Improved Identifiability of Kinetic Parameters in Lithium‐Ion Batteries via Nonlinear Frequency Response Analysis

Model parameterization is essential, on one side, to offer insights into the internal states of a Li-ion battery, and on the other side, to deliver realistic predictions of the battery performance. Multistep parameterization, including the C-rate test, electrochemical impedance spectroscopy, and for the first time, nonlinear frequency response analysis, has been implemented in this study. Via nonlinear frequency response analysis, an asymmetrical charge transfer process at the positive electrode is identified, whereby the charge transfer coefficient at the positive electrode is no longer 0.5, as assumed in many simulation works. Further, it is shown that nonlinear frequency response analysis in combination with electrochemical impedance spectroscopy can improve the uniqueness of the kinetic model parameters. Specifically, ambiguous sets of kinetic parameters, that is, rate constant and charge transfer coefficient, are identified via only electrochemical impedance spectroscopy. The ambiguity can be resolved with additional nonlinear frequency response analysis.