Preparation And Electrochemical Properties Of Nanofilaments Arrays And Their Composite Materials

In this paper, the controlled synthesis of morphology of the electrodematerial is designed as a starting point. The controlled synthesis of carbonnanoflament is carefully studied. As the basis for the growth mechanism ofcarbon nanotubes （CNTs） and carbon nanofibers （CNFs）, a novel binder-freeelectrode of helical carbon nanofiber clusters （HCNFs） is prepared bychemical vapor deposition （CVD） method. And the correspondence betweenits structure and electrochemical properties is discussed in detail. Another partof this paper is building nanocable-like structure of the composite electrode. Asimple, effective and reproducible precipitation method has been carried outby electrochemical deposition for synthesizing CNTs–Fe₃O₄nanocomposites.These works presented here give a clear example that the electrochemicalproperties of the electrode materials can be modulated in a way by carefuldesigning and controlling synthesis of the target materials.The major workshave been described as follows:（1） A novel binder-free electrode of HCNFs grown on copper foil hasbeen successfully fabricated by using of a CVD method. The HCNFs wereconstructed by its basic unit of platelet carbon nanofibers （CNFs）, of which were helically twining each other to form a unique helical structure. Moreinterestingly is that these primary platelet carbon nanofibers were found to befurther created by numerous small graphene layers with the diameter of about10nm and stacked perpendicularly to the growth axial of the CNFs, thereby aopen and smooth insertion/extraction pathway for lithium ions was generated.The electrochemical results demonstrate that the present HCNFs are of a goodanode material for rechargeable lithium-ion batteries with excellent high-ratecapabilities, together with a good cycling stability. A reversible capacity of550mAh·g^-1at400mA·g^-1and467.3mAh·g^-1at2000mA·g^-1could beobtained. The superior electrochemical properties of HCNFs may be attributedto its opened structure and shorten path for lithium ions.（2） A simple, effective and reproducible precipitation method has beencarried out by electrochemical deposition for synthesizing CNTs–Fe₃O₄nanocomposites. Product morphology can be precisely controlled by adjustingthe experimental conditions. Fe₃O₄nanosheets could strongly attach to thesurface of CNTs array. The initial discharge and charge capacity of TheCNTs–Fe₃O₄（37wt.%of Fe₃O₄） nanocomposite electrode are1033mAhg^-1and741.2mAh·g^-1respectively. The recharge capacity retention after longcycles remains620mAh·g^-1,which is signficantly higher than both of theCNTs array and Fe₃O₄nanopartical. The excellent cycleability and the highcapacity retention of the electrodes are attributed to the framework of CNTsarray and deposition of nanosized Fe₃O₄sheets on CNTs array.