High-performance graphite-based composite bipolar plate, preparation method, and application

Abstract

The present invention relates to the field of flow battery materials, and specifically provides a high-performance graphite-based composite bipolar plate, a preparation method, and an application. The method comprises: mixing powder in a powder mixing system; under a vacuum condition, in a mold pressing system, heating and pressing the mixed powder in a mold; then finishing heating and continuing to maintain a forming pressure; when the temperature drops below the curing forming temperature of a resin, releasing the forming pressure and filling with air; and demolding; wherein the mixed powder comprises 75 wt.%-85 wt.% of graphite powder, 15 wt.%-25 wt.% of resin powder, and the balance of carbon black, carbon nanotubes and carbon fibers. The bipolar plate obtained by the method has high conductivity and high airtightness, and is suitable for industrial production.

Description

High-performance graphite-based composite material bipolar plate, preparation method and application Technical Field

[0001] The present invention relates to the field of liquid flow battery materials, and specifically provides a high-performance graphite-based composite material bipolar plate, a preparation method and applications. Background Art

[0002] Graphite-based composite bipolar plates are composite plates with a double-sided flow channel structure, made with graphite as the matrix and an organic resin as the binder. They are used in energy storage technologies such as flow batteries. Compared to pure graphite and metal bipolar plates, composite bipolar plates offer advantages such as high density, excellent corrosion resistance, high production efficiency, and ease of industrialization. However, the organic resin binder content in these bipolar plates is inversely proportional to electrical conductivity and directly proportional to mechanical properties. Therefore, achieving composite bipolar plates with both high mechanical properties and high electrical conductivity is a critical challenge in this field. Currently, there are two main methods for producing these bipolar plates using flexible graphite sheets. One involves forming low-density flexible graphite sheets into flow field plates in a single step, followed by resin impregnation and final curing. The other involves mixing expanded graphite powder with an organic solvent, semi-curing the mixture, and then performing compression molding. These processes are then followed by resin impregnation and final curing. Both methods require subsequent resin impregnation and cleaning, significantly reducing production efficiency.

[0003] CN 114937785 A discloses a composite graphite bipolar plate for a liquid flow battery and a preparation method thereof. By using a graphite fiber layer as an intermediate support layer, the prepared bipolar plate has both excellent conductivity and extremely high strength, thereby improving the bipolar plate's anti-bending and anti-flexural strength. At the same time, by using a low-density flexible graphite prefabricated plate, the pores inside the flexible graphite plate are fully filled, thereby improving the strength of the flexible graphite plate and preventing the bipolar plate from delamination or cracking during use. However, this process involves the preparation of graphite fiber paper, which places high demands on air stirring, screening equipment and the preparation process of graphite fiber paper; it involves the preparation of polymer support layers on both sides of the graphite fiber paper. Since the selected thermoplastic polymer material does not have good conductivity, after the graphite fiber paper is wrapped, while the mechanical properties are improved, it will also affect the overall conductivity; it involves hot pressing of flexible graphite prefabricated plates. During the process, the heating temperature is 30-100°C higher than the melting point of the polymer film, which will cause the polymer film between the graphite fiber paper and the flexible graphite prefabricated plate to melt, and some liquefied polymer materials will fill the pores of the flexible graphite, resulting in a decrease in the overall conductivity of the flexible graphite plate.

[0004] CN113346097B discloses a method for preparing graphite-based composite bipolar plates for proton exchange membrane fuel cells. The method comprises preparing a bulk molding compound (BMC) using graphite powder, thermosetting resin, amino-modified carbon nanotubes, and reinforcing fibers. The BMC is then subjected to a single compression molding process to produce the graphite-based composite bipolar plates. This process introduces bubbles during both the mixing and hot-pressing stages, which can negatively impact the density of the final product, and thus its electrical conductivity and mechanical properties. Furthermore, to improve the mechanical properties and chemical stability of the bipolar plates, acyl chloride-amidated carbon nanotubes must first be prepared. A multi-component resin slurry and the carbon nanotubes are then mixed. The resulting slurry is then mixed with graphite powder and glass fiber and allowed to stand for 36 hours for thickening and maturation, resulting in the BMC. The maturated BMC is then separated, weighed, and placed in a heated mold for hot pressing to produce the finished graphite-based composite bipolar plates. The entire process requires numerous steps and stations, resulting in low production efficiency.

[0005] CN111261893B discloses a highly conductive flexible graphite bipolar plate for flow batteries and its preparation and application. The process involves uniformly mixing expanded graphite powder and polyvinylidene fluoride (PVDF) powder in a mixer at a high loading factor, followed by cold pressing into a low-density blank. The blank is then vacuum-hot-pressed or roller-pressed into a high-density finished bipolar plate. To achieve uniform mixing of two powders with a significant density difference, the two powders are mechanically mixed in a paddle mixer with an ultra-high filler content (over 90%). This method allows for a single mixing volume of no more than 500g, and the mixing time is long, making it unsuitable for large-scale production, which requires efficient powder preparation. The process also requires the transfer, molding, and two or more pressing steps of the green sheet, resulting in a complex forming process. While the thermoplastic PVDF binder exhibits good mechanical properties, it lacks thermal stability and creep resistance, making it susceptible to deformation and failure at high operating temperatures.

[0006] CN115483403A discloses a highly conductive composite bipolar plate for fuel cells and its preparation method. The method involves uniformly mixing graphite powder and powdered ammonium bicarbonate, then pressing the mixture at room temperature and high pressure to form a bipolar plate-shaped graphite / ammonium bicarbonate composite plate. The mixture is then heated to volatilize the ammonium bicarbonate, resulting in a three-dimensional graphite skeleton. Finally, a liquid thermosetting resin is impregnated into the three-dimensional graphite skeleton under vacuum conditions and cured to produce a composite bipolar plate with a three-dimensional graphite conductive network. The ammonium bicarbonate used as a pore-forming agent in this process is thermally unstable and acutely toxic. The process requires numerous steps and has low production efficiency.

[0007] It can be seen that the currently provided processes are difficult to achieve industrial production of graphite-based composite bipolar plates with high conductivity and high air tightness.

[0008] In view of this, the present invention is proposed.

[0009] Summary of the Invention

[0010] The first object of the present invention is to provide a method for preparing a high-performance graphite-based composite material bipolar plate.

[0011] The second object of the present invention is to provide a high-performance graphite-based composite material bipolar plate prepared by the above preparation method.

[0012] The third object of the present invention is to provide the above-mentioned preparation method or application of the high-performance graphite-based composite material bipolar plate.

[0013] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0014] A method for preparing a high-performance graphite-based composite material bipolar plate comprises: mixing powders in a powder mixing system using a high-speed airflow; then heating and pressurizing the mixed powders in a mold under vacuum conditions in a molding system; then terminating the heating while maintaining the molding pressure; and when the temperature drops below the curing molding temperature of the resin, releasing the molding pressure, filling with air, and performing demolding.

[0015] The mold has a vacuum system.

[0016] The pressing operation is completed by a servo forming press with adjustable press speed and pressure holding function.

[0017] The heating operation is completed by a heating system with adjustable heating rate and heat preservation function.

[0018] The heating is performed to a temperature equal to or higher than the curing temperature of the selected resin.

[0019] Graphite paper is laid between the mold and the mixed powder, or a special release agent is coated on the molding surface of the mold.

[0020] The mixed powder comprises: 75wt.% to 85wt.% graphite powder, 15wt.% to 25wt.% resin powder, and the remainder is carbon black, carbon nanotubes and carbon fibers, wherein the mass ratio of carbon black: carbon nanotubes: carbon fibers is 1:(1-2):(1-2).

[0021] In some embodiments, the powder mixing method is to pass a high-speed airflow at a certain temperature into a sealed tank to ensure that the different powders are fully mixed in the airflow. The resin powder is softened by the airflow heating during the powder mixing process and is wrapped to a certain extent with other powders, especially graphite powder, to achieve a pre-bonding effect.

[0022] Furthermore, during the powder mixing operation, the high-speed air flow introduced is air, high-purity argon or high-purity nitrogen, preferably high-purity argon or high-purity nitrogen, the gas temperature is 10-280°C, the fluid velocity is 150-500m / s, and the air flow powder mixing time is 10-60min.

[0023] Preferably, the high-speed air flow velocity is 150 to 350 m / s, and the powder mixing time is 30 to 45 min.

[0024] Furthermore, the vacuum degree of the vacuum condition is 2.0×10 -3 ~5.5×10 -3 Pa, preferably 2.0×10 -3 ~3.5×10 -3 Pa.

[0025] Furthermore, during the heating and pressurizing operation, the pressurizing process involves increasing the forming pressure to a target value of 50-100 MPa at a predetermined rate. The heating process involves heating the mold to a temperature of 100-120°C at a predetermined rate once the forming pressure reaches 5-10 MPa. After a period of holding at this temperature, the mold temperature is then increased to a target temperature of 160-330°C at a predetermined rate, ensuring that the forming pressure reaches the target value simultaneously. The mold temperature is then held at this temperature for 1-10 minutes. The forming pressure is calculated by dividing the pressure displayed on the forming press's digital pressure gauge by the cross-sectional area of ​​the workpiece. The temperature is measured by contacting a tungsten-rhenium thermocouple with the mold's outer surface.

[0026] Furthermore, the heating and pressurizing operation includes: increasing the forming pressure to 70-85 MPa at a pressure increase rate of 3-5 MPa / min; when the forming pressure rises to above 10 MPa, increasing the temperature to 110-120°C at a heating rate of 25-35°C / min; keeping warm for 3-5 minutes; and then continuing to increase the mold temperature to the target value of 170-330°C at a heating rate of 10-15°C / min to ensure that the forming pressure reaches the target pressure value at the same time; and then keeping warm and pressurizing for 5-8 minutes.

[0027] Furthermore, the graphite powder has a size of 50 to 300 μm, the resin powder has a size of 10 to 100 μm, the carbon black powder has a size of 10 to 50 nm, the carbon nanotube has a size of 10 to 50 nm, and the carbon fiber has a size of 7 to 10 μm.

[0028] Preferably, the graphite powder is one or more of natural flake graphite powder, artificial graphite powder, and expanded graphite powder.

[0029] Furthermore, the mixed powder includes: 77wt.% to 80wt.% graphite powder, 18wt.% to 21wt.% resin powder, and the remainder is carbon black, carbon nanotubes and carbon fibers, wherein the mass ratio of carbon black: carbon nanotubes: carbon fibers is 1:(1-2):(1-2).

[0030] Preferably, the content of carbon black is 0.7 wt.% to 2.2 wt.%.

[0031] Preferably, the content of carbon nanotubes is 1.2 wt.% to 2.1 wt.%.

[0032] Preferably, the content of carbon fiber is 0.7 wt.% to 2.2 wt.%.

[0033] Furthermore, the resin powder as a binder phase can be one or more of thermoplastic phenolic resin powder, thermosetting phenolic resin powder, polypropylene resin powder, polyimide resin powder, polyphenylene sulfide powder, etc., preferably thermoplastic phenolic resin powder or polyphenylene sulfide powder.

[0034] The high-performance graphite-based composite material bipolar plate prepared by the above preparation method.

[0035] The above preparation method or application of high-performance graphite-based composite material bipolar plates in liquid flow batteries.

[0036] Compared with the prior art, the technical effects of the present invention are:

[0037] (1) The present invention uses high-speed airflow powder mixing technology to mix graphite-based composite material powders. On the one hand, it avoids the uneven distribution of powders caused by differences in density and particle size of different powder particles, especially improving the uniformity of carbon nanotubes and carbon fibers in the powder, which are more prone to entanglement and agglomeration. On the other hand, the increased kinetic energy of the powder under high-speed airflow promotes the pre-bonding of the resin powder with higher plasticity and other powders, especially graphite powder, to form a more uniform wrapping effect, thus laying the foundation for improving the structural uniformity of the final graphite-based composite material bipolar plate. In addition, compared with the traditional ball milling powder mixing process, this powder mixing technology process eliminates the process of separating the balls and powders after mixing, and is more suitable for the production requirements of large-scale, high-quality mixed powders.

[0038] (2) The present invention removes air from the surface of the graphite-based composite material powder through vacuum degassing, resulting in a more uniform distribution of the conductive phase particles, primarily graphite powder particles. This is a key factor in the material ultimately achieving a dense and uniform structure (see Figure 2). Vacuum degassing is performed before powder forming to increase the bulk density of the powder and achieve better filling properties. During the powder forming process, the forming powder inside the mold cavity is evacuated to ensure that no air gaps remain in the powder particles during the forming process.

[0039] (3) The present invention improves the overall electrical conductivity of the material by introducing carbon black, carbon nanotubes, etc., wherein the carbon nanotubes also play a bridging role between graphite particles, which can effectively increase the conductive path and avoid excessive resistivity caused by the graphite particles being completely wrapped by the resin.

[0040] (4) The present invention introduces carbon fibers and carbon nanotubes, which, on the one hand, can play a bridging role between graphite particles, increase the conductive path, and thus improve the overall conductivity of the material; on the other hand, carbon fibers and carbon nanotubes can enhance the mechanical properties of the material, especially the bending strength. By observing the microstructure of the material fracture (see Figure 3), it can be found that the carbon nanotubes are mostly in a pulled-out shape rather than a smooth cross-section, indicating that they play a role in hindering the development of cracks during the fracture process.

[0041] (5) The present invention lays flexible graphite paper between the graphite-based composite material powder and the upper and lower molds. On the one hand, this avoids the difficulty of demolding caused by the adhesion of resin to the mold during the forming process; on the other hand, the flexible graphite paper retained on the surface of the bipolar plate after forming has excellent conductivity, which avoids the appearance of resin residue on the surface and eliminates the need for surface cleaning and other processes. Although it has no effect on the bulk conductivity, it can improve the overall surface conductivity of the product and at the same time improve the production efficiency of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The various technical features of the present invention and the relationships between them are further explained below with reference to the accompanying drawings. The accompanying drawings are exemplary, and some technical features are not shown in actual proportion. In addition, some drawings may omit technical features that are commonly used in the technical field to which the present invention belongs and are not essential for understanding and implementing the present invention, or additional technical features that are not essential for understanding and implementing the present invention may be shown. In other words, the combination of the various technical features shown in the accompanying drawings is not intended to limit the present invention. In addition, throughout the present invention, the same figure numbers refer to the same content. The specific description of the drawings is as follows:

[0043] FIG1 is a schematic flow diagram of a preparation method according to the present invention;

[0044] FIG2 is a low-magnification fracture microscopic morphology of a high-performance graphite-based composite material bipolar plate product prepared according to Example 1 of the preparation method of the present invention;

[0045] FIG3 is a high-magnification fracture microscopic morphology of a high-performance graphite-based composite material bipolar plate product prepared according to Example 2 of the preparation method of the present invention. DETAILED DESCRIPTION

[0046] Hereinafter, specific embodiments of the present invention will be described in detail.

[0047] Flow batteries: Flow batteries consist of a stack unit, electrolyte, electrolyte storage and supply unit, and management and control unit. Flow batteries store and release electrical energy through reactions between active substances in the battery's positive and negative electrolytes, controlled by cyclic conversion between different electrolytes. Flow batteries offer advantages such as high safety, long cycle life, flexible design, and low maintenance costs. They are an emerging area of ​​the battery industry, facilitating parallel design and promising the rapid fulfillment of large and medium-sized energy storage and peak-shaving needs.

[0048] Bipolar plates: As an important component of flow batteries, bipolar plates serve to separate and connect cells in series, conduct current, and provide structural support for the battery stack. Currently, the cost of bipolar plates accounts for approximately 40% of the total cost of flow batteries. The bipolar plate material must be a good conductor of heat and electricity to ensure uniform temperature distribution throughout the flow battery during operation, facilitate heat dissipation, conduct electricity, and improve the efficiency of the flow battery. At the same time, since the electrolyte in the flow battery is corrosive, the material must have stable chemical properties and good corrosion resistance. In addition, as the connection between single cells, the bipolar plate is responsible for supporting the entire flow battery. Therefore, the bipolar plate is required to have good mechanical properties and high strength to ensure the stability of the battery stack during assembly. Common materials used to make bipolar plates are graphite, metal, and composite materials.

[0049] Composite bipolar plates: Composite bipolar plates are simple to manufacture, significantly reducing costs and enabling large-scale production. Made from a polymer resin and carbon composite material, they offer advantages over metal bipolar plates, such as corrosion resistance and lightweight.

[0050] In some embodiments, the preparation method provided by the present invention is implemented using the following system:

[0051] The powder mixing system is used to mix the mixed powders obtained according to the proportion. The high-speed airflow is introduced into the closed mixing tank to achieve uniform mixing of the powders, and the mixed powders are collected at the bottom of the mixing tank.

[0052] The vacuum system is controlled to evacuate the powder in the mold cavity in the mold; the mold is provided with a vacuum system.

[0053] The controlled forming system is used to fill the powder into the mold cavity for molding, and cooperates with the heating system to pressurize the liquefied resin into the gaps between the graphite powder, carbon black, carbon nanotubes and carbon fibers. The pressing operation is completed by a servo forming press with settable pressurization rate and pressure holding function.

[0054] The heating system is controlled to set the heating rate and the holding time, so as to liquefy the resin powder in the mixed powder and cooperate with the forming system to complete the compression forming of the graphite-based composite material bipolar plate.

[0055] The present invention provides a method for preparing a high-performance graphite-based composite material bipolar plate, wherein graphite powder is used as a matrix powder, a resin is used as an organic binder, carbon black and carbon nanotubes are used as reinforcing phases to improve electrical conductivity, and carbon nanotubes and carbon fibers are used as reinforcing phases to improve mechanical properties. The above raw materials are mixed to obtain a mixed powder. In a powder mixing system, a high-speed airflow is used to mix the powders. Then, in a molding system, the mixed powders in the mold are heated and pressurized under vacuum conditions. The specific heating temperature is heated to above the curing forming temperature of the resin, and the heat and pressure are maintained for a period of time. Then, the heating is terminated and the forming pressure is continued to be maintained (applied to the powder surface by a press through the mold). When the temperature drops below the curing forming temperature of the resin, the forming pressure is removed (the press stops pressurizing) and air is filled in (ensuring that the air pressure in the mold cavity is equal to the external air pressure, facilitating smooth opening of the mold and smooth demolding of the sample), and demolding is performed. During the preparation process, graphite paper is laid between the mold and the mixed powder or a special release agent is applied to the mold forming surface to prevent the product from adhering to the mold.

[0056] The present invention designs a new graphite-based resin composite mixed powder for bipolar plates, which adopts airflow powder mixing and vacuum powder forming technology to achieve efficient production of high-performance graphite-based composite material bipolar plates. In the present invention, high-efficiency and high-quality mixing of powders is achieved through high-speed airflow, which can not only improve the uniformity of powders, especially fiber powders (such as carbon nanotubes and carbon fiber powders), but also promote the resin powder to form a good pre-bonding effect on graphite powder, providing a good foundation for the uniformity of the structure and high conductivity and high mechanical properties of the final product; a layer of conductive flexible graphite paper is laid between the powder and the mold, or a special release agent is applied to the mold forming surface to ensure that there is no adhesion between the product and the mold during the heating and forming process and after the forming process is completed; vacuum conditions are maintained during the heating and forming process, and the vacuum degassing process method is used to significantly reduce the adverse effects of gas adsorbed on the powder surface during the forming process on the structure density; the mixed powder is subjected to pressurized heating treatment under vacuum conditions to achieve one-step forming, and a graphite-based composite material bipolar plate with high conductivity, high airtightness and high mechanical properties is obtained. Compared with the current forming method of pressing followed by resin impregnation and post-treatment, the process method of the present invention is more suitable for the mass production of high-performance graphite-based composite material bipolar plates.

[0057] Specifically, the mixed powder includes: 75wt.% to 85wt.% graphite powder, 15wt.% to 25wt.% resin powder, and the remainder is carbon black, carbon nanotubes and carbon fibers, wherein the mass ratio of carbon black, carbon nanotubes and carbon fibers is 1:(1~2):(1~2). Among them, the content of graphite powder can be but is not limited to 75wt.%, 76wt.%, 77wt.%, 78wt.%, 79wt.%, 80wt.%, 81wt.%, 82wt.%, 83wt.%, 84wt.% or 85wt.%; the graphite powder can be, for example, artificial graphite powder, natural flake graphite powder, expanded graphite powder, etc.; the content of resin powder can be but is not limited to 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.%, 20wt.%, 21wt.%, 22wt.%, 23wt.%, 24wt.% or 25wt.%; the resin powder can be, for example, thermosetting phenolic resin powder, thermoplastic phenolic resin powder, polypropylene resin powder, polyimide resin powder, polyphenylene sulfide powder, etc.

[0058] In some embodiments, a mold with a flow channel cavity can be selected for efficient production of high-performance graphite-based composite bipolar plates.

[0059] The preparation method of the present invention can be carried out according to the following steps, and the process flow is shown in Figure 1:

[0060] Step 1: Weigh the graphite-based composite material powder: After mixing graphite powder (mass fraction 75wt.% to 85wt.%), resin powder (mass fraction 15wt.% to 25wt.%), carbon black, carbon nanotubes and carbon fibers (mass fraction 0 to 10wt.%) in a certain proportion, put them into an air flow powder mixing system for mixing.

[0061] In a preferred embodiment, the graphite powder has a size range of 50 to 300 μm and a mass fraction of 77 wt.% to 80 wt.%; the resin powder is preferably one or more of thermosetting phenolic resin powder, thermoplastic phenolic resin powder, polypropylene resin powder, polyimide resin powder, and polyphenylene sulfide powder as a binder phase, and its powder size range is 10 to 100 μm, and its mass fraction is 18 wt.% to 21 wt.%; the carbon black powder has a size range of 10 to 50 nm and a mass fraction of 0.7 wt.% to 2.2 wt.%; the carbon nanotube has a size range of 10 to 50 nm and a mass fraction of 1.2 wt.% to 2.1 wt.%; and the remainder is carbon fiber, and the size of the carbon fiber ranges from 7 to 10 μm. ； The ball-to-material ratio is 2:1.

[0062] In a preferred embodiment, the batched graphite-based composite material powder is placed in a powder mixing system, which is then sealed and introduced with compressed air at a temperature of 130 to 280°C at a high-speed airflow rate of 150 to 350 m / s for 30 to 45 minutes. The air flow is then stopped, and the mixed powder is collected and removed.

[0063] Step 2: Lay conductive graphite paper (carbon content>99wt.%, thickness 0.1-0.5mm) on the upper and lower surfaces of the mold press head, or spray a special release agent on the upper and lower surfaces of the mold press head.

[0064] Step 3: Fill the powder and smooth the surface of the powder.

[0065] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.0 -3 ~5.5×10 -3 Pa, vacuum for 5 to 10 minutes. The vacuum degree is maintained at 2.0 by vacuuming for 5 to 10 minutes. -3 ~5.5×10 -3 Pa, continuous vacuuming is also required to maintain the vacuum degree in the subsequent process.

[0066] In a preferred embodiment, the vacuum degree in the mold cavity is drawn to 2.0 before the powder is formed. -3 ~3.5×10 -3 Pa, vacuum for 10 minutes.

[0067] Step 5: Continue to evacuate the mold and increase the forming pressure to 50-100 MPa at a certain rate. When the forming pressure reaches 5-10 MPa, start heating the mold at a certain rate. When the mold temperature reaches 100-120°C, keep it warm for a while, then continue to heat it at a certain rate until the target temperature reaches 160-330°C. Ensure that the forming pressure reaches the target pressure value of 50-100 MPa at the same time, and keep it warm and pressurized for 1-10 minutes.

[0068] It should be noted that pressurization and heating are carried out in stages (the time used for the two may be different). The first stage is the pressurization stage. In the unheated stage, the forming pressure is increased to 50-100MPa at a certain pressure increase rate. Heating begins when the forming pressure rises to 5-10MPa, first rising to 100-120°C at a certain temperature increase rate, keeping warm for a period of time, and then rising to the final target temperature of 160-330°C at a certain temperature increase rate. When setting the pressure increase rate, temperature increase rate and holding time, it should be ensured that the forming pressure and forming temperature reach the target values ​​at the same time, that is, when the forming pressure rises to the final target pressure value of 50-100MPa, the heating temperature is raised to the target value of 160-330°C, followed by holding and pressure for 1-10 minutes.

[0069] In a preferred embodiment, the forming pressure is increased to 70-85 MPa at a pressure increase rate of 3-5 MPa / min. When the forming pressure rises to above 10 MPa, the temperature in the forming chamber is increased to 110-120°C at a heating rate of 25-35°C / min. After keeping warm for 3-5 minutes, the temperature is continued to be increased to 170-330°C at a heating rate of 10-15°C / min, and then kept warm and pressurized for 5-8 minutes.

[0070] Step 6: After the insulation is completed, continue to maintain the molding pressure, cool it down with the furnace to below the resin curing temperature, release the molding pressure and fill the mold with air, and demold the molded product from the mold.

[0071] In a preferred embodiment, after the heat preservation and pressure preservation are completed, the mold is cooled to below 80° C. in the furnace, air is filled into the mold, and the molded product is demolded and taken out from the mold.

[0072] Example 1

[0073] This example uses vacuum powder forming to produce graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), and a mold wall thickness of 80 mm. A bidirectional pressing process is used, with the upper and lower pressing molds measuring 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plate is formed in a vacuum powder forming furnace. The specific steps are as follows:

[0074] Step 1: Using graphite-based composite material powder: 80wt.% of 75-150μm natural flake graphite powder, 15wt.% of BR2123F thermoplastic phenolic resin powder, 1wt.% of 10-30nm carbon black, 2wt.% of 10-30nm carbon nanotubes, and 2wt.% of 5-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed air for mixing. The gas temperature is 130°C, the air flow velocity is 200m / s, and the mixing time is 45min.

[0075] Step 2: Lay conductive graphite paper (carbon content > 99%, thickness 0.1 mm) on the upper and lower surfaces of the mold press head.

[0076] Step 3: Fill the powder and smooth the surface of the powder.

[0077] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0078] Step 5: Continue to evacuate the chamber and increase the forming pressure to 75 MPa at a rate of 3 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 110°C at a rate of 25°C / min. Keep warm for 5 minutes, then continue to increase the temperature to 175°C at a rate of 10°C / min, and then keep warm and maintain pressure for 5 minutes.

[0079] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 80°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0080] Example 2

[0081] This example uses vacuum powder forming to produce graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), and a mold wall thickness of 80 mm. A bidirectional pressing process is used, with the upper and lower pressing molds measuring 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plate is formed in a vacuum powder forming furnace. The specific steps are as follows:

[0082] Step 1: Using graphite-based composite material powder: 78wt.% of 48-70μm expanded graphite powder, 18wt.% of P-4 polyphenylene sulfide powder, 1wt.% of 30-50nm carbon black, 2wt.% of 10-30nm carbon nanotubes, and 1wt.% of 7-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed high-purity nitrogen for mixing. The gas temperature is 280°C, the air flow velocity is 150m / s, and the mixing time is 35min.

[0083] Step 2: Spray 717 super dry release agent on the forming surface of the mold, place it in a drying oven, dry it at 100°C for 10 minutes, and take out the mold for use.

[0084] Step 3: Fill the powder and smooth the surface of the powder.

[0085] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0086] Step 5: Continue to evacuate the chamber and increase the forming pressure to 85 MPa at a rate of 5 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 120°C at a rate of 30°C / min. Keep warm for 4 minutes, then continue to increase the temperature to 310°C at a rate of 10°C / min, and then keep warm and maintain pressure for 10 minutes.

[0087] Step 6: After the insulation is completed, the forming pressure is continued to be maintained, and the furnace is cooled to 120°C. The forming pressure is released and air is filled into the mold. The mold is opened and the molded product is demolded and taken out.

[0088] Example 3

[0089] This example uses vacuum powder forming to produce graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), and a mold wall thickness of 80 mm. A bidirectional pressing process is used, with the upper and lower pressing molds measuring 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plate is formed in a vacuum powder forming furnace. The specific steps are as follows:

[0090] Step 1: Using graphite-based composite material powder: 76wt.% of 150-300μm natural flake graphite powder, 18wt.% of SA-848 thermoplastic solid acrylic resin, 2wt.% of 10-30nm carbon black, 2wt.% of 30-50nm carbon nanotubes, and 2wt.% of 7-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed air for mixing. The gas temperature is 155°C, the air flow velocity is 300m / s, and the mixing time is 35min.

[0091] Step 2: Lay conductive graphite paper (carbon content > 99%, thickness 0.2 mm) on the upper and lower surfaces of the mold press head.

[0092] Step 3: Fill the powder and smooth the surface of the powder.

[0093] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0094] Step 5: Continue to evacuate the chamber and increase the forming pressure to 70 MPa at a rate of 5 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 120°C at a rate of 35°C / min. Keep warm for 5 minutes, then continue to increase the temperature to 185°C at a rate of 15°C / min, and then keep warm and maintain pressure for 8 minutes.

[0095] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 85°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0096] Comparative Example 1

[0097] This comparative example uses vacuum powder forming to produce graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), and a mold wall thickness of 80 mm. A bidirectional pressing process is used, with the upper and lower pressing mold dimensions of 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plates are formed in a vacuum powder forming furnace. The specific steps are as follows:

[0098] Step 1: Using graphite-based composite material powder: 69wt.% of 75-150μm natural flake graphite powder, 26wt.% of BR2123F thermoplastic phenolic resin powder, 1wt.% of 10-30nm carbon black, 2wt.% of 10-30nm carbon nanotubes, and 2wt.% of 5-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed air for mixing. The gas temperature is 130°C, the air flow velocity is 200m / s, and the mixing time is 45min.

[0099] Step 2: Lay conductive graphite paper (carbon content > 99%, thickness 0.1 mm) on the upper and lower surfaces of the mold press head.

[0100] Step 3: Fill the powder and smooth the surface of the powder.

[0101] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0102] Step 5: Continue to evacuate the chamber and increase the forming pressure to 75 MPa at a rate of 3 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 110°C at a rate of 25°C / min. Keep warm for 5 minutes, then continue to increase the temperature to 175°C at a rate of 10°C / min, and then keep warm and maintain pressure for 5 minutes.

[0103] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 80°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0104] Compared with Example 1, the difference of this comparative example is that the ratio of the graphite-based composite material powder in step 1 is different.

[0105] Comparative Example 2

[0106] This comparative example uses vacuum powder forming to prepare graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), a mold wall thickness of 80 mm, and a bidirectional pressing process. The upper and lower pressing molds measure 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plates are formed in a vacuum powder forming furnace. The specific steps are as follows:

[0107] Step 1: Using graphite-based composite material powder: 78wt.% of 48-70μm expanded graphite powder, 18wt.% of P-4 polyphenylene sulfide powder, 1wt.% of 30-50nm carbon black, 2wt.% of 10-30nm carbon nanotubes, and 1wt.% of 7-10μm carbon fiber are mixed and placed in a planetary ball mill with a ball-to-material ratio of 1:1, a rotation speed of 300r / min, and a ball mill mixing time of 120min.

[0108] Step 2: Spray 717 super dry release agent on the forming surface of the mold, place it in a drying oven, dry it at 100°C for 10 minutes, and take out the mold for use.

[0109] Step 3: Fill the powder and smooth the surface of the powder.

[0110] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0111] Step 5: Continue to evacuate the chamber and increase the forming pressure to 85 MPa at a rate of 5 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 120°C at a rate of 30°C / min. Keep warm for 4 minutes, then continue to increase the temperature to 310°C at a rate of 10°C / min, and then keep warm and maintain pressure for 10 minutes.

[0112] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 120°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0113] Compared with Example 2, this comparative example is different in that a planetary ball mill is used for powder mixing in step 1.

[0114] Comparative Example 3

[0115] This comparative example uses vacuum powder forming to prepare graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), a mold wall thickness of 80 mm, and a bidirectional pressing process. The upper and lower pressing molds measure 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plates are formed in a vacuum powder forming furnace. The specific steps are as follows:

[0116] Step 1: Using graphite-based composite material powder: 78wt.% of 48-70μm expanded graphite powder, 18wt.% of P-4 polyphenylene sulfide powder, 1wt.% of 30-50nm carbon black, 2wt.% of 10-30nm carbon nanotubes, and 1wt.% of 7-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed high-purity nitrogen for mixing. The gas temperature is room temperature, the air flow velocity is 150m / s, and the mixing time is 35min.

[0117] Step 2: Spray 717 super dry release agent on the forming surface of the mold, place it in a drying oven, dry it at 100°C for 10 minutes, and take out the mold for use.

[0118] Step 3: Fill the powder and smooth the surface of the powder.

[0119] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0120] Step 5: Continue to evacuate the chamber and increase the forming pressure to 85 MPa at a rate of 5 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 120°C at a rate of 30°C / min. Keep warm for 4 minutes, then continue to increase the temperature to 310°C at a rate of 10°C / min, and then keep warm and maintain pressure for 10 minutes.

[0121] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 120°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0122] Compared with Example 2, this comparative example is different in that the gas temperature in step 1 is room temperature.

[0123] Comparative Example 4

[0124] This comparative example uses vacuum powder forming to prepare graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), a mold wall thickness of 80 mm, and a bidirectional pressing process. The upper and lower pressing molds measure 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plates are formed in a vacuum powder forming furnace. The specific steps are as follows:

[0125] Step 1: Using graphite-based composite material powder: 76wt.% of 150-300μm natural flake graphite powder, 18wt.% of SA-848 thermoplastic solid acrylic resin, 2wt.% of 10-30nm carbon black, 2wt.% of 30-50nm carbon nanotubes, and 2wt.% of 7-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed air for mixing. The gas temperature is 155°C, the air flow velocity is 300m / s, and the mixing time is 35min.

[0126] Step 2: Lay conductive graphite paper (carbon content > 99%, thickness 0.2 mm) on the upper and lower surfaces of the mold press head.

[0127] Step 3: Fill the powder and smooth the surface of the powder.

[0128] Step 4: Increase the forming pressure to 70 MPa at a rate of 5 MPa / min. When the forming pressure rises to above 10 MPa, increase the temperature in the forming chamber to 120°C at a rate of 35°C / min. Keep warm for 5 minutes, then continue to increase the temperature to 185°C at a rate of 15°C / min, and then keep warm and pressurized for 8 minutes.

[0129] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 85°C with the furnace, remove the forming pressure, open the mold and demold the molded product.

[0130] Compared with Example 3, this comparative example is different in that there is no vacuum treatment in steps 3 and 4.

[0131] Comparative Example 5

[0132] Comparative Example 5 uses vacuum powder forming to prepare graphite-based composite bipolar plates with dimensions of 400 × 300 × 5 mm (length × width × thickness). The bipolar plate forming mold has an inner cavity dimension of 400 × 300 × 15 mm (length × width × height), a mold wall thickness of 80 mm, and a bidirectional pressing process. The upper and lower pressing molds have dimensions of 399.9 × 299.9 × 12 mm and 399.9 × 299.9 × 20 mm, respectively. The bipolar plate is formed in a vacuum powder forming furnace. The specific steps are as follows:

[0133] Step 1: Using graphite-based composite material powder: 76wt.% of 150-300μm natural flake graphite powder, 18wt.% of SA-848 thermoplastic solid acrylic resin, 2wt.% of 10-30nm carbon black, 2wt.% of 30-50nm carbon nanotubes, and 2wt.% of 7-10μm carbon fiber are mixed and placed in a powder mixing system, sealed and introduced with compressed air for mixing. The gas temperature is 155°C, the air flow velocity is 300m / s, and the mixing time is 35min.

[0134] Step 2: Lay conductive graphite paper (carbon content > 99%, thickness 0.2 mm) on the upper and lower surfaces of the mold press head.

[0135] Step 3: Fill the powder and smooth the surface of the powder.

[0136] Step 4: Close the mold and perform vacuum degassing in a vacuum powder forming furnace with a vacuum degree of 2.5×10 -3 Pa, vacuum for 10 minutes.

[0137] Step 5: Continue to evacuate the chamber, increase the forming pressure to 70 MPa at a rate of 5 MPa / min, and simultaneously increase the temperature in the forming chamber to 185°C at a rate of 13°C / min, and then maintain the temperature and pressure for 8 minutes.

[0138] Step 6: After the insulation is completed, continue to maintain the forming pressure, cool to 85°C with the furnace, remove the forming pressure and fill the mold with air, open the mold and demold the molded product.

[0139] Compared with Example 3, the difference in this comparative example is that in step 5, the temperature and pressure are increased simultaneously.

[0140] Example 4

[0141] The high-performance graphite-based composite bipolar plate products prepared in Example 1 and Example 2 were used as samples for fracture morphology observation.

[0142] 90×30×5 mm specimens were cut from the middle of the products of Example 1, Example 2, and Example 3 by wire cutting. Three specimens were cut from each example. The flexural strength of the specimens was tested using the three-point bending method on a universal testing machine with a support span of 50 mm. The flexural strength of the tested specimens was calculated according to the following formula:

[0143] Where:

[0144] σ—flexural strength, unit is MPa;

[0145] P—breaking load value, unit is Newton (N);

[0146] L—support span, in millimeters (mm);

[0147] b—the width of the plate sample being tested, in millimeters (mm);

[0148] h—the thickness of the plate sample being tested, in millimeters (mm).

[0149] Three valid test samples were taken as a group, and the average value was calculated as the test result. The results are shown in Table 1.

[0150] The fracture morphology of the specimens from Examples 1 and 2 after three-point bending was observed under a Zeiss Gemini SEM 500 field emission scanning electron microscope. Figure 2 shows a 500x magnification, and Figure 3 shows a 30,000x magnification. It can be seen that the conductive phase particles, primarily graphite powder particles, are evenly distributed, while the carbon nanotubes mostly have an extended shape rather than a smooth cross-section, indicating that they hinder crack growth during the fracture process.

[0151] Example 5

[0152] 45×45×5 mm specimens were cut from the middle of the products of Example 1, Example 2, and Example 3 by wire cutting. Three specimens were cut from each example sample. The compressive strength of the specimens was tested on a universal testing machine. The compressive strength of the tested specimens was calculated according to the following formula:

[0153] Where:

[0154] P—compressive strength, unit is MPa;

[0155] Q—the maximum load value when the sample breaks, in Newton (N);

[0156] S—the area of ​​the sample's pressure surface, in square millimeters (mm 2 ).

[0157] Three valid test samples were taken as a group, and the average value was calculated as the test result. The results are shown in Table 1.

[0158] Example 6

[0159] The electrical conductivity, contact resistance, air tightness, density, hardness, etc. of the composite material bipolar plates prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were tested. The test results are shown in Table 1.

[0160] Table 1 Performance of composite bipolar plates of Examples 1 to 3 and Comparative Examples 1 to 5

[0161] The preferred powder forming process conditions of the above embodiment are obtained based on a single-variable scientific experimental design and a large number of experimental explorations. Under these conditions, the comprehensive performance of the graphite-based composite material bipolar plate prepared by the vacuum powder forming method is better. Comparative experiments were conducted on the following process parameters, which are described in detail as follows: (1) In the process of selecting powder components, mixed powders with different graphite and resin contents were prepared and standard-sized samples were prepared. Performance testing and microstructure analysis found that when the resin powder content was higher than 25wt.%, the conductivity of the sample was significantly reduced. For example, the sample with a resin powder content of 26wt.% had a conductivity of 51.8S / cm due to the reduced contact between the graphite powders caused by the high content of resin. (2) Using powders of the same composition as raw materials, powder mixing experiments were conducted in an air flow mixing system and an ordinary planetary ball mill (the ball-to-material ratio was 1:1). The mixed powders were then used to prepare samples under the same subsequent process conditions. Comparison of the microstructures revealed that the samples obtained from the powders prepared in the air flow mixing system had a more uniform microstructure, especially the distribution of fiber powders (such as carbon fibers and carbon nanotubes) was significantly more uniform than that of the samples prepared from ball milled powders, with no obvious agglomeration observed. (3) When the temperature of the injected gas was controlled at 30-45°C below the curing temperature of the selected resin powder, the distribution of the resin phase between the graphite powders in the final sample was further improved compared to the sample prepared from room temperature gas. After preparing multiple groups of samples, it was found that the electrical conductivity of the different samples obtained from the powders prepared in the air flow mixing system was basically consistent, and the mechanical properties were also better than those of the samples prepared from ball milled powders. (4) Using powders of the same composition and airflow as raw materials, samples were prepared under vacuum and non-vacuum conditions. Comparison of the tissues revealed that the sample prepared after vacuum had a higher density and no microscopic holes were observed in the tissue. The density of the sample prepared without vacuum was relatively low, only 1.66 g / cm 3 , there are tiny holes in the microstructure. (5) The experimental results show that the samples prepared by simultaneous temperature and pressure increase are not completely discharged due to the separation of gas on the surface of the graphite powder during heating. The gas enters the liquid resin solution and cannot be completely discharged, which eventually leads to the formation of pores inside the resin phase. On the one hand, it reduces the density of the product, and on the other hand, it also reduces the final mechanical properties of the product. After a large number of comparative experiments, it was found that the graphite-based composite bipolar plate prepared by the vacuum powder forming method of the present invention has the best comprehensive performance.

[0162] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the technical concept of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance graphite-based composite material bipolar plate, characterized in that: The preparation method comprises: mixing powders by using high-speed airflow in a powder mixing system, then heating and pressurizing the mixed powders in a mold under vacuum conditions in a molding system, then terminating the heating and continuing to maintain the molding pressure, and when the temperature drops below the curing molding temperature of the resin, removing the molding pressure and filling with air to perform demolding; The mold is provided with a vacuum system; The pressurizing operation is performed by a servo forming press machine with a settable pressurizing rate and pressure holding function; The heating operation is completed by a heating system with a settable heating rate and heat preservation function; The heating is heating to a temperature above the curing temperature of the selected resin; In the heating and pressurizing operation, the pressurizing includes continuously increasing the forming pressure to 50-100 MPa at a certain pressure increase rate; the heating includes starting to increase the temperature to 100-120° C. when the forming pressure increases to 5-10 MPa, and after heat preservation, continuing to increase the temperature to 160-330° C. at a certain temperature increase rate to achieve the forming pressure and temperature reaching the target value at the same time, and then heat preservation and pressure preservation for 1-10 minutes; Graphite paper is laid between the mold and the mixed powder; The mixed powder comprises: 75wt.% to 85wt.% of graphite powder, 15wt.% to 25wt.% of resin powder, and the remainder is carbon black, carbon nanotubes and carbon fibers, the sum of the weight percentages of the above components is 100%, wherein the mass ratio of carbon black: carbon nanotubes: carbon fibers is 1:(1-2):(1-2); In the powder mixing operation, the gas used in the high-speed air flow is air, high-purity argon or high-purity nitrogen, the gas temperature is 10-280° C., the gas flow rate is 150-500 m / s, and the air flow powder mixing time is 10-60 min; The vacuum degree of the vacuum condition is 2.0×10 -3 ~5.5×10 -3 Pa.

2. The preparation method according to claim 1, characterized in that: The forming pressure value is obtained by dividing the pressure value displayed by the digital pressure gauge of the forming press by the cross-sectional area of ​​the workpiece; The temperature is obtained by contacting the outer surface of the mold with a tungsten-rhenium thermocouple.

3. The preparation method according to claim 1, characterized in that: The heating and pressurizing operation includes: increasing the forming pressure to 70-85MPa at a pressure increase rate of 3-5MPa / min; when the forming pressure rises to above 10MPa, increasing the mold temperature to 110-120°C at a heating rate of 25-35°C / min; keeping the temperature for 3-5min; and then continuing to increase the mold temperature to a target value of 170-330°C at a heating rate of 10-15°C / min to ensure that the forming pressure reaches the target pressure value at the same time; and then keeping the temperature and pressure for 5-8min.

4. The preparation method according to claim 1, characterized in that: The size of graphite powder is 50-300 μm, the size of resin powder is 10-100 μm, the size of carbon black powder is 10-50 nm, the size of carbon nanotube is 10-50 nm, and the size of carbon fiber is 7-10 μm; The graphite powder is one or more of natural flake graphite powder, artificial graphite powder and expanded graphite powder; The resin powder is one or more of thermoplastic phenolic resin powder, thermosetting phenolic resin powder, polypropylene resin powder, polyimide resin powder and polyphenylene sulfide powder.

5. The preparation method according to claim 1, characterized in that: The mixed powder includes: 77wt.% to 80wt.% graphite powder, 18wt.% to 21wt.% resin powder, and the remainder is carbon black, carbon nanotubes and carbon fibers, wherein the mass ratio of carbon black: carbon nanotubes: carbon fibers is 1:(1-2):(1-2).

6. The preparation method according to claim 4, characterized in that: The content of carbon black is 0.7wt.% to 2.2wt.%, the content of carbon nanotubes is 1.2wt.% to 2.1wt.%, and the content of carbon fiber is 0.7wt.% to 2.2wt.%.

7. A high-performance graphite-based composite material bipolar plate prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the preparation method according to any one of claims 1 to 6 or the high-performance graphite-based composite bipolar plate according to claim 7 in a liquid flow battery.

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