Lithium Insertion/Extraction Properties of Nanocarbon Materials

Five kinds of nanocarbon materials (NCMs)—single-walled carbon nanotubes (SWNTs), C60@SWNTs (C60-peapod), multiwalled carbon nanotubes (MWNTs), graphite nanoflakes, and graphite nanoparticles containing some MWNTs—were systematically investigated as anode materials for Li ion batteries via scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and a variety of electrochemical testing techniques. Galvanostatic charge−discharge indicated that lithium storage capacity, Coulombic efficiency, and cyclability strongly depended on both the subtle structures and the subsequent treatments of NCMs. It was proved by cyclic voltammetry that lithium oxidation potentials increase with the increase of the length of lithium reversible insertion/extraction route. Raman spectroscopy revealed a mechanism of lithium insertion/extraction in SWNT and C60-peapod electrodes, suggesting that lithium can enter the inner space of the tubes, the trigonal interstitial channels of the bundles, and the intercalation site between adjacent tubes, and that the dominant reversible sites for lithium storage are the trigonal interstitial channels.