Li-Ion Conductivity of Single-Step Synthesized Glassy-Ceramic Li 10 GeP 2 S 12 and Post-heated Highly Crystalline Li 10 GeP 2 S 12 .

Li 10 GeP 2 S 12 is a phosphosulfide solid electrolyte that exhibits exceptionally high Li-ion conductivity, reaching a conductivity above 10 -3 S cm -1 at room temperature, rivaling that of liquid electrolytes. Herein, a method to produce glassy-ceramic Li 10 GeP 2 S 12 via a single-step utilizing high-energy ball milling was developed and systematically studied. During the high energy milling process, the precursors experience three different stages, namely, the 'Vitrification zone' where the precursors undergo homogenization and amorphization, 'Intermediary zone' where Li 3 PS 4 and Li 4 GeS 4 are formed, and the 'Product stage' where the desired glassy-ceramic Li 10 GeP 2 S 12 is formed after 520 min of milling. At room temperature, the as-milled sample achieved a high ionic conductivity of 1.07 × 10 -3 S cm -1 . It was determined via quantitative phase analyses (QPA) of transmission X-ray diffraction results that the as-milled Li 10 GeP 2 S 12 possessed a high degree of amorphization (44.4 wt %). To further improve the crystallinity and ionic conductivity of the Li 10 GeP 2 S 12 , heat treatment of the as-milled sample was carried out. The optimal heat-treated Li 10 GeP 2 S 12 is almost fully crystalline and possesses a room temperature ionic conductivity of 3.27 × 10 -3 S cm -1 , an over 200% increase compared to the glassy-ceramic Li 10 GeP 2 S 12 . These findings help provide previously lacking insights into the controllable preparation of Li 10 GeP 2 S 12 material.