7Li nuclear magnetic resonance studies of hard carbon and graphite/hard carbon anode for Li ion battery

The hard carbon is attractive for the Li ion battery because of its higher capacity than the theoretical value of 372 Ah kg(-1) based on the composition of stage 1 Li-intercalated graphite, LiC(6). However, since the Li-doping reaction occurs at the potential of around 0 V versus Li/Li(+) reference electrode, it is often pointed out the possibility of Li metal deposition on the surface of anode. From the viewpoint of the safety it may be a moot point. In the present study, (7)Li NMR measurement was performed to estimate the degree of Li metal deposition on the surface of graphite and hard carbon anode. As a result, it is clarified that the Li metal deposition does not occur up to 110% over-discharge of the reversible capacity of hard carbon, whereas in the case of graphite anode, Li metal deposition occurred above 105% over-discharge of the capacity. From the (7)Li NMR spectroscopy, the safety limit of hard carbon is rather superior to that of graphite. (C) 2010 Elsevier B.V. All rights reserved.