Aqueous solution synthesis of Na3SbS4–Na2WS4 superionic conductors

We report a route for the synthesis of Na3SbS4–Na2WS4 superionic conductors from aqueous solution. Na3SbS4–Na2WS4 has the highest high sodium-ion conductivity (4.28 mS cm−1 at 25 °C) of reported sulfide-based solid electrolytes prepared via liquid-phase methods. The antimony in Na3SbS4 is replaced by tungsten in a higher valence state, which is charge-compensated by sodium vacancies in the form Na3−xSb1−xWxS4. Introducing sodium vacancies while maintaining the 3D conduction pathways increases the pre-exponential factor in the Arrhenius plots of ionic conduction. The development of a facile synthetic protocol, as well as the high ionic conductivity and excellent chemical stability of Na3SbS4–Na2WS4 in the presence of water, is a major step towards the realization of all-solid-state sodium batteries.