Caging Nb₂ O₅ Nanowires in PECVD-Derived Graphene Capsules toward Bendable Sodium-Ion Hybrid Supercapacitors

Sodium-ion hybrid supercapacitors (Na-HSCs) by virtue of synergizing the merits of batteries and supercapacitors have attracted considerable attention for high-energy and high-power energy-storage applications. Orthorhombic Nb₂ O₅ (T-Nb₂ O₅ ) has recently been recognized as a promising anode material for Na-HSCs due to its typical pseudocapacitive feature, but it suffers from intrinsically low electrical conductivity. Reasonably high electrochemical performance of T-Nb₂ O₅ -based electrodes could merely be gained to date when sufficient carbon content was introduced. In addition, flexible Na-HSC devices have scarcely been demonstrated by far. Herein, an in situ encapsulation strategy is devised to directly grow ultrathin graphene shells over T-Nb₂ O₅ nanowires (denoted as Gr-Nb₂ O₅ composites) by plasma-enhanced chemical vapor deposition, targeting a highly conductive anode material for Na-HSCs. The few-layered graphene capsules with ample topological defects would enable facile electron and Na⁺ ion transport, guaranteeing rapid pseudocapacitive processes at the Nb₂ O₅ /electrolyte interface. The Na-HSC full-cell comprising a Gr-Nb₂ O₅ anode and an activated carbon cathode delivers high energy/power densities (112.9 Wh kg^-1 /80.1 W kg^-1 and 62.2 Wh kg^-1 /5330 W kg^-1 ), outperforming those of recently reported Na-HSC counterparts. Proof-of-concept Na-HSC devices with favorable mechanical robustness manifest stable electrochemical performances under different bending conditions and after various bending-release cycles.