Synthesis And Electrochemical Properties Of Nickel And Cobalt Oxides/sulfides

Supercapacitors are new electrochemical energy storage devices with broad application prospects.Preparation of electrode materials with excellent properties is the key to develop high-performance supercapacitor.Oxides and sulfides of transition metal elements such as nickel and cobalt are promising electrode materials with high theoretical specific capacitance and abundant reserves.However,their electrochemical properties are still difficult to meet the requirements of practical application due to the limited conductivity,insufficient electroactive sites and sluggish reaction kinetics.In order to improve their electrochemical properties,NiCo2O4,NiCO2S4 and CoSx were selected as the research objects in this thesis.Their electrochemical performances were enhanced by designing microstructure,synthesizing composite material and incorporating proper guest elements.The main contents of this thesis are listed:1.Hierarchical NiCo2O4@Co-Fe LDHs core-shell nanowire arrays on Ni foam were synthesized by hydrothermal and calcination methods.The crystal structure,morphology and electrochemical properties of NiCo2O4@Co-Fe LDHs,NiCo2O4 and Co-Fe LDHs were investigated and compared with each other.It was found that the unique core-shell structural composite material could combine the advantages of NiCo2O4 nanowires and Co-Fe LDHs nanoflakes to obtain a high specific capacitance.However,the low conductivity of Co-Fe LDHs leaded to a decrease in rate capability and cycling stability.2.Mixed metal sulfide NixCu1-xCo2S4 with different Ni/Cu molar ratios was fabricated and its influences on the phase composition,morphology and electrochemical performances of NixCu1-xCo2S4 were investigated.It was found that proper substitution of Ni by Cu can effectively improve the electrochemical performance of electrode material.The enhancement can be attributed to the high crystallinity,modified microstructure,increased electrochemical sites,improved electroconductivity as well as the synergistic effects of Ni and Cu.Whereas when the substitution amount of Cu is excessive,the electrochemical property of the material was reduced due to the lowed redox performance of Cu compared to Ni.Among all the metal sulfides,sample Ni0.67Cu0.33Co2S4 showed the best electrochemical performance.3.Two-dimensional CoSx nanoplates can be easily fabricated by anion-exchange at room temperature.The CoSx nanoplates were low crystalline,nearly amorphous,and showed a porous structure,which was basically different from their precursor.Such a porous nanostructure can facilitate the diffusion of electrolyte and favor the sufficient contact between the active material and electrolyte,resulting in excellent electrochemical properties.