Electrochemical system analysis from impedance data to system identification

Electrochemical impedance spectroscopy is a non-destructive experimental technique for the operando characterization of electrochemical systems. Here, we develop electrochemical system analysis (ELSA) as a data-driven, systems-theoretical approach to the analysis of measured impedance spectra. It solves the problem of finding an interpretable model description that explains given impedance data with high accuracy and without prior model assumptions. ELSA adopts the comprehensive analysis of the generalized distribution of relaxation time analysis and builds upon the data-driven and regularization-free Loewner method. ELSA systematically interprets the transfer function resulting from the Loewner method to reliably identify serial elements and resistive-capacitive and resistive-inductive processes with characteristic time constants. It also finds resonant elements by identifying conjugate complex poles. Based on the Shannon entropy of the residuals and the curvature of the locus, ELSA automatically and reproducibly identifies the minimal model order, thus avoiding overfitting. System characterization results are presented for different types of electrochemical power sources: batteries, fuel cells, and double-layer capacitors.