Investigation on thermal and fire propagation behaviors of multiple lithium-ion batteries within the package

•Pioneering study of large-scale lithium-ion batteries fire propagation.•Continuously acceleration of thermal and fire propagation is revealed.•Simultaneous ignition, combustion and ejection of multiple batteries is analyzed.•Innovative measurement of impact pressure in lithium-ion batteries fire. Understanding the fire hazard of lithium-ion battery (LIB) is important for the safety issues during their manufacture, storage, transportation, and usage. In this work, experiments are conducted to analyze the mechanisms of thermal and fire propagation of multiple LIBs in the package. According to the results, it is found that the thermal and fire propagation of multiple LIBs can be triggered easily, and will accelerate continuously. In the later stage of the fire, more and more batteries can be ignited simultaneously. The maximum of 5.6 batteries in Test A ignite at the same time, and in Test B, there can be 32 batteries burning together to reach the largest mass loss rate (MLR). The package with more batteries has higher average MLR and fire propagation has a great effect on the combustion efficiency of LIB. The heat flux and impact pressure results also indicate the simultaneous combustion and ejection of multiple batteries. This work can provide more useful data for fire protection in large-scale battery storage systems.