Fabrication of a Rigid‐Flexible and Dual‐Conductive Interphase on an Aluminum Current Collector for Ultra‐Stable Anode‐Free Sodium Batteries

Anode‐free sodium batteries (AFSBs) guarantee enhanced energy density and safety; however, their practical applications are hindered by uncontrolled dendritic growth and fragile solid electrolyte interphase formation. Hence, a novel interface engineering strategy is adopted in the present work to construct an in situ 3D porous interphase with dual ion/electron conductive channels on aluminum (Al) foil. The interphase consisting of a fast ion‐conducting sodium aluminate (NaAlO 2 )framework, a highly conductive carbon nanotube network, and a flexible carboxymethyl cellulose binder is fabricated through a simple in situ chemical etching method. The unique architecture of the as‐prepared interface synergistically regulates the sodiophilic nature and the ion/electron flux distribution, dramatically reducing the sodium nucleation overpotential from 35 mV for bare Al to 15 mV, and enabling ultra‐stable sodium plating/stripping in the half cells for over 6000 h at 1 mA cm −2 with a low polarization of 30 mV. When the resultant anode‐free full cell is paired with a sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ) cathode, it yields impressive high‐rate cyclic stability with a retention capacity of 90.7% after 100 cycles at 1 C and a remarkable energy density of 314 Wh kg −1 . This work presents a scalable and effective method for stabilizing anode‐free configurations and offers valuable insights for next‐generation metal‐based battery fabrication.