Amorphization-Induced Enhancement of Ionic Conductivity of ZrO2–NaTaCl6 Composites

Abstract

The development of solid electrolytes with a high ionic conductivity is crucial for realizing all-solid-state sodium batteries. Chloride solid electrolytes, particularly NaTaCl6, have garnered significant attention because of their high conductivity, favorable formability, and good electrochemical stability at high potentials. Mechanochemically synthesized NaTaCl6 consists of both amorphous and crystalline phases, with the former being closely associated with its high ionic conductivity. In this study, xZrO2·NaTaCl6 (x = 0–2) samples were prepared by the mechanochemical method, in which the addition of ZrO2 is intended to facilitate the amorphization of the NaTaCl6 crystalline phase. This approach yielded NaTaCl6 with nanocrystalline ZrO2 particles dispersed in the amorphous phase. The 1.1ZrO2·NaTaCl6 sample exhibited an ionic conductivity of 1.3 × 10–3 S cm–1 at 25 °C and an electrochemical stability window of approximately 1.4–4.1 V versus Na+/Na. The amorphization of NaTaCl6, induced by the addition of ZrO2, contributed to its high ionic conductivity and improved electrochemical stability. This study demonstrates that the amorphization of NaTaCl6-based solid electrolytes leads to enhanced ionic conductivity.