The Study of Resistance Variation between Charging and Discharging Process by Current-Interrupt Technique and Dynamic Electrochemical Impedance Spectroscopy (DEIS)

In this study, resistances of charging and discharging process were distinguished both by current-interrupt technique in time-domain and dynamic electrochemical impedance spectroscopy (DEIS) in frequency-domain. It is found that when the SOC varies from 0 to 0.4, the resistances of discharging process are larger than that of charging process. However, the difference between these two resistances decrease as the SOC increases, and then two resistances almost equal in the SOC range of 0.4 to 0.8. Then as the SOC increases further and approaches 1.0, the latter resistance exceeds the former one. A mathematical model to fit the voltage change in the current-interrupt experiments and an equivalent circuit to fit the impedance in the DEIS experiments are employed to find out the component of the total resistance which dominates the shift of resistance magnitude of charging/discharging process as the SOC increases from 0 to 1. It is concluded that the charge transfer resistance R_CT and the diffusion resistance R_D, contributed to a large proportion of the magnitude shift.