JP2001237147A - Solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid-state electrolytic capacitor in which a solid-state electrolytic layer composed of fine uniform conductive high molecules is formed into a winding type capacitor element and which has excellent electrical characteristics and large capacitance. SOLUTION: A capacitor element 10 in which an anode electrode foil 1 and a cathode electrode foil 2 are wound through separators 3 is impregnated with a polymerizable monomer and an oxidizing agent having concentration exceeding 40 wt.% to a solvent, and conductive high molecules formed by a chemical polymerization reaction are held by the separators 3. The degree of polymerization is improved by the oxidizing agent, and the solid electrolytic layer consisting of fine uniform conductive high molecules is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, 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.

[0010] The conductive polymer represented by polypyrrole is mainly produced by a chemical oxidation polymerization method (chemical polymerization) or an electrolytic oxidation polymerization method (electrolysis polymerization). Was difficult to produce. On the other hand, in the case of electrolytic polymerization, it is necessary to apply a voltage to an object on which a film is to be formed, 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. On the surface of the coating layer, there is a method in which a conductive precoat layer, for example, a conductive polymer film chemically polymerized using an oxidizing agent is used as a precoat layer, and then the electrolyte layer is formed by electrolytic polymerization using the precoat layer as an electrode. It has been proposed (JP-A-63-173313,
JP-A-63-158829: Manganese dioxide is used as a 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 consisting of a conductive polymer film formed only by chemical polymerization by impregnating 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.

However, when a capacitor element is impregnated with a mixed solution obtained by mixing a monomer solution and an oxidizing agent, the solid electrolyte layer is not formed inside the capacitor element, and the expected electrical characteristics cannot be obtained. It turned out to be impossible.

[0015]

Therefore, when the monomer solution and the oxidizing agent were separately impregnated or the polymerization temperature of the solution during the reaction was lowered, good electrical characteristics could be obtained to some extent. There has been a demand for a solid electrolytic capacitor having more excellent electric characteristics, and it is still not satisfactory in ESR characteristics. In addition, because the variation in capacitance and life characteristics is still large, the cause is that the degree of polymerization of the conductive polymer is still insufficient, and the solid electrolyte layer in the capacitor element is sufficiently dense and uniform. It may not have been done.

Therefore, the present invention provides a method for forming a solid electrolyte layer in a capacitor element in a dense and uniform manner, thereby improving the ES.
The purpose is to improve the R characteristic. for that reason,
The present inventor has conducted experimental studies, and as a result of using an oxidizing agent having a certain concentration or more, it is possible to sufficiently cause a polymerization reaction in a capacitor element, and thus it is possible to form a dense and uniform solid electrolyte layer. I got the knowledge.

[0017]

According to the present invention, an oxidizing agent having a concentration exceeding 40% by weight based on a polymerizable monomer and a solvent is provided on a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator. And a conductive polymer produced by a chemical polymerization reaction by impregnation with the above is held by a separator.

[0018]

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 made of a non-woven fabric mainly composed of vinylon fibers. The capacitor element 10 is formed by being wound with the separator 3 interposed therebetween.
The capacitor element 10 is impregnated with a polymerizable monomer, 3,4-ethylenedioxythiophene, and an oxidizing agent in a solvent, and is a conductive polymer, polyethylene, formed by a chemical polymerization reaction in the capacitor element 10. Dioxythiophene is held by the separator 3 as a solid electrolyte layer 5.

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 in the same manner as 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 separator 3 is a non-woven fabric mainly composed of vinylon fibers. In addition, a non-woven fabric obtained by mixing vinylon fibers with paper fibers such as glass fibers, polyester fibers, nylon fibers, rayon fibers, and manila paper is used. Can also. The nonwoven fabric has a basis weight of 6 to 36 g / m ² ,
Fiber diameter 5-30 μm, thickness 30-150 μm, density 0.
Those having a density of 2 to 0.5 g / cm ³ are used.

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 as a polymerizable monomer can be obtained by a known production method disclosed in Japanese Patent Application Laid-Open No. 2-15611. Further, an oxidizing agent such as ferric p-toluenesulfonate dissolved in a solvent such as butanol was used, and good results were obtained when the oxidizing agent had a concentration exceeding 40% by weight based on the solvent. Although the reason is not clear, it is considered that a high concentration of the oxidizing agent promotes the chemical polymerization reaction to increase the degree of polymerization, and as a result, the conductivity of the solid electrolyte layer made of a conductive polymer is improved.

The distribution of the oxidizing agent to the solvent is 40% by weight.
However, if the concentration exceeds 40% by weight, sufficient capacitance characteristics and ESR characteristics cannot be obtained. Further, the substantial upper limit is about 60% by weight, and the oxidizing agent exceeding the upper limit makes the synthesis extremely difficult. A range of 50% by weight to 55% by weight is desirable as a range in which desired characteristics can be obtained and synthesis is easy.

[0026]

Next, a method for manufacturing a solid electrolytic capacitor according to the present invention and a solid electrolytic capacitor obtained by the method 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 their surfaces are subjected to an etching process 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 a non-woven fabric mainly composed of vinylon fibers to obtain a capacitor element 10.

In this embodiment, the capacitor element 10
Has a diameter of 4φ, a vertical dimension of 7 mm, a rated voltage of 6.3 WV, and a rated capacitance of 33 μF. 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.
It protrudes from the end face of the capacitor element 10.

Next, the capacitor element 10 is impregnated with 3,4-ethylenedioxythiophene as a polymerizable monomer and an oxidizing agent. The oxidizing agent uses butanol as a solvent,
P dissolved in the butanol in a distribution of 52% by weight
Using ferric toluenesulfonate to impregnate 3,4-ethylenedioxythiophene with an oxidizing agent at a ratio of 1: 5 to produce polyethylenedioxythiophene, which is a solid electrolyte made of a conductive polymer;

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

Next, in the solid electrolytic capacitor according to the embodiment, a change in characteristics due to the blending of the oxidizing agent in the solvent will be described. Here, butanol was used as a solvent for the capacitor element according to the example, and the butanol contained 40% by weight or less.
Ferric p-toluenesulfonate dissolved in a distribution of 60% by weight was used as oxidizing agent. The results are shown below.

[0031]

[Table 1]

As is clear from Table 1, 4
With an oxidizing agent dissolved at 0% by weight, sufficient ESR characteristics cannot be obtained, and the capacitance characteristics are only about 93% of the rated capacitance. On the other hand, when the oxidizing agent has a concentration of more than 40% by weight, the ESR characteristics are remarkably improved, and it is understood that the solid electrolyte layer in the capacitor element is dense and uniform.

[0033]

According to the present invention, a conductive polymer produced by a chemical polymerization reaction between a polymerizable monomer and an oxidizing agent having a concentration exceeding 40% by weight with respect to a solvent is held as a solid electrolyte by a separator. Therefore, the solid electrolyte layer made of a conductive polymer inside the capacitor element is dense and uniform, and as a result, a solid electrolytic capacitor having excellent ESR characteristics can be obtained.

[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 conceptual diagram 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

Claims (1)

[Claims] 1. A method in which a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator is impregnated with a polymerizable monomer and an oxidizing agent having a concentration of more than 40% by weight with respect to a solvent. A solid electrolytic capacitor in which a conductive polymer generated by the reaction is held by a separator.