Solid electrolytic capacitor, smoothing circuit, filter circuit, and manufacturing method

Abstract

A solid electrolytic capacitor including a solid electrolyte layer and an electrolyte solution is prevented from deteriorating in capacitance in a low-temperature environment. The solid electrolytic capacitor includes an anode foil, a cathode foil, a solid electrolyte layer containing a conductive polymer, and an electrolyte solution. The solid electrolyte layer, the electrolyte solution, or both contain an aromatic compound having a HOMO level of-9.35 eV or more and having one or more hydroxyl groups.

Description

Technical Field

[0001] The present invention relates to a hybrid solid electrolytic capacitor using a solid electrolyte and an electrolyte solution, a manufacturing method thereof, and a smoothing circuit and a filter circuit including the solid electrolytic capacitor. Background Art

[0002] Capacitors are used in various applications, particularly in filter circuits. Examples of filter circuits include low-pass filters, high-pass filters, band-pass filters, and ripple filters, also known as smoothing circuits. Smoothing circuits are provided in power converters, and smoothing capacitors are incorporated into these circuits. Power converters convert power from an AC power source into DC power using a converter circuit, and then convert this DC power into the required AC power using an inverter circuit. The smoothing circuit, located between the converter and inverter circuits, suppresses ripples in the DC output from the converter circuit and smoothes the output before inputting it into the inverter circuit.

[0003] Electrolytic capacitors are already a common type of capacitor. Electrolytic capacitors utilize valve metals such as tantalum or aluminum, and utilize anode electrodes formed from sintered valve metal powders, or expanded valve metal foils etched to increase surface area, achieving high capacity in a compact design. In particular, solid electrolytic capacitors, which are dielectric oxide films coated with a solid electrolyte, offer advantages such as small size, high capacity, and low equivalent series resistance. They are also easily integrated into chips and suitable for surface mounting, making them essential for miniaturization, enhanced functionality, and cost-effectiveness in electronic devices.

[0004] As solid electrolytes, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known. In recent years, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which have excellent adhesion to dielectric oxide films, have rapidly gained popularity as solid electrolytes.

[0005] Conductive polymers include those that exhibit conductivity through the use of external dopants. External dopants are low-molecular-weight anions, polyanions such as organic sulfonic acids, and the like, and are used during chemical oxidation polymerization or electrolytic oxidation polymerization to exhibit high conductivity. Self-doping conductive polymers are also examples of conductive polymers. Self-doping conductive polymers have molecules within the monomer molecule that function as dopants, imparting conductivity and solubility in solvents.

[0006] However, solid electrolytic capacitors lack the ability to repair defects in the dielectric oxide film compared to liquid-type electrolytic capacitors, which impregnate the capacitor element with an electrolyte and lack a solid electrolyte layer. Therefore, so-called hybrid solid electrolytic capacitors, which form a solid electrolyte layer in the capacitor element where the anode and cathode foils face each other and impregnate the gaps between the capacitor elements with an electrolyte, have attracted attention (see, for example, Patent Document 1).

[0007] In particular, solid electrolytic capacitors that use a solid electrolyte layer and an electrolyte solution deteriorate in conductivity due to dedoping reactions of the dopant, increasing the ESR of the solid electrolytic capacitor. Furthermore, in high-temperature environments, such as those at 105°C, the solid electrolyte layer oxidizes and degrades, increasing the ESR of the solid electrolytic capacitor.

[0008] Regarding the increase in ESR associated with the dedoping reaction, Patent Document 1 reports that the dedoping reaction can be suppressed by making the molar ratio of the solute component, i.e., the acid component, to the alkaline component in the electrolyte excessive. In this report, it is presumed that the dedoping reaction is suppressed because the acid component, i.e., the dopant, maintains a state of equilibrium with the acid component in the electrolyte.

[0009] To address the issue of promoting oxidation of the solid electrolyte layer in a high-temperature environment, Patent Document 1 discloses that the electrolyte solution contains antioxidants such as aromatic compounds such as phenol, cresol, ethylphenol, pyrogallol, hydroquinone, pyrocatechol, tocopherol, butylated hydroxyanisole, butylated hydroxytoluene, benzoic acid, salicylic acid, resorcinol, and benzotriazole, amine compounds, silane compounds, quinone compounds, and carboxylic acid compounds. Patent Document 1 states that the acid component forms hydrogen bonds with the antioxidant, resulting in stabilization of the electronic resonance structure of the aromatic compound. Therefore, it is presumed that the antioxidant is activated, increasing the ability to inhibit degradation.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 4536625 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] It was confirmed that by including the antioxidant of Patent Document 1 in the electrolyte solution, even if the increase in ESR of a solid electrolytic capacitor using a solid electrolyte and an electrolyte solution can be suppressed under high-temperature conditions, deterioration in the electrostatic capacitance of a solid electrolytic capacitor using a solid electrolyte and an electrolyte solution under low-temperature conditions may not be suppressed.

[0015] Figure 1This is a graph showing the change in electrostatic capacitance (ΔCap) per charge and discharge cycle in various temperature atmospheres of a solid electrolytic capacitor using a solid electrolyte layer and an electrolyte solution. Figure 1 In the graph, the circle-marked graph is a graph under an atmosphere of 150°C, the triangle-marked graph is a graph under an atmosphere of 0°C, and the quadrilateral-marked graph is a graph under an atmosphere of -40°C.

[0016] For charge and discharge, a voltage of 25V is applied, a peak current of 27A is passed, and charge and discharge are repeated every 10 seconds, which is considered one cycle. Figure 1 As shown in FIG, even in a temperature environment of 150°C, the deterioration of ΔCap of a solid electrolytic capacitor using a solid electrolyte layer and an electrolyte solution is suppressed. Figure 1 As shown, when the temperature environment becomes 0° C. or lower, the ΔCap of the solid electrolytic capacitor using a solid electrolyte layer and an electrolyte solution is significantly deteriorated.

[0017] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to suppress deterioration of the electrostatic capacitance of a solid electrolytic capacitor including a solid electrolyte layer and an electrolyte solution in a low-temperature environment.

[0018] Means for solving problems

[0019] The inventors' intensive research has led to the following understanding: Unlike deterioration caused by thermally accelerated chemical reactions, such as dedoping and oxidative degradation, in conductive polymers at high temperatures, degradation occurs due to electrochemical reactions within the conductive polymer at low temperatures. Specifically, during storage, a voltage partial pressure is applied to the solid electrolyte layer and the electrolyte due to the current transient response during charging. Furthermore, the inventors have discovered that, in low-temperature environments, this partial pressure application causes overoxidation of the conductive polymer, leading to degradation of the conductive polymer and a decrease in the capacitance of the solid electrolytic capacitor.

[0020] However, the present inventors have confirmed that the phenomenon of peroxidative degradation of conductive polymers due to charge and discharge in a low-temperature environment significantly occurs in so-called hybrid solid electrolytic capacitors using a solid electrolyte layer containing a conductive polymer and an electrolyte solution.

[0021] Table 1 below shows a solid electrolytic capacitor (Reference Example 1) with only a solid electrolyte layer and a solid electrolytic capacitor (Reference Example 2) with a solid electrolyte layer and an electrolyte solution. The capacitors were placed in a -40°C environment and subjected to a DC load of 25V, undergoing 3100 cycles of charge and discharge. One cycle consisted of a 10-second charge and a 10-second discharge. Changes in capacitance were measured before and after the 3100 cycles.

[0022] The measurement results are shown in Table 1 below.

[0023] (Table 1)

[0024] electrolytes ΔCap (%) Reference Example 1 Solid electrolyte layer -2.6 Reference Example 2 Solid electrolyte layer + electrolyte -16.6

[0025] As shown in Table 1, the solid electrolytic capacitor of Reference Example 1, which had only a solid electrolyte layer, showed no degradation in capacitance under low-temperature conditions despite the presence of a conductive polymer. On the other hand, the solid electrolytic capacitor of Reference Example 2, which had both a solid electrolyte layer and an electrolyte solution, experienced significant degradation in capacitance due to overoxidation of the conductive polymer.

[0026] Based on this understanding, the present inventors conducted further in-depth research and confirmed that the addition of an aromatic compound with a higher HOMO level than the conductive polymer effectively suppresses oxidative degradation of the conductive polymer. This significantly increases the difference in HOMO levels between the conductive polymer and the aromatic compound, while also minimizing the potential difference between the aromatic compound and the electrode. Consequently, the aromatic compound readily donates electrons to the electrode, replacing the conductive polymer and facilitating oxidation.

[0027] In particular, when the HOMO level is -9.35 eV or higher, the difference in HOMO level between the conductive polymer and the aromatic compound is large, and the difference in potential between the aromatic compound with a high HOMO level and the electrode is small, resulting in a higher improvement in capacitance. Based on this finding, the present inventors have completed the present invention.

[0028] That is, in order to solve the above-mentioned problems, the solid electrolytic capacitor of this embodiment includes an anode body and a cathode body, a solid electrolyte layer containing a conductive polymer, and an electrolyte solution, wherein the solid electrolyte layer, the electrolyte solution, or both contain an aromatic compound having a HOMO energy level of greater than -9.35 eV and one or more hydroxyl groups.

[0029] The aromatic compound may be contained in an amount of 3.2 μmol or more per 1 mF of the foil capacity of the anode body.

[0030] The HOMO energy level of the aromatic compound may be set to -8.88 eV or higher.

[0031] The LUMO energy level of the aromatic compound can be set to -1.88 eV or lower. A LUMO energy level of -1.88 eV or lower not only makes it more susceptible to sacrificial oxidation on the anode side compared to conductive polymers, but also facilitates reduction on the cathode side after oxidation. A HOMO energy level of -9.35 eV or higher makes aromatic compounds with one or more hydroxyl groups more susceptible to regeneration on the cathode side. Consequently, the aromatic compound is less likely to be depleted, preventing the deterioration of the capacitance of the solid electrolytic capacitor over a long period of time.

[0032] In particular, when the HOMO energy level of the aromatic compound is set to be -8.88 eV or higher and the LUMO energy level is set to be -1.88 eV or lower, the improvement rate of the electrostatic capacitance of the solid electrolytic capacitor is significantly improved.

[0033] The aromatic compound may have hydroxyl groups at the 1-position and the 4-position.

[0034] The aromatic compound may further have one or more substituents.

[0035] The substituent may be an electron-donating substituent or an acetyl group.

[0036] The electron-donating substituent may be an alkyl group, an alkylene group, a vinyl group, a phenyl group, an amino group, a hydroxyl group, or an alkoxy group.

[0037] The electron-donating substituent may be arranged only at the 2-position of 1,4-hydroxybenzene.

[0038] The electrolyte solution may contain a polyol compound as a solvent.

[0039] The electrolyte solution may contain glycerin as the polyol compound.

[0040] The conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and contain 9.0 μg / mm 3 above.

[0041] Furthermore, in order to solve the above-mentioned problems, a smoothing circuit including the solid electrolytic capacitor of this embodiment and a filter circuit including the solid electrolytic capacitor of this embodiment are also aspects of the present invention.

[0042] In addition, in order to solve the above-mentioned problems, the manufacturing method of the solid electrolytic capacitor of this embodiment includes: a process of forming a solid electrolyte layer containing a conductive polymer between the anode body and the cathode body; and a process of immersing the solid electrolyte layer in an electrolyte after the solid electrolyte layer is formed, wherein the solid electrolyte layer, the electrolyte or both contain an aromatic compound having a HOMO energy level of greater than -9.35 eV and one or more hydroxyl groups.

[0043] Effects of the Invention

[0044] According to the present invention, it is possible to suppress deterioration in capacitance of a solid electrolytic capacitor including a solid electrolyte layer and an electrolytic solution in a low-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a graph showing the change in electrostatic capacitance (ΔCap) per charge and discharge cycle in various temperature atmospheres of a solid electrolytic capacitor using a solid electrolyte layer and an electrolyte solution.

[0046] Figure 2 This is an example of a smoothing circuit including a solid electrolytic capacitor.

[0047] Figure 3 This is an example of a filter circuit including a solid electrolytic capacitor.

[0048] Figure 4 The horizontal axis represents the potential, and the vertical axis represents the current density, and the cyclic voltammograms of the conductive polymer films measured in the electrolyte solutions of Example 1 and Comparative Example 1 are shown.

[0049] Figure 5 It is a graph showing the relationship between the HOMO level and the improvement rate of electrostatic capacitance.

[0050] Figure 6 It is a graph showing the relationship between the HOMO level, the LUMO level, and the improvement rate of the electrostatic capacitance.

[0051] Figure 7 This is a graph showing the relationship between the ratio of glycerin in the solvent and the capacitance improvement rate. DETAILED DESCRIPTION

[0052] Hereinafter, a solid electrolytic capacitor according to an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[0053] (Overall composition)

[0054] Solid electrolytic capacitors are passive components that utilize capacitance to store and discharge charge, leveraging the dielectric polarization of a dielectric oxide film. They are classified as hybrid types, using both a solid electrolyte layer and an electrolyte solution. Hybrid solid electrolytic capacitors are hereinafter referred to as solid electrolytic capacitors.

[0055] Solid electrolytic capacitors are constructed by housing a capacitor element in a housing, with the housing opening sealed with a sealing member. The capacitor element consists of an anode foil, a cathode foil, a separator, and an electrolyte layer. A dielectric oxide film is formed on the surface of the anode foil. The anode and cathode foils are wound or stacked relative to each other with a separator interposed therebetween. The electrolyte layer comprises a solid electrolyte layer and an electrolyte solution.

[0056] The solid electrolyte layer contains a conductive polymer such as poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid. The solid electrolyte layer is interposed between the anode foil and the cathode foil and is in close contact with the dielectric oxide film. The electrolyte is filled in the gap of the capacitor element. The electrolyte layer functions as a true cathode. A specific aromatic compound (hereinafter referred to as a specific aromatic compound) is added to the electrolyte layer, i.e., the electrolyte, the solid electrolyte layer, or both, which suppresses the oxidative degradation of the conductive polymer by replacing the conductive polymer and causing oxidation.

[0057] An example of a method for manufacturing the solid electrolytic capacitor is briefly described below: First, as a first step, an anode foil and a cathode foil having a dielectric oxide film formed on their surfaces are wound with a separator interposed therebetween to form a capacitor element, and the capacitor element is subjected to a repair chemical formation.

[0058] Next, as a second step, a solid electrolyte layer is formed on the capacitor element. In the second step, for example, a conductive polymer liquid containing dispersed or dissolved conductive polymer particles or powder is impregnated into the capacitor element, and the solvent is evaporated by drying. Then, as a third step, the capacitor element is impregnated with an electrolyte solution. A specific aromatic compound is added to the conductive polymer liquid, the electrolyte solution, or both.

[0059] Next, as a fourth step, the open end of the case into which the capacitor element has been inserted is sealed with a sealing member and then aged to form a solid electrolytic capacitor.

[0060] (Specific aromatic compounds)

[0061] An aromatic compound (hereinafter referred to as a specific aromatic compound) is added to the solid electrolyte layer, the electrolyte solution, or both, replacing the conductive polymer oxide. When the specific aromatic compound is added to the solid electrolyte layer, the specific aromatic compound can be added to the conductive polymer solution and impregnated into the capacitor element. Alternatively, a conductive polymer solution containing the specific aromatic compound can be attached between the anode and cathode. This specific aromatic compound has a HOMO energy level of -9.35 eV or higher and contains one or more hydroxyl groups.

[0062] The HOMO energy level, also known as the highest occupied molecular orbital energy level, is the molecular orbital with the highest energy occupied by electrons. Oxidation is the process of electron loss from a molecule. Electrons are initially lost from the high-energy HOMO, the most unstable occupied molecular orbital. In other words, the higher the HOMO energy level, the easier it is for electrons to escape, making oxidation more likely to occur. Furthermore, the higher the HOMO energy level, the smaller the difference with the electrode potential, making it easier to donate electrons to the electrode. Therefore, relatively speaking, the higher the HOMO energy level, the more susceptible a molecule is to oxidation.

[0063] For example, the calculated HOMO energy level of poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid is approximately -9.6 eV. Certain aromatic compounds with a HOMO energy level of -9.35 eV or higher have a large difference in HOMO energy from that of the conductive polymer and a small difference in electrode potential. Consequently, these aromatic compounds readily donate electrons to the electrode, easily replacing the conductive polymer in oxidation. Aromatic compounds with one or more hydroxyl groups undergo an oxidation reaction in which the hydrogen atom of the hydroxyl group is dissociated to form a carbonyl group.

[0064] Therefore, in a low-temperature environment of -20°C to -40°C, the conductive polymer in the solid electrolyte layer undergoes oxidative deterioration. However, a specific aromatic compound oxidizes prior to the oxidation of the conductive polymer, that is, sacrificially oxidizes, suppressing the oxidation of the conductive polymer and suppressing the deterioration of the electrostatic capacitance of the solid electrolytic capacitor. In particular, aromatic compounds having a HOMO energy level of -8.88 eV or higher and one or more hydroxyl groups are preferred because they have a good effect of suppressing the deterioration of the electrostatic capacitance. In addition, for example, the HOMO energy level of the specific aromatic compound is -8.39 eV or lower.

[0065] Furthermore, the HOMO energy level of poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid is calculated using a semi-empirical molecular orbital method (MO-G) as a calculation program and the PM6 method as a calculation method, with a 16-mer of poly(3,4-ethylenedioxythiophene) in which 5 molecules at both ends of the molecular chain are undoped and 6 molecules in the center are doped as a molecular model.

[0066] As aromatic compounds having a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups, they can be selected from aromatic compounds of the hydroxybenzene series, aromatic compounds having substituents on dihydroxybenzene, and carboxylic acids.

[0067] Among them, as aromatic compounds having a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups, aromatic compounds having hydroxyl groups at the 1-position and 4-position are preferred, and they tend to have a high HOMO energy level and an increased effect of suppressing the oxidation of the conductive polymer. More preferably, they are aromatic compounds having hydroxyl groups at the 1-position and 4-position and further having one or more electron-donating substituents or acetyl groups, and they tend to have a further increased HOMO energy level and a further improved effect of suppressing the oxidation of the conductive polymer. For example, aromatic compounds having hydroxyl groups at the 1-position and 3-position can suppress thermal energy-promoted de-doping and oxidative deterioration, but relatively, the effect of suppressing the oxidation of the conductive polymer is reduced compared to aromatic compounds having hydroxyl groups at the 1-position and 4-position.

[0068] As such a specific aromatic compound, for example, from the hydroxybenzene series, 1,4-dihydroxybenzene of the following chemical structural formula (1) can be cited.

[0069]

Chemical Formula 1

[0070]

[0071] In addition, for example, from the hydroxybenzene series, sesamol of the following chemical structural formula (2) can be cited.

[0072]

Chemical Formula 2

[0073]

[0074] In addition, for example, from the hydroxybenzene series, 1,2-dihydroxybenzene represented by the following chemical structural formula (3) can be cited.

[0075]

Chemistry 3

[0076]

[0077] In addition, for example, from the hydroxybenzene series, 1,2,3-trihydroxybenzene represented by the following chemical formula (4) can be cited.

[0078]

Chemistry 4

[0079]

[0080] In addition, examples of specific aromatic compounds include aromatic compounds having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents, such as those represented by the following chemical formula (5).

[0081]

Chemistry 5

[0082]

[0083] In the chemical structural formula (5), the electron-donating substituent R is an acyl group such as an alkylene group, a vinyl group, a phenyl group, an amino group, a hydroxyl group, an alkoxy group, an acetyl group, an alkynyl group, or an alkyl group having 1 or more carbon atoms. Furthermore, in addition to the 2-position, the electron-donating substituent R may be present at other positions such as the 3-position and the 5-position.

[0084] Examples of the aromatic compound having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents include methoxyhydroquinone represented by the following chemical formula (6).

[0085]

Chemistry 6

[0086]

[0087] Examples of the aromatic compound having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents include tert-butylhydroquinone represented by the following chemical formula (7).

[0088]

Chemistry 7

[0089]

[0090] Examples of the aromatic compound having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents include methylhydroquinone represented by the following chemical formula (8).

[0091]

Chemistry 8

[0092]

[0093] Examples of the aromatic compound having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents include phenylhydroquinone represented by the following chemical formula (9).

[0094]

Chemistry 9

[0095]

[0096] Examples of the aromatic compound having hydroxyl groups at the 1- and 4-positions and one or more electron-donating substituents include 1,2,4-trihydroxybenzene represented by the following chemical formula (10).

[0097]

Chemistry 10

[0098]

[0099] In addition, as the specific aromatic compound, from among aromatic compounds having a hydroxyl group at the 1-position and the 4-position and an acetyl group, there can be mentioned acetylhydroquinone represented by the following chemical formula (11).

[0100]

Chemistry 11

[0101]

[0102] In addition, as a specific aromatic compound, for example, from the carboxylic acid series, there can be mentioned vanillic acid represented by the following chemical formula (12).

[0103]

Chemistry 12

[0104]

[0105] In addition, as a specific aromatic compound, for example, from the carboxylic acid series, gallic acid represented by the following chemical formula (13) can be cited.

[0106]

Chemistry 13

[0107]

[0108] In addition, as a specific aromatic compound, for example, from the carboxylic acid series, 3,5-dihydroxybenzoic acid represented by the following chemical formula (14) can be cited.

[0109]

Chemistry 14

[0110]

[0111] More preferably, among the specific aromatic compounds, the LUMO energy level is -1.88 eV or less. The LUMO energy level is the lowest unoccupied molecular orbital energy level, also known as the lowest unoccupied molecular orbital energy level. It is the lowest energy molecular orbital in the orbital where no electrons enter. A reduction reaction is the phenomenon of electron donation to a molecule. Electrons are applied to the LUMO. The lower the LUMO energy level, the smaller the difference with the electrode potential, making it easier for electrons to be donated from the electrode. Therefore, relatively speaking, the lower the LUMO energy level, the easier it is to reduce.

[0112] In specific aromatic compounds with a HOMO energy level of -9.35 eV or higher, electrons are donated from the electrode, causing the hydrogen atom of the hydroxyl group to dissociate and transform into a carbonyl group. If the specific aromatic compound has a low LUMO energy level, it easily accepts electrons from the electrode and receives the dissociated hydrogen atom from the electrolyte. In other words, the carbonyl group returns to the hydroxyl group, regenerating the specific aromatic compound.

[0113] This regenerated specific aromatic compound has the function of sacrificially oxidizing the conductive polymer again before the overoxidation, which helps suppress the overoxidation of the conductive polymer. In particular, it has been found that specific aromatic compounds with a LUMO energy level of -1.88 eV or less are difficult to deplete due to regeneration, and the sacrificial oxidation before the overoxidation of the conductive polymer is sustained within the solid electrolytic capacitor. Therefore, specific aromatic compounds with a LUMO energy level of -1.88 eV or less are preferred. Using such specific aromatic compounds, the effect of suppressing the deterioration of the electrostatic capacitance of the solid electrolytic capacitor is prolonged. For example, the LUMO energy level of the specific aromatic compound is -2.31 eV or higher.

[0114] Examples of specific aromatic compounds having a LUMO level of -1.88 eV or less include 1,4-dihydroxybenzene, 1,2-dihydroxybenzene, 1,2,3-trihydroxybenzene, tert-butylhydroquinone, methylhydroquinone, phenylhydroquinone, 1,2,4-trihydroxybenzene, acetylhydroquinone, and gallic acid.

[0115] In particular, when the HOMO energy level of the aromatic compound is set to -8.88 eV or higher and the LUMO energy level is set to -1.88 eV or lower, the improvement rate of the electrostatic capacitance of the solid electrolytic capacitor is significantly improved.

[0116] The specific aromatic compound can be added as a mixture of one or more. The amount of the specific aromatic compound added is preferably 3.2 μmol or more per 1 mF of the anode foil capacity. When the amount of the specific aromatic compound added is within this range, the deterioration of the electrostatic capacitance of the solid electrolytic capacitor is particularly suppressed. In particular, when the amount of the specific aromatic compound added is 6.7 μmol or more per 1 mF of the anode foil capacity, the deterioration of the electrostatic capacitance of the solid electrolytic capacitor is significantly suppressed.

[0117] The capacitance of the anode foil is measured by cutting a test piece of a predetermined area from the anode foil, immersing it in a capacitance measurement solution in a glass measuring tank with a platinum plate as the counter electrode, and using a capacitance meter. For example, the predetermined area is 1 cm 2 The electrostatic capacitance measuring liquid is set to an aqueous solution of ammonium adipate at 30°C, the electrostatic capacitance meter is set to a potentiometer and a frequency response analyzer, an electrochemical impedance analyzer or an LCR meter, etc. As measurement conditions, the DC bias is set to 1.5V and the AC amplitude is set to 1V.

[0118] Regarding the amount of specific aromatic compound added, the preferred numerical range is obtained based on the foil capacity of the anode foil, which is inferred and not limited to this mechanism. As the foil capacity of the anode foil increases, the amount of conductive polymer tends to increase. This is believed to be because the molecular weight of the conductive polymer on the anode foil has a positive correlation with the foil capacity of the anode foil.

[0119] (Solid electrolyte layer)

[0120] The conductive polymer contained in the solid electrolyte layer is a conjugated polymer of the self-doping type doped with a dopant molecule within the molecule or an externally doped type doped with an external dopant molecule. The conjugated polymer is obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of a monomer or a derivative thereof having a π conjugated double bond. The dopant is an acceptor that easily accepts electrons in the conjugated polymer or a donor that easily donates electrons. In the case of an acceptor, π electrons are extracted from the conjugated polymer to form a negatively charged carrier (hole). In the case of a donor, electrons are donated to form a negatively charged carrier, and the conductive polymer exhibits conductivity.

[0121] The conductive polymer is subject to peroxidation degradation in low-temperature environments of -20°C to -40°C. However, the specific aromatic compound oxidizes before the peroxidation of the conductive polymer, thereby suppressing peroxidation. Consequently, deterioration of the electrostatic capacitance of the solid electrolytic capacitor is suppressed. When the specific aromatic compound is added, the content of the conductive polymer is preferably 9.0 μg / mm2 per unit volume of the capacitor element consisting of the anode foil, cathode foil, and electrolyte layer. 3 When the content of the conductive polymer is within this range, the proportion of the conductive polymer that suppresses oxidative degradation increases, and deterioration of the electrostatic capacitance of the solid electrolytic capacitor is further suppressed.

[0122] Furthermore, as the conjugated polymer, known conjugated polymers can be used without particular limitation. For example, polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. can be listed. These conjugated polymers can be used alone or in combination of two or more, and can be copolymers of two or more monomers.

[0123] As the conjugated polymer, known conjugated polymers can be used without particular limitation. For example, polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. can be listed. These conjugated polymers can be used alone or in combination of two or more, and can be copolymers of two or more monomers.

[0124] Among the above-mentioned conjugated polymers, preferred are those obtained by polymerizing thiophene or its derivatives, and preferably those obtained by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or their derivatives. Thiophene derivatives are preferably selected from thiophenes having substituents at the 3- and 4-positions. The substituents at the 3- and 4-positions of the thiophene ring may form a ring together with the carbon atoms at the 3- and 4-positions. The number of carbon atoms in the alkyl and alkoxy groups is preferably 1 to 16.

[0125] In particular, a polymer of 3,4-ethylenedioxythiophene called EDOT, that is, poly(3,4-ethylenedioxythiophene) called PEDOT, is particularly preferred. Furthermore, monomers having substituents added to 3,4-ethylenedioxythiophene can be used. For example, alkylated ethylenedioxythiophenes having alkyl groups added as substituents can be used, such as methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), and butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin).

[0126] The dopant may be a substituent of a conjugated polymer, may be chemically or electrochemically added in small amounts, and may be used without particular limitation. The dopant may be used alone or in combination of two or more. The dopant may be a homopolymer or a copolymer of two or more monomers. In addition, the dopant may be a polymer or a monomer.

[0127] For example, as dopants, there can be listed polyanions, inorganic acids such as boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodipic acid, cresic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalatoboric acid, sulfonimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0128] Examples of the polyanion include substituted or unsubstituted polyalkylene groups, substituted or unsubstituted polyalkenylene groups, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, that is, polymers composed only of structural units having anionic groups, and polymers composed of structural units having anionic groups and structural units not having anionic groups. Specific examples of the polyanion include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacryloylsulfonic acid, polymethacryloylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0129] In addition to the conductive polymer, the solid electrolyte layer may contain various additives such as polyols. Examples of the polyol include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerol, polyglycerol, polyoxyethylene glycerol, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, or a combination of two or more thereof. Since the polyol has a high boiling point, it can remain in the solid electrolyte layer even after the drying process, thereby reducing ESR and improving the withstand voltage.

[0130] The method for forming the solid electrolyte layer is not particularly limited. For example, a conductive polymer liquid in which particles or powder of a conductive polymer are dispersed or dissolved can be impregnated into a capacitor element, causing the conductive polymer to adhere to the dielectric oxide film to form the solid electrolyte layer. To promote the impregnation of the capacitor element, a reduced pressure treatment or a pressurized treatment can be applied as needed. The impregnation process can be repeated multiple times. As for the dispersion medium or solvent of the conductive polymer liquid, drying can be used to evaporate and remove it as needed. Heat drying or reduced pressure drying can be performed as needed.

[0131] Alternatively, a conductive polymer liquid can be applied or dispensed between the anode and cathode to form a solid electrolyte layer. By depositing the conductive polymer liquid between the anode and cathode, the conductive polymer liquid adheres to the anode's dielectric coating, cathode, separator, or a combination thereof. Prior to assembling the capacitor element, the conductive polymer liquid can be individually deposited on the anode's dielectric coating, cathode, separator, or a combination thereof.

[0132] Furthermore, a conductive polymer liquid is obtained by, for example, adding a monomer, an acid or an alkali metal salt thereof that releases the dopant, and an oxidant, stirring until chemical oxidative polymerization is completed, and then removing the oxidant and residual monomers by purification means such as ultrafiltration, cation exchange, and anion exchange.

[0133] (Electrolyte)

[0134] The electrolyte can be impregnated between the anode body and the cathode body. For example, the electrolyte is impregnated in a capacitor element having a solid electrolyte layer formed therein. The electrolyte is a solution in which anionic components and cationic components are added to a solvent. The anionic components and cationic components are typically salts of organic acids, salts of inorganic acids, or salts of complex compounds of organic acids and inorganic acids, and are ion-dissociated salts that dissociate into anionic components and cationic components are added to the solvent. The acid that becomes the anionic component and the base that becomes the cationic component can be added to the solvent separately. In addition, the electrolyte may not contain anionic components or cationic components, or both anionic components and cationic components in the solvent.

[0135] The solvent of the electrolyte solution can be a protic organic polar solvent or an aprotic organic polar solvent. Examples of the protic organic solvent include monohydric alcohols, polyhydric alcohols, and oxyhydric alcohol compounds. Examples of the monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and oxyhydric alcohol compounds include alkylene oxide adducts of polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, glycerol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, polyethylene glycol, and polyoxyethylene glycerol.

[0136] As aprotic organic polar solvents, sulfones, amides, lactones, cyclic amides, nitrile, and sulfoxides can be used. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, and N,N-diethylacetamide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitrile solvents include acetonitrile, 3-methoxypropionitrile, and glutaronitrile. Examples of sulfoxides include dimethyl sulfoxide.

[0137] When a specific aromatic compound is added to the solvent, a polyol compound is preferably used. Combining a specific aromatic compound with a polyol compound improves the effect of suppressing the deterioration of the electrostatic capacitance of the solid electrolytic capacitor. Examples of the polyol compound include alkylene glycols such as ethylene glycol and propylene glycol, polyalkylene glycols such as polyethylene glycol, and glycerols such as glycerol and polyglycerol. In particular, combining a specific aromatic compound with a glycerol further improves the effect of suppressing the deterioration of the electrostatic capacitance of the solid electrolytic capacitor.

[0138] For example, glycerol is contained in the solvent in an amount of 20 wt% or more. Preferably, glycerol is contained in the solvent in an amount of 60 wt% or more. When the amount is 60 wt% or more, the effect of suppressing the deterioration of electrostatic capacitance is suppressed to the same level as when glycerol is contained in the solvent in an amount of 100 wt%.

[0139] Furthermore, the specific aromatic compound is preferably added to the electrolyte in the solid electrolyte and the electrolyte. When the specific aromatic compound is added to the electrolyte, the deterioration of the electrostatic capacitance of the solid electrolytic capacitor is suppressed compared to the case where the specific aromatic compound is added to the solid electrolyte.

[0140] Examples of the anion component in the electrolyte include oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, heptanoic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcinic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and carboxylic acids such as pyromellitic acid, phenols, and sulfonic acids, and various organic acids. Examples of the anion component of the inorganic acid in the electrolyte include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic acids and inorganic acids include boron disalicylic acid, boron dioxalic acid, boron diglycolic acid, boron dimalonic acid, boron disuccinic acid, boron diadipic acid, boron diazelaic acid, boron dibenzoic acid, boron dimaleic acid, boron dilactic acid, boron dimalic acid, boron ditartaric acid, boron dicitric acid, boron diphthalic acid, boron di(2-hydroxy)isobutyric acid, boron diresorcinolic acid, boron dimethylsalicylic acid, boron dinaphthoic acid, boron dimandelic acid, and boron di(3-hydroxy)propionic acid.

[0141] In addition, examples of salts of at least one of an organic acid, an inorganic acid, and a composite compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidine salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidine salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0142] Furthermore, other additives can also be added to the electrolyte. As additives, phosphoric acid, phosphoric acid esters and other phosphoric acid compounds, boric acid, boric acid esters and other boric acid compounds, boric acid and mannitol, sorbitol and other sugar alcohol complexes, colloidal silicon dioxide, silicone oil, etc. can be included. In addition, as additives, nitro compounds can be included. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzene, p-nitrobenzyl alcohol, m-nitroacetophenone, o-nitroanisole, etc. As other additives, for the purpose of improving chemical formation, phosphoric acid esters and other phosphoric acid compounds are preferably added, or for the purpose of gas absorption, p-nitro compounds such as nitrobenzoic acid are preferably added.

[0143] (Electrode Foil)

[0144] The anode and cathode foils, which face each other across the electrolyte, are long strips of valve metal. Examples of valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode foil is preferably 99.9% or higher, and that of the cathode foil is preferably around 99% or higher. Impurities such as silicon, iron, copper, magnesium, and zinc may be present.

[0145] The anode foil is expanded as a sintered body obtained by sintering the powder of the valve metal, an etched foil obtained by etching the foil obtained by stretching the valve metal, or an evaporation body obtained by evaporating the particles of the valve metal on the surface of the foil. The expanded surface structure is composed of tunnel-shaped pits, sponge-shaped pits, or gaps between dense powders. The tunnel-shaped pits can be dug into the deep part of the anode foil, or can be formed in a way that penetrates the anode foil. The expanded surface structure is formed by electrolytic etching, chemical etching, sandblasting, etc., or by evaporating or sintering metal particles on the foil. As electrolytic etching, DC etching or AC etching in which DC or AC is applied in an acidic aqueous solution in the presence of halogen ions such as hydrochloric acid can be cited. In addition, in chemical etching, the metal foil is immersed in an acid solution or an alkaline solution.

[0146] The dielectric oxide film is typically formed on the surface of the anode foil. If the anode foil is made of aluminum, it is aluminum oxide formed by oxidizing the porous structure. This dielectric oxide film is formed by applying voltage in an aqueous solution of adipic acid, boric acid, or phosphoric acid.

[0147] The cathode foil may be a flat foil without an expanded surface structure, or it may be provided with an expanded surface structure by vapor deposition, sintering, or etching, similar to the anode foil. An oxide film may be formed intentionally or naturally on the expanded surface layer. Intentionally, a thin dielectric oxide film (approximately 1 to 10 Vfs) may be formed by chemical conversion treatment. The natural oxide film is formed by the cathode foil reacting with oxygen in the air. In addition, an inorganic conductive layer may be formed on the cathode foil. Examples of the inorganic conductive layer include metal compounds such as titanium and titanium carbide, and carbon.

[0148] (Spacer)

[0149] Examples of spacers include cellulose such as kraft paper, Manila hemp, straw, hemp, and rayon, and mixed papers thereof; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polyamide resins such as polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0150] (Circuit)

[0151] Such solid electrolytic capacitors are suitable for various filter circuits, such as low-pass filters, high-pass filters, band-pass filters, and ripple filters, also known as smoothing circuits.

[0152] Figure 2 This circuit diagram shows an example of a smoothing circuit including this solid electrolytic capacitor. This smoothing circuit 1 includes a diode 2, a solid electrolytic capacitor 3, and an inrush current limiting circuit 4. Diode 2 is connected in series with the circuit, allowing the rectified input voltage Vin to pass while preventing reverse connection. Solid electrolytic capacitor 3 is placed after diode 2 and connected in parallel with the circuit to smooth the rectified input voltage Vin.

[0153] The inrush current limiting circuit 4 is inserted in series between the diode 2 and the solid electrolytic capacitor 3. The inrush current limiting circuit 4 includes a resistor 41 and a switch 42 connected in parallel. The resistor 41 limits the peak value of the inrush current input to the solid electrolytic capacitor 3. The switch 42 opens when an inrush current occurs and closes after the solid electrolytic capacitor 3 is charged, thereby short-circuiting the resistor 41 and suppressing power loss.

[0154] In this smoothing circuit 1, in low-temperature environments, inrush current can cause peroxidative degradation of the conductive polymer in solid electrolytic capacitor 3, reducing its capacitance. Therefore, solid electrolytic capacitor 3 is replaced with one containing an aromatic compound with a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups in the solid electrolyte layer, the electrolyte, or both. This suppresses peroxidative degradation of the conductive polymer in solid electrolytic capacitor 3 caused by inrush current and also reduces capacitance reduction. Consequently, a smoothing circuit 1 can be implemented by replacing resistor 41, which limits the peak value of inrush current, with a resistor of a lower resistance.

[0155] In this smoothing circuit 1, power loss is reduced due to the reduced resistance of the resistor 41. Therefore, by omitting the switch 42, not only can the resistor 41 with a smaller resistance be replaced, but also the smoothing circuit 1 without the switch 42 can be realized.

[0156] Figure 3 4 is a circuit diagram showing an example of a filter circuit including the solid electrolytic capacitor. Figure 3 The filter circuit 5 shown includes a solid electrolytic capacitor 3 and an inrush current limiting circuit 4. The solid electrolytic capacitor 3 is connected in parallel with the circuit, and the inrush current limiting circuit 4 is connected in series with the circuit before the solid electrolytic capacitor 3. The inrush current limiting circuit 4 includes a resistor 41 and a switch 42 connected in parallel.

[0157] In this filter circuit 5, in low-temperature environments, inrush current can cause peroxidative degradation of the conductive polymer in solid electrolytic capacitor 3, reducing capacitance. Therefore, solid electrolytic capacitor 3 is replaced with one containing an aromatic compound with a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups in the solid electrolyte layer, electrolyte, or both. This allows for a filter circuit 5 in which resistor 41, which limits the peak value of the inrush current, is replaced with a resistor with a lower resistance.

[0158] The filter circuit 5 has a reduced power loss due to the reduced resistance of the resistor 41. Therefore, the switch 42 can be omitted, and not only can the resistor 41 with a smaller resistance be replaced, but the filter circuit 5 without the switch 42 can also be realized.

[0159] Example

[0160] The solid electrolytic capacitor of the present invention is described in more detail below based on examples. However, the present invention is not limited to the following examples.

[0161] (Electrolyte of Example 1)

[0162] The electrolyte solution of Example 1 was prepared. The electrolyte solution of Example 1 contained 0.16 mol of ammonium azelaic acid salt per kg of ethylene glycol solvent as a solute. Furthermore, 0.025 mol / kg of methoxyhydroquinone was added to the electrolyte solution of Example 1 as a specific aromatic compound. Methoxyhydroquinone is an aromatic compound having hydroxyl groups at the 1- and 4-positions and a methoxy group as an electron-donating substituent at the 2-position.

[0163] (Electrolyte of Comparative Example 1)

[0164] An electrolyte solution of Comparative Example 1 was prepared corresponding to the electrolyte solution of Example 1. The electrolyte solution of Comparative Example 1 had the same composition and composition ratio as the electrolyte solution of Example 1, except that methoxyhydroquinone was not added.

[0165] (Peroxidation potential measurement test)

[0166] For Example 1 and Comparative Example 1, cyclic voltammograms showing the relationship between current and potential at a temperature of -40°C were analyzed. 2 The glassy carbon electrode was pre-coated with a conductive polymer. The conductive polymer was PEDOT / PSS, a compound consisting of PEDOT doped with polystyrenesulfonic acid (PSS). This conductive polymer was applied to the glassy carbon electrode using a solution casting method. Specifically, a dispersion of PEDOT / PSS was applied to the glassy carbon electrode and then dried to evaporate the solvent. 10 μL of the dispersion was applied to the glassy carbon electrode and dried at 110°C for 30 minutes.

[0167] A platinum electrode was used as the counter electrode, and an Ag / AgCl reference electrode was used as the reference electrode. The measurement solution consisted of a mixed solution of ethylene glycol as the solvent and ammonium azelate as the supporting electrolyte (solute). 0.16 mol of ammonium azelate was dissolved per 1 kg of the electrolyte. Then, at room temperature, a potential sweep was performed, starting from the immersion potential toward the positive side, repeating the sweep from 1.5 V (a potential exceeding 1.2 V) to -0.4 V.

[0168] Figure 4 (a) is the result of the cyclic voltammogram of the conductive polymer film measured in the electrolyte of Example 1, and (b) is the result of the cyclic voltammogram of the conductive polymer film measured in the electrolyte of Comparative Example 1, with the horizontal axis being the potential and the vertical axis being the current density.

[0169] like Figure 4 As shown in (b), it can be confirmed that the oxidation current and reduction current of the conductive polymer film decrease sharply when the potential is swept to 1.5V. During the charge-discharge test, the current transient response during charge and discharge also divides the voltage between the conductive polymer film and the electrolyte during the charge storage period. Therefore, in Comparative Example 1, under a temperature environment of -40°C, the voltage is divided and applied to the solid electrolyte layer during charge and discharge. Due to the 1.5V voltage division, the conductive polymer degrades due to overoxidation during the electrochemical reaction.

[0170] On the other hand, Figure 4 As shown in (a), it can be confirmed that in the electrolyte of Example 1, the changes in the oxidation current and reduction current of the conductive polymer film are small even when the potential is swept up to 1.5 V. In other words, the results of Comparative Example 1 and Example 1 confirm that under low-temperature environments such as -40°C, the conductive polymer undergoes peroxidative degradation due to electrochemical reactions, and that the addition of a specific aromatic compound suppresses peroxidative degradation of the conductive polymer due to electrochemical reactions.

[0171] (Capacitor of Example 1)

[0172] The solid electrolytic capacitor of Example 1 was fabricated using the electrolyte solution of Example 1. The anode foil was aluminum foil, expanded by etching, and then subjected to a dielectric oxide film by chemical conversion. During the chemical conversion, a voltage was applied to the anode foil in an aqueous adipic acid solution. The cathode foil was aluminum foil, expanded by etching, then subjected to a chemical conversion to form an oxide film, and then a titanium compound was vapor-deposited. During the chemical conversion, a voltage was applied to the cathode foil in an aqueous adipic acid solution.

[0173] The anode foil and cathode foil were connected to lead wires, and wound with the anode foil and cathode foil facing each other via a Manila separator. The capacitor element was repaired by immersing it in an aqueous solution of ammonium dihydrogen phosphate for 10 minutes.

[0174] Next, a dispersion of polyethylenedioxythiophene (PEDOT) doped with polystyrenesulfonic acid (PSS) was prepared and impregnated into the capacitor element. The capacitor element was then lifted and dried at 150°C for 30 minutes. This immersion and drying process was repeated several times. Thus, a solid electrolyte layer was formed on the capacitor element. The electrolyte of Example 1 was then impregnated into the capacitor element having the solid electrolyte layer formed thereon. At this time, the electrolyte was impregnated into the capacitor element in such a manner that the specific aromatic compound, methoxyhydroquinone, became 6.7 μmol / mF relative to the foil capacitance of the anode foil of 1 mF.

[0175] The capacitor element was inserted into a cylindrical shell with a bottom, a sealing body was installed at the open end, and it was sealed by fastening. Then, voltage was applied for 45 minutes at a temperature of 115°C, and an aging treatment was performed on the solid electrolytic capacitor of Comparative Example 1. Thus, the wound capacitor element with a diameter of 8.0 mm and a height of 10.0 mm was inserted into an aluminum outer shell with a bottom, a sealing rubber was installed at the open end, and it was sealed by fastening. The rated withstand voltage of this solid electrolytic capacitor is 25WV and the rated capacity is 330μF.

[0176] (Capacitors of Examples 2 to 12)

[0177] Next, solid electrolytic capacitors of Examples 2 to 12 were produced. These solid electrolytic capacitors were produced using the same configuration, manufacturing conditions, and manufacturing method as Example 1, except that the type of specific aromatic compound added to the electrolyte solution was different from that of Example 1. Furthermore, a solid electrolytic capacitor of Comparative Example 2 was produced. The solid electrolytic capacitor of Comparative Example 2 was produced using the same configuration, manufacturing conditions, and manufacturing method as Example 1, except that 3,5-dihydroxybenzoic acid was added to the electrolyte solution instead of the specific aromatic compound.

[0178] In Example 2, tert-butylhydroquinone (t-BHQ) was added to the electrolyte as a specific aromatic compound. In Example 3, methylhydroquinone (MHQ) was added to the electrolyte as a specific aromatic compound. In Example 4, phenylhydroquinone (PhAHQ) was added to the electrolyte as a specific aromatic compound. In Example 5, 1,2,4-trihydroxybenzene was added to the electrolyte as a specific aromatic compound. In Example 6, sesamol was added to the electrolyte as a specific aromatic compound.

[0179] In Example 7, 1,4-dihydroxybenzene was added to the electrolyte as a specific aromatic compound.

[0180] In Example 8, 1,2-dihydroxybenzene was added to the electrolyte as a specific aromatic compound. In Example 9, acetylhydroquinone was added to the electrolyte as a specific aromatic compound. In Example 10, 1,2,3-trihydroxybenzene was added to the electrolyte as a specific aromatic compound. In Example 11, vanillic acid was added to the electrolyte as a specific aromatic compound. In Example 12, gallic acid was added to the electrolyte as a specific aromatic compound.

[0181] (Charge and discharge test)

[0182] The capacitance improvement rate (ΔCap) of the solid electrolytic capacitors of Examples 1 to 12 and Comparative Example 2 was measured. The capacitance was measured after 540 cycles of 10-second charge and 10-second discharge, each at -40°C, with a 25V DC load applied. The capacitance improvement rate was calculated using the following formula 1.

[0183] (Calculation formula 1)

[0184] ΔCap=(Ca-Cb)÷Ca×100

[0185] Where Ca is the capacitance of the solid electrolytic capacitor of Comparative Example 1, to which no specific aromatic compound was added, and Cb is the capacitance of the solid electrolytic capacitor of each Example and Comparative Example. The capacitance was measured using an LCR meter (4284A, manufactured by Agilent Technologies). The measurement was performed at an ambient temperature of 21°C, an AC current level of 1.0 Vrms, and a measurement frequency of 120 Hz.

[0186] The results of the capacitance improvement rates for Examples 1 to 12 and Comparative Example 2 are shown in Table 2 below. Table 2 also shows the positions of hydroxyl groups, substituent types, HOMO levels, and LUMO levels in the specific aromatic compounds of each Example and the additive of Comparative Example 2. The HOMO and LUMO levels were calculated using the PM6 method using a semi-empirical molecular orbital (MO-G) calculation program (Fujitsu SCIGRESS).

[0187] (Table 2)

[0188]

[0189] In addition, based on Table 2, the relationship between the HOMO level and the improvement rate of electrostatic capacitance is shown in Figure 5 As shown in Table 2 and Figure 5 As shown, the capacitance improvement rate of Comparative Example 1 is only 3.9%, while the capacitance improvement rate of Examples 1 to 12 exceeds at least 20%. Examples 1 to 12 are solid electrolytic capacitors containing an aromatic compound having a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups.

[0190] Examples 1 to 9 achieved capacitance improvements exceeding at least 30%. Examples 1 to 9 are solid electrolytic capacitors containing aromatic compounds having a HOMO energy level of -8.88 eV or higher. Examples 1 to 9 are solid electrolytic capacitors containing dihydroxybenzene- and hydroxybenzene-based aromatic compounds. Most of these examples 1 to 9 are solid electrolytic capacitors containing aromatic compounds having hydroxyl groups at the 1 and 4 positions.

[0191] In addition, based on Table 2, the relationship between the HOMO level, LUMO level and the improvement rate of electrostatic capacitance is shown in Figure 6 in the coordinate diagram. Figure 6 The horizontal axis represents the HOMO energy level, the vertical axis represents the LUMO energy level, and the electrostatic capacitance is shown next to the graph.

[0192] As shown in Table 2 and Figure 6 As shown, if the HOMO energy level is -8.88 eV or higher, the electrostatic capacitance improvement rate exceeds at least 30%. Furthermore, the electrostatic capacitance improvement rate of Example 6, which has a LUMO energy level exceeding -1.88 eV at a HOMO energy level of -8.88 eV or higher, is 33%, while for Examples 1 to 5 and Examples 7 to 9, which have a LUMO energy level below -1.88 eV, the electrostatic capacitance improvement rate reaches 38% or higher. This result was obtained after 540 cycles of charge and discharge testing, indicating that the regeneration of the specific aromatic compound suppresses the deterioration of the electrostatic capacitance even after this number of cycles.

[0193] In particular, it was confirmed that the capacitance improvement rate significantly exceeded 40% for Examples 1 to 4 and Example 9. Examples 1 to 4 and Example 9 are aromatic compounds having hydroxyl groups at the 1 and 4 positions and further having an electron-donating substituent or a substituent such as an acetyl group.

[0194] (Add target comparison test)

[0195] Solid electrolytic capacitors of Examples 13 and 14 were further produced. Examples 13 and 14 used methylhydroquinone as the specific aromatic compound. Examples 13 and 14 differed in the target of adding the specific aromatic compound. That is, the objects to which the specific aromatic compound was added differed. Similar to Examples 1 to 9, Example 13 added the specific aromatic compound to the electrolyte. On the other hand, in Example 14, the specific aromatic compound was added to a conductive polymer solution, and the capacitor element was immersed in the conductive polymer solution to form a solid electrolyte layer. In other words, the solid electrolytic capacitor of Example 14 contained the specific aromatic compound in the solid electrolyte layer, and no specific aromatic compound was added to the electrolyte solution.

[0196] The capacitor element was filled with the electrolyte solution so that the concentration of the specific aromatic compound was 14 μmol / mF per 1 mF of the anode foil capacitance. The solid electrolytic capacitors of Examples 10 and 11 were fabricated using the same configuration, manufacturing conditions, and manufacturing method as Examples 1 to 9.

[0197] The improvement rate (ΔCap) of the electrostatic capacitance of the solid electrolytic capacitors of Examples 13 and 14 was measured. The electrostatic capacitance was measured in the same manner as in Examples 1 to 9, including placing each solid electrolytic capacitor in a temperature environment of -40°C.

[0198] The results of the improvement rates of the electrostatic capacitance in Examples 13 and 14 are shown in Table 3 below.

[0199] (Table 3)

[0200]

[0201] As shown in Table 3, the capacitance improvement rate for both Examples 13 and 14 reached 45% or more. Therefore, it was confirmed that regardless of whether the specific aromatic compound was added to the electrolyte solution or the solid electrolyte layer, it effectively suppressed the peroxidative degradation of the conductive polymer, thereby suppressing the deterioration of the capacitance of the solid electrolytic capacitor. Furthermore, Example 13 showed a better capacitance improvement rate than Example 14. This confirms that when the specific aromatic compound is added to the electrolyte solution, peroxidative degradation of the conductive polymer within the solid electrolyte layer is more effectively suppressed.

[0202] (Addition amount test)

[0203] Solid electrolytic capacitors were further produced according to Examples 15 to 18, Reference Example 1, and Comparative Examples 3 and 4. In Examples 15 to 17 and Reference Example 1, the same acetylhydroquinone as in Example 9 was added to the electrolyte as the specific aromatic compound, but the amount added was different from that in Example 9. Furthermore, the solid electrolytic capacitors of Examples 15 to 17 and Reference Example 1 were produced using the same configuration, manufacturing conditions, and manufacturing method as in Example 9.

[0204] In Example 18, the same gallic acid as in Example 12 was added to the electrolyte as the specific aromatic compound, but the amount added was different from that in Example 12. Furthermore, the solid electrolytic capacitor of Example 18 was produced using the same configuration, production conditions, and production method as in Example 12.

[0205] Comparative Examples 3 and 4 added the same 3,5-dihydroxybenzoic acid as in Comparative Example 2 to the electrolyte solution, but in different amounts compared to Comparative Example 2. Furthermore, the solid electrolytic capacitors of Comparative Examples 3 and 4 were fabricated using the same configuration, manufacturing conditions, and manufacturing method as in Comparative Example 2.

[0206] The capacitance improvement rate (ΔCap) was measured for the solid electrolytic capacitors of Examples 15 and 18, Reference Example 1, and Comparative Examples 3 and 4. The capacitance was measured using the same method as for Examples 1 to 9, including placing each solid electrolytic capacitor at a temperature of -40°C.

[0207] The capacitance improvement results of Examples 9, 15 to 18, Reference Example 1, and Comparative Examples 2 to 4 are shown in Table 4 below, along with the amounts of specific aromatic compounds added. The amounts in the table are expressed as μmol / mF per 1 mF of anode foil capacity.

[0208] (Table 4)

[0209]

[0210] As shown in Reference Example 1, Example 9, and Examples 15 to 18 in Table 4, it can be confirmed that increasing the amount of the specific aromatic compound added increases the rate of improvement in the capacitance of the solid electrolytic capacitor. Specifically, as the amount of the specific aromatic compound added increases, the effect of suppressing the peroxidative degradation of the conductive polymer further improves, and the effect of suppressing the deterioration of the capacitance of the solid electrolytic capacitor improves. This trend is also observed in Comparative Examples 2 to 4, but the rate of improvement in capacitance in these Comparative Examples 2 to 4 is very small.

[0211] However, as shown in Reference Example 1, it was confirmed that if the amount of the specific aromatic compound added was too small, the capacitance improvement rate was small. As shown in Examples 15 and 18, the amount of the specific aromatic compound added was preferably 3.2 μmol or greater per 1 mF of the anode foil capacitance. Furthermore, as shown in Examples 9 and 17, the capacitance improvement rate was further improved when the amount of the specific aromatic compound added was 6.7 μmol or greater per 1 mF of the anode foil capacitance.

[0212] (Electrolyte Solvent Amount Test)

[0213] Solid electrolytic capacitors of Examples 19 to 21 were also produced. The solid electrolytic capacitors of Examples 19 to 21 were filled with electrolytes containing 0.16 mol of triethylamine azelaic acid salt per kg of solute in the solvent. Furthermore, 0.025 mol / kg of methylhydroquinone was added to the electrolytes as a specific aromatic compound.

[0214] The types of solvents used in the electrolyte solutions used in Examples 19 to 21 differed. The electrolyte solution in Example 19 contained ethylene glycol as a solvent, the electrolyte solution in Example 20 contained glycerol as a solvent, and the electrolyte solution in Example 21 contained γ-butyrolactone as a solvent. The solid electrolytic capacitors in Examples 19 to 21 were fabricated using the same configuration, manufacturing conditions, and manufacturing methods as those in Examples 1 to 9.

[0215] The improvement rate (ΔCap) of the electrostatic capacitance of the solid electrolytic capacitors of Examples 19 to 21 was measured. The electrostatic capacitance was measured in the same manner as in Examples 1 to 9, including placing each solid electrolytic capacitor in a temperature environment of -40°C.

[0216] The results of the improvement rates of the electrostatic capacitance of Examples 19 to 21 are shown in Table 5 below, along with the types of solvents in the electrolyte solutions.

[0217] (Table 5)

[0218]

[0219] Compared to Example 21, Examples 19 and 20 in Table 5 show a higher improvement rate in the capacitance of the solid electrolytic capacitor. This indicates that, when a specific aromatic compound is added to the electrolyte layer, the selection of a polyol compound as the solvent for the electrolyte solution further enhances the effect of suppressing peroxidative degradation of the conductive polymer, thereby improving the effect of suppressing capacitance degradation of the solid electrolytic capacitor. Furthermore, the selection of glycerol as the polyol compound significantly enhances the effect of suppressing peroxidative degradation of the conductive polymer and capacitance degradation.

[0220] (Conductive high molecular weight test)

[0221] Solid electrolytic capacitors of Examples 22 to 25 were further produced. The solid electrolytic capacitors of Examples 22 to 25 were the same as the solid electrolytic capacitor of Example 3 in that the conductive polymer was polyethylenedioxythiophene (PEDOT) doped with polystyrenesulfonic acid (PSS), but the amount of the conductive polymer was different.

[0222] The solid electrolytic capacitor of Example 25 differs from the solid electrolytic capacitor of Example 3 in the amount of the specific aromatic compound added. Furthermore, the solid electrolytic capacitors of Examples 22 to 25 were produced using the same configuration, production conditions, and production method as Example 3.

[0223] The improvement rate (ΔCap) of the electrostatic capacitance of the solid electrolytic capacitors of Examples 22 to 25 was measured. The electrostatic capacitance was measured in the same manner as in Examples 1 to 9, including placing each solid electrolytic capacitor in a temperature environment of -40°C.

[0224] The results of the improvement rate of the electrostatic capacitance of Examples 19 to 21 are shown in Table 6 below together with the amount of the conductive polymer. In the table, the amount of the conductive polymer is expressed as a unit volume of 1 mm2 per unit volume of the capacitor element consisting of the anode foil, cathode foil, separator, and electrolyte layer. 3 To express.

[0225] (Table 6)

[0226]

[0227] As shown in Table 6, Examples 3, 22, and 23 showed a higher improvement rate in the capacitance of the solid electrolytic capacitor than Examples 24 and 25. That is, when the specific aromatic compound was added to the electrolyte layer, it was confirmed that the capacitance of the solid electrolytic capacitor was improved by increasing the amount of the conductive polymer to 1 mm2 per unit volume of the capacitor element. 3 , which is 9.0 μg or more, further improves the effect of suppressing the overoxidative degradation of the conductive polymer, and improves the effect of suppressing the deterioration of the electrostatic capacitance of the solid electrolytic capacitor.

[0228] In this example, a cathode foil on which a titanium compound was deposited after etching was used. However, it was confirmed that the same effects as those of this example were obtained even when a cathode foil on which no metal compound was deposited was used.

[0229] Furthermore, solid electrolytic capacitors of Examples 26 to 30 were produced. The solid electrolytic capacitors of Examples 26 to 30 differed from those of Example 21 in the solvent ratio of glycerol to γ-butyrolactone. The solid electrolytic capacitors of Examples 26 to 30 were produced using the same configuration, manufacturing conditions, and manufacturing method as Example 21. As shown in Table 7 below, the glycerol ratio in the solvent of the electrolytic capacitors of Examples 26 to 30 ranged from 20 wt% to 60 wt%, varying in 10 wt% increments.

[0230] Next, the capacitance improvement rate (ΔCap) was measured for the solid electrolytic capacitors of Examples 26 to 30. The capacitance was measured using the same method as for Examples 1 to 9, including placing each solid electrolytic capacitor at a temperature of -40°C.

[0231] The results of the improvement rate of electrostatic capacitance are shown in Table 7 below together with Examples 21 and 20. Figure 7 . Figure 7 This is a graph showing the relationship between the ratio of glycerin in a solvent and the capacitance improvement rate.

[0232] (Table 7)

[0233]

[0234] As shown in Table 7 and Figure 7 As shown, Example 26, in which the ratio of glycerol in the solvent was 20 wt%, further improved the capacitance improvement rate compared to Example 21, in which no glycerol was added. When the glycerol ratio was increased to 60 wt% or more, as can be seen from a comparison with Example 20, an improvement effect comparable to that obtained with 100 wt% glycerol was achieved.

Claims

1. A solid electrolytic capacitor, characterized in that The invention comprises an anode body and a cathode body, a solid electrolyte layer containing a conductive polymer, and an electrolyte solution, wherein the solid electrolyte layer, the electrolyte solution, or both contain an aromatic compound having a HOMO energy level of -9.35 eV or higher and one or more hydroxyl groups.

2. The solid electrolytic capacitor according to claim 1, wherein The anode body contains 3.2 μmol or more of the aromatic compound per 1 mF of foil capacity.

3. The solid electrolytic capacitor according to claim 1 or 2, characterized in that: The HOMO energy level of the aromatic compound is -8.88 eV or higher.

4. The solid electrolytic capacitor according to claim 1 or 2, characterized in that: The LUMO energy level of the aromatic compound is -1.88 eV or less.

5. The solid electrolytic capacitor according to claim 1 or 2, characterized in that: The aromatic compound has hydroxyl groups at the 1-position and the 4-position.

6. The solid electrolytic capacitor according to claim 5, characterized in that The aromatic compound may also have one or more substituents.

7. The solid electrolytic capacitor according to claim 6, wherein: The substituent is an electron-donating substituent or an acetyl group.

8. The solid electrolytic capacitor according to claim 7, wherein: The electron-donating substituent is an alkyl group, an alkylene group, a vinyl group, a phenyl group, an amino group, a hydroxyl group or an alkoxy group.

9. The solid electrolytic capacitor according to claim 7, wherein: The electron-donating substituent is disposed only at the 2-position of 1,4-hydroxybenzene.

10. The solid electrolytic capacitor according to claim 1 or 2, characterized in that: The electrolyte solution contains a polyol compound as a solvent.

11. The solid electrolytic capacitor according to claim 10, wherein: The electrolyte solution contains glycerin as the polyol compound.

12. The solid electrolytic capacitor according to claim 1 or 2, characterized in that: The conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and the unit volume of the capacitor element contains 9.0 μg / mm 3 above.

13. A smoothing circuit, characterized in that The solid electrolytic capacitor according to claim 1 or 2 is included.

14. A filter circuit, characterized in that The solid electrolytic capacitor according to claim 1 or 2 is included.

15. A method for manufacturing a solid electrolytic capacitor, characterized in that: The invention comprises: a process of forming a solid electrolyte layer comprising a conductive polymer between an anode body and a cathode body; and a process of immersing the solid electrolyte layer in an electrolyte after the solid electrolyte layer is formed, wherein the solid electrolyte layer, the electrolyte or both contain an aromatic compound having a HOMO energy level of greater than -9.35 eV and one or more hydroxyl groups.

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