A layered ultra-thin carbon-based bipolar plate and its preparation method

Abstract

The present invention relates to the field of fuel cell technology, and in particular to a layered ultra-thin carbon-based bipolar plate and a method for preparing the same. The layered ultra-thin carbon-based bipolar plate is a sandwich-shaped layered composite structure, comprising a conductive additive layer, with a prepreg layer and a conductive substrate / resin composite layer provided on both sides of the conductive additive layer, from the inside to the outside, and the outer surface of the conductive substrate / resin composite layer having a flow channel structure. Compared with the prior art, the present invention solves the problem of excessive thickness of traditional carbon-based composite bipolar plates to meet strength requirements, as well as the contradiction between process performance and conductivity of carbon-based composite bipolar plates; the prepreg layer can effectively reduce the thickness of the bipolar plate while ensuring good bending strength of the plate, while avoiding the problem of high molding difficulty caused by low molding thickness; the thickness is within 1.4 mm, which can significantly reduce the overall volume and weight of the fuel cell, has low manufacturing difficulty, requires fewer steps, and is suitable for mass production.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a layered ultra-thin carbon-based bipolar plate and a preparation method thereof. Background Art

[0002] Compared to internal combustion engines, fuel cells are power generation devices that directly convert chemical energy into electrical energy. This differs from the complex energy conversion process of internal combustion engines, resulting in a high energy conversion rate. Proton exchange membrane fuel cells (PEMFCs) operate by introducing hydrogen and oxygen into the anode and cathode, respectively. Catalyzed by these catalysts, oxidation and reduction reactions occur, respectively. Electrons are conducted through an external circuit to generate electricity, while hydrogen ions are transported through the proton exchange membrane to the cathode to form water.

[0003] During the power generation process of a proton exchange membrane fuel cell (PEMFC), bipolar plates play a crucial role in the proper operation of the fuel cell. They must completely separate the reactant gases at the two poles to prevent mixing of the gases and the resulting violent oxidation reaction. Furthermore, electron conduction in the external circuit must pass through the bipolar plates, requiring them to have excellent electrical conductivity. The transport of reactant gases and the removal of generated water rely on the gas flow channels on the bipolar plates, requiring them to have well-formed flow channels to ensure minimal fluid resistance and excellent water-gas transport. Bipolar plates account for a significant portion of the mass and volume of a fuel cell system, and their thickness and mass significantly impact the fuel cell's specific power.

[0004] Currently, various companies and research institutions have developed bipolar plates made of various materials, mainly including metal bipolar plates, graphite bipolar plates, and composite bipolar plates. Graphite has good electrical conductivity and corrosion resistance, but poor mechanical strength, requiring a greater thickness to maintain safe operation of the stack under the clamping force and gas pressure of the stack assembly. Metal bipolar plates have high mechanical strength and good gas isolation performance, and can be formed into ultra-thin bipolar plates through mechanical processing methods such as stamping. However, they are prone to electrochemical corrosion when the fuel cell is operating, and require surface treatment methods such as adding coatings. Carbon-based composite bipolar plates use graphite polymer composite materials as the matrix, have good mechanical strength and corrosion resistance, and can be processed using injection molding and compression molding methods, making them suitable for mass production. However, properties such as conductivity, gas barrier properties, and structural strength are difficult to balance. Summary of the Invention

[0005] The present invention aims to provide a layered, ultra-thin carbon-based bipolar plate and its preparation method. The functional layers of the carbon-based composite bipolar plate are fabricated using a conductive substrate / resin composite outer layer and a prepreg inner layer sandwiched between a conductive additive layer. This layered, ultra-thin carbon-based composite bipolar plate can reduce the volume and mass of fuel cell stacks, improve specific power, and simplify production, facilitating mass production.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first aspect of the present invention provides a layered ultra-thin carbon-based bipolar plate, which is a sandwich-shaped layered composite structure, including a conductive additive layer, and prepreg layers and conductive substrate / resin composite layers are arranged on both sides of the conductive additive layer from the inside to the outside, respectively, and a flow channel structure is formed on the surface of the plate through hot molding and curing.

[0008] As a preferred technical solution of the present invention, the flow channel structure has a flow channel depth less than the thickness of the conductive substrate / resin composite layer, and the prepreg layer and conductive additive layer are planar structures. Due to different orientations, if the prepreg layer is involved in the molding process, it will cause internal stress imbalance between the layers, greatly affecting the flatness of the electrode plate. Furthermore, the prepreg layer is strong, but the flow channel precision molding performance is poor. Therefore, in the present invention, only the conductive substrate / resin composite layer is involved in molding the flow channel structure.

[0009] As a preferred technical solution of the present invention, the prepreg layer is a prepreg of unidirectional carbon fiber or unidirectional carbon fiber fabric, and the orientations of the prepreg layers on both sides of the conductive additive layer are perpendicular to each other. The prepreg layer has good in-plane conductivity and high mechanical strength, and is an industrial intermediate material for producing composite materials. The use of prepreg to prepare layered ultra-thin carbon-based composite bipolar plates can ensure that the plates have good bending strength while effectively reducing the thickness of the bipolar plates, and ultra-thin bipolar plates can be prepared through a relatively easy production process.

[0010] Unidirectional carbon fiber prepreg or unidirectional carbon fiber fabric prepreg has excellent mechanical strength and helps control the thickness of the composite bipolar plate, reducing the difficulty of the ultra-thin composite bipolar plate molding process. The outer layer uses a conductive substrate / resin composite material to ensure good flow channel molding performance.

[0011] A unidirectional carbon fiber or unidirectional carbon fiber fabric prepreg layer is used as the middle layer. Compared with chopped fibers, unidirectional carbon fiber or unidirectional carbon fiber fabric can not only improve the in-plane conductivity of the bipolar plate, but also significantly enhance the mechanical properties of the carbon-based composite bipolar plate. Compared with non-unidirectional carbon fiber fabric, the conductivity has a single fiber orientation. By vertically stacking two unidirectional carbon fiber or unidirectional carbon fiber fabric prepreg layers, not only can the in-plane conductivity of the bipolar plate in both axial directions be improved, but the in-plane conductivity of the bipolar plate in both axial directions can also be evenly distributed. This increases the strength of the bipolar plate, improves the in-plane conductivity of the bipolar plate, reduces the thickness and weight of the bipolar plate, and effectively improves the specific power of the fuel cell stack.

[0012] As a preferred technical solution of the present invention, the thickness of the prepreg layer is 0.06mm to 0.20mm.

[0013] As a preferred technical solution of the present invention, the prepreg layer contains a single or combined semi-solid thermosetting resin, and the semi-solid thermosetting resin includes epoxy resin, phenolic resin, polyimide resin, ammonium cyanate resin, bismaleimide resin or unsaturated polyester resin.

[0014] A conductive additive layer is prepared between the prepregs as a separator. Excessive resin applied to the prepreg surface during hot molding can be squeezed out, increasing the through-plane resistance of the bipolar plate. The conductive additive layer sandwiched between the two prepreg layers absorbs the resin squeezed out of the prepreg layers during the molding process, creating a conductive path between adjacent prepreg layers and improving the through-plane conductivity of the layered carbon-based composite bipolar plate.

[0015] As a preferred technical solution of the present invention, the conductive additive layer contains graphite powder (mainly composed of graphite powder).

[0016] As a preferred technical solution of the present invention, the graphite powder has a diameter of 1 μm to 200 μm. More preferably, the graphite powder has a diameter of 3 μm to 50 μm. Even more preferably, the graphite powder has a diameter of 6 μm to 20 μm.

[0017] As a preferred technical solution of the present invention, the amount of graphite powder contained in the conductive agent addition layer is 25g / m 2 ~135g / m 2 .

[0018] As a preferred technical solution of the present invention, the graphite powder includes natural flake graphite, and / or expanded graphite, and / or carbon fiber, and / or highly conductive carbon black.

[0019] As a preferred technical solution of the present invention, the conductive agent added layer is obtained by dispersing graphite powder in a dispersant to form a slurry, which is then applied to the surface of the prepreg layer and dried. Furthermore, the coating is preferably performed using a coating machine.

[0020] As a preferred technical solution of the present invention, during the preparation of the conductive agent addition layer, the dispersant is a volatile solvent, including anhydrous ethanol, methanol or acetone. More preferably, the dispersant is anhydrous ethanol or acetone.

[0021] As a preferred technical solution of the present invention, during the preparation of the conductive agent addition layer, a dispersant is added to the graphite powder, ultrasonically dispersed, and centrifuged to obtain a uniformly dispersed graphite slurry. Furthermore, preferably, the ultrasonic dispersion time is 10 minutes and the centrifugation time is 30 minutes.

[0022] As a preferred technical solution of the present invention, during the preparation of the conductive agent addition layer, the mass ratio of the dispersant to the graphite powder is 0.18:1 to 0.48:1.

[0023] As a preferred technical solution of the present invention, during the preparation of the conductive additive layer, the slurry is applied only to one side of the prepreg layer. After coating, the conductive additive layer is dried in a vacuum oven to form a conductive additive layer located between the two prepreg layers. The purpose is to ensure that the conductive additive layer adheres evenly and stably to the prepreg surface.

[0024] As a preferred technical solution of the present invention, during the preparation of the conductive agent added layer, drying refers to drying in a vacuum oven.

[0025] As a preferred technical solution of the present invention, during the preparation of the conductive agent added layer, the drying temperature is 40°C to 120°C.

[0026] As a preferred technical solution of the present invention, the thickness of the conductive substrate / resin composite layer is 0.01 mm to 0.4 mm.

[0027] A conductive substrate / resin composite layer serves as a surface buffer layer to improve flow channel forming performance. Prepregs have poor fine flow channel forming performance during hot compression molding, and excessive resin content in the prepreg is easily squeezed out of the bipolar plate flow channel surface, increasing the surface contact resistance of the bipolar plate. Using a conductive substrate / resin composite layer as a buffer layer can significantly improve the surface forming performance of the bipolar plate, absorb excess resin squeezed out of the prepreg, and reduce the contact resistance of the bipolar plate.

[0028] As a preferred technical solution of the present invention, the conductive substrate / resin composite layer is made from a masterbatch of a conductive substrate and a thermosetting resin. The conductive substrate may include natural graphite, artificial graphite, or expanded graphite. The thermosetting resin should be the same type as the prepreg layer. Using a thermosetting resin with the same composition as the prepreg resin in the masterbatch for the conductive substrate / resin composite layer ensures adhesion between the layers after molding of the layered structure.

[0029] As a preferred technical solution of the present invention, the masterbatch is obtained by dissolving the conductive substrate and the resin in a solvent in sequence, stirring and mixing them at room temperature, and then evenly placing them in a flat mold of a preset thickness and drying and removing the solvent.

[0030] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the diameter of the conductive substrate is 4 μm to 120 μm.

[0031] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the mass ratio of the conductive substrate to the resin is 1:9 to 9:1.

[0032] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the mass ratio of the solvent to the masterbatch is 1:9-3:7.

[0033] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the solvent includes acetone, and / or anhydrous ethanol, and / or n-butanol, and / or ethylene glycol, and / or isopropyl alcohol. Methods for sequentially dissolving the conductive substrate and the resin in the solvent include ball milling and centrifugal stirring.

[0034] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the preset thickness of the flat plate mold is 0.1 mm to 2.8 mm.

[0035] As a preferred technical solution of the present invention, during the preparation of the masterbatch, the drying and desolventizing conditions are to treat at a temperature of 80° C. for 0.1 h to 10 h.

[0036] A second aspect of the present invention provides a method for preparing the layered ultra-thin carbon-based bipolar plate, which adopts hot molding and comprises the following steps:

[0037] (1) In a mold with a runner structure, a masterbatch, a prepreg layer coated with a conductive additive layer, a prepreg layer, and a masterbatch are placed in order from bottom to top.

[0038] (2) Pressurizing and molding according to the set molding pressure and molding temperature, then naturally cooling to room temperature while maintaining the pressure, and releasing the pressure to obtain the layered ultra-thin carbon-based bipolar plate.

[0039] As a preferred technical solution of the present invention, in step (1), the conductive additive layer coated on the prepreg layer should be located between two prepreg layers, and the orientations of two adjacent prepreg layers should be perpendicular to each other.

[0040] As a preferred technical solution of the present invention, in step (1), a release agent is sprayed on the inner surface of the mold.

[0041] As a preferred technical solution of the present invention, in step (2), the thickness of the conductive substrate / resin composite layer after molding is 0.01 mm to 0.4 mm.

[0042] As a preferred technical solution of the present invention, in step (2), the molding pressure is 20 MPa, the molding temperature is 150° C., and the pressing time is 1 h.

[0043] The thickness of the final layered ultra-thin carbon-based composite bipolar plate is generally less than 1.4 mm.

[0044] 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), and the flexural strength is between 50 and 90 MPa.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] Through the layered structure, the requirements of the carbon-based composite bipolar plate for thickness (volume), air tightness, structural strength, conductivity, process difficulty, etc. are met respectively, thereby achieving the optimization of the overall performance of the composite graphite bipolar plate. The use of unidirectional carbon fiber prepreg is not only conducive to optimizing the structural strength of the ultra-thin carbon-based composite bipolar plate, but also has good auxiliary functions for air tightness and the molding of ultra-thin plates. The graphite / resin composite layer can achieve high-precision molding of the flow channel structure, and the contact surface resistance of the plate can be maintained at a low level. At the same time, the process difficulty of the present invention is low, the steps are simple, and it is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the layered stacking structure during the hot molding process of the present invention.

[0048] Figure 2 This is a schematic diagram of the structure of the layered ultra-thin carbon-based composite bipolar plate after hot molding of the present invention.

[0049] Figure 3 for Figure 2 A partial enlarged view of .

[0050] In the figure, 1 is a conductive substrate / resin composite layer, 2 is a prepreg layer, 3 is a conductive additive layer, and 4 is a flow channel structure. DETAILED DESCRIPTION

[0051] A layered ultra-thin carbon-based bipolar plate, which is a sandwich-shaped layered composite structure, includes a conductive additive layer 3, and two sides of the conductive additive layer 3 are sequentially provided with a prepreg layer 2 and a conductive substrate / resin composite layer 1 from the inside to the outside, and a flow channel structure 4 is formed on the surface of the plate by hot pressing and curing. Figure 2 and Figure 3 shown.

[0052] In a preferred embodiment, the depth of the flow channel structure 4 is less than the thickness of the conductive substrate / resin composite layer 1, and the prepreg layer 2 and conductive additive layer 3 are planar structures. Due to their different orientations, if the prepreg layer is involved in the molding process, it will cause an imbalance in internal stress between the layers, significantly affecting the flatness of the electrode plate. Furthermore, the prepreg layer is strong, but the flow channel precision molding performance is poor. Therefore, only the conductive substrate / resin composite layer is involved in the molding of the flow channel structure.

[0053] As a preferred embodiment, the prepreg layer 2 is a prepreg of unidirectional carbon fiber or unidirectional carbon fiber fabric, and the orientations of the prepreg layers 2 on both sides of the conductive additive layer 3 are perpendicular to each other. The prepreg layer 2 has good in-plane conductivity and high mechanical strength, and is an industrial intermediate material for producing composite materials. The use of prepreg to prepare layered ultra-thin carbon-based composite bipolar plates can effectively reduce the thickness of the bipolar plates while ensuring that the plates have good bending strength, and ultra-thin bipolar plates can be prepared through a relatively easy production process.

[0054] As a preferred embodiment, the thickness of the prepreg layer 2 is 0.06 mm to 0.20 mm.

[0055] As a preferred embodiment, the prepreg layer 2 contains a single or combined semi-solid thermosetting resin, and the semi-solid thermosetting resin includes epoxy resin, phenolic resin, polyimide resin, ammonium cyanate resin, bismaleimide resin or unsaturated polyester resin.

[0056] As a preferred embodiment, the conductive additive layer 3 contains graphite powder (mainly composed of graphite powder).

[0057] As a preferred embodiment, the graphite powder has a diameter of 1 μm to 200 μm. More preferably, the graphite powder has a diameter of 3 μm to 50 μm. Even more preferably, the graphite powder has a diameter of 6 μm to 20 μm.

[0058] As a preferred embodiment, the amount of graphite powder contained in the conductive agent added layer is 25g / m 2 ~135g / m 2 .

[0059] As a preferred embodiment, the graphite powder includes natural flake graphite, and / or expanded graphite, and / or carbon fiber, and / or highly conductive carbon black.

[0060] As a preferred embodiment, the conductive agent added layer is obtained by dispersing graphite powder in a dispersant to form a slurry, which is then coated on the surface of the prepreg layer 2 and dried. It is further preferred that the coating is performed using a coating machine.

[0061] As a preferred embodiment, during the preparation of the conductive agent addition layer, the dispersant is a volatile solvent, including anhydrous ethanol, methanol or acetone. More preferably, the dispersant is anhydrous ethanol or acetone.

[0062] As a preferred embodiment, during the preparation of the conductive agent addition layer, a dispersant is added to the graphite powder, ultrasonically dispersed, and centrifuged to obtain a uniformly dispersed graphite slurry. Furthermore, preferably, the ultrasonic dispersion time is 10 minutes and the centrifugation time is 30 minutes.

[0063] As a preferred embodiment, during the preparation of the conductive agent addition layer, the mass ratio of the dispersant to the graphite powder is 0.18:1 to 0.48:1.

[0064] In a preferred embodiment, during the preparation of the conductive additive layer, the slurry is applied only to one side of the prepreg layer 2. After application, the slurry is dried in a vacuum oven to obtain a conductive additive layer 3 located between the two prepreg layers 2. The purpose is to ensure that the conductive additive layer 3 adheres evenly and stably to the prepreg surface.

[0065] As a preferred embodiment, during the preparation of the conductive agent added layer, drying refers to drying in a vacuum oven.

[0066] As a preferred embodiment, during the preparation of the conductive agent added layer, the drying temperature is 40°C to 120°C.

[0067] As a preferred technical solution of the present invention, the thickness of the conductive substrate / resin composite layer 1 is 0.01 mm to 0.4 mm.

[0068] In a preferred embodiment, the conductive substrate / resin composite layer 1 is formed from a masterbatch of a conductive substrate and a thermosetting resin. The conductive substrate includes natural graphite, artificial graphite, or expanded graphite, and the thermosetting resin is the same type as the prepreg layer 2. The masterbatch of the conductive substrate / resin composite layer 1 uses a thermosetting resin with the same composition as the prepreg resin to ensure adhesion between the layers after molding of the layered structure.

[0069] As a preferred embodiment, the masterbatch is obtained by dissolving the conductive substrate and the resin in a solvent in sequence, stirring and mixing them at room temperature, and then evenly placing them into a flat plate mold of a preset thickness, and drying and removing the solvent.

[0070] As a preferred embodiment, during the preparation of the masterbatch, the diameter of the conductive substrate is 4 μm to 200 μm.

[0071] As a preferred embodiment, during the preparation of the masterbatch, the mass ratio of the conductive substrate to the resin is 1:9 to 9:1.

[0072] As a preferred embodiment, during the preparation of the masterbatch, the mass ratio of the solvent to the masterbatch is 1:9 to 3:7.

[0073] In a preferred embodiment, during the preparation of the masterbatch, the solvent includes acetone, and / or anhydrous ethanol, and / or n-butanol, and / or ethylene glycol, and / or isopropyl alcohol. Methods for sequentially dissolving the conductive substrate and the resin in the solvent include ball milling and centrifugal stirring.

[0074] As a preferred embodiment, during the preparation of the masterbatch, the preset thickness of the flat plate mold is 0.1 mm to 2.8 mm.

[0075] As a preferred embodiment, during the preparation of the masterbatch, the drying and desolventizing conditions are to treat at a temperature of 80° C. for 0.1 h to 10 h.

[0076] The preparation method of layered ultra-thin carbon-based bipolar plates adopts hot molding, such as Figure 1 As shown, the following steps are included:

[0077] (1) In a mold with a runner structure, a masterbatch, a prepreg layer 2 coated with a conductive additive layer 3, a prepreg layer 2, and a masterbatch are placed in order from bottom to top.

[0078] (2) Pressurizing and molding according to the set molding pressure and molding temperature, then naturally cooling to room temperature while maintaining the pressure, and releasing the pressure to obtain the layered ultra-thin carbon-based bipolar plate.

[0079] As a preferred embodiment, in step (1), the conductive additive layer 3 coated on the prepreg layer 2 should be located between two prepreg layers 2, and the orientations of two adjacent prepreg layers 2 should be perpendicular to each other.

[0080] As a preferred embodiment, in step (1), a release agent is sprayed on the inner surface of the mold.

[0081] As a preferred embodiment, in step (2), the thickness of the conductive substrate / resin composite layer 1 after molding is 0.01 mm to 0.4 mm.

[0082] As a preferred embodiment, in step (2), the molding pressure is 20 MPa, the molding temperature is 150° C., and the pressing time is 1 hour.

[0083] The thickness of the final layered ultra-thin carbon-based composite bipolar plate is generally less than 1.4 mm.

[0084] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0085] Example 1

[0086] A layered ultra-thin carbon-based composite bipolar plate has a sandwich-shaped layered composite structure, including a conductive additive layer 3, with prepreg layers 2 and conductive substrate / resin composite layers 1 arranged on both sides from the inside to the outside (i.e., including two layers of conductive substrate / resin composite layers 1 on the surface and an inner layer consisting of two prepreg layers 2 sandwiching the conductive additive layer 3), and the outer surface of the conductive substrate / resin composite layer 1 has a flow channel structure.

[0087] The prepreg layer 2 is an epoxy prepreg with a thickness of 0.2 mm (unidirectional carbon fiber prepreg with epoxy resin as the matrix); the conductive additive layer 3 sandwiched by the prepreg layer 2 is prepared by coating a natural flake graphite slurry with a particle size of 10 μm; the conductive substrate / resin composite outer layer is natural flake graphite powder and epoxy resin in a mass ratio of 8:2, and the graphite particle size is 40 μm.

[0088] A method for preparing a layered ultra-thin carbon-based composite bipolar plate comprises the following steps:

[0089] Step 1: Use epoxy resin as the matrix of unidirectional carbon fiber prepreg as the middle layer to enhance mechanical properties, with a thickness of 0.2mm (fiber unit area mass of 200g / m 2 , resin content is 20% to 40%).

[0090] Step 2: Pour acetone as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite of 0.3:1. Ultrasonic dispersion is performed for 10 minutes, followed by centrifugation for 30 minutes to obtain a slurry with uniformly dispersed graphite.

[0091] Step 3: Use a coating machine to evenly coat the graphite slurry in step 2 on a single surface of the prepreg, with a coating thickness of no more than 50 μm, so that the graphite content is 50 to 134 g / m 2 The prepreg coated with the conductive additive layer 3 was placed in a vacuum drying oven and dried at 60° C. for 24 h, and a die-cutting machine was used to cut the dried prepreg into the target bipolar plate shape and size.

[0092] Step 4: Select epoxy resin and natural flake graphite powder to prepare a masterbatch of the surface conductive substrate / resin composite layer 1, where the diameter of the natural flake graphite is 40 μm. Dissolve the natural flake graphite powder and the resin in acetone in sequence and stir and mix at room temperature. The mass ratio of the natural flake graphite powder to the resin is 8:2; the mass ratio of the acetone solvent to the masterbatch is 1:9. Place the evenly mixed masterbatch into a frame-shaped flat plate mold with a filling thickness of 0.8 mm, and place it in a blast drying oven at 80°C to desolventize for 1 hour to prepare the surface conductive substrate / resin composite layer 1 masterbatch.

[0093] Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer 1 masterbatch, the prepreg layer 2 coated with the conductive additive layer 3, the prepreg layer 2, and the conductive substrate / resin composite layer 1 masterbatch. The carbon fibers of the two prepreg layers 2 should be oriented vertically, and the conductive additive layer 3 should be located between the two prepreg layers 2. Before loading the mold, spray methyl silicone oil on the inner surface of the mold cavity for demolding.

[0094] In step 6, the assembled mold is mounted on a flat-plate vulcanizer for hot compression molding. The molding pressure is set to 20 MPa and the molding temperature is set to 150°C. The pressurization is applied for 1 hour. After that, the pressure is maintained and the plate is naturally cooled to room temperature. The pressure is then released. The molded bipolar plate is removed from the mold to obtain the layered ultra-thin composite graphite bipolar plate. The maximum thickness of the molded plate is measured to be 1.00 ± 0.05 mm, the thickness of the composite layer is 0.2 ± 0.02 mm, and the depth of the flow channel is 0.15 ± 0.01 mm.

[0095] Example 2

[0096] A layered ultra-thin carbon-based composite bipolar plate has a sandwich-shaped layered composite structure, including a conductive additive layer 3, with prepreg layers 2 and conductive substrate / resin composite layers 1 arranged on both sides from the inside to the outside (i.e., including two layers of conductive substrate / resin composite layers 1 on the surface and an inner layer consisting of two prepreg layers 2 sandwiching the conductive additive layer 3), and the outer surface of the conductive substrate / resin composite layer 1 has a flow channel structure.

[0097] The prepreg layer 2 is an epoxy prepreg with a thickness of 0.1 mm (unidirectional carbon fiber prepreg with epoxy resin as the matrix); the conductive additive layer 3 sandwiched by the prepreg layer 2 is prepared by coating a natural flake graphite slurry with a particle size of 20 μm; the conductive substrate / resin composite outer layer is natural flake graphite powder and epoxy resin in a mass ratio of 8:2, and the graphite particle size is 40 μm.

[0098] A method for preparing a layered ultra-thin carbon-based composite bipolar plate comprises the following steps:

[0099] Step 1: Use epoxy resin as the matrix of unidirectional carbon fiber prepreg as the middle layer to enhance the mechanical properties, with a thickness of 0.1mm (the fiber unit area mass is 100g / m 2 , resin content is 20% to 40%).

[0100] Step 2: Pour anhydrous ethanol as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite being 0.3:1. Ultrasonic dispersion is performed for 10 minutes, followed by centrifugation for 30 minutes to obtain a slurry with uniformly dispersed graphite.

[0101] Step 3: Use a coating machine to evenly coat the graphite slurry in step 2 on a single surface of the prepreg. The coating thickness is no more than 50 μm, and the graphite content is 25 g / m 2 ~67g / m 2 The prepreg coated with the conductive additive layer 3 was placed in a vacuum drying oven and dried at 60° C. for 24 h, and a die-cutting machine was used to cut the dried prepreg into the target bipolar plate shape and size.

[0102] Step 4: Prepare a surface conductive substrate / resin composite layer 1 masterbatch using epoxy resin and natural flake graphite powder, where the natural flake graphite has a diameter of 40 μm. Dissolve the natural flake graphite powder and resin in acetone, respectively, and stir and mix at room temperature. The mass ratio of natural flake graphite powder to resin is 8:2; the mass ratio of acetone solvent to masterbatch is 1:9. Place the evenly mixed masterbatch into a frame-shaped flat plate mold in a forced air drying oven at 80°C for 1 hour to remove the solvent. This will produce the surface conductive substrate / resin composite layer 1 masterbatch.

[0103] Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer 1 masterbatch, the prepreg layer 2 coated with the conductive additive layer 3, the prepreg layer 2, and the conductive substrate / resin composite layer 1 masterbatch. The carbon fibers of the two prepreg layers 2 should be oriented vertically, and the conductive additive layer 3 should be located between the two prepreg layers 2. Before loading the mold, spray methyl silicone oil on the inner surface of the mold cavity for demolding.

[0104] In step 6, the assembled mold is mounted on a flat-plate vulcanizer for hot compression molding. The molding pressure is set to 20 MPa and the molding temperature is set to 150°C. The pressurization is applied for 1 hour. After that, the pressure is maintained and the plate is naturally cooled to room temperature. The pressure is then released. The molded bipolar plate is removed from the mold to obtain the layered ultra-thin carbon-based composite bipolar plate. The maximum thickness of the molded plate is measured to be 0.80 ± 0.05 mm, the thickness of the composite layer is 0.2 ± 0.02 mm, and the depth of the flow channel is 0.15 ± 0.01 mm.

[0105] Example 3

[0106] A layered ultra-thin carbon-based composite bipolar plate has a sandwich-shaped layered composite structure, including a conductive additive layer 3, with prepreg layers 2 and conductive substrate / resin composite layers 1 arranged on both sides from the inside to the outside (i.e., including two layers of conductive substrate / resin composite layers 1 on the surface and an inner layer consisting of two prepreg layers 2 sandwiching the conductive additive layer 3), and the outer surface of the conductive substrate / resin composite layer 1 has a flow channel structure.

[0107] The prepreg layer 2 is an epoxy prepreg with a thickness of 0.06 mm (unidirectional carbon fiber prepreg with epoxy resin as the matrix); the conductive additive layer 3 sandwiched by the prepreg layer 2 is prepared by coating a natural flake graphite slurry with a particle size of 40 μm; the conductive substrate / resin composite outer layer is natural flake graphite powder and epoxy resin in a mass ratio of 8:2, and the graphite particle size is 40 μm.

[0108] A method for preparing a layered ultra-thin carbon-based composite bipolar plate comprises the following steps:

[0109] Step 1: Use epoxy resin as the matrix of unidirectional carbon fiber prepreg as the middle layer to enhance the mechanical properties, with a thickness of 0.06mm (fiber unit area mass of 54g / m 2 , resin content is 35% to 40%).

[0110] Step 2: Pour acetone as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite of 0.3:1. Ultrasonic dispersion is performed for 10 minutes, followed by centrifugation for 30 minutes to obtain a slurry with uniformly dispersed graphite.

[0111] Step 3: Use a coating machine to evenly coat the graphite slurry in step 2 on a single surface of the prepreg, with a coating thickness of no more than 50 μm, so that the graphite content is 29-36 g / m 2 The prepreg coated with the conductive additive layer 3 was placed in a vacuum drying oven and dried at 60° C. for 24 h, and a die-cutting machine was used to cut the dried prepreg into the target bipolar plate shape and size.

[0112] Step 4: Select epoxy resin and natural flake graphite powder to prepare a masterbatch of the surface conductive substrate / resin composite layer 1, where the diameter of the natural flake graphite is 40 μm. Dissolve the natural flake graphite powder and the resin in acetone in sequence and stir and mix at room temperature. The mass ratio of the natural flake graphite powder to the resin is 8:2; the mass ratio of the acetone solvent to the masterbatch is 1:9. Place the evenly mixed masterbatch into a frame-shaped flat plate mold with a filling thickness of 0.8 mm, and place it in a blast drying oven at 80°C to desolventize for 1 hour to prepare the surface conductive substrate / resin composite layer 1 masterbatch.

[0113] Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer 1 masterbatch, the prepreg layer 2 coated with the conductive additive layer 3, the prepreg layer 2, and the conductive substrate / resin composite layer 1 masterbatch. The carbon fibers of the two prepreg layers 2 should be oriented vertically, and the conductive additive layer 3 should be located between the two prepreg layers 2. Before loading the mold, spray methyl silicone oil on the inner surface of the mold cavity for demolding.

[0114] In step 6, the assembled mold is mounted on a flat-plate vulcanizer for hot compression molding. The molding pressure is set to 20 MPa and the molding temperature is set to 150°C. The pressurization is applied for 2 hours. After that, the pressure is maintained and the plate is naturally cooled to room temperature. The pressure is then released. The molded bipolar plate is removed from the mold to obtain the layered ultra-thin composite graphite bipolar plate. The maximum thickness of the molded plate is measured to be 0.70 ± 0.05 mm, the thickness of the composite layer is 0.20 ± 0.02 mm, and the depth of the flow channel is 0.15 ± 0.01 mm.

[0115] Example 4

[0116] A layered ultra-thin carbon-based composite bipolar plate has a sandwich-shaped layered composite structure, including a conductive additive layer 3, with prepreg layers 2 and conductive substrate / resin composite layers 1 arranged on both sides from the inside to the outside (i.e., including two layers of conductive substrate / resin composite layers 1 on the surface and an inner layer consisting of two prepreg layers 2 sandwiching the conductive additive layer 3), and the outer surface of the conductive substrate / resin composite layer 1 has a flow channel structure.

[0117] The prepreg layer 2 is a phenolic prepreg with a thickness of 0.2 mm (a unidirectional carbon fiber prepreg with a phenolic resin matrix); the conductive additive layer 3 sandwiched by the prepreg layer 2 is prepared by coating a natural flake graphite slurry with a particle size of 10 μm; the conductive substrate / resin composite outer layer is natural flake graphite powder and phenolic resin in a mass ratio of 8:2, and the graphite particle size is 40 μm.

[0118] A method for preparing a layered ultra-thin carbon-based composite bipolar plate comprises the following steps:

[0119] Step 1: Use unidirectional carbon fiber prepreg with phenolic resin as the matrix as the middle layer to enhance mechanical properties, with a thickness of 0.2 mm (the fiber unit area mass is 200 g / m 2 , resin content is 20% to 40%).

[0120] Step 2: Pour acetone as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite of 0.3:1. Ultrasonic dispersion is performed for 10 minutes, followed by centrifugation for 30 minutes to obtain a slurry with uniformly dispersed graphite.

[0121] Step 3: Use graphite spraying equipment to evenly spray the graphite slurry in step 2 on a single surface of the prepreg, with a coating thickness of no more than 50 μm, so that the graphite content is 50 to 134 g / m 2 The prepreg coated with the conductive additive layer 3 was placed in a vacuum drying oven and dried at 60° C. for 24 h, and a die-cutting machine was used to cut the dried prepreg into the target bipolar plate shape and size.

[0122] Step 4: Prepare a masterbatch of the surface conductive substrate / resin composite layer 1 by selecting phenolic resin and natural flake graphite powder, wherein the particle size of the natural flake graphite is 40 μm. Dissolve the natural flake graphite powder and the resin in acetone in turn and stir and mix them at room temperature. The mass ratio of the natural flake graphite powder to the resin is 8:2; the mass ratio of the acetone solvent to the masterbatch is 1:9. Fill the evenly mixed masterbatch into a frame-shaped flat plate mold with a thickness of 0.6 mm, place it in a blast drying oven at 80°C to desolventize for 1 hour, and thus prepare the masterbatch of the surface conductive substrate / resin composite layer 1.

[0123] Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer 1 masterbatch, the prepreg layer 2 coated with the conductive additive layer 3, the prepreg layer 2, and the conductive substrate / resin composite layer 1 masterbatch. The carbon fibers of the two prepreg layers 2 should be oriented perpendicularly, and the conductive additive layer 3 should be located between the two prepreg layers 2. Before loading the mold, spray polytetrafluoroethylene on the inner surface of the mold cavity for demolding.

[0124] In step 6, the assembled mold is mounted on a flat-plate vulcanizer for hot compression molding. The molding pressure is set to 25 MPa and the molding temperature is set to 160°C. Pressurization is performed for 2 hours. After maintaining the pressure, the mold is naturally cooled to room temperature and the pressure is released. The molded bipolar plate is removed from the mold to obtain the layered ultra-thin composite graphite bipolar plate. The maximum thickness of the molded plate is measured to be 0.6±0.05 mm, the thickness of the composite layer is 0.12±0.02 mm, and the depth of the flow channel is 0.09±0.01 mm.

[0125] Example 5

[0126] A layered ultra-thin carbon-based composite bipolar plate has a sandwich-shaped layered composite structure, including a conductive additive layer 3, with prepreg layers 2 and conductive substrate / resin composite layers 1 arranged on both sides from the inside to the outside (i.e., including two layers of conductive substrate / resin composite layers 1 on the surface and an inner layer consisting of two prepreg layers 2 sandwiching the conductive additive layer 3), and the outer surface of the conductive substrate / resin composite layer 1 has a flow channel structure.

[0127] The prepreg layer 2 is a phenolic prepreg with a thickness of 0.1 mm (a unidirectional carbon fiber prepreg with a phenolic resin matrix); the conductive additive layer 3 sandwiched by the prepreg layer 2 is prepared by coating a natural flake graphite slurry with a particle size of 20 μm; the conductive substrate / resin composite outer layer is natural flake graphite powder and phenolic resin in a mass ratio of 8:2, and the graphite particle size is 40 μm.

[0128] A method for preparing a layered ultra-thin carbon-based composite bipolar plate comprises the following steps:

[0129] Step 1: Use unidirectional carbon fiber prepreg with phenolic resin as the matrix as the middle layer to enhance mechanical properties, with a thickness of 0.1 mm (the fiber unit area mass is 200 g / m 2 , resin content is 20% to 40%).

[0130] Step 2: Pour acetone as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite of 0.4:1. Ultrasonic dispersion is performed for 15 minutes, followed by centrifugation for 40 minutes to obtain a slurry with uniformly dispersed graphite.

[0131] Step 3: Use graphite spraying equipment to evenly spray the graphite slurry in step 2 on a single surface of the prepreg, with a coating thickness of no more than 50 μm, so that the graphite content is 50 to 134 g / m 2 The prepreg coated with the conductive additive layer 3 was placed in a vacuum drying oven and dried at 60° C. for 24 h, and a die-cutting machine was used to cut the dried prepreg into the target bipolar plate shape and size.

[0132] Step 4: Prepare a masterbatch of the surface conductive substrate / resin composite layer 1 using phenolic resin and natural flake graphite powder, where the diameter of the natural flake graphite is 40 μm. Dissolve the natural flake graphite powder and resin in acetone in sequence and stir and mix at room temperature. The mass ratio of the natural flake graphite powder to the resin is 8:2; the mass ratio of the acetone solvent to the masterbatch is 1:9. Place the evenly mixed masterbatch into a frame-shaped flat plate mold with a filling thickness of 0.6 mm, and place it in a blast drying oven at 80°C to desolventize for 1 hour. This is the prepared masterbatch of the surface conductive substrate / resin composite layer 1.

[0133] Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer 1 masterbatch, the prepreg layer 2 coated with the conductive additive layer 3, the prepreg layer 2, and the conductive substrate / resin composite layer 1 masterbatch. The carbon fibers of the two prepreg layers 2 should be oriented perpendicularly, and the conductive additive layer 3 should be located between the two prepreg layers 2. Before loading the mold, spray polytetrafluoroethylene on the inner surface of the mold cavity for demolding.

[0134] In step 6, the assembled mold is mounted on a flat-plate vulcanizer for hot compression molding. The molding pressure is set to 25 MPa and the molding temperature is set to 160°C. Pressurization is performed for 2 hours. After maintaining the pressure, the mold is naturally cooled to room temperature and the pressure is released. The molded bipolar plate is removed from the mold to obtain the layered ultra-thin composite graphite bipolar plate. The maximum thickness of the molded plate is measured to be 0.45 ± 0.05 mm, the thickness of the composite layer is 0.12 ± 0.02 mm, and the depth of the flow channel is 0.09 ± 0.01 mm.

[0135] Example 6

[0136] The only difference between this embodiment and embodiment 1 is that the mass ratio of natural flake graphite powder and phenolic resin in the conductive substrate / resin composite outer layer is 9:1, and the remaining materials and preparation methods are the same as those in embodiment 1.

[0137] Example 7

[0138] The only difference between this embodiment and embodiment 1 is that the molding and curing temperature is 180° C., and the remaining materials and preparation methods are the same as those in embodiment 1.

[0139] Example 8

[0140] The only difference between this embodiment and embodiment 1 is that the natural flake graphite used for the conductive substrate / resin composite layer 1 is 80 μm, and the remaining materials and preparation methods are the same as those in embodiment 1.

[0141] Example 9

[0142] The only difference between this embodiment and embodiment 2 is that the natural flake graphite used for the conductive substrate / resin composite layer 1 is 80 μm, and the remaining materials and preparation methods are the same as those in embodiment 2.

[0143] Example 10

[0144] The only difference between this embodiment and embodiment 3 is that the natural flake graphite used for the conductive substrate / resin composite layer 1 is 80 μm, and the remaining materials and preparation methods are the same as those in embodiment 3.

[0145] The electrical conductivity of the bipolar plates prepared in Examples 1 to 10 was tested according to the test standard: GB / T 2004 2.6-2011, and the results shown in Table 1 were obtained.

[0146] Table 1

[0147] Example 1 2 3 4 5 Conductivity (S / cm) 169 153 58 171 147 Example 6 7 8 9 10 Conductivity (S / cm) 181 175 177 156 64

[0148] As shown in Table 1, the layered, ultra-thin carbon-based composite bipolar plates prepared by using a prepreg interlayer to enhance flexural properties exhibit excellent electrical conductivity. Comparisons with Examples 1-3 show that increasing the graphite particle size used in the conductive additive layer 3 sandwiched between the prepregs significantly decreases the in-plane conductivity of the bipolar plate. When the graphite particle size is 40 μm, the in-plane conductivity drops to 58 S / m, falling short of the ideal fuel cell bipolar plate. This indicates that when the graphite particle size of the conductive additive layer 3 sandwiched between the prepregs exceeds the optimal range of the present invention, the in-plane conductivity of the bipolar plate is significantly affected. Comparisons with Examples 1-3 and Examples 8-10 show that, within the optimal range, increasing the graphite particle size of the conductive substrate / resin composite layer 1 is beneficial for improving the in-plane conductivity of the bipolar plate.

[0149] 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), and the flexural strength is between 50 and 90 MPa.

[0150] 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 ultra-thin carbon-based bipolar plate, characterized in that: It is a sandwich-shaped layered composite structure, including a conductive additive layer, with prepreg layers and conductive substrate / resin composite layers arranged on both sides of the conductive additive layer from the inside to the outside, and a flow channel structure is formed on the surface of the plate through hot molding and curing; The prepreg layer is a prepreg of unidirectional carbon fiber or unidirectional carbon fiber fabric, and the orientations of the prepreg layers on both sides of the conductive additive layer are perpendicular to each other. The flow channel depth of the flow channel structure is less than the thickness of the conductive substrate / resin composite layer. The prepreg layer and the conductive additive layer are planar structures. The conductive additive layer sandwiched between the two prepreg layers is used to absorb the resin extruded from the prepreg layers during the compression molding process, thereby constructing a conductive path between adjacent prepreg layers and improving the through-conductivity of the layered carbon-based composite bipolar plate. A conductive substrate / resin composite layer is used as a buffer layer to improve the surface forming performance of the bipolar plate, absorb excess resin squeezed out of the prepreg, and reduce the contact resistance of the bipolar plate; The thickness of the prepreg layer is 0.20 mm, and it is a unidirectional carbon fiber prepreg based on epoxy resin with a resin content of 20% to 40%; The conductive additive layer is prepared by coating a 10 μm particle size natural flake graphite slurry; the conductive additive layer contains a graphite content of 50 to 134 g / m 2 , The conductive substrate / resin composite layer is composed of natural flake graphite powder and epoxy resin in a mass ratio of 8:2, with a graphite particle size of 40 μm; The maximum thickness of the formed plate is 1.00±0.05 mm, the thickness of the composite layer is 0.2±0.02 mm, and the depth of the flow channel is 0.15±0.01 mm.

2. The method for preparing a layered ultra-thin carbon-based bipolar plate according to claim 1, wherein: The hot molding process includes the following steps: Step 1: Use unidirectional carbon fiber prepreg with epoxy resin as the matrix as the middle layer to enhance mechanical properties. The thickness is 0.2 mm and the fiber unit area mass is 200 g / m 2 , resin content is 20%~40%; Step 2: Pour acetone as a dispersant into the natural flake graphite powder, with a mass ratio of dispersant to graphite of 0.3:1, and ultrasonically disperse for 10 minutes, followed by centrifugation for 30 minutes to obtain a slurry with uniformly dispersed graphite; Step 3: Use a coating machine to evenly coat the graphite slurry in step 2 on a single surface of the prepreg. The coating thickness is no more than 50 μm, and the graphite content is between 50 and 134 g / m 2 , put it into a vacuum drying oven and dry it at 60°C for 24 hours, and use a die-cutting machine to cut the dried prepreg coated with the conductive additive layer 3 into the target bipolar plate shape and size; Step 4, epoxy resin and natural flake graphite powder are selected to prepare a surface conductive substrate / resin composite layer masterbatch, the natural flake graphite has a diameter of 40 μm, the natural flake graphite powder and the resin are dissolved in acetone in sequence, and stirred and mixed at room temperature, wherein the mass ratio of natural flake graphite powder to resin is 8:2; the mass ratio of acetone solvent to masterbatch is 1:9, the mixed masterbatch is placed in a frame-shaped flat plate mold with a filling thickness of 0.8 mm, and placed in a blast drying oven at 80°C for desolvation for 1 hour, i.e., the prepared surface conductive substrate / resin composite layer masterbatch; Step 5: Load the laminated structure into a mold with a runner structure in the order of the conductive substrate / resin composite layer masterbatch, the prepreg layer coated with the conductive additive layer, the prepreg layer, and the conductive substrate / resin composite layer masterbatch. The carbon fibers of the two prepreg layers should be oriented perpendicularly, and the conductive additive layer is located between the two prepreg layers. Before loading the mold, spray methyl silicone oil on the inner surface of the mold cavity to facilitate demolding. In step 6, the assembled mold is installed on a flat vulcanizer for hot compression molding, the molding pressure is set to 20 MPa, the molding temperature is set to 150°C, and the pressurization is performed for 1 hour. After that, the pressure is maintained and naturally cooled to room temperature. The pressure is released and the molded bipolar plate is removed from the mold to obtain the layered ultra-thin composite graphite bipolar plate.

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