Fiber-Shaped Supercapacitors Fabricated Using Hierarchical Nanostructures of NiCo 2 O 4 Nanoneedles and MnO 2 Nanoflakes on Roughened Ni Wire

Electrostatic capacitors have high power density but low energy density. In contrast, batteries and fuel cells have high energy density but low power density. However, supercapacitors can simultaneously achieve both high power density and energy density. Herein, we propose a supercapacitor, in which etched nickel wire was used as a current collector due to its high conductivity. Two redox reactive materials, MnO 2 nanoflakes and NiCo 2 O 4 nanoneedles, were used in a hierarchical structure to cover the roughened surface of the Ni wire to maximize the effective surface area. Thus, a specific capacitance, energy density, and power density of 14.4 F/cm 3 , 2 mWh/cm 3 , and 0.1 W/cm 3 , respectively, was obtained via single-electrode experiments. A fiber-shaped supercapacitor was prepared by twisting two electrodes with solid electrolytes made of KOH and polyvinyl alcohol. Although the solid electrolyte had a low ionic conductivity, the energy density and power density were determined to be 0.97 mWh/cm 3 and 49.8 mW/cm 3 , respectively.