JPH07331201A - Electrically conductive adhesive and bonded structure using the same - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive adhesive highly effective for bonding between polarizable electrodes and a collector, hard to disintegrate due to intercalation, also contributing to improving ion mobility, by incorporating a rubber material with expanded graphite and a pore-forming material. CONSTITUTION:This electrically conductive adhesive contains 30-250 pts.wt. of a rubber material as binder, 100 pts.wt. of expanded graphite and 1-1000 pts.wt. of a pore-forming material. The rubber material is a chemical-resistant butyl rubber, isobutyl-isopropylene copolymer rubber, butadiene rubber, styrene rubber, silicone rubber, ethylene-propylene rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber, urethane rubber, or fluororubber. The pore-forming material, is such as to be solid at normal temperatures and reduce its volume or vanish by melting, fusing, sublimation, or decomposition on heating. This adhesive is prepared by blending a total of 100 pts.wt. of the above three components with 100-1000 pts.wt. of a solvent such as toluene, acetone, water, or methanol. The other objective pored bonded structure is made by putting this adhesive in between a pair of adherends followed by heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive adhesive, and more particularly to a conductive adhesive suitable for use in bonding a polarizable electrode and a current collector.

[0002]

2. Description of the Related Art A secondary battery such as an electric double layer capacitor is used as a backup power source for a microcomputer memory or the like as a small and large-capacity capacitor. This type of battery has a polarizable electrode, a current collector and However, there is a drawback that the internal resistance becomes high when the battery is assembled.

In order to reduce the internal resistance, it is necessary to increase both electric conductivity and ion mobility contained in the electrolytic solution. In order to increase the electric conductivity of one of them, For example, it has been proposed to reduce the contact resistance between the polarizable electrode and the current collector by using a conductive adhesive for bonding the polarizable electrode and the current collector.

As the above-mentioned conductive adhesive, for example, a method in which an electrode obtained by sintering and hardening carbon fine particles and a current collector such as conductive rubber are bonded together by thermocompression bonding The conductive adhesive (see Japanese Patent Application Laid-Open No. 2-083816) or powder such as carbon black or graphite is used as a polycarbodiimide resin type, ABS resin type, epoxy resin type, polyphenylene sulphate resin. Examples thereof include conductive adhesives (see JP-A-5-082396) which are mixed with a resin of a resin type, a urethane resin type, a polyester resin type, or an acrylic resin type.

[0005]

However, Japanese Unexamined Patent Publication (Kokai) No. 2-0.
Since the conductive adhesive used in Japanese Patent No. 83816 is a simple one in which graphite powder is mixed with a thermosetting resin, the electrode and the current collector are separated from each other by applying a little heat, or However, there is a drawback in that the electrolyte is separated from the current collector simply by impregnating the electrode.

Further, the conductive adhesive used in JP-A-5-082396 contains graphite powder as a conductive material, but graphite collapses due to an intercalation phenomenon caused by charging and discharging. However, there is a drawback that the conductivity is deteriorated and the cycle life is remarkably reduced.

As described above, none of the conductive adhesives used for increasing the electric conductivity have sufficient characteristics, let alone the adhesives for the purpose of improving the mobility of the ions. It never existed.

The present invention overcomes the above-mentioned drawbacks of the prior art,
To provide a conductive adhesive that not only has high adhesive performance when used for bonding a polarizable electrode material and a current collector, but also does not easily collapse due to intercalation and contributes to improved ion mobility. Was made for the main purpose.

[0009]

In order to achieve the above object, the constitution of the conductive adhesive used in the present invention is 30 to 250 parts by weight of a rubber material as a binder and 100 parts by weight of expanded graphite as a conductive material. Parts and 1 to 1000 parts by weight of the pore-forming material.

That is, the inventors of the present invention have conducted earnest research to achieve the above-mentioned object, and as a result, the expanded graphite powder has a sufficiently opened interlayer, so that the intercalation can be performed even if charging and discharging are repeated. It does not cause expansion and contraction between layers due to, and therefore, it is less likely to collapse like graphite powder, and the rubber material is disclosed in JP-A-5-0.
As a result of further research, the present invention was completed as a result of the idea that it has excellent characteristics with respect to the adhesive force with the current collector, compared with the plastics listed as the binder in Japanese Patent No. 82396. It was made.

The present invention will be specifically described below.

The rubber material used as the binder in the present invention can be selected from those known in the art, and is used for bonding a polarizable electrode and a collector in a capacitor such as an electric double layer capacitor. In this case, it is desirable that the chemical resistant rubber has sufficient durability against the organic solvent used as the electrolytic solution in the capacitor, the strongly acidic and the strongly alkaline solution. Specifically, butyl rubber is preferable. , Isoptyl-isoprene copolymer rubber, butadiene rubber, styrene rubber, silicone rubber,
Examples thereof include ethylene propylene rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber, urethane rubber, and fluorine rubber. In addition, these rubber materials may be used alone or as a mixture of two or more thereof.

The expansive graphite used as a conductive material in the present invention is conventionally known, and is a mixture of natural flake graphite with a mixed acid of concentrated nitric acid and concentrated sulfuric acid, potassium chlorate, potassium dichromate, and permanganese. Wet-oxidize together with a strong oxidant such as potassium acid, and rapidly heat the wet-oxidized graphite at a high temperature of 900 ° C. or higher to decompose the oxidant contained in the graphite layers, to increase the oxidant by 50 to 300 times. It is graphite whose layers are expanded, and its powder is particularly used in the present invention.

Further, the pore-forming material used in the present invention is for making fine holes in the adhesive layer after adhesion before and after the adhesion of the adherend with the adhesive of the present invention, The fine pores enhance the impregnation property of the electrolytic solution into the adhesive layer and the mobility of ions in the electrolytic solution, thereby making it possible to significantly reduce the resistance of the adhesive layer as compared with the conventional conductive adhesive. It is for.

The above-mentioned pore-forming material is, for example, solid at room temperature or in a temperature range around it, and is dissolved, melted, sublimated, or decomposed by heating to reduce the volume of the solid portion. Alternatively, there may be mentioned ones that disappear, that is, the pore-forming material used in the present invention is, in principle, after the adherend is substantially adhered by the conductive adhesive of the present invention, it is heated by heating as described above. Although the volume of the solid portion is reduced or eliminated to form a hole in the conductive adhesive layer, the hole forming material used in the present invention is not limited to this, and can be used for adhesion of an adherend. At the same time, the volume may be reduced or eliminated, and further, the volume may be reduced or eliminated prior to adhering the adherend.

Examples of such pore formers include stearic acid, naphthol, polystyrene, paraffin wax, polypropylene, polymethyl methacrylate, ethylene-vinyl acetate copolymer, wheat flour, methyl cellulose, methyl ethyl cellulose, carboxymethyl cellulose, carboxy. Methyl cellulose sodium or the like can be applied, and the shape of these pore-forming materials can be powder, granular, or fibrous.

The size of the pore-forming material may be determined according to the purpose of use of the conductive adhesive of the present invention and is not particularly limited, but one example is powder or In the case of granular particles, those having a particle size distribution of several μm to 50 μm can be exemplified, and in the case of fibrous particles, the range of several tens of μm in diameter and 1 to 5 mm in length can be exemplified. Incidentally, these sizes are, for example, when the volume of the solid portion of the pore-forming material is reduced or disappeared by heating, the adhesive of the present invention may expand at the same time, so that the size of the hole in the adhesive structure after adhesion is Does not correspond directly.

Table 1 below shows the relationship between the heating temperature and the volume reduction rate of the pore-forming material.

[Table 1]

In consideration of work efficiency and the like, it is preferable that the expanded graphite, the rubber material, and the pore-forming material (these may be collectively referred to as solid contents hereinafter) be dissolved or suspended in a solvent. Examples of such a solvent include toluene, acetone, water, methanol, ethanol, propanol, tetrachloroethylene, trichloroethylene, promchloromethane, diacetone, dimethylformamide, ethyl ether, cresol, xylene, chloroform, butanol, and dimethyl ether. However, it is not particularly limited.

The mixing ratio of the above components will be described below. First, the amount ratio of the expanded graphite to the rubber material may be in the range of 30 parts by weight to 250 parts by weight of the rubber material with respect to 100 parts by weight of the expanded graphite. If the amount of the rubber material is less than this range, sufficient adhesive strength cannot be obtained, and if it is more than this range, sufficient conductivity cannot be obtained.

Next, the amount ratio of the expanded graphite and the pore former is
The range of 1 to 1000 parts by weight of the pore-forming material can be applied to 100 parts by weight of the expanded graphite. If the pore-forming material is less than this range, there is a problem that the ion mobility is not improved, and if it is more than this range, sufficient adhesive performance is not obtained and the polarizable electrode and the current collector are separated. Occurs.

The amount ratio of the solvent to the solid content is 100 parts by weight to 100 parts by weight of the solvent based on 100 parts by weight of the solid content.
A range of 0 parts by weight can be mentioned. If the amount of solvent is more than this range, the amount of solid content occupying the bonded portion will be insufficient, and the problem will occur that the adhesive strength will decrease. If the amount of the solvent is less than this range, the conductive adhesive lacks fluidity, and it is difficult to uniformly apply the conductive adhesive on the polarizable electrode and the current collector. Since it is uniform, the problem that the adhesive strength is lowered still arises.

The conductive adhesive of the present invention thus obtained is applied to an appropriate adherend, for example, a polarizable electrode or a collector in a capacitor such as an electric double layer capacitor. They are used by adhering them, or by applying them between adherends and further heat-treating or hot-pressing at an appropriate temperature. The conditions for heat treatment, etc. are the components in the conductive adhesive to be used, Specifically, it may be determined based on the heat resistant temperature of the rubber material and the like.

For example, when butyl rubber, isobutyl-isobutylene copolymer rubber, styrene rubber, nitrile rubber, ethylene propylene rubber, or epichlorohydrin rubber is used as the rubber material, the temperature is about 160 ° C. or lower, and when acrylic rubber is used, it is 200. Since the heat treatment is performed at a temperature of about ℃ or less, or about 300 ℃ or less when using fluorine rubber or silicon rubber, therefore, at the latest, in order to reduce the volume or disappear in the step of this heat treatment or the like, the pouring is completed, It suffices to select the pore former.

When a solvent is used, it is applied to an appropriate adherend, for example, a polarizable electrode in a capacitor such as an electric double layer capacitor or an adherend such as a current collector to bring them into contact with each other. Since it can be bonded, the pore-forming material reduces the volume of its solid portion after considering the components in the conductive adhesive used in the same manner as described above, specifically, the heat resistant temperature of the rubber material, or the like. It only has to be heated to a temperature at which it disappears.

The size of the hole thus formed between the adhesive layers is about 10 nm in the case of the examples described below as a result of observation by the mercury penetration method and the scanning electron microscope.
It was found to be in the range of 100 μm to 100 μm.

[0027]

The present invention will be described in more detail with reference to the following examples.

Examples 1 to 8 Isobutyl-isoprene copolymer rubber (rubber material), expanded graphite powder (conductive material, average particle size 10 μm), methylcellulose (pore former), and toluene (solvent) After mixing, a conductive adhesive was prepared, and using this conductive adhesive, a polarizable electrode (which was obtained by binding activated carbon and phenol resin by hot press and firing in an inert atmosphere) and a current collector ( After adding carbon powder to unvulcanized butyl rubber and kneading,
The sheet was molded into a sheet) and heat-treated at 160 ° C. for 3 minutes to evaporate the methylcellulose in the adhesive. This adhesive product was vacuum impregnated into a 30 wt% H ₂ SO ₄ aqueous solution to prepare an electric double layer capacitor. This electricity 2
20 times up to 1000 cycles using multilayer capacitors
Constant current charge / discharge at 1, 100, 500, 10
The equivalent series resistance at the 00th cycle was measured, and at the same time, the appearance of the electrode at that time was observed. The results are shown in Table 2 together with the composition of the conductive adhesive. The equivalent series resistance is 1 kHz.
A constant current of 10 mA of 10 mA was applied to this electric double layer capacitor, and the voltage was calculated from the voltage between the electrodes (the same applies to Examples and Comparative Examples below).

[Table 2]

Examples 9 to 16 Isobutyl-isoprene copolymer rubber, expanded graphite powder (average particle size 10 μm), pore former (stearic acid),
A solvent (toluene) was mixed to prepare a conductive adhesive. Using this conductive adhesive, polarizable electrodes (active carbon and phenolic resin bonded by hot press and fired in an inert atmosphere) and current collectors (unvulcanized isobutyl-isoprene copolymer rubber) After adding carbon powder and kneading,
The sheet was molded into a sheet) and heat-treated at 160 ° C. for 3 minutes to evaporate the stearic acid in the adhesive. This adhesive product was vacuum-impregnated in a 30 wt% H ₂ SO ₄ aqueous solution to prepare an electric double layer capacitor, which was subjected to constant current charging / discharging at 20 mA up to 1000 cycles, 1, 100, 50.
The equivalent series resistance at the 0th and 1000th cycles was measured, and at the same time, the appearance of the electrodes at that time was observed. The results are shown in Table 3 together with the composition of the conductive adhesive.

[Table 3]

Examples 17 to 24 Acrylic rubber and expanded graphite powder (average particle size 10 μm)
Then, the pore-forming material (stearic acid) and the solvent (toluene) were mixed to prepare a conductive adhesive. Using this conductive adhesive, polarizable electrodes (active carbon and phenol resin were bonded by hot press and fired in an inert atmosphere) and a current collector (Nisshinbo glassy carbon) were bonded, 200
Heat treatment was performed at 0 ° C. for 3 minutes to evaporate the stearic acid in the adhesive. This adhesive product was vacuum impregnated into a 30 wt% H ₂ SO ₄ aqueous solution to prepare an electric double layer capacitor,
Constant current charge and discharge at 20mA until cycle, 1, 10
The equivalent series resistance at the 0th, 500th, and 1000th cycles was measured, and at the same time, the appearance of the electrodes at that time was observed. The results are shown in Table 4 together with the composition of the conductive adhesive.

[Table 4]

Examples 25 to 32 Fluorine rubber, expanded graphite powder (average particle size 10 μm),
A pore former (stearic acid) and a solvent (toluene) were mixed to prepare a conductive adhesive. Using this conductive adhesive, polarizable electrodes (active carbon and phenol resin were bonded by hot press and fired in an inert atmosphere) and a current collector (Nisshinbo glassy carbon) were bonded, The stearic acid in the adhesive was evaporated by heat treatment at 300 ° C. for 3 minutes. This adhesive product was vacuum-impregnated in a 30 wt% H ₂ SO ₄ aqueous solution to produce an electric double layer capacitor, which was charged and discharged at a constant current of 20 mA up to 1000 cycles for 1,100,
Measure the equivalent series resistance at the 500th and 1000th cycles,
At the same time, the appearance of the electrodes at that time was observed. The results are shown in Table 5 together with the composition of the conductive adhesive.

[Table 5]

Comparative Examples 1 to 8 ABS resin, expanded graphite powder (average particle size 10 μm),
A pore former (stearic acid) and a solvent (toluene) were mixed to prepare a conductive adhesive. Using this conductive adhesive, polarizable electrodes (active carbon and phenolic resin bonded by hot press and fired in an inert atmosphere) and current collectors (unvulcanized isobutyl-isoprene copolymer rubber rubber) Carbon powder was added and kneaded, and the mixture was then molded into a sheet) and heat-treated at 160 ° C. for 3 minutes to evaporate the stearic acid in the adhesive. 30 wt% of this adhesive
Of H ₂ SO ₄ aqueous solution was vacuum-impregnated to prepare an electric double layer capacitor, which was subjected to constant current charge / discharge at 20 mA up to 1000 cycles, and the equivalent series resistances at the 1st, 100th, 500th and 1000th cycles were measured, and at the same time, The appearance of the electrodes at that time was observed. The results are shown in Table 6 together with the composition of the conductive adhesive.
Shown in.

[Table 6]

Comparative Examples 9 to 16 Isobutyl-isoprene copolymer rubber, graphite lead powder (average particle size 10 μm), pore former (stearic acid), and solvent (toluene) were mixed to obtain a conductive adhesive. Was produced. Using this conductive adhesive, polarizable electrodes (active carbon and phenolic resin bonded by hot press and fired in an inert atmosphere) and current collectors (unvulcanized isobutyl-isoprene copolymer rubber) Carbon powder was added to and kneaded, and then molded into a sheet)) and adhered at 160 ° C.
Then, the stearic acid in the adhesive was evaporated by heat treatment for 3 minutes. This adhesive product was vacuum-impregnated in a 30 wt% H ₂ SO ₄ aqueous solution to produce an electric double layer capacitor, which was charged and discharged at a constant current of 20 mA up to 1000 cycles for 1,100,
Measure the equivalent series resistance at the 500th and 1000th cycles,
At the same time, the appearance of the electrodes at that time was observed. The results are shown in Table 7 together with the composition of the conductive adhesive.

[Table 7]

Comparative Examples 17 to 24 Isobutyl-isoprene copolymer rubber, expanded graphite powder (average particle size 10 μm), pore former (stearic acid),
A solvent (toluene) was mixed to prepare a conductive adhesive. Using this conductive adhesive, polarizable electrodes (active carbon and phenolic resin bonded by hot press and fired in an inert atmosphere) and current collectors (unvulcanized isobutyl-isoprene copolymer rubber) After adding carbon powder and kneading,
The sheet was molded into a sheet) and heat-treated at 160 ° C. for 3 minutes to evaporate the stearic acid in the adhesive. This adhesive product was vacuum-impregnated in a 30 wt% H ₂ SO ₄ aqueous solution to prepare an electric double layer capacitor, which was subjected to constant current charging / discharging at 20 mA up to 1000 cycles, 1, 100, 50.
The equivalent series resistance at the 0th and 1000th cycles was measured, and at the same time, the appearance of the electrodes at that time was observed. The results are shown in Table 8 together with the composition of the conductive adhesive.

[Table 8]

[0035]

As is apparent from the above, the conductive adhesive of the present invention contains 30 to 250 parts by weight of a rubber material as a binder, 100 parts by weight of expanded graphite as a conductive material, and pore forming materials of 1 to 1000. The adhesive structure of the present invention comprises 30 to 250 parts by weight of a rubber material as a binder, 100 parts by weight of expanded graphite as a conductive material, and a pore-forming material between appropriate adherends. Since the adherend is adhered by disposing a conductive adhesive containing 1 to 1000 parts by weight of the material, and the hole is formed in the layer of the conductive adhesive by the hole forming material. If this structure is used, for example, in the bonding structure of the polarizable electrode material and the current collector in the electric double layer capacitor, they can be firmly bonded together, and collapse due to intercalation does not easily occur, and the ion mobility is also improved. Electrode It is possible to provide.

Claims (12)

[Claims] 1. A rubber material 30 to 250 as a binder.
Parts by weight, and 100 parts by weight of expanded graphite as a conductive material,
An electrically conductive adhesive comprising 1 to 1000 parts by weight of a pore-forming material. 2. The conductive adhesive according to claim 1, wherein the rubber material as the binder has chemical resistance. 3. The chemical resistant rubber is butyl rubber, isobutyl-isoprene copolymer rubber, butadiene rubber, styrene rubber, silicone rubber, ethylene propylene rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber,
The conductive adhesive according to claim 2, which is one or more of urethane rubber and fluororubber. 4. The conductive adhesive according to claim 1, wherein the pore-forming material is a solid at around room temperature and reduces or disappears in volume by heating. 5. The conductive adhesive according to claim 4, wherein the pore-forming material dissolves, melts, sublimes, or decomposes by heating and reduces or disappears the volume of its solid portion. 6. The conductive adhesive according to claim 1, which contains a solvent. 7. The solvent is toluene, acetone, water, methanol, ethanol, propanol, tetrachloroethylene, trichloroethylene, bromochloromethane, diacetone, dimethylformamide, ethyl ether, cresol, xylene, chloroform, butanol, dimethyl ether or a solvent thereof. The conductive adhesive according to claim 6, which is a mixture. 8. The ratio of the solvent to the mixture of the rubber material, the expanded graphite and the pore-forming material is 100 parts by weight of the solvent to 100 parts by weight of the mixture of the rubber material, the expanded graphite and the pore-forming material. 10
The conductive adhesive according to claim 6, which is 100 parts by weight. 9. A conductive material containing 30 to 250 parts by weight of a rubber material as a binder, 100 parts by weight of expanded graphite as a conductive material, and 1 to 1000 parts by weight of a pore-forming material between appropriate adherends. An adhesive structure using a conductive adhesive, characterized in that the adherend is bonded by disposing an adhesive, and the hole is formed in the layer of the conductive adhesive by the hole forming material. 10. The adhesive structure with a conductive adhesive according to claim 9, wherein the pore-forming material is solid at around room temperature, and its volume is reduced or eliminated by heating. 11. The pore-forming material is melted by heating,
The adhesive structure with a conductive adhesive according to claim 10, which melts, sublimes, or decomposes to reduce or eliminate the volume of its solid portion. 12. The hole forming is performed by heating.
An adhesive structure using the conductive adhesive as described in 1.