Numerical simulation of initial gas-jet fire evolution under thermal runaway of lithium-ion batteries

Abstract

The instantaneous gas-jet explosion behavior following thermal runaway in batteries poses significant hazards. In this study, a novel three-dimensional numerical model of lithium battery thermal runaway is developed by combining the internal pressure buildup of pyrolysis gases with the subsequent initial jet fire. It is predicted that the internal pressure buildup is caused by the generation of multi-component pyrolysis gases produced by the thermal runaway. The initial jet fire evolution driven by the internal pressure buildup is investigated by focusing on its instantaneous velocity, fire temperature, and concentrations of combustion components. The simulated results reveal that the pressure buildup within the battery follows a distinct power law vs time which causes rupture of the safety valve. The pyrolysis gas jetting initiated at a high temperature of 1750 K and a speed of 450 m/s is over within just 2 milliseconds (ms), while the initial fire lasts for about 6 ms. Due to high-speed jet effects, two vortex currents are initially formed on both sides above the outlet of the safety valve, shifting downstream over time. This causes downstream propagation of the initial jet fire and changes its flame morphology. These results offer crucial insights into the thermal management and safety features required for lithium-ion batteries.