An ultrathin high-strength flexible graphite bipolar plate and a preparation method thereof

Abstract

The application relates to an ultrathin high-strength flexible graphite bipolar plate and a preparation method thereof, and comprises the following steps: S1, a flexible graphite blank plate is molded to obtain a flexible graphite bipolar plate P1; S2, the flexible graphite bipolar plate P1 is placed in a vacuum environment, an impregnation solvent is added, and standing is carried out to obtain a flexible graphite bipolar plate P2; S3, the flexible graphite bipolar plate P2 is immersed in the impregnation solvent, and ultrasonic treatment is carried out to obtain a flexible graphite bipolar plate P3; S4, the flexible graphite bipolar plate P3 is heated and evaporated to obtain a flexible graphite bipolar plate P4; S5, the flexible graphite bipolar plate P4 is placed in a vacuum environment, a resin solution is added, and standing is carried out to obtain a flexible graphite bipolar plate P5; and S6, the flexible graphite bipolar plate P5 is cleaned, solidified and dried to obtain an ultrathin high-strength flexible graphite bipolar plate. Compared with the prior art, the application avoids cracks and other defects caused by the use of huge molding pressure by combining the mode of molding and solvent evaporation shrinkage.

Description

Technical Field

[0001] This invention relates to the field of batteries, and in particular to an ultrathin, high-strength, flexible graphite bipolar plate and its preparation method. Background Technology

[0002] Bipolar plates are a crucial component of fuel cells, consisting of plates and a flow field. Their main functions are gas distribution, current collection, heat conduction, and sealing. Based on the matrix material, bipolar plates can be mainly classified into metallic bipolar plates, graphite bipolar plates, and composite graphite bipolar plates. Among these, graphite bipolar plates are highly favored by researchers due to their low raw material cost, corrosion resistance, and low density.

[0003] With the trend towards lighter fuel cells, higher demands are being placed on the production of bipolar plates. Although current technologies have reduced the thickness of composite graphite bipolar plates to below 1 mm, the manufacturing process is complex and industrial production is challenging. Directly processing flake graphite using rolling and molding techniques to produce ultra-thin flexible graphite bipolar plates requires pressures as high as 100-250 MPa, thus demanding high-quality rolling and molding equipment and increasing equipment costs. Furthermore, the immense pressure increases the risk of cracking in high-density graphite plates, leading to a higher defect rate.

[0004] Patent CN109950569A discloses a molding method for preparing bipolar plates for fuel cells. This patent describes a flexible graphite bipolar plate prepared by first molding flake graphite powder and then impregnating it with vacuum resin. The thinnest possible thickness is 0.5 mm. However, the molding pressure is 50-250 MPa, which is extremely high. This process inevitably requires high-quality molding equipment, increasing costs. Furthermore, the immense pressure subjected to this material makes it prone to surface and internal cracks, reducing its mechanical properties.

[0005] Patent CN113013432A discloses a method for preparing graphite bipolar plates. This method involves first rolling a flexible graphite preform, then vacuum impregnating it with resin, and finally high-temperature molding and curing to obtain a graphite bipolar plate with a thickness of 0.5-2 mm. However, in this method, the resin impregnation followed by molding and curing results in resin overflowing onto the surface of the bipolar plate, which is difficult to remove and significantly affects the conductivity of the bipolar plate. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems mentioned above regarding the ultra-thinness, high compression pressure, easy generation of micro-cracks and defects, and low mechanical strength of graphite bipolar plates under conventional processing conditions, and to provide an ultra-thin, high-strength, flexible graphite bipolar plate and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide a method for preparing an ultrathin, high-strength, flexible graphite bipolar plate, comprising the following steps:

[0009] S1. A flexible graphite blank is molded to obtain a flexible graphite bipolar plate P1.

[0010] S2. Place the flexible graphite bipolar plate P1 from step S1 in a vacuum environment, add an impregnation solvent, and let it stand to obtain the flexible graphite bipolar plate P2.

[0011] S3. Immerse the flexible graphite bipolar plate P2 obtained in step S2 in the impregnation solvent of step S2, and sonicate it to obtain the flexible graphite bipolar plate P3.

[0012] S4. The flexible graphite bipolar plate P3 obtained in step S3 is heated and evaporated to obtain the flexible graphite bipolar plate P4.

[0013] S5. Place the flexible graphite bipolar plate P4 obtained in step S4 in a vacuum environment, add resin solution, and let it stand to obtain the flexible graphite bipolar plate P5.

[0014] S6. The flexible graphite bipolar plate P5 obtained in step S5 is sequentially cleaned, cured, and dried to obtain an ultrathin, high-strength flexible graphite bipolar plate.

[0015] Furthermore, in step S1, the molding pressure is 10–50 MPa, and the molding time is 5–30 min.

[0016] Furthermore, in step S1, the thickness of the flexible graphite bipolar plate P1 is 0.1 to 0.4 times the thickness of the flexible graphite blank.

[0017] Furthermore, in step S2, the vacuum level is -0.08 to -0.1 MPa and is maintained for 1 to 4 hours.

[0018] Furthermore, in step S2, the impregnation solvent is selected from solvents with a boiling point of 50–100°C under normal pressure, and the standing time is 4–12 h.

[0019] Furthermore, in step S3, the frequency of ultrasound is 10–50 kHz, and the duration of ultrasound is 2–15 min.

[0020] Furthermore, in step S4, the heating and evaporation temperature is 25–90°C, and the heating and evaporation time is 2–10 hours.

[0021] Furthermore, in step S5, the vacuum degree is -0.08 to -0.1 MPa and is maintained for 1 to 4 hours; the resin solution is prepared by thermosetting resin, organic solvent and curing agent in a volume ratio of 100:(5 to 15):(0.1 to 3); and the standing time is 4 to 12 hours.

[0022] Further, in step S6, the cleaning solvent is water, the cleaning method is rinsing, the cleaning temperature is 60-95℃, and the cleaning time is 5-15 minutes; the curing method is water bath curing, the curing temperature is 80-120℃, and the curing time is 2-6 hours; the drying method is forced air drying, the drying temperature is 40-90℃, and the drying time is 2-8 hours. The thickness of the ultrathin high-strength flexible graphite bipolar plate is 0.06-0.4 times the thickness of the flexible graphite blank.

[0023] The second technical solution of the present invention is to provide an ultrathin, high-strength, flexible graphite bipolar plate based on the preparation method described in one of the above technical solutions.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) This invention prepares ultrathin flexible graphite bipolar plates by combining molding and solvent evaporation shrinkage. Compared with complete molding, it avoids the use of huge molding pressure during the compression process, reducing equipment requirements and costs.

[0026] (2) The present invention reduces the macroscopic thickness of the flexible graphite bipolar plate by shrinking the micro-pores, making the material more uniformly stressed, less prone to compression cracks, improving the product yield, and suitable for industrial production.

[0027] (3) The flexible graphite bipolar plate of the present invention is thin, which can make flexible graphite bipolar plates of 0.3-0.8mm thick obtained from flexible graphite blanks with a thickness of 0.5-2mm, effectively reducing the stack volume of fuel cells and increasing their volumetric power density. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation process of the present invention.

[0029] Figure 2 This is a schematic diagram illustrating the principle of the present invention. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0031] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are all conventional commercially available raw materials or conventional processing techniques in the art.

[0032] Modified acrylic resin: Duco New Materials Co., Ltd., model DB41812-V00.

[0033] Example 1:

[0034] A method for preparing an ultrathin, high-strength, flexible graphite bipolar plate includes the following steps:

[0035] (1) Select an areal density of 45 mg / cm³ 2 A 3.5mm thick flexible graphite blank is molded under 20MPa pressure for 10 minutes to produce a 0.6mm thick flexible graphite bipolar plate P1.

[0036] (2) A flexible graphite bipolar plate P1 is placed in an impregnation vessel and vacuumed until the vacuum degree inside the impregnation vessel is -0.08 to -0.1 MPa. The vacuum is maintained for 2 hours, an aqueous solution is injected, and the plate is left to stand for 5 hours to obtain a flexible graphite bipolar plate P2.

[0037] (3) Immerse the flexible graphite bipolar plate P2 in an aqueous solution and place it in an ultrasonic instrument with a frequency of 15KHz. After ultrasonication for 5 minutes, the flexible graphite bipolar plate P3 is obtained.

[0038] (4) Place the flexible graphite bipolar plate P3 in a drying oven and heat it at 40°C for 8 hours to obtain the flexible graphite bipolar plate P4.

[0039] (5) Place the flexible graphite bipolar plate P4 in the impregnation vessel, evacuate the vessel to a vacuum level of -0.08 to -0.1 MPa, maintain for 3 hours, inject the resin solution (modified acrylic resin: tetrahydrofuran: polyurethane = 100:10:0.5), let stand for 6 hours, and obtain the flexible graphite bipolar plate P5.

[0040] (6) The flexible graphite bipolar plate P5 was rinsed repeatedly with an 80°C aqueous solution for 5 minutes, then placed in a 95°C hot water solution for 3 hours to cure, and finally placed in a 60°C forced-air drying oven for 6 hours to obtain a flexible graphite bipolar plate P6 with a thickness of 0.35 mm and a bending strength of 50.78 MPa.

[0041] Example 2:

[0042] A method for preparing an ultrathin, high-strength, flexible graphite bipolar plate includes the following steps:

[0043] (1) Select an areal density of 60 mg / cm³ 2 A 4mm thick flexible graphite blank is molded under 35MPa pressure for 15 minutes to form a 1.2mm thick flexible graphite bipolar plate P1.

[0044] (2) Place the flexible graphite bipolar plate P1 in an impregnation vessel, evacuate the vessel to a vacuum of -0.08 to -0.1 MPa, maintain the vacuum for 1.5 h, inject ethanol solvent, and let stand for 4 h to obtain the flexible graphite bipolar plate P2.

[0045] (3) Immerse the flexible graphite bipolar plate P2 in ethanol solvent, place it in an ultrasonic instrument with a frequency of 35KHz, and sonicate for 2 minutes to obtain the flexible graphite bipolar plate P3.

[0046] (4) Place the flexible graphite bipolar plate P3 in a drying oven and heat it at 60°C for 2 hours to obtain the flexible graphite bipolar plate P4.

[0047] (5) Place the flexible graphite bipolar plate P4 in an impregnation vessel, evacuate the vessel to a vacuum of -0.08 to -0.1 MPa, maintain for 3 hours, inject a resin solution (modified acrylic resin: acetone: epoxy resin = 100:15:1), and let stand for 8 hours to obtain the flexible graphite bipolar plate P5.

[0048] (6) The flexible graphite bipolar plate P5 was rinsed repeatedly with a 90℃ aqueous solution for 10 minutes, then placed in a 95℃ hot water solution for 2 hours to solidify, and finally placed in a 60℃ forced-air drying oven for 8 hours to obtain a flexible graphite bipolar plate P6 with a thickness of 0.7 mm and a bending strength of 54.29 MPa.

[0049] The embodiments of this invention utilize the principle of creating negative pressure through solvent evaporation within a relatively sealed cavity to compress flexible graphite bipolar plates. The negative pressure created between the pore cavities and atmospheric pressure regulates the internal pore structure of the flexible graphite bipolar plate material. During the compression process, the shrinkage of the microscopic pores in the flexible graphite leads to a reduction in its macroscopic thickness, resulting in more uniform stress distribution and reducing the likelihood of compression cracks. First, a flexible graphite preform is molded, impregnated with solvent, ultrasonically treated, and then evaporated to obtain an ultrathin flexible graphite plate. Next, the strength of the ultrathin flexible graphite plate is improved through vacuum impregnation, curing, and drying with resin, ultimately yielding an ultrathin, high-strength flexible graphite bipolar plate. Furthermore, the entire preparation process requires minimal equipment, is simple, suitable for industrial production, and has broad development prospects.

[0050] In conclusion, Figure 1 This is a schematic diagram illustrating the fabrication process of an ultrathin, high-strength, flexible graphite bipolar plate according to the present invention. The fabrication is achieved through a combination of molding and solvent evaporation shrinkage. First, a low-density flexible graphite preform is molded under low pressure. Then, the bipolar plate is made ultrathin through solvent evaporation shrinkage. In the solvent evaporation shrinkage step, the open and closed pores of the flexible graphite plate are filled with solvent through solvent vacuum impregnation and ultrasonic treatment (controlling the ultrasonic frequency and time), ensuring uniform material shrinkage during solvent evaporation. Finally, through solvent evaporation, resin impregnation, and other operations, an ultrathin, high-strength, flexible graphite bipolar plate with a thickness of 0.06 to 0.4 times that of the original flexible graphite preform and a bending strength of 40 to 60 MPa is obtained.

[0051] Figure 2This is a schematic diagram illustrating the solvent evaporation compression mechanism of a method for preparing an ultrathin, high-strength, flexible graphite bipolar plate according to the present invention. Solvent evaporates from the pores near the surface of the graphite bipolar plate, while solvent in the adjacent internal pores fills these pores near the surface under capillary action, creating a negative pressure space inside. This creates a pressure difference with atmospheric pressure, ultimately forcing the pores to contract. Because this process is based on the contraction characteristics of the microporous structure of the graphite bipolar plate, the contraction force is relatively gentle. Solvent evaporation compression changes the macroscopic thickness of the flexible graphite bipolar plate by altering its microporous structure. Compared to high-pressure molding (which changes thickness through macroscopic pressure transmission), this method results in fewer microcracks and defects inside the graphite bipolar plate, and can, to some extent, eliminate larger microcracks and defects generated during molding.

[0052] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing an ultrathin, high-strength, flexible graphite bipolar plate, characterized in that, Includes the following steps: S1. A flexible graphite blank is molded to obtain a flexible graphite bipolar plate P1. S2. Place the flexible graphite bipolar plate P1 from step S1 in a vacuum environment, add an impregnation solvent, and let it stand to obtain the flexible graphite bipolar plate P2. S3. Immerse the flexible graphite bipolar plate P2 obtained in step S2 in the impregnation solvent of step S2, and sonicate it to obtain the flexible graphite bipolar plate P3. S4. The flexible graphite bipolar plate P3 obtained in step S3 is heated and evaporated to obtain the flexible graphite bipolar plate P4. S5. Place the flexible graphite bipolar plate P4 obtained in step S4 in a vacuum environment, add resin solution, and let it stand to obtain the flexible graphite bipolar plate P5. S6. The flexible graphite bipolar plate P5 obtained in step S5 is sequentially cleaned, cured, and dried to obtain an ultrathin high-strength flexible graphite bipolar plate. In step S1, the molding pressure is 10~50 MPa and the molding time is 5~30 min. In step S2, the impregnation solvent is selected from solvents with a boiling point of 50~100℃ under normal pressure, and the standing time is 4~12 h; In step S3, the frequency of ultrasound is 10~50 KHz and the duration of ultrasound is 2~15 min. In step S4, the heating and evaporation temperature is 25~90℃, and the heating and evaporation time is 2~10 h; In step S5, the vacuum degree is -0.08~-0.1 MPa and is maintained for 1~4 h; the resin solution is prepared by thermosetting resin, organic solvent and curing agent in a volume ratio of 100:(5~15):(0.1~3); the standing time is 4~12 h.

2. The method for preparing an ultrathin, high-strength, flexible graphite bipolar plate according to claim 1, characterized in that, In step S1, the thickness of the flexible graphite bipolar plate P1 is 0.1 to 0.4 times the thickness of the flexible graphite blank.

3. The method for preparing an ultrathin, high-strength, flexible graphite bipolar plate according to claim 1, characterized in that, In step S2, the vacuum level is -0.08 to -0.1 MPa, and it is maintained for 1 to 4 hours.

4. The method for preparing an ultrathin, high-strength, flexible graphite bipolar plate according to claim 1, characterized in that, In step S6, the cleaning solvent is water, the cleaning method is rinsing, the cleaning temperature is 60~95℃, and the cleaning time is 5~15min; the curing method is water bath curing, the curing temperature is 80~120℃, and the curing time is 2~6h; the drying method is forced air drying, the drying temperature is 40~90℃, and the drying time is 2~8h. The thickness of the ultrathin high-strength flexible graphite bipolar plate is 0.06~0.4 times the thickness of the flexible graphite blank.

5. An ultrathin, high-strength, flexible graphite bipolar plate, characterized in that, Prepared according to the preparation method described in any one of claims 1-4.

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