A method for manufacturing a fuel cell graphite bipolar plate and a bipolar plate manufactured thereby

Abstract

The application relates to the technical field of fuel cells, and particularly discloses a fuel cell graphite bipolar plate preparation method and a bipolar plate prepared by the method. The fuel cell graphite bipolar plate comprises resol, graphite powder, carbon fibers and an impregnating agent; and the preparation method comprises the following steps: batching, granulating, hot pressing and impregnating. The fuel cell graphite bipolar plate can be used for preparing a fuel cell, has the advantages that the adverse effects on the service life of the fuel cell are reduced, and the prepared bipolar plate has the advantages that the air tightness is improved, the adverse effects on the service life of the bipolar plate are reduced, and the effects on the application of the fuel cell prepared by the bipolar plate to vehicles such as automobiles are reduced.

Description

Technical Field

[0001] This application relates to the technical field of fuel cells, and more specifically, to a method for preparing a graphite bipolar plate for a fuel cell and the resulting bipolar plate. Background Technology

[0002] A fuel cell is a device that continuously converts the chemical energy of fuel and oxidant directly into electrical energy through a chemical reaction. Due to its high efficiency and low emissions, fuel cells have been widely used in automobiles and other transportation vehicles in recent years.

[0003] Graphite composite bipolar plates are key components of fuel cells, typically manufactured by mixing graphite powder with resin and then molding. The resins used are usually thermosetting or thermoplastic. Compared to thermoplastic resins, methyl phenolic resins have shorter cooling times and higher efficiency. Compared to thermosetting resins such as epoxy resins, they can be dried at low temperatures, facilitating material distribution. When the viscosity of methyl phenolic resin is suitable, it can disperse more evenly with graphite powder, resulting in a stronger bond and easier formation of a continuous conductive network. Therefore, methyl phenolic resin is often used to mix with graphite powder to prepare graphite composite bipolar plates for fuel cells.

[0004] However, since methyl phenolic resin contains a large amount of alcohol solvents, the solvents evaporate during curing, causing a certain shrinkage rate. Therefore, when hot-pressing the mixture of methyl phenolic resin and graphite powder, bipolar plates made with high molding pressure are prone to cracking or warping, resulting in a low product qualification rate. Bipolar plates made with low molding pressure have a high qualification rate, but poor density and internal pores, leading to unqualified air tightness. Consequently, during the use of the fuel cell stack, acidic electrolytes can easily enter the pores and corrode the bipolar plates, affecting their service life and thus impacting the application of the fuel cell in automobiles and other transportation vehicles. Summary of the Invention

[0005] In order to improve the airtightness of the fabricated bipolar plate, reduce the adverse effects on the service life of the bipolar plate, and reduce the impact on the application of fuel cells in automobiles and other transportation vehicles, this application provides a method for preparing a graphite bipolar plate for a fuel cell and the bipolar plate prepared therefrom.

[0006] In a first aspect, this application provides a method for preparing a graphite bipolar plate for a fuel cell, employing the following technical solution:

[0007] A method for preparing a graphite bipolar plate for a fuel cell includes the following steps:

[0008] S1. Ingredients: Mix the first-stage phenolic thermosetting resin, graphite powder and conductive material in a weight ratio of (10-40):(60-90):(1-10) to obtain a composite wet powder, wherein the conductive material is carbon fiber.

[0009] S2. Granulation: The wet composite powder obtained in S1 is dried at 150±10℃ for 15±1min, cooled and crushed, and then sieved to obtain composite powder with a particle size of 200±100 mesh.

[0010] S3. Hot pressing: The composite powder obtained in S2 is evenly spread into the mold. After the mold is closed, it is heated to 160±1℃ at 5-15MPa and hot pressed for 30-60min to obtain the primary graphite bipolar plate.

[0011] S4. Impregnation: The primary graphite bipolar plate obtained in S3 is subjected to vacuum treatment. The vacuum-treated primary graphite bipolar plate is then immersed in an impregnating agent and impregnated at 0.4-0.7 MPa for 3-6 hours. The impregnated primary graphite bipolar plate is then removed and cleaned. The cleaned primary graphite bipolar plate is then cured at 0.5-0.8 MPa for 2±1 hours at a curing temperature of 150-180℃ to obtain the graphite bipolar plate.

[0012] By adopting the above technical solution, the raw materials are mixed and the mixed wet material is granulated to obtain composite powder, thereby enabling the methyl phenolic thermosetting resin in the wet material to be initially cross-linked and cured, which facilitates the uniform distribution of the raw materials in the mold, and at the same time reduces the possibility of some methyl phenolic thermosetting resin being squeezed out and causing uneven distribution when the wet material is hot-pressed.

[0013] By using low-pressure hot pressing, the density of the primary graphite bipolar plate is appropriately reduced and channels are formed, making it easier for the solution in the methyl phenolic thermosetting resin to drain out from the formed channels. The relatively loose structure is more conducive to stress dispersion, making the flatness of the graphite bipolar plate easier to control and the yield of finished products with different shapes.

[0014] After the primary graphite bipolar plate is prepared, it is impregnated. At this time, the impregnating agent is cured and fills the pores on the surface of the primary graphite bipolar plate, which improves the airtightness and strength of the prepared graphite bipolar plate and reduces the adverse effects on the airtightness and strength of the graphite bipolar plate caused by the use of low-pressure hot pressing.

[0015] When impregnating the primary graphite bipolar plate, a vacuum treatment is first used to remove the gas in the pores of the primary graphite bipolar plate. Then, the primary graphite bipolar plate is immersed in the impregnating agent and pressurized, thereby forcing the impregnating agent into the pores. This reduces the possibility that the impregnating agent is not easy to enter the pores, which helps to improve the airtightness and strength of the graphite bipolar plate, reduces the adverse effects on the service life of the bipolar plate, and thus reduces the impact on the application of fuel cells made from the bipolar plate in automobiles and other transportation vehicles.

[0016] Preferably, in step S4, the vacuum treatment method is to maintain the primary graphite bipolar plate at -0.2±0.1MPa for 1-3 hours.

[0017] By adopting the above technical solution, the prepared primary graphite bipolar plate is vacuum-treated under the above pressure for 1-3 hours to remove the gas in the pores of the primary graphite bipolar plate. This facilitates the impregnating agent to fully fill the pores on the surface of the primary graphite bipolar plate, thereby improving the airtightness and strength of the primary graphite bipolar plate and reducing the impact on the application of fuel cells made from the bipolar plate in automobiles and other transportation vehicles. When the pressure and time of vacuum treatment exceed the above range, the structure of the primary graphite bipolar plate may be damaged, thus affecting the airtightness and strength of the primary graphite bipolar plate. When the pressure and time of vacuum treatment are less than the above range, it is difficult to completely remove the gas from the pores of the primary graphite bipolar plate, which may make it difficult for the impregnating agent to completely fill the pores, affecting the airtightness and strength of the graphite bipolar plate.

[0018] Preferably, in step S4, the viscosity of the impregnating agent at 25°C is 100-500 mPa·s.

[0019] By adopting the above technical solution, when the primary graphite bipolar plate is impregnated in an impregnating agent with a viscosity within the above range, it facilitates the impregnating agent to fully penetrate and fill the pores, while improving the adhesion between the impregnating agent and the primary graphite bipolar plate, and reducing the possibility of the impregnating agent falling off after curing. When the viscosity of the impregnating agent is less than the above range, the bonding force between the impregnating agent and the primary graphite bipolar plate is weak, which may easily cause the impregnating agent to fall off, affecting the airtightness and strength of the graphite bipolar plate. When the viscosity of the impregnating agent is greater than the above range, it may be difficult for the impregnating agent to penetrate into the pores, thereby affecting the airtightness and strength of the graphite bipolar plate.

[0020] Preferably, in S1, the average particle size of the graphite powder is 5-30 μm, and the viscosity of the methyl phenolic thermosetting resin is 50-100 mPa·s.

[0021] By adopting the above technical solution, selecting graphite powder within the above particle size range and methyl phenolic thermosetting resin within the above viscosity range, it is easier for graphite powder and methyl phenolic thermosetting resin to be fully mixed and bonded, reducing the possibility of cracking. When the particle size of graphite powder and the viscosity of methyl phenolic thermosetting resin are smaller than the above range, graphite powder is prone to agglomeration due to its increased specific surface area, making it difficult to mix evenly with methyl phenolic thermosetting resin. Furthermore, the viscosity of methyl phenolic resin decreases, thereby reducing the bonding force with graphite powder and affecting the strength of the graphite bipolar plate. When the particle size of graphite powder and the viscosity of methyl phenolic thermosetting resin are larger than the above range, the contact area between graphite powder and methyl phenolic thermosetting resin decreases, and the viscosity of methyl phenolic thermosetting resin increases, making it difficult to mix evenly with graphite powder. This is not conducive to the formation of a continuous conductive network in the graphite bipolar plate, thus affecting the quality of the graphite bipolar plate.

[0022] Preferably, in step S4, the impregnating agent is prepared from epoxy resin, dicyclopentadienol-type epoxy resin, and methyltetrahydroanhydride in a weight ratio of (5-10):(30-45):(50-60), and the impregnating agent is prepared by the following method:

[0023] The epoxy resin, dicyclopentadienol-type epoxy resin and methyltetrahydroanhydride were mixed and stirred for 10±1 min and allowed to stand for 40±1 min to obtain the impregnating agent.

[0024] By adopting the above technical solution, dicyclopentadienol-type epoxy resin is selected as a diluent, and methyltetrahydroanic anhydride is selected as a curing agent to prepare an impregnating agent with epoxy resin. Dicyclopentadienol-type epoxy resin is used as an active diluent to dilute epoxy resin. It has low hygroscopicity, and methyltetrahydroanic anhydride forms a cross-linked network with epoxy resin, which is convenient for filling the pores of the primary graphite bipolar plate and improving the airtightness of the graphite bipolar plate.

[0025] Preferably, the dicyclopentadienol type epoxy resin is prepared by mixing hyperbranched polysiloxane and dicyclopentadienol type epoxy resin in a weight ratio of (3-5):100.

[0026] By adopting the above technical solution, hyperbranched polysiloxane is selected to blend with dicyclopentadienol-type epoxy resin, which facilitates the bonding of dicyclopentadienol-type epoxy resin with primary graphite bipolar plates through hyperbranched polysiloxane. This allows the impregnating agent to physically fill the pores of the primary graphite bipolar plate while further decoupling the impregnating agent from the primary graphite bipolar plate, thereby improving the bonding force between the impregnating agent and the primary graphite bipolar plate. At the same time, the hyperbranched polysiloxane, being a dendritic molecule, has entanglement between molecular chains and low viscosity characteristics that can absorb impact energy and disperse stress, thus toughening the graphite bipolar plate and reducing the possibility of crack propagation.

[0027] Preferably, the hyperbranched polysiloxane is prepared from diethylene glycol and 3-(2,3-epoxypropoxy)propyltrimethoxysilane in a weight ratio of 5:(3-5), and the preparation method of the hyperbranched polysiloxane is as follows:

[0028] Diethylene glycol and 3-(2,3-epoxypropoxy)propyltrimethoxysilane were mixed in a weight ratio and slowly heated to 130±10℃ under a nitrogen atmosphere while stirring continuously until distillate was produced. The distillation temperature was controlled at 55±1℃ and gradually increased to 150-170℃ until no distillate was produced. After cooling to room temperature, the residual distillate was removed under vacuum to obtain hyperbranched polysiloxane.

[0029] By adopting the above technical solution, hyperbranched polysiloxane is prepared by using diethylene glycol to react 3-(2,3-epoxypropoxy)propyltrimethoxysilane. This allows 3-(2,3-epoxypropoxy)propyltrimethoxysilane to form dendritic molecules, which facilitates toughening of the impregnating agent. 3-(2,3-epoxypropoxy)propyltrimethoxysilane is also easily bonded to graphite, thus facilitating the bonding of dicyclopentadienol-type epoxy resin to the primary graphite bipolar plate, further improving the bonding force between the impregnating agent and the primary graphite bipolar plate. Furthermore, 3-(2,3-epoxypropoxy)propyltrimethoxysilane contains epoxy groups, which further facilitates cross-linking and curing to form a three-dimensional network. During curing, the curing temperature causes the molecular chains of the hyperbranched polysiloxane and dicyclopentadienol-type epoxy resin to curl up, facilitating the impregnating agent to enter the pores of the primary graphite bipolar plate, further improving the airtightness and strength of the graphite bipolar plate.

[0030] Secondly, this application provides a graphite bipolar plate for a fuel cell, employing the following technical solution:

[0031] A graphite bipolar plate for a fuel cell is prepared by the above-described method for preparing a graphite bipolar plate for a fuel cell.

[0032] By adopting the above technical solution, the graphite bipolar plate prepared by the preparation method of this application is integrally formed. Compared with the graphite bipolar plate prepared by machining, the thickness is reduced and the production efficiency is high. It can meet the requirements of flatness and shape yield of graphite bipolar plate while improving the airtightness and strength of graphite bipolar plate.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. By using low-pressure hot pressing, the density of the primary graphite bipolar plate is appropriately reduced and channels are formed, making it easier for the solution in the methyl phenolic thermosetting resin to drain out through the formed channels. The relatively loose structure is also more conducive to stress dispersion, making the flatness of the graphite bipolar plate easier to control and the yield of finished products higher. When impregnating and filling the pores on the surface of the primary graphite bipolar plate, a vacuum treatment is first used to remove the gas in the pores of the primary graphite bipolar plate. The primary graphite bipolar plate is then immersed in the impregnating agent and pressurized, thereby forcing the impregnating agent into the pores.

[0035] 2. When the primary graphite bipolar plate is impregnated in an impregnating agent with a viscosity within the above-mentioned range, it facilitates the impregnating agent to fully penetrate and fill the pores, while improving the adhesion between the impregnating agent and the primary graphite bipolar plate, and reducing the possibility of the impregnating agent falling off after curing. When the viscosity of the impregnating agent is less than the above-mentioned range, the adhesion between the impregnating agent and the primary graphite bipolar plate is weak, which may easily cause the impregnating agent to fall off. When the viscosity of the impregnating agent is greater than the above-mentioned range, the impregnating agent is difficult to penetrate into the pores, thereby affecting the airtightness and strength of the graphite bipolar plate.

[0036] 3. Selecting graphite powder within the above particle size range and methyl phenolic thermosetting resin within the above viscosity range facilitates thorough mixing and bonding of the graphite powder and methyl phenolic thermosetting resin, reducing the possibility of cracking. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the embodiments.

[0038] The methods for testing the flexural strength, shear strength, electrical conductivity, airtightness, and flatness of the graphite bipolar plates prepared in all embodiments and comparative examples are as follows:

[0039] 1. Bending strength

[0040] The bending strength of the graphite composite plate was tested according to the test method in the national standard GBT-20042.6-2024 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics".

[0041] 2. Shear strength

[0042] The shear strength of graphite composite plates was tested according to the test method in the national standard GB / T 40388-2021 "Test Method for Shear Strength of Carbon / Carbon Composite Materials".

[0043] 3. Electrical conductivity

[0044] The conductivity of the graphite composite board was tested according to the testing method of the National Metrological Verification Regulation JJG 508-2004 "Four-Probe Resistivity Tester".

[0045] 4. Air tightness

[0046] The airtightness of the graphite composite plate was tested according to the test method in the national standard GBT-20042.6-2024 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics".

[0047] 5. Flatness

[0048] The flatness of the graphite composite plate was tested according to the test method in the national standard GBT-20042.6-2024 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics".

[0049] raw material

[0050] The raw materials used in the embodiments and comparative examples of this application are all commercially available. The epoxy resin used is E-51, and the solid content of the methyl phenolic thermosetting resin is 80±10%.

[0051] Preparation Example

[0052] Preparation Example 1: Hyperbranched Polysiloxane

[0053] Preparation Example 1.1

[0054] A hyperbranched polysiloxane, the preparation method of which is as follows:

[0055] 5g of diethylene glycol and 3g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane were mixed and slowly heated to 130°C under a nitrogen atmosphere while stirring continuously until a distillate was produced. The distillation temperature was controlled at 55°C, and the temperature was gradually increased to 150°C until no more distillate was produced. After cooling to room temperature, the residual distillate was removed under vacuum to obtain hyperbranched polysiloxane.

[0056] Preparation Example 1.2

[0057] Unlike Preparation Example 1.1, in Preparation Example 1.2, the amount of 3-(2,3-epoxypropoxy)propyltrimethoxysilane added was 4g.

[0058] Preparation Example 1.3

[0059] Unlike Preparation Example 1.1, the amount of 3-(2,3-epoxypropoxy)propyltrimethoxysilane added in Preparation Example 1.3 was 5g.

[0060] Preparation Example 1.4

[0061] Unlike Preparation Example 1.2, Preparation Example 1.4 involved a gradient temperature increase to 160°C.

[0062] Preparation Example 1.5

[0063] Unlike Preparation Example 1.2, Preparation Example 1.5 involved a gradient temperature increase to 170°C.

[0064] Preparation Example 2: Modified Dicyclopentadienol Type Epoxy Resin

[0065] Preparation Example 2.1

[0066] A modified pentadienylphenol type epoxy resin, the preparation method of which is as follows:

[0067] 3g of hyperbranched polysiloxane from Preparation Example 1.1 and 100g of dicyclopentadienol type epoxy resin were mixed to obtain modified dicyclopentadienol type epoxy resin.

[0068] Preparation Example 2.2

[0069] Unlike Preparation Example 2.1, in Preparation Example 2.2, the amount of hyperbranched polysiloxane from Preparation Example 1.1 added was 4g.

[0070] Preparation Example 2.3

[0071] Unlike Preparation Example 2.1, the amount of hyperbranched polysiloxane added in Preparation Example 2.3 from Preparation Example 1.1 is 5g.

[0072] Preparation Examples 2.4-2.7

[0073] Unlike Preparation Example 2.2, the hyperbranched polysiloxanes in Preparation Examples 2.4-2.7 were derived in equal amounts from Preparation Examples 1.2-1.5.

[0074] Preparation Example 2.8

[0075] Unlike Preparation Example 2.2, Preparation Example 2.8 uses an equal amount of 3-(2,3-epoxypropoxy)propyltrimethoxysilane to replace the hyperbranched polysiloxane.

[0076] Preparation Example 3 Impregnating Agent

[0077] Preparation Example 3.1

[0078] An impregnating agent, the preparation method of which is as follows:

[0079] 5g of epoxy resin, 45g of dicyclopentadienol-type epoxy resin and 50g of methyltetrahydroanic anhydride were mixed and stirred for 10 minutes and allowed to stand for 40 minutes to obtain an impregnating agent. The viscosity of the impregnating agent at 25℃ was 100mPa·s.

[0080] Preparation Example 3.2

[0081] Unlike Preparation Example 3.1, in Preparation Example 3.2, the amount of epoxy resin added was 10g, the amount of dicyclopentadienol type epoxy resin was 35g, and the amount of methyltetrahydroanic anhydride added was 55g.

[0082] Preparation Example 3.3

[0083] Unlike Preparation Example 3.1, Preparation Example 3.3 contained 7.5 g of epoxy resin, 30 g of dicyclopentadienol epoxy resin, and 60 g of methyltetrahydroanic anhydride.

[0084] Preparation Example 3.4

[0085] Unlike Preparation Example 3.2, the impregnating agent prepared in Preparation Example 3.4 has a viscosity of 300 mPa·s at 25°C.

[0086] Preparation Example 3.5

[0087] Unlike Preparation Example 3.2, the impregnating agent prepared in Preparation Example 3.5 has a viscosity of 500 mPa·s at 25°C.

[0088] Preparation Examples 3.6-3.13

[0089] Unlike Preparation Example 3.4, the dicyclopentadienol type epoxy resin in Preparation Examples 3.6-3.13 was replaced with an equal amount of modified pentadienol type epoxy resin from Preparation Examples 2.1-2.8. Example

[0090] Example 1: Dicyclopentadienol type epoxy resin

[0091] Example 1.1

[0092] A graphite bipolar plate, the preparation method of which is as follows:

[0093] S1. Ingredients: Mix 20g of methyl phenolic thermosetting resin with a viscosity of 50mPa·s, 180g of graphite powder with an average particle size of 5μm and 11g of carbon fiber at a speed of 800r / min for 120s to obtain composite powder wet material.

[0094] S2. Granulation: The wet composite powder obtained in S1 is dried at 150℃ for 15 minutes, cooled and crushed, and then sieved to obtain composite powder with a particle size of 200 mesh.

[0095] S3. Hot pressing: The composite powder obtained in S2 is evenly spread into the mold. After the mold is closed, the temperature is raised to 160℃ at 5MPa and held for 10 minutes. The heating time is 20 minutes to obtain the primary graphite bipolar plate.

[0096] S4. Impregnation: The primary graphite bipolar plate obtained in S3 is kept at -0.2 MPa for 2 hours. The vacuum-treated primary graphite bipolar plate is then immersed in 100 g of the impregnating agent from Preparation Example 3.1 and impregnated at 0.4 MPa for 3 hours. The impregnated primary graphite bipolar plate is then removed and cleaned. The cleaned primary graphite bipolar plate is then cured at 0.5 MPa for 2 hours at a curing temperature of 160°C to obtain a graphite bipolar plate with a thickness ≤1 mm, a length of 360 mm, a width of 140 mm, and flow channels on both sides.

[0097] Examples 1.2-1.5

[0098] Unlike Example 1.1, the raw material ratios and process parameters in Examples 1.2-1.5 are different, as detailed in Table 1.

[0099] Table 1 Raw material ratios and process parameters for Examples 1.1-1.5

[0100]

[0101] Comparative Example 1

[0102] Unlike Example 1.1, the hot pressing pressure in Comparative Example 1 was 30 MPa, and the primary graphite bipolar plate was not impregnated.

[0103] Comparative Example 2

[0104] Unlike Example 1.1, the primary graphite bipolar plate prepared in Comparative Example 2 was not impregnated.

[0105] The graphite bipolar plates prepared in Examples 1.1-1.5 and Comparative Examples 1-2 were tested for bending strength, shear strength, electrical conductivity, airtightness and flatness, as detailed in Table 2.

[0106] Table 2 Performance test data for Examples 1.1-1.5 and Comparative Examples 1-2

[0107]

[0108] As shown in Table 2, Comparative Example 1 used high hot-pressing pressure and did not impregnate the primary graphite bipolar plate. Although the resulting graphite bipolar plate had better bending strength and electrical conductivity, and its airtightness was within the acceptable range, its performance in terms of flatness and shear strength was poor, and it did not meet the usage requirements. Comparative Example 2 used the same low-pressure hot-pressing method as this application but did not impregnate the resulting primary graphite bipolar plate. Although the resulting graphite bipolar plate met the requirements for flatness and electrical conductivity, its performance in terms of bending strength and shear strength was poor, and its airtightness was significantly reduced, with the possibility of air leakage. It also did not meet the usage requirements.

[0109] The graphite bipolar plates prepared in Examples 1.1-1.5 of this application exhibit better performance in terms of flatness, airtightness, and shear strength than those in Comparative Examples 1-2. Furthermore, their electrical conductivity and bending strength also meet the requirements for use. This indicates that the method of using low-pressure hot pressing and impregnation treatment of the primary graphite bipolar plate in this application is beneficial to improving the flatness, airtightness, and shear strength without affecting the electrical conductivity and bending strength of the graphite bipolar plate.

[0110] Examples 1.1-1.3 investigated the effect of the raw material ratio of graphite bipolar plates. The results showed that the graphite bipolar plate prepared in Example 1.2 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the raw material ratio of the graphite bipolar plate selected in Example 1.2 is beneficial to improve the flatness, airtightness, and shear strength without affecting the electrical conductivity and bending strength of the graphite bipolar plate.

[0111] Compared with Example 1.2, Examples 1.4-1.5 investigated the effects of hot pressing pressure, hot pressing time, vacuum time, impregnation pressure, impregnation time, curing time, and curing temperature. The results showed that the graphite bipolar plate prepared in Example 1.4 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the process parameters selected in Example 1.4 for preparing the graphite bipolar plate are beneficial to improving the flatness, airtightness, and shear strength without affecting the electrical conductivity and bending strength of the graphite bipolar plate.

[0112] Example 2: Viscosity of methyl phenolic thermosetting resin and average particle size of graphite powder

[0113] Example 2.1

[0114] Unlike Example 1.4, in Example 2.1 the average particle size of graphite powder is 20 μm and the viscosity of the methyl phenolic thermosetting resin is 75 mPa·s.

[0115] Example 2.2

[0116] Unlike Example 1.4, in Example 2.2 the average particle size of graphite powder is 30 μm and the viscosity of the methyl phenolic thermosetting resin is 150 mPa·s.

[0117] The graphite bipolar plates prepared in Examples 2.1-2.2 were tested for bending strength, shear strength, electrical conductivity, airtightness and flatness, as detailed in Table 3.

[0118] Table 3 Performance test data for Examples 2.1-2.2

[0119]

[0120] Referring to Tables 2 and 3, and using Example 1.4 as a control, the effects of the average particle size of graphite powder and the viscosity of the first-order phenolic thermosetting resin were investigated in Examples 2.1-2.2. The results showed that the graphite bipolar plate prepared in Example 2.1 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the average particle size of graphite powder and the viscosity of the first-order phenolic thermosetting resin selected in Example 2.1 are beneficial to improving the performance of the graphite bipolar plate in terms of electrical conductivity, bending strength, flatness, airtightness, and shear strength.

[0121] Example 3: Modified dicyclopentadienol type epoxy resin

[0122] Examples 3.1-3.12

[0123] Unlike Example 1.4, the impregnating agents in Examples 3.1-3.12 were derived in equal amounts from Preparation Examples 3.2-3.13.

[0124] The graphite bipolar plates prepared in Examples 3.1-3.12 were tested for bending strength, shear strength, electrical conductivity, airtightness and flatness, as detailed in Table 4.

[0125] Table 4 Performance test data for Examples 3.1-3.12

[0126]

[0127] As shown in Tables 3 and 4, with Example 2.1 as a control, Examples 3.1-3.2 investigated the effect of the impregnating agent raw material ratio. The results showed that the graphite bipolar plate prepared in Example 3.1 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the impregnating agent raw material ratio selected in Example 3.1 is beneficial to improving the performance of the graphite bipolar plate in terms of electrical conductivity, bending strength, flatness, airtightness, and shear strength.

[0128] Compared with Example 3.1, Examples 3.3-3.4 investigated the effect of impregnating agent viscosity. The results showed that the graphite bipolar plate prepared in Example 3.3 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness and flatness. This may be because the impregnating agent selected in Example 3.3 had a moderate viscosity, which made it easier for the impregnating agent to fill the primary graphite bipolar plate while improving the bonding force between the impregnating agent and the primary graphite bipolar plate, thereby improving the performance of the graphite bipolar plate in terms of electrical conductivity, bending strength, flatness, airtightness and shear strength.

[0129] Compared with Example 3.3, Examples 3.5-3.12 investigated the effect of modified dicyclopentadienol epoxy resin. The results showed that the graphite bipolar plates prepared in Examples 3.5-3.12 performed better in terms of flexural strength, shear strength, electrical conductivity, airtightness, and flatness. This may be because in Examples 3.5-3.12, an equal amount of modified dicyclopentadienol epoxy resin was used to replace the dicyclopentadienol epoxy resin. This allows the impregnating agent to physically fill the pores of the primary graphite bipolar plate under pressure while chemically bonding with it, thus facilitating pore filling, improving the bonding force with the primary graphite bipolar plate, and consequently improving the performance of the graphite bipolar plate in terms of electrical conductivity, flexural strength, flatness, airtightness, and shear strength.

[0130] Examples 3.5-3.7 investigated the effect of the raw material ratio of the modified dicyclopentadienol epoxy resin. The results showed that the graphite bipolar plate prepared in Example 3.6 exhibited better performance in terms of flexural strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the raw material ratio of the modified dicyclopentadienol epoxy resin selected in Example 3.6 is beneficial to improving the performance of the graphite bipolar plate in terms of electrical conductivity, flexural strength, flatness, airtightness, and shear strength.

[0131] Compared with Example 3.6, the influence of the proportion of hyperbranched polysiloxane raw materials was investigated in Examples 3.8-3.9. The results showed that the graphite bipolar plate prepared in Example 3.8 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness and flatness. This indicates that the proportion of hyperbranched polysiloxane raw materials selected in Example 3.8 is beneficial to improving the performance of graphite bipolar plate in terms of electrical conductivity, bending strength, flatness, airtightness and shear strength.

[0132] Compared with Example 3.8, Examples 3.10-3.11 investigated the effect of gradient heating temperature during the preparation of hyperbranched polysiloxanes. The results showed that the graphite bipolar plate prepared in Example 3.10 performed better in terms of bending strength, shear strength, electrical conductivity, airtightness, and flatness. This indicates that the gradient heating temperature selected in Example 3.10 during the preparation of hyperbranched polysiloxanes is beneficial to improving the performance of graphite bipolar plates in terms of electrical conductivity, bending strength, flatness, airtightness, and shear strength.

[0133] Compared with Example 3.10, in Example 3.12, an equal amount of 3-(2,3-epoxypropoxy)propyltrimethoxysilane was used to replace the hyperbranched polysiloxane, thereby modifying the dicyclopentadienol-type epoxy resin. The results showed that the graphite bipolar plate prepared in Example 3.10 performed better than that in Example 3.12 in terms of flexural strength, shear strength, conductivity, airtightness, and flatness. This may be because the hyperbranching of 3-(2,3-epoxypropoxy)propyltrimethoxysilane forms dendritic molecules, which, in contrast, enhance the properties of the polysiloxane. When dicyclopentadienol-type epoxy resin is blended and modified, it facilitates the toughening of the impregnating agent and the bonding of the dicyclopentadienol-type epoxy resin to the primary graphite bipolar plate, thereby improving the bonding force between the impregnating agent and the primary graphite bipolar plate. Furthermore, the curing temperature during curing causes the molecular chains of the hyperbranched polysiloxane and dicyclopentadienol-type epoxy resin to coil, which facilitates the impregnating agent to enter the pores of the primary graphite bipolar plate, thereby improving the performance of the graphite bipolar plate in terms of electrical conductivity, flexural strength, flatness, airtightness, and shear strength.

[0134] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a graphite bipolar plate for a fuel cell, characterized in that, Includes the following steps: S1. Ingredients: Mix the first-stage phenolic thermosetting resin, graphite powder and conductive material in a weight ratio of (10-40):(60-90):(1-10) to obtain a composite wet powder, wherein the conductive material is carbon fiber. S2. Granulation: The wet composite powder obtained in S1 is dried at 150±10℃ for 15±1min, cooled and crushed, and then sieved to obtain composite powder with a particle size of 200±100 mesh. S3. Hot pressing: The composite powder obtained in S2 is evenly spread into the mold. After the mold is closed, it is heated to 160±1℃ at 5-15MPa and hot pressed for 30-60min to obtain the primary graphite bipolar plate. S4. Impregnation: The primary graphite bipolar plate obtained in S3 is subjected to vacuum treatment. The vacuum-treated primary graphite bipolar plate is then immersed in an impregnating agent and impregnated at 0.4-0.7 MPa for 3-6 hours. The impregnated primary graphite bipolar plate is then removed and cleaned. The cleaned primary graphite bipolar plate is then cured at 0.5-0.8 MPa for 2±1 hours at a curing temperature of 150-180℃ to obtain the graphite bipolar plate. In step S4, the vacuum treatment method is as follows: the primary graphite bipolar plate is kept at -0.2±0.1MPa for 1-3 hours; in step S4, the viscosity of the impregnating agent at 25°C is 100-500mPa·s; in step S1, the average particle size of the graphite powder is 5-30μm, and the viscosity of the methyl phenolic thermosetting resin is 50-100mPa·s. In step S4, the impregnating agent is prepared from epoxy resin, dicyclopentadienol-type epoxy resin, and methyltetrahydroanhydride in a weight ratio of (5-10):(30-45):(50-60), and the preparation method of the impregnating agent is as follows: The epoxy resin, dicyclopentadienol type epoxy resin and methyltetrahydroanhydride were mixed and stirred for 10±1 min and allowed to stand for 40±1 min to obtain the impregnating agent. The dicyclopentadienol type epoxy resin is prepared by mixing hyperbranched polysiloxane and dicyclopentadienol type epoxy resin in a weight ratio of (3-5):

100.

2. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, characterized in that: The hyperbranched polysiloxane is prepared by diethylene glycol and 3-(2,3-epoxypropoxy)propyltrimethoxysilane in a weight ratio of 5:(3-5). The preparation method of the hyperbranched polysiloxane is as follows: Diethylene glycol and 3-(2,3-epoxypropoxy)propyltrimethoxysilane were mixed in a weight ratio and slowly heated to 130±10℃ under a nitrogen atmosphere while stirring continuously until distillate was produced. The distillation temperature was controlled at 55±1℃ and gradually increased to 150-170℃ until no distillate was produced. After cooling to room temperature, the residual distillate was removed under vacuum to obtain hyperbranched polysiloxane.

3. A graphite bipolar plate for a fuel cell, characterized in that: It is prepared by the method for preparing graphite bipolar plates for fuel cells according to any one of claims 1-2.

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