Heavily Tungsten Doped Sodium Thioantimonate Solid State Electrolytes with Exceptionally Low Activation Energy for Ionic Diffusion

Abstract A strategy for modifying the structure of solid‐state electrolytes (SSEs) to reduce the cation diffusion activation energy is presented. Two heavily W‐doped sodium thioantimonate SSEs, Na 2.895 W 0.3 Sb 0.7 S 4 and Na 2.7 W 0.3 Sb 0.7 S 4 are designed, both exhibiting exceptionally low activation energy and enhanced room temperature (RT) ionic conductivity; 0.09 eV, 24.2 mS/cm and 0.12 eV, 14.5 mS/cm. At −15 °C the Na 2.895 W 0.3 Sb 0.7 S 4 displays a total ionic conductivity of 5.5 mS/cm. The 30 % W content goes far beyond the 10–12 % reported in the prior studies, and results in novel pseudo‐cubic or orthorhombic structures. Calculations reveal that these properties result from a combination of multiple diffusion mechanisms, including vacancy defects, strongly correlated modes and excessive Na‐ions. An all‐solid‐state battery (ASSB) using Na 2.895 W 0.3 Sb 0.7 S 4 as the primary SSE and a sodium sulfide (Na 2 S) cathode achieves a reversible capacity of 400 mAh g −1 .