Hydrothermal synthesis of a flower-like nano-nickel hydroxide for high performance supercapacitors

•Flower-like nickel hydroxide was synthesized by a facile hydrothermal process.•The as-prepared nickel hydroxide exhibits high specific capacitance.•The as-prepared nickel hydroxide exhibits excellent high rate performance. To construct suitable nanostructures for electronic and ionic transport in the electrode of a supercapacitor, a flower-like nanostructured nickel hydroxide (Ni(OH)2) was synthesized by a facile hydrothermal process in this study. For comparison, an additional two Ni(OH)2 samples were synthesized to investigate the formation mechanism of the flower-like Ni(OH)2. Physicochemical characterizations indicate that the Ni(OH)2 nanoflower was formed by stacked hexagonal β-phase of the Ni(OH)2 nanoflakes. The dissolution-recrystallization of Ni(OH)2 and the stacking of nanoflakes play important roles in the formation of Ni(OH)2 nanoflowers. Due to the higher conductivity and the suitable macropores for ionic transport, the nanoflower-like Ni(OH)2 exhibits a high specific capacitance of 2653.2Fg−1 at 2Ag−1 and 1998.5Fg−1 at 40Ag−1. An asymmetric supercapacitor, which was assembled with Ni(OH)2 as the positive material and HNO3-treated activated carbon as the negative material, exhibited a high cell voltage of 1.6V. Due to the high specific capacitance and high cell voltage, the as-prepared asymmetric supercapacitor exhibited a high energy density of 32.7Whkg−1 at 71.5Wkg−1 and 25.5Whkg−1 at 1.28kWkg−1.