Sulfone-assisted-NH4I as electrolyte additive with synergistic dissolution and catalysis effects on reducing the activation voltage of Li2S cathode

Abstract

Li2S is highly desired for high energy-density lithium sulfur batteries since it allows to be matched with Li metal-free anodes and alleviates the volume expansion of S cathode. However, Li+ extraction from Li2S usually suffers from a huge voltage barrier due to its poor electron conductivity and sluggish Li+ ion diffusion during activation. In this work, trace sulfone-assisted-NH4I is adopted as an electrolyte additive with synergistic dissolution and catalysis effects to alleviate the voltage barrier of Li2S. On one hand, the intercalation between sulfone-NH4+ and Li2S turns solid Li2S into liquid phase, which significantly speeding up the transport of electrons and Li+ ions during activation. On the other hand, I− works as a redox mediator, which further facilitates the oxidation of Li2S to polysulfides. By taking the advantages of synergistic dissolution and catalysis effects from sulfone-NH4+ and I−, the Li2S cathode can be activated at ~3.0 V with a very flat plateau. Finally, the Li2S cathode cycled in the electrolyte with optimized 0.5% sulfone-assisted-NH4I additive shows a high initial discharge capacity of 1160 mAh g−1 at 0.05C, along with enhanced cycling performances and rate capabilities.