Measurement approaches for Thermal Impedance Spectroscopy of Li-ion batteries

This work introduces two novel measurement methods for capturing the thermal behaviour of Li-ion cells in the frequency domain. For the validation, we compare them to the state of the art measurement method, in which the battery is thermally stimulated by a set of discrete frequencies, each tested individually in a sequential manner. All experiments are conducted with a cylindrical 18650 LFP-Graphite cell and lead to similar thermal impedance spectra. We validate a 0-D thermal model fitted to the respective measurement results with a thermal step response in the time domain. The results show, that all three models accurately represent the thermal behaviour of a Li-ion cell, with a mean absolute error below 0.3 K on the validation test. A spider-web diagram classifies and compares the given methods based on five values showing, that the state of art thermal measurement time can be reduced by 62% while also increasing the impedance measurement resolution by measuring multiple frequencies simultaneously.