Anion type-dependent confinement effect on glass transitions of solutions of LiTFSI and LiFSI

Abstract

We present findings on the effect of nanometer-sized silica-based pores on the glass transition of aqueous solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and lithium difluorosulfimide (LiFSI), respectively. Our experimental results demonstrate a clear dependence of the confinement effect on the anion type, particularly for water-rich solutions, in which the precipitation of crystalized ice under cooling process induces the formation of freeze-concentrated phase confined between pore wall and core ice. As this liquid layer becomes thinner, the freeze-concentrated phase experiences glass transition at increasingly higher temperatures in solutions of LiTFSI. However, differently, for solutions of LiFSI and LiCl, this secondary confinement has a negligible effect on the glass transition of solutions confined wherein. These different behaviors emphasize the obvious difference in the dynamic properties’ response of LiTFSI and LiFSI solutions to spatial confinement and particularly to the presence of the hydrophilic pore wall.