Electrolytic capacitor, filter circuit, and power converter

Abstract

To provide: an electrolytic capacitor that, when used at 120 Hz in an extremely low-temperature environment, can extract a capacitance of 80% or more of the nominal capacitance specified under the conditions of 20°C and 120 Hz; a filter circuit including the electrolytic capacitor; and a power converter including the electrolytic capacitor.SOLUTION: Under a temperature environment of -40°C, the electrolytic capacitor has an ESR at 120 Hz that is less than 7.2 times the ESR at 100 kHz. The filter circuit includes the electrolytic capacitor, and the power converter includes the electrolytic capacitor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrolytic capacitor, a filter circuit, and a power converter. [Background technology]

[0002] An electrolytic capacitor has valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil is enlarged by forming the valve metal into a sintered body or an etched foil, and has a dielectric oxide film on the enlarged surface. An electrolyte is interposed between the anode foil and the cathode foil. The electrolyte is in close contact with the uneven surface of the anode foil and functions as a true cathode. The electrolytic capacitor has the advantage that the specific surface area can be increased by enlarging the surface of the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors. In addition, the electrolyte can be in close contact with the dielectric oxide film of the anode foil, making it easier to further increase the capacitance of the electrolytic capacitor.

[0003] Capacitors are used in various applications, and are particularly widely used in filter circuits. For example, in the field of power electronics, a smoothing capacitor is provided in a power converter that converts the power of an AC power source into DC power using a converter circuit and then converts the DC power into a desired AC power using an inverter circuit, in order to suppress and smooth the pulsation of the DC output from the converter circuit before inputting it to the inverter circuit. In addition, a decoupling capacitor is provided near a semiconductor switching element such as gallium nitride to ensure stable operation of the semiconductor switching element and to remove noise.

[0004] As power electronics devices become increasingly power-intensive, there is a growing demand for capacitors with higher capacity. Electrolytic capacitors can be made to have a higher capacity more easily than film capacitors, and can easily meet this demand for higher capacity. Furthermore, as devices become more powerful, the withstand voltage required of electrolytic capacitors is also increasing. In order to increase the spark voltage of the electrolyte, a voltage-resistance improver is added to the electrolyte. Examples of voltage-resistance improvers include polymer compounds such as polyvinyl alcohol and polyethylene glycol, and inorganic fine particles such as silica and alumina (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-176102 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the use of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), which use electric power obtained from a battery to drive the motor, has been rapidly increasing. These vehicles are equipped with power converters that charge the drive batteries. The power converters in EVs and PHEVs are also called on-board chargers (OBCs). OBCs are equipped with, for example, smoothing capacitors in parallel with bridge diodes, or capacitors included in a step-up converter of a power factor correction (PFC) circuit. Step-up converters often use power semiconductors such as MOSFETs and IGBTs, which have low on-resistance and high-speed switching, in order to achieve high efficiency by suppressing power loss.

[0007] For rapid charging, electrolytic capacitors for vehicle use are also required to have high capacity and high withstand voltage at 120Hz. Generally, however, the nominal capacitance of an electrolytic capacitor is indicated under the conditions of 20℃ and 120Hz. Therefore, filter circuits and power converters are designed taking this nominal capacitance into consideration.

[0008] However, electrolytic capacitors for automotive applications may be exposed to extremely low temperature environments, such as -40°C. In such extremely low temperature environments, the electrolytic capacitor may experience a rapid decrease in capacitance. One of the causes of the decrease in capacitance in extremely low temperature environments is the high freezing point of the voltage resistance improver that is sometimes added to electrolytic capacitors to accommodate high voltage resistance.

[0009] If the capacitance of the electrolytic capacitor fluctuates beyond the design range, for example, there is a risk that the rated voltage of the electrolytic capacitor mounted in the power converter may be exceeded, which may cause the power converter to stop. To avoid this, it is necessary to reduce the output voltage by suppressing quick charging until the electrolytic capacitor warms up.

[0010] Here, the JIS standard (JIS C 5101-4-1), which specifies standards for Japanese industrial products, recommends a tolerance of -20% to +20% for nominal capacitance. Therefore, circuits should be designed so that electrolytic capacitors can achieve 80% of their nominal capacitance. In other words, the ideal electrolytic capacitor is one that, when used at 120Hz in an extremely low-temperature environment, achieves a capacitance of 80% or more of its nominal capacitance at 20°C and 120Hz.

[0011] The present invention has been proposed to solve the above-mentioned problems, and its object is to provide an electrolytic capacitor that, when used at 120 Hz in an extremely low temperature environment, delivers a capacitance of 80% or more of the nominal capacitance under the conditions of 20°C and 120 Hz, a filter circuit including this electrolytic capacitor, and a power converter including this electrolytic capacitor. [Means for solving the problem]

[0012] In order to solve the above problem, in the electrolytic capacitor of this embodiment, the ESR at 120 Hz in a temperature environment of -40°C is less than 7.2 times the ESR at 100 kHz.

[0013] The battery also includes an electrolyte solution containing colloidal silica and a separator made of cellulose, The thickness L of the separator (cm), the density ρ of the separator (g / cm 3 ), and the specific resistance Rs (Ω·cm) of the electrolytic solution at 20° C. may satisfy the following formula (1):

number

[0014] In order to solve the above problem, the filter circuit and the power converter of the present embodiment include this electrolytic capacitor. Effect of the Invention

[0015] According to the present invention, when the electrolytic capacitor is used at 120 Hz in an extremely low temperature environment, it is possible to obtain a capacitance that is 80% or more of the nominal capacitance at 20° C. and 120 Hz. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a scatter diagram showing the relationship between the capacitance appearance rate and the ESR increase rate of an electrolytic capacitor. [Diagram 2] FIG. 1 is a scatter diagram showing the relationship between ESR×S at −40° C. and 120 Hz of an electrolytic capacitor and the capacitance appearance rate at −40° C. relative to 20° C. [Diagram 3] This is a scatter plot showing the relationship between ESR×S at -40° C. and 120 Hz and ESR×S at 20° C. and 100 kHz for an electrolytic capacitor. [Figure 4] FIG. 11 is a scatter diagram showing the relationship between the tortuosity τ and the density ρ of the separator. [Diagram 5] FIG. 2 is a circuit diagram of a power converter. [Figure 6] FIG. 11 is a diagram showing waveforms of output voltages at each temperature of a power converter including electrolytic capacitors of an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the preferred embodiments. However, the present invention is not limited to the preferred embodiments described below.

[0018] (Overall composition) An electrolytic capacitor is a passive element that obtains capacitance through the dielectric polarization of a dielectric oxide film and stores and discharges electric charge. When used at 120 Hz in an extremely low temperature environment, this electrolytic capacitor produces 80% or more of the nominal capacitance at 20°C and 120 Hz, making it suitable for, but not limited to, filter circuits used at 120 Hz in an extremely low temperature environment and power converters equipped with this filter circuit.

[0019] A power converter is a device that converts AC voltage into DC voltage, and examples of such a converter include the OBC of an EV or PHEV. Examples of filter circuits include a low-pass filter, a high-pass filter, a band-pass filter, and a ripple filter, also known as a smoothing circuit.

[0020] The capacitor element of this electrolytic capacitor is composed of a pair of electrodes, one or both of which have a dielectric oxide film, facing each other through a separator, and impregnated with an electrolyte. The electrolyte is in close contact with the uneven surface of the dielectric oxide film on the anode foil, and functions as a true cathode. The separator retains the electrolyte and insulates the pair of electrodes to prevent short circuits.

[0021] The ESR of this electrolytic capacitor when operated at a frequency of 120 Hz in a temperature environment of -40°C is less than 7.2 times the ESR when operated at a frequency of 100 kHz in a temperature environment of -40°C. 120Hz The ESR when driven at a frequency of 100 kHz in a temperature environment of -40°C is ESR 100kHz Then, this electrolytic capacitor satisfies the following formula (2).

number

[0022] Here, Fig. 1 is a scatter diagram showing the relationship between the capacitance appearance rate and the ESR increase rate of an electrolytic capacitor. In Fig. 1, the vertical axis is the capacitance appearance rate, and the horizontal axis is the ESR increase rate. The capacitance appearance rate is a percentage value of the ratio of the capacitance when the electrolytic capacitor is driven at -40°C and 120Hz to the capacitance when the electrolytic capacitor is driven at 20 and 120Hz. The ESR increase rate is the magnification of the ESR when the electrolytic capacitor is driven at -40°C and 120Hz to the ESR when the electrolytic capacitor is driven at -40°C and 100kHz.

[0023] As shown in Figure 1, the capacitance appearance rate decreases as the ESR increase rate increases, and is inversely proportional to the ESR increase rate. Also, as shown in Figure 1, when the ESR increase rate is less than 7.2 times, the capacitance appearance rate is 80% or more. Therefore, by satisfying the ESR ratio of the above formula (2), this electrolytic capacitor has a capacitance of 80% or more of the nominal capacitance under the conditions of 20°C and 120 Hz when used at 120 Hz in an extremely low temperature environment of -40°C.

[0024] In Figure 1, the gradient is steep until the ESR increase rate is less than 20 times, so the capacitance appearance rate and the ESR increase rate are considered to be proportional. Also, in the ESR increase rate in Figure 1, the ESR of the electrolytic capacitor when operated at -40°C and 100kHz shows little change according to the electrolytic capacitor specifications. Therefore, the ESR increase rate is calculated by multiplying the ESR when the electrolytic capacitor is operated at -40°C and 120Hz by the surface area (S) of the dielectric oxide film, ESR × S (kΩ cm 2 In addition, in an electrolytic capacitor, ESR×S is approximately equal to resistivity ρ.

[0025] As a result, Figure 1 is replaced by the scatter diagram in Figure 2. In Figure 2, the horizontal axis is ESR x S at -40°C and 120Hz, and the vertical axis is the capacitance appearance rate at -40°C to 20°C. Here, the equivalent circuit of an electrolytic capacitor in an extremely low temperature environment of -40°C can be expressed as an equivalent circuit of a parallel circuit of capacitance and resistance components, with the bulk consisting of the electrolyte and separator, and the dielectric oxide film, respectively, and can be expressed as an equivalent circuit in which each parallel circuit is connected in series. When the resistance component of the bulk decreases, the impedance of the bulk decreases, and the capacitance of the equivalent circuit of the bulk increases, which is considered to increase the electrostatic capacitance of the electrolytic capacitor as a composite capacitance with the dielectric oxide film capacitance. Therefore, the capacitance appearance rate at -40°C to 20°C correlates with ESR x S at -40°C and 120Hz.

[0026] In Figure 2, a regression analysis using the least squares method gives Y = -3.0443X + 100, where Y is the vertical axis of capacitance appearance rate and X is the horizontal axis of ESR × S. In order for the capacitance appearance rate of -40°C to be 80% or more relative to 20°C, the ESR × S at -40°C and 120Hz must be 6.57kΩ cm 2 You will know what you should do.

[0027] Next, the ESR of an electrolytic capacitor is generally considered to be in the bulk region when it does not show frequency dependence. In a 20°C environment, the 100kHz region is the region where ESR does not show frequency dependence, so the 100kHz region is the bulk resistance. On the other hand, in a low temperature environment of -40°C, the 120Hz region is the region where ESR does not show frequency dependence, so the 120Hz region is the bulk resistance. Therefore, ESR×S at -40°C and 120Hz and ESR×S at 20°C and 100kHz are correlated because they both show bulk resistance. Therefore, there is a high correlation between ESR×S at -40°C and 120Hz and ESR×S at 20°C and 100kHz.

[0028] Figure 3 is a scatter plot showing the relationship between ESR×S at -40°C and 120Hz and ESR×S at 20°C and 100kHz when colloidal silica is added to the electrolyte. Based on Figure 3, a regression analysis was performed using the least squares method with ESR×S at -40°C and 120Hz as Y and ESR×S at 20°C and 100kHz as X, resulting in Y=81.278X. The ESR×S at -40°C and 120Hz was 6.57kΩ·cm 2 Then, the ESR×S of the electrolytic capacitor containing colloidal silica at 20°C and 100kHz is 80.8Ω cm 2 It was.

[0029] Combining Figures 2 and 3, in an electrolytic capacitor with colloidal silica added to the electrolyte, in order for the capacitance appearance rate at -40°C to be 80% or more at 20°C, the resistivity at 20°C and 100kHz must be 80.8 Ω cm 2 It needs to be as follows.

[0030] Here, we use the tortuosity, which is an index showing the complexity of the current path. If the tortuosity is τ, ESR×S in the tortuosity is the value of ESR×S at 20°C and 100kHz, ε is the porosity, L is the thickness of the separator (cm), and Rs is the resistivity of the electrolyte at 20°C (Ω cm), then the tortuosity can be expressed by the following formula (3).

number

[0031] Expanding the above formula (3), ESR×S at 20° C. and 100 kHz is given by the following formula (4).

number

[0032] Here, the tortuosity τ and the separator density ρ (g / cm 3 ) is correlated when the separator is made of cellulose, and the relationship between the tortuosity τ and the density ρ of the separator is expressed by the following formula (5). [Table 5]

[0033] In addition, the porosity (ε) and the separator density ρ (g / cm 3 ) is expressed by the following relational formula (6) when the separator is cellulose. [Table 6]

[0034] From the above formulas (4) to (6), ESR×S at 20° C. and 100 kHz is given by the following formula (7). [Table 7]

[0035] The ESR×S at 20℃ and 100kHz is 80.8Ω cm in order for the capacitance appearance rate at -40℃ to be 80% or more compared to 20℃. 2 Therefore, when the electrolyte of the electrolytic capacitor contains colloidal silica and the separator is made of cellulose, the thickness L (cm) of the separator and the density ρ (g / cm 3 ) and the specific resistance Rs (Ω cm) of the electrolyte at 20°C.

number

[0036] When the electrolyte of the electrolytic capacitor contains colloidal silica and the separator is made of cellulose, the capacitance appearance rate at -40°C to 20°C is 80% or more by satisfying the above formula (8). When formula (8) is satisfied, the ESR when driven at a frequency of 120 Hz in a temperature environment of -40°C is less than 7.2 times the ESR when driven at a frequency of 120 Hz in a temperature environment of -40°C.

[0037] However, the ESR ratio of the above formula (2) can be satisfied by changing the types and parameters of the electrolyte and separator, not limited to the electrolyte containing colloidal silica and the separator made of cellulose. As long as the ESR ratio of the above formula (2) can be satisfied, the anode body, cathode body, separator, and electrolyte of the electrolytic capacitor may be of any known type, and the electrolyte may contain any known type of pressure resistance improver.

[0038] For example, the electrolyte may be a solution in which an anion component and a cation component are added to a solvent. The anion component and the cation component are typically a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, and are added to the solvent by an ion dissociative salt that dissociates into an anion component and a cation component. An acid that becomes an anion component and a base that becomes a cation component may be added separately to the solvent. In addition, the electrolyte may not include an anion component or a cation component, or both an anion component and a cation component in the solvent.

[0039] The solvent of the electrolyte may be a protic organic polar solvent or an aprotic organic polar solvent. Examples of the protic organic solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of the monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and oxyalcohol compounds include ethylene glycol, diethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol and polyoxyethylene glycerin.

[0040] As the aprotic organic polar solvent, sulfones, amides, lactones, cyclic amides, nitriles, sulfoxides, etc. may be used. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, etc. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, etc. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, etc. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, glutaronitrile, etc. The sulfoxides include dimethyl sulfoxide.

[0041] Examples of anion components in the electrolyte include 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, resorcylic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, and other carboxylic acids, phenols, and sulfonic acids, and various other organic acids. Examples of inorganic acid anion components in the electrolyte include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic acids and inorganic acids include borodisalicylic acid, borodioxalic 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, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0042] In addition, examples of at least one salt of an organic acid, an inorganic acid, and a complex compound of an organic acid and an inorganic acid include ammonium salt, quaternary ammonium salt, quaternary amidinium salt, amine salt, sodium salt, potassium salt, etc. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of quaternary amidinium salts include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, propylamine, etc., examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc., and examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0043] Furthermore, the electrolyte may contain a pressure resistance improver other than colloidal silica. Examples of the pressure resistance improver include polymer compounds such as polyvinyl alcohol and polyethylene glycol, inorganic fine particles such as alumina, in addition to colloidal silica. Other additives may also be added to the electrolyte. As additives for improving chemical conversion properties, phosphoric acid compounds such as phosphoric acid and phosphoric acid esters, boric acid compounds such as boric acid and boric acid esters, complex compounds of boric acid and sugar alcohols such as mannitol and sorbitol, etc. may be included. As additives for absorbing gas, nitro compounds may be included in o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzene, p-nitrobenzyl alcohol, m-nitroacetophenone, o-nitroanisole, etc.

[0044] Examples of the separator include cellulose such as kraft, Manila hemp, esparto, hemp, and rayon, as well as mixed papers thereof, polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof, polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins, polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides, polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0045] (electrode body) The anode and cathode elements are arranged in a laminated form in which they are alternately laminated with a separator sandwiched therebetween, or in a wound form in which they are alternately laminated with a separator sandwiched therebetween and wound. In the laminated form, in addition to a flat plate form in which an exterior is omitted, for example, the capacitor element is covered with a laminate film, or sealed by molding, dip coating, or printing with a resin such as a heat-resistant resin or an insulating resin.

[0046] Alternatively, the anode body and the cathode body are arranged in a wound type in which they are alternately stacked with a separator sandwiched therebetween and wound. In the wound type, for example, the capacitor element is inserted into a cylindrical exterior case with a bottom, and the open end of the exterior case is sealed with a sealing body by crimping. The sealing body is made of, for example, rubber, or a laminate of rubber and a hard substrate. Examples of rubber include ethylene propylene rubber and butyl rubber.

[0047] The anode body is a foil made of a valve metal. In a wound electrolytic capacitor, the valve metal is stretched into a long strip shape, while in a laminated electrolytic capacitor, it is a flat plate or a sintered body made by molding and sintering powder into a flat plate shape. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be included.

[0048] The anode body has a surface-expanding layer formed on one or both sides thereof. The surface-expanding layer is an etching layer formed by etching a foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto a foil. That is, the surface-expanding layer has a porous structure, and is composed of tunnel-like pits, spongy pits, or voids between densely packed powder or particles.

[0049] The tunnel-shaped etching pit is a hole dug in the foil thickness direction. This tunnel-shaped etching pit is typically formed by passing a direct current in an acidic aqueous solution containing halogen ions such as hydrochloric acid. The tunnel-shaped etching pit is further enlarged by passing a direct current in an acidic aqueous solution such as nitric acid. The spongy etching pit makes the surface-enlarged layer into a sponge-like layer with fine voids extending in a space. This spongy etching pit is formed by passing an alternating current in an acidic aqueous solution containing halogen ions such as hydrochloric acid.

[0050] The sintered layer is produced by obtaining a powder of a valve metal of the same or different type as the foil body by a pulverization method, an atomization method, a melt spinning method, a rotating disk method, a rotating electrode method, or the like, forming a paste with a binder or a solvent, applying it to the foil body, drying it, and heating and sintering it in a vacuum or a reducing atmosphere, or the like. The atomization method may be any of a water atomization method, a gas atomization method, and a water gas atomization method. The vapor deposition layer is produced by, for example, a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and evaporating a valve metal of the same or different type as the foil body by resistance heat or electron beam energy, and depositing the vapor of the valve metal particles on the surface of the foil body.

[0051] The dielectric oxide film is formed on one or both sides of the anode body on which the surface-expanding layer is formed. The dielectric oxide film is typically an oxide film formed on the surface layer 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 surface-expanding layer. In the chemical conversion treatment for forming the dielectric oxide film, a voltage is applied to the anode body in a chemical conversion solution so as to achieve a desired withstand voltage. The chemical conversion solution is a solution that does not contain halogen ions, and is, for example, a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate.

[0052] In the case of a wound-type electrolytic capacitor, the cathode body is preferably a foil body made of a valve metal and stretched. The purity of the cathode body is preferably 99% or more. A surface-expanding layer is formed on the cathode body, as with the anode body. A plain foil without a surface-expanding layer may be used as the cathode body. The cathode body may have a natural oxide film or a thin oxide film (about 1 to 10 V) formed by chemical conversion treatment. The natural oxide film is formed by the reaction of the cathode body with oxygen in the air. Furthermore, a layer made of a metal nitride, a metal carbide, or a metal carbonitride may be formed on the cathode body by a vapor deposition method, or a layer containing carbon may be formed on the surface.

[0053] Alternatively, a carbon layer may be laminated on the cathode body. The carbon material contained in the carbon layer is graphite, carbon black, or a mixture thereof. Examples of graphite include natural graphite, artificial graphite, graphitized ketjen black, etc. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black. In addition, the carbon layer may contain activated carbon, carbon nanohorn, or fibrous carbon as the carbon material. Activated carbon is made from natural plant tissue such as coconut shell, synthetic resin such as phenol, or fossil fuel such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes (hereinafter, CNT), carbon nanofibers (hereinafter, CNF), etc. Activated carbon and fibrous carbon are preferable because pi electrons are delocalized and the specific surface area is large.

[0054] 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, and the slurry is coated on the cathode foil by a slurry casting method, a doctor blade method, a spray atomization method, or the like, and dried. In the deposition method, the carbon material is evaporated by applying an electric current to heat the carbon material in a vacuum, or evaporated by applying an electron beam to the carbon material in a vacuum, and a film of the carbon material is formed on the cathode foil. In addition, in the sputtering method, a target made of a carbon material and the cathode foil are placed in a vacuum container, and an inert gas is introduced into the vacuum container and a voltage is applied to cause the plasmatized inert gas to collide with the target, and the particles of the carbon material knocked out from the target are deposited on the cathode foil.

[0055] 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. 2As 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, but if a carbon material is forced into the pores of the surface-expanding layer by pressing and the carbon material is deformed along the uneven surface of the surface-expanding layer, the adhesion and fixation between the carbon layer and the cathode foil can be further improved.

[0056] The carbon material may also be subjected to a porous treatment such as an activation treatment or an opening treatment. As the porous treatment, a conventionally known activation treatment such as a gas activation method or a chemical activation method can be used. Examples of the gas used in the gas activation method include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or a gas consisting of a mixture of these. Examples of the chemical used in the chemical activation method 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. During this activation treatment, a heat treatment is performed as necessary.

[0057] An anode lead and a cathode lead are connected to the anode body and the cathode body and are extended to the outside of the capacitor element. The anode lead and the cathode lead are connected to the anode body and the cathode body by cold welding, ultrasonic welding, laser welding, or the like. EXAMPLES

[0058] The electrolytic capacitor, the filter circuit, and the power converter will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0059] Various electrolytic capacitors were produced. The anode body was common to all electrolytic capacitors, and the base material of the anode body was aluminum foil. The aluminum foil of the anode body was enlarged by etching. In the process of enlarging the surface of the anode body, a direct current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid to form pits, and then a direct current was passed through the aluminum foil in an aqueous solution containing nitric acid to enlarge the pits. As a result, tunnel-shaped etching pits were formed in the anode body. Furthermore, the anode body was immersed in an aqueous solution of boric acid and subjected to a chemical conversion treatment at 650 V to form a dielectric oxide film on the surface of the aluminum foil.

[0060] Two types of cathode bodies were prepared. The base material of both cathode bodies was aluminum foil. The aluminum foil of the cathode bodies was enlarged by etching. In the process of enlarging the surface of the cathode bodies, an alternating current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid. As a result, spongy etching pits were formed in the cathode bodies. One type of cathode body has a carbon layer on the surface-enlarged aluminum foil. The carbon material of the carbon layer was carbon black, and the carbon layer was laminated on the surface-enlarged aluminum foil by a coating method. After the carbon layer was laminated, the cathode body was pressed.

[0061] A lead wire was connected to each of the anode and cathode bodies, and the anode and cathode bodies were wound facing each other with a separator interposed between them. The wound body had a diameter of 30 mm and a height of 60 mm. The wound body was impregnated with an electrolyte to complete the capacitor element. The capacitor element was housed in an exterior case, and the opening of the exterior case was sealed with a sealant. The sealant and the exterior case were tightly attached by crimping. After this, the electrolytic capacitor was subjected to an aging treatment by applying a voltage of 550 V at room temperature for one hour.

[0062] Each electrolytic capacitor was produced by combining any one of the various electrolytes in Table 1 below with any one of the various separators in Table 2 below.

[0063] (Table 1) TIFF2025034972000010.tif81163

[0064] (Table 2) TIFF2025034972000011.tif41164

[0065] As shown in Table 1, the various electrolytes have the same composition, but by varying the composition ratio, the resistivity (Ω·cm) differs. Specifically, by adjusting the content of the solute azelaic acid, other additives, and water, the various electrolytes have various resistivities. Other additives include phosphoric acid and nitro compounds, as shown in Table 1. In addition, as shown in Table 2, the various separators are all made of kraft paper, i.e., cellulose. The various separators were adjusted to various thicknesses and average densities by combining multiple types of kraft paper with different thicknesses and densities.

[0066] The separators and electrolytes provided in the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 4 are as shown in Table 3 below. In Table 3 below, the resistivity Re (Ω cm 2 ) is the right side of the above formula (8), as shown in the following formula (9).

[0067]

number

[0068] (Table 3) TIFF2025034972000013.tif127166

[0069] (ESR and capacitance appearance rate measurements) The ESR of the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 4 in Table 3 above was measured. The ESR was measured using an LCR meter (manufactured by NF Corporation, model number ZM2376). The ESR measurement environment was -40°C, the frequencies were 120Hz and 100kHz, the DC bias was 1.5V, and the AC current level was a sine wave of 1.0Vrms.

[0070] And the ESR when driven at a frequency of 120Hz in a temperature environment of -40℃ 120HzWhen driven at a frequency of 100 kHz in a temperature environment of -40°C, 100kHz This division was used to calculate the ESR ratio, which is the ratio of the ESR when driven at a frequency of 120 Hz in a temperature environment of -40°C to the ESR when driven at a frequency of 100 kHz in a temperature environment of -40°C.

[0071] The electrostatic capacitance (Cap) of the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 4 in Table 3 above was measured. The Cap was measured using an LCR meter (model number ZM2376, manufactured by NF Corporation). Two types of Cap were measured. The measurement environment for one Cap was 20°C, the frequency was 120Hz, the DC bias was 1.5V, and the AC current level was a sine wave of 1.0Vrms. The measurement environment for the other Cap was -40°C, the frequency was 120Hz, the DC bias was 1.5V, and the AC current level was a sine wave of 1.0Vrms.

[0072] Then, the Cap when driven at a frequency of 120 Hz in a temperature environment of -40° C. was divided by the Cap when driven at a frequency of 120 Hz in a temperature environment of 20° C. This division was used to calculate the capacitance appearance rate of the Cap when driven at a frequency of 120 Hz in a temperature environment of -40° C., i.e., the capacitance appearance rate of -40° C. to 20° C., based on the Cap when driven at a frequency of 120 Hz in a temperature environment of 20° C.

[0073] The ESR ratios and capacitance appearance rates at -40°C to 20°C of the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 4 in Table 3 above are shown in Table 4 below. (Table 4) TIFF2025034972000014.tif126163

[0074] As shown in Table 4 above, in the electrolytic capacitors of Examples 1 to 7, the resistivity Re (ESR x S) was set to 80.8 or less by adjusting the electrolytic solution and the separator. As a result, the ESR of Examples 1 to 7 was all less than 7.2. And, in the electrolytic capacitors of Examples 1 to 7, the capacitance appearance ratios of -40°C to 20°C were all 80% or more. On the other hand, in Comparative Examples 1 to 4, in which the resistivity Re (ESR x S) was significantly more than 80.8, the ESR ratios all significantly exceeded 7.2, and the capacitance appearance ratios of -40°C to 20°C were significantly less than 80%.

[0075] It was confirmed that an ESR ratio of less than 7.2 results in a capacity appearance rate of 80% or more at -40°C relative to 20°C. It was also confirmed that the method of calculating resistivity Re and the standard value of 80.8 are highly accurate when colloidal silica is contained in the electrolyte and cellulose is used as the separator.

[0076] 1 to 3 are plots of Examples 1 to 7 and Comparative Examples 1 to 4. In Fig. 1, the plots of filled square marks are Example 1, the plots of open circles are Example 2, the plots of open diamond marks are Example 3, the plots of open triangle marks are Example 4, the plots of open square marks are Example 5, the plots of filled diamond marks are Example 6, the plots of filled circles are Example 7, the plots of asterisk marks are Comparative Example 1, the plots of x marks are Comparative Example 2, the plots of filled triangle marks are Comparative Example 3, and the plots of plus marks are Comparative Example 4. In Figs. 1 to 3, good correlations are shown respectively.

[0077] In addition, Fig. 4 shows the relationship between the tortuosity τ and the separator density ρ (g / cm 3 4 is a scatter diagram showing the relationship between the tortuosity τ and the density ρ of the separator. The tortuosity τ was calculated from various measured values ​​of the electrolytes and separators of Examples 1 to 7 and Comparative Examples 1 to 4 and plotted. The types of plots are the same as those in Figs. 1 to 3. As shown in Fig. 4, when the electrolyte contains colloidal silica and the separator is made of cellulose, it can be confirmed that there is a good correlation between the tortuosity τ and the density ρ of the separator.

[0078] In addition, in Figure 4, the relationship between the tortuosity τ and the density ρ of the separator is plotted with negative symbols when the electrolyte contains colloidal silica and various polycarbonate separators are used. As shown in Figure 4, these plots are concentrated near 1, including when the tortuosity τ is less than 1, and it can be confirmed that there is no correlation.

[0079] In this way, when the electrolyte contains colloidal silica and the separator is made of cellulose, the thickness L (cm) of the separator and the density ρ (g / cm 3 ), and the specific resistance Rs (Ω cm) of the electrolyte at 20°C as parameters, it is possible to define a relationship equation for achieving a capacity appearance rate of 80% or more at -40°C relative to 20°C.

[0080] Next, the power converter using the electrolytic capacitors of Example 4 and Comparative Example 5 was simulated using software (LTSpice XVII version 17.0.34, manufactured by Analog Devices Inc.). The electrolyte used in the electrolytic capacitor of Comparative Example 5 is composed of 4.5 wt% water, 63.4 wt% ethylene glycol, 6 wt% azelaic acid, 2.2 wt% additive, 17 wt% polyether polyol, and 2 wt% dimethylamine. The additive contains phosphoric acid and a nitro compound. The polyether polyol is a pressure resistance improver. The separator used in the electrolytic capacitor of Comparative Example 5 is separator 2 in Table 2.

[0081] As a result, the electrolytic capacitor of Comparative Example 5 had a specific resistance of 825 Ω·cm at 20° C. The ESR ratio was 10.9. And, in the electrolytic capacitor of Comparative Example 5, the capacitance appearance rate from −40° C. to 20° C. was 63.2%.

[0082] Fig. 5 is a circuit diagram of a power converter. As shown in Fig. 5, the power converter is an active power factor correction circuit, and includes an AC power source 1, a bridge diode 2, and a step-up converter 3. The bridge diode 2 is connected to the AC power source 1 and full-wave rectifies the AC voltage.

[0083] The step-up converter 3 is connected to the bridge diode 2, and includes a reactor 31, a switching element 32, a diode 33, and an electrolytic capacitor 34. The step-up converter 3 improves the decrease in power factor caused by the electrolytic capacitor 34, which smoothes the output voltage of the bridge diode 2 and outputs the DC voltage Vout.

[0084] The reactor 31 and the diode 33 are inserted in series with the bridge diode 2. The reactor 31 is inserted after the bridge diode 2, and the diode 33 is inserted after the reactor 31. The switching element 32 and the electrolytic capacitor 34 are inserted in parallel with the bridge diode 2. The switching element 32 is inserted between the reactor 31 and the diode 33, and the electrolytic capacitor 34 is inserted after the diode 33.

[0085] This electrolytic capacitor 34 was replaced with the electrolytic capacitors of Example 4 and Comparative Example 5, and the output voltage Vout was measured in each temperature range. Here, the power converter was designed so that the output voltage Vout would be 400±50 V, based on the nominal capacitance at 20° C. and 120 Hz of the electrolytic capacitors of Example 4 and Comparative Example 5.

[0086] 6 is a graph showing waveforms of output voltage Vout in each temperature range in the power converter including the electrolytic capacitors of Example 4 and Comparative Example 5. The temperature ranges are -40°C, -25°C, 0°C, 20°C, and 85°C.

[0087] As shown in Fig. 6, when the operating environment is set to -40°C, the power converter including the electrolytic capacitor of Comparative Example 5 exhibits large voltage fluctuations in the output voltage Vout, exceeding the expected 400±50V and resulting in an output voltage Vout of 650V. For this reason, until the electrolytic capacitor of Comparative Example 5 warms up, it is necessary to suppress the output power so as not to exceed the rated voltage of the electrolytic capacitor of Comparative Example 5. Therefore, for example, when the power converter is an OBC for an EV or PHEV, the output power for quick charging of the EV or PHEV must be suppressed.

[0088] On the other hand, as shown in Fig. 6, even when the operating environment is set to -40°C, the power converter including the electrolytic capacitor of Example 4 has a small voltage fluctuation in the output voltage Vout, remaining within the expected range of 400±50V. Therefore, even in an extremely low temperature environment of -40°C, there is no need to suppress the output power. Therefore, for example, when the power converter is an OBC for an EV or PHEV, the EV or PHEV can be rapidly charged with a large output power even in an extremely low temperature environment of -40°C. [Explanation of symbols]

[0089] 1 AC power supply 2 Bridge Diode 3. Step-up converter 31 Reactor 32 Switching element 33 Diode 34 Electrolytic capacitor

Claims

1. An electrolytic capacitor in which the ESR at 120 Hz is less than 7.2 times the ESR at 100 kHz in a temperature environment of -40°C.

2. The battery is provided with an electrolyte solution containing colloidal silica and a separator made of cellulose, The thickness L (cm) of the separator, the density ρ (g / cm ３ ) and the specific resistance Rs (Ω cm) of the electrolytic solution at 20° C. satisfies the following mathematical formula (1):

2. The electrolytic capacitor according to claim 1 . [0010]

3. 3. A filter circuit comprising the electrolytic capacitor according to claim 1.

4. A power converter comprising the electrolytic capacitor according to claim 1 or 2.

Images