic stability, increasing the solubility of PVDF, and accelerating the dissolution rate.

[0095] 2. The experimental data of Examples 1-3 and Comparative Examples 1-3 were tested and analyzed respectively, and the results are shown in Table 2.

[0096] Table 2. Data Results Analysis of Examples 1-3 and Comparative Examples 1-3

[0097]

[0098]

[0099] As can be seen from the data in Examples 1-3 in Table 2, the processing method of the present invention can disperse the current collector and the positive electrode material, achieve fast filtration and good circulation, and the NMP recovery rate can reach more than 97%. In the examples, heating to 70°C, stirring speed of 350 rpm, and ultrasonic reaction for 60 min until the black powder of the positive electrode sheet is completely dispersed, the addition of different flocculants can cause the positive electrode material in the mixture to agglomerate, thereby accelerating the filtration speed. After filtration, the addition of a dehydrating agent can increase the NMP concentration while avoiding the hydrolysis of NMP, ensuring efficient recovery and subsequent recycling and stripping of waste positive electrode sheet current collector and positive electrode material.

[0100] Furthermore, comparing Example 1 with Comparative Example 1, it can be seen that when other conditions remain unchanged, reducing the NMP concentration to 90% reduces the solubility of PVDF to insoluble, resulting in poor dispersion of the current collector and positive electrode material. Comparing Example 1 with Comparative Example 2, it can be seen that when other conditions remain unchanged and no flocculant is added, the positive electrode material disperses and forms a uniform state with the NMP solution, and the PVDF colloid easily clogs the filter paper, greatly reducing the filtration effect. At the same time, there is also a significant loss of NMP solution, resulting in a low recovery rate. Comparing Example 1 with Comparative Example 3, it can be seen that when other conditions remain unchanged and no dehydrating agent is added for direct circulation, the NMP concentration will be reduced to less than 90% in the previous cleaning, so it cannot act on the dispersion of the current collector and positive electrode material again. In addition, Comparative Example 3 did not add a dehydrating agent to remove excess water from the system in time, and the NMP hydrolyzed, resulting in a low recovery rate.

[0101] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP, characterized in that, Includes the following steps: S1: Add the positive electrode sheet to the NMP solution, stir, and sieve to obtain the positive electrode cleaning filtrate and aluminum foil; S2: Add flocculant to the positive electrode cleaning filtrate obtained in step S1, stir, let stand, and then separate the solid and liquid to obtain NMP crude liquid and positive electrode material powder. S3: Add a dehydrating agent to the crude NMP solution obtained in step S2, filter to remove solids and obtain NMP recovery solution, which is used for the separation of positive electrode current collector and positive electrode material in steps S1-S2. In step S1, the NMP solution concentration is 95wt%-99wt%, and the solid-liquid ratio of the positive electrode to the NMP solution is 1g:(2-100)mL; In step S3, water is added to make the concentration of the NMP recovery solution 95wt%-97wt%.

2. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 1, characterized in that, In step S1, the stirring is accompanied by heating, the heating temperature is 60-90℃, and the heating time is 60-120min.

3. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 1, characterized in that... In step S1, the stirring is accompanied by ultrasound, the frequency of which is 30-60 kHz and the duration of which is 60-120 min.

4. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 1, characterized in that, In step S2, the flocculant includes a flocculant solution and a coagulant aid, wherein the flocculant solution is at least one of a polyacrylamide solution and a ferrous sulfate solution.

5. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 4, characterized in that, The concentration of the flocculant solution is 0.5 wt%-5.0 wt%.

6. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 4, characterized in that, The coagulant is at least one of diatomaceous earth, activated carbon, and graphite.

7. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 4, characterized in that, In step S2, the amount of flocculant used is 8%-12% of the mass of the positive electrode cleaning filtrate, wherein the ratio of the flocculant to the coagulant aid is (10:0)-(3:7).

8. The method for cyclically stripping current collectors and positive electrode materials from waste positive electrode sheets using NMP as described in claim 1, characterized in that, In step S3, the dehydrating agent is at least one of calcium chloride and magnesium chloride.

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