First-Principles Study of Oxyhydride H^– Ion Conductors: Toward Facile Anion Conduction in Oxide-Based Materials

H– ion conductor materials have the great potential to enable high-energy density electrochemical storage based on hydrogen. Fast H– conduction has been recently demonstrated in the La2–x–ySrx+yLiH1–x+yO3–y oxyhydride materials. However, little is known about the H– diffusion mechanism in this new material and its unique structure. The origin of such exceptional H– conduction in the oxide-based materials is of great interest. Using first-principles calculations, we studied the energetics and diffusion mechanisms of H– ions as a function of structures and compositions in this oxyhydride system. Our study identified that fast H– diffusion is mediated by H– vacancies and that the fast two-dimensional or three-dimensional H– diffusion is activated by different anion sublattices in different compositions. In addition, novel doping was predicted from ab initio computation to increase H– conductivity in these materials. The unique two-anion-site feature in this structural framework enables highly tunable lattice and minimizes the blocking of anion diffusion by oxygen sublattice, allowing high mobile-carrier concentration and good diffusion network. This conclusion offers general guidance for future design and discovery of novel oxide-based anion conductors.