Study On The Performance Of Nickel Nanowire Based Composite Electrode Materials For Supercapacitors

Supercapacitors are considered as one of the most promising energy storage device for their outstanding strength,such as high power density,fast charging and discharging,long life and so on.However,the energy density of supercapacitors is lower than secondary battery,which limits their wide application in various electronic devices.It is an effective way to improve the energy density of supercapacitors by designing an efficient new electrode structure based on the active material of transition metal compounds.However,based on the high pseudocapacitance mechanism,the loss of cyclic stability under the redox reaction is a difficult problem to limit their wide application.The effective way to solve this problem is to design the composite electrode with high pseudocapacitance active materials.In this paper,we successfully designed and fabricated a composite electrode with high specific surface area,which was constructed with Ni-Co oxides/hydroxides nanoarray on Ni nanowire(NiNW),and the energy storage mechanism of the ultra-long cycle stability of this structure was studied.The main research contents are as follows:The nickel nanowire(NiNW)was synthesized by a simple water bath method,and the effects of different experimental conditions(reaction temperature,Ni2+ concentration and volume ratio)on the size of NiNW were studied.The results show that the volume ratio(volume of solution to container)is the key factor in controlling the different size of NiNW.Besides,based on the preparation method of NiNW,a composite basement of nickel nanowires/nickel foam(NiNW/NF)is conducted.The results show that different morphology of the nickel and cobalt compounds are highly uniform and solidly growed in NiNW.Meanwhile,it is confimed that NiNW/NF composite structure can be used as a base for constructing high-performance three-dimensional(3D)core-shell structure.A three dimensional hierarchical nanostructure composed of nickel nano wires(NiNW)and nickel-cobalt oxide nanorods(NiCo-NR)on the surface of nickel foam(NF)is designed and successfully fabricated.By controlling annealing conditions,the formation of mesoporous NiCo204 nanorod on NiNW/NF composite substrain was realized by controlling the annealing conditions.The resulting NiNW@NiCo-NR/NF electrode shows a high areal specific capacitance(7.436 F cm-2 at 5 mA cm-2),good cycling stability(74.08%retained after 1500 cycles)and excellent rate capability(88.04%retained at 100 mA cm-2).A three-dimensional hierarchical composite electrode composed of nickel nanowires@nickel-cobalt double hydroxide aligned on nickel foam(NiNW@NiCo-DH/NF)is successfully fabricated by an in-situ growth route.Compared with the one without nickel nano wires,the electrochemical performance of the obtained composite electrode is apparently improved,which shows a high areal specific capacitance(2.25 F cm-2 at 5 mA cm-2),excellent rate capability(1.65 F cm-2 at 100 mA cm-2)and superior cycle stability(151.2%retained in the 20000th cycle).And the activation mechanism of ultra-long cycle life of the obtained composite electrode is studied in this work,which indicates that the transforms of surface atoms on Ni nanowires into high-pseudocapacitance Ni(OH)2 and NiOOH during cycles make major contributions for the performance improvement.