LiFSI as a functional additive of the fluorinated electrolyte for rechargeable Li-S batteries

Novel electrolyte consisting of ethyl 1,1,2,2-tetrafluoroethyl ether (ETFE), conventional ether 1,3-dioxolane (DOL) and film-forming additive LiFSI was investigated for rechargeable lithium sulfur batteries. It is found that the addition of LiFSI promotes ionic conduction, reduces polysulfide solubility in the electrolyte, and enhances the compatibility of the electrolyte with metallic Li. Consequently, increased reversible capacity, improved cycle stability and rate capability are exhibited in an additive-contained fluorinated electrolyte with moderate amount of DOL. It further reveals that the synergistic function of the fluorinated ether and LiFSI greatly modify and stabilize Li surface. However, rich DOL employed in the fluorinated electrolyte results in excessive polysulfide dissolution and inferior interface quality despite the raised ionic conductivity, which is unfavorable for the overall cell performance instead even though the additive was employed.