Redox Active Glyme-Li Salt Solvate Ionic Liquids Based on Tetrabromoferrate(III)

抄録

An equimolar mixture of oligoether solvents, glymes, and Li salt yields a new subclass of ionic liquids (ILs), referred to as solvate ILs, when using an appropriate combination of glyme and Li salt. In this paper a triglyme-Li tetrabromoferrate complex [Li(G3)][FeBr₄] is prepared by combining a crystalline glyme-Li salt complex, [Li(G3)]Br, and an iron(III) bromide Lewis acid, FeBr₃, to demonstrate a solvate IL comprised entirely of complex ions. [Li(G3)][FeBr₄] is characterized in terms of thermal properties, coordination structure, and transport properties. This study reveals that the melting point of [Li(G3)][FeBr₄] is lower than 100°C and that highly dissociated complex ions, [Li(G3)]⁺ and [FeBr₄]⁻, are present both in the molten state and in polar acetonitrile solutions. [Li(G3)][FeBr₄] is thus deemed a good solvate IL. The reversible redox property of the [FeBr₄]⁻/[FeBr₄]²⁻ couple is exploited for the catholytes of rechargeable lithium batteries. The catholyte based on this redox active solvate IL exhibits a highly reversible charge-discharge behavior.