A study of the effect of short-term relaxation on the EIS test technique for EV battery cells

Abstract

Electrochemical impedance spectroscopy (EIS) is a powerful tool employed to investigate the fundamental electrochemical parameters of a Li-ion battery cell. Its effectiveness has established it as a core method to study electrochemical behavior of batteries in laboratory environments. An industry-wide interest currently exists to employ EIS as part of battery management systems (BMSs) for state of charge, internal temperature and state of health measurements. The major issue of employing EIS for online measurement as part of BMS is the reliability. In this work, it is shown that not all the parameters extracted by the EIS technique are reliable when measurement is performed shortly after charge/discharge. While pure Ohmic resistance was found to be consistent, the change transfer resistance and double layer capacitance are not reproducible. Therefore, only Ro can be reliably employed for the fast online measurement by BMS.