Flexible graphite bipolar plate, method of making same, and flow battery

Abstract

The application belongs to the technical field of liquid flow batteries, and discloses a flexible graphite bipolar plate, a preparation method thereof and a liquid flow battery. The flexible graphite bipolar plate comprises a flexible graphite bipolar plate base body and a conductive resin, the conductive resin is filled in the pores of the flexible graphite bipolar plate base body, and the conductive resin is prepared through a preparation method comprising the following steps: S1, adding 3,4-ethylenedioxythiophene and resin into water, stirring to obtain a 3,4-ethylenedioxythiophene-resin mixed solution; S2, adding an oxidizing agent into the 3,4-ethylenedioxythiophene-resin mixed solution, stirring, and obtaining a reaction product after reaction; and S3, filtering, cleaning and drying the reaction product to obtain the conductive resin. The flexible graphite bipolar plate has good in-plane electrical conductivity and contact resistance, and is beneficial to improving the energy conversion efficiency of the liquid flow battery.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, and specifically relates to a flexible graphite bipolar plate, its preparation method, and a flow battery. Background Technology

[0002] As the global energy structure shifts towards renewable energy, the large-scale integration of intermittent power sources such as wind and solar power places higher demands on energy storage technologies. Traditional batteries have limitations in cost, safety, and lifespan in large-scale energy storage scenarios, making it difficult to meet the demands. Flow batteries, with their advantages of independent power and capacity design, high safety, and long cycle life, are gradually becoming a core technology in the energy storage field through continuous optimization of material systems, cost reduction, and improved system integration.

[0003] Flexible graphite bipolar plates possess excellent flexibility, high-temperature resistance, and corrosion resistance, making them highly promising for applications in flow batteries and other fields. Currently, non-conductive resins are commonly used as micropore fillers in the fabrication of flexible graphite bipolar plates to effectively improve the overall strength and sealing of the material. However, since the resin itself is not conductive, when it fills the micropores of the flexible graphite bipolar plate, it forms a barrier in the conductive pathways of the graphite, leading to a decrease in the conductivity of the flexible graphite bipolar plate and significantly limiting its application in flow batteries.

[0004] Therefore, improving the conductivity of flexible graphite bipolar plates is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention provides a flexible graphite bipolar plate, a method for preparing the same, and a flow battery. This flexible graphite bipolar plate has good in-plane conductivity and contact resistance, which is beneficial for improving the energy conversion efficiency of the flow battery.

[0006] In a first aspect, the present invention provides a flexible graphite bipolar plate, comprising a flexible graphite bipolar plate substrate and a conductive resin, wherein the conductive resin fills the pores of the flexible graphite bipolar plate substrate, and the conductive resin is prepared by a method comprising the following steps:

[0007] S1. Add 3,4-ethylenedioxythiophene and resin to water and stir to obtain a 3,4-ethylenedioxythiophene-resin mixed solution.

[0008] S2. Add the oxidant to the 3,4-ethylenedioxythiophene-resin mixed solution, stir, and the reaction product is obtained after the reaction.

[0009] S3. The reaction product is filtered, washed, and dried to obtain the conductive resin.

[0010] Preferably, in step S1, the mass ratio of 3,4-ethylenedioxythiophene to the resin is 1:(5-20), and the stirring time is 2-8 hours.

[0011] More preferably, in step S1, the mass ratio of the 3,4-ethylenedioxythiophene to the resin is 1:(8-15).

[0012] More preferably, in step S1, the stirring time is 3-6 hours.

[0013] Preferably, the resin includes at least one of polyvinylidene fluoride, epoxy resin, and phenolic resin.

[0014] Preferably, in step S2, the mass ratio of the oxidant to the 3,4-ethylenedioxythiophene is 1:(1-3), and the stirring time is 12-36 h.

[0015] Preferably, the oxidant includes one of ferric chloride, ammonium persulfate, and ferric p-toluenesulfonate.

[0016] Preferably, in step S3, the filtration uses a dialysis bag to retain the solution inside the dialysis bag, which is used to filter out unreacted substances (monomers and oxidants). The unreacted substances will diffuse outside the dialysis bag.

[0017] Preferably, in step S3, the cleaning is performed using a water-alcohol mixture solution, which is a mixture of water and alcohol in a mass ratio of 1:(2-4).

[0018] Preferably, the alcohol includes at least one of methanol, ethanol, and isopropanol.

[0019] In a second aspect, the present invention provides a method for preparing the flexible graphite bipolar plate described in the first aspect, comprising the following steps:

[0020] The flexible graphite bipolar plate is obtained by filling the pores of the flexible graphite bipolar plate matrix with conductive resin through vacuum impregnation, followed by curing and drying.

[0021] Preferably, the vacuum impregnation method specifically includes the following steps:

[0022] The flexible graphite bipolar plate substrate, which is normally pressurized, is placed in a sealed cavity. The air inside the pores is removed by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, the pressure is slowly released to normal pressure.

[0023] Preferably, prior to curing, the impregnated flexible graphite bipolar plate substrate is rinsed with a cleaning agent. Rinsing removes excess resin.

[0024] Preferably, the cleaning agent comprises one of water, perfluoroisobutyl methyl ether, or methoxynonfluorobutane.

[0025] Preferably, the curing temperature is 50-95℃ and the curing time is 60-180 min.

[0026] Preferably, the curing is water bath curing.

[0027] Preferably, after the conductive resin is filled, cured, and dried by vacuum impregnation, the resin loading ratio in the flexible graphite bipolar plate is 20-45 wt%.

[0028] Preferably, the drying temperature in this invention is 40-80℃, and the drying time is 12-36h.

[0029] In a third aspect, the present invention provides a flow battery, the flow battery comprising the flexible graphite bipolar plate described in the first aspect of the present invention.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention utilizes the conjugated polymer poly(3,4-ethylenedioxythiophene) whose conjugated main chain allows free electrons to be transported relatively easily through π orbitals, to achieve in-situ polymerization of poly(3,4-ethylenedioxythiophene) in resin used to fill the micropores of flexible graphite bipolar plate matrix, thereby obtaining a conductive resin.

[0032] (2) By using conductive resin to impregnate the flexible graphite bipolar plate substrate, the present invention can not only achieve the micropore sealing effect, but also avoid the reduction of the conductivity of the graphite bipolar plate by traditional resin. The prepared flexible graphite bipolar plate has good in-plane conductivity and contact resistance, which is beneficial to improving the energy conversion efficiency of flow battery. Detailed Implementation

[0033] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0034] Example 1

[0035] A flexible graphite bipolar plate includes a flexible graphite bipolar plate substrate and a conductive resin, wherein the conductive resin fills the pores of the flexible graphite bipolar plate substrate.

[0036] The above-mentioned method for preparing flexible graphite bipolar plates includes the following steps:

[0037] S1. Add 3,4-ethylenedioxythiophene and phenolic resin in a mass ratio of 1:15 to water and stir for 3 hours to obtain a 3,4-ethylenedioxythiophene-resin mixed solution.

[0038] S2. Ferric chloride oxidant was added to a mixed solution of 3,4-ethylenedioxythiophene and resin, and the mixture was stirred and dispersed for 24 hours. The reaction product was obtained after the reaction. The mass ratio of oxidant to 3,4-ethylenedioxythiophene was 1:2.

[0039] S3. Filter the reaction product using a dialysis bag, retain the solution in the dialysis bag, wash it multiple times with a water-methanol mixture with a mass ratio of 1:3, and dry it at 50°C for 24 hours to obtain the conductive resin.

[0040] S4. The flexible graphite bipolar plate substrate, which is normally press-formed, is placed in a sealed cavity. The air inside the pores is removed by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, the pressure is slowly released to normal pressure. Then, the impregnated flexible graphite bipolar plate substrate is rinsed with water, cured in a 90°C water bath for 90 minutes, and dried at 80°C for 12 hours to obtain the flexible graphite bipolar plate. The resin loading ratio in the flexible graphite bipolar plate is 20wt%.

[0041] Example 2

[0042] A flexible graphite bipolar plate includes a flexible graphite bipolar plate substrate and a conductive resin, wherein the conductive resin fills the pores of the flexible graphite bipolar plate substrate.

[0043] The above-mentioned method for preparing flexible graphite bipolar plates includes the following steps:

[0044] S1. Add 3,4-ethylenedioxythiophene and epoxy resin in a mass ratio of 1:12 to water and stir for 6 hours to obtain a 3,4-ethylenedioxythiophene-resin mixed solution.

[0045] S2. Add ammonium persulfate oxidant to a 3,4-ethylenedioxythiophene-resin mixed solution and stir continuously for 30 hours to disperse. The reaction product is obtained after the reaction. The mass ratio of oxidant to 3,4-ethylenedioxythiophene is 1:1.

[0046] S3. Filter the reaction product using a dialysis bag, retain the solution in the dialysis bag, wash it multiple times with a water-ethanol mixture with a mass ratio of 1:2, and dry it at 55°C for 18 hours to obtain the conductive resin.

[0047] S4. The flexible graphite bipolar plate substrate, which is normally press-formed, is placed in a sealed cavity. The air inside the pores is removed by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, the pressure is slowly released to normal pressure. Then, the impregnated flexible graphite bipolar plate substrate is rinsed with water, cured in a 90°C water bath for 90 minutes, and dried at 80°C for 12 hours to obtain the flexible graphite bipolar plate. The resin loading ratio in the flexible graphite bipolar plate is 35wt%.

[0048] Example 3

[0049] A flexible graphite bipolar plate includes a flexible graphite bipolar plate substrate and a conductive resin, wherein the conductive resin fills the pores of the flexible graphite bipolar plate substrate.

[0050] The above-mentioned method for preparing flexible graphite bipolar plates includes the following steps:

[0051] S1. Add 3,4-ethylenedioxythiophene and polyvinylidene fluoride in a mass ratio of 1:8 to water and stir for 6 hours to obtain a 3,4-ethylenedioxythiophene-resin mixed solution.

[0052] S2. Add the ferric p-toluenesulfonate oxidant to the 3,4-ethylenedioxythiophene-resin mixed solution and stir continuously for 15 hours to disperse. The reaction product is obtained after the reaction. The mass ratio of oxidant to 3,4-ethylenedioxythiophene is 1:3.

[0053] S3. Filter the reaction product using a dialysis bag, retain the solution in the dialysis bag, wash it multiple times with a water-isopropanol mixed solution with a mass ratio of 1:4, and dry it at 60°C for 20 hours to obtain the conductive resin.

[0054] S4. The flexible graphite bipolar plate substrate, which is normally press-formed, is placed in a sealed cavity. The air inside the pores is removed by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, the pressure is slowly released to normal pressure. Then, the impregnated flexible graphite bipolar plate substrate is rinsed with water, cured in a 90°C water bath for 90 minutes, and dried at 80°C for 12 hours to obtain the flexible graphite bipolar plate. The resin loading ratio in the flexible graphite bipolar plate is 45wt%.

[0055] Comparative Example 1 (the only difference from Example 2 is that the conductive resin is replaced with conventional epoxy resin)

[0056] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0057] A flexible graphite bipolar plate substrate, which is normally press-formed, is placed in a sealed cavity. The air inside the pores is removed by vacuuming. Under negative pressure, epoxy resin fully penetrates into the pores of the flexible graphite bipolar plate substrate. Finally, the pressure is slowly released to normal pressure. The substrate is then rinsed with water, cured in a 90°C water bath for 90 minutes, and dried at 80°C for 12 hours to obtain the flexible graphite bipolar plate.

[0058] The epoxy resin used in Comparative Example 1 is the same as the epoxy resin used in Example 2.

[0059] Comparative Example 2 (the only difference from Example 2 is that it was not polymerized in situ in the resin)

[0060] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0061] S1. Add 3,4-ethylenedioxythiophene to water and stir for 6 hours to obtain a 3,4-ethylenedioxythiophene solution.

[0062] S2. Add ammonium persulfate oxidant to 3,4-ethylenedioxythiophene solution and stir continuously for 30 hours to disperse. After the reaction, the reaction product is obtained. The mass ratio of oxidant to 3,4-ethylenedioxythiophene is 1:1.

[0063] S3. Filter the reaction product using a dialysis bag, retain the solution in the dialysis bag, wash it multiple times with a water-ethanol mixture with a mass ratio of 1:2, dry it at 55°C for 18 hours, and then mix it with epoxy resin to obtain a conductive resin; wherein the mass ratio of 3,4-ethylenedioxythiophene to epoxy resin is 1:12.

[0064] S4. Place the conventionally sized flexible graphite bipolar plate substrate in a sealed cavity. Remove the air from the pores by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, slowly depressurize to normal pressure. Then, rinse the impregnated flexible graphite bipolar plate substrate with water, cure it in a 90°C water bath for 90 minutes, and dry it at 80°C for 12 hours to obtain the flexible graphite bipolar plate.

[0065] Comparative Example 3 (the only difference from Example 2 is that 3,4-ethylenedioxythiophene is replaced with pyrrole)

[0066] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0067] S1. Add pyrrole and epoxy resin in a mass ratio of 1:12 to water and stir for 6 hours to obtain a 3,4-ethylenedioxythiophene-resin mixed solution.

[0068] S2. Add ammonium persulfate oxidant to a 3,4-ethylenedioxythiophene-resin mixed solution and stir continuously for 30 hours to disperse. The reaction product is obtained after the reaction. The mass ratio of oxidant to 3,4-ethylenedioxythiophene is 1:1.

[0069] S3. Filter the reaction product using a dialysis bag, retain the solution in the dialysis bag, wash it multiple times with a water-ethanol mixture with a mass ratio of 1:2, and dry it at 55°C for 18 hours to obtain the conductive resin.

[0070] S4. Place the conventionally sized flexible graphite bipolar plate substrate in a sealed cavity. Remove the air from the pores by vacuuming. Under negative pressure, the conductive resin will fully penetrate into the pores of the flexible graphite bipolar plate substrate. Finally, slowly depressurize to normal pressure. Then, rinse the impregnated flexible graphite bipolar plate substrate with water, cure it in a 90°C water bath for 90 minutes, and dry it at 80°C for 12 hours to obtain the flexible graphite bipolar plate.

[0071] Performance testing

[0072] 1. Conductivity test

[0073] The in-plane conductivity of the flexible graphite bipolar plates prepared in each embodiment and comparative example was tested using a four-probe resistance meter.

[0074] 2. Air tightness

[0075] The air tightness of the flexible graphite bipolar plates prepared in each embodiment and comparative example was tested using a flow meter method air tightness tester.

[0076] 3. Bending strength

[0077] The bending strength of the flexible graphite bipolar plates prepared in each embodiment and comparative example was tested by a three-point bending test using a mechanical testing machine.

[0078] 4. Contact resistance

[0079] The contact resistance of the flexible graphite bipolar plates prepared in each embodiment and comparative example at 1.5 MPa was tested using a contact resistance tester.

[0080] The performance test results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As shown in Table 1, Examples 1-3 and Comparative Examples 1-3 all exhibit good airtightness and bending strength. Among them, the flexible graphite bipolar plates in Examples 1-3 with conductive resin have an in-plane conductivity of 507-525 S / cm and a contact resistance (1.5 MPa) of 2.34-2.44 mΩ·cm.2 Compared to Comparative Example 1, it exhibits superior conductivity. However, the conductive polymer (poly3,4-ethylenedioxythiophene) in Comparative Example 2 is not synthesized in situ with high dispersion in the resin, which is still not conducive to the construction of the conductive network. As a result, the in-plane conductivity and contact resistance of the flexible graphite bipolar plate prepared in Comparative Example 3 are not significantly improved due to the use of other conductive polymers. The conductivity and contact resistance of the flexible graphite bipolar plate prepared in Comparative Example 3 are also not as good as those of the present invention, and the improvement in in-plane conductivity and contact resistance is also limited.

[0084] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A flexible graphite bipolar plate, characterized in that, The flexible graphite bipolar plate includes a flexible graphite bipolar plate substrate and a conductive resin. The conductive resin fills the pores of the flexible graphite bipolar plate substrate and is prepared by a method including the following steps: S1. Add 3,4-ethylenedioxythiophene and resin to water and stir to obtain a 3,4-ethylenedioxythiophene-resin mixed solution. S2. Add the oxidant to the 3,4-ethylenedioxythiophene-resin mixed solution, stir, and the reaction product is obtained after the reaction. S3. The reaction product is filtered, washed, and dried to obtain the conductive resin.

2. The flexible graphite bipolar plate according to claim 1, characterized in that, In step S1, the mass ratio of 3,4-ethylenedioxythiophene to the resin is 1:(5-20), and the stirring time is 2-8 hours.

3. The flexible graphite bipolar plate according to claim 1, characterized in that, The resin includes at least one of polyvinylidene fluoride, epoxy resin, and phenolic resin.

4. The flexible graphite bipolar plate according to claim 1, characterized in that, In step S2, the mass ratio of the oxidant to the 3,4-ethylenedioxythiophene is 1:(1-3), and the stirring time is 12-36h.

5. The flexible graphite bipolar plate according to claim 1, characterized in that, The oxidant includes one of ferric chloride, ammonium persulfate, and ferric p-toluenesulfonate.

6. The flexible graphite bipolar plate according to claim 1, characterized in that, In step S3, the cleaning is performed using a water-alcohol mixture solution, which is composed of water and alcohol mixed in a mass ratio of 1:(2-4).

7. The flexible graphite bipolar plate according to claim 6, characterized in that, The alcohol includes at least one of methanol, ethanol, and isopropanol.

8. The method for preparing the flexible graphite bipolar plate according to any one of claims 1-7, characterized in that, Includes the following steps: The flexible graphite bipolar plate is obtained by filling the pores of the flexible graphite bipolar plate matrix with conductive resin through vacuum impregnation, followed by curing and drying.

9. The preparation method according to claim 8, characterized in that, The curing temperature is 50-95℃, and the curing time is 60-180 min.

10. A flow battery, characterized in that, The flow battery includes the flexible graphite bipolar plate as described in any one of claims 1-7.

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