Preparation method and application of flexible graphite paper high-strength bipolar plate

Abstract

The invention belongs to the technical field of bipolar plates, and particularly relates to a preparation method and application of a flexible graphite paper high-strength bipolar plate. Uniformly mixing the modified polyphenylene sulfide powder and the expanded graphite worms according to an air convection principle, uniformly dispersing and stacking the mixture by material distribution equipment, and calendering the mixture by a calender to obtain a sheet; and finally, melting and curing the modified polyphenylene sulfide by utilizing high temperature of a hot press, so that the prepared bipolar plate has relatively good conductivity, heat insulation performance and mechanical performance, is simple in processing technology and light in weight, and is suitable for the field of flow batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of bipolar plates, and in particular relates to a preparation method and application of a flexible graphite paper high-strength bipolar plate. Background Art

[0002] Bipolar plates are key components in flow batteries, and they support membrane electrodes, collect current, isolate, and dissipate heat in flow batteries. Therefore, bipolar plates need to have properties such as gas barrier, conductivity, and corrosion resistance. The common bipolar plates on the market are metal bipolar plates, which have the advantages of high mechanical strength and good conductivity, but are heavy and easy to corrode. Therefore, flexible graphite paper with the characteristics of being thin, bendable, and corrosion-resistant is gradually used to prepare bipolar plates. Graphite paper is made by chemically treating high-carbon phosphorus flake graphite and expanding and rolling it at high temperature. However, the toughness of graphite paper prepared from pure graphite is poor, and it is easy to break or crack during use, thus affecting the performance of the material. In order to improve the flexibility of graphite paper, graphite powder is often used as a filler and added to the resin, and then prepared into a bipolar plate through heating, pressurization, curing and other operations.

[0003] Patent CN102569834A discloses a high-strength flexible graphite bipolar plate and a preparation method thereof. The bipolar plate is prepared by adding expanded graphite worms into a mold, directly molding or step-by-step molding by molding or rolling, and then the bipolar plate is immersed in phenolic resin for heat treatment to obtain a flexible graphite bipolar plate that is corrosion-resistant, lightweight, and has good electrical and thermal conductivity. However, the expanded graphite worms and the resin cannot be evenly mixed by the immersion method, resulting in poor mechanical properties of the flexible graphite electrode.

[0004] Patent CN116638697B discloses a high-performance graphite-based composite bipolar plate, preparation method and application. The method comprises mixing graphite powder, resin powder, carbon black and carbon fiber in a powder mixing system, and then heating and pressurizing the mixed powder in a mold in a molding system. The heating is then terminated and the molding pressure is continued to be maintained. When the temperature drops below the curing molding temperature of the resin, the molding pressure is removed and air is filled in. The bipolar plate with high conductivity and good air tightness is obtained by demolding. However, the graphite powder used includes natural flake powder and artificial graphite powder, which will increase the weight of the bipolar plate and reduce the thermal insulation performance.

[0005] Therefore, there is an urgent need in the market for a flexible graphite paper bipolar plate that has good thermal insulation and mechanical properties and is lightweight. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to obtain a flexible graphite paper high-strength bipolar plate with good electrical conductivity, thermal insulation and mechanical properties, simple processing technology and light weight.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In one aspect, the present invention provides a method for preparing a flexible graphite paper high-strength bipolar plate, comprising the following steps:

[0009] (1) adding expandable graphite into a high-temperature expansion furnace and expanding at 900-1000° C. until the volume does not change to obtain expanded graphite worms;

[0010] (2) adding the expanded graphite worms and modified polyphenylene sulfide powder obtained in step (1) into a powder mixing system, introducing gas to mix the powders, and obtaining a mixed powder;

[0011] (3) adding the mixed powder obtained in step (2) to a material distribution device for dispersion and stacking, and then sending it to a calender for heating and pressurization to obtain a sheet;

[0012] (4) placing the sheet obtained in step (3) into a hot press, hot pressing at 330-350° C. and 20-40 MPa for 7-9 min, cooling to 50-70° C., and releasing the sheet by passing air to obtain a flexible graphite paper high-strength bipolar plate.

[0013] Preferably, the temperature of the gas is 280-290°C.

[0014] The present application prepares expanded graphite worms by subjecting expandable flake graphite to a special high-temperature puffing furnace, then uniformly mixes modified polyphenylene sulfide powder and expanded graphite worms by the principle of air convection, and then uniformly disperses and stacks them by special distribution equipment, and then calenders them to obtain sheets by a calender. Finally, a hot press is used to melt and solidify the modified polyphenylene sulfide at high temperature to prepare a bipolar plate having the characteristics of low resistance, high conductivity, high mechanical strength, corrosion resistance, and easy cutting, and is suitable for the fields of liquid flow batteries and fuel cells.

[0015] In some embodiments, the method for preparing the expandable graphite is: adding natural flake graphite, mixed acid, potassium permanganate and potassium dichromate into a reaction container, reacting at 40-60° C. for 50-70 min, and centrifugally washing and drying to obtain the expandable graphite.

[0016] Preferably, the mass ratio of the natural flake graphite, mixed acid, potassium permanganate and potassium dichromate is 1:(30-40):(0.1-0.3):(0.08-0.12).

[0017] In some embodiments, the mixed acid is a mixture of acetic anhydride, phosphoric acid, and perchloric acid, and the mass ratio of the three is 1: (0.90-0.94): (1.2-1.4).

[0018] The present application prepares expandable graphite by oxidizing natural flake graphite with a specific ratio of mixed acid, potassium permanganate, and potassium dichromate. In the oxidation process, the mixed acid can play a role in assisting oxidation, and acetic anhydride can absorb water in the solution to reduce the pH of the solution, further improving the oxidizability of potassium permanganate and potassium dichromate, which helps to increase the volume of expandable graphite after expansion and lighten the weight of the bipolar plate. Moreover, after intercalation oxidation of natural flake graphite by acetic anhydride, phosphoric acid, perchloric acid, potassium permanganate, and potassium dichromate, a large number of oxygen-containing groups such as hydroxyl, carboxyl, and phosphate groups can be introduced into the graphite, which is conducive to the generation of a large amount of gas at high temperature, and the expansion graphite worms with high purity and well-developed pores are obtained.

[0019] In some embodiments, the mass ratio of the expanded graphite worms to the modified polyphenylene sulfide powder in step (2) is 1:(0.2-0.3).

[0020] The present application limits the ratio of expanded graphite worms and modified polyphenylene sulfide powder, thereby improving the mechanical properties of the bipolar plate without affecting the conductive properties of the bipolar plate.

[0021] In some embodiments, the gas is high-purity nitrogen, high-purity argon, or dry air.

[0022] Preferably, the gas is dry air.

[0023] In some embodiments, the temperature of the heating and pressing is 140-160° C., and the pressure is 70-90 MPa.

[0024] The present application can play a pre-bonding role by limiting the temperature and pressure of heating and pressing, embedding the expanded graphite worms into the modified polyphenylene sulfide resin, and pressing them into a certain thickness, thereby improving the subsequent hot pressing effect of the bipolar plate, which is beneficial to improving the conductive performance of the bipolar plate.

[0025] In some embodiments, the method for preparing the modified polyphenylene sulfide powder comprises the following steps:

[0026] A1. Add 1,3,5-tribromobenzene, 2,4-dichlorobenzenethiol and sodium bicarbonate to N-methylpyrrolidone, heat to 170-190°C and react for 10-15h, cool to room temperature and pour into 20-22wt% hydrochloric acid to obtain a precipitate, wash, filter and dry to obtain a hyperbranched polyphenylene sulfide powder;

[0027] A2. Add the hyperbranched polyphenylene sulfide powder obtained in step A1, triethylamine and tetrahydrofuran into a reaction vessel, heat to 65-70°C, react for 7-9 hours, cool to room temperature, add copper sulfate methanol solution, stir for 30-40 minutes, wash, filter and dry to obtain modified polyphenylene sulfide powder.

[0028] Preferably, the mass ratio of the 1,3,5-tribromobenzene, 2,4-dichlorothiophenol and sodium bicarbonate is (0.03-0.04):1:(1.3-1.4).

[0029] Polyphenylene sulfide has good corrosion resistance, heat resistance and mechanical properties, but its electrical conductivity is poor. This application prepares a hyperbranched polyphenylene sulfide resin so that it has multiple benzene rings and sulfur atoms on a plane, which has a strong conjugation effect and hydrogen bonding effect, which is beneficial to improving the mechanical properties of the bipolar plate, and can improve the mobility of electrons on the polyphenylene sulfide chain segment, further improving the electrical conductivity of polyphenylene sulfide, and then improving the electrical conductivity of the bipolar plate. In addition, this application introduces quaternary ammonium salt groups on the polyphenylene sulfide chain segment by reacting the hyperbranched polyphenylene sulfide resin with triethylamine and then complexing it with copper ions, which can further improve the electron mobility between the modified polyphenylene sulfide and the expanded graphite worms, which is beneficial to improving the electrical conductivity of the bipolar plate.

[0030] In some embodiments, the weight average molecular weight of the hyperbranched polyphenylene sulfide is 20,000-30,000.

[0031] The present application limits the molecular weight of polyphenylene sulfide to ensure that the modified polyphenylene sulfide resin has good heat resistance and mechanical properties while having good processing properties, which is beneficial to improving the mechanical properties and conductive properties of the bipolar plate.

[0032] In some embodiments, the mass ratio of the hyperbranched polyphenylene sulfide powder to triethylamine is 1:(0.1-0.2).

[0033] The present application limits the mass ratio of the hyperbranched polyphenylene sulfide powder and triethylamine, so that the sulfur atoms on the hyperbranched polyphenylene sulfide are not easily affected by triethylamine, thereby preventing the problem of decreased mechanical properties of the modified polyphenylene sulfide resin due to the breakage of chain segments.

[0034] On the other hand, the present invention provides a method for preparing a flexible graphite paper high-strength bipolar plate and application of the obtained flexible graphite paper high-strength bipolar plate in the field of liquid flow batteries.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention prepares graphite worms from expandable flake graphite through a special high-temperature puffing furnace, then uniformly mixes modified polyphenylene sulfide powder and expanded graphite worms using the principle of air convection, and then uniformly disperses and stacks them through a special material distribution equipment, and then calenders them to obtain sheets. Finally, a hot press is used to melt and solidify the modified polyphenylene sulfide at high temperature to prepare a bipolar plate with low resistance, high conductivity, high mechanical strength, corrosion resistance, and easy cutting characteristics, and is suitable for the field of fuel cells.

[0037] (2) The present invention prepares expandable graphite by oxidizing natural flake graphite using mixed acid, potassium permanganate, and potassium dichromate. By introducing a large number of oxygen-containing groups such as hydroxyl, carboxyl, and phosphate groups into the graphite, a large amount of gas can be generated at high temperature, so that the volume of the expanded graphite worms is larger, which is beneficial to reducing the weight of the flexible graphite paper high-strength bipolar plate.

[0038] (3) The present invention prepares a hyperbranched polyphenylene sulfide resin so that it has multiple benzene rings and sulfur atoms on a plane, which has a strong conjugation effect and hydrogen bonding effect, which is beneficial to improving the mechanical properties and electrical conductivity of the bipolar plate. In addition, the present application further improves the electron mobility between the modified polyphenylene sulfide and the expanded graphite worms by reacting the hyperbranched polyphenylene sulfide resin with triethylamine to introduce quaternary ammonium salt groups on the polyphenylene sulfide chain segments and then complexing them with copper ions, thereby further improving the electrical conductivity of the flexible graphite paper high-strength bipolar plate. DETAILED DESCRIPTION

[0039] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0040] In the following embodiments and comparative examples, except for modified polyphenylene sulfide, the other compounds and related reagents used can be purchased from the market. The average particle size of natural flake graphite is 80 mesh, purchased from Hebei Runhuabang New Material Technology Co., Ltd.; the number average molecular weight of polyphenylene sulfide powder is 25,000, purchased from Ningbo Rongsu New Material Co., Ltd.

[0041] Preparation Example 1

[0042] The preparation method of modified polyphenylene sulfide powder-1 comprises the following steps:

[0043] A1. Add 0.35 g 1,3,5-tribromobenzene, 10 g 2,4-dichlorobenzenethiol and 13.5 g sodium bicarbonate to 100 ml N-methylpyrrolidone, heat to 180° C. for reaction, cool to room temperature, pour into 300 ml 21 wt % hydrochloric acid to obtain a precipitate, wash, filter and dry to obtain a hyperbranched polyphenylene sulfide powder with a number average molecular weight of 25443;

[0044] A2. Add 20 g of the hyperbranched polyphenylene sulfide powder obtained in step A1, 3 g of triethylamine and 30 g of tetrahydrofuran into a reaction vessel, heat to 68 ° C, react for 8 hours, cool to room temperature, add 10 ml of 2 wt% copper sulfate methanol solution, stir for 35 minutes, wash, filter and dry to obtain modified polyphenylene sulfide powder-1.

[0045] Preparation Example 2

[0046] The preparation method of modified polyphenylene sulfide powder-2 is the same as that of Preparation Example 1, except that the number average molecular weight of the hyperbranched polyphenylene sulfide powder is 43288.

[0047] Preparation Example 3

[0048] The preparation method of modified polyphenylene sulfide powder-3 is the same as that of Preparation Example 1, except that the amount of triethylamine added is 5 g.

[0049] Preparation Example 4

[0050] The preparation method of expandable graphite-1 is as follows: 1g natural flake graphite, 35g mixed acid, 0.2g potassium permanganate and 0.1g potassium dichromate are added into a reaction container, reacted at 45°C for 60min, and centrifuged, washed and dried to obtain the expandable graphite-1;

[0051] The mixed acid is a mixture of acetic anhydride, 85 wt % phosphoric acid and 60 wt % perchloric acid, and the mass ratio of the three is 1:0.92:1.3.

[0052] Preparation Example 5

[0053] The preparation method of expandable graphite-2 is the same as that of Preparation Example 4, except that the mixed acid is replaced by 68wt% nitric acid in equal amounts.

[0054] Preparation Example 6

[0055] The preparation method of expandable graphite-3 is the same as that of Preparation Example 4, except that the mixed acid is a mixture of acetic anhydride, 85wt% phosphoric acid, and 60wt% perchloric acid, and the mass ratio of the three is 0.5:0.92:1.3.

[0056] Example 1

[0057] A method for preparing a flexible graphite paper high-strength bipolar plate comprises the following steps:

[0058] (1) adding expandable graphite-1 into a high-temperature expansion furnace and expanding at 950° C. until the volume does not change to obtain expanded graphite worms;

[0059] (2) adding 10 g of the expanded graphite worms obtained in step (1) and 2.5 g of modified polyphenylene sulfide powder-1 into a powder mixing system, introducing dry air at a flow rate of 250 m / s at 285° C. to mix the powders to obtain a mixed powder;

[0060] (3) adding the mixed powder obtained in step (2) to a material distribution device for dispersion and stacking, and then feeding it into a calender for heating and pressing at 150° C. and 80 MPa to obtain a sheet;

[0061] (4) The sheet obtained in step (3) is placed in a hot press, hot-pressed at 340° C. and 30 MPa for 8 min, cooled to 60° C., and demolded by passing air to obtain a flexible graphite paper high-strength bipolar plate with a thickness of 0.8 mm.

[0062] Example 2

[0063] A method for preparing a flexible graphite paper high-strength bipolar plate comprises the following steps:

[0064] (1) adding expandable graphite-1 into a high-temperature expansion furnace and expanding at 950° C. until the volume does not change to obtain expanded graphite worms;

[0065] (2) adding 10 g of the expanded graphite worms obtained in step (1) and 20 g of the modified polyphenylene sulfide powder-1 into a powder mixing system, introducing dry air at a flow rate of 200 m / s at 290° C. to mix the powders to obtain a mixed powder;

[0066] (3) adding the mixed powder obtained in step (2) into a material distribution device and spreading it, and then sending it into a calender to heat and pressurize it at 140° C. and 90 MPa to obtain a sheet;

[0067] (4) The sheet obtained in step (3) was placed in a hot press, hot pressed at 330° C. and 40 MPa for 7 min, cooled to 50° C., and air was introduced to demold the sheet to obtain a flexible graphite paper high-strength bipolar plate with a thickness of 0.8 mm.

[0068] Example 3

[0069] A method for preparing a flexible graphite paper high-strength bipolar plate comprises the following steps:

[0070] (1) adding expandable graphite-1 into a high-temperature expansion furnace and expanding at 950° C. until the volume does not change to obtain expanded graphite worms;

[0071] (2) adding 10 g of the expanded graphite worms obtained in step (1) and 3 g of modified polyphenylene sulfide powder-1 into a powder mixing system, introducing dry air at a flow rate of 300 m / s at 280° C. to mix the powders to obtain a mixed powder;

[0072] (3) adding the mixed powder obtained in step (2) into a material distribution device and spreading it, and then sending it into a calender to heat and pressurize it at 150° C. and 80 MPa to obtain a sheet;

[0073] (4) The sheet obtained in step (3) was placed in a hot press, hot pressed at 350° C. and 20 MPa for 9 min, cooled to 70° C., and air was introduced to demold the sheet to obtain a flexible graphite paper high-strength bipolar plate with a thickness of 0.8 mm.

[0074] Example 4

[0075] A method for preparing a high-strength bipolar plate of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that the added amount of modified polyphenylene sulfide powder-1 is 4g.

[0076] Example 5

[0077] A method for preparing a high-strength bipolar plate of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that an equal amount of modified polyphenylene sulfide powder-1 is replaced by modified polyphenylene sulfide powder-2.

[0078] Example 6

[0079] A method for preparing a high-strength bipolar plate of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that an equal amount of modified polyphenylene sulfide powder-1 is replaced by modified polyphenylene sulfide powder-3.

[0080] Example 7

[0081] A method for preparing a high-strength bipolar plate made of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that an equal amount of expandable graphite-1 is replaced by expandable graphite-2.

[0082] Example 8

[0083] A method for preparing a high-strength bipolar plate made of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that an equal amount of expandable graphite-1 is replaced by expandable graphite-3.

[0084] Comparative Example 1

[0085] A method for preparing a high-strength bipolar plate of flexible graphite paper, the specific implementation method is the same as that of Example 1, except that an equal amount of modified polyphenylene sulfide powder-1 is replaced by polyphenylene sulfide powder.

[0086] Performance Testing

[0087] The flexible graphite paper high-strength bipolar plates obtained in the above embodiments and comparative examples were tested:

[0088] (1) Mechanical properties: Tested in accordance with NB / T42007-2013;

[0089] (2) Conductivity: Tested in accordance with NB / T42007-2013;

[0090] (3) Density: A density meter is used to test the density of the flexible graphite paper high-strength bipolar plate.

[0091] The test results are shown in Table 1:

[0092] Table 1

[0093] Group Flexural strength(MPa) Compressive strength(MPa) Conductivity (S / cm) <![CDATA[Density (g / cm 3 )]]> Example 1 45.6 93.5 429.1 1.63 Example 2 44.5 91.8 426.2 1.65 Example 3 44.4 92.3 425.8 1.62 Example 4 47.2 95.2 417.2 1.83 Example 5 45.5 93.3 421.2 1.73 Example 6 40.2 85.1 423.5 1.67 Example 7 48.0 96.7 422.7 1.87 Example 8 45.7 93.5 423.8 1.72 Comparative Example 1 37.9 81.5 415.3 1.66

[0094] It can be seen from the data in Table 1 that the flexible graphite paper high-strength bipolar plates prepared in Examples 1-3 have excellent mechanical properties, electrical conductivity and low density. From the comparison between Example 4 and Example 1, it can be seen that the change in the ratio of expanded graphite worms and modified polyphenylene sulfide powder will cause the conductive properties of the flexible graphite paper high-strength bipolar plate to decrease and the density to increase; from the comparison between Example 5 and Example 1, it can be seen that the increase in the molecular weight of hyperbranched polyphenylene sulfide will cause the conductive properties of the flexible graphite paper high-strength bipolar plate to decrease and the density to increase; from the comparison between Example 6 and Example 1, it can be seen that the change in the ratio of hyperbranched polyphenylene sulfide powder and triethylamine will cause the modified polyphenylene sulfide to increase. The ether chain segments are destroyed, which reduces the mechanical properties and conductive properties of the flexible graphite paper high-strength bipolar plate; from the comparison between Example 7 and Example 1, it can be seen that after the mixed acid is replaced with nitric acid, the density of the expanded graphite is larger, which increases the density of the flexible graphite paper high-strength bipolar plate; from the comparison between Example 8 and Example 1, it can be seen that the change in the ratio of the mixed acid will make the water in the system less likely to be absorbed by acetic anhydride, resulting in a larger density of the expanded graphite worms, which increases the density of the flexible graphite paper high-strength bipolar plate; from the comparison between Comparative Example 1 and Example 1, it can be seen that the mechanical properties and conductive properties of the flexible graphite paper high-strength bipolar plate prepared by adding conventional polyphenylene sulfide ketone are poor.

[0095] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-strength bipolar plate made of flexible graphite paper, characterized in that: The following steps are involved: (1) adding expandable graphite into a high-temperature expansion furnace and expanding at 900-1000° C. until the volume does not change to obtain expanded graphite worms; (2) adding the expanded graphite worms and modified polyphenylene sulfide powder obtained in step (1) into a powder mixing system, introducing gas to mix the powders, and obtaining a mixed powder; (3) adding the mixed powder obtained in step (2) to a material distribution device for dispersion and stacking, and then sending it to a calender for heating and pressurization to obtain a sheet; (4) placing the sheet obtained in step (3) into a hot press, hot pressing at 330-350° C. and 20-40 MPa for 7-9 min, cooling to 50-70° C., and releasing the sheet by passing air to obtain a flexible graphite paper high-strength bipolar plate.

2. The method for preparing a flexible graphite paper high-strength bipolar plate according to claim 1, characterized in that: The preparation method of the expandable graphite is as follows: natural flake graphite, mixed acid, potassium permanganate and potassium dichromate are added into a reaction container, reacted at 40-60° C. for 50-70 minutes, and centrifuged, washed and dried to obtain the expandable graphite.

3. The method for preparing a flexible graphite paper high-strength bipolar plate according to claim 2, characterized in that: The mixed acid is a mixture of acetic anhydride, phosphoric acid and perchloric acid, and the mass ratio of the three is 1: (0.90-0.94): (1.2-1.4).

4. The method for preparing a flexible graphite paper high-strength bipolar plate according to claim 1, characterized in that: The mass ratio of the expanded graphite worms to the modified polyphenylene sulfide powder in step (2) is 1:(0.2-0.3).

5. The method for preparing a high-strength bipolar plate made of flexible graphite paper according to claim 1, characterized in that: The gas is high-purity nitrogen, high-purity argon or dry air.

6. The method for preparing a high-strength bipolar plate made of flexible graphite paper according to claim 1, characterized in that: The temperature of the heating and pressing is 140-160° C., and the pressure is 70-90 MPa.

7. The method for preparing a flexible graphite paper high-strength bipolar plate according to claim 1, characterized in that: The preparation method of the modified polyphenylene sulfide powder comprises the following steps: A1. Add 1,3,5-tribromobenzene, 2,4-dichlorobenzenethiol and sodium bicarbonate to N-methylpyrrolidone, heat to 170-190°C for reaction for 10-15h, cool to room temperature and pour into hydrochloric acid to obtain a precipitate, wash, filter and dry to obtain a hyperbranched polyphenylene sulfide powder; A2. Add the hyperbranched polyphenylene sulfide powder obtained in step A1, triethylamine and tetrahydrofuran into a reaction vessel, heat to 65-70° C., react for 7-9 hours, cool to room temperature, add copper sulfate methanol solution, stir for 30-40 minutes, wash, filter and dry to obtain modified polyphenylene sulfide powder.

8. The method for preparing a high-strength flexible graphite paper bipolar plate according to claim 7, characterized in that: The weight average molecular weight of the hyperbranched polyphenylene sulfide is 20,000-30,000.

9. The method for preparing a high-strength bipolar plate made of flexible graphite paper according to claim 7, characterized in that: The mass ratio of the hyperbranched polyphenylene sulfide powder to triethylamine is 1:(0.1-0.2).

10. Application of the high-strength flexible graphite paper bipolar plate obtained by the method for preparing the high-strength flexible graphite paper bipolar plate according to any one of claims 1 to 9 in the field of liquid flow batteries.