Cathode current collector and electrolytic capacitor

Abstract

The present invention provides an electrolytic capacitor with low ESR, long life, and high reliability, and a cathode current collector capable of realizing such a capacitor. The cathode current collector has an oxide layer made of a valve metal oxide provided on the surface of a cathode substrate, and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer. The organic conductive layer either consists of a dense layer provided on the surface of the oxide layer and a porous layer provided on the surface of the dense layer, or the organic conductive layer consists of a dense layer provided on the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm. The organic conductive layer of the electrolytic capacitor is provided in close contact with the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm.

Description

[Technical Field]

[0001] The present invention relates to a cathode current collector and an electrolytic capacitor. [Background technology]

[0002] In recent years, with the miniaturization and increasing speed of electronic devices, there has been a strong demand in the field of solid electrolyte electrolytic capacitors for small, large-capacity capacitors with low equivalent series resistance (ESR) at high frequencies. Solid electrolyte electrolytic capacitors use a cathode substrate made of a valve metal, an oxide layer made of an oxide of the valve metal formed on the cathode substrate, and a cathode current collector that, if necessary, is further provided on the cathode substrate with an inorganic conductive layer containing an inorganic conductive material. The cathode current collector surface has contact resistance with the electrolyte components, and this contact resistance has a significant effect on the capacitor's ESR.

[0003] Generally, when forming a solid electrolyte layer, a dispersion containing a conductive polymer dispersion is often used. This dispersion can cause problems, particularly by reducing the adhesion between the solid electrolyte layer and the cathode current collector, resulting in increased contact resistance. In particular, in hybrid electrolytic capacitors, the solid electrolyte layer formed using the dispersion tends to retain the electrolyte, and the electrolyte seeps between the solid electrolyte layer and the cathode current collector, reducing adhesion and increasing contact resistance.

[0004] For example, Patent Document 1 proposes that a cathode current collector having an inorganic conductive layer on the surface of a cathode substrate be roughened before the inorganic conductive layer is formed, thereby improving adhesion between the cathode current collector and a solid electrolyte layer. The surface of the inorganic conductive layer is also roughened along the roughened structure formed on the surface of the cathode substrate. The recessed regions on the surface of the inorganic conductive layer are not in contact with the solid electrolyte layer. The electrolyte solution used as the capacitor electrolyte is guided into the recessed regions on the surface of the inorganic conductive layer, thereby improving adhesion between the cathode current collector and the solid electrolyte layer. Furthermore, a hybrid electrolytic capacitor obtained using such a cathode current collector exhibits reduced initial ESR and suppressed increases in ESR after a no-load test.

[0005] Furthermore, for example, Patent Document 2 proposes that a cathode current collector having an oxide layer and an inorganic conductive layer sequentially provided on the surface of a cathode substrate be further provided with an organic conductive layer on the inorganic conductive layer to improve adhesion between the cathode current collector and a solid electrolyte layer. By providing an organic conductive layer with low electrolyte impregnation ability on the surface of the inorganic conductive layer, most of the electrolyte used as the capacitor's electrolyte is retained in the solid electrolyte layer. This improves adhesion between the cathode current collector and the solid electrolyte layer. Furthermore, hybrid electrolytic capacitors obtained using such cathode current collectors exhibit reduced initial ESR and suppressed increases in ESR after load testing.

[0006] Furthermore, for example, Patent Document 3 proposes that in a solid electrolytic capacitor, the impedance in the high frequency range is reduced by using a conductive separator, and further the impedance is reduced by forming an organic conductive layer on the surface of the cathode current collector. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 174806 [Patent Document 2] International Publication No. 2021 / 125182 [Patent Document 3] Japanese Patent Application Publication No. 7-283086 Summary of the Invention [Problem to be solved by the invention]

[0008] As shown in Patent Document 1, by using a cathode current collector having an inorganic conductive layer provided on a roughened cathode substrate, it is possible to improve adhesion to a certain extent with a solid electrolyte layer. However, as described in Patent Document 1, even if the electrolyte solution is guided to the recessed regions on the surface of the inorganic conductive layer where the solid electrolyte layer and the inorganic conductive layer are not in contact, the solid electrolyte layer formed using a dispersion liquid tends to retain the electrolyte solution. Therefore, this does not lead to a fundamental solution to the problem of the electrolyte solution seeping between the solid electrolyte layer and the cathode current collector, resulting in poor adhesion.

[0009] Patent Document 2 discloses that the application of an organic conductive layer to the surface of an inorganic conductive layer improves adhesion between the cathode current collector and the solid electrolyte layer to a certain extent. However, extensive research has revealed that further improvements in performance are possible by optimizing the structure of the organic conductive layer. Specifically, Patent Document 2 states that a dense organic conductive layer with a density within a predetermined range is preferable. However, even when such a dense organic conductive layer is combined with a solid electrolyte layer that easily retains electrolyte, penetration of the electrolyte into the interface between the cathode current collector and the solid electrolyte layer reduces adhesion between the cathode current collector and the solid electrolyte layer, and the problem of contact resistance is considered to be insufficiently resolved. This penetration of the electrolyte into the interface between the cathode current collector and the solid electrolyte layer particularly deteriorates long-life and high reliability. Patent Document 2 also discloses that the thickness of the organic conductive layer is generally 1 to 2,000 nm. However, such a thin organic conductive layer alone cannot sufficiently prevent penetration of the electrolyte into the interface between the inorganic conductive layer and the organic conductive layer, resulting in reduced adhesion between the inorganic conductive layer and the organic conductive layer. The penetration of the electrolyte into the interface between the inorganic conductive layer and the organic conductive layer deteriorates the ESR, particularly at an initial stage. Therefore, in Patent Document 2, the adhesion between the cathode current collector and the solid electrolyte layer, and the adhesion between the inorganic conductive layer and the organic conductive layer within the cathode current collector are not sufficient, and the initial ESR and long life are not highly reliable.

[0010] While Patent Documents 1 and 2 both relate to hybrid electrolytic capacitors that use both solid electrolytes and liquid electrolytes as electrolyte components, the adhesion between the cathode current collector and the solid electrolyte layer is also an issue in solid electrolytic capacitors that do not use liquid electrolytes as electrolyte components. For example, Patent Document 3 shows that an organic conductive layer formed on the surface of the cathode current collector reduces impedance, but does not mention the specific structure of the organic conductive layer. However, as described above, after extensive research, it was found that further improvements in performance could be achieved by optimizing the structure of the organic conductive layer.

[0011] The above-mentioned conventional techniques have problems with contact resistance, namely, (1) there is room for improvement in the rate of change of ESR over time due to deterioration in adhesion between the cathode current collector and the solid electrolyte layer, and (2) there is room for improvement in the initial ESR value due to deterioration in adhesion within the cathode current collector (adhesion between the oxide layer provided on the surface of the cathode substrate and the organic conductive layer, or adhesion between the inorganic conductive layer provided on the surface of the oxide layer and the organic conductive layer).

[0012] The solid electrolyte layer used in electrolytic capacitors that include a cathode current collector with a cathode substrate made of valve metal can be formed using a dispersion liquid containing a dispersion medium and a conductive polymer particle dispersion, or it can be formed by chemical polymerization using a monomer and an oxidizing agent. Chemical polymerization can cause the cathode current collector surface to become acidic during the chemical polymerization of the monomer and the oxidizing agent, resulting in damage.

[0013] Therefore, one object of the present invention is to provide a cathode current collector and an electrolytic capacitor that can improve at least one of the above-mentioned problems of contact resistance and damage to the surface of the cathode current collector. [Means for solving the problem]

[0014] A first aspect of the present invention provides a cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer and a porous layer provided on the surface of the dense layer.

[0015] A second aspect of the present invention provides a cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm.

[0016] In the cathode current collector provided in the first and second aspects of the present invention, an inorganic conductive layer containing an inorganic conductive material may be further provided between the oxide layer and the organic conductive layer, and the dense layer may be provided on a surface of the inorganic conductive layer.

[0017] In the cathode current collectors provided by the first and second aspects of the present invention, the surface of the cathode substrate may be smooth.

[0018] In the cathode current collector provided by the first aspect of the present invention, the porous layer may have a thickness of 2 μm or more and 25 μm or less.

[0019] In the cathode current collector provided by the first aspect of the present invention, the dense layer may have a thickness of 0.02 μm or more and less than 15 μm.

[0020] In the cathode current collector provided by the first aspect of the present invention, the porosity of the porous layer may be 0.1 or more and 0.7 or less.

[0021] In the cathode current collectors provided by the first and second aspects of the present invention, the organic conductive layer may be an electrolytically polymerized film.

[0022] In the cathode current collector provided by the first and second aspects of the present invention, the conductive polymer may be poly(3,4-ethylenedioxythiophene).

[0023] An electrolytic capacitor provided by a third aspect of the present invention contains at least a solid electrolyte as an electrolyte component, and uses a cathode current collector provided by the present invention.

[0024] A fourth aspect of the present invention provides an electrolytic capacitor comprising: a cathode substrate made of a valve metal; a cathode current collector having: an oxide layer made of an oxide of the valve metal provided on the surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer; and at least a solid electrolyte as an electrolyte component, wherein the organic conductive layer is provided in close contact with the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm.

[0025] In the electrolytic capacitor provided by a fourth aspect of the present invention, an inorganic conductive layer containing an inorganic conductive material may be further provided between the oxide layer and the organic conductive layer, and the organic conductive layer may be provided in close contact with the surface of the inorganic conductive layer.

[0026] In the electrolytic capacitor provided by the fourth aspect of the present invention, the surface of the cathode substrate may be smooth.

[0027] In the electrolytic capacitor provided by the fourth aspect of the present invention, the organic conductive layer may be an electrolytic polymerized film.

[0028] In the electrolytic capacitor provided by the fourth aspect of the present invention, the conductive polymer may be poly(3,4-ethylenedioxythiophene).

[0029] The electrolytic capacitors provided by the third and fourth aspects of the present invention may further contain an electrolytic solution as an electrolyte component. [Effects of the Invention]

[0030] The cathode current collector and electrolytic capacitor according to each aspect of the present invention can improve at least one of the contact resistance problems of the prior art. In particular, the cathode current collector and electrolytic capacitor according to each aspect of the present invention can achieve low ESR and high durability in the high-frequency range. Here, the term "high frequency" is not clearly defined and refers to a frequency range that varies depending on the field of application. In the electrical field, high frequency may refer to a frequency range of several kHz to tens of MHz. Although not limited thereto, in certain capacitor fields, high frequency may refer to a frequency range of several kHz to hundreds of kHz. The aspects of the present invention are particularly effective when using a solid electrolyte layer formed using a dispersion liquid, but are also effective when using a solid electrolyte layer formed using chemical polymerization. That is, the cathode current collector and electrolytic capacitor according to each aspect of the present invention can suppress damage to the cathode current collector surface during chemical polymerization by forming an organic conductive layer on the surface of the cathode current collector that prevents penetration of a polymerization solution such as a monomer and an oxidizing agent, thereby achieving low ESR and high durability. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view showing a layer structure of a cathode current collector which is an embodiment according to a first aspect of the present invention. [Figure 2] 1 is a cross-sectional view showing the layer structure of a cathode current collector which is another embodiment relating to the first aspect of the present invention, and FIG. 2 is a cross-sectional view showing the layer structure of a cathode foil which is one embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing the layer structure of a cathode current collector which is an embodiment according to the second aspect of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing the layer structure of a cathode current collector in an electrolytic capacitor that is an embodiment according to a third aspect of the present invention. [Figure 5] 10 is an enlarged cross-sectional photograph of a portion of an organic conductive layer in a cathode current collector that is another embodiment related to the first aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The cathode current collector and electrolytic capacitor of the present invention will be described below with reference to the drawings. Note that the drawings are used for explaining the present invention, and the present invention is not limited to the contents of the drawings. Furthermore, the embodiments and examples disclosed herein are illustrative in all respects, and the scope of the present invention is not limited to these contents. The scope of the present invention includes equivalents to the claims and all modifications within the scope.

[0033] 1. Cathode current collectors 7, 8 and 10 FIG. 1 shows a schematic diagram of a cathode current collector according to one embodiment of the first aspect of the present invention. The cathode current collector 7 includes a cathode substrate 1 made of a valve metal, an oxide layer 2 made of an oxide of the valve metal constituting the cathode substrate 1 and disposed on the surface of the cathode substrate 1, and an organic conductive layer 6 containing a conductive polymer and disposed on the surface of the oxide layer 2. The organic conductive layer 6 includes a dense layer 4 disposed on the surface of the oxide layer 2 and a porous layer 5 disposed on the surface of the dense layer 4. The porous layer 5 has many voids observed in the thickness direction. The dense layer 4 is a denser layer with fewer voids than the porous layer 5. The dense layer 4 has almost no voids. The specific configurations of the dense layer 4 and the porous layer 5 and how to determine their presence or absence will be described in detail later.

[0034] Here, by providing the dense layer 4 on the surface of the oxide layer 2 that is in contact with the organic conductive layer 6, it is possible to ensure adhesion between the oxide layer 2 and the organic conductive layer 6. This is because the dense layer 4 is characterized by being continuously present between the oxide layer 2 and the organic conductive layer 6, which increases the number of contact points between the oxide layer 2 and the organic conductive layer 6 (dense layer 4), thereby reducing the space for substances that deteriorate adhesion to enter between the oxide layer 2 and the organic conductive layer 6. Furthermore, by ensuring adhesion between the oxide layer 2 and the organic conductive layer 6, it is possible to reduce the contact resistance and the initial ESR value.

[0035] Furthermore, by providing the porous layer 5 on the surface of the dense layer 4, i.e., by providing the porous layer 5 on the side where the organic conductive layer 6 contacts the solid electrolyte layer, adhesion between the organic conductive layer 6 and the solid electrolyte layer can be ensured. This is thought to be due to an anchor effect in which the conductive polymer dispersion penetrates into the porous layer 5 during the formation of the solid electrolyte layer, integrating the organic conductive layer 6 and the solid electrolyte layer. Ensuring adhesion between the organic conductive layer 6 and the solid electrolyte layer can suppress an increase in contact resistance due to peeling of the solid electrolyte layer, ensure sufficient adhesion between the cathode current collector 7 and the solid electrolyte layer, and reduce the rate of change in ESR over time.

[0036] The configuration of a cathode current collector according to another embodiment of the first aspect of the present invention is shown schematically in Fig. 2, and a cross-sectional photograph thereof is shown in Fig. 5. Cathode current collector 8 is a cathode current collector having cathode substrate 1 made of a valve metal, oxide layer 2 made of an oxide of the valve metal constituting cathode substrate 1 and provided on the surface of cathode substrate 1, inorganic conductive layer 3 provided on the surface of oxide layer 2, and organic conductive layer 6 containing a conductive polymer provided on the surface of inorganic conductive layer 3, and organic conductive layer 6 has dense layer 4 provided on the surface of oxide layer 2 and porous layer 5 provided on the surface of dense layer 4.

[0037] Here, by providing the dense layer 4 on the surface of the inorganic conductive layer 3 with which the organic conductive layer 6 is in contact, it is possible to ensure adhesion between the inorganic conductive layer 3 and the organic conductive layer 6. This is because the dense layer 4 has the characteristic of being continuously present between the inorganic conductive layer 3 as described above, which increases the number of contact points between the inorganic conductive layer 3 and the organic conductive layer 6 (dense layer 4), thereby reducing the space for substances that deteriorate adhesion to enter between the inorganic conductive layer 3 and the organic conductive layer 6. Furthermore, by ensuring adhesion between the inorganic conductive layer 3 and the organic conductive layer 6, it is possible to reduce the contact resistance and the initial value of ESR.

[0038] Furthermore, by providing porous layer 5 on the surface of dense layer 4, i.e., by providing a porous layer on the side where organic conductive layer 6 contacts the solid electrolyte layer, it is possible to ensure adhesion between organic conductive layer 6 and the solid electrolyte layer. This is also due to the anchor effect described above, and by ensuring sufficient adhesion between cathode current collector 8 and the solid electrolyte layer, it is possible to reduce the rate of change in ESR over time.

[0039] Generally, when a solid electrolyte layer using a conductive polymer dispersion is used, contact resistance problems can occur due to poor adhesion between the cathode current collector and the solid electrolyte layer and / or poor adhesion within the cathode current collector. In contrast, cathode current collectors 7 and 8, which are embodiments of the present invention, have an organic conductive layer 6 with a multilayer structure including a dense layer 4 and a porous layer 5, which are structured appropriately for each interface, thereby at least partially alleviating the contact resistance problem. More specifically, providing the dense layer 4 on the surface of the oxide layer 2 or the inorganic conductive layer 3 improves adhesion within the cathode current collector (i.e., adhesion between the oxide layer and the organic conductive layer provided on the surface of the cathode substrate, or adhesion between the inorganic conductive layer and the organic conductive layer provided on the surface of the oxide layer), thereby reducing the initial ESR value. Furthermore, providing the porous layer 5 on the surface of the dense layer 4 improves adhesion between the cathode current collector and the solid electrolyte layer, thereby suppressing the rate of change in ESR over time.

[0040] The configuration of a cathode current collector according to one embodiment of the second aspect of the present invention is shown schematically in Fig. 3. Cathode current collector 10 includes cathode substrate 1 made of a valve metal, oxide layer 2 made of an oxide of the valve metal constituting cathode substrate 1 and provided on the surface of cathode substrate 1, inorganic conductive layer 3 provided on the surface of oxide layer 2, and organic conductive layer 9 containing a conductive polymer and provided on the surface of inorganic conductive layer 3, where organic conductive layer 9 is a dense layer provided on the surface of inorganic conductive layer 3, and the thickness of organic conductive layer 9 is greater than 2 µm and not greater than 22 µm.

[0041] Here, by providing a dense layer as the organic conductive layer 9 on the surface of the inorganic conductive layer 3 that is in contact with the organic conductive layer 9, it is possible to prevent the conductive polymer dispersion from penetrating into the interface between the inorganic conductive layer 3 and the organic conductive layer 9. Furthermore, by making the thickness of the organic conductive layer 9 greater than 2 μm, it is possible to sufficiently prevent the electrolyte from penetrating into the interface between the inorganic conductive layer 3 and the organic conductive layer 9, ensuring adhesion, sufficiently reducing the initial ESR value, and solving the problem of contact resistance. On the other hand, by making the thickness of the organic conductive layer 9 22 μm or less, it is possible to suppress an increase in ESR due to an increase in the distance between the capacitor electrodes.

[0042] 3 also shows an inorganic conductive layer 3, but the present invention also includes a cathode current collector in which the inorganic conductive layer 3 is not provided. In this case, the relationship between the inorganic conductive layer 3 and the organic conductive layer 9 is replaced by the relationship between the oxide layer 2 and the organic conductive layer 9. In other words, when the inorganic conductive layer 3 is not provided, the organic conductive layer 9 (dense layer) is provided on the surface of the oxide layer 2.

[0043] (1) Cathode substrate 1 The cathode substrate 1 can be any substrate made of a valve metal that is used as a cathode substrate in conventional electrolytic capacitors, without any particular limitation. For example, a foil made of a valve metal such as aluminum, tantalum, niobium, or titanium can be used as the cathode substrate 1, with aluminum foil being particularly preferred. Here, the foil can refer to, but is not limited to, a sheet-like member having a thickness of 200 μm or less.

[0044] The cathode substrate 1 may be either one that has been subjected to a surface roughening treatment such as etching, or one that is smooth and not subjected to a surface roughening treatment. When etching is used as the surface roughening treatment, it may be a known chemical etching method or a known electrolytic etching method. The pits formed by etching may be tunnel pits or spongy pits, or may be a combination of these.

[0045] However, when a roughened cathode substrate is used, the residue of the electrolyte solution during electrolytic polymerization tends to remain in the etched structure, but when the surface is smooth, it is easy to remove by washing and the residue is less likely to remain. Since the residue leads to performance degradation, a smooth cathode substrate is preferred.

[0046] In this context, "smooth" refers to a surface that has not been roughened by etching or other processes, as described above, and the surface may be completely flat, but does not necessarily have to be completely flat. "Smooth" also includes surfaces with slight roughness or undulations due to unavoidable rolling streaks or scars that occur during the foil manufacturing process, such as rolling. The degree of unavoidable rolling streaks or undulations may depend on the finishing roller used in the final rolling step.

[0047] (2) Oxide layer 2 The oxide layer 2 formed on the surface of the cathode substrate 1 may be an anodized film or a natural oxide film. When the oxide layer 2 is an anodized film, it may be a barrier film or a porous film. A known anodization method may be used to form the oxide layer 2, and for example, chemical conversion treatment using a chemical conversion solution such as an aqueous solution of ammonium borate, ammonium adipate, or ammonium phosphate may be used.

[0048] (3) Inorganic conductive layer 3 Whether or not to provide an inorganic conductive layer 3 between the oxide layer 2 and the organic conductive layer 6 can be arbitrarily selected depending on the final configuration of the capacitor to be obtained. For example, conventional solid electrolytic capacitors often use a cathode current collector having an inorganic conductive layer 3 formed as the outermost layer. On the other hand, conventional hybrid electrolytic capacitors use both a cathode current collector having an oxide layer (including an oxide of a valve metal constituting the cathode substrate) formed as the outermost layer and a cathode current collector having an inorganic conductive layer formed as the outermost layer. Therefore, whether or not to provide an inorganic conductive layer can also be arbitrarily selected for the cathode current collector of the present invention.

[0049] The dense layer 4 in the present invention has high adhesion not only to the oxide layer 2 but also to the inorganic conductive layer 3. Therefore, by providing the dense layer 4, it is possible to improve the adhesion between the layer on the cathode substrate 1 side (meaning the oxide layer 2 when the inorganic conductive layer 3 is not provided, or the inorganic conductive layer 3 when the inorganic conductive layer 3 is provided; the same applies hereinafter) and the organic conductive layer 6, regardless of whether the inorganic conductive layer 3 is provided or not, and to obtain the effects of the present invention.

[0050] The inorganic conductive layer 3 may be a single layer, or may be formed of two or more inorganic conductive layers using different inorganic conductive materials.

[0051] The type of inorganic conductive material forming the inorganic conductive layer 3 and the method for forming the inorganic conductive layer 3 include current collector There are no particular limitations as long as sufficient adhesion to the oxide layer in the cathode substrate 1 can be ensured, or ions of the inorganic conductive material can penetrate the oxide layer to firmly adhere to the cathode substrate 1.

[0052] Examples of inorganic conductive materials that can be used include carbon, titanium, aluminum, tantalum, chromium, niobium, vanadium, tungsten, hafnium, copper, platinum, gold, silver, cobalt, nickel, and iron. Examples of forming methods that can be used include vacuum deposition, sputtering, ion plating, CVD (chemical vapor deposition), ALD (atomic layer deposition), coating, electroplating, and electroless plating.

[0053] (4) Organic conductive layer (4-1) Organic Conductive Layer 6 The organic conductive layer 6 in the cathode current collectors 7 and 8 is composed of a dense layer 4 provided on the surface of the layer on the cathode substrate 1 side, and a porous layer 5 provided on the surface of the dense layer 4 and coming into contact with the solid electrolyte layer. The porous layer 5 may have a multilayer structure composed of a plurality of porous layers in which adjacent layers have different porosities.

[0054] On the cathode substrate 1 side, in order to reduce the contact resistance between the layer on the cathode substrate 1 side and the organic conductive layer 6, it is preferable to increase the number of contact points between the layer on the cathode substrate 1 side and the organic conductive layer 6. Because there is an issue with the adhesion between the solid electrolyte layer and the cathode substrate 1, it is necessary to avoid providing contact points between the solid electrolyte layer and the cathode substrate 1. Therefore, in order to reduce the space for the solid electrolyte to get between the layer on the cathode substrate 1 side and the organic conductive layer 6, a dense organic conductive layer (dense layer 4) is formed on the surface of the layer on the cathode substrate 1 side.

[0055] Regarding the organic conductive layer 11 in the electrolytic capacitor described below, in hybrid electrolytic capacitors, the element is fabricated by impregnation with an electrolyte solution. This impregnation with the electrolyte solution is performed after the solid electrolyte layer is formed. That is, in the solid electrolyte layer formation process, a conductive polymer dispersion first penetrates the porous layer 5, and then, through vacuum impregnation, it adheres to the surface of the dense layer 4 formed underneath, reducing voids and making it denser, and becoming integrated with the solid electrolyte layer. Before the solid electrolyte layer was formed, the organic conductive layer 6 consisted of the dense layer 4 and the porous layer 5. This then becomes the organic conductive layer 11, consisting of the dense layer 4 and the porous layer 5, which has reduced voids and become denser.

[0056] On the solid electrolyte layer side, it is preferable to increase the contact area between the organic conductive layer 6 and the solid electrolyte layer by the anchor effect, thereby reducing the resistance between the organic conductive layer 6 and the solid electrolyte layer. Therefore, in the cathode current collectors 7 and 8, which are an embodiment related to the first aspect of the present invention, a porous organic conductive layer (porous layer 5) is formed on the surface of the dense layer 4 as a layer that will come into contact with the solid electrolyte layer.

[0057] For example, Patent Document 2 describes that providing a dense organic conductive layer improves adhesion, but the problem of electrolyte solution penetrating the interface between the cathode current collector and the solid electrolyte layer and deteriorating contact still remains. However, since the solid electrolyte layer retains the electrolyte solution due to the impregnation with the electrolyte solution, there is a risk that the electrolyte solution will penetrate into the interface between the organic conductive layer and the solid electrolyte layer and deteriorate contact. However, in the cathode current collectors 7 and 8 of the present invention, the outermost layer is not smooth but porous, and therefore it is possible to suppress deterioration of contact by the anchor effect.

[0058] The organic conductive layer 6 is preferably an electrolytic polymerized film, since it can be formed with good adhesion on the surface of the layer on the cathode substrate 1 side.

[0059] In the case of a cathode current collector 7 that does not include an inorganic conductive layer 3, an electrolytically polymerized film is formed on the surface of the oxide layer 2. Therefore, electropolymerization is performed using a working electrode that has a power supply layer pre-formed on the surface of the oxide layer 2. The power supply layer can be formed using a known method. For example, a very thin conductive polymer dispersion is pre-coated on the surface of the oxide layer 2. This pre-coated power supply layer may be made of an inorganic conductive material (e.g., manganese dioxide). This pre-coated power supply layer may also be made of an organic conductive material. In the case of an organic conductive material, the pre-coated power supply layer becomes part of the organic conductive layer 6 after subsequent electropolymerization.

[0060] On the other hand, in the case of the cathode current collector 8, the inorganic conductive layer 3 is already formed on the surface of the oxide layer 2. Therefore, the cathode substrate 1 on which the oxide layer 2 and the inorganic conductive layer 3 are formed in this order can be used as a working electrode for electrolytic polymerization.

[0061] The electropolymerized film is formed by constant-current or constant-potential polymerization, in which a cathode substrate 1 having a precoat layer or inorganic conductive layer 3 formed on the surface of an oxide layer 2 and a counter electrode made of platinum or the like are immersed in a polymerization solution containing at least a monomer, a supporting electrolyte, and a solvent, and a voltage is applied between the precoat layer or inorganic conductive layer 3 and the counter electrode. The solvent for electropolymerization is not particularly limited as long as it can dissolve the desired amount of monomer and supporting electrolyte and does not adversely affect the electropolymerization, but water is included. Depending on the electrolysis conditions for electropolymerization, a dense layer 4 or a porous layer 5 can be formed.

[0062] The conductive polymer contained in the organic conductive layer 6 is not particularly limited, and conductive polymers derived from known monomers having π-conjugated double bonds can be used. However, thiophene or its derivatives are preferably used because they provide high conductivity and high-temperature durability. Examples of thiophene derivatives include 3,4-ethylenedioxythiophene, 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, and alkylated ethylenedioxythiophene, which is 3,4-ethylenedioxythiophene modified with an alkyl group. Furthermore, sulfonated polyester can be used as a supporting electrolyte serving as a dopant. The sulfonated polyester is a polymer anion and is incorporated into the polymer of thiophene or its derivative obtained by electrolytic polymerization, functioning as a dopant.

[0063] (4-1-a) Dense layer 4 The dense layer 4 of the organic conductive layer 6 is present at the interface between the organic conductive layer 6 and the oxide layer 2 of the cathode current collector 7, or at the interface between the organic conductive layer 6 and the inorganic conductive layer 3 of the cathode current collector 8. Here, "present at the interface" means that the dense layer 4 is formed by a layer structure that is continuously present between the organic conductive layer 6 and the oxide layer 2 of the cathode current collector 7 or the inorganic conductive layer 3 of the cathode current collector 8.

[0064] The dense layer 4 refers to a layer in which the materials forming the organic conductive layer are bonded so continuously that there is no room for other materials to penetrate into the layer, and there are almost no voids. The term "almost no voids" means that when cross-sections are observed with a scanning electron microscope at a magnification of 50,000 times, the number of voids with a maximum diameter of 20 nm or more observable with the naked eye is less than 5 per 1 μm of thickness in all 10 fields of view.

[0065] Even if there are parts that are not continuous due to the presence of voids, as long as there are no voids that continuously connect the oxide layer 2 of the cathode current collector 7 or the inorganic conductive layer 3 of the cathode current collector 8 to the porous layer 5, and there are no voids with a diameter equal to or greater than the thickness of the dense layer 4 between the oxide layer 2 of the cathode current collector 7 or the inorganic conductive layer 3 of the cathode current collector 8 and the porous layer 5, such a structure is also included in the "continuous layer structure."

[0066] If the surface of the cathode substrate 1 is previously roughened by etching or other such treatment, the organic conductive layer 6 grows to fill the surface of the recesses formed by the roughening treatment. When the organic conductive layer 6 reaches a surface area where no recesses are formed, it grows uniformly on the surface, just as it would if the surface of the cathode substrate 1 were smooth. By adjusting the electrolysis conditions for electropolymerization, the organic conductive layer grown uniformly on the surface can be made almost void-free. Therefore, even if the cathode substrate 1 has previously been roughened, the dense layer 4 prevents the dispersion liquid containing a conductive polymer dispersion serving as a solid electrolyte or the electrolyte from penetrating into the recesses formed from the surface to the interior of the cathode substrate 1 by the roughening treatment.

[0067] In the cathode current collectors 7 and 8, which are embodiments related to the first aspect of the present invention, the thickness of the dense layer 4 is not particularly limited. However, in order to more reliably ensure contact with the layer on the cathode substrate 1 side so as to sufficiently suppress penetration of the dispersion liquid of the conductive polymer that serves as the solid electrolyte, the thickness of the dense layer 4 is preferably equal to or greater than a certain thickness, and is preferably equal to or greater than 0.02 μm.

[0068] However, if the dense layer 4 is too thick, the thermal expansion coefficients of the cathode substrate 1 and the organic conductive layer 6 differ, and therefore peeling of the organic conductive layer 6 due to stress caused by long-term thermal load during use may become a problem, resulting in an increase in ESR. For this reason, the thickness of the dense layer 4 is preferably a certain thickness or less, and is preferably less than 15 μm. The oxide layer 2 of the cathode current collector used in an electrolytic capacitor is generally 0.1 μm or less, and the inorganic conductive layer 3 generally has an average thickness of 3 μm or less, which are sufficiently thin and do not cause peeling due to differences in thermal expansion coefficients.

[0069] Therefore, the thickness of the dense layer 4 is preferably 0.02 μm or more and less than 15 μm, because this can sufficiently and reliably prevent the conductive polymer dispersion from penetrating between the layer on the cathode substrate 1 side and the organic conductive layer 6, and can also more reliably prevent peeling of the organic conductive layer 6 due to long-term thermal load during use.

[0070] The dense layer 4 is preferably an electrolytically polymerized film. The formation of the dense layer 4 and the porous layer 5 is determined by the polymerization conditions.

[0071] Specifically, it is determined by the growth rate (polymerization rate) which represents the electrochemical charge transfer, and if the monomer concentration (the water to organic solvent ratio must also be adjusted) is low, the diffusion of the monomer is rate-limiting, or the polymerization rate is slow, a dense layer 4 is formed.

[0072] On the other hand, if the monomer concentration (the water to organic solvent ratio must also be adjusted) is sufficient and there is no problem with the diffusion of the monomer, increasing the polymerization rate will result in a structure in which fibrous polymers are folded over one another, and porous layer 5 will be formed.

[0073] The dense layer 4 grows to cover the surface of the conductive substrate. However, since the slower the polymerization rate, the longer the manufacturing process and the higher the cost, the more preferably the thickness of the dense layer 4 is 20 nm or more and less than 2.5 μm. Note that, during the electrolytic polymerization process, ions released from the supporting electrolyte are contained as dopants in the organic conductive layer, which is a conductive polymer.

[0074] (4-1-b) Porous layer 5 The porous layer 5 refers to a layer in which the material forming the organic conductive layer is formed with spaces (voids) within the layer that allow other materials to enter, and in which numerous voids are visible to the naked eye in the thickness direction when observed in cross section at 50,000x magnification using a scanning electron microscope. For example, when viewed in cross section as shown in Figure 5, the porous layer has voids within it that extend to the outer surface of the cathode current collector.

[0075] The thickness of the porous layer 5 is not particularly limited, but if it is too thin, a sufficient anchoring effect may not be obtained, and sufficient adhesion may not be obtained. If the thickness of the porous layer 5 is less than 2 μm, the anchoring effect and adhesion tend to be insufficient. Therefore, the thickness of the porous layer 5 is preferably 2 μm or more.

[0076] However, if the porous layer 5 is too thick, the capacitor element size increases, and the distance between the cathode substrate 1 and the anode substrate increases, which may result in an increase in ESR. Furthermore, residues of the electrolyte used in electropolymerization increase the ESR change rate. If the porous layer 5 is thicker than 25 μm, it may be difficult to completely remove the residues in the pores of the porous layer 5 even after washing, which may result in an increase in the ESR change rate. For this reason, the thickness of the porous layer 5 is preferably 25 μm or less.

[0077] Therefore, since a sufficient anchoring effect with the solid electrolyte layer can be obtained, sufficient adhesion with the solid electrolyte layer can be more reliably obtained, and an increase in the ESR change rate due to the residue of the electrolyte solution in the voids of the porous layer 5 can be more reliably suppressed, the thickness of the porous layer 5 is preferably 2 μm or more and 25 μm or less.

[0078] Furthermore, when the conductive polymer that forms the solid electrolyte is impregnated, the conductive polymer is incorporated into the porous layer, and even if the thickness is greater than 12 μm, the anchoring effect remains unchanged. Furthermore, the thicker the porous layer 5, the longer the cleaning process for removing the residual electrolyte solution must be. For these reasons, it is more preferable that the thickness of the porous layer 5 be between 2 μm and 12 μm, inclusive, to ensure sufficient adhesion to the solid electrolyte layer, more reliably suppress an increase in the ESR change rate due to the residual electrolyte solution, and shorten the cleaning process for removing the residual electrolyte solution, i.e., the manufacturing process for the cathode current collectors 7 and 8.

[0079] The porosity of the porous layer 5 is not particularly limited, but if the porosity is too small, the contact area with the solid electrolyte layer becomes too small, resulting in an insufficient anchoring effect and insufficient adhesion. Furthermore, if the cathode current collector 7 or 8 having a low porosity of the porous layer 5 is used in the electrolytic capacitor of the present invention, it becomes difficult to further improve durability. Furthermore, if the porosity is too large, the porous layer 5 is likely to peel off from the dense layer 4, resulting in adhesion problems such as peeling during winding of the element.

[0080] Therefore, the porosity of the porous layer 5 is preferably 0.1 or more and 0.7 or less, because a sufficient anchoring effect with the solid electrolyte layer and sufficient adhesion with the solid electrolyte layer can be obtained, thereby enabling further improvement in durability and suppressing peeling from the dense layer 4. Furthermore, the porosity of the porous layer 5 is more preferably 0.3 or more and 0.7 or less, because the anchoring effect with the solid electrolyte layer can be further enhanced while suppressing peeling from the dense layer 4.

[0081] Here, the anchoring effect of the porous layer 5 on the solid electrolyte layer will be described. In the process of forming the solid electrolyte layer of an electrolytic capacitor, a dispersion containing a conductive polymer that will become the solid electrolyte layer is vacuum-impregnated, and then dried and solidified by heat treatment. During solidification, since the outermost layers of the cathode current collectors 7 and 8 are the porous layer 5, the porous layer 5 shrinks while enclosing the solid electrolyte in the voids, and adheres more firmly to the solid electrolyte layer.

[0082] The porous layer 5 is preferably an electrolytically polymerized film. In the case of electrolytic polymerization, if the monomer concentration (the ratio of water to organic solvent must also be adjusted) is sufficient and there are no problems with monomer diffusion, increasing the polymerization rate will result in a large pore structure, such as an aggregate of fibrous structures. The porosity of the porous layer 5 can be controlled by the drying conditions after forming an organic conductive layer having such a large pore structure. The higher the drying temperature, the lower the porosity, i.e., the lower the porosity. The higher the drying temperature, the lower the porosity, i.e., the higher the porosity. The higher the drying temperature, the lower the porosity and the higher the density of the porous layer 5, resulting in a thinner porous layer 5.

[0083] The porous layer 5 may have a multilayer structure in which adjacent layers have different porosities. The porosity of each layer constituting the porous layer 5 may increase or decrease in order from the side formed on the surface of the dense layer 4. Alternatively, the porosity may alternate between high and low. Furthermore, the porosity of adjacent layers may be the same for some of the layers constituting the porous layer 5, or the porosity of all layers constituting the porous layer 5 may be the same. In other words, the porosity of each layer constituting the porous layer 5 may be set arbitrarily.

[0084] When the porous layer 5 has a multi-layer structure, there is no particular upper limit to the number of layers that constitute the porous layer 5.

[0085] To form porous layer 5 into a multilayer structure in which adjacent layers have different porosities, the layer can be formed by controlling drying conditions in multiple stages or by a multiple-stage manufacturing process with intermediate drying. For example, to improve adhesion to the solid electrolyte layer without deteriorating adhesion to the cathode substrate 1, the porosity of the porous structure can be increased sequentially from the cathode substrate 1 side toward the outer layer by repeatedly performing electrolytic polymerization and subsequent drying, with the drying temperature successively lowered with each repetition.

[0086] (4-2) Organic Conductive Layer 9 The organic conductive layer 9 of the cathode current collector 10, which is one embodiment relating to the second aspect of the present invention, is made of a dense layer provided on the surface of the layer on the cathode substrate 1 side.

[0087] On the cathode substrate 1 side, a dense layer is formed on the surface of the layer on the cathode substrate 1 side to suppress penetration of a conductive polymer dispersion liquid between the layer on the cathode substrate 1 side and the organic conductive layer 9 during impregnation with the conductive polymer that serves as a solid electrolyte. The thickness of the organic conductive layer 9 is set to more than 2 μm to sufficiently suppress penetration of the electrolyte during impregnation. Furthermore, the thickness of the organic conductive layer 9 is preferably 2.5 μm or more, since this can sufficiently reduce the effect of deterioration of adhesion over time due to penetration of the electrolyte.

[0088] However, if the organic conductive layer 9 is too thick, the capacitor element size increases, the distance between the cathode substrate 1 and the anode substrate increases, and the ESR increases. Therefore, the thickness of the organic conductive layer 9 is set to 22 μm or less. Furthermore, if the organic conductive layer 9 is too thick, the thermal expansion coefficients of the cathode substrate and the organic conductive layer differ, which can cause peeling of the organic conductive layer 9 due to stress caused by long-term thermal load during use, resulting in an increase in ESR. Therefore, the thickness of the organic conductive layer 9 is preferably 15 μm or less.

[0089] Therefore, in order to sufficiently suppress the penetration of the conductive polymer dispersion and the electrolyte solution and to suppress an increase in ESR due to the distance between the cathode substrate 1 and the anode substrate, the organic conductive layer 9 is made of a dense layer provided on the surface of the layer on the cathode substrate 1 side, and the thickness of the organic conductive layer 9 is set to more than 2 μm and not more than 22 μm. Furthermore, the thickness of the organic conductive layer 9 is preferably set to be 2.5 μm or more and 15 μm or less, in order to sufficiently reduce the influence of deterioration of adhesion over time due to penetration of the electrolyte solution and to suppress peeling of the organic conductive layer 6 due to long-term thermal load during use.

[0090] The definition of the dense layer in the organic conductive layer 9 is the same as the definition of the dense layer 4 in the organic conductive layer 6. The manufacturing method of the dense layer in the organic conductive layer 9 is also the same as the manufacturing method of the dense layer 4 in the organic conductive layer 6. The evaluation method of the dense layer in the organic conductive layer 9 is also the same as the evaluation method of the dense layer 4 in the organic conductive layer 6.

[0091] 2. About electrolytic capacitors The electrolytic capacitors according to the third and fourth aspects of the present invention are solid electrolytic capacitors or hybrid electrolytic capacitors that use a solid electrolyte containing at least a conductive polymer as an electrolyte component. Note that, with regard to the cathode current collector, only the organic conductive layer will be described here.

[0092] (1) About the anode Any anode used in a conventional electrolytic capacitor can be used without particular limitation. For example, an anode made of a valve metal can be used, which has its surface subjected to a surface enlargement treatment and then anodized to form a dielectric oxide film on the surface of the surface-enlarged anode.

[0093] The anode substrate may be made of, for example, aluminum, tantalum, niobium, or titanium. The anode substrate may be in the form of, for example, a foil or a wire. The anode substrate is preferably aluminum foil.

[0094] Examples of methods that can be used for the surface-enlarging treatment include etching, vapor deposition, and sintering. When the surface-enlarging treatment is etching, it may be chemical or electrochemical. The pits formed by etching may be spongy pits, tunnel pits, or a combination of both. When the surface-enlarging treatment is vapor deposition or sintering, the material of the valve metal particles deposited on the surface of the anode substrate may be the same as or different from the material of the anode substrate.

[0095] As the electrolyte used in the anodizing treatment, for example, an aqueous solution of ammonium adipate, an aqueous solution of ammonium phosphate, or an aqueous solution of ammonium borate can be used.

[0096] (2) Solid electrolyte layer The conductive polymer in the solid electrolyte layer is not particularly limited in type, and a conductive polymer derived from a monomer having a π-conjugated double bond, which is used in conventional electrolytic capacitors, can be used. The conductive polymer may be derived from the same monomer as the conductive polymer contained in the organic conductive layer 6 or 9, or may be derived from a different monomer. However, it is more preferable that the conductive polymer in the solid electrolyte layer, as well as the conductive polymer contained in the organic conductive layer 6 or 9, be poly(3,4-ethylenedioxythiophene), since this provides particularly high conductivity and high-temperature durability.

[0097] Currently, solid electrolyte layers used in electrolytic capacitors with cathode current collectors using valve metal cathode substrates are generally formed using two types of electrolyte layers: one formed using a dispersion containing a dispersion of conductive polymer particles and a dispersion medium, and the other formed using chemical polymerization of a monomer and an oxidizing agent. As described above, the present invention is particularly effective when using a solid electrolyte layer formed using a dispersion, but it is also effective when using chemical polymerization. In other words, a problem with chemical polymerization is that the cathode current collector surface becomes acidic and is damaged during the chemical polymerization of the monomer and oxidizing agent. Therefore, by forming an organic conductive layer on the surface of the cathode current collector that prevents penetration of the polymerization solution, such as the monomer and oxidizing agent, damage to the cathode current collector surface during chemical polymerization can be suppressed, resulting in a low ESR and high durability.

[0098] (3) Electrolyte Electrolytes used in conventional electrolytic capacitors, containing at least a solvent and a solute dissolved therein, can be used, and are appropriately selected depending on the operating temperature and other requirements of the hybrid electrolytic capacitor. Examples of electrolytes include those prepared by dissolving solutes such as benzoates, phthalates, terephthalates, salicylates, tartrates, oxalates, glutarates, adipates, azelates, maleates, fumarates, and citrates in solvents such as γ-butyrolactone, ethylene glycol, diethylene glycol, ethylene glycol monomethyl ether, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, acetonitrile, and water. Examples of salts include quaternary ammonium salts such as ammonium salts, tetramethylammonium salts, and triethylmethylammonium salts; quaternary amidinium salts such as ethyldimethylimidazolinium salts and tetramethylimidazolinium salts; and amine salts such as trimethylamine salts and triethylamine salts. The above solvents may be used alone or in combination. The above solutes may be used alone or in combination of two or more. These electrolyte solutions may contain known additives in addition to the above solvents and solutes.

[0099] (4) Separators Any separator used in conventional electrolytic capacitors can be used without any particular limitation, such as a woven or nonwoven fabric or mixed paper made of cellulose fibers or their derivative resins.

[0100] (5) Capacitors Terminals are connected to the anode and cathode current collector 7, 8, or 10 obtained as described above, respectively, and a capacitor element is formed by arranging the dielectric layer of the anode and the organic conductive layer 6 of the cathode current collector 7 or 8, or the organic conductive layer 9 of the cathode current collector 10, with a separator interposed between them. The capacitor element may be of a wound type or a laminated type. Terminals used in conventional electrolytic capacitors can be used for both the anode terminal and the cathode terminal, without any particular limitation.

[0101] Next, the capacitor element is repaired and then dried. The capacitor element is then impregnated with a dispersion containing conductive polymer particles and dried repeatedly as needed to form a solid electrolyte layer. The resulting capacitor element is then sealed in an exterior case to obtain a solid electrolytic capacitor.

[0102] Here, when a hybrid electrolytic capacitor is obtained, the process is carried out in the same manner as when a solid electrolytic capacitor is obtained up to the formation of a solid electrolyte layer, and then the obtained element is impregnated with an electrolytic solution and then enclosed in an outer case.

[0103] (6) Organic conductive layer 11 in electrolytic capacitor The organic conductive layer 11 in the electrolytic capacitor is provided in close contact with the surface of the oxide layer 2, and the thickness of the organic conductive layer 11 is set to be more than 2 μm and not more than 22 μm. When the inorganic conductive layer 3 is formed on the surface of the oxide layer 2, the organic conductive layer 11 is provided in close contact with the surface of the inorganic conductive layer 3. As a result, the number of contact points between the layer on the cathode substrate 1 side and the organic conductive layer 11 is increased, which reduces the resistance between the layer on the cathode substrate 1 side and the organic conductive layer 11 and also sufficiently suppresses penetration of the dispersion containing the conductive polymer dispersion and the electrolyte. A method for checking whether the organic conductive layer 11 is in close contact with the layer on the cathode substrate 1 side will be described in detail later.

[0104] The structure of the cathode current collector 12 in the electrolytic capacitor of the present invention is shown schematically in FIG. 4. As described above, the process of incorporating the cathode current collector into a capacitor element involves a step of impregnating the capacitor element with a dispersion of a conductive polymer that will form the solid electrolyte layer, followed by a heat treatment. Vacuum impregnation is typically used for the impregnation. During this process, if the organic conductive layer contains a porous layer 5 prior to the formation of the solid electrolyte layer, the porous layer 5 is compressed and adheres to the surface of the underlying dense layer 4, inorganic conductive layer 3, or oxide layer 2, reducing voids and making the porous layer denser. (Note that if the porous layer 5 has a multilayer structure in which adjacent layers have different porosities, all layers constituting the porous layer 5 are compressed, reducing voids and making the porous layer denser.) Therefore, even when the organic conductive layer before the formation of the solid electrolyte layer consists of only the dense layer 4, or when it consists of the dense layer 4 and the porous layer 5 formed on the surface thereof, or when it consists of only the porous layer 5, the organic conductive layer 11 is provided in close contact with the surface of the layer on the cathode substrate 1 side, as shown in the schematic diagram of FIG. 4 .

[0105] In organic conductive layer 11, it is difficult to distinguish between dense layer 4 and porous layer 5 before being incorporated into a capacitor element.

[0106] As described above, after the solid electrolyte layer is formed, the layer is impregnated with an electrolyte solution. To adequately suppress the penetration of the electrolyte solution, which penetrates more easily between the layer on the cathode substrate 1 side and the organic conductive layer 11 than the conductive polymer dispersion liquid that forms the solid electrolyte, the organic conductive layer 11 must have a certain thickness. However, if the organic conductive layer 11 is too thick, the capacitor element size increases, the distance between the cathode substrate 1 and the anode substrate increases, and the ESR increases. Therefore, to adequately suppress the penetration of the electrolyte solution and suppress the increase in ESR due to the distance between the cathode substrate 1 and the anode substrate, the thickness of the organic conductive layer 11 is set to more than 2 μm and not more than 22 μm.

[0107] Furthermore, if the thickness is too thin, the effect of deterioration in adhesion due to permeation of the electrolyte solution over time cannot be sufficiently reduced, whereas if the thickness is too thick, the difference in thermal expansion coefficients between the cathode substrate 1 and the organic conductive layer 11 causes stress-induced peeling of the organic conductive layer 11 due to long-term thermal load during use, resulting in an increase in ESR. Therefore, the thickness of the organic conductive layer 11 is preferably 2.5 μm or more and 15 μm or less, because this can reduce the effect of deterioration in adhesion by suppressing permeation of the electrolyte solution over time and can suppress not only the increase in ESR due to the distance between the cathode substrate 1 and the anode substrate but also the increase in ESR due to long-term thermal load during use.

[0108] The cathode current collector removed by disassembling the capacitor is obtained with a solid electrolyte layer adhered to its surface. Next, the solid electrolyte layer is removed as much as possible by washing. Because the adhesion of the solid electrolyte layer is weaker than that of the organic conductive layer, it is possible to remove only the solid electrolyte layer without removing the solid electrolyte layer incorporated into the organic conductive layer 11. The solid electrolyte layer is removed by washing with water or an organic solvent. The thickness can then be measured using the same method as for the organic conductive layer of the cathode current collector before it is made into a capacitor. The solid electrolyte layer incorporated into the organic conductive layer 11 may be treated as part of the organic conductive layer 11.

[0109] In order to obtain the electrolytic capacitor provided by the fourth aspect of the present invention, if the dense layer 4 in the cathode current collector before being incorporated into the capacitor element is 2 μm or less, it is necessary to further form a porous layer 5, and the thinner the dense layer 4, the thicker the porous layer 5 must be formed.

[0110] 3. Evaluation method (1) Whether or not dense layer 4 is formed A cross-section sample of a cathode current collector with an organic conductive layer formed thereon was prepared using a cross-section polisher before being incorporated into a capacitor element. Ten fields of view were observed under a scanning electron microscope at 50,000x magnification, varying the observation position. The number of voids observable in the image of the layer on the cathode substrate 1 side was then counted for each field of view. If the number of voids with a maximum diameter of 20 nm or more observable in the image was found to be less than five per 1 μm of thickness in all 10 observed fields, it was determined that a dense layer 4 had formed on the cathode substrate 1 side. Here, "a frequency of less than five voids per 1 μm of thickness" refers to the number of voids found within a 1 μm-thick range, measured from the interface between the layer on the cathode substrate 1 side and the organic conductive layer toward the outer surface of the cathode current collector. The dense layer extends up to the uppermost void where the number of voids is found to be five or more per 1 μm of thickness. Furthermore, if five or more voids are present within a range of 1 μm from the interface between the layer on the cathode substrate 1 side and the organic conductive layer, the thickness is reduced by 1 μm toward the cathode substrate 1 side to check the thickness at which the number of voids is less than five, and the portion up to just before the uppermost void at which the number of voids is five or more is regarded as a dense layer.

[0111] If the thickness of the layer formed on the surface of the layer on the cathode substrate 1 side exceeds the thickness that can be captured in one field of view at a magnification of 50,000 times, be sure to check the number of voids in all parts in the film thickness direction by sequentially changing the observation position in the film thickness direction.

[0112] (2) Thickness of dense layer 4 Once the layer on the cathode substrate 1 side is confirmed to be the dense layer 4, its thickness is measured in 10 fields of view at different observation positions using the length measurement function of a scanning electron microscope. Specifically, the number of voids is counted in the film thickness direction from the interface with the layer on the cathode substrate 1 side, and the thickness is measured up to just before the uppermost void where the number of voids with a maximum diameter of 20 nm or more is at a frequency of 5 or more per μm of thickness. The observation magnification used for measuring the thickness is the maximum magnification that can fit the dense layer 4 on the cathode substrate 1 side in one field of view in the film thickness direction. The thickness of the dense layer 4 is determined by averaging the thicknesses in each field of view. Note that the observation positions for the 10 fields of view used to measure the thickness and the 10 fields of view used to confirm whether a dense layer has been formed may be different or the same.

[0113] (3) Presence or absence of porous layer 5 When the layer formed on the surface of the layer on the cathode substrate 1 side is confirmed to be a dense layer 4 and its thickness is measured, the number of voids observable in images of the organic conductive layer formed on the surface of the dense layer 4 is counted in 10 fields of view at different observation positions, as in (1). If the number of voids with a maximum diameter of 20 nm or more observable in images is 5 or more per 1 μm of thickness in all 10 observed fields of view, it is determined that a porous layer 5 has been formed. The presence or absence of a porous layer is determined by the number of voids that fit within a 1 μm thickness when the number of voids is counted sequentially from the boundary with the dense layer 4 in the film thickness direction.

[0114] (4) Thickness of the porous layer 5 Once it has been confirmed that the layer provided on the surface of the dense layer 4 is the porous layer 5, the thickness from the interface between the dense layer 4 and the porous layer 5 to the outer surface of the porous layer 5 is measured in 10 fields of view at different observation positions using the length measurement function of the scanning electron microscope. The observation magnification when measuring the thickness is the maximum magnification in the film thickness direction that can fit the porous layer 5 provided on the surface of the dense layer 4 in one field of view. The thickness of the porous layer 5 is then determined by averaging the thicknesses of the layers confirmed to be the porous layer 5 in each field of view.

[0115] (5) Porosity of the porous layer 5 Here, the porosity of the porous layer 5 is calculated using the film thickness a of the porous layer 5 and the film thickness c of the organic conductive layer (hereinafter referred to as the "compressed densified layer") in which the voids have been compressed and densified. First, the organic conductive layer 6 is compressed in a wet state and dried, thereby crushing the voids in the porous layer 5 and turning the porous layer 5 into a compressed densified layer. Therefore, the change in film thickness before and after compression and densification indicates the degree of porosity. Therefore, a wet cathode current collector 7 or 8 is sandwiched between a separator and a glass plate and dried under pressure at a temperature between 100°C and 150°C, forming a compressed densified layer from the organic conductive layer 6 consisting of the porous layer 5 and the densified layer 4. The thickness of the compressed densified layer thus formed is c The porosity d is defined as the sum of the thickness a of the porous layer determined in (4) and the thickness b of the dense layer determined in (2), minus c, and then divided by the thickness a of the porous layer before compression and densification (Equation 1). d = (a + bc) / a (Equation 1)

[0116] When the porous layer 5 has a multilayer structure in which adjacent layers have different porosities, the overall porosity of the layers can be calculated using the above formula 1. This overall porosity may be treated as the porosity of the porous layer 5.

[0117] To determine whether the porous layer 5 has a multilayer structure in which adjacent layers have different porosities, the void ratio determined by binarizing the image can be used. Specifically, an image of the porous layer 5 is observed at the maximum magnification that can fit all layers on the surface of the cathode substrate 1 in a single field of view in the thickness direction of the porous layer 5. The void ratio of each layer constituting the porous layer 5 is then binarized to determine the void ratio. If there is a layer whose void ratio differs from that of its adjacent layer by 15% or more, the porous layer 5 is determined to have a multilayer structure in which adjacent layers have different porosities. To identify the boundaries between layers, a scanning electron microscope is used to obtain 10,000x images of the entire porous layer 5 in the thickness direction. The images are then binarized in 1-μm squares in the thickness direction to determine the void ratio. If there are any locations where the void ratio changes by 15% or more, the 1-μm squares are further subdivided in the thickness direction to determine the void ratio, and the boundary positions where the void ratio differs by 15% or more are determined. The subdivision is generally at least 0.1 μm (not more than 10 equal divisions). Furthermore, when the film thickness is thinner than 1 μm or when the portion cannot be contained in 1 μm increments, the evaluation is also made by appropriately dividing the film thickness into smaller parts. Note that instead of the porosity calculated using Equation 1, the porosity may be estimated from the ratio of voids in each layer calculated in this manner. Furthermore, the multilayer structure may be expressed by using both the relative comparison of the ratio of voids in each layer and the overall porosity.

[0118] (6) Confirmation of adhesion of the organic conductive layer 11 to the cathode substrate 1 in the electrolytic capacitor The capacitor element is disassembled, and the removed cathode current collector 12 is washed with water or an organic solvent to remove the solid electrolyte, followed by drying. A cross-section polisher is then used to prepare a cross-section sample of the cathode current collector 12 on which the organic conductive layer is formed. Ten fields of view at the interface between the cathode substrate 1 and the organic conductive layer are observed at 50,000x magnification using a scanning electron microscope, varying the observation position. The number of voids present at the interface that can be observed in the image is then confirmed. If the number of voids with a maximum diameter of 20 nm or more that can be observed with the naked eye is less than five per field of view in all 10 observed fields, and if more than 90% of the interface is void-free, the organic conductive layer 11 in the electrolytic capacitor is determined to be in close contact with the cathode substrate 1.

[0119] (7) Thickness of the organic conductive layer 11 in the electrolytic capacitor After disassembling the capacitor element and confirming that the organic conductive layer provided on the cathode current collector 12 is the organic conductive layer 11 provided in close contact with the cathode substrate 1, the thickness is measured in 10 fields of view at different observation positions using the length measurement function of a scanning electron microscope. The thickness of the organic conductive layer 11 is measured in a portion where there is no residue of the solid electrolyte layer. The solid electrolyte layer incorporated into the organic conductive layer 11 is treated as part of the organic conductive layer 11. The observation magnification is the maximum magnification in the film thickness direction that can fit the organic conductive layer 11 in one field of view. The thickness of the organic conductive layer 11 is determined by averaging the thicknesses in each field of view. The observation positions of the 10 fields of view used to measure the thickness and the 10 fields of view used to check adhesion may be different or the same.

[0120] (8) ESR (load test) Before conducting the load test, measure the ESR (initial value) of the electrolytic capacitor at 100kHz. Next, apply the rated voltage to the electrolytic capacitor in a constant temperature bath at 125°C for 2000 hours. After that, return the electrolytic capacitor to room temperature and measure the ESR of the electrolytic capacitor at 100kHz. [Example]

[0121] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples. Wound hybrid electrolytic capacitors with a rated voltage of 35 V and having a cathode current collector as shown in Table 1 were fabricated and evaluated according to the following procedure. In addition, wound solid electrolytic capacitors with a rated voltage of 25 V and having a cathode current collector as shown in Table 2 were fabricated and evaluated.

[0122] Example 1 (1) Preparation of cathode current collector A smooth aluminum foil was used as a cathode substrate to obtain a cathode current collector. A natural oxide film was present on the surface of the cathode substrate. An inorganic conductive layer containing carbon was formed on the natural oxide film by ion plating. 5 g of sulfonated polyester, 785 g of water, 197 g of acetonitrile, and 10 g of 3,4-ethylenedioxythiophene (EDOT) were mixed and stirred, and the mixture was visually confirmed to have not separated into two layers to prepare an electropolymerization solution. Next, the aluminum foil (working electrode) on which the inorganic conductive layer had been formed and a SUS plate counter electrode were immersed in this polymerization solution, and a current of 0.1 mA / cm was applied as the first step. 2 After performing constant current electropolymerization for 2.5 minutes under the conditions of 2 Constant-current electrolytic polymerization was carried out for 14.3 minutes under the conditions of . The working electrode after polymerization was washed with water and then dried at 60°C for 30 minutes to obtain a cathode current collector in which an organic conductive layer was formed on an inorganic conductive layer. The organic conductive layer in the cathode current collector of Example 1 was a PEDOT (poly(3,4-ethylenedioxythiophene)) layer having a 0.2 μm-thick dense layer and a 10.0 μm-thick porous layer, and having a porosity of 0.46. (2) Preparation of the anode An etched aluminum foil was used as the anode substrate for obtaining the anode. This aluminum foil was anodized using an aqueous solution of ammonium adipate as the chemical conversion solution, forming an anodized film (dielectric layer) on the surface of the aluminum foil at a chemical conversion voltage of 56.0 V, thereby obtaining the anode. (3) Preparation of capacitor element Terminals were connected to the anode and cathode current collectors, and the dielectric layer of the anode and the organic conductive layer of the cathode current collector were stacked facing each other with a separator interposed between them, and then wound. Then, an ammonium dihydrogen phosphate solution was used to apply a voltage of 53.0 V and 1 mA / cm. 2 After the anode was repaired and formed under the above conditions for 10 minutes, it was dried at 30°C for 6 hours to obtain a capacitor element. (4) Formation of solid electrolyte layer A dispersion liquid for forming a solid electrolyte layer was obtained by dispersing poly(3,4-ethylenedioxythiophene) microparticles (dispersion) doped with polystyrene sulfonic acid in a dispersion medium of 5% by mass of ethylene glycol in water. The capacitor element was impregnated with the resulting dispersion liquid under a reduced pressure (90 kPa) for 120 seconds and then dried at 150°C for 20 minutes. This dispersion liquid impregnation and drying process was repeated again to obtain a capacitor element with an added solid electrolyte layer. Note that after fabrication of this capacitor element, the organic conductive layer was provided in close contact with the inorganic conductive layer and had a thickness of 5.6 μm. (5) Fabrication of hybrid electrolytic capacitors An electrolyte solution was prepared by dissolving 5% by mass of ammonium borodisalicylate in ethylene glycol. This electrolyte solution was dispensed into the capacitor element with the solid electrolyte layer added, impregnating the solid electrolyte layer with the electrolyte, yielding a capacitor element with a composite electrolyte layer. The resulting element was sealed in an exterior case. Next, a voltage of 35 V was applied at 125°C for 45 minutes to perform an aging treatment, yielding a hybrid electrolytic capacitor with a rated voltage of 35 V. (6) Evaluation of capacitor characteristics As the initial characteristics of the obtained capacitors, ESR was measured at 100 kHz under conditions of 20°C. Next, as a durability test, the capacitors were left under high-temperature conditions of 125°C for 2000 hours, and then ESR was measured again at 100 kHz as the characteristics after the durability test.

[0123] <Example 2> An aluminum foil with spongy etching pits formed was used as a cathode substrate for obtaining a cathode current collector. This aluminum foil was anodized using an aqueous solution of ammonium dihydrogen phosphate as the chemical conversion solution, forming an anodized film (oxide layer) with a chemical conversion voltage of 2.0 V on the surface of the aluminum foil. The aluminum foil with the anodized film formed was dipped into an aqueous dispersion of a conductive polymer (PEDOT) to form a very thin conductive polymer layer on the anodized film. Note that the conductive polymer layer formed by dipping was so thin that it could not be distinguished or measured using a scanning electron microscope, and therefore is not included in the thickness of the organic conductive layer in this invention. Electropolymerization was performed using this conductive polymer layer formed by dipping as a power supply layer in the same manner as in Example 1, to obtain a cathode current collector in which the same PEDOT layer as in Example 1 was formed on the power supply layer as the organic conductive layer. Thereafter, the same procedure as in Example 1 was repeated. Note that after the capacitor element was fabricated (after the solid electrolyte layer was formed, the same applies below), the organic conductive layer was formed in close contact with the oxide layer consisting of the anodized film.

[0124] Example 3 The same procedure as in Example 1 was carried out for constant-current electropolymerization, except that the first stage time was 7.5 seconds. The organic conductive layer in the cathode current collector of Example 3 was a PEDOT layer having a 0.01 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.47. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 5.4 μm.

[0125] Example 4 The same procedure as in Example 1 was carried out for constant-current electropolymerization, except that the first stage time was 22.5 seconds. The organic conductive layer in the cathode current collector of Example 4 was a PEDOT layer having a 0.03 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.47. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 5.4 μm.

[0126] <Example 5> The same procedure as in Example 1 was carried out for constant-current electropolymerization, except that the first stage time was 25 minutes. The organic conductive layer in the cathode current collector of Example 5 was a PEDOT layer having a 2.0 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 7.4 μm.

[0127] Example 6 The same procedure as in Example 1 was carried out for constant-current electropolymerization, except that the first stage time was 37.5 minutes. The organic conductive layer in the cathode current collector of Example 6 was a PEDOT layer having a 3.0 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 8.4 μm.

[0128] Example 7 The same procedure as in Example 1 was carried out, except that the constant-current electrolytic polymerization was carried out for 175 minutes in the first stage, 2.9 minutes in the second stage, and 120 minutes at 50°C for drying after rinsing. The organic conductive layer in the cathode current collector of Example 7 was a PEDOT layer having a 14 μm-thick dense layer and a 2.0 μm-thick porous layer, with a porosity of 0.60. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 14.8 μm.

[0129] Example 8 The same procedure as in Example 7 was carried out for constant-current electropolymerization, except that the first stage time was 200 minutes. The organic conductive layer in the cathode current collector of Example 8 was a PEDOT layer having a 16 μm-thick dense layer and a 2.0 μm-thick porous layer, with a porosity of 0.60. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 16.8 μm.

[0130] Example 9 For constant current electropolymerization, the electropolymerization process was performed in one step instead of two steps, and the current was set at 0.1 mA / cm 2 The same procedure as in Example 1 was carried out, except that the heating was carried out for 26.3 minutes under the conditions of 1. The organic conductive layer in the cathode current collector of Example 9 was a PEDOT layer having a dense layer with a thickness of 2.1 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 2.1 μm.

[0131] Example 10 The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 31.3 minutes. The organic conductive layer in the cathode current collector of Example 10 was a PEDOT layer having a dense layer with a thickness of 2.5 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 2.5 μm.

[0132] Example 11 The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 175 minutes. The organic conductive layer in the cathode current collector of Example 11 was a PEDOT layer having a dense layer with a thickness of 14 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 14 μm.

[0133] Example 12 The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 200 minutes. The organic conductive layer in the cathode current collector of Example 12 was a PEDOT layer having a dense layer with a thickness of 16 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 16 μm.

[0134] Example 13 The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 271 minutes. The organic conductive layer in the cathode current collector of Example 13 was a PEDOT layer having a dense layer with a thickness of 21.7 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 21.7 μm.

[0135] Example 14 The same procedure as in Example 1 was carried out, except that the constant-current electropolymerization time was 25 minutes for the first stage and 2.7 minutes for the second stage. The organic conductive layer in the cathode current collector of Example 14 was a PEDOT layer having a 2.0 μm-thick dense layer and a 1.9 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer and had a thickness of 3.0 μm.

[0136] Example 15 The same procedure as in Example 14 was carried out for constant-current electropolymerization, except that the second stage time was 3.6 minutes. The organic conductive layer in the cathode current collector of Example 15 was a PEDOT layer having a 2.0 μm-thick dense layer and a 2.5 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and had a thickness of 3.4 μm.

[0137] Example 16 The same procedure as in Example 1 was carried out, except that the constant-current electrolytic polymerization was carried out for 6.3 minutes in the first stage and 15.7 minutes in the second stage. The organic conductive layer in the cathode current collector of Example 16 was a PEDOT layer having a 0.5 μm-thick dense layer and an 11.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer and had a thickness of 6.5 μm.

[0138] Example 17 The same procedure as in Example 16 was carried out, except that the second stage of constant-current electropolymerization was carried out for 18.6 minutes. The organic conductive layer in the cathode current collector of Example 17 was a PEDOT layer having a 0.5 μm-thick dense layer and a 13.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 7.6 μm.

[0139] Example 18 The same procedure as in Example 16 was carried out, except that the second stage of constant-current electropolymerization was carried out for 34.3 minutes. The organic conductive layer in the cathode current collector of Example 18 was a PEDOT layer having a 0.5 μm-thick dense layer and a 24.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 13.5 μm.

[0140] Example 19 The same procedure as in Example 16 was carried out, except that the second stage of constant-current electropolymerization was carried out for 37.1 minutes. The organic conductive layer in the cathode current collector of Example 19 was a PEDOT layer having a 0.5 μm-thick dense layer and a 26.0 μm-thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 14.6 μm.

[0141] Example 20 The same procedure as in Example 1 was carried out, except that the first stage of constant-current electropolymerization was carried out for 6.3 minutes and drying after water washing was carried out at 30°C for 120 minutes. The organic conductive layer in the cathode current collector of Example 20 was a PEDOT layer having a 0.5 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.80. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer and had a thickness of 2.5 μm.

[0142] Example 21 The same procedure as in Example 1 was performed, except that drying after water washing was performed at 40°C for 120 minutes. The organic conductive layer in the cathode current collector of Example 21 was a PEDOT layer having a 0.2 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.70. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer and had a thickness of 3.2 μm.

[0143] Example 22 The same procedure as in Example 21 was performed, except that the drying temperature after water washing was 50°C. The organic conductive layer in the cathode current collector of Example 22 was a PEDOT layer having a 0.2 μm thick dense layer and a 10.0 μm thick porous layer, and had a porosity of 0.60. After fabrication of the capacitor element, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 4.2 μm.

[0144] Example 23 The same procedure as in Example 1 was performed, except that the drying temperature after water washing was 120°C. The organic conductive layer in the cathode current collector of Example 23 was a PEDOT layer having a 0.2 μm thick dense layer and a 10.0 μm thick porous layer, and had a porosity of 0.31. After fabrication of the capacitor element, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 7.1 μm.

[0145] Example 24 The same procedure as in Example 1 was performed, except that the drying temperature after water washing was 150°C. The organic conductive layer in the cathode current collector of Example 24 was a PEDOT layer having a 0.2 μm thick dense layer and a 10.0 μm thick porous layer, and had a porosity of 0.14. After fabrication of the capacitor element, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 8.8 μm.

[0146] Example 25 The same procedure as in Example 1 was performed, except that the drying temperature after water washing was 160°C. The organic conductive layer in the cathode current collector of Example 25 was a PEDOT layer having a 0.2 μm-thick dense layer and a 10.0 μm-thick porous layer, with a porosity of 0.05. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer, and its thickness was 9.7 μm.

[0147] Example 26 The same procedure as in Example 1 was carried out, except that pyrrole was used instead of 3,4-ethylenedioxythiophene (EDOT) as the monomer contained in the electropolymerization solution. 0.2 The organic conductive layer was a PPY (polypyrrole) layer having a 10.0 μm thick dense layer and a 10.0 μm thick porous layer, with a porosity of 0.46. After fabrication of the capacitor element, the organic conductive layer was in close contact with the inorganic conductive layer and had a thickness of 5.6 μm.

[0148] <Comparative Example 1> The same procedure as in Example 1 was carried out, except that electropolymerization was not carried out.

[0149] <Comparative Example 2> The same procedure as in Example 2 was carried out, except that electropolymerization was not carried out.

[0150] <Comparative Example 3> The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 2.5 minutes. The organic conductive layer in the cathode current collector of Comparative Example 3 was a PEDOT layer having only a 0.2 μm-thick dense layer. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 0.2 μm.

[0151] <Comparative Example 4> The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 21.3 minutes. The organic conductive layer in the cathode current collector of Comparative Example 4 was a PEDOT layer having a dense layer with a thickness of 1.7 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 1.7 μm.

[0152] <Comparative Example 5> The same procedure as in Example 9 was carried out, except that the constant current electrolytic polymerization time was 289 minutes. The organic conductive layer in the cathode current collector of Comparative Example 5 was a PEDOT layer having a dense layer with a thickness of 23.1 μm. After the capacitor element was fabricated, the organic conductive layer was provided in close contact with the inorganic conductive layer, and its thickness was 23.1 μm.

[0153] Example 27 (1) Fabrication of solid electrolytic capacitors The capacitor element with the added solid electrolyte layer obtained by the same procedure as in Example 1 was sealed in an exterior case. A voltage of 25 V was applied at 125°C and aging treatment was performed for 45 minutes to obtain a solid electrolytic capacitor with a rated voltage of 25 V. (2) Evaluation of capacitor characteristics As the initial characteristics of the obtained capacitors, ESR was measured at 100 kHz under conditions of 20°C. Next, as a durability test, the capacitors were left under high-temperature conditions of 125°C for 2000 hours, and then ESR was measured again at 100 kHz as the characteristics after the durability test.

[0154] Example 28 The capacitor element with the added solid electrolyte layer obtained by the same procedure as in Example 2 was sealed in an exterior case. Thereafter, the same procedure as in Example 27 was carried out.

[0155] <Comparative Example 6> The same procedure as in Example 27 was carried out, except that electropolymerization was not carried out.

[0156] <Comparative Example 7> The same procedure as in Example 28 was carried out, except that electropolymerization was not carried out.

[0157] [Table 1]

[0158] [Table 2]

[0159] (A) Test results for hybrid electrolytic capacitors in Table 1 All of the hybrid electrolytic capacitors produced in the examples in Table 1 had lower initial ESR values ​​and lower ESR change rates after the heat resistance test compared to the comparative examples.

[0160] First, the cathode current collector other than the organic conductive layer will be described.

[0161] The surface condition of the cathode substrate, the structure of the oxide layer, and the presence or absence of an inorganic conductive layer can be examined by comparing Example 1 and Example 2. In Example 1, the surface of the cathode substrate is smooth, the oxide layer is made of a natural oxide film, and an inorganic conductive layer is formed. In Example 2, the surface of the cathode substrate is rough due to the formation of etching pits, the oxide layer is made of an anodic oxide film, and no inorganic conductive layer is formed. The initial ESR value and the ESR change rate were 53.29 in Example 1 and 59.32 in Example 2, and both the initial ESR value and the ESR change rate were lower in Example 1 than in Example 2. Therefore, with respect to the cathode current collector other than the organic conductive layer, it is preferable that the surface of the cathode substrate is smooth, the oxide layer is made of a natural oxide film, and an inorganic conductive layer is formed.

[0162] Next, a cathode current collector before fabrication of a capacitor element (before incorporation into a capacitor element) will be described in the case where the organic conductive layer is composed of a dense layer and a porous layer.

[0163] The organic conductive layer consisting of a dense layer and a porous layer can be examined by comparing Example 1 with Comparative Examples 1 and 3. In Example 1, a dense layer having the same thickness of 0.2 μm as in Comparative Example 3 was formed, followed by a porous layer (thickness: 10 μm, porosity: 0.46). Comparative Example 1 had the same structure as Example 1 and Comparative Example 3, except that an organic conductive layer was not formed. The initial ESR value and ESR change rate were 53.29 for Example 1, 96.95 for Comparative Example 3, and 100.100 for Comparative Example 1. Thus, Example 1 had lower initial ESR value and ESR change rate than Comparative Examples 1 and 3. This demonstrates that the formation of an organic conductive layer consisting of a dense layer and a porous layer can reduce both the initial ESR value and the ESR change rate.

[0164] In an investigation of changes in the thickness of the dense layer, the dense layer thickness increased in the following order: Example 3 (0.01 μm), Example 4 (0.03 μm), Example 1 (0.2 μm), Example 5 (2 μm), Example 6 (3 μm), Example 7 (14 μm), and Example 8 (16 μm). In Examples 1 and 4 to 7, in which the dense layer thickness was 0.02 μm or more but less than 15 μm, the initial ESR value was 61 or less and the ESR change rate was 33 or less. These initial values ​​and rates of change were lower than the initial ESR value of 68 and the ESR change rate of 49 in Example 3, in which the dense layer thickness was 0.01 μm. This indicates that when the dense layer thickness is 0.02 μm or less, penetration of the dispersion liquid cannot be sufficiently suppressed, resulting in problems with adhesion between the cathode substrate and the organic conductive layer, and consequently increasing the initial ESR value and the ESR change rate. On the other hand, Example 8, with a dense layer thickness of 16 μm, had a lower initial ESR value compared to the comparative example, but a higher ESR change rate compared to the other examples. This indicates that when the dense layer thickness is 15 μm or greater, the difference in thermal expansion coefficients between the cathode substrate and the organic conductive layer causes stress-induced peeling of the organic conductive layer due to long-term thermal load during use, resulting in a higher ESR change rate. Furthermore, Examples 6 and 7, with dense layer thicknesses of 3 μm and 14 μm, respectively, had no problems with performance. However, when the organic conductive layer is composed of a dense layer and a porous layer, forming a thick porous layer is advantageous in manufacturing because it provides greater manufacturing efficiency and allows for a thicker film thickness to be achieved in a shorter time. From the perspective of manufacturing tasks, a thinner dense layer is preferable. Therefore, it was found that a dense layer thickness of less than 2.5 μm is preferable. From the above, it was found that the dense layer thickness is preferably 0.02 μm or more and less than 15 μm, and more preferably 0.02 μm or more and less than 2.5 μm.

[0165] In the study of varying the thickness of the porous layer, the porous layer thickness increased in the following order: Example 14 (1.9 μm), Example 15 (2.5 μm), Example 1 (10 μm), Example 16 (11 μm), Example 17 (13 μm), Example 18 (24 μm), and Example 19 (26 μm). In Examples 1 and 15 to 18, in which the porous layer thickness was 2 μm or more and 25 μm or less, the ESR change rate was 33 or less, which was lower than the ESR change rate of 54 in Examples 14 and 19, in which the porous layer thickness was 1.9 μm and 26 μm, respectively. On the other hand, in Examples 14 and 19, in which the porous layer thickness was 1.9 μm and 26 μm, respectively, the ESR change rate was lower than that of the comparative example, but higher than that of the other Examples. This indicates that a porous layer thickness less than 2 μm does not provide a sufficient anchoring effect with the solid electrolyte layer. Furthermore, it was found that if the thickness of the porous layer is greater than 25 μm, it becomes difficult to completely remove the residual electrolyte solution used in the electrolytic polymerization, which adversely affects the ESR, from the pores of the porous layer. Furthermore, in Examples 17 and 18, in which the thickness of the porous layer was 12 μm or more and 25 μm or less, there was no problem with the ESR change rate, but the anchoring effect with the solid electrolyte layer remained unchanged, but the manufacturing task of cleaning the residual electrolyte solution from the porous layer was found to be longer. From the above, it was found that the thickness of the porous layer is preferably 2 μm or more and 25 μm or less, and more preferably 2 μm or more and 12 μm or less.

[0166] In the study of varying porosity, the porosity, i.e., the porosity, decreased in the following order: Example 20 (0.8), Example 21 (0.7), Example 22 (0.6), Example 1 (0.46), Example 23 (0.31), Example 24 (0.14), and Example 25 (0.05). Furthermore, in Examples 1 and 21 to 24, where the porosity was 0.1 to 0.7, the ESR change rate was 41 or less, which was lower than the ESR change rates of 51 and 52 for Examples 20 and 25, where the porosity was 0.8 and 0.05, respectively. Furthermore, in Examples 1 and 21 to 23, where the porosity was 0.3 to 0.7, the ESR change rate was particularly low (31 or less). From the above, it was found that the porosity is preferably 0.1 to 0.7, more preferably 0.3 to 0.7.

[0167] From the above, it was found that the initial ESR value and the ESR change rate can be kept low by configuring the organic conductive layer structure to consist of a dense layer and a porous layer formed on top of it.

[0168] It was found that by making the dense layer 0.02 μm or more and less than 15 μm thick, sufficient contact with the substrate can be ensured, and by making the porous layer 0.1 to 0.7 in porosity and 2 to 25 μm in thickness, a sufficient anchor effect with the solid electrolyte layer can be obtained, and in particular, the initial ESR value and ESR change rate can be kept low, making it possible to maintain good adhesion between the cathode current collector and the solid electrolyte layer when a load is applied.

[0169] The dense layer preferably has a certain thickness to ensure contact with the layer on the cathode substrate 1 side. However, since this lengthens the manufacturing process, it is preferable to make the dense layer as thin as possible and to form a thick porous layer, which allows for high manufacturing efficiency and the formation of a thick organic conductive layer in a short time. The porous layer must be thick enough to achieve an anchoring effect and to suppress the penetration of the electrolyte into the capacitor element. However, it is preferable for the thickness to be within a range that allows the electrolyte residue in the porous layer to be easily removed by washing. Furthermore, the porosity is preferably such that it provides high adhesion to the dense layer and a sufficient anchoring effect with the solid electrolyte layer. Based on the above, an example of an optimal combination of a dense layer and a porous layer may include a dense layer thickness of 0.02 μm to 0.5 μm, a porous layer thickness of 3 μm to 12 μm, and a porosity of 0.3 to 0.7.

[0170] In Example 26, the organic conductive layer was formed by electrolytic polymerization of pyrrole instead of EDOT as a monomer. Among the examples, Examples 1 and 26 have relatively similar geometric structures of the organic conductive layer, but when compared, Example 1, which had a PEDOT layer, exhibited a lower ESR change rate after the heat resistance test. From the above, it was found that PEDOT is the preferred component of the organic conductive layer.

[0171] Next, a cathode current collector before fabrication of a capacitor element will be described in the case where the organic conductive layer is a dense layer and has a predetermined thickness.

[0172] In an investigation in which the thickness of the organic conductive layer (dense layer only) was varied, the dense layer thickness increased in the following order: Comparative Example 3 (0.2 μm), Comparative Example 4 (1.7 μm), Example 9 (2.1 μm), Example 10 (2.5 μm), Example 11 (14 μm), Example 12 (16 μm), Example 13 (21.7 μm), and Comparative Example 5 (23.1 μm). In Examples 9 to 13, in which the organic conductive layer had a thickness of more than 2 μm and not more than 22 μm, the initial ESR value was 70 or less, which was lower than the initial ESR value of 84 or more in Comparative Examples 3 to 5, in which the dense layer had a thickness of not more than 2 μm or more than 22 μm. This indicates that if the organic conductive layer is a dense layer and its thickness is 2 μm or less, the penetration of the electrolyte cannot be sufficiently suppressed, and the adhesion between the inorganic conductive layer (an inorganic conductive layer was formed in all of the above examples, but if no inorganic conductive layer was formed, an oxide layer was used) and the organic conductive layer is insufficient. Furthermore, if the thickness is greater than 22 μm, the distance between the cathode substrate and the anode substrate becomes too long, and the effect of the increased ESR cannot be ignored.

[0173] Furthermore, among the above examples, Example 9 (2.1 μm) had a relatively high initial ESR value (70). This indicates that if the thickness of the organic conductive layer is thinner than 2.5 μm, the permeation of the electrolyte over time cannot be sufficiently suppressed even when the layer is left at room temperature without load.

[0174] Furthermore, in Examples 12 and 13, in which the thickness of the organic conductive layer was more than 15 μm, there was no problem with the initial ESR value, but the ESR change rate was higher than in the other Examples. This indicates that, because the thermal expansion coefficients of the cathode substrate and the organic conductive layer differ, peeling of the organic conductive layer due to stress caused by long-term thermal load during use becomes a problem, resulting in an increase in ESR.

[0175] From the above, it was found that when the organic conductive layer is made of a dense layer, the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm, and preferably 2.5 μm or more and 15 μm or less.

[0176] In Comparative Examples 3 and 4, similar to Patent Document 2, only a dense layer was formed as an organic conductive layer on the surface of an inorganic conductive layer, with a thickness within the range disclosed in Patent Document 2. Examples 1, 3 to 8, and 14 to 26, in which a porous layer was further formed on the surface of a dense layer as an organic conductive layer, had lower initial ESR values ​​and ESR change rates after a heat resistance test than Comparative Examples 3 and 4. Furthermore, Examples 9 to 13, in which only a dense layer was formed as an organic conductive layer with a thickness within the range of more than 2 μm and 22 μm, had lower initial ESR values ​​and ESR change rates after a heat resistance test than Comparative Examples 3 and 4.

[0177] From the above, it was found that the present invention, in which the organic conductive layer on the cathode current collector before fabrication of a capacitor element consists of a dense layer and a porous layer provided on the surface of the dense layer, can further improve the adhesion within the cathode current collector (adhesion between the oxide layer or inorganic conductive layer and the organic conductive layer) and the adhesion between the cathode current collector and the solid electrolyte layer, thereby solving the problem of contact resistance.Furthermore, it was found that the present invention, in which the organic conductive layer on the cathode current collector before fabrication of a capacitor element consists of a dense layer with a thickness of more than 2 μm and 22 μm or less, can further improve the adhesion within the cathode current collector (adhesion between the oxide layer or inorganic conductive layer and the organic conductive layer), thereby solving the problem of contact resistance.

[0178] Next, the organic conductive layer in the electrolytic capacitor after the capacitor element is fabricated will be described.

[0179] Focusing on the thickness of the organic conductive layer, Comparative Examples 3 and 4, which were thinner than 2 μm, and Comparative Example 5, which was thicker than 22 μm, had larger initial ESR values ​​and ESR change rates after heat resistance tests than Examples 1, 3, and 25. Furthermore, Example 9, which was thinner than 2.5 μm, and Examples 8, 12, and 13, which were thicker than 15 μm, had larger ESR change rates than the other Examples. Those with a thickness of 2.5 μm to 15 μm had particularly low initial ESR values ​​and ESR change rates. For the same reasons as those found from the results of Examples 9 to 13 and Comparative Examples 3 and 4, in which the organic conductive layer before capacitor element fabrication consisted only of a dense layer, it was found that the thickness of the organic conductive layer in electrolytic capacitors should be greater than 2 μm and less than 22 μm, preferably greater than 2.5 μm to 15 μm.

[0180] (B) Test results for solid electrolytic capacitors in Table 2 In the examples of Table 2, the initial ESR value and the rate of change in ESR after the heat resistance test were kept low compared to the comparative examples of Table 2.

[0181] As in the results for the hybrid electrolytic capacitor (A) where the organic conductive layer is composed of a dense layer and a porous layer, in the solid electrolytic capacitor, the organic conductive layer obtained in the examples has a dense layer formed on the side in contact with the oxide layer or inorganic conductive layer, and a porous layer formed on the side in contact with the solid electrolyte layer. This improves the adhesion within the cathode current collector and between the cathode current collector and the solid electrolyte layer, achieving a low ESR and suppressing the rate of change in ESR after the heat resistance test. [Industrial Applicability]

[0182] The present invention can be applied to an electrolytic capacitor that uses a solid electrolyte containing at least a conductive polymer as an electrolyte component.

[0183] [Note] The present disclosure discloses the following configurations. [Configuration 1] A cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer and a porous layer provided on the surface of the dense layer. [Configuration 2] 2. The cathode current collector according to claim 1, further comprising an inorganic conductive layer containing an inorganic conductive material between the oxide layer and the organic conductive layer, and the dense layer is provided on a surface of the inorganic conductive layer. [Configuration 3] 3. The cathode current collector according to claim 1, wherein the surface of the cathode substrate is smooth. [Configuration 4] 4. The cathode current collector according to any one of configurations 1 to 3, wherein the porous layer has a thickness of 2 μm or more and 25 μm or less. [Configuration 5] Any of configurations 1 to 4, wherein the thickness of the dense layer is 0.02 μm or more and less than 15 μm. Kaichi The cathode current collector according to any one of the preceding claims. [Configuration 6] 6. The cathode current collector according to any one of configurations 1 to 5, wherein the porosity of the porous layer is 0.1 or more and 0.7 or less. [Configuration 7] 7. The cathode current collector according to any one of configurations 1 to 6, wherein the organic conductive layer is an electrolytically polymerized film. [Configuration 8] 8. The cathode current collector according to any one of configurations 1 to 7, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene). [Configuration 9] 1. A cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm. [Configuration 10] 10. The cathode current collector according to claim 9, wherein an inorganic conductive layer containing an inorganic conductive material is further provided between the oxide layer and the organic conductive layer, and the dense layer is provided on a surface of the inorganic conductive layer. [Configuration 11] 11. The cathode current collector according to aspect 9 or 10, wherein the surface of the cathode substrate is smooth. [Configuration 12] 12. The cathode current collector according to any one of configurations 9 to 11, wherein the organic conductive layer is an electrolytically polymerized film. [Configuration 13] 13. The cathode current collector according to any one of aspects 9 to 12, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene). [Configuration 14] 14. An electrolytic capacitor using the cathode current collector according to any one of aspects 1 to 13, which contains at least a solid electrolyte as an electrolyte component. [Configuration 15] 15. The electrolytic capacitor according to claim 14, further comprising an electrolytic solution as the electrolyte component. [Configuration 16] a cathode current collector having a cathode substrate made of a valve metal, an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate, and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer; At least a solid electrolyte as an electrolyte component; An electrolytic capacitor comprising: An electrolytic capacitor, characterized in that the organic conductive layer is provided in close contact with the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and 22 μm or less. [Configuration 17] 17. The electrolytic capacitor according to claim 16, further comprising an inorganic conductive layer containing an inorganic conductive material between the oxide layer and the organic conductive layer, the organic conductive layer being provided in close contact with the surface of the inorganic conductive layer. [Configuration 18] 18. The electrolytic capacitor according to claim 16 or 17, wherein the surface of the cathode substrate is smooth. [Configuration 19] 19. The electrolytic capacitor according to any one of aspects 16 to 18, wherein the organic conductive layer is an electrolytic polymerized film. [Configuration 20] 20. The electrolytic capacitor according to any one of aspects 16 to 19, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene). [Configuration 21] 21. The electrolytic capacitor according to any one of aspects 16 to 20, further comprising an electrolytic solution as the electrolyte component. [Explanation of symbols]

[0184] 1 Cathode substrate 2. Oxide layer 3. Inorganic conductive layer 4 Layer compacta 5 Porous layer 6, 9, 11 Organic conductive layer 7, 8, 10, 12 Cathode current collector

Claims

1. 1. A cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer and a porous layer provided on the surface of the dense layer.

2. 1. A cathode current collector comprising: a cathode substrate made of a valve metal; an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate; and an organic conductive layer containing a conductive polymer provided on the surface of the oxide layer, wherein the organic conductive layer comprises a dense layer provided on the surface of the oxide layer, and the thickness of the organic conductive layer is more than 2 μm and not more than 22 μm.

3. 3. The cathode current collector according to claim 1, further comprising an inorganic conductive layer containing an inorganic conductive material between the oxide layer and the organic conductive layer, and the dense layer is provided on a surface of the inorganic conductive layer.

4. 3. The cathode current collector according to claim 1, wherein the surface of the cathode substrate is smooth.

5. The cathode current collector according to claim 1 , wherein the porous layer has a thickness of 2 μm or more and 25 μm or less.

6. The cathode current collector according to claim 1 , wherein the dense layer has a thickness of 0.02 μm or more and less than 15 μm.

7. The cathode current collector according to claim 1 , wherein the porous layer has a porosity of 0.1 or more and 0.7 or less.

8. The cathode current collector according to claim 1 , wherein the organic conductive layer is an electrolytically polymerized film.

9. 3. The cathode current collector according to claim 1, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene).

10. 3. An electrolytic capacitor using the cathode current collector according to claim 1 or 2, which contains at least a solid electrolyte as an electrolyte component.

11. The electrolytic capacitor according to claim 10 , further comprising an electrolyte solution as the electrolyte component.

12. a cathode current collector having a cathode substrate made of a valve metal, an oxide layer made of an oxide of the valve metal provided on a surface of the cathode substrate, and an organic conductive layer containing a conductive polymer provided on a surface of the oxide layer; At least a solid electrolyte as an electrolyte component; An electrolytic capacitor comprising: the organic conductive layer is composed of a dense layer provided on the surface of the oxide layer and a porous layer provided on the surface of the dense layer, or is composed of a dense layer provided on the surface of the oxide layer; 1. An electrolytic capacitor, comprising: the organic conductive layer provided in intimate contact with a surface of the oxide layer; and a thickness of the organic conductive layer ranging from more than 2 μm to 22 μm.

13. 13. The electrolytic capacitor according to claim 12, further comprising an inorganic conductive layer containing an inorganic conductive material between the oxide layer and the organic conductive layer, the organic conductive layer being provided in close contact with a surface of the inorganic conductive layer.

14. 13. The electrolytic capacitor according to claim 12, wherein the surface of the cathode substrate is smooth.

15. The electrolytic capacitor according to claim 12 , wherein the organic conductive layer is an electrolytic polymerized film.

16. 13. The electrolytic capacitor of claim 12, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene).

17. The electrolytic capacitor according to claim 12 , further comprising an electrolyte solution as the electrolyte component.

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