JP3251580B2 - Electrode sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrode sheet used for electrodes of electric double layer capacitors, batteries and the like.

(Prior art) In an electric double layer capacitor, for example, a polarizable electrode is impregnated with an electrolytic solution, separated by a separator, and housed in a case so as to be charged or discharged through a collector electrode to constitute a capacitor cell. This capacitor cell is stacked as required to produce a multilayer electric double layer capacitor.In this case, a gap and insulation are provided between the capacitor cell and the outer case to avoid a short circuit between the collector electrode and the outer metal case. A rubber plate or a resin sheet provided with conductivity by a carbon material is used as a collector electrode because it is necessary to form a sealed form by pressing and laminating capacitor cells (Japanese Utility Model Application Laid-Open No. 2-120819). ~ 120821).

Further, as the polarizable electrode, it is necessary to impregnate the electrolyte, the larger the surface area, and the lower the electric resistance of the entire capacitor, it is preferable that the electric resistance is small.It is preferable to use activated carbon having a high electric resistance but a large surface area. It is desired to use together with graphite having a small electric resistance, and a paste obtained by mixing 20 to 80% by weight of graphite powder in a mixture of powdered activated carbon and an electrolyte solution is filled in the recesses of the conductive sheet to form electrodes ( JP-A-2-7509), 20 to 80% by weight of powdered activated carbon and 10 to 20% by weight of graphite or carbon black and 5 to 5% by weight.
A sheet obtained by wet-kneading 40% by weight of an organic binder to form a sheet (Japanese Patent Laid-Open No. 1-165108) has been proposed.

(Problems to be Solved by the Invention) By the way, when imparting a certain elasticity or formability to an electrode sheet using graphite, it is necessary to limit the ratio of the graphite for imparting conductivity to a certain amount or less. In order to be able to charge and discharge as quickly as possible without loss, there is a problem that the overall electrical resistance is increased, though the electrical resistance of the collector electrode sheet of the capacitor is preferably as small as possible.

Further, regarding the polarizable electrode, when the kneaded material is in the form of a paste, the configuration of the capacitor cell is limited. On the other hand, in the case of forming a sheet, it is difficult to adjust the average pore diameter and pore volume by stretching.

Accordingly, a first object of the present invention is to provide a resin sheet for an electrode having a small graphite ratio and a small electric resistance.

It is a second object of the present invention to provide a resin sheet for an electrode having a small graphite ratio and not only a small electric resistance but also a large electric capacity.

Further, the present invention also provides an integrated composite electrode which can be used as a collector electrode and a polarizable electrode of an electric double layer capacitor.

(Means for Solving the Problems) The present invention has been made by focusing on the fact that it is possible to obtain a low electric resistance even with a small blending amount by using an elastic graphite body as the graphite. Alternatively, the present invention resides in an electrode sheet which is formed by bonding using a dispersed resin.

This elastic graphite body is electrically conductive, similar to ordinary graphite, but has a spongy internal structure, so it is lightweight, has excellent compression recovery properties, and has a small weight ratio due to its low bulk density. This elastic graphite body can be produced by the method described in Japanese Patent Application No. 62-164808, etc.
Conventionally known ones can also be used.

In the present invention, this elastic graphite body is used as a granular material,
The particle size is preferably about 0.1 μm to 1 mm from the viewpoint of molding operability.

As a binder resin for binding these, it is particularly preferable to use a tetrafluoroethylene resin, an epoxy resin, a phenol resin, and an unsaturated polyester resin,
It is preferable to use a powdered resin or a dispersed resin dispersed in an appropriate dispersion medium, water, alcohols, inorganic acids, or the like. The reason is that the former is used as a binder to form a bond in a state where the resin is in partial contact with the elastic graphite particles, and the latter is used as a binder to bind the particles in a state where the resin wraps the elastic graphite body. This is because, as a result, it is possible to obtain a good molded product without penetrating the resin into the sponge structure of the elastic graphite body and impairing the structure and the elasticity.

The blending ratio of the elastic graphite body and the binder resin varies depending on the strength required for the product, but sheeting is possible in the range of 100: 1 to 500, and preferably 100: 10 to 200.

When impregnating the electrolyte, it is necessary to increase the surface area by mixing with activated carbon, but when the elastic graphite body is contained,
When activated carbon is filled and pressed, the elastic graphite body is compressed and the adhesion to activated carbon is increased, so that sheeting is facilitated.

Then, the 2nd structure of this invention is the sheet | seat for electrodes which makes the elastic graphite body and powdered activated carbon combine by using a powdery resin or a dispersed resin.

Here, activated carbon is generally a microporous material having a high surface area, but preferably has a surface area of 3000 to 5000 m ² / g.

The blending ratio of the elastic graphite body and the activated carbon is determined by the desired relative ratio between the electric resistance and the electric capacity, but usually a weight ratio of 30 to 300: 100 is appropriate.

In addition, since an electric double layer capacitor is assembled by laminating a polarizable electrode and a collector electrode via a separator, the polarizable electrode and the collector electrode are integrated in assembling and reducing the contact resistance between them. Is preferred. Thus, the present invention also provides an integrated composite electrode obtained by laminating and bonding the above two types of resin sheets for electrodes.

Although the lamination of the two sheets is performed by simple pressing such as roll rolling, it is preferable that the polarizing electrode be pressed before the resin is cured or in a state of low crystallinity. In particular, when used as a capacitor electrode, a composite electrode can also be prepared by cutting a polarizable electrode sheet into a necessary size in advance before bonding both sheets and bonding the obtained sheet to a collector electrode sheet, and then punching out. (See FIG. 3) (Action) According to the present invention, since the resin sheet containing the elastic graphite body is light even if its content is small, it is widely dispersed in the resin matrix, and the binder resin is used as the graphite particles. The graphite particles do not lose elasticity because they adhere to the surface of the graphite particles and function as a binder without adhering in the form of a thread or a web and penetrating into the interior of the sponge. This phenomenon is the same when the activated carbon is contained. As shown in FIG. 4, the elastic graphite particles 5 and the activated carbon particles 6 are not damaged by the resin in the surface porosity by the dispersed resin 4 as the binder resin. The electrolyte can be sufficiently impregnated with the electrolyte and has a large electric capacity. However, the electric resistance can be kept low and the electrolyte is thermochemically durable.

Hereinafter, the present invention will be described in detail based on specific examples shown in the accompanying drawings.

(Production Example 1 ... Electrode collector sheet) Elastic graphite powder adjusted to an average particle size of 1 μm (specific surface area 40 m ² / g, electrical resistance 0.28 Ωcm, bulk density 0.35
g / cm ² , trade name: L-fight particles: manufactured by Koa Oil Co., Ltd.) 100 parts by weight of PTFE dispersion (30-J, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.) having a solid content of 60% in advance
A mixture obtained by adding 60 parts by weight of monoethanolamine to 0 parts by weight was added and kneaded until the mixture became viscous to obtain a sticky kneaded product. The kneaded material is flattened while being folded, then placed on a 1 mm PTFE sheet by a rolling machine and rolled to form a sheet. Put this in a container and place it in an electric furnace under nitrogen gas flow.
The temperature is raised to 370 ° C. at 0 / hr, held for 2 hours, taken out and cooled to produce electrode sheets having a thickness of 140 μm and 200 μm.

(Comparative Examples 1 to 3) Natural graphite (scale: CSSP made by Nippon Graphite) and artificial graphite particles (HAG made by Nippon Graphite) adjusted to an average particle size of 1 μm as graphite powder
-150), and an electrode sheet is produced in the same manner as in Production Example 1 except that the same amount of natural graphite (AUP made by Nippon Graphite) is used.

As a result, 5 × 10 mm
The electrical resistivity and bulk density of the test piece of × 200 μmt were as follows.

(Test Example 1) A change in electric resistance value was measured while applying a load to the 200 μm electrode sheet manufactured in Production Example 1 and Comparative Example 1 as described below. As a result, as shown in FIG. 1, at the time of about 20 kg / cm ² in the case of Production Example 1, the resistance dropped to about 0.2 Ω, but in Comparative Example 1, it stopped at 0.4 Ω. In this case, a large difference occurs in the resistance value of the electrode.

(Production Example 2) The surface of the electrode sheet produced in Production Example 1 was coated with an acrylic conductive carbon paint of 30 to 50 μm, and the diameter was 13 mmφ.
To obtain a collector electrode sheet. Applying a carbon coating to the surface will reduce the contact electrical resistance.

(Production Example 3 ... Polarizable electrode) Activated carbon powder (specific surface area 3100) adjusted to an average particle size of 5 μm was added to 100 parts by weight of the elastic graphite body adjusted to an average particle size of 1 μm.
m ² / g, particle size distribution 0.5μ ~ 80μ, pore volume 1.78ml / g high purity, high surface area fine porous activated carbon particles prepared from petroleum coke) 300 parts by weight, add a Henschel mixer And mixed at 2000 rpm for 5 minutes. The PTFE enamel (Primer 850-300, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.) having a solid content of 38% was previously added to 100 parts by weight of the PTFE enamel.
Add 250 parts by weight of ethanol to parts by weight,
The mixture was kneaded until it became viscous to obtain a sticky kneaded product. The kneaded material is flattened so as to be woven and then rolled by a rolling machine to form a sheet. This is dried in an oven at 80 ° C. for 1 hour, then placed in an electric furnace at 300 ° C., held for 30 minutes, taken out and cooled to produce a 700 μm thick sheet.

(Comparative Example 2) An electrode sheet is manufactured in the same manner as in Manufacturing Example 3 except that the same amount of artificial graphite particles (HAG-150 manufactured by Nippon Graphite Co., Ltd.) adjusted to an average particle size of 1 µm is used as graphite powder.

(Test Example 2) A change in electric resistance was measured while applying a load to the electrode sheets manufactured in Production Example 3 and Comparative Example 2 as described below. As a result, as shown in FIG.
At 20 kg / cm ² , the resistance drops to about 0.1Ω, but stops at 0.3Ω in Comparative Example 1, and a large difference occurs in the resistance value as an electrode under the compression condition of the multilayer electric double layer capacitor.

(Production Example 4) As shown in FIG. 3, a sheet for a collector (a) produced in Production Example 1 and a polarizable electrode (b) produced in Production Example 3 were prepared, and both were laminated and rolled. The composite sheet (c) is prepared by pressing. This is fired or cured as required, and punched out to produce a composite electrode (d).

By stacking the composite electrodes via a separator, a multilayer electric double layer capacitor can be easily assembled.

(Effects of the Invention) As is clear from the above description, according to the present invention, in the electrode resin sheet containing graphite, since the elastic graphite body is used as graphite, the electric resistance can be reduced even in a small amount, An electrode material having excellent moldability can be provided. Further, since the reduction ratio of the electric resistance during pressurization is large, it can be used as a collector electrode of a multilayer capacitor. Furthermore, according to the present invention, the electrode sheet containing the activated carbon and the elastic graphite body can sufficiently reduce the electric resistance by a small amount of the elastic graphite body. Can provide an electrode material having a large value. When a polarizable electrode is manufactured from this electrode material, the capacity of the electric double layer capacitor can be increased by activated carbon, and its internal electric resistance can be reduced by the network of elastic activated carbon particles, thereby exhibiting excellent capacitor characteristics.

Further, since the two types of electrode sheets can be joined by pressing, the contact resistance between them can be reduced.

[Brief description of the drawings]

FIGS. 1 and 2 are logarithmic graphs showing the change in electric resistance under pressure of the first and second electrode sheets according to the present invention, and FIGS. 3 (a) to (d) show the relationship between the polarization electrode and the collector electrode. FIG. 4 is a schematic diagram showing a process of assembling the composite electrode, and FIG. 4 is a schematic diagram showing a bonding state between the dispersed resin, the elastic graphite particles, and the activated carbon particles. DESCRIPTION OF SYMBOLS 1 ... Collecting electrode sheet, 2 ... Polarizable electrode 3 ... Composite electrode 4, ... Dispersed resin 5 ... Elastic graphite particles, 6 ... Activated carbon particles

Claims (1)

(57) [Claims] 1. A polarizable electrode sheet formed by dispersing a binder resin in a material containing activated carbon fine particles having a specific surface area of 3000 to 5000 m ² / g and elastic graphite fine particles, and a material containing elastic graphite fine particles. A composite electrode sheet obtained by laminating and bonding under pressure pressure a sheet for collector formed by dispersing a binder resin into a sheet.