| With the rapid development and popularization of portable electronic devices such as smart phones and tablet PCs,people pay more and more attention to energy storage devices.Compared with the lithium ion battery,the high power density,the fast charging and discharging characteristics and the excellent cycle stability of the supercapacitor make it become a focus in the energy storage equipment.At the same time,the electrode is the key to the performance of energy storage equipment.Now researchers are trying to use a variety of methods to push the limit of performance of energy storage devices.From the aspect of materials,transition metal oxides and transition metal sulfides are popular research directions due to their much higher specific capacitance than carbon based materials.From the aspect of structure,the improvement of the morphology and structure of the nanotubes,nanowires,nanorods,nano flowers,holes,core-shell are also step by step to improve the performance of electrode materials.Based on the above aspects,the effects of different loading densities on the electrochemical characteristics for supercapacitor,such as cycle stability and rate performance,are investigated by means of the preparation of different loading densities of Ni-Co-S nano arrays.Then,we also study the effect of nickel-cobalt sulfide arrays compound with polypyrrole on the electrochemical performance for supercapacitor.The main contents include the following aspects:(1)In the second chapter of this thesis,we study the synthesis,morphology and electrochemical properties of Ni-Co-S nano arrays with different loading densities.Different loading densities of Ni-Co-S nano arrays are grown on the same size of nickel foam by hydro-thermal reaction respectively.Their loading densities can be controlled by changing the amount of the reactants.The experimental result shows that the electrochemical properties of the supercapacitor electrode are the best only when the loading density of the Ni-Co-S nano arrays is moderate.The best experimental group shows an excellent areal capacitance of 4.84 F cm-2 under the current density of 10mA cm-2 Moreover,compared with experimental groups with other loading densities,it also shows the best rate performance and electrochemical stability.It is worth noting that the method of controling loading densities of Ni-Co-S nano arrays may not only provide a new strategy of researching on supercapacitor,but also provide a new idea to study the nano arrays growing at different substrate and applying in the field of catalysis,lithium ion battery.(2)In the third chapter of the paper,we first prepare the nickel-cobalt sulfide nano arrays by the method of the previous experiment.Then,the nickel-cobalt sulfide arrays are combined with polypyrrole.A polypyrrole film is formed on the surface of the nickel-cobalt sulfide arrays.Transition metal sulfide and polymers both have high electrochemical activity.Moreover,polypyrrole has high electronic conductivity,which makes up the poor conductivity of the transition metal sulfide.The Ni-Co-S@PPY arrays electrode exhibits an outstanding initial capacitance of 4.89F cm-2 at the current density of 10mA cm-2,and it can maintain 3.75 F cm-2 when the current density reaches 60mA cm-2.After polymerization of pyrrole,not only the capacitance is significantly improved,but also the rate performance exhibits better stability.After 3000 cycles,Ni-Co-S nano arrays remained 75.3%retention of the original areal capacitance(2.53 F cm-2)at current density of 20 mA cm-2.After the polymerization of polypyrrole film on the surface of the arrays,the Ni-Co-S@PPY arrays electrode has almost no capacity loss after 3000 charging and discharging cycles.The experimental results show that,compared with the composite of Ni-Co-S nano arrays,the Ni-Co-S nano arrays compounded with the polypyrrole exhibits better cycle stability,rate performance,and electrochemical activity. |
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