Electrochemical Impedance Spectroscopy (EIS) is a widely-used measurement technique to analyse properties of Lithium-Ion Batteries, since impedance spectra are sensitive to changes of battery parameters like surface layer thicknesses, material conductivities and reaction rate constants. Physico-chemical models of Lithium-ion batteries are a useful tool to correlate changes of measured impedance spectra to changes of Lithium-ion battery parameters. We will present a model based on the work of Doyle and Newman [1] extended with double layers and aging processes to simulate EIS during degradation of a Lithium-ion battery. The model has been used to simulate impedance spectra and to fit them to measured impedance spectra with a linear least square fitting tool.

Within this study, we provide fits of a physico-chemical battery model to cycle aged cell EIS measurements. Achieving reliable results is only possible if measured and simulated impedance spectra meet linearity, causality and stationarity requirements for EIS. Various ageing induced changes in the charge distributions at the anode surface interphases have been assumed and compared under the preconditions mentioned above. These ageing model approaches differ in their passivated specific surface area for reactions and double layers. Each of these ageing models aim to describe the effect of the Solid Electrolyte Interphase (SEI) on the impedance spectrum during cyclical ageing. It is assumed that the aging model providing the best possible agreement between simulation and experiment for all spectra of a cycled Lithium-ion battery is also the best approximation of the real physical behavior. We will show that the SEI influences the reaction and the double layer at the anode/SEI interphase as well as the reaction at the SEI/electrolyte interphase. Figure 1 shows a good agreement between experiment and simulation results for the assumed aging model. Relative deviations between measurements and simulations, e.g. in the second semicircle, can be reduced to 10^-6.

References:

[1] M. Doyle, T.F. Fuller, J. Newman, J. Electrochem. Soc. 140 (1993) 1526