Solid electrolytic capacitor and manufacturing method

Abstract

Provided are a solid electrolytic capacitor that has a low equivalent series resistance, and a manufacturing method. This solid electrolytic capacitor comprises: an anode body that has a dielectric film; a cathode body that faces the anode body; and a solid electrolyte layer that is interposed between the anode body and the cathode body. A capacitor element is obtained by superimposing the anode body and the cathode body with the solid electrolyte layer interposed therebetween. The solid electrolyte layer contains a conductive polymer and tannic acid. The content ratio of the conductive polymer (A) and the tannic acid (B) is A:B=100:185 or more by weight ratio, and the weight of the conductive polymer relative to the volume of the capacitor element is 0.003 mg / mm3 to 0.018 mg / mm3. The solid electrolyte layer is formed using a conductive polymer solution in which conductive polymer particles are dispersed. The conductive polymer solution contains the conductive polymer and tannic acid at the aforementioned weight ratio.

Description

Solid electrolytic capacitor and manufacturing method

[0001] The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof.

[0002] Electrolytic capacitors have anode and cathode foils made of valve metals such as tantalum or aluminum. The anode foil is enlarged by shaping the valve metal into a sintered or etched foil, and the enlarged surface is coated with a dielectric film. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the irregular surface of the anode foil and functions as the true cathode.

[0003] Capacitors are used in a variety of applications. For example, in the field of power electronics, power from an AC power source is converted into DC power by a converter circuit, and this DC power is then converted into desired AC power by an inverter circuit. A smoothing capacitor is provided in a power supply circuit to suppress pulsation in the DC output from the converter circuit and smooth the DC before inputting it to the inverter circuit. Furthermore, a decoupling capacitor is provided near a semiconductor switching element such as a gallium nitride element to ensure stable operation of the semiconductor switching element and remove noise. Furthermore, with the trend toward higher power in the field of power electronics, there is a growing demand for capacitors with higher capacitance.

[0004] In this regard, electrolytic capacitors have the advantage that the specific surface area can be increased by expanding the surface area of ​​the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors such as film capacitors. Electrolytic capacitors contain an electrolyte in the form of an electrolytic solution. The contact area between the electrolytic solution and the dielectric film on the anode foil increases. This makes it easier to further increase the capacitance of electrolytic capacitors.

[0005] A method of adding tannic acid to an electrolyte to improve capacitance has also been proposed (see, for example, Patent Document 1). Tannic acid dissolves the oxide film on the anode body, which is believed to improve the initial capacitance of an electrolytic capacitor. Regarding tannic acid, a method of adding it to an electrolyte together with a phosphorus oxoacid ion-generating compound has also been proposed (see, for example, Patent Document 2). Tannic acid acts as a chelating agent to form a water-soluble aluminum chelate complex. This complex further combines with phosphate ions to form a bond. The formation of this bond inhibits the dissolution of the aluminum oxide film by phosphoric acid, thereby suppressing an increase in leakage current.

[0006] In recent years, solid electrolytic capacitors that use a solid electrolyte with higher conductivity than the electrolyte solution have also become popular (see, for example, Patent Document 3). Solid electrolytic capacitors are small and have large capacitance, and use a solid electrolyte with higher conductivity than the electrolyte solution, enabling low equivalent series resistance (ESR). Known solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex.

[0007] Known solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. In recent years, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which has a slow reaction rate and excellent adhesion to dielectric films, have rapidly become popular as solid electrolytes. Conductive polymers use acid compounds such as polyanions as dopants, and the monomer molecules contain a partial structure that acts as a dopant, resulting in high conductivity.

[0008] In addition to low equivalent series resistance, solid electrolytic capacitors have the advantage of being long-lasting, as they are not susceptible to drying-up due to evaporation of the electrolyte over time. However, so-called hybrid-type solid electrolytic capacitors, which use both a conductive polymer and an electrolyte to repair defects in the dielectric film and reduce leakage current in solid electrolytic capacitors, are also becoming popular.

[0009] JP 2002-110470 A JP 2012-84568 A JP 2011-60980 A

[0010] If a solid electrolytic capacitor has a high equivalent series resistance (ESR), it generates heat, which causes thermal degradation of the conductive polymer, shortening the capacitor's lifespan. Therefore, the solid electrolytic capacitor is affected by the equivalent series resistance, limiting the allowable ripple current. When a solid electrolytic capacitor is used in a voltage smoothing circuit of a power converter, many solid electrolytic capacitors are connected in parallel to handle the ripple current. Therefore, there is a demand for solid electrolytic capacitors with a lower equivalent series resistance.

[0011] Furthermore, if the ESR of a solid electrolytic capacitor is high, a voltage drop occurs due to the ESR when the solid electrolytic capacitor is discharged, and a voltage rise occurs due to the ESR when the solid electrolytic capacitor is charged. In other words, the solid electrolytic capacitor causes voltage fluctuations. Therefore, a solid electrolytic capacitor with a high ESR has a low voltage smoothing ability.

[0012] The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a solid electrolytic capacitor with a low equivalent series resistance and a manufacturing method thereof.

[0013] In order to solve the above-described problems, the solid electrolytic capacitor of the present embodiment includes an anode body having a dielectric film, a cathode body facing the anode body, a solid electrolyte layer interposed between the anode body and the cathode body, and a capacitor element including the anode body, the cathode body, and the solid electrolyte layer, wherein the solid electrolyte layer contains a conductive polymer and tannic acid, the content ratio of the conductive polymer (A) to the tannic acid (B) in the solid electrolyte layer is A:B=100:185 or more by weight, and the weight of the conductive polymer is 0.003 mg / mm ３ More than 0.018 mg / mm ３ The following is the result.

[0014] The ratio of the conductive polymer (A) to the tannic acid (B) in the solid electrolyte layer may be set to A:B=100:185 to 100:1400 by weight.

[0015] The weight of the conductive polymer per volume of the capacitor element is 0.005 mg / mm ３ 0.015mg / mm or more ３ The following may be true:

[0016] The solid electrolyte layer may include ethylene glycol, glycerin, or both.

[0017] The solid electrolyte layer may contain sorbitol.

[0018] The ratio of the conductive polymer (A) to the sorbitol (D) in the solid electrolyte layer may be set to A:D=1:4 to 1:28 by weight.

[0019] An electrolyte may also be provided.

[0020] In order to solve the above-described problems, a method for manufacturing a solid electrolytic capacitor according to the present embodiment includes an element forming step of forming a solid electrolyte layer between an anode body having a dielectric film and a cathode body using a conductive polymer solution in which conductive polymer particles are dispersed, thereby forming a capacitor element having the anode body, the cathode body, and the solid electrolyte layer, the conductive polymer solution including a conductive polymer and tannic acid, the conductive polymer solution including the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B of 100:185 or more, and the conductive polymer is added to the solid electrolyte layer in an amount of 0.003 mg / mm ３ More than 0.018 mg / mm ３ Included in the following weights:

[0021] The conductive polymer solution may contain the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B=100:185 to 100:1400.

[0022] The conductive polymer is added to the solid electrolyte layer in an amount of 0.005 mg / mm ３ 0.015mg / mm or more ３ The following weight amounts may be included:

[0023] The conductive polymer liquid may contain a polyhydric alcohol, which is ethylene glycol, glycerin, or both of these, and the content ratio of the conductive polymer (A) to the polyhydric alcohol (C) may be A:C=1:9 to 1:54 by weight.

[0024] The capacitor element may be impregnated with an electrolyte.

[0025] According to the present invention, the solid electrolytic capacitor has a low ESR.

[0026] 1 is a graph showing the relationship between the amount of tannic acid added and the rate of change in ESR. 2 is a graph showing the relationship between the conductive polymer and the ESR, divided into the cases of adding tannic acid and not adding tannic acid. 3 is a graph showing the relationship between the conductive polymer and the rate of change in ESR. 4 is a graph showing the relationship between the amount of ethylene glycol and the ESR. 5 is a graph showing the relationship between the amount of sorbitol and the ESR.

[0027] Hereinafter, a solid electrolytic capacitor and a manufacturing method thereof according to an embodiment will be described, but the present invention is not limited to the embodiment described below.

[0028] (Solid Electrolytic Capacitor) A solid electrolytic capacitor is a passive element that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. This solid electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body, a cathode body, and a solid electrolyte layer. A dielectric film is formed on the anode body. The anode body and the cathode body face each other with the solid electrolyte layer between them. The solid electrolyte layer is interposed between the dielectric film of the anode body and the cathode body, and functions as a true cathode in close contact with the dielectric film of the anode body. The solid electrolytic capacitor may include a solid electrolyte layer and an electrolytic solution as an electrolyte. The electrolytic solution is impregnated into the voids of the capacitor element on which the solid electrolyte layer is formed.

[0029] A separator may be interposed between the anode body and the cathode body. The separator holds the solid electrolyte layer and prevents short-circuiting between the anode body and the cathode body. If the solid electrolyte layer can maintain its shape by itself and separates the anode body from the cathode body, the separator can be omitted from the configuration of the solid electrolytic capacitor.

[0030] Solid electrolytic capacitors are classified into, for example, stacked, wound, and flat types. In stacked types, anode bodies and cathode bodies are alternately stacked with a separator sandwiched between them. In wound types, anode bodies and cathode bodies are wound with a separator sandwiched between them. In flat types, a solid electrolyte layer and a cathode body are stacked on an anode body.

[0031] (Electrode Body) The anode body and cathode body are foil bodies made of a valve metal. The foil bodies may be formed by stretching a valve metal or the like, or by sintering a valve metal powder. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the valve metal is preferably 99.9% or more for the anode body and 99% or more for the cathode body, and may contain silicon, iron, copper, magnesium, zinc, and the like.

[0032] In wound electrolytic capacitors, the anode body is a long, strip-shaped anode foil, while in laminated and flat electrolytic capacitors, the anode body is a flat anode foil. A surface-expanding layer is formed on one or both sides of the anode body. The surface-expanding layer can be an etched layer formed by etching the foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto the foil. That is, the surface-expanding layer has a porous structure consisting of tunnel-shaped pits, spongy pits, or voids between densely packed powder or particles.

[0033] The dielectric coating is formed on one or both sides of the anode body on which the surface-expanding layer is formed. When a surface-expanding layer is formed, it is formed on the surface of the surface-expanding layer, following the irregularities of the surface-expanding layer. The dielectric coating is typically an oxide coating formed on the surface of the anode body. If the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the surface-expanding layer. In the chemical conversion treatment to form the dielectric coating, a voltage is applied to the anode body in a chemical conversion solution until the desired withstand voltage is achieved. The chemical conversion solution is a solution free of halogen ions, such as a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate.

[0034] In the case of a wound-type electrolytic capacitor, the cathode body is preferably a cathode foil made of a valve metal and stretched. A surface-expanding layer is formed on the cathode body, just like on the anode body. Plain foil without a surface-expanding layer may also be used as the cathode body. The cathode body may have a natural oxide film or a thin oxide film of about 1 to 10 Vfs formed by chemical conversion treatment. The natural oxide film is formed when the cathode body reacts with oxygen in the air.

[0035] The cathode body may further include a conductive layer. The conductive layer may contain primarily an inorganic substance or an inorganic compound. Examples of the inorganic substance or inorganic compound include titanium, zirconium, tantalum, niobium, nitrides or carbides thereof, aluminum carbide, carbon materials, and composites or mixtures thereof.

[0036] In the case of a laminated electrolytic capacitor, the cathode body is preferably a laminate of a metal layer and a carbon layer. The carbon layer of the cathode body is arranged facing the anode body. The carbon layer is formed in a paste form by coating the electrolyte layer on the anode body after the electrolyte layer is formed on the anode body, and then curing the layer by heating. The metal layer is, for example, a silver layer, and is formed by coating the paste form on the carbon layer and then curing the layer by heating.

[0037] (Solid electrolyte layer) The solid electrolyte layer is a layer containing a conductive polymer. The conductive polymer is a self-doped conjugated polymer doped with an intramolecular dopant, or a conjugated polymer doped with an external dopant molecule. The conjugated polymer is obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of a monomer having a π-conjugated double bond or a derivative thereof. The dopant or external dopant molecule is an acceptor that easily accepts electrons into the conjugated polymer, or a donor that easily donates electrons, which allows the conductive polymer to exhibit high conductivity.

[0038] As the conjugated polymer, any known polymer can be used without any particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. These conjugated polymers may be used alone or in combination of two or more types, or may even be a copolymer of two or more types of monomers.

[0039] Among the above conjugated polymers, preferred are conjugated polymers obtained by polymerizing thiophene or a derivative thereof, and preferred are conjugated polymers 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 derivatives thereof. The thiophene derivative is preferably a compound selected from thiophenes having substituents at the 3rd and 4th positions, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbon atoms at the 3rd and 4th positions. The alkyl group or alkoxy group preferably has 1 to 16 carbon atoms.

[0040] In particular, a polymer of 3,4-ethylenedioxythiophene, known as EDOT, i.e., poly(3,4-ethylenedioxythiophene), known as PEDOT, is preferred. Furthermore, a substituent may be added to 3,4-ethylenedioxythiophene. For example, an alkylated ethylenedioxythiophene having an alkyl group having 1 to 5 carbon atoms added as a substituent may be used. Examples of alkylated ethylenedioxythiophenes include 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), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

[0041] Any known dopant can be used without any particular limitation. A single dopant may be used, or two or more dopants may be used in combination. Furthermore, a polymer or a monomer may be used. Examples of dopants include inorganic acids such as polyanions, boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0042] Examples of the polyanion include a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, and a substituted or unsubstituted polyester, and include a polymer consisting only of a structural unit having an anionic group, and a polymer consisting of a structural unit having an anionic group and a structural unit not having an anionic group. Specific examples of the polyanion include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0043] An example of the conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and hereinafter this conductive polymer will be referred to as PEDOT:PSS.

[0044] This solid electrolyte layer can be formed using a conductive polymer liquid. The conductive polymer liquid is a dispersion or solution in which a conductive polymer is dispersed or dissolved. In the solid electrolyte layer forming step, the anode body and cathode body, or a wound body formed by adding a separator to these, is immersed in the conductive polymer liquid to impregnate the wound body with the conductive polymer liquid. Alternatively, the conductive polymer liquid is applied to the anode body or the separator. The conductive polymer liquid may be immersed or applied once or multiple times. The wound body may be placed in a reduced pressure environment to be impregnated with the conductive polymer liquid.

[0045] The solid electrolyte layer contains a conductive polymer and a compound represented by the following formula (1), the chemical formula of which is C ７６ H ５２ O ４６ It also contains tannic acid.

[0046] In the solid electrolyte layer, the ratio of the conductive polymer (A) to the tannic acid (B) is A:B=100:185 or more by weight. Furthermore, when tannic acid is contained in the solid electrolyte layer, the weight of the conductive polymer is 0.003 mg / mm ３ More than 0.018 mg / mm ３ The following is the result.

[0047] When tannic acid is contained in the solid electrolyte layer together with the conductive polymer, the conductive polymer and tannic acid may chemically interact as follows, although this is not intended to be limiting: That is, during the polymerization process, a large amount of dopant, such as twice the molar amount of the conjugated polymer, may be added to disperse the conjugated polymer. Excess dopant that does not contribute to doping increases the ESR of the solid electrolytic capacitor because the dopant is insulating.

[0048] On the other hand, when tannic acid is added, hydrogen bonds are formed between the hydroxyl groups of the tannic acid and functional groups such as sulfo groups of the dopant. Alternatively, π-π interactions occur between the phenyl groups of the tannic acid and the benzene rings of the dopant. As a result, the insulating dopant is phase-separated from the conjugated polymer. Tannic acid phase-separates the dopant from the conjugated polymer and removes excess dopant.

[0049] This results in improved conductivity due to the structural change of the conjugated polymer, and a reduction in the ESR of the solid electrolytic capacitor. The structural change of the conjugated polymer refers to the change of the conjugated polymer from a coiled benzoid structure to a linear quinoid structure. The coiled benzoid structure is a low-conductivity structure, while the linear quinoid structure is a high-conductivity structure.

[0050] The interaction between the conductive polymer and tannic acid occurs when the weight of the conductive polymer is 0.003 mg / mm ３ More than 0.018 mg / mm ３ Unless the weight of the conductive polymer is below this range, it will not lead to a reduction in ESR. If the weight of the conductive polymer deviates above or below this range, the ESR will actually be higher than that of a solid electrolytic capacitor without tannic acid added to the solid electrolyte layer. This is speculation and not intended to be limiting, but tannic acid is a resistive material. However, above the lower limit of this conductive polymer weight range, the contribution of the conductive polymer's increased conductivity to lower ESR outweighs the adverse effect on ESR of tannic acid, which is a resistive material. On the other hand, if the weight of the conductive polymer exceeds the upper limit of the conductive polymer weight range, the amount of tannic acid relative to the conductive polymer becomes too small to completely convert the conjugated polymer into a highly conductive structure, resulting in a limit to the ESR improvement effect.

[0051] Furthermore, such an interaction between the conductive polymer and tannic acid does not lead to a significant ESR reduction effect unless the weight ratio of the conductive polymer (A) to the tannic acid (B) is A:B=100:185 or more. If the weight ratio of the conductive polymer (A) to the tannic acid (B) is less than A:B=100:185, the effect of reducing the ESR of the solid electrolytic capacitor is small.

[0052] Preferably, the weight ratio of the conductive polymer (A) to the tannic acid (B) is A:B = 100:185 to 100:1400. If the weight ratio of the conductive polymer (A) to the tannic acid (B) is A:B = 100:1400, further reduction in the ESR of the solid electrolytic capacitor cannot be expected. On the other hand, if the weight ratio of the conductive polymer (A) to the tannic acid (B) is more than A:B = 100:1400, the adverse effect of tannic acid on the ESR as a resistive material becomes significant.

[0053] Preferably, the weight of the conductive polymer is 0.005 mg / mm 3 per volume of the capacitor element. ３ 0.015mg / mm or more ３ Within this range, a large difference occurs in the effect of reducing the ESR of the solid electrolytic capacitor compared to when tannic acid is not contained in the solid electrolyte layer.

[0054] When a solid electrolyte layer is formed using a conductive polymer liquid, tannic acid may be included in the conductive polymer liquid as an additive. When the conductive polymer liquid is impregnated into or applied to a wound body or an anode body, the tannic acid contained in the conductive polymer liquid adheres to the wound body or the anode body together with the conductive polymer. In this case, the conductive polymer liquid contains a conductive polymer (A) and tannic acid (B) in a weight ratio of A:B=100:185 or more.

[0055] The solid electrolyte layer may further contain ethylene glycol, glycerin, or both. Ethylene glycol and glycerin change the higher-order structure of the conductive polymer and reorient the crystalline structure of the polymer chain. Therefore, ethylene glycol and glycerin improve the carrier mobility and the electrical conductivity of the conductive polymer. This further improves the ESR of the solid electrolytic capacitor.

[0056] Ethylene glycol, glycerin, or both are added to a conductive polymer liquid and impregnated into a capacitor element together with the conductive polymer liquid, thereby being incorporated into the solid electrolyte layer. The conductive polymer liquid is preferably adjusted so that the weight ratio of the conductive polymer (A) to the polyhydric alcohol (C), which is ethylene glycol, glycerin, or both, in the conductive polymer liquid is within the range of A:C = 1:9 to 1:54. Below this range, the beneficial effect of ethylene glycol and glycerin in improving the electrical conductivity of the conductive polymer cannot be obtained. Furthermore, ethylene glycol and glycerin have high viscosities. Therefore, above this range, combined with the high viscosity of tannic acid, the ease of impregnation with the conductive polymer liquid decreases, resulting in an increase in the ESR of the solid electrolytic capacitor.

[0057] Preferably, the ratio by weight of the conductive polymer (A) to the polyhydric alcohol (C), which is ethylene glycol, glycerin, or both, in the conductive polymer liquid is A:C=1:19 to 1:46. When a separator is impregnated with the conductive polymer liquid and then dried, the concentration of the conductive polymer in the central region of the separator tends to be low due to the coffee ring effect.

[0058] However, when the weight ratio of the conductive polymer (A) to the polyhydric alcohol (C), which is ethylene glycol, glycerin, or both, is set to A:C=1:19 or more, the coffee-ring effect is suppressed. Therefore, the concentration of the conductive polymer in the central region of the separator also increases. As a result, the conductive polymer is uniformly deposited between the anode and cathode bodies, further reducing the ESR of the solid electrolytic capacitor.

[0059] However, in order to strike a balance between the increase in viscosity due to the inclusion of ethylene glycol, glycerin, or both of these and the suppression of the coffee ring effect, the weight ratio of the conductive polymer (A) to the polyhydric alcohol (C) which is ethylene glycol, glycerin, or both of these is preferably A:C=1:46 or less. If this range is exceeded, the ESR of the solid electrolytic capacitor will start to increase, although it will still be suppressed by the effect of tannic acid.

[0060] The solid electrolyte layer may further contain sorbitol. Sorbitol also changes the higher-order structure of the conductive polymer and reorients the crystalline structure of the polymer chain. Therefore, sorbitol also improves the carrier mobility and the electrical conductivity of the conductive polymer. This further improves the ESR of the solid electrolytic capacitor.

[0061] In the solid electrolyte layer, the ratio of the conductive polymer (A) to the sorbitol (D) is within the range of A:D = 1:4 to 1:28 by weight. In particular, when the ratio of the conductive polymer (A) to the sorbitol (D) is A:D = 1:9 or more by weight, the ESR of the solid electrolytic capacitor is significantly improved. However, if the ratio is below this range, the beneficial effects of including sorbitol cannot be obtained. Furthermore, even if the amount of sorbitol is increased beyond this range, the beneficial effects of including sorbitol are not increased.

[0062] Ethylene glycol, glycerin, or sorbitol may be contained in the conductive polymer liquid. Ethylene glycol, glycerin, and sorbitol have high boiling points, so they can remain in the solid electrolyte layer even after the drying process.

[0063] The conductive polymer liquid may contain a dispersion medium or solvent, a pH adjuster, and additives in addition to the conductive polymer, tannic acid, ethylene glycol, glycerin, and sorbitol. The dispersion medium or solvent may be any one that disperses or dissolves conductive polymer particles or powder. The pH adjuster improves the acidity of the conductive polymer liquid so that the anode body, cathode body, and separator do not dissolve. Examples of additives include organic binders, surfactants, dispersants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0064] The dispersion medium or solvent for the conductive polymer liquid is not particularly limited as long as the conductive polymer is soluble or unlikely to aggregate and tannic acid is soluble in it. The dispersion medium or solvent for the conductive polymer liquid is water or a mixture of water and an organic solvent. Suitable examples of the organic solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, heterocyclic compounds, and nitrile compounds.

[0065] Examples of polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Examples of alcohols include methanol, ethanol, propanol, butanol, ethylene glycol, and glycerin. That is, ethylene glycol, glycerin, or both may be contained in the conductive polymer liquid as a dispersion medium or solvent for the conductive polymer liquid. Examples of esters include ethyl acetate, propyl acetate, and butyl acetate. Examples of hydrocarbons include hexane, heptane, benzene, toluene, and xylene. Examples of carbonate compounds include ethylene carbonate and propylene carbonate. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

[0066] Tannic acid may be contained in the conductive polymer liquid or may be impregnated into the solid electrolyte layer by a known method. For example, a tannic acid solution such as an aqueous or ethanolic solution of tannic acid may be prepared separately from the conductive polymer liquid, and the tannic acid may be impregnated into the capacitor element simultaneously with the conductive polymer liquid, at the latest before the conductive polymer liquid is dried.

[0067] (Electrolyte) The solid electrolytic capacitor may be a so-called hybrid type that uses an electrolytic solution in addition to a solid electrolyte layer. The electrolytic solution is a solution in which a solute is added to a solvent. The solute is an organic acid or its salt, an inorganic acid or its salt, or a complex compound of an organic acid and an inorganic acid or its salt, and is an ion-dissociable salt that dissociates into an anion component and a cation component. The solvent may be used alone or in combination of two or more types.

[0068] Examples of organic acids that serve as anionic solutes include carboxylic acids such as 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, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of the composite compound of an organic acid and an inorganic acid include borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0069] Furthermore, examples of at least one salt of an organic acid, an inorganic acid, or a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium 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 amidinium 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.

[0070] The solvent may be either a protic polar solvent or an aprotic polar solvent. Typical examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Typical examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0071] Furthermore, other additives can be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, borate esters, nitro compounds, phosphate esters, colloidal silica, and high-boiling-point solvents. These may be used alone or in combination. The nitro compounds suppress the generation of hydrogen gas within the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, and p-nitrophenol. The high-boiling-point solvent acts as a pressure resistance improver, and examples include polyols or derivatives thereof to which alkylene oxides have been added.

[0072] The capacitor element is immersed in the electrolyte solution, and the electrolyte solution is impregnated into the voids within the capacitor element. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte solution into smaller voids. The electrolyte solution impregnation process may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte solution may be injected into the capacitor element while pressurizing the electrolyte solution.

[0073] (Separator) The separator may be made of cellulose such as kraft, Manila hemp, esparto, hemp, rayon, or a mixture thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins; and these resins may be used alone or in combination.

[0074] The solid electrolytic capacitors of the examples will be described in more detail below, but the present invention is not limited to the examples described below.

[0075] (Examples 1-6) Solid electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 and 2 were fabricated. Examples 1 to 6 and Comparative Examples 1 and 2 used the same anode body and cathode body. The anode body was an aluminum anode foil, and the cathode body was an aluminum cathode foil. A surface-enlarging layer consisting of spongy etching pits was formed on the anode foil by etching. The anode foil was then subjected to a chemical conversion treatment to form a dielectric film. During the chemical conversion treatment, the anode foil was immersed in an aqueous ammonium borate solution at a liquid temperature of 85°C, and a constant current of 2 mA was applied until a voltage of 35 V was reached.

[0076] The cathode foil was a plain foil that had not been subjected to surface enlargement or chemical conversion treatment. A kraft paper separator was prepared, and the anode and cathode foils were stacked and wound together to form a wound capacitor. The capacitor element had a diameter of 8 mm, a length of 10 mm, and a theoretical capacitance of 150 μF.

[0077] This capacitor element was impregnated with a conductive polymer solution, resulting in conductive polymer particles adhering to the dielectric film of the anode foil, the cathode foil, and the inside of the separator. The conductive polymer solution was prepared as follows: PEDOT:PSS was used as the conductive polymer. PEDOT:PSS was added to water as a dispersion medium to prepare a conductive polymer dispersion with a conductive polymer concentration of 1.2 wt%. Ethylene glycol was added to the aqueous dispersion at a ratio of 10 wt% relative to the aqueous dispersion, and ammonia was added to adjust the pH to 4. Furthermore, 0 to 15 wt% of tannic acid was added to the dispersion depending on each example and comparative example, and ultrasonic dispersion treatment was performed for 5 minutes. Tannic acid was not added except for Comparative Example 1.

[0078] The conductive polymer solution was impregnated for 3 minutes in an environment reduced in pressure to 10 kPa. After impregnation with the conductive polymer solution, the capacitor element was dried for 10 minutes in an environment at a temperature of 60°C, and further dried at 120°C or 150°C. This produced a capacitor element in which a solid electrolyte layer was formed between the anode foil and the cathode foil.

[0079] The capacitor element is charged to a concentration of 0.005 mg / mm ３ The weight of the capacitor element was measured before and after impregnation with the conductive polymer solution, and the difference in weight between the capacitor element before and after impregnation was taken as the remaining amount of conductive polymer solution. The amount of PEDOT:PSS adhered was then calculated from the remaining amount and the concentration of the conductive polymer in the conductive polymer solution after preparation was completed.

[0080] The capacitor element was subjected to a repair chemical treatment. In the repair chemical treatment, the capacitor element was immersed in a boric acid aqueous solution at a liquid temperature of 85°C, and a voltage of 35 V was applied while passing a constant current of 2 mA, and the voltage was maintained for 20 minutes. Thereafter, the boric acid aqueous solution was washed off the wound body with pure water, and the wound body was dried in a temperature environment of 105°C.

[0081] The capacitor element was housed in an aluminum case with one end closed and the other end open. A rubber seal was inserted into the opening of the aluminum case, and the outside of the aluminum case was crimped to seal the capacitor element. The fabrication of the solid electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 and 2 was then completed.

[0082] (ESR Test 1) The ESR of the solid electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 and 2 was measured. The ESR was measured using an LCR meter (Agilent ZM2376, manufactured by NF Corporation). The ambient temperature during the measurement was 25°C, the DC bias was 1.5 V, the AC current level was a sine wave of 1.0 Vrms, and the measurement frequency was 100 kHz.

[0083] The amount of tannic acid added and the ESR change rate for each example and comparative example were calculated, and the amount of tannic acid added, the ESR change rate, and the ESR measurement results are shown in Table 1 below. The amount of tannic acid added is the weight content of tannic acid when the weight content of PEDOT:PSS in the solid electrolyte layer is taken as 100. The ESR change rate is the ESR ratio when the ESR of Comparative Example 1 is taken as 100.

[0084] (Table 1)

[0085] Based on Table 1 above, the relationship between the amount of tannic acid added and the rate of change in ESR is shown in the graph of Figure 1. As shown in Table 1 above and Figure 1, in Examples 1 to 6 in which the amount of tannic acid added, i.e., the content ratio of conductive polymer (A) to tannic acid (B) was A:B = 100:185 or more by weight, the ESR was reduced to 75% or less compared to Comparative Example 1 in which no tannic acid was added.

[0086] (Examples 7-12) Solid electrolytic capacitors were fabricated in Examples 7 to 12, Comparative Examples 3 and 4, and Comparative Examples 5 to 12. The anode bodies, cathode bodies, and separators in Examples 7 to 12 and Comparative Examples 3 to 12 were the same as those in Examples 1 to 6. The conductive polymer solutions in Examples 7 to 12 and Comparative Examples 3 to 12 were prepared as follows: An aqueous dispersion with a PEDOT:PSS concentration of 2.0 wt % was prepared. Ethylene glycol and water were added to this aqueous dispersion, and the PEDOT:PSS concentration was adjusted to a range of 0.2 to 1.8 wt %, which varied for each of Examples 7 to 12 and Comparative Examples 3 to 12.

[0087] Ammonia was added to adjust the pH to 4. Furthermore, 5 wt % of tannic acid was added to the dispersions of Examples 7 to 12 and Comparative Examples 3 and 4, and ultrasonic dispersion treatment was performed for 5 minutes. That is, the amount of tannic acid added was the same in Examples 7 to 12 and Comparative Examples 3 and 4, but the amount of conductive polymer was different. On the other hand, tannic acid was not added to the dispersions of Comparative Examples 5 to 12.

[0088] The conductive polymer solutions of Comparative Example 3 and Comparative Example 5, Comparative Example 4 and Comparative Example 6, Example 7 and Comparative Example 7, Example 8 and Comparative Example 8, Example 9 and Comparative Example 9, Example 10 and Comparative Example 10, Example 11 and Comparative Example 11, and Example 12 and Comparative Example 12 have the same PEDOT:PSS concentration in the range of 0.2 to 1.8 wt %, but are distinguished by the presence or absence of tannic acid.

[0089] The conductive polymer solution was impregnated for 3 minutes in an environment reduced in pressure to 10 kPa. After impregnation with the conductive polymer solution, the capacitor element was dried for 10 minutes in an environment at a temperature of 60°C, and further dried at 120°C or 150°C. This produced a capacitor element in which a solid electrolyte layer was formed between the anode foil and the cathode foil.

[0090] The capacitor elements were repaired under the same conditions and by the same method as in Examples 1 to 6. The capacitor elements were housed in an aluminum case with one end closed and the other end open. A rubber seal was inserted into the opening of the aluminum case, and the outside of the aluminum case was crimped to seal the capacitor elements. The solid electrolytic capacitors of Examples 7 to 12 and Comparative Examples 3 and 4 were then fabricated.

[0091] (ESR Test Part 2) The ESR of the solid electrolytic capacitors of Examples 7 to 12 and Comparative Examples 3 to 12 was measured. The ESR measurement method and conditions were the same as those of Examples 1 to 6. The amount of PEDOT:PSS per volume of the capacitor element (hereinafter referred to as conductive polymer) was calculated, and Table 2 below shows the conductive polymer, ESR change rate, and ESR measurement results for Comparative Examples 3 and 4 and Examples 7 to 12. Table 3 below also shows the conductive polymer and ESR measurement results for Comparative Examples 5 to 12.

[0092] (Table 2)

[0093] (Table 3)

[0094] Based on Tables 2 and 3 above, the relationship between the conductive polymer and the ESR is shown in the graph of Figure 2, dividing the results into those with and without tannic acid. In Figure 2, the plots with filled circles represent the series containing tannic acid of Comparative Examples 3 and 4 and Examples 7 to 12. In Figure 2, the plots with open circles represent the series without tannic acid of Comparative Examples 5 to 12. Based on Table 2 above, the relationship between the conductive polymer and the rate of change in ESR is shown in the graph of Figure 3.

[0095] As shown in Tables 2 and 3 above and FIG. 2, the weight of the conductive polymer is 0.003 mg / mm ３ When the concentration of tannic acid in the solid electrolyte layer is less than 100%, the ESR is actually higher when tannic acid is added to the solid electrolyte layer. As shown in Figure 3, when tannic acid is added to the solid electrolyte layer, the ESR increases to 140% compared to when tannic acid is not added.

[0096] On the other hand, as shown in FIG. 2, the weight of the conductive polymer is 0.003 mg / mm ３ In this case, the inclusion of tannic acid in the solid electrolyte layer reduces the ESR. As shown in Figure 3, when tannic acid is included in the solid electrolyte layer, the ESR is reduced to 75% or less compared to when tannic acid is not included.

[0097] However, as shown in FIGS. 2 and 3, the weight of the conductive polymer is 0.018 mg / mm ３ In this case, even if tannic acid is contained in the solid electrolyte layer, an advantageous ESR is not obtained. ３ If the content is less than this, the effect of reducing the ESR due to the inclusion of tannic acid in the solid electrolyte layer is exerted, and the ESR is lower than that of a solid electrolytic capacitor not containing tannic acid in the solid electrolyte layer.

[0098] 1 to 3, it was confirmed that simply adding tannic acid to the solid electrolyte layer does not result in a solid electrolytic capacitor with a low ESR. First, tannic acid must be included in the solid electrolyte layer, second, the weight ratio of the conductive polymer (A) to the tannic acid (B) in the solid electrolyte layer must be A:B=100:185 or more, and third, the weight of the conductive polymer must be 0.003 mg / mm3 or less per volume of the capacitor element. ３ More than 0.018 mg / mm ３ It was confirmed that by satisfying these conditions, the solid electrolytic capacitor has a low ESR.

[0099] In particular, as shown in FIG. 3, the weight of the conductive polymer is 0.005 mg / mm ３ Above, 0.015mg / mm ３ It was confirmed that in the following ranges, the ESR was reduced to 50% or less compared to when tannic acid was not contained in the solid electrolyte layer.

[0100] (Examples 13-17) Solid electrolytic capacitors of Examples 13 to 17 were fabricated. The anode body, cathode body, and separator of Examples 13 to 17 were the same as those of Examples 1 to 6. The conductive polymer solution of Examples 13 to 17 had a different amount of ethylene glycol added than that of Example 1, and the amount of ethylene glycol contained in the solid electrolyte layer was different from that of Example 1. The solid electrolytic capacitors of Examples 13 to 17 were fabricated using the same method and conditions as those of Examples 13 to 17, except that they were fabricated using conductive polymer solutions with different ethylene glycol contents.

[0101] The conductive polymer liquid of Example 1 was prepared so that the ethylene glycol content was 10 wt % relative to the total amount of the conductive polymer liquid. The conductive polymer liquid of Example 13 had 20 wt % ethylene glycol added relative to the total amount of the conductive polymer liquid. The conductive polymer liquid of Example 14 had 30 wt % ethylene glycol added relative to the total amount of the conductive polymer liquid. The conductive polymer liquid of Example 15 had 40 wt % ethylene glycol added relative to the total amount of the conductive polymer liquid. The conductive polymer liquid of Example 16 had 50 wt % ethylene glycol added relative to the total amount of the conductive polymer liquid. The conductive polymer liquid of Example 17 had 58 wt % ethylene glycol added relative to the total amount of the conductive polymer liquid. The amount of solvent in the conductive polymer liquid was not changed, and instead of increasing or decreasing ethylene glycol, the water content was increased or decreased.

[0102] In the conductive polymer solution of Example 1, the content ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C = 1:9.3 by weight. In the conductive polymer solution of Example 13, the content ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C = 1:18.5 by weight. In the conductive polymer solution of Example 14, the content ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C = 1:27.8 by weight. In the conductive polymer solution of Example 15, the content ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C = 1:37.0 by weight. In the conductive polymer solution of Example 16, the content ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C = 1:46.3 by weight. In the conductive polymer solution of Example 17, the weight ratio of the conductive polymer (A) to the ethylene glycol (C) was A:C=1:53.7.

[0103] (ESR Test Part 3) The ESR of the solid electrolytic capacitors of Examples 13 to 17 was measured. The ESR measurement method and conditions were the same as those of Example 1. Table 4 below shows the ESR measurement results and ESR change rates for Comparative Example 1, Examples 1, and 13 to 17. The ESR change rates are ESR ratios when the ESR of Comparative Example 1 is set to 100. Furthermore, based on Table 4 below, the relationship between the amount of ethylene glycol and ESR is shown in FIG. 4.

[0104] (Table 4)

[0105] As shown in Table 4 above and in Example 1 and Examples 13 to 17 in FIG. 4, even without increasing the amount of tannic acid, the content ratio of the conductive polymer (A) to the tannic acid (B) in the solid electrolyte layer is A:B=100:185 or more by weight, and the weight of the conductive polymer is 0.003 mg / mm ３ More than 0.018 mg / mm ３ If it is equal to or less than this, the ESR of the solid electrolytic capacitor can be kept low.

[0106] It has been confirmed that the ESR of the solid electrolytic capacitor can be kept low when the weight ratio of the conductive polymer (A) to the ethylene glycol (C) in the conductive polymer solution is at least A:C=1:9 to 1:54.

[0107] Moreover, Example 13 has a lower ESR than Example 1, and Example 14 has a lower ESR than Example 13. That is, up to a content ratio A:C of 1:27.8 between the conductive polymer (A) and ethylene glycol (C), the ESR of the solid electrolytic capacitor decreases as the ethylene glycol content increases. It can be confirmed that the coffee ring effect is suppressed to a high degree, and the effect of ethylene glycol in improving the conductivity of the conductive polymer is efficiently achieved.

[0108] However, Example 15 has a higher ESR than Example 14. That is, when the content ratio of conductive polymer (A) to ethylene glycol (C) A:C becomes equal to or greater than 1:37.0, the ESR of the solid electrolytic capacitor increases with the increase in the ethylene glycol content. It can be confirmed that the conductivity-enhancing effect of the conductive polymer and the degree of suppression of the coffee-ring effect, as well as the increase in viscosity of the conductive polymer solution due to the increase in the amount of ethylene glycol, affect the ESR of the solid electrolytic capacitor.

[0109] However, the solid electrolytic capacitors of Examples 14 to 16 are in a range in which a particularly low ESR is maintained. From this, it was confirmed that when the content ratio of the conductive polymer (A) to the ethylene glycol (C) is within the range of A:C = 1:19 to 1:46 by weight, the conductive polymer's effect of improving conductivity and the degree of suppression of the coffee ring effect are strongly exhibited, the adverse effects of an increase in the viscosity of ethylene glycol are suppressed, and in particular, the ESR of the solid electrolytic capacitor is further suppressed.

[0110] (Examples 18-25) Solid electrolytic capacitors of Examples 18 to 25 were fabricated. The anode body, cathode body, and separator of Examples 18 to 25 were the same as those of Examples 13 and 15. However, the conductive polymer solution of Examples 13 and 15 did not contain sorbitol. In contrast, the conductive polymer solution of Examples 18 to 22 had the same ethylene glycol content as that of Example 13, but differed from Example 13 in that it contained sorbitol. The conductive polymer solution of Examples 23 to 25 had the same ethylene glycol content as that of Example 15, but differed in that it contained sorbitol.

[0111] The solid electrolytic capacitors of Examples 18 to 25 were produced using conductive polymer solutions with different sorbitol contents, and were produced using the same method and conditions as those of Examples 13 or 15. The amount of solvent in the conductive polymer solution was not changed, and instead of increasing or decreasing ethylene glycol, the amount of water was increased or decreased.

[0112] To the conductive polymer solution of Example 18, 1 wt % of sorbitol was added relative to the total amount of the conductive polymer solution. To the conductive polymer solution of Example 19, 5 wt % of sorbitol was added relative to the total amount of the conductive polymer solution. To the conductive polymer solution of Example 20, 10 wt % of sorbitol was added relative to the total amount of the conductive polymer solution. To the conductive polymer solution of Example 21, 20 wt % of sorbitol was added relative to the total amount of the conductive polymer solution. To the conductive polymer solution of Example 22, 30 wt % of sorbitol was added relative to the total amount of the conductive polymer solution.

[0113] 1 wt % of sorbitol was added to the conductive polymer solution of Example 23, 10 wt % of sorbitol was added to the conductive polymer solution of Example 24, and 18 wt % of sorbitol was added to the conductive polymer solution of Example 25.

[0114] These conductive polymer solutions were impregnated into capacitor elements, and the capacitor elements were dried for 10 minutes in a 60°C environment and then further dried at 120°C or 150°C. As a result, in the solid electrolyte layer of the solid electrolytic capacitor of Example 18, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:0.93 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 19, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:4.63 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 20, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:9.26 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 21, the content ratio of the conductive polymer (A) to the sorbitol (D) in the solid electrolyte layer was A:D = 1:18.52 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 22, the content ratio of the conductive polymer (A) to the sorbitol (D) in the solid electrolyte layer was A:D = 1:27.78 by weight.

[0115] In the solid electrolyte layer of the solid electrolytic capacitor of Example 23, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:0.93 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 24, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:9.26 by weight. In the solid electrolyte layer of the solid electrolytic capacitor of Example 25, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:16.67 by weight.

[0116] (ESR Test No. 4) The ESR of the solid electrolytic capacitors of Examples 18 to 25 was measured. The ESR measurement method and conditions were the same as those of Example 1. Tables 5 and 6 below show the ESR measurement results and ESR change rates for Comparative Example 1 and Examples 13, 15, and 18 to 25. The ESR change rates are ESR ratios when the ESR of Comparative Example 1 is set to 100.

[0117] (Table 5)

[0118] (Table 6)

[0119] Based on Tables 5 and 6 above, the relationship between the amount of sorbitol and ESR is shown in Figure 5. The series of Examples listed in Table 5 are plotted with black circles, and the series of Examples listed in Table 6 are plotted with triangles.

[0120] As shown in Tables 5 and 6 above and FIG. 5 , the difference in ESR between Example 13 and Example 18, and the difference in ESR between Example 15 and Example 23, are small. However, Example 19 has an ESR change rate improved by 10% or more compared to Example 13, and the ESR is lower. In Example 19, the content ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer is A:D = 1:4 by weight. This confirms that the ESR of the solid electrolytic capacitor can be further reduced when the content ratio of the conductive polymer (A) to sorbitol (D) is A:D = 1:4 by weight or more.

[0121] Moreover, Example 20 has an approximately 20% improvement in ESR change rate and a decrease in ESR compared to Examples 13 and 15. Similarly, Example 24 has a difference of 2.38 mΩ, nearly ten times the difference in ESR between Example 23 and Example 15, which was 0.26 mΩ. In Examples 20 and 24, the weight ratio of the conductive polymer (A) to sorbitol (D) in the solid electrolyte layer was A:D = 1:9.26.

[0122] However, the difference in ESR between Examples 21 and 22 and Example 20 is small, and the difference between Example 25 and Example 24 is small. That is, it was confirmed that when the content ratio of conductive polymer (A) to sorbitol (D) is in the range of A:D = 1:28 or less by weight, an ESR reduction effect commensurate with the sorbitol content is achieved. This confirmed that the ESR of the solid electrolytic capacitor is kept particularly low when the content ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:9 to 1:28 by weight.

Claims

1. A capacitor element comprising: an anode body having a dielectric film; a cathode body facing the anode body; a solid electrolyte layer interposed between the anode body and the cathode body; and the anode body, the cathode body, and the solid electrolyte layer, wherein the solid electrolyte layer contains a conductive polymer and tannic acid, the content ratio of the conductive polymer (A) to the tannic acid (B) in the solid electrolyte layer is A:B=100:185 or more by weight, and the weight of the conductive polymer is 0.003 mg / mm ３ More than 0.018 mg / mm ３ 1. A solid electrolytic capacitor comprising:

2. The solid electrolytic capacitor according to claim 1, wherein the ratio by weight of the conductive polymer (A) and the tannic acid (B) in the solid electrolyte layer is A:B=100:185 to 100:1400.

3. The weight of the conductive polymer is 0.005 mg / mm ３ 0.015mg / mm or more ３ 2. The solid electrolytic capacitor according to claim 1, wherein:

4. The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer contains ethylene glycol, glycerin, or both.

5. The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer contains sorbitol.

6. The solid electrolytic capacitor according to claim 5, wherein the ratio by weight of the conductive polymer (A) and the sorbitol (D) in the solid electrolyte layer is A:D=1:4 to 1:

28.

7. The solid electrolytic capacitor according to any one of claims 1 to 6, further comprising an electrolyte.

8. An element forming step of forming a capacitor element having the anode body, the cathode body and the solid electrolyte layer by forming a solid electrolyte layer between an anode body having a dielectric film and a cathode body using a conductive polymer solution in which conductive polymer particles are dispersed, the conductive polymer solution containing a conductive polymer and tannic acid, the conductive polymer solution containing the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B of 100:185 or more, and in the element forming step, the conductive polymer is added to the solid electrolyte layer in an amount of 0.003 mg / mm ３ More than 0.018 mg / mm ３ The method for producing a solid electrolytic capacitor, comprising the steps of:

9. The method for producing a solid electrolytic capacitor according to claim 8, wherein the conductive polymer solution contains the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B=100:185 to 100:1400.

10. The conductive polymer is added to the solid electrolyte layer in an amount of 0.005 mg / mm ３ 0.015mg / mm or more ３ The method for producing a solid electrolytic capacitor according to claim 8, wherein the content is the following by weight:

11. The method for producing a solid electrolytic capacitor according to claim 8, wherein the conductive polymer liquid contains a polyhydric alcohol which is ethylene glycol, glycerin or both of these, and the content ratio of the conductive polymer (A) to the polyhydric alcohol (C) is A:C=1:9 to 1:54 by weight.

12. The method for producing a solid electrolytic capacitor according to any one of claims 8 to 11, further comprising the step of impregnating the capacitor element with an electrolyte.

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