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 (NaAlO₂)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 (Na₃V₂(PO₄)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.