Structure and interaction of mixed ionic liquids with lithium using first-principles calculations

This study employs first-principles and ab initio molecular dynamics (AIMD) calculations to investigate the interactions between mixed ionic-liquid systems (ILs) and lithium-metal surfaces. The systems contain two cations, [C₄mpyr]⁺ and [C₄mpip]⁺, and five anions: [FSI]^-, [TFSI]^-, [FTFSI]^-, [MCTFSI]^-, and [OTF]^-. They were arranged in checkerboard configurations on Li(100), and their interfacial interactions were analyzed using the independent gradient model (IGM), electron density difference (EDD), and charge analysis. Replacing [C₄mpyr]⁺ with [C₄mpip]⁺ produces stronger adsorption in the FSI-, FTFSI-, and MCTFSI-containing systems, but weaker adsorption in the TFSI- and OTF-containing systems. Cation and anion mixing also reduces hydrogen bonding in selected systems, suggesting a potentially favorable effect on electrolyte transport; however, the present vacuum-monolayer model cannot directly quantify bulk viscosity or ionic conductivity. AIMD simulations further indicate that adding [FSI]^- leads to an earlier onset of [MCTFSI]^- decomposition within the simulated trajectories. These findings provide microscopic insight into the initial interactions of mixed ionic liquids with lithium.