Na 3.8 [Sn 0.67 Si 0.33 ] 0.8 Sb 0.2 S 4: A quinary sodium fast ionic conductor for all -solid-state sodium battery

Strategy of Sb-substitution is carried out on the template structure Na4Sn0.67M0.33S4 (M = Si, Ge), which affords a series of quinary sulfide-based sodium fast ionic conductors formulated as Na4-x[Sn0.67M0.33]1-xSbxS4 (M = Si, x = 0.1, 0.2, 0.3; M = Ge, x = 0.2.). Among them, the highest ambient ionic conductivity (1.75 × 10−4 S cm−1) is achieved when M = Si and x = 0.2. The new fast ionic conductor Na3.8[Sn0.67Si0.33]0.8Sb0.2S4 is isostructural to its structure template Na4Sn0.67Si0.33S4 and thus crystallizes in the space group of I41/acd. It is shown that the incorporation of Sb improves the ionic conductivity. The study of lattice parameters shows that the improvement of the ion conductivity by Sb-substitution is mainly due to the enlarged crystal lattice. Furthermore, using Na3.8[Sn0.67Si0.33]0.8Sb0.2S4 as solid electrolytes, room temperature all-solid-state sodium battery of Se0.05S0.95@pPAN/Na3Sn is realized, which proves the novel fast ionic conductor a potential candidate to apply in sodium solid state battery. This work not only extends the scope of Na4[Sn0.67Si0.33]S4, the I41/acd space group template, but also deepens the understanding of the lattice size effect on the structure and property relationship by aliovalent substitution. © 2020