Faster, higher quality and more efficient: a new coating process is set to optimise the production of battery electrodes. This will ultimately lower the costs of battery production as a whole.
With their new coating process, researchers at the Karlsruhe Institute of Technology (KIT) have succeeded in producing electrodes for lithium-ion batteries at what they claim is a record speed. The new process also improves the quality of electrodes and reduces production costs.
To achieve this, the scientists took a very close look at the electrode coating. Until now, manufacturers of battery electrodes have applied the electrode material in the form of a thin paste on a copper or aluminium foil in a rectangular pattern. This pattern is interrupted by short sections of uncoated foil, which are vital for electron discharge. To produce these sections, the coating process has to be repeatedly interrupted and restarted. A particular challenge consists in producing sharp edges without smearing the material, all while maintaining very high production speeds. "Precision of electrode coating is an essential factor for efficiency and costs of battery cell production,” says Professor Wilhelm Schabel from the Institute of Thermal Process Engineering – Thin Film Technology (TVT-TFT), who is responsible for research into this field at KIT.
Faster coating by membrane nozzle
Doctoral researcher Ralf Diehm, who works in Schabel’s team, has now succeeded in making decisive progress. He 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. “This membrane is much lighter than mechanical valves, as a result of which quick reaction times and high speeds can be reached,” explains Diehm.
“So far, manufacturing speeds have been limited to about 30 to 40 metres per minute. With the new technology, we reach up to 150 metres per minute in electrode coating.” Another advantage is that since the membrane can be controlled more precisely than mechanical valves, production quality is improved and the reject rate is reduced. On a typical production line, electrodes can be produced for three times as many battery cells, therefore helping to meet growing demand for electric mobility.
Optimising the drying process
For battery production as a whole to benefit from faster electrode coating, the production process also has to be adapted elsewhere, however, because faster coating demands shorter drying times. Otherwise, the drying section and therefore the entire plant would have to be enlarged. So KIT carried out fundamental research on different drying conditions and applied this knowledge to optimise the drying process. The result is a drying time that is about 40% shorter, with no adverse impact on electrode properties. The technology will now be developed and readied for industrial production by a spin-off established by Ralf Diehm and his team.