Theoretical Design of Defects as a Driving Force for Ion Transport in Li3OBr Solid Electrolyte

Abstract

Due to ever-increasing concerns about safety issues in using Li ionic batteries, solid electrolytes have extensively explored. The Li-rich anti-perovskite Li3OBr has been considered as a promising solid electrolyte candidate, but it still suffers challenges to achieve a high ionic conductivity owing to the high intrinsic symmetry of the crystal lattice. Herein, we presented a design strategy that introduces various point defects and grain boundaries to break the high lattice symmetry of Li3OBr crystal, and their effect and microscopic mechanism of promoting the migration of Li-ion were explored theoretically. It has been found that (Formula presented.) are the dominant defects responsible for the fast Li-ion diffusion in bulk Li3OBr and its surface, but they are easily trapped by the grain boundaries, leading to the annihilating of the Frenkel defect pair (Formula presented.) and thus limits the (Formula presented.) diffusion at the grain boundaries. The (Formula presented.) defect near the grain boundaries can effectively drive (Formula presented.) across the grain boundary, thereby converting the carrier of Li+ migration from (Formula presented.) in the bulk and surface to (Formula presented.) at the grain boundary, and thus improving the ionic conductivity in the whole Li3OBr crystal. This work provides a comprehensive insight into the Li+ transport and conduction mechanism in the Li3OBr electrolyte. It opens a new way of improving the conductivity for all-solid-state Li electrolyte material through the defect design.