All-Solid-State Fiber-Shaped Asymmetric Supercapacitors with Ultrahigh Energy Density Based on Porous Vanadium Nitride Nanowires and Ultrathin Ni(OH)2 Nanosheet Wrapped NiCo2O4 Nanowires Arrays Electrode

Fiber-shaped supercapacitors (FSC), among the most promising next-generation flexible energy storage devices, attract tremendous attention due to their high power density and rapid charging and discharging. However, their practical application is hindered by the low energy density that results from inferior specific capacitance and a limited voltage window. Herein, we design a flexible fiber-shaped asymmetric supercapacitor (FASC) with high energy density using vanadium nitride (VN) nanowires (NWs) on carbon nanotube fiber (CNTF) as negative electrode and ultrathin Ni(OH)2 nanosheet wrapped nickel cobalt oxide (NiCo2O4) to form a hierarchical nanowire array (HNWA) structure on CNTF as positive electrode. As-assembled FASC device has a maximum operational voltage of 1.6 V, with a highest areal capacitance of 291.9 mF/cm2 (106.1 F/cm3) and an energy density of 103.8 μWh/cm2 (37.7 mW/cm3). The FASC device possesses excellent reliability and achieves a retaining capacitance of more than 90% after 3000 bending cycles, which boosts practical applications for next-generation flexible energy storage devices.