On-line state estimation of automotive batteries using in-situ impedance spectroscopy

Safe operation of Li-ion traction batteries in electric cars is one of the main requirements for a broad acceptance of this technology. Safety critical factors such as over-temperature conditions must be reliably monitored and captured. Increasingly strict safety regulations in the automotive sector imply rising challenges to both car manufacturers and battery system suppliers and hence resilient, reliable yet inexpensive tools for battery state diagnosis are necessary to address these topics. The approach presented here is a battery diagnosis tool based on in-situ galvanostatic electrochemical impedance spectroscopy which can be integrated into a standard battery management system. The algorithms which are used to convert the impedance measurements into valuable battery temperature estimations are based on numeric correlations between the impedance and these state variables. It is shown that the method can be used even in non-equilibrium state of the battery thus improving the functional safety in electric cars during the usage of a battery pack by redundant monitoring of the battery temperature.