JPH0255929B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to solid electrolytic capacitors, and particularly to improvements in capacitors having a solid electrolyte layer made of an organic semiconductor. [Prior art] Solid electrolytic capacitors use a film-forming metal such as aluminum or tantalum in the form of a foil or block as an anode, and in order to enlarge the area of the anode, the anode is etched or fine powder is burned. It has a structure in which the surface is made porous by bonding, an oxide film layer serving as a dielectric is formed on this surface, a solid electrolyte layer is formed on this surface, and a means for extracting a conductive cathode is provided on the outside. Conventionally, manganese dioxide has been used as this solid electrolyte layer. This manganese dioxide is formed as the electrolyte layer on the dielectric oxide film by impregnating the anode electrode in liquid manganese nitrate, and then thermally decomposing the manganese nitrate at a temperature of around 300°C to denature it into manganese dioxide. was. However, according to this forming method, only a small amount of manganese dioxide is deposited in a single process, so it is necessary to repeat the same process several times 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).
It uses various complex salts of. Since the complex salt of TCNQ is a solid substance at room temperature, a conventional method of attaching it to a capacitor element using it as an electrolyte has been proposed. The anode body is impregnated in a solution in which a complex salt is dissolved, and then the anode body is removed from the solution and an organic solvent is dispersed to form a TCNQ complex salt layer on the surface of the anode body. 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. A method has also been proposed in which a dispersion of a polymer substance and fine powder of TCNQ complex salt is attached to the electrode surface, as in (Japanese Patent Publication No. 51-32303). However, in these methods, the solvent is
Since TCNQ complex salt is dispersed in a crystalline state,
Sufficient contact cannot be obtained with the dielectric oxide film on the surface of the anode body, which has an enlarged surface and complex irregularities.
There was a drawback that the desired capacitance could not be obtained. Recently, as in (Unexamined Japanese Patent Publication No. 57-173928)
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 the liquefied material, and then the anode body is pulled up 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 heat, and many TCNQ
Some complex salts decompose when heated before they reach their melting point, making it virtually impossible to use this method. For example, 4,4'-
An example of this is a complex salt of dimethylbipyridinium or 4,4'-isopropylbipyridinium and TCNQ. When heated above 240°C, these complex salts emit smoke and decompose before melting, becoming an insulator. [Problems to be Solved by the Invention] This invention improves the above-mentioned drawbacks.
The purpose is to form a solid electrolyte layer by heating and melting impregnation with a complex salt of dimethylbipyridinium or 4,4'-isopropylbipyridinium and TCNQ, and to obtain a solid electrolytic capacitor with excellent characteristics. [Means for solving the problems] The present invention provides 4,4'-dimethylbipyridinium
TCNQ complex salt or 4,4′-isopropylbipyridinium TCNQ complex salt, γ-hexalactone,
A mixture obtained by adding one or more lactone compounds selected from the group of γ-octalactone, γ-nonalactone, γ-decalactone, γ-undecalactone, and γ-dodecalactone is used as a solid electrolyte forming material. Use this mixture as described above.
It is characterized by heating to a temperature lower than the melting point or decomposition temperature of TCNQ complex salt to liquefy it, impregnating a capacitor element in this liquid mixture, and cooling and solidifying after impregnation to obtain a desired solid electrolyte layer. Focusing on the phenomenon that the melting point (freezing point) of TCNQ is lower than that of pure substances, the mixture of TCNQ complex salt and additives is melted by heating and impregnated into the anode body. This invention will be explained in detail based on the following examples. [Example] First, a solid electrolytic capacitor according to the present invention will be explained along with an example of a manufacturing procedure. FIG. 1 is a sectional view of a solid electrolytic capacitor manufactured according to the present invention, and FIG. 2 shows the anode body, ie, the capacitor element, used in this embodiment. In FIG. 2, a capacitor element 1 is formed by winding a band-shaped electrode body, and an 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 slightly wider than the anodes 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 a method for 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 buried inside and a recess 11 on the top surface, and the capacitor element 1 is placed in the recess 11 to preheat the capacitor element 1 and bring it to a high temperature state. I'll keep it. 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 bottomed cylindrical outer case 20, 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. As conventional examples, examples of a normal dry electrolytic capacitor using a liquid electrolyte, a solid electrolytic capacitor made using an isopropyl-isoquinolinium TCNQ complex salt that can be melted and impregnated with only a TCNQ complex salt, and a 4,4'- In comparison with the present invention, attempts were made to impregnate dimethylbipyridinium TCNQ complex salt and 4,4'-isopropylbipyridinium TCNQ complex salt by heating and melting each of them. 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, for Conventional Examples 2 to 4 and Invention Examples 1 to 6, the capacitor element was heated to 300°C in a preheating block using the impregnation apparatus shown in FIG. 3, and was kept on standby.
Into the impregnation block, TCNQ complex salt alone or a mixture of it and a lactone additive is injected, heated and melted, and the capacitor element is immersed in this for 10 seconds, then taken out from the melting tank and allowed to cool naturally. Impregnation with solid electrolyte was performed. 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
Completed a 10μF electrolytic capacitor. At this time, the external dimensions of the capacitor main body were 3 mm in diameter and 5 mm in length. 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. The electrical characteristics were determined by measuring capacitance (μF), tangent of loss angle at 120Hz, equivalent series resistance [ESR] at 100KHz (Ω), and leakage current value (μA/2 minute value), Table 1, The results shown in Table 2 were obtained.

【table】

【table】

[Effect]

Looking at the results of these examples, it was found that 4,4'-dimethylbipyridinium or 4,4'-isopropylbipyridinium TCNQ complex, which could not be used as a solid electrolyte due to thermal decomposition before melting when conventionally heated and melted, It can be seen that by adding and heating a lactone compound, it can be liquefied at a temperature that does not lead to decomposition and can be impregnated into capacitor elements. 4,4'-dimethylbipyridinium or 4,
4′-isopropyl bipyridinium TCNQ complex salt is
As shown in Conventional Examples 3 and 4, even if the salt is heated and melted for use, thermal decomposition occurs before melting. Incidentally, 4,4'-dimethylbipyridinium TCNQ complex salt, 4,4'-isopropylbipyridinium TCNQ
When any of the complex salts is heated alone, it thermally decomposes with smoke emission at a temperature exceeding approximately 240°C, and after decomposition, the TCNQ complex salt turns into an insulator with high resistance. However, as can be seen from the examples, although there are differences depending on the type of additive and the mixing ratio, in each example of the present invention in which a lactone-based compound was added, it melted and liquefied at a low temperature of 200°C or less, and did not affect the capacitor element. Impregnation is now possible. In addition, when comparing the characteristics of solid electrolytic capacitors after impregnation, it is found that in conventional dry electrolytic capacitors using a liquid electrolyte as shown in Conventional Example 1, the electrolyte is held in a liquid state inside the capacitor element, so the anode expands. The electrolyte penetrates into the fine etching holes (pits) created by the etching process to create a surface.
It has sufficient contact with the dielectric oxide film and exhibits a high capacitance value. However, the specific resistance value of the electrolyte is as high as 200-300 Ω cm, whereas the specific resistance value of the TCNQ complex salt is about several tens of Ω cm, resulting in product loss or high equivalent series resistance. There is. In addition, the solid electrolytic capacitor impregnated with isopropyl-isoquinolinium TCNQ complex salt, which can be heat-melted and impregnated without adding additives, shown in Conventional Example 2,
Loss, equivalent series resistance value is TCNQ as mentioned above.
Since the specific resistance value of the complex salt is lower than that of the electrolyte, excellent characteristics are obtained, but sufficient capacitance is not obtained. Although the reason for this is not clear, the molten isopropyl-isoquinolinium TCNQ complex salt
Although it penetrates into the etching pit of the anode, during subsequent cooling and solidification, the isopropyl-isoquinolinium TCNQ complex crystallizes into needle-like crystals.
This is thought to be because contact with the dielectric oxide film in the etching pit 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. In this example, a capacitor element is constructed in which foil-shaped aluminum is used for the anode, and a dielectric oxide film is formed on the surface after surface expansion treatment, and a current collecting electrode is wound with a separator paper interposed. I used
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. In addition, 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. [Effect] As described above, according to the present invention, 4,4'-dimethylbipyridinium or 4,4'-isopropylpyridinium
It becomes possible to obtain a solid electrolytic capacitor having a solid electrolyte layer by impregnating a capacitor element by heating and melting TCNQ complex salt. 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 the anode metal, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer, the solid electrolyte layer comprising tetracyanoquinodimethane, 4, A solid electrolytic capacitor comprising a mixture of a complex salt of 4'-dimethylbipyridinium or 4,4'-isopropylbipyridinium and a lactone compound. 2 The lactone compound is γ-hexalactone,
The solid according to claim 1, which is one or more selected from the group of γ-octalactone, γ-nonalactone, γ-decalactone, γ-undecalactone, and γ-dodecalactone. Electrolytic capacitor.