Asymmetric supercapacitors based on β-Ni(OH)2 nanosheets and activated carbon with high energy density

Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy and scanning electron microscopy. The XRD and SEM results show that Ni(OH)2 has a beta -phase structure and covers the nickel foam skeleton with nanosheets. This beta -Ni(OH)2/Ni-foam electrode exhibits a high specific electric quantity of 790.3 C g-1 approaching the theoretical value (1040.6 C g-1) and high electrochemical activity. Asymmetric supercapacitor has been fabricated successfully using beta -Ni(OH)2/Ni-foam nanosheets as positive electrode and activated carbon as negative electrode in a KOH aqueous electrolyte. The electrochemical capacitances of this supercapacitor are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. An asymmetric supercapacitor AC/6 mol L-1 KOH/ beta -Ni(OH)2/Ni-foam could be cycled reversibly in the high-voltage region of 0-1.6 V and displays intriguing performances with a specific capacitance of 105.8 F g-1 and high energy density of 36.2 W h kg-1. Importantly, this asymmetric supercapacitor device exhibits an excellent long cycle life along with 92% specific capacitance retained after 1000 cycles.