Laminar burning velocity of lithium-ion battery thermal runaway vent gas in air

In this study, a spherically propagating flame of vent gas generated during the thermal runaway of lithium-ion batteries with different states of charge (SOC) was experimentally and numerically investigated. The vent gas is mainly composed of H2, CO, CO2, and some hydrocarbons. With increasing SOC, the CO2 fraction tends to decrease while the H2 and CO fractions tend to increase. Combustion experiments were conducted using a closed vessel, and the combustion progression was captured using a high-speed Schlieren image system to measure the unstretched laminar burning velocity, Su0. In addition, the combustion was computationally estimated under the experimental conditions by performing 1D planar flame simulations using Chemkin-Pro with the Aramco Mech 1.3 reaction model. Remarkably, the calculated values of Su0 closely matched the experimental ones, demonstrating good agreement. The results showed that Su0 tended to increase with increasing SOC. Furthermore, the effects of the chemical reaction mechanism, which plays a pivotal role in driving this increase in Su0 with increasing SOC, were investigated. Specifically, the heightened SOC levels promoted the H2 branching reaction led to an increased concentration of OH radicals in the mixture. This consequently accelerated the rate-determining reaction for the oxidation of hydrocarbons, leading to an increase in Su0. As an effect of the hydrocarbons in the vent gas mixtures, the number of moles of CO increased slightly near the flame because the rate of CO production in the flame zone was more dominant than that of consumption under the condition of SOC 50.