In-Plane Assembled Orthorhombic Nb2O5 Nanorod Films with High-Rate Li+ Intercalation for High-Performance Flexible Li-Ion Capacitors

Organic hybrid supercapacitors that consist of a battery electrode and a capacitive electrode show greatly improved energy density, but their power density is generally limited by the poor rate capability of battery-type electrodes. In addition, flexible organic hybrid supercapacitors are rarely reported. To address the above issues, herein an in-plane assembled orthorhombic Nb2O5 nanorod film anode with high-rate Li+ intercalation to develop a flexible Li-ion hybrid capacitor (LIC) is reported. The binder-/additive-free film exhibits excellent rate capability (approximate to 73% capacity retention with the rate increased from 0.5 to 20 C) and good cycling stability (>2500 times). Kinetic analyses reveal that the high rate performance is mainly attributed to the excellent in-plane assembly of interconnected single-crystalline Nb2O5 nanorods on the current collector, ensuring fast electron transport, facile Li-ion migration in the porous film, and greatly reduced ion-diffusion length. Using such a Nb2O5 film as anode and commercial activated carbon as cathode, a flexible LIC is designed. It delivers both high gravimetric and high volumetric energy/power densities (approximate to 95.55 Wh kg(-1)/5350.9 W kg(-1); 6.7 mW h cm(-3)/374.63 mW cm(-3)), surpassing previous typical Li-intercalation electrode-based LICs. Furthermore, this LIC device still keeps good electrochemical attributes even under serious bending states (30 degrees-180 degrees).