Effect of surface structure on the irreversible capacity of various graphitic carbon electrodes

In order to understand the structural effect on irreversible capacity, the electrochemical lithium intercalation of various graphitic carbons was studied in 1 M LiPF6 solution of ethylene carbonate/propylene carbonate/diethyl carbonate (EC/PC/DEC), as a function of PC content. Because the irreversible capacity was increased by PC only for the carbons with a considerable edge fraction, it was possible to selectively amplify and monitor the reaction on the edge surface. The important role of the edge surface was confirmed qualitatively by high resolution transmission electron microscope images of the surface structure and quantitatively by further analysis on the results, using a simple model that explicitly considered the different reactivity of EC and PC toward the basal and edge surfaces. Exfoliation behavior, emerging as the PC content increased above a certain structure- dependent threshold, was examined also. The structural effect could be explained by assuming that the cointercalation of PC gave rise to exfoliation. Two controlling factors were suggested: the structural integrity affecting the expansion of layer spacing and the geometry of the edge surface affecting the cointercalation of PC. (C) 1999 The Electrochemical Society. S0013-4651(98)03-036-5. All rights reserved.