Stable Na Deposition/Dissolution Enabled by 3D Bimetallic Carbon Fibers with Artificial Solid Electrolyte Interface

3D bimetallic carbon nanofibers (CNFs) are promising interlayers for regulating Na deposition/dissolution on the Na metal or directly on current collectors like Cu. However, uncontrollable solid electrolyte interface (SEI) growth on the interlayer during the repeated Na plating/stripping process leads to low initial Coulombic efficiency (CE), impeding the practical applications of such a protective layer in Na metal batteries. Herein, an artificial SEI-coated interlayer decorated with sodiophilic Ag and sodiophobic Cu on CNF is applied on Cu foil to regulate the Na deposition/dissolution behavior. The artificial SEI, consisting of organic components like RCO₂Na/RCONa and inorganic reactants Na₂CO₃/Na_xO_y, minimizes irreversible electrolyte decomposition at the interlayer. The sodiophobic-sodiophilic bimetallic CNF interlayer is lightweight, porous, and mechanically robust. It can guide Na deposition toward the sodiophilic Ag-rich region of the CNF matrix and cluster in the open pores facing the current collector, effectively preventing Na dendrite formation. The interlayer features with artificial SEI synergistically enhance the stability of Na deposition/dissolution on Cu foil, resulting in a high average CE of over 99.5% for 600 cycles spanning 6500 h. Furthermore, post-analysis confirms the high electrochemical stability of the artificial SEI of the interlayer during cycling.