On explosion limits of NCA battery vent gas

Using Li_x (Ni_0.80Co_0.15Al_0.05)O₂ (NCA) battery vent gas (BVG) as an archetypical multi-component mixture, a comprehensive computational investigation with detailed chemical kinetics is conducted on its pressure-temperature explosion limits response characteristics under different states of charge (SOC) and equivalence ratios conditions. The results show that the BVG explosion limits exhibit the characteristics Z-shaped curve under all of the SOC conditions, which demonstrates the dominance of H₂ in the explosion response of the BVG. Furthermore, with increasing SOC, the explosion limit of the BVG mixture moves significantly to the lower temperature regime at high pressures condition. That is because the proportion of C₂H₄ in the BVG increases with increasing SOC, and the nonlinear characteristics of the C₂H₄ on the third explosion limit become more prominent. The more intriguing result is that with increasing equivalence ratio, the explosion limit curve rotates counterclockwise around a crossover point, and it is determined by the chain branching reaction with oxygen and the chain propagation reactions related to H₂ and C₂H₄ for the low- and high-pressure conditions, respectively. To elucidate the key controlling mechanisms, the sensitivity and reaction path analyses under the conditions near the explosion limits of the typical battery vent gas are performed. The dominant kinetic pathways are found to be these of H₂ and CO with the highly reactive H₂[sbnd]O₂ kinetics dominating. Moreover, the small amount of C2 species in BVG has been found to significantly influence the explosion boundary especially at elevated pressures. Results of this study are expected to offer potential options in the anti-fire BVG mixture design strategies, and provide useful guidance for the safety valve control strategy as well as the post-processing of the lithium-ion battery catch on fire.