| The development of portable electronics in conjunction with declining fossil fuel supplies has produced a demand for versatile power sources. Theoretically; Lithium ion batteries are the premier electrochemical energy storage chemistry, however materials and engineering issues presently hinder this technology from attaining optimal performance. The work presented in this dissertation has focused on understanding and controlling issues associated with graphtic negative electrode materials (e.g. capacity fade, irreversible losses). We have examined the effects of fullerene soot as an additive to graphite electrodes. Through physical and electrochemical characterization it was found that the composite electrodes exhibit synergistically favorable characteristics attributable to both the graphite and fullerene soot, but not observed with electrodes containing the individual materials.; Composite electrodes containing graphite and a small fraction of arc-generated fullerene soot show superior capacity retention upon extended cycling compared to electrodes containing only graphite. Electroanalytical techniques were used to demonstrate that the SEI layer formed on the composite electrode during the initial lithiation is much denser, and less porous than the SEI layer formed on the pure graphite electrode. Results of impedance spectroscopy also make it apparent that the fullerene soot facilitates Li+ transfer into the graphite particles, enabling the electrode to utilize its full capacity during prolonged cycling. Pure graphite electrodes exhibit isolation of some graphite particles, resulting in permanent loss of Li+ intercalation sites, which is observed as Coulombic losses and capacity fade. In addition, our results suggest that some high molecular weight fullerenic species or carbon onions preferentially account for the observed suppression of capacity fade, and that limiting the soot content to these species allows lower overall soot content in the composite material thus increasing the first cycle Coulombic efficiency significantly. These efforts have resulted in an increased understanding of the electrochemical nature of carbon materials and possibly a technologically useful composite electrode material. |
