Electrolytic capacitor

Abstract

This electrolytic capacitor comprises a capacitor element and a liquid component. The capacitor element comprises an anode body having a chemical conversion coating, and a solid electrolyte in contact with the chemical conversion coating. The ratio V / Vw of a chemical conversion voltage of V volts applied to the anode body to form the chemical conversion coating and a rated voltage of Vw volts of the electrolytic capacitor is 1.80 or less. The liquid component includes a solvent with a melting point and a freezing point of 60°C or less and an acid component. The solvent includes a first solvent having a hydroxy group. The acid component includes a carboxylic acid compound. The number of moles of the hydroxy group per 100 g of the solvent is greater than 0.10 moles but not greater than 1.00 mole.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Hybrid electrolytic capacitors, which contain a solid electrolyte and an electrolytic solution, are considered promising as small, high-capacity capacitors with low equivalent series resistance (ESR). The electrolytic solution may be a solution in which a solute or an acid component is dissolved in a non-aqueous solvent, or a liquid component such as a non-aqueous solvent.

[0003] Patent Document 1 proposes an electrolytic capacitor including a capacitor element and an electrolyte solution, wherein the capacitor element includes an anode body having a chemical conversion coating, and a solid electrolyte in contact with the chemical conversion coating, the electrolyte solution including a solvent, a polymer component, and a solute, the solvent including at least one selected from the group consisting of lactone compounds, glycol compounds, and sulfone compounds, the concentration of the polymer component in the electrolyte solution being 15% by mass or less, the solute including at least one benzenedicarboxylic acid and its derivatives as a first acid component, and at least one amine and amidine as a base component, the concentration of the solute in the electrolyte solution being 15% by mass or more and 40% by mass or less, and the ratio V / Vw of a chemical conversion voltage V applied to the anode body to form the chemical conversion coating to a rated voltage Vw of the electrolytic capacitor being 1.7 or less.

[0004] International Publication No. 2019 / 065951

[0005] When the V / Vw ratio is equal to or less than a predetermined value (1.7 or less in Patent Document 1), as in Patent Document 1, it is expected that a higher initial capacity will be obtained compared to when the V / Vw ratio is higher. Furthermore, by using a liquid component having a composition as in Patent Document 1, it is believed that when the V / Vw ratio is equal to or less than a predetermined value, fluctuations in ESR will be suppressed compared to when the V / Vw ratio is higher. However, when the V / Vw ratio is equal to or less than a predetermined value, performing a long-term reliability test in a high-temperature environment (e.g., at a temperature of 100°C or higher) can result in a significant increase in ESR.

[0006] One aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element and a liquid component, wherein the capacitor element includes an anode body having a chemical conversion coating, and a solid electrolyte in contact with the chemical conversion coating, wherein a ratio of a chemical conversion voltage V (volts) applied to the anode body to form the chemical conversion coating to a rated voltage V (volts) of the electrolytic capacitor is 1.80 or less, the liquid component includes a solvent having a melting point and a freezing point of 60°C or less, and an acid component, the solvent includes a first solvent having a hydroxy group, the acid component includes a carboxylic acid compound, and the number of moles of the hydroxy group per 100 g of the solvent is greater than 0.10 and equal to or less than 1.00 moles.

[0007] According to the present disclosure, when the V / Vw ratio is equal to or less than a predetermined value and the electrolytic capacitor is exposed to a high-temperature environment (for example, a temperature of 100° C. or higher and 200° C. or lower) for a long period of time, fluctuations in ESR can be suppressed.

[0008] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure; 2 is a schematic view of a portion of a capacitor element of the electrolytic capacitor of FIG. 1 developed; 3 is a graph of Δcap in Examples, Comparative Examples, and Reference Examples; 4 is a graph of ΔESR in Examples, Comparative Examples, and Reference Examples;

[0009] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] As the V / Vw ratio decreases, the thickness of the conversion coating tends to decrease. Therefore, it is expected that a high capacitance can be obtained in an electrolytic capacitor. However, in an electrolytic capacitor with a solid electrolyte, since the conversion coating and the solid electrolyte are in contact with each other, as the thickness of the conversion coating decreases, leakage current becomes more likely to occur. Therefore, in electrolytic capacitors with a solid electrolyte, the V / Vw ratio is generally set to a relatively large value (e.g., a value greater than 1.80) to form a conversion coating of a certain thickness and suppress leakage current.

[0011] Patent Document 1 teaches that even when the V / Vw ratio is equal to or less than a predetermined value, the rate of change in capacitance and ESR during long-term use of an electrolytic capacitor can be kept relatively small. The evaluation of each rate of change in Patent Document 1 is based on the rate of change in capacitance and ESR after 2,500 hours of aging at 90°C while applying a rated voltage, compared to the initial capacitance and ESR. However, when the V / Vw ratio is equal to or less than a predetermined value, the ESR of the electrolytic capacitor may increase significantly if a long-term reliability test is performed in a high-temperature environment (e.g., a temperature of 100°C to 200°C).

[0012] Technique (1) In view of the above, an electrolytic capacitor according to one aspect of the present disclosure includes a capacitor element and a liquid component. The capacitor element includes an anode body having a chemical conversion coating, and a solid electrolyte in contact with the chemical conversion coating. The ratio of a chemical conversion voltage (V volts) applied to the anode body to form the chemical conversion coating to a rated voltage (Vw volts) of the electrolytic capacitor (V / Vw) is 1.80 or less. The liquid component includes a solvent having a melting point and a freezing point of 60°C or less, and an acid component. The solvent includes a first solvent having a hydroxy group. The acid component includes a carboxylic acid compound. The number of moles of the hydroxy group per 100 g of the solvent is greater than 0.10 and less than or equal to 1.00 moles.

[0013] When V / Vw>1.80, a relatively thick chemical conversion coating is formed, suppressing leakage current and preventing localized large currents from flowing through the solid electrolyte. This suppresses degradation of the solid electrolyte, thereby suppressing fluctuations in ESR and making it easier to maintain high capacitance, even when the electrolytic capacitor is exposed to high-temperature environments (e.g., temperatures between 100°C and 200°C) for extended periods. In contrast, when V / Vw≦1.80, the chemical conversion coating is thinner than when V / Vw>1.80, making it more difficult to suppress leakage current. Localized large currents flowing through the solid electrolyte due to leakage current accelerate degradation of the solid electrolyte. Solid electrolyte degradation is particularly pronounced in high-temperature environments. Therefore, when an electrolytic capacitor is exposed to high-temperature environments for extended periods, the solid electrolyte deteriorates, resulting in a decrease in conductivity and an increase in ESR. Furthermore, the occurrence of leakage current and degradation of the solid electrolyte reduce the initial capacitance, and prolonged exposure of the electrolytic capacitor to high-temperature environments can easily further reduce the capacitance. As described above, the fluctuation in ESR and the decrease in capacitance when an electrolytic capacitor is exposed to a high-temperature environment are almost no problem when V / Vw>1.80, but can become significant when V / Vw≦1.80.

[0014] When an electrolytic capacitor uses a liquid component containing a solvent (first solvent) having hydroxy groups, the first solvent tends to enhance the repairability of the chemical conversion coating and reduce leakage current. However, when the liquid component contains a carboxylic acid compound in addition to the first solvent, an esterification reaction between the carboxylic acid compound and the first solvent is likely to proceed, increasing the pH of the liquid component, causing the dopant contained in the solid electrolyte to be eliminated and reducing the conductivity of the solid electrolyte. In contrast, in the electrolytic capacitor according to the above aspect of the present disclosure, the number of moles of hydroxy groups in the first solvent per 100 g of solvent in the liquid component is greater than 0.10 and not more than 1.00 moles. This range of moles of hydroxy groups ensures the film repair effect of the first solvent and the film repair effect of the moisture appropriately generated by the esterification reaction between the first solvent and the carboxylic acid compound, even though V / Vw≦1.80 is satisfied, thereby suppressing leakage current. Furthermore, by suppressing the progress of the esterification reaction to some extent, the low pH of the liquid component is maintained, and the high conductivity of the solid electrolyte is maintained. Therefore, fluctuations in ESR when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be suppressed. In addition, a decrease in capacitance can also be suppressed.

[0015] When the number of moles of the hydroxyl group is 0.10 moles or less, the first solvent has a low film repair effect, and the amount of water generated by the esterification of the first solvent with the carboxylic acid compound is small, so the film repair effect of this water is also small. Therefore, when V / Vw≦1.80, leakage current tends to be significant. In particular, when a large current flows through the solid electrolyte in the initial stage, the solid electrolyte becomes locally insulated, reducing its conductivity and therefore reducing the initial capacitance.

[0016] When V / Vw≦1.80, if the number of moles of hydroxy groups exceeds 1.00, the esterification reaction between the first solvent and the carboxylic acid compound is likely to proceed, resulting in an increase in the pH of the liquid component and accelerated degradation of the solid electrolyte. When an electrolytic capacitor is exposed to a high-temperature environment for a long period of time, the degradation of the solid electrolyte becomes significant, resulting in significant fluctuations in ESR and a significant decrease in capacitance. Note that when V / Vw>1.80, even if the number of moles of hydroxy groups exceeds 1.00, the ESR remains relatively low, eliminating the problem of increased ESR. This is thought to be because, when V / Vw>1.80, leakage current is suppressed, which tends to suppress solid electrolyte degradation, and the pH of the liquid component has a greater effect on the solid electrolyte than the leakage current. When V / Vw>1.80 and the number of moles of hydroxy groups exceeds 1.00, the low pH of the liquid component is thought to maintain high conductivity of the solid electrolyte.

[0017] In this specification, the solvent contained in the liquid component is a solvent whose melting point and freezing point are 60° C. or lower. The melting point and freezing point of the first solvent included in the category of solvent are also 60° C. or lower.

[0018] The first solvent having a hydroxy group is an organic solvent and is classified as a protic organic solvent. In the first solvent, the hydroxy group is bonded to an organic group.

[0019] The chemical conversion coating is not limited to a coating formed by a method (hereinafter referred to as the first method) in which a predetermined chemical conversion voltage is applied to an anode body while the anode body is immersed in an acidic aqueous solution (hereinafter referred to as the chemical conversion solution). For example, the chemical conversion coating may be formed by heat treating the anode body while the anode body is immersed in the chemical conversion solution (hereinafter referred to as the second method). When a chemical conversion coating is formed by the first method, a chemical conversion coating having a thickness T corresponding to the chemical conversion voltage is formed. In other words, the chemical conversion voltage can be calculated from the thickness T of the chemical conversion coating. Even when a chemical conversion coating is formed by the second method, the chemical conversion voltage required to form the chemical conversion coating by the first method can be calculated from the thickness T. In other words, the chemical conversion voltage V includes the voltage applied to the anode body to form a chemical conversion coating with thickness T and the voltage required to form a chemical conversion coating with thickness T. Furthermore, because a chemical conversion coating grows by 1.3 nm per 1 V, the chemical conversion voltage can be estimated by dividing the thickness (nm) of the chemical conversion coating on the product by 1.3 nm.

[0020] The rated voltage Vw is the upper limit voltage determined as a rating, and is the maximum value of the voltage that can be applied between the electrodes of the electrolytic capacitor.

[0021] Technique (2) In the technique (1), the liquid component may contain 0.1% by mass or more and 6.0% by mass or less of water. By ensuring that the water content in the liquid component is within this range, the chemical conversion coating can be more resilient and the liquid component can more easily maintain a low pH to a certain extent. Therefore, even if V / Vw≦1.80, fluctuations in ESR can be suppressed when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time. Furthermore, leakage current can be reduced.

[0022] The water concentration in the liquid component can be measured using a Karl Fischer moisture content analyzer using a liquid component sampled from an electrolytic capacitor. The liquid component is preferably sampled from an initial electrolytic capacitor. The initial electrolytic capacitor is an electrolytic capacitor after aging or break-in charging and discharging, or an unused electrolytic capacitor if it is a commercially available product.

[0023] Technique (3) In the technique (1) or technique (2), the first solvent may contain a polyol compound. This provides a higher film repair effect and enhances the effect of suppressing leakage current. This ensures a higher initial capacitance.

[0024] Technique (4) In the technique (3), the polyol compound may contain polyethylene glycol (PEG). The weight-average molecular weight (Mw) of the PEG may be 150 or more and 2000 or less. Using a PEG with such an Mw makes it easy to adjust the number of moles of hydroxyl groups within the above range while maintaining a high film repair effect. Because esterification between the carboxylic acid compound and the first solvent is easily suppressed, fluctuations in ESR and reductions in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be further suppressed. Furthermore, because the viscosity of the liquid component can be easily maintained relatively low, dissociation of the acid component and the base component can be enhanced.

[0025] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0026] Technique (5) In any one of the techniques (1) to (4), the first solvent may contain a first ether compound having the hydroxy group. The first ether compound may also be included in the polyol compound. When the first solvent contains the first ether compound, a higher film repair effect is achieved, enhancing the effect of suppressing leakage current. This ensures a higher initial capacitance. Furthermore, when the first ether compound is used, it is easy to adjust the number of moles of hydroxy groups within the above range. Because esterification between the carboxylic acid compound and the first solvent is easily suppressed, fluctuations in ESR and reductions in capacitance can be further suppressed when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0027] Technique (6) In any one of the techniques (1) to (5), the solvent may include a second solvent. The second solvent may include a second ether compound that does not have a hydroxy group. In this case, dehydration reactions such as esterification reactions are suppressed, and excess water is not generated in the liquid component, thereby stabilizing the characteristics of the electrolytic capacitor.

[0028] Technique (7) In any one of Techniques (1) to (6), the content of the first solvent in the solvent may be 30% by mass or more. By keeping the content of the first solvent within this range, a higher film repair effect can be achieved and leakage current can be suppressed, even though V / Vw≦1.80 is satisfied. Furthermore, by suppressing the progress of the esterification reaction to some extent, the low pH of the liquid component is maintained, and high conductivity of the solid electrolyte is maintained. Therefore, fluctuations in ESR and reductions in capacitance can be further suppressed when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0029] Technique (8) In any one of the techniques (1) to (7), the carboxylic acid compound may include at least one selected from the group consisting of aromatic carboxylic acids and aliphatic carboxylic acids. Such carboxylic acid compounds initially result in a low pH of the liquid component, but the esterification reaction proceeds relatively easily. However, in the present disclosure, the number of moles of hydroxy groups per 100 g of solvent is within a specific range, thereby suppressing the progression of esterification and maintaining a low pH of the liquid component, thereby ensuring high conductivity of the solid electrolyte. Therefore, fluctuations in ESR and reductions in capacitance can be further suppressed when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0030] The electrolytic capacitor of the present disclosure will be described in more detail below, including the above techniques (1) to (8). At least one selected from the components described below can be arbitrarily combined with at least one of the above techniques (1) to (8) for the electrolytic capacitor of the present disclosure, as long as such combination is technically possible.

[0031] [Electrolytic Capacitor] In the electrolytic capacitor of the present disclosure, the V / Vw ratio is 1.80 or less, and may be 1.75 or less, or even 1.70 or less. When the V / Vw ratio is in this range, leakage current tends to be significant. However, in the present disclosure, by using a liquid component with a specific composition, leakage current can be suppressed and the initial capacitance can be ensured within the above V / Vw ratio range, and fluctuations in ESR and reductions in capacitance can be suppressed when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time. Considering surge voltage, the lower limit of the V / Vw ratio is usually preferably 1.25 or more, and more preferably 1.35 or more.

[0032] The V / Vw ratio may be 1.25 or more (or 1.35 or more) and 1.80 or less, 1.25 or more (or 1.35 or more) and 1.75 or less, or 1.25 or more (or 1.35 or more) and 1.70 or less.

[0033] The formation voltage V is selected, for example, according to the rated voltage Vw so that V / Vw falls within the above range.

[0034] The rated voltage Vw is not particularly limited. When the rated voltage Vw is 100 V or less, and particularly when it is 50 V or less, the effect of suppressing the fluctuation in ΔESR and the decrease in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time is more likely to be achieved.

[0035] The electrolytic capacitor of the present disclosure includes a capacitor element and a liquid component.

[0036] (Liquid Component) The liquid component contains a solvent and an acid component. The liquid component may further contain a base component.

[0037] (Solvent) Examples of the solvent contained in the liquid component include organic solvents. The organic solvent is preferably a non-aqueous solvent. It may be a protic solvent. The solvent may contain one organic solvent (e.g., a non-aqueous solvent) or a combination of two or more organic solvents.

[0038] (First Solvent) The solvent includes a first solvent having hydroxy groups. The number of moles of hydroxy groups per 100 g of solvent is greater than 0.10 mol, and may be 0.15 mol or more, or 0.20 mol or more. By having the number of moles of hydroxy groups in this range, leakage current can be suppressed and a high initial capacitance can be obtained even when V / Vw is 1.80 or less. The number of moles of hydroxy groups per 100 g of solvent is 1.00 mol or less. By having the number of moles of hydroxy groups in this range, the progress of the esterification reaction between the first solvent and the carboxylic acid compound can be suppressed, thereby suppressing fluctuations in ESR and decreases in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time. From the perspective of further suppressing fluctuations in ESR and decreases in capacitance, the number of moles of hydroxy groups per 100 g of solvent may be 0.85 mol or less, 0.83 mol or less, or 0.70 mol or less.

[0039] The number of moles of hydroxy groups per 100 g of solvent may be greater than 0.10 mol and less than or equal to 0.85 mol (or less than or equal to 0.83 mol), greater than or equal to 0.15 mol and less than or equal to 0.85 mol (or less than or equal to 0.83 mol), greater than or equal to 0.20 mol and less than or equal to 0.85 mol (or less than or equal to 0.83 mol), greater than or equal to 0.10 mol and less than or equal to 0.70 mol, or greater than or equal to 0.15 mol (or greater than or equal to 0.20 mol) and less than or equal to 0.70 mol.

[0040] In the first solvent, the hydroxy group may be an alcoholic hydroxy group. From the viewpoint of easily obtaining a higher film repair effect, it is preferable that the first solvent has at least one alcoholic hydroxy group.

[0041] The first solvent may be a polyol compound having one hydroxy group or two or more hydroxy groups. Examples of the first solvent include monovalent hydroxy compounds and polyol compounds (polyols, partial ethers of polyols, etc.). The polyol compound preferably has at least one alcoholic hydroxy group. The polyol compound may have an alcoholic hydroxy group and a phenolic hydroxy group. In the polyol compound, all of the hydroxy groups may be alcoholic hydroxy groups.

[0042] Examples of monovalent hydroxy compounds include aliphatic alcohols (C hydroxy compounds such as hexanol, octanol, and lauryl alcohol) ６－１８ alkyl alcohols, etc.) and aralkyl alcohols (benzyl alcohol, phenethyl alcohol, etc.).

[0043] Examples of polyols include glycol compounds (alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), polyalkylene glycols (PEG (diethylene glycol (DEG), triethylene glycol (including TEG), polypropylene glycol (PPG), polyoxyethylene-polyoxypropylene copolymer (EOPO)), etc.)), glycerin compounds (glycerin (SGC), polyglycerin, etc.), sugar alcohol compounds, and alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.). Examples of partial ethers of polyols include partial ethers (e.g., alkyl ethers) corresponding to the above polyols. Examples of alkyl ethers include methyl ether, ethyl ether, propyl ether, isopropyl ether, n-butyl ether, isobutyl ether, tert-butyl ether (C １－６ Alkyl ether or C １－４ The first solvent may contain one polyol compound or a combination of two or more polyol compounds. In this specification, the term "polyol compound" also includes a first solvent that is a partial ether of a polyol and has only one hydroxy group.

[0044] From the viewpoint of further suppressing leakage current and easily ensuring a higher initial capacitance, the first solvent may contain a polyol compound. In particular, when the polyol compound contains PEG, it is easy to adjust the number of moles of hydroxyl groups within the above range while ensuring a high film repair effect, and it is possible to further suppress fluctuations in ESR and decreases in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0045] The weight-average molecular weight (Mw) of the PEG may be 150 to 2,000, 150 to 1,000, 150 to 500, or 200 to 400. When the polyol compound contains PEG with such Mw, leakage current can be suppressed while further suppressing fluctuations in ESR and reductions in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time. In addition, the viscosity of the liquid component can be easily maintained relatively low, thereby enhancing the dissociation of the acid component and the base component.

[0046] It is also preferable that the first solvent contains a first ether compound having a hydroxy group. In this case, leakage current can be further suppressed, and fluctuations in ESR and decreases in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be further suppressed. Examples of the first ether compound include partial ethers of the above-mentioned polyols. The first solvent may contain one type of first ether compound or a combination of two or more types.

[0047] The first ether compound may be at least one selected from the group consisting of monoalkyl ethers of alkylene glycols and monoalkyl ethers of polyalkylene glycols. Among them, monoalkyl ethers of PEG (mono C ) including diethylene glycol, triethylene glycol, etc. １－６ Alkyl ether or mono C １－４ Alkyl ethers, etc. are preferred. Examples of the first ether compound include diethylene glycol monomethyl ether (DEGMM), triethylene glycol monomethyl ether, hexaethylene glycol monomethyl ether (HEGMM), and monomethyl ether of PEG (PEGMM). Examples include PEGMM200, PEGMM240, PEGMM300, and PEGMM400. The number following PEGMM is the Mw of the corresponding PEG. For example, the monomethyl ether of PEG400 is represented as PEGMM400. However, these first ether compounds are merely examples, and the first ether compound is not limited to these specific examples.

[0048] (Second Solvent) The solvent contained in the liquid component may further contain a second solvent in addition to the first solvent. The second solvent may be an aprotic solvent. Examples of the second solvent include sulfone compounds, lactone compounds, carbonate compounds, and ether compounds (second ether compounds) that do not have a hydroxy group. The solvent may contain one type of second solvent or a combination of two or more types.

[0049] Examples of sulfone compounds include cyclic sulfone compounds (such as sulfolane (SL)) and sulfoxide compounds (such as dimethyl sulfoxide and diethyl sulfoxide). Examples of lactone compounds include γ-butyrolactone (GBL) and γ-valerolactone. Examples of carbonate compounds include chain carbonates (such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate), and cyclic carbonates (such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate).

[0050] Examples of the second ether compound include alkyl ethers of the above monohydric alcohols (for example, dialkyl ethers such as dimethyl ether and diethyl ether), and ethers of the above polyols (for example, alkyl ethers). Examples of the polyol ethers include compounds in which all hydroxy groups of a polyol are etherified with alkyl groups or the like. Examples of such ethers include dialkyl ethers of PEG (di-C alkyl ethers such as dimethyl ether and diethyl ether), １－６ Alkyl ether or diC １－４ Specific examples of PEG dialkyl ethers include diethylene glycol dimethyl ether (DEGDM), hexaethylene glycol dimethyl ether (HEGDM), and ethyl methyl ether of PEG240 (PEGDEM240). The solvent may contain one type of second ether compound or a combination of two or more types.

[0051] (Others) The solvent may contain, for example, a first ether compound, or may contain a first ether compound and a second ether compound. The first solvent may contain only the first ether compound, or may contain the first ether compound and at least one selected from the group consisting of the monovalent hydroxy compounds and polyol compounds (excluding the first ether compound), or may contain a second ether compound in addition to these.

[0052] The content of the first solvent in the solvent may be 30% by mass or more, or 50% by mass or more. When the content of the first solvent is in this range, leakage current can be further suppressed, and fluctuations in ESR and reductions in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be further suppressed. The content of the first solvent in the solvent may be 100% by mass or less. Alternatively, the solvent may consist solely of the first solvent.

[0053] (Moisture) The liquid component may contain moisture. The moisture content of the liquid component contained in the electrolytic capacitor may be 0.1% by mass or more and 6.0% by mass or less, 0.2% by mass or more and 4.0% by mass or less, or 0.5% by mass or more and 2.0% by mass or less. When the moisture content of the liquid component is within this range, high film repairability is easily achieved despite V / Vw≦1.80, and fluctuations in ESR when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be further suppressed.

[0054] (Acid Component) The acid component includes a carboxylic acid compound (first acid component). The liquid component may include an acid component (second acid component) other than the carboxylic acid compound.

[0055] (Carboxylic Acid Compound (First Acid Component)) When the liquid component contains a carboxylic acid compound, the pH of the liquid component can be kept low. Furthermore, although esterification easily proceeds in carboxylic acid compounds, in the present disclosure, by setting the number of moles of hydroxy groups within a specific range, the proceeding of esterification can be suppressed and a low pH can be maintained, thereby suppressing fluctuations in ESR and reductions in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0056] Examples of the carboxylic acid compound include carboxylic acids, carboxylic acid anhydrides, and coordination compounds of carboxylic acids.

[0057] Examples of the carboxylic acid include aliphatic carboxylic acids, alicyclic carboxylic acids, and aromatic carboxylic acids. The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid. Examples of the acid anhydrides include anhydrides of polycarboxylic acids. The aliphatic carboxylic acids and alicyclic carboxylic acids may be saturated or unsaturated. The carbon number of the aliphatic carboxylic acid may be 1 to 30 or 2 to 30. The alicyclic carboxylic acid may be 4 to 10 or 5 to 8. The carbon number of the aromatic carboxylic acid may be 7 to 15 or 7 to 12. The aliphatic ring in the alicyclic carboxylic acid may be a crosslinked ring or a fused ring in which an aromatic ring is fused to an aliphatic ring. In the aromatic carboxylic acid, an aliphatic ring may be fused to the aromatic ring. In the alicyclic carboxylic acid and the aromatic carboxylic acid, the aliphatic ring or aromatic ring may be a heterocycle containing a heteroatom (such as an oxygen atom or a sulfur atom) as a ring constituent atom.

[0058] Examples of aliphatic polycarboxylic acids include saturated polycarboxylic acids (oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, etc.) and unsaturated polycarboxylic acids (maleic acid, fumaric acid, itanoic acid, etc.). Examples of alicyclic polycarboxylic acids include cyclohexane-1,2-dicarboxylic acid and cyclohexene-1,2-dicarboxylic acid. Examples of aromatic polycarboxylic acids include phthalic acid, trimellitic acid, and pyromellitic acid.

[0059] Examples of aliphatic monocarboxylic acids include saturated monocarboxylic acids (such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, and behenic acid), and unsaturated monocarboxylic acids (such as acrylic acid, methacrylic acid, and oleic acid). Examples of aromatic monocarboxylic acids include benzoic acid, cinnamic acid, naphthoic acid, aromatic hydroxycarboxylic acids (such as salicylic acid, mandelic acid, and resorcylic acid), sulfoaromatic carboxylic acids (such as p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylic acid), and nitroaromatic carboxylic acids (such as nitrobenzoic acid).

[0060] Examples of the coordination compound include a coordination compound having at least one central atom selected from the group consisting of boron, aluminum, and silicon, and an acid having a carbonyloxy bond bound to the central atom. Specific examples of the coordination compound include borodisalicylic acid, borodisalic acid, borodiglycolic acid, and borodigallic acid.

[0061] The acid component may contain one or more carboxylic acid compounds.

[0062] Among carboxylic acid compounds, at least one selected from the group consisting of aromatic carboxylic acids (phthalic acid, salicylic acid, benzoic acid, nitrobenzoic acid, etc.) and aliphatic carboxylic acids is preferred. From the viewpoint of easily obtaining high heat resistance, aromatic carboxylic acids are preferred. In addition, the above-mentioned coordination compounds (borodisalicylic acid, borodisalic acid, borodiglycolic acid, etc.) are also preferred.

[0063] In the liquid component, the carboxy group and other acid groups (such as sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups) of the carboxylic acid compound may each be in any form, such as a free form, a salt form, an anion form, or a form interacting (e.g., complexing) with a conductive polymer. The carboxy group of the carboxylic acid compound and other acid groups each include all of these forms.

[0064] (Second Acid Component) The acid component may include an acid (second acid component) other than a carboxylic acid compound. Examples of such other acids include acids having a carbonyloxy bond other than carboxylic acid (such as oxocarbonic acid and Meldrum's acid) or coordination compounds thereof, phenolic compounds (such as picric acid, p-nitrophenol, hydroquinone, pyrogallol, catechol, resorcinol, and phloroglucinol) or coordination compounds thereof, sulfur-containing acids (such as sulfuric acid, sulfonic acids (such as aromatic sulfonic acids such as benzenesulfonic acid and naphthalenesulfonic acid), and oxyaromatic sulfonic acids (such as phenol-2-sulfonic acid)), compounds having a sulfonylimide bond, boron-containing acids (such as boric acid, halogenated boric acids (such as boric fluoride and tetrafluoroboric acid), and partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halogenated phosphoric acids (such as hexafluorophosphoric acid), phosphonic acid, phosphinic acid, and partial esters thereof (such as butyl phosphate)), and nitrogen-containing acids (such as nitric acid and nitrous acid).

[0065] Examples of compounds having a sulfonylimide bond include saccharin, 1,2-benzenedisulfonimide, cyclohexafluoropropane-1,3-bis(sulfonyl)imide, 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide, dibenzenesulfonimide, trifluoromethanesulfonanilide, N-[(4-methylphenyl)sulfonyl]acetamide, benzenesulfonanilide, and N,N'-diphenylsulfamide.

[0066] Examples of the coordination compound include a coordination compound having at least one central atom selected from the group consisting of boron, aluminum, and silicon, and an acid or phenol compound having a carbonyloxy bond bound to the central atom. Specific examples of the coordination compound include borodicatechol and borodipyrogallol.

[0067] The acid component may contain one or more of the above-mentioned second acid components.

[0068] (Others) The proportion of the carboxylic acid compound in the acid component may be 30% by mass or more, or 50% by mass or more. In this case, fluctuations in ESR and reductions in capacitance when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time can be further suppressed. The proportion of the carboxylic acid compound in the acid component is 100% by mass or less. From the viewpoint of improving the film repairability of the chemical conversion coating, the proportion of the carboxylic acid compound in the acid component may be 80% by mass or less.

[0069] The proportion of the carboxylic acid compound in the acid component may be 30% by mass or more (or 50% by mass or more) and 100% by mass or less, or 30% by mass or more (or 50% by mass or more) and 80% by mass or less.

[0070] The concentration of the carboxylic acid compound contained in the liquid component may be 1% by mass or more and 30% by mass or less, or may be 1% by mass or more and 20% by mass or less.

[0071] The above ratios and concentrations are values ​​determined based on the mass of each acid when it is in a free form.

[0072] (Base Component) When the liquid component contains a base component, the dissociation of an acid component such as a carboxylic acid compound is enhanced, making it easier for an acid group such as a carboxyl group to act on the solid electrolyte. This makes it easier to obtain higher conductivity of the solid electrolyte. The liquid component may be an electrolyte solution containing a solute. The solute may contain an acid component and a base component, or may contain a salt of the acid component and the base component.

[0073] Examples of the basic component include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The liquid component may contain one type of basic component or two or more types.

[0074] The amine may be any of aliphatic, aromatic, and heterocyclic. Examples of the amine include dialkylamines (diethylamine, etc.), trialkylamines (trimethylamine, ethyldimethylamine, triethylamine (TEA), tri-n-butylamine (TBA), dimethyl-n-octylamine (DMOA), etc.), alkylenediamines (ethylenediamine, etc.), aromatic amines (aniline, etc.), and heterocyclic amines (pyrrolidine, imidazole compounds (imidazole (Imd), 1,2,3,4-tetramethylimidazolinium, etc.), pyridine (Pyr), 4-dimethylaminopyridine, diazabicycloundecene (DBU), N-methylmorpholine (MMP), N-butylmorpholine, and N-isobutylmorpholine). Each of the aromatic amines and heterocyclic amines may be monocyclic or polycyclic (fused ring, bridged ring, etc.). Examples of the quaternary ammonium compound include amidine compounds (including imidazole compounds).

[0075] The liquid component may contain the base component in a free form, a cationic form, or a salt form, and all of these forms may be referred to as the base component.

[0076] The equivalent ratio of the carboxylic acid compound to the base component (=carboxylic acid compound / base component) may be 0.5 or more and 10 or less, 1.0 or more and 9.0 or less, or 1.3 or more and 8.9 or less. In this case, a high degree of dissociation of the carboxylic acid compound can be ensured and corrosion of the electrode can be suppressed.

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

[0078] The equivalent ratio of the acid component to the base component (=acid component / base component) may be 0.5 or more and 15 or less, or 1.0 or more and 10 or less. The equivalent ratio of the acid component / base component may be selected from the above-mentioned numerical range described for the equivalent ratio of the carboxylic acid compound / base component.

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

[0080] (Capacitor Element) The capacitor element included in the electrolytic capacitor includes an anode body having a chemical conversion coating and a solid electrolyte in contact with the chemical conversion coating. The solid electrolyte includes a conductive polymer and constitutes at least a part of the cathode body of the capacitor element. The cathode body may further include a cathode extraction layer (e.g., a cathode foil).

[0081] (Anode Body) The anode body may contain a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. These materials may be used alone or in combination of two or more. Preferred valve metals include aluminum, tantalum, niobium, and titanium.

[0082] The anode body is preferably an anode foil. The anode body preferably has a porous portion having pores at least in the surface layer. Anode bodies other than anode foil include a porous sintered body or a porous molded body of particles containing a valve metal.

[0083] The porous anode foil can be obtained by roughening the surface of a valve metal-containing substrate (e.g., a foil or plate-shaped substrate). The roughening can be performed by etching (e.g., electrolytic etching or chemical etching).

[0084] (Chemical Conversion Coating) The chemical conversion coating is also called a dielectric layer. The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body.

[0085] The chemical conversion coating contains, for example, an oxide of a valve metal. For example, when tantalum is used as the valve metal, the chemical conversion coating contains Ta ２ O ５ When aluminum is used as the valve metal, the conversion coating contains Al ２ O ３ However, the chemical conversion coating is not limited to these, and any coating that functions as a dielectric may be used.

[0086] The chemical conversion coating is usually formed on the surface of the anode body. When the chemical conversion coating is formed on the surface of the porous portion of the anode body, the coating is formed along the inner wall surfaces of the pores in the porous portion and the depressions (pits) on the surface of the anode body.

[0087] (Solid Electrolyte) The conductive polymer constituting the solid electrolyte includes, for example, a conjugated polymer and a dopant. The solid electrolyte covers, for example, at least a portion of the chemical conversion coating. This embodiment includes a case where the solid electrolyte is in contact with at least a portion of the chemical conversion coating. When the capacitor element includes an anode foil and a cathode foil, the solid electrolyte may be interposed between these foils. In this case, the solid electrolyte may be impregnated into a separator interposed between the anode foil and the cathode foil. The solid electrolyte may be in contact with at least a portion of the cathode foil in addition to at least a portion of the chemical conversion coating. The solid electrolyte may form a layer. The solid electrolyte may further include an additive in addition to the conductive polymer, as necessary.

[0088] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0089] The conjugated polymer may be used alone or in combination of two or more kinds.

[0090] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0091] (Dopants) Examples of dopants include relatively low molecular weight anions and polymeric anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that generate these anions are used as dopants. Examples of dopants that generate sulfonate ions include aromatic sulfonic acid compounds (such as paratoluenesulfonic acid and naphthalenesulfonic acid). The aromatic sulfonic acid compound may have at least one group selected from the group consisting of a carboxy group and a hydroxy group.

[0092] Examples of polymeric anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolac resin, and polyacrylic acid. The polymeric anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having a substituent. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0093] However, these dopants are merely examples and are not limited to these. One dopant may be used alone, or two or more dopants may be used in combination.

[0094] The conductive polymer may be formed, for example, by chemically polymerizing or electrolytically polymerizing a conjugated polymer precursor on a chemical conversion coating in the presence of a dopant. Alternatively, a conductive polymer (e.g., a solid electrolyte layer) may be formed by contacting a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed with the chemical conversion coating. 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, and oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination.

[0095] The Mw of the dopant is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0096] The amount of the dopant contained in the conductive polymer is, for example, 10 parts by mass or more and 1000 parts by mass or less, and may be 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0097] (Cathode Extraction Layer) The cathode extraction layer may include, for example, a first layer covering at least a portion of the solid electrolyte. The cathode extraction layer may include a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil (cathode foil). Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may include a first layer containing conductive carbon (e.g., graphite) (also referred to as a carbon layer) and a second layer containing metal powder or a metal foil. When a metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil. The cathode extraction layer can be formed by a known method depending on the layer configuration.

[0098] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such a second layer include a metal paste layer (e.g., a silver paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). The resin may be a thermosetting resin such as an imide resin or an epoxy resin, or a thermoplastic resin.

[0099] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0100] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0101] (Separator) A separator may be disposed between the cathode body (e.g., cathode foil) and the anode body (e.g., anode foil). The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0102] When the capacitor element includes a separator, the separator may be impregnated with the solid electrolyte. The conductive polymer may be interposed between the anode body (e.g., anode foil) and the cathode body (e.g., cathode foil), and may be in contact with at least a portion of the chemical conversion coating and at least a portion of the cathode body.

[0103] (Other) An electrolytic capacitor can be obtained, for example, by housing a capacitor element and a liquid component in a case and sealing the case with a sealing material or the like. The capacitor element is formed according to the description of the components of the capacitor element. The liquid component is prepared by dissolving the components, such as an acid component and a base component, in a solvent.

[0104] The electrolytic capacitor may be a wound type, and may be either a chip type or a laminate type. The electrolytic capacitor has at least one capacitor element. The electrolytic capacitor may have multiple capacitor elements. For example, the electrolytic capacitor may have a laminate of two or more capacitor elements, or may have two or more wound capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0105] In the capacitor element, one end of a cathode lead is electrically connected to the cathode extraction layer. One end of an anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the exterior body or case. The other end of each lead exposed from the exterior body or case is used for soldering to a substrate on which the electrolytic capacitor is to be mounted, for example. Each lead may be a lead wire or a lead frame.

[0106] Fig. 1 is a cross-sectional schematic diagram of an electrolytic capacitor according to this embodiment, and Fig. 2 is a schematic diagram showing a portion of a capacitor element of the electrolytic capacitor in an exploded view. However, the electrolytic capacitor of the present disclosure is not limited to the following embodiments. Furthermore, the components of the following embodiments may be arbitrarily combined with at least one of the above-described techniques (1) to (8) for the electrolytic capacitor of the present disclosure, or may be arbitrarily combined with at least one of the above-described techniques (1) to (8) and the components described above.

[0107] The electrolytic capacitor includes, for example, a capacitor element 10, a bottomed case 101 that contains capacitor element 10 and a liquid component (not shown), a sealing member 102 that closes the opening of bottomed case 101, a seat plate 103 that covers sealing member 102, lead wires 104A and 104B that extend from sealing member 102 and pass through seat plate 103, and lead tabs 105A and 105B that connect the lead wires to electrodes of capacitor element 10. The vicinity of the open end of bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to sealing member 102.

[0108] Capacitor element 10 is, for example, a wound body as shown in Fig. 2. The wound body includes anode foil 11 connected to lead tab 105A, cathode foil 12 connected to lead tab 105B, and separator 13. Anode foil 11 and cathode foil 12 are wound with separator 13 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 14. Note that Fig. 2 shows a partially unfolded state of the wound body before the outermost periphery is secured.

[0109] In capacitor element 10, a chemical conversion coating (not shown) is formed on at least a portion of the surface of anode foil 11. Separator 13 and a solid electrolyte (e.g., a conductive polymer) (not shown) are interposed between anode foil 11 and cathode foil 12. The solid electrolyte is in contact with at least a portion of the chemical conversion coating. The solid electrolyte is also in contact with at least a portion of cathode foil 12. The solid electrolyte and separator are impregnated with a liquid component.

[0110] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0111] Examples 1 to 13, Comparative Examples 1 to 4, and Reference Examples 1 to 17 Wound electrolytic capacitors (diameter 10 mm, length 10 mm) with a rated voltage of 25 V and a rated capacitance of 680 μF were fabricated and evaluated according to the following procedure.

[0112] (Preparation of anode body) An aluminum foil with a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Then, a chemical conversion coating 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 of 42.5 V (chemical conversion coating 32.7 nm) in the Examples and Comparative Examples, and 47.5 V (chemical conversion coating 36.5 nm) in the Reference Example. The aluminum foil was then cut into a size of 6 mm length x 120 mm width to prepare an anode body. The V / Vw ratio was 1.70 in the Examples and Comparative Examples, and 1.90 in the Reference Example.

[0113] (Preparation of Cathode Body) An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and then cut into a size of 6 mm length×120 mm width to prepare a cathode body.

[0114] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode body and the cathode body, respectively, and the anode body and the cathode body were wound around the lead tabs, with a separator interposed therebetween. An anode lead wire and a cathode lead wire were connected to the ends of each lead tab protruding from the wound body, respectively. The prepared wound body was then subjected to a chemical conversion treatment again, and a chemical conversion coating was formed on the cut ends of the anode body. Next, the ends of the outer surface of the wound body were fixed with a winding tape to prepare the wound body.

[0115] (Preparation of Polymer Dispersion Containing Conductive Polymer) 3,4-ethylenedioxythiophene and the polymer dopant poly(4-styrenesulfonic acid) (PSS, Mw 100,000) were dissolved in ion-exchanged water to prepare a mixed solution. While stirring the mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymer dispersion containing poly(3,4-ethylenedioxythiophene) doped with PSS (PEDOT / PSS) as the conductive polymer. The Mw of the polymer dopant is the value measured under the conditions described above.

[0116] (Coating of Chemical Conversion Coating with Solid Electrolyte) The wound body was immersed in a polymer dispersion contained in a designated container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the polymer dispersion. The wound body impregnated with the polymer dispersion was then dried in a drying oven at 150°C for 20 minutes to form a solid electrolyte containing a conductive polymer so as to cover at least a portion of the chemical conversion coating. In this way, a capacitor element was formed.

[0117] (Preparation of Liquid Component and Impregnation into Capacitor Element) A mixed solvent was prepared by mixing the solvents shown in Table 1. By adjusting the mass ratio of each solvent as shown in Table 1, the number of moles of hydroxyl groups (OH) per 100 g of the mixed solvent was adjusted as shown in Table 1.

[0118] A liquid component was prepared by dissolving a salt of phthalic acid and TEA and phthalic acid in the resulting mixed solvent. The amounts of each component were adjusted so that the salt concentration in the liquid component was 13% by mass and the total acid concentration was approximately 10% by mass. The pH of the prepared liquid component was approximately 4.0±0.5.

[0119] (Assembly of Electrolytic Capacitor) The capacitor element was immersed in the liquid component and placed in a reduced pressure atmosphere (40 kPa) for 5 minutes to allow the liquid component to be impregnated into the capacitor element.

[0120] The capacitor element impregnated with the liquid component was placed inside a bottomed case, with the lead wires positioned on the open side of the case. A sealing member (made of an elastic material containing butyl rubber as a rubber component) formed to allow the lead wires to pass through was placed above the capacitor element. The bottomed case was then drawn near the open end, and the open end was further curled to adhere to the sealing member. In this way, the capacitor element and liquid component were sealed inside the bottomed case. An electrolytic capacitor as shown in Figure 1 was completed by placing a seat plate on the curled portion. A total of 40 electrolytic capacitors were produced for each example. The produced electrolytic capacitors were then aged at 95°C for 90 minutes while applying a rated voltage Vw.

[0121] [Evaluation] The capacitance change (Δcap) and ESR change (ΔESR) of the electrolytic capacitors prepared above were evaluated using the following procedure. For 20 electrolytic capacitors after the aging treatment, the capacitance at a frequency of 120 Hz and the ESR at a frequency of 100 kHz were measured using an LCR meter in an environment of 20°C, and the average values ​​(initial capacitance value: c0 (F) and initial ESR value: r0 (Ω)) were calculated. After measuring c0 and r0, a high-temperature load test (accelerated test) was conducted. That is, a rated voltage Vw was applied to the electrolytic capacitors at a temperature of 145°C for 1500 hours. For the electrolytic capacitors after 1500 hours of accelerated testing, the average capacitance value (c1 (F)) and ESR value (r1 (Ω)) were calculated in accordance with the initial capacitance value and initial ESR value. Using the obtained c0 and c1, and r0 and r1, the capacitance change (Δcap) and ESR change (ΔESR) were calculated according to the following formulas: Δcap=(c1-c0) / c0 ΔESR=r1 / r0

[0122] The water content in the liquid component determined by the above-mentioned procedure was 0.5% by mass to 2.0% by mass.

[0123] The number of moles of hydroxy groups per 100 g of solvent can be determined, for example, by the following procedure. An example will be described in which a mixed solvent of PEG300 (polyethylene glycol Mw 300) and EG (ethylene glycol) mixed in a 1:1 mass ratio is used as the solvent. The mass per mole of PEG300 is 300 g / mol. PEG300 has two hydroxy groups per molecule, and the number of moles per 100 g is 100 g / 300 g ≒ 0.333. Therefore, the number of moles of hydroxy groups per 100 g of PEG300 is calculated as 0.333 x 2 = 0.666. Next, the number of moles of hydroxy groups per 100 g of EG is calculated in the same manner as for PEG300. Specifically, EG has two hydroxy groups per molecule, and the number of moles per 100 g is 100 g / 62.068 g ≒ 1.611. Therefore, the number of moles of hydroxy groups per 100 g of EG is calculated as 1.611 x 2 = 3.222. These values ​​are then multiplied by the mass ratio of each solvent and added together to determine the number of moles of hydroxy groups per 100 g of mixed solvent. Specifically, this is calculated as 0.666 x 1 / 2 + 3.222 x 1 / 2 ≒ 1.94. Note that the calculation is performed using a value to three decimal places and then rounded to two decimal places.

[0124] The evaluation results for each electrolytic capacitor are shown in Table 1. In Table 1, A1 to A13 are working examples, B1 to B4 are comparative examples, and R1 to R17 are reference examples. The results for Δcap and ΔESR in Table 1 are shown in Figures 3 and 4, respectively.

[0125]

[0126] The solvents in Table 1 are as follows: (First solvent) (Polyol compound) PEG300: Polyethylene glycol Mw 300 PEG400: Polyethylene glycol Mw 400 PEG200: Polyethylene glycol Mw 200 EOPO1700: Polyoxyethylene-polyoxypropylene copolymer (Mw 1700) EG: Ethylene glycol DEG: Diethylene glycol TEG: Triethylene glycol GLY: Glycerin (First ether compound) DEGMM: Diethylene glycol monomethyl ether PEGMM400: Monomethyl ether of polyethylene glycol (Mw 400) HEGMM: Hexaethylene glycol monomethyl ether (Second solvent) GBL: γ-butyrolactone SL: Sulfolane PEGDM240: Dimethyl ether of polyethylene glycol (Mw 240)

[0127] As shown in Table 1, Figures 3 and 4, in the Reference Examples where V / Vw > 1.80, even if the number of moles of hydroxy groups per 100 g of solvent changes, both ΔESR and Δcap after accelerated testing at high temperatures remain almost unchanged (R1 to R17). In contrast, in the Examples and Comparative Examples where V / Vw ≦ 1.80, as the number of moles of hydroxy groups increases, the increase in ΔESR and the decrease in Δcap after accelerated testing become significant. In the Examples, by setting the number of moles of hydroxy groups to 1.00 moles or less, fluctuations in ΔESR and decreases in Δcap can be suppressed even when V / Vw ≦ 1.80. Furthermore, when V / Vw ≦ 1.80, leakage current tends to be significant. However, by increasing the number of moles of hydroxy groups to more than 0.10 moles, leakage current can be reduced and high initial capacitance can be maintained.

[0128] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0129] The electrolytic capacitor of the present disclosure can be used as a hybrid electrolytic capacitor. The electrolytic capacitor exhibits small fluctuations in ESR when exposed to high-temperature environments for long periods of time, suppresses capacitance reduction, and has high reliability. Therefore, it is particularly suitable for applications requiring high reliability or long life. However, the applications of the electrolytic capacitor are not limited to these.

[0130] 100: Electrolytic capacitor 101: Bottomed case 102: Sealing member 103: Seat plate 104A, 104B: Lead wire 105A, 105B: Lead tab 10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 14: Winding tape

Claims

1. An electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises an anode body having a chemical conversion coating, and a solid electrolyte in contact with the chemical conversion coating, wherein a ratio of a chemical conversion voltage V volts applied to the anode body to form the chemical conversion coating to a rated voltage Vw volts of the electrolytic capacitor: V / Vw is 1.80 or less, wherein the liquid component comprises a solvent having a melting point and a freezing point of 60°C or less, and an acid component, wherein the solvent comprises a first solvent having a hydroxyl group, and the acid component comprises a carboxylic acid compound, and the number of moles of the hydroxyl group per 100 g of the solvent is greater than 0.10 and less than or equal to 1.00 moles.

2. The electrolytic capacitor according to claim 1, wherein the liquid component contains 0.1% by mass or more and 6.0% by mass or less of water.

3. The electrolytic capacitor according to claim 1, wherein the first solvent comprises a polyol compound.

4. The electrolytic capacitor according to claim 3, wherein the polyol compound contains polyethylene glycol, and the weight average molecular weight of the polyethylene glycol is 150 or more and 2,000 or less.

5. The electrolytic capacitor according to claim 1 or 3, wherein the first solvent contains a first ether compound having a hydroxy group.

6. The electrolytic capacitor according to claim 1 or 3, wherein the solvent includes a second solvent, and the second solvent includes a second ether compound not having a hydroxy group.

7. The electrolytic capacitor according to claim 1 or 2, wherein the content of the first solvent in the solvent is 30 mass % or more.

8. The electrolytic capacitor according to claim 1 or 2, wherein the carboxylic acid compound includes at least one selected from an aromatic carboxylic acid and an aliphatic carboxylic acid.

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