German Scientists Redesign Stack to Make Cheaper Redox Flow Batteries

Researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT, located in Germany, claim that thorough redesigning the stack, they have contrived a way to bring down production costs of redox flow batteries which are used to store renewable energy. As a result, Christian Doetsch and Lukas Kopietz from Fraunhofer UMSICHT and Dr. Thorsten Seipp from Volterion, who developed the new stack, have been awarded with the Joseph von Fraunhofer Prize by the institute.

Prof. Doetsch explains that the redesigned stack is 40 percent more cost-effective in terms of material costs. Additionally, the stack weighs 80 percent less than a conventional stack and is only about half the size. It is being marketed by the spin-off Volterion. The Joseph von Fraunhofer Prize jury commented on the scientists’ win by saying, “the spin-off and its successful exit from Fraunhofer, serve as a prototype for marketing new manufacturing technologies.” The stack has been developed with an electrically conductive plastic so that it remains flexible and can be welded.

The German researchers laid out the process of making the device as follows: Plastic in the form of pellets is cooled to temperatures as low as minus 80 degrees, then ground into powder and mixed with 80 percent graphite by weight. This powder is sent through a system comprising several rollers heated to different temperatures and moving at different speeds. The powder is briefly melted between the rollers at moderate temperatures and low pressures. It is then kneaded, rolled into an “endless sheet” and finally rolled up. Kopietz said, “This gives the new material thermoplastic properties, so it’s flexible and can be welded even though only 20 percent of it is plastic.” The resulting flexible material is said to have thermoplastic properties and to be easy to weld, due to which the stack uses neither gaskets nor screws- the cells are simply welded together.

Another reason why production costs are reduced is because the plates can be produced as an endless roll through a powder-to-roll process, which requires much less material. The scientists explain, “Very thin plates can be produced in this way. In the injection moulding process, the plate thickness is limited to several millimeters due to the production method, but in the powder-to-roll process it can be between 0.1 and 0.4 millimeters.” Consequently, light-weight and low-priced stacks can be produced.

Seipp said that this development opens up totally new possibilities in design, which have been implemented right through to the complete battery at Volterion. More than a thousand stacks have already been sold by Volterion.