Fabrication Of CNTs/Cobalt Nickel Oxide Composite Supercapacitor Powders And Its Performance Research

Electrochemical supercapacitor?ES?is a promising new energy storage device.It has higher power density and longer cycle life than batteries,and it also has higher energy density than conventional capacitor.Meanwhile,.It has great potential applicatio ns in aerospace,defense technology,digital communications system,electric vehicles,smart grid and so on,due to its advantages of high specific capacitance,high power density,green environmental protection and long cycle life,so supercapacitor has attracted broad.attention of global scientific research workers.Electrode material is the key to determine its characteristics.Transition metal oxides NiCo₂O₄ with high specific capacitance,reversible electrochemical capacity and stable cycle performance,is considered as the most promising electrode material taking the place of precious metal electrode materials..Although the the electrical conductivity of NiCo₂O₄ is twice higher than that of Co3O4 and NiO,it is just 10-2S/cm.So it can't be applied in high current,due to the poor electrical conductivity affecting rate performance of the metal oxide.In order to solve the problem of the poor electrical conductivity,it is the most common method of combining NiCo₂O₄ with carbon materials.In carbon materials,carbon nanotubes?CNTs?with low density,large specific surface and hollow one dimensional structure,can form a considerable double layer capacitor,but its application is limited because of easy aggregation,low capacitance and energy density.NiCo₂O₄ compositing with the carbon nanotube,not only can improve the electrical conductivity of NiCo₂O₄,but also can improve the specific capacitance of carbon nanotubes.So the excellent electrochemical performance of the composite electrode materials can be obtained.The purpose of the paper is to prepare the excellent electrochemical performance of the CNTs/NiCo₂O₄ composite electrode materials,then a new method of improving the dispersion of CNTs is supplied,meanwhile,the NiCo₂O₄ powders and CNTs/NiCo₂O₄ composite powders can be prepared by hydrothermal process-calcination method and the CO1.29Ni1.71O4powders and CNTs/CO1.29Ni1.71O4 composite powders can be synthetized by the one-step hydrothermal method.The main contents are as follows:?1?The dispersion of CNTs is improved by two-step oxidation method.CNTs are heated at 75? in the strong alkaline solution of NaCIO and KMnO4 and then titrated by H₂O₂ solution After the oxidation treatment,the length of CNTs is shorten and the hydrophilic hydroxyl groups are introduced into the surface of CNTs with increasing defects.Simultaneously,the dispersion and stability of CNTs in aqueous are improved,and the electrochemical property is also ameliorated.Besides,the paper expounds the mechanism of improving the dispersion of CNTs by two-step oxidation method.?2?The layered NiCo₂O₄ powders and CNTs/NiCo₂O₄ composite powders are prepared by hydrothermal process-calcination method.The reaction temperature,the holding time and the types of CNTs are affecting on the phase,morphology and electrochemical properties of the products.The result shows the petals morphology of NiCo₂O₄ is obtained under the condition of 180? with 4h heat preservation,and in 0-0.4V voltage window,its specific capacitance can reach 1022F/g in the current density of 1 A/g.After adding the treated CNTs,CNTs can be uniformly dispersed in the matrix,at the same time the layered NiCo₂O₄ is curled up into a well crystalline spherical particles distributing three-dimensional network structure of CNTs,and the specific capacitance ofcomposite powders can reach 1725 F/g.?3?The well-crystallized Co_1.29Ni_1.71O₄nano-microsphere powders with the diameter of 20 nm,are obtained ne-step hydrothermal method.When the current density is 1A/g,the specific capacitance can reach 503 F/g.However,its rate performance is poor,because the specific capacitance only 282 F/g in high current density of 10 A/g,and specific capacitance is reduced by 44%.The synthesis of CNTs/Co_1.29Ni_1.71O₄ composite materials by the same method,can maintain high specific capacitance under the big current density.The specific capacitance of composites can reach 1315F/g and 929 F/g;respectively in the current density of 1 A/g and 10A/g.