Recycling method of waste lithium battery polyvinylidene fluoride adhesive

Abstract

The invention belongs to the technical field of waste battery recycling, and particularly relates to a recycling method of a waste lithium battery polyvinylidene fluoride adhesive. The method comprises the following steps: leaching, soaking and dissolving crushed parts of the waste lithium batteries by adopting an organic solvent, fully dissolving a polyvinylidene fluoride adhesive, carrying out centrifugal separation treatment, and removing impurities to obtain an extracting solution containing the polyvinylidene fluoride adhesive; separating and recovering the organic mixed solvent and the polyvinylidene fluoride solution by adopting filter membrane filtration and vacuum rotary evaporation; adding a pore-foaming agent into the polyvinylidene fluoride solution to prepare a membrane casting solution; and preparing the regenerated flat sheet membrane by adopting a non-solvent induced phase inversion method. According to the method, impurities are effectively separated and removed through leaching, soaking and dissolving of the organic solvent and subsequent treatment of the extracting solution, and the quality and performance of the regenerated flat sheet membrane are ensured. The regenerated flat sheet membrane is prepared by adopting a non-solvent induced phase inversion method, so that the environmental pollution is reduced, the energy consumption is reduced, and the requirement of sustainable development is met.

Description

Technical Field

[0001] The invention belongs to the technical field of waste battery recycling, and in particular relates to a method for recycling polyvinylidene fluoride adhesive of waste lithium batteries. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries are being used in more and more scenarios, such as tower base stations, new energy vehicles, 3C products, robots and other industries. The life of lithium-ion batteries generally ranges from 3 to 7 years. When lithium-ion batteries are in abnormal use such as overcharge, over-discharge, high temperature, low temperature, high humidity, or collision, extrusion, etc., their service life will be shortened. When lithium-ion batteries serving in different environments reach the end of their life, they will face the problem of recycling and disposal.

[0003] Lithium-ion batteries are usually composed of a shell, positive active material, negative active material, positive binder (usually PVDF), negative binder (usually SBR), Al current collector, Cu current collector, diaphragm, electrolyte, etc. At present, the recycling of waste lithium-ion battery elements has become a hot topic in global research, but there are still many problems in actual production. The peeling of broken parts and aluminum foil of waste lithium-ion batteries is one of the severe challenges. The most commonly used methods for separating broken parts and current collectors include dissolving polyvinylidene fluoride (PVDF) with organic solvents, high-temperature calcination and decomposition of PVDF, crushing and screening, dissolving aluminum foil with alkaline solution, molten salt treatment, etc. Ultrasound is often used as an auxiliary means. In current research, although there are various methods for separating broken parts and current collectors, there are still problems such as high energy consumption, environmental pollution, and high prices in actual applications.

[0004] There are few research reports on the recycling and reuse of positive electrode adhesives. Chinese patent CN105990617A discloses a method for recycling and regenerating waste lithium-ion battery electrode materials as follows: the dried positive electrode sheet and / or negative electrode sheet are roasted at 250°C to 650°C for 1 to 6 hours, and then the positive and negative electrode powder materials are separated from the current collector by mechanical methods to obtain positive electrode powder materials and / or negative electrode powder materials. The purpose of roasting in this step is to render the adhesive ineffective by heat treatment.

[0005] Therefore, in order to cope with the recycling of a large number of waste lithium batteries and effectively recycle all resources, it is urgent to develop a green and economical process for recycling PVDF binders. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for recycling and reusing polyvinylidene fluoride adhesives from waste lithium batteries. After separating the adhesive, a non-solvent induced phase transformation method is used to prepare a regenerated flat membrane, thus establishing a green and economical method for recycling and reusing adhesive materials for lithium batteries. The technical solution adopted is:

[0007] A method for recycling polyvinylidene fluoride adhesive of waste lithium batteries comprises the following steps:

[0008] (1) washing, soaking and dissolving the broken parts of the waste lithium battery with an organic solvent, fully dissolving the polyvinylidene fluoride binder and centrifuging to remove impurities, thereby obtaining an extract containing the polyvinylidene fluoride binder;

[0009] (2) using membrane filtration and vacuum rotary evaporation to separate and recover the organic mixed solvent and the polyvinylidene fluoride solution;

[0010] (3) adding a porogen to the polyvinylidene fluoride solution to prepare a film casting solution;

[0011] (4) The regenerated flat membrane was prepared by non-solvent induced phase inversion method.

[0012] Preferably, in step (1), the organic solvent is at least one of diethyl ether, ethylene glycol dimethyl ether, petroleum ether, ethyl acetate, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dichloromethane, chloroform, dichloroethane, dichloroethylene, trichloroethylene, tetrachloroethylene, acetonitrile, acetone, tetrahydrofuran, methanol, ethanol, propanol, and isopropanol; and the volume ratio of the crushed parts to the organic solvent is 1:1 to 10, preferably 1:1.

[0013] Preferably, the broken pieces are completely immersed in an organic solvent by elution and immersion at a temperature of 20 to 60° C., and ultrasonic stirring or mechanical stirring is performed simultaneously to fully dissolve the polyvinylidene fluoride adhesive.

[0014] Preferably, during the centrifugal separation, an organic solvent is added for dilution, and centrifugation is performed at 5000 rpm for 20 minutes; the centrifugation is repeated 2 to 3 times.

[0015] Preferably, in step (2), a polytetrafluoroethylene membrane with a pore size of 0.2 to 1 micron is used for membrane filtration; the organic mixed solvent and the polyvinylidene fluoride adhesive solution are separated in a vacuum rotary evaporator. The vacuum rotary evaporator can be purchased through conventional commercial channels, and the setting conditions are set according to different solvents.

[0016] Preferably, in step (3), the porogen added is dibutyl phthalate.

[0017] Preferably, the specific method of preparing the casting solution is to add the porogen into the polyvinylidene fluoride solution, and stir and mix at room temperature to obtain the casting solution; wherein, the amount of the porogen added is 3-15% of the mass of the polyvinylidene fluoride solution.

[0018] Preferably, in step (4), the method for preparing the regenerated flat membrane by the non-solvent induced phase inversion method is:

[0019] a. Injecting the casting solution into the non-solvent induced phase inversion device and applying pressure to promote the phase inversion of the casting solution;

[0020] b. Solidify the liquid after phase inversion into a flat film under low temperature conditions.

[0021] Preferably, in step a, the applied pressure is 2-10 MPa and the temperature is 20-60°C.

[0022] Preferably, in step b, after the phase conversion is completed, the temperature is lowered to 0-20° C. and the curing time is 2-12 hours.

[0023] The thickness of the prepared regenerated flat membrane is 20 to 50 microns; the porosity of the membrane is above 20%, preferably 30 to 50%.

[0024] The tensile strength of the regenerated flat membrane is greater than 20 MPa; the thermal stability of the membrane remains intact at 200°C, and the tensile strength is greater than 25 MPa.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a green and efficient method for recovering polyvinylidene fluoride as a binder in positive electrode materials. The method effectively separates the polyvinylidene fluoride binder through treatments such as eluting, soaking and dissolving with an organic solvent, and then prepares a regenerated flat membrane by a non-solvent induced phase transformation method. This method not only avoids environmental pollution, but also enables the recycling of resources, thus meeting the requirements of sustainable development.

[0027] The present invention provides an economical, environmentally friendly and sustainable method for recycling PVDF binders from waste lithium batteries. The binder in the positive electrode powder of retired lithium-ion batteries recovered by the technology has high purity and a recovery rate of more than 98%. It is suitable for the recycling and reuse of waste PVDF materials in the field of waste lithium battery recycling and industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0029] The accompanying drawings are only used for exemplary description. The technical solution of the present invention is described in detail below through embodiments in combination with the accompanying drawings. For those skilled in the art, some well-known structures and their descriptions in the accompanying drawings may be omitted, and therefore, they should not be understood as limitations on the present invention.

[0030] The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer shall be followed. The raw materials, instruments and equipment used, if the manufacturer is not specified, are all conventional products that can be purchased commercially. Other technical methods not described herein adopt existing technologies.

[0031] Example 1

[0032] Organic solvent selection and elution process:

[0033] In the implementation process of the present invention, ethyl acetate is first selected as the organic solvent to improve the solubility and recovery rate of the PVDF adhesive. The broken pieces of the waste lithium battery are sent to the organic solvent elution system, and the system evenly covers the organic solvent on the surface of the broken pieces by spraying or soaking to ensure that the PVDF adhesive is fully dissolved and separated. The elution process can be carried out in a closed reactor to minimize the loss of solvent volatilization and maintain the safety of the operating environment.

[0034] Extraction treatment and impurity removal:

[0035] The mixture of broken parts and organic solvent after elution, soaking and dissolution is called extract, which contains dissolved PVDF adhesive and other impurities. The extract enters the high-speed centrifuge or membrane filtration device for treatment through the conveying system. During the high-speed centrifugation process, organic solvent is added and centrifuged multiple times. The setting condition is 5000rpm centrifugation for 20 minutes to ensure that PVDF and organic solvent are effectively separated. The organic solvent is collected and enters the subsequent recovery system, while the solid residue is discharged through the discharge port.

[0036] Configuration and preparation of casting solution:

[0037] After most of the impurities are removed from the treated extract, its cleanliness meets the requirements for the preparation of the casting solution. During the preparation of the casting solution, an appropriate amount of fresh resin, porogen and other additives are added to the extract according to a predetermined formula ratio. The amount of these additives is fine-tuned according to actual needs to optimize the performance of the regenerated flat membrane, such as increasing the tensile strength or improving thermal stability.

[0038] Preparation of regenerated flat membrane by non-solvent-induced phase inversion:

[0039] The prepared casting solution is transported to the non-solvent induced phase inversion device. In the device, pressure is applied and temperature is controlled (such as the pressure in the device is 2MPa and the temperature is 60°C) to promote the phase inversion process of the liquid. This conversion process is carried out under low temperature conditions to ensure the high quality and good physical properties of the regenerated flat membrane. The liquid after phase inversion solidifies to form a film, and finally a regenerated flat membrane with a set thickness (20 to 50 microns) and porosity (30% to 50%) is prepared.

[0040] The embodiment of the present invention describes in detail the whole process of recycling PVDF adhesive from waste lithium batteries, and realizes the effective utilization of resources and environmental protection by preparing a regenerated flat membrane through organic solvent elution, extract solution treatment, casting solution configuration and non-solvent induced phase transformation. These steps are not only technically feasible and practical, but also conform to the concept of sustainable development, providing a new solution for the field of battery recycling.

[0041] Example 2

[0042] like Figure 1 As shown, a method for recycling polyvinylidene fluoride adhesive of waste lithium batteries comprises the following steps:

[0043] (1) Ethyl acetate is used to rinse, soak and dissolve the broken parts of the waste lithium battery, and the volume ratio of the broken parts to the organic solvent is 1:1. The rinsing and soaking are carried out in a reaction kettle, and all the broken parts are immersed in ethyl acetate at a temperature of 60°C. At the same time, mechanical stirring is performed to fully dissolve the polyvinylidene fluoride adhesive.

[0044] The polyvinylidene fluoride adhesive is fully dissolved and subjected to high-speed centrifugal separation. During the centrifugal separation, an organic solvent is added to the reactor for dilution, and centrifugal separation is performed at 5000 rpm for 20 minutes. The centrifugation is repeated 3 times to extract as cleanly as possible and remove impurities.

[0045] After removing impurities, an extract containing polyvinylidene fluoride binder is obtained. The organic solvent can be recycled and reused without causing waste.

[0046] (2) When filtering with a membrane, a polytetrafluoroethylene membrane with a pore size of 0.2 micrometers was used; the organic mixed solvent and the polyvinylidene fluoride adhesive solution were separated in a vacuum rotary evaporator. The recovery rate of the polyvinylidene fluoride adhesive was 98.5%.

[0047] (3) Adding a porogen to the polyvinylidene fluoride solution in an amount of 5% by mass of the polyvinylidene fluoride solution to prepare a casting solution.

[0048] (4) The non-solvent induced phase inversion method is used to prepare the regenerated flat membrane. The method for preparing the regenerated flat membrane by the non-solvent induced phase inversion method is as follows:

[0049] a. Inject the casting solution into the non-solvent induced phase inversion device, apply a pressure of 2MPa and a temperature of 50°C to promote the phase inversion of the casting solution;

[0050] b. Solidify the phase-converted liquid into a flat membrane at 0°C, i.e., a regenerated flat membrane. The thickness of the regenerated flat membrane is 20 microns; the porosity of the membrane is 30%.

[0051] Example 3

[0052] A method for recycling polyvinylidene fluoride adhesive of waste lithium batteries comprises the following steps:

[0053] (1) Ethyl acetate is used to rinse, soak and dissolve the broken parts of the waste lithium battery, and the volume ratio of the broken parts to the organic solvent is 1:2. The rinsing and soaking are carried out in a reaction kettle, and all the broken parts are immersed in ethyl acetate at a temperature of 60°C. At the same time, mechanical stirring is performed to fully dissolve the polyvinylidene fluoride adhesive.

[0054] The polyvinylidene fluoride adhesive is fully dissolved and centrifuged. During the centrifugal separation, an organic solvent is added to the reaction kettle for dilution, and centrifugation is performed at 4000 rpm for 30 minutes; the centrifugation is repeated twice to extract as cleanly as possible and remove impurities. Impurities are removed to obtain an extract containing the polyvinylidene fluoride adhesive. The organic solvent can be recycled and reused without causing waste.

[0055] (2) When filtering with a membrane, a polytetrafluoroethylene membrane with a pore size of 0.2 to 1 micron was used; the organic mixed solvent and the polyvinylidene fluoride adhesive solution were separated in a vacuum rotary evaporator. The recovery rate of the polyvinylidene fluoride adhesive was 97.8%.

[0056] (3) Add a porogen to the polyvinylidene fluoride solution, wherein the amount of the porogen added is 10% of the mass of the polyvinylidene fluoride solution to prepare a casting solution.

[0057] (4) The non-solvent induced phase inversion method is used to prepare the regenerated flat membrane. The method for preparing the regenerated flat membrane by the non-solvent induced phase inversion method is as follows:

[0058] a. Inject the casting solution into the non-solvent induced phase inversion device, apply a pressure of 5 MPa; the temperature is 60 ° C to promote the phase inversion of the casting solution;

[0059] b. Solidify the liquid after phase conversion into a flat membrane at a temperature of 0-20°C, i.e., a regenerated flat membrane. The thickness of the regenerated flat membrane is 30 microns; the porosity of the membrane is 40%.

[0060] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for recycling polyvinylidene fluoride adhesive from waste lithium batteries, characterized in that: The steps include: (1) washing, soaking and dissolving the broken parts of the waste lithium battery with an organic solvent, fully dissolving the polyvinylidene fluoride binder and centrifuging to remove impurities, thereby obtaining an extract containing the polyvinylidene fluoride binder; (2) separating and recovering the organic mixed solvent and the polyvinylidene fluoride solution by stirring, membrane filtration and vacuum rotary evaporation; (3) adding a porogen to the polyvinylidene fluoride solution to prepare a film casting solution; (4) The regenerated flat membrane was prepared by non-solvent induced phase inversion method.

2. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (1), the organic solvent is at least one of ether, ethylene glycol dimethyl ether, petroleum ether, ethyl acetate, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dichloromethane, chloroform, dichloroethane, dichloroethylene, trichloroethylene, tetrachloroethylene, acetonitrile, acetone, tetrahydrofuran, methanol, ethanol, propanol, and isopropanol; and the volume ratio of the crushed parts to the organic solvent is 1:1 to 10.

3. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (1), during the centrifugal separation, an organic solvent is added to the reaction kettle for dilution, and centrifugal separation is performed at 5000 rpm for 20 minutes; the centrifugation is repeated 2 to 3 times.

4. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (2), the rotary evaporation temperature is 20 to 100°C.

5. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (2), a polytetrafluoroethylene membrane with a pore size of 0.2 to 1 micron is used for membrane filtration; and the organic mixed solvent and the polyvinylidene fluoride binder solution are separated in a vacuum rotary evaporator.

6. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (3), the porogen is dibutyl phthalate.

7. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: The specific method of preparing the casting solution is to add the porogen into the polyvinylidene fluoride solution, and stir and mix at room temperature to obtain the casting solution; wherein, the amount of the porogen added is 3-15% of the mass of the polyvinylidene fluoride solution.

8. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 1, characterized in that: In the step (4), the method for preparing the regenerated flat membrane by the non-solvent induced phase inversion method is: a. Injecting the casting solution into the non-solvent induced phase inversion device and applying pressure to promote the phase inversion of the casting solution; b. Solidify the liquid after phase inversion into a flat film under low temperature conditions.

9. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 8, characterized in that: In the step a, the applied pressure is 2-10 MPa and the temperature is 20-60°C.

10. The method for recycling polyvinylidene fluoride adhesive of waste lithium batteries according to claim 8, characterized in that: In the step b, after the phase conversion is completed, the temperature is lowered to 0-20° C. for curing, and the curing time is 2-12 hours.

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