Solid electrolytic capacitor and manufacturing method

Abstract

The invention provides a solid electrolytic capacitor with low equivalent series resistance and a manufacturing method. A solid electrolytic capacitor includes an anode body having a dielectric film, a cathode body facing the anode body, and a solid electrolyte layer interposed between the anode body and the cathode body. The capacitor element overlaps an anode body and a cathode body with a solid electrolyte layer interposed therebetween. The solid electrolyte layer contains a conductive polymer and tannic acid. The content ratio of the conductive polymer (A) to the tannic acid (B) is A: B = 100: 185 or more in terms of weight ratio, and the weight of the conductive polymer is 0.003 mg / mm3 or more and 0.018 mg / mm3 or less relative to the volume of the capacitor element. The solid electrolyte layer is formed using a conductive polymer liquid in which conductive polymer particles are dispersed. The conductive polymer liquid contains a conductive polymer and tannic acid in the above weight ratio.

Description

Technical Field

[0001] This invention relates to solid electrolytic capacitors and methods for manufacturing them. Background Technology

[0002] Electrolytic capacitors have a valve-acting metal such as tantalum or aluminum as the anode and cathode foils. The anode foil is enlarged by shaping the valve-acting metal into a sintered body or etched foil, and a dielectric coating layer is formed on the enlarged surface. An electrolyte is present between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil, functioning as the actual cathode.

[0003] Capacitors are used in a variety of applications. For example, in the field of power electronics, in power supply circuits that convert AC power to DC power using a converter circuit and then convert the DC power back to the required AC power using an inverter circuit, smoothing capacitors are used to suppress and smooth the DC output from the converter circuit before it is input to the inverter circuit. Additionally, decoupling capacitors are placed near semiconductor switching elements such as gallium nitride (GaN) to ensure stable operation and reduce noise. Furthermore, with the increasing power requirements in the field of power electronics, the demand for high-capacitance capacitors is increasing.

[0004] In this respect, electrolytic capacitors can increase their specific surface area by expanding the anode foil, giving them the advantage of easily achieving large capacitance compared to other types of capacitors such as film capacitors. Electrolytic capacitors contain an electrolyte in the form of a liquid. The increased contact area between the electrolyte and the dielectric coating of the anode foil allows for a larger capacitance in electrolytic capacitors.

[0005] To improve capacitance, a method of adding tannic acid to the electrolyte has been proposed (see, for example, Patent Document 1). It is believed that tannic acid dissolves the oxide coating of the anode, thus increasing the initial capacitance of the electrolytic capacitor. Furthermore, a method has also been proposed to add tannic acid together with a phosphorus oxyacid ion-forming compound to the electrolyte (see, for example, Patent Document 2). Tannic acid acts as a chelating agent, forming a water-soluble aluminum chelate complex. This complex further binds with phosphate ions. By forming this complex, the dissolution of the alumina coating caused by phosphoric acid is inhibited, thereby suppressing the increase in leakage current.

[0006] In recent years, solid electrolytic capacitors using solid electrolytes with higher conductivity than liquid electrolytes have become widespread (see, for example, Patent Document 3). Solid electrolytic capacitors are small and have high capacitance; by using solid electrolytes with higher conductivity than liquid electrolytes, they can achieve low equivalent series resistance (ESR). Manganese dioxide and 7,7,8,8-tetracyanoquinone dimethane (TCNQ) complexes are known as solid electrolytes.

[0007] As solid electrolytes, manganese dioxide and 7,7,8,8-tetracyanoquinone dimethane (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 exhibit slow reaction rates and excellent adhesion to dielectric coatings, have rapidly gained popularity as solid electrolytes. These conductive polymers utilize acidic compounds such as polyanions as dopants, and also possess partial structures within the monomer molecule that function as dopants, exhibiting high conductivity.

[0008] Solid electrolytic capacitors, in addition to having low equivalent series resistance, do not have the advantage of long lifespan due to the electrolyte evaporating and drying out over time. However, in order to provide the dielectric coating with a repair function and reduce the leakage current of solid electrolytic capacitors, so-called hybrid solid electrolytic capacitors that combine conductive polymers and electrolytes are becoming increasingly popular.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2002-110470

[0012] Patent Document 2: Japanese Patent Application Publication No. 2012-84568

[0013] Patent Document 3: Japanese Patent Application Publication No. 2011-60980 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] If the equivalent series resistance (ESR) of a solid electrolytic capacitor is high, the capacitor will heat up, causing thermal degradation of the conductive polymer and thus shortening its lifespan. Therefore, the allowable ripple current of a solid electrolytic capacitor is limited by its ESR. When using solid electrolytic capacitors in voltage smoothing circuits of power converters, a large number of capacitors are connected in parallel to handle the ripple current. Therefore, solid electrolytic capacitors with lower ESRs are desirable.

[0016] Furthermore, if a solid electrolytic capacitor has a high ESR, the voltage drop caused by ESR occurs during the capacitor's discharge, and the voltage rise caused by ESR occurs during its charging. In other words, the solid electrolytic capacitor causes voltage fluctuations. Therefore, a solid electrolytic capacitor with a high ESR has reduced voltage smoothing capability.

[0017] The present invention is proposed to solve the above-mentioned problems, and its purpose is to provide a solid electrolytic capacitor with low equivalent series resistance and a method for manufacturing it.

[0018] Methods for solving problems

[0019] To address the aforementioned issues, the solid electrolytic capacitor of this embodiment comprises: an anode having a dielectric coating, a cathode opposite to the anode, a solid electrolyte layer between the anode and the cathode, and a capacitor element comprising the anode, the cathode, and the solid electrolyte layer. The solid electrolyte layer contains a conductive polymer and tannic acid. Within the solid electrolyte layer, the ratio of the conductive polymer (A) to the tannic acid (B) is at least A:B = 100:185 by weight, and the weight of the conductive polymer relative to the volume of the capacitor element is 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 the following.

[0020] Within the solid electrolyte layer, the ratio of the conductive polymer (A) to the tannic acid (B) by weight can be A:B = 100:185 to 100:1400.

[0021] The weight of the conductive polymer relative to the volume of the capacitor element can be 0.005 mg / mm². 3 Above and 0.015 mg / mm 3 the following.

[0022] The solid electrolyte layer may contain ethylene glycol, glycerol, or both.

[0023] The solid electrolyte layer may contain sorbitol.

[0024] Within the solid electrolyte layer, the ratio of the conductive polymer (A) to the sorbitol (D) by weight can be A:D = 1:4 to 1:28.

[0025] It may also include electrolyte.

[0026] Furthermore, to address the aforementioned issues, the method for manufacturing a solid electrolytic capacitor according to this embodiment includes an element forming step of forming a capacitor element having the anode, the cathode, and the solid electrolyte layer by forming a solid electrolyte layer between an anode and a cathode having a dielectric coating using a conductive polymer liquid in which conductive polymer particles are dispersed. The conductive polymer liquid comprises a conductive polymer (A) and tannic acid (B), and the conductive polymer liquid contains the conductive polymer and the tannic acid in a weight ratio of A:B = 100:185 or higher. In the element forming step, the solid electrolyte layer contains 0.003 mg / mm³ of the solid electrolyte layer relative to the volume of the capacitor element. 3 Above and 0.018 mg / mm3 The following weight includes the conductive polymer.

[0027] The conductive polymer liquid may contain the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B = 100:185 to 100:1400.

[0028] In the solid electrolyte layer, the concentration can be 0.005 mg / mm³ relative to the volume of the capacitor element. 3 Above and 0.015 mg / mm 3 The following weight includes the conductive polymer.

[0029] The conductive polymer liquid may contain ethylene glycol, glycerol, or both, i.e., polyols, and the ratio of the conductive polymer (A) to the polyol (C) by weight is A:C = 1:9 to 1:54.

[0030] Electrolyte may be impregnated in the capacitor element.

[0031] Invention Effects

[0032] According to the present invention, solid electrolytic capacitors achieve low ESR. Attached Figure Description

[0033] Figure 1 A graph showing the relationship between the amount of tannic acid added and the rate of change in ESR.

[0034] Figure 2 The graph shows the relationship between conductive high molecular weight and ESR, with and without the addition of tannic acid.

[0035] Figure 3 A graph showing the relationship between conductive high molecular weight and ESR change rate.

[0036] Figure 4 A graph showing the relationship between ethylene glycol content and ESR.

[0037] Figure 5 A graph showing the relationship between sorbitol content and ESR. Detailed Implementation

[0038] The following describes the solid electrolytic capacitor and its manufacturing method according to the embodiments. It should be noted that the present invention is not limited to the embodiments described below.

[0039] (Solid electrolytic capacitor)

[0040] Solid electrolytic capacitors are passive components that utilize the dielectric polarization of a dielectric film to obtain capacitance for charge storage and discharge. The solid electrolytic capacitor includes a capacitor element. The capacitor element includes an anode, a cathode, and a solid electrolyte layer. A dielectric film is formed on the anode. The anode and cathode sandwich the solid electrolyte layer. The solid electrolyte layer is located between the dielectric film of the anode and the cathode, and is tightly sealed to the dielectric film of the anode, functioning as the true cathode. The electrolyte in the solid electrolytic capacitor may include a solid electrolyte layer and an electrolyte solution. The electrolyte solution is impregnated in the voids of the capacitor element where the solid electrolyte layer is formed.

[0041] A separator may be present between the anode and cathode. The separator maintains the solid electrolyte layer. Furthermore, the separator prevents short circuits between the anode and cathode. The solid electrolyte layer maintains its shape on its own; when the solid electrolyte layer isolates the anode and cathode, the separator can be omitted from the configuration of the solid electrolytic capacitor.

[0042] Solid electrolytic capacitors are classified into, for example, multilayer, wound, and flat types. In the multilayer type, the anode body and cathode body are alternately stacked, sandwiching a separator. In the wound type, the anode body and cathode body are wound together, sandwiching a separator. In the flat type, a solid electrolyte layer and a cathode body are stacked on the anode body.

[0043] (Electrode)

[0044] The anode and cathode are foils made of a valve-acting metal. The foil can be formed by stretching the valve-acting metal or by sintering powdered valve-acting metal. Valve-acting metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Regarding the purity of the valve-acting metal, for the anode, 99.9% or higher is preferred; for the cathode, 99% or higher is preferred, and it may contain silicon, iron, copper, magnesium, zinc, etc.

[0045] In wound electrolytic capacitors, the anode is a strip-shaped anode foil, while in stacked and flat electrolytic capacitors, the anode is a flat anode foil. An expansion layer is formed on one or both sides of the anode. This expansion layer can be an etched layer (where the foil has been etched), a sintered layer (where valve-acting metal powder has been sintered), or a vapor-deposited layer (where valve-acting metal particles have been deposited onto the foil). In other words, the expansion layer has a porous structure, consisting of tunnel-like pits, sponge-like pits, or dense gaps between powders or particles.

[0046] The dielectric coating is formed on one or both sides of the anode body where the extended surface layer has been formed. When the extended surface layer has been formed, it is formed on the surface of the extended surface layer along its unevenness. 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 alumina layer formed by oxidizing the surface of the extended surface layer. In the formation process for forming the dielectric coating, a voltage is applied to the anode body in a formation solution, with the desired withstand voltage as the target. The formation solution is a solution in which halide ions are absent, such as a phosphoric acid-based formation solution like ammonium dihydrogen phosphate, a boric acid-based formation solution like ammonium borate, or an adipic acid-based formation solution like ammonium adipate.

[0047] Regarding the cathode, in the case of wound-type electrolytic capacitors, a stretched cathode foil made of valve-acting metal is preferred. An expansion layer is formed in the cathode, similar to that formed in the anode. A flat foil without an expansion layer can also be used as the cathode. The cathode may have a natural oxide coating or a thin oxide coating of approximately 1–10 Vfs formed through a chemical formation process. The natural oxide coating is formed by the reaction of the cathode with oxygen in the air.

[0048] Furthermore, a conductive layer can be provided in the cathode body. As a conductive layer, it is sufficient that it mainly contains inorganic materials or inorganic compounds. Examples of inorganic materials or inorganic compounds include titanium, zirconium, tantalum, niobium, their nitrides or carbides, aluminum carbide, carbon materials, and their composites or mixtures.

[0049] In the case of a multilayer electrolytic capacitor, the cathode is preferably a laminate of a metal layer and a carbon layer. The carbon layer of the cathode is positioned facing the anode. The carbon layer is formed by preparing a paste, coating the electrolyte layer onto the anode, and then curing it by heating. The metal layer, for example, is a silver layer, which is prepared as a paste, coated onto the carbon layer, and then cured by heating.

[0050] (Solid electrolyte layer)

[0051] The solid electrolyte layer is a layer containing conductive polymers. These conductive polymers are either self-doped conjugated polymers doped with intramolecular dopants or conjugated polymers doped with external dopants. Conjugated polymers are obtained through chemical oxidative polymerization or electrolytic oxidative polymerization of monomers or their derivatives possessing π-conjugated double bonds. The dopants or external dopants act as electron acceptors or electron donors, thus giving the conductive polymers high conductivity.

[0052] As a conjugated polymer, known conjugated polymers can be used without particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylidene, poly(phenylene oxide), and polythiophene vinylidene. These conjugated polymers can be used alone or in combination of two or more, and can be copolymers of two or more monomers.

[0053] Among the aforementioned conjugated polymers, conjugated polymers polymerized from thiophene or its derivatives are preferred, especially those polymerized from 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothiophene[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or their derivatives. As thiophene derivatives, compounds selected from thiophenes having substituents at the 3 and 4 positions are preferred, where the substituents at the 3 and 4 positions of the thiophene ring can form a ring together with the carbons at the 3 and 4 positions. The alkyl and alkoxy groups preferably have 1 to 16 carbon atoms.

[0054] Polymers of 3,4-ethylenedioxythiophene, known as EDOT, are particularly preferred, namely poly(3,4-ethylenedioxythiophene) known as PEDOT. Furthermore, substituents can be added to 3,4-ethylenedioxythiophene. For example, alkylated ethylenedioxythiophene with alkyl groups having 1 to 5 carbon atoms can be used as substituents. Examples of alkylated ethylenedioxythiophene 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.

[0055] Dopant can be any known substance without particular limitation. Dopant can be used alone or in combination of two or more. In addition, polymers or monomers can be used. Examples of dopant include inorganic acids such as polyanionic acid, boric acid, nitric acid, and phosphoric acid, as well as organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, stearic acid, rosin acid, crotonic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borosilicate, bis(oxalato)boronic acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0056] Polyanionic compounds include, for example, substituted or unsubstituted polyalkylene compounds, substituted or unsubstituted polyolefin compounds, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters. Examples include polymers containing only structural units with anionic groups, and polymers composed of structural units with and without anionic groups. Specifically, examples of polyanionic compounds include polyvinylsulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylamide sulfonic acid, polymethacrylamide sulfonic acid, poly(2-acryloylamino-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0057] As a conductive polymer, an example is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate, which will be referred to as PEDOT:PSS below.

[0058] This solid electrolyte layer can be formed using a conductive polymer liquid. The conductive polymer liquid is a dispersion or solution of conductive polymers. In the solid electrolyte layer formation process, the anode and cathode bodies, or a wound body with spacers added therein, are immersed in the conductive polymer liquid, so that the conductive polymer liquid is impregnated in the wound body. Additionally, the conductive polymer liquid is coated onto the anode body or spacers. The conductive polymer liquid can be applied once or multiple times. The wound body can be placed under reduced pressure while impregnating with the conductive polymer liquid.

[0059] In the solid electrolyte layer, along with the conductive polymer, there is also a component represented by the following formula (1), with the chemical formula C. 76 H 52 O 46 Tannic acid.

[0060] [Chemistry 1]

[0061]

[0062] Within the solid electrolyte layer, the weight ratio of conductive polymer (A) to tannic acid (B) is A:B = 100:185 or higher. Furthermore, when tannic acid is included in the solid electrolyte layer, the weight of the conductive polymer relative to the volume of the capacitor element is 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 the following.

[0063] While speculative, it is not limited to the inclusion of tannic acid within the solid electrolyte layer along with conductive polymers. The conductive polymers and tannic acid exhibit the chemical interactions described below. Specifically, during polymerization, dopants are sometimes added in large quantities, sometimes at a molar ratio of twice the amount of the conjugated polymer, to disperse the conjugated polymer. The excess dopant that is not involved in doping, being an insulating agent, increases the ESR of the solid electrolytic capacitor.

[0064] On the other hand, if tannic acid is added, hydrogen bonds are formed between the hydroxyl groups of tannic acid and functional groups such as the sulfonyl groups of the dopant. Alternatively, π-π interactions are formed between the phenyl groups of tannic acid and the benzene rings of the dopant. As a result, the insulating dopant separates from the conjugated polymer phase. Tannic acid separates the dopant from the conjugated polymer phase, removing excess dopant.

[0065] Therefore, by achieving increased conductivity due to structural changes in conjugated polymers, the ESR of solid electrolytic capacitors can be reduced. The structural change in conjugated polymers refers to the transformation of the conjugated polymer from a coil-like benzene structure to a linear quinone structure. The coil-like benzene structure has low conductivity, while the linear quinone structure has high conductivity.

[0066] Furthermore, regarding the interaction between such a conductive polymer and tannic acid, if the weight of the conductive polymer relative to the volume of the capacitor element is not 0.003 mg / mm², 3 Above and 0.018 mg / mm 3 Below this range, there is no decrease in ESR. If the weight of the conductive polymer deviates significantly from this range, the ESR increases compared to a solid electrolytic capacitor without added tannic acid within the solid electrolyte layer. This is speculative, but not limited to, as tannic acid is a resistive material. However, if the weight exceeds the lower limit of the conductive polymer's weight range, the contribution of the high conductivity of the conductive polymer to the resulting low ESR outweighs the adverse effect of tannic acid as a resistive material on ESR. On the other hand, if the weight exceeds the upper limit of the conductive polymer's weight range, the amount of tannic acid relative to the conductive polymer decreases, failing to completely transform the conjugated polymer into a highly conductive structure, thus creating a limit to the ESR improvement effect.

[0067] Furthermore, regarding the interaction between such a conductive polymer and tannic acid, if the weight ratio of conductive polymer (A) to tannic acid (B) is not greater than A:B = 100:185, it will not lead to a significant reduction in ESR. If the weight ratio of conductive polymer (A) to tannic acid (B) is less than A:B = 100:185, the reduction in ESR of the solid electrolytic capacitor will be small.

[0068] Preferably, the weight ratio of the conductive polymer (A) to tannic acid (B) is A:B = 100:185 to 100:1400 or less. If the weight ratio of the conductive polymer (A) to tannic acid (B) is A:B = 100:1400, further ESR reduction in the solid electrolytic capacitor cannot be expected. On the other hand, if the weight ratio of the conductive polymer (A) to tannic acid (B) is greater than A:B = 100:1400, the adverse effect of tannic acid as a resistive material on ESR becomes greater.

[0069] Preferably, the weight of the conductive polymer relative to the volume of the capacitor element is 0.005 mg / mm². 3 Above and 0.015 mg / mm 3 Below. If it falls within this range, there will be a significant difference in the ESR reduction effect of solid electrolytic capacitors compared to the case where there is no tannic acid in the solid electrolyte layer.

[0070] When using a conductive polymer solution to form a solid electrolyte layer, tannic acid can be included as an additive in the conductive polymer solution. When the conductive polymer solution is impregnated or coated onto a winding or anode body, the tannic acid in the conductive polymer solution adheres to the winding or anode body along with the conductive polymer. In this case, the conductive polymer solution contains conductive polymer (A) and tannic acid (B) in a weight ratio of A:B = 100:185 or higher.

[0071] The solid electrolyte layer can be further incorporated with ethylene glycol, glycerol, or both. Ethylene glycol and glycerol alter the higher-order structure of the conductive polymer and, in addition, reorient the crystal structure of the polymer chains. Therefore, ethylene glycol and glycerol increase carrier mobility and improve the conductivity of the conductive polymer. Moreover, the ESR of the solid electrolytic capacitor is further improved.

[0072] Ethylene glycol, glycerol, or both are added to a conductive polymer solution, and the capacitor element is impregnated with the conductive polymer solution, thereby being contained within a solid electrolyte layer. Preferably, the conductive polymer solution is adjusted so that the weight ratio of the conductive polymer (A) to the polyol (C), i.e., ethylene glycol, glycerol, or both, is within the range of A:C = 1:9 to 1:54. If the ratio is below this range, the beneficial effect of increased conductivity from the conductive polymers produced by ethylene glycol and glycerol is not achieved. Furthermore, ethylene glycol and glycerol have high viscosity. Therefore, if the ratio is above this range, combined with the high viscosity of tannic acid, the ease of impregnation with the conductive polymer solution decreases, and the ESR of the solid electrolytic capacitor increases.

[0073] Preferably, in the conductive polymer liquid, the content ratio of conductive polymer (A) to ethylene glycol, glycerol, or both, i.e., polyol (C), is within the range of A:C = 1:19 to 1:46 by weight. When the conductive polymer liquid is impregnated in the separator and dried, due to the coffee ring effect, the concentration of conductive polymer in the central band of the separator tends to decrease.

[0074] However, if the weight ratio of the conductive polymer (A) to ethylene glycol, glycerol, or both (i.e., polyols, C) is greater than 1:19, the coffee ring effect is suppressed. Consequently, the concentration of the conductive polymer in the central band of the separator also increases. As a result, the conductive polymer adheres uniformly between the anode and cathode, further reducing the ESR of the solid electrolytic capacitor.

[0075] However, based on the balance between the increase in viscosity caused by the inclusion of ethylene glycol, glycerol, or both and the suppression of the coffee ring effect, the weight ratio of the conductive polymer (A) to ethylene glycol, glycerol, or both, i.e., polyol (C), is preferably A:C = 1:46 or less. If this range is exceeded, although the ESR of the solid electrolytic capacitor is still suppressed by the effect of tannic acid, the ESR of the solid electrolytic capacitor begins to rise.

[0076] Furthermore, sorbitol can be further incorporated into the solid electrolyte layer. Sorbitol also causes a higher-order structural change in the conductive polymer, and further reorients the crystal structure of the polymer chains. Therefore, sorbitol also increases carrier mobility and the conductivity of the conductive polymer. Moreover, the ESR of the solid electrolytic capacitor is further improved.

[0077] Within the solid electrolyte layer, the weight ratio of the conductive polymer (A) to sorbitol (D) is in the range of 1:4 to 1:28. Specifically, if the weight ratio of the conductive polymer (A) to sorbitol (D) is 1:9 or higher, the ESR of the solid electrolytic capacitor is significantly improved. However, if it is below this range, the beneficial effect of containing sorbitol is not obtained. Furthermore, even if sorbitol is contained beyond this range, the effect of containing sorbitol does not increase.

[0078] The presence of ethylene glycol, glycerol, or sorbitol in conductive polymer liquids is preferable. Ethylene glycol, glycerol, and sorbitol, due to their high boiling points, can remain in the solid electrolyte layer even after the drying process.

[0079] In conductive polymeric liquids, in addition to the conductive polymer, tannic acid, ethylene glycol, glycerol, and sorbitol, a dispersion medium or solvent, a pH adjuster, and additives may be included. Regarding the dispersion medium or solvent, any dispersion or dissolution of the conductive polymer particles or powder is sufficient. The pH adjuster improves the acidity of the conductive polymeric liquid by ensuring that the anodic, cathodic, and separator components remain insoluble. Examples of additives include, for instance, organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, and UV absorbers.

[0080] Regarding the dispersion medium or solvent of the conductive polymer liquid, there are no particular limitations as long as the conductive polymer is soluble or difficult to aggregate, and tannic acid is soluble. The dispersion medium or solvent of the conductive polymer liquid is water, or a mixture of water and an organic solvent. Examples of preferred organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, heterocyclic compounds, and nitrile compounds.

[0081] 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 glycerol. That is, ethylene glycol, glycerol, or both can be used as dispersion media or solvents in conductive polymeric liquids. 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-oxazolinone. Examples of nitrile compounds include acetonitrile, glutaronitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

[0082] In the case of tannic acid, besides being contained in conductive polymer liquids, it can be impregnated into solid electrolyte layers using known methods. For example, a tannic acid solution, such as an aqueous solution or an ethanol solution, can be prepared separately from the conductive polymer liquid, and can be impregnated into the capacitor element simultaneously with the conductive polymer liquid, at the latest before the conductive polymer liquid is dried.

[0083] (Electrolyte)

[0084] Solid electrolytic capacitors can be so-called hybrid types, where an electrolyte is used in addition to a solid electrolyte layer. The electrolyte 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 organic and inorganic acids or its salt, and is an ionic dissociation salt that dissociates into anionic and cationic components. Solvents are used alone or in combination of two or more.

[0085] Organic acids that become anionic components as solutes include oxalic acid, succinic acid, glutaric acid, pimelic acid, octanoic 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, 2,4-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, gallic acid, gentianic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, etc., as well as carboxylic acids, phenols, and sulfonic acids. Additionally, inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphite, carbonic acid, and silicic acid. Examples of compounds that are complex compounds of organic and inorganic acids include borosilicate, borosilicate oxalic acid, borosilicate diethanolic acid, borosilicate dimalonic acid, borosilicate disuccinic acid, borosilicate diadipic acid, borosilicate diazolic acid, borosilicate dibenzoic acid, borosilicate dimaleic acid, borosilicate dilactic acid, borosilicate dimalic acid, borosilicate ditartaric acid, borosilicate dicitric acid, borosilicate diphthalic acid, borosilicate di(2-hydroxy)isobutyric acid, borosilicate di(2,4-dihydroxybenzoic acid), borosilicate dimethylsalicylic acid, borosilicate dinaphtholic acid, borosilicate dimandelic acid, and borosilicate di(3-hydroxy)propionic acid.

[0086] In addition, salts of at least one of organic acids, inorganic acids, and complex compounds of organic and inorganic acids include, for example, ammonium salts, quaternary ammonium salts, quaternary amidine salts, amine salts, sodium salts, and potassium salts. Quaternary ammonium ions, as quaternary ammonium salts, include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Quaternary amidine salts include ethyldimethylimidazolium and tetramethylimidazolium. Amine salts include salts of primary amines, secondary amines, and tertiary amines. Primary amines include methylamine, ethylamine, and propylamine; secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine; and tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0087] In terms of solvents, both protic and non-protic polar solvents are acceptable. Examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and hydroxyl alcohols. Examples of non-protic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0088] Furthermore, other additives can be added to the electrolyte. Examples of additives include complexes of boric acid with polysaccharides (mannitol, sorbitol, etc.), complexes of boric acid with polyols, borate esters, nitro compounds, phosphate esters, colloidal silica, and high-boiling-point solvents. These can be used individually or in combination of two or more. 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. High-boiling-point solvents act as voltage withstand enhancers; examples include polyols with added olefin oxides or their derivatives.

[0089] Regarding the electrolyte, it is applied by immersing the capacitor element in the electrolyte, thereby impregnating the voids within the capacitor element. To impregnate even finer voids, depressurization or pressurization can be performed as needed. The electrolyte impregnation process can be repeated multiple times. For example, the internal pressure of the capacitor element can be reduced, while the electrolyte is simultaneously pressurized and injected into the capacitor element.

[0090] (Separator)

[0091] The separators are made of cellulose and its mixtures, such as kraft paper, Manila hemp, esparto grass, hemp, rayon, etc.; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and their derivatives; polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins; aliphatic polyamides, semi-aromatic polyamides, fully aromatic polyamides and other polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins, etc. These resins can be used alone or in combination.

[0092] Example

[0093] The solid electrolytic capacitors of the embodiments will now be described in more detail. However, the present invention is not limited to the embodiments described below.

[0094] (Examples 1-6)

[0095] 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 common anode and cathode bodies. The anode body was an aluminum anode foil, and the cathode body was an aluminum cathode foil. For the anode foil, an etch process was used to form an expanded layer consisting of sponge-like etch pits. Next, a dielectric coating was formed by performing a formation process on the anode foil. During the formation process, the anode foil was immersed in an ammonium borate aqueous solution at a liquid temperature of 85°C, and a constant current of 2mA was applied while a voltage was applied until the voltage reached 35V.

[0096] The cathode foil is a flat foil that has not undergone any surface enlargement or formation treatment. A wound structure is created by overlapping and winding the anode and cathode foils through kraft paper separators. The capacitor element has a diameter of 8 mm and a length of 10 mm, with a theoretical capacitance of 150 μF.

[0097] By impregnating the capacitor element with a conductive polymer liquid, the conductive polymer particles are attached to the dielectric coating of the anode foil, the cathode foil, and the separator. The preparation of the conductive polymer liquid is as follows: PEDOT:PSS is used as the conductive polymer. PEDOT:PSS is added to water as the dispersion medium to prepare a conductive polymer dispersion with a concentration of 1.2 wt%. Ethylene glycol is added to the aqueous dispersion at a ratio of 10 wt%, and ammonia is added to bring the pH to 4. Furthermore, 0–15 wt% tannic acid is added to the dispersion according to each example and comparative example, and ultrasonic dispersion is performed for 5 minutes. Only in Comparative Example 1 was tannic acid not added.

[0098] The conductive polymer solution is impregnated for 3 minutes under reduced pressure of 10 kPa. After impregnation, the capacitor element is dried at 60°C for 10 minutes, and then dried at 120°C or 150°C. This process produces a capacitor element with a solid electrolyte layer formed between the anode and cathode foils.

[0099] In the capacitor element, there is an adhering material with a volume relative to the capacitor element of 0.005 mg / mm². 3 PEDOT:PSS was prepared. The weight of the capacitor element was measured before and after impregnation with the conductive polymer liquid, and the weight difference of the capacitor element before and after impregnation was taken as the residual amount of conductive polymer liquid. Furthermore, the amount of PEDOT:PSS attached was calculated from the residual amount and the concentration of conductive polymer in the prepared conductive polymer liquid.

[0100] Repair formation is performed on the capacitor element. In the repair formation, the capacitor element is immersed in a boric acid aqueous solution at 85°C, and a constant current of 2mA is applied while a voltage is maintained until the voltage reaches 35V for 20 minutes. Then, the boric acid aqueous solution is rinsed from the winding body with pure water, and dried at 105°C.

[0101] The capacitor element is housed in an aluminum casing with a bottom at one end and an opening at the other. A sealing rubber is inserted into the opening of the aluminum casing, and the outer side of the aluminum casing is tightened to seal the capacitor element. Thus, the solid electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 and 2 are manufactured.

[0102] (One of the ESR trials)

[0103] The ESR of the solid electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 and 2 was measured. For ESR, an LCR meter (MF Circuit Design Block, Agilent ZM2376) was used. The ambient temperature during measurement was 25°C, the DC bias was set to 1.5V, the AC current level was set to a 1.0Vrms sine wave, and the measurement frequency was set to 100kHz.

[0104] The amount of tannic acid added and the ESR change rate for each example and each comparative example were calculated, and the tannic acid addition amount, ESR change rate, and ESR measurement results are shown in Table 1 below. The amount of tannic acid added is the weight of tannic acid when the weight of PEDOT:PSS in the solid electrolyte layer is set to 100. The ESR change rate is the ESR ratio when the ESR of Comparative Example 1 is set to 100.

[0105] (Table 1)

[0106]

[0107] Based on Table 1 above, the relationship between the amount of tannic acid added and the ESR change rate is shown in Table 1. Figure 1 The coordinate graph. As shown in Table 1 above and Figure 1 As shown, in Examples 1 to 6, where the amount of tannic acid added, i.e. the ratio of conductive polymer (A) to tannic acid (B) by weight is A:B = 100:185 or more, the ESR was reduced to below 75% compared to Comparative Example 1, which did not contain tannic acid.

[0108] (Examples 7-12)

[0109] Solid electrolytic capacitors of Examples 7 to 12, Comparative Examples 3 and 4, and Comparative Examples 5 to 12 were fabricated. The anode, cathode, and separator of Examples 7 to 12 and Comparative Examples 3 to 12 were common to those of Examples 1 to 6. The preparation of the conductive polymer liquid of Examples 7 to 12 and Comparative Examples 3 to 12 is as follows. That is, 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 concentration of PEDOT:PSS varied in Examples 7 to 12 and Comparative Examples 3 to 12, ranging from 0.2 to 1.8 wt%.

[0110] Ammonia was added to achieve a pH of 4. Furthermore, 5 wt% tannic acid was added to the dispersions of Examples 7 to 12 and Comparative Examples 3 and 4, and the mixtures were subjected to ultrasonic dispersion treatment for 5 minutes. That is, the amount of tannic acid added was consistent in Examples 7 to 12 and Comparative Examples 3 and 4, but the amount of conductive polymer differed. On the other hand, no tannic acid was added to the dispersions of Comparative Examples 5 to 12.

[0111] For the conductive polymer liquids of Comparative Examples 3 and 5, 4 and 6, 7 and 7, 8 and 8, 9 and 9, 10 and 10, 11 and 11, 12 and 12, the concentration of PEDOT:PSS between each pair is the same in the range of 0.2 to 1.8 wt%, but there is a difference in the presence or absence of tannic acid.

[0112] The conductive polymer solution is impregnated for 3 minutes under reduced pressure of 10 kPa. After impregnation, the capacitor element is dried at 60°C for 10 minutes, and then dried at 120°C or 150°C. This process produces a capacitor element with a solid electrolyte layer formed between the anode and cathode foils.

[0113] For the capacitor element, repair formation was performed using the same method and under the same conditions as in Examples 1 to 6. The capacitor element was housed in an aluminum casing with a bottom at one end and an opening at the other. A sealing rubber was inserted into the opening of the aluminum casing, and the outer side of the aluminum casing was tightened to seal the capacitor element. Furthermore, the solid electrolytic capacitors of Examples 7 to 12 and Comparative Examples 3 and 4 were thus completed.

[0114] (ESR Experiment 2)

[0115] The ESR of the solid electrolytic capacitors of Examples 7 to 12 and Comparative Examples 3 to 12 was measured. The methods and conditions for ESR measurement were the same as those for Examples 1 to 6. The amount of PEDOT:PSS relative to the volume of the capacitor element (hereinafter referred to as conductive high molecular weight) was calculated, and the conductive high molecular weight, ESR change rate, and ESR measurement results involved in Comparative Examples 3 and 4 and Examples 7 to 12 are shown in Table 2 below. In addition, the conductive high molecular weight and ESR measurement results involved in Comparative Examples 5 to 12 are shown in Table 3 below.

[0116] (Table 2)

[0117]

[0118] (Table 3)

[0119]

[0120] Based on Tables 2 and 3 above, the relationship between conductive high molecular weight and ESR is divided into tannic acid addition and no tannic acid addition, as shown in Tables 2 and 3 above. Figure 2 In the coordinate graph. Figure 2 In the diagram, the black circles mark the series containing tannic acid, including Comparative Examples 3 and 4, and Examples 7 to 12. Additionally, in... Figure 2In the diagram, the white circles represent the series of Comparative Examples 5 to 12 without added tannic acid. Furthermore, based on Table 2 above, the relationship between conductive high molecular weight and ESR change rate is shown. Figure 3 In the coordinate graph.

[0121] As shown in Table 2 above, Table 3 above and Figure 2 As shown, the conductivity of the high molecular weight polymer relative to the volume of the capacitor element is less than 0.003 mg / mm². 3 In the case of tannins in the solid electrolyte layer, the ESR increases. For example... Figure 3 As shown, when the solid electrolyte layer contains tannic acid, the ESR increases by 140% compared to the case without tannic acid.

[0122] On the other hand, such as Figure 2 As shown, if the conductivity of the high molecular weight polymer relative to the volume of the capacitor element is 0.003 mg / mm², 3 The above method reduces ESR by including tannins in the solid electrolyte layer. For example... Figure 3 As shown, when the solid electrolyte layer contains tannic acid, the ESR decreases to below 75% compared to the case without tannic acid.

[0123] However, as Figure 2 and Figure 3 As shown, if the conductivity of the high molecular weight polymer relative to the volume of the capacitor element is 0.018 mg / mm², 3 Even with the presence of tannic acid in the solid electrolyte layer, a favorable ESR was not achieved. This was only possible with a high molecular weight relative to the volume of the capacitor element being 0.018 mg / mm². 3 The following utilizes the low ESR effect generated by the presence of tannic acid in the solid electrolyte layer, resulting in a lower ESR compared to solid electrolytic capacitors without tannic acid in the solid electrolyte layer.

[0124] Thus, Tables 1 to 3 and Figures 1 to 3 In summary, it was confirmed that adding tannic acid only to the solid electrolyte layer did not result in a low ESR in solid electrolytic capacitors. It was confirmed that: first, tannic acid was present in the solid electrolyte layer; second, the weight ratio of the conductive polymer (A) to tannic acid (B) in the solid electrolyte layer was A:B = 100:185 or higher; and third, the weight of the conductive polymer relative to the volume of the capacitor element was 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 The following conditions are met, thus solid electrolytic capacitors achieve low ESR.

[0125] In particular, such as Figure 3As shown, it was confirmed that if the conductive high molecular weight relative to the volume of the capacitor element is 0.005 mg / mm², 3 Above and 0.015 mg / mm 3 In the following range, compared to the case where there is no tannic acid in the solid electrolyte layer, the ESR is reduced to below 50%.

[0126] (Examples 13-17)

[0127] Solid electrolytic capacitors of Examples 13 to 17 were fabricated. The anode, cathode, and separator of Examples 13 to 17 are common to those of Examples 1 to 6. Regarding the conductive polymer liquid of Examples 13 to 17, the amount of ethylene glycol added differs from that of Example 1, and the amount of ethylene glycol contained in the solid electrolyte layer also differs from that of Example 1. The solid electrolytic capacitors of Examples 13 to 17 were fabricated using the same method and manufacturing conditions, except that they used conductive polymer liquids with different ethylene glycol contents.

[0128] The conductive polymer liquid of Example 1 was prepared with ethylene glycol accounting for 10 wt% of the total conductive polymer liquid. In the conductive polymer liquid of Example 13, 20 wt% ethylene glycol was added relative to the total conductive polymer liquid. In the conductive polymer liquid of Example 14, 30 wt% ethylene glycol was added relative to the total conductive polymer liquid. In the conductive polymer liquid of Example 15, 40 wt% ethylene glycol was added relative to the total conductive polymer liquid. In the conductive polymer liquid of Example 16, 50 wt% ethylene glycol was added relative to the total conductive polymer liquid. In the conductive polymer liquid of Example 17, 58 wt% ethylene glycol was added relative to the total conductive polymer liquid. It should be noted that the amount of solvent in the conductive polymer liquid remained constant, instead of adjusting the amount of water by increasing or decreasing the amount of ethylene glycol.

[0129] In the conductive polymer liquid of Example 1, the weight ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:9.3. In the conductive polymer liquid of Example 13, the weight ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:18.5. In the conductive polymer liquid of Example 14, the weight ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:27.8. In the conductive polymer liquid of Example 15, the weight ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:37.0. In the conductive polymer liquid of Example 16, the weight ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:46.3. In the conductive polymer liquid of Example 17, the ratio of conductive polymer (A) to ethylene glycol (C) by weight is A:C = 1:53.7.

[0130] (ESR Experiment 3)

[0131] The ESR of the solid electrolytic capacitors in Examples 13 to 17 was measured. The methods and conditions for ESR measurement were the same as in Example 1. Table 4 below shows the ESR measurement results and ESR change rates for Comparative Example 1, Example 1, and Examples 13 to 17. The ESR change rate is the ESR ratio 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. Figure 4 .

[0132] (Table 4)

[0133]

[0134] As shown in Table 4 above and Figure 4 As shown in Examples 1 and 13 to 17, even without increasing the amount of tannic acid, as long as the weight ratio of conductive polymer (A) to tannic acid (B) in the solid electrolyte layer is A:B = 100:185 or higher, the weight of the conductive polymer relative to the volume of the capacitor element is 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 The following approach will suppress the ESR of solid electrolytic capacitors to a low level.

[0135] It can be confirmed that in a conductive polymer liquid, as long as the weight ratio of conductive polymer (A) to ethylene glycol (C) is at least A:C = 1:9 to 1:54, the ESR of the solid electrolytic capacitor will be suppressed to a low level.

[0136] Furthermore, compared to Example 1, Example 13 exhibited a lower ESR, and compared to Example 13, Example 14 exhibited a lower ESR. That is, up to a conductivity polymer (A) to ethylene glycol (C) content ratio of A:C = 1:27.8, the higher the ethylene glycol content ratio, the lower the ESR of the solid electrolytic capacitor. This confirms a high degree of suppression of the coffee ring effect and efficient utilization of the conductivity-enhancing effect of the conductivity polymer produced by ethylene glycol.

[0137] However, Example 15 exhibits a higher ESR compared to Example 14. Specifically, if the ratio of conductive polymer (A) to ethylene glycol (C) is A:C = 1:37.0 or higher, the ESR of the solid electrolytic capacitor increases with the increase in the ethylene glycol content. It can be confirmed that, in addition to the conductivity-enhancing effect of the conductive polymer and the degree of suppression of the coffee ring effect, the increase in viscosity of the conductive polymer liquid accompanying the increase in ethylene glycol content also affects the ESR of the solid electrolytic capacitor.

[0138] In particular, the solid electrolytic capacitors of Examples 14 to 16 maintain a particularly low ESR range. It has been confirmed that as long as the weight ratio of the conductive polymer (A) to ethylene glycol (C) is within the range of A:C = 1:19 to 1:46, the conductivity-enhancing effect of the conductive polymer and the suppression of the coffee ring effect are strongly exerted, the adverse effects of increased viscosity of ethylene glycol are suppressed, and especially the ESR of the solid electrolytic capacitor is suppressed even lower.

[0139] (Examples 18-25)

[0140] Solid electrolytic capacitors of Examples 18 to 25 were fabricated. The anode, cathode, and separator of Examples 18 to 25 were common to those of Examples 13 and 15. However, the conductive polymer liquids of Examples 13 and 15 did not contain sorbitol. The conductive polymer liquids of Examples 18 to 22 had the same ethylene glycol content as Example 13, but differed from Example 13 in that they contained sorbitol. The conductive polymer liquids of Examples 23 to 25 had the same ethylene glycol content as Example 15, but differed from Example 15 in that they contained sorbitol.

[0141] Furthermore, the solid electrolytic capacitors of Examples 18 to 25 were manufactured under the same method and manufacturing conditions as those of Examples 13 or 15, except that they were made using conductive polymer liquids with different sorbitol contents. It should be noted that the amount of solvent in the conductive polymer liquid remained unchanged, while the amount of water was adjusted instead of adding or subtracting ethylene glycol.

[0142] In the conductive polymer liquid of Example 18, 1 wt% sorbitol was added relative to the total amount of the conductive polymer liquid. In the conductive polymer liquid of Example 19, 5 wt% sorbitol was added relative to the total amount of the conductive polymer liquid. In the conductive polymer liquid of Example 20, 10 wt% sorbitol was added relative to the total amount of the conductive polymer liquid. In the conductive polymer liquid of Example 21, 20 wt% sorbitol was added relative to the total amount of the conductive polymer liquid. In the conductive polymer liquid of Example 22, 30 wt% sorbitol was added relative to the total amount of the conductive polymer liquid.

[0143] In the conductive polymer liquid of Example 23, 1 wt% sorbitol was added relative to the total amount of conductive polymer liquid. In the conductive polymer liquid of Example 24, 10 wt% sorbitol was added relative to the total amount of conductive polymer liquid. In the conductive polymer liquid of Example 25, 18 wt% sorbitol was added relative to the total amount of conductive polymer liquid.

[0144] The capacitor elements were immersed in these conductive polymer liquids and dried at 60°C for 10 minutes, followed by drying at 120°C or 150°C. As a result, in the solid electrolyte layer of the solid electrolytic capacitor of Example 18, the weight ratio of conductive polymer (A) to sorbitol (D) was A:D = 1:0.93. In the solid electrolyte layer of the solid electrolytic capacitor of Example 19, the weight ratio of conductive polymer (A) to sorbitol (D) was A:D = 1:4.63. In the solid electrolyte layer of the solid electrolytic capacitor of Example 20, the weight ratio of conductive polymer (A) to sorbitol (D) was A:D = 1:9.26. In the solid electrolyte layer of the solid electrolytic capacitor of Example 21, the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:18.52. In the solid electrolyte layer of the solid electrolytic capacitor of Example 22, the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:27.78.

[0145] In the solid electrolyte layer of the solid electrolytic capacitor of Example 23, the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:0.93. In the solid electrolyte layer of the solid electrolytic capacitor of Example 24, the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:9.26. In the solid electrolyte layer of the solid electrolytic capacitor of Example 25, the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:16.67.

[0146] (ESR Experiment 4)

[0147] The ESR of the solid electrolytic capacitors of Examples 18 to 25 was measured. The methods and conditions for ESR measurement were the same as those for Example 1. The ESR measurement results and ESR change rates for Comparative Example 1, Examples 13, 15, 18 to 25 are shown in Tables 5 and 6 below. The ESR change rate is the ESR ratio when the ESR of Comparative Example 1 is set to 100.

[0148] (Table 5)

[0149]

[0150] (Table 6)

[0151]

[0152] Based on Tables 5 and 6 above, the relationship between sorbitol content and ESR is shown in... Figure 5 The series of embodiments described in Table 5 are plotted with black circles, while the series of embodiments described in Table 6 are plotted with triangles.

[0153] As shown in Tables 5 and 6 above, and Figure 5 As shown, the differences in ESR between Examples 13 and 18, and between Examples 15 and 23, are small. However, in Example 19, the rate of change in ESR is increased by more than 10% compared to Example 13, resulting in a decrease in ESR. In Example 19, the weight ratio of conductive polymer (A) to sorbitol (D) in the solid electrolyte layer is A:D = 1:4. This confirms that as long as the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:4 or higher, the ESR of the solid electrolytic capacitor can be suppressed to a lower level.

[0154] Furthermore, compared to Example 13, Example 20 showed an approximately 20% increase in ESR change rate and a decrease in ESR. Compared to Example 24, the difference in ESR between Example 23 and Example 15 was 0.26 mΩ, representing a nearly tenfold difference of 2.38 mΩ compared to the ESR of Example 15. In Examples 20 and 24, the weight ratio of the conductive polymer (A) to sorbitol (D) within the solid electrolyte layer was A:D = 1:9.26.

[0155] However, the differences in ESR between Examples 21 and 22 and Example 20 are small, as are the differences between Examples 25 and Example 24. That is, it was confirmed that when the weight ratio of conductive polymer (A) to sorbitol (D) is below A:D = 1:28, an ESR reduction effect consistent with the sorbitol content is observed. Therefore, it was confirmed that as long as the weight ratio of conductive polymer (A) to sorbitol (D) is A:D = 1:9 to 1:28, the ESR of the solid electrolytic capacitor is suppressed to a particularly low level.

Claims

1. A solid electrolytic capacitor, characterized in that, have: Anode with dielectric coating, The cathode body opposite to the anode body, The solid electrolyte layer between the anode and the cathode, and A capacitor element comprising the anode, the cathode, and the solid electrolyte layer. The solid electrolyte layer comprises a conductive polymer and tannic acid. Within the solid electrolyte layer, the ratio of the conductive polymer (A) to the tannic acid (B) by weight is A:B = 100:185 or higher. The weight of the conductive polymer relative to the volume of the capacitor element is 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 the following.

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

3. The solid electrolytic capacitor according to claim 1, characterized in that, The weight of the conductive polymer relative to the volume of the capacitor element is 0.005 mg / mm². 3 Above and 0.015 mg / mm 3 the following.

4. The solid electrolytic capacitor according to claim 1, characterized in that, The solid electrolyte layer contains ethylene glycol, glycerol, or both.

5. The solid electrolytic capacitor according to claim 1, characterized in that, The solid electrolyte layer contains sorbitol.

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

28.

7. The solid electrolytic capacitor according to any one of claims 1 to 6, characterized in that, It also contains an electrolyte.

8. A method for manufacturing a solid electrolytic capacitor, characterized in that, include: A capacitor element is formed by forming a solid electrolyte layer between an anode and a cathode having a dielectric coating using a conductive polymer liquid in which conductive polymer particles are dispersed, thereby forming the anode, the cathode, and the solid electrolyte layer. The conductive polymer liquid comprises a conductive polymer (A) and tannic acid (B), and the conductive polymer liquid contains the conductive polymer (A) and the tannic acid (B) in a weight ratio of A:B = 100:185 or higher. In the element formation process, in the solid electrolyte layer, the volume relative to the capacitor element is 0.003 mg / mm². 3 Above and 0.018 mg / mm 3 The following weight includes the conductive polymer.

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

10. The method for manufacturing a solid electrolytic capacitor according to claim 8, characterized in that, In the solid electrolyte layer, the volume relative to the capacitor element is 0.005 mg / mm². 3 Above and 0.015 mg / mm 3 The following weight includes the conductive polymer.

11. The method for manufacturing a solid electrolytic capacitor according to claim 8, characterized in that, The conductive polymer liquid contains ethylene glycol, glycerol, or both, i.e., polyols. The ratio of the conductive polymer (A) to the polyol (C) by weight is A:C = 1:9 to 1:

54.

12. A method for manufacturing a solid electrolytic capacitor according to any one of claims 8 to 11, characterized in that, The capacitor element is impregnated with electrolyte.

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