Method for separating positive current collector and positive active material in positive plate

Abstract

The invention provides a method for separating a positive current collector and a positive active material in a positive plate, which comprises the following steps: S1, providing a positive plate which comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector; wherein the positive electrode film layer comprises polyvinylidene fluoride and a positive electrode active material; s2, the positive plate is placed in a composite leaching agent to be subjected to leaching treatment, polyvinylidene fluoride in the positive plate is dissolved in the composite leaching agent, a positive current collector and a positive film layer are stripped, and the positive current collector and a leaching solution are obtained; s3, filtering the leaching solution to obtain a filtrate and a filter cake; wherein the filter cake comprises a positive electrode active material. The method provided by the invention can effectively reduce the use of high-polarity and high-boiling-point organic solvents, so that the cost can be saved, the environmental pollution can be reduced, and the method is more suitable for industrial production and application.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium battery material recycling, and specifically relates to a method for separating a positive electrode current collector and a positive electrode active material in a positive electrode sheet. Background Art

[0002] Driven by the goal of carbon neutrality, the global electric vehicle and chemical energy storage industries have developed rapidly. As the basic component of new energy vehicles and chemical energy storage equipment, the production and sales of lithium batteries have increased rapidly. However, the average service life of lithium batteries is 6 to 8 years, and we will face a large-scale retirement wave of lithium batteries. According to data from the China Automotive Engineering Society, the scale of retired batteries in my country will reach 1.04 million tons in 2023, and it is expected that the scale of retired power batteries will reach 3.5 million tons by 2030. On the one hand, retired batteries contain a large number of heavy metals, organic electrolytes, plastics and other substances. If they are not properly planned and handled, they will cause great harm to the environment; on the other hand, retired power batteries are rich in a large number of valuable metals such as lithium, nickel, manganese, cobalt, iron, copper, and aluminum. If they can be planned and recycled, it will be of great significance to promote the healthy and sustainable development of the new energy industry and solve the problem of resource shortage. Whether from the perspective of environmental protection or resource reuse, retired batteries have huge recycling value. Therefore, the retired battery recycling industry has ushered in a booming development in recent years. The development of simple, efficient and environmentally friendly retired battery recycling processes has become a research direction of concern in the current battery recycling industry.

[0003] At present, whether it is lithium iron phosphate battery or ternary battery, the mainstream recycling process is to discharge, disassemble, roast and screen the retired battery into battery black powder through the pretreatment process, and then recover the lithium, nickel, manganese, cobalt, iron phosphate and other substances in the battery black powder through wet or fire process. The role of roasting in the pretreatment process is mainly to pyrolyze the binder polyvinylidene fluoride (PVDF) in the positive electrode material, so that the binder is ineffective to separate and disperse the positive electrode aluminum foil and the electrode active material. However, PVDF will produce a large amount of volatile fluoride during the decomposition process. The volatile fluoride corrodes the equipment and will dissipate into the air if not properly handled, which will harm the environment. In addition, the pyrolyzed PVDF cannot be recycled, resulting in a waste of resources. In order to solve the problem of PVDF pyrolysis during the pretreatment roasting process of retired batteries, some companies soak the pole pieces after disassembly of the battery in strong polar organic solvents such as NMP and DMF, dissolve PVDF in the organic solvent, and then separate and disperse the current collector and the electrode active material, and the organic solvent is reused by evaporation. Although this process has high separation efficiency, the highly polar organic solvents used are expensive, large in quantity, and have high boiling points (high evaporation energy consumption), making them unsuitable for large-scale industrialization. In the process of pre-treating retired batteries to remove battery black powder, it is urgent to find a new efficient and environmentally friendly process to solve the problem of separating the positive current collector and the positive active material. Summary of the invention

[0004] In view of this, the present application provides a method for separating the positive electrode current collector and the positive electrode active material in the positive electrode sheet, aiming to solve the problem that the existing technical solutions use a large amount of high-polarity solvents with high boiling points / high prices and cannot be industrialized on a large scale.

[0005] The present application provides a method for separating a positive electrode current collector and a positive electrode active material in a positive electrode sheet, comprising the following steps:

[0006] Step S1: providing a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector; wherein the positive electrode film layer comprises polyvinylidene fluoride and a positive electrode active material;

[0007] Step S2: placing the positive electrode sheet in a composite leaching agent for leaching treatment, so that the polyvinylidene fluoride in the positive electrode sheet is dissolved in the composite leaching agent, and the positive electrode collector and the positive electrode film layer are peeled off to obtain a positive electrode collector and a leaching solution; wherein the composite leaching agent comprises component A and component B; the component A comprises at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide, and the component B comprises C 1 ~C 3 Alcohol compounds, C 2 ~C 4 At least one of an ester compound, acetone and ether;

[0008] Step S3: filtering the leaching solution to obtain a filtrate and a filter cake; wherein the filter cake includes a positive electrode active material.

[0009] According to the present application, the inventors have discovered that the use of a composite leachate comprising components A and B can effectively dissolve the polyvinylidene fluoride in the positive electrode sheet, thereby achieving the separation of the positive electrode current collector and the positive electrode active material, wherein component A is mainly a high-polarity, high-boiling point organic solvent, and component B is a low-polarity, low-boiling point organic solvent, wherein component A plays a major role in dissolving polyvinylidene fluoride. Although component B cannot directly dissolve PVDF, it can be miscible with component A. When the positive electrode sheet is placed in the composite leachate for leach treatment, component B in the composite leachate can swell the positive electrode film layer, thereby making it easier for component A to penetrate the positive electrode film layer, thereby dissolving the polyvinylidene fluoride in the positive electrode film layer in the composite leachate, thereby dispersing the positive electrode active material in the positive electrode film layer in the composite leachate, and the positive electrode current collector and the positive electrode film layer are peeled off, thereby separating the positive electrode current collector from the positive electrode active material.

[0010] Based on this, the method provided in the present application can effectively reduce the use of high-polarity and high-boiling point organic solvents, thereby saving costs and reducing environmental pollution, and is more suitable for industrial production applications.

[0011] It should also be noted that component A in the present application may include but is not limited to the above-mentioned ones, and those skilled in the art may select other strongly polar organic solvents that can dissolve polyvinylidene fluoride according to actual needs; component B also includes but is not limited to the above-mentioned ones, and other low-boiling point organic solvents that are miscible with component A may be selected according to actual needs.

[0012] In some embodiments, the positive electrode film layer further contains conductive carbon.

[0013] In some embodiments, in step S2, the mass ratio of the positive electrode sheet to the composite solvent is 1:0.5-5.

[0014] In some of the above embodiments, under this condition, the composite solvent can fully leached the positive electrode sheet, so that the polyvinylidene fluoride is fully dissolved in the composite solvent, so that the positive electrode film layer and the positive electrode current collector are more easily separated and improved. The separation efficiency can also reduce the subsequent recovery of the polyvinylidene fluoride in the leaching solution. For example, the mass ratio of the positive electrode sheet to the composite solvent can be 1:0.5, 1:0.8, 1:1.1, 1:1.5, 1:2.1, 1:2.5, 1:3, 1:3.6, 1:3.8, 1:4, 1:5, or within the range of any of the above values.

[0015] In some embodiments, in step S2, the conditions for the leaching treatment include: leaching treatment at 10-50° C. for 0.5-3 h.

[0016] In some of the above embodiments, under this condition, the polyvinylidene fluoride in the positive electrode film layer can be fully dissolved in the composite solvent, so that the positive electrode film layer and the positive electrode current collector are fully separated, thereby improving the recovery rate of the polyvinylidene fluoride.

[0017] In some embodiments, in step S2, the mass proportion of component A in the composite leachate is 5% to 20%.

[0018] In some of the above embodiments, under this condition, the composite leachate has a better dissolving effect on polyvinylidene fluoride, which can further improve the separation efficiency of the positive electrode current collector and the positive electrode film layer, and obtain a better PVDF yield (up to 96% or more). At the same time, reducing the amount of component A can further reduce costs. For example, the mass proportion of component A in the composite leachate can be 5%, 7%, 9%, 10%, 13%, 15%, 18%, 20%, or within the range of any of the above values. Further preferably, the mass proportion is 10% to 15%. Within this range, the yield of PVDF can be further improved (greater than 98%) while ensuring a lower cost.

[0019] In some embodiments, the composite leachate consists of an A component and a B component.

[0020] In some of the above implementations, under this condition, in the filtrate obtained by filtering the leachate in step S3, the solvent consists only of component A and component B. Therefore, when recovering polyvinylidene fluoride in the filtrate, it is only necessary to distill component A and component B separately to obtain polyvinylidene fluoride with higher purity, thereby improving the recovery efficiency and reducing the recovery cost.

[0021] In some embodiments, in step S2, the B component includes C 1 ~C 3 Alcohol compounds and C 2 ~C 4 Ester compound; wherein the C 1 ~C 3 Alcohol compounds and the C 2 ~C 4 The mass ratio of the ester compound is 1 to 10:1.

[0022] In some of the above embodiments, the inventors found that component B includes C 1 ~C 3 Alcohol compounds and C 2 ~C 4 ester compounds, and the mass ratio of the two is 1 to 10:1, the composite leaching agent has a better leaching effect, which can further improve the solubility of polyvinylidene fluoride in the composite leaching agent, thereby further improving the recovery rate of polyvinylidene fluoride (for example, the yield reaches more than 99%). 1 ~C 3 Alcohol compounds and the C 2 ~C 4 The mass ratio of the ester compounds can be 1:1, 1.6:1, 2:1, 2.8:1, 3.5:1, 4.2:1, 5:1, 5.5:1, 6:1, 6.8:1, 7.2:1, 7.8:1, 8.2:1, 9:1, 9.5:1, 10:1, or within the range of any of the above values.

[0023] In some embodiments, the C 1 ~C 3 The alcohol compound includes at least one of methanol, ethanol or propanol; the C 2 ~C 4 The ester compound includes at least one of ethyl acetate and methyl acetate. Based on the above embodiment, the use of the above types of alcohol compounds and ester compounds can further reduce costs.

[0024] In some embodiments, the B component is C 1 ~C 3 Alcohol compounds and C2 ~C 4 Based on the above implementation, the composite solvent has fewer components and the cost of recovering polyvinylidene fluoride is lower.

[0025] In some embodiments, the method further comprises: step S4: distilling the filtrate to distill out the composite leachate to obtain polyvinylidene fluoride. Based on the above embodiment, the composite leachate is separated from polyvinylidene fluoride by distillation to improve the recovery rate of polyvinylidene fluoride.

[0026] In some embodiments, in step S4, the conditions of the distillation treatment include: distilling at 90-120°C for 1-3h to distill out component B in the composite leachate, and then distilling at 190-260°C for 1-3h to distill out component A in the composite leachate. Based on the above embodiment, since there is a large difference in the boiling points of component A and component B in the composite leachate, a method of segmented distillation at different temperatures can be used to distill out component A and component B respectively, and the distilled component A and component B can be reconfigured into a new composite leachate for repeated use, further reducing costs.

[0027] In some embodiments, in step S1, the positive electrode sheet is obtained by at least a discharge step and a disassembly step. Based on the above embodiment, the positive electrode sheet is obtained by discharging and disassembling the battery, and this method can be used to recycle various materials in the positive electrode sheet.

[0028] In some embodiments, in step S2, before the leaching treatment, the step further includes: shearing the positive electrode sheet to obtain a plurality of pieces with an area of ​​1 to 25 cm 2 Based on the above embodiment, the positive electrode sheet is sheared to increase the contact area between the positive electrode sheet and the composite solvent, thereby further improving the separation efficiency.

[0029] In some embodiments, step S2 includes applying stirring during the leaching process, and the stirring speed is 100 to 500 r / min.

[0030] In some embodiments, the method further comprises: step S5: washing the filter cake with a composite solvent and drying the filter cake to obtain a positive electrode active material. Based on the above embodiment, the filter cake is further washed with a composite solvent to further improve the recovery efficiency of polyvinylidene fluoride.

[0031] In some embodiments, the washing in step S5 is specifically countercurrent washing for 2 to 10 times, which can reduce the usage of the composite leaching agent and reduce the cost.

[0032] In some embodiments, the drying in step S5 is specifically drying at 190-260° C. for 1-3 hours.

[0033] It should be noted that, generally, the positive electrode film layer also includes a conductive agent, so the positive electrode active material obtained in step S5 also includes a conductive agent.

[0034] Compared with the prior art, the method provided in the present application for separating the positive electrode current collector and the positive electrode active material in the positive electrode sheet can effectively reduce the use of high-polarity and high-boiling point organic solvents, and at the same time has a higher recycling rate for PVDF in the positive electrode sheet, thereby saving costs and reducing environmental pollution, and is more suitable for industrial production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow chart of some embodiments of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0037] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the implementation or examples are included in at least one implementation or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more implementations or examples in a suitable manner.

[0038] The main purpose of the present invention is to provide a process for separating aluminum foil and active materials of lithium battery positive electrode sheets, aiming to solve the process problems in the existing technical solutions that a large amount of high-boiling point / high-price high-polarity solvents are used, large-scale industrialization is impossible, and PVDF cannot be effectively recovered.

[0039] To achieve the above-mentioned purpose, the present invention provides a method for separating the positive electrode current collector and the positive electrode active material in the positive electrode sheet, and the process flow chart thereof is as follows: Figure 1 As shown, the following steps are included:

[0040] S1, discharging the lithium battery and disassembling it to obtain the positive electrode sheet.

[0041] S2, putting the positive electrode sheet obtained in S1 into the composite leaching agent for leaching, and after leaching, the active material is detached and dispersed from the surface of the aluminum foil. The aluminum foil after stripping the active material is taken out and washed with an organic solvent to obtain an aluminum foil product. After leaching, the aluminum foil is taken out to obtain a leaching solution.

[0042] S3, filtering the leaching solution obtained in S2 to obtain a filtrate and a filter cake.

[0043] S4, the filtrate is distilled to obtain PVDF product and distillate, and the distillate is returned to the leaching process for recycling.

[0044] S5, the filter cake obtained in S3 is countercurrently washed with a composite solvent, and then dried at high temperature to obtain an active material. The washing liquid obtained by the countercurrent washing is returned to the leaching step for recycling.

[0045] Furthermore, the lithium battery described in the above step S1 is lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese ternary, nickel cobalt aluminum ternary, etc.

[0046] Furthermore, the positive electrode sheet obtained by disassembling in the above step S1 can be cut into pieces with an area of ​​1-25 cm 2 of fragments.

[0047] Furthermore, in the above step S2, the mass ratio of the positive electrode sheet to the composite solvent during leaching is 1:0.5-5.

[0048] Further, in the above step S2, the composite leaching agent is composed of two components, A and B, and the A component is composed of a high-boiling point strong polar organic solvent, and the strong polar solvent is composed of NMP (N-methylpyrrolidone), DMAC (dimethylacetamide), DMF (N, N-dimethylformamide), TEP (triethyl phosphate) and DMSO (dimethyl sulfoxide) or a mixture of several substances. The A component accounts for 5% to 20% in the composite leaching agent, preferably 10% to 15%, which plays a role in dissolving PVDF. The B component is composed of a low-boiling point low-polarity organic solvent, and the low-polarity solvent is composed of methanol, ethanol, ethyl acetate, methyl acetate, ether, acetone or a mixture of several substances. The B component accounts for 80 to 95% in the composite leaching agent. The B component is preferably a mixture of low-chain alcohols (such as methanol, ethanol, etc.) and low-chain esters (ethyl acetate, methyl acetate, etc.), and the mass ratio of low-chain alcohols to low-chain esters in the B component is preferably 1 to 10:1.

[0049] Furthermore, in the above step S2, stirring is applied during the leaching process, the stirring speed is 100-500 r / min, the leaching temperature is 10-50° C., and the leaching time is 0.5-3 h.

[0050] In the above step S4, the distillation is a temperature-stage distillation, the first distillation temperature stage is 90-120°C, the distillation time is 1-3h, and the main purpose is to distill out component B. The second distillation temperature stage is 190-260°C, the distillation time is 1-3h, and the main purpose is to distill out component A and purify PVDF. The components A and B obtained by the two distillations are mixed as a composite solvent and returned to the leaching process for recycling.

[0051] Furthermore, in the above step S5, the countercurrent washing times are 2-10 times, the evaporation drying temperature is 190-260° C., and the drying time is 1-3 hours.

[0052] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels. During the experiment, the positive electrode sheet will inevitably be stuck with electrolyte.

[0053] Example 1

[0054] Disassemble 20 lithium iron phosphate batteries to obtain 245.5g of positive electrode sheets, and cut the positive electrode sheets into pieces with an area of ​​1cm 2 The initial ratio of the battery is lithium iron phosphate: conductive carbon: PVDF mass = 94%: 4%: 2%; the compacted density of the battery positive electrode is 210g / m 2 The total amount of positive electrode material used in 20 batteries except aluminum foil is 197.4g, of which PVDF is 3.948g. The thickness of the aluminum foil used is 16μm, and the amount of aluminum foil used in 20 batteries is 41.1g.

[0055] The obtained 245.5g positive electrode sheet was immersed in 491g composite leaching agent at 30°C and 100r / min stirring speed for 1h. Among the components of the composite leaching agent, component A accounts for 10% of the solvent mass, component A is NMP (N-methylpyrrolidone), component B accounts for 90% of the solvent mass, and component B is ethanol and ethyl acetate, wherein ethanol accounts for 90% of the B component mass. After leaching, the aluminum foil was separated, and the mass of the aluminum foil obtained after washing and drying was 41.08g, and the yield of the positive electrode sheet was 99.97%. The leaching solution obtained by leaching was filtered and separated to obtain a filter cake and a filtrate. The filter cake was washed 5 times with a composite solvent in countercurrent and dried at 200°C for 3h to obtain 191.6g of filter cake (i.e., positive electrode material, including positive electrode active material and conductive carbon at this time). The filtrate was distilled at 120°C for 2 h, and the distillate components mainly included ethanol and ethyl acetate. The temperature was then raised to 200°C for distillation for 2 h, and the distillate components mainly included NMP. After distillation, 3.92 g of PVDF product was obtained, and the PVDF yield was 99.29%.

[0056] Embodiment 2-3

[0057] The method is substantially the same as Example 1, except that the mass ratio of ethanol to ethyl acetate in component B of the composite leachate is different, as shown in Table 1.

[0058] In addition, the mass of initial PVDF, the mass of PVDF after distillation, and the PVDF yield are shown in Table 1.

[0059] Example 4

[0060] Disassemble 20 lithium iron phosphate batteries from the same batch as Example 1 to obtain 241.6 g of positive electrode sheets. Cut the positive electrode sheets into pieces with an area of ​​1 cm 2 The initial ratio of the battery is lithium iron phosphate: conductive carbon: PVDF mass = 94%: 4%: 2%; the compacted density of the battery positive electrode is 210g / m 2 The total amount of positive electrode material used in 20 batteries except aluminum foil is 197.8g, of which PVDF is 3.956g. The thickness of the aluminum foil used is 16μm, and the amount of aluminum foil used in 20 batteries is 41.3g.

[0061] The obtained 241.6g positive electrode sheet was immersed in 491g composite solvent at 30℃ and 100r / min stirring speed for 1h. Among them, component A in the composite solvent accounts for 10% of the solvent mass, component A is NMP, component B accounts for 90% of the solvent mass, and component B is pure ethanol. After leaching, the aluminum foil was separated, and the mass of the aluminum foil obtained after washing and drying was 41.07g, and the yield of the positive electrode sheet was 99.44%. The leaching solution obtained by leaching was filtered and separated to obtain the filter cake and the filtrate. The filter cake was washed with the composite solvent in countercurrent for 5 times and dried at 200℃ for 3h to obtain 191.72g of filter cake (i.e., positive electrode material). The filtrate was distilled at 120℃ for 2h, and the distillate components mainly included ethanol, and then heated to 200℃ for distillation for 2h. The distillate components mainly included NMP. After distillation, 3.88g of PVDF product was obtained, and the PVDF yield was 98.08%.

[0062] Embodiments 5 to 7

[0063] The same as Example 4, except that the mass proportion of component A in the composite leachate is different, see Table 1 for details;

[0064] In addition, the mass of initial PVDF, the mass of PVDF after distillation, and the PVDF yield are shown in Table 1.

[0065] Example 8

[0066] The embodiment is substantially the same as the embodiment 1, except that the component B in the composite leaching agent is acetone and ethyl acetate in a mass ratio of 9:1, as shown in Table 1;

[0067] In addition, the mass of initial PVDF, the mass of PVDF after distillation, and the PVDF yield are shown in Table 1.

[0068] Comparative Example 1

[0069] Disassemble 20 lithium iron phosphate batteries from the same batch as Example 1 to obtain 243.9 g of positive electrode sheets. Cut the positive electrode sheets into pieces with an area of ​​1 cm 2 The initial ratio of the battery is lithium iron phosphate: conductive carbon: PVDF mass = 94%: 4%: 2%; the compacted density of the battery positive electrode is 210g / m 2 The total amount of positive electrode material used in 20 batteries except aluminum foil is 198.1g, of which PVDF is 3.96g. The thickness of the aluminum foil used is 16μm, and the amount of aluminum foil used in 20 batteries is 41.2g.

[0070] The obtained 243.9g positive electrode sheet was immersed in 491g of leaching agent at 30°C and 100r / min stirring speed for 1h. The leaching agent was pure NMP. After leaching, the aluminum foil was separated. After washing and drying, the mass of the aluminum foil was 41.09g, and the yield of the positive electrode sheet was 99.98%. The leaching solution obtained by leaching was filtered and separated to obtain the filter cake and the filtrate. The filter cake was washed 5 times with a composite solvent in countercurrent and dried at 200°C for 3h to obtain 191.56g of filter cake (i.e., positive electrode material). The filtrate was distilled at 120°C for 2h, then heated to 200°C for distillation for 2h. After distillation, 3.89g of PVDF product was obtained, and the yield of PVDF was 98.18%.

[0071] In Example 1, the mass of component A accounts for 10% of the mass of the solvent, the material of component A is NMP, the mass of component B accounts for 90% of the mass of the solvent, and the material of component B is ethanol and ethyl acetate, wherein ethanol accounts for 90% of the mass of component B. The current market price of NMP is 11,366 yuan / ton, the price of ethanol is 6,000 yuan / ton, and the price of ethyl acetate is 4,200 yuan / ton. After conversion, the total price of the solvent in Example 1 is 3.13 yuan. The corresponding PVDF yield in Comparative Example 1 is about 1% lower than that in Example 1, and the solvent price is 5.58 yuan after conversion, which is 78.3% higher than that in Example 1, and the amount of toxic solvent NMP in Example 1 is greatly reduced by 90%.

[0072] Table 1

[0073]

[0074]

[0075] Note: “--” in Table 1 means that the parameter is not included.

[0076] According to the results in Table 1, each embodiment can separate the positive electrode current collector from the positive electrode film layer by using the composite leachate, and has a high recycling rate for PVDF. At the same time, the high polarity and high boiling point component A in the composite leachate accounts for a low proportion, which can effectively reduce the recycling cost.

[0077] Furthermore, according to Examples 1 to 3, the mass ratio of alcohol to ester in component B has a certain influence on the recovery rate of PVDF. When the mass ratio of alcohol to ester satisfies the condition of 1 to 10:1, the recovery rate of PVDF is higher.

[0078] According to Examples 1, 4, and 8, the composition of component B has a certain influence on the recycling rate of PVDF. Using a combination of alcohol and ester as component B can further improve the recycling rate of PVDF.

[0079] According to Examples 4 to 7, the mass proportion of component A in the composite leachate has a certain influence on the recovery rate of PVDF. When the mass proportion of component A in the composite leachate meets the condition of 10% to 15%, the recovery rate of PVDF is higher.

[0080] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for separating a positive electrode current collector and a positive electrode active material in a positive electrode sheet, characterized in that: The following steps are involved: Step S1: providing a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector; Wherein, the positive electrode film layer comprises polyvinylidene fluoride and positive electrode active material; Step S2: placing the positive electrode sheet in a composite leaching agent for leaching treatment, so that the polyvinylidene fluoride in the positive electrode sheet is dissolved in the composite leaching agent, and the positive electrode current collector and the positive electrode film layer are peeled off to obtain the positive electrode current collector and the leaching solution; Wherein, the composite leaching agent comprises component A and component B; The component A includes at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide, and the component B includes at least one of C1-C3 alcohol compounds, C2-C4 ester compounds, acetone and ether; Step S3: filtering the leaching liquid to obtain a filtrate and a filter cake; Wherein, the filter cake includes positive electrode active material.

2. The method according to claim 1, characterized in that: In the step S2, the mass ratio of the positive electrode sheet to the composite solvent is 1:0.5-5.

3. The method according to claim 1, characterized in that In the step S2, the conditions of the leaching treatment include: leaching treatment at 10-50° C. for 0.5-3 h.

4. The method according to claim 1, characterized in that: In the step S2, the mass proportion of the component A in the composite leaching agent is 5% to 20%; Preferably, the mass proportion of the component A in the composite leachate is 10% to 15%.

5. The method according to claim 1 or 4, characterized in that: The composite leaching agent consists of component A and component B.

6. The method according to claim 1, characterized in that In the step S2, the component B includes C1-C3 alcohol compounds and C2-C4 ester compounds; Wherein, the mass ratio of the C1-C3 alcohol compounds to the C2-C4 ester compounds is 1-10:

1.

7. The method according to claim 1 or 6, characterized in that: The C1-C3 alcohol compound includes at least one of methanol, ethanol or propanol; The C2-C4 ester compound includes at least one of ethyl acetate and methyl acetate.

8. The method according to claim 6, characterized in that The B component is a mixture of C1-C3 alcohol compounds and C2-C4 ester compounds.

9. The method according to claim 1, characterized in that: Also includes: Step S4: performing a distillation treatment on the filtrate to distill out the composite solvent to obtain polyvinylidene fluoride; Preferably, in step S4, the distillation treatment conditions include: distilling at 90-120° C. for 1-3 hours to distill out component B in the composite solvent, and then distilling at 190-260° C. for 1-3 hours to distill out component A in the composite solvent.

10. The method according to claim 1, characterized in that In the step S1, the positive electrode sheet is obtained through at least a discharge step and a disassembly step; Preferably, in the step S2, before the leaching treatment, the step further includes: cutting the positive electrode sheet to obtain a plurality of pieces with an area of ​​1 to 25 cm 2 Fragments of positive electrode; Preferably, it also includes: Step S5: washing and drying the filter cake with a composite solvent to obtain a positive electrode active material.

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