Preparation of Li7P2S8X-Type Solid Electrolytes with Complex Anions for All-Solid-State Lithium Battery Applications

To improve the energy/power density and safety of all-solid-state lithium batteries (ASSBs), sulfide-based solid electrolytes have recently attracted attention. Li7P2S8X solid electrolytes are believed to show highly comparable ionic conductivity and stability against lithium metal. In this study, complex anion-based Li7P2S8X solid electrolytes were prepared for the first time to achieve good stability against lithium metal anodes. The crystalline structure and the role of complex anions in tuning the crystal structure were analyzed using powder X-ray diffraction techniques. Laser Raman and nuclear magnetic spectroscopy analyses were performed to reveal the structural characteristics of complex anion-based Li7P2S8X solid electrolytes. Among all prepared solid electrolytes, the Li7.05Sn0.05P1.95S8(OH)0.25I0.75 solid electrolyte exhibited the highest ionic conductivity of 4.3 mS cm–1 at room temperature. Cyclic voltammetry and DC polarization analysis were carried out to study the stability of solid electrolytes against lithium metal anodes. Interestingly, complex anion:halogen anion-based solid electrolytes exhibited a high critical current density and a long DC cycle stability (>250 cycles).