Preparation Of Ni-Co-O Composites And Their Supercapacity Performance

The supercapacitors (also called electrochemical capacitors), as a new energy storage device, have drawn much attention in recent years due to their advantages such as fast charge-discharge, high specific capacity and long cycle life. It has been found that the electrode material is one of the key factors to determine the supercapacitor performance. In recent years, researchers have found the excellent electrochemical properties of Ni-Co-O composites due to the synergistic effects between Ni and Co. In this study, we have prepared Ni-Co-O composites by Micro Impinging Stream Reactor (MISR) or by MISR combined with hydrothermal method. Details are as follows:(1) By mixing the raw material NiSO4·6H2O, Co(NO3)2·6H2O and the precipitant ammonia in MISR, the precursor of Ni-Co-O composites, Ni(OH)2and Co(OH)2, were formed very quickly and Ni-Co-O composites were then obtained after aging and calcining. This MISR technology can prepare fine dispersed Ni-Co-O composites with higher performance due to the intensified micro-mixing behaviors of the reactor and hence forming a more homogeneous precipitating environment. The optimal preparation conditions were determined by studying the effects of different flow rates, calcination temperature, calcination time, pH value and so on. Under the optimal preparation conditions, the particle diameter of Ni-Co-O composites was about50～80nm and the specific capacitance reached about2060F/g. After2000cycles, the specific capacitance remained about1750F/g, which was only15%of reduction, demonstrating excellent cycle stability.(2) Urea, as a precipitating agent, was premixed with the reactant mixture in MISR to prepare the precursors under hydrothermal conditions, which would form Ni-Co-O composites after calcining. It showed that MISR combined with hydrothermal method can prepare more dispersed and controllable Ni-Co-O composites. The hydrothermal time and hydrothermal temperature also had influence on the growth pattern of the composite materials. A porous spherical flower-like structure was formed with this method and Ni-Co-O composites with a size of4～5μm and a specific capacitance of1972F/g were prepared.