JPS6364890B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electric double layer capacitor that utilizes an electric double layer formed by a polarizable electrode and an electrolyte interface, and in particular has a current collecting electrode made of a thermally sprayed metal layer on activated carbon fiber or the like. This invention relates to a small, high-capacity, low-internal-resistance electric double layer capacitor using composite electrode materials. Structure of the conventional example and its problems The basic structure of the electric double layer capacitor used conventionally is as shown in FIG.
and current collection layers 6 and 7 for taking out the leads 4 and 5 from the polarizable electrodes 1 and 2. The specific capacitor shapes are roughly divided into two types. The first type has the structure shown in FIGS. 2a and 2b. That is, a paste-like polarizable material made of graphite, carbon black, activated carbon, etc. and a binder such as tetrafluoroethylene or polyvinylpyrrolidone is placed on a net-like current collector 10 such as expanded metal made of aluminum metal. A separator 12 on which an electrode 11 is rolled and impregnated with an electrolytic solution, a current collector 10, and a polarizable electrode 11
It is wound and sealed in a cylindrical aluminum case 13. 14 is a lead. The second type, for example, as shown in Figure 3, uses a cloth, paper, or felt-like material 15 made of activated carbon fibers as a polarizable electrode, and collects current by plasma spraying on the electrode. A body 16 is formed and housed in a flat aluminum case 18 via a separator 17 impregnated with an electrolytic solution. 19 is an insulator. In electric double layer capacitors having these structures, characteristic values such as element capacitance, self-discharge characteristics, and internal resistance are cited as performance factors of the capacitor. Among these performance values, if we focus on the internal resistance of the element, the resistance component within the element is divided as shown in FIG. That is, the contact resistance R ₁ between the current collecting electrode 20 and the polarizable electrode 21, and the resistance inside the polarizable electrode
R ₂ , interfacial resistance between the polarizable electrode 21 and the electrolyte 23 impregnated in the separator 22 R ₃ , electrolyte 2
3 resistance R ₄ and a symmetrically existing resistance R ₃ ′,
R ₂ ′ and R ₁ ′. In the latter type of the above-mentioned two types of electric double layer capacitor configuration examples, that is, in the case of using activated carbon fiber as the polarizable electrode, the above-mentioned resistances R ₂ and R ₂ ' are larger than those of the first type. there is a possibility. In other words, as shown in Fig. 5, if the activated carbon fibers 25 are intertwined with each other in twill weave or plain weave, the carbon fiber density per unit area is low, and the so-called powdered activated carbon paste type. This is because the electrical resistance in both the thickness direction and the planar direction is greater than that using polarizable electrodes. In addition, as shown in FIG. 6, the electric double layer capacity at the interface between the polarizable electrode 31 and the electrolytic solution 32 in the microscopic pores 30 of the activated carbon fibers is calculated as the electric double layer capacity at the interface between the polarizable electrode 31 and the electrolyte 32. In consideration of the thickness of the activated carbon fibers, density per unit area, conductivity, etc., leading to the collector electrode 34 depends on R ₂ and
It cannot be ignored that R ₂ ′ becomes a high resistance. An electric double layer capacitor using activated carbon fiber as a polarizable electrode was invented by the present inventors (Japanese Patent Application Laid-Open No.
As detailed in Japanese Patent No. 55-99714), a small, flat button-shaped structure is possible, but in such a structure, the area of the polarizable electrode is particularly small, so it is necessary to lower the internal resistance. is required. Purpose of the Invention As described above, the present invention aims to improve the internal resistance of a small capacitor using activated carbon fiber as a polarizable electrode, and provides an electric double layer capacitor with low internal resistance. With the goal. Structure of the Invention The present invention is characterized in that, in an electric double layer capacitor using activated carbon fibers as polarizable electrodes, activated carbon fibers carrying a conductivity improver are used as polarizable electrodes. DESCRIPTION OF EMBODIMENTS FIG. 7 shows the basic structure of an electric double layer capacitor according to an embodiment. That is, the current collecting electrode 40,
It basically consists of an activated carbon fiber layer 41 that is in contact with the current collecting electrode 40 and carries a conductivity improving layer 42 on its surface, and a separator 43 impregnated with an electrolyte. Furthermore, when the surface of the polarizable electrode is shown microscopically, it becomes as shown in FIGS. 8a and 8b. As shown in Figure a, a conductivity improving layer 51 is supported over the entire surface of the activated carbon fiber 50, and as shown in Figure b, the pores 52 of the activated carbon are also coated with a conductivity improving layer 53. ing. The conductivity improving layer used here includes oxides of transition metals such as ruthenium, osmium, iridium, indium, and platinum, organic resins,
Three types of materials can be considered: conductive paint with carbon particles or other metal particles dispersed in CMC, tin oxide, indium oxide, and conductive metal layers formed by vapor deposition, sputtering, etc. It is essential that only the electric double layer formation reaction occurs in the plane between the polarizable electrode and the electrolyte, and considering the chemical and electrical stability of the polarizable electrode, stable conductivity as described above is required. It is preferable to use a conductive oxide such as a transition metal oxide, a conductive paint, or even tin oxide as the conductivity improving layer. When using an activated carbon fiber polarizable electrode having such a conductivity improving layer on its surface, for example, the resistance of activated carbon fiber is 10 ^-1 to 10 Ωcm, and the resistance of ruthenium oxide is 10 ^-5 .
As can be seen from the comparison of Ωcm, a low resistance layer is formed on the surface of the activated carbon fiber, and as shown in FIG. 9, the electric double layer formed on the inner surface of the polarizable electrode 55 is It is connected to the current collecting electrode 57 with low resistance through the path of the conductivity improving layer 56 formed on the surface. For example, if activated carbon fibers are immersed in an aqueous solution of ruthenium chloride for a certain period of time and thermal decomposition is performed with the ruthenium chloride aqueous solution sufficiently impregnated into the pores of the activated carbon fibers, it is possible to It is also coated with a ruthenium oxide layer. As a result, the resistance within the polarizable electrode mentioned above
In _other words, the resistance within the activated carbon fibers, as well as the contact resistance R ₃ between the polarizable electrode and the electrolyte and the contact resistance R ₁ between the polarizable electrode and the current collecting electrode, decrease, reducing the internal resistance of the electric double layer capacitor. Can be made very small. In addition, when a conductivity improving layer is formed using a thermally decomposable salt such as ruthenium chloride as described above,
Since electrodes can be easily taken out from the micropores of the activated carbon fibers, the entire surface area of these portions also contributes to the formation of an electric double layer, increasing the output capacity per unit volume. Methods for forming the conductivity improving layer used in the present invention include immersion pyrolysis using a thermally decomposable salt such as ruthenium chloride, coating or impregnation with a carbon colloid liquid, and forming a conductive oxide such as tin oxide. A method of forming the layer by vacuum evaporation may be mentioned.
Although this method is disadvantageous considering the formation of a conductivity-improving layer in the activated carbon pores, the type of activated carbon fiber used,
When considering heat resistance, etc., each method has its own characteristics, and exhibits superior characteristics to conventional electric double layer capacitors that do not have a conductivity improving layer. The activated carbon fiber used as the base material may be rayon-based, acrylic-based, phenolic-based, etc. In particular, phenolic novolac carbon fiber (for example, Kynor fiber manufactured by Nippon Kynor Co., Ltd.) is used because of its strength and surface area per unit weight. ) is preferred. Plasma spraying, arc spraying, etc. are effective for the current collecting electrode used, and nickel, aluminum,
Materials composed of zinc, copper, tin, lead, and one or more of their alloys are suitable. The following specific embodiments of the present invention will be described. (Example 1) Thickness woven from novolak activated carbon fiber
A 0.2 mm activated carbon cloth was dipped in a 0.5 mole/l ruthenium chloride aqueous solution for 5 minutes and then kept in a furnace at 300°C to coat the surface of the activated carbon fiber with a ruthenium oxide layer. An aluminum layer (thickness: 20 μm) is formed on one side of the activated carbon fiber cloth thus prepared by plasma spraying, and then a circle with a diameter of 10 mm is cut out. A polypropylene separator 60 is sandwiched between the two circular polarizable electrodes as shown in FIG. to be sealed. 63 and 64 are activated carbon cloths carrying a ruthenium oxide layer, and 65 is an aluminum layer. (Example 2) Thickness woven with novolak activated carbon fiber
A 0.2 mm activated carbon cloth was immersed in colloidal carbon liquid (manufactured by Acheson, USA, trade name: Aquadak).
After taking it out, dry it at 100℃ for 10 minutes. An aluminum layer (thickness: 20 μm) is formed on one side of the activated carbon fiber cloth thus prepared by plasma spraying, and then a circle with a diameter of 10 mm is cut out. A polypropylene separator was sandwiched between the two circular polarizable electrodes in the same configuration as shown in Figure 10, and a mixed solution of propylene carbonate and tetraethylammonium perchlorate was injected as an electrolyte, and the mixture was inserted into the metal case through a gasket. Seal it. (Example 3) Thickness woven with novolak activated carbon fiber
A tin oxide layer (5 μm thick) is formed on a 0.2 mm activated carbon cloth by vacuum evaporation. Furthermore, an aluminum layer (thickness 20μm) is applied on top of this by plasma spraying.
After forming, cut out a circle with a diameter of 10 mm. A polypropylene separator with the same configuration as shown in FIG. 10 is sandwiched between the two circular polarizable electrodes, and a mixed solution of propylene carbonate and tetraethylammonium perchlorate is injected as an electrolyte.
Seal the metal case via a gasket. (Example 4) Thickness woven with novolak activated carbon fiber
Soak a 0.2 mm activated carbon cloth in an aqueous ruthenium chloride solution (0.5 mole/) for 5 minutes. Next, the activated carbon fibers are kept in a thermal decomposition furnace for 10 minutes at 300°C to form a ruthenium oxide layer on the surface of the activated carbon fibers. An aluminum layer (thickness: 20 μm) is formed on one side of the thus-produced material by plasma spraying, and a 3 cm x 3 cm piece is cut out to form a polarizable electrode. Next, Figure 11a,
As shown in b, the polypropylene separator 70 is sandwiched between the polarizable electrodes 73 and 74, and the electrodes 71 and 72 are taken out. Then, the whole is sealed with a cylindrical aluminum case 76 and a rubber cap 77, and external electrode leads 78 and 79 are taken out. 75 is a sprayed aluminum layer. The characteristics of the electric double layer capacitors obtained in the four examples described above are shown in the table below. The same table shows the characteristics of a circular button type electric double layer capacitor without a conductivity improving layer and a wound type capacitor as conventional examples for comparison.

[Table] Effects of the Invention As is clear from the above explanation, according to the present invention, by using activated carbon fibers carrying a conductivity improver as polarizable electrodes, the resistance of the activated carbon fiber layer itself and the activated carbon fiber layer can be improved. Both the contact resistance between the electrode and the current collecting electrode, as well as the contact resistance between the activated carbon fiber layer and the electrolyte, are reduced compared to conventional methods, especially in button-type configurations that require high internal resistance.
One to two orders of magnitude lower internal resistance is achieved. Therefore, the electric double layer capacitor of the present invention can be adapted to miniaturization of electronic equipment and has great industrial value.

[Brief explanation of drawings]

Figure 1 is a diagram showing the basic configuration of a conventional electric double layer capacitor, Figures 2a and b are diagrams showing an example of the configuration of a conventional electric double layer capacitor, and Figure 3 is a diagram showing the basic configuration of a conventional electric double layer capacitor. 4 is a diagram showing an equivalent circuit of internal resistance of a conventional electric double layer capacitor, FIG. 5 is a diagram showing an activated carbon fiber cloth, and FIG. 6 is a diagram showing activated carbon in a polarizable electrode. A diagram showing the positional relationship between fibers and current collecting electrodes, FIG. 7 is a diagram showing the basic configuration of the electric double layer capacitor according to the present invention, and FIGS. FIG. 9 is a diagram showing the current collection mechanism of the electric double layer capacitor according to the present invention; FIG. 10 is a diagram showing the configuration of the electric double layer capacitor according to an embodiment of the present invention; FIGS. 11a and 11b are diagrams showing the structure of an electric double layer capacitor which is another embodiment of the present invention. 1, 2, 11, 21, 31, 55, 73, 74
... Polarizable electrode, 23, 32 ... Electrolyte, 33,
50... activated carbon fiber, 40, 57... current collecting electrode,
42, 51, 53, 56... Conductivity improving layer.

Claims (1)

[Scope of Claims] 1. A polarizable electrode that is in contact with an electrolyte and utilizes an electric double layer formed at the interface with the electrolyte, and the polarizable electrode carries a conductivity improver for increasing conductivity. An electric double layer capacitor is characterized in that it is composed of activated carbon fibers and has a current collecting electrode on one side. 2. The electric double layer capacitor according to claim 1, wherein the activated carbon fiber is a novolac type activated carbon fiber obtained by activation of phenolic carbon fiber. 3. The electric double layer capacitor according to claim 1, wherein the conductivity improver contains at least one of a conductive paint and a conductive transition metal oxide. 4 The current collecting electrode material is nickel, aluminum,
The electric double layer capacitor according to claim 1, characterized in that the electric double layer capacitor is made of at least one member selected from the group consisting of zinc, copper, tin, lead, and alloys thereof. 5. The transition metal oxide according to claim 3, wherein the transition metal oxide is at least one selected from the group consisting of oxides of ruthenium, iridium, osmium, tin, indium, and platinum. Electric double layer capacitor.