The electric double-layer capacitor uses a pair of electric charge layers (electric double-layer capacitor) each of which having different codes and which is generated on a boundary between a conductive material composing an electrode and an electrolyte impregnated in the conductive material; and the electric double-layer capacitor is characterized by not causing deterioration which occurs as a result of charge and discharge. Therefore, for example, the electric double-layer capacitor is used in such a manner that it is connected to a power supply (a battery or a power supply converting a commercial AC power supply into a direct current) in parallel to accumulate electric charges and, by discharging the electric charges accumulated in the power supply on a short transmission interruption of the power supply, it backups various electric and electronic devices (for example, a D-RAM or the like).
The existing electric double-layer capacitor uses an active carbon powder or the like as a conductor material for an electrode (a carbon material) because a capacitance of the electric double-layer capacitor is determined by an amount of the electric charges to be accumulated in the electric double-layer capacitor. As a surface area of the electrode becomes larger, the amount of the electric charges becomes larger. The active carbon has a high specific surface area which is not less than 1,000 m2/g so that the active carbon is suitable for the electrode material of the amount of the electric double-layer capacitor requiring a large surface area.
The electric double-layer capacitor using the active carbon power as a polarizing electrode is described, for example, in JP-A-4-44407. The polarizing electrode described in this publication is a solid active carbon electrode which is solidified by mixing the active carbon power with a heat hardening phenol resin such as a phenol resin or the like.
Among the electric double-layer capacitors, the one with a high capacity is expected to be used for a power supply for a pulse power. However, a conventional electric double-layer capacitor cannot supply a large current in an instant so that it cannot carry out a function which is required to serve as a power supply for the pulse power. This is because the movement of ions is inhibited inside of a microscopic fine pore with a diameter of a several nm contained in the active carbon powder. In details, as described in JP-A-4-288361, the solid active carbon electrode using the active carbon power has the fine pore with a diameter of a several nm contained in the active carbon powder, and a pore with a diameter of a 100 nm or more formed upon carbonizing the phenol resin. Among these fine pores, inside of the microscopic fine pore with a diameter of a several nm contained in the active carbon powder, movement of ions is inhibited. As a result, the conventional electric double-layer capacitor involves a problem such that, when a large current is discharged, a capacity is decreased by appearance and the conventional electric double-layer capacitor cannot sufficiently offer a performance. Therefore, it is expected to realize an electrode having a fine pore structure (a distribution of seized of the fine pore) so that the ions can be moved more easily.
In addition, the maximum current value capable of being supplied to an electrode per unit area is proportion to a capacitance per unit area of the electrode. Therefore, it is preferable that the capacitance per unit area of the electrode is large.
In order to solve the above-described problems, an object of the present invention is to provide a polarizing electrode having a fine pore size distribution (a structure of a fine pore) so as to make moving of ions easier and its manufacturing method; and to provide an electric double-layer capacitor using the polarizing electrode, which has a large capacitance and is capable of taking out a large current in a moment of time.
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