CARBON MATERIALS FOR LITHIUM-ION (SHUTTLECOCK) CELLS

Carbon materials as possible alternatives to metallic lithium were described with emphasis on the electrochemical characters of carbon materials, such as (natural and artificial) graphite, petroleum coke, pitch-based carbon fibers, high-area carbons, and other carbonaceous materials. Well-defined graphite showed the lowest operating voltage (0-0.3 V versus Li) and the highest volumetric capacity (about 0.6 Ah.cm-3 based on the observed density and rechargeable capacity) in addition to excellent rechargeability. The theoretical capacity of graphite was 372 mAh.g-1 or 850 mAh.cm-3 based on the graphite sample for the reaction to form the first-stage compound (LiC6). Among the materials examined, some of them showed the capacity more than 372 mAh.g-1, while the operating voltage was higher and the density was lower than that of graphite. To understand such an anomalous behavior of carbonaceous materials, we modeled carbon electrodes and explained why some of carbonaceous materials exceed a capacity limit of 372 mAh.g-1. According to our model, high-capacity materials more than 500 mAh.g-1 were possible but traded off volumetric capacity, operating voltage, and consequently energy density. A lithium-ion (shuttlecock) cell consisting of natural graphite and LiNiO2 was also reported and the specific problems in applying carbon materials to lithium-ion cells were discussed.