LiI-Modified Glass-Ceramic Lithium Thioborate: From Fundamentals to Applications in Solid-State Batteries

Solid-state batteries are an emerging battery technology rivaling lithium-ion batteries, but before commercialization can occur, new classes of solid-state electrolytes (SSEs) must be investigated to better understand the fundamental properties of these materials and to extend the capabilities of fast charging and cycle life. In this work, we investigate glass-ceramic lithium thioborate (LBS) SSEs with the stoichiometry of Li10B10S20 and utilize a rapid synthesis that enables lithium iodide (LiI) modification in Li10B10S20. We study the structures of four materials with varying amounts of LiI using X-ray diffraction, pair distribution function, and solid-state NMR and find that LiI breaks down the B10S20 supertetrahedra that make up the unit cell of Li10B10S20. More LiI increases ionic conductivity by increasing the unit cell volume and the fraction of the glassy phase in the electrolyte. LiI-modified Li10B10S20 as an anode-facing SSE enables all-solid-state batteries to cycle well with theoretical capacities up 6.37 mAh/cm2 at 0.1C, validating the relevance of LBS SSEs as separators for solid-state batteries.