A Physically-Based Electrical Model for Lithium-Ion Cells

Prediction of battery performance is essential in assessing the technical and economic viability of battery systems. We present a novel impedance-based model of a lithium-ion cell that accounts for the dynamic response of battery cells as a nonlinear function of the state of charge (SoC). The model is composed of impedance blocks connected in series. Each block is derived from a specific electrochemical equation linked to the battery operation. The state of charge is estimated from the voltage of a nonlinear capacitance, thereby addressing the intercalation of ions into the electrode structure. The developed procedure to identify the parameters of the individual impedance blocks is applied to a commercial lithium-ion cell (lithium nickel oxide). Validation in the time domain shows high accuracy of the model (RMSE < 1% at ambient temperature for SoCs between 20% and 80% and for all current rates allowed by the manufacturer) in estimating the voltage at the device's terminals, efficiency, power and energy density under different current rates.