Miscibility of Li4GeO4 into Li3PS4 Solid Electrolytes from First-Principles Methods

Lithium-based oxysulfide solid electrolytes are currently being researched for all-solid-state batteries, as they offer a combination of high electrochemical stabilities and elevated Li-ion conductivities, thus combining the best characteristics of sulfide and oxide solid electrolytes. In this work, we investigated the miscibility of Li3PS4 and Li4GeO4 polyanions. Building upon a robust multiscale first-principles methodology, we explore the configurational disorder arising from the mixing of GeO44- and PS43- in the (1 - x)Li3PS4-xLi(4)GeO(4) tie line. The computed phase diagram reveals a stable ordered phase with the composition Li7PO4GeS4. In Li7PO4GeS4, the sulfur atoms initially bound to pentavalent phosphorus as PS43- are fully exchanged with oxygen atoms (from GeO44-), giving rise to GeS44- moieties. Ab initio molecular dynamics simulations predicted a high Li-ion conductivity of similar to 13.31 mS cm(-1) for Li7PO4GeS4 at 573 K. These results reveal the structural complexity and flexibility of these polyanion systems.