Atomistic Insights into the Role of Grain Boundary in Ionic Conductivity of Polycrystalline Solid-State Electrolytes

It is widely accepted that grain
boundary (GB) in polycrystalline
solid-state electrolytes (SSEs) can substantially reduce ionic conduction,
which is regarded as the most essential property for SSEs. However,
the physical origin of the GB-induced retardation effects remains
unanswered. In this study, molecular dynamics simulations and first-principle
calculations were combined to reveal the role of GBs in ionic conduction
via the evaluation of the thermodynamic–kinetic interaction
between GBs and vacancy in cubic Na3PS4. Our
results suggest that the reduced ionic conduction in GBs is attributed
to the segregation of Na vacancy in the GB core. The GB-blocking effects
strongly depend on both vacancy segregation energy and the number
of segregation sites in the GB core, which are determined by the GB
structure. This study will shed new light on the future design of
polycrystalline SSEs with a high ionic conductivity via grain boundary
engineering.