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

"Abstract— 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
... mehr
microindenters are already used in current research to estimate
the relaxation behavior of battery electrodes. In order to reduce
scattering, a 5 mm² 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."