Designs,synthesis And Electrochemical Performances Of Heterostructured Cobalt-based Metal Oxides Electrode Materials For Supercapacitors

Supercapacitors,as a kind of novel energy storage devices,has attracted considerable attention due to their fast charging/discharging rate,environmental friendliness,high energy and power densities.Electrode material is the key factor that influences the electrochemical behaviors of supercapacitors.Cobalt-based metal oxides,as electrode materials of pseudocapacitors,have high theoretical specific capacitance and simple preparation.However,low electrical conductivity,low rate capability and poor cyclability have limited their application in electronic devices.Therefore,to research and improve rate capability and cycling stability of cobalt-based metal oxides,the nanostructured material and their composites were prepared by chemical methods in this paper.The main researchful contents are as follows:Hierarchical Ni Co₂O₄@MnO₂ mesoporous nanoneedles on a nickel foam conductive substrate are synthesized by a simple hydrothermal method combined with precipitation method.The material with a needle-like shape has uniform diameters and lengths of about 2 μm.And MnO₂ nanoparticles were observed on the surface of nanoneedle arrays.The HRTEM images also reveal that MnO₂ nanoparticles successfully covered on the surface of the NiCo₂O₄ nanoneedles.Electrochemical tests show that heterostructured NiCo₂O₄@MnO₂（S2）nanoneedles deliver a remarkable capacitance value of 2353.4 F·g^-1 at a current density of 1 A·g^-1.The NiCo₂O₄@MnO₂（S2）electrode also remains 92.9% initial capacitance after 3000 cycles at 8 A·g^-1.Even after 10000 cycles at 15 A·g^-1,the specific capacitance of the composite is as high as 736.2 F·g^-1,indicating their excellent cycling stability.The NiCo₂O₄ nanoparticles and Co₃O₄ microspheres are synthesized by hydrothermal method,respectively.The Ni Co₂O₄ nanoparticles and the Co₃O₄ microspheres at a weight ratio of 9:1,4:1,3:1 were prepared through a cooperative assembly process.The diameter of the Co₃O₄ microspheres is about 4 μm,and the materials are constructed by numerous nanoparticles with high porosity.The Co₃O₄/NiCo₂O₄（4:1）composite shows the best electrochemical performance.Electrochemical tests show that Co₃O₄/NiCo₂O₄（4:1）delivers a specific discharge capacitance of 1278.1 F·g^-1 at a current density of 1 A·g^-1,and even 809.4 F·g^-1 at 10A·g^-1,indicating their outstanding electrochemical properties.Mesoporous ZnCo₂O₄/NiO nanoflakes on a nickel foam conductive substrate areprepared by a simple hydrothermal method combined with chemical bath deposition method.The two dimensional nanoflakes have a large surface area,which reduces the ions and electron diffusion distance.Electrochemical tests show that ZnCo₂O₄/NiO（M3）nanoflakes deliver a capacitance value of 2797 F·g^-1 at a current density of 1A·g^-1,and 2287.2 F·g^-1 at 10 A·g^-1 with a capacitance retention of 81.8%,even 1079.2F·g^-1at 40 A·g^-1.It retains approximate 100% initial capacitance at 30 A·g^-1after 4000 cycles.The electrochemical cycling stability of the ZnCo₂O₄/NiO（M3）composite material is excellent.