JP2022144218A - Electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

To suppress the occurrence of a short circuit and suppress an increase in ESR when an overvoltage or the like is applied to an electrolytic capacitor.SOLUTION: A capacitor element 5 of an electrolytic capacitor includes a positive electrode 11 having a dielectric oxide film, a negative electrode 12, a separator 13, and a first conductive polymer layer and a second conductive polymer layer formed between the dielectric oxide film and the separator 13. In the dielectric oxide film, the contact area with the first conductive polymer layer is larger than the contact area with the second conductive polymer layer. The polymer contained in the first conductive polymer layer and the polymer contained in the second conductive polymer layer are the same. The boiling point of the first dopant contained in the first conductive polymer layer is lower than the boiling point of the second dopant contained in the second conductive polymer layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electrolytic capacitor and its manufacturing method.

As an electrolytic capacitor, a capacitor element having an anode having a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode, an exterior case containing the capacitor element, and an opening of the exterior case being sealed. There is known an electrolytic capacitor provided with a sealing member (sealing means) for sealing (see Patent Document 1).

In Patent Document 1, at least the round bar portion for penetrating the sealing member and the welded portion of the electrode lead-out means connected to the anode are coated with polyimide silicon in advance, and then a solid body is formed between both electrodes of the capacitor element. It forms an electrolyte layer. This suppresses the occurrence of a short when the solid electrolyte adheres to the welded portion.

JP-A-2004-296931

The electrolytic capacitor described above is coated with polyimide silicon, which is an insulator, before the solid electrolyte layer is formed. Therefore, when an overvoltage or the like is applied, the occurrence of a short circuit can be suppressed, but the insulator acts as a resistance. Therefore, the equivalent series resistance (ESR) of the electrolytic capacitor increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic capacitor capable of suppressing the occurrence of a short circuit and suppressing an increase in ESR when an overvoltage or the like is applied to the electrolytic capacitor, and a method of manufacturing the same.

An electrolytic capacitor of the present invention includes a capacitor element having an anode having a dielectric oxide film, a cathode, a separator disposed between the anode and the cathode, and an exterior body housing the capacitor element. wherein the capacitor element has a first conductive polymer layer and a second conductive polymer layer formed between the dielectric oxide film and the separator; The contact area of the first conductive polymer layer with the dielectric oxide film is larger than the contact area of the second conductive polymer layer with the dielectric oxide film, and The layer contains a polymer and a first dopant, and the second conductive polymer layer contains the same polymer as the polymer contained in the first conductive polymer layer and a second dopant. wherein the boiling point of the first dopant is lower than the boiling point of the second dopant.

The findings of the present inventors have revealed the following.
According to the above configuration, the boiling point of the first dopant contained in the first conductive polymer layer, which has a large contact area with the dielectric oxide film, is higher than the boiling point of the second dopant contained in the second conductive polymer layer. low. When overvoltage or the like is applied to the electrolytic capacitor, the first dopant contained in the first conductive polymer layer decomposes faster than the second dopant. As a result, the first conductive polymer layer, which has a large contact area with the dielectric oxide film, loses its conductivity faster than the second conductive polymer layer and becomes insulated. As a result, it was found that the occurrence of short circuits was suppressed.
On the other hand, the second conductive polymer layer, which has a small contact area with the dielectric oxide film, is more difficult to insulate than the first conductive polymer layer. Therefore, the second conductive polymer layer does not easily become a resistor. As a result, it was found that the ESR of the electrolytic capacitor hardly increased even when overvoltage was applied.
As described above, according to the present invention, it is possible to provide an electrolytic capacitor that can suppress the occurrence of a short circuit and suppress an increase in ESR when an overvoltage or the like is applied.

In the above configuration, it is preferable that the weight of the polymer in the second conductive polymer layer is larger than the weight of the polymer in the first conductive polymer layer.

According to the above configuration, in the first conductive polymer layer and the second conductive polymer layer, the weight of the polymer in the second conductive polymer layer, which is difficult to insulate, increases the weight of the polymer in the first conductive polymer layer, which is easy to insulate. greater than the weight of the polymer in the flexible polymer layer. This indicates that there are relatively many polymers in the second conductive polymer layer that are less likely to become resistance. Therefore, even if overvoltage is applied, the ESR of the electrolytic capacitor is less likely to increase.

A method of manufacturing an electrolytic capacitor according to the present invention includes a first step of winding an anode and a cathode having a dielectric oxide film with a separator interposed therebetween to form a capacitor element, and at least the dielectric oxide film of the capacitor element. a second step of forming a first conductive polymer layer between the separator and the second step of forming a second conductive polymer layer on the capacitor element on which the first conductive polymer layer is formed; and a fourth step of housing the capacitor element having the second conductive polymer layer formed thereon in an outer package, wherein the second step includes at least a first monomer and a first dopant. After the capacitor element is immersed in the first liquid and pulled out, the first conductive polymer layer is formed by heat treatment, and the third step includes using at least the same second monomer as the first monomer. After the capacitor element having the first conductive polymer layer formed thereon is immersed in a second liquid containing a second dopant and pulled out, the second conductive polymer layer is formed by heat treatment. The boiling point of one dopant is lower than the boiling point of the second dopant.

According to the above configuration, the first conductive polymer layer formed earlier has a larger contact area with the dielectric oxide film than the second conductive polymer layer formed later. The boiling point of the first dopant contained in the first conductive polymer layer, which has a large contact area with the dielectric oxide film, is lower than the boiling point of the second dopant contained in the second conductive polymer layer. Therefore, when overvoltage or the like is applied to the electrolytic capacitor, the first dopant contained in the first conductive polymer layer decomposes faster than the second dopant. As a result, the first conductive polymer layer, which has a large contact area with the dielectric oxide film, loses its conductivity faster than the second conductive polymer layer and becomes insulated. As a result, it was found that the occurrence of short circuits was suppressed.
On the other hand, in the dielectric oxide film, the second conductive polymer layer having a small contact area is more difficult to insulate than the first conductive polymer layer. Therefore, the second conductive polymer layer does not easily become a resistor. As a result, it was found that the ESR of the electrolytic capacitor hardly increased even when overvoltage was applied.
As described above, according to the present invention, it is possible to provide an electrolytic capacitor that can suppress the occurrence of a short circuit and suppress an increase in ESR when an overvoltage or the like is applied.

In the above configuration, it is preferable that the concentration of the second monomer in the second liquid is higher than the concentration of the first monomer in the first liquid.

According to the above configuration, the weight of the polymer in the second conductive polymer layer formed by the second liquid is greater than the weight of the polymer in the first conductive polymer layer formed by the first liquid. growing. As a result, the amount of polymer in the second conductive polymer layer, which does not readily become resistance, is relatively large. Therefore, even if overvoltage is applied, the ESR of the electrolytic capacitor is less likely to rise.

In the above configuration, it is preferable that the second liquid further contains iron ions, and the molar ratio of the second dopant to the iron ions contained in the second liquid is 2.6 or more and 3.0 or less.

With the above configuration, it is possible to provide an electrolytic capacitor with low initial ESR before overvoltage or the like is applied.

In the above configuration, it is preferable that the first liquid further contains iron ions, and the molar ratio of the first dopant to the iron ions contained in the first liquid is 2.6 or more and 3.4 or less.

With the above configuration, it is possible to provide an electrolytic capacitor with high capacitance and low leakage current.

According to the present invention, it is possible to provide an electrolytic capacitor that can suppress the occurrence of a short circuit and suppress an increase in ESR when an overvoltage or the like is applied to the electrolytic capacitor.

1 is a front view of a main part cut away of an electrolytic capacitor according to an embodiment of the present invention; FIG. FIG. 2 is an exploded perspective view of the capacitor element shown in FIG. 1;

Preferred embodiments of the present invention will be described below with reference to the drawings.

The electrolytic capacitor 1, as shown in FIG. .

As shown in FIG. 2, the capacitor element 5 is formed by winding an anode 11 and a cathode 12 through a separator 13 in a cylindrical shape, and the winding is stopped by a tape 14 attached to the outer peripheral surface.

Lead tabs (not shown) are connected to the anode 11 and the cathode 12, respectively. Anode 11 is connected to lead terminal 21 via a lead tab. Cathode 12 is connected to lead terminal 22 via a lead tab. The lead terminals 21 and 22 are led out to the outside through holes 31 and 32 formed in the sealing member 3, respectively, as shown in FIG.

The anode 11 shown in FIG. 2 is a valve action metal having a dielectric oxide film formed on its surface. Examples of valve metals include at least one selected from the group consisting of aluminum, tantalum, niobium and titanium. The dielectric oxide film is formed, for example, by roughening the surface of the foil of the valve metal by etching and then subjecting it to chemical conversion treatment.

Cathode 12 is formed using a valve metal. As the cathode 12, for example, a foil obtained by roughening the surface of a valve metal foil by etching, or a foil obtained by subjecting the roughened surface to a chemical conversion treatment is used. As the cathode 12, a plain foil that is not etched may be used. Furthermore, at least one selected from the group consisting of titanium, nickel, titanium carbide, nickel carbide, titanium nitride, nickel nitride, titanium carbonitride and nickel carbonitride is coated on the surface of the roughened foil or plain foil. A coating foil on which a metal thin film containing the seed metal is formed may be used. Also, a coating foil obtained by forming a carbon thin film on the surface of a roughened foil or a plain foil may be used.

The material of the separator 13 is not particularly limited. As the separator 13, for example, a material mainly composed of cellulose may be used.

Capacitor element 5 has a first conductive polymer layer and a second conductive polymer layer at least between the dielectric oxide film of anode 11 and separator 13 . The contact area between the first conductive polymer layer and the dielectric oxide film is larger than the contact area between the second conductive polymer layer and the dielectric oxide film. The contact area between the second conductive polymer layer and the dielectric oxide film is preferably 50% or more of the contact area between the first conductive polymer layer and the dielectric oxide film. The first conductive polymer layer and the second conductive polymer layer may be formed on portions other than between the dielectric oxide film of anode 11 and separator 13 .

In the form in which the first conductive polymer layer and the second conductive polymer layer exist, the contact area of the first conductive polymer layer with respect to the dielectric oxide film is that of the second conductive polymer layer. It is not particularly limited as long as it is larger than the contact area. For example, a first conductive polymer layer may be formed on the dielectric oxide film, and a second conductive polymer layer may be formed on the first conductive polymer layer. A first conductive polymer layer and a second conductive polymer layer may be present on the dielectric oxide film. A second conductive polymer layer may exist between the first conductive polymer layers. The "layer" here may or may not be flat.

The first conductive polymer layer includes a polymer and a first dopant. A polymer is not limited to a specific one. Molecules include, for example, polyethylenedioxythiophene (PEDOT), polythiophene, polypyrrole, polyaniline, or derivatives thereof. The first dopant is not limited to a specific one. Examples of the first dopant include p-toluenesulfonic acid, polystyrenesulfonic acid (PSS), ethanesulfonic acid, and benzenesulfonic acid.

The first conductive polymer layer may further contain an oxidizing agent containing iron. Examples of iron-containing oxidizing agents include ferric p-toluenesulfonate and ferric benzenesulfonate. The oxidizing agent is used, for example, to chemically oxidatively polymerize monomers when forming the first conductive polymer layer. The first conductive polymer layer may separately contain an iron-containing oxidizing agent and a dopant, or may contain a compound of iron and the acid of the dopant. A compound of iron and a dopant acid functions as both an oxidant and a dopant.

The second conductive polymer layer includes a polymer and a second dopant. The polymer contained in the second conductive polymer layer is the same polymer as the polymer contained in the first conductive polymer layer. Here, "the same polymer as the polymer contained in the first conductive polymer layer" is obtained by polymerizing the same monomer as the polymer contained in the first conductive polymer layer. It is a polymer. If the monomers are the same, that is, if "the polymer monomer contained in the first conductive polymer layer" and "the polymer monomer contained in the second conductive polymer layer" are the same. For example, whether the "degree of polymerization of the polymer contained in the first conductive polymer layer" and the "degree of polymerization of the polymer contained in the second conductive polymer layer" are the same or different, "The polymer contained in the first conductive polymer layer" and "the polymer contained in the second conductive polymer layer" are the same.

The second dopant is not limited to a specific one. Examples of the second dopant include p-toluenesulfonic acid, polystyrenesulfonic acid (PSS), and benzenesulfonic acid.

The second conductive polymer layer may further contain an oxidizing agent containing iron. Examples of iron-containing oxidizing agents include ferric p-toluenesulfonate and ferric 1-naphthalenesulfonate. The oxidizing agent is used, for example, to chemically oxidatively polymerize monomers when forming the second conductive polymer layer. The second conductive polymer layer may separately contain an iron-containing oxidizing agent and a dopant, or may contain a compound of iron and the acid of the dopant. A compound of iron and a dopant acid functions as both an oxidant and a dopant.

When both the first conductive polymer layer and the second conductive polymer layer contain an iron-containing oxidizing agent, the oxidizing agent (iron-containing oxidizing agent) contained in the first conductive polymer layer and The oxidizing agent contained in the second conductive polymer layer may be the same or different.

The boiling point of the first dopant contained in the first conductive polymer layer is lower than the boiling point of the second dopant contained in the second conductive polymer layer. In other words, the thermal stability of the first dopant is lower than the thermal stability of the second dopant.

The boiling point of the first dopant is not particularly limited. The boiling point of the second dopant is not particularly limited. The boiling point of the first dopant is, for example, preferably 200° C. or lower, more preferably 150° C. or lower. The boiling point of the second dopant is, for example, preferably 140° C. or higher, more preferably 300° C. or higher. The difference between the boiling point of the first dopant and the boiling point of the second dopant is, for example, preferably 2° C. or higher, more preferably 15° C. or higher, and more preferably 150° C. or higher.

The weight of the polymer in the second conductive polymer layer is greater than the weight of the polymer in the first conductive polymer layer. For example, the second monomer concentration of the second liquid in which the capacitor element is immersed to form the second conductive polymer layer is changed to the first monomer concentration in which the capacitor element is immersed to form the first conductive polymer layer. By making the concentration of the liquid higher than the first monomer concentration, the weight of the polymer in the second conductive polymer layer can be made larger than the weight of the polymer in the first conductive polymer layer. When the concentration of the first monomer and the concentration of the second monomer are the same or less, the amount of polymer in the first conductive polymer layer can also be obtained by repeating the number of times of immersion in the second solution, pulling out and heat treatment a plurality of times. can do more. On the other hand, since repeated immersion and heat treatment reduce productivity, the concentration of the second monomer is preferably two times or more, more preferably three times or more, that of the first monomer.

The electrolytic capacitor 1 described above is produced, for example, by the following method. Here, a method of chemically oxidatively polymerizing a monomer when forming the first conductive polymer layer and the second conductive polymer layer will be described.

Lead tabs for external extraction electrodes are connected to the anode 11 and the cathode 12 (see FIG. 2) cut to a predetermined width. By winding the anode 11 and the cathode 12 to which the lead tabs are connected, with the separator 13 interposed therebetween, the main body portion to be the capacitor element 5 is produced (first step). The anode 11 is a valve action metal with a dielectric oxide film formed thereon.

In order to repair the cut end of the main body which will be the capacitor element 5 and the dielectric oxide film that was damaged during the fabrication of the main body, the main body is subjected to chemical conversion treatment. The chemical conversion treatment is performed by applying a voltage to the main body in a chemical conversion solution. Examples of chemical conversion liquids used for chemical conversion treatment include aqueous solutions containing at least one of adipic acid and adipic acid salts.

Subsequently, in order to form the first conductive polymer layer, the main body is immersed in a first liquid containing a first monomer, a first dopant, and an iron-containing oxidizing agent, and then subjected to heat treatment. The first dopant and the iron-containing oxidant may be different from each other, or may be the first dopant and oxidant. Polymerization of the first monomer forms a first conductive polymer layer at least between the dielectric oxide film and the separator 13 (second step). After the heat treatment, the main body may be dried if necessary.

Next, in order to form a second conductive polymer layer, the first conductive polymer layer is formed in a second liquid containing a second monomer, a second dopant, and an iron-containing oxidizing agent. After immersing the main body, heat treatment is performed. The second monomer is the same monomer as the first monomer contained in the first liquid used to form the first conductive polymer layer. The concentration of the second monomer contained in the second liquid is higher than the concentration of the first monomer contained in the first liquid. For example, the concentration of the first monomer contained in the first liquid is 10 wt % or more and 30 wt % or less, and the concentration of the second monomer contained in the second liquid is 30 wt % or more and 70 wt % or less. The concentration of the second monomer contained in the second liquid is preferably twice or more, more preferably three times or more, that of the first monomer contained in the first liquid. A second conductive polymer layer is formed by polymerizing the second monomer (third step). After the heat treatment, the main body may be dried if necessary. Capacitor element 5 is thus obtained. By housing capacitor element 5 in a metal case (fourth step), electrolytic capacitor 1 is obtained.

By the above method, the first conductive polymer layer and the second conductive polymer layer are formed at least between the dielectric oxide film of the anode 11 and the separator. By forming the first conductive polymer layer first, the first conductive polymer layer is formed on most of the dielectric oxide film. Therefore, the contact area between the previously formed first conductive polymer layer and the dielectric oxide film is larger than the contact area between the later formed second conductive polymer layer and the dielectric oxide film.

In the method described above, since the concentration of the second monomer contained in the second liquid is higher than the concentration of the first monomer contained in the first liquid, in the obtained electrolytic capacitor, the second conductive polymer layer has a high The weight of the molecule is greater than the weight of the polymer in the first conductive polymer layer.

From the findings of the inventors, it has been found that the electrolytic capacitor 1 according to the present embodiment provides the following effects.
In the dielectric oxide film, the boiling point of the first dopant contained in the first conductive polymer layer with a large contact area is lower than the boiling point of the second dopant contained in the second conductive polymer layer. When an overvoltage or the like is applied to the electrolytic capacitor 1, the first dopant contained in the first conductive polymer layer decomposes faster than the second dopant. As a result, the first conductive polymer layer, which has a large contact area with the dielectric oxide film, loses its conductivity faster than the second conductive polymer layer and becomes insulated. This suppresses the occurrence of a short circuit.
On the other hand, in the dielectric oxide film, the second conductive polymer layer having a small contact area is more difficult to insulate than the first conductive polymer layer. Therefore, the second conductive polymer layer does not easily become a resistor. As a result, it was found that the ESR of the electrolytic capacitor 1 hardly increased even when an overvoltage was applied.
According to the electrolytic capacitor 1 described above, when an overvoltage or the like is applied, the occurrence of a short circuit can be suppressed, and an increase in ESR can be suppressed.

Also, the weight of the polymer in the second conductive polymer layer, which is difficult to insulate, is greater than the weight of the polymer in the first conductive polymer layer. This indicates that there are many polymers in the second conductive polymer layer that are less likely to become resistance. Therefore, even if overvoltage is applied, the ESR of the electrolytic capacitor is less likely to rise.

In the above, the concentration of the second monomer contained in the second liquid was made higher than the concentration of the first monomer contained in the first liquid in the manufacturing process of the electrolytic capacitor. As a result, the weight of the polymer in the second conductive polymer layer becomes greater than the weight of the polymer in the first conductive polymer layer. However, the concentration of the first monomer contained in the first liquid is the same as the concentration of the second monomer contained in the second liquid, or the concentration of the first monomer contained in the first liquid is the same as the concentration of the second monomer contained in the second liquid. It may be higher than the concentration of two monomers. In this case, for example, the main body portion of the capacitor element on which the first conductive polymer layer is formed is immersed in the second liquid containing the second monomer, and then pulled out and subjected to heat treatment. In the resulting electrolytic capacitor, the weight of the polymer in the second conductive polymer layer is greater than the weight of the polymer in the first conductive polymer layer.

Further, in the manufacturing process of the electrolytic capacitor, when the second liquid contains iron ions, the molar ratio of the second dopant to the iron ions contained in the second liquid is preferably 2.6 or more and 3.0 or less. . When the second conductive polymer layer contains an oxidizing agent containing iron, the molar ratio of iron contained in the oxidizing agent to the second dopant in the second conductive polymer layer is 1:2. It is preferably 6 to 3.0. In this case, the initial ESR of the electrolytic capacitor 1 (ESR before overvoltage or the like is applied) tends to be relatively low.

Further, in the manufacturing process of the electrolytic capacitor, when the first liquid contains iron ions, the molar ratio of the first dopant to the iron ions contained in the first liquid is 2.6 or more and 3.4 or less. is preferred. When the first conductive polymer layer contains an iron-containing oxidizing agent, in the first conductive polymer layer, the molar ratio of iron contained in the oxidizing agent to the first dopant is 1:2.6 to 3.4 is preferred. In this case, an electrolytic capacitor with high capacitance and low leakage current can be provided.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

An electrolytic capacitor was produced by the following method.

Aluminum lead tabs for external extraction electrodes were connected to the anode foil and the cathode foil cut to a predetermined width. The anode aluminum foil is formed by subjecting the surface of aluminum foil, which is a valve metal, to etching to roughen the surface and then to chemical conversion treatment at 60 V to form a dielectric oxide film. The cathode foil is a carbon-supported aluminum foil. By winding the anode aluminum foil and the cathode aluminum foil through an electrolytic paper (separator) mainly composed of cellulose, a main body portion to be a capacitor element was produced.

A chemical conversion treatment was performed to repair the dielectric oxide film that had been damaged at the cut end of the anode foil and the mounting portion of the lead tab. The chemical conversion treatment was performed by applying a voltage close to the chemical conversion voltage value of the dielectric oxide film while the main body, which was to be the capacitor element, was immersed in the chemical conversion solution. An aqueous ammonium adipate solution having a concentration of 2 wt % ammonium adipate was used as an anodizing solution.

Next, under the following conditions (under [Conditions for preparing the first conductive polymer layer and the second conductive polymer layer] described later), ethylenedioxythiophene (EDOT), a first dopant, and a first dopant After immersing the main body, which will be the capacitor element, in the first liquid in which 30% by weight of iron salt (dopant and oxidizing agent) is mixed with ethanol for 30 minutes, the main body is lifted from the first liquid and heated at 40° C. for 1 hour. A first conductive polymer layer was formed by heat treatment.

Subsequently, under the following conditions, ethylenedioxythiophene (EDOT), a second dopant, an iron salt of the second dopant (dopant and oxidizing agent) of 30 wt %, and ethanol were added to a second liquid, which was a mixture of the main body portion to be the capacitor element. for 30 minutes, the main body was pulled up from the second liquid, heat-treated at 40° C. for 1 hour, and then heat-treated at 220° C. for 15 minutes. After that, the main body portion to be the capacitor element was immersed in ethylene glycol for 5 minutes to remove excess iron and dopant, and then dried at 160° C. for 30 minutes. Thus, a second conductive polymer layer was formed.

The lead wires of the resulting capacitor element were inserted through the holes of the sealing body, and after the capacitor element and the sealing body were housed in an aluminum case, the periphery of the opening of the case was curled. A rated voltage (25 V) was applied to the capacitor element accommodated in the case in a constant temperature bath set at 150° C., and aging treatment was performed to produce an electrolytic capacitor. The electrolytic capacitor produced in this experiment has a rated voltage of 25 WV, a rated capacitance of 150 μF, and a product size of φ8×10 L (mm).

[Preparation conditions for the first conductive polymer layer and the second conductive polymer layer]
<Conventional conditions>
Monomer (EDOT) concentration 30 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
Under conventional conditions, only one conductive polymer layer was produced.
<Example 1>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant 1-naphthalenesulfonic acid (molar ratio of iron:dopant = 1:2.6)
<Example 2>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt%/dopant ethanesulfonic acid (molar ratio of iron: dopant = 1:2.6)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
<Example 3>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt%/dopant ethanesulfonic acid (molar ratio of iron: dopant = 1:3.2)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
<Example 4>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt%/dopant benzenesulfonic acid (molar ratio of iron: dopant = 1:2.6)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant 1-naphthalenesulfonic acid (molar ratio of iron: dopant = 1:3.0)
<Comparative example 1>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt%/dopant benzenesulfonic acid (molar ratio of iron: dopant = 1:2.6)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt%/dopant benzenesulfonic acid (molar ratio of iron: dopant = 1:2.6)
<Comparative example 2>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant 1-naphthalenesulfonic acid (molar ratio of iron:dopant = 1:2.8)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant benzenesulfonic acid (molar ratio of iron:dopant = 1:2.8)
<Comparative Example 3>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant 1-naphthalenesulfonic acid (molar ratio of iron:dopant = 1:2.8)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
<Example 5>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant p-toluenesulfonic acid (molar ratio of iron: dopant = 1: 2.8)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant 1-naphthalenesulfonic acid (molar ratio of iron:dopant = 1:3.2)
<Example 6>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant benzenesulfonic acid (molar ratio of iron:dopant = 1:3.4)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt% / dopant p-toluenesulfonic acid (molar ratio of iron:dopant = 1:3.4)
<Comparative Example 4>
First conductive polymer layer: Monomer (EDOT) concentration 10 wt% / dopant benzenesulfonic acid (molar ratio of iron:dopant = 1:3.0)
Second conductive polymer layer: Monomer (EDOT) concentration 30 wt%/dopant benzenesulfonic acid (molar ratio of iron: dopant = 1:3.0)

Table 1 shows capacitor fabrication conditions.

(evaluation)
As initial characteristics, the capacitance (Cap.), tangent of loss angle (tan δ), equivalent series resistance (ESR) and leakage current (μA) of the capacitor were measured in an environment of 20°C. After applying 100 V to each capacitor for 60 minutes (after the overvoltage test), the capacitor's capacitance (Cap.), loss angle tangent (tan δ), equivalent series resistance (ESR) and leakage current (μA) were measured. Table 2 shows the evaluation results.

Under conventional conditions in which only one conductive polymer layer was formed, a short circuit occurred during the overvoltage test.
Also in Comparative Examples 1 and 4, a short circuit occurred during the overvoltage test. In Comparative Examples 1 and 4, the first conductive polymer layer and the second conductive polymer layer were formed in the capacitor element, but the first conductive polymer layer and the second conductive polymer layer were not formed. A polymer layer was formed under the same conditions (see Table 1).

As shown in Table 2, no short circuit occurred in Comparative Examples 2 and 3, but the ESR significantly increased after the overvoltage test. In Comparative Examples 2 and 3, the boiling point of the second dopant contained in the second conductive polymer layer was lower than the boiling point of the first dopant contained in the first conductive polymer layer (see Table 1). . The second conductive polymer layer, which has a polymer with a relatively large weight compared to the polymer of the first conductive polymer layer, lost its conductivity earlier than the first conductive polymer layer and became insulated. It is considered that the ESR increased significantly due to this.

The above experiments have revealed the following.
The boiling point of the first dopant contained in the first conductive polymer layer, which has a large contact area with the dielectric oxide film of the anode, is lower than the boiling point of the second dopant contained in the second conductive polymer layer, and When the weight of the polymer in the second conductive polymer layer, which has a small contact area with the dielectric oxide film of the anode, is greater than the weight of the polymer in the first conductive polymer layer, an overvoltage is applied to the electrolytic capacitor. It has been found that the occurrence of a short circuit can be suppressed and an increase in the ESR of the electrolytic capacitor can be suppressed in this case.

Further, in Examples 1 to 4, as shown in Table 2, the initial ESR is low. From this, in the second conductive polymer layer, when the molar ratio of iron contained in the oxidizing agent to the second dopant is 1:2.6 to 3.0 (see Table 1), the initial ESR was found to be low.

In the above experiment, in order to form the first conductive polymer layer and the second conductive polymer layer, ethylenedioxythiophene (EDOT) was polymerized as a monomer to form a high-density polyethylenedioxythiophene (PEDOT). I got the molecule. However, the monomers and polymers for forming the first conductive polymer layer and the second conductive polymer layer were ethylenedioxythiophene (EDOT) and polyethylenedioxythiophene (PEDOT) used in the above experiments. is not limited to Monomers and polymers other than the above may also be used. Other monomers and polymers can also provide similar effects.

It is not limited to the first dopant and oxidant contained in the first conductive polymer layer and the first dopant and oxidant used in the above experiments. It is not limited to the second dopant and oxidizing agent contained in the second conductive polymer layer, and the second dopant and oxidizing agent used in the above experiments. Similar effects are obtained with other dopants and oxidizing agents.

Although the embodiments of the present invention have been described above based on the examples, it should be considered that the specific configuration is not limited to these embodiments. The scope of the present invention is indicated by the scope of the claims rather than the above description, and includes all modifications within the scope and meaning equivalent to the scope of the claims.

For example, in the above description, the case where the first conductive polymer layer and the second conductive polymer layer are formed between the dielectric oxide film and the separator has been described. However, the first conductive polymer layer and the second conductive polymer layer may be formed other than between the dielectric oxide film and the separator. For example, it may also be formed on a dielectric oxide film and/or a separator.

In the above description, the case where the first conductive polymer layer and the second conductive polymer layer are formed between the dielectric oxide film and the separator has been described. However, another conductive polymer layer may be formed between the dielectric oxide film and the separator in addition to the first conductive polymer layer and the second conductive polymer layer.

In the above experiment, an electrolytic capacitor having a rated voltage of 25 WV, a rated capacity of 150 μF, and a product size of φ8×10 L (mm) was produced, but the rated voltage, rated capacity and product size of the electrolytic capacitor of the present invention are not limited to the above. .

REFERENCE SIGNS LIST 1 electrolytic capacitor 2 exterior case 3 sealing body 4 exterior body 5 capacitor element 11 anode 12 cathode 21, 22 lead terminal

Claims (6)

An electrolytic capacitor comprising: a capacitor element having an anode having a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode; and an exterior housing housing the capacitor element,
The capacitor element has a first conductive polymer layer and a second conductive polymer layer formed between the dielectric oxide film and the separator,
In the dielectric oxide film, the contact area with the first conductive polymer layer is larger than the contact area with the second conductive polymer layer,
The first conductive polymer layer includes a polymer and a first dopant,
The second conductive polymer layer contains the same polymer as the polymer contained in the first conductive polymer layer and a second dopant,
An electrolytic capacitor, wherein the boiling point of the first dopant is lower than the boiling point of the second dopant. 2. The electrolytic capacitor according to claim 1, wherein the weight of polymer in said second conductive polymer layer is greater than the weight of polymer in said first conductive polymer layer. a first step of winding an anode and a cathode having a dielectric oxide film with a separator interposed therebetween to form a capacitor element;
a second step of forming a first conductive polymer layer between at least the dielectric oxide film and the separator of the capacitor element;
a third step of forming a second conductive polymer layer on the capacitor element on which the first conductive polymer layer is formed;
and a fourth step of housing the capacitor element having the second conductive polymer layer formed thereon in an exterior body,
In the second step, after the capacitor element is immersed in a first liquid containing at least a first monomer and a first dopant and pulled out, a first conductive polymer layer is formed by heat treatment,
In the third step, the capacitor element having the first conductive polymer layer formed thereon is immersed in a second liquid containing at least the same second monomer as the first monomer and a second dopant, pulled out, and then heat-treated. to form the second conductive polymer layer,
A method of manufacturing an electrolytic capacitor, wherein the boiling point of the first dopant is lower than the boiling point of the second dopant. 4. The method of manufacturing an electrolytic capacitor according to claim 3, wherein the second monomer concentration in the second liquid is higher than the first monomer concentration in the first liquid. The second liquid further contains iron ions,
4. The method of manufacturing an electrolytic capacitor according to claim 3, wherein the molar ratio of the second dopant to the iron ions contained in the second liquid is 2.6 or more and 3.0 or less. The first liquid further contains iron ions,
4. The method of manufacturing an electrolytic capacitor according to claim 3, wherein the molar ratio of the first dopant to the iron ions contained in the first liquid is 2.6 or more and 3.4 or less.

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