A toughened flexible graphite bipolar plate and a method for making the same

Abstract

The application belongs to the field of fuel cell bipolar plates, and particularly discloses a toughened flexible graphite bipolar plate and a preparation method thereof.The toughened flexible graphite bipolar plate comprises the following components in parts by weight: graphite 40-80 parts, resin 10-50 parts, curing agent 10-25 parts, conductive agent 1-10 parts, and auxiliary agent 3-20 parts.The toughened flexible graphite bipolar plate has the advantages of high bending strength, good toughness, low bending modulus and high conductivity, wherein the bending strength of the toughened flexible graphite bipolar plate is greater than 50 MPa, and the bending modulus is less than 8000 MPa.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell bipolar plates, specifically relating to a toughened flexible graphite bipolar plate and its preparation method. Background Technology

[0002] In a hydrogen fuel cell, hydrogen gas is delivered to the anode (negative electrode). Through the action of a catalyst (platinum), an electron is separated from the hydrogen atom. The hydrogen ion (proton), having lost its electron, passes through the proton exchange membrane and reaches the cathode (positive electrode). Electrons, however, cannot pass through the proton exchange membrane. This electron travels through an external circuit to the cathode, generating an electric current. The electrical energy generated by the fuel cell is transmitted to an electric motor via an inverter and controller, and then through a transmission system and drive axle to rotate the wheels, enabling the vehicle to move. Compared to traditional automobiles, the energy conversion efficiency is as high as 60-80%, which is 2-3 times that of an internal combustion engine. As a core component of the fuel cell, the bipolar plate needs to separate hydrogen and oxygen and conduct electricity; therefore, it requires high mechanical strength, high conductivity, high impermeability, chemical stability, and heat resistance, among other properties.

[0003] Currently, the main materials for bipolar plates include metal bipolar plates, graphite bipolar plates, and composite graphite bipolar plates. Among them, metal bipolar plates have high coating costs and poor corrosion resistance. Graphite bipolar plates have complex manufacturing processes, resulting in high costs, and their brittleness hinders widespread adoption. Composite graphite bipolar plates possess strong corrosion resistance and excellent conductivity, and their manufacturing process is relatively simple, leading to their widespread use. However, the bending strength of composite graphite bipolar plates is lower than that of metal and graphite bipolar plates, leaving significant room for improvement. Furthermore, composite graphite bipolar plates suffer from insufficient toughness, making them prone to damage during fuel cell assembly. Summary of the Invention

[0004] In view of the problems of insufficient bending strength and toughness of composite graphite bipolar plates in the prior art, the present invention will provide a toughened flexible graphite bipolar plate and its preparation method.

[0005] To achieve the above objectives, the following technical solutions are specifically included:

[0006] On one hand, the present invention provides a toughened flexible graphite bipolar plate, comprising the following components in parts by weight: 40-80 parts graphite, 10-50 parts resin, 10-25 parts curing agent, 1-10 parts conductive agent, and 3-20 parts additives; wherein the resin comprises phenolic resin; the curing agent comprises at least two of hexamethylenetetramine (urotropine), bisphenol A, epoxy resin, vinyl ester resin, polyethylene resin, acrylic resin, polyamide resin, unsaturated polyester resin, dicyandiamide, and polythiolated compounds; the additives comprise coupling agents and toughening agents; and the toughening agent comprises at least one of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl butyral.

[0007] This invention, by selecting specific component ratios, produces toughened flexible graphite bipolar plates with advantages such as high flexural strength, good toughness, low flexural modulus, and high conductivity. Specifically, the toughened flexible graphite bipolar plate exhibits a compressive strength greater than 50 MPa, a flexural modulus less than 8000 MPa, and a gas permeability less than 0.002 sccm / cm. 2 Surface resistivity is less than 10.5 mΩcm 2 .

[0008] In a preferred embodiment of the present invention, the phenolic resin includes at least one of thermoplastic phenolic resin, thermosetting phenolic resin, boron phenolic resin, polyamide-modified phenolic resin, aniline-modified phenolic resin, and bisacrylamide-modified phenolic resin.

[0009] As a further preferred embodiment of the present invention, the phenolic resin is a thermoplastic phenolic resin or a thermosetting phenolic resin.

[0010] As a preferred embodiment of the present invention, it comprises the following components in parts by weight: 60 parts graphite, 35 parts resin, 15-20 parts curing agent, 5 parts conductive agent, and 3-15 parts additives.

[0011] As a further preferred embodiment of the present invention, it comprises the following components in parts by weight: 60 parts graphite, 35 parts resin, 16-20 parts curing agent, 5 parts conductive agent, and 6-15 parts additives.

[0012] In a preferred embodiment of the present invention, the curing agent is any two of hexamethylenetetramine, epoxy resin, and bisphenol A.

[0013] As a further preferred embodiment of the present invention, the hexamethylenetetramine, epoxy resin and bisphenol A are in the following weight parts: 15 parts, 5 parts and 5 parts, respectively.

[0014] When the epoxy resin is selected as the curing agent, the epoxy resin may be the same as or different from the epoxy resin selected for the resin, but it is preferred that the two are the same.

[0015] In a preferred embodiment of the present invention, the coupling agent includes at least one of silane coupling agents and titanate esters; the toughening agent is polypropylene.

[0016] As a further preferred embodiment of the present invention, the silane coupling agent is any one of KH550, KH560, and KH570.

[0017] In a preferred embodiment of the present invention, the graphite includes at least one of expanded graphite (flexible graphite), natural graphite, and artificial graphite.

[0018] As a further preferred embodiment of the present invention, the expanded graphite is flexible graphite with an expansion degree of 100-500.

[0019] In a preferred embodiment of the present invention, the conductive agent includes at least one of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, and graphene.

[0020] As a further preferred embodiment of the present invention, the mesh size of the conductive agent is 10 to 3000 mesh.

[0021] On the other hand, the present invention also includes a method for preparing a toughened flexible graphite bipolar plate, which includes the following steps: (1) stirring and mixing graphite, resin, curing agent, conductive agent and additives to obtain powder;

[0022] (2) Place the powder described in step (1) in a mold and press it to obtain a bipolar plate preform;

[0023] (3) The bipolar plate preform described in step (2) is placed in a mold for hot pressing to obtain a toughened flexible graphite bipolar plate.

[0024] In a preferred embodiment of the present invention, the stirring speed in step (1) is 2000-20000 rpm and the stirring time is 1-10 minutes; the pressing pressure in step (2) is 10-100 MPa and the pressing time is 1-10 minutes; the hot pressing pressure in step (3) is 10-100 MPa and the hot pressing time is 30-360 seconds.

[0025] In a preferred embodiment of the present invention, the thickness of the bipolar plate preform is 0.3-1.0 mm.

[0026] In a preferred embodiment of the present invention, the toughened flexible graphite bipolar plate has a thickness of 0.35mm-1.5mm.

[0027] Compared with existing technologies, the present invention has the following advantages: the toughened flexible graphite bipolar plate of the present invention has the advantages of high bending strength, good toughness, low flexural modulus, and high conductivity. Specifically, the toughened flexible graphite bipolar plate has a compressive strength greater than 50 MPa, a flexural modulus less than 8000 MPa, and a gas permeability less than 0.002 sccm / cm. 2 Surface resistivity is less than 10.5 mΩcm 2 . Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific embodiments.

[0029] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0030] In the following examples, the silane coupling agent used is KH550; the flexible graphite used is flexible graphite with an expansion degree of 100-500.

[0031] Examples 1-6

[0032] The composition of the toughened flexible graphite bipolar plates in Examples 1-6 is shown in Table 1 and Table 2, respectively.

[0033] The preparation methods of the toughened flexible graphite bipolar plates in Examples 1-6 are as follows:

[0034] (1) Preparation of powder: Pre-dehydrated graphite, resin, curing agent, conductive agent and additives are put into a high-speed mixer. Under the strong shearing action of high-speed rotation (20,000 rpm), the block and powder materials are fully mixed. The mixing time is 10 minutes to obtain a uniformly mixed powder.

[0035] (2) Preparation of bipolar plate preform: Place the well-stirred powder in the mold, spread the powder in the mold with a scraper, scrape off the excess powder, press 100MPa at room temperature and hold the pressure for 10 minutes to obtain a flat plate with a thickness of 0.3mm.

[0036] (3) Curing of electrode preform: The pressed preform electrode is placed in a mold with a flow channel that has been preheated to 150°C and hot-pressed at 50MPa for 300s in a constant temperature hot press. Then the molded electrode is taken out while it is still hot. The base thickness is 0.35mm and the electrode thickness is 0.5mm.

[0037] Example 7

[0038] (1) Preparation of powder: According to the component content of Example 1 in Table 1, the pre-dehydrated graphite, high-strength resin, curing agent, conductive agent and additives are put into a high-speed mixer. Under the strong shearing action of high-speed rotation (10000 rpm), the block and powder materials are fully mixed. The mixing time is 5 minutes to obtain a uniformly mixed powder.

[0039] (2) Preparation of bipolar plate preform: Place the well-stirred powder in the mold, spread the powder evenly in the mold with a scraper, scrape off the excess powder, press at 80MPa at room temperature and hold for 5 minutes to obtain a flat plate with a thickness of 0.5mm.

[0040] (3) Curing of electrode preform: The pressed preform electrode is placed in a mold with a flow channel that has been preheated to 200°C and hot-pressed at 70MPa for 360s in a constant temperature hot press. Then the molded electrode is taken out while it is still hot. The electrode thickness is 0.8mm and the base thickness is 0.5mm.

[0041] Example 8

[0042] (1) Preparation of powder: According to the component content of Example 1 in Table 1, the pre-dehydrated graphite, high-strength resin, curing agent, conductive agent and additives are put into a high-speed mixer. Under the strong shearing action of high-speed rotation (2000 rpm), the block and powder materials are fully mixed. The mixing time is 2 minutes to obtain a uniformly mixed powder.

[0043] (2) Preparation of bipolar plate preform: Place the well-stirred powder in the mold, spread the powder in the mold with a scraper, scrape off the excess powder, press at 20MPa at room temperature and hold for 7 minutes to obtain a flat plate with a thickness of 1.0mm.

[0044] (3) Curing of electrode preform: The pressed preform electrode is placed in a mold with a flow channel that has been preheated to 150°C and hot-pressed at 20MPa for 100s in a constant temperature hot press. Then the molded electrode is taken out while it is still hot. The electrode thickness is 0.8mm and the base thickness is 0.5mm.

[0045] Comparative Example 1

[0046] The components of the comparative graphite bipolar plates are shown in Table 2.

[0047] The comparative graphite bipolar plate was prepared using the same method as in Example 1, and its performance test results are shown in Table 2.

[0048] Comparative Example 2

[0049] The components of the comparative graphite bipolar plates are shown in Table 2.

[0050] The preparation method of the comparative graphite bipolar plate is the same as that of Example 1, and its performance test results are shown in Table 2.

[0051] Table 1. Composition, weight percentages, and properties of the toughened flexible graphite bipolar plates in Examples 1-5

[0052]

[0053] Table 2. Composition, weight percentages, and performance of the graphite bipolar plates in Example 6, Comparative Examples 1 and 2

[0054]

[0055]

[0056] The toughened flexible graphite bipolar plate of this invention was tested according to the specific test methods in the national standard GB / T 20042.6-2011. The results show that the flexural strength of the hot-pressed toughened flexible graphite bipolar plate of this invention is greater than 50 MPa. Under the same flexural strength, the greater the deformation, the smaller the flexural modulus, indicating stronger deformation capacity and greater toughness. Under the same flexural strength, the toughened flexible graphite bipolar plate of this invention exhibits high toughness with a flexural modulus < 8000 MPa; the gas leakage rate is less than 0.002 sccm / cm. 2 Surface resistivity is less than 10.5 mΩcm 2 .

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A toughened flexible graphite bipolar plate characterized by, The composition comprises the following components by weight: graphite 40-80 parts, resin 10-50 parts, curing agent 16-20 parts, conductive agent 1-10 parts, and auxiliary agent 3-20 parts; the resin is phenolic resin, or phenolic resin and epoxy resin; the curing agent is any two of hexamethylene tetramine, epoxy resin, and bisphenol A; the auxiliary agent comprises coupling agent and toughening agent; the toughening agent is polypropylene.

2. The toughened flexible graphite bipolar plate of claim 1 wherein The composition comprises the following components by weight: graphite 60 parts, resin 35 parts, curing agent 15-20 parts, conductive agent 5 parts, and auxiliary agent 3-15 parts.

3. The toughened flexible graphite bipolar plate of claim 2 wherein The composition comprises the following components by weight: graphite 60 parts, resin 35 parts, curing agent 16-20 parts, conductive agent 5 parts, and auxiliary agent 6-15 parts.

4. The toughened flexible graphite bipolar plate of claim 1 wherein The weight parts of the hexamethylene tetramine, epoxy resin, and bisphenol A are 15 parts, 5 parts, and 5 parts respectively.

5. The toughened flexible graphite bipolar plate according to any one of claims 1 to 3, wherein The coupling agent comprises at least one of silane coupling agent and titanate; the toughening agent is polypropylene.

6. The toughened flexible graphite bipolar plate according to any one of claims 1 to 3, wherein The graphite comprises at least one of expanded graphite, natural graphite, and artificial graphite.

7. The toughened flexible graphite bipolar plate of any one of claims 1 to 3, wherein The conductive agent comprises at least one of acetylene black, conductive carbon black, carbon nanotube, carbon fiber, and graphene.

8. The method of producing a flexible graphite bipolar plate according to any one of claims 1 to 7, characterized by, The method comprises the following steps, (1) mixing graphite, resin, curing agent, conductive agent, and auxiliary agent by stirring to obtain powder; (2) pressing the powder obtained in step (1) in a mold under pressure to obtain a bipolar plate preform; (3) performing hot-pressing treatment on the bipolar plate preform obtained in step (2) in a mold to obtain a toughened flexible graphite bipolar plate.

9. The production method according to claim 8, wherein The stirring speed in step (1) is 2000-20000 revolutions per minute, and the stirring time is 1-10 minutes; the pressing pressure in step (2) is 10-100 MPa, and the pressing time is 1-10 minutes; the hot-pressing pressure in step (3) is 10-100 MPa, and the hot-pressing time is 30-360 seconds.

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