Structure and lithium insertion properties of carbon nanotubes

Carbon nanotubes were obtained by pyrolysis of acetylene or ethylene cataly zed by iron or iron oxide nanoparticles. The morphology, microstructure, an d lithium insertion properties of these carbon nanotubes were investigated by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and electrochemical meas urements, respectively. The results showed that the structures of the carbo n nanotubes play major roles in both specific capacity and cycle life. Slig htly graphitized carbon nanotubes showed a specific capacity of 640 mAh/g d uring the first charge, whereas well-graphitized carbon nanotubes showed a specific capacity of 282 mAh/g during the first charge. After 20 charge/dis charge cycles the charge capacity of the slightly graphitized samples degra ded to 65.3% of their original charge capacities, but the well-graphitized samples maintained 91.5% of their original charge capacities. The effects o f charge-discharge rates and cycling temperature on lithium insertion prope rties of carbon nanotubes with different extents of graphitization are disc ussed. (C) 1999 The Electrochemical Society. S0013-4651(98)08-024-0. All ri ghts reserved.