Thiotetrelates Li₂ZnXS₄ (X = Si, Ge, and Sn) As Potential Li-Ion Solid-State Electrolytes

A novel inorganic solid-state electrolyte (ISSE) with high ionic conductivity is a crucial part of all-solid-state lithium-ion (Li-ion) batteries (ASSLBs). Herein, we first report on Li2ZnXS4 (LZXS, X = Si, Ge, and Sn) semiconductor-based ISSEs, crystallizing in the corner-sharing tetrahedron orthorhombic space group, to provide valuable insights into the structure, defect chemistry, phase stability, electrochemical stability, H2O/ CO2 chemical stability, and Li-ion conduction mechanisms. A key feature for the Li-ion transport and low migration barrier is the interconnected and corner-shared [LiS4] units along the a-axis, which allows Li-ion transport via empty or occupied tetrahedron sites. A major finding is the first indication that Li-ion migration in Li2ZnSiS4 (LZSiS) has lower energy barriers (similar to 0.24 eV) compared to Li2ZnGeS4 (LZGS) and Li2ZnSnS4 (LZSnS), whether through vacancy migration or interstitial migration. However, LZGS and LZSnS exhibit greater H2O/CO2 stability compared to LZSiS. The novel framework of LZXS with relatively low Li-ion migration barriers and moderate electrochemical stability could benefit the ASSLB communities.