Synthesis, structure, and electrochemical properties of crystalline Li–P–S–O solid electrolytes: Novel lithium-conducting oxysulfides of Li10GeP2S12 family

Abstract

Novel lithium-ion (Li+)-conducting oxysulfides of the Li10GeP2S12 family were found in the ternary Li2S–P2S5–P2O5 system; Li10GeP2S12-type solid solutions with compositions Li3+5xP1−xS4−zOz (x=0.03–0.08, z=0.4–0.8) were confirmed. The solid solutions showed ionic conductivities from 4.14×10−5 to 2.64×10−4Scm−1 at 298K and a wide electrochemical window of 0–5.0V (vs. Li/Li+). Among the solid solutions synthesized, the purest phase had the composition Li3.35P0.93S3.5O0.5 (x=0.07, z=0.5). Structural analysis revealed that the novel oxysulfides are isostructural to the original Li10GeP2S12 structure and the (P/□)(S/O)4 tetrahedra, which indicates the presence of cation defects with oxygen substitution in the crystal structure. Electrochemical stability of the oxysulfides was confirmed in the voltage range of 0–5.0V. The solid-electrolyte interphase (SEI) resistivity and its cycle-dependence evaluation for new materials demonstrated that the oxysulfides had lower resistivities and furnished well-contacted SEI layers during the charge–discharge process.