Investigation on the Synthesis, Structure, and Transport Properties of Double-Perovskite-Type Tungsten-Substituted NaLa₂TaO₆ as a Solid Electrolyte for All-Solid-State-Sodium Batteries

All-solid-state sodium batteries (SSSBs) with improved energy density, broad electrochemical windows, and reduced safety issues have been regarded as propitious energy storage systems to substitute for commercial organic liquid electrolytes. This study summarizes the electrical properties of solid-state Na-ion conductors Na_1–xLa₂Ta_1–xW_xO₆ (x = 0, 0.01, 0.02, 0.05, and 0.1) possessing a double perovskite-oxide-like structure. The title compounds were synthesized by a solid-state reaction method. The phase identification, structural characterization, and morphological studies were performed by powder X-ray diffraction (PXRD), Raman spectroscopy, and scanning electron microscopy; in addition, impedance spectroscopy was used to study their sodium-ion (Na⁺) conductivity. Among the investigated compounds, Na_0.99La₂Ta_0.99W_0.01O₆ exhibits a maximized Na⁺ conductivity of 10^–5 S cm^–1 at 30 °C. Moreover, Na_0.99La₂Ta_0.99W_0.01O₆ is chemically and electrochemically stable (up to 4.2 V) against the sodium metal anode.