The Interaction Between Fluorinated Additives and Imidazolyl Ionic Liquid Electrolytes in Lithium Metal Batteries: A First-Principles Study

Abstract

This investigation employs first-principles calculations to explore the interaction between imidazolium ionic liquids (ILs) and fluoride additives on lithium metal surface. Our focus lies in the comprehensive analysis of three distinct categories of fluorinated additives, each differing in their degree of fluorination. The computations reveal that fluorination plays a significant role in determining both the ionic conductivity and the formation of the solid–electrolyte interphase (SEI) film. Specifically, heightened fluorination enhances the oxidative stability of the system but diminishes the strength of solvent binding, resulting in the formation of larger salt/anion clusters and a decrease in ionic conductivity. Conversely, increased fluorination facilitates the interaction between fluorinated additives and the lithium metal surface, thereby aiding in the formation of a stable SEI film characterized by an abundance of inorganic LiF components. This is important as it serves to suppress dendrite growth and mitigate interface side reactions. Considering the combined influences of ionic conductivity and film formation, 1FP is suggested as the optimal candidate for pyridine-based additive systems, with FEC preferred for cyclic ester-based additive systems and BC for chain ester-based additive systems. This study provides theoretical references for the design of ionic liquid-fluorinated additive electrolyte systems that can protect the lithium metal anode.