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 carbon! to 250 m(2)/ g (composite). 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 degreesC. (C) 2004 The Electrochemical Society.