LiI-ModifiedGlass-Ceramic Lithium Thioborate: FromFundamentals 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.