Construction of hierarchical three-dimensional interspersed flower-like nickel hydroxide for asymmetric supercapacitors

Abstract

Low-cost and easily obtainable electrode materials are crucial for the application of supercapacitors. Nickel hydroxides have recently attracted intensive attention owning to their high theoretical specific capacitance, high redox activity, low cost, and eco-friendliness. In this study, novel three-dimensional (3D) interspersed flower-like nickel hydroxide was assembled under mild conditions. When ammonia was used as the precipitant and inhibitor and CTAB was used as an exfoliation agent, the obtained exfoliated ultrathin Ni(OH)₂ nanosheets were assembled into 3D interspersed flower-like nickel hydroxide. In this novel 3D structure, the ultrathin Ni(OH)₂ nanosheets not only provided a large contact area with the electrolyte, reducing the polarization of the electrochemical reaction and providing more active sites, but also reduced the concentration polarization in the electrode solution interface. Consequently, the utilization efficiency of the active material was improved, yielding a high capacitance. The electrochemical performance was improved via promoting the electrical conductivity by mixing the as-synthesized Ni(OH)₂ with carbon tubes (N-4-CNT electrode), yielding excellent specific capacitances of 2,225.1 F·g^–1 at 0.5 A·g^–1 in a three-electrode system and 722.0 F·g^–1 at 0.2 A·g^–1 in a two-electrode system. The N-4-CNT//active carbon (AC) device exhibited long-term cycling performance (capacitance-retention ratio of 111.4% after 10,000 cycles at 5 A·g^–1) and a high specific capacitance of 180.5 F·g^–1 with a high energy density of 33.5 W·h·kg^–1 and a power density of 2,251.6 W·kg^–1.