Evaluation of the electrochemical stability, interfacial reaction, and molecular behavior of ether-functionalized pyrrolidinium as novel electrolyte for lithium metal battery by quantum and molecular dynamics simulations

Abstract

Commercial lithium (Li) ion batteries (LIBs) do not satisfy the energy density requirements for vehicle electrification (>350 Wh kg−1); therefore, alternative materials are required. Ionic liquid (IL) electrolytes can meet the energy density requirements using a Li metal anode and have the advantage of being non-flammable. However, a better understanding of the chemical properties of IL electrolytes is essential, as the associated chemical and interfacial stabilities are not well-understood. In this study, potential ILs were explored through ether functionalization (R-O-R’). Using density functional theory calculations, the charge distribution was evaluated with respect to the inclusion of an ether functional group. Electrochemical stability was investigated based on high occupied molecular orbital and low unoccupied molecular orbital energy levels. Furthermore, the decomposition mechanism and interfacial stability were explored through ab initio molecular dynamics simulations. Diffusivity, which is the most important property of electrolytes, was evaluated for [cations+], [anions−], and [Li+] in ILs. The results from this study highlight that the ether functionalization further causes more conductive behavior of lithium ions, makes more electrochemically stable, and determines the time of the ionic liquid-based electrolyte decomposition reaction on the surface of lithium metal. It provides a foundation for ether functionalization and the development of promising IL electrolytes for Li metal battery commercialization.