In current batteries, the housing and contacting structures occupy more than 50% of the volume, which means cells can’t be packed densely. Meanwhile, electrical resistance is found at the connections between the small-scale cells.
Rather than stringing battery cells side-by-side in small sections, the bipolar approach sees cells stacked one above the other across a large area. Built directly into the vehicle's chassis , the EMBATT bipolar battery is said to eliminate the housing and contacting structure. Through the direct connection of the cells in the stack, current flows over the entire surface of the battery, reducing electrical resistance ‘considerably’.
“With our new packaging concept, we hope to increase the range of electric cars in the medium term to 1000km,” said project manager Dr Mareike Wolter.
The bipolar electrode is a metallic tape coated on both sides with ceramic storage materials – one side becomes the anode, the other the cathode. The anode is currently made using lithium-titanate, while the cathode is a lithium nickel-manganese spinel. This arrangement is said to support high cell voltages and an energy density of 500Wh/l.
“We have used our expertise in ceramic technologies to design the electrodes in such a way that they need as little space as possible, save a lot of energy, are easy to manufacture and have a long life,” Dr Wolter noted.
Fraunhofer IKTS applies ceramics to the tape using a roll-to-roll process. “One of our core competencies is to adapt ceramic materials from the laboratory to a pilot scale and to reproduce them reliably,” said Dr Wolter.
The next step is the development of larger battery cells and their installation in electric cars, with initial tests planned in vehicles by 2020.
Working with IKTS in the EMBATT project are ThyssenKrupp System Engineering, which is manufacturing the batteries, and IAV Automotive Engineering, which is integrating them into electric vehicles.