Effects of Overdischarge Rate on Thermal Runaway of NCM811 Li-Ion Batteries

Overdischarge often occurs during the use of battery packs, owing to cell inconsistency in the pack. In this study, the overdischarge behavior of 2.9 Ah cylindrical NCM811 [Li(Ni0.8Co0.1Mn0.1)O2] batteries in an adiabatic environment was investigated. A higher overdischarge rate resulted in a faster temperature increase in the batteries. Moreover, the following temperatures increased: Tu, at which the voltage decreased to 0 V; Ti, at which the current decreased to 0 A; and the maximum temperature during the battery overdischarge (Tm). The following times decreased: tu, when the voltage decreased from 3 to 0 V, and ti, when the current decreased to 0 A. The discharge capacity of the batteries was 3.06–3.14 Ah, and the maximum discharge depth of the batteries was 105.51–108.27%. Additionally, the characteristic overdischarge behavior of the batteries in a high-temperature environment (55 °C) was investigated. At high temperatures, the safety during overdischarging decreased, and the amount of energy released during the overdischarge phase and short-circuiting decreased significantly. Shallow overdischarging did not significantly affect the battery capacity recovery. None of the overdischarging cases caused fires, explosions, or thermal runaway in the batteries. The NCM811 batteries achieved good safety performance under overdischarge conditions: hence, they are valuable references for battery safety research.