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

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 7Li NMR and electrochemistry data and may thus analyse: the detailed chronology of the events, the Knight shift, the line width, the relaxation time T1. 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 graphiteʹs 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.