Lithium-titanate-oxide (LTO) batteries are one of the most promising technologies for various types of future applications in electric mobility, stationary storage systems and hybrid applications with high-power demands due to their long cyclic stability and superior safety.
The cyclic and calendar ageing of 43 LTO cells under 16 different operation conditions have been investigated using an incremental capacity analysis (ICA). Our investigation showed, that the cells exhibit a multi-stage ageing mechanism with stagewise increasing degradation gradient. In the first ageing stage, the LTO anode limits the amount of extractable capacity. After a certain amount of cathode degradation is reached an inflexion point occurs and the cathode starts limiting the amount of extractable capacity and thus determine the ageing gradient. This initiates the second ageing stage with much stronger occuring capacity fading gradient (see Fig.2). Additionally, due to an anode overhang, some cells experience a reversible increase in extractable capacity before any degradation becomes visible. Hence, for these cells an initial capacity gain stage becomes apparent.
These multi-stage ageing mechanisms are modelled using a physical motivated as well as a purely data-driven approach based on the separate degradation of the anode and cathode. Therefore, the investigated LTO cell is modelled in its electrical and thermal properties and simulated using the ISEA Framework simulation environment. The multi-stage ageing models are embedded an compared with regards to their accuracy and complexity.