Fluoroalkoxyaluminate-based ionic liquids as electrolytes for sodium-ion batteries

Ionic liquids (ILs) are a promising class of materials because of their unique properties such as high elec-trochemical stability window and intrinsic conductive nature, which are desirable in the development of high-performance electrolytes for energy storage applications. However, the strong Coulombic interac-tions between cation and anion, which contributes to the high viscosity of the ILs, are the main bottleneck in their applications as electrolytes. Weakly coordinated anions-based ILs are a class of electrolytes with high degree of charge delocalization, which leads to weak ionic interactions and improves the ionic trans-port. Here, we have performed molecular dynamics simulations and density functional theory calcula-tions of imidazolium and ammonium-based ionic liquids in different Na' mole fractions comprising the weakly coordinated fluoroalkoxyaluminate anion ([Al(Ohfip)4]-). The results have shown that the 0.8-scaled OPLS-AA based force field predicted the transport properties of neat systems with good accu-racy. The Na'-[anion] pair structural and lifetime analysis suggest that the fluoroalkoxyaluminate pro-motes lower lifetimes and facilitates the mobility of Na' in these systems. Although the cations provided similar transport and structural results for Na', the theoretical electrochemical stability win-dows of the ammonium-derived ILs exhibited values above 5.0 eV, which indicates good performance for energy storage applications.(c) 2022 Elsevier B.V. All rights reserved.