Electrolytic capacitor and method of manufacturing the same

Abstract

To provide an electrolytic capacitor for uses under middle and high voltages of 160 V or higher, which is arranged so that the total amount of gas generated in the electrolytic capacitor is reduced.SOLUTION: An electrolytic capacitor comprises an anode foil with a dielectric oxide film formed thereon, and a cathode body. The cathode body includes a negative electrode foil made of a valve action metal, and a carbon layer formed on the negative electrode foil. The anode foil and the cathode body are regulated in electrostatic capacitance so as to have such an electrostatic capacitance that as for the proportion of X and Y of an electrostatic capacitance X per unit area of the anode foil vs. an electrostatic capacitance Y per unit area of the cathode body, Y becomes 10 or more to X of 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present 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 consists of a capacitor element impregnated with an electrolyte housed in an outer case, sealed with a seal, and a lead terminal extending from the seal. The capacitor element consists of an anode foil, made of a valve metal foil with a dielectric oxide film formed thereon, facing a cathode foil made of the same or another metal, with a separator interposed between the anode and cathode foils.

[0003] The electrolyte is interposed between the anode and cathode foils, in close contact with the uneven surface of the anode foil, and functions as a true cathode. This electrolytic capacitor can be considered a series capacitor, 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 calculated by dividing the effective area of ​​the anode foil facing the cathode foil by S [m 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 -12 If the velocity is [F / m], it can be approximated by the following equation 1. (Formula 1) C=8.854×10 -12 ×ε S / d

[0004] Electrolytic capacitors may be required to withstand voltages of 160V or higher, such as in automotive applications like electric vehicles and power applications. The thickness d of the dielectric oxide film on the anode foil significantly affects the withstand voltage of an electrolytic capacitor. Therefore, electrolytic capacitors capable of withstanding medium- to high-voltage 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, thereby decreasing the capacitance C. Therefore, electrolytic capacitors for medium- to high-voltage applications of 160V or higher incorporate a surface-expanding layer on the anode foil, which is composed of numerous tunnel-shaped pits. Furthermore, electrolytic capacitors for medium- to high-voltage applications of 160V or higher incorporate a surface-expanding layer on the anode foil, which has tunnel-shaped pits that penetrate the foil partially or entirely. This surface-expanding technology allows electrolytic capacitors for medium- to high-voltage applications of 160V or higher to achieve a large surface area for the anode foil while maintaining the thickness of the dielectric oxide film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-181368 Summary of the Invention [Problem to be solved by the invention]

[0006] Gases are generated in electrolytic capacitors due to various phenomena. For example, on the anode side, when the dielectric oxide film dissolves and the moisture in the electrolyte comes into contact with the valve metal, hydrogen gas is generated due to hydration degradation of the valve metal. Hydrogen gas is also generated at the foil interface on the cathode side. If the amount of gas generated in an electrolytic capacitor increases, it may cause swelling of the exterior case, opening of the valve, or leakage of the electrolyte.

[0007] On the other hand, in recent years, electrolytic capacitors for medium to high voltage applications of 160V or more are required to have even larger capacitance. In other words, there is also a demand for thinner dielectric oxide films while maintaining the withstand voltage. However, as the thickness of the dielectric oxide film decreases, the withstand voltage of the anode foil decreases and the leakage current increases. When leakage current occurs, hydroxide ions (OH) present due to the dissociation of water in the electrolyte are released. - ) reacts with oxygen ions (O 2- ) is generated, and aluminum ions (Al 3+ ) reacts with the electrolyte to form a dielectric oxide film, and electrons are generated. In other words, an increase in leakage current significantly increases the amount of electrons generated. At this time, protons (H + ) increases.

[0008] As the leakage current increases, the electrons that increase on the anode foil move to the cathode foil. On the cathode foil side, protons in the electrolyte near the cathode foil receive the 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, which corresponds to the leakage current of the capacitor, according to Faraday's law. In other words, if the dielectric oxide film on the anode foil is made thinner to increase the capacitance C, the amount of molecular hydrogen generated increases with the increase in leakage current, causing the internal pressure of the capacitor to rise in a short period of time, resulting in a problem of shortening the capacitor's lifespan.

[0009] To address this issue, it has been considered to add gas absorbents or gas control agents such as nitro compounds to the electrolyte of electrolytic capacitors. However, nitro compounds tend to lower the withstand voltage of electrolytic capacitors, so it is desirable to reduce the amount added for electrolytic capacitors that require medium to high voltages of 160V or more.

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

[0011] First, let us define the capacitance appearance rate. The capacitance appearance rate is the ratio of the capacitance of an electrolytic capacitor to the capacitance of the anode side. In other words, the capacitance appearance rate is the percentage obtained by dividing the total capacitance by the anode side capacitance, assuming that the electrolytic capacitor is a capacitor with the anode and cathode sides connected in series. The total capacitance is obtained by multiplying the anode side capacitance and the cathode side capacitance and dividing the result by the sum of the anode side capacitance and the cathode side capacitance. Therefore, the capacitance appearance rate is expressed by the following equation 2.

[0012] (Formula 2) TIFF0007760829000001.tif16161

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

[0014] In the field of electrolytic capacitors, anode foils for electrolytic capacitors intended for so-called medium- to high-voltage applications (160 V or higher) have a smaller capacitance per unit area than anode foils for electrolytic capacitors intended for low-voltage applications. In electrolytic capacitors intended for medium- to high-voltage applications, the difference in capacitance between the anode and cathode sides is large. This is because the dielectric oxide film on the surface of the surface-expanded layer is thicker in anode foils for electrolytic capacitors intended for medium- to high-voltage applications to ensure sufficient withstand voltage. From the perspective of improving the capacitance appearance rate, in electrolytic capacitors in the low-voltage range where the anode capacitance is large, increasing the cathode capacitance is highly effective in increasing the capacitance appearance rate. However, in electrolytic capacitors intended for medium- to high-voltage applications where the anode capacitance is small, or where the cathode capacitance is more than one order of magnitude larger than the anode capacitance, increasing the cathode capacitance has little effect on the capacitance appearance rate.

[0015] In other words, when the anode capacitance is large, increasing the cathode capacitance increases the capacitance appearance rate. In other words, for electrolytic capacitors intended for low-voltage applications (less than 160 V) with a large anode capacitance, increasing the cathode capacitance is significant. On the other hand, when the anode capacitance is small, the cathode capacitance only contributes little to the capacitance appearance rate, and increasing the cathode capacitance has almost no effect on the capacitance appearance rate. In other words, for electrolytic capacitors intended for medium- to high-voltage applications (160 V or higher) with a small anode capacitance, increasing the cathode capacitance is extremely insignificant.

[0016] In electrolytic capacitors for medium- to high-voltage applications, where improving the capacitance on the cathode side has little effect on the capacitance appearance rate, the capacitance of the cathode foil has not been improved due to the increased number of processes that would be required if a carbon material were used. However, as a result of extensive research by the present inventors, it was found that in electrolytic capacitors for medium- to high-voltage applications of 160 V or more, the total amount of gas generated within the electrolytic capacitor can be suppressed by forming a carbon layer on the cathode foil and making the capacitance on the cathode side 10 times or more the capacitance on the anode side.

[0017] The present invention was made based on this finding obtained by the present inventors, and in order to solve the above-mentioned problems, the present invention provides an electrolytic capacitor comprising an anode foil on which a dielectric oxide film is formed 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 the anode foil and the cathode body have capacitances such that the anode foil has a capacitance X per unit area and the cathode body has a capacitance Y per unit area equal to that of the anode foil, such that the ratio of X to Y is 1:10 or greater.

[0018] The anode foil and the cathode body may have a capacitance such that a ratio of X to Y is 1 to Y greater than 14, where X is a capacitance per unit area of ​​the anode foil and Y is a capacitance per unit area of ​​the cathode body equal to that of the anode foil.

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

[0020] The anode foil has a capacitance of 3.5 μF / cm 2 The capacitance X may be as follows:

[0021] It may also be used for medium to high voltage applications of 160V or more. [Effects of the Invention]

[0022] According to the present invention, even in electrolytic capacitors for medium to high voltage applications, the amount of gas generated in the electrolytic capacitor can be suppressed. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a graph showing the amount of swelling of the electrolytic capacitors of Examples 1 and 2 and Comparative Example 1. [Figure 2] 10 is a graph showing the amount of swelling of the electrolytic capacitors of Example 3 and Comparative Example 2. [Figure 3]1 is a graph showing the amount of swelling of the electrolytic capacitors of Examples 4 and 5 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0024] (electrolytic capacitor) An electrode assembly according to an embodiment of the present invention and an electrolytic capacitor using this electrode assembly as a cathode are described below. An electrolytic capacitor is a passive element that stores and discharges electric charge according to its capacitance. This electrolytic capacitor has a wound or stacked capacitor element. The capacitor element is formed by placing an anode foil having a dielectric oxide film formed on its surface and a cathode body facing each other via a separator, and impregnating the anode foil with an electrolytic solution. The electrolytic solution is in close contact with the uneven surface of the dielectric oxide film on the anode foil, and functions as a true cathode. The electrolytic solution may be solidified into a gel.

[0025] (cathode body) The cathode body has a cathode foil made of elongated valve metal as a current collector. The cathode foil has a natural oxide film or a chemical conversion film formed on its surface. The oxide film is formed naturally or intentionally. A natural oxide film is formed when the cathode foil reacts with oxygen in the air, while a chemical conversion film is formed intentionally by applying a voltage in a solution without halogen ions, such as an aqueous solution of adipic acid, boric acid, or phosphoric acid. When the valve metal is aluminum foil, the oxide film is aluminum oxide.

[0026] A carbon layer containing a carbon material as a main material is formed on the surface of this cathode foil. That is, the cathode body has an oxide film as an insulating layer on the cathode foil, which is a current collector, and a carbon layer on this oxide film. The carbon layer is located on the outermost surface of the cathode body. It is preferable that the carbon layer is in close contact with the cathode foil and is not easily peeled off from the cathode foil even when subjected to impact. To improve the adhesion between the carbon layer and the cathode foil, it is preferable to form a surface-expanding layer on the surface of the cathode foil and then form the carbon layer on the surface-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 now be described in detail. The valve metals constituting the cathode foil include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity is preferably about 99% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be included. For example, the cathode foil may be made of an aluminum material designated by the temper code H in accordance with JIS standard H0001, known as an H material, or an aluminum material designated by the temper code O in accordance with JIS standard H0001, known as an O material.

[0028] The surface-expanding layer is formed by electrolytic etching, chemical etching, sandblasting, or the like, or by vapor deposition or sintering of metal particles or the like onto the foil. Examples of electrolytic etching include AC etching. In AC etching, the cathode foil is immersed in an acidic aqueous solution containing halogen ions, such as hydrochloric acid, and an AC current is passed through it. In chemical etching, the metal foil is immersed in an acid or alkaline solution. In other words, the surface-expanding layer refers to a region where spongy etching pits are formed or a 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 tunnel-shaped pits formed so as to penetrate the cathode foil.

[0029] Examples of carbon materials contained in the carbon layer include activated carbon, graphite, carbon black, carbon nanohorns, and fibrous carbon. Activated carbon is made from natural plant tissues such as coconut husks, synthetic resins such as phenols, and fossil fuels such as coal, coke, and pitch. Examples of graphite include natural graphite, artificial graphite, and graphitized ketjen black. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs) and carbon nanofibers (hereinafter referred to as CNFs).

[0030] As the carbon material contained in the carbon layer, carbon black, which is spherical carbon, is particularly preferred. When the surface-expanding layer formed on the surface of the cathode foil has etching pits, using carbon black with a particle size smaller than the opening diameter of the etching pits allows the carbon layer to easily penetrate deeper into the etching pits, and the carbon layer adheres 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 material contained in the carbon layer may suitably be a combination of flaky or scale-like graphite and spherical carbon (carbon black). The flaky or scale-like graphite preferably has an aspect ratio of its minor axis to its major axis in the range of 1:5 to 1:100. The spherical carbon (carbon black) preferably has an average primary particle diameter of 100 nm or less. When a carbon layer containing this combination of carbon materials is laminated on a cathode foil, the carbon black is easily rubbed into the pores of the surface-expanding layer by the graphite. The graphite easily deforms along the uneven surface of the surface-expanding layer and easily accumulates on the uneven surface. The graphite then acts as a pressing lid to hold down the spherical carbon rubbed into the pores. This further enhances the adhesion and fixation between the carbon layer and the cathode foil.

[0032] In addition, activated carbon and fibrous carbon have delocalized pi electrons and a large specific surface area, and therefore may be added to the carbon layer together with carbon black, which is spherical carbon, or may be added to the carbon layer together with a mixture of flake-like or scaly graphite and carbon black, which is spherical carbon.

[0033] Methods for forming a carbon layer on a cathode foil include vacuum deposition, sputtering, ion plating, CVD, coating, electrolytic plating, and electroless plating. In the coating method, a carbon material is dispersed in a dispersion solvent to prepare a slurry, which is then coated on the cathode foil by a slurry casting method, doctor blade method, spray atomization method, or the like, and dried. In the deposition method, the carbon material is evaporated by heating with electrical current in a vacuum, or by irradiating the carbon material with an electron beam in a vacuum, forming a film of the carbon material on the cathode foil. In the sputtering method, a target made of a 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, causing the plasma-generated inert gas to collide with the target, and carbon material particles knocked out from the target are deposited on the cathode foil.

[0034] After laminating the carbon layer and the cathode foil, it is preferable to press them together. In the press process, for example, the cathode body consisting of the carbon layer and the cathode foil is sandwiched between press rollers and a linear press pressure is applied. The press pressure is 0.01 to 100 t / cm. 2 As long as the carbon layer and the cathode foil can be pressure-welded, there are no particular limitations on the pressure-welded structure formed at the interface of the cathode foil. However, if a pressing process is used to force the carbon material into the pores of the surface-expanding layer and deform the carbon material along the uneven surface of the surface-expanding 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 surface-expanding layer by graphite under pressure, and the graphite is likely to deform and pile up along the uneven surface of the surface-expanding layer.

[0035] The carbon material may also be subjected to a porous treatment such as an activation treatment or an opening treatment. Conventional activation treatments, such as gas activation and chemical activation, can be used as the porous treatment. Examples of gases used in gas activation include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, and mixtures of these. Examples of chemicals used in chemical activation 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, and inorganic salts such as zinc chloride. Heat treatment is optionally performed during this activation treatment.

[0036] (anode foil) The anode foil is a long foil made of a valve metal. The purity of the anode foil is preferably about 99.9% or higher. This anode foil is made by forming a surface-expanding layer on a stretched foil and then forming a dielectric oxide film on the surface of the surface-expanding layer. The surface-expanding layer is suitable for medium- to high-voltage applications of 160 V or higher, and has numerous tunnel-shaped pits dug into the foil surface in the thickness direction by direct current etching. To accommodate higher capacities in medium- to high-voltage applications of 160 V or higher, the tunnel-shaped pits may be formed so as to penetrate the anode foil. Alternatively, the surface-expanding layer may be made 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 chemical conversion treatment in which a voltage is applied in a solution free of halogen ions, such as an acid such as ammonium borate, ammonium phosphate, or ammonium adipate, or an aqueous solution of such an acid. By having a thickness of 200 nm or more, the dielectric oxide film can contribute to the withstand voltage of electrolytic capacitors, even in medium- to high-voltage applications of 160 V or more.

[0038] (Capacitance ratio of anode foil to cathode body) In this electrolytic capacitor, the cathode capacitance is generated by the electric double layer action that occurs at the interface between the electrolyte and the cathode body, and the anode capacitance is generated by the dielectric polarization action. The anode foil used in medium- to high-voltage electrolytic capacitors has a capacitance of 3.5 μF / cm 2 The following anode capacitance is generated:

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

[0040] The method for adjusting the capacitance includes, for example, adjusting the thickness of the dielectric oxide film and adjusting the surface area of ​​the surface-expanding layer by etching, and is not limited to any known method.

[0041] (electrolyte) The electrolyte is a mixed solution in which a solute is dissolved in a solvent, and additives are added 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 160 V or more. However, as long as the required withstand voltage can be obtained through surface expansion treatment and chemical conversion treatment of the anode foil, the solvent may be either a protic polar solvent or an aprotic polar solvent. 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 electrolytic solution includes anionic and cationic components, and is typically an organic acid or its salt, an inorganic acid or its salt, or a composite 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. An acid that becomes an anion and a base that becomes a cation may be added separately to the electrolytic solution 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 (mannite, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, and phosphate esters. These may be used alone 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-nitrobenzene, o-nitrophenol, m-nitrophenol, and p-nitrophenol. Nitro compounds have the ability to absorb hydrogen gas.

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

[0045] (Example) The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0046] (Examples 1 and 2) Example 1 An electrolytic capacitor of Example 1 was fabricated for high-voltage applications, having 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 an AC etching process, and a surface-enlarging layer consisting of spongy etching pits was formed on both sides of the foil. In the AC etching process, the cathode foil was immersed in an acidic aqueous solution containing approximately 8% by weight of hydrochloric acid as the main electrolyte at a liquid temperature of 25°C, and an AC current of 10 Hz and a current density of 0.14 A / cm was applied. 2 A current of 1000kJ / cm2 was applied to the substrate for approximately 5 minutes to expand both sides of the aluminum foil. The aluminum foil was then subjected to a chemical conversion treatment to form a dielectric oxide film on the surface of the surface-expanding layer. For the chemical conversion treatment, chlorine that had adhered during the AC etching process was removed using a phosphoric acid solution, and then a voltage was applied in an ammonium dihydrogen phosphate solution.

[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 carboxymethyl cellulose sodium (CMC-Na) as a dispersant-containing solution.

[0048] This slurry was uniformly applied to the cathode foil. The slurry was then heated and dried to volatilize the solvent, after which the cathode body was pressed. In the press process, the cathode body was sandwiched between press rollers and pressed with a pressure of 5.38 kNcm. -1 The carbon layer was fixed onto the cathode foil by applying a linear pressure of 180 mm. The linear pressure was applied using a press machine manufactured by Takumi Giken Co., Ltd. The diameter of the press roller was 180 mm, the press width was 130 mm, and the cathode body was transported once at a speed of 3 m / min.

[0049] A strip of aluminum foil was used as the anode foil. The aluminum foil was subjected to a direct current etching process to form a surface-expanding layer consisting of tunnel-shaped etching pits. The direct current etching process involved a first step to form pits and a second step to expand the pits. In the first step, the aluminum foil was electrochemically etched with a direct current in an aqueous solution containing chloride ions. The etching in the first step was carried out at a current density of 400 mA / cm. 2 In the second step, in order to enlarge the pits formed in the aluminum foil after the first step, an electrochemical etching treatment was carried out using a direct current in an aqueous solution containing nitrate ions. The current density of the etching treatment in the second step was 300 mA / cm. 2 This was done for about 2 minutes.

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

[0051] An aluminum tab-shaped lead terminal was ultrasonically connected to each of the anode foil and cathode body. A separator was sandwiched between the anode foil and cathode body and then wound. A kraft separator was used as the separator. The wound anode foil, cathode body, and separator was impregnated with an electrolyte. The electrolyte contained ethylene glycol as a solvent and azelaic acid salt as a solute. Paranitrobenzyl alcohol, a nitro compound, was also added to the electrolyte so that its concentration was 2 wt % of the total electrolyte volume.

[0052] The sealing body had external terminals attached to a phenolic laminate plate. After impregnation with the electrolyte, the lead terminals extending from the wound body were connected to the external terminals of the sealing body, and the wound body and sealing body were 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 was subjected to an aging treatment. The aging treatment involved applying a voltage of 481 V for 95 minutes at room temperature (30°C). This resulted in the production of an electrolytic capacitor according to Example 1, which was cylindrical with a diameter of 30 mm and a height of 60 mm and a rated voltage of 450 V.

[0053] Example 2 An electrolytic capacitor of Example 2 was fabricated for high-voltage applications, having a cylindrical shape with a diameter of 30 mm and a height of 60 mm and a rated voltage of 450 V. The electrolytic capacitor of Example 2 used a cathode body on which a carbon layer was formed by sputtering. No surface-enlarging layer was formed on the cathode foil, and no press working was performed in the process of forming the carbon layer. The electrolytic capacitor of Example 2 was fabricated using the same method and conditions as Example 1, including the composition of the carbon layer formed on the cathode foil.

[0054] (Comparative Example 1) An electrolytic capacitor of Comparative Example 1 was fabricated for high-voltage applications, having a cylindrical shape with a diameter of 30 mm and a height of 60 mm and a rated voltage of 450 V. In the electrolytic capacitor of Comparative Example 1, a surface-enlarging layer was formed on the cathode foil, but no carbon layer was formed. Furthermore, no press working was performed. Otherwise, the electrolytic capacitor of Comparative Example 1 was fabricated using the same method and under the same conditions as Example 1.

[0055] (Configuration comparison) 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 were connected in series within the electrolytic capacitor. That is, the combined capacitance was obtained by multiplying the anode-side capacitance X by the cathode-side capacitance Y per unit area and dividing the result by the sum of the anode-side capacitance X and the cathode-side capacitance Y per unit area. The capacitance appearance ratio is the ratio of the combined capacitance to the anode-side capacitance. (Table 1) TIFF0007760829000002.tif45145

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

[0057] The measurement results of the amount of gas generated are shown in Figure 1. Figure 1 is a graph showing the change in the amount of swelling ΔL over time for Examples 1 and 2 and Comparative Example 1. As shown in Figure 1, from 250 hours to 500 hours after voltage application, the rate of change in the amount of swelling ΔL is the same for Examples 1 and 2 and Comparative Example 1. However, from 500 hours to approximately 750 hours after voltage application, only the electrolytic capacitor of Comparative Example 1 shows rapid expansion. The rate of change in the amount of swelling ΔL for the electrolytic capacitors of Examples 1 and 2 does not change between 250 hours to 500 hours after voltage application and between 500 hours to approximately 750 hours after voltage application.

[0058] These results confirm the occurrence of the following phenomenon. That is, even in the electrolytic capacitor of Comparative Example 1, from 250 hours after voltage application until 500 hours had passed, the nitro compounds that bonded with hydrogen atoms remained, suppressing the generation of hydrogen gas. However, in the electrolytic capacitor of Comparative Example 1, around 500 hours after voltage application, all the nitro compounds had bonded with hydrogen atoms, and there was no nitro compound left to bond with hydrogen atoms. As a result, the nitro compounds no longer worked to suppress hydrogen gas generation, and the electrolytic capacitor of Comparative Example 1 suddenly expanded after 500 hours had passed since voltage application.

[0059] On the other hand, the electrolytic capacitors of Examples 1 and 2 include a cathode body with a carbon layer formed on the cathode foil, and the capacitances of the anode foil and cathode body are adjusted so that the ratio of the capacitance per unit area of ​​the anode foil (X) to the capacitance per unit area of ​​the cathode body (Y) is 10 or greater. This suppresses hydrogen gas generation. 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 the nitro compound occur simultaneously. This is thought to be due to the fact that many nitro compounds capable of bonding with hydrogen atoms remain even 500 hours after voltage application. Therefore, the electrolytic capacitors of Examples 1 and 2 did not suddenly expand even after 500 hours of voltage application. Thus, the results of Examples 1 and 2 and Comparative Example 1 confirm that the electrolytic capacitors of Examples 1 and 2 suppress hydrogen gas generation.

[0060] Example 3 An electrolytic capacitor of Example 3 was fabricated. The electrolytic capacitor of Example 3 used an output terminal composed of an aluminum wire and a metal wire. Specifically, the aluminum wire had a flat portion formed by crushing one end of a round bar shape using a press or other process, and an unpressed round bar portion at the other end. The tip of the round bar portion was connected to the metal wire by arc welding or other process. The flat portion was connected to the cathode body and the anode foil, respectively, using various connection methods. A rubber seal was used, with a through hole formed therein for inserting the metal wire. The metal wire leading from the wound body was passed through the insertion hole in the seal body to be integrated, and the wound body and seal body were inserted into an aluminum exterior case. Other than being cylindrical with a diameter of 16 mm and a height of 50 mm, the capacitor was fabricated using the same configuration, composition, manufacturing method, and conditions as Example 1, and was intended for high-voltage applications with a rated voltage of 450 V.

[0061] (Comparative Example 2) An electrolytic capacitor of Comparative Example 2 was produced. The electrolytic capacitor of Comparative Example 2 had the same structures as those of Example 3 in terms of the lead-out terminal and sealing body. In addition, except for the fact that it was a cylindrical capacitor with the same dimensions as those of Example 3 and the cathode-side capacitance Y of the cathode body, it was produced with the same structure, composition, manufacturing method, and conditions as those of Comparative Example 1, and was intended for high-voltage use with a rated voltage of 450 V.

[0062] (Configuration comparison) 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 were connected in series within the electrolytic capacitor. That is, the combined capacitance was obtained by multiplying the anode-side capacitance X by the cathode-side capacitance Y per unit area and dividing the result by the sum of the anode-side capacitance X and the cathode-side capacitance Y per unit area. The capacitance appearance ratio is the ratio of the combined capacitance to the anode-side capacitance. (Table 2) TIFF0007760829000003.tif35145

[0063] (Gas generation amount measurement test) The gas generation amount was measured for the electrolytic capacitors of Example 3 and Comparative Example 2. The high voltage application conditions and the method and conditions for measuring the swelling amount of the outer case 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 amount of gas generated are shown in Figure 2. Figure 2 is a graph showing the change in the amount of swelling ΔL over time for Example 3 and Comparative Example 2. As shown in Figure 2, the electrolytic capacitor of Comparative Example 2 began to expand suddenly 500 hours after voltage application. On the other hand, the amount of swelling ΔL of the electrolytic capacitor of Example 3 remained almost unchanged, 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 consumed completely in the electrolytic capacitor of Comparative Example 2, and the suppression of hydrogen gas generation by the nitro compound was no longer effective, but in the electrolytic capacitor of Example 3, even after 3,000 hours, a large amount of nitro compound capable of bonding with hydrogen atoms remained, and hydrogen gas generation was suppressed. Thus, the results of Example 3 and Comparative Example 2 also confirmed that hydrogen gas generation was suppressed by providing a cathode body having a carbon layer formed on the cathode foil, and by adjusting the capacitances of the anode foil and the cathode body so that the ratio of the capacitance X per unit area of ​​the anode foil to the capacitance Y per unit area of ​​the cathode body is 1:10 or greater.

[0066] (Examples 4 to 5) Example 4 An electrolytic capacitor of Example 4 was fabricated. The electrolytic capacitor of Example 4 was a laminate cell with a rated voltage of 200 V. The anode foil was subjected to a chemical conversion treatment by applying a voltage of 286 V. Aluminum tab-shaped lead-out terminals were ultrasonically connected to the anode foil and cathode body, respectively. A separator folded zigzag was then prepared, and the cathode body and anode foil were alternately sandwiched between the folds, thereby fabricating a laminate of the cathode body, anode foil, and separator, with the cathode body and anode foil facing each other with the separator interposed therebetween.

[0067] After the laminate was impregnated with the electrolyte, the laminate was sealed in a laminate material. The solvent for the electrolyte was ethylene glycol, to which azelaic acid salt was added as a solute. However, no nitro compounds such as paranitrobenzyl alcohol were added to the electrolyte. After the laminate cell was fabricated, it was subjected to an aging treatment. For the aging treatment, a voltage of 230 V was applied to the laminate cell at room temperature (25°C) for 120 minutes, and then a voltage of 230 V was applied for 60 minutes in a temperature environment of 85°C.

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

[0069] Example 5 An electrolytic capacitor of Example 5, which is a laminate cell with a rated voltage of 200 V, was fabricated. The electrolytic capacitor of Example 5 used a cathode body on which a carbon layer was formed by sputtering. A surface-expanding layer was not formed on the cathode foil, and no press working was performed in the process of forming the carbon layer. The electrolytic capacitor of Example 5 was fabricated using the same method and under the same conditions as Example 4, including the composition of the carbon layer formed on the cathode foil.

[0070] (Comparative Example 3) An electrolytic capacitor of Comparative Example 3 was fabricated as a laminate cell with a rated voltage of 200 V. In the electrolytic capacitor of Comparative Example 3, a surface-expanding layer was formed on the cathode foil, but no carbon layer was formed. Otherwise, the electrolytic capacitor of Comparative Example 3 was fabricated by the same method and under the same conditions as Example 4.

[0071] (Configuration comparison) 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-side and cathode-side capacitors were connected in series within the electrolytic capacitor. That is, the combined capacitance was obtained by multiplying the anode-side capacitance X by the cathode-side capacitance Y per unit area and dividing the result by the sum of the anode-side capacitance X and the cathode-side capacitance Y per unit area. The capacitance appearance ratio is the ratio of the combined capacitance to the anode-side capacitance. (Table 3) TIFF0007760829000004.tif45145

[0072] As shown in Table 3, the anode-side capacitance X of the anode foils of Examples 4 and 5 and Comparative Example 3 was 1.77 μF / cm 2The difference from the anode-side capacitance X in Example 1 and the like is due to the fact that the voltage for the chemical conversion treatment was relatively low, resulting in a relatively thin dielectric oxide film.

[0073] (Gas generation amount measurement test) The gas generation amounts of the electrolytic capacitors of Examples 4 and 5 and Comparative Example 3 were measured. A DC voltage of 214 V was continuously applied to each electrolytic capacitor in a temperature environment of 105°C, and the gas generation amount was measured at each elapsed time. The gas generation amount was measured by the swelling amount ΔV of the laminate cell. The swelling amount ΔV of the laminate cell was measured by 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] The measurement results of the amount of gas generated are shown in Figure 3. Figure 3 is a graph showing the change over time in the swelling amount 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 swelled by about 1.5 times compared to Examples 4 and 5. Furthermore, Example 5 began to expand suddenly after 250 hours. On the other hand, although the swelling amount ΔV of the electrolytic capacitor of Example 4 increased, it was found that the electrolytic capacitor of Example 4 expanded more slowly than Example 5 and Comparative Example 3.

[0075] These results confirm the following phenomenon: In the electrolytic capacitor of Comparative Example 3, a hydrogen gas generation reaction accompanied by a proton reduction reaction occurred immediately after the start of the test, and the electrolytic capacitor of Comparative Example 3 had a larger expansion amount ΔV per unit time from the start of voltage application compared to Examples 4 and 5.

[0076] On the other hand, the electrolytic capacitors of Examples 4 and 5 were equipped with a cathode body in which a carbon layer was formed on a cathode foil, and the capacitances of the anode foil and the cathode body were adjusted so that the ratio of the capacitance X per unit area of ​​the anode foil to the capacitance Y per unit area of ​​the cathode body was 1:10 or more. This confirmed that hydrogen gas generation was suppressed.

[0077] Furthermore, the electrolytic capacitor of Example 5, which includes a cathode body with a carbon layer formed on the cathode foil, in which the ratio of the capacitance X per unit area of ​​the anode foil to the capacitance Y per unit area of ​​the cathode body is 1:14, has a larger swelling amount ΔV after 500 hours than the electrolytic capacitor of Example 4, in which the ratio of X to Y is 1:14. This demonstrates that even when the cathode body includes a carbon layer formed on the cathode foil, adjusting the capacitances of the anode foil and the cathode body so that the ratio of the capacitance X per unit area of ​​the anode foil to the capacitance Y per unit area of ​​the cathode body is 1:14, further suppresses the generation of hydrogen gas.

Claims

1. An electrolytic capacitor used for medium to high voltage applications of 160 V or more, comprising an anode foil on which a dielectric oxide film is formed, a cathode body, and an electrolyte, The cathode body is a cathode foil made of a valve metal; a carbon layer formed on the cathode foil; and the anode foil and the cathode body have a capacitance such that a ratio of X to Y is 1:10 or greater, where X is a capacitance per unit area of ​​the anode foil and Y is a capacitance per unit area of ​​the cathode body equal to that of the anode foil; The anode foil has a resistance of 3.5 μF / cm ２ Having the following capacitance X: An electrolytic capacitor characterized by:

2. the anode foil and the cathode body have a capacitance such that a ratio of X to Y is 1 to Y greater than 14, where X is a capacitance per unit area of ​​the anode foil and Y is a capacitance per unit area of ​​the cathode body equal to that of the anode foil; 2. The electrolytic capacitor according to claim 1,

3. The anode foil is an enlarged surface portion formed on the foil surface; a dielectric oxide film having a thickness of 200 nm or more formed on the surface of the enlarged surface portion; having 3. The electrolytic capacitor according to claim 1 or 2,

4. the electrolyte solution contains water; 4. The electrolytic capacitor according to claim 1, wherein:

5. the electrolyte solution contains a nitro compound; 5. The electrolytic capacitor according to claim 1, wherein:

6. the cathode foil has a natural oxide film or a chemical conversion film on its surface; 6. The electrolytic capacitor according to claim 1, wherein:

7. the anode foil has a surface-expanding layer having tunnel-shaped pits, a surface-expanding layer formed by sintering valve metal powder, or a surface-expanding layer formed by vapor-depositing a film of metal particles; 7. The electrolytic capacitor according to claim 1, wherein:

8. A method for manufacturing an electrolytic capacitor used for medium to high voltage applications of 160 V or more, the electrolytic capacitor comprising an anode foil having a dielectric oxide film formed thereon, a cathode body, and an electrolyte, the method comprising: the cathode body includes a cathode foil made of a valve metal and a carbon layer formed on the cathode foil, the anode foil and the cathode body are adjusted so that a capacitance X per unit area of ​​the anode foil and a capacitance Y per unit area of ​​the cathode body equal to that of the anode foil are such that a ratio of X to Y is 1:10 or more, and the capacitance X per unit area of ​​the anode foil is 3.5 μF / cm2 or less; A method for manufacturing an electrolytic capacitor, comprising:

Images