Hierarchical NiO@NiCo2O4 Core–shell Nanosheet Arrays on Ni Foam for High-Performance Electrochemical Supercapacitors

A facile solvothermal method followed by a postannealing process is used to prepare NiO@NiCo2O4 core–shell nanosheet arrays supported on Ni foam substrate for a high-performance supercapacitor. The hybrid electrode possesses a three-dimensional structure with the “shell” of NiCo2O4 nanoflakes anchored on the “core” of ordered NiO nanosheets. It shows high specific capacitance of 1623.6 F g–1 (or specific capacity of 225.5 mAh g–1) at 2 A g–1 and excellent rate performance with a 96% capacitance retention rate at 20 A g–1. The high cycling stability is proved by nearly 90% capacitance retention at 10 A g–1 after 10000 cycles. Its asymmetric supercapacitor, assembled with NiO@NiCo2O4/Ni foam and the activated carbon/Ni foam as the positive and negative electrode, respectively, displays the specific energy of 52.5 W h kg–1 at 387.5 W kg–1. The excellent electrochemical performance of NiO@NiCo2O4 electrode indicates its great potential in applications of energy storage devices.