Single-atom-anchored hierarchically nanopores hard carbon toward high-performance sodium storage

Abstract

Hard carbon anodes for sodium-ion batteries (SIBs) face a critical challenge in simultaneously achieving high capacity and rapid reaction kinetics, particularly in the low-voltage plateau region, due to the ambiguous storage mechanism and sluggish ion transport. Herein, we demonstrate a one-step metal salt-catalyzed strategy that enables the concurrent construction of hierarchical nanopores and the immobilization of single-atom Zn-N4 sites within hard carbon derived from lignosulfonate biomass. The resulting material achieves a remarkable reversible capacity of 354 mAh/g at 0.02 A/g and outstanding rate capability (238 mAh/g at 3.0 A/g). In situ X-ray diffraction (XRD) and Raman spectroscopy (Raman) spectroscopy elucidate a cooperative layer-insertion/nanopore-filling mechanism governing sodium storage in the plateau region. Furthermore, theoretical simulations reveal that Zn-N4 sites do not dominate the Na-storage behavior alone, but cooperate with the hierarchical pore structure by optimizing the local sodium ions (Na+) adsorption strength and facilitating ion transport. Compared with pure carbon nanopores, Zn-N4 modified nanopores show moderated Na+ binding over the whole pore-size range, indicating a more balanced interaction between Na+ and the carbon framework. This work highlights the advantages of integrating an ordered hard carbon framework with single-atom sites and provides new insights into high-performance sodium storage. The synergistic combination of hierarchical nanopores with single-atom sodium-affinity sites offer a general design paradigm for next-generation sodium-ion battery anodes.