Static-electricity-enhanced multi-level pore composite membrane for vanadium battery and preparation method and application thereof

Abstract

The application relates to the technical field of vanadium redox flow battery diaphragm, and particularly discloses an electrostatic enhancement type multi-stage pore composite membrane for a vanadium battery as well as a preparation method and application thereof. The composite membrane is prepared by introducing positively charged small-molecule organic matter, a pore-forming agent and a sacrificial template agent into an ion exchange resin solution, forming a double-layer membrane through flow casting and blade coating, and then performing acid etching treatment to obtain the composite membrane with a multi-stage pore structure. The composite membrane has both electrostatic repulsion and size screening effects, large pores promote fast proton transmission, and small pores effectively block vanadium ions, so that the ion selectivity and conductivity are synergistically improved. The preparation method is simple, the prepared composite membrane has high coulomb efficiency, high energy efficiency and good cycle stability in the vanadium battery, and is suitable for a vanadium redox flow battery system.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery separator technology, and more particularly to an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, its preparation method, and its application. Background Technology

[0002] Ion-conducting membranes are a crucial component of flow batteries, responsible for transferring charge carriers and forming a current loop while simultaneously blocking the active materials at the positive and negative electrodes to prevent cross-contamination. An ideal ion-conducting membrane should possess high ionic conductivity and high selectivity, along with good chemical stability in corrosive electrolytes. Porous ion-conducting membranes, due to their large pore size and wide pore distribution (far exceeding the hydration diameter of vanadium ions), struggle to fully utilize their pore size sieving effect. The phase inversion method used in their preparation makes it difficult to achieve both high ionic conductivity and high ionic selectivity simultaneously, leaving significant room for performance improvement. Therefore, developing a composite membrane that synergistically combines electrostatic repulsion and size sieving, exhibits both high proton conductivity and high vanadium ion selectivity, and boasts a simple manufacturing process is of great significance. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide an electrostatically enhanced multi-level porous ion membrane for vanadium batteries, its preparation method, and its application.

[0004] In a first aspect, the present invention provides a method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, comprising the following steps:

[0005] S1. Take 10-20 parts by weight of ion exchange resin to prepare an ion exchange resin solution with a mass concentration of 2%-5%.

[0006] S2. Add 1-3 parts by weight of positively charged small molecule organic matter, 2-4 parts by weight of pore-forming agent and 1-2 parts by weight of sacrificial template agent to the ion exchange resin solution to form a uniform casting solution 1.

[0007] S3. Add 1-3 parts by mass of positively charged small molecule organic matter and 1-2 parts by mass of sacrificial template agent to the ion exchange resin solution to form a uniform casting solution 2.

[0008] S4. Cast the casting solution 1 into a film, heat it to obtain a cast film; then coat the casting solution 2 onto the cast film, heat it to obtain a double-layer film;

[0009] S5. The bilayer membrane is immersed in hydrochloric acid solution for ultrasonic etching, washed with water and dried to obtain an electrostatically enhanced multi-level porous composite membrane.

[0010] Preferably, the ion exchange resin in S1 is selected from at least one of perfluorosulfonic acid resin, sulfonated polyphenylene imidazole, and sulfonated polyether ether ketone; the organic solvent in the ion exchange resin solution is selected from at least one of N-methylpyrrolidone and dimethylacetamide.

[0011] Preferably, the positively charged small molecule organic compound in S2 or S3 is selected from at least one of Rhodamine B, 6-carboxyrhodamine 110, and tetramethylrhodamine B isocyanate.

[0012] Preferably, the pore-forming agent in S2 includes lithium chloride and polyethylene glycol, and the mass ratio of lithium chloride to polyethylene glycol is 1:20-1:10.

[0013] Preferably, the sacrificial template agent in S2 or S3 is zeolite imidazole ester skeleton-8, and the preparation method of zeolite imidazole ester skeleton-8 includes:

[0014] Dissolve 5-10 parts by weight of zinc nitrate hexahydrate and 100-150 parts by weight of 2-methylimidazole in deionized water. Pour the resulting zinc nitrate hexahydrate solution into the resulting 2-methylimidazole solution. After the reaction, centrifuge, wash, and dry to obtain the sacrificial template agent.

[0015] Preferably, the thickness of the cast film in S4 is 50-80 μm, and the thickness of the double-layer film is 100-120 μm.

[0016] Preferably, the concentration of the hydrochloric acid solution in step S5 is 3-4 mol / L, the temperature of the ultrasonic etching is 45-55℃, and the time of the ultrasonic etching is 1-2 h.

[0017] Preferably, the electrostatically enhanced multi-level porous composite membrane in S5 has a macropore size distribution of 5-15 μm and a micropore size distribution of 10-100 nm.

[0018] Secondly, the present invention provides an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, which is prepared by the above-described method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries.

[0019] Thirdly, the present invention provides the application of an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, wherein the electrostatically enhanced multi-level porous composite membrane for vanadium batteries prepared by the above-described method for preparing the electrostatically enhanced multi-level porous composite membrane for vanadium batteries or the above-described electrostatically enhanced multi-level porous composite membrane for vanadium batteries is applied to an all-vanadium redox flow battery.

[0020] The beneficial effects of this invention are:

[0021] 1. The composite membrane of this invention is composed of positively charged small-molecule organic compounds, which are stably and firmly loaded onto the polymer network and the inner wall of the pores through electrostatic interactions and hydrogen bonding. This not only enables the battery to have a good capacity retention rate, but also provides strong and lasting electrostatic repulsion, effectively blocking vanadium ions and improving the battery's coulombic efficiency.

[0022] 2. This invention uses a pore-forming agent and a sacrificial template agent to form a regular and interconnected multi-level pore structure in the composite membrane. The large pores ensure rapid proton transport, while the small pores achieve size sieving. This can improve the proton transport speed and the vanadium blocking ability, thereby improving both voltage efficiency and coulombic efficiency, and thus improving the energy efficiency of the fuel cell stack.

[0023] 3. The composite membrane electrostatic repulsion composite network and multi-level pore structure of the present invention work together. The positive charge in the pores can enhance the charge sieving ability, thereby achieving precise synergy and spatial coupling of "electrostatic repulsion" and "size sieving" at the molecular level, further improving the coulombic efficiency of the battery, and thus improving the energy efficiency of the stack. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of a cross-section of the electrostatically enhanced multi-level porous composite membrane of Embodiment 1 of the present invention.

[0025] Figure 2 This is a Zeta potential diagram of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0026] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0027] A method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries includes the following steps:

[0028] S1. Dissolve 10-20 parts by weight of ion exchange resin in an organic solvent to prepare an ion exchange resin solution with a mass concentration of 2% to 5%.

[0029] S2. Preparation of the sacrificial template agent zeolite imidazole ester skeleton-8: Dissolve 5-10 parts by weight of zinc nitrate hexahydrate and 100-150 parts by weight of 2-methylimidazole in 40-60 parts by weight and 400-600 parts by weight of deionized water, respectively. Then, quickly pour the zinc nitrate hexahydrate solution into the 2-methylimidazole solution. The mixed solution immediately turns milky white. After 5 minutes, centrifuge the synthesized product at 11,000 rpm and wash with deionized water. Finally, dry the product in a vacuum oven at 70℃-90℃. Then add 1-3 parts by weight of positively charged small molecule organic matter, 2-4 parts by weight of porogen lithium chloride and polyethylene glycol (mass ratio 1:20-1:10), and 1-2 parts by weight of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution of step S1 to form a uniform casting solution 1.

[0030] S3. Add 1-3 parts by mass of positively charged small molecule organic matter and 1-2 parts by mass of sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution in step S1 to form a uniform casting solution 2.

[0031] S4. Cast the casting solution 1 from step S2 into a film and heat it at 35-50℃ for 2-4 hours to obtain a cast film; then coat the casting solution 2 from step S3 onto the cast film and heat it at 35-50℃ for 2-4 hours to obtain a double-layer film; wherein, the thickness of the cast film is 50-80μm, and the total thickness of the double-layer film is 100-120μm;

[0032] S5. Immerse the bilayer membrane from step S4 in a 3-4 mol / L hydrochloric acid solution for ultrasonic etching at a temperature of 45-55℃ for 1-2 hours. Wash with water and dry to obtain an electrostatically enhanced multi-level porous composite membrane. The macropore size distribution of the composite membrane is 5-15 μm, and the micropore size distribution is 10-100 nm.

[0033] Example 1: A method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, comprising the following steps:

[0034] S1. Dissolve 15 parts by mass of perfluorosulfonic acid resin in the organic solvent N-methylpyrrolidone to prepare an ion exchange resin solution with a mass concentration of 3%.

[0035] S2. Preparation of the sacrificial template agent zeolite imidazole ester skeleton-8: Dissolve 6 parts by mass of zinc nitrate hexahydrate and 120 parts by mass of 2-methylimidazole in 50 parts by mass and 500 parts by mass of deionized water, respectively. Then, quickly pour the zinc nitrate hexahydrate solution into the 2-methylimidazole solution. The mixed solution immediately turns milky white. After 5 minutes, centrifuge the synthesized product at 11,000 rpm and wash with deionized water. Finally, dry the product in a vacuum oven at 80°C. Then, add 3 parts by mass of the positively charged small molecule organic compound rhodamine B, 3 parts by mass of the porogen lithium chloride and polyethylene glycol (mass ratio 1:10), and 2 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution of step S1 to form a uniform casting solution 1.

[0036] S3. Add 2 parts by mass of the positively charged small molecule organic compound Rhodamine B and 2 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution in step S1 to form a uniform casting solution 2.

[0037] S4. Cast the casting solution 1 from step S2 into a film and heat it at 40°C for 3 hours to obtain a cast film; then coat the casting solution 2 from step S3 onto the cast film and heat it at 40°C for 3 hours to obtain a double-layer film; the thickness of the cast film is 70 μm and the total thickness of the double-layer film is 120 μm.

[0038] S5. Immerse the bilayer membrane from step S4 in a 4 mol / L hydrochloric acid solution for ultrasonic etching at a temperature of 50℃ for 2 hours; wash with water and dry to obtain an electrostatically enhanced hierarchical porous composite membrane. The macropore size distribution of the composite membrane is 5-15 μm, and the micropore size distribution is 10-100 nm. Figure 1 As shown, the cross-sectional scanning electron microscope image of the composite membrane reveals a multi-level pore structure, with macropores ranging from 5 to 15 μm and micropores ranging from 10 to 100 nm in diameter.

[0039] Example 2: A method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, comprising the following steps:

[0040] S1. Take 10 parts by mass of sulfonated polyphenylene imidazole resin and dissolve it in the organic solvent N-methylpyrrolidone to prepare an ion exchange resin solution with a mass concentration of 2%.

[0041] S2. Preparation of the sacrificial template agent zeolite imidazole ester skeleton-8: Dissolve 8 parts by mass of zinc nitrate hexahydrate and 140 parts by mass of 2-methylimidazole in 50 parts by mass and 500 parts by mass of deionized water, respectively. Then, quickly pour the zinc nitrate hexahydrate solution into the 2-methylimidazole solution. The mixed solution immediately turns milky white. After 5 minutes, centrifuge the synthesized product at 11,000 rpm and wash it with deionized water. Finally, dry the product in a vacuum oven at 90°C. Then, add 3 parts by mass of the positively charged small molecule organic compound 6-carboxyrhodamine 110, 2 parts by mass of the porogen lithium chloride and polyethylene glycol (mass ratio 1:20), and 1 part by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution of step S1 to form a uniform casting solution 1.

[0042] S3. Add 3 parts by mass of the positively charged small molecule organic compound 6-carboxyrhodamine 110 and 1 part by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution in step S1 to form a uniform casting solution 2.

[0043] S4. Cast the casting solution 1 from step S2 into a film and heat it at 35°C for 4 hours to obtain a cast film; then coat the casting solution 2 from step S3 onto the cast film and heat it at 35°C for 4 hours to obtain a double-layer film; the thickness of the cast film is 50 μm and the total thickness of the double-layer film is 100 μm.

[0044] S5. The bilayer membrane from step S4 is immersed in a 3 mol / L hydrochloric acid solution for ultrasonic etching at a temperature of 45°C for 2 hours. After washing and drying, an electrostatically enhanced multi-level porous composite membrane is obtained. The macropore size distribution of the composite membrane is 5-15 μm, and the micropore size distribution is 10-100 nm.

[0045] Example 3: A method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, comprising the following steps:

[0046] S1. Dissolve 20 parts by mass of sulfonated polyether ether ketone resin in the organic solvent dimethylacetamide to prepare an ion exchange resin solution with a mass concentration of 5%.

[0047] S2. Preparation of the sacrificial template agent zeolite imidazole ester skeleton-8: Dissolve 10 parts by mass of zinc nitrate hexahydrate and 150 parts by mass of 2-methylimidazole in 60 parts by mass and 600 parts by mass of deionized water, respectively. Then, quickly pour the zinc nitrate hexahydrate solution into the 2-methylimidazole solution. The mixed solution immediately turns milky white. After 5 minutes, centrifuge the synthesized product at 11,000 rpm and wash it with deionized water. Finally, dry the product in a vacuum oven at 70°C. Then, add 1 part by mass of the positively charged small molecule organic compound tetramethylrhodamine B isocyanate, 4 parts by mass of the porogen lithium chloride and polyethylene glycol (mass ratio 1:15), and 1.5 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution of step S1 to form a uniform casting solution 1.

[0048] S3. Add 1 part by mass of the positively charged small molecule organic compound tetramethylrhodamine B isocyanate and 1.5 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution in step S1 to form a uniform casting solution 2.

[0049] S4. Cast the casting solution 1 from step S2 into a film and heat it at 45°C for 2 hours to obtain a cast film; then coat the casting solution 2 from step S3 onto the cast film and heat it at 45°C for 2 hours to obtain a double-layer film; the thickness of the cast film is 60 μm and the total thickness of the double-layer film is 120 μm.

[0050] S5. The bilayer membrane from step S4 is immersed in a 3.5 mol / L hydrochloric acid solution for ultrasonic etching at a temperature of 55°C for 1 hour. After washing and drying, an electrostatically enhanced multi-level porous composite membrane is obtained. The macropore size distribution of the composite membrane is 5-15 μm, and the micropore size distribution is 10-100 nm.

[0051] Example 4: A method for preparing an electrostatically enhanced hierarchical porous composite membrane for vanadium batteries, comprising the following steps:

[0052] S1. Dissolve 15 parts by mass of perfluorosulfonic acid resin in the organic solvent N-methylpyrrolidone to prepare an ion exchange resin solution with a mass concentration of 4%.

[0053] S2. Preparation of the sacrificial template agent zeolite imidazole ester skeleton-8: Dissolve 5 parts by mass of zinc nitrate hexahydrate and 100 parts by mass of 2-methylimidazole in 40 parts by mass and 400 parts by mass of deionized water, respectively. Then, quickly pour the zinc nitrate hexahydrate solution into the 2-methylimidazole solution. The mixed solution immediately turns milky white. After 5 minutes, centrifuge the synthesized product at 11,000 rpm and wash it with deionized water. Finally, dry the product in a vacuum oven at 85°C. Then, add 2 parts by mass of the positively charged small molecule organic compound rhodamine B, 3 parts by mass of the porogen lithium chloride and polyethylene glycol (mass ratio 1:10), and 2 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution of step S1 to form a uniform casting solution 1.

[0054] S3. Add 2 parts by mass of the positively charged small molecule organic compound Rhodamine B and 2 parts by mass of the sacrificial template agent zeolite imidazole ester skeleton-8 to the ion exchange resin solution in step S1 to form a uniform casting solution 2.

[0055] S4. Cast the casting solution 1 from step S2 into a film and heat it at 50°C for 3 hours to obtain a cast film; then coat the casting solution 2 from step S3 onto the cast film and heat it at 50°C for 3 hours to obtain a double-layer film; the thickness of the cast film is 80 μm and the total thickness of the double-layer film is 120 μm.

[0056] S5. The bilayer membrane from step S4 is immersed in a 4 mol / L hydrochloric acid solution for ultrasonic etching at a temperature of 50°C for 2 hours. After washing and drying, an electrostatically enhanced multi-level porous composite membrane is obtained. The macropore size distribution of the composite membrane is 5-15 μm, and the micropore size distribution is 10-100 nm.

[0057] Comparative Example 1:

[0058] Consistent with Example 1, steps S2 and S3 do not involve positively charged small molecule organic compounds.

[0059] Comparative Example 2:

[0060] Similar to Example 1, the positively charged small molecule organic compounds in steps S2 and S3 are replaced with Chrome Black T.

[0061] Comparative Example 3:

[0062] Consistent with Example 1, lithium chloride and polyethylene glycol are not added in steps S2 and S3.

[0063] Comparative Example 4:

[0064] Consistent with Example 1, in step S3, the same mass fractions of porogen lithium chloride and polyethylene glycol are added as in step S2.

[0065] Comparative Example 5:

[0066] Consistent with Example 1, no pore-forming agent or sacrificial template agent is added in steps S2 and S3.

[0067] Comparative Example 6:

[0068] Consistent with Example 1, there is no blank membrane in steps S2, S3, and S4.

[0069] Zeta potential assay: The surface charge properties of the films in the examples and comparative examples were characterized using a solid surface zeta potential meter. A flow potential assay was performed using 1 mmol L⁻¹. -1 A KCl solution was used as the electrolyte solution. A 0.1 mol / L solution was employed. -1 Hydrochloric acid and 0.1 mol L -1 The pH of the solution was adjusted with sodium hydroxide solution, the Zeta potential at pH=3 was recorded, and the Zeta potentials of Example 1 and Comparative Example 1 were tested in the pH range of 3-10.

[0070] Battery performance testing: The films prepared in the examples and comparative examples were assembled into battery stacks and subjected to charge-discharge tests under the same test conditions. The coulombic efficiency, voltage efficiency, energy efficiency, and capacity retention after 100 cycles were recorded. The test results are shown in Table 1.

[0071] Table 1. Test Results of Membrane and Battery Performance

[0072]

[0073] As shown in Table 1, Example 1 exhibits higher Zeta potential and coulombic efficiency compared to Comparative Example 1. This is because the positive charge on the membrane surface enhances the membrane's repulsion of vanadium ions, strengthens its vanadium-blocking properties, and thus demonstrates higher coulombic efficiency in battery testing. Further... Figure 2As shown, Comparative Example 1 exhibits strong negative charge across the entire pH range of 3-10, while the potential of the composite membrane in Example 1, although not all values ​​are positive, shows a significant increase, indicating that its positive charge is indeed enhanced. Furthermore, Examples 1 and 2 demonstrate that the addition of different positively charged organic compounds, Rhodamine B and Eriochrome Black T, affects the coulombic efficiency and capacity retention of the battery. This is because Rhodamine B is positively charged, and the negatively charged perfluorosulfonic acid has a strong charge-force interaction with it, allowing it to be introduced into the internal structure of the membrane through electrostatic adsorption. However, the negatively charged small molecule Eriochrome Black T cannot be firmly loaded into the membrane due to charge repulsion. In summary, the composite membrane of this invention is composed of positively charged small molecule organic compounds, which are stably and firmly loaded onto the polymer network and pore walls through electrostatic interactions and hydrogen bonding. This not only enables the battery to have a good capacity retention rate but also provides strong and persistent electrostatic repulsion, effectively blocking vanadium ions and improving the battery's coulombic efficiency.

[0074] As shown in Table 1, Example 1 exhibits higher energy and voltage efficiencies compared to Comparative Examples 3-4. This is because Example 1 contains a pore-forming agent and a sacrificial template agent, forming a regular and interconnected multi-level pore structure in the composite membrane. Large pores ensure rapid proton transport, while small pores achieve size sieving, improving both proton transport speed and vanadium blocking capability. This enhances both voltage and coulombic efficiency, thereby improving the energy efficiency of the fuel cell stack. Comparative Example 3, lacking a pore-forming agent, provides pore size sieving and electrostatic repulsion, resulting in higher coulombic efficiency, but lacks large-pore proton transport, leading to slightly lower energy and voltage efficiencies. Comparative Example 4, with the addition of a pore-forming agent in step S3, lacks a multi-level pore structure in the composite membrane, allowing large pores to penetrate the ion exchange membrane, resulting in low coulombic efficiency and low capacity retention. Furthermore, Comparative Example 5, without a sacrificial template agent, has a slightly lower coulombic efficiency than Example 1, but higher than the blank membrane of Comparative Example 6. This indicates that the small pores generated by the sacrificial template agent can improve the coulombic efficiency of the battery by facilitating vanadium ion shuttle passage through size sieving. Furthermore, Examples 1-4 exhibit superior battery efficiency and capacity retention, demonstrating that the composite membrane electrostatic repulsion composite network and multi-level pore structure of the present invention work synergistically. The positive charge within the pores enhances charge sieving ability, thereby achieving precise synergy and spatial coupling of "electrostatic repulsion" and "size sieving" at the molecular level. This can further improve the coulombic efficiency of the battery, thereby enhancing the energy efficiency of the fuel cell stack.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an electrostatically enhanced multi-level porous composite membrane for vanadium batteries, characterized in that, Includes the following steps: S1. Take 10-20 parts by weight of ion exchange resin to prepare an ion exchange resin solution with a mass concentration of 2%-5%. S2. Add 1-3 parts by weight of positively charged small molecule organic matter, 2-4 parts by weight of pore-forming agent and 1-2 parts by weight of sacrificial template agent to the ion exchange resin solution to form a uniform casting solution 1. The pore-forming agent includes lithium chloride and polyethylene glycol, and the mass ratio of lithium chloride to polyethylene glycol is 1:20-1:10; S3. Add 1-3 parts by mass of positively charged small molecule organic matter and 1-2 parts by mass of sacrificial template agent to the ion exchange resin solution to form a uniform casting solution 2. The positively charged small molecule organic compound is selected from at least one of Rhodamine B, 6-carboxyrhodamine 110, and tetramethylrhodamine B isocyanate. The sacrificial template agent is zeolite imidazole ester skeleton-8. The preparation method of zeolite imidazole ester skeleton-8 includes: dissolving 5-10 parts by weight of zinc nitrate hexahydrate and 100-150 parts by weight of 2-methylimidazole in deionized water, pouring the obtained zinc nitrate hexahydrate solution into the obtained 2-methylimidazole solution, centrifuging, washing and drying after reaction to obtain the sacrificial template agent. S4. Cast the casting solution 1 into a film, heat it to obtain a cast film; then coat the casting solution 2 onto the cast film, heat it to obtain a double-layer film; S5. The bilayer membrane is immersed in hydrochloric acid solution for ultrasonic etching, washed with water and dried to obtain an electrostatically enhanced multi-level porous composite membrane.

2. The preparation method according to claim 1, characterized in that, The ion exchange resin in S1 is selected from at least one of perfluorosulfonic acid resin, sulfonated polyphenylene imidazole, and sulfonated polyether ether ketone; the organic solvent in the ion exchange resin solution is selected from at least one of N-methylpyrrolidone and dimethylacetamide.

3. The preparation method according to claim 1, characterized in that, The thickness of the cast film in S4 is 50-80 μm, and the thickness of the double-layer film is 100-120 μm.

4. The preparation method according to claim 1, characterized in that, The concentration of the hydrochloric acid solution in S5 is 3-4 mol / L, the temperature of the ultrasonic etching is 45-55℃, and the time of the ultrasonic etching is 1-2 h.

5. The preparation method according to claim 1, characterized in that, The electrostatically enhanced multi-level porous composite membrane in S5 has a macropore size distribution of 5-15 μm and a micropore size distribution of 10-100 nm.

6. An electrostatically enhanced multi-level porous composite membrane for vanadium batteries, characterized in that, It is prepared by the method for preparing the electrostatically enhanced multi-level porous composite membrane for vanadium batteries according to any one of claims 1-5.

7. The application of electrostatically enhanced multi-level porous composite membranes for vanadium batteries, characterized in that, The vanadium battery electrostatically enhanced multi-level porous composite membrane prepared by the method of any one of claims 1-5 or the vanadium battery electrostatically enhanced multi-level porous composite membrane of claim 6 is applied to a vanadium redox flow battery.

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