Dense, Melt Cast Sulfide Glass Electrolyte Separators for Li Metal Batteries

Abstract

The data presented here are the first to show, at a device scale, that dense sulfide glass electrolyte films are effective at blocking the penetration of Li metal deposits through a symmetric Li | glass | Li cell. Monolithic glass wafers 4–5 cm in diameter and 400–500 μm thick with a nominal composition of (Li2S)60(SiS2)28(P2S5)12 were made by melt casting. The resulting glass had an ionic conductivity of 1.8 mS/cm and blocks Li deposits at current densities of between 1,400–1,800 μA/cm2 at 25°C. For comparison, porous separators formed by cold compaction of the same glass powder have an ionic conductivity of 0.81 mS/cm and block Li deposits at current densities of only 400 μA/cm2 at 25°C. The lower conductivity of the cold compacted separator suggests that percolation and interparticle impedance of sulfide glass electrolytes is significant. Furthermore, macrocracking and cathodic decomposition versus Li metal were identified as failure modes in the fully dense as-cast glasses and provide insight on how to improve the technology.