Influence of Calendar Aging on Cell‐To‐Cell Variation of 18650 NCA Cells With Blended Si‐ and SiO x ‐Based/Graphite Electrodes

Silicon‐containing negative electrodes increase the energy density of lithium‐ion batteries but promote heterogeneous degradation due to their large volume expansion. This study compares calendar aging of Si–graphite (Si–Gr) and SiO x ‐graphite (SiO x ‐Gr) cells, focusing on degradation mechanisms and statistical variation. 30 commercial 18650 cells per cell type were aged for up to 323 days at 100% state of charge and 35 °C. Capacity, resistance, and voltage relaxation were monitored, and degradation modes were identified via differential analysis and electrode balancing. Si–Gr cells show initially lower capacity variation but higher resistance variation. With aging, their coefficient of variation increases significantly across capacity, resistance, and degradation modes, indicating increasingly heterogeneous behavior. SiO x ‐Gr cells exhibit low and stable variation, reflecting homogeneous aging. SiO x ‐Gr cells show higher capacity fade but moderate resistance increase, whereas Si–Gr cells show lower capacity fade and about three times higher, more widely spread resistance growth. Degradation is dominated by loss of lithium inventory, with more pronounced loss of active material in Si–Gr cells, with silicon being the dominant factor. Voltage relaxation correlates with capacity fade and serves as a noninvasive indicator of aging. The dataset is publicly available.