Electrolytic capacitor and method for producing electrolytic capacitor

Abstract

The disclosed electrolytic capacitor includes a capacitor element and an electrolytic solution with which the capacitor element is impregnated. The capacitor element includes: an anode foil having a dielectric layer formed on the surface thereof; a cathode foil; and a solid conductor layer disposed between the anode foil and the cathode foil. The solid conductor layer has a first surface facing the dielectric layer and a second surface facing the cathode foil. The solid conductor layer has a patterned uneven shape on the first surface. The first surface has a contact region that is in contact with the dielectric layer and a non-contact region that is not in contact with the dielectric layer. The electrolytic solution is disposed at least in the non-contact region.

Description

Electrolytic Capacitor and Method for Manufacturing Electrolytic Capacitor

[0001] The present disclosure relates to an electrolytic capacitor and a method for manufacturing an electrolytic capacitor.

[0002] Various electrolytic capacitors have been conventionally proposed. Claim 1 of Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2022-144278) describes "a solid electrolytic capacitor comprising: a capacitor element formed by opposing an anode foil and a cathode body; a conductive polymer layer formed by impregnation with a dispersion containing particles or powder of a conductive polymer and a solvent; and an electrolytic solution with which the capacitor element is impregnated, wherein the cathode body includes a cathode foil made of a valve metal and having a surface-enlarging layer formed on a surface thereof, and a carbon layer laminated on the surface-enlarging layer and in contact with the conductive polymer layer on a surface opposite to the surface-enlarging layer, and an amount of the conductive polymer particles or powder contained in the surface-enlarging layer is less than an amount of the conductive polymer particles or powder contained in a surface layer side of the carbon layer facing the conductive polymer layer".

[0003] Japanese Unexamined Patent Application Publication No. 2022-144278

[0004] At present, there is a demand for electrolytic capacitors with low equivalent series resistance (ESR). However, it is difficult to reduce ESR in conventional electrolytic capacitors using a separator. If the separator is thinned to reduce ESR, the anode and the cathode are likely to directly short-circuit. On the other hand, when a diaphragm other than a separator is used, the retention of the electrolytic solution may decrease. Under such circumstances, one object of the present invention is to provide an electrolytic capacitor that has high electrolytic solution retention and can suppress short circuits.

[0005] One aspect of the present disclosure relates to an electrolytic capacitor comprising a capacitor element and an electrolyte impregnated in the capacitor element, wherein the capacitor element comprises an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil, the solid conductor layer having a first surface facing the dielectric layer and a second surface facing the cathode foil, the solid conductor layer having a patterned uneven shape on the first surface, the first surface having a contact region in contact with the dielectric layer and a non-contact region not in contact with the dielectric layer, and the electrolyte is disposed in at least the non-contact region.

[0006] According to this disclosure, an electrolytic capacitor can be obtained that has high electrolyte retention and can suppress short circuits. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of its structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0007] This is a schematic cross-sectional view showing an example of a capacitor element used in the electrolytic capacitor according to this embodiment. This is a schematic cross-sectional view showing the cross-section along line II-II in Figure 1. This is a schematic cross-sectional view showing an example of one step in the manufacturing method according to this embodiment. This is a schematic cross-sectional view showing an example of one step following the step in Figure 3A. This is a schematic cross-sectional view showing an example of one step following the step in Figure 3B.

[0008] Embodiments of the present invention will be described below with examples, but the present invention 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 ​​and other materials may be applied as long as the invention relating to this disclosure can be carried out. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "numerical value A or greater and numerical value B or less". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined as long as the lower limit does not exceed the upper limit. In the following description, when examples of components or methods are listed, unless otherwise specified, only one of the listed examples may be used, or multiple of the listed examples may be used in combination.

[0009] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment may be referred to as "electrolytic capacitor (C)" below. The electrolytic capacitor (C) includes a capacitor element and an electrolyte impregnated in the capacitor element. The capacitor element includes an anode foil with a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil. The solid conductor layer has a first surface facing the dielectric layer and a second surface facing the cathode foil. The solid conductor layer has a patterned uneven shape on the first surface. The first surface has a contact region that contacts the dielectric layer and a non-contact region that does not contact the dielectric layer. At least the non-contact region is disposed of with the electrolyte.

[0010] Typically, an electrolytic capacitor (C) does not include a separator between the anode and cathode foils. Therefore, the electrolytic capacitor (C) can significantly reduce ESR. However, a very thin porous insulating layer may be placed between the anode and cathode foils of the electrolytic capacitor (C). For example, a very thin porous insulating layer formed by electrospinning may be placed between the anode and cathode foils.

[0011] In an electrolytic capacitor (C), a solid conductive layer is placed between the anode foil and the cathode foil. Therefore, direct short circuits between the anode foil and the cathode foil can be suppressed. In other words, the electrolytic capacitor (C) is an electrolytic capacitor that can reduce ESR and suppress short circuits. The solid conductive layer may be placed in a range of 80-100% (area ratio) or 90-100% of the region where the anode foil and cathode foil face each other.

[0012] The uneven surface of the first surface is patterned. That is, the uneven surface is not formed randomly, but in a predetermined pattern. The pattern of the uneven surface is not particularly limited, and any pattern that can achieve the effects of this disclosure is acceptable.

[0013] In one example pattern, multiple recesses are arranged at a certain distance from each other. For example, when polygons are tiled without gaps, the recesses are placed at the vertices of each polygon. The polygons may be triangles, quadrilaterals, or hexagons. However, the distances between adjacent recesses do not all have to be the same; they may be different. The pattern of recesses and depressions may be formed by combining linear recesses and dot-shaped recesses.

[0014] As mentioned above, a separator does not necessarily have to be placed between the anode foil and the cathode foil. This makes it possible to particularly reduce ESR. Examples of separators include known separators (insulating sheets) that are placed between the anode foil and the cathode foil to prevent short circuits between them. Such insulating sheets can be handled independently during the manufacturing process of the capacitor element. Examples of such insulating sheets include insulating cloth (e.g., nonwoven fabric) and insulating porous films. However, a thin insulating layer formed on the capacitor element material by the electrospinning method is treated as an integral part of the material and is difficult to handle independently. Therefore, insulating layers formed by the electrospinning method are not included as examples of separators.

[0015] The ratio Rs of the contact area to the area of ​​the first surface may be 40% or more, 60% or more, or 65% or more, and may be 97% or less, 95% or less, or 93% or less. Here, the area of ​​the first surface and the area of ​​the contact area are the areas of the solid conductive layer when viewed from above. Setting the ratio Rs to 65% or more makes it easier to maintain the uneven shape. Setting the ratio Rs to 95% or less increases the area in contact between the dielectric layer and the electrolyte. This makes it easier to repair the dielectric layer, resulting in a highly reliable electrolytic capacitor.

[0016] The solid conductive layer may include a plurality of protrusions that constitute at least a part of the uneven shape. For example, the solid conductive layer may include a sheet-like portion disposed on the cathode foil side and protrusions disposed on the anode foil side of the sheet-like portion. The sheet-like portion is sheet-like with no through holes formed therein.

[0017] The solid conductive layer may have at least one through-hole, selected from the group consisting of through-holes and through-grooves. In this case, the through-hole constitutes at least a part of the uneven shape.

[0018] The thickness Tc of the solid conductive layer between the bottom surface of the recessed area of ​​the uneven shape and the second surface may be 3 μm or more, 5 μm or more, or 10 μm or more, and may be 30 μm or less, 27 μm or less, 15 μm or less, or 10 μm or less. For example, the thickness Tc may be in the range of 3 μm to 30 μm. By setting the thickness Tc to 3 μm or more, direct short circuits between the anode foil and the cathode foil can be easily suppressed. By setting the thickness Tc to 30 μm or less, it becomes possible to reduce ESR compared to when using a conventional separator. By setting the thickness Tc in the range of 5 μm to 25 μm, it is possible to achieve a good balance between suppressing short circuits and reducing ESR.

[0019] The maximum thickness Tmax of the solid conductive layer may be 3 μm or more, or 5 μm or more, and may be 30 μm or less, 27 μm or less, or 15 μm or less. By setting the maximum thickness Tmax to 3 μm or more, direct short circuits between the anode foil and the cathode foil can be suppressed. By setting the maximum thickness Tmax to 30 μm or less (for example, 27 μm or less or 15 μm or less), ESR can be particularly reduced. The maximum difference in height between the contact area and the non-contact area adjacent to the contact area may be in the range of 3 μm to 27 μm (for example, in the range of 3 μm to 15 μm).

[0020] The maximum thickness Tmax of a solid conductive layer can be determined by the distance between a first component (e.g., an anode foil) in contact with the first surface of the solid conductive layer and a second component (e.g., a cathode foil) in contact with the second surface of the solid conductive layer. The thickness Tc and the maximum thickness Tmax can be measured using a cross-sectional image of the solid conductive layer. In a typical solid conductive layer, the thickness of the solid conductive layer in the contact region is generally constant. Therefore, in a typical solid conductive layer, the thickness in the contact region can be considered as the maximum thickness Tmax of the solid conductive layer.

[0021] The solid conductive layer may contain a conductive polymer. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and their derivatives. These derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as the basic skeleton. For example, a derivative of polythiophene is poly(3,4-ethylenedioxythiophene). These conductive polymers may be used individually or in combination. The conductive polymer may also 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, for example, 1,000 to 100,000. A preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0022] Conductive polymers may be doped with dopants. From the viewpoint of suppressing dedoping from conductive polymers, polymer dopants may be used as dopants. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually or in combination of two or more. At least some of these may be added in the form of salts. A preferred example of a dopant is polystyrene sulfonic acid (PSS).

[0023] 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.

[0024] The solid conductive layer may be composed solely of conductive polymers. The solid conductive layer may also contain components other than conductive polymers. The content of conductive polymers in the solid conductive layer may be in the range of 50% to 100% by mass.

[0025] (Method for Manufacturing Electrolytic Capacitors) The manufacturing method (M) according to this embodiment is described below. Electrolytic capacitors (C) can be manufactured by manufacturing method (M). However, electrolytic capacitors (C) may be manufactured by methods other than manufacturing method (M). Matters described regarding electrolytic capacitors (C) are applicable to manufacturing method (M). Matters described regarding manufacturing method (M) are also applicable to electrolytic capacitors (C). Manufacturing method (M) includes steps (i) and (ii). These steps are described below.

[0026] (Step (i)) Step (i) is a step of forming a capacitor element including an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil. In step (i), a solid conductor layer is formed having a patterned uneven shape on its first surface such that the first surface has a contact region that contacts the dielectric layer and a non-contact region that does not contact the dielectric layer.

[0027] As described above, the solid conductive layer may contain a conductive polymer. In that case, the solid conductive layer may be formed in step (i) by coating a dispersion of the conductive polymer onto the cathode foil and then drying it. For example, step (i) may include a step of coating a dispersion of the conductive polymer onto a predetermined area using a mask.

[0028] In one example of step (i), a solid conductive layer is formed on the cathode foil. For example, first, a first layer (sheet-like portion) without recesses or through holes is formed on the surface of the cathode foil. The method for forming the first layer is not particularly limited. For example, the first layer may be formed by coating a raw material solution containing the material for the solid conductive layer (such as a conductive polymer) onto the cathode foil and then drying it. The material for the solid conductive layer may be dissolved in the liquid medium of the raw material solution or dispersed in the liquid medium of the raw material solution. The liquid medium of the raw material solution is not limited and may include water, organic solvents, and mixtures thereof. Examples of organic solvents include alcohols (ethanol, isopropyl alcohol, etc.) and other organic solvents. The method for coating the raw material solution is not limited and may include spraying or printing.

[0029] In one example of step (i), a second layer having through holes is then formed on the sheet-like portion. The second layer may be formed in the same way as the first layer by applying a raw material solution containing the material for the solid conductive layer (such as a conductive polymer) to the cathode foil and then drying it. The liquid medium and application method of the raw material solution may be the same as described above. However, in forming the second layer, an application method that can form through holes is used. For example, the raw material solution may be applied only to the areas other than the parts that will become through holes using a mask. Alternatively, the raw material solution may be applied only to the areas other than the parts that will become through holes using a screen printing method or the like.

[0030] As described above, a solid conductive layer is formed consisting of a first layer without through holes and a second layer with through holes. The portions with through holes become recesses. In the example described above, the through holes are formed in such a way that a patterned uneven shape is created.

[0031] Alternatively, instead of forming the first layer (sheet-like portion), a solid conductive layer having through holes may be formed on the anode foil (more specifically, the dielectric layer) or cathode foil. Next, a capacitor element may be formed by placing the foil on which the solid conductive layer is formed opposite the foil on which the solid conductive layer is not formed. In this case, one end of the through hole faces the dielectric layer, and the other end of the through hole faces the cathode foil.

[0032] In another example of step (i), a solid conductive layer is first formed on the substrate. At this time, as described above, the first layer and the second layer are formed sequentially on the substrate. Next, the solid conductive layer is transferred to the anode foil. At this time, the transfer is carried out so that the first layer is in contact with the dielectric layer on the surface of the anode foil. Next, the cathode foil is placed on the second layer. In this way, a capacitor element can be formed. Alternatively, a very thin insulating layer (for example, a very thin separator) may be formed on the second layer, and then the cathode foil may be placed on the insulating layer. The insulating layer may be formed by depositing insulating fibers by electrospinning or the like.

[0033] The solid conductive layer is formed on at least one side of the anode foil or one side of the cathode foil. The solid conductive layer is formed on both sides of the anode foil or both sides of the cathode foil, if necessary. If the capacitor element is of the multilayer type, the anode foil and cathode foil are stacked alternately with the solid conductive layer in between. If the capacitor element is of the wound type, the anode foil and cathode foil are wound with the solid conductive layer in between.

[0034] (Step (ii)) Step (ii) is the step of impregnating the capacitor element with an electrolyte. The method of impregnating the capacitor element with an electrolyte is not limited. In one example, the capacitor element is impregnated with an electrolyte by immersing it in the electrolyte. Step (ii) ensures that the electrolyte is placed in at least the non-contact area.

[0035] After step (ii), other steps may be performed as needed. For example, a step may be performed in which the capacitor elements impregnated with electrolyte are placed in a container. In this way, an electrolytic capacitor is manufactured.

[0036] As mentioned above, in a capacitor element, a separator may or may not be placed between the anode foil and the cathode foil.

[0037] Examples of components used in electrolytic capacitors (C) are described below. However, the components used in electrolytic capacitors (C) are not limited to the examples described below. Components other than those specific to electrolytic capacitors (C) are not particularly limited, and known components may be used.

[0038] (Anode Foil) Examples of anode foil include metal foil containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode foil may also be a metal foil of the valve metal (e.g., aluminum foil). The surface of the anode foil may be roughened by etching or the like. That is, the surface of the anode foil may be porous. The thickness of the anode foil may be 15 μm or more, or 50 μm or more, or 300 μm or less, or 100 μm or less. If the capacitor element is a wound type element, the anode foil has a strip shape.

[0039] A dielectric layer is formed on the surface of the anode foil. The dielectric layer may be formed by chemical conversion treatment of the anode foil. In this case, the dielectric layer may contain an oxide of the valve metal (e.g., aluminum oxide). The dielectric layer may be formed of any dielectric material other than the oxide of the valve metal, as long as it functions as a dielectric.

[0040] (Cathode Foil) A conductive sheet may be used for the cathode foil, or a metal foil (e.g., aluminum foil) may be used. The metal constituting the metal foil may be valve metal or an alloy containing valve metal. The surface of the cathode foil may be roughened by etching or the like. That is, the surface of the cathode may be porous. The thickness of the cathode foil may be 15 μm or more, or 50 μm or more, or 300 μm or less, or 100 μm or less. If the capacitor element is a wound type element, the cathode foil has a strip shape.

[0041] As described above, a solid conductive layer and an electrolyte are placed between the anode foil and the cathode foil. The electrolyte is not particularly limited, and known electrolytes used in electrolytic capacitors may be used. The electrolyte may contain a non-aqueous solvent and a solute (e.g., an organic salt) dissolved in the non-aqueous solvent.

[0042] 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 (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.

[0043] The non-aqueous solvent may contain a polymer solvent. Examples of polymer solvents include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group in a polyhydric alcohol is substituted with a polyalkylene glycol (including derivatives). Specifically, 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. Examples of polymer solvents further 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 as a mixture.

[0044] Examples of solutes include inorganic salts and organic salts. An organic salt is a salt in which at least one of an anion and a cation contains 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.

[0045] (Exterior Case) The capacitor element is housed in an exterior case. The exterior case is not particularly limited, and a known exterior case may be used.

[0046] Hereinafter, an example of the present disclosure will be specifically described with reference to the drawings. The constituent elements described above can be applied to the constituent elements of the example described below. Further, the constituent elements of the example described below can be modified based on the above description. Further, the matters described below may be applied to the above-described embodiments. In addition, in the example described below, constituent elements that are not essential to the electrolytic capacitor according to the present disclosure may be omitted.

[0047] (Embodiment 1) In Embodiment 1, a part of an example of the electrolytic capacitor (C) according to the present embodiment will be described. FIG. 1 is a top view schematically showing a part of a capacitor element 100 used in the electrolytic capacitor (C). FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. FIG. 1 also shows the arrangement of the non-contact area Suc. The capacitor element 100 includes an anode foil 101, a cathode foil 102, a solid conductor layer 103, and an electrolytic solution (not shown). A dielectric layer 101a is formed on the surface of the anode foil 101. The dielectric layer 101a is a layer formed by oxidizing the surface of a metal foil 101b. The solid conductor layer 103 has a first surface 103s1 facing the dielectric layer 101a and a second surface 103s2 facing the cathode foil 102. A plurality of recesses 103c arranged at regular intervals are formed on the first surface 103s1 of the solid conductor layer 103. That is, the solid conductor layer 103 has a patterned uneven shape on the first surface 103s1. The area where the recess 103c is formed in the first surface 103s1 is the non-contact area Suc that does not contact the dielectric layer 101a. The area where the recess 103c is not formed in the first surface 103s1 is the contact area Sc that contacts the dielectric layer 101a. The electrolytic solution is disposed in the non-contact area Suc. Note that the electrolytic solution may also be disposed in the voids of the solid conductor layer 103.

[0048] (Embodiment 2) In Embodiment 2, an example of the manufacturing method (M) will be described. In the manufacturing method of Embodiment 2, first, as shown in FIG. 3A, a first layer 103a is formed on the cathode foil 102. The first layer 103a is a sheet-like layer in which no through-hole is formed. Next, as shown in FIG. 3B, a second layer 103b is formed on the first layer 103a. The second layer 103b is a layer in which a through-hole is formed. The first layer 103a and the second layer 103b constitute the solid conductor layer 103. In this way, the solid conductor layer 103 composed of the first layer 103a and the second layer 103b is formed. A patterned uneven shape is formed on the surface (first surface 103s1) of the solid conductor layer 103.

[0049] Next, as shown in Figure 3C, the anode foil 101 is placed on the first surface 103s1 of the solid conductive layer 103. In this way, the capacitor element 100 is formed. Next, the capacitor element 100 is impregnated with an electrolyte. This places the electrolyte in the non-contact area Suc. After that, other steps are performed as needed to obtain an electrolytic capacitor. For example, the capacitor element 100 is housed in an outer casing.

[0050] (Note) The above description discloses the following technologies: (Technology 1) An electrolytic capacitor comprising a capacitor element and an electrolyte impregnated in the capacitor element, wherein the capacitor element comprises an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil, the solid conductor layer having a first surface facing the dielectric layer and a second surface facing the cathode foil, the solid conductor layer having a patterned uneven shape on the first surface, the first surface having a contact region in contact with the dielectric layer and a non-contact region not in contact with the dielectric layer, and the electrolyte being disposed in at least the non-contact region. (Technology 2) The electrolytic capacitor according to Technology 1, wherein no separator is disposed between the anode foil and the cathode foil. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the ratio of the area of ​​the contact region to the area of ​​the first surface is 65% or more and 95% or less. (Technology 4) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the solid conductive layer includes a plurality of protrusions that constitute at least a part of the uneven shape. (Technology 5) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the solid conductive layer has at least one through-hole selected from the group consisting of through-holes and through-grooves, and the through-hole constitutes at least a part of the uneven shape. (Technology 6) The electrolytic capacitor according to any one of Technology 1 to 5, wherein the thickness of the solid conductive layer between the bottom surface of the recess of the uneven shape and the second surface is in the range of 3 μm to 30 μm. (Technology 7) The electrolytic capacitor according to any one of Technology 1 to 6, wherein the solid conductive layer includes a conductive polymer.(Technical 8) A method for manufacturing an electrolytic capacitor, comprising the steps of: (i) forming a capacitor element including an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil; and (ii) impregnating the capacitor element with an electrolyte, wherein the solid conductor layer has a first surface facing the dielectric layer and a second surface facing the cathode foil, and in step (i), the solid conductor layer is formed having a patterned uneven shape on the first surface such that the first surface has a contact region that contacts the dielectric layer and a non-contact region that does not contact the dielectric layer, and in step (ii), the electrolyte is disposed in at least the non-contact region. (Technical 9) The method for manufacturing an electrolytic capacitor according to Technical 8, wherein in the capacitor element, no separator is disposed between the anode foil and the cathode foil. (Technical 10) The manufacturing method according to Technical 8 or 9, wherein the solid conductive layer comprises a conductive polymer, and in step (i), the solid conductive layer is formed by applying a dispersion of the conductive polymer to the cathode foil and then drying it. (Technical 11) The manufacturing method according to Technical 10, wherein step (i) includes a step of applying the dispersion to a predetermined area using a mask.

[0051] 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 this example, multiple electrolytic capacitors were fabricated and evaluated. In this example, a parallel plate type capacitor including one anode and one cathode was fabricated.

[0052] (Experiment 1) First, a solid conductive layer was formed on the cathode foil according to the procedure shown in Figures 3A and 3B. Aluminum foil was used as the cathode foil. The solid conductive layer was formed from a conductive polymer. Specifically, first, a raw material solution was prepared by dispersing PEDOT:PSS (poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid) in pure water. Next, a solid conductive layer was formed by applying the raw material solution according to the procedure described above. When forming the second layer, through holes were formed at regular intervals using a mask, as shown in Figure 2. Next, an anode foil with a dielectric layer formed on its surface was placed on the second layer. In this way, the capacitor element shown in Figure 3C was fabricated. Next, the solid conductive layer was impregnated with an electrolyte. The electrolyte was prepared by dissolving triethylamine phthalate in a solvent mainly composed of ethylene glycol.

[0053] Multiple capacitor elements were formed by varying the ratio Rs of the contact area to the area of ​​the first surface from 40% to 100%. Then, pressure was applied between the anode foil and cathode foil of these capacitor elements, and the pressure when the anode foil and cathode foil were short-circuited was measured. The ratio (%) of the non-contact area to the area of ​​the first surface is expressed as (100 - Rs). The measured results are shown in Table 1. In Table 1, the pressure during a short circuit is a relative value with the pressure of capacitor C1 during a short circuit set to 1. A higher pressure during a short circuit indicates that the short circuit is more suppressed.

[0054]

[0055] Capacitors A1 to A6 are electrolytic capacitors (C) according to the present disclosure. Capacitor C1 is a comparative example. The pressure during short-circuiting of capacitors A1 to A6 was equal to or greater than the pressure during short-circuiting of capacitor C1. In other words, the electrolytic capacitors (C) according to the present disclosure were able to suppress short circuits to the same extent as or better than when using conventional separators. When the ratio Rs was in the range of 65% to 95%, the pressure during short circuits was higher. This result indicates that by setting the ratio Rs in the range of 65% to 95%, short circuits between the anode foil and cathode foil can be particularly suppressed.

[0056] (Reference Experiment) In the reference experiment, parallel plate type capacitors were fabricated using the same method and conditions as in Experiment 1. However, the solid conductive layer was a uniform thickness layer without any uneven surface. Capacitors R1 to R6 were fabricated by varying the thickness of the solid conductive layer in the range of 3.0 μm to 40 μm. In addition, a parallel plate type capacitor R7 was fabricated using the same method and conditions as in Experiment 1, except that a conventional separator (thickness: 50 μm) was used instead of the solid conductive layer. A nonwoven fabric made of cellulose fibers was used as the separator.

[0057] The capacitance Cap and equivalent series resistance (ESR) were measured for the fabricated capacitors. Table 2 shows the measurement results for the thickness of the solid conductive layer and the characteristics of the capacitor. However, the thickness of capacitor R7 is the thickness of the separator. Note that the capacitance Cap and ESR in Table 2 are expressed as relative values ​​when the measured value of capacitor R7 is set to 1.00. A large capacitance Cap and a low ESR are preferable.

[0058]

[0059] As shown in Table 2, the capacitance Cap of capacitors R1 to R6 was large, as was the capacitance Cap of capacitor R7. The ESR of capacitors R1 to R5 was lower than that of capacitor R7. The results of this reference experiment indicate that it is possible to increase capacitance and reduce ESR by reducing the thickness of the solid conductive layer to 30 μm or less. Furthermore, when a capacitor is made using a separator that has been thinned to 40 μm or less than the conventional separator, the number of short circuits between the anode foil and cathode foil increases compared to a capacitor using a solid conductive layer of the same thickness as the separator.

[0060] This disclosure is applicable to electrolytic capacitors. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be constrained. 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 construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0061] 100: Capacitor element 101: Anode foil 101a: Dielectric layer 102: Cathode foil 103: Solid conductor layer 103s1: First surface 103s2: Second surface Sc: Contact area Suc: Non-contact area

Claims

1. An electrolytic capacitor comprising a capacitor element and an electrolyte impregnated in the capacitor element, wherein the capacitor element comprises an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil, the solid conductor layer having a first surface facing the dielectric layer and a second surface facing the cathode foil, the solid conductor layer having a patterned uneven shape on the first surface, the first surface having a contact region in contact with the dielectric layer and a non-contact region not in contact with the dielectric layer, and the electrolyte is disposed in at least the non-contact region.

2. The electrolytic capacitor according to claim 1, wherein no separator is placed between the anode foil and the cathode foil.

3. The electrolytic capacitor according to claim 1 or 2, wherein the ratio of the area of ​​the contact region to the area of ​​the first surface is 65% or more and 95% or less.

4. The electrolytic capacitor according to claim 1 or 2, wherein the solid conductive layer includes a plurality of protrusions that constitute at least a part of the uneven shape.

5. The electrolytic capacitor according to claim 1 or 2, wherein the solid conductive layer has at least one through portion selected from the group consisting of through holes and through grooves, and the through portion constitutes at least a part of the uneven shape.

6. The electrolytic capacitor according to claim 1 or 2, wherein the thickness of the solid conductive layer between the bottom surface of the recess of the uneven shape and the second surface is in the range of 3 μm to 30 μm.

7. The electrolytic capacitor according to claim 1 or 2, wherein the solid conductive layer comprises a conductive polymer.

8. A method for manufacturing an electrolytic capacitor, comprising the steps of: (i) forming a capacitor element including an anode foil having a dielectric layer formed on its surface, a cathode foil, and a solid conductor layer disposed between the anode foil and the cathode foil; and (ii) impregnating the capacitor element with an electrolyte, wherein the solid conductor layer has a first surface facing the dielectric layer and a second surface facing the cathode foil, and in step (i), the solid conductor layer is formed having a patterned uneven shape on the first surface such that the first surface has a contact region that contacts the dielectric layer and a non-contact region that does not contact the dielectric layer, and in step (ii), the electrolyte is disposed in at least the non-contact region.

9. The manufacturing method according to claim 8, wherein no separator is disposed between the anode foil and the cathode foil in the capacitor element.

10. The manufacturing method according to claim 8 or 9, wherein the solid conductive layer comprises a conductive polymer, and in step (i), the solid conductive layer is formed by applying a dispersion of the conductive polymer to the cathode foil and then drying it.

11. The manufacturing method according to claim 10, wherein step (i) includes a step of applying the dispersion to a predetermined area using a mask.

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