Degradation modes of large-format stationary-storage LFP-based lithium-ion cells during calendaric and cyclic aging

Lithium-ion batteries exhibit capacity loss as a result of the combined degrading effects of calendaric and cyclic aging. In this study, we quantify the lifetime of large-format (180 Ah) commercial stationary-storage lithium iron phosphate-based lithium-ion cells by performing 1500 cycles of cyclic aging and ca. 850 days of calendaric aging. The aging tests were performed at two different temperatures (35 °C and 50 °C) to observe the effect of temperature on aging. The calendaric aging cells were stored at two different states of charge (SOC) (100 % and 75 %) to observe the effect of SOC. At the end of aging tests, the capacity loss of all cells at 50 °C exceeded those of all cells at 35 °C. Temperature was thus identified as major aging driver. The observed global activation energy over all investigated aging protocols was 37.3 kJ/mol. Furthermore, aging modes (loss of lithium inventory and loss of active material) were investigated by differential voltage analysis of the charge-discharge curves; for the cyclic aging cells, this was performed on the cycling data directly. The degradation mode analysis showed that loss of lithium inventory is mainly responsible for capacity loss. • Investigation of large-format (180 Ah) LFP cell aging for 1500 cycles or 850 days • Influence of aging protocol (cyclic/calendaric), temperature, and SOC investigated • High temperature is the dominant aging driver, 35 °C to 50 °C doubles capacity loss. • Loss of lithium inventory (LLI) is the dominant degradation mode.