A layered graphite composite bipolar plate and its preparation method

Abstract

The present invention relates to a layered graphite composite bipolar plate and a preparation method. The layered graphite composite bipolar plate includes an intermediate layer and surface layers disposed on both sides of the intermediate layer. The intermediate layer is a thermoplastic resin / graphite composite plate, and the surface layer is a thermosetting resin / graphite composite layer. The outer surface of the surface layer has a flow channel structure. Compared with the prior art, the present invention utilizes a thermoplastic composite material to make the intermediate layer, which helps improve the feeding accuracy of the thermosetting composite material during the production process and helps alleviate the problem of low molding reliability of thermosetting composite materials with high carbon content. In addition, the high resin content of the intermediate layer in the layered plate improves the bending strength and airtightness of the bipolar plate, and the high carbon content of the surface layer improves its electrical conductivity. The overall performance of the bipolar plate is improved by optimizing the different functional layers separately. At the same time, the preparation process is simple, which is conducive to mass production and has high practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells and relates to a proton exchange membrane fuel cell, in particular to a layered graphite composite bipolar plate and a preparation method thereof. Background Art

[0002] Fuel cell technology, with its clean and efficient energy conversion mechanism, holds broad application prospects. Proton exchange membrane fuel cells (PEMFCs), in particular, offer fast startup and low operating temperatures, making them the most suitable fuel cell type for large-scale deployment. Bipolar plates are key fuel cell components, performing multiple functions, including isolating and distributing anode and cathode reactants, collecting current, conducting heat, sealing, and supporting the membrane electrode. Therefore, the size and performance of the bipolar plates have a direct impact on fuel cell performance.

[0003] Bipolar plates currently used in PEMFCs can be categorized as graphite, metal, and composite bipolar plates based on their manufacturing materials. Graphite bipolar plates offer excellent conductivity and corrosion resistance, but suffer from poor flexural strength and airtightness, typically requiring thicker plates for practical applications. Furthermore, the difficulty in machining the fine flow channel structures on the bipolar plate surface is a significant factor limiting the widespread application of graphite bipolar plates. Metal bipolar plates offer significant advantages in terms of conductivity, flexural strength, and machinability. However, metal bipolar plates are exposed to the high-temperature, acidic environment of PEMFCs, making them susceptible to corrosion and dissolution, or the formation of an oxide layer on the plate surface. This not only reduces the metal bipolar plate's conductivity, but also allows the dissolved metal ions to diffuse into the proton exchange membrane, significantly impacting PEMFC performance. Composite bipolar plates, with a graphite-reinforced resin polymer matrix, offer key advantages such as low cost, simplified manufacturing, lightweight, and excellent corrosion resistance. The performance of composite bipolar plates is influenced by factors such as graphite content and manufacturing process, resulting in significant variations in conductivity, flexural strength, and processability. The current optimization ideas mainly focus on optimizing the performance of resins and improving the hot molding process, which makes it difficult to fundamentally improve the contradiction between conductivity and flexural strength.

[0004] To address the inability of a single composite material to effectively balance bipolar plate performance, the Institute of Metal Research, Chinese Academy of Sciences, disclosed a flexible graphite bipolar plate and its preparation method in Chinese Patent CN107819137A. The patent proposes using metal mesh and carbon cloth as a conductive framework, coating it with a graphite / resin composite, and finally laminating it with flexible graphite paper and then molding it to form a composite bipolar plate. The patent introduces the concept of a reinforced structure to improve the overall performance of the bipolar plate.

[0005] Guangdong Guohong Hydrogen Energy Technology Co., Ltd. disclosed an ultra-thin flexible graphite bipolar plate and its preparation method in Chinese patent CN109921051A, and proposed a method of reinforcing flexible graphite plates with graphene films. Summary of the Invention

[0006] The existing technologies do not effectively solve the problem of reducing the thickness of graphite composite bipolar plates and the precision of forming flow channels. The purpose of the present invention is to provide a layered graphite composite bipolar plate and a preparation method to solve this problem.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] On the one hand, the present invention provides a layered graphite composite bipolar plate, comprising an intermediate layer and surface layers arranged on both sides of the intermediate layer, wherein the intermediate layer is a thermoplastic resin / graphite composite material plate, the surface layer is a thermosetting resin / graphite composite material layer, and the outer surface of the surface layer has a flow channel structure.

[0009] As a preferred embodiment of the present invention, the flow channel structure is solidified and formed on the surface layer through hot molding. Its depth is less than the thickness of the surface layer. The intermediate layer maintains a planar structure and does not participate in the flow channel formation. This structure effectively enables the intermediate layer to ensure the bending strength of the plate. The goal of improving the flow channel structure's forming accuracy can be achieved simply by optimizing the formulation of the surface layer. This facilitates the formulation optimization of layered composite plates and provides a solution to the difficult problem of balancing forming performance and usability.

[0010] As a preferred embodiment of the present invention, the thermoplastic resin / graphite composite material plate is formed by processing a composite material made of thermoplastic resin and graphite material.

[0011] As a further preferred embodiment of the present invention, the thermoplastic resin includes fluorinated ethylene-propylene (FEP), and / or polypropylene (PP), and / or polyphenylene sulfide (PPS), and / or polyvinylidene fluoride (PVDF), and / or polycarbonate (PC), and / or polyoxymethylene resin (POM).

[0012] As a further preferred embodiment of the present invention, the graphite material includes natural flake graphite, and / or expanded graphite, and / or carbon fiber powder, and / or chopped carbon fiber.

[0013] As a further preferred embodiment of the present invention, the mass ratio of the thermoplastic resin to the graphite material is 3:7-7:3. More preferably, the mass ratio of the thermoplastic resin to the graphite material is 5:5.

[0014] As a further preferred embodiment of the present invention, the particle size of the graphite material is 1 μm-200 μm. When the graphite material contains chopped carbon fibers, the length of the chopped carbon fibers is 1 mm-5 mm. More preferably, the particle size of the graphite material is 40 μm-80 μm.

[0015] As a further preferred embodiment of the present invention, the thickness of the thermoplastic resin / graphite composite material plate is 0.1 mm to 0.4 mm, and more preferably, the thickness of the thermoplastic resin / graphite composite material plate is 0.1 mm to 0.2 mm.

[0016] As a preferred embodiment of the present invention, the thermosetting resin / graphite composite material layer is made of a masterbatch of a mixture of thermosetting resin and graphite material.

[0017] As a further preferred embodiment of the present invention, the graphite material includes natural flake graphite, and / or expanded graphite, and / or carbon fiber, and / or graphene nanosheets, and / or highly conductive carbon black.

[0018] As a further preferred embodiment of the present invention, the thermosetting resin is a thermosetting resin with a relatively low curing temperature, including epoxy resin (EP), and / or phenolic resin (PF), and / or polyimide resin (PI), and / or vinyl ester resin (VER), and / or polybenzoxazine resin (PBA), and / or urea-formaldehyde resin (UR), and / or polyurethane resin (PU).

[0019] As a further preferred embodiment of the present invention, the mass ratio of the graphite material to the thermosetting resin is 7:3-9:1.

[0020] As a further preferred embodiment of the present invention, the particle size of the graphite material is 1 μm-100 μm.

[0021] As a further preferred embodiment of the present invention, the thickness of the thermosetting resin / graphite composite material layer is 0.1 mm-0.5 mm, and the thickness of the formed electrode plate is less than 1.4 mm.

[0022] A second aspect of the present invention provides a method for preparing a layered graphite composite bipolar plate, comprising the following steps:

[0023] S1: Preparation of thermoplastic resin / graphite composite sheet by roll forming;

[0024] S2: preparing a masterbatch of thermosetting resin / graphite composite material;

[0025] S3: filling the masterbatch of thermosetting resin / graphite composite material, the thermoplastic resin / graphite composite material plate and the masterbatch of thermosetting resin / graphite composite material into the drying mold in sequence and performing a drying process;

[0026] S4: placing the dried material from step S3 together with the drying mold into a hot pressing mold, pressurizing and heating to form the material, and cooling the material to obtain the layered graphite composite bipolar plate.

[0027] As a preferred embodiment of the present invention, step S1 includes the following process:

[0028] S11: Dry-mix the thermoplastic resin and graphite powder, mix them evenly and then dry them to obtain a masterbatch A:

[0029] S12: preheating the masterbatch A in a preheating box while maintaining a constant feeding rate;

[0030] S13: The preheated masterbatch A is conveyed by a conveying mechanism, and processed into a continuous plate of target thickness through rough rolling and finish rolling. The continuous plate is cut and cooled to obtain the thermoplastic resin / graphite composite material plate.

[0031] The layered structure of the intermediate and surface layers in this invention achieves the performance requirements of graphite composite bipolar plates for structural strength and airtightness, in-plane conductivity, and reliable molding, thereby optimizing overall plate performance. Furthermore, the intermediate layer serves as a substrate to assist in molding the surface layer, reducing the difficulty of molding ultra-thin graphite composite plates.

[0032] The present invention uses rolling to press the composite material into a smooth-surfaced plate, which serves as the intermediate layer of the graphite composite bipolar plate. Rolling is a fast process that allows for precise control of the thickness of the intermediate layer, making it suitable for mass production.

[0033] The composite material required for the intermediate layer must meet multiple requirements. It must exhibit good flowability during the rolling process, ensure reliable molding, and minimize shrinkage. The formed sheet must also exhibit high airtightness, flexural strength, and through-plane electrical conductivity. To achieve these requirements, strict requirements must be met for the ratio of thermoplastic resin to graphite.

[0034] As a further preferred embodiment of the present invention, in step S1, the feeding rate of the masterbatch A and the conveying rate of the conveying mechanism are adjusted according to the fluidity of the thermoplastic resin and the content of the graphite powder in the masterbatch A. If the fluidity of the thermoplastic resin in the masterbatch A is low or the graphite content is high, the feeding rate is reduced, and the conveying rate of the conveying mechanism is also reduced accordingly; if the fluidity of the resin in the masterbatch A is high or the graphite content is low, the feeding rate and the conveying rate are increased.

[0035] As a further preferred embodiment of the present invention, in step S1 , the preheating temperature of the masterbatch A is adjusted according to the type of thermoplastic resin in the masterbatch A and the content of graphite powder.

[0036] As a further preferred embodiment of the present invention, in step S1, rough rolling and finishing rolling are completed by a combined roll group consisting of horizontal rolls and vertical rolls, and the horizontal rolls and vertical rolls respectively realize processing of the thickness and width of the formed plate.

[0037] As a further preferred embodiment of the present invention, in step S1, depending on the type of thermoplastic resin and the graphite powder content in masterbatch A, the finishing process can be performed by 3-10 finishing roller sets. If the thermoplastic resin content in masterbatch A is greater than the graphite content, the finishing process can be performed by 3-6 finishing roller sets. This number can be adjusted based on the high-temperature fluidity of the resin to improve production efficiency. If the graphite content in masterbatch A is greater than the thermoplastic resin content, the finishing process can be performed by 7-10 finishing roller sets to ensure reliable molding.

[0038] As a further preferred embodiment of the present invention, in step S1, the continuous plate is cut into plates of target length by limiting rollers.

[0039] After the plate is formed, the surface layer should exhibit high electrical and thermal conductivity, thus requiring a high graphite content. Furthermore, the surface layer must maintain a low thickness while ensuring reliable molding. Therefore, the thermosetting resin and graphite should be mixed using a combination of mechanical stirring and ultrasonic dispersion with a solvent to ensure the most uniform mixing possible. The amount of solvent used must balance the graphite dispersion effect with the need for easy drying. To meet these performance requirements, the ratio of resin, graphite, and solvent must be strictly controlled.

[0040] As a preferred embodiment of the present invention, in step S2, a masterbatch of a thermosetting resin / graphite composite material is obtained by sequentially adding a solvent and a graphite material to a thermosetting resin and mixing them thoroughly;

[0041] The solvent is a volatile polar solvent, including acetone, and / or anhydrous ethanol, and / or n-butanol, and / or ethylene glycol, and / or isopropanol;

[0042] The ratio of the mass of the solvent to the total mass of the thermosetting resin and the graphite material is 1:9-2:8.

[0043] The raw materials for the intermediate and surface layers are dried together in a drying mold before being hot-pressed to form a layered graphite composite bipolar plate. This preforming method not only allows for convenient and efficient control of the surface layer feed rate, but also quickly achieves uniform distribution of the masterbatch within the mold before pressing, improving production efficiency.

[0044] As a preferred embodiment of the present invention, in step S3, the drying process is vacuum drying at 80° C. for 1 h to 2 h.

[0045] As a preferred embodiment of the present invention, in step S3, vibration is performed before drying to achieve uniform distribution of the masterbatch of the thermosetting resin / graphite composite material in the drying mold, and the filling thickness of the masterbatch of the thermosetting resin / graphite composite material after vibration is 0.8 mm-2.0 mm.

[0046] As a preferred embodiment of the present invention, in step S4, during the pressurized and heated molding process, a pre-pressing pressure of 1 MPa-10 MPa is first applied for 1 minute, the molding temperature is then raised to 140°C-180°C, and the hot molding pressure is raised to 15 MPa-30 MPa, maintained for 0.5-1 hour; after cooling, the mold is demolded to obtain the layered graphite composite bipolar plate. Using the GBT20042.6 standard test, the hydrogen permeability coefficient of the plate obtained by the present invention is less than 1×10 -14 cm 3 / (s·cm 2 Pa), flexural strength is between 50-90 MPa, and electrical conductivity is between 100-180 S / cm.

[0047] The present invention uses thermoplastic composite materials to produce the intermediate layer, which helps improve the feeding accuracy of thermosetting composite materials during the production process, and at the same time helps to alleviate the problem of low molding reliability of thermosetting composite materials with high carbon content; in addition, the high resin content intermediate layer in the layered plate improves the bending strength and air tightness of the bipolar plate, and the high carbon content surface layer improves its electrical conductivity; relying on the separate optimization of different functional layers, the overall performance of the bipolar plate is improved, and the preparation process is simple, which is conducive to mass production and has high practical value.

[0048] A third aspect of the present invention provides a processing system for a layered graphite composite bipolar plate, the processing system comprising:

[0049] The intermediate layer processing device is used for processing the intermediate layer, and has a conveying mechanism for conveying the intermediate layer material and a feeder, a preheating box, a roughing roller group, a finishing roller group, a limit roller group and a cooling mechanism arranged in sequence along the conveying direction of the conveying mechanism.

[0050] The drying device comprises a drying box and a drying mold, wherein the drying mold is used to hold the surface layer material and the middle layer.

[0051] The molding device comprises a hot molding die with a flow channel structure and is used for hot molding the surface layer material and the middle layer contained in the drying die.

[0052] As a preferred embodiment of the present invention, the conveying mechanism is a conveyor belt, and the feeder, preheating box, roughing roller group, finishing roller group, limiting roller group and cooling mechanism are arranged in sequence on the conveyor belt along the conveying direction of the conveyor belt.

[0053] As a preferred embodiment of the present invention, the feeder is a vibrating feeder.

[0054] As a preferred embodiment of the present invention, there are multiple finishing roller groups, which are arranged in sequence along the conveying direction of the conveying mechanism to gradually thin the intermediate layer material on the conveying mechanism.

[0055] As a preferred embodiment of the present invention, a plurality of convex tooth mechanisms are distributed along the circumferential direction on the roller body of the limiting roller group.

[0056] As a preferred embodiment of the present invention, the cooling mechanism is an air-cooled cooling mechanism having a cooling air duct facing the conveying mechanism.

[0057] As a preferred embodiment of the present invention, the drying mold has side walls and a detachable bottom plate. The bottom plate is removed during hot molding.

[0058] Compared with the prior art, the present invention meets the requirements of graphite composite bipolar plates for low thickness (volume), high air tightness, high structural strength, good electrical conductivity, and low processing difficulty through a layered structure, thereby achieving a combination of processability and practicality of composite graphite bipolar plates. The composite material with thermoplastic resin as the base has good processability, and thinner plates can be quickly processed through a rolling process. The preparation of the middle layer with graphite / thermoplastic resin composite material not only has low processing difficulty, but also, as a base, can reduce the process difficulty of forming ultra-thin plates with thermosetting resin composite materials. In the bipolar plate, the higher resin content of the middle layer can improve the air tightness and structural strength of the bipolar plate. Thermosetting resin / graphite composite material as the surface layer can ensure that the plate has a higher in-plane conductivity, while avoiding flow field deformation caused by local high temperature during use, and ensuring long-term reliable operation of the plate. The preparation process of the present invention is relatively simple and suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The figure shows the cross-sectional structure of the layered graphite composite bipolar plate formed by the present invention.

[0060] Figure 2 Schematic diagram of the preparation process of a layered graphite composite bipolar plate in one embodiment of the present invention.

[0061] Figure 3 It is a schematic diagram of the intermediate layer processing device of the present invention (which embodies the processing process of the intermediate layer).

[0062] Figure 4 The figure shows the hot compression molding process of the layered graphite composite bipolar plate of the present invention.

[0063] In the figure, 101 is the middle layer, 102 is the surface layer, 103 is the flow channel structure, 201 is the feeder, 202 is the feeding valve, 203 is the preheating box, 204 is the roughing roller group, 205 is the finishing roller group, 206 is the limiting roller group, 207 is the cooling mechanism, 208 is the conveying mechanism, 301 is the hot molding mold, 302 is the drying mold, and 303 is the surface layer material. DETAILED DESCRIPTION

[0064] A layered graphite composite bipolar plate, such as Figure 1 As shown, it includes an intermediate layer 101 and surface layers 102 arranged on both sides of the intermediate layer 101, the intermediate layer 101 is a thermoplastic resin / graphite composite material plate, the surface layer 102 is a thermosetting resin / graphite composite material layer, and the outer surface of the surface layer 102 has a flow channel structure 103.

[0065] The present invention preferably forms the flow channel structure 103 by heat-molding and curing the surface layer 102, with its depth being less than the thickness of the surface layer 102. The intermediate layer 101 is a planar structure and does not participate in the flow channel formation. This structure effectively leverages the intermediate layer 101's function of ensuring the plate's bending strength. The goal of improving the forming accuracy of the flow channel structure 103 can be achieved simply by optimizing the formulation of the surface layer 102. This facilitates the formulation optimization of layered composite plates and provides a solution to the difficult problem of balancing forming performance and usability.

[0066] The present invention preferably uses a thermoplastic resin / graphite composite material sheet formed from a composite material made of a thermoplastic resin and a graphite material. It is further preferred that the thermoplastic resin includes fluorinated ethylene-propylene (FEP), and / or polypropylene (PP), and / or polyphenylene sulfide (PPS), and / or polyvinylidene fluoride (PVDF), and / or polycarbonate (PC), and / or polyoxymethylene resin (POM). It is further preferred that the graphite material includes natural flake graphite, and / or expanded graphite, and / or carbon fiber powder, and / or chopped carbon fiber. For example, the thermoplastic resin can be fluorinated ethylene-propylene (FEP), and the graphite material can be natural flake graphite. Alternatively, the thermoplastic resin can be fluorinated ethylene-propylene (FEP) and polypropylene (PP) mixed in a ratio of 1:1 or any other ratio, and the graphite material can be carbon fiber powder. Alternatively, the thermoplastic resin can be polycarbonate (PC), and the graphite material can be carbon fiber powder and chopped carbon fiber mixed in a ratio of 9:1 or any other ratio, etc. It is further preferred that the mass ratio of the thermoplastic resin to the graphite material can be 3:7 to 7:3. More preferably, the mass ratio of the thermoplastic resin to the graphite material is 5:5. More preferably, the particle size of the graphite material is 1 μm to 200 μm. When the graphite material contains chopped carbon fibers, the length of the chopped carbon fibers is 1 mm to 5 mm. More preferably, the particle size of the graphite material is 40 μm to 80 μm. More preferably, the thickness of the thermoplastic resin / graphite composite material sheet is 0.1 mm to 0.4 mm. Even more preferably, the thickness of the thermoplastic resin / graphite composite material sheet is 0.1 mm to 0.2 mm.

[0067] The preferred thermosetting resin / graphite composite material layer of the present invention is made of a masterbatch mixed with a thermosetting resin and a graphite material. Preferably, the graphite material includes natural flake graphite, and / or expanded graphite, and / or carbon fiber, and / or graphene nanosheets, and / or highly conductive carbon black. Preferably, the thermosetting resin is a thermosetting resin with a lower curing temperature, including epoxy resin (EP), and / or phenolic resin (PF), and / or polyimide resin (PI), and / or vinyl ester resin (VER), and / or polybenzoxazine resin (PBA), and / or urea-formaldehyde resin (UR), and / or polyurethane resin (PU). For example, the thermosetting resin selects epoxy resin (EP), and the graphite material includes natural flake graphite. Alternatively, the thermosetting resin selects phenolic resin (PF) and polyimide resin (PI) to mix in a ratio of 1:1 or other arbitrary ratios, and the graphite material selects graphene nanosheets. Alternatively, the thermosetting resin selects polyurethane resin (PU), and the graphite material selects expanded graphite and carbon fiber to mix in a ratio of 8:2 or other arbitrary ratios. The preferred mass ratio of thermosetting resin to graphite is 7:3 to 9:1. The graphite particle size is 1 μm to 100 μm. Furthermore, the thickness of the thermosetting resin / graphite composite layer is preferably 0.1 mm to 0.5 mm, and the thickness of the formed composite graphite plate is less than 1.4 mm.

[0068] A method for preparing a layered graphite composite bipolar plate comprises the following steps:

[0069] S1: Preparation of thermoplastic resin / graphite composite sheet by roll forming;

[0070] S2: preparing a masterbatch of thermosetting resin / graphite composite material;

[0071] S3: filling the masterbatch of thermosetting resin / graphite composite material, the thermoplastic resin / graphite composite material plate and the masterbatch of thermosetting resin / graphite composite material into the drying mold in sequence and performing a drying process;

[0072] S4: placing the dried material from step S3 together with the drying mold into a hot pressing mold, pressurizing and heating to form the material, and cooling the material to obtain a layered graphite composite bipolar plate.

[0073] Preferably, step S1 includes the following process:

[0074] S11: Dry-mix the thermoplastic resin and graphite powder, mix them evenly and then dry them to obtain a masterbatch A:

[0075] S12: preheating the masterbatch A in a preheating box while maintaining a constant feeding rate;

[0076] S13: The preheated masterbatch A is conveyed by a conveying mechanism, and is processed into a continuous plate of target thickness through rough rolling and finish rolling. The continuous plate is cut and cooled to obtain a thermoplastic resin / graphite composite material plate.

[0077] The layered structure of the intermediate and surface layers in this invention achieves the performance requirements of graphite composite bipolar plates for structural strength and airtightness, in-plane conductivity, and reliable molding, thereby optimizing overall plate performance. Furthermore, the intermediate layer serves as a substrate to assist in molding the surface layer, reducing the difficulty of molding ultra-thin graphite composite plates.

[0078] The present invention uses rolling to press the composite material into a smooth-surfaced plate, which serves as the intermediate layer of the graphite composite bipolar plate. Rolling is a fast process that allows for precise control of the thickness of the intermediate layer, making it suitable for mass production.

[0079] The composite material required for the intermediate layer must meet multiple requirements. It must exhibit good flowability during the rolling process, ensure reliable molding, and minimize shrinkage. The formed sheet must also exhibit high airtightness, flexural strength, and through-plane electrical conductivity. To achieve these requirements, strict requirements must be met for the ratio of thermoplastic resin to graphite.

[0080] In the preferred step S1, the feeding rate of the masterbatch A and the conveying rate of the conveying mechanism are adjusted according to the fluidity of the thermoplastic resin in the masterbatch A and the content of the graphite powder. If the fluidity of the thermoplastic resin in the masterbatch A is low or the graphite content is high, the feeding rate is reduced, and the conveying rate of the conveying mechanism is also reduced accordingly; if the fluidity of the resin in the masterbatch A is high or the graphite content is low, the feeding rate and the conveying rate are increased. In the preferred step S1, the preheating temperature of the masterbatch A is adjusted according to the type of the thermoplastic resin in the masterbatch A and the content of the graphite powder; in the preferred step S1, the rough rolling and the finishing rolling are completed by a combined roller group composed of horizontal rollers and vertical rollers, and the horizontal rollers and vertical rollers respectively realize the processing of the thickness and width of the formed plate. In the preferred step S1, according to the type of the thermoplastic resin in the masterbatch A and the content of the graphite powder, the finishing rolling process can be completed by 3-10 groups of finishing rollers. If the thermoplastic resin content in masterbatch A is greater than the graphite content, the finishing process can be performed by 3-6 sets of finishing rollers. This can be adjusted based on the high-temperature fluidity of the resin to improve production efficiency. If the graphite content in masterbatch A is greater than the thermoplastic resin content, the finishing process can be performed by 7-10 sets of finishing rollers to ensure reliable forming. Preferably, in step S1, the continuous sheet is cut into sheets of the target length by limiting rollers.

[0081] After the plate is formed, the surface layer should exhibit high electrical and thermal conductivity, thus requiring a high graphite content. Furthermore, the surface layer must maintain a low thickness while ensuring reliable molding. Therefore, the thermosetting resin and graphite should be mixed using a combination of mechanical stirring and ultrasonic dispersion with a solvent to ensure the most uniform mixing possible. The amount of solvent used must balance the graphite dispersion effect with the need for easy drying. To meet these performance requirements, the ratio of resin, graphite, and solvent must be strictly controlled.

[0082] Preferably, in step S2, a masterbatch of a thermosetting resin / graphite composite material is obtained by sequentially adding a solvent and a graphite material to a thermosetting resin and thoroughly mixing them; the solvent is a volatile polar solvent, including acetone, and / or anhydrous ethanol, and / or n-butanol, and / or ethylene glycol, and / or isopropanol; and the ratio of the mass of the solvent to the total mass of the thermosetting resin and the graphite material is 1:9-2:8.

[0083] The raw materials for the intermediate and surface layers are dried together in a drying mold before being hot-pressed to form a layered graphite composite bipolar plate. This preforming method not only allows for convenient and efficient control of the surface layer feed rate, but also quickly achieves uniform distribution of the masterbatch within the mold before pressing, improving production efficiency.

[0084] Preferably, in step S3, the drying process is vacuum drying at 80° C. for 1-2 hours. Preferably, in step S3, the masterbatch of the thermosetting resin / graphite composite material is vibrated before drying to achieve uniform distribution of the masterbatch in the drying mold, and the filling thickness of the masterbatch of the thermosetting resin / graphite composite material after vibrating is 0.8 mm to 2.0 mm.

[0085] Preferably, in step S4, during the pressurized and heated molding process, pre-pressing is first performed at a pressure of 1 MPa-10 MPa for 1 minute, then the molding temperature is raised to 140°C-180°C, and the hot molding pressure is raised to 15 MPa-30 MPa and maintained for 0.5 h-1 h; after cooling, demolding is performed to obtain a layered graphite composite bipolar plate.

[0086] Figure 2 A schematic flow chart of a method for preparing a layered graphite composite bipolar plate of the present invention is shown in an embodiment.

[0087] A processing system for layered graphite composite bipolar plates, such as Figure 3-4 As shown, the processing system includes an intermediate layer processing device, a drying device and a forming device, wherein: the intermediate layer processing device is used for processing the intermediate layer 101, and has a conveying mechanism 208 for conveying the intermediate layer material, and a feeder 201, a preheating box 203, a roughing roller group 204, a finishing roller group 205, a limiting roller group 206 and a cooling mechanism 207 arranged in sequence along the conveying direction of the conveying mechanism 208; the drying device has a drying box and a drying mold 302, and the drying mold 302 is used to hold the surface layer material 303 and the intermediate layer 101; the forming device has a hot molding mold 301 with a flow channel structure, which is used to hot mold the surface layer material 303 and the intermediate layer 101 held in the drying mold 302.

[0088] As a preferred embodiment of the present invention, the conveying mechanism 208 is a conveyor belt, and the feeder, preheating box, roughing roller group, finishing roller group, limiting roller group and cooling mechanism are arranged in sequence on the conveyor belt along the conveying direction of the conveyor belt.

[0089] In the present invention, the feeder 201 is preferably a vibrating feeder, and a feeding valve 202 is provided at the outlet of the vibrating feeder. In the present invention, it is preferred that a plurality of finishing roller groups 205 are provided, which are arranged in sequence along the conveying direction of the conveying mechanism, and are used to gradually thin the intermediate layer material on the conveying mechanism. In the present invention, the limiting roller group 206 is preferably provided with a plurality of convex tooth structures distributed along the circumferential direction on the roller body. In the present invention, the two pressure rollers of the roughing roller group 204, the finishing roller group 205 and the limiting roller group 206 can be respectively arranged on the upper and lower surfaces of the conveyor belt for processing the materials conveyed on the conveyor belt. In the present invention, the cooling mechanism 207 is preferably an air-cooled cooling mechanism, and the air-cooled cooling mechanism has a cooling air duct facing the conveying mechanism. The drying mold 302 has a side enclosure and a detachable bottom plate, and the bottom plate is removed during hot molding.

[0090] In the present invention, the preheating box 203, the cooling mechanism 207 and the drying box and other equipment can adopt commercially available corresponding equipment.

[0091] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0092] Example 1:

[0093] Preparation of a layered graphite composite bipolar plate comprises the following steps:

[0094] (1) Fluorinated ethylene-propylene (FEP) with an average particle size of 8 μm and flake graphite with an average particle size of 50 μm were dry-mixed in a plastic kneader for 2 h. The mass ratio of FEP to flake graphite was 4:6. The mixed masterbatch was then placed in a vacuum drying oven and dried at 70°C for 2 h to obtain masterbatch A.

[0095] (2) Masterbatch A is fed into the preheating box 203 by the vibrating feeder 201. Figure 3 As shown, the preheating temperature is 360°C.

[0096] (3) Conveyor mechanism 208 conveys masterbatch A to the roughing rolls, where it is rough-rolled into a 2.0 mm thick plate. Seven final finishing rolls are used to produce thicknesses of 1.5 mm, 1.0 mm, 0.7 mm, 0.5 mm, 0.4 mm, 0.35 mm, and 0.3 mm, respectively. The roughing and finishing rolls are heated during operation to maintain a surface temperature of approximately 300°C.

[0097] (4) The convex tooth structure on the limiting roller group 206 cuts the continuous plate into independent plates.

[0098] (5) The cooling mechanism 207 continuously blows clean and dry air to cool the plate by air cooling. When the plate temperature drops below 80°C, the middle layer is obtained.

[0099] (6) The thermosetting resin in masterbatch B is granular phenolic resin, and the graphite material is natural flake graphite with a particle size of 60 μm. Anhydrous ethanol is used as the solvent. The mass ratio of resin, graphite, and solvent is 1:9:1.1. The masterbatch is stirred with a mechanical stirrer for 30 minutes, followed by ultrasonic dispersion for 10 minutes.

[0100] (7) The mixed masterbatch B (surface layer material 303), the intermediate layer 101, and the masterbatch B (surface layer material 303) are sequentially filled into the drying mold 302, wherein the filling thickness of the masterbatch B is 2.4 mm. The filling is carried out on a vibration compactor. After the filling is completed, the masterbatch B is vibrated for 1 minute to ensure that the masterbatch B is evenly distributed in the drying mold 302. The drying mold 302 is then placed in a vacuum drying oven at 80°C for 1 hour to remove the solvent.

[0101] (8) Place the drying mold 302 together with the masterbatch B and the intermediate layer 101 therein into the hot molding mold 301, as shown in FIG. Figure 4 The process is then heated to 180°C, the pressure increased to 20 MPa, and maintained for 1 hour. The mold is then closed, the pressure is removed, and the hot pressing mold is cooled with water. Once the temperature drops below 60°C, the mold is demolded to produce a layered graphite composite bipolar plate. Measurements show that the thickness of the formed plate is 1.2 ± 0.04 mm, with the surface layer thickness being 0.45 ± 0.02 mm and the flow channel depth being 0.35 ± 0.01 mm.

[0102] Example 2:

[0103] Preparation of a layered graphite composite bipolar plate comprises the following steps:

[0104] (1) Based on Example 1, complete the production of the middle layer.

[0105] (2) Preheat the liquid epoxy resin (E-44) and curing agent phthalic anhydride (HHPA) to 110°C and maintain for 2 minutes.

[0106] (3) Weigh epoxy resin and HHPA in a mass ratio of 5:4, pour them into a beaker and stir for 5 minutes at the same temperature. During the stirring process, 0.5% of the mass of the epoxy resin, benzyldimethylamine, is added to the epoxy resin as an accelerator.

[0107] (4) Add flake graphite with a particle size of 60 μm to 80 μm to the homogeneously mixed resin. The mass ratio of the resin to graphite mixture is 2:8. Maintain a constant temperature of 110°C and mechanically stir for 20 minutes until uniformly mixed to obtain masterbatch B.

[0108] (5) Add masterbatch B, intermediate layer 101, and masterbatch B to the drying mold in sequence. The filling thickness of masterbatch B in the drying mold is 1 mm. Place the mold in a blast drying oven at 110° C. for semi-curing treatment for 30 minutes.

[0109] (6) A PTFE film is laid in the hot molding die 301 as an auxiliary demoulding aid, and the dry mold 302 together with the material therein is placed in the hot molding die preheated to 110°C, pressurized to 30 MPa, pressurized for 5 minutes, then the pressure is removed, the temperature is raised to 120°C, and kept warm for 90 minutes.

[0110] (7) The finalized composite bipolar plate sample was removed and placed in a forced air drying oven at 180°C for 2 h to further cure. After curing, a layered ultra-thin graphite composite bipolar plate was obtained. Measurements showed that the thickness of the formed plate was 0.9 ± 0.04 mm, the thickness of the surface layer was 0.3 ± 0.02 mm, and the flow channel depth was 0.25 ± 0.01 mm.

[0111] Example 3

[0112] To prepare a layered ultra-thin graphite composite bipolar plate, the following steps are required:

[0113] (1) Polypropylene (PP) with an average particle size of 8 μm and carbon fiber powder with an average length of 100 μm were dry-mixed in a ball mill for 2 h. The mass ratio of PP to carbon fiber was 5:5. The mixed masterbatch was then placed in a vacuum drying oven and dried at 70°C for 5 h to obtain masterbatch A.

[0114] (2) Masterbatch A is fed into the filler preheating box 203 by the vibrating feeder 201. Figure 3 As shown, the preheating temperature is 200°C.

[0115] (3) Conveyor mechanism 208 conveys masterbatch A to the roughing roll set 204, where it is rough-rolled into a sheet with a thickness of 1.5 mm. The final four finishing rolls reduce the thickness to 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm, respectively. The roughing roll set 204 and the finishing roll set 205 are heated during operation to maintain a surface temperature of approximately 170°C.

[0116] (4) The convex tooth structure on the limiting roller group 206 cuts the continuous plate into independent plates.

[0117] (5) The cooling mechanism 207 continuously blows clean and dry air to cool the plate by air cooling, and the middle layer is obtained when the plate is cooled to room temperature.

[0118] (6) The thermosetting resin in masterbatch B is granular phenolic resin, and the graphite material is natural flake graphite with a particle size of 60 μm. Anhydrous ethanol is used as the solvent. The mass ratio of resin, graphite, and solvent is 2:8:1.5. The masterbatch is stirred with a mechanical stirrer for 30 minutes, followed by ultrasonic dispersion for 10 minutes.

[0119] (7) The mixed masterbatch B, the intermediate layer 101, and the masterbatch B are sequentially filled into the drying mold 302, wherein the filling thickness of the masterbatch B is 2.0 mm. The filling is carried out on a vibration compactor. After the filling is completed, the masterbatch B is vibrated for 1 minute to ensure that the masterbatch B is evenly distributed in the drying mold 302. The drying mold 302 is then placed in a vacuum drying oven at 70°C to remove the solvent for 90 minutes.

[0120] (8) Place the dry mold 302 together with the masterbatch B303 and the intermediate layer 101 therein into a hot molding mold, as shown in FIG. Figure 4The process is then heated to 180°C, the pressure increased to 30 MPa, and maintained for 1 hour. The mold is then closed, the pressure is removed, and the hot pressing mold is cooled with water. Once the temperature drops below 60°C, the mold is demolded to produce a layered, ultra-thin graphite composite bipolar plate. Measurements show that the thickness of the formed plate is 0.8±0.04mm, with the surface layer thickness being 0.35±0.02mm and the flow channel depth being 0.25±0.01mm.

[0121] According to the GBT20042.6 standard test, the hydrogen permeability coefficient of the plate obtained by the present invention is less than 1×10 -14 cm 3 / (s·cm 2 Pa), flexural strength is between 50-90 MPa, and electrical conductivity is between 100-180 S / cm.

[0122] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A layered graphite composite bipolar plate, characterized in that: It includes an intermediate layer and surface layers arranged on both sides of the intermediate layer, wherein the intermediate layer is a thermoplastic resin / graphite composite material plate, the surface layer is a thermosetting resin / graphite composite material layer, and the outer surface of the surface layer is formed by thermal curing to form a flow channel structure; The thermoplastic resin / graphite composite material plate is formed by processing a composite material made of thermoplastic resin and graphite material, the mass ratio of thermoplastic resin to graphite material is 5:5, the particle size of the graphite material is 40μm-80μm; the thickness of the thermoplastic resin / graphite composite material plate is 0.1mm-0.2mm; The thermosetting resin / graphite composite material layer is made of a masterbatch of a thermosetting resin and a graphite material, the mass ratio of the graphite material to the thermosetting resin is 7:3-9:1, the particle size of the graphite material is 1 μm-100 μm, the thickness of the thermosetting resin / graphite composite material layer is 0.1 mm-0.5 mm, and the thickness of the formed plate is less than 1.4 mm; The flow channel structure is solidified and formed on the surface layer by hot molding, and its depth is less than the thickness of the surface layer. The intermediate layer maintains a planar structure and does not participate in the flow channel molding; The preparation method comprises the following steps: S1: Preparation of thermoplastic resin / graphite composite sheet by roll forming; S2: preparing a masterbatch of thermosetting resin / graphite composite material; S3: filling the masterbatch of thermosetting resin / graphite composite material, the thermoplastic resin / graphite composite material plate and the masterbatch of thermosetting resin / graphite composite material into the drying mold in sequence and performing a drying process; S4: placing the dried material from step S3 together with the drying mold into a hot pressing mold, pressurizing and heating to form the material, and cooling the material to obtain the layered graphite composite bipolar plate; Step S1 includes the following process: S11: Dry-mix the thermoplastic resin and graphite powder, mix them evenly and then dry them to obtain a masterbatch A: S12: preheating the masterbatch A in a preheating box while maintaining a constant feeding rate; S13: The preheated masterbatch A is conveyed by a conveying mechanism, subjected to rough rolling and finish rolling, and processed into a continuous sheet of target thickness. The continuous sheet is cut and cooled to obtain the thermoplastic resin / graphite composite material sheet; In step S1, the feed rate of masterbatch A and the conveying rate of the conveying mechanism are adjusted according to the fluidity of the thermoplastic resin in masterbatch A and the content of graphite powder; the preheating temperature of masterbatch A is adjusted according to the type of thermoplastic resin and the content of graphite powder in masterbatch A; rough rolling and finishing rolling are performed by a combined roller group consisting of horizontal rollers and vertical rollers, and the horizontal rollers and vertical rollers respectively process the thickness and width of the formed sheet; depending on the type of thermoplastic resin in masterbatch A and the content of graphite powder, the finishing rolling process can be completed by 3-10 sets of finishing rollers; the continuous sheet is cut into sheets of target length by limit rollers; In step S2, a masterbatch of a thermosetting resin / graphite composite material is obtained by sequentially adding a solvent and a graphite material to a thermosetting resin and thoroughly mixing them; the solvent is a volatile polar solvent, including acetone, and / or anhydrous ethanol, and / or n-butanol, and / or ethylene glycol, and / or isopropanol; and the ratio of the mass of the solvent to the total mass of the thermosetting resin and the graphite material is 1:9-2:8; In step S3, the drying process is vacuum drying at 80° C. for 1 hour to 2 hours. In step S3, the drying process is vibrated before the drying process to achieve uniform distribution of the masterbatch of the thermosetting resin / graphite composite material in the drying mold. After vibrating, the filling thickness of the masterbatch of the thermosetting resin / graphite composite material is 0.8 mm to 2.0 mm. In step S4, during the pressurized and heated molding process, pre-pressing is first performed at a pressure of 1 MPa-10 MPa for 1 minute, then the molding temperature is raised to 140°C-180°C, and the hot molding pressure is raised to 15 MPa-30 MPa and maintained for 0.5 h-1 h; after cooling, demolding is performed to obtain the layered graphite composite bipolar plate.

2. The layered graphite composite bipolar plate according to claim 1, characterized in that: The thermoplastic resin / graphite composite material sheet is formed by processing a composite material made of thermoplastic resin and graphite material, including any one or more of the following conditions: (i) The thermoplastic resin comprises fluorinated ethylene-propylene, and / or polypropylene, and / or polyphenylene sulfide, and / or polyvinylidene fluoride, and / or polycarbonate, and / or polyoxymethylene resin; (ii) The graphite material includes natural flake graphite, and / or expanded graphite, and / or carbon fiber powder, and / or chopped carbon fiber.

3. The layered graphite composite bipolar plate according to claim 1, characterized in that: The thermosetting resin / graphite composite material layer is made of a masterbatch of a thermosetting resin and a graphite material, and includes any one or more of the following conditions: (i) the graphite material comprises natural flake graphite, and / or expanded graphite, and / or carbon fiber, and / or graphene nanosheets, and / or highly conductive carbon black; (ii) The thermosetting resin is a thermosetting resin with a relatively low curing temperature, including epoxy resin, and / or phenolic resin, and / or polyimide resin, and / or vinyl ester resin, and / or polybenzoxazine resin, and / or urea-formaldehyde resin, and / or polyurethane resin.

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