Thermal runaway features of lithium sulfur pouch cells at various states of charge evaluated by extended volume-accelerating rate calorimetry

High energy density lithium-sulfur (Li-S) batteries are regarded as the promising next-generation energy stroge devices. The thermal runaway (TR) issues posed by Li-S batteries have been less investigated, while they are critical for the practical application of Li-S batteries. Herein, we first evaluate the TR features of the 1.5 Ah Li-S pouch cell (LSPC) at various states of charge (SOC) using extended volume-accelerating rate calorimetry (EVARC). The specific heat capacity and thermodynamic parameters have been calculated from the recorded data. An intermittent pulse technique has been used to quantify the internal resistance of LSPC during the EV-ARC test. The heat sources in the TR processes of LSPC composed of different chemistries have been probed using EV-ARC and differential thermal analysis (DTA). Moreover, it takes as long as 15.7 min for LSPC with 100% SOC from the sharp drop of voltage to the instantaneous rise of temperature, while it takes 16 s for lithium ion pouch cell (LIPC). The experiment results indicate that the major heat source during TR may not be the internal short circuit but the redox reaction between cathode and anode, which can provide an important insight into the rational design of safe Li-S battery system.