Cell-level comparative ARC study on thermal runaway and gas hazards of LFP and polyanionic Na-ion batteries for residential energy storage

To support cell-level safety assessment for residential energy storage systems, this study compares commercial lithium iron phosphate (LFP) and polyanionic sodium-ion (SIB) batteries under identical accelerating rate calorimetry (ARC) conditions. The surface temperature, voltage, and internal pressure of the batteries were measured to characterize thermal runaway (TR) evolution, while post-test gas chromatography (GC) was used to analyze the final mixed gas composition after thermal runaway. The results indicate that both batteries follow a four-stage TR evolution process, including thermal latency, thermal incubation, thermal eruption, and cooling decay. However, their safety characteristics differ substantially. The LFP battery shows stronger resistance to thermal initiation, with a self-heating onset temperature of 131.48 °C and a thermal runaway warning time of 262.07 min. In comparison, the SIB battery exhibits a milder eruption stage, with a peak temperature of 296.36 °C and a mass-specific heat release of 142.5 kJ/kg, both lower than those of the LFP battery. The SIB battery also shows a more uniform spatial temperature distribution and weaker localized hot-spot formation. Post-test gas analysis shows that the final mixed gas from the SIB battery is dominated by CO₂ (68.12%), with flammable components accounting for 26.18%. However, the SIB battery also produces a higher absolute CO yield than the LFP battery, indicating that CO-related exposure risk requires dedicated attention. This work provides a cell-level comparative dataset for commercial LFP and polyanionic Na-ion batteries under identical ARC conditions, clarifying their trade-offs among thermal stability, eruption intensity, gas yield, flammability, and CO-related toxicity risk.