All-solid-state flexible supercapacitor based on nanotube-reinforced polypyrrole hollowed structures

Supercapacitors are strong future candidates for energy storage devices owing to their high power density, fast charge-discharge rate, and long cycle stability. Here, a flexible supercapacitor with a large specific capacitance of 443 F g^-1 at a scan rate of 2 mV s^-1 is demonstrated using nanotube-reinforced polypyrrole nanowires with hollowed cavities grown vertically on a nanotube/graphene based film. Using these electrodes, we obtain improved capacitance, rate capability, and cycle stability for over 3000 cycles. The assembled all-solid-state supercapacitor exhibits excellent mechanical flexibility, with the capacity to endure a 180° bending angle along with a maximum specific and volumetric energy density of 7 W h kg^-1 (8.2 mW h cm^-3) at a power density of 75 W kg^-1 (0.087 W cm^-3), and it showed an energy density of 4.13 W h kg^-1 (4.82 mW h cm^-3) even at a high power density of 3.8 kW kg^-1 (4.4 W cm^-3). Also, it demonstrates a high cycling stability of 94.3% after 10 000 charge/discharge cycles at a current density of 10 A g^-1. Finally, a foldable all-solid-state supercapacitor is demonstrated, which confirms the applicability of the reported supercapacitor for use in energy storage devices for future portable, foldable, or wearable electronics.