Electrolytic capacitor and method for manufacturing electrolytic capacitor

Abstract

The disclosed electrolytic capacitor includes: an anode having a dielectric layer on the surface thereof; a cathode; a porous insulating layer that is formed on at least one electrode selected from the group consisting of the anode and the cathode, and that is disposed between the anode and the cathode; and an electrolyte that is disposed in voids in the insulating layer. An outer edge of at least a part of the anode and / or the cathode is located inward of the outer edge of the insulating layer adjacent to said part of the anode and / or the cathode.

Description

Electrolytic capacitor and method for manufacturing an electrolytic capacitor

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

[0002] As an electrolytic capacitor, an electrolytic capacitor including a wound body of an anode foil, a separator, and a cathode foil is known. On the other hand, an electrolytic capacitor that does not use a separator has also been proposed.

[0003] In claim 1 of Patent Document 1 (Japanese Patent No. 5072857), "a step of forming an anode member in which a first conductive polymer layer is coated on the surface of a first metal foil, a step of forming a cathode member in which a second conductive polymer layer is coated on the surface of a second metal foil, a step of connecting a first lead tab terminal to the anode member, a step of connecting a second lead tab terminal to the cathode member, a step of winding the anode member and the cathode member without any intervening member, and a step of forming a third conductive polymer layer by polymerization in the gap between the anode member and the cathode member after the winding step" are described.

[0004] Japanese Patent No. 5072857

[0005] In order to increase the capacitance of an electrolytic capacitor using a separator, it is necessary to make the separator thinner. However, when the separator is made thinner, it becomes difficult to handle the separator, and short circuits are likely to occur, and the difficulty of manufacturing the electrolytic capacitor increases. On the other hand, when a separator is not used, a decrease in withstand voltage and a decrease in reliability at high temperatures are likely to occur. In such a situation, one of the objects of the present disclosure is to provide a new electrolytic capacitor that enables an increase in capacitance and is less likely to cause a short circuit.

[0006] One aspect of the present disclosure relates to an electrolytic capacitor comprising: an anode having a dielectric layer on its surface; a cathode; a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode, and disposed between the anode and the cathode; and an electrolyte disposed in the voids of the insulating layer, wherein the outer edges of at least a portion of the anode and / or the cathode are located inward from the outer edges of the insulating layer adjacent to that portion.

[0007] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor having an anode and a cathode having a dielectric layer on their surfaces, comprising: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; (ii) stacking the anode and the cathode such that the insulating layer is positioned between the anode and the cathode; further comprising (a) arranging an electrolyte in the voids of the insulating layer, wherein step (ii) is performed such that the outer edges of at least a portion of the anode and / or the cathode are located inward from the outer edges of the insulating layer adjacent to that portion.

[0008] According to this disclosure, electrolytic capacitors that can be made high-capacitance and are less prone to short circuits can be obtained. Novel features of the present invention are described in the appended claims, but the present invention, in conjunction with other objects and features of the present invention, will be better understood by the following detailed description with reference to the drawings, relating to both the structure and content.

[0009] Figure 1 is a schematic side view showing an example of an electrolytic capacitor according to an embodiment of this disclosure. Figure 2 is a schematic exploded perspective view showing an example of a capacitor element included in the electrolytic capacitor shown in Figure 1. Figure 3A is a schematic cross-sectional view showing a part of the laminated structure of an example of a capacitor element. Figure 3B is a schematic diagram for explaining the arrangement of plates in the capacitor element shown in Figure 3A. Figure 4A is a schematic cross-sectional view showing a part of the laminated structure of an example of a capacitor element. Figure 4B is a schematic diagram for explaining the arrangement of plates in the capacitor element shown in Figure 4A. Figure 5 is a schematic diagram for explaining an example of an electrospinning method.

[0010] 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.

[0011] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment may be referred to as "electrolytic capacitor (C)" below. The electrolytic capacitor (C) includes an anode having a dielectric layer on its surface, a cathode, a porous insulating layer, and an electrolyte disposed in the voids of the insulating layer. The porous insulating layer is formed on at least one electrode selected from the group consisting of an anode and a cathode, and is disposed between the anode and the cathode. The at least one electrode may be referred to as "electrode (E)" or "at least one electrode (E)" below. The porous insulating layer formed on electrode (E) may be referred to as "insulating layer (L)" below.

[0012] At least a portion of the outer edge of the anode and / or cathode is located inward from the outer edge of the insulating layer (L) adjacent to that portion. This configuration suppresses short circuits between the anode and cathode. When viewed from the stacking direction Ds of the anode and cathode, if the outer edge of a portion of the electrode is located closer to the center of the insulating layer (L) than the outer edge of the insulating layer (L) adjacent to that portion, it can be determined that the outer edge of that portion of the electrode is located inward from the outer edge of the insulating layer (L). Note that if the anode and cathode are wound, the stacking direction Ds is the radial direction of the winding.

[0013] The insulating layer (L) functions as an insulating layer in place of the separator. Because the insulating layer (L) is formed on top of the electrodes (E), it is easy to handle even when thin. Therefore, it can be made thinner compared to a separator. By using a thin insulating layer (L), it is possible to increase the capacitance per unit volume. In other words, the electrolytic capacitor (C) can be made with high capacitance.

[0014] In the electrolytic capacitor described in Patent Document 1, which does not have a separator between the anode and cathode, a decrease in breakdown voltage and reliability is likely to occur. On the other hand, an insulating layer (L) is placed between the anode and cathode of the electrolytic capacitor (C). Therefore, in the electrolytic capacitor (C), a decrease in breakdown voltage and reliability can be suppressed.

[0015] Electrolytic capacitors (C) typically do not include a separator. However, electrolytic capacitors (C) may include a separator. For example, an insulating layer may be formed on only one side of the electrode (E), and a separator may be placed on the other side. In this specification, a separator means a porous insulating film that is treated as a component existing independently of the electrode. Examples of separators include nonwoven fabrics and microporous membranes. An insulating layer (L) formed by depositing fibers has a different structure from known nonwoven fabrics used as separators.

[0016] The insulating layer (L) may be attached to the dielectric layer and integrated with the anode, or attached to the cathode and integrated with the cathode. Integration with the electrode (E) facilitates handling. Here, "integrated" means a state in which it can be handled as a single component in the manufacturing process. The insulating layer (L) may be formed only on the anode, only on the cathode, or on both the anode and the cathode. More specifically, being attached to the anode means being attached to the dielectric layer on the anode surface.

[0017] The capacitor element of an electrolytic capacitor (C) may include a wound body formed by winding an anode and a cathode. In this case, the anode and cathode are stacked in the radial direction of the wound body. The electrolytic capacitor (C) may also include a laminate in which the anode and cathode are stacked. For example, the capacitor element of an electrolytic capacitor (C) may include a laminated type formed by stacking a flat anode and a flat cathode in one direction. For example, a laminate may be formed by stacking multiple anodes and multiple cathodes in one direction. In this case, the anodes and cathodes are arranged alternately.

[0018] The region on the electrode (E) where the insulating layer (L) is formed can be selected according to the form of the electrolytic capacitor (C). Depending on the form of the capacitor element, the insulating layer (L) is formed on one or both sides of the electrode (E). The insulating layer (L) is usually formed on both sides of the electrode (E). The insulating layer (L) may be formed on 90% or more (for example, 95% or more) of the area of ​​both sides of the electrode (E). However, it is preferable that the insulating layer (L) is not formed in the part where leads or the like are connected. Furthermore, in the case of electrodes (E) arranged at both ends of a laminated body, the insulating layer (L) only needs to be formed on the side of the adjacent electrode.

[0019] In a capacitor element, it is preferable that electrodes without an insulating layer (L) do not protrude beyond the insulating layer (L). For example, it is preferable that the width (length in the shorter direction) of an electrode without an insulating layer (L) is smaller than the width of the insulating layer (L). This configuration can suppress short circuits of the electrodes.

[0020] In one example of an electrolytic capacitor (Cx), an insulating layer (L) is formed on both sides of one electrode (sometimes referred to as "electrode X"), while no insulating layer (L) is formed on the other electrode (sometimes referred to as "electrode Y"). In this case, at least a portion of the outer edge of electrode Y is located inside the outer edge of the insulating layer (L). This configuration helps to suppress short circuits between the electrodes.

[0021] When the anode and cathode are wound, the anode and cathode each have a strip-like shape (a long, narrow rectangle). In this case, the anode and cathode each have two long sides. Preferably, the two long sides of electrode Y are located inside the two long sides of the insulating layer (L) adjacent to electrode Y. In this case, the width (length in the short direction) of electrode Y is shorter than the width (length in the short direction) of the insulating layer (L) adjacent to electrode Y. The entire outer edge of electrode Y may be located inside the outer edge of the insulating layer (L) adjacent to electrode Y. The ratio R of the length of the portion of the outer edge of electrode Y that is located inside the outer edge of the insulating layer (L) to the total length of the outer edge of electrode Y may be 45% or more, 50% or more, 80% or more, 90% or more, or 95% or more. The ratio R is 100% or less.

[0022] The distance L between the portion of the outer edge of electrode Y that is located inside the outer edge of the insulating layer (L) and the outer edge of the insulating layer (L) may be 0.3 mm or more, 0.5 mm or more, 1.0 mm or more, or 2.0 mm or more, and may be 3.0 mm or less, 2.0 mm or less, 1.0 mm or less, or 0.5 mm or less. By setting the distance L to 0.3 mm or more, short circuits can be particularly suppressed. By setting the distance L to 3.0 mm or less, a decrease in capacitance can be suppressed. The proportion of the outer edge of electrode Y that is within the above range of distance L may be within the range exemplified for the above proportion R.

[0023] An example electrolytic capacitor (C1) has the following configuration: (1) The electrolytic capacitor (C) includes a wound body in which the anode and cathode are wound. (2) An insulating layer (L) is formed on both sides of one electrode (electrode X) of the anode and cathode. (3) The two long sides of the other electrode (electrode Y) of the anode and cathode are located inside the two long sides of the insulating layer (L).

[0024] Another example of an electrolytic capacitor (C2) has the following configuration: (1') The electrolytic capacitor (C2) includes a laminate in which multiple anodes and multiple cathodes are alternately stacked. (2') An insulating layer (L) is formed on both sides of one electrode (electrode X) of the anode and cathode. (3') The outer edge of the other electrode (electrode Y) of the anode and cathode is located inward from the outer edge of the insulating layer (L).

[0025] Furthermore, an insulating layer (L) may be formed on one side of the anode and one side of the cathode. In that case, the anode and cathode are wound or laminated such that an insulating layer is placed between them.

[0026] The insulating layer (L) may include fibers deposited on at least one electrode (E). The insulating layer (L) may consist solely of these fibers, or may contain these fibers as a main component. The fiber content in the material constituting the insulating layer (L) may be 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more.

[0027] The average diameter of the fibers constituting the insulating layer (L) may be 0.05 μm or more, 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 2.0 μm or less, 1.5 μm or less, 1.0 μm or less, or 0.6 μm or less. The average diameter of the fibers may be in the range of 0.1 to 1.5 μm. The lower and / or upper limits of this range may be replaced with the above lower and / or upper limits, provided that the lower limit does not exceed the upper limit. By setting the average diameter of the fibers to 0.1 μm or more, it becomes possible to increase the density of the insulating layer, improving its withstand voltage performance. By setting the average diameter of the fibers to 1.5 μm or less, it becomes easier to form a structure in which the fibers overlap in a complex manner, improving the withstand voltage performance of the insulating layer.

[0028] The average diameter of a fiber is determined by taking the arithmetic mean of the diameters of 30 arbitrarily selected fibers. The diameter of each fiber is determined by measuring the diameter at one arbitrarily selected point. If the cross-section of a fiber is not circular, the equivalent circular diameter calculated from the area of ​​the fiber's cross-section is taken as the fiber's diameter.

[0029] The fibers constituting the insulating layer (L) are not particularly limited. Any material that is insulating and stable within the electrolytic capacitor can be used for the fibers. The fibers may be made of polymers. Examples of fiber materials include various insulating polymers. For example, examples of fiber materials include polyacrylonitrile, fluoropolymers (such as polyvinylidene fluoride), polyurethane, polyethylene oxide, polyvinyl alcohol, poly-L-lactic acid, nylon 6, polyethylene terephthalate, polystyrene, polymethyl methacrylate, polypropylene, polysulfone, polyethersulfone, polycaprolactone, polyimide, and cellulosin polymers. Cellulosin polymers include cellulose and cellulose derivatives. Examples of cellulosin polymers include cellulose, alkylcellulose, and cellulose acetate. The fibers constituting the insulating layer (L) may consist of at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. Polyacrylonitrile and polyvinylidene fluoride are easily spun by electrospinning. By using these fibers, it is possible to particularly enhance the characteristics of electrolytic capacitors (C).

[0030] The insulating layer (L) may contain materials other than fibers, or may be composed of materials other than fibers. An example of an insulating layer (L) composed of materials other than fibers is an insulating layer formed by depositing a polymer or a polymer-containing composition onto an electrode (E). The method of depositing the polymer onto the electrode (E) is not particularly limited. For example, a porous insulating layer (L) may be formed by spraying a coating liquid containing a polymer. The polymer used may be one of the polymers exemplified as a fiber material.

[0031] The thickness of the insulating layer (L) may be 0.5 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more, and may be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. The thickness of the insulating layer (L) may be in the range of 0.5 to 30 μm. The lower and / or upper limits of this range may be replaced with the lower and / or upper limits mentioned above, as long as the lower limit does not exceed the upper limit. By setting the thickness of the insulating layer (L) to 0.5 μm or more, it is possible to increase the dielectric strength and reduce the leakage current. By setting the thickness of the insulating layer (L) to 30 μm or less, it becomes particularly easy to increase the capacitance.

[0032] The insulating layer (L) is usually formed to be as uniform in thickness as possible. The thickness of the insulating layer (L) can be measured using a cross-sectional image of the insulating layer (L) in a cross-sectional image of the electrode (E) on which the insulating layer (L) is formed.

[0033] The anode and cathode may each contain or be metal foil. Examples of metal foil will be described later. The cathode may contain metal foil and other layers formed on the surface of the metal foil. Examples of other layers include conductive layers made of a material different from the metal foil.

[0034] The anode and cathode of an electrolytic capacitor (C) face each other with an insulating layer (L) in between. The arrangement of the anode and cathode is not particularly limited. The anode and cathode may be wound together. That is, the electrolytic capacitor (C) may include a wound body in which the anode and cathode are wound together.

[0035] (Method for Manufacturing Electrolytic Capacitors) The manufacturing method according to this embodiment may be referred to as "Manufacturing Method (M)" below. According to Manufacturing Method (M), electrolytic capacitors (C) can be manufactured. However, electrolytic capacitors (C) may be manufactured by methods other than Manufacturing Method (M). Matters described for electrolytic capacitors (C) can be applied to Manufacturing Method (M), so redundant explanations may be omitted. Matters described for Manufacturing Method (M) may also be applied to electrolytic capacitors (C).

[0036] Manufacturing method (M) is a method for manufacturing an electrolytic capacitor comprising an anode and a cathode having a dielectric layer on their surfaces. Manufacturing method (M) includes the steps of: (i) forming a porous insulating layer (insulating layer (L)) on at least one electrode (electrode (E)) selected from the group consisting of an anode and a cathode; and (ii) stacking the anode and the cathode such that the insulating layer (L) is positioned between the anode and the cathode. Manufacturing method (M) further includes the step (a) of placing an electrolyte in the voids of the insulating layer (L). Step (ii) is carried out such that the outer edges of at least a portion of the anode and / or cathode are located inward from the outer edges of the insulating layer adjacent to that portion.

[0037] (Step (i)) The method for forming the insulating layer (L) in step (i) is not particularly limited. As described above, a porous insulating layer (L) may be formed by spraying a coating solution containing a polymer. Alternatively, the insulating layer (L) may be formed in step (i) by depositing fibers on at least one electrode (E). For example, in step (i), fibers may be deposited on at least one electrode (E) by an electrospinning method. The insulating layer (L) can be formed in step (i) so as to adhere to the electrode (E). By adhering the insulating layer (L) to the electrode (E), the electrode (E) and the insulating layer (L) can be handled as a single integrated component in step (ii).

[0038] When forming an insulating layer (L) by electrospinning, a higher conductivity on the surface of the electrode (E) makes it easier to improve the adhesion of fibers to the electrode (E). Therefore, from the viewpoint of improving the adhesion of the insulating layer (L) to the electrode (E), the cathode may be used as the electrode (E). When forming an insulating layer (L) by electrospinning, fibers can be deposited on the electrode (E) by extruding a polymer solution from a nozzle. The polymer in the polymer solution can be the polymer described above. The solvent of the polymer solution is not limited, and depending on the type of polymer, a known solvent used in the electrospinning method may be used. Examples of solvents include water and organic solvents. Examples of organic solvents include alcohol, acetone, dichloromethane, dimethylformamide, dimethylacetamide, tetrahydrofuran, and dimethyl sulfoxide. One type of solvent may be used alone, or multiple types may be used in mixture. The polymer solution may contain additives (e.g., known additives).

[0039] The concentration of the polymer solution (the ratio of the mass of polymer to the mass of the polymer solution) is not limited and can be selected according to the fiber to be formed. By changing the conditions under which the electrospinning method is performed (nozzle diameter, applied voltage, type of solvent, concentration of polymer solution, etc.), the physical properties of the formed fiber (e.g., fiber diameter) can be changed. The concentration of the polymer solution may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, or it may be 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0040] In step (i), an insulating layer (L) may be formed on electrodes (E) cut to the size used in an electrolytic capacitor (C). Alternatively, in step (i), an insulating layer (L) may be formed on a large conductive sheet, and then the electrodes (E) may be formed by cutting the conductive sheet. In this case, the outer edge of the insulating layer (L) and the outer edge of the electrodes (E) are usually equal. That is, in this case, the length and width of the insulating layer (L) and the length and width of the electrodes (E) are usually equal. However, the length and width of the insulating layer (L) and the length and width of the electrodes (E) may be different. The conductive sheet is a sheet that becomes an anode or cathode when cut. Therefore, a metal foil with a dielectric layer formed on it, or the like, is used for the conductive sheet.

[0041] A dielectric layer is formed on the surface of the anode used in step (i). The dielectric layer may be formed by a known method (e.g., chemical conversion treatment). The surface of the anode is usually porous. The surface of the cathode may also be porous. By making these surfaces porous, the surface area of ​​the electrodes can be increased. Furthermore, by making the surface of electrode (E) porous, the adhesion of the insulating layer (L) to electrode (E) can be improved. The method for making the electrode surface porous is not limited, and known methods may be used. For example, the electrode surface may be made porous by etching.

[0042] (Step (ii)) In step (ii), the method for stacking the anode and cathode is not particularly limited, and known methods may be used. In step (ii), the anode and cathode may be stacked by winding them together. Alternatively, in step (ii), one or more flat anodes and one or more flat cathodes may be stacked in one direction.

[0043] As described above, in step (ii), step (ii) is performed such that at least a part of the outer edge of the anode and / or the cathode is positioned inside the outer edge of the insulating layer adjacent to that part. When manufacturing the electrolytic capacitor (C1) described above, step (i) is performed so as to satisfy the above (2), and step (ii) is performed so as to satisfy the above (3). When manufacturing the electrolytic capacitor (C2) described above, step (i) is performed so as to satisfy the above (2'), and step (ii) is performed so as to satisfy the above (3').

[0044] (Step (a)) Step (a) is a step of disposing an electrolyte in the voids of the insulating layer (L). It is also possible to consider that step (a) is a step of disposing an electrolyte between the anode and the cathode. By disposing an electrolyte between the anode and the cathode, the electrolyte is disposed in the voids of the insulating layer (L).

[0045] The step (a) of disposing an electrolyte in the voids of the insulating layer (L) may be performed simultaneously with the step (ii) of forming the insulating layer (L), but is usually performed after forming the insulating layer (L). When the electrolyte contains a conductive polymer (solid electrolyte), the conductive polymer may be disposed in the voids of the insulating layer (L) before forming the wound body (or laminate) of the anode and the cathode. In this case, the conductive polymer may be disposed in the insulating layer (L) by applying a liquid containing the conductive polymer to the insulating layer (L) and then drying it. Thereafter, a wound body (or laminate) of the anode and the cathode is formed.

[0046] The conductive polymer may be disposed in the voids of the insulating layer (L) after forming the wound body (or laminate) of the anode and the cathode. In this case, the conductive polymer may be disposed in the insulating layer (L) by impregnating the wound body (or laminate) with a liquid containing the conductive polymer and then drying it.

[0047] When the electrolyte contains an electrolytic solution, the electrolytic solution may be disposed in the voids of the insulating layer (L) after forming a wound body (or laminate) of an anode and a cathode. For example, the electrolytic solution may be disposed in the insulating layer (L) by impregnating the wound body (or laminate) with the electrolytic solution. The impregnation of the electrolytic solution may be performed before accommodating the wound body (or laminate) in the exterior body, or may be performed after accommodating the wound body (or laminate) in the exterior body.

[0048] As described above, a capacitor element containing an electrolyte is formed. An electrolytic capacitor is manufactured using the formed capacitor element. For example, an electrolytic capacitor can be obtained by accommodating the capacitor element in an exterior body. The processes other than the above-described processes are not particularly limited, and the processes used in known manufacturing methods may be used.

[0049] Examples of the components used in the electrolytic capacitor (C) will be described below. However, the components used in the electrolytic capacitor (C) are not limited to the examples described below. The components other than the components peculiar to the electrolytic capacitor (C) are not particularly limited, and known components may be used.

[0050] (Anode) Examples of the anode include a metal foil containing at least one kind of valve metal such as titanium, tantalum, aluminum, and niobium. The anode may be a valve metal foil (for example, an 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 type element, the anode has a strip shape.

[0051] The anode has a dielectric layer on its surface. The dielectric layer may be formed by subjecting the anode to a forming treatment. In this case, the dielectric layer may contain an oxide of the valve metal (for example, aluminum oxide). Note that the dielectric layer only needs to function as a dielectric, and may be formed of a dielectric other than the oxide of the valve metal.

[0052] (Cathode) A conductive sheet may be used as the cathode, 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 may be roughened by etching or the like. That is, the surface of the cathode may be porous. The thickness of the cathode 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 has a strip shape.

[0053] (Electrolyte) The electrolyte is placed between the anode and the cathode (for example, in the void of the insulating layer (L)). A solid electrolyte (e.g., a conductive polymer) and / or an electrolyte solution may be used as the electrolyte. The electrolytic capacitor (C) preferably contains a conductive polymer and an electrolyte solution. The electrolytic capacitor (C) may contain a conductive polymer and a liquid component placed between the anode and the cathode. The liquid component may be an electrolyte solution or a non-aqueous solvent used in the electrolyte solution. When an insulating layer (L) is used, using a conductive polymer and an electrolyte solution as the electrolyte is preferable because it is easier to achieve high reliability and high withstand voltage while reducing ESR.

[0054] 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, derivatives of polythiophene include poly(3,4-ethylenedioxythiophene). These conductive polymers may be used individually or in combination of multiple types. 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, for example, 1,000 to 100,000. A preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0055] 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).

[0056] 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.

[0057] When a conductive polymer is placed between the anode and cathode, a liquid containing the conductive polymer may be used, as described above. The liquid medium is not particularly limited. Examples of liquid mediums include water, organic solvents (alcohol, ethylene glycol), and mixed solvents thereof. The liquid containing the conductive polymer may be a dispersion in which particles of the conductive polymer are dispersed in a liquid mainly composed of water (content: 50% by mass or more).

[0058] The content of the conductive polymer in a 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.

[0059] The electrolyte is not particularly limited, and any known electrolyte 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.

[0060] 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.

[0061] The non-aqueous solvent may include polymeric 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. Examples of polymeric solvents further include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. The non-aqueous solvent may be used alone or as a mixture of two or more.

[0062] Examples of solutes include inorganic and organic salts. Organic salts are salts 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.

[0063] (Enclosure) The capacitor element is housed in an enclosure. The enclosure is not particularly limited, and known enclosures may be used.

[0064] Hereinafter, an example of this disclosure will be specifically described with reference to the drawings. The components of the example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiments. Furthermore, in the example described below, components that are not essential to the electrolytic capacitor according to this disclosure may be omitted.

[0065] (Embodiment 1) Figure 1 is a schematic cross-sectional view showing an example of an electrolytic capacitor 100 according to this embodiment. Figure 2 is a schematic diagram showing a part of the capacitor element 10 included in the electrolytic capacitor 100 unfolded. The electrolytic capacitor 100 is a wound-type capacitor including a wound body.

[0066] The electrolytic capacitor 100 comprises a capacitor element 10, a bottomed case 101 housing the capacitor element 10, a sealing member 102 closing the opening of the bottomed case 101, a base plate 103 covering the sealing member 102, lead wires 104A and 104B extending from the sealing member 102 and passing through the base plate 103, and lead tabs 105A and 105B connecting the lead wires to the electrodes of the capacitor element 10. The open end of the bottomed case 101 is curled inward.

[0067] An example of a capacitor element 10 is schematically shown in Figure 2. The capacitor element 10 is a wound body formed by winding an anode (anode foil) 11 and a cathode (cathode foil) 12. The anode 11 has a dielectric layer 11a on its surface. A porous insulating layer 21 is formed on the anode 11 and / or cathode 12. Figure 2 shows an example in which the insulating layer 21 is formed on both sides of the cathode 12. The insulating layer 21 is integrated with the cathode 12 and is wound together with the cathode 12. The outermost circumference of the wound body is fixed by a winding stopper tape 14. Note that Figure 2 shows a state in which a portion of the wound body is unfolded before the outermost circumference is fixed. As described above, the surfaces of the anode 11 and / or cathode 12 may be porous.

[0068] Figure 3A schematically shows a partial cross-sectional view of an example of a wound-type capacitor element 10. Figure 3B shows a top view of a portion of the anode 11 and cathode 12 of the capacitor element 10 when they are laid flat without changing their relative positions. Figures 3A and 3B show the axial direction Da of the winding axis of the capacitor element 10. Figure 3A shows the stacking direction Ds of the anode 11 and cathode 12. In the case of a wound-type capacitor element 10, the stacking direction Ds of the anode 11 and cathode 12 is the radial direction of the cylindrical capacitor element 10. In the capacitor element 10 shown in Figures 3A and 3B, the insulating layer 21 is formed on both sides of the cathode 12.

[0069] The anode 11 and cathode 12 used in the wound capacitor element 10 each have a strip shape. The anode 11 has two long sides (outer edges 11e). The cathode 12 has two long sides (outer edges 12e). The insulating layer 21 in one example shown in Figures 3A and 3B is formed over the entire surface of the cathode 12. Therefore, the planar shape of the insulating layer 21 is the same as the planar shape of the cathode 12. That is, the insulating layer 21 has a strip shape and two long sides (outer edges 21e). As shown in Figure 3B, the width W11 of the anode 11 is shorter than the width W21 of the insulating layer 21. As shown in Figures 3A and 3B, the two long sides (outer edges 11e) of the anode 11 are located inward from the two long sides (outer edges 21e) of the insulating layer 21 adjacent to the anode 11. This configuration makes it possible to suppress short circuits between the anode 11 and the cathode 12.

[0070] Figure 4A schematically shows a partial cross-sectional view of another example of a multilayer capacitor element 10. Figure 4B schematically shows the arrangement of the anode 11 and cathode 12 of the capacitor element 10. Figure 4A shows the stacking direction Ds of the anodes 11 and 12 in the capacitor element 10. In Figure 4B, this stacking direction Ds is perpendicular to the surface of the insulating layer 21. In the capacitor element 10 shown in Figures 4A and 4B, the insulating layer 21 is formed on both sides of the cathode 12.

[0071] As shown in Figure 4B, the outer edge 11e of the anode 11 is located inside the outer edge 21e of the insulating layer 21 adjacent to the anode 11. This configuration suppresses short circuits between the anode 11 and the cathode 12.

[0072] In the examples shown in Figures 3A to 4B, the insulating layer 21 is formed on the cathode 12, and an anode 11 smaller than the cathode 12 is used. However, the configuration of the electrolytic capacitor (C) is not limited to these configurations, and other configurations are also possible. For example, in another example of an electrolytic capacitor, the insulating layer 21 is formed on the anode 11, and a cathode 12 smaller than the anode 11 is used.

[0073] In another example of an electrolytic capacitor, an insulating layer 21 is formed on one side of the anode 11 and one side of the cathode 12, and they are wound or stacked. In this case, the anode 11 and cathode 12 are wound or stacked such that an insulating layer is placed between the anode 11 and cathode 12. In this example, the anode 11 is either larger than the cathode 12 or smaller than the cathode 12. This example also provides an effect of suppressing short circuits, but the effect may be smaller than that obtained in the electrolytic capacitor example described above.

[0074] The apparatus for carrying out the electrospinning method is not particularly limited. An example of an apparatus 200 for carrying out the electrospinning method is schematically shown in Figure 5. The apparatus 200 includes a syringe 201 having a conductive nozzle 201a and a power supply 202. A polymer solution 211 is placed inside the syringe 201. A high voltage is applied between the nozzle 201a and the electrode 221 (anode or cathode) by the power supply 202. Fibers 212 are formed by ejecting the polymer solution 211 from the nozzle 201a. The formed fibers 212 are deposited on the electrode 221, forming a porous insulating layer. By increasing the number of nozzles 201a, it is possible to deposit a large number of fibers 212 simultaneously.

[0075] (Note) The above description discloses the following technologies: (Technology 1) An electrolytic capacitor comprising: an anode having a dielectric layer on its surface; a cathode; a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode, and disposed between the anode and the cathode; and an electrolyte disposed in the voids of the insulating layer, wherein the outer edge of at least a portion of the anode and / or the cathode is located inward of the outer edge of the insulating layer adjacent to that portion. (Technology 2) The electrolytic capacitor according to Technology 1, comprising a wound body in which the anode and the cathode are wound, wherein the insulating layer is formed on both sides of one of the electrodes, the anode and the cathode, and the two long sides of the other electrode, the anode and the cathode, are located inward of the two long sides of the insulating layer adjacent to the other electrode. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the insulating layer is attached to the dielectric layer or to the cathode. (Technology 4) An electrolytic capacitor according to any one of Techniques 1 to 3, wherein the insulating layer includes fibers deposited on the at least one electrode. (Technology 5) An electrolytic capacitor according to Technique 4, wherein the average diameter of the fibers is in the range of 0.1 to 1.5 μm. (Technology 6) An electrolytic capacitor according to Technique 4 or 5, wherein the fibers consist of at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. (Technology 7) An electrolytic capacitor according to any one of Techniques 1 to 6, wherein the thickness of the insulating layer is in the range of 0.5 to 30 μm. (Technology 8) An electrolytic capacitor according to any one of Techniques 1 to 7, wherein the anode and the cathode are each metal foils. (Technology 9) An electrolytic capacitor according to any one of Techniques 1, 3 to 8, comprising a wound body in which the anode and the cathode are wound. (Technology 10) An electrolytic capacitor according to any one of Techniques 1, 3 to 8, comprising a laminate in which the anode and the cathode are laminated.(Technical 11) A method for manufacturing an electrolytic capacitor including an anode and a cathode having a dielectric layer on their surfaces, comprising: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; and (ii) stacking the anode and the cathode such that the insulating layer is positioned between the anode and the cathode, further comprising (a) arranging an electrolyte in the voids of the insulating layer, wherein step (ii) is performed such that the outer edge of at least a portion of the anode and / or the cathode is located inward from the outer edge of the insulating layer adjacent to that portion. (Technical 12) The manufacturing method according to Technical 11, wherein in step (i), the insulating layer is formed by depositing fibers on the at least one electrode. (Technical 13) The manufacturing method according to Technical 12, wherein in step (i), the fibers are deposited on the at least one electrode by an electrospinning method. (Technical 14) A manufacturing method according to any one of Technical 11 to 13, wherein in step (i), the insulating layer is formed on both sides of one of the anode and the cathode, and in step (ii), the anode and the cathode are laminated by winding them such that the other two long sides of the anode and the cathode are located inside the two long sides of the insulating layer.

[0076] 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 capacitor including one anode and one cathode was fabricated.

[0077] (Capacitor A1) An electrolytic capacitor (capacitor A1) was manufactured by the following method: (1) Preparation of the anode foil (anode) The surface of an aluminum foil (thickness: 100 μm) was roughened (porous) by etching. A dielectric layer was formed on the roughened surface of the aluminum foil by chemical conversion treatment. Next, the aluminum foil with the dielectric layer formed on it was cut to the size shown in Table 1. In this way, an anode foil with dielectric layers formed on both sides was obtained.

[0078] (2) Preparation of Cathode Foil (Cathode) An aluminum foil (thickness: 50 μm) was etched to roughen (make porous) the surface of the aluminum foil and obtain a cathode foil. Next, a porous insulating layer was formed on the cathode foil (aluminum foil) by depositing fibers on the surface using the electrospinning method. A polyacrylonitrile solution was used as the polymer solution for the electrospinning method. An aprotic polar solvent was used as the solvent for the polymer solution. By using this polymer solution, a porous insulating layer (thickness: 15 μm) made of polyacrylonitrile fibers was formed on the cathode foil. Next, the cathode foil with the insulating layer formed was cut to the size shown in Table 1. In this way, a cathode foil with an insulating layer formed on one side was obtained. The size of the insulating layer is the same as the size of the cathode foil.

[0079] (3) Assembly of electrolytic capacitors The porous insulating layer of the cathode foil has a solid content surface density of 0.3 mg / cm². ２ A dispersion of conductive polymer was dropped onto the plate in such a manner. Subsequently, the anode foil and cathode foil were stacked on top of each other with an insulating layer in between to form a laminate. At this time, the anode foil and cathode foil were stacked so that the centers of the anode foil and cathode foil coincided, and each of the four sides of the anode foil was parallel to the four sides of the cathode foil.

[0080] Next, the laminate was dried at 150°C for 20 minutes to form a conductive polymer between the anode foil and the cathode foil. At this time, the conductive polymer was placed in the voids of the insulating layer. The conductive polymer used was poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS). In addition, a liquid containing 5% by mass of ethylene glycol added to water was used as the dispersion medium for the conductive polymer dispersion.

[0081] Next, the electrolyte was impregnated into the laminate to place it within the voids of the insulating layer. The electrolyte 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 set to 2.0. By aging the electrolytic capacitor thus fabricated, a parallel plate type capacitor A1 was obtained. Aging was performed by applying the rated voltage to the capacitor for 30 minutes.

[0082] Ten capacitors A1 were fabricated and evaluated for short circuits. Furthermore, the capacitance (Cap) at 120 Hz and the equivalent series resistance (ESR) at 100 kHz were measured for five capacitors A1 that were not short-circuited. The capacitance and ESR of capacitor A1 were then calculated by arithmetic mean of the measurement results for the five capacitors A1.

[0083] (Capacitors Z1-Z3) Capacitors Z1-Z3 were manufactured using the same method and conditions as capacitor A1, except that the electrode sizes were changed as shown in Table 1, and a separator was used instead of forming an insulating layer. In other words, in capacitors Z1-Z3, no insulating layer was formed on the cathode, and a separator was placed between the anode and cathode. A nonwoven fabric made of cellulose (thickness: 50 μm) was used as the separator. The size of the separator was 22 mm x 22 mm. Ten capacitors Z1 were manufactured and evaluated in the same way as capacitor A1.

[0084] (Other Capacitors) Other capacitors were manufactured using the same method and conditions as capacitor A1, except that the size of the electrodes and / or the electrodes on which the insulating layer was formed were changed as shown in Table 1. In all capacitors, the insulating layer was formed over the entire surface of one side of the electrode on which it was formed. That is, the size of the insulating layer was the same as the size of the electrode on which it was formed. Ten of each type of capacitor were manufactured and evaluated in the same way as capacitor A1.

[0085] Table 1 shows some of the manufacturing conditions and evaluation results for each capacitor. "Size" in Table 1 indicates the length × width of the planar shape. "Formation Position" in Table 1 indicates the electrode where the fibers were deposited by the electrospinning method. The capacitance and ESR values ​​in Table 1 are relative values ​​when the evaluation result of capacitor Z1 is set to 1.00. "Insulator" in Table 1 refers to the insulator placed between the anode and cathode. A high capacitance is preferable, and a low ESR and short-circuit rate are preferable.

[0086]

[0087] Capacitors A1 and A2 are electrolytic capacitors (C) according to the present disclosure. Capacitors Z1 to Z4 are comparative examples. As shown in Table 1, capacitors A1 and A2 had large capacitance and low ESR and short-circuit rate. The increase in capacitance is thought to be due to the increased amount of conductive polymer filled into the porous anode because the insulating layer is thin. The decrease in ESR in capacitors A1 and A2 is thought to be due to the thinner insulating layer compared to the separator. The short-circuit rate of capacitors A1 and A2 was lower than that of capacitor Z4. When a wound (or multilayer) capacitor element is formed using the insulating layer used in capacitors A1 and A2, it is possible to increase the capacitance per unit volume because the insulating layer is thin.

[0088] 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.

[0089] 10: Capacitor element 11: Anode 11a: Dielectric layer 12: Cathode 21: Porous insulating layer 100: Electrolytic capacitor

Claims

1. An electrolytic capacitor comprising: an anode having a dielectric layer on its surface; a cathode; a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode, and disposed between the anode and the cathode; and an electrolyte disposed in the voids of the insulating layer, wherein the outer edges of at least a portion of the anode and / or the cathode are located inward from the outer edges of the insulating layer adjacent to that portion.

2. The electrolytic capacitor according to claim 1, comprising a wound body in which the anode and the cathode are wound, wherein the insulating layer is formed on both sides of one of the electrodes, the anode and the cathode, and the two long sides of the other electrode, the anode and the cathode, are located inward from the two long sides of the insulating layer adjacent to the other electrode.

3. The electrolytic capacitor according to claim 1 or 2, wherein the insulating layer is attached to the dielectric layer or to the cathode.

4. The electrolytic capacitor according to claim 1 or 2, wherein the insulating layer includes fibers deposited on the at least one electrode.

5. The electrolytic capacitor according to claim 4, wherein the average diameter of the fibers is in the range of 0.1 to 1.5 μm.

6. The electrolytic capacitor according to claim 4, wherein the fiber comprises at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

7. The electrolytic capacitor according to claim 1 or 2, wherein the thickness of the insulating layer is in the range of 0.5 to 30 μm.

8. The electrolytic capacitor according to claim 1 or 2, wherein the anode and the cathode are each metal foils.

9. The electrolytic capacitor according to claim 1, comprising a wound body in which the anode and the cathode are wound.

10. The electrolytic capacitor according to claim 1, comprising a laminate in which the anode and the cathode are stacked.

11. A method for manufacturing an electrolytic capacitor, comprising an anode and a cathode having a dielectric layer on their surfaces, comprising: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; (ii) stacking the anode and the cathode such that the insulating layer is positioned between the anode and the cathode; further comprising (a) arranging an electrolyte in the voids of the insulating layer, wherein step (ii) is performed such that the outer edge of at least a portion of the anode and / or the cathode is located inward from the outer edge of the insulating layer adjacent to that portion.

12. The manufacturing method according to claim 11, wherein the insulating layer is formed by depositing fibers on the at least one electrode in step (i).

13. The manufacturing method according to claim 12, wherein in step (i), the fibers are deposited on the at least one electrode by electrospinning.

14. The manufacturing method according to claim 11 or 12, wherein in step (i), the insulating layer is formed on both sides of one of the anode and the cathode, and in step (ii), the anode and the cathode are laminated by winding them such that the other two long sides of the anode and the cathode are located inside the two long sides of the insulating layer.

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