Characterization of Uncertainty in EIS and DRT Analysis of Lithium Batteries

The analysis of electrochemical impedance spectroscopy (EIS) measurement results by means of the distribution of relaxation times (DRT) technique enables accurate battery diagnostics in a variety of applications, including the automotive field. In order to provide meaningful insight, such analysis must be performed by taking into account the measurement uncertainty associated with DRT results. We provide a method for characterizing the DRT uncertainty based on repeated measurements. First, we validate the proposed method by numerical Monte Carlo simulations, which allow for relating the uncertainty in the DRT curve to the signal-to-noise ratio of the voltage and current waveforms measured in the time domain. Furthermore, we also investigate the impact of the number of frequency points and of the choice of the DRT regularization parameter. Finally, we apply the proposed uncertainty characterization method to experimental data obtained from a rechargeable 18650 lithium-ion cell. The method provides an easily interpretable visual representation of the DRT uncertainty, thus potentially supporting both the designer and the user of battery measurement systems.