Preparation method for cryptocrystalline-graphite-based fuel cell bipolar plate

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 an aphanitic graphite-based bipolar plate of a fuel cell TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid flow battery materials, in particular to a method for preparing an aphanitic graphite-based bipolar plate of a fuel cell. BACKGROUND

[0002] Fuel cells, as one of the representatives of clean energy, are an indispensable part of the new energy development system of "new energy + energy storage", and are regarded as the most effective, cleanest and most promising clean energy technology in the 21st century. Fuel cells have the advantages of fast start at room temperature, no electrolyte loss, long service life, high specific power and specific energy density, and are a new type of power source for military and civilian use.

[0003] A typical fuel cell stack is composed of a diffusion layer (cathode and anode), a catalyst layer (cathode and anode), and a proton exchange membrane to form a membrane electrode assembly. The bipolar plate is placed on both sides of the membrane electrode and connected to other single cells. The structure of the entire stack is similar to a plate-and-frame filter press. The bipolar plate is a key component in the stack, which plays a role in distributing fuel gas and air (oxygen), electrically connecting single cells, removing waste heat from the active area, preventing gas and coolant leakage, and promoting water management. At present, the cost of the bipolar plate accounts for about 30% to 45% of the total cost of the stack, and the mass accounts for about 80% of the total weight of the stack.

[0004] To ensure the performance indicators of the bipolar plate, the materials for preparing the bipolar plate mainly include metals, graphite and graphite composite materials. Although metal bipolar plates have the advantages of low cost, easy forming and good electrical conductivity, they have the fatal defects of poor corrosion resistance and poor safety. Graphite bipolar plates have the advantages of low contact resistance and good corrosion resistance, but they have problems such as fragility and gas permeability. At present, the mainstream preparation process (natural crystalline graphite or artificial graphite multiple impregnation, calcination + slicing + CNC engraving forming) is complex, the yield is low, and the cost is high. Graphite composite bipolar plates have the advantages of good corrosion resistance, high preparation efficiency and easy industrialization, and are the focus of current research and the mainstream trend of subsequent bipolar plate material development. However, they have problems such as high raw material cost, complex molding process, and conflict between product electrical conductivity and mechanical properties.

[0005] From the perspective of controlling production cost and meeting product performance indicators, reducing the formulation cost of graphite composite bipolar plates, simplifying the preparation process, and developing new molding processes are the fundamental solutions. Aphanitic graphite is abundant in reserves and low in price, which is the best choice to replace the commonly used natural crystalline graphite, artificial graphite, flexible graphite paper and expanded graphite powder. However, it has problems such as small particle size, many surface impurities and poor electrical conductivity.

[0006] CN111261893B discloses a high-conductivity flexible graphite bipolar plate for flow battery and its preparation and application, which is prepared by mixing the expanded graphite powder and polyvinylidene fluoride (PVDF) powder in a mixer at a high loading coefficient, then cold-pressing into a low-density blank, and then vacuum hot-pressing or roll-pressing into a bipolar plate. The method is complex and not suitable for large-scale application, and the product has poor thermal stability.

[0007] CN116638697A discloses a high-performance graphite-based composite bipolar plate, a preparation method and application, which mixes the powders in a powder mixing system using high-speed airflow, then heats and presses the mixed powders in the mold under vacuum conditions in a mold pressing system, then stops heating and continues to maintain the forming pressure, waits for the temperature to drop below the solidification forming temperature of the resin, removes the forming pressure and fills in air, and demolds. The method creatively adds carbon nanotube conductive fillers to ensure powder forming while improving the conductivity of the bipolar plate. However, the method uses natural flake graphite as raw material, and the preparation process involves complicated processes such as mixing, vacuumizing and hot-pressing, which is high in raw material cost and complex in process.

[0008] CN115483403A discloses a high-conductivity composite bipolar plate for fuel cell and a preparation method thereof, which mixes graphite powder and powdered ammonium bicarbonate uniformly, then presses the graphite / ammonium bicarbonate composite plate into a bipolar plate shape at room temperature and high pressure, then heats to volatilize the ammonium bicarbonate to obtain a three-dimensional graphite skeleton, and finally impregnates the three-dimensional graphite skeleton with a liquid thermosetting resin under vacuum conditions to obtain a composite bipolar plate with a three-dimensional graphite conductive network after curing. The pore-forming agent ammonium bicarbonate used in the process has thermal instability and acute toxicity, and the preparation process requires more processes and has low production efficiency.

[0009] It can be seen that there is no technology disclosed for preparing a high-conductivity, high-strength and high-airtightness graphite composite bipolar plate using aphanitic graphite as the main material, and the preparation processes of the graphite composite bipolar plates disclosed are difficult to realize large-scale industrial production. In view of this, in view of the above problems, after in-depth research, the present case is produced.

[0010] SUMMARY

[0011] The purpose of the present application is to provide a method for preparing a aphanitic graphite-based fuel cell bipolar plate to solve the problems raised in the background art.

[0012] To achieve the above-mentioned purpose, the present application provides the following technical solution: a method for preparing a aphanitic graphite-based fuel cell bipolar plate, comprising the following steps:

[0013] (1) Weigh a certain amount of high-carbon aphanitic graphite, add an appropriate amount of oxidizing agent solution, and stir at a certain temperature for a certain time for oxidation treatment;

[0014] (2) Collecting the solid product after the oxidation treatment, rinsing, filtering and drying to obtain product I;

[0015] (3) Mixing product I with binder A, pyrolyzing, crushing into powder after pyrolyzing, and purifying to obtain product II;

[0016] (4) Mixing product II with binder B and conductive filler, hot-pressing the powder in the mold in a mold system, shaping, cooling, unloading, demolding and trimming to obtain the final product.

[0017] Further, the fixed carbon content of the high-carbon aphanitic graphite in step (1) is greater than 94%, the oxidizing agent is one or a combination of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid and potassium permanganate, the reaction temperature is room temperature to 100°C, and the reaction time is 0.5 to 4 hours.

[0018] Preferably, the reaction temperature is 50 to 90°C, and the reaction time is 3 to 4 hours.

[0019] Further, the binder A in step (3) includes one or a combination of coke, fat coal, lean coal, semi-coke, petroleum pitch and coal pitch, the pyrolysis temperature is 500 to 900°C, and the pyrolysis time is 0.5 to 2 hours.

[0020] Preferably, the pyrolysis temperature is 600 to 800°C, and the pyrolysis time is 1 to 1.5 hours.

[0021] Further, the binder B in step (4) includes one or a combination of epoxy resin, phenolic resin, polyimide resin and polypropylene resin, the conductive filler is one or a combination of graphene, carbon fiber, carbon black and carbon nanotube, the molding pressure is 60 to 100 MPa, and the molding temperature is 150 to 350°C.

[0022] Preferably, the resin powder has a size of 10 to 50 μm.

[0023] Preferably, the conductive filler is a mixture of graphene, carbon fiber and carbon nanotube at a mass ratio of 1: (1 to 1.2): (1 to 1.2).

[0024] Preferably, the molding pressure is 80 to 100 MPa, and the molding temperature is 150 to 250°C.

[0025] Further, the product II has a size of 20 to 100 μm.

[0026] Further, the mixing ratio of product II, adhesive B and conductive filler is: 80wt.% to 90wt.% of product II, 7wt.% to 17wt.% of adhesive B, and the balance is conductive filler.

[0027] Compared with the prior art, the method has the following advantages:

[0028] 1. The surface properties of the aphanitic graphite are improved by oxidation modification, and the dispersibility and conductivity thereof are improved, which is beneficial to the subsequent interface compounding with resin and conductive filler.

[0029] 2. The aphanitic graphite is co-pyrolyzed with high-temperature adhesive high-carbon substances to effectively solve the problem of small particle size of the aphanitic graphite, reduce the problem of preferred orientation of the aphanitic graphite, improve the stability between the aphanitic graphite and interface carbon atoms, and improve the mechanical properties of the bipolar plate.

[0030] 3. The conductive filler such as graphene, carbon fiber, carbon black, carbon nanotube and metal fiber is introduced, which not only plays a bridging role between aphanitic graphite particles to pass through the conductive path and reduce the contact resistance, thereby improving the overall electrical conductivity of the bipolar plate, but also improves the mechanical properties of the material, especially the bending strength.

[0031] 4. The aphanitic graphite has small particle size, many surface impurities and poor electrical conductivity, and the bipolar plate meeting the use requirements is prepared by oxidation modification, co-pyrolysis granulation, doping of conductive filler and hot pressing forming, and the mechanism is clear, the process is simple, the product is excellent, the use prospect is wide, and the method is suitable for industrial promotion. BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 is a process flow diagram of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] Please refer to Fig. 1, the present application provides the following technical solutions:

[0035] Embodiment 1

[0036] A kind of aphanitic graphite-based fuel cell bipolar plate preparation method, comprising the following steps:

[0037] Step (1) amorphous graphite with a fixed carbon content of 94.77% and H2O2 (concentration of 30 wt.%) accounting for 20% of the mass fraction of amorphous graphite were placed in a beaker to form a mixture, deionized water was used to set the volume according to a solid-liquid ratio of 1:100 to form a suspension, the reaction temperature was 60℃, the reaction time was 4h, and the product I was collected after the reaction was completed;

[0038] Step (2) product I was mixed with coke at a mass ratio of 10:1 and pyrolyzed, the pyrolysis temperature was 700℃, the pyrolysis time was 1h, the pyrolysis product was crushed to D50 of 45μm, and product II with a fixed carbon content of 99.9% was purified;

[0039] Step (3) 85wt.% product II, 12wt.% epoxy resin, 1wt.% graphene, 1wt.% carbon fiber, and 1wt.% carbon nanotube were uniformly mixed, and the powder in the mold with an inner cavity size of 400×200×15mm was hot-pressed in a molding system, the hot-pressing temperature was 250℃, the molding pressure was 100MPa, after molding and cooling, the pressure was released, demolding, and edge trimming were performed, and the final product was obtained.

[0040] Example 2

[0041] A preparation method of an amorphous graphite-based fuel cell bipolar plate, comprising the following steps:

[0042] Step (1) amorphous graphite with a fixed carbon content of 94.77% and solid potassium permanganate powder accounting for 20% of the mass fraction of amorphous graphite were placed in a beaker to form a mixture, deionized water was used to set the volume according to a solid-liquid ratio of 1:50 to form a suspension, the reaction temperature was 90℃, the reaction time was 4h, and the product I was collected after the reaction was completed;

[0043] Step (2) product I was mixed with coal tar pitch at a mass ratio of 8:1 and pyrolyzed, the pyrolysis temperature was 600℃, the pyrolysis time was 1.5h, the pyrolysis product was crushed to D50 of 45μm, and product II with a fixed carbon content of 99.9% was purified;

[0044] Step (3) 80wt.% product II, 17wt.% polypropylene resin, 1wt.% graphene, 1wt.% carbon fiber, and 1wt.% carbon nanotube were uniformly mixed, and the powder in the mold with an inner cavity size of 400×200×15mm was hot-pressed in a molding system, the hot-pressing temperature was 200℃, the molding pressure was 80MPa, after molding and cooling, the pressure was released, demolding, and edge trimming were performed, and the final product was obtained.

[0045] Example 3

[0046] A preparation method of an amorphous graphite-based fuel cell bipolar plate, comprising the following steps:

[0047] Step (1) a mixture of aphanitic graphite with a fixed carbon content of 94.77% and 3% of sulfuric acid (concentration of 98.8wt.%) by mass fraction of aphanitic graphite and 15% of H2O2(concentration of 30wt.%) by mass fraction in a beaker, and then constant volume with deionized water at a solid-liquid ratio of 1:100 to form a suspension, the reaction temperature is 50℃, the reaction time is 3h, and the product I is collected after the reaction is completed;

[0048] Step (2) after mixing product I and semi-coke at a mass ratio of 5:1, pyrolysis, pyrolysis temperature is 800℃, pyrolysis time is 1h, the pyrolysis product is crushed to D50 of 45μm, and then purified to product II with a fixed carbon content of 99.9%;

[0049] Step (3) after mixing 85wt.% product II, 12wt.% epoxy resin, 1wt.% graphene, 1wt.% carbon fiber and 1wt.% carbon nanotube uniformly, the powder in the mold with an inner cavity size of 400×200×15mm is hot-pressed in a molding system, the hot-pressing temperature is 250℃, the forming pressure is 80MPa, after forming and cooling, the pressure is released, demolded, and trimmed to obtain the final product.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the aphanitic graphite is not subjected to step (1) of oxidation regulation, and the others are the same as Example 1.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 2 is that it is not subjected to step (2) of mixed pyrolysis, but directly uses product I purified to a fixed carbon content of 99.9%, and the others are the same as Example 2.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 3 is that 1wt.% graphene, 1wt.% carbon fiber and 1wt.% carbon nanotube are not added in step (3), and the remaining 3wt.% is replaced by epoxy resin, and the others are the same as Example 3.

[0056] The bipolar plates prepared in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2 and Comparative Example 3 are respectively tested for bending strength, electrical conductivity, contact resistance and gas permeability, and the test results are shown in Table 1.

[0057] Table 1

[0058] From Table 1, the test results of Comparative Example 1 and Comparative Example 1 show that the oxidation regulation can significantly improve the electrical performance of the aphanitic graphite-based bipolar plate, and can also improve the gas permeability performance of the material; the test results of Comparative Example 2 and Comparative Example 2 show that the bending strength of the bipolar plate prepared by mixing and pyrolyzing Product 1 and the binder A is significantly improved, in addition, the electrical performance and the gas permeability performance are also significantly improved; the test results of Comparative Example 3 and Comparative Example 3 show that the electrical performance of the bipolar plate can be significantly improved by adding the conductive filler in the mixed material, in addition, the bending strength is also significantly improved.

[0059] It should be noted that the bipolar plate preparation conditions preferred in the above examples are obtained based on a large number of exploration experiments and scientific experimental design of single variable and orthogonal test, but the present application is not limited to the specific details in the above examples, and various simple modifications can be made to the technical solutions of the present application within the technical concept range of the present application, and these simple modifications all belong to the protection scope of the present application.

[0060] The contents not described in detail in the specification belong to the prior art known to those skilled in the art. Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method of making an agraphitic graphite-based fuel cell bipolar plate, the method comprising: It comprises the following steps: ​ Step (1) a certain amount of high-carbon aphanitic graphite is weighed and added with a proper amount of oxidant solution, and stirred at a certain temperature for a certain time for oxidation treatment; Step (2) the solid product after oxidation treatment is collected, washed, filtered and dried to obtain product I; Step (3) product I is mixed with binder A, pyrolyzed, crushed into powder after pyrolysis is completed, and purified to obtain product II; Step (4) product II is mixed with binder B and conductive filler, and then the powder in the mold is subjected to hot-pressing operation in a mold pressing system, and after shaping, cooling, pressure release, demolding and edge trimming, the final product is obtained.

2. A method of making an amorphous graphite-based bipolar plate for a fuel cell according to claim 1, characterized in that: In step (1), the fixed carbon content of the high-carbon aphanitic graphite is greater than 94%, the oxidant is one or a combination of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid and potassium permanganate, the reaction temperature is room temperature to 100℃, and the reaction time is 0.5 to 4h.

3. A method of making an amorphous graphite-based bipolar plate for a fuel cell according to claim 2, wherein: The reaction temperature is 50 to 90℃, and the reaction time is 3 to 4h.

4. The method of claim 1, wherein the method further comprises: In step (3), binder A comprises one or a combination of coke, fat coal, lean coal, semi-coke, petroleum pitch and coal pitch, the pyrolysis temperature is 500 to 900℃, and the pyrolysis time is 0.5 to 2h.

5. A method of making an amorphous graphite-based bipolar plate for a fuel cell according to claim 4, characterized in that: The pyrolysis temperature is 600 to 800℃, and the pyrolysis time is 1 to 1.5h.

6. The method of claim 1, wherein the method further comprises: In step (4), binder B comprises one or a combination of epoxy resin, phenolic resin, polyimide resin and polypropylene resin, the conductive filler is one or a combination of graphene, carbon fiber, carbon black, carbon nanotube and metal fiber, the molding pressure is 60 to 100MPa, and the molding temperature is 150 to 350℃.

7. A method of making an amorphous graphite-based bipolar plate for a fuel cell according to claim 6, characterized in that: The powder size of the resin is 10 to 50μm; The conductive filler is a mixture of graphene, carbon fiber and carbon nanotube at a mass ratio of 1: (1 to 1.2) : (1 to 1.2); The molding pressure is 80 to 100MPa, and the molding temperature is 150 to 250℃.

8. The method of claim 1, wherein the method further comprises: The D50 of product II is 20 to 100μm.

9. The method of claim 1, wherein the method further comprises: The mixing ratio of product II, binder B and conductive filler is: 80wt.% to 90wt.% product II, 7wt.% to 17wt.% binder B, and the rest is conductive filler.

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