Molecular Design of Nitrile Electrolytes Enabling Lithiated Silicon–Sulfur Batteries with Quasi‐Solid‐State Sulfur Reaction

Abstract The development of lithium–sulfur (Li−S) batteries is hindered by the polysulfide dissolving, cross‐over and the inherent lithium metal anode instability. We herein instead describe a lithiated silicon−sulfur (LiSi−S) battery enabled by molecular engineering of highly solvating nitrile electrolytes toward weakly solvating to fundamentally decouple the reactions of the two electrodes and eliminate their cross‐talk. Specifically, by controlled fluorination of the ethoxy‐nitrile base solvent, the charge distribution on the solvent is manipulated which suppresses the solvation for polysulfides promoting a quasi‐solid‐state sulfur reaction (QSSSR) mechanism. The promoted anion participation in Li + solvation, along with the fluoroethylene carbonate additive, further stabilizes the interphases at both sulfur cathode and LiSi anode mitigating the mechanical degradations. The QSSSR‐based LiSi−S cell shows a high capacity of 1499.0 mA h g sulfur −1 at 0.1C, and achieves a high capacity retention of 90.2% over 100 cycles at 0.2C with an average Coulombic efficiency of 99.9%. This work highlights the essence of molecular engineering for manipulating the primary reactions and interphasial behaviors at both electrodes toward high performance sulfur batteries.