Numerical Investigation of Thermal Runaway and Fire Characteristics in Large-Format Lithium-ion Batteries

Abstract: As the demand for lithium-ion batteries with higher energy density increases, so does the attention towards fire safety. Adoption of larger batteries intensifies energy density, thereby increasing the risk of energy release during thermal runaway. Given the excessively expensive nature of experimental tests, numerical techniques offer a valuable alternative for investigating fire behaviour and flame dynamics in lithium-ion batteries. Consequently, this study employs a modeling approach for vent gas fire simulation on large-format pouch-type batteries with a 100% state of charge (SOC) and a lithium iron phosphate (LFP) cathode. The open-source Fire Dynamics Simulation (FDS) solver was used for the modeling process. The battery's thermal runaway is considered to initiate as a pyrolysis process, producing flammable gases-termed battery vent gases-and a residue representing the solid components post-thermal runaway, analogous to char. The model's validity is verified through experimental tests. Our study introduces novel insights: unlike previous research, our approach demonstrates that modeling the process of thermal runaway beforehand is unnecessary to predict the heat release rate from flaming. Additionally, we comprehensively analyse flame characteristics, including flaming temperature and length, to forecast environmental risks and the potential spread of thermal runaway. The peak heat release rate, flame temperature, and flame length reached 90 kW, 885C, and about 1.9 m, respectively. Keywords: Lithium-ion batteries, Fire behavior, Thermal runaway modelling, Flame characteristics