Insights into the differences in ionic conductivities of Na3PS4 solid electrolytes synthesized by Liquid-Phase and ball mill methods

Abstract

This study sheds more light on the reasons for the lower ionic conductivity of cubic Na3PS4 (NPS) synthesized via liquid phase (LP) compared to ball mill (BM) methods. X-ray diffraction (XRD) analysis revealed distinct patterns for the NPS precursors obtained by the two methods. Raman spectroscopy was employed to track the evolution of NPS during the LP and BM processes. In both cases, the intermediate phase Na4P2S6 was detected, but its conversion to Na3PS4 was significantly faster in the BM method. This disparity in conversion rates correlates with the observed differences in ionic conductivity and implies that the amount of the residual intermediate phase may contribute to this difference. TGA-FTIR analysis was performed on the LP-THF-synthesized precursor and revealed the presence of THF residues even at elevated temperatures. These findings may help clarify challenges limiting the improvement of LP as a reliable method for synthesizing thiophosphate-based solid electrolytes.