Thermal runaway of Li-ion batteries caused by hemispherical indentation under different temperatures: Flame formation process and wreckage analysis

Mechanical abuse leads to deformation and damage of the internal laminate structure of the lithium-ion battery, which in turn affects the thermal runaway (TR) propagation within the battery and flame formation. In this paper, the TR propagation path, TR spray, TR flame ignition mechanism, and battery wreckage characteristics of soft pack batteries in hemispherical indentation tests are investigated. The results show that the propagation path of the high-temperature area on the battery is consistent with the propagation path of the internal gas. Due to the tight constraints under indentation in the laminated structure, gases generated by TR reactions and the electrolyte vapor lead to high internal pressure, triggering ejection behaviour. The ejected flammable gas is ignited by the ejected high-temperature particles and forms the jet fire, which in turn accelerates the propagation of TR, ultimately leading to the formation of radiating cracks in the battery wreckage. As the temperature increases, the TR spreads faster and the ejection becomes more violent, causing the weight of the battery wreckages to drop significantly.