Electrolytic capacitor and method for manufacturing the same

Abstract

To provide a technique for solving a problem in which storage stability of an electrolyte deteriorates due to deposition of a solute component of the electrolyte at low temperature, resulting in deterioration in ESR (equivalent series resistance) characteristics of an electrolytic capacitor.SOLUTION: A method for manufacturing an electrolytic capacitor including a foil-shaped anode body 21 having a dielectric layer on a surface and a foil-shaped cathode body 22 includes the steps of: forming a capacitor element precursor by winding or laminating a separator 23 and an anode body and a cathode body facing each other with the separator interposed therebetween; impregnating the capacitor element precursor with a treatment liquid containing a polyhydric alcohol, a solvent, and a conductive polymer component; impregnating the capacitor element precursor with a liquid component; and eluting the polyhydric alcohol into the liquid component to obtain a capacitor element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] As a small, large-capacity, low-ESR capacitor, there is an electrolytic capacitor that has an anode foil with a dielectric layer, a cathode body, and a conductive polymer attached to the dielectric layer. Among them, a hybrid electrolytic capacitor that uses a conductive polymer as a solid electrolyte in combination with a liquid component (electrolytic solution) is expected to reduce leakage current (for example, Patent Document 1).

[0003] In the hybrid electrolytic capacitor, attempts have been made to include various solute components (supporting salts) in the liquid component in order to provide a repair function for the dielectric layer or to improve characteristics such as withstand voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4916416 specification Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electrolyte contains a large amount of various solute components (supporting salts), which results in poor storage stability and easy precipitation of the solute components, especially at low temperatures (e.g., below freezing). As a result, the capacitor's performance is likely to deteriorate after long-term use or in low-temperature environments. Furthermore, the solute components may react with the conductive polymer, degrading the capacitor's performance or accelerating the deterioration of the conductive polymer's performance. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor including a foil-shaped anode body having a dielectric layer on a surface thereof, and a foil-shaped cathode body, the method including: step (i) of forming a capacitor element precursor by winding or stacking a separator and the anode body and the cathode body facing each other with the separator interposed therebetween; step (ii) of impregnating the capacitor element precursor with a treatment liquid containing a polyhydric alcohol, a solvent, and a conductive polymer component; step (iii) of impregnating the capacitor element precursor that has been subjected to step (ii) with a liquid component; and step (iv) of eluting the polyhydric alcohol into the liquid component to obtain a capacitor element.

[0007] Another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element, the capacitor element including a separator, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator sandwiched therebetween, a solid electrolyte layer interposed between the anode body and the cathode body, and a liquid component, the solid electrolyte layer containing a polyhydric alcohol and a conductive polymer, and the solid electrolyte layer having an unevenly distributed portion where the polyhydric alcohol is unevenly distributed. [Effects of the Invention]

[0008] The manufacturing method of the present disclosure can improve the characteristics of electrolytic capacitors. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic view showing a partially developed winding body included in the electrolytic capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for manufacturing an electrolytic capacitor according to an embodiment of the present disclosure is a method for manufacturing an electrolytic capacitor including a foil-shaped anode body having a dielectric layer on a surface thereof and a foil-shaped cathode body, and includes the following steps (i) to (iv): (i) forming a capacitor element precursor by winding or stacking a separator and an anode body and a cathode body facing each other with the separator in between; (ii) a step of impregnating a capacitor element precursor with a treatment liquid containing a polyhydric alcohol, a solvent, and a conductive polymer component; (iii) impregnating the capacitor element precursor obtained in step (ii) with a liquid component; and (iv) A step of dissolving the polyhydric alcohol into the liquid component to obtain a capacitor element.

[0011] According to the manufacturing method of this embodiment, in step (ii), the polyhydric alcohol and the conductive polymer component are attached to the capacitor element precursor, and then in step (iii), the liquid component is condensed. By impregnating the capacitor element precursor with the conductive polymer, the conductive polymer adheres to the surface of the anode body and / or separator, allowing for the production of electrolytic capacitors with excellent characteristics. In particular, electrolytic capacitors with low ESR (equivalent series resistance) can be realized. Furthermore, deterioration of characteristics in low-temperature environments can be suppressed.

[0012] Polyhydric alcohols include organic compounds (e.g., non-polymeric organic compounds) containing multiple hydroxyl groups (-OH) bonded to carbon atoms, including sugars such as glucose. Other examples of polyhydric alcohols include mannitol, sorbitol, xylitol, volemitol, pentaerythritol, trimethylolpropane, and glycerin. Mannitol, sorbitol, xylitol, volemitol, and pentaerythritol are also called sugar alcohols. Compounds having three or more hydroxy groups may also be used as polyhydric alcohols.

[0013] Polyhydric alcohols, which contain multiple hydroxyl groups, easily bond with the hydroxyl groups present on the surfaces of the anode body and separator. Therefore, by impregnating a capacitor element precursor with a treatment liquid containing polyhydric alcohols, a solvent, and a conductive polymer component, and then removing the solvent by drying, the conductive polymer adheres to the anode body and separator. As a result, the conductive polymer adheres tightly to the anode body, reducing the ESR of the electrolytic capacitor.

[0014] Furthermore, in step (iv), the polyhydric alcohols are dissolved into the liquid component, which lowers the melting point of the liquid component due to freezing point depression, allowing the viscosity of the liquid component to be maintained low even in low-temperature environments. This improves low-temperature properties. After step (iv), the polyhydric alcohols are contained in the liquid component in an amount ranging from 0.1% by mass to 1% by mass.

[0015] In step (ii), the polyhydric alcohols adhere to the conductive polymer layer so as to be incorporated therein, and may be unevenly distributed near the conductive polymer. A conductive polymer layer (solid electrolyte layer) may be formed between the anode body or cathode body and the separator. Some of the polyhydric alcohols may be unevenly distributed in a precipitated state within the conductive polymer layer without dissolving even after impregnation with the liquid component. The polyhydric alcohols are thought to be unevenly distributed in a dispersed state within the conductive polymer layer. In other words, the solid electrolyte layer is not dense but has hollow portions, such as a sponge, and the polyhydric alcohols are thought to be precipitated in the hollow portions. Even after step (iv), the liquid component and the polyhydric alcohols (not dissolved in the liquid component) may be unevenly distributed in the hollow portions. This structure can improve the characteristics of electrolytic capacitors.

[0016] In step (ii), the treatment liquid may contain an acid component in addition to the polyhydric alcohol. In addition to the polyhydric alcohol and the acid component, the treatment liquid may also contain a base component. That is, in step (ii), the acid component may be contained in the treatment liquid in the form of a salt with the base component.

[0017] The acid component contained in electrolytic capacitors supplies oxygen to the damaged area when the oxide film that makes up the dielectric layer is damaged, repairing the damage. The inclusion of the acid component in the liquid component allows damage to the dielectric layer to be repaired, maintaining low leakage current (LC) and high breakdown voltage. However, if the acid component in the liquid component is excessive, it can precipitate in low-temperature environments, leading to a deterioration in performance. Furthermore, the ESR (equivalent series resistance) is likely to increase with long-term use.

[0018] In the manufacturing method of this embodiment, by adding an acid component to the treatment liquid in step (ii), the acid component can be unevenly distributed near the conductive polymer, similar to the polyhydric alcohols. After step (iv), some of the acid component dissolves in the liquid component, but some is unevenly distributed near the conductive polymer and near the anode body. This allows for a high dielectric layer repair effect while limiting the amount of acid component contained in the liquid component. As a result, leakage current can be reduced and breakdown voltage can be increased while suppressing deterioration of low-temperature characteristics and increase in ESR due to long-term use.

[0019] The acid component can also have the effect of suppressing deterioration caused by the desorption of dopants contained in the conductive polymer. Therefore, by including an acid component in the liquid component, the decrease in conductivity caused by dedoping of the conductive polymer is suppressed, and the ESR can be maintained low even during long-term use. In addition, the withstand voltage is improved.

[0020] The liquid component may contain an aprotic solvent or a protic solvent. The aprotic solvent easily dissolves acid components but poorly dissolves polyhydric alcohols. Therefore, the acid components can be selectively eluted into the liquid component relative to the polyhydric alcohols. This suppresses the degradation of the conductive polymer due to dedoping, and maintains a low ESR. Meanwhile, the protic solvent easily dissolves acid components but poorly dissolves polyhydric alcohols. Therefore, the polyhydric alcohols can be selectively eluted into the liquid component relative to the acid components. This allows the acid components to be unevenly distributed near the anode body, enhancing the repair effect of the dielectric layer and effectively suppressing an increase in leakage current. Furthermore, the effect of the polyhydric alcohols in improving low-temperature characteristics can be enhanced.

[0021] The liquid component may also contain a non-polar solvent. The ratio of the aprotic solvent, the protic solvent, and the non-polar solvent in the liquid component can be adjusted appropriately depending on the desired properties of the electrolytic capacitor.

[0022] The protic solvent refers to a solvent having a Hildebrand solubility parameter (SP value) of 14 or more. The aprotic solvent refers to a solvent having a solubility parameter (SP value) of 5 or more and less than 14.

[0023] The present embodiment will be described in more detail below with reference to the accompanying drawings, although the present invention is not limited to the following embodiment.

[0024] (Step (i)) First, a separator and an anode body and a cathode body that face each other with the separator sandwiched therebetween are wound or stacked to form a capacitor element precursor, which is an element before an electrolyte layer is formed.

[0025] The foil-shaped anode body may be formed by a known method. For example, first, a metal foil, which is the raw material for the anode body, is prepared, and the surface of the metal foil is roughened. The roughening can be performed, for example, by etching using direct current electrolysis or alternating current electrolysis. Next, a dielectric layer is formed on the surface of the roughened metal foil. The dielectric layer can be formed, for example, by subjecting the metal foil to a chemical conversion treatment. The chemical conversion treatment of the metal foil oxidizes the surface of the metal foil, thereby forming a dielectric layer, which is an oxide film. In this manner, the anode body is formed.

[0026] If necessary, lead terminals for electrical connection are connected to the anode body and the cathode body.

[0027] When the electrolytic capacitor is a wound type capacitor, the capacitor element precursor can be formed, for example, by winding together a foil-shaped anode body, a foil-shaped cathode body, and a separator, with the separator disposed between the anode body and the cathode body.

[0028] When the electrolytic capacitor is a stacked type capacitor, for example, a capacitor element precursor can be formed by folding a foil-shaped anode body, a foil-shaped cathode body, and a separator together in a zigzag pattern, with the separator disposed between the anode body and the cathode body.

[0029] (Step (ii)) Next, the capacitor element precursor is impregnated with a treatment liquid containing a polyhydric alcohol, a solvent, and a conductive polymer component. The solvent may be water, a mixture of water and a nonaqueous solvent, or a nonaqueous solvent. The nonaqueous solvent is not particularly limited, but protic solvents and aprotic solvents can be used. Examples of protic solvents include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol, and ethers such as formaldehyde and 1,4-dioxane. Examples of aprotic solvents include amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, and ketones such as methyl ethyl ketone.

[0030] The polyhydric alcohols may be any of the compounds listed above. Polyhydric alcohols preferably have a high melting point. The higher the melting point, the more easily the polyhydric alcohol penetrates deep into the pores of the porous anode body during the solvent drying process after impregnation with the treatment solution. Therefore, hydroxy groups of the polyhydric alcohol bond with hydroxy groups on the surface of the anode body deep in the porous portion of the anode body, enhancing the adhesion of the conductive polymer. This improves the ESR. The melting point of the polyhydric alcohols may be 80°C or higher, 100°C or higher, or 150°C or higher. Among the polyhydric alcohols listed above, the melting point of glucose is approximately 146 to 150°C, that of mannitol is approximately 165 to 169°C, that of sorbitol is approximately 93 to 95°C, that of xylitol is approximately 92 to 97°C, that of pentaerythritol is approximately 257 to 260°C, and that of trimethylolpropane is approximately 56 to 58°C. Note that the melting points of these substances may vary depending on their structures (stereoisomers).

[0031] The solvent of the treatment liquid may be, for example, water. The impregnation can be performed, for example, by immersing the capacitor element precursor in the aqueous treatment liquid. The aqueous treatment liquid is a treatment liquid containing water. The amount of water contained in the liquid (solvent) constituting the aqueous treatment liquid is, for example, in the range of 50 to 100 mass %.

[0032] The immersion time is not particularly limited, but may be, for example, 1 minute or more and 20 minutes or less. The entire capacitor element precursor may be immersed in the aqueous treatment liquid, or only a portion of the capacitor element precursor may be immersed in the aqueous treatment liquid. For example, only 50% or less of the capacitor element precursor in the longitudinal direction (axial direction in the case of a wound body) may be immersed in the aqueous treatment liquid.

[0033] The impregnation with the treatment liquid may be carried out at room temperature or at a temperature other than room temperature (for example, a temperature higher than room temperature), and may be carried out under atmospheric pressure or under an environment other than atmospheric pressure (for example, under reduced pressure).

[0034] The content of polyhydric alcohols in the treatment liquid may be 0.1% by mass or more and 10% by mass or less. By making the content of polyhydric alcohols 0.1% by mass or more, the effect of reducing ESR can be obtained. On the other hand, as the content of polyhydric alcohols increases, the viscosity of the treatment liquid increases, which may make it difficult to impregnate the conductive polymer. From the viewpoint of facilitating impregnation of the conductive polymer, the content of polyhydric alcohols may be 10% by mass or less.

[0035] In the treatment liquid, the conductive polymer component may be a conductive polymer or a precursor of a conductive polymer. That is, a treatment liquid in which a conductive polymer is dispersed may be impregnated into a capacitor element precursor to form a conductive polymer layer (solid electrolyte layer) in the space between the anode body and the separator, or a solid electrolyte layer may be formed by polymerizing a conductive polymer precursor (e.g., a raw material monomer) on the dielectric layer of the anode body. The solid electrolyte layer may be composed of a single layer, or may be composed of two or more layers made of different materials by performing impregnation multiple times. The conductive polymer material may be one described below.

[0036] The concentration of the conductive polymer contained in the treatment liquid (polymer dispersion) in which the conductive polymer is dispersed is preferably 0.5 to 10% by mass. The average particle size D50 of the conductive polymer is preferably, for example, 0.01 to 0.5 μm. Here, the average particle size D50 is the median diameter in the volumetric particle size distribution determined by a particle size distribution measuring device using dynamic light scattering. The polymer dispersion can be obtained, for example, by a method of dispersing a conductive polymer in a liquid dispersion medium, or a method of polymerizing a precursor monomer in a liquid dispersion medium to generate conductive polymer particles.

[0037] The treatment liquid may contain an acid component in addition to the conductive polymer component and polyhydric alcohol. The acid component has the effect of suppressing dedoping of the conductive polymer. The treatment liquid may further contain a base component.

[0038] The acid component may include a compound containing an acidic functional group. Examples of the acidic functional group include a carboxy group, a hydroxy group, a sulfo group, a phosphate group, a nitro group, and an oxo group. The acid component may include a carboxylic acid, a phosphoric acid, a sulfonic acid, a boric acid, and / or a salt thereof. More specifically, the acid component may include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, resorcylic acid, borodisalicylic acid, etc. The compound containing an acidic functional group may be a polycarboxylic acid or a compound having a phenolic hydroxy group.

[0039] As the acid component, polycarboxylic acids and monocarboxylic acids can be used. Examples of polycarboxylic acids include aliphatic polycarboxylic acids (saturated polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, and 5,6-decanedicarboxylic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, and itanoic acid), aromatic polycarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid), and alicyclic polycarboxylic acids (cyclohexane-1,2-dicarboxylic acid and cyclohexene-1,2-dicarboxylic acid). Examples of the monocarboxylic acid include aliphatic monocarboxylic acids (having 1 to 30 carbon atoms) ([saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, and behenic acid]; [unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, and naphthoic acid), and oxycarboxylic acids (such as salicylic acid, mandelic acid, and resorcylic acid). Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcylic acid are preferably used because they have high conductivity and thermal stability.

[0040] Inorganic acids include carbon compounds, hydrogen compounds, boron compounds, sulfur compounds, nitrogen compounds, and phosphorus compounds. Representative examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, fluoroboric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. Furthermore, a composite compound of an organic acid and an inorganic acid can be used as the acid component, such as borodiglycolic acid, borodisoxalic acid, and borodisalicylic acid.

[0041] In addition to the acid component, the processing solution may contain a base component. Examples of basic components include metal hydroxides such as sodium hydroxide and potassium hydroxide, and nitrogen-containing basic compounds such as aliphatic amines and cyclic amines. Among these, compounds having an alkyl-substituted amidine group, such as imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds), can provide capacitors with high conductivity and excellent impedance performance. Examples of compounds having an alkyl-substituted amidine group include 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole. Quaternary salts of compounds having an alkyl-substituted amidine group may also be used as the base component. Specific examples include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) quaternized with an alkyl group or arylalkyl group having 1 to 11 carbon atoms.

[0042] Tertiary amines can also be used as the base component, and examples thereof include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, and tri-tert-butylamine), and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, and diethylphenylamine). Among these, trialkylamines are preferred due to their high conductivity, and it is more preferable to use at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia may also be used as the base component.

[0043] The base component may be contained in the treatment solution in the form of a salt with an acid component, such as trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, or mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0044] After the impregnation, the solvent contained in the treatment solution is removed by drying, thereby forming a solid electrolyte layer between the anode body and the separator, and the polyhydric alcohol precipitates, with at least a portion of the polyhydric alcohol adhering to the anode body, the separator, and the solid electrolyte layer. Furthermore, if the treatment solution contains an acid component or a base component, these components may also precipitate and adhere to the anode body, the separator, and the solid electrolyte layer.

[0045] The conductive polymer, polyhydric alcohol, and acid component may be attached so as to cover at least a portion of the dielectric layer on the surface of the anode body, and to fill at least a portion of the pores of the roughened anode body.

[0046] Drying is usually performed by heating. Drying may be performed under atmospheric pressure or under an environment other than atmospheric pressure (e.g., reduced pressure). The drying temperature may be a temperature equal to or higher than the melting point of the polyhydric alcohol, and may also be a temperature equal to or higher than the boiling point of the solvent under the pressure at which drying is performed (e.g., 100°C or higher). In a preferred example, the drying temperature is a temperature equal to or higher than the boiling point of the solvent under the pressure at which drying is performed (e.g., 100°C or higher), and is a temperature equal to or higher than the melting point but lower than the boiling point of the polyhydric alcohol under the pressure at which drying is performed. Drying at a temperature equal to or higher than the melting point of the polyhydric alcohol can enhance the permeability of the polyhydric alcohol into the capacitor element precursor. The drying temperature may be, for example, 150°C or higher or 180°C or higher.

[0047] If necessary, the impregnation with the treatment liquid (step (ii)) and the drying step may be repeated. By repeating step (ii), the amounts of polyhydric alcohols and acid components precipitated can be increased.

[0048] (Step (iii)) The capacitor element precursor is then impregnated with a liquid component, which may be a substance that is liquid at room temperature (25°C) or at the temperature at which the electrolytic capacitor is used.

[0049] The method for impregnating the liquid component is not particularly limited. For example, a method of immersing the capacitor element precursor in the liquid component contained in a container is simple and preferable. The impregnation is preferably carried out under reduced pressure, for example, in an atmosphere of 10 to 100 kPa. Examples of the liquid component include the materials described above.

[0050] The liquid component contains a solvent that dissolves the polyhydric alcohol. If necessary, it may contain other solutes that dissolve in the solvent. The liquid component may contain the above-mentioned acid component and / or base component. The acid component and / or base component can be selected from the compounds exemplified in the above-mentioned treatment liquid.

[0051] The liquid component may be a non-aqueous solvent, or a mixture of a non-aqueous solvent and an ionic substance (solute, for example, an organic salt) dissolved therein (i.e., an electrolyte). The non-aqueous solvent may be an organic solvent or an ionic liquid. A high-boiling-point solvent is preferred as the non-aqueous solvent. Examples of non-aqueous solvents include polyhydric alcohols such as ethylene glycol (EG) and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (GBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde.

[0052] Furthermore, a polymer solvent may be used as the non-aqueous solvent. Examples of polymer solvents include polyalkylene glycol, polyalkylene glycol derivatives, and compounds in which at least one hydroxyl group in a polyhydric alcohol has been substituted with polyalkylene glycol (including derivatives). Specific examples of polymer solvents include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol. Further examples of polymer solvents include ethylene glycol-propylene glycol copolymer, ethylene glycol-butylene glycol copolymer, and propylene glycol-butylene glycol copolymer. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0053] In order to suppress dedoping of the dopant in the conductive polymer, the pH of the liquid component may be set to less than 7, or may be set to 5 or less. The pH of the liquid component may be adjusted after step (iv) so that the liquid component has the above-mentioned acidity after elution of the acid component.

[0054] The liquid component may be a protic solvent or an aprotic solvent. Protic solvents tend to elute polyhydric alcohols in the step (iv) described below. Therefore, the eluted polyhydric alcohols can improve low-temperature characteristics. On the other hand, aprotic solvents tend to elute polyhydric alcohols in the step (iv). In this case, the adhesion of the conductive polymer to the anode body is improved, and the ESR can be reduced. It is preferable that 50% by mass or more of the entire liquid component is an aprotic solvent and less than 50% by mass is a protic solvent. It is even more preferable that 60% by mass or more of the entire liquid component is an aprotic solvent and less than 40% by mass is a protic solvent. That's fine.

[0055] The liquid component may or may not be an electrolytic solution. The liquid component may be substantially free of solutes and may not have substantial electrical conductivity. For example, in step (iii), the electrical conductivity X1 of the liquid component is preferably 1 μS / cm or less.

[0056] (Step (iv)) Subsequently, the polyhydric alcohol is dissolved into the liquid component, thereby obtaining a capacitor element. Step (iv) can be carried out simultaneously with or in parallel to step (iii).

[0057] By impregnating the liquid component, at least a portion of the polyhydric alcohols, acid components and / or base components precipitated in step (ii) is eluted, resulting in an increase in the electrical conductivity of the liquid component.

[0058] After step (iv), the liquid component into which the polyhydric alcohols and / or acid components have been eluted has an electrical conductivity X2 higher than X1 (X2>X1) and preferably 500 μS / cm or less. The electrical conductivity X2 of the liquid component may be 0.1 μS / cm or more and 500 μS / cm or less, more preferably 0.1 μS / cm or more and 100 μS / cm or less, 0.5 μS / cm or more and 500 μS / cm or less, or 0.5 μS / cm or more and 100 μS / cm or less.

[0059] When a treatment liquid containing an acid component is used in step (ii), the acid component may be eluted into the liquid component in step (iv). The eluted acid component suppresses a decrease in conductivity due to dedoping of the conductive polymer, allowing the ESR to be maintained low even during long-term use. It also improves the withstand voltage. However, if the elution of the acid component is excessive, the ESR may increase and the low-temperature characteristics may deteriorate over long-term use. In order to suppress an increase in ESR and a deterioration in low-temperature characteristics over long-term use, the content of the acid component in the liquid component after step (iv) is preferably 0.01% by mass or more and 2% by mass or less, based on the total amount of the liquid component containing the acid component.

[0060] When a treatment liquid containing a base component is used in step (ii), the base component may leach out into the liquid component. In this case, in order to further suppress an increase in ESR due to long-term use, the content of the base component in the liquid component after step (iv) is preferably 2 mass% or less based on the total amount of the liquid component containing the base component.

[0061] The content of each solute, such as an acid component, a base component, or a polyhydric alcohol, in the liquid component can be measured by extracting the liquid component from the electrolytic capacitor using a centrifuge and then subjecting it to microscopic FT-IR analysis or liquid chromatography.

[0062] The liquid component after step (iv) may contain the solvent (e.g., water) of the treatment liquid that was not removed in the drying step after step (ii). If the liquid component contains a large amount of water, the water may evaporate when heat is applied to the electrolytic capacitor during a reflow process or the like, and the vapor may reduce the airtightness of the case sealing the electrolytic capacitor. After step (iv), the water content of the liquid component is preferably 5% by mass or less, more preferably 3% by mass or less.

[0063] An electrolytic capacitor is manufactured using the capacitor element obtained in step (iv). There is no particular limitation on the method for manufacturing an electrolytic capacitor using the capacitor element, and a known method may be applied. For example, the capacitor element may be placed in a case and sealed.

[0064] An example of the structure of an electrolytic capacitor manufactured by the manufacturing method of this embodiment will be described in detail below.

[0065] [Electrolytic capacitor] An electrolytic capacitor according to one embodiment of the present invention is an electrolytic capacitor including a capacitor element, the capacitor element including a separator, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator sandwiched therebetween, a solid electrolyte layer interposed between the anode body and the cathode body, and a liquid component. The solid electrolyte layer contains a polyhydric alcohol and a conductive polymer. The solid electrolyte layer has an unevenly distributed portion where the polyhydric alcohol is unevenly distributed. The liquid component (electrolytic solution or solvent) and the conductive polymer are used as an electrolyte.

[0066] FIG. 1 is a cross-sectional view of the electrolytic capacitor according to this embodiment, and FIG. 2 is a schematic view showing a partially developed wound body included in the electrolytic capacitor.

[0067] 1, the electrolytic capacitor includes, for example, a capacitor element 10, a bottomed case 11 that houses the capacitor element 10, a sealing member 12 that closes the opening of the bottomed case 11, a seat plate 13 that covers the sealing member 12, lead wires 14A and 14B that extend from the sealing member 12 and pass through the seat plate 13, lead tabs 15A and 15B that connect the lead wires to electrodes of the capacitor element 10, and a liquid component (not shown). The capacitor element 10 and the liquid component are housed in an outer case. The vicinity of the open end of the bottomed case 11 is drawn inward, and the open end is curled so as to be crimped to the sealing member 12.

[0068] Capacitor element 10 is fabricated, for example, by attaching a conductive polymer to a wound body as shown in Fig. 2. The wound body includes anode body 21 having a dielectric layer, cathode body 22 including a first metal having valve action, and separator 23 interposed therebetween. The conductive polymer is attached so as to cover at least a portion of the surface of the dielectric layer of anode body 21, forming a solid electrolyte layer. Capacitor element 10 further includes lead tab 15A connected to anode body 21 and lead tab 15B connected to cathode body 22.

[0069] Anode body 21 and cathode body 22 are wound with separator 23 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 24. Note that FIG. 2 shows a partially unfolded state of the wound body before the outermost periphery is fixed. Anode body 21 includes a metal foil whose surface has been roughened to have projections and recesses, and a dielectric layer is formed on a main surface of the metal foil having projections and recesses.

[0070] (anode body) The anode body has a dielectric layer on its surface. The anode body can be a metal foil with a dielectric layer formed on its surface. The type of metal contained in the metal foil is not particularly limited, but valve-acting metals such as aluminum, tantalum, niobium, and titanium, and alloys of valve-acting metals are preferred because they facilitate the formation of a dielectric layer. Among these, simple metals such as aluminum and alloys such as aluminum alloys are preferred. Usually, the surface of the anode body is roughened, and a dielectric layer is formed on the roughened surface of the metal foil.

[0071] (cathode body) The cathode body can be made of a metal foil. The type of metal contained in the metal foil is not particularly limited, and examples thereof include valve-action metals such as aluminum, tantalum, niobium, and titanium, or alloys of valve-action metals. The metal contained in the metal foil can be a single metal such as aluminum or an alloy such as an aluminum alloy. The surface of the cathode body can be roughened or not. Furthermore, the surface of the cathode body can be provided with a chemical conversion coating, or with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the cathode body. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon.

[0072] (separator) The separator may be a sheet-like material that can be impregnated with an electrolyte, such as an insulating sheet-like material that can be impregnated with an electrolyte. The separator may be a woven fabric, a nonwoven fabric, or a porous membrane. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0073] (conductive polymer) Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and polyaniline. These may be used alone, or two or more types may be used in combination, or a copolymer of two or more types of monomers may be used. The weight-average molecular weight of the conductive polymer is not particularly limited, but is, for example, 1,000 to 100,000.

[0074] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, etc. refer to polymers having a basic skeleton of polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, etc., respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT), etc.

[0075] A dopant may be added to the conductive polymer. From the viewpoint of suppressing dedoping from the conductive polymer, it is desirable to use a polymer dopant. Examples of polymer dopants include anions of polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used alone or in combination of two or more. Furthermore, these may be homopolymers or copolymers of two or more monomers. Among these, polystyrene sulfonic acid (PSS) is preferred.

[0076] The weight average molecular weight of the dopant is not particularly limited, but is preferably, for example, 1,000 to 100,000 in terms of facilitating the formation of a homogeneous solid electrolyte layer.

[0077] The conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0078] Polyhydric alcohols (not shown) are unevenly distributed within the solid electrolyte layer. Some of the polyhydric alcohols are dissolved into the liquid component, while the remaining part is unevenly distributed and precipitated in a dispersed state within the solid electrolyte layer.

[0079] In the above embodiment, a wound-type electrolytic capacitor has been described, but the scope of application of the present invention is not limited to the above, and the present invention can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a metal sintered body as an anode body, and stacked-type electrolytic capacitors that use a metal plate as an anode body.

[0080] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0081] Example 1 In this example, a wound electrolytic capacitor (diameter 8 mm×length 12 mm) was fabricated with a rated voltage of 100 V and a rated capacitance of 18 μF. A specific method for fabricating the electrolytic capacitor will be described below.

[0082] The electrolytic capacitor shown in Figure 1 was fabricated as follows, and its characteristics were evaluated. (1) Fabrication of capacitor elements

[0083] (Preparation of the cathode body) As the cathode body, an Al foil (aluminum foil) having a thickness of 50 μm was used.

[0084] (Preparation of the anode body) An Al foil with a thickness of 120 μm was prepared. This Al foil was subjected to a DC etching treatment to roughen the surface. Next, the Al foil was subjected to a chemical conversion treatment to form a dielectric layer (thickness: approximately 70 nm), thereby obtaining an anode body. The dielectric layer was formed by immersing the Al foil in an ammonium adipate solution and performing a chemical conversion treatment at 70°C for 30 minutes while applying a voltage of 180 V to the Al foil. The anode body was then cut to a predetermined size to prepare an anode body.

[0085] (Production of wound body) An anode lead tab and a cathode lead tab, each connected to a lead wire, were connected to the prepared anode body and a cathode body having a conductor layer on their end surfaces, respectively. The anode body and the cathode body were wound with a separator interposed therebetween while rolling up the lead tabs, and the outer surfaces were fixed with a winding stop tape to produce a wound body, thereby obtaining a capacitor element precursor. The capacitor element precursor was immersed in an ammonium adipate solution, and a voltage of 180 V was applied to the anode body while performing chemical conversion treatment again at 70°C for 60 minutes, thereby forming a dielectric layer mainly on the end surface of the anode body.

[0086] (Preparation of processing solution) A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and polystyrene sulfonic acid as a dopant in ion-exchanged water. Iron (III) sulfate (oxidant) dissolved in ion-exchanged water was added to the resulting mixed solution while stirring, and a polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidant, yielding a polymer dispersion containing polyethylenedioxythiophene doped with approximately 2% by mass of polystyrene sulfonic acid.

[0087] Mannitol (MAN) was added as a polyhydric alcohol to the polymer dispersion and mixed to obtain a treatment liquid. The amount of mannitol added was adjusted to 5% by mass based on the total amount of the treatment liquid.

[0088] (Impregnation of treatment liquid and drying) The capacitor element precursor was then immersed in a treatment liquid contained in a predetermined container at room temperature under reduced pressure for 5 minutes. At this time, the capacitor element precursor was immersed in the first aqueous treatment liquid from the side where the lead tab was not connected. Thereafter, the capacitor element precursor was pulled out of the treatment liquid. Thereafter, the capacitor element precursor impregnated with the treatment solution was dried for 30 minutes in a drying oven at 180° C. In this way, the polyhydric alcohol and the conductive polymer were adhered to the capacitor element precursor so as to cover the dielectric layer of the anode body.

[0089] (Impregnation of liquid components) The capacitor element precursor was impregnated with γ-butyrolactone (GBL) as a liquid component at room temperature and atmospheric pressure.

[0090] (Sealing of capacitor elements) The capacitor element impregnated with the liquid component was sealed to complete the electrolytic capacitor, which was then subjected to aging treatment at 130°C for 2 hours while applying the rated voltage.

[0091] (evaluation) The initial ESR value and low-temperature characteristics of the obtained electrolytic capacitor were evaluated according to the following procedures. First, in an environment of 20° C., the initial ESR value X1 (mΩ) at a frequency of 100 kHz was measured using an LCR meter for four-terminal measurement.

[0092] Next, the electrolytic capacitor was charged at the rated voltage for 60 seconds in an environment of 20°C, and the current flowing when the rated voltage was applied to the charged electrolytic capacitor was measured and taken as the initial leakage current value LC0.

[0093] Next, the electrolytic capacitor was placed in a -55°C environment for 30 minutes. After that, the electrolytic capacitor was placed in a 125°C environment for 30 minutes. This cycle was repeated 1000 times. After 1000 cycles, the electrolytic capacitor was placed in a 20°C environment, and the ESR was measured in the same manner as the initial ESR measurement, and this was taken as the ESR value after the evaluation test, X2. The ratio of the ESR value after the test to the initial ESR value, X2 / X1, was also evaluated.

[0094] Examples 2 to 7 In Example 1, the polyhydric alcohols and the like added to the treatment liquid and the amounts thereof, and the solvent of the liquid component were changed as shown in Table 1. Otherwise, electrolytic capacitors were produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1.

[0095] In Example 2, a mixed solvent of γ-butyrolactone (GBL) and sulfolane (SL) in a mass ratio of 50:50 was used as the liquid component. In Example 3, in addition to mannitol, mono(triethylamine) borodisalicylate (BSA / TEA) was added as an acid component at a ratio of 3% by mass relative to the total amount of the treatment solution. Also, a mixed solvent of γ-butyrolactone (GBL) and sulfolane (SL) in a mass ratio of 50:50 was used as the liquid component.

[0096] In Example 4, ethylene glycol (EG) was used as the liquid component. In Example 5, a mixed solvent of ethylene glycol (EG) and polyethylene glycol (PEG) (weight average molecular weight 200) mixed in a mass ratio of 50:50 was used as the liquid component.

[0097] In Example 6, volemitol (VOL) was added as a polyhydric alcohol to the treatment liquid at a ratio of 5 mass % relative to the entire treatment liquid, and ethylene glycol (EG) was used as a liquid component. In Example 7, xylitol (XYL) was added as a polyhydric alcohol to the treatment liquid at a ratio of 5 mass % relative to the entire treatment liquid, and ethylene glycol (EG) was used as a liquid component. In Example 8, sorbitol (SOR) was added as a polyhydric alcohol to the treatment liquid at a ratio of 5 mass % relative to the entire treatment liquid, and ethylene glycol (EG) was used as a liquid component. In Example 9, a mixed solvent of ethylene glycol (EG) and γ-butyrolactone (GBL) in a mass ratio of 30:70 was used as the liquid component.

[0098] Comparative Examples 1 to 3 No polyhydric alcohols were added to the processing solution. In Comparative Example 1, a solvent in which γ-butyrolactone (GBL) and mannitol (MAN) were mixed in a mass ratio of 98:2 was used as the liquid component. In Comparative Example 2, GBL was used as the liquid component, as in Example 1. In Comparative Example 3, ethylene glycol (EG) was used as the liquid component. Other than that, an electrolytic capacitor was produced in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0099] Comparative Example 4 In Example 1, no polyhydric alcohols were added to the treatment liquid, and borodisalicylic acid mono(triethylamine) (BSA / TEA) was added as an acid component in a proportion of 3% by mass relative to the total treatment liquid. Other than that, an electrolytic capacitor was produced in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0100] Comparative Example 5 In Example 1, an electrolytic capacitor (solid electrolytic capacitor) was produced without impregnating with a liquid component, and evaluated in the same manner as in Example 1.

[0101] Table 1 shows the polyhydric alcohols and acid components added to the treatment solution, the amounts of these components added, the composition of the liquid components, and the electrical conductivity of the liquid components after aging treatment for the electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 5. Table 2 shows the evaluation results of the initial ESR and leakage current for the electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 5.

[0102] [Table 1]

[0103] [Table 2]

[0104] As can be seen from Tables 1 and 2, the electrolytic capacitors of Examples 1 to 9, which were fabricated by impregnating the capacitors with a treatment solution containing a conductive polymer and polyhydric alcohols, removing the solvent component of the treatment solution by drying, and then impregnating the capacitors with a liquid component, have smaller LC1 / LC0 and suppressed increases in ESR after repeated exposure to high-temperature and low-temperature environments compared to the electrolytic capacitors of Comparative Examples 1 to 5. Furthermore, the initial ESR is also low.

[0105] In Examples 1 to 3, an aprotic solvent or a mixed solvent of aprotic solvents is used as the solvent for the treatment solution. In this case, polyhydric alcohols are difficult to elute, so most of the polyhydric alcohols are unevenly distributed on the surface of the anode body and in the conductive polymer layer. In this case, the conductive polymer layer (solid electrolyte layer) has good adhesion to the anode body, and the initial ESR is significantly reduced.

[0106] In Examples 4 to 6, a protic solvent or a mixed solvent of protic solvents is used as the solvent for the treatment liquid. In this case, polyhydric alcohols are easily eluted, and the concentration of polyhydric alcohols present in the liquid component is higher than in Examples 1 to 3. In this case, the change in ESR, X2 / X1, tends to be smaller than in Examples 1 to 3.

[0107] In Examples 7 and 8, the initial ESR and X2 / X1 were slightly higher than those in Examples 1 to 6. This is thought to be because the melting points of the polyhydric alcohols used in Examples 7 and 8 (xylitol 94°C, sorbitol 95°C) were lower than those of the polyhydric alcohols used in Examples 1 to 6 (mannitol 167°C, volemitol 152°C). The melting points of the polyhydric alcohols are preferably 100°C or higher, and more preferably 150°C or higher.

[0108] In Example 9, a mixed solvent of a protic solvent and an aprotic solvent was used as the solvent for the treatment liquid, which made it possible to reduce the initial ESR and also reduce X2 / X1. [Industrial Applicability]

[0109] The present invention can be used in a hybrid electrolytic capacitor that uses a conductive polymer and a liquid component. [Explanation of symbols]

[0110] 10: Capacitor element, 11: Bottomed case, 12: Sealing member, 13: Seat plate, 14A, 14B: Lead wires, 15A, 15B: Lead tabs, 21: Anode body, 22: Cathode body, 23: Separator, 24: Winding tape

Claims

1. The capacitor element includes a foil-shaped anode body having a dielectric layer on its surface and a foil-shaped cathode body. A method for manufacturing an electrolytic capacitor comprising: A separator, and the anode body and the cathode body facing each other with the separator in between. forming a capacitor element precursor by rolling or laminating; A treatment liquid containing polyhydric alcohols, a solvent, and a conductive polymer component is applied to the capacitor. impregnating a device precursor; After the step of impregnating the capacitor element precursor with the treatment liquid, impregnating the precursor with a liquid component; The polyhydric alcohol is eluted into the liquid component, thereby forming the capacitor element and obtaining In the step of impregnating the capacitor element precursor with the liquid component, The content of the aprotic solvent is 50% by mass or more, After the step of obtaining the capacitor element, the polyvalent ammonium salt is The content of the alcohols is 0.1% by mass or more and 1% by mass or less, and the content of the polyhydric alcohols is The electrical conductivity X2 of the liquid component into which the eluate is dissolved is 0.1 μS / cm or more and 500 μS / cm or less. A method for manufacturing an electrolytic capacitor.

2. In the step of impregnating the capacitor element precursor with the liquid component, 2. The method for producing an electrolytic capacitor according to claim 1, wherein the electrical conductivity X1 is 1 μS / cm or less.

3. After the step of obtaining the capacitor element, the liquid into which the polyhydric alcohols have been dissolved is The electrical conductivity X2 of the liquid component is 3. The electrolytic capacitor according to claim 1, wherein the electrical conductivity of the liquid component is higher than X1. Manufacturing method.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the liquid component contains a protic solvent. Capacitor manufacturing method.

5. In the step of impregnating the capacitor element precursor with the liquid component, 5. The electrolytic solution according to claim 4, wherein the content of the protic solvent is less than 50 mass %. How to manufacture a capacitor.

6. The proportion of the treatment liquid in the step of impregnating the capacitor element precursor with the treatment liquid is 2. The method according to claim 1, wherein the content of the polyhydric alcohol is 0.1% by mass or more and 10% by mass or less.

6. A method for producing an electrolytic capacitor according to any one of claims 1 to 5.

7. The method according to any one of claims 1 to 6, wherein the melting point of the polyhydric alcohol is 150°C or higher. A method for manufacturing the electrolytic capacitor described above.

8. In the step of impregnating the capacitor element precursor with the treatment liquid, the treatment liquid is an acid compound. minutes, The acid component is contained in the entire liquid component after the step of obtaining the capacitor element. The method for producing an electrolytic capacitor according to any one of claims 1 to 7, wherein the proportion of the hydroxyl group is 2 mass % or less. Construction method.

9. After the step of impregnating the capacitor element precursor with the treatment liquid, a step of removing the solvent by drying before the step of impregnating the liquid component into the semiconductor element precursor; With a degree, The drying temperature in the step of removing the solvent is 150° C. or higher.

10. A method for producing the electrolytic capacitor according to claim 1.

10. An electrolytic capacitor including a capacitor element, The capacitor element is A separator; a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween; a solid electrolyte layer interposed between the anode body and the cathode body; a liquid component, the solid electrolyte layer contains a polyhydric alcohol and a conductive polymer, the solid electrolyte layer has an uneven distribution portion in which the polyhydric alcohol is unevenly distributed, The content of the aprotic solvent in the liquid component is 50% by mass or more, The content of the polyhydric alcohols in the liquid component is 0.1% by mass or more and 1% by mass or less. The electrical conductivity of the liquid component is 0.1 μS / cm or more and 500 μS / cm or less. Electrolytic capacitor.

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