JP2001110685A - Solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a large capacitance solid electrolytic capacitor with superior electrical characteristics by forming a precise and a uniform solid electrolyte layer made of conductive polymer in a wound capacitor element. SOLUTION: An anode foil 1 and a cathode foil 2 are wound with separators 3 therebetween, to compose a capacitor element 10. The separators 3 are impregnated with 3,4-ethylene dioxythiophene and oxidizing agent, which forms polyethylene dioxythiophene electrolyte layers supported by the separators 3 through polymerization reaction. The solid electrolyte layers are formed by gentle polymerization reaction during, and after the impregnation process of 3,4-ethylene dioxythiophene and oxidizaing agent, and further the solid electrolyte layers are supported by the separators from the beginning of their formation process, so that precise and uniform solid electrolyte layers can be formed in the capacitor element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

[0002]

2. Description of the Related Art An electrolytic capacitor is formed by forming an oxide film layer serving as a dielectric on the surface of an anode electrode made of a valve metal such as tantalum or aluminum and having fine holes and etching pits. Is drawn out.

[0003] The extraction of the electrode from the oxide film layer is performed by a conductive electrolyte layer. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. For example, in an aluminum electrolytic capacitor, a liquid electrolyte is used as a true electrode, and a cathode electrode merely serves to electrically connect the liquid electrolyte to an external terminal.

[0004] The electrolyte layer functioning as a true cathode is required to have adhesion, denseness, uniformity, etc. with the oxide film layer.
In particular, the adhesion in the fine holes of the anode electrode and the inside of the etching pits has a great effect on the electrical characteristics, and a number of electrolyte layers have been proposed.

The solid electrolytic capacitor uses a solid electrolyte having conductivity instead of a liquid electrolyte which lacks impedance characteristics in a high frequency range because of ionic conduction. Among them, manganese dioxide, 7, 7, and 8 are used. , 8-
Tetracyanoquinodimethane (TCNQ) complexes are known.

[0006] The solid electrolyte layer made of manganese dioxide is
The anode element made of a sintered body of tantalum is immersed in an aqueous solution of manganese nitrate, and is produced by thermal decomposition at a temperature of about 300 to 400 ° C. In such a capacitor using a solid electrolyte layer, the oxide film layer is easily damaged during the thermal decomposition of manganese nitrate, which tends to increase the leakage current, and the specific resistance of manganese dioxide itself is high. It has been difficult to obtain sufficiently satisfactory impedance characteristics. In addition, the lead wire was damaged by the heat treatment, and it was necessary to separately provide an external terminal for connection as a later process.

As a solid electrolytic capacitor using a TCNQ complex, one disclosed in Japanese Patent Application Laid-Open No. 58-191414 is known. An electrolyte layer is formed. This TCNQ complex has high conductivity and can obtain good results in frequency characteristics and temperature characteristics.

However, since the TCNQ complex has a property of being transferred to an insulator in a short time after being melted, it is difficult to control the temperature in the manufacturing process of the capacitor. A remarkable characteristic change is seen due to solder heat at the time of mounting.

In order to solve the disadvantages of the manganese dioxide and the TCNQ complex, attempts have been made to use a conductive polymer such as polypyrrole as the solid electrolyte layer.

The conductive polymer represented by polypyrrole is mainly produced by a chemical oxidative polymerization method (chemical polymerization) or an electrolytic oxidative polymerization method (electrolytic polymerization). It was difficult to form a film densely. On the other hand, in the electrolytic oxidation polymerization method, it is necessary to apply a voltage to an object to form a film, and therefore, it is difficult to apply the method to an anode electrode for an electrolytic capacitor having an oxide film layer as an insulator formed on the surface. A method in which an electroconductive precoat layer, for example, a conductive polymer film chemically polymerized using an oxidizing agent is used as a precoat layer on the surface of the oxide film layer, and then an electrolyte layer is formed by electrolytic polymerization using the precoat layer as an electrode. And the like have been proposed (JP-A-63-173).
313, JP-A-63-158829: Manganese dioxide is used as the precoat layer).

However, the manufacturing process becomes complicated because the pre-coat layer is formed in advance, and in the electrolytic polymerization, a solid electrolyte layer is generated from the vicinity of the external electrode for polymerization arranged on the surface of the anode electrode to be coated. It has been very difficult to continuously produce a conductive polymer film having a uniform thickness over a wide range.

Therefore, a foil-like anode electrode and a cathode electrode are
An electrolyte layer made of a conductive polymer film formed only by chemical polymerization by immersing a monomer solution such as pyrrole and an oxidizing agent into this capacitor element by winding it up through a separator to form a so-called winding type capacitor element Tried to form

[0013] Such a wound type capacitor element is well known for an aluminum electrolytic capacitor, but by holding a conductive polymer layer with a separator, it is possible to avoid the complication of electrolytic polymerization and also to increase the surface area. It was expected that the capacity would be expanded by the foil-like electrode. Furthermore,
It was expected that the use of a wound-type capacitor element would maintain both electrodes and the separator with a constant tightening force and contribute to the adhesion between the electrodes and the electrolyte layer.

[0014]

However, when a capacitor element is impregnated with a mixed solution obtained by mixing a monomer solution and an oxidizing agent, a solid electrolyte layer is not formed even inside the capacitor element, and the expected electric power is not obtained. It turned out that the characteristic could not be obtained.

Therefore, when the monomer solution and the oxidizing agent are separately impregnated or the polymerization temperature of the solution at the time of the reaction is lowered, good electrical properties are obtained to some extent, but only the pressure resistance is insufficient. There was a problem. The cause is that even with these means, the solid electrolyte layer generated near the end face of the capacitor element hinders the subsequent permeation of the solution, and a sufficient solution has not penetrated into the inside,
As a result, it was considered that the reason was that a dense and uniform solid electrolyte layer was not formed.

In addition, when chemical polymerization is carried out at a low temperature, strict temperature control is required, and the production equipment becomes complicated, resulting in an increase in product cost.

On the other hand, as a result of repeated studies on various conductive polymers, attention was paid to polyethylenedioxythiophene (PEDT), which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode ( JP-A-2-1561
No. 1).

The present invention focuses on the fact that the polymerization reaction rate of polyethylenedioxythiophene is slow, and forms a solid electrolyte layer made of a dense and uniform conductive polymer inside a wound capacitor element, An object of the present invention is to provide a solid electrolytic capacitor having excellent electric characteristics and a large capacity, and a method for manufacturing the same.

[0019]

A solid electrolytic capacitor according to the present invention comprises a capacitor element in which an anode electrode foil and a cathode electrode foil are wound with a separator interposed therebetween, and 3,4-ethylenedioxythiophene permeated into the separator. It is characterized in that polyethylenedioxythiophene produced by a polymerization reaction between the polymer and an oxidizing agent is held by a separator as an electrolyte layer.

[0020] Ferric p-toluenesulfonate is used as the oxidizing agent.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a solid electrolytic capacitor of the present invention, in which an anode electrode foil 1 made of a valve metal such as aluminum and having an oxide film layer formed on its surface, and a cathode electrode foil 2 are wound via a separator 3. Form a capacitor element. Then, the capacitor element is impregnated with a mixed solution obtained by mixing 3,4-ethylenedioxythiophene and an oxidizing agent, and the polyethylenedioxythiophene generated by a polymerization reaction in the mixed solution that has permeated the separator 3 is applied to the solid electrolyte layer. 5 is held by the separator 3.

The anode electrode foil 1 is made of a valve metal such as aluminum. As shown in FIG. 2, the surface of the anode electrode foil 1 is roughened by electrochemical etching in a chloride aqueous solution to form a large number of etching pits. 8 are formed. Further, on the surface of the anode electrode foil 1, a voltage is applied in an aqueous solution of ammonium borate or the like to form an oxide film layer 4 serving as a dielectric.

The cathode electrode foil 2 is made of aluminum or the like, similarly to the anode electrode foil 1, and has only a surface subjected to etching.

Lead wires 6 and 7 for connecting the respective electrodes to the outside are connected to the anode electrode foil 1 and the cathode electrode foil 2 by known means such as stitching and ultrasonic welding. The lead wires 6 and 7 are made of aluminum or the like,
It comprises an external connection portion for electrically connecting the connection portion between the anode electrode foil 1 and the cathode electrode foil 2 and the outside, and is led out from the end face of the wound capacitor element 10.

The capacitor element 10 is formed by winding the above-mentioned anode electrode foil 1 and cathode electrode foil 2 with the separator 3 interposed therebetween. The dimensions of the bipolar electrode foils 1 and 2 are arbitrary according to the specifications of the solid electrolytic capacitor to be manufactured, and the separator 3 may have a width slightly larger than this according to the dimensions of the bipolar electrode foils 1 and 2. .

3,4-ethylenedioxythiophene is
It can be obtained by a known production method disclosed in JP-A-2-15611 and the like. As the oxidizing agent, ferric p-toluenesulfonate dissolved in ethylene glycol is used. The ratio of ethylene glycol to ferric p-toluenesulfonate in this oxidizing agent may be arbitrary, but in the present invention, a ratio of 1: 1 is used. The mixing ratio of the oxidizing agent to 3,4-ethylenedioxythiophene is preferably in the range of 1: 3 to 1:15.

[0027]

Next, the solid electrolytic capacitor according to the present invention will be specifically described.

The anode electrode foil 1 and the cathode electrode foil 2 are made of a valve metal, for example, aluminum or tantalum, and the surfaces thereof have been subjected to an etching treatment in advance to increase the surface area. The anode electrode foil 1 is further subjected to a chemical conversion treatment to form an oxide film layer 4 made of aluminum oxide on the surface.

The anode electrode foil 1 and the cathode electrode foil 2 are wound via a separator 3 made of glass paper having a thickness of 80 to 200 μm to obtain a capacitor element 10.

In this embodiment, the capacitor element 10
Is used having a diameter of 4φ and a vertical dimension of 7 mm. Note that lead wires 6 and 7 are electrically connected to the anode electrode foil 1 and the cathode electrode foil 2 of the capacitor element 10, respectively, and protrude from the end face of the capacitor element 10.

The capacitor element 10 having the above configuration is impregnated with a mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent. As the oxidizing agent, ferric p-toluenesulfonate dissolved in ethylene glycol was used.
The mixing ratio of 4-ethylenedioxythiophene to the oxidizing agent is preferably in the range of 1: 3 to 1:15.

In the impregnation, the capacitor element 10 is immersed in an impregnation tank storing a fixed amount of the mixed solution, and the pressure is reduced if necessary.

Next, the capacitor element 10 impregnated with the mixed solution is pulled up from the impregnation tank, and left at a polymerization temperature of 25 ° C. to 100 ° C. for 15 hours to 2 hours to remove the polyethylene dioxythiophene, ie, the solid electrolyte layer 5 by the polymerization reaction. Generate.

The ranges of the polymerization temperature and the standing time are as follows. As the polymerization temperature increases, the electric capacity, tan δ, and impedance characteristics among the electrical characteristics of the manufactured solid electrolytic capacitor improve, but the leakage current characteristics deteriorate. Is observed, the capacitor element 10 to be manufactured is
Can be arbitrarily changed within the above range in accordance with the specifications. In addition, about 15 hours at a polymerization temperature of 25 ° C, 50 ° C
For about 4 hours at 100 ° C. and about 2 hours at 100 ° C., it was optimal to leave at a temperature of 50 ° C. for 4 hours in consideration of the coating state of the solid electrolyte layer 5 and the process time.

Then, the capacitor element is washed with water, an organic solvent or the like for about 120 minutes and dried at 100 ° C. to 180 ° C. for about 30 minutes. Thereafter, at room temperature, 40% of the withstand voltage of the anode electrode foil 1 is obtained. Through a so-called aging step in which a voltage of about 60% is applied, a series of steps of forming the solid electrolyte layer 5 is completed. Note that the above-described step of forming the solid electrolyte layer 5 may be repeated a plurality of times as necessary.

The capacitor element 10 in which the solid electrolyte layer 5 is formed on the separator 3 interposed between the anode electrode foil 1 and the cathode electrode foil 2 as described above, for example, by coating the outer periphery with an exterior resin, Form a capacitor.

Next, the electrical characteristics of the solid electrolytic capacitor according to the above embodiment and the conventional solid electrolytic capacitor will be compared. As a comparative example, a capacitor element having the same configuration as in the example was used, and (Comparative Example 1) a capacitor element was impregnated with a monomer solution composed of pyrrole and an oxidizing agent at room temperature to form a solid electrolyte layer. (Comparative Example 2) A monomer solution composed of pyrrole and an oxidizing agent at -10 ° C
At a low temperature, the capacitor element was impregnated to form a solid electrolyte layer. Ten samples were manufactured for each, and the average value of each initial characteristic was measured. The results are shown below.

[0038]

As is clear from these results, the solid electrolytic capacitor according to the example has the same capacitance, tan δ, and the like as compared with Comparative Example 2 in which polypyrrole was produced in a low temperature range, and has a withstand voltage characteristic. Shows excellent properties

[0040]

According to the present invention, a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator,
Impregnate 4-ethylenedioxythiophene with an oxidizing agent. And the process of infiltration and occurring after infiltration 3,
Polyethylenedioxythiophene, that is, a solid electrolyte layer is formed inside the capacitor element by a mild polymerization reaction of 4-ethylenedioxythiophene and an oxidizing agent, and the solid electrolyte layer is held by a separator from the formation process. As a result, a dense and uniform solid electrolyte layer can be formed even inside the capacitor element, and as a result, the electrical characteristics of the solid electrolytic capacitor are improved.In particular, the withstand voltage characteristics are the same as those of polyethylene dioxythiophene itself. Together, the improvement is remarkable as compared with a conventional solid electrolytic capacitor using a conductive polymer for a solid electrolyte layer.

Further, in the capacitor element, since the anode electrode foil and the cathode electrode foil are wound up with a constant tightening force via the separator, the anode electrode foil, the cathode electrode foil and the separator adhere to each other at a constant pressure. As a result, the solid electrolyte layer held by the separator is also in close contact with the anode electrode foil at a constant pressure. Therefore, the adhesion between the oxide film layer on the anode electrode foil and the solid electrolyte layer is improved, and it becomes easy to obtain desired electrical characteristics.

Furthermore, in the step of producing polyethylene dioxythiophene, heat treatment in a high temperature range is not performed unlike the conventional manganese dioxide and TCNQ complex, so that damage to the oxide film layer is suppressed, and the reliability of the product is reduced. In addition, the lead wire can be used as an external connection terminal without damage to the lead wire due to heat treatment.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a capacitor element used in the present invention.

FIG. 2 is a partially enlarged view of an anode electrode foil used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode electrode foil 2 Cathode electrode foil 3 Separator 4 Oxide film layer 5 Solid electrolyte layer 6, 7 Lead wire 8 Etching pit 10 Capacitor element

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[Procedure amendment]

[Submission date] September 14, 2000
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

[0038]

Claims (2)

[Claims] 1. A capacitor element comprising an anode electrode foil and a cathode electrode foil wound around a separator, and polyethylenedioxy produced by a polymerization reaction of 3,4-ethylenedioxythiophene permeated into the separator and an oxidizing agent. A solid electrolytic capacitor in which thiophene is held as an electrolyte layer by a separator. 2. The solid electrolytic capacitor according to claim 1, wherein the oxidizing agent is ferric p-toluenesulfonate.