JPS6314860B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a small-sized, large-capacity, wet-type electric double layer capacitor. Conventional Structure and Problems Conventionally, this type of electric double layer capacitor, as shown in FIG. It is constructed by injecting liquid. Further, as shown in FIG. 2, a paste made by adding graphite, carbon black, polytetrafluoroethylene, polyvinylpyrrolidone, etc. to activated carbon powder is used as the polarizable electrode 1, and a metal paste is used as the conductive electrode 2. A polarizable electrode material is formed and pressed onto the surface of a thin plate, net, or punched metal, or a rubber-like material is applied to a rolling roller to form a polarizable electrode body and a conductive electrode. Then, a polarizable electrode body having a pair of conductive electrodes is wound up with a separator 3 interposed therebetween, and an electrolyte is injected therein. A specific example of the configuration shown in FIG. 1 is shown in FIG.
It has a structure in which an activated carbon fiber cloth is used as the polarizable electrode body 1, and a metal layer of aluminum, titanium, etc., or a conductive resin layer is formed as the conductive electrode 2. These are superimposed via a separator 3,
After injecting the electrolyte, the positive and negative electrodes are insulated with a gasket 4, and then sealed with a coin-shaped case 5. Here, the metal conductive electrode is formed by a plasma spraying method or an arc spraying method, and the conductive resin layer is formed by a screen printing method, a spray method, or a dip method. It is formed by When a conductive resin is used, the internal impedance becomes larger than when a metal layer is used, resulting in a capacitor that is not suitable for strong discharge applications. Next, we will discuss the withstand voltage of the capacitor, which is a problem with conventional construction methods. The withstand voltage largely depends on the conductive electrode and electrolyte used. Therefore (1)
We will discuss the withstand voltage when using an aqueous electrolyte and (2) a non-aqueous electrolyte. (1) When using an aqueous electrolyte Aqueous electrolytes have two orders of magnitude higher conductivity than non-aqueous electrolytes and can provide capacitors suitable for strong discharge. However, in aqueous solutions of acids or bases, the decomposition voltage remains almost constant regardless of the type of electrolyte.
Indicates 1.7V. For example, 1N.25℃, H ₂ SO ₄ ; 1.67V,
HaOH: 1.69V. That is, at this voltage, oxygen begins to be generated at the anode and hydrogen begins to be generated at the cathode.
However, the theoretical reversible potential difference between the oxygen and hydrogen electrodes for this reaction at 1 atm is approximately 1.23V and 1.7V.
The value of is much more polarized than this. In reality, the residual current gradually increases as it approaches the decomposition voltage of around 1.7V, and unless the voltage applied to the capacitor is controlled below 1.23V, the leakage current will increase and the capacitor characteristics, including reliability, will significantly deteriorate. descend. As long as an aqueous electrolyte is used in this way, it is impossible to obtain a highly reliable capacitor that has a withstand voltage of 1.23 V or more. (2) When using a nonaqueous electrolyte Organic electrolysis in which a solute such as lithium perchlorate or tetraethylammonium perchlorate is dissolved in a solvent such as propylene carbonate, γ-butyrolactone, N-N-dimethylformamide, or acetonitrile. It is widely known that the electrolyte has a lower electrical conductivity than an aqueous electrolyte, but has a higher withstand voltage. Here, the withstand voltage is regulated at the anode by oxidative decomposition of the electrolyte and dissolution of the anode electrode, while at the cathode it is regulated by the reductive decomposition of the electrolyte or the cathode electrode. When stainless steel or aluminum is used for the conductive electrode on the anode side, when the anode is polarized, it does not become passivated but dissolves, and the potential at which a current begins to flow due to this dissolution is the same as that of the activated carbon electrode in the electrolyte using the above organic solvent. Since it is lower than the anodic oxidation or electrolyte decomposition potential, when stainless steel or aluminum is used as the current collector, the anodic potential is limited by these dissolution potentials, and the electrochemical potential determined by the polarizable electrode and electrolyte is The stable potential region cannot be used effectively. Furthermore, when titanium is used as the cathode side conductive electrode, titanium oxide in titanium becomes titanium bronze through a reaction as shown in the following formula. TiO ₂ +H ⁺ +e→HTiO ₂ Due to this reaction, current begins to flow due to cathode polarization, resulting in leakage current of the capacitor. Thus, it can be seen that the withstand voltage of this capacitor is greatly influenced by the electrolyte and conductive electrode used. Furthermore, electric double layer capacitors are currently used as backup power sources for memory devices, and since many memories operate at 5.5V, when using an aqueous electrolyte, seven or eight layers of single cells are stacked together, and non-aqueous electrolyte Even if liquid is used, withstand voltage cannot be obtained unless three-layer single cells are connected in series. Therefore, when stacked in series, the combined capacity is reduced to 1/7 to 1/8 of a single cell in the case of an aqueous electrolyte, and 1/3 of a single cell in the case of a non-aqueous electrolyte. This shows how advantageous it is to obtain a capacitor with high withstand voltage. As described above, with the conventional conductive electrode configuration, it is difficult to increase the maximum usable breakdown voltage to 2.3 V or more per single cell. OBJECT OF THE INVENTION The object of the present invention is to obtain an electric double layer capacitor with high withstand voltage by improving the conductive electrode structure of a conventional electric double layer capacitor. Structure of the Invention In order to achieve this object, the present invention forms a conductive electrode made of titanium on one side of an anode-side polarizable electrode body, and forms a conductive electrode made of aluminum on one side of a cathode-side polarizable electrode body. death,
The anode-side and cathode-side polarizable electrode bodies on which the conductive electrodes are formed are opposed to each other with a separator interposed therebetween, and an electrolytic solution is injected thereinto. Description of Examples Before describing specific examples, the withstand voltage of an electric double layer capacitor will be explained. The ideal breakdown voltage of a capacitor is that when the capacitor is polarized as an anode or a cathode, the decomposition potential of the polarizable electrode and conductive electrode is greater than the decomposition potential of the electrolyte, and the decomposition current is caused by oxidation and reduction of the electrolyte. It is regulated by decomposition. Therefore, as shown in the iE curve shown in FIG. 4, it is sufficient that the decomposition potential 6 of the polarizable electrode and the conductive electrode is greater than the decomposition potential 7 of the electrolytic solution. In addition, the current and potential curves (i-E curves) when the constituent materials of this capacitor are polarized anode and cathode are obtained using the usual three-electrode method using silver for the opposing electrode and carbon for the reference electrode. It was calculated by (Example 1) Activated carbon fibers with a specific surface area of 2000 m ² /g were used for the polarizable electrode, and a titanium conductive electrode 9 was formed on one side of the anode-side polarizable electrode body 8 by plasma spraying, and the cathode-side polarizability An aluminum conductive electrode 11 is formed on one side of the electrode body 10 by plasma spraying, and is overlapped with a polypropylene separator 12 interposed therebetween to prevent electronic short circuits, and tetraethylammonium perchlorate is dissolved in propylene carbonate. After injecting the solution as electrolyte A, it is enclosed in a coin-shaped case 5 as shown in FIG. 5 and cased. Here, the electrochemical behavior of the polarizable electrode and conductive electrode of this example was investigated. The electrolyte solution used was A in all cases. FIG. 6 shows the iE curve of carbon obtained by the three-electrode method. Currents 13 and 14 flowing due to anode and cathode polarization are considered to be caused by decomposition of the electrolyte, and current 15 in the intermediate region is a charging current to the electric double layer. In addition, a similar iE curve of titanium is shown in Figure 7.
Figure 8 shows the iE curve of aluminum. 7th
As shown in the figure, titanium produces titanium bronze when cathodically polarized, so when cathodically polarized, a current flows due to this reaction. From FIG. 8, it can be seen that since aluminum is dissolved by anode polarization, a large withstand voltage cannot be expected by anodic polarization. In Example 1, since titanium is used for the anode conductive electrode and aluminum is used for the cathode conductive electrode, a breakdown voltage of about 2.9 is obtained. Table 1 shows the various characteristics of the capacitor when the polarizable electrode is a circle with a diameter of 15 mm. Compared to the conventional model, the withstand voltage is improved from 2.3V to 2.9V.

[Table] (Example 2) Using polarizable electrodes and conductive electrodes that were exactly the same as in Example 1, a capacitor having the structure shown in FIG. 2 was created. Table 2 shows the capacitor characteristics in this example. It can also be seen from Table 2 that the capacitor of this structure exhibits a higher withstand voltage than the conventional capacitor. The polarizable electrode used had a size of 10 cm x 5 cm.

[Table] (Example 3) Using the same polarizable electrodes and conductive electrodes as in Examples 1 and 2, the withstand voltage was measured when an electrolytic solution with the combination of solvent and electrolyte shown in Table 3 was used. It is shown in the right column of Table 3. From Table 3, it can be seen that the capacitor using the organic electrolyte exhibits a withstand voltage of 2.8 to 3.0V.

【table】

[Table] 〓α: Lithium perchlorate 〓

Claims (1)

[Claims] 1. A conductive electrode made of titanium is formed on one side of the polarizable electrode body on the anode side, and a conductive electrode made of aluminum is formed on one side of the polarizable electrode body on the cathode side. An electric double layer capacitor constructed by placing cathode-side polarizable electrode bodies facing each other with a separator in between and injecting an electrolyte. 2. The electric double layer capacitor according to claim 1, wherein the conductive electrode formed on one side of the polarizable electrode body is in contact with the conductive case. 3. The electric double layer capacitor according to claim 1, wherein the conductive electrode is formed on the polarizable electrode body by either a thermal spraying method such as plasma spraying or arc spraying, or a vapor deposition method. . 4. The electric double layer capacitor according to claim 1, wherein activated carbon in the form of fiber cloth, paper, felt, or porous body is used for the polarizable electrode body.