JP2000277393A - Electric double-layer capacitor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor using an electrode body with a small internal resistance, and a method for manufacturing the electric double-layer capacitor. SOLUTION: In this capacitor, an electrode body 50, where a conductive layer is formed between a pyroelectric 54 and a polarization electrode 53, us used. The conductive layer is made of an organic adhesive and a conductive filler 51. When the diameter of the particles of the conductive filler 51 and the thickness of an adhesion layer 52 are set to (d), and (t), respectively, at least the partial conductive filler 51 satisfies to relation 0.2t<=d<=3t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor using an electrode body having a small internal resistance and a method for manufacturing the same.

[0002]

2. Description of the Related Art Currently, the development of electric double layer capacitors, in other words, the use of capacitors, is being actively conducted in various fields. For example, a drastic reduction in fossil fuel consumption is required in the context of environmental and resource issues. One of the measures to reduce the use of fossil fuels in the automotive industry is fossil fuel and electricity. It shows a positive stance on the development and market introduction of so-called hybrid cars that combine the use of energy. In such applications, a higher output density of the high output density type electric double layer capacitor is required.

In addition, the use of personal computers and various electronic devices as so-called backup power sources is increasing. In these fields, high energy density type electric double layer capacitors are used, but further higher energy density is required.

As shown in FIG. 1, a single electrode cell 10, which is one of the basic structures of such an electric double layer capacitor, has a positive electrode side and a current collector 20, 22 which are generally made of a metal material. The polarizable electrode 24 and the polarizable electrode 26 on the negative electrode side are formed, and the polarizable electrodes 24
8 and a polarizable electrode 2
4. 26 is impregnated with an electrolytic solution composed of a solvent and an electrolyte.

FIG. 2 shows the structure of a single capacitor cell 12 in which a plurality of single electrode cells 10 are connected to current collectors 20 and 22.
Are formed in such a manner that the electrode take-out portions 30 and 32 formed in the above are electrically connected in parallel. Such a single-capacitor cell 12 is suitably used as an electric double layer capacitor having a relatively large capacity used for automobiles and the like. These single electrode cells 10 and single capacitor cells 12
Both are flat, and have characteristics that high filling and easy area enlargement are easy, but the internal resistance tends to increase.

[0006] For such a flat-type electric double-layer capacitor, there is also a wound-type electric double-layer capacitor 70 as shown in FIG. 3. It is a structure suitable for. In the wound type electric double layer capacitor 70, the positive electrode sheet 72 in which the positive electrode side polarizable electrode 24 is formed on the current collector 20, and the current collector 22.
Sheet 74 on which a negative polarizable electrode 26 is formed
Is wound in a cylindrical shape through a separator 28. For example, the wound body 76 is accommodated in a case 78, filled with an electrolytic solution, and each electrode sheet 72
-While ensuring continuity between 74 and each of the electrode terminals 80,
It is manufactured by sealing the opening end surface of the case 78 with the sealing plate 82 on which the electrode terminals 80 are formed.

[0007]

However, in the above-described electrode bodies of various shapes including the current collector and the polarizable electrode, and the electric double-layer capacitor including the separator and the electrolytic solution, the current collector and the electrolytic solution are separated. In order to reduce the contact resistance between the polar electrodes, there is a means of maintaining the pressure at ² kg / cm ² or more, or providing a conductive layer between the current collector and the polarizable electrode to form a laminated integrated electrode body. Has been adopted.

[0008] However, in the case of pressure holding, the pressure fluctuates due to vibration or impact, and the characteristics change and the change with time increase. When the pressing area is large, it is difficult to press uniformly, and the characteristic variation increases. And so on.

When a conductive layer is provided between the current collector and the polarizable electrode to form a laminated electrode body, the material for the conductive layer is usually a mixture of a conductive filler and an organic adhesive. A conductive organic adhesive is often used. However, if the amount of the conductive filler is increased in order to sufficiently contact the conductive filler, the adhesive strength is weakened, and the adherend (the current collector and the adhesive In order to make the contact between the polar electrode and the conductive filler sufficiently, there is a problem that the fixing must be performed with a large pressing force.

[0010] For the reasons described above, the manufacturing workability is good and the contact resistance can be reduced by securing reliable electrical contact without lowering the adhesiveness between the current collector and the polarizable electrode. There is a demand for an electrode body having excellent long-term reliability.

[0011]

Means for Solving the Problems The present invention has been made in view of the above-mentioned problems of the prior art. That is, according to the present invention, there is provided an electric double-layer capacitor using an electrode body in which a conductive layer is formed between a current collector and a polarizable electrode, and the conductive layer includes an organic adhesive and a conductive filler. When the particle size of the conductive filler is d and the thickness of the adhesive layer is t, at least a part of the conductive filler satisfies the relationship of 0.2t ≦ d ≦ 3t. An electric double layer capacitor is provided.

Here, it is more preferable that the particle size d of at least a part of the conductive filler is in the range of 0.5t to 2t. Further, the thickness of the conductive layer is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 60 μm. As the conductive filler, particles of a carbon-based material, for example, graphite are preferably used.

Further, according to the present invention, there is provided a method for manufacturing an electric double layer capacitor using an electrode body having a conductive layer formed between a current collector and a polarizable electrode, wherein a surface of the current collector is provided. Then, after forming an adhesive layer composed of a conductive filler and an organic adhesive, the collector and the polarizable electrode are pressed with the adhesive layer interposed therebetween, and the particle size of the conductive filler is d. Forming a conductive layer in which at least a part of the conductive filler satisfies a relationship of 0.2t ≦ d ≦ 3t, where t is a layer thickness, and a step of manufacturing the electrode body. And a method for manufacturing an electric double layer capacitor.

Another method of manufacturing an electric double layer capacitor provided by the present invention is a method of manufacturing an electric double layer capacitor using an electrode body having a conductive layer formed between a current collector and a polarizable electrode. A method, wherein the surface of the current collector comprises:
After forming an adhesive layer having a thickness t ₁ comprising an organic adhesive and a conductive filler having a particle diameter d ₁ of 0.2 t ₁ or less, another conductive filler having a particle diameter d is formed on the adhesive layer. To form a preliminary adhesive layer, press the current collector and the polarizable electrode with the preliminary adhesive layer interposed therebetween, and at least a part of the another conductive filler reduces the adhesive layer thickness. forming a conductive layer that satisfies the relationship of 0.2t ≦ d ≦ 3t when t, and manufacturing the electrode body. is there.

In such a method for manufacturing an electric double layer capacitor, it is also preferable to simultaneously heat the current collector and the polarizable electrode with the preliminary adhesive layer interposed therebetween. It is more preferable that at least a part of the conductive filler having a particle diameter d satisfies the relationship of 0.5t ≦ d ≦ 2t. Further, the thickness of the conductive layer is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 60 μm.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An electric double layer capacitor according to the present invention uses an electrode body in which a conductive layer is formed between a current collector and a polarizable electrode. The structure of the electrode body is not limited, and the electrode body can be used for any of the above-described single electrode cell 10, single capacitor cell 12, and wound type electric double layer capacitor 70 (wound body). Here, as the current collector, for example, a metal foil having a thickness of 10 to 60 μm or a perforated metal foil (a punching metal or an expander metal) is suitably used, and aluminum is preferably used as a material.

Further, as the polarizable electrode, a sheet-shaped molded body mainly composed of a carbon material mainly contributing to the development of a capacitance, and further comprising a conductive auxiliary material for imparting conductivity and an organic binder is preferable. Used for In particular, the carbon material is activated carbon, and 70% to 97% of the carbon material
Is a material that contributes to the development of capacitance. When the amount of the carbon material mainly contributing to the development of the capacitance is out of the above range, a sufficient capacitance cannot be obtained, which is not preferable. Further, carbon fine powder such as carbon black is preferably used as the conductive auxiliary, and fluororesin-based organic binder is suitably used as the organic binder.

The sheet-shaped molded body (polarizable electrode) can be produced by, for example, a method described in Japanese Patent Publication No.
In addition to the method described in JP-A-105316, those manufactured by those skilled in the art using known methods can be used. Further, the present inventors have previously described Japanese Patent Application No. Hei 10-33021.
The sheet-shaped molded body manufactured by the manufacturing method disclosed in No. 4 is also particularly preferably used in terms of high density and high strength.

The conductive layer formed between the current collector and the polarizable electrode is mainly composed of an organic adhesive and a conductive filler. Here, as the organic adhesive, a fluororesin,
Various resin materials such as silicone resin, acrylic resin, rubber adhesive, and resin adhesive can be used, and various resins such as solution type, emulsion type, and hot melt type in which these resins are dissolved or dispersed are available. It is possible to provide for bonding by using one having the form described above.

On the other hand, as the conductive filler, any of a conductive carbon-based material, a metal-based material, and an oxide-based material can be used. The polarizable electrode mainly contributes to the development of capacitance. When it is composed of a carbon material, it is preferable to use a carbon-based material, and it is particularly preferable to use graphite. In addition, examples of the form of other conductive fillers include a particle form, a granulated particle form, a flat form, and a fiber form.

In the present invention, when the particle size of the conductive filler is d and the thickness of the adhesive layer is t, at least a part of the conductive filler satisfies the relationship of 0.2t ≦ d ≦ 3t. Conductive layer, more preferably 0.5t ≦ d ≦
A conductive layer satisfying the relation of 2t is formed. FIG.
It is sectional drawing which shows typically the structure of the electrode body satisfying such conditions. Here, the adhesive layer thickness t refers to the distance between the average boundary between the current collector 54 and the organic adhesive and the average boundary between the polarizable electrode 53 and the organic adhesive. Also,
The particle size d of the conductive filler refers to the value of the average particle size. When the conductive filler is in the form of a fiber, the fiber diameter corresponds to the particle size d.

In the electrode body 50, since the particle diameter d of the conductive filler 51 is large in the range of 0.2 t to 3 t, the number of times of contact between the conductive fillers 51 in the adhesive layer 52 decreases. , The polarizable electrode 53 and the current collector 5 directly through the conductive filler 51 penetrating the adhesive layer 52.
4 has an electrically and structurally contacting structure.
Due to the presence of the conductive filler 51, the conductivity between the polarizable electrode 53 and the current collector 54 is improved, so that the amount of the conductive filler 51 added to the organic adhesive can be reduced. In addition, the adhesion is improved at the same time, and the reliability is ensured. In addition, since the polarizable electrode 53 and the current collector 54 can be fixed by an appropriate pressure at the time of bonding, the workability is improved. The organic adhesive has a conductive filler (conductive additive) having a small particle size of, for example, 0.2 t or less, separately from the conductive filler 51.
It is also preferable to add activated carbon or carbon black, which is a constituent material of the polarizable electrode, as long as the adhesiveness is not reduced.

By the way, as for the conductive layer having a structure in which the conductive filler 51 partially penetrates the adhesive layer 52 as shown in FIG. 4, the width in which the conductive filler 51 is distributed (the vertical direction in FIG. 4) Width, that is, polarizable electrode 53
When the approximate average value of the distribution width of the conductive layer and the current collector 54 in the stacking direction is defined as the thickness w of the conductive layer, the thickness w is 1 to 1
It is preferable to be in the range of 00 μm. Conductive layer thickness w
Is thinner than 1 μm, the adhesive strength becomes weak, while
This is because if the thickness is larger than m, the capacitance density per volume decreases, which is not preferable. From such a viewpoint, it is more preferable that the thickness w of the conductive layer be in the range of 5 to 60 μm in order to secure a good balance between the adhesive force and the capacitance density.

Next, a method for manufacturing the above-described electrode body will be described. In one manufacturing method, an adhesive layer composed of a conductive filler and an organic adhesive is formed on the surface of the current collector by various methods, and the current collector and the polarizable electrode are applied across the formed adhesive layer. The conductive layer is formed by applying pressure and, if necessary, applying heat while heating to form an electrode body.

For example, first, a solution comprising a conductive filler and an organic adhesive and a solvent is spray-coated on one or both surfaces of a foil-like current collector such as an aluminum foil, and then the solvent is removed by evaporation or the like. To form an adhesive layer. Next, a polarizable electrode is laminated on one or both surfaces of the current collector so as to sandwich the obtained adhesive layer, and is adhered and joined by a uniaxial press or a roll press, so that the particle diameter d of the conductive filler described above is obtained. And an electrode body having a conductive layer that satisfies the relationship between the thickness and the adhesive layer thickness t can be obtained.

It is also preferable to use the following method. That is, first, the organic adhesive, the solvent, and the particle size d ₁
To produce a slurry comprising a conductive filler having
Using a doctor blade method or the like, the slurry was coated on one side or both sides of the foil-like current collector, such as aluminum foil, to form an adhesive layer having a thickness of t _1. Here, the forming conditions of the adhesive layer are determined in advance so that the particle diameter d ₁ of the conductive filler added to the slurry is not more than 0.2 times the thickness t ₁ of the adhesive layer. Next, on the adhesive layer, another conductive filler having a particle size of d is scattered and adhered to form a pre-adhesive layer, and a polarizable electrode is provided on one or both sides of the current collector so as to sandwich the pre-adhesive layer. Are laminated and bonded and joined by a uniaxial press or a roll press. In this way, it is also possible to obtain an electrode body on which a conductive layer is formed in which at least a part of the conductive filler having the particle diameter d satisfies the relationship between the particle diameter d of the conductive filler and the thickness t of the adhesive layer.

Further, a sheet-like molded body containing a conductive filler is prepared in advance by various methods such as a doctor blade method or an extrusion molding method, and the current collector, the sheet-like molded body, and the polarizable electrode are heated in this order. It is also possible to form an electrode body by bonding using means such as pressure and pressure. In this case, in the formed conductive layer, the particle diameter d of at least a part of the conductive filler
It is preferable to control the heating condition and the pressing condition such that a predetermined relationship is satisfied between the pressure and the adhesive layer thickness t.

The method for applying the organic adhesive, that is, the method for forming the adhesive layer is not limited to the above-described spray method and doctor blade method, and other methods such as a screen printing method, a roll coater method, and a brush coating method are used. You can also.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that these Examples do not limit the present invention. 0.5 g of carbon material powder consisting of 10 g of activated carbon and 1.2 g of carbon black
Of polytetrafluoroethylene at 19 ° C. for about 1 hour, and then kneading for about 20 minutes in a mortar while applying a shearing force while heating to 40 ° C. or higher. It was spread as evenly as possible on an aluminum sheet of about 30 μm, covered with an aluminum sheet of the same thickness, sandwiched, and passed through a roller to obtain a primary molded body of a polarizable electrode having a thickness of about 2 mm. Next, the obtained primary compact was roll-pressed five times with a roller or the like to obtain a polarizable electrode sheet (hereinafter, referred to as an “electrode sheet”) having a thickness of about 0.5 mm. This electrode sheet was cut into a desired size to obtain a target polarizable electrode for an electric double layer capacitor.

Next, on one side of an aluminum foil having a thickness of 50 μm, graphite powder having a particle size of 3 μm as a conductive filler and a conductive organic adhesive made of a silicon resin and a solvent are applied, and dried at 120 ° C. An adhesive layer was formed. The thickness of the adhesive layer after drying was about 17 μm. Then, a graphite powder having the same material as the conductive filler and having an average particle diameter of 20 μm was adhered to the surface of the adhesive layer so as to be almost a single layer to form a preliminary adhesive layer.

Two current collectors having such a pre-adhesive layer formed thereon are prepared, and a polarizable electrode having an area of 2.8 cm ² is sandwiched between the pre-adhesive layer and the polarizable electrode so that the pre-adhesive layer is bonded to the polarizer. After pressing by ² kg / cm ² by pressing, 150
It dried at ℃, and produced the resistance measurement sample (Example 1).
In addition, the manufacturing method of the above-mentioned electrode body (resistance measurement sample)
This is the same as the method disclosed by the inventors in Production Example 1 of Japanese Patent Application No. 10-330214.

A resistance measurement sample having the same structure as in Example 1 (Comparative Example) except that a conductive filler having an average particle diameter of 20 μm is not attached on the adhesive layer in the same manner as in the manufacturing method of Example 1 described above. 1) was produced. Then, the electric resistance of Example 1 and Comparative Example 1 was changed to 2 kgf using an electrode compression jig.
/ Cm ² was measured under a load. After the electrical resistance measurement, a part of the sample was cut and the cross section was observed, and the thickness of the adhesive layer was examined. Table 1 shows the results. In Example 1 using a conductive filler having a large particle diameter, it was confirmed that the electric resistance was extremely low as compared with Comparative Example 1.

[0033]

[Table 1]

Next, the particle size of the conductive filler to be attached to the surface of the adhesive layer is 3 μm, 5 μm, 10 μm, 40 μm,
A resistance measurement sample was prepared in the same manner as in Example 1 except that the thickness was variously changed to 60 μm and 100 μm, and was used for measurement of electric resistance. After the resistance measurement, a part of the sample was cut and the cross section was observed, and the thickness of the adhesive layer was examined. Table 2 shows the measurement results.

[0035]

[Table 2]

Table 2 shows that the particle size of the conductive filler deposited on the adhesive layer was 3 μm (Comparative Example 2),
In the case of 0 μm (Comparative Example 3), it has a large electric resistance almost equal to or slightly smaller than that of Comparative Example 1 described above, and the effect of reducing the electric resistance due to the adhesion of the conductive filler is remarkable. Did not appear. On the other hand, the particle size is 5 to 60.
In the samples containing the conductive filler of μm (Examples 2 to 5), it was found that the electric resistance between the current collectors was favorably reduced. The above Examples 1 to 5 and Comparative Examples 1 to 3
When the electrical resistance value is compared based on the relationship between the particle size of the conductive filler deposited on the adhesive layer and the thickness of the obtained adhesive layer, the particle size in the range of 0.2 to 3 times the adhesive layer thickness is obtained. It is understood that it is preferable to use a conductive filler having a diameter.

Next, under the same manufacturing conditions as in the above-described Examples 2 to 5 and Comparative Examples 2 and 3, the blank portions of the two current collectors 54 as shown in the cross-sectional view of FIG. By preparing a sample 55 formed in the same direction and pulling the blank portions of the respective current collectors 54 in the opposite directions, the adhesiveness of the adhesive layer 52 is destroyed at the portion of the polarizable electrode 53. , And the case of peeling at the adhesive layer 52 was determined as “poor”. As shown in Table 2, the samples of Examples 2 to 5 provided good adhesiveness in which the polarizable electrode 53 was broken, but Comparative Examples 2 and 3 showed that the adhesive layer 5 was not used.
2, it was confirmed that not only the effect of reducing the resistance but also the improvement of the adhesiveness were not achieved.

[0038]

As described above, according to the present invention, the resistance can be reduced without lowering the adhesiveness of the conductive layer formed between the current collector and the polarizable electrode in the electrode body. In addition, a remarkable effect that an electric double layer capacitor excellent in charge and discharge characteristics and reliability can be manufactured can be obtained. In addition, since the manufacture of the electrode body is easy, the productivity is improved, and an excellent effect that the characteristic variation of each electric double layer capacitor is suppressed and the quality is stabilized is also exhibited.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of the structure of a single electrode cell.

FIG. 2 is a perspective view showing an example of the structure of a single capacitor cell.

FIG. 3 is a perspective view showing an example of the structure of a wound electric double layer capacitor.

FIG. 4 is a cross-sectional view schematically showing a structure of an electrode body suitably used for the electric double layer capacitor of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration of a tensile test sample.

[Explanation of symbols]

10 single electrode cell, 12 single capacitor cell, 22.2
4 ... current collector, 26 ... polarizable electrode, 28 ... separator, 3
0, 32: electrode extraction portion, 50: electrode body, 51: conductive filler, 52: adhesive layer, 53: polarizable electrode, 54:
Current collector, 55: tensile test sample, 70: wound type electric double layer capacitor, 72: positive electrode sheet, 74: negative electrode sheet, 7
6: wound body, 78: case, 80: electrode terminal, 82: sealing plate.

Claims (10)

[Claims] An electric double layer capacitor using an electrode body having a conductive layer formed between a current collector and a polarizable electrode, wherein the conductive layer comprises an organic adhesive and a conductive filler,
When the particle size of the conductive filler is d and the thickness of the adhesive layer is t, at least a part of the conductive filler is 0.2%.
An electric double layer capacitor characterized by satisfying a relationship of t ≦ d ≦ 3t. 2. The electric double layer capacitor according to claim 1, wherein at least a part of the conductive filler satisfies a relationship of 0.5t ≦ d ≦ 2t. 3. The electric double layer capacitor according to claim 1, wherein the thickness of the conductive layer is in a range of 1 to 100 μm. 4. The electric double layer capacitor according to claim 3, wherein the thickness of the conductive layer is in the range of 5 to 60 μm. 5. The electric double layer capacitor according to claim 1, wherein the conductive filler is a carbon-based material. 6. A method for manufacturing an electric double layer capacitor using an electrode body having a conductive layer formed between a current collector and a polarizable electrode, wherein a conductive filler and a conductive filler are provided on the surface of the current collector. After forming an adhesive layer composed of an organic adhesive, the current collector and the polarizable electrode are pressed with the adhesive layer interposed therebetween, and the particle size of the conductive filler is d, and the thickness of the adhesive layer is t. Forming a conductive layer in which at least a part of the conductive filler satisfies the relation of 0.2t ≦ d ≦ 3t, and manufacturing the electrode body. Production method. 7. A method for manufacturing an electric double layer capacitor using an electrode body having a conductive layer formed between a current collector and a polarizable electrode, wherein an organic adhesive is provided on the surface of the current collector. , Particle size d ₁ is 0.2
After forming the adhesive layer having a thickness of t ₁ consisting of a conductive filler is t ₁ or less, on the adhesive layer, by adhering another electrically conductive filler having a particle size d to form a pre-adhesive layer, the The current collector and the polarizable electrode are pressurized with the preliminary adhesive layer interposed therebetween, and at least a part of the other conductive filler is 0.2t ≦ d ≦ 3t when the thickness of the adhesive layer is t. By forming the conductive layer that satisfies the relationship of
A method for manufacturing an electric double layer capacitor, comprising a step of manufacturing the electrode body. 8. The method for manufacturing an electric double layer capacitor according to claim 6, wherein at least a part of said another conductive filler satisfies a relationship of 0.5t ≦ d ≦ 2t. 9. The method for manufacturing an electric double layer capacitor according to claim 6, wherein the thickness of the conductive layer is in a range of 1 to 100 μm. 10. The method according to claim 9, wherein the thickness of the conductive layer is in the range of 5 to 60 μm.