Hierarchical NiCo2O4@ NiCoAl-layered double hydroxide core/shell nanoforest arrays as advanced electrodes for high-performance asymmetric supercapacitors

A combination of hydrothermal synthesis and a step-by-step in situ structure fabrication process for growing a hierarchical core/shell structure of NiCo2O4@ NiCoAl-LDH onto nickel foam without binders and conductive agents is presented. For supercapacitor electrodes, the as-obtained NiCo2O4@ NiCoAl-LDH nanoforest displays an enhanced specific capacitance of 1814.24 F g(-1) at a current density of 1 A g(-1) and a cycling performance with a retention of 93% after 2000 cycles at 10 A g(-1). Moreover, an asymmetric supercapacitor based on NiCo2O4@ NiCoAl-LDH nanoforest electrode and activated carbon electrode achieves an excellent electrochemical property with the energy density of 74.64 Wh kg(-1) at the power density of 800 W kg(-1) and good cycling stability (retaining 86% after 2000 cycles). The improved electrochemical performance is attributed to the hierarchical core/shell structure and synergistic effect of active materials, which enhance the interfacial charge transmission and shorten the diffusion path of ions. These results demonstrate that the hierarchical core/shell NiCo2O4@ NiCoAl-LDH nanoforest arrays are promising for supercapacitor applications. (C) 2017 Elsevier B.V. All rights reserved.