《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. Na₄Sn_0.67Si_0.33S₄shows a distinctly new structure with space groupI4₁/acdand 3D diffusion pathway by silicon doping in Na₄SnS₄, which exhibits 2 orders of magnitude conductivity improvement than that of the mother compound Na₄SnS₄. And the Na₄Sn_0.67Si_0.33S₄can be taken as a high tolerance structural template for chemical manipulation. Based on the structural template, aliovalent substitution of P⁵⁺for M⁴⁺leads to a wide range of solid solutions of Na_4-x[Sn_0.67Si_0.33]_1-xP_xS₄(0 ≤ x ≤ 0.4) with enhanced sodium conductivity. The highest ionic conductivity reaches 1.6 × 10⁻³ S cm⁻¹withx = 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.