Design and Synthesis of Cubic K Ba SbSe Solid Electrolytes for K-O Batteries.

Developing K-ion conducting solid-state electrolytes (SSEs) plays a critical role in the safe implementation of potassium batteries. In this work, a chalcogenide-based potassium ion SSE is reported, K SbSe , which adopts a trigonal structure at room temperature. Single-crystal structural analysis reveals a trigonal-to-cubic phase transition at the low temperature of 50 °C, which is the lowest among similar compounds and thus provides easy access to the cubic phase. The substitution of barium for potassium in K SbSe leads to the creation of potassium vacancies, expansion of lattice parameters, and a transformation from a trigonal phase to a cubic phase. As a result, the maximum conductivity of K Ba SbSe reaches around 0.1 mS cm at 40 °C for K Ba SbSe , which is over two orders of magnitude higher than that of undoped K SbSe . This novel SSE is successfully employed in a K-O battery operating at room temperature where a polymer-laminated K Ba SbSe pellet serves as a separator between the oxygen cathode and the potassium metal anode. Effective protection of the K metal anode against corrosion caused by O is demonstrated.