Preparation method of graphite composite bipolar plate

Abstract

The invention discloses a preparation method of a graphite composite bipolar plate, which comprises the processes of raw material homogenization, preheating treatment, hot press molding, demolding, stress relief and cutting and trimming, the raw material homogenization and stress relief processes can significantly improve the yield and product quality, and the problems of low yield, poor batch stability and the like in the prior art are solved; meanwhile, conductive fillers such as graphene, carbon fibers, carbon black, carbon nanotubes and metal fibers are introduced, so that a bridging effect among graphite particles is achieved, a conductive path is broken through, contact resistance is reduced, the overall conductivity of the bipolar plate is improved, the mechanical property of the material can be improved, and the service life of the bipolar plate is prolonged. Particularly, the bending strength is obviously improved; in addition, the method is simple in process, flexible to adjust, low in special equipment requirement, low in equipment investment and suitable for popularization.

Description

Technical Field

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

[0002] Fuel cells have the advantages of fast start-up at room temperature, no electrolyte loss, long service life, high specific power and specific energy density, etc., and are a new type of power source for both military and civilian use. Bipolar plates are a key component in fuel cell stacks, which play the role of distributing fuel gas and air (oxygen), achieving electrical connection between single cells, removing waste heat from active areas, preventing gas and coolant leakage, and promoting water management.

[0003] The materials used to make bipolar plates mainly include metals, graphite and graphite composite materials. Among them, graphite composite bipolar plates have the advantages of good corrosion resistance, high preparation efficiency and easy industrialization. They are the focus of current research and the mainstream trend of subsequent bipolar plate material development. However, they have problems such as difficulty in material homogenization, harsh composite conditions, large fluctuations in product quality, low yield and high production costs. From the perspective of controlling production costs and meeting product performance indicators, simplifying the preparation process and developing new composite processes are the fundamental solutions.

[0004] Prior art CN116638697A discloses a high-performance graphite-based composite bipolar plate, preparation method and application, wherein a high-speed airflow is used in a powder mixing system to mix the powder, and then the mixed powder in the mold is heated and pressurized under vacuum conditions, and then the heating is terminated and the molding pressure is continued. When the temperature drops below the curing temperature of the resin, the molding pressure is removed and air is filled in for demolding. This method adds carbon nanotube conductive fillers to ensure that the powder is molded while improving the conductivity of the bipolar plate. However, the preparation process of this method is complicated, involving cumbersome processes such as mixing, vacuuming, and hot pressing.

[0005] Prior art CN116512634A discloses a composite graphite bipolar plate molding production system and method for fuel cells, including a ring production line, and a material laying device, a hot molding device, a curing device and a demoulding device arranged in sequence along the direction of travel of the ring production line. The present invention solves the problems of low efficiency, large equipment investment, and long production cycle in the traditional hot molding process by separating the preheating, molding and curing processes in the production and preparation of composite graphite bipolar plates. However, key processes such as raw material homogenization and stress elimination are not mentioned, which may cause problems such as large fluctuations in product quality and low yield.

[0006] Therefore, in order to solve the above problems, the present invention provides a method for preparing graphite composite bipolar plates, which can realize batch preparation of graphite composite bipolar plates and solve the problems of complex process, low yield and poor batch stability in the prior art. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a graphite composite bipolar plate, so as to realize batch preparation of graphite composite bipolar plates and solve the problems of complex process, low yield and poor batch stability in the prior art.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for preparing a graphite composite bipolar plate includes raw material homogenization, preheating treatment, hot pressing, demoulding, stress elimination, and cutting and trimming processes.

[0010] Furthermore, the raw material homogenization is selected from one or more of segmented grinding, air flow crushing, ultrasonic dispersion, solvent dispersion, and multi-stage vibration.

[0011] Furthermore, the raw materials include graphite, resin, and conductive filler; the graphite is selected from at least one of flake graphite, cryptocrystalline graphite, artificial graphite, spherical graphite, and expanded graphite; the resin is selected from at least one of epoxy resin, phenolic resin, polyimide resin, and polypropylene resin; the conductive filler is selected from at least one of graphene, carbon fiber, carbon black, carbon nanotubes, and metal fiber.

[0012] Preferably, the graphite is flake graphite with a fixed carbon content greater than 99.9% and a size of 20 to 100 microns.

[0013] Preferably, the resin is epoxy resin, and the powder size is 10 to 50 microns.

[0014] Preferably, the conductive filler is a mixture of graphene, carbon fiber and carbon nanotubes in a mass ratio of 1:(1-1.2):(1-1.2).

[0015] Furthermore, the mixing ratio of graphite, resin and conductive filler is: 80wt.% to 85wt.% graphite, 13wt.% to 17wt.% resin, and 1wt.% to 4wt.% conductive filler.

[0016] Preferably, the mixing ratio of graphite, resin and conductive filler is: 83wt.% graphite, 15wt.% resin and 2wt.% conductive filler.

[0017] Furthermore, the preheating treatment is carried out in a mold; the mold includes an upper mold, a lower mold, a scraping device, and a demoulding device, which is made of metal and has a built-in heating unit with temperature control.

[0018] Preferably, the preheating temperature is 100-140° C., and the preheating time is 30-60 min.

[0019] Furthermore, the hot pressing is carried out under a hydraulic press; the pressure of the hydraulic press is not less than 100 MPa, and has pressure control and pressure maintenance functions.

[0020] Preferably, the hot pressing molding pressure is 100-150 MPa, the hot pressing molding temperature is 150-250° C., and the holding time is 5-10 min.

[0021] Furthermore, demoulding is completed by a demoulding device in the mold after cooling to a certain temperature; the demoulding device is selected from one of mechanical, wind, and vibration.

[0022] Furthermore, the stress relief is selected from at least one of heat treatment, sandblasting, mechanical treatment, and roller pressing treatment.

[0023] Furthermore, trimming and trimming include cutting, grinding and blowing processes.

[0024] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0025] 1. The present invention includes raw material homogenization and stress elimination processes, which solves the problems of low yield and poor batch stability in the prior art;

[0026] 2. The present invention introduces conductive fillers such as graphene, carbon fiber, carbon black, carbon nanotubes, and metal fibers, which not only play a bridging role between graphite particles to open up the conductive path and reduce the contact resistance, thereby improving the overall conductivity of the bipolar plate, but also can improve the mechanical properties of the material, especially the bending strength.

[0027] 3. The process of the present invention is simple, the adjustment is flexible, the demand for special equipment is small, the equipment investment is small, and it is suitable for promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, some of the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be made based on these drawings without paying any creative work.

[0029] Figure 1 is a process flow chart of Example 1 of the present invention;

[0030] Figure 2 It is a schematic diagram of preheating treatment, hot pressing molding, and demoulding in Example 1 of the present invention;

[0031] Figure 3 This is an infrared spectrum of the graphite composite bipolar plate material under different ratios of Examples 1-3 of the present invention;

[0032] in, Figure 2 Middle: 101-raw materials filled into the mold after homogenization, 201-lower mold, 202-upper mold, 203-heating unit with temperature control system, 301-hydraulic press, 401-demolding device. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the following implementation manners or examples, unless otherwise specified, functional components or structures are conventional components or conventional structures used in the art to achieve corresponding functions.

[0035] The present invention provides a method for preparing a graphite composite bipolar plate, including the steps of raw material homogenization, preheating, hot pressing, demoulding, stress relief, cutting and trimming, etc. The process flow and some structures thereof can be referred to Figure 1 and Figure 2 .

[0036] In some specific embodiments, raw material homogenization includes one or more of segmented grinding, air flow milling, ultrasonic dispersion, solvent dispersion, and multi-stage vibration.

[0037] In a more specific embodiment, the raw material is homogenized by segmented grinding or segmented grinding + air flow milling.

[0038] In some specific embodiments, the raw materials include graphite, resin, and conductive filler; the graphite includes at least one of flake graphite, cryptocrystalline graphite, artificial graphite, spherical graphite, and expanded graphite; the resin includes at least one of epoxy resin, phenolic resin, polyimide resin, and polypropylene resin. The conductive filler is at least one of graphene, carbon fiber, carbon black, carbon nanotube, and metal fiber.

[0039] In a more specific embodiment, the graphite is flake graphite having a fixed carbon content greater than 99.9% and a size of 20 to 100 μm, more preferably 50 to 60 μm; the resin is epoxy resin having a powder size of 10 to 50 μm, more preferably 25 to 30 μm; and the conductive filler is a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:(1 to 1.2):(1 to 1.2), more preferably a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1.

[0040] In a more specific embodiment, the mixing ratio of graphite, resin and conductive filler is: 80wt.%~85wt.% graphite, 13wt.%~17wt.% resin, 1wt.%~4wt.% conductive filler; more preferably, the mixing ratio of graphite, resin and conductive filler is: 83wt.% graphite, 15wt.% resin, 2wt.% conductive filler.

[0041] In some specific embodiments, preheating is performed in the mold; the mold includes a lower mold 201, an upper mold 202, a scraping device, and a demoulding device 401, which are made of metal and have a built-in heating unit 203 with temperature control.

[0042] In a more specific embodiment, the preheating temperature is 120±20° C., and the preheating time is 30 to 60 minutes. More preferably, the preheating temperature is 120° C., and the preheating time is 50 minutes.

[0043] In some specific embodiments, the hot pressing is performed under a hydraulic press 301. The pressure of the hydraulic press should be no less than 100 MPa, and it has pressure control and pressure maintenance functions.

[0044] In a more specific embodiment, the molding pressure is 100-150 MPa, the molding temperature is 150-250° C., and the holding time is 5-10 min; more preferably, the molding pressure is 130 MPa, the molding temperature is 220° C., and the holding time is 10 min.

[0045] In some specific embodiments, demoulding is completed by a demoulding device in the mold after cooling to a certain temperature; the demoulding device is one of mechanical, wind, and vibration; in a more specific embodiment, the demoulding device 401 is a mechanical device.

[0046] In some specific embodiments, the stress relief comprises at least one of heat treatment, sandblasting, mechanical treatment, and rolling treatment.

[0047] In some specific embodiments, trimming includes cutting, grinding, and blowing processes.

[0048] The above embodiments may be implemented individually or in any combination of two or more.

[0049] The above implementation is described in more detail below in conjunction with specific examples.

[0050] Example 1

[0051] See attached Figure 1-3 This embodiment provides a method for preparing a graphite composite bipolar plate, comprising the following steps:

[0052] (1) 15 wt.% of epoxy resin was weighed and ground in a ball mill for 40 min. Then, 84 wt.% of flake graphite with a fixed carbon content of 99.92% and 1 wt.% of a conductive filler were weighed. The conductive filler was a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1. After being mixed with the epoxy resin, the mixture was further ground for 20 min to homogenize. Then, 201 was filled in and 101 was formed after being vibrated and flattened.

[0053] (2) Close 202, open 203, preheat temperature is 120°C, preheat time is 50 min.

[0054] (3) After preheating, turn on 301, linearly increase the pressure to 130 MPa within 5 minutes, linearly increase the temperature to 220°C within 5 minutes, and then maintain this pressure and temperature for 10 minutes.

[0055] (4) As the mold cools to less than 50°C, open 202 and push 401 to demold to obtain a rough bipolar plate.

[0056] (5) After heating both sides of the rough blank to 80°C and holding for 5 min, a 5 MPa flat press is used to release stress and correct deflection to form a bipolar plate stress release part.

[0057] (6) The burrs on the edge of the stress release part of the bipolar plate are removed, and the plate is polished with a wool wheel. After the dust is removed by high-pressure air gun, the finished graphite composite bipolar plate is obtained.

[0058] The infrared spectrum of the graphite composite bipolar plate material under this ratio is as follows Figure 3 shown.

[0059] Example 2

[0060] See attached Figure 3 This embodiment provides a method for preparing a graphite composite bipolar plate, comprising the following steps:

[0061] (1) 15 wt.% of epoxy resin was weighed and ground in a ball mill for 40 min, then 83 wt.% of flake graphite with a fixed carbon content of 99.92% and 2 wt.% of a conductive filler were weighed, wherein the conductive filler was a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1, mixed with the epoxy resin, and then ground for 20 min to homogenize, and then filled with 201, vibrated, and flattened to form 101;

[0062] (2) Close 202, open 203, preheat temperature is 120°C, preheat time is 50 min;

[0063] (3) After the preheating is completed, 301 is turned on, and the pressure is linearly increased to 130 MPa within 5 minutes, and the temperature is linearly increased to 220°C within 5 minutes, and then maintained at this pressure and temperature for 10 minutes;

[0064] (4) As the mold cools to less than 50° C., 202 is opened and 401 is pushed to demold to obtain a rough bipolar plate blank;

[0065] (5) After heating both sides of the rough blank to 80°C and holding for 5 min, use 5 MPa flat pressing to release stress and correct deflection to form a bipolar plate stress release part;

[0066] (6) The burrs on the edge of the stress release part of the bipolar plate are removed, and the plate is polished with a wool wheel. After the dust is removed by high-pressure air gun, the finished graphite composite bipolar plate is obtained.

[0067] The infrared spectrum of the graphite composite bipolar plate material under this ratio is as follows Figure 3 shown.

[0068] Example 3

[0069] See attached Figure 3 This embodiment provides a method for preparing a graphite composite bipolar plate, comprising the following steps:

[0070] (1) 15 wt.% of epoxy resin was weighed and ground in a ball mill for 40 min, then 82 wt.% of flake graphite with a fixed carbon content of 99.92% and 3 wt.% of a conductive filler were weighed, wherein the conductive filler was a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1, mixed with the epoxy resin, and then ground for 20 min to homogenize, and then 201 was filled in, and 101 was formed after vibration and flattening;

[0071] (2) Close 202, open 203, preheat temperature is 120°C, preheat time is 50 min;

[0072] (3) After the preheating is completed, 301 is turned on, and the pressure is linearly increased to 130 MPa within 5 minutes, and the temperature is linearly increased to 220°C within 5 minutes, and then maintained at this pressure and temperature for 10 minutes;

[0073] (4) As the mold cools to less than 50° C., 202 is opened and 401 is pushed to demold to obtain a rough bipolar plate blank;

[0074] (5) After heating both sides of the rough blank to 80°C and holding for 5 min, use 5 MPa flat pressing to release stress and correct deflection to form a bipolar plate stress release part;

[0075] (6) The burrs on the edge of the stress release part of the bipolar plate are removed, and the plate is polished with a wool wheel. After the dust is removed by high-pressure air gun, the finished graphite composite bipolar plate is obtained.

[0076] The infrared spectrum of the graphite composite bipolar plate material under this ratio is as follows Figure 3 shown.

[0077] Example 4

[0078] This embodiment provides a method for preparing a graphite composite bipolar plate, comprising the following steps:

[0079] (1) 15 wt.% of epoxy resin was weighed and ground in a ball mill for 30 min, then 83 wt.% of flake graphite with a fixed carbon content of 99.92% and 2 wt.% of a conductive filler were weighed, wherein the conductive filler was a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1, mixed with the epoxy resin, and then ground for 20 min, and then air flow crushed for 5 min to homogenize, and then filled with 201, vibrated, and flattened to form 101;

[0080] (2) Close 202, open 203, preheat temperature is 120°C, preheat time is 50 min;

[0081] (3) After the preheating is completed, 301 is turned on, and the pressure is linearly increased to 130 MPa within 5 minutes, and the temperature is linearly increased to 220°C within 5 minutes, and then maintained at this pressure and temperature for 10 minutes;

[0082] (4) As the mold cools to less than 50° C., 202 is opened and 401 is pushed to demold to obtain a rough bipolar plate blank;

[0083] (5) After heating both sides of the rough blank to 80°C and holding for 5 min, use 5 MPa flat pressing to release stress and correct deflection to form a bipolar plate stress release part;

[0084] (6) The burrs on the edge of the stress release part of the bipolar plate are removed, and the plate is polished with a wool wheel. After the dust is removed by high-pressure air gun, the finished graphite composite bipolar plate is obtained.

[0085] Example 5

[0086] This embodiment provides a method for preparing a graphite composite bipolar plate, comprising the following steps:

[0087] (1) 15 wt.% of epoxy resin was weighed and ground in a ball mill for 40 min, then 83 wt.% of spherical graphite with a fixed carbon content of 99.96% and 2 wt.% of a conductive filler were weighed, wherein the conductive filler was a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1:1:1, mixed with the epoxy resin, and then ground for 20 min to homogenize, and then 201 was filled in, and 101 was formed after vibration and flattening;

[0088] (2) Close 202, open 203, preheat temperature is 120°C, preheat time is 50 min;

[0089] (3) After the preheating is completed, 301 is turned on, and the pressure is linearly increased to 130 MPa within 5 minutes, and the temperature is linearly increased to 220°C within 5 minutes, and then maintained at this pressure and temperature for 10 minutes;

[0090] (4) As the mold cools to less than 50° C., 202 is opened and 401 is pushed to demold to obtain a rough bipolar plate blank;

[0091] (5) After heating both sides of the rough blank to 80°C and holding for 5 min, use 5 MPa flat pressing to release stress and correct deflection to form a bipolar plate stress release part;

[0092] (6) The burrs on the edge of the stress release part of the bipolar plate are removed, and the plate is polished with a wool wheel. After the dust is removed by high-pressure air gun, the finished graphite composite bipolar plate is obtained.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 2 is that the homogenization treatment in step (1) is not performed but simply mixed and then filled into 201 to form 101. The rest is the same as Example 2.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 4 is that the stress relief process in step (5) is not performed, and the other aspects are the same as Example 4.

[0097] The graphite composite bipolar plates prepared in Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1 and Comparative Example 2 were tested for bending strength, electrical conductivity, contact resistance, and gas permeability. The test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] Depend on Figure 3, there is obvious -CH2CH2-O- vibration in Example 1, and the epoxy resin grafting is successful; the -CH2CH2-O- vibration of Examples 2 and 3 is weakened, which is attributed to the infrared shielding of graphene, carbon fiber and carbon nanotubes; It can be seen from Table 1 that with the increase of the amount of conductive filler added, the conductivity of the graphite composite bipolar plate gradually increases, the contact resistance gradually decreases, the bending strength first increases and then decreases, the gas permeability first decreases and then increases, and the yield rate and maximum deflection do not change significantly; On the whole, the comprehensive index when the conductive filler is added at 2wt.% is better; Comparing Example 2 and Example 4, the homogenization method of segmented grinding + air flow crushing is better than segmented grinding; Comparing Example 2 and Example 5, flake graphite is better than spherical graphite; Comparing Example 4 and Comparative Example 1, the yield rate and product quality can be significantly improved after raw material homogenization; Comparing Example 4 and Comparative Example 2, the rough blank can be significantly improved by stress elimination process and the maximum deflection can be reduced.

[0101] In summary, the present invention includes raw material homogenization and stress elimination processes, which solve the problems of low yield and poor batch stability in the prior art; the present invention introduces conductive fillers such as graphene, carbon fiber, carbon black, carbon nanotubes, metal fibers, etc., which not only play a bridging role between graphite particles to open up the conductive path and reduce the contact resistance, thereby improving the overall conductivity of the bipolar plate, but also can improve the mechanical properties of the material, especially the bending strength. The present invention has a simple process, flexible adjustment, less demand for special equipment, and small equipment investment, and is suitable for promotion.

[0102] The preferred conditions of the above embodiments are obtained based on a large number of exploratory experiments and scientific experimental designs of single variable and orthogonal experiments. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, the technical scheme of the present invention can be subjected to a variety of simple modifications, and these simple modifications all belong to the protection scope of the present invention.

[0103] The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further explain various possible combinations.

[0104] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0105] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a graphite composite bipolar plate, characterized in that: It includes raw material homogenization, preheating treatment, hot pressing molding, demoulding, stress relief, cutting and trimming processes.

2. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: The raw material homogenization is selected from one or more of segmented grinding, air flow pulverization, ultrasonic dispersion, solvent dispersion, and multi-stage vibration.

3. The method for preparing a graphite composite bipolar plate according to claim 2, characterized in that: The raw materials include graphite, resin, and conductive filler; the graphite is selected from at least one of flake graphite, cryptocrystalline graphite, artificial graphite, spherical graphite, and expanded graphite; the resin is selected from at least one of epoxy resin, phenolic resin, polyimide resin, and polypropylene resin; the conductive filler is selected from at least one of graphene, carbon fiber, carbon black, carbon nanotubes, and metal fiber.

4. The method for preparing a graphite composite bipolar plate according to claim 3, characterized in that: The mixing ratio of graphite, resin and conductive filler is: 80wt.%-85wt.% graphite, 13wt.%-17wt.% resin, and 1wt.%-4wt.% conductive filler.

5. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: The preheating treatment is carried out in the mold; the mold includes an upper mold, a lower mold, a scraping device, and a demoulding device, which is made of metal and has a built-in heating unit with temperature control.

6. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: The hot pressing is carried out under a hydraulic press; the pressure of the hydraulic press is not less than 100 MPa.

7. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: The demoulding is completed by a demoulding device in the mold after cooling to a certain temperature; the demoulding device is selected from one of mechanical, wind and vibration.

8. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: The stress relief is selected from at least one of heat treatment, sandblasting, mechanical treatment, and roller pressing treatment.

9. The method for preparing a graphite composite bipolar plate according to claim 1, characterized in that: Trimming includes cutting, grinding and blowing processes.

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