An experimental study of the robustness of electrochemical impedance spectroscopy measurements within consecutive cycles

Diffusion of lithium ions into the electrodes (relaxation effect) was shown to affect the electrochemical impedance spectroscopy (EIS) measurements hours after the load is removed. Previous research primarily examined the influence of rest time following individual charge or discharge cycles while the robustness of the measurements remained mostly unexplored. This study experimentally examined the effects of rest periods between successive cycles. For the first time to the authors’ knowledge, it demonstrated that the repeatability of EIS measurements can be significantly affected by rest periods in between cycles and the SOC level. Additionally, it was discovered that repeatable impedance measurements can be obtained after a very short relaxation period of 15 minutes, supporting the reduction of relaxation period. While additional investigations are required to understand some of the observations and their implications on onboard SOH estimation strategies, this study serves to experimentally demonstrate that the impedance dispersion between successive cycles can be significant and should not be overlooked.