A method for preparing resin / scale graphite / carbon black composite bipolar plate for all-vanadium redox flow battery

Abstract

The application belongs to the field of energy storage battery materials, and particularly relates to a high-content flake graphite / carbon black composite bipolar plate and application thereof in a vanadium redox flow battery. The bipolar plate is prepared by using thermoplastic phenolic resin as a matrix, high-content natural flake graphite as a main conductive filler, and carbon black as a second conductive filler, and is formed by die molding. The carbon black nanoparticles are filled in the interlayer gap of the flake graphite, a three-dimensional 'point-surface' conductive network is constructed, and the interface bonding between the resin and the filler is improved. When the content of the flake graphite is 68% and the addition amount of the carbon black is 7%, the in-plane conductivity and the bending strength of the bipolar plate are significantly improved, the ohmic polarization internal resistance of the battery is effectively reduced, the stability of the battery stack assembly and the long-term operation reliability are ensured, and the service life of the battery is prolonged. The material has the advantages of simple preparation process, low raw material cost, stable performance and suitability for mass production.

Description

Technical Field

[0001] This invention relates to a composite bipolar plate material for vanadium redox flow batteries and its preparation method, and more particularly to a composite bipolar plate based on the results of curing kinetic analysis, which adds carbon black as a second filler under high-content flake graphite filling conditions. Background Technology

[0002] Vanadium redox flow batteries (VRFBs) have attracted much attention in the field of large-scale energy storage due to their advantages such as high safety, long cycle life, and the ability to independently design power and capacity. As one of the key components of VRFBs, bipolar plates need to simultaneously possess high conductivity, good bending strength, excellent corrosion resistance, and dimensional stability.

[0003] Resin / flake graphite composite bipolar plates have become a research hotspot due to their low cost and ease of processing. However, when the flake graphite content is high (e.g., ≥ 70%), the resin content is relatively insufficient, leading to a significant decrease in the mechanical properties of the bipolar plate. Conversely, while reducing the graphite content can improve strength, it deteriorates electrical conductivity. Existing technologies have reported improving the conductive network structure by adding a second conductive filler (such as carbon black or carbon nanotubes), but the impact of the introduction of the second filler on the curing behavior, interfacial bonding, and final properties of the composite material in highly filled systems lacks systematic research.

[0004] The kinetic parameters of thermosetting or thermoplastic resins during the curing process (such as activation energy, reaction order, and gel time) directly affect resin flow, wetting, and the quality of interfacial bonding with fillers. In high-content flake graphite-filled systems, fillers exert significant physical and chemical effects on resin curing behavior, such as dilution effects, hindering molecular chain movement, and interfacial adsorption. Therefore, optimizing the resin-filler ratio and process conditions based on curing kinetic analysis results is of great significance for the preparation of high-performance composite bipolar plates. Summary of the Invention

[0005] The present invention aims to solve the problem of balancing electrical conductivity and flexural strength in high-content flake graphite-filled composite bipolar plates, and provides a composite bipolar plate with carbon black as a second filler and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A resin / flake graphite / carbon black composite bipolar plate is characterized in that the bipolar plate is composed of a resin matrix, flake graphite and carbon black, wherein the mass percentage of flake graphite is 70% to 75%, the mass percentage of carbon black is 1% to 5%, and the resin matrix is ​​thermoplastic phenolic resin.

[0007] The resin matrix is ​​2130 phenolic resin; The flake graphite has a particle size of 75 μm and a fixed carbon content of ≥ 99%; The carbon black has a particle size of 20 nm to 50 nm and a specific surface area of ​​100 to 300 m² / g; The composite bipolar plate has a thickness of 2–4 mm, an in-plane conductivity ≥150 S / cm, and a bending strength ≥40 MPa.

[0008] This invention also provides a method for preparing a resin / flake graphite / carbon black composite bipolar plate based on curing kinetic analysis, characterized by comprising the following steps: (1) Weigh out flake graphite, carbon black and resin powder according to the mass ratio, wherein the flake graphite accounts for 70% to 75%, the carbon black accounts for 1% to 5%, the resin accounts for 25%, and the total mass is 10 g, and mix them evenly. (2) Add an appropriate amount of anhydrous ethanol to the mixed powder obtained in step (1) and stir magnetically at room temperature until it becomes a paste, so that the filler is evenly dispersed. (3) Fill the paste material into the bipolar plate mold, place it on the flat vulcanizing machine, set the molding temperature (200℃), molding pressure (80 kN) and molding time (2 h) and perform hot pressing molding; (4) Cool the molded bipolar plate to room temperature with the mold, and obtain the resin / flake graphite / carbon black composite bipolar plate after demolding.

[0009] In step (1), the preferred mass percentage of flake graphite is 65% to 75%, the mass percentage of carbon black is 1% to 10%, and the mass percentage of resin is 25%.

[0010] The present invention has the following advantages: (1) In this invention, carbon black is introduced as a second conductive filler. Carbon black nanoparticles can fill the gaps between flake graphite layers to build more three-dimensional conductive pathways. At the same time, they form a "point-to-surface" contact conductive network with flake graphite, which further improves the in-plane conductivity under a higher flake graphite content.

[0011] (2) Adding an appropriate amount of carbon black can improve the wettability between the resin and the inorganic filler, and enhance the flexural strength of the composite material through physical cross-linking points; at the same time, the high specific surface area of ​​carbon black is conducive to adsorbing resin molecules, reducing the fluidity of the resin, and reducing resin loss during the molding process.

[0012] (3) The raw materials of the present invention are inexpensive, the process is simple and controllable, and the resulting bipolar plates have excellent comprehensive performance, making them suitable for large-scale application of all vanadium redox flow batteries. Attached Figure Description

[0013] Figure 1 This is a comparison of the in-plane conductivity of the composite bipolar plates prepared in this invention with different carbon black addition amounts. Figure 2This is a comparison of the resistivity of the composite bipolar plates prepared according to the present invention with different carbon black addition amounts; Figure 3 This is a comparison diagram of the bending strength of the composite bipolar plates prepared according to different carbon black addition amounts in this invention; Figure 4 This is a cross-sectional SEM image of the composite bipolar plate prepared by the present invention with a carbon black addition of 4%. Detailed Implementation

[0014] The invention will be described in detail below through specific examples: Weigh out 10g of flake graphite (75μm), carbon black (30nm), and 2130 phenolic resin according to the specified mass ratio. Add an appropriate amount of anhydrous ethanol and stir magnetically at room temperature for 1 hour until a paste is formed. Fill the paste into a mold, place it on a flat vulcanizing machine, and hot-press it at 200℃ and 80 kN for 2 hours. After cooling with the mold, demold to obtain a composite bipolar plate. The in-plane conductivity is 161 S / cm, and the flexural strength is 46 MPa.

[0015] like Figure 1 As shown, when the phenolic resin content is fixed at 25%, the in-plane conductivity of the bipolar plate initially increases and then slightly decreases as the carbon black addition increases from 1% to 5%. When the carbon black addition is 4%, the conductivity increases to 161 S / cm. This is because the carbon black nanoparticles fill the spaces between the flake graphite layers, increasing the conductive contact points and forming a more complete "point-to-surface" conductive network. When the carbon black addition exceeds 7%, the carbon black particles locally agglomerate, which disrupts the uniformity of the conductive network, leading to a decrease in conductivity. Higher conductivity is beneficial for reducing the ohmic polarization of the bipolar plate and improving the energy efficiency of the battery.

[0016] like Figure 2 As shown, the resistivity of the bipolar plate gradually decreases with increasing carbon black content. In particular, the resistivity decreases rapidly as the carbon black content increases from 1% to 4%. Lower resistivity helps reduce the ohmic internal resistance of the battery, thereby improving battery performance. Therefore, a carbon black content of around 4% is ideal. When the carbon black content exceeds 4%, the resistivity increases slightly. This may be because excessive carbon black content leads to localized agglomeration in the resin matrix, disrupting the uniform conductive network structure and thus slightly increasing the resistivity. Considering both conductivity and manufacturing cost, the preferred carbon black content is 3%–5%, and more preferably 4%.

[0017] like Figure 3As shown, the flexural strength of the bipolar plate initially increases slightly and then gradually decreases as the carbon black content increases from 0 to 10%. When the carbon black content is 7%, the flexural strength is 46 MPa. An appropriate amount of carbon black can enhance the interfacial bonding between the resin and graphite, but excessive carbon black weakens the continuity of the resin matrix, leading to a decrease in mechanical properties. Higher flexural strength is beneficial for ensuring the stability of the fuel cell stack assembly and its long-term operational reliability.

[0018] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the bipolar plate with the best performance of this invention. As can be seen from the image, the cross-section is generally flat and dense, with no obvious pores, cracks, or filler debonding defects, indicating good interfacial bonding between the resin, graphite, and carbon black. This microstructure endows the bipolar plate with excellent electrical conductivity and synergistic improvement in flexural strength.

[0019] In summary, by optimizing the molding process based on the curing kinetics analysis results and adding 1% to 10% carbon black as a second filler to a high-content flake graphite (>70%) system, the in-plane conductivity and flexural strength of the composite bipolar plate can be significantly improved, achieving synergistic optimization of electrical conductivity and mechanical properties.

[0020] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A composite bipolar plate for an all-vanadium redox flow battery, characterized in that: This bipolar plate uses thermoplastic phenolic resin as the matrix, high-content natural flake graphite as the main conductive filler, and carbon black as the second conductive filler.

2. The composite bipolar plate as described in claim 1, characterized in that: The flake graphite accounts for 70% to 75% of the mass, the carbon black accounts for 1% to 5% of the mass, and the phenolic resin accounts for 25%.

3. The composite bipolar plate as described in claim 1, characterized in that: The thermoplastic phenolic resin is 2130 phenolic resin.

4. The composite bipolar plate as described in claim 1, characterized in that: The flake graphite has a particle size of 75 μm and a fixed carbon content of ≥ 99%; the carbon black has a particle size of 20 nm to 50 nm and a specific surface area of ​​100 to 300 m² / g.

5. The composite bipolar plate as described in claim 1, characterized in that: The composite bipolar plate has a thickness of 2–4 mm, an in-plane conductivity ≥150 S / cm, and a bending strength ≥40 MPa.

6. The composite bipolar plate as described in claim 1, wherein the molding process parameters are: molding temperature 200℃, molding pressure 80 kN, and molding time 2 h.

7. The preparation method according to claim 6, characterized in that: Weigh out the flake graphite, carbon black and resin powder according to the mass ratio, add anhydrous ethanol, stir at room temperature until a paste is formed, and then fill it into a mold for hot pressing.

8. An application of the composite bipolar plate according to any one of claims 1-7, characterized in that: The composite bipolar plate is used as the bipolar plate in a vanadium redox flow battery.

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