New Amorphous Quaternary Sulfide Compounds as Solid Electrolyte for All-Solid-State Li-Ion Batteries

In recent years, interest in all-solid-state lithium secondary batteries with high energy density and output performance has increased due to the possibility of mitigating safety issues related to liquid electrolytes. However, the development of a suitable solid electrolyte (SE) remains a major challenge in advancing all-solid-state battery technology. Sulfide-based compounds are advantageous as solid-state electrolytes due to their high ionic conductivity and efficient transport of lithium ions, which can be attributed to their high polarizability and low electronegativity. In this work, an amorphous new sulfide compound, LiSbGeS₄, was synthesized as a Li-ion conductor. The amorphous characteristics of LiSbGeS₄ were investigated using PXRD, XAS, XRS, Raman spectroscopy, and thermal analysis. XPS and Raman spectroscopy provided information about into the local structure and chemical bonding of LiSbGeS₄, indicating the presence of metal-metal bonds and metal-S polyhedral units. LiSbGeS₄ was modified to have a high ionic conductivity through anion aliovalent substitution of the Cl^- on S^2- sites while maintaining amorphous phase. LiSbGe_0.8625S_3.45Cl_0.55 exhibited a significantly higher lithium-ion conductivity, reaching 7.26 mS/cm, which is approximately 2400 times higher than that of pristine LiSbGeS₄. This study presents new amorphous sulfide compounds with enhanced Li-ion conductivity as a promising solid electrolyte for Li-ion batteries.