The stability and reaction mechanism of a LiF/electrolyte interface: insight from density functional theory

Abstract

In a Li-metal battery, a solid lithium fluoride (sLiF) film, as a coating layer, is widely used to stabilize both the Li-metal and the liquid electrolyte (LE) to suppress unwanted redox shuttles. The sLiF/LE interface significantly affects the performance of the Li-metal battery. Here, to understand the chemistry and the Li-ion transport properties of the solid–liquid interface, we study interfacial reactions and dynamics at the interface between sLiF and a liquid electrolyte (EC, DMC, and LiPF₆) by using a quantum mechanics method. LiPF₆ is found to be chemically unstable at the sLiF/LE interface, and a resistive solid–liquid electrolyte interphase (SLEI) for Li-ion transport forms at the interface. The mobility of the electrolyte molecules and Li-ions near the sLiF/LE interface is much lower than that in a bulk liquid electrolyte. Such a molecular-level understanding of the interfacial processes provides the basis to develop a new interface between a solid and a liquid electrolyte for better Li-ion batteries.