Graphite-based Composite Bipolar Plates for Flow Batteries

Flow battery is considered a promising technology for large-scale energy storage, because of its high safety, long service life, and scalability. It can assist the power grid in peak shaving and energy storage, which will help to improve the energy utilization. Bipolar plate is a key component in a flow battery, which can separate single cells, connect the adjacent electrodes in series, help to conduct electric current and provide structural support for the stack. However, the cost of bipolar plate accounts for a big proportion of the total stack cost. It is of great significance to develop high-performance and low-cost bipolar plates, which will significantly accelerate the commercialization of flow batteries. Thus, its development has become an urgent need in the flow battery industry. Although much work related to the development of bipolar plates has been carried out, there is still lack of ideal bipolar plate products in the market, taking both their performance and cost into consideration. This article focuses on the introduction of current research status on graphite-based composite bipolar plates for flow batteries and the influence of material selection and processing techniques on the performance of bipolar plates, including electrical conductivity, mechanical strength, barrier properties, and corrosion resistance. Based on the review, some suggestions are made for the further developments of bipolar plates for flow batteries.

Graphite-based composite bipolar plates have the advantages of low density and good corrosion resistance, which have great development potential and will have a significant impact on the large-scale application of liquid flow batteries. In this paper, the research progress of graphite-based composite bipolar plates in recent years is introduced from the performance and economic needs of bipolar plates. In terms of material selection, many researches start from the nature of the resin matrix itself, targeted to make up for the shortcomings in performance, and a variety of secondary fillers (carbon black, carbon nanotubes, carbon fibers, graphene, etc.) are compared or even used in combination. In terms of preparation process, some researches have been carried out on the mixing method of materials, molding parameters, process optimization, etc. At the same time, some surface treatment methods have been proposed to remove the influence of resin-rich layer of composite bipolar plate and reduce the contact resistance. At present, the production cost of high-performance graphite-based composite bipolar plates is still high, and it is difficult to meet the needs of large-scale applications. The balance between performance, production efficiency and cost is the main problem that needs to be solved in the future of liquid flow battery bipolar plates. Commonly used molding method of high cost and low production rate; injection molding in the cost and production rate has certain advantages, but in the choice of material system has some limitations; impregnated graphite plate also exists in the high cost and long preparation time; compared with the previous processes, roll molding has the advantages of high productivity and low cost, but usually the resin has a lower content of carbon and insufficient performance. In the future, it is necessary to carry out innovative design on the material components of bipolar plates to develop graphite-based composite bipolar plates with low carbon content and high electrical conductivity, and at the same time, it is possible to utilize highly efficient production methods for large-scale production. In addition, graphite-based composite bipolar plate corrosion resistance and stability of the study is relatively limited, taking into account the liquid flow battery electrolyte often has a strong acidic and chemical corrosion, the future need to explore more in this area, especially on the non-graphite carbon materials and resins need to be further verified oxidation resistance and acid resistance. In the face of the above challenges, it is necessary to continue to study the new material system, further study of the synergistic effect of conductive fillers, adjust the components and preparation process to promote the formation and optimization of the conductive network, reduce the production cost of graphite-based composite bipolar plates under the premise of taking into account the performance and improve the production efficiency, so as to reduce the cost of energy storage in the liquid flow battery.