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

The paper analyzes the effects of fast charge on a lithium-ion battery module made by 4 lithium-iron-phosphate cells series connected, submitted to a test profile which includes a fast charge step at current rate 3C. This test profile simulates the real working profile requested to the batteries of a electric bus to perform a particular service of local public transportation with recharge of the batteries at the end of line. More than 3,000 shallow cycles were performed: the battery module did not show a significant reduction of performances in terms of capacity and energy, but, on the other side, a relevant increase of the inner resistance was observed. As an effect of this, the autonomy of the electric bus is reduced correspondingly. 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 and all through the vehicle life, 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 with fast charge is cheaper and the fast charge can be a valid instrument to solve the problem of short autonomy of electric vehicles. © 2017 MOBI -Mobility, Logistics and Automotive Technology Research Centre.