Flow channel integrated carbon fiber bipolar plate for flow battery as well as preparation method and application of flow channel integrated carbon fiber bipolar plate
By impregnating carbon fiber woven fabric with a mixture of conductive materials and resin, an integrated carbon fiber bipolar plate with a flow channel was prepared. This solved the problems of the contradiction between conductivity and mechanical properties, high contact resistance, and simple flow channel design in flow batteries, thus improving battery performance and production efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- THREE GORGES NEW ENERGY JIMUSAR POWER GENERATION CO LTD
- Filing Date
- 2026-01-14
- Publication Date
- 2026-05-19
AI Technical Summary
Existing flow battery bipolar plates suffer from problems such as a contradiction between conductivity and mechanical properties, high contact resistance, simple flow channel design, and complex manufacturing process, resulting in high internal resistance, low energy conversion efficiency, and difficulty in large-scale production.
The process involves impregnating a mixture of carbon fiber woven fabric, conductive materials, and resin, and then directly forming an integrated carbon fiber bipolar plate in the flow channel mold through a molding process. Combined with an irregular flow field structure, this solves the requirements for conductivity, corrosion resistance, and mechanical strength.
It achieves low contact resistance, good electrolyte distribution and mechanical stability, improves battery voltage efficiency and production efficiency, and reduces production costs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of flow battery technology, and relates to an integrated carbon fiber bipolar plate for flow batteries, its preparation method and application. Background Technology
[0002] Traditional bipolar plate materials for flow batteries mainly include graphite, metals, and carbon-plastic composites. While graphite bipolar plates possess excellent conductivity and corrosion resistance, their high brittleness and processing costs make them unsuitable for large-scale production. Metal bipolar plates, while exhibiting good conductivity, suffer from poor corrosion resistance, particularly in highly oxidizing and reducing electrolytes, leading to shortened battery life. Carbon-plastic composite bipolar plates, made by combining conductive carbon materials (such as graphite, carbon black, and carbon fiber) with polymer resins (such as polyethylene and polypropylene), offer advantages such as low cost, high mechanical strength, and good corrosion resistance. However, bipolar plates prepared using current processes still suffer from insufficient conductivity and high contact resistance with the electrodes, resulting in high internal resistance and limited energy conversion efficiency.
[0003] To address these issues, researchers have attempted to improve the overall performance of bipolar plates by optimizing the material system and structural design. For example, using nano-conductive fillers such as carbon nanotubes and graphene in combination with polymer resins can significantly improve the conductivity of bipolar plates; fabricating bipolar plates with flow channel structures through molding or extrusion molding processes can optimize electrolyte distribution and reduce flow resistance. However, existing technologies still have the following shortcomings: 1. Conflict between conductivity and mechanical properties: Although the addition of highly conductive fillers can reduce the bulk resistance, it can easily lead to increased material brittleness and affect the mechanical stability of the bipolar plate. 2. High contact resistance: The contact resistance between the bipolar plates and the electrodes accounts for a large proportion of the battery's internal resistance, and existing processes make it difficult to achieve a tight bond between the two. 3. Simple flow channel design: Traditional flow channel structures have limited effect on optimizing electrolyte distribution, which can easily lead to uneven local reactions and affect battery performance; 4. Complex preparation process: Some processes involve multiple steps or high temperature and high pressure conditions, which increases production costs and makes it difficult to achieve large-scale application.
[0004] The bipolar plate described in patent CN 116565244 A is located between a first carbon felt and a second carbon felt. Grooves are formed on the surface of the bipolar plate that contact the first and second carbon felts, and these grooves are filled with an adhesive. Fibers extending outward from the grooves are also present within the grooves, forming a fiber layer on the surface of the flocked bipolar plate. This fiber layer serves as the contact surface with the carbon felt, significantly increasing the friction between them. After 5000 charge-discharge cycles within the fuel cell stack, the carbon felt did not slip or shift, and the contact resistance between the carbon felt and the bipolar plate is also reduced. However, the bipolar plate is not treated as a single unit. In highly corrosive systems, if the flocked material falls off during long-term cycling, the risk of fuel cell blockage increases.
[0005] CN 109732943 A patent describes a method for preparing a bipolar plate for a fuel cell. This involves mixing multiple layers of woven carbon fiber with resin powder, allowing the resin to uniformly fill the pores between the carbon fibers. The resin-mixed woven carbon fiber layer is then placed in a mold for curing to obtain a carbon fiber preform. The carbon fiber preform is then polished and shaped to form airflow channels, cooling channels, and hydrogen flow channels. Compared to the flow field design of fuel cells, the bipolar plate of a flow battery is much larger, with flow field depth and ridge width approximately 3-5 times that of a fuel cell. Therefore, post-processing is not conducive to mass production, and it also damages the appearance of the bipolar plate, increasing the contact area with the electrolyte and making electrochemical corrosion more likely. Although this patent addresses the air permeability problem of the bipolar plate, the increased resin content actually reduces the conductivity. Summary of the Invention
[0006] Most bipolar plates used in existing flow cell stacks are flat, directly contacting the electrodes. This results in poor electrolyte distribution consistency, increased concentration polarization at the stack inlet and outlet, leading to reduced energy efficiency and low electrode utilization. Increasing flow field design improves efficiency; an integrated design is superior to a separate design, primarily by eliminating interfacial resistance between different materials, reducing assembly difficulty, and improving production efficiency. Traditional molding processes are demanding in material selection; therefore, a carbon fiber reinforced structure is used, employing impregnation molding to achieve integrated molding. This ensures both bipolar plate consistency and allows for the design of irregular flow field structures.
[0007] To develop bipolar plates for flow batteries that simultaneously possess certain conductivity, resistance to electrolyte corrosion, and high mechanical strength, this invention provides an integrated carbon fiber bipolar plate for flow batteries, its preparation method, and its application. This method effectively solves the difficulties in the integrated molding process for synthesized bipolar plates.
[0008] The technical solution of this invention is as follows: An integrated carbon fiber bipolar plate for flow batteries is provided. The bipolar plate is first made by impregnating carbon fiber woven fabric with a liquid resin containing conductive material, transferring the carbon fiber fabric to a flow channel mold, and then curing it to obtain the integrated bipolar plate.
[0009] The integrated carbon fiber bipolar plate of the flow battery is an assembly of bipolar plate and flow channel. The bipolar plate with different flow channel forms is directly formed by hot pressing and curing in a mold. The carbon fiber woven fabric can be selected from different woven filaments such as 1K, 3K, 12K, 48K or pre-oxidized filaments to weave carbon cloth, with plain weave or twill weave process.
[0010] The conductive material is one or more of the following: expanded graphite, natural graphite, flake graphite, microcrystalline graphite, artificial graphite, graphene, conductive carbon black, and mesophase carbon microspheres.
[0011] The resin material is one or more of phenolic resin, epoxy resin, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride, polyphenylene sulfide, and acrylic resin.
[0012] The thickness of the integrated flow channel substrate is 0.5~1.0mm, the flow channel depth is 1.0~2.5mm, and the flow channel width is 0.5~1.0mm.
[0013] A method for preparing an integrated carbon fiber bipolar plate for a flow battery includes the following steps: (1) The conductive material and the resin material are mechanically mixed under vacuum conditions to obtain mixture A, wherein the proportion of conductive material in the total mass fluctuates between 40% and 60%. (2) The carbon fiber material is woven to obtain carbon fiber cloth B, with a thickness of about 5~8 mm and a bulk density of about 1.4~1.6 g / cm³. 3 ; (3) Immerse B in mixture A, and spread the liquid onto carbon fiber cloth under vacuum to obtain C; (4) Transfer C to a mold with a flow field and cure it at 120-140°C under a pressure of 10-20 MPa to obtain the final bipolar plate product.
[0014] Furthermore, the temperature for mechanical mixing is 40~60℃, and the stirring time is 20~40min.
[0015] Furthermore, the inert gas used for mechanical mixing is N2, and the vacuum pressure only needs to reach 0.1 MPa.
[0016] Furthermore, the finished bipolar plate has a ridge-to-groove or ridge-to-ridge structure.
[0017] An application of an integrated carbon fiber bipolar plate for flow batteries, used in vanadium redox flow batteries, zinc-bromine flow batteries, zinc-nickel flow batteries, lead flow batteries, and iron-chromium flow batteries, serves as a current collector in the battery material, responsible for the collection and transfer of electrons.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a composite bipolar plate for flow batteries and its preparation method. Due to the addition of carbon fiber, it is similar to the electrode material in flow batteries. The contact between carbon fibers reduces the contact resistance between the two components in the stack and improves the voltage efficiency. (2) The bipolar plate for flow batteries prepared in this invention uses carbon fiber cloth as the substrate, which is easy to shape and adapt to different flow field molds, solving the problem of traditional materials being difficult to shape and demold, and enabling the development of more irregular flow fields. (3) Impregnation with a liquid mixture of resin and conductive material ensures the air permeability of the bipolar plate after the holes are plugged, and the conductive material contained in the resin and the carbon fiber form more conductive paths, thus ensuring the conductivity of the bipolar plate. Detailed Implementation
[0019] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0020] The embodiment and the comparative sample have the same flow channel width, ridge width, flow field depth, etc. The only difference in flow field structure is that the ridge is to the groove and the ridge is to the ridge. It is directly molded into one piece, and the sample is a single cell with a length, width and thickness of about 150*120*2mm.
[0021] Example 1 (1) Natural graphite and acrylic modified fluororesin were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, in which the mass ratio of conductive material to resin material was 40:60. (2) 1K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 5mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and cure it at 120°C under a pressure of 15MPa to obtain the final bipolar plate product.
[0022] Example 2 (1) A mixture of natural graphite and artificial graphite (mass fraction ratio of 2:1) and a mixture of phenolic resin and epoxy resin (mass fraction ratio of 1:1) are mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, wherein the mass fraction ratio of conductive material to resin material is 50:50. (2) 3K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 7mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge to ridge structure), and cure it at 120°C under a pressure of 18MPa to obtain the final bipolar plate product.
[0023] Example 3 (1) A mixture of graphene and artificial graphite (mass fraction ratio of 2:1) and a mixture of acrylic monomer and epoxy modified (mass fraction ratio of 1:1) were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, wherein the mass fraction ratio of conductive material to resin material was 50:50. (2) 3K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 5mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and perform curing treatment at 120°C under a pressure of 20MPa to obtain the final bipolar plate product.
[0024] Example 4 (1) A mixture of graphene and conductive carbon black (mass fraction ratio of 2:1) and acrylic modified fluororesin were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, with the mass fraction ratio of conductive material to resin material being 40:60. (2) 3K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 8mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and perform curing treatment at 120°C under a pressure of 20MPa to obtain the final bipolar plate product.
[0025] Example 5 (1) Graphene and acrylic modified fluororesin were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, in which the mass ratio of conductive material to resin material was 40:60. (2) The pre-oxidized filaments are woven into a plain weave carbon fiber cloth with a thickness of about 5 mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and perform curing treatment at 120°C under a pressure of 20MPa to obtain the final bipolar plate product.
[0026] Comparative Example 1 (1) Expanded graphite worms and acrylic modified fluororesin were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, with the mass ratio of conductive material to resin material being 50:50. (2) 1K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 5mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and perform curing treatment at 120°C under a pressure of 20MPa to obtain the final bipolar plate product.
[0027] Comparative Example 2 (1) Natural graphite and acrylic modified fluororesin were mechanically mixed under vacuum and stirred at 50°C for 30 min until homogeneous to obtain mixture A, with the mass ratio of conductive material to resin material being 40:50. (2) 1K carbon fiber bundles are woven into plain weave carbon fiber cloth with a thickness of about 5mm to obtain B; (3) Impregnate B in mixture A, and spread the liquid onto the carbon fiber cloth under a vacuum of 0.1 MPa to obtain C; (4) Transfer C to a mold with a flow field (ridge-to-groove structure), and cure it at 180°C under a pressure of 20MPa to obtain the final bipolar plate product.
[0028] Comparative Example 3 (1) The ridge-to-ridge structure in the same embodiment is consistent (the ridge-to-groove structure is difficult to demold and the groove has low strength and is easily broken). Bipolar plates that can be integrally molded are purchased from commercial manufacturers for testing. Flake graphite, artificial graphite and PVDF resin are mechanically mixed and hot-pressed in a mold.
[0029] Table 1 Performance data of the bipolar plates prepared in the examples The compression ratio of a single cell is 25%. When two cells are assembled, the battery pack operates at 200 mA / cm². 2 Constant current charge-discharge tests were conducted, and the overall efficiency of the two sections was recorded for comparison (vanadium concentration 2 mol, ion-exchange membrane Nafion 212, carbon felt 4.35 mm). Table 1 shows that the bipolar plate prepared by the method of this invention has high voltage efficiency. Comparative Example 1 illustrates the poor uniformity of the conductive material dispersion (the body density of the expanded graphite worms is approximately 0.02~0.2 g / cm³). 3 Meanwhile, its expanded particle size is relatively large (approximately 100-200 micrometers), making it difficult to disperse in liquid resin, resulting in poor bipolar plate molding. Comparative Example 2 illustrates that excessively high curing temperatures damage the mechanical strength of the molded bipolar plate, reduce the contact between materials, and decrease electrical performance. Comparative Example 3 currently only produces ridge-to-ridge structures for purchased bipolar plates. Ridge-to-groove structures, due to their thicker bipolar plates, have a larger conductive path, resulting in some loss of electrical efficiency and increased raw material costs. If a ridge-to-groove structure is used, the groove area is thinner after molding and curing, leading to lower mechanical strength and making mass production difficult.
[0030] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A flow channel integrated carbon fiber bipolar plate for flow batteries, characterized in that, The bipolar plate and flow channel are integrally molded. The bipolar plate with different flow channels is directly formed by hot pressing and curing the molding material in the mold. The molding material is carbon fiber cloth impregnated with liquid resin containing conductive material.
2. The integrated carbon fiber bipolar plate for flow batteries according to claim 1, characterized in that, The carbon fiber cloth is made of different woven filament bundles or pre-oxidized filaments, using plain weave or twill weave processes.
3. The integrated carbon fiber bipolar plate for flow batteries according to claim 1, characterized in that, The conductive material is one or more of the following: expanded graphite, natural graphite, flake graphite, microcrystalline graphite, artificial graphite, graphene, conductive carbon black, and mesophase carbon microspheres.
4. The integrated carbon fiber bipolar plate for flow batteries according to claim 1, characterized in that, The resin material is one or more of phenolic resin, epoxy resin, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride, polyphenylene sulfide, and acrylic resin.
5. The integrated carbon fiber bipolar plate for flow batteries according to claim 1, characterized in that, The integrated carbon fiber bipolar plate has a thickness of 0.5~1.0mm, a flow channel depth of 1.0~2.5mm, and a flow channel width of 0.5~1.0mm.
6. A method for preparing an integrated carbon fiber bipolar plate for a flow battery, characterized in that, Includes the following steps: (1) The conductive material and the resin material are mixed to obtain mixture A, wherein the proportion of conductive material in the total mass fluctuates between 40% and 60%. (2) The carbon fiber material is woven to obtain carbon fiber cloth B, with a thickness of about 5~8 mm and a bulk density of about 1.4~1.6 g / cm³. 3 ; (3) Immerse B in mixture A, and spread the liquid onto carbon fiber cloth under vacuum to obtain C; (4) Transfer C to a mold with a flow field and cure it at 120-140°C under a pressure of 10-20 MPa to obtain the final bipolar plate product.
7. The method for preparing an integrated carbon fiber bipolar plate for a flow battery according to claim 6, characterized in that, The mixing temperature in step (1) is 40~60℃ and the stirring time is 20~40min.
8. The method for preparing an integrated carbon fiber bipolar plate for a flow battery according to claim 6, characterized in that, The inert gas used in step (1) is N2, and the vacuum pressure can reach 0.1 MPa.
9. The method for preparing an integrated carbon fiber bipolar plate for a flow battery according to claim 6, characterized in that, In step (4), the finished bipolar plate is a ridge-to-groove or ridge-to-ridge structure.
10. An application of an integrated carbon fiber bipolar plate for a flow battery, characterized in that, Integrated carbon fiber bipolar plates are used in vanadium redox flow batteries, zinc-bromine flow batteries, zinc-nickel flow batteries, lead flow batteries, and iron-chromium flow batteries.