Enhanced Accuracy of Broadband Li-Ion Battery Impedance Measured by Portable Discharge Paradigm

Abstract

Electrochemical impedance spectroscopy (EIS) is a non-invasive characterization method widely used in lithium-ion battery studies and management. In particular, based on the algorithm of generalized S transform (GST), a discharge paradigm measuring EIS of next-generation battery management system (BMS) through the discharge of a battery with one resistor is proposed for its simplicity and portability. However, extracting impedance from the discharge paradigm is still challenging due to the factors of resistance selection and sampling frequency. Herein, the mechanism by which factors affect the accuracy of EIS data measured by the discharge paradigm is analyzed. The experimental results indicate that resistance determined the variation of state of charge (SoC) and signal-noise ratio (SNR) in the high-frequency range, and the influence of sampling frequency can be ignored when sampling frequency is above 5kHz. To minimize impedance errors in the low frequency by enlarging applied resistance, the periodic step wave is employed to maintain a high SNR in the high frequency. The proposed method is verified at different SoCs, states of health (SoHs) and temperatures, and the results reveal good accuracy in differentiating the variation of characteristics under these conditions. Overall, the proposed method looks promising for future application of impedance.

Keywords: Lithium-ion battery, Discharge paradigm, Periodic step wave, Electrochemical impedance spectroscopy, Generalized S transform