Fabrication Of Hierarchical Ni-based Core-shell Composite Electrode Materials And Its Application In Electrochemical-capacitors

The transition metal oxides/hydroxides（such as Ni,Co,Mn,etc.）are considered to be the most one of promising electrode materials,due to their advantages such as low cost,abundant resources,excellent pseudo-capacitance performance,stable cycle performance,and good corrosion resistance et,al.However,because the metal oxide/hydroxide itself has poor electrical conductivity,limiting its practical application in the electrochemical system,giving rise to a poor active material utilization,and hindering its commercialization process.Therefore,researchers have studied the transition metal compounds in a variety of ways,including the effective design of the morphological structure,particle size,composition and microstructure,which expect to enhance the electronic and ion conductivity of the materials and improve its electrochemistry performance.In this work,a series of hierarchical core-shell structure transition metal compounds composite materials were synthesized,which employ an eco-friendly and economic friendly synthesis method.The morphological structure,composition,particle size,microstructure,element distribution,and the electrochemical performance in the capacitor were characterized and explored.The thesis consists of three parts as following:Part Ⅰ:Preparation of hierarchical core-shell NiO@Co₃O₄ composite electrode materials and its application in electrochemical capacitors.Hierarchical Ni O assembledby porous nanosheet was prepared using nickel acetate and urea as raw materials,and employ hydrothermal method,Co₃O₄ was coated on the surface for the core-shell NiO@Co₃O₄ composite.The morphological structure,composition,microstructure and electrochemical properties of the electrode material were investigated by various characterization methods.The results show that NiO@Co₃O₄ composites still have uniform particle size,large specific surface area,rich graded pore structure and good faraday-capacitance performance and cycle performance.Part Ⅱ:Preparation of hierarchical core-dual-shell NiO@Co₃O₄@MnO₂composite electrode materials and its application in electrochemical capacitors.Hierarchical NiO assembled by porous nanosheet was prepared using nickel acetate and urea as raw materials employ hydrothermal method,Co₃O₄ and MnO₂were coated on the surface for the core-dual-shell composite.The morphological structure,composition,microstructure and electrochemical properties of the electrode material were investigated by various characterization methods.The results show that the morphology of NiO@Co₃O₄@MnO₂ ternary composite material maintains NiO original peony flower,show a uniform particle size,a large specific surface area and rich pore size distribution.NiO@Co₃O₄@MnO₂ demonstrated a superior pseudo-capacitance performance,better cycle performance and magnification performance than NiO@Co₃O₄ composite material.Part Ⅲ:Preparation of hierarchical core-shell Ni（OH）₂@Mn₂O₃ composite electrode materials and its application in electrochemical capacitors.Hierarchical Ni（OH）₂,which was assembled by ultra thin nanosheets,was prepared using nickel acetate as raw materials,which employ hydrothermal method,coated Mn₂O₃ on the surface of Ni（OH）₂ for prepared core-shell Ni（OH）₂@Mn₂O₃composites.The morphological structure,composition,microstructure and electrochemical properties of the electrode material were investigated by various characterization methods.The results show that the morphology of Ni（OH）₂@Mn₂O₃composites is similar to ranunculus,and present uniform particle size,excellent electrochemical performance,good cycle performance and magnification.When the load of Mn₂O₃ is 7.8%,the material displays the largest specific capacitance.