| Supercapacitors(SCs) have the characteristics of fast charge and discharge ability,long cycle life and high power density,which makes it an ideal choice to meet the demand for high-efficiency energy storage equipment,and therefore strong interest in the development of high-performance electrode materials has been aroused.However,compared with batteries,SCs still have the problem of low energy density.According to the calculation formula of energy density,the effective way to solve this problem is to combine the battery-type material with large specific capacity(C)and the capacitive material to assemble the asymmetric supercapacitor(ASC)with a wide working potential window(V).Transition metal oxides and hydroxides,especially layered double hydroxides(LDH),are ideal battery-type materials because of their low cost and high electrochemical activity.In order to further improve the electrochemical performance of LDH,LDH with a variety of nanostructures have been developed.Among various reported structures,three-dimensional core-shell nanostructured compounds are considered to be ideal electrode materials for supercapacitors because of their more accessible active sites and high conductivity.However,due to the weak binding force between the active material and the substrate,their energy storage or cycle stability is still poor.In view of this,improving the interface between core-shell LDH and conductive substrate is an important way to improve the electrochemical performance of materials and capacitor equipment.In this paper,copper based oxide-cobalt nickel layered double hydroxide materials with three-dimensional core-shell structure were synthesized by wet chemical oxidation and electrodeposition.Through the orthogonal design experiment and study on the influence of dry or wet copper surface,the reaction conditions were further optimized,and the electrode materials with the best electrochemical performance and interface adhesion were obtained.X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)to characterize the crystal structure,composition and nanostructure of the materials.Then,the electrochemical properties of the materials were characterized by cyclic voltammetry(CV),galvanostatic charge discharge(GCD),cyclic stability test and electrochemical impedance spectroscopy(EIS),and the practical value of the materials was studied by assembling the asymmetric capacitor equipment.The work of this paper can be summarized as follows:Firstly,utilizing a water-enhanced Cu surface as original substrate for in-situ growth of robust CuO(CuO/Cu).Subsequently,the CN LDH is coated on the CuO/Cu substrate by means of a typical electrodeposition method.The adhesive force of the as-obtained core-shell-like CN LDH@CuO nanoarchitectures on Cu substrate is largely improved,which thus efficiently inhibits the common“broken circuit”problems between the loaded active materials and conductive substrate.Meanwhile,due to the unique three-dimensional nanostructure,the as-prepared materials show excellent electrochemical performance.In 2 M KOH aqueous solution,the CN LDH@CuO/Cu as working electrode indicates a high specific capacitance of 3010.8 F g-1 at 1 A g-1,superior rate capability of 59.3%at 50 A g-1,and good capacitance retention of 67.8%after 10000cycles at 20 A g-1.These are obviously better than that of the dried,naked Cu surface as growth substrate.Fabricated into an asymmetry supercapacitor(ASC),it shows a high energy density of 52 Wh kg-1 at a power density of 800 W kg-1,and after 8000 cycles at5 A g-1,only 10.7%of the initial capacitance is lost.Secondly,based on the design of orthogonal experiment,a series of Cu based oxide/hydroxide materials with Cu foam(CF)as core/substrate were prepared by alkali assisted wet chemical oxidation.The morphological characteristics and the growing laws of these materials were studied by SEM.It was found that when the concentration of sodium hydroxide was low or the ratio of sodium hydroxide to ammonium persulfate was low,the ordered and stable nanostructures were difficult to form on the surface of copper foams.The morphology and shedding of these materials after ultrasonic treatment were studied by SEM and the weight changes of the materials before and after the treatment.The stability of the material structure and the adhesion between the material and the substrate were also investigated.Meanwhile,based on the electrochemical properties and the structural stability of 18 kinds of orthogonal experimental products,the primary and secondary order of influencing factors of wet chemical reaction conditions on the properties of these materials were studied by the orthogonal experimental range analysis.It was found that the concentration ratio between sodium hydroxide and ammonium persulfate,and the concentration of sodium hydroxide were the main and secondary factors affecting the specific capacitance of copper-based electrode materials,repectively,while the reaction time and hydrogen content were the main and secondary factors affecting the structural stability of copper-based electrode materials.By combining the results of orthogonal data analysis and the morphology of the materials,No.3,No.9 and No.3,No.9,and No.10 were selected as the potential core/substrate materials.Through observing the morphologies of these materials,the morphological characteristics and the growing laws of these materials were explored.The stability of the material structure and the adhesion between the material and the substrate were investigated by the research of the morphologies of these ultrasonic treated materials.Meanwhile,based on the electrochemical properties and the structural stability of 18kinds of orthogonal experimental products,the primary and secondary order of influencing factors of wet chemical reaction conditions on the properties of these materials were studied by the orthogonal experimental range analysis.Combined with the results of orthogonal range analysis and the morphologies of these materials,several core/substrate materials such as No.7were selected as the potential electrode core materials.Thirdly,the ultrathin cobalt-nickel layered double hydroxides(CoNi LDH)was synthesized onto the above mentioned several potential core/substrate materials by the method of electrodepositon,and then the obtained several core/shell materials were characterized by their electrochemical performances.The results show that the CoNi LDH with cross-linked nanosheet aggregates deposited on the 3D CF@CuO core/substrate materials exhibited the best electrochemical performance.Besides,the synergistic effect of Co and Ni was studied by the optimization of their ratio in the LDHs.The results show that when the ratio of Co toNiequal to 1:4,the obtained CoNi LDH exhibits the best electrochemical performances.The as-prepared core-shell nanohybrid(CF@CuO@CoNi LDH 1-4)is featured with a high specific capacitance(3123.8 F·g-1 at1 A·g-1),an excellent rate performance and a long cycle life.The assembled CF@CuO@CoNi LDH 1-4//RGO ASC delivers an ultra-high energy density of 92.5Wh·kg-1 at a power density of 400 W·kg-1,and only 16.2%capacitance loss after 8000cycles at 5 A·g-1.These results indicate that the cross-linked hybrid is an ideal electrode material providing high performances. |
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