Graphitized Carbons of Variable Morphology and Crystallinity: A Comparative Study of Their Performance in Lithium Cells

Six different carbons in variable particle size ranging from micrometric to nanometric and morphology (microbeads, flakes, nanofibers, and short and long multiwalled nanotubes) were tested as electrodes for Li-ion batteries. Their performance (particularly in regard to rate capability and cycling properties) was analyzed in terms of textural and structural properties as determined from N-2 adsorption and X-ray diffraction data, respectively. All carbons exhibited irreversible capacity (IC) to an extent governed by a combination of textural [(S-BET) and pore volume] and structural properties (average layer stacking height and orientation index). However, no direct correlation between IC and cell performance in terms of the rate capability and cycling properties was observed. These two properties are more markedly influenced by structural ordering in the graphite layers. At low rates, high particle sizes and crystallinity resulted in enhanced cell performance. Ensuring good performance at high rates, however, required both a highly layered ordering and a nanometric particle size in the carbon. Carbons with special morphologies such as nanotubes or nanofibers possess a high structural disorder which is detrimental for use as electrode materials in Li-ion batteries. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3231489] All rights reserved.