State estimation of a reduced electrochemical model of a lithium-ion battery

Batteries are the key technology for enabling further mobile electrification and energy storage. Accurate prediction of the state of the battery is needed not only for safety reasons, but also for better utilization of the battery. In this work we present a state estimation strategy for a detailed electrochemical model of a lithium-ion battery. The benefit of using a detailed model is the additional information obtained about the battery, such as accurate estimates of the state of charge within the individual electrodes, overpotential, concentration and current distribution across the electrodes, which can be utilized for safety and optimal operation. We propose an observer based on a reduced set of partial differential-algebraic equations, which are solved on a coarse spatial grid. The reduced model has a less complex structure, while still capturing the main dynamics. The observer is tested in experiments for actual electric-vehicle drive cycles. Experimental results show the observer to be robust with respect to unmodeled dynamics, as well as to noisy and biased voltage and current measurements. The available state estimates can be used for monitoring purposes, or incorporated into a model based controller to improve the performance of the battery while guaranteeing safe operation.