Initiation and propagation of curved reaction front in solids: Insights into solid combustion and battery thermal runaway

Abstract

As decarbonization and carbon neutrality become increasingly important, battery research has received more and more attention. One of the great challenges in battery is thermal runaway and its propagation, which is fundamentally a combustion problem featured by reaction-conduction coupling, with negligible effects from mass diffusion in the time scale of interest. In this work, a large Ze number asymptotic analysis was performed to describe spherical and cylindrical reaction front initiation and propagation in solid combustion, assuming one-step global chemistry and infinite Le number. Although the reaction front dynamics bear some similarity to a regular flame with finite, greater-than-unity Le number, a theory based on finite Le number is fundamentally inapplicable to describe the combustion behavior with infinite Le. Analytical results are derived to describe to evolution of reaction front velocity and temperature accounting for the effects of changing curvature as well as the ignition energy. A simplified, explicit formula is also derived to describe the reaction front propagation velocity by directly linking to the burnt temperature, exhibiting very good performance in thermal runaway propagation prediction and experimental design. The results also show smaller critical radius and minimum ignition energy for cylindrical reaction front, leading to greater concerns for thermal runaway propagation triggered by nail penetration, as compared to a local hot spot.