Decoding NASICON and Its Metal Interface for Solid‐State Batteries

Solid-state batteries (SSBs) are among the most promising next-generation energy storage technologies, offering exceptional safety, high energy density, and fast-charging capability. Among all kinds of solid electrolytes, sodium super ionic conductor (NASICON) is one of the most promising candidates due to its inexpensive material precursors, air stability, and high ionic conductivity. However, it faces a critical challenge: interfacial instability with metal anodes, leading to dendrite formation and penetration that ultimately cause battery failure. Addressing this issue requires a systematic understanding of the solid electrolyte itself, interfacial failure mechanisms, and robust mitigation strategies. Therefore, this review focuses on NASICON as a model system for both sodium- and lithium-based SSBs, providing a comprehensive overview and new insights into NASICON and its metal interfaces. A top-down approach is adopted, beginning with the fundamentals of NASICON's crystallography, thermodynamics, and kinetics to elucidate its intrinsic properties and interfacial degradation behaviors. Advanced characterization techniques for probing such failures are then reviewed, followed by a comprehensive discussion of mitigation strategies targeting the electrolyte, electrode, and their interface, along with practical insights into NASICON manufacturing. Finally, future research directions are proposed to guide the advancement of NASICON-based SSBs toward practical commercialization.