Electrolytic capacitors and electrolyte

Abstract

To provide an electrolytic capacitor and electrolyte in which the hydration reaction between the electrode foil and water is suppressed, thereby suppressing the deterioration of reliability due to the generation of hydrogen gas over a long period of time. [Solution] An electrolytic capacitor comprising a capacitor element including an anode foil, a cathode foil and a separator, a case housing the capacitor element, and an electrolyte filled in the case, wherein the cathode foil comprises aluminum and at least one selected from copper and iron in an amount of 0.05% to 0.50% by mass relative to the total mass of the cathode foil, and the electrolyte comprises 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, relative to the total mass of the electrolyte, an electrolytic capacitor and electrolyte.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor and an electrolytic solution.

Background Art

[0002] Electrolytic capacitors are used in various applications such as smoothing of voltage input from a power supply, noise removal, and DC bias voltage elimination. In particular, electrolytic capacitors using an electrolytic solution with a high water content are suitably used for low-voltage products, and are used, for example, for decoupling, coupling, and stable power supply to the Central Processing Unit (CPU) of personal computers. Electrolytic capacitors are required to have reduced impedance (Z) in order to fully exhibit their performance, and especially in small electrolytic capacitors, the specific resistance of the electrolytic solution is a major dominant factor of the impedance.

[0003] A method of reducing the specific resistance of an electrolytic solution by increasing the amount of water used as part of the solvent in an electrolytic capacitor has also been proposed (see Patent Document 1). However, when the water content in the electrolytic solution is increased, there are problems such as reaction with the anode foil, cathode foil and the like that significantly degrades the characteristics of the capacitor, and an increase in the internal pressure of the capacitor due to hydrogen gas generated during the reaction. Further, as a method for suppressing the hydration reaction when the water content is increased, an electrolytic solution for driving an electrolytic capacitor has been proposed, which is prepared by dissolving at least one kind of alkoxycarbonyldicarboxylic acid having a specific structure in a mixed solvent composed of 30.0 to 80.0 wt% of water and an organic solvent (see Patent Document 2).

[0004] On the other hand, as the cathode foil of an electrolytic capacitor, an aluminum foil is generally used, but there are also examples in which a metal such as copper or iron is contained in aluminum.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-186188 [Patent Document 2] Japanese Patent Publication No. 2005-197614 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the case of cathode foil containing metals such as copper and iron in aluminum, there is an advantage in that the processability of the cathode foil is improved because the area around the copper or iron dissolves more easily than the aluminum. However, since copper and iron have a lower ionization tendency compared to aluminum, it has been found that using aluminum foil containing metals such as copper and iron as cathode foil increases the reactivity of aluminum, making it easier for hydrogen gas to be generated. Increased hydrogen gas generation tends to require improvement in terms of product stability.

[0007] While the electrolytes described in Patent Documents 1 and 2 can be expected to have some ability to suppress hydrogen gas generation in cathode foil, there is room for improvement in the hydrogen gas generation suppression effect when applied to highly reactive cathode foil containing copper or iron in addition to aluminum.

[0008] One embodiment of this disclosure aims to solve the problem of an electrolytic capacitor in which the hydration reaction between the electrode foil and water is suppressed, thereby suppressing the deterioration of reliability due to the generation of hydrogen gas over a long period of time. Another embodiment of the present disclosure aims to solve the problem of providing an electrolyte that suppresses the decrease in reliability due to the generation of hydrogen gas when applied to an electrolytic capacitor having a highly reactive cathode foil. [Means for solving the problem]

[0009] The following embodiments are included as means to solve the above problems. <1> An electrolytic capacitor comprising a capacitor element including an anode foil, a cathode foil, and a separator, a case housing the capacitor element, and an electrolyte filled in the case, The cathode foil comprises aluminum and at least one selected from copper and iron in an amount of 0.05% to 0.50% by mass relative to the total mass of the cathode foil. The electrolyte comprises, in proportion to the total mass of the electrolyte, 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, or a salt thereof, in an electrolytic capacitor. <2> The compounds selected from dibasic carboxylic acids having 8 to 24 carbon atoms and having a methyl group in the molecular chain, or salts thereof, include compounds with the following structure: <1> The electrolytic capacitors listed above.

[0010] [ka]

[0011] <3> The electrolyte further comprises at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and having a methoxycarbonyl group in the molecular chain, or salts thereof. <1> or <2> The electrolytic capacitors listed above.

[0012] <4> The electrolyte comprises 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in the molecular chain, or salts thereof, relative to the total mass of the electrolyte. <1> ~ <3> The electrolyte used in electrolytic capacitors as described in any one of the following. [Effects of the Invention]

[0013] According to one embodiment of the present disclosure, an electrolytic capacitor is provided in which the hydration reaction between the electrode foil and water is suppressed, thereby suppressing the deterioration of reliability due to the generation of hydrogen gas over a long period of time. According to another embodiment of the present disclosure, there is provided an electrolytic solution that, when applied to an electrolytic capacitor having a highly reactive cathode foil, suppresses a decrease in reliability caused by generation of hydrogen gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of an electrolytic capacitor. [Figure 2] FIG. 2(A) is a schematic perspective view showing a configuration of a capacitor element included in the electrolytic capacitor of FIG. 1, and FIG. 2(B) is a partially enlarged view of a laminate constituting the capacitor element. DETAILED DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the present disclosure, the term "step" includes not only a step independent of other steps but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range indicated by "to" in the present disclosure, the numerical values stated before and after "to" are included as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another stepwise described numerical range. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When a plurality of substances corresponding to each component are present in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, when embodiments are described with reference to the drawings, the configurations of the embodiments are not limited to those shown in the drawings. In addition, the dimensions of the members in each drawing are conceptual, and the relative dimensional relationships between members are not limited to the aspects shown in the drawings.

[0016] <Electrolytic Capacitor> The electrolytic capacitor of the present disclosure is an electrolytic capacitor comprising a capacitor element including an anode foil, a cathode foil and a separator, a case for accommodating the capacitor element, and an electrolytic solution filled in the case, wherein the cathode foil comprises aluminum and at least one selected from copper and iron in an amount of 0.05 mass% to 0.50 mass% based on the total mass of the cathode foil, and the electrolytic solution comprises, based on the total mass of the electrolytic solution, 15 mass% to 80 mass% of an organic solvent, 10 mass% to 70 mass% of water, and at least one selected from dibasic carboxylic acids having 8 to 24 carbon atoms and having a methyl group in the molecular chain, or salts thereof.

[0017] The form of the electrolytic capacitor of the present disclosure is not particularly limited, and any electrolytic capacitor having a known configuration may be used. The electrolytic capacitor of the present disclosure may be modified or improved in any way within the scope of the present disclosure, and may be, for example, an electrolytic capacitor having a wound structure as shown in Figure 1. The electrolytic capacitor of the present disclosure includes, for example, an electrolytic capacitor of the type having an oxide film on both electrode foils, an electrolytic capacitor of the type having an electrode foil with a functional substance such as a silane coupling agent attached to the surface, and electrolytic capacitors other than those having a wound structure.

[0018] One embodiment of the configuration of the electrolytic capacitor of the present disclosure will be described with reference to the drawings. Figure 1 is a schematic cross-sectional view showing one embodiment of the electrolytic capacitor of the present disclosure. Figure 2(A) is a schematic perspective view showing the configuration of the capacitor element of the electrolytic capacitor shown in Figure 1, and Figure 2(B) is a partially enlarged view of the laminate constituting the capacitor element. The electrolytic capacitor 10 shown in Figure 1 is an aluminum electrolytic capacitor, in which a capacitor element 12 impregnated with an electrolyte (not shown) is housed in a metal case 14, and the opening of the case 14 is closed with a sealing body 16. The anode foil and cathode foil of the electrolytic capacitor 10 are each connected to electrode lead tabs 18. The capacitor element 12 housed in the metal case 14 has the shape of a wound sheet-like laminate 20 as shown in Figure 2(B).

[0019] As shown in Figure 2(B), the laminate 20 includes an aluminum foil (anodic foil) 24 having an aluminum oxide film 22 over its entire surface, an aluminum foil (cathode foil) 26 containing at least one selected from copper and iron in an amount of 0.05% to 0.50% by mass relative to the total mass of the cathode foil, and a first separator (isolation paper) 28 and a second separator (isolation paper) 30 sandwiched between these electrodes. The first separator 28 and the second separator 30 used in the laminate 20 may be the same or they may be different from each other. As shown in Figure 1, the capacitor element 12 is impregnated with an electrolyte (not shown) inside a metal case 14. -------------------------------------------------------------------------------

[0020] (Anode foil) The anode foil of the electrolytic capacitor of this disclosure can be one of known types. The anode foil of the electrolytic capacitor of this disclosure is preferably made of high-purity aluminum foil with a purity of 99% or higher. The anode foil can be formed by electrochemically etching aluminum foil, then anodizing it to form an oxide film on the surface, and finally attaching lead tabs for electrode extraction.

[0021] (Cathode foil) The cathode foil contains aluminum and at least one selected from copper and iron in an amount ranging from 0.05% to 0.50% by mass relative to the total mass of the cathode foil. The cathode foil can be formed by electrochemically etching the above-mentioned aluminum foil. For the cathode foil, chemical conversion treatments such as anodizing to form an oxide film on the surface are optional. Normally, a natural oxide film (not shown) is formed on the surface of the cathode foil by oxygen in the air, so any special oxide film formation treatment may or may not be performed. Alternatively, the surface of the etched cathode foil may be subjected to a chemical conversion treatment similar to that of the anode foil to form an oxide film, for example. The cathode foil contains at least one selected from copper and iron in an amount ranging from 0.05% to 0.50% by mass relative to the total mass of the cathode foil, thereby exhibiting excellent etching properties and better processability compared to aluminum foil. Due to its good processability, such as etching properties, its resistance to electrolyte tends to be lower than that of aluminum foil. However, because the electrolytic capacitor of this disclosure contains an electrolyte described later, even when using cathode foil with good processability, the hydration reactivity between the electrode foil and water is low, and the generation of hydrogen gas due to reaction with water is effectively suppressed.

[0022] Of the copper and iron metals contained in the cathode foil, copper is preferred from the viewpoint of having a lower ionization tendency. The content of at least one selected from copper and iron relative to the total mass of the cathode foil is in the range of 0.05% to 0.50% by mass, preferably in the range of 0.10% to 0.40% by mass, and more preferably in the range of 0.20% to 0.30% by mass. After etching, the cathode foil can be fitted into an electrolytic capacitor by attaching lead tabs for electrode extraction.

[0023] (Electrolytic capacitor configuration) In one embodiment of the electrolytic capacitor of this disclosure, a capacitor element can be obtained by winding up an anode foil and a cathode foil with their surfaces facing each other via a separatory paper. The isolation paper used in capacitor elements is not particularly limited. For example, isolation paper can be made from naturally occurring cellulose materials (e.g., Manila hemp, plant pulp, etc.) and manufactured through processes such as dust removal, washing, beating, and papermaking. Furthermore, paper derived not only from natural fibers but also from synthetic fibers can be used as isolation paper.

[0024] The resulting capacitor element is housed in a metal case. The case containing the capacitor element is filled with electrolyte, and the opening of the case is sealed with a sealing element to obtain an electrolytic capacitor.

[0025] The sealing material used in electrolytic capacitors is preferably made of a material that has high hardness, moderate elasticity, is impermeable to electrolyte, and has good airtightness as a sealing material. The sealing material can be selected and used from a variety of known materials. Examples of materials for the sealing body include elastic rubbers such as natural rubber (NR), styrene-butadiene rubber (SBR), ethylene-propylene polymer (EPT), and isobutylene-isoprene rubber (IIR). Furthermore, isobutylene-isoprene rubber (IIR) is also preferable because it offers high airtightness and suppresses the permeation of electrolyte as vapor. In particular, it is even more preferable to use IIRs that have good heat resistance, such as sulfur vulcanization, quinoid vulcanization, resin vulcanization, and peroxide vulcanization. In manufacturing the electrolytic capacitors of this disclosure, instead of the above-mentioned known sealing material, a hybrid material can also be used, which is made by laminating a resin material plate (for example, a fluororesin plate such as a polytetrafluoroethylene (hereinafter referred to as PTFE) plate) that is airtight and has sufficiently high strength with elastic rubber.

[0026] (electrolyte) The electrolyte used in the electrolytic capacitor of this disclosure comprises, with respect to the total mass of the electrolyte, 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, or a salt thereof (hereinafter also referred to as a specific compound), and may further contain other components depending on the purpose. The electrolyte according to this disclosure contains a specific compound, which is thought to suppress the reaction between the water in the electrolyte and the cathode foil, thereby effectively suppressing the generation of unwanted hydrogen gas. Therefore, the electrolytic capacitor according to this disclosure can suppress the decrease in reliability due to hydrogen generation over a long period of time, even when using a highly reactive cathode foil.

[0027] Examples of at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in the molecular chain, or salts thereof (i.e., specific compound), include 1,7-octanedicarboxylic acid, 3-methylpimelic acid, 4-methylpimelic acid, 3-methylseveric acid, 4-methylseveric acid, 3-methylazelaic acid, 5-methylazelaic acid, 2-methylsebacic acid, 4-methylsebacic acid, 5-methylsebacic acid, 2-methylundecanediic acid, 5-methylundecanediic acid, and among these, 1,7-octanedicarboxylic acid having the structure shown below is preferred. When a specific compound is a carboxylate salt, examples of salts include ammonium salts, amine salts, alkylammonium salts, amidine salts, sodium salts, potassium salts, etc. Examples of amine salts include dimethylamine, diethylamine, trimethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, methanolamine, ethanolamine, dimethanolamine, diethanolamine, trimethanolamine, triethanolamine, pyrrolidine, piperidine, piperazine, morpholine, methylmorpholine, ethylmorpholine, oxazolidine, thiomorpholine, thiazolidine, etc. In particular, as a specific compound, an ammonium salt of 1,7-octanedicarboxylic acid having the following structure is more preferred from the viewpoint of its effect in suppressing the reaction between the electrolyte and the cathode foil.

[0028] [ka]

[0029] The electrolyte relating to this disclosure may contain only one specific compound, or it may contain two or more specific compounds. The content of the specific compound is preferably 0.05% to 2.5% by mass, more preferably 0.15% to 2.0% by mass, and even more preferably 0.5% to 1.8% by mass, based on the total mass of the electrolyte. By keeping the content of the specific compound within the above range, a hydrogen generation suppression effect is achieved, and there is no concern about increased leakage current during high-temperature no-load standing tests that may occur due to excessive content of the specific compound.

[0030] The electrolyte may further contain at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and having a methoxycarbonyl group in their molecular chain, or salts thereof. Examples of dibasic carboxylic acids having 8 to 24 carbon atoms and a methoxycarbonyl group in the molecular chain include 7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid, 7,9-dimethyl-7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, and 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid, which may also be salts. The salts of the above dibasic carboxylic acids are preferably included as ammonium salts.

[0031] (solvent) The electrolyte according to this disclosure contains 15% to 80% by mass of an organic solvent and 10% to 70% by mass of water as a solvent for the specified components, etc.

[0032] -Organic solvents- The organic solvent can be either protic or aprotic, and each solvent can be used individually or in combination of two or more. If necessary, one or more protic solvents and one or more aprotic solvents may be used in any combination. Examples of proton-based solvents include alcohol compounds. Suitable examples of alcohol compounds include monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol; dihydric alcohols (glycols) such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol; and trihydric alcohols such as glycerin. Among these, dihydric alcohols are preferred, and from the viewpoint of availability and stability, ethylene glycol and diethylene glycol are preferred.

[0033] Examples of aprotic solvents include lactone compounds such as γ-butyrolactone, sulfolanes, methylsulfolanes, dimethylsulfolanes, ethylene carbonates, propylene carbonates, pyrrolidines, 2-pyrrolidinones, N-methyl-2-pyrrolidinones, 1,3-dimethyl-2-imidazolidinones, tetrahydrofurans, acetonitriles, N-methylformamides, N,N-dimethylformamides, nitrobenzenes, and other intramolecular polarizing compounds and their derivatives.

[0034] Protic solvents and aprotic solvents may be used individually, or two or more may be used in any combination as needed. The content of the organic solvent relative to the total mass of the electrolyte is 15% to 80% by mass, preferably 30% to 80% by mass, and more preferably 45% to 75% by mass.

[0035] -water- The water used should preferably have a low impurity content, and purified water, distilled water, or ion-exchanged water can be used. The water content as a solvent is 10% to 70% by mass, preferably 10% to 60% by mass, and more preferably 12% to 50% by mass, based on the total mass of the electrolyte. By including water as a solvent in the electrolyte, the dissociation of organic acids and organic acid salts into ions is promoted, thereby improving the conductivity of the electrolyte. Furthermore, it lowers the freezing point of the solvent, thereby improving the resistivity characteristics of the electrolyte at low temperatures, and achieving good low-temperature characteristics, as indicated by a small difference in resistivity between low temperature and room temperature. As described above, the electrolyte according to this disclosure contains a specific compound, and therefore, even if the electrolyte contains water, the hydration reaction between the electrolyte and the cathode foil is suppressed, thereby effectively suppressing the generation of unwanted hydrogen gas.

[0036] -Other dibasic carboxylic acids- The electrolyte relating to this disclosure may contain other dibasic carboxylic acids other than the specified compound. Other dibasic carboxylic acids include linear dibasic carboxylic acids, which may be salts thereof. Examples of linear dibasic carboxylic acids include adipic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, and 1,10-decanedicarboxylic acid. Other dibasic carboxylic acids may be included as salts, and ammonium salts are preferred as the salts.

[0037] -Other ingredients- In addition to specific compounds, the electrolyte may contain other components for purposes such as suppressing hydrogen gas generation, inhibiting electrode degradation, and improving voltage resistance. Other components include, for example, nitro compounds such as p-nitrophenol, m-nitroacetophenone, p-nitrobenzoic acid, p-nitrobenzyl alcohol, o-nitroanisole, and p-nitrotoluene, which are used to suppress hydrogen gas generation. Components intended to suppress electrode degradation include phosphoric acid compounds such as orthophosphoric acid, phosphorous acid, hypophosphoric acid, pyrophosphoric acid, polyphosphoric acid, methyl phosphate, ethyl phosphate, butyl phosphate, isopropyl phosphate, dibutyl phosphate, and dioctyl phosphate; chelating agents such as citric acid, gluconic acid, gluconolactone, ethylenediaminetetraacetic acid (EDTA), glycol etherdiaminetetraacetic acid (GEDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), trans-1,2-diaminocyclohexane-N,N,N',N',N'-tetraacetic acid hydrate (CyDTA), and triethylenetetraminehexaacetic acid (TTHA), as well as their salts. Components intended to improve voltage resistance include boric acid compounds such as boric acid and its complex compounds, polyhydric alcohols such as mannitol, sorbitol, xylitol, and pentaerythritol, and silicon compounds such as colloidal silica.

[0038] The electrolyte may also contain, as other components, at least one selected from organic acids and inorganic acids, and derivatives thereof. Examples of organic acids include monocarboxylic acids and their derivatives such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, and caprylic acid; dicarboxylic acids and their derivatives such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, and 1,10-decanedicarboxylic acid; and hydroxycarboxylic acids and their derivatives such as citric acid and salicylic acid. Examples of inorganic acids include boric acid, sulfamic acid, and their derivatives. Furthermore, the compound may also contain a complex of an organic acid and an inorganic acid, i.e., a boron complex of a dicarboxylic acid or hydroxycarboxylic acid. Examples of complex compounds of organic and inorganic acids include borodisuoic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodimaleic acid, borodiphthalic acid, borodiglycolic acid, borodicitric acid, borosalicylic acid, and their derivatives.

[0039] (Preparation of electrolyte solution) The electrolyte can be prepared by adding the aforementioned components to a mixed solvent of an organic solvent and water, and then stirring and mixing them. The order in which each component, including the specific compound, is added is arbitrary. When preparing the electrolyte, the mixture may be heated to improve the solubility of each component. The heating temperature should be appropriately selected considering the stability of each component. Generally, heating to 100°C or below is preferable.

[0040] <Electrolyte> The electrolyte of this disclosure comprises, in proportion to the total amount of the electrolyte, 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, or salts thereof. The electrolyte of this disclosure has a good hydrogen generation suppression effect and can therefore be suitably used in known electrolytic capacitors. In particular, its effect is remarkable when used in the electrolytic capacitor of this disclosure described above, which uses a highly reactive cathode foil.

[0041] (Manufacturing method for electrolytic capacitors) There are no particular restrictions on the manufacturing method of electrolytic capacitors; known methods can be appropriately selected and applied according to the configuration of the electrolytic capacitor. For example, in the case of the electrolytic capacitor illustrated in Figure 1, first, an aluminum foil containing a specified amount of copper or iron is prepared, electrochemically etched to form an oxide film on the surface (either a natural oxide film or a chemically converted film), and then electrode lead tabs are attached to produce the cathode foil according to this disclosure. In a separate process, the aluminum foil is electrochemically etched, then anodized to form an oxide film on the surface, and electrode lead tabs are attached to produce the aluminum anode foil. (Cathode foil preparation process) and (Anode foil preparation process) A capacitor element is fabricated by inserting a separator (isolation paper) between the obtained anode foil and cathode foil and winding them into a roll. (Capacitor element formation process)

[0042] As a separate process, the electrolyte solution is prepared. An electrolytic capacitor can be obtained by impregnating the resulting electrolyte into a capacitor element, housing it in a case, and sealing it with a sealing element. Here, when housing the capacitor element in the case, the electrode lead tabs are positioned so that they protrude from the case. The order in which the anode foil manufacturing process, cathode foil manufacturing process, and electrolyte preparation process are carried out is arbitrary, and they may be performed simultaneously as separate processes. Here, we have provided an example of a method for manufacturing an electrolytic capacitor with a wound structure, but it goes without saying that the method for manufacturing an electrolytic capacitor is not limited to the above method and can be appropriately selected depending on the configuration of the electrolytic capacitor.

[0043] As described above, the electrolytic capacitor of this disclosure has a highly reactive cathode foil, and even when an electrolyte with increased water content is used to reduce resistance, the hydration reaction between the electrode foil and water is suppressed, and the decrease in reliability due to the generation of hydrogen gas is suppressed over a longer period of time, making it suitable for use in various applications. Furthermore, the electrolytic capacitor of this disclosure exhibits the above effect by using the electrolyte of this disclosure. The electrolyte according to this disclosure can be used in various electrolytic capacitors because it exhibits a hydrogen generation suppression effect not only when used in electrolytic capacitors containing the highly reactive cathode foil mentioned above, but also when used in electrolytic capacitors containing commonly used aluminum cathode foil. [Examples]

[0044] The present disclosure will be described in more detail below with reference to the examples. However, the present disclosure is not limited to what is described in the following examples. Unless otherwise specified, "%" represents "mass%".

[0045] [Examples 1, 2, and 1 Comparative Example] <Fabrication of electrolytic capacitors> An aluminum electrolytic capacitor with a rating of 35WV, φ18, 35L, 3300μF, and lead type (CE04) was fabricated using the following procedure. (1) Preparation of anode foil and cathode foil After electrochemically etching aluminum foil, an oxide film was formed on the surface, and then lead tabs for electrode extraction were attached to fabricate an aluminum anode foil. Next, an aluminum foil containing 0.25% copper was electrochemically etched, and lead tabs for electrode extraction were attached to create an aluminum-containing cathode foil.

[0046] (2) Preparation of the electrolyte Based on the composition shown in Table 1 below, the solvent and electrolyte components were sequentially added to the container and then stirred to prepare the electrolyte solution. In Tables 1 and 2 below, the values ​​listed in the electrolyte formulation represent the percentage content of each component. First, the solvent, ethylene glycol, and water were thoroughly mixed in a container. Then, the other components were added to the container, mixed, and uniformly dissolved to prepare the electrolyte solution. In preparing the electrolyte, the solution was heated to 50°C to improve the solubility of each component.

[0047] (3) Fabrication of capacitor elements A capacitor element was fabricated by winding a separator (isolation paper) between the anode foil and cathode foil obtained in (1) into a roll. Paper made from Manila hemp pulp was used as the separator.

[0048] (4) Placement in case The capacitor element was impregnated with the electrolyte obtained in (2) and housed in a bottomed aluminum case. At this time, the electrode lead tabs were housed so that they were outside the case, and the opening of the case was sealed with an elastic sealant. After that, an aging treatment was performed to fabricate a wound electrolytic capacitor. IIR rubber was used as the elastic sealant.

[0049] (5) Durability evaluation of electrolytic capacitors Each of the obtained electrolytic capacitors was subjected to a continuous DC 35V in a 105°C forced convection constant temperature chamber. Subsequently, the time until the explosion-proof valve of the electrolytic capacitor activated due to the increase in internal pressure caused by hydrogen gas generation was measured. As a result, both the example and comparative example showed durability of more than 1000 hours before the explosion-proof valve activated. The time until the explosion-proof valve activated in Comparative Example 1 was set to 100, and the times until the explosion-proof valve activated in Examples 1 and 2 were converted and relatively evaluated. The results are shown in Table 1 below. Note that the values ​​listed in the electrolyte formulations in the table below are in mass percent.

[0050] [Table 1]

[0051] As shown in Table 1, the electrolytic capacitors using the electrolytes of Example 1 and Example 2 had 4 to 6 times the durability of the electrolytic capacitor of Comparative Example 1. From the above results, it was confirmed that the electrolytic capacitors of each example had a good effect in suppressing hydrogen generation.

[0052] [Examples 3 to 5 and Comparative Example 2] <Fabrication of electrolytic capacitors> Electrolytic capacitors were manufactured in the same manner as in Example 1, except that the electrolyte formulation was as described in Table 2 below, and evaluated in the same manner as in Example 1. As a result, both the examples and comparative examples demonstrated durability of over 1000 hours before the explosion-proof valves activated. The time until the explosion-proof valve activated in Comparative Example 2 was set to 100, and the times until the explosion-proof valve activated in Examples 3 to 5 were converted and evaluated relatively. The results are shown in Table 2 below.

[0053] [Table 2]

[0054] As shown in Table 2, the electrolytic capacitors using the electrolytes of Examples 3 to 5 had 2 to 5 times the durability of the electrolytic capacitor of Comparative Example 2. From the above results, it was confirmed that the electrolytic capacitors of each example had a good effect in suppressing hydrogen generation. [Explanation of symbols]

[0055] 10... Electrolytic capacitor, 12... Capacitor element, 14... Electrolytic capacitor case (metal case), 16... Sealing body, 18... Lead tab for electrodes 20...Laminate, 22...Anodized layer, 24...Anode foil, 26...Cathode foil, 28...First separator, 30...Second separator

Claims

1. An electrolytic capacitor comprising a capacitor element including an anode foil, a cathode foil, and a separator, a case housing the capacitor element, and an electrolyte filled in the case, The cathode foil comprises aluminum and at least one selected from copper and iron in an amount of 0.05% to 0.50% by mass relative to the total mass of the cathode foil. The electrolyte comprises, in proportion to the total mass of the electrolyte, 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, or a salt thereof. Electrolytic capacitor.

2. The electrolytic capacitor according to claim 1, wherein the compound selected from a dibasic carboxylic acid having 8 to 24 carbon atoms and having a methyl group in the molecular chain, or a salt thereof, includes a compound having the following structure. 【Chemistry 1】

3. The electrolytic capacitor according to claim 1, wherein the electrolyte further comprises at least one compound selected from a dibasic carboxylic acid having 8 to 24 carbon atoms and a methoxycarbonyl group in its molecular chain, or a salt thereof.

4. An electrolyte used in an electrolytic capacitor according to any one of claims 1 to 3, comprising 15% to 80% by mass of an organic solvent, 10% to 70% by mass of water, and at least one compound selected from dibasic carboxylic acids having 8 to 24 carbon atoms and a methyl group in their molecular chain, based on the total mass of the electrolyte.

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