JPH026211B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and particularly to improvements in a solid electrolyte layer made of an organic semiconductor and a method for forming the same. Solid capacitors use a film-forming metal such as aluminum or tantalum for the anode, and in order to enlarge the surface of the anode, it is made porous by etching or sintering, and an oxide film layer that serves as a dielectric is formed on the surface. However, it has a structure in which a solid electrolyte layer is formed on this surface, and a conductive cathode extraction layer is further formed on the outside of this solid electrolyte layer. Conventionally, manganese dioxide has been used as this solid electrolyte layer. As a means of forming this manganese dioxide on the dielectric oxide film layer, the anode electrode is impregnated in liquid manganese nitrate, and then,
Manganese nitrate was thermally decomposed at a temperature of around 300°C and denatured into manganese dioxide. However, according to this method, only a small amount of manganese dioxide is deposited in one process, so 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 materials in this electrolyte layer. This organic electrolyte is known as tetracyanoquinodimethane (hereinafter referred to as TCNQ).
This method uses various complex salts of Since TCNQ complex salt is a solid substance at room temperature, the conventional method of attaching it to capacitor elements using it as an electrolyte is to impregnate the anode body in a solution of TCNQ complex salt dissolved in an organic solvent. After that, the anode is removed from the solution and an organic solvent is dispersed to form a TCNQ complex salt layer on the surface of the anode. However, in this method, the concentration of TCNQ complex salt in the solvent is low, so
It is not possible to deposit enough TCNQ complex salt in a single impregnation, and as with the formation of the manganese dioxide layer, it is necessary to repeat this process several to ten times, which again complicates the manufacturing process. Furthermore, since the TCNQ complex salt crystallizes after the solvent evaporates, sufficient contact with the dielectric oxide film on the surface of the anode body cannot be obtained, resulting in the drawback that a predetermined capacitance cannot be obtained. Recently, a method has been proposed in which only the TCNQ complex salt is heated above its melting point to liquefy, the anode body is impregnated with it, and then the liquefied TCNQ complex salt is pulled out and cooled to adhere the TCNQ complex salt. According to this method, since the highly concentrated TCNQ complex salt itself is deposited on the anode body, sufficient TCNQ complex salt can be deposited in one impregnation step. However, TCNQ complex salts are sensitive to heating, and many TCNQ complex salts are
Some substances decompose before they reach a melting point, making it virtually impossible to use this method. An example of this is 4,4'-dimethylbipyridinium or a complex salt of bipyridinium such as 4,4'-dimethylbipyridinium and TCNQ. It becomes a thing. This invention improves on these drawbacks, and it is possible to improve TCNQ, which has conventionally been impossible to heat-melt and impregnate.
The aim is to make it possible to impregnate complex salts by heating and melting, and to obtain solid electrolytic capacitors with excellent characteristics. This invention relates to 4,4'-dimethylbipyridinium
A mixture formed by adding a lactone compound to TCNQ complex salt or 4,4'-isopropylbipyridinium TCNQ complex salt is heated to a temperature lower than the decomposition temperature of the TCNQ complex salt to liquefy it, and a capacitor element is placed in this liquid mixture. It is characterized by impregnation and cooling and solidification after impregnation.
Focusing on the phenomenon that the melting point (freezing point) of a mixture is lower than that of a pure substance, a mixture of TCNQ complex salt and additives is heated and melted and impregnated into the anode body. This invention will be explained in detail based on the following examples. First, the manufacturing procedure of the solid electrolytic capacitor according to the present invention will be explained. FIG. 1 shows the capacitor element used in this example. This capacitor element 1 is formed by winding a band-shaped electrode body, and the anode 2 is made of high-purity aluminum foil. A dielectric oxide film is formed on the surface of this anode 2 by anodizing treatment. This strip-shaped anode 2 has a collector electrode 3 of approximately the same size disposed oppositely, and a separator paper 4, which is slightly wider than the electrodes 2 and 3, is sandwiched between the anode 2 and the collector electrode 3. The stuffed material 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. 2 shows a method 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,
Powder mixture 1 consisting of TCNQ complex salt and additives
4 is injected and the mixture 14 is melted by heating. The capacitor element 1, which has been kept on standby in the preheating block 10, is moved here and impregnated for a predetermined period of time.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. The capacitor element 1 on which the solid electrolyte layer has been formed in this manner is housed in a cylindrical outer case 20 with a bottom, as shown in FIG. 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. In addition, as conventional examples, a normal dry electrolytic capacitor using a liquid electrolyte and a solid electrolytic capacitor made using an isopropyl-isoquinolinium TCNQ complex salt that can be melted and impregnated only with a TCNQ complex salt are used as conventional examples in this invention. A comparison will be shown. First, the capacitor element used was made of high-purity aluminum (purity
99.99%) was 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 was formed on the surface by anodizing treatment. Aluminum (purity 99.94%) of the same size as the anode is placed oppositely as a current collecting electrode, and an aluminum tab for external extraction is connected approximately at the center of both electrodes by cold welding. It is wound into a cylindrical shape with a separator paper interposed between them. Next, for Conventional Example 1, this capacitor element was impregnated with an ethylene glycol-ammonium adipate based electrolyte. In addition, in Conventional Example 2, only isopropyl-isoquinolinium TCNQ complex salt, which can be heated and melted by TCNQ complex salt, was heated and melted at 240°C and impregnated into the capacitor element. An attempt was made to impregnate the 4,4'-dimethylbipyridinium TCNQ complex salt and the 4,4'-isopropylbipyridinium TCNQ complex salt used in this invention by heating only these complex salts. For Examples 1 to 14 of the present invention, the capacitor element was heated to 210°C in a preheating block using the impregnating apparatus shown in Fig. 2 and kept on standby. The capacitor element was immersed in the mixture for 10 seconds, and then taken out of the melting tank and allowed to cool naturally to impregnate the solid electrolyte. Then, the impregnated capacitor element is stored in an aluminum exterior case, the opening is closed with a rubber sealing body, and the opening end of the exterior case is wrapped tightly to seal the rated voltage of 6.3V. Capacity 10μ
I completed the electrolytic capacitor below. At this time, the external dimensions of the capacitor body are 3 mm in diameter and 5 mm in length.
It was hot. Among these capacitors, the rated voltage was applied to each capacitor for aging for 15 minutes for the conventional example 1, and for 1 hour for the capacitor using a solid electrolyte, and then the electrical characteristics were examined. Electrical characteristics include capacitance (μF), tangent of loss angle,
Equivalent series resistance value [ESR] at 100KHz, (Ω),
When the leakage current value (μA/2 minute value) was measured,
The results shown in the table below were obtained. Regarding Table 1,
For an example using a mixture of 4,4'-dimethylbipyridinium TCNQ complex salt and a lactone compound, Table 2, 4,4'-isopropylbipyridinium
An example using a mixture of TCNQ complex salt and a lactone compound is shown.

【table】

【table】

[Table] Looking at the results of these examples, as shown in Conventional Example 3 or Conventional Example 4, when conventionally heated and melted, thermal decomposition occurred before melting and it could not be used as a solid electrolyte4,4 It can be seen that by adding and heating a lactone compound, the '-dimethylbipyridinium TCNQ complex salt or the 4,4'-isopropylbipyridinium TCNQ complex salt can be liquefied at a temperature that does not lead to decomposition and can be impregnated into a capacitor element. 4,4'-dimethylbipyridinium or 4,
As mentioned above, when the complex salt of 4'-isopropyl bipyridinium and TCNQ is heated to a temperature exceeding 260°C, it is recognized that it turns into an insulator while emitting light. However, as can be seen from the examples, although there are differences depending on the type of additive and the mixing ratio, in all examples, the additive is melted and liquefied at a temperature below 210°C, making it possible to impregnate capacitor elements. I can see that I am getting used to it. In addition, when examining the characteristics of the solid electrolytic capacitor after electrolyte impregnation, it was found that in the conventional dry electrolytic capacitor using a liquid electrolyte shown in Conventional Example 1, the electrolyte is held in a liquid state inside the capacitor element.
The electrolyte penetrates into the fine etched holes (pits) created by etching to enlarge the surface of the anode, making sufficient contact with the dielectric oxide film, resulting in a high capacitance value. However, the specific resistance value of the electrolyte and the specific resistance value of the TCNQ complex salt are several tens of Ω・cm.
However, since it is high at 200-300Ωcm, the loss value or equivalent series resistance value is high. In addition, in the solid electrolytic capacitor manufactured by heating and melting only the isopropyl-isoquinolinium TCNQ complex salt and impregnating it into the capacitor element, as shown in Conventional Example 2, the loss and equivalent series resistance value are as follows: Since the specific resistance value is lower than that of the electrolytic solution, excellent characteristics are obtained, but the capacitance value is not sufficiently obtained. The reason for this is not clear, but although the molten isopropyl-isoquinolinium TCNQ complex permeates into the etching pit of the anode, during subsequent cooling and solidification, the isopropyl-isoquinolinium TCNQ complex crystallizes into needle-like crystals and is removed from the etching pit. This is thought to be because contact with the dielectric oxide film inside is only partially made. On the other hand, all of the solid electrolytic capacitors manufactured by the method of the present invention exhibit larger capacitance values than Conventional Example 2. This is because the solid electrolyte of this invention is a mixture of a TCNQ complex salt and a lactone compound, so crystallization is prevented during cooling after melting and impregnation, and it remains in the etching pit in an amorphous state, resulting in dielectric oxidation. This is thought to be due to sufficient contact with the film being maintained. Also, some
Even if the TCNQ complex salt crystallizes, the presence of the lactone compound between the crystals is thought to provide intercrystalline conductivity and ensure capacitance. 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. Regarding the lactone compounds to be added,
Lactone compounds other than those exemplified in this example may also be used. Furthermore, in the examples, only one type of additive was used, but the same effect can be expected even if two or more types of lactone compounds are mixed and added. As described above, according to the present invention, 4,4'-dimethylbipyridinium
The capacitor element can be impregnated by heating and melting TCNQ complex salt or 4,4'-isopropylbipyridinium TCNQ complex salt. Further, according to the present invention, the impregnation rate of TCNQ complex salt can be improved and the capacitance value per unit volume can be increased, which contributes to miniaturization of solid electrolytic capacitors. Furthermore, since the concentration of the TCNQ complex salt itself is much higher than that dissolved in conventional solvents, sufficient properties can be brought out in a single impregnation process. Furthermore, since it becomes liquid at a temperature lower than the decomposition temperature of TCNQ complex salt, sufficient time can be secured for the properties of TCNQ complex salt to change due to heating, making impregnation work easier and allowing the use of expensive TCNQ complex salt without wasting it. There are effects such as being able to
This is extremely useful for improving the characteristics of solid electrolytic capacitors and improving workability.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the structure of a capacitor element used in an embodiment of the present invention, FIG. 2 is a sectional view showing a solid electrolyte impregnation device of the present invention, and FIG. FIG. 2 is a cross-sectional view showing a completed state of the solid electrolytic capacitor. 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)

[Claims] 1. 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, the solid electrolyte layer comprising:
It is characterized by consisting of a mixture obtained by adding a lactone compound to a complex salt of tetracyanoquinodimethane and 4,4'-dimethylbipyridinium or 4,4'-isopropylbipyridinium, which is melted and then solidified. Solid electrolytic capacitor. 2 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone. 3. A solid electrolytic capacitor in which a dielectric oxide film is formed on the surface of the anode metal, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer, in which the solid electrolyte layer is formed using tetracyanoquinodimethane and 4,4′- A mixture obtained by adding a lactone compound to a complex salt of dimethylbipyridinium or 4,4'-isopropylbipyridinium is liquefied by heating to a temperature lower than the decomposition temperature of the tetracyanoquinodimethane complex salt, and this liquid mixture is 1. A method for manufacturing a solid electrolytic capacitor, which comprises impregnating a capacitor element inside the solid electrolytic capacitor, and cooling and solidifying the capacitor element after impregnation. 4 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The method for manufacturing a solid electrolytic capacitor according to claim 3, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone.