Polymer/ionic liquid thermoplastic electrolytes for energy storage processed by solvent free procedures

Alberto Mejia, Esperanza Benito, Julio Guzman, Leoncio Garrido, Nuria García, Mario Hoyos, and Pilar Tiemblo
ACS Sustainable Chemistry & Engineering, 4 2016, 2114–2121

A series of poly(ethylene oxide) (PEO)/lithium trifluoromethanesulfonate (LiTf)/room temperature ionic liquids (RTIL) composite electrolytes has been prepared by melt compounding, using sepiolite modified with D-α-tocopherol polyethylene glycol 1000 succinate (TPGS-Sep) as filler. These electrolytes have been extensively characterized, including thermal stability, relaxations and transitions, rheology, conductivity, ion diffusivity and salt dissociation. The work shows how the ability of TPGS-S to act as a physical crosslinking site for PEO allows these electrolytes to behave as solids at T>70ºC, while the abundance of an ionic liquid phase makes the ion diffusion coefficients at 25ºC to be considerably high, closer to those of a viscous liquid than to those of a solid phase. This combination of rheological and electrical properties, together with their simple and scalable preparation by melt-compounding makes them a very appealing new class of sustainable electrolytes. This same concept can be applied to electrolytes with other types of salts and therefore electrolytes incorporating Al3+, Mg2+ or Na+ salts can be similarly prepared.