Contaminant‐to‐Protection: In Situ Built Tri‐Component Barrier Enables Ultralong‐Cycling <scp>NASICON</scp> ‐Based Sodium Metal Batteries

NASICON‐type Na 3 Zr 2 Si 2 PO 12 (NZSP) is a promising electrolyte for solid‐state sodium battery due to its high ionic conductivity and wide electrochemical window. Unfortunately, the sodiophobicity of NZSP leads to extremely poor interfacial contact, which represents a substantial hindrance to its practical application. Herein, a “one stone two birds” strategy is proposed to decompose the contamination layer of NZSP and form a super‐sodiophilic and electron‐blocking hybrid interlayer consisting of Na 3 Sb alloy, NaCl and Na 2 O. The hybrid interlayer can not only improve the wettability of NZSP to Na and promote the rapid migration of Na + ions, but also effectively prevent the electron from intruding into the electrolyte at the interface and inhibit the growth of dendrites. Consequently, a dendrite‐free sodium plating/stripping can be achieved even at critical current densities as high as 1.4 mA cm −2 and the sodium symmetric cell can be stably cycled for more than 3600 h at 0.5 mA cm −2 /0.5 mAh cm −2 . In addition, the solid‐state full cell coupled with the Na 3 V 2 (PO 4 ) 3 cathode delivers capacities of 103.3 mAh g −1 under 0.5 C for 300 cycles at room temperature. This work offers an effective and innovative strategy to address the interfacial issues of solid‐state sodium metal batteries.