Shelf life of lithium-ion batteries: Recommissioning LiFePO4/C cells after ten years of uninterrupted calendar aging

We analyze the impact of ten years of uninterrupted shelf storage at 50% state of charge and 6 °C on 100 commercial 26650 LiFePO 4 /C lithium-ion cells. By comparing measurements taken before storage with those performed in this study after shelf storage, we assess capacity fade, resistance changes, performance at high loads, and cycle aging. Initial check-up measurements performed directly after storage reveal minimal aging, with all cells retaining 96%–98% of their initial capacity, and resistance changes being negligibly small. The cell-to-cell variations in capacity and resistance remain within the range of fresh production batches. Pseudo-open-circuit voltage measurements and differential voltage analysis imply no active material loss on the anode side, indicating that aging is primarily attributed to SEI growth. The rate capability of long-term stored cells remains unchanged compared to fresh cells for C-rates up to 3 C. Long-term cycling tests of up to ten months reveal a stable operation with aging trajectories similar to those of fresh cells. Our results demonstrate that long-term storage leads only to minor degradation, with no negative effects on performance or lifetime. This suggests that shelf-stored cells can be used in applications just like fresh cells, without any additional precautions.