Online Estimation of Electrochemical Impedance Spectra for Lithium-Ion Batteries via Discrete Fractional Order Model

An electrochemical impedance spectrum is one critical non-destructive approach to indicate the health status of lithium-ion batteries. This paper presents an online model-based method of estimating the electrochemical impedance spectra based on discrete fractional order model. Firstly, a discrete fractional order model (FOM) is employed to model the dynamic behavior of the lithium-ion battery, especially the diffusion kinetics. In addition, another highlight of FOM lay on its significant performance in the impedance modeling for Li-ion battery over a wide range of frequency domain. Secondly, the Levenberg-Marquardt algorithm is adopted to identify parameters of FOM recursively. Based on identification results, the electrochemical impedance spectra can be obtained by simulation. Finally, a verifying experiment is carried out based on hybrid pulse power characterization test (HPPC) mixed by EIS test. The first order and second order equivalent circuits (short as, EC1 & EC2) have been imported here as the comparison with the fractional order model. The simulation results reveal that the fractional order model can ensure an acceptable accuracy of the RMS of impedance spectra, with a maximum error being less than 0.1mohm.