Anion sublattice design enables superionic conductivity in crystalline oxyhalides.

Solid-state batteries are attractive energy storage systems as a result of their inherent safety, but their development hinges on advanced solid-state electrolytes (SSEs). Most SSEs remain largely confined to single-anion systems (e.g., sulfides, oxides, halides, and polymers). Through mixed-anion design strategy, we develop crystalline Li3Ta3O4Cl10 (LTOC) and its derivatives with excellent ionic conductivities (up to 13.7 millisiemens per centimeter at 25°C) and electrochemical stability. The LTOC structure features mixed-anion spiral chains, consisting of corner-shared oxygen and terminal chlorine atoms, which induces continuous "tetrahedron-tetrahedron" Li-ion migration pathways with low energy barriers. Additionally, LTOC demonstrates holistic cathode compatibility, enabling solid-state batteries operation at 4.9 volts versus Li/Li+ and low temperature, down to −50°C. These findings describe a promising class of superionic conductors for high-performance solid-state batteries. Editor's summary: Theoretical predictions have shown that crystalline structures with a lithium-hopping path of tetrahedral to tetrahedral are likely to display a higher lithium ionic conductivity than those with the more commonly observed tetrahedral-octahedral-tetrahedral diffusion pathway. Zhao et al. report on the synthesis, characterization, and electrochemical testing of a solid-state lithium tantalum oxychloride electrolyte with the formula Li3Ta3O4Cl10. The material has high ionic conductivity and low activation energy, even at lower temperatures. These properties are due to the mixed-anion chemistry, which enables facile lithium-ion migration pathways. The broad applicability of the mixed-anion strategy was validated using niobium and other cost-effective or earth-abundant elements to replace the tantalum, although with some decrease in conductivity. —Marc S. Lavine [ABSTRACT FROM AUTHOR]