WO2025218042A1 - Preparation method for cryptocrystalline-graphite-based fuel cell bipolar plate - Google Patents

Abstract

Disclosed in the present invention is a preparation method for a cryptocrystalline-graphite-based fuel cell bipolar plate. The preparation method comprises the following steps: weighing a certain amount of high-carbon cryptocrystalline graphite, adding an appropriate amount of an oxidant solution, and stirring same at a certain temperature for a certain time to perform an oxidation treatment; collecting a solid product after the oxidation treatment, washing same clean, then filtering and drying same to obtain a product I; uniformly mixing the product I with a binder A, performing pyrolyzing, and then crushing same into a powder, and purifying same to obtain a product II; uniformly mixing the product II with a binder B and a conductive filler, and then performing a hot-pressing operation on the powder in a mold in a mold pressing system, followed by shaping and cooling same, then depressurizing, demolding and trimming same to obtain a final product. The present invention involves creatively preparing, by means of oxidation modification, co-pyrolysis granulation, hot-press molding with incorporation of conductive fillers, etc., a cryptocrystalline-graphite-based fuel cell bipolar plate that meets use requirements. The present invention involves a clear mechanism, a simple process and an excellent product, and has broad application prospects and is suitable for industrial promotion.

Description

A method for preparing cryptocrystalline graphite-based fuel cell bipolar plates Technical Field

The present invention relates to the technical field related to liquid flow battery materials, and specifically to a method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate.

Background Art

Fuel cells, a representative example of clean energy, are an integral part of the emerging "new energy + energy storage" energy development system and are considered the most efficient, cleanest, and most promising clean energy technology of the 21st century. Fuel cells offer advantages such as rapid start-up at room temperature, no electrolyte loss, a long service life, and high specific power and energy density, making them a new power source for both military and civilian use.

A typical fuel cell stack consists of a membrane electrode assembly (MEA) consisting of a diffusion layer (cathode), a catalyst layer (cathode), and a proton exchange membrane. Bipolar plates are placed on either side of the MEA and connected to the other cells. The entire stack structure resembles a plate-and-frame filter press. Bipolar plates are a key component in the fuel cell stack, distributing fuel gas and air (oxygen), providing electrical connections between individual cells, removing waste heat from the active area, preventing gas and coolant leakage, and facilitating water management. Currently, bipolar plates account for approximately 30% to 45% of the total stack cost and approximately 80% of the stack weight.

To ensure the performance indicators of bipolar plates, the materials used to prepare them mainly include metals, graphite, and graphite composites. Although metal bipolar plates have advantages such as low cost, easy molding, and good conductivity, they have fatal flaws such as poor corrosion resistance and poor safety. Graphite bipolar plates have advantages such as low contact resistance and good corrosion resistance, but they are fragile and permeable to gas. At the same time, the current mainstream preparation process (multiple impregnation of natural crystalline graphite or artificial graphite, roasting + slicing + CNC engraving) is complex, has low yield, and high cost. Graphite composite bipolar plates have advantages such as good corrosion resistance, high preparation efficiency, and easy industrialization. They are the current research focus and the mainstream trend of subsequent bipolar plate material development, but they are also subject to problems such as high raw material costs, complex molding processes, and conflicts between product conductivity and mechanical properties.

From the perspective of controlling production costs and meeting product performance indicators, reducing the cost of graphite composite bipolar plates The fundamental solution is to reduce formulation costs, simplify the preparation process, and develop a new molding process. Cryptocrystalline graphite is abundant and inexpensive, making it an excellent alternative to commonly used natural crystalline graphite, artificial graphite, flexible graphite paper, and expanded graphite powder. However, it has problems such as small particle size, high surface impurities, and poor conductivity.

CN111261893B discloses a highly conductive flexible graphite bipolar plate for flow batteries, as well as its preparation and application. The process involves mixing expanded graphite powder and polyvinylidene fluoride (PVDF) powder in a mixer at a high loading factor, cold-pressing the mixture into a low-density billet, and then vacuum hot-pressing or roller-pressing the resulting bipolar plate. This method is complex, unsuitable for large-scale application, and the resulting product suffers from poor thermal stability.

CN116638697A discloses a high-performance graphite-based composite material bipolar plate, preparation method, and application. In a powder mixing system, high-speed airflow is used to mix the powders. Then, in a molding system, the mixed powders in the mold are heated and pressurized under vacuum conditions. The heating is then terminated while the molding pressure is maintained. Once the temperature drops below the curing temperature of the resin, the molding pressure is released, air is introduced, and demolding is performed. This method creatively incorporates carbon nanotube conductive fillers to ensure powder molding while improving the conductivity of the bipolar plate. However, this method uses natural flake graphite as raw material, and the preparation process involves tedious processes such as mixing, vacuuming, and hot pressing. The raw material cost is high and the process is complex.

CN115483403A discloses a highly conductive composite bipolar plate for fuel cells and its preparation method. The method involves uniformly mixing graphite powder and powdered ammonium bicarbonate, then pressing the mixture at room temperature and high pressure to form a bipolar plate-shaped graphite/ammonium bicarbonate composite plate. The plate is then heated to volatilize the ammonium bicarbonate, resulting in a three-dimensional graphite skeleton. Finally, a liquid thermosetting resin is impregnated into the three-dimensional graphite skeleton under vacuum conditions and cured to produce a composite bipolar plate with a three-dimensional graphite conductive network. The ammonium bicarbonate used in this process is thermally unstable and acutely toxic, and the preparation process requires numerous steps, resulting in low production efficiency.

As can be seen, there is currently no published technology for producing graphite composite bipolar plates with high conductivity, high strength, and high airtightness using cryptocrystalline graphite as the primary material. Furthermore, the published processes for preparing graphite composite bipolar plates are difficult to implement for large-scale industrial production. In light of this, in-depth research into the aforementioned issues led to the present case.

Summary of the Invention

The object of the present invention is to provide a method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate to solve the problems raised in the above background technology.

To achieve the above object, the present invention provides the following technical solution: a method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate, comprising the following steps:

(1) Weigh a certain amount of high-carbon cryptocrystalline graphite, add an appropriate amount of oxidant solution, and stir for a certain time at a certain temperature for oxidation treatment;

(2) collecting the solid product after oxidation treatment, rinsing it, filtering it, and drying it to obtain product I;

(3) Product I is mixed evenly with binder A and then pyrolyzed. After the pyrolysis is completed, the product is crushed into powder and purified to obtain product II;

(4) Product II is mixed evenly with binder B and conductive filler, and then the powder in the mold is hot-pressed in a molding system. After molding and cooling, the pressure is released, the mold is demolded, and the edges are trimmed to obtain the final product.

Furthermore, in step (1), the fixed carbon content of the high-carbon cryptocrystalline graphite is greater than 94%, the oxidant is one or more combinations of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, etc., the reaction temperature is room temperature to 100° C., and the reaction time is 0.5 to 4 hours.

Preferably, the reaction temperature is 50-90° C., and the reaction time is 3-4 h.

Furthermore, in step (3), the binder A comprises one or more combinations of coking coal, fat coal, lean coal, semi-coke, petroleum asphalt, coal tar, etc., the pyrolysis temperature is 500-900° C., and the pyrolysis time is 0.5-2 h.

Preferably, the pyrolysis temperature is 600-800° C., and the pyrolysis time is 1-1.5 h.

Furthermore, in step (4), the binder B includes one or more combinations of resins such as epoxy resin, phenolic resin, polyimide resin, polypropylene resin, etc., the conductive filler is one or more combinations of graphene, carbon fiber, carbon black, carbon nanotubes, and metal fiber, the molding pressure is 60-100 MPa, and the molding temperature is 150-350°C.

Preferably, the resin powder has a size of 10 to 50 μm.

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

Preferably, the molding pressure is 80-100 MPa, and the molding temperature is 150-250°C.

Furthermore, the size of product II is 20 to 100 μm.

Furthermore, the mixing ratio of product II, binder B, and conductive filler is: 80wt.% to 90wt.% product II, 7wt.% to 17wt.% binder B, and the balance is conductive filler.

Compared with the prior art, the beneficial effects of the present invention are: the cryptocrystalline graphite-based fuel cell bipolar plate preparation method has the following advantages over the prior art:

1. The present invention improves the surface properties of cryptocrystalline graphite through oxidative modification, enhances its dispersibility and conductivity, and is beneficial to its subsequent interface composite with resin and conductive filler.

2. The present invention oxidatively modifies cryptocrystalline graphite and co-pyrolyzes and granulates it with a high-temperature adhesive high-carbon material, thereby effectively solving the problem of small particle size of cryptocrystalline graphite and reducing the problem of preferred orientation of cryptocrystalline graphite, thereby improving the stability between cryptocrystalline graphite and interface carbon atoms, and is beneficial to improving the mechanical properties of the bipolar plate.

3. The present invention introduces conductive fillers such as graphene, carbon fiber, carbon black, carbon nanotubes, and metal fibers. In addition to playing a bridging role between cryptocrystalline graphite particles to open up conductive paths and reduce contact resistance, thereby improving the overall conductivity of the bipolar plate, it can also improve the mechanical properties of the material, especially the bending strength.

4. The present invention addresses the problems of cryptocrystalline graphite with small particle size, many surface impurities, and poor electrical conductivity. By creatively preparing fuel cell bipolar plates that meet the requirements through oxidation modification, co-pyrolysis granulation, and hot pressing molding by incorporating conductive fillers, the present invention has a clear mechanism, a simple process, and an excellent product. It has broad prospects for use and is suitable for industrial promotion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the process flow of the present invention.

DETAILED DESCRIPTION

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

Please refer to Figure 1, the present invention provides the following technical solutions:

Example 1

A method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate comprises the following steps:

Step (1) placing cryptocrystalline graphite having a fixed carbon content of 94.77% and H2O2 (concentration of 30 wt.%) accounting for 20% of the mass fraction of the cryptocrystalline graphite in a beaker to form a mixture, and adding deionized water to the mixture at a solid-liquid ratio of 1:100 to form a suspension, the reaction temperature is 60°C, the reaction time is 4 hours, and after the reaction is completed, product I is collected;

Step (2) Product I is fully mixed with coking coal in a mass ratio of 10:1 and then pyrolyzed at a pyrolysis temperature of 700° C. for 1 hour. The pyrolysis product is crushed to a D50 of 45 μm and then purified to obtain Product II with a fixed carbon content of 99.9%;

Step (3) After uniformly mixing 85 wt.% of product II, 12 wt.% of epoxy resin, 1 wt.% of graphene, 1 wt.% of carbon fiber, and 1 wt.% of carbon nanotubes, the powder is hot-pressed in a mold with an inner cavity size of 400×200×15 mm in a molding system at a hot-pressing temperature of 250° C. and a molding pressure of 100 MPa. After molding and cooling, the product is pressure-relieved, demolded, and trimmed to obtain the final product.

Example 2

A method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate comprises the following steps:

Step (1) placing cryptocrystalline graphite having a fixed carbon content of 94.77% and solid potassium permanganate powder accounting for 20% by mass of the cryptocrystalline graphite in a beaker to form a mixture, and diluting the mixture with deionized water at a solid-liquid ratio of 1:50 to form a suspension, reacting at a temperature of 90° C. for 4 hours, and collecting product I after the reaction is completed;

Step (2) Product I and coal tar pitch are fully mixed in a mass ratio of 8:1 and then pyrolyzed at a pyrolysis temperature of 600℃, pyrolysis time is 1.5h, the pyrolysis product is crushed to D50 of 45μm and then purified to product II with a fixed carbon content of 99.9%;

Step (3) After uniformly mixing 80 wt.% of product II, 17 wt.% of polypropylene resin, 1 wt.% of graphene, 1 wt.% of carbon fiber, and 1 wt.% of carbon nanotubes, the powder is hot-pressed in a mold with an inner cavity size of 400×200×15 mm in a molding system at a hot-pressing temperature of 200° C. and a molding pressure of 80 MPa. After molding and cooling, the product is pressure-relieved, demolded, and trimmed to obtain the final product.

Example 3

A method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate comprises the following steps:

Step (1) placing cryptocrystalline graphite with a fixed carbon content of 94.77%, sulfuric acid (concentration of 98.8 wt.%) accounting for 3% of the mass fraction of the cryptocrystalline graphite, and H2O2 (concentration of 30 wt.%) with a mass fraction of 15% in a beaker to form a mixture, and adding deionized water to the mixture at a solid-liquid ratio of 1:100 to form a suspension, the reaction temperature is 50°C, the reaction time is 3 hours, and after the reaction is completed, product I is collected;

Step (2) Product I is fully mixed with semi-coke in a mass ratio of 5:1 and then pyrolyzed at a pyrolysis temperature of 800° C. for 1 hour, and the pyrolysis product is crushed to a D50 of 45 μm and then purified to obtain Product II with a fixed carbon content of 99.9%;

Step (3) After uniformly mixing 85 wt.% of product II, 12 wt.% of epoxy resin, 1 wt.% of graphene, 1 wt.% of carbon fiber, and 1 wt.% of carbon nanotubes, the powder is hot-pressed in a mold with an inner cavity size of 400×200×15 mm in a molding system at a hot-pressing temperature of 250° C. and a molding pressure of 80 MPa. After molding and cooling, the powder is depressurized, demolded, and trimmed to obtain the final product.

Comparative Example 1

The difference between this comparative example and Example 1 is that the cryptocrystalline graphite is not subjected to the oxidation regulation of step (1), and the other conditions are the same as those of Example 1.

Comparative Example 2

The difference between this comparative example and Example 2 is that the mixed pyrolysis in step (2) is not performed, but the product I is directly purified to a fixed carbon content of 99.9% before use. The other steps are the same as those in Example 2.

Comparative Example 3

The difference between this comparative example and Example 3 is that 1 wt.% graphene, 1 wt.% carbon fiber and 1 wt.% carbon nanotubes are not added in step (3), and the remaining 3 wt.% is replaced by epoxy resin. The rest is the same as Example 3.

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

Table 1

From Table 1, it can be seen from the test results of Example 1 and Comparative Example 1 that oxidation regulation can significantly improve the electrical properties of the cryptocrystalline graphite-based bipolar plate, and can also improve the gas permeability performance of the material; from the test results of Example 2 and Comparative Example 2, it can be seen that the flexural strength of the bipolar plate obtained by mixing and pyrolyzing the product 1 and the binder A is significantly improved, and the electrical properties and gas permeability performance are also significantly improved; from the test results of Example 3 and Comparative Example 3, it can be seen that the addition of a conductive filler to the mixture can significantly improve the electrical properties of the bipolar plate, and the flexural strength is also significantly improved.

It should be noted that the preferred bipolar plate preparation conditions in the above embodiments are obtained based on a large number of exploratory experiments and scientific experimental designs of single variable and orthogonal experiments. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, the technical solution of the present invention can be subjected to various simple modifications, and these simple modifications all fall within the scope of protection of the present invention.

The contents not described in detail in this specification belong to the prior art known to those skilled in the art. Although the embodiments of the present invention have been shown and described, it is not difficult for those skilled in the art to In other words, it should be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims (9)

A method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate, characterized by comprising the following steps: Step (1) weighing a certain amount of high-carbon cryptocrystalline graphite, adding an appropriate amount of oxidant solution, and stirring for a certain time at a certain temperature to perform oxidation treatment; Step (2) collecting the solid product after oxidation treatment, rinsing it, filtering it, and drying it to obtain product I; Step (3) mixing the product I and the binder A uniformly and then pyrolyzing them, crushing them into powder after the pyrolysis is completed, and purifying them to obtain the product II; Step (4) uniformly mixes the product II with the binder B and the conductive filler, and then hot presses the powder in the mold in a molding system, forms and cools, and then releases the pressure, demolds, and trims the edges to obtain the final product. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 1 is characterized in that: the fixed carbon content of the high-carbon cryptocrystalline graphite in step (1) is greater than 94%, the oxidant is one or more combinations of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, etc., the reaction temperature is room temperature to 100°C, and the reaction time is 0.5 to 4 hours. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 2 is characterized in that the reaction temperature is 50-90°C and the reaction time is 3-4 hours. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 1 is characterized in that: in the step (3), the binder A includes one or more combinations of coking coal, fat coal, lean coal, semi-coke, petroleum asphalt, coal tar, etc., the pyrolysis temperature is 500-900°C, and the pyrolysis time is 0.5-2h. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 4 is characterized in that the pyrolysis temperature is 600-800°C and the pyrolysis time is 1-1.5 hours. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 1 is characterized in that: the binder B in step (4) comprises epoxy resin, phenolic resin, polyimide The conductive filler is one or more combinations of resins such as polypropylene resin, graphene, carbon fiber, carbon black, carbon nanotubes, and metal fiber. The molding pressure is 60-100 MPa and the molding temperature is 150-350°C. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 6, wherein the resin powder has a size of 10 to 50 μm; The conductive filler is a mixture of graphene, carbon fiber, and carbon nanotubes in a mass ratio of 1: (1 to 1.2): (1 to 1.2); The molding pressure is 80-100 MPa, and the molding temperature is 150-250°C. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 1, wherein the D50 of the product II is 20 to 100 μm. The method for preparing a cryptocrystalline graphite-based fuel cell bipolar plate according to claim 1, characterized in that the mixing ratio of the product II, binder B, and conductive filler is: 80wt.% to 90wt.% product II, 7wt.% to 17wt.% binder B, and the balance is conductive filler.