Diversion of Aging of Battery Cells in Automotive Systems

Automotive battery systems for hybrid or full battery electric vehicles have a voltage level of up to 400 V and therefore consist of a vast serial connection of battery cells. Hence, the worst cell in the string defines the overall pack performance and lifetime. A fact nowadays mostly neglected in system design is the spread in cell aging and also their initial behavior due to the production process, the cooling gradient and the position within the pack. This paper will show that it is mandatory to consider the diversification of the cells in system layout and packaging to optimize the lifetime on system level tremendously. Results of aging experiments with hundreds of cells regarding pack architectures under laboratory and therefore comparable conditions are given.