A preparation and molding process for a composite bipolar plate

Abstract

The present invention relates to a preparation and molding process for a composite bipolar plate. S1: Graphite, resin, curing agent, accelerator, and additives are thoroughly mixed in a certain proportion by a mixer; S2: A certain proportion of the obtained mixture is pre-taken and placed into a molding die, scraped flat, and molded into a bipolar plate with a specific flow field under a certain pressure and time; S3: The remaining mixture is placed into the molding die once or multiple times, scraped flat, and molded into a bipolar plate with a specific flow field under a certain pressure and time; S4: The molded bipolar plate is fixed by a clamp, placed in an oven, solidified at a specific heating rate and holding time, and cooled. The present invention divides the molding feeding into two or more times, thereby improving the force uniformity at different heights of the bipolar plate, reducing the compression ratio difference at different positions of the bipolar plate, effectively reducing cracking and residual stress during molding, and improving the bipolar plate molding rate and performance uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a preparation and molding process of a composite bipolar plate. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are a promising green power battery technology, particularly favored by countries around the world and receiving extensive research and development. Bipolar plates, a key component in fuel cell structures, account for 60% to 80% of a fuel cell's mass and cost, making them crucial. Three main types of bipolar plates exist: graphite, metal, and composite. Composite plates hold the greatest potential due to their corrosion resistance, high strength, lightweight, and low cost. However, due to their thinness, complex flow fields, and poor flowability of the graphite and resin mixture, composite plates can experience varying compression ratios at different locations during molding, making them susceptible to cracking.

[0003] In order to overcome the above-mentioned deficiencies, the present invention provides a preparation and molding process for a composite bipolar plate. Summary of the Invention

[0004] The present invention aims to address the problem of graphite / resin composite bipolar plates in existing fuel cells, which are prone to cracking due to different compression ratios at different locations during molding due to their thinness, complex flow fields, and poor fluidity of the graphite, resin, and other mixtures. The specific solution is as follows:

[0005] A preparation and molding process for a composite bipolar plate comprises the following steps:

[0006] Step 1: Mix the graphite, resin, curing agent, accelerator and additives in a certain proportion through a mixer;

[0007] Step 2: Pre-take a certain proportion of the obtained mixture and put it into a molding die, scrape it flat, and then press-mold it into a bipolar plate with a specific flow field under a certain pressure and time;

[0008] Step 3: The remaining mixture is put into a compression mold, scraped flat, and compression molded into a bipolar plate with a specific flow field under a certain pressure and time;

[0009] Step 4: Fix the formed bipolar plate with a fixture, place it in an oven, solidify it at a specific heating rate and holding time, and cool it.

[0010] Furthermore, the graphite is flexible graphite, the carbon content in the flexible graphite is greater than 99.9wt%, and the particle size is 10 to 300μm.

[0011] Furthermore, the particle size of the resin, curing agent, accelerator and additive is 10 to 300 μm.

[0012] Furthermore, the resin is a thermosetting resin, the curing agent is any one of an aromatic curing agent, an acid anhydride curing agent, or a phenolic resin curing agent; and the additive is any one of carbon black, carbon nanotubes, or graphene.

[0013] Furthermore, the certain proportions described in step 1 are specifically: graphite content is 50wt% to 90wt%, thermosetting resin content is 5wt% to 30wt%, curing agent content is 3wt% to 20wt%, accelerator content is 0.01wt% to 5wt%, and additive content is 0.01wt% to 5wt%.

[0014] Furthermore, the mixer in step 1 is any one of a three-dimensional motion mixer, a V-shaped mixer, a two-dimensional motion mixer, or an airflow stirring mixer.

[0015] Furthermore, the pre-taking of a certain proportion in step 2 is specifically: the amount of the mixture of graphite, resin, curing agent, accelerator, and additive is 10wt% to 60wt% of the total feed, the pressure is 2MPa to 60MPa, and the molding method is: from small pressure to large pressure, the holding time is 1s to 60s, and the press feed speed is 0.1mm / s to 100mm / s.

[0016] Furthermore, the mixing time in step 1 is 15 to 30 minutes.

[0017] Furthermore, in step 3, the remaining mixed material is added to the compression mold in one or more steps. The pressure is 10 MPa to 100 MPa, and the compression molding method is as follows: from low pressure to high pressure, the holding time is 1 second to 60 seconds, and the press feed speed is 0.1 mm / s to 100 mm / s.

[0018] Furthermore, the oven in step 4 is any one of a hot air circulation oven, an electric blast drying oven or a vacuum oven, the curing temperature is 100°C to 300°C, the heating rate is 2°C / min to 50°C / min, the holding time is 15min to 300min, the cooling method is air cooling or furnace cooling, and the clamping force of the fixture is 500Pa to 10MPa.

[0019] In summary, the technical solution of the present invention has the following beneficial effects:

[0020] This solution addresses the problem of existing fuel cell graphite / resin composite bipolar plates, which are thin, have complex flow fields, and poor fluidity of the graphite, resin, and other mixtures, resulting in different compression ratios at different locations during compression molding, which can easily lead to cracking. The present invention divides the molding process into two or more times, improving the force uniformity at different heights of the bipolar plate, reducing the difference in compression ratio at different locations of the bipolar plate, effectively reducing cracking and residual stress during molding, and improving the bipolar plate molding rate and performance uniformity. Using the molding process of this solution, graphite / resin composite bipolar plates with improved appearance integrity and more uniform performance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Attachment Figure 1 This is a step diagram of a preparation and molding process of a composite bipolar plate of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] like Figure 1 As shown, a preparation and molding process of a composite bipolar plate adopts the following steps:

[0024] Step S1, graphite, resin, curing agent, accelerator, and additives are mixed in a certain proportion (graphite content is 50wt% to 90wt%, thermosetting resin content is 5wt% to 30wt%, curing agent content is 3wt% to 20wt%, accelerator content is 0.01wt% to 5wt%, and additive content is 0.01wt% to 5wt%) by a mixer (mixing time is: 15 to 30 minutes);

[0025] Step S2: Pre-take a certain proportion of the obtained mixture and place it into a compression mold, scrape it flat, and then compression mold it into a bipolar plate with a specific flow field under a certain pressure and time. (Specifically, the pre-taken certain proportion is: the amount of the mixture of graphite, resin, curing agent, accelerator, and additives is 10wt% to 60wt% of the total material, the pressure is 2MPa to 60MPa, and the compression molding method is: from low pressure to high pressure, the holding time is 1s to 60s, and the press feed speed is 0.1mm / s to 100mm / s)

[0026] In step S3, the remaining mixture is added to the mold in one or more portions, scraped flat, and molded into a bipolar plate with a specific flow field under a certain pressure and time. (The pressure in step S3 is 10 MPa to 100 MPa, the molding method is: from low pressure to high pressure, the holding time is 1 second to 60 seconds, and the press feed speed is 0.1 mm / s to 100 mm / s)

[0027] In step S4, the formed bipolar plate is secured with a fixture and placed in an oven for curing at a specified heating rate and holding time, followed by cooling. The oven in step S4 can be any of a hot air circulation oven, an electric blast drying oven, or a vacuum oven. The curing temperature is 100°C to 300°C, the heating rate is 2°C / min to 50°C / min, the holding time is 15 minutes to 300 minutes, and the cooling method is air cooling or furnace cooling. The clamping force of the fixture is 500 Pa to 10 MPa.

[0028] Furthermore, the graphite is flexible graphite, containing greater than 99.9% by weight of carbon and having a particle size of 10 to 300 μm. The particle sizes of the resin, curing agent, accelerator, and additive are 10 to 300 μm. The resin is a thermosetting resin, and the curing agent is an aromatic curing agent, an acid anhydride curing agent, or a phenolic resin curing agent. The additive is carbon black, carbon nanotubes, or graphene. Depending on the actual product, no additive may be added.

[0029] Furthermore, the mixer in step 1 is any one of a three-dimensional motion mixer, a V-shaped mixer, a two-dimensional motion mixer, or an airflow stirring mixer.

[0030] Example 1:

[0031] In this embodiment 1, the raw materials for the graphite / resin composite bipolar plate are provided in the following proportions by mass: 65-85 parts of flexible graphite, 15-35 parts of epoxy resin, 5-20 parts of phenolic resin curing agent, and the mass of accelerators and other additives is 0.01% to 5% of the total mass.

[0032] Preferably, the particle size of the graphite powder is 20 to 150 μm, and the particle sizes of other raw materials are the same as or close to that of the graphite powder.

[0033] Put the mixture of graphite, epoxy resin, curing agent, accelerator and other accelerators into a three-dimensional motion mixer and mix them thoroughly for 15 to 30 minutes.

[0034] Take 50wt% of the mixture required for a composite bipolar plate and pre-put it into the molding die, scrape it flat, and mold it; the press feed speed is 0.1mm / s~40mm / s, the molding pressure is 10MPa~50MPa, from small to large, the holding time is 5s~35s, and it is not taken out from the cavity.

[0035] The remaining material of the mixture required for a composite bipolar plate is put into the molding die, scraped flat, and molded; the press feed speed is 0.1mm / s to 40mm / s, the molding pressure is 40MPa to 80MPa, from small to large, and the pressure holding time is 5s to 35s.

[0036] The molded bipolar plate is fixed by a clamp with a clamping force of 500Pa to 6kPa; the bipolar plate is heated in a hot air circulation oven with a heating rate of 2°C / min to 25°C / min, a holding time of 30min to 120min, and air-cooled.

[0037] Example 2:

[0038] In this embodiment 2, the raw materials for the graphite / resin composite bipolar plate are provided in the following proportions by mass: 60-80 parts of flexible graphite, 15-40 parts of epoxy resin, 5-20 parts of phenolic resin curing agent, and the mass of accelerators and other additives is 0.01% to 5% of the total mass.

[0039] Preferably, the particle size of the graphite powder is 30 to 160 μm, and the particle sizes of other raw materials are the same as or close to that of the graphite powder.

[0040] Put the mixture of graphite, epoxy resin, curing agent, accelerator and other accelerators into a three-dimensional motion mixer and mix them thoroughly for 15 to 30 minutes.

[0041] Take 20wt% of the mixture required for a composite bipolar plate and pre-put it into the molding die, scrape it flat, and mold it; the press feed speed is 0.1mm / s~40mm / s, the molding pressure is 10MPa~50MPa, from small to large, the holding time is 5s~35s, and it is not taken out from the cavity.

[0042] 30 wt% of the mixture required for a composite bipolar plate is put into the molding die, scraped flat, and molded; the press feed speed is 0.1 mm / s to 40 mm / s, the molding pressure is 10 MPa to 50 MPa, from small to large, and the holding time is 5 s to 35 s.

[0043] The remaining material of the mixture required for a composite bipolar plate is put into the molding die, scraped flat, and molded; the press feed speed is 0.1mm / s to 40mm / s, the molding pressure is 30MPa to 85MPa, from small to large, and the pressure holding time is 5s to 35s.

[0044] The molded bipolar plate is fixed by a clamp with a clamping force of 500Pa to 6kPa; the bipolar plate is heated in a hot air circulation oven with a heating rate of 2°C / min to 25°C / min, a holding time of 30min to 120min, and air-cooled.

[0045] Example 3:

[0046] In this embodiment 3, the raw materials for the graphite / resin composite bipolar plate are provided in the following proportions by mass: 50-70 parts of flexible graphite, 20-40 parts of epoxy resin, 10-25 parts of aromatic curing agent, and the mass of accelerators and other additives is 0.01% to 5% of the total mass.

[0047] Preferably, the particle size of the graphite powder is 50 to 170 μm, and the particle sizes of other raw materials are the same as or close to that of the graphite powder.

[0048] Put the mixture of graphite, epoxy resin, curing agent, accelerator and other accelerators into a three-dimensional motion mixer and mix them thoroughly for 15 to 30 minutes.

[0049] Take 30wt% of the mixture required for a composite bipolar plate and pre-put it into the molding die, scrape it flat, and mold it; the press feed speed is 0.1mm / s~40mm / s, the molding pressure is 10MPa~50MPa, from small to large, and the pressure holding time is 5s~35s.

[0050] The remaining material of the mixture required for a composite bipolar plate is put into the molding die, scraped flat, and molded; the press feed speed is 0.1mm / s to 40mm / s, the molding pressure is 50MPa to 90MPa, from small to large, and the pressure holding time is 5s to 35s.

[0051] The molded bipolar plate is fixed by a clamp with a clamping force of 500Pa to 6kPa; the bipolar plate is heated in a hot air circulation oven with a heating rate of 5°C / min to 30°C / min, a holding time of 30min to 150min, and air-cooled.

[0052] Comparative Example 1:

[0053] The only difference between Comparative Example 1 and Example 1 is that the mixed material is not fed in batches during the molding process, but is fed into the mold all at once for molding. The rest of the contents are the same as in Example 1 and will not be repeated here.

[0054] Comparative Example 2:

[0055] The only difference between Comparative Example 2 and Example 2 is that the mixed material is not fed in batches during the molding process, but is fed into the mold all at once for molding. The rest of the contents are the same as Example 2 and will not be repeated here.

[0056] Comparative Example 3:

[0057] The only difference between Comparative Example 3 and Example 3 is that the mixed material is not fed in batches during the molding process, but is fed into the mold all at once for molding. The rest of the contents are the same as in Example 3 and will not be repeated here.

[0058] The standard deviation reflects the degree of dispersion of a data set or the stability or uniformity of a physical quantity, specifically the degree of dispersion of a set of data relative to its mean. In this experiment, the density standard deviation and the surface conductivity standard deviation were used to characterize the distribution uniformity of the bipolar plate's post-molding performance. Smaller standard deviations indicate better uniformity, while larger standard deviations indicate poorer uniformity.

[0059] In order to fully verify the beneficial effects of the present invention and reflect the effective improvement of bipolar plate molding by the improved process of batch feeding and molding during molding, the present invention is compared with the existing common molding process, and corresponding performance tests are carried out on Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3, respectively. Among them, Examples 1, 2, and 3 are the processes of the present invention, and Comparative Examples 1, 2, and 3 are the existing common molding processes. The results are shown in Table 1:

[0060] Table 1 Comparison of relevant properties of Examples 1, 2, 3 and Comparative Examples 1, 2, 3

[0061]

[0062] Comparative Examples 1, 2, and 3 in Table 1 represent existing commonly used molding processes. Comparison of Example 1, Comparative Example 1 with Example 2, Comparative Example 2, and Example 3, Comparative Example 3 shows that the standard deviation of density and the standard deviation of surface conductivity of Example 1 are both smaller than those of Comparative Example 1, and the same is true for Examples 2 and 3, indicating that the present invention can effectively improve the density uniformity and surface conductivity uniformity of the bipolar plate. In addition, no cracking occurs in Examples 1, 2, and 3 after molding, while creases or cracking occur to varying degrees in Comparative Examples 1, 2, and 3, indicating that the present invention effectively improves the compression ratio and effective pressure at different positions by changing the material for batch molding, thereby effectively reducing cracking during the bipolar plate molding process and improving the effective molding of the bipolar plate.

[0063] In summary, the technical solution of the present invention has the following beneficial effects:

[0064] This solution addresses the problem of existing fuel cell graphite / resin composite bipolar plates, which are thin, have complex flow fields, and poor fluidity of the graphite, resin, and other mixtures, resulting in different compression ratios at different locations during compression molding, which can easily lead to cracking. The present invention divides the molding process into two or more times, improving the force uniformity at different heights of the bipolar plate, reducing the difference in compression ratio at different locations of the bipolar plate, effectively reducing cracking and residual stress during molding, and improving the bipolar plate molding rate and performance uniformity. Using the molding process of this solution, graphite / resin composite bipolar plates with improved appearance integrity and more uniform performance can be obtained.

[0065] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. A process for preparing and forming a composite bipolar plate, characterized in that: Use the following steps: Step 1: Mix the graphite, resin, curing agent, accelerator and additives in a certain proportion through a mixer; Step 2: Pre-take a certain proportion of the obtained mixture and put it into a molding die, scrape it flat, and then press-mold it into a bipolar plate with a specific flow field under a certain pressure and time; Step 3: The remaining mixture is put into a compression mold, scraped flat, and compression molded into a bipolar plate with a specific flow field under a certain pressure and time; Step 4: Fix the formed bipolar plate with a fixture, place it in an oven, solidify it at a specific heating rate and holding time, and cool it; The certain proportions in step 1 are specifically: graphite content of 50wt% to 90wt%, thermosetting resin content of 5wt% to 30wt%, curing agent content of 3wt% to 20wt%, accelerator content of 0.01wt% to 5wt%, and additive content of 0.01wt% to 5wt%; The mixer in step 1 is any one of a three-dimensional motion mixer or an air flow stirring mixer; The mixing time in step 1 is: 15 to 30 minutes; The pre-taking of a certain proportion in step 2 specifically comprises: the amount of the mixture of graphite, resin, curing agent, accelerator, and additives is 10wt% to 60wt% of the total feed, the pressure is 2MPa to 60MPa, the compression molding method is: from low pressure to high pressure, the holding time is 1s to 60s, and the press feed speed is 0.1mm / s to 100mm / s; The remaining mixture in step 3 is put into the compression mold in one or more steps. The pressure is 10 MPa to 100 MPa, and the compression molding method is from low pressure to high pressure, the holding time is 1 s to 60 s, and the press feed speed is 0.1 mm / s to 100 mm / s. The oven in step 4 is any one of a hot air circulation oven, an electric blast drying oven or a vacuum oven. The curing temperature is 100°C to 300°C, the heating rate is 2°C / min to 50°C / min, the holding time is 15min to 300min, the cooling method is air cooling or furnace cooling, and the clamping force of the fixture is 500Pa to 10MPa.

2. The process for preparing and forming a composite bipolar plate according to claim 1, characterized in that: The graphite is flexible graphite, the carbon content in the flexible graphite is greater than 99.9wt%, and the particle size is 10-300μm.

3. The process for preparing and forming a composite bipolar plate according to claim 1, characterized in that: The particle size of the resin, curing agent, accelerator and additive is 10 to 300 μm.

4. The process for preparing and forming a composite bipolar plate according to claim 1, characterized in that: The resin is a thermosetting resin, the curing agent is any one of an aromatic curing agent, an acid anhydride curing agent or a phenolic resin curing agent; and the additive is any one of carbon black, carbon nanotubes or graphene.

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