High-strength graphite bipolar plate and method for manufacturing the same

Abstract

This invention relates to the field of bipolar plate technology, specifically to a high-strength graphite bipolar plate and its preparation method, which is prepared from the following raw materials in parts by weight: 60-80 parts of natural graphite powder, 12-18 parts of modified epoxy resin, 8-12 parts of reinforcing additives, 2-4 parts of conductive agent, 1-3 parts of curing agent, 0.5-2 parts of dispersant, and 0.3-1 parts of coupling agent. This invention uses a ternary compound of bisphenol A epoxy resin, phenolic epoxy resin, and organic fluorine epoxy resin, and combines it with binary graft modification of KH560 and fluorosilicone coupling agent. This significantly improves the interfacial compatibility, bonding strength, and hydrophobic and humid heat resistance of the resin matrix and inorganic fillers, enabling the bipolar plate to maintain high strength while significantly improving flexibility and dimensional stability. It effectively solves the defects of traditional epoxy resins, such as high brittleness, poor weather resistance, and weak bonding with fillers, laying a foundation for high strength, high toughness, and high weather resistance from the matrix level.

Description

Technical Field

[0001] This invention relates to the field of bipolar plate technology, specifically to a high-strength graphite bipolar plate and its preparation method. Background Technology

[0002] Graphite bipolar plates are one of the core components of automotive fuel cells, undertaking key functions such as separating reactant gases, conducting current, supporting membrane electrode assemblies, and dissipating waste heat from the reaction. Their performance directly determines the power density, lifespan, and safety stability of the automotive fuel cell. With the rapid development of new energy vehicle technologies, higher requirements are being placed on the comprehensive performance of graphite bipolar plates. They not only need to possess excellent conductivity and weather resistance, but also good mechanical strength and flexibility to adapt to complex operating conditions such as vibration and temperature changes during vehicle operation.

[0003] Currently, existing graphite bipolar plates for automotive batteries generally suffer from the following technical defects: First, poor coordination between flexibility and strength; either insufficient mechanical strength, making them prone to breakage and damage during assembly and use, or poor flexibility, failing to adapt to the vibration conditions of automobiles and easily cracking; second, poor weather resistance; under complex automotive operating environments such as high and low temperature cycles and humidity changes, they are prone to aging and deformation, leading to decreased sealing performance and affecting the normal operation of fuel cells; third, insufficient conductivity; the high resistance of graphite bipolar plates causes energy loss and reduces the energy conversion efficiency of fuel cells; fourth, poor overall product coordination; often, improving one performance aspect leads to a decline in other performance aspects, making it difficult to achieve a synergistic improvement in strength, flexibility, conductivity, and weather resistance, seriously affecting their performance and service life in automotive fuel cells.

[0004] To address the aforementioned issues, existing technologies often employ single modification methods, such as modifying epoxy resin alone to improve strength, or simply adding carbon fibers to enhance conductivity. However, these methods cannot achieve synergistic optimization of various properties, and the modification effects are limited, failing to meet the high-performance requirements of graphite bipolar plates for automotive fuel cells. Therefore, developing a high-strength graphite bipolar plate with excellent overall performance, capable of synergistically optimizing strength, flexibility, conductivity, and weather resistance, and its preparation method, has become an urgent technical problem to be solved in the current automotive battery industry. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the purpose of this invention is to provide a high-strength graphite bipolar plate and its preparation method, so as to solve the problems mentioned in the background art.

[0006] The present invention solves the technical problem by adopting the following technical solution: This invention provides a high-strength graphite bipolar plate, which is prepared from the following raw materials in parts by weight: 60-80 parts of natural graphite powder, 12-18 parts of modified epoxy resin, 8-12 parts of reinforcing additives, 2-4 parts of conductive agent, 1-3 parts of curing agent, 0.5-2 parts of dispersant, and 0.3-1 parts of coupling agent.

[0007] Preferably, the modified epoxy resin is a compound of bisphenol A epoxy resin, phenolic epoxy resin, and organic fluorine modified epoxy resin, and is obtained by binary grafting modification with KH560 and fluorosilicone coupling agent. The mass ratio of the bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin is (2-4):(1-2):1.

[0008] Preferably, the reinforcing additive is lanthanum oxide coated hexagonal boron nitride@carbon fiber core-shell particles, in situ loaded with nano-silica sol, and chitosan is used as a dispersant and interfacial crosslinking agent; The mass ratio of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in the reinforcing additive is (7-9):1:(1.5-2):(11-13).

[0009] Preferably, the conductive agent is a micron-nano gradient conductive network formed by a composite of graphene, carbon black nanoparticles, and carbon nanotubes; The mass ratio of graphene, nano-carbon black, and carbon nanotubes in the conductive agent is (5-7):(2-4):1.

[0010] Preferably, the curing agent is composed of methyltetrahydrophthalic anhydride, 2-ethyl-4-methylimidazole, and a latent epoxy curing agent.

[0011] Preferably, the natural graphite powder has a particle size of 150-200 mesh; The carbon fiber is polyacrylonitrile-based carbon fiber with a diameter of 10-20 μm and a length of 50-100 μm; The hexagonal boron nitride has a particle size of 50-100 nm.

[0012] In addition, the present invention also provides a method for preparing a high-strength graphite bipolar plate, comprising the following steps: Preparation of S100 modified epoxy resin Bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin are added to a reaction vessel and stirred at 80-100℃ for 30-60 minutes. KH560 and fluorosilicone coupling agent are added, and the mixture is kept at the temperature for 2-3 hours for grafting. After cooling, the modified epoxy resin is obtained. Preparation of S200 Enhanced Additive Lanthanum oxide-coated hexagonal boron nitride was added to a mixture of carbon fiber, nano-silica sol, and chitosan, stirred, intermittently sonicated for 1-1.5 hours, and then centrifuged, dried, and pulverized to obtain the reinforcing additive. Preparation of S300 conductive agent Graphene, carbon black nanoparticles, and carbon nanotubes are added to a high-speed mixer and mixed for 10-20 minutes to obtain a conductive agent. S400 raw material mixing Add natural graphite powder, modified epoxy resin, reinforcing additive, conductive agent, dispersant, and coupling agent in sequence, keep the temperature ≤50℃, stir for 30-60 minutes, then add curing agent and continue stirring for 20-30 minutes. S500 Hot Press Molding Pre-cur the mixture at 60-90℃ for 10-15 minutes, then raise the temperature to 120-140℃ and hold it at 12MPa for 30-60 minutes, and let it cool naturally before demolding and removing the electrode plate. S600 Curing and Post-treatment The electrode plates are placed in a constant temperature oven and kept at 80-120℃ for 1.5-2.5 hours. After cooling to room temperature, internal stress is eliminated, and the plates are polished, trimmed, and surface burrs and excess material are removed to obtain a high-strength graphite bipolar plate. Preferably, the amount of KH560 and fluorosilicone coupling agent in step S100 is 3-6% of the total mass of bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin, and the mass ratio of KH560 to fluorosilicone coupling agent is 1:1.

[0013] Preferably, the preparation method of the lanthanum oxide-coated hexagonal boron nitride powder in step S200 is as follows: Hexagonal boron nitride was added to ethanol and ultrasonically dispersed. Lanthanum oxide was then added, with a mass ratio of hexagonal boron nitride to lanthanum oxide of 3:1. The mixture was stirred for 20-40 minutes and then dried by rotary evaporation at 80°C to obtain lanthanum oxide-coated hexagonal boron nitride powder.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a ternary compound of bisphenol A epoxy resin, phenolic epoxy resin, and organic fluorine epoxy resin, and combines it with binary grafting modification of KH560 and fluorosilicone coupling agent. This significantly improves the interfacial compatibility, bonding strength, and hydrophobic and humid heat resistance of the resin matrix and inorganic fillers. As a result, the bipolar plate maintains high strength while significantly improving flexibility and dimensional stability. This effectively solves the defects of traditional epoxy resins, such as high brittleness, poor weather resistance, and weak bonding with fillers, laying a foundation for high strength, high toughness, and high weather resistance from the matrix level. This invention employs lanthanum oxide-coated hexagonal boron nitride@carbon fiber core-shell structure reinforcing agent. Through core-shell interface design, filler agglomeration and interface defects are eliminated, enabling carbon fiber to provide a mechanical skeleton, lanthanum oxide and boron nitride to toughen and reinforce and optimize the conductive pathway, and nano-silica sol and chitosan to further improve dispersibility and interfacial bonding, achieving simultaneous improvement in strength, toughness and conductivity, breaking the technical prejudice in the industry that reinforcement and toughening and conductivity are mutually restrictive. A micron-nano conductive network composed of graphene, carbon black nanoparticles, and carbon nanotubes was constructed. Through the synergistic formation of multi-scale conductive fillers, a continuous, stable, and low-impedance electron transport pathway was formed, which significantly reduced the volume resistivity and improved the energy conversion efficiency of fuel cells. At the same time, the problems of large addition amount, easy agglomeration, and impact on mechanical properties of single conductive agents were avoided, thus achieving the optimal balance between conductivity and mechanical properties. This invention employs a step-by-step molding process of pre-curing, main curing, and post-curing, which effectively releases air bubbles and thermal stress inside the material, avoiding warping, cracking, and deformation caused by internal stress concentration. This significantly improves the appearance flatness, dimensional accuracy, and long-term reliability of the bipolar plate, enabling the bipolar plate to maintain an extremely low performance degradation rate after high and low temperature cycling from -40℃ to 80℃, fully meeting the stringent vibration, temperature change, and long-term durability requirements of automotive fuel cells. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 A high-strength graphite bipolar plate is prepared from the following raw materials in parts by weight: 65 parts of natural graphite powder (150 mesh, 99.6% purity), 15 parts of modified epoxy resin, 10 parts of reinforcing additives, 3 parts of conductive agent, 2 parts of curing agent, 1 part of dispersant, and 0.5 parts of coupling agent. Among them, the modified epoxy resin is a compound of bisphenol A epoxy resin, phenolic epoxy resin and organic fluorine modified epoxy resin in a mass ratio of 3:1:1, which is then modified by binary grafting of KH560 and fluorosilicone coupling agent. The mass ratio of KH560 to fluorosilicone coupling agent is 1:1, and the fluorosilicone coupling agent is heptadecafluorodecyltrimethoxysilane. The reinforcing additive consists of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 8:1:1.8:12. The carbon fiber is polyacrylonitrile-based carbon fiber with a diameter of 20 μm and a length of 50 μm. The conductive agent is obtained by compounding graphene, nano carbon black, and carbon nanotubes in a mass ratio of 6:3:1. The curing agent consists of methyltetrahydrophthalic anhydride, 2-ethyl-4-methylimidazolium, and a latent epoxy curing agent in a mass ratio of 93:2:5. The latent epoxy curing agent is micronized dicyandiamide (DICY). 10; The dispersant is PEG400.

[0017] The preparation method of high-strength graphite bipolar plates includes the following steps: Preparation of S100 modified epoxy resin S101: Add bisphenol A epoxy resin, phenolic epoxy resin, and organic fluorine modified epoxy resin to a closed reactor according to the specified ratio, under nitrogen protection, start stirring at 400 r / min, heat to 90℃, keep stirring at this temperature for 45 min, until the system is transparent and homogeneous. S102: Add 5% of the total mass of the above resin to a mixed coupling agent of KH560 and fluorosilicone coupling agent, maintain 90℃ and 400r / min, and continue stirring for 2.5h. S103: Stop heating, cool down to ≤40℃ with cooling water, filter out the material, seal and store away from light, and use within 24 hours. Preparation of S200 Enhanced Additive S201: Prepare a 1.5wt% acetic acid aqueous solution, add chitosan, stir until completely dissolved, prepare a 3wt% chitosan solution, keep warm at 60℃ and stir for 60 minutes, degas, filter, and set aside; S202: Add hexagonal boron nitride (50nm) to ethanol, disperse by ultrasonication at 300W for 30min, add lanthanum oxide, the mass ratio of hexagonal boron nitride to lanthanum oxide is 3:1, stir for 30min, dry by rotary evaporation at 80℃ to obtain lanthanum oxide coated hexagonal boron nitride powder; S203: First, pour the chitosan solution into a mixing tank and stir at 500 r / min. Then, add carbon fiber, nano-silica sol, and lanthanum oxide-coated hexagonal boron nitride powder in sequence. Stir for 1.5 h until there are no visible agglomerates and the mixture is evenly dispersed. S204: Adjust the system temperature to 30℃, ultrasonic power to 400W, and use intermittent ultrasound: ultrasound for 30 minutes, pause for 10 minutes, and then ultrasound for 30 minutes, for a total effective ultrasound time of 1 hour. The temperature is controlled at 25-35℃ throughout the process to prevent overheating and degradation. S205: Centrifuge at 3500 r / min for 15-20 min, discard the supernatant, wash twice with anhydrous ethanol, wash once with deionized water, vacuum dry at 70℃ for 4 h until the moisture content is ≤0.3%, pulverize using an ultrafine pulverizer, pass through a 200 mesh sieve, the powder is loose, without lumps, and has a uniform particle size, and is sealed for later use. Preparation of S300 conductive agent S301: Add graphene, nano carbon black, and carbon nanotubes to a high-speed mixer and mix at 800 r / min for 15 min to obtain a gradient conductive agent for later use. S400 raw material mixing S401: Add natural graphite powder, modified epoxy resin, reinforcing additive, conductive agent, dispersant, and coupling agent in sequence, control the material temperature to ≤50℃, and stir at 650r / min for 40min. S402: Add curing agent, stir at 500 r / min for 25 min to obtain a loose wet powder mixture without clumping, with a mixing uniformity RSD ≤ 5%; S500 Hot Press Molding S501: Spread the mixture evenly into the flow field mold, level it, control the thickness tolerance to ±0.02mm, pre-cur it for 10 minutes at 80℃ and 3MPa, and degas twice. S502: Heat to 130℃ at a constant rate, pressurize to 12MPa, and keep at the temperature and pressure for 40 minutes to cure; S503: Maintain a slight pressure (2-3MPa) and allow it to cool naturally to ≤40℃ to obtain the electrode plate.

[0018] S600 Post-curing and Post-treatment S601: Place the electrode plate in a constant temperature oven and keep it at 100℃ for 2 hours. Then cool it to room temperature with the oven to eliminate internal stress. After grinding, trimming, cleaning and drying, a high-strength graphite bipolar plate is obtained.

[0019] Example 2 A high-strength graphite bipolar plate is prepared from the following raw materials in parts by weight: 60 parts of natural graphite powder (200 mesh, 99.6% purity), 18 parts of modified epoxy resin, 12 parts of reinforcing additives, 4 parts of conductive agent, 2.5 parts of curing agent, 1.2 parts of dispersant, and 0.6 parts of coupling agent. The modified epoxy resin was obtained by compounding bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin in a mass ratio of 4:1.5:1, and then performing binary grafting modification with KH560 and a fluorosilicone coupling agent. The mass ratio of KH560 to the fluorosilicone coupling agent was 1:1, and the fluorosilicone coupling agent was γ-ray. (2,2,3,3 (Tetrafluoropropyl)propyltrimethoxysilane; The reinforcing additive consists of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 9:1:2:13. The carbon fiber is polyacrylonitrile-based carbon fiber with a diameter of 10 μm and a length of 100 μm. The conductive agent is obtained by compounding graphene, nano carbon black, and carbon nanotubes in a mass ratio of 7:4:1. The curing agent consists of methyltetrahydrophthalic anhydride, 2-ethyl-4-methylimidazolium, and a latent epoxy curing agent in a mass ratio of 93:2:5. The latent epoxy curing agent is micronized dicyandiamide (DICY). 10; The dispersant is PEG400.

[0020] The preparation method of the high-strength graphite bipolar plate is the same as in Example 1.

[0021] Example 3 A high-strength graphite bipolar plate is prepared from the following raw materials in parts by weight: 70 parts of natural graphite powder (150 mesh, 99.6% purity), 12 parts of modified epoxy resin, 8 parts of reinforcing additives, 2 parts of conductive agent, 1.5 parts of curing agent, 0.8 parts of dispersant, and 0.4 parts of coupling agent. The modified epoxy resin was obtained by compounding bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin in a mass ratio of 2.5:1:1, and then performing binary grafting modification with KH560 and a fluorosilicone coupling agent. The mass ratio of KH560 to the fluorosilicone coupling agent was 1:1, and the fluorosilicone coupling agent was γ-ray... (2,2,3,3 (Tetrafluoropropyl)propyltrimethoxysilane; The reinforcing additive consists of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 7:1:1.5:11. The carbon fiber is polyacrylonitrile-based carbon fiber with a diameter of 20 μm and a length of 50 μm. The conductive agent is obtained by compounding graphene, carbon black nanoparticles and carbon nanotubes in a mass ratio of 5:2:1; The curing agent consists of methyltetrahydrophthalic anhydride, 2-ethyl-4-methylimidazolium, and a latent epoxy curing agent in a mass ratio of 93:2:5. The latent epoxy curing agent is micronized dicyandiamide (DICY). 10; The dispersant is PEG400.

[0022] The preparation method of the high-strength graphite bipolar plate is the same as in Example 1.

[0023] Comparative Example 1 The difference from Example 1 is as follows: Replace the modified epoxy resin with an equal part by weight of unmodified bisphenol A epoxy resin. The remaining formulas and preparation methods are the same as in Example 1.

[0024] Comparative Example 2 The difference from Example 1 is as follows: The modified epoxy resin uses only bisphenol A epoxy resin and phenolic epoxy resin in a mass ratio of 3:1. Only KH560 coupling agent is used; fluorinated silicone coupling agent is not used. The remaining formulas and preparation methods are the same as in Example 1.

[0025] Comparative Example 3 The difference from Example 1 is as follows: The modified epoxy resin is a compound of bisphenol A epoxy resin, phenolic epoxy resin and organofluorine modified epoxy resin in a mass ratio of 5:1:1. The remaining formulas and preparation methods are the same as in Example 1.

[0026] Comparative Example 4 The difference from Example 1 is as follows: The modified epoxy resin is a compound of bisphenol A epoxy resin, phenolic epoxy resin and organofluorine modified epoxy resin in a mass ratio of 1:1:1. The remaining formulas and preparation methods are the same as in Example 1.

[0027] Comparative Example 5 The difference from Example 1 is as follows: No enhancers added; The remaining formulas and preparation methods are the same as in Example 1.

[0028] Comparative Example 6 The difference from Example 1 is as follows: The reinforcing additive is composed of carbon fiber, hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 8:1:1.8:12, and has no coating or core-shell structure. The remaining formulas and preparation methods are the same as in Example 1.

[0029] Comparative Example 7 The difference from Example 1 is as follows: The reinforcing additive consists of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 11:1:1.8:12. The remaining formulas and preparation methods are the same as in Example 1.

[0030] Comparative Example 8 The difference from Example 1 is as follows: The reinforcing additive consists of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in a mass ratio of 6:1:1.8:12. The remaining formulas and preparation methods are the same as in Example 1.

[0031] Comparative Example 9 The difference from Example 1 is as follows: The conductive agent is obtained by compounding graphene and nano carbon black in a mass ratio of 6:3, without carbon nanotubes or gradient conductive network; The remaining formulas and preparation methods are the same as in Example 1.

[0032] Comparative Example 10 The difference from Example 1 is as follows: The conductive agent is prepared by compounding graphene, carbon black nanoparticles and carbon nanotubes in a mass ratio of 8:3:1. The remaining formulas and preparation methods are the same as in Example 1.

[0033] Comparative Example 11 The difference from Example 1 is as follows: The conductive agent is prepared by compounding graphene, carbon black nanoparticles and carbon nanotubes in a mass ratio of 3:3:1. The remaining formulas and preparation methods are the same as in Example 1.

[0034] Comparative Example 12 The difference from Example 1 is as follows: Step S501 is not included in S500; The remaining formulas and preparation methods are the same as in Example 1.

[0035] Performance testing According to GB / T20042.6-2024 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics", the graphite bipolar plates prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests. The test items included bending strength, elongation at break (flexibility index), volume resistivity (conductivity index), and weathering stability (performance decay rate after 50 cycles of high and low temperature cycling (-40℃~80℃)). Weathering stability (performance decay rate, %) refers to the comprehensive decay rate of the three core performance indicators of volume resistivity, bending strength, and elongation at break after the sample has undergone 50 cycles of high and low temperature cycling at -40℃~80℃. The calculation method is as follows: test the volume resistivity, flexural strength and elongation at break of the sample before and after aging, calculate the decay rate of each individual property, and take the arithmetic mean of the three decay rates as the final decay rate of weather resistance stability performance.

[0036] The formula for calculating the degradation rate of a single performance component is: Degradation rate of a single component = (1 - Performance value after aging / Performance value before aging) × 100%. The test results are shown in the table below.

[0037] In Examples 1-3 of this invention, the graphite bipolar plate simultaneously possesses high strength, high flexibility, high conductivity, and high weather resistance through the synergistic effect of ternary fluorosilicone modified epoxy resin, lanthanum oxide-coated hexagonal boron nitride@carbon fiber core-shell reinforcing agent, gradient conductive network, and stepwise curing process.

[0038] The embodiment has a flexural strength ≥82MPa, elongation at break ≥2.03%, volume resistivity ≤5.1mΩ・cm, and a comprehensive performance degradation rate of ≤3.56% after 50 high and low temperature cycles. All performance characteristics are well-balanced and excellent, far superior to all comparative examples, achieving unexpected technical results.

[0039] Comparative Example 1 used unmodified single bisphenol A epoxy resin without ternary compounding or fluorosilicone grafting modification. This resulted in extremely poor interfacial compatibility with the inorganic filler, high resin matrix brittleness, and weak resistance to damp heat. This indicates that unmodified epoxy resin cannot provide sufficient strength, flexibility, and interfacial bonding for the bipolar plate, and exhibits extremely poor weather resistance.

[0040] Comparative Example 2 did not add organic fluorine-modified epoxy resin and only used a single KH560 coupling agent. It lacked the hydrophobic, aging-resistant and interface-reinforcing effects brought by the fluorosilicone structure, resulting in insufficient toughness and high and low temperature resistance of the resin system.

[0041] In Comparative Example 3, the ratio of ternary epoxy resin was adjusted to 5:1:1. The proportion of bisphenol A epoxy resin was too high, which destroyed the synergistic effect of phenolic epoxy resin and organic fluorine epoxy resin, and reduced the cross-linking structure and toughness of the resin.

[0042] In Comparative Example 4, the ratio of ternary epoxy resin was adjusted to 1:1:1. The proportion of bisphenol A epoxy resin was insufficient, resulting in low strength and crosslinking density of the resin matrix, and decreased load-bearing capacity and structural stability.

[0043] Comparative Example 5, without any reinforcing additives, lacks the synergistic effect of carbon fiber and lanthanum oxide-coated BN skeleton reinforcement, toughening, and conductivity provided by the electrode plate. The matrix has no effective support, and the mechanical and weather resistance properties completely collapse.

[0044] Comparative Example 6 used ordinary physical mixed reinforcement components, but did not prepare lanthanum oxide-coated BN@carbon fiber core-shell structure. The filler interface had large defects and uneven dispersion, which could not form a continuous reinforcement and conductive network, and was prone to interface debonding.

[0045] Comparative Example 7 increased the carbon fiber ratio to 11:1, which exceeds the scope of this invention. Excessive carbon fiber is prone to agglomeration, resulting in increased internal defects and decreased dispersibility and molding uniformity.

[0046] Comparative Example 8 reduced the carbon fiber ratio to 6:1, resulting in insufficient reinforcing phase, weakened skeletal support, and limited improvement in mechanical properties.

[0047] Comparative Example 9 used only graphene and carbon black as conductive agents, without adding carbon nanotubes. It was unable to construct a micron-nano gradient conductive network, lacked nanoscale conductive bridging, and the resistance to electron transport increased significantly.

[0048] In Comparative Example 10, the ratio of conductive agent was adjusted to 8:3:1. The graphene ratio was too high, which made it easy for the layers to agglomerate and stack, destroying the uniformity of the matrix and affecting the continuous construction of the conductive network.

[0049] Comparative Example 11 had the conductive agent ratio adjusted to 3:3:1. The graphene ratio was insufficient, resulting in a decrease in the density of macroscopic conductive pathways and a deterioration in the continuity of the conductive network.

[0050] Comparative Example 12 omitted the 80℃ pre-curing step and adopted one-step hot pressing molding. As a result, the air bubbles and thermal stress inside the material were not released, the curing was uneven, and internal stress concentration was caused.

[0051] In summary, this invention achieves simultaneous improvements in four key performance indicators of graphite bipolar plates: flexural strength, elongation at break, volume resistivity, and weather resistance, through a combination of ternary epoxy resin compounding and fluorosilicone binary grafting modification, lanthanum oxide-coated hexagonal boron nitride@carbon fiber core-shell structure reinforcement, graphene / carbon black / carbon nanotube gradient conductivity construction, and stepwise curing to eliminate internal stress. Compared with comparative examples, this invention maintains high flexibility without reducing strength and extremely low performance degradation rate while maintaining high conductivity. It overcomes the technical bias in the field of "reinforcement reducing toughness, toughening reducing strength, and improving weather resistance reducing conductivity," and solves the long-standing technical challenge of synergistically optimizing the overall performance of graphite bipolar plates for automotive fuel cells.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0053] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-strength graphite bipolar plate, characterized in that, It is prepared from the following raw materials in parts by weight: 60-80 parts of natural graphite powder, 12-18 parts of modified epoxy resin, 8-12 parts of reinforcing additives, 2-4 parts of conductive agent, 1-3 parts of curing agent, 0.5-2 parts of dispersant, and 0.3-1 parts of coupling agent.

2. The high-strength graphite bipolar plate according to claim 1, characterized in that, The modified epoxy resin is a compound of bisphenol A epoxy resin, phenolic epoxy resin, and organic fluorine modified epoxy resin, and is obtained by binary grafting modification with KH560 and fluorosilicone coupling agent. The mass ratio of the bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin is (2-4):(1-2):

1.

3. The high-strength graphite bipolar plate according to claim 1, characterized in that, The reinforcing additive is lanthanum oxide coated hexagonal boron nitride@carbon fiber core-shell particles, in situ loaded with nano-silica sol, and chitosan as a dispersant and interfacial crosslinking agent. The mass ratio of carbon fiber, lanthanum oxide-coated hexagonal boron nitride, silica sol, and chitosan in the reinforcing additive is (7-9):1:(1.5-2):(11-13).

4. A high-strength graphite bipolar plate according to claim 1, characterized in that, The conductive agent is a micron-nano gradient conductive network formed by a combination of graphene, nano carbon black, and carbon nanotubes. The mass ratio of graphene, nano-carbon black, and carbon nanotubes in the conductive agent is (5-7):(2-4):

1.

5. A high-strength graphite bipolar plate according to claim 1, characterized in that, The curing agent is composed of methyltetrahydrophthalic anhydride, 2-ethyl-4-methylimidazole, and a latent epoxy curing agent.

6. A high-strength graphite bipolar plate according to claim 3, characterized in that, The natural graphite powder has a particle size of 150-200 mesh; The carbon fiber is polyacrylonitrile-based carbon fiber with a diameter of 10-20 μm and a length of 50-100 μm; The hexagonal boron nitride has a particle size of 50-100 nm.

7. A method for preparing a high-strength graphite bipolar plate as described in any one of claims 1-6, characterized in that, Includes the following steps: Preparation of S100 modified epoxy resin Bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin are added to a reaction vessel and stirred at 80-100℃ for 30-60 minutes. KH560 and fluorosilicone coupling agent are added, and the mixture is kept at the temperature for 2-3 hours for grafting. After cooling, the modified epoxy resin is obtained. Preparation of S200 Enhanced Additive Lanthanum oxide-coated hexagonal boron nitride was added to a mixture of carbon fiber, nano-silica sol, and chitosan, stirred, intermittently sonicated for 1-1.5 hours, and then centrifuged, dried, and pulverized to obtain the reinforcing additive. Preparation of S300 conductive agent Graphene, carbon black nanoparticles, and carbon nanotubes are added to a high-speed mixer and mixed for 10-20 minutes to obtain a conductive agent. S400 raw material mixing Add natural graphite powder, modified epoxy resin, reinforcing additive, conductive agent, dispersant, and coupling agent in sequence, keep the temperature ≤50℃, stir for 30-60 minutes, then add curing agent and continue stirring for 20-30 minutes. S500 Hot Press Molding Pre-cur the mixture at 60-90℃ for 10-15 minutes, then raise the temperature to 120-140℃ and hold it at 12MPa for 30-60 minutes, and let it cool naturally before demolding and removing the electrode plate. S600 Curing and Post-treatment The electrode plates are placed in a constant temperature oven and kept at 80-120℃ for 1.5-2.5 hours. After cooling to room temperature, internal stress is eliminated, and the plates are polished, trimmed, and surface burrs and excess material are removed to obtain high-strength graphite bipolar plates.

8. The method for preparing the high-strength graphite bipolar plate according to claim 7, characterized in that, In step S100, the amount of KH560 and fluorosilicone coupling agent is 3-6% of the total mass of bisphenol A epoxy resin, phenolic epoxy resin, and organofluorine modified epoxy resin, and the mass ratio of KH560 to fluorosilicone coupling agent is 1:

1.

9. The method for preparing a high-strength graphite bipolar plate according to claim 7, characterized in that, The preparation method of lanthanum oxide-coated hexagonal boron nitride powder in step S200 is as follows: Hexagonal boron nitride was added to ethanol, ultrasonically dispersed, and then lanthanum oxide was added. The mass ratio of hexagonal boron nitride to lanthanum oxide was 3:

1. The mixture was stirred for 20-40 minutes and then dried by rotary evaporation at 80°C to obtain lanthanum oxide-coated hexagonal boron nitride powder.

Images