A high energy density fiber-shaped supercapacitor based on zinc-cobalt bimetallic oxide nanowire forests on carbon nanotube fibers

Zn-Co bimetallic oxide (ZCO) nanowire forests were grown on carbon nanotube (CNT) fibers by a hydrothermal method and the resulting hybrid fiber was used to construct an all solid high energy density fiber-shaped supercapacitor (FSSC). Results indicated that the electrochemical performance of the hybrid fiber was greatly improved due to a synergistic effect between ZnO_x, CoO_x and the CNT fiber. The ZnO_x and CNTs are electrically conductive species that increase the utilization rate of the pseudocapacitive CoO_x while the acid-oxidized CNTs provide active sites for the growth of high-density aligned ZCO nanowire forests. The hybrid fiber reaches a high capacitance of 112.67 mF·cm^-2 and an energy density of 12.68 μwh·cm^-2 at a power density of 0.45 mw·cm^-2. Its capacitance retention is 90.63% after 10,000 cycles at a current density of 1 mA·cm^-2, showing good cycling stability. The changes in the cyclic voltammetry curve and capacitance at several different bending angles are negligible, indicating its excellent flexibility and mechanical stability. These outstanding features of the FSSC are attractive for developing portable and wearable electronic devices.