NASICON-type Na1+xZr2SixP3-xO12 Electrolytes Progress and Perspectives for Solid-state Sodium Metal Batteries

All-solid-state sodium metal batteries (ASSMBs) are considered as the most attractive alternative to lithium-ion batteries on account of their remarkable safety and low cost. Solid-state electrolytes as a key component have great effects on the performance of ASSMBs. Sodium super ionic conductors (NASICON)-type Na1+xZr2SixP3-xO12 (NZSP) electrolytes with excellent mechanical stability, high thermal/chemical stability as well as high ionic conductivity have become one of the most promising electrolytes for ASSMBs. The good compatibility of NASICON-type electrolytes with Na metal anodes and high-voltage cathodes is of great significance for ASSMBs. This paper reviews the structural characteristics, ion transport mechanism, strategies for enhancing conductivity, and synthesis methods of Na1+xZr2SixP3-xO12 based ceramic electrolytes. Simultaneously, it also introduces the approaches to addressing the interfacial issues between Na1+xZr2SixP3-xO12 electrolytes and solid electrodes. Finally, the prospective research directions are also presented to tackle the challenges for the practical application of Na1+xZr2SixP3-xO12 electrolytes.