Equivalent circuit modeling of sodium-ion batteries

Accurate modeling of sodium-ion batteries (SIBs) plays a vital role in the optimal development of the battery management system (BMS). In this study, the equivalent circuit models (ECMs) with different resistance capacitance (RC) numbers are thoroughly investigated. The relationship between circuit parameters and state of charge (SOC) is modeled as polynomial functions. The Bayesian information criterion is used to assist in optimal model selection by balancing the trade-off between model accuracy and model complexity. Two typical types of operation conditions, i.e. hybrid pulse power characterization/dynamic stress tests and constant current discharge tests, are conducted to evaluate the model performance. Both fitting and prediction results demonstrate that the ECMs with three-RC network can describe the terminal voltage response of a 1 Ah pouch-type SIB. The accurate modeling strategy provides a promising tool to state monitoring and control in BMS.