A Large-Scale Cycle and Calendar Ageing Study on a Large Commercial Li-Ion Pouch Cell

The Li-ion battery has become the most used commercial rechargeable battery technology. Since its commercial launch in the 1990’s Li-ion batteries have developed steadily. Initially the Li-ion battery replaced other secondary batteries as e.g. NiMH in portable electronics (e.g. mobile phones and portable computers), while Li-ion batteries were introduced in the first commercial electric vehicles in 2008/2009. Later, the Li-ion battery has also been introduced into large electric ships (2014) [1] as well as in large-scale electric energy storage (BESS) [2]. During the Li-ion battery’s development, its cycle and calendar life has improved steadily. However, a battery’s life is still dependent on its quality, chemistry and energy density, as well as how the battery is used and mounted, i.e., operating and storage temperature, maximum, average and minimum state-of-charge (SoC), as well as the current during charge and discharge. It is also well known that a battery’s life can be strongly dependent on the mounting of the pouch-cell with and without a mechanical fixture [3]. This work presents results from a large-scale ageing study initiated in 2020 involving more than 150 cells and some are still running. The cell was a large-format Li-ion pouch cell (64 Ah) optimized for power, with an NMC532 cathode and graphite anode, and an energy density of approximately 200 Wh/kg. The calendar life was tested as a function of temperature (5 to 45°C) and SoC (0-100%) while the cycle life was scrutinized with respect to temperature (5 to 45°C), current (0.2C to 1.5C), average SoC as well as SoC window, in addition to the effect of mechanical fixture or not. We observed a strong correlation between mechanical fixture and cycle life [3], as well as the cell’s cycle temperature, where the highest temperature gave the lowest cycle life, while cycle life at 5, 15 and 25°C were almost similar when reaching 80% remaining capacity (SoH). However, we observed strong differences in ageing diagnostics [3, 4] as well as safety of these aged cells, depending on the ageing temperature [5, 6]. The effect on cycle life of different currents showed that the cell was virtually insensitive and had similar cycle life for all tested currents. However, we could observe significant differences in the homogeneity of the ageing patterns from the ICA analysis, where the cells aged at higher C-rates had aged in a more inhomogeneous manner. The effects of SoC, showed a strong correlation between SoC for both cycle and calendar life. The lower SoC, the better it was for both cycle and calendar life. For cycle life at 25°C the best observed cycle life was observed in the 0-40% SoC window, while the worst cycle life was observed in the 10-90 and 0-100% SoC windows. Cycling from 0-40% SoC has so far reached 90% SoH after 4500 equivalent full cycles (EFC) (still cycling), while cycling from 0-100% SoC to 80% SoH obtained an average cycle life of 3000 EFC. By limiting the maximum SoC to 80%, the cycle life is doubled to more than 6000 EFC. The ageing study is complemented by ICA, DC resistance and EIS measurements, as well as the analysis on mechanical pressure increase and gas formation during both, calendar and cyclic ageing. References Sæther, S.R. and E. Moe, A green maritime shift: Lessons from the electrification of ferries in Norway. Energy Research & Social Science, 2021. 81: p. 11. Chen, T.M., et al., Applications of Lithium-Ion Batteries in Grid-Scale Energy Storage Systems. Transactions of Tianjin University, 2020. 26(3): p. 208-217. Spitthoff, L., et al., Incremental Capacity Analysis (dQ/dV) as a Tool for Analysing the Effect of Ambient Temperature And Mechanical Clamping on Degradation. Journal of Electroanalytical Chemistry, 2023. Wind, J. and P.J.S. Vie, Revisiting Pulse-Based OCV Incremental Capacity Analysis for Diagnostics of Li-Ion Batteries. Batteries-Basel, 2024. 10(8): p. 12. Vie, P.J.S., et al. Diagnostics of Safety Hazardous Ageing Conditions for Commercial Lithium-Ion Pouch Cells. in The 244th ECS meeting. 2023. Gothenburg, Sweden: The Electrochemical Society. Lian, T., et al. (Invited) Thermal Stability and Thermal Energy Measurements for a Lithium-Ion Pouch Cell with Different State of Health. in The 244th ECS Meeting. 2023. Gothenburg, Sweden: The Electrochemical Society.