Impact of Co-Solvent and LiTFSI Concentration on Ionic Liquid-Based Electrolytes for Li-S Battery

Various organic compounds were investigated as co-solvents in an ionic liquid (IL), N,N -butylmethyl pyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr 14 TFSI), based electrolyte for Li-S batteries. For the Pyr 14 TFSI/Co-solvent binary system, only 1,3-dioxolane (DOL) afforded stable cycling performance with reasonable Coulombic efficiency (CE). Further increase in DOL concentration leads to a higher initial capacity but deteriorated CE. In an attempt to balance CE and capacity, 2.0 M LiTFSI Pyr 14 TFSI/DOL (2:1) exhibited optimal performance in terms of initial discharge capacity of 896 mAhg −1 and CE of 98.1% for over 200 cycle. The role of DOL and salt concentration interplay in the binary electrolyte was simulated by ab-initio molecular dynamics (AIMD). The solvation energy with varying co-solvent and LiTFSI salt concentration provides useful information when looking toward implementing other IL-based electrolyte systems for Li-S chemistry.