Electrode material, cathode foil for electrolytic capacitor, and electrolytic capacitor

Abstract

The present invention realizes an electrode material or the like that can be used for a cathode foil or the like for an electrolytic capacitor, the electrode material or the like having all the advantages of having good adhesion to a conductive polymer and low interfacial contact resistance, having a layer (geometric structure / surface modification) for holding the conductive polymer and an electrolytic solution, being excellent in resistance to deterioration due to a solid electrolyte, an electrolytic solution, and moisture, having no or a low capacitance component and behaving as a low-resistance conductor (exhibiting no or low combined capacitance), being capable of being thinned, being low in cost, and being less likely to cause winding deviation.SOLUTION: Provided is an electrode material including an oxide layer on a smooth substrate, and further including an inorganic conductive layer on the oxide layer, in which the inorganic conductive layer includes a first conductive layer containing a metal and / or a metal compound and a second conductive layer containing carbon, the first conductive layer has an uneven portion on a surface layer side thereof, and the second conductive layer is located on an outermost layer of the inorganic conductive layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode material, in particular to a cathode foil for an electrolytic capacitor that can be used in electrolytic capacitors such as solid electrolytic capacitors and hybrid capacitors, and to an electrolytic capacitor. [Background technology]

[0002] The functions and characteristics required for the cathode of a hybrid capacitor are as follows: (i) It has good adhesion to the conductive polymer and low contact resistance at the interface. (ii) There is a layer (geometric structure / surface modification) to hold the conductive polymer and electrolyte. (iii) Resistance to degradation caused by solid electrolytes, chemical polymerization chemicals, electrolytes, and moisture. (iv) It has no capacitance or a low capacitance and behaves as a low-resistance conductor. (v) Thinning is feasible. (vi) Low cost. These are among the above (ii) and (iii), and apart from compatibility with the electrolyte, these are extremely important functions and properties for the cathode of a solid electrolytic capacitor.

[0003] For example, a foil with a smooth titanium layer and a smooth carbon layer on top of it exhibits poor adhesion (i), particularly with aqueous conductive polymer dispersions, and poor electrolyte retention (ii), making it difficult to maintain a healthy doped state of the conductive polymer, resulting in high resistance when fabricated into a device. Chemically etched cathode foils are difficult to miniaturize due to their thickness, and when combined with an anode to form a capacitor, they generate combined capacitance, resulting in a low anode capacitance extraction rate. Furthermore, while the ESR (equivalent series resistance) is low at high frequencies such as 100 kHz, it significantly increases at low frequencies such as 120 Hz, resulting in a narrow frequency range for low ESR. The high contact resistance with the conductive polymer and the electrolyte-dependent portions of the foil not covered by the conductive polymer raise concerns about low-temperature performance. Furthermore, there is a risk of localized chemical transformation of the cathode foil during the aging anodization process after device fabrication, which could result in reduced capacity and increased resistance. For example, a chemical conversion coating applied to an aluminum substrate provides a certain level of protection against electrolytes. However, it is difficult to completely prevent chemical reactions with the chemical polymerization solution for the conductive polymer or the acidic electrolyte used to maintain the conductive polymer in a doped state, or with traces of moisture and other substances present in the substrate. On the other hand, if a natural oxide coating or a chemical conversion coating comes into direct contact with a conductive polymer in its intact state, a depletion layer will form at the contact interface, resulting in high contact resistance.

[0004] Foils with an intermediate layer (titanium layer) and a carbon layer applied to a chemically etched foil are thin, and the etched layer can hold the conductive polymer and electrolyte. However, it is difficult to completely coat the interior of the etched layer with titanium or carbon layers, and an aluminum oxide layer is required to protect it from the electrolyte, conductive polymer, and chemical polymerization chemicals (for example, a chemical conversion coating of several volts is required). This chemical conversion coating layer also functions to protect from the electrolyte, as described above, but it also behaves as an insulator if left untreated, which is likely to cause high resistance. It can be said that many of these problems also apply to solid electrolytic capacitors that do not use an electrolyte and whose electrolyte is made solely of conductive polymer.

[0005] Various cathode foils have been developed for use in electrolytic capacitors such as solid electrolytic capacitors and hybrid capacitors. Patent documents 1 and 3 describe electrolytic capacitors in which an inorganic conductive layer is formed on the surface of a cathode foil that has been roughened by etching (surface expansion ratio 1.5 to 500 times). However, these cathode foils have the following problems: When using an etched substrate, which is a smooth substrate with an enlarged surface due to etching, it is difficult for the inorganic conductive layer material to reach the inside of the etched layer, and it is difficult to completely cover the inside of the etched layer with the inorganic conductive layer material, so there will be areas where the aluminum, a component of the substrate, is exposed. The exposed aluminum surface has a coating of aluminum oxide, which is an insulator and therefore has high resistance. Exposed aluminum has poor chemical resistance and has problems with durability against polymers and electrolytes. - Because the substrate is dissolved by etching, there are significant issues with regard to handling strength, thin foil production, residual chlorine, waste liquid treatment, and manufacturing costs. There are problems such as:

[0006] Patent Document 4 describes a cathode foil for an aluminum electrolytic capacitor, which comprises a first layer made of at least one of a metal and its nitride, carbide, carbonitride, and oxide formed on the surface of an aluminum foil, and a second layer made of at least one of a metal and its nitride, carbide, carbonitride, and oxide formed on the first layer, the first layer having a denser structure than the second layer. However, the invention described in Patent Document 4 is primarily aimed at improving hydration resistance as a cathode for a capacitor using only an electrolyte containing water, and there is room for improvement in reducing the resistance and improving the durability of cathodes that can be used in electrolytic capacitors such as hybrid capacitors and solid electrolytic capacitors.

[0007] Patent Document 2 describes a cathode foil for a hybrid capacitor that uses a smooth substrate on which a carbon layer is formed. Patent Document 5 describes a cathode foil for a solid electrolytic capacitor that uses a smooth substrate on which carbon exists on a metal layer. However, because the surface layer of these cathode foils does not have any irregularities, it is believed that there is room for further improvement in ESR and durability. Furthermore, because the surface layer of the cathode foil does not have any irregularities, the frictional force with the separator paper (isolating paper) is weak. When the winding core jig is removed during the element winding process of an electrolytic capacitor, the cathode foil is prone to popping out in the direction of the winding core jig, resulting in winding misalignment. Other prior art technologies include Patent Documents 6 to 24, but it is believed that there is room for improvement in function and performance in all of them. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 174806 [Patent Document 2] International Publication No. 2016 / 174807 [Patent Document 3] International Publication No. 2016 / 189779 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-022707 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-174865 [Patent Document 6] International Publication No. 2017 / 090241 [Patent Document 7] Japanese Patent Application Publication No. 2019-179884 [Patent Document 8] Japanese Patent Application Laid-Open No. 2007-243203 [Patent Document 9] Japanese Patent Application Laid-Open No. 2015-073015 [Patent Document 10] Japanese Patent Application Publication No. 2019-179884 [Patent Document 11] U.S. Patent No. 10,896,783 [Patent Document 12] International Publication No. 2021 / 107063 [Patent Document 13] International Publication No. 2012 / 115050 [Patent Document 14] Japanese Patent Application Laid-Open No. 2004-281223 [Patent Document 15] Japanese Patent Application Laid-Open No. 2012-195527 [Patent Document 16] Japanese Patent Application Laid-Open No. 2011-192924 [Patent Document 17] Patent Publication No. 2021-145135 [Patent Document 18] US Patent Application Publication No. 2009 / 0161299 [Patent Document 19] European Patent Application Publication No. 3817020 [Patent Document 20] US Patent Application Publication No. 2014 / 0036416 [Patent Document 21] US Patent Application Publication No. 2021 / 0383981 [Patent Document 22] Japanese Patent Application Laid-Open No. 2005-294500 [Patent Document 23] International Publication No. 2010 / 029598 [Patent Document 24] Japanese Patent Application Laid-Open No. 2006-190878 [Patent Document 25] Japanese Patent Publication No. 2022-057601 [Patent Document 26] Japanese Patent Publication No. 2022-057985 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, the present invention provides the following (1) to (7): (1) It has good adhesion to the conductive polymer and low contact resistance at the interface. (2) It has a layer (geometric structure and surface modification) for holding the conductive polymer and electrolyte. (3) Excellent resistance to deterioration caused by solid electrolytes, chemical polymerization chemicals, electrolytic solutions, and moisture. (4) It has no capacitance or a low capacitance and behaves as a low-resistance conductor. (5) It is possible to make it thinner. (6) Low cost. (7) It is difficult for the winding to slip. The present invention aims to provide an electrode material that can be used for cathode foils for electrolytic capacitors and has at least one of the above advantages, or an electrolytic capacitor that includes a cathode foil using such an electrode material. [Means for solving the problem]

[0010] To address the above-mentioned problems, the present invention provides an electrode material having an oxide layer on a smooth substrate and an inorganic conductive layer on the oxide layer, the inorganic conductive layer comprising a first conductive layer containing a metal and / or a metal compound and a second conductive layer containing carbon, the first conductive layer having an uneven surface, and the second conductive layer being the outermost layer of the inorganic conductive layer. Here, the "smooth substrate" refers to a substrate that has not undergone a surface roughening treatment such as etching, but the substrate surface does not necessarily have to be completely flat. Smooth substrates also include those with minor surface roughness or undulations due to unavoidable rolling streaks or scars that occur during the foil manufacturing process, such as rolling (although the substrate surface may, of course, be completely smooth). The "oxide layer" may be an oxide layer formed without any special treatment, such as a natural oxide film, or an oxide layer intentionally formed by a treatment such as a chemical conversion treatment. The oxide layer may completely or partially cover the smooth substrate, or the smooth substrate and the first conductive layer may be in direct contact with each other, for example, by the material of the dense layer of the first conductive layer penetrating the oxide layer (forming the dense layer by the arc ion plating (AIP) method described later, or the like). Furthermore, when the second conductive layer is formed on the uneven portion of the first conductive layer, the second conductive layer may be divided into multiple parts due to the shape of the uneven portion (see FIG. 1, etc., in the embodiment described later). In the above and subsequent descriptions, the term "layer" may refer to a "layer" formed in such multiple parts (this applies not only to the second conductive layer, but also to any layer).

[0011] The smooth substrate and the first conductive layer may be made of different materials.

[0012] The second conductive layer may be a layer consisting essentially of carbon.

[0013] In the above description, "consisting essentially of carbon" or "consisting of carbon" does not necessarily mean that the second conductive layer does not contain any components other than carbon. The actual composition of the components may vary depending on factors such as control of component purity within the layer, limitations in manufacturing technology regarding the inclusion of impurities, and the level of resistance as an allowable error for the electrode material in individual products (the second conductive layer may contain components other than carbon, as long as the functionality of the electrode material is maintained at an allowable level). This also applies to descriptions such as "consisting essentially of," "consisting of," "comprising substantially only of," and "comprising only of."

[0014] The inorganic conductive layer may further have a dense layer in which metals and / or metal compounds are densely present, and the dense layer may be formed between the oxide layer and the first conductive layer. Note that "densely present" here means that (metals and / or metal compounds) are densely present compared to the "uneven portion."

[0015] Of the inorganic conductive layers, both the first conductive layer and the second conductive layer, or at least the first conductive layer, may be layers made of particle deposition layers, and the first conductive layer may be a layer containing at least one of titanium, aluminum, and their nitrides, oxides, oxynitrides, carbides, and carbonitrides. Materials that can be used for the first conductive layer are not limited to these, but when an aluminum substrate is used as the substrate, it is desirable to use metals, particularly titanium (Ti) and aluminum (Al) (alloys containing multiple components may be used as long as they do not impair adhesion to the substrate or the conductivity of the first conductive layer).

[0016] The oxide layer may be a phosphorus-containing oxide layer.

[0017] The smooth substrate may be a substrate containing aluminum or an aluminum alloy. However, the material that can be used as the substrate is not limited to aluminum, and any other material, such as valve metals tantalum (Ta), titanium (Ti), niobium (Nb), hafnium (Hf), zirconium (Zr), zinc (Zn), or tungsten (W), or an aluminum alloy containing any of these materials added to aluminum, can also be used.

[0018] A mixed layer may be formed between the first conductive layer and the second conductive layer, where the material constituting the first conductive layer and the material constituting the second conductive layer are mixed, and the composition of the mixed layer may change from a component containing substantially only the material constituting the first conductive layer to a component containing substantially only the material constituting the second conductive layer, from the first conductive layer to the second conductive layer. As already mentioned, "containing substantially only the material constituting the first conductive layer" and "containing only the material constituting the first conductive layer" do not necessarily mean that the mixed layer contains no components other than the "material constituting the first conductive layer," and "containing substantially only the material constituting the second conductive layer" do not necessarily mean that the mixed layer contains no components other than the "material constituting the second conductive layer" (other components may be included as long as the functionality of the electrode material is maintained to an acceptable degree).

[0019] Furthermore, in the above description, the phrase "changing from a component containing substantially only the material constituting the first conductive layer to a component containing substantially only the material constituting the second conductive layer from the first conductive layer to the second conductive layer" does not necessarily mean that the content of the material constituting the second conductive layer in the mixed layer increases monotonically in the direction from the first conductive layer to the second conductive layer. The actual composition at each position in the mixed layer may vary depending on variations in the concentration of each component due to limitations in manufacturing technology. However, preferably, the mixed layer is formed so that the content of the material constituting the second conductive layer continuously increases from the first conductive layer to the second conductive layer.

[0020] The carbon may be graphite-like carbon.

[0021] There is no particular restriction on the type of material to be used as carbon, but graphite-like carbon, which has particularly excellent electrical conductivity among carbon materials, is preferred in terms of reducing the ESR of the electrolytic capacitor. It is also preferred in terms of manufacturing costs. Here, graphite-like carbon is a material that has diamond bonds (sp 3 Hybrid orbital bonds) and graphite bonds (carbon-carbon sp 2 Among the amorphous carbons with a mixture of both bonds (sp and sp hybrid orbital bonds), those with a graphite bond ratio of more than 50% (those with more graphite bonds than diamond bonds). However, in addition to the amorphous structure, there are also those with a crystalline structure that is partially composed of graphite structures (i.e., sp 2 This also includes those that have a phase consisting of a hexagonal crystal structure with hybrid orbital bonding.

[0022] The static friction coefficient and dynamic friction coefficient of the surface of the surface layer side of the electrode material provided by the present invention against the separator paper may be higher than the static friction coefficient and dynamic friction coefficient of the surface of the surface layer side of an electrode material that has a conductive layer made of carbon as the outermost layer on the surface layer side on a smooth base material and has no uneven portion on the surface layer side.

[0023] The present invention also provides a cathode foil for an electrolytic capacitor, in which at least a conductive polymer is interposed between an anode foil and a cathode foil, the cathode foil using the above-mentioned electrode material of the present invention.

[0024] The present invention also provides an electrolytic capacitor having at least a conductive polymer interposed between an anode foil and a cathode foil, the electrolytic capacitor having the cathode foil of the present invention. In one example, a solid electrolytic capacitor is provided.

[0025] The electrolytic capacitor may be an electrolytic capacitor in which an electrolyte is further interposed between the anode foil and the cathode foil. In one example, a hybrid capacitor is provided. [Effects of the Invention]

[0026] The present invention provides an electrode material that can be used for cathode foils for electrolytic capacitors, etc., that has at least one of the advantages (1) to (7) listed above regarding the problems to be solved by the invention, or an electrolytic capacitor that includes a cathode foil using such an electrode material. Specifically, for example, the following advantages are provided. By using a smooth foil instead of an etched substrate, there is no need to worry about residual chlorine, and it is also possible to avoid the problem of exposed aluminum due to the difficulty of the inorganic conductive layer material penetrating deep into the etched layer. This makes it possible to improve resistance to deterioration (chemical resistance and durability) caused by solid electrolytes, chemical polymerization solutions, electrolytic solutions, and moisture ((3)), making it possible to make the product thinner while maintaining its strength ((5)), and by eliminating the etching process, it is possible to reduce costs, including the issue of wastewater treatment facilities ((6)). By applying an inorganic conductive layer with a rough surface, for example by vapor deposition, to a smooth foil, it is possible to obtain a layer with a geometric structure suitable for holding a conductive polymer and an electrolyte ((2)). The geometrical uneven structure on the surface layer improves adhesion with the conductive polymer ((1)). The geometric uneven structure on the surface layer increases the static and dynamic friction (friction coefficients) with the separator paper, suppressing misalignment, which is likely to occur when the winding core jig is removed during the element winding process for electrolytic capacitors ((7)). By providing a carbon-containing layer on the outermost inorganic conductive layer, it is possible to create a cathode foil with low resistance and no capacitance component. (The formation of a depletion layer due to contact between the conductive polymer and, for example, an aluminum oxide film is suppressed by forming a first conductive layer containing a metal and / or metal compound and a second conductive layer containing carbon on the aluminum oxide layer, significantly reducing the contact resistance with the conductive polymer) ((1) and (4)). [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 2 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material according to an embodiment of the present invention (Modification 1). [Figure 3] FIG. 3 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material according to an embodiment of the present invention (Modification 2). [Figure 4] FIG. 3 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material according to one embodiment of the present invention (Modification 3). [Figure 5] 2 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in which each layer is laminated only on one side of a substrate, unlike in FIG. 1, in one embodiment of the present invention. [Figure 6] 3 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in which each layer is laminated on only one side of a substrate, unlike in FIG. 2, in one embodiment of the present invention. [Figure 7] 4 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in which each layer is laminated on only one side of a substrate, unlike in FIG. 3, in one embodiment of the present invention. [Figure 8] 5 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in which layers are laminated only on one side of a substrate, unlike FIG. 4, in one embodiment of the present invention. [Figure 9] 1A and 1B are exploded views showing the structures of a wound-type solid electrolytic capacitor and a wound-type hybrid capacitor according to an embodiment of the present invention. [Figure 10]1 is a TEM (Transmission Electron Microscopy) photograph (cross-sectional image) of a cathode foil (Example 2 described below) using an electrode material according to one embodiment of the present invention. [Figure 11] 4 is a TEM photograph (cross-sectional image) of a cathode foil (Example 4 described later) using an electrode material that is another embodiment of the present invention. [Figure 12] 11 is a STEM (Scanning Transmission Electron Microscopy) photograph (cross-sectional image) of the same cathode foil (Example 2) as in FIG. 10. [Figure 13] 12 is a STEM photograph (cross-sectional image) of the same cathode foil (Example 4) as in FIG. 11. [Figure 14] TEM photographs (bright field image, cross-sectional image) of the same cathode foil (Example 2) as in FIG. 10. [Figure 15] TEM photographs (bright field image, cross-sectional image) of the same cathode foil (Example 4) as in FIG. 11. [Figure 16] 11 is a graph showing the analysis results of the same cathode foil (Example 2) as in FIG. 10 by ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) (showing the profile distribution of the chemical bond state). [Figure 17] 12 is a graph showing the analysis results by ToF-SIMS of the same cathode foil (Example 4) as in FIG. 11 (showing the profile distribution of the chemical bond state). [Figure 18] 12 is a graph of the Raman scattering spectrum (all wavenumber range) obtained by laser microscopic Raman spectroscopy of the same cathode foils (Examples 2 and 4) as those in FIGS. 10 and 11. FIG. [Figure 19] 12 is a graph of the Raman scattering spectrum (CC bond region) obtained by laser microscopic Raman spectroscopy of the same cathode foils (Examples 2 and 4) as those in FIGS. 10 and 11. FIG. [Figure 20] 1 is a table showing the results of ESR measurements carried out on hybrid capacitor Examples 1 to 4 and hybrid capacitor Comparative Examples 1 to 3. [Figure 21]1 is a table showing the results of ESR measurements carried out on solid electrolytic capacitors of Examples 1 to 4 and solid electrolytic capacitors of Comparative Examples 1 to 3. [Figure 22] 11 is a profile distribution of elements obtained by TEM-EDS (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy) of the same cathode foil (Example 2) as in FIG. 10. [Figure 23] 12 shows the element profile distribution obtained by TEM-EDS for the same cathode foil (Example 4) as in FIG. 11. [Figure 24] 25 shows the element profile distribution (on the carbon conductive layer side of FIG. 25) obtained by STEM-EELS (Scanning Transmission Electron Microscopy-Electron Energy Loss Spectroscopy) of the same cathode foil (Example 2) as in FIG. 10. [Figure 25] 24 shows the element profile distribution (on the substrate side of FIG. 24) obtained by STEM-EELS for the same cathode foil (Example 2) as in FIG. [Figure 26] 27 shows the element profile distribution (on the carbon conductive layer side of FIG. 27) obtained by STEM-EELS for the same cathode foil (Example 4) as in FIG. [Figure 27] 26 shows the element profile distribution (on the substrate side of FIG. 26) obtained by STEM-EELS for the same cathode foil (Example 4) as in FIG. 11. [Figure 28] 12 is a table showing the results of a tape adhesion test carried out on the same cathode foils (Examples 2 and 4) as those in FIGS. 10 and 11 and the cathode foil of Comparative Example 1. [Figure 29] 10 and 11 (Examples 2 and 4) and the cathode foil of Comparative Example 1, and the results of contact angle measurements, and a table showing the breakdown of the surface free energy (hydrogen bonding component and dispersion force component) calculated from the results. DETAILED DESCRIPTION OF THE INVENTION

[0028] As one embodiment of the present invention, a cathode foil for an electrolytic capacitor using the electrode material and an electrolytic capacitor using the cathode foil will be described below. However, as already mentioned, the aluminum foil used as the substrate and the titanium (Ti) or aluminum (Al) used to form the first conductive layer in the following description can be replaced with other materials. For example, materials for forming the first conductive layer include tantalum (Ta), titanium (Ti), chromium (Cr), aluminum (Al), niobium (Nb), vanadium (V), tungsten (W), hafnium (Hf), copper (Cu), zirconium (Zr), zinc (Zn), and nitrides of these metals, oxides of these metals, oxynitrides of these metals, carbides of these metals, and carbonitrides of these metals. (The first conductive layer may contain any other material. The same applies to other layers.) The carbon is not limited to graphite-like carbon, and any carbon material may be used. Furthermore, the use of the electrode material of the present invention is not limited to cathode foil for solid electrolytic capacitors or hybrid capacitors, but can also be used for electrodes (any electrode, such as a cathode, anode, positive electrode, or negative electrode) of any other storage element, such as other secondary batteries, electric double layer capacitors, and lithium ion capacitors. The electrolytic capacitor of the present invention is not limited to the wound electrolytic capacitor described below, but may be any type, such as a stacked type or a chip type. The uneven portion of the first conductive layer shown in FIG. 1 described below does not need to be formed on the entire surface of the surface side of the first conductive layer, and the uneven portion may be provided only partially on the surface side of the first conductive layer (naturally, the uneven portion may be formed on the entire surface of the surface side of the first conductive layer). The "smooth" substrate referred to in Figure 1 and other figures below does not necessarily have to have a smooth surface over the entire surface; for example, a "smooth substrate" may include a substrate having slight roughness or undulations on the surface due to unavoidable rolling lines or scars that occur slightly during the foil manufacturing process, such as rolling (naturally, the substrate surface may be completely smooth).The "second conductive layer" described below with reference to FIG. 1 and other figures may be a layer consisting essentially of carbon, or may contain other components besides carbon, such as tantalum (Ta), titanium (Ti), chromium (Cr), aluminum (Al), niobium (Nb), vanadium (V), tungsten (W), hafnium (Hf), copper (Cu), zirconium (Zr), zinc (Zn), nitrides of these metals, oxides of these metals, oxynitrides of these metals, carbides of these metals, and carbonitrides of these metals. The carbon content in the second conductive layer may be any desired content. Furthermore, it is not essential that the electrode material, cathode foil for electrolytic capacitor, or electrolytic capacitor of the present invention include all of the layers, components, and structures described in the following embodiments. The electrode material and cathode foil for electrolytic capacitor may not include at least one or more of the dense layer and the mixed layer. In the following illustrations, such as FIG. 1, a first conductive layer is formed on both sides of the smooth substrate. However, various layers or elements such as concave-convex portions may be formed on only one side or both sides of the smooth substrate. It is also possible to construct an electrode material or an electrolytic capacitor having a cathode foil using the electrode material, with different layer structures on the first and second sides of the substrate, such as by providing an oxide layer on the first side (front side) of the smooth substrate but not on the second side (rear side). The presence or absence, arrangement, etc. of elements such as concave-convex portions may also differ from those of the present invention on one side. Other layers, elements, structures, features, etc. may be omitted as appropriate as long as the electrode material, cathode foil for electrolytic capacitor, or electrolytic capacitor of the present invention can function. Furthermore, as long as the electrode material or electrolytic capacitor of the present invention can function, the electrode material, cathode foil for electrolytic capacitor, or electrolytic capacitor of the present invention may have layers, elements, structures, and features other than those described in the following embodiments. Furthermore, any of the electrode materials of the present invention can be used as the cathode foil in the electrolytic capacitor of the present invention. The layers, elements, structures, features, and the like described may be arbitrarily selected and combined as appropriate, and electrode materials, cathode foils for electrolytic capacitors, electrolytic capacitors, and the like obtained through such selection and combination are all included in the scope of the present invention.

[0029] The above-mentioned resistance to deterioration due to the solid electrolyte, the chemical polymerization agent, the electrolytic solution, and moisture can be further improved by the following measures. If the adhesion at the interface between the smooth foil and the vapor deposition layer is insufficient, the vapor deposition layer may be applied after covering it with a dense inorganic conductive layer. By covering the smooth foil with a dense inorganic conductive layer, it is possible to completely eliminate the exposed aluminum portion in some cases, thereby improving chemical resistance and durability. By applying an oxide film containing phosphorus (P) to the smooth foil and then covering it with a dense inorganic conductive layer, it is possible to further improve chemical resistance and durability (even if a dense layer is not formed, it is possible to improve chemical resistance and durability by applying an oxide film containing phosphorus to the smooth base material using chemical conversion treatment, etc.).

[0030] Cathode foil using the electrode material of the present invention 1 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material according to one embodiment of the present invention. The cathode foil (electrode material) 1 comprises a substrate (smooth aluminum foil) 2 that has not been roughened by etching or other processes, an oxide layer 3 formed on the smooth aluminum foil 2, such as a natural oxide film or an artificially formed oxide film containing phosphorus, a first conductive layer 4 formed on the oxide layer 3 and having projections and depressions, made of Ti or Al, and a second conductive layer 5 formed on the first conductive layer 4.

[0031] A commercially available high-purity aluminum sheet can be used as the smooth aluminum foil 2. The thickness of the aluminum sheet is not particularly limited, but if it is used as a cathode foil for a wound-type electrolytic capacitor (such as a solid electrolytic capacitor or a hybrid capacitor), it is preferably 10 μm or more and 50 μm or less.

[0032] The oxide layer 3 is an oxide layer such as a natural oxide film or an oxide film intentionally formed by a chemical conversion treatment such as anodizing or immersion treatment containing phosphorus, and is formed by exposing the smooth aluminum foil 2 to air, anodizing treatment using an ammonium dihydrogen phosphate solution, or immersing in an aqueous phosphoric acid solution or an aqueous aluminum biphosphate solution followed by heat treatment.

[0033] The first conductive layer 4 is formed, for example, by arranging a smooth aluminum foil 2 on which an oxide layer 3 has been formed (or, if a dense layer 6, as described below, is to be formed, by arc ion plating or the like) in a vacuum chamber, and a metal material (Ti or Al) as an evaporation source, evaporating the metal material, and depositing the evaporated metal material on the oxide layer 3 (or on the dense layer 6, if a dense layer 6 is to be formed) (evaporation method). Vapor deposition methods include the above-mentioned vacuum evaporation, chemical vapor deposition (CVD), sputtering, etc., but electron beam evaporation is preferred among vacuum evaporation methods in terms of controlling the geometric structure. Electron beam evaporation is a method in which an accelerated electron beam is irradiated on an evaporation material to heat and vaporize it, which is then deposited on a substrate. The fineness of the irregularities in the first conductive layer can be controlled, for example, by adjusting the particle size of the metal material to be deposited. The particle size of the metal material can be appropriately controlled by adjusting conditions during vapor deposition, such as the type of gas introduced, the degree of vacuum, and the temperature of the substrate. In an embodiment in which a first conductive layer 4 made of a nitride, oxide, or carbide of a metal such as Ti or Al is formed on a smooth aluminum foil 2 on which an oxide layer 3 and, if a dense layer 6 is formed, a further dense layer 6 are formed, the first conductive layer 4 may be formed by carrying out the above method in an atmosphere of, for example, nitrogen gas, oxygen gas, or a hydrocarbon gas such as acetylene gas or methane gas. In an embodiment in which a first conductive layer 4 made of an oxynitride or carbonitride of a metal such as Ti or Al is formed, the first conductive layer 4 may be formed in an atmosphere of, for example, nitrogen gas and oxygen gas, or nitrogen gas and a hydrocarbon gas such as acetylene gas or methane gas.

[0034] The second conductive layer 5 of the present invention is preferably formed using a vapor deposition method such as ion plating, rather than by dispersing carbon particles in a binder such as a resin binder and then applying the resulting mixture. In a layer of carbon particles formed by mixing the carbon particles with a binder, the carbon occupancy rate is substantially reduced by the amount of binder added. Furthermore, the contact between the material of the first conductive layer and the carbon particles in the lower layer is point contact, making it difficult to form a mixed layer. Furthermore, the above-mentioned application method makes it difficult to increase the electrical conductivity at the interface, resulting in increased interface resistance and poor adhesion, and making it difficult to achieve a thin, uniform coating. The second conductive layer 5 is preferably formed as a smooth and dense GLC (Graphite-Like Carbon) coating. When the second conductive layer 5 is formed on the uneven portion of the first conductive layer 4, the shape of the second conductive layer 5 depends on the shape of the uneven portion of the first conductive layer 4, so the second conductive layer 5 does not necessarily need to have unevenness (its thickness is substantially constant) and may be a smooth and dense coating. As shown in Figures 1 to 8, by having unevenness on the surface on the surface side of the electrode material 1 (however, having unevenness on the surface is not essential for the electrode material 1), the static friction coefficient and dynamic friction coefficient of the surface on the surface side of the electrode material 1 against the separator paper are thought to be higher than the static friction coefficient and dynamic friction coefficient of the surface on the surface side of an electrode material that has a conductive layer made of carbon as the outermost layer on the surface side on a smooth base material and does not have unevenness on the surface side.

[0035] The second conductive layer 5 can be obtained by the same method as the dense layer 6. Among these, ion plating methods such as arc ion plating, which have a high ionization rate and adhesion energy of the film-forming material, are particularly preferred because they facilitate the formation of an interdiffusion state with the first conductive layer and are highly effective in reducing interfacial resistance. Specifically, a laminate in which an oxide layer 3 and a first conductive layer 4 are formed on a smooth aluminum foil 2 (when forming a dense layer 6, an additional dense layer 6 is formed between the oxide layer 3 and the first conductive layer 4) and a carbon material serving as an evaporation source (for example, a graphite material when forming the second conductive layer 5 as a GLC coating) are placed in a vacuum chamber. A vacuum arc discharge is then generated between the evaporation source target as a cathode and an anode to evaporate and ionize the carbon material, and the resulting carbon cations are introduced into the laminate. Arc ion plating is suitable for forming high-melting-point compound films, such as carbides and nitrides, because it can locally generate high Joule heat on the target using an arc current. Furthermore, the high plasma density can increase the ionization rate of the evaporated film-forming material. A negative bias voltage may be applied to the laminate to accelerate the carbon cations toward the laminate. To impart a textured geometric shape to the second conductive layer 5, a carbon material (e.g., a graphite material when forming the second conductive layer 5 as a GLC coating) may be deposited using the same electron beam deposition method as used for the textured portion of the first conductive layer 4. The second conductive layer 5 may contain any component other than carbon. However, when forming a second conductive layer 5 containing components other than carbon, any other material may be prepared as an evaporation source in addition to the carbon material, and the other material may be evaporated and ionized in the same manner to be deposited on the laminate.

[0036] Fig. 2 is a cross-sectional view (Variation 1) showing the layer structure of a cathode foil using an electrode material according to one embodiment of the present invention. Unlike the layer structure shown in Fig. 1, a dense layer 6 is formed between an oxide layer 3 and a first conductive layer 4.

[0037] The dense layer 6 is formed by placing the smooth aluminum foil 2 with the oxide layer 3 formed thereon and a metal material (Ti or Al) serving as an evaporation source in a vacuum chamber, evaporating and ionizing the Ti or Al using an electron beam and a plasma generating electrode, and then directing the resulting metal cations, ionized by arc discharge, toward the smooth aluminum foil 2. A negative bias voltage may be applied to the smooth aluminum foil 2 to accelerate the metal cations toward the smooth aluminum foil 2. Therefore, the Ti or Al ions penetrate the oxide layer 3 formed on the surface of the smooth aluminum foil 2 and firmly adhere to the smooth aluminum foil 2. However, it is not essential that the material of the first conductive layer 4 penetrate the oxide layer 3 to adhere to the smooth aluminum foil 2. An oxide layer 3, such as a natural oxide film or an oxide film formed by an anodizing process containing phosphorus, may be present between the first conductive layer 4 and the smooth aluminum foil 2 without forming holes. In an embodiment in which a dense layer 6 made of a nitride, oxide, or carbide of a metal such as Ti or Al is formed on the smooth aluminum foil 2 on which the oxide layer 3 has been formed, the dense layer 6 may be formed by carrying out the above method in an atmosphere of, for example, nitrogen gas, oxygen gas, or a hydrocarbon gas such as acetylene gas or methane gas. In an embodiment in which a dense layer 6 made of an oxynitride or carbonitride of a metal such as Ti or Al is formed, the dense layer 6 may be formed in an atmosphere of, for example, nitrogen gas and oxygen gas, or nitrogen gas and a hydrocarbon gas such as acetylene gas or methane gas.

[0038] In addition to ion plating methods such as arc ion plating, other methods that can be used to form the dense layer 6 include vacuum deposition, chemical vapor deposition, sputtering, atomic layer deposition, sol-gel deposition, plating, coating, and printing. In one example, the ion plating method can be used because the dense layer 6 and the smooth aluminum foil 2 are firmly attached to each other through the oxide layer 3, thereby keeping the ESR of the capacitor low, and because a smooth metal coating can be easily formed.

[0039] 3 is a cross-sectional view (Variation 2) showing the layer structure of a cathode foil using an electrode material according to one embodiment of the present invention. Unlike the layer structure shown in FIG. 1, a mixed layer 7 is formed between the first conductive layer 4 and the second conductive layer 5.

[0040] In one example, the mixed layer 7 can be formed by not completely separating the time periods of the step of forming the first conductive layer 4 by a vapor deposition method such as vacuum deposition and the step of forming the second conductive layer 5 by arc ion plating, but by performing both steps so that there is a period of time when the steps of forming the first conductive layer 4 and the second conductive layer 5 are performed simultaneously. The introduction of such a mixed layer 7 improves the adhesion and chemical stability between the material constituting the first conductive layer 4 (a metal, or any material including a metal nitride, oxide, oxynitride, carbide, or carbonitride as described above) and the material constituting the second conductive layer 5 (carbon such as GLC, and, if the second conductive layer 5 also contains materials other than carbon, any other material contained in the second conductive layer 5), thereby preventing deterioration of the metal due to chemical reactions.

[0041] It is preferable that the mixed layer 7 is configured so that the boundary region with the first conductive layer 4 contains substantially only the material that constitutes the first conductive layer 4, and the boundary region with the second conductive layer 5 contains substantially only the material that constitutes the second conductive layer 5, and that the content of the material that constitutes the second conductive layer 5 increases continuously from the first conductive layer 4 toward the second conductive layer 5. Such a mixed layer 7 can be configured, for example, as follows: (i) At the start of the formation of the mixed layer 7, only the vapor deposition process, which is the process for forming the first conductive layer 4, is performed, and electron beam irradiation is not performed on the carbon material such as graphite material (and, in the case where the second conductive layer 5 also contains materials other than carbon, on any other material of the second conductive layer 5); (ii) gradually reducing the amount of electron beam irradiation onto the material constituting the first conductive layer 4 over time to reduce the amount of evaporation of the metal material in the vapor deposition method that is the process of forming the first conductive layer 4, and at the same time increasing the amount of electron beam irradiation onto the carbon material such as graphite material (and, in the case where the second conductive layer 5 also contains materials other than carbon, any other material of the second conductive layer 5), thereby forming a mixed coating in which the material constituting the first conductive layer 4 and the material constituting the second conductive layer 5 are mixed and the content of the material constituting the second conductive layer 5 increases toward the upper layer; (iii) At the end of the film formation, the vapor deposition method, which is the step of forming the first conductive layer 4, is terminated, and only the arc ion plating method, which is the step of forming the second conductive layer 5, is carried out, thereby forming a film essentially consisting of only the material that constitutes the second conductive layer. Alternatively, when forming the mixed layer 7 by a vapor deposition method (first conductive layer 4) and a sputtering method (second conductive layer 5), the mixed layer 7 of such a preferred embodiment can be formed by any method, such as by decreasing the evaporation rate of the material of the first conductive layer 4 over time and increasing the voltage applied to a carbon target such as a graphite target (and, if the second conductive layer 5 contains materials other than carbon, any other target of the material of the second conductive layer) (by increasing the sputtering rate of the graphite target and, if used, any other target of the material of the second conductive layer). Furthermore, (i) to (iii) are processes primarily suited to batch-type single-wafer processing. Alternatively, the mixed layer can also be formed by a roll-to-roll method in which a material target for the first conductive layer, followed by a material target for the second conductive layer, is sequentially arranged in a chamber, and continuous film formation is performed in the order of first and second layers while the foil is being transported. The mixed layer is formed by arranging the first and second evaporation source targets adjacent to each other so that the vapors and ions of the deposition materials emitted from the first and second evaporation source targets in a conical shape toward the substrate overlap (contact) before reaching the substrate. By appropriately controlling the distance between the evaporation source targets and the distance between each evaporation source target and the substrate, the mixed, diffused, and bonded states of the mixed layer can be optimized. In this case, the electron beam irradiation dose can be kept constant without adjusting it as described above, making it a more suitable process for mass production. Alternatively, the mixed layer can be obtained by heating the substrate temperature to, for example, several hundred degrees Celsius, regardless of the distance between the evaporation source targets or the distance between each evaporation source target and the substrate.

[0042] Fig. 4 is a cross-sectional view (Variation 3) showing the layer structure of a cathode foil using an electrode material according to one embodiment of the present invention. Unlike the layer structure shown in Fig. 1, a dense layer 6 is formed between the oxide layer 3 and the first conductive layer 4, and a mixed layer 7 is formed between the first conductive layer 4 and the second conductive layer 5.

[0043] As already mentioned, it is not essential to laminate each layer on both sides of the substrate 2 as shown in FIGS. 1 to 4 . Each layer may be laminated on only one side of the substrate 2 as shown in FIGS. 5 to 8 . Alternatively, different layer structures may be formed on the front and back sides of the substrate 2, for example, by laminating each layer shown in FIG. 5 on one side of the substrate 2 and laminating each layer shown in FIG. 6 on the other side of the substrate 2.

[0044] The thickness of the oxide layer 3, dense layer 6, first conductive layer 4, mixed layer 7, and second conductive layer 5 is sufficient if each is approximately 0.005 μm or more and 1 μm or less, and good characteristics as a cathode foil can be obtained as long as the total thickness of each layer excluding the substrate 2 is at least 0.05 μm on one side of the substrate 2. However, each layer may be formed thicker or thinner. The thickness of each layer in FIGS. 1 to 8 is merely an example, and the thickness of each layer can be determined as desired.

[0045] Furthermore, when an electrode material according to one embodiment of the present invention using a valve metal as the substrate 2 is used as a cathode foil for an electrolytic capacitor, the potential corresponding to a current that falls within the current density range of the leakage current of the electrolytic capacitor due to electrochemical polarization may be more noble than the natural immersion potential of a control cathode foil of the same type as the valve metal used in the substrate 2 and having a purity of 99.99% or higher. Furthermore, the natural immersion potential when immersed in an electrolyte may be more noble than the natural immersion potential of a control cathode foil of the same type as the valve metal used in the substrate 2 and having a purity of 99.99% or higher when immersed in the same electrolyte (Patent Documents 25 and 26). This can prevent hydrogen gas from being generated on the cathode side when the dielectric oxide film formed on the anode foil is repaired by leakage current. To further explain this point, the control cathode foil has a natural oxide film formed thereon and has a natural immersion potential at which the cathodic reaction of reducing hydrogen ions occurs predominantly. The cathode foil of the present invention has a natural immersion potential that is more noble than that of the control cathode foil. Therefore, even when the cathode foil of the present invention is incorporated into an electrolytic capacitor and leakage current occurs, the potential of the cathode foil of the present invention can be maintained on the nobler side than the natural immersion potential of the control cathode foil. Therefore, when leakage current occurs in the electrolytic capacitor, the potential of the cathode foil of the present invention is within a potential range in which the cathodic reaction that reduces dissolved oxygen occurs predominantly, and the cathodic reaction that reduces hydrogen ions is suppressed. As a result, an increase in internal pressure of the electrolytic capacitor due to the generation of hydrogen gas is suppressed, thereby reducing the risk of swelling of the case that houses the capacitor element.

[0046] Electrolytic capacitor of the present invention Hereinafter, a solid electrolytic capacitor and a hybrid capacitor will be described as examples of electrolytic capacitors that can be fabricated using the cathode foil of the present invention. Here, we will describe the case where a cathode foil 1 having the layer structure shown in Figures 1 to 4 in which each layer is laminated on both sides of a substrate 2 is used. However, the electrolytic capacitor of the present invention can also be fabricated using a cathode foil 1 having a layer structure in which each layer is laminated on only one side of a substrate 2.

[0047] (Solid electrolytic capacitor) FIG. 9 is an exploded view of a wound type solid electrolytic capacitor 8 fabricated using a cathode foil 1 having any of the layer structures shown in FIGS. 1 to 4. The solid electrolytic capacitor 8 has: (i) Anode foil 9, which is obtained by forming an oxide film on anode aluminum foil by anodizing treatment, and cathode foil 10 having any of the layer structures shown in FIGS. 1 to 4 are stacked together with separator paper 11 interposed therebetween, and anode terminal 13 is connected to anode foil 9 and cathode terminal 14 is connected to cathode foil 10, and the resulting structure is then wound together to produce capacitor element 12. (ii) The capacitor element 12 is immersed in a mixed solution of 3,4-ethylenedioxythiophene and iron(II) p-toluenesulfonate as an oxidant, containing n-butyl alcohol as a diluent, and then heated to form a solid electrolyte layer of polyethylenedioxythiophene (PEDOT) by thermal polymerization. Alternatively, the solid electrolyte layer may be formed by immersing and impregnating the capacitor element 12 in a PEDOT / PSS aqueous dispersion solution, which is made by mixing polyethylenedioxythiophene with polystyrene sulfonic acid (PSS) to disperse the polyethylenedioxythiophene in an aqueous solution, and then drying the PEDOT / PSS aqueous dispersion solution. (iii) Capacitor element 12 with the solid electrolyte layer formed thereon is housed in aluminum case 15 and sealed with sealing rubber 16 . The solid electrolyte layer may also be formed from conductive polymers such as polypyrrole, polyaniline, polyacene, polyparaphenylene vinylene, and polyisothianaphthene, or from manganese dioxide (MnO2) or TCNQ (tetracyanoquinodimethane) complex salts.

[0048] (hybrid capacitor) The hybrid capacitor is manufactured by carrying out steps (i) and (ii) in the same manner as in the case of manufacturing the solid electrolytic capacitor 8, and then: (ii-2) The capacitor element having the solid electrolyte layer formed thereon is impregnated with an electrolytic solution containing at least one of γ-butyl lactone, ethylene glycol, and water as a solvent. (iii) A solid electrolyte layer is formed, and the capacitor element impregnated with an electrolyte solution is housed in an aluminum case and sealed with sealing rubber. The solid electrolyte layer may also be formed from conductive polymers such as polypyrrole, polyaniline, polyacene, polyparaphenylene vinylene, and polyisothianaphthene, or from manganese dioxide (MnO2) or TCNQ (tetracyanoquinodimethane) complex salts. [Example]

[0049] The structures, analysis results, performance test results, etc. of various cathode foils and electrolytic capacitors produced as examples of the present invention will be described below.

[0050] Figure 10 is a TEM (transmission electron microscope) photograph (cross-sectional image) of a cathode foil (Example 2 described below) using an electrode material according to one embodiment of the present invention. The cathode foil of Figure 10 has the layer structure shown in Figure 6 (the layer structure on one side shown in Figure 2) (a natural oxide film is thought to be formed between the smooth substrate and the dense layer), and is produced by forming a dense layer 6 of Ti by arc ion plating on a smooth aluminum substrate 2 (on which a natural oxide film 3 has been formed), forming a first conductive layer 4 of Ti by vacuum deposition, and forming a carbon layer (second conductive layer 5) of GLC by arc ion plating. Such a cathode foil is By using a smooth substrate as the substrate 2, the Al surface can be coated with Ti without any gaps. The granular deposition structure allows for adhesion and retention of polymers and electrolytes. -Ti pretreatment using the arc ion plating method can eliminate the influence of residual oil and oxides on the substrate surface. 11 shows a TEM photograph (cross-sectional image) of a cathode foil (Example 4 described later) different from the cathode foil shown in FIG. 10. The cathode foils shown in FIGS. 10 and 11 are both produced by forming a dense layer 6 of Ti on a smooth aluminum substrate 2 (having a natural oxide film 3 formed thereon) by arc ion plating, forming a first conductive layer 4 of Ti by vacuum deposition, and forming a carbon layer (second conductive layer 5) of GLC by arc ion plating. However, the particle diameter of the metal material (Ti in the samples shown in FIGS. 10 and 11) contained in the first conductive layer 4 is different, and therefore the fineness of the irregularities in the first conductive layer 4 is different.

[0051] Fig. 12 is a STEM (scanning transmission electron microscope) photograph (cross-sectional image) of the same cathode foil (Example 2) as in Fig. 10, and Fig. 13 is a STEM photograph (cross-sectional image) of the same cathode foil (Example 4) as in Fig. 11. As described above, the particle size of the metal material in the first conductive layer 4 can be appropriately controlled by adjusting conditions during vapor deposition, such as the type of gas introduced, the degree of vacuum, and the temperature of the substrate, and therefore the first conductive layer 4 can be formed with various particle sizes, i.e., various irregularity finenesses.

[0052] Figure 14 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil (Example 2) as in Figure 10, and Figure 15 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil (Example 4) as in Figure 11. In both the samples of Example 2 and Example 4, a native oxide film (about several nm thick) on the substrate can be identified.

[0053] FIG. 16 is a graph showing the results of analysis (showing a profile distribution of chemical bonding states) by ToF-SIMS (time-of-flight secondary ion mass spectrometry) of the same cathode foil (Example 2) as in FIG. 10 , and FIG. 17 is a graph showing the results of analysis (showing a profile distribution of chemical bonding states) by ToF-SIMS of the same cathode foil (Example 4) as in FIG. 11 . In the graphs in FIGS. 16 and 17 , the vertical axis represents secondary ion intensity, measured in counts, which represents the number of secondary ions detected at each measurement depth. In the graphs in FIGS. 16 and 17 , carbon C6 derived from carbon deposition is a fragment (cluster) ion consisting of six C atoms and is a monovalent negative ion; metallic titanium Ti2 ions are monovalent negative ions consisting of two Ti atoms; metallic aluminum (base metal) Al5 ions are monovalent negative ions consisting of five Al atoms; and other species such as TiC2, TiO2, TiN, TiNO, and Al2O3 are negative ions of their respective molecular bonding states. For example, in Example 4 shown in Figure 17, it can be seen that metallic Ti is present only in small amounts at the substrate interface, with most of it existing as carbides, oxides, nitrides, or oxynitrides. Furthermore, in both the samples of Example 2 and Example 4, a mixed layer of oxides and Ti compounds, and a mixed layer of Ti compounds and C are formed on the aluminum substrate, and the mixed layers are formed as gradient coatings in which the proportion of C increases toward the outermost layer (carbon layer).

[0054] Fig. 18 is a graph (all wavenumber region) of the Raman scattering spectrum obtained by laser microscopic Raman spectroscopy of a cathode foil as a sample prepared under the same conditions as the samples shown in Figs. 10 and 17, and Fig. 19 is a graph (CC bond region) of the Raman scattering spectrum obtained by laser microscopic Raman spectroscopy of a cathode foil as a sample prepared under the same conditions as the samples shown in Figs. 10 and 17. In the graph of Fig. 18, the horizontal axis indicates the Raman shift at 1500 cm -1 The graph with a larger Raman intensity [counts] on the vertical axis corresponds to the sample of Example 2, and the Raman shift on the horizontal axis is 1500 cm -1The graph with the smaller Raman intensity [counts] on the vertical axis in the vicinity corresponds to the sample of Example 4. In the graph of FIG. 19, the Raman shift on the horizontal axis is 1100 cm -1 The graph with the smaller Raman intensity [counts] on the vertical axis corresponds to the sample of Example 2, and the Raman shift on the horizontal axis is 1100 cm -1 The graph with a larger Raman intensity [counts] on the vertical axis in the vicinity corresponds to the sample of Example 4. In particular, from the graph shown in FIG. 19, it can be seen that in both the samples of Example 2 and Example 4, sp 3 (D band) than the Raman intensity in sp 2 The Raman intensity at (G band) is higher than that at (G band), indicating that the carbon layer (second conductive layer) in both samples is formed by containing GLC.

[0055] Performance test of the hybrid capacitor of the present invention Cathode foils of Examples 1 to 4 were prepared as cathode foils of the present invention, and cathode foils of Comparative Examples 1 to 3 were prepared as cathode foils of comparative examples. Hybrid capacitors of Examples 1 to 4 were fabricated using the cathode foils of Examples 1 to 4, respectively, and hybrid capacitors of Comparative Examples 1 to 3 were fabricated using the cathode foils of Comparative Examples 1 to 3, respectively, and a performance test (ESR measurement) was performed on each of the fabricated hybrid capacitors. The fabrication conditions and ESR measurement conditions for each hybrid capacitor are as follows: Example 1: Ar gas was introduced into a chamber evacuated to 0.003 Pa. A first target made of Ti and a second target made of graphite were sequentially placed adjacent to each other so that the vapor and ions of the deposition materials emitted from the first and second targets in a conical shape toward the substrate overlapped (contacted) before reaching the substrate. A smooth aluminum foil was then transported through the process in this order. A 200 nm uneven Ti layer was deposited by electron beam evaporation, followed by a carbon film by arc ion plating. This continuous roll-to-roll deposition process produced mixed layers at the interface between the oxide layer on the smooth substrate and the first conductive layer, and at the interface between the first and second conductive layers. This foil was used as the cathode and combined with an anode foil (etched aluminum foil anodized at 53 V) to fabricate a hybrid capacitor. The initial ESR (100 kHz) was measured, and the ESR (100 kHz) was measured after leaving the anode foil and the cathode foil at 125°C for 2000 hours (1 hour = 60 minutes). The hybrid capacitor was fabricated as follows: First, the anode foil and the cathode foil fabricated as described above were stacked with a separator paper between them. An anode terminal was connected to the anode foil, and a cathode terminal was connected to the cathode foil. The resulting stack was then wound to fabricate a capacitor element. Next, the capacitor element was immersed in a water-based polymer dispersion solution in a container evacuated to approximately 7000 Pa and then dried at 150°C for 30 minutes in an air environment to form a solid electrolyte layer. The capacitor element was then impregnated with an electrolyte solution containing ethylene glycol as a solvent in a container evacuated to approximately 5000 Pa. Finally, the capacitor element was housed in an aluminum case and sealed with sealing rubber. Example 2: The same amount of Ar gas as in Example 1 was introduced into a chamber vessel evacuated to 0.003 Pa, and a smooth aluminum foil was transported through the same film-forming process as in Example 1, and a 10 nm Ti film was formed by arc ion plating. A 200 nm Ti layer with irregularities was then applied by vapor deposition, and a carbon film was then formed by arc ion plating. The subsequent steps were the same as in Example 1. Example 3: The same treatment as in Example 2 was carried out, except that a smooth substrate was used that had been anodized in an ammonium dihydrogen phosphate solution at an applied voltage of 5V. Example 4: This example is the same as Example 2, except that the gases introduced are two types: Ar and N2. Comparative Example 1: A smooth substrate was used, the same amount of Ar gas as in Examples 1 to 3 was introduced, a Ti film was formed by arc ion plating, and then a carbon film was formed by arc ion plating. The other conditions were the same as in Example 1. Comparative Example 2: The substrate was an etched foil anodized at 2V, and the same amount of Ar gas as in Examples 1 to 3 was introduced. After a Ti film was formed by arc ion plating, a carbon film was formed by arc ion plating. The other conditions were the same as in Example 1. Comparative Example 3: A (dense) Ti layer was formed by vacuum deposition on a smooth substrate without introducing any gas, and then N2 gas was introduced until the pressure inside the container became equivalent to that of Examples 1 to 3, and a (rough) Ti layer was formed by vacuum deposition. This cathode was used. The other conditions were the same as in Example 1. The coating structure of the cathode foil in Comparative Example 3 was the same as the coating structure disclosed in the specification of JP 2014-022707 A. In the cathode foils of Examples 1 to 4 and Comparative Examples 1 and 2, in which a carbon conductive layer is formed, a mixed layer is formed below the carbon conductive layer. In the mixed layer, carbon and a material constituting the layer below the mixed layer are mixed together. Furthermore, the carbon layers in Examples 1 to 4 and Comparative Examples 1 and 2 contain GLC.

[0056] FIG. 20 is a table showing the results of ESR measurements performed on hybrid capacitors in Examples 1 to 5 and Comparative Examples 1 to 3. In FIG. 20, "after 2000 hours of aging" indicates that the ESR was measured after the hybrid capacitors were aged for 2000 hours in an atmospheric environment at 125°C. As can be seen from the ESR measurement results in FIG. 20, in the initial state, the ESR of the hybrid capacitors in Examples 1 to 3 was lower than that of the hybrid capacitors in Comparative Examples 1 to 3, and the ESR of the hybrid capacitor in Example 4 was lower than that of the hybrid capacitors in Comparative Examples 1 and 3 (note that the ESR of the hybrid capacitor in Comparative Example 2 was almost equivalent). After 2000 hours of aging, the ESR of the hybrid capacitors in Examples 1 to 4 was lower than that of the hybrid capacitors in Comparative Examples 1 to 3.

[0057] Performance test of the solid electrolytic capacitor of the present invention In addition, the cathode foils of Examples 1 to 4 and Comparative Examples 1 to 3 were used to fabricate solid electrolytic capacitors of Examples 1 to 4 and Comparative Examples 1 to 3, respectively (these were fabricated using a fabrication method that differed from the fabrication method for the hybrid capacitors of Examples 1 to 4 and Comparative Examples 1 to 3 only in that no process of impregnating the capacitor element with an electrolyte solution was performed after the solid electrolyte layer was formed). Performance tests (ESR measurements) were performed on each of the fabricated solid electrolytic capacitors.

[0058] 21 is a table showing the results of ESR measurements of the solid electrolytic capacitors of Examples 1 to 4 and Comparative Examples 1 to 3. In the initial state, the ESR of the solid electrolytic capacitors of Examples 1 to 4 is lower than that of the solid electrolytic capacitors of Comparative Examples 1 and 3, and the ESR of the solid electrolytic capacitor of Example 3 is particularly lower than that of the solid electrolytic capacitors of Comparative Examples 1 to 3.

[0059] The following figures relate to ultrathin section samples taken in the thickness direction of the entire coating portion, including the substrate portion closer to the coating. Fig. 22 shows the elemental profile distribution of the same cathode foil (Example 2) as in Fig. 10, obtained by TEM-EDS (transmission electron microscopy-energy dispersive X-ray analysis). Fig. 23 shows the elemental profile distribution of the same cathode foil (Example 4) as in Fig. 11, obtained by TEM-EDS. Fig. 24 shows the elemental profile distribution of the same cathode foil (Example 2) as in Fig. 10, obtained by STEM-EELS (scanning transmission electron microscopy-electron energy loss spectroscopy) (closer to the carbon conductive layer than Fig. 25), and Fig. 25 shows the elemental profile distribution of the same cathode foil (Example 2) as in Fig. 10, obtained by STEM-EELS (closer to the substrate than Fig. 24). Fig. 26 shows the element profile distribution (closer to the carbon conductive layer than Fig. 27) obtained by STEM-EELS for the same cathode foil (Example 4) as Fig. 11, and Fig. 27 shows the element profile distribution (closer to the substrate than Fig. 26) obtained by STEM-EELS for the same cathode foil (Example 4) as Fig. 11. Here, in Figs. 22 to 27, K indicates the K-shell electron shell, and in Figs. 24 to 27, L indicates the L-shell electron shell. It can be seen that in both Examples 2 and 4, a mixed layer is present below the carbon conductive layer.

[0060] The adhesive mechanism between the conductive polymer and the cathode foil was an adhesive tape. Figure 28 shows comparative data on adhesion using industrial adhesive tape. A 10 mm wide Nitto Denko polypropylene adhesive tape was used. It was cut into 15 cm lengths and placed adhesive side down, parallel to the length, on a 50 mm wide x 200 mm long test piece. A press roller with a load of 20 N was run back and forth over the tape for a length of at least 100 mm, applying a uniform load. One end of the test piece was firmly clamped, and the tape opposite the side bonded to the test piece was folded 180° near the clamp. The end was then secured with a clip connected to a push-pull gauge and pulled at a constant speed of 10 mm / s. The average tensile load (gf / cm) at which the tape peeled was measured and recorded as the tape adhesion. Examples 2 and 4 demonstrated significantly stronger tape adhesion than Comparative Example 1, which lacked an uneven surface structure, reflecting the anchoring effect of the uneven surface structure. In other words, it was found that the uneven structure provided on the surface side of the first conductive layer can have the effect of improving adhesion with the conductive polymer.

[0061] In recent hybrid capacitors, in order to achieve heat resistance, conductivity, voltage resistance, manufacturing costs, etc., polyethylenedioxythiophene (PEDOT) is often dispersed in an aqueous solution by mixing it with polystyrene sulfonate (PSS), and then drying it to form a solid electrolyte layer. The adhesion and retention of conductive polymers are thought to depend on the wettability and surface free energy of the cathode foil. Figure 29 shows the contact angles (°) for water, a highly polar solvent, and diiodomethane (methylene iodide, CH2I2), a less polar solvent, and the surface free energy (mJ / m) calculated from these angles using the Owens and Wendt model. 2) (polar hydrogen-bonding component and nonpolar dispersion force component). The polar hydrogen-bonding component is related to affinity with aqueous solvents, while the nonpolar dispersion force component is related to affinity with hydrocarbons, organic solvents, polymers, etc. A 1 μL droplet of water or diiodomethane was dropped onto a horizontally placed sample piece, and the contact angle of the droplet after 60 seconds was measured using a contact angle meter (DM-501Hi) manufactured by Kyowa Interface Science Co., Ltd. For Examples 2 and 4, the uneven surface structure provided on the surface layer side resulted in significantly lower contact angles (excellent wettability) with both solvents and well-balanced high surface free energy values ​​with both components compared to Comparative Example 1, which did not have an uneven surface structure on the surface layer side. In other words, the uneven surface structure provided on the surface layer side of the first conductive layer improved adhesion with the conductive polymer and also provided a geometric structure suitable for retaining the conductive polymer and electrolyte.

[0062] [Note] The present disclosure discloses the following configurations. [Configuration 1] An oxide layer is provided on a smooth substrate, and an inorganic conductive layer is provided on the oxide layer, the inorganic conductive layer has a first conductive layer containing a metal and / or a metal compound and a second conductive layer containing carbon; the first conductive layer has an uneven portion on its surface side, the second conductive layer is located on the outermost layer of the inorganic conductive layer; electrode material. [Configuration 2] 2. The electrode material of claim 1, wherein the smooth substrate and the first conductive layer are made of different materials. [Configuration 3] 3. The electrode material of claim 1, wherein the second conductive layer consists essentially of carbon. [Configuration 4] 4. The electrode material according to any one of configurations 1 to 3, wherein the inorganic conductive layer further has a dense layer in which the metal and / or metal compound is densely present, and the dense layer is formed between the oxide layer and the first conductive layer. [Configuration 5] 5. The electrode material according to any one of Aspects 1 to 4, wherein both the first conductive layer and the second conductive layer, or at least the first conductive layer, of the inorganic conductive layer is made of a particle deposition layer, and the first conductive layer contains at least one of titanium, aluminum, and nitrides, oxides, oxynitrides, carbides, and carbonitrides thereof. [Configuration 6] 6. The electrode material according to any one of aspects 1 to 5, wherein the oxide layer is an oxide layer containing phosphorus. [Configuration 7] 7. The electrode material according to any one of aspects 1 to 6, wherein the smooth substrate comprises aluminum or an aluminum alloy. [Configuration 8] 8. The electrode material according to any one of configurations 1 to 7, wherein a mixed layer is formed between the first conductive layer and the second conductive layer, the mixed layer being a mixture of the material constituting the first conductive layer and the material constituting the second conductive layer, and the composition of the mixed layer changes from a component containing substantially only the material constituting the first conductive layer to a component containing substantially only the material constituting the second conductive layer, from the first conductive layer to the second conductive layer. [Configuration 9] 9. The electrode material according to any one of aspects 1 to 8, wherein the carbon is graphite-like carbon. [Configuration 10] 10. The electrode material according to any one of configurations 1 to 9, wherein the static friction coefficient and dynamic friction coefficient of the surface of the surface layer side against the separator paper are higher than the static friction coefficient and dynamic friction coefficient of the surface of the surface layer side against the separator paper of an electrode material having a conductive layer made of carbon as the outermost layer on a smooth base material and no uneven portion on the surface layer side. [Configuration 11] 11. A cathode foil for an electrolytic capacitor, comprising an anode foil and a cathode foil, and at least a conductive polymer interposed between the anode foil and the cathode foil, the cathode foil using the electrode material according to any one of configurations 1 to 10. [Configuration 12] 12. An electrolytic capacitor having at least a conductive polymer interposed between an anode foil and a cathode foil, the electrolytic capacitor having the cathode foil according to claim 11. [Configuration 13] 13. The electrolytic capacitor of claim 12, further comprising an electrolyte interposed between the anode foil and the cathode foil. [Industrial Applicability]

[0063] The electrode material of the present invention can be used as a cathode foil for electrolytic capacitors such as hybrid capacitors, solid electrolytic capacitors, etc. Furthermore, the electrode material of the present invention can be used in various capacitors, various power storage devices such as electric double layer capacitors, lithium ion capacitors, and lithium ion batteries, and various power generation elements such as fuel cells, solar cells, thermoelectric power generation elements, and vibration power generation elements. [Explanation of symbols]

[0064] 1. Cathode foil (electrode material) 2 Base material 3. Oxide layer 4. First conductive layer (concave-convex layer) 5 Second conductive layer 6 Layer compacta 7 Mixed Layer 8 Wound solid electrolytic capacitors, wound hybrid capacitors 9 Anode foil 10 Cathode foil 11 Separator paper 12 Capacitor element 13 Anode terminal 14 Cathode terminal 15 Aluminum case 16 Sealing rubber

Claims

1. An oxide layer is provided on a smooth substrate, and an inorganic conductive layer is provided on the oxide layer, the inorganic conductive layer has a first conductive layer containing a metal and / or a metal compound and a second conductive layer containing carbon; the first conductive layer has an uneven portion on its surface side, the second conductive layer is located on the outermost layer of the inorganic conductive layer; electrode material.

2. The electrode material according to claim 1 , wherein the smooth substrate and the first conductive layer are made of different materials.

3. 3. The electrode material according to claim 1, wherein the second conductive layer consists essentially of carbon.

4. 3. The electrode material according to claim 1, wherein the inorganic conductive layer further comprises a dense layer in which the metal and / or metal compound is densely present, the dense layer being formed between the oxide layer and the first conductive layer.

5. 3. The electrode material according to claim 1, wherein both the first conductive layer and the second conductive layer, or at least the first conductive layer, of the inorganic conductive layers are made of particle deposition layers, and the first conductive layer contains at least one of titanium, aluminum, and nitrides, oxides, oxynitrides, carbides, and carbonitrides thereof.

6. 3. The electrode material according to claim 1, wherein the oxide layer is an oxide layer containing phosphorus.

7. The electrode material according to claim 1 or 2, wherein the smooth substrate comprises aluminum or an aluminum alloy.

8. 3. The electrode material according to claim 1, wherein a mixed layer is formed between the first conductive layer and the second conductive layer, the mixed layer being a mixture of a material constituting the first conductive layer and a material constituting the second conductive layer, and the composition of the mixed layer changes from a component containing substantially only the material constituting the first conductive layer to a component containing substantially only the material constituting the second conductive layer, from the first conductive layer to the second conductive layer.

9. 3. The electrode material according to claim 1, wherein the carbon is graphite-like carbon.

10. 3. The electrode material according to claim 1 or 2, wherein the static friction coefficient and dynamic friction coefficient of the surface of the surface layer side relative to the separator paper are higher than the static friction coefficient and dynamic friction coefficient of the surface of the surface layer side relative to the separator paper of an electrode material having a conductive layer made of carbon as the outermost layer on a smooth base material and no uneven portion on the surface layer side.

11. 3. A cathode foil for an electrolytic capacitor, comprising an anode foil and a cathode foil, and at least a conductive polymer interposed between the anode foil and the cathode foil, the cathode foil using the electrode material according to claim 1 or 2.

12. An electrolytic capacitor having at least a conductive polymer interposed between an anode foil and a cathode foil, the electrolytic capacitor comprising the cathode foil according to claim 11.

13. 13. The electrolytic capacitor according to claim 12, further comprising an electrolyte interposed between the anode foil and the cathode foil.

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