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 (∼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.