The impact of DC bias current on the modeling of lithium iron phosphate and lead-acid batteries observed using electrochemical impedance spectroscopy

This paper deploys electrochemical impedance spectroscopy (EIS) to investigate the impact of temperature and dc bias current on battery impedance characteristics. Measured test results are used to demonstrate that, under conditions where the nonlinear Butler-Volmer equation is necessary to model the electrode charge transfer characteristics, the semicircular trajectory that typically appears in the EIS results shrinks in diameter as the battery's dc bias current increases. For a lithium-based battery, the nonlinearity introduced by the Butler-Volmer relationship is more pronounced at low temperature, while lead-acid batteries typically exhibit this nonlinearity even at room temperature. The impact of dc bias current on the battery model and EIS characteristics are thoroughly investigated using a combination of experimental tests combined with theoretical justification based on the Arrhenius equation. The value of using this observed relationship to improve the accuracy of battery models and condition monitors (e.g., state-of charge, etc.) is discussed in the paper.