New design reduces costs for bipolar plates
Redox flow batteries have a relatively complex structure and are prone to error. Researchers have therefore now integrated a bipolar plate directly into a stack. This saves on components and at the same time reduces costs. In addition, it makes the system easier to assemble and more reliable.
Vanadium redox flow batteries store electrical energy in suitable electrolyte solutions and are ideal for applications with a high capacity to power ratio, such as the intermediate storage of electrical energy from solar and wind energy systems. The central component of redox flow batteries is the bipolar plate. Until now graphite plates have been used, which are connected to a separate plastic frame. This frame not only ensures that the stack remains stable and tight but also guarantees the media flow to the cathode and anode. This structure, however, is relatively complex and prone to errors. Only with a precision-fit assembly can leaks be avoided later. The different thermal expansion of the materials used can also cause problems.
The Redox Flow Plate research project was therefore aimed at developing an integrated plate where the bipolar plate and frame are made from a single material or are integrated into a single component. This is intended to simplify the assembly, reduce the number of components and thus make the system more reliable and cheaper.
Quick and error-free production
When assembling the stack, a time-consuming and error-prone production step is the assembly of the membrane and electron unit, the seals and the bipolar plate. “Here it is extremely important that the components are precisely assembled to prevent leaks occurring during the subsequent operation,” explains Project Manager Thorsten Hickmann and adds: “Integrating a mono- or bipolar plate in a plastic frame has the advantage that this assembly step is greatly simplified.” The scientists have furnished the plate frame with a guide. This enables several plates to be quickly and precisely fixed together using a bolt. In addition, channel structures integrated in the frame increase the efficiency in battery mode. The more even distribution of the electrolytic liquid on the bipolar plate surface reduces unwanted short circuits.
Bipolar plates in redox flow battery systems are expensive. Another aspect of the research was therefore concerned with reducing costs. “Only then will the newly developed design be able to compete on the market,” explains the Project Manager.
“During our tests, the injection moulding process proved to be the most promising method for producing bipolar plates with integrated seals in one piece,” says Hickmann. Because only one part is manufactured in a single piece and the gasket is integrated, fewer components are needed. Even complex structures can be produced in this way. The researchers believe that this will make a decisive contribution to reducing costs.