Investigation of the sodium-ion transport mechanism and elastic properties of double anti-perovskite Na 3 S 0.5 O 0.5 I.

Sodium-rich anti-perovskites have unique advantages in terms of composition tuning and electrochemical stability when used as solid-state electrolytes in sodium-ion batteries. However, their Na + transport mechanism is not clear and Na + conductivity needs to be improved. In this paper, we investigate the stability, elastic properties and Na + transport mechanisms of both the double anti-perovskite Na 3 S 0.5 O 0.5 I and anti-perovskite Na 3 OI. The results indicate that the NaI Schottky defect is the most favorable intrinsic defect for Na + transport and due to the substitution of S 2- for O 2- , Na 3 S 0.5 O 0.5 I has stronger ductility and higher Na + conductivity compared to Na 3 OI, despite the electrochemical window being slightly narrower. Divalent alkaline earth metal dopants can increase the Na + vacancy concentration, while impeding Na + migration. Among the dopants, Sr 2+ and Ca 2+ are the optimal dopants for Na 3 S 0.5 O 0.5 I and Na 3 OI, respectively. Notably, the Na + conductivity of the non-stoichiometric Na 3 S 0.5 O 0.5 I at room temperature is 1.2 × 10 -3 S cm -1 , indicating its great potential as a solid-state electrolyte. Moreover, strain effect calculations show that biaxial tensile strain is beneficial for Na + transport. Our work reveals the sodium-ion transport mechanism and elastic properties of double anti-perovskites, which is of great significance for the development of solid-state electrolytes.