Design of S-Substituted Fluorinated Aryl Sulfonamide-Tagged (S-FAST) Anions to Enable New Solvate Ionic Liquids for Battery Applications

Electrolytes with improved thermal and oxidative stability must be developed to achieve greater power and energy densities without compromising safety in modern energy storage devices. Because of their much-reduced solvent vapor pressure and expanded electrochemical windows, solvate ionic liquids (SILs) of lithium salts have recently attracted significant attention in this regard. The current palette of SILs is, however, limited to only a few suitable anions with limited chemical functionality. Guided by fundamental physical organic chemistry principles, we designed a new family of S-substituted fluorinated aryl sulfonamide-tagged anions that feature variable numbers of electronically neutral or withdrawing sulfide, sulfoxide, and sulfone substituents. Several salts of these electron deficient anions display very high electrochemical oxidative stability, good solubility, and a weakly coordinating nature that enables the synthesis of Li-based SILs with high thermal and electrochemical oxidative stability. This new family of functional, noncoordinating anions will potentially expand the scope of applications of SILs as safe electrolytes in battery devices.