Electrolytic capacitor and method for manufacturing electrolytic capacitor

Abstract

Disclosed is an electrolytic capacitor (100) comprising: an anode (11) having a dielectric layer (11a) on the surface thereof; a separator (21) disposed adjacent to the dielectric layer (11a); an electrolyte disposed in the separator (21); and a cathode layer (12). The separator (21) has a first surface on the dielectric layer (11a) side and a second surface on the side opposite to the first surface. The cathode layer (12) is disposed on the second surface of the separator. A part of the cathode layer (12) enters a part of the separator (21) on the second surface side.

Description

Electrolytic capacitor and method for manufacturing the same

[0001] The present disclosure relates to electrolytic capacitors and methods for manufacturing electrolytic capacitors.

[0002] While electrolytic capacitors that include a wound body of an anode foil, a separator, and a cathode foil are known, electrolytic capacitors that do not use a cathode foil have also been proposed.

[0003] Claim 1 of Patent Document 1 (JP 2007-180404 A) describes, "A solid electrolytic capacitor comprising: an anode element formed by winding an anode foil made of a valve metal having a dielectric oxide film formed on the surface thereof, with a separator interposed therebetween; a solid electrolyte formed of a conductive polymer and provided between the anode foil and the separator; an anode-side terminal connected to the anode foil and drawn out from the wound end surface of the anode element; and a cathode layer formed by forming a conductor layer on the solid electrolyte on the cathode-side end surface opposite the wound end surface."

[0004] Claim 1 of Patent Document 2 (WO 2012 / 086407) describes "a method for manufacturing a solid electrolytic capacitor, comprising: a step of cutting a metal foil having a dielectric coating formed on its surface to produce an anode foil; a step of forming an electrically insulating resin film covering at least an end surface region of an end surface of the anode foil that is positioned in the width direction of the anode foil, the step of attaching an anode lead tab terminal to the anode foil after the resin film is formed, and then winding the anode foil with a conductive separator superimposed thereon but without a cathode foil superimposed thereon to produce a wound body; a step of forming a solid electrolyte layer inside and outside the wound body; a step of forming a cathode layer on the solid electrolyte layer outside the wound body; and a step of electrically connecting a cathode lead frame to the cathode layer."

[0005] JP 2007-180404 A International Publication No. 2012 / 086407

[0006] One approach to increasing the capacitance of an electrolytic capacitor is to thin the cathode foil. However, thinning the cathode foil reduces the current collection function and increases the equivalent series resistance (ESR). In this situation, one of the objectives of the present disclosure is to provide an electrolytic capacitor that can achieve both high capacitance and low ESR.

[0007] One aspect of the present disclosure relates to an electrolytic capacitor including: an anode having a dielectric layer on a surface thereof; a separator disposed adjacent to the dielectric layer; an electrolyte disposed within the separator; and a cathode layer, wherein the separator has a first surface on the dielectric layer side and a second surface opposite to the first surface, the cathode layer is disposed on the second surface of the separator, and a portion of the cathode layer extends into a portion of the separator on the second surface side.

[0008] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on a surface thereof and a separator having first and second surfaces, the method including: step (i) of forming a cathode layer on the second surface of the separator; and step (ii) of stacking the anode and the separator such that the first surface of the separator on which the cathode layer is formed is adjacent to the dielectric layer; and further including step (a) of disposing an electrolyte in the separator.

[0009] According to the present disclosure, an electrolytic capacitor capable of achieving both high capacitance and low ESR can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] Fig. 1 is a side view schematically illustrating an example of an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 2 is an exploded perspective view schematically illustrating an example of a capacitor element included in the electrolytic capacitor shown in Fig. 1. Fig. 3 is a cross-sectional view schematically illustrating an example of a separator on which a cathode layer is formed. Fig. 4 is a cross-sectional view schematically illustrating a portion of an example of a laminate structure of a capacitor element.

[0011] The following describes embodiments of the present invention using examples, but the present invention is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified. However, other numerical values ​​and other materials may be applied as long as the invention according to the present disclosure can be implemented. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0012] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment may be referred to as an "electrolytic capacitor (C)" below. The electrolytic capacitor (C) includes an anode having a dielectric layer on its surface, a separator disposed adjacent to the dielectric layer, an electrolyte disposed within the separator, and a cathode layer. The separator has a first surface on the dielectric layer side and a second surface opposite the first surface. The cathode layer is disposed on the second surface of the separator. A portion of the cathode layer extends into a portion of the separator on the second surface side.

[0013] The electrolytic capacitor (C) does not include a cathode foil. Therefore, the electrolytic capacitor (C) can have a large capacitance. Furthermore, the decrease in ESR can be suppressed compared to when the cathode foil is made thinner. Therefore, the electrolytic capacitor (C) can achieve both a large capacitance and a low ESR.

[0014] One way to increase the capacity of an electrolytic capacitor is to make the separator thinner. However, making the separator thinner makes it more susceptible to breakage, making it difficult to handle and increasing the risk of short circuits. On the other hand, in the electrolytic capacitor (C), it is possible to increase the capacity without making the separator thinner.

[0015] The density of the separator is 0.10 mg / cm ３ Above, 0.30mg / cm ３ or more, or 0.50 mg / cm ３ or more, and may be 1.0 mg / cm ３ , or 0.8 mg / cm ３ The density of the separator may be 0.30 mg / cm or less. ３ By setting the density of the separator to 0.30 mg / cm or more, short-circuiting between the anode and cathode layers can be particularly suppressed. ３ By doing so, it is possible to prevent the cathode layer from coming too close to the dielectric layer, which in turn makes it possible to particularly prevent a short circuit between the anode and the cathode layer.

[0016] The density of a separator is the density obtained by dividing the mass of the separator by the apparent volume of the separator. The apparent volume of the separator is determined by measuring the area and thickness of the separator. The thickness of the separator can be measured by observing the cross section of the separator. The density of a separator with a cathode layer formed thereon can be measured after removing the cathode layer.

[0017] The separator may include polymer fibers. For example, the separator may be a nonwoven fabric. Examples of fiber materials will be described later.

[0018] The cathode layer extends into the separator on the second surface side of the separator but does not reach the first surface. No cathode layer is present on the first surface of the separator. That is, the separator has a cathode layer-absent portion where no cathode layer is present and a cathode layer-present portion where a cathode layer is present. The dielectric layer on the anode surface faces the cathode layer-present portion via the cathode layer-absent portion.

[0019] When the thickness of the separator is Ds (μm), the depth Din (depth from the second surface) of the cathode layer into the separator is preferably 0.5Ds or less. By setting Din to 0.5Ds or less, short-circuiting between the anode and the cathode layer can be suppressed.

[0020] The thickness Dn of the cathode layer may be 10 μm or more, or 20 μm or more, or may be 100 μm or less, 50 μm or less, or 30 μm or less. By making the thickness of the cathode layer 50 μm or less (e.g., 30 μm or less), it is particularly easy to achieve high capacity. By making the thickness of the cathode layer 20 μm or more, it is particularly possible to reduce ESR.

[0021] In order to increase the conductivity of the cathode layer, the cathode layer preferably contains a metal. Examples of metals contained in the cathode layer include metals with high conductivity such as silver. The cathode layer may contain metal particles (e.g., silver particles). For example, the cathode layer may contain metal particles (e.g., silver particles) and a resin. When the cathode layer is formed from a metal paste (e.g., silver paste), the cathode layer contains metal particles and a resin. The metal content in the cathode layer may be 80% by mass or more, or 90% by mass or more.

[0022] The average particle size of the metal particles may be 0.001 μm or more, or 0.01 μm or more, or may be 10.0 μm or less, or 5.0 μm or less. By setting the average particle size of the metal particles to 5.0 μm or less, the gaps between the metal particles can be filled, thereby increasing the conductivity. On the other hand, by increasing the average particle size of the metal particles, the metal particles can be prevented from coming too close to the dielectric layer.

[0023] The average particle size of metal particles can be measured using an electron microscope (SEM, TEM). Specifically, first, a cross-sectional image of the cathode layer is obtained using the electron microscope. Next, 100 metal particles are randomly selected from the image and their particle sizes are measured. At this time, the equivalent circle diameter (the diameter of a circle having the same area as the cross-sectional area of ​​the particle) is taken as the particle size of each metal particle. The arithmetic mean of the 100 measured particle sizes is then taken as the average particle size.

[0024] The metal particles may include particles having an average particle size of 5.0 μm or less (non-flake particles) and flake particles. With this configuration, the non-flake particles fill the gaps between the flake particles, thereby improving the electrical conductivity.

[0025] In this specification, flake-like particles refer to flat-plate-shaped particles with an aspect ratio of 2 or more. The aspect ratio of a particle can be determined based on a cross-sectional image of the particle taken with an electron microscope (e.g., SEM). First, the length of the particle's major axis (maximum diameter of the particle) and the length of the particle's minor axis (minimum diameter of the particle) are measured in the cross-sectional image. The aspect ratio is determined by dividing the length of the major axis by the length of the minor axis.

[0026] The density of the separator is 0.30 mg / cm ３ Above 0.40 mg / cm ３ When the separator density is less than 0.40 mg / cm, the average particle size of the metal particles contained in the cathode layer is preferably in the range of 0.1 μm to 5 μm. In this case, the metal particles preferably include both non-flake-shaped particles and flake-shaped particles. ３ In this case, the average particle size of the metal particles contained in the cathode layer is preferably in the range of 0.01 μm to 5 μm. In this case, the metal particles may not be in the form of flakes.

[0027] The electrolyte may be a solid electrolyte (e.g., a conductive polymer) and / or an electrolytic solution. The electrolyte may contain a conductive polymer and an electrolytic solution. The conductive polymer is less likely to be contained in the cathode layer. Therefore, the cathode layer can be efficiently retained on the anode surface and the separator. The use of an electrolytic solution improves the repairability of the dielectric layer. The conductive polymer may contain at least one selected from the group consisting of polyaniline, polypyrrole, polyethylenedioxythiophene, and derivatives thereof.

[0028] The separator on which the cathode layer is disposed and the anode may be stacked in one direction to form a laminate. The separator of an example electrolytic capacitor (C) may include a first separator and a second separator. The first separator and the second separator may each have a first surface on the dielectric layer side and a second surface opposite the first surface. The cathode layer is disposed on the second surface of the first separator. The anode, the first separator, and the second separator may be stacked such that the second separator faces the cathode layer (the cathode layer disposed on the second surface of the first separator). From another perspective, the second separator may be disposed adjacent to the cathode layer (the cathode layer disposed on the second surface of the first separator). That is, the first separator and the second separator may be disposed so as to face each other with the cathode layer interposed therebetween. The anode foil, first separator, second separator, and cathode layer may be stacked in the following order: anode foil / first separator / cathode layer / second separator. The cathode layer may not be disposed on the surface of the second separator. Alternatively, a cathode layer may also be formed on the second surface of the second separator. The cathode layer may not extend into a portion of the second surface side of the second separator. Alternatively, the cathode layer may extend into a portion of the second surface side of the second separator. The stack may include a plurality of flat first separators, a plurality of flat second separators, and a plurality of flat anodes. The anodes and cathode layers are alternately arranged with the separators sandwiched between them.

[0029] The anode and the separator may be wound to form a wound body. Here, the separator may include a first separator and a second separator. The cathode layer is disposed on a second surface of the first separator. The first separator and the second separator may each have a first surface on the dielectric layer side and a second surface opposite the first surface. The anode, the first separator, and the second separator may be wound such that the second separator is adjacent to the cathode layer. From another perspective, the second separator may be disposed so as to face the cathode layer. That is, the first separator and the second separator may be disposed so as to face each other with the cathode layer interposed therebetween. The anode foil, the first separator, the second separator, and the cathode layer may be stacked in the following order: anode foil / first separator / cathode layer / second separator. In the wound body, the anode faces the cathode layer with the separator sandwiched therebetween. The cathode layer may not be formed on the surface of the second separator. Alternatively, a cathode layer may also be formed on the second surface of the second separator. The cathode layer may not extend into a portion of the second surface side of the second separator. Alternatively, the cathode layer may extend into a portion of the second surface side of the second separator. The first separator and the second separator may be the same separator. In this case, the first and second separators are arranged so that their respective cathode layers are adjacent to each other.

[0030] (Method for manufacturing electrolytic capacitor) The manufacturing method according to this embodiment may be referred to as "manufacturing method (M)" below. According to the manufacturing method (M), the electrolytic capacitor (C) can be manufactured. However, the electrolytic capacitor (C) may also be manufactured by a method other than the manufacturing method (M). The matters described for the electrolytic capacitor (C) may also be applied to the manufacturing method (M), and therefore, redundant explanations may be omitted. The matters described for the manufacturing method (M) may also be applied to the electrolytic capacitor (C).

[0031] Manufacturing method (M) is a method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on its surface and a separator having first and second surfaces. Manufacturing method (M) includes step (i) of forming a cathode layer on the second surface of the separator, and step (ii) of laminating the anode and the separator so that the first surface of the separator on which the cathode layer is formed is adjacent to the dielectric layer. Manufacturing method (M) further includes step (a) of disposing an electrolyte in the separator.

[0032] (Step (i)) The method for forming the cathode layer in step (i) is not particularly limited. The cathode layer may be formed using a metal paste. For example, the cathode layer may be formed by applying a metal paste containing metal particles and a resin to the second surface of the separator, followed by heat treatment. Alternatively, the cathode layer may be formed by vapor-depositing a metal on the second surface of the separator. In either method, a portion of the cathode layer penetrates into a portion of the separator on the second surface side. More specifically, a portion of the cathode layer penetrates into a portion of the voids in the separator on the second surface side.

[0033] The cathode layer may be formed on 90% or more (area ratio) of the second surface of the separator, or may be formed on the entire second surface. In one example of step (i), a separator and a cathode layer having a size to be used in a capacitor element may be formed by forming a cathode layer on the second surface of a large separator sheet and then cutting the separator sheet to a predetermined size.

[0034] (Step (ii)) Step (ii) is performed after step (i). In step (ii), the separator on which the cathode layer has been formed and the anode are laminated. At this time, the separator and the anode are laminated such that the dielectric layer on the surface of the anode and the cathode layer-existing portion of the separator face each other with the cathode layer-absent portion of the separator sandwiched between them. In step (ii), a laminate (or a wound body) is formed without using a cathode foil.

[0035] In step (ii), a flat separator and a flat anode may be stacked in one direction. Alternatively, in step (ii), the separator and the anode may be stacked by being wound in a stacked state. In step (ii), the cathode layer is stacked or wound together with the separator. The above-mentioned stacked structure can be formed by step (ii).

[0036] The separator on which the cathode layer is formed may be the first separator. In this case, the electrolytic capacitor to be manufactured may include a first separator and a second separator. In step (ii), the anode, the first separator, and the second separator may be stacked by winding them so that the second separator is adjacent to the cathode layer. In the wound body to be formed, the anode, the first separator, and the second separator are stacked in the radial direction of the wound body. In the wound body, one surface of the cathode layer faces the dielectric layer on the anode surface across the cathode layer-absent portion of the first separator. The other surface of the cathode layer faces the dielectric layer on the anode surface across the second separator. As described above, a cathode layer may also be formed on the second surface of the second separator.

[0037] (Step (a)) Step (a) is a step of disposing an electrolyte in a separator. In other words, step (a) is a step of disposing an electrolyte between an anode (more specifically, a dielectric layer on the surface of the anode) and a cathode layer. The timing of performing step (a) is not particularly limited, and step (a) may be performed after step (i). Step (a) may be performed after step (i) and before step (ii). Alternatively, step (a) may be performed after step (ii).

[0038] When the electrolyte includes a conductive polymer, the separator may be impregnated with a liquid containing the conductive polymer and then dried to dispose the conductive polymer in the separator. For example, the wound body formed in step (ii) may be impregnated with a liquid containing the conductive polymer and then dried to dispose the conductive polymer in the separator. When the electrolyte includes an electrolytic solution, the wound body formed in step (ii) may be impregnated with the electrolytic solution to dispose the electrolytic solution in the separator.

[0039] In this manner, a capacitor element containing an electrolyte is formed. An electrolytic capacitor is manufactured using the formed capacitor element. For example, an electrolytic capacitor is obtained by housing the capacitor element in an outer casing. Steps other than those described above are not particularly limited, and steps used in known manufacturing methods may be used.

[0040] Examples of components used in the electrolytic capacitor (C) are described below. However, the components used in the electrolytic capacitor (C) are not limited to the examples described below. Components other than those specific to the electrolytic capacitor (C) are not particularly limited, and known components may be used.

[0041] (Anode) Examples of the anode include a metal foil containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode may be a metal foil of a valve metal (e.g., aluminum foil). The anode may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. The surface of the anode may be roughened by etching or the like. That is, the surface of the anode may be made porous. The thickness of the anode may be 15 μm or more, or 50 μm or more, and may be 300 μm or less, or 100 μm or less. When the capacitor element is a wound element, the anode has a strip shape.

[0042] A dielectric layer is formed on the surface of the anode. The dielectric layer may be formed by chemically treating the anode. In this case, the dielectric layer may contain an oxide of a valve metal (e.g., aluminum oxide). Note that the dielectric layer may be formed of any dielectric other than an oxide of a valve metal as long as it functions as a dielectric.

[0043] (Cathode Layer) The cathode layer may be the same as the cathode layer described above.

[0044] (Separator) A porous sheet can be used for the separator. The porous sheet is preferably made of fibers. For example, the porous sheet may be a nonwoven fabric. Examples of fiber materials that make up the separator include cellulose, cellulose derivatives, polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0045] The thickness of the separator is not particularly limited, but a thin separator is preferable from the viewpoint of increasing capacity. On the other hand, a thick separator is preferable from the viewpoint of preventing short circuits. The thickness of the separator may be 5 μm or more, or 10 μm or more, or may be 50 μm or less, or 30 μm or less.

[0046] The separator may be made of a plurality of laminated porous insulating sheets (e.g., nonwoven fabrics). The laminate of the plurality of porous insulating sheets may be a commercially available product, or may be formed by laminating together a plurality of nonwoven fabrics that are used as separators. The separator may be a laminate of a plurality of nonwoven fabrics with different densities. For example, the separator may be made of a laminate of a plurality of nonwoven fabrics with a density of 0.30 mg / cm. ３ and a porous insulating sheet (e.g., nonwoven fabric) having a density of 0.30 mg / cm or more. ３ The insulating sheet may be a laminate with a porous insulating sheet (e.g., nonwoven fabric) having a density of less than 0.30 mg / cm ３ A cathode layer may be formed on the surface of the porous insulating sheet, which can reduce leakage current.

[0047] (Electrolyte) The electrolyte is disposed between the anode and the cathode (for example, in the voids of the separator). The electrolyte may be a solid electrolyte (for example, a conductive polymer) and / or an electrolytic solution. The electrolytic capacitor (C) preferably contains a conductive polymer and an electrolytic solution. The electrolytic capacitor (C) may contain a conductive polymer and a liquid component disposed between the anode and the cathode. The liquid component may be the electrolytic solution or a nonaqueous solvent used in the electrolytic solution.

[0048] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and derivatives thereof. These derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as their basic skeletons. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene). These conductive polymers may be used alone or in combination. Furthermore, the conductive polymer may be a copolymer of two or more monomers. The weight-average molecular weight of the conductive polymer is not particularly limited and may be in the range of 1,000 to 100,000, for example. One preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0049] The conductive polymer may be doped with a dopant. From the viewpoint of suppressing dedoping from the conductive polymer, a polymer dopant may be used as the dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, and the like. These may be used alone or in combination of two or more. At least a portion of these may be added in the form of a salt. A preferred example of the dopant is polystyrene sulfonic acid (PSS).

[0050] The dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0051] When a conductive polymer is disposed in a wound body (or laminate) of a separator on which a cathode layer is formed and an anode, a liquid containing the conductive polymer may be used, as described above. The liquid medium is not particularly limited. Examples of the liquid medium include water, organic solvents (alcohol, ethylene glycol, etc.), and mixed solvents thereof. The liquid may be a liquid containing a conductive polymer or a dispersion in which conductive polymer particles are dispersed in water.

[0052] The content of the conductive polymer in the liquid containing the conductive polymer may be 0.5% by mass or more, or 1.0% by mass or more, and may be 4.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less.

[0053] The electrolytic solution is not particularly limited, and may be a known electrolytic solution used in electrolytic capacitors. The electrolytic solution may contain a non-aqueous solvent and a solute (e.g., an organic salt) dissolved in the non-aqueous solvent.

[0054] Examples of the non-aqueous solvent include polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (γBL), 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.

[0055] The non-aqueous solvent may contain a polymer solvent. Examples of polymer solvents include polyalkylene glycol, polyalkylene glycol derivatives, and compounds in which at least one hydroxyl group in a polyhydric alcohol has been substituted with polyalkylene glycol (including derivatives). Specific examples of polymer 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 polymer solvents include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0056] Examples of solutes include inorganic salts and organic salts. Organic salts are salts in which at least one of the anion and cation contains an organic compound. 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.

[0057] (Exterior Body) The capacitor element is housed in an exterior body. The exterior body is not particularly limited, and a known exterior body may be used.

[0058] An example of the present disclosure will be specifically described below with reference to the drawings. The components described above can be applied to the components of the example described below. Furthermore, the components of the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Furthermore, in the example described below, components that are not essential for the electrolytic capacitor according to the present disclosure may be omitted.

[0059] (Embodiment 1) Fig. 1 is a cross-sectional view schematically illustrating an example of an electrolytic capacitor 100 according to this embodiment. Fig. 2 is a partially exploded schematic view of an example of a capacitor element 10 included in the electrolytic capacitor 100. The electrolytic capacitor 100 is a wound-type capacitor including a wound body.

[0060] Electrolytic capacitor 100 includes capacitor element 10, bottomed case 101 that houses capacitor element 10, sealing member 102 that closes the opening of bottomed case 101, seat plate 103 that covers sealing member 102, lead wires 104A and 104B that extend from sealing member 102 and pass through seat plate 103, and lead tabs 105A and 105B that connect the lead wires to electrodes of capacitor element 10. The open end of bottomed case 101 is curled inward.

[0061] 2, capacitor element 10 is a wound body formed by winding anode (anode foil) 11, first separator 21, and second separator (not shown). The outermost periphery of the wound body is fixed by winding tape 14. Note that FIG. 2 shows a partially unfolded state of the wound body before the outermost periphery is fixed.

[0062] FIG. 3 is a schematic cross-sectional view of a portion of a first separator 21. The separator 21 has a first surface 21sa disposed on the anode 11 side (dielectric layer side) and a second surface 21sb opposite the first surface. A cathode layer 12 is formed on the second surface 21sb. Part of the cathode layer 12 extends into a portion of the separator 21 on the second surface 21sb side. The separator 21 has a cathode layer-existing portion 21x where the cathode layer 12 is present and a cathode layer-absent portion 21y where the cathode layer 12 is not present. FIG. 3 also shows the thickness Ds of the separator 21 and the depth Din (depth from the second surface 21sb) of the cathode layer 12 extending into the separator 21.

[0063] A cross section of a portion of capacitor element 10 is shown schematically in Fig. 4. Note that although Fig. 4 shows anode 11, cathode layer 12, first separator 21, and second separator 22 as flat members, they are curved within capacitor element 10, which is a wound body.

[0064] As shown in Fig. 4, the capacitor element 10 includes a laminate (wound body) of an anode 11, a cathode layer 12, a first separator 21, and a second separator 22. Dielectric layers 11a are formed on both sides of the anode 11. One surface of the cathode layer 12 faces the dielectric layer 11a on the surface of the anode 11, with the cathode layer-absent portion 21y of the first separator 21 interposed therebetween. The other surface of the cathode layer 12 faces the dielectric layer 11a on the surface of the anode 11, with the second separator 22 interposed therebetween. As described above, the surface of the anode 11 may be porous.

[0065] (Additional Notes) The above description discloses the following technologies. (Technology 1) An electrolytic capacitor including: an anode having a dielectric layer on its surface; a separator disposed adjacent to the dielectric layer; an electrolyte disposed within the separator; and a cathode layer, the separator having a first surface on the dielectric layer side and a second surface opposite the first surface, the cathode layer being disposed on the second surface of the separator, and a portion of the cathode layer extending into a portion of the separator on the second surface side. (Technology 2) The density of the separator is 0.30 mg / cm ３The electrolytic capacitor according to Technology 1, wherein the cathode layer contains metal particles and a resin. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the cathode layer contains metal particles and a resin. (Technology 4) The electrolytic capacitor according to Technology 3, wherein the metal particles have an average particle size of 5 μm or less. (Technology 5) The electrolytic capacitor according to Technology 3, wherein the metal particles include particles having an average particle size of 5 μm or less and flaky particles. (Technology 6) The electrolytic capacitor according to any one of Technology 1 to 5, wherein the electrolyte includes a conductive polymer and an electrolytic solution. (Technology 7) The electrolytic capacitor according to any one of Technology 1 to 6, wherein the separator includes a first separator and a second separator, the cathode layer is disposed on the second surface of the first separator, and the anode, the first separator, and the second separator are stacked such that the second separator faces the cathode layer. (Technology 8) The electrolytic capacitor according to any one of Techniques 1 to 6, wherein the separator includes a first separator and a second separator, the cathode layer is disposed on the second surface of the first separator, and the anode, the first separator, and the second separator are wound together so that the second separator is adjacent to the cathode layer. (Technology 9) A method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on its surface and a separator having first and second surfaces, comprising: a step (i) of forming a cathode layer on the second surface of the separator; and a step (ii) of stacking the anode and the separator so that the first surface of the separator on which the cathode layer is formed is adjacent to the dielectric layer, and further comprising a step (a) of disposing an electrolyte in the separator. (Technology 10) The manufacturing method according to Technique 9, wherein the cathode layer is formed using a metal paste in the step (i). (Technology 11) The manufacturing method according to Technology 9 or 10, wherein the separator is a first separator, and in the step (ii), the anode, the first separator, and the second separator are stacked by winding the anode, the first separator, and the second separator so that the second separator is adjacent to the cathode layer.

[0066] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the examples described below. In these examples, a plurality of electrolytic capacitors were fabricated and evaluated. In these examples, parallel plate capacitors including one anode and one cathode were fabricated.

[0067] (Capacitor A1) An electrolytic capacitor (Capacitor A1) was produced by the following method. (1) Preparation of anode An aluminum foil (thickness: 100 μm) was subjected to an etching treatment to roughen (make porous) the surface of the aluminum foil. The roughened surface of the aluminum foil was subjected to a chemical conversion treatment to form a dielectric layer on the surface of the aluminum foil. The obtained aluminum foil was cut to a predetermined size. In this way, an anode foil having a dielectric layer formed on its surface was obtained.

[0068] (2) Formation of Cathode Layer A nonwoven fabric (thickness: 50 μm) made of cellulose-based fibers was prepared as a separator. The density of the nonwoven fabric was 0.25 mg / cm ３ Silver paste was applied to one side of the nonwoven fabric using an applicator, and then the silver paste was cured by heating at 150°C for 30 minutes. In this way, a cathode layer (thickness: 20 μm) was formed on one side of the separator. Part of the cathode layer was embedded in the separator. The obtained separator was cut to a predetermined size. In this way, a separator with a cathode layer formed on the surface was obtained.

[0069] (3) Formation of Capacitor Element An anode lead tab was connected to the anode foil formed in the above step (1). A cathode lead tab was connected to the cathode layer formed in the above step (2). Next, a conductive polymer dispersion was dropped onto the portion of the separator where the cathode layer was absent. The conductive polymer dispersion used was a dispersion containing fine particles of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. The dispersion medium used was a mixture of water and ethylene glycol in a mass ratio of 95:5. The conductive polymer dispersion had a surface density of solids of 0.3 mg / cm. ２ The mixture was dropped onto the separator so that the temperature became

[0070] Next, the anode foil and a separator were laminated to form a laminate. At this time, the separator was positioned so that the cathode layer-free portion of the separator was adjacent to the dielectric layer of the anode foil. Next, the laminate was heated at 150°C for 20 minutes to remove the dispersion medium of the conductive polymer. In this way, the conductive polymer was disposed in the portion between the anode foil and the cathode layer (mainly within the separator).

[0071] Next, the laminate and the electrolyte solution were placed in a pouch made of laminate film. The electrolyte solution was prepared by dissolving 5-sulfosalicylic acid and triethylamine in ethylene glycol (solvent) to a total concentration of 25% by mass. The equivalent ratio of 5-sulfosalicylic acid to triethylamine was 2.0. The pouch was then held in a reduced pressure atmosphere (40 kPa) for 5 minutes and then sealed. In this way, the electrolyte solution was placed between the anode foil and the cathode layer (mainly in the separator). A capacitor element was thus formed. The formed capacitor element was subjected to an aging treatment for 60 minutes while applying a rated voltage. Using the above procedure, a parallel-plate electrolytic capacitor (Capacitor A1) was fabricated.

[0072] The capacitance (Cap) of the capacitor A1 was measured at 120 Hz. Furthermore, the equivalent series resistance (ESR) of the capacitor A1 was measured at 100 kHz. Furthermore, the leakage current (LC) of the capacitor A1 at the rated voltage was measured.

[0073] (Capacitor A2) Capacitor A2 was produced in the same manner and under the same conditions as those for producing capacitor A1, except that the density of the separator in capacitor A2 was changed. ３ Capacitor A2 was evaluated in the same manner as capacitor A1.

[0074] (Capacitor C1) In capacitor C1, a cathode foil was used instead of a cathode layer formed on a separator. The cathode foil was formed by etching aluminum foil (thickness: 50 μm). That is, the surface of the cathode foil was roughened (made porous) by etching. A cathode lead tab was connected to the cathode foil. The laminate was formed by stacking an anode foil and a cathode foil with a separator sandwiched between them. Except for these points, capacitor C1 was fabricated using the same method and conditions as capacitor A1. That is, the electrolyte of capacitor C1 was composed of a conductive polymer and an electrolytic solution, just like capacitor A1. Capacitor C1 was evaluated in the same manner as capacitor A1.

[0075] Table 1 shows some of the manufacturing conditions and evaluation results for capacitors A1, A2, and C1. The evaluation values ​​in Table 1 are relative values, with the evaluation value for capacitor C1 being 1.0. A high capacitance is preferable. A low ESR and leakage current are preferable.

[0076]

[0077] Capacitors A1 and A2 are electrolytic capacitors (C) according to the present disclosure. Capacitor C1 is a comparative example. As shown in Table 1, capacitors A1 and A2 had large capacitance and small ESR.

[0078] When a cathode foil (aluminum foil) is used, a natural oxide film exists on the surface of the cathode foil. In this case, it is thought that the capacitance of capacitor C1 decreases due to the combined capacitance of the capacitance of the anode foil and the capacitance of the cathode foil. On the other hand, a cathode layer using silver particles does not form a dielectric, so no capacitance is generated in the cathode foil, resulting in a single-pole capacitance of the anode only. This is thought to be why the capacitance of capacitors A1 and A2 increased.

[0079] The leakage current was large in capacitor A1, which is believed to be due to the large depth Din (depth from the second surface) of the cathode layer into the separator. The leakage current was small in capacitor A2, which used a high-density separator, due to the small depth Din. In capacitor A2, the depth Din was 0.5 times or less the separator thickness Ds (μm).

[0080] When a wound (or laminated) capacitor element is formed using the separator used in the capacitors A1 and A2, the absence of a cathode foil makes it possible to increase the capacitance per volume.

[0081] The present disclosure is applicable to electrolytic capacitors. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to cover all modifications and alterations without departing from the true spirit and scope of the present invention.

[0082] 10: Capacitor element 11: Anode 11a: Dielectric layer 12: Cathode layer 21: Separator (first separator) 21sa: First surface 21sb: Second surface 22: Second separator 100: Electrolytic capacitor 101: Bottomed case 102: Sealing member 103: Seat plate 104A: Anode lead wire 104B: Cathode lead wire 105A: Anode lead tab 105B: Cathode lead tab

Claims

1. An electrolytic capacitor comprising: an anode having a dielectric layer on a surface thereof; a separator disposed adjacent to the dielectric layer; an electrolyte disposed within the separator; and a cathode layer, wherein the separator has a first surface facing the dielectric layer and a second surface opposite the first surface, the cathode layer being disposed on the second surface of the separator, and a portion of the cathode layer extending into a portion of the separator on the second surface side.

2. The density of the separator is 0.30 mg / cm ３ 2. The electrolytic capacitor according to claim 1 .

3. The electrolytic capacitor according to claim 1 or 2, wherein the cathode layer contains metal particles and a resin.

4. The electrolytic capacitor according to claim 3, wherein the average particle size of the metal particles is 5 μm or less.

5. The electrolytic capacitor according to claim 3, wherein the metal particles include particles having an average particle size of 5 μm or less and flaky particles.

6. The electrolytic capacitor according to claim 1 or 2, wherein the electrolyte contains a conductive polymer and an electrolytic solution.

7. The electrolytic capacitor according to claim 1 or 2, wherein the separator includes a first separator and a second separator, the cathode layer is disposed on the second surface of the first separator, and the anode, the first separator, and the second separator are stacked such that the second separator faces the cathode layer.

8. The electrolytic capacitor according to claim 1 or 2, wherein the separator includes a first separator and a second separator, the cathode layer is disposed on the second surface of the first separator, and the anode, the first separator, and the second separator are wound together such that the second separator is adjacent to the cathode layer.

9. A method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on a surface thereof and a separator having a first and second surface, comprising: a step (i) of forming a cathode layer on the second surface of the separator; and a step (ii) of stacking the anode and the separator so that the first surface of the separator on which the cathode layer is formed is adjacent to the dielectric layer; and further comprising a step (a) of disposing an electrolyte in the separator.

10. The manufacturing method according to claim 9, wherein in step (i), the cathode layer is formed using a metal paste.

11. The manufacturing method according to claim 9 or 10, wherein the separator is a first separator, and in step (ii), the anode, the first separator, and the second separator are stacked by winding the anode, the first separator, and the second separator so that the second separator is adjacent to the cathode layer.

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