Self‐Confinement of Na Metal Deposition in Hollow Carbon Tube Arrays for Ultrastable and High‐Power Sodium Metal Batteries

Abstract Sodium metal batteries are promising next‐generation energy storage technology by using energy‐dense and affordable Na metal anodes, yet suffering uncontrollable Na dendritic growth issues. Herein, Au nanoparticle@hollow amorphous carbon tube yolk/shell arrays (Au/HCT‐CC) is rationally designed on carbon cloth as a dynamic host. In situ transmission electron microscopy observations reveal a regulated dendrite‐free Na metal plating/stripping within the Au/HCT‐CC host. The self‐confinement of Na metal deposition in the hollow carbon can further stabilize the electrolyte/electrode interface and homogenize Na ion flux, as evidenced by rigorous experimental and theoretical characterizations, thus successfully accommodating the hurdles to Na metal anodes. When cycling in half cells, the Au/HCT‐CC electrodes deliver remarkably high coulombic efficiencies (CEs) of 99.96% over 2200 h at 5 mA cm −2 . The high CE of 99.54% is preserved even under harsh cycling conditions of 10 mA cm −2 and 20 mAh cm −2 for 250 cycles. These values rival the state‐of‐the‐art electrochemical performance for Na metal anodes in literature. Finally, the practical feasibility of the new anode is demonstrated by cycling in Na 3 V 2 (PO 4 ) 3 @C||Na‐Au/HCT‐CC full cells over 900 cycles with an extremely low capacity degradation rate of 0.017% per cycle.