A new approach to measure the non-linear Butler–Volmer behavior of electrochemical systems in the time domain

Abstract

A new approach to measure the non-linear Butler–Volmer behavior of electrochemical systems in the time domain is presented. The method is based on two superimposed currents, one large pulse as an offset and a small pulse which is transformed into the frequency domain. The advantage of this new method is the decreased measurement time compared to frequency domain measurements. This allows the characterization at lower frequencies with less distortion from change in SOC and temperature. In order to reduce spectral leakage of the fast Fourier transform the derivative of the measured signals is taken. The measurement time can be as small as the theoretical limit T=1/f with a negligible error. For the characterization of large automotive cells high currents are needed which were provided by a reprogrammed BaSyTeC HPS cell test system, also used to conduct dynamic electrochemical impedance spectroscopy measurements to validate the new method. The equality of the two completely different hardware and software systems is shown for a 50Ah cell for automotive applications at −20°C in a current range from 0 to 100A.