JP7574133B2 - Solid electrolytic capacitor and method for manufacturing the same - Google Patents

Description

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

A known electrolytic capacitor is one that includes a capacitor element having an anode with a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode, and an exterior body that houses the capacitor element.

Patent Document 1 describes an electrolytic capacitor in which a polyhydroxy compound is contained in a conductive polymer layer formed on a dielectric oxide film. Patent Document 1 describes that when a polyhydroxy compound with a melting point of 40°C or higher and 150°C or lower is used, it is possible to improve conductivity and reduce ESR (equivalent series resistance).

Patent Document 2 describes that the electrolyte of an electrolytic capacitor contains a first aromatic compound having a hydroxyl group as a solute acid component. Patent Document 2 also describes that the first aromatic compound having a hydroxyl group makes it possible to maintain a low ESR for a long period of time.

Patent No. 6767630 International Publication No. 2017/056447

In recent years, there has been a demand for electrolytic capacitors that can maintain a lower ESR than conventional capacitors in high temperature environments. In addition, there is a demand for electrolytic capacitors that have a low initial ESR.

The object of the present invention is to provide an electrolytic capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments.

Patent Documents 1 and 2, etc., describe technologies that can reduce ESR. However, the inventors' research has shown that even if these technologies are adopted, they are insufficient to achieve the desired low ESR in the initial stage and in high-temperature environments.

The inventors have furthered their research and discovered that the following invention makes it possible to provide an electrolytic capacitor that can maintain a lower E.S.R. than conventional capacitors in high-temperature environments. They have also discovered that this electrolytic capacitor can reduce the initial E.S.R.

The method for manufacturing an electrolytic capacitor of the present invention is a method for manufacturing an electrolytic capacitor having a capacitor element body having an anode with a dielectric oxide film, a cathode, and a separator arranged between the anode and the cathode, and includes a first step of impregnating the capacitor element body with a first liquid containing a conductive polymer and an antioxidant at 0.2 wt% to 2.0 wt% and then heat treating the capacitor element body to form a conductive polymer layer on the dielectric oxide film, and a second step of impregnating the capacitor element body with a second liquid containing an organic solvent and an antioxidant at 0.2 wt% to 10.0 wt% and forming an organic solvent layer after the conductive polymer layer is formed, the first liquid and the second liquid are at least one selected from benzenetriol and derivatives of benzenetriol, and the concentration of the antioxidant in the second liquid is the same as the concentration of the antioxidant in the first liquid or higher than the concentration of the antioxidant in the first liquid.

According to the present invention, the first liquid forming the conductive polymer layer and the second liquid forming the organic solvent layer each contain at least one antioxidant selected from benzenetriol and derivatives of benzenetriol. Within the above range of antioxidant concentrations, the concentration of the antioxidant in the second liquid forming the organic solvent layer is set to be the same as the concentration of the antioxidant in the first liquid forming the conductive polymer layer, or higher than the concentration of the antioxidant in the first liquid. It has been found that this makes it possible to manufacture an electrolytic capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments.

The organic solvent contained in the second liquid may be at least one selected from polyalkylene glycol, polyglycerin, and derivatives thereof.

By using an organic solvent such as polyalkylene glycol to form the organic solvent layer, the repair performance of the dielectric oxide film on the anode is improved, which is expected to reduce leakage current.

The polyalkylene glycol may be at least one selected from polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol.

By using the above compounds, which are easily available to form an organic solvent layer, it is expected that leakage current will be reduced.

The electrolytic capacitor according to the present invention is an electrolytic capacitor having a capacitor element body having an anode having a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode, and a conductive polymer layer containing at least a conductive polymer and an antioxidant, and an organic solvent layer containing at least an organic solvent and an antioxidant are formed in the capacitor element body, the antioxidant contained in the conductive polymer layer and the antioxidant contained in the organic solvent layer are at least one selected from benzenetriol and derivatives of benzenetriol, and the weight ratio of the antioxidant contained in the conductive polymer layer to the antioxidant contained in the organic solvent layer is 1:1 to 1:50.

According to the above configuration, the conductive polymer layer and the organic solvent layer each contain at least one antioxidant selected from benzenetriol and derivatives of benzenetriol. The ratio of the antioxidant in the conductive polymer layer to the antioxidant in the organic solvent layer is 1:1 to 1:50. It has been found that this makes it possible to provide an electrolytic capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments.

In the above configuration, the organic solvent contained in the organic solvent layer may be at least one selected from polyalkylene glycol, polyglycerin, and derivatives thereof.

By including an organic solvent such as polyalkylene glycol in the organic solvent layer, the repair performance of the dielectric oxide film on the anode is improved, which is expected to reduce leakage current.

The polyalkylene glycol may be at least one selected from polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol.

By using the above compounds, which are easily available as organic solvents, it is expected that leakage current can be reduced.

The present invention provides an electrolytic capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments.

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

A preferred embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the electrolytic capacitor 1 includes an exterior body 4 having an exterior case 2 and a sealing body 3 that seals the opening of the exterior case 2, and a capacitor element 5 housed in the exterior body 4.

As shown in FIG. 2, the capacitor element 5 is formed by winding an anode 11 and a cathode 12 into a cylindrical shape with a separator 13 between them, and is secured to the outer periphery by tape 14.

Lead tabs (not shown) are connected to the anode 11 and the cathode 12. The anode 11 is connected to a lead terminal 21 via a lead tab. The cathode 12 is connected to a lead terminal 22 via a lead tab. The lead terminals 21 and 22 are respectively led out to the outside through holes 31 and 32 formed in the sealing body 3 as shown in FIG. 1.

The anode 11 shown in FIG. 2 is a valve metal having a dielectric oxide film formed on its surface. The valve metal may be, for example, 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 a valve metal foil by etching, and then subjecting it to a chemical conversion treatment.

The cathode 12 is formed using a valve metal. For example, a valve metal foil whose surface is roughened by etching, or a foil whose surface is roughened and then chemically treated, is used as the cathode 12. A plain foil that is not etched may be used as the cathode 12. Furthermore, a coating foil in which a metal thin film containing at least one metal selected from the group consisting of titanium, nickel, titanium carbide, nickel carbide, titanium nitride, nickel nitride, titanium carbonitride, and nickel carbonitride is formed on the surface of the roughened foil or plain foil may be used. A coating foil in which a carbon thin film is formed on the surface of the roughened foil or plain foil may also be used.

The material of the separator 13 is not particularly limited. For example, a material mainly made of cellulose may be used as the separator 13.

A conductive polymer layer held by a separator 13 is formed between the dielectric oxide film of the anode 11 and the cathode 12. The conductive polymer layer contains a conductive polymer and an antioxidant. The conductive polymer layer is a layer formed by impregnating the dielectric oxide film with a first liquid containing a conductive polymer and 0.2 wt % to 2.0 wt % of an antioxidant and subjecting the first liquid to heat treatment.

For example, polythiophene, polypyrrole, polyaniline, or derivatives thereof are used as the polymer contained in the conductive polymer layer. Polyethylenedioxythiophene (PEDOT) is generally used as the polymer. The polymer is not limited to these.

The conductive polymer layer further includes a dopant. As the dopant, p-toluenesulfonic acid, polystyrenesulfonic acid (PSS), etc. are generally used. The dopant is not limited to these. A self-doped conductive polymer may also be used.

The conductive polymer layer may contain other additives in addition to the polymer, dopant, and antioxidant. The antioxidant will be described later.

The capacitor element 5 shown in FIG. 2 further has an organic solvent layer. The organic solvent layer contains an organic solvent and an antioxidant. The organic solvent layer is a layer formed by impregnating the capacitor element body having the anode 11, the cathode 12, and the separator 13 with a second liquid containing an organic solvent and 0.2 wt % to 10.0 wt % of an antioxidant after the conductive polymer layer is formed. The organic solvent layer is formed or held in the voids of the capacitor element 5 in which the conductive polymer layer is formed.

The organic solvent may be, for example, at least one selected from polyalkylene glycol, polyglycerin, and derivatives thereof. These enhance the repair performance of the dielectric oxide film of the anode, and are expected to reduce leakage current. The polyalkylene glycol may be at least one selected from polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol. These compounds are easily available and are expected to reduce leakage current. The organic solvent contained in the organic solvent layer is not particularly limited.

The organic solvent layer may contain other additives in addition to the organic solvent and the antioxidant. The organic solvent layer may or may not contain an electrolyte.

The antioxidant contained in the conductive polymer layer and the antioxidant contained in the organic solvent layer are at least one selected from benzenetriol and derivatives of benzenetriol. Examples of benzenetriol include pyrogallol, hydroxynol, and phloroglucinol. The derivatives of benzenetriol may be, for example, derivatives in which the hydrogen group of benzenetriol is etherified, esterified, halogenated, aminated, or carbonylated. Specifically, the derivatives of benzenetriol may be derivatives in which the hydrogen group of benzenetriol is replaced with an atom or functional group other than the hydrogen group. Examples of functional groups include amino groups and carboxyl groups. Examples of derivatives of benzenetriol include propyl gallate. The antioxidant contained in the conductive polymer layer and the antioxidant contained in the organic solvent layer may be the same or different.

The amount of the antioxidant contained in the organic solvent layer is the same as or greater than the amount of the antioxidant contained in the conductive polymer layer. It is presumed that the relationship between the "amount of the antioxidant contained in the organic solvent layer" and the "amount of the antioxidant contained in the conductive polymer layer" has a tendency similar to the relationship between the "concentration of the antioxidant in the first liquid" for forming the conductive polymer layer and the "concentration of the antioxidant in the second liquid" for forming the organic solvent layer in the manufacturing method of the electrolytic capacitor 1 described later. In other words, when the "concentration of the antioxidant in the second liquid" for forming the organic solvent layer is the same as the "concentration of the antioxidant in the first liquid" for forming the conductive polymer layer, it is presumed that the "amount of the antioxidant contained in the organic solvent layer" is the same as the "amount of the antioxidant contained in the conductive polymer layer". If the "concentration of the antioxidant in the second liquid" for forming the organic solvent layer is higher than the "concentration of the antioxidant in the first liquid" for forming the conductive polymer layer, it is presumed that the "amount of the antioxidant contained in the organic solvent layer" is greater than the "amount of the antioxidant contained in the conductive polymer layer."

The conductive polymer layer and/or the organic solvent layer may contain other antioxidants in addition to the antioxidants described above.

The electrolytic capacitor 1 described above is manufactured, for example, by the following method.

Lead tabs for external extraction electrodes are connected to the anode 11 and cathode 12 (see Figure 2), which have been cut to a specified width. The anode 11 and cathode 12 to which the lead tabs are connected are wound with a separator 13 in between to create the capacitor element body. The anode 11 is a valve metal on which a dielectric oxide film is formed.

The capacitor element body is subjected to a chemical conversion treatment to repair the cut edge of the capacitor element body or the dielectric oxide film that was damaged during the production of the capacitor element body. The chemical conversion treatment is carried out by applying a voltage to the capacitor element body in a chemical conversion liquid. The chemical conversion liquid used for the chemical conversion treatment is, for example, an aqueous solution containing at least one of adipic acid and an adipate salt.

Next, the capacitor element body is impregnated with a first liquid containing a conductive polymer and 0.2 wt % to 2.0 wt % of an antioxidant, and then heat-treated (for example, heated at 40° C. to 220° C.) (first step). The antioxidant is at least one selected from benzenetriol and derivatives of benzenetriol. The conductive polymer of the first liquid may be the polymer and dopant exemplified above. The polymer and dopant are not limited to a specific polymer and dopant. A self-doped conductive polymer may also be used. In addition to the polymer and antioxidant, the first liquid may further contain other additives. In addition to at least one antioxidant selected from benzenetriol and derivatives of benzenetriol, the first liquid may also contain other antioxidants.

As a result of the above, a conductive polymer layer is formed on the main body of the capacitor element.

Next, the capacitor element body on which the conductive polymer layer is formed is impregnated with a second liquid containing an organic solvent and 0.2 wt % to 10.0 wt % of the above-mentioned antioxidant (second step). The antioxidant is at least one selected from benzenetriol and derivatives of benzenetriol. The concentration of the antioxidant in the second liquid is the same as the concentration of the antioxidant in the first liquid or is higher than the concentration of the antioxidant in the first liquid. The antioxidant (at least one selected from benzenetriol and derivatives of benzenetriol) contained in the second liquid may be the same as or different from the above-mentioned antioxidant (at least one selected from benzenetriol and derivatives of benzenetriol) contained in the first liquid. The organic solvent may be any of the organic solvents exemplified above. The type of organic solvent is not particularly limited. The second liquid may further contain other additives. The second liquid may contain other antioxidants in addition to at least one antioxidant selected from benzenetriol and derivatives of benzenetriol.

As a result of the above, an organic solvent layer is formed. This results in the capacitor element 5.

The capacitor element 5 is housed in the exterior case 2 (see FIG. 1), and the opening of the exterior case 2 is closed with the sealing body 3. This results in the electrolytic capacitor 1.

The inventors have obtained the following findings:

It is believed that the reason why the E.S.R. becomes high in a high-temperature environment is due to the thermal oxidative degradation of the conductive polymer contained in the conductive polymer layer. In the past, it was thought that the reason that the thermal oxidative degradation of the conductive polymer could not be sufficiently suppressed was, for example, because oxygen flowed into the conductive polymer layer, causing the conductive polymer to deteriorate by thermal oxidation. It is also thought that it was not possible to sufficiently suppress the thermal oxidative degradation caused by the conductive polymer present on the surface of the dielectric oxide film reacting with oxygen in the dielectric oxide film.

In contrast, it is believed that the electrolytic capacitor manufactured by the above-mentioned method can sufficiently suppress the thermal oxidative degradation of the conductive polymer.
Specifically, it is believed that the benzenetriol and/or derivatives of benzenetriol contained in the conductive polymer layer as an antioxidant suppresses thermal oxidative degradation of the conductive polymer even if oxygen flows into the conductive polymer layer. Also, an organic solvent layer containing benzenetriol and/or derivatives of benzenetriol as an antioxidant is formed on the surface of the conductive polymer layer, and the antioxidant present in the organic solvent layer is secured to a certain extent. It is believed that this sufficiently suppresses thermal oxidative degradation of the conductive polymer present on the surface of the dielectric oxide film.
It was found that these features make it possible to maintain a lower ESR than before in high temperature environments.

In addition, when the conductive polymer layer contains a large amount of antioxidant, the initial E.S.R. tends to be high, but by including an antioxidant in the organic solvent layer, the concentration of the antioxidant in the first liquid that forms the conductive polymer layer can be reduced. This is thought to prevent the initial E.S.R. of the electrolytic capacitor from becoming too high.

As described above, according to this embodiment, it is possible to manufacture an electrolytic capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments. Furthermore, the above-mentioned electrolytic capacitor is a capacitor that has a low initial ESR and can maintain a lower ESR than conventional capacitors in high temperature environments.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

The electrolytic capacitor was made using the following method.

Aluminum lead tabs for external extraction electrodes were connected to the anode and cathode foils cut to a specified width. The anode aluminum foil was made by roughening the surface of the valve metal aluminum foil by etching, and then forming a dielectric oxide film by chemical conversion treatment at 100 V. The cathode foil was aluminum foil on which carbon was vapor-deposited. The main body of the capacitor element was made by winding the anode aluminum foil and cathode aluminum foil with nylon-based electrolytic paper (separator) in between.

A chemical conversion treatment was performed to repair the dielectric oxide film that was missing from the cut edge of the anode foil and the attachment part of the lead tab. The chemical conversion treatment was performed by immersing the main body part that will become the capacitor element in a chemical conversion solution and applying a voltage that is close to the chemical conversion voltage value of the dielectric oxide film. The chemical conversion solution used was an aqueous solution of ammonium adipate with an ammonium adipate concentration of 2 wt%.

Next, the capacitor element body was impregnated with the first liquid under reduced pressure under the following conditions (see [Conditions for preparing the conductive polymer layer and organic solvent layer] below), and the capacitor element body was then held in a thermostatic chamber set at 40°C for 30 minutes, after which it was heat-treated by holding it in a thermostatic chamber set at 160°C for 30 minutes. This impregnation and heat treatment was repeated twice. As a result, a conductive polymer layer was formed in the capacitor element body.

Then, the capacitor element body was impregnated with the second liquid under reduced pressure under the following conditions (see [Conditions for preparing the conductive polymer layer and organic solvent layer] below). The capacitor element body was then left in a thermostatic chamber at 135°C for 30 minutes to form an organic solvent layer.

The resulting capacitor element was placed in an aluminum case, and the edges of the opening of the case were curled. A rated voltage (63 V) was applied to the capacitor element placed in the case in a thermostatic chamber set at 125°C, and an aging process was performed to produce an electrolytic capacitor. The electrolytic capacitor produced in this experiment had a category upper limit temperature of 125°C, a rated voltage of 63 WV, a rated capacitance of 22 μF, and a product size of φ8 × 7L (mm).

[Conditions for preparing conductive polymer layer and organic solvent layer]
<Conventional Condition 1>
Conductive polymer layer: Dispersion liquid (containing no antioxidant) made by mixing PEDOT/PSS (concentration 2.0 wt%) and ethylene glycol (concentration 10 wt%)
Organic solvent layer: None
<Conventional Condition 2>
Conductive polymer layer: Dispersion liquid (containing no antioxidant) made by mixing PEDOT/PSS (concentration 2.0 wt%) and ethylene glycol (concentration 10 wt%)
Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration: 0.5 wt %). "PEG400" is a polyethylene glycol having a number average molecular weight of 400.
<Conventional Condition 3>
Conductive polymer layer: Dispersion of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution (no antioxidant)
<Example 1>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.2 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 0.2 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:1
<Example 2>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.2 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:25
<Example 3>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 1.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:2
<Example 4>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Example 5>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 10.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:20
<Example 6>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 2.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:2.5
<Example 7>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.2 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 10.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:50
<Example 8>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), phloroglucinol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing phloroglucinol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Example 9>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), phloroglucinol (concentration 1.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing phloroglucinol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:5
<Example 10>
Conductive polymer layer: Dispersion of PEDOT/PSS (concentration 2.0 wt%), hydroxynol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing hydroxynol (concentration 5.0 wt%) Antioxidant contained in conductive polymer layer: Antioxidant contained in organic solvent layer = 1:10
<Example 11>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), propyl gallate (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing propyl gallate (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Example 12>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing phloroglucinol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Example 13>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), hydroxynol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Comparative Example 1>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 0.2 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 0.1 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:0.5
<Comparative Example 2>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 1.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 0.5 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:0.5
<Comparative Example 3>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 5.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 0.5 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:0.1
<Comparative Example 4>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), pyrogallol (concentration 10.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 0.5 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:0.05
<Comparative Example 5>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), catechol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing catechol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Comparative Example 6>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), p-nitrophenol (concentration 0.5 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing p-nitrophenol (concentration 5.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:10
<Comparative Example 7>
Conductive polymer layer: Dispersion liquid of a mixture of PEDOT/PSS (concentration 2.0 wt%), hydroxynol (concentration 5.0 wt%), and ethylene glycol (concentration 10 wt%) Organic solvent layer: Polyethylene glycol (PEG400) solution containing pyrogallol (concentration 1.0 wt%) Antioxidant contained in the conductive polymer layer: Antioxidant contained in the organic solvent layer = 1:0.2

(evaluation)
As the initial characteristics, the equivalent series resistance (ESR) of the electrolytic capacitor was measured in an environment of 20°C.
Next, the electrolytic capacitor was subjected to application of a rated voltage (63 V) in a high-temperature atmosphere of 150° C. for 1000 hours (hereinafter, sometimes referred to as "after high-temperature test"), and then the equivalent series resistance (ESR) of the capacitor was measured.

Table 1 shows the experimental conditions and the evaluation results.
In Table 1, "Avg." is the arithmetic mean value of E.S.R. (n=30). "C.F." of "150°C rated application test after 1000 hours"("after high temperature test") is the rate of increase of E.S.R. after high temperature test with respect to the initial E.S.R. "C.F." is calculated from the following formula.
cf = (Avg. ESR after high temperature test - Initial Avg. ESR) / Initial Avg. ESR

As shown in Table 1, the electrolytic capacitor under conventional condition 1 is a capacitor that does not contain an antioxidant in the conductive polymer layer and does not have an organic solvent layer, the electrolytic capacitor under conventional condition 2 is a capacitor that contains benzenetriol as an antioxidant only in the organic solvent layer, and the electrolytic capacitor under conventional condition 3 is a capacitor that contains benzenetriol as an antioxidant only in the conductive polymer layer. As shown in Table 1, the E.S.R. after high-temperature testing was high under conventional conditions 1 to 3. In addition, the rate of increase (c.f.) of E.S.R. was large under conventional conditions 1 to 3.

As shown in Table 1, the electrolytic capacitors of Examples 1 to 13 are capacitors in which both the conductive polymer layer and the organic solvent layer contain benzenetriol or a derivative of benzenetriol as an antioxidant. In Example 1, the concentration of the antioxidant in the second liquid is the same as the concentration of the antioxidant in the first liquid. In this case, it is presumed that the amount of antioxidant in the organic solvent layer is the same as the amount of antioxidant in the conductive polymer layer. In Examples 2 to 13, the concentration of the antioxidant in the second liquid is higher than the concentration of the antioxidant in the first liquid. In this case, it is presumed that the amount of antioxidant in the organic solvent layer is greater than the amount of antioxidant in the conductive polymer layer.

In Examples 1 to 13, as shown in Table 1, the initial ESR was low and the ESR after the high temperature test was also low. Also, the rate of increase (cf) of ESR was small.
That is, the electrolytic capacitors of Examples 1 to 13 were electrolytic capacitors that had a low initial ESR and were capable of maintaining an ESR lower than conventional ones in a high temperature environment.

Although the antioxidants in Examples 1 to 7 and Examples 8 to 13 were of different types, the effects of Examples 1 to 7 and Examples 8 to 13 were comparable. From this, it is believed that when the antioxidant is benzenetriol and/or a derivative of benzenetriol, the initial E.S.R. is low, regardless of the type of antioxidant, and it is possible to maintain a lower E.S.R. than conventional methods in high temperature environments.

As shown in Table 1, in the electrolytic capacitors of Comparative Examples 1 to 4 and 7, both the conductive polymer layer and the organic solvent layer contained benzenetriol or a derivative of benzenetriol as an antioxidant, but the ESR after the high temperature test was high.
In Comparative Examples 1 to 4 and 7, unlike Examples 1 to 12, the concentration of the antioxidant in the first liquid was higher than the concentration of the antioxidant in the second liquid. In this case, it is presumed that the amount of the antioxidant in the conductive polymer layer was greater than the amount of the antioxidant in the organic solvent layer. This is considered to have affected the E.S.R. after the high temperature test.

The initial ESR was high in Comparative Examples 3 and 4. Furthermore, the initial ESR in Comparative Example 7 was higher than that in Example 13 in which the same antioxidant as in Comparative Example 7 was used.
In Comparative Examples 3, 4, and 7, the concentration of the antioxidant in the first liquid was higher than in Examples 1 to 13. In these cases, it is presumed that the amount of the antioxidant in the conductive polymer layer was large. This is considered to have affected the initial E.S.R.

In Comparative Examples 5 and 6, the ESR after the high temperature test was high. Also, the rate of increase (cf) of the ESR was large.
In Comparative Example 5, catechol, which is a benzenediol, was used as the antioxidant.
In Comparative Example 6, p-nitrophenol, in which the hydrogen atom of phenol is substituted with a nitro group, was used as the antioxidant.
It was found that these antioxidants were unable to sufficiently suppress the increase in E.S.R. in a high-temperature environment.

From the above experiment, the following was found.
The first liquid forming the conductive polymer layer and the second liquid forming the organic solvent layer each contain benzenetriol or a derivative of benzenetriol as an antioxidant, the first liquid containing 0.2 wt % to 2.0 wt % of the antioxidant, and the second liquid containing 0.2 wt % to 10.0 wt % of the antioxidant. Furthermore, the concentration of the antioxidant in the second liquid is the same as that in the first liquid or is higher than that in the first liquid. In this case, it is presumed that the amount of the antioxidant contained in the organic solvent layer is the same as that contained in the conductive polymer layer, or is greater than that contained in the conductive polymer layer.
It was found that the electrolytic capacitor manufactured under the above conditions had a low initial ESR and was capable of maintaining a lower ESR than conventional electrolytic capacitors in a high temperature environment.

In the above experiments, in Examples 1 to 13, benzenetriol or a derivative of benzenetriol was used. However, the effects of the present invention can be obtained even when two or more selected from benzenetriol and a derivative of benzenetriol are used. In addition, in the above experiments, propyl gallate or phloroglucinol was used as the derivative of benzenetriol, but the effects of the present invention can be obtained even when other derivatives of benzenetriol are used.

In the above experiments, in Examples 1 to 13, PEDOT was used as the polymer and PSS was used as the dopant to form the conductive polymer layer. However, the polymer and dopant are not limited to the above. The effects of the present invention can be obtained even when other polymers are used. The effects of the present invention can be obtained even when other dopants are used.

In the above experiments, in Examples 1 to 13, polyethylene glycol was used as the organic solvent for the organic solvent layer and the second liquid. However, other organic solvents may be used as the organic solvent for the organic solvent layer and the second liquid. The effects of the present invention can be obtained even when other organic solvents are used as the organic solvent for the organic solvent layer and the second liquid.

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

In addition, in the above experiment, an electrolytic capacitor was produced with a category upper limit temperature of 125°C, a rated voltage of 63 WV, a rated capacity of 22 μF, and a product size of φ8 × 7L (mm), but the category upper limit temperature, 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)

A method for manufacturing a solid electrolytic capacitor including a capacitor element body having an anode having a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode,
a first step of impregnating the capacitor element body with a first liquid containing a conductive polymer and an antioxidant at 0.2 wt % or more and 2.0 wt % or less, and then performing a heat treatment to form a conductive polymer layer on the capacitor element body;
a second step of forming an organic solvent layer by impregnating the capacitor element body with a second liquid containing an organic solvent and an antioxidant at 0.2 wt % or more and 10.0 wt % or less, and not containing an electrolyte , after the conductive polymer layer is formed;
having
the antioxidant contained in the first liquid and the antioxidant contained in the second liquid are at least one selected from benzenetriol and derivatives of benzenetriol,
A method for manufacturing a solid electrolytic capacitor, wherein a concentration of the antioxidant in the second liquid is the same as or higher than a concentration of the antioxidant in the first liquid. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the organic solvent contained in the second liquid is at least one selected from the group consisting of polyalkylene glycol, polyglycerin, and derivatives thereof. 3. The method for producing a solid electrolytic capacitor according to claim 2, wherein the polyalkylene glycol is at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol. A solid electrolytic capacitor comprising a capacitor element body having an anode having a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode,
a conductive polymer layer including at least a conductive polymer and an antioxidant in the capacitor element body;
An organic solvent layer is formed, the organic solvent layer containing at least an organic solvent and an antioxidant and not containing an electrolyte ,
the antioxidant contained in the conductive polymer layer and the antioxidant contained in the organic solvent layer are at least one selected from benzenetriol and derivatives of benzenetriol,
a weight ratio of the antioxidant contained in the conductive polymer layer to the antioxidant contained in the organic solvent layer being 1:1 to 1:50; 5. The solid electrolytic capacitor according to claim 4, wherein the organic solvent contained in the organic solvent layer is at least one selected from the group consisting of polyalkylene glycol, polyglycerin, and derivatives thereof. 6. The solid electrolytic capacitor according to claim 5, wherein the polyalkylene glycol is at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol.

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