Thermal runaway inhibition and propagation blocking in 18650 cylindrical lithium-ion battery under controlled oxygen environments

Thermal runaway (TR) in lithium-ion batteries (LIBs) poses a significant safety hazard to electric vehicles and energy storage systems. This work systematically investigates the thermal runaway behavior and the corresponding inhibition mechanisms in 18650 LIBs. Repeated thermal abuse tests were conducted in accordance with the GB 38031-2025 standard, utilizing a nitrogen injection system to achieve precise oxygen level control. The flame extinction thresholds during the intense jetting and burning stage were determined to be 9% O2 for a 75% state of charge (SOC) battery and 5% O2 for a 100% SOC battery. At this point, inhibition efficiency is calculated to be 0.28 and 0.29, respectively, with the corresponding mass losses reduced to 25.25 g and 27.35 g. Notably, a critical reignition phenomenon was observed, which highlights the dynamic instability of combustion under oxygen-limited conditions. To characterize the coupling relationship between heat diffusion and the TR intensity under different oxygen levels, a dimensionless model was proposed, which accurately captures the temperature decay above the safety valve. Furthermore, module scale tests verified the effectiveness of the critical inhibition thresholds and revealed the mechanism for blocking the TR propagation. When the oxygen level was reduced to 9%, the TR propagation speed was decelerated from 0.499 layer/min to 0.288 layer/min. The 5% critical oxygen threshold can completely prevent combustion and substantially weaken inter-cell thermal radiation and convection, thereby successfully blocking cascading TR propagation. These findings provide practical and actionable design guidelines for evaluating inert gas inhibition strategies for lithium-ion battery systems.