Preparation And Electrochemical Properties Of Nickel-based Composites

Supercapacitors have been widely used in many fields owe to their favorable properties of faster charge and discharge rates,high power density and high energy density,longer cycle life,and so on.Electrode materials play an important role in the performance of supercapacitors.Transition metal hydroxides and oxides have excellent electrochemical properties and are inexpensive and environmentally friendly.In recent years,they have attracted wide attention of scientists and engineers as potential electrode materials for supercapacitors.The dissertation focusses on nickel hydroxides,nickel oxides,and their composites,and the influences of synthesis conditions,structure modification,and materials composition on the electrochemical properties of electrode materials have been investigated.The main research contents are as follows.1.The Ni?OH?₂ nanosheets were synthesized on nickel foam?NF?substrate through an in-situ growth method with nickel foam serving as both substrate and nickel source.And Ni?OH?₂/NF electrodes were obtained.Their morphologies and phase were characterized by using scanning electron microscope?SEM?and powder X-ray diffraction?XRD?.The optimum synthetic conditions for Ni?OH?₂ nanosheets have been investigated.Acting as working electrode,the supercapacitor performance of Ni?OH?₂/NF electrode was investigated through a series of electrochemical performance testing methods,such as,cyclic voltammetry,constant current charge discharge,AC impedance and cycle stability.The experimental results showed that the Ni?OH?₂/NF electrode prepared at 180? for 6 h possesses higher specific capacitance and better cycle stability in 2 mol/L KOH solution.The specific capacity was as high as 850 F/g when the current density was 1A/g.The specific capacity of the electrode can still maintain 95% of the initial specific capacity even after 1000 cycles of charging-discharging,which indicates that the prepared Ni?OH?₂/NF electrode has good cycle stability.2.MnCO₃/Ni?OH?₂ nanocomposites with hierarchical structures were grown onnickel foam via an in-situ growth method to prepare MnCO₃/Ni?OH?₂/NF composite electrodes.Electrochemical experimental results show that the specific capacitance of the composite electrode increases greatly after MnCO₃ being composited.The specific capacitance can reach 2150 F/g at the charge-discharge rate of 1 A/g.And 91% of the specific capacitance can still be maintained after 1000 cycles of charging-discharging.3.CeO₂/Ni/NiO porous composite microspheres have been prepared through thermal decomposition of the precursor obtained by spray drying technique.The morphology and composition of the composite microspheres were characterized by means of SEM and XRD.The electrochemical properties of porous composite microspheres with different morphologies were investigated.And the experimental results showed that porous composite microspheres with regular morphology and uniform particle size possessed superior specific capacitance and impedance.