Solvent-free and low temperature synthesis of chalcogenide Na superionic conductors for solid-state batteries

Sodium chalcogenide ionic conductors are attractive candidates as solid electrolytes (SEs) in solid-state Na metal batteries. They show the advantages of high ionic conductivity of 10-4-10- 2 S cm- 1 at room temperature and great chemical stability in air. However, simple and efficient approaches for the scalable synthesis of chalco-genide solid electrolytes (SEs) are required. In this work, we report a solvent-free mixing to form dry interme-diate products, which are subjected to different treatments (electron-beam assisted method or low temperature heating (& LE;150 degrees C)) to produce pure phase of Na3SbS4-ySey (0 & LE; y & LE; 2) chalcogenides. Heavy Se-doping in Na3SbS4 results in the tetragonal-to -cubic phase transition as well as a significant change of Sb-S bonding in Raman spectra. Among all chalcogenide SEs, Na3SbS3Se showed the highest ionic conductivity of 3.75 x 10-4 S cm-1 at room temperature, 47% higher than that of pristine Na3SbS4. Moreover, the Se-dopant also enhanced the electrochemical stability towards Na metal in solid-state batteries. The solid-state Na||FeS2 battery with Na3SbS3Se SE displayed long-term cycling ability up to 1,000 cycles within the voltage window of 1.0-2.7 V and retained a specific discharge capacity of 105 mAh g-1 after 600 cycles. This technique promotes the practical applications of chalcogenide SEs in solid-state Na batteries.