High Ionic Conductivity with Improved Lithium Stability of CaS- and CaI₂‑Doped Li₇P₃S₁₁ Solid Electrolytes Synthesized by Liquid-Phase Synthesis

Li₇P₃S₁₁ solid electrolytes (SEs) subjected to liquid-phase synthesis with CaS or CaI₂ doping were investigated in terms of their ionic conductivity and stability toward lithium anodes. No peak shifts were observed in the XRD patterns of CaS- or CaI₂-doped Li₇P₃S₁₁, indicating that the doping element remained at the grain boundary. CaS- or CaI₂-doped Li₇P₃S₁₁ showed no internal short circuit, and the cycling continued, indicating that not only CaI₂ including I^– but also CaS could help increase the lithium stability. These results provide insights for the development of sulfide SEs for use in all-solid-state batteries in terms of their ionic conductivity and stability toward lithium anodes.