Although extensive efforts have been made to stabilize metal sodium anodes and prevent dendrite formation, it is still difficult to achieve long‐term stability at large area capacity and high current density due to a series of complex failure modes, including uneven Na nucleation and subsequent dendrite formation. Herein, an oxygen‐containing carbonized coconut framework (O‐CCF) with a 3D tubular structure is designed to inhibit dendrite growth. The 3D tubular structure can regulate the uniform distribution of electric field, making Na+ diffuse evenly on the electrode surface. The oxygen functional groups with sodiophilicity contribute to the adsorption of Na+ and reduce the Na nucleation energy on the surface of O‐CCF. The interaction of 3D tubular structure and oxygen functional groups enable Na stripping/plating over 10 000 cycles at 50 mA cm−2, as well as cycling stably for 1000 cycles with coulombic efficiency of 99.6% at 5 mA cm−2 and high areal capacity of 10 mAh cm−2. As a proof of concept, full cells of O‐CCF//Na‐Na3V2(PO4)3 (NVP) and Na‐O‐CCF//Fe7S8 are assembled and exhibit outstanding electrochemical performance. This work presents a promising strategy for fabrication of safe Na metal anodes.

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Magnesium ion batteries (MIBs) have attracted a lot of attention because of the natural abundance of magnesium, high volumetric energy density, and superior safety. Nevertheless, MIBs are still in their infancy because of the significant challenge in developing a suitable electrolyte with low flammability, high ionic conductivity, and compatibility with the Mg anode. Herein, we construct rechargeable quasi-solid-state MIBs based on tailored polymer electrolytes. The quasi-solid state electrolyte of poly­(vinylidene fluoride-co-hexafluoropropylene)-nanosized SiO2–Mg­(TFSI)2 combines the outstanding dynamic property of a liquid electrolyte and the good stability of a solid-state electrolyte. It exhibits a highly reversible Mg2+ deposition–dissolution capability, high ion conductivity (0.83 mS cm–1), and superior compatibility with the Mg metal and cathode. The quasi-solid-state MIBs with a layered titanic oxide cathode show a high reversible capacity of 129 mA h g–1 at 50 mA g–1 (150 W h kg–1) without any decay after 100 cycles.

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