Explosion characteristics of thermal runaway gases from nickel cobalt manganese (NCM) and lithium iron phosphate (LFP) batteries under elevated temperatures and pressures: Experiments and chemical kinetic analysis

This study systematically elucidates the explosion characteristics and kinetic mechanisms of gases released during thermal runaway in lithium-ion batteries with varying cathode chemistries. Experiments were conducted in a 60 L constant-volume explosion vessel for using reconstructed combustible vent gas mixtures derived from nickel cobalt manganese (NCM) and lithium iron phosphate (LFP) batteries. Specifically, the effects of initial pressure variation at 300 K and initial temperature variation at 100 kPa on the explosion parameters, flame propagation characteristics, and reaction kinetics were investigated. The explosion experiments showed that, for both systems, the maximal explosion pressure ( P max ) and the maximal pressure rise rate ((d P /dt) max ) initially increase and subsequently decrease with increasing equivalent ratio ( φ ), whilst the characteristic time exhibits a U-shaped trend. An increase in the initial pressure ( P 0 ) markedly intensifies the explosion, whereas an increase in the initial temperature ( T 0 ) promotes reaction initiation and accelerates flame propagation. Compared with the LFP system, the NCM system exhibits higher explosion index ( K G ) and laminar burning velocity (LBV), indicating a greater explosion hazard. Analyses of rate of production (ROP), sensitivity, and reaction pathways indicate that the key elementary reactions in the combustion of both systems are R3 (H 2 + OH <=> H 2 O + H), R1 (H + O 2 <=> OH + O) and R2 (H 2 + O <=> OH + H), with the NCM system exhibiting higher sensitivity coefficients. At the moment of maximum temperature rise rate, the dominant reaction networks of the two systems are broadly similar. Notably, compared to an increase in T 0 , an increase in P 0 has a more pronounced influence on key elementary reactions and sensitivity coefficients, proving more effective in strengthening the dominant reaction pathways.