JPH04206920A - Electrode and electric double layer capacitor - Google Patents

Abstract

PURPOSE:To make the manufacture of an apparatus easy, the separation of a collector difficult and an electric resistance sufficiently low also in the direction of thickness by equipping the apparatus with a block containing an activated carbon and with a collector part being a metal film formed on the surface of the block. CONSTITUTION:An activated carbon block is formed by carbonization and activation of a phenol formalin resin foam, substantially has an open-cell structure and has 0.1g/cm<3> or more bulk density and 500m<2>/g or more specific surface area. A pair of polarizable electrodes 1, 1 equipped with this block and a collector part being a metal film formed by plasma spraying on the surface of the block and separator 3 arranged between are housed in a case 5 and impregnated with an electrolytic solution. The collector is composed of at least one sort selected from the group consisting of Al, Ta, Cu and Ti.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to electrodes and electric double layer capacitors, and more particularly to carbon-based electrodes and devices using the electrodes that have been conventionally used in lead-acid batteries, Ni-Cd storage batteries, etc. The present invention relates to a large-capacity electric double layer capacitor that can be used for applications such as secondary batteries.

TECHNICAL BACKGROUND OF THE INVENTION In recent years, electric double layer capacitors, which have a long life and are capable of high-speed charging and discharging, have been used as backup power sources for electronic devices. An electric double layer capacitor is a capacitor that consists of a polarizable electrode and an electrolyte in contact with the polarizable electrode, and at the interface between these electrodes, positive and negative electrodes are arranged and distributed to accumulate charge in the electric double layer. , the capacitance of the electric double layer increases depending on the area of the electrode interface.

Such an electric double layer capacitor consists of a pair of polarizable electrodes, a separator placed between the polarizable electrodes, a case that houses them, and a gasket ring to maintain watertightness of the case. is common.

Polarizable electrodes must have good electrical conductivity, and conventionally electrodes made of a single metal were used, but in recent years, in order to increase the surface area of polarizable electrodes, one side of a facepiece made of activated carbon fibers has been made of metal. A polarizable electrode with a current collector formed therein has been used (Japanese Patent Application Laid-Open No. 61-203618,
JP-A-63-268221 and JP-A-64-1
(See Publication No. 220).

By the way, electric double layer capacitors require low electrical resistance between the activated carbon fiber and metal layer, electrochemical inertness, and low cost in order to efficiently draw out the electric double layer accumulated in the polarizable electrode. is required.

For example, Japanese Patent Application Laid-Open No. 1220/1983 discloses a polarizable electrode in which aluminum metal is formed as a current collector by plasma spraying on the surface of cloth or the like made of activated carbon fibers.

However, when fabrics made of activated carbon fibers are cut out into disc-like shapes using a punching die to produce polarizable electrodes, there is a problem in that the sprayed aluminum metal tends to peel off from the activated carbon fibers.

This is because although the aluminum metal adheres to the aluminum metal due to the ``anchor effect'' during thermal spraying, since the activated carbon fibers are flexible, voids are created at the interface between the activated carbon fibers and the aluminum metal during punching.

Further, in such a polarizable electrode, when it is housed in a case, an external force is applied to the electrode, and there is a possibility that a void may be generated at the interface between the activated carbon fiber and the aluminum metal, and the current collector may peel off.

As a countermeasure, it has been proposed to first form a film of aluminum metal on activated carbon fibers by ion beam irradiation or sputtering, and then perform plasma spraying to increase the adhesion strength of the metal film as a current collector (Japanese Patent Application Laid-Open No. 64-122
(See Publication No. 0).

However, such a method is industrially disadvantageous because the manufacturing process of the polarizable electrode is complicated and costs are high.

In addition, although this polarizable electrode has a low electrical resistance in the fiber direction, the contact surface between the fibers is small, so the contact resistance is high, and therefore the electrical resistance in the thickness direction is high. There is a drawback of increasing internal resistance.

Furthermore, when manufacturing large-capacity polarizable electrodes using activated carbon fiber cloth, the cloth must be laminated, which increases the contact resistance between the fibers and increases the resistance between the cloths that are in surface contact with each other. As a result, the electrical resistance in the lamination direction of the cloth, that is, in the thickness direction, becomes even higher and unstable.

In order to lower the electrical resistance of such polarizable electrodes, polarizable electrodes in which a porous aluminum layer is formed on the entire surface of the electrode body by plasma spraying have been proposed (Japanese Patent Laid-Open No. 61-203618). reference).

However, for this polarizable electrode, the thickness is still 4.
Although it was not possible to sufficiently reduce the electrical resistance in the - direction, the problem especially when laminating activated carbon fiber cloth was not solved at all.

Purpose of the Invention The present invention aims to solve the problems associated with the conventional technology, and provides an electrode that is easy to manufacture, hardly causes peeling of the current collector, and has sufficiently low electrical resistance even in the thickness direction. The object of the present invention is to provide an electric double layer capacitor using the same as a polarizable electrode.

Summary of the Invention The electrode according to the present invention is characterized by comprising a block containing activated carbon and a current collector portion that is a thin metal film formed on the surface of the block.

The electric double layer capacitor according to the present invention is characterized by having a polarizable electrode including a block containing activated carbon and a current collector that is a thin metal film formed on the surface of the block.

According to the electrode and electric double layer capacitor according to the present invention, the metal thin film formed on the block surface as a current collector,
Due to the "anchor effect" that enters the countless micropores of the activated carbon contained in the above block, it is firmly bonded to the block, and the block is strong and will not be distorted, so it will not be affected by external forces applied during processing and assembly into the electrode. There is no peeling of the current collector part.

DETAILED DESCRIPTION OF THE INVENTION The electrode and electric double layer capacitor according to the present invention will be specifically described below.

In the electrode according to the present invention, a current collector portion is provided in a block containing activated carbon. In the present invention, it is also possible to use an activated carbon-containing block made by mixing activated carbon fibers or powdered activated carbon with an appropriate binder and solidifying it, but considering the activated carbon content, strength, specific surface area, etc., resin foaming It is preferable to use an activated carbon block obtained by carbonizing and activating the body.

The resin foam used in manufacturing the activated carbon block is a resin porous body having a cellular structure obtained by mixing a resin prepolymer with a foaming agent, a curing agent, etc., and foaming and curing the mixture.

Specifically, such resins include polyurethane,
Thermosetting resins such as phenol resin, furfural resin, epoxy resin, furan resin, polyisocyanurate-1 resin, polyimide resin, and urea resin are mainly used.

Among these resin foams, phenolic resins, especially resol-type phenolic resins that use resol as a prepolymer, are expected to have uniform cell shapes, are easy to manufacture, and have good yields when carbonized and activated. Foam is preferred.

Resoles can be obtained by reacting phenols and aldehydes in the presence of an alkali catalyst according to known methods.

Specific examples of such phenols include phenol, cresol, xylenol, and resorcinol, with phenol being particularly preferred.

Specifically, the aldehydes used include formaldehyde, 1-lioxane, acetaldehyde, and furfural, with formaldehyde being particularly preferred.

Further, as the alkali catalyst, specifically, L i O
Examples include H, KOH, NaOH, NH, 11NH40H, ethanolamine, ethylenediamine, and triethylamine.

As a blowing agent for obtaining a resin foam, conventionally known decomposition type, reaction type and evaporation type blowing agents can be used, but among these, it is preferable to use an evaporation type blowing agent that operates at a relatively low temperature. Specifically, butane, pentane, hexadi,
Examples include paraffinic hydrocarbons such as heptane, alcohols such as methanol, ethanol and butanol, halogenated hydrocarbons such as dichlorotrifluoroethane (Freon 123), ethers and mixtures thereof.

For foaming and curing, a curing agent is used together with a foaming agent. As this curing agent, a conventionally known curing agent is selected and used depending on the type of prepolymer. In the case of a prepolymer or resol type phenol-formalin resin, specifically, inorganic acids such as sulfuric acid, phosphoric acid, and hydrochloric acid, and organic acids such as paratoluenesulfonic acid and cresolsulfonic acid are used.

Resin foams can be obtained by mixing, for example, the above-mentioned resol-type phenolic resin prepolymer with a blowing agent, a curing agent, and if necessary, additives such as a foam stabilizer, filler, and stabilizer, either all at once or sequentially. The creamy material is heated and supplied into a heated mold, wooden mold, or cardboard box, or between a double belt conveyor, and foamed and hardened.
It can be obtained by cropping as needed. Among these methods, the method of supplying a creamy substance into a mold and gradually foaming it at a slow speed is preferable in order to obtain a uniform foamed product. On the contrary, the cellular structure of rapidly foamed and hardened foam tends to be non-uniform and the direction and location of the foaming is not uniform, so there is a problem that the internal resistance value varies. It is desirable to make the foam as uniform as possible. Further, it is desirable that the bubbles have a large number of open cells in consideration of contact with the electrolytic solution and ion mobility.

The activated carbon block used in the present invention is produced by processing such a molded resin foam as it is, or by cutting or cutting it into a desired shape such as a plate, followed by carbonization and activation treatment.

The carbonization treatment is performed by firing the resin foam in a non-oxidizing atmosphere. That is, the resin foam is prepared under reduced pressure or in Ar.
Gas, He gas, N, gas, CO.

gas, halogen gas, ammonia gas, H2 scum, mixed gas thereof, etc., preferably 500 to 120
It is fired at a temperature of 0°C, especially 600 to 900°C.

In this way, the foam is carbonized and a porous carbon body is obtained. Although there is no particular restriction on the temperature increase rate during firing, it is preferable to increase the temperature gradually around 200 to 600°C, where decomposition of the resin generally starts.

The activation treatment is performed by heating the obtained porous carbon material in the presence of an oxidizing gas. Processing temperature is usually 800-1200°C
I will do it. If the treatment temperature is too low, activation will not proceed sufficiently,
Only small specific surface areas can be obtained. On the other hand, if the treatment temperature is too high, cracks will easily form in the carbide foam.

The oxidizing gas in the present invention refers to an oxygen-containing gas such as water vapor, carbon dioxide, air, oxygen, etc., but it is usually replaced with an inert gas such as combustion gas, N2 gas, etc. for ease of operation. Used as a mixed gas. The exposure time to the oxidizing gas depends on the concentration of the oxidizing gas and the processing temperature, but 1) For safety, it is necessary to maintain the shape of the carbide foam within a range that does not damage it.

Further, the activation treatment may be a chemical activation method other than the above-mentioned gas activation, or a method using both of them in combination. The chemical activation method is a method in which chemicals such as zinc chloride, phosphoric acid, potassium sulfide, etc. are added to the resin foam, and then heated in an inert gas atmosphere to perform carbonization and activation at the same time.

The activated carbon block that can be used in the present invention has a substantially open cell structure as a whole, and has a bulk density of 0.1 g/Cm.
2 or more, preferably O, 15g/cm3 to 0.7
0 g/cm3, specific surface area of 500 m''/= 1 1-g or more, preferably 700 d/g or more, and more preferably 700 to 2000 rrr/g to improve contact with the electrolyte and increase capacity. This is desirable for making a large capacitor.

In the present invention, a substantially open-cell structure means that the volume of the electrolyte impregnated into the activated carbon block under vacuum (10-'torr or less) is smaller than the theoretically calculated spatial volume of the activated carbon block. The ratio is 60% or more, preferably 8096 or more, and more preferably 90% or more.

In the present invention, the open cell ratio was determined as follows.

Examples of the types of electrolytes used during measurement include 3
0% by weight sulfuric acid (density 1,215g/cc (25°C))
Alternatively, an electrolytic solution (density 1.088 g/cc (25° C.)) containing 10% by weight of tetraethylammonium tetrafluoroborate in propylene carbonate is used.

Theoretical space volume (■1) is the volume of activated carbon block (V)
It is calculated from the bulk density (AD) of the activated carbon block, the dustiness (DC') of the activated carbon, and the bulk density (AD) of the activated carbon block.

After pulverization and drying, measurements were made using a pycnometer with a Kaelsack thermometer, using toluene as an immersion liquid.

The volume of electrolyte impregnated into the activated carbon block (■,) is
How many weights (W, ) of the activated carbon block is impregnated and the amount of mold after impregnation (
W2) and the density (DL) of the electrolytic solution.

vt - (W2-W,')/DL Therefore, the open cell ratio is VL/VTX100 (%) It is calculated by

Since such an activated carbon block has a substantially open cell structure, it has a large specific surface area and is easily infiltrated with an electrolyte. In addition, this activated carbon block exhibits high strength because of its continuous skeleton, and has a large specific surface area that makes it possible to manufacture self-supporting electrodes that are difficult to break, especially polarizable electrodes. Low resistance and stable.

Furthermore, activated carbon blocks can be made into electrodes of any shape by trimming them to the desired thickness and shape, and when used as polarizable electrodes, they can be used to create large, thick, and high-capacity electric double layers. Not only can the capacitor be easily manufactured, but also the volume of the polarizable electrode can be reduced by increasing the bulk density, thereby reducing the overall size of the capacitor.

Since the activated carbon block used in the present invention has a moderate average pore diameter, ions in the electrolyte, especially the organic electrolyte, can freely move in and out, making it possible to obtain an electrode with a substantially large surface area. I can do it.

A thin metal film is formed on one side of the block containing activated carbon to serve as a current collector and an electrode.The method for forming this thin film is a method that allows the metal to enter the micropores of the activated carbon that makes up the block. Any method may be used, such as plasma spraying, vapor deposition, sputtering,
Ion beam irradiation method etc. can be applied. Among these, plasma spraying is preferred because it embeds the surface of the metal or activated carbon block, provides strong adhesion, and improves productivity.

In the plasma spraying method, first, argon gas, nitrogen gas, etc. are heated to a high temperature by direct current arc discharge to create a partially electrolyzed plasma state, and working gas is supplied from behind and heated by the arc, which is then ejected from the nozzle as ultra-high temperature plasma. let

Next, powdered thermal spray material is placed on a carrier gas, blown into this ultra-high temperature plasma, heated and melted, and accelerated to collide with the surface of the activated carbon block at high speed to form a sprayed metal thin film layer. .

Argon or nitrogen is generally used as the working gas, and helium or hydrogen may be added to these gases. Further, thermal spraying onto a base material is generally performed in an atmospheric atmosphere, but it may also be performed in a reduced pressure inert atmosphere.

In the present invention, the thermal spray ion material is not particularly limited, but examples thereof include A1, Ta, Cu, and Ti, and these metals may be used alone or in combination of two or more types.

In addition, the formed metal thin film is usually 50 to 300 μm1
The thickness is preferably 100 to 200 μm.

When metal is sprayed onto a block containing activated carbon in this way, a thin film can be formed that is firmly adhered due to the anchor effect of the metal entering into the micropores of the activated carbon block. As shown in Figure 3, the entire activated carbon block has a substantially open-cell structure, and the anchor effect increases the surface area for solid adhesion, making the adhesion between the activated carbon block and the current collector even stronger. There are advantages.

Although the electrode 1 can be used for various purposes, it is particularly preferred as a polarizable electrode for an electric double layer capacitor. That is, the electric double layer capacitor of the present invention is characterized by having this electrode as a polarizable electrode.

Here, the structure and manufacturing method of an electric double layer capacitor using the above-mentioned electrode as a polarizable electrode will be explained with reference to the accompanying drawings.

The attached FIG. 1 shows an example of an electric double layer capacitor according to the present invention. As shown in the figure, this electric double layer capacitor includes a pair of polarizable electrodes 1 and A case 5 houses a separator 3 disposed therebetween.

The polarizable electrodes 1 and 1 are manufactured, for example, by cutting the activated carbon block obtained as described above into a predetermined thickness, and plasma-spraying aluminum onto one surface thereof to form the current collector portion 2.

Further, the case 5 consists of case halves 5a and 5b and an insulating packing 4 interposed between them.

To assemble an electric double layer capacitor equipped with such members, first, the polarizable electrodes 1, 2 and separator 3 are degassed and then impregnated with an electrolyte, and then current is collected with the separator 3 in between. The polarizable electrodes are arranged facing each other with a distance of ±1.1 between the polarizable electrodes with the body 2 facing outward, and then housed in the case halves 5a and 5b. This is done by tightening and/or oozing.

The electric double layer capacitor according to the present invention is not particularly limited in terms of structure other than the use of the polarizable electrodes, and a conventionally known aqueous electrolyte or organic electrolyte can be used as the electrolyte.

Further, there are no particular limitations on the structure and shape of the case, and the case may have a structure as shown in the attached FIG. 2, for example. FIG. 2 is a cross-sectional view showing another embodiment of the electric double layer capacitor according to the present invention, and as shown, the case 1
5 consists of an inner half 15a and an outer half 15a, and the outer half 151) is shaped like a bowl. In such case 11, the distance between the separator 3 and the polarizable electrode is ±1.
．． 1 accommodated in the outer half 15b, the inner half 15a
An electric double layer capacitor is manufactured by covering the two halves 5a and 5b with each other and caulking the two halves 5a and 5b together via the packing 4.

Effects of the Invention According to the electrode according to the present invention, the metal thin film formed on the block surface as a current collector part is firmly attached to the block due to the "anchor effect" in which it enters the countless micropores of the activated carbon block. In addition to being bonded to the block, the block is strong and not easily distorted, so the current collector part will not peel off due to external forces applied during processing and assembly of electrodes, especially polarizable electrodes.
It is possible to maintain the initial characteristics for a long period of time.

In addition, in the electric double layer capacitor according to the present invention, a block containing activated carbon is used for the polarizable electrode, so that large electrodes with the thickness and size required for energy storage devices such as secondary batteries can be easily manufactured. In other words, the industrial value is extremely large.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 First, 100 parts by weight of resol (phenol-formalin resin prepolymer), 10 parts by weight of paratoluenesulfonic acid as a hardening agent, and 1.5 M parts of dichlorotrifluoroethane as a blowing agent were sufficiently stirred with a high-speed mixer. rear,
Pour this mixture into the mold, cover it, and then heat it to 80°C.
By leaving it in the air oven for 30 minutes,
0cm, width 30cm, thickness 3cm, bulk density 0.3g/
A plate-shaped phenolic resin foam of ci was obtained.

This molded plate has a length of 20 cm+, a width of 10 cm, and a thickness],
After cutting into pieces of 0 cm, they were placed in a Matsufuru furnace and heated under a nitrogen atmosphere at a heating rate of 60°C/hour to a temperature of 600°C. After maintaining this temperature for 1 hour, they were cooled and vertically heated. 1
6cm, width 8cm, thickness 0.8cm, bulk density 0.29
A plate-like porous carbon material of g/cnr was obtained.

Further, the temperature of this plate-shaped carbon porous body was raised to 950°C, steam was introduced into the combustion gas, and the temperature was maintained for 16 hours and then cooled.

The bulk density, strength, and specific surface area of the obtained activated carbon block were examined. Further, the open cell rate of this activated carbon block was 99% by the measurement method described above.

The results are shown in Table 1.

Table 1 Next, this activated carbon block was band sawed to a length of 12cm.

It was cut to a width of 7.5 cm and a thickness of 0.5 cm, and aluminum was plasma sprayed on one side of the surface in an air atmosphere.

Table 2 shows the appearance, film thickness, and electrical resistivity of activated carbon after thermal spraying.

A cross-sectional photograph of the activated carbon block showing the state of the sprayed metal layer is shown in FIG.

The film thickness was calculated by measuring the plate thickness before and after thermal spraying with a micro gauge.

The electrical resistivity was calculated by performing plasma spraying on both surfaces, passing a direct current of 50 mA/g (weight of activated carbon) through the surfaces, and measuring the voltage on both surfaces.

Example 2 In Example I, the appearance, film thickness, and electrical resistivity of activated carbon after spraying were measured in the same manner as in Example 1 except that tantalum was used as the sprayed metal.

The results are shown in Table 2.

Example 3 Example 1 except that the sprayed metal was copper.
In the same manner as above, the appearance, film thickness, and electrical resistivity of activated carbon after thermal spraying were measured.

The results are shown in Table 2.

Comparative Example 1 In Example 1, a graphite plate measuring 12 cm in length, 7.5 cm in width, and 0.1 cm in thickness was pressure-bonded to serve as a current collector instead of plasma spraying of aluminum. , the electrical resistivity was measured.

The results are shown in Table 2.

Comparative Example 2 The electrical resistivity was determined in the same manner as in Example 1, except that instead of plasma spraying aluminum, a nickel plate of 12 cm in length and 7.5 cm in width was pressure-welded as a current collector. It was measured.

The results are shown in Table 2.

[Brief explanation of the drawing]

Attached Figures 1 and 2 are cross-sectional views showing an electric double layer capacitor using the polarizable electrode of the present invention, and Figure 3 is a cross-sectional view of the polarizable electrode plasma-sprayed onto the activated carbon block of the present invention. This is a photo. In the figure, 1 is a polarizable electrode, 2 is a current collector, 3 is a separator, 4 and I4 are insulating packings, and 5.15 is a case. Patent applicant Mitsui Petrochemical Industries Co., Ltd. Agent Patent attorney Shunichi Suzuki -)') - Figure 1 Figure 2

Claims (6)

[Claims] (1) An electrode comprising a block containing activated carbon and a current collector portion that is a thin metal film formed on the surface of the block. (2) The electrode according to claim 1, wherein the metal thin film is formed by plasma spraying. (3) The electrode according to claim 1 or 2, wherein the activated carbon block is made by carbonizing and activating a phenol-formalin resin foam and has a substantially open cell structure. . (4) The above block is made by carbonizing and activating resin foam, has a bulk density of 0.1 g/cm^3 or more, and a specific surface area of 50
4. The electrode according to claim 1, wherein the electrode is an activated carbon block of 0 m^2/g or more. (5) The electrode according to any one of claims 1 to 4, wherein the current collector is made of at least one member selected from the group consisting of Al, Ta, Cu, and Ti. (6) An electric double layer capacitor characterized by having a polarizable electrode comprising a block containing activated carbon and a current collector portion that is a thin metal film formed on the surface of the block.