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

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 Lii 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 V0Li + Li and thus limits the V0Li diffusion at the grain boundaries. The V?Br defect near the grain boundaries can effectively drive V0Li across the grain boundary, thereby converting the carrier of Li+ migration from Lii in the bulk and surface to V0Li 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.

Automated summary

Due to safety concerns with Li ionic batteries, solid electrolytes have been extensively researched. Li-rich anti-perovskite Li3OBr is considered a promising candidate, but achieving high ionic conductivity is challenging due to the crystal lattice's high intrinsic symmetry. This study presents a design strategy that introduces various point defects and grain boundaries to break the high lattice symmetry of Li3OBr crystal, and explores their effect and microscopic mechanism in promoting Li-ion migration.