When producing electrodes for batteries, electrode material in the form of a thin paste is applied to a copper or aluminum foil in a rectangular pattern. The pattern is interrupted by short sections of uncoated foil, which are needed for electron discharge. To produce these sections, the coating process has to be interrupted and restarted repeatedly. A special challenge consists in producing sharp edges without smearing of material at maximum production speeds. Because, smallest production errors make battery cells unusable. Due to the high reject rate and the low throughput, lithium-ion batteries today are more expensive than actually necessary.
The Karlsruhe Institute of Technology (KIT) has now succeeded in making decisive progress. The nozzle for the electrode material was optimized and equipped with an oscillating membrane that cyclically stops and restarts the application of the coating paste. Advantage: »This membrane is much lighter than mechanical valves, as a result of which quick reaction times and high speeds can be reached«, Doctoral researcher Ralf Diehm says. »So far, manufacturing speeds have been limited to about 30 to 40 meters per minute. With the new technology, we reach up to 150 meters per minute in electrode coating.« Absence of some formerly used mechanical components in the nozzle does not only increase production speed, it also results in other advantages in electrode production: as the membrane can be controlled more precisely than mechanical valves, production quality is improved and the reject rate is reduced. The technology will now be developed to industrial maturity by a spinoff.
Quicker Drying necessary
For entire battery production to profit from quicker electrode coating, the production process has to be readjusted at another point. Quicker coating requires shorter drying times. Otherwise, the drying section and, hence, the complete plant would have to be enlarged. Based on studies of different drying conditions, the drying process has already been optimized in a knowledge-based way. As a result, drying time was reduced by about 40 per cent with electrode properties being maintained. Within the ProZell II Research Cluster funded by the Federal Ministry of Education and Research (BMBF), this work is now planned to be continued in cooperation with partners from Technische Universität Braunschweig and the Center for Solar Energy and Hydrogen Research Baden-Württemberg.
Electrode production at a record speed and high production quality considerably reduces costs of cell production. On a typical production line, electrodes can be produced for three times as many battery cells, thus meeting the growing need for electric mobility. TFT develops its technologies for electrode production and for future new material systems as part of the Center for Electrochemical Energy Storage Ulm & Karlsruhe. New findings relating to production technology will also be incorporated directly in the Post Lithium Storage Cluster of Excellence, within which KIT develops batteries for the future together with Ulm University.