High-surface-conductivity flexible graphite bipolar plate, preparation method and application thereof

Abstract

This invention relates to the field of flow battery technology, specifically disclosing a flexible graphite bipolar plate with high surface conductivity, its preparation method, and its application. The preparation method includes the following steps: (1) chemically and thermally treating flake graphite to obtain expanded graphite sheets; (2) spraying a PEDOT:PSS solution onto the first layer of expanded graphite sheets, then laying a second layer of expanded graphite sheets, and pre-pressing to obtain an EG-PEDOT:PSS composite material; (3) impregnating the EG-PEDOT:PSS composite material with an epoxy resin solution, and performing water bath curing and drying treatment to obtain a PEDOT:PSS-EG-EP composite material; (4) using a hot-pressing molding process to obtain a flexible graphite bipolar plate with high surface conductivity. This invention improves the overall conductivity of the graphite bipolar plate and enhances the energy storage efficiency of flow batteries.

Description

Technical Field

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

[0002] The global energy system is accelerating its transformation towards green, low-carbon, and intelligent technologies. Flow batteries, as a representative of new long-term energy storage technologies, are playing an increasingly important role in ensuring stable grid operation and promoting the integration of renewable energy, thanks to their advantages such as high safety, long lifespan, and scalability. Especially with the large-scale integration of wind and solar power, flow batteries effectively alleviate the temporal and spatial mismatch between energy output and electricity demand through peak shaving, valley filling, frequency regulation, and voltage regulation, and have become one of the key supporting technologies for building new power systems.

[0003] As a crucial component in flow batteries, the bipolar plate serves as both a current collector and an electrolyte separator, and its conductivity directly impacts the battery's energy conversion efficiency and overall system performance. However, traditional flexible graphite bipolar plates often employ resin impregnation during manufacturing to enhance structural density and corrosion resistance. But because resin itself is an electrically insulating material, it easily forms localized enrichment layers on the surface or interface of the bipolar plate during high-temperature molding and curing, obstructing the conductive path and significantly increasing surface contact resistance. This phenomenon not only limits the battery's power output but can also lead to stability issues such as localized overheating, becoming a key technological bottleneck restricting the performance improvement and large-scale application of flow batteries.

[0004] Therefore, it is necessary to provide a flexible graphite bipolar plate with high surface conductivity, its preparation method, and its application, so as to improve the overall conductivity of the graphite bipolar plate, reduce the amount of non-conductive resin, improve the energy storage efficiency of flow batteries, and at the same time, fill the micropores to a certain extent, ensure the reliable mechanical strength and airtightness of the bipolar plate, and facilitate the stable operation of the bipolar plate under extreme mechanical conditions. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a flexible graphite bipolar plate with high surface conductivity, a preparation method and application, which improves the overall conductivity of the graphite bipolar plate, reduces the amount of non-conductive resin, improves the energy storage efficiency of flow batteries, and at the same time plays a certain role in filling micropores, ensuring the reliable mechanical strength and airtightness of the bipolar plate, which is conducive to the stable operation of the bipolar plate under extreme mechanical conditions.

[0006] A first aspect of the present invention provides a flexible graphite bipolar plate with high surface conductivity.

[0007] Specifically, a method for preparing a flexible graphite bipolar plate with high surface conductivity includes the following steps:

[0008] (1) Chemical and heat treatment of flake graphite to obtain expanded graphite sheets;

[0009] (2) Spray PEDOT:PSS solution onto the first layer of expanded graphite sheet, then lay the second layer of expanded graphite sheet, and pre-press it in a mold to obtain EG-PEDOT:PSS composite material.

[0010] (3) The epoxy resin solution containing SiO2 is impregnated into the internal micropores of the EG-PEDOT:PSS composite material by vacuum impregnation, and then the impregnated material is rinsed with a cleaning agent, and then cured and dried in a water bath to obtain the PEDOT:PSS-EG-EP composite material.

[0011] (4) A flexible graphite bipolar plate with high surface conductivity was prepared by hot pressing of PEDOT:PSS-EG-EP composite material.

[0012] Preferably, in step (1), the purity of the flake graphite is 95-99.5%.

[0013] More preferably, in step (1), the purity of the flake graphite is 97-99.5%.

[0014] More preferably, in step (1), the purity of the flake graphite is 98-99.5%.

[0015] Preferably, in step (1), the reagents for the chemical treatment include at least one of nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, hydrofluoric acid, hydrogen peroxide, and potassium permanganate.

[0016] Preferably, in step (1), the temperature of the chemical treatment is 30-90°C and the time is 1-3 hours.

[0017] More preferably, in step (1), the temperature of the chemical treatment is 50-90°C and the time is 1.2-3 hours.

[0018] More preferably, in step (1), the temperature of the chemical treatment is 50-80°C and the time is 1.5-3 hours.

[0019] Preferably, in step (1), the temperature of the heat treatment is 500 to 800°C.

[0020] More preferably, in step (1), the temperature of the heat treatment is 700-800°C.

[0021] More preferably, in step (1), the temperature of the heat treatment is 750-800°C.

[0022] Preferably, in step (2), the thickness ratio of the first layer of expanded graphite sheet to the second layer of expanded graphite sheet is 1:1 to 5.

[0023] More preferably, in step (2), the thickness ratio of the first layer of expanded graphite sheet to the second layer of expanded graphite sheet is 1:1 to 1.5.

[0024] More preferably, in step (2), the thickness ratio of the first layer of expanded graphite sheet to the second layer of expanded graphite sheet is 1:1.

[0025] Preferably, in step (2), the spraying amount of the PEDOT:PSS solution is 15-25 mg / cm³. 2 .

[0026] Preferably, in step (2), the thickness of the EG-PEDOT:PSS composite material is 1.2–1.8 mm, and the average density is 0.2–0.7 g / cm³. 3 .

[0027] More preferably, in step (2), the thickness of the EG-PEDOT:PSS composite material is 1.4–1.8 mm, and the average density is 0.3–0.6 g / cm³. 3 .

[0028] More preferably, in step (2), the thickness of the EG-PEDOT:PSS composite material is 1.44–1.75 mm, and the average density is 0.4–0.5 g / cm³. 3 .

[0029] Preferably, in step (3), the water bath curing temperature is 50-95°C and the time is 60-180 min.

[0030] More preferably, in step (3), the water bath curing temperature is 70-85°C and the time is 60-150 min.

[0031] More preferably, in step (3), the water bath curing temperature is 70-80°C and the time is 70-150 min.

[0032] Preferably, in step (4), the temperature of the hot pressing process is 110-150°C, the time is 5-10 min, and the pressure is 15-30 MPa.

[0033] More preferably, in step (4), the temperature of the hot pressing process is 120-140°C, the time is 5-8 min, and the pressure is 18-30 MPa.

[0034] More preferably, in step (4), the temperature of the hot pressing process is 120-130°C, the time is 5-7 min, and the pressure is 18-25 MPa.

[0035] A second aspect of the present invention provides a flexible graphite bipolar plate with high surface conductivity.

[0036] Specifically, the flexible graphite bipolar plate with high surface conductivity is prepared by the preparation method provided in the first aspect.

[0037] A third aspect of the present invention provides the application of a flexible graphite bipolar plate with high surface conductivity in a flow battery.

[0038] Specifically, the flow battery includes a flexible graphite bipolar plate with high surface conductivity.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The present invention improves the overall conductivity of graphite bipolar plates by enriching the thermoplastic conductive polymer PEDOT:PSS on the surface of flexible graphite and reduces the amount of non-conductive resin, thereby improving the energy storage efficiency of flow batteries.

[0041] (2) The present invention fills the interior of the flexible graphite bipolar plate with thermosetting epoxy resin, which fills the micropores and ensures the reliable mechanical strength and airtightness of the bipolar plate, which is beneficial to the stable operation of the bipolar plate under extreme mechanical conditions. Detailed Implementation

[0042] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0043] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0044] Example 1

[0045] A method for preparing a flexible graphite bipolar plate with high surface conductivity includes the following steps:

[0046] (1) Mix 98% pure flake graphite with a mixed acid consisting of sulfuric acid / nitric acid (3:1), chemically treat at 70°C for 2 hours, wash with pure water until neutral, and heat treat at 750°C to obtain expanded graphite sheets.

[0047] (2) A PEDOT:PSS solution was sprayed onto a first layer of expanded graphite sheet with a thickness of 1 mm, and then a second layer of expanded graphite sheet with a thickness of 1 mm was laid on top. The mixture was then pre-pressed in a mold at a pressure of 10 MPa to obtain an EG-PEDOT:PSS composite material with a total thickness of 1.6 mm and a density of 0.45 g / cm³. 3 ;

[0048] (3) The epoxy resin solution with 40% solid content containing SiO2 release agent was vacuum impregnated into the internal micropores of EG-PEDOT:PSS composite material. Then the impregnated material was rinsed with cleaning agent, cured in water bath at 70°C for 120 min and dried to obtain PEDOT:PSS-EG-EP composite material.

[0049] (4) PEDOT:PSS-EG-EP composite material was hot-pressed at 130°C for 6 minutes at a pressure of 18MPa to obtain a flexible graphite bipolar plate with high surface conductivity.

[0050] Example 2

[0051] A method for preparing a flexible graphite bipolar plate with high surface conductivity includes the following steps:

[0052] (1) Mix 98% pure flake graphite with sulfuric acid, chemically treat at 50°C for 1.5 h, wash with pure water until neutral, and heat treat at 750°C to obtain expanded graphite sheets.

[0053] (2) A PEDOT:PSS solution was sprayed onto a first layer of expanded graphite sheet with a thickness of 0.9 mm, and then a second layer of expanded graphite sheet with a thickness of 0.9 mm was laid on top. The mixture was then pre-pressed in a mold at a pressure of 10 MPa to obtain an EG-PEDOT:PSS composite material with a total thickness of 1.44 mm and a density of 0.5 g / cm³. 3 ;

[0054] (3) The epoxy resin solution with 40% solid content containing SiO2 release agent was vacuum impregnated into the internal micropores of EG-PEDOT:PSS composite material. Then the impregnated material was rinsed with cleaning agent, cured in water bath at 75°C for 150 min and dried to obtain PEDOT:PSS-EG-EP composite material.

[0055] (4) PEDOT:PSS-EG-EP composite material was hot-pressed at 120°C for 7 minutes at a pressure of 20MPa to obtain a flexible graphite bipolar plate with high surface conductivity.

[0056] Example 3

[0057] A method for preparing a flexible graphite bipolar plate with high surface conductivity includes the following steps:

[0058] (1) Mix 99.5% pure flake graphite with sulfuric acid, chemically treat at 80°C for 3 hours, wash with pure water until neutral, and heat treat at 800°C to obtain expanded graphite sheets.

[0059] (2) A PEDOT:PSS solution was sprayed onto a first layer of expanded graphite sheet with a thickness of 1.1 mm, and then a second layer of expanded graphite sheet with a thickness of 1.1 mm was laid on top. The mixture was then pre-pressed in a mold at a pressure of 12 MPa to obtain an EG-PEDOT:PSS composite material with a total thickness of 1.75 mm and a density of 0.4 g / cm³. 3 ;

[0060] (3) The epoxy resin solution with 40% solid content containing SiO2 is impregnated into the internal micropores of the EG-PEDOT:PSS composite material by vacuum impregnation, and then the impregnated material is rinsed with a cleaning agent, cured in a water bath at 80°C for 150 min and dried to obtain the PEDOT:PSS-EG-EP composite material.

[0061] (4) PEDOT:PSS-EG-EP composite material was hot-pressed at 120°C for 5 minutes at a pressure of 25MPa to obtain a flexible graphite bipolar plate with high surface conductivity.

[0062] Comparative Example 1

[0063] A method for preparing a bipolar plate includes the following steps:

[0064] (1) Use flake graphite with a purity of 99.5% to mix with sulfuric acid, chemically treat at 70°C for 2 hours, wash with pure water until neutral, and heat treat at 750°C to obtain expanded graphite sheets.

[0065] (2) Expanded graphite sheets are pre-pressed in a mold at a pressure of 25 MPa to obtain a pre-fabricated flexible graphite plate with a thickness of 0.6 mm and an average density of 0.7 g / cm³. 3 ;

[0066] (3) The epoxy resin solution is impregnated into the micropores of the flexible graphite plate semi-finished product through vacuum. Then the impregnated graphite plate is rinsed with a cleaning agent, cured in a water bath at 70°C for 100 minutes, and then dried to obtain the bipolar plate.

[0067] Performance testing:

[0068] 1. Vertical conductivity test

[0069] The contact resistance of the bipolar plates prepared in each embodiment and comparative example was tested using a bipolar plate contact resistance meter at a pressure of 2 MPa.

[0070] 2. Horizontal conductivity test

[0071] The in-plane conductivity of the bipolar plates prepared in each embodiment and comparative example was tested using a four-probe resistance meter.

[0072] 3. Bending strength

[0073] The bending strength of the bipolar plates prepared in each embodiment and comparative example was tested by a mechanical testing machine through a three-point bending test.

[0074] Table 1. Performance test results of bipolar plates in each embodiment and comparative example.

[0075] Group <![CDATA[Contact resistance (mΩ·cm 2 )]]> In-plane conductivity (S / cm) Flexural strength (MPa) Example 1 4.3 464.2 48.8 Example 2 3.1 466.7 48.2 Example 3 5.8 481.1 46.7 Comparative Example 1 9.7 389.4 44.5

[0076] As shown in Table 1, Examples 1-3 and Comparative Example 1 all exhibit good flexural strength, indicating that the thermosetting epoxy resin filling the flexible graphite bipolar plate effectively fills the micropores, ensuring reliable airtightness and mechanical strength, which is beneficial for the stable operation of the bipolar plate under extreme mechanical conditions. Meanwhile, the contact resistance of Examples 1-3 ranges from 3.1 to 5.8 mΩ·cm. 2 With an in-plane conductivity of 464.2–481.1 S / cm, it exhibits excellent conductivity, thereby improving the energy storage efficiency of flow batteries.

[0077] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, any technical solutions obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concept of the present invention and on the existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a flexible graphite bipolar plate with high surface conductivity, characterized in that, Includes the following steps: (1) Chemical and heat treatment of flake graphite to obtain expanded graphite sheets; (2) Spray PEDOT:PSS solution onto the first layer of expanded graphite sheet, then lay the second layer of expanded graphite sheet, and pre-press it in a mold to obtain EG-PEDOT:PSS composite material. (3) The epoxy resin solution containing SiO2 is impregnated into the internal micropores of the EG-PEDOT:PSS composite material by vacuum impregnation, and then the impregnated material is rinsed with a cleaning agent, and then cured and dried in a water bath to obtain the PEDOT:PSS-EG-EP composite material. (4) A flexible graphite bipolar plate with high surface conductivity was prepared by hot pressing of PEDOT:PSS-EG-EP composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the purity of the flake graphite is 95-99.5%.

3. The preparation method according to claim 1, characterized in that, In step (1), the reagents for the chemical treatment include at least one of nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, hydrofluoric acid, hydrogen peroxide, and potassium permanganate.

4. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the chemical treatment is 30-90°C and the time is 1-3 hours.

5. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the heat treatment is 500 to 800°C.

6. The preparation method according to claim 1, characterized in that, In step (2), the thickness ratio of the first layer of expanded graphite sheet to the second layer of expanded graphite sheet is 1:1 to 5.

7. The preparation method according to claim 1, characterized in that, In step (3), the water bath curing temperature is 50-95℃ and the time is 60-180min.

8. The preparation method according to claim 1, characterized in that, In step (4), the temperature of the hot pressing process is 110-150℃, the time is 5-10 min, and the pressure is 15-30 MPa.

9. A flexible graphite bipolar plate with high surface conductivity, characterized in that, The highly surface conductive flexible graphite bipolar plate is prepared by any one of claims 1 to 8.

10. The application of the highly surface conductive flexible graphite bipolar plate of claim 9 in a flow battery, characterized in that, The flow battery includes a flexible graphite bipolar plate with high surface conductivity.