Conformal coating of ultratin Ni(OH)₂ on ZnO nanowires grown on textile fiber for efficient flexible energy storage devices

Abstract

A highly flexible supercapacitor is fabricated through a simple solution-based method in which conformal ultrathin (2 nm) nickel hydroxide (Ni(OH)₂) layer is deposited on vertically grown zinc oxide (ZnO) nanowires on a three-dimensional, highly conductive textile substrate. The conformal ultrathin Ni(OH)₂ layer enables a fast and reversible redox reaction which improves the specific capacitance by utilizing the maximum number of active sites for the redox reaction, while vertically grown ZnO nanowires on wearable textile fibers effectively transport electrolytes and shorten the ion diffusion path. The Ni(OH)₂ coated ZnO nanowire electrodes show a high specific capacitance of 3150 F g−1 in a 1 M LiOH aqueous solution. Moreover, the asymmetric electrochemical capacitors with Ni(OH)₂-coated ZnO nanowires as the positive electrode and multiwall carbon nanotubes-textile as the negative electrode exhibit promising characteristics with a maximum power density of 110 kW kg−1, an energy density of 54 W h kg−1, and excellent cycling performance of ∼96% capacitance retention over 5000 cycles.