Design and Synthesis of Cubic K 3-2 x Ba x SbSe 4 Solid Electrolytes for K-O 2 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 ₃ SbSe ₄ , 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 ₃ SbSe ₄ 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 _{3-2 x} Ba _x SbSe ₄ reaches around 0.1 mS cm ^-1 at 40 °C for K _2.2 Ba _0.4 SbSe ₄ , which is over two orders of magnitude higher than that of undoped K ₃ SbSe ₄ . This novel SSE is successfully employed in a K-O ₂ battery operating at room temperature where a polymer-laminated K _2.2 Ba _0.4 SbSe ₄ 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 ₂ is demonstrated.
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