Impedance spectroscopy of battery cells: Theory versus experiment

Abstract

Electrochemical impedance spectroscopy (EIS) is an accurate electrochemical method able to identify various electrochemical steps that occur in complex electrochemical systems such as battery cells. In order to extract the maximum information from given battery system, systematic experiments that combine EIS with other (complementary) techniques are needed, as reported occasionally in the recent literature. Additionally, a proper quantitative evaluation of measured spectra has to be based on physical models which, however, tend to be quite elaborate and frequently less accessible to the wide battery community. In various cases of practical interest, however, the models can be simplified as shown in this review. One level of simplification reduces the full solution to the well-known de Levie model and is frequently used for description of the effects of porous electrodes. The ultimate level of simplification, in turn, leads to a Randles-like equivalent circuit for each insertion electrode and a pure resistor for the electrolyte phase in separator. This review shows that care has to be taken when using these simplifications in order to keep the analysis consistent and physically sound.