Valence state of Mo and electrochemical properties of Na3-2xSb1-xMoxS4-xIx based solid-state electrolytes

Among the chalcogenide solid-state electrolytes (SSEs), Na3SbS4 is of particular importance because of its high ionic conductivity and compatibility with moist air, which reduces processing costs and favors large-scale industrial deployment. However, the cation doping effects on the electrochemical properties of the Na3SbS4 remain elusive. Here, a series of Na(3-2x)Sb(1-x)MoxS(4-x)Ix (x = 0.05, 0.1 0.15, 0.2) SSEs were fabricated via the ball milling and melt quenching strategy. The valence state of Mo is revealed to be 4+ not 6+. A high ionic conductivity of 0.54 mS cm−1 and an excellent critical current density of 1.5 mA cm−2 was obtained at room temperature. The cycling life of the symmetric cell is up to 112 h. The as-prepared SSEs also exhibit outstanding chemical stability. This work provides insightful understanding of the valence state of cations and impacts on the electrochemical performance of chalcogenide SSEs, which are vital for designing optimal SSEs.