On Simplification of a Solid-State Battery Model for State Estimation

This paper studies the state estimation of a solid-state battery. Partial differential equations based on a nonporous insertion model are presented to model the solid state battery. Two assumptions simplifying the battery model under-lie the study of state estimation: that the Li-ion concentration in the solid electrolyte is uniform and the charge transfer coefficient at the positive electrode is 0.5. The assumptions made resolve the issue of very weak observability: the diffusion dynamics in the electrolyte and positive electrode are connected via Butler-Volmer equation and the contribution of the charge transfer overpotential is found to be insignificant. For state estimation, an extended Kalman filter (EKF) is applied based on the simplified battery model using measurements of current and voltage of the cell. Simulation results show that the state-of-charge (SOC) of the battery can be accurately estimated by the EKF in specific SOC ranges, i.e., SOC <; 0.2 and SOC >0.4.