Characterization of fire behaviors associated with a thermal runaway in large-scale commercial LiNi0.8Co0.1Mn0.1O2/graphite cells under external ignition

The fire behaviors of large-format commercial batteries at varying states of charge (SOCs) under an external ignition source were experimentally studied. The thermal runaway of the battery mainly starts in the temperature interval of 470.1-526.5 K. The trigger time and temperature of the thermal runaway present a relatively stronger decreasing tendency with an increase in SOC. This implies that the thermal stability of the battery decreases with SOC. The maximum flame temperature is found in the temperature range of 1062.5-1492.0 K, which depends on the combustion efficiency and flame shape. Two peaks of the observed heat release rate (HRR) show that the battery undergoes two intense burning processes at a low SOC. There is no monotonically increasing relationship between total heat release (THR) and SOC. However, the remaining mass of the battery decreases as SOC increases. This indicates that the materials eject fiercely so that some of them are extremely fast to be ignited, resulting in insufficient combustion, particularly for a battery at a high SOC. The gas emission and physicochemical analysis of residue can support this point. The fire hazards involving thermal risk and gas toxicity are also evaluated and discussed.