Analyzing the coupling characteristics of real-time key parameters in the thermal runaway of NCM523 batteries

Lithium-ion batteries (LIBs) based on LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) are widely used in electric vehicles, yet thermal runaway (TR) remains a critical safety challenge. In real battery packs, materials filled between batteries reduce heat transfer during TR, frequently inducing a low-power heating phenomenon that is prevalent yet not fully understood, hindering the development of effective TR suppression and hazard mitigation strategies. Herein, this work investigates NCM523 LIBs' TR characteristics via low-power heating experiments, delineating TR into four stages and identifying key gaseous products. Deflagration is mainly triggered by CO and H₂ from polyvinylidene fluoride decomposition at 260°C, with flame behaviors strongly dependent on state of charge (SOC): high-SOC (>60%) batteries show significant deflagration, while low-SOC ones exhibit variable combustion duration and larger residual mass fluctuation. This work clarifies the gas-flame coupling mechanisms, addresses existing research deficiencies, and provides theoretical support for NCM523 LIB safety design and fire-suppression optimization.