Research progress on NASICON-type solid electrolytes in all-solid-state sodium batteries: bulk optimization and...

All-solid-state sodium batteries (ASSSBs) are regarded as prominent candidates for next-generation sustainable energy storage systems due to the natural abundance of sodium resources, intrinsic safety, and potential for high energy density. Among the solid electrolytes that serve as core components, Na₃Zr₂Si₂PO₁₂ (NZSP) has emerged as one of the most promising ceramic electrolyte systems owing to its three-dimensional open framework structure, appreciable room-temperature ionic conductivity, wide electrochemical stability window, and excellent air stability. Nevertheless, the transition from laboratory realization of high-performance materials to practical solid-state devices is hindered by two principal bottlenecks for NZSP-based ASSSBs: insufficient bulk ion transport efficiency and poor electrode/electrolyte interfacial compatibility. To address these challenges, this review systematically encompasses the entire chain of research progress on NZSP solid electrolytes, spanning from the fundamentals of crystal structure to intrinsic modification strategies and further to interfacial engineering. Finally, the major challenges confronting current investigations are summarized, and future development directions are envisioned from the perspectives of synergistic bulk-interface optimization, integration of advanced characterization with theoretical computations, electrolyte thin-film fabrication, and full-cell integration.