A high performance solid state asymmetric supercapacitor device based upon NiCo₂O₄ nanosheets//MnO₂ microspheres

A high performance solid state asymmetric supercapacitor (SSASCs) device is successfully fabricated by combining NiCo₂O₄ as positive and MnO₂ as negative electrode materials. Herein, we also report a facile strategy to synthesize mesoporous layered NiCo₂O₄ nanosheets and 3D hierarchical MnO₂ microspheres by a simple microwave heating method. Both materials exhibit excellent electrochemical performance due to their unique morphological features along with nanocrystallite size, high specific surface area, narrow pore size distribution and large pore volume. The SSASCs device operates within the potential window of 1.5 V and exhibits high volumetric capacity and energy density of 0.954 mA h cm^-3 (2.3 F cm^-3) and 0.715 mW h cm^-3 at 1 mA cm^-2 respectively. The device also demonstrates excellent cyclic stability with capacity retention of 83% by the end of 10000 cycles at a current density of 2 mA cm^-2. This work constitutes the first demonstration of using 3D hierarchical MnO₂ microspheres as a high energy negative electrode for a SSASCs device. A SSASCs device with high volumetric capacity and energy density has significant potential applications in portable electronics and electrical vehicles.