Interfacial structures and decomposition reactions of hybrid anion-based ionic liquids at lithium metal surface from first-principles and ab initio molecular dynamics

Abstract

Ionic liquids (ILs) based on hybrid anions have recently been investigated as appealing alternative electrolytes for energy storage devices, because such asymmetric anions have the potential to reduce melting point and inhibit crystallization of ILs without losing advantages found for the common symmetric ones. In this work, interfacial structures and decomposition reactions of the ILs consisting of two hybrid anions (FTFSI− and MCTFSI−) with the [BMP] cation at lithium metal surface were intensively studied using the combination of first-principles DFT calculations and ab initio molecular dynamics (AIMD) simulations. The corresponding ILs comprising the symmetric anions (TFSI− and FSI−) were also considered for comparison. The adsorption of the ILs on the surface is governed by the interactions between the anions and the substrate mainly via the Li−O bonds. For [BMP][FTFSI] rapid decomposition of the anion triggered by the S−F and S−N bond cleavage was observed, while the first reaction step for [BMP][MCTFSI] involves the breaking of the C−S and S−N bonds of the anion. Particularly, the differences of adsorption properties and reaction mechanisms for these two classes of ILs on the Li surface were demonstrated in detail.