Research on the thermal runaway mechanism and eruption flame dynamics of NCM811 lithium-ion battery stimulated by the coupling abuse of heat and penetration

•As the initial thermal load increases, the maximum temperature of cell increases.•The thermal-penetration coupled stimulation increases fire risk of thermal runaway.•A phenomenon of “separator melt protection channel” is found.•A micro short circuit model of “kebab”-type is proposed.•Failure mechanism of LIBs under coupled thermal-penetration stimulus is revealed. Thermal abuse and mechanical abuse are the main triggers of thermal runaway (TR) in lithium-ion batteries (LIBs). With the emergence of stimulus superposition application scenarios makes the TR mechanism of LIBs under a single stimulus no longer applicable, and the TR characteristics of LIBs induced by heat-penetration coupled stimulation has become one of the key bottlenecks constraining the intrinsic safety design and control of LIBs. In this paper, an experimental platform for heat-penetration coupled stimulation on LIBs was built, and an experimental research on the TR mechanism and eruption dynamics of LIBs under penetration with different initial thermal load was carried out. The results show that the maximum temperature of cell induced by penetration increases from 537.4 °C to 746 °C, an increase of 38.8 %, as the initial thermal load of the cell increases from 10 °C to 130 °C. When the initial thermal load is further increased to 160 °C, the penetration stimulation no longer induces TR, which is closely related to the “separator melt protection channel”. Based on this, a “kebab” micro-short circuit model is proposed. At 10 °C, 40 °C, 70 °C, and 100 °C, the cell safety valve is destroyed and a “column fire” is formed above the positive electrode. And at 100 °C, the flame eruption height is the largest, up to 185.10 cm, and the jet flame area is the largest, up to 5687.62 cm2.And with the initial thermal load increases, the eruption particles are smaller in size. Increasing content of O in eruption particles, which characterizes the strength of the reaction within the cell, and F elements characterizing toxicity are detected in the eruption particles. The results enrich the theory of TR induced by thermal–mechanical abuse, which is of great guiding significance for the intrinsic safety design of LIBs and the prevention and control of TR risk.