The effect of cycling on the state of health of the electric vehicle battery

This paper provides an analysis of the experimental results available for lithium ion battery degradation which has been used to create a model of the effect of the identified parameters on the ageing of an EV battery. The parameters affecting degradation are generally accepted to be; state of charge, depth of discharge, charging rate and battery temperature. Values for each of these parameters have been found for three versions of a typical daily cycling scenario; uncontrolled charging, delayed charging and V2G. A comparison is made of the expected overall degradation using four different charging rates and different charging patterns based on the model. A link is made between the charging patterns and the effect on the power flow at the transformer of a typical section of LV network using a ADMD profile. The analysis shows that delayed charging and V2G slow down the rate of battery degradation. However, fast charging appears to accelerate battery degradation. Delayed charging also helps avoid excessive evening loading and thus will help delay distribution network asset upgrading. Uncontrolled charging increases evening loading and V2G can reduce it. However, the EV then needs more power for charging and the charging after V2G needs to be managed if it is not to create another spike in demand at a later time.