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 Art]

[0002] As a small-sized, large-capacity capacitor with low ESR, there is known an electrolytic capacitor that includes an anode foil having a dielectric layer and a cathode body, and includes a conductive polymer adhering to the dielectric layer. Among these, hybrid electrolytic capacitors, which use a conductive polymer as a solid electrolyte in combination with a liquid component (electrolyte), are expected to reduce leakage current (see, for example, Patent Document 1).

[0003] In the above hybrid electrolytic capacitor, attempts have been made to incorporate various solute components (supporting salts) into the liquid component in order to provide a repair function for the dielectric layer and to improve properties such as withstand voltage. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent No. 4916416 Specification [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, when a large amount of various solute components (supporting salts) are contained in the electrolyte, the storage stability of the electrolyte deteriorates, and the solute components tend to precipitate particularly at low temperatures (e.g., below freezing). As a result, the properties of the capacitor tend to degrade after long-term use or in low-temperature environments. In addition, the solute components may react with the conductive polymer to degrade the properties of the capacitor, or may promote the degradation of the properties of the conductive polymer in some cases. [Means for Solving the Problem]

[0006] One aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor, comprising a foil-shaped anode having a dielectric layer on its surface and a foil-shaped cathode, the method comprising: (i) forming a capacitor element precursor by winding or stacking a separator and the anode and cathode facing each other with the separator in between; (ii) impregnating the capacitor element precursor with a processing solution containing polyhydric alcohols, a solvent, and a conductive polymer component; (iii) impregnating the capacitor element precursor that has gone through step (ii) with a liquid component; and (iv) dissolving the polyhydric alcohols in the liquid component to obtain a capacitor element.

[0007] Another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element, wherein the capacitor element includes a separator, a foil-shaped anode and a foil-shaped cathode facing each other with respect to the separator, a solid electrolyte layer interposed between the anode and the cathode, and a liquid component, wherein the solid electrolyte layer contains polyhydric alcohols and a conductive polymer, and the solid electrolyte layer has a segregated portion in which the polyhydric alcohols are segregated. [Effects of the Invention]

[0008] The manufacturing method disclosed herein can improve the characteristics of electrolytic capacitors. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing an electrolytic capacitor according to one embodiment of the present disclosure. [Figure 2] This is a schematic diagram showing a portion of the windings contained in the electrolytic capacitor unfolded. [Modes for carrying out the invention]

[0010] A method for manufacturing an electrolytic capacitor according to one embodiment of the present disclosure is a method for manufacturing an electrolytic capacitor comprising a foil-shaped anode having a dielectric layer on its surface and a foil-shaped cathode, comprising the following steps (i) to (iv): (i) A step of forming a capacitor element precursor by winding or stacking a separator and an anode and cathode facing each other with the separator in between, (ii) A step of impregnating a capacitor element precursor with a treatment solution containing polyhydric alcohols, a solvent, and conductive polymer components. (iii) A step of impregnating the capacitor element precursor that has gone through step (ii) with a liquid component, and (iv) A step of dissolving polyhydric alcohols in a liquid component to obtain a capacitor element.

[0011] According to the manufacturing method of this embodiment, in step (ii), polyhydric alcohols and conductive polymer components are attached to the capacitor element precursor, and then in step (iii), the liquid component is converted into a capacitor element. By impregnating the capacitor element precursor with the conductive polymer, the polymer adheres closely to the surface of the anode and / or separator, enabling the manufacture of electrolytic capacitors with superior characteristics. In particular, it is possible to realize electrolytic capacitors with low ESR (equivalent series resistance). Furthermore, it is possible to suppress the deterioration of characteristics in low-temperature environments.

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

[0013] Because polyhydric alcohols have multiple hydroxyl groups, they readily bond with hydroxyl groups present on the surfaces of the anode and separator. Therefore, by impregnating the capacitor element precursor with a treatment solution containing polyhydric alcohols, a solvent, and a conductive polymer component, and then removing the solvent by drying, the conductive polymer adheres to the anode and separator. As a result, the conductive polymer adheres closely to the anode, reducing the ESR of the electrolytic capacitor.

[0014] Furthermore, in step (iv), the dissolution of polyhydric alcohols into the liquid component lowers the melting point of the liquid component due to freezing point depression, allowing the viscosity of the liquid component to be maintained at a low temperature even in low-temperature environments. This improves the low-temperature properties. After step (iv), the polyhydric alcohols are present in an amount of 0.1% by mass or more and 1% by mass or less relative to the total liquid component.

[0015] In step (ii), the polyhydric alcohols adhere to the conductive polymer layer and may be unevenly distributed near the conductive polymer. A layer of conductive polymer (solid electrolyte layer) may be formed between the anode or cathode and the separator. Some of the polyhydric alcohols may remain unevenly distributed within the conductive polymer layer without dissolving even after impregnation with the liquid component. The polyhydric alcohols are thought to be unevenly distributed within the conductive polymer layer. That is, the solid electrolyte layer is not dense and has hollow parts, such as a sponge, and it is thought that the polyhydric alcohols precipitate in these hollow parts. Even after going through step (iv), the liquid component and the polyhydric alcohols (that have not dissolved in the liquid component) may be unevenly distributed in these hollow parts. This structure can improve the characteristics of the electrolytic capacitor.

[0016] In step (ii), the treatment solution may contain an acid component in addition to polyhydric alcohols. In addition to polyhydric alcohols and acid components, a basic component may be included in the treatment solution. That is, in step (ii), the acid component may be included in the treatment solution in the form of a salt with the basic component.

[0017] The acid component contained in an electrolytic capacitor has the function of supplying oxygen to a damaged portion of an oxide film constituting a dielectric layer when damage occurs to the oxide film, thereby repairing the damaged portion. When a liquid component contains the acid component, damage occurring in the dielectric layer can be repaired, leakage current (LC) can be kept low, and withstand voltage can be maintained at a high level. However, if the acid component contained in the liquid component is excessive, the acid component precipitates in a low-temperature environment, which tends to cause characteristic degradation. In addition, ESR (equivalent series resistance) tends to increase due to long-term use.

[0018] In the manufacturing method of the present embodiment, by including an acid component in the treatment liquid of step (ii), the acid component can be unevenly distributed in the vicinity of the conductive polymer similarly to polyhydric alcohols. After step (iv), a part of the acid component elutes into the liquid component, while a part of the acid component is unevenly distributed in the vicinity of the conductive polymer and also in the vicinity of the anode body. This makes it possible to obtain a high repair effect on the dielectric layer while limiting the amount of the acid component contained in the liquid component. As a result, leakage current can be lowered and withstand voltage can be increased while suppressing degradation of low-temperature characteristics and an increase in ESR due to long-term use.

[0019] The acid component may also have the function of suppressing deterioration caused by desorption of a dopant contained in the conductive polymer. Therefore, when the liquid component contains the acid component, a decrease in conductivity caused by dedoping of the conductive polymer is suppressed, and ESR can be maintained at a low level even during long-term use. In addition, the withstand voltage is improved.

[0020] The liquid component may contain an aprotic solvent, or may contain a protic solvent. An aprotic solvent easily dissolves acid components, but hardly dissolves polyhydric alcohols. Therefore, the acid component can be selectively eluted into the liquid component with respect to the polyhydric alcohols. This suppresses degradation of the conductive polymer caused by dedoping, and allows ESR to be maintained at a low level. On the other hand, a protic solvent hardly dissolves acid components, but easily dissolves polyhydric alcohols. Therefore, the polyhydric alcohols can be selectively eluted into the liquid component with respect to the acid component. This allows the acid component to be unevenly distributed in the vicinity of the anode body, enhances the repairing effect on the dielectric layer, and provides an excellent effect of suppressing an increase in leakage current. Furthermore, the effect of improving low-temperature characteristics by the polyhydric alcohols can be enhanced.

[0021] The liquid component may also contain a non-polar solvent. The proportions of the aprotic solvent, protic solvent, and non-polar solvent in the liquid component can be appropriately adjusted according to the required characteristics of the electrolytic capacitor.

[0022] Note that a protic solvent means a solvent having a Hildebrand solubility parameter (SP value) of 14 or more. An aprotic solvent means a solvent having the above solubility parameter (SP value) of 5 or more and less than 14.

[0023] Hereinafter, the present embodiment will be described more specifically with appropriate reference to the drawings. However, the following embodiments do not limit the present invention.

[0024] (Step (i)) First, a capacitor element precursor is formed by winding or laminating a separator, and an anode body and a cathode body facing each other with the separator interposed therebetween. The capacitor element precursor is an element before the electrolyte layer is formed.

[0025] The foil-shaped anode may be formed by known methods. For example, first, a metal foil, which is the raw material for the anode, is prepared, and the surface of the metal foil is roughened. Roughening can be done, for example, by etching using a DC electrolytic method or an AC electrolytic method. Next, a dielectric layer is formed on the surface of the roughened metal foil. The dielectric layer can be formed, for example, by chemical conversion treatment of the metal foil. 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 way, the anode is formed.

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

[0027] If the electrolytic capacitor is a wound-type capacitor, a capacitor element precursor can be formed by winding together, for example, a foil-shaped anode, a foil-shaped cathode, and a separator. In this case, the components are wound so that the separator is positioned between the anode and the cathode.

[0028] If the electrolytic capacitor is a multilayer capacitor, a capacitor element precursor can be formed, for example, by folding a foil-shaped anode, a foil-shaped cathode, and a separator together in a zigzag pattern. In this case, they are folded so that the separator is positioned between the anode and the cathode.

[0029] (Step (ii)) Next, a processing solution containing polyhydric alcohols, a solvent, and a conductive polymer component is impregnated into the capacitor element precursor. The solvent may be water, a mixture of water and a non-aqueous solvent, or a non-aqueous solvent. The non-aqueous solvent is not particularly limited, but for example, 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 compounds mentioned above can be used as polyhydric alcohols. Polyhydric alcohols with high melting points are preferred. The higher the melting point, the easier it is for the polyhydric alcohol to penetrate deep into the pores of the porous anode body during the solvent drying process after impregnation with the treatment solution. Therefore, the hydroxyl groups of the polyhydric alcohol and the hydroxyl groups on the anode body surface bond in the deep parts of the porous anode body, improving the adhesion of the conductive polymer. This improves the ESR. The melting points of the polyhydric alcohols may be 80°C or higher, 100°C or higher, or 150°C or higher. For the polyhydric alcohols listed above, the melting points are approximately 146-150°C for glucose, 165-169°C for mannitol, 93-95°C for sorbitol, 92-97°C for xylitol, 257-260°C for pentaerythritol, and 56-58°C for trimethylolpropane. Furthermore, the melting points of these substances may vary depending on their structure (stereoisomers).

[0031] The solvent in the treatment solution may be, for example, water. Impregnation can be carried out, for example, by immersing the capacitor element precursor in an aqueous treatment solution. The aqueous treatment solution is a treatment solution containing water. The amount of water contained in the liquid (solvent) that makes up the aqueous treatment solution is, for example, in the range of 50 to 100% by mass.

[0032] The immersion time is not particularly limited, but may be, for example, between 1 minute and 20 minutes. The entire capacitor element precursor may be immersed in the aqueous treatment solution, or only a part of the capacitor element precursor may be immersed in the aqueous treatment solution. 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 solution.

[0033] The impregnation with the treatment solution may be carried out at room temperature or at a temperature other than room temperature (for example, a temperature higher than room temperature). Furthermore, the impregnation with the treatment solution 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 solution may be 0.1% by mass or more and 10% by mass or less. A polyhydric alcohol content of 0.1% by mass or more provides an ESR reduction effect. On the other hand, as the polyhydric alcohol content increases, the viscosity of the treatment solution increases, which may make impregnation of the conductive polymer difficult. From the viewpoint of facilitating impregnation of the conductive polymer, the polyhydric alcohol content may be 10% by mass or less.

[0035] In the processing solution, the conductive polymer component may be a conductive polymer or a precursor of a conductive polymer. That is, a processing solution containing dispersed conductive polymer may be impregnated into a capacitor element precursor to form a layer of conductive polymer (solid electrolyte layer) in the space between the anode and the separator, or a solid electrolyte layer may be formed by polymerizing a precursor of conductive polymer (e.g., raw material monomer) on the dielectric layer of the anode. The solid electrolyte layer may consist of a single layer, or it may consist of two or more layers made of different materials by performing the impregnation in multiple stages. The conductive polymer material can be one of those described later.

[0036] The concentration of conductive polymer in the processing solution (polymer dispersion) containing the conductive polymer is preferably 0.5 to 10% by mass. Furthermore, 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 volume particle size distribution determined by a particle size distribution analyzer using dynamic light scattering. The polymer dispersion can be obtained, for example, by dispersing the conductive polymer in a liquid dispersion medium, or by polymerizing a precursor monomer in a liquid dispersion medium to produce conductive polymer particles.

[0037] The treatment solution may contain not only conductive polymer components and polyhydric alcohols, but also acidic components. The acidic components have the effect of suppressing the dedoping of the conductive polymer. The treatment solution may further contain basic components.

[0038] The acidic component may include compounds containing acidic functional groups. Examples of acidic functional groups include carboxyl groups, hydroxyl groups, sulfo groups, phosphoric acid groups, nitro groups, and oxo groups. The acidic component may also include carboxylic acids, phosphoric acid, sulfonic acid, boric acid, and / or salts thereof. More specifically, acidic components include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, resorcinic acid, borogisalicylic acid, and the like. Compounds containing acidic functional groups may be polycarboxylic acids or compounds having phenolic hydroxyl groups.

[0039] Polycarboxylic acids and monocarboxylic acids can be used as the acidic component. Examples of polycarboxylic acids include aliphatic polycarboxylic acids ([saturated polycarboxylic acids, e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebatic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids, e.g., maleic acid, fumaric acid, eicotanoic acid]), aromatic polycarboxylic acids (e.g., phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.). Examples of the above monocarboxylic acids include aliphatic monocarboxylic acids (1 to 30 carbon atoms) ([saturated monocarboxylic acids, e.g., 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, behenic acid]; [unsaturated monocarboxylic acids, e.g., acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (e.g., benzoic acid, cinnamic acid, naphthoic acid), and oxycarboxylic acids (e.g., salicylic acid, mandelic acid, resorcinic acid). Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcinic acid are preferred because they have high conductivity and are thermally stable.

[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, borofluoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. Furthermore, composite compounds of organic and inorganic acids can be used as the acid component. Examples include borodiglycolic acid, borodisalicylic acid, and borodisalicylic acid.

[0041] In addition to the acidic component, a basic component may also be included in the treatment solution. 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 alkyl-substituted amidine groups, 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 alkyl-substituted amidine groups 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-ethylimidazoline, 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. A quaternary salt of a compound having an alkyl-substituted amidine group may be used as the base component. Specifically, these include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) that have been quaternized with alkyl or arylalkyl groups having 1 to 11 carbon atoms.

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

[0043] The basic component may be included in the treatment solution in the form of a salt with the acid component. Examples of salts with the acid component include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0044] After impregnation, drying removes the solvent contained in the treatment solution, forming a solid electrolyte layer between the anode and the separator, and causing polyhydric alcohols to precipitate, with at least a portion of the polyhydric alcohols adhering to the anode, separator, and solid electrolyte layer. Furthermore, if the treatment solution contains acidic or basic components, these components may also precipitate and adhere to the anode, separator, and solid electrolyte layer.

[0045] The conductive polymer, polyhydric alcohols, and acidic components may adhere to cover at least a portion of the dielectric layer on the surface of the anode and to fill at least a portion of the pores within the roughened anode.

[0046] Drying is usually carried out by heating. Drying may be carried out under atmospheric pressure or under conditions other than atmospheric pressure (e.g., under reduced pressure). The drying temperature may be above the melting point of the polyhydric alcohols, and further, above the boiling point of the solvent under the drying pressure (e.g., 100°C or higher). In a preferred example, the drying temperature is above the boiling point of the solvent under the drying pressure (e.g., 100°C or higher), and above the melting point of the polyhydric alcohols under the drying pressure, but below the boiling point. By drying at a temperature above the melting point of the polyhydric alcohols, the permeability of the polyhydric alcohols to the capacitor element precursor can be increased. The drying temperature may be, for example, 150°C or higher or 180°C or higher.

[0047] Furthermore, if necessary, the impregnation with the treatment solution (step (ii)) and the drying step may be repeated. By repeating step (ii), the amount of precipitated polyhydric alcohols and acidic components can be increased.

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

[0049] The method for impregnating with the liquid component is not particularly limited. For example, a simple and preferred method is to immerse the capacitor element precursor in a liquid component contained in a container. 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 mentioned above.

[0050] The liquid component contains a solvent for dissolving polyhydric alcohols. It may also contain other solutes that dissolve in the solvent, if necessary. The liquid component may also contain the aforementioned acidic and / or basic components. The acidic and / or basic components can be selected from the compounds exemplified in the treatment solution described above.

[0051] The liquid component may be a non-aqueous solvent, or a mixture of a non-aqueous solvent and an ionic substance (solute, e.g., 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, polymeric solvents may be used as non-aqueous solvents. Examples of polymeric solvents include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group in a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specifically, examples of polymeric 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. Examples of polymeric solvents further include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. Non-aqueous solvents may be used individually or as a mixture of two or more.

[0053] To suppress dopant dedoping in conductive polymers, the pH of the liquid component may be set to less than 7, or to 5 or less. The pH of the liquid component may be adjusted after step (iv) and after the elution of the acid component to achieve the above acidity.

[0054] The liquid component may be a protic solvent or an aprotic solvent. Protic solvents readily elute polyhydric alcohols in step (iv) described below. Therefore, the low-temperature properties can be improved by eluting polyhydric alcohols. On the other hand, aprotic solvents readily elute polyhydric alcohols in step (iv). In this case, the adhesion of the conductive polymer to the anode is improved, and the ESR can be lowered. Preferably, 50% by mass or more of the liquid component is an aprotic solvent and less than 50% by mass is a protic solvent. More preferably, 60% by mass or more of the 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 electrolyte. The liquid component may not substantially contain a solute and may not substantially have electrical conductivity. For example, in step (iii), the conductivity X1 of the liquid component is preferably 1 μS / cm or less.

[0056] (Step (iv)) Next, polyhydric alcohols are dissolved into the liquid component. This yields a capacitor element. Step (iv) may be performed simultaneously with or in parallel with step (iii).

[0057] The impregnation with the liquid component causes at least some of the polyhydric alcohols, acidic components, and / or basic components precipitated in step (ii) to dissolve. As a result, the conductivity of the liquid component increases.

[0058] After step (iv), the conductivity X2 of the liquid component from which polyhydric alcohols and / or acidic components have been eluted is higher than X1 (X2 > X1), preferably 500 μS / cm or less. The conductivity X2 of the liquid component may be 0.1 μS / cm or more and 500 μS / cm or less, and 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 processing solution containing an acid component is used in step (ii), the acid component may dissolve into the liquid component in step (iv). The dissolved acid component suppresses the decrease in conductivity due to dedoping of the conductive polymer, and the ESR can be kept low even with long-term use. Furthermore, the dielectric strength is improved. However, if the dissolution of the acid component is excessive, the ESR may increase with long-term use, and the low-temperature characteristics may deteriorate. To suppress the increase in ESR and the deterioration of low-temperature characteristics with 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 relative to the total amount of the liquid component containing the acid component.

[0060] If a treatment solution containing a basic component is used in step (ii), the basic component may leach into the liquid component. In that case, in order to further suppress the increase in ESR due to long-term use, it is preferable that the content of the basic component in the liquid component after step (iv) be 2% by mass or less relative to the total amount of the liquid component containing the basic component.

[0061] Furthermore, the content of each solute, such as acidic components, basic components, and polyhydric alcohols, in the liquid component can be measured by extracting the liquid component from the inside of the electrolytic capacitor using a centrifuge and performing micro-FT-IR analysis or liquid chromatography.

[0062] The liquid component after step (iv) may contain solvent (e.g., water) from the processing solution that was not removed in the drying step after step (ii). If the amount of water in the liquid component is high, the water may vaporize when heat is applied to the electrolytic capacitor in the reflow process, and the airtightness of the case sealing the electrolytic capacitor may decrease due to the vapor. After step (iv), the amount of water in the liquid component is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0063] An electrolytic capacitor is manufactured using the capacitor elements obtained in step (iv). There are no particular limitations on the method of manufacturing the electrolytic capacitor using the capacitor elements, and known methods may be applied. For example, the capacitor elements can be placed in a case and sealed.

[0064] The configuration 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 and a foil-shaped cathode facing each other with the separator in between, a solid electrolyte layer interposed between the anode and the cathode, and a liquid component. The solid electrolyte layer contains polyhydric alcohols and a conductive polymer. The solid electrolyte layer has a segregated portion in which the polyhydric alcohols are unevenly distributed. The liquid component (electrolyte or solvent) and the conductive polymer are used as electrolytes.

[0066] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to this embodiment, and Figure 2 is a schematic diagram showing a portion of the windings contained in the electrolytic capacitor unfolded.

[0067] As shown in Figure 1, an electrolytic capacitor comprises, for example, a capacitor element 10, a bottomed case 11 housing the capacitor element 10, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, lead tabs 15A and 15B connecting the lead wires to the electrodes of the capacitor element 10, and a liquid component (not shown). The capacitor element 10, together with the liquid component, is housed in the outer case. The area near the opening end of the bottomed case 11 is tapered inward, and the opening end is curled so as to be crimped to the sealing member 12.

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

[0069] The anode 21 and cathode 22 are wound around a separator 23. The outermost circumference of the winding is secured by a winding stopper tape 24. Figure 2 shows the winding in a partially unfolded state before securing the outermost circumference. The anode 21 comprises a metal foil with a roughened surface that has irregularities, and a dielectric layer is formed on the main surface of the metal foil with irregularities.

[0070] (Anode) The anode body has a dielectric layer on its surface. A metal foil with a dielectric layer formed on its surface can be used as the anode body. The type of metal contained in the metal foil is not particularly limited, but metals with valve properties such as aluminum, tantalum, niobium, and titanium, and alloys of metals with valve properties are preferred because the dielectric layer is easy to form. Among these, elemental metals such as aluminum and alloys such as aluminum alloys are preferred. Typically, the surface of the anode body is roughened, and a dielectric layer is formed on the roughened surface of the metal foil.

[0071] (Cathole body) A metal foil can be used as the cathode body. The type of metal contained in the metal foil is not particularly limited, but for example, a valve-forming metal such as aluminum, tantalum, niobium, or titanium, or an alloy of a valve-forming metal, can be used. The metal contained in the metal foil may be a pure metal such as aluminum, or an alloy such as an aluminum alloy. The surface of the cathode body may or may not be roughened. In addition, a chemical conversion coating may be provided on the surface of the cathode body, and a coating of a metal different from the metal constituting the cathode body (a dissimilar metal) or a nonmetal may be provided. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon.

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

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

[0074] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene, respectively, refer to polymers whose basic structure is polypyrrole, polythiophene, polyfuran, polyaniline, or polyacetylene. Therefore, derivatives of polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene may also be included. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT).

[0075] Dopants may be added to conductive polymers. From the viewpoint of suppressing dedoping from conductive polymers, it is desirable to use polymer dopants. Examples of polymer dopants include anions such as polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually 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 1,000,000, as it facilitates 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 dissolve into the liquid component, while the remaining portion precipitates unevenly within the solid electrolyte layer.

[0079] Although the above embodiments described wound electrolytic capacitors, the scope of application of the present invention is not limited to those described above. It can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode, and multilayer electrolytic capacitors that use a metal plate as the anode.

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

[0081] Example 1 In this embodiment, a wound electrolytic capacitor (8 mm in diameter x 12 mm in length) with a rated voltage of 100 V and a rated capacitance of 18 μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0082] An electrolytic capacitor, as shown in Figure 1, was fabricated according to the following procedure, and its characteristics were evaluated. (1) Fabrication of capacitor elements

[0083] (Preparation of the cathode) A 50 μm thick aluminum foil was used as the cathode.

[0084] (Preparation of the anode) A 120 μm thick aluminum foil was prepared. The surface of this aluminum foil was roughened by DC etching. Next, a dielectric layer (thickness: approximately 70 nm) was formed by chemical conversion treatment of the aluminum foil to obtain an anode. The dielectric layer was formed by immersing the aluminum foil in an ammonium adipate solution and performing chemical conversion treatment at 70°C for 30 minutes while applying a voltage of 180 V to the aluminum foil. After that, the anode was cut to a predetermined size to prepare the anode.

[0085] (Preparation of coiled bodies) Anode lead tabs and cathode lead tabs, each with a lead wire attached, were connected to the prepared anode body and cathode body having a conductive layer on its end face, respectively. The anode body and cathode body were then wound around each other via a separator, incorporating the lead tabs, and the outer surface was secured with winding tape to create a wound body, thereby obtaining a capacitor element precursor. A dielectric layer was formed mainly on the end face of the anode by immersing the capacitor element precursor in an ammonium adipate solution and then performing a conversion treatment again at 70°C for 60 minutes while applying a voltage of 180V to the anode.

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

[0087] A polymer dispersion was mixed with mannitol (MAN) as a polyhydric alcohol to obtain a treatment solution. The amount of mannitol added was adjusted to 5% by mass of the total treatment solution.

[0088] (Impregnation and drying of the treatment solution) Next, the capacitor element precursor was immersed in a treatment solution contained in a designated container for 5 minutes under reduced pressure at room temperature. At this time, the capacitor element precursor was immersed in the first aqueous treatment solution from the side without the lead tabs connected. After that, the capacitor element precursor was removed from the treatment solution. Subsequently, the capacitor element precursor impregnated with the treatment solution was dried in a drying oven at 180°C for 30 minutes. In this way, polyhydric alcohols and conductive polymers were deposited on the capacitor element precursor so as to cover the dielectric layer of the anode.

[0089] (Impregnation with liquid components) A 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 electrolytic capacitor was completed by sealing the capacitor element impregnated with liquid components. Afterward, it underwent an aging process 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 capacitors were evaluated using the following procedure. First, the initial ESR value X1 (mΩ) at a frequency of 100 kHz was measured using a 4-terminal LCR meter in an environment of 20°C.

[0092] Next, the electrolytic capacitor was charged at its rated voltage for 60 seconds in a 20°C environment. The current flowing through the electrolytic capacitor after charging was measured when the rated voltage was applied, and this was defined as the initial leakage current value LC0.

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

[0094] Examples 2-7 In Example 1, the polyhydric alcohols and other substances added to the processing solution, their amounts, and the solvent of the liquid component were changed as shown in Table 1. Otherwise, an electrolytic capacitor was fabricated 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 was used as the liquid component, consisting of γ-butyrolactone (GBL) and sulfolane (SL) in a mass ratio of 50:50. In Example 3, in addition to mannitol, borodisalicylic acid mono(triethylamine) (BSA / TEA) was added to the treatment solution as an acid component at a ratio of 3% by mass relative to the total treatment solution. A mixed solvent was also used, consisting of γ-butyrolactone (GBL) and sulfolane (SL) mixed in a 50:50 mass ratio as liquid components.

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

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

[0098] Comparative Examples 1-3 No polyhydric alcohols were added to the treatment solution. In Comparative Example 1, a solvent was used as the liquid component, which consisted of a mixture of γ-butyrolactone (GBL) and mannitol (MAN) in a mass ratio of 98:2. In Comparative Example 2, GBL was used as the liquid component, similar to Example 1. In Comparative Example 3, ethylene glycol (EG) was used as the liquid component. Electrolytic capacitors were fabricated 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 solution, and instead, borogisalicylic acid mono(triethylamine) (BSA / TEA) was added as the acid component at a ratio of 3% by mass relative to the total treatment solution. Electrolytic capacitors were fabricated and evaluated in the same manner as in Example 1.

[0100] Comparative Example 5 In Example 1, an electrolytic capacitor (solid electrolytic capacitor) was fabricated without impregnation with liquid components and evaluated in the same manner as in Example 1.

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

[0102] [Table 1]

[0103] [Table 2]

[0104] Tables 1 and 2 show that the electrolytic capacitors of Examples 1-9, which were fabricated by impregnating the capacitors with a treatment solution containing conductive polymers and polyhydric alcohols, then removing the solvent component of the treatment solution by drying and impregnating with the liquid component, have a smaller LC1 / LC0 ratio and suppress the increase in ESR after repeated exposure to high and low temperature environments compared to the electrolytic capacitors of Comparative Examples 1-5. In addition, their initial ESR is also lower.

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

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

[0107] In Examples 7 and 8, the initial ESR and X2 / X1 were slightly higher compared to Examples 1-6. 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) are lower than those of the polyhydric alcohols used in Examples 1-6 (mannitol 167°C, boremitol 152°C). The melting point of the polyhydric alcohol is 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 solution. In this case, the initial ESR could be lowered, and the X2 / X1 ratio could also be lowered. [Industrial applicability]

[0109] This invention can be used in hybrid electrolytic capacitors that utilize conductive polymers and liquid components. [Explanation of Symbols]

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

Claims

1. A method for manufacturing an electrolytic capacitor, which includes a capacitor element having a foil-shaped anode having a dielectric layer on its surface and a foil-shaped cathode, A step of forming a capacitor element precursor by winding or stacking a separator and the anode and cathode bodies facing each other with the separator in between, A step of impregnating the capacitor element precursor with a treatment solution containing polyhydric alcohols, a solvent, and conductive polymer components, The process of impregnating the capacitor element precursor with the processing solution is followed by the process of impregnating the capacitor element precursor with a liquid component, The process includes the step of obtaining the capacitor element by dissolving the polyhydric alcohols in the liquid component, The aforementioned polyhydric alcohols are at least one selected from glucose, mannitol, sorbitol, xylitol, boremitol, pentaerythritol, trimethylolpropane, and derivatives thereof. In the step of impregnating the capacitor element precursor with the liquid component, the content of the aprotic solvent in the liquid component is 50% by mass or more. A method for manufacturing an electrolytic capacitor, wherein, after the step of obtaining the capacitor element, the conductivity X2 of the liquid component from which the polyhydric alcohols have dissolved is 0.1 μS / cm or more and 500 μS / cm or less.

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

3. A method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein, after the step of obtaining the capacitor element, the conductivity X2 of the liquid component from which the polyhydric alcohols have dissolved is higher than the conductivity X1 of the liquid component in the step of impregnating the capacitor element precursor with the liquid component.

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

5. The method for manufacturing an electrolytic capacitor according to claim 4, wherein, in the step of impregnating the capacitor element precursor with the liquid component, the content of the protic solvent in the liquid component is less than 50% by mass.

6. A method for manufacturing an electrolytic capacitor according to any one of claims 1 to 5, wherein the content of the polyhydric alcohols in the processing solution in the step of impregnating the capacitor element precursor with the processing solution is 0.1% by mass or more and 10% by mass or less.

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

8. The processing solution used in the step of impregnating the capacitor element precursor with the processing solution contains an acidic component. A method for manufacturing an electrolytic capacitor according to any one of claims 1 to 7, wherein the content of the acid component in the entire liquid component after the step of obtaining the capacitor element is 2% by mass or less.

9. The process includes a step of removing the solvent by drying, after the step of impregnating the capacitor element precursor with the processing solution, but before the step of impregnating the capacitor element precursor with the liquid component. A method for manufacturing an electrolytic capacitor according to any one of claims 1 to 8, wherein the drying temperature in the step of removing the solvent is 150°C or higher.

10. An electrolytic capacitor including a capacitor element, The aforementioned capacitor element is Separator and, A foil-shaped anode and a foil-shaped cathode are facing each other with the separator in between, A solid electrolyte layer interposed between the anode and the cathode, It contains a liquid component, The solid electrolyte layer contains polyhydric alcohols and a conductive polymer. The solid electrolyte layer has a segregated portion in which the polyhydric alcohols are unevenly distributed, The proportion of aprotic solvent in the aforementioned liquid component is 50% by mass or more. The aforementioned polyhydric alcohols are at least one selected from glucose, mannitol, sorbitol, xylitol, boremitol, pentaerythritol, trimethylolpropane, and derivatives thereof. An electrolytic capacitor wherein the conductivity of the liquid component is 0.1 μS / cm or more and 500 μS / cm or less.

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