We have developed a device using a novel composite material as the negative electrode and ordinary activated carbon as the positive electrode. The composite material was obtained by heat-treatment of activated carbon with pitch. The structure of this composite was shown to be amorphous based on the X-ray diffraction pattern, and the surface area decreased from 2200 m 2 /g ͑activated carbon͒ to 250 m 2 /g ͑composite͒. This device can discharge at an extremely high current density of 10,000 mA/g based on the composite weight. The power density of around 2.2 kW/L was two times higher than EDLCs, and the energy density of around 20 Wh/L was three times higher. The discharge capacity maintained its initial capacity for at least 100,000 cycles. This device also had excellent storage characteristics at 60°C.

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One of the possible ways to obtain a safe and high-energy-density anode (negative electrode) for a rechargeable lithium battery is the replacement of lithium by carbon materials. Rechargeable lithium-ion batteries (LIB) using two kinds of carbon as the anode material have been accepted in the marketplace. One is graphite with a theoretical capacity 372 mAh/g (C 6 Li). Another is hard carbon with very low H/C atomic ratios (smaller than 0.1), which can store more lithium, with discharge capacities surpassing the theoretical capacity of graphite.On the other hand, there is another kind of interesting carbonaceous material that has not been used in the LIB industry. Carbon materials with high H/C atomic ratios in the range of 0.2 to 0.4 can store much more lithium, with discharge capacities surpassing those of hard carbons with low H/C atomic ratios. We reported that polyacenic semiconductor (PAS) material with an H/C of 0.25 obtained by pyrolyzing phenolic resins showed a reversible capacity of 850 mAh/g. 1 Dahn et al. 2 reported that polyvinyl chloride (PVC)-based disordered carbon with an H/C of 0.36 had a reversible capacity of 940 mAh/g. 2 Takami showed that perylene-based disordered carbon with an H/C of 0.26 had a reversible capacity of 804 mAh/g. 3 Although these materials have high capacities, they show low efficiency (65-75%) during the first charge and discharge. In particular, Li charged into the carbon electrode cannot be discharged from these electrodes. It is well known that the lithium supply in the LIB arises from the cathode when the cell is manufactured. In order to compensate for the loss of lithium that is irreversibly consumed, an excess of cathode material must be used. As a result, the energy density of the cell decreases and the cost of the cell increases. In order to make practical use of this kind of material, not only a large capacity is important, but also a high efficiency is necessary.In this study, we report the devleopment of a new carbonaceous material with a discharge capacity of 1017 mAh/g and efficiency of 81.5% for LIB using isotropic pitch as the raw material. According to our solid-state 13 C-nuclear magnetic resonance (NMR) results, a crystallite of the carbonaceous materials consists of graphene sheets with a disk-like shape. Therefore, we call these materials polycyclic aromatic hydrocarbons (PAHs) in this study. ExperimentalPreparation of PAHs.-The PAHs were produced in a tube furnace for general experiments. Generally, 30 g of isotropic pitch was placed in a ceramic boat and introduced into the tube furnace. Air in the furnace was replaced by N 2 for at least 20 min. The raw material was heated at a rate of 10ЊC /min to 650ЊC under a nitrogen atmosphere, which was maintained for 4 h. The obtained carbonaceous material was cooled to room temperature under a nitrogen atmosphere. As a reference material, PAS using phenolic resin as the raw material was also prepared under the same conditions.Structural characteristics of the carbonaceous material.-13 C NMR measurements were ...

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