Extensive aging analysis of high-power lithium titanate oxide batteries: Impact of the passive electrode effect

Abstract

Partial electrification of vehicle drive trains, for example by the usage of 48 V systems, require high-power batteries with extreme robustness to temperatures, current rates and energy throughputs. In this study, the application-relevant lifetime performance of 33 state-of-the-art high-power lithium titanate oxide nickel manganese cobalt oxide (LTO|NMC) cells is measured under cyclic, calendar, and drive cyclic aging regimes. Regular extended check-ups reveal the cell performance in terms of capacity loss and internal resistance increase, which allows for the identification of critical operating conditions. For the first time a passive electrode effect is identified in calendar aging tests of LTO cells in which the cathode is geometrically and capacitively oversized. Passive electrode areas lead to a change in cell balancing, which can be illustrated by the shift of the half-cell voltage curves. Generally, the investigated cells show an excellent cycle stability for shallow cycles, even at high ambient temperatures and high current rates. Only large cycle depths greater than 70% at elevated temperatures reduce the battery life significantly. Furthermore, the results show that cells cycled in areas of low state of charge age faster than in areas of high state of charge. The rise in internal resistance under calendar aging has the most detrimental influence on lifetime in a 48 V battery.