Ethylene Carbonate Reduction on Lithiated Surfaces of Hydroxylated Amorphous Silicon Dioxide

Abstract

Ab-initio molecular dynamics simulations are used to elucidate the reactivity between ethylene carbonate (EC) molecules and lithiated amorphous hydroxylated silicon dioxide films. The EC molecules are modeled in liquid phase, while the amorphous hydroxylated silicon dioxide films are modeled at various Li contents. It is observed that EC molecules always interact with the film surface via electrostatic interactions between the EC carbonyl oxygen and the Li-ions on the film surface and these interactions were observed to be independent of the Li content. Reduction of EC molecules was observed only in films with a Li/Si ratio above 2.22 where it proceeds via a simultaneous two-electron transfer mechanism. This study clarifies how the EC molecules approach the lithiated film surface and their reactivity changes on films with Li/Si ratios below 2.22 where the reaction is thermodynamically not favorable. Dissociation of hydroxyl groups on the film surface and posterior formation of Si-H and O-Li bonds triggered by surface interactions with the EC liquid phase are observed. It is suggested that O atoms in the oxidized films play an important role as sinks of negative charge in the post-lithiation film. Plausible reasons for the slightly lower reactivity of the lithiated oxidized films are given.