A High-Precision and Fast Measurement Method for Li-Ion Battery EIS

Fast and accurate measurement of the lithium-ion (Li-ion) battery electrochemical impedance spectroscopy (EIS) is essential for the safe and reliable operation of energy storage systems. However, existing methods for measuring battery EIS are of low efficiency. Hence, this article proposes a high-precision and fast measurement method for Li-ion battery EIS. In terms of the excitation signal, the optimized sinc pulse signal and linear frequency modulation (LFM) pulse signal (chirp) are introduced for EIS measurement of low- and medium-to-high frequency bands, respectively, and the spectrum is calculated by chirp Z transform (CZT). In terms of the measurement device, the method proposes a terminal voltage balancing capacitor to achieve high-precision measurement of the small terminal voltage variations of the battery. Then, the measured EIS is fit into a fractional-order equivalent circuit model (ECM). Finally, simulations and experiments under different working conditions are conducted to inspect the effectiveness of the proposed method on lithium-iron-phosphate (LiFePO4) battery cell. The duration of the proposed excitation signal is shortened to 7.3% of the traditional frequency sweeping method, the sensitivity of the measurement circuit is improved by about three orders of magnitude compared with the traditional method and the normalized root-mean-square error (NRMSE) of the full-frequency band EIS is within 2%, which indicates that the proposed method can achieve fast and high-precision measurement of battery EIS and provides a guidance for further study of battery ECM parameters.