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

Li 2 S 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 Li 2 S 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-NH 4 I is adopted as an electrolyte additive with synergistic dissolution and catalysis effects to alleviate the voltage barrier of Li 2 S. On one hand, the intercalation between sulfone-NH 4 + and Li 2 S turns solid Li 2 S 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 Li 2 S to polysulfides. By taking the advantages of synergistic dissolution and catalysis effects from sulfone-NH 4 + and I − , the Li 2 S cathode can be activated at ~3.0 V with a very flat plateau. Finally, the Li 2 S cathode cycled in the electrolyte with optimized 0.5% sulfone-assisted-NH 4 I additive shows a high initial discharge capacity of 1160 mAh g −1 at 0.05C, along with enhanced cycling performances and rate capabilities.