A comparative study of Li_(10.35)Ge_(1.35)P_(1.65)S_(12) and Li_(10.5)Ge_(1.5)P_(1.5)S_(12) superionic conductors

摘要

Since the lithium-ion conductor Li10GeP2S12 (LGPS) with a super high room-temperature conductivity of 12 mS/cm was first reported in 2011, sulfide-type solid electrolytes have been paid much attention. It was suggested by Kwon et al. [J. Mater Chem. A 3, 438 (2015)] that some excess lithium ions in LGPS, namely, Li10+delta Ge1+delta P2-delta S12, could further improve their ionic conductivities, and the highest conductivity of 14.2 mS/cm was obtained at delta = 0.35 though a larger lattice parameter that occurred at delta = 0.5. In this study, we focus on these two different chemical compositions of LGPS with delta = 0.35 and delta = 0.5, respectively. Both samples were prepared using the same experimental process. Their lattice parameter, microstructure and room-temperature ionic conductivity were compared in detail. The results show that the main phase is the tetragonal LGPS phase but with a nearly identical amount of orthorhombic LGPS phase coexisting in both samples. Bigger lattice parameters, larger grain sizes and higher ionic conductivities are simultaneously achieved in Li10.5Ge1.5P1.5S12 (delta = 0.5), exhibiting an ultrahigh room-temperature ionic conductivity of 18.8 mS/cm.