JPH09293639A - Solid electrolytic capacitor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor, which is superior in electrical characteristics and is large in capacitance, by a method wherein a solid electrolyte layer consisting of conductive molecules, which are dense and even, is formed in the interior of a wound capacitor element, and a method of manufacturing the capacitor. SOLUTION: A capacitor element 10 formed by winding anode electrode foils 1 and cathode electrode foils 2 via separators 3 is impregnated with a mixed solution formed by mixing a 3,4-ethylene dioxy thiophene with an oxidiizng agent, whereby this mixed solution infiltrates up to the interior of the element 10 and a polyethylene dioxy thiophene layer, that is, a solid electrolyte layer is formed also in the interior of the element 10 by the, gentle polymerization of the 3,4-ethylene dioxy thiophene with the oxidizing agent, which is caused in the process of the infiltration of the mixed solution and after the infiltration.

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.

The electrode is pulled out from the oxide film layer by the 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 only serves to electrically connect this liquid electrolyte to an external terminal.

The electrolyte layer functioning as a true cathode is required to have adhesion, denseness, and uniformity with the oxide film layer.
In particular, the adhesiveness inside the fine holes of the anode electrode or inside the etching pit has a great influence on the electrical characteristics, and various electrolyte layers have been proposed in the past.

A solid electrolytic capacitor uses a solid electrolyte having conductivity instead of a liquid electrolyte lacking impedance characteristics in a high frequency region because it is ionic conductive. 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 a capacitor using such 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 was difficult to obtain satisfactory impedance characteristics. Further, the lead wires are damaged by the heat treatment, and it is necessary to separately provide an external terminal for connection as a post 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, the TCNQ complex has a property of being transferred to an insulator in a short time after being melted, which makes it 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.

A conductive polymer represented by polypyrrole is mainly produced by a chemical oxidative polymerization method (chemical polymerization) or an electrolytic oxidative polymerization method (electrolytic polymerization), but the chemical oxidative polymerization method has a high strength. It was difficult to form a film with high precision. On the other hand, in the electrolytic oxidative polymerization method, it is necessary to apply a voltage to an object that forms a film, and therefore it is difficult to apply it to an anode electrode for an electrolytic capacitor having an oxide film layer that is an insulator formed on the surface. , A method of forming a conductive precoat layer on the surface of the oxide film layer in advance, for example, a conductive polymer film chemically polymerized using an oxidizing agent as a precoat layer, and then forming an electrolyte layer by electrolytic polymerization using this precoat layer as an electrode Has been proposed (Japanese Patent Laid-Open No. 63-173).
313, JP-A-63-158829: Manganese dioxide is used as a precoat layer).

However, since the precoat layer is formed in advance, the manufacturing process becomes complicated, and in the electrolytic polymerization, the solid electrolyte layer is formed in the vicinity of the external electrode for polymerization arranged on the coated surface of the anode electrode. It was very difficult to continuously produce a conductive polymer film having a uniform thickness over a wide range.

Therefore, the foil-shaped anode and cathode electrodes are replaced by
By winding through a separator to form a so-called wound type capacitor element, an electrolyte layer made of a conductive polymer film formed only by chemical polymerization by dipping a monomer solution such as pyrrole and an oxidant into the capacitor element. Tried to form.

Such a wound-type capacitor element is well known in aluminum electrolytic capacitors. By holding the conductive polymer layer with a separator, the complexity of electrolytic polymerization is avoided and the surface area is also large. It was expected that the capacity would be expanded by using foil electrodes. 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.

Further, when the chemical polymerization is carried out at a low temperature, strict temperature control is required, and the manufacturing apparatus 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).

In the present invention, paying attention to the slow polymerization reaction rate of polyethylenedioxythiophene, a dense and uniform solid electrolyte layer made of a conductive polymer is formed inside a wound capacitor element. It is an object of the present invention to provide a large-capacity solid electrolytic capacitor having excellent electrical characteristics and a method for manufacturing the same.

[0019]

In the solid electrolytic capacitor of the present invention, a mixed solution prepared by mixing 3,4-ethylenedioxythiophene and an oxidizing agent is used as a separator, and a separator made of glass paper for an anode electrode foil and a cathode electrode foil is used. The polyethylene dioxythiophene produced by the polymerization reaction in the mixed solution which has been impregnated into the capacitor element wound through the separator and which has permeated the separator is held by the separator as an electrolyte layer.

As the oxidant, ferric p-toluenesulfonate dissolved in ethylene glycol is used.

In this solid electrolytic capacitor,
Instead of glass paper, a separator prepared by mixing paper with glass paper can be used. At this time, a separator having a paper mixing ratio of 80% or less is suitable.

In order to manufacture such a solid electrolytic capacitor, a mixed solution prepared by mixing 3,4-ethylenedioxythiophene and an oxidizing agent is used as a positive electrode foil and a negative electrode foil with glass paper or glass paper. A capacitor element wound with a paper-mixed separator is impregnated, and polyethylenedioxythiophene is produced by a polymerization reaction in the mixed solution that has permeated the separator.

Further, a mixed solution prepared by mixing 3,4-ethylenedioxythiophene and an oxidizing agent was wound around an anode electrode foil and a cathode electrode foil via glass paper or a separator made of a mixture of glass paper and paper. After impregnating the capacitor element, at 25 ℃ to 100 ℃ for 15 hours to 2
The polyethylene dioxythiophene is produced by repeating the step of standing for 4 hours at 50 ° C. for a predetermined number of times.

The mixing ratio of 3,4-ethylenedioxythiophene and the oxidizing agent is preferably in the range of 1: 3 to 1:15.

As described above, according to the present invention, a mixed solution prepared by mixing 3,4-ethylenedioxythiophene and an oxidizing agent in a capacitor element obtained by winding an anode electrode foil and a cathode electrode foil with the separator interposed therebetween. By impregnating the mixed solution, the mixed solution permeates into the inside of the capacitor element, and polyethylene dioxythiophene, by a gentle polymerization reaction of 3,4-ethylenedioxythiophene and an oxidizing agent that occurs during the permeation process and after the permeation. That is, the solid electrolyte layer is also formed inside the capacitor element, and the solid electrolyte layer is formed in a state of being held by the separator during the generation process.

[0026]

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, which comprises an anode electrode foil 1 made of a valve metal such as aluminum and having an oxide film layer formed on the surface thereof, and a cathode electrode foil 2, glass paper or glass paper and paper. The mixed element is wound through the separator 3 to form a capacitor element. Then, this capacitor element is impregnated with a mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent, and polyethylenedioxythiophene produced by a polymerization reaction in the mixed solution which has permeated the separator 3 is 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 foil 1 is roughened by an electrochemical etching process in a chloride aqueous solution to form a large number of etching pits. 8 forming. 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 a surface which is only subjected to etching treatment.

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 made of glass paper or a mixture of glass paper and paper such as manila paper or kraft paper. When a mixed separator is used, the paper mixing ratio per unit area is 80 paper. % Or less is desirable. Further, the thickness of the separator 3 may be arbitrary, but when a thick separator is used, the diameter dimension of the wound capacitor element 10 becomes large, and therefore 80 μm.
To 200 μm. The reason for using the glass separator or the separator 3 in which glass paper is mixed with paper is to suppress the oxidation reaction between the oxidizing agent and the separator 3 in the mixed solution with which the capacitor element 10 is impregnated and maintain the oxidizing ability of the oxidizing agent. This is for improving the permeability of the mixed solution.

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. The oxidizing agent used is ferric p-toluenesulfonate dissolved in ethylene glycol. The ratio of ethylene glycol to ferric p-toluenesulfonate in this oxidizing agent may be arbitrary, but in the present invention, the ratio is 1: 1. The mixing ratio of this oxidizing agent to 3,4-ethylenedioxythiophene is preferably in the range of 1: 3 to 1:15.

As a method of impregnating the capacitor element 10 with a mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent, a known means, for example, a reduced pressure impregnation method,
A pressure impregnation method or the like can be used.

[0034]

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.

(Embodiment 1) The anode electrode foil 1 and the cathode electrode foil 2 are made of a valve metal such as aluminum or tantalum, and the surface of the anode electrode foil 1 and the cathode electrode foil 2 is enlarged by the etching treatment in advance. 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 around 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
Has 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 structure is impregnated with a mixed liquid of 3,4-ethylenedioxythiophene and an oxidizing agent. As the oxidant, ferric iron p-toluenesulfonate dissolved in ethylene glycol was used.
The mixing ratio of 4-ethylenedioxythiophene and the oxidizing agent is preferably in the range of 1: 3 to 1:15.

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

Then, the capacitor element 10 impregnated with the mixed solution is pulled out from the impregnation tank and left at a polymerization temperature of 25 ° C. to 100 ° C. for 15 hours to 2 hours to form polyethylene dioxythiophene, that is, the solid electrolyte layer 5 by the polymerization reaction. To generate.

Regarding the ranges of the polymerization temperature and the standing time, among the electric characteristics of the manufactured solid electrolytic capacitor, the electrostatic capacity, tan δ and impedance characteristics are improved when the polymerization temperature is increased, but the leakage current characteristics are poor. Since there is a tendency that
It can be arbitrarily changed within the above range according to the specification of. At a polymerization temperature of 25 ° C for about 15 hours, 50 ° C
It is suitable to leave it for about 4 hours and at 100 ° C. for about 2 hours, and it is optimal to leave it 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.

Next, 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, and then at room temperature, 40% of the withstand voltage of the anode electrode foil 1 is applied. Through a so-called aging step of applying a voltage of about 60% to 60%, the series of steps for forming the solid electrolyte layer 5 is completed. The above-described solid electrolyte layer 5 producing step may be repeated a plurality of times as necessary.

In this way, 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, the solid electrolytic layer is formed by coating the outer periphery of the capacitor element 10 with an exterior resin, for example. Form a capacitor.

(Embodiment 2) A capacitor element 10 manufactured in the same manner as in Embodiment 1 described above was used as the separator 3, which was a mixture of glass paper and paper. The paper can be selected from Manila paper, kraft paper, etc., but in this example, Manila paper was used. The paper mixing ratio in weight per unit area is 80% or less when the paper is 80% or less.
.About.200 .mu.m was used.

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

[0046]

As is clear from these results, the solid electrolytic capacitor according to Example 1 is equivalent in capacitance, tan δ, etc., even in comparison with Comparative Example 2 in which polypyrrole is produced in the low temperature range, and has a withstand voltage characteristic. Show excellent characteristics.

Next, a solid electrolytic capacitor according to Example 2 and a solid electrolytic capacitor having a solid electrolyte layer made of polyethylenedioxythiophene produced by the same manufacturing method as in Example 2 as a comparative example Example 3) Manila paper was used as a separator, (Comparative Example 4) Manila paper was used as a separator at about 350 ° C to 40 ° C.
A comparison is made with carbonized paper carbonized at 0 ° C. Ten samples each were manufactured in the same manner as the above comparison, and the average value of the initial characteristics of each sample was measured. The results are shown below.

[0049]

As is clear from this result, in Comparative Example 3 using ordinary Manila paper, an oxidizing reaction occurs with the oxidizing agent in the mixed solution with which the capacitor element is impregnated, and the oxidizing ability of the oxidizing agent is lowered. As a result, the adhesion between the anode electrode foil and the oxide film layer is poor, and desired characteristics cannot be obtained in terms of capacitance and impedance characteristics. Also,
When the carbonized separator is used, the leakage current characteristic is significantly inferior in addition to the impedance characteristic.

[0051]

According to the present invention, a capacitor element obtained by winding an anode electrode foil and a cathode electrode foil with the separator interposed therebetween is impregnated with a mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent. By doing so, this mixed solution penetrates into the inside of the capacitor element. Then, polyethylene dioxythiophene, that is, a solid electrolyte layer is formed inside the capacitor element by a gentle polymerization reaction between 3,4-ethylenedioxythiophene and an oxidizing agent that occurs during the permeation process and after the permeation, and the solid electrolyte is also formed. The layer is held by the separator from its production process.
Therefore, 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, and especially in the withstand voltage characteristics, the characteristics of polyethylenedioxythiophene itself are also improved. Together, the improvement is remarkable compared to the conventional solid electrolytic capacitor using a conductive polymer in the solid electrolyte layer.

Further, in the capacitor element, since the anode electrode foil and the cathode electrode foil are wound with a constant tightening force via the separator, the anode electrode foil, the cathode electrode foil and the separator are brought into close contact with each other with a constant pressure. As a result, the solid electrolyte layer held by the separator is also adhered to the anode foil with a constant pressure. Therefore, the adhesion between the oxide film layer on the anode electrode foil and the solid electrolyte layer is improved, and desired electrical characteristics can be easily obtained.

When a separator made of glass paper or a mixture of glass paper and paper is used as the separator,
The mixed solution in which 3,4-ethylenedioxythiophene and the oxidant are mixed easily penetrates into the capacitor element, and polyethylenedioxythiophene is also produced inside the capacitor element. Therefore, the product characteristics are improved as a result.

Further, unlike the conventional manganese dioxide or TCNQ complex, heat treatment in a high temperature range is not carried out in the step of producing polyethylenedioxythiophene, so that damage to the oxide film layer is suppressed and product reliability is improved. In addition, the lead wire is not damaged by heat treatment and can be directly used as a terminal for external connection.

[Brief description of 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 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

[Procedure amendment]

[Submission date] September 24, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claim 9

[Correction method] Change

[Correction contents]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

As the oxidant, ferric p-toluenesulfonate dissolved in ethylene glycol is used.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction contents]

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

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01G 9/24 A

Claims (11)

[Claims] 1. A mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent is impregnated into a capacitor element obtained by winding an anode electrode foil and a cathode electrode foil through a separator made of glass paper, A solid electrolytic capacitor in which polyethylenedioxythiophene produced by a polymerization reaction in the mixed solution that permeates the separator is held by the separator as an electrolyte layer. 2. The solid electrolytic capacitor according to claim 1, wherein the oxidizing agent is ferric p-toluenesulfonate dissolved in ethylene glycol. 3. The solid electrolytic capacitor according to claim 1, wherein the electrolytic layer is held by a separator made of paper mixed with glass paper instead of glass paper. 4. The solid electrolytic capacitor according to claim 3, which is a separator having a paper mixing ratio of 80% or less. 5. A mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent is impregnated into a capacitor element in which an anode electrode foil and a cathode electrode foil are wound around a separator made of glass paper, A method for producing a solid electrolytic capacitor, characterized in that polyethylenedioxythiophene is produced by a polymerization reaction in the mixed solution that permeates the separator. 6. A capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator made of glass paper is impregnated with a mixed solution of 3,4-ethylenedioxythiophene and an oxidizing agent. 25 ℃ to 100 ℃
A method for manufacturing a solid electrolytic capacitor, characterized in that the step of leaving for 15 hours to 2 hours is repeated a predetermined number of times. 7. The solid electrolytic capacitor according to claim 6, wherein the mixed solvent obtained by mixing 3,4-ethylenedioxythiophene and the oxidizing agent is impregnated into the capacitor element and then left at 50 ° C. for 4 hours. Manufacturing method. 8. The method for producing a solid electrolytic capacitor according to claim 5, wherein the mixing ratio of 3,4-ethylenedioxythiophene and the oxidizing agent is 1: 3 to 1:15. 9. The method for producing a solid electrolytic capacitor according to claim 5, wherein the oxidizing agent is ferric p-toluenesulfonate dissolved in ethylene glycol. 10. The method for producing a solid electrolytic capacitor according to claim 5, wherein a separator made by mixing paper into glass paper is used instead of glass paper. 11. A method for producing a solid electrolytic capacitor according to claim 10, wherein the separator has a paper mixing ratio of 80% or less.