Thermal runaway response and structural early warning of large-format sodium-ion batteries in a confined chamber under different triggering modes

The thermal safety of large-format sodium-ion batteries (SIBs) in confined spaces is critical for the deployment of next-generation energy storage systems. In this study, the thermal runaway (TR) behavior and structural early-warning characteristics of 50 Ah prismatic SIBs were investigated under heating, overcharge, and heating + overcharge conditions in a confined chamber. Synchronized temperature, pressure, and expansion-force measurements were combined with heat-source analysis to clarify trigger-dependent failure pathways and precursor signals. The results show that, after safety valve opening, side-reaction heat becomes the dominant heat source under all three triggering modes, indicating that the cell gradually transitions from externally driven or current-assisted heating to internally sustained exothermic reactions. The heating + overcharge condition significantly accelerates cell destabilization and amplifies the thermal hazard, with only 7 s between safety valve opening and TR and the highest maximum temperature-rise rate and peak temperature of 44.9 °C/s and 552.1 °C, respectively. In contrast, overcharge produces the strongest pressure and mechanical responses, with the peak pressure and maximum expansion force reaching 0.539 MPa and 4216.2 N, respectively. Moreover, the rate of force change shows clear precursor characteristics earlier than the surface temperature signal. Warning thresholds of 1.5 N/s for heating and heating + overcharge conditions and 5.0 N/s for overcharge conditions are proposed, providing a force-based criterion for early TR identification of large-format SIBs in confined environments.