A Coupled Thermal Runaway and Fire Dynamics Model for a 100 Ah Cylindrical Lithium-ion Battery Module

Abstract This study presents a coupled model incorporating a thermal propagation model and a fire model to investigate the fire safety of a large lithium-ion battery (Li-ion) module. The thermal propagation model employs a three-dimensional (3D) finite element method (FEM), while the fire model utilizes computational fluid dynamics (CFD). Literature data on material properties and thermal runaway characteristics of 18650 cells with Nickel-Manganese-Cobalt (NMC) chemistry, including the onset temperature of rapid thermal runaway (TR), maximum cell temperature, vent gas composition, and volume, are used as input data. Simulation results highlight that thermal convection serves as the dominant heat transfer mechanism, contributing over 50 % of the total heat flux driving TR propagation. TR propagation initiates gradually but accelerates rapidly in a string-wise pattern. The gas temperature inside the module significantly influences TR process through convective heat transfer. The computed heat release exhibits linear correlation with experimental values, but underpredicts total heat release by approximately a factor of three. This discrepancy is likely due to the omission of combustion of solid particles as well as heat release from ancillary components (e.g., cables, insulation in the module). The calculated total heat release correlates linearly with the cumulative number of cells entering TR, confirming that accurate TR propagation modelling is critical for reliable prediction of overall energy release.