A Distribution of Relaxation Time Approach on Equivalent Circuit Model Parameterization to Analyse Li-ion Battery Degradation

The time-varying and complex electrochemical behaviour inherent to Li-ion batteries cause a great challenge to its diagnostics and prognostics. Electrochemical impedance spectroscopy (EIS) based mapping of the impedance datasets as a function of frequency to equivalent electrical elements specific to physical/chemical characteristics is vital to validate the equivalent circuit models (ECM). Distribution of relaxation times (DRT) is a method to convert the EIS impedance spectra as a function of frequency to a distribution of time constants representing an RC network in a battery ECM. Modeling the battery with detailed consideration of EIS data is the main advantage of the DRT technique. In this work, the whole process of modeling a large amount of EIS data has been done automatically, selecting only the dominant peaks present during the entire battery ageing to increase computational efficiency. The results show that good accuracy is achieved in monitoring the degradation of a Li-ion cell and that the dispersion of the different fits is consistent throughout the data set.