Electrolytic capacitor

Abstract

This electrolytic capacitor has a rated voltage of 150 V or more, and comprises a capacitor element and an electrolyte solution. The capacitor element includes: an anode foil having a dielectric layer on a surface thereof; a cathode foil; and a separator and a conductive polymer interposed between the anode foil and the cathode foil. The electrolyte solution contains a solute and a solvent in which the solute is dissolved. The solute is a salt of an organic carboxylate anion as a first acid component and an organic cation as a base component. The electrolyte solution further contains a free second acid component. The solvent includes a first organic solvent having a molecular weight of 200 or lower and a second organic solvent having a molecular weight higher than the molecular weight of the first organic solvent. The concentration of the solute in the electrolyte solution is 5-12 mass%. The conductivity of the electrolyte solution at 30°C is 0.05-0.29 mS / cm.

Description

Electrolytic Capacitor

[0001] The present disclosure relates to an electrolytic capacitor.

[0002] Hybrid electrolytic capacitors are regarded as promising as capacitors that are small in size, large in capacity, and have low ESR (equivalent series resistance). Such an electrolytic capacitor includes a capacitor element and an electrolytic solution. The capacitor element includes, for example, an anode foil having a dielectric layer formed on a surface thereof, a cathode foil, and a separator and a conductive polymer interposed therebetween. As the electrolytic solution, a solution obtained by dissolving a solute in an organic solvent is used. Also, in recent years, hybrid electrolytic capacitors having high voltage resistance have been regarded as promising.

[0003] Patent Document 1 proposes a solid electrolytic capacitor characterized in that: a solid electrolyte layer is formed on a capacitor element obtained by winding an anode electrode foil and a cathode electrode foil with a separator interposed therebetween using a conductive polymer dispersion in which conductive polymer particles are dispersed in a solvent; and an electrolytic solution containing less than 9 wt% of a salt of a composite compound of an inorganic acid and an organic acid as a solute is filled into voids in the capacitor element on which the solid electrolyte layer is formed.

[0004] Patent Document 2 proposes a solid electrolytic capacitor characterized in that: the capacitor has a capacitor element formed by winding an anode foil and a cathode foil with a separator interposed therebetween; the capacitor element has a solid electrolyte layer; voids in the capacitor element are filled with an electrolytic solution; the electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent; and an addition amount of the acid of the solute relative to the solvent is 0.6 mol / kg or less.

[0005] Japanese Patent Application Laid-Open No. 2019-145835, Japanese Patent Application Laid-Open No. 2017-38010

[0006] One aspect of the present disclosure relates to an electrolytic capacitor comprising a capacitor element and an electrolyte, wherein the capacitor element comprises an anode foil having a dielectric layer on its surface, a cathode foil, a separator and a conductive polymer interposed between the anode foil and the cathode foil, the electrolyte comprises a solute and a solvent for dissolving the solute, the solute is a salt of an organic carboxylic acid anion as a first acid component and an organic cation as a base component, the electrolyte further comprises a free second acid component, the solvent comprises a first organic solvent having a molecular weight of 200 or less and a second organic solvent having a molecular weight higher than the molecular weight of the first organic solvent, the concentration of the solute in the electrolyte is 5% by mass or more and 12% by mass or less, the conductivity of the electrolyte at 30°C is 0.05 mS / cm or more and 0.29 mS / cm or less, and the rated voltage is 150 V or more.

[0007] According to this disclosure, in an electrolytic capacitor comprising an electrolyte and a conductive polymer and having a rated voltage of 150V or higher, a high convergence rate of leakage current during re-formation can be obtained, and a low ESR can be obtained after re-formation.

[0008] This is a schematic cross-sectional view showing 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 in Figure 1 unfolded.

[0009] Generally, electrolytic capacitors using conductive polymers and electrolytes undergo an aging process after assembly by heating while applying the rated voltage. During the aging process, the anode foil is re-formed by applying voltage to it in the electrolyte, which can converge leakage current. However, in recent years, with the expansion of applications for electrolytic capacitors, there has been a demand for high-voltage products with a rated voltage of 150V or more. However, it has become clear that in electrolytic capacitors with such very high rated voltages, leakage current may not converge through re-formation. Furthermore, even if leakage current can be converged through re-formation, it has become clear that the equivalent series resistance (ESR) after re-formation may not be sufficiently reduced.

[0010] In electrolytic capacitors that use anode foil and also contain conductive polymer and electrolyte, corrosion of the anode foil, as well as degradation of the conductive polymer, can occur. Therefore, in order to ensure excellent capacitor performance, such as low ESR, the electrolyte needs to have various functions and characteristics. In particular, when the rated voltage of the electrolytic capacitor is very high, such as 150V or above, degradation of the conductive polymer when the rated voltage is applied tends to become significant. In particular, the increase in ESR becomes significant due to the degradation of the conductive polymer. For this reason, even if the electrolyte of an electrolytic capacitor that does not use conductive polymer is used as is in an electrolytic capacitor that contains conductive polymer, sufficient characteristics cannot be obtained.

[0011] Furthermore, electrolytic capacitors typically undergo an aging process after assembly, in which they are heated while the rated voltage is applied. This aging process regenerates the anode foil, reduces leakage current, and yields an electrolytic capacitor with sufficient performance for practical use. However, it has become clear that while leakage current may converge when the applied voltage during the aging process is less than 150V, it may not converge when the voltage is 150V or higher. This type of problem is previously unknown.

[0012] Technical Information (1) An electrolytic capacitor according to one aspect of the present disclosure comprises a capacitor element and an electrolyte, and has a rated voltage of 150V or more. The capacitor element comprises an anode foil having a dielectric layer on its surface, a cathode foil, a separator and a conductive polymer interposed between the anode foil and the cathode foil. The electrolyte comprises a solute and a solvent for dissolving the solute. The solute is a salt of an organic carboxylic acid anion as a first acid component and an organic cation as a base component. The electrolyte further comprises a free second acid component. The solvent comprises a first organic solvent with a molecular weight of 200 or less and a second organic solvent with a molecular weight higher than the molecular weight of the first organic solvent. The concentration of the solute in the electrolyte is 5% by mass or more and 12% by mass or less. The conductivity of the electrolyte at 30°C is 0.05 mS / cm or more and 0.29 mS / cm or less.

[0013] In this disclosure, by using the above-mentioned electrolyte, when the rated voltage of the electrolytic capacitor is high, such as 150V or more, the re-formation of the anode foil can be promoted by aging treatment, resulting in a high leakage current convergence rate. In addition, the ESR of the electrolytic capacitor can be kept low. Furthermore, in the electrolytic capacitor of this disclosure, by using the above-mentioned electrolyte, high voltage withstand capability can be obtained even before the aging treatment.

[0014] The exact reasons for the above effects are unclear, but they are thought to be due to the balance of the electrolyte's conductivity and composition. For example, the inclusion of both a first and second organic solvent in the electrolyte makes it easier to achieve an appropriate viscosity. Furthermore, the electrolyte's conductivity being 0.29 mS / cm or less suppresses short circuits through the electrolyte while maintaining a certain level of conductivity. This allows for high dielectric strength even before aging (re-reformation). In addition, the electrolyte's conductivity being 0.29 mS / cm or less, and the aforementioned composition of the electrolyte, allows for a more uniform formation of the dielectric layer on the anode foil surface during aging. Therefore, a high convergence rate of leakage current during re-reformation is thought to be achieved. The inclusion of a second acid component in the electrolyte allows for a low pH even with relatively low solute concentrations and relatively low conductivity. As a result, degradation and de-doping of the conductive polymer during aging (re-reformation) are thought to be suppressed. Furthermore, a certain degree of conductivity is ensured by the electrolyte having a conductivity of 0.05 mS / cm or higher. These factors allow for a low ESR (Energy Stress Ratio) in the re-formed electrolytic capacitor.

[0015] In this specification, the state in which leakage current has converged refers to the state in which, after performing aging treatment (re-formation) of an electrolytic capacitor for a predetermined time, the leakage current becomes less than 0.01 CV (= 0.01 × capacitance × rated voltage). The leakage current convergence rate refers to the ratio (%) of the number of electrolytic capacitors in which the leakage current has converged to the total number of electrolytic capacitors that have undergone aging treatment (re-formation) for multiple electrolytic capacitors (for example, 10). The aging treatment (re-formation) is performed, for example, by applying the rated voltage to the electrolytic capacitor at 130°C for 2 hours.

[0016] Technology (2) In Technology (1) above, the concentration of the second acid component in the electrolyte is preferably 6% by mass or more and 15% by mass or less. In this case, it is easy to adjust the conductivity of the electrolyte to the above range, and it is easy to obtain a high convergence rate of leakage current during re-formation. In addition, it is easy to obtain a low ESR of the electrolytic capacitor.

[0017] Technology (3) In Technology (1) or Technology (2) described above, the second organic solvent preferably contains at least one selected from the group consisting of polyalkylene glycol, polyglycerin, and polyalkylene oxide adducts of polyhydric alcohols. These second organic solvents make it easy to maintain the viscosity of the electrolyte within an appropriate range. Furthermore, since the second organic solvent readily acts as an oxygen source for the dielectric layer, it is advantageous in ensuring higher dielectric strength and a high leakage current convergence rate.

[0018] Technology (4) In any one of the above technologies (1) to (3), it is preferable that the first organic solvent includes at least one selected from the group consisting of sulfone-based solvents, glycol-based solvents, and lactone-based solvents. These first organic solvents make it easy to adjust the conductivity of the electrolyte to the above range, and when combined with the second organic solvent, make it easy to adjust the viscosity of the electrolyte to an appropriate range.

[0019] Technology (5) In any one of the above technologies (1) to (4), it is preferable that the second acid component includes an aromatic compound having at least one acid group selected from the group consisting of a carboxyl group and a phenolic hydroxyl group. By using such a second acid component, the pH of the electrolyte can be kept low, which suppresses dedoping and degradation of the conductive polymer and makes it easier to obtain high conductivity. As a result, the ESR of the electrolytic capacitor can be further reduced.

[0020] Technology (6) In the above technology (5), the aromatic compound comprises an aromatic carboxylic acid and a polyhydric phenol, and it is preferable that in the electrolyte, the mass ratio of the aromatic carboxylic acid to 100 parts by mass of the solute is 90 parts by mass or more and 120 parts by mass or less, and the mass ratio of the polyhydric phenol is 10 parts by mass or more and 35 parts by mass or less. In this case, a high convergence rate of leakage current during re-formation can be obtained, and the ESR of the electrolytic capacitor after re-formation can be further reduced.

[0021] Technology (7) In any one of the above technologies (1) to (6), it is preferable that the viscosity of the electrolyte at 25°C is 150 mPa·s or more and 1000 mPa·s or less. In this case, appropriate ion diffusion is easily obtained, low ESR can be ensured, and higher dielectric strength is easily obtained.

[0022] For viscosity measurement, the electrolyte used in the assembly of electrolytic capacitors may be used, or the electrolyte extracted from an early electrolytic capacitor may be used. The viscosity is measured using a vibrating viscometer for the electrolyte at 25°C.

[0023] In this specification, an "initial electrolytic capacitor" refers to an electrolytic capacitor that has not been used after assembly or aging treatment, and in the case of commercially available products, it refers to an unused electrolytic capacitor.

[0024] The electrolytic capacitor of this disclosure will be described in more detail below, including the above-mentioned technologies (1) to (7), with reference to the drawings as necessary. To the extent that it is not technically inconsistent, at least one of the above-mentioned technologies (1) to (7) may be combined with at least one of the elements described below. Note that each figure is for illustrative purposes only, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of the actual components.

[0025] The following descriptions may include examples of embodiments of the Disclosure, but the Disclosure is not limited to these examples. The following descriptions may include specific numerical values ​​and materials, but other numerical values ​​and materials may be used as long as the effects of the Disclosure are achieved. In the following descriptions, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0026] [Electrolytic Capacitor] The electrolytic capacitor of this disclosure includes a capacitor element and an electrolyte. The electrolytic capacitor comprises a case for housing the capacitor element and the electrolyte, and optionally a sealing body. The electrolytic capacitor of this disclosure has a rated voltage of 150V or more, preferably 160V or more. The rated voltage of the electrolytic capacitor may be 150V or more and 220V or less (or 210V or less), or 160V or more and 210V or less.

[0027] (Electrolyte) The electrolyte contains a solute and a solvent that dissolves the solute. The solute is a salt of an organic carboxylic acid anion as the first acid component and an organic cation as the base component. The electrolyte further contains a free second acid component. The electrolyte is prepared by dissolving the solute and the second acid component in the solvent.

[0028] In an electrolyte, the solute may be in the form of a salt, but it is usually dissociated into anions and cations. Furthermore, the anions and cations may form salts with components contained in the electrolyte or electrolytic capacitor, or they may interact or be in a complex form. All of these forms are collectively referred to as the solute, the organic carboxylic acid anion constituting the solute, or the organic cation, etc.

[0029] The free second acid component added during the preparation of the electrolyte may be converted into anions, cations, salts, etc., in the electrolyte, but at least a portion of it remains in a free state. In the electrolyte, the acid component that exists in a free state is referred to as the second acid component.

[0030] (Solute) The solute is composed of an organic carboxylic acid anion (first acid component) and an organic cation (basic component).

[0031] (First Acid Component) Examples of organic carboxylic acid anions include anions of organic carboxylic acids (aliphatic carboxylic acids, aromatic carboxylic acids, etc.). From the viewpoint of easily obtaining higher heat resistance and durability, it is preferable that the organic carboxylic acid anion contains an aromatic carboxylic acid anion. Examples of aromatic carboxylic acids corresponding to aromatic carboxylic acid anions include aromatic hydroxy acids (benzoic acid, salicylic acid, gallic acid, etc.), aromatic polycarboxylic acids (phthalic acid, pyromellitic acid, etc.), and sulfo-aromatic carboxylic acids (m-sulfobenzoic acid, 4-sulfophthalic acid, 5-sulfosalicylic acid, etc.). The content of aromatic carboxylic acid anions in the first acid component (anion) is preferably 70% by mass or more, and more preferably 85% by mass or more. The content of aromatic carboxylic acid anions in the first acid component (anion) is 100% by mass or less.

[0032] It is preferable that the organic carboxylic acid anion does not contain the borodisalicylic acid anion. This is because, if moisture is present in the electrolyte, the salicylic acid produced by the decomposition of borodisalicylic acid will accelerate the corrosion of the anodic foil (in other words, its moisture resistance will decrease). Also, from a similar viewpoint, it is preferable that the organic carboxylic acid anion does not contain the anion of the coordination compound of the organic carboxylic acid. Examples of such coordination compounds include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodigallic acid, borodicatechol, and borodipyrogallol.

[0033] (Organic cations) Examples of organic cations include at least one organic cation selected from the group consisting of organic amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds.

[0034] Organic amines may be aliphatic, aromatic, or heterocyclic. Examples of organic amines include dialkylamines (such as diethylamine), trialkylamines (such as trimethylamine, ethyldimethylamine, triethylamine, tri-n-butylamine, and dimethyl-n-octylamine), alkylenediamines (such as ethylenediamine), aromatic amines (such as aniline), and heterocyclic amines (such as pyrrolidine, imidazole compounds (such as imidazole and 1,2,3,4-tetramethylimidazolinium), pyridine, 4-dimethylaminopyridine, diazabicycloundecene, and morpholine compounds (such as morpholine and 4-methylmorpholine)). Aromatic amines and heterocyclic amines may each be monocyclic or polycyclic (such as fused rings or cross-linked rings). Examples of quaternary ammonium compounds include amidine compounds.

[0035] Organic cations are used in the preparation of the electrolyte in the form of salts with organic carboxylic acid anions as the first acid component. In the electrolyte, organic cations as basic components are present in cation form. Some organic cations may be present in the form of salts.

[0036] Since the first acid component and the base component are used in the form of a salt, the equivalent ratio of the first acid component to the base component (= first acid component / base component) may be, for example, 0.8 or more and 1.2 or less. The equivalent ratio of the first acid component to the base component is (total number of acid groups per molecule of the first acid component) / (OH that can be produced per molecule of the base component). － This is the ratio of the total number of moles.

[0037] The concentration of the solute in the electrolyte is 5% by mass or more and 12% by mass or less. This range of solute concentration ensures appropriate conductivity of the electrolyte, resulting in a high convergence rate of leakage current during re-formation. Furthermore, the combined use of the solute and a second acid component suppresses the degradation of the conductive polymer during re-formation, resulting in a low ESR. From the viewpoint of easily obtaining an even lower ESR, the concentration of the solute in the electrolyte is preferably 7% by mass or more and 12% by mass or less, and more preferably 8% by mass or more and 12% by mass or less.

[0038] (Second Acid Component) Examples of the second acid component include carboxylic acid compounds, acids other than carboxylic acids that have a carbonyloxy bond (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 a sulfonyliimide bond, boron-containing acids other than the first acid component (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).

[0039] Examples of carboxylic acid compounds include carboxylic acids (aliphatic carboxylic acids, aromatic carboxylic acids, etc.), carboxylic acid anhydrides, and coordination compounds of carboxylic acids. Examples of aromatic carboxylic acids include aromatic hydroxy acids (benzoic acid, salicylic acid, etc.), aromatic polycarboxylic acids (phthalic acid, pyromellitic acid, etc.), and sulfo-aromatic carboxylic acids (m-sulfobenzoic acid, 4-sulfophthalic acid, 5-sulfosalicylic acid, etc.).

[0040] 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.

[0041] Examples of the above-mentioned coordination compounds include coordination compounds having at least one central atom selected from the group consisting of boron, aluminum and silicon, wherein a carboxylic acid, an acid having a carbonyloxy bond, or a phenol compound is bonded to the central atom via an oxygen atom of these compounds. Specific examples of coordination compounds include borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodigallic acid, borodicatechol, and borodipyrogallol.

[0042] The electrolytic solution may contain one type of the second acid component, or may contain two or more types in combination.

[0043] The second acid component preferably contains an aromatic compound having at least one or more acid groups selected from the group consisting of a carboxy group and a phenolic hydroxy group. In the second acid component, the content of such an aromatic compound is preferably 70% by mass or more, more preferably 85% by mass or more.

[0044] The above-mentioned aromatic compound preferably contains at least one selected from the group consisting of aromatic carboxylic acids (phthalic acid, salicylic acid, gallic acid, etc.) and polyhydric phenols (pyrogallol, catechol, etc.). From the viewpoint of obtaining a high convergence rate of leakage current during re-formation and further reducing the ESR of the electrolytic capacitor after re-formation, it is preferable that the aromatic compound contains both an aromatic carboxylic acid and a polyhydric phenol.

[0045] The concentration of the second acid component in the electrolytic solution is preferably 6% by mass or more and 15% by mass or less, more preferably 8% by mass or more and 15% by mass or less. From the viewpoint that a lower ESR is likely to be obtained after re-formation, the concentration of the second acid component in the electrolytic solution is preferably 11% by mass or more and 15% by mass or less.

[0046] When the second acid component contains an aromatic carboxylic acid, in the electrolytic solution, the mass ratio of the aromatic carboxylic acid relative to 100 parts by mass of the solute is preferably not less than 90 parts by mass and not more than 120 parts by mass, and more preferably not less than 90 parts by mass and not more than 110 parts by mass. In these cases, the combination of the solute and the aromatic carboxylic acid not only makes it easy to adjust the ionic conductivity of the electrolytic solution within the above-mentioned range, but also can keep the pH of the electrolytic solution low. Therefore, a high convergence rate of leakage current during reformation can be obtained, dedoping and deterioration of the conductive polymer are suppressed, and ESR after reformation can be further reduced.

[0047] When the second acid component contains a polyhydric phenol, in the electrolytic solution, the mass ratio of the polyhydric phenol relative to 100 parts by mass of the solute is preferably not less than 10 parts by mass and not more than 35 parts by mass, and more preferably not less than 15 parts by mass and not more than 25 parts by mass. In these cases, it is easy to suppress deterioration of the conductive polymer during reformation. Therefore, ESR after reformation can be further reduced.

[0048] (Solvent) The solvent comprises a first organic solvent having a molecular weight of 200 or less, and a second organic solvent having a molecular weight higher than that of the first organic solvent. As these organic solvents, it is preferable to use at least a polar solvent. Polar solvents include aprotic polar solvents and protic polar solvents.

[0049] (First Organic Solvent) Examples of the first organic solvent include sulfone-based solvents, lactone-based solvents, carbonate-based solvents, and alcohol-based solvents. The electrolytic solution may contain one type of the first organic solvent, or may contain two or more types in combination.

[0050] Examples of aprotic polar solvents include sulfone-based solvents such as cyclic sulfones (e.g., sulfolane (SL)) and sulfoxides (e.g., dimethyl sulfoxide and diethyl sulfoxide). Examples of lactone-based solvents include γ-butyrolactone (GBL) and γ-valerolactone. Examples of carbonate-based solvents include linear carbonates (e.g., dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate) and cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, and fluoroethylene carbonate).

[0051] Protic polar solvents, specifically alcoholic solvents, include monohydric alcohols (methanol, ethanol, etc.) and polyhydric alcohols. Examples of polyhydric alcohols include glycol-based solvents (alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), diethylene glycol, triethylene glycol, etc.), glycerin-based solvents (glycerin, diglycerin, etc.), sugar alcohol-based solvents (erythritol, pentaerythritol, mannitol, etc.), or alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.).

[0052] From the viewpoint of easily adjusting the conductivity and viscosity of the electrolyte to an appropriate range, the first organic solvent preferably contains at least one selected from the group consisting of sulfone-based solvents, glycol-based solvents, and lactone-based solvents. The total ratio of these solvents in the first organic solvent is preferably 70% by mass or more and 100% by mass or less, and more preferably 85% by mass or more and 100% by mass or less. It is also preferable that the first organic solvent contains a glycol-based solvent (solvent Ia) and at least one selected from the group consisting of sulfone-based solvents and lactone-based solvents (solvent Ib).

[0053] From the viewpoint of easily adjusting the conductivity and viscosity of the electrolyte to an appropriate range, the mass ratio of the first organic solvent in the solvent is preferably 20% by mass or more and 65% by mass or less, and more preferably 22% by mass or more and 60% by mass or less. In the solvent, it is preferable that the remainder of the first organic solvent is the second organic solvent. When the first organic solvent contains solvent Ia and solvent Ib, the mass ratio of solvent Ia to solvent Ib (= solvent Ia / solvent Ib) is preferably 0.5 or more and 2 or less, and more preferably 0.8 or more and 1.2 or less.

[0054] (Second organic solvent) As the second organic solvent, an organic solvent with a molecular weight of more than 200 is preferred. Furthermore, as the second organic solvent, an organic solvent having a repeating monomer unit structure is more preferred.

[0055] The second organic solvent preferably contains at least one selected from the group consisting of polyalkylene glycol, polyglycerin, and polyalkylene oxide adducts of polyhydric alcohols (such as polyethylene oxide adducts). Examples of polyalkylene glycols include polyethylene glycol (PEG), polypropylene glycol (PG), and polyoxyethylene-polyoxypropylene copolymer (POE-POP copolymer). Examples of polyhydric alcohols include the polyhydric alcohols described for the first organic solvent (such as glycol-based solvents, glycerin-based solvents, and sugar alcohol-based solvents).

[0056] From the viewpoint of easily adjusting the conductivity and viscosity of the electrolyte to an appropriate range, the number-average molecular weight (Mn) or weight-average molecular weight (Mw) of the second organic solvent is preferably 250 or more and 4000 or less, and more preferably 300 or more and 3000 or less.

[0057] (Conductivity) In this disclosure, it is preferable that the conductivity of the electrolyte at 30°C is 0.05 mS / cm or more and 0.29 mS / cm or less. By using an electrolyte with conductivity in this range, high dielectric strength can be obtained even before re-formation, and a high convergence rate of leakage current during re-formation can be obtained. In addition, a low ESR can be obtained for the electrolytic capacitor after re-formation. From the viewpoint of further reducing ESR, it is even more preferable that the conductivity of the electrolyte at 30°C is 0.12 mS / cm or more and 0.29 mS / cm or less.

[0058] The conductivity (electrical conductivity) of the electrolyte is measured at 30°C using a commercially available conductivity meter. The electrolyte used for measuring conductivity may be the electrolyte used in the assembly of electrolytic capacitors, or the electrolyte extracted from an early electrolytic capacitor.

[0059] (Other) The viscosity of the electrolyte at 25°C is preferably 150 mPa·s to 1000 mPa·s, and more preferably 150 mPa·s to 600 mPa·s. In this case, appropriate ion diffusion is easily obtained, low ESR can be ensured, and higher dielectric strength can be easily obtained.

[0060] Since the electrolytic capacitors of this disclosure contain a conductive polymer, the pH of the electrolyte is relatively low from the viewpoint of suppressing degradation and dedoping of the conductive polymer. The pH of the electrolyte at 25°C is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. The pH of the electrolyte at 25°C may be 2 or more. For pH measurement, the electrolyte used in the assembly of the electrolytic capacitor may be used, or the electrolyte extracted from an initial electrolytic capacitor may be used.

[0061] (Capacitor element) The capacitor element includes an anode foil, a cathode foil, a separator and a conductive polymer interposed between them. A dielectric layer is formed on at least the surface of the anode foil.

[0062] (Anode foil) The anode foil contains aluminum. The anode foil may be formed of aluminum or an aluminum-containing alloy.

[0063] From the viewpoint of easily securing a higher capacity, it is preferable that the anode foil has a porous portion having pores in at least the surface layer. An anode foil having a porous portion can be obtained, for example, by roughening the surface of a substrate containing aluminum (such as a foil-like or plate-like substrate containing aluminum). Roughening may be performed by etching (for example, electrolytic etching or chemical etching).

[0064] (Dielectric layer) The dielectric layer is formed, for example, by anodizing the surface of the anode foil. 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 foil. When the dielectric layer is formed on the surface of the porous portion of the anode foil, it is formed along the inner walls of the pores in the porous portion or the depressions (pits) on the surface of the anode foil.

[0065] The dielectric layer is, for example, aluminum oxide (Al ２ O ３ This includes (etc.). However, the dielectric layer is not limited to these; any material that functions as a dielectric is acceptable.

[0066] (Cathode Foil) Examples of cathode foil include metal foil. Preferably, the metal constituting the metal foil is a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. However, the type of metal is not limited to these. The surface of the metal foil may be roughened as needed.

[0067] A chemical conversion coating may be provided on the surface of the metal foil. Alternatively, a coating of a different metal (a dissimilar metal) or a nonmetal may be provided on the surface of the metal foil. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0068] (Separator) A separator is placed between the anode foil and the cathode foil. The separator is not particularly limited, and may be a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0069] (Conductive Polymer) The conductive polymer is interposed between the anode foil and the cathode foil, each having a dielectric layer formed on its surface. The conductive polymer may also be impregnated into the separator. The conductive polymer may be in contact with at least a portion of the dielectric layer and at least a portion of the cathode foil (or the dielectric layer if one is formed on the surface of the cathode foil).

[0070] The conductive polymer may include, for example, a conjugated polymer and a dopant. The conductive polymer may form layers. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer may further contain additives as needed.

[0071] (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).

[0072] Conjugated polymers may be used individually or in combination of two or more types.

[0073] 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.

[0074] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polysaccharide-converted values ​​measured by gel permeation chromatography (GPC). Mw and Mn may also be determined by electrospray ionization mass spectrometry (ESIMS). The GPC of conjugated polymers and dopants is measured, for example, using a polyhydroxymethacrylate gel column and an aqueous sodium nitrate mobile phase.

[0075] (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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The Dopant's Mw is not particularly limited and may be between 1,000 and 1,000,000.

[0080] 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.

[0081] (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.

[0082] In a capacitor element, one end of the cathode lead is electrically connected to the cathode foil. One end of the anode lead is electrically connected to the anode foil. The other end of the anode lead and the other end of the cathode lead are drawn out from the case. The other ends of each lead exposed from the case are used for soldering to the substrate on which the electrolytic capacitor is to be mounted. Lead wires or lead frames may be used for each lead.

[0083] The case may be made of resin or metal. For example, an electrolytic capacitor can be obtained by housing a capacitor element in a case having an opening and sealing the opening with a sealing body or the like.

[0084] 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 of Figure 1 in an unfolded state. 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 (7) of the present disclosure, or arbitrarily combined with at least one of the above technologies (1) to (7) and the components described above.

[0085] An electrolytic capacitor comprises, for example, a capacitor element 10, an electrolyte (not shown), 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 the 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.

[0086] 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.

[0087] 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 are interposed between the anode foil 11 and the cathode foil 12. The conductive polymer may be impregnated into the separator 13. The capacitor element 10 is impregnated with an electrolyte.

[0088] [Examples] The electrolytic capacitors of this disclosure will be described below in detail based on examples and comparative examples, but this disclosure is not limited to the following examples.

[0089] Examples 1-8 and Comparative Examples 1-5: Wind-wound electrolytic capacitors (rated voltage 150V and rated capacitance 12μF) were fabricated and evaluated using the following procedure.

[0090] (1) Preparation of the anode foil 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 in length and 120 mm in width to prepare the anode foil.

[0091] (2) Preparation of the cathode foil An aluminum foil with a thickness of 50 μm was etched to roughen the surface of the aluminum foil. Then, a chemical conversion treatment was performed in the same manner as for the anode foil. After that, the aluminum foil was cut to a size of 8 mm in length and 120 mm in width to prepare the cathode foil.

[0092] (3) Fabrication of the winding The anode lead tabs and cathode lead tabs were connected to the anode foil and cathode foil, and the anode foil and cathode foil were wound together with a paper separator, while winding the lead tabs. The anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the winding. Then, the fabricated winding was subjected to a chemical conversion treatment to form a dielectric layer on the cut end of the anode. Next, the ends of the outer surface of the winding were fixed with winding tape to fabricate the winding.

[0093] (4) Preparation of polymer dispersion containing conductive polymer A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and the polymer dopant poly(4-styrenesulfonic acid) (PSS, Mw 100,000) in deionized water. 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.

[0094] (5) 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 conductive polymer. A capacitor element was formed in this way.

[0095] (6) Preparation of the electrolyte The electrolyte was prepared by dissolving triethylamine phthalate (solute) and the second acid component (pyrogallol and phthalic acid) in a solvent. As the solvent, a mixed solvent of the first organic solvent (EG and SL) and the second organic solvent shown in Table 1 was used. As the second organic solvent, POE-POP copolymer (Mw: 2000), PEG300 (polyethylene glycol, Mn300), or PEG2000 (polyethylene glycol, Mn2000) was used. The concentrations of each component in the electrolyte are shown in Table 1.

[0096] (7) 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 impregnate the capacitor elements with the electrolyte. The electrolyte-impregnated capacitor elements were placed in a bottomed case so that the lead wires were located 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 elements. Then, a drawing process was performed near the opening end of the bottomed case, and the opening end was further curled to make it tightly adhere to the sealing member. In this way, the capacitor elements 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. A total of 20 electrolytic capacitors were manufactured for each example.

[0097] (8) Of the electrolytic capacitors that were reprocessed, 10 were subjected to aging treatment at 130°C for 2 hours while applying the rated voltage, thereby reprocessing the anode foil.

[0098] [Evaluation] The following evaluation was conducted.

[0099] (a) Conductivity of the electrolyte The conductivity (electrical conductivity (unit: mS / cm)) of the electrolyte prepared in the example or comparative example was measured at 30°C using a commercially available conductivity meter.

[0100] (b) Withstand voltage before re-formation Ten electrolytic capacitors manufactured in the process described in (7) above were subjected to voltage application at 20°C while boosting the voltage at a rate of 1.0 V / sec, and the breakdown withstand voltage (BDV) at which an overcurrent of 0.5 A flows was measured, and the average value (unit: V) was calculated.

[0101] (c) Leakage current (LC) convergence rate during reprocessing For the 10 electrolytic capacitors obtained in the process of (8) above, the current value (leakage current value) flowing through the electrolytic capacitors was measured using a 4-terminal LCR meter in an environment of 20°C. For each electrolytic capacitor, the state in which the leakage current value was less than 0.01 CV was defined as the LC convergence state. The ratio (%) of the number of electrolytic capacitors in the LC convergence state out of the 10 electrolytic capacitors was determined, and this value was defined as the LC convergence rate.

[0102] (d) ESR after re-formation Of the 10 electrolytic capacitors obtained in step (8) above after re-formation, the ESR values ​​at a frequency of 100 kHz were measured at a 20°C environment using a four-terminal LCR meter for measurement in which the LC was in a converged state. The average value (mΩ) of the measured values ​​for these electrolytic capacitors was then determined.

[0103] The evaluation results are shown in Table 1. In Table 1, E1 to E8 are Examples 1 to 8, and C1 to C5 are Comparative Examples 1 to 5.

[0104]

[0105] As shown in Table 1, in the examples, the LC convergence rate during re-reformation was high, and the ESR of the electrolytic capacitors was kept low. Furthermore, in the examples, high withstand voltage was obtained even before re-reformation. In contrast, in Comparative Examples 1 and 5, the conductivity of the electrolyte was high, resulting in a low LC convergence rate during re-reformation. In addition, in these comparative examples, the withstand voltage before re-reformation tended to be lower compared to the examples. In Comparative Examples 2 to 4, although the LC convergence rate during re-reformation was high, the ESR of the electrolytic capacitors tended to be high even after re-reformation.

[0106] The electrolytic capacitors of this disclosure can be used as hybrid electrolytic capacitors. These electrolytic capacitors contain a conductive polymer and have a rated voltage of 150V or higher, but leakage current during re-formation is contained, resulting in a low ESR. Furthermore, these electrolytic capacitors offer high voltage withstand capability. Therefore, these electrolytic capacitors are particularly suitable for applications requiring a rated voltage of 150V or higher or high voltage withstand capability. However, the applications of electrolytic capacitors are not limited to these.

[0107] 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 electrolytic capacitor comprising a capacitor element and an electrolyte, wherein the capacitor element comprises an anode foil having a dielectric layer on its surface, a cathode foil, a separator and a conductive polymer interposed between the anode foil and the cathode foil, the electrolyte comprises a solute and a solvent for dissolving the solute, the solute is a salt of an organic carboxylic acid anion as a first acid component and an organic cation as a base component, the electrolyte further comprises a free second acid component, the solvent comprises a first organic solvent with a molecular weight of 200 or less and a second organic solvent with a molecular weight higher than the molecular weight of the first organic solvent, the concentration of the solute in the electrolyte is 5% by mass or more and 12% by mass or less, the conductivity of the electrolyte at 30°C is 0.05 mS / cm or more and 0.29 mS / cm or less, and the rated voltage is 150V or more.

2. The electrolytic capacitor according to claim 1, wherein the concentration of the second acid component in the electrolyte is 6% by mass or more and 15% by mass or less.

3. The electrolytic capacitor according to claim 1 or 2, wherein the second organic solvent comprises at least one selected from the group consisting of polyalkylene glycol, polyglycerin, and polyalkylene oxide adducts of polyhydric alcohols.

4. The electrolytic capacitor according to claim 1 or 2, wherein the first organic solvent comprises at least one selected from the group consisting of sulfone-based solvents, glycol-based solvents, and lactone-based solvents.

5. The electrolytic capacitor according to claim 1 or 2, wherein the second acid component comprises an aromatic compound having at least one acid group selected from the group consisting of a carboxyl group and a phenolic hydroxyl group.

6. The electrolytic capacitor according to claim 5, wherein the aromatic compound comprises an aromatic carboxylic acid and a polyhydric phenol, and in the electrolyte, the mass ratio of the aromatic carboxylic acid to 100 parts by mass of the solute is 90 parts by mass or more and 120 parts by mass or less, and the mass ratio of the polyhydric phenol is 10 parts by mass or more and 35 parts by mass or less.

7. The electrolytic capacitor according to claim 1 or 2, wherein the viscosity of the electrolyte at 25°C is 150 mPa·s or more and 1000 mPa·s or less.

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