Electrochemical Impedance Spectroscopy Based Power-Mix Control Strategy for Improved Lifetime Performance in Second-Life Battery Systems

In this paper, a control strategy is described that increases the longevity of degraded Electric Vehicle (EV) batteries used in off-grid stationary-storage applications. The control strategy relies on battery impedance data measured using online Electrochemical Impedance Spectroscopy (EIS) to determine the time-varying degradation rates and electrical models for each battery module. The power-mix between battery modules at different State-of-Health (SOH) is set by the controller to reduce the rate of total capacity fade. A photovoltaic (PV) energy generation curtailing technique is used to reduce the battery charge rates in order to further reduce degradation. In simulation, the control strategy is shown to increase the battery system lifetime by an average of 56%. Experimental validation of the control strategy is performed using two custom 3.85kWh battery modules, and an online EIS system is demonstrated.