States of charge and temperature estimation for cylindrical li-ion batteries based on an electrochemical-thermal coupling model considering ageing calibration

Though full-order electrochemical models provide precise descriptions of the reactions occurring within batteries, their complexity cannot be afforded by real-time embedded applications. This paper constructs a coupled electrochemical-thermal model to estimate the state of charge (SoC) and state of temperature (SoT) of li-ion batteries (LiBs). Firstly, an extended single particle model (eSPM) is elaborated and enhanced with a thermal part, thereby facilitating an effective interplay between electrochemical behavior and thermal state. Furthermore, the calibration of battery aging state is accomplished by identifying aging-related parameters utilizing a particle swarm optimization. Subsequently, the electrochemical process within the LiB is articulated in a statespace formulation, and the distribution of Li+ concentrations at different locations is estimated via the unscented Kalman filter (UKF). Eventually, the SoC and entropy change are obtained using the estimated Li+ concentrations, while the SoT is deduced from the thermal model. Experimental verifications, utilizing 18650 LiB cells under two dynamic loads and a temperature range of 0-50 degrees C, showcase the remarkable accuracy and superior robustness of the developed model across diverse operating conditions. Notably, a maximum voltage simulation RMSE of 0.055V, a commendable SoC estimation RMSE of 0.016 %, and an exceptionally low SoT estimation RMSE of 0.18 degrees C, are achieved.