Lithium-ion batteries is pervasively used for electric vehicles and energy storage stations, however, it is causing fire hazard because it has the thermal runaway problem. Micro-scale defects in lithium-ion batteries can trigger thermal runaway which subsequently propagates from localized points to other areas within the battery. While extensive research has been conducted on the dynamics of thermal runaway propagation of batteries, the specific mechanisms governing the evolution of thermal chemical reactions coupled with heat transfer remain unclear. This study focuses on the thermal runaway front (TRF) in lithium-ion batteries, which is characterized by intense reactions and complex failure mechanisms, serving as the boundary between the failure and intact regions during thermal runaway. Similar to the flame front in combustion science, the thermal runaway front velocity (vTR) derived from the principles of energy conservation and flame front theory, is found to correlate positively with the 1/2 of both the thermal conductivity and reaction rate. High-speed camera in-situ observations of the TR propagation dynamics showed that gas diffusion on the anode creates micro-channel flow paths, that influenced the heat and mass transfer processes, leading to a maximum acceleration of velocity by 28.28%. The velocity formula is capable of predicting various explosive modes driven by gas-solid interaction within the battery and provides an explanation for phenomena such as sustained thermal runaway venting and events resulting in sudden death type thermal runaway. Additionally, a “reaction cone” physical model is proposed, outlining self-limiting conditions for reaction suppression, heat transfer inhibition, and enhanced cooling in extensive thermochemical reactions, which guides the design of safe battery