Native Defects in Li10GeP2S12 and Their Effect on Lithium Diffusion

Defects in crystals alter the intrinsic nature of pristine materials including their electronic/crystalline structure and charge-transport characteristics. The ionic transport properties of solid-state ionic conductors, in particular, are profoundly affected by their defect structure. Nevertheless, a fundamental understanding of the defect structure of one of the most extensively studied lithium superionic conductors, Li 10 GeP 2 S 12, remains elusive because of the complexity of the structure; the effects of defects on lithium diffusion and the potential to control defects by varying synthetic conditions also remain unknown. Herein, we report, for the first time, a comprehensive first-principles study on native defects in Li 10 GeP 2 S 12 and their effect on lithium diffusion. We provide the complete defect profile of Li 10 GeP 2 S 12 and identify major defects that are easily formed regardless of the chemical environment while the presence of path-blocking defects is sensitively dependent on the synthetic conditions. Moreover, using ab initio molecular dynamics simulation, it is demonstrated that the major defects in Li 10 GeP 2 S 12 significantly alter the diffusion process. The defects generally facilitate lithium diffusion in Li 10 GeP 2 S 12 by enhancing the charge carrier concentration and flattening the site energy landscape. This work delivers a comprehensive picture of the defect chemistry and structural insights for fast lithium diffusion of Li 10 GeP 2 S 12 -type conductors.