Time and Temperature Dependent Aging Mechanisms in Commercial Lithium-Ion Cells with SiO$_x$/Graphite Anodes

This work addresses the limited understanding of how changes in SiO$_x$/graphite anodes and the N/P ratio induced by aging influence the temperature-dependent transition between degradation mechanisms. It provides insight into the potentially evolving risk of lithium plating and its implications for the safe and durable operation of batteries. Commercial 3.5 Ah Li-ion 18 650 cells with SiOx/graphite anodes (∼2.5 wt.% Si) and Ni-rich LiNi$_{1−x−y}$Mn$_x$Co$_y$O$_2$ cathodes were systematically aged in the temperature range from −10 °C to +45 °C at 0.5 C and 0.85 C. Aging rates were evaluated at both beginning-of-life, i.e. 100%–95% state-of-health and mid-of-life (92.5%–87.5% state-of-health) using Arrhenius plots. The V-shaped Arrhenius plots at beginning-of-life exhibited minima, while the minima of the mid-of-life aged cells were either shifted to higher temperatures or even vanished in the investigated temperature range, indicating an increased susceptibility to lithium plating in the aged cells. Post-mortem analyses using FIB-SEM/EDX mapping revealed that SiO$_x$ degradation and related side reactions are more pronounced at high temperatures, while most likely lithium plating predominates at low temperatures. Loss of anode active material in the form of SiO$_x$ degradation and the resulting decrease in the N/P ratio is most likely the cause of the observed changes in the Arrhenius plots after cycling.