Fast Battery EIS Measurement Using Flexible Local Rational Method

Electrochemical impedance spectroscopy (EIS) is one of the most widely used techniques for battery monitoring and characterization. However, EIS measurement is a time-consuming process, since it must be performed after the battery relaxation time interval. In this article, a method for performing fast broadband EIS during battery relaxation by compensating for the effect of the transient is proposed. The approach is based on the local rational method (LRM), which is a nonparametric frequency-domain system identification technique, and eliminates the need for long waiting time before starting the measurement process. The proposed approach is validated by numerical simulations and experiments, proving its capability of compensating the effect of the transient and outperforming other nonparametric techniques, such as the local polynomial method (LPM). In particular, experimental tests performed on a 18650 lithium-ion battery show that the proposed flexible LRM approach is capable of compensating the transient behavior and providing usable EIS estimates immediately after the battery discharge is finished. This behavior is demonstrated using a broadband multisine excitation signal of 20 s duration, spanning a frequency range from 50 mHz to 100 Hz.