Electrolytic capacitor and method for manufacturing electrolytic capacitor

Abstract

The subject of this invention is an electrolytic capacitor capable of suppressing leakage current and extending lifespan in an aqueous electrolyte containing a relatively large amount of phosphate ion source, and a method for manufacturing the same. As a solution, the electrolytic capacitor (1) of this invention comprises: a capacitor element (2) having an anode foil (8) with a dielectric layer formed thereon, a cathode foil (9), and a separator (10) disposed between the anode foil (8) and the cathode foil (9); an electrolyte (3) impregnated within the capacitor element (2), the electrolyte (3) comprising a solvent containing water, a phosphate ion source, and a phosphonic acid chelating agent (excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure), and the electrolyte (3) containing 40% by mass or more of the aforementioned water.

Description

Technical Field

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

[0002] An electrolytic capacitor is an energy storage device. Its basic structure involves introducing (impregnating) an electrolyte into a capacitor element, which has a separator between an anode foil and a cathode foil. The anode foil has an oxide coating that serves as a dielectric layer. Electrolytic capacitors come in two types: those that introduce a non-solid electrolyte into the capacitor element; and those that introduce a solid electrolyte, such as a conductive polymer, into the capacitor element. Furthermore, there is a so-called "hybrid type" of electrolytic capacitors where an electrolyte is introduced into the capacitor element along with a solid electrolyte, allowing for the utilization of the advantages of both solid and non-solid electrolytes.

[0003] The electrolyte in an electrolytic capacitor contains at least a solute as the electrolyte and a solvent to dissolve or disperse the solute. Furthermore, regarding the composition of the electrolyte in an electrolytic capacitor, sometimes the water content in the solvent is increased to achieve lower resistance, aiming for lower ESR and lower impedance. However, if the water content, which readily undergoes chemical reactions in the electrolyte, is increased, especially at high temperatures, the leaching of metallic elements from the electrode foil (e.g., Al) can lead to problems. 3+ ) and water (i.e., OH-) - A hydration reaction occurs, and the resulting hydroxides (e.g., Al(OH)3) precipitate on the electrode foil surface, degrading the foil and leading to increased leakage current. Additionally, the hydrogen gas produced by the hydration reaction and water electrolysis increases internal pressure, causing the explosion-proof valve to open within a relatively short time, thus shortening its lifespan.

[0004] Therefore, in the past, for electrolytes containing a water-based solvent with a specified amount of water, phosphoric acid was mixed in to suppress the hydration degradation of the electrode foil (Patent Document 1: Japanese Patent Application Publication No. 2004-186239).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2004-186239 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] While the inhibitory effect of phosphoric acid on hydration degradation of electrode foil is well-known, the limited amount of phosphoric acid in the electrolyte means that this inhibitory effect is only partially achieved. Specifically, the free phosphate ions in the electrolyte react with the dissolved metal elements (e.g., Al) in the electrode foil. 3+ The resulting inorganic phosphate (e.g., AlPO4) forms a water-resistant coating on the electrode foil surface, inhibiting hydration degradation. However, phosphoric acid (phosphate ions) gradually disappears from the electrolyte. Therefore, with a relatively small amount of phosphoric acid, it is insufficient to adequately inhibit hydration degradation of the electrode foil, and the inhibitory effect is difficult to maintain. Conversely, if a relatively large amount of phosphoric acid is added to improve the inhibition of hydration degradation, the acidic nature of phosphoric acid, coupled with its inherent ability to degrade the electrode foil, may actually exacerbate degradation, leading to increased leakage current and accelerated hydration, thus shortening the electrode foil's lifespan.

[0010] Solution for solving the problem

[0011] The present invention was made in view of the above circumstances, and its object is to provide an electrolytic capacitor and a method for manufacturing an electrolytic capacitor, wherein, in an electrolyte composition in which a predetermined amount of phosphate ion source is mixed in an aqueous electrolyte containing a predetermined amount of water, leakage current can be suppressed and a long lifespan can be achieved even though a relatively large amount of the phosphate ion source is contained.

[0012] The present invention addresses the aforementioned problems through the following solution as one embodiment.

[0013] The electrolytic capacitor of the present invention is characterized by comprising: a capacitor element having an anode foil and a cathode foil having a dielectric layer formed thereon, and a separator disposed between the anode foil and the cathode foil; and an electrolyte impregnated within the capacitor element, the electrolyte comprising a solvent containing water, a phosphate ion source, and a phosphonic acid chelating agent (excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), and ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure), wherein the electrolyte contains 40% by mass or more of the aforementioned water.

[0014] According to the present invention, the phosphonic acid chelating agent is adsorbed onto the surface of the electrode foil to act as a protective film, protecting the electrode foil from the effects of excessive phosphate ions. Furthermore, this protective film moderately slows down the reaction of Al... 3+The reaction between the metal elements of the electrode foil and phosphate ions proceeds excessively, suppressing the loss of phosphate ions. As a result, although the present invention contains a relatively large amount (e.g., 154.0–500.0 mmol / kg) of phosphate ion source in the electrolyte, it can suppress leakage current and achieve a long lifetime.

[0015] The characteristic is that the aforementioned phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of these three acids, esters of these three acids and salts of the esters, and condensates of these three acids and salts of the condensates. Furthermore, the aforementioned phosphate ion source is preferably one or more substances selected from the group consisting of phosphoric acid, phosphates, phosphate esters, and salts of phosphate esters.

[0016] The aforementioned phosphonic acid chelating agent may be one or more substances selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, nitrotris(methylenephosphonic acid) and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0017] The electrolyte contains 154.0 to 500.0 mmol / kg of the aforementioned phosphate ion source (excluding cases where the content is less than 0.75 wt% in the aforementioned electrolyte).

[0018] The method for manufacturing the electrolytic capacitor of the present invention is characterized in that a solvent containing water, a phosphate ion source, and a phosphonic acid chelating agent (excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), and ethylenediamine-N,N'-bis(methylenephosphonic acid), and substances having the same chemical structure as these) are mixed into the electrolyte, and at least 40% by mass of the aforementioned water is mixed into the electrolyte.

[0019] According to the present invention, the phosphonic acid chelating agent is adsorbed onto the surface of the electrode foil to act as a protective film, protecting the electrode foil from the effects of excessive phosphate ions. Furthermore, this protective film moderately slows down the reaction of Al... 3+ The reaction between the metal elements of the electrode foil and phosphate ions proceeds excessively, suppressing the loss of phosphate ions. As a result, although the present invention contains a relatively large amount (e.g., 154.0–500.0 mmol / kg) of phosphate ion source in the electrolyte, it can suppress leakage current and achieve a long lifetime.

[0020] The characteristic is that the aforementioned phosphate ion source is selected from one or more substances chosen from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of these three acids, esters of these three acids and salts of the esters, and condensates of these three acids and salts of the condensates. Furthermore, it is preferable that the aforementioned phosphate ion source is selected from one or more substances chosen from the group consisting of phosphoric acid, phosphates, phosphate esters, and salts of phosphate esters.

[0021] The aforementioned phosphonic acid chelating agent may be selected from one or more substances comprising 1-hydroxyethylidene-1,1-diphosphonic acid, nitrotris(methylenephosphonic acid) and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0022] The feature is that the aforementioned phosphate ion source is mixed in the aforementioned electrolyte at a concentration of 154.0 to 500.0 mmol / kg (excluding cases where the concentration in the aforementioned electrolyte is less than 0.75 wt%).

[0023] The effects of the invention

[0024] According to the present invention, in an electrolyte composition in which a specified amount of phosphate ion source is mixed in an aqueous electrolyte containing a specified amount of water, leakage current can be suppressed and long lifespan can be achieved even though a relatively large amount of the phosphate ion source is contained. Attached Figure Description

[0025] Figure 1 This is a schematic diagram (front sectional view) showing an example of an electrolytic capacitor according to this embodiment.

[0026] Figure 2 This is an explanatory diagram illustrating an example of a capacitor element in an electrolytic capacitor according to this embodiment.

[0027] Figure 3 This is a flowchart illustrating an example of a method for manufacturing an electrolytic capacitor according to this embodiment.

[0028] Figure 4 This is an explanation Figure 3 An explanatory diagram illustrating an example of the capacitor element forming process in the method shown.

[0029] Figure 5 A and Figure 5 B is a graph showing the results of Experiment 1.

[0030] Figure 6 This is a graph showing the results of Experiment 3.

[0031] Figure 7 This is a graph showing the results of Experiment 4. Detailed Implementation

[0032] This invention relates to an electrolytic capacitor with structural features in its electrolyte composition and a method for manufacturing the same. Hereinafter, as an example of an electrolytic capacitor (a type in which a non-solid electrolyte is introduced into the capacitor element) for carrying out the invention, an example will be provided. However, the electrolytic capacitor of the present invention is not limited to the type described herein, as the nature of the invention suggests. For example, it also includes so-called "hybrid type" electrolytic capacitors in which a solid electrolyte, such as a conductive polymer, is introduced into the capacitor element.

[0033] Hereinafter, this specification will describe in detail the methods for carrying out the present invention with reference to the accompanying drawings. Figure 1 This is a schematic diagram (front sectional view) showing an example of the electrolytic capacitor 1 of this embodiment. However, for ease of understanding, the cross-sectional structure of the capacitor element 2 is not shown. Figure 2 This is an explanatory diagram illustrating an example of the capacitor element 2 in the electrolytic capacitor 1 of this embodiment, schematically showing a basic configuration example of the capacitor element 2. Hereinafter, as one embodiment, this specification describes an electrolytic capacitor 1 having a wound capacitor element 2, but is not limited to this element form; for example, it could also be a stacked type, a coin type, etc. Furthermore, as one embodiment, this specification describes a leaded electrolytic capacitor 1 having lead terminals 4, but is not limited to this terminal form; for example, it could also be a threaded terminal type, a self-supporting substrate type, etc. Additionally, as one embodiment, this specification describes an aluminum electrolytic capacitor 1 having electrode foils 8 and 9 primarily made of aluminum or aluminum alloy, but is not limited to this foil form; for example, it could also be an electrode foil primarily made of a valve metal or valve metal alloy other than aluminum.

[0034] like Figure 1 As shown, in this embodiment, the electrolytic capacitor 1 houses a capacitor element 2 impregnated with electrolyte 3 within a bottomed cylindrical casing 6. The opening of the casing 6 is sealed with a sealing material 5. Lead terminals 4 (anode terminal 4a and cathode terminal 4b) that engage with the capacitor element 2 are fitted into through holes provided in the sealing material 5 and lead out to the outside of the electrolytic capacitor 1 through the through holes. The opening edge 6a of the casing 6 is tightly fitted into the sealing material 5, thereby sealing the inside of the casing 6. An explosion-proof valve 7, which serves as a pressure valve, is provided in the casing 6. When the internal pressure of the electrolytic capacitor 1 reaches a certain level, the valve opens to release the gas inside the electrolytic capacitor 1, thereby achieving explosion prevention. The number and position of the explosion-proof valve 7 are not limited; for example, it can be provided on the sealing material 5, or on both the casing 6 and the sealing material 5. Furthermore, the casing 6 is typically encased by an outer casing material (not shown).

[0035] Next, as Figure 2As shown, the capacitor element 2 of this embodiment includes an anode foil 8, a cathode foil 9, and a separator 10 disposed between the anode foil 8 and the cathode foil 9. An anode terminal 4a is bonded to the anode foil 8. A cathode terminal 4b is bonded to the cathode foil 9.

[0036] The electrode foils (anode foil 8 and cathode foil 9) are primarily made of aluminum or aluminum alloy. Here, "primary material" refers to other elements that are permitted to be present in trace amounts, for example, less than 1.0% by mass (e.g., less than 0.5%, 0.1%, 0.05%, or 0.01% by mass). On the other hand, other elements intentionally included in the aluminum alloy may 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. Other metals constituting the aluminum alloy are not limited to valve metals; they may also be metallic elements other than valve metals and other non-metallic elements. These other elements may be present in any amount within the range necessary for the electrode foils 8 and 9 to function as electrodes in the aluminum electrolytic capacitor 1. Even when the content (by mass%) of intentionally added substances is relatively small, there may still be cases where the content (by mass) of impurities exceeds the unintentional amount. It should be noted that, as foil forms other than those described in this embodiment that are applicable to the present invention, foil forms in which the aluminum is replaced with other valve metals can be listed.

[0037] Electrode foils 8 and 9 can also be formed from two layers: a core substrate and a covering material covering the substrate. In this case, at least the outer covering material can be made primarily of aluminum or an aluminum alloy. That is, the composition of the substrate and the composition of the covering material can be the same or different.

[0038] Electrode foils 8 and 9 have an expanded surface area structure. This expanded surface area structure is typically formed through etching. Alternatively, it can be formed by vapor deposition, sintering, or other processes using a base metal powder. In this case, for example, aluminum or aluminum alloy powder is deposited or sintered onto the core substrate, thereby forming the expanded surface area structure simultaneously with the electrode foils 8 and 9 themselves. The expanded surface area structure of the electrode foils 8 and 9 increases the specific surface area and thus increases the electrostatic capacitance.

[0039] An oxide coating 8a, serving as a dielectric layer, is formed on the surface of the expanded anode foil 8 through a chemical conversion treatment. Specifically, the chemical conversion treatment is an anodizing process in which the target metal (here, the anode foil 8) is used as the anode, and a voltage is applied between the metal and the chemical conversion solution to form the oxide coating 8a.

[0040] The chemical conversion process can be performed, for example, by immersing capacitor element 2 in a chemical conversion solution bath, with anode terminal 4a as the anode, and applying a predetermined voltage (e.g., 100V for 5 minutes) between the capacitor element 2 and the chemical conversion solution for a predetermined time. Then, capacitor element 2 is removed from the chemical conversion solution bath and dried. Examples of chemical conversion solutions include aqueous solutions of ammonium adipate, ammonium borate, ammonium phosphate, ammonium glutarate, ammonium azelaate, ammonium tartrate, ammonium sebate, ammonium pimecrolate, and ammonium octanoate.

[0041] On the other hand, the expanded cathode foil 9 is not further processed, and a natural oxide coating (not shown) is formed on its surface by oxygen in the air. However, this configuration is not limited to this; for example, valve metal or valve metal alloy powder such as titanium may be further deposited on the surface of the expanded cathode foil 9. This can increase the dielectric constant and thus the electrostatic capacitance. Alternatively, the surface of the expanded cathode foil 9 may be chemically converted in the same way as the anode foil 8 to form a non-polar electrolytic capacitor 1.

[0042] The separator 10 separating the anode foil 8 and the cathode foil 9 is made of paper or other natural cellulose fibers such as Manila hemp pulp, or of fabric, sheet, or film made of synthetic fibers such as nylon, or of blends or blends thereof. Among these, synthetic fibers have the advantage of allowing for the selection of materials with particularly excellent heat resistance. Examples of such synthetic fibers include nylon, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polyphenylene sulfide (PPS). It should be noted that... Figure 2 This diagram schematically illustrates a basic configuration example of capacitor element 2, showing one separator 10, but its number is not limited; for example, as shown... Figure 4 As shown, three pieces can also be set.

[0043] In addition, electrolyte 3 is impregnated inside capacitor element 2. For example... Figure 2 As schematically shown, the electrolyte 3 exists in the gap between the anode foil 8 and the cathode foil 9. Through contact with the dielectric layer (oxide coating 8a) formed on the anode foil 8 and the cathode foil 9, it essentially functions as the true cathode, replacing the cathode foil 9 as the counter electrode of the anode foil 8. However, as long as the electrolyte 3 can perform this function, it may not completely fill the space between the two electrode foils 8 and 9, and there may be areas between the two electrode foils 8 and 9 that are not filled with electrolyte 3. It should be noted that the separator 10 allows the components of the electrolyte 3 to freely pass through the anode foil 8 side and the cathode foil 9 side, but depending on the structure and material of the separator 10, the electrolyte 3 may also permeate within the separator 10.

[0044] The electrolyte 3 comprises a solute as an electrolyte and a solvent for dissolving or dispersing the solute. In this embodiment, the solvent is an aqueous solvent containing a predetermined amount of water. The water content is not limited; the electrolyte 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. This increased water content in the electrolyte 3 is achieved by containing a phosphate ion source and a phosphonic acid chelating agent. This aqueous solvent may further contain components other than water (e.g., organic solvents), or may consist solely of water. Such an aqueous solvent, through the action of water, can increase the solubility of the electrolyte and the mobility of ions, thereby reducing the resistivity of the electrolyte 3. Furthermore, by reducing the resistivity of the electrolyte 3, it is possible to achieve low ESR and low impedance in the electrolytic capacitor 1.

[0045] Examples of organic solvents that can be used as solvent components include protic solvents such as monohydric alcohols like methanol, ethanol, propanol, and butanol; dihydric alcohols like ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol; trihydric alcohols like glycerol; and their derivatives. Examples of aprotic solvents include lactones such as γ-butyrolactone; sulfolane, methylsulfolane, dimethylsulfolane, ethylene carbonate, propylene carbonate, pyrrolidine, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolinone, tetrahydrofuran, acetonitrile, N-methylformamide, N,N-dimethylformamide, nitrobenzene, and their derivatives. One solvent can be used alone, or two or more can be used in combination. For example, protic and aprotic solvents can be used simultaneously.

[0046] Furthermore, the solute used as the electrolyte can be an organic acid, an inorganic acid, a compound of organic and inorganic acids, or their derivatives, or their salts. One type can be used alone, or two or more can be used in combination. For example, organic acids and inorganic acids can be used simultaneously.

[0047] Examples of organic acids and their derivatives include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, octanoic acid, and their derivatives. 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, 1,10-decanedicarboxylic acid, and their derivatives. Examples of hydroxycarboxylic acids include citric acid, salicylic acid, and their derivatives. Examples of inorganic acids and their derivatives include boric acid, aminosulfonic acid, and their derivatives. In addition, as complex compounds of organic and inorganic acids and their derivatives, examples include boron complexes of dicarboxylic acids or hydroxycarboxylic acids, such as boron dioxalic acid, boron dimalonic acid, boron disuccinic acid, boron diadipic acid, boron dimaleic acid, boron diphenylcarboxylic acid, boron diethanolic acid, boron dicitric acid, boron disalicylic acid, etc., and their derivatives.

[0048] In addition, examples of salts of organic acids, inorganic acids, complex compounds of organic and inorganic acids, and their derivatives include ammonium salts, alkylammonium salts, amine salts, amidine salts, sodium salts, and potassium salts. Examples of amine salts include dimethylamine, diethylamine, trimethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, methanolamine, ethanolamine, diethanolamine, diethanolamine, triethanolamine, triethanolamine, pyrrolidine, piperidine, piperazine, morpholine, methylmorpholine, ethylmorpholine, oxazolidine, thiomorpholine, and thiazoline.

[0049] It should be noted that in the following embodiments, a mixture of ammonium adipate and ammonium formate was used as the solute for electrolyte.

[0050] Furthermore, the electrolyte 3 in this embodiment contains a phosphate ion source. A phosphate ion source is a general term for compounds that generate phosphate ions in the electrolyte 3. The phosphate ions (PO4) generated by the phosphate ion source... 3- ) Inhibit the formation of water (OH) in aqueous solvents - ) and aluminum ions (Al 3+ The hydration degradation of electrode foils 8 and 9 is caused by the hydration reaction product (Al(OH)3). Phosphate ions (PO4) 3- The adsorption or adhesion of ions to the surfaces of electrode foils 8 and 9 is significantly stronger than that of hydroxide ions (OH-). - ), suppressing the interaction between electrode foils 8 and 9 and hydroxide ions (OH-). - The water resistance is improved by contact with phosphate ions (PO4). 3- ) and aluminum ions (Al) dissolved from electrode foils 8 and 9 3+ The reaction produces aluminum phosphate (AlPO4), which forms a water-resistant coating that protects the surfaces of electrode foils 8 and 9. Furthermore, the phosphate ions (PO4)...3- ) and aluminum ions (Al 3+ The reaction of the electrolyte 3 with phosphate ions competes with the hydration reaction, thereby suppressing the hydration reaction. Thus, the electrolytic capacitor 1 with electrolyte 3 containing phosphate ions suppresses the hydration degradation of electrode foils 8 and 9, resulting in suppression of leakage current. Furthermore, the electrolytic capacitor 1 also suppresses the generation of hydrogen gas caused by the hydration reaction and the electrolysis of water, thereby suppressing the rise in internal pressure of the electrolytic capacitor 1 and extending its lifespan.

[0051] On the other hand, in the existing electrolyte 3 composition, when the amount of phosphate ions is relatively small, it is not enough to sufficiently suppress the hydration degradation of electrode foils 8 and 9, and the suppression effect is also difficult to sustain. If the content of phosphate ions is increased, the leakage current will increase and the life of electrolytic capacitor 1 will be shortened because the phosphate ions themselves will promote the side reaction of the degradation of electrode foils 8 and 9. Therefore, it is not possible to increase the content of phosphate ions in electrolyte 3.

[0052] In contrast, the electrolyte 3 of this embodiment contains both a phosphate ion source and a phosphonic acid chelating agent. The phosphonic acid chelating agent adsorbs onto the surfaces of the electrode foils 8 and 9, acting as a protective film to protect the electrode foils 8 and 9 from the effects of excessive phosphate ions. Therefore, even with a relatively large amount of phosphate ions, no adverse effects caused by side reactions occur, and the desired hydration degradation inhibition effect of the electrode foils 8 and 9 can be fully achieved. Furthermore, this protective film formed by the phosphonic acid chelating agent moderately slows down the degradation of Al... 3+ The reaction with phosphate ions proceeds excessively, thereby suppressing the loss of phosphate ions. Therefore, the desired hydration degradation suppression effect of electrode foils 8 and 9, achieved through a relatively large amount of phosphate ions, can be maintained for a long period. As a result, the electrolytic capacitor 1 of this embodiment, containing a relatively large amount of water and a relatively large amount of phosphate ion source in the electrolyte 3, achieves low resistance in the electrolyte 3 due to water, thereby achieving low ESR and low impedance in the electrolytic capacitor 1, while also sufficiently suppressing leakage current caused by the phosphate ion source and extending the lifespan of the electrolytic capacitor 1.

[0053] Specifically, for the electrolyte 3 of this embodiment, although the electrolyte 3 contains a relatively large amount of phosphate ion source in the following range, as an example, the range of all combinations of the upper and lower limits can be freely selected from the range of 120.0 mmol / kg to 500.0 mmol / kg, for example 120.0~500.0 mmol / kg, 120.0~400.0 mmol / kg, 120.0~300.0 mmol / kg, 120.0~210. 0mmol / kg, 120.0~205.0mmol / kg, 120.0~200.0mmol / kg, 120.0~170.0mmol / kg, 120.0~160.0mmol / kg, 12 0.0~155.0mmol / kg, 120.0~154.0mmol / kg, 125.0~155.0mmol / kg, 130.0~155.0mmol / kg, 130.0~150.0mmo l / kg, 150.0~500.0mmol / kg, 151.0~500.0mmol / kg, 152.0~500.0mmol / kg, 153.0~500.0mmol / kg, 154.0~ 500.0mmol / kg, 154.0~400.0mmol / kg, 154.0~300.0mmol / kg, 155.0~500.0mmol / kg, 160.0~500.0mmol / k While exhibiting values ​​of g, 170.0–500.0 mmol / kg, 180.0–500.0 mmol / kg, 190.0–500.0 mmol / kg, 200.0–500.0 mmol / kg, 205.0–500.0 mmol / kg, 210.0–500.0 mmol / kg, 205.0–400.0 mmol / kg, and 205.0–300.0 mmol / kg, these methods can suppress leakage current and achieve long lifespans. For this concentration (120.0–500.0 mmol / kg), for example, when the phosphate ion source is phosphoric acid (H3PO4), it corresponds to a mixture of approximately 1.2–5.0% by mass in electrolyte 3. This is a high concentration compared to the standard mixture (proper mixture) of phosphoric acid in electrolyte 3 without the addition of phosphonic acid chelating agents, which is approximately 1.0% by mass or approximately 100.0 mmol / kg–105.0 mmol / kg. Furthermore, for 205.0–500.0 mmol / kg, for example, when the phosphate ion source is phosphoric acid (H3PO4), it corresponds to a mixture of approximately 2.0–5.0% by mass (more precisely, a concentration exceeding 2.0% by mass but not exceeding 5.0% by mass) in electrolyte 3.However, according to other viewpoints, based on phosphonic acid chelating agents, the mixed phosphate ions can be utilized more efficiently. Therefore, it is not necessary to make the phosphate ion source extremely large (e.g., 500.0 mmol / kg) but moderately large (e.g., 120.0 mmol / kg) to adequately suppress leakage current and achieve sufficient long lifetime.

[0054] The phosphate ion source can be used for phosphoric acid (orthophosphoric acid), phosphorous acid, hypophosphoric acid, their respective salts, their respective esters and salts, as well as their respective condensates and salts. One type can be used alone, or two or more types can be used in combination.

[0055] Examples of salts of phosphoric acid, phosphorous acid, and hypophosphite include ammonium salts, aluminum salts, sodium salts, calcium salts, and potassium salts. Examples of esters of phosphoric acid, phosphorous acid, and hypophosphite 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.

[0056] Examples of condensates of phosphoric acid, phosphorous acid, and hypophosphite include condensed phosphoric acid, which is a condensate of phosphoric acid. Examples of such condensed phosphoric acid include linear condensed phosphoric acid such as pyrophosphoric acid, tripolyphosphoric acid, and tetrapolyphosphoric acid; cyclic condensed phosphoric acid such as metaphosphoric acid and hexametaphosphoric acid; and condensed phosphoric acid formed by combining such linear and cyclic condensed phosphoric acid. Examples of salts of condensates of phosphoric acid, phosphorous acid, and hypophosphite include ammonium salts, aluminum salts, sodium salts, potassium salts, and calcium salts.

[0057] Phosphoric acid and phosphoric acid compounds decompose in electrolyte 3 to produce phosphate ions. Phosphorous acid and phosphorous acid compounds decompose in electrolyte 3 to produce phosphite ions, which are then oxidized to produce phosphate ions. Hypophosphoric acid and hypophosphoric acid compounds decompose in electrolyte 3 to produce hypophosphoric acid, which is then oxidized to produce phosphate ions. The condensate is relatively stable in electrolyte 3 in the neutral region at room temperature, but depending on temperature or pH conditions, or through slow decomposition over time, it may produce phosphate ions, phosphite ions, hypophosphoric acid ions, etc. Therefore, phosphoric acid, phosphates, phosphate esters, and salts of phosphate esters, which can directly produce phosphate ions, are preferably suitable as the phosphate ion source, and even more preferably, phosphoric acid and phosphates are suitable.

[0058] In addition, phosphonic acid chelating agents are compounds that possess phosphonic acid (H3PO3), i.e., the phosphonic acid group (-P(=O)(OH)2), and have chelating ability (the function of forming complexes with metal ions). Examples of phosphonic acid chelating agents include 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), nitrotris(methylenephosphonic acid) (NTMP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), and ethylenediamine-N,N'-bis(methylenephosphonic acid). One type can be used alone, or two or more can be used in combination. The appropriate type of phosphonic acid chelating agent should be selected according to the specifications of the electrolytic capacitor 1 (e.g., heat resistance temperature). Based on the various tests (examples) described below, EDTMP is more preferred among the four phosphonic acid chelating agents listed above, and HEDP and NTMP are even more preferred. As a phosphonic acid chelating agent, for example, one or more substances selected from the group consisting of phosphonic acid chelating agents other than EDTMP, EDTPO, and ethylenediamine-N,N'-bis(methylenephosphonic acid) can be used. Alternatively, as a phosphonic acid chelating agent, one or more substances selected from the group consisting of HEDP, NTMP, PBTC, and EDTMP can be used. It should be noted that the same substance, which differs in name and / or description from the substance exemplified herein, should be understood as the exemplified substance.

[0059] For phosphonic acid chelating agents, the phosphonic acid groups in the chelating agent can be considered to effectively act on the adsorption and protective film formation on the surfaces of the aforementioned electrode foils 8 and 9, distinguishing them from chelating agents without phosphonic acid groups. In fact, according to the following examples, by including a phosphonic acid chelating agent in the electrolyte 3, a particularly significant suppression effect on leakage current and a particularly significant long lifespan effect on the electrolytic capacitor 1 under high-temperature conditions were observed. As an example, the content of the phosphonic acid chelating agent in the electrolyte 3 can be set within the range of 0.1% by mass to 5.0% by mass, freely selecting any combination of the upper and lower limits, such as 0.1–5.0% by mass, 0.1–4.0% by mass, 0.1–3.5% by mass, 0.1–3.0% by mass, 0.1–2.5% by mass, 0.1–2.0% by mass, 0.1–1.6% by mass, etc.

[0060] Furthermore, the electrolyte 3 may also contain known functional substances that can be mixed into the electrolyte 3 of the electrolytic capacitor 1. The functional substances referred to here are substances that possess certain functions useful to the electrolytic capacitor 1, such as oxide coating 8a repair function, high-temperature resistance function, low-temperature resistance function, and hydrogen absorption function. Among the functional substances, there are also substances that can function as electrolytes (solutes). When such substances are mixed as functional substances, the primary purpose of mixing them is to achieve the effects of useful functions other than those of functioning as electrolytes (solutes).

[0061] [Manufacturing Method of Electrolytic Capacitors]

[0062] Next, this specification will describe the manufacturing method of the electrolytic capacitor 1 of this embodiment. Figure 3 This is a flowchart illustrating an example of a method for manufacturing the electrolytic capacitor 1 according to this embodiment. Figure 4 This is an explanation Figure 3 An explanatory diagram (schematic perspective view) of an example of the capacitor element forming process S01 in the method shown.

[0063] like Figure 3 As shown, the electrolytic capacitor 1 of this embodiment is manufactured by performing a capacitor element forming process S01, an electrolyte introduction process S02, a sealing process S03, and an aging process S04. The electrolyte introduction process S02, which introduces an electrolyte 3 of a specific composition, includes novel and advantageous features common to all electrolytic capacitors of the present invention. On the other hand, processes S01, S03, and S04 include unnecessary or different operations for types other than those of this embodiment (e.g., hybrid types, element forms other than wound types, terminal forms other than leaded types, etc.). Such operations can be appropriately omitted or modified for types other than those of this embodiment.

[0064] As an example of capacitor element formation process S01, the anode foil 8 is pre-treated with the aforementioned surface-expanding treatment, such as etching, and the aforementioned chemical conversion treatment, and then the anode terminal 4a is joined. The cathode foil 9 is pre-treated with the aforementioned surface-expanding treatment, such as etching, and then the cathode terminal 4b is joined. Then, as... Figure 4As shown, the anode foil 8 and cathode foil 9 are separated by a separator 10 held between them. These anode foils 8, cathode foils 9, and separator 10 are wound to form a cylindrical shape. Then, a retaining material such as tape or film (not shown) is attached to a predetermined portion of the outer periphery of the cylindrical shape to maintain the wound state. It should be noted that this is not typically performed in the electrolytic capacitor 1 of this embodiment, but in hybrid types, the cylindrical capacitor element 2 is usually subjected to a chemical conversion treatment to repair defects in the oxide coating 8a. This chemical conversion treatment involves re-performing the anodizing treatment already performed on the anode foil 8, and then performing a re-chemical conversion treatment to repair the defects in the oxide coating 8a. This re-chemical conversion treatment is arbitrary; for example, it is not prohibited to perform a re-chemical conversion treatment on the electrolytic capacitor 1 of this embodiment type, and conversely, it is not prohibited not to perform a re-chemical conversion treatment on hybrid types.

[0065] Next, in the electrolyte introduction step S02, an electrolyte 3 of a specific composition is introduced into the capacitor element 2. Regarding the composition of the electrolyte 3, as described in this embodiment, it is an aqueous solvent prepared by mixing at least water. The water content is not limited; it can be 40% by mass or more, and further, 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. This aqueous solvent can be further mixed with components other than water (e.g., organic solvents), or it can consist solely of water. Appropriately used solvent components other than water and solute components can be used.

[0066] In addition to the solvent and solute, electrolyte 3 also contains a phosphate ion source and a phosphonic acid chelating agent. Regarding the mixing amount, as an example, the phosphate ion source is mixed in electrolyte 3 at a concentration ranging from 120.0 mmol / kg to 500.0 mmol / kg, freely choosing any combination of the upper and lower limits. For example, in electrolyte 3, the concentrations are 120.0–500.0 mmol / kg, 120.0–400.0 mmol / kg, 120.0–300.0 mmol / kg, and 120.0–210.0 mmol / kg. / kg, 120.0~205.0mmol / kg, 120.0~200.0mmol / kg, 120.0~170.0mmol / kg, 120.0~160.0mmol / kg, 120.0~155.0mmol / kg, 120.0~154.0mmol / kg, 125.0~155.0mmol / kg, 130.0~155.0mmol / kg, 130.0~150.0 mmol / kg, 150.0~500.0mmol / kg, 151.0~500.0mmol / kg, 152.0~500.0mmol / kg, 153.0~500.0mmol / kg , 154.0~500.0mmol / kg, 154.0~400.0mmol / kg, 154.0~300.0mmol / kg, 155.0~500.0mmol / kg, 160.0~5 Concentrations include 0.0 mmol / kg, 170.0~500.0 mmol / kg, 180.0~500.0 mmol / kg, 190.0~500.0 mmol / kg, 200.0~500.0 mmol / kg, 205.0~500.0 mmol / kg, 210.0~500.0 mmol / kg, 205.0~400.0 mmol / kg, and 205.0~300.0 mmol / kg. Furthermore, as an example, phosphonic acid chelating agents can be mixed in electrolyte 3 at concentrations ranging from 0.1% to 5.0% by mass, where the upper and lower limits can be freely selected from any combination of the upper and lower limits. For example, concentrations in electrolyte 3 could be 0.1–5.0% by mass, 0.1–4.0% by mass, 0.1–3.5% by mass, 0.1–3.0% by mass, 0.1–2.5% by mass, 0.1–2.0% by mass, or 0.1–1.6% by mass. Furthermore, known functional substances that can be mixed in the electrolyte 3 of the electrolytic capacitor 1 can also be mixed in electrolyte 3.

[0067] Regarding the introduction of electrolyte 3, as an example, capacitor element 2 is immersed in the prepared electrolyte 3 tank. After a predetermined time, capacitor element 2 is removed from the electrolyte 3 tank. It should be noted that, as described above, although known functional substances can be mixed in during the preparation stage of electrolyte 3, the functional substances can also be introduced into capacitor element 2 by immersing it in a tank containing a liquid containing the functional substances, either before or after the introduction of electrolyte 3. The introduction of electrolyte 3 and functional substances can be carried out under pressure controlled as needed.

[0068] Next, refer to Figure 1 The steps of the sealing process S03 will be explained. As an example, the capacitor element 2 is housed within a bottomed cylindrical casing 6. The lead terminals 4 (anode terminal 4a and cathode terminal 4b) that connect to the capacitor element 2 are fitted into the through holes of the sealing material 5, and the opening of the casing 6 is sealed with the sealing material 5. Thus, the lead terminals 4 are in a state where they are led out to the outside of the electrolytic capacitor 1. Next, a tight-fitting process is performed on the opening edge 6a of the casing 6 to seal the inside of the casing 6. It should be noted that an explosion-proof valve 7 may also be provided on the casing 6 and / or the sealing material 5. This allows for the manufacture of... Figure 1 The electrolytic capacitor 1 is shown. Furthermore, the casing 6 can also be packaged with an outer material (not shown). This packaging can be performed before or after the aging process S04 described below.

[0069] Finally, the aging process S04 applies a specified voltage to the manufactured electrolytic capacitor 1 under high temperature conditions for a specified time. This allows the oxide coating 8a repair function of the specified components in the electrolyte 3 to function, repairing portions of the oxide coating 8a that were peeled off during manufacturing, as well as relatively thin portions of the oxide coating 8a, thereby suppressing leakage current and stabilizing performance. Furthermore, the aging process can also unexpectedly achieve a smoothing effect, such as the removal of initial defects.

[0070] Example

[0071] [Experiment 1]

[0072] According to the aforementioned embodiment, an aluminum electrolytic capacitor with a rated voltage of 16V was manufactured using conventional methods. The anode and cathode foils were made of etched aluminum foil, and the anode foil underwent chemical conversion treatment to form an oxide coating. The capacitor element was assembled, and then an electrolyte with the composition shown in Table 1 was introduced into the capacitor element. It should be noted that the functional materials in Table 1 include multiple substances, and their composition ratios are the same in all examples (hereinafter, the functional materials are the same for all tests). The electrolytic capacitor was assembled, and then a prescribed aging treatment was performed. The manufactured electrolytic capacitors were exposed to a temperature environment of 115°C without applied voltage, and the leakage current under 16V applied for 1 minute was measured after each prescribed period. Five units were tested in each example. Figure 5 A and Figure 5 The results are shown in B.

[0073] [Table 1]

[0074]

[0075] The following commercially available products were used as phosphate and phosphonic acid chelating agents (the same applies to all tests).

[0076] Phosphoric acid (manufactured by RASA Industries, LTD.)

[0077] HEDP: 1-Hydroxyethylidene-1,1-Diphosphonic acid (manufactured by CHELEST, CHELEST PH-210, "CHELEST" is a registered trademark. The same applies below.)

[0078] NTMP: Nitrogenotris(methylenephosphonic acid) (manufactured by CHELEST, CHELEST PH-320)

[0079] PBTC: 2-phosphonobutane-1,2,4-tricarboxylic acid (manufactured by CHELEST, CHELEST PH-430)

[0080] EDTMP: Ethylenediaminetetra(methylenephosphonic acid) (manufactured by CHELEST, CHELEST PH-540)

[0081] Figure 5 A is a graph showing the average of each example, and the error range representing the maximum and minimum values. However, there are areas where the error range is too small to be visually discernible. Additionally, Figure 5 B is to Figure 5 The graph in chart A has a narrowed vertical axis range to make the results of each embodiment easier to observe. However, for ease of observation, the error range has been omitted from the display. It should be noted that... Figure 5 Comparative Example 2 is not shown in B.

[0082] like Figure 5 A and Figure 5 As shown in B, compared to Reference Example 1, which contained 104.9 mmol / kg of phosphoric acid in the existing standard electrolyte, Comparative Example 1 (130.7 mmol / kg), with a higher phosphoric acid content, exhibited a significantly increased leakage current. Furthermore, in Comparative Example 2 (156.4 mmol / kg), which contained an even higher phosphoric acid content than Comparative Example 1, the leakage current increased even more significantly. In contrast, in Examples 1-4, which used various phosphonic acid chelating agents in approximately the same amount of phosphoric acid as Comparative Example 1 (128.4–129.6 mmol / kg), the leakage current was lower than that of Reference Example 1. Additionally, in Examples 5-8, which used various phosphonic acid chelating agents in approximately the same amount of phosphoric acid as Comparative Example 2 (153.6–155.0 mmol / kg), the leakage current was also lower than that of Reference Example 1.

[0083] Specifically, in Reference Example 1, the increase in leakage current became significant after approximately 3000 hours from the start of the test, reaching a maximum of 115.98 μA after 9469 hours. In Comparative Example 1, the increase in leakage current began to increase sharply after approximately 500 hours from the start of the test, reaching a maximum of 369.56 μA after 4060 hours. In Comparative Example 2, the increase in leakage current began to increase sharply after approximately 500 hours from the start of the test, exceeding 500 μA and thus exceeding the measurement range before 1000 hours had elapsed.

[0084] In contrast, the leakage current of Examples 1 to 8 was below 16.15 μA throughout the entire test period (Example 6: after 508 hours), which was significantly less than that of Comparative Examples 1, 2 and Reference Example 1. Furthermore, the leakage current of Examples 1 to 5, 7 and 8 was below 12.62 μA throughout the entire test period (Example 8: after 1084 hours).

[0085] Furthermore, in all Examples 1-8, Examples 1-4, which had a relatively low phosphoric acid content, showed a tendency for lower leakage current compared to Examples 5-8, which had a relatively high phosphoric acid content. It can be considered that since phosphate ions can be utilized more efficiently through phosphonic acid chelating agents, the leakage current was sufficiently suppressed by moderately increasing the phosphate ion source. Among the phosphonic acid chelating agents, in Examples 5-8, which had a relatively high phosphoric acid content, HEDP (Example 5) and PBTC (Example 7) showed a tendency for lower leakage current compared to NTMP (Example 6) and EDTMP (Example 8), which is favorable. Furthermore, regardless of the amount of phosphoric acid, PBTC (Examples 3, 7) showed a particularly low tendency for leakage current, which is favorable. Considering the experimental conditions, for electrolytic capacitors (e.g., electrolytic capacitors with a heat resistance temperature set at 110-120°C) intended for use at around 115°C, NTMP and EDTMP are preferred among the phosphonic acid chelating agents, HEDP is more preferred, and PBTC is even more preferred.

[0086] [Experiment 2]

[0087] According to the aforementioned embodiment, an aluminum electrolytic capacitor with a rated voltage of 16V was manufactured using conventional methods. The anode and cathode foils were made of etched aluminum foil, and the anode foil underwent chemical conversion treatment to form an oxide coating. The capacitor element was assembled, and then an electrolyte with the composition shown in Table 2 was introduced into the capacitor element. The electrolytic capacitor was then assembled and subjected to a prescribed aging treatment. The manufactured electrolytic capacitors were exposed to the electrical conditions and temperature environment shown in Table 3, and the presence of any faults (opening of the explosion-proof valve or unusable state due to lack of power) was investigated every 500 hours. Five units were tested for each example. The results are shown in Table 3.

[0088] [Table 2]

[0089]

[0090] [Table 3]

[0091]

[0092] As shown in Table 3, overall, the lifetime of Comparative Example 3 (130.7 mmol / kg), which had a higher phosphoric acid content (104.9 mmol / kg) than Reference Example 2 (which had a higher phosphoric acid content than Comparative Example 3), was shortened. Furthermore, in Comparative Example 4 (156.4 mmol / kg), which had a higher phosphoric acid content than Comparative Example 3, the lifetime was further shortened compared to Comparative Example 3 or to the same extent. In contrast, in Examples 9-12, which used various phosphonic acid chelating agents in approximately the same amount of phosphoric acid (128.4–129.6 mmol / kg) as Comparative Example 3, the lifetime was extended compared to Reference Example 2. Additionally, in Examples 13-16, which used various phosphonic acid chelating agents in approximately the same amount of phosphoric acid (153.6–155.0 mmol / kg) as Comparative Example 4, the lifetime was also extended compared to Reference Example 2.

[0093] Specifically, under a temperature condition of 115°C without applied voltage, all five units in Comparative Example 4 failed after 5500 hours, all five units in Comparative Example 3 failed after 6500 hours, and all five units in Reference Example 2 failed after 9500 hours. In contrast, in Examples 9-16, none of the five units failed after 9500 hours, demonstrating an extended lifespan compared to Comparative Examples 3 and 4 and Reference Example 2.

[0094] Under conditions of 115°C and a rated voltage of 16V, all five units in Comparative Example 4 failed after 5500 hours, all five units in Comparative Example 3 failed after 6500 hours, and all five units in Reference Example 2 failed after 9500 hours. In contrast, in Examples 9-16, none of the five units failed after 9500 hours, demonstrating an extended lifespan compared to Comparative Examples 3 and 4 and Reference Example 2.

[0095] Under conditions of 125°C without applied voltage, all five units in Comparative Examples 4 and 3 failed after 3000 hours, while all five units in Reference Example 2 failed after 3500 hours. In contrast, all five units in Examples 15 and 16 failed after 5000 hours, all five units in Examples 11 and 14 failed after 7000 hours, and some units in Examples 9, 10, 12, and 13 failed after 8000 hours. Although there are differences between the examples, the lifespan of all Examples 9-16 was extended compared to Comparative Examples 3 and 4 and Reference Example 2.

[0096] At 115°C, there was no difference between the examples, but at 125°C, Examples 9-12, with relatively less phosphoric acid, showed a tendency for longer lifespan compared to Examples 13-16, which had relatively higher phosphoric acid content. It can be considered that the use of phosphonic acid chelating agents allows for more efficient utilization of phosphate ions, thus moderately increasing the phosphate ion source and sufficiently suppressing leakage current. As described above, at 125°C, Comparative Examples 3, 4, and Reference Example 2 experienced failures very early, while all Examples 9-16 maintained a certain lifespan, especially Examples 9-14, some of which maintained more than twice the lifespan of Comparative Examples 3, 4, and Reference Example 2. Thus, the combined use of phosphoric acid and phosphonic acid chelating agents particularly demonstrates a very significant effect in achieving a very stable long lifespan even under relatively harsh high-temperature conditions.

[0097] Among phosphonic acid chelating agents, in Examples 13-16 with relatively high phosphoric acid content at 125°C, HEDP (Example 13) and NTMP (Example 14) showed a tendency for longer lifespan compared to PBTC (Example 15) and EDTMP (Example 16), and were therefore preferred. Considering the conditions of this test, for electrolytic capacitors intended to be used at around 125°C (e.g., electrolytic capacitors with a heat resistance temperature set at 120-130°C), PBTC and EDTMP are preferred among phosphonic acid chelating agents, and HEDP and NTMP are more preferred.

[0098] [Experiment 3]

[0099] Furthermore, to investigate the mixing amount (content) of the phosphate ion source, electrolytes with the compositions shown in Table 4 were prepared for each example. An aluminum electrode and a platinum electrode, both made of 2cm × 5cm aluminum foil, were connected to a galvanometer (Yokogawa Electric Corporation, digital multimeter TY710). The two electrodes were placed in a glass beaker containing 70g of electrolyte at room temperature, forming the experimental setup. In this setup, the current value was measured 5 minutes after the electrodes were immersed in the electrolyte. Table 4 shows the electrolyte composition and the measured current values. Additionally, in Figure 6 The results of this measurement are presented in the form of a chart.

[0100] [Table 4]

[0101]

[0102] The electrode reactions in this experimental setup are described below.

[0103] Aluminum electrode reaction

[0104] Al Al 3＋ +3e - (Al + 3OH)- Al(OH)3+ 3e - )

[0105] Platinum electrode reaction

[0106] 3H₂O + 3e - 3OH - + 3 / 2H2

[0107] That is, the magnitude of the current value measured here indicates the degree of progression of hydration degradation of the aluminum foil. At the same time, in each case, the lower the current value, the better the hydration degradation of the foil is suppressed by the phosphoric acid in the electrolyte.

[0108] As shown in Table 4 and Figure 6 As shown, compared to Comparative Example 5, which contained an electrolyte composition without the addition of phosphonic acid chelating agents to phosphoric acid, Examples 17-20, which contained various phosphonic acid chelating agents to phosphoric acid, exhibited lower current values ​​regardless of the phosphoric acid concentration, and foil hydration degradation was suppressed. More specifically, at the phosphoric acid concentration (approximately 100 mmol / kg) in existing standard electrolytes, the difference in current values ​​between Examples 17-20 and Comparative Example 5 was relatively small. However, when the phosphoric acid concentration was increased by 2 times (approximately 200 mmol / kg), 3 times (approximately 300 mmol / kg), 4 times (approximately 400 mmol / kg), and 5 times (approximately 500 mmol / kg), the current value in Comparative Example 5 increased relatively sharply, while the increase in current values ​​in Examples 17-20 was relatively slow, particularly in Examples 17, 18, and 20. As a result, the difference in current values ​​between Examples 17-20 and Comparative Example 5 became relatively larger. Therefore, by mixing phosphoric acid with a phosphonic acid chelating agent and adding an extremely large amount of phosphoric acid (phosphate ion source) to the electrolyte at about 5 times the standard amount, the degradation of the electrode foil can be effectively suppressed, thereby achieving the reduction of leakage current and extension of life in the electrolytic capacitor confirmed in Experiments 1 and 2.

[0109] Based on the experimental results to date, in this invention, by using phosphonic acid chelating agents, the mixing amount (content) of the phosphate ion source in the electrolyte can be set within a range of all combinations of upper and lower limits, from 120.0 mmol / kg to 500.0 mmol / kg, for example 120.0–500.0 mmol / kg, 120.0–400.0 mmol / kg, 120.0–300.0 mmol / kg, 120.0– 210.0mmol / kg, 120.0~205.0mmol / kg, 120.0~200.0mmol / kg, 120.0~170.0mmol / kg, 120.0~160.0mmol / kg, 120.0~155.0mmol / kg, 120.0~154.0mmol / kg, 125.0~155.0mmol / kg, 130.0~155.0mmol / kg, 130.0 ~150.0mmol / kg, 150.0~500.0mmol / kg, 151.0~500.0mmol / kg, 152.0~500.0mmol / kg, 153.0~500.0mmo l / kg, 154.0~500.0mmol / kg, 154.0~400.0mmol / kg, 154.0~300.0mmol / kg, 155.0~500.0mmol / kg, 160. The ranges are as follows: 0–500.0 mmol / kg, 170.0–500.0 mmol / kg, 180.0–500.0 mmol / kg, 190.0–500.0 mmol / kg, 200.0–500.0 mmol / kg, 205.0–500.0 mmol / kg, 210.0–500.0 mmol / kg, 205.0–400.0 mmol / kg, 205.0–300.0 mmol / kg, etc.

[0110] Among phosphonic acid chelating agents, HEDP (Example 17), NTMP (Example 18), and EDTMP (Example 20) showed a tendency to have lower current values ​​compared to PBTC (Example 19), which is favorable. Even with a very high amount of phosphoric acid in the electrolyte (approximately 500 mmol / kg), the current was suppressed to a low value of 54.09 μA in PBTC (Example 19), an even lower value of 20.65 μA in HEDP (Example 17), a significantly lower value of 14.87 μA in NTMP (Example 18), and a more significantly lower value of 15.53 μA in EDTMP (Example 20). Considering the conditions of this test, for electrolytic capacitors and the like intended for use at room temperature, PBTC is preferred among phosphonic acid chelating agents, HEDP is more preferred, and NTMP and EDTMP are even more preferred.

[0111] [Experiment 4]

[0112] Furthermore, to investigate the mixing amount (content) of phosphonic acid chelating agents, electrolytes with the compositions shown in Table 5 were prepared for each example. In the same test apparatus as in Experiment 3, the current value was measured 5 minutes after the electrodes were placed in the electrolyte. Table 5 shows the electrolyte composition and the measured current values. Additionally, in Figure 7 The results of this measurement are presented in the form of a chart.

[0113] [Table 5]

[0114]

[0115] As shown in Table 5 and Figure 7 As shown, compared to Comparative Example 6, which did not contain an electrolyte composition incorporating phosphonic acid chelating agents with phosphoric acid, Examples 21-24, which contained various phosphonic acid chelating agents incorporating phosphoric acid, exhibited low current values ​​at any phosphonic acid chelating agent dosage, and foil hydration degradation was suppressed. Specifically, compared to the 27.45 μA of the Comparative Example, the current value was suppressed to a significantly low value of less than 13.5 μA when 0.2% by mass of phosphonic acid chelating agent was incorporated (Examples 21-1, 22-1, 23-1, 24-1), and to an even more significantly low value of less than 9.0 μA when 0.6% by mass or more of phosphonic acid chelating agent was incorporated (Examples 21-2-21-4, 22-2-22-4, 23-2-23-4, 24-2-24-4). Thus, when 0.2% by mass of phosphonic acid chelating agent was mixed in, it already showed a significant effect compared to the comparative example. The significant effect continued stably until 1.5% by mass of phosphonic acid chelating agent was mixed in. Therefore, by mixing at least 0.1% or even 0.2% by mass of phosphonic acid chelating agent with phosphoric acid, the degradation of the electrode foil can be sufficiently suppressed, thereby achieving the reduction of leakage current and extension of life in the electrolytic capacitor confirmed in Experiments 1 and 2.

[0116] Based on the experimental results to date, in this invention, the mixing amount (content) of the phosphonic acid chelating agent in the electrolyte can be set to 0.1% or even 0.2% by mass or more. For example, if a portion of the functional material in this embodiment is replaced with a phosphonic acid chelating agent to set the upper limit, the upper and lower limits can be freely selected from any combination of the upper and lower limits within the range of 0.1% to 5.0% by mass, such as 0.1–5.0% by mass, 0.1–4.0% by mass, 0.1–3.5% by mass, 0.1–3.0% by mass, 0.1–2.5% by mass, 0.1–2.0% by mass, 0.1–1.6% by mass, 0.2–5.0% by mass, 0.2–4.0% by mass, 0.2–3.5% by mass, 0.2–3.0% by mass, 0.2–2.5% by mass, 0.2–2.0% by mass, 0.2–1.6% by mass, 0.2–1.5% by mass, etc.

[0117] [Experiment 5]

[0118] Furthermore, the protective effect of the electrode foil provided by the phosphonic acid chelating agent was verified. The test was conducted according to the JEITA standard of the Japan Electronics and Information Technology Industries Association (formerly the Electronic Industries Association of Japan): EIAJ RC-2364A "Test Method for Electrode Foil for Aluminum Electrolytic Capacitors" (revised March 1999) (https: / / www.jeita.or.jp / japanese / standard / book / RC-2364A / #target / page_no=1) (hereinafter referred to as the EIAJ standard). The aluminum foil used for the test electrode foil was a product with a rated coating withstand voltage (Vf) of 36V or higher from aluminum low-voltage anodic chemical conversion foil (manufactured by JAPAN CAPACITOR INDUSTRIAL CO., LTD., low-voltage chemical conversion foil 100LV20B). For this aluminum foil, the measurement range was set to 5cm. 2 The electrode foil, measuring 10mm x 50mm, was punched to form the test piece.

[0119] Electrode foils were immersed in 100g of the electrolyte solutions shown in Table 6 and left at room temperature (25°C) for 24 hours. Then, the electrode foils were removed from the electrolyte and rinsed with pure water. For the resulting electrode foils, a constant DC current was passed through an EIAJ-based test circuit for the coating withstand voltage of low-voltage anodic chemical conversion foils (i.e., the electrode foil was immersed in the test solution (test range portion) and connected to a DC power supply). The rise time (Tr), the coating withstand voltage (Vt) of the electrode foil, and the voltage reached after 3 minutes were measured using a method based on the EIAJ standard.

[0120] Composition of the test solution: 1000ml pure water, 150g ammonium adipate

[0121] Measurement temperature: 85±2℃

[0122] Measurement current: 1.0 ± 0.1 mA (per 5 cm test piece) 2 (current value)

[0123] Rise time (Tr): The time from the start of current flow until the applied voltage to the electrode foil rises to 90% (32.4V) of the rated coating withstand voltage (Vf) (36V) (seconds).

[0124] Coating withstand voltage (Vt): Voltage after 3 minutes from the rise time (Tr) (unit [V (volts)])

[0125] Voltage reached after 3 minutes: Voltage (unit: V (volts)) three minutes after the current begins flowing.

[0126] [Table 6]

[0127]

[0128] [Table 7]

[0129]

[0130] As shown in Table 7, compared to Reference Example 3 with a phosphoric acid content of 104.9 mmol / kg in the existing standard electrolyte, Comparative Example 8-1 (130.7 mmol / kg), with a higher phosphoric acid content, exhibited a longer rise time (Tr), and decreased voltage reached after 3 minutes and coating withstand voltage (Vt). In Comparative Example 8-2 (156.4 mmol / kg), with an even higher phosphoric acid content than Comparative Example 8-1, the rise time (Tr) was significantly longer, and decreased voltage reached after 3 minutes and coating withstand voltage (Vt). This confirms the degradation of the electrode foil caused by the relatively large increase in phosphoric acid.

[0131] Furthermore, compared to the electrolyte compositions of Comparative Examples 8-1 and 8-2, even in Comparative Examples 7-1 and 7-2, where EDTA, a chelating agent without phosphonic acid groups, was increased by more than 2.7 times, the rise time (Tr) was longer than in Reference Example 3, and the voltage reached after 3 minutes and the coating withstand voltage (Vt) were also lower. That is, even with an electrolyte containing sufficient EDTA, the degradation of the electrode foil due to the relatively large amount of phosphoric acid added was confirmed. Here, it can be considered that even chelating agents without phosphonic acid groups, as exemplified by EDTA, as chelating agents, will, through their chelating properties, interact with aluminum ions (Al... 3+ This chelating agent forms a complex and traps phosphoric acid, thus contributing to the suppression of leakage current associated with hydration degradation of the electrode foil, together with phosphoric acid. On the other hand, based on the results of this experiment, chelating agents without phosphonic acid groups are almost unable to suppress the degradation of the electrode foil caused by a relatively large amount of phosphoric acid. Therefore, it is speculated that even with the addition of this chelating agent, a significantly longer lifespan cannot be achieved in electrolyte compositions containing relatively large or extremely large amounts of phosphoric acid.

[0132] In contrast, in Examples 25-1, 25-2, 26-1, and 26-2, where HEDP or EDTMP, as phosphonic acid chelating agents, were mixed with the electrolyte composition of Comparative Examples 8-1 and 8-2, the rise time (Tr) was shortened compared to Reference Example 3, and the voltage reached after 3 minutes and the coating withstand voltage (Vt) both increased. That is, the degradation of the electrode foil caused by the relatively large amount of phosphoric acid was suppressed. This indicates that the electrode foil was protected by the phosphonic acid chelating agent, confirming the electrode foil protection effect brought about by the phosphonic acid chelating agent. It should be noted that among phosphonic acid chelating agents, HEDP (Examples 25-1 and 25-2) tends to have a higher electrode foil protection effect compared to EDTMP (Examples 26-1 and 26-2). From the viewpoint of electrode foil protection, it can be said that among phosphonic acid chelating agents, EDTMP is preferred, and HEDP is more preferred.

[0133] It can be considered that phosphonic acid chelating agents function effectively through their phosphonic acid groups, thereby adsorbing onto the electrode foil surface and acting as a protective film, protecting the electrode foil from the effects of excessive phosphate ions. As a result, in this experiment, it was able to suppress the electrode foil degradation caused by a relatively large increase in phosphoric acid, which is impossible to achieve with chelating agents without phosphonic acid groups. Specifically, the effect is that, for example, as shown in the results of Experiment 3, mixing approximately five times the standard amount of phosphoric acid (phosphate ion source) into the electrolyte sufficiently suppresses electrode foil degradation, and, as shown in the results of Experiments 1 and 2, achieves a reduction in leakage current and an extension of lifespan in the electrolytic capacitor.

Claims

1. An electrolytic capacitor, characterized in that, have: A capacitor element having an anode foil, a cathode foil having a dielectric layer formed thereon, and a spacer disposed between the anode foil and the cathode foil; and, The electrolyte permeating the capacitor element The electrolyte contains an aqueous solvent, a phosphate ion source, and a phosphonic acid chelating agent, but excludes ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), and ethylenediamine-N,N'-bis(methylenephosphonic acid), as well as substances having the same chemical structure. The electrolyte contains more than 40% by mass of water.

2. The electrolytic capacitor according to claim 1, characterized in that, The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of these three acids, esters of these three acids and salts of these esters, and condensates of these three acids and salts of these condensates.

3. The electrolytic capacitor according to claim 2, characterized in that, The phosphate ion source is one or more substances selected from the group consisting of phosphoric acid, phosphates, phosphate esters, and salts of phosphate esters.

4. The electrolytic capacitor according to claim 1, characterized in that, The phosphonic acid chelating agent is one or more substances selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, nitrotris(methylenephosphonic acid) and 2-phosphonobutane-1,2,4-tricarboxylic acid.

5. The electrolytic capacitor according to claim 1, characterized in that, The electrolyte contains 154.0 to 500.0 mmol / kg of the phosphate ion source, except where the phosphate ion source is less than 0.75 wt% in the electrolyte.

6. A method for manufacturing an electrolytic capacitor, characterized in that, The electrolyte shall be mixed with at least a water-containing solvent, a phosphate ion source, and a phosphonic acid chelating agent, but excluding ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N,N',N'-tetra(phosphonomethyl)ethylenediamine (EDTPO), and ethylenediamine-N,N'-bis(methylenephosphonic acid), as well as substances having the same chemical structure as these. The electrolyte contains at least 40% by mass of water.

7. The method for manufacturing an electrolytic capacitor according to claim 6, characterized in that, The phosphate ion source is selected from one or more substances in the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, salts of each of the 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.

8. The method for manufacturing an electrolytic capacitor according to claim 7, characterized in that, The phosphate ion source is selected from one or more substances in the group consisting of phosphoric acid, phosphate, phosphate ester and salts of phosphate ester.

9. The method for manufacturing an electrolytic capacitor according to claim 6, characterized in that, The phosphonic acid chelating agent is selected from one or more substances comprising 1-hydroxyethylidene-1,1-diphosphonic acid, nitrotris(methylenephosphonic acid) and 2-phosphonobutane-1,2,4-tricarboxylic acid.

10. The method for manufacturing an electrolytic capacitor according to claim 6, characterized in that, The phosphate ion source is mixed in at a concentration of 154.0–500.0 mmol / kg in the electrolyte, except where the phosphate ion source is less than 0.75 wt% in the electrolyte.

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