Calendar aging model for lithium-ion batteries considering the influence of cell characterization

To optimize costs and ensure safety, investigation and modeling of battery aging is very important. Calendar aging analysis consist of a periodic sequence of calendar aging and cell characterization. The influence of the characterization on the results of the calendar aging investigation has been assumed to be negligible so far. Nevertheless, the characterization measurements of different studies, especially the important capacity measurement, differ fundamentally. This could have an impact on the results of capacity and resistance change in calendar aging. In this paper, the effect of characterization is quantified for the first time, using periodic characterization measurements. A significant influence in the form of capacity increase and resistance decrease is found. It can be explained by an increase in the active electrode surface area caused by the characterization measurement. Therefore, the cell characterization is a new possible source for capacity increase in calendar aging. As an important result, in future studies capacity measurements should be performed with small currents below 1C to reduce the influence of characterization on the results. Additionally, a correction of the characterization effect can be done according to the presented method. •Study of the characterization measurement effect on calendar aging investigations.•New explanation of capacity gain and resistance drop in calendar aging measurements.•Recommendation for using a lower current rate than 1C in the capacity measurement.•Semi-empirical capacity loss model for NMC lithium-ion cells.•Determination of a change in aging behavior at long-term calendar aging.