Electrolytic capacitor element

Abstract

An electrolytic capacitor element 1 comprises: a positive electrode 10 that is formed from a valve-action metal substrate 11, and has a leading end surface 10a and a base end surface 10b; a dielectric layer 20 provided on at least one of main surfaces 10c, 10d of the positive electrode 10, excluding at least the base end surface 10b; a mask layer 30 made from an insulating material and provided on the dielectric layer 20 along the base end surface 10b; and a negative electrode 40 provided on the dielectric layer 20 more on the leading end surface 10a side than the mask layer 30. The negative electrode 40 has a solid-state electrolyte layer 50 provided on the dielectric layer 20, and an electroconductive layer 60 provided on the solid-state electrolyte layer 50. The solid-state electrolyte layer 50 includes a first layer 51 containing a first electroconductive polymer doped with a first dopant, and a second layer 52 containing a second electroconductive polymer doped with a second dopant. The second layer 52 is disposed locally within the plane of the solid electrolyte layer 50, and the first layer 51 is disposed at least in a region where the second layer 52 is not disposed within the plane of the solid electrolyte 50. The second electroconductive polymer is more susceptible to de-doping than the first electroconductive polymer.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor element.

Background Art

[0002] Patent Document 1 discloses a solid electrolytic capacitor having a first oxide dielectric layer formed on the surface of an anode body, a second oxide dielectric layer formed on an exposed end face formed by cutting the anode body, a first conductive polymer layer formed on the first oxide dielectric layer, and a second conductive polymer layer formed on the second oxide dielectric layer. It is described that the second conductive polymer layer is more likely to be insulated than the first conductive polymer layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, by covering the second oxide dielectric layer with a low breakdown voltage formed on the cut surface of the anode body with the second conductive polymer layer, the second conductive polymer layer is insulated. Therefore, it is said that a solid electrolytic capacitor with a small leakage current defect rate without a decrease in capacitance can be provided. However, the insulation mechanism is not clear, and since the measure for making the second conductive polymer layer easily insulated is the addition of an insulating binder, there is room for improvement in that the conductivity of the entire second conductive polymer layer decreases and an increase in equivalent series resistance (ESR) is caused. In addition, since a portion where the electric field is likely to concentrate, for example, a corner portion, is not covered with the second conductive polymer layer when a voltage is applied, there is also room for further improvement in that the reduction of leakage current is not sufficient.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide an electrolytic capacitor element capable of suppressing leakage current while suppressing an increase in equivalent series resistance.

Means for Solving the Problems

[0006] The electrolytic capacitor element of the present invention is composed of a valve-acting metal substrate, an anode having a front end face and a base end face, a dielectric layer provided on at least one main surface of the anode except at least the base end face, a mask layer composed of an insulating material and provided on the dielectric layer along the base end face, and a cathode provided on the dielectric layer on the front end face side of the mask layer. The cathode has a solid electrolyte layer provided on the dielectric layer and a conductive layer provided on the solid electrolyte layer. The solid electrolyte layer includes a first layer containing a first conductive polymer doped with a first dopant and a second layer containing a second conductive polymer doped with a second dopant. The second layer is partially disposed in the plane of the solid electrolyte layer, and the first layer is disposed at least in a region where the second layer is not disposed in the plane of the solid electrolyte layer. The second conductive polymer is more likely to be dedoped than the first conductive polymer.

Effects of the Invention

[0007] According to the present invention, it is possible to provide an electrolytic capacitor element capable of suppressing leakage current while suppressing an increase in equivalent series resistance.

Brief Description of the Drawings

[0008]

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[0009] The electrolytic capacitor element of the present invention will now be described. However, the present invention is not limited to the following configurations, and can be appropriately modified and applied within the scope of the present invention. Note that the present invention also includes a combination of two or more of the individual desirable configurations described below.

[0010] Furthermore, the embodiments described below are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. Repetition of descriptions of matters common to multiple embodiments will be omitted, and only differences will be described.

[0011] [Electrolytic capacitor element] Fig. 1 is a plan view schematically illustrating an example of an electrolytic capacitor element according to an embodiment of the present invention. Fig. 2 is a cross-sectional view of the electrolytic capacitor element shown in Fig. 1 taken along line XX. In Fig. 1, a solid electrolyte layer 50 covered with a conductive layer 60 is indicated by a dashed line. In Figs. 1 and 2, the solid electrolyte layer 50 is shown without distinguishing between a first layer 51 and a second layer 52.

[0012] The electrolytic capacitor element 1 shown in FIGS. 1 and 2 is a solid electrolytic capacitor element, and includes: an anode 10 made of a valve metal substrate 11 and having a tip end surface 10a and a base end surface 10b; a dielectric layer 20 provided on the surface of the anode 10 except for the base end surface 10b; a mask layer 30 made of an insulating material provided on the dielectric layer 20 along the base end surface 10b; and a cathode 40 provided on the dielectric layer 20 closer to the tip end surface 10a than the mask layer 30. The cathode 40 has a solid electrolyte layer 50 provided on the dielectric layer 20 and a conductive layer 60 provided on the solid electrolyte layer 50.

[0013] Fig. 3 is a perspective view of the electrolytic capacitor element shown in Fig. 1. Fig. 4 is a cross-sectional view of the electrolytic capacitor element shown in Fig. 3 taken along line AA. Fig. 5 is a cross-sectional view of the electrolytic capacitor element shown in Fig. 3 taken along line BB. Figs. 3, 4, and 5 show the state before the conductive layer 60 of the cathode 40 is formed. Fig. 3 does not show the dielectric layer 20, and the first layer 51 of the solid electrolyte layer 50 is indicated by a dashed dotted line, showing a see-through state of the first layer 51.

[0014] 3, 4, and 5, the solid electrolyte layer 50 includes a first layer 51 including a first conductive polymer doped with a first dopant and a second layer 52 including a second conductive polymer doped with a second dopant, the second layer 52 being partially disposed within the plane of the solid electrolyte layer 50, and the first layer 51 being disposed at least in an area within the plane of the solid electrolyte layer 50 where the second layer 52 is not disposed. The second conductive polymer is more susceptible to undoping than the first conductive polymer. This makes it possible to suppress leakage current while suppressing an increase in the equivalent series resistance of the electrolytic capacitor element 1. The reason (action) for obtaining this effect is thought to be as follows. That is, it is believed that local dedoping of the conductive polymer occurs in areas where leakage current occurs, resulting in the insulating nature of the conductive polymer. In electrolytic capacitor element 1, second layer 52, which contains a second conductive polymer prone to dedoping, is partially disposed within the plane of solid electrolyte layer 50. This allows second layer 52 to be selectively disposed in areas prone to leakage current, thereby insulating the second conductive polymer and suppressing leakage current. That is, second layer 52 can function as a local self-healing layer. Meanwhile, conductive polymers prone to dedoping generally have relatively poor conductivity, which tends to increase the equivalent series resistance of the electrolytic capacitor element. However, in electrolytic capacitor element 1, second layer 52, which may increase the equivalent series resistance, is partially disposed within the plane of solid electrolyte layer 50, while first layer 51, which includes a first conductive polymer that is less susceptible to dedoping than the second conductive polymer, i.e., which can suppress an increase in equivalent series resistance, is disposed at least in an area within the plane of solid electrolyte layer 50 where second layer 52 is not disposed, thereby preventing an increase in the equivalent series resistance of the entire electrolytic capacitor element 1. From the above, it is believed that leakage current can be reduced without an increase in the equivalent series resistance of the entire electrolytic capacitor element 1.

[0015] Here, "the second conductive polymer is more susceptible to undoping than the first conductive polymer" means that the bonding strength between the second main chain and the second dopant of the second conductive polymer is weaker than the bonding strength between the first main chain and the first dopant of the first conductive polymer.

[0016] Regarding the mechanism by which dedoping of a conductive polymer occurs due to leakage current, it is thought that dedoping occurs when the leakage current inhibits the electrical bond between the main chain of the conductive polymer and the dopant, or when Joule heat generated when the leakage current flows through the conductive polymer causes thermal motion of the dopant.

[0017] Furthermore, from the perspective of preventing leakage current alone, it is conceivable to dispose only the second conductive polymer, which is prone to dedoping, over the entire surface of the solid electrolyte layer 50. However, this may reduce the conductivity of the entire solid electrolyte layer 50, potentially increasing the equivalent series resistance of the electrolytic capacitor element 1. Furthermore, since conductive polymers that are prone to dedoping generally tend to have poor heat resistance, disposing only the second conductive polymer, which is prone to dedoping, over the entire surface of the solid electrolyte layer 50 may reduce the high-temperature reliability of the electrolytic capacitor element 1.

[0018] Thus, in this specification, the term "conductive polymer" refers to a polymer that includes a main chain and a dopant. That is, a first conductive polymer includes a first main chain and a first dopant, and a second conductive polymer includes a second main chain and a second dopant.

[0019] 3, 4, and 5, the anode 10 has six surfaces: a tip surface 10a, a base surface 10b, a pair of main surfaces 10c and 10d, and a pair of side surfaces 10e and 10f, and also has corners where three of these six surfaces intersect and ridges where two of these six surfaces intersect, and the second layer 52 covers each corner 10g of the tip surface 10a. Generally, leakage current is likely to occur at the corners of an anode, so this can more effectively suppress leakage current.

[0020] Fig. 6 is a perspective view schematically illustrating one example of an electrolytic capacitor element according to another embodiment of the present invention. Fig. 7 is a cross-sectional view taken along line CC of the electrolytic capacitor element shown in Fig. 6. Fig. 8 is a cross-sectional view taken along line DD of the electrolytic capacitor element shown in Fig. 6. Note that Figs. 6, 7, and 8 show the state before the conductive layer 60 of the cathode 40 is formed. Furthermore, Fig. 6 omits the illustration of the dielectric layer 20, and shows the first layer 51 of the solid electrolyte layer 50 with a dashed dotted line, with the first layer 51 seen through.

[0021] As shown in FIGS. 6, 7, and 8, the second layer 52 may further cover the front end surface 10a and each ridge line portion 10h formed by the front end surface 10a. Generally, leakage current is likely to occur at the ridge line portion of the anode. Therefore, this can further effectively suppress the leakage current. Also, compared with the case shown in FIG. 6, it is easier to form the second layer 52 in the case shown in FIG. 3.

[0022] In this specification, a corner portion is a portion where three surfaces intersect, and a ridge line portion is a portion where two surfaces intersect. Also, a corner portion formed by a certain surface means a corner portion where three surfaces including that surface intersect, and a ridge line portion formed by a certain surface means a ridge line portion where two surfaces including that surface intersect.

[0023] FIG. 9 is a perspective view schematically showing an example of an electrolytic capacitor element according to still another embodiment of the present invention. FIG. 10 is a cross-sectional view taken along line E-E of the electrolytic capacitor element shown in FIG. 9. FIG. 11 is a cross-sectional view taken along line F-F of the electrolytic capacitor element shown in FIG. 9. Note that FIGS. 9, 10, and 11 show the state before the conductive layer 60 of the cathode 40 is formed. Also, in FIG. 9, the illustration of the dielectric layer 20 is omitted, and the first layer 51 of the solid electrolyte layer 50 is shown by a dashed line, showing a state in which the first layer 51 is seen through.

[0024] As shown in FIGS. 9, 10, and 11, the second layer 52 may further cover each side surface 10e, 10f and each ridge line portion 10j formed by each side surface 10e, 10f. Thereby, the leakage current can be particularly effectively suppressed.

[0025] FIG. 12 is a perspective view schematically showing an example of an electrolytic capacitor element according to still another embodiment of the present invention. FIG. 13 is a cross-sectional view taken along line G-G of the electrolytic capacitor element shown in FIG. 12. FIG. 14 is a cross-sectional view taken along line H-H of the electrolytic capacitor element shown in FIG. 12. Note that FIGS. 12, 13, and 14 show the state before the conductive layer 60 of the cathode 40 is formed. Also, in FIG. 12, the illustration of the dielectric layer 20 is omitted, and the first layer 51 of the solid electrolyte layer 50 is shown by a dashed line, showing a state in which the first layer 51 is seen through.

[0026] As shown in FIGS. 12, 13, and 14, the second layer 52 may be disposed along the mask layer 30. At locations along the mask layer, the solid electrolyte layer becomes thin, and as a result, there is a risk of leakage current occurring. However, by disposing the second layer 52 along the mask layer 30, it is possible to effectively suppress the leakage current at locations along the mask layer 30.

[0027] Furthermore, although not shown, a second layer having both the structure shown in FIG. 3, FIG. 6, or FIG. 9 and the structure shown in FIG. 12 may be formed. That is, for example, by combining the structures shown in FIGS. 6 and 12, the second layer 52 may cover each corner portion 10g by the front end surface 10a, the front end surface 10a, and each ridge line portion 10h by the front end surface 10a, and may be disposed along the mask layer 30.

[0028] Each component in the electrolytic capacitor element 1 will be described in detail below.

[0029] The anode 10 is a thin film (foil) having a rectangular shape in plan view formed from a valve-acting metal substrate 11, and preferably has a rectangular shape (strip shape) in plan view having a pair of long sides and a pair of short sides. The front end surface 10a and the base end surface 10b are end surfaces located on a pair of sides (preferably a pair of short sides) of the anode 10. The base end surface 10b is an exposed end surface not covered by the dielectric layer 20, and is exposed at one end surface of the electrolytic capacitor and connected to an external electrode described later. The anode 10 has a front end surface 10a, a base end surface 10b, main surfaces 10c and 10d, and side surfaces 10e and 10f.

[0030] In this specification, "in plan view" means viewing from the normal direction of the main surface of the anode (valve-acting metal substrate).

[0031] FIG. 15 is an enlarged cross-sectional view of the mask layer portion of the electrolytic capacitor element shown in FIG. 2.

[0032] As shown in Fig. 15, a plurality of recesses are provided on each main surface of the valve-actuating metal substrate 11 (anode 10). Therefore, each main surface of the valve-actuating metal substrate 11 is in a porous state. As a result, the surface area of the valve-actuating metal substrate 11 is increased. Note that it is not limited to the case where both main surfaces of the valve-actuating metal substrate 11 are porous, and only one of the two main surfaces of the valve-actuating metal substrate 11 may be porous.

[0033] The valve-actuating metal substrate 11 is composed of, for example, a single metal such as aluminum, tantalum, niobium, titanium, zirconium, or a valve-actuating metal such as an alloy containing these metals. An oxide film can be formed on the surface of the valve-actuating metal.

[0034] Note that the valve-actuating metal substrate 11 may be composed of a core part and a porous part provided on at least one main surface of the core part, and those obtained by etching the surface of a metal foil, forming a porous powder sintered body on the surface of a metal foil, etc. can be appropriately adopted.

[0035] Here, the dielectric layer 20 is provided on the surface of the anode 10 except for the base end surface 10b. That is, the dielectric layer 20 is provided on the tip end surface 10a of the anode 10, on the main surfaces 10c and 10d, and on the side surfaces 10e and 10f, but is not provided on the base end surface 10b of the anode 10. However, the dielectric layer 20 only needs to be provided on at least one of the main surfaces 10c and 10d of the anode 10 except for at least the base end surface 10b.

[0036] The dielectric layer 20 is preferably composed of an oxide film provided on the surface of the valve-actuating metal substrate 11. For example, the dielectric layer 20 is composed of an oxide of aluminum. The oxide of aluminum is formed by anodizing the surface of the valve-actuating metal substrate 11 as will be described later.

[0037] The mask layer 30 is a linear (strip-shaped extending) insulating member provided on the dielectric layer 20 along the base end surface 10b of the anode 10, preferably along the short side of the anode 10, which separates the anode 10 and the cathode 40 and ensures insulation therebetween. By the mask layer 30, the anode 10 is partitioned into a region on the base end surface 10b side and a region on the tip end surface 10a side. Here, the mask layer 30 is arranged at a predetermined interval from the base end surface 10b, but it may be arranged up to the base end surface 10b. Further, the mask layer 30 is provided on the main surfaces 10c and 10d and the side surfaces 10e and 10f of the anode 10 via the dielectric layer 20. However, similar to the dielectric layer 20, it may be provided on at least one of the main surfaces 10c and 10d of the anode 10 (however, the main surface on which the dielectric layer 20 is provided).

[0038] As shown in FIG. 15, the mask layer 30 is preferably provided so as to fill a plurality of pores (recesses) of the valve-acting metal substrate 11. However, it is sufficient that a part of the outer surface of the dielectric layer 20 is covered by the mask layer 30, and there may be pores (recesses) of the valve-acting metal substrate 11 that are not filled by the mask layer 30.

[0039] The mask layer 30 is made of an insulating material. The mask layer 30 is formed, for example, by applying a mask material such as a composition containing an insulating resin. Examples of the insulating resin include polyphenyl sulfone (PPS), polyether sulfone (PES), cyanate ester resin, fluororesin (tetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, etc.), a composition composed of soluble polyimide siloxane and epoxy resin, polyimide resin, polyamideimide resin, and their derivatives or precursors, etc.

[0040] The application of the mask material can be performed, for example, by screen printing, roller transfer, dispenser, inkjet printing, etc.

[0041] The cathode 40 has a solid electrolyte layer 50 provided on the dielectric layer 20 and a conductive layer 60 provided on the solid electrolyte layer 50. Also, the cathode 40 is provided on the dielectric layer 20 on the tip surface 10a side of the mask layer 30. That is, it is provided on the dielectric layer 20 in the region on the tip surface 10a side of the anode 10 partitioned by the mask layer 30.

[0042] The solid electrolyte layer 50 is provided on the dielectric layer 20. As shown in FIG. 15, it is preferable that the solid electrolyte layer 50 is provided so as to fill a plurality of pores (recesses) of the valve action metal substrate 11. However, it is sufficient that a part of the outer surface of the dielectric layer 20 is covered by the solid electrolyte layer 50, and there may be pores (recesses) of the valve action metal substrate 11 that are not filled by the solid electrolyte layer 50.

[0043] The solid electrolyte layer 50 is provided on the dielectric layer 20 on the tip surface 10a side of the mask layer 30. That is, it is provided on the dielectric layer 20 in the region on the tip surface 10a side of the anode 10 partitioned by the mask layer 30.

[0044] As described above, the solid electrolyte layer 50 includes a first layer 51 containing a first conductive polymer doped with a first dopant and a second layer 52 containing a second conductive polymer doped with a second dopant. The second layer 52 is disposed only in a partial region, not in the entire region, within the plane of the solid electrolyte layer 50. That is, the second layer 52 is unevenly distributed in the in-plane direction of the solid electrolyte layer 50, not in the thickness direction. On the other hand, the first layer 51 is disposed at least in a region within the plane of the solid electrolyte layer 50 where the second layer 52 is not disposed. Therefore, in the plane of the solid electrolyte layer 50, at least one of the first layer 51 and the second layer 52 is disposed.

[0045] Here, as shown in FIG. 3 and the like, the first layer 51 is disposed over the entire area in the plane of the solid electrolyte layer 50, and the second layer 52 is provided on the first layer 51. That is, the second layer 52 is disposed only in a part of the region on the first layer 51.

[0046] The thickness of the first layer 51 is not particularly limited, and for example, it may be about the same thickness as a general solid electrolyte layer. Specifically, the maximum thickness of the first layer 51 is preferably 2 μm or more and 50 μm or less, more preferably 3 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0047] The thickness of the second layer 52 is also not particularly limited, but specifically, the maximum thickness of the second layer 52 is preferably 2 μm or more and 50 μm or less, more preferably 3 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0048] The location where the second layer 52 is disposed can be set as appropriate. As described above, (1) a form in which the second layer 52 covers each corner portion 10g of the anode 10 (see FIG. 3 and the like), (2) a form in which the second layer 52 further covers the front end surface 10a of the anode 10 and each ridge line portion 10h formed by the front end surface 10a (see FIG. 6 and the like), (e) a form in which the second layer 52 further covers each side surface 10e, 10f of the anode 10 and each ridge line portion 10j formed by each side surface 10e, 10f (see FIG. 9 and the like), and (4) a form in which the second layer 52 is disposed along the mask layer 30 (see FIG. 12 and the like) are preferable.

[0049] In the case of (1), the second layer 52 may cover at least one of the four corner portions 10g formed by the front end surface 10a, but preferably covers each of the four corner portions 10g. Further, FIG. 3 shows a case where two corner portions 10g (corner portions 10g arranged vertically in FIG. 3) on the same side surface 10e or 10f are each independently covered by the second layer 52, but these two corner portions 10g may be integrally covered by the second layer 52. That is, the four ridge line portions 10h formed by the front end surface 10a include two ridge line portions 10ha formed by the side surface 10e or 10f and the front end surface 10a, but the second layer 52 may further cover the ridge line portion 10ha.

[0050] (2) In this case, the second layer 52 may cover at least one of the four ridge line portions 10h formed by the front end surface 10a, but it is preferable to cover each of the four ridge line portions 10h. Thus, the second layer 52 preferably covers the tip portion (the portion including the front end surface 10a as a part) of the anode 10, and is preferably provided across each of the main surface 10c, the main surface 10d, the side surface 10e, and the side surface 10f from the front end surface 10a.

[0051] (3) In this case, the second layer 52 may cover at least one of the two side surfaces 10e and 10f, but it is preferable to cover each of the two side surfaces 10e and 10f. Also, the second layer 52 may cover at least one of the four ridge line portions 10j formed by the side surfaces 10e and 10f, but it is preferable to cover each of the four ridge line portions 10j. Also, in this case, the second layer 52 may not cover the front end surface 10a and each ridge line portion 10h formed by the front end surface 10a.

[0052] (4) In this case, the second layer 52 may be arranged along the mask layer 30 on at least one of the main surfaces 10c and 10d of the anode 10 and the side surfaces 10e and 10f, but it is preferable to be arranged along the mask layer 30 on each of these surfaces. Also, in this case, it is preferable that no gap is provided between the second layer 52 and the mask layer 30, and the second layer 52 is preferably arranged side by side with the mask layer 30 in a state of being in contact with the mask layer 30. Furthermore, although a gap may occur between only the first layer 51 and the mask layer 30, it is preferable that the second layer 52 fills the gap between the first layer 51 and the mask layer 30.

[0053] In any case, the shape of the second layer 52 is not particularly limited. For example, as shown in FIG. 3 and the like, the shape may be such that the peripheral contour line is formed by a plurality of straight lines orthogonal to each other, or a shape in which at least two straight lines of the peripheral contour line intersect obliquely in this shape, or a shape in which at least one straight line of the peripheral contour line is curved in this shape.

[0054] As the material constituting the solid electrolyte layer 50, for example, conductive polymers such as polypyrrole, polythiophene, and polyaniline are used. Among these, polythiophene is preferable, and poly(3,4-ethylenedioxythiophene) called PEDOT is particularly preferable. Further, the above conductive polymer contains a dopant such as polystyrene sulfonic acid (PSS).

[0055] Here, preferred examples of the first conductive polymer (first main chain and first dopant) contained in the first layer 51 and the second conductive polymer (second main chain and second dopant) contained in the second layer 52 will be described.

[0056] The second dopant contained in the second conductive polymer preferably has a smaller molecular size than the first dopant contained in the first conductive polymer. Thereby, it is possible to make the second conductive polymer more easily undergo dedoping than the first conductive polymer.

[0057] Here, the "molecular size" is the volume occupied by the molecular model in which the electron density of each element constituting the dopant is visualized. Note that this "molecular size" may be expressed as the diameter of a sphere having an equivalent volume when the volume occupied by the molecular model in which the electron density is visualized is represented by a sphere.

[0058] Suitable combinations of the first dopant and the second dopant include, for example, the following.

[0059] That is, the first dopant contained in the first conductive polymer may be paratoluenesulfonate ion, and the second dopant contained in the second conductive polymer may be sulfate ion.

[0060] Also, the first dopant contained in the first conductive polymer may be anthraquinonesulfonate ion, and the second dopant contained in the second conductive polymer may be paratoluenesulfonate ion.

[0061] Also, the first dopant contained in the first conductive polymer may be polystyrenesulfonate ion, and the second dopant contained in the second conductive polymer may be paratoluenesulfonate ion.

[0062] Thus, the first dopant may be a molecule having more aromatic rings or a molecule having a wider conjugated system than the second dopant.

[0063] ]> Regarding the ease of dedoping and the molecular size of these dopants, dedoping is more likely to occur in the order of polystyrenesulfonate ion, anthraquinonesulfonate ion, paratoluenesulfonate ion, and sulfate ion, and the molecular size becomes smaller.

[0064] The second main chain contained in the second conductive polymer may have the same skeleton as the first main chain contained in the first conductive polymer.

[0065] Specifically, the first main chain and the second main chain may be polythiophene, and PEDOT is particularly preferred.

[0066] On the other hand, the second main chain contained in the second conductive polymer may have a different skeleton from the first main chain contained in the first conductive polymer.

[0067] The first main chain contained in the first conductive polymer is polythiophene (particularly preferably PEDOT), and the second main chain contained in the second conductive polymer may be polypyrrole or polyaniline.

[0068] The solid electrolyte layer 50 is formed, for example, by a method of forming a polymer film of a conductive polymer such as poly(3,4-ethylenedioxythiophene) on the surface of the dielectric layer 20 using a liquid containing a polymerizable monomer such as 3,4-ethylenedioxythiophene, or a method of applying a dispersion liquid of a conductive polymer such as poly(3,4-ethylenedioxythiophene) on the surface of the dielectric layer 20 and drying it. In particular, in the method of forming a polymer film of a conductive polymer using a liquid containing a polymerizable monomer, compared with the method using a dispersion liquid of a conductive polymer, the thickness of the solid electrolyte layer 50 tends to be thinner on each corner portion 10g of the anode 10 and each ridge line portion 10h, 10j, and on the region in the case of the mask layer 30. Therefore, leakage current can be suppressed more effectively.

[0069] The first layer 51 is preferably formed by forming an inner layer that fills the pores (recesses) of the valve-action metal substrate 11 and then forming an outer layer that covers the entire dielectric layer 20. The inner layer can be formed, for example, by an immersion method, sponge transfer, screen printing, dispenser, inkjet printing, etc. Similarly, the outer layer can be formed, for example, by an immersion method, sponge transfer, screen printing, dispenser, inkjet printing, etc. Similarly, the second layer 52 can be formed, for example, by an immersion method, sponge transfer, screen printing, dispenser, inkjet printing, etc. However, in the cases of (1), (3), and (4) above, inkjet printing is preferable, and in the case of (2) above, the immersion method is preferable.

[0070] The conductive layer 60 is provided on the solid electrolyte layer 50. The conductive layer 60 covers substantially the entire area of the solid electrolyte layer 50 and is in contact with the mask layer 30. Note that the conductive layer 60 may be arranged up to in front of the mask layer 30. The conductive layer 60 has a substantially constant thickness.

[0071] The conductive layer 60 includes, for example, a carbon layer or a cathode conductor layer. The conductive layer 60 may also be a composite layer in which a cathode conductor layer is provided on the outer surface of the carbon layer, or a mixed layer containing carbon and a cathode conductor layer material.

[0072] The carbon layer is formed, for example, by a method such as applying a carbon paste containing carbon particles and a resin to the surface of the solid electrolyte layer 50 and drying it.

[0073] The application of the carbon paste can be performed, for example, by dipping, sponge transfer, screen printing, spray coating, dispenser, inkjet printing, or the like.

[0074] The cathode conductor layer is formed, for example, by a method such as applying a conductive paste containing metal particles such as gold, silver, copper, platinum, etc. and a resin to the surface of the solid electrolyte layer or the carbon layer and drying it. The cathode conductor layer is preferably a silver layer.

[0075] The application of the conductive paste can be performed, for example, by dipping, sponge transfer, screen printing, spray coating, dispenser, inkjet printing, or the like.

[0076] [Method for manufacturing an electrolytic capacitor element] The method for manufacturing the electrolytic capacitor element 1 will be described below. In the following example, a method for simultaneously manufacturing a plurality of electrolytic capacitor elements using a large-sized valve action metal substrate will be described.

[0077] FIG. 16 is a schematic diagram showing an example of a step of preparing a valve action metal substrate on which a mask layer is formed.

[0078] As shown in FIG. 16, a valve action metal substrate 11A having a dielectric layer 20 on its surface is prepared. The valve action metal substrate 11A includes a plurality of element portions 12 and a support portion 13. Each element portion 12 is strip-shaped and protrudes from the support portion 13. A mask layer 30 is formed on the dielectric layer 20 of each element portion 12.

[0079] First, a valve-action metal substrate 11A having a porous portion on its surface is cut by laser processing, punching, or the like to be processed into a shape including a plurality of element portions 12 and a support portion 13.

[0080] Next, a mask layer 30 is formed on both main surfaces and both side surfaces of each element portion 12 along the short sides of the element portion 12.

[0081] Thereafter, an anodic oxidation treatment is performed on the valve-action metal substrate 11A to form an oxide film serving as a dielectric layer 20 on the surface of the valve-action metal substrate 11A. At this time, an oxide film is also formed on the side surfaces of the element portions 12 cut by laser processing, punching, or the like. Note that a formed foil on which an oxide of the valve-action metal is already formed may be used as the valve-action metal substrate 11A. Also in this case, an anodic oxidation treatment is performed on the valve-action metal substrate 11A after cutting to form an oxide film on the side surfaces of the cut element portions 12.

[0082] FIG. 17 is a schematic diagram showing an example of a process of forming the first layer of the solid electrolyte layer.

[0083] The first layer 51 (see FIG. 3 and the like) of the solid electrolyte layer 50 is formed on the dielectric layer 20 of the element portion 12. As shown in FIG. 17, it is preferable to apply a treatment liquid for forming the first conductive polymer to the valve-action metal substrate 11A by an immersion method. FIG. 17 shows a state in which a treatment liquid 70 for forming the first conductive polymer is supplied to a treatment tank 75.

[0084] As the treatment liquid 70 for forming the first conductive polymer, for example, a dispersion liquid of the first conductive polymer is used. A conductive polymer film can be formed by applying the dispersion liquid of the first conductive polymer to the outer surface of the dielectric layer 20 and drying it. Alternatively, a liquid containing a polymerizable monomer, such as 3,4-ethylenedioxythiophene, and an oxidizing agent, such as iron (III) paratoluenesulfonate, may be used as the treatment liquid 70 for forming the first conductive polymer. A conductive polymer film can be formed by applying the liquid containing the polymerizable monomer to the outer surface of the dielectric layer 20 and chemically polymerizing it. This conductive polymer film becomes the first layer 51 of the solid electrolyte layer 50.

[0085] 17, the valve metal substrate 11A is immersed in a treatment liquid 70, whereby the treatment liquid 70 is impregnated into the porous portion of the valve metal substrate 11A. After immersion for a predetermined time, the valve metal substrate 11A is removed from the treatment liquid 70 and dried at a predetermined temperature for a predetermined time. By repeating the process of immersion in the treatment liquid 70, removal, and drying a predetermined number of times, the first layer 51 of the solid electrolyte layer 50 is formed.

[0086] For example, the valve metal substrate 11A is immersed in a first dispersion liquid (which may be a liquid containing a polymerizable monomer) containing a first conductive polymer, pulled out, and then dried to form the inner layer of the first layer 51 (a portion provided on the dielectric layer 20 and filling the pores of the valve metal substrate 11). The immersion in the first dispersion liquid, pulling out, and drying may be performed multiple times.

[0087] After forming the inner layer of the first layer 51, the valve metal substrate 11A may be immersed in a solution containing a primer compound, pulled out, and dried to form a primer layer.

[0088] Thereafter, the valve metal substrate 11A is immersed in a second dispersion liquid (which may be a liquid containing a polymerizable monomer) containing the first conductive polymer, pulled out, and then dried to form the outer layer of the first layer 51 (the part that is connected to the inner layer and covers the entire dielectric layer 20).

[0089] When the primer layer is formed, the valve-acting metal substrate 11A is washed with pure water to remove the excess primer compound. After washing, a drying process is performed. Thus, the first layer 51 of the solid electrolyte layer 50 is formed in a predetermined region.

[0090] FIG. 18 is a schematic diagram showing an example of a process for forming the second layer of the solid electrolyte layer.

[0091] After forming the first layer 51 of the solid electrolyte layer 50, for example, as shown in FIG. 18, a treatment liquid for forming a second conductive polymer is applied by dipping method to the region where the second layer 52 (see FIG. 6 etc.) is to be formed. FIG. 18 shows a state in which the treatment liquid 71 for forming the second conductive polymer is supplied to the treatment tank 76.

[0092] As the treatment liquid 71 for forming the second conductive polymer, for example, a dispersion liquid of the second conductive polymer is used. By attaching and drying the dispersion liquid of the second conductive polymer on the outer surface of the first layer 51, a conductive polymer film can be formed. Alternatively, as the treatment liquid 71 for forming the second conductive polymer, a liquid containing a polymerizable monomer, for example, 3,4-ethylenedioxythiophene, and an oxidizing agent, for example, iron(III) p-toluenesulfonate, may be used. By attaching the liquid containing the polymerizable monomer to the outer surface of the first layer 51, a conductive polymer film can be formed by chemical polymerization. This conductive polymer film becomes the second layer 52 of the solid electrolyte layer 50.

[0093] As shown in FIG. 18, by immersing the tip of the valve-acting metal substrate 11A in the treatment liquid 71, the treatment liquid 71 adheres to the outer surface of the first layer 51. After immersion for a predetermined time, the valve-acting metal substrate 11A is pulled out of the treatment liquid 71 and dried at a predetermined temperature and for a predetermined time. By repeating the immersion, pulling out, and drying in the treatment liquid 71 a predetermined number of times, the second layer 52 of the solid electrolyte layer 50 as shown in FIG. 6 is formed.

[0094] Alternatively, a treatment liquid for forming a second conductive polymer (for example, the dispersion liquid of the second conductive polymer or the liquid containing a polymerizable monomer and an oxidizing agent described above) may be discharged onto the outer surface of the first layer 51 by inkjet printing to form the second layer 52 of the solid electrolyte layer 50 in a predetermined region. Thereby, the second layer 52 of the solid electrolyte layer 50 as shown in FIGS. 3, 9, and 12 can be formed.

[0095] After forming the solid electrolyte layer 50, the carbon layer is formed in a predetermined region by immersing, pulling up, and drying the valve-acting metal substrate 11A in the carbon paste.

[0096] After forming the carbon layer, the cathode conductor layer is formed in a predetermined region by immersing, pulling up, and drying the valve-acting metal substrate 11A in a conductive paste containing metal particles such as silver paste.

[0097] Then, the valve-acting metal substrate 11A is cut to separate the element portion 12, and a strip-shaped anode 10 is formed in which the cut surface becomes the base end surface 10b.

[0098] Through the above steps, the electrolytic capacitor element 1 is obtained.

[0099] [Electrolytic Capacitor] Hereinafter, an example of an electrolytic capacitor including the electrolytic capacitor element of the present invention will be described. Note that the electrolytic capacitor element of the present invention may be included in an electrolytic capacitor having other configurations. For example, a lead frame may be used as an external electrode. Further, the electrolytic capacitor may include an electrolytic capacitor element other than the electrolytic capacitor element of the present invention (that is, an electrolytic capacitor element having a structure different from the structure of the electrolytic capacitor element of the present invention).

[0100] FIG. 19 is a perspective view schematically showing an example of an electrolytic capacitor including the electrolytic capacitor element according to the embodiment of the present invention. FIG. 20 is a cross-sectional view taken along the Z-Z line of the electrolytic capacitor shown in FIG. 19.

[0101] In FIGS. 19 and 20, the length direction of the electrolytic capacitor 100 and the exterior body 110 is denoted by L, the width direction by W, and the height direction by T. Here, the length direction L, the width direction W, and the height direction T are perpendicular to each other.

[0102] As shown in FIGS. 19 and 20, the electrolytic capacitor 100 has a substantially rectangular parallelepiped outer shape. The electrolytic capacitor 100 is a solid electrolytic capacitor and includes an exterior body 110, a first external electrode 120, a second external electrode 130, and a plurality of electrolytic capacitor elements 1.

[0103] The exterior body 110 seals a plurality of electrolytic capacitor elements 1. That is, a plurality of electrolytic capacitor elements 1 are embedded in the exterior body 110. Note that the exterior body 110 may seal one electrolytic capacitor element 1. That is, one electrolytic capacitor element 1 may be embedded inside the exterior body 110.

[0104] The exterior body 110 has a substantially rectangular parallelepiped outer shape. The exterior body 110 has a first main surface 110a and a second main surface 110b that face each other in the height direction T, a first side surface 110c and a second side surface 110d that face each other in the width direction W, and a first end surface 110e and a second end surface 110f that face each other in the length direction L.

[0105] As described above, the exterior body 110 has a substantially rectangular parallelepiped outer shape, but it is preferable that the corners and the ridge lines are rounded.

[0106] The exterior body 110 is made of, for example, a sealing resin.

[0107] The sealing resin contains at least a resin, and preferably contains a resin and a filler.

[0108] As the resin, an epoxy resin, a phenol resin, a polyimide resin, a silicone resin, a polyamide resin, a liquid crystal polymer, etc. are preferably used.

[0109] As the filler, silica particles, alumina particles, etc. are preferably used.

[0110] As the sealing resin, a material containing a solid epoxy resin, a phenolic resin, and silica particles is preferably used.

[0111] When a solid sealing resin is used, resin molding such as compression molding or transfer molding is preferably used, with compression molding being more preferred. When a liquid sealing resin is used, molding methods such as dispensing or printing are preferably used. Among these, compression molding is preferred to seal the periphery of the electrolytic capacitor element 1 with the sealing resin to form the exterior body 110.

[0112] The exterior body 110 may be composed of a substrate and a sealing resin provided on the substrate. The substrate is, for example, an insulating resin substrate such as a glass epoxy substrate. In this case, the bottom surface of the substrate forms the second main surface 110b of the exterior body 110. The thickness of the substrate is, for example, 100 μm.

[0113] The multiple electrolytic capacitor elements 1 are stacked in the height direction T via a conductive adhesive 140. The extending direction of each of the multiple electrolytic capacitor elements 1 is approximately parallel to the first main surface 110a and the second main surface 110b of the exterior body 110. The electrolytic capacitor elements 1 are bonded to each other via the conductive adhesive 140.

[0114] The conductive adhesive 140 contains, for example, metal particles such as gold, silver, copper, platinum, etc., and resin, but here, silver is used as the metal particles and acrylic resin is used as the resin. Other examples of the resin contained in the conductive adhesive 140 include urethane resin, epoxy resin, polyimide resin, and phenol resin.

[0115] The first external electrode 120 is provided on the first end surface 110e of the exterior package 110. In Fig. 19, the first external electrode 120 is provided from the first end surface 110e of the exterior package 110 to each of the first main surface 110a, the second main surface 110b, the first side surface 110c, and the second side surface 110d. The first external electrode 120 is electrically connected to the conductive layer 60 of the cathode 40 of the electrolytic capacitor element 1 exposed from the exterior package 110 at the first end surface 110e. The first external electrode 120 may be directly or indirectly connected to the conductive layer 60 at the first end surface 110e of the exterior package 110.

[0116] The second external electrode 130 is provided on the second end surface 110f of the package 110. In Fig. 19, the second external electrode 130 is provided from the second end surface 110f of the package 110 to each of the first main surface 110a, the second main surface 110b, the first side surface 110c, and the second side surface 110d. The second external electrode 130 is electrically connected to the anode 10 (valve metal base 11) of the electrolytic capacitor element 1 exposed from the package 110 at the second end surface 110f. The second external electrode 130 may be directly or indirectly connected to the anode 10 (valve metal base 11) at the second end surface 110f of the package 110.

[0117] It is preferable that the first external electrode 120 and the second external electrode 130 are each formed by at least one method selected from the group consisting of a dip coating method, a screen printing method, a transfer method, an inkjet printing method, a dispensing method, a spray coating method, a brush coating method, a drop casting method, an electrostatic coating method, a plating method, and a sputtering method.

[0118] The first external electrode 120 preferably has a resin electrode layer containing a conductive component and a resin component. When the first external electrode 120 contains a resin component, the adhesion between the first external electrode 120 and the sealing resin of the exterior body 110 is improved, thereby improving reliability.

[0119] The second external electrode 130 preferably has a resin electrode layer containing a conductive component and a resin component. Since the second external electrode 130 contains a resin component, the adhesion between the second external electrode 130 and the sealing resin of the exterior body 110 is enhanced, improving the reliability.

[0120] The conductive component preferably contains, as a main component, a single metal such as silver, copper, nickel, tin, or an alloy containing at least one of these metals.

[0121] The resin component preferably contains, as a main component, an epoxy resin, a phenolic resin, or the like.

[0122] The resin electrode layer is formed by a method such as dip coating, screen printing, transfer printing, inkjet printing, dispensing, spray coating, brush coating, drop casting, electrostatic coating, or the like. Among these, the resin electrode layer is preferably a printed resin electrode layer formed by coating a conductive paste by screen printing. When the resin electrode layer is formed by coating a conductive paste by screen printing, the first external electrode 120 and the second external electrode 130 are more likely to be flat compared to the case where the conductive paste is coated by dip coating. That is, the thicknesses of the first external electrode 120 and the second external electrode 130 are likely to be uniform.

[0123] When the first external electrode 120 has a resin electrode layer, since both the first external electrode 120 and the cathode conductor layer contain a resin component, the adhesion between the first external electrode 120 and the cathode conductor layer is enhanced, improving the reliability.

[0124] At least one of the first external electrode 120 and the second external electrode 130 may have a so-called plating layer formed by a plating method. Examples of the plating layer include a zinc-silver-nickel layer, a silver-nickel layer, a nickel layer, a zinc-nickel-gold layer, a nickel-gold layer, a zinc-nickel-copper layer, a nickel-copper layer, and the like. On these plating layers, for example, a copper plating layer, a nickel plating layer, and a tin plating layer are preferably provided in this order (or except for some plating layers).

[0125] At least one of the first external electrode 120 and the second external electrode 130 may have both a resin electrode layer and a plating layer. For example, the second external electrode 130 may have a resin electrode layer connected to the anode 10 (the valve-acting metal substrate 11) and an outer-layer plating layer provided on the surface of the resin electrode layer. Further, the second external electrode 130 may have an inner-layer plating layer connected to the anode 10 (the valve-acting metal substrate 11), a resin electrode layer provided so as to cover the inner-layer plating layer, and an outer-layer plating layer provided on the surface of the resin electrode layer.

[0126] In the above embodiment, the case where the second layer 52 is formed on the first layer 51 after the first layer 51 is formed has been described. However, the first layer 51 may be formed on the second layer 52 after the second layer 52 is formed. In this case, similar to the first layer 51, it is preferably formed by forming an inner layer (a portion provided on the dielectric layer 20 and filling the pores of the valve-acting metal substrate 11) and then an outer layer (a portion connected to the inner layer and covering the entire dielectric layer 20 in the region) for the second layer 52.

[0127] In the above embodiment, the case where the first layer 51 is disposed over the entire in-plane area of the solid electrolyte layer 50 has been described. However, the first layer 51 may be partially disposed in the plane of the solid electrolyte layer 50. That is, the first layer 51 may be selectively disposed only in a region where the second layer 52 is not disposed in the plane of the solid electrolyte layer 50. In this case, inkjet printing is preferably used as the method for forming the first layer 51.

[0128] Further, in the above embodiment, the case where the electrolytic capacitor element 1 is a solid electrolytic capacitor using a conductive polymer as an electrolyte material has been described. However, the electrolytic capacitor element of the present invention may be a so-called hybrid type electrolytic capacitor element that uses an electrolytic solution in addition to a solid electrolyte such as a conductive polymer as an electrolyte material.

[0129] Also, in the above embodiment, the case where the electrolytic capacitor element 1 is used in the chip-type electrolytic capacitor 100 has been described. However, the electrolytic capacitor element of the present invention may be used, for example, by being embedded in a package substrate included in a semiconductor device. Here, examples of the semiconductor device include a semiconductor composite device in which a voltage regulator (voltage control device) and a load are mounted on a package substrate.

Example

[0130] Hereinafter, examples specifically disclosing the electrolytic capacitor element of the present invention will be shown. Note that the present invention is not limited only to these examples.

[0131] (Example 1) As an anode (valve-acting metal substrate), an aluminum foil having an etching layer on its surface was prepared, and it was immersed in an ammonium adipate aqueous solution and anodized to form a dielectric layer on the surface of the aluminum foil.

[0132] Next, a composition composed of a soluble polyimide siloxane and an epoxy resin was roller-transferred onto the aluminum foil having a dielectric layer formed on its surface, and a mask layer was formed on both main surfaces and both side surfaces of the foil via the dielectric layer.

[0133] Next, an aluminum foil was immersed in a mixed solution of iron(III) p-toluenesulfonate, 3,4-ethylenedioxythiophene, and 1-butanol up to just below the mask layer, pulled out, and then dried. As a result, 3,4-ethylenedioxythiophene was chemically polymerized on the dielectric layer to form a first layer of the solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was p-toluenesulfonate ion. Note that the p-toluenesulfonate ion is incorporated into the first layer from iron(III) p-toluenesulfonate, which is an oxidizing agent used in the chemical polymerization reaction, to become the first dopant.

[0134] Next, only the tip (lower end) of the aluminum foil was immersed in an aqueous solution of ammonium persulfate, pulled out, then immersed in a mixed solution of 3,4-ethylenedioxythiophene and ethanol, pulled out, and then dried to partially form a second layer of the solid electrolyte layer on the first layer (see Fig. 6). The second main chain of the second layer was poly(3,4-ethylenedioxythiophene), and the second dopant of the second layer was sulfate ion. Note that the sulfate ion from ammonium persulfate becomes the second dopant.

[0135] Next, an electrolytic capacitor element was obtained by sequentially forming a carbon layer and a silver layer.

[0136] Four obtained electrolytic capacitor elements were laminated using a conductive adhesive to obtain a laminate. Thereafter, the laminate was sealed using an epoxy resin and diced to form a solid piece. Next, a silver paste containing a resin component was screen-printed on the cathode-side and anode-side end faces of the solidified sealed body to form external electrodes on the cathode and anode, thereby obtaining a finished product of the electrolytic capacitor.

[0137] (Example 2) A finished product of the electrolytic capacitor was obtained in the same manner as in Example 1, except that the formation of the solid electrolyte layer was performed as follows.

[0138] That is, an aluminum foil with a dielectric layer formed on its surface was immersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, pulled out, and then dried to form a first layer of a solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was polystyrene sulfonic acid ions.

[0139] Next, only the tip (lower end) of the aluminum foil was immersed in a mixed solution of iron(III) p-toluenesulfonate, 3,4-ethylenedioxythiophene, and 1-butanol, pulled out, and then dried. Thereby, 3,4-ethylenedioxythiophene was chemically polymerized on the first layer, and a second layer of the solid electrolyte layer was partially formed on the first layer (see Fig. 6). The second main chain of the second layer was poly(3,4-ethylenedioxythiophene), and the second dopant of the second layer was p-toluenesulfonic acid ions. Note that, similar to the case of the first layer, p-toluenesulfonic acid ions are incorporated into the second layer from iron(III) p-toluenesulfonate, which is the oxidizing agent used in the chemical polymerization reaction, to become the second dopant.

[0140] (Example 3) In Example 1, a finished electrolytic capacitor was obtained in the same manner except that the formation of the solid electrolyte layer was performed as follows.

[0141] That is, an aluminum foil with a dielectric layer formed on its surface was immersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, pulled out, and then dried to form a first layer of a solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was polystyrene sulfonic acid ions.

[0142] Next, a polyaniline N-methyl-2-pyrrolidone (NMP) solution containing no second dopant was applied by inkjet printing only to each corner on the tip surface side (lower end side) of the aluminum foil, and dried, thereby partially forming a second layer of the solid electrolyte layer on the first layer (see FIG. 3). Further, by immersing it in an aqueous sodium p-toluenesulfonate solution, it was doped with the second dopant. The second main chain of the second layer was polyaniline, and the second dopant of the second layer was p-toluenesulfonate ions.

[0143] (Example 4) In Example 1, a finished electrolytic capacitor was obtained in the same manner except that the formation of the solid electrolyte layer was performed as follows.

[0144] That is, an aluminum foil having a dielectric layer formed on its surface was immersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, pulled up, and then dried, thereby forming a first layer of the solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was polystyrene sulfonate ions.

[0145] Next, a polyaniline N-methyl-2-pyrrolidone (NMP) solution containing no second dopant was applied by inkjet printing to the tip surface (lower end surface), each side surface, each corner, and each ridge line portion of the aluminum foil, and dried, thereby partially forming a second layer of the solid electrolyte layer on the first layer (see FIG. 9). Further, by immersing it in an aqueous sodium p-toluenesulfonate solution, it was doped with the second dopant. The second main chain of the second layer was polyaniline, and the second dopant of the second layer was p-toluenesulfonate ions.

[0146] (Comparative Example 1) In Example 1, a finished electrolytic capacitor was obtained in the same manner except that the formation of the solid electrolyte layer was performed as follows.

[0147] That is, an aluminum foil with a dielectric layer formed on its surface was immersed in a mixed solution of iron(III) p-toluenesulfonate, 3,4-ethylenedioxythiophene, and 1-butanol. After being pulled out and dried, a first layer of the solid electrolyte layer was formed on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was p-toluenesulfonate ion. The second layer of the solid electrolyte layer was not formed.

[0148] (Comparative Example 2) In Example 1, a finished electrolytic capacitor was obtained in the same manner except that the formation of the solid electrolyte layer was performed as follows.

[0149] That is, an aluminum foil with a dielectric layer formed on its surface was immersed in a mixed solution of iron(III) p-toluenesulfonate, 3,4-ethylenedioxythiophene, and 1-butanol. After being pulled out and dried, a first layer of the solid electrolyte layer was formed on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was p-toluenesulfonate ion.

[0150] Next, the aluminum foil was immersed in an aqueous solution of ammonium persulfate so as to cover the entire first layer. After being pulled out, it was immersed in a mixed solution of 3,4-ethylenedioxythiophene and ethanol. After being pulled out and dried, a second layer of the solid electrolyte layer was formed over the entire area on the first layer. The second main chain of the second layer was poly(3,4-ethylenedioxythiophene), and the second dopant of the second layer was sulfate ion.

[0151] (Comparative Example 3) In Example 1, a finished electrolytic capacitor was obtained in the same manner except that the formation of the solid electrolyte layer was performed as follows.

[0152] Specifically, aluminum foil with a dielectric layer formed on its surface was immersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, pulled out, and then dried to form a first layer of a solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was polystyrene sulfonate ions. A second layer of a solid electrolyte layer was not formed.

[0153] Comparative Example 4 A finished electrolytic capacitor was obtained in the same manner as in Example 1, except that the solid electrolyte layer was formed as follows.

[0154] Specifically, aluminum foil with a dielectric layer formed on its surface was immersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, pulled out, and then dried to form a first layer of the solid electrolyte layer on the dielectric layer. The first main chain of the first layer was poly(3,4-ethylenedioxythiophene), and the first dopant of the first layer was polystyrene sulfonate ions.

[0155] Next, aluminum foil was immersed in a solution of polyaniline in N-methyl-2-pyrrolidone (NMP) so as to cover the entire first layer, and then removed and dried to form a second solid electrolyte layer over the entire first layer. The second main chain of the second layer was polyaniline, and the second dopant of the second layer was paratoluenesulfonate ions.

[0156] The equivalent series resistance (ESR) and leakage current (LC) yield of the finished electrolytic capacitors obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated. The results are shown in Table 1 below. The ESR indicates a relative value to the ESR of the electrolytic capacitor obtained in Comparative Example 1.

[0157] [Table 1]

[0158] In Example 1, the second layer of the solid electrolyte layer covering the tip end (including each corner) of the aluminum foil is doped with sulfate ions that are prone to dedoping, and therefore the LC yield rate is improved compared to Comparative Example 1. Furthermore, in Example 1, the conductive polymer that is prone to dedoping is formed only in a part of the solid electrolyte layer, and therefore the increase in ESR was reduced compared to Comparative Example 2.

[0159] In other examples, the second layer of the solid electrolyte layer, which selectively covers only the areas where leakage current is likely to occur, such as the corners of the tip of the aluminum foil, is doped with a dopant that is likely to be dedoped, thereby achieving a high LC yield rate while suppressing an increase in ESR. [Explanation of symbols]

[0160] 1. Electrolytic capacitor element 10 Anode 10a Tip surface 10b Proximal surface 10c, 10d main surface 10e, 10f side 10g corner 10h, 10ha, 10j ridgeline area 11, 11A Valve metal substrate 12 Element section 13 Support part 20 dielectric layer 30 mask layers 40 cathode 50 Solid electrolyte layer 51 1st layer 52 2nd layer 60 Conductive layer 70, 71 Processing liquid 75, 76 Treatment tank 100 Solid electrolytic capacitor 110 Exterior body 110a 1st main surface 110b 2nd principal surface 110c 1st side 110d 2nd side 110e 1st end face 110f 2nd end face 120 First external electrode 130 Second external electrode 140 Conductive adhesive

Claims

1. An anode composed of a valve-acting metal substrate, having a tip surface and a base surface, a dielectric layer provided on at least one main surface of the anode except at least the base surface, a mask layer composed of an insulating material, provided on the dielectric layer along the base surface, and a cathode provided on the dielectric layer on the tip surface side of the mask layer, comprising: the cathode having a solid electrolyte layer provided on the dielectric layer and a conductive layer provided on the solid electrolyte layer, the solid electrolyte layer including a first layer containing a first conductive polymer doped with a first dopant and a second layer containing a second conductive polymer doped with a second dopant, the second layer being partially disposed in the plane of the solid electrolyte layer, the first layer being disposed at least in a region where the second layer is not disposed in the plane of the solid electrolyte layer, the second conductive polymer being more likely to be dedoped than the first conductive polymer, an electrolytic capacitor element.

2. The anode has six surfaces including the tip surface, the base surface, a pair of main surfaces, and a pair of side surfaces, and has a corner portion where three of the six surfaces intersect and an edge portion where two of the six surfaces intersect, the second layer covering the corner portion formed by the tip surface, the electrolytic capacitor element according to claim 1.

3. The second layer further covers the tip surface and the edge portion formed by the tip surface, the electrolytic capacitor element according to claim 2.

4. The second layer further covers each side surface and the edge portion formed by each side surface, the electrolytic capacitor element according to claim 2 or 3.

5. The second layer is disposed along the mask layer, the electrolytic capacitor element according to claim 1 or 2.

6. The second dopant contained in the second conductive polymer has a smaller molecular size than the first dopant contained in the first conductive polymer, the electrolytic capacitor element according to claim 1 or 2.

7. The first dopant contained in the first conductive polymer is para-toluenesulfonic acid ion, the second dopant contained in the second conductive polymer is sulfate ion, the electrolytic capacitor element according to claim 1 or 2.

8. The first dopant contained in the first conductive polymer is anthraquinonesulfonic acid ion, The second dopant contained in the second conductive polymer is para-toluenesulfonic acid ion, the electrolytic capacitor element according to claim 1 or 2.

9. The first dopant contained in the first conductive polymer is polystyrene sulfonic acid ion, The second dopant contained in the second conductive polymer is para-toluenesulfonic acid ion, the electrolytic capacitor element according to claim 1 or 2.

10. The second main chain contained in the second conductive polymer has the same skeleton as the first main chain contained in the first conductive polymer, the electrolytic capacitor element according to claim 1 or 2.

11. The first main chain and the second main chain are polythiophene, the electrolytic capacitor element according to claim 10.

12. The first main chain contained in the first conductive polymer is polythiophene, The second main chain contained in the second conductive polymer is polypyrrole or polyaniline, the electrolytic capacitor element according to claim 1 or 2.

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