Faster production for battery electrodes

Researchers from the Karlsruhe Institute of Technology (KIT) have produced electrodes for lithium-ion batteries at what they claim to be record speed, while also improving the quality of the electrodes and reducing production costs.

When producing electrodes for batteries, electrode material in the form of a thin paste is applied to a copper or aluminium 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. It is particularly challenging to produce sharp edges without smearing of material at high production speeds.

“Precision of electrode coating is an essential factor for efficiency and costs of battery cell production,” said Professor Wilhelm Schabel from KIT’s Institute of Thermal Process Engineering–Thin Film Technology (TVT-TFT), who is responsible for the research. “Even [the] 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.”

Doctoral researcher Ralf Diehm, who works in Prof Schabel’s team, has now optimised the nozzle for the electrode material and equipped it with an oscillating membrane that cyclically stops and restarts the application of the coating paste. Diem explained, “This membrane is much lighter than mechanical valves, as a result of which quick reaction times and high speeds can be reached. So far, manufacturing speeds have been limited to about 30–40 m/min. With the new technology, we reach up to 150 m/min in electrode coating.”

Absence of some formerly used mechanical components in the nozzle not only increases 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 established by Diehm and his team.

But in order for battery production to profit from quicker electrode coating, the production process has to be readjusted at another point, noted Dr Philip Scharfer, Head of the TFT group. He said, “Quicker coating requires shorter drying times. Otherwise, the drying section and hence the complete plant would have to be enlarged.”

Based on fundamental studies of different drying conditions, the drying process has now been optimised in a knowledge-based way. As a result, drying time was reduced by about 40% with electrode properties being maintained.

These breakthroughs have considerably reduced the cost of cell production, according to the researchers; on a typical production line, electrodes can be produced for three times as many battery cells, thus meeting the growing need for electric mobility. Further findings relating to production technology will be incorporated directly in the Post Lithium Storage (POLiS) Cluster of Excellence, within which KIT develops batteries for the future together with Ulm University.

Image caption: The new process considerably increases production capacity of battery electrodes. Image credit: Ralf Diehm, KIT.

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