Degradation of Lithium Ion Batteries under Complex Conditions of Use

It is well known that lithium ion batteries degrade due to cycling (cycle life), but also when in standby mode with little or no current throughput (calendar life). Experimental results exist which show the lifetime of a battery under either of these conditions, cycling or standby operation. Results for an application specific mix of cycling and standby operation are, however, not readily available in the scientific literature. The ageing mechanisms of these two modes of operation differ in their impact on capacity and internal resistance as the two most important performance characteristics of a battery. The question is how the ageing mechanisms interact and how certain ageing mechanisms occurring particularly in one mode of operation affect ageing mechanisms which occur predominantly in the other mode of operation. As the conditions of use are very different in terms of current amplitude, state-of-charge and temperature, it is clear that the interaction needs to be considered taking the application into account by using application specific load collectives. This paper will discuss how to approach this problem, shows first results and their relevance for vehicle batteries when used for vehicle to grid operation.