Three kinds of carbon have been used for commercial cells: graphite, soft carbon and hard carbon. The difference in the structures of these three kinds of carbon is shown clearly using our new model for soft and hard carbon structure. The lithium-doped state of these three kinds of carbon is discussed using the new structural model and published Li-7 NMR data. A large reversible capacity is demonstrated in the hard carbons derived from some vegetable fibers. Two mechanisms-one enhancing the adsorbing force of pseudo-metallic lithium atoms and one reducing the repulsion force between doped lithium atoms-which together produce a high reversible capacity, are explained.