Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor and a method for manufacturing an electrolytic capacitor that can suppress the generation of hydrogen gas using a nitro compound, suppress a decrease in withstand voltage after high-temperature loading, and stably operate in temperature ranges including high temperatures.SOLUTION: An electrolytic capacitor 1 includes: a capacitor element 2 having an anode foil 3 on which a dielectric layer is formed, a cathode foil 4, and a separator 5 disposed between the anode foil 3 and the cathode foil 4; and an electrolyte solution 6 impregnated in the capacitor element 2. The electrolyte solution 6 contains a 4-nitropyridine N-oxide compound.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Electrolytic capacitors are energy storage devices that are essentially composed of an anode foil with a dielectric layer formed thereon, a cathode foil, and a separator disposed between them, and are impregnated with an electrolyte. 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 another in which a solid electrolyte such as a conductive polymer is introduced. Furthermore, there are also so-called "hybrid" electrolytic capacitors in which both a solid electrolyte and an electrolytic solution are introduced into the capacitor element, thereby taking advantage of the advantages of both solid and non-solid electrolytes.

[0003] In conventional electrolytic capacitors, in order to meet various market demands, for example, increasing the water content in the electrolyte to lower impedance increases the amount of hydrogen gas generated by the hydration reaction between the metal elements in the electrode foil and water. Alternatively, in an attempt to reduce the size and increase the capacity of the product, increasing the capacity of the foil increases the amount of hydrogen gas generated, which increases the internal pressure of the reduced outer casing space. This hydrogen gas generation can lead to problems such as swelling, leakage, and the activation (opening) of explosion-proof valves.

[0004] Therefore, conventionally, a nitro compound having a nitro group has been blended into the electrolytic solution (see Patent Document 1: JP-A-4-10512). The nitro compound has the effect of suppressing the generation of hydrogen gas in the electrolytic capacitor by absorbing hydrogen ions through reduction of the nitro group. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-10512 [Patent Document 2] Japanese Patent Application Publication No. 2023-145741 Summary of the Invention [Problem to be solved by the invention]

[0006] As exemplified in Patent Document 1 (JP 4-10512 A), the hydrogen gas generation inhibitory effect of nitro compounds (nitro groups) is well known. Conventionally, limited nitrobenzene compounds among nitro compounds have been used in electrolytes for electrolytic capacitors (Patent Document 2: JP 2023-145741 A, paragraph 0032).

[0007] However, the nitro compounds that have been used up to now have relatively low solubility in polar solvents such as ethylene glycol, and at relatively high concentrations they reduce the withstand voltage of electrolytic capacitors, so their blending amounts have been limited to relatively low concentrations. [Means for solving the problem]

[0008] Furthermore, the inventors have newly discovered a problem that conventional nitro compounds suffer a significant decrease in withstand voltage, particularly after being subjected to a high-temperature load (exposed at a high temperature for a certain period of time).

[0009] Therefore, the present invention aims to provide an electrolytic capacitor and a method for manufacturing an electrolytic capacitor that can suppress the generation of hydrogen gas using a nitro compound, suppress a decrease in voltage resistance after high-temperature loading, and can operate stably in temperature ranges including high temperatures.

[0010] The present invention solves the above problems by the solution means described below as one embodiment.

[0011] An electrolytic capacitor according to the present invention includes a capacitor element having 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, wherein the electrolyte solution contains a 4-nitropyridine N-oxide compound.

[0012] The 4-nitropyridine N-oxide compound is preferably 4-nitropyridine N-oxide.

[0013] Furthermore, the generation of hydrogen in an electrolytic capacitor becomes more of a problem as the water content in the electrolyte increases, so the present invention is more suitable for an embodiment in which the solvent for the electrolyte contains water.

[0014] The method for producing an electrolytic capacitor according to the present invention is characterized in that a 4-nitropyridine N-oxide compound is blended in the electrolytic solution.

[0015] The 4-nitropyridine N-oxide compound is preferably 4-nitropyridine N-oxide.

[0016] As the solvent for the electrolytic solution, a solvent containing water can be suitably used. [Effects of the Invention]

[0017] The electrolytic capacitor according to the present invention can suppress the generation of hydrogen gas in the electrolytic capacitor by using the 4-nitropyridine N-oxide compound, and can suppress the decrease in withstand voltage after high-temperature loading, thereby enabling stable operation in temperature ranges including high temperatures. [Brief explanation of the drawings]

[0018] [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 a schematic diagram (exploded perspective view) showing an example of a capacitor element in the electrolytic capacitor according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram (a schematic diagram of the basic configuration) showing an example of a capacitor element in the electrolytic capacitor according to this embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of a method for manufacturing an electrolytic capacitor according to this embodiment. [Figure 5] 5A and 5B are graphs showing the results of Example 1, Comparative Examples 1 and 2, and Reference Example 1 in Test 3. [Figure 6] 6A and 6B are graphs showing the results of Example 2, Comparative Example 4, and Reference Example 1 in Test 3. [Figure 7] FIG. 7 is a graph showing the results of Example 3, Comparative Example 5, and Reference Example 1 in Test 4. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to an electrolytic capacitor having a structural characteristic in the composition of the electrolyte solution and to a method for manufacturing the same. Therefore, the present invention is applicable to electrolytic capacitors in which the capacitor element is impregnated with the electrolyte solution. Hereinafter, as an embodiment of the present invention, an electrolytic capacitor 1 will be described using an example of a type in which an electrolyte solution 6 is introduced as a non-solid electrolyte (a type in which a solid electrolyte is not introduced) into the capacitor element 2. However, due to the nature of the present invention, the electrolytic capacitor of the present invention is not limited to the electrolytic capacitor 1 described here. That is, the electrolytic capacitor of the present invention 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. Furthermore, as an embodiment of the present invention, an electrolytic capacitor 1 having lead terminals (lead wires) 10 and 11 will be described as an example. However, due to the nature of the present invention, the electrolytic capacitor of the present invention is not limited to this terminal type. That is, the electrolytic capacitor of the present invention also includes electrolytic capacitors with terminal types such as screw terminals, board-standing types with riveted external terminals, and other surface-mounted types. Furthermore, as an embodiment of the present invention, an electrolytic capacitor 1 having a wound-type capacitor element 2 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 this element form. In other words, the electrolytic capacitor according to the present invention also includes electrolytic capacitors with element forms such as stacked types and coin types.

[0020] 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) showing an example of an electrolytic capacitor 1 according to this embodiment. However, for ease of viewing, the cross-sectional structure of the capacitor element 2 is not shown. FIGS. 2 and 3 are schematic diagrams illustrating an example of the capacitor element 2 in the electrolytic capacitor 1 according to this embodiment. FIG. 2 is an exploded perspective view illustrating the forming (winding) step S01 of the capacitor element 2. FIG. 3 is an explanatory diagram schematically illustrating the basic configuration of the capacitor element 2.

[0021] As shown in FIG. 1 , the electrolytic capacitor 1 according to this embodiment includes a capacitor element 2 impregnated with an electrolyte solution 6 housed in a cylindrical, bottomed outer case 7. A filler (not shown) made of an insulating material such as epoxy resin may fill the gap between the capacitor element 2 and the inner wall of the outer case 7. The outer case 7 may be made of, for example, an aluminum case, which is relatively airtight, heat-resistant, and corrosion-resistant. An explosion-proof valve 8, which functions as a pressure valve, is provided at the bottom of the outer case 7. The explosion-proof valve 8 is formed by thinning a portion of the bottom surface of the outer case 7. When a relatively large amount of gas is generated relatively suddenly within the electrolytic capacitor 1 and the internal pressure rises to a certain level, the thinned portion breaks, allowing the gas to escape to the outside. For packaging purposes, the outer case 7 is further covered by an outer sleeve (not shown) made of an insulating material such as vinyl chloride.

[0022] A sealing body 9 is attached to the opening 7a of the outer case 7. Lead terminals (anode lead terminal 10 and cathode lead terminal 11) connected to the capacitor element 2 pass through through holes provided in the sealing body 9 and are drawn out from the through holes to the outside of the electrolytic capacitor 1. A first crimped portion 7c is provided by crimping the sealing body 9 by the opening 7a of the outer case 7 in a direction perpendicular to the installation direction of the sealing body 9 (Z direction in the drawing). A second crimped portion 7d is provided by crimping the sealing body 9 by the open end 7b of the outer case 7 in a direction parallel to the installation direction of the sealing body 9 (Z direction in the drawing). In this way, the outer case 7 is sealed by the sealing body 9 and is also hermetically sealed by the crimped portions 7c and 7d at two locations.

[0023] Next, as shown in FIG. 2, the wound capacitor element 2 according to this embodiment is formed by stacking an anode foil 3 and a cathode foil 4 with a separator 5 sandwiched between them and winding them together, and holding them together with a holding material (not shown) such as tape, to form a cylindrical capacitor element 2.

[0024] As shown in Fig. 3, the basic configuration includes an anode foil 3, a cathode foil 4, and a separator 5 disposed between the anode foil 3 and the cathode foil 4. An anode lead terminal 10 is connected to the anode foil 3. A cathode lead terminal 11 is connected to the cathode foil 4.

[0025] The electrode foils (anode foil 3 and cathode foil 4) are made of valve metals such as aluminum and tantalum. Alternatively, valve metal alloys made of multiple types of valve metals may be used. Alternatively, valve metal alloys may be used in which metal elements other than valve metals or other non-metal elements are added to one or multiple valve metals to the extent that they can function as the electrode foils 3 and 4. Note that these valve metals or valve metal alloys are permitted to contain unintentional impurities to the extent that they can function as the electrode foils 3 and 4.

[0026] The electrode foils 3 and 4 may be formed of multiple layers, including 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 made of the valve metal or valve metal 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 3 and 4 have an expanded surface structure due to a surface expansion process. A typical example of the surface expansion process is etching. Alternatively, the expanded surface structure may be formed by vapor deposition or sintering of a metal powder. In this case, for example, the electrode foils 3 and 4 themselves can be formed and the expanded surface structure can be formed by coating the core substrate with the valve metal or valve metal alloy powder by vapor deposition or sintering. The expanded surface structure of the electrode foils 3 and 4 can increase the specific surface area and thus the capacitance.

[0028] The surface of the surface-enlarged anode foil 3 is subjected to a chemical conversion treatment to form an oxide film 3a as a dielectric layer. On the other hand, the chemical conversion treatment is optional for the surface-enlarged cathode foil 4. That is, in a polar electrolytic capacitor 1, no chemical conversion treatment is performed, and a natural oxide film (not shown) is usually formed on the surface of the cathode foil 4 by oxygen in the air. Alternatively, a treatment other than chemical conversion treatment may be performed, for example, the surface of the surface-enlarged cathode foil 4 may be further coated with a valve metal or valve metal alloy powder. This can increase the dielectric constant and improve the capacitance. Alternatively, the surface of the surface-enlarged cathode foil 4 may be subjected to a chemical conversion treatment similar to that of the anode foil 3 to form a non-polar electrolytic capacitor 1.

[0029] Lead terminals 10 and 11 are connected to electrode foils 3 and 4 by stitch connection, cold pressure welding, or the like, and are drawn out from capacitor element 2.

[0030] Separator 5 (electrolytic paper) can be made of natural cellulose fibers such as Manila hemp pulp, or cloth, sheet, or film made of synthetic fibers such as nylon, or a blend or blend of these. Synthetic fibers have the advantage of being able to be selected from materials with particularly excellent heat resistance. Examples of such synthetic fibers include nylon, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polyphenylene sulfide (PPS). While FIG. 3 shows a schematic diagram of the basic configuration of capacitor element 2 and illustrates one separator 5, the number of separators is not limited; multiple separators (e.g., three in FIG. 2) may be used as needed to separate anode foil 3 from cathode foil 4.

[0031] The capacitor element 2 is also impregnated with an electrolyte 6. As shown schematically in FIG. 3, the electrolyte 6 in the polar electrolytic capacitor 1 exists in the gap between the anode foil 3 and the cathode foil 4. The electrolyte 6 comes into contact with the dielectric layer (oxide film 3a) formed on the anode foil 3 and the cathode foil 4, thereby functioning as a true cathode that essentially serves as the counter electrode to the anode foil 3 in place of the cathode foil 4. The separator 5 allows the components of the electrolyte 6 to pass freely between the anode foil 3 side and the cathode foil 4 side, but depending on the configuration and material of the separator 5, the electrolyte 6 may also be impregnated within the separator 5.

[0032] The electrolytic solution 6 contains an electrolyte and a solvent that dissolves or disperses the electrolyte.

[0033] The electrolyte may be an organic acid, an inorganic acid, a composite compound of an organic acid and an inorganic acid, a derivative thereof, or a salt thereof. One of these may be used alone, or two or more may be mixed and used. For example, an organic acid and an inorganic acid may be used together.

[0034] 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.

[0035] 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.

[0036] The solvent may be a composition consisting of one or more organic solvents, a composition consisting of one or more organic solvents and water, or a composition consisting of water only.

[0037] 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.

[0038] The electrolyte solution 6 according to this embodiment further contains a 4-nitropyridine N-oxide compound (NpNO compound), which is a nitro compound. The 4-nitropyridine N-oxide compound here is a compound containing 4-nitropyridine N-oxide (C5H4N2O3) or a derivative thereof, as shown in the following chemical formula (1):

[0039] [ka]

[0040] In chemical formula (1), X 1 , X 2 , X 3 and X 4 each independently represents a hydrogen atom or an atom other than hydrogen or a group, and may be the same or different.

[0041] In a basic embodiment, 4-nitropyridine N-oxide is used, and as shown in the above chemical formula (1), the hydrogen atom X of 4-nitropyridine N-oxide is 1 -X 4 One or more of the hydrogen atoms of 4-nitropyridine N-oxide may be substituted with other atoms or groups. Examples of such derivatives include compounds in which one or more of the hydrogen atoms of 4-nitropyridine N-oxide are substituted with alkyl groups (represented by chemical formula (1), X 1 , X 2 , X 3 and X 4 Each of the groups independently represents a hydrogen atom or an alkyl group, and each group may be the same or different. Specifically, for example, 3-methyl-4-nitropyridine N-oxide (C6H6N2O3) (represented by the chemical formula (1), X 1 , X 3 and X 4 is a hydrogen atom (H), and X 2 NpNO compounds in which the aryl group is a methyl group (-CH3) can be used.

[0042] As a nitro compound having a nitro group, the NpNO compound has the effect of suppressing the generation of hydrogen gas within the electrolytic capacitor 1, thereby suppressing an increase in the internal pressure of the electrolytic capacitor 1. As a result, it is possible to prevent external swelling, leakage, and even the activation (opening) of the explosion-proof valve 8 that accompany an increase in internal pressure. Since the generation of hydrogen within the electrolytic capacitor 1 is more likely to become a problem the higher the water content in the electrolyte 6, blending an NpNO compound into the electrolyte 6, particularly one that uses a solvent containing water, effectively suppresses the generation of hydrogen gas and suppresses an increase in internal pressure.

[0043] Furthermore, NpNO compounds have superior solubility in polar solvents such as ethylene glycol compared to conventional substances such as nitroacetophenone and nitrobenzoic acid. This is presumably because NpNO compounds have a pyridine ring and an oxygen coordinate bond, which gives them relatively high polarity and excellent solubility in polar solvents. In fact, the inventors investigated the solubility of a target substance in ethylene glycol, one of the major solvents, by heating and dissolving it in a solvent, leaving it at room temperature for one day, and then visually evaluating the presence or absence of crystals. They found that 4-nitropyridine N-oxide could be dissolved in a concentration (mass %) more than twice that of 3'-nitroacetophenone and nitrobenzoic acid.

[0044] Furthermore, the NpNO compound hardly causes a decrease in the withstand voltage of the electrolytic capacitor 1, which occurs when conventional nitro compounds are blended at relatively high concentrations or after high-temperature loading. In other words, the NpNO compound clearly suppresses the decrease in withstand voltage compared to conventional substances. According to the examples described below, when an electrolyte solution 6 containing 4-nitropyridine N-oxide was used, the electrolytic capacitor 1 operated normally even after applying a constant voltage at a high temperature of 125°C for 500 hours without short circuits due to dielectric breakdown or other causes that would otherwise occur if the withstand voltage decreased. In fact, the withstand voltage (spark voltage) measured using a foil with an oxide film 3a formed on the electrolyte solution 6 after high-temperature loading at 125°C showed almost no decrease compared to the value before high-temperature loading, both at 0.03 mol / L, which is within the conventional normal concentration range, and at 0.12 mol / L, which exceeds this range. In another example, it was confirmed that the withstand voltage did not decrease even when 4-nitropyridine N-oxide was blended at an even higher concentration (0.18 mol / L). Thus, stable and favorable results were obtained regardless of the amount (concentration) of the NpNO compound. Therefore, the amount (concentration) of the NpNO compound in the electrolyte 6 can be set to, for example, 0.03 to 0.30 mol / L, 0.06 to 0.30 mol / L, 0.12 to 0.30 mol / L, 0.18 to 0.30 mol / L, etc., which is increased up to the upper limit of solubility in ethylene glycol, approximately 0.3 mol / L. Furthermore, the NpNO compound can be blended at an even higher concentration in a solvent such as water, in which it is more easily soluble.

[0045] In addition to the NpNO compound, the electrolyte 6 may contain known functional substances that can be incorporated into the electrolyte 6 of the electrolytic capacitor 1. The functional substances referred to here refer to substances that have some useful function in the electrolytic capacitor 1, such as the ability to repair the oxide film 3a, withstand pressure, withstand high temperatures, withstand low temperatures, or absorb hydrogen gas. Some functional substances can function as electrolytes (solutes), but when such substances are incorporated as functional substances, they are incorporated primarily for the purpose of achieving a useful function other than their function as an electrolyte (solute). Examples of such functional substances include phosphate compounds, chelate compounds, specific polymers, and carbohydrates.

[0046] [Manufacturing method of electrolytic capacitors] Next, this specification will explain a method for manufacturing the electrolytic capacitor 1 according to this embodiment. Figure 4 is a flowchart showing an example of the method for manufacturing the electrolytic capacitor 1 according to this embodiment.

[0047] As shown in Figure 4, the electrolytic capacitor 1 according to this embodiment is manufactured by, for example, performing a capacitor element forming step S01, an electrolyte solution introducing step S02, a sealing step S03, and an aging step S04. Of these steps, the operation of preparing an electrolyte solution 6 of a specific composition in the electrolyte solution introducing step S02 is a novel and advantageous feature common to all electrolytic capacitors according to the present invention. Meanwhile, for the other operations, in addition to the methods exemplified here, known manufacturing processes and operations can be used for this embodiment and types other than this embodiment, such as hybrid types, terminal configurations other than lead-type, and element configurations other than wound types.

[0048] In the capacitor element formation step S01, the anode foil 3 is subjected to a surface expansion treatment and a chemical conversion treatment in advance. For example, in the surface expansion treatment, a DC or AC voltage is applied to a raw metal foil such as an aluminum foil in an etching solution (a strongly acidic aqueous solution such as hydrochloric acid). This unevenness is created on the surface of the metal foil, thereby increasing the specific surface area. Subsequently, in the chemical conversion treatment, a DC voltage is applied to the etched foil in a chemical conversion solution (a weakly acidic aqueous solution such as ammonium borate). This forms an oxide film 3a as a dielectric layer on the surface of the etched foil. The cathode foil 4 is also subjected to a surface expansion treatment in advance, and, if necessary, a chemical conversion treatment or other treatments.

[0049] Furthermore, an anode lead terminal 10 and a cathode lead terminal 11 are connected to the anode foil 3 and the cathode foil 4 by stitch connection, cold pressure welding, etc. The connection of the lead terminals 10, 11 can be performed before or after the chemical conversion treatment.

[0050] 2, the anode foil 3 and the cathode foil 4 are stacked with the separator 5 sandwiched between them and wound into a cylindrical shape, and a holding material (not shown) such as tape is attached to hold the wound state, thereby forming the capacitor element 2.

[0051] In the case of the hybrid type, chemical conversion treatment may be performed again at any time after the formation of the capacitor element 2 to repair the missing oxide film 3a. This re-chemical conversion treatment is an optional treatment, and for example, performing re-chemical conversion treatment on the present embodiment is not prohibited, and conversely, not performing re-chemical conversion treatment on the hybrid type is not prohibited.

[0052] Next, in the electrolyte introduction step S02, the electrolyte solution 6 is prepared and introduced into the capacitor element 2 to impregnate the electrolyte solution 6. The preparation of the electrolyte solution 6 can be performed at any time before the introduction of the electrolyte solution 6. The composition of the electrolyte solution 6 is as already described for the electrolyte solution 6 according to this embodiment. That is, a 4-nitropyridine N-oxide compound (NpNO compound) is further blended into the basic structure in which an electrolyte is dissolved or dispersed in a solvent. As a specific composition, for example, the NpNO compound can be blended in the electrolyte solution 6 at 0.03 to 0.30 mol / L. Furthermore, for example, the NpNO compound can be blended as 4-nitropyridine N-oxide or a derivative thereof. Furthermore, the electrolyte solution 6 may optionally be blended with a known functional substance.

[0053] The electrolytic solution 6 is introduced by immersing the capacitor element 2 in the electrolytic solution 6 for a predetermined period of time. As described above, the NpNO compound and other functional substances may be blended in the preparation stage of the electrolytic solution 6. Alternatively, before or after introducing the electrolytic solution 6 into the capacitor element 2, the capacitor element 2 may be immersed in a liquid containing the NpNO compound and other functional substances, separate from the electrolytic solution 6, to introduce the functional substances into the capacitor element 2. The introduction of the electrolytic solution 6 and the functional substances may be carried out under controlled pressure as necessary. After introduction, excess liquid may be removed using a centrifuge as necessary.

[0054] Next, in the sealing step S03, the capacitor element 2 is housed in a cylindrical outer case 7 with a bottom, and a sealing body 9 is attached to the opening 7a of the outer case 7. The lead terminals 10 and 11 extending from the capacitor element 2 are passed through the through-holes in the sealing body 9 and are then extended to the outside of the electrolytic capacitor 1. The opening 7a of the outer case 7 is crimped in a direction perpendicular to the direction in which the sealing body 9 is attached (the Z direction in the drawing). This forms the first crimped portion 7c shown in FIG. 1. The open end 7b of the outer case 7 is crimped in a direction parallel to the direction in which the sealing body 9 is attached (the Z direction in the drawing). This forms the second crimped portion 7d shown in FIG. 1. As a result, the outer case 7 is sealed by the sealing body 9 and is hermetically sealed by the two crimped portions 7c and 7d. In this way, the electrolytic capacitor 1 is completed. For packaging, the outer case 7 is further covered with an outer sleeve made of an insulating material such as vinyl chloride. The coating can be performed before or after the aging step S04 described below.

[0055] Finally, in the aging step S04, a DC voltage is applied to the formed electrolytic capacitor 1 under high-temperature conditions. This activates the oxide film 3a repair function of specific components in the electrolyte 6, repairing areas where the oxide film 3a peeled off during the manufacturing process or relatively thin areas of the oxide film 3a, thereby suppressing leakage current and stabilizing performance. The aging process also has a debugging effect, such as eliminating unexpected initial defects. [Example]

[0056] The basic composition was prepared by dissolving a predetermined organic acid as an electrolyte and a predetermined functional substance as an additive in ethylene glycol and water as the solvent. The nitro compounds shown in Table 1 were added to the basic composition so that the concentrations in the electrolyte solution after addition were as shown in Table 1. The electrolyte solutions of the examples and comparative examples were prepared by adding the nitro compounds shown in Table 1. Tests were conducted using the electrolyte solutions of each example. However, for Comparative Example 3, the entire amount of the nitro compound, 3'-nitroacetophenone, could not be dissolved in the solvent, and an electrolyte solution could not be prepared. Therefore, all of the tests described below could not be conducted for Comparative Example 3. The basic composition without the addition of a nitro compound was approximately 65% ​​by mass of ethylene glycol, approximately 5% by mass of water, approximately 10% by mass of electrolyte, and 20% by mass of other additives. The electrolyte solution of this basic composition was used in Test 3, described below as Reference Example 1.

[0057] [Table 1]

[0058] [Test 1] An aluminum electrolytic capacitor with a rated voltage of 450 V was manufactured using a conventional method in accordance with the present embodiment described above. Etched aluminum foil was used for the anode and cathode foils, and the anode foil was subjected to a chemical conversion treatment to form an oxide film. The anode and cathode foils, each with a lead terminal connected, were stacked and wound with a separator sandwiched between them to form a capacitor element. The electrolyte solution for each example was then introduced into the capacitor element, which was then housed in an outer case and sealed to produce an electrolytic capacitor. The capacitor was then subjected to a predetermined aging treatment.

[0059] A DC voltage of 450V was applied to each electrolytic capacitor at a temperature of 105°C, and the time until the explosion-proof valve operated (opened) was measured. Ten units were tested for each example. The results are shown in Table 2.

[0060] [Test 2] Furthermore, a DC voltage of 450V was applied to each electrolytic capacitor for 500 hours at a temperature of 125°C, and the occurrence of short circuits was checked. Ten units were tested for each example. The results are shown in Table 2.

[0061] [Test 3] In addition, anode foil pieces (10 × 20 mm) were prepared by etching and chemically treating aluminum foil pieces to form an oxide film, and cathode foil pieces, which were plain aluminum foil pieces of the same size. The anode foil piece and the cathode foil piece were immersed in the electrolyte of each example by 2 cm 2 After immersion, a load was applied by passing a constant current while controlling the temperature of the electrolyte at 85°C, and the voltage behavior (initial voltage behavior) was measured.

[0062] In addition, the medium bottle containing each electrolyte solution was kept at 125°C for 500 hours in a forced convection incubator (PH-202, manufactured by Espec Corporation). Then, using the electrolyte solution of each example after high-temperature storage, voltage behavior (voltage behavior after high-temperature storage) was measured at 85°C while applying a constant current, as described above. One test piece was used for each example. Figure 5A shows the initial voltage behavior of Example 1, Comparative Examples 1 and 2, and Reference Example 1. Figure 5B shows the voltage behavior after high-temperature storage of Example 1, Comparative Examples 1 and 2, and Reference Example 1. Figure 6A shows the initial voltage behavior of Example 2, Comparative Example 4, and Reference Example 1. Figure 6B shows the voltage behavior after high-temperature storage of Example 2, Comparative Example 4, and Reference Example 1. Reference Example 1 shown in Figures 6A and 6B is a reprint of Reference Example 1 shown in Figures 5A and 5B. In the graphs of Figures 5A and 5B, the time range (minimum to maximum) on the horizontal axis and the voltage range (minimum to maximum) on the vertical axis are the same. In addition, the graphs in Figures 6A and 6B have the same time range (minimum to maximum) on the horizontal axis and the same voltage range (minimum to maximum) on the vertical axis. The voltage range on the vertical axis is the same in all of Figures 5A, 5B, 6A, and 6B. The same voltage value α is indicated by a dashed line in all of the figures as a reference value for comparison. In all of the figures, a constant is added to the time value to shift the plots in each example except for Reference Example 1, so that the voltage behaviors of each example do not overlap. In the voltage behavior of each example shown in each figure, the voltage at the time when a disturbance in the rising curve due to spark or scintillation was first observed was defined as the spark voltage. A higher spark voltage indicates a higher withstand voltage.

[0063] [Table 2]

[0064] As shown in Table 2, in Example 1 and Comparative Examples 1 and 2, in which the nitro compound in the reagent was added at 0.03 mol / L, within the conventional range, all reagents were dissolved in a solvent to prepare an electrolyte. Furthermore, in a test (Test 1) in which the rated voltage was applied at a high temperature of 105°C, the explosion-proof valve of all test devices activated within 2000 to 2500 hours for all examples in which any reagent was added. When voltage was applied under the same conditions as in Test 1 to electrolytic capacitors with the same specifications as the test devices using electrolytes with the same basic composition but without nitro compounds, most of the devices activated the explosion-proof valve within 500 to 1000 hours. In comparison, in Test 1, all examples in which any reagent was added demonstrated the effect of suppressing hydrogen gas generation in the electrolytic capacitor, resulting in an extended explosion-proof valve activation time and an extended lifespan for the electrolytic capacitor. There was no difference in the explosion-proof valve activation time for each example in the categories listed in Table 2, indicating that the hydrogen gas absorption performance of each reagent was comparable.

[0065] On the other hand, in an accelerated test (Test 2) in which a constant voltage was applied for 500 hours at an even higher temperature of 125°C, short circuits occurred in multiple devices due to dielectric breakdown caused by a decrease in withstand voltage in Comparative Examples 1 and 2, in which 3'-nitroacetophenone or 4-nitrobenzyl alcohol was added. In contrast, in Example 1, in which 4-nitropyridine N-oxide was added, no short circuits occurred in any of the devices, and the electrolytic capacitors operated without any problems.

[0066] In Test 3, in which the withstand voltages of the electrolytes of each example were measured after a high-temperature load of 125°C, the same as in Test 2, a decrease in withstand voltage was observed after high-temperature load compared to the initial value, as shown in Figures 5A and 5B. In contrast, Example 1, which added 4-nitropyridine N-oxide, did not show a decrease in withstand voltage after high-temperature load, and instead tended to increase compared to the initial value. As shown in Figure 5A, the initial withstand voltages of each example, including Reference Example 1, which did not contain any nitro compound, were similar. Therefore, comparing the graphs of each example after high-temperature storage in Figure 5B, it is clear that after high-temperature load, Reference Example 1 showed almost no change in withstand voltage, Comparative Examples 1 and 2 showed a decrease in withstand voltage, and Example 1 showed no decrease in withstand voltage at all.

[0067] Next, in Example 2 and Comparative Examples 3 and 4, in which 0.12 mol / L of nitro compound was added as a reagent, exceeding the conventional normal amount range, as mentioned above, the entire amount of 3'-nitroacetophenone in Comparative Example 3 could not be dissolved in the solvent, and an electrolyte could not be prepared. On the other hand, for 4-nitrobenzyl alcohol (Comparative Example 4) and 4-nitropyridine N-oxide (Example 2), the entire amount of the reagent was dissolved in the solvent to prepare an electrolyte. Furthermore, in a test (Test 1) in which the rated voltage was applied at a high temperature of 105°C, the explosion-proof valves of all test devices operated within 6,000 to 6,500 hours for each reagent added. That is, in these examples, the effect of suppressing hydrogen gas generation in the electrolytic capacitor improved as the amount of reagent increased, resulting in a further extension of the explosion-proof valve operation time and a further extension of the life of the electrolytic capacitor.

[0068] On the other hand, in an accelerated test (Test 2) in which a constant voltage was applied for 500 hours at an even higher temperature of 125°C, the incidence of short circuits after exposure to high temperature in Comparative Example 4, in which 4-nitrobenzyl alcohol was added, increased by twice as much as in Comparative Example 2, in which the same reagent was added in a normal amount. While the initial withstand voltages of Comparative Example 2 shown in Fig. 5A and Comparative Example 4 shown in Fig. 6A are almost the same, a comparison of the withstand voltages after exposure to high temperature in each example shown in Fig. 5B and Fig. 6B reveals that the decrease in withstand voltage in Comparative Example 4 was significant, and that the decrease in withstand voltage increased further as the amount of reagent increased.

[0069] In Example 2, in which 4-nitropyridine N-oxide was added, no short circuits occurred in any of the devices, and the electrolytic capacitors operated without problems, even when the amount of reagent was increased, as shown in Table 2, compared to Example 1. Looking at the actual withstand voltage, as shown in Figures 6A and 6B, there was almost no change after high-temperature storage compared to the initial value, and almost no decrease in withstand voltage was observed even after high-temperature loading. Therefore, it can be seen that increasing the amount (addition concentration) of 4-nitropyridine N-oxide does not cause much decrease in withstand voltage, and almost no malfunction occurs.

[0070] [Test 4] Furthermore, for electrolytes prepared from the basic composition (Reference Example 1) containing no nitro compound, 4-nitropyridine N-oxide (Example 3) or 4-nitrophenol (Comparative Example 5) was added so that the electrolyte concentration after addition was 0.18 mol / L. A constant current was applied while controlling the temperature at 85°C, and a load was applied, and the voltage behavior (initial voltage behavior) was measured in the same manner as in Test 3. The results are shown in Figure 7. Reference Example 1 shown in Figure 7 is a reprint of Reference Example 1 shown in Figure 5A. The voltage range (from minimum to maximum) on the vertical axis in Figure 7 coincides with that shown in Figures 5A-6B. The voltage value α shown in Figures 5A-6B is also shown by a dashed line in Figure 7. In Figure 7, in each example except Reference Example 1, a constant was added to the time value to shift the plots, thereby preventing overlapping of the voltage behaviors of each example.

[0071] As shown in FIG. 7, Comparative Example 5, in which 4-nitrophenol was added, had a lower withstand voltage than Reference Example 1, in which no 4-nitrophenol was added, but Example 3, in which 4-nitropyridine N-oxide was added, had almost the same withstand voltage as Reference Example 1.

[0072] From the above, it was confirmed that nitro compounds have the effect of suppressing hydrogen gas generation in electrolytic capacitors, and that this effect improves as the amount of nitro compounds is increased. On the other hand, it was revealed that conventional substances, such as nitrobenzene compounds, reduce the withstand voltage of electrolytic capacitors, particularly after high-temperature loading (Comparative Examples 1 and 2), and that the decrease in withstand voltage also increases with increasing the amount of nitro compounds (Comparative Example 4). Furthermore, some conventional substances reduce the withstand voltage at high concentrations even without high-temperature loading (Comparative Example 5), and some have insufficient solubility in polar solvents such as ethylene glycol, making it difficult to increase the amount of nitro compounds (Comparative Example 3). In contrast, the 4-nitropyridine N-oxide compound of the present invention has excellent solubility in polar solvents such as ethylene glycol, allowing for sufficient increase in amount, and does not reduce the withstand voltage even at high concentrations. Furthermore, the 4-nitropyridine N-oxide compound does not reduce the withstand voltage even after high-temperature loading, and maintains approximately the same effect of suppressing withstand voltage reduction regardless of the amount added and the temperature.

[0073] Therefore, by incorporating a 4-nitropyridine N-oxide compound into the electrolyte at a high concentration, hydrogen gas generation is significantly suppressed, and the electrolytic capacitor can operate stably at temperatures including high temperatures without significant reduction in withstand voltage. The amount (concentration) of the 4-nitropyridine N-oxide compound in the electrolyte can be, for example, 0.03 to 0.12 mol / L, 0.03 to 0.18 mol / L, or 0.03 to 0.20 mol / L, which correspond to the concentration ranges in the examples. Furthermore, as other examples, concentrations higher than the conventional range of 0.03 to 0.06 mol / L, such as 0.06 to 0.12 mol / L, 0.06 to 0.18 mol / L, 0.06 to 0.20 mol / L, 0.12 to 0.18 mol / L, or 0.12 to 0.20 mol / L, can also be used. In addition, the concentration can be increased to approximately 0.3 mol / L, which is the upper limit of solubility in ethylene glycol, and can be set to 0.03 to 0.30 mol / L, 0.06 to 0.30 mol / L, 0.12 to 0.30 mol / L, 0.18 to 0.30 mol / L, etc., and can also be blended at an even higher concentration in a solvent such as water in which it is more easily soluble.

[0074] After the electrolyte is impregnated into the capacitor element, some of the NpNO compounds are adsorbed onto the electrode foil or consumed during the aging process, resulting in a slightly lower content (concentration) in the electrolyte of the electrolytic capacitor compared to the blending amount (concentration). Furthermore, some NpNO compounds may be lost during sample centrifugation, a common analytical technique in this field. It is difficult to uniformly specify the content (concentration) corresponding to the blending amount (concentration), as it depends on the product specifications. However, for relatively high blending concentrations, such as 0.12 mol / L or 0.18 mol / L, the content (concentration) in the electrolyte of the electrolytic capacitor is typically 0.03 mol / L or higher. On the other hand, for relatively low blending concentrations, such as 0.03 mol / L, the content (concentration) can be as low as 0.01 mol / L or even 0.001 mol / L. From this, the content (concentration) of the NpNO compound according to the present invention in the electrolyte of the electrolytic capacitor is, for example, 0.001 to 0.12 mol / L, 0.001 to 0.18 mol / L, 0.001 to 0.20 mol / L, 0.001 to 0.30 mol / L, 0.01 to 0.12 mol / L, 0.01 to 0.18 mol / L, 0.01 to 0.20 mol / L, 0.01 to 0.30 mol / L, 0. 03~0.12mol / L, 0.03~0.18mol / L, 0.03~0.20mol / L, 0.03~0.30mol / L, 0.06~0.12mol / L, 0.06~0.18mol / L, 0.06 It can be defined as ~0.20mol / L, 0.06~0.30mol / L, 0.12~0.18mol / L, 0.12~0.20mol / L, 0.12~0.30mol / L, 0.18~0.30mol / L, etc. [Explanation of symbols]

[0075] 1 electrolytic capacitor 2 Capacitor elements 3 Anode foil 3a Oxide film 4 cathode foil 5 Separator 6 Electrolyte 7. Outer case 7a opening 7b Open end 7c First crimping part 7d Second crimping part 8 Explosion-proof valve 9 Sealing body 10 Anode lead terminal 11 Cathode lead terminal S01 Capacitor element formation process S02 Electrolyte introduction process S03 Sealing process S04 Aging process

Claims

1. 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; an electrolyte impregnated in the capacitor element; The electrolyte solution contains a 4-nitropyridine N-oxide compound. An electrolytic capacitor characterized by:

2. The 4-nitropyridine N-oxide compound is 4-nitropyridine N-oxide.

2. The electrolytic capacitor according to claim 1,

3. The solvent of the electrolytic solution contains water.

3. The electrolytic capacitor according to claim 1 or 2, wherein:

4. Adding a 4-nitropyridine N-oxide compound to the electrolyte A method for manufacturing an electrolytic capacitor, comprising:

5. The 4-nitropyridine N-oxide compound is 4-nitropyridine N-oxide.

5. The method for producing an electrolytic capacitor according to claim 4,

6. The solvent for the electrolyte solution is a solvent containing water.

6. The method for manufacturing an electrolytic capacitor according to claim 4 or 5,

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