KR102018538B1 - A Separator for Zn-Br Redox Flow Battery, Manufacturing method thereof and A Zn-Br Redox Flow Battery containing the same - Google Patents

Abstract

The separator for zinc-bromine redox flow battery according to the present invention comprises a polyolefin resin porous film; A fluorine-based surfactant coating layer coated on at least one surface of the porous film; And a polymer coating layer coated on the surface of the fluorine-based surfactant coating layer and having sulfonic acid group introduced into the polytetrafluoromethylene skeleton.
The membrane for zinc-bromine redox flow battery according to the present invention is impregnated with Nafion in the polyolefin-based resin porous film and has the advantages such as mechanical strength of the polyolefin-based resin porous film and wettability of the electrolyte of Nafion. In addition, the wettability of the liquid electrolyte containing water is further improved due to the fluorine-based surfactant coating layer coated on at least one surface of the porous film, thereby improving the voltage efficiency and energy efficiency of the zinc-bromine redox flow battery having the separator. Is improved.

Description

Separator for Zn-Br Redox Flow Battery, Manufacturing method, and A Zn-Br Redox Flow Battery containing the same }

The present invention relates to a separator used in a zinc-bromine redox flow battery, a method of manufacturing the same, and a zinc-bromine redox flow battery having the same.

Conventional energy is being replaced by renewable energy because of energy crisis and environmental pollution. Renewables such as wind and solar power are developing into large-scale facilities. However, the wind and solar energy is a situation that the impact on the grid is getting worse due to the limitations of the power generation stability.

Accordingly, in order to obtain stable renewable energy that realizes load-shifting, research and development on a low cost, high efficiency, high capacity energy storage system is required.

Among the various energy storage systems, the redox flow cell has the advantages of low capacity, long life, high reliability and low operation and maintenance, such as adjustable capacity, no solid phase reaction, and no microstructure change of the electrode material. As a result, research and development has been concentrated.

Among the redox flow cells, zinc-bromine redox flow cells use Zn and Br as redox couples, and use the principle that Br reacts with oxidation at the cathode and Zn reacts with the cathode during charging.

Zinc-bromine redox flow cells necessarily contain water as a component of the liquid electrolyte. The separator made of a polyolefin resin porous film has excellent mechanical strength but poor wettability with such an electrolyte. Meanwhile, polymers in which sulfonic acid groups are introduced into a polytetrafluoromethylene skeleton, such as Nafion (Dupont), are thermally stable, have high chemical stability against Br, and have proton conductivity. Good wettability to liquid electrolyte and low membrane resistance. In addition, there is an advantage of reducing the Br ₂ crossover. Therefore, by impregnating Nafion to this polyolefin-based resin porous film, a composite membrane using simultaneously the mechanical strength of the polyolefin-based resin porous film and the wettability of the electrolyte of Nafion and the like has been proposed (SF-600 by Asahi Kasehi).

However, since the composite separator such as SF-600 is provided with a polyolefin resin porous film, it is necessary to further improve the wettability of the liquid electrolyte of the zinc-bromine redox flow battery including water.

Korean Unexamined Patent Publication No. 10-2016-0064545 Korean Unexamined Patent Publication No. 10-2015-0145309

SUMMARY OF THE INVENTION The present invention has been made in view of the above technical background, and has a polyolefin resin porous film and a zinc-bromine redox flow battery having a polymer coating layer having sulfonic acid group introduced into a polytetrafluoromethylene skeleton formed on its surface. Disclosed is a separator for a zinc-bromine redox flow battery, which further improves the wettability of a liquid electrolyte of the separator, a method of manufacturing the same, and a zinc-bromine redox flow battery having the same.

Another technical problem of the present invention is to provide a manufacturing method for efficiently increasing the porosity of a polyolefin resin porous film as a manufacturing method for the zinc-bromine redox flow battery described above.

In order to achieve the above object, the membrane for zinc-bromine redox flow battery according to the present invention,

Polyolefin resin porous film;

A fluorine-based surfactant coating layer coated on at least one surface of the porous film; And

It is coated on the surface of the fluorine-based surfactant coating layer, and is provided with a polymer coating layer in which sulfonic acid groups are introduced into the polytetrafluoromethylene skeleton.

In the separator of the present invention,

The polyolefin-based resin is polypropylene, the fluorine-based surfactant is a compound represented by the following formula (1), and the polymer in which the sulfonic acid group is introduced into the polytetrafluoromethylene skeleton is preferably Nafion.

 In the separator of the present invention, the porous film is preferably a polyolefin resin stretched film in which inorganic fine particle filler is dispersed, the thickness of the porous film is preferably 10 to 500, the thickness of the fluorine-based surfactant coating layer is It is preferable that it is 0.1-1 micrometer, and it is preferable that the thickness of the said polymer coating layer is 1-3 micrometers.

The present invention also provides a zinc-bromine redox flow battery having a positive electrode, a negative electrode, a liquid electrolyte containing water, and a separator for the zinc-bromine redox flow battery described above.

In addition, the manufacturing method of the separator for zinc-bromine redox flow battery of the present invention,

(S1) preparing a polyolefin resin porous film;

(S2) coating and drying a fluorine-based surfactant solution on at least one surface of the porous film to form a fluorine-based surfactant coating layer; And

(S3) coating a polymer solution having a sulfonic acid group introduced into the polytetrafluoromethylene skeleton and drying the surface of the fluorine-based surfactant coating layer to form a polymer coating layer having a sulfonic acid group introduced into the polytetrafluoromethylene skeleton.

In the method for preparing a separator for a zinc-bromine redox flow battery of the present invention, in the preparing of the porous film of (S1), an unstretched film is prepared by extruding a mixture of the kneaded polyolefin resin and an inorganic fine particle filler. A first step of doing;

Drawing a stretched film by stretching the unstretched film; And

It is preferable that a third step of treating the stretched film with an acidic solution. As the inorganic microparticle filler, any one or more selected from the group consisting of calcium carbonate, silica, magnesium carbonate, alumina, mica, titanium oxide and kaoring may be used. At this time, it is preferable that the average particle diameter of an inorganic fine particle filler is 0.1-300 micrometers.

In addition, the first step is preferably performed to uniaxially stretch the unstretched film in the MD direction, and the acidic solution preferably contains acetic acid solution.

The separator for zinc-bromine redox flow battery of the present invention is impregnated with Nafion in a polyolefin resin porous film, and has the advantages of mechanical strength of the polyolefin resin porous film and wettability of the electrolyte of Nafion. In addition, the wettability of the liquid electrolyte containing water is further improved due to the fluorine-based surfactant coating layer coated on at least one surface of the porous film, thereby improving the voltage efficiency and energy efficiency of the zinc-bromine redox flow battery having the separator. Is improved.

In addition, when the polyolefin-based resin porous film is prepared by a predetermined method in the preparation of the zinc-bromine redox flow battery separator of the present invention, the surface of the inorganic fine particle filler included in the stretched film by treatment of an acidic solution As this elutes, the porosity of the porous film can be improved. That is, since the acidic solution can dissolve the inorganic fine particle filler, since the surface of the inorganic fine particle filler mixed in the stretched film is dissolved and extracted by the acidic solution, pores are further formed by the volume of the dissolved inorganic fine particle filler. The porosity of the porous film is improved. Pores are also formed around the inorganic fine particle filler that is mixed during the stretching process, and the pores formed around the inorganic fine particle filler become larger according to the treatment of the acidic solution, so that the pore distribution hardly increases. do. Therefore, it is possible to use a porous film having increased porosity efficiently without adopting harsh conditions.

1 and 2 is a view showing the specification of the calcium carbonate used in the production of a polyolefin resin porous film constituting the separator according to Example 1 of the present application,
3 is an SEM photograph of unstretched films according to the blending ratio of the inorganic filler when preparing the polyolefin-based resin porous film constituting the separator according to Example 1 of the present application,
FIG. 4 is SEM images of unstretched films having a blending ratio of an inorganic filler 50 wt% and films according to a draw ratio when preparing a polyolefin-based resin porous film constituting the separator according to Example 1 of the present application,
5 is a cross-sectional SEM photograph of a stretched film treated with acetic acid when preparing a polyolefin-based resin porous film constituting the separator according to Example 1 of the present application;
6 is a SEM image of the surface of the stretched film treated with acetic acid when preparing a polyolefin-based resin porous film constituting the separator according to Example 1 of the present application,
7 is a cross-sectional SEM photograph of the non-oriented film treated with acetic acid according to Reference Example 2,
8 is a SEM image of the surface of a non-oriented film treated with acetic acid according to Reference Example 2. FIG.
9 is a SEM photograph of the surface and cross section before and after forming the Nafion coating layer of the polyolefin resin porous film with a fluorine-based surfactant coating layer constituting the separator according to Example 1 of the present application,
10 is a process schematic diagram of preparing a zinc-bromine redox flow cell using the membranes of Example 1 and Comparative Examples 1-2;
11 and 12 are graphs of measuring the voltage efficiency and the energy efficiency of a cell having a separator prepared in Example 1 and a cell having a separator according to Comparative Examples 1 and 2, respectively. to be.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

Separation membrane for zinc-bromine redox flow battery according to the present invention,

Polyolefin resin porous film;

A fluorine-based surfactant coating layer coated on at least one surface of the porous film; And

It is coated on the surface of the fluorine-based surfactant coating layer, and is provided with a polymer coating layer in which sulfonic acid groups are introduced into the polytetrafluoromethylene skeleton.

Polyolefin-based resin porous films used as separators for zinc-bromine redox flow batteries are well known in the art. Typically, a polypropylene resin is used a lot, but is not limited thereto. A uniaxially stretched porous film or a biaxially stretched porous film is also widely used, but is not limited thereto. It is preferable that the thickness is 10-500 micrometers.

A fluorine-based surfactant coating layer is formed on at least one surface of the porous film. The fluorine-based surfactant is a compound containing two or more fluorine groups, and helps the liquid electrolyte containing water to wet well into the pores of the hydrophobic polyolefin resin porous film through the polymer coating layer having sulfonic acid group introduced into the polytetrafluoromethylene skeleton described below. give. It is preferable that the thickness is 0.1-1 micrometer.

As the fluorine-based surfactant, a compound represented by the following Chemical Formula 1 may be used, but is not limited thereto.

<Formula 1>

On the surface of the fluorine-based surfactant coating layer, a polymer coating layer in which a sulfonic acid group is introduced into a polytetrafluoromethylene skeleton is formed. Polymers in which sulfonic acid groups are introduced into polytetrafluoromethylene backbone, such as Nafion, are thermally stable, chemically stable against Br, and proton-conducting polymers, as described above, for liquid electrolyte in zinc-bromine redox flow cells. Good wettability and low membrane resistance. In addition, there is an advantage of reducing the Br ₂ crossover. However, since it is expensive, it is preferable to form in thickness of 1-3 micrometers, for example.

Separation membrane (not shown) of the three-layer structure as described above is a fluorine-based surfactant coating layer is formed on at least one surface of the polyolefin-based resin porous film, and thus the fluorine-based surfactant is located on the surface and pores of the polyolefin-based resin porous film. In addition, by the polymer coating layer formed on the surface of the fluorine-based surfactant coating layer, the polymer component may be located on the surface of the fluorine-based surfactant coating layer, and may be located in the surface and pores of the polyolefin-based resin porous film.

The separator described above is provided with a liquid electrolyte including a positive electrode, a negative electrode, and water to constitute a zinc-bromine redox flow battery.

On the other hand, the manufacturing method of the separator for zinc-bromine redox flow battery of the present invention,

(S1) preparing a polyolefin resin porous film;

(S2) coating and drying a fluorine-based surfactant solution on at least one surface of the porous film to form a fluorine-based surfactant coating layer; And

(S3) coating a polymer solution having a sulfonic acid group introduced into the polytetrafluoromethylene skeleton and drying the surface of the fluorine-based surfactant coating layer to form a polymer coating layer having a sulfonic acid group introduced into the polytetrafluoromethylene skeleton.

First, prepare a polyolefin resin porous film (step S1). As described above, the polyolefin resin porous film used as the use of the separator for the zinc-bromine redox flow battery is well known in the art and is not particularly limited.

In particular, in order to efficiently increase the porosity of the polyolefin resin porous film, a first step of extruding a mixture of the kneaded polyolefin resin and the inorganic fine particle filler to prepare an unstretched film; Drawing a stretched film by stretching the unstretched film; And a third step of treating the stretched film with an acidic solution.

First, a mixture of the kneaded polyolefin resin and the inorganic fine particle filler is extruded to prepare an unstretched film (first step).

As the polyolefin resin, any resin that can be used for the production of a separator for an electrochemical device such as polyethylene and polypropylene can be used. In addition, the inorganic fine particle filler may be used as long as it can be dissolved in an acidic solution such as calcium carbonate, silica, magnesium carbonate, alumina, mica, titanium oxide, kaoring, and the like. Preferably calcium carbonate can be used. The average particle diameter of the inorganic fine particle filler can be appropriately selected according to the desired pore size, for example, preferably 0.1 to 300 µm, more preferably 0.3 to 50 µm, still more preferably 0.5 to 30 µm. .

A method for producing an unstretched film by extruding a mixture of polyolefin resins and inorganic fine particles is a well-known dry manufacturing method, for example, using a polyolefin resin and 20 to 60% by weight of inorganic fine particle filler as required. After kneading, the kneaded material may be prepared into pellets and then extruded to produce an unstretched film.

Next, the unstretched film is stretched to prepare a stretched film (second step).

Although the stretching method can be used for both uniaxial stretching or biaxial stretching, it is preferable to perform uniaxial stretching of the unstretched film in the MD direction in view of economics and productivity.

The draw ratio for stretching the unstretched film may be selected in consideration of the desired mechanical strength and pore size of the separator, but may be stretched 2 to 6 times, but is not limited thereto.

The stretched stretched film is then treated with an acidic solution (third step).

As described above, since the acidic solution can dissolve the inorganic microparticle filler, the surface of the inorganic microparticle filler mixed into the stretched film is dissolved and extracted by the acidic solution, so that the pores are as large as the volume of the dissolved inorganic microparticle filler. It is further formed to improve the porosity of the film. Pores are also formed around the inorganic fine particle filler that is mixed during the stretching process, and the pores formed around the inorganic fine particle filler become larger according to the treatment of the acidic solution, so that the pore distribution hardly increases. do. Therefore, the porosity of the porous film can be efficiently increased without adopting harsh conditions such as increasing the draw ratio.

As the acidic solution, both strong and weak acids may be used, but it is preferable to use a weak acid such as acetic acid which has little effect on the mechanical properties of the stretched film. In this respect, the pH of the acidic solution treated on the stretched film is preferably 1 to 5, more preferably 1.5 to 4, and even more preferably 1 to 3 pH. .

The treatment method of the acidic solution is not limited, for example, a method of immersing the stretched film in a bath containing the acidic solution may be used. The temperature of the acidic solution can also be controlled, preferably at room temperature for ease of processing.

In the above-described method for producing a porous film, it will be obvious that the extruded unstretched film may be annealed before the second step, or hot set after the second step.

When the polyolefin resin porous film is prepared, at least one surface of the porous film is coated with a fluorine-based surfactant solution and dried to form a fluorine-based surfactant coating layer (step S2).

Introduction of the fluorine-based surfactant coating layer improves the hydrophilicity of the polyolefin-based resin, thereby improving the wettability of the liquid electrolyte solution containing water.

The above-mentioned compounds may be used as the fluorine-based surfactant, and a coating layer may be formed by coating a solution in which a fluorine-based surfactant is dissolved in a solvent such as N-methyl pyrrolidone (NMP) on at least one surface of the porous film and then drying it. And the coating method is not limited.

Subsequently, the polymer solution in which the sulfonic acid group is introduced into the polytetrafluoromethylene skeleton is coated on the surface of the fluorine-based surfactant coating layer and dried to form the polymer coating layer in which the sulfonic acid group is introduced into the polytetrafluoromethylene skeleton (step S3).

A polymer coating layer can be formed by coating a solution in which a sulfonic acid group is introduced into a polytetrafluoromethylene skeleton such as Nafion in a solvent such as N-methyl pyrrolidone (NMP) and then drying it, thereby forming a polymer coating layer. It doesn't work. When coating the polymer solution, it is preferable to remove the excess solution after performing the first coating for uniformity of solution impregnation, and then to perform the second coating again, but is not limited thereto.

The separator of the present application prepared by the above method is assembled into a zinc-bromine redox flow cell by a conventional method with a liquid electrolyte including a positive electrode, a negative electrode, and water.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example  One

<Production of Porous Film>

Method of measuring porosity and pore size

As a pore rule analyzer (mercury method), porosity was measured using a Micromeritics Autopore IV9520.

Pore size was measured using a Porometer (POROLUX 1000, IB-FT GmbH). The porewick solution having a surface tension of 16.0 dynes / cm was impregnated with the specimen for at least 10 minutes, and then subjected to room temperature.

Calcium carbonate

Calcium carbonate in the specifications shown in FIGS. 1 and 2 was used.

Stretch  Process conditions

It carried out as Table 1 below.

division Unit Pilot No extension Extension Stretch three times Stretch 4 times Screw RPM RPM 30 50 63 75 Casting roll m / min 1.4 1.4 1.4 1.4 MDO 1st Stretch m / min 1.4 2.0 2.5 2.7 2nd stretch m / min 1.4 2.5 3.5 4.0 3rd Stretch m / min 1.4 2.8 4.5 6.5 Ratio % 0 200 300 400 Thickness Μm 200 200 200 200 Machine speed 1st Cooling m / min 2.0 3.5 5.0 6.5

Reference Example  One

Polyethylene resin (LG Chemical Trade Name: LB7500N) was blended and kneaded with calcium carbonate in the ratio of the following Table 2 to prepare an unstretched film.

Inorganic filler
Compounding ratio (% by weight) Thickness
(Μm) Pore size
(Μm) Porosity (%) 30 200 16.12 25 40 200 16.78 26.1 50 200 17.1 27.2

SEM images of the unstretched films obtained according to Table 2 are shown in FIG. 3.

Subsequently, it was stretched according to Table 3 below using an unstretched film having an inorganic filler formulation of 50% by weight, and the pore size and the like accordingly are shown in Table 3 below.

division Thickness
(Μm) Pore size
(Μm) Porosity (%) No extension 200 17.1 27.2 Draw twice 200 19.78 (14% ↑) 30.1 (9% ↑) Stretch three times 200 32.9 (48% ↑) 35.1 (23% ↑) Stretch 4 times 200 29.3 (42% ↑) 39.1 (31% ↑)

SEM photographs of the films obtained according to Table 3 are shown in FIG. 4.

Production Example  One

According to the reference example 1, the stretched 4 times film containing 50 weight% of calcium carbonate was immersed for 5 minutes in 15weight% of acetic acid aqueous solution, and the SEM photograph of the obtained film was shown in FIG.

The average pore size was measured at 49 nm and porosity was 60%. From these figures, it can be seen that the pore size was increased from 29.3 nm and porosity 39.1%. This can be confirmed that the pores are increased from the cross-sectional photograph of Figure 5 and the surface photograph of FIG.

Reference Example  2

Acetic acid was treated in the same manner as in Production Example 1 using the unstretched film of Table 3 having an inorganic filler formulation of 50% by weight, and SEM photographs of the obtained film were shown in FIGS. 7 and 8. From the cross-sectional photograph of FIG. 7 and the surface photograph of FIG. 8, it can be seen that the pores were not greatly increased even when the acid-treated inorganic filler-containing film was not subjected to stretching.

From the above results, when preparing a polyolefin-based resin porous film according to Preparation Example 1 in the preparation of the zinc-bromine redox flow battery separator of the present invention, the surface of the inorganic microparticle filler contained in the stretched film by treatment of an acidic solution As it is eluted, it can be seen that the porosity of the porous film can be improved. That is, since the acidic solution can dissolve the inorganic fine particle filler, since the surface of the inorganic fine particle filler mixed in the stretched film is dissolved and extracted by the acidic solution, pores are further formed by the volume of the dissolved inorganic fine particle filler. The porosity of the porous film is improved. Pores are also formed around the inorganic fine particle filler that is mixed during the stretching process, and the pores formed around the inorganic fine particle filler become larger according to the treatment of the acidic solution, so that the pore distribution hardly increases. do. Therefore, it is possible to use a porous film having increased porosity efficiently without adopting harsh conditions.

<Formation of Fluorine-Based Surfactant Coating Layer>

After preparing a solution in which the fluorine-based surfactant represented by Formula 1 was dissolved in NMP at a concentration of 30% by weight, it was cast on one surface of a porous film having a thickness of 20 μm prepared according to the preparation method of Preparation Example 1, and dried. A fluorine-based surfactant coating layer having a thickness of 1 μm was formed.

< Polytetrafluoromethylene  On the skeleton Sulfonic acid  Formation of Introduced Polymer Coating Layer>

After the Nafion D520 solution purchased from DuPont was dried, a solution dissolved in N-methyl pyrrolidone (NMP) at a concentration of 10% by weight was prepared. After removing the excess solution, the second casting and drying again to form a polymer coating layer in which sulfonic acid groups were introduced into a polytetrafluoromethylene skeleton having a thickness of about 2 μm.

9 is a SEM photograph of the surface and the cross section before and after the formation of the Nafion coating layer of the polyolefin resin porous film with a fluorine-based surfactant coating layer constituting the separator according to Example 1 of the present application.

Comparative example  One

A SF-600 membrane (Nafion-filled porous polypropylene membrane) purchased from Asahi Kaseihisa was used.

Comparative example  2

Nafion 212 membrane (Nara Cell Tech Co., Ltd.) having a thickness of 50 µm was pretreated with pure water for 12 hours, and used in a state of improving wettability with water.

<Measurement of Voltage Efficiency and Energy Efficiency>

Zinc-bromine redox flow cells each having a size of 120 cm 2 were prepared according to the process of FIG. 10 using the membranes of Example 1 and Comparative Examples 1-2.

FIG. 11 is a view showing a cell (PP_Nafion 80DI12hr) having a separator prepared according to Example 1, a cell (SF600) having a separator according to Comparative Example 1, and a separator (Nafion 212 80DI12hr) according to Comparative Example 2. It is a graph which measures the voltage efficiency of a cell.

In addition, Figure 12 is a graph showing the measurement of the energy efficiency of the cell having a membrane in accordance with an embodiment having a membrane cell according to a cell and, in Comparative Example 1 having the manufactured membrane according to 1, and Comparative Example 2 .

Since the separators of Example 1 and Comparative Example 1 have a polyolefin-based resin porous film, the mechanical strength is superior to that of the Nafion membrane of Comparative Example 2. 11 and 12, the cell with the separator of Example 1, in which the fluorine-based surfactant coating layer was formed before the Nafion coating layer was formed, had a voltage higher than that of the cell of Comparative Example 1, which did not form the fluorine-based surfactant coating layer. It can be seen that the efficiency and energy efficiency have been improved.

Claims (14)

delete delete delete delete delete (S1) preparing a polyolefin resin porous film;
(S2) coating and drying a fluorine-based surfactant solution on at least one surface of the porous film to form a fluorine-based surfactant coating layer; And
(S3) coating a polymer solution having a sulfonic acid group introduced into a polytetrafluoromethylene skeleton on a surface of the fluorine-based surfactant coating layer and drying the same to form a polymer coating layer having a sulfonic acid group introduced into a polytetrafluoromethylene skeleton;
The preparing of the porous film of (S1) may include a first step of extruding a mixture of the kneaded polyolefin resin and the inorganic fine particle filler to prepare an unstretched film;
Drawing a stretched film by stretching the unstretched film; And
A method of manufacturing a separator for a zinc-bromine redox flow battery comprising a third step of treating the stretched film with an acidic solution. delete The method of claim 6,
The inorganic fine particle filler is any one or more selected from the group consisting of calcium carbonate, silica, magnesium carbonate, alumina, mica, titanium oxide and kaoring, wherein the zinc-bromine redox flow battery separator. The method of claim 6,
The average particle diameter of the inorganic fine particle filler is 0.1 to 300㎛ method for producing a separator for zinc-bromine redox flow battery. The method of claim 6,
The first step is a method for producing a separator for zinc-bromine redox flow battery, characterized in that the uniaxial stretching of the unstretched film in the MD direction. The method of claim 6,
The acid solution is a method for producing a zinc-bromine redox flow battery separator, characterized in that the acetic acid solution. The method of claim 6,
The polyolefin-based resin is polypropylene, the fluorine-based surfactant is a compound represented by the following formula (1), the polymer in which the sulfonic acid group is introduced into the polytetrafluoromethylene skeleton is Nafion (Nafion), characterized in that Method for preparing a separator for a redox flow battery:
<Formula 1>

The method of claim 6,
The porous film is a method for producing a separator for zinc-bromine redox flow battery, characterized in that the polyolefin resin stretched film in which inorganic fine particle filler is dispersed. The method of claim 6,
Separation membrane of the zinc-bromine redox flow battery, characterized in that the thickness of the porous film is 10 to 500㎛, the thickness of the fluorine-based surfactant coating layer is 0.1 to 1㎛, the thickness of the polymer coating layer is 1 to 3㎛. Manufacturing method.

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