Electrolytic capacitor and method for manufacturing an electrolytic capacitor

Abstract

To provide an electrolytic capacitor for medium-to-high voltage applications of 160 V or higher, which suppresses the total amount of gas generated within the capacitor.SOLUTION: The electrolytic capacitor includes an anode foil with a dielectric oxide film formed thereon and a cathode body. The cathode body includes a cathode electrode foil made of a valve-acting metal and a carbon layer formed on the cathode electrode foil. The capacitance per unit area of the anode foil X, and the capacitance per unit area of the cathode body Y, are adjusted such that the ratio of X to Y is 1 to 10 or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor is a passive element that stores and discharges electric charge through capacitance. An electrolytic capacitor is constructed by housing a capacitor element impregnated in an electrolyte solution in an outer casing, sealing the outer casing with a sealing element, and drawing out terminals from the sealing element. The capacitor element consists of an anode foil, which has a dielectric oxide film formed on a valve metal foil, and a cathode foil, which is made of the same or other metal foil, facing each other, with a separator interposed between the anode foil and the cathode foil.

[0003] The electrolyte is interposed between the anode and cathode foils, making close contact with the uneven surface of the anode foil and functioning as a true cathode. This electrolytic capacitor can be considered as a series capacitor formed by combining the capacitance of the anode foil and the capacitance of the cathode in series. However, if the capacitance of the cathode foil is sufficiently larger than the capacitance of the anode foil, the capacitance C [F] of the electrolytic capacitor is given by the effective area S [m²] of the surface of the anode foil facing the cathode foil. 2 ], the thickness of the dielectric oxide film formed on the surface of the anode foil is d [m], the relative permittivity of the dielectric oxide film is ε, and the permittivity of vacuum is 8.85 × 10⁻⁶. -12 If we denote it as [F / m], it can be approximated by the following equation 1. (Formula 1) C = 8.854 × 10 -12 ×ε·S / d

[0004] Electrolytic capacitors are sometimes required to withstand voltages of 160V or higher, such as in automotive applications like electric vehicles and power applications. The withstand voltage of an electrolytic capacitor is greatly affected by the thickness d of the dielectric oxide film on the anode foil. Therefore, electrolytic capacitors that can withstand medium to high voltages of 160V or higher require a thick dielectric oxide film. However, increasing the thickness of the dielectric oxide film increases the thickness d in Equation 1, which reduces the capacitance C. Therefore, electrolytic capacitors for medium to high voltage applications of 160V or higher are equipped with a surface-expanding layer on the anode foil, which consists of numerous tunnel-shaped pits. Electrolytic capacitors are equipped with a surface-expanding layer on the anode foil that has tunnel-shaped pits penetrating the foil, either partially or entirely. In this way, surface-expanding technology allows electrolytic capacitors for medium to high voltage applications of 160V or higher to achieve a large surface area of ​​the anode foil while maintaining the thickness of the dielectric oxide film. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-181368 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, gas is generated inside electrolytic capacitors due to various phenomena. For example, on the anode side, when the dielectric oxide film dissolves and comes into contact with the water in the electrolyte and the valve metal, hydrogen gas is generated as the valve metal deteriorates due to hydration. Hydrogen gas is also generated at the foil interface on the cathode side. If the amount of gas generated inside the electrolytic capacitor increases, it may cause the outer casing to bulge, the valve to open, or electrolyte leakage.

[0007] On the other hand, in recent years, electrolytic capacitors for medium- and high-voltage applications above 160V are required to have even larger capacitances. In other words, it is also required to thin the dielectric oxide film while maintaining the dielectric strength. However, the dielectric strength of the anode foil decreases and the leakage current increases as the thickness of the dielectric oxide film decreases. When leakage current occurs, hydroxide ions (OH) present in the electrolyte are released due to the dissociation of water. - ) is reacted by an oxygen ion (O 2- ) is generated, and aluminum ions (Al) are generated by the anode reaction of the aluminum in the anode foil. 3+ ) reacts with the dielectric oxide film to form, and electrons are generated. In other words, an increase in leakage current significantly increases the amount of electrons generated. At that time, protons (H) are generated at the interface between the electrolyte and the dielectric oxide film on the anode foil. + ) increases.

[0008] As the leakage current increases, the electrons that have increased on the anode foil side move to the cathode foil. On the cathode foil side, as a cathode reaction, protons in the electrolyte present near the cathode foil accept electrons and atomic hydrogen (H) ad ) is produced. When two atomic hydrogen atoms combine, molecular hydrogen (H2 gas) is produced. Here, the reaction rate of the cathode reaction that produces molecular hydrogen increases in proportion to the reaction rate of the anode reaction corresponding to the leakage current of the capacitor, according to Faraday's law. In other words, if the dielectric oxide film of the anode foil is thinned in order to increase the capacitance C, the internal pressure of the capacitor will rise in a short period of time due to the increase in the amount of molecular hydrogen produced with the increase in leakage current, which shortens the lifespan of the capacitor.

[0009] Therefore, it is conceivable to add gas absorbers or gas control agents such as nitro compounds to the electrolyte of electrolytic capacitors. However, nitro compounds tend to lower the voltage rating of electrolytic capacitors, so it is desirable to reduce the amount added in electrolytic capacitors that require medium to high voltages of 160V or more.

[0010] The present invention was proposed to solve the above problems, and its objective is to provide an electrolytic capacitor for medium-to-high voltage applications of 160V or higher that suppresses the total amount of gas generated inside the electrolytic capacitor. [Means for solving the problem]

[0011] First, let's define the capacitance emergence rate. The capacitance emergence rate is the ratio of the capacitance of the electrolytic capacitor to the capacitance of the anode. That is, the capacitance emergence rate is the percentage obtained by considering the electrolytic capacitor as having a combined capacitance when the anode and cathode are connected in series, and dividing it by the capacitance of the anode. The combined capacitance is obtained by dividing the product of the anode capacitance and the cathode capacitance by the sum of the anode capacitance and the cathode capacitance. Therefore, the capacitance emergence rate is expressed by the following equation 2.

[0012] (Formula 2) TIFF0007917026000001.tif16161

[0013] As shown in Equation 2, when the capacitance of the anode is large, the influence of the cathode on the capacitance appearance rate becomes large. On the other hand, when the capacitance of the anode is small, the influence of the cathode on the capacitance appearance rate becomes small.

[0014] In the field of electrolytic capacitors, the anode foil for electrolytic capacitors intended for so-called medium-high voltage applications (160V and above) has a smaller capacitance per unit area than the anode foil for electrolytic capacitors intended for low voltage applications. In electrolytic capacitors intended for medium-high voltage applications, the difference in capacitance between the anode and cathode sides is large. This is because, in the anode foil for electrolytic capacitors intended for medium-high voltage applications, the dielectric oxide film on the surface of the expanding layer becomes thicker in order to ensure withstand voltage. From the perspective of improving the capacitance appearance rate, in electrolytic capacitors in the low-voltage region where the capacitance on the anode side is large, increasing the capacitance on the cathode side has a significant effect in increasing the capacitance appearance rate. However, in electrolytic capacitors intended for medium-high voltage applications where the capacitance on the anode side is small, or in electrolytic capacitors where the capacitance on the cathode side is an order of magnitude larger than that on the anode side, improving the capacitance on the cathode side has little effect on the capacitance appearance rate.

[0015] In other words, when the anode capacitance is large, increasing the cathode capacitance will increase the capacitance appearance rate. That is, for electrolytic capacitors for low-voltage applications below 160V where the anode capacitance is large, there is a reason to increase the cathode capacitance. On the other hand, when the anode capacitance is small, the contribution of the cathode capacitance to the capacitance appearance rate is small, and increasing the cathode capacitance has almost no effect on the capacitance appearance rate. That is, for electrolytic capacitors for medium-to-high voltage applications above 160V where the anode capacitance is small, there is very little reason to increase the cathode capacitance.

[0016] In electrolytic capacitors for medium- and high-voltage applications, where improving the capacitance on the cathode side has little effect on the capacitance appearance rate, improving the capacitance of the cathode foil has not been done due to considerations such as the increased number of processes required by using carbon materials. However, as a result of our diligent research, we have found that in electrolytic capacitors for medium- and high-voltage applications of 160V or higher, forming a carbon layer on the cathode foil and making the capacitance on the cathode side 10 times or more than the capacitance on the anode side suppresses the total amount of gas generated inside the electrolytic capacitor.

[0017] The present invention was accomplished based on the obtaining of this finding by the present inventors. In order to solve the above problem, the electrolytic capacitor of the present invention is an electrolytic capacitor comprising an anode foil having a dielectric oxide film formed thereon and a cathode body, wherein the cathode body has a cathode foil made of a valve metal and a carbon layer formed on the cathode foil, and with respect to the anode foil and the cathode body, the capacitance X per unit area of the anode foil and the capacitance Y per unit area of the cathode body that is the same unit area as the anode foil have a capacitance such that in the ratio of X to Y, when X is 1, Y is 10 or more.

[0018] With respect to the anode foil and the cathode body, the capacitance X per unit area of the anode foil and the capacitance Y per unit area of the cathode body that is the same unit area as the anode foil may have a capacitance such that in the ratio of X to Y, when X is 1, Y is more than 14.

[0019] The anode foil may comprise an enlarged surface portion formed on the foil surface and a dielectric oxide film formed on the surface of the enlarged surface portion and having a thickness of 200 nm or more.

[0020] The anode foil has 3.5 μF / cm 2 may be configured to have the following capacitance X.

[0021] The electrolytic capacitor may be configured to be used for medium and high voltage applications of 160 V or more. Effects of the Invention

[0022] According to the present invention, the amount of gas generated inside an electrolytic capacitor can be suppressed even for electrolytic capacitors for medium and high voltage applications. Brief Description of Drawings

[0023] [Figure 1] It is a graph showing the swelling amount of the electrolytic capacitors of Examples 1 and 2 and Comparative Example 1. [Figure 2] It is a graph showing the swelling amount of the electrolytic capacitors of Example 3 and Comparative Example 2. [Figure 3]This graph shows the amount of bulging of the electrolytic capacitors in Examples 4 and 5 and Comparative Example 3. [Modes for carrying out the invention]

[0024] (Electrolytic capacitor) An electrode body and an electrolytic capacitor using this electrode body as a cathode according to an embodiment of the present invention will be described. An electrolytic capacitor is a passive element that stores and discharges charge according to its capacitance. This electrolytic capacitor has a wound type or a laminated type capacitor element. The capacitor element consists of an anode foil with a dielectric oxide film formed on its surface and a cathode body facing each other via a separator, and impregnated with an electrolyte. The electrolyte is in close contact with the uneven surface of the dielectric oxide film on the anode foil and functions as a true cathode. The electrolyte may be solidified into a gel.

[0025] (Cathole body) The cathode body has a cathode foil formed by stretching a valve metal as a current collector. A natural oxide film or a chemical conversion film is formed on the surface of the cathode foil. The oxide film is formed naturally or intentionally. The natural oxide film is formed by the reaction of the cathode foil with oxygen in the air, while the chemical conversion film is an oxide film that is intentionally formed by a chemical conversion treatment in which a voltage is applied in a halogen ion-free solution such as an aqueous solution of adipic acid, boric acid, or phosphoric acid. If the valve metal is aluminum foil, the oxide film is aluminum oxide.

[0026] A carbon layer containing carbon material as the main component is formed on the surface of the cathode foil. That is, the cathode body has an oxide film, which is an insulating layer, on top of the cathode foil, which is the current collector, and a carbon layer on top of this oxide film. The carbon layer is located on the outermost surface of the cathode body. It is preferable that the carbon layer adheres closely to the cathode foil and is resistant to peeling off from the cathode foil even under impact. To improve the adhesion between the carbon layer and the cathode foil, it is preferable to form an expanding layer on the surface of the cathode foil and form the carbon layer on top of the expanding layer. Furthermore, to improve the adhesion between the carbon layer and the cathode foil, it is preferable to press-form the cathode body consisting of the carbon layer and the cathode foil.

[0027] The cathode body will be described in detail. The valve metals that make up the cathode foil include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. A purity of 99% or higher is desirable, but impurities such as silicon, iron, copper, magnesium, and zinc may be present. As the cathode foil, for example, aluminum material with a temper symbol of H as defined in JIS standard H0001, so-called H material, or aluminum material with a temper symbol of O as defined in JIS standard H0001, so-called O material may be used.

[0028] The expanded layer is formed by electrolytic etching, chemical etching, sandblasting, etc., or by depositing or sintering metal particles onto a foil body. Electrolytic etching includes AC etching. In AC etching, for example, the cathode foil is immersed in an acidic aqueous solution containing halogen ions, such as hydrochloric acid, and an alternating current is passed through it. Chemical etching involves immersing the metal foil in an acidic or alkaline solution. In other words, the expanded layer refers to the region where spongy etching pits are formed, or the region with a porous structure consisting of voids between densely packed powder particles. The etching pits may be tunnel-shaped pits formed by DC etching, or they may be formed so as to penetrate the cathode foil.

[0029] Carbon materials to be included in the carbon layer include activated carbon, graphite, carbon black, carbon nanohorns, or fibrous carbon. Activated carbon is made from natural plant tissues such as coconut shells, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Graphite includes natural graphite, artificial graphite, and graphitized Ketjenblack. Carbon black includes Ketjenblack, acetylene black, channel black, and thermal black. Fibrous carbon includes carbon nanotubes (CNTs) and carbon nanofibers (CNFs).

[0030] As the carbon material to be contained in the carbon layer, spherical carbon, specifically carbon black, is particularly preferred. When the expanded layer formed on the surface of the cathode foil is an etching pit, using carbon black with a particle size smaller than the opening diameter of the etching pit allows it to penetrate deeper into the etching pit, resulting in the carbon layer adhering closely to the cathode foil.

[0031] The carbon layer may contain a mixture of two or more of these carbon materials. For example, the carbon materials contained in the carbon layer may include flaky or scale-like graphite and carbon black, which is spherical carbon. The flaky or scale-like graphite preferably has an aspect ratio of 1:5 to 1:100 between its short axis and long axis. The carbon black, which is spherical carbon, preferably has a primary particle diameter of 100 nm or less on average. When a carbon layer containing this combination of carbon materials is laminated onto the cathode foil, the carbon black is easily rubbed into the pores of the expansion layer by the graphite. The graphite is easily deformed along the uneven surface of the expansion layer and easily accumulates on the uneven surface. The graphite then acts as a pressing lid, holding in the spherical carbon that has been rubbed into the pores. As a result, the adhesion and fixation between the carbon layer and the cathode foil are further improved.

[0032] Furthermore, activated carbon and fibrous carbon have delocalized pi electrons and a large specific surface area, so they may be added to the carbon layer together with spheroidal carbon, such as carbon black, or added to the carbon layer together with a mixture of flake-like or scaly graphite and spheroidal carbon, such as carbon black.

[0033] Methods for forming a carbon layer on the cathode foil include vacuum deposition, sputtering, ion plating, CVD, coating, electroplating, and electroless plating. In the coating method, a slurry is prepared by dispersing the carbon material in a dispersion solvent, and the slurry is applied to the cathode foil and dried using methods such as slurry casting, doctor blade method, or spray atomization. In the deposition method, the carbon material is evaporated by electrically heating it in a vacuum, or by irradiating the carbon material with an electron beam in a vacuum, thereby forming a carbon film on the cathode foil. In the sputtering method, a target made of carbon material and the cathode foil are placed in a vacuum chamber, and an inert gas is introduced into the vacuum chamber and a voltage is applied to cause the plasma-generated inert gas to collide with the target, depositing the carbon material particles knocked out from the target onto the cathode foil.

[0034] After laminating the carbon layer and the cathode foil, it is preferable to press-weld them together. In press-welding, for example, the cathode body consisting of the carbon layer and the cathode foil is sandwiched between press rollers and press pressure is applied. The press pressure is 0.01 to 100 t / cm². 2 A certain degree of pressure is desirable. As long as the carbon layer and the cathode foil can be pressure-welded together, there are no particular limitations on the pressure-welding structure that occurs at the interface of the cathode foil. However, if the carbon material is pressed into the pores of the expansion layer by press working, and the carbon material is deformed along the uneven surface of the expansion layer, the adhesion and fixation between the carbon layer and the cathode body will be further improved. In particular, carbon black, which is spherical carbon, is rubbed into the pores of the expansion layer by the graphite subjected to press pressure, and the graphite is easily deformed and piled up along the uneven surface of the expansion layer.

[0035] Furthermore, carbon materials may also be subjected to porous treatments such as activation treatment and opening treatment. Conventional known activation treatments such as gas activation methods and chemical activation methods can be used for porous treatment. Examples of gases used in gas activation methods include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or mixtures thereof. Examples of chemicals used in chemical activation methods include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, inorganic acids such as boric acid, phosphoric acid, sulfuric acid, and hydrochloric acid, or inorganic salts such as zinc chloride. Heat treatment may be applied as needed during this activation treatment.

[0036] (Anode foil) The anode foil is a long foil made of valve metal. A purity of 99.9% or higher is desirable for the anode foil. This anode foil is formed by creating a surface expansion layer on a stretched foil, and then forming a dielectric oxide film on the surface of the surface expansion layer. The surface expansion layer, suitable for medium-to-high voltage applications of 160V or higher, has numerous tunnel-shaped pits carved into the foil surface in the thickness direction by DC etching. To accommodate high capacity applications of 160V or higher, the tunnel-shaped pits may be formed to penetrate the anode foil. Alternatively, the surface expansion layer may be formed by sintering valve metal powder, or by depositing a film of metal particles or the like onto the foil.

[0037] The dielectric oxide film formed on the anode foil is typically an oxide film formed on the surface layer of the anode foil. If the anode foil is made of aluminum, it is an aluminum oxide layer formed by oxidizing the porous structure region. This dielectric oxide film is formed by a chemical conversion treatment in which a voltage is applied in a halogen-free solution such as an acid, ammonium borate, ammonium phosphate, ammonium adipate, or an aqueous solution of these acids. By having a thickness of 200 nm or more, the dielectric oxide film can contribute to the voltage withstand capability of electrolytic capacitors, even in medium-to-high voltage applications of 160 V or more.

[0038] (Capacitance ratio of anode foil to cathode) In this electrolytic capacitor, a cathode-side capacitance is generated by the electric double-layer effect at the interface between the electrolyte and the cathode, and a anode-side capacitance is generated by dielectric polarization. The anode foil used in electrolytic capacitors for medium and high-voltage applications is 3.5 μF / cm². 2 The following anode-side capacitance is generated.

[0039] In such electrolytic capacitors, the anode foil and cathode body are adjusted so that the anode capacitance X per unit area of ​​the anode foil and the cathode capacitance Y per unit area of ​​the cathode body are 10 or more for every 1 X, i.e., X:Y = 1:10 or more. It has been found that when the cathode capacitance Y per unit area is 10 times or more the anode capacitance X, and the cathode body contains a carbon layer, the total amount of gas generated in electrolytic capacitors for medium and high-voltage applications is suppressed.

[0040] Furthermore, methods for adjusting capacitance include, for example, adjusting the thickness of the dielectric oxide film and adjusting the surface area of ​​the expanded layer by etching, and are not limited to any known method.

[0041] (electrolyte) The electrolyte is a mixture obtained by dissolving a solute in a solvent and adding additives as needed. Ethylene glycol is preferred as the solvent. Using ethylene glycol as the solvent improves the withstand voltage of the electrolytic capacitor, making it suitable for medium to high voltage applications of 160V or higher. However, any solvent, protic or aprotic, may be used as long as the required withstand voltage can be obtained by surface treatment and chemical treatment of the anode foil. Representative examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and oxides.

[0042] The solute contained in the electrolyte contains anionic and cationic components, and is typically an organic acid or its salt, an inorganic acid or its salt, or a complex compound of an organic acid and an inorganic acid or an ionically dissociable salt thereof, and is used alone or in combination of two or more. The acid that becomes an anion and the base that becomes a cationic may be added separately to the electrolyte as solute components.

[0043] Furthermore, other additives can be added to the electrolyte. Examples of additives include polyethylene glycol, complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, and phosphate esters. These may be used individually or in combination of two or more. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobencene, o-nitrophenol, m-nitrophenol, and p-nitrophenol. Nitro compounds have a hydrogen gas absorption effect.

[0044] (Separator) The separator is interposed between the anode foil and the cathode body to prevent short circuits between the anode foil and the cathode body, and also holds the electrolyte. Examples of separators include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives; polyamide resins such as polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; and acrylic resins. These resins can be used individually or in mixtures, or mixed with cellulose.

[0045] (Examples) The present invention will be described in more detail below based on the following examples. However, the present invention is not limited to the following examples.

[0046] (Examples 1-2) (Example 1) An electrolytic capacitor for high-voltage applications, Example 1, was fabricated in a cylindrical shape with a diameter of 30 mm and a height of 60 mm, and a rated voltage of 450 V. A strip of aluminum foil was used as the cathode foil. The aluminum foil was subjected to AC etching to form a widened surface layer consisting of spongy etching pits on both sides of the foil. In the AC etching process, the cathode foil was immersed in an acidic aqueous solution with a liquid temperature of 25°C and approximately 8 wt% hydrochloric acid as the main electrolyte, and an AC current of 10 Hz and a current density of 0.14 A / cm² was applied. 2 The current was applied to the substrate for approximately 5 minutes to expand both sides of the aluminum foil. Next, the aluminum foil was subjected to a chemical conversion treatment to form a dielectric oxide film on the surface of the expanded layer. In the chemical conversion treatment, chlorine that had adhered during the AC etching treatment was removed with an aqueous phosphoric acid solution, and then a voltage was applied in an aqueous solution of ammonium dihydrogen phosphate.

[0047] The carbon layer of the cathode body contained carbon black as the carbon material. Specifically, a slurry was prepared by mixing and kneading carbon black powder, styrene-butadiene rubber (SBR) as a binder, and an aqueous solution of carboxymethylcellulose sodium (CMC-Na) as a dispersant.

[0048] This slurry was uniformly applied to the cathode foil. Then, the slurry was heated and dried to evaporate the solvent, and the cathode body was pressed. In the pressing process, the cathode body was sandwiched between press rollers and subjected to 5.38 kNcm -1 Press pressure was applied to fix the carbon layer onto the cathode foil. The press pressure was applied using a press machine manufactured by Takumi Giken Co., Ltd. The press roller diameter was 180 mm, the press processing width was 130 mm, and the cathode body was transported once at a speed of 3 m / min.

[0049] Furthermore, a strip of aluminum foil was used as the anode foil. The aluminum foil was subjected to DC etching to form an expanded surface layer consisting of tunnel-shaped etching pits. The DC etching process consisted of a first step to form the pits and a second step to enlarge the pits. In the first step, the aluminum foil was electrochemically etched with a DC current in an aqueous solution containing chloride ions. The etching process in the first step was performed at a current density of 400 mA / cm². 2 This was performed for approximately 1 minute. In the second step, electrochemical etching was performed using a direct current in an aqueous solution containing nitrate ions to enlarge the pits formed in the aluminum foil after the first step. The current density for the etching process in the second step was 300 mA / cm². 2 This was done for approximately 2 minutes.

[0050] After forming the expanded layer, a chemical conversion treatment was performed on the anode foil to form a dielectric oxide film on the surface of the expanded layer. Specifically, a voltage of 650V was applied in a chemical conversion solution of 4% by weight boric acid at a liquid temperature of 85°C.

[0051] The anode foil and cathode body were ultrasonically connected to aluminum tab-shaped lead terminals. A separator was placed between the anode foil and cathode body during the winding process. A kraft-type separator was used. The wound assembly of the anode foil, cathode body, and separator was impregnated with an electrolyte. The electrolyte consisted of ethylene glycol as the solvent and azelaate as the solute. In addition, para-nitrobenzyl alcohol was added to the electrolyte as a nitro compound at a concentration of 2% by weight relative to the total volume of the electrolyte.

[0052] The sealing body had external terminals attached to a phenolic laminate. After impregnation with electrolyte, lead terminals from the wound body were connected to the external terminals of the sealing body. The wound body and the sealing body were then inserted into an aluminum outer case and sealed with the sealing body. The outer case was cylindrical with a diameter of 30 mm and a height of 60 mm. After sealing with the sealing body, the electrolytic capacitor underwent an aging treatment. The aging treatment involved applying a voltage of 481 V for 95 minutes at room temperature (30 °C). As a result, an electrolytic capacitor according to Example 1 was manufactured, which was cylindrical with a diameter of 30 mm and a height of 60 mm and had a rated voltage of 450 V.

[0053] (Example 2) An electrolytic capacitor for high-voltage applications, specifically Example 2, was fabricated. This capacitor is cylindrical with a diameter of 30 mm and a height of 60 mm, and has a rated voltage of 450 V. The electrolytic capacitor of Example 2 used a cathode body with a carbon layer formed by sputtering. No expanding layer was formed on the cathode foil, and no press working was performed during the carbon layer formation process. Furthermore, the electrolytic capacitor of Example 2, including the composition of the carbon layer formed on the cathode foil, was fabricated using the same method and under the same conditions as Example 1.

[0054] (Comparative Example 1) A cylindrical electrolytic capacitor for high-voltage applications, Comparative Example 1, with a diameter of 30 mm and a height of 60 mm, and a rated voltage of 450 V, was fabricated. In the electrolytic capacitor of Comparative Example 1, an expanded surface layer was formed on the cathode foil, but the carbon layer was not formed. Pressing was not performed. Otherwise, the electrolytic capacitor of Comparative Example 1 was fabricated using the same method and under the same conditions as in Example 1.

[0055] (Comparison of configurations) The similarities and differences between the electrolytic capacitors of Examples 1 and 2 and Comparative Example 1 are shown in Table 1 below. In Table 1, the combined capacitance was calculated assuming that the anode and cathode capacitors are in series within the electrolytic capacitor. That is, the combined capacitance was obtained by dividing the product of the anode capacitance X and cathode capacitance Y per unit area by the sum of the anode capacitance X and cathode capacitance Y per unit area. The capacitance occurrence rate is the ratio of the combined capacitance to the anode capacitance. (Table 1) TIFF0007917026000002.tif45145

[0056] (Gas generation amount measurement test) The amount of gas generated by the electrolytic capacitors in Examples 1 and 2 and Comparative Example 1 was measured. A high voltage of DC 450V was continuously applied to each electrolytic capacitor at a temperature of 105°C, and the amount of gas generated at each elapsed time was measured. The amount of gas generated was measured by the amount of bulge ΔL of the outer casing of the electrolytic capacitor. The gas causes the bottom surface of the electrolytic capacitor to expand in the direction of the height of the electrolytic capacitor (along the line connecting the opening of the outer casing and the bottom surface). The amount of bulge ΔL of the outer casing is the amount of change in the height of the capacitor due to this expansion.

[0057] The measurement results of the gas generation amount are shown in Figure 1. Figure 1 is a graph showing the time change of the swelling amount ΔL for Examples 1 and 2 and Comparative Example 1. As shown in Figure 1, from 250 hours after voltage application until 500 hours have passed, the degree of change in the swelling amount ΔL is the same among Examples 1 and 2 and Comparative Example 1. However, from 500 hours after voltage application until approximately 750 hours have passed, only the electrolytic capacitor of Comparative Example 1 shows rapid expansion. The degree of change in the swelling amount ΔL of the electrolytic capacitors in Examples 1 and 2 is unchanged in the intervals from 250 hours after voltage application until 500 hours have passed, and from 500 hours after voltage application until approximately 750 hours have passed.

[0058] The following phenomenon was observed in the electrolytic capacitor of Comparative Example 1: From 250 hours after voltage application until 500 hours after voltage application, nitro compounds that bonded with hydrogen atoms persisted, suppressing the generation of hydrogen gas. However, around 500 hours after voltage application, all the nitro compounds in the electrolytic capacitor of Comparative Example 1 bonded with hydrogen atoms, leaving no nitro compounds that could bond with hydrogen atoms. As a result, the suppression of hydrogen gas generation by the nitro compounds ceased, and the electrolytic capacitor of Comparative Example 1 rapidly expanded after 500 hours of voltage application.

[0059] On the other hand, the electrolytic capacitors of Examples 1 and 2 are equipped with a cathode body having a carbon layer formed on the cathode foil, and the capacitance of the anode foil and the cathode body are adjusted so that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body have a capacitance such that the ratio of X to Y is 10 or more for every 1 X, thereby suppressing the generation of hydrogen gas. This is thought to be because, in the electrolytic capacitors of Examples 1 and 2, the cathode reaction that reduces dissolved oxygen in the electrolyte and the reduction reaction of nitro compounds occur simultaneously, and even after 500 hours have passed since the voltage was applied, a large amount of nitro compounds that can bond with hydrogen atoms remain. Therefore, the electrolytic capacitors of Examples 1 and 2 did not rapidly expand even after 500 hours had passed since the voltage was applied. Thus, the results of Examples 1 and 2 and Comparative Example 1 confirm that the electrolytic capacitors of Examples 1 and 2 suppress the generation of hydrogen gas.

[0060] (Example 3) An electrolytic capacitor of Example 3 was fabricated. The electrolytic capacitor of Example 3 used lead terminals made of aluminum wire and metal wire. Specifically, the aluminum wire consisted of a flat portion formed by pressing one end of a round bar shape and an unpressed round bar portion on the other end, with the tip of the round bar portion and the metal wire connected by arc welding or the like. The flat portion was connected to the cathode and anode foil using various connection methods. In addition, a rubber seal with a through hole for inserting the metal wire was used. The metal wire led out from the winding body was passed through the through hole in the seal and integrated, and the winding body and seal were inserted into an aluminum outer case. Except for being cylindrical with a diameter of 16 mm and a height of 50 mm, it was manufactured with the same configuration, composition, manufacturing method and conditions as Example 1, and is for high-voltage applications with a rated voltage of 450 V.

[0061] (Comparative Example 2) A comparative example electrolytic capacitor was fabricated. The electrolytic capacitor of comparative example 2 had the same configuration as Example 3 in terms of the structure of the lead terminals and the sealing body. Except for being cylindrical with the same dimensions as Example 3 and having the cathode side capacitance Y of the cathode body, it was manufactured under the same configuration, composition, manufacturing method, and conditions as Comparative Example 1, and is intended for high-voltage applications with a rated voltage of 450V.

[0062] (Comparison of configurations) The similarities and differences between the electrolytic capacitors of Example 3 and Comparative Example 2 are shown in Table 2 below. In Table 2, the combined capacitance was calculated assuming that the anode and cathode capacitors are in series within the electrolytic capacitor. That is, the combined capacitance was obtained by dividing the product of the anode capacitance X and cathode capacitance Y per unit area by the sum of the anode capacitance X and cathode capacitance Y per unit area. The capacitance occurrence rate is the ratio of the combined capacitance to the anode capacitance. (Table 2) TIFF0007917026000003.tif35145

[0063] (Gas generation amount measurement test) The amount of gas generated by the electrolytic capacitors in Example 3 and Comparative Example 2 was measured. The high voltage application conditions and the measurement method and conditions for the amount of bulging of the outer casing in the gas generation amount measurement test were the same as those in Examples 1 and 2 and Comparative Example 1.

[0064] The measurement results of the gas generation amount are shown in Figure 2. Figure 2 is a graph showing the time change of the swelling amount ΔL for Example 3 and Comparative Example 2. As shown in Figure 2, after 500 hours of voltage application, the electrolytic capacitor of Comparative Example 2 began to swell rapidly. On the other hand, the electrolytic capacitor of Example 3 remained almost unchanged in swelling amount ΔL, never exceeding 0.2 mm, until 3000 hours had passed.

[0065] In the electrolytic capacitors of Example 3 and Comparative Example 2, the nitro compound was completely consumed in the electrolytic capacitor of Comparative Example 2, and the suppression of hydrogen gas generation by the nitro compound became ineffective. However, in the electrolytic capacitor of Example 3, even after 3000 hours, a large amount of nitro compound that could bond with hydrogen atoms remained, indicating that hydrogen gas generation was suppressed. Thus, the results from Example 3 and Comparative Example 2 confirm that hydrogen gas generation is suppressed by providing a cathode body with a carbon layer formed on the cathode foil, and by adjusting the capacitance of the anode foil and the cathode body such that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body have a capacitance ratio of X to Y of 10 or more for every 1 X.

[0066] (Examples 4-5) (Example 4) An electrolytic capacitor of Example 4 was fabricated. The electrolytic capacitor of Example 4 is a laminate cell with a rated voltage of 200V. The anode foil was chemically treated by applying a voltage of 286V. Aluminum tab-shaped lead terminals were ultrasonically connected to the anode foil and cathode body, respectively. A separator folded in a zigzag pattern was prepared, and the cathode body and anode foil were alternately sandwiched in each fold, thereby creating a laminate of the cathode body, anode foil, and separator while the cathode body and anode foil faced each other via the separator.

[0067] After impregnating the laminate with an electrolyte, the laminate was sealed in a laminate material. The solvent for the electrolyte was ethylene glycol, to which azelaate was added as a solute. However, no nitro compounds such as paranitrobenzyl alcohol were added to the electrolyte. After fabricating the laminate cells, an aging treatment was performed. The aging treatment involved applying a voltage of 230V to the laminate cells for 120 minutes at room temperature (25°C), and then applying a voltage of 230V for 60 minutes in a temperature environment of 85°C.

[0068] The other configurations, composition, manufacturing method, and conditions of the electrolytic capacitor in Example 4 are the same as those of Example 1, with the same configuration, composition, manufacturing method, and conditions, except for the anode-side capacitance X of the anode foil and the cathode-side capacitance Y of the cathode body, and it is intended for medium-voltage applications with a rated voltage of 200V.

[0069] (Example 5) An electrolytic capacitor of Example 5, which is a laminate cell with a rated voltage of 200V, was fabricated. In the electrolytic capacitor of Example 5, a cathode body with a carbon layer formed by sputtering was used. No widening layer was formed on the cathode foil, and no pressing was performed in the process of forming the carbon layer. In addition, the electrolytic capacitor of Example 5 was fabricated using the same method and conditions as Example 4, including the composition of the carbon layer formed on the cathode foil.

[0070] (Comparative Example 3) Comparative Example 3, an electrolytic capacitor with a laminate cell rated at 200V, was fabricated. In the electrolytic capacitor of Comparative Example 3, a widened surface layer was formed on the cathode foil, but the carbon layer was not formed. Otherwise, the electrolytic capacitor of Comparative Example 3 was fabricated using the same method and conditions as in Example 4.

[0071] (Comparison of configurations) The similarities and differences between the electrolytic capacitors of Examples 4 and 5 and Comparative Example 3 are shown in Table 3 below. In Table 3, the combined capacitance was calculated assuming that the anode and cathode capacitors are in series within the electrolytic capacitor. That is, the combined capacitance was obtained by dividing the product of the anode capacitance X and cathode capacitance Y per unit area by the sum of the anode capacitance X and cathode capacitance Y per unit area. The capacitance occurrence rate is the ratio of the combined capacitance to the anode capacitance. (Table 3) TIFF0007917026000004.tif45145

[0072] As shown in Table 3, the anode-side capacitance X of the anode foil in Examples 4 and 5 and Comparative Example 3 was 1.77 [μF / cm²]. 2The difference from the anode-side capacitance X in Example 1, etc., is that the dielectric oxide film became relatively thinner because the voltage of the chemical conversion treatment was relatively lowered.

[0073] (Gas generation amount measurement test) The amount of gas generated by the electrolytic capacitors in Examples 4 and 5 and Comparative Example 3 was measured. A voltage of DC 214V was continuously applied to each electrolytic capacitor at a temperature of 105°C, and the amount of gas generated at each elapsed time was measured. The amount of gas generated was measured by the amount of swelling ΔV of the laminate cell. The amount of swelling ΔV of the laminate cell was measured by the Archimedes method. That is, the volume of liquid displaced by the laminate cell was measured by measuring the weight increase when the laminate cell was immersed in water.

[0074] Figure 3 shows the measurement results of the amount of gas generated. Figure 3 is a graph showing the time change in the amount of swelling ΔV of the electrolytic capacitors of Examples 4 and 5 and Comparative Example 3. As shown in Figure 3, after 500 hours of voltage application, Comparative Example 3 has swollen to about 1.5 times the amount of Examples 4 and 5. Also, after 250 hours, Example 5 began to expand rapidly. On the other hand, although the amount of swelling ΔV of the electrolytic capacitor of Example 4 is increasing, it can be seen that the electrolytic capacitor of Example 4 is expanding more slowly compared to Example 5 and Comparative Example 3.

[0075] From these results, the following phenomenon can be confirmed: In the electrolytic capacitor of Comparative Example 3, a hydrogen gas generation reaction associated with the reduction of protons occurred immediately after the start of the test, and the electrolytic capacitor of Comparative Example 3 showed a larger expansion amount ΔV per unit time compared to Examples 4 and 5 from the time the voltage was first applied.

[0076] On the other hand, it was confirmed that the electrolytic capacitors of Examples 4 and 5 are equipped with a cathode body having a carbon layer formed on the cathode foil, and that the capacitance of the anode foil and the cathode body are adjusted so that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body have a capacitance such that the ratio of X to Y is 1 to 10 or more for every 1 X, thereby suppressing the generation of hydrogen gas.

[0077] Furthermore, even when a cathode body has a carbon layer formed on the cathode foil, the electrolytic capacitor of Example 5, where the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body are in a ratio of X to Y of 14 for X to 1, exhibits a larger swelling ΔV after 500 hours than the electrolytic capacitor of Example 4, where the ratio of X to Y is greater than 14 for X to 1. This confirms that even when a cathode body has a carbon layer formed on the cathode foil, the generation of hydrogen gas is further suppressed by adjusting the capacitances of the anode foil and cathode body so that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body are in a ratio of X to Y greater than 14 for X to 1.

Claims

1. An electrolytic capacitor used for medium-to-high voltage applications of 160V or higher, comprising an anode foil with a dielectric oxide film formed thereon, a cathode body, and an electrolyte, The cathode body is A cathode foil made of valve-acting metal, A carbon layer formed on the cathode foil, It has, The anode foil and the cathode body have capacitances such that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body, which is the same as that of the anode foil, have a capacitance such that the ratio of X to Y is 10 or more for every 1 X. An electrolytic capacitor characterized by the following features.

2. The anode foil and the cathode body have capacitances such that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body, which is the same as that of the anode foil, have a capacitance such that, in the ratio of X to Y, Y is greater than 14 for every 1 X. The electrolytic capacitor according to claim 1, characterized by the above.

3. The anode foil is The expanded portion formed on the foil surface, A dielectric oxide film with a thickness of 200 nm or more is formed on the surface of the enlarged portion, Having The electrolytic capacitor according to claim 1 or 2, characterized by the above.

4. The electrolyte contains water. An electrolytic capacitor according to any one of claims 1 to 3, characterized by the above.

5. The electrolyte contains a nitro compound. An electrolytic capacitor according to any one of claims 1 to 4, characterized by the above.

6. The cathode foil has a native oxide film or a chemical conversion film on its surface. An electrolytic capacitor according to any one of claims 1 to 5, characterized by the above.

7. The anode foil has a widening layer having tunnel-shaped pits, a widening layer formed by sintering valve-acting metal powder, or a widening layer formed by depositing a film of metal particles. An electrolytic capacitor according to any one of claims 1 to 6, characterized by the above.

8. A method for manufacturing an electrolytic capacitor used for medium-to-high voltage applications of 160V or higher, comprising an anode foil with a dielectric oxide film formed thereon, a cathode body, and an electrolyte, The cathode body comprises a cathode foil made of a valve-acting metal and a carbon layer formed on the cathode foil. The anode foil and the cathode body are adjusted so that the capacitance X per unit area of ​​the anode foil and the capacitance Y per unit area of ​​the cathode body, which is the same as that of the anode foil, have a capacitance such that the ratio of X to Y is 1 for every 10 or more units of X. A method for manufacturing electrolytic capacitors characterized by the following.

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