Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present disclosure includes a capacitor element and a liquid component. The capacitor element includes an anode body, a dielectric layer that is formed on the surface of the anode body, and a conductive polymer that is in contact with at least part of the surface of the dielectric layer. The liquid component includes a non-aqueous solvent and an acid component. The non-aqueous solvent includes an aprotic solvent. The proportion of aprotic solvent in the non-aqueous solvent is more than 50 mass%. The acid component includes a first acid that is an aliphatic hydroxycarboxylic acid and a second acid that is a boric acid compound.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Electrolytic capacitors are considered promising as capacitors with small size, large capacity, and low ESR (equivalent series resistance). The electrolytic capacitors include an anode body having a dielectric layer formed on its surface, a conductive polymer in contact with at least a portion of the dielectric layer, and an electrolyte. The electrolyte may be a solution in which a solute is dissolved in a non-aqueous solvent, or a liquid component such as a non-aqueous solvent.

[0003] Patent Document 1 proposes an electrolyte solution to be used in an electrolytic capacitor including an anode having a dielectric oxide film, a cathode, a separator disposed between the anode and the cathode, and a conductive polymer and an electrolyte solution held by the separator, the electrolyte solution containing a solvent containing at least one selected from the group consisting of ethylene glycol, polyethylene glycol, and derivatives thereof, and a solute containing at least one selected from the group consisting of a dicarboxylic acid having a hydroxyl group at the α-position, a polycarboxylic acid having a hydroxyl group at the α-position, and salts thereof.

[0004] Patent Document 2 proposes a method for manufacturing an electrolytic capacitor, which comprises: preparing a wound element by winding an anode foil and a cathode foil, to which tab terminals for external lead electrodes are connected, with a separator interposed therebetween; subjecting the cut cross section of the anode foil and the attachment portion for the tab terminal to a chemical conversion treatment; forming a conductive polymer layer to prepare a capacitor element; storing the capacitor element, to which a sealing member is attached, and an electrolyte in a cylindrical metal case with a bottom; sealing the opening of the metal case; and performing an aging treatment; the method is characterized in that the electrolyte has a resistivity of 5 kΩ cm or more; and performing a heat treatment at 150 to 210°C for 10 to 30 minutes after sealing the opening of the metal case and before performing the aging treatment.

[0005] Patent Document 3 proposes an electrolyte solution for electrolytic capacitors that contains an organic carboxylic acid having a hydroxy group, a boron compound, and a solvent, in which the content of the boron compound is 0.6 mol or more per mol of the organic carboxylic acid having a hydroxy group, and the solvent contains a protic organic solvent, so that an increase in pressure inside the outer container can be suppressed even when the electrolytic capacitor is exposed to a high temperature of 250°C or higher.

[0006] Patent Document 4 proposes an electrolyte solution for use in an electrolytic capacitor including an anode having a dielectric oxide film, a cathode, a separator disposed between the anode and the cathode, a capacitor element having a conductive polymer and an electrolyte solution held by the separator, and an outer casing housing the capacitor element. The electrolyte solution is characterized by containing a solvent containing at least one selected from the group consisting of alkylene glycol, polyalkylene glycol, polyglycerin, polyoxyethylene glycerin fatty acid ester, polyoxyethylene glycerin ether, and derivatives thereof; and a solute containing at least one selected from the group consisting of a dicarboxylic acid having a hydroxyl group at the α-position, a polycarboxylic acid having a hydroxyl group at the α-position, and salts thereof, and an aliphatic dicarboxylic acid having an unsaturated bond and a molecular weight of 150 or more and / or a salt thereof.

[0007] Patent Document 5 proposes an electrolyte solution to be used in an electrolytic capacitor including an anode and a cathode having a dielectric oxide film, a separator disposed between the anode and the cathode, and a conductive polymer and an electrolyte solution held by the separator, the electrolyte solution including a solute containing 3 wt % to 30 wt % of at least one selected from the group consisting of aliphatic hydroxy acids and salts thereof, and a solvent.

[0008] Japanese Patent Application Laid-Open No. 2021-163877 Japanese Patent Application Laid-Open No. 2022-017716 International Publication No. 2021 / 095815 Japanese Patent Application Laid-Open No. 2024-006100 Japanese Patent Application Laid-Open No. 2018-198248

[0009] When a liquid component containing an aliphatic hydroxycarboxylic acid is used, the dielectric layer is easily repaired. However, when an electrolytic capacitor is exposed to high temperatures, such as during a reflow process, the use of an aliphatic hydroxycarboxylic acid can easily generate gas, which can cause significant swelling of the electrolytic capacitor.

[0010] One aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element and a liquid component, wherein the capacitor element includes an anode body, a dielectric layer formed on a surface of the anode body, and the conductive polymer in contact with at least a portion of a surface of the dielectric layer, wherein the liquid component includes a non-aqueous solvent and an acid component, wherein the non-aqueous solvent includes an aprotic solvent, and a ratio of the aprotic solvent in the non-aqueous solvent is greater than 50 mass %, and the acid component includes a first acid that is an aliphatic hydroxycarboxylic acid and a second acid that is a boric acid compound.

[0011] According to the present disclosure, swelling of an electrolytic capacitor when exposed to high temperatures can be reduced.

[0012] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure, showing a portion of a capacitor element of the electrolytic capacitor shown in FIG. 1 that is expanded, and FIG. 2 is a schematic cross-sectional view showing a portion of the electrolytic capacitor shown in FIG. 1 that is measured to evaluate swelling.

[0013] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0014] In aromatic hydroxycarboxylic acids such as salicylic acid, the carboxyl and hydroxyl groups attached to the benzene ring have a planar structure, whereas in aliphatic hydroxycarboxylic acids, the carboxyl and hydroxyl groups attached to the carbon chain can rotate to form a three-dimensional structure. Therefore, aliphatic hydroxycarboxylic acids have a selective affinity with hydrophilic dielectric layers and are thought to promote the repair of the oxide film that constitutes the dielectric layer. On the other hand, aliphatic hydroxycarboxylic acids are more susceptible to decomposition at high temperatures than aromatic hydroxycarboxylic acids. Therefore, when electrolytic capacitors are exposed to high temperatures (e.g., 220°C or higher in the case of reflow soldering) during the board mounting process or when used in a high-temperature environment, decomposition of the aliphatic hydroxycarboxylic acids within the electrolytic capacitor can generate gas, potentially resulting in significant swelling of the electrolytic capacitor.

[0015] On the other hand, the electrolytic capacitor according to the present disclosure uses a liquid component containing an aliphatic hydroxycarboxylic acid, thereby reducing swelling when the electrolytic capacitor is exposed to high temperatures. Additionally, the use of the liquid component reduces the effects of voltage-induced changes in the electrolytic capacitor's characteristics. The voltage-induced changes in characteristics are affected, for example, by the ratio V / Vw of the formation voltage V (unit: V (volts)) of the dielectric layer to the rated voltage Vw (unit: V (volts)) of the electrolytic capacitor. Hereinafter, the V / Vw ratio may be referred to as the Vt ratio. When this Vt ratio is equal to or less than a predetermined value, the effects of voltage-induced changes in characteristics are particularly significant.

[0016] (Technology 1) An electrolytic capacitor according to one aspect of the present disclosure includes a capacitor element and a liquid component. The capacitor element includes an anode body, a dielectric layer formed on the surface of the anode body, and the conductive polymer in contact with at least a portion of the surface of the dielectric layer. The liquid component includes a non-aqueous solvent and an acid component. The non-aqueous solvent includes an aprotic solvent. The proportion of the aprotic solvent in the non-aqueous solvent is greater than 50 mass%. The acid component includes a first acid that is an aliphatic hydroxycarboxylic acid and a second acid that is a boric acid compound.

[0017] When the ratio of aprotic solvents to the nonaqueous solvent contained in the liquid component is high, it is difficult to achieve the dielectric layer film repair effect of the nonaqueous solvent. When such a nonaqueous solvent is used, the dielectric layer film repair effect can be enhanced by using an aliphatic hydroxycarboxylic acid. However, aliphatic hydroxycarboxylic acids have low heat resistance and tend to decompose when exposed to high temperatures, causing swelling of the electrolytic capacitor. In the present disclosure, by including a first acid that is an aliphatic hydroxycarboxylic acid and a second acid that is a boric acid compound in the liquid component, swelling of the electrolytic capacitor when exposed to high temperatures can be reduced when using an aliphatic hydroxycarboxylic acid.

[0018] Furthermore, in order to increase the capacitance of electrolytic capacitors, the thickness of the dielectric layer may be reduced. On the other hand, as the thickness of the dielectric layer decreases (i.e., the Vt ratio decreases), changes in characteristics are more likely to occur. Therefore, the film repairability of the dielectric layer using a liquid component becomes important. For example, when a dielectric layer is formed by chemical conversion of the surface of an anode body, the thickness of the dielectric layer decreases if the chemical conversion is performed at a low chemical conversion voltage. When a thin dielectric layer is subjected to an accelerated test in which the layer is left in a relatively high-temperature environment (e.g., a temperature of 120°C or higher and 150°C or lower) while a voltage is applied, a decrease in capacity and an increase in ESR after the accelerated test may become more pronounced compared to when the layer is chemically converted at a general chemical conversion voltage. In particular, it has been found that the decrease in capacity and the increase in ESR after the accelerated test become more pronounced when a liquid component containing a first acid but not a second acid is used. In contrast, in the present disclosure, by using a liquid component containing a first acid and a second acid and having a high ratio of aprotic solvent in the nonaqueous solvent, capacity loss and ESR increase after accelerated testing are significantly suppressed even when the dielectric layer thickness is relatively small (in other words, the Vt ratio is small). This suppression effect is greater than when a liquid component containing a second acid but not a first acid is used, and is thought to be due to a synergistic effect between the first acid and the second acid. This synergistic effect is obtained when a liquid component containing a high ratio of aprotic solvent in the nonaqueous solvent is used.

[0019] (Technology 2) In the above (Technology 1), the acid component may further include a tertiary acid that is an aromatic carboxylic acid. In this case, relatively high film repairability can be obtained and electrode corrosion can be suppressed. The tertiary acid also has relatively high heat resistance, so when the electrolytic capacitor is exposed to high temperatures, de-doping, in which the dopant is detached from the conductive polymer, is reduced. Therefore, deterioration of the conductive polymer is suppressed, making it easier to maintain high capacity after accelerated testing when the Vt ratio is small, and further suppressing an increase in ESR.

[0020] (Technology 3) In the above-described (Technology 1) or (Technology 2), the total mass ratio of the first acid and the second acid in the liquid component may be less than the mass ratio of the third acid. The swelling of an electrolytic capacitor is largely influenced by the first acid, and even if the mass ratio of the first acid and the second acid is less than the mass ratio of the third acid, the swelling suppression effect is sufficiently exhibited. Furthermore, when the Vt ratio is small, the decrease in capacitance and increase in ESR of the electrolytic capacitor after an accelerated test are largely influenced by the first acid. In the present disclosure, even if the total mass ratio of the first acid and the second acid is less than the mass ratio of the third acid, excellent performance (specifically, high capacity and low ESR) after an accelerated test can be obtained when the Vt ratio is small. Furthermore, a high mass ratio of the third acid facilitates obtaining higher heat resistance and suppressing electrode corrosion.

[0021] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the liquid component may further contain a base component. When the liquid component contains a base component, the acid component is more likely to be dissociated, which acts on the conductive polymer, making it easier to obtain high conductivity of the conductive polymer. Therefore, it is easier to obtain high initial capacity and low ESR. It is also easier to ensure high conductivity of the liquid component.

[0022] (Technology 5) In any one of the above (Technology 1) to (Technology 4), the aprotic solvent may include at least one selected from the group consisting of sulfone-based solvents, lactone-based solvents, and carbonate-based solvents. Using these solvents makes it easier to ensure high electrical conductivity of the liquid component. Furthermore, while these solvents themselves have a low film repair effect on the dielectric layer, the present disclosure uses a first acid and a second acid, which provides a high film repair effect and further suppresses deterioration of the conductive polymer.

[0023] (Technology 6) In any one of the above (Technology 1) to (Technology 5), the first acid may include an aliphatic hydroxycarboxylic acid having three or more functional groups selected from the group consisting of hydroxy groups and carboxy groups. Such aliphatic hydroxycarboxylic acid may be at least one of an aliphatic hydroxycarboxylic acid having two or more hydroxy groups and one or more carboxy groups, and an aliphatic hydroxycarboxylic acid having one or more hydroxy groups and two or more carboxy groups. When the first acid includes such an aliphatic hydroxycarboxylic acid, swelling can be further reduced when combined with a second acid and an aprotic solvent. Furthermore, when the Vt ratio is small, deterioration of characteristics after accelerated testing can be further suppressed.

[0024] (Technology 7) In any one of the above (Technology 1) to (Technology 6), the first acid may include an aliphatic hydroxycarboxylic acid having two or more hydroxy groups and two or more carboxy groups. When the first acid includes such an aliphatic hydroxycarboxylic acid, swelling can be further reduced when combined with the second acid and an aprotic solvent. Furthermore, when the Vt ratio is small, deterioration of characteristics after accelerated testing can be further suppressed.

[0025] (Technology 8) In any one of the above (Technology 1) to (Technology 7), the first acid may include an aliphatic hydroxycarboxylic acid having at least one α-hydroxy group. When the first acid includes such an aliphatic hydroxycarboxylic acid, swelling can be further reduced when combined with the second acid and an aprotic solvent. This makes it easier to maintain the high performance of the electrolytic capacitor after accelerated testing when the Vt ratio is small.

[0026] (Technology 9) In any one of (Technology 1) to (Technology 8) above, the molar ratio of the second acid to the first acid (=second acid / first acid) in the liquid component may be 0.5 or more. In this case, swelling of the electrolytic capacitor can be further reduced. Furthermore, even if the formation voltage is low (in other words, even if the Vt ratio is small or the thickness of the dielectric layer is small), the decrease in capacitance and the increase in ESR after an accelerated test can be further reduced.

[0027] (Technology 10) In any one of (Technology 1) to (Technology 9) above, the molar ratio of the second acid to the first acid (=second acid / first acid) in the liquid component may be 3.0 or less. In this case, swelling of the electrolytic capacitor can be further reduced. Furthermore, even if the formation voltage is low (in other words, even if the Vt ratio is small or the thickness of the dielectric layer is small), the decrease in capacitance and the increase in ESR after an accelerated test can be further reduced. In addition, a low initial ESR can be easily achieved.

[0028] (Technology 11) In any one of (Technology 1) to (Technology 10) above, the second acid may include at least one selected from the group consisting of boric acid, a partial ester of boric acid, and a borate. The use of such a second acid can further reduce swelling when combined with the first acid and an aprotic solvent. Furthermore, it can further reduce the deterioration of electrolytic capacitor performance after accelerated testing when the Vt ratio is small.

[0029] (Technology 12) In any one of (Technology 1) to (Technology 11) above, the ratio V / Vw (i.e., Vt ratio) of the formation voltage V of the dielectric layer to the rated voltage Vw of the electrolytic capacitor may be 1.80 or less. A Vt ratio in this range indicates that the formation voltage is lower than typical values ​​and the thickness of the dielectric layer is small. In the present disclosure, because the liquid component is used, high film repairability is achieved and high conductivity of the conductive polymer is maintained, even when the Vt ratio is as small as described above (in other words, the thickness of the dielectric layer is small). Therefore, a Vt ratio of 1.80 or less is advantageous in maintaining high capacitance and low ESR after accelerated testing.

[0030] The electrolytic capacitor of the present disclosure will be described in more detail below, including the above (Technology 1) to (Technology 12), with reference to the drawings as necessary. To the extent that there is no technical contradiction, at least one of the above (Technology 1) to (Technology 12) may be combined with at least one of the elements described below. Note that each figure is a schematic illustration, and the dimensional ratios (e.g., thickness) of each component may differ from the actual ratios.

[0031] [Electrolytic Capacitor] An electrolytic capacitor includes a capacitor element and a liquid component, which are usually contained in a container.

[0032] (Liquid Component) The liquid component includes a non-aqueous solvent and an acid component. The liquid component may further include a base component. The liquid component may include a solute (specifically, a salt). The salt may be a salt of an acid component and a base component. In an electrolytic capacitor, the acid component may form a salt, may be in a free state, may be in an anionic state, or may be in a state of interaction with a component contained in the liquid component or the capacitor element. For convenience, all of these states may be referred to as the acid component in this specification. In an electrolytic capacitor, the base component may form a salt, may be in a free state, may be in a cationic state, or may be in a state of interaction with a component contained in the liquid component or the capacitor element. For convenience, all of these states may be referred to as the base component in this specification.

[0033] (Non-aqueous solvent) The non-aqueous solvent includes an aprotic solvent. The aprotic solvent includes, for example, at least one selected from the group consisting of sulfone-based solvents, lactone-based solvents, and carbonate-based solvents. From the viewpoint of ensuring high conductivity of the liquid component, it is preferable that the non-aqueous solvent includes at least an aprotic polar solvent.

[0034] Examples of sulfone solvents include cyclic sulfone compounds (such as sulfolane (SL)) and sulfoxide compounds (such as dimethyl sulfoxide and diethyl sulfoxide). Examples of lactone solvents include γ-butyrolactone (GBL) and γ-valerolactone. Examples of carbonate solvents include chain carbonates (such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) and cyclic carbonates (such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate).

[0035] The non-aqueous solvent may contain one aprotic solvent or a combination of two or more aprotic solvents.

[0036] The nonaqueous solvent may contain a protic solvent. The protic solvent may be a protic polar solvent. Examples of the protic solvent include alcohol compounds. Examples of the alcohol compounds include monohydric alcohols and polyhydric alcohols. Examples of the polyhydric alcohols include glycol compounds (alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), polyalkylene glycols (polyethylene glycol (PEG), polypropylene glycol, etc.)), glycerin compounds (glycerin, polyglycerin, etc.), sugar alcohol compounds, and alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.). The nonaqueous solvent may contain one type of protic solvent or a combination of two or more types. From the viewpoint of further suppressing swelling when the electrolytic capacitor is exposed to high temperatures, polyalkylene glycols such as PEG, glycerin compounds, etc. are preferred as the protic solvent.

[0037] However, in the present disclosure, the ratio of the aprotic solvent to the nonaqueous solvent may be greater than 50% by mass, 60% by mass or more, 65% by mass or more, or 70% by mass or more. When the ratio of the aprotic solvent is this high, it is difficult to achieve film repair of the dielectric layer using the nonaqueous solvent. In such cases, using a first acid more effectively demonstrates the film repair effect of the first acid. Furthermore, combining the first acid with a second acid can reduce swelling when the electrolytic capacitor is exposed to high temperatures. Furthermore, even when the Vt ratio is relatively small, such as 1.80 or less, a high film repair effect of the dielectric layer can be ensured, thereby reducing the decrease in capacitance and the increase in ESR during accelerated testing.

[0038] (Acid Component) (First Acid) The first acid contained in the liquid component is an aliphatic hydroxycarboxylic acid. The aliphatic hydroxycarboxylic acid has one or more hydroxy groups and one or more carboxy groups in an aliphatic chain (such as an aliphatic hydrocarbon chain).

[0039] Specific examples of aliphatic hydroxycarboxylic acids include glycolic acid, lactic acid, tartronic acid, glyceric acid, hydroxybutyric acid, malic acid, tartaric acid, citric acid, pantoic acid, and galactaric acid. However, the aliphatic hydroxycarboxylic acids are not limited to these specific examples. The acid component may contain one or more aliphatic hydroxycarboxylic acids.

[0040] The number of carbon atoms in the aliphatic hydroxycarboxylic acid is 2 or more, and may be 3 or more. The number of carbon atoms in the aliphatic hydroxycarboxylic acid may be 10 or less, or may be 8 or less. The number of carbon atoms in the aliphatic hydroxycarboxylic acid may be 2 or more (or 3 or more) and 10 or less, or 2 or more (or 3 or more) and 8 or less.

[0041] The first acid may include an aliphatic hydroxycarboxylic acid having three or more functional groups selected from the group consisting of hydroxy groups and carboxy groups. Such aliphatic hydroxycarboxylic acids are sometimes referred to as aliphatic hydroxycarboxylic acids IA in this specification. The first acid may include an aliphatic hydroxycarboxylic acid having two or more hydroxy groups and two or more carboxy groups. Such aliphatic hydroxycarboxylic acids are sometimes referred to as aliphatic hydroxycarboxylic acids Ia. The aliphatic hydroxycarboxylic acid IA may include aliphatic hydroxycarboxylic acids Ia. The use of aliphatic hydroxycarboxylic acids IA or Ia, in combination with a secondary acid and an aprotic solvent, can further suppress swelling of electrolytic capacitors exposed to high temperatures. Furthermore, the decrease in capacitance and the increase in ESR after accelerated testing can be further suppressed. Examples of aliphatic hydroxycarboxylic acids IA include tartronic acid, glyceric acid, malic acid, tartaric acid, citric acid, pantoic acid, and galactaric acid. Examples of aliphatic hydroxycarboxylic acids Ia include tartaric acid and galactaric acid. From the viewpoint of easy availability and obtaining a higher effect, it is preferable to use at least tartaric acid.

[0042] The proportion of the aliphatic hydroxycarboxylic acid IA (or Ia) in the first acid may be more than 50% by mass, 75% by mass or more, or 90% by mass or more. The proportion of the aliphatic hydroxycarboxylic acid IA (or Ia) in the first acid is 100% by mass or less. The first acid may also be composed solely of the aliphatic hydroxycarboxylic acid IA or the aliphatic hydroxycarboxylic acid Ia. In such cases, the effects of the aliphatic hydroxycarboxylic acid IA or the aliphatic hydroxycarboxylic acid Ia are more likely to be exerted, and a combination with the second acid and an aprotic solvent can provide even greater effects.

[0043] The first acid may include an aliphatic hydroxycarboxylic acid having at least one α-hydroxy group. It is believed that the use of such an aliphatic hydroxycarboxylic acid will result in higher film repair properties. The aliphatic hydroxycarboxylic acid IA or Ia may have at least one α-hydroxy group. For example, when the aliphatic hydroxycarboxylic acid has two carboxy groups, and a hydroxy group is present at the α-position of each carboxy group, the number of α-hydroxy groups is two. The number of α-hydroxy groups in the aliphatic hydroxycarboxylic acid may be four or less, or may be three or less.

[0044] The content (concentration) of the first acid in the liquid component may be 1.0% by mass or more and 10.0% by mass or less, 1.5% by mass or more and 7.0% by mass or less, or 2.0% by mass or more and 5.0% by mass or less. When the content of the first acid is within such a range, swelling of the electrolytic capacitor can be further reduced. In addition, a decrease in capacitance and an increase in ESR when the Vt ratio is small can be further suppressed.

[0045] (Second Acid) The second acid is a boric acid compound. The boric acid compound functions as an acid. The second acid may contain at least one selected from the group consisting of boric acid, partial esters of boric acid, and borate salts. Examples of boric acid include orthoboric acid, metaboric acid, tetraboric acid, and halogenated boric acids (such as tetrafluoroboric acid). Examples of partial esters of boric acid include monoesters or diesters of orthoboric acid, and partial esters of halogenated borate salts. The ester may be, for example, an alkyl ester or an alkenyl ester. The borate salt may be a salt with a base component or a metal salt. Of these boric acid compounds, orthoboric acid is preferred because it is easy to obtain the acid effect and can easily achieve a higher effect when combined with the first acid and an aprotic solvent.

[0046] The proportion of orthoboric acid in the second acid may be more than 50% by mass, 75% by mass or more, or 90% by mass or more. The proportion of orthoboric acid in the second acid is 100% by mass or less. The second acid may consist solely of orthoboric acid.

[0047] The molar ratio of the second acid to the first acid (=second acid / first acid) may be 0.3 or more, or may be 0.5 or more. From the viewpoint of further reducing swelling of the electrolytic capacitor, the molar ratio of the second acid to the first acid (=second acid / first acid) may be 1.0 or more. From the viewpoint of suppressing corrosion of the electrode, the molar ratio of the second acid to the first acid (=second acid / first acid) may be 3.0 or less.

[0048] (Tertiary Acid) The acid component may further include a tertiary acid, which is an aromatic carboxylic acid. Because the tertiary acid has relatively high heat resistance, it can further reduce swelling of the electrolytic capacitor and easily achieve high film repairability. Furthermore, the use of the tertiary acid can suppress corrosion of the electrodes. The high heat resistance of the tertiary acid suppresses deterioration of the conductive polymer when the electrolytic capacitor is exposed to high temperatures. Therefore, it is possible to further suppress performance degradation when the Vt ratio is small.

[0049] Tertiary acids include aromatic monocarboxylic acids, aromatic polycarboxylic acids, aromatic hydroxy acids, and sulfoaromatic carboxylic acids.

[0050] Examples of aromatic monocarboxylic acids include benzoic acid and methylbenzoic acid. Examples of aromatic polycarboxylic acids include phthalic acid, trimellitic acid, and pyromellitic acid. Examples of aromatic hydroxy acids include salicylic acid. Examples of sulfoaromatic carboxylic acids include p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylic acid. However, the tertiary acid is not limited to these specific examples.

[0051] The acid component may contain one or more tertiary acids.

[0052] From the viewpoint of easily obtaining higher heat resistance and easily suppressing electrode corrosion, it is preferable that the third acid contains at least an aromatic polycarboxylic acid (e.g., phthalic acid). The proportion of aromatic polycarboxylic acid (e.g., phthalic acid) in the third acid is greater than 50 mass%, may be 75 mass% or more, or may be 90 mass% or more. The proportion of aromatic polycarboxylic acid (e.g., phthalic acid) in the third acid is 100 mass% or less. The third acid may be composed solely of aromatic polycarboxylic acid (e.g., phthalic acid). If necessary, the acid component may not contain an aromatic hydroxycarboxylic acid such as salicylic acid. Aromatic hydroxycarboxylic acids have relatively high heat resistance and are less likely to cause the problem of swelling of electrolytic capacitors caused by hydroxycarboxylic acids than aliphatic hydroxycarboxylic acids.

[0053] In the liquid component, the total mass ratio of the first acid and the second acid may be equal to or greater than the mass ratio of the third acid. The swelling of electrolytic capacitors and performance degradation when the Vt ratio is small are largely influenced by the first acid. Therefore, in the present disclosure, even if the mass ratio of the first acid and the second acid is less than the mass ratio of the third acid, the swelling suppression effect is sufficiently exerted and the performance degradation after accelerated testing when the Vt ratio is small can be further suppressed. Furthermore, a high mass ratio of the third acid makes it easier to obtain higher heat resistance and suppress electrode corrosion.

[0054] The content (concentration) of the tertiary acid in the liquid component may be 1% by mass or more and 30% by mass or less, or may be 1% by mass or more and 20% by mass or less.

[0055] (Quaternary Acid) The acid component may further include an acid (quaternary acid) other than the primary, secondary, and tertiary acids. Examples of quaternary acids include carboxylic acids other than the primary and tertiary acids (e.g., aliphatic carboxylic acids and alicyclic carboxylic acids having no hydroxy groups), acids having a carbonyloxy bond other than carboxylic acids (e.g., oxocarbonic acids and Meldrum's acid), or coordination compounds thereof, phenolic compounds (e.g., picric acid, p-nitrophenol, pyrogallol, and catechol), or coordination compounds thereof, sulfur-containing acids (e.g., sulfuric acid, sulfonic acids (e.g., aromatic sulfonic acids), oxyaromatic sulfonic acids (e.g., phenol-2-sulfonic acid), compounds having a sulfonylimide bond, phosphorus-containing acids (e.g., phosphoric acid, halogenated phosphoric acids (e.g., hexafluorophosphoric acid), phosphonic acids, phosphinic acids, and partial esters thereof), and nitrogen-containing acids (e.g., nitric acid and nitrous acid). The acid component may include one or more quaternary acids.

[0056] The total amount of the first acid, second acid, and tertiary acid in the entire acid component may be 80 mass% or more, or may be 90 mass% or more. The total amount of the first acid, second acid, and tertiary acid in the entire acid component is 100 mass% or less. The entire acid component may be composed only of the first acid and the second acid, or may be composed only of the first acid, the second acid, and the tertiary acid.

[0057] In this specification, the contents and ratios (molar ratios, mass ratios, mass ratios, etc.) of acid components are values ​​determined based on the mass or moles of each acid when it is in a free form. Furthermore, the contents and ratios (molar ratios, mass ratios, mass ratios, etc.) of acid components are values ​​in the liquid component of the initial electrolytic capacitor.

[0058] In this specification, the initial electrolytic capacitor refers to an electrolytic capacitor after aging or break-in charging and discharging, or an unused electrolytic capacitor if it is a commercially available product.

[0059] (Base Component) The liquid component may further contain a base component. In this case, the dissociation property of the acid component is enhanced, making it easier for acid groups such as carboxyl groups to act on the conductive polymer. This makes it easier to obtain higher conductivity of the conductive polymer. In addition, the conductivity of the liquid component is also enhanced.

[0060] Examples of the basic component include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The liquid component may contain one type of basic component or two or more types.

[0061] The amine may be any of aliphatic, aromatic, and heterocyclic. Examples of the amine include dialkylamines (diethylamine, etc.), trialkylamines (trimethylamine, ethyldimethylamine, triethylamine (TEA), tri-n-butylamine (TBA), dimethyl-n-octylamine (DMOA), etc.), alkylenediamines (ethylenediamine, etc.), aromatic amines (aniline, etc.), and heterocyclic amines (morpholine, pyrrolidine, imidazole compounds (imidazole (Imd), 1,2,3,4-tetramethylimidazolinium, etc.), pyridine (Pyr), 4-dimethylaminopyridine, diazabicycloundecene (DBU), etc.). Each of the aromatic amines and heterocyclic amines may be monocyclic or polycyclic (fused ring, bridged ring, etc.). Examples of the quaternary ammonium compound include amidine compounds (including imidazole compounds).

[0062] The equivalent ratio of the acid component to the base component (=acid component / base component) may be 0.5 or more and 15 or less, 1.0 or more and 10 or less, or 1.3 or more and 5 or less.

[0063] The equivalent ratio of the acid component to the base component is the ratio of the amount of H generated per molecule of each acid. ＋ (total number of moles of OH that can be generated per molecule of base component) / (OH that can be generated per molecule of base component) － The ratio is the sum of the moles of

[0064] (Capacitor Element) The electrolytic capacitor may include one capacitor element, or may include two or more capacitor elements.

[0065] The capacitor element includes, for example, an anode body having an uneven surface, a dielectric layer formed on the surface of the anode body, and a cathode part in contact with at least a portion of the surface of the dielectric layer. The cathode part includes a conductive polymer in contact with at least a portion of the surface of the dielectric layer. The cathode part may include a cathode body such as a cathode extraction layer in addition to the conductive polymer.

[0066] (Anode Body) The anode body may contain a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. These materials may be used alone or in combination of two or more. Preferred valve metals include aluminum, tantalum, niobium, and titanium.

[0067] The anode body may have an uneven surface. Such an anode body may have a porous portion having pores at least in the surface layer. The anode body is preferably an anode foil. Examples of anode bodies other than an anode foil include a porous sintered body or a porous molded body of particles containing a valve metal.

[0068] An anode foil having a textured surface can be obtained, for example, by roughening the surface of a substrate (e.g., a foil or plate-shaped substrate) containing a valve metal. The roughening may be performed by etching (e.g., electrolytic etching or chemical etching).

[0069] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body. Anodization is performed, for example, by chemical conversion treatment. The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body. The voltage applied to the anode body during chemical conversion treatment is the chemical conversion voltage. The film thickness of the dielectric layer is proportional to the chemical conversion voltage in the chemical conversion treatment, and can be adjusted by the magnitude of the chemical conversion voltage. Therefore, the chemical conversion voltage can be calculated conversely from the film thickness of the dielectric layer depending on the material of the dielectric layer.

[0070] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O３ However, the dielectric layer is not limited to this, and may be any layer that functions as a dielectric.

[0071] The dielectric layer is usually formed on the surface of the anode body. When the dielectric layer is formed on the surface of the porous portion of the anode body, the dielectric layer is formed along the inner wall surfaces of the pores in the porous portion and the depressions (pits) on the surface of the anode body.

[0072] In the present disclosure, even if the Vt ratio is relatively low (in other words, the thickness of the dielectric layer is relatively small), the liquid component provides high film repairability and reduces the effects of property changes, thereby suppressing the progression of degradation of the conductive polymer.

[0073] The average thickness T of the dielectric layer may be 15 nm or more and 300 nm or less. When the thickness T is in this range, a higher capacitance can be obtained. Even when the thickness T is relatively small, such as 200 nm or less (e.g., 15 nm or more and 200 nm or less, or 20 nm or more and 150 nm or less), the liquid component can reduce the influence of characteristic changes when the Vt ratio is small.

[0074] The thickness of the dielectric layer is determined from an image taken with a scanning electron microscope (SEM). The average thickness of the dielectric layer is determined by measuring the thickness of the dielectric layer at any multiple locations (for example, 10 locations) and averaging the measurements. As the measurement sample, for example, an anode body on which a dielectric layer is formed is used. In this case, an aluminum foil with a side length of 10 mm or more and 50 mm or less is used as the anode body. Hereinafter, this sample will be referred to as sample A. An anode body on which a dielectric layer is formed, which is obtained in the process of manufacturing an electrolytic capacitor, may also be used as the sample. Hereinafter, this sample will be referred to as sample B.

[0075] More specifically, first, a cross section parallel to the thickness direction of sample A or sample B is exposed, and an image is taken using an SEM. The thickness of the dielectric is determined at any multiple locations in the field of view of any multiple locations on this image. The sample for taking the above cross-sectional image is obtained by the following procedure. First, sample A or sample B is embedded in a curable resin, and the curable resin is cured. The cured product is wet-polished or dry-polished to expose a cross section parallel to the thickness direction of the dielectric (a cross section in which the layer structure of the dielectric can be confirmed). The exposed cross section is smoothed by ion milling to obtain the sample for taking the image.

[0076] (Conductive Polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer may cover at least a portion of the dielectric layer. This embodiment includes a case where the conductive polymer is in contact with at least a portion of the dielectric layer. When the capacitor element includes an anode foil and a cathode foil, the conductive polymer may be interposed between these foils. In this case, the conductive polymer may be impregnated into a separator interposed between the anode foil and the cathode foil. The conductive polymer may be in contact with at least a portion of the cathode foil in addition to at least a portion of the dielectric layer. The conductive polymer may form a layer. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer forms at least a portion of the cathode body in an electrolytic capacitor. The conductive polymer may further include an additive, if necessary.

[0077] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0078] The conjugated polymer may be used alone or in combination of two or more kinds.

[0079] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0080] In this specification, the weight average molecular weight (Mw) is a value calculated as polysaccharide as measured by gel permeation chromatography (GPC). GPC is usually performed using a polyhydroxymethacrylate gel column and an aqueous sodium nitrate solution as the mobile phase.

[0081] (Dopants) Examples of dopants include relatively low molecular weight anions and polymeric anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that generate these anions are used as dopants. Examples of dopants that generate sulfonate ions include aromatic sulfonic acid compounds (such as paratoluenesulfonic acid and naphthalenesulfonic acid). The aromatic sulfonic acid compound may have at least one group selected from the group consisting of a carboxy group and a hydroxy group.

[0082] Examples of polymeric anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolac resin, and polyacrylic acid. The polymeric anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having a substituent. Among these, polyanions derived from polystyrene sulfonic acid (such as a homopolymer or copolymer) or a derivative thereof are preferred.

[0083] However, these dopants are merely examples and are not limited to these. One dopant may be used alone, or two or more dopants may be used in combination.

[0084] The conductive polymer may be formed, for example, by chemically polymerizing or electrolytically polymerizing a conjugated polymer precursor on a dielectric layer in the presence of a dopant. Alternatively, a conductive polymer (e.g., a conductive polymer layer) may be formed by contacting a dielectric layer with a treatment liquid containing the conductive polymer. Examples of such treatment liquids include a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed. The conductive polymer used in these treatment liquids can be obtained by polymerizing a conjugated polymer precursor in the presence of a dopant. Examples of conjugated polymer precursors include raw material monomers for the conjugated polymer, and oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination.

[0085] The Mw of the dopant is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0086] The amount of the dopant contained in the conductive polymer is, for example, 10 parts by mass or more and 1000 parts by mass or less, and may be 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0087] (Cathode Extraction Layer) The cathode extraction layer may include, for example, a first layer covering at least a portion of the conductive polymer. The cathode extraction layer may include a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil (cathode foil). Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may include a first layer containing conductive carbon (e.g., graphite) (also referred to as a carbon layer) and a second layer containing metal powder or a metal foil. When a metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil. The cathode extraction layer can be formed by a known method depending on the layer configuration.

[0088] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such a second layer include a metal paste layer (e.g., a silver paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). The resin may be a thermosetting resin such as an imide resin or an epoxy resin, or a thermoplastic resin.

[0089] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0090] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0091] (Separator) A separator may be disposed between the cathode body (e.g., cathode foil) and the anode body (e.g., anode foil). The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0092] When the capacitor element includes a separator, the separator may be impregnated with the conductive polymer. The conductive polymer may be interposed between the anode body (e.g., anode foil) and the cathode body (e.g., cathode foil), and may be in contact with at least a portion of the dielectric layer and at least a portion of the cathode body.

[0093] (Vt Ratio) In the electrolytic capacitor of the present disclosure, the Vt ratio may be 1.80 or less, 1.75 or less, or even 1.70 or less. When the Vt ratio is within this range, the thickness of the dielectric layer is small, and the effect of characteristic changes is likely to be significant. However, in the present disclosure, by using a liquid component with a specific composition, the initial capacitance can be ensured with a Vt ratio within the above range, and an increase in ESR and a decrease in capacitance can be suppressed when the electrolytic capacitor is exposed to high temperatures. Considering surge voltage, the lower limit of the Vt ratio is usually preferably 1.25 or more, and more preferably 1.35 or more.

[0094] The Vt ratio may be 1.25 or more (or 1.35 or more) and 1.80 or less, 1.25 or more (or 1.35 or more) and 1.75 or less, or 1.25 or more (or 1.35 or more) and 1.70 or less.

[0095] The formation voltage V is selected, for example, according to the rated voltage Vw so that the Vt ratio falls within the above range.

[0096] The rated voltage Vw is not particularly limited. When the rated voltage Vw is 100 V or less (particularly, when it is 50 V or less), the effect of suppressing an increase in ESR and a decrease in capacitance when the electrolytic capacitor is exposed to high temperatures is more easily achieved.

[0097] (Other) The electrolytic capacitor may be a wound type, and may be either a chip type or a laminated type. The electrolytic capacitor has at least one capacitor element. The electrolytic capacitor may have multiple capacitor elements. For example, the electrolytic capacitor may have a laminate of two or more capacitor elements, or may have two or more wound capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0098] In the capacitor element, one end of a cathode lead is electrically connected to the cathode extraction layer. One end of an anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the case. The other end of each lead exposed from the case is used for soldering to a substrate on which the electrolytic capacitor is to be mounted, for example. Each lead may be a lead wire or a lead frame.

[0099] The container may have any shape as long as it can accommodate the capacitor element and the liquid component inside. The opening of the container is sealed with, for example, a sealing member (e.g., a sealing body) while the capacitor element and the liquid component are accommodated inside.

[0100] Fig. 1 is a cross-sectional schematic diagram of an electrolytic capacitor according to this embodiment, and Fig. 2 is a schematic diagram showing a portion of a capacitor element of the electrolytic capacitor in an exploded view. However, the electrolytic capacitor of the present disclosure is not limited to the following embodiments. Furthermore, the components of the following embodiments may be arbitrarily combined with at least one of the above-described (Technology 1) to (Technology 12) of the electrolytic capacitor of the present disclosure, or may be arbitrarily combined with at least one of the above-described (Technology 1) to (Technology 12) and the components described above.

[0101] The electrolytic capacitor 100 includes, for example, a capacitor element 10, a bottomed case 101, a sealing member 102 that closes the opening of the bottomed case 101, a seat plate 103 that covers the sealing member 102, lead wires 104A and 104B, and lead tabs 105A and 105B. The bottomed case 101 accommodates the capacitor element 10 and a liquid component (not shown). The vicinity of the open end of the bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to the sealing member 102. The lead wires 104A and 104B are led out of the sealing member 102 and pass through the seat plate 103. The lead tabs 105A and 105B connect the lead wires 104A and 104B to electrodes of the capacitor element 10, respectively.

[0102] Capacitor element 10 is, for example, a wound body as shown in Fig. 2. The wound body includes anode foil 11 connected to lead tab 105A, cathode foil 12 connected to lead tab 105B, and separator 13. Anode foil 11 and cathode foil 12 are wound with separator 13 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 14. Note that Fig. 2 shows a partially unfolded state of the wound body before the outermost periphery is secured.

[0103] In capacitor element 10, a dielectric layer (not shown) is formed on at least a portion of the surface of anode foil 11. Separator 13 and a conductive polymer (not shown) are interposed between anode foil 11 and cathode foil 12. The conductive polymer is in contact with at least a portion of the dielectric layer. The conductive polymer is also in contact with at least a portion of cathode foil 12. The conductive polymer and separator are impregnated with a liquid component.

[0104] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0105] <Electrolytic Capacitors E1 to E4 and C1 to C2> Wound electrolytic capacitors (diameter 10 mm, length 10 mm) with a rated voltage of 25 V and a rated capacitance of 390 μF (for a Vt ratio of 1.70) or 330 μF (for a Vt ratio of 1.96) were fabricated and evaluated according to the following procedure.

[0106] (Preparation of Anode Body) An aluminum foil with a thickness of 100 μm was etched to roughen the surface of the aluminum foil. Then, a chemical conversion coating (dielectric layer) was formed on the surface of the aluminum foil by chemical conversion treatment. The chemical conversion treatment was performed by immersing the aluminum foil in an ammonium adipate solution and applying a voltage. The aluminum foil was then cut into a size of 6 mm long x 120 mm wide to prepare an anode body. By applying a voltage of 49 V in the chemical conversion treatment, the Vt ratio was set to 1.96 (dielectric layer thickness: 64 nm). Furthermore, by applying a voltage of 42.5 V in the chemical conversion treatment, the Vt ratio was set to 1.70 (dielectric layer thickness: 55 nm).

[0107] (Preparation of Cathode Body) An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and then cut into a size of 6 mm length×120 mm width to prepare a cathode body.

[0108] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode body and the cathode body, and the anode body and the cathode body were wound around the lead tabs, with a separator interposed therebetween. At this time, the ends of the outer surface of the wound body were fixed with a winding stop tape. An anode lead wire and a cathode lead wire were connected to the ends of the lead tabs protruding from the wound body, respectively. The prepared wound body was then subjected to a chemical conversion treatment again, and a chemical conversion coating was formed on the cut ends of the anode body. In this manner, a wound body was prepared.

[0109] (Preparation of polymer dispersion containing conductive polymer) 3,4-ethylenedioxythiophene and the polymer dopant poly(4-styrenesulfonic acid) (PSS, Mw: 100,000) were dissolved in ion-exchanged water to prepare a mixed solution. While stirring the mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymer dispersion containing PSS-doped poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) as the conductive polymer.

[0110] (Coating of Dielectric Layer with Conductive Polymer) The wound body was immersed in a polymer dispersion contained in a designated container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the polymer dispersion. Next, the wound body impregnated with the polymer dispersion was dried in a drying oven at 150°C for 20 minutes, thereby applying the conductive polymer to the wound body. The conductive polymer was interposed between the anode body and the cathode body and was in contact with at least a portion of each of the anode body and the cathode body. In this manner, a capacitor element was formed.

[0111] (Preparation of Liquid Component and Impregnation into Capacitor Element) A liquid component in solution form was prepared by blending the solute and acid shown in Table 1 into a non-aqueous solvent so that the concentrations in the liquid component were the values ​​shown in Table 1. As the non-aqueous solvent, a mixed solvent of sulfolane, γ-butyrolactone, and polyethylene glycol 300 (number average molecular weight 300) mixed in a mass ratio of 70:15:15 was used. Tartaric acid was used as the first acid, and orthoboric acid was used as the second acid. Phthalic acid corresponds to the tertiary acid, and TEA corresponds to the base component.

[0112] (Assembly of Electrolytic Capacitor) The capacitor element was immersed in the liquid component and placed in a reduced pressure atmosphere (40 kPa) for 5 minutes to allow the liquid component to be impregnated into the capacitor element.

[0113] The capacitor element impregnated with the liquid component was placed inside a bottomed case, with the lead wires positioned on the open side of the case. A sealing member (made of an elastic material containing butyl rubber as a rubber component) formed to allow the lead wires to pass through was placed above the capacitor element. The bottomed case was then drawn near the open end, and the open end was further curled to adhere to the sealing member. In this way, the capacitor element and liquid component were sealed inside the bottomed case. An electrolytic capacitor as shown in Figure 1 was completed by placing a seat plate on the curled portion. A total of 40 electrolytic capacitors were produced for each example. The produced electrolytic capacitors were then aged at 95°C for 90 minutes while applying a rated voltage Vw.

[0114] [Evaluation] (1) Swelling of Electrolytic Capacitor Fig. 3 shows the portion of the electrolytic capacitor that was measured to evaluate swelling. Fig. 3 is a schematic cross-sectional view of the electrolytic capacitor 100 portion in Fig. 1. Swelling of the electrolytic capacitor was evaluated by the following procedure.

[0115] First, for each of 20 electrolytic capacitors (electrolytic capacitor 100 in FIG. 3 ) after the aging treatment, the height h0 from the top 101t of the case 101 to the bottom end 102a of the sealing member 102 and the height H0 from the top 101t of the case to the bottom end 101b of the case were measured. After the measurements, the electrolytic capacitors were heated at a maximum temperature of 260°C for a maximum of 30 seconds, simulating reflow. For each of the heated electrolytic capacitors 100, the height h1 from the top 101t of the case 101 to the bottom end of the sealing member and the height H1 from the top 101t of the case 101 to the bottom end 101b of the case were measured in the same manner as for the height h0 and height H0. For each electrolytic capacitor, the amount of swelling of the electrolytic capacitor (= (h1-h0)-(H1-H0)) was calculated from the change in these heights, and the average value for the 20 capacitors was calculated. This average value was calculated as the amount of swelling of the electrolytic capacitor (unit: mm).

[0116] (2) Capacitance and ESR The capacitance change (Δcap) and ESR change (ΔESR) after the accelerated test were measured for 20 electrolytic capacitors after the aging treatment described above, and the average values ​​were calculated using the following procedure. Each value was measured for a Vt ratio of 1.70 and a Vt ratio of 1.96.

[0117] The capacitance of the electrolytic capacitor at a frequency of 120 Hz and the ESR value at a frequency of 100 kHz were measured using an LCR meter in an environment of 20°C, and the average initial capacitance value (c0 (μF)) and the average initial ESR value (r0 (mΩ)) were calculated.

[0118] After measuring c0 and r0, a high-temperature load test (accelerated test) was conducted. That is, a rated voltage Vw was applied to the electrolytic capacitor for 500 hours at a temperature of 145°C. After 500 hours of the accelerated test, the average capacitance value (c1 (μF)) and average ESR value (r1 (mΩ)) of the electrolytic capacitor were determined in accordance with the initial capacitance value and initial ESR value.

[0119] The capacity change rate Δcap (%) due to the accelerated test was calculated using the following formula: Δcap=(c1−c0) / c0×100

[0120] The evaluation results of each electrolytic capacitor are shown in Table 1. In Table 1, E1 to E4 are electrolytic capacitors of examples, and C1 and C2 are electrolytic capacitors of comparative examples.

[0121]

[0122] As shown in Table 1, when the liquid component did not contain the first acid but contained the second acid, the swelling of the electrolytic capacitor when exposed to high temperatures was 0.25 mm (electrolytic capacitor C1). In contrast, when the liquid component contained the first acid but not the second acid, the swelling of the electrolytic capacitor was very large, at 0.62 mm (electrolytic capacitor C2).

[0123] In contrast, when the liquid component contained the same mass ratio of the first acid as electrolytic capacitor C2 and the same mass ratio of the second acid as electrolytic capacitor C1, the swelling of the electrolytic capacitor was 0.18 mm (electrolytic capacitor E4). This value was reduced from 0.25 mm for electrolytic capacitor C1, which did not contain the first acid, and significantly reduced from 0.62 mm for electrolytic capacitor C2, which did not contain the second acid. The reduction in swelling in electrolytic capacitor E4 is thought to be due to the synergistic effect of the first acid and the second acid. It is surprisingly small and significant compared to the results for electrolytic capacitors C1 and C2. This reduction in swelling was achieved depending on the amount of second acid, and sufficient swelling reduction was also achieved in electrolytic capacitors E1 to E3.

[0124] Furthermore, in both the comparative example and the example electrolytic capacitors, a low ESR (r0) of approximately 10 mΩ to 11 mΩ was obtained in the initial stage, demonstrating the high conductivity of the conductive polymer. When the Vt ratio was 1.96, a conventional value, the capacitance change rate (Δcap) and ESR (r1) after accelerated testing did not differ significantly between the case where the liquid component contained a first acid but not a second acid (electrolytic capacitor C2) and the case where the liquid component contained a second acid but not the first acid (electrolytic capacitor C1). However, when the Vt ratio was small, at 1.70, the case where the liquid component contained a first acid but not a second acid (electrolytic capacitor C2) showed a significant decrease in capacitance after accelerated testing (larger capacitance change rate) and a significant increase in ESR (r1) after accelerated testing. In contrast, in the electrolytic capacitors of the examples, even when the Vt ratio was as small as 1.70 after the accelerated test, the decrease in capacitance (increase in the rate of capacitance change) and the increase in ESR (r1) after the accelerated test were suppressed (comparison between electrolytic capacitors E1 to E4 and electrolytic capacitors C1 and C2).

[0125] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0126] The electrolytic capacitor of the present disclosure can be used as a solid-liquid hybrid electrolytic capacitor. The electrolytic capacitor is particularly suitable for applications requiring high heat resistance and high reliability. However, the applications of the electrolytic capacitor are not limited to these.

[0127] 100: Electrolytic capacitor 101: Bottomed case 101t: Top of case 100 101b: Lower end of case 100 102: Sealing member 102a: Lower end of sealing member 102 103: Seat plate 104A, 104B: Lead wires 105A, 105B: Lead tabs 10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 14: Winding tape

Claims

1. An electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises an anode body, a dielectric layer formed on the surface of the anode body, and the conductive polymer in contact with at least a portion of the surface of the dielectric layer, wherein the liquid component comprises a non-aqueous solvent and an acid component, wherein the non-aqueous solvent comprises an aprotic solvent, and the ratio of the aprotic solvent in the non-aqueous solvent is greater than 50 mass %, and the acid component comprises a first acid which is an aliphatic hydroxycarboxylic acid and a second acid which is a boric acid compound.

2. The electrolytic capacitor of claim 1, wherein the acid component further comprises a tertiary acid that is an aromatic carboxylic acid.

3. The electrolytic capacitor according to claim 2, wherein the total mass ratio of the first acid and the second acid in the liquid component is less than the mass ratio of the third acid.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the liquid component further contains a base component.

5. The electrolytic capacitor according to any one of claims 1 to 3, wherein the aprotic solvent includes at least one selected from the group consisting of sulfone-based solvents, lactone-based solvents, and carbonate-based solvents.

6. The electrolytic capacitor according to any one of claims 1 to 3, wherein the first acid comprises an aliphatic hydroxycarboxylic acid having three or more functional groups selected from the group consisting of hydroxy groups and carboxy groups.

7. The electrolytic capacitor according to any one of claims 1 to 3, wherein the first acid comprises an aliphatic hydroxycarboxylic acid having two or more hydroxy groups and two or more carboxy groups.

8. The electrolytic capacitor according to any one of claims 1 to 3, wherein the first acid comprises an aliphatic hydroxycarboxylic acid having at least one α-hydroxy group.

9. The electrolytic capacitor according to any one of claims 1 to 3, wherein the molar ratio of the second acid to the first acid in the liquid component is 0.5 or more.

10. The electrolytic capacitor according to claim 9, wherein the molar ratio of the second acid to the first acid in the liquid component is 3.0 or less.

11. The electrolytic capacitor according to any one of claims 1 to 3, wherein the second acid includes at least one selected from the group consisting of boric acid, a partial ester of boric acid, and a borate.

12. The electrolytic capacitor according to any one of claims 1 to 3, wherein the ratio V / Vw of the formation voltage V of the dielectric layer to the rated voltage Vw of the electrolytic capacitor is 1.80 or less.

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