Method for preparing diaphragm for flow battery with interlayer structure by utilizing electrodeposition technology

Abstract

The invention relates to the field of flow battery diaphragms, in particular to a method for preparing a diaphragm for a flow battery with a sandwich structure by utilizing an electrodeposition technology, which comprises the following steps of: preparing a resin solution from film-forming resin, and putting the resin solution and an electrode substrate into an electrodeposition device; by controlling current and voltage, the charged resin ions are driven by an electric field to move towards the film-forming electrode, and a layer of thin film is formed on the electrode substrate through enrichment. And after drying and curing, the thin film and the electrode substrate are placed in another set of electro-deposition device, and the electro-deposition device contains dispersion liquid containing charged filler. Then, voltage is applied to the electrode plate, so that the filler is enriched on the surface of the thin film; and finally, placing the electrode substrate in a resin solution to prepare a film through electro-deposition, and depositing a layer of thin film on the surface of the filler to form the film for the flow battery with a sandwich structure. The process is simple, the interlayer filler is properly introduced, the performance of the membrane is improved, and meanwhile, the environmental protection and safety problems caused by volatilization of a large amount of solvents in a traditional tape casting method can be effectively avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flow battery separators, in particular to a method for preparing a sandwich structure flow battery separator by electrodeposition. BACKGROUND

[0002] Wind energy, solar energy and biomass energy, as the main renewable energy, are clean and abundant, and have attracted widespread attention. However, these energies are derived from nature and have certain intermittency, resulting in unstable power generation capacity, which leads to the contradiction between seasonal and unstable power generation and the demand for continuous and stable power supply. In the face of this situation, developing effective energy storage technology to ensure the stability of power supply has become the key to the widespread application of renewable energy.

[0003] Flow redox batteries (RFBs) are an advanced energy storage technology, and due to their unique structure and excellent performance, they have become an important solution to energy storage problems with high energy density, long cycle life and excellent safety. The separator is the core component of the flow battery, and its main function is to prevent the mixing of positive and negative electrode solutions, while allowing ions to freely migrate inside the battery, thereby completing the closure of the current and the conversion of electrical energy. The performance of the separator directly affects the overall efficiency and stability of the battery. An ideal separator not only needs to have excellent mechanical strength and chemical stability, but also must achieve an effective balance between proton conductivity and ion selectivity. This balance determines the diffusion ability and selective conduction ability of active ions, thereby affecting the energy efficiency and power density of the battery.

[0004] Traditional flow battery separators often face the problems of insufficient ion conductivity, high resistance or insufficient ion selectivity, which limit the power density and energy efficiency of the battery. Sandwich structure separators can effectively overcome these deficiencies, and are usually composed of two or more layers of functional fillers. This design can improve the overall performance of the separator while optimizing its conductivity, selectivity and mechanical strength.

[0005] Preparation of sandwich structure separators by electrodeposition not only allows the uniform coating of charged fillers on the surface of the membrane, improving the efficiency of the separator, but also simplifies the operation steps and equipment requirements. In addition, electrodeposition can significantly reduce the amount of organic solvent volatilization and reduce environmental pollution. SUMMARY

[0006] The purpose of the present application is to provide a method for preparing a sandwich structure flow battery separator by electrodeposition, which is simple in process and avoids the environmental and safety problems caused by the large amount of solvent volatilization in traditional casting method.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: Step (1), dissolve the film-forming resin in an organic solvent to prepare a film-forming resin solution with a mass percentage of 2-75%, and then add it to the electrodeposition device I. The resin molecules are uniformly enriched on the film-forming electrode substrate by controlling the current, voltage, and time parameters. The electrode opposite to the film-forming electrode is the counter electrode. Step (2), take out the film-forming electrode substrate in step (1) and dry it to obtain a film-forming electrode substrate with a resin film attached to its surface. Step (3), add the charged filler to be added to the film into a solvent, and use a magnetic stirrer to fully stir and ultrasonically treat it to uniformly disperse the charged filler in the solvent. A filler dispersion liquid with a concentration range of 1-70% is prepared, and then the filler dispersion liquid is added to the electrodeposition device II. The electrode opposite to the film-forming electrode is the counter electrode. Step (4), place the film-forming electrode substrate with the resin film attached to its surface in step (2) into the electrodeposition device II. Then, under the condition of continuous dispersion by ultrasonic or magnetic stirring, the charged filler is uniformly enriched on the surface of the film attached to the electrode substrate by controlling the current, voltage, and time parameters. A film-forming electrode substrate with a charged filler and a film-forming resin film is obtained. Step (5), take out the film-forming electrode substrate in step (4), slowly rinse the film surface with a solvent to remove the loosely attached filler, and then place the film-forming electrode substrate into the electrodeposition device I. Repeat step (1) with the electrode opposite to the film-forming electrode being the counter electrode. Step (6), take out the film-forming electrode substrate in step (5) and repeat step (2). Step (7), if a separator for a flow battery with a multi-layer structure is to be manufactured, steps (1) to (6) are repeated multiple times, and the type of filler in step (3) is changed according to actual use requirements.

[0008] Further, in step (1) of the above method for preparing a separator for a flow battery with a multi-layer structure using electrodeposition technology, the film-forming resin is one or more of perfluorosulfonic acid resin, sulfonated polyether ether ketone, polybenzothiazole, polybenzimidazole, sulfonated polyethylene, polyether sulfone, sulfonated polypropylene, polyimide, polysulfone, polyether ether ketone, perfluorocarboxylic acid resin, polyvinylidene fluoride resin, polypropylene, polyethylene, and polyvinylidene fluoride. The organic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dichloromethane.

[0009] Further, in the method for preparing a separator for a sandwich structure flow battery by using an electrodeposition technique, in step (3), the charged filler is selected from graphene-based fillers, carbon nanotube-based fillers, oxide-based fillers, or organic-based fillers; the charged filler is added in an amount of 1-10 wt%; the ultrasonic treatment time is 0.5-6 h; and the solvent is selected from organic solvents or inorganic solvents, wherein the organic solvents include one or more than two of ethanol, propanol, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl pyrrolidone, or dichloromethane, and the inorganic solvents include pure water or an inorganic salt aqueous solution.

[0010] Further, in the method for preparing a separator for a sandwich structure flow battery by using an electrodeposition technique, the graphene-based fillers are graphene, graphene oxide, multi-layer graphene, or nanographite; the carbon nanotube-based fillers are hydroxyl carbon nanotubes, carboxyl carbon nanotubes, carbonyl carbon nanotubes, single-walled carbon nanotubes, or multi-walled carbon nanotubes; and the organic-based fillers are polypyrrole, sulfamic acid, methyl sulfonic acid, amino acetic acid, or dodecyl ethoxy sulfobetaine.

[0011] Further, in the method for preparing a separator for a sandwich structure flow battery by using an electrodeposition technique, in step (4), the area ratio of the anode to the cathode in the electrodeposition device II is 1:10-10:1, and the distance between the anode and the cathode is 1 mm-100 mm; the film-forming electrode is the anode or the cathode; when the film-forming electrode is the anode, the counter electrode corresponding to the film-forming electrode is the cathode, and a negative resin ion enrichment film is formed on the film-forming electrode; and when the film-forming electrode is the cathode, the counter electrode corresponding to the film-forming electrode is the anode, and a positive resin ion enrichment film is formed on the film-forming electrode.

[0012] Further, in the method for preparing a separator for a sandwich structure flow battery by using an electrodeposition technique, the film-forming electrode is one of a boron-doped diamond thin film electrode, a titanium-based ruthenium-iridium electrode, a titanium-based iridium-tantalum electrode, a titanium-based ruthenium-indium-tin electrode, a titanium-based tin-antimony oxide electrode, a titanium-based sub-titanium oxide electrode, and a titanium-based lead dioxide electrode; at least one of a metal material electrode of stainless steel, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, tantalum, zirconium, tungsten, cerium, aluminum, bismuth, rhenium, barium, osmium, tin, lead, gold, silver, platinum, palladium, iridium, rhodium, molybdenum, and ruthenium; and any one of a carbon material electrode of graphite felt, carbon felt, graphite, glassy carbon, boron-doped diamond, activated carbon, graphene, carbon fiber, carbon nanotube, and carbon sponge.

[0013] Further, in the method for preparing a separator for a sandwich structure flow battery by using an electrodeposition technique, the film-forming electrode is in a sheet shape or a rod shape, and the counter electrode is in any one of a sheet shape, a rod shape, a wire shape, a particle shape, a sponge shape, a mesh shape, and a porous structure.

[0014] Further, in the method for preparing the membrane for the flow battery with the sandwich structure by the electro-deposition technology, in the step (1) and the step (4), when the constant current electro-deposition is used, the current density ranges from 10 mA·cm -2 ~1000 mA·cm -2 , the electro-deposition time is 1~120 min, and the electro-deposition temperature is 25 ℃~70 ℃; when the constant voltage electro-deposition is used, the voltage ranges from 1 V to 150 V, the electro-deposition time is 1~120 min, and the electro-deposition temperature is 25 ℃~70 ℃; when the constant current pulse electro-deposition is used, the current density ranges from 10 mA·cm -2 ~1000 mA·cm -2 , the electro-deposition time is 1~120 min, the frequency is 200~2000 Hz, the duty cycle is 20 %~80 %, and the electro-deposition temperature is 25 ℃~70 ℃.

[0015] Further, in the method for preparing the membrane for the flow battery with the sandwich structure by the electro-deposition technology according to claim 1, in the step (2), the film drying temperature is 80~150 ℃, and the time is 1~4 h.

[0016] Further, in the method for preparing the membrane for the flow battery with the sandwich structure by the electro-deposition technology according to claim 1, the sandwich structure membrane prepared by the method is 10~100 μm, the filler sandwich thickness is 1~20 μm, the membrane thickness is 5~99 μm, and the applicable flow battery system includes any one or more of the iron-chromium, all-vanadium, zinc-iron, all-iron, zinc-bromine, sodium polysulfide / bromine, titanium-manganese or organic system flow batteries.

[0017] The design idea of the present application is: The present application dissolves the film-forming resin in an organic solvent, prepares an anionic or cationic resin solution, and then adds it to the electrodeposition device I. By controlling the current, voltage, and time parameters, the electrode substrate is uniformly enriched with resin molecules, and then the film-forming electrode and the thin film are placed in the electrodeposition device II containing a modified charged filler dispersion liquid, and under the condition of continuous dispersion by ultrasonic or magnetic stirring, the charged filler is uniformly enriched on the surface of the thin film by controlling the current, voltage, and time parameters. Then, the film-forming electrode and the thin film with the charged filler are taken out and placed in the electrodeposition device I to deposit another layer of resin thin film, and then taken out and dried. If a multi-layer structure is desired for the flow battery separator, the above steps can be repeated multiple times, and different types of charged fillers can also be used. Finally, the prepared multi-layer separator is taken off the electrode plate. The obtained multi-layer separator has high ion selective permeability, high conductivity, and good mechanical strength, and the technical indicators are as follows: thickness range 10-100 μm, tensile strength > 20 MPa, elongation at break > 90 %, ion conductivity > 12 mS·cm -1 , vanadium ion permeability constant <2 0×10 -7 cm·min, flow battery energy efficiency: 200 mA·cm -2 , >75 %, 150 mA·cm -2 , >80 %, 100 mA·cm -2 , >81 %.

[0018] The advantages and beneficial effects of the present application are as follows: 1. The present application uses electrodeposition technology to prepare a multi-layer structure flow battery separator, which uniformly distributes the charged filler inside the separator, reduces the internal resistance of the battery, improves the vanadium resistance, and thus improves the battery efficiency, providing a new idea for the manufacturing method of flow battery separator, and having important reference value for improving the performance of flow battery.

[0019] 2. The preparation method of the multi-layer structure flow battery separator of the present application can greatly reduce the volatilization of organic solvent, avoid environmental pollution, reduce the safety hazard, and also can significantly reduce the production cost of the separator. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Structure diagram of a single-layer structure flow battery separator prepared by the electrodeposition method of the present application; Figure 2 Structure diagram of a multi-layer structure flow battery separator prepared by the electrodeposition method of the present application; Figure 3 Schematic diagram of the electrodeposition device I; Figure 4 Schematic diagram of the electrodeposition device II. DETAILED DESCRIPTION

[0021] In the process of implementation, the film-forming resin is made into a resin solution, and then the resin solution is placed in the electrodeposition device I. As shown in the figure, by controlling the current, voltage, and time, the charged negative resin ions and the positive resin ions are enriched on the positive film-forming electrode and the negative film-forming electrode, respectively, under the driving of the electric field. After drying and curing, the film is formed. Subsequently, the film-forming electrode and the thin film are placed in the electrodeposition device II filled with a modified charged filler dispersion liquid. As shown in the figure, under the condition of ultrasonic continuous dispersion or magnetic stirring, the charged filler is uniformly enriched on the surface of the thin film by controlling the current, voltage, and time. Then, the film-forming electrode and the thin film with the charged filler attached are taken out and placed in the electrodeposition device I to deposit another layer of resin thin film. After taking out and drying, if a multi-layer structure of the flow battery separator is to be manufactured, the above steps can be repeated multiple times, and different types of charged fillers can also be used. Finally, the prepared layered separator is taken off from the electrode plate, as shown in the figure. Figure 1 Figure 2 Figure 1 Figure 2 The layered structure flow battery separator prepared by the electrodeposition method of the present application has good ion selectivity, mechanical properties, and good electrical conductivity, which makes the flow battery have good battery performance, and provides a new idea for the development of flow battery separators.

[0022] In order to further understand the present application, the present application is described below in conjunction with examples, but the examples are only for further illustrating the features and advantages of the present application, and are not a limitation on the claims of the present application. Example 1

[0023] In this embodiment, the method for preparing a layered structure flow battery separator by using electrodeposition technology is as follows: (1) Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to prepare a 10% by mass film-forming resin solution, and then add it to the electrodeposition device I. Constant voltage electrodeposition is adopted. The film-forming electrode and the counter electrode are both smooth 316L stainless steel plates. The area ratio of the film-forming electrode to the counter electrode is 1:1. The distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm. The current density is 10 mA·cm -2 , the voltage is 15 V, the time is 5 min, and the electrodeposition temperature is 15 ℃. The perfluorosulfonic acid resin molecules are uniformly enriched on the electrode substrate; (2) Take out the electrode substrate in step (1) and dry it at 140 ℃ for 30 min to obtain a layer of perfluorosulfonic acid thin film attached to the electrode substrate; (3) Dissolve Ti3C2T x ​​​MXene was added into solvent, and stirred for 1 h using a magnetic stirrer and treated with ultrasound for 20 min to make it uniformly dispersed in the solvent, to prepare a dispersion liquid with a concentration of 10 %wt. Then the MXene dispersion liquid was added into the electrodeposition device II; (4) The perfluorosulfonic acid thin film obtained from the film-forming electrode in step (3) was placed in the electrodeposition device II together with the electrode substrate. Then, under the condition of continuous magnetic stirring, constant voltage electrodeposition was adopted, the distance between the film-forming electrode and the counter electrode was controlled to be 1.5 cm, the current density was 10 mA·cm -2 , the voltage was 15 V, the time was 15 min, and the electrodeposition temperature was 15 ℃, and the MXene was uniformly enriched on the surface of the perfluorosulfonic acid thin film attached to the electrode substrate to form a filler layer; (5) The film-forming electrode substrate in step (4) was taken out, and the filler loosely attached to the surface of the thin film was washed away slowly with solvent, and then the electrode substrate was placed into the electrodeposition device I to repeat step (1); (6) The film-forming electrode substrate in step (5) was taken out, and step (2) was repeated.

[0024] In this embodiment, the obtained perfluorosulfonic acid thin film-MXene sandwich film had a thickness of 60 μm, in which the filler part was 10 μm thick, and the film surface was smooth and uniformly distributed. The basic performance and the performance applied to vanadium flow batteries were tested, and the results are shown in Table 1. Example 2

[0025] In this embodiment, the method for preparing a sandwich structure separator for flow batteries by using electrodeposition technology is as follows: (1) The sulfonated polyether ether ketone resin was dissolved in N,N-dimethylformamide to prepare a film-forming resin solution with a mass percentage of 10 %, which was then added into the electrodeposition device I. Constant current electrodeposition was adopted, the film-forming electrode and the counter electrode were both titanium-based ruthenium-iridium electrodes with rough surfaces, the area ratio of the film-forming electrode to the counter electrode was 1:1.2, the distance between the film-forming electrode and the counter electrode was controlled to be 1.5 cm, the current density was 30 mA·cm -2 , the voltage was 25 V, the time was 3 min, and the electrodeposition temperature was 25 ℃, and the sulfonated polyether ether ketone resin molecules were uniformly enriched on the electrode substrate; (2) The electrode substrate in step (1) was taken out and dried at 120 ℃ for 30 min to obtain a layer of sulfonated polyether ether ketone thin film attached to the electrode substrate; (3) Hydroxyl carbon nanotubes were added into solvent, and stirred for 1 h using a magnetic stirrer and treated with ultrasound for 20 min to make them uniformly dispersed in the solvent, to prepare a dispersion liquid with a concentration of 7.5 %wt. Then the hydroxyl carbon nanotube dispersion liquid was added into the electrodeposition device II; (4) The sulfonated polyether ether ketone film obtained from the film-forming electrode in step (3) is placed in the electrodeposition device II together with the electrode substrate. Then, under the condition of continuous magnetic stirring, constant voltage electrodeposition is adopted, the distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm, the current density is 10 mA·cm -2 , the voltage is 15 V, the time is 15 min, and the electrodeposition temperature is 25 ℃, and the hydroxyl nanocarbon tube is uniformly enriched on the surface of the sulfonated polyether ether ketone film to form a filler layer; (5) The film-forming electrode substrate in step (4) is taken out, and the filler attached loosely on the surface of the film is washed away slowly with a solvent, and then the electrode substrate is placed in the electrodeposition device I, and step (1) is repeated; (6) The film-forming electrode substrate in step (5) is taken out, and step (2) is repeated; In this embodiment, the obtained sulfonated polyether ether ketone-hydroxyl nanocarbon tube sandwich film has a thickness of 50 μm, the filler layer has a thickness of 15 μm, the film surface is smooth, the distribution is uniform, and there is no delamination phenomenon. The basic performance and the performance applied to the vanadium flow battery are tested, and the results are shown in Table 1. Example 3

[0026] In this embodiment, the method for preparing the sandwich structure separator for flow battery by using the electrodeposition technology is as follows: (1) The perfluorosulfonic acid resin is dissolved in N,N-dimethylformamide to prepare a film-forming resin solution with a mass percentage of 10 %, and then added to the electrodeposition device I. Constant voltage electrodeposition is adopted, the film-forming electrode is a titanium mesh with a mesh number of 500, the counter electrode is a 316L stainless steel plate with a smooth surface, the area ratio of the film-forming electrode to the counter electrode is 1:1.5, the distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm, the current density is 10 mA·cm -2 , the voltage is 15 V, the time is 4 min, and the electrodeposition temperature is 15 ℃, and the perfluorosulfonic acid resin molecules are uniformly enriched on the electrode substrate; (2) The electrode substrate in step (1) is taken out and dried at 140 ℃ to obtain a perfluorosulfonic acid film attached to the electrode substrate; (3) The pyrrole monomer and sulfuric acid are added to a solvent to prepare a 10 % pyrrole monomer+15 % H2SO4 aqueous solution, and then a magnetic stirrer is used for fully stirring for 1 h and ultrasonic treatment for 40 min to prepare a pyrrole monomer solution with a concentration of 0.1 M. Then the pyrrole monomer solution is added to the electrodeposition device II; (4) The perfluorosulfonic acid film obtained from the film-forming electrode in step (3) is placed in the electrodeposition device II together with the electrode substrate. Then, under the condition of continuous magnetic stirring, constant voltage electrodeposition is adopted, the distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm, the current density is 5 mA·cm -2, the electrodeposition temperature is 25 °C, and a layer of polypyrrole will be deposited on the surface of the perfluorosulfonic acid film to form a filler layer; (5) The film-forming electrode substrate in step (4) is taken out, and the filler that is not tightly attached to the surface of the film is slowly washed away with a solvent. Then, the electrode substrate is placed in the electrodeposition device I, and step (1) is repeated. (6) The film-forming electrode substrate in step (5) is taken out, and step (2) is repeated.

[0027] In this embodiment, the obtained perfluorosulfonic acid-polypyrrole sandwich film has a thickness of 40 μm, in which the filler layer has a thickness of 10 μm. The film surface is smooth, uniform, and has no delamination phenomenon. The basic performance and the performance of the film applied to a vanadium flow battery are tested, and the results are shown in Table 1. Example 4

[0028] In this embodiment, the method for preparing a sandwich structure separator for a flow battery by using electrodeposition technology is as follows: (1) The polybenzothiazole resin is dissolved in N,N-dimethylformamide to prepare a film-forming resin solution with a mass percentage of 45%. Then, the solution is added to the electrodeposition device I. Constant current pulse electrodeposition is adopted. The film-forming electrode is a porous graphite plate, the counter electrode is a 316L stainless steel plate with a smooth surface, the area ratio of the film-forming electrode to the counter electrode is 1:1, the distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm, the current density is 10 mA·cm -2 , the electrodeposition time is 20 min, the frequency is 200 Hz, the duty cycle is 20%, and the electrodeposition temperature is 25 °C. The polybenzothiazole resin molecules will be uniformly enriched on the electrode substrate; (2) The electrode substrate in step (1) is taken out and dried at 100 °C to obtain a layer of polybenzothiazole film attached to the electrode substrate; (3) The short carboxyl carbon nanotubes are added to pure water, and a magnetic stirrer is used to fully stir for 1 h and ultrasonic treatment for 2 h to prepare a 15% wt short carboxyl carbon nanotube dispersion liquid. Then, the dispersion liquid is placed in the electrodeposition device II; (4) The polybenzothiazole film obtained by the film-forming electrode in step (3) is placed in the electrodeposition device II together with the electrode substrate. Then, constant voltage electrodeposition is adopted under the condition of continuous magnetic stirring. The distance between the film-forming electrode and the counter electrode is controlled to be 1.5 cm, the current density is 5 mA·cm -2 , the voltage is 15 V, the time is 10 min, the electrodeposition temperature is 25 °C, and a layer of short carboxyl carbon nanotubes will be deposited on the surface of the polybenzothiazole film to form a filler layer; (5) The film-forming electrode substrate in step (4) is taken out, and the filler that is not tightly attached to the surface of the film is slowly washed away with a solvent. Then, the electrode substrate is placed in the electrodeposition device I, and step (1) is repeated. (6) Take out the film electrode substrate in step (5), and repeat step (2).

[0029] In this embodiment, the obtained polybenzothiazole-short carboxyl carbon nanotube sandwich film has a thickness of 60 μm, wherein the filler layer has a thickness of 20 μm, the film surface is smooth, the distribution is uniform, and there is no delamination phenomenon. The basic performance and the performance applied to the vanadium flow battery are tested, and the results are shown in Table 1.

[0030] Table 1 Performance test results of the membrane of the embodiment

[0031] The results of the embodiment show that the sandwich structure membrane prepared by the electrodeposition method has the advantages of good vanadium resistance, good conductivity, and good battery performance, and the method is green and environmentally friendly, and no large amount of solvent volatilization is generated during operation, which meets the use requirements of the flow battery and can be widely applied in the field of flow batteries.

Claims

1. A method for preparing a separator for a sandwich-structured flow battery using electrodeposition technology, characterized in that, Includes the following steps: Step (1): Dissolve the film-forming resin in an organic solvent to prepare a film-forming resin solution with a mass percentage of 2-75%, and then add it to electrodeposition device I. By controlling the current, voltage, and time parameters, resin molecules will be uniformly enriched on the film-forming electrode substrate. The counter electrode is opposite to the film-forming electrode. Step (2): Take out the film-forming electrode substrate from step (1) and dry it to obtain a film-forming electrode substrate with a resin film attached to its surface. Step (3): Add the charged filler to be added to the membrane into the solvent, stir thoroughly with a magnetic stirrer and sonicate to make the charged filler disperse evenly in the solvent, and prepare a filler dispersion with a concentration range of 1-70%. Then add the filler dispersion into electrodeposition device II, with the counter electrode opposite to the film forming electrode. Step (4): Place the film-forming electrode substrate with resin film attached to the surface in step (2) into electrodeposition apparatus II. Then, under the conditions of continuous ultrasonic dispersion or magnetic stirring, by controlling the current, voltage and time parameters, the charged filler will be uniformly enriched on the surface of the film attached to the electrode substrate, and a film-forming electrode substrate with charged filler and film-forming resin film attached is obtained. Step (5): Take out the film-forming electrode substrate from step (4), slowly rinse off the loosely attached filler on the film surface with solvent, and then put the film-forming electrode substrate into electrodeposition apparatus I. Repeat step (1). The electrode opposite to the film-forming electrode is the counter electrode. Step (6): Remove the film-forming electrode substrate from step (5) and repeat step (2). Step (7): If it is necessary to manufacture a separator for a flow battery with a multi-layer structure, repeat steps (1) to (6) multiple times, and change the type of filler in step (3) according to the actual usage requirements.

2. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, In step (1), the film-forming resin is one or more of the following: perfluorosulfonic acid resin, sulfonated polyether ether ketone, polybenzothiazole, polybenzimidazole, sulfonated polyethylene, polyether sulfone, sulfonated polypropylene, polyimide, polysulfone, polyether ether ketone, perfluorocarboxylic acid resin, polyvinylidene fluoride resin, polypropylene, polyethylene, and polyvinylidene fluoride. The organic solvent is selected from one or more of the following: dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dichloromethane.

3. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, In step (3), the charged filler is selected from graphene-based fillers, carbon nanotube-based fillers, oxide fillers, or organic fillers; the amount of charged filler added is 1-10 wt%, and the ultrasonic dispersion treatment time is 0.1-6 h; the solvent can be an organic solvent or an inorganic solvent. The organic solvent includes one or more of ethanol, propanol, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dichloromethane, and the inorganic solvent includes pure water and inorganic salt aqueous solution.

4. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 3, characterized in that, Graphene-based fillers include graphene, graphene oxide, multilayer graphene, or nanographite sheets; carbon nanotube-based fillers include hydroxyl carbon nanotubes, carboxyl carbon nanotubes, carbonyl carbon nanotubes, single-walled carbon nanotubes, or multi-walled carbon nanotubes; organic fillers include polypyrrole, aminosulfonic acid, methanesulfonic acid, aminoacetic acid, or dodecylethoxysulfobetaine.

5. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, In step (4), the area ratio of the positive electrode to the negative electrode in electrodeposition apparatus I and II is 1:10 to 10:1, and the distance between the positive electrode and the negative electrode is 1 mm to 100 mm. The film-forming electrode is either a positive electrode or a negative electrode: when the film-forming electrode is a positive electrode, the corresponding counter electrode is a negative electrode, and an anion enrichment film is formed on the film-forming electrode; when the film-forming electrode is a negative electrode, the corresponding counter electrode is a positive electrode, and a cation enrichment film is formed on the film-forming electrode.

6. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, The film-forming electrode is one of the following: boron-doped diamond thin film electrode, titanium-based ruthenium-iridium electrode, titanium-based iridium-tantalum electrode, titanium-based ruthenium-indium-tin electrode, titanium-based tin-antimony oxide electrode, titanium-based titanium suboxide electrode, and titanium-based lead dioxide electrode; at least one of the following metallic material electrodes: stainless steel, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, tantalum, zirconium, tungsten, cerium, aluminum, bismuth, rhenium, barium, osmium, tin, lead, gold, silver, platinum, palladium, iridium, rhodium, molybdenum, and ruthenium; or any one of the following carbon material electrodes: graphite felt, carbon felt, graphite, glassy carbon, boron-doped diamond, activated carbon, graphene, carbon fiber, carbon nanotube, and carbon sponge.

7. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, The film-forming electrode is in the shape of a sheet or a rod, and the counter electrode is in any of the following shapes: sheet, rod, filament, granular, sponge-like, mesh, and porous structure.

8. The method for preparing a separator for a sandwich-structured flow battery using electrodeposition technology according to claim 1, characterized in that, In steps (1) and (4), when using constant current electrodeposition, the current density range is 10 mA·cm⁻¹. -2 ~1000mA·cm -2 The electrodeposition time ranged from 1 to 120 min, and the electrodeposition temperature ranged from 25 ℃ to 70 ℃. For constant voltage electrodeposition, the voltage ranged from 1 V to 150 V, the electrodeposition time from 1 to 120 min, and the electrodeposition temperature from 25 ℃ to 70 ℃. For constant current pulse electrodeposition, the current density ranged from 10 mA·cm⁻¹. -2 ~1000 mA·cm -2 The electrodeposition time was 1–120 min, the frequency was 200–2000 Hz, the duty cycle was 20%–80%, and the electrodeposition temperature was 25 ℃–70 ℃.

9. The method for preparing a sandwich-structured flow battery separator using electrodeposition technology according to claim 1, characterized in that, In step (2), the film drying temperature is 80-180 ℃ and the time is 1-4 h.

10. The method for preparing a sandwich structure flow battery separator using electrodeposition technology according to claim 1, wherein the sandwich structure separator prepared by the method has a thickness of 10 to 100 μm, wherein the thickness of the filler sandwich layer is 1 to 20 μm, and the applicable flow battery system includes any one or more of iron-chromium, vanadium, zinc-iron, iron, zinc-bromine, sodium / bromine polysulfide, titanium-manganese, or organic system flow batteries.

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