Selective integration of hierarchical nanostructured energy materials: an effective approach to boost the energy storage performance of flexible hybrid supercapacitors

High energy density, fast charge-discharge capability, high flexibility, and sustained cycle life are the key challenges in the application of flexible supercapacitors (SCs) in modern electronics. These primary requirements could be accomplished by engineering a new class of current collectors consisting of hierarchical combinations of various active materials. This study reports the selective integration of hierarchical Ni(OH)(2) nanoneedle arrays with NiO-NiCo2O4 nanosheet arrays (Ni(OH)(2) NNAs@NiO-NiCo2O4 NSAs) on flexible fabric for high-performance electrodes. The novel core-shell-like hetero-nanoarchitectures not only enhance the electrochemical activity and specific surface area but also, more importantly, provide superhighways for the ultrafast transport of electrons and ions. As a battery-type material, the core-shell-like Ni(OH)(2) NNAs@NiO-NiCo2O4 NSAs display a high specific capacity of 326.7 mA h g(-1) at 2 A g(-1) in aqueous 3 M KOH; this value is 1.89, 1.23 and 1.14 times those of NiO-NiCo2O4, NiO@NiO-NiCo2O4 and Co3O4@NiO-NiCo2O4 electrodes, respectively. Most importantly, a flexible hybrid SC (FHSC, Ni(OH)(2) NNAs@NiO-NiCo2O4 NSAs//graphene-ink) demonstrates a superhigh energy density of 97.1 W h kg(-1) and a superior long cycling lifespan with 94.7% retention over 5000 cycles. Utilizing these excellent energy storage properties, the fabricated FHSC operated a multifunction electronic display and light up different colored light emitting diodes for real-time applications.