JP2024079211A - Electrolytic capacitor having conductive polymer compound and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive polymer capacitor that shows excellent durability under high temperature.

SOLUTION: An electrolytic capacitor includes: a solid electrolyte interface having an anode foil having a surface with an oxide film formed thereon, a cathode foil, and a separator provided between the anode foil and the cathode foil, and including a conductive polymer compound in a gap between the anode foil and the cathode foil; and a liquid material interface including a liquid material. The liquid material interface contains 1.0 or more mass% of aromatic nitro compounds. The liquid material is polyethylene glycol. The ratio of pentaethylene glycol in the polyethylene glycol or polyethylene glycol larger than that is 30 mass % or less.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an electrolytic capacitor having a conductive polymer compound and a manufacturing method thereof. In particular, the present invention relates to an electrolytic capacitor having a solid electrolyte phase containing a conductive polymer compound and a liquid substance phase containing polyethylene glycol, and a manufacturing method thereof.

Solid electrolytic capacitors that use conductive polymer compounds as the electrolyte (solid electrolyte) are known. Also known are electrolytic capacitors that use conductive polymer compounds and an electrolytic solution as the electrolyte (hybrid capacitors).

In electrolytic capacitors that contain such conductive polymer compounds, nitro compounds may be used to suppress thermal degradation, etc.

Patent Document 1 describes a solid electrolytic capacitor including a conductive polymer layer, and describes how the conductive polymer layer is obtained using a mixed solution in which a conductive polymer compound is dispersed in a solution containing at least ethylene glycol and a nitro compound.

Patent Document 2 describes an electrolytic capacitor that contains a conductive polymer and a conductive auxiliary liquid. This conductive auxiliary liquid contains a high-boiling organic solvent with a boiling point of 150°C or higher, and an aromatic compound that has a nitro group and a carboxyl group or a carboxy ester moiety, but does not have a hydroxyl group.

Patent document 3 describes an electrolyte used in a hybrid electrolytic capacitor containing a conductive polymer, and describes that the electrolyte contains a first solvent containing a lactone, a second solvent containing a specific compound such as 1,3-propanediol, and an aromatic nitro compound.

Patent document 4 describes an electrolytic capacitor having a capacitor element, in which the capacitor element is impregnated with a liquid containing at least one of a polyalkylene glycol and a derivative of a polyalkylene glycol, and in which the liquid further contains an aromatic compound containing a nitro group and at least one of a hydroxyl group and a carboxyl group.

Patent Document 5 describes an electrolytic capacitor that includes an anode body having a dielectric layer formed on its surface, a solid electrolyte layer that is in contact with the dielectric layer and contains a conductive polymer, and an electrolyte. The electrolyte contains a first base component, a first acid component, and a second acid component. This document also describes that the solvent of the electrolyte can contain a glycol compound, and that the electrolyte can contain a nitro compound as the third acid component.

It is also known to incorporate a liquid water-soluble polymer compound into a solid electrolytic capacitor that contains a conductive polymer.

Patent document 6 describes a solid electrolytic capacitor in which a solid electrolyte made of a fine particle conductive polymer compound and a water-soluble polymer solution made of a liquid water-soluble polymer compound, water, and an alcohol having a nitro group are introduced so that the water-soluble polymer solution surrounds the solid electrolyte.

JP 2013-131514 A JP 2015-2274 A JP 2021-40036 A U.S. Pat. No. 1,067,9800 International Publication No. 2019/225523 JP 2018-26542 A

Conventional electrolytic capacitors that use conductive polymer compounds as solid electrolytes sometimes have insufficient durability at high temperatures.

The present disclosure aims to provide an electrolytic capacitor that has a conductive polymer compound and exhibits excellent durability at high temperatures.

The above problems related to the present disclosure can be solved by the inventions related to the present disclosure described below.
<Aspect 1>
an anode foil having an oxide film formed on its surface;
A cathode foil;
a separator disposed between the anode foil and the cathode foil;
Equipped with
In the gap between the anode foil and the cathode foil,
A solid electrolyte phase including a conductive polymer compound;
A liquid material phase including a liquid material;
An electrolytic capacitor comprising:
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0% by mass or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is 30 mass% or less.
Electrolytic capacitor.
<Aspect 2>
2. The electrolytic capacitor of claim 1, wherein the liquid substance phase contains water in an amount of 0.1% to 10% by weight.
<Aspect 3>
3. The electrolytic capacitor of claim 1 or 2, wherein the aromatic nitro compound is selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, and nitrobenzaldehyde.
<Aspect 4>
The electrolytic capacitor according to any one of aspects 1 to 3, wherein the solid electrolyte phase contains polyethylenedioxythiophene as the conductive polymer compound and polystyrenesulfonic acid as a dopant.
<Aspect 5>
forming a capacitor element by stacking an anode foil having an oxide film formed on its surface and a cathode foil that has been optionally etched, with a separator interposed therebetween, and winding the stack;
impregnating the capacitor element with an aqueous solution or dispersion of a conductive polymer compound to form a solid electrolyte phase in the gap between the anode foil and the cathode foil; and
impregnating the capacitor element having a solid electrolyte phase formed therein with a liquid substance phase containing a liquid substance;
Including,
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0% by mass or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is 30 mass% or less.
A method for manufacturing electrolytic capacitors.

The electrolytic capacitor according to the present disclosure is an electrolytic capacitor having a conductive polymer compound, and can provide an electrolytic capacitor that exhibits excellent durability at high temperatures.

FIG. 1a is a cross-sectional schematic diagram of an electrolytic capacitor according to one embodiment of the present disclosure. FIG. 1b is a perspective schematic diagram of a capacitor element according to one embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of a main part of the solid electrolyte phase of FIG.

<< Capacitor >>
The electrolytic capacitor according to the present disclosure comprises:
an anode foil having an oxide film formed on its surface;
A cathode foil;
a separator disposed between the anode foil and the cathode foil;
Equipped with
In the gap between the anode foil and the cathode foil,
A solid electrolyte phase including a conductive polymer compound;
A liquid material phase including a liquid material;
Including,
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0 mass% or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol is 30 mass % or less.

Conventionally, in electrolytic capacitors having a conductive polymer compound as a solid electrolyte, polyethylene glycol (PEG) has been used as the electrolyte or solution medium used together with the conductive polymer compound.

The inventors of the present invention discovered that in an electrolytic capacitor that includes a solid electrolyte phase containing a conductive polymer compound and a liquid substance phase containing a liquid substance, the durability at high temperatures can be improved by optimizing the degree of polymerization (molecular weight) of the polyethylene glycol contained in the liquid substance phase, and thus arrived at the present invention.

More specifically, it was found that durability at high temperatures is particularly good when the ratio of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the liquid polyethylene glycol is below a certain level.

Without intending to be limited by theory, it is believed that when the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is relatively small, the arrangement of the aromatic nitro compound in the solid electrolyte phase containing the conductive polymer compound is optimized, and as a result, the effect of suppressing thermal degradation by the aromatic nitro compound (particularly as a gas absorbent) is improved.

More specifically, when the molecular weight of the polyethylene glycol contained in the liquid substance phase is relatively low, it is considered that the degree of compatibility of the polyethylene glycol with the conductive polymer compound (e.g., PEDOT) constituting the solid electrolyte phase (particularly, the degree of penetration of the polyethylene glycol into the gaps of the solid electrolyte phase formed from the conductive polymer compound) is improved. Since the liquid substance phase contains an aromatic nitro compound, it is considered that the degree of penetration of the aromatic nitro compound into the solid electrolyte phase is improved with the improvement in the degree of compatibility of the polyethylene glycol with the solid electrolyte phase. On the other hand, when the molecular weight of the polyethylene glycol contained in the liquid substance phase is relatively high, for example, the gaps of the solid electrolyte layer are blocked by the polyethylene glycol having a relatively large molecular weight, and contact or proximity between the conductive polymer constituting the solid electrolyte and the aromatic nitro compound is inhibited.

When the aromatic nitro compound is more effectively absorbed into the solid electrolyte phase, hydrogen gas generated due to leakage currents, etc. is more effectively removed by the aromatic nitro compound before it can adversely affect the conductive polymer compound that constitutes the solid electrolyte phase, and as a result, the durability of the electrolytic capacitor is improved.

The drawings are used to explain exemplary embodiments of the present invention in more detail. It should be noted that these drawings and exemplary embodiments are not intended to limit the present invention. The drawings are schematic and are not necessarily drawn to scale.

<Configuration of electrolytic capacitor 1 according to embodiment>
1A and 1B are diagrams for explaining an electrolytic capacitor 1 according to an embodiment of the present invention. Fig. 1A is a cross-sectional view of the electrolytic capacitor 1, and Fig. 1B is a perspective view of a capacitor element 20.

Figure 2 is a diagram for explaining the main parts of the electrolytic capacitor 1 according to the embodiment. Figure 2 is a cross-sectional view of the main parts of the electrolytic capacitor 1.

The electrolytic capacitor 1 according to the embodiment is a wound-type electrolytic capacitor, and as shown in FIG. 1, includes a cylindrical metal case 10 with a bottom, a capacitor element 20, and a sealing member 40.

The bottom surface of the metal case 10 is substantially circular, with a valve (not shown) located near the center. This allows the valve to break and release the internal pressure to the outside when the internal pressure rises. The side surface of the metal case 10 stands upright in a substantially vertical direction from the outer edge of the bottom surface. The opening of the metal case 10 is sealed with a sealing member 40, and the two leads 29, 30 of the capacitor element 20 are pulled out to the outside through a through hole provided in the sealing member 40.

The capacitor element 20 is housed inside the metal case 10, and as shown in Figs. 1(b) and 2, it comprises an anode foil 21, a cathode foil 23, and a separator 25 disposed between the anode foil 21 and the cathode foil 23, and the anode foil 21 and the cathode foil 23 are overlapped and wound with the separator 25 interposed therebetween.

In the embodiment shown in FIG. 2, a solid electrolyte phase consisting of a fine particle conductive polymer compound 26 and a liquid substance phase 27 containing a liquid substance are introduced into the gap between the anode foil 21 and the cathode foil 23, and the liquid substance phase 27 is present so as to surround the solid electrolyte consisting of the conductive polymer compound 26. The anode foil 21 and the cathode foil 23 have oxide films 22 and 24 on their surfaces, respectively.

<Gaps>
In the present disclosure, the term "gap between the anode foil and the cathode foil" includes not only "gaps between the anode foil and the separator and between the cathode foil and the separator" but also "gaps between fibers in the separator." In addition, the term "gap between the anode foil and the cathode foil" also includes "gaps in etching pits (recesses) formed in the surface of the anode foil or cathode foil by roughening through etching."

<Liquid substance phase>
The capacitor according to the present disclosure includes a liquid substance phase. The liquid substance phase includes at least a liquid substance and a nitro-aromatic compound.

The liquid phase can be present surrounding the solid electrolyte phase.

The liquid substance phase is preferably substantially composed of a liquid substance, an aromatic nitro compound, and optionally water. That is, the liquid substance phase is preferably composed of a liquid substance, an aromatic nitro compound, and optionally water, and contains other components in a proportion of 10% by mass or less, 5% by mass or less, 2% by mass or less, 1% by mass or less, or even 0.1% by mass or less.

In the capacitor according to the present disclosure, the proportion of the liquid substance phase occupying the gap between the anode foil and the cathode foil may be 10 vol% to 99 vol%, particularly 50 vol% to 99 vol%, or even 60 vol% to 99 vol%.

(Liquid substance)
The liquid substance contained in the liquid substance phase is polyethylene glycol (PEG). The liquid substance phase may contain ethylene glycol. When the liquid substance phase contains ethylene glycol, the content of ethylene glycol may be 5% by mass or less, or even 1% by mass or less, based on the liquid substance phase. In a preferred embodiment, the liquid substance phase does not contain ethylene glycol.

(Polyethylene glycol)
Polyethylene glycol (PEG) is
Diethylene glycol (abbreviated as "PEG-2"),
Triethylene glycol (abbreviated as "PEG-3"),
Tetraethylene glycol (abbreviated as "PEG-4"),
Pentaethylene glycol (abbreviated as "PEG-5"),
Hexaethylene glycol (abbreviated as "PEG-6"),
heptaethylene glycol (abbreviated as "PEG-7"),
Octaethylene glycol (abbreviated as "PEG-8"), and nonaethylene glycol (abbreviated as "PEG-9")
The polyethylene glycol is not limited to these examples, and also includes polyethylene glycols having a higher degree of polymerization (higher molecular weight) than the above polyethylene glycols.

The liquid substance (polyethylene glycol) may be a mixture of two or more types of polyethylene glycol with different molecular weights, or it may be a single type of polyethylene glycol with a single molecular weight.

A mixture of two or more polyethylene glycols with different molecular weights can be prepared, for example, by mixing two or more polyethylene glycols having specific molecular weights (e.g., triethylene glycol, tetraethylene glycol).

In one of the preferred embodiments of the present disclosure, the liquid substance (polyethylene glycol) comprises a mixture of triethylene glycol (PEG-3) and tetraethylene glycol (PEG-4) or consists essentially of this mixture (i.e., contains 0.1% by weight or less of other components).

The content of the liquid substance (polyethylene glycol) is preferably 80 to 99% by mass, more preferably 85 to 98% by mass, even more preferably 90 to 96% by mass, and particularly preferably 92 to 95% by mass, relative to the liquid substance phase.

(Proportion of PEG with relatively high molecular weight)
As described above, in the capacitor according to the present disclosure, the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is 30 mass % or less.

This proportion may be 28% by weight or less, 26% by weight or less, 24% by weight or less, or 22% by weight or less.

In a particularly preferred embodiment of the present invention, the proportion of pentaethylene glycol or larger polyethylene glycol in the polyethylene glycol is 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, or 1% by mass or less. The lower limit of this proportion is not particularly limited, but may be 0.1% by mass or more, 1% by mass or more, 2% by mass or more, 4% by mass or more, 6% by mass or more, 8% by mass or more, or 10% by mass or more.

It is particularly preferred that the polyethylene glycol is substantially free of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol. "Substantially free" means that the content of the component is 0.1% by mass or less.

There is no particular limitation on the method for producing a liquid substance (polyethylene glycol) in which the proportion of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol in polyethylene glycol is 30 mass % or less. For example, it can be obtained by using only at least one of the polyethylene glycols smaller than pentaethylene glycol (diethylene glycol, triethylene glycol, and tetraethylene glycol).

In addition, by incorporating at least one of polyethylene glycols smaller than pentaethylene glycol (diethylene glycol, triethylene glycol, and tetraethylene glycol) into a mixture of polyethylene glycols in which the proportion of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol exceeds 30% by mass, or into pentaethylene glycol or polyethylene glycols having a molecular weight larger than pentaethylene glycol, the proportion of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol can be made to be 30% by mass or less.

(Proportion of PEG with a relatively small molecular weight)
In a particularly preferred embodiment of the present invention, the proportion of tetraethylene glycol or smaller polyethylene glycol in the polyethylene glycol liquid substance is 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more. The upper limit of this proportion is not particularly limited, but may be less than 100% by mass or less than 99.9% by mass.

(Molecular Weight)
Preferably, the liquid material polyethylene glycol has an average molecular weight or molecular weight of less than 200. The average molecular weight or molecular weight of the liquid material polyethylene glycol is more preferably 190 or less, 180 or less, 170 or less, or 160 or less, and/or 100 or more, 110 or more, 120 or more, 130 or more, or 140 or more.

In the present disclosure, the "average molecular weight" of the liquid substance polyethylene glycol can be calculated from the amounts (proportions) of the polyethylene glycols used in preparing the liquid substance polyethylene glycol. Alternatively, the average molecular weight measured by GPC analysis (gel permeation chromatography analysis) can be used as the "average molecular weight" of the liquid substance polyethylene glycol.

<Aromatic nitro compounds>
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0 mass % or more, whereby a capacitor having excellent durability at high temperatures can be obtained.

Aromatic nitro compounds are aromatic compounds that contain a nitro group.

The aromatic nitro compound may be at least one selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, nitrobenzaldehyde, nitrobenzene carboxylic acid, nitrobenzene dicarboxylic acid, nitroaniline, nitroanisole, nitrotoluene, nitroacetanilide, nitrocresol, nitrophenyl acetic acid, methyl nitrobenzoic acid, dinitrobenzoic acid, nitroterephthalic acid, and nitroisophthalic acid. These may be used alone or in combination of two or more.

Preferably, the aromatic nitro compound is at least one selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, and nitrobenzaldehyde.

The aromatic nitro compound is preferably nitroacetophenone. When nitroacetophenone is used as the aromatic nitro compound, a capacitor with particularly good thermal durability can be obtained.

The content of aromatic nitro compounds may be 1.1% by mass or more, 1.2% by mass or more, 1.3% by mass or more, 1.4% by mass or more, 1.5% by mass or more, 2% by mass or more, or 3% by mass or more, and/or 10% by mass or less, 8% by mass or less, or 6% by mass or less, based on the liquid substance phase.

The content of the aromatic nitro compound is preferably 1.0 to 10 mass % relative to the liquid substance phase, more preferably 1.2 to 8 mass %, and even more preferably 1.4 to 6 mass %. In this case, a capacitor with particularly excellent durability at high temperatures is obtained.

<Water>
The liquid phase may contain water.

When the liquid substance phase present in the gap between the anode foil and the cathode foil contains "water" in addition to the liquid water-soluble polymer compound, even if defects occur in the oxide film during the process of manufacturing the electrolytic capacitor, it is possible to use the moisture from the "water" to repair the defects in addition to the moisture held by the water-soluble polymer compound. As a result, particularly good effects can be obtained in terms of reducing the defect density in the oxide film and reducing leakage current.

The water content may be 0% to 10% by mass, preferably 0.1% to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the liquid substance phase. When the water content is within this range, the oxide film defect repair effect can be sufficiently obtained, and adverse effects caused by an excessive water content (such as expansion of the capacitor that can occur when used for a long period of time in a high-temperature environment) can be avoided or suppressed.

The liquid substance phase may contain an ionic compound in addition to the liquid substance and the aromatic nitro compound. An example of the ionic compound is an organic salt. An organic salt is a salt in which at least one of the base and the acid that constitute the salt is organic. In one embodiment of the present disclosure, the liquid substance phase contains a liquid substance and an aromatic nitro compound, but does not contain an ionic compound (particularly an organic salt).

<Anode foil>
A capacitor according to the present disclosure includes an anode foil having an oxide film formed on its surface.

The anode foil may be formed from a valve metal such as aluminum, tantalum, or niobium.

The anode foil has an oxide film on its surface. For example, an oxide film can be formed on the surface of the anode foil by roughening the surface through an etching process according to a known method and then performing a chemical conversion treatment.

<Cathode foil>
A capacitor according to the present disclosure includes a cathode foil.

The cathode foil, like the anode foil, may be formed from a valve metal such as aluminum, tantalum, or niobium.

The cathode foil may have an oxide film formed on its surface. The surface of the cathode foil may be roughened by etching in the same manner as the anode foil, and then an oxide film may be formed by natural oxidation. The cathode foil may also be subjected to a chemical conversion treatment at a desired voltage (e.g., 2 V), which may result in the formation of an oxide film.

<Separator>
A capacitor according to the present disclosure includes a separator disposed between the anode foil and the cathode foil.

As the separator, those formed of cellulose fibers, which are chemically compatible with conductive polymer particles and water-soluble polymers, and synthetic resins such as nylon, PET, and PPS, which have excellent heat resistance, are preferable, and for example, heat-resistant cellulose paper and heat-resistant flame-retardant paper can be used. More specifically, examples of the separator include cellulose and mixed papers thereof, polyester resins, polyamide resins, polyimide resins, polyethylene resins, polypropylene resins, polyphenylene sulfide resins, acrylic resins, polyvinyl alcohol resins, and trimethylpentene resins, and these resins can be used alone or in combination. In addition, polytetrafluoroethylene resins, polyvinylidene fluoride resins, and vinylon resins can also be used. Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof. Examples of polyamide resins include aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides. Examples of cellulose include kraft, Manila hemp, esparto, hemp, and rayon.

<Solid electrolyte phase>
Capacitors according to the present disclosure include a solid electrolyte phase in the gap between the anode and cathode foils.

(Conductive polymer compound)
The solid electrolyte phase contains a conductive polymer compound, and in particular is substantially composed of a conductive polymer compound.

The conductive polymer compound may be at least one selected from polythiophene, polypyrrole, and polyaniline, and derivatives thereof. The conductive polymer compound may be at least one of these. A preferred conductive polymer compound is polyethylenedioxythiophene (PEDOT) (particularly poly(3,4-ethylenedioxythiophene)).

The solid electrolyte phase may further include a dopant. Examples of dopants include polystyrene sulfonic acid (PSS), toluene sulfonic acid, alkylbenzene sulfonic acid, and naphthalene sulfonic acid, as well as derivatives thereof. These may be used alone or in combination of two or more.

The polystyrene sulfonic acid preferably has a weight average molecular weight of 10,000 to 1,000,000.

In a preferred embodiment, the solid electrolyte phase comprises polyethylenedioxythiophene (PEDOT) and polystyrenesulfonic acid (PSS) as a dopant.

The conductive polymer compound may be in the form of fine particles. The average particle size of the fine particle conductive polymer compound is preferably in the range of 1 nm to 300 nm, or even 5 nm to 200 nm (e.g., 20 nm).

In the capacitor according to the present disclosure, the proportion of the conductive polymer compound in the gap between the anode foil and the cathode foil may be 0.5 vol% to 20 vol%, or even 1 vol% to 10 vol%.

(Formation of solid electrolyte phase)
The method for forming the solid electrolyte phase containing the conductive polymer compound is not particularly limited, but for example, it can be formed by a dipping impregnation method. For example, the solid electrolyte phase can be formed by filling a dispersion liquid (conductive polymer compound dispersion liquid) in which the conductive polymer compound is dispersed in a dispersion medium or a solution (conductive polymer compound solution) in which the conductive polymer compound is dissolved in a solvent into the voids, and then removing the dispersion medium or the solvent from the voids by heating and drying or the like.

More specifically, for example, a capacitor element is immersed in a conductive polymer dispersion or a conductive polymer solution using an introduction tank. The capacitor element is then removed from the conductive polymer dispersion or the conductive polymer solution, and the capacitor element is heat-treated to form a solid electrolyte phase. This operation may be repeated multiple times, thereby increasing the amount of filling of the solid electrolyte phase.

The solid electrolyte phase containing the conductive polymer compound may be formed by polymerizing the monomer in a so-called "in situ polymerization".

The conductive polymer content in the conductive polymer dispersion or conductive polymer solution may be 0.1 to 10% by mass, particularly 1 to 3% by mass.

As a dispersion medium for the conductive polymer compound dispersion, for example, protic solvents such as water, alcohol (methanol, ethanol, 1-propanol, butanol), and mixtures thereof can be used. As a solvent for the conductive polymer compound solution, for example, protic solvents such as water, alcohol (methanol, ethanol, 1-propanol, butanol), and mixtures thereof can be used. An aromatic nitro compound may be contained in the conductive polymer compound dispersion or the conductive polymer compound solution.

The conductive polymer dispersion or conductive polymer solution may contain other compounds as additives, for example, high-boiling point compounds (particularly compounds having a boiling point of 150°C or higher). Examples of additives include polyols (ethylene glycol, polyethylene glycol, and derivatives thereof; glycerin, diglycerin, polyglycerin, and derivatives thereof), sugar alcohols (sorbitol, mannitol, etc.), γ-butyrolactone, butanediol, dimethyl sulfoxide, sulfolane, N-methylpyrrolidone, and dimethyl sulfolane. These may be used alone or in combination of two or more.

The content of the additive in the conductive polymer compound dispersion or conductive polymer compound solution may be 1 to 40% by mass, particularly 2 to 30% by mass, or even 5 to 25% by mass. The content of the additive may be 1 to 20% by mass.

<Capacitor>
(CAP)
Capacitors according to the present disclosure may have a capacitance of 200-400 μF, or even 220-350 μF, when measured at 120 Hz according to the method described in the Examples.

(tan δ)
Capacitors according to the present disclosure may have a tan delta of 0.5 to 4.0%, or even 1.0 to 3.0%, when measured at 120 Hz according to the method described in the Examples.

(ESR)
Capacitors according to the present disclosure may have an ESR of 5 to 30 mΩ, or even 8 to 20 mΩ, when measured at 100 kHz according to the method described in the Examples.

<<Capacitor manufacturing method>>
The method for producing the capacitor according to the present disclosure is not particularly limited. In particular, the capacitor according to the present disclosure can be produced by the following production method according to the present disclosure:
forming a capacitor element by stacking an anode foil having an oxide film formed on its surface and a cathode foil that has been optionally etched, with a separator interposed therebetween, and winding the stack;
impregnating the capacitor element with an aqueous solution or dispersion of a conductive polymer compound to form a solid electrolyte phase in the gap between the anode foil and the cathode foil; and
impregnating a capacitor element having a solid electrolyte phase formed therein with a liquid substance phase containing a liquid substance;
Including,
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0% by mass or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol is 30 mass% or less.
A method for manufacturing electrolytic capacitors.

For details of each component of the manufacturing method according to the present disclosure (anode foil, cathode foil, solid electrolyte phase, liquid substance phase, liquid substance, etc.), please refer to the above description of the electrolytic capacitor according to the present disclosure.

A method for manufacturing an electrolytic capacitor in an exemplary embodiment is described below. This exemplary manufacturing method includes, in this order, a capacitor element fabrication process, a chemical conversion treatment process, a solid electrolyte phase introduction process, a liquid substance phase introduction process, and an assembly and sealing process.

(1) Capacitor Element Preparation Process In an exemplary method of an electrolytic capacitor, first, an aluminum foil is provided as an anode foil 21. After the surface of the aluminum foil is roughened by a surface enlarging process, a predetermined voltage of 2V to 500V is applied to the roughened surface of the aluminum foil to perform a chemical conversion process, thereby forming an oxide film 22 on the surface of the aluminum foil. Then, a capacitor element is prepared that includes an anode foil 21 having an oxide film 22, a cathode foil 23 that has been optionally etched, and a separator 25 disposed between the anode foil 21 and the cathode foil 23 (see FIG. 1(b)). Specifically, the anode foil 21 having an uneven surface (rough surface) and the oxide film 22 formed on the uneven surface and the cathode foil 23 having an uneven surface are overlapped and wound through the separator 25 to prepare a capacitor element 20. At this time, a lead 30 is connected to the anode foil 21, and a lead 29 is connected to the cathode foil 23.

(2) Chemical Conversion Treatment Step Next, the capacitor element 20 is immersed in a chemical conversion solution in a chemical conversion solution tank, and a predetermined voltage (e.g., 100 V) is applied between the anode lead 30 and the chemical conversion solution for 5 minutes. This operation repairs defects in the oxide film present at the edge of the anode foil 21 and defects in the oxide film that may be present on the surface.

The chemical conversion liquid may be an aqueous solution of, for example, ammonium adipate, ammonium borate, ammonium phosphate, ammonium glutarate, ammonium azelaate, ammonium tartrate, ammonium sebacate, ammonium pimelate, or ammonium suberate.

(3) Solid Electrolyte Phase Introducing Step Next, a solid electrolyte phase consisting of fine particle conductive polymer compound 26 is introduced into the gap between the anode foil 21 and the cathode foil 23 so that the ratio of the solid electrolyte phase occupying the gap is within a range of, for example, 2 vol % to 30 vol %. In the solid electrolyte phase introducing step, for example, a conductive polymer compound dispersion liquid in which a conductive polymer compound is dispersed in a dispersion medium is filled into the gap, and then the dispersion medium is removed from the gap, thereby introducing the solid electrolyte phase into the gap. Instead of the conductive polymer compound dispersion liquid, a solution in which a conductive polymer compound is dissolved in a solvent (conductive polymer compound solution) may be used.

More specifically, the solid electrolyte phase introduction step can be performed by a dipping impregnation method. That is, after filling an introduction tank with a conductive polymer compound dispersion liquid (e.g., polymer concentration 2 vol%), the capacitor element is immersed in the conductive polymer compound dispersion liquid. Next, the capacitor element is removed from the introduction tank, and then the capacitor element is heat-treated.

The conductive polymer dispersion liquid can be produced by polymerizing (radical polymerization or oxidative polymerization) a monomer (e.g., PEDOT monomer) in suspension to produce a conductive polymer compound in the form of fine particles (e.g., PEDOT polymer) to which a dopant or emulsifier has been added, and dispersing the fine particles of the conductive polymer compound in a predetermined dispersion medium. The average particle size of the conductive polymer compound can be adjusted by appropriately setting the polymerization reaction conditions (e.g., the concentrations of the initiator, monomer, polymerization aid, etc., the reaction temperature, the stirring conditions of the reaction solution, etc.). It can also be adjusted by carrying out a known crushing process (e.g., agitation crushing process, vibration crushing process, etc.). The particle size can also be made uniform by a separation filtration process.

In order to increase the proportion of the solid electrolyte phase in the voids, the number of repetitions of the above operation can be increased and/or the polymer concentration in the conductive polymer compound dispersion can be increased. On the other hand, in order to decrease the proportion of the solid electrolyte phase in the voids, the number of repetitions of the above operation can be decreased and/or the polymer concentration in the conductive polymer compound dispersion can be decreased.

(4) Liquid substance phase introducing step In the liquid substance phase introducing step, for example, the liquid substance phase 27 is introduced into the gap between the anode foil 21 and the cathode foil 23 so as to surround the solid electrolyte and so that the ratio of the liquid substance phase 27 occupying the gap is within a range of 10 vol % to 99 vol %. Specifically, the liquid substance phase introducing step can be performed as follows (a) and (b).

(a) Preparation of liquid substance phase The liquid substance phase can be prepared by providing a liquid substance (polyethylene glycol), adding an aromatic nitro compound and optionally water to the liquid substance, and then stirring. These operations may be carried out at, for example, 40°C.

(b) Introduction of Liquid Material Phase When the filling of the liquid material phase is carried out by the immersion impregnation method, the liquid material phase is filled into an introduction tank, and then the capacitor element is immersed in the liquid material phase to introduce the liquid material phase into the voids.

(5) Assembly and sealing process In the assembly and sealing process, the sealing member 40 is attached to the capacitor element 20, and the capacitor element 20 is inserted into the metal case 10, and then the metal case 10 is crimped near the open end of the metal case 10. As the sealing member 40, for example, isobutylene-isoprene rubber (IIR) can be used. Instead of isobutylene-isoprene rubber (IIR), rubber materials such as ethylene-propylene terpolymer (EPT), EPT-IIR blend rubber, silicone rubber, and rubber composite materials in which resins such as phenolic resin (Bakelite), epoxy resin, and fluororesin are bonded to rubber can also be used. Thereafter, an aging process is performed by applying a predetermined voltage in a high-temperature atmosphere as desired. This completes the electrolytic capacitor 1 according to the embodiment.

The following describes the embodiments of the present invention in more detail with reference to examples. The following examples and comparative examples are not intended to limit the present invention.

<<Measurement method>>
The measurement methods used in the examples and comparative examples are as follows.

<CAP>
The CAP (μF) of the capacitor was measured at 120 Hz in a thermostatic chamber at 25° C. using an LCR meter (Precision LCR Meter (E4980A) manufactured by Keysight Technologies).

<tan δ>
The tan δ (%) of the capacitor was measured at 120 Hz in a thermostatic chamber at 25° C. using an LCR meter (Precision LCR Meter (E4980A) manufactured by Keysight Technologies).

<ESR>
The ESR (mΩ) of the capacitor was measured at 100 kHz in a thermostatic chamber at 25° C. using an LCR meter (Precision LCR Meter (E4980A) manufactured by Keysight Technologies).

<Average molecular weight>
The average molecular weight of polyethylene glycol was measured by the GPC method using a high performance liquid chromatograph (Shimadzu Corporation, Prominence).

<<Examples 1 to 5 and Comparative Examples 1 to 2>>
In Examples 1 to 5 and Comparative Examples 1 and 2, the composition of the polyethylene glycol contained in the liquid substance phase of the capacitor was examined.

Example 1
(Capacitor manufacturing)
Anode foil (made of aluminum) and cathode foil (made of aluminum) with a withstand voltage of about 60V were wound with a separator (made of cellulose) between them, and then the end faces and defects were chemically formed using a chemical formation solution, and then the solid electrolyte was vacuum-impregnated and dried to produce a capacitor element having a solid electrolyte phase. The solid electrolyte phase contained polyethylenedioxythiophene (PEDOT) as a conductive polymer compound and polystyrenesulfonic acid (PSS) as a dopant. The capacitor element was impregnated with the liquid constituting the liquid substance phase to obtain the capacitor according to Example 1.

The liquid phase of the capacitor of Example 1 had the following composition:
94% by weight of tetraethylene glycol (PEG-4) (molecular weight 194.23)
5% by weight nitroacetophenone 1% by weight water

In the liquid substance phase of Example 1, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0% by mass.

<Performance evaluation (initial value)>
For the produced capacitor according to Example 1, an initial performance evaluation and a performance evaluation after a durability test were respectively performed.

In the durability test, the capacitor was left at rest for 500 hours at 135°C with a voltage of 42 V applied to it, and then the performance of the capacitor was evaluated.

The results for Example 1 are shown in Table 1 below.

Example 2
A capacitor according to Example 2 was produced in the same manner as in Example 1, except that a mixture (mass ratio 2:8) of PEG-4 and PEG-3 (triethylene glycol, molecular weight 150.17) was used instead of the above-mentioned PEG-4, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 2, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 1 below.

Example 3
A capacitor according to Example 3 was produced in the same manner as in Example 1, except that PEG-3 was used instead of the above-mentioned PEG-4, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 3, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 1 below.

Example 4
A capacitor according to Example 4 was produced in the same manner as in Example 1, except that PEG-2 (diethylene glycol, molecular weight 106.12) was used instead of the above-mentioned PEG-4, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 4, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 1 below.

Example 5
A capacitor according to Example 5 was manufactured in the same manner as in Example 1, except that a mixture of PEG-4 and PEG200 (mass ratio 5:5) was used instead of the PEG-4, and the performance of the capacitor was evaluated.

The PEG 200 used in Example 5 has a molecular weight distribution, i.e., it is a mixture of multiple polyethylene glycols with different degrees of polymerization. Measurements by gel chromatography (GPC method) showed that in the liquid substance phase of Example 5, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 21.6 mass %. The results are shown in Table 1 below.

<Comparative Example 1>
A capacitor according to Comparative Example 1 was manufactured in the same manner as in Example 1, except that PEG300 was used instead of the above-mentioned PEG-4, and the performance of the capacitor was evaluated.

The PEG300 used in Comparative Example 1 has a molecular weight distribution, i.e., it is a mixture of multiple polyethylene glycols with different degrees of polymerization. Measurements by gel chromatography (GPC method) showed that in the liquid substance phase of Comparative Example 1, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 79.6 mass %. The results are shown in Table 1 below.

<Comparative Example 2>
A capacitor according to Comparative Example 2 was manufactured in the same manner as in Example 1, except that PEG200 was used instead of the above-mentioned PEG-4, and the performance of the capacitor was evaluated. As a result of measuring the molecular weight distribution by gel chromatography, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol in the liquid substance phase according to Comparative Example 2 was 43.3 mass %. The results are shown in Table 1 below.

<Reference Example 1>
A capacitor according to Reference Example 1 was produced in the same manner as in Example 1, except that ethylene glycol (EG) was used instead of the PEG-4, and the performance of the capacitor was evaluated.

From Table 1, it can be seen that by using nitroacetophenone as the aromatic nitro compound and by using a relatively low proportion (mass%) of PEG-5 or higher, the capacitor's properties are maintained after endurance testing.

<<Example 6 and Comparative Example 3>>
In Example 6 and Comparative Example 3, the contents of nitroacetophenone as an aromatic nitro compound contained in the liquid substance phase of the capacitor were set to 10 mass % and 0 mass %, respectively.

Example 6
A capacitor according to Example 6 was manufactured in the same manner as in Example 3, except that the contents of nitroacetophenone (10% by mass) and PEG-3 were changed, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 6, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0% by mass. The results are shown in Table 2 below.

<Comparative Example 3>
A capacitor according to Comparative Example 3 was produced in the same manner as in Example 6, except that nitroacetophenone was not added, and the performance of the capacitor was evaluated. In the liquid substance phase according to Comparative Example 3, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 2 below.

From Table 2, it can be seen that the effect shown in Table 1, that is, the effect of using nitroacetophenone as the aromatic nitro compound and having a low proportion (mass %) of PEG-5 or higher to maintain the capacitor characteristics well after endurance testing, is obtained when the nitroacetophenone content is 5 or 10 parts by weight, but is not obtained when nitroacetophenone is not contained.

<<Examples 7 to 12>>
In Examples 7 to 12, the cases where an aromatic nitro compound other than nitroacetophenone was used as the aromatic nitro compound contained in the liquid substance phase of the capacitor were examined.

Example 7
A capacitor according to Example 7 was manufactured in the same manner as in Example 3, except that nitrobenzoic acid was used instead of nitroacetophenone, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 7, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 3 below.

Example 8
A capacitor according to Example 8 was manufactured in the same manner as in Example 3, except that nitrobenzyl alcohol was used instead of nitroacetophenone, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 8, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 3 below.

<Example 9>
A capacitor according to Example 9 was manufactured in the same manner as in Example 8, except that the contents of nitrobenzyl alcohol (10% by mass) and PEG-3 were changed, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 9, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0% by mass. The results are shown in Table 3 below.

Example 10
A capacitor according to Example 10 was manufactured in the same manner as in Example 3, except that nitrophenol was used instead of nitroacetophenone, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 10, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 3 below.

Example 11
A capacitor according to Example 11 was produced in the same manner as in Example 10, except that the contents of nitrophenol (10% by mass) and PEG-3 were changed, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 11, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0% by mass. The results are shown in Table 3 below.

Example 12
A capacitor according to Example 12 was manufactured in the same manner as in Example 3, except that nitrobenzaldehyde was used instead of nitroacetophenone, and the performance of the capacitor was evaluated. In the liquid substance phase according to Example 12, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 3 below.

From Table 3, it can be seen that the effect shown in Table 1, that is, the effect of using nitroacetophenone as the aromatic nitro compound and having a low proportion (mass %) of PEG-5 or higher, thereby maintaining the capacitor characteristics well after endurance testing, can also be obtained with aromatic nitro compounds other than nitroacetophenone.

<<Examples 13 to 16>>
In Examples 13 to 16, PEG-3 and nitroacetophenone were added, and the water content was varied to various values for investigation.

The capacitors of Examples 13 to 16 were manufactured in the same manner as in Example 3, except that the content of PEG-3 and water was changed as shown in Table 4 below, and the performance of the capacitors was evaluated. In the liquid substance phase of Examples 13 to 16, the proportion of pentaethylene glycol (PEG-5) or polyethylene glycols larger than pentaethylene glycol in the polyethylene glycol was 0 mass %. The results are shown in Table 4 below.

From Table 4, it can be seen that the effect shown in Table 1, that is, the effect of using nitroacetophenone as the aromatic nitro compound and having a low ratio (mass %) of PEG-5 or higher, which allows the capacitor characteristics to be well maintained after endurance testing, can be obtained even when the amount of water is changed.

<<Examples 17A to 20A and Comparative Examples 4A to 5A>>
In Examples 17A to 20A and Comparative Examples 4A to 5A, the component contents in the liquid substance phase containing PEG-3, nitroacetophenone, and water were changed to various values as shown in Table 5 below, and evaluation was performed.

In the durability test, the capacitor was left at rest for 60 hours at 135°C with a voltage of 42 V applied to it, and then the performance of the capacitor was evaluated.

The results are shown in Table 5 below.

<<Examples 17B to 20B and Comparative Examples 4B to 5B>>
In Examples 17B to 20B and Comparative Examples 4B to 5B, the performance evaluation of the capacitors was performed in the same manner as in Examples 17A to 20A and Comparative Examples 4A to 5A, respectively, except that the duration of the durability test was changed from 60 hours to 80 hours. The results are shown in Table 6 below.

As can be seen from Tables 5 and 6, the effect of maintaining the capacitor characteristics well after endurance testing by using nitroacetophenone as the aromatic nitro compound and having a low proportion (mass %) of PEG-5 or higher is obtained when the nitroacetophenone content is 1.0 to 5.0 mass %, but it can be seen that this effect is not obtained when the nitroacetophenone content is 0.5 mass % or when no nitroacetophenone is contained.

As can be seen from Table 6, the capacitor with a nitroacetophenone content of 1.0% by mass showed a slight decrease in durability in the 80-hour durability test, but showed superior durability compared to capacitors with a nitroacetophenone content of 0.5% by mass or no nitroacetophenone. Capacitors with a nitroacetophenone content of 1.5 to 5.0% by mass showed very excellent durability even in the 80-hour durability test.

REFERENCE SIGNS LIST 1 electrolytic capacitor 10 metal case 20 capacitor element 21 anode foil 22, 24 oxide film 23 cathode foil 25 separator 26 solid electrolyte phase 27 liquid material phase 29, 30 lead 40 sealing member

Claims (5)

an anode foil having an oxide film formed on its surface;
A cathode foil;
a separator disposed between the anode foil and the cathode foil;
Equipped with
In the gap between the anode foil and the cathode foil,
A solid electrolyte phase including a conductive polymer compound;
A liquid material phase including a liquid material;
An electrolytic capacitor comprising:
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0% by mass or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is 30 mass% or less.
Electrolytic capacitor. The electrolytic capacitor according to claim 1, wherein the liquid substance phase contains water in an amount of 0.1% by mass to 10% by mass. The electrolytic capacitor according to claim 1 or 2, wherein the aromatic nitro compound is selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, and nitrobenzaldehyde. The electrolytic capacitor according to claim 1 or 2, wherein the solid electrolyte phase contains polyethylenedioxythiophene as the conductive polymer compound and polystyrenesulfonic acid as a dopant. forming a capacitor element by stacking an anode foil having an oxide film formed on its surface and a cathode foil that has been optionally etched, with a separator interposed therebetween, and winding the stack;
impregnating the capacitor element with an aqueous solution or dispersion of a conductive polymer compound to form a solid electrolyte phase in the gap between the anode foil and the cathode foil; and
impregnating the capacitor element having a solid electrolyte phase formed therein with a liquid substance phase containing a liquid substance;
Including,
The liquid substance phase contains an aromatic nitro compound in an amount of 1.0% by mass or more,
The liquid substance is polyethylene glycol, and the proportion of pentaethylene glycol or polyethylene glycol larger than pentaethylene glycol in the polyethylene glycol is 30 mass% or less.
A method for manufacturing electrolytic capacitors.