Reversible ionic liquids (RevILs) are a class of solvents which are promising for a range of applications. RevILs have shown structurally dependent properties by changing their functional group and exhibited dramatic property changes between their molecular liquid (ML) and ionic liquid (IL) states. These unique characteristics of RevILs suggest a method of creating a suite of designer solvents that meet various chemical applications[1, 2]. The concept of “reversibility” lies in the ability of the RevIL to switch from ML to IL with CO₂ addition and to switch back from IL to ML with a mild heating, showing dramatic difference of properties [1]. Non-electrochemical applications using RevIL systems include CO₂ capture and separation [1].

The RevIL will exist in the ionically-insulating and relatively non-polar ML state, as synthesized, while IL state can be ionically conducting and relatively polar compared to the ML. Additionally, the RevIL properties will change as different functional groups are introduced. The tunability and switchability of the RevILs also make them promising for alternative uses in electrochemical systems[3].

This work investigates the feasibility of RevIL switchable solvents for use as switchable electrolytes in electrochemical applications. Silylamine RevILs are used in this study, and their properties as switchable electrolytes including conductivity, viscosity, and reversibility are primarily investigated. We will also show the change of properties as functional group changes. The change in conductivity and viscosity have signaled the possibility of implementing silylamines as a co-solvent in battery electrolytes to serve as a thermally-activated safety switch. Because these electrolytes have phase change from IL to ML with polarity and conductivity change at reversal temperature, the reversal temperature has also been studied to provide information about the temperature dynamics of the IL.

[1] J.R. Switzer, A.L. Ethier, E.C. Hart, K.M. Flack, A.C. Rumple, J.C. Donaldson, A.T. Bembry, O.M. Scott, E.J. Biddinger, M. Talreja, M.G. Song, P. Pollet, C.A. Eckert, C.L. Liotta, Design, synthesis, and evaluation of nonaqueous silylamines for efficient CO₂ capture, ChemSusChem, 7 (2014) 299-307.

[2] P.G. Jessop, D.J. Heldebrant, X. Li, C.A. Eckert, C.L. Liotta, Reversible nonpolar-to-polar solvent, Nature, 436 (2005) 1102.

[3] J.D. Jimenez, S. Jung, E.J. Biddinger, Ionicity analysis of silylamine-type reversible ionic liquids as a model switchable electrolyte, Journal of the Electrochemical Society, 162 (2015) H460-H465.