Preparation Of Metal Oxide/carbon Nanofiber Composites And Their Lithium Storage Properties

Active metal oxides have recently attracted tremendous attention as appealing anode materials due to their great theoretical capacities and high reserves abundances.Among these alternatives,FeOx and SnO2 can be the most reliable candidates because of their high specific capacity,improved safety,low cost and environmental friendliness.In recent years,it has been proved that carbon nanofibers(CNFs)as matrix for iron oxide composites possess electrochemically kinetic properties due to their good interconnectivity,preferable electrical conductivity and high specific surface area.Electrospinning technique has been lately emerged as a facile and efficient method to fabricate metal oxide/carbon nanofibrous anodes with superior electrochemical performance.Here,nanosized metal oxides can buffer the pulverization of electrodes induced by Li+ insertion/extractions,provide high activity in the redox reactions,and facilitate the transport of ions and electrons.Meanwhile,carbon matrices with outstanding conductivity,stable structural property can be beneficial to improve the electrical connections of the whole electrodes and further alleviate the huge volume change during continuous cycling.The specific studies were as follows:(1)Iron oxide/carbon nanofibers(FeOx/CNFs)were prepared by electrospinning FeCl3·6H2O-polyacrylonitrile(PAN)precursors and heat treating at 400,600,800,1000?.As carbonization temperature increased,granular FeOx gradually migrated from nanofiber interior,oxidation states of iron in FeOx/CNFs changed from Fe2O3 to FeO and Fe,graphitization process of carbon matrices proceed with less defective structures and heteroatom contents,leading to an increase of conductivity and a diminution of irreversible reactions during cycling.As systematically studied and compared in electrochemical performance,FeOx/CNFs with the FeO,Fe state,highly graphitized carbon matrices and migration structure with FeO and Fe both embedded in and dispersed on carbon matrices presented stable cycling performance and outstanding rate capability.The above trade-off study of all the cooperative factors that affected the electrochemical property might make an effective guidance for preparation of promising FeOx/CNF anodes.(2)A novel flexible SnO2/CNFs electrode was synthesized by simultaneouslyelectrospinning/electrospraying followed by pre-oxidation and carbonization.The combined technology allows uniform incorporation of SnO2 nanoparticles into a carbon nanofiber matrix to form a SnO2/CNFs composite without damages to carbon nanofiber matrix and the adhesion between carbon fibers and SnO2 nanoparticle clusters were relativey strong.The flexible SnO2/CNFs electrode demonstrate an overall capacity of?520 mAhg-1 after 50cycles with coulombic efficiencies above 98%and excellent rate capability.Moreover,the cooperative structure factors that affected the electrochemical property have been mainly studied.