Characterization of lithiated natural graphite before and after mild oxidation

Partial oxidation of natural graphite utilized in lithium ion batteries was found to increase its reversible capacity, while decreasing the irreversib le capacity. Several chemically distinct Li sites in lithiated graphite wer e identified by solid state Li-7 nuclear magnetic resonance (NMR): intercal ated Li, and Li chemically bonded within the surface passivation layer or s olid electrolyte interface (SEI). The partially oxidized graphite exhibited a third site, attributed to Li bonded to armchair, zigzag, or other edge s ites in the carbon. In addition, the NMR signal from the SEI in the partial ly oxidized graphite is consistent with earlier work suggesting that oxidat ion lays the foundation for a chemically bonded SEI that is implicated in i mproved electrochemical performance. Electron paramagnetic resonance (EPR) signals observed in lithiated graphite are attributed to conduction electro ns, as noted by other authors. EPR in unlithiated graphite, however, failed to detect a correlation between possible radical sites to which Li could b ond and excess Li capacity in the partially oxidized graphite. (C) 1998 Els evier Science S.A. All rights reserved.