Preparation method of graphite bipolar plate of fuel cell
By modifying natural flake graphite with sulfuric acid and nitric acid and using a multi-gradient molding process, the problems of high porosity and poor mechanical strength of graphite bipolar plates were solved, and high-density, high-mechanical-strength graphite bipolar plates were prepared, improving the performance and stability of fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI DUKE NEW MATERIALS CO LTD
- Filing Date
- 2025-12-10
- Publication Date
- 2026-04-17
AI Technical Summary
Traditional graphite bipolar plates have high porosity and poor mechanical strength, which affects battery performance and stability.
Graphite bipolar plates were prepared by modifying natural flake graphite with sulfuric acid and nitric acid, combined with multi-gradient molding and segmented curing processes, forming a stable conductive network and mechanical properties.
The density and mechanical strength of graphite bipolar plates were increased, the risk of gas leakage was reduced, and the conductivity and corrosion resistance of the battery were improved, thus achieving a low-cost, high-performance bipolar plate.
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Abstract
Description
Technical Field
[0001] This application relates to the field of fuel cell technology, and in particular to a method for preparing a graphite bipolar plate for a fuel cell. Background Technology
[0002] Common proton exchange membrane fuel cell (PEMFC) or solid oxide fuel cell (SOFC) stacks consist of core components such as bipolar plates, membrane electrode assemblies (MEAs), and seals. As a key supporting and functional component in fuel cells, the bipolar plate has a decisive impact on the stack's power density, efficiency, lifespan, and cost.
[0003] Currently, common fuel cell bipolar plates are mainly classified into metal bipolar plates, composite bipolar plates, and graphite bipolar plates. While metal bipolar plates (such as stainless steel and titanium alloys) possess excellent mechanical strength and conductivity, effectively blocking gases, they are prone to corrosion in long-term acidic and humid environments, leading to poor electrochemical performance. Furthermore, some metal materials are expensive. Composite bipolar plates are mostly made with polymers (such as resins) as the matrix and conductive fillers (such as graphite, carbon black, and carbon nanotubes) added. However, their conductivity is greatly affected by the type and distribution of fillers, resulting in poor stability and a significant impact on the overall performance of the fuel cell stack. Graphite bipolar plates are considered an ideal choice due to their excellent chemical stability and corrosion resistance. However, traditional graphite bipolar plates have high porosity (typically >3%) and poor mechanical strength, leading to gas leakage and affecting battery performance and stability. Summary of the Invention
[0004] This application provides a method for preparing graphite bipolar plates for fuel cells to solve the technical problems of high porosity and poor mechanical strength of traditional graphite bipolar plates.
[0005] To address the aforementioned technical problems, in a first aspect, this application provides a method for preparing a graphite bipolar plate for a fuel cell, comprising the following steps: Step 1: Take natural flake graphite with a fixed carbon content of ≥99% and a mesh size of 60-100. Add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite to modify it, and obtain modified graphite. Step 2: Mix the modified graphite with a conductive medium, and then spray granulate to obtain granular material; Step 3: Add the granular material into a mold preheated to 60℃~200℃, and use a multi-gradient molding process for molding. Cool and demold to obtain a bipolar plate blank. Step four: After the bipolar plate preform is heat-treated and cured in sections under inert gas protection, a hydrophobic coating is uniformly sprayed onto the semi-finished bipolar plate and dried to obtain the finished graphite bipolar plate.
[0006] In some embodiments, step one includes: Take natural flake graphite with fixed carbon ≥99% and 60-100 mesh, add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite, stir at a constant temperature of 60℃±2℃ for 2h, wash with water until neutral, vacuum dry at 80℃±2℃ for 12h, grind, and sieve to obtain modified graphite. Alternatively, take natural flake graphite with a fixed carbon content of ≥99% and a mesh size of 60-100. Add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite. After ultrasonic treatment at 45℃±2℃ for 1 hour, wash with water until neutral, freeze dry, and then immerse in an ethanol dispersion containing 0.5wt% graphene oxide. Stir at 60℃±2℃ for 3 hours, separate, wash, and dry to obtain modified graphite.
[0007] In some embodiments, step two includes: 82% modified graphite, 8% conductive carbon black, 7% carbon fiber and 3% polytetrafluoroethylene by weight were added to a high-speed mixer and dry-mixed at 800 rpm for 30 minutes until uniform to obtain a dry mixture. Add a phenolic resin-ethanol solution with a solid content of 20wt% to the dry mixture, ultrasonically disperse for 30 min, dry at 80℃, and mix at 2000 rpm for 45 min to form a uniform slurry. The uniform slurry was sprayed and granulated at an inlet temperature of 180℃±5℃, an atomization pressure of 0.8Mpa, and an outlet temperature of 85℃±2℃ to obtain the first granules with a particle size of 0.85~0.95mm and a moisture content of ≤0.5%.
[0008] In some embodiments, step three includes: The first granular material is added to a mold preheated to 60°C and molded using a multi-gradient molding process. After cooling and demolding, a bipolar plate blank is obtained. The multi-gradient molding process includes: the first stage process is to hold at 10MPa pressure and 60℃±2℃ for 30s; the second stage process is to hold at 30MPa pressure and 80℃±2℃ for 30s; and the third stage process is to hold at 50MPa and 100℃±2℃ for 30s. Alternatively, the multi-gradient molding process includes: a first-stage process of holding at 10 MPa pressure and 60℃±2℃ for 30 seconds; and a second-stage process of holding at 50 MPa and 100℃±2℃ for 30 seconds.
[0009] In some embodiments, step four includes: The bipolar plate blank was placed in an inert gas protected atmosphere furnace and heated to 80℃±2℃ at 2℃ / min and held for 1h. Then it was heated to 120℃±5℃ at 1℃ / min and held for 2h. Then it was heated to 180℃±5℃ at 1℃ / min and held for 3h. Finally, it was cooled to room temperature with the furnace. A 5wt% polyvinylidene fluoride-N-methylpyrrolidone solution was sprayed onto the bipolar plate preform, and then dried at 120℃±5℃ for 1 hour to obtain the finished graphite bipolar plate.
[0010] In some embodiments, step two includes: The modified graphite (90%~95%), graphene powder (2%~5%), and polytetrafluoroethylene emulsion (3%~5%) or carbon nanotubes (3%~5%) by weight are melt-blended and extruded in a twin-screw extruder at 260℃~280℃, then water-cooled and pelletized to obtain the second granules. 75%~85% modified graphite, 10%~15% carbon fiber, and 10% polyetheretherketone or polyethersulfone by weight are melt-blended and extruded in a twin-screw extruder at 360℃~380℃, and then rapidly cooled and pelletized with liquid nitrogen to obtain the third granular material.
[0011] In some embodiments, step three includes: Preheat the mold to 200°C, fill part of the second granular material into the bottom layer of the mold, fill the third granular material into the middle layer of the mold, fill part of the second granular material into the top layer of the mold, and then use a multi-gradient molding process to mold the material. After cooling and demolding, a bipolar plate blank is obtained. The multi-gradient molding process includes: the first stage process is to hold at 25MPa pressure and 280℃~340℃ for 5min~10min; the second stage process is to hold at 40MPa pressure and 300℃~380℃ for 10min~15min; and the third stage process is to hold at 50MPa and 250℃±5℃ for 5min.
[0012] In some embodiments, step four includes: The bipolar plate blank was placed in an inert gas protected atmosphere furnace, heated to 250℃±5℃ at 2℃ / min and held for 2h, then heated to 300℃±5℃ at 1℃ / min and held for 3h, and finally cooled to room temperature with the furnace. 8wt% perfluoroethylene propylene copolymer-NMP liquid was sprayed onto the bipolar plate preform, and then sintered at 220℃±5℃ for 30 min to obtain the finished graphite bipolar plate.
[0013] In some embodiments, step three, cooling and demolding, includes: After cooling the mold to 70℃~100℃ using circulating cooling water at a cooling rate of ≤1.5℃ / min, the mold is demolded.
[0014] Secondly, this application provides an application of a graphite bipolar plate in a fuel cell, wherein the graphite bipolar plate is prepared by the above-mentioned graphite bipolar plate preparation method.
[0015] Compared with the prior art, this application has the following beneficial effects: Natural flake graphitic acid is oxidized and modified with sulfuric acid and nitric acid to introduce oxygen-containing functional groups into the graphite interlayer, improving the hydrophilicity and reactivity of graphite and facilitating subsequent bonding with conductive media. The modified graphite is then spray-granulated with the conductive media to ensure a uniform distribution of the conductive network, resulting in granules with better flowability and packing density. A multi-gradient molding process at 60℃~200℃ reduces internal stress in the granules, minimizing bubbles and defects, thereby improving the density and mechanical strength of the bipolar plate. Segmented curing and hydrophobic treatment remove residual solvents and small molecules at low temperatures and allow the resin to cure and crosslink at high temperatures, forming a stable three-dimensional network, enhancing mechanical properties and corrosion resistance. This enables the low-cost preparation of graphite bipolar plates with high conductivity and high mechanical properties. Detailed Implementation
[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.
[0017] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.
[0018] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.
[0019] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of this invention do not impose any limitation on the quantity requirement (i.e., the number of times) of the elements or components. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Example 1
[0021] A method for preparing graphite bipolar plates for fuel cells includes the following steps: Step 1: Take 1000g of natural flake graphite with fixed carbon ≥99% and 80 mesh, add 2000mL of a mixed acid of sulfuric acid and nitric acid with a volume ratio of 3:1 to the natural flake graphite, stir at a constant temperature of 60℃±2℃ for 2h, wash with water until the pH of the filtrate is 7.0, vacuum dry at 80℃±2℃ for 12h, grind, and sieve to obtain modified graphite; Step two, by weight percentage, 82% (410g) of modified graphite and conductive carbon black (acetylene black, particle size 35nm, specific surface area 75m²) are added. 2 8% (40g) of phenolic resin (7μm in diameter, 2μm in length), 7% (35g) of carbon fiber (7μm in diameter, 2μm in length), and 3% (15g) of polytetrafluoroethylene micro powder were added to a high-speed mixer and dry-mixed at 800rpm for 30min until uniform to obtain a dry mixture. A phenolic resin-ethanol solution with a solid content of 20% was added to the dry mixture, ultrasonically dispersed for 30min, dried in an oven at 80℃, and then mixed at 2000rpm for 45min to form a uniform slurry. The uniform slurry was spray-granulated at an inlet temperature of 180℃±5℃, an atomization pressure of 0.8Mpa, and an outlet temperature of 85℃±2℃ to obtain the first granules with a particle size of 0.85~0.95mm and a moisture content of ≤0.5%. Step 3: The first granular material is added to a mold preheated to 60℃, and after molding using a multi-gradient molding process, the mold is cooled to 70℃ by circulating cooling water at a cooling rate of ≤1.5℃ / min. The mold is then demolded to obtain the bipolar plate preform. The multi-gradient molding process includes: a first stage of holding at 10MPa pressure and 60℃±2℃ for 30s; a second stage of holding at 30MPa pressure and 80℃±2℃ for 30s; and a third stage of holding at 50MPa and 100℃±2℃ for 30s. Step 4: Place the bipolar plate preform in an inert gas atmosphere furnace, heat it at 2℃ / min to 80℃±2℃ and hold for 1 hour, then heat it at 1℃ / min to 120℃±5℃ and hold for 2 hours, then continue to heat it at 1℃ / min to 180℃±5℃ and hold for 3 hours, finally cool it to room temperature in the furnace; spray a 5wt% polyvinylidene fluoride-N-methylpyrrolidone solution onto the bipolar plate preform (10g / m² per side). 2 Then, dry the graphite bipolar plate in an oven at 120℃±5℃ for 1 hour to obtain the finished graphite bipolar plate. Example 2
[0022] The difference from Example 1 is that step two of Example 2, the multi-gradient molding process, includes: the first stage process is to keep warm at 10MPa pressure and 60℃±2℃ for 30s; the second stage process is to keep warm at 50MPa and 100℃±2℃ for 30s. Example 3
[0023] A method for preparing graphite bipolar plates for fuel cells includes the following steps: Step 1: Take 1000g of natural flake graphite with fixed carbon ≥99% and 80 mesh, add 2000mL of a mixed acid of sulfuric acid and nitric acid with a volume ratio of 3:1 to the natural flake graphite, sonicate at 45℃±2℃ for 1h, wash with water until the pH of the filtrate is 7.0, freeze dry, and then immerse in an ethanol dispersion containing 0.5wt% graphene oxide, stir at 60℃±2℃ for 3h, separate, wash, and dry to obtain modified graphite; Step 2: 95% modified graphite, 2% graphene powder, and 3% polytetrafluoroethylene emulsion (60% solid content) by weight are melt-blended and extruded in a twin-screw extruder at 280℃, then water-cooled and pelletized to obtain a second batch of 1.0mm~1.2mm particles; 85% modified graphite, 10% carbon fiber, and 10% polyetheretherketone by weight are melt-blended and extruded in a twin-screw extruder at 380℃, then rapidly cooled and pelletized with liquid nitrogen to obtain a third batch of 1.2mm~1.5mm particles. Step 3: Preheat the mold to 200℃, fill part of the second granular material into the bottom layer of the mold, fill the third granular material into the middle layer of the mold, and fill part of the second granular material into the top layer of the mold to form a "sandwich" structure. After molding using a multi-gradient molding process, cool the mold to 100℃ using circulating cooling water at a cooling rate of ≤1℃ / min, and then demold to obtain the bipolar plate preform. The multi-gradient molding process includes: the first stage process is to hold at 25MPa pressure and 340℃±5℃ for 10min; the second stage process is to hold at 40MPa pressure and 380℃±5℃ for 15min; and the third stage process is to hold at 50MPa pressure and 250℃±5℃ for 5min. Step four: Place the bipolar plate preform in an inert gas atmosphere furnace, heat it to 250℃±5℃ at 2℃ / min and hold for 2 hours, then heat it to 300℃±5℃ at 1℃ / min and hold for 3 hours, finally cool it to room temperature in the furnace; spray 8wt% perfluoroethylene-propylene copolymer-NMP liquid onto the bipolar plate preform (10g / m² per side). 2 Then, sinter at 220℃±5℃ for 30 minutes to obtain the finished graphite bipolar plate. Example 4
[0024] The difference from Example 2 is that in step two of Example 4, 90% modified graphite, 5% graphene powder, and 5% carbon nanotubes by mass are melt-blended and extruded in a twin-screw extruder at 260°C, and then water-cooled and pelletized to obtain a second batch of 1.0mm~1.2mm particles; 75% modified graphite, 15% carbon fiber, and 10% polyetheretherketone by mass are melt-blended and extruded in a twin-screw extruder at 300°C, and then rapidly cooled and pelletized with liquid nitrogen to obtain a third batch of 1.2mm~1.5mm particles; in step three, the multi-gradient molding process includes: the first stage process is a holding time of 5 minutes at 280°C under 25MPa pressure; the second stage process is a holding time of 10 minutes at 300°C under 40MPa pressure; and the third stage process is a holding time of 5 minutes at 250°C±5°C under 50MPa pressure.
[0025] Comparative Example 1 Commercially available traditional graphite bipolar plates were used as comparative example 1.
[0026] Comparative Example 2 Commercially available composite bipolar plates were used as comparative example 2.
[0027] Comparative Example 3 Commercially available metal bipolar plates were used as comparative example 3.
[0028] Comparative Example 4 Compared with Example 1, Comparative Example 4 removed step one and replaced modified graphite with natural flake graphite.
[0029] Comparative Example 5 Compared with Example 1, Comparative Example 5 uses the following steps instead of Step 3: the first granular material is added to a mold preheated to 60°C, and after being kept at 50 MPa and 100°C ± 2°C for 90 seconds, the mold is cooled to 70°C by circulating cooling water at a cooling rate of ≤1.5°C / min, and then demolded to obtain a bipolar plate blank.
[0030] Comparative Example 6 Compared with Example 1, Comparative Example 6 uses the following steps instead of step four: the bipolar plate preform is placed in an inert gas atmosphere furnace and held at 180℃±5℃ for 6 hours, and finally cooled to room temperature with the furnace; a 5wt% polyvinylidene fluoride-N-methylpyrrolidone solution is sprayed onto the bipolar plate preform (10g / m² per side). 2 Then, dry the graphite bipolar plate in an oven at 120℃±5℃ for 1 hour to obtain the finished graphite bipolar plate.
[0031] Referring to GB / T20042.6—2024 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics", the contact resistance (mΩ·cm) of the bipolar plates was tested using a low-resistance meter. 2 The flexural strength of the bipolar plate was tested using a universal testing machine, and the electrical conductivity (S / cm) was tested using a four-probe tester. The tensile strength (MPa) of the bipolar plate was tested according to GB / T2567-2008 "Test Methods for Properties of Resin Castings". The performance results of the graphite bipolar plate are shown in Table 1.
[0032] Table 1 Performance Results of Graphite Bipolar Plates
[0033] As shown in Table 1, the electrical conductivity (conductivity, contact resistance), mechanical properties (flexural strength, tensile strength), corrosion resistance (corrosion current density), and cost management of Examples 1 to 4 are significantly better than those of Comparative Examples 1 to 6. The specification demonstrates that graphitic acid modification, multi-gradient molding, and segmented curing can effectively improve the electrical conductivity and mechanical properties of the bipolar plate. Compared to the commercially available bipolar plates of Comparative Examples 1 to 3, this invention better balances product performance and cost advantages; compared to the different processes used in Comparative Examples 4 to 6, this invention exhibits better product performance.
[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0035] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application for those skilled in the art.
Claims
1. A method for preparing a graphite bipolar plate for a fuel cell, characterized in that, Includes the following steps: Step 1: Take natural flake graphite with a fixed carbon content of ≥99% and a mesh size of 60-100. Add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite to modify it, and obtain modified graphite. Step 2: Mix the modified graphite with the conductive medium, and then spray granulate to obtain granular material; Step 3: Add the granular material into a mold preheated to 60℃~200℃, and use a multi-gradient molding process for molding. Cool and demold to obtain a bipolar plate blank. Step four: After the bipolar plate preform is heat-treated and cured in sections under inert gas protection, a hydrophobic coating is uniformly sprayed onto the semi-finished bipolar plate and dried to obtain the finished graphite bipolar plate.
2. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 1, characterized in that, Step one includes: Take natural flake graphite with fixed carbon ≥99% and 60-100 mesh, add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite, stir at a constant temperature of 60℃±2℃ for 2h, wash with water until neutral, vacuum dry at 80℃±2℃ for 12h, grind, and sieve to obtain modified graphite. Alternatively, take natural flake graphite with a fixed carbon content of ≥99% and a mesh size of 60-100. Add sulfuric acid and nitric acid in a volume ratio of 3:1 to the natural flake graphite. After ultrasonic treatment at 45℃±2℃ for 1 hour, wash with water until neutral, freeze dry, and then immerse in an ethanol dispersion containing 0.5wt% graphene oxide. Stir at 60℃±2℃ for 3 hours, separate, wash, and dry to obtain modified graphite.
3. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 1, characterized in that, Step two includes: 82% modified graphite, 8% conductive carbon black, 7% carbon fiber and 3% polytetrafluoroethylene by weight were added to a high-speed mixer and dry-mixed at 800 rpm for 30 minutes until uniform to obtain a dry mixture. Add a phenolic resin-ethanol solution with a solid content of 20wt% to the dry mixture, ultrasonically disperse for 30 min, dry at 80℃, and mix at 2000 rpm for 45 min to form a uniform slurry. The uniform slurry was sprayed and granulated at an inlet temperature of 180℃±5℃, an atomization pressure of 0.8Mpa, and an outlet temperature of 85℃±2℃ to obtain the first granules with a particle size of 0.85~0.95mm and a moisture content of ≤0.5%.
4. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 3, characterized in that, Step three includes: The first granular material is added to a mold preheated to 60°C and molded using a multi-gradient molding process. After cooling and demolding, a bipolar plate blank is obtained. The multi-gradient molding process includes: the first stage process is to hold at 10MPa pressure and 60℃±2℃ for 30s; the second stage process is to hold at 30MPa pressure and 80℃±2℃ for 30s; and the third stage process is to hold at 50MPa and 100℃±2℃ for 30s. Alternatively, the multi-gradient molding process includes: a first-stage process of holding at 10 MPa pressure and 60℃±2℃ for 30 seconds; and a second-stage process of holding at 50 MPa and 100℃±2℃ for 30 seconds.
5. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 3, characterized in that, Step four includes: The bipolar plate blank was placed in an inert gas protected atmosphere furnace, heated to 80℃±2℃ at 2℃ / min and held for 1h, then heated to 120℃±5℃ at 1℃ / min and held for 2h, then heated to 180℃±5℃ at 1℃ / min and held for 3h, and finally cooled to room temperature with the furnace. A 5wt% polyvinylidene fluoride-N-methylpyrrolidone solution was sprayed onto the bipolar plate preform, and then dried at 120℃±5℃ for 1 hour to obtain the finished graphite bipolar plate.
6. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 1, characterized in that, Step two includes: The modified graphite (90%~95%), graphene powder (2%~5%), and polytetrafluoroethylene emulsion (3%~5%) or carbon nanotubes (3%~5%) by weight are melt-blended and extruded in a twin-screw extruder at 260℃~280℃, then water-cooled and pelletized to obtain the second granules. 75%~85% modified graphite, 10%~15% carbon fiber, and 10% polyetheretherketone or polyethersulfone by weight are melt-blended and extruded in a twin-screw extruder at 360℃~380℃, and then rapidly cooled and pelletized with liquid nitrogen to obtain the third granular material.
7. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 6, characterized in that, Step three includes: Preheat the mold to 200°C, fill part of the second granular material into the bottom layer of the mold, fill the third granular material into the middle layer of the mold, fill part of the second granular material into the top layer of the mold, and then use a multi-gradient molding process to mold the material. After cooling and demolding, a bipolar plate blank is obtained. The multi-gradient molding process includes: the first stage process is to hold at 25MPa pressure and 280℃~340℃ for 5min~10min; the second stage process is to hold at 40MPa pressure and 300℃~380℃ for 10min~15min; and the third stage process is to hold at 50MPa and 250℃±5℃ for 5min.
8. The method for preparing a graphite bipolar plate for a fuel cell as described in claim 6, characterized in that, Step four includes: The bipolar plate blank was placed in an inert gas protected atmosphere furnace, heated to 250℃±5℃ at 2℃ / min and held for 2h, then heated to 300℃±5℃ at 1℃ / min and held for 3h, and finally cooled to room temperature with the furnace. 8wt% perfluoroethylene propylene copolymer-NMP liquid was sprayed onto the bipolar plate preform, and then sintered at 220℃±5℃ for 30 min to obtain the finished graphite bipolar plate.
9. The method of claim 1, wherein the graphite bipolar plate is used for a fuel cell. Step three, cooling and demolding, includes: After cooling the mold to 70℃~100℃ using circulating cooling water at a cooling rate of ≤1.5℃ / min, the mold is demolded.
10. Use of a graphite bipolar plate in a fuel cell, characterized in that The graphite bipolar plate is prepared by the graphite bipolar plate preparation method according to any one of claims 1 to 9.