Understanding Temperature, Transient-Current, and Historical-State Effects in Dynamic Electrochemical Impedance Spectroscopy of Lithium-Ion Batteries

Abstract

Dynamic electrochemical impedance spectroscopy (DEIS) shows strong potential for online state estimation of lithium-ion batteries (LIBs), yet its practical application remains limited by the interplay among relaxation, temperature, transient operating conditions, and historical cell states. In this work, the differences between stationary electrochemical impedance spectroscopy (SEIS) and DEIS are systematically investigated using a single commercial 18650 cell. First, DEIS measured shortly after discharge is analyzed. Within the investigated post-discharge period and experimental resolution, temperature variation accounts for most of the observable impedance evolution, whereas an independent relaxation contribution is not resolved. The coupled effects of transient current and temperature on operando DEIS are then examined using a simplified characteristic-feature framework intended to approximately separate their contributions. In addition, SEIS hysteresis is observed, indicating that the impedance measured after a long rest depends not only on the present state of charge (SOC) but also on the preceding operating history. Accordingly, a normalization strategy based on the ratio of the dynamic impedance feature to its corresponding local SEIS reference is evaluated and produces more consistent qualitative trends across the tested historical conditions and SOC levels. These results provide a novel perspective on the effects of temperature, transient current, and historical state on DEIS, offer useful guidance for developing DEIS-based online state-estimation methods for LIBs, and establish a basis for further quantitative validation using additional cells and operating conditions.