Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor and a method for manufacturing the same, which has an electrolyte composition in which a predetermined amount of a phosphate ion source is blended with an aqueous electrolyte containing a predetermined amount of water, and which can suppress leakage current and achieve a long life despite containing a relatively large amount of the phosphate ion source.SOLUTION: An electrolytic capacitor (1) according to the present invention includes a capacitor element (2) having an anode foil (8) on which a dielectric layer is formed, a cathode foil (9), and a separator (10) disposed between the anode foil (8) and the cathode foil (9), and an electrolyte (3) impregnated in the capacitor element (2), and the electrolyte (3) contains a water-containing solvent, a phosphate ion source, and a phosphonic acid-based chelating agent, and the phosphate ion source is contained in the electrolyte at 120.0 to 500.0 mmol / kg.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] An electrolytic capacitor is an electricity storage device that is basically constructed by disposing a separator between an anode foil with an oxide film formed as a dielectric layer and a cathode foil, and then introducing (impregnating) an electrolyte into the capacitor element. There are two types of electrolytic capacitors: one in which an electrolytic solution is introduced as a non-solid electrolyte into the capacitor element, and one in which a solid electrolyte such as a conductive polymer is introduced. Furthermore, there is also a so-called "hybrid type" of electrolytic capacitor, in which both the solid electrolyte and the electrolytic solution are introduced into the capacitor element, and which takes advantage of the advantages of both solid and non-solid electrolytes.

[0003] The electrolytic solution in an electrolytic capacitor contains at least a solute, which is an electrolyte, and a solvent that dissolves or disperses the solute. Regarding the composition of the electrolytic solution in an electrolytic capacitor, the water content in the solvent is sometimes increased to lower the resistance of the electrolytic solution, with the aim of lowering the ESR and impedance of the electrolytic capacitor. However, if the water content in the electrolytic solution is increased, which is prone to chemical reactions, the metal elements (e.g., Al) of the electrode foil that have dissolved out may be dissolved, especially at high temperatures. 3+ ) and water (i.e., OH - ) undergoes a hydration reaction, and the resulting hydroxides (e.g., Al(OH)3) precipitate on the surface of the electrode foil, degrading the foil and increasing leakage current. In addition, hydrogen gas produced by the hydration reaction and electrolysis of water increases the internal pressure, causing the explosion-proof valve to open in a relatively short time, shortening its lifespan.

[0004] Therefore, conventionally, phosphoric acid has been added to an electrolyte solution having an aqueous solvent containing a predetermined amount of water to suppress hydration deterioration of electrode foil (Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-186239). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-186239 Summary of the Invention [Problem to be solved by the invention]

[0006] The effect of phosphoric acid in inhibiting the hydration degradation of electrode foils is well known, but the amount of phosphoric acid added to the electrolyte is limited, so there is a problem that the effect of phosphoric acid in inhibiting the hydration degradation of electrode foils is also insufficient. That is, the phosphate ions released in the electrolyte are converted into the metal elements (e.g., Al) of the electrode foil that have been dissolved. 3+ ), and the resulting inorganic phosphate (e.g., AlPO4) forms a water-resistant film on the surface of the electrode foil, suppressing hydration degradation of the electrode foil; however, phosphoric acid (phosphate ions) gradually disappears from the electrolyte. Therefore, if a relatively small amount of phosphoric acid is added, hydration degradation of the electrode foil is not sufficiently suppressed, and the suppression effect is difficult to sustain. Therefore, if a relatively large amount of phosphoric acid is added to enhance the effect of suppressing hydration degradation of the electrode foil, phosphoric acid, being an acid, itself has the property of degrading the electrode foil, and this actually accelerates the deterioration of the electrode foil, increasing leakage current and accelerating the hydration reaction, thereby shortening the lifespan. [Means for solving the problem]

[0007] The present invention has been made in view of the above circumstances, and aims to provide an electrolytic capacitor and a method for manufacturing an electrolytic capacitor, which have an electrolyte solution composition in which a predetermined amount of a phosphate ion source is blended with an aqueous electrolyte solution containing a predetermined amount of water, and which can suppress leakage current and achieve a long life despite containing a relatively large amount of the phosphate ion source.

[0008] The present invention solves the above problems by the solution means described below as one embodiment.

[0009] The electrolytic capacitor according to the present invention comprises: A low-voltage electrolytic capacitor, a capacitor element including an anode foil having a dielectric layer formed thereon, a cathode foil, and a separator disposed between the anode foil and the cathode foil; and an electrolyte solution impregnated in the capacitor element, wherein the electrolyte solution is 55wt% or more Contains water water system a solvent; a phosphate ion source; Phosphonic acid group Phosphonic acid chelating agents, which are compounds with chelating ability, (However, ethylenediaminetetra(methylenephosphonic acid) (EDTMP), ethylenediaminetetrakis(methylenephosphonic acid) (EDTPO), ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure as these are excluded.)

[0010] According to the present invention, the phosphonic acid-based chelating agent is adsorbed onto the surface of the electrode foil and acts as a protective film, protecting the electrode foil from the action of excess phosphate ions. 3+ The present invention moderately slows down the excessive reaction between the metal elements of the electrode foil and phosphate ions, thereby suppressing the loss of phosphate ions. for example Although the content is relatively large, at 120.0 to 500.0 mmol / kg, leakage current can be suppressed and a long life can be achieved.

[0011] The electrolyte solution is The organic acid ammonium salt is contained. The ammonium salt is mainly ammonium adipate with ammonium formate added. It is preferable.

[0012] The phosphate ion source may be one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of each of these three acids, esters of each of the three acids and salts of the esters, and condensates of each of the three acids and salts of the condensates.Furthermore, the phosphate ion source is preferably one or more substances selected from the group consisting of phosphoric acid, phosphate salts, phosphate esters, and salts of phosphate esters.

[0013] The phosphonic acid chelating agent includes 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylenephosphonic acid), and 2-Phosphonobutane-1,2,4-tricarboxylic acid Acid The substance may be one or more substances selected from the group including:

[0014] The method for producing an electrolytic capacitor according to the present invention comprises adding at least 55wt% or more An aqueous solvent containing water, a phosphate ion source, and a phosphonic acid group having chelating ability Phosphonic acid chelating agent (but ethylenediaminetetra(methylenephosphoric acid) phosphonic acid) (EDTMP), ethylenediaminetetrakis(methylenephosphonic acid) (EDTP O), and ethylenediamine-N,N'-bis(methylenephosphonic acid), and (excluding substances with the same chemical structure as these.) It is characterized by being blended.

[0015] According to the present invention, the phosphonic acid-based chelating agent is adsorbed onto the surface of the electrode foil and acts as a protective film, protecting the electrode foil from the action of excess phosphate ions. 3+ The present invention moderately slows down the excessive reaction between the metal elements of the electrode foil and phosphate ions, thereby suppressing the loss of phosphate ions. for example Although the content is relatively large, at 120.0 to 500.0 mmol / kg, leakage current can be suppressed and a long life can be achieved.

[0016] The electrolyte solution is It is characterized by containing an organic acid ammonium salt. Ammonium adipate is a compound mainly composed of ammonium adipate and ammonium formate. It is preferable that

[0017] The phosphate ion source may be one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of each of these three acids, esters of each of the three acids and salts of the esters, and condensates of each of the three acids and salts of the condensates.Furthermore, the phosphate ion source is preferably one or more substances selected from the group consisting of phosphoric acid, phosphate salts, phosphate esters, and salts of phosphate esters.

[0018] The phosphonic acid chelating agent includes 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylenephosphonic acid), and 2-Phosphonobutane-1,2,4-tricarboxylic acid Acid The substance may be one or more substances selected from the group including: [Effects of the Invention]

[0019] According to the present invention, in an electrolyte composition in which a predetermined amount of a phosphate ion source is blended with an aqueous electrolyte containing a predetermined amount of water, leakage current can be suppressed and a long life can be achieved while containing a relatively large amount of the phosphate ion source. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram (front cross-sectional view) showing an example of an electrolytic capacitor according to this embodiment. [Figure 2] FIG. 2 is an explanatory diagram illustrating an example of a capacitor element in the electrolytic capacitor according to this embodiment. [Figure 3] FIG. 3 is a flowchart showing an example of a method for manufacturing an electrolytic capacitor according to this embodiment. [Figure 4] FIG. 4 is an explanatory diagram illustrating an example of a capacitor element forming step in the method shown in FIG. [Figure 5] 5A and 5B are graphs showing the results of Test 1. [Figure 6] FIG. 6 is a graph showing the results of Test 3. [Figure 7] FIG. 7 is a graph showing the results of Test 4. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to an electrolytic capacitor having a structural feature in the composition of the electrolyte solution, and to a method for manufacturing the same. Hereinafter, as an embodiment of the present invention, an electrolytic capacitor of a type in which an electrolyte solution is introduced as a non-solid electrolyte into the capacitor element (a type in which a solid electrolyte is not introduced) will be described as an example. However, due to the nature of the present invention, the electrolytic capacitor according to the present invention is not limited to the type described here, and also includes, for example, so-called "hybrid type" electrolytic capacitors in which an electrolyte solution is introduced into the capacitor element together with a solid electrolyte such as a conductive polymer.

[0022] Hereinafter, this specification will describe in detail embodiments of the present invention with reference to the drawings. FIG. 1 is a schematic diagram (front cross-sectional view) illustrating an example of an electrolytic capacitor 1 according to this embodiment. However, for ease of understanding, the cross-sectional structure of the capacitor element 2 is not shown. FIG. 2 is an explanatory diagram illustrating an example of the capacitor element 2 in the electrolytic capacitor 1 according to this embodiment, and schematically illustrates an example of the basic configuration of the capacitor element 2. Hereinafter, this specification will describe an electrolytic capacitor 1 having a wound-type capacitor element 2 as an example of an embodiment, but this element configuration is not limited to this and may be, for example, a stacked type or a coin type. Also, this specification will describe an example of a lead-type electrolytic capacitor 1 having lead terminals 4 as an example of an embodiment, but this terminal configuration is not limited to this and may be, for example, a screw terminal type or a board-mounted type. Also, this specification will describe an example of an aluminum electrolytic capacitor 1 having electrode foils 8 and 9 primarily made of aluminum or an aluminum alloy as an example of an embodiment, but this foil configuration is not limited to this and may be, for example, an electrode foil primarily made of a valve metal other than aluminum or a valve metal alloy.

[0023] As shown in FIG. 1 , the electrolytic capacitor 1 according to this embodiment includes a capacitor element 2 impregnated with an electrolyte solution 3 housed in a cylindrical case 6 with a bottom. The opening of the case 6 is sealed with a sealing material 5. Lead terminals 4 (anode terminal 4a and cathode terminal 4b) joined to the capacitor element 2 are fitted into through-holes in the sealing material 5 and extend from the through-holes to the outside of the electrolytic capacitor 1. The opening edge 6a of the case 6 is crimped to the sealing material 5, thereby sealing the inside of the case 6. The case 6 is provided with an explosion-proof valve 7, which is a pressure valve. When the internal pressure of the electrolytic capacitor 1 reaches a certain level, the valve opens to release gas within the electrolytic capacitor 1, thereby preventing explosion. The number and location of the explosion-proof valves 7 are not limited; for example, they may be provided in the sealing material 5, or in both the case 6 and the sealing material 5. Furthermore, in a packaged product, the case 6 is typically packaged in an exterior packaging material (not shown).

[0024] 2, capacitor element 2 according to this embodiment includes an anode foil 8, a cathode foil 9, and a separator 10 disposed between anode foil 8 and cathode foil 9. An anode terminal 4a is joined to anode foil 8. A cathode terminal 4b is joined to cathode foil 9.

[0025] The electrode foils (anode foil 8 and cathode foil 9) are primarily made of aluminum or an aluminum alloy. The term "primary material" here refers to the tolerance of unintentional inclusion of trace amounts of other elements, such as less than 1.0% by mass (e.g., less than 0.5%, 0.1%, 0.05%, or 0.01% by mass). Meanwhile, other elements intentionally included in the aluminum alloy include one or more of the following elements: Ta, Nb, Ti, Cr, Hf, Zr, Zn, W, Ni, V, Fe, Cu, Mn, Mg, Ga, Si, and B. The other metals constituting the aluminum alloy are not limited to valve metals; they may also include metal elements other than valve metals or other nonmetallic elements. These other elements may be included in any amount within the range that allows the electrode foils 8 and 9 in the aluminum electrolytic capacitor 1 to function. When the content (by mass) of the intended additive is relatively small, the composition may contain a content (by mass) that exceeds the content (by mass) of unintentional impurities. Note that foil forms that can be applied to the present invention other than this embodiment include foil forms in which the aluminum is replaced with other valve metals.

[0026] The electrode foils 8 and 9 may be formed of two layers: a core substrate and a coating material that covers the substrate. In this case, it is sufficient that at least the outer layer of the coating material is primarily made of aluminum or an aluminum alloy. That is, the composition of the substrate and the composition of the coating material may be the same or different.

[0027] The electrode foils 8, 9 have an expanded surface structure. The expanded surface structure is typically formed by etching. Alternatively, the expanded surface structure may be formed by vapor deposition, sintering, or the like of a metal powder as a main material. In this case, for example, the electrode foils 8, 9 themselves can be formed and the expanded surface structure can be formed by coating the core substrate with aluminum or aluminum alloy powder by vapor deposition or sintering. The expanded surface structure of the electrode foils 8, 9 can increase the specific surface area and thus the capacitance.

[0028] An oxide film 8a serving as a dielectric layer is formed by chemical conversion treatment on the surface of the enlarged anode foil 8. Specifically, the chemical conversion treatment is an anodization process in which a voltage is applied between the target metal (here, the anode foil 8) as the anode and a chemical conversion solution to form the oxide film 8a.

[0029] The chemical conversion treatment can be performed, for example, by the following procedure. That is, in the chemical conversion treatment, for example, capacitor element 2 is immersed in a chemical conversion solution tank, and a predetermined voltage is applied between anode terminal 4a as the anode and the chemical conversion solution for a predetermined time (for example, a voltage of 100 V is applied for 5 minutes). Thereafter, capacitor element 2 is removed from the chemical conversion solution tank and dried. Examples of chemical conversion solutions include aqueous solutions of ammonium adipate, ammonium borate, ammonium phosphate, ammonium glutarate, ammonium azelaate, ammonium tartrate, ammonium sebacate, ammonium pimelate, ammonium suberate, etc.

[0030] On the other hand, the surface-enlarged cathode foil 9 is not further processed, and a natural oxide film (not shown) is formed on the surface of the cathode foil 9 by oxygen in the air. However, this configuration is not limited thereto, and for example, a valve metal or valve metal alloy powder such as titanium may be further vapor-deposited on the surface of the surface-enlarged cathode foil 9. This increases the dielectric constant and improves the capacitance. Alternatively, the surface of the surface-enlarged cathode foil 9 may be subjected to a chemical conversion treatment similar to that of the anode foil 8, resulting in a non-polar electrolytic capacitor 1.

[0031] The separator 10 separating the anode foil 8 and the cathode foil 9 is made of paper or the like made of natural cellulose fibers such as Manila hemp pulp, or cloth, sheet, film, or the like made of synthetic fibers such as nylon, or a blend or blended product thereof. Of these, synthetic fibers have the advantage of being able to select materials with particularly excellent heat resistance. Examples of such synthetic fibers include nylon, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polyphenylene sulfide (PPS). Note that while FIG. 2 is a diagram schematically illustrating an example of the basic configuration of the capacitor element 2 and shows one separator 10, the number is not limited; for example, three separators may be provided, as shown in FIG. 4.

[0032] In addition, the capacitor element 2 is impregnated with an electrolyte solution 3. As shown schematically in FIG. 2, the electrolyte solution 3 is present in the gap between the anode foil 8 and the cathode foil 9. By contacting the dielectric layer (oxide film 8a) formed on the anode foil 8 and the cathode foil 9, the electrolyte solution 3 functions in place of the cathode foil 9 as a true cathode that essentially serves as the counter electrode of the anode foil 8. However, as long as the electrolyte solution 3 can perform its function, it does not have to completely fill the space between the electrode foils 8 and 9, and there may be areas between the electrode foils 8 and 9 that are not filled with the electrolyte solution 3. Note that the separator 10 allows components of the electrolyte solution 3 to pass freely between the anode foil 8 side and the cathode foil 9 side, but depending on the configuration and material of the separator 10, the electrolyte solution 3 may also be impregnated into the separator 10.

[0033] The electrolytic solution 3 contains a solute, which is an electrolyte, and a solvent that dissolves or disperses the solute. The solvent according to this embodiment is an aqueous solvent containing a predetermined amount of water. The water content is not limited, but the electrolytic solution 3 may contain 40% by mass or more of water, and may further contain 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more. The water content of the electrolytic solution 3 can be increased by the inclusion of a phosphate ion source and a phosphonic acid chelating agent, which will be described later. The aqueous solvent may further contain components other than water (e.g., an organic solvent) or may be composed solely of water. Such an aqueous solvent can increase the solubility of the electrolyte and the mobility of ions by the action of water, thereby reducing the resistivity of the electrolytic solution 3. The reduced resistance of the electrolytic solution 3 can result in a reduced ESR and impedance of the electrolytic capacitor 1.

[0034] Examples of organic solvents that can be used as solvent components include protic solvents such as monohydric alcohols (e.g., methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol), dihydric alcohols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol), and trihydric alcohols (e.g., glycerin), as well as derivatives thereof. Examples of aprotic solvents include lactone compounds (e.g., γ-butyrolactone), sulfolane, methylsulfolane, dimethylsulfolane, ethylene carbonate, propylene carbonate, pyrrolidine, 2-pyrrolidinone, N-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, tetrahydrofuran, acetonitrile, N-methylformamide, N,N-dimethylformamide, nitrobenzene, and derivatives thereof. One of these solvents may be used alone, or two or more may be used in combination. For example, both a protic solvent and an aprotic solvent may be used.

[0035] The solute, which is an electrolyte, can be an organic acid, an inorganic acid, a composite compound of an organic acid and an inorganic acid, or a derivative or salt thereof. Of these, one kind may be used alone, or two or more kinds may be used in combination. For example, an organic acid and an inorganic acid may be used together.

[0036] Examples of organic acids and their derivatives include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, and caprylic acid, as well as derivatives thereof. Examples of dicarboxylic acids include 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, as well as derivatives thereof. Examples of hydroxycarboxylic acids include citric acid and salicylic acid, as well as derivatives thereof. Examples of inorganic acids and their derivatives include boric acid, sulfamic acid, and derivatives thereof. Furthermore, examples of composite compounds of organic acids and inorganic acids and derivatives thereof include boron complexes of dicarboxylic acids or hydroxycarboxylic acids, and examples thereof include borodisalic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodimaleic acid, borodiphthalic acid, borodiglycolic acid, borodicitric acid, borodisalicylic acid, and derivatives thereof.

[0037] Furthermore, examples of salts of organic acids, inorganic acids, composite compounds of organic acids and inorganic acids, and derivatives thereof include ammonium salts, alkylammonium salts, amine salts, amidine salts, sodium salts, potassium salts, etc. Examples of amine salts include salts of dimethylamine, diethylamine, trimethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, methanolamine, ethanolamine, dimethanolamine, diethanolamine, trimethanolamine, triethanolamine, pyrrolidine, piperidine, piperazine, morpholine, methylmorpholine, ethylmorpholine, oxazolidine, thiomorpholine, thiazolidine, etc.

[0038] In the examples described below, a mixture of two types of solute, ammonium adipate and ammonium formate, is used as the electrolyte.

[0039] Furthermore, the electrolyte solution 3 according to this embodiment contains a phosphate ion source. The phosphate ion source is a general term for compounds that generate phosphate ions in the electrolyte solution 3. The phosphate ions (PO4 3- ) is the water (OH) in an aqueous solvent. - ) and aluminum ions (Al 3+ ) and phosphate ions (PO4 3- ) has an adsorption or adhesion property to the surfaces of the electrode foils 8 and 9 due to hydroxide ions (OH - ) and the electrode foils 8 and 9, and hydroxide ions (OH - ) and improves water resistance. 3- ) is the aluminum ion (Al 3+ ), and the resulting aluminum phosphate (AlPO4) forms a water-resistant film that protects the surfaces of the electrode foils 8 and 9. 3- ) and aluminum ions (Al 3+ ) competes with the hydration reaction, thereby suppressing the hydration reaction. In this way, the electrolytic capacitor 1 having the electrolyte solution 3 containing the phosphate ion source is able to suppress hydration deterioration of the electrode foils 8, 9, thereby suppressing leakage current. Furthermore, the electrolytic capacitor 1 is able to suppress the generation of hydrogen gas due to the hydration reaction and the electrolysis of water, thereby suppressing an increase in the internal pressure of the electrolytic capacitor 1 and extending the life of the electrolytic capacitor 1.

[0040] On the other hand, in the conventional composition of electrolyte solution 3, when the amount of phosphate ions is relatively small, the hydration deterioration of electrode foils 8 and 9 is not sufficiently suppressed, and the suppression effect is difficult to sustain. Furthermore, if the amount of phosphate ions is increased, the phosphate ions themselves cause a side reaction that accelerates the deterioration of electrode foils 8 and 9, thereby increasing leakage current and shortening the life of electrolytic capacitor 1. Therefore, it was not possible to increase the amount of phosphate ions in electrolyte solution 3.

[0041] In contrast, the electrolyte solution 3 according to this embodiment contains a phosphonic acid chelating agent in addition to a phosphate ion source. The phosphonic acid chelating agent is adsorbed onto the surface of the electrode foils 8 and 9, acting as a protective film, protecting the electrode foils 8 and 9 from the effects of excess phosphate ions. Therefore, even if the electrode foils 8 and 9 contain a relatively large amount of phosphate ions, the electrode foils 8 and 9 can fully exhibit the expected effect of suppressing hydration degradation without suffering from side reactions. In addition, the protective film formed by the phosphonic acid chelating agent prevents Al 3+ By appropriately slowing the excessive reaction between the phosphate ions and the electrolyte, the loss of phosphate ions is suppressed. Therefore, the effect of suppressing hydration degradation of the electrode foils 8, 9, which is expected from having a relatively large amount of phosphate ions, can be exerted for a long period of time. As a result, the electrolytic capacitor 1 according to this embodiment contains a relatively large amount of water and a relatively large amount of a phosphate ion source in the electrolyte solution 3, and the water reduces the resistance of the electrolyte solution 3, thereby achieving a low ESR and low impedance of the electrolytic capacitor 1, while the phosphate ion source sufficiently suppresses leakage current and extends the life of the electrolytic capacitor 1.

[0042] Specifically, the electrolyte solution 3 according to this embodiment contains a relatively large amount of phosphate ion source, such as 120.0 to 500.0 mmol / kg, 120.0 to 400.0 mmol / kg, 120.0 to 300.0 mmol / kg, 120.0 to 200.0 mmol / kg, 120.0 to 170.0 mmol / kg, 120.0 to 160.0 mmol / kg, or 125.0 to 155.0 mmol / kg, while still being able to suppress leakage current and achieve a long life. When the phosphate ion source is phosphoric acid (H3PO4), for example, this content (120.0 to 500.0 mmol / kg) corresponds to a blending amount of about 1.2 to 5.0 mass% in electrolyte solution 3, which is a higher concentration than the standard blending amount (appropriate blending amount) of about 1.0 mass% to about 100.0 mmol / kg to 105.0 mmol / kg of phosphoric acid in the composition of electrolyte solution 3 without the addition of a phosphonic acid chelating agent. However, from another perspective, the phosphonic acid chelating agent allows the blended phosphate ions to be utilized more efficiently, so that the amount of the phosphate ion source does not necessarily need to be extremely large (e.g., 500.0 mmol / kg), but can be made moderately large (e.g., 120.0 mmol / kg), thereby sufficiently suppressing leakage current and sufficiently achieving a long life.

[0043] The phosphate ion source may be phosphoric acid (orthophosphoric acid), phosphorous acid, hypophosphorous acid, salts of each of these three acids, esters of each of the three acids and salts of the esters, and condensates of each of the three acids and salts of the condensates. One of these may be used alone, or two or more may be used in combination.

[0044] Examples of salts of phosphoric acid, phosphorous acid, and hypophosphorous acid include ammonium salts, aluminum salts, sodium salts, calcium salts, and potassium salts. Examples of esters of phosphoric acid, phosphorous acid, and hypophosphorous acid include alkyl phosphate esters such as ethyl phosphate, diethyl phosphate, butyl phosphate, and dibutyl phosphate. Examples of salts of these esters include ammonium salts, aluminum salts, sodium salts, potassium salts, and calcium salts.

[0045] Condensates of phosphoric acid, phosphorous acid, and hypophosphorous acid include, for example, condensed phosphoric acid, which is a condensate of phosphoric acid. Examples of condensed phosphoric acids include linear condensed phosphoric acids such as pyrophosphoric acid, tripolyphosphoric acid, and tetrapolyphosphoric acid, cyclic condensed phosphoric acids such as metaphosphoric acid and hexametaphosphoric acid, and compounds in which such linear condensed phosphoric acids are combined with cyclic condensed phosphoric acids. Examples of salts of condensates of phosphoric acid, phosphorous acid, and hypophosphorous acid include ammonium salts, aluminum salts, sodium salts, potassium salts, and calcium salts.

[0046] Phosphoric acid and phosphoric acid compounds decompose in the electrolyte solution 3 to generate phosphate ions. Phosphorous acid and phosphorous acid compounds decompose in the electrolyte solution 3 to generate phosphite ions, which are then oxidized to generate phosphate ions. Hypophosphorous acid and hypophosphite compounds decompose in the electrolyte solution 3 to generate hypophosphorous acid, which is then oxidized to generate phosphate ions. Condensates are relatively stable in the electrolyte solution 3 at room temperature in the neutral range, but can gradually decompose depending on temperature or pH conditions or over time to generate phosphate ions, phosphite ions, hypophosphite ions, and the like. Therefore, phosphoric acid, phosphate salts, phosphate esters, and salts of phosphate esters, which can directly generate phosphate ions, are suitable as phosphate ion sources, and phosphoric acid and phosphate salts are even more suitable.

[0047] The phosphonic acid chelating agent is a compound having phosphonic acid (H3PO3), i.e., a phosphonic acid group (-P(=O)(OH)2), and chelating ability (the ability to form a complex with a metal ion). Examples of the phosphonic acid chelating agent include 1-hydroxyethylidene-1,1-diphosphonic acid (abbreviated as HEDP), nitrilotris(methylenephosphonic acid) (abbreviated as NTMP), 2-phosphonobutane-1,2,4-tricarboxylic acid (abbreviated as PBTC), and ethylenediaminetetra(methylenephosphonic acid) (abbreviated as EDTMP). One of these may be used alone, or two or more may be used in combination. The phosphonic acid chelating agent may be selected appropriately depending on the specifications of the electrolytic capacitor 1 (e.g., heat resistance temperature, etc.). Taking into account the tests (examples) described below, it can be seen that, overall, of the four phosphonic acid chelating agents listed above, EDTMP, HEDP, and NTMP are more preferable, and HEDP and NTMP are even more preferable.

[0048] Phosphonic acid chelating agents are distinguished from chelating agents that do not have phosphonic acid groups, because the phosphonic acid groups in the chelating agent are thought to be effective in adsorbing to the surfaces of the electrode foils 8 and 9 and forming protective films. In fact, according to the examples described below, the inclusion of a phosphonic acid chelating agent in electrolyte 3 resulted in particularly significant suppression of leakage current and particularly significant longevity of electrolytic capacitor 1 under high-temperature conditions. The content of the phosphonic acid chelating agent in electrolyte 3 can be set within a range of 0.1 to 5.0 mass%, 0.1 to 4.0 mass%, 0.1 to 3.5 mass%, 0.1 to 3.0 mass%, 0.1 to 2.5 mass%, 0.1 to 2.0 mass%, or 0.1 to 1.6 mass%, for example.

[0049] Furthermore, the electrolytic solution 3 may contain a known functional substance that can be blended into the electrolytic solution 3 of the electrolytic capacitor 1. The functional substance here refers to a substance that has some useful function in the electrolytic capacitor 1, such as the function of repairing the oxide film 8a, the function of resisting high temperatures, the function of resisting low temperatures, or the function of absorbing hydrogen gas. Some functional substances can function as electrolytes (solutes), but when such substances are blended as functional substances, they are blended primarily for the purpose of achieving the effect of a useful function other than their function as an electrolyte (solute).

[0050] [Manufacturing method of electrolytic capacitors] Next, this specification will describe a method for manufacturing the electrolytic capacitor 1 according to this embodiment. Fig. 3 is a flowchart showing an example of the method for manufacturing the electrolytic capacitor 1 according to this embodiment. Fig. 4 is an explanatory view (schematic perspective view) illustrating an example of the capacitor element formation step S01 in the method shown in Fig. 3.

[0051] As shown in FIG. 3 , the electrolytic capacitor 1 according to this embodiment is manufactured by, for example, performing a capacitor element formation step S01, an electrolyte introduction step S02, a sealing step S03, and an aging step S04. Among these steps, the electrolyte introduction step S02, which introduces an electrolyte 3 of a specific composition, includes a novel and advantageous feature common to all electrolytic capacitors according to this embodiment. Meanwhile, steps S01, S03, and S04 include operations that are unnecessary or different for types other than this embodiment (e.g., hybrid types, element configurations other than wound types, terminal configurations other than lead wire types, etc.). These operations may be omitted or modified as appropriate for types other than this embodiment.

[0052] In the capacitor element formation step S01, for example, the anode foil 8 is subjected to the aforementioned surface-expanding treatment, such as etching, and the aforementioned chemical conversion treatment, and then the anode terminal 4a is bonded to it. The cathode foil 9 is subjected to the aforementioned surface-expanding treatment, such as etching, and then the cathode terminal 4b is bonded to it. Then, as shown in FIG. 4 , a separator 10 is sandwiched between the anode foil 8 and the cathode foil 9 to separate them, and the anode foil 8, cathode foil 9, and separator 10 are wound together to form a cylindrical shape. A holding material (not shown), such as tape or film, is then attached to a predetermined portion of the outer periphery of the cylindrical shape to maintain the wound state. While not typically performed in the electrolytic capacitor 1 according to this embodiment, in the case of a hybrid type, a chemical conversion treatment is typically performed on the cylindrically formed capacitor element 2 to repair any missing oxide film 8a. This chemical conversion treatment is a re-chemical conversion treatment in which the anodization treatment already performed on the anode foil 8 is repeated to repair any missing oxide film 8a. This re-chemical conversion treatment is an optional treatment, and for example, it is not prohibited to perform the re-chemical conversion treatment on the electrolytic capacitor 1 of the type of this embodiment, and conversely, it is not prohibited to not perform the re-chemical conversion treatment on the hybrid type.

[0053] Next, in the electrolyte solution introducing step S02, an electrolyte solution 3 having a specific composition is introduced into the capacitor element 2. The composition of the electrolyte solution 3 is as already described for the electrolyte solution 3 according to this embodiment. That is, the solvent is an aqueous solvent containing at least water. The water content is not limited, but may be 40% by mass or more of water in the electrolyte solution 3, and may further be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more. The aqueous solvent may further contain components other than water (e.g., organic solvents), or may be composed solely of water. The solvent components other than water and the solute components may be the same as those described above.

[0054] In addition to the solvent and the solute, a phosphate ion source and a phosphonic acid chelating agent are blended into the electrolytic solution 3. The blending amount of the phosphate ion source is adjusted to a concentration in the electrolytic solution 3 of 120.0 to 500.0 mmol / kg, 120.0 to 400.0 mmol / kg, 120.0 to 300.0 mmol / kg, 120.0 to 200.0 mmol / kg, 120.0 to 170.0 mmol / kg, 120.0 to 160.0 mmol / kg, 125.0 to 155.0 mmol / kg, or the like. Furthermore, a phosphonic acid-based chelating agent is blended into the electrolytic solution 3 to a concentration of 0.1 to 5.0 mass%, 0.1 to 4.0 mass%, 0.1 to 3.5 mass%, 0.1 to 3.0 mass%, 0.1 to 2.5 mass%, 0.1 to 2.0 mass%, 0.1 to 1.6 mass%, or the like. Furthermore, the electrolytic solution 3 may be blended with a known functional substance that can be blended into the electrolytic solution 3 of the electrolytic capacitor 1.

[0055] As an example of introducing the electrolytic solution 3, the capacitor element 2 is immersed in a tank of prepared electrolytic solution 3. After a predetermined time has elapsed, the capacitor element 2 is removed from the tank of electrolytic solution 3. As described above, a known functional substance may be added during the preparation of the electrolytic solution 3. Alternatively, the functional substance may be introduced into the capacitor element 2 by immersing the capacitor element 2 in a tank of a liquid containing the functional substance before or after introducing the electrolytic solution 3 into the capacitor element 2. The introduction of the electrolytic solution 3 and the functional substance may be carried out under controlled pressure as necessary.

[0056] Next, the procedure for the sealing step S03 will be described with reference to FIG. 1. As an example, the capacitor element 2 is housed in a cylindrical case 6 with a bottom. The lead terminals 4 (anode terminal 4a and cathode terminal 4b) joined to the capacitor element 2 are fitted into through holes in the sealing material 5, and the opening of the case 6 is closed with the sealing material 5. As a result, the lead terminals 4 are extended to the outside of the electrolytic capacitor 1. Next, the opening edge 6a of the case 6 is crimped to seal the inside of the case 6. Note that an explosion-proof valve 7 may be provided in the case 6 and / or the sealing material 5. In this way, the electrolytic capacitor 1 shown in FIG. 1 is manufactured. Furthermore, the case 6 may be packaged in an exterior material (not shown). This packaging may be performed before or after the aging step S04 described below.

[0057] Finally, in the aging step S04, the manufactured electrolytic capacitor 1 is subjected to an aging treatment in which a predetermined voltage is applied for a predetermined time under high-temperature conditions. This activates the oxide film 8a repair function of a predetermined component in the electrolyte 3, repairing areas where the oxide film 8a peeled off during the manufacturing process or relatively thin areas of the oxide film 8a, thereby suppressing leakage current and stabilizing performance. The aging treatment also has a debugging effect, such as eliminating unexpected initial defects. [Example]

[0058] [Test 1] Aluminum electrolytic capacitors with a rated voltage of 16 V were manufactured using a conventional method in accordance with the present embodiment. Etched aluminum foil was used for the anode and cathode foils, and an oxide film was formed on the anode foil by chemical conversion treatment. Capacitor elements were assembled, and then an electrolyte solution with the composition shown in Table 1 was introduced into the capacitor elements. The functional materials in Table 1 contained multiple substances, and the composition ratios were the same for each example (hereinafter, the same applies to all functional materials tested). The electrolytic capacitors were assembled and then subjected to the specified aging treatment. Each manufactured electrolytic capacitor was exposed to a temperature environment of 115°C with no applied voltage, and the leakage current was measured after 1 minute of application of 16 V at specified intervals. Five capacitors were tested for each example. The results are shown in Figures 5A and 5B.

[0059] [Table 1]

[0060] The following commercially available products were used as phosphoric acid and phosphonic acid chelating agents (the same applies to all tests below). Phosphoric acid (Rasa Industries) HEDP: 1-hydroxyethylidene-1,1-diphosphonic acid (manufactured by Chelest Corporation, Chelest PH-210; "Chelest" is a registered trademark; the same applies hereinafter) NTMP: Nitrilotris(methylenephosphonic acid) (Chelest PH-320, manufactured by Chelest Corporation) PBTC: 2-phosphonobutane-1,2,4-tricarboxylic acid (Chelest PH-430, manufactured by Chelest) EDTMP: Ethylenediaminetetra(methylenephosphonic acid) (Chelest PH-540, manufactured by Chelest Corporation)

[0061] FIG. 5A is a graph showing the average values ​​of each example and the error ranges representing the maximum and minimum values. However, there are some areas where the error range is too small to be seen. FIG. 5B is a graph in which the vertical axis range of the graph in FIG. 5A has been reduced to make the results of each example easier to see. However, for ease of viewing, the error ranges have been omitted. Note that Comparative Example 2 is not shown in FIG. 5B.

[0062] As shown in FIGS. 5A and 5B, the leakage current was significantly higher in Comparative Example 1 (130.7 mmol / kg), which had a higher amount of phosphoric acid than Reference Example 1, which had a conventional standard amount of phosphoric acid in the electrolyte (104.9 mmol / kg). Furthermore, the leakage current was even more significantly higher in Comparative Example 2 (156.4 mmol / kg), which had an even higher amount of phosphoric acid than Comparative Example 1. In contrast, Examples 1 to 4, which used approximately the same amount of phosphoric acid as Comparative Example 1 (128.4 to 129.6 mmol / kg) in combination with various phosphonic acid chelating agents, showed lower leakage current than Reference Example 1. Furthermore, Examples 5 to 8, which used approximately the same amount of phosphoric acid as Comparative Example 2 (153.6 to 155.0 mmol / kg) in combination with various phosphonic acid chelating agents, also showed lower leakage current than Reference Example 1.

[0063] Specifically, in Reference Example 1, the increase in leakage current began to become noticeable approximately 3,000 hours after the start of the test, reaching a maximum value of 115.98 μA after 9,469 hours. In Comparative Example 1, the increase in leakage current began to increase sharply approximately 500 hours after the start of the test, reaching a maximum value of 369.56 μA after 4,060 hours. In Comparative Example 2, the increase in leakage current began to increase sharply approximately 500 hours after the start of the test, exceeding 500 μA and dropping out of the range before 1,000 hours had elapsed.

[0064] In contrast, the leakage current in Examples 1 to 8 was 16.15 μA or less throughout the entire test period (Example 6: after 508 hours had elapsed), which was significantly lower than those in Comparative Examples 1 and 2 and Reference Example 1. Furthermore, the leakage current in Examples 1 to 5, 7, and 8 was 12.62 μA or less throughout the entire test period (Example 8: after 1084 hours had elapsed).

[0065] Furthermore, among all Examples 1 to 8, Examples 1 to 4, which contained relatively less phosphoric acid, tended to have lower leakage current than Examples 5 to 8, which contained relatively more phosphoric acid. It is believed that the phosphonic acid chelating agent enabled more efficient utilization of phosphate ions, allowing for a moderate increase in the phosphate ion source to adequately suppress leakage current. Among the phosphonic acid chelating agents, in Examples 5 to 8, which contained relatively more phosphoric acid, HEDP (Example 5) and PBTC (Example 7) tended to have lower leakage current than NTMP (Example 6) and EDTMP (Example 8), which were favorable. Furthermore, regardless of the amount of phosphoric acid, PBTC (Examples 3 and 7) particularly tended to have lower leakage current, which was favorable. Considering the test conditions, for electrolytic capacitors expected to be used at temperatures up to approximately 115°C (e.g., electrolytic capacitors with a heat-resistant temperature set to 110 to 120°C), NTMP and EDTMP are preferred among the phosphonic acid chelating agents, HEDP is more preferred, and PBTC is even more preferred.

[0066] [Test 2] Aluminum electrolytic capacitors with a rated voltage of 16 V were manufactured using a conventional method in accordance with the present embodiment. Etched aluminum foil was used for the anode and cathode foils, and an oxide film was formed on the anode foil by chemical conversion treatment. A capacitor element was assembled, and then an electrolyte solution with the composition shown in Table 2 was introduced into the capacitor element. The electrolytic capacitor was assembled and then subjected to a predetermined aging treatment. The electrolytic capacitors of each example manufactured were exposed to the electrical conditions and temperature environment shown in Table 3, and the presence or absence of failure (open explosion-proof valve or inoperable state due to inability to pass current) was investigated every 500 hours. Five capacitors were tested for each example. The results are shown in Table 3.

[0067] [Table 2]

[0068] [Table 3]

[0069] As shown in Table 3, overall, the lifespan was shorter in Comparative Example 3 (130.7 mmol / kg), which had a higher amount of phosphoric acid than Reference Example 2, which had a conventional standard amount of phosphoric acid in the electrolyte (104.9 mmol / kg). Furthermore, in Comparative Example 4 (156.4 mmol / kg), which had an even higher amount of phosphoric acid than Comparative Example 3, the lifespan was either shorter than Comparative Example 3 or comparable to that of Comparative Example 3. In contrast, Examples 9 to 12, which used approximately the same amount of phosphoric acid (128.4 to 129.6 mmol / kg) as Comparative Example 3 in combination with various phosphonic acid chelating agents, showed longer lifespans than Reference Example 2. Furthermore, Examples 13 to 16, which used approximately the same amount of phosphoric acid (153.6 to 155.0 mmol / kg) as Comparative Example 4 in combination with various phosphonic acid chelating agents, also showed longer lifespans than Reference Example 2.

[0070] Specifically, under the temperature condition of 115°C with no voltage applied, all five devices failed after 5500 hours in Comparative Example 4, all five devices failed after 6500 hours in Comparative Example 3, and all five devices failed after 9500 hours in Reference Example 2. In contrast, in Examples 9 to 16, none of the five devices failed even after 9500 hours, and the lifespan was longer than that of Comparative Examples 3 and 4 and Reference Example 2.

[0071] Under the temperature condition of 115°C with an applied rated voltage of 16V, all five devices failed after 5500 hours in Comparative Example 4, all five devices failed after 6500 hours in Comparative Example 3, and all five devices failed after 9500 hours in Reference Example 2. In contrast, in Examples 9 to 16, none of the five devices failed even after 9500 hours, and the lifespan was longer than in Comparative Examples 3 and 4 and Reference Example 2.

[0072] Under the temperature condition of 125°C with no applied voltage, all five devices failed after 3000 hours in Comparative Examples 4 and 3, and all five devices failed after 3500 hours in Reference Example 2. In contrast, all five devices failed after 5000 hours in Examples 15 and 16, all five devices failed after 7000 hours in Examples 11 and 14, and some devices failed after 8000 hours in Examples 9, 10, 12, and 13. Although there were differences between Examples, all Examples 9 to 16 had a longer lifespan than Comparative Examples 3 and 4 and Reference Example 2.

[0073] At 115°C, there was no difference between the Examples. However, at 125°C, Examples 9 to 12, which contained relatively less phosphoric acid, tended to have a longer lifespan than Examples 13 to 16, which contained relatively more phosphoric acid. It is believed that the phosphonic acid chelating agent enabled more efficient use of phosphate ions, allowing for a moderate increase in the phosphate ion source and sufficient suppression of leakage current. As described above, at 125°C, Comparative Examples 3 and 4 and Reference Example 2 failed very quickly, whereas all Examples 9 to 16 maintained a certain lifespan. In particular, Examples 9 to 14 had a lifespan more than twice that of Comparative Examples 3 and 4 and Reference Example 2. Thus, the combined use of phosphoric acid and a phosphonic acid chelating agent provided a particularly significant effect, achieving a very stable and long lifespan, especially under relatively harsh high-temperature conditions.

[0074] Among the phosphonic acid chelating agents, HEDP (Example 13) and NTMP (Example 14) tended to have a longer life than PBTC (Example 15) and EDTMP (Example 16) in Examples 13-16, which contained relatively large amounts of phosphoric acid, at 125°C. Considering the test conditions, for electrolytic capacitors expected to be used at temperatures up to about 125°C (for example, electrolytic capacitors with a heat-resistant temperature set to 120-130°C), among the phosphonic acid chelating agents, PBTC and EDTMP are preferred, and HEDP and NTMP are more preferred.

[0075] [Test 3] Furthermore, to investigate the blending amount (content) of the phosphate ion source, electrolytes of each example with the compositions shown in Table 4 were prepared. An aluminum electrode made of 2 cm x 5 cm plain aluminum foil and a platinum electrode were connected to an ammeter (Yokogawa Measurement Corporation, Digital Multimeter TY710). Both electrodes were placed in 70 g of electrolyte at room temperature in a glass beaker to form a test apparatus. The current value was measured 5 minutes after placing the electrodes in the electrolyte using the test apparatus. Table 4 shows the electrolyte composition and the measurement results of the current value. The measurement results are also shown graphically in Figure 6.

[0076] [Table 4]

[0077] The electrode reaction in this test device is as follows: Aluminum electrode reaction Al ⇒ Al 3+ + 3e - (Al + 3OH - ⇒ Al(OH)3+ 3e - ) Platinum electrode reaction 3H2O + 3e - ⇒ 3OH - + 3 / 2H2

[0078] That is, the magnitude of the measured current value indicates the progress of hydration deterioration of the aluminum foil. At the same time, in each example, the lower the current value, the better the hydration deterioration of the foil is suppressed by the phosphoric acid in the electrolyte.

[0079] As shown in Table 4 and FIG. 6 , compared to Comparative Example 5, which had an electrolyte composition that did not contain a phosphonic acid chelating agent together with phosphoric acid, Examples 17-20, which contained various phosphonic acid chelating agents together with phosphoric acid, exhibited low current values ​​and suppressed foil hydration degradation at any phosphoric acid content. More specifically, at a conventional standard amount of phosphoric acid in an electrolyte (approximately 100 mmol / kg), the difference in current value between Examples 17-20 and Comparative Example 5 was relatively small. However, when the amount of phosphoric acid was doubled (approximately 200 mmol / kg), tripled (approximately 300 mmol / kg), quadrupled (approximately 400 mmol / kg), or five times (approximately 500 mmol / kg), Comparative Example 5 exhibited a relatively steep increase in current value, whereas Examples 17-20 exhibited a relatively slow increase in current value, and Examples 17, 18, and 20 exhibited a particularly slow increase in current value. As a result, the difference in current value between Examples 17-20 and Comparative Example 5 became relatively large. Therefore, by using a phosphonic acid chelating agent in combination with phosphoric acid, an extremely large amount of phosphoric acid (phosphate ion source), up to about five times the standard amount, can be incorporated into the electrolyte, which can sufficiently suppress the deterioration of the electrode foil. This in turn can reduce the leakage current and extend the life of the electrolytic capacitor, as confirmed in Tests 1 and 2.

[0080] From the test results so far, in the present invention, by using a phosphonic acid-based chelating agent in combination, the blending amount (content) of the phosphate ion source in the electrolyte can be set within the ranges of 120.0 to 500.0 mmol / kg, 120.0 to 400.0 mmol / kg, 120.0 to 300.0 mmol / kg, 120.0 to 200.0 mmol / kg, 120.0 to 170.0 mmol / kg, 120.0 to 160.0 mmol / kg, 125.0 to 155.0 mmol / kg, 130.0 to 155.0 mmol / kg, 130.0 to 150.0 mmol / kg, etc.

[0081] Among the phosphonic acid chelating agents, HEDP (Example 17), NTMP (Example 18), and EDTMP (Example 20) tended to exhibit lower current values ​​compared to PBTC (Example 19). Even when the amount of phosphoric acid in the electrolyte was extremely high at approximately 500 mmol / kg, the current was suppressed to a low value of 54.09 μA for PBTC (Example 19), an even lower value of 20.65 μA for HEDP (Example 17), an even lower value of 14.87 μA for NTMP (Example 18), and an even lower value of 15.53 μA for EDTMP (Example 20). Considering the test conditions, for electrolytic capacitors and the like expected to be used at room temperature, among the phosphonic acid chelating agents, PBTC is preferred, HEDP is more preferred, and NTMP and EDTMP are even more preferred.

[0082] [Test 4] Furthermore, in order to investigate the blending amount (content) of the phosphonic acid chelating agent, electrolyte solutions of each example with the compositions shown in Table 5 were prepared. Using a test device with the same configuration as in Test 3, the current value was measured 5 minutes after placing the electrodes in the electrolyte solution. Table 5 shows the electrolyte solution composition and the measurement results of the current value. The measurement results are also shown in a graph in Figure 7.

[0083] [Table 5]

[0084] 7, compared with Comparative Example 6, which had an electrolyte composition that did not contain a phosphonic acid chelating agent together with phosphoric acid, Examples 21 to 24, which contained various phosphonic acid chelating agents together with phosphoric acid, had low current values ​​and suppressed foil hydration degradation at any phosphonic acid chelating agent content. That is, the current value was already significantly reduced to less than 13.5 μA when 0.2% by mass of phosphonic acid chelating agent was added (Examples 21-1, 22-1, 23-1, and 24-1), compared with 7.45 μA in Comparative Example 2, and was further reduced to less than 9.0 μA when 0.6% by mass or more of phosphonic acid chelating agent was added (Examples 21-2 to 21-4, 22-2 to 22-4, 23-2 to 23-4, and 24-2 to 24-4). Thus, a significant effect was already achieved compared to the comparative example when the phosphonic acid chelating agent was added at 0.2 mass%, and the significant effect was maintained stably up to a phosphonic acid chelating agent addition of 1.5 mass%. Therefore, by adding at least 0.1 to 0.2 mass% of a phosphonic acid chelating agent together with phosphoric acid, deterioration of the electrode foil can be sufficiently suppressed, and ultimately, the leakage current of the electrolytic capacitor confirmed in Tests 1 and 2 can be reduced and the lifespan extended.

[0085] From the test results so far, in the present invention, the blending amount (content) of the phosphonic acid chelating agent in the electrolyte can be set to 0.1 to 0.2 mass% or more. For example, when the upper limit is set by replacing a part of the functional substance of this example with a phosphonic acid chelating agent, the blending amount (content) can be set in the range of 0.1 to 5.0 mass%, 0.1 to 4.0 mass%, 0.1 to 3.5 mass%, 0.1 to 3.0 mass%, 0.1 to 2.5 mass%, 0.1 to 2.0 mass%, 0.1 to 1.6 mass%, 0.2 to 5.0 mass%, 0.2 to 4.0 mass%, 0.2 to 3.5 mass%, 0.2 to 3.0 mass%, 0.2 to 2.5 mass%, 0.2 to 2.0 mass%, 0.2 to 1.6 mass%, 0.2 to 1.5 mass%, etc. [Explanation of symbols]

[0086] 1 electrolytic capacitor 2 Capacitor elements 3 Electrolyte 4 Lead terminals 4a Anode terminal 4b Cathode terminal 5. Encapsulating material 6 cases 6a Opening edge 7 Explosion-proof valve 8 Anode foil 8a Oxide film 9 Cathode foil 10 Separator S01 Capacitor element formation process S02 Electrolyte introduction process S03 Sealing process S04 Aging process

Claims

1. A low-voltage electrolytic capacitor, a capacitor element including an anode foil on which a dielectric layer is formed, a cathode foil, and a separator disposed between the anode foil and the cathode foil; and an electrolyte solution impregnated in the capacitor element, The electrolyte solution contains an aqueous solvent containing 55 wt % or more of water, a phosphate ion source, and a phosphonic acid chelating agent which is a compound having a phosphonic acid group and chelating ability (excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), ethylenediaminetetrakis(methylenephosphonic acid) (EDTPO), ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure as these). An electrolytic capacitor characterized by:

2. The electrolytic solution contains an organic acid ammonium salt.

2. The electrolytic capacitor according to claim 1,

3. The organic acid ammonium salt is mainly composed of ammonium adipate to which ammonium formate is added.

3. The electrolytic capacitor according to claim 2,

4. The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of each of these three acids, esters of each of the three acids and salts of the esters, and condensates of each of the three acids and salts of the condensates.

2. The electrolytic capacitor according to claim 1,

5. The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphate salts, phosphate esters, and salts of phosphate esters.

5. The electrolytic capacitor according to claim 4,

6. The phosphonic acid chelating agent is one or more substances selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylenephosphonic acid), and 2-phosphonobutane-1,2,4-tricarboxylic acid.

2. The electrolytic capacitor according to claim 1,

7. The phosphate ion source is contained in the electrolyte solution at a content of 120.0 to 500.0 mmol / kg (excluding 0.75 wt % or less in the electrolyte solution).

2. The electrolytic capacitor according to claim 1,

8. A low-voltage electrolytic capacitor, The electrolyte solution is blended with an aqueous solvent containing at least 55 wt % or more of water, a phosphate ion source, and a phosphonic acid chelating agent which is a compound having a phosphonic acid group and chelating ability (excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), ethylenediaminetetrakis(methylenephosphonic acid) (EDTPO), ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure as these). A method for manufacturing an electrolytic capacitor, comprising:

9. The electrolyte solution may contain an organic acid ammonium salt.

9. The method for manufacturing an electrolytic capacitor according to claim 8,

10. The organic acid ammonium salt is mainly composed of ammonium adipate to which ammonium formate is added.

10. The method for manufacturing an electrolytic capacitor according to claim 9,

11. The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of each of these three acids, esters of each of the three acids and salts of the esters, and condensates of each of the three acids and salts of the condensates.

9. The method for manufacturing an electrolytic capacitor according to claim 8,

12. The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphate salts, phosphate esters, and salts of phosphate esters. The method for manufacturing an electrolytic capacitor according to claim 11,

13. The phosphonic acid chelating agent is one or more substances selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylenephosphonic acid), and 2-phosphonobutane-1,2,4-tricarboxylic acid.

9. The method for manufacturing an electrolytic capacitor according to claim 8,

14. The phosphate ion source is blended in the electrolyte solution in an amount of 120.0 to 500.0 mmol / kg (excluding an amount of 0.75 wt % or less in the electrolyte solution).

9. The method for manufacturing an electrolytic capacitor according to claim 8,

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