KTaCl6: High-voltage stable potassium-ion conducting chloride solid electrolyte

Abstract

The exceptional electrochemical oxidative stabilities of halide solid electrolytes (SEs) have led to extensive research on Li and Na all-solid-state batteries. In this study, we report a new K+ SE, cubic KTaCl6, with a remarkable K+ conductivity of 1.0 × 10−5 S cm−1, synthesized via a mechanochemical method. This value represents a 1000-fold enhancement over that of samples prepared through heat treatment, which is remarkable among halide K+ SEs reported to date. Through structural characterization via X-ray diffraction, Rietveld analysis, and bond valence energy landscape calculations, we reveal three-dimensional K+ migration pathways facilitated by face-sharing KCl1211− cuboctahedra. This configuration is in contrast to that of the monoclinic KTaCl6 produced through annealing, which features discontinuous K+ migration pathways. These pathways are formed by the edge- or corner-sharing of KCl1211− anti-cuboctahedra, resulting in a significantly reduced K+ conductivity. Cyclic voltammetry measurements employing three-electrode cells indicate high electrochemical stability up to ≈3.7 V (vs. K/K+).