Mechanochemistry in Sodium Thioantimonate Solid Electrolytes: Effects on Structure, Morphology, and Electrochemical Performance.

Sodium thioantimonate (Na 3 SbS 4 ) and its W-substituted analogue Na 2.88 Sb 0.88 W 0.12 S 4 have been identified as potential electrolyte materials for all-solid-state sodium batteries due to their high Na + conductivity. Ball milling mechanochemistry is a frequently employed synthetic approach to produce such Na + -conductive solid solutions; however, changes in the structure and morphology introduced in these systems via the mechanochemistry process are poorly understood. Herein, we combined X-ray absorption fine structure spectroscopy, Raman spectroscopy, solid-state nuclear magnetic resonance spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy characterization techniques to provide an in-depth analysis of these solid electrolytes. We report unique changes seen in the structure and morphology of Na 3 SbS 4 and Na 2.88 Sb 0.88 W 0.12 S 4 resulting from ball milling, inducing changes in the electrochemical performance of the solid-state batteries. Specifically, we observed a tetragonal-to-cubic crystal phase transition within Na 3 SbS 4 following the ball mill, resulting in an increase in Na + conductivity. In contrast, the Na + conductivity was reduced in mechanochemically treated Na 2.88 Sb 0.88 W 0.12 S 4 due to the formation and accumulation of a WS 2 phase. In addition, mechanochemical treatment alters the surface morphology of densified Na 2.88 Sb 0.88 W 0.12 S 4 pellets, providing intimate contact at the solid electrolyte/Na interface. This phenomenon was not observed in Na 3 SbS 4 . This work reveals the structural and morphological origin of the changes seen in these materials' electrochemical performance and how mechanochemical synthesis can introduce them.