Fast Lithium Ion Diffusion in Brownmillerite ${\mathrm{Li}}_x{\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_5$

Abstract

Ionic conductors have great potential for interesting tunable physical properties via ionic liquid gating and novel energy storage applications such as all-solid-state lithium batteries. In particular, low migration barriers and high hopping attempt frequency are the keys to achieve fast ion diffusion in solids. Taking advantage of the oxygen-vacancy channel in ${\mathrm{Li}}_x{\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_5$, we show that migration barriers of lithium ion are as small as 0.28~0.17eV depending on the lithium concentration rates. Our first-principles calculation also investigated hopping attempt frequency and concluded the room temperature ionic diffusivity and ion conductivity is high as ${10}^{-7}\sim {10}^{-6}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$ and ${10}^{-3}\sim {10}^{-2}\mathrm{S}\cdot {\mathrm{cm}}^{-1}$ respectively, which outperform most of perovskite-type, garnet-type and sulfide Li-ion solid-state electrolytes. This work proves ${\mathrm{Li}}_x{\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_5$ as a promising super-ionic conductor.

8 pages, 7 figures