Electronic Structure and Binding Characteristics of Ionic Liquid Ions on Li-Metal Surfaces Through a DFT Approach

Understanding the interactions between ionic liquid ions and lithium-metal surfaces is critical for designing safer and more efficient lithium metal batteries. In this work, we use density functional theory to investigate the electronic structure, binding energies, work-function shifts and interfacial charge redistribution of several ionic liquid ions, including FSI−, TFSI−, PF6−, BF4−, DFOB−, Pyr14+, and EMIM+, on a Li-metal anode (Lim). Absorption orientation-dependent effects are examined for each molecule. Specifically, differences in charge density and electron localization function analyses revealed unique patterns of electron accumulation and delocalization that highlighted specific atomic roles in interfacial bonding. Interfacial charge transfer is analyzed through Bader charges, revealing a moderate charge redistribution for the cations (EMIM+, Pyr14+), and a more significant charge uptake for the reactive anions (FSI−, TFSI−, DFOB−). Among cations, EMIM+ was determined to have the most interfacial stability, while Pyr14+ displayed mid-level reactivity. For the anions, varying tendencies for bond formation with lithium metal and potential fragmentation could be determined. Overall, these discoveries detail an atomistic analysis of ionic liquid to Lim interactions providing additional pathways for molecular design techniques to stabilize electrolytes performing not high-cost computational calculations.