High-performance Spinel NiMn2O4 Microspheres Self-assembled with Nanosheets by Microwave-assisted Synthesis for Supercapacitor

Spinel NiMn2O4 microspheres self-assembled with nanosheets directly growing on 3D nickel foam were successfully prepared by a facile microwave-assisted hydrothermal process. The structural and morphology evolution behavior, and the charge storage mechanism of as-prepared samples were thoroughly characterized and assessed. It was found that the formation of product stepwise underwent nucleation, regular growth, and self-assembled process (from nanosheets to small microspheres and further aggregating to large microspheres) to display in a flower-like microspheres structure. Further study on energy storage mechanism of the prepared spinel NiMn2O4 indicates that the diffusion-controlled process dominates charge storage at low scan rates, while the capacitive process occupied dominance as the scan rate rise. As a result, the as-prepared NiMn2O4 showed high specific capacitance up to 768.9 F/g measured by the charge-discharge at 1 A/g and excellent cycling stability (85.8 % capacity retention and near 100 % Columbic efficiency after 6000 cycles at 5 A/g), which indicated that the fabricated products show great potential application in commercial supercapacitors application.