When manufacturing electrodes for batteries, electrode material is applied as a thin paste in a rectangular pattern to a copper or aluminum foil. The pattern is interrupted by short sections of uncoated foil, which are essential to conduct away the electrical current. For these sections, the coating process must be interrupted and restarted again and again. A particular challenge is to enable sharp edges without smearing the material at very high production speeds. Precision is the key to electrode coating: even small production errors render battery cells unusable. “Due to the high reject rate and low throughput, lithium-ion batteries are now more expensive than they should be,” says Professor Wilhelm Schabel of KIT.
Doctoral student Ralf Diehm in Schabel’s research group has now achieved a decisive further development. He equipped the nozzle for the electrode material with a vibrating membrane that cyclically stops and restarts the application of the coating paste. “Since this membrane is much lighter than mechanical valves, very fast reaction times and thus high speeds are possible,” explains Diehm. “Previously, the manufacturing process was limited to speeds of about 30 to 40 meters per minute. With the new technology we can achieve up to 150 meters per minute for electrode coating.
In addition to a higher production speed, the elimination of mechanical parts in the application nozzle has further advantages for electrode production: Because the membrane can be controlled much more precisely than mechanical valves, production quality improves and rejects are reduced. The technology will now be transferred from the laboratory to industrial production as part of a spin-off by Ralf Diehm and his team.
Dr. Philip Scharfer, who is doing research at KIT together with Professor Schabel, explains that the production process also has to be readjusted elsewhere in order for battery production to benefit from faster electrode coating. “A faster coating requires shorter drying times. Otherwise, the dryer section and thus the entire system would have to be enlarged accordingly”. On the basis of fundamental investigations of different drying conditions, the KIT has already been able to optimize the drying process based on knowledge, which reduces the drying time by about 40 percent while maintaining the same electrode properties. In the ProZell II research cluster funded by the German Ministry of Education and Research (BMBF), this work will now be continued together with partners from the Technical University of Braunschweig and the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Ulm.
More information: https://www.energy.kit.edu/index.php