JPS6226566B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to electrochemical devices such as electrolytic capacitors and batteries that utilize electrochemical reactions, and particularly relates to electrochemical devices that are coated with a special coating material. Flat, oval electrolytic capacitors have the property of being extremely deformable due to the increase in internal pressure due to gas generation during operation. Furthermore, even in thin batteries, internal gas generation occurs due to self-discharge and other factors, resulting in separation between electrodes and deterioration of characteristics. For this reason, the flat electrochemical device
Although it has great advantages, such as being thinner than normal cylindrical electrochemical elements and being able to be manufactured by heat sealing, the complicated sealing process can be omitted and costs can be reduced, it is difficult to put it into practical use. It was possible or extremely difficult. An object of the present invention is to eliminate the above-mentioned drawbacks and provide an electrochemical element such as an electrolytic capacitor or a thin battery that has a dramatically improved lifespan. For example, an electrolytic capacitor always involves several electrochemical reactions during its operation. Taking an aluminum electrolytic capacitor as an example, an electrochemical reaction occurs where the exposed Al reacts with the electrolyte and is repaired by turning into Al ₂ O ₃ at the edges of the anode foil without an oxide film or at the defective parts of the dielectric. This reaction occurs continuously throughout the operation of the capacitor, and is expressed by the following reaction equation. Here, the current represented by "6e ^- " is the DC leakage current of the electrolytic capacitor, and it will not disappear even if it decreases due to aging. Therefore, it is impossible for an electrolytic capacitor to be completely airtight. The reason why electrolytic capacitors fail is not only due to the failure of the seal due to an increase in the internal gas pressure is because the gas permeates through the rubber sealing material and escapes, so if the gas is generated below a certain level, the internal pressure will not increase. Seem. By the way, since the above reaction is an electrochemical reaction between Al and the electrolyte, it follows the so-called Arrhenius law, so it is considered that twice as much gas is generated per unit time for every 10° C. increase in the operating temperature of the electrolytic capacitor. Therefore, how to deal with gas generation is an important issue in improving the life of electrolytic capacitors. In particular, the most common electrolytic capacitors with an aluminum case are mechanically strong and can withstand a certain degree of internal pressure rise, but in the case of flat electrolytic capacitors like the one shown in Figure 2, Since the electrical strength is weak, the appearance changes due to gas generation, and the capacitor characteristics deteriorate significantly. For this reason, several countermeasures against gas generation have been considered. One method is to package the capacitor element with a film made of polypropylene or polyethylene, which are materials with high hydrogen permeability and low water vapor permeability, and a metal foil between these films. (Japanese Patent Publication No. 54-7151) However, according to experiments by the present inventors, in the case of the polypropylene or polyethylene exterior shown here, hydrogen gas permeability does not cause any problem and prevents internal pressure from rising, but inside the capacitor The electrolyte also permeated at the same time, and its lifespan was extremely short. In addition, if a metal foil of Al 9 μm thickness is placed between these films, the electrolyte,
It was found that almost no hydrogen gas permeated through the capacitor, leading to damage to the capacitor due to an increase in internal pressure. In the method described in the above-mentioned patent publication, another method has been proposed in which most of the film is made up of a film with metal foil, part of it is used as a base film, and a window is provided to control the permeation amount of electrolyte and hydrogen gas. However, in this case, there is a drawback that the manufacturing cost of the film and the manufacturing cost of the flat electrolytic capacitor increases, and even if the amount of permeation can be essentially controlled, the selectivity cannot be improved. Another method is to use high-density polyethylene, which has very low moisture and gas permeability, or a layered layer of vinylidene chloride and polyethylene, or a layered layer of synthetic resin and aluminum foil. (Japanese Patent Publication No. 52-5702) In this case, as well as the method of the above-mentioned Japanese Patent Publication No. 54-7151, the electrolyte solution is The permeability of the capacitor was so high that the deterioration of the capacitor characteristics was severe. In particular, when vinylidene chloride film was present, Cl ions entered the electrolyte and further deteriorated the characteristics. In addition, since the film made of aluminum foil was hardly permeable to hydrogen gas or electrolyte, the capacitor was destroyed. These problems are caused by thin batteries (paper batteries)
Although the degree of gas generation differs, the same situation is exhibited for both, and gas generation causes separation between the electrodes, resulting in deterioration of both voltage and current capacity. This is a particularly serious problem for Li batteries that use polar organic solvents as electrolytes. In order to solve the above problems, the present inventors investigated the gas permeability and electrolyte permeability of various films, and as a result, the general formula is (However, R ₁ is

【formula】

【formula】

【formula】

It has been discovered that a polyoxadiazole film represented by any of the following formulas has relatively low gas permeability and is suitable as a coating material for electrochemical devices such as flat electrolytic capacitors and thin batteries. Therefore, the present inventors used these films to prototype flat electrolytic capacitors and thin dry batteries, and also prototyped conventional products and compared their lifespans. As a result, the flat electrolytic capacitor using the coating material of the present invention is 2 times smaller than the conventional product.
The lifespan has been extended by ~3 times. Table 1 shows the results using a flat electrolytic capacitor as a model.

[Table] Such effects can be inferred from the gas and electrolyte permeability of each film shown in Table 1. One is that the separation coefficient value is larger than that of conventional materials, and hydrogen gas selectivity is high. The other is carbon dioxide,
It has excellent barrier properties against polar gases and vapors such as electrolytes. In other words, these coating materials have excellent electrolyte barrier properties and selectively permeate hydrogen gas, so their lifespan is dramatically improved compared to conventional electrochemical devices such as flat electrolytic capacitors or thin dry batteries. . As is clear from the above, the advantages of the present invention are that hydrogen gas generated during operation or when left unused is released to the outside of the device, and the electrolyte has excellent barrier properties, which reduces the increase in internal pressure of the device and the deterioration of electrochemical characteristics. This means that lifespan can be dramatically improved. Specific examples will be described in detail below. Figure 1 shows the appearance of a flat electrolytic capacitor. A 16WV 500μF rated electrode foil 1 was used, and an electrolytic solution containing ethylene glycol as the main solvent was impregnated into it. This electrode foil 1 was inserted into a bag body 2 made of a film laminated with polyoxadiazole (manufactured by Furukawa Electric Co., Ltd.) and polyamide (NT-120, manufactured by Nippon Matai Co., Ltd.) as a heat sealing material. In order to improve the adhesion of the electrode foil 1, the inside of the bag 2 is evacuated and the insertion opening is sealed by heat sealing.
A flat electrolytic capacitor shown in FIG. 2 was manufactured.
(3 indicates the seal part). At this time, the thickness of the polyoxadiazole film was found to be good in the range of 50 μm to 200 μm in terms of its permeability and heat sealability. For comparison, conventional flat electrolytic capacitors were manufactured using polyethylene film, polypropylene film, and a composite film of polypropylene film and aluminum foil. The compositions of these films are shown in Table 2.

[Table] Table 3 shows the characteristics of each flat electrolytic capacitor. The experimental conditions were as follows: 16V DC load was applied for 500 hours in an oven at 85℃, and the number of samples was n.
was set to 5. When a polyethylene or polypropylene film is used in the conventional example, hydrogen gas permeability is good, but it is clear from the change in weight that the electrolyte also permeates at the same time. Therefore, the rate of change in tan δ is also quite large. Furthermore, in the case of a composite film with aluminum foil, neither hydrogen nor electrolyte permeate through it, making it impossible to prevent an increase in internal pressure, resulting in damage to the heat-sealed portion.

[Table] Compared to these conventional examples, the product of the present invention selectively transmits hydrogen gas to the outside of the element, prevents internal pressure from increasing, and has excellent electrolyte barrier properties.
The weight change after being left at 85℃ for 500 hours is polyethylene.
Very small compared to polypropylene film,
The rate of change in tanδ was also small. Furthermore, no change in the appearance of the device was observed. In the case of thin dry batteries, the internal structure consists of an anode without a dielectric layer, as well known by those skilled in the art;
A cathode is present with a spacer interposed therebetween, and a carbonate ester such as propylene keybonate is used as the electrolyte, and other conditions are the same as in the case of the flat electrolytic capacitor described above. In this case, there is no change in the appearance of the element due to gas generation, and the problem is peeling between the electrodes.Comparing the exterior covering material of the present invention with the conventional exterior covering material using aluminum foil, the lifespan is 60℃. In tests, the product of the present invention was found to have a lifespan of at least twice as long as that of the conventional product. As described above, the present invention utilizes polyoxadiazole, which is a material that selectively permeates hydrogen, as a coating material for electrochemical devices such as flat electrolytic capacitors or thin batteries, thereby preventing deformation and destruction of the device due to increased internal pressure. In addition to preventing this, the excellent electrolyte barrier property improves property deterioration. The above explanation mainly takes the flat electrolytic capacitor as an example, but other electrolytic capacitors such as cylindrical and long cylindrical electrolytic capacitors, thin batteries, cylindrical batteries, rectangular parallelepiped batteries, etc. Of course, it can also be applied to electrochemical devices that utilize chemical reactions.

[Brief explanation of the drawing]

FIG. 1 is an exploded view of a flat electrolytic capacitor as an embodiment of the present invention, and FIG. 2 is a perspective view of a flat electrolytic capacitor as an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Electrode foil, 2...Bag body, 3...Seal part, 4...Lead wire.

Claims (1)

[Scope of Claims] 1 Consists of an electrode portion, an electrolyte portion, and a coating material covering at least them, the coating material having hydrogen selective permeability, and whose general formula is: (However, R ₁ is any one of [Formula] [Formula] [Formula] [Formula]) An electrochemical device characterized in that it is a polyoxadiazole represented by the following formula. 2. The electrochemical device according to claim 1, wherein the electrochemical device is a flat capacitor. 3. The electrochemical device according to claim 1, wherein the electrochemical device is a flat battery.