Electrolytic capacitor and electrolytic solution used for same

Abstract

This electrolytic solution is used in an electrolytic capacitor provided with a capacitor element containing a conductive polymer. The electrolytic solution contains an organic solvent, a first acid, and a base component. The first acid is an aromatic carboxylic acid (excluding mono(2-hydroxyethyl) phthalate) having an aromatic moiety, a first ester group bonded to the aromatic moiety, and a first carboxy group bonded to the aromatic moiety. The first ester group does not have a carboxy group. The first carboxy group is positioned at the ortho position with respect to the first ester group.

Description

Electrolytic capacitors and the electrolytes used therein Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2024-191029, filed with the Japan Patent Office on 30 October 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to an electrolytic capacitor and an electrolyte used therein.

[0003] Electrolytic capacitors are considered promising as small, high-capacity capacitors with low ESR (equivalent series resistance). These capacitors comprise an anode with a dielectric layer, a conductive polymer covering at least a portion of the dielectric layer, and an electrolyte. The conductive polymer includes, for example, a conjugated polymer and a dopant. As the electrolyte, a solution obtained by dissolving a solute in a non-aqueous solvent is used.

[0004] As the solute, salts of acidic and basic components are used. Aromatic carboxylic acids such as phthalic acid are sometimes used as the acidic component.

[0005] Patent Document 1 proposes an electrolyte for electrolytic capacitors (C) containing a salt (A) of a carboxylic acid (a) and an amine (b) or ammonia, and a solvent (B), wherein the carboxylic acid (a) contains an ester compound (a1) of a dicarboxylic acid (e) and an alcohol (d) of 1 to 8 valent, an aromatic carboxylic acid (a2), and a chain-like aliphatic carboxylic acid (a3), and the ester compound (a1) is an ester compound having at least one carboxyl group.

[0006] Patent Document 2 proposes an electrolytic capacitor comprising a conductive polymer and a conductive auxiliary liquid, wherein the conductive auxiliary liquid comprises a high-boiling point organic solvent with a boiling point of 150°C or higher, and an aromatic compound having a nitro group and a carboxyl group or carboxyester portion, but lacking a hydroxyl group.

[0007] Patent Document 3 proposes an electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer covering at least a portion of the dielectric layer, the liquid component comprises an acid component and a solvent, the acid component comprises a first carboxylic acid compound having a plurality of first sites, and each of the plurality of first sites independently comprises a first carboxyl group containing a first carbonyl group, a second carbonyl group, and a first linking group that links the first carbonyl group and the second carbonyl group.

[0008] Japanese Patent Publication No. 2019-102791, Japanese Patent Publication No. 2015-2274, International Publication No. 2024 / 010063

[0009] The first aspect of this disclosure relates to an electrolyte used in an electrolytic capacitor comprising a capacitor element containing a conductive polymer, wherein the electrolyte comprises an organic solvent, a first acid, and a basic component, the first acid being an aromatic carboxylic acid (excluding mono(2-hydroxyethyl) phthalate) having an aromatic moiety, a first ester group bonded to the aromatic moiety, and a first carboxyl group bonded to the aromatic moiety, the first ester group lacking a carboxyl group, and the first carboxyl group located in the ortho position relative to the first ester group.

[0010] A second aspect of this disclosure relates to an electrolytic capacitor comprising a capacitor element and the electrolyte, wherein the capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer covering at least a portion of the dielectric layer.

[0011] According to this disclosure, it is possible to provide an electrolytic capacitor with excellent voltage resistance and heat resistance, and an electrolyte used therein.

[0012] This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present disclosure. This is a schematic diagram showing a portion of the capacitor element of the electrolytic capacitor shown in Figure 1 in an unfolded view.

[0013] Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0014] Aromatic carboxylic acids have higher heat resistance compared to aliphatic carboxylic acids, etc. However, aromatic carboxylic acids are prone to degradation in the electrolyte of electrolytic capacitors. When aromatic carboxylic acids degrade, the function of the electrolyte deteriorates, or the conductive polymer contained in the electrolytic capacitor degrades. Furthermore, when a salt of an aromatic carboxylic acid with a basic component is used as the solute in the electrolyte, the dielectric strength of the electrolyte is still insufficient.

[0015] Technical (1) An electrolyte according to a first aspect of the present disclosure is used in an electrolytic capacitor comprising a capacitor element containing a conductive polymer. The electrolyte comprises an organic solvent, a first acid, and a basic component. The first acid is an aromatic carboxylic acid (excluding mono(2-hydroxyethyl) phthalate) having an aromatic moiety, a first ester group bonded to the aromatic moiety, and a first carboxyl group bonded to the aromatic moiety. The first ester group does not have a carboxyl group. The first carboxyl group is located in the ortho position relative to the first ester group.

[0016] The electrolyte relating to the first aspect of this disclosure is an organic electrolyte containing a specific first acid and a basic component, as described above. The first acid, an aromatic carboxylic acid, has a first ester group (but without a carboxyl group) in addition to a first carboxyl group, thereby ensuring high dielectric strength. Furthermore, because the first carboxyl group is located in the ortho position relative to the first ester group, deactivation of the first carboxyl group is suppressed even in high-temperature environments. As a result, a low pH of the electrolyte is maintained, the function of the electrolyte is preserved, and the degradation of the conductive polymer is suppressed. Therefore, high heat resistance of the electrolytic capacitor is obtained. Thus, this disclosure provides an electrolytic capacitor with excellent dielectric strength and heat resistance.

[0017] Technology (2) In the above technology (1), the first ester group may include an oxyalkylene group or a poly(oxyalkylene) group. This makes it easier to suppress the deactivation of the first carboxyl group, and a higher heat resistance of the electrolytic capacitor can be obtained.

[0018] Technology (3) In Technology (1) or Technology (2) above, the aromatic carboxylic acid may further have a second ester group bonded to the aromatic moiety and a second carboxyl group bonded to the aromatic moiety. The second carboxyl group may be located in the ortho position relative to the second ester group. The second carboxyl group makes it easier to obtain a low pH of the electrolyte. By having the second carboxyl group in the ortho position relative to the second ester group, the deactivation of the second carboxyl group is suppressed, and it becomes easier to maintain a low pH. In addition to making it easier to maintain the function of the electrolyte, the deterioration of the conductive polymer is further suppressed. Therefore, higher heat resistance of the electrolytic capacitor can be obtained.

[0019] Technology (4) In Technology (3) above, the aromatic moiety may have a first benzene ring. The first ester group, the second ester group, the first carboxyl group, and the second carboxyl group may be bonded to the first benzene ring. In this case, the initial equivalent series resistance (ESR) is kept low, and the increase in ESR when exposed to high temperatures is suppressed. It is thought that the low pH of the electrolyte is obtained by the action of the first and second carboxyl groups, which leads to high conductivity of the conductive polymer and keeps the initial ESR low. The deactivation of the first and second carboxyl groups is further suppressed by the action of the first and second ester groups. It is thought that the low pH of the electrolyte is maintained even in high-temperature environments, and the deterioration of the conductive polymer is suppressed, thus maintaining high conductivity of the conductive polymer and suppressing the increase in ESR.

[0020] Technology (5) In Technology (3) above, the aromatic moiety may have a first benzene ring, a second benzene ring, and a single bond or linking group connecting the first benzene ring and the second benzene ring. In this case, the first ester group and the first carboxyl group may be bonded to the first benzene ring, and the second ester group and the second carboxyl group may be bonded to the second benzene ring. In this case, for reasons similar to those of Technology (4) above, the initial ESR can be kept relatively low, and the increase in ESR when exposed to high temperatures can be kept relatively small.

[0021] Technology (6) In Technology (5) above, in the first benzene ring, one of the first ester group and the first carboxyl group may be located in the meta position relative to the single bond or the linking group, and the other of the first ester group and the first carboxyl group may be located in the para position relative to the single bond or the linking group. Also, in the second benzene ring, one of the second ester group and the second carboxyl group may be located in the meta position relative to the single bond or the linking group, and the other of the second ester group and the second carboxyl group may be located in the para position relative to the single bond or the linking group. Such aromatic carboxylic acids are relatively easy to obtain, and because the relationship between the ester group and the carboxyl group tends to be in the ortho position, higher heat resistance is easily obtained.

[0022] Technology (7) In any one of the above technologies (3) to (6), the first ester group may include an oxyalkylene group or a poly(oxyalkylene) group. The second ester group may include an oxyalkylene group or a poly(oxyalkylene) group. In these cases, the deactivation of the first and second carboxyl groups is further suppressed, and higher heat resistance is more easily obtained.

[0023] Technology (8) The present disclosure also includes electrolytic capacitors containing the above-described electrolyte. An electrolytic capacitor relating to a second aspect of the present disclosure includes a capacitor element and an electrolyte described in any one of the above technologies (1) to (7). The capacitor element includes an anode having a dielectric layer on its surface and a conductive polymer covering a portion of the dielectric layer. By combining the above-described electrolyte with a capacitor element containing a conductive polymer, high heat resistance can be ensured while suppressing the degradation of the conductive polymer and ensuring high voltage resistance.

[0024] The electrolyte and electrolytic capacitor of this disclosure will be described in more detail below, including the above techniques (1) to (8), with reference to the drawings as necessary. To the extent that it is not technically inconsistent, at least one of the above techniques (1) to (8) may be combined with at least one of the elements described below. Note that the figures are schematic representations, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of the actual components.

[0025] [Electrolyte] The electrolyte of this disclosure is used in an electrolytic capacitor comprising a capacitor element containing a conductive polymer. The electrolyte comprises an organic solvent, an acid component, and a basic component. At least a first acid is used as the acid component. The acid component may optionally further contain a second acid different from the first acid in addition to the first acid. The electrolyte may also further contain additives.

[0026] (Acid component) (First acid) The first acid, which is classified as an aromatic carboxylic acid, has an aromatic moiety, an ester group bonded to this aromatic moiety, and a carboxyl group bonded to the aromatic moiety. The first acid may have one ester group bonded to the aromatic moiety, or two or more. The number of ester groups bonded to the aromatic moiety in the first acid may be 6 or less, or 4 or less, depending on the number of carbon atoms and members of the aromatic moiety, the number of carboxyl groups, etc. The number of ester groups bonded to the aromatic moiety in the first acid may be 1 or more and 6 or less (or 4 or less), or 2 or more and 6 or less (or 4 or less). Also, the number of ester groups bonded to the aromatic moiety in the first acid may be 1 or 2.

[0027] The first acid may have one carboxyl group bonded to the aromatic moiety, or two or more. The number of carboxyl groups bonded to the aromatic moiety in the first acid may be 6 or less, or 4 or less, depending on the number of carbon atoms and members of the aromatic moiety, the number of ester groups, etc. The number of carboxyl groups bonded to the aromatic moiety in the first acid may be 1 to 6 (or 4 or less), or 2 to 6 (or 4 or less). Furthermore, the number of carboxyl groups bonded to the aromatic moiety in the first acid may be 1 or 2.

[0028] The first acid has at least an ester group (first ester group) bonded to the aromatic moiety and a carboxyl group (first carboxyl group) bonded to the aromatic moiety. The first carboxyl group is located in the ortho position relative to the first ester group. This suppresses the deactivation of the first carboxyl group, resulting in high heat resistance for the electrolytic capacitor. The first acid may further have a second carboxyl group bonded to the aromatic moiety. The first acid may further have a second ester group bonded to the aromatic moiety. The second carboxyl group may be located in the ortho position relative to the first ester group. The second carboxyl group may also be located in the ortho position relative to the second ester group. In these cases, the deactivation of the second carboxyl group can be suppressed by the first or second ester group, making it easier to maintain a low pH of the electrolyte and resulting in higher heat resistance.

[0029] In the first acid, the aromatic moiety may consist of a single aromatic ring. Alternatively, the aromatic moiety may consist of two or more aromatic rings linked together by a single bond or a linking group.

[0030] Examples of aromatic rings included in the aromatic moiety include benzene rings and condensed rings. Examples of condensed rings include condensed rings between benzene rings (naphthalene ring, anthracene ring, phenanthrene ring, acenaphthene ring, etc.) and condensed rings between a benzene ring and another ring (hydrocarbon ring, oxygen-containing ring, etc.) (fluorene ring, indene ring, benzopyran ring, xanthene ring, etc.). The number of members in the condensed ring may be 20 or less. From the viewpoint of easily obtaining a lower pH of the electrolyte, the number of members in the condensed ring is preferably 12 or less, and more preferably 10 or less. It is also preferable that the aromatic moiety consists of a single benzene ring. The aromatic ring is preferably an aromatic hydrocarbon ring.

[0031] Among structures in which two or more aromatic rings are linked, biphenyl is an example of a structure linked by a single bond. The linking group is a polyvalent group. Examples of linking groups include polyvalent groups corresponding to aliphatic hydrocarbons (such as alkanes), ether groups (-O-), thioether groups (-S-), and carbonyl groups (-C(=O)-). The number of carbon atoms in the aliphatic hydrocarbon may be 1 to 6 or 1 to 4. From the viewpoint of easily obtaining a lower pH of the electrolyte, a divalent or trivalent group is preferred, and a divalent group is more preferred. Examples of aromatic moieties having a structure linked by a linking group include diphenylmethane, 2,2-diphenylpropane, diphenyl ether, and diphenyl ketone.

[0032] The aromatic moiety may have a first benzene ring, or it may have a first benzene ring and a second benzene ring, and a single bond or linking group connecting them. The first and second benzene rings may each be benzene rings that are not fused with other rings (in other words, monocyclic rings). In these cases, the molecular size is relatively small, and the effect of the carboxyl group is easily exerted, making it easier to obtain a lower pH of the electrolyte.

[0033] The aromatic moiety may have substituents other than ester and carboxyl groups (hereinafter referred to as first substituents). The aromatic moiety may have the first substituent on an aromatic ring or on a linking group. Examples of first substituents include aliphatic hydrocarbon groups, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyl groups, hydroxyalkyl groups, and alkoxy groups (for example, methoxy groups, ethoxy groups, propoxy groups, butoxy groups, tert-butoxy groups, and other alkoxy groups with 1 to 6 or 1 to 4 carbon atoms). Examples of aliphatic hydrocarbon groups include alkyl groups and alkenyl groups. Examples of alkyl groups include methyl groups, ethyl groups, propyl groups, iso-propyl groups, butyl groups, tert-butyl groups, hexyl groups, 2-ethylhexyl groups, decyl groups, and dodecyl groups. Examples of alkenyl groups include vinyl groups and allyl groups. The number of carbon atoms in an aliphatic hydrocarbon group (alkyl group, alkenyl group) may be 1 to 20, 1 to 10, 1 to 6, or 1 to 4. In the case of an alkenyl group, the lower limit of these carbon number ranges is 2. Examples of hydroxyalkyl groups include hydroxymethyl, 2-hydroxyethyl, and 3-hydroxypropyl groups. The number of carbon atoms in a hydroxyalkyl group is selected from a range similar to that of the aliphatic hydrocarbon group described above.

[0034] The aromatic moiety may have one first substituent, or two or more. It is also preferable that it has no first substituents. The number of first substituents is selected according to, for example, the number of members in the aromatic ring in the aromatic moiety, the number of ester groups and carboxyl groups, and in the case of linking groups, the type of linking group and chain length. The number of first substituents may be, for example, four or less.

[0035] In the first acid, the ester groups bonded to aromatic moieties such as the first and second ester groups are represented, for example, as R-O-(C=O)-. The group R is preferably a linear group. The group R may be an aliphatic hydrocarbon group or a heteroatom-containing linear group. These groups may also have substituents (hereinafter referred to as second substituents). The aliphatic hydrocarbon group and the heteroatom-containing linear group may be linear or branched. The heteroatom of the heteroatom-containing linear group is preferably oxygen or sulfur, and more preferably oxygen.

[0036] For example, at least the first ester group (more specifically, the heteroatom-containing chain group) may contain an oxyalkylene group or a poly(oxyalkylene) group. Also, both the first and second ester groups, or all of the ester groups bonded to the aromatic moiety, may contain an oxyalkylene group or a poly(oxyalkylene) group. Examples of oxyalkylene moieties in the oxyalkylene group and poly(oxyalkylene) group include oxyalkylenes having 1 to 4 carbon atoms (preferably 2 to 4), such as oxyethylene, oxypropylene, and oxytrimethylene. In the poly(oxyalkylene) group, the number of oxyalkylene repeats (for example, n1 or n2 as described later) may be 2 to 20, 2 to 10, or 2 to 6.

[0037] When an ester group (more specifically, group R) bonded to an aromatic moiety such as a primary or secondary ester group contains an oxyalkylene group or a poly(oxyalkylene) group, an aliphatic hydrocarbon group, for example, is bonded to the terminal end of the oxyalkylene group or poly(oxyalkylene) group.

[0038] The aliphatic hydrocarbon group R described above, or the aliphatic hydrocarbon group bonded to the end of the oxyalkylene group or poly(oxyalkylene) group, may be saturated or unsaturated. Each aliphatic hydrocarbon group may be linear or branched. Examples of aliphatic hydrocarbon groups include alkyl groups and alkenyl groups. Examples of alkyl groups include methyl, ethyl, propyl, iso-propyl, butyl, tert-butyl, hexyl, 2-ethylhexyl, decyl, and dodecyl groups. Examples of alkenyl groups include vinyl and allyl groups. The number of carbon atoms in each aliphatic hydrocarbon group (alkyl group or alkenyl group) may be 1 to 20, 1 to 10, 1 to 6, or 1 to 4. For alkenyl groups, the lower limit of these carbon number ranges is 2. The ester group may have a second substituent on the aliphatic hydrocarbon group bonded to its end.

[0039] The second substituent can be a hydrocarbon group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyl group, a hydroxyalkyl group, or an alkoxy group (for example, an alkoxy group with 1 to 6 or 1 to 4 carbon atoms, such as a methoxy group, ethoxy group, propoxy group, butoxy group, or tert-butoxy group). Examples of hydrocarbon groups include alkyl groups such as methyl group, ethyl group, propyl group, iso-propyl group, butyl group, and tert-butyl group (alkyl groups with 1 to 6 or 1 to 4 carbon atoms). Examples of hydroxyalkyl groups include hydroxymethyl group, 2-hydroxyethyl group, and 3-hydroxypropyl group, which have 1 to 6 (or 1 to 4) carbon atoms. Such hydrocarbon groups and hydroxyalkyl groups may also be the second substituent of a heteroatom-containing chain group. When the aliphatic hydrocarbon group at the terminus of an oxyalkylene group or a poly(oxyalkylene) group has a second substituent, at least one of the second substituents exemplified above can be selected from the group consisting of, for example, a hydroxyl group, a halogen atom, and an alkoxy group.

[0040] Group R may not have a second substituent. Group R may have one second substituent or two or more. If group R has two or more second substituents, at least two of the second substituents may be the same, or all of the second substituents may be different.

[0041] The second substituent may be a hydroxyl group or a group having a hydroxyl group. From the viewpoint of easily obtaining higher heat resistance, the second substituent may be a group without a hydroxyl group (such as the hydrocarbon group, halogen atom, or alkoxy group mentioned above). In other words, in the first acid, at least the first ester group does not have to have a hydroxyl group, and not all ester groups bonded to the aromatic moiety have to have a hydroxyl group. From the viewpoint of easily obtaining higher heat resistance, for example, the first acid may be an aromatic carboxylic acid other than mono(2-hydroxyethyl) phthalate.

[0042] From the viewpoint of suppressing the deactivation of carboxyl groups in the first acid, it is preferable that at least the first ester group in the first acid does not have a carboxyl group. From a similar viewpoint, it is preferable that all of the ester groups bonded to the aromatic moiety in the first acid (for example, the first ester group and the second ester group) do not have a carboxyl group.

[0043] In the electrolyte, carboxyl groups (first carboxyl group, second carboxyl group, etc.) bonded to the aromatic moiety may be in a free state, an ionic state, or a salt state. In electrolytic capacitors, in addition to the above states, carboxyl groups (first carboxyl group, second carboxyl group, etc.) bonded to the aromatic moiety may interact with or complex with components contained in the electrolytic capacitor (e.g., conductive polymer). In this specification, all of these states may be collectively referred to as carboxyl groups.

[0044] The first acid has at least a first carboxyl group and may have two or more carboxyl groups bonded to the aromatic moiety. The first acid may have a first carboxyl group and a second carboxyl group.

[0045] If the aromatic moiety of the first acid has a first benzene ring and a first ester group and a second ester group, as well as a first carboxyl group and a second carboxyl group, the first ester group, the second ester group, the first carboxyl group and the second carboxyl group may be bonded to the first benzene ring. The first carboxyl group is located in the ortho position relative to the first ester group. The second carboxyl group may be located in the ortho position relative to the first ester group or the second ester group (especially the second ester group). When the first acid has such a structure, the initial ESR tends to be kept low, and the change in ESR when the electrolytic capacitor is exposed to a high-temperature environment also tends to be small.

[0046] The aromatic moiety of the first acid has a first benzene ring, a second benzene ring, and a single bond or linking group connecting them, and may also have a first ester group and a second ester group, as well as a first carboxyl group and a second carboxyl group. In this case, the first ester group and the first carboxyl group may be bonded to the first benzene ring, and the second ester group and the second carboxyl group may be bonded to the second benzene ring. The first carboxyl group is located in the ortho position relative to the first ester group, and the second carboxyl group is located in the ortho position relative to the second ester group. When the first acid has such a structure, the initial ESR tends to be kept low, and the change in ESR when the electrolytic capacitor is exposed to a high-temperature environment also tends to be small. Furthermore, in the first benzene ring, one of the first ester group and the first carboxyl group may be located in the meta position relative to the single bond or linking group, and the other of the first ester group and the first carboxyl group may be located in the para position relative to the single bond or linking group. Similarly, in the second benzene ring, one of the second ester group and the second carboxyl group may be located in the meta position relative to the single bond or linking group, and the other of the second ester group and the second carboxyl group may be located in the para position relative to the single bond or linking group. First acids having such a structure are readily available, and the ester group and carboxyl group tend to be in an ortho position, making it easier to obtain higher heat resistance.

[0047] The first acid having a first ester group and a first carboxy group includes, for example, an aromatic carboxylic acid represented by the following formula (I). The first acid having a first ester group, a second ester group, a first carboxy group and a second carboxy group includes an aromatic dicarboxylic acid represented by the following formula (II).

[0048]

[0049] In formula (I) and formula (II), A １ and A ２ are each an aromatic moiety, and reference may be made to the above description. -C(=O)-O-R １ corresponds to the first ester group, and -C(=O)-O-R １ａ corresponds to the first ester group or the first carboxy group, and -C(=O)-O-R ２ａ corresponds to the second ester group or the second carboxy group. R １ａ is R １ or a hydrogen atom H, and R ２ａ is R ２ or a hydrogen atom H. One of R １ａ and R １ｂ is the first carboxy group and the other is the first ester group. One of R ２ａ and R ２ｂ is the second carboxy group and the other is the second ester group. R １ and R ２ each correspond to the above-mentioned group R. In formula (II), R １ and R ２ may be the same or different. m represents the number of carboxy groups and is an integer of 0 or 1 or more. The upper limit of m may be selected according to the number of members of the aromatic moiety A １ . m is 4 or less, may be 2 or less, and may be 1 or less.

[0050] Formula (I) includes, for example, an aromatic carboxylic acid represented by the following formula (i). Formula (II) includes, for example, an aromatic carboxylic acid represented by the following formula (iia), an aromatic carboxylic acid represented by the following formula (iib). However, the first acid is not limited to these only.

[0051]

[0052] In these equations, R １ａ , R １ｂ , R ２ａ , R ２ｂ , R １ , and m are the same as in formula (I) or formula (II). −X− is a single bond or a linking group. For linking groups, see the explanation above.

[0053] In formula (i), m is preferably 0 or 1. When m is 1, if the position of one carboxyl group is considered to be position 1, the position of the second carboxyl group may be any of positions 2, 3, 4, or 5. With respect to the first carboxyl group, the second carboxyl group may be at the m-position or the p-position.

[0054] For these formulas, the first ester group is -C(=O)-O-R １ and the second ester group -C(=O)-O-R ２ (More specifically, R １ and R ２ Each of these may contain an oxyalkylene group or a poly(oxyalkylene) group. Such first and second ester groups are represented by the following formulas (g1) and (g2), respectively.

[0055]

[0056] In these equations, -(-R １ｄ ―O-) ｎ１ - and - (-R ２ｄ ―O-) ｎ２ Each of these corresponds to an oxyalkylene group or a poly(oxyalkylene) group. Group R １ｃ and R ２ｃ Each of these corresponds to an aliphatic hydrocarbon bonded to the end of an oxyalkylene group or poly(oxyalkylene) group, as described above.

[0057] -R １ｄ - and -R ２ｄEach of the following is an alkylene group. The number of carbon atoms in the alkylene group may be between 1 and 4, or between 2 and 4. n1 and n2 are the number of repeating oxyalkylene groups and are integers of 1 or more. Each of n1 and n2 is selected, for example, from the range of repeating oxyalkylene groups described above.

[0058] Specific examples of the first acid represented by formula (i) include the compound represented by formula (i-1) below, the compound represented by formula (i-2a) below, and the compound represented by formula (i-2b) below.

[0059]

[0060] Specific examples of compounds represented by formula (ii) include the compounds represented by formulas (iiia-1a) and (iiia-1b), respectively, the compounds represented by formulas (iib-1a), (iib-1b), and (iib-1c), respectively, the compounds represented by formulas (iib-2a), (iib-2b), and (iib-2c), respectively, and the compounds represented by formulas (iib-3a), (iib-3b), and (iib-3c), respectively.

[0061]

[0062] In equations (i-1), (i-2), (iia-1), and (iib-1) to (iib-3), R １ａ , R １ｂ , R ２ａ , and R ２ｂ (R １ and R ２ (including) is the same as in formula (i) or formula (ii). First ester group -C(=O)-O-R １ It is preferable that the group is represented by the above formula (g1) or a hydroxyalkyl ester group. Second ester group -C(=O)-O-R ２ It is preferable that the first acid is a group represented by formula (g2) or a hydroxyalkyl ester group. However, the first acid is not limited to these specific examples.

[0063] The electrolyte may contain one primary acid, or a combination of two or more primary acids.

[0064] The concentration of the first acid in the electrolyte may be 1% by mass or more and 20% by mass or less, 3% by mass or more and 18% by mass or less, or 4% by mass or more and 16% by mass or less. When the concentration of the first acid is within these ranges, higher dielectric strength and higher heat resistance are easily obtained.

[0065] The electrolyte may contain, in addition to the primary acid, a secondary acid other than the primary acid as an acid component. The proportion of the primary acid in the acid component may be 25% by mass or more, 30% by mass or more, 50% by mass or more, or 70% by mass or more. The proportion of the primary acid in the acid component is 100% by mass or less.

[0066] (Secondary Acids) Examples of acids other than primary acids (secondary acids) include carboxylic acid compounds other than primary acids, acids having carbonyloxy bonds other than carboxylic acids (such as oxocarbonic acid and meldrumic acid) or their coordination compounds, phenolic compounds (such as picric acid, p-nitrophenol, pyrogallol, and catechol) or their coordination compounds, sulfur-containing acids (such as sulfuric acid, sulfonic acid (such as aromatic sulfonic acid), oxyaromatic sulfonic acid (such as phenol-4-sulfonic acid)), compounds having sulfonyliimide bonds, boron-containing acids (such as boric acid, halide boric acid (such as tetrafluoroboric acid), or partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halide phosphoric acid (such as hexafluorophosphate), phosphonic acid, phosphinic acid, or partial esters thereof), and nitrogen-containing acids (such as nitric acid and nitrite).

[0067] Examples of carboxylic acid compounds include carboxylic acids other than primary acids (aliphatic carboxylic acids, aromatic carboxylic acids, etc.), carboxylic acid anhydrides, and coordination compounds of carboxylic acids. Examples of aliphatic carboxylic acids include aliphatic polycarboxylic acids (such as adipic acid and other aliphatic polycarboxylic acids with 4 to 10 carbon atoms). Examples of aromatic carboxylic acids include aromatic hydroxy acids (such as benzoic acid and salicylic acid), aromatic polycarboxylic acids (such as phthalic acid and pyromellitic acid), and sulfo-aromatic carboxylic acids (such as m-sulfobenzoic acid, 4-sulfophthalic acid, and 5-sulfosalicylic acid).

[0068] Examples of compounds containing a sulfonylimide bond include saccharin, 1,2-benzenedisulfonamide, cyclohexafluoropropane-1,3-bis(sulfonyl)imide, 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide, dibenzenesulfonamide, trifluoromethanesulfonanilide, N-[(4-methylphenyl)sulfonyl]acetamide, benzenesulfonanilide, and N,N'-diphenylsulfamide.

[0069] Examples of the coordination compounds mentioned above include those comprising at least one central atom selected from the group consisting of boron, aluminum, and silicon, to which a carboxylic acid, an acid having a carbonyloxy bond, or a phenolic compound is bonded. Specific examples of coordination compounds include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodigallic acid, borodicatechol, and borodipyrogallol.

[0070] The acid component may contain one secondary acid, or a combination of two or more. Among the secondary acids, aromatic carboxylic acids (phthalic acid, salicylic acid, benzoic acid, etc.) and the above-mentioned coordination compounds (borodisalicylic acid, borodisuoic acid, borodiglycolic acid, etc.) are preferred, with phthalic acid, salicylic acid, borodisalicylic acid, etc. being particularly preferred.

[0071] In the electrolyte, the acidic groups of the secondary acid (carboxyl groups, sulfonic acid groups, phosphate groups, phosphonic acid groups, phenolic hydroxyl groups, etc.) may exist in any of the following forms: free form, salt form, anionic form, or form interacting with (compounding with) a conductive polymer. Each of the acidic groups of the secondary acid encompasses all of these forms.

[0072] (Basic component) The presence of a basic component in the electrolyte increases the dissociability of the acid component, making it easier for acidic groups such as carboxyl groups to act on the conductive polymer. Therefore, it is easier to obtain higher conductivity from the conductive polymer.

[0073] Examples of basic components include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The electrolyte may contain one of these basic components or a combination of two or more.

[0074] The amine may be aliphatic, aromatic, or heterocyclic. Examples of amines include dialkylamines (such as diethylamine), trialkylamines (such as trimethylamine, ethyldimethylamine, triethylamine (TEA), tri-n-butylamine (TBA), dimethyl-n-octylamine (DMOA), and dimethyldecylamine (DMDA)), alkylenediamines (such as ethylenediamine), aromatic amines (such as aniline), and heterocyclic amines (such as pyrrolidine, imidazole compounds (such as imidazole (Imd), 1,2,3,4-tetramethylimidazolinium), pyridine (Pyr), 4-dimethylaminopyridine, and diazabicycloundecene (DBU)). Both aromatic amines and heterocyclic amines may be monocyclic or polycyclic (such as fused rings or cross-linked rings). Examples of quaternary ammonium compounds include amidine compounds (including imidazole compounds).

[0075] The electrolyte may contain basic components in free form, in cation form, or in salt form. All of these forms are sometimes collectively referred to as basic components.

[0076] The equivalent ratio of the first acid to the base component (= first acid / base component) may be 0.5 or more and 10 or less, or 1.0 or more and 9.0 or less. Preferably, the first acid / base component (equivalent ratio) is 2.5 or more and 10 or less, and more preferably 3.0 or more and 8.0 or less. In these cases, a high degree of dissociation of the first acid can be ensured, and electrode corrosion can be suppressed. In addition, it is easier to ensure higher dielectric strength.

[0077] The equivalent ratio of the first acid to the base component is (total number of carboxyl groups per molecule of the first acid) / (OH groups that can be generated per molecule of the base component). －This is the ratio of the total number of moles.

[0078] 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 12 or less, or 3.0 or more and 10 or less. The equivalent ratio of the acid component / base component may be selected from the above numerical range described for the equivalent ratio of the first acid / base component.

[0079] The equivalent ratio of the acid component to the base component is (total number of acid groups per molecule of acid component) / (OH groups that can be generated per molecule of base component). － This is the ratio of the total number of moles.

[0080] (Organic solvents) Non-aqueous solvents are examples of organic solvents included in the electrolyte. It is preferable to use at least a polar solvent as the organic solvent. Polar solvents include aprotic polar solvents and protic polar solvents. Examples of such organic solvents include sulfone compounds, lactone compounds, carbonate compounds, and alcohol compounds. The electrolyte may contain one of these organic solvents, or a combination of two or more.

[0081] Among aprotic polar solvents, sulfone compounds include cyclic sulfone compounds (such as sulfolane (SL)) and sulfoxide compounds (such as dimethyl sulfoxide and diethyl sulfoxide). Lactone compounds include γ-butyrolactone (GBL) and γ-valerolactone. Carbonate compounds include linear carbonates (such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) and cyclic carbonates (such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate).

[0082] Alcohol compounds, which are protic polar solvents, include monohydric alcohols and polyhydric alcohols. Examples of polyhydric alcohols include glycol compounds (alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), polyalkylene glycols (polyethylene glycol (PEG), polypropylene glycol, etc.)), glycerol compounds (glycerol, polyglycerol, etc.), sugar alcohol compounds, or alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.).

[0083] From the viewpoint of easily obtaining higher conductivity of the electrolyte, the organic solvent may contain glycol compounds and sulfone compounds (such as cyclic sulfone compounds like SL). Furthermore, it is also preferable to include polyalkylene glycols (such as PEG) in addition to these solvents.

[0084] [Electrolytic Capacitors] The components of an electrolytic capacitor other than the electrolyte will be explained in more detail below.

[0085] (Capacitor element) The capacitor element includes an anode having a dielectric layer on its surface and a conductive polymer covering at least a portion of the dielectric layer. The conductive polymer constitutes at least a portion of the cathode of the capacitor element. The cathode may further include a cathode extraction layer (such as a cathode foil).

[0086] (Anode) The anode may include a valve metal, an alloy containing a valve metal, and a compound containing a valve metal. These materials may be used individually or in combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferred, for example.

[0087] An anode foil is preferred as the anode body. Preferably, the anode body has a porous portion with pores in at least its surface layer. Other anode bodies include porous sintered bodies or porous molded bodies of particles containing valve metal.

[0088] An anode foil having a porous portion can be obtained, for example, by roughening the surface of a substrate containing a valve-acting metal (such as a foil-shaped or plate-shaped substrate). Surface roughening may be carried out by etching (for example, electrolytic etching or chemical etching).

[0089] (Dielectric layer) The dielectric layer is formed, for example, by anodizing the valve metal on the surface of the anode. Anodizing is carried out, for example, by chemical conversion treatment. The dielectric layer is formed, for example, to cover at least a portion of the surface of the anode.

[0090] The dielectric layer contains, for example, an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta ２ O ５ It includes. When aluminum is used as the valve metal, the dielectric layer is Al ２ O ３ This includes [the specified element]. However, the dielectric layer is not limited to this; any material that functions as a dielectric is acceptable.

[0091] The dielectric layer is typically formed on the surface of the anode. When the dielectric layer is formed on the surface of a porous portion of the anode, it forms along the inner walls of the pores in the porous portion or the depressions (pits) on the anode surface.

[0092] (Conductive Polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer covers at least a portion of the dielectric layer. This embodiment includes cases where the conductive polymer is in contact with at least a portion of the dielectric layer. If 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 constitute a layer. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer constitutes at least a portion of the cathode body in an electrolytic capacitor. The conductive polymer may further contain additives as needed.

[0093] (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 polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeleton. The above polymers only need to contain at least one monomer unit that constitutes the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (such as substituted products having substituents). For example, polythiophene also includes poly(3,4-ethylenedioxythiophene) (PEDOT).

[0094] Conjugated polymers may be used individually or in combination of two or more types.

[0095] The weight-average molecular weight (Mw) of the conjugated polymer is not particularly limited, and is, for example, between 1,000 and 1,000,000.

[0096] In this specification, weight-average molecular weight (Mw) is a polysaccharide-converted value measured by gel permeation chromatography (GPC). GPC is typically performed using a polyhydroxymethacrylate gel column and an aqueous sodium nitrate solution as the mobile phase.

[0097] (Dopants) Examples of dopants include relatively low-molecular-weight anions and high-molecular-weight anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that produce these anions are used as dopants. Examples of dopants that produce sulfonate ions include aromatic sulfonic acid compounds (such as p-toluenesulfonic acid and naphthalenesulfonic acid). Aromatic sulfonic acid compounds may have, for example, at least one selected from the group consisting of a carboxyl group and a hydroxyl group.

[0098] Examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenol sulfonic acid novolac resin, and polyacrylic acid. The polymer anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having substituents. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0099] However, these dopants are merely examples and are not limited to them. A single dopant may be used alone, or two or more may be used in combination.

[0100] The conductive polymer may be formed, for example, by performing at least one of chemical polymerization and / or electropolymerization of a conjugated polymer precursor on a dielectric layer in the presence of a dopant. Alternatively, a conductive polymer (e.g., a layer of conductive polymer) may be formed by contacting a dielectric layer with 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 solutions or dispersions 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 conjugated polymers, oligomers and prepolymers in which multiple molecular chains of raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination.

[0101] The Dopant's Mw is not particularly limited and may be between 1,000 and 1,000,000.

[0102] The amount of dopant contained in the conductive polymer may be 10 parts by mass or more and 1000 parts by mass or 20 parts by mass or more and 500 parts by mass per 100 parts by mass of the conjugated polymer.

[0103] (Cathode Extraction Layer) The cathode extraction layer comprises, for example, a first layer covering at least a portion of a conductive polymer. The cathode extraction layer may also comprise 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 conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be composed of a layer containing conductive carbon (such as graphite) as the first layer (also referred to as a carbon layer) and a layer containing metal powder or a metal foil as the second layer. When a metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil. The cathode extraction layer can be formed by known methods depending on the layer configuration.

[0104] A second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder onto the surface of the first layer. Examples of such a second layer include a metal particle-containing layer (such as a silver particle-containing layer) formed using a composition containing metal particles such as silver particles and a resin (binder resin). As the resin, a thermosetting resin such as an imide resin or epoxy resin may be used, or a thermoplastic resin may be used.

[0105] When using metal foil as the first layer, the type of metal is not particularly limited, but it is preferable to use valve metals such as aluminum, tantalum, or niobium, or alloys containing valve metals. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a metal different from the metal constituting the metal foil (dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (conductive carbon, etc.).

[0106] The above-mentioned dissimilar metal or nonmetal (for example, conductive carbon) coating may be used as the first layer, and the above-mentioned metal foil may be used as the second layer.

[0107] (Separator) A separator may be placed between the cathode (cathode foil, etc.) and the anode (anode foil, etc.). The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used.

[0108] If the capacitor element includes a separator, the conductive polymer may be impregnated into the separator. The conductive polymer may be interposed between the anode (such as an anode foil) and the cathode (such as a cathode foil), and may be in contact with at least a portion of the dielectric layer and at least a portion of the cathode.

[0109] (Other) Electrolytic capacitors may be wound type, chip type, or multilayer type. Electrolytic capacitors have at least one capacitor element. Electrolytic capacitors may have multiple capacitor elements. For example, an electrolytic capacitor may have a multilayer structure of two or more capacitor elements, or it may have two or more wound type capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0110] In a capacitor element, one end of the cathode lead is electrically connected to the cathode lead-out layer. One end of the 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 led out from the outer casing or case, respectively. The other ends of each lead exposed from the outer casing or case are used for soldering to the substrate on which the electrolytic capacitor is to be mounted. Each lead may be a lead wire or a lead frame.

[0111] The electrolyte of this disclosure can be used in electrolytic capacitors, such as hybrid electrolytic capacitors. The electrolytic capacitors of this disclosure have high voltage resistance and high heat resistance. Therefore, the electrolytic capacitors of this disclosure are particularly suitable for a variety of applications where high voltage resistance, high reliability, or long lifespan are required. However, the applications of electrolytic capacitors are not limited to these.

[0112] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present disclosure, and Figure 2 is a schematic diagram showing a part of the capacitor element relating to the electrolytic capacitor unfolded. 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 technologies (1) to (8) relating to the electrolytic capacitor of the present disclosure, or at least one of the above technologies (1) to (8) and the components described above.

[0113] An electrolytic capacitor comprises, for example, a capacitor element 10, a bottomed case 101, a sealing member 102 that closes the opening of the bottomed case 101, a base plate 103 that covers the sealing member 102, lead wires 104A, 104B, and lead tabs 105A, 105B. The bottomed case 101 houses the capacitor element 10 and an electrolyte (not shown). The area near the opening end of the bottomed case 101 is tapered inward, and the opening end is curled so as to be crimped to the sealing member 102. The lead wires 104A and 104B are led out from the sealing member 102 and pass through the base plate 103. The lead tabs 105A and 105B connect the lead wires 104A and 104B to the electrodes of the capacitor element 10, respectively.

[0114] The capacitor element 10 is, for example, a wound body as shown in Figure 2. The wound body comprises an anode foil 11 connected to a lead tab 105A, a cathode foil 12 connected to a lead tab 105B, and a separator 13. The anode foil 11 and the cathode foil 12 are wound around the separator 13. The outermost circumference of the wound body is secured by a winding stopper tape 14. Note that Figure 2 shows the state in which a portion of the wound body is unfolded before securing the outermost circumference.

[0115] In the capacitor element 10, a dielectric layer (not shown) is formed on at least a portion of the surface of the anode foil 11. A separator 13 and a conductive polymer (not shown) are interposed between the anode foil 11 and the 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 the cathode foil 12. The conductive polymer and the separator are impregnated with an electrolyte. As the electrolyte, the electrolyte described herein, which contains an organic solvent, a first acid, and a basic component, is used.

[0116] [Examples] The electrolyte and electrolytic capacitor according to the present disclosure will be described in detail below based on examples and comparative examples. However, the electrolyte and electrolytic capacitor according to the present disclosure are not limited to the following examples. The components described in the following examples may be combined with the conceptual descriptions above, which include at least one of the technologies (1) to (8).

[0117] <Production Example 1> The compound represented by formula (i-1) above, which is the first acid (-R １ａ -H, -R １ｂ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ The following procedure was used to manufacture it.

[0118] A mixture of phthalic anhydride (50 mmol) and triethylene glycol monomethyl ether (50 mmol) was heated at 170°C for 2 hours to produce compound (i-1) as the first acid. The endpoint of the reaction was determined by the acid value, and the structure of the obtained first acid was determined by liquid chromatography-mass spectrometry (LC / MS) (ion source: ESI). － This was confirmed by [the organization / method].

[0119] <Production Example 2> The first acid was produced using the same procedure as in Production Example 1, except that trimellitic anhydride was used instead of phthalic anhydride. The obtained first acid was a compound represented by the above formula (i-2a) (-R １ａ -H, -R １ｂ (= group R １ ): - (CH ２ CH ２-O) ３ -CH ３ ), and a compound represented by the formula (i-2b) (-R １ａ (= group R １ ): -(CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ : -H) was a mixture of

[0120] Production Example 3 Instead of phthalic anhydride, pyromellitic dianhydride was used, and 100 mmol of triethylene glycol monomethyl ether was used. The first acid was produced in the same procedure as in Production Example 1 except for these. The obtained first acid was a compound represented by the formula (iia-1a) (-R １ａ : -H, -R １ｂ (= group R １ ): -(CH ２ CH ２ -O) ３ -CH ３ , -R ２ａ : -H, -R ２ｂ (= group R ２ ): -(CH ２ CH ２ -O) ３ -CH ３ ), and a compound represented by the formula (iia-1b) (-R １ａ : -H, -R １ｂ (= group R １ ): -(CH ２ CH ２ -O) ３ -CH ３ , -R ２ａ (= group R ２ ): -(CH ２ CH ２ -O) ３ -CH ３ , -R ２ｂ : -H) was a mixture of

[0121] <Production Example 4> Instead of phthalic anhydride, 4,4'-biphthalic anhydride was used, and 100 mmol of triethylene glycol monomethyl ether was added. The reaction was carried out at 170°C for 4 hours. The first acid was produced using the same procedure as in Production Example 1, except for these steps. The obtained first acid is a compound represented by the formula (iib-1a) (-R １ａ -H, -R １ｂ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), the compound represented by the formula (iib-1b) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), and the compound represented by the formula (iib-1c) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ｂ It was a mixture of :-H.

[0122] <Production Example 5> Instead of phthalic anhydride, 4,4'-oxydiphthalic anhydride was used, and 100 mmol of triethylene glycol monomethyl ether was added. The reaction was carried out at 170°C for 4 hours. The first acid was produced using the same procedure as in Production Example 1, except for these steps. The obtained first acid is a compound represented by the formula (iib-2a) (-R １ａ -H, -R １ｂ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), the compound represented by the formula (iib-2b) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), and the compound represented by the formula (iib-2c) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ｂ It was a mixture of :-H.

[0123] <Production Example 6> Instead of phthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride was used, and 100 mmol of triethylene glycol monomethyl ether was added. The reaction was carried out at 170°C for 4 hours. The first acid was produced using the same procedure as in Production Example 1, except for these steps. The obtained first acid is a compound represented by the formula (iib-3a) (-R １ａ -H, -R １ｂ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), the compound represented by the formula (iib-3b) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ -H, -R ２ｂ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ ), and the compound represented by the formula (iib-3c) (-R １ａ (= group R １ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R １ｂ -H, -R ２ａ (= group R ２ ): - (CH ２ CH ２ -O) ３ -CH ３ , -R ２ｂ It was a mixture of :-H.

[0124] <Production Example 7> Instead of phthalic anhydride, pyromellitic dianhydride was used, and 100 mmol of ethylene glycol was used. The first acid was produced using the same procedure as in Production Example 3, except for these differences. The obtained first acid was a compound represented by the above formula (iia-1b) (-R １ａ -H, -R １ｂ (= group R １ ): -CH ２ CH ２ -OH, -R ２ａ (= group R ２ ): -CH ２ CH ２ -OH, -R2 ｂ : -H)

[0125] <Production Example 8> Instead of phthalic anhydride, isophthalic acid was used, and 50 mmol of ethylene glycol was used. Except for these, the isophthalic acid mono(2-hydroxyethyl) ester, which corresponds to the second acid, was produced using the same procedure as in Production Example 1. In isophthalic acid mono(2-hydroxyethyl) ester, one carboxyl group of isophthalic acid is replaced with -C(=O)-O-CH ２ CH ２ It is a compound in which an -OH group has been replaced.

[0126] Examples 1-11 and Comparative Examples 1-2: Wound-wound electrolytic capacitors (electrolytic capacitor I with a rated voltage of 25V and a rated capacitance of 330μF, and electrolytic capacitor II with a rated voltage of 100V and a rated capacitance of 18μF) were fabricated and evaluated according to the following procedure.

[0127] (Preparation of the anode) A 100 μm thick aluminum foil was etched to roughen its surface. Then, a 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 to it. After that, the aluminum foil was cut to a size of 8 mm x 120 mm to prepare the anode.

[0128] (Preparation of the cathode) A 50 μm thick aluminum foil was etched to roughen its surface. Then, the aluminum foil was cut to a size of 8 mm x 120 mm to prepare the cathode.

[0129] (Fabrication of the wound body) Anode lead tabs and cathode lead tabs were connected to the anode and cathode bodies, and the anode and cathode bodies were wound together with paper separators, winding the lead tabs as they were wound. Anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the wound body. Then, the fabricated wound body was subjected to another chemical conversion treatment to form a dielectric layer on the cut end of the anode body. Next, the ends of the outer surface of the wound body were fixed with winding tape to fabricate the wound body.

[0130] (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 deionized water to prepare a mixed solution. While stirring the mixed solution, an oxidizing agent (ferrous sulfate and ammonium persulfate) dissolved in deionized water was added to carry out the polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, and a polymer dispersion containing PSS-doped poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) as the conductive polymer was obtained. The Mw of the polymer dopant is the value measured under the conditions described above.

[0131] (Coating of the dielectric layer with conductive polymer) The wound body was immersed in a polymer dispersion contained in a predetermined container for 5 minutes in a reduced-pressure atmosphere (40 kPa), and then the wound body was 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, and at least a portion of the dielectric layer was coated with a conductive polymer. A capacitor element was formed in this way. However, in Comparative Examples 8 to 10, the capacitor element was formed without performing this step of coating the dielectric layer with a conductive polymer.

[0132] (Impregnation of electrolyte) As the solvent for the electrolyte, a mixture obtained by mixing EG, PEG (number average molecular weight Mn: 300), and SL in a volume ratio of EG:PEG:SL = 1:1:1 was used. The electrolyte was prepared by dissolving the acid and base components shown in Table 1 or Table 2 in this mixture. The concentration of the first acid (or second acid) in the electrolyte was set to 4% by mass to 16% by mass. Tables 1 and 2 also show the equivalent ratio of the first acid to the base component. For comparative examples in Table 1 or Table 2, the equivalent ratio of the second acid to the base component is shown in parentheses in the column for the equivalent ratio of the first acid / base component. As the acid component, in the examples, the first acid shown in Table 1, which was produced in Production Examples 1 to 7, was used, in Comparative Example 1, phthalic acid, which is the second acid, was used, and in Comparative Example 2, mono(2-hydroxyethyl) isophthalic acid produced in Production Example 8 was used.

[0133] The basic components used were triethylamine (TEA), tributylamine (TBA), dimethyldecylamine (DMDA), pyridine (Pyr), or diazabicycloundecene (DBU).

[0134] (Assembly of electrolytic capacitors) The capacitor elements were immersed in the electrolyte and placed in a reduced pressure atmosphere (40 kPa) for 5 minutes to allow the electrolyte to penetrate the capacitor elements.

[0135] A capacitor element impregnated with electrolyte was housed in a bottomed case, with the lead wires positioned on the opening side of the bottomed case. A sealing member, formed to allow the lead wires to pass through, was placed above the capacitor element. Then, a drawing process was performed near the opening end of the bottomed case, and the opening end was further curled to create a tight seal with the sealing member. In this way, the capacitor element and electrolyte were sealed inside the bottomed case. By placing a base plate on the curled portion, an electrolytic capacitor as shown in Figure 1 was completed. For each example, a total of 40 electrolytic capacitors I and a total of 20 electrolytic capacitors II were manufactured. The manufactured electrolytic capacitors were subjected to an aging process at 130°C for 2 hours while applying the rated voltage.

[0136] [Evaluation] The electrolytic capacitors fabricated as described above were evaluated according to the following (1) and (2).

[0137] (1) ESR values ​​were measured for electrolytic capacitors I and II after ESR aging treatment using an LCR meter at a frequency of 100 kHz in an environment of 20°C. The average value of the measured values ​​for 40 electrolytic capacitors I and 20 electrolytic capacitors II (initial ESR value: r0 (Ω)) was then calculated.

[0138] After determining r0, accelerated tests were performed on electrolytic capacitors I under the following conditions 1 and 2, and on electrolytic capacitors II under the following condition 3. Condition 1 (No-load accelerated test): 20 of the 40 electrolytic capacitors I were left standing at 145°C for 750 hours. Condition 2 (25V load accelerated test): The remaining 20 electrolytic capacitors I from the no-load accelerated test were subjected to a rated voltage (25V) at 145°C for 750 hours. Condition 3 (100V load accelerated test): 20 electrolytic capacitors II were subjected to a voltage of 100V at 145°C for 750 hours.

[0139] For each electrolytic capacitor I and II after each accelerated test, the average ESR value (r1 (Ω)) after the accelerated test was calculated in the same manner as for the initial ESR value.

[0140] Using the obtained values ​​of r0 and r1, the ESR change (ΔESR) was calculated using the following formula: ΔESR = r1 / r0

[0141] (2) Withstand Voltage Characteristics The withstand voltage characteristics were measured using the following procedure. First, a sample of electrolytic capacitor for evaluating the withstand voltage characteristics was prepared in accordance with the example or comparative example. More specifically, a 120 μm thick aluminum foil was treated by applying a voltage of 630 V while immersed in an ammonium adipate solution, and then cut to a size of 14 mm in length and 110 mm in width. In this way, an anode foil (anode body) having a dielectric layer was prepared. A 22 μm thick aluminum foil was treated by applying a voltage of 2 V while immersed in an ammonium adipate solution, and then cut to a size of 14 mm in length and 135 mm in width. In this way, a cathode foil (cathode body) having a dielectric layer was prepared. The obtained anode foil and cathode foil having a dielectric layer were used. Except for these, a total of five electrolytic capacitors were prepared using the same procedure as in the example or comparative example, and then subjected to aging treatment.

[0142] An electrolytic capacitor was placed in a constant temperature bath set to 145°C, and a DC current was applied to the electrolytic capacitor by connecting the leads to a power supply. At this time, the current density per unit area was 3 mA / cm² relative to the area of ​​the anode foil (the area of ​​the projected shape when the anode foil is projected in the thickness direction). ２ The applied DC current was adjusted to achieve the following result. This caused voltage fluctuations, such as increases and decreases in the electrolytic capacitor's voltage. During this time, when the voltage increase of the electrolytic capacitor subsided and several points of voltage decrease appeared, the voltage at the second point was measured. This voltage was measured for five electrolytic capacitors, and the average value was calculated. This average value was used as an indicator of the voltage withstand characteristic. The table shows the relative values ​​when the value of the capacitor in Comparative Example 1 is set to 100. A larger value indicates better voltage withstand characteristics and superior performance of the electrolytic capacitor.

[0143] The evaluation results for each electrolytic capacitor are shown in Table 1 or Table 2. In Tables 1 and 2, E1 to E11 are examples, and C1 to C2 are comparative examples.

[0144]

[0145] As shown in Table 1, the ESR increase was suppressed in the examples compared to the comparative examples, even after the no-load accelerated test and the 25V and 100V load accelerated tests. In the 100V load accelerated test, the electrolytic capacitor of Comparative Example 1 was deemed undetectable (ND) because the internal pressure increased during the test and the safety valve opened. Furthermore, high voltage withstand capability was obtained in the examples.

[0146]

[0147] As shown in Table 2, high voltage resistance was obtained even when using base components other than TEA, and the rise in ESR was suppressed after both the no-load accelerated test and the 25V and 100V load accelerated tests.

[0148] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0149] 100: Electrolytic capacitor 101: Bottomed case 102: Sealing material 103: Base 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 electrolyte for use in an electrolytic capacitor comprising a capacitor element containing a conductive polymer, wherein the electrolyte comprises an organic solvent, a first acid, and a basic component, the first acid being an aromatic carboxylic acid (excluding mono(2-hydroxyethyl) phthalate) having an aromatic moiety, a first ester group bonded to the aromatic moiety, and a first carboxyl group bonded to the aromatic moiety, the first ester group not having a carboxyl group, and the first carboxyl group being located in the ortho position relative to the first ester group.

2. The electrolyte according to claim 1, wherein the first ester group comprises an oxyalkylene group or a poly(oxyalkylene) group.

3. The electrolyte according to claim 1, wherein the aromatic carboxylic acid further comprises a second ester group bonded to the aromatic moiety and a second carboxyl group bonded to the aromatic moiety, the second carboxyl group being located in the ortho position relative to the second ester group.

4. The electrolyte according to claim 3, wherein the aromatic moiety has a first benzene ring, and the first ester group, the second ester group, the first carboxyl group, and the second carboxyl group are bonded to the first benzene ring.

5. The electrolyte according to claim 3, wherein the aromatic moiety has a first benzene ring, a second benzene ring, and a single bond or linking group connecting the first benzene ring and the second benzene ring, the first ester group and the first carboxyl group being bonded to the first benzene ring, and the second ester group and the second carboxyl group being bonded to the second benzene ring.

6. The electrolyte according to claim 5, wherein in the first benzene ring, one of the first ester group and the first carboxyl group is located in the meta position relative to the single bond or the linking group, and the other of the first ester group and the first carboxyl group is located in the para position relative to the single bond or the linking group, and in the second benzene ring, one of the second ester group and the second carboxyl group is located in the meta position relative to the single bond or the linking group, and the other of the second ester group and the second carboxyl group is located in the para position relative to the single bond or the linking group.

7. The electrolyte according to any one of claims 3 to 6, wherein the first ester group comprises an oxyalkylene group or a poly(oxyalkylene) group, and the second ester group comprises an oxyalkylene group or a poly(oxyalkylene) group.

8. An electrolytic capacitor comprising a capacitor element and an electrolyte according to any one of claims 1 to 6, wherein the capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer covering at least a portion of the dielectric layer.

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