Speciation and dipole reorientation dynamics of glass-forming liquid electrolytes: Li[N(SO2CF3)2] mixtures of 1,3-propane sultone or tetrahydrothiophene-1,1-dioxide†

Recently new ionic fluids such as super-concentrated electrolyte solutions, solvate ionic liquids and deep eutectic solvents have attracted much attention in the field of liquid electrolytes for next-generation electrochemical devices and processes. The basic composition of these new ionic fluids is similar among them; a solvent and a large/excess amount of salt mixtures, though the solvent is sometimes a solid at ambient temperatures. Here, we found and demonstrated that LiTFSA (TFSA = (CF₃SO₂)₂N⁻) mixtures with 1,3-propane sultone (PS) or tetrahydrothiophene-1,1-dioxide (SL) yield a homogeneous liquid at room temperature within a wide range of compositions. In order to clarify the uniquely high Li⁺ transference number in these mixtures, speciation and dipole reorientation dynamics were studied to provide evidence of large-size aggregate formation in these mixtures.