Diffusion mechanism in a sodium superionic sulfide-based solid electrolyte: Na11Sn2AsS12

Abstract Recently, in all solid-state batteries, sulfide-based solid electrolytes have received increased attention due to their high ionic conductivity, good mechanical features, and better chemical stability. Therefore, in the present study, we have synthesized a novel sodium superionic conducting sulfide-based inorganic solid electrolyte (Na 11 Sn 2 AsS 12 ) using a solid-state reaction method. The prepared solid electrolyte (Na 11 Sn 2 AsS 12 ) is characterized by different techniques such as x-ray diffractometry (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy, thermogravimetric analysis (TGA), electrochemical impedance spectroscopy, and linear sweep voltammetry to study its various properties such as structure, surface morphology, thermal stability, dielectric properties, ionic conductivity, and electrochemical stability window for sodium ion battery (SIB) applications. The XRD analysis confirms two coexisting phases—tetragonal and cubic, with phase fractions of 0.69 and 0.31, respectively. The SEM study reveals the irregular shape and dense morphology of the solid electrolyte. On the other hand, TGA shows that the prepared solid electrolyte is suitable for high temperature battery applications. The ionic and transport studies confirm that the synthesized Na 11 Sn 2 AsS 12 is purely ionic in nature, with ionic conductivity found to be 1.14 × 10 − 4 S cm −1 and negligible electronic conductivity ∼ 1.43 × 10 − 10 S cm −1 at room temperature. Furthermore, the detailed ionic conduction mechanism is studied using temperature and frequency-dependent AC impedance analysis. In addition, the synthesized solid electrolyte Na 11 Sn 2 AsS 12 exhibits a wide electrochemical window (∼7.0 V) and a high diffusion coefficient ( 1.3 × 10 − 7 cm 2 s −1 ) showing suitable electrolyte properties for solid-state SIB applications.