The mechanism of Li2S activation in lithium-sulfur batteries: Can we avoid the polysulfide formation?

Abstract

Abstract Electrochemical reactions in the Li S batteries are considered as a multistep reaction process with at least 2–3 equilibrium states. Here we report a possibility of having a conversion of Li 2 S into sulfur without detectible formation of polysulfides. That was confirmed by using a novel material system consisting of carbon coated Li 2 S particles prepared by carbothermal reduction of Li 2 SO 4 . Two independent in operando measurements showed direct oxidation of Li 2 S into sulfur for this system, with almost negligible formation of polysulfides at potentials above 2.5 V vs. Li/Li + . Our results link the diversity of first charge profiles in the literature to the Li 2 S oxidation mechanism and show the importance of ionic wiring within the material. Furthermore, we demonstrate that the Li 2 S oxidation mechanism depends on the relative amount of soluble sulfur in the electrolyte. By controlling the type and the amount of electrolyte within the encapsulating carbon shell, it is thereby possible to control the reaction mechanism of Li 2 S activation.