The first in situ 7Li NMR study of the reversible lithium insertion mechanism in disorganised carbons

We study a disordered carbon designed to be used as negative electrode in a secondary lithium battery. We perform in situ magnetic resonance, i.e. we run several electrochemical cycles inside the magnet while recording NMR spectra. We obtain simultaneous Li-7 NMR and electrochemistry data and may thus analyse: the detailed chronology of the events, the Knight shift, the line width, the relaxation time T-1. This experimental work allows us to evidence a quasi metallic lithium, less diffusive than in metal and in graphite. The quasi metallic lithium is responsible for the very good reversible capacity, at a very low voltage. We indicate a model for the insertion/extraction of lithium in the fibers. The disordered carbon under study exhibits better qualities than graphite's for secondary battery applications. Only one drawback remains: a 0.5 V hysteresis; NMR shows that it occurs when the lasts quasi metal lithium are to be extracted. We evaluate the energy barrier. (C) 2003 Elsevier Ltd. All rights reserved.