Flexible graphite bipolar plate adaptive to high-temperature fuel cell as well as preparation method and application of flexible graphite bipolar plate

Abstract

The invention provides a flexible graphite bipolar plate adaptive to a high-temperature fuel cell as well as a preparation method and application of the flexible graphite bipolar plate. By optimizing a bismaleimide impregnation liquid formula and a vacuum pressure impregnation and stepped curing process, the flexible graphite bipolar plate has a high TG point (greater than 260 DEG C), excellent mechanical properties and long-term stability at a high temperature, not only meets the long-term service demand of a traditional medium-temperature fuel cell, but also can be adapted to a high-temperature fuel cell scene of 120-200 DEG C, and has a wide application prospect. The technical blank of the high-temperature bipolar plate is filled.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature fuel cells, and particularly relates to a flexible graphite bipolar plate suitable for high-temperature fuel cells and a preparation method and application thereof. BACKGROUND

[0002] The flexible graphite bipolar plate is a core structure and a conductive component of a fuel cell stack, and its performance needs to be highly matched with the working environment of the fuel cell. Currently, the mainstream of the industry adopts an acrylic resin solution as an impregnation carrier.

[0003] For example, a patent application with the publication number CN117855511A discloses a preparation method of a flexible composite bipolar plate and a fuel cell. The preparation method comprises the following steps: S1, oxidizing, intercalating, washing and drying flaky graphite; S2, uniformly mixing an organic binder with the dried flaky graphite and heating in an inert gas atmosphere to form a high-strength expanded graphite polymer; S3, pressing and cutting the expanded graphite polymer to form a flexible graphite original plate; S4, pressing the flexible graphite original plate into a semi-finished polar plate with a flow channel feature; and S5, impregnating, washing, curing and drying the semi-finished polar plate to obtain a finished polar plate. In step S2, the organic binder is an epoxy resin solution or an acrylic resin solution.

[0004] After optimization of the process, the gas tightness of the bipolar plate prepared by using the acrylic resin can meet the basic needs (air permeability ≤1.5×10 -8 cm 2 / s) of traditional medium-temperature fuel cells (80-90℃), but there are still insurmountable limitations in high-temperature scenarios and long-term service: (1) Insufficient heat resistance, unable to adapt to high-temperature fuel cells: the glass transition temperature (TG point) of the acrylic resin after curing is lower than 150℃, when the working temperature of the fuel cell is increased to above 120℃, the resin is easy to soften and creep, resulting in a decrease in the structural stability of the polar plate, and unable to meet the use requirements of high-temperature proton exchange membrane fuel cells (such as fuel cells based on phosphoric acid doped polybenzimidazole membranes, working temperature 160-200℃); (2) Poor long-term mechanical stability: in the long-term operation (more than 5000 hours) of the medium-temperature fuel cell, the acrylic resin is easy to undergo thermal oxidative aging, resulting in an attenuation rate of the bending strength of the bipolar plate exceeding 20%, and an attenuation rate of the impact strength exceeding 30%, increasing the risk of cracking and gas leakage of the stack; (3) Significant attenuation of gas tightness at high temperature: even if the initial gas tightness meets the requirements, the molecular chain movement of the acrylic resin is intensified at a high temperature above 120℃, and the micro-pore plugging structure is easy to be damaged, and the air permeability rate increases by more than 30% after 1000 hours of high-temperature aging, which cannot guarantee the gas isolation requirements of the long-term operation of the high-temperature fuel cell.

[0005] Bismaleimide resin is an ideal choice to solve the above problems due to its inherent high TG point (≥ 250℃ after curing), high modulus characteristics. However, how to optimize the resin formulation and process to fully exert its heat resistance advantage, while ensuring the synergistic improvement of mechanical properties and long-term stability, to adapt to the harsh demands of high-temperature fuel cells, is a key technical problem that needs to be broken through in this field.

[0006] Patent application CN119050396A discloses a high-strength, high-temperature-resistant flexible graphite composite bipolar plate and its preparation method. The bipolar plate product is obtained by impregnating and hot pressing expanded graphite treated with carbohydrates. To further improve the heat resistance of the bipolar plate, a thermosetting resin with high crosslinking density is used for impregnation, including but not limited to bismaleimide resin, furan resin, vinyl ester resin, etc. However, there is still great significance in researching and developing high-temperature-resistant flexible graphite bipolar plates using bismaleimide resin. SUMMARY

[0007] To solve the above technical problems in the prior art, the present application provides a flexible graphite bipolar plate suitable for high-temperature fuel cells and its preparation method and application.

[0008] The present application provides a preparation method of a flexible graphite bipolar plate suitable for high-temperature fuel cells, comprising the following steps: (1) Expandable graphite is expanded and pressed into a flexible graphite blank bipolar plate; (2) Dissolve 100 parts of bismaleimide resin in an organic solvent to prepare a base solution with a solid content of 20wt%-25wt% by weight; add 10-15 parts of carboxyl-terminated nitrile rubber and 3-5 parts of conductive carbon black to the base solution and disperse uniformly to obtain an impregnating solution; (3) Place the flexible graphite blank bipolar plate prepared in step (1) in the impregnating solution prepared in step (2) for impregnation, so that the impregnating solution penetrates into the micropores of the flexible graphite blank bipolar plate; after impregnation, wash and dry the flexible graphite blank bipolar plate to remove the solvent; (4) Cure the flexible graphite blank bipolar plate completed in step (3).

[0009] Preferably, in step (4), the curing is stepwise vacuum curing, the vacuum degree is ≤10 Pa, and the curing temperature is increased in stages in the range of 110-230℃; during the curing, the curing temperature of the first stage is increased to 110-120℃ at a temperature increasing rate of 1.5-2.0℃ / min, and then the temperature is kept constant for 1.5-2.0 hours; the curing temperature of the second stage is increased to 160-170℃ at a temperature increasing rate of 1.5-2.0℃ / min, and then the temperature is kept constant for 2.5-3.0 hours; the curing temperature of the third stage is increased to 210-230℃ at a temperature increasing rate of 1.5-2.0℃ / min, and then the temperature is kept constant for 3.0-4.0 hours; finally, the temperature is cooled to room temperature at a temperature decreasing rate of 1.0-1.5℃ / min, to obtain the flexible graphite bipolar plate for high-temperature fuel cells.

[0010] In step (4), more than 98% of the residual solvent is removed in the first stage, and at the same time, the bismaleimide resin and the carboxyl-terminated butynorubber are preliminarily crosslinked to avoid solvent boiling at high temperature; the second stage promotes the copolymerization grafting reaction of the bismaleimide resin and the carboxyl-terminated butynorubber to form a "rigid main chain-flexible side chain" structure to balance the high-temperature rigidity and the low-temperature toughness; and the third stage ensures that the bismaleimide resin and the carboxyl-terminated butynorubber form a highly crosslinked three-dimensional network structure.

[0011] Preferably, in step (1), the expandable graphite has a carbon content of not less than 99.5%, and an ash content of not more than 0.3%; the expansion temperature is 880-950℃, and the expansion time is 40-60 seconds.

[0012] Preferably, in step (1), the pressing method is first to make a flexible graphite loose cake plate with a bulk density of 0.25-0.4g / cm 3 by a rolling process, and then to press the flexible graphite loose cake plate into a flexible graphite green bipolar plate with a bulk density of 0.7-0.9g / cm 3 and a thickness of 1.0-1.3mm by a high-precision vacuum molding process under a pressure of 30-50MPa; the micropore aperture of the flexible graphite green bipolar plate is 1.0-3μm, which takes into account the resin permeation efficiency and the structural stability at a subsequent high temperature.

[0013] Preferably, in step (2), the number average molecular weight of the bismaleimide resin is 1100-1500, and the bismaleimide resin is a 4,4'-diamino diphenyl sulfone modified bismaleimide resin; the 4,4'-diamino diphenyl sulfone modified bismaleimide resin is obtained by addition reaction of 4,4'-diamino diphenyl sulfone and bismaleimide resin; during the modification process, the amino group of 4,4'-diamino diphenyl sulfone reacts with the maleimide group in the bismaleimide resin to form a new chemical bond, realizing chain extension modification of the bismaleimide resin; through this modification method, the crosslinking density of the bismaleimide resin can be reduced to a certain extent, and the flexibility of the molecular chain is improved, thereby improving the toughness of the bismaleimide resin; The organic solvent is N-methyl pyrrolidone (NMP), and the solubility parameter difference between NMP and the bismaleimide resin is ≤1.5 (cal / cm 3 ) 0.5 , which ensures that the resin is completely dissolved and has strong interfacial bonding force with the graphite element blank electrode plate, and is not easy to delaminate at high temperature; The content of acrylonitrile in the carboxyl-terminated butyl nitrile rubber (CTBN) is 28wt%-32wt%, which has good low-temperature toughness and high-temperature compatibility; The particle size of the conductive carbon black is 15-30 nm, which can reduce the high-temperature contact resistance. The viscosity of the impregnating solution obtained in step (2) is 12-15 mPa·s at 25℃.

[0014] Preferably, in step (2), the dispersion process adopts high-speed shearing dispersion machine for 25-30 minutes at a speed of 2800-3200 r / min, and the dispersion temperature is controlled at 20-25℃ during the process to avoid premature crosslinking of the resin.

[0015] Preferably, in step (3), vacuum pressure impregnation is used during impregnation; first, the flexible graphite element blank electrode plate is placed in an impregnation tank, vacuum is extracted to an absolute pressure lower than 30 Pa and maintained for 30-60 minutes; then, the impregnating solution is injected into the impregnation tank and covers the flexible graphite element blank electrode plate under vacuum condition, and vacuum impregnation is maintained for 50-90 minutes; finally, the impregnation is continued under 0.6-0.8 MPa for 60-90 minutes.

[0016] Preferably, in step (3), the solvent used for cleaning is a reagent with a boiling point lower than 80℃ and capable of being mutually soluble with the organic solvent in step (2), and is further preferably anhydrous ethanol or acetone.

[0017] The application also provides a flexible graphite bipolar plate suitable for high-temperature fuel cells, which is prepared by the above method.

[0018] The application further provides application of the flexible graphite bipolar plate for adapting to the high-temperature fuel cell in preparation of the fuel cell.

[0019] Compared with the prior art, the application has the following beneficial effects: The application optimizes the bismaleimide impregnating solution formula, the vacuum pressure impregnation and the stepwise curing process, so that the flexible graphite bipolar plate has a high TG point (> 260 DEG C), excellent mechanical properties and long-term stability at high temperature, meets the long-term service requirement of traditional medium-temperature fuel cells, can be adapted to the 120-200 DEG C high-temperature fuel cell scene, and fills the technical gap of high-temperature bipolar plates.

[0020] (1) Ultra-high TG point, perfect adaptation to high-temperature fuel cells: the TG point of the bismaleimide resin after optimized curing is higher than 260 DEG C, the structure is stable in the 120-200 DEG C high-temperature environment, there is no softening and creep phenomenon, and the bismaleimide resin can be directly adapted to the high-temperature proton exchange membrane fuel cell (160-200 DEG C), filling the current technical gap of high-temperature bipolar plates; the acrylic resin system appears obvious softening above 120 DEG C, and cannot meet the demand of high-temperature scene; (2) Excellent mechanical properties and high-temperature stability: the initial bending strength of the bipolar plate is greater than or equal to 40 MPa, and the impact strength is greater than or equal to 6.5 kJ / m 2 , which is increased by 21.6% and 51.2% respectively compared with the acrylic resin system; after 1000 hours of high-temperature aging at 180 DEG C, the attenuation rate of the bending strength is less than 6%, and the attenuation rate of the impact strength is less than 8%, which is far lower than that of the acrylic resin system (the attenuation rate is more than 30% after high-temperature aging), ensuring the structural reliability of the long-term operation of the high-temperature fuel cell; (3) Low long-term air tightness decay rate: the initial air permeability is not higher than 0.8*10 -8 cm 2 / s, which is equivalent to that of the optimized acrylic resin system; but after 1000 hours of high-temperature aging at 180 DEG C, the air permeability increases by less than 10%, while the air permeability of the acrylic resin system increases by more than 30%; after 10000 hours of long-term operation of the traditional medium-temperature fuel cell (80 DEG C), the air permeability is still not higher than 1.2*10 -8 cm 2 / s, and the air tightness stability is significantly better than that of the acrylic resin system; (4) High-temperature conductivity stability: the interface bonding force between the modified conductive carbon black and the bismaleimide resin is strong, the in-plane conductivity of the bipolar plate is greater than 360 S / cm at 180 DEG C, the contact resistance is less than 4 mΩ·cm 2 , and the conductivity decreases by less than 5% after 1000 hours of high-temperature aging, ensuring the conductivity efficiency and stability of the high-temperature fuel cell. DETAILED DESCRIPTION

[0021] Example 1 Substrate preparation: Select expandable graphite with carbon content of 99.8% and ash content of 0.2%, put it in a high-temperature furnace at 920℃ for 50 seconds, then get flexible graphite mat with bulk density of 0.3 g / cm 3 by rolling process; then the flexible graphite mat is molded under a pressure of 35 MPa (control accuracy ± 0.1 MPa, pressure holding for 4 minutes) to make a green plate with a bulk density of 0.8 g / cm 3 and a thickness of 1.1 mm, and the micropore size is concentrated in 1.2-2.8 μm.

[0022] Impregnating solution preparation: 100 g of 4,4'-diamino diphenyl sulfone modified bismaleimide resin with a number average molecular weight of 1300 is dissolved in 350 g of NMP (solid content of 22.2%), 12 g of CTBN (acrylonitrile content in CTBN is 30%) and 4 g of conductive carbon black (particle size is 20 nm) are added, and a high-speed shearing disperser is used to disperse at 3000 r / min and 23℃ for 28 minutes to obtain an impregnating solution with a viscosity of 13.5 mPa·s at 25℃.

[0023] Vacuum pressure impregnation: the green plate is placed in a 316L stainless steel customized impregnation tank, vacuumed to 50 Pa and kept for 55 minutes; the impregnation tank is injected with the above-mentioned impregnating solution at a rate of 10 mL / min under vacuum, and vacuum impregnation is kept for 75 minutes; then the vacuum is broken, and a positive pressure of 0.8 MPa is applied to the tank body, and pressure holding impregnation is kept for 90 minutes.

[0024] Controllable solvent cleaning: after impregnation, the plate is taken out and dripped for 5 minutes; then the plate is quickly immersed in low-boiling anhydrous ethanol at a temperature of 10℃ for 5 seconds, and after gentle shaking, it is immediately taken out and placed in a well-ventilated place for volatilization for 40 seconds.

[0025] High-temperature adaptive precise curing: the plate is placed in a vacuum oven and heated to 115℃ at a heating rate of 1.8℃ / min, then kept for 1.8 hours, continues to heat to 165℃ at the same heating rate, then kept for 2.8 hours, then heats to 220℃ at the same heating rate, then kept for 3.5 hours, finally cools to room temperature (25℃, same below) at a cooling rate of 1.2℃ / min, to get high-performance flexible graphite bipolar plate adapted to high-temperature fuel cells.

[0026] Example 2 Substrate preparation: Select expandable graphite with carbon content of 99.5% and ash content of 0.3%, put it in a high-temperature furnace at 880℃ for 40 seconds; make flexible graphite mat with bulk density of 0.25 g / cm 3 by rolling process, then vacuum mold the flexible graphite mat under a pressure of 30 MPa to get a green plate with a bulk density of 0.7 g / cm 3A green anode plate with a thickness of 1.0 mm (pore size of 1.0-2 μm).

[0027] Impregnation liquid preparation: 100 g of 4,4'-diamino diphenyl sulfone modified bismaleimide resin with a number average molecular weight of 1100 was dissolved in 400 g of NMP (solid content of 20%), 10 g of CTBN (acrylonitrile content of 28 wt%) and 3 g of conductive carbon black (particle size of 15 nm) were added, and a high-speed shearing disperser was used to disperse at 2800 r / min and 20℃ for 25 minutes to obtain an impregnation liquid with a viscosity of 12 mPa·s at 25℃.

[0028] Vacuum pressure impregnation: the green anode plate was placed in a 316L stainless steel customized impregnation tank, vacuumed to 25 Pa and maintained for 30 minutes; the impregnation tank was injected with the above impregnation liquid at a rate of 10 mL / min under vacuum, vacuum impregnated for 50 minutes, and then pressure impregnated at 0.6 MPa for 60 minutes.

[0029] Controllable solvent cleaning: after impregnation, the anode plate was taken out and dripped for 5 minutes; then, the anode plate was quickly immersed in low-boiling anhydrous ethanol at a temperature of 10℃ for 5 seconds, and then taken out immediately after gentle shaking, and placed in a well-ventilated place to volatilize for 40 seconds.

[0030] High-temperature adaptive precise curing: the anode plate was placed in a vacuum oven and heated to 110℃ at a rate of 1.5℃ / min, then heated to 160℃ at a rate of 1.5℃ / min and maintained for 2.5 hours, then heated to 210℃ at the same rate and maintained for 3.0 hours, and finally cooled to room temperature at a rate of 1.0℃ / min.

[0031] Example 3 Substrate preparation: expandable graphite with a carbon content of 99.8% and an ash content of 0.2% was selected and placed in a 950℃ high-temperature furnace for 60 seconds; a flexible graphite sponge cake plate with a bulk density of 0.4 g / cm 3 was prepared by rolling process, and then the flexible graphite sponge cake plate was vacuum molded at a pressure of 50 MPa to obtain a green anode plate with a bulk density of 0.9 g / cm 3 and a thickness of 1.3 mm (pore size of 2-3 μm).

[0032] Impregnation liquid preparation: 100 g of 4,4'-diamino diphenyl sulfone modified bismaleimide resin with a number average molecular weight of 1500 was dissolved in 300 g of NMP (solid content of 25%), 15 g of CTBN (acrylonitrile content of 32 wt%) and 5 g of conductive carbon black (particle size of 30 nm) were added, and a high-speed shearing disperser was used to disperse at 3200 r / min and 25℃ for 30 minutes to obtain an impregnation liquid with a viscosity of 15 mPa·s at 25℃.

[0033] Vacuum pressure impregnation: Place the blank electrode plate into a customized 316L stainless steel impregnation tank, evacuate to 20Pa and maintain for 60 minutes; while maintaining vacuum, inject the above impregnation liquid into the impregnation tank at a rate of 10mL / min, maintain vacuum impregnation for 90 minutes, and then apply pressure impregnation at 0.8MPa for 90 minutes.

[0034] Controlled solvent cleaning: After immersion, remove the electrode plate and drip for 5 minutes; then, quickly immerse the electrode plate in acetone at 10°C for 5 seconds, gently shake it, and immediately remove it. Let it stand in a ventilated place to evaporate for 40 seconds.

[0035] High-temperature adaptable precision curing: Place the electrode plate in a vacuum oven and heat it to 120℃ at a rate of 2.0℃ / min, then hold it at that temperature for 2.0 hours. Continue heating it to 170℃ at a rate of 2.0℃ / min and hold it at that temperature for 3.0 hours. Then heat it to 230℃ at the same rate and hold it at that temperature for 4.0 hours. Finally, cool it down to room temperature at a rate of 1.5℃ / min.

[0036] Example 4 Substrate preparation: Same as in Example 1.

[0037] Preparation of impregnation solution: 100g of 4,4'-diaminodiphenyl sulfone modified bismaleimide resin with a number average molecular weight of 1300 was dissolved in 333g of NMP (solid content of 23.1%), 14g of CTBN (acrylonitrile content of 31wt%) and 4g of conductive carbon black (particle size of 22nm) were added, and the mixture was sheared and dispersed for 28 minutes at 3000r / min and 23℃ using a high-speed shear disperser to obtain an impregnation solution with a viscosity of 14mPa·s at 25℃.

[0038] Vacuum pressure impregnation: Same as in Example 1.

[0039] Controlled solvent cleaning: Same as in Example 1.

[0040] High-temperature adaptable precision curing: Same as in Example 1.

[0041] Comparative Example 1 Substrate preparation: Same as in Example 1, ensuring substrate consistency.

[0042] Impregnating solution preparation: 100 g of acrylic resin with a number average molecular weight of 3000 was dissolved in 130 g of ethyl acetate to prepare a base solution, 12 g of CTBN (the content of acrylonitrile in CTBN was 30%) and 4 g of conductive carbon black (the particle size was 20 nm) were added to the base solution, and 2 ‰ of the mass of the base solution of VAZO52 and 2.5 ‰ of the mass of the base solution of VAZO64 were added as initiators to facilitate the subsequent curing process. A high-speed shearing disperser was used to disperse at 2800 r / min and 25℃ for 25 minutes to obtain an impregnating solution with a viscosity of 12 mPa·s at 25℃.

[0043] Vacuum pressure impregnation: the green plate was placed in a 316L stainless steel customized impregnation tank, vacuumed to 50 Pa and maintained for 55 minutes; the impregnating solution was injected into the impregnation tank at a rate of 10 mL / min under vacuum, and vacuum impregnation was maintained for 75 minutes; then the vacuum was broken, and a positive pressure of 0.8 mpa was applied to the tank body, and pressure impregnation was maintained for 90 minutes.

[0044] Cleaning: after impregnation, the plate was taken out and dripped for 5 minutes; then, the plate was immersed in deionized water at a temperature of 25℃ for tumbling cleaning, and four thousandths of surfactant (the main component is octylphenol polyoxyethylene ether) was added to the deionized water, and the cleaning time was 10 minutes; then it was put into pure deionized water for tumbling rinsing, and the cleaning time was 10 minutes.

[0045] Curing: the plate was immersed in 95℃ deionized water, and cured at 95℃ for 1.5 hours to obtain a flexible graphite bipolar plate.

[0046] Comparative Example 2 The difference from Example 1 is that no CTBN is added in the preparation of the impregnating solution.

[0047] Comparative Example 3 The difference from Example 1 is that the mass of CTBN added in the preparation of the impregnating solution is 5 g.

[0048] Test Example 1 The flexible graphite bipolar plates obtained in Examples 1-4 and Comparative Examples 1-3 were tested for performance, and the performance comparison is shown in Table 1.

[0049] The test method refers to the following documents: GB / T 11998-2018 "Determination of Glass Transition Temperature of Plastics by Thermomechanical Analysis (TMA)"; GB / T 1043.1-2008 "Determination of Impact Properties of Plastics by Simple Beam Method Part 1: Non-Instrumented Impact Test"; GB / T 1735-2009 "Determination of Heat Resistance of Color Coatings and Clear Coatings"; GB / T 32793-2016 Determination of volume and surface resistivity of conductive plastics; GBT 20042.6-2024 Proton exchange membrane fuel cells - Part 6: Test methods for bipolar plate properties.

[0050] Table 1

[0051] The initial mechanical properties of the embodiment of the present application are significantly better than the acrylic resin system (Comparative Example 1), and the amount of CTBN added has a direct impact on the mechanical properties. When there is no CTBN or low CTBN ratio (Comparative Examples 2 or 3), the impact strength is greatly reduced.

[0052] The high-temperature aging attenuation rate of the embodiment of the present application is less than 10%, which is much lower than that of Comparative Example 1 (> 30%) and Comparative Examples 2-3, proving that the synergistic effect of the formulation and process of the present application can significantly improve the high-temperature long-term stability.

[0053] The Tg of the embodiment of the present application is higher than 260℃, while the Tg of the acrylic resin system (Comparative Example 1) is only 148℃, which directly reflects the high-temperature adaptation advantage of the bipolar plate of the present application; at the same time, Comparative Examples 2-3 show that the addition of CTBN has little effect on Tg, and the core heat resistance is guaranteed by the bismaleimide resin.

Claims

1. A method of making a flexible graphite bipolar plate suitable for high temperature fuel cells, characterized by, The method comprises the following steps: (1) expandable graphite is expanded and pressed into a flexible graphite element plate; (2) 100 parts of bismaleimide resin is dissolved in an organic solvent to prepare a base solution with a solid content of 20wt%-25wt%; 10-15 parts of carboxyl-terminated butyl nitrile rubber and 3-5 parts of conductive carbon black are added to the base solution and uniformly dispersed to obtain an impregnating solution; (3) the flexible graphite element plate prepared in step (1) is immersed in the impregnating solution prepared in step (2) to allow the impregnating solution to fully penetrate into the micropores of the flexible graphite element plate; after the immersion is completed, the flexible graphite element plate is cleaned and dried to remove the solvent; (4) the flexible graphite element plate after step (3) is cured.

2. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (4), the curing is stepwise vacuum curing, the vacuum degree is ≤10 Pa, and the curing temperature is increased in stages in the range of 110-230℃; During the curing, the first-stage curing temperature is increased to 110-120℃ at a temperature increasing rate of 1.5-2.0℃ / min and then kept for 1.5-2.0 hours; the second-stage curing temperature is increased to 160-170℃ at a temperature increasing rate of 1.5-2.0℃ / min and then kept for 2.5-3.0 hours; the third-stage curing temperature is increased to 210-230℃ at a temperature increasing rate of 1.5-2.0℃ / min and then kept for 3.0-4.0 hours; finally, the temperature is cooled to room temperature at a temperature decreasing rate of 1.0-1.5℃ / min to obtain the flexible graphite bipolar plate suitable for high-temperature fuel cells.

3. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (2), the number average molecular weight of the bismaleimide resin is 1100-1500, and the bismaleimide resin is a 4,4'-diamino diphenyl sulfone modified bismaleimide resin; the 4,4'-diamino diphenyl sulfone modified bismaleimide resin is obtained by addition reaction of 4,4'-diamino diphenyl sulfone and bismaleimide resin.

4. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (1), the carbon content of the expandable graphite is not less than 99.5%, and the ash content of the expandable graphite is not more than 0.3%; the expansion temperature is 880-950℃, and the expansion time is 40-60 seconds.

5. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (1), the method for pressing is to first make a flexible graphite fluffy cake board with a bulk density of 0.25-0.4 g / cm 3 by a rolling process, and then to press the flexible graphite fluffy cake board into a flexible graphite green plate with a bulk density of 0.7-0.9 g / cm 3 and a thickness of 1.0-1.3 mm by a high-precision vacuum molding process under a pressure of 30-50 MPa; the flexible graphite green plate has a micropore size of 1.0-3 μm.

6. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (2), the organic solvent is N-methyl pyrrolidone; The content of acrylonitrile in the carboxyl-terminated butyl nitrile rubber is 28wt%-32wt%; The particle size of the conductive carbon black is 15-30nm; The viscosity of the impregnating solution obtained in step (2) is 12-15mPa·s at 25℃.

7. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (3), vacuum pressure impregnation is used during the impregnation; the flexible graphite element plate is first placed in an impregnation tank, vacuum is applied to an absolute pressure lower than 30Pa and maintained for 30-60 minutes; then the impregnating solution is injected into the impregnation tank and covers the flexible graphite element plate under vacuum, and vacuum impregnation is maintained for 50-90 minutes; finally, the impregnation is continued under 0.6-0.8MPa for 60-90 minutes.

8. The method of claim 1, wherein the graphite bipolar plate is flexible. In step (3), the solvent used for cleaning is a reagent with a boiling point lower than 80℃ and miscible with the organic solvent in step (2).

9. A flexible graphite bipolar plate adapted for use in a high temperature fuel cell, characterized by It is prepared by the method for preparing flexible graphite bipolar plates adapted to high-temperature fuel cells according to any one of claims 1 to 8.

10. The application of the flexible graphite bipolar plate adapted to high-temperature fuel cells as described in claim 9 in the fabrication of fuel cells.

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