Modeling thermal runaway propagation of lithium-ion batteries under impacts of ceiling jet fire

Thermal runaway (TR) of lithium-ion batteries (LIBs) is always accompanied by the emission of combustible gases and the resulting jet fire may promote TR propagation in the battery module. An accurate TR propagation model incorporating jet fire provides insights into the cell-to-cell failure mechanism and aids the safety-optimal design of battery pack. In this work, a modeling framework based on conjugate heat transfer is developed to explore the interaction between jet fire and propagation behavior during TR. The LIBs are modelled by integrating chemical reactions, gas generation and jet dynamics, while the jet fire outside the cells is simulated by the CFD models involving combustion. The heat balance is employed to address TR propagation, which fully considers the energy flows between various elements of battery pack. The proposed model is capable of capturing the flame morphology and temperature evolution of cells, fire and ceiling plate, as confirmed by the TR propagation experiment under ceilings. Simulation results demonstrate that increasing the space confinement degrees shortens the propagation time interval by enhancing the convection from ejected gases and the radiation from flame. The reduction of ceiling height extends the flame extension length and significantly accelerates the cell-to-cell failure, highlighting the impacts of jet fire on TR propagation. This work presents a more realistic model for TR propagation, which can provide a pragmatic guidance for the battery pack's fire protection design and process safety assurance in the practical application.