Understanding lithium transport in SEI films: a nonequilibrium molecular dynamics simulation

Abstract

ABSTRACTThe transport properties of the solid electrolyte interphase (SEI) play an important role in the charging and discharging process of lithium-ion batteries (LIBs). We used nonequilibrium molecular dynamics (NEMD) simulation to mimic the lithium permeability of SEI films with different chemical compositions, thicknesses and densities. We found the order of permeability to be Li2CO3 > LiF > compound > Li2O > LiOH. Permeability is likely more affected by the binding energy between the lithium ions and the SEI atoms than by structural qualities such as surface area and porosity. The density profiles indicate lithium ions tend to accumulate on the SEI–vacuum interface when the film is less permeable. The transport process does not satisfy Einstein’s diffusion equation, thereby revealing the nonequilibrium nature. The relationship between the chemical compositions, densities, thicknesses and permeabilities of each film is expressed by an empirical equation, which can be used to quickly predict the transport properties of SEI films.