Comprehensive analysis of sidewall-rupture-induced thermal runaway propagation in cylindrical lithium-ion batteries

Thermal runaway (TR) propagation in a battery module can cause catastrophic failures. However, the role of sidewall rupture in lithium-ion batteries in promoting TR propagation remains poorly understood. This work presents an in-depth investigation of TR propagation behaviour in a planar cell cluster consisting of eight high-specific-energy 21,700-format cells. The TR propagation behaviour, including the temperature distribution of gases, ejecta, and cell surfaces, was first characterized using a high-speed infrared camera. The results indicate that, within the present dataset and over the spacing range tested (0.0–1.5 mm), cell spacing had no clear effect on propagation order. The failure morphology of the adjacent cells after flame exposure could be classified into four types: normal venting, sidewall rupture, collapse, and mixed failure involving both sidewall rupture and collapse. Any effect of spacing appeared to be reflected primarily in a redistribution of morphology categories rather than in a change in the dominant failure mode. Although cell spacing influenced several aspects of TR propagation, no clear dependence of residual battery mass on cell spacing was observed in the present dataset, suggesting that residual battery mass was not strongly associated with cell spacing under the tested conditions. Finally, the quantitative relationships between internal pressure and sidewall rupture, as well as between external loads applied to the cell and its buckling behaviour, were analysed. These results provide a foundation for elucidating TR propagation mechanisms associated with sidewall rupture and for reducing TR propagation risk through optimized battery-can design to enhance overall battery safety.