Electrolytic capacitors

Abstract

An electrolytic capacitor according to the present invention includes a capacitor element and a liquid component. The capacitor element comprises an anode body having a dielectric layer on a surface thereof, and a conductive polymeric compound covering at least a portion of the dielectric layer. The liquid component includes an acid component, a base component, a solvent, and an antioxidant. The solvent includes water and a polyol compound. The acid component includes a coordination compound containing a central atom and an organic molecule having a plurality of coordinating atoms bonded to the central atom, and at least one of the plurality of coordinating atoms is an oxygen atom bonded to a carbonyl group.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor including a conductive polymer compound and a liquid component.

Background Art

[0002] An electrolytic capacitor includes a capacitor element and a liquid component (electrolyte). The capacitor element includes an anode body having a dielectric layer on its surface and a conductive polymer compound covering at least a part of the dielectric layer. The liquid component includes an acid component, a base component, and a solvent. Various studies have been conducted on the liquid component.

[0003] In Patent Document 1, it is proposed to use a composite acid compound of an organic acid and an inorganic acid, such as borodisalicylic acid, as the acid component of the liquid component. By using the composite acid compound, deterioration of the acid component due to heat is suppressed. Further, in Patent Document 2, it is proposed to include an antioxidant such as phenol in the electrolyte. The antioxidant is used for the purpose of suppressing deterioration due to oxidation of the conductive polymer compound.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the liquid component contains water, oxygen is supplied to the anode, making it easier for the liquid component to repair defects in the dielectric layer. However, when the liquid component contains both water and a complex acid compound, the water in the liquid component hydrolyzes the complex acid compound, and the resulting acid (e.g., salicylic acid) can corrode the anode, potentially increasing the equivalent series resistance (ESR). Furthermore, the corrosion of the anode can lead to insufficient repair of defects in the dielectric layer, potentially increasing leakage current. [Means for solving the problem]

[0006] One aspect of the present invention relates to 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 compound covering at least a portion of the dielectric layer, the liquid component comprising an acid component, a base component, a solvent, and an antioxidant, the solvent comprising water and a polyol compound, and the acid component comprising a coordination compound having a central atom and an organic molecule having a plurality of coordination atoms bonded to the central atom, and at least one of the plurality of coordination atoms being an oxygen atom bonded to a carbonyl group. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the increase in ESR and leakage current of electrolytic capacitors. While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, in conjunction with other objects and features of the present invention. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the configuration of the capacitor element according to the same embodiment. [Modes for carrying out the invention]

[0009] An electrolytic capacitor according to one embodiment of the present invention comprises a capacitor element and a liquid component. The capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer. The liquid component comprises an acid component, a base component, a solvent, and an antioxidant. The solvent comprises water and a polyol compound. The acid component comprises a coordination compound. The coordination compound comprises a central atom and an organic molecule having a plurality of coordination atoms bonded to the central atom. At least one of the plurality of coordination atoms is an oxygen atom bonded to a carbonyl group.

[0010] Coordination compounds have a strong bond between their central atom and the coordination atom, resulting in excellent thermal stability. Therefore, liquid components containing coordination compounds are advantageous for improving the heat resistance of electrolytic capacitors. Furthermore, if the liquid component contains water, oxygen is supplied to the anode, improving the repair function of the dielectric layer. For example, if the anode contains aluminum, the oxygen supplied to the anode can contribute to the formation of aluminum oxide at defects in the dielectric layer.

[0011] On the other hand, coordination compounds contain organic molecules that have an oxygen atom bonded to a carbonyl group as a coordination atom. These compounds can be hydrolyzed by water in the liquid component, producing acids with carboxyl groups or both carboxyl and hydroxyl groups. This decomposition acid can corrode the anode, leading to the formation of impurities (e.g., chelated aluminum) on the anode surface. This increases the interfacial resistance between the anode and the conductive polymer compound, potentially increasing the ESR. The impurities may also prevent sufficient repair of defects in the dielectric layer, potentially increasing leakage current.

[0012] In contrast, the present invention incorporates an antioxidant and a polyol compound into a liquid component containing water and a coordination compound. This suppresses corrosion of the anode body by the aforementioned decomposition acids, and reduces the increase in ESR and leakage current associated with anode body corrosion. The effect of suppressing the increase in ESR and leakage current is particularly pronounced when used at high temperatures and for extended periods.

[0013] When an antioxidant and a polyol compound are used in combination with a liquid component containing water and a coordination compound, a significant effect in suppressing the increase of ESR and other factors is obtained. The detailed reason for this is unknown, but it is speculated as follows: The COOH (carboxyl group) of the decomposition acid is converted to a CHO group (converted to an aldehyde group) by the action of the antioxidant. The decomposition acid having a carboxyl group reacts with the polyol compound having a hydroxyl group to esterify. It is speculated that the combined effects of the CHO conversion and esterification of the decomposition acid result in the significant effect described above.

[0014] The liquid components will be described in detail below.

[0015] (Liquid component) The liquid component is in direct contact with the dielectric layer or via a conductive polymer compound. The liquid component, together with the conductive polymer compound, may be present between the dielectric layer of the anode and the cathode. In the liquid component, the acidic and basic components may exist as anions and cations, respectively. Therefore, the liquid component can function as an electrolyte with high conductivity. The liquid component enhances the contact between the dielectric layer and the conductive polymer compound and also repairs defects in the dielectric layer.

[0016] (first acid component) The acid component includes a coordination compound as the first acid component. The proportion of the coordination compound in the liquid component is, for example, 0.5% by mass or more, may be 3% by mass or more, may be 0.5% by mass or more and 30% by mass or less, or may be 3% by mass or more and 30% by mass or less.

[0017] The coordination compound contains a central atom and an organic molecule. The organic molecule has a plurality of coordination atoms bonded to the central atom. Since the coordination atoms can form strong bonds, it is preferable that the central atom of the coordination compound contains at least one selected from the group consisting of boron atoms, aluminum atoms, and silicon atoms. The organic molecule may form a complex anion together with the central atom. At this time, the organic molecule may exist, for example, as an organic group in which a proton bonded to the coordination atom has been deprotonated. The number of organic molecules coordinated per one central atom may be 1 molecule or 2 or more molecules. From the viewpoint of the stability of the complex anion, an organic molecule in which 2 or more molecules (for example, 2 molecules or 3 molecules) of organic molecules are coordinated per two central atoms may be selected.

[0018] The quantitative and qualitative analysis of the complex anion can be carried out, for example, by the following method.

[0019] <Qualitative analysis> First, 30 mL of the liquid component is weighed into a glass container having a sealed lid, and the infrared absorption spectrum (IR) of the liquid component in the container is measured with a predetermined measuring device (IRSprit [manufactured by Shimadzu Corporation]). Next, the container containing the liquid component is sealed and held in a high-temperature environment for a certain period of time. Then, after allowing the liquid component in the container to cool, IR is measured again. The stability of the complex anion can be evaluated by the change in the stretching vibration spectrum of the bond between the central atom and the coordination atom. It can be said that the smaller the spectral change, the higher the stability of the complex anion.

[0020] <Quantitative analysis> First, weigh 30 mL of the liquid component into a glass container with a sealed lid, measure the nuclear magnetic resonance spectrum (NMR) of the liquid component in the container using a predetermined measuring device ([AVANCE III HD [manufactured by BRUKER]]), and determine the initial formation ratio (G0) of the complex anion from the peak intensity. Next, seal the container containing the liquid component and hold it in a high-temperature environment for a certain period of time. Then, after allowing the liquid component in the container to cool, measure the NMR again and determine the formation ratio (G1) of the complex anion and the unreacted organic molecules. The decomposition rate of the complex anion can be determined using the following formula, and the stability of the complex anion can be evaluated. It can be said that the smaller the decomposition rate, the higher the stability of the complex anion.

[0021] Formation ratio G1 (%) of complex anion = (peak intensity of complex anion) / (peak intensity of complex anion + peak intensity of unreacted organic molecules) × 100 Decomposition rate (%) of complex anion = initial formation ratio G0 (%) of complex anion - formation ratio G1 (%) of complex anion

[0022] At least one of the plurality of coordinating atoms contained in the coordination compound is an oxygen atom bonded to a carbonyl group. The plurality of coordinating atoms may include a plurality of oxygen atoms, or all of the plurality of coordinating atoms may be oxygen atoms. The plurality of coordinating atoms includes at least an oxygen atom bonded to a carbonyl group, and may further include an oxygen atom bonded to a carbon atom having no oxo group (=O).

[0023] When the coordinating atom is an oxygen atom bonded to a carbonyl group, an organic compound having a carboxy group derived from an organic molecule can be formed by hydrolysis. When the coordinating atom is an oxygen atom bonded to a carbon atom having no oxo group (=O), an organic compound having a hydroxy group derived from an organic molecule can be formed by hydrolysis.

[0024] The organic molecule preferably contains at least one selected from the group consisting of hydroxy acids and polycarboxylic acids. Examples of hydroxy acids include aliphatic hydroxy acids (glycolic acid, lactic acid, tartonic acid, α-, β- or γ-hydroxybutyric acid, malic acid, citric acid, etc.) and aromatic hydroxy acids (salicylic acid, mandelic acid, benzyl acid, etc.). Examples of polycarboxylic acids include aliphatic polycarboxylic acids (oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, etc.) and aromatic polycarboxylic acids (phthalic acid, etc.). When the organic molecule is a hydroxy acid, in the coordination compound, the central atom is bonded to at least two oxygen atoms, one oxygen atom bonded to a carbonyl group and the other oxygen atom bonded to a carbon atom that does not have an oxo group.

[0025] Furthermore, the coordination compounds may contain multiple coordination atoms, including oxygen atoms bonded to a carbonyl group and nitrogen atoms. The number of oxygen atoms and nitrogen atoms may be one or multiple. If there are multiple oxygen atoms, at least one of the oxygen atoms must be bonded to a carbonyl group. In this case, the compounds may also contain oxygen atoms bonded to carbon atoms that do not have an oxo group. Examples of organic molecules containing the above-mentioned oxygen atoms and nitrogen atoms as coordination atoms include aminocarboxylic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, hydroxyethyliminodiacetic acid, L-aspartic acid-N,N-diacetic acid, and hydroxyiminodisuccinic acid.

[0026] When the central atom is boron or aluminum, for example, a four-coordinate complex anion can be formed. Typically, this is a complex anion in which two organic molecules (e.g., hydroxy acids, dicarboxylic acids) are coordinated to the boron or aluminum atom. Also, when the central atom is silicon, for example, a five-coordinate or six-coordinate complex anion can be formed. Typically, this is a complex anion in which three organic molecules are coordinated to the silicon atom.

[0027] From the viewpoint of excellent thermal stability, it is preferable that the coordination compound includes at least one selected from the group consisting of borodisalicylic acid, borodiglycolic acid, and borodisuoic acid.

[0028] (Second acid component) The acid component may include an oxoacid other than the first acid component as a second acid component. The oxoacid of the second acid component does not contain an organic carboxylic acid. When an organic carboxylic acid (an organic molecule having a carboxyl group) and an oxoacid other than an organic carboxylic acid are produced by the hydrolysis of the coordination compound, including the second acid component together with the coordination compound in the liquid component suppresses the hydrolysis reaction of the coordination compound, which is an equilibrium reaction, and thus suppresses the production of organic carboxylic acids that corrode the anode. From the viewpoint of easily controlling the hydrolysis reaction (equilibrium reaction) of the coordination compound, it is preferable that the second acid component is the same as the oxoacid other than an organic carboxylic acid produced by the hydrolysis of the coordination compound.

[0029] The second acid component may be an inorganic acid. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, and sulfuric acid. Among these, boric acid is preferred as the second acid component. This is because the hydrolysis of the coordination compound formed by organic carboxylic acids such as salicylic acid and boric acid is easily suppressed, and corrosion of the anode by decomposing acids is easily suppressed. The above coordination compound, which has excellent thermal stability, remains undecomposed, and thermal degradation of the acid component is easily suppressed.

[0030] The molar ratio of oxoacids (second acid component) other than the coordination compound to the organic molecule (oxoacid / organic molecule) is preferably 0.05 or more and 30 or less, more preferably 0.5 or more and 30 or less. In this case, the pH of the liquid component is appropriately maintained, and the hydrolysis of the coordination compound is efficiently suppressed.

[0031] (Basic components) As the base component, an amine compound can be used. Amine compounds are advantageous for maintaining a low ESR during long-term use of electrolytic capacitors. Aliphatic amines, aromatic amines, heterocyclic amines, etc., can be used as amine compounds. Among these, aliphatic amines with molecular weights of 72 or more and 102 or less are preferred due to their high degree of dissociation.

[0032] The amine compound may include at least one selected from the group consisting of primary amine compounds, secondary amine compounds, and tertiary amine compounds. In this case, the thermal stability of the liquid component is enhanced, and the heat resistance of the electrolytic capacitor is improved. Examples of primary to tertiary amine compounds include methylamine, dimethylamine, monoethyldimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, N,N-diisopropylethylamine, tetramethylethylenediamine, hexamethylenediamine, spermidine, spermine, amantadine, aniline, phenethylamine, toluidine, pyrrolidine, piperidine, piperazine, morpholine, imidazole, imidazoline, pyridine, pyridazine, pyrimidine, pyrazine, and 4-dimethylaminopyridine. The amine compound may be used alone or in combination of two or more. Among these, tertiary amines such as triethylamine and monoethyldimethylamine are preferred.

[0033] The liquid component preferably contains more acidic components than basic components. The acidic components lower the pH of the electrolyte from the beginning, suppressing the dedoping of dopants from the conductive polymer. By containing more acidic components than basic components, the dedoping of dopants from the conductive polymer (degradation of the solid electrolyte) can be suppressed. Furthermore, since the acidic components contribute to the repair function of the dielectric layer of the liquid component, it is preferable to contain more acidic components than basic components.

[0034] From the viewpoint of suppressing the dedoping of dopants from conductive polymers, the molar ratio of the acid component to the base component (acid component / base component) is, for example, 1 or more, may be 1.1 or more, preferably 1.5 or more, and more preferably 1.5 or more and 10.0 or less.

[0035] From the viewpoint of suppressing the dedoping of dopants from conductive polymers, the pH of the liquid component may be 4.0 or less, or 0.1 or more, or 3.5 or less.

[0036] The total content of acidic and basic components in the liquid component may be, for example, 3% by mass or more and 30% by mass or 5% by mass or more and 25% by mass or less, relative to the total liquid component. In the above range, the repairability of the dielectric layer is improved, and a liquid component with good conductivity is easily obtained.

[0037] (solvent) The solvent comprises at least water and a polyol compound. The water in the liquid component may originate from the water contained in the dispersion of the conductive polymer compound used in the process of covering the surface of the dielectric layer with a film of the conductive polymer compound. Alternatively, it may originate from the water contained in each component such as the separator or metal foil, or in the polyol compound.

[0038] The water content relative to the total liquid component may be 0.1% by mass or more and 30% by mass or less, 0.1% by mass or more and 15% by mass or less, or 0.1% by mass or more and 10% by mass or less. Furthermore, the water content relative to the total liquid component may be 1% by mass or more and 15% by mass or 1% by mass or less.

[0039] When the water content is 0.1% by mass or more, the repair function of the dielectric layer of the liquid component is easily exhibited. When the water content is 1% by mass or more, the repairability of the dielectric layer of the liquid component is further improved. When the water content is 15% by mass or less, the liquid component contains an antioxidant, which easily suppresses oxidative degradation of the conductive polymer compound and thus easily suppresses the increase in ESR due to the degradation of the conductive polymer compound. When the water content is 10% by mass or less, the oxidative degradation of the conductive polymer compound described above is further suppressed.

[0040] The water content relative to the total liquid component may be 0.1% by mass or more and 5% by mass or less, 0.5% by mass or more and 5% by mass or less, or 1% by mass or more and 5% by mass or less. When the water content is 5% by mass or less, the rise in internal pressure of the electrolytic capacitor during reflow processing and the resulting deformation of the sealing portion are easily suppressed.

[0041] Furthermore, the water content relative to the total liquid component may be 5% by mass or more and 10% by mass or less. When the water content is 5% by mass or more, a large amount of decomposition acid is generated by the hydrolysis of the coordination compound, but by using antioxidants and polyol compounds, a significant effect of suppressing anode corrosion due to decomposition acid can be obtained.

[0042] The water content in the liquid component can be determined by disassembling the electrolytic capacitor, taking a sample of the liquid component, and measuring the amount of water in the sample using a Karl Fischer moisture meter.

[0043] Polyol compounds readily dissolve coordination compounds and readily esterify the decomposition acids of coordination compounds. The proportion of polyol compounds in the solvent is, for example, 5% by mass or more, and may be 50% by mass or more. All solvents other than water may be polyol compounds. Polyol compounds may be used individually or in combination of two or more. Gas chromatography-mass spectrometry (GC / MS) or the like can be used to analyze polyol compounds.

[0044] The polyol compound preferably contains a glycerin compound. When a glycerin compound is used, the conductive polymer compound swells, improving its orientation. This improves the conductivity of the conductive polymer compound and makes it easier to reduce ESR. In addition, glycerin compounds have a high boiling point, which suppresses permeation from the sealing portion of the electrolytic capacitor to the outside. Therefore, the reduction of solvent in the liquid component due to exposure of the electrolytic capacitor to high temperatures is suppressed, improving the repairability of the dielectric layer and improving the dielectric strength. Furthermore, decomposition acids having a carboxyl group are more easily esterified with glycerin compounds than phenolic antioxidants having a hydroxyl group bonded to the aromatic ring. When the solvent contains a glycerin compound, the effect of esterification of decomposition acids having a carboxyl group on phenolic antioxidants is reduced, and the function of CHO conversion of decomposition acids and the function of suppressing oxidative degradation of conductive polymer compounds in phenolic antioxidants are more easily and efficiently exhibited.

[0045] Glycerin compounds include glycerin, polyglycerin, and their derivatives. Examples of glycerin or polyglycerin derivatives include esters in which at least some of the hydroxyl groups of glycerin or polyglycerin are esterified, and alkylene oxide adducts of glycerin or polyglycerin. Examples of polyglycerin include diglycerin and triglycerin.

[0046] Polyglycerin contains a repeating structure of glycerin units. The number of repeating glycerin units in polyglycerin is, for example, 2 or more and 15 or less, may be 2 or more and 12 or less, may be 2 or more and 10 or less, or may be 2 or more and 6 or less. The weight-average molecular weight of polyglycerin is preferably, for example, 200 or more and 1000 or less, and more preferably 300 or more and 800 or less.

[0047] Furthermore, the polyol compound preferably contains a glycol compound. When a glycol compound (for example, alkylene glycol such as ethylene glycol) is used, the conductive polymer compound swells, improving the orientation of the conductive polymer compound. This improves the conductivity of the conductive polymer compound, making it easier to reduce ESR. In addition, the glycol compound does not evaporate easily, which suppresses the reduction of solvent in the liquid component when the electrolytic capacitor is exposed to high temperatures, improving the repairability of the dielectric layer and improving the dielectric strength.

[0048] Glycol compounds include alkylene glycols, polyalkylene glycols, and the like. Polyalkylene glycols may be homopolymers or copolymers (for example, copolymers containing ethylene oxide (EO) units and propylene oxide (PO) units). The weight-average molecular weight of polyalkylene glycols is, for example, 100 or more and 3000 or less, or 100 or more and 2000 or less. The weight-average molecular weight of polyethylene glycols is, for example, 100 or more and 600 or less, or 100 or more and 400 or less. Specific examples of glycol compounds include ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, triethylene glycol, and the like, with ethylene glycol being preferred. Ethylene glycol has low viscosity among glycol compounds and readily dissolves acidic and basic components containing coordination compounds. Furthermore, ethylene glycol has high thermal conductivity and excellent heat dissipation, which is advantageous for improving the heat resistance of electrolytic capacitors.

[0049] The solvent may contain components other than the polyol compound and water. Examples of such components include sulfone compounds, sulfoxide compounds, lactone compounds, and carbonate compounds.

[0050] Examples of sulfone compounds include dimethyl sulfone, diethyl sulfone, sulfolane, and 3-methylsulfolane. Examples of sulfoxide compounds include dimethyl sulfoxide and diethyl sulfoxide. Examples of lactone compounds include γ-butyrolactone and γ-valerolactone. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Other components besides the polyol compounds may be used individually or in combination of two or more.

[0051] From the viewpoint of the dissociability of acidic and basic components, ionic conductivity, and heat resistance, other components other than organic compounds having hydroxyl groups are preferably γ-butyrolactone and sulfolane.

[0052] (Antioxidant) The antioxidant may include at least one selected from the group consisting of phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, and aliphatic antioxidants. Among these, phenolic antioxidants are preferred from the viewpoint of reactivity with oxygen.

[0053] The phenolic antioxidant preferably includes at least one selected from the group consisting of monophenolic antioxidants, bisphenolic antioxidants, and polyphenolic antioxidants. Among these, polyphenols are preferred from the viewpoint of having many functional groups that react well with oxygen.

[0054] The monophenol antioxidants preferably include 2,6-di-tert-butyl-4-methylphenol, butylhydroxyanisole, sesamol, tocopherol, tocotrienol, p-nitrophenol, etc. The monophenol antioxidants may also include mono, di, or tri(α-methylbenzyl)phenol, trolox, normelatonin, ferulic acid, etc.

[0055] The material may also contain a bisphenol-based antioxidant, preferably an anoxomer. Furthermore, it may contain other bisphenol-based antioxidants such as 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-ethyl-6-tert-butylphenol), 4,4'-thiobis(3-ethyl-6-tert-butylphenol), or the butylation reaction product of p-cresol and dicyclopentadiene.

[0056] The polyphenol antioxidants preferably include 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, gallic acid, propyl gallate, chlorogenic acid, catechin, epigallocatechin, epigallocatechin gallate, rosmarinic acid, genkwanin, luteolin, carnosic acid, carnosol, ursolic acid, pyrogallol, kebradic acid, hydroxytyrosol, dopamine, caffeic acid, adrenaline, noradrenaline, catechol, ushiol, hydroquinone, resorcinol, etc.

[0057] Furthermore, the polyphenol antioxidants may include protocatechuic acid, rutin, gnetin C, theaflavin, luteolin, resveratrol, pinosembrin, pinobanksin, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4,4',4”-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), etc.

[0058] Amine-based antioxidants include aromatic secondary amine antioxidants, benzotriazole antioxidants, benzimidazole antioxidants, amine-ketone antioxidants, and the like.

[0059] Aromatic secondary amine antioxidants include N-phenyl-1-naphthylamine, diphenylamine antioxidants, and phenylenediamine antioxidants. Diphenylamine antioxidants include alkylated diphenylamines such as p,p'-dioctyldiphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and p-(p-toluenesulfonylamide)diphenylamine. Phenylenediamine antioxidants include N,N'-di-2-naphthyl-p-phenylenediamine, N-phenyl-N'-isopyropyr-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, and N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine.

[0060] Benzotriazole antioxidants include benzotriazole, etc. Benzimidazole antioxidants include benzimidazole, 2-mercapto-benzoimidazole, 2-mercaptomethyl-benzoimidazole, imidazole dipeptide, etc. Amine-ketone antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, a reaction product of diphenylamine and acetone, acetylcysteine, melatonin, and the like.

[0061] Phosphorus-based antioxidants include phosphate ester antioxidants and phosphite ester antioxidants. Examples of esters include monoalkyl esters, dialkyl esters, and trialkyl esters. Examples of phosphite ester antioxidants include tris(nonylphenyl) phosphite.

[0062] Sulfur-based antioxidants include thioether-based antioxidants, isothiocyanates, sulfites, pyrosulfites, etc. Thioether-based antioxidants include phenothiazines, dibenzyl disulfide, diacetyl sulfide, dilauryl thiodipropionate, etc.

[0063] Aliphatic antioxidants include citric acid, L-ascorbic acid, erythorbic acid, ethylenediaminetetraacetic acid, and others.

[0064] The antioxidant may be used alone or in combination of two or more types. The antioxidant content in the liquid component is, for example, 0.5% by mass or more and 30% by mass or less of the total liquid component. Liquid chromatography (LC), gas chromatography-mass spectrometry (GC / MS), etc., can be used for the analysis of the antioxidant.

[0065] In the liquid component, the molar ratio of antioxidant to organic molecules in the coordination compound (antioxidant / organic molecule) may be 0.05 or more and 30 or less, or 0.5 or more and 30 or less. In this case, the CHO conversion of the decomposition acid derived from the organic molecule by the antioxidant is more efficiently carried out.

[0066] (Capacitor element) The capacitor element includes at least an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer. The following provides a detailed explanation of capacitor elements.

[0067] (Anode) The anode body may include valve metals, alloys containing valve metals, and compounds containing valve metals. These materials can be used individually or in combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used. An anode body with a porous surface can be obtained, for example, by roughening the surface of a substrate containing a valve metal (such as a foil or plate-shaped substrate) by etching. Alternatively, the anode body may be a molded body of particles containing a valve metal or a sintered body thereof. The sintered body has a porous structure.

[0068] (Dielectric layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body through chemical conversion treatment or the like. The dielectric layer only needs to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Because the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner walls of holes and depressions (pits) on the surface of the anode body.

[0069] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these; any material that functions as a dielectric is acceptable. If the surface of the anode is porous, the dielectric layer is formed along the surface of the anode (including the inner walls of the pores).

[0070] (Conductive polymer compound) Examples of conductive polymer compounds include π-conjugated polymer compounds. Examples of conductive polymer compounds include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene. These may be used individually, in combination of two or more, or as copolymers of two or more monomers. The weight-average molecular weight of the conductive polymer compound is, for example, 1,000 to 1,000,000.

[0071] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, polyaniline, etc., as their basic skeletons. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0072] Conductive polymer compounds can be doped with dopants. The dopants may be polyanions. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually or in combination of two or more. Furthermore, these may be polymers of a single monomer or copolymers of two or more monomers. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0073] At least a portion of the surface of the dielectric layer is covered with a conductive polymer layer (solid electrolyte layer). The conductive polymer layer may contain a dopant along with the conductive polymer compound. In an electrolytic capacitor, the conductive polymer layer, together with the cathode body, constitutes part of the cathode. The conductive polymer layer may further contain additives as needed.

[0074] The conductive polymer layer can be formed, for example, by chemical polymerization and / or electrolytic polymerization of raw material monomers on the dielectric layer. Alternatively, it can be formed by bringing a solution in which a conductive polymer compound is dissolved, or a dispersion in which a conductive polymer compound is dispersed, into contact with the dielectric layer. The conductive polymer layer only needs to be formed so as to cover at least a portion of the dielectric layer.

[0075] (Cathole body) By including a polyol compound and an antioxidant in the liquid component containing the coordination compound and water, the CHO conversion and esterification of the decomposition acids produced by the hydrolysis of the coordination compound are promoted, thereby suppressing the corrosion of the cathode body by the decomposition acids. As the corrosion of the cathode body progresses and impurities are formed on the surface of the cathode body, the interfacial resistance between the cathode body and the conductive polymer compound increases, and the ESR increases.

[0076] A metal foil may be used as the cathode. The type of metal is not particularly limited, but it is preferable to use a valve metal or an alloy containing a valve metal such as aluminum, tantalum, or niobium. The surface of the metal foil may be roughened as needed. A chemical conversion coating may be provided on the surface of the metal foil, and a coating of a different metal (dissimilar metal) or a nonmetal may be provided. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon.

[0077] (Separator) When a metal foil is used as the cathode, a separator may be placed between the metal foil and the anode. The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamides, aromatic polyamides such as aramids) may be used.

[0078] (others) An electrolytic capacitor only needs to have at least one capacitor element, but it may also have multiple capacitor elements. The number of capacitor elements included in an electrolytic capacitor should be determined according to its application.

[0079] The present invention will be described more specifically below based on embodiments. However, the present invention is not limited to the following embodiments.

[0080] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to this embodiment, and Figure 2 is a schematic diagram showing a portion of the capacitor elements related to the electrolytic capacitor unfolded.

[0081] The electrolytic capacitor shown in Figure 1 comprises a capacitor element 10, a liquid component (not shown), a bottomed case 11 housing the capacitor element 10 and the liquid component, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, and lead tabs 15A and 15B connecting the lead wires to the electrodes of the capacitor element 10. The open end of the bottomed case 11 is curled so as to be crimped to the sealing member 12.

[0082] The capacitor element 10 is manufactured from a wound body as shown in Figure 2. The wound body is a semi-finished product of the capacitor element 10, and it is characterized by the absence of a conductive polymer compound between the anode 21, which has a dielectric layer on its surface, and the cathode 22. The wound body is made by winding the anode 21, which is connected to a lead tab 15A, and the cathode 22, which is connected to a lead tab 15B, with a separator 23 in between. The outermost circumference of the wound body is fixed with a winding stopper tape 24. Note that Figure 2 shows a partially unfolded state of the wound body before the outermost circumference is fixed.

[0083] The anode body 21 comprises a metal foil with a roughened surface, and a dielectric layer is formed on the roughened surface. A capacitor element 10 is formed by attaching a conductive polymer compound to at least a portion of the surface of the dielectric layer.

[0084] The following describes an example of a manufacturing method for electrolytic capacitors. (Step of preparing an anode 21 and a cathode 22 having a dielectric layer) The anode 21 and cathode 22 are made from metal foil containing a valve metal. In the case of the anode 21, the surface of the metal foil is roughened by etching or the like, creating multiple irregularities on the surface of the metal foil. Next, a dielectric layer is formed on the roughened surface of the metal foil by chemical conversion treatment or the like. The surface of the cathode 22 may also be roughened as needed.

[0085] (Process for creating a coiled body) The anode 21 and cathode 22 are wound together via a separator 23 to form a wound body. At this time, lead tabs 15A and 15B may be wound along with the winding, and the lead tabs 15A and 15B may be raised from the wound body as shown in Figure 2. A winding stopper tape 24 is placed on the outer surface of the cathode 22, which is located in the outermost layer of the wound body, to fix the end of the cathode 22. When a large sheet of metal foil cut into pieces is used as the anode 21, the wound body may be further treated with a chemical conversion process to form a dielectric layer on the cut surface of the anode 21.

[0086] (Process for forming capacitor elements) For example, a dispersion of a conductive polymer compound is impregnated into a dielectric layer to form a film of the conductive polymer compound that covers at least a portion of the dielectric layer. This yields a capacitor element 10 in which the conductive polymer compound is positioned between the anode 21 and the cathode 22. The step of applying the dispersion of the conductive polymer compound to the surface of the dielectric layer may be repeated two or more times. After that, the capacitor element 10 can be impregnated with a liquid component. This yields an electrolytic capacitor comprising a conductive polymer compound and a liquid component. By impregnating the capacitor element 10 with a liquid component, an electrolytic capacitor with excellent dielectric layer repair function can be obtained.

[0087] (Process of sealing capacitor elements) The capacitor element 10 is housed in the bottomed case 11 along with its liquid component, such that the lead wires 14A and 14B are positioned on the opening side of the bottomed case 11. The material of the bottomed case 11 can be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy containing these materials. Next, the opening of the bottomed case 11 is closed with a sealing member 12 through which the lead wires 14A and 14B pass, the opening ends are crimped to the sealing member 12 and curled, and a base plate 13 is placed on the curled portion to obtain an electrolytic capacitor as shown in Figure 1. After that, an aging process may be performed while applying the rated voltage.

[0088] Although the above embodiments described wound electrolytic capacitors, the scope of application of the present invention is not limited to those described above. It can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode, and multilayer electrolytic capacitors that use a metal plate as the anode.

[0089] [Examples] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0090] Examples 1-14, Comparative Examples 1-11 A wound electrolytic capacitor (10mm diameter x 10mm length) with a rated voltage of 25V and a rated capacitance of 330μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0091] (Preparation of the anode) A 100 μm thick aluminum foil was etched to roughen its surface. Subsequently, a dielectric layer was formed on the surface of the aluminum foil by a chemical conversion treatment. This treatment involved immersing the aluminum foil in an ammonium adipate solution and applying a voltage of 45 V. Afterward, the aluminum foil was cut to prepare the anode.

[0092] (Preparation of the cathode) A 50 μm thick aluminum foil was etched to roughen its surface. Then, the aluminum foil was cut to prepare the cathode.

[0093] (Preparation of coiled bodies) 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 separators, incorporating the lead tabs. Next, the ends of the outer surface of the wound body were secured with winding tape to create the wound body. Anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the wound body. The fabricated wound body was subjected to another chemical conversion treatment to form a dielectric layer on the cut ends of the anode bodies.

[0094] (Preparation of polymer dispersions) A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000), a high molecular weight dopant, in deionized water. While stirring the mixed solution, iron(III) sulfate (oxidizing agent) dissolved in deionized water was added. A polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymer dispersion containing polyethylene dioxythiophene (PEDOT / PSS) doped with approximately 5% by mass of PSS.

[0095] (Formation of conductive polymer layer) A coiled body was immersed in a polymer dispersion contained in a designated container for 5 minutes in a reduced-pressure atmosphere (40 kPa), and then the coiled body was removed from the polymer dispersion. Next, the coiled body impregnated with the polymer dispersion was dried in a drying oven at 150°C for 20 minutes to form a conductive polymer layer that covers at least a portion of the dielectric layer. A capacitor element was thus formed.

[0096] (Preparation of liquid components) Liquid components shown in Tables 1 and 2 were prepared by adding an acid component, a base component, and an antioxidant to a solvent containing an organic solvent and water and mixing. The water content of the liquid component relative to the total liquid component was as shown in Tables 1 and 2. Ethylene glycol (EG), glycerin (GLY), or γ-butyrolactone (GBL) was used as the organic solvent. The acid component was either a first acid component or a first and second acid component. Borosalicylic acid (BS) or phthalic acid (FS) was used as the first acid component. Boric acid was used as the second acid component. Ethyldimethylamine was used as the base component. 12% by mass of the salt formed by the above acid and base components was added to the liquid component. The molar ratio of the first acid component to the base component was 1.0. Pyrogallol was used as the antioxidant. The antioxidant content in the liquid component was 6% by mass relative to the total liquid component. In Comparative Examples 1-3, 6, 9, and 11, the liquid component did not contain an antioxidant. In Examples 9-13 and Comparative Examples 1, 3-4, and 6-7, the liquid component did not contain a second acid component.

[0097] (Assembly of electrolytic capacitors) The above-mentioned wound body, which had a conductive polymer layer formed on it, was immersed in the liquid component in a reduced-pressure atmosphere (40 kPa) for 5 minutes. This resulted in obtaining a capacitor element impregnated with the liquid component. The obtained capacitor element was sealed to complete an electrolytic capacitor as shown in Figure 1. Subsequently, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage.

[0098] The following evaluations were performed using the electrolytic capacitors of Examples 1 to 14 and Comparative Examples 1 to 11.

[0099] [Evaluation: Measurement of ESR and leakage current] Under 20°C conditions, the ESR (initial ESR (Z0)) of an electrolytic capacitor at a frequency of 100kHz was measured using a 4-terminal LCR meter. Additionally, under 20°C conditions, the leakage current (initial leakage current L0) was measured after applying the rated voltage to the electrolytic capacitor and elapsed for 2 minutes.

[0100] Next, the electrolytic capacitors were stored for 2000 hours at 145°C. After storage, the ESR (Z1) and leakage current (L1) were measured at 20°C using the same procedure as described above.

[0101] The evaluation results are shown in Tables 1 and 2.

[0102] [Table 1]

[0103] [Table 2]

[0104] In the electrolytic capacitors of Examples 1 to 14, ESR and leakage current were low both initially and after storage, and the increase in ESR and leakage current during storage was suppressed. In Examples 1 to 8, in which boric acid was further added as a second acid component to the liquid component, the ESR and leakage current after storage were further reduced.

[0105] In the electrolytic capacitors of Examples 5-7, the water content was high, ranging from 5% to 10% by mass, resulting in significant decomposition acid generation. However, the ESR and leakage current after storage were sufficiently reduced. Thus, by including antioxidants and polyol compounds in the liquid component, a remarkable effect in suppressing corrosion of the anode and cathode due to decomposition acid was obtained. In Example 14, the electrolytic capacitor using GLY exhibited lower ESR and leakage current after storage compared to the electrolytic capacitor using EG in Example 3.

[0106] In the electrolytic capacitors of Comparative Examples 1-3, 6, 9, and 11, the conductive polymer deteriorated during storage because the liquid component did not contain an antioxidant. In the electrolytic capacitors of Comparative Examples 1-3, 6, 9, and 11, the anode and cathode deteriorated due to decomposition acids. Therefore, the ESR increased after storage in the electrolytic capacitors of Comparative Examples 1-3, 6, 9, and 11.

[0107] In the electrolytic capacitors of Comparative Examples 6-10, GBL was used as the solvent, and the esterification of the decomposition acid (salicylic acid) of BS did not proceed. As a result, the anode and cathode deteriorated due to the decomposition acid, and the ESR and leakage current increased after storage. In the electrolytic capacitors of Comparative Examples 3-5, since BS was not used as the acid component, the acid component deteriorated due to heat during storage of the electrolytic capacitors, resulting in increased ESR and leakage current after storage. [Industrial applicability]

[0108] The electrolytic capacitor according to the present invention has low ESR and leakage current, and is suitable for use in applications where high reliability is required. 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. [Explanation of symbols]

[0109] 10: Capacitor element, 11: Bottomed case, 12: Sealing material, 13: Base plate, 14A, 14B: Lead wires, 15A, 15B: Lead tabs, 21: Anode, 22: Cathode, 23: Separator, 24: Winding tape

Claims

1. It includes a capacitor element and a liquid component, The capacitor element comprises an anode having a dielectric layer on its surface, and a conductive polymer compound covering at least a portion of the dielectric layer. The aforementioned liquid component comprises an acid component, a basic component, a solvent, and an antioxidant. The solvent comprises water and a polyol compound. The water content relative to the total liquid component is 5% by mass or more and 10% by mass or less. The aforementioned acid component includes a coordination compound. The coordination compound comprises a boron atom and an organic molecule that coordinates to the boron atom. The coordination compound comprises at least one selected from the group consisting of borodisalicylic acid, borodiglycolic acid, and borodisuoic acid. The aforementioned antioxidant is an electrolytic capacitor containing a polyphenol-based antioxidant.

2. The electrolytic capacitor according to claim 1, wherein in the liquid component, the molar ratio of the antioxidant to the organic molecules: antioxidant / organic molecules is 0.05 or more and 30 or less.

3. The electrolytic capacitor according to claim 1 or 2, wherein the acid component includes an oxoacid other than the coordination compound.

4. The electrolytic capacitor according to claim 3, wherein the oxoacid includes boric acid.

5. The electrolytic capacitor according to claim 3 or 4, wherein the molar ratio of the oxo acid to the organic molecule, i.e., oxo acid / organic molecule, is 0.05 or more and 30 or less.

6. The electrolytic capacitor according to any one of claims 1 to 5, wherein the polyol compound comprises a glycerin compound.

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