Fe-Single-Atom Incorporated Wood-Derived Anode with Fe─N─C/FeC 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─N─O active sites closely coupled with FeC 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─N─O-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─N─O-WNC anode, assembled with sodium foil as counter electrodes in a coin cell, exhibits a significant discharge-specific capacity of 318 mAh g at a current density of 50 mAg. The electrochemical analysis support the role of Fe─N bonding in modulating the electronic environment of Na diffusion sites. The incorporation of Fe─N─O 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─N─O-WNC anode promises for the manufacturing of advanced SIBs from a renewable material and thereby enhancing the investigation of sodiophilic Fe─N sites.