JPS6348113Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to the improvement of electric double layer capacitors, and in particular to the structure of electric double layer capacitors that improves self-discharge characteristics and reduces leakage current by improving separators constituting capacitor elements. Generally, an electric double layer capacitor consists of an electrode composed of activated carbon mixed with an aqueous electrolyte such as dilute sulfuric acid, polarized by an ion-permeable separator, an insulating gasket made of butyl rubber, etc., and an electrically conductive butyl rubber made of an insulating gasket. It is constructed by stacking several electric double layer capacitor elements sealed with a current collector and enclosing them in an outer container. In the case of an electric double layer capacitor with this structure,
The ion-permeable separator is made of porous polypropylene that has been subjected to hydrophilic treatment to block electron conduction between both electrodes. This hydrophilic treatment of the separator is generally carried out by applying a surfactant dissolved in an organic solvent to the entire porous polypropylene and then drying it. However, even if the ends of the separator are glued to an insulating gasket with an adhesive or the like and both electrodes are sealed, the separator as a whole is hydrophilic.
The electrolytic solution permeated to the ends of the separator through the contact surfaces with both electrodes, and as a result, there were cases in which the self-discharge characteristics as well as the leakage current characteristics of the completed electric double layer capacitor were adversely affected. Also, generally in electric double layer capacitors,
It is said that leakage current characteristics are proportional to the area of the separator, and it has been considered that the leakage current characteristics can be improved by reducing the separator area. When reducing the electrode area in contact with the separator and seeking the same capacitance as before, it is necessary to increase the vertical dimension of both electrodes because capacitance is proportional to the amount of activated carbon. As the impedance increases, the impedance also increases, which adversely affects the electrical characteristics. Therefore, there is a limit to the reduction in the area of the separator with which the electrodes come into contact. In view of the above drawbacks, the present invention aims to improve the self-discharge characteristics of electric double layer capacitors and to improve the leakage current characteristics by improving the separator. The present invention proposes a capacitor that utilizes an electric double layer formed between a polarizable electrode mainly made of activated carbon and an aqueous electrolyte, in which at least a portion of the separator made of porous polypropylene, excluding the peripheral edge, is subjected to hydrophilic treatment. It consists of a structure with applied parts. The present invention will be explained below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of an electric double layer capacitor according to the present invention. In the drawing, an outer container 2 forming an electric double layer capacitor is made of a highly conductive metal such as iron or aluminum, and an opening of the outer container 2 is sealed with an insulating lid 3. This electric double layer capacitor element 1 has at least one or a plurality of laminated electrodes 6 and 7 made by adding dilute sulfuric acid to activated carbon, and a separator is provided in the gap between the electrodes 6 and 7 to separate the electrodes 6 and 7. It is formed with 8 interposed therebetween. The separator 8 is made of porous polypropylene, and its central portion 13 is made of porous polypropylene, as shown in FIG.
A surfactant consisting of an ethanol solution of a nonionic surfactant such as polyoxyethylene oleyl ether is coated and dried to make it hydrophilic, while the peripheral edge 12 of the separator is hydrophobic. is retained. Each electrode 6, 7 is separated by sandwiching the peripheral end 12 of the separator 8, which has not been subjected to hydrophilic treatment, between an insulating gasket 5 made of butyl rubber, etc., and covers the end surface of each electrode 6, 7. It is sealed with conductive butyl rubber 4 to form electric double layer capacitor element 1. At least one or more electric double layer capacitor elements 1 thus formed are stacked in a known structure and housed in an outer container 2, and electrode lead terminals 9 and 10 led out from each electrode 6 and 7 are placed in the outer container. The electric double layer capacitor 2 is made to protrude outside, and a lid 3 is attached to the opening of the outer container 2 to seal the electric double layer capacitor. In the case of this embodiment, the only part through which ions permeate is the hydrophilically treated central part 13, so there is no possibility that the electrolyte will permeate into the peripheral part 12 of the separator 8 sandwiched between the insulating gaskets 5. ,
Improvements in leakage current characteristics can be expected. Further, since the area of the separator 8 to be hydrophilized can be easily adjusted, it is possible to easily suppress leakage current to the minimum level while functioning as an electric double layer capacitor. FIG. 3 is a plan view of a separator showing a second embodiment of the present invention. In this embodiment, the separator 11 that separates the electrodes 6 and 7 has a grid-like hydrophilic portion 14 with a constant density, and the peripheral edge 1 of the separator
5 retains hydrophobicity. The separator 11 according to this embodiment is partially hydrophilized in a lattice shape, and a surfactant can be used effectively. In this embodiment, the separator 11 is hydrophilic-treated in a grid pattern, but any other shape may be used as long as the separator 11 is uniformly hydrophilic-treated. Next, the characteristics of the electric double layer capacitor according to this example will be compared with those of the conventional example. As samples, we prepared 10 electric double layer capacitors with a rated voltage of 5 volts (V) and a rated capacity of 1 flat (F), and measured the average values of each capacitance (F), leakage current (μA), and impedance (Ω). . The leakage current is 60
The minute value is being measured. The results are shown below.

[Table] Furthermore, the self-discharge characteristics of the electric double layer capacitor (A) according to this example and the electric double layer capacitor B of the conventional example having the same rated voltage and rated capacity as the above samples were measured. The measurements were performed by charging each of the 10 samples with the rated voltage, leaving them at room temperature, and measuring the average value of the residual voltage after 75 hours, 1000 hours, and 300 hours. The results are shown in FIG. As is clear from the above characteristic measurement results, although the leakage current characteristics of the electric double layer capacitor according to this example are improved by approximately 25% compared to the leakage current characteristics of the conventional electric double layer capacitor, the capacitance No notable differences were observed in the characteristics or impedance characteristics. Furthermore, as shown in Figure 4, the residual voltage of the conventional electric double layer capacitor after 300 hours is approximately 20% lower than the rated voltage, whereas the electric double layer capacitor of the present invention has a The decrease was only about 10%, indicating that the self-discharge characteristics were improved. As described above, the present invention provides a capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode mainly made of activated carbon and an aqueous electrolyte, at least at the peripheral edge of a separator made of porous polypropylene that separates both electrodes. Since the separator is characterized in that a portion other than the separator is hydrophilically treated, the peripheral edge of the separator sandwiched by the insulating gasket is kept hydrophobic, and the electrolyte can penetrate into the peripheral edge of the separator. This eliminates the problem, reduces the overall separator area, and improves leakage current characteristics. Further, by improving the leakage current characteristics, the self-discharge characteristics of the electric double layer capacitor are also improved. Furthermore, since the improvement in leakage current characteristics can be achieved without increasing the amount of activated carbon, impedance characteristics are not affected. Furthermore, since the separator is subjected to the minimum necessary hydrophilic treatment to make it ion permeable, it becomes possible to work more efficiently. In summary, the present invention is a useful invention that can suppress the leakage current of the electric double layer capacitor to a minimum and achieve extremely efficient ion permeation of the electrolyte.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an electric double layer capacitor according to the present invention, and FIGS. 2 and 3 are plan views showing a separator of the electric double layer capacitor according to the present invention. FIG. 4 is a graph showing the electrical characteristics of the electric double layer capacitor according to the present invention. DESCRIPTION OF SYMBOLS 1... Electric double layer capacitor element, 2... Outer container, 3... Lid, 4... Conductive rubber, 5... Gasket, 6, 7... Electrode, 8, 11... Separator, 9, 10 ...External connection terminal, A...This embodiment, B...Conventional example.

Claims (1)

[Claims for Utility Model Registration] (1) A capacitor that utilizes an electric double layer formed between a polarizable electrode mainly made of activated carbon and an aqueous electrolyte, excluding at least the periphery of a separator made of a hydrophobic material. An electric double layer capacitor characterized by having a hydrophilic part in a part. (2) The electric double layer capacitor according to claim 1, wherein at least a portion of the separator made of porous polypropylene is treated to make it hydrophilic.