JPH0697004A - Polarizable electrode and its manufacture - Google Patents

Abstract

PURPOSE:To provide a polarizable electrode wherein the strength and the resistivity of the polarizable electrode which is used to an electric double layer capacitor, a battery or an electrochromic display and which is composed of active carbon have been improved. CONSTITUTION:The surface of active carbon fine particles 1 is covered with bonding agents 2, and the active carbon fine particles 1 are bonded densely because the bonding agents 2 are boned to each other. When the bonding agents 2 are carbonized, the active carbon fine particles 1 and the bonding agents 2 are bonded firmly and the high electric conductivity of the title electrode is kept.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizable electrode made of activated carbon for use in an electric double layer capacitor, a battery, an electrochromic display and the like, and a method for producing the polarizable electrode.

[0002]

2. Description of the Related Art A conventional technique will be described by taking an electric double layer capacitor as an example.

An electric double layer capacitor is a large-capacity capacitor which uses activated carbon powder or activated carbon fibers as a polarizable electrode and utilizes an electric double layer generated at the interface between activated carbon and an electrolytic solution. The electric double layer capacitor is a small-sized and large-capacity rechargeable capacitor, and is widely used for backing up microcomputers, memories, and timers.

Such electric double layer capacitors are roughly classified into the following two types. That is, an aqueous solution type electrolytic solution such as a sulfuric acid aqueous solution and an organic solution type electrolytic solution obtained by adding an electrolyte to an organic solvent such as propylene carbonate are used.

When powdered activated carbon is used, dilute sulfuric acid as an electrolyte is generally mixed to form a slurry paste which is incorporated in a capacitor. In this case, in order to increase the packing density of activated carbon and to improve the contact resistance between activated carbons, it is necessary to pressurize and seal the polarizable electrode, which requires a large case and complicates the manufacturing process. However, there were problems such as poor handling.

When using fibrous activated carbon, there are problems that the packing density is lower and the contact resistance is higher than that of powdered activated carbon.

Therefore, the development of a solid activated carbon electrode has been proposed as a polarizable electrode which has a simple structure and a high energy density and which does not require an electrode pressing means.

FIG. 3 shows activated carbon powder or activated carbon fibers obtained by pressurizing and molding a dry mixture of activated carbon powder or activated carbon fibers and a binder and then heating the mixture in an inert gas atmosphere to carbonize the binder. 2 shows a cross section of a solid activated carbon electrode composed of carbon and carbon (for example, see JP-A-63-226019). Activated carbon fine particles 1 is a binder 2
Are bonded together by carbonizing the binder 2. There are holes 3 between each particle.

[0009]

However, in the case of the solid activated carbon electrode produced by dry-mixing the activated carbon 1 and the binder 2, the activated carbon 1 and the binder 2 are dispersed independently of each other. The contact area of 2 is small, and a large amount of binder 2 is required to increase the strength of the activated carbon electrode when solidifying. As a result, there is a problem that the content rate of the activated carbon 1 decreases, and when the electric double layer capacitor is configured, the capacity density decreases and the internal resistance increases.

In view of the above, the present invention solves the above problems of the conventional solid activated carbon electrode, and when an electric double layer capacitor is constructed, a solid polarizable electrode having dramatically improved capacity density and internal resistance is provided. The purpose is to provide.

[0011]

The present invention is a polarizable electrode characterized in that at least a part of the surface of activated carbon is coated with a binder.

The present invention also provides a highly dispersed mixture of activated carbon and a binder obtained by removing the solvent from a solution obtained by dispersing activated carbon in a solution obtained by dissolving the binder in a solvent. Is a method of manufacturing a polarizable electrode which is formed by pressurizing, molding and carbonizing.

[0013]

In the present invention, a part of the activated carbon is coated with the binder to increase the affinity between the activated carbon and the binding agent, and the activated carbon and the binding agent are strongly bound to increase the strength of the electrode. Since the contact resistance is reduced, the internal resistance is lowered, and a highly reliable polarizable electrode suitable for rapid charging and large current discharging can be realized.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional view of a polarizable electrode according to one embodiment of the present invention. The surface of the activated carbon fine particles 1 is thinly coated with the binder 2, and the activated carbon fine particles 1 are tightly bound to each other due to the binding of the binding agents 2 with each other. By carbonizing the binder 2, the activated carbon fine particles 1 and the binder 2 are firmly bonded and high electric conductivity is maintained.
There are holes 3 between each particle. (Example 1) A solution obtained by dissolving a phenol resin as a binder in ethanol was mixed with 4 times the weight of the phenol-based activated carbon powder in weight ratio to the phenol resin and dispersed to obtain a solution. Then, the ethanol was removed to obtain a highly dispersed mixture of activated carbon and a binder. The mixture is press-molded under a press pressure of 120 kg / cm ² and a press temperature of 180 ° C. to form a polarizable electrode material, which is heated at 800 ° C. in an inert gas atmosphere to carbonize the phenol resin. A polarizable electrode was obtained by.

Regarding the polarizable electrode manufactured in this example,
Bending strength and specific resistance were measured and shown in (Table 1).

In order to measure the characteristics of the electric double layer capacitor as an electrode, the test cell of the electric double layer capacitor shown in FIG. 2 was prototyped, and the capacitance and internal resistance were measured.
The results are shown in (Table 1). The pair of polarizable electrodes 4 obtained by cutting the polarizable electrode manufactured in this example into a cylindrical shape having a diameter of 20 mm and a thickness of 1.5 mm is impregnated with a 30 wt% sulfuric acid aqueous solution as an electrolytic solution, and a polyethylene separator 6 is interposed therebetween. To face each other,
An electric double layer capacitor was formed using the current collector 5 and the insulating gasket 7.

For comparison with the conventional example, the bending strength, the specific resistance, and the electrostatic capacity and the internal resistance of the electrode of the electric double layer capacitor were similarly measured for the polarizable electrode manufactured by the following comparative example. (Table 1). (Comparative Example 1) Phenolic activated carbon powder is mixed with phenol resin as a binder and activated carbon obtained by dry-blending four times the weight ratio of phenolic activated carbon powder to the phenol resin. Press the product at a pressure of 120 kg / c
The material for the polarizable electrode is formed by press molding under the conditions of m ² and a pressing temperature of 180 ° C., and 800 ° C. in an inert gas atmosphere.
A polarizable electrode was obtained by heating the phenol resin to carbonize it.

[0019]

[Table 1]

As is clear from (Table 1), the polarizable electrode of this example has a large bending strength and a small specific resistance as compared with the conventional example. Further, when used as the polarizable electrode of the electric double layer capacitor, it is understood that the polarizable electrode of the present embodiment has a large capacitance and a small internal resistance as compared with the conventional example.

In the above embodiments, the case where the activated carbon is in the form of powder has been described, but the same effect can be obtained when the activated carbon is in the form of particles or fibers.

Further, although powdery materials are used as the current collector material and the polarizable electrode material in the above embodiments, the material is not limited to these and may be granular or fibrous.

Further, in the above embodiment, the phenolic resin-based activated carbon was used as the polarizable electrode material, but the activated carbon is not limited to this, and the phenolic resin also has a heat that melts below the curing temperature. It is not limited to this as long as it is a curable binder.

Further, in the above embodiment, the electrolytic solution is 30
Although a wt% sulfuric acid aqueous solution was used, the present invention is not limited to this, and an organic electrolytic solution may be used.

Although a polyethylene porous film is used as the separator in the above embodiment, it is not limited to this as long as it is non-electroconductive and ion-permeable.

The polarizable electrode of the present invention can be widely used not only in the electric double layer capacitor as described above but also in batteries, electrochromic displays and the like.

[0027]

As is apparent from the above description,
In the present invention, the affinity of the activated carbon and the binder is increased by coating a part of the activated carbon with the binder, the strength of the electrode is increased due to the strong binding of the activated carbon and the binder, and the contact resistance between the activated carbons is increased. Is reduced, the internal resistance is lowered, and a highly reliable polarizable electrode suitable for rapid charging and large current discharging can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a polarizable electrode formed through a process according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an electric double layer capacitor test cell.

FIG. 3 is a sectional view of a polarizable electrode formed through a process according to a comparative example.

[Explanation of symbols]

 1 Activated carbon fine particles 2 Binder 3 Void 4 Polarizing electrode 5 Current collector 6 Separator 7 Gasket

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Yoshida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A polarizable electrode in which activated carbon is bound with a binder, wherein at least a part of the surface of the activated carbon is coated with the binder. 2. The polarizable electrode according to claim 1, wherein the binder comprises a sintered body of polymer and pitch. 3. A highly dispersed mixture of activated carbon and a binder obtained by removing the solvent from a solution obtained by dispersing activated carbon in a solution obtained by dissolving the binder in a solvent is pressed. A method of manufacturing a polarizable electrode, which comprises forming, carbonizing, and forming.