Group 14 element based sodium chalcogenide Na4Sn0.67Si0.33S4 as structure template for exploring sodium superionic conductors

Sodium superionic conductors are keys to realize room-temperature and high safety all-solid-state sodium batteries . Sulfide based sodium superionic conductors are promising but most reported examples are based on group 15 elements. To extend the horizon, we demonstrate a development route from group 14 elements based sodium chalcogenide . Na 4 Sn 0.67 Si 0.33 S 4 shows a distinctly new structure with space group I 4 1 / acd and 3D diffusion pathway by silicon doping in Na 4 SnS 4 , which exhibits 2 orders of magnitude conductivity improvement than that of the mother compound Na 4 SnS 4 . And the Na 4 Sn 0.67 Si 0.33 S 4 can be taken as a high tolerance structural template for chemical manipulation. Based on the structural template, aliovalent substitution of P 5+ for M 4+ leads to a wide range of solid solutions of Na 4- x [Sn 0.67 Si 0.33 ] 1- x P x S 4 (0 ≤  x  ≤ 0.4) with enhanced sodium conductivity. The highest ionic conductivity reaches 1.6 × 10 −3  S cm −1 with x  = 0.25. Change of vacancy population and weak Na-S interaction induced from P doping are main reasons for the improvement of ionic conductivity. In addition, excellent air stability is demonstrated. This work expands the exploration opportunities and provides further understanding of structure-property relationship for sodium superionic conductors.