Effect of Heat-treatment Atmosphere on Structural Properties of Li-Y-Cl Solid Electrolytes

Chloride-based solid electrolytes (SEs) exhibit high ionic conductivity and wide electrochemical stability windows, 11 which have attracted much attention as ion conductors in all-solid-state lithium-ion batteries.However, a scalable 12 liquid-phase synthesis method for highly conductive chloride SEs has not yet been established owing to a limited 13 understanding of the effects of synthesis conditions on structural properties.In this study, highly crystalline 14 orthorhombic Li-Y-Cl SEs were synthesized via a pyridine-mediated liquid-phase synthesis method followed by 15 post-heat treatment under an Ar atmosphere.The synthesized Li 2.5 YCl 5.5 exhibited an ionic conductivity of 2.4 16 10 -4 S cm -1 at 25 C and oxidation stability up to 3.14 V versus Li-In.X-ray photoelectron spectroscopy analysis 17 revealed that heat treatment under an Ar atmosphere suppresses Cl release during crystallization, leading to the 18 formation of a highly crystalline orthorhombic phase.This study provides important insights into the role of 19 atmosphere control in the crystallization process of chloride SEs.20