Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor capable of favorably suppressing leakage current by using a non-liquid component for a defect portion of a dielectric film.SOLUTION: The electrolytic capacitor includes: an anode body with a dielectric film; a cathode body facing the anode body; and an electrolyte layer interposed between the anode body and the cathode body. The electrolyte layer includes a conductive polymer and a plastic crystal. The plastic crystal contains boron in a molecular structure and does not contain halogen in the molecular structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Electrolytic capacitors use valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil is enlarged by forming a powder sintered layer made of valve metal powder on the foil surface, or by etching the foil. The enlarged surface has a dielectric coating. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil and functions as the true cathode.

[0003] Capacitors are used in a variety of applications. In all applications, there is a growing demand for higher capacitance. In this regard, electrolytic capacitors have the advantage that the specific surface area can be increased by expanding the surface of the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors such as film capacitors. Furthermore, electrolytic capacitors contain electrolyte in the form of an electrolytic solution. The contact area of the electrolytic solution with the dielectric film on the anode foil increases. This makes it easier to further increase the capacitance of electrolytic capacitors.

[0004] In recent years, solid electrolytic capacitors that use a solid electrolyte as the electrolyte have become widespread as electrolytic capacitors (see, for example, Patent Document 1). Because solid electrolytic capacitors use a highly conductive solid electrolyte, they can be miniaturized, have a large capacity, and have a low equivalent series resistance (ESR). In addition to being small, having a large capacity, and having a low equivalent series resistance, solid electrolytic capacitors also have other characteristics, such as being easy to fabricate into chips and being suitable for surface mounting, making them essential for miniaturizing, improving functionality, and reducing the cost of electronic devices.

[0005] Known examples of solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. In recent years, conductive polymers have rapidly become popular as solid electrolytes. Conductive polymers are derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT has a slow reaction rate and excellent adhesion to dielectric films. Conductive polymers use acid compounds such as polyanions as dopants, and the monomer molecules contain substructures that act as dopants, resulting in high conductivity and promoting low ESR in electrolytic capacitors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2007 / 091656 Summary of the Invention [Problem to be solved by the invention]

[0007] However, solid electrolytes have poor repair properties for defects in the dielectric film, which can lead to increased leakage current. So-called hybrid electrolytic capacitors have been proposed, in which the voids in the capacitor element are impregnated with an electrolytic solution or an ionic liquid. However, it is also desirable for the solid electrolyte itself to have the ability to suppress leakage current.

[0008] The present invention has been proposed to solve the above-mentioned problems, and its object is to provide an electrolytic capacitor and a manufacturing method that can effectively suppress leakage current by using a non-liquid component in defective parts of a dielectric film. [Means for solving the problem]

[0009] In order to solve the above problems, the electrolytic capacitor of the present embodiment includes an anode body having a dielectric coating, a cathode body facing the anode body, and an electrolyte layer interposed between the anode body and the cathode body, wherein the electrolyte layer includes a conductive polymer and a plastic crystal, and the plastic crystal includes boron in its molecular structure but does not include a halogen in its molecular structure.

[0010] The anion component of the plastic crystal is a chelate complex consisting of a polydentate ligand which is an organic compound having the boron and at least two hydroxyl groups in its molecular structure, and sp 2 It may have a double bond formed by a hybrid orbital.

[0011] The anode body may have a deposit containing boron and carbon deposited on at least a portion of the anode body.

[0012] The cationic component of the plastic crystal may be a quaternary ammonium cation.

[0013] The anion component of the plastic crystal may be a bis(salicylate)borate anion, and the cation component of the plastic crystal may be an N-ethyl-N-methylpyrrolidinium cation, a tetramethylammonium anion, or a spiropyrrolidinium cation.

[0014] The plastic crystal may be an ionic organic material having a solid-solid transition point, ionic conductivity, and a melting point lower than room temperature. The solid-solid transition point occurs at a lower temperature than the melting point during the temperature rise process in differential scanning calorimetry (DSC), and is the point at which a negative peak occurs in the value of heat flow per unit weight.

[0015] The conductive polymer may have π conjugation.

[0016] The conductive polymer may include poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid.

[0017] In order to solve the above problems, the manufacturing method of the electrolytic capacitor of this embodiment includes an electrolyte layer forming process for forming an electrolyte layer between a pair of electrodes, and the electrolyte layer forming process includes a polymer attachment process for attaching a conductive polymer to one or both of the pair of electrodes, and a plastic crystal attachment process for attaching a plastic crystal, the molecular structure of which contains boron and does not contain halogen, to one or both of the pair of electrodes. [Effects of the Invention]

[0018] According to the present invention, even in an electrolytic capacitor using a solid electrolyte such as a conductive polymer and a plastic crystal, leakage current can be suppressed to a low level. [Brief explanation of the drawings]

[0019] [Figure 1] This is a photograph of the elemental distribution of carbon, oxygen, and aluminum in the layer of the anode body, mapped using SEM-EDX. [Figure 2] This is a photograph of the elemental distribution of boron in the layer of the anode body mapped using SEM-EDX. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0021] (Overall composition) An electrolytic capacitor is a passive device that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. An electrolytic capacitor includes a pair of electrodes and an electrolyte layer sandwiched between the electrodes. One electrode is an anode body, with a dielectric film formed on its surface. The other electrode is a cathode body. The electrolyte layer is in close contact with the dielectric film of the anode body and is arranged so as to be continuous between the dielectric film and the cathode body, creating a conductive path and functioning as a true cathode.

[0022] A separator is interposed between the anode body and the cathode body. This separator separates the anode body and the cathode body to prevent short-circuiting between them, and also maintains the electrolyte layer between the anode body and the cathode body. If the shape of the electrolyte layer can be maintained by itself and the cathode body can be separated by the electrolyte layer, the separator can be eliminated from the electrolytic capacitor.

[0023] The electrolyte layer contains a conductive polymer and a plastic crystal. The conductive polymer is a self-doped conjugated polymer doped with an internal dopant molecule, 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 readily accepts electrons into the conjugated polymer, or a donor that readily donates electrons, thereby causing the conductive polymer to exhibit high conductivity. Note that the electrolyte layer of the present application contains a conductive polymer and a plastic crystal, thereby forming a solid electrolyte layer, but may also contain a liquid component.

[0024] Plastic crystals, also known as plastic crystals, have an ordered arrangement and a disordered orientation. That is, plastic crystals have a three-dimensional crystal lattice structure in which anions and cations are regularly arranged, but these anions and cations have rotational disorder. Because of their ordered arrangement, plastic crystals lose fluidity, making them non-liquid components and capable of being treated as solid electrolytes.

[0025] The plastic crystal of the present application may be an ionic organic substance having a solid-solid transition point, ionic conductivity, and a melting point lower than room temperature. Furthermore, the solid-solid transition point is located lower than the operating temperature range of the electrolytic capacitor, and the melting point is located higher than the operating temperature range of the electrolytic capacitor. For example, the operating temperature range of the electrolytic capacitor is -40°C or higher and 150°C or lower when the electrolytic capacitor is intended for outdoor use, such as in an automotive application. Note that room temperature in the present application is 25°C. The melting point may be located, for example, above room temperature, or above 100°C. Furthermore, the melting point may be located, for example, above 150°C.

[0026] The solid-solid phase transition point is an endothermic peak that occurs below the melting point during the temperature rise process in differential scanning calorimetry (DSC), i.e., a peak where the heat flow per unit weight is negative. Below this solid-solid phase transition point, the material has a regular crystalline structure with regular molecular orientation and center of gravity. Above this solid-solid phase transition point and below the melting point, the material is in a plastic crystalline phase. The plastic crystalline phase transitions to a plastic crystalline phase at room temperature. Therefore, this electrolytic capacitor operates while maintaining the ionic organic material, which has a melting point higher than room temperature and a solid-solid phase transition point lower than room temperature, in a plastic crystalline state.

[0027] The plastic crystal contained in the electrolyte layer contains boron in its molecular structure. On the other hand, the molecular structure of the plastic crystal does not contain halogen. Plastic crystals containing boric acid in their molecular structure reduce the leakage current of electrolytic capacitors. Although this is speculation and not intended to be limiting, it is believed that the effect of reducing leakage current by containing such plastic crystals is achieved through the following mechanism.

[0028] That is, the mechanism for reducing leakage current is thought to be the formation of deposits derived from plastic crystals at the defect area. Because plastic crystals have ionic conductivity, when they exist at the dielectric film interface, a strong electric field is generated at the interface. When a defect occurs in the dielectric film, the plastic crystals are decomposed by an electrochemical oxidation reaction due to the flow of current, and deposits are formed at the defect in the dielectric film. These deposits have insulating properties and seal the defect. Alternatively, the deposits function pseudo-as part of the dielectric film, repairing the defect in the dielectric film. Note that the deposits may also be partially attached.

[0029] However, if the molecular structure of the plastic crystal contains a halogen, the electrochemical oxidation reaction of the plastic crystal will result in the formation of a deposit of liberated halogen ions. If the deposit of liberated halogen ions covers defects in the dielectric film, it may not repair the defects but may instead act as a starting point for accelerating the progression of corrosion and deterioration from the defects.

[0030] Particularly preferably, the anion component of the plastic crystal has the following four characteristics. First, the molecular structure has a chelate complex with boron as the central atom. Second, the multidentate ligand of this chelate complex is an organic compound having at least two hydroxy groups. In other words, it is an organic compound having at least two coordination or bonding sites. Third, the anion component of the plastic crystal has a molecular structure containing sp 2 It has a double bond formed by hybrid orbitals. 2 The double bond due to hybrid orbitals includes the double bond between two carbon atoms and the double bond between a carbon atom and an oxygen atom. In particular, the anion component of plastic crystals has a molecular structure in which each carbon atom is sp 2 The aromatic ring may have a hybrid orbital and further have a structure in which π electrons are delocalized.

[0031] The structure of an anion component in which a multidentate ligand coordinates to the central boron atom is more likely to have a three-dimensionally symmetric molecular structure and a spherical shape that allows rotational disorder than a structure in which a monodentate ligand coordinates. Therefore, when combined with a cation, it is thought to have a solid / solid phase transition point lower than room temperature and a plastic crystalline phase that exhibits ionic conductivity.

[0032] When plastic crystals having these four characteristics are contained in the electrolyte layer, the following mechanism is assumed to occur, although it is not limited to this, and the leakage current of the electrolytic capacitor is further reduced compared to when boric acid is simply contained in the molecule.

[0033] That is, in the ligand that coordinates or bonds to the boron-centered chelate complex, the bond between boron and oxygen is weaker than the other bonds in the ligand, and therefore is easily separated by the electrochemical oxidation reaction of the plastic crystal. Furthermore, it is thought that the aromatic ring acts as an electron-withdrawing group, making the bond between oxygen and boron easier to break. On the other hand, since the plastic crystal has oxygen atoms derived from hydroxyl groups in the anion structure, a cross-linked structure is formed in part of the separation. Therefore, it is thought that deposits are more likely to occur in defects in the dielectric film. Each carbon in the structure of the ligand is sp 2 It is believed that the presence of hybrid orbitals allows some carbon atoms to act as the starting point for bonding between anions in the plastic crystal, making it easier for the material to function as a pseudo-dielectric film.

[0034] If the leakage current of electrolytic capacitors can be reduced by using such plastic crystals, the dependency on repairing defects in the dielectric film by liquid components can be reduced, and electrolytic capacitors with no or reduced liquid components can be realized.

[0035] The liquid component may permeate the outer shell of the electrolytic capacitor, such as the sealing body, and leak out, resulting in a decrease in the capacitance of the electrolytic capacitor and possibly causing dry-up. However, if the leakage current of the electrolytic capacitor can be reduced using a plastic crystal, the decrease in capacitance of the electrolytic capacitor due to the decrease in the liquid component can be suppressed, and theoretically dry-up can be eliminated. Alternatively, when used in combination with a liquid component, the plastic crystal can maintain the reduction in leakage current even if the amount of the liquid component is reduced.

[0036] In other words, even if a solid electrolytic capacitor contains a liquid component, the effect of reducing leakage current due to the plastic crystals can be enjoyed. If a liquid component is not used in combination, the liquid component will leak out when the valve opens due to an increase in internal pressure of the electrolytic capacitor, and there is no risk of short-circuiting the electronic circuit. Furthermore, the main cation is not a metal ion.

[0037] (anode body) In such electrolytic capacitors, the anode body is a foil made of a valve metal. In wound electrolytic capacitors, the valve metal is stretched into a long strip shape, while in laminated electrolytic capacitors, it is a flat plate or a sintered body made by molding and sintering powder into a flat plate. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be present.

[0038] 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 a foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto a foil. That is, the surface-expanding layer has a porous structure consisting of tunnel-like pits, spongy pits, or voids between densely packed powder or particles.

[0039] The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pits turn the surface-expanding layer into a sponge-like layer with fine, interconnected voids. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0040] The sintered layer is produced by obtaining a powder of a valve action metal of the same or different type as the foil by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc., forming a paste with a binder or solvent, applying it to the foil, drying it, and heating and sintering it in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization method, gas atomization method, and water gas atomization method. The vapor deposition layer is produced by, for example, a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and evaporating a valve action metal of the same or different type as the foil by resistance heat or electron beam energy, and depositing the vapor of the valve action metal particles on the surface of the foil.

[0041] The dielectric coating is formed on one or both sides of the anode body on which the surface-expanding layer is formed. The dielectric coating is typically an oxide coating formed on the surface layer 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 a 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.

[0042] An anode lead is connected to the anode body and extends outside the capacitor element. The capacitor element is an assembly of the anode body, cathode body, electrolyte layer, and separator. The anode lead is connected to the anode body by stitching, cold welding, ultrasonic welding, laser welding, or the like.

[0043] (cathode body) In the case of a wound-type electrolytic capacitor, the cathode body is preferably a foil made of a valve metal and stretched. The purity of the cathode body is preferably 99% or higher. 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 (about 1 to 10 V) formed by chemical conversion treatment. The natural oxide film is formed by the cathode body reacting with oxygen in the air. Furthermore, a layer made of metal nitride, metal carbide, or metal carbonitride may be formed on the cathode body by vapor deposition, or a carbon-containing layer may be formed on the surface.

[0044] Alternatively, in the case of a stacked 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 disposed facing the anode body. The carbon layer is formed by applying a paste onto the electrolyte layer after the electrolyte layer is formed on the anode body, and then curing the paste by heating. The metal layer is, for example, a silver layer, and is formed by applying a paste onto the carbon layer and then curing the paste by heating.

[0045] A cathode lead is connected to the cathode body and is drawn out of the capacitor element by stitching, cold welding, ultrasonic welding, laser welding, or the like.

[0046] (electrolyte layer) (conductive polymer) 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.

[0047] Among the above conjugated polymers, preferred are conjugated polymers obtained by polymerizing thiophene or its derivatives, 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.

[0048] In particular, a polymer of 3,4-ethylenedioxythiophene, known as EDOT, i.e., poly(3,4-ethylenedioxythiophene), known as PEDOT, is particularly preferred. A substituent may be added to 3,4-ethylenedioxythiophene. For example, alkylated ethylenedioxythiophene, in which an alkyl group having 1 to 5 carbon atoms is added as a substituent, may be used. 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.

[0049] 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.

[0050] Examples of polyanions include substituted or unsubstituted polyalkylenes, substituted or unsubstituted polyalkenylenes, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, and include polymers consisting only of structural units having anionic groups, and polymers consisting of structural units having anionic groups and structural units not having anionic groups.Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0051] This conductive polymer is produced by chemical oxidative polymerization or electrolytic oxidative polymerization. In chemical oxidative polymerization, a solution containing a monomer that will become the monomer unit of the conductive polymer is mixed with an oxidizing agent to cause a polymerization reaction. The oxidizing agent may be any known compound that releases a dopant. Examples of the oxidizing agent include trivalent iron salts such as iron(III) p-toluenesulfonate, iron(III) naphthalenesulfonate, and iron(III) anthraquinonesulfonate, and peroxodisulfates such as peroxodisulfate, ammonium peroxodisulfate, and sodium peroxodisulfate. A single compound may be used, or two or more compounds may be used. The polymerization temperature is not strictly limited, but is generally in the range of 10 to 200°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0052] In electrolytic oxidation polymerization, a monomer that will become a monomer unit of a conductive polymer is mixed with a supporting electrolyte and polymerized by a constant potential method, a constant current method, or a potential sweep method. The supporting electrolyte includes at least one compound selected from the group consisting of borodisalicylic acid and borodisalicylic acid salts. Examples of the salt include alkali metal salts such as lithium salt, sodium salt, and potassium salt; alkylammonium salts such as ammonium salt, ethylammonium salt, and butylammonium salt; dialkylammonium salts such as diethylammonium salt and dibutylammonium salt; trialkylammonium salts such as triethylammonium salt and tributylammonium salt; and tetraalkylammonium salts such as tetraethylammonium salt and tetrabutylammonium salt.

[0053] In the case of the constant potential method, a potential of 1.0 to 1.5 V relative to the reference electrode is suitable, and in the case of the constant current method, a potential of 1 to 10,000 μA / cm 2 In the case of a potential sweep method, it is preferable to sweep the potential in the range of 0 to 1.5 V with respect to the reference electrode at a rate of 5 to 200 mV / sec. There is no strict limit to the polymerization temperature, but it is generally in the range of 10 to 60°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0054] In chemical oxidation polymerization or electrolytic oxidation polymerization, the solvent to which the monomer, oxidizing agent, or supporting electrolyte is added can be any solvent that can dissolve the desired amount of monomer and supporting electrolyte and does not adversely affect the electrolytic oxidation polymerization. Examples of suitable solvents include water, methanol, ethanol, isopropanol, butanol, ethylene glycol, acetonitrile, butyronitrile, acetone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, γ-butyrolactone, methyl acetate, ethyl acetate, methyl benzoate, ethyl benzoate, ethylene carbonate, propylene carbonate, nitromethane, nitrobenzene, sulfolane, and dimethyl sulfolane. These solvents may be used alone or in combination.

[0055] The conductive polymer is formed in the electrolytic capacitor by immersing an object to which the conductive polymer is to be attached in a solution of a monomer that will become a monomer unit of the conductive polymer and an oxidizing agent or a supporting electrolyte, and generating the conductive polymer through a polymerization reaction. The object to be attached includes at least an anode body. In addition to the anode body, one or both of the cathode body and the separator may also be used as the object to which the conductive polymer is to be attached. Alternatively, a capacitor element, which is an assembly incorporating an anode body, a cathode body, and a separator, may be used as the object to be attached, and immersed in a solution of a monomer that will become a monomer unit of the conductive polymer and an oxidizing agent or a supporting electrolyte, and generating a polymerization reaction.

[0056] Alternatively, the conductive polymer may be formed in the electrolytic capacitor by using an impregnation method in which a conductive polymer liquid in which conductive polymer particles or powder are dispersed or dissolved is impregnated into an object to be attached. Using a conductive polymer liquid in which conductive polymer particles or powder are dispersed or dissolved makes it easier for the plastic crystals to mix with the conductive polymer when attached. The conductive polymer liquid is prepared by purifying the solution after chemical oxidation polymerization or electrolytic oxidation polymerization by ultrafiltration, cation exchange, anion exchange, etc., to remove residual monomers and impurities, and dispersing the resulting solution in the solution.

[0057] The solvent for the conductive polymer solution may be any solvent that disperses or dissolves the conductive polymer, and is preferably water or a mixture of water and an organic solvent. Examples of the organic solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

[0058] 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, and butanol. 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 ether compounds include dioxane and diethyl ether. Examples of linear ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

[0059] The conductive polymer solution may contain a pH adjuster, a polyhydric alcohol, and various additives as needed. The pH adjuster neutralizes the dopant to improve the acidity of the conductive polymer solution so that the anode body, cathode body, and separator do not dissolve. Examples of pH adjusters include ammonia, water-soluble alkylamines such as ethylamine and diethylamine, water-soluble arylamines such as aniline and benzylamine, and water-soluble heterocyclic amines such as pyridine and imidazole. Examples of pH adjusters include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide and calcium hydroxide, alkali metal or alkaline earth metal carbonates such as sodium carbonate and calcium carbonate, and alkali metal or alkaline earth metal alkoxides such as sodium methoxide and calcium methoxide.

[0060] Polyhydric alcohols change the higher-order structure of conductive polymers and enhance the reorientation of the crystalline structure of polymer chains. This reduces the ESR of electrolytic capacitors and improves their withstand voltage. Examples of polyhydric alcohols include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerin, polyoxyethyleneglycerin, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, and combinations of two or more of these. Because of their high boiling points, polyhydric alcohols remain in the electrolyte layer even after the conductive polymer solution is impregnated into the substrate and dried. Polyhydric alcohols change the higher-order structure of conductive polymers and reorient the crystalline structure of polymer chains. This improves carrier mobility and the electrical conductivity of conductive polymers, reducing the ESR of electrolytic capacitors and improving their withstand voltage.

[0061] Examples of the additives include organic binders, surfactants, dispersants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0062] After the conductive polymer solution has been impregnated into the object to be attached, the solvent is removed by a drying process. The temperature environment in the drying process is, for example, 40°C or higher and 200°C or lower, and the drying time is, for example, in the range of 3 minutes to 180 minutes. The drying process may be repeated multiple times. Drying may be performed in a reduced pressure environment, for example, by reducing the pressure to 5 kPa to 100 kPa. The drying process may be divided into a preliminary drying process and a main drying process. In addition to immersion, the conductive polymer solution may be applied by drop coating or spray coating.

[0063] (flexible crystal) The types of anion and cation components that make up the plastic crystal are not particularly limited, as long as they are solid rather than ionic liquid within the target temperature range in which the electrolytic capacitor is used, contain boric acid in their molecular structure, and do not contain halogens.

[0064] Examples of anion components constituting the plastic crystal include various borate anions, various sulfone-based anions, and tetrafluoroaluminate anions.

[0065] The various borate anions include a borate anion represented by the following chemical formula (1).

[0066] (chemical 1) TIFF2025121410000002.tif29161In the formula, R1 and R2 are each independently a ketone group, or R1 and R2 are carbon atoms in a common six-membered aromatic ring.In the formula, R3 and R4 are each independently a ketone group, or R3 and R4 are carbon atoms in a common six-membered aromatic ring.

[0067] In the chemical formula (1), when R1, R2, R3, and R4 are all ketone groups, the anion is a bis(oxalato)borate anion (BoB anion) represented by the following chemical formula (2).

[0068] (Case 2) TIFF2025121410000003.tif42161

[0069] Furthermore, in chemical formula (1), if R1 and R2 are carbon atoms that form a common six-membered aromatic ring, and R3 and R4 are carbon atoms that form a common six-membered aromatic ring, then the anion is a bis(pyrocatecholato)borate anion represented by the following chemical formula (3).

[0070] (3) TIFF2025121410000004.tif29161

[0071] Further, the various borate anions include a borate anion represented by the following chemical formula (4).

[0072] (C4) TIFF2025121410000005.tif32161In the formula, R1 to R6 are each independently a ketone group or a methylene group. Alternatively, in the formula, either R1 or R3 is a ketone group or a methylene group, and the other combination of R1 and R2 or the other combination of R2 and R3 is a carbon atom of a common aromatic six-membered ring. In the formula, either R4 or R6 is a ketone group or a methylene group, and the other combination of R4 and R5 or the other combination of R5 and R6 is a carbon atom of a common aromatic six-membered ring. The aromatic six-membered ring may have one or four methyl groups, or the aromatic six-membered ring may be part of a polycyclic aromatic ring having two or more aromatic rings, such as a naphthalene ring.

[0073] In the chemical formula (4), if R1 and R6 are ketone groups, R2 and R3 are carbon atoms that form a common six-membered aromatic ring, and R4 and R5 are carbon atoms that form a common six-membered aromatic ring, the anion is a bis(salicylato)borate anion (BScB anion) represented by the following chemical formula (5).

[0074] (C5) TIFF2025121410000006.tif55161

[0075] In the chemical formula (4), when R1 and R6 are ketone groups, R2 and R3 are carbon atoms constituting a common six-membered aromatic ring, R4 and R5 are carbon atoms constituting a common six-membered aromatic ring, and both aromatic six-membered rings each have four methyl groups, the resulting anion is bis(tetramethylsalicylate)borate, as represented by the following chemical formula (6).

[0076] (6) TIFF2025121410000007.tif59161

[0077] In the chemical formula (4), when R1 and R6 are ketone groups, R2 and R3 are carbon atoms constituting a common six-membered aromatic ring, R4 and R5 are carbon atoms constituting a common six-membered aromatic ring, and both aromatic six-membered rings each have one methyl group, the resulting anion is a bis(methylsalicylate)borate anion (BmScB anion) represented by the following chemical formula (7).

[0078] (7) TIFF2025121410000008.tif48161

[0079] Examples of cationic components constituting the plastic crystal include various quaternary ammonium cations, various pyrrolidinium cations, various piperidinium cations, various imidazolium cations, various phosphonium cations, and various trialkylsulfonyl cations. When various pyrrolidinium cations or various piperidinium cations are used as the quaternary ammonium cation, the melting point tends to be high.

[0080] Examples of the quaternary ammonium cation include tetraalkylammonium cations represented by the following chemical formula (8) and substituted with a linear alkyl group, regardless of the number of carbon atoms.

[0081] (C8) TIFF2025121410000009.tif47161In the formula, a, b, c, and d are integers of 1 or more, and the number of carbon atoms may be any number.

[0082] In the above chemical formula (8), when a, b, c, and d are 2, it is a tetramethylammonium cation (TMA cation) represented by the following chemical formula (9).

[0083] (9) TIFF2025121410000010.tif38161

[0084] In the above chemical formula (8), when a, b, c, and d are 2, it is a tetraethylammonium cation (TEA cation) represented by the following chemical formula (10).

[0085] (C10) TIFF2025121410000011.tif38165

[0086] In the above chemical formula (8), when a, b, and c are 2 and d is 1, it is a triethylmethylammonium cation (TEMA cation) represented by the following chemical formula (11).

[0087] (Chem.11) TIFF2025121410000012.tif38161

[0088] In the above chemical formula (8), when a, b, and c are 1, d is 2, and one of the hydrogen atoms of the ethyl group is substituted with a hydroxy group to form a hydroxyethyl group, the resulting cation is a choline cation (CHL cation) represented by the following chemical formula (12).

[0089] (C12) TIFF2025121410000013.tif34161

[0090] Furthermore, examples of the quaternary ammonium cation include a five-membered ring pyrrolidinium cation represented by the following chemical formula (13) to which a methyl group, an ethyl group, or an isopropyl group is bonded.

[0091] (C13) TIFF2025121410000014.tif46161In the formula, R1 and R2 are methyl groups, ethyl groups, or isopropyl groups.

[0092] Specific examples of the five-membered ring pyrrolidinium cation generalized by the above chemical formula (13) include the N-ethyl-N-methylpyrrolidinium cation (P12 cation) represented by the following chemical formula (14), the N-isopropyl-N-methylpyrrolidinium cation (P13iso cation) represented by the following chemical formula (15), and the N,N-diethylpyrrolidinium cation (P22 cation) represented by the following chemical formula (16).

[0093] (C14) TIFF2025121410000015.tif49161

[0094] (C15) TIFF2025121410000016.tif52161

[0095] (C16) TIFF2025121410000017.tif48161

[0096] Furthermore, examples of the quaternary ammonium include spiro-type pyrrolidinium cations (SBP cations) represented by the following chemical formula (17).

[0097] (C17) TIFF2025121410000018.tif52161

[0098] Various piperidinium cations are represented by the following chemical formula (18), and examples thereof include piperidinium cations in which a methyl group, an ethyl group, or an isopropyl group is a six-membered ring.

[0099] (C18) TIFF2025121410000019.tif41161In the formula, R3 and R4 are methyl groups, ethyl groups, or isopropyl groups.

[0100] A specific example of the six-membered ring piperidinium cation generalized by the above chemical formula (18) is, for example, the 1-ethyl-1-methylpiperidinium cation represented by the following chemical formula (19), in which R3 is a methyl group and R4 is an ethyl group.

[0101] (C19) TIFF2025121410000020.tif36161

[0102] The various imidazolium cations are 1,3-dialkylimidazolium or 1,2,3-trialkylimidazolium cations represented by the following chemical formula (20).

[0103] (20) TIFF2025121410000021.tif46161In the formula, h and i are integers between 1 and 3, and j is 0 or 1.

[0104] In chemical formula (20), when j is 0 and h and i are 1, the compound is a 1,3-dimethylimidazolium cation (DMI cation) represented by the following chemical formula (21). The 2-position of this DMI cation may be substituted with a methyl group.

[0105] (21) TIFF2025121410000022.tif30161

[0106] In the chemical formula (20), when j is 0, h is 1, and i is 2, it is a 1-ethyl-3-methylimidazolium cation (EMI cation) represented by the following chemical formula (22). The 2-position of this EMI cation may be substituted with a methyl group.

[0107] (22) TIFF2025121410000023.tif30161

[0108] In chemical formula (20), when j is 0, h is 1, and i is 3, the cation is a 1-methyl-3-propylimidazolium cation (MPI cation) represented by the following chemical formula (23). The 2-position of this MPI cation may be substituted with a methyl group.

[0109] (23) TIFF2025121410000024.tif30161

[0110] The various phosphonium cations are represented by the following chemical formula (24), and examples thereof include tetraalkylphosphonium cations substituted with a linear alkyl group, regardless of the number of carbon atoms. Examples of the tetraalkylphosphonium cations include tetraethylphosphonium cations (TEP cations).

[0111] (24) TIFF2025121410000025.tif47161In the formula, e, f, g, and h are integers of 1 or more, and the number of carbon atoms may be any.

[0112] Examples of various trialkylsulfonyl cations include the trimethylsulfonium cation represented by the following chemical formula (25), in which all hydrogen atoms of the sulfonium are substituted with methyl groups.

[0113] (25) TIFF2025121410000026.tif37161

[0114] Two or more types of plastic crystals may be included in the electrolyte layer. When two or more types of plastic crystals are included, plastic crystals of the same anion type may be included in the electrolyte layer, plastic crystals of the same cation type may be included in the electrolyte layer, or plastic crystals with different anion and cation components may be included in the electrolyte layer. The blending ratio of different plastic crystals in the electrolyte layer may be equimolar or may be different.

[0115] Plastic crystals can be produced by, for example, the following manufacturing method, but various other methods can also be used. Specifically, alkali metal salts of the anion components constituting the plastic crystal and halogenated cation components are dissolved in a solvent. Examples of alkali metals include Na, K, Li, and Cs.

[0116] Alkali metal salts are synthesized by heating a mixture of a boron source and an alkali metal source while mixing with an organic substance that will form the anion skeleton. The organic substance that will form the anion skeleton has at least two hydroxyl groups in the molecule, such as salicylic acid, various methyl salicylates, and oxalic acid. Examples of halogens include F, Cl, Br, and I. Water is the preferred solvent. An ion exchange reaction is carried out by gradually adding a solution of the anion metal salt to a solution of the halogenated cation. An equimolar amount of the anion metal salt solution is added to the solution of the halogenated cation and stirred.

[0117] At this time, ion exchange produces plastic crystals and alkali metal halides. When an organic solvent such as dichloromethane is mixed and allowed to stand, the mixture separates into an aqueous layer and an organic solvent layer. The alkali metal halides are removed by removing the aqueous layer. This operation can be repeated multiple times. After removing the alkali metal halides, the organic solvent such as dichloromethane is evaporated to obtain plastic crystals.

[0118] Alternatively, a halogenated cationic component may be added to a mixture of a boron source and an organic substance that will form an anionic skeleton while heating. Ethanol is a preferred solvent for the mixture, and plastic crystals can be obtained by extraction and drying in ion exchange, as well as by washing with ethanol.

[0119] The plastic crystals are dissolved in a solvent in which the plastic crystals are soluble. The solvent is preferably a polar solvent. Examples of polar solvents include acetonitrile, propylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, sulfolane, acetone, methanol, ethanol, isopropyl alcohol, and mixtures thereof. These polar solvents efficiently dissolve the plastic crystals, resulting in excellent productivity of the electrolyte layer.

[0120] The object to which the electrolyte layer is to be attached is then impregnated with a solution of plastic crystals. After impregnation with the solution of plastic crystals, the object is left in a temperature environment at which the solvent volatilizes, such as at 100°C, to volatilize the solvent by drying, and then left in a temperature environment at 150°C, etc., to volatilize any remaining moisture. This allows plastic crystals to be formed on the object to be attached.

[0121] (separator) Examples of separators include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers 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. These resins can be used alone or in combination.

[0122] (Method of manufacturing electrolytic capacitors) (wound type) An example of the assembly process for a wound-type electrolytic capacitor is shown below. First, a surface-expanding layer is formed on one or both sides of the valve metal foil on the anode side, and a dielectric film is formed on the surface-expanding layer by chemical conversion treatment. If necessary, a surface-expanding layer is also formed on one or both sides of the valve metal foil on the cathode side, and an oxide film is formed on the surface. The anode and cathode leads are connected to the anode and cathode bodies, for example, by stitching, cold welding, ultrasonic welding, or laser welding.

[0123] Long anode and cathode bodies are wound with a separator interposed therebetween to produce a cylindrical wound body. The separator is overlapped so that one end protrudes beyond one end of the anode and cathode bodies. The protruding separator is wound first so that the core of the wound body is aligned with the short sides of the anode and cathode bodies to produce a winding core. Then, the anode and cathode bodies are wound by rolling up the long sides of the anode and cathode bodies using the winding core as a winding shaft.

[0124] After the winding, a repair chemical conversion step is performed to repair bare metal portions of the valve metal exposed when the anode body and cathode body are cut to the desired width, and to repair defects in the anode body and cathode body caused by physical stress such as winding.

[0125] In the repair anodization process, the wound body is immersed in an anodization solution and a voltage is applied. Examples of anodization solutions include phosphoric acid-based anodization solutions such as ammonium dihydrogen phosphate, boric acid-based anodization solutions such as ammonium borate, adipic acid-based anodization solutions such as ammonium adipate, and an anodization solution containing a mixture of boric acid and dicarboxylic acid such as citric acid. The repair anodization voltage is preferably 0.1 to 1.2 times the anodization voltage of the anode body. The voltage application method during repair anodization can be appropriately selected from methods such as applying a constant voltage from the start of repair anodization or increasing the applied voltage stepwise at regular intervals.

[0126] Next, the process moves to the electrolyte formation process, where an electrolyte layer is formed between the anode and cathode bodies. The electrolyte formation process is broadly divided into a polymer attachment process and a plastic crystal attachment process. In the polymer attachment process, a conductive polymer is attached between the anode and cathode bodies, and in the plastic crystal attachment process, a plastic crystal is attached between the anode and cathode bodies.

[0127] In the polymer application process using a conductive polymer liquid, the wound body is immersed in the conductive polymer liquid to impregnate the wound body with the conductive polymer liquid. To promote the impregnation of the wound body with the conductive polymer liquid, a decompression treatment or a pressurization treatment may be performed as necessary. The impregnation process may be repeated multiple times. After the wound body is impregnated with the conductive polymer liquid, a drying process is performed to remove the solvent of the conductive polymer liquid.

[0128] When the conductive polymer is deposited while being produced, the wound body is immersed in a solution of a monomer that will become the monomer unit of the conductive polymer, and an oxidizing agent or a supporting electrolyte to cause a polymerization reaction. After the conductive polymer is deposited, the solvent is removed by a drying process.

[0129] Next, in the plastic crystal attachment step, the roll is immersed in a solution of plastic crystals to impregnate the roll. To promote the impregnation of the roll with the plastic crystal solution, a decompression treatment or a pressurization treatment may be performed as necessary. The impregnation step may be repeated multiple times. After the roll is impregnated with the plastic crystal solution, the solvent is removed by a drying step.

[0130] In this example, the conductive polymer is first attached to the wound body, followed by the plastic crystal, but it is also possible to attach the plastic crystal first and then the conductive polymer. However, from the perspective of forming a conductive path between the anode body and the cathode body, it is preferable to attach the conductive polymer first. By attaching the conductive polymer first, an electrolyte layer including the plastic crystal and the conductive polymer layer can be formed uniformly, resulting in good capacitance characteristics and good ESR characteristics.

[0131] The conductive polymer and the plastic crystal may be attached to the anode body, and then the anode body and the cathode body may be wound facing each other with a separator interposed therebetween. Alternatively, the conductive polymer and the plastic crystal may be attached to the anode body, the cathode body, the separator, or both, and then the anode body and the cathode body may be wound facing each other with a separator interposed therebetween.

[0132] The capacitor element is housed in an outer case that is closed at one end and open at the other end, and the capacitor element is sealed in the outer case with a sealing member. After the capacitor element is sealed in the outer case, the electrolytic capacitor undergoes an aging process to complete its production. In the aging process, a DC voltage is applied to the electrolytic capacitor to repair defects in the dielectric film. In this case, applying a voltage in the aging process may form a deposit layer made of decomposed material derived from plastic crystals, thereby repairing defects in the dielectric oxide film. In addition to the aging process, a step of applying a voltage to form a deposit layer may be provided.

[0133] (Laminated type) An example of the assembly process for a laminated type electrolytic capacitor is shown below. First, a surface-expanding layer is formed on the surface of the valve metal foil that serves as the anode body. Next, the foil with the surface-expanding layer is subjected to a chemical conversion treatment in a chemical conversion solution to form a dielectric film on the surface of the valve metal foil. An insulating resist layer is printed and dried on the area that will later become the anode terminal, excluding the area that will become the anode. In other words, the insulating resist layer is printed so that an electrolyte layer does not form on the area that will become the anode terminal.

[0134] After printing the insulating resist layer, the process moves to the conductive polymer deposition process, where the foil is immersed in a conductive polymer solution to deposit the conductive polymer so that it covers the dielectric film. After the solvent in the conductive polymer solution is removed by drying, the process moves to the plastic crystal deposition process, where the foil is immersed in a plastic crystal solution to deposit additional plastic crystals. The solvent in the plastic crystals is then removed by drying. An electrolyte layer is formed by this deposition of the conductive polymer and plastic crystals.

[0135] Next, a carbon paste is printed on the electrolyte layer using a screen printer or the like and dried. This drying process forms a carbon layer on the electrolyte layer. Furthermore, a metal paste such as silver paste is printed on the carbon layer and dried. This drying process forms a silver layer on the carbon layer. These carbon and silver layers correspond to the cathode body of the electrolytic capacitor.

[0136] After the cathode body is formed, the insulating resist layer is peeled off. The insulating resist layer may be peeled off by laser irradiation or mechanical peeling using a jig. The exposed portion is plated to complete the anode terminal.

[0137] The capacitor element thus fabricated is then covered with, for example, a laminate film, or encapsulated by molding, dip-coating, or printing with a resin such as a heat-resistant resin or an insulating resin. After encapsulating the capacitor element, a step of applying a voltage to form a deposit layer may be added. [Example]

[0138] The electrolytic capacitor and its manufacturing method will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0139] Example 1 The electrolytic capacitor of Example 1 was fabricated as follows. First, a pair of electrodes was fabricated using aluminum foil. Both electrode foils were subjected to an etching process to enlarge the surface. One electrode was used as an anode body, and its surface was enlarged by AC etching. In the anode body surface enlargement process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid to form spongy pits. The other electrode was used as a cathode body, and its surface was enlarged by AC etching. In the formation of the cathode body surface enlargement layer, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid to form spongy etching pits.

[0140] For the anode body, a dielectric film was formed on the foil surface by chemical conversion treatment. In the chemical conversion treatment process, aluminum foil with a surface expansion layer formed was subjected to chemical conversion treatment in an ammonium adipate aqueous solution to form a 63.6V dielectric film on the surface of the aluminum foil. For the cathode body, a dielectric film of 3V was formed on aluminum foil with a surface expansion layer formed.

[0141] Lead wires were connected to each of the anode and cathode bodies, and the anode and cathode foils were wound facing each other with a manila paper separator in between. The wound body had a diameter of 6.3 mm and a height of 5.8 mm. Repair and chemical conversion were performed by passing a voltage of 58 V and a current density of 2 mA through the wound body in an ammonium dihydrogen phosphate solution at a liquid temperature of 90°C.

[0142] The wound body was first impregnated with a conductive polymer liquid. The conductive polymer liquid contained a dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) doped with polystyrene sulfonic acid (PSS). PEDOT / PSS was added at a ratio of 2 wt% to the total conductive polymer liquid. The pH of this conductive polymer liquid was adjusted to 4.0 with ammonia water. Ethylene glycol was also added to the conductive polymer liquid at a ratio of 10 wt% to the conductive polymer dispersion.

[0143] The wound body was impregnated with the conductive polymer solution for 5 minutes at room temperature and under a pressure of -0.3 MPa. The impregnation process was performed twice in total. After the wound body was removed from the conductive polymer solution, it was left to stand at room temperature for 10 minutes and then left to stand in a temperature environment of 110°C for 30 minutes to dry the wound body. This resulted in the formation of an electrolyte layer containing the conductive polymer on the dielectric film of the anode body.

[0144] Next, a plastic crystal was attached between the anode and cathode bodies in addition to the conductive polymer. The plastic crystal was P12BScB. That is, a plastic crystal containing P12 cations and BScB anions in a 1:1 molar ratio was attached. The P12 cation is an N-ethyl-N-methylpyrrolidinium cation represented by chemical formula (17). The BScB anion is a bis(salicylate)borate anion represented by chemical formula (5).

[0145] First, lithium bis(salicylato)borate was synthesized by heating an aqueous solution of 1 equivalent of boric acid and 2 equivalents of lithium carbonate to 60°C, adding 2 equivalents of salicylic acid to the solution, and allowing it to cool. An ion exchange reaction was then carried out by adding dropwise an aqueous solution of 1 equivalent of N-ethyl-N-methylpyrrolidinium tetrafluoroborate to this lithium bis(salicylato)borate.

[0146] The alkali metal halide was removed by removing the aqueous layer from the separated solution. After removing the alkali metal halide, the dichloromethane was evaporated to obtain plastic crystals of P12BScB.

[0147] Furthermore, differential scanning calorimetry (DSC) showed that the solid-solid transition point of P12BScB was -46.4°C during the heating process, and the melting point of P12BScB was 153.4°C during the heating process, indicating that it was a plastic crystal in the operating temperature range of electrolytic capacitors and at room temperature.

[0148] The P12BScB plastic crystals were added to acetonitrile at a ratio of 40 wt% to the total solution. This acetonitrile solution was dripped onto the wound body, allowing the wound body to be impregnated with the acetonitrile solution. After impregnation, the wound body was left to stand in an argon atmosphere at 90°C for 14 hours to dry the acetonitrile solution. This resulted in the formation of an electrolyte layer containing conductive polymer and plastic crystals. The amount of plastic crystals attached was 20 mg per wound body.

[0149] The capacitor element of Example 1 was housed in an outer case, and the opening of the outer case was sealed with a sealant. The sealant and the outer case were tightly attached by crimping. The electrolytic capacitor of Example 1 was then subjected to an aging treatment by applying a voltage of 40.25 V for 1 hour in a temperature environment of 105°C. As a result, an electrolytic capacitor with a diameter of 6.3 mm, a height of 5.8 mm, a rated voltage of 35 WV, and 47 μF was produced.

[0150] Example 2 An electrolytic capacitor of Example 2 was fabricated. The electrolytic capacitor of Example 2 differs from Example 1 in the type of plastic crystal. In Example 2, SBPBScB was attached as the plastic crystal. That is, plastic crystals containing SBP cations and BScB anions in a 1:1 molar ratio were attached. The SBP cation is a spiro-pyrrolidinium cation represented by chemical formula (20). Differential scanning calorimetry (DSC) showed that the solid-solid phase transition point of SBPBScB was −50.9°C during the heating process, and the melting point of SBPBScB was 170.5°C during the heating process, indicating that the SBPBScB was a plastic crystal within the operating temperature range of the electrolytic capacitor and at room temperature.

[0151] (Comparative Example 1) An electrolytic capacitor of Comparative Example 1 was fabricated. The electrolytic capacitor of Comparative Example 1 differed from Examples 1 and 2 in the type of plastic crystal. The other configurations, compositions, manufacturing methods, and manufacturing conditions of the electrolytic capacitor of Comparative Example 1 were the same as those of Examples 1 and 2. In Comparative Example 1, P12FSA was attached as the plastic crystal. That is, plastic crystals containing P12 cations and FSA anions in a 1:1 molar ratio were attached. The FSA cation was a spiro-type pyrrolidinium cation represented by chemical formula (26), and its molecular structure did not contain boron. However, differential scanning calorimetry (DSC) revealed that the solid-solid phase transition point of P12FSA was -20°C during the heating process, and the melting point of P12FSA was 190°C during the heating process, indicating that it was a plastic crystal within the operating temperature range of the electrolytic capacitor and at room temperature.

[0152] (26) TIFF2025121410000027.tif37161

[0153] (Comparative Example 2) An electrolytic capacitor of Comparative Example 2 was fabricated. The electrolytic capacitor of Comparative Example 2 differed from Examples 1 and 2 in the type of plastic crystal. The other configurations, compositions, manufacturing methods, and manufacturing conditions of the electrolytic capacitor of Comparative Example 2 were the same as those of Examples 1 and 2. In Comparative Example 2, P12BF4 was attached as the plastic crystal. That is, plastic crystals containing P12 cations and BF4 anions in a 1:1 molar ratio were attached. The BF4 cations were tetrafluoroborate. Differential scanning calorimetry (DSC) revealed that the solid-solid phase transition point of P12BF4 was -29°C during the heating process, and the melting point of P12BF4 was 280°C during the heating process, indicating that the P12BF4 was a plastic crystal within the operating temperature range of the electrolytic capacitor and at room temperature.

[0154] (Comparative Examples 3 and 4) Electrolytic capacitors of Comparative Examples 3 and 4 were produced. Comparative Example 3 differs from Example 1 in that it does not contain plastic crystals, and the other configurations, composition, manufacturing method, and manufacturing conditions of the electrolytic capacitor of Comparative Example 3 are the same as those of Example 1. Comparative Example 4 differs from Example 1 in that it does not contain a conductive polymer, and the other configurations, composition, manufacturing method, and manufacturing conditions of the electrolytic capacitor of Comparative Example 4 are the same as those of Example 1.

[0155] (Reference example 1) An electrolytic capacitor of Reference Example 1 was fabricated. The electrolytic capacitor of Reference Example 1 is a hybrid capacitor in which an electrolytic solution is used together with a conductive polymer instead of a plastic crystal. The electrolytic solution contains ethylene glycol as the main solvent and azelaic acid as the main solute. After the conductive polymer is attached and dried, the wound body is immersed in the electrolytic solution, and the electrolytic solution is impregnated while the pressure inside the wound body is reduced. The other configurations, compositions, manufacturing methods, and manufacturing conditions of the electrolytic capacitor of Reference Example 1 are the same as those of Examples 1 and 2.

[0156] (Characteristics test) The electrolytic capacitance (Cap), equivalent series resistance (ESR), and leakage current (LC) of the electrolytic capacitors of Examples 1 and 2, Comparative Examples 1 to 4, and Reference Example 1 were measured. Cap and ESR were measured at 20°C using an LCR meter (model ZM2376, manufactured by NF Corporation). The Cap measurement frequency was 120 Hz, and the AC current level was a sine wave of 1.0 Vms. The ESR measurement frequency was 100 kHz, and the AC current level was a sine wave of 1.0 Vms. The leakage current was measured after applying a voltage of 35 V for 2 minutes at 20°C.

[0157] The measurement results of Cap, ESR and leakage current of the electrolytic capacitors of Examples 1 and 2, Comparative Examples 1 to 4 and Reference Example 1 are shown in Table 1 below.

[0158] (Table 1) TIFF2025121410000028.tif91161

[0159] As shown in Table 1 above, the electrolytic capacitor of Comparative Example 1 has a reduced capacitance and a significantly worsened ESR due to the inclusion of plastic crystals in the electrolyte layer, as can be seen when compared with Comparative Example 3. The electrolytic capacitor of Comparative Example 2 has an increased leakage current due to the inclusion of plastic crystals in the electrolyte layer, as can be seen when compared with Comparative Example 3.

[0160] However, it can be seen that the leakage current of the electrolytic capacitors of Examples 1 and 2 is kept low. In the plastic crystals of Examples 1 and 2, boron is included in the molecular structure of the anion, whereas the plastic crystal of Comparative Example 1 does not contain boron in the molecular structure of the anion. Furthermore, in the plastic crystals of Examples 1 and 2, halogen is not included in the molecular structure of the anion, whereas the plastic crystal of Comparative Example 2 contains halogen in the molecular structure of the anion.

[0161] Thus, it can be confirmed that the leakage current of the electrolytic capacitor is reduced by including in the electrolyte layer plastic crystals whose anion molecular structure contains boron and no halogen. Moreover, it can be seen that the leakage current of the electrolytic capacitors of Examples 1 and 2 is reduced to a level comparable to or even lower than that of Reference Example 1. In the electrolytic capacitor of Reference Example 1, it can be seen that the electrolyte repairs defects in the dielectric film upon voltage application, reducing the leakage current, but Examples 1 and 2 are not impregnated with the electrolyte.

[0162] The electrolytic capacitor of Comparative Example 4 contains the same plastic crystal as Example 1, but does not contain a conductive polymer, and therefore does not exhibit capacitance. Therefore, it was confirmed that an electrolytic capacitor can be established by incorporating a conductive polymer into the electrolyte layer, and that the leakage current of the electrolytic capacitor can be reduced by incorporating plastic crystals whose anion molecular structure contains boron and no halogen into the electrolyte layer. Furthermore, this electrolytic capacitor also has good capacitance and is less likely to increase ESR.

[0163] Example 3 An electrolytic capacitor according to the third embodiment was fabricated. First, a pair of electrodes was fabricated using aluminum foil. Both electrode foils were used without surface expansion. One electrode was used as an anode, and a dielectric film was formed on the surface of the anode by chemical conversion treatment. In the chemical conversion treatment process, the aluminum foil with the surface expansion layer was subjected to chemical conversion treatment in an ammonium adipate solution, and a 10V dielectric film was formed on the surface of the aluminum foil. In addition, for the cathode, a 3V dielectric film was formed on the aluminum foil with the surface expansion layer.

[0164] A manila paper separator was placed between the anode and cathode bodies, which were stacked alternately. Plastic crystals were attached to the separator. P12BScB was used as the plastic crystals. P12BScB was purified using the same method and conditions as in Example 1. The P12BScB plastic crystals were added to acetonitrile at a ratio of 40 wt% to the total solution. This acetonitrile solution was dripped onto the separator, impregnating the separator with the acetonitrile solution. After impregnation, the stack of anode bodies, cathode bodies, and separators was left in a vacuum atmosphere at 90°C for 14 hours to dry the acetonitrile solution. This resulted in the formation of an electrolyte layer containing a conductive polymer and plastic crystals. The amount of plastic crystals attached was 20 mg per cell.

[0165] (Characteristics test) A voltage was applied to the electrolytic capacitor of Example 3. A voltage of 50 V was applied to the electrolytic capacitor of Example 3 in a temperature environment of 140°C, and a current of 0.2 mA was continuously passed for 100 hours. After this voltage application, the electrolytic capacitor was disassembled, the anode body was removed, and the anode body was washed with water and acetonitrile.

[0166] The cross-sectional sample of the removed anode body was analyzed using energy dispersive X-ray spectroscopy (SEM-EDX), and photographs were obtained that mapped the distribution of each element. Figure 1 is a photograph that maps the distribution of each element: carbon, oxygen, and aluminum. Figure 2 is a photograph that maps the distribution of boron.

[0167] The photograph in Figure 1 confirms the presence of an oxide layer B, in which oxygen is distributed, on top of the base metal layer A of the aluminum foil, in which aluminum is distributed. This oxide layer B is a dielectric film layer obtained when the aluminum foil is oxidized through chemical conversion treatment. The presence of a deposit layer C, in which carbon is distributed, can be confirmed on top of this oxide layer B. Oxygen distribution can also be confirmed in the deposit layer C. The photograph in Figure 2 confirms the presence of a deposit layer C, in which boron is distributed, in the same position as the deposit layer in the photograph in Figure 1.

[0168] That is, a deposit layer C containing carbon and boron exists on top of the oxide layer B, which is a layer of the dielectric film. Because this deposit layer C contains boron, it is believed to be a deposit layer formed by electrochemical oxidation of plastic crystals upon application of voltage. It can be seen that this deposit covers defects in the dielectric film. Furthermore, because carbon in the ligands that serve as the starting point for bonding between the anions of these plastic crystals is a component of the deposit, it can be seen that this deposit easily functions as a pseudo-repair film. Therefore, it can be seen that the leakage current of the electrolytic capacitors of Examples 1 and 2 is kept low.

Claims

1. an anode body having a dielectric coating, a cathode body facing the anode body, and an electrolyte layer interposed between the anode body and the cathode body; the electrolyte layer includes a conductive polymer and a plastic crystal; the plastic crystal contains boron in its molecular structure and does not contain halogen in its molecular structure; An electrolytic capacitor characterized by:

2. The anion component of the plastic crystal is a chelate complex consisting of a polydentate ligand which is an organic compound having the boron and at least two hydroxyl groups in its molecular structure, and sp ２ Having a double bond formed by hybrid orbitals; 2. The electrolytic capacitor according to claim 1,

3. having a deposit containing boron and carbon deposited on at least a portion of the anode body; 3. The electrolytic capacitor according to claim 1 or 2,

4. the cationic component of the plastic crystal is a quaternary ammonium cation; 4. The electrolytic capacitor according to claim 3,

5. the anion component of the plastic crystal is a bis(salicylate)borate anion; the cationic component of the plastic crystal is an N-ethyl-N-methylpyrrolidinium cation or a spiro-type pyrrolidinium cation; 4. The electrolytic capacitor according to claim 3,

6. the plastic crystal is an ionic organic substance having a solid-solid phase transition point, ionic conductivity, the solid-solid phase transition point being lower than room temperature, and the melting point being higher than room temperature; 2. The electrolytic capacitor according to claim 1,

7. The solid-solid phase transition point occurs at a temperature lower than the melting point during a temperature rise in differential scanning calorimetry (DSC), and is a point at which a negative peak occurs in the value of heat flow per unit weight.

7. The electrolytic capacitor according to claim 6,

8. the conductive polymer has π-conjugation; 2. The electrolytic capacitor according to claim 1,

9. the conductive polymer contains poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid; 9. The electrolytic capacitor according to claim 8,

10. an electrolyte layer forming step of forming an electrolyte layer between a pair of electrodes, The electrolyte layer forming step includes: a polymer attachment step of attaching a conductive polymer to one or both of the pair of electrodes; a plastic crystal attachment step of attaching a plastic crystal having a molecular structure containing boron and no halogen to one or both of the pair of electrodes; having A method for manufacturing an electrolytic capacitor, comprising:

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