Affinity‐Engineered Flexible Scaffold toward Energy‐Dense, Highly Reversible Na Metal Batteries

The practical deployment of metallic anodes in the energy‐dense batteries is impeded by the thermodynamically unstable interphase in contact with the aprotic electrolyte, structural collapse of the substrates as well as their insufficient affinity toward the metallic deposits. Herein, the mechanical flexible, lightweight (1.2 mg cm −2 ) carbon nanofiber scaffold with the monodispersed, ultrafine Sn 4 P 3 nanoparticles encapsulation (Sn 4 P 3 NPs@CNF) is proposed as the deposition substrate toward the high‐areal‐capacity sodium loadings up to 4 mAh cm −2 . First‐principles calculations manifest that the alloy intermediates, namely the Na 15 Sn 4 and Na 3 P matrix, exhibit the intimate Na affinity as the “sodiophilic” sites. Meanwhile, the porous CNF regulates the heterogeneous alloying process and confines the deposit propagation along the nanofiber orientation. With the precise control of pairing mode with the NaVPO 4 F cathode (8.7 mg cm −2 ), the practical feasibility of the Sn 4 P 3 NPs@CNF anode (1* Na excess) is demonstrated in 2 mAh single‐layer pouch cell prototype, which achieves the 95.7% capacity retention for 150 cycles at various mechanical flexing states as well as balanced energy/power densities.