Controlled Synthesis And Lithium-Storage Performances Of Graphene-based Composites

By virtue of their extraordinary physicochemical properties, graphene-basedcomposites (GBC) have been intensively explored for electrochemical lithium-storageand other applications. Artful control of the structure, morphology, and coupling ofthe units should be a key importance to improve the conductance, structure stability,and electrode interface of the composites, and pave the way to the design andfabrication of novel GBC with high energy, high power density and long life. In thisdissertation, mechanism of lithium storage in graphene nanosheets (GNS), effects ofGNS to the lithium storage performances of transition metal compounds, controlledsynthesis and electrochemical performances of GBC, and effects of nitrogen dopantsto the electrochemical performances of GNS have been investigated.The first cathode polarization of the GNS electrode has been systematicallyinvestigated by using electrochemical impedance spectroscopy. Variations of solidelectrolyte interphase films resistance and charge transfer resistance with the electrodepotential have been studied, relational kinetic parameters of the lithium intercalationin GNS electrode have been calculated.Fe2O3-graphene hybrid materials have been fabricated by a hydrothermal strategy,graphene oxide has been directly utilized without any reduction. In the fabricatedmaterials, both graphene sheets and Fe2O3nanoparticles play roles in lithium storage,moreover, extra capacity could also been given due to the synergetic effect. Enhancedreversible capacity, perfect cycling stability and excellent rate capability have beenachieved accordingly.Appropriate mineralizers and heat processing have been explored respectively totailoring the morphologies and structures of GBC, and consequent improving theconductance, structure stability, and electrode interface performances of thecomposite. Enhanced capacity and superior cycling stability of GBC have beenachieved, effects of morphologies and structures to the lithium storage in GBC havebeen clarified.High concentration nitrogen doped graphene sheets (NGS) have been synthesized,effects of nitrogen dopants and structure defects to the electrochemical performancesof graphene sheets have been investigated. It have been found that the NGS presented a superior lithium storage performance with a hybrid feature of lithium ion batteryand faradic capacitor at a low rate and a faradic capacitor feature at a high rate.