Achieving Superconformal Sodium Deposition on Carbon Nanofiber Film by Constructing Axial Oxygen Coordinated Copper Atomic Sites

Achieving superconformal deposition of metallic sodium on 3D matrices is a critical challenge for sodium metal batteries (SMBs). Herein, flexible 3D carbon nanofiber films anchored with axial O-coordinated CuN 4 O 2 single-atom sites (CuN 4 O 2 -CNF) by a ZnCl 2 -mediated thermal activation strategy is designed. Unlike conventional planar CuN 3 configurations obtained without ZnCl 2 , the axial O in CuN 4 O 2 sites exhibits a high density of states near the Fermi level, modulating the electronic structure of neighboring Cu and N. This lowers Na + adsorption energy, accelerates charge transfer and enhances electrolyte permeability, enabling superconformal sodium deposition. As a result, the CuN 4 O 2 -CNF achieves an ultra-low nucleation overpotential of 10 mV, a coulombic efficiency of 99.92% over 8,000 h, and exceptional cycling stability exceeding 10,000 h in symmetric cells. The full coin cells paired with a Na 3 V 2 (PO 4 ) 3 cathode retain 89.5 mA h g −1 after 1,000 cycles at 1 A g −1 and deliver 80.3 mA h g −1 at 5 A g −1 , demonstrating superior rate capability. The pouch cells also maintain a stable capacity of 75.8 mA h g −1 after 150 cycles at 58.5 mA g −1 . These results highlight the transformative potential of axial-coordination for designing high-performance metal batteries, offering insights into interfacial dynamics and host architectures for next-generation energy-storage systems.