Synthesis of cubic Na₃SbS₄ solid electrolyte with enhanced ion transport for all-solid-state sodium-ion batteries

A comprehensive research coupling experiment and computation has been performed to understand the phase transition of Na₃SbS₄ and to synthesize cubic Na₃SbS₄ (c-Na₃SbS₄), a high temperature phase of Na₃SbS₄ that is difficult to be preserved when cooled down to ambient temperature. The formation of c-Na₃SbS₄ is verified by Rietveld refinement, nuclear magnetic resonance spectroscopy as well as electrochemical impedance spectroscopy. Unlike tetragonal Na₃SbS₄ (t-Na₃SbS₄) appearing phase transition at high temperature, c-Na₃SbS₄ is stable not just at room temperature but also sustaining thermal cycling up to at least 200 °C. Both experiment and theoretical calculation reveal that the ionic conductivity of c-Na₃SbS₄ is higher than that of t-Na₃SbS₄, though the values are in the same order of magnitude. Both structures allow fast ion transport. All-solid-state cells with c-Na₃SbS₄ solid electrolyte demonstrate superior Coulombic efficiency, high specific capacity, and relatively good cycling stability. Na₃SbS₄ solid electrolyte is promising for all-solid-state sodium-ion batteries.