Two-dimensional impedance data analysis by the distribution of relaxation times

Abstract

Electrochemical impedance spectroscopy of batteries and fuel cells suffers from ambiguity due to overlapping features of different electrochemical processes. One approach to mitigate this problem is the analysis of impedance data by the distribution of relaxation times (DRT) of the underlying physico-chemical processes. In this work an evolution of DRT analysis using generalized Tikhonov regularization with a uniform penalty and an RC kernel is discussed. By conducting the transformation without discriminating or constraining the sign of the distribution and by using both the imaginary and the real part of the RC kernel it can be distinguished between impedance contributions of RQ-like physico-chemical processes, pure ohmic resistances and inductances in the system under investigation. Furthermore, regularization can be simultaneously applied in a second, non-inverted dimension, which affords an increased resolution of the spectrum. The properties of the algorithm are demonstrated by analyzing synthetic impedance data.