Preparation method of ultrathin anion exchange membrane and application of ultrathin anion exchange membrane in organic flow battery

Abstract

The invention discloses a preparation method of a double-layer ultrathin anion exchange membrane and application of the anion exchange membrane in an aqueous organic flow battery, the anion exchange membrane is composed of a functional anion exchange layer and a porous polyethylene membrane mixed layer filled with a functional polymer, and the mixed layer needs hydrophilic treatment; the mixed layer subjected to hydrophilic treatment is arranged on the negative electrode carbon felt side of the water-based flow battery, and the functional anion exchange layer is arranged on the positive electrode carbon felt side of the water-based flow battery; the thickness of the functional anion exchange layer of the ultrathin anion exchange membrane is only 2-3 [mu] m, the cost of the anion exchange membrane can be remarkably reduced, and electrolyte permeation can be effectively reduced due to the compact structure; the thickness of the mixed layer is 7-20 microns, the ion transfer distance is relatively short, and the ion transfer resistance can be remarkably reduced; in addition, the PE membrane has a rough and porous structure, filling of membrane liquid is facilitated, a compact anion membrane which is good in adhesiveness and free of defects is formed, and the reliability of the anion membrane is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of organic flow batteries, and specifically provides a preparation method of a double-layer ultra-thin anion exchange membrane (DLM) and its application in organic flow batteries. Background Art

[0002] Organic flow batteries are a new type of energy storage technology. As a key component, the anion exchange membrane (AEM) not only separates the positive and negative electrolyte solutions but also conducts anions to form the internal circuit of the battery. However, traditional anion membranes have poor mechanical strength (low tensile strength and elongation at break), resulting in the necessity to maintain a certain thickness (≥50 μm) to maintain their integrity and high cost. In addition, due to the relatively thick thickness of the anion membranes prepared by traditional processes, the ion transfer resistance is relatively large, and during the curing and drying process of the membrane solution (curing from the surface to the inside), the evaporation of high-boiling solvents inside is not smooth, and there is a situation of "boiling over" of the solvent, resulting in defects such as porous interiors and hole-like surfaces in the anion membranes, which in turn leads to cross-permeation of the positive and negative electrolyte solutions, seriously affecting the service life of the battery. Therefore, it is necessary to develop new ion exchange membrane manufacturing technologies, reduce the cost of anion exchange membranes, improve ion transfer capabilities, fundamentally solve the mechanical strength problem and the defect problem on the membrane surface, and thus promote the industrial development of organic flow batteries. Summary of the Invention

[0003] To solve the problems raised in the above background art, the purpose of the present invention is to provide a preparation method of a double-layer ultra-thin anion exchange membrane (DLM) and its application in organic flow batteries. The anion exchange membrane prepared by the method of the present invention is composed of a functional anion exchange layer and a porous polyethylene membrane (PE) mixed layer filled with a functional polymer; the thickness of the functional anion exchange layer is only 2-3 μm, which can significantly reduce the cost of the anion exchange membrane by at least 90%, and has a dense structure (no defects inside and on the surface), which can effectively reduce the penetration of the electrolyte solution; the thickness of the mixed layer is 7-20 μm, with a relatively short ion transfer distance, which can significantly reduce the ion transfer resistance; in addition, the PE membrane has a rough and porous structure, which is beneficial to the filling of the membrane solution and the formation of a dense anion membrane with good adhesion and no defects, improving the reliability of the anion membrane. Most importantly, when this ultra-thin anion membrane is applied in aqueous organic batteries, it can significantly reduce the resistance of the battery, improve the energy efficiency and service life of the battery.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of a double-layer ultra-thin anion membrane (DLM), comprising the following steps:

[0006] (1) Preparation of membrane solution: dissolving a functional polymer with anion exchange capacity in an organic solvent to prepare a uniform membrane solution with good fluidity;

[0007] (2) Adding additives: adding 0.05wt%-0.2wt% of a surfactant to the above-mentioned membrane liquid, fully dispersing it and letting it stand to defoam, so as to reduce the surface tension of the membrane liquid, inhibit the generation of surface defects during the drying process of the membrane liquid, and improve the uniformity of the membrane surface;

[0008] (3) Laboratory-level manufacturing: PE film positioning - PVC aqueous solution is sprayed on the smooth and flat surface of the glass plate, the PE film is placed on the surface of the PVC aqueous solution, and the PET substrate is placed on the surface of the PE film. Finally, the PE film is wiped with dust-free paper through the PET until it is evenly attached, and then the PET is removed and the PE film is dried;

[0009] Manufacturing level processing: Place the PE film on the head of the coating machine, manually pull the PE film to the machine position, and adjust the tension of the reel to make the surface of the PE film flat;

[0010] (4) Membrane liquid coating: The membrane liquid obtained in (2) is evenly coated on the surface of the PE membrane, and then heated, dried and solidified into a film to obtain an ultra-thin anion exchange membrane DLM;

[0011] (5) Preparation of hydrophilic agent: alcohol and pure water are mixed in a volume ratio of 1:1 to obtain a hydrophilic solvent, and then an appropriate amount of hydrophilic polymer material is added and heated to dissolve;

[0012] (6) DLM hydrophilic treatment: The ultra-thin anion exchange membrane is immersed in a hydrophilic agent, taken out and washed with water, and the hydrophilic treatment is completed; a double-layer ultra-thin anion exchange membrane is obtained.

[0013] Furthermore, in step (1), the mass percentage of the functional polymer in the membrane solution is 15%-21%; the functional polymer is one or more of quaternized polyalkyltriphenylpyridine, quaternized polyalkyltriphenylpiperidine and other high molecular polymers with positive charge and anion adsorption function; the organic solvent can be one or more of nitrogen-methylpyrrolidone, dimethyl sulfoxide, and dimethylformamide.

[0014] Furthermore, in step (2), the surfactant is one or more of a fluorocarbon surfactant, a polyethylene oxide ether surfactant, an amine salt surfactant and a quaternary ammonium salt surfactant.

[0015] Furthermore, in step (3), the PE membrane is a porous membrane with a thickness of 7-17 μm and a pore size of 30-50 nm. Before use, the surface of the PE membrane cannot be directly subjected to force (such as wiping or scratching).

[0016] Further, in step (4), the thickness of the film formed by heating, drying, and curing is 2 - 3 μm.

[0017] Further, in step (5), 0.5 wt.% - 1.5 wt.% of a hydrophilic polymer material is added to the hydrophilic solvent. The hydrophilic polymer material is ethylene - vinyl alcohol copolymer; the alcohol is one or more of ethanol and isopropanol.

[0018] Further, in step (6), the anion exchange membrane is composed of a functional anion exchange layer and a mixed layer of a porous polyethylene membrane (PE) filled with a functional polymer. Among them, the mixed layer needs to be hydrophilically treated. During the hydrophilization treatment, the soaking temperature is 35 - 45 °C; if the temperature of the hydrophilizing agent is too low, the ethylene - vinyl alcohol copolymer will be affected, and if the temperature of the hydrophilizing agent is too high, the polymer in the functional layer will swell and become unstable.

[0019] Further, in step (6), the thickness of the double - layer ultra - thin anion exchange membrane is 7 - 20 μm.

[0020] The present invention also provides a double - layer ultra - thin anion exchange membrane prepared by the preparation method as described above.

[0021] The present invention also provides the application of the double - layer ultra - thin anion exchange membrane as described above in an aqueous organic flow battery.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] The thickness of the functional anion exchange layer of the DLM of the present invention is only about 2 - 3 μm, which can significantly reduce the cost of the anion exchange membrane by at least 90%.

[0024] The anion exchange layer of the DLM of the present invention is relatively thin, which is convenient for solvent evaporation to form a dense structure. Moreover, the PE membrane in the mixed layer has a rough and porous structure, which is conducive to the filling of the membrane liquid and the formation of a dense anion membrane with good adhesion and no defects, and has a stronger ability to block the penetration of the electrolyte, significantly improving the service life of the battery.

[0025] The thickness of the mixed layer of the DLM of the present invention is 7 - 20 μm, which has a relatively short ion transfer distance, can significantly reduce the ion transfer resistance, and improve the energy efficiency of the battery.

[0026] The preparation process of the DLM of the present invention is simple and suitable for large - scale production. Description of the Drawings

[0027] Figure 1 Cross - sectional SEM pictures of a 7 - μm PE membrane (left) and an ultra - thin anion membrane (DLM, right) fabricated by the laboratory - level method of the present invention for a 7 - μm PE membrane;

[0028] Figure 2 SEM image of the surface of the PE film according to the present invention;

[0029] Figure 3 Cross-sectional SEM images of 17μm PE film (left) and the ultrathin anion exchange membrane (DLM, right) prepared by the laboratory-level method according to the present invention;

[0030] Figure 4 Adhesion image of the ultrathin anion exchange membrane (DLM) prepared by the method according to the present invention;

[0031] Figure 5 Surface SEM image of the ultrathin anion exchange membrane prepared by the method according to the present invention;

[0032] Figure 6 Capacity decay graph of the anion exchange membrane (T-AEM) in Example 3 in a single cell;

[0033] Figure 7 Capacity decay graph of the double-layer ultrathin anion exchange membrane (DLM) prepared by the process according to the present invention in Example 4 in a single cell;

[0034] Figure 8 Surface images of the ultrathin anion exchange membranes prepared from the membrane solutions of Comparative Example 1 and Comparative Example 2;

[0035] Figure 9 Cross-sectional SEM image of the anion exchange membrane (T-AEM) prepared in Comparative Example 3;

[0036] Figure 10 Surface SEM image of the anion exchange membrane (T-AEM) prepared in Comparative Example 3. Detailed implementation manners

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] In the embodiments of the present invention, the application is in a flow battery, and the organic flow energy storage battery of the TEMPO-MV system with the most commercial potential is selected as an example for description, but it does not limit the application of the solution described in the present invention in other flow batteries.

[0039] Single cell performance test conditions:

[0040] (1) Current density is: 80mA / cm 2 ;

[0041] (2) Charge and discharge experiment: Charge to 1.5 V and discharge to 0.9 V;

[0042] (3) Electrode parameters: Thickness is 4 mm, assembly compression ratio is 20%, and effective working area is 49 cm 2 ;

[0043] (4) Anion exchange membrane: The anion exchange membrane and ultra-thin anion membrane prepared in Comparative Example 3;

[0044] (5) Electrolyte: 50 mL of 1.5 M TEMPO aqueous solution is used for the positive electrode, and 50 mL of 1.5 M MV aqueous solution is used for the negative electrode;

[0045] (6) Other conditions: Laboratory temperature is 25 ± 2 °C, and the pump speeds of the positive and negative electrodes are both 35 r / min.

[0046] Example 1

[0047] Preparation process of double-layer ultra-thin anion membrane (DLM): (1) Dissolve the functional polymer (name: quaternized polyalkyltriphenylpyridine, manufacturer: Suqian Zhongke Times New Materials Co., Ltd., the same below) in DMSO solvent to form a homogeneous membrane solution (solid content 21%); (2) Add 0.15% of polyether silicone (name: Wet 270, manufacturer: Evonik Operations GmbH, Germany; the same below) to the membrane solution, fully disperse it, and let it stand until there are no visible bubbles in the membrane solution; (3) 7 μm PE membrane positioning - Spray PVC aqueous solution on the surface of a smooth and flat glass plate, place the PE membrane on the surface of the PVC aqueous solution, then place a PET substrate on the surface of the PE membrane, and finally wipe the PE membrane through the PET with dust-free paper until it fits evenly, then remove the PET and dry the PE membrane; (4) Coating the membrane solution on the PE membrane, the coating thickness of the membrane solution is 55 μm, heat it to 90 °C and dry for 0.5 h to prepare an anion exchange membrane (DLM-10) with a functional coating thickness of 2.8 μm (as shown in Figure 1 (right)).

[0048] Characterization and performance testing of double-layer ultra-thin anion membrane (DLM): Figure 2 It is the SEM image of the surface of the PE membrane after positioning. It can be seen from the figure that the positioned PE membrane is still rough and porous, which is beneficial to the penetration of the membrane solution and improves the bonding strength between the functional layer and the PE membrane; Figure 1It is a cross-sectional SEM image of PE and DLM. It can be seen from the figure that compared with the PE film, the mixed layer of DLM is denser, and the dense layer can reduce the ion transfer channel, which is manifested as the ion conductivity of DLM-10 is lower than that of T-AEM (see Table 2 for details), and the functional layer is very dense and has a thickness of 2.8 μm; by comparing the morphology of T-AEM in Comparative Example 3 and DLM in Example 1, it can be seen that the double-layer ultra-thin anionic membrane (DLM) has a denser cross-sectional structure. The reason is that the functional layer is thin, the solvent is easy to escape, and then a dense structure is produced.

[0049] Example 2

[0050] Preparation process of double-layer ultra-thin anion membrane (DLM): (1) dissolving the functional polymer in DMSO solvent to form a uniform membrane solution (solid content 21%); (2) adding 0.15% polyether siloxane to the membrane solution and fully dispersing it and letting it stand until there are no bubbles visible to the naked eye in the membrane solution; (3) positioning of 17 μm PE membrane - spraying PVC aqueous solution on the smooth and flat surface of the glass plate, placing the PE membrane on the surface of the PVC aqueous solution, and then placing the PET substrate on the surface of the PE membrane, and finally wiping the PE membrane with dust-free paper through the PET until it is evenly attached, then removing the PET and drying the PE membrane; (4) coating the membrane solution on the PE film, the membrane solution coating thickness is 40 μm, heating to 90°C and drying for 0.5h, and an anion exchange membrane (DLM-19) with a functional coating thickness of 1.8 μm can be prepared (such as Figure 3 (shown on the right).

[0051] Double-layer ultra-thin anion membrane (DLM) characterization and performance testing: Figure 3 It is the cross-sectional SEM image of PE and DLM. It can be seen from the figure that compared with the 17μm PE membrane, the mixed layer of DLM is still denser. This dense layer can reduce the ion transfer channel, which is manifested as the ion conductivity of DLM-19 is lower than that of T-AEM (see Table 2 for details), and the functional layer is very dense and the thickness is 1.8μm; Figure 4 This is the adhesion test chart of DLM-19 (immerse the DLM-19 film in water to make it fully wet, take out the wet film, and use the tip of a utility knife to scrape the functional coating surface of the wet film. The adhesion is judged by whether the functional coating falls off.) From the figure, it can be seen that the functional layer and the PE film have a high bonding strength and there is no shedding phenomenon; Figure 5It is the surface SEM image of DLM-19. It can be seen from the figure that the functional layer is very dense and there are no obvious hole-like defects. By comparing the morphologies of T-AEM in Comparative Example 3 and DLM-19 in Example 2, it can be known that the double-layer ultra-thin anion membrane has a more dense and "zero" defect perfect structure. The reason is that the functional layer is relatively thin, and the solvent is easy to escape, thus generating a dense structure. In addition, from the mechanical strength comparison data of T-AEM, DLM-10 and DLM-19 diaphragms in Table 1, it can be known that there is a qualitative change in the tensile strength of the double-layer ultra-thin anion membrane (DLM), and the elongation at break is significantly improved.

[0052] Table 1 Mechanical strength parameters of the diaphragms prepared in Comparative Example 3, Example 1 and Example 2

[0053] Diaphragm Thickness (μm) Tensile strength (MPa) Elongation at break (%) T-AEM 50 68.9(±3) 112.1(±4) DLM-10 10 143(±6) 120(±5) DLM-19 19 183(±5) 126(±3)

[0054] Example 3

[0055] The diaphragm of the single cell is a 50-μm T-AEM ion membrane, and the test results are as Figure 6 shown. From this, it can be known that: the capacity of the battery decays by 3.5% in the first 200 weeks; the capacity decay is relatively fast. The speculated reason is that the anion membrane (T-AEM) prepared in Comparative Example 3 has the characteristics of cross-section ( Figure 9 ) and surface defects ( Figure 10 ), the penetration of the electrolyte is relatively fast, and the order of magnitude of the permeability coefficient is similar to that of the commercial DSVN membrane (see Table 2 for details). Therefore, the capacity decay of the single cell test is fast.

[0056] Example 4

[0057] The diaphragm of the single cell is a 19-μm DLM ion membrane, and the test results are as Figure 7 shown. From this, it can be known that: the capacity of the battery decays by 3.0% in the first 1000 weeks; the capacity decay is significantly lower than that of T-AEM. The speculated reason is that it can be seen from Figure 3 that the functional layer of DLM is very dense and there are no obvious hole-like defects on the surface ( Figure 5 ), the penetration of the electrolyte is significantly reduced, and the permeability coefficient is much lower than that of the commercial DSVN membrane (see Table 2 for details). Therefore, the capacity decay of the single cell test is extremely low.

[0058] Table 2 Test parameters of various anion membranes and commercial membrane DSVN prepared in Comparative Example 3, Example 1 and Example 2

[0059]

[0060] Example 5

[0061] In this example, the test data of single cells assembled with DLM-19 anion membranes treated with hydrophilizing agents of different concentrations are given. The DLM-19 hydrophilization treatment method is as follows: DLM-19 diaphragms with a thickness of 19 μm are respectively immersed in ethylene-vinyl alcohol copolymer hydrophilizing agents with a mass concentration of 0.5%, 1%, and 1.5%. After complete infiltration, they are left standing at 45°C for 40 minutes, and then the DLM-19 is immersed in deionized water. After taking it out, the battery is assembled for testing. The energy efficiency of the single cell is shown in Table 3. The energy efficiencies of the single cells assembled with ion membranes treated with ethylene-vinyl alcohol copolymer hydrophilizing agents with a mass concentration of 0.5%, 1%, and 1.5% are 83.2%, 83.5%, and 83.3% respectively, indicating that the hydrophilization treatment effects of the hydrophilizing agents at the three concentrations on the membrane are not very different, and all can be used.

[0062] Table 3 Comparison table of energy efficiency of DLM-19 diaphragms treated with hydrophilizing agents of different concentrations in single cells in Example 5

[0063] Serial number Concentration of hydrophilic agent (%) Diaphragm Energy efficiency (%) 1 0.5 DLM-19 83.2 2 1 DLM-19 83.5 3 1.5 DLM-19 83.3

[0064] Example 6

[0065] Other conditions are the same as in Example 1, except that PE membranes with different thicknesses (7 μm, 12 μm, 17 μm) are used. In this example, the comparative test data of the energy efficiency of single cells assembled with DLM anion membranes prepared with PE membranes of different thicknesses and anion membranes (T-AEM-50) with a thickness of 50 μm prepared in Comparative Example 3 are given. The DLM hydrophilization treatment method is as follows: DLM diaphragms with different thicknesses are respectively immersed in ethylene-vinyl alcohol copolymer hydrophilizing agents with a mass concentration of 1%. After complete infiltration, they are left standing at 45°C for 40 minutes, and then the DLM is immersed in deionized water. After taking it out, the battery is assembled for testing. The energy efficiency of the single cell is shown in Table 4. The energy efficiencies of the single cells assembled with ion membranes prepared with 7-μm, 12-μm, and 17-μm PE membranes and anion membranes (T-AEM-50) with a thickness of 50 μm prepared in Comparative Example 3 are 83%, 83.5%, 83.2%, and 80.5% respectively, indicating that the three commercially available PE membranes with different thicknesses have little effect on the resistance of the DLM membrane, and all can be used and the energy efficiency is at least 2.5% higher than that of the anion membrane prepared in Comparative Example 3.

[0066] Table 4 Comparison table of energy efficiency of DLM prepared with PE membranes of different thicknesses and anion exchange membranes (T-AEM-50) with a thickness of 50 μm prepared in Comparative Example 3 in single cells in Example 6

[0067] Serial number Thickness of PE film (μm) Diaphragm Energy efficiency % 1 7 DLM-10 83 2 12 DLM-14 83.5 3 17 DLM-19 83.2 4 - T-AEM-50 80.5

[0068] Example 7

[0069] Other steps are the same as those in Example 2, except that three different functional polymers are used to prepare the DLM membrane, and the stability of the DLM membrane in a single cell is compared. The comparison data are shown in Table 5. The hydrophilic treatment methods of the three DLM membranes are the same, and the process is as follows: Immerse the DLM diaphragm in a hydrophilic agent containing ethylene-vinyl alcohol copolymer with a mass concentration of 1%, let it soak completely, then stand still at 45 °C for 40 min, and then immerse the DLM in deionized water. After taking it out, assemble the battery for testing. The performance comparison of single cells is shown in Table 5. The DLM membranes prepared by using quaternized polyalkyltriphenylpyridine, quaternized polyalkyltriphenylpiperidine, and a mixture of quaternized polyalkyltriphenylpyridine and quaternized polyalkyltriphenylpiperidine (volume ratio 1:1) polymers have a capacity decay of less than that of the T-AEM-50 diaphragm battery in Comparative Example 3 after 1000 cycles in a single cell, indicating that the technology of the present invention is applicable to the preparation of DLM membranes with different functional polymers.

[0070] Table 5 Comparison table of the influence of DLM membranes prepared with different functional polymers on the capacity decay of single cells

[0071]

[0072] Comparative Example 1

[0073] Preparation process of a bilayer ultra-thin anion membrane (DLM) without additives: (1) Dissolve the functional polymer (name: quaternized polyalkyltriphenylpyridine, manufacturer: Suqian Zhongke Times New Materials Co., Ltd.) in DMSO solvent to form a homogeneous membrane solution (solid content 21%), and stand still until there are no visible bubbles in the membrane solution; (2) Position the 7-μm PE membrane - Spray an aqueous PVC solution on the surface of a smooth and flat glass plate, place the PE membrane on the surface of the aqueous PVC solution, then place a PET substrate on the surface of the PE membrane, and finally wipe the PE membrane through the PET with dust-free paper until it fits evenly, then remove the PET and dry the PE membrane; (3) Coat the membrane solution on the PE membrane, with the coating thickness of the membrane solution being 55 μm, heat it to 90 °C and dry it for 0.5 h to prepare a bilayer ultra-thin anion membrane without additives (as shown in Figure 8 (left)).

[0074] Comparative Example 2

[0075] Prepare a bilayer ultra-thin anion membrane with additives by the method of Example 1 (as shown in Figure 8 (right)).

[0076] The membrane solution in Comparative Example 1 has no additives, and there are a large number of "white spots" on the surface of the prepared bilayer ultra-thin anion membrane. There are exposed sites on the PE membrane at these places, and there are large pores that will accelerate the penetration of the electrolyte, seriously affecting the stability of the battery; the membrane solution in Comparative Example 2 has additives, which can reduce the surface tension of the PE membrane and significantly improve the spreading property of the membrane solution on the surface of the PE membrane. The surface of the prepared bilayer ultra-thin anion membrane has no "white spots" and is uniform.

[0077] Comparative Example 3

[0078] Preparation process of anion exchange membrane (T-AEM): (1) Dissolve the functional polymer in DMSO solvent to form a uniform membrane solution (solid content 21%); (2) Add 0.15% polyether silicone in the membrane solution, disperse it fully and then let it stand until there are no visible bubbles in the membrane solution; (3) Coat the membrane solution on the PET substrate, the coating thickness of the membrane solution is 500 μm, heat it to 90 °C and dry it for 2 h, then an anion exchange membrane with a thickness of 50 μm can be prepared.

[0079] Characterization and performance test of anion exchange membrane (T-AEM): Figure 9 This is the cross-sectional SEM image of the T-AEM prepared in Comparative Example 3. It can be seen from the figure that the diaphragm is not dense and the cross-section is porous; Figure 10 This is the surface SEM image of the T-AEM prepared in Comparative Example 3. It can be seen from the figure that the surface of the diaphragm is uneven and porous; According to the above morphology, it can be known that the anion exchange membrane prepared in Comparative Example 3 has the characteristics of cross-sectional and surface defects. The possible reason is that the anion exchange membrane prepared in Comparative Example 3 has a relatively thick thickness (50 μm), a relatively large ion transfer resistance, and during the curing and drying process of the membrane solution (curing from the surface to the inside), the evaporation of the high-boiling solvent inside is not smooth, and there is a situation of "boiling over" of the solvent, resulting in the internal porosity and surface porosity defects of the anion exchange membrane.

[0080] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0081] It should be noted that the above content only illustrates the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a double-layer ultra-thin anion exchange membrane, characterized in that: The following steps are involved: (1) dissolving a functional polymer having anion exchange ability in an organic solvent to prepare an intermediate membrane solution; (2) adding 0.05 wt% to 0.2 wt% of a surfactant to the intermediate membrane solution, fully dispersing the surfactant and allowing it to stand for defoaming to obtain a membrane solution; (3) Spraying a PVC aqueous solution on a smooth, flat surface of a glass plate, placing a PE film on the surface of the PVC aqueous solution, and then placing a PET substrate on the surface of the PE film. Finally, wiping the PE film with dust-free paper through the PET until it is evenly attached, then removing the PET and drying the PE film; the surface of the PE film is in a flat state; (4) uniformly coating the film liquid in step (2) on the surface of the PE film in step (3), and then heating, drying and curing to form a film; (5) mixing alcohol and pure water in a volume ratio of 1:1 to obtain a hydrophilic solvent, and then adding a hydrophilic polymer material and heating and dissolving it to obtain a hydrophilic agent; (6) Soaking the membrane obtained in step (4) in a hydrophilic agent, taking it out and washing it with water, thereby completing the hydrophilic treatment; and obtaining a double-layer ultra-thin anion exchange membrane.

2. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (1), the mass percentage of the functional polymer in the membrane solution is 15%-21%; the functional polymer is one or more high molecular polymers with positive charge and anion adsorption function; the organic solvent can be one or more of nitrogen methyl pyrrolidone, dimethyl sulfoxide, and dimethylformamide.

3. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (2), the surfactant is one or more of a fluorocarbon surfactant, a polyethylene oxide ether surfactant, an amine salt surfactant and a quaternary ammonium salt surfactant.

4. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (3), the PE membrane is a porous membrane with a thickness of 7-17 μm and a pore size of 30-50 nm. Before use, the surface of the PE membrane cannot be directly subjected to force.

5. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (4), the thickness of the film formed by heating, drying and curing is 2-3 μm.

6. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (5), 0.5wt.%-1.5wt.% of a hydrophilic polymer material is added to a hydrophilic solvent, wherein the hydrophilic polymer material is an ethylene-vinyl alcohol copolymer; and the alcohol is one or more of ethanol and isopropanol.

7. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (6), the soaking temperature is 35-45°C.

8. The method for preparing a double-layer ultra-thin anion exchange membrane according to claim 1, characterized in that: In step (6), the thickness of the double-layer ultra-thin anion exchange membrane is 7-20 μm.

9. A double-layer ultra-thin anion exchange membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the double-layer ultra-thin anion exchange membrane as claimed in claim 9 in an aqueous organic liquid flow battery.

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