Electrochemistry and structure of locally concentrated surface-active ionic liquids

Diluting the surface-active ionic liquid 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (BMIM AOT) with the non-solvating diluent 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE) will reduce viscosity while preserving essential nanostructures and electrochemical properties, creating locally concentrated ionic liquids (LCILs) suitable for energy storage applications.

BMIM AOT:TFTFE mixtures at 2:1, 1:1, and 1:2 weight ratios were investigated using rheological measurements, conductivity analysis, cyclic voltammetry, electrochemical impedance spectroscopy, small- and wide-angle X-ray scattering (S/WAXS), and atomic force microscopy (AFM).

TFTFE addition at 1:1 weight ratio reduced BMIM AOT viscosity by 99 % and increased conductivity by over one order of magnitude while maintaining electrochemical stability (>4 V). S/WAXS revealed preservation of characteristic sponge-like nanostructures in the bulk for all BMIM AOT:TFTFE mixtures investigated. Differential capacitance measurements showed enhanced charge storage capabilities, with maximum performance at 1:1 ratio due to improved ion mobility. AFM showed that TFTFE enhances solvophobic segregation at neutral interfaces but reduces interfacial nanostructures at charged surfaces. These findings reveal that SAIL-based LCILs achieve optimal balance between low viscosity and stable nanostructures, making them promising electrolytes for energy storage devices requiring fast charge-discharge rates and electrochemical stability.