Fast-charge life cycle test on a lithium-ion battery module

This study addresses the effects of fast charge on a lithium-ion battery module made by four lithium-iron-phosphate cells connected in series, submitted to a test profile which included a fast-charge step at a current rate of 3 C. This test profile simulated the real working profile requested by the batteries of an electric bus to perform a particular service of local public transportation, with the batteries recharging at the end of line. More than 3000 shallow cycles were performed. The battery module did not show a significant reduction in performance in terms of capacity and energy; however, a relevant increase in resistance was observed. Due to this change, the autonomy of the electric bus was reduced correspondingly. By fixing a minimum value for the autonomy, a life estimate of the battery module was made. Finally, on the base of this result, a cost estimate and comparison between slow and fast charge was made, under the same service conditions throughout the vehicle's lifespan, for a real case of a minibus equipped with a battery system sized for fast charge at the end of line, and a larger battery system sized for slow charge at the end of a working day. This comparison proved that, in the case study considered, the solution using fast charge was cheaper, and fast charge can be a valid approach to solve the problem of short autonomy of electric vehicles. © 2018 by the authors.