An Analysis of Calendaric Aging over 5 Years of Ni‐rich 18650‐Cells with Si/C Anodes

AbstractCalendaric lifetime testing of lithium‐ion cells is time‐consuming and resource‐intensive. As Dubarry et al.[1] state, testing is often limited to a few aging conditions. This paper presents the results of a long‐term aging study on lithium‐ion cells with a nickel‐rich NCA cathode and a graphite‐silicon anode. 69 cells were stored at 5 different voltages and under 4 different temperatures for 5 years. Regular reference performance tests (RPT) provide insights for State of Health (SoH) calculation and further analysis through differential voltage analysis. The results are verified against post‐mortem analyses. The long aging period enables accurate determination of aging rates. Our results demonstrate that the storage voltage level strongly influences the degradation rate, with temperature playing a minor role. The identified aging effects include loss of active material on the cathode side and loss of lithium inventory. Initial degradation follows a ‐trajectory but is caused by overhang effects. The long‐term aging is rather linear.