High-Performance All-Inorganic Solid-State Sodium–Sulfur Battery

All-inorganic solid-state sodium-sulfur batteries (ASSBs) are promising technology for stationary energy storage due to their high safety, high energy, and abundant resources of both sodium and sulfur. However, current ASSB shows poor cycling and rate performances mainly due to the huge electrode/electrolyte interfacial resistance arising from the insufficient triple-phase contact among sulfur active material, ionic conductive solid electrolyte, and electronic conductive carbon. Herein, we report an innovative approach to address the interfacial problem using a Na₃PS₄-Na₂S-C (carbon) nanocomposite as the cathode for ASSBs. Highly ionic conductive Na₃PS₄ contained in the nanocomposite can function as both solid electrolyte and active material (catholyte) after mixing with electronic conductive carbon, leading to an intrinsic superior electrode/electrolyte interfacial contact because only a two-phase contact is required for the charge transfer reaction. Introducing nanosized Na₂S into the nanocomposite cathode can effectively improve the capacity. The homogeneous distribution of nanosized Na₂S, Na₃PS₄, and carbon in the nanocomposite cathode could ensure a high mixed (ionic and electronic) conductivity and a sufficient interfacial contact. The Na₃PS₄-nanosized Na₂S-carbon nanocomposite cathode delivered a high initial discharge capacity of 869.2 mAh g^-1 at 50 mA g^-1 with great cycling and rate capabilities at 60 °C, representing the best performance of ASSBs reported to date and therefore constituting a significant step toward high-performance ASSBs for practical applications.