Hierarchical structure electrodes of NiO ultrathin nanosheets anchored to NiCo2O4 on carbon cloth with excellent cycle stability for asymmetric supercapacitors

To fabricate free-standing electrodes with hierarchical structured redox-type metal oxides has become a wise strategy for the development of high-performance energy storage systems. Two types of NiCo2O4 with needle-like and slice-like morphologies act as the conducting cores and hydrothermally grow on carbon cloth (CC/NiCo2O4-N and CC/NiCo2O4-S). The mesoporous NiO ultrathin nanosheets further are anchored on the surface of the two types of CC/NiCo2O4 to form the novel high-performance electrodes (CC/NiCo2O4-N@0NiO and CC/NiCo2O4-S@NiO). Particularly, the formation mechanism of NiO ultrathin nanosheets is proposed. The two integrated electrodes of CC/NiCo2O4-N@NiO and CC/NiCo2O4-S@NiO exhibit high specific capacitance of 921.9 and 852.9 mF/cm(2) (or 709.1 and 775.1 F/g) at 2 mA/cm(2), respectively and excellent long cycling lifespan (both 100% retention after 10,000 cycles). The assembled asymmetric supercapacitors, CC/NiCo2O4-N@NiO//graphene and CC/NiCo2O4-S@NiO//graphene, can still deliver the high energy density and power density, and possess excellent cycling stability (95.2% and 92.3% retention after 10,000 cycles, respectively). Our work not only provides an attractive strategy and a two-step facile method for construction of hierarchical electrodes based on ultrathin NiO sheets and nanostructured NiCo2O4, but also offers a strategy for high-performance supercapacitors.