Facile one-pot synthesis of high-purity sodium antimony chalcogenides in polar solvents

Abstract

Alkali metal chalcogenides have emerged as a new class of inorganic materials with diverse applications in energy conversion and storage owing to their structural versatility and wide range of properties. Strategies are needed for simple and cost-efficient synthetic approaches that enable the composition and functional properties of these materials to be systematically tuned. Herein, we present a novel wet-chemistry approach to produce ternary Na-based metal chalcogenides with varying compositions. Phase-pure Na₃SbCh₄ (Ch = S, Se) solid-state electrolytes are synthesized in a single-step fashion by reacting an ethanolic solution of Na chalcogenides with appropriately selected metal halides at room temperature. This process simplifies the reaction protocols, improves yield, and decreases the raw material loss incurred in multistep systems by eliminating the need for phase-pure binary metal chalcogenides. The reaction mechanisms and impurity profile of various sodium metal chalcogenides introduced in this work were methodically investigated through characterization techniques such as X-ray diffraction (XRD) and Raman spectroscopy. Among the chalcogenides, synthesis of the sulfide compounds (∼99 wt% purity) was straightforward, achieving a yield of 92–95% whereas the selenides required more control to generate the appropriate mix of precursors, which resulted in a lower yield of 74–79% but with a high purity of 97.5–99.6 wt%. Electrochemical impedance spectroscopy of as-synthesized Na₃SbCh₄ (Ch = S, Se) showed a high ionic conductivity of 0.17–0.38 mS cm⁻¹ and low activation energy of 0.19–0.21 eV comparable with other reports of solution-based synthesis. The one-pot scheme was successfully extended to the NaSbCh₂ (Ch = S, Se) system, producing phase pure ternary sodium metal chalcogenides with tunable band gaps (1.6–1.8 eV) appropriate for solar energy conversion applications. The “one-pot” approach offers a simple yet economical route for scalable production of bulk sodium ternary chalcogenides at ambient conditions.