New hydrophobic ionic liquids based on (fluorosulfonyl)(polyfluorooxaalkanesulfonyl)imides with various oniums

Sixteen ionic liquids (ILs) based on two new asymmetric imide anions, (fluorosulfonyl)(polyfluorooxaalkanesulfonyl)imide {[(FSO2)(XCF2CF2OCF2CF2SO2)N]−, [5X3O-FOFSI]−, X = H and I}, are synthesized and characterized by in combination with various oniums, including 1,3-dialkylimidazolium, quaternary alkyl (or ether-functionalized alkyl)ammonium, N-alkyl-N-methyl-pyrrolidinium and -piperidinium. Their physicochemical properties are investigated, in terms of phase transitions, thermal stability, density, viscosity, ionic conductivity, electrochemical stability, and the capability as electrolytes to allow Li deposition/stripping. The influences of the structural variations in both the cations and anions, particularly introduction of an ether group into the anion, on the above properties are systematically studied. All the ILs are liquids at room temperature and show low glass transition temperatures, suggesting the high flexibility of the ether-functionalized imide anion. It has been demonstrated that only having an ether group into the polyfluoroalkyl chain of the imide anion affect neither the cathodic nor anodic stability of the anion and their ILs. The ILs based on the [5H3O-FOFSI]− anion have an enough electrochemical stability to allow Li deposition/striping, while those based on the [5I3O-FOFSI]− anion show relatively low cathodic stability due to the presence of a CI bond in the anion.

► Ionic liquids based on (fluorosulfonyl)(polyfluorooxaalkanesulfonyl)imides are prepared.
► Fundamental physical and electrochemical properties are measured.
► They show low melting points or low glass transitions without melting.
► They show wide electrochemical windows.