2D Combustion Modeling of Cell Venting Gas in a Lithium-Ion Battery Pack

With the rapid development of lithium-ion battery technology, powertrain electrification has been widely applied in vehicles. However, if thermal runaway occurs in a lithium-ion battery pack, the venting gas in the cells will spread and burn rapidly, which poses a great threat to safety. In this study, a 2D CFD simulation of the combustion characteristics of cell venting gas in a lithium-ion battery pack is performed, and the possibility of detonation of the battery pack is explored. First, a numerical model for the premixed combustion of venting gas is established using a two-step combustion mechanism. The combustion characteristics are then simulated in a 2D channel for the stoichiometric combustible mixture, and the variations in the flame velocity and pressure increment in the flow channel are analyzed. Next, the effects of the initial conditions inside the battery pack, including the pressure, temperature, and excess air coefficient, on the flame propagation process and pressure variation are evaluated. The results indicate that the flame velocity increases with the increase in the initial pressure or temperature and that the influence of the initial temperature is more acute. The maximum flame speed is achieved with a slightly rich mixture, about 450 mm·s⁻¹. When the excess air coefficient is around 0.9, the flame propagation changes from a slow deflagration to a fast deflagration, which causes a high risk of explosion for the battery pack.