Revealing particle venting of lithium-ion batteries during thermal runaway: A multi-scale model toward multiphase process

Safety issues raised by thermal runaway (TR) are the main obstacle hindering the booming of lithium-ion batteries. A comprehensive model can potentially help improve understanding of the TR mechanisms and assist the battery pack design. However, previous models generally neglected the particle ejection, which is integral to predicting TR. In this study, a multi-scale model for the multiphase process of battery venting has been proposed, covering the entire chain of chemical reactions and physical transformation during TR. A lumped model in battery scale unveiled the interplay of thermal abuse progression and pressure accumulation. The computational fluid dynamics coupled with the discrete phase model was adopted to simulate both generated gases and ejected particles. The newly developed model was checked quantitatively by experimental measurements for battery temperature, jet velocity and mass evolution under thermal abuse. Simulation results highlight two violent ejections of particles and gases with inverted conical contours, consistent with visualization by laser technique in the experiment. The electrolyte vapours are found to dominate the gas release before TR, while the generated reaction gases become the major release after the burst of chain reactions. The developed model fulfils the TR prediction including particle ejection, which can provide new references for the thermal safety design of battery packs.