A novel method for preparing composite graphite bipolar plate

Abstract

The present invention provides a novel method for preparing a composite graphite bipolar plate, comprising the following steps: (1) adding a thermosetting phenolic resin to a good solvent at a certain temperature and stirring to dissolve it; (2) adding a poor solvent and a bridging agent, stirring to diffuse the resin droplets into the poor solvent and crystallize them, filtering and drying to obtain resin spherulites; (3) calcining the resin spherulites for a period of time to solidify 90% of the resin and coat the resin surface with the remaining amorphous carbon; (4) blending the resin obtained in step (3) with graphite and then molding it, and then calcining the bipolar plate at 1000°C to convert the amorphous carbon into glassy carbon; (5) impregnating and curing the calcined bipolar plate to obtain the novel composite graphite bipolar plate. This method avoids the problems of slow resin curing rate and long curing time by adopting the resin spherulite molding method, facilitates blending with graphite, avoids the problem of uneven distribution, and improves the bending strength of the molded plate.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and in particular relates to a method for preparing a novel composite graphite bipolar plate. Background Art

[0002] Fuel cells conduct fuel protons through a proton exchange membrane, generating electricity by outputting current through an external path. Their product consists solely of water, making them a highly efficient and environmentally friendly energy conversion method. Fuel cells offer high energy conversion efficiency and are not limited by the Carnot cycle. They are currently widely used in new energy vehicles, ships, drones, and combined heat and power generation.

[0003] Fuel cells are mainly composed of a stack and system components, and the stack is the core of the entire fuel cell. It includes a battery unit composed of a membrane electrode and a bipolar plate, as well as a current collector, end plate, sealing ring, etc. The bipolar plate plays the role of separating the reaction gas, removing heat, and discharging the chemical reaction products (water). The airtightness, electrical and thermal conductivity, mechanical properties, and corrosion resistance of the bipolar plate will affect the performance of the entire stack, thereby affecting the performance of the battery. Traditional composite graphite bipolar plates are mainly mass-produced by compression molding. The performance of the prepared composite graphite bipolar plates mainly depends on the composition and ratio of graphite and resin. There is a contradiction between the difficulty in optimizing the electrical conductivity and bending strength simultaneously. In addition, the thickness of the graphite bipolar plate needs to be continuously reduced, and the performance of the composite graphite bipolar plate needs to be further improved. Summary of the Invention

[0004] The present invention aims to solve the technical problem that the electrical conductivity and bending strength of existing composite graphite bipolar plates need to be improved simultaneously, and proposes a novel method for preparing composite graphite bipolar plates.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a novel composite graphite bipolar plate comprises the following steps:

[0007] (1) adding a thermosetting phenolic resin to a good solvent at a certain temperature and stirring to dissolve it;

[0008] (2) adding a certain amount of poor solvent and bridging agent, stirring to allow the resin droplets to diffuse into the poor solvent and crystallize, filtering and drying to obtain resin spherulite particles;

[0009] (3) calcining the resin spherulites at 500°C-700°C for a period of time to solidify 90% of the resin and coat the surface of the resin with the remaining amorphous carbon;

[0010] (4) blending the resin obtained in step (3) with graphite and then performing molding, and then calcining the molded bipolar plate at 800° C. to 1200° C. to convert the amorphous carbon into glassy carbon;

[0011] (5) The calcined bipolar plate is impregnated with glue and solidified to obtain a novel composite graphite bipolar plate.

[0012] Preferably, in step (1), the good solvent is one of methanol, ethanol, isopropanol and acetone, and the poor solvent is water.

[0013] Preferably, the bridging agent in step (2) is one of carbon tetrachloride, isopropyl acetate, toluene and isobutyl acetate.

[0014] Preferably, in step (1) and step (2), the stirring temperature is 30-50° C., the stirring speed is 200-500 rpm / min, and the stirring time is 0.5-2 h.

[0015] Preferably, the mass ratio of graphite to resin in step (4) is (3-4): (1-2).

[0016] Preferably, the molding method in step (4) is cold pressing with a pressure of 5 to 45 MPa in nine sections.

[0017] Preferably, in step (5), the curing temperature is 350° C. and the curing time is 2 h.

[0018] Preferably, the impregnated glue in step (5) is acrylic resin, and the impregnation time is 24 hours.

[0019] Preferably, the calcination temperature in step (3) is 600°C.

[0020] Preferably, the calcination temperature in step (4) is 1000°C.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are:

[0022] The novel composite graphite bipolar plate preparation method employs resin spherulite molding, avoiding the slow and long curing times of the resin. This facilitates blending with graphite and avoids uneven distribution. After molding, the plate is cured at 1000°C, improving its flexural strength. Compared to conventional resin-graphite blended plates, the composite bipolar plates produced using this method exhibit higher conductivity, more uniform thickness, and improved flexural strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the process of spherulite forming of the present invention;

[0024] Figure 2This is a flow chart of the method for preparing the novel composite graphite bipolar plate of the present invention; DETAILED DESCRIPTION

[0025] In order to better understand the present invention, Figure 1 and Figure 2 And embodiments are described in detail.

[0026] Example 1

[0027] A method for preparing a novel composite graphite bipolar plate comprises the following steps:

[0028] (1) Weigh 40 g of Sumitomo PR12603 resin and place it in a round-bottom container. Add 100 ml of ethanol solvent and stir at 30°C for 1 h using a magnetic stirrer with a heating capacity of 350 rpm / min to dissolve it.

[0029] (2) After stirring, 100 ml of water and 30 ml of isopropyl acetate solution were added to the solution obtained in step (1). The mixture was magnetically stirred at 30°C for 2 h at a stirring speed of 350 rpm / min. Since ethanol is a good solvent for the resin and water is a poor solvent for the resin, under the action of isopropyl acetate as a bridging agent, the resin droplets precipitated from the good solvent into the poor solvent to form resin spherulites.

[0030] (3) The solution obtained in step (2) was filtered and dried in a thermostat at 28° C. to obtain resin spherulite particles.

[0031] (4) The obtained resin spherulites were calcined in a muffle furnace at 600° C. for 2 h to obtain cured resin spherulites. At this time, 90% of the resin was cured, and the remaining amorphous carbon was wrapped around the resin surface.

[0032] (5) The solidified resin spherulites were mixed with 60 g of expanded graphite (200 mesh, Hebei Fengming) in an internal mixer and then placed in a molding machine. Silicone oil was used as a release agent and cold pressing was performed at a pressure of 5 to 45 MPa in nine sections. After demolding, a bipolar plate with a flow channel was obtained.

[0033] (6) The molded bipolar plate is placed in a muffle furnace and cured at 1000°C for 2 hours. After cooling, the bipolar plate is taken out and vacuum-impregnated in acrylic resin for 24 hours.

[0034] (7) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0035] The specific test methods are as follows:

[0036] (1) Thickness test: Take six different locations in the flow channel area of ​​the bipolar plate, use a thickness gauge to measure the thickness, and record and calculate the average value.

[0037] (2) Conductivity test: The conductivity of the composite board was measured using an RTS-9 dual-electricity four-probe measuring instrument. In order to eliminate the contact resistance between the metal probe and the sample, the DC four-probe method was used to directly test the conductivity.

[0038] (3) Bending strength test: The WD-10D universal testing machine was used to measure the bending resistance of the composite board. The three-point bending method was used to test the bending strength of the composite board. The test steps are as follows:

[0039] ① Make the sample into a long strip with a width of 10mm.

[0040] ② Adjust the support span so that the pressure head and support head are perpendicular to the specimen axis.

[0041] ③The pressure head is 10mm / s 2 The load is applied uniformly and without shock until the sample breaks, and the breaking load value is read.

[0042] The flexural strength is calculated according to the following formula:

[0043] δ F =3PL / 2bh 2’

[0044] Wherein, δF is the flexural strength (MPa), P is the breaking load value (N), L is the support span (30 mm), b is the sample width (mm), and h is the sample thickness (mm).

[0045] Example 2

[0046] (1) Weigh 50 g of PR55147 resin and place it in a round-bottom container. Add 150 ml of acetone solvent and stir at 25°C for 1 h using a magnetic stirrer with a heating capacity of 300 rpm / min.

[0047] (2) After stirring, add 150 ml of water and 50 ml of carbon tetrachloride solution to the solution obtained in step (1). Stir magnetically at 30° C. for 2 h at a stirring speed of 300 rpm / min until resin spherulites precipitate from the good solvent into the poor solvent.

[0048] (3) The solution obtained in step (2) was filtered and dried in a thermostat at 28° C. to obtain resin spherulite particles.

[0049] (4) The obtained resin spherulites were calcined in a muffle furnace at 600° C. for 3 h to obtain solidified resin spherulites.

[0050] (5) The solidified resin spherulites were mixed with 80 g of flake graphite (250 mesh, Hebei Fengming) in an internal mixer and then placed in a molding machine. Silicone oil was used as a release agent and cold pressing was performed at a pressure of 5 to 45 MPa in nine sections. After demolding, a bipolar plate with a flow channel was obtained.

[0051] (6) The molded bipolar plate is placed in a muffle furnace and cured at 1000°C for 2 hours. After cooling, the bipolar plate is taken out and vacuum-impregnated in acrylic resin for 24 hours.

[0052] (7) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0053] Example 3

[0054] (1) Weigh 60 g of PR55738 resin and place it in a round-bottom container. Add 180 ml of methanol solvent and stir at 27.5 °C for 2 h using a magnetic stirrer with a heating capacity of 200 rpm / min.

[0055] (2) After stirring, add 200 ml of water and 60 ml of toluene solution to the solution obtained in step (1). Stir magnetically at 20°C for 1 hour at a stirring speed of 250 rpm / min until resin spherulites precipitate from the good solvent into the poor solvent.

[0056] (3) The solution obtained in step (2) was filtered and dried in a thermostat at 28° C. to obtain resin spherulite particles.

[0057] (4) The obtained resin spherulites were calcined in a muffle furnace at 600° C. for 3 h to obtain solidified resin spherulites.

[0058] (5) The solidified resin spherulites were mixed with 100 g of microcrystalline graphite (300 mesh Guiyang Tansha) in an internal mixer and then placed in a molding machine. Silicone oil was used as a release agent and cold pressing was performed at a pressure of 5 to 45 MPa in nine sections. After demolding, a bipolar plate with a flow channel was obtained.

[0059] (6) The molded bipolar plate is placed in a muffle furnace and cured at 1000°C for 2 hours. After cooling, the bipolar plate is taken out and vacuum-impregnated in acrylic resin for 24 hours.

[0060] (7) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0061] Comparative Example 1

[0062] (1) Weigh 40 g of PR12603 resin and place it in a round-bottom container. Add 100 ml of ethanol solvent and stir at 30°C for 1 h using a magnetic stirrer with a heating capacity of 350 rpm / min.

[0063] (2) 60 g of expanded graphite (200 mesh, Hebei Fengming) was blended with the resin solution from step (1) and stirred at 350 rpm / min for 8 h. The mixture was then filtered and dried to obtain a graphite resin mixture. The mixture was then placed in a molding press, cold pressed using silicone oil as a release agent at a pressure of 5 to 45 MPa in nine stages, and demolded to obtain a bipolar plate with flow channels.

[0064] (3) Vacuum impregnate the molded bipolar plate in acrylic resin for 24 hours.

[0065] (4) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0066] Comparative Example 2

[0067] (1) Weigh 50 g of PR55147 resin and place it in a round-bottom container. Add 150 ml of acetone solvent and stir at 25°C for 1 h using a magnetic stirrer with a heating capacity of 300 rpm / min.

[0068] (2) 80 g of flake graphite (250 mesh, Hebei Fengming) was blended with the resin solution from step (1) and stirred at 300 rpm / min for 8 h. The mixture was then filtered and dried to obtain a graphite resin mixture. The mixture was then placed in a molding press, cold pressed using silicone oil as a release agent at a pressure of 5 to 45 MPa in nine stages, and demolded to obtain a bipolar plate with flow channels.

[0069] (3) Vacuum impregnate the molded bipolar plate in acrylic resin for 24 hours.

[0070] (4) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0071] Comparative Example 3

[0072] (1) Weigh 60 g of PR55738 resin and place it in a round-bottom container. Add 180 ml of methanol solvent and stir at 27.5 °C for 2 h using a magnetic stirrer with a heating capacity of 200 rpm / min.

[0073] (2) 100 g of microcrystalline graphite (300 mesh Guiyang Tansha) was blended with the resin solution of step (1), stirred at 200 rpm / min for 8 h, and then filtered and dried to obtain a graphite resin mixture. The mixture was then placed in a molding press, cold pressed using silicone oil as a release agent at a pressure of 5 to 45 MPa in nine stages, and demolded to obtain a bipolar plate with flow channels.

[0074] (3) Vacuum impregnate the molded bipolar plate in acrylic resin for 24 hours.

[0075] (4) The bipolar plate was taken out and placed in a muffle furnace at 350°C for 2 h to obtain the final bipolar plate with flow channels. Physical parameters such as thickness, conductivity, and bending strength were tested.

[0076] Spherulite granulation technology is primarily divided into three systems: good solvent, poor solvent, and bridging agent. However, depending on the material system, only two systems are required: the poor solvent and bridging agent. A good solvent is a solvent with good solubility for the resin, while a poor solvent is a solvent with poor solubility for the resin. A bridging agent is a solvent that has good solubility for the resin but is immiscible with the poor solvent. Spherulite granulation technology can be divided into two types: wet spherical aggregation and emulsifier diffusion. The emulsifier diffusion method is a new spherulite granulation method characterized by the resin first forming droplets in the good solvent liquid phase. As the solvent in the droplets diffuses into the poor solvent, the good solvent precipitates, and the resin crystallizes and solidifies, maintaining a spherical shape. Spherulite granulation technology redistributes poorly soluble resins among the good solvent, poor solvent, and bridging agent based on their solubility differences. As the good solvent evaporates, the resin eventually reprecipitates into microspheres in the bridging agent.

[0077] The bipolar plates prepared using the methods described in the above examples and comparative examples were tested for thickness, conductivity, and flexural strength. The test results are shown in Table 1. The comparison shows that the bipolar plates prepared using the novel composite graphite bipolar plate preparation method of the present invention are thinner and have higher conductivity. This is due to a higher curing ratio of the resin after spheroidization, resulting in a more uniform mixing of the graphite resin. The bipolar plates also exhibit higher flexural strength due to the glass transition of the resin, which enhances the strength of the entire composite plate.

[0078] Table 1 Physical Characterization Coefficients of Examples and Comparative Examples

[0079] Bipolar plate thickness / mm Conductivity S / cm Bending strength / MPa Example 1 1.34 370 75 Example 2 1.46 420 67 Example 3 1.54 280 54 Comparative Example 1 1.78 145 32 Comparative Example 2 1.87 196 28 Comparative Example 3 1.68 203 21

[0080] The novel composite graphite bipolar plate manufacturing method utilizes resin spherulite molding, avoiding the slow and long curing times of the resin. This facilitates blending with graphite and avoids uneven distribution. After molding, the plate is cured at 1000°C, enhancing its bending strength.

[0081] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a novel composite graphite bipolar plate, characterized in that: The steps include: (1) adding a thermosetting phenolic resin to a good solvent at a certain temperature and stirring to dissolve it; (2) adding a certain amount of poor solvent and bridging agent, stirring to allow the resin droplets to diffuse into the poor solvent and crystallize, filtering and drying to obtain resin spherulite particles; (3) calcining the resin spherulites at 500°C to 700°C for a period of time to solidify 90% of the resin and coat the surface of the resin with the remaining amorphous carbon; (4) blending the resin obtained in step (3) with graphite and then performing molding, and then calcining the molded bipolar plate at 800° C. to 1200° C. to convert the amorphous carbon into glassy carbon; (5) The calcined bipolar plate is impregnated with glue and solidified to obtain a novel composite graphite bipolar plate.

2. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: In step (1), the good solvent is one of methanol, ethanol, isopropanol and acetone, and the poor solvent is water.

3. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: The bridging agent in step (2) is one of carbon tetrachloride, isopropyl acetate, toluene and isobutyl acetate.

4. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: In step (1) and step (2), the stirring temperature is 30-50° C., the stirring speed is 200-500 rpm / min, and the stirring time is 0.5-2 h.

5. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: The mass ratio of graphite to resin in step (4) is (3-4): (1-2).

6. The method for preparing the novel composite graphite bipolar plate according to claim 5, characterized in that: The molding method in step (4) is cold pressing with a pressure of 5 to 45 MPa in nine sections.

7. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: In step (5), the curing temperature is 350° C. and the curing time is 2 h.

8. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: The glue used for impregnation in step (5) is acrylic resin, and the impregnation time is 24 hours.

9. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: The calcination temperature in step (3) is 600°C.

10. The method for preparing the novel composite graphite bipolar plate according to claim 1, characterized in that: The calcination temperature in step (4) is 1000°C.

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