Pilot-scale production of the bipolar electrode. Source: Photo Fraunhofer IKTSThe hundreds to thousands of separate battery cells muscled into electric vehicles occupy quite a lot of space. Each one is surrounded by a housing, connected to the car via terminals and cables, and monitored by sensors. The cells cannot be densely packed, and electrical resistances, which reduce the power, are generated at the connections of small-scale cells.

A spatial solution devised by Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden, Germany, and partners ThyssenKrupp System Engineering and IAV Automotive Engineering borrows the bipolar principle known from fuel cells and applies it to the lithium battery. In this approach, individual battery cells are not strung separately side-by-side in small sections, but instead are stacked directly one above the other across a large area. The entire structure for the housing and the contacting is therefore eliminated and more batteries can be installed.

With the direct connection of cells in the stack, the current flows over the entire surface of the battery, considerably reducing electrical resistance. The battery electrodes are designed to release and absorb energy very quickly.

"With our new packaging concept, we hope to increase the range of electric cars in the medium term up to 1000 kilometers [621 miles]," says Dr. Mareike Wolter, Project Manager at Fraunhofer IKTS.

The bipolar electrode is a metallic tape coated on both sides with ceramic storage materials; one side becomes the anode, the other the cathode. Ceramic materials used as powders are mixed with polymers and electrically conductive materials to form a suspension, which is applied to the tape in a roll-to-roll process.

The next planned step is the development of larger battery cells and their installation in electric cars, with initial vehicular tests by 2020.