Oxygenation promoting Se-coordination of amorphous adjacent Nb-Nb diatomic pairs for high-performance sodium-ion hybrid capacitors

Abstract

Transition metal selenides as sodium-ion hybrid capacitor (SIHC) anodes still suffer from amorphization difficulties and capacity degradation triggered by polyselenide dissolution. Herein, an atomistic amorphous strategy is proposed to construct adjacent Nb-Nb diatomic pairs with Se/O-coordination (Se₄-Nb₂-O₂) in N-doped carbon-confined amorphous selenide clusters (a-Nb-Se/O@NC). Synergistic carbon confinement and hydrothermal oxygenation induce amorphization of Nb–Se bonds, eliminating crystalline rigidity while creating isotropic dual-ion transport channels and high-density active sites enriched with dangling bonds, thereby enhancing structural integrity and Na⁺ storage capacity. The unique Se/O-coordinated Nb-Nb diatomic configuration establishes an electron-delocalized system, where the low electronegativity of Se counterbalances electron withdrawal from coordinated O at Nb centers. These strengthen d-p orbital hybridization, reduce Na⁺ adsorption energy, and optimize charge transfer pathways and reaction kinetics in the amorphous clusters. Electrochemical tests reveal that the a-Nb-Se/O@NC anode delivers a high reversible capacity of 312.57 mAh g⁻¹ and exceptional cyclic stability (103 % capacity retention) after 5000 cycles at 10.0 A g⁻¹. Assembled SIHCs achieve outstanding energy/power densities (207.1 Wh kg⁻¹/18966 W kg⁻¹), surpassing most amorphous and crystalline counterparts. This work provides methodological insights for the design of electrodes in high-power storage devices through atomic modulation and electronic optimization of amorphous selenides.