Na₃SbS₄: A Solution Processable Sodium Superionic Conductor for All‐Solid‐State Sodium‐Ion Batteries

Abstract All‐solid‐state sodium‐ion batteries that operate at room temperature are attractive candidates for use in large‐scale energy storage systems. However, materials innovation in solid electrolytes is imperative to fulfill multiple requirements, including high conductivity, functional synthesis protocols for achieving intimate ionic contact with active materials, and air stability. A new, highly conductive (1.1 mS cm −1 at 25 °C, E a =0.20 eV) and dry air stable sodium superionic conductor, tetragonal Na 3 SbS 4 , is described. Importantly, Na 3 SbS 4 can be prepared by scalable solution processes using methanol or water, and it exhibits high conductivities of 0.1–0.3 mS cm −1 . The solution‐processed, highly conductive solidified Na 3 SbS 4 electrolyte coated on an active material (NaCrO 2 ) demonstrates dramatically improved electrochemical performance in all‐solid‐state batteries.