Electrochemical Properties Of Nickel/Cobalt-based Metallic Oxide Core/Shell Nanofibers

The development of new energy can be effectively alleviated the energy shortage and environmental pollution.The study of energy storage devices has played a vital role in the effective utilization of new energy.As a kind of efficient energy storage device,supercapacitors both have high power density and high energy density and being widely used in hybrid electric vehicles,portable electronic products and military.Electrode material is an important influencing factor of supercapacitors.As an inexpensive,environmently friendly electrode material with high theoretical capacity,cobalt/nickel-based metallic oxide has received extensive attention.This thesis starts with the preparation of excellent electrode material,and a series of cobalt/nickel-based metallic oxide nanofibers with core-shell structure have been fabricated via a co-electrospinning method.The morphologies and structures of samples were characterized by XRD,SEM,and TEM measurements.The performance of electrochemical has been tested by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectra through a electrochemical workstation.The main research contents are as follows:1.NiO,Co₃O₄ single nanofibers and NiO@Co₃O₄ core/shell nanofibres were prepared using PVP/Ni?NO₃?₂ and PVP/Co?NO₃?₂ as precursors by electrospinning method.The structure,morphology and electrochemical performance of all the electrode material were characterized.Through generating synergistic effects,the electrochemical performance has been greatly improved.The capacitance of NiO@Co₃O₄ core/shell nanofibers reduces from 437Fg^-1(1Ag^-1)to 276Fg^-1(40Ag^-1)with 63% remaining,more than NiO(221Fg^-1)and Co₃O₄(283Fg^-1)single nanofibers,with good rate capability.The electrochemical impedance spectra results show that all the Rs,Rct and Zw of NiO@Co₃O₄ core/shell nanofibers were the least.After continuous 1000 cycles(5Ag^-1),the capacitance retention of NiO@Co₃O₄ core/shell nanofibers were 82.9%,more than NiO?77.4%?and Co₃O₄?78.8%?single nanofibers.2.NiCo₂O₄@MnCo₂O₄ core/shell nanofibres were prepared using PVP/Ni?NO₃?₂/ Co?NO₃?₂ and PVP/Mn?CH3COO?2/Co?NO₃?₂ as precursors by co-electrospinning method with different annealing process.The structure,morphology and electrochemical performance of the electrode materials were characterized.The heat treatment temperature was set to 500?,600? and 700?.The structure and morphology analysis results showed that all samples were well crystallized.When the temperature was 500?,the NiCo₂O₄@MnCo₂O₄ core/shell nanofibres have a complete and continuous structure.Along with the rise of temperature,both molecular's thermal motion and the growth of crystal became rapid.When the temperature increased to 600?,the nanofibres were broken micrometer size,and broken into pieces at 700?.The electrochemical performance tested results indicate that the NiCo₂O₄@MnCo₂O₄ core/shell nanofibres at 500? with complete structure had the best electrochemical properties.The capacitance of NiCo₂O₄@MnCo₂O₄ core/shell nanofibres at 1Ag^-1 was 463Fg^-1?500??,362Fg^-1?600??and 283Fg^-1?700??respectively.1D nanofibres provided electrons and ions with migration channel,therefore,the sample at 500? had the lowest impedance as well as best cycle stability.After continuous 1000 cycles(5Ag^-1),the capacitance retention was 82.4%.