Effect of a rhombohedral phase on lithium intercalation capacity in graphite

Five natural graphites with different rhombohedral phase (3R phase) content have been investigated as anode materials for rechargeable lithium-ion batteries. The reversible capacity varies from 250 mA h/g to 350 mA h/g for the same intercalation conditions depending on the content of the 3R-phase. With increasing rhombohedral phase in the graphite, the intercalation capacity will be high. A peak at about 10 mV in the cyclic voltammograms (CV) of a sample with a large 3R-phase content is caused by lithium ions occupying boundaries between the rhombohedral (3R) phase and the hexagonal (2H) phase and is responsible for a capacity exceeding the theoretical value.