Sulfinyl-functionalized fluorinated imide anions for ionic liquids and battery electrolytes

To expediate the development of ionic liquids (ILs) as electrolyte materials for battery application, an adequate correlation between chemical structures of ILs and their inherent properties is essential. Herein, a series of ILs containing sulfinyl-functionalized fluorinated imide anions with a lower valence state sulfur [i.e., S(IV)] are synthesized and suggested as electrolyte candidates for battery use. Our results show that structural modifications of the sulfinyl-functionalized fluorinated imide anions allow precise control of the physical and electrochemical properties of the corresponding ILs, including thermal properties, transport behaviors, and electrochemical stability. Replacing classic sulfonyl group (–SO₂–) with sulfinyl moiety (–SO–) affords ILs with higher structural flexibility, and stronger resistance towards crystallization. The incorporation of longer perfluoroalkyl functionalities slightly increases the oxidative tolerance of the ILs with sulfinyl-functionalized fluorinated imide anions, which may allow more positive participation in building the electrode-electrolyte interface. The present work brings new opportunities for customizing IL-based electrolytes for the conversion-type electrode materials with lower working potentials.