Study On The Nanostructure Controlling And Electrochemical Performance Of Transition Metal Chalcogenides

Supercapacitor have become a research hotspot in the field of energy storage because of their high power density,excellent cycle stability and good temperature characteristics.However,there are still some disadvantages,such as low energy density and high cost,which limit the prospect of large-scale commercial application of supercapacitors.Transition metal chalcogenides have become a category of widely concerned electrode material for supercapacitors because of their high theoretical specific capacity,high redox activity and low price.However,the disadvantages of transition metal chalcogenides such as poor rate performance and low cycling stability,seriously hindering their application in supercapacitors.In order to solve the above problems,some strategies including compositing with conductive matrix,cibtrolling microstructure and optimizing composition were used in this dissertation to improve the specific capacity,rate performance and cycle stability of transition metal chalcogenides,and the relation between structure and performance was explored.The main findings of this dissertation are as follows:(1)Preparation and investigation on the synergistically nanostructured NiCo₂S₄electrodes:in order to increase the loading of electrochemically active materials and expose more active sites to improve the electron transport in electrode,the pristine nickel foam was engineered by electrochemical deposition to form porous nanostructure.Then,NiCo₂S₄ nanosheets were further grown on the surface of the nanoengieered nickel foam to form a synergistically nanostructured NiCo₂S₄ electrode.The as-prepared electrode has a large specific surface area and short path for the ion diffusion,thus presenting much improved specific capacity,rate performance and cycle stability.The specific capacity of electrode is 1223.8 C g^-1 at current density of 2.5 A g^-1.When the current density increases to 148.5 A g^-1,the capacitance retention is 53.4%.After 10000 charge discharge cycles,the capacitance retention of electrde keeps 94.56%of its intial value.The assembled device has a power density of 425.7 W kg^-1 at energy density of 76.7 Wh kg^-1.(2)Preparation and investigation on the Co-doped Ni₃Se₄ hierarchical nanostructures:in order to obtain electrode materials with high intrinsic conductivity and good structural stability efficiently,the hierarchical nanostructured Co-doped Ni₃(NO₃)₂(OH)₄ as precursor was prepared by a chemical bath method.Then,the Co-doped Ni₃Se₄ was prepared through ion exchange reaction by a hydrothermal method.The strategy of utilizing the intrinsic high conductivity of transition metal selenides and the doping of Co ions is in favor of improving the electrical conductivity of electrode.The self-supporting structure in eletrode and the synergistic effect between Ni and Co ions enhances the structural stability of electrode.The specific capacity of electrode is 1321.8 C g^-1 at current density of 2.2 A g^-1.When the current density increases to 44 A g^-1,the capacitance retention keeps 50.6%.After 40000 charge discharge cycles,the capacitance retention of electrode keepts 77.2%of its intial value.The assembled device has a power density of404.0 W kg^-1 at energy density of 58.7 Wh kg^-1.