Synthesis Of Nanostructured CO₃O₄and Their Electrochemical Properties

Lithium-ion batteries, which have high capacity and long life span, are now thedominant power sources for portable electronic devices. To meet the growing need for highperformance lithium-ion batteries, searching for alternative electrode materials is an essentialstrategy. Cobalt oxide （Co₃O₄） is a promising anode material for lithium-ion batteries on thebasis that it has a high theoretical value of890mAh/g. Besides, nanostructured electrodematerials can exhibait enhanced electrochemical properties compared with their bulkcounterparts. In this thesis, nanostructured Co₃O₄were successfully synthesized and theirlithium storage performances were studied.Porous Co₃O₄hexapods were successfully grown on copper foil through a facilehydrothermal method followed by a thermal treatment. The as-prepared Co₃O₄hexapodswere highly central symmetric with six blades. The as-prepared Co₃O₄hexapods on copperfoil used as anodes for lithium-ion batteries exhibited a very high reversible capacity of900mAh/g and an excellent cycling stability after30cycles at a current density of100mA/g.The good electrochemical performance was attributed to the unique porous structure of theCo₃O₄hexapods and the good contact with copper foil. After the carbon coating treatment tothe Co₃O₄hexapods, the samples exhibited an enhanced reversible capacity of1200mAh/gand better cycling stability under the same test condition. The rate capability of the Co₃O₄hexapods was also improved after the carbon coating treatment. From the results, we canconfirm that the carbon coating treatment to the Co₃O₄hexapods increases the wholeelectrical conductivity of the electrode and facilitates the lithium ion insertion/extractionprocesses.Co₃O₄arrays grown directly on carbon cloth were also successfully prepared throughthe same synthetic strategy. The Co₃O₄arrays were consisted of numerous brush-likebranches with tight connection to the carbon fibers. The Co₃O₄arrays on carbon clothshowed excellent flexible and bendable properties. The lithium storage property of thesample was investigated. When cycling at a current density of100mA/g, the Co₃O₄arrayson carbon cloth showed a reversible capacity as high as819mAh/g after40cycles. Ratecapability of the sample was studied by discharging/charging at various current densities. A reversible capacity of421.6mAh/g was obtained even at a current density as high as800mA/g. The high capacity, excellent cycling stability, and the good rate capability can beattributed to the unique morphology and hierarchical structure of the Co₃O₄arrays and thegood electrical conductivity of the carbon cloth.