NiCo₂O₄ Nanosheets on Hollow\nCarbon Nanofibers for Flexible Solid-State Supercapacitors

Abstract

The carbon nanofiber-based all-solid-state supercapacitors\nhold\ngreat promise in powering portable electronics, while the low specific\ncapacitance and intrinsic fragility have hindered their practical\napplication. Here, flexible N-doped hollow carbon nanofibers (HCNFs)\nwere prepared using poly(acrylonitrile-<i>co</i>-acrylamide)\nas a precursor by the coaxial electrospinning method. The leaf-like\nNiCo₂O₄ nanosheets are located on the inner\nand outer walls of the carbon layer <i>via</i> a simple\nsolvothermal method to construct 3D freestanding NiCo₂O₄/HCNFs electrodes for a flexible all-solid-state supercapacitor.\nThe hollow structure of HCNFs provides both inner and outer surfaces\nfor NiCo₂O₄ nanosheets and shortens the distance\nof ion transportation. NiCo₂O₄/HCNFs possesses\nan enhanced specific capacitance of 1864.0 F g^–1 at 1 A g^–1 and a good capacitance retention capability\nof 91.7% after 5000 times cycling, which is one of the best reported\ncycling stabilities to date. The symmetrical all-solid-state supercapacitors\n(ASSCs) were directly prepared with NiCo₂O₄/HCNFs\nas an electrode without adding any conductive agents and binders,\nwhich have good flexibility and a maximum energy density of 44.3 W\nh kg^–1 at a specific power of 814.8 W kg^–1. Five series-connected ASSCs assembled by NiCo₂O₄/HCNFs can lighten a “DHU” logo composed of\n36 light-emitting diodes, indicating their potential application prospect\nin wearable and portable devices.