Preparation And Electrochemical Performances Of Cobalt-based Oxide Electrode Materials

The increasing energy consumption makes the research of clean and renewable energy become the primary issue of global common concern.The core of developing new energy is energy storage technology.Among numerous energy storage systems,supercapacitor plays an important role in urban rail transit,electronic equipment,military industry and other fields.In most cases,supercapacitor and other energy storage devices form a hybrid system due to its high power density characteristic.Further improving energy density of supercapacitor has been a hot spot of research.Its performance is closely related to electrode materials.Cobalt-based oxides with tailoring band gap,high theoretical capacity and abundant resources at home are idea electrode materials for supercapacitors.However,the instability of material structures during cycling and low actual specific capacity cannot be ignored.Designing and developing the performance of materials is an important part of electrochemical research.In this thesis,several cobalt-based oxides and their composites are synthesized and the structures and electrochemical performance of materials are characterized in detail.The main content is as follow:（1）The cauliflower-like Co₃O₄@Ni（OH）₂ electrode materials are synthesized via a two-step hydrothermal method using Nifoam as collector.The maximum capacity of electrode materials is 464.5 C g^-1(0.5 A g^-1)and 91.67%capacity retention after 20000 cycles(6 A g^-1).The as-assembled asymmetric device with composite as cathode delivers a maximum energy density of 112.5 Wh kg^-1at 1350 W kg^-1.（2）The materials of PPy decorated MnCo₂O₄ urchins are fabricated via a hydrothermal strategy and an electro-polymerization process.Due to the synergistic effect of PPy and MnCo₂O₄ materials,the composite electrode material exhibits excellent charge storge ability and long cycling stability.The results show that the capacity of composite is 2.862 m Ah cm^-2at 1 m A cm^-2 and capacity retention is 88%after 20000 cycles(10 m A cm^-2).The asymmetric supercapacitor with composite as cathode possesses a maximum energy density of 0.785 m Wh cm^-3 at a power density of 7.49 W cm^-3.（3）Three dimensional MnCo₂O₄/NiCo₂S₄ nanomaterials are grown in situ on a Nifoam substrate via a multistep hydrothermal process.The obtained composite delivers a specific capacity of 600 C g^-1 at 0.5 A g^-1 and retains 75%of the initial capacity after 10000 cycles at 6 A g^-1.Furthermore,an assembled asymmetric capacitor possesses an energy density of 90.37Wh kg^-1 at 1349.9 W kg^-1 and exhibits a capacity retention of 68%after cycling.