Graphite bipolar plates, their preparation methods and applications

Abstract

This invention provides a graphite bipolar plate, its preparation method, and its application. The preparation method includes: expanding graphite raw material to obtain graphite worms, mixing them with reinforcing materials and binders, performing mechanochemical activation treatment to obtain a modified graphite substrate, molding, and sequentially performing resin impregnation and curing treatments to obtain impregnated monopolar plates, which are then bonded together to obtain a graphite bipolar plate. The reinforcing material includes carbon materials, and the binder includes one or more of polyarylacetylene, polyurethane, dicyandiamide, and resorcinol. This invention introduces a mechanochemical activation process in the preparation of graphite bipolar plates for fuel cells. It utilizes reinforcing materials to improve the bending resistance of the final product, and uses binders to increase the density and formability of the substrate and further increase its mechanical strength, resulting in a modified graphite substrate for electrode preparation. This significantly improves the bending strength of the electrode without affecting its conductivity, thereby increasing the overall lifespan of the fuel cell system.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and more specifically, to a graphite bipolar plate, its preparation method, and its application. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is a type of fuel cell that converts chemical energy into electrical energy. It comprises an anode plate, a cathode plate, and a solid polymer proton exchange membrane. The bipolar plate is one of the core components of a PEMFC, serving to disperse gas and transfer current; its cost accounts for approximately 30% of the entire fuel cell stack. Therefore, bipolar plates must possess excellent corrosion resistance, electrical conductivity, hydrophilicity, and low cost.

[0003] The internal environment of a proton exchange membrane fuel cell is generally acidic. This acidic environment corrodes the bipolar plates, and areas rich in acidic liquid exhibit strong electrochemical corrosion behavior during prolonged operation. The basic materials for fuel cell bipolar plates are broadly classified into carbon-based and metal-based materials. Since no single material can perfectly meet all the requirements for a bipolar plate, such as gas permeability resistance, electrical conductivity, mechanical strength, corrosion resistance, and low cost, composite materials or coating materials are also used in bipolar plate manufacturing. Based on the material, bipolar plates can be classified into graphite bipolar plates, metal bipolar plates, and composite bipolar plates.

[0004] Graphite materials possess excellent corrosion resistance and electrical conductivity, making them ideal bipolar plate materials for fuel cells. However, they suffer from drawbacks such as low strength, high brittleness, high processing costs, and difficulty in thinning. Metallic materials, including stainless steel, aluminum alloys, and titanium alloys, offer advantages such as high strength, low cost, and ease of processing. However, metallic materials are highly susceptible to corrosion and oxidation during fuel cell operation, affecting the conductivity of the bipolar plate, increasing ohmic losses, and thus impacting the lifespan of the entire system. Therefore, metallic bipolar plates generally require surface treatment or coating to improve their corrosion resistance. Composite materials, which combine graphite, metallic materials, and various resins or polymers, can balance electrical conductivity, corrosion resistance, and mechanical properties. However, their manufacturing processes are complex and generally costly.

[0005] Currently, due to the inherent drawbacks of graphite bipolar plates, such as brittleness, low strength, and processing difficulties, the common solution is to incorporate polymer resins into the graphite substrate. The resulting composite graphite plates possess bending resistance, corrosion resistance, and excellent electrical and thermal conductivity, making them one of the most commonly used bipolar plates. However, current methods for preparing composite graphite plates primarily focus on improving the strength and other properties of graphite bipolar plates through adjustments to graphite resin formulations and impregnation ratios. At present, the low strength and high brittleness of the graphite substrate remain largely unresolved, constituting a major limitation to their widespread application.

[0006] Currently, the graphite bipolar plates used in conventional proton exchange membrane fuel cells are generally produced by first modifying and expanding natural graphite raw materials at high temperatures to form expanded graphite substrates. These expanded graphite substrates are then rolled into flexible pre-pressed plates, which are then vacuum-injected and impregnated with polymer resins before being pressed into shape to obtain monopolar plates with flow channels. Finally, they are bonded and cured to form commercially viable bipolar plates. However, due to the high porosity of expanded graphite, two issues arise: firstly, it affects the conductivity of the bipolar plate, and secondly, it affects the overall airtightness of the plate. Furthermore, the bending strength of bipolar plates formed using this method is not well addressed, failing to meet the requirements for long-term support of fuel cells. Summary of the Invention

[0007] The main objective of this invention is to provide a graphite bipolar plate, its preparation method, and its application, in order to solve the problem that existing fuel cell bipolar plates cannot simultaneously achieve conductivity and bending strength.

[0008] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a graphite bipolar plate is provided, comprising the following steps: Step S1, expanding graphite raw material to obtain graphite worms; Step S2, mixing the graphite worms with reinforcing materials and binders, and performing mechanochemical activation treatment to obtain a modified graphite substrate; Step S3, molding the modified graphite substrate to obtain a monopolar plate; Step S4, sequentially subjecting the monopolar plate to resin impregnation and curing treatment to obtain an impregnated monopolar plate; Step S5, bonding the impregnated monopolar plates to obtain a graphite bipolar plate; wherein the reinforcing material includes carbon materials, and the binder includes one or more of polyarylacetylene, polyurethane, dicyandiamide, and resorcinol.

[0009] Further, in step S2, the reinforcing material includes one or more of carbon fiber, carbon black and carbon nanotubes; and / or the weight ratio of the reinforcing material to the graphite worm is (0.5 to 10.0):100, preferably (3.0 to 5.0):100.

[0010] Further, in step S2, the weight ratio of the binder to the graphite worm is (0.1-2.0):100, preferably (1.0-1.5):100; more preferably, the weight ratio of the reinforcing material to the binder is (2-5):1.

[0011] Further, in step S2, the rotation speed of the mechanochemical activation is 200-800 rpm, preferably 400-600 rpm; and / or the weight ratio of the ball material to the mechanochemical activation is 1:(10-80), preferably 1:(20-30).

[0012] Further, in step S1, the natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying and expansion treatment in sequence to obtain graphite worms; preferably, the expansion treatment temperature is 800-1200℃; and / or the length of the graphite worms is 1-2cm.

[0013] Furthermore, in step S3, the molding pressure is 30-60 MPa, and the pressing time is 10-100 min, preferably 40-60 min.

[0014] Further, in step S4, the resin impregnation treatment includes one or more of epoxy resin, phenolic resin, unsaturated polyester and furan resin, and the weight ratio of resin to monopolar plate is 1:(1-5), preferably 1:(2-3); and / or the impregnation temperature is 50-150°C, preferably 60-80°C, and the impregnation time is 5-100 min, preferably 30-50 min; and / or the curing treatment is carried out in a vacuum drying oven with a vacuum degree of 0.1-0.3 MPa, a curing temperature of 50-80°C, and a curing time of 10-100 min.

[0015] According to another aspect of the present invention, a graphite bipolar plate is provided, which is obtained using the preparation method described above.

[0016] Furthermore, the contact resistance of the graphite bipolar plate is 2–6 mΩ·cm. 2 @0.6Mpa, flexural strength is 25~50MPa.

[0017] According to another aspect of the present invention, a fuel cell is provided, comprising the graphite bipolar plate described above.

[0018] By applying the technical solution of this invention, a mechanochemical activation process is introduced in the preparation of graphite bipolar plates for fuel cells. Before pressing the expanded graphite material into a single plate, the expanded graphite is mixed with reinforcing materials and binders for activation treatment. The reinforcing materials are used to improve the bending resistance of the final product, and the binders are used to improve the density and formability of the substrate and further increase the mechanical strength, resulting in modified graphite substrate for plate preparation. Without affecting the conductivity of the plate, the bending strength of the plate is greatly improved, thereby improving the overall lifespan of the fuel cell system. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 A flowchart illustrating the fabrication process of a graphite bipolar plate according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] As described in the background section of this invention, existing fuel cell bipolar plates suffer from the problem of not being able to simultaneously achieve conductivity and bending strength. To address this issue, in a typical embodiment of this invention, a method for preparing a graphite bipolar plate is provided, comprising the following steps: Step S1, expanding graphite raw material to obtain graphite worms; Step S2, mixing the graphite worms with reinforcing materials and binders, and performing mechanochemical activation treatment to obtain a modified graphite substrate; Step S3, molding the modified graphite substrate to obtain a monopolar plate; Step S4, sequentially impregnating and curing the monopolar plate with resin to obtain an impregnated monopolar plate; Step S5, bonding the impregnated monopolar plates to obtain a graphite bipolar plate; wherein the reinforcing material includes carbon materials, and the binder includes one or more of polyarylacetylene, polyurethane, dicyandiamide, and resorcinol.

[0023] Specifically, the graphite raw material is first expanded to obtain graphite worms with excellent softness and resilience. Then, the graphite worms are mixed with reinforcing materials and binders and subjected to mechanochemical activation treatment (such as ball milling). In this process, not only can the particle size of the material be reduced and the specific surface area increased, but the mutual conversion of mechanical energy and chemical energy will also occur, causing structural and physicochemical changes in the reinforcing materials and the substrate to maximize their activity, thereby improving the bending resistance of the final product.

[0024] The binder can improve the density and formability of the substrate, and further increase the mechanical strength. The binder includes one or more of polyarylacetylene, polyurethane, dicyandiamide and resorcinol, preferably polyarylacetylene. Its function is to improve the adhesion between the graphite substrates themselves and between the graphite substrates and the reinforcing materials, thereby improving the mechanical properties of the material without affecting the overall conductivity of the plate, including reducing its brittleness and improving its bending strength, to obtain a modified graphite substrate. Then the modified graphite substrate is molded and demolded to obtain a monopolar plate.

[0025] Expanded graphite worms generally have high porosity, which directly results in high gas permeability of the manufactured electrode plates. This does not meet the purpose of bipolar plates in fuel cells, which aim to isolate the anode and cathode gases. Therefore, the single-electrode plates need to be resin-impregnated. The resin is applied to the electrode plate surface using spraying or brushing, followed by curing. This process seals the pores while improving the strength and processability of the modified graphite substrate, resulting in an impregnated single-electrode plate. After resin impregnation, the single-electrode plates are coated with adhesive using methods such as coating or screen printing. Finally, the impregnated single-electrode plates are bonded together to obtain a high-strength graphite bipolar plate for fuel cells.

[0026] In the preparation of graphite bipolar plates for fuel cells, this invention introduces a mechanochemical activation process. Before pressing expanded graphite material into monopolar plates, the expanded graphite is mixed with reinforcing materials and binders for activation treatment to obtain modified graphite substrate. Without affecting the conductivity of the plate, the mechanical strength of the plate is greatly improved (the bending strength of the bipolar plate can be increased by 30-60% compared with existing products), thereby improving the overall lifespan of the fuel cell system.

[0027] In a preferred embodiment, in step S2, the reinforcing material includes one or more of carbon fibers, carbon black, and carbon nanotubes; and / or the weight ratio of the reinforcing material to graphite worms is (0.5–10.0):100, preferably (3.0–5.0):100. The aforementioned reinforcing material has higher specific strength and specific modulus, which can significantly enhance the flexural strength and toughness of the graphite substrate and reduce its brittleness without significantly affecting the conductivity of the graphite bipolar plate. Furthermore, it helps to improve the conductivity and surface activity of the graphite substrate, allowing the specific type of binder of this invention to be better distributed and bonded, thereby further improving the overall mechanical properties of the bipolar plate while ensuring high conductivity. The preferred addition ratio can further ensure that the reinforcing material is evenly distributed, reducing the decrease or insufficiency of conductivity caused by local excess, while providing a better reinforcing effect, making the bipolar plate less prone to fracture or deformation when subjected to mechanical stress during fuel cell operation.

[0028] To achieve a more stable structural connection between the graphite worms, in a preferred embodiment, in step S2, the weight ratio of binder to graphite worms is (0.1–2.0):100, preferably (1.0–1.5):100; more preferably, the weight ratio of reinforcing material to binder is (2–5):1. An appropriate amount of binder is more conducive to establishing a good interfacial bond between the reinforcing materials and between them and the graphite worms, without introducing excessive non-conductive components and affecting the conductivity of the bipolar plate. This improves the integrity of the material and enhances the overall mechanical strength, especially the bending strength, making it less prone to damage during fuel cell operation. The preferred weight ratio range between reinforcing material and binder allows for a more uniform distribution of the reinforcing material and full coverage by the binder, forming a composite network structure. This utilizes the reinforcing material to improve the mechanical properties of the bipolar plate, effectively addressing the problems of high brittleness and low strength in traditional graphite bipolar plates while maintaining their excellent conductivity.

[0029] In the mechanochemical activation process, parameter control has a significant impact on the activation effect, directly affecting the improvement of bipolar plate strength. In a preferred embodiment, in step S2, the rotation speed of the mechanochemical activation is 200–800 rpm, preferably 400–600 rpm; and / or the weight ratio of the ball material to the mechanochemical activation material is 1:(10–80), preferably 1:(20–30). The above rotation speed range allows the reinforcing material, binder, and graphite worms to come into more complete contact and disperse during the activation process, forming a more uniform composite structure. The shear force generated by high-speed rotation helps to break the constraints of the graphite interlayer structure, allowing the reinforcing material to be better embedded between the graphite layers. This not only enhances the mechanical strength of the graphite material but also helps to maintain its original conductivity. The ball-to-material weight ratio within the above range allows the graphite worms to be subjected to more appropriate mechanical stress, further promoting the uniform distribution and effective bonding of reinforcing materials and binders in the graphite structure, reducing conductivity loss caused by excessive graphite crushing or insufficient activation of reinforcing materials due to insufficient stress, thereby enabling the bipolar plate to have excellent conductivity while significantly improving its bending strength.

[0030] Graphite worms (expanded graphite) are typically prepared from natural flake graphite. In a preferred embodiment, in step S1, the natural flake graphite is sequentially subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment to obtain graphite worms. Preferably, the expansion treatment temperature is 800–1200℃; and / or the length of the graphite worms is 1–2 cm. Strong acid oxidation allows the insertion of corresponding atoms, ions, or molecules, thereby forming graphite intercalation compounds and altering the relatively weak van der Waals forces between the layers of natural graphite. Graphite intercalation compounds can be classified into covalent bonds, ionic bonds, mixed bonds, and molecular bonds. After sufficient oxidation, the graphite undergoes deacidification, water washing, and drying processes to remove residual intercalating agents. Simultaneously, appropriate antioxidants, such as citric acid or vitamins, can be added to reduce the oxidation of graphite under high-temperature conditions. After drying, graphite is subjected to high-temperature expansion treatment at 800–1200℃, which rapidly decomposes the interlayer compounds and uses the thrust generated by the decomposition to widen the interlayer spacing, resulting in worm-like graphite strips with a length of 1–2 cm. Under these conditions, the interlayer distance of graphite can be increased while retaining the original continuous phase structure of graphite, thereby changing some of the original properties of graphite, such as low thermal conductivity and low self-lubricating properties, to form a material with excellent softness and resilience, better meeting the requirements for electrode material applications.

[0031] In a preferred embodiment, in step S3, the molding pressure is 30–60 MPa, and the molding time is 10–100 min, preferably 40–60 min. High-pressure molding can promote a tighter bond between the reinforcing material and the binder in the modified graphite substrate, forming a dense structure. This not only helps to improve the mechanical strength of the material, especially the flexural strength, but also reduces the internal porosity of the substrate, lowers the gas permeability, optimizes the airtightness of the bipolar plate, and is beneficial for isolating the anode and cathode gases and maintaining the stability of the internal environment of the fuel cell stack. Within the above-mentioned molding time range, it is beneficial to allow the composite material to flow fully and fill the mold cavity under sufficient pressure, while giving the binder an appropriate time for initial curing, forming a stable structure without excessive hardening that would affect subsequent processing. It also reduces the problems of insufficient molding due to too short a molding time or changes in material properties such as decreased conductivity due to too long a molding time, further improving the performance of the fuel cell bipolar plate.

[0032] Resins used for impregnation are generally divided into two main categories: thermoplastic resins and thermosetting resins. Because thermoplastic resins need to be cooled to room temperature before the next step can be performed, which is less efficient, thermosetting resins are generally used. In a preferred embodiment, in step S4, the resin impregnation treatment includes one or more of epoxy resin, phenolic resin, unsaturated polyester and furan resin, preferably epoxy resin, and the weight ratio of resin to monopolar plate is 1:(1-5), preferably 1:(2-3); and / or the impregnation temperature is 50-150°C, preferably 60-80°C, and the impregnation time is 5-100 min, preferably 30-50 min; and / or the curing treatment is carried out in a vacuum drying oven with a vacuum degree of 0.1-0.3 MPa, a curing temperature of 50-80°C, and a curing time of 10-100 min.

[0033] Taking epoxy resin as an example, its main molecular structure is characterized by the presence of active epoxy groups in the molecular chain. These epoxy groups can be located at the ends, in the middle, or in a cyclic structure. Due to the presence of these active epoxy groups, it can undergo cross-linking reactions with various types of curing agents to form polymers with a three-dimensional network structure. Cured epoxy resin exhibits excellent physicochemical properties, superior adhesion strength to both metallic and non-metallic surfaces, good dielectric properties, low shrinkage, good dimensional stability, high hardness, good flexibility, and excellent resistance to alkalis, acids, and solvents.

[0034] Furthermore, a resin-to-monopolar plate weight ratio within the aforementioned range is more conducive to the proper distribution of resin in the composite material, reducing the decrease in conductivity due to excessive resin or the insufficient mechanical strength due to insufficient resin. Suitable impregnation temperature and time promote the resin's full penetration into the microporous structure of the monopolar plate, forming a dense coating, enhancing the material's adhesion, while preserving its original conductive network. This optimizes the resin's flowability and curing properties, allowing for rapid curing at lower temperatures, reducing the impact of thermal stress on the material's conductivity. Additionally, it improves the uniformity and strength of the resin coating, providing a stable foundation for subsequent bonding. Vacuum curing effectively removes air bubbles from the resin, preventing the formation of voids and further improving the density and airtightness of the bipolar plate. Simultaneously, gentle curing conditions help reduce thermal stress, protecting the material's conductive network from damage, thus enabling the bipolar plate to maintain better conductivity while possessing higher mechanical strength.

[0035] In another typical embodiment of the present invention, a graphite bipolar plate is also provided, obtained using the preparation method described above. Due to the use of the method of the present invention, by introducing a mechanochemical activation process and combining preferred reinforcing materials and binders, the prepared graphite bipolar plate exhibits significantly improved mechanical strength, especially a substantial increase in flexural strength. This allows the bipolar plate to better withstand mechanical stress during fuel cell operation, extending its service life and enhancing the overall stability of the fuel cell stack. Simultaneously, it ensures that the conductive network of the bipolar plate is not damaged, thereby maintaining high conductivity, reducing ohmic losses, and improving the efficiency of the fuel cell.

[0036] Furthermore, the mechanochemical activation treatment further enhances the corrosion resistance of the graphite substrate, making it more stable in the acidic environment of fuel cells and reducing the impact of electrochemical corrosion on bipolar plate performance. Resin impregnation effectively reduces the porosity of the bipolar plate, improves airtightness, isolates anode and cathode gases, optimizes the working environment of the fuel cell, and ensures efficient system operation. In summary, the graphite bipolar plate of this invention significantly improves conductivity, mechanical strength, corrosion resistance, and airtightness, making it a valuable and reliable core component for fuel cells and possessing significant application value.

[0037] Specifically, in a preferred embodiment, the contact resistance of the graphite bipolar plate is 2–6 mΩ·cm. 2 @0.6Mpa, flexural strength is 25~50MPa.

[0038] In another typical embodiment of the present invention, a fuel cell is also provided, including the graphite bipolar plate described above. Because the performance of the core component, the graphite bipolar plate, of the fuel cell of the present invention is significantly optimized, it can balance conductivity and bending strength, resulting in significantly improved energy conversion efficiency, enhanced system stability, excellent durability, and improved sealing performance. By improving the overall performance of the graphite bipolar plate, the efficiency, stability, and service life of the fuel cell are significantly improved.

[0039] Typical, but not limiting, weight ratios of reinforcing material to graphite worms are 0.5:100, 1.0:100, 2.0:100, 3.0:100, 4.0:100, 5.0:100, 6.0:100, 7.0:100, 8.0:100, 9.0:100, 10.0:100, or any two of these values.

[0040] Typical, but not limiting, weight ratios of binder to graphite worms are 0.1:100, 0.5:100, 1.0:100, 1.5:100, 2.0:100, or any two of these values.

[0041] Typical, but not limiting, weight ratios of reinforcing material to binder are 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any two of these ratios.

[0042] Typical, but not limited, rotational speeds for mechanochemical activation are 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, or any combination of two of these values.

[0043] Typical, but not limiting, mechanochemically activated pellet weight ratios are 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, or any two of these values.

[0044] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0045] Example 1

[0046] The fabrication process of graphite bipolar plates is shown in the following flowchart. Figure 1 As shown.

[0047] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0048] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0049] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0050] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0051] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0052] Example 2

[0053] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0054] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:3.0:1.5 and subjected to mechanochemical activation treatment (rotation speed of 400 rpm, ball weight ratio of 1:20) to obtain modified graphite substrate.

[0055] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0056] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0057] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0058] Example 3

[0059] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0060] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:5.0:1.0 and subjected to mechanochemical activation treatment (rotation speed of 600 rpm, ball weight ratio of 1:30) to obtain modified graphite substrate.

[0061] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0062] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0063] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0064] Example 4

[0065] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0066] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0067] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 40 min), and after demolding, a monopolar plate is obtained.

[0068] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2, the impregnation temperature is 60℃, and the impregnation time is 50min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0069] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0070] Example 5

[0071] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0072] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0073] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 60 min), and after demolding, a monopolar plate is obtained.

[0074] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:3, the impregnation temperature is 80℃, and the impregnation time is 30min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0075] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0076] Example 6

[0077] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 800℃) in sequence to obtain graphite worms (1cm in length);

[0078] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0079] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0080] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0081] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0082] Example 7

[0083] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1200℃) in sequence to obtain graphite worms (2cm in length);

[0084] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0085] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0086] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0087] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0088] Example 8

[0089] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0090] Step S2: Graphite worms are mixed with reinforcing material (carbon black) and binder (polyarylacetylene) at a weight ratio of 100:0.5:2.0 and subjected to mechanochemical activation treatment (rotation speed of 200 rpm, ball weight ratio of 1:10) to obtain modified graphite substrate;

[0091] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0092] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0093] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0094] Example 9

[0095] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0096] Step S2: Graphite worms are mixed with reinforcing material (carbon nanotubes) and binder (dicyandiamide) at a weight ratio of 100:10.0:0.1 and subjected to mechanochemical activation treatment (rotation speed of 800 rpm, ball weight ratio of 1:80) to obtain modified graphite substrate;

[0097] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0098] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0099] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0100] Example 10

[0101] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0102] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0103] Step S3: The modified graphite substrate is molded (pressure 30 MPa, pressing time 100 min), and after demolding, a monopolar plate is obtained.

[0104] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0105] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0106] Example 11

[0107] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0108] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0109] Step S3: The modified graphite substrate is molded (pressure 60 MPa, pressing time 10 min), and after demolding, a monopolar plate is obtained.

[0110] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:2.5, the impregnation temperature is 70℃, and the impregnation time is 40min), and then perform curing treatment (vacuum degree is 0.2MPa, curing temperature is 75℃, and curing time is 55min) to obtain the impregnated monopolar plate.

[0111] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0112] Example 12

[0113] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0114] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0115] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0116] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:1, the impregnation temperature is 50℃, the impregnation time is 100min, and then perform curing treatment (vacuum degree is 0.1MPa, curing temperature is 80℃, curing time is 10min) to obtain the impregnated monopolar plate.

[0117] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0118] Example 13

[0119] Step S1: Natural flake graphite is subjected to acid oxidation, deacidification, water washing, drying, and expansion treatment (at a temperature of 1000℃) in sequence to obtain graphite worms (1.5cm in length);

[0120] Step S2: Graphite worms are mixed with reinforcing material (carbon fiber) and binder (resorcinol) at a weight ratio of 100:4.0:1.2 and subjected to mechanochemical activation treatment (rotation speed of 500 rpm, ball weight ratio of 1:25) to obtain modified graphite substrate.

[0121] Step S3: The modified graphite substrate is molded (pressure 45 MPa, pressing time 50 min), and after demolding, a monopolar plate is obtained.

[0122] Step S4: Apply impregnation resin to the surface of the monopolar plate by spraying to impregnate the monopolar plate with resin (epoxy resin impregnation, the weight ratio of resin to monopolar plate is 1:5, the impregnation temperature is 150℃, and the impregnation time is 5min), and then perform curing treatment (vacuum degree is 0.3MPa, curing temperature is 50℃, and curing time is 100min) to obtain the impregnated monopolar plate.

[0123] Step S5: Apply adhesive to the coating area of ​​the electrode plate using a coating method, and then bond the impregnated monopolar plate to obtain a graphite bipolar plate.

[0124] Comparative Example 1

[0125] The difference from Example 1 is that no reinforcing material (carbon fiber) is added in step S2.

[0126] Comparative Example 2

[0127] The difference from Example 1 is that no binder (resorcinol) is added in step S2.

[0128] Comparative Example 3

[0129] The difference from Example 1 is that manual grinding is used to mix the ingredients in step S2.

[0130] Comparative Example 4

[0131] The difference from Example 1 is that in step S2, graphite worms are mixed with reinforcing material (carbon black) and binder (polyarylacetylene) in a weight ratio of 100:0.3:0.05 and subjected to mechanochemical activation treatment (rotation speed of 200 rpm, ball weight ratio of 1:10) to obtain modified graphite substrate.

[0132] Comparative Example 5

[0133] The difference from Example 1 is that in step S2, graphite worms are mixed with reinforcing material (carbon nanotubes) and binder (dicyandiamide) at a weight ratio of 100:15.0:3.0 and subjected to mechanochemical activation treatment (rotation speed of 800 rpm, ball weight ratio of 1:80) to obtain modified graphite substrate.

[0134] The graphite bipolar plates prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0135] Test method:

[0136] The conductivity of the bipolar plate, i.e., the contact resistance, is measured by a contact resistance tester. The test standard refers to GB / T-20042.6-2024 Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics.

[0137] Bending strength of bipolar plates: refers to the maximum bending stress that a bipolar plate can withstand during bending under specified conditions. The testing equipment is a universal tensile testing machine, and the testing standard refers to GB / T-20042.6-2024 Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics.

[0138] Table 1

[0139]

[0140]

[0141] As can be seen from the above, compared with the comparative example, the embodiments of the present invention introduce a mechanochemical activation process in the preparation of graphite bipolar plates for fuel cells. Before pressing the expanded graphite material into a single plate, the expanded graphite is mixed with reinforcing materials and binders for activation treatment. The reinforcing materials are used to improve the bending resistance of the final product, and the binders are used to improve the density and formability of the substrate and further increase the mechanical strength, resulting in modified graphite substrate for plate preparation. Without affecting the conductivity of the plate, the bending strength of the plate is greatly improved, thereby improving the overall lifespan of the fuel cell system.

[0142] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite bipolar plate, characterized in that, Includes the following steps: Step S1: The graphite raw material is expanded to obtain graphite worms; Step S2: The graphite worms are mixed with reinforcing materials and binders, and subjected to mechanochemical activation treatment to obtain modified graphite substrate; Step S3: The modified graphite substrate is molded to obtain a single-electrode plate; Step S4: The monopolar plate is subjected to resin impregnation and curing treatment in sequence to obtain an impregnated monopolar plate; Step S5: The impregnated monopolar plates are bonded together to obtain the graphite bipolar plate; The reinforcing material includes carbon materials, and the binder includes one or more of polyarylacetylene, polyurethane, dicyandiamide, and resorcinol.

2. The preparation method according to claim 1, characterized in that, In step S2 The reinforcing material includes one or more of carbon fibers, carbon black, and carbon nanotubes; and / or The weight ratio of the reinforcing material to the graphite worm is (0.5-10.0):100, preferably (3.0-5.0):

100.

3. The preparation method according to claim 1 or 2, characterized in that, In step S2 The amount of adhesive added is in a weight ratio of (0.1-2.0):100 to the graphite worms, preferably (1.0-1.5):

100. Preferably, the weight ratio of the reinforcing material to the adhesive is (2-5):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2 The rotational speed for the mechanochemical activation is 200–800 rpm, preferably 400–600 rpm; and / or The weight ratio of the mechanochemically activated balls is 1:(10-80), preferably 1:(20-30).

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step S1 Natural flake graphite was subjected to acid oxidation, deacidification, water washing, drying, and expansion treatments in sequence to obtain the graphite worms; Preferably, the temperature of the expansion treatment is 800–1200°C; and / or the length of the graphite worm is 1–2 cm.

6. The preparation method according to any one of claims 1 to 5, characterized in that, In step S3 The molding pressure is 30-60 MPa, and the pressing time is 10-100 min, preferably 40-60 min.

7. The preparation method according to any one of claims 1 to 6, characterized in that, In step S4 In the resin impregnation treatment, the resin includes one or more of epoxy resin, phenolic resin, unsaturated polyester, and furan resin, and the weight ratio of the resin to the monopolar plate is 1:(1-5), preferably 1:(2-3); and / or The impregnation treatment is performed at an impregnation temperature of 50–150°C, preferably 60–80°C, for a duration of 5–100 min, preferably 30–50 min; and / or The curing process is carried out in a vacuum drying oven with a vacuum degree of 0.1 to 0.3 MPa, a curing temperature of 50 to 80°C, and a curing time of 10 to 100 min.

8. A graphite bipolar plate, characterized in that, It is obtained using the preparation method according to any one of claims 1 to 7.

9. The graphite bipolar plate according to claim 8, characterized in that, The contact resistance of the graphite bipolar plate is 2–6 mΩ·cm. 2 @0.6Mpa, flexural strength is 25~50MPa.

10. A fuel cell, characterized in that, Includes the graphite bipolar plate as described in claim 8 or 9.

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