Multi-scale thermal runaway analysis of sodium-ion batteries and comparative safety assessment with lithium-ion batteries

As a burgeoning alternative to traditional energy storage, sodium-ion batteries (SIBs) offer distinct advantages for large-scale energy storage due to their cost-effectiveness. However, knowledge gaps of the safety of SIBs still remain. This paper addresses these gaps by providing a comprehensive analysis of the thermal and explosion hazards of SIBs with Na_xNiFeMnO₂ (NFM) cathodes, compared with similar capacity lithium-ion batteries (LIBs), LiFePO₄ (LFP) and LiNi_xCo_yMn_1-x-yO₂ (NCM) batteries, using an accelerated calorimeter. Additionally, differential scanning calorimetry is employed to probe the heat sources in the thermal runaway (TR) processes of SIBs. Results indicate that the self-heating temperature and TR occurrence temperature of the NFM cell are 55.02 °C and 215.81 °C, respectively, with a mass loss ratio is close to that of NCM cell, posing a high explosion severity. Gas chromatography revealed similar gas compositions to LIBs, with a notable CH₄ concentration. The lower and upper explosive limits for NFM cells are calculated to be 5.18 % and 30.48 %, respectively. The explosion limit range for NFM cells falls between those of NCM and LFP cells. Eight key parameters corresponding to the likelihood and severity of the thermal and explosive hazards are considered, to establish multiscale safety assessment. The overall risk of TR can be ranked as: NCM > NFM > LFP cells. However, the NFM cells showed lower tolerance to side reactions and slightly lower explosive hazards compared to NCM cells. This study provides guidance for designing high-safety SIBs and offers a novel safety assessment framework for secondary batteries.