Electrochemical insertion of Li and irreversibility in disordered carbons prepared from oxygen and sulfur-containing pitches

Starting from pitches with oxygen and sulfur contents varying from 0.13 to 2.7% by weight, we prepared a series of pregraphitic carbons by pyrolysis a t 1000 degrees C. The presence of O and S has no apparent physical or struc tural effect on the final carbon, However, a direct link was found between oxygen and sulfur contents and the irreversible capacity of the electrochem ical reaction of Li with these carbons. Apparently Li reacts irreversibly w ith sulfur and oxygen to form Li-O and Li-S bonds as are found in Li2O and Li2S. According to this model, the irreversible capacity should be directly proportional to the chalcogen content, and this is approximately observed at high chalcogen content. For lower concentrations, the formation of the s olid electrolyte interphase (SEI) is the dominant cause of Li loss, (C) 199 9 Elsevier Science Ltd. All rights reserved.