Composite Quasi‐Solid‐State Electrolytes with Organic–Inorganic Interface Engineering for Fast Ion Transport in Dendrite‐Free Sodium Metal Batteries

Abstract Quasi‐solid‐state electrolytes (QSSE) are a promising candidate for addressing the limitations of liquid and solid electrolytes. However, different ion transport capacities between liquid solvents and polymers can cause localized heterogeneous distribution of Na⁺ fluxes. In addition, the continuous side reactions occurring at the interface between QSSE and sodium anode lead to uncontrollable dendrites growth. Herein, a novel strategy is designed to integrate the composite electrospun membrane of Na₃Zr₂Si₂PO₁₂ and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) into QSSE, aiming to introduce new fast ion conducting channels at the organic–inorganic interface. The efficient ion transfer pathways can effectively promote the homogenization of ion migration, enabling composite QSSE to achieve an ultrahigh ionic conductivity of 4.1 mS cm⁻¹ at room temperature, with a Na⁺ transference number as high as 0.54. Moreover, the PVDF‐HFP is preferentially reduced upon contact with the sodium anode to form a “NaF‐rich” solid electrolyte interphase, which effectively suppresses the growth of dendrites. The synergistic combination of multiple strategies can realize exceptional long‐term cycling stability in both sodium symmetric batteries (≈700 h) and full batteries (2100 cycles). This study provides a new insight for constructing high performance and dendrite‐free solid‐state sodium metal batteries.