The derivation process of the Nyquist plot for partial equivalent circuits and the relationship between the AC impedance spectra and the variation law of resistance during battery DC charging and discharging

Abstract

This paper reveals the relationship between resistance changes during battery DC charging/discharging and the very low-frequency data points in the Nyquist plot of the battery’s AC impedance spectrum and derives the corresponding Nyquist plots for common equivalent circuits. This provides a theoretical basis for understanding the rationality of fitting the AC impedance spectrum’s Nyquist plot with equivalent circuits. During derivation, notable conclusions were drawn: for example, the Nyquist plot of the “capacitance-inductance adsorption” equivalent circuit in the “adsorption-type impedance system” does not consist of standard semicircles; additionally, for the “adsorption-type impedance system,” not all component parameter information can be deduced from the zero-point data of its Nyquist plot.