Comparative Analysis of Battery Degradation Using EIS and Differential Capacity Methods for Single Cells and Modules

Battery degradation plays a critical role in determining battery performance and in predicting the remaining useful life (RUL). Several methods exist to monitor degradation. Differential capacity analysis, expressed as differential capacity versus voltage (dQ/dV), can be applied to both single cells and modules. EIS allows tracking the deterioration of specific internal mechanisms within a cell. Typically, the dQ/dV curve exhibits distinct peaks, which can be monitored over time to quantitatively assess the degree of degradation. This, in turn, enables the estimation of the state of health (SOH). A practically useful method for determining degradation of battery SOH is to measure the increased % ΔSOC for running the same tour repeatedly. As the battery capacity is decreased the % ΔSOC is increased. By following this by time we get a measure of SOH at each point in time. This has been demonstrated for buses in Luleå for 6 years operation in commercial traffic.