Electrolytic capacitor, electrolyte, and method for manufacturing an electrolytic capacitor

Abstract

This invention provides an electrolytic capacitor with improved capacitance retention under extremely low temperature conditions using silicone oil, its electrolyte, and a method for manufacturing the electrolytic capacitor. [Solution] The electrolytic capacitor comprises an anode body on which a dielectric film is formed, a cathode body facing the anode body with the dielectric film in between, and an electrolyte. The electrolyte contains a polyhydric alcohol and silicone oil. The silicone oil contains, as a partial structure in its molecule, a linear polysiloxane and side chains of organic groups formed by substituting some of the methyl groups of the polysiloxane. The molecular weight of the polysiloxane accounts for 30% to 60% of the molecular weight of the silicone oil. This electrolytic capacitor includes an element formation step of forming a capacitor element including an anode body and a cathode body, and an impregnation step of impregnating the capacitor element with the electrolyte.

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor that obtains capacitance through the dielectric polarization effect of a dielectric film and stores and discharges electric charge, its electrolyte, and a method for manufacturing an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor is a passive element that stores and discharges electric charge by obtaining capacitance through the dielectric polarization effect of a dielectric film. An electrolytic capacitor is equipped with valve metals such as tantalum or aluminum as the anode and cathode. The anode is enlarged by shaping the valve metal into a sintered body or etched foil, and a dielectric film is formed on the enlarged surface by a treatment such as anodizing. An electrolyte is interposed between the anode and cathode. The electrolyte is in close contact with the uneven surface of the anode and functions as a true cathode.

[0003] The electrolyte is interposed between the dielectric film of the anode and the cathode foil, facilitating ion conduction between the anode and cathode. Therefore, the conductivity and temperature characteristics of the electrolyte significantly affect the electrical characteristics of the electrolytic capacitor, such as impedance, dielectric loss tangent (tanδ), and equivalent series resistance (ESR). Furthermore, the electrolyte repairs deterioration and damage to the dielectric film formed on the anode, affecting the leakage current (LC) and lifespan characteristics of the electrolytic capacitor.

[0004] Therefore, electrolytic capacitors should ideally use an electrolyte with at least high electrical conductivity. However, increasing the electrical conductivity of the electrolyte tends to lower the spark voltage, which may impair the voltage withstand characteristics of the electrolytic capacitor. From a safety standpoint, it is desirable for electrolytic capacitors to have high voltage withstand capabilities to prevent short circuits or fires even under harsh conditions where abnormal voltages exceeding the rated voltage are applied. Furthermore, electrolytic capacitors using electrolytes are susceptible to leakage. If electrolyte leaks from an electrolytic capacitor, in the worst case, it can damage surrounding electronic equipment.

[0005] Therefore, silicone oil is sometimes added to the electrolyte as a pressure-resistant agent. In addition, modified silicone oil is sometimes added to the electrolyte to facilitate miscibility with polyhydric alcohols such as ethylene glycol and glycerin, butyrolactone, dimethylformamide, etc., which are commonly used as solvents for electrolytes (see, for example, Patent Document 1). Modified silicone oil has hydrophilic groups such as hydroxyl groups, carboxyl groups, epoxy groups, polyether groups, polyoxyalkylenes, polyethylene oxides, and polypropylene oxides introduced into the polysiloxane skeleton. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 64-84617 [Overview of the project] [Problems that the invention aims to solve]

[0007] For example, in applications such as automotive use, electrolytic capacitors may be exposed to extremely low temperatures of -40°C. In such extremely low temperatures, the capacitance of electrolytic capacitors can decrease rapidly. One reason for this decrease in capacitance in extremely low temperatures is the high freezing point of the voltage-improving agent.

[0008] The present invention was proposed to solve the above problems, and its objective is to provide an electrolytic capacitor with further improved capacitance retention rate in an extremely low-temperature environment using silicone oil, the electrolyte, and a method for manufacturing the electrolytic capacitor. [Means for solving the problem]

[0009] To solve the above problems, the electrolytic capacitor of this embodiment comprises an anode body on which a dielectric film is formed, a cathode body facing the anode body with the dielectric film in between, and an electrolyte containing a polyhydric alcohol and silicone oil. The silicone oil contains, as a partial structure in its molecule, a linear polysiloxane and a side chain of an organic group formed by substituting some of the functional groups of the polysiloxane, and the molecular weight of the polysiloxane accounts for 30% to 60% of the molecular weight of the silicone oil.

[0010] The electrolyte may contain two or more types of silicone oils with different molecular weights of polysiloxane.

[0011] The molecular weight ratio of the polysiloxane in the total silicone oil accounts for, on average, 30% to 60% of the molecular weight of the silicone oil, and a portion of the silicone oil may have a molecular weight of polysiloxane that is less than 30% or more than 60% of the molecular weight of the silicone oil.

[0012] The aforementioned polyhydric alcohol may be ethylene glycol.

[0013] The electrolyte may further contain dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, diethyl adipate, or a combination thereof as a solvent.

[0014] The electrolyte may contain water.

[0015] To solve the above problems, the electrolyte of this embodiment contains a polyhydric alcohol and a silicone oil, wherein the silicone oil contains, as a partial structure in the molecule, a linear polysiloxane and a side chain of an organic group formed by substituting some of the functional groups of the polysiloxane, and the molecular weight of the polysiloxane accounts for 30% to 60% of the molecular weight of the silicone oil.

[0016] An element formation step of forming a capacitor element including an anode body and a cathode body, and an impregnation step of impregnating the capacitor element with an electrolytic solution, wherein the electrolytic solution contains a polyhydric alcohol and a silicone oil, and the silicone oil includes, as a partial structure in the molecule, a linear polysiloxane and a side chain of an organic group formed by substituting a part of the functional groups of the polysiloxane, and the molecular weight of the polysiloxane accounts for 30% or more and 60% or less of the molecular weight of the silicone oil.

Effect of the Invention

[0017] According to the present invention, the capacitance of the electrolytic capacitor can be further improved under a temperature environment of -40°C.

Brief Description of the Drawings

[0018] [Figure 1] It is a graph showing the results of 29Si-NMR analysis. [Figure 2] It is a graph showing the results of 1H-NMR analysis. [Figure 3] It is a graph showing the adhesion amount of the voltage withstand improver to each element of the capacitor element. [Figure 4] It is a scatter diagram plotting the measurement results of viscosity and a graph showing the theoretical values of viscosity. [Figure 5] (a) is the 1H-NMR analysis result of the first mixed liquid sample, (b) is the 1H-NMR analysis result of the second mixed liquid sample, (c) is the 1H-NMR analysis result of the third mixed liquid sample, and (d) is the 1H-NMR analysis result of the fourth mixed liquid sample.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the electrolytic capacitor according to the embodiment will be described. It should be noted that the present invention is not limited to the embodiments described below.

[0020] (Electrolytic Capacitor) An electrolytic capacitor is a passive element that stores and discharges electric charge by obtaining capacitance through the dielectric polarization effect of a dielectric film. An electrolytic capacitor comprises a capacitor element. The capacitor element comprises an anode, a cathode, and an electrolyte. A dielectric film is formed on the surface of the anode. The anode and cathode face each other with a separator in between. The electrolyte is impregnated into the capacitor element. By impregnating the capacitor element, the electrolyte is interposed between the dielectric film of the anode and the cathode, and functions as a true cathode in close contact with the dielectric film of the anode.

[0021] (Anode) The anode body is the anode-side electrode made of a valve metal, and is, for example, in the form of a thin plate or foil. This anode body may be formed by stretching a valve metal or by sintering a powder of a valve metal. Furthermore, the anode body may be formed by laminating powders of the same or different valve metals onto the surface of a stretched valve metal substrate by sintering or vapor deposition. Examples of valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the valve metal for the anode body is preferably 99.9% or higher, and other elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, and zirconium may be included.

[0022] An expanded surface layer is formed on one or both sides of the anode. The expanded surface layer is an etched layer obtained by etching the surface of the stretched anode, a sintered layer obtained by sintering valve metal powder, or a vapor-deposited layer obtained by depositing valve metal particles onto a foil. In other words, the expanded surface layer has a porous structure and consists of tunnel-shaped pits, sponge-like pits, or densely packed powder or voids between particles.

[0023] Tunnel-shaped etching pits are holes carved in the direction of the foil thickness. These tunnel-shaped etching pits are typically formed by passing a direct current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current through an acidic aqueous solution containing nitric acid, for example. Sponge-like etching pits cause the expanded layer to become a sponge-like layer with a series of fine voids. These sponge-like etching pits are formed by passing an alternating current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0024] The sintered layer is produced by pasteuring powder with a binder or solvent, applying it to a substrate and drying it, or by press-molding it in a mold and heating and sintering it in a vacuum or reducing atmosphere. The vapor-deposited layer is produced, for example, by resistance heating vapor deposition or electron beam heating vapor deposition. This vapor-deposited layer is formed by heating the same or different valve metal as the foil body with resistance heat or electron beam energy to evaporate it, and depositing the vapor of valve metal particles onto the surface of the foil body. In addition, a separation portion may be formed in the sintered layer to separate the sintered layers from each other.

[0025] The dielectric film is formed on one or both sides of the anode body on which the expanding layer is formed. The dielectric film is formed on the surface of the expanding layer, following the irregularities of the expanding layer. Typically, the dielectric film is an oxide film formed on the surface of the anode body, and if the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the expanding layer.

[0026] In the chemical conversion treatment for forming a dielectric film, a voltage is applied to the anode in the conversion solution to achieve a desired withstand voltage. Furthermore, in the chemical conversion treatment for forming a dielectric film, it is preferable to form a dielectric film with a thickness of 0.9 to 1.5 nm per 1 V of the target withstand voltage. For example, a dielectric film with a thickness of 270 nm or more may be formed to create a dielectric film with a withstand voltage of 300 V or more. Alternatively, a dielectric film with a thickness of 405 nm or more may be formed to create a dielectric film with a withstand voltage of 450 V or more. The conversion solution is a halogen-ion-free solution, such as a phosphoric acid-based conversion solution like ammonium dihydrogen phosphate, a boric acid-based conversion solution like ammonium borate, or an adipic acid-based conversion solution like ammonium adipate.

[0027] A pseudo-boehmite layer may be formed on the dielectric film. The pseudo-boehmite layer contains a hydrated aluminum oxide, such as AlOOH·xH2O or Al2O3·xH2O. On the other hand, the dielectric film is a layer of aluminum oxide containing γ-alumina, which is a crystalline oxide. This pseudo-boehmite layer is dense internally and functions as a resistive layer, improving the voltage withstand capability of the electrolytic capacitor.

[0028] (Cathole body) The cathode body is the cathode-side electrode made of a valve metal, and is, for example, in the form of a thin plate or foil. The purity of the valve metal with respect to the cathode body is preferably 99% or higher. A widening layer is formed on the cathode body. A plain foil without a widening layer may also be used as the cathode body. The cathode body may have a native oxide film or a thin oxide film of about 1 to 10 Vfs formed by chemical conversion treatment. The native oxide film is formed when the cathode body reacts with oxygen in the air.

[0029] Furthermore, the cathode body may be provided with a conductive layer. The conductive layer is laminated on the cathode body. The conductive layer may mainly contain inorganic materials or inorganic compounds. Examples of inorganic materials or inorganic compounds include titanium, zirconium, tantalum, niobium, nitrides or carbides thereof, aluminum carbide, carbon materials, and composites or mixtures thereof. Specifically, examples include a carbon layer which is a conductive layer of carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer which is a mixture of titanium and carbon material, and a conductive layer which is a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2). The conductive layer containing carbon material, i.e., the carbon layer, contains graphite, carbon black, or a mixture thereof as the carbon material.

[0030] (electrolyte) The electrolyte contains silicone oil. The silicone oil is a siloxane represented by the following structural formula (1). [ka] In the formula, R1 to R9 are each a methyl group, an ethyl group, a propyl group, or an isopropyl group, m is an integer including 0, n is an integer of 1 or more, and X is an organic group.

[0031] As shown in structural formula (1) above, the molecule of silicone oil has a backbone consisting of a linear polysiloxane. Some or all of the monomer units of polysiloxane have side chains of organic group X. Typically, the monomer unit of polysiloxane is dimethylsiloxane. In some or all of the dimethylsiloxane groups that make up this monomer unit, one functional group such as a methyl group is substituted with organic group X.

[0032] When this silicone oil contains dimethylsiloxane, i.e., when m is 1 or greater, it becomes a block copolymer, alternating copolymer, or random copolymer of monomer units of dimethylsiloxane and monomer units of methylsiloxane partially substituted with organic group X.

[0033] Organic group X is a polyether represented by the following structural formula (2). [ka] The organic group X is a hydrophilic group, in the formula R is either none (connecting directly to the C (carbon) in the repeating structure of X), CH2, or C2H4, R' is H, CH3, or C2H5, and a and b are integers, including the case where either one is 0.

[0034] As shown in the structural formula (2) above, the organic group X is a polyether in which one or more ethylene oxide groups, propylene oxide groups, or both are arranged in a linear chain, with a hydroxyl group or alkyl group at the end. The organic group X of the polyether may be a block copolymer, alternating copolymer, or random copolymer of monomer units of ethylene oxide groups and propylene oxide groups.

[0035] The molecular weight of polysiloxane, or in other words, the molecular weight of silicone oil excluding the molecular weight of organic group X, accounts for between 30% and 60% of the total molecular weight of the silicone oil. With this silicone oil, electrolytic capacitors maintain a high capacitance retention rate even in extremely low temperature environments of -40°C. The capacitance retention rate is the percentage of capacitance at a temperature of -40°C compared to capacitance at a temperature of 20°C.

[0036] When the molecular weight of polysiloxane exceeds 60% of the molecular weight of silicone oil, the number of hydrophilic organic groups X becomes insufficient, making it insoluble in the electrolyte. When the molecular weight of polysiloxane is 30% or more of the molecular weight of silicone oil, the silicone oil readily bonds with the dielectric film through hydrogen bonding, resulting in a significant depression of the silicone oil's freezing point. Therefore, the decrease in discharge capacity of electrolytic capacitors in extremely low temperature environments is suppressed, and electrolytic capacitors maintain a high capacitance retention rate even in extremely low temperature environments of -40°C.

[0037] It is preferable to include two or more types of silicone oils with different polysiloxane molecular weights in the electrolyte. Including two or more types of silicone oils in the electrolyte further improves the volume retention rate at extremely low temperatures of -40°C. Although this is an estimate and not limited to this estimated mechanism, the further improvement in volume retention rate is presumed to be due to the following mechanism.

[0038] In other words, it is presumed that the mixing of different types of silicone oils created intermolecular repulsion, causing the silicone oils to disperse and the viscosity of the electrolyte to decrease. The intermolecular repulsion is presumed to have occurred because the self-diffusion coefficient of the siloxane bond (Si-CH3) in the molecular structure of the silicone oil increased, thereby increasing the degrees of freedom of the polysiloxane skeleton. As a result, it is presumed that the solidification of the silicone oil became less likely to progress even in an extremely low temperature environment of -40°C, and the capacitance retention rate of the electrolytic capacitor improved.

[0039] If at least one type of silicone oil contains polysiloxane in a proportion of 30% to 60% of the molecular weight of the silicone oil, other types of silicone oil may contain polysiloxane in a proportion of less than 30% or more than 60%. If at least one type of silicone oil contains polysiloxane in a proportion of 30% to 60% of the molecular weight of the silicone oil, the effect of improving the volume retention rate by including two or more types of silicone oils will be further enhanced. In particular, if the molecular weight of polysiloxane in the other types of silicone oil exceeds 60%, the improvement in volume retention rate at extremely low temperatures of -40°C will be remarkable.

[0040] However, the silicone oils included in the electrolyte are selected such that the molecular weight of the polysiloxane contained in two or more types of silicone oils averages between 30% and 60% of the molecular weight of the silicone oils.

[0041] The electrolyte is not particularly limited as long as it can contain silicone oil. The electrolyte may include 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 its salt, and may also include an ionic dissociable salt that dissociates into an acidic component and a basic component. The acidic component and the basic component may be added separately as solutes.

[0042] The solvent includes a hydrophilic solvent, preferably a polyhydric alcohol that has a pressure-reducing effect, or a mixture of a polyhydric alcohol and water. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol.

[0043] Alternatively, the solvent preferably includes a mixture of a polyhydric alcohol and a dicarboxylic acid diester, or a mixture of a polyhydric alcohol, a dicarboxylic acid diester, and water. However, the dicarboxylic acid diester has the structure of the following chemical formula (3). In the structural formula, n is a natural number less than or equal to 4, and X is 1 or 2.

[0044] TIFF2026060935000004.tif39152

[0045] This dicarboxylic acid diester is a specific dicarboxylic acid diester selected from the group consisting of dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, and diethyl adipate (hereinafter, these are also referred to as specific dicarboxylic acid diesters). Two or more specific dicarboxylic acid diesters may be selected and used as solvents. When specific dicarboxylic acid diesters are used as solvents for the electrolyte, the volume retention rate at extremely low temperatures of -40°C is further improved.

[0046] While this is a hypothesis and not limited to this hypothetical mechanism, it is estimated that the interaction between the OH groups of the silicone oil and the polyhydric alcohol is promoted when the three components—a dicarboxylic acid diester, a polysiloxane (whose molecular weight is 30% or more of the silicone oil's molecular weight), a silicone oil, and a polyhydric alcohol are present. This interaction between the OH groups of the silicone oil and the polyhydric alcohol suppresses aggregation of the silicone oil molecules, leading to further freezing point depression. As a result, it is estimated that electrolytic capacitors exhibit even higher capacitance retention rates even in extremely low-temperature environments of -40°C.

[0047] Organic acids that can be added to a solvent include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcinic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, t-butyladipic acid, and 11-vinyl-8-octadecenediic acid, as well as phenols and sulfonic acids. Inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic and inorganic acids include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinic acid, borodimethylsalicylic acid, borodinafthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0048] Basic components include ammonium, quaternary ammonium, amidinium quaternary, amines, sodium, potassium, etc. Quaternary ammonium components include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Amidinium quaternary components include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Amines include primary amines, secondary amines, and tertiary amines. Primary amines include methylamine, ethylamine, propylamine, etc. Secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0049] Furthermore, other additives can be added to the electrolyte. Examples of additives include 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, phosphate esters, and colloidal silica. These may be used individually or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, and m-nitroacetophenone.

[0050] (Separator) The 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; 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; acrylic resins; and polyvinyl alcohol resins, and these resins are used individually or in mixtures.

[0051] The separator may be fibrillated by generating thin fibers that branch out from the surface of the original fibers, such as fibrillated cellulose. Fibrillation can be achieved, for example, by beating. The fibrillated fibers intertwine using the thin fibrillated fibers, improving the strength of the separator. As a result, the separator can be made thinner. Thinning the separator allows for longer anodes and cathodes per unit volume, improving the capacitance of the electrolytic capacitor.

[0052] (Capacitor element) A capacitor element is a laminate formed by stacking an anode and a cathode with a separator in between. The separator is stacked so that one end extends beyond the other end of the anode and cathode. The core of the capacitor element is created by first winding the protruding separator so that it aligns with the short sides of the anode and cathode. Then, using this core as the winding axis, the long sides of the anode and cathode are wound around it. In this way, the laminate of the anode, cathode and separator is wound in multiple layers in a spiral pattern, forming a cylindrical capacitor element.

[0053] Each of the anode and cathode is connected to a lead terminal. The lead terminals protrude from one end face of the capacitor element and are conductors that electrically connect the electrolytic capacitor to the mounting substrate. The lead terminals are electrically and mechanically connected to the anode and cathode by stitch connections, cold welding, ultrasonic welding, or laser welding. In the capacitor element, these lead terminals are led out from one end face of the cylindrical shape.

[0054] After forming the capacitor elements, a repair and chemical conversion process may be provided to repair the exposed base metal portion of the valve acting metal when the anode and cathode bodies are cut to the desired width, as well as any defects in the anode and cathode bodies caused by physical stress such as winding.

[0055] In the repair chemical conversion process, the capacitor element is immersed in a conversion solution and a voltage is applied. The conversion solution can be a phosphoric acid-based solution such as ammonium dihydrogen phosphate, a boric acid-based solution such as ammonium borate, an adipic acid-based solution such as ammonium adipate, or a solution made by mixing boric acid and dicarboxylic acids such as citric acid. The voltage is preferably, for example, 0.1 to 1.2 times the conversion voltage. Furthermore, as appropriate, methods for applying the voltage during repair chemical conversion include applying a constant voltage from the start of the repair chemical conversion, or gradually increasing the applied voltage at regular intervals.

[0056] The electrolyte is impregnated into the voids within the capacitor element by immersing it in the electrolyte. To ensure the electrolyte penetrates even finer voids, depressurization or pressurization may be performed as needed. The electrolyte impregnation process may be repeated multiple times. For example, the inside of the capacitor element may be depressurized, and the electrolyte may be injected into the capacitor element while pressurizing the electrolyte.

[0057] The capacitor element, impregnated with electrolyte, is housed in an outer casing. The outer casing is made of aluminum, a manganese-containing aluminum alloy, or stainless steel. The outer casing is, for example, a cylindrical body with one end closed and the other end open. A pressure relief valve may be formed at the bottom of the outer casing. The pressure relief valve opens when the internal pressure of the outer casing exceeds a set pressure.

[0058] The opening of the outer casing is sealed by a sealing body. The sealing body is an elastic insulator such as a rubber sheet, or a laminate of a rigid substrate insulating board such as a synthetic resin sheet and an elastic insulator. The sealing body is attached to the opening of the outer casing. Then, by crimping, the sealing body is folded and crushed inward around the opening edge of the outer casing, and it adheres tightly to the entire circumference of the opening edge of the outer casing. A press-fit hole is formed in the sealing body, and the lead terminal is pulled out to the outside through the press-fit hole.

[0059] After sealing the capacitor elements in the outer casing, it is preferable to perform an aging treatment on the electrolytic capacitors. In the aging treatment, a DC voltage is applied to the electrolytic capacitors to repair defects such as the dielectric film. [Examples]

[0060] The electrolytic capacitors of the embodiments will be described in more detail below. However, the present invention is not limited to the embodiments described below.

[0061] (Examples 1 and 2) Electrolytic capacitors were fabricated for Examples 1 and 2, Comparative Examples 1 to 3, and Comparative Examples 4 and 5. Each electrolytic capacitor, except for Comparative Example 1, contained silicone oil in its electrolyte. The silicone oil in each electrolytic capacitor differed in the molecular weight of the polysiloxane, the molecular weight of the polyether organic group X, and the ratio of the polysiloxane molecular weight to the molecular weight of the silicone oil. Only in Comparative Example 1 was the electrolyte a glycerin derivative instead of silicone oil.

[0062] The electrolyte composition is the same for both. The electrolyte contains 65 wt% ethylene glycol, 4 wt% water, 1.4 wt% boric acid and mannitol, 12 wt% azelaic acid and diethylamine, and 17 wt% silicone oil. In Comparative Example 1, instead of 17 wt% silicone oil, a glycerin derivative in which ethylene oxide chains and propylene oxide chains are attached to a glycerin backbone is included.

[0063] The structures of the silicone oils in Examples 1 and 2, Comparative Examples 1 to 3, and Comparative Examples 4 and 5 are shown in Table 1 below. (Table 1) TIFF2026060935000005.tif114168

[0064] The molecular structures of the silicone oils in each example and comparative example were identified by nuclear magnetic resonance spectroscopy. First, 29 Si-NMR analysis revealed peaks at 8 ppm and -22 ppm, as shown in Figure 1. The 8 ppm peak represents silicon with three methyl groups attached. In other words, the 8 ppm peak represents both ends of the linear structure of the silicone oil. The -22 ppm peak represents silicon with two methyl groups attached. By combining the integral value of this -22 ppm peak with the integral value of the peaks representing silicon at both ends of the linear structure of the silicone oil, the chain length excluding both ends of the linear structure of the silicone oil was determined.

[0065] In other words, the number of Si was calculated by comparing the integral values ​​of the 8 ppm peak and the -22 ppm peak, using the integral values ​​of the peaks indicating Si at both ends of the linear structure of the silicone oil as a reference, and the chain length excluding both ends of the linear structure of the silicone oil was determined. 29 For Si-NMR analysis, since there was a risk of overlap between the peak of the silicone oil and the reference substance (tetramethylsilane, TMS), the measurement was performed by mixing the silicone oil only with the deuterated solvent.

[0066] Also, 1¹H-NMR analysis reveals a peak in the range of 4 ppm to 3.5 ppm, as shown in Figure 2. However, as shown in Figure 2, no peak is observed near 1.5 ppm. The 1.5 ppm peak represents the H (hydrogen) of the CH3 group of the propylene oxide group. Since this 1.5 ppm peak is not observed, the organic group X attached to the silicone oil in each example and comparative example does not contain a propylene oxide group. The peak in the range of 4 ppm to 3.5 ppm represents the H (hydrogen) of the O-CH2 bond between the ethylene oxide group and the propylene oxide group. However, since the propylene oxide group is not present, the peak in the range of 4 ppm to 3.5 ppm represents the H (hydrogen) of the O-CH2 bond of the ethylene oxide group. 1 ¹H-NMR analysis was performed using a deuterated solvent containing tetramethylsilane (TMS) as the reference substance. 1 The identification of each peak in 1H-NMR analysis was performed based on TMS.

[0067] The 0.5 ppm peak represents the H atoms in the Si-CH3 bond when R1 to R9 in the above structural formula (1) of the silicone oil are methyl groups, and the 0.8 ppm peak represents the H atoms in the Si-CH2 bond to which the organic group X is attached. The integral value of this 0.5 ppm peak and 29 Based on the results of Si-NMR analysis, the molecular structure of organic group X and the molecular weight of organic group X relative to the polysiloxane were determined from the integral values ​​of the peak at 0.8 ppm and the peaks in the range of 4 ppm to 3.5 ppm.

[0068] Based on the above, we determined the average molecular weight of the polysiloxane shown in Table 1, the average molecular weight of the polyether organic group X, the average molecular weight of the entire silicone oil, the ratio of the average molecular weight of the polysiloxane to the average molecular weight of the silicone oil, the number of organic groups X, the number of repeating ethylene oxide chains within organic group X, the number of Si at the ends of the silicone oil, and the number of Si excluding the ends of the silicone oil.

[0069] The anode, cathode, and separator in each example and comparative example are identical. The anode was made of stretched aluminum foil. The aluminum foil was immersed in an aqueous hydrochloric acid solution, and a DC current was passed through the aluminum foil in the aqueous hydrochloric acid solution to form an expanded surface layer consisting of tunnel-shaped etching pits. Then, a conversion treatment was applied to the aluminum foil having the expanded surface layer to form a dielectric film along the irregularities of the expanded surface layer. An aqueous ammonium borate solution was used as the conversion solution. The dielectric film was formed by applying voltage in the conversion solution.

[0070] The cathode body is an enlarged aluminum foil. The aluminum foil was enlarged by etching, and an oxide film was formed by chemical conversion treatment at a conversion voltage of 3Vfs. Lead wires were connected to the anode and cathode bodies, and the anode and cathode bodies were wound together with a cellulose-based separator in between. The capacitor element fabricated by winding was immersed in an electrolyte solution, impregnating the voids within the capacitor element with the electrolyte solution. The electrolyte-impregnated capacitor element was placed in an outer case, the opening of the outer case was sealed with a sealing element, and each electrolytic capacitor was completed by aging treatment.

[0071] (Adsorption amount survey) A mixture was prepared by mixing the pressure-improving agent used in Comparative Example 1, Comparative Example 3, and Example 1 with ethylene glycol in a weight ratio of 1:1. The anode, cathode, and separator were immersed separately in this mixture. After removing the anode, cathode, and separator, the amount of pressure-improving agent remaining in the mixture was measured. 1 The pressure was measured by 1H-NMR analysis. From the measurement results, the amount of pressure-improving agent attached to the anode, cathode, and separator was calculated. The immersion time was 1 day, and the mixed solution was maintained at 60°C during immersion. Two sets of anodes, cathodes, and separators were prepared, and the test was performed twice.

[0072] The results of the adsorption amount investigation are shown in Figure 3. Figure 3 is a graph showing the amount of pressure improver adhering. The horizontal axis BLK is blank, and the amount of pressure improver was investigated without immersing the anode, cathode, and separator. 1The results were measured by 1H-NMR analysis. In the horizontal axis, (+) in parentheses represents the anode, (-) in parentheses represents the cathode, and (sepa) in parentheses represents the separator. The sample number follows the hyphen in the horizontal axis. The vertical axis in Figure 3 shows the percentage of pressure-resistant agent attached to the immersed object. This percentage is calculated by subtracting the percentage of pressure-resistant agent contained in the remaining mixture from 50%.

[0073] The white graph shows the results for Comparative Example 1, in which a glycerin derivative with ethylene oxide chains and propylene oxide chains attached to a glycerin skeleton was used as a pressure-resistant agent. The hatched graph shows the results for Comparative Example 3, in which a silicone oil with a polysiloxane content of 26% by molecular weight ratio was used as a pressure-resistant agent. The black-filled graph shows the results for Example 1, in which a silicone oil with a polysiloxane content of 50.7% by molecular weight ratio was used as a pressure-resistant agent.

[0074] In Figure 3, among the (+) graphs related to the anode, the graphs filled in black indicate that the anode of Example 1 had the most adsorbent pressure improver. As shown in Table 1, when the molecular weight of the polysiloxane is 50.7%, which is within the range of 30% to 60% of the molecular weight of the silicone oil, the silicone oil is adsorbed most effectively onto the dielectric film of the anode.

[0075] In Figure 3, among the (+) graphs related to the anode, the hatched and white graphs indicate that the amount of pressure-resistant agent adsorbed onto the anode in Comparative Example 3 is not significantly different from that in Comparative Example 1. From this, as shown in Table 1, it can be seen that when the molecular weight of polysiloxane is 26.0%, which is less than 30% of the molecular weight of silicone oil, the amount of silicone oil adsorbed onto the dielectric film is no different from that of a glycerin derivative in which ethylene oxide chains and propylene oxide chains are added to a glycerin backbone.

[0076] (Capacity retention rate test) The capacitance retention rates of the electrolytic capacitors in Comparative Examples 1 to 3 and Examples 1 and 2 were measured. In Comparative Examples 4 and 5, the silicone oil was insoluble in the electrolyte, and the electrolyte could not be prepared. As shown in Table 1, in Comparative Example 3, the molecular weight of the polysiloxane was 69.2% of the molecular weight of the silicone oil. Therefore, it was confirmed that the upper limit for the molecular weight of the polysiloxane is 60.0% or less of the molecular weight of the silicone oil.

[0077] For the capacitance retention test, the electrolytic capacitors of Comparative Examples 1 to 3 and Examples 1 and 2 were placed in temperature environments of 20°C, -20°C, -30°C, and -40°C, and the capacitance at each temperature environment was measured. Specifically, measurements were taken using an LCR meter (Agilent ZM2376, manufactured by NF Circuit Design Block Co., Ltd.). The DC bias was set to 1.5V, the AC signal level to a 1.0Vrms sine wave, and the measurement frequency to 120Hz. Furthermore, the capacitance retention rate was calculated as the percentage of the capacitance at each temperature relative to the capacitance at 20°C.

[0078] The measurement results for the volume retention rate are shown in Table 2 below. (Table 2) TIFF2026060935000006.tif134156

[0079] As shown in Table 2, Comparative Examples 1 and 2 have a maximum volume retention rate of the high 68% range at -40°C, while Examples 1 and 2 have a volume retention rate of well over 70% at -40°C. As shown in Table 1, in Examples 1 and 2, the molecular weight of the polysiloxane is within the range of 30% to 60% of the molecular weight of the silicone oil. In addition, the molecular weight of the silicone oil, which is the sum of the molecular weight of the polysiloxane and the molecular weight of the organic group, is larger in Examples 1 and 2 compared to Comparative Examples 1 and 2. While a larger molecular weight of a molecule makes it more prone to solidification and worsens the volume retention rate in an extremely low temperature environment, Examples 1 and 2 exhibit better volume retention rates even in an extremely low temperature environment of -40°C compared to Comparative Examples 1 and 2.

[0080] From this, it was confirmed that when the silicone oil contains, as a partial structure in its molecule, a linear polysiloxane and a side chain of an organic group formed by substituting a methyl group, which is a substituent of the polysiloxane, and when the molecular weight of the polysiloxane accounts for 30% to 60% of the molecular weight of the silicone oil, the silicone oil is adsorbed onto the dielectric film, causing a freezing point depression in the silicone oil, and thus the capacitance retention rate of the electrolytic capacitor containing this silicone oil in the electrolyte under cryogenic conditions is increased.

[0081] (Examples 3 to 10) Electrolytic capacitors were fabricated according to Examples 3 to 10. The composition and composition ratio of the electrolyte in the electrolytic capacitors of Examples 3 to 10 are the same as those in Example 2. Furthermore, the structure of the electrolytic capacitors of Examples 3 to 10 is the same as that of Example 2, and they were manufactured using the same manufacturing method and under the same manufacturing conditions. In Example 2, the electrolyte contained a silicone oil with a polysiloxane molecular weight of 51.5%, whereas the electrolyte in the electrolytic capacitors of Examples 3 to 10 contained the same silicone oil as in Example 2, as well as another silicone oil with a different polysiloxane molecular weight than the silicone oil in Example 2. The other silicone oil has the same structure as the silicone oil in Example 2, except for the difference in polysiloxane molecular weight.

[0082] (Capacity retention rate test) The capacitance retention rate of the electrolytic capacitors of Examples 3 to 10 was measured when placed in a temperature environment of -40°C. The test method and test conditions for capacitance retention rate were the same as in Example 2.

[0083] Table 3 below shows the results of other silicone oils, the molecular weight ratio of polysiloxane contained in other silicone oils to the silicone oil, the average molecular weight ratio of polysiloxane in the total silicone oil, and the volume retention rate, along with the results of Example 2 and the improvement rate based on Example 2.

[0084] (Table 3) TIFF2026060935000007.tif166161

[0085] As shown in Table 3, Examples 3 to 10, like Example 2, also showed a volume retention rate of well over 70% at -40°C. This confirms that even when the electrolyte contains two or more types of silicone oils with different polysiloxane molecular weights, a good volume retention rate can be achieved in an extremely low temperature environment of -40°C.

[0086] Moreover, in most of Examples 3 to 10, the volume retention rate at -40°C was further improved compared to Example 2. The molecular weight percentage of polysiloxane in the total silicone oil contained in Examples 3 to 10 was, on average, within the range of 30% to 60% of the molecular weight of the silicone oil. However, in Examples 3 to 10, silicone oil with a polysiloxane molecular weight percentage of less than 30% or more than 60% was mixed in the electrolyte at a concentration of 10 wt% to 30 wt%.

[0087] From this, it was confirmed that while the molecular weight ratio of polysiloxane in the total silicone oil must, on average, be within the range of 30% to 60% of the molecular weight of the silicone oil, deliberately including silicone oil with a polysiloxane molecular weight ratio of less than 30% or more than 60% in the electrolyte further improves the volume retention rate under extremely low temperature conditions of -40°C.

[0088] In particular, as can be seen by comparing the improvement rates of Examples 3 to 6 with those of Example 2, it was confirmed that the volume retention rate at an extremely low temperature of -40°C is improved by deliberately including a silicone oil with a polysiloxane molecular weight ratio of over 60% in the electrolyte.

[0089] Here, a liquid was prepared by changing the mixing ratio of a silicone oil with a molecular weight ratio of 50.7% of the polysiloxane used in Example 1 (referred to as the first silicone oil) and a silicone oil with a molecular weight ratio of 62.4% of the polysiloxane mixed in Examples 4 to 6 (referred to as the second silicone oil) at a ratio of 100:0 to 0:100. Then, the viscosity of this actually prepared liquid was measured. Also, the theoretical value of the viscosity of the liquid with the mixing ratio of the first silicone oil and the second silicone oil changed at a ratio of 100:0 to 0:100 was calculated by the following mathematical formula (Equation 1).

[0090] [Equation] In the formula, η 1,2 is the viscosity of the liquid obtained by mixing the first silicone oil and the second silicone oil. η1 is the viscosity of the first silicone oil. η2 is the viscosity of the second silicone oil. w1 is the weight fraction of the first silicone oil in the liquid. w2 is the weight fraction of the second silicone oil in the liquid.

[0091] A scatter plot showing the measurement results of the viscosity and a graph showing the theoretical values of the viscosity are combined and shown in FIG. 4. As shown in FIG. 4, the measured values of each viscosity are plotted below the graph showing the theoretical values of the viscosity. This result indicates that the interaction between different silicone oils generates an intermolecular repulsive force, the silicone oil is dispersed, and the viscosity decreases deviating from the theoretical value. And it can be confirmed that in Examples 3 to 10, due to the viscosity decrease deviating from the theory of this electrolyte, the capacity retention rate was further improved in an extremely low temperature environment of -40°C.

[0092] (Examples 11 to 18) Electrolytic capacitors of Examples 11 to 18 were fabricated. Electrolytic capacitors of Comparative Examples 6 and 7 were also fabricated. The electrolytes in the electrolytic capacitors of Examples 11 to 18 and Comparative Examples 6 and 7 contain 59.5 wt% ethylene glycol, with an additional 6.5 wt% dicarboxylic acid diester, compared to the electrolyte of Example 2 which contains 65 wt% ethylene glycol. The other components and their contents in the electrolytes of Examples 11 to 18 and Comparative Examples 6 and 7 are the same as those in Example 2. Furthermore, the electrolytic capacitors of Examples 11 to 18 and Comparative Examples 6 and 7 have the same configuration as those of Example 2 and were fabricated using the same manufacturing method and under the same manufacturing conditions.

[0093] The electrolyte in Example 11 contains dimethyl malonate. The electrolyte in Example 12 contains dimethyl succinate. The electrolyte in Example 13 contains diethyl succinate. The electrolyte in Example 14 contains dimethyl glutarate. The electrolyte in Example 15 contains diethyl glutarate. The electrolyte in Example 16 contains dimethyl adipate. The electrolyte in Example 17 contains diethyl adipate.

[0094] The electrolyte of Example 18 contains diisopropyl adipate. The electrolyte of Comparative Example 6 contains dimethyl glutarate, but the molecular weight percentage of polysiloxane in the silicone oil is 0%. The electrolyte of Comparative Example 7 contains dimethyl glutarate, but the molecular weight percentage of polysiloxane in the silicone oil is less than 30%, at 26.0%.

[0095] (Capacity retention rate test) The capacitance retention rate of the electrolytic capacitors of Examples 11 to 18 and Comparative Examples 6 and 7 was measured when placed in a -40°C temperature environment. The test method and test conditions for capacitance retention rate were the same as in Example 2. The measurement results of capacitance retention rate, along with the results from Example 2, are shown in Table 4 below.

[0096] (Table 4) TIFF2026060935000009.tif131165

[0097] As shown in Table 4 above, the electrolyte of Example 18, which contains diisopropyl adipate, has good volume retention when placed in a -40°C environment. However, Examples 11 to 17, which contain dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, or diethyl adipate in the electrolyte, have even better volume retention when placed in a -40°C environment than Example 2.

[0098] On the other hand, Comparative Example 6, which contains dimethyl glutarate but has a polysiloxane molecular weight ratio of 0% in the silicone oil, and Comparative Example 7, which contains dimethyl glutarate but has a polysiloxane molecular weight ratio of 26.0% in the silicone oil, did not show improvement in volume retention when placed in a -40°C environment. In other words, when Comparative Example 1 was placed in a -40°C environment, the volume retention rate was 62.3%, and even with the addition of dimethyl glutarate as in Comparative Example 6, the improvement was only 0.3%, reaching 62.6%. Similarly, when Comparative Example 3 was placed in a -40°C environment, the volume retention rate was 68%, and even with the addition of dimethyl glutarate as in Comparative Example 7, the improvement was only 0.4%, reaching 68.4%.

[0099] Based on this, assuming that the electrolyte contains a polyhydric alcohol and silicone oil, and that the molecular weight of polysiloxane in the silicone oil is between 30% and 60%, it was confirmed that the volume retention rate when placed in a -40°C environment is further improved when dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, or diethyl adipate is further added to the electrolyte.

[0100] Here, various mixtures of silicone oil, dimethyl glutarate, and ethylene glycol from Example 1 were prepared. The first mixture sample was a liquid containing only ethylene glycol, with no silicone oil or dimethyl glutarate from Example 1 added. The second mixture sample contained ethylene glycol and dimethyl glutarate in a weight ratio of 9:1, with no silicone oil from Example 1 added. The third mixture sample contained silicone oil and dimethyl glutarate from Example 1 in a weight ratio of 1:1, with no ethylene glycol added. The fourth mixture sample contained equal amounts of silicone oil, dimethyl glutarate, and ethylene glycol from Example 1 by weight.

[0101] These first to fourth mixed liquid samples 1 The results were measured by 1H-NMR analysis. These results are shown in Figure 5. Figure 5(a) shows the analysis results for the first mixed solution sample, (b) shows the analysis results for the second mixed solution sample, (c) shows the analysis results for the third mixed solution sample, and (d) shows the analysis results for the fourth mixed solution sample.

[0102] Compared to Figures 5(a) through (c), only the analysis results shown in Figure 5(d) show that the peak P, which indicates the OH group derived from ethylene glycol, has shifted from between 6 ppm and 5 ppm as shown in Figures 5(a) and (b) to between 5 ppm and 4 ppm. As shown in Figures 5(a) through (d), this phenomenon occurs only when all three types—silicone oil, specific dicarboxylic acid diesters, and ethylene glycol—are present together.

[0103] These results indicate that only when these three components—dicarboxylic acid diesters, polysiloxanes, silicone oil, and polyhydric alcohols—are present, with the total molecular weight of the dicarboxylic acid diesters being 30% or more of the silicone oil's molecular weight, do the OH groups of the silicone oil and polyhydric alcohols interact, causing a further freezing point depression of the silicone oil. This results in electrolytic capacitors exhibiting even higher capacitance retention rates, even in extremely low-temperature environments of -40°C.

Claims

1. an anode body on which a dielectric film has been formed, A cathode body facing the anode body with the dielectric film in between, An electrolyte containing polyhydric alcohol and silicone oil, Equipped with, The silicone oil comprises, as a partial structure in the molecule, a linear polysiloxane and a side chain of an organic group formed by substituting some of the functional groups of the polysiloxane. The molecular weight of the polysiloxane is 30% to 60% of the molecular weight of the silicone oil. An electrolytic capacitor characterized by the following features.

2. The aforementioned silicone oil is a siloxane represented by the following structural formula (1), The aforementioned organic group is a polyether represented by the following structural formula (2). The electrolytic capacitor according to claim 1, characterized by the above. 【Chemistry 1】 【Chemistry 2】 In the formula, R １ ~R ９ Each of the groups is a methyl group, an ethyl group, a propyl group, or an isopropyl group, m is an integer including 0, n is an integer of 1 or more, and R is either absent or CH ２ or C ２ H ４ And R' is H, CH ３ , or C ２ H ５ The integers a and b are such that a and b are both zero.

3. The electrolyte contains two or more types of silicone oils with different molecular weights of polysiloxane. The electrolytic capacitor according to claim 1 or 2, characterized by the above.

4. The molecular weight ratio of the polysiloxane in the total silicone oil accounts for, on average, 30% to 60% of the molecular weight of the silicone oil. A portion of the silicone oil is such that the molecular weight of the polysiloxane is less than 30% or more than 60% of the molecular weight of the silicone oil. The electrolytic capacitor according to claim 3, characterized by the above.

5. The aforementioned polyhydric alcohol is ethylene glycol. The electrolytic capacitor according to claim 1 or 2, characterized by the above.

6. The electrolyte further comprises dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, diethyl adipate, or a combination thereof as a solvent. The electrolytic capacitor according to claim 1 or 2, characterized by the above.

7. The electrolyte contains water. The electrolytic capacitor according to claim 1 or 2, characterized by the above.

8. Contains polyhydric alcohols and silicone oils, The silicone oil comprises, as a partial structure in the molecule, a linear polysiloxane and a side chain of an organic group formed by substituting some of the functional groups of the polysiloxane. The molecular weight of the polysiloxane is 30% to 60% of the molecular weight of the silicone oil. An electrolyte characterized by the following.

9. A device formation step for forming a capacitor element including an anode and a cathode, An impregnation step in which the capacitor element is impregnated with an electrolyte, Includes, The electrolyte comprises a polyhydric alcohol and a silicone oil. The silicone oil comprises, as a partial structure in the molecule, a linear polysiloxane and a side chain of an organic group formed by substituting some of the functional groups of the polysiloxane. The molecular weight of the polysiloxane is 30% to 60% of the molecular weight of the silicone oil. A method for manufacturing electrolytic capacitors characterized by the following.

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