Search

The usage of electric vehicle batteries to assist the main electric grid for the storage of energy provided by intermittent sources should become an essential tool to increase the penetration of green energies. However, this service induces additional usage on the cells and, therefore, could degrade them further. Since degradation is path-dependent, it is of paramount importance to test the impact of all the different grid applications on the batteries. In this work, we tested the additional usage induced by using electric vehicle batteries for frequency regulation at moderate rates during rest or charge and found no detrimental effect after around 2000 cycles on the cells.

This paper presents results from a field test performed on commercial power-optimized lithium-ion battery cells cycled on three heavy-duty trucks. The goal with this study was to age battery cells in a hybrid electric vehicle (HEV) environment and find suitable methods for identifying cell ageing. The battery cells were cycled on in-house developed equipment intended for testing on conventional vehicles by emulating an HEV environment. A hybrid strategy that allows battery usage to vary within certain limits depending on driving patterns was used. This concept allows unobtrusive and low-cost testing of battery cells under realistic conditions. Each truck was equipped with one cell cycling equipment and two battery cells. One cell per vehicle was cycled during the test period while a reference cell on each vehicle experienced the same environmental conditions without being cycled. Differential voltage analysis and electrochemical impedance spectroscopy were used to identify ageing of the tested battery cells. Analysis of driving patterns and battery usage was performed from collected vehicle data and battery cell data.