Ab Initio Computation Design for Fast Ionic Conductors

Abstract

Fast ionic conductor materials are the key component in enabling a variety of electrochemical devices. It is crucial to understand why only a few materials exhibit faster ionic conduction than typical solids and how one can design fast ion conductors following simple principles. Using ab initio modeling techniques, we studied a range of novel fast Li-ion conductor materials and identified the mechanisms leading to fast Li-ion conduction in solid materials. In lithium super-ionic conductors, we show that fast diffusion in super-ionic conductors happens through unique concerted migration mechanism of multiple ions with low energy barrier in contrast to isolated ion hopping in typical solids. We elucidate that low energy barriers of the concerted ionic diffusion are a result of unique mobile-ion configurations and strong mobile-ion interactions in these super-ionic conductor materials. Our theory provides a conceptually simple framework for guiding the design of super-ionic conductor materials. Using first principles computation, we demonstrate this strategy by designing a number of novel fast ion conducting materials. Furthermore, we highlight the design principles for having such crystal structures.