KONTIFLEX: Mass production of graphite bipolar plates

In the “KONTIFLEX“ project, the weldable, flexible polymer bipolar plates already developed by Fraunhofer UMSICHT for flow batteries are being further developed for use in LT-PEM (low-temperature polymer electrolyte membrane fuel cells). As part of this, the manufacturing process is to be transferred from the laboratory plant to large-scale roll-to-roll production. SAUERESSIG GmbH + Co KG supports the implementation of the production process on an industrial scale with its expertise as an alliance partner in order to tap into the cost-reduction potential of a large-scale production process over the medium term. For the first time, the aim is to enable the continuous production of thin, highly filled graphite plates with integrated complex structures and to develop, test, and implement continuous production. In addition, the bipolar plate for high-temperature PEM will be upgraded through the use of new plastic mixtures.

Challenges

As alternative, hydrogen-based energy converters, fuel cells offer a wide range of applications in stationary and mobile applications – but the investment costs are still very high. Bipolar plates are a major component of fuel cell stacks. They separate the reaction gases and cooling media from each other and distribute them to the corresponding fuel cell reaction area. Bipolar plates must have good electrical and thermal conductivity and be robust against chemical influences and high mechanical contact pressures in the cell. In addition, they should be coolable and as thin as possible. High requirements, but also high costs: Bipolar plates account for about a quarter of stack costs.

The technology already developed by Fraunhofer UMSICHT for the continuous production of graphite-plastic composites enables roll-to-roll processing as well as the direct use of powdery starting materials. In contrast to conventional processes, processing is extremely gentle on the material, enabling a thermoplastic-based plastic compound that can be welded.

New, cost-effective design

The bipolar plates can be bonded firmly to each other and with other joining partners, are very flexible and thus open up completely new design possibilities for fuel cells. Since the bipolar plates can be welded directly to other elements, sealing surfaces can be almost completely dispensed with. Due to the smaller number of components and the new flexibility, stack construction is also simpler and safer, more compact, and considerably less expensive due to effective assembling.

From laboratory to large-scale production

The transfer of this process from the laboratory plant to large-scale production makes it possible for the first time to demonstrate continuous production of thin, highly filled bipolar plates and to further develop the technology as a cost-effective component for further applications.

The new production plant is currently in test operation. As part of the project, Fraunhofer UMSICHT researchers developed and produced a 3.2 m² bipolar plate together with SAUERESSIG GmbH + Co KG. The plate is so far unique in terms of its size.

SAUERESSIG GmbH + Co. KG