Indentation tests on battery electrodes to estimate the target gap of battery calenders

The increasing electrification of everyday life is largely based on lithium-ion batteries. Depending on the application, different requirements are placed on the batteries in terms of energy and power density. On the production side, these parameters are influenced in particular by the calendering process step. This is a rolling process in which coated and dried porous electrodes with elastoplastic material behavior are compacted to their target thickness. At present, the quantitative interactions between the calender gap, electrode and target thickness are still largely unknown, so that in practice the calender gap is set iteratively in the µm range. After each iteration, a tactile thickness measurement is usually carried out in order to adjust the actual electrode thickness to the target thickness. The setting of the calender gap as a significant factor influencing the electrode thickness is then based on empirical values.This work investigates whether it is possible to estimate the calender target gap on the basis of indentation tests in order to reduce the setting time of the target gap. Nano- and microindenters are already used in current research to estimate the relaxation behavior of battery electrodes. In order to reduce scattering, a 5 mm round indenter is used in this work for the mechanical characterization of the electrodes. Due to their industrial relevance, indentation tests are carried out on LFP cathodes and graphite-based anodes. A calender target gap for different target thicknesses is estimated from the indentation curves. Finally, to validate the approach for the LFP cathode and the graphite-based anode, the required calender gap is determined on a gap-controlled laboratory calendar to obtain a desired target thickness. The tests show that both the estimated and the real calender gap electrode thickness curve are linear. The current discrepancy between the estimated and real calender gap in the two-digit µm range is to be reduced in further work using an empirical correction value.