Preventing Capacity Fading in Lithium-Sulfur Batteries Using Sulfur Confinement in Mesoporous Carbon and Fluorinated Solvent-Based Electrolytes

The capacity of lithium-sulfur (Li-S) batteriesfadescontinuously with the increasing number of charge-dischargecycles as a result of the dissolution of lithium polysulfides (Li2S x , x = 4-8)generated during charge and discharge into the electrolyte. To mitigatethis, a fluorinated solvent-based electrolyte was applied to a mesoporouscarbon cathode containing confined sulfur for use in a Li-Sbattery. During operation, a solid electrolyte interface (SEI) wasformed at the surface of the positive electrode because of electrolytedecomposition, and the SEI significantly suppressed the dissolutionof the lithium polysulfides. The chemical composition and formationmechanism of the SEI were determined through X-ray photoelectron spectroscopyand operando soft X-ray absorption spectroscopy analyses. Crucially,the Li-S battery assembled with the fluorinated electrolyteexhibited favorable discharge rate performance (620 mAh/g-of-sulfurat a 5C rate) and good cycling stability.