(Invited) A Critical View on the Application of Distribution of Relaxation Times

Electrochemical Impedance Spectroscopy (EIS) has been an important tool in Solid State Ionics since the sixties of the 20th century. Evolving from graphical analysis to fully automated Complex Nonlinear Least Squares analysis (CNLS), it has contributed to a better understanding of charge and mass transfer and storage processes in solid state devices, e.g. batteries, sensors, fuel cells etc. In many cases the use of an Equivalent Circuit (EqC) gave access to important materials parameters. Due to the increasing complexity of e.g. electrodes, it is not always simple to find an appropriate EqC. The transformation of the impedance spectra to a distribution of relaxation times in the τ-domain has gained increased attention over the last decades, as it is seen as a model independent representation. The main problem, however, is that this transformation is an ill-posed inverse problem. Various methods (e.g. FFT, Tikhonov Regularization, Max Entropy) have been designed to provide the distributions, but they all require adjustment of a ‘smoothing’ parameter. In this presentation the advantages and limitations of the use of a DRT will be presented with selected practical examples.