Fe‐Single‐Atom Incorporated Wood‐Derived Anode with Fe─N─C/Fe₃C Structural Unit and Hollow Diffusion Sites for Enhanced Sodium‐Ion Storage

Sluggish diffusion kinetics of Na+ drastically restrain the rate capability and capacitance of the anode for sodium-ion batteries (SIBs). Herein, a Fe single-atom strategy is employed to construct Fe─N4─O2 active sites closely coupled with Fe3C species, establishing strong electronic interactions and, more importantly, an optimized coordination environment through precise tuning of their composition ratio with wood-derived nanoporous carbon (WNC) support. The charging Na+ through nanoporous carbon of Fe─N4─O2-WNC anode is revealed by electrochemical capacitive and charge-discharge studies to establish a reversible conversion and diffusion of Na+ supported by theoretical calculation of Na+ migration energy (eV) against the diffusion path. Fe─N4─O2-WNC anode, assembled with sodium foil as counter electrodes in a coin cell, exhibits a significant discharge-specific capacity of 318 mAh g-1 at a current density of 50 mAg-1. The electrochemical analysis support the role of Fe─N bonding in modulating the electronic environment of Na+ diffusion sites. The incorporation of Fe─N4─O2 in WNC results in 1) faster Na+ diffusion through hollow (H) sites, 2) stretching of the Fe─N bond during discharge cycles. In addition, Fe─N4─O2-WNC anode promises for the manufacturing of advanced SIBs from a renewable material and thereby enhancing the investigation of sodiophilic Fe─N sites.