JPH0410728B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to solid electrolytic capacitors, and particularly to improvements in solid electrolytes made of organic semiconductors. [Prior Art] Solid electrolytic capacitors use film-forming metals such as aluminum and tantalum for the anode, and in order to enlarge the area of the anode, the surface of the foil-shaped anode body is etched or a powder of the metal is used. is sintered to make it porous, an oxide film layer serving as a dielectric is formed on this surface by means such as anodizing treatment, a solid electrolyte layer is further formed on this upper surface, and a cathode is drawn out from this solid electrolyte layer. The device is configured to include electrical connection means for. Conventionally, manganese dioxide has been used for this solid electrolyte layer. The method for forming this manganese dioxide on the dielectric oxide film layer is to impregnate the anode electrode in liquid manganese nitrate, and then
Manganese nitrate was thermally decomposed at temperatures around ℃ and denatured into manganese dioxide. However, in this method of electrolyte formation, since only a small amount of manganese dioxide is deposited in one process, it is necessary to repeat the same process several to more than ten times. As a result, the manufacturing process becomes extremely complicated, and the dielectric oxide film deteriorates due to the high temperature and gas generated during thermal decomposition. Therefore, recently, instead of this manganese dioxide,
It has been proposed to use conductive organic substances as electrolytes. This organic electrolyte is known as tetracyanoquinodimethane (hereinafter referred to as TCNQ).
This method uses various complex salts of Although TCNQ complex salt is an organic substance, it has moderate conductivity, and its use is being attempted as it is suitable for the electrolyte layer of solid electrolytic capacitors. Since TCNQ complex salt is a solid substance at room temperature, the challenge is how to attach it to the derivative oxide film as an electrolyte. For example, as previously proposed,
(U.S. Patent No. 3,214,648), etc.
It is known to dissolve TCNQ complex salt in an organic solvent, impregnate the anode body in this solution, and then pull it out of the solution and evaporate the organic solvent to form a TCNQ complex salt layer on the surface of the anode body. However, with this method, because the concentration of TCNQ complex salt in the solvent is low, it is not possible to deposit enough TCNQ complex salt in one impregnation, and this process is repeated several to more than ten times, similar to the formation of a manganese dioxide layer. Repetition was necessary and the complexity of the manufacturing process could not be avoided. In addition, as in (Japanese Patent Publication No. 51-32303), a method has been proposed in which a dispersion consisting of a polymer substance and fine powder of TCNQ complex salt is adhered to the electrode surface. However, in these methods, after evaporation of the solvent
Because the TCNQ complex salt crystallizes or is dispersed in a crystalline state, sufficient contact cannot be obtained with the derivative oxide film on the surface of the anode body, which has been expanded and has complex irregularities. However, there was a drawback that the desired capacitance could not be obtained. Recently, as shown in (Japanese Unexamined Patent Publication No. 57-173928),
Heat and dissolve only the TCNQ complex salt above its melting point,
A solid electrolytic capacitor has been proposed in which the anode body is impregnated, then pulled up and cooled, and TCNQ complex salt is attached. Solid electrolytic capacitors made using this method are
Since the highly concentrated TCNQ complex salt itself is attached to the anode body, a sufficient TCNQ complex salt layer can be formed in a single impregnation operation. However, in the solid electrolyte layer produced by this method, the TCNQ complex salt is crystallized as described above, and sufficient contact with the dielectric oxide film layer cannot be established, making it impossible to obtain the desired capacitance. Moreover, the TCNQ complex salt itself is extremely sensitive to heating.
If kept in a molten state, thermal decomposition will occur in a short time,
It turns into an insulator. Furthermore, some TCNQ complex salts undergo thermal decomposition at temperatures below their melting point, making it virtually impossible to form a solid electrolyte layer using this method. For example, isopropyl-isoquinolinium TCNQ complex salt can be impregnated by heating and dissolving it, but the time that it can remain in a molten state is extremely short. Also, methylisoquinolinium
TCNQ complex salt, 4,4'-dimethylbipyridinium
TCNQ complex salt, 4,4'-isopropylbipyridinium TCNQ complex salt, etc. undergo thermal decomposition from the heating stage before melting, and impregnation with electrolyte by melting is virtually impossible. [Problems to be Solved by the Invention] This invention improves on these conventional drawbacks, and is capable of impregnating TCNQ complex salts that cannot be impregnated by melting or impregnating in a very short time even if it is possible to impregnate by melting. must end
TCNQ complex salt is formed on the surface of the anode body as a solid electrolyte, and the insufficiency of contact with the dielectric oxide film due to crystallization after impregnation of TCNQ complex salt is improved, making it a solid with excellent properties and high impregnation efficiency. The purpose is to obtain electrolytic capacitors. [Means for Solving the Problems] The present invention provides a solid electrolytic capacitor in which a dielectric oxide film is formed on a metal surface of an anode, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer. A complex salt consisting of one or more selected from the group of isoquinolinium, methylisoquinolinium, 4,4'-dimethylbipyridinium, and 4,4'-isopropylbipyridinium and TCNQ, N,N-dimethyl A solid electrolytic capacitor characterized in that it is formed by dissolving and solidifying a mixture to which formamide is added. The present invention will be described in detail below based on examples. [Example] First, a solid electrolytic capacitor according to the present invention was
An example of the manufacturing procedure will be explained below. FIG. 1 is a cross-sectional view showing a completed solid electrolytic capacitor manufactured according to this example, and FIG. 2 shows an anode body, ie, a capacitor element, used in this example. The capacitor element 1 shown in FIG. 2 is formed by winding a band-shaped electrode body, and the anode 2 is made of high-purity aluminum foil. This anode 2 has
A dielectric oxide film is formed on the surface by anodizing. This strip-shaped anode 2 has a collector electrode 3 of approximately the same size disposed oppositely, and a separator paper 4 slightly wider than the electrodes 2 and 3 is sandwiched between the anode 2 and the collector electrode 3. The capacitor element 1 is wound from one end to form a cylindrical capacitor element 1. Note that tabs 5 and 6 for obtaining electrical connection with the outside are connected to each of the anode 2 and the collector electrode 3 by means such as welding, and protrude in parallel from one end surface. Furthermore, external leads 7 and 8 are connected to the tips of these tabs by welding. FIG. 3 shows an example of impregnating the capacitor element 1 with a solid electrolyte layer, and a preheating block 10 is placed on the left side of the figure. This preheating block 10 has a heating heater embedded inside and a recess 11 on the top surface.
The capacitor element 1 is placed in the recess 11, and the capacitor element 1 is heated in advance to maintain a high temperature state. Next, an impregnating block 12 is placed on the right side of the figure, and this impregnating block 12 also has a heating heater embedded therein and a recess 13 formed in its upper surface. And in this recess 13,
A powder mixture 14 consisting of TCNQ complex salt and N,N-dimethylformamide as an additive is injected, and the mixture 14 is melted by heating. The capacitor element 1 that has been kept on standby in the preheating block 10 is moved here and impregnated for a predetermined period of time, and then the capacitor element 1 is pulled up from the recess 13 and the liquid mixture 14 is solidified by natural cooling to form a solid electrolyte layer. form. As shown in FIG. 1, the capacitor element 1 with the solid electrolyte layer formed thereon is housed in a cylindrical outer case 20 with a bottom, and the open end of the outer case 20 is sealed with an elastic sealant 21. Closed, outer case 2
Tighten the open end of 0 to seal it. Note that the external leads 7 and 8 drawn out from the capacitor element 1 protrude to the outside from the through hole provided in the elastic sealing body 21, so that an electrical connection between the capacitor element 1 and the outside can be established. Next, we will show the results of fabricating an actual solid electrolytic capacitor using the procedure described above and determining its characteristics. First, as a capacitor element, the width is 2.2 mm and the length is 10 mm.
A high-purity (99.99%) aluminum foil with a thickness of 80 μm is prepared as an anode, and after enlarging the surface of this anode by electrolytic etching using alternating current, a dielectric oxide film with a withstand voltage of 9 V is applied to the surface. was formed by anodizing. Then, as a current collecting electrode, aluminum foil (99.94% purity) of the same size as the anode was placed oppositely, and an aluminum tab for external extraction was connected to the approximate center of both electrodes by cold welding. A cylindrical structure, which was wound as shown in FIG. 2 with mixed paper separator paper interposed therebetween, was used in all Examples. Next, as Comparative Example 1 for this capacitor element,
It was impregnated with an ethylene glycol-ammonium adipate electrolyte. In addition, as Comparative Examples 2 to 5, only the complex salts of four types of TCNQ complex salts, isopropyl-isolinium complex salt, methylisoquinolinium complex salt, 4,4'-dimethylbipyridinium complex salt, and 4,4'-isopropylbipyridinium complex salt, were heated. The solution was dissolved, and the capacitor element was impregnated into the solution using the impregnating apparatus described above. Next, as invention examples 1 to 4, the above four types of
A mixture of TCNQ complex salt and N,N-dimethylformamide was impregnated using the impregnation apparatus while changing the heating temperature. Then, the capacitor element that has been impregnated is stored in a cylindrical aluminum outer case, the case opening is closed with a rubber sealing body, and the outer case opening end is wrapped and sealed. Rated voltage
We have completed a 6.3V electrolytic capacitor with a rated capacity of 10μF. Among these electrolytic capacitors, Comparative Example 1, which uses a liquid electrolyte, has a capacitance of 15
After aging was performed by applying the rated voltage to each capacitor for 1 hour for the capacitors that could be impregnated among other comparative examples and for 1 hour for the capacitors of this invention example, the electrical characteristics were examined. Regarding the electrical characteristics, we measured the capacitance, the tangent of the loss angle, the equivalent series resistance value at 100KHz, and the leakage current after 2 minutes of applying the rated voltage.
The characteristics of each were compared. The results are shown in the table below.

[Effect]

Looking at the results of these examples, it can be seen that in the normal dry electrolytic capacitor using a liquid electrolyte shown in Comparative Example 1, the electrolyte is held in a liquid state inside the capacitor element, so the area of the anode can be enlarged. The electrolyte penetrates into the fine etching holes (pits) formed by the etching process, and makes sufficient contact with the dielectric oxide film, resulting in a high capacitance value. However, the specific resistance value of the electrolyte is about 200 Ωcm, whereas the specific resistance value of the TCNQ complex salt is about several tens of Ωcm.
Since it is high at -300Ω・cm, the loss value or equivalent series resistance value is high. In addition, in the comparison example, only the isopropyl-isoquinolinium TCNQ complex salt of Comparative Example 2 can be impregnated by heating and melting, and other TCNQ complex salts of Comparative Examples 3 to 5 can be impregnated by heating and melting. In all cases, thermal decomposition occurred before reaching the molten state, and impregnation was impossible. In addition, looking at the characteristics of Comparative Example 2, which was able to be impregnated, excellent characteristics were obtained in terms of loss and equivalent series resistance, as the specific resistance value of the TCNQ complex salt is lower than that of the electrolyte, as mentioned above. However, sufficient capacitance values have not been obtained. The reason for this is not clear, but TCNQ
In the case of heating and melting only the complex salt, the TCNQ complex salt penetrates into the etching pit of the anode, but upon subsequent cooling and solidification, the TCNQ complex salt crystallizes into needle-shaped crystals, and dielectric oxidation within the etching pit forms capacitance. This is thought to be due to the fact that contact with the film was only partially made. On the other hand, as is clear from the characteristics of Invention Examples 1 to 4, the solid electrolytic capacitor of the present invention exhibits a larger capacitance value than Comparative Example 2 in all of them. This is because the solid electrolyte of this invention
Since it is a mixture of TCNQ complex salt and N,N-dimethylformamide, crystallization is prevented during cooling after melting and impregnation, and it remains in the etching pit in an amorphous state, so contact with the dielectric oxide film is prevented. This is thought to be because it is sufficiently maintained. Furthermore, even if some of the TCNQ complex salt crystallizes, it is thought that the presence of N,N-dimethylformamide between the crystals provides electrical conduction between the crystals and ensures capacitance. For the same reason, excellent conductivity can be obtained even in contact with the collector electrode side, contributing to improved characteristics. This example uses a capacitor element in which foil-shaped aluminum is used as the anode, the surface of which is enlarged and then a dielectric oxide film is formed, and a current collecting electrode is wound with a separator paper interposed. However, the capacitor element is not limited to such a structure, and the metal constituting the anode may be other film-forming metals such as tantalum or alloys thereof. Further, the structure is not limited to such a wound structure, but may be a porous body obtained by sintering film-forming metal powder. Moreover, even if it is a wound structure, the separator paper may be omitted, the collecting electrode may be made of a metal other than aluminum, or a heat-resistant conductive resin film may be used. Regarding the exterior structure, in this example, the case is housed in a metal exterior case, but the exterior body may be a resin case, a resin dip or mold, a laminate film exterior, etc. However, this does not deviate from the scope of this invention. [Effects] As described above, according to the present invention, a solid electrolyte layer can be formed by heating and melting impregnation with a mixture of TCNQ complex salt and N,N-dimethylformamide, which is impossible to impregnate by heating and melting conventionally. It was hot
TCNQ complex salts can be used. Furthermore, since the melting temperature of the TCNQ complex salt, which could be impregnated by heating and melting, is lowered, the time required for thermal decomposition is extended, and deterioration of properties can be prevented and impregnation becomes easier. Further, according to the present invention, the impregnation rate of the TCNQ complex salt can be improved and the capacitance value per unit volume can be increased, which contributes to miniaturization of the solid electrolytic capacitor. Furthermore, since the TCNQ complex salt is in sufficient contact with the dielectric oxide film, a solid electrolytic capacitor with low loss and excellent impedance characteristics can be obtained, which is extremely useful for improving the characteristics of solid electrolytic capacitors.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the completed state of the solid electrolytic capacitor of the present invention, FIG. 2 is an exploded perspective view showing the structure of a capacitor element used in an embodiment of the invention, and FIG. FIG. 2 is a cross-sectional view showing a solid electrolyte impregnation device used in Examples. 1... Capacitor element, 2... Anode, 3... Collector electrode, 4... Separator paper, 5, 6... Tab,
7, 8... External lead, 10... Preheating block, 11, 13... Recess, 12... Impregnation block, 14... Mixture, 20... Exterior case, 21
...Elastic sealant.

Claims (1)

[Scope of Claims] 1. A solid electrolytic capacitor in which a dielectric oxide film is formed on the surface of an anode metal, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer, wherein the solid electrolyte layer is composed of a complex salt of tetracyanoquinodimethane and N. A solid electrolytic capacitor, characterized in that it is formed by melting and solidifying a mixture to which N-dimethylformamide is added. 2 Complex salts of tetracyanoquinodimethane include isopropyl-isoquinolinium, methylisoquinolinium, 4,4'-dimethylbipyridinium, 4,
The solid electrolytic capacitor according to claim 1, which is a complex salt consisting of one or more selected from the group of 4'-isopropyl bipyridinium.