Lifespan prediction of Li-ion batteries in electrical vehicles by applying coulombic efficiency: from anode material to battery cell to vehicle application

Coulombic efficiency (CE) is widely considered to be an important parameter for indicating the loss of reversibility of lithium, which can be used to reflect battery performance and safety to predict the lifespan in Li-ion battery research. However, the quantifiable relationship between CE and lifespan, as well as its application in lifespan prediction for real-world electrical vehicles (EV), are not fully understood. In this paper, the battery cycle degradation test is performed, which explores the close relationship between the CE and the cycle life through the study of an experimental cell with graphite anodes (AG) coated with different proportions of pitch-based carbon (PbC), indicating that a high CE is associated with a long battery life. Furthermore, the CE evolution is explored through cycling experiments of the standard cell under imitated real-world EV working conditions and the logarithmic relation with upper and lower branches between the CE and cycle number is constructed. Based on this relationship, a quantitative lifespan prediction method for EVs is proposed. It was found that the failure behavior of the degradation trend could be identified through the mass EVs operating data by using this method, and the false alarm for normal EVs is low, at only about 2% by cycle number, indicating that CE in EVs reflects the health status of lifespan (HSoL) of battery. Therefore, the detection method is helpful for predicting the cycle life and offers an early failure warning for battery management systems. The evolution of CE in each cycle follows a time-variable logarithmic function closely related to the cycle number, which can be used for predicting the lifespan of LIBs.