Restoring the gas diffusion field before the fire of the LiNi0.7Co0.2Mn0.1O2 lithium-ion battery thermal runaway

Although ternary lithium-ion batteries promise high energy density, their safety issues have aroused widespread social concern. The thermal runaway phenomenon of ternary lithium-ion batteries presents a violent fire or explosion induced by the sparks. However, the reason for the disaster of thermal runaway remains unclear. This study restores gas diffusion before a fire or explosion using computational fluid dynamics(CFD) in order to explain the germination of the disaster. The calculation results revealed that the diffusion field cane divided into three zones:(1) fuel-surplus zone; (2) fuel‑oxygen zone; (3) oxygen surplus zone. The combustible zone (fuel‑oxygen zone) quickly enlarges after the safety valve is opened and is located on the top of the safety valve, so the deflagration tended to happen on the top of the safety valve a few seconds after the safety valve opened. Besides, the study also established the relationship between venting parameters and time based on the Sigmoid function. The established relationship function could provide boundary conditions for the fire dynamics of lithium-ion battery thermal runaway. Overall, the method could not only be used to further explore the combustion mechanism of lithium-ion thermal runaway, but also provided insight into the safety design of the battery pack structures.