Electrolytic capacitors and their manufacturing methods

Abstract

A method for manufacturing an electrolytic capacitor comprising a capacitor element having a foil-shaped anode and a foil-shaped cathode, the foil-shaped anode having a dielectric layer on its surface, the method comprising: a step of forming a capacitor element precursor by winding or stacking a spacer and an anode and cathode positioned opposite each other with the spacer between them; a step of impregnating the capacitor element precursor with a treatment liquid containing an acid component, a solvent, and a conductive polymer component; a step of impregnating the capacitor element precursor with a liquid component after the step of impregnating the capacitor element precursor with the treatment liquid; and a step of obtaining the capacitor element by dissolving the acid component into the liquid component.

Description

Technical Field

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

[0002] Electrolytic capacitors, which are small, have large capacitance, and low ESR, include an anode foil with a dielectric layer and a cathode body, and have a conductive polymer attached to the dielectric layer. Among them, hybrid electrolytic capacitors that use a conductive polymer as a solid electrolyte and a liquid component (electrolyte) are expected to reduce leakage current (e.g., Patent Document 1).

[0003] In the above-mentioned hybrid electrolytic capacitors, in order to have the function of repairing the dielectric layer and improve the voltage withstand capability, it has been tried to make the liquid component contain various solute components (supporting electrolyte).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 4916416 Specification Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, the presence of a large amount of various solute components (supporting electrolyte) in the electrolyte results in poor storage stability, especially at low temperatures (e.g., below freezing), where solute components are prone to precipitation. Consequently, the capacitor's characteristics tend to degrade after prolonged use or in low-temperature environments. Furthermore, there are cases where solute components react with conductive polymers, leading to a decrease in capacitor characteristics, or cases where the characteristics of conductive polymers are accelerated to degrade.

[0009] Methods for solving problems

[0010] One aspect of the present invention is a method for manufacturing an electrolytic capacitor comprising a capacitor element having a foil-shaped anode and a foil-shaped cathode, wherein the foil-shaped anode has a dielectric layer on its surface. The manufacturing method includes the following steps (i), (ii), (iii), and (iv). In step (i), a capacitor element precursor is formed by winding or stacking a spacer and the anode and cathode, which are positioned opposite each other and separated by the spacer. In step (ii), a treatment liquid containing an acid component, a solvent, and a conductive polymer component is impregnated into the capacitor element precursor. In step (iii), after step (ii), a liquid component is impregnated into the capacitor element precursor. In step (iv), the capacitor element is obtained by dissolving the acid component into the liquid component.

[0011] Another aspect of the present invention provides an electrolytic capacitor comprising a capacitor element. The capacitor element includes a spacer, a foil-shaped anode and a foil-shaped cathode separated by the spacer, a solid electrolyte layer disposed between the anode and the cathode, and a liquid component. The solid electrolyte layer contains an acidic component and a conductive polymer. Furthermore, the solid electrolyte layer has a biased portion containing the acidic component.

[0012] Invention Effects

[0013] The manufacturing method of the present invention can improve the characteristics of electrolytic capacitors. Attached Figure Description

[0014] Figure 1 This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram showing a portion of the winding contained in the same electrolytic capacitor after it has been unwound. Detailed Implementation

[0016] One embodiment of the present invention discloses a method for manufacturing an electrolytic capacitor comprising a capacitor element, wherein the capacitor element has a foil-shaped anode and a foil-shaped cathode, and the foil-shaped anode has a dielectric layer on its surface. The manufacturing method includes the following steps (i) to (iv):

[0017] (i) The process of forming a capacitor element precursor by winding or stacking a spacer and an anode and a cathode body facing each other with the spacer between them;

[0018] (ii) A process of impregnating a treatment solution containing acidic components, solvents and conductive polymeric components into the capacitor element precursor.

[0019] (iii) The process of impregnating the liquid component into the capacitor element precursor after process (ii); and

[0020] (iv) A process of obtaining a capacitor element by dissolving an acidic component into a liquid component.

[0021] According to the manufacturing method of this embodiment, in step (ii), after the acid component and the conductive polymer component are attached to the capacitor element precursor, in step (iii), the liquid component is impregnated into the capacitor element precursor, thereby controlling the amount of acid component contained in the liquid component and manufacturing an electrolytic capacitor with excellent characteristics.

[0022] When the acid component in an electrolytic capacitor causes damage to the oxide film constituting the dielectric layer, it acts as a supplier of oxygen to the damaged area, thus repairing it. By including acid in the liquid component (electrolyte), damage in the dielectric layer can be repaired, leakage current (LC) can be reduced, and high withstand voltage can be maintained. However, if the liquid component (electrolyte) contains too much acid, acid precipitates at low temperatures, easily leading to a deterioration in performance. Furthermore, the ESR (equivalent series resistance) is prone to increase with prolonged use.

[0023] From the perspective of repairing damage to the dielectric layer, the acid component is preferably located near the surface of the anode body where the dielectric layer is formed. Therefore, in the manufacturing method of this embodiment, a treatment liquid containing an acid component, a solvent, and a conductive polymer component is impregnated into the capacitor element precursor, and then the solvent is removed by drying, thereby allowing the acid component to adhere to the anode body. Next, a liquid component is impregnated into the capacitor element precursor. At this time, some of the acid component dissolves into the liquid component, while some can remain near the anode body. Thus, a high dielectric layer repair effect can be obtained while limiting the amount of acid component contained in the liquid component. As a result, it does not lead to a decrease in low-temperature characteristics or an increase in ESR due to long-term use, and it can reduce leakage current and improve withstand voltage.

[0024] Furthermore, the acid component adheres by being introduced into the conductive polymer layer, and after the liquid component penetrates, a portion of the acid component does not dissolve but remains in a precipitated state within the conductive polymer layer. In the conductive polymer layer, at least one portion selected from the portion in contact with the anode, the portion in contact with the cathode, and the portion in contact with the spacer can contain a portion with the acid component. The acid component in the portion in contact with the anode effectively participates in the repair of the dielectric layer.

[0025] Furthermore, the acid component can suppress the degradation caused by the removal of dopants contained in the conductive polymer. Therefore, by including an acid component in the liquid component, the decrease in conductivity caused by the dedoping of the conductive polymer can be suppressed, maintaining a low ESR even during long-term use. Additionally, voltage withstand capability is improved. The acid component is preferably located near the conductive polymer.

[0026] In step (ii), the treatment solution may contain alkali components and / or polyols in addition to acid components. That is, in the liquid component after step (iv), alkali components and / or polyols may be dissolved in addition to acid components. Using polyols, conductive polymers can be tightly bonded to the surface of the anode and / or spacer, thereby maintaining low ESR. Furthermore, the addition of polyols improves low-temperature characteristics.

[0027] The liquid component can contain either aprotic or protic solvents. Aprotic solvents readily dissolve acidic components but struggle to dissolve polyols. Therefore, acidic components can be selectively dissolved into the liquid component relative to polyols. This suppresses degradation caused by dedoping of conductive polymers and maintains a low ESR. On the other hand, protic solvents struggle to dissolve acidic components but readily dissolve polyols. Therefore, polyols can be selectively dissolved into the liquid component relative to acidic components. This concentrates the acidic component near the anode, improving the repair effect of the dielectric layer and effectively suppressing the increase in leakage current. Furthermore, it enhances the improvement of low-temperature properties based on polyols.

[0028] In addition, the liquid component may contain nonpolar solvents. The proportions of nonprotic solvents, protic solvents, and nonpolar solvents in the liquid component can be appropriately adjusted according to the required characteristics of the electrolytic capacitor.

[0029] It should be noted that protic solvents refer to solvents with a solubility parameter (SP value) of 14 or higher based on the Hildebrand method. Aprotic solvents refer to solvents with a solubility parameter (SP value) of 5 or higher but less than 14.

[0030] Hereinafter, this embodiment will be described in more detail with appropriate reference to the accompanying drawings. However, the following embodiments do not limit the present invention.

[0031] (Process (i))

[0032] First, a capacitor element precursor is formed by winding or stacking spacers and anode and cathode bodies that are positioned opposite each other and separated by the spacers. The capacitor element precursor is the element before the electrolyte layer is formed.

[0033] A foil-shaped anode can be formed using 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 performed, for example, by etching based on direct current electrolysis or alternating current electrolysis. Then, a dielectric layer is formed on the surface of the roughened metal foil. The dielectric layer can be formed, for example, by performing a formation treatment on the metal foil. The surface of the metal foil is oxidized by the formation treatment, thereby forming a dielectric layer as an oxide film. By operating in this manner, the anode is formed.

[0034] It should be noted that, as needed, lead terminals for electrical connection are connected to the anode and cathode bodies.

[0035] In the case of a wound-type electrolytic capacitor, for example, a capacitor element precursor can be formed by winding a foil-shaped anode body, a foil-shaped cathode body, and spacers together. In this case, they are wound in such a way that spacers are arranged between the anode body and the cathode body.

[0036] In the case of a multilayer electrolytic capacitor, for example, a capacitor element precursor can be formed by bending a foil-shaped anode, a foil-shaped cathode, and a spacer together into a zigzag shape. In this case, they are bent such that a spacer is placed between the anode and the cathode.

[0037] (Process (ii))

[0038] Then, a treatment solution containing acidic components, solvents, and conductive polymeric components is impregnated into the capacitor element precursor. The solvent can be water, a mixture of water and a non-aqueous solvent, or a non-aqueous solvent. There are no particular limitations on the non-aqueous solvent; 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.

[0039] The solvent of the treatment solution can be, for example, water. Impregnation can be carried out, for example, by impregnating 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) constituting the aqueous treatment solution is, for example, in the range of 50 to 100% by mass.

[0040] There is no particular limitation on the immersion time; for example, it can be more than 1 minute and less than 20 minutes. The entire capacitor element precursor can be immersed in the aqueous treatment solution, or only a portion of the capacitor element precursor can be immersed in the aqueous treatment solution. For example, less than 50% of the length direction (axial direction in the case of a wound body) of the capacitor element precursor can be immersed in the aqueous treatment solution.

[0041] The impregnation of the treatment solution can be carried out at room temperature or at a temperature higher than room temperature. Furthermore, the impregnation can be carried out at atmospheric pressure or in an environment other than atmospheric pressure (e.g., under reduced pressure).

[0042] In the processing solution, the conductive polymer component can be either a conductive polymer or a precursor of a conductive polymer. That is, the processing solution containing dispersed conductive polymers can be impregnated into the capacitor element precursor to form a layer of conductive polymer (solid electrolyte layer) in the space between the anode and the spacer. Alternatively, a solid electrolyte layer can be formed by polymerizing a precursor of the conductive polymer (e.g., a raw material monomer) on the dielectric layer of the anode. The solid electrolyte layer can be formed as a single layer or as two or more layers with different constituent materials through multiple impregnation processes. Materials described later can be used as the conductive polymer material.

[0043] The concentration of the conductive polymer in the treatment liquid (polymer dispersion) 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 volumetric particle size distribution determined using a particle size distribution measuring device based on dynamic light scattering. The polymer dispersion can be obtained, for example, by dispersing the conductive polymer in a liquid dispersion medium, or by polymerizing precursor monomers in a liquid dispersion medium to generate conductive polymer particles.

[0044] In addition to conductive polymer components, the treatment solution also contains acid components. The acid components inhibit the dedoping of the conductive polymers. The treatment solution may also contain alkaline components and / or polyols.

[0045] Acidic components can contain compounds with acidic functional groups. Examples of acidic functional groups include carboxyl, hydroxyl, sulfonyl, phosphate, nitro, and oxo groups. Acidic components can contain carboxylic acids, phosphoric acids, sulfonic acids, boric acids, and / or their salts. More specifically, acidic components include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, resorcinic acid, and borosilicate acid. Compounds containing acidic functional groups can be polycarboxylic acids or compounds with phenolic hydroxyl groups.

[0046] As an acid component, both polycarboxylic acids and monocarboxylic acids can be used.

[0047] 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, octanoic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids, such as maleic acid, fumaric acid, itaconic acid]), aromatic polycarboxylic acids (such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (such as cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.).

[0048] Examples of the aforementioned monocarboxylic acids include aliphatic monocarboxylic acids (1 to 30 carbon atoms) ([saturated monocarboxylic acids, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids, such as acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, naphtholic acid), and hydroxycarboxylic acids (such as salicylic acid, mandelic acid, m-dihydroxybenzoic acid).

[0049] Among them, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and m-dihydroxybenzoic acid have high electrical conductivity and are thermodynamically stable, and are therefore preferred.

[0050] Examples of 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, hypophosphite, alkyl phosphates, boric acid, fluoroboric acid, boric acid tetrafluoride, phosphoric acid hexafluoride, benzenesulfonic acid, and naphthalenesulfonic acid.

[0051] Alternatively, complex compounds of organic and inorganic acids can be used as the acid component. Examples include borodiglycolic acid, borodioxalic acid, and borodisalicylic acid.

[0052] In addition to acidic components, the treatment solution may also contain alkaline components and / or polyols.

[0053] Examples of alkaline components include metal hydroxides such as sodium hydroxide and potassium hydroxide, as well as nitrogen-containing alkaline compounds such as aliphatic amines and cyclic amines. Among these, imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds and 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]undec-7-ene, 1,5-diazabicyclo[4,3,0]non-5-ene, 1,2-dimethylimidazoline, 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-methylimidazolium, and 1-methylbenzimidazole. Quaternary salts of compounds having alkyl-substituted amidine groups can also be used as the base component. Specifically, examples include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) that have undergone quaternization of alkyl or arylalkyl groups having 1 to 11 carbon atoms.

[0054] Alternatively, tertiary amines can be used as the base component, such as 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-containing amines (dimethylaniline, methylethylaniline, diethylaniline, etc.). Among these, trialkylamines are preferred from the perspective of high conductivity, and it is more preferable that they contain at least one selected from trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Alternatively, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia can also be used as the base component.

[0055] The alkaline component may also be present in the treatment solution in the form of a salt of the acid component. Examples of salts of the acid component include trimethylamine maleate, triethylamine borosilicate, ethyl dimethylamine phthalate, mono-1,2,3,4-tetramethylimidazoline phthalate, and mono-1,3-dimethyl-2-ethylimidazoline phthalate.

[0056] Polyols include organic compounds (e.g., non-polymer organic compounds) containing multiple hydroxyl groups (-OH) bonded to carbon atoms, such as sugars like glucose. Other examples of polyols include mannitol, sorbitol, xylitol, pentaerythritol, trimethylolpropane, and glycerol. It should be noted that mannitol, sorbitol, xylitol, and pentaerythritol are also called sugar alcohols. Compounds with three or more hydroxyl groups can also be used as polyols.

[0057] Polyols, possessing multiple hydroxyl groups, readily bond to hydroxyl groups present on the surfaces of the anode and spacers. This facilitates the fixation of the conductive polymer to the anode and spacers, effectively binding it to the anode. Consequently, the ESR of the electrolytic capacitor can be reduced. Furthermore, the polyols dissolved from the liquid component in step (iv) described later contribute to improving the low-temperature characteristics of the electrolytic capacitor.

[0058] After impregnation, the solvent contained in the treatment solution is removed by drying, thereby forming a solid electrolyte layer between the anode and the spacer, and acid components are precipitated, with at least a portion of the acid components adhering to the anode, spacer, and solid electrolyte layer. Additionally, if the treatment solution contains alkaline components or polyols, these components will also precipitate and adhere to the anode, spacer, and solid electrolyte layer.

[0059] The conductive polymer and acid components are attached in a manner that covers at least a portion of the dielectric layer on the surface of the anode body and in a manner that fills at least a portion of the pores within the roughened anode body.

[0060] Drying is typically performed using heat. Drying can be carried out at atmospheric pressure or in an environment other than atmospheric pressure (e.g., under reduced pressure). The drying temperature can be above the melting point of the acid component, or above the boiling point of the solvent under the drying pressure (e.g., above 100°C). In a preferred embodiment, the drying temperature is above the boiling point of the solvent under the drying pressure (e.g., above 100°C), and above the melting point but below the boiling point of the acid component under the drying pressure. By drying at a temperature above the melting point of the acid component, the permeability of the first compound to the capacitor element precursor can be improved. The drying temperature can be, for example, above 150°C or above 180°C.

[0061] It should be noted that, as needed, the impregnation (step (ii)) and drying steps of the treatment solution can be repeated. By repeating step (ii), the amount of precipitated acid components can be increased.

[0062] (Process (iii))

[0063] Next, the liquid component is impregnated into the capacitor element precursor. The liquid component can be a substance that is liquid at room temperature (25°C) or a substance that is liquid at the temperature at which the electrolytic capacitor is used.

[0064] There are no particular limitations on the method of impregnating the liquid component. For example, immersing the capacitor element precursor in a liquid component contained in a container is a simple and preferred method. Impregnation is preferably carried out under reduced pressure, for example, an atmosphere of 10 to 100 kPa. The materials described above can be cited as liquid components.

[0065] The liquid component contains a solvent that dissolves the acid component. Other solutes dissolved in the solvent may also be included, if desired. The liquid component may also contain the aforementioned basic components and / or polyols. For the basic components and / or polyols, compounds exemplified in the above-described treatment solutions may be selected.

[0066] The liquid component can be a non-aqueous solvent or a mixture of a non-aqueous solvent and an ionic substance (solute, such as an organic salt) dissolved therein (i.e., an electrolyte). The non-aqueous solvent can be an organic solvent or an ionic liquid. High-boiling-point solvents are preferred as non-aqueous solvents. Examples of non-aqueous solvents include polyols 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.

[0067] Alternatively, polymeric solvents can also be used as non-aqueous solvents. Examples of polymeric solvents include polyalkylene glycols, polyalkylene glycol derivatives, and compounds in which at least one hydroxyl group in a polyol is replaced by a polyalkylene glycol (including its derivatives). Specifically, examples of polymeric solvents include polyethylene glycol (PEG), polyethylene glycol glycerol ether, polyethylene glycol diglycerol ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glycerol ether, polypropylene glycol diglycerol ether, polypropylene glycol sorbitol ether, and polybutanediol. Examples of polymeric solvents also include copolymers of ethylene glycol and propylene glycol, copolymers of ethylene glycol and butanediol, and copolymers of propylene glycol and butanediol. A single non-aqueous solvent can be used, or two or more can be used in combination.

[0068] To suppress the dedoping of dopants in conductive polymers, the pH of the liquid component can be set to less than 7, or even below 5. The pH of the liquid component can be adjusted to achieve the aforementioned acidity after the acid component has dissolved in step (iv).

[0069] The liquid component can be either a protic or aprotic solvent. Protic solvents make it difficult for the acid component to dissolve in step (iv) described later. Therefore, the acid component tends to concentrate near the anode, improving the repair effect of the dielectric layer and increasing withstand voltage and leakage current. On the other hand, aprotic solvents readily dissolve the acid component in step (iv). In this case, dedoping of conductive polymers can be suppressed, reducing ESR.

[0070] The liquid component may or may not be an electrolyte. The liquid component may substantially not contain a solute and may substantially lack electrical conductivity. For example, in step (iii), the conductivity X1 of the liquid component is preferably 1 μS / cm or less.

[0071] (Process (iv))

[0072] Next, the acid component is dissolved into the liquid component. This yields a capacitor element. Step (iv) can be performed simultaneously or in parallel with step (iii).

[0073] Through the infiltration of the liquid component, at least a portion of the acidic, alkaline, and / or polyol components precipitated in step (ii) dissolves. As a result, the conductivity of the liquid component increases.

[0074] After step (iv), the conductivity X2 of the liquid component after the acid component has dissolved is higher than X1 (X2 > X1), preferably 500 μS / cm or less. The conductivity X2 of the liquid component can 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. In the manufacturing method of this embodiment, the dissolution of the acid component into the liquid component is minimal, and the conductivity of the liquid component is lower than conventional. However, since the acid component is concentrated near the anode, even with minimal dissolution, the increase in leakage current can be suppressed, and a high-voltage electrolytic capacitor can be achieved.

[0075] On the other hand, if the proportion of acid component is greater than 2% by mass, the ESR may increase due to long-term use and the low-temperature performance may decrease. In order to suppress the increase of ESR and the decrease of low-temperature performance caused by long-term use, in the liquid component after step (iv), it is preferable that the proportion of acid component is 0.01% by mass or more and 2% by mass or less relative to the total liquid component containing acid component.

[0076] In the case where a treatment liquid containing an alkaline component is used in step (ii), the alkaline component may dissolve into the liquid component. In this case, in order to suppress the increase in ESR due to long-term use, it is preferable that the content of the alkaline component in the liquid component after step (iv) is less than 2% by mass relative to the total liquid component containing the alkaline component.

[0077] Furthermore, when a processing solution containing polyols is used in process (ii), the alkaline component may dissolve into the liquid component. The dissolved polyols contribute to the improvement of the low-temperature characteristics of the electrical capacitor. Although the reason for this is not yet fully understood, it can be attributed to the lowering of the freezing point of the liquid component due to the addition of polyols.

[0078] It should be noted that the content of various solutes such as acid components, alkali components, and polyols in the liquid component can be extracted from the electrolytic capacitor using a centrifuge and determined using microscopic FT-IR analysis or liquid chromatography.

[0079] The liquid component after step (iv) may contain solvents (e.g., water) from the processing liquid that were not removed during the drying step after step (ii). If the liquid component contains a high amount of water, the water will vaporize when the electrolytic capacitor is heated using a reflux process or similar method, potentially reducing the airtightness of the sealed electrolytic capacitor casing due to the vapor. After step (iv), the water content in the liquid component is preferably 5% by mass or less, more preferably 3% by mass or less.

[0080] Electrolytic capacitors can be manufactured using the capacitor elements obtained in step (iv). There are no particular limitations on the method used to manufacture electrolytic capacitors using the capacitor elements; known methods can be applied. For example, simply placing the capacitor elements in a casing and sealing it is sufficient.

[0081] Hereinafter, a detailed description will be given of an example of the structure of an electrolytic capacitor manufactured using the manufacturing method of this embodiment.

[0082] Electrolytic capacitors

[0083] One embodiment of the electrolytic capacitor of the present invention is an electrolytic capacitor comprising a capacitor element, the capacitor element comprising a spacer, a foil-shaped anode and a foil-shaped cathode disposed opposite each other with respect to the spacer, a solid electrolyte layer disposed between the anode and the cathode, and a liquid component. The solid electrolyte layer contains an acidic component and a conductive polymer. The solid electrolyte layer has a portion biased towards the acidic component. The liquid component (electrolyte or solvent) and the conductive polymer are used as the electrolyte.

[0084] Figure 1 This is a cross-sectional schematic diagram of the electrolytic capacitor according to this embodiment. Figure 2This is a schematic diagram showing a portion of the winding contained in the same electrolytic capacitor after it has been unwound.

[0085] like Figure 1 As shown, an electrolytic capacitor includes, for example, a capacitor element 10, a bottomed housing 11 housing the capacitor element 10, a sealing member 12 blocking the opening of the bottomed housing 11, a base plate 13 covering the sealing member 12, leads 14A and 14B extending from the sealing member 12 and through the base plate 13, lead connectors 15A and 15B connecting the leads to the electrodes of the capacitor element 10, and a liquid component (not shown). The capacitor element 10 is housed together with the liquid component in the outer housing. The bottomed housing 11 is necked inward near the opening end, and the opening end is crimped by riveting to the sealing member 12.

[0086] Capacitor element 10 can be, for example, made by attaching a conductive polymer to a substrate such as... Figure 2 The capacitor element 10 is manufactured using a wound body as shown. The wound body includes an anode body 21 having a dielectric layer, a cathode body 22 containing a first metal having a valve function, and a spacer 23 sandwiched between them. A conductive polymer is attached to at least a portion of the surface of the dielectric layer of the anode body 21 to form a solid electrolyte layer. The capacitor element 10 also includes a lead connector 15A connected to the anode body 21 and a lead connector 15B connected to the cathode body 22.

[0087] The anode body 21 and the cathode body 22 are wound together with a spacer 23 in between. The outermost circumference of the wound body is fixed by a winding fixing tape 24. It should be noted that... Figure 2 This indicates that a portion of the wound body has been unwound before its outermost periphery is fixed. The anode body 21 has a metal foil with a roughened surface, and a dielectric layer is formed on the main surface of the roughened metal foil.

[0088] (Anode)

[0089] The anode has a dielectric layer on its surface. The anode 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; however, from the perspective of ease of forming the dielectric layer, metals with valve-like properties such as aluminum, tantalum, niobium, and titanium, as well as alloys of such metals, are preferred. Among these, elemental metals such as aluminum and alloys such as aluminum alloys are preferred. Typically, the surface of the anode is roughened, and the dielectric layer is formed on the roughened surface of the metal foil.

[0090] (Cathode)

[0091] The cathode can be made of metal foil. There are no particular limitations on the type of metal contained in the foil; for example, it can use metals with valve-like properties such as aluminum, tantalum, niobium, and titanium, or alloys of such metals. The metal contained in the foil can also be an elemental metal such as aluminum or an alloy such as an aluminum alloy. The surface of the cathode can be roughened or left unroughened. Furthermore, a metallization film or a film of a different metal (dissimilar metal) or non-metal can be provided on the surface of the cathode. Examples of dissimilar metals or non-metals include metals such as titanium and non-metals such as carbon.

[0092] (spacer)

[0093] The spacer can be an electrolyte-impregnable sheet material, such as an insulating sheet material that is also electrolyte-impregnable. The spacer can be woven fabric, nonwoven fabric, or a porous membrane. Examples of materials that can be used as spacers include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamides, polyimides, polyamide-imides, polyether-imides, rayon, and vitreous materials.

[0094] (Conductive polymer)

[0095] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and polyaniline. They can be used alone, in combination of two or more monomers, or as copolymers of two or more monomers. The weight-average molecular weight of conductive polymers is not particularly limited, but can range from 1,000 to 100,000.

[0096] It should be noted that in this specification, polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene refer to polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as their basic backbones, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene may also contain their respective derivatives. For example, polythiophene may include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0097] Dopants can be added to conductive polymers. From the viewpoint of suppressing dedoping from conductive polymers, it is desirable to use polymeric dopants. Examples of polymeric dopants include anions of polyvinylsulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylamide sulfonic acid, polymethacrylamide sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. They can be used alone or in combination of two or more. Furthermore, they can be homopolymers or copolymers of two or more monomers. Among these, polystyrene sulfonic acid (PSS) is preferred.

[0098] The weight-average molecular weight of the dopant is not particularly limited, but from the perspective of facilitating the formation of a uniform solid electrolyte layer, it is preferably, for example, 1,000 to 100,000.

[0099] Conductive polymers can also be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0100] An acidic component (not shown) is present within the solid electrolyte layer. A portion of the acidic component dissolves into the liquid component, while the remaining portion is partially precipitated within the solid electrolyte layer. This portion of the acidic component may be present in at least one of the portions selected from the portions in contact with the anode, the cathode, and the spacer.

[0101] Although the above embodiments describe a wound electrolytic capacitor, the application scope of the present invention is not limited to the above description, and can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode body, and laminated electrolytic capacitors that use a metal plate as the anode body.

[0102] Example

[0103] The present invention will now be described in detail based on embodiments and comparative examples; however, the present invention is not limited to the following embodiments.

[0104] Example 1

[0105] In this embodiment, a wound electrolytic capacitor (8mm in diameter × 12mm in length) with a rated voltage of 100V and a rated capacitance of 18μF is manufactured. The specific manufacturing method of the electrolytic capacitor will be described below.

[0106] Make according to the following guidelines. Figure 1 The electrolytic capacitor shown is evaluated, and its characteristics are assessed.

[0107] (1) Fabrication of capacitor components

[0108] (Preparation of the cathode)

[0109] A 50μm thick Al foil (aluminum foil) was used as the cathode.

[0110] (Preparation of the anode)

[0111] An Al foil with a thickness of 120 μm was prepared. The Al foil was then subjected to DC etching to roughen its surface. Next, a formation process was performed on the Al foil to form a dielectric layer (thickness: approximately 70 nm), thereby obtaining the anode. The Al foil was immersed in an ammonium adipate solution, and a formation process was performed at 70°C for 30 minutes while applying a voltage of 180 V, thereby forming the dielectric layer. Afterwards, the anode was cut to a given size to prepare the anode body.

[0112] (Making of the wound body)

[0113] Anode lead connectors and cathode lead connectors with leads are connected to the prepared anode body and cathode body with conductor layers on the end face, respectively. While winding the lead connectors, the anode body and cathode body are wound with spacers in between. The outer surface is fixed with winding and fixing tape, thereby making a wound body and obtaining the capacitor element precursor.

[0114] The capacitor element precursor is immersed in an ammonium adipate solution, and while applying a voltage of 180V to the anode body, it undergoes a formation treatment at 70°C for 60 minutes, thereby forming a dielectric layer mainly on the end face of the anode body.

[0115] (Preparation of the treatment solution)

[0116] A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and polystyrene sulfonic acid as a dopant in ion-exchanged water. While stirring the resulting mixed solution, ferric sulfate (III) dissolved in ion-exchanged water (an oxidizing agent) was added to initiate a polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymeric dispersion of polyethylenedioxythiophene doped with polystyrene sulfonic acid containing approximately 2% by mass.

[0117] In a polymer dispersion, borosilicate mono(triethylamine) (BSA / TEA) is added as a salt containing both acidic and basic components and mixed to obtain a treatment solution. The total content of borosilicate mono(triethylamine) in the treatment solution is 1% by mass.

[0118] (Immersion and drying of the treatment solution)

[0119] Next, at room temperature and under reduced pressure, the capacitor element precursor is immersed in a processing solution contained in a given container for 5 minutes. During this time, the capacitor element precursor is immersed in the processing solution from the side without the lead connector. Afterward, the capacitor element precursor is removed from the processing solution.

[0120] Then, the capacitor element precursor impregnated with the treatment solution is dried in a drying oven at 180°C for 30 minutes. This process, as described, allows the acid components and conductive polymers to adhere to the capacitor element precursor in a manner that covers the dielectric layer of the anode body.

[0121] (Infiltration of liquid components)

[0122] At room temperature and atmospheric pressure, γ-butyrolactone (GBL) is impregnated into the capacitor element precursor as a liquid component.

[0123] (Sealing of capacitor components)

[0124] The capacitor element, impregnated with the liquid component, is sealed to complete the electrolytic capacitor process. Then, it undergoes an aging treatment at 130°C for 2 hours while the rated voltage is applied.

[0125] In addition, the samples of the aged electrolytic capacitors were decomposed and the liquid components were extracted by centrifugation. The conductivity of the liquid components was then measured using a conductivity meter.

[0126] (evaluate)

[0127] The initial ESR value and leakage current of the obtained electrolytic capacitors were evaluated according to the following steps. First, the ESR value and leakage current were measured using a 4-terminal LCR meter at 20°C.

[0128] The initial ESR value X1 (mΩ) at a frequency of 100kHz.

[0129] Then, at 20°C, the electrolytic capacitor was charged with its rated voltage for 60 seconds, and the current flowing through it when the rated voltage was applied to the charged electrolytic capacitor was measured and set as the leakage current value LC1.

[0130] Next, the charged electrolytic capacitors were placed under no-load conditions at 145°C for 500 hours. Afterward, the leakage current and ESR were measured similarly at 20°C, and the ESR value X2 and leakage current value LC2 after the reliability test were calculated. The ratio of the ESR value after the test to the initial ESR value, X2 / X1, was evaluated. Additionally, the ratio of the leakage current value after the test to the leakage current value before the test, LC2 / LC1, was evaluated.

[0131] Examples 2-7

[0132] In Example 1, the acid components added to the treatment solution and their amounts, as well as the solvent for the liquid components, were varied as shown in Table 1. Otherwise, the electrolytic capacitor was fabricated in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0133] In Example 2, a mixed solvent consisting of γ-butyrolactone (GBL) and sulfolane (SL) in a mass ratio of 50:50 was used as the liquid component.

[0134] In Example 3, the amount of borosilicate mono(triethylamine) (BSA / TEA) added to the treatment solution was changed to 0.2% by mass.

[0135] In Example 4, ethylene glycol (EG) was used as the liquid component.

[0136] In Example 5, a mixed solvent consisting of ethylene glycol (EG) and polyethylene glycol (PEG) (weight average molecular weight 200) in a mass ratio of 50:50 was used as the liquid component.

[0137] In Example 6, 3% by mass of monoethyldimethylamine phthalate (PA / EDMA) was added as the acid component, and ethylene glycol (EG) was used as the liquid component.

[0138] In Example 7, a mixed solvent consisting of ethylene glycol (EG) and γ-butyrolactone (GBL) in a mass ratio of 50:50 was used as the liquid component.

[0139] Example 8

[0140] In Example 1, after impregnation with the treatment solution, the temperature inside the drying oven in the drying process was changed to 100°C. Otherwise, the electrolytic capacitor was manufactured in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0141] Comparative Examples 1 and 2

[0142] No acid was added to the treatment solution.

[0143] In Comparative Example 1, an electrolyte in which ethylene glycol (EG) and monoethyldimethylamine phthalate (PA / EDMA) were mixed at a mass ratio of 75:25 was used as the liquid component.

[0144] In Comparative Example 2, the same GBL as in Example 1 was used as the liquid component.

[0145] Otherwise, the electrolytic capacitor was fabricated in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0146] Comparative Example 3

[0147] In Example 1, an electrolytic capacitor (solid electrolytic capacitor) was fabricated without impregnation of liquid components, and the evaluation was performed in the same manner as in Example 1. The amount of borosilicate mono(triethylamine) (BSA / TEA) added to the treatment solution was set to 0.5% by mass.

[0148] Table 1 shows the acid components and their amounts added to the treatment solution in the electrolytic capacitors of Examples 1-8 and Comparative Examples 1-3, the composition of the liquid components, and the conductivity of the liquid components after aging treatment. Table 2 shows the evaluation results of the ESR and leakage current of the electrolytic capacitors of Examples 1-8 and Comparative Examples 1-3.

[0149]

[0150]

[0151] According to Tables 1 and 2, after impregnating the capacitor element precursor with a treatment solution containing conductive polymers and acid components, the solvent components of the treatment solution were removed by drying, allowing the liquid components to impregnate. The electrolytic capacitors of Examples 1-8 produced in this manner showed significantly smaller LC2 / LC1 ratios compared to the electrolytic capacitors of Comparative Examples 1-3, and the increase in ESR and leakage current during reliability evaluation tests was significantly suppressed. Furthermore, the leakage current LC1 was also smaller in the initial manufacturing stage, and the initial ESR was also lower.

[0152] In the electrolytic capacitors of Examples 1 to 7, where the drying temperature was set to 180°C, the initial ESR and initial leakage current LC1 were significantly improved compared to the electrolytic capacitor of Example 8, where the drying temperature was set to 100°C. Based on the comparison between Examples 1 to 7 and Example 8, it is more preferable to remove the processing liquid at a temperature of 150°C or higher.

[0153] In Examples 1-3, aprotic solvents or mixtures of aprotic solvents were used as the solvent for the treatment liquid. In this case, the acid component was readily leached, and the conductivity of the liquid component tended to be higher compared to Examples 4-6, which used protic solvents. In this case, the ESR change X2 / X1 could be reduced. This can be attributed to the fact that the greater leaching of the acid component allows for its effective configuration near the conductive polymer, suppressing dedoping of the conductive polymer and maintaining its high conductivity.

[0154] In Examples 4-6, protic solvents or mixtures of protic solvents were used as the solvent for the treatment solution. In this case, since the acid component is difficult to dissolve, most of the acid component is concentrated on the surface of the anode and the conductive polymer layer. It can be seen that the repair effect of the dielectric layer is excellent in this case, especially in Example 5, which combines a glycol-based solvent and a polyalkylene-based solvent, and can further reduce the initial leakage current change LC2 / LC1.

[0155] In Example 7, a mixed solvent of protic and non-protic solvents was used as the solvent for the treatment liquid. In this case, the initial ESR and the initial leakage current LC1 can be reduced.

[0156] Industrial availability

[0157] This invention can be used in hybrid electrolytic capacitors that utilize conductive polymers and liquid components.

[0158] Explanation of reference numerals in the attached figures

[0159] 10 Capacitor element, 11 Bottomed housing, 12 Sealing component, 13 Base plate, 14A, 14B Leads, 15A, 15B Lead connectors, 21 Anode body, 22 Cathode body, 23 Spacer, 24 Wrapped fixing tape.

Claims

1. A method for manufacturing an electrolytic capacitor, comprising a capacitor element having a foil-shaped anode and a foil-shaped cathode, wherein the foil-shaped anode has a dielectric layer on its surface. The manufacturing method has the following characteristics: The process of forming a capacitor element precursor by winding or stacking a spacer and an anode body and a cathode body that are positioned opposite each other with the spacer between them; The process of impregnating the capacitor element precursor with a treatment solution containing acidic components, solvents, and conductive polymeric components; A process of impregnating the capacitor element precursor with the processing liquid followed by a process of impregnating the capacitor element precursor with liquid components; as well as The process of obtaining the capacitor element by dissolving the acid component into the liquid component. The acid component is a compound containing at least one functional group selected from carboxyl, hydroxyl, phosphate, nitro, and oxo groups. The liquid component contains a protic solvent. After the process of obtaining the capacitor element, the conductivity X2 of the liquid component after the acid component is dissolved is higher than the conductivity X1 of the liquid component in the process of impregnating the liquid component into the capacitor element precursor, and is 0.1 μS / cm or more and 100 μS / cm or less.

2. The method for manufacturing an electrolytic capacitor according to claim 1, wherein, After the process of obtaining the capacitor element, the acid component is present in a proportion of 0.01% by mass or more and 2% by mass or less in the total liquid component.

3. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein, In the process of impregnating the liquid component into the capacitor element precursor, the conductivity X1 of the liquid component is less than 1 μS / cm.

4. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein, The liquid component contains an aprotic solvent.

5. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein, The liquid component following the process of obtaining the capacitor element contains an alkaline component. In the liquid components after the process of obtaining the capacitor element, the content of the alkaline component is less than 2% by mass.

6. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein, After the step of impregnating the processing liquid into the capacitor element precursor and before the step of impregnating the liquid component into the capacitor element precursor, there is a step of removing the solvent by drying. The drying temperature in the process of removing the solvent is above 150°C.

7. An electrolytic capacitor, formed using the manufacturing method of an electrolytic capacitor according to any one of claims 1 to 6, the electrolytic capacitor comprising capacitor elements. The capacitor element comprises: Spacer A foil-shaped anode body and a foil-shaped cathode body are sandwiched between the spacer and opposite each other. The solid electrolyte layer sandwiched between the anode and the cathode, and Liquid components The solid electrolyte layer contains acidic components and conductive polymers. The solid electrolyte layer has a biased portion containing the acid component. The acid component is a compound containing at least one functional group selected from carboxyl, hydroxyl, phosphate, nitro and oxo groups.

8. The electrolytic capacitor according to claim 7, wherein, The biased portion exists in at least one portion selected from the portion in contact with the anode body, the portion in contact with the cathode body, and the portion in contact with the spacer.

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