An electric double-layer capacitor using the formation of an electric double layer for energy storage performs charging and discharging only through the movement of ions without requiring an oxidation-reduction reaction required by a secondary battery. Therefore, the electric double-layer capacitor has the advantages of an excellent output characteristic and reduced degradation. Since the electric double-layer capacitor utilizes the natural phenomenon of the formation of the electric double layer, the device structure thereof is simpler than that of a parallel-plate condenser or the like. In addition, because the spacing between electrode plates in the condenser is on the order of the size of an ion in the electric double-layer capacitor, the electric double-layer capacitor has the advantage of a large capacitance. On the other hand, a low energy density and the like can be listed as disadvantages of the electric double-layer capacitor.
The electric double-layer capacitor is used in two different applications. In one of the two applications, the electric double-layer capacitor is primarily used alone. In the other application, the electric double-layer capacitor is used in conjunction with another type of energy conversion device such as a secondary battery or a fuel battery. In either case, the electric double-layer battery performs an important function as an energy conversion device.
In recent years, improvements in the performance of equipment using the above-mentioned energy conversion device, including the electric double-layer capacitor, are remarkable. With the improvements in the performance of the equipment, there has been a growing demand for an improvement in the performance of the energy conversion device.
Among numerous existing energy conversion devices, a lead acid battery for an automobile can be listed as one of the most frequently used devices. As the lead acid battery for an automobile, a high-output type capable of instantaneously extracting a large current is demanded to allow constant starting from a state where an engine is cool. A temporal scale is in the range of, e.g., about 0.2 seconds to 1 second, and a characteristic which allows retention of a high voltage within the time is required. In consideration of the tendency of a load, such as a motor mounted in a vehicle or the like, to keep increasing, a lead acid battery which provides a higher output than a conventional lead acid battery has done is in demand. In an idle stopping vehicle and a hybrid vehicle in which the charging and discharging of a lead acid battery is repeatedly and frequently performed also, a lead acid battery which provides a higher output more stably than the conventional lead acid battery has done is in demand.
In Patent Document 1, it is proposed to add a substance having a desulfurization catalytic effect or a SOx oxidation catalytic effect to a carbon material containing activated carbon or cause the carbon material to support such a substance and add the resulting material to a negative electrode, thereby improving the charge acceptance of a battery.
In Patent Document 2, it is proposed to produce an electrode using an active material mixture paste produced by adding conductive carbon and activated carbon to a negative-electrode active material, thereby achieving an improvement in conductivity and an increase in the capacity of an electric double layer and holding a battery voltage high immediately after discharging.
In Patent Document 3, it is proposed to cover a surface of the positive electrode of a lead acid battery with a porous carbon material, thereby improving the charge acceptance of the lead acid battery.
In Patent Document 4, it is proposed to remove an impurity in an electrolytic solution by bringing activated carbon into contact with the electrolytic solution to cause adsorption of the impurity, thereby reducing self-discharging.                Patent Document 1: JP-2002-367613 A        Patent Document 2: JP-2003-51306 A        Patent Document 3: JP-H8-180858 A        Patent Document 4: JP-2001-210354 A        
The task of the present invention is to provide a lead acid battery having an output characteristic more excellent than that of a conventional lead acid battery and an electrode for the lead acid battery used therein. An object of the present invention in an energy conversion device to which an electric-double-layer capacitor material capable of high-speed charging and discharging is added is to enhance the effect of the addition of activated carbon by making most effective use of the electric-double-layer capacitor material and provide a device with a higher input/output capability and a higher energy density.