Electrolytic capacitors

Abstract

The present invention addresses the problem of providing an electrolytic capacitor with which an etching treatment of an electrode material is not required and with which it is possible to achieve higher electrostatic capacitance than conventional electrolytic capacitors using electrode foils having surface areas increased only by etching. This electrolytic capacitor (10), as a solution, comprises: a capacitor element (1) having a positive electrode foil (20), a negative electrode foil (23), and separators (24), (25) interposed between the positive electrode foil (20) and the negative electrode foil (23); and an electrolyte into which the capacitor element (1) is impregnated, wherein the positive electrode foil (20) or the negative electrode foil (23) is characterized by having a sintered body formed by powder sintered grains composed of at least one among aluminum and an aluminum alloy.

Description

Technical Field

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

Background Art

[0002] Electrolytic capacitors have the characteristics of being small-sized, having a large capacitance, and being inexpensive, and are widely used as one of the important components in electronic devices, electrical devices, vehicle-mounted devices, etc.

[0003] Conventional electrolytic capacitors, for example, the most widely used aluminum electrolytic capacitors, can be manufactured by chemically or electrochemically etching high-purity aluminum foil to increase its surface area, and then forming an anode foil with a film formed by anodic oxidation on the surface of the aluminum foil, and using a cathode foil with an etched surface. Next, the obtained anode foil and cathode foil are arranged facing each other, and further, a separator is interposed between these foils to form an element having a wound structure, and this structure element is impregnated with an electrolytic solution. The element after impregnation with the electrolytic solution is housed in a case and sealed with an elastic sealing body to complete the electrolytic capacitor.

[0004] Increasing the capacitance of electrolytic capacitors is an important market requirement directly related to the miniaturization of mounted devices, and attempts have been made to increase the capacitance by expanding the etching ratio. However, there is a theoretical limit to the increase in surface area by etching, and it is becoming increasingly difficult to meet the ever-increasing requirement for higher capacitance. Also, in order to reduce the environmental load caused by hydrochloric acid containing sulfuric acid, phosphoric acid, nitric acid, etc. used in the etching process, a method for increasing the surface area to replace the etched foil is desired.

[0005] Here, as a method for increasing the surface area to replace the etched foil, a capacitor using a metal sintered body as an anode has been proposed conventionally (Patent Document 1: Japanese Utility Model Laid-Open No. 59-140430).

[0006] However, such a capacitor has a drawback that since the distance from the anode to the cathode current collector is long, the resistance component through the electrolytic solution becomes large, and the capacitance at high frequencies decreases.

[0007] Another method for increasing surface area has been proposed, which involves using an aluminum electrolytic capacitor characterized by the use of foil on which fine aluminum powder is attached to the surface of the electrode foil (Patent Document 2: Japanese Patent Application Publication No. 2-267916, and Patent Document 3: Japanese Patent Application Publication No. 2006-108159).

[0008] However, the electrode foils disclosed in these documents have drawbacks: because the particle size of the aluminum powder is small, there is a risk that the gaps between the sintered grains will be filled when forming the anodic oxide film, leading to a decrease in capacitance; and when using an electrolyte for medium- and high-voltage capacitors with relatively high viscosity and resistivity, the capacitance at high frequencies decreases. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Utility Model Publication No. 59-140430 [Patent Document 2] Japanese Patent Application Publication No. 2-267916 [Patent Document 3] Japanese Patent Publication No. 2006-108159 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] This invention has been made in view of the above-mentioned demand for higher capacitance and reduction of environmental impact, and aims to provide an electrolytic capacitor that does not require etching of the electrode material and can achieve higher capacitance than conventional electrolytic capacitors that use electrode foil whose surface area is increased by etching alone. [Means for solving the problem]

[0011] The electrolytic capacitor according to the present invention comprises an anode foil, a cathode foil, a capacitor element having a separator interposed between the anode foil and the cathode foil, and an electrolyte impregnated in the capacitor element, wherein the anode foil or the cathode foil has a sintered body composed of sintered particles of powder made from at least one of aluminum and an aluminum alloy. Furthermore, the resistivity of the electrolyte is 1500 Ω·cm or less, and the average particle size (D50) of the powder or sintered grains is 6 μm or less. It is characterized by the following.

[0012] The anode foil or the cathode foil preferably consists of the sintered body and a substrate that supports the sintered body. 。

[0013] Furthermore, the electrolyte preferably contains a solvent consisting of an organic solvent, or a solvent consisting of a mixture of water and an organic solvent, and at least one electrolyte selected from the group consisting of an organic acid or organic acid salt, an inorganic acid or inorganic acid salt, and a mixture of an organic acid or organic acid salt and an inorganic acid or inorganic acid salt. [Effects of the Invention]

[0014] According to the electrolytic capacitor of the present invention, the electrode foil has a surface area greater than the pit area of ​​conventional etched foil, thus enabling the realization of a large capacitance. Furthermore, since etching of the electrode foil is not always necessary, the environmental impact can be reduced. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of an electrolytic capacitor according to this embodiment. [Figure 2] Figure 2 is an explanatory diagram illustrating an example of a capacitor element according to this embodiment. [Figure 3] Figure 3 is a graph showing the leakage current values ​​of the electrolytic capacitors in Examples 13 and 14 during high-temperature load testing. [Modes for carrying out the invention]

[0016] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to only these embodiments. FIG. 1 is a cross-sectional view showing an outline of the overall configuration of the electrolytic capacitor 10 according to the present embodiment, and FIG. 2 is an explanatory view of the capacitor element 1. The electrolytic capacitor 10 according to the present embodiment has a capacitor element 1 disposed inside a bottomed cylindrical exterior case 4 formed of a metal such as aluminum. The opening of the exterior case 4 is sealed with a sealing body 3, and the sealing body 3 is fixed by caulking the opening edge (crimp 14).

[0017] The capacitor element 1 according to the present embodiment is a wound capacitor element 1 configured by winding an anode foil 20 having a sintered body 22 of aluminum powder formed on the surface of a core material (base material) 21, a cathode foil 23, a first separator 24 disposed between the anode foil 20 and the cathode foil 23, and a second separator 25. After being impregnated with an electrolytic solution, it is sealed inside the exterior case 4. Reference numeral 2 denotes a lead wire 2 connected to each of the anode foil 20 and the cathode foil 23. Each lead wire 2 has a lead tab 5 and a terminal 6, which are connection portions with the anode foil 20 or the cathode foil 23. However, the form of the electrolytic capacitor 10 according to the present invention is not limited. In addition to the wound type shown in FIG. 1, for example, a multilayer type, a coin type, etc. may also be used. Also, the form of the terminal portion (the entire portion connected to the electrode foils 20 and 23 and exposed outside the electrolytic capacitor 10) is not limited. In addition to the lead form shown in FIG. 1, for example, a substrate self-supporting form, a screw terminal form, etc. may also be used. Therefore, the shape, number, and connection form of the members constituting the terminal portion are not limited either.

[0018] As an example, in a substrate - self - standing electrolytic capacitor (not shown) where the terminal 6 stands on a substrate composed of, for example, a two - layer sealing body 3, the lead tab 5, which is the connection part to the electrode foils 20 and 23, may be connected to the respective electrode foils 20 and 23 at a plurality of locations. This configuration may be understood as a configuration in which a plurality of lead tabs 5 are provided, or may be understood as a configuration in which the lead tab 5 branches at the end. According to this configuration, compared with a configuration in which one lead tab 5 is connected to each of the electrode foils 20 and 23 (one location each), the metal resistance and inductance of each of the electrode foils 20 and 23 can be reduced, achieving a lower impedance of the electrolytic capacitor and an improvement in the allowable ripple current. Also, the lead tabs 5 connected to a plurality of locations of the electrode foils 20 and 23 gather and are fixed to the terminal 6 and the sealing body 3, thereby improving the stability of the capacitor element 1 and enhancing the vibration resistance of the electrolytic capacitor.

[0019] Also, the sintered body 22 of aluminum powder according to the present embodiment is formed on both sides or one side of the base material 21. However, the base material 21 does not necessarily have to be included, and the electrode foil (anode foil 20) may be composed only of the sintered body 22 of aluminum powder. Thus, regardless of the presence or absence of the base material 21, the electrode foil (here, the anode foil 20) at least whose surface is formed of the sintered body 22 is referred to as a "sintered body foil" in the present application. In the electrolytic capacitor 10 according to the present embodiment, the anode foil 20 is composed of a sintered body foil and the cathode foil 23 is composed of an etched foil. However, in the electrolytic capacitor 10 according to the present invention, at least one of the two electrode foils (anode foil 20 and cathode foil 23), either the anode foil 20 or the cathode foil 23, may be composed of a sintered body foil. For example, both the anode foil 20 and the cathode foil 23 may be composed of sintered body foils.

[0020] According to this embodiment, the electrode foil (anodic foil 20) has a surface area greater than the pit area of ​​conventional etched foil, thus enabling a large capacitance. Furthermore, compared to conventionally proposed aluminum sintered body capacitors (e.g., Patent Document 1), this embodiment has a structure in which the sintered body 22 is wound in a foil shape, so the distance between the anode and cathode current collector is reduced, which reduces the resistance component through the electrolyte and results in superior capacitance at high frequencies (around 10 kHz). Moreover, this embodiment also offers superior capacitance at high frequencies (around 10 kHz) compared to electrolytic capacitors using foil with fine aluminum powder attached (e.g., Patent Documents 2 or 3).

[0021] Here, the sintered powder body 22 refers to a sintered body composed of sintered powder particles. These sintered particles refer to sintered particles (referred to as "sintered particles" in this application) that have been sintered from powder particles (referred to as "powder particles" in this application). The sintered aluminum powder body 22 according to this embodiment is composed of sintered grains of powder made from at least one of aluminum and an aluminum alloy. The aluminum in the aluminum and aluminum alloys preferably has an aluminum purity of 99.8% by weight or higher, from the viewpoint of preventing defects caused by impurities. In particular, to suppress the increase in leakage current under high-temperature loads, an aluminum purity of 99.99% by weight or higher is more preferable. In the case of aluminum alloys, for example, alloys containing one or more elements such as silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), boron (B), and zirconium (Zr) can be used. In this case, the content of each of these elements is preferably 100 ppm by weight or less, and particularly preferably 50 ppm by weight or less.

[0022] The sintered body 22 is formed by sintering sintered particles of at least one of aluminum and aluminum alloy powders while maintaining voids between them. That is, each sintered particle is connected while maintaining voids, and it has a three-dimensional network structure. By using such a porous sintered body, it is possible to obtain the desired capacitance without etching. The porosity of the sintered body 22 can be appropriately set within a range of 10% or more, depending on the desired capacitance, etc. Furthermore, the porosity can be controlled by, for example, the particle size of the starting material aluminum or aluminum alloy powder, the composition of the paste composition containing the powder (resin binder), etc.

[0023] The shape of the sintered body 22 is not particularly limited, but in the case of a configuration including the base material 21, it is generally preferable that the average thickness of one side is 5 μm or more and 100 μm or less, and particularly preferably 5 μm or more and 60 μm or less, in the form of a foil. The average thickness can be calculated by observing the cross-section of the sintered foil with a scanning electron microscope (SEM) or the like, measuring the thickness at any 10 points, and averaging them.

[0024] Furthermore, the average particle size of the sintered grains is preferably 80 μm or less. If the average particle size is greater than 80 μm, the desired capacitance may not be obtained. The average particle diameter of the sintered grains is preferably 1 μm or larger. If the average particle diameter is smaller than 1 μm, the desired dielectric strength may not be obtained. While a smaller average particle diameter is advantageous for increasing the surface area, if the average particle diameter is made too small, the gaps between the sintered grains may be filled when forming the anodic oxide film as needed, potentially reducing the capacitance. From the viewpoint of preventing such a reduction in capacitance, it is more preferable to have an average particle diameter of 2.5 μm or larger. In particular, from the viewpoint of improving capacitance characteristics around 10 kHz, it is preferable that the average particle diameter is between 2.5 μm and 6 μm.

[0025] The base material 21 is not particularly limited, but aluminum foil can be suitably used. The base material 21 can be used without etching, but etching may be performed as needed. The aluminum foil used as the base material 21 can be aluminum or an aluminum alloy having the same composition as the aluminum or aluminum alloy powder described above. In particular, to suppress the increase in leakage current under high-temperature loads, it is more preferable that the aluminum purity be 99.99% by weight or higher. The thickness of the aluminum foil used as the base material 21 is not particularly limited, but is preferably within the range of 5 μm to 100 μm, and particularly within the range of 5 μm to 60 μm.

[0026] The method for forming a sintered body 22 on a substrate 21 to create an electrode foil 20 (23) is as follows: 1. A first step of forming a film on a substrate 21 consisting of a composition containing at least one type of aluminum and aluminum alloy powder, and 2. A second step in which the coating is sintered at a temperature of 560°C to 660°C. Includes.

[0027] 1st process In the first step, a coating is formed on the substrate 21, consisting of a composition containing at least one type of aluminum and aluminum alloy powder. The aforementioned compositions and components can be used for aluminum or aluminum alloys. The particle shape of the aforementioned powder, i.e., powder granules, is not particularly limited, and any of the following powder granules can be suitably used: spherical, irregularly shaped, flaky, etc., but spherical powder granules are particularly suitably used. The average particle size of the powder, i.e., the powder particles, is preferably 80 μm or less. If the average particle size is greater than 80 μm, the desired capacitance may not be obtained. The average particle size of the aforementioned powder, i.e., the powder particles, is preferably 1 μm or larger. If the average particle size is smaller than 1 μm, the desired dielectric strength may not be obtained. While a smaller average particle size is advantageous for increasing the surface area, if the average particle size is made too small, the gaps between the sintered particles may be filled when forming the anodic oxide film as needed, potentially reducing the capacitance. From the viewpoint of preventing such a reduction in capacitance, it is more preferable to have an average particle size of 2.5 μm or larger. In particular, from the viewpoint of improving capacitance characteristics around 10 kHz, it is preferable that the average particle diameter is between 2.5 μm and 6 μm. Furthermore, the particle size of the powder particles does not change significantly even after sintering in the second step, and by adjusting the average particle size of the powder particles, the average particle size of the sintered particles can be adjusted to a similar extent.

[0028] The aforementioned composition may optionally contain a resin binder, a solvent, a sintering aid, a surfactant, etc. All of these can be known or commercially available. In particular, it is preferable to use a paste-like composition containing at least one of a resin binder and a solvent. This allows for efficient film formation.

[0029] Furthermore, known solvents can be used. For example, in addition to water, organic solvents such as ethanol, toluene, ketones, and esters can be used.

[0030] 2nd process In the second step, the coating is sintered at a temperature of 560°C to 660°C. The sintering temperature should be between 560°C and 660°C, preferably between 560°C and less than 660°C, and more preferably between 570°C and 659°C. The sintering time varies depending on the sintering temperature and other factors, but can usually be appropriately determined within a range of about 5 to 24 hours.

[0031] The sintering atmosphere is not particularly limited and may be any of the following: a vacuum atmosphere, an inert gas atmosphere, an oxidizing gas atmosphere (including an atmospheric atmosphere), or a reducing atmosphere, but a vacuum atmosphere or a reducing atmosphere is particularly preferred. The pressure conditions may also be normal pressure (atmospheric pressure), reduced pressure, or increased pressure.

[0032] Furthermore, if the composition contains organic components such as a resin binder, it is preferable to perform a heat treatment (degreasing treatment) at a temperature range of 100°C to 600°C for a holding time of 5 hours or more before the second step after the first step. The heat treatment atmosphere is not particularly limited and may be any of the following: a vacuum atmosphere, an inert gas atmosphere, or an oxidizing gas atmosphere. The pressure conditions may also be normal pressure (atmospheric pressure), reduced pressure, or increased pressure. The electrode material of the present invention can be obtained through the second step described above. This can be used as an electrode (electrode foil 20(23)) for the aluminum electrolytic capacitor 10 without etching, but etching may be performed as necessary. When used as an electrode foil 20(23), the electrode material is slit to an appropriate size after the second step, or after the third step if the third step described below is performed.

[0033] 3rd process The electrode material can be subjected to a chemical conversion treatment as a third step, if necessary, to form a chemical conversion film (oxide film). For example, by forming an oxide film that is a dielectric with voltage resistance through a predetermined anodic oxidation treatment, an anode foil 20 for an electrolytic capacitor 10 with a desired voltage resistance can be obtained.

[0034] On the other hand, the electrode material that has undergone the second or third step may be used as the cathode foil 23. However, the cathode foil 23 according to this embodiment is constructed as an etched foil in which aluminum foil or aluminum alloy foil is used as the electrode material and the electrode material is etched. In the case of aluminum alloy foil, for example, an aluminum alloy foil containing one or more elements such as silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), boron (B), and zirconium (Zr) in a total content of 1% by weight or less can be used. Of these, for example, an aluminum alloy foil containing copper can be etched by a chemical etching method, so the cathode foil 23 can be manufactured at a relatively low cost.

[0035] The cathode foil 23, which is an etched foil, is usually not subjected to chemical conversion treatment. Instead, a natural oxide film is formed, or chemical conversion (formation of an oxide film) progresses due to the use of the electrolytic capacitor 10 (for example, repeated charging and discharging). Therefore, the cathode foil 23 may be subjected to chemical conversion treatment in advance, particularly for the purpose of suppressing the progression of chemical conversion during charging and discharging, so that a chemical conversion film (oxide film) is formed. This makes it possible to suppress the progression of chemical conversion of the cathode foil 23 even when charging and discharging is repeated. The chemical conversion voltage of the chemically converted cathode foil 23 is preferably set in the range of 2V to 6V.

[0036] Furthermore, as in this embodiment, when at least one electrode foil (anode foil 20 in this embodiment) is made of a sintered foil, it is preferable to set the other electrode foil (cathode foil 23 in this embodiment) to have a relatively large foil capacitance to match the sintered foil which has a large foil capacitance. If, in this embodiment, the foil capacitance of the cathode foil 23 (etched foil) is significantly smaller than that of the anode foil 20 (sintered foil), then when the electrolytic capacitor 10 is repeatedly charged and discharged, the neutralization of the charge between the electrode foils 20 and 23 during discharge becomes insufficient. This charge creates a potential difference between the cathode foil 23 and the electrolyte, causing the cathode foil 23 to undergo chemical deformation. As a result, the foil capacitance of the cathode foil 23 decreases, and the capacitance of the electrolytic capacitor 10 decreases. From the viewpoint of preventing such deterioration of the electrolytic capacitor 10, when one electrode foil is made of a sintered foil, the foil capacitance of the other electrode foil should be 30 μF / cm². 2 It is preferable to set it to the above, 80 μF / cm 2 It is more preferable to have a value of 100 μF / cm or higher. 2 It is even more preferable if the values ​​are greater than or equal to the above. The foil capacitance referred to here is the capacitance of the foil measured according to the JEITA standard: EIAJ RC-2364A "Test Method for Electrode Foils for Aluminum Electrolytic Capacitors" (revised March 1999) (https: / / www.jeita.or.jp / japanese / standard / book / RC-2364A / #target / page_no=1) by the Japan Electronics and Information Technology Industries Association (formerly the Electronic Industries Association of Japan).

[0037] In addition to etched foil or sintered foil, the cathode foil 23 according to this embodiment may be made of titanium-deposited foil, in which titanium is deposited on an aluminum foil or aluminum alloy foil which is the base material 21. Since the titanium-deposited foil has a larger foil capacity compared to etched foil, sufficient foil capacity can be secured for the cathode foil 23.

[0038] Next, I will explain the electrolyte. In this invention, it is preferable that the resistivity of the electrolyte is 1500 Ω·cm or less. This brings the ratio of the capacitance at 10 kHz to the capacitance at 120 Hz closer to 1 compared to conventional methods, resulting in good capacitance characteristics over a wide frequency range. Furthermore, from the viewpoint of ensuring the desired dielectric strength, it is preferable that the resistivity of the electrolyte is 100 Ω·cm or more. The electrolyte of the present invention contains at least an electrolyte and a solvent. Additives, as described later, may also be added. Preferably, an organic solvent alone can be used as the solvent for dissolving the electrolyte and additives, or a water-organic solvent system, i.e., a mixture of an organic solvent and water, can be used.

[0039] As the organic solvent, protic solvents or aprotic solvents can be used individually or in combination of two or more. If necessary, one or more protic solvents and one or more aprotic solvents may be used in any combination. Suitable protic solvents include, for example, alcohol compounds. Specific examples of alcohol compounds that can be advantageously used here are not particularly limited, but include monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol; dihydric alcohols (glycols) such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol; dihydric alcohols (glycols) such as 1,4-butanediol and 1,3-butanediol; trihydric alcohols such as glycerin; or derivatives thereof. Furthermore, suitable aprotic solvents are not particularly limited, but include lactone compounds such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone, sulfolane, methylsulfolane, dimethylsulfolane, propylene carbonate, ethylene carbonate, isobutylene carbonate, methylpyrrolidone, imidazolidinone, pyrrolidine, pyrrolidinone, methylpyrrolidinone, tetrahydrofuran, acetonitrile, N-methylformamide, N,N-dimethylformamide, nitrobenzene, their derivatives, and other intramolecular polarizing compounds.

[0040] In the electrolyte according to this embodiment, as described above, instead of using an organic solvent alone, a water-organic solvent system can also be used. By using such a water-organic solvent system, the freezing point of the solvent can be lowered. As a result, the resistivity characteristics of the electrolyte at low temperatures can be improved, and good low-temperature characteristics, indicated by a small difference in resistivity between low temperature and room temperature, can be achieved.

[0041] To explain in more detail, taking the case where ethylene glycol is used as the organic solvent as an example, this protic organic solvent has a boiling point of 198°C and a melting point of approximately -13°C. Since the temperature range required for capacitors is generally -40°C to 105°C, an electrolyte using this solvent has a margin of safety at high temperatures, but at low temperatures, the electrical properties may deteriorate due to increased viscosity or solidification of the electrolyte.

[0042] Therefore, the electrolyte in this embodiment uses an organic solvent with excellent temperature characteristics, either alone or in a mixture of several types. When using an organic solvent with a relatively high freezing point, water is added to create a water-organic solvent system, thereby lowering the freezing point of the solvent and ensuring electrical properties at low temperatures. This water-organic solvent system has very high electrolyte solubility and ion mobility, so it can achieve a much lower resistivity than an electrolyte using an organic solvent alone. Furthermore, at low temperatures, the solvent characteristics are improved, resulting in an electrolyte with the groundbreaking characteristic of having a small difference in resistivity between low and room temperature. Consequently, an electrolytic capacitor 10 using such an electrolyte can naturally have good temperature characteristics, reflecting the characteristics of the electrolyte.

[0043] The amount of water added to the water-organic solvent system is preferably in the range of 0.1% to 20% by mass of the total mass of the electrolyte. This allows for the achievement of the low resistivity and good oxide film repair characteristics mentioned above, and also allows water molecules to be utilized in the repair of the oxide films on electrode foils 20 and 23, resulting in relatively excellent oxide film repair characteristics.

[0044] Furthermore, as electrolytes, organic acids, preferably carboxylic acids or their salts, boron complexes of dicarboxylic acids or hydroxycarboxylic acids or their salts, and inorganic acids or their salts are used. These electrolyte components may be used individually, or two or more electrolyte components may be used in any combination. When inorganic acids or their salts are used in combination with carboxylic acids or their salts, or boron complexes of dicarboxylic acids or hydroxycarboxylic acids or their salts as electrolyte components, a freezing point depression of the electrolyte can be expected, thereby contributing to a further improvement in the low-temperature properties of the electrolyte.

[0045] Examples of carboxylic acids that can be used as electrolyte components are not limited to those listed below, but include monocarboxylic acids and their derivatives such as formic acid, acetic acid, propionic acid, butyric acid, p-nitrobenzoic acid, salicylic acid, benzoic acid, methylbenzoic acid, ethylbenzoic acid, isobutylbenzoic acid, sec-butylbenzoic acid, tert-butylbenzoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid, azelaic acid, and sebaci acid. Examples of dicarboxylic acids and their derivatives include nic acid, caprylic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, methyl adipic acid, ethyl adipic acid, isobutyl adipic acid, sec-butyl adipic acid, tert-butyl adipic acid, 2-methyl nonanandioic acid, 3-tert-butylhexandioic acid, brassic acid, octadecenediic acid, 12-vinyl-8-octadecenediic acid, and dimethyloctadecadienetetracarboxylic acid. Carboxylic acids containing hydroxyl groups, such as citric acid, can also be used.

[0046] Furthermore, the dicarboxylic acids or hydroxycarboxylic acids in boron complexes of dicarboxylic acids or hydroxycarboxylic acids that can also be used as electrolyte components are not limited to those listed below, but examples include borodioxalic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodimaleic acid, borodiglycolic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borosalicylic acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0047] Furthermore, examples of inorganic acids that can also be used as electrolyte components include, but are not limited to, phosphoric acid, phosphorous acid, phosphonic acid, hypophosphorous acid, phosphinic acid, alkyl phosphoric acid, phosphomolybdic acid, boric acid, and sulfamic acid. Derivatives of such inorganic acids may also be used as needed.

[0048] Furthermore, various commonly known salts can be used as the salts of the carboxylic acids or inorganic acids mentioned above. Suitable salts are not particularly limited, but may include one or more selected from sodium salts, potassium salts, ammonium salts, alkylammonium salts, and the amine salts and amidine salts listed below. As amine salts, salts of primary amines, secondary amines, and tertiary amines can be used, and examples include salts of methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, methanolamine, ethanolamine, dimethanolamine, diethanolamine, trimethanolamine, triethanolamine, pyrrolidine, piperidine, piperazine, morpholine, methylmorpholine, ethylmorpholine, oxazolidine, thiomorpholine, thiazolidined morpholine, methylmorpholine, ethylmorpholine, oxazolidine, thiomorpholine, and thiazolidined. Examples of amidine salts include salts of 1,3-dimethylimidazolinium, 1,3-diethylimidazolinium, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,3-dimethyl-2-ethylimidazolinium, 1,2-dimethyl-3-ethylimidazolinium, 1,2-dimethyl-3-ethylimidazolinium, 1,2,3-triethylimidazolinium, and 1,2,3,4-tetraethylimidazolinium. Other examples include tetraalkylammonium salts and imidazolium salts.

[0049] Furthermore, using inorganic acids or their salts as electrolyte components can be expected to lower the freezing point of the electrolyte, contributing to the improvement of the electrolyte's low-temperature properties.

[0050] Furthermore, by using an electrolyte component such as an inorganic acid or its salt in combination with the aforementioned electrolyte component such as a carboxylic acid or its salt, the lifespan of the electrolytic capacitor 10 is significantly extended compared to when the carboxylic acid or its salt is used alone.

[0051] In the electrolyte according to this embodiment, the amount of electrolyte contained therein can be appropriately determined according to conditions such as the required characteristics of the electrolyte, the type of solvent used, and the type of electrolyte used. Generally speaking, for example, when a carboxylic acid or its salt is used as the electrolyte, the amount is preferably about 3% to 30% by mass of the total mass of the electrolyte. If the amount of electrolyte is less than 3% by mass, the desired conductivity cannot be sufficiently secured, and if it exceeds 30% by mass, the effect will saturate and it will become less soluble in the solvent.

[0052] Furthermore, when using inorganic acids or their salts as electrolytes, the amount is generally preferably around 0.1% to 15% by mass of the total mass of the electrolyte. If the amount of electrolyte is less than 0.1% by mass, it becomes difficult to secure the desired conductivity sufficiently, and if it exceeds 15% by mass, the conductivity gradually saturates and the electrolyte becomes less soluble in the solvent. When using carboxylic acids or their salts in combination with inorganic acids or their salts, the amount can be used within the range of 0.1% to 15% by mass of the total mass of the electrolyte. However, as mentioned above, the amount of electrolyte can be appropriately determined according to conditions such as the required characteristics of the electrolyte and the type of electrolyte used. For example, phosphorus oxyacids (phosphoric acid, phosphorous acid, hypophosphorous acid, etc.) extend the lifespan of the electrolytic capacitor 10 by suppressing the hydration reaction of electrode foils 20 and 23, and this effect is achieved if phosphorus oxyacids or their salts are contained in at least 0.01% by mass of the total mass of the electrolyte. Therefore, by combining multiple electrolyte components as needed and adjusting the amount of each electrolyte component, the desired conductivity and desired characteristics can be obtained.

[0053] Furthermore, the electrolyte according to this embodiment may optionally contain additives such as (1) chelate compounds, (2) sugars, (3) gluconic acid and / or gluconolactone, (4) nitro compounds, (5) polymer compounds, and (6) phosphate esters. These additives may be used individually or in any combination of two or more additives. Each additive will be described below.

[0054] (1) Chelate compounds Examples of chelating compounds that can be used include ethylenediaminetetraacetic acid (EDTA), trans-1,2-diaminocyclohexane-N,N,N',N',N'-tetraacetic acid-hydrate (CyDTA), dihydroxyethylglycine (DHEG), ethylenediaminetetrakis(methylenephosphonic acid) (EDTPO), diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA), diaminopropanoltetraacetic acid (DPTA-OH), ethylenediaminediacetic acid (EDDA), ethylenediamine-N,N'-bis(methylenephosphonic acid) 1 / 2 hydrate (EDDPO), glycol etherdiaminetetraacetic acid (GEDTA), and hydroxyethylethylenediaminetriacetic acid (EDTA-OH). Generally, it is preferable to add the chelating compound in an amount ranging from 0.01% to 3% by mass of the total mass of the electrolyte. Such chelate compounds can provide several benefits in low-impedance capacitors, including extending the lifespan of the electrolytic capacitor 10 by suppressing the hydration reaction of the aluminum (Al) electrode foils 20 and 23, improving the low-temperature characteristics of the electrolytic capacitor 10 (because the solvent has a composition close to that of a nonfreezing state, the change in impedance between room temperature and low temperature is small), and improving corrosion resistance.

[0055] (2) Sugars Examples of sugars include monosaccharides such as glucose, fructose, xylose, galactose, ribose, mannose, arabinose, lyxose, allose, altose, growth, and idostalose, as well as their derivatives; sugar alcohols such as erythritol, xylitol, and mannitol; disaccharides such as maltose, sucrose, lactose, cellobiose, sucrose, and agarobiose, as well as their derivatives; trisaccharides such as maltotriose, as well as their derivatives; and polysaccharides such as starch, glycogen, alginic acid, agar, and mannan, as well as their derivatives. Generally, it is preferable to add sugars in an amount ranging from 0.01% to 5% by mass of the total mass of the electrolyte. Such sugars can provide several benefits, including extending the lifespan of the electrolytic capacitor 10 by protecting the electrode foils 20 and 23, extending the lifespan of the electrolytic capacitor 10 in low-impedance capacitors by suppressing the hydration reaction of the aluminum (Al) electrode foils 20 and 23, suppressing the degradation of certain electrolyte components (for example, suppressing the decomposition and activation of carboxylic acids), and improving the low-temperature characteristics of the electrolytic capacitor 10 (because the solvent has a composition close to that of a non-freezing state, the change in impedance between room temperature and low temperature becomes smaller). When such sugars are used together with boric acid or its derivatives, the solubility of the sugars is improved by the formation of esters. Therefore, it becomes possible to reliably add a predetermined amount of sugars and allow them to act sufficiently in the electrolyte. As a result, a stable and sufficiently long lifespan for the electrolytic capacitor 10 can be achieved. In this case, boric acid or its derivatives may be added to the electrolyte as an electrolyte component (solute component), or they may be added solely for the purpose of reacting with sugars. On the other hand, mannitol and the like are suitably applied as sugars added together with boric acid or its derivatives. Furthermore, the preferred ratio of boric acid or its derivatives to sugars is within the range of "boric acid or its derivatives:sugars = 10:1 to 1:5". If too much sugar is added, it will become less soluble in the solvent.

[0056] (3) Gluconic acid and / or gluconolactone The electrolyte according to this embodiment may contain gluconic acid and / or gluconolactone, either alone or in combination, as needed. Generally, it is preferable to add these additives in an amount ranging from 0.01% to 5% by mass of the total mass of the electrolyte.

[0057] (4) Nitro compounds The electrolyte according to this embodiment may, if necessary, contain at least one nitro compound selected from nitrobenzene, nitrophenol (e.g., p-nitrophenol), nitrobenzoic acid (e.g., p-nitrobenzoic acid, dinitrobenzoic acid), nitroacetophenone (e.g., p-nitroacetophenone), nitroanisole, nitrobenzyl alcohol, nitroxylene, and other aromatic nitro compounds.

[0058] In the electrolyte according to this embodiment, when the nitro compound described above is used, it has the effect of absorbing hydrogen gas generated at the electrode foils 20 and 23. Furthermore, a more favorable effect can be expected when two or more nitro compounds are mixed and used rather than using the nitro compound alone. In addition, it is generally preferable to add the nitro compound in an amount ranging from 0.01% to 5% by mass of the total mass of the electrolyte. If the amount of nitro compound added is less than 0.01% by mass, the desired effect cannot be obtained to any extent, and conversely, if it exceeds 5% by mass, further improvement of the desired effect cannot be expected, and in some cases, adverse effects on other properties may occur.

[0059] To further explain the use of nitro compounds, the absorption of hydrogen gas generated during the reaction of aluminum and water tends to decrease as the water content in the solvent increases when nitro compounds are used alone. This decrease in absorption effect becomes more pronounced when the electrolyte is exposed to high temperatures. However, these problems arising from the use of nitro compounds alone can be resolved by using two or more nitro compounds in combination.

[0060] (5) Polymer compounds Examples of polymer compounds that can be used include water-soluble silicones, polyacrylic acid and its derivatives, polymethacrylic acid and its derivatives, polyacrylamide and its derivatives, polyglutamic acid and its derivatives, polyglycerin and its derivatives, polyethylene glycol and its derivatives, polypropylene glycol and its derivatives, polyvinyl alcohol and its derivatives, polyoxyethylene glycol and its derivatives, polyoxyalkylene compounds, polysiloxanes, silicon dioxide, etc. These may be used individually or in any combination of two or more types. The total amount of these added is preferably in the range of 0.1% to 30% by mass of the total mass of the electrolyte. Such polymer compounds can provide effects corresponding to the action of each polymer compound, such as improving the voltage withstand characteristics of the electrolytic capacitor 10 and extending the lifespan of the electrolytic capacitor 10. The molecular weight of polymer compounds can be broadly used, ranging from relatively low molecular weights (oligomers) to high molecular weights, depending on the function of each polymer compound, its solubility and dispersibility in solvents, and the desired effect.

[0061] (6) Phosphate ester Examples of phosphate esters that can be used include methyl phosphate ester, ethyl phosphate ester, dimethyl phosphate ester, diethyl phosphate ester, trimethyl phosphate ester, and triethyl phosphate ester. Similar to chelate compounds, such phosphate esters suppress the hydration reaction of the electrode foils 20 and 23, thereby suppressing the degradation of the electrode foils 20 and 23 and the generation of hydrogen gas, thus extending the lifespan of the electrolytic capacitor 10.

[0062] Furthermore, the electrolyte according to this embodiment may also contain, in addition to the additives described above, other additives commonly used in the field of aluminum electrolytic capacitors and other electrolytic capacitors. Suitable additives include, for example, silane coupling agents, polymer electrolytes, and colloidal silica.

[0063] The separators 24 and 25 in this embodiment are not particularly limited, but preferably, naturally occurring cellulose materials such as Manila hemp or plant pulp are used as raw materials, and it is advantageous to use those manufactured by going through a dust removal process, washing process, beating process, papermaking process, etc. Woven fabrics, nonwoven fabrics, sheets, and films made from synthetic fibers such as rayon, nylon, polyester, polyvinyl compounds, aramid, acrylic, and polyurethane can also be used. Furthermore, blended products and mixed spun products of natural and synthetic fibers can also be used.

[0064] Here, the path to the depths of the pits (here, meaning the voids formed in the sintered body) in the sintered foil is relatively long, and there is a risk that the high-viscosity electrolyte may not impregnate the sintered foil sufficiently. For example, if a certain amount or more of a polymer compound or the like that has a voltage resistance improving effect is added to the electrolyte applied to the electrolytic capacitor 10 for high voltage, the viscosity of the polymer compound or the like will make the electrolyte highly viscous, and there is a risk that the impregnation will be insufficient. Therefore, for example, in the electrolytic capacitor 10 for high voltage, it is preferable to pre-coat the separators 24 and 25 with an electrolyte additive that has a voltage resistance improving effect, such as a polymer compound, prior to the fabrication of the capacitor element 1 (winding in this embodiment). This makes it possible to make a relatively low-viscosity electrolyte that does not contain any additive or contains only a small amount of the additive, and a decrease in impregnation can be prevented.

[0065] Furthermore, since sintered foil is prone to generating fine powder and burrs during slitting, these factors contribute to a relatively higher short-circuit rate in electrolytic capacitors 10 having sintered foil. Therefore, in the electrolytic capacitor 10 according to this embodiment, the thickness of the separators 24 and 25 is in the range of 20 μm to 150 μm, and the density is 0.2 g / cm³. 3 ~1.0g / cm 3 It is preferable to set it within this range. This can reduce the rate of short circuits.

[0066] The capacitor element 1 according to this embodiment comprises an anode foil 20 which is a sintered foil, a cathode foil 23 which is an etched foil, and separators 24 and 25 interposed between the anode foil 20 and the cathode foil 23, as described above. The manufacturing procedure is as follows: First, the anode foil 20, which has undergone a chemical conversion process after sintering, is slit to an appropriate size. Similarly, the cathode foil 23, which has undergone an etching process, is also slit to an appropriate size. Next, lead tabs 5 are joined to the anode foil 20 and the cathode foil 23, respectively. For joining the electrode foils 20 and 23 to the lead tabs 5, known methods such as crimping, cold pressure welding, ultrasonic bonding, and laser welding can be used. In the case of crimping, in order to prevent foil cracking during joining, through holes may be formed in advance at the joining portions of the electrode foils 20 and 23 prior to joining by press working. In cold welding, the die that comes into contact with the electrode foils 20 and 23 may be coated with a high-hardness, low-friction material such as diamond-like carbon (DLC) or titanium carbide (TiC). This ensures the wear resistance of the die and prevents the adhesion and accumulation of fine powder from the electrode foils 20 and 23.

[0067] Next, in the wound electrolytic capacitor 10, as shown in Figure 2, the anode foil 20, cathode foil 23, and separators 24 and 25 are wound so that the anode foil 20 and cathode foil 23 are separated by the first separator 24 or the second separator 25 to create the capacitor element 1 (however, in Figure 2, the lead wires 2 (lead tabs 5 and terminals 6) are omitted). Subsequently, the capacitor element 1 is immersed in an electrolyte to impregnate the capacitor element 1 with the electrolyte. Impregnation with the electrolyte may be carried out under normal pressure (atmospheric pressure), but it is more preferable to carry it out under reduced pressure. In this reduced pressure method, the capacitor element 1 is immersed in the electrolyte in a reduced pressure atmosphere, and after a certain period of time, the immersion state is maintained while returning to an atmospheric pressure atmosphere to impregnate it with the electrolyte. Alternatively, after returning to an atmospheric atmosphere, the immersion state may be maintained while further pressurizing the atmosphere. The reduced pressure is preferably 1.5 kPa or less in absolute pressure, and the increased pressure is preferably in the range of 0.15 MPa to 1.0 MPa in gauge pressure. Furthermore, the electrolyte may be heated throughout the process from reduced pressure to increased pressure, within a range where evaporation of electrolyte components is permissible. Heating the electrolyte reduces its viscosity, thereby improving its impregnation properties.

[0068] Next, the capacitor element 1 impregnated with electrolyte is placed inside the outer case 4. Then, the opening of the outer case 4 is sealed with a sealing body 3 and the opening edge is crimped. By following these steps, the electrolytic capacitor 10 can be manufactured. After that, aging treatment may be performed as needed.

[0069] The lead wires 2 are drawn out from the lead wire through-holes in the sealing body 3. The terminals 6, which are used as external connection terminals or external electrode terminals, may be integrally formed with the lead tabs 5, or they may be connected to the lead tabs 5 in a timely manner during the manufacturing process of the electrolytic capacitor 10. The lead wires 2 (lead tabs 5 and terminals 6) can be formed from various metallic materials such as iron, copper, tin, lead, silver, gold, zinc, bismuth, tungsten, nickel, titanium, and chromium. For the purpose of lowering the ESR of the electrolytic capacitor 10, it is advantageous to form the lead wires 2 from highly conductive metallic materials such as copper, silver, iron, and gold, and it is particularly advantageous to form them from copper or silver.

[0070] Furthermore, the lead tabs 5, which are the connection points with the electrode foils 20 and 23, undergo chemical conversion due to repeated charging and discharging of the electrolytic capacitor 10, similar to the etched foil (cathode foil 23) mentioned above, as a potential difference is generated between them and the electrolyte. Therefore, to suppress the progression of chemical conversion during charging and discharging, a chemical conversion treatment may be performed on the lead tabs 5 to form a chemical conversion film (oxide film). This provides an effect of reducing leakage current. In this case, phosphorylation or adipine oxidation is preferred for the chemical conversion treatment. This allows a substance with good chemical conversion properties to be placed on the lead tabs 5 and electrode foils 20 and 23, so that film repair can be performed in a shorter time, and an increase in leakage current can be prevented even when mechanical stress is applied.

[0071] Furthermore, if the chemical deformation of the lead tab 5 connected to the cathode foil 23 (etched foil) progresses due to repeated charging and discharging of the electrolytic capacitor 10, there is a risk of a short circuit occurring between the lead tab 5 and the anode foil 20 (sintered foil) due to heat generated by charging and discharging. Therefore, the lead tab 5 connected to the cathode foil 23 may be subjected to etching and further chemical deformation treatment. This further suppresses the progression of chemical deformation, thereby preventing a short circuit. Note that the lead tab 5 connected to the anode foil 20 may also be subjected to etching.

[0072] The outer case 4 housing the capacitor element 1 can preferably be made of aluminum, which is commonly used in the past. If greater strength is required, non-heat-treated aluminum with a purity of 99.0% or higher (for example, non-heat-treated aluminum 1100), heat-treated aluminum with a purity of 99.0% or higher (for example, H22 material of 1000 series aluminum), or tempered aluminum alloy containing manganese (Mn) and / or magnesium (Mg) can be used (for example, O material of aluminum alloy 3003, H22 material of 3000 series aluminum alloy, or O material of aluminum alloy 3004).

[0073] The capacitor element 1 may be bonded and housed inside the outer case 4 using an adhesive. This fixes the capacitor element 1 and improves the vibration resistance of the electrolytic capacitor 10. Any known adhesive can be used as the adhesive.

[0074] The sealing body 3 used in the electrolytic capacitor 10 in this embodiment can be formed from various commonly used materials, as long as the material has high hardness, appropriate elasticity, is impermeable to the electrolyte, and has good airtightness as a sealing body 3. Suitable sealing body 3 materials include, for example, elastic rubbers such as natural rubber (NR), styrene-butadiene rubber (SBR), ethylene-propylene polymer (EPT), and isobutylene-isoprene rubber (IIR). In particular, isobutylene-isoprene rubber (IIR) is preferred because it has high airtightness and does not allow the electrolyte to permeate as vapor. Furthermore, it is even more preferable to use IIR with superior heat resistance, such as sulfur vulcanization, quinoid vulcanization, resin vulcanization, or peroxide vulcanization. Furthermore, to suppress mechanical stress, it is also possible to use rubber materials with higher hardness. In terms of hardness, using sealing rubber with a rubber hardness measurement (30-second value) of 80 (IRHD / M) or higher using an IRHD hardness tester reduces mechanical stress and suppresses the increase in leakage current.

[0075] Furthermore, instead of the sealing body 3 material described above, a hybrid material formed by bonding an airtight and sufficiently strong resin material with elastic rubber can also be advantageously used. Examples of such resin materials include fluororesins such as PTFE, polyphenylene sulfide (PPS), polyarylate (PAR), liquid crystal polymer, polysulfone (PSF), polyethersulfone, polyetheretherketone (PEEK), polyetherimide (PEI), polyamide (aromatic polyamide, aliphatic polyamide), polyimide (PI), polyamideimide (PAI), polycarbonate, polyacetal, phenolic resin, and modified polyphenylene ether. Such a sealing body 3, consisting of two layers of resin material and rubber material, is suitably applied to substrate-free electrolytic capacitors. [Examples]

[0076] Next, the present invention will be further described with reference to examples. The examples listed herein are for illustrative purposes only and are not intended to limit the present invention. In the table, "%" indicates "mass%".

[0077] Example 1 In this example, a wound aluminum electrolytic capacitor was fabricated following the procedure described below.

[0078] An anode foil was prepared from an aluminum powder sintered body using the manufacturing method disclosed above (steps 1 to 3), and then lead wires for electrode extraction were attached. A cathode foil was prepared by electrochemically etching another aluminum foil, and then lead wires for electrode extraction were attached. Subsequently, a capacitor element was fabricated by winding the anode foil and cathode foil with a separator (isolation paper) in between. Meanwhile, based on the composition table shown in Table 1 below, solvent components and electrolyte components were sequentially added to a certain container and then stirred and dissolved to prepare an electrolyte solution.

[0079] After impregnating the capacitor elements with the electrolyte prepared by the above mixing method, they were housed in a bottomed aluminum case with the electrode lead wires protruding outside the case. The opening of the case was then sealed with an elastic seal, and an aging treatment was performed to fabricate a wound electrolytic capacitor.

[0080] Comparative Example 1 In Comparative Example 1, aluminum foil was electrochemically etched, and then an oxide film was formed on the surface by anodizing, which was used as the anode foil. The other electrolytic capacitor manufacturing methods were the same as those described in Example 1.

[0081] In both Example 1 and Comparative Example 1, foil-tipped samples with a capacitor voltage rating equivalent to 400 WV were prepared.

[0082] Next, the capacitance of the electrolytic capacitors fabricated in Example 1 and Comparative Example 1 was measured at 25°C, 120Hz, and 10kHz, and the measured values ​​shown in Table 1 below were obtained.

[0083] [Table 1]

[0084] Comparing the capacitor capacitance of Example 1 and Comparative Example 1, it can be seen that the capacitance of Example 1, which uses an aluminum powder sintered anode foil, is greater than that of Comparative Example 1, which uses an etched anode foil.

[0085] Examples 2-12 Next, for capacitors fabricated using the same method as in Example 1, the relationship between the resistivity of the electrolyte and the capacitance of the capacitor will be compared for average powder particle sizes of 2.5 μm and 6 μm. The electrolytic capacitors in Examples 2 to 12 were fabricated by repeatedly using the same method as in Example 1, and the electrolyte was prepared using the same components as in Example 1, but with adjustments to the composition to produce capacitors with resistivity of 100 Ω·cm at 30°C to 2000 Ω·cm at 30°C, respectively. For the capacitor with an average powder particle size of 2.5 μm, a foil breakdown voltage equivalent to 400 WV was produced, and for the capacitor with an average powder particle size of 6 μm, a foil breakdown voltage equivalent to 450 WV was produced.

[0086] Comparative Examples 2-12 The method for fabricating the aluminum etched foil capacitors used in Comparative Examples 2 to 12 was the same as that used in Comparative Example 1, and the method for preparing the electrolyte was the same as that used in Examples 2 to 12. As in Examples 2 to 12, samples with foil breakdown voltages equivalent to 400 WV and 450 WV were fabricated.

[0087] Next, the capacitance of the electrolytic capacitors fabricated in Examples 1-12 and Comparative Examples 1-12 was measured at 25°C, 120Hz and 10kHz, and the measured values ​​shown in Tables 2 and 3 below were obtained.

[0088] [Table 2]

[0089] [Table 3]

[0090] Tables 2 and 3 show the capacitance values ​​at 120 Hz and 10 kHz. A typical application of capacitors is for smoothing the primary side of switching power supplies. In addition to smoothing the input voltage from the commercial power line, this also absorbs current noise from elements such as MOS-FETs that repeatedly switch at frequencies around 10 kHz in the later stages of the circuit. This noise is called EMI and is subject to regulation under the EMC Directive (89 / 336 / EEC) because it adversely affects other electrical equipment through the commercial power line. Increasing the capacitance around 10 kHz is important because it contributes to reducing this noise. The reason why the "ratio" of the capacitance values ​​at 120 Hz and 10 kHz is listed here is that if we were to compare the capacitance values ​​at 10 kHz themselves, it would be natural that electrolytic capacitors using aluminum powder sintered foil, which has a larger foil capacitance, would have a larger value than electrolytic capacitors using etched foil. By listing the "ratio," we can compare the ease with which the 10 kHz capacitance can be obtained relative to the capacitance specified at 120 Hz.

[0091] Tables 2 and 3 show the capacitance ratios at 120 Hz and 10 kHz. For electrolyte resistivity between 100 Ω·cm and 1500 Ω·cm, the aluminum powder sintered foil shows a higher value than the etched foil. At 2000 Ω·cm, the powder sintered foil shows a lower value than the etched foil. This is thought to be because the structure of the aluminum powder sintered foil is not a tunnel-shaped etching pit like that seen in conventional etched foils, but rather a structure of aggregated particles, resulting in a longer path length to the back of the pit. Therefore, when using an electrolyte with high resistivity, it becomes difficult to obtain capacitance at high frequencies. In other words, in aluminum electrolytic capacitors, combining aluminum powder sintered foil with an electrolyte with resistivity of 1500 Ω·cm or less makes it easier to obtain a 10 kHz capacitance relative to the 120 Hz capacitance than with conventionally used aluminum etched foil.

[0092] Examples 13 and 14 Next, we will compare the relationship between the purity of the aluminum substrate and the lifespan of the capacitor. The electrolytic capacitor of Example 13 was manufactured using an aluminum powder sintered foil in which the aluminum purity of the substrate was 99.99% by weight or higher, and the aluminum purity of the powder was 99.99% by weight or higher. The other capacitor manufacturing methods were repeated according to the method described in Example 1. Furthermore, the electrolytic capacitor of Example 14 was manufactured using an aluminum powder sintered foil in which the aluminum purity of the base material was 99.8% by weight or more and less than 99.95% by weight, and the aluminum purity of the powder was 99.99% by weight or more. The other capacitor manufacturing methods were repeated using the method described in Example 1.

[0093] Next, high-temperature load tests were performed on the electrolytic capacitors of Examples 13 and 14 at 425V and 105°C. Figure 3 shows the leakage current values ​​of the electrolytic capacitors during the high-temperature load test. In all examples, the leakage current was kept low at less than 12 μA, but in particular, the capacitor with a substrate purity of 99.99% by weight or higher (Example 13) showed no increasing trend in leakage current after 3000 hours, indicating that the increase in leakage current was suppressed. An increase in leakage current leads to an increase in the amount of gas generated inside the capacitor, which gradually increases the internal pressure and increases the risk of premature valve operation. Therefore, to achieve good life characteristics, it is more preferable that the aluminum purity of the substrate be 99.99% by weight or higher. Furthermore, it is clear that for the same reasons, it is preferable that the aluminum powder electrically bonded to the substrate also be aluminum pure at 99.99% by weight or higher.

[0094] In this specification, "average particle size (D50)" refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering in the case of powders, and to the particle size at 50% of the cumulative value in the volume-based particle size distribution of sintered grains measured by observing the surface or cross-section of the sintered body with a scanning electron microscope. The diameter of the observed sintered grains is measured as the particle size. However, sintered grains may be in a state where the sintered powder grains have melted and partially lost their shape, or where the sintered powder grains are partially connected to each other. In such cases, a portion with a roughly circular shape is approximately considered as a single sintered grain, and its maximum diameter is measured as the particle size. On the other hand, portions where the roughly circular shape is difficult to discern are excluded. The particle size of a predetermined number of sintered grains is measured, and the volume-based particle size distribution is calculated from these number-based particle size distributions. The particle size at 50% of the cumulative value in this particle size distribution is then obtained as the average particle size (D50) of the sintered grains. Furthermore, the particle size of the powder particles hardly changes before and after sintering, and the average particle size (D50) of the powder obtained by the above method is substantially the same as the average particle size (D50) of the sintered particles of that powder.

Claims

1. An electrolytic capacitor comprising an anode foil, a cathode foil, a capacitor element having a separator interposed between the anode foil and the cathode foil, and an electrolyte impregnated in the capacitor element, The anode foil or the cathode foil has a sintered body composed of sintered particles of powder made from at least one of aluminum and aluminum alloys. The resistivity of the electrolyte is 1500 Ω·cm or less. The average particle size (D50) of the powder or sintered grains is 6 μm or less. An electrolytic capacitor characterized by the following features.

2. The anode foil or the cathode foil consists of the sintered body and a substrate that supports the sintered body. The electrolytic capacitor according to claim 1, characterized in that...

3. The electrolyte comprises a solvent consisting of an organic solvent, or a solvent consisting of a mixture of water and an organic solvent, and at least one electrolyte selected from the group consisting of organic acids or organic acid salts, inorganic acids or inorganic acid salts, and mixtures of organic acids or organic acid salts and inorganic acids or inorganic acid salts. The electrolytic capacitor according to claim 1 or 2, characterized by the above.

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