The importance of clean and efficient energy storage has grown enormously over the past decades, driven primarily by concerns over global warming, diminishing fossil-fuel reserves, and increasing demand for portable electronics and grid storage systems. The performance of energy storage devices depends crucially on the properties of their component materials. Rechargeable lithium ion batteries (LIBs), due to their high energy density superior to all other secondary batteries, have become instrumental in powering nearly all of our small, portable electronics. However, LIBs have their drawbacks. One of the most pressing challenges for LIBs is overheating. During charging, a tendency for growth of small Li filaments, known as dendrites, occurs. The dendrites can short-circuit the cells and trigger a process known as thermal runaway, which can lead to violent overheating reactions. When a LIB overheats, the components inside are at risk of decomposing and undergoing a series of reactions that can generate even more heat and gaseous products. This will induce the liquid electrolyte that comprises organic chemicals to combust. In order to extend the battery life between charges and create a smaller, higher-energy battery, today’s LIBs have twice as much active material and thinner separators, setting the stage for a new generation of heat-triggered recalls. Despite many safety mechanisms have already been incorporated into batteries to prevent inadvertent charging and excessive current, there is little research focusing on exploring the fundamental mechanism of heat transport in LIBs in both stationary and charging conditions and how the excess heat is generated. In this work, by performing first-principles and molecular dynamics simulations, for the first time we give a robust and detailed explanation of the thermal transport mechanism in superionic material Li2S. At the temperature range in which the system can be regarded as a solid, the large hopping of Li is found to be responsible for phonon thermal conductivity’s deviation from the traditional 1/T relationship. At the high temperature range, the contribution of convection and liquid-phonon interaction increase significantly due to the fluidization of Li ions. Furthermore, there is an interplay between the enhanced phonon scattering and the increased force hopping between neighboring atoms as temperature arises, which results in a dip in the evolution of the virial term around 1200K. When the temperature is higher than 1200 K, the virial thermal conductivity increases with temperature due to the contribution of vibrations with extremely short mean free path (diffusons). At 1300 K, more than 46% of the heat carried by the S sublattice is contributed by the carriers with mean free path smaller than a few angstroms, which is the typical hopping distance. Our study provides a clear physical map of the heat transport in superionic battery materials and describes the key mechanisms to guide the design of thermal management in battery electrodes.