Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present invention comprises: an anode foil having a dielectric layer on a surface thereof; a cathode foil; a separator interposed between the anode foil and the cathode foil; a conductive polymer attached to the separator; and a liquid component impregnated into the separator, wherein the anode foil has a core part and a pair of porous parts continuous with both surfaces of the core part, the separator contains first fibers and second fibers, the first fibers and the second fibers are mixed, a fiber diameter D1 of the first fibers is 10 μm to 50 μm, a fiber diameter D2 of the second fibers is 5 μm or less, and a density of the separator is 0.37 g / cm3 to 0.50 g / cm3.

Description

Electrolytic capacitors Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2025-025167, filed with the Japan Patent Office on 19 February 2025, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to electrolytic capacitors.

[0003] Patent Document 1 describes an electrolytic capacitor comprising: a capacitor element having a dielectric layer on its surface, a cathode foil laminated on it via a separator, and a solid electrolyte layer made of conductive polymer fine particles formed on the surfaces of the anode foil, cathode foil and separator; a pair of lead wires, each with one end connected to the capacitor element; a driving electrolyte impregnated in the capacitor element; and an outer casing that seals the capacitor element together with the driving electrolyte, with the other ends of the pair of lead wires being led out to the outside, wherein the airtightness of the separator is 2.0 s / 100 ml or less, and furthermore, the conductive polymer fine particles have a particle size of 100 nm or less and a density of 0.3 mg / cm² per unit area of ​​the anode foil. ２ 1.2mg / cm or more ２ The following range of electrolytic capacitors is proposed.

[0004] Japanese Patent Publication No. 2013-26536

[0005] From the perspective of increasing capacitance, increasing the thickness of the anode foil and the thickness of the porous portion of the anode foil is being considered. However, using such an anode foil may reduce the short-circuit resistance of the electrolytic capacitor.

[0006] One aspect of the present invention comprises an anode foil having a dielectric layer on its surface, a cathode foil, a separator interposed between the anode foil and the cathode foil, a conductive polymer adhering to the separator, and a liquid component impregnated into the separator, wherein the anode foil has a core portion and a pair of porous portions continuous on both sides of the core portion, the separator comprises a first fiber and a second fiber, the first fiber and the second fiber are mixed together, the fiber diameter D1 of the first fiber is 10 μm to 50 μm, the fiber diameter D2 of the second fiber is 5 μm or less, and the density of the separator is 0.37 g / cm³. ３ ~0.50 g / cm ３ This concerns electrolytic capacitors.

[0007] According to the present invention, an electrolytic capacitor with high capacitance and excellent short-circuit resistance can be obtained.

[0008] This is a schematic cross-sectional view showing an example of an electrolytic capacitor according to one embodiment of the present invention. This is a perspective view showing a portion of the winding shown in Figure 1 unfolded.

[0009] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0010] In the following explanation, when examples are given of lower and upper limits for specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0011] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0012] [Electrolytic Capacitor] The electrolytic capacitor according to this disclosure (hereinafter also referred to as "electrolytic capacitor (C)") includes an anode foil having a dielectric layer on its surface, a cathode foil, a separator interposed between the anode foil and the cathode foil, a conductive polymer adhering to the separator, and a liquid component impregnated into the separator. In other words, the electrolytic capacitor according to this disclosure is a solid-liquid hybrid type electrolytic capacitor.

[0013] The electrolytic capacitor (C) may be a wound-type electrolytic capacitor comprising a wound body formed by winding an anode foil and a cathode foil with a separator interposed between the anode foil and the cathode foil. Alternatively, the electrolytic capacitor (C) may be a laminated-type electrolytic capacitor comprising a laminate formed by folding an anode foil and a cathode foil in a zigzag pattern with a separator interposed between the anode foil and the cathode foil.

[0014] An anode foil having a dielectric layer on its surface comprises a core and a pair of porous portions continuous on both sides of the core. In other words, the anode foil is a metal foil with a dielectric layer formed on its surface. The type of metal constituting the metal foil is not particularly limited. Examples of metals constituting the metal foil include valve-forming metals and alloys of valve-forming metals, such as aluminum, tantalum, niobium, and titanium, as the formation of the dielectric layer is easy. A preferred example is aluminum and aluminum alloys. The surface of the anode foil is roughened to form porous portions, and the dielectric layer is formed on the roughened surface. The dielectric layer of the anode foil is in contact with a conductive polymer.

[0015] Anode foil can be obtained, for example, by roughening the surface of a metal foil through etching, and then forming a dielectric layer (oxide film) on the roughened metal foil surface through chemical conversion treatment.

[0016] Metal foil can be used for the cathode foil. The type of metal that makes up the metal foil is not particularly limited. Examples of metals that make up the metal foil include valve-forming metals and alloys of valve-forming metals such as aluminum, tantalum, niobium, and titanium. A preferred example is aluminum and aluminum alloys. In addition, a chemical conversion coating may be provided on the surface of the cathode foil, and a coating of a different metal (dissimilar metal) or a nonmetal may be provided. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon.

[0017] The thickness of the anode foil is, for example, 100 μm or more, the thickness of the core is, for example, 35 μm or less, and the thickness of the porous portion is, for example, 32.5 μm or more, or may be 35 μm or more. Here, the thickness of the porous portion refers to the thickness of the porous portion on one side of the core. Therefore, the total thickness of the pair of porous portions is, for example, 65 μm or more, or may be 70 μm or more. The dielectric layer is formed in the porous portion.

[0018] The thickness of the core of the anode foil can be determined by measuring the thickness of the core at five arbitrary locations in a cross-section parallel to the thickness direction of the anode foil (for example, a cross-sectional SEM image) and averaging the results.

[0019] The thickness of the porous portion of the anode foil is determined by measuring the thickness of a pair of porous portions continuous on both sides of the core at five arbitrary locations in a cross-section parallel to the thickness direction of the anode foil (e.g., a cross-sectional SEM image), and then averaging these measurements. Typically, the thicknesses of a pair of porous portions are approximately the same. Therefore, if the thicknesses of a pair of porous portions differ, the average of both thicknesses is used as the thickness of the porous portion.

[0020] If the dielectric strength of an anode foil having a dielectric layer on its surface is 80V or more and less than 90V, the CV value of the anode foil is, for example, 1200V·μF / cm. ２ The above is also acceptable. Furthermore, if the dielectric strength of the anode foil having a dielectric layer on its surface is 90V or more and less than 105V, the CV value of the anode foil is 1100V・μF / cm ２The above is also acceptable. Furthermore, if the dielectric strength of the anode foil having a dielectric layer on its surface is 105V or more and less than 110V, the CV value of the anode foil is 1000V・μF / cm ２ The above is also acceptable. Furthermore, if the dielectric strength of the anode foil having a dielectric layer on its surface is 110V or higher, the CV value of the anode foil is 970V・μF / cm ２ That's fine too.

[0021] The CV value is the product of the capacitance per unit area (foil capacitance) C of the anode foil and the breakdown voltage (the breakdown voltage of an anode foil with a dielectric layer on its surface) V. The CV value is calculated by measuring the capacitance C and breakdown voltage V of the anode foil with a dielectric layer. The capacitance C and breakdown voltage V are measured in accordance with the EIAJ standard (RC-2364A). Then, the product of capacitance C and breakdown voltage V (CV value) is calculated.

[0022] In solid-liquid hybrid electrolytic capacitors, there is a strong demand for higher capacitance, so the thickness of the anode foil and the porous section are designed to be considerably large. However, if the thickness of the porous section exceeds conventional levels, the short-circuit resistance of the electrolytic capacitor can rapidly decrease. For example, it has been found that when using anode foil with a thickness of 100 μm or more, a core thickness of 35 μm or less, and a porous section thickness of 32.5 μm or more, the problem of short-circuit resistance becomes apparent, making countermeasures an urgent necessity. Hereinafter, anode foil with a thickness of 100 μm or more, a core thickness of 35 μm or less, and a porous section thickness of 32.5 μm or more will be referred to as "anode foil (P)".

[0023] The following phenomena are suspected to be the reason why the short-circuit resistance decreases when anode foil (P) is used. First, because the anode foil (P) has a large overall thickness and a large porous portion, it is thought that cracks are likely to form on the surface of the porous portion when it is bent. In other words, the porous portion of the anode foil (P) may have cracks.

[0024] In the vicinity of a crack, the strength of the porous part decreases, and it is considered that minute fragments of the porous part may break off starting from the crack. When the thickness of the porous part is 32.5 μm or more, if a crack occurs in the porous part, fragments having a length of about 70 μm, for example, can be generated even though they are of minute size. If fragments of about 70 μm break off and the fragments enter a pinhole or a low-density portion of the separator, the probability of a short circuit occurring increases significantly. On the other hand, the separator is a nonwoven fabric and is formed, for example, by papermaking fibers by the papermaking method. Therefore, it is likely that unevenness in papermaking occurs, and even a small amount of fragments can cause a short circuit.

[0025] In contrast, when the separator includes a first fiber and a second fiber, the first fiber and the second fiber are mixedly formed, the fiber diameter D1 of the first fiber is 10 μm to 50 μm, the fiber diameter D2 of the second fiber is 5 μm or less, and the density of the separator is 0.37 g / cm ３ to 0.50 g / cm ３ (hereinafter, also referred to as "separator (S)"), it is considered that the density of the separator (S) is homogenized and the generation of pinholes is highly suppressed. The first fiber having a large fiber diameter D1 imparts sufficient strength to the separator (S), but it is difficult to prevent unevenness in papermaking with only the first fiber. By mixedly forming the second fiber having a fiber diameter D2 sufficiently smaller than the fiber diameter D1 with the first fiber, for example, even when a pinhole is generated due to unevenness in papermaking of the first fiber, the pinhole is filled with a plurality of second fibers. Therefore, when minute fragments of the porous part have a length of about 70 μm, the movement between the electrodes is significantly restricted.

[0026] However, if the density of the separator (S) is less than 0.37 g / cm ３ it is likely that unevenness in papermaking occurs in the separator, and it becomes difficult to suppress a short circuit caused by minute fragments of the porous part. To suppress the intrusion of minute fragments of the porous part into the separator, it is important to increase the density of the separator. Even if the first fiber and the second fiber are mixedly formed, if the density of the separator is insufficient, the intrusion of fragments of the porous part into the separator may be allowed. On the other hand, if the density of the separator is 0.50 g / cm３ If the density exceeds this value, it becomes difficult to adhere a sufficient amount of conductive polymer to the separator, and the resistance between the anode foil and cathode foil may increase. The density of the separator (S) is 0.37 g / cm³. ３ ~0.43 g / cm ３ It is preferable that this be the case.

[0027] The second fiber is preferably fibrillated. Fibrillation is a phenomenon in which a fiber is split and subdivided in the axial direction. Fibrillation of a fiber occurs by applying friction or pressure to the fiber. Fibrillation may also be performed by beating or other methods. Fibrillated fibers are usually highly crimped and have a high ability to trap minute foreign matter. By fibrillating the second fiber, if minute fragments are generated in the porous section, the movement of these fragments between poles is severely restricted.

[0028] The separator (S) may contain only one type of first fiber or multiple types. The fiber diameter D1 can be determined by arbitrarily selecting 20 first fibers having a fiber diameter of 10 μm to 50 μm from the separator, measuring the fiber diameter of the selected first fibers (length in the direction perpendicular to the axial direction of the first fiber), and averaging the results. If the number of arbitrarily selected first fibers is sufficiently large, the fiber diameter D1 will converge to a single value even if the separator (S) contains multiple types of first fibers. The fiber diameter D1 is preferably 40 μm or less, and more preferably 20 μm to 35 μm.

[0029] The separator (S) may contain only one type of second fiber or multiple types. The fiber diameter D2 can be determined by arbitrarily selecting 20 second fibers with a fiber diameter of 5 μm or less from the separator, measuring the fiber diameter of the selected second fibers (length in the direction perpendicular to the axial direction of the second fiber), and averaging the results. If the number of arbitrarily selected second fibers is sufficiently large, the fiber diameter D2 will converge to a single value even if the separator (S) contains multiple types of first fibers.

[0030] If the second fiber is fibrillated, the fiber diameter D2 is measured by considering each fibril as a separate fiber, rather than the fiber before fibrillation. The fiber diameter D2 is preferably between 1 μm and 5 μm.

[0031] The content rate of the second fiber in the total of the first fiber and the second fiber contained in the separator is, for example, 10% by mass to 50% by mass, may be 10% by mass to 30% by mass, or may be 30% to 50% by mass. By including the second fiber in the separator (S) at such a content rate, both the strength and the density homogeneity of the separator (S) can be sufficiently enhanced.

[0032] The ratio of the fiber diameter D1 of the first fiber to the fiber diameter D2 of the second fiber: D1 / D2 is, for example, 3 to 15, and may be 3 to 10. When the first fiber and the second fiber are mixed and formed in such a D1 / D2 ratio, since there is a sufficiently large difference between the fiber diameter D1 and the fiber diameter D2, it is considered that pinholes of the separator (S) that may be caused by uneven formation of the first fiber are more likely to be filled with a plurality of second fibers. The D1 / D2 ratio is, for example, 5 or more, and may be 8 or more.

[0033] The separator (S) may contain fibers other than the first fiber and the second fiber. That is, the separator (S) may contain fibers with a fiber diameter exceeding 50 μm (third fiber) or fibers with a fiber diameter exceeding 5 μm and less than 10 μm (fourth fiber). However, it is preferable to limit the content rates of the third fiber and the fourth fiber contained in the separator (S) to 5% by mass or less.

[0034] The thickness of the separator (S) is, for example, 45 μm or less, and may be 37 μm to 43 μm. When the separator (S) is formed by the mixed weaving of the first fiber and the second fiber and has a sufficiently large density, even a thin separator (S) has a sufficiently high barrier property. When the second fiber is fibrillated, the barrier property of the separator (S) becomes even higher. Therefore, by making the separator (S) thin as described above, the resistance between the anode foil and the cathode foil can be reduced. Also, the thinner the separator (S), the larger the volume of the anode foil in the electrolytic capacitor can be, which is more advantageous for increasing the capacitance. The thickness measurement is obtained by measuring ten arbitrary locations with a push-pull micrometer in a state where a plurality of separators (S) (for example, ten sheets) are stacked, and dividing the average value of the measurement values by the number of stacked sheets to calculate the thickness per sheet.

[0035] The first fiber may be at least one of a synthetic fiber and a cellulose-based fiber. The second fiber may be at least one of a synthetic fiber and a cellulose-based fiber. That is, as the separator (S) combining the first fiber and the second fiber, for example, the following modes are conceivable.

[0036] A separator (S) in which both the first fiber and the second fiber are synthetic fibers. A separator (S) in which both the first fiber and the second fiber are cellulose-based fibers. A separator (S) in which the first fiber is a synthetic fiber and the second fiber is a cellulose-based fiber. A separator (S) in which the second fiber is a synthetic fiber and the first fiber is a cellulose-based fiber. A separator (S) in which the first fiber includes a synthetic fiber and a cellulose-based fiber and the second fiber is a synthetic fiber. A separator (S) in which the first fiber includes a synthetic fiber and a cellulose-based fiber and the second fiber is a cellulose-based fiber. A separator (S) in which the second fiber includes a synthetic fiber and a cellulose-based fiber and the first fiber is a synthetic fiber. A separator (S) in which the second fiber includes a synthetic fiber and a cellulose-based fiber and the first fiber is a cellulose-based fiber. A separator (S) in which the first fiber includes a synthetic fiber and a cellulose-based fiber and the second fiber includes a synthetic fiber and a cellulose-based fiber.

[0037] Cellulosic fibers include natural cellulose fibers. Examples of natural cellulose fibers include Manila hemp pulp, esparto pulp, coniferous pulp, hardwood pulp, and sisal pulp. Cellulosic fibers may also include regenerated cellulose fibers and semi-synthetic cellulose fibers. Regenerated cellulose fibers include those spun using a solution of natural cellulose dissolved in a solvent (e.g., rayon). Semi-synthetic cellulose fibers include those produced by adding other materials to natural cellulose to form fibers (e.g., acetate). Cellulosic fibers may be used individually or in combination of two or more types.

[0038] The synthetic fiber preferably contains at least one selected from the group consisting of aramid (aromatic polyamide), polyethylene terephthalate (PET), and vinylon (acetalized PVA). Among these, aramid is more preferred from the viewpoint of improving heat resistance and fiber strength (tensile strength). The synthetic fiber may be used alone or in combination of two or more types.

[0039] The synthetic fibers may include, in addition to those exemplified above, polybutylene terephthalate, polyphenylene sulfide, nylon, polyimide, polyamide-imide, polyetherimide, and the like. The separator may also include glass fibers. At least a portion of the separator may be carbonized.

[0040] The conductive polymer adhering to the separator (S) is preferably formed by conductive polymer particles. Examples of conductive polymers include polypyrrole, polythiophene, polyaniline, and their derivatives. The conductive polymer may be used alone or in combination of two or more types. The conductive polymer may also be a copolymer of two or more monomers. A derivative of a conductive polymer means a polymer that has a conductive polymer as its basic skeleton. For example, derivatives of polythiophene include poly(3,4-ethylenedioxythiophene).

[0041] The conductive polymer may contain a dopant. The dopant can be appropriately selected depending on the type of conductive polymer. Various known dopants may be used as dopants. Examples of dopants include naphthalene sulfonic acid, p-toluenesulfonic acid, polystyrene sulfonic acid, and salts thereof. An example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS). The conductive polymer may be formed from particles of poly(3,4-ethylenedioxythiophene) (PEDOT) (hereinafter also referred to as PEDOT / PSS) doped with polystyrene sulfonic acid (PSS).

[0042] Preferably, the conductive polymer is also attached to the dielectric layer of the anode foil and the cathode foil. This allows the conductive polymer to form a sufficient conductive path between the anode foil and the cathode foil. As a result, the equivalent series resistance (ESR) of the electrolytic capacitor can be reduced, thereby improving the reliability of the electrolytic capacitor.

[0043] The conductive polymer may also adhere to the voids in the separator (S) (i.e., the surface of the separator's constituent material surrounding the voids in the separator (S)). This allows for the formation of stronger conductive paths between the anode foil and the cathode foil due to the conductive polymer. It is preferable that the conductive polymer adheres to at least the surface of the dielectric layer of the anode foil, and more preferably adheres to both the surface of the dielectric layer and the surface of the cathode foil, and further, adheres to the voids in the separator (S). It is preferable that the conductive polymer exists in such a way that it continuously connects the surface of the dielectric layer and the surface of the cathode foil.

[0044] A conductive polymer can be formed, for example, by applying a polymer dispersion, in which a conductive polymer containing a dopant is dispersed in a liquid medium, to the dielectric layer of the anode foil, the separator (S), and the cathode foil, and then removing at least a portion of the liquid medium. Alternatively, the conductive polymer may be formed by impregnating the separator with the polymer dispersion or coating the separator (S) with the polymer dispersion, and then removing at least a portion of the liquid medium. In the above case, the conductive polymer containing the dopant is dispersed in the liquid medium in particulate form.

[0045] From the viewpoint of enhancing entanglement with the second fibers constituting the separator (S), the median diameter of the conductive polymer particles in the polymer dispersion is preferably, for example, 0.01 μm to 0.5 μm. In this case, even when a densely formed separator (S) is used, the conductive polymer can adhere to the voids in the separator.

[0046] The median diameter of conductive polymer particles is the median diameter in the volume particle size distribution measured by a particle size analyzer using dynamic light scattering. The median diameter of conductive polymer particles can be controlled by polymerization conditions, dispersion conditions, and other factors.

[0047] Conductive polymers can also be formed by applying a polymerization solution containing monomers and dopants, which are the constituent units of the conductive polymer, to a dielectric layer, and then chemically or electrolytically polymerizing the monomers in the presence of the dielectric layer and the dopant. From the viewpoint of exhibiting excellent voltage withstand characteristics in electrolytic capacitors, it is preferable to apply the conductive polymer to the separator (S) using a polymer dispersion.

[0048] The weight-average molecular weight of the conductive polymer is not particularly limited, but from the viewpoint of controlling the median diameter of the conductive polymer particles in the polymer dispersion to the range described above, it is preferably, for example, 100,000 or less. The weight-average molecular weight of the conductive polymer may be between 1,000 and 100,000. Note that the weight-average molecular weight is the weight-average molecular weight on a polystyrene basis measured by gel permeation chromatography.

[0049] Electrolytic capacitors may contain a non-aqueous solvent or electrolyte as a liquid component. The liquid component may be a substance that is liquid at room temperature (25°C) or a substance that is liquid at the temperature at which the electrolytic capacitor is used. The liquid component can improve the contact between the conductive polymer and the dielectric layer, and can also improve the repairability of defects in the dielectric layer. The electrolyte may also function as an electrolyte together with the conductive polymer.

[0050] The non-aqueous solvent may be an organic solvent or an ionic liquid. Examples of non-aqueous solvents include polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (GBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde.

[0051] Polymeric solvents may be used as non-aqueous solvents. Examples of polymeric solvents include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group in a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specifically, examples of polymeric solvents include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol. Further examples of polymeric solvents include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. Non-aqueous solvents may be used individually or as a mixture of two or more.

[0052] The liquid component may contain acidic and basic components. Examples of acidic components include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcinic acid. Examples of basic components include 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethylimidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole.

[0053] The electrolyte contains a non-aqueous solvent and a solute (e.g., an organic salt) dissolved therein. Examples of non-aqueous solvents that constitute the electrolyte include those mentioned above. Examples of solutes include inorganic salts and organic salts. An organic salt is a salt in which at least one of the anion and cation is an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0054] To suppress the dedoping of dopants from conductive polymers, the pH of the liquid component may be set to less than 7, or to 5 or less.

[0055] The components of an electrolytic capacitor (C) will be explained further below.

[0056] Figure 1 is a schematic cross-sectional view showing an example of an electrolytic capacitor (C) according to an embodiment of the present invention. Figure 2 is a schematic perspective view showing the configuration of the wound body. Figure 2 is a diagram showing a part of the wound body of Figure 1 unfolded.

[0057] The electrolytic capacitor (C) 200 comprises a winding body 100. The winding body 100 is constructed by winding an anode foil (P) 10 and a cathode foil 20 with a separator (S) 30 in between.

[0058] The wound body 100 contains a conductive polymer (not shown). That is, the conductive polymer is interposed between the anode foil 10 (dielectric layer) and the cathode foil 20, and is attached to the surface and interior of the separator (S) 30.

[0059] One end of lead tabs 50A and 50B are connected to the anode foil (P) 10 and the cathode foil 20, respectively, and the winding body 100 is formed by winding the lead tabs 50A and 50B. Lead wires 60A and 60B are connected to the other end of lead tabs 50A and 50B, respectively.

[0060] A winding stopper tape 40 is placed on the outer surface of the cathode foil 20, which is located in the outermost layer of the winding body 100, and the end of the cathode foil 20 is fixed by the winding stopper tape 40. If the anode foil (P) 10 is prepared by cutting from a large sheet of foil, the winding body 100 may be further treated with a chemical conversion process to provide a dielectric layer on the cut surface.

[0061] The winding body 100 is housed in the closed-bottom case 211 such that the lead wires 60A and 60B are located on the opening side of the closed-bottom case 211. The material of the closed-bottom case 211 can be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy thereof.

[0062] The winding body 100 is sealed inside the bottomed case 211 by placing a sealing member 212 at the opening of the bottomed case 211, crimping the open end of the bottomed case 211 to the sealing member 212 to create a curl, and placing a seat plate 213 on the curled portion.

[0063] The sealing member 212 is formed so that the lead wires 60A and 60B pass through it. The sealing member 212 can be made of an insulating material, and an elastic material is preferred. Among these, silicone rubber, fluororubber, ethylene propylene rubber, Hypalon rubber, butyl rubber, isoprene rubber, etc., which have high heat resistance are preferred.

[0064] [Method for Manufacturing Electrolytic Capacitors] The method for manufacturing electrolytic capacitors (C) includes, but is not limited to, the following steps.

[0065] (First Step) The first step is to obtain a capacitor element intermediate (hereinafter also simply referred to as the intermediate). In the case of a wound electrolytic capacitor, an electrode group (wound body) may be formed by winding an anode foil (P) and a cathode foil with a separator (S) interposed between the anode foil (P) and the cathode foil. In the case of a multilayer capacitor, an electrode group (multilayer body) may be formed by bending an anode foil (P) and a cathode foil in a zigzag pattern with a separator (S) interposed between the anode foil (P) and the cathode foil.

[0066] (Second Step) The second step is to impregnate the intermediate with a processing solution containing a conductive polymer to obtain a capacitor element. In the second step, for example, the intermediate may be immersed in a processing solution containing a conductive polymer. The immersion time is, for example, 30 seconds or more and 30 minutes or less. The second step may be carried out at room temperature or at a temperature other than room temperature (for example, a temperature higher than room temperature). Furthermore, the second step may be carried out under atmospheric pressure or under reduced pressure.

[0067] The processing solution containing the conductive polymer is usually a polymer dispersion containing water as the liquid medium. The amount of water in the liquid medium is, for example, in the range of 2 to 100% by mass of the dispersion. The liquid medium may be water. The conductive polymer is dispersed in the aqueous medium. That is, the polymer dispersion may be a suspension in which particulate conductive polymer is dispersed in water. The content of the conductive polymer in the suspension may be, for example, 0.1% to 20% by mass, or 0.5% to 3% by mass.

[0068] The viscosity of the polymer dispersion (suspension) may be, for example, in the range of 1 mPa·s to 100 mPa·s, or in the range of 1 mPa·s to 40 mPa·s (for example, in the range of 1 mPa·s to 25 mPa·s). The lower the viscosity of the polymer dispersion (suspension), the easier it is for the intermediate to be impregnated.

[0069] The second step may further include drying the intermediate impregnated in the polymer dispersion (suspension). Drying may be carried out under atmospheric pressure or under reduced pressure. Drying of the intermediate may also be carried out by heating the intermediate. The heating temperature is, for example, 100°C or higher and 120°C or lower.

[0070] (Third step) The method for manufacturing an electrolytic capacitor (C) includes a third step of impregnating the capacitor element with a liquid component (non-aqueous solvent or electrolyte). The third step may be carried out, for example, by injecting the liquid component into a bottomed case for an electrolytic capacitor in which the capacitor element is housed. The method for manufacturing an electrolytic capacitor may also include a step of sealing the bottomed case in which the capacitor element is housed.

[0071] (Note) The above description discloses the following technology: (Technology 1) an anode foil having a dielectric layer on its surface, a cathode foil, a separator interposed between the anode foil and the cathode foil, a conductive polymer adhering to the separator, and a liquid component impregnated into the separator, wherein the anode foil has a core and a pair of porous portions continuous on both sides of the core, the separator includes a first fiber and a second fiber, the first fiber and the second fiber are mixed together, the fiber diameter D1 of the first fiber is 10 μm to 50 μm, the fiber diameter D2 of the second fiber is 5 μm or less, and the density of the separator is 0.37 g / cm³ ３ ~0.50 g / cm ３(Technology 2) An electrolytic capacitor, wherein the thickness of the anode foil is 100 μm or more, the thickness of the core is 35 μm or less, and the thickness of the porous part is 32.5 μm or more. (Technology 3) An electrolytic capacitor, wherein the ratio of the fiber diameter D1 of the first fiber to the fiber diameter D2 of the second fiber, D1 / D2, is 3 to 15. (Technology 4) An electrolytic capacitor, wherein the second fiber is fibrillated, wherein the second fiber is fibrillated, wherein the electrolytic capacitor, wherein the thickness of the separator is 45 μm or less, wherein the electrolytic capacitor, wherein the weight-average molecular weight of the conductive polymer is 100,000 or less, wherein the electrolytic capacitor, wherein the electrolytic capacitor, wherein the thickness of the separator is 45 μm or less, wherein the weight-average molecular weight of the conductive polymer is 100,000 or less, wherein the electrolytic capacitor, wherein the electrolytic capacitor, wherein the conductive polymer contains poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, wherein the electrolytic capacitor, wherein the electrolytic capacitor, wherein the weight-average molecular weight of the conductive polymer is 100,000 or less. (Technology 7) An electrolytic capacitor, wherein the electrolytic capacitor, wherein the conductive polymer contains poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, wherein the electrolytic capacitor, wherein the electrolytic polymer, wherein the weight-average molecular weight of the conductive polymer is 100,000 or less. (Technology 8) An electrolytic capacitor according to any one of Techniques 1 to 7, wherein the porous portion has cracks. (Technology 9) The anode foil has a dielectric strength of 80V or more and less than 90V, and the CV value of the anode foil is 1200V・μF / cm ２ The electrolytic capacitor described in any one of the above technologies 1 to 8. (Technology 10) The anode foil has a withstand voltage of 90V or more and less than 105V, and the CV value of the anode foil is 1100V・μF / cm ２ The electrolytic capacitor described in any one of the above technologies 1 to 8. (Technology 11) The anode foil has a withstand voltage of 105V or more and less than 110V, and the CV value of the anode foil is 1000V・μF / cm ２ The electrolytic capacitor described in any one of the above technologies 1 to 8. (Technology 12) The anode foil has a dielectric strength of 110V or more, and the CV value of the anode foil is 970V・μF / cm ２ The electrolytic capacitor described above is one of the technologies 1 to 8.

[0072] The present invention will be described in more detail below based on experimental examples.

[0073] 《Experimental Examples 1-3》 Pseudo-capacitors were fabricated, and the withstand voltage of each pseudo-capacitor was determined. Each pseudo-capacitor was made by sandwiching a predetermined separator between a pair of smooth-surfaced electrodes (aluminum plates (thickness 0.1 mm)). One main surface of the separator was sprinkled with 1 mg of aluminum powder, with a volume-based median diameter of 70 μm as measured by laser scattering diffraction, and then the main surface of the separator was lightly wiped with a wiper to intentionally introduce foreign matter.

[0074] The aluminum powder is a foreign substance that mimics fragments that may break off from the thick porous portion of the anode foil. Here, it was considered that when using anode foil with a core thickness of 35 μm or less, a porous portion thickness of 32.5 μm or more, and a total thickness of 100 μm or more, fragments with a maximum diameter of approximately 70 μm may be generated.

[0075] A circuit was formed by connecting each of the pair of electrodes to a voltmeter. Then, a pseudo-capacitor was clamped between the clamping parts of a micrometer, and the distance between the clamping parts was reduced to a predetermined distance (fixed at 30 μm), thereby fixing the separator sandwiched between the pair of electrodes.

[0076] Subsequently, a voltage was applied between the pair of electrodes using a voltmeter, and the voltage was increased at a predetermined rate. The voltage at which the voltage rapidly decreased was measured as the withstand voltage. The results are shown in Table 1.

[0077] The following four types were prepared as separators: (Separator A1) Papermaking using a mixture of first fibers (cellulose fibers) and fibrillated second fibers (regenerated cellulose fibers (rayon)) Fiber diameter of the first fiber D1 = 15 μm Fiber diameter of the second fiber D2 = 2 μm D1 / D2 ratio = 7.5 Thickness = 37 μm Density = 0.37 g / cm³ ３

[0078] (Separator A2) Papermaking process using a mixture of first fibers (cellulose fibers) and fibrillated second fibers (regenerated cellulose fibers (rayon)). Fiber diameter of first fibers D1 = 15 μm. Fiber diameter of second fibers D2 = 2 μm. D1 / D2 ratio = 7.5. Thickness = 40 μm. Density = 0.40 g / cm³. ３

[0079] (Separator A3) Papermaking process using a mixture of first fibers (cellulose fibers) and fibrillated second fibers (regenerated cellulose fibers (rayon)). Fiber diameter of first fibers D1 = 15 μm. Fiber diameter of second fibers D2 = 2 μm. D1 / D2 ratio = 7.5. Thickness = 43 μm. Density = 0.43 g / cm³ ３

[0080] (Separator B1) Papermaking consisting only of first fibers. Fiber diameter D1 of the first fiber = 15 μm, Thickness = 50 μm, Density = 0.35 g / cm³ ３

[0081]

[0082] From the above experimental example, when using an anode foil with a core thickness of 35 μm or less, a porous portion thickness of 35 μm or more, and a total thickness of 100 μm or more, a first fiber with a fiber diameter D1 of 10 μm to 50 μm and a second fiber with a fiber diameter D2 of 5 μm or less are mixed to form a foil with a density of 0.37 g / cm³. ３ ~0.50 g / cm ３ It can be understood that using a separator like this reduces the rate of short circuits.

[0083] This invention can be used in electrolytic capacitors equipped with anode foil suitable for high capacitance.

[0084] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0085] 10: Anode foil, 20: Cathode foil, 30: Separator, 40: Winding stopper tape, 50A, 50B: Lead tab, 60A, 60B: Lead wire, 100: Winding body, 200: Electrolytic capacitor, 211: Bottomed case, 212: Sealing member, 213: Base plate

Claims

1. The material comprises: an anode foil having a dielectric layer on its surface; a cathode foil; a separator interposed between the anode foil and the cathode foil; a conductive polymer adhering to the separator; and a liquid component impregnated into the separator, wherein the anode foil has a core and a pair of porous portions continuous on both sides of the core; the separator comprises a first fiber and a second fiber, the first fiber and the second fiber are mixed together, the fiber diameter D1 of the first fiber is 10 μm to 50 μm, the fiber diameter D2 of the second fiber is 5 μm or less, and the density of the separator is 0.37 g / cm³. ３ ~0.50 g / cm ３ This is an electrolytic capacitor.

2. The electrolytic capacitor according to claim 1, wherein the thickness of the anode foil is 100 μm or more, the thickness of the core is 35 μm or less, and the thickness of the porous portion is 32.5 μm or more.

3. The electrolytic capacitor according to claim 1, wherein the ratio of the fiber diameter D1 of the first fiber to the fiber diameter D2 of the second fiber, D1 / D2, is 3 to 15.

4. The electrolytic capacitor according to claim 1, wherein the second fiber is fibrillated.

5. The electrolytic capacitor according to claim 1, wherein the thickness of the separator is 45 μm or less.

6. The electrolytic capacitor according to claim 1, wherein the weight-average molecular weight of the conductive polymer is 100,000 or less.

7. The electrolytic capacitor according to claim 1, wherein the conductive polymer comprises poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

8. The electrolytic capacitor according to claim 1, wherein the porous portion has cracks.

9. The withstand voltage of the anode foil is 80V or more and less than 90V, and the CV value of the anode foil is 1200V・μF / cm ２ The electrolytic capacitor described in claim 1 is as described above.

10. The withstand voltage of the anode foil is 90V or more and less than 105V, and the CV value of the anode foil is 1100V・μF / cm ２ The electrolytic capacitor described in claim 1 is as described above.

11. The withstand voltage of the anode foil is 105V or more and less than 110V, and the CV value of the anode foil is 1000V・μF / cm ２ The electrolytic capacitor described in claim 1 is as described above.

12. The anode foil has a dielectric strength of 110V or more, and the CV value of the anode foil is 970V・μF / cm ２ The electrolytic capacitor described in claim 1 is as described above.

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