Li10GeP2S12-Type Superionic Conductors: Synthesis, Structure, and Ionic Transportation

Ever since the first report on Li10GeP2S12(LGPS) in 2011, its unique structure and exceptionally high lithium conductivity (>1 x 10(-2)S cm(-1)) have attracted extensive interest, especially for applications in solid-state ionics and batteries. Herein, studies of LGPS and its modifications are reviewed with a focus on the synthesis, structure, and ionic transportation of LGPS. For material synthesis, the relationships between LGPS and its precursor compounds such as Li(3)PS(4)and Li(4)GeS(4)are discussed. A technique for single-crystal growth and a family of LGPS-type materials that are chemically or structurally related to LGPS are then described. The crystal structure of LGPS is analyzed from the viewpoints of tetrahedral framework units, anion sublattice, and Li distributions; furthermore, the conduction mechanism is qualitatively analyzed. Subsequently, ionic transportation in LGPS is studied quantitatively. The origin of the high conductivity is discussed in terms of the activation energy, diffusion coefficient, and its related parameters; and these factors are compared to those of other non-LGPS-type conductors. Then, the battery applications are briefly summarized to indicate the potential merits of using LGPS-type solid electrolytes with high lithium conductivity. Any remaining issues and possible research directions that have emerged from the aforementioned studies are finally highlighted.