Insight into the thermal behavior and thermal runaway propagation prevention of large capacity sodium-ion battery

Sodium-ion battery (SIB) is rapidly gaining adoption due to their wide operating temperature range and cost-effectiveness. However, the safety of large-capacity SIB faces increasing challenges with their widespread application. This study focuses on a 220 Ah SIB and its battery module, establishing a three-dimensional thermal abuse model to investigate thermal runaway characteristics under two distinct triggers: external overheating and internal short circuit. Based on these characteristics, a thermal runaway propagation resistance strategy is proposed, integrating high flame-retardant thermal insulation materials and active liquid cooling management. It is found that under external overheating (800 W) and internal short circuit (0.01 Ω, 5 mm radius) conditions, thermal runaway is triggered at 325 s and within 7 s, respectively, with the entire process lasting only 60 s and 79 s; peak temperatures reach 1240 °C (external surface) and 1697 °C (short-circuit point). Moreover, ceramic fiber and basalt fiber insulation layers (4 mm thick) extend the thermal runaway propagation time of the battery module by 1,590 s and 12,710 s, respectively, effectively delaying failure. Additionally, active liquid cooling reduces the battery module temperature by up to 25.3 °C, maintaining it below 60 °C and safely below the SEI decomposition threshold. This work provides quantitative theoretical insights and protective strategies for the safety design of large-capacity sodium-ion batteries under complex operating conditions.