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

Abstract

The objective is to realize an electrode material, etc., that can be used for a negative electrode foil for an electrolytic capacitor, having at least one of the following advantages: good adhesion to a solid electrolyte and low contact resistance at the interface; having a layer (geometric structure / surface modification) for maintaining the solid electrolyte and electrolyte solution; excellent heat resistance to the solid electrolyte, electrolyte solution, and moisture; having no capacitance component or having a low capacitance component and acting as a low-resistance conductor (not exhibiting synthetic capacitance or having low synthetic capacitance); being capable of being thinned; being low-cost; and not easily causing winding misalignment. An electrode material is provided having an oxide layer on a smooth substrate and an inorganic conductive layer on the oxide layer, wherein the inorganic conductive layer comprises a first conductive layer comprising a metal and / or a metal compound and a second conductive layer comprising carbon, wherein the first conductive layer has an uneven portion on its surface side and the second conductive layer is located on the outermost side of the inorganic conductive layer.

Description

Technology Field

[0001] The present invention relates to a negative electrode foil for an electrolytic capacitor and an electrolytic capacitor, which can be used in electrode materials, particularly in electrolytic capacitors such as solid-state electrolytic capacitors and hybrid capacitors. Background Technology

[0002] The functions and characteristics required for the negative electrode of a hybrid capacitor are,

[0003] (i) It should have good adhesion to the solid electrolyte and low contact resistance at the interface.

[0004] (ii) There shall be a solid electrolyte and a layer (geometric structure / surface modification) to retain the electrolyte.

[0005] (iii) It shall be resistant to deterioration caused by solid electrolytes, chemical polymerization solutions, electrolytes, and moisture.

[0006] (iv) It shall act as a conductor having no capacitance component, or having a low capacitance component and low resistance.

[0007] (v) Park Hyung-hwa will be able to realize it.

[0008] (vi) It should be low-cost.

[0009] Examples include the above, and excluding compatibility with the electrolyte among (ii) and (iii) above, these can be considered very important functions and characteristics for the cathode of a solid electrolytic capacitor.

[0010] In this regard, for example, a foil having a smooth titanium layer and a smooth carbon layer on top of it has insufficient adhesion to the dispersion of a solid electrolyte, particularly an aqueous solution as the dispersion medium (i), and poor retention of the electrolyte (ii). In particular, it is difficult to maintain a sound dope state with respect to a solid electrolyte made of a conductive polymer, and thus it becomes high resistance when used as a device. The etched cathode foil is difficult to miniaturize because of its thick thickness, and when combined with an anode to form a capacitor, it generates a composite capacitance, which lowers the capacitance extraction rate of the anode. Furthermore, while the ESR (Equivalent Series Resistance) is low at high frequencies such as 100 kHz, it becomes significantly higher at low frequencies such as 120 Hz, and there are problems such as a narrow frequency range with low ESR. There is a concern regarding low-temperature performance because the contact resistance with the solid electrolyte is high and the parts not coated with the solid electrolyte are dependent on the electrolyte. Additionally, there is a risk that the cathode foil may become locally oxidized during the aging anodic oxidation process after device formation, leading to concerns about reduced capacitance or increased resistance. For example, the oxidized film layer applied to an aluminum substrate provides a certain protective function against the electrolyte. However, for solid electrolytes made of conductive polymers, it is difficult to completely suppress chemical reactions with chemical polymerization agents or acidic electrolytes used to maintain the dope state of the solid electrolyte, as well as chemical reactions with the substrate due to small amounts of moisture. Furthermore, if the natural oxide film or the oxidized film comes into direct contact with the solid electrolyte in its original state, a depletion layer forms at the contact interface, which causes a problem of increased contact resistance.

[0011] In the case of a etched foil with an intermediate layer (titanium layer) and a carbon layer, the thickness is thin, and it is possible to retain the conductive polymer or electrolyte in the etched layer. However, the titanium layer or carbon layer applied to the etched layer cannot completely coat the interior of the etched layer, so an aluminum oxide layer is required to protect it from the electrolyte, solid electrolyte, and chemical polymerization solution (for example, a etched film of about a few volts is required). Although this etched film layer also has the same function of protecting from the electrolyte as above, it acts as an insulator as is, so it is highly likely to cause high resistance. Furthermore, most of these problems can be said to apply to solid electrolytic capacitors in which the electrolyte consists only of a solid electrolyte and no electrolyte is interposed.

[0012] Various types of cathode foils have been conventionally developed for use in electrolytic capacitors, such as solid-state electrolytic capacitors and hybrid capacitors. Patent documents 1 and 3 describe an electrolytic capacitor in which an inorganic conductive layer is formed on the surface of a cathode foil that has been roughened by etching (a surface expansion rate of 1.5 to 500 times). However, regarding these cathode foils,

[0013] · When using an etched substrate that has been flattened by etching a smooth substrate, it is difficult for the material of the inorganic conductive layer to penetrate into the interior of the etched layer, and since it is difficult to completely cover the interior of the etched layer with the material of the inorganic conductive layer, there are parts where the aluminum component of the substrate is exposed.

[0014] · An aluminum oxide film exists on the surface of the exposed aluminum, and since aluminum oxide is an insulator, it becomes high resistance.

[0015] · Exposed aluminum has poor chemical resistance and has durability issues with polymers or electrolytes.

[0016] · Since the substrate is dissolved by etching, there are significant challenges in terms of handling strength, thinning, residual chlorine, wastewater treatment, and manufacturing costs.

[0017] There are problems such as the above.

[0018] In addition, Patent Document 4 describes a negative electrode foil for an aluminum electrolytic capacitor, characterized by having a first layer formed on the surface of an aluminum foil, the first layer being composed of at least one of a metal and its nitride, carbide, carbonitride, or oxide, and a second layer formed on the first layer being composed of at least one of a metal and its nitride, carbide, carbonitride, or oxide, wherein the first layer has a denser structure than the second layer. However, the invention described in Patent Document 4 is a negative electrode for a capacitor that uses only an electrolyte containing water as the electrolyte, and focuses on improving water resistance, so there is room for improvement in lowering the resistance and enhancing the durability of the negative electrode that can be used in electrolytic capacitors such as hybrid capacitors and solid electrolytic capacitors.

[0019] Patent Document 2 describes a negative electrode foil for a hybrid capacitor in which a carbon layer is formed thereon using a smooth substrate. Additionally, Patent Document 5 describes a negative electrode foil for a solid electrolytic capacitor in which carbon is present on a metal layer using a smooth substrate. However, since there are no uneven parts on the surface side of these negative electrode foils, it is believed that there is room for further improvement in terms of ESR and durability. Furthermore, because the surface side of the negative electrode foil does not have uneven parts, the frictional force with the separator paper is weak, making it prone to causing a winding misalignment problem in which the negative electrode foil protrudes in the drawing direction of the winding jig during the drawing process of the electrolytic capacitor element winding process.

[0020] Patent Document 9 describes an electrolytic capacitor using a cathode comprising a plurality of metal particles having a median diameter of about 20 to about 500 micrometers, which are disposed on the surface of a substrate and sintered. However, the size in micrometer units is excessively large, making it impossible to obtain the geometric structure necessary for maintaining the solid electrolyte and the electrolyte, thus leaving room for improvement. Additionally, prior art can be cited in Patent Documents 6 to 8 and 10 to 24, but it is believed that there is room for improvement in function and performance in all of them. Prior art literature

[0021] International Publication No. 2016 / 174806 International Publication No. 2016 / 174807 International Publication No. 2016 / 189779 Japanese Published Patent Application No. 2014-022707 Japanese Published Patent Application No. 2012-174865 Japanese Published Patent Application No. 2023-002273 International Publication No. 2017 / 090241 Japanese Published Patent Application No. 2019-179884 Japanese Published Patent Application No. 2007-243203 Japanese Published Patent Application No. 2015-073015 Japanese Published Patent Application No. 2019-179884 U.S. Patent No. 10896783 Specification International Publication No. 2021 / 107063 International Publication No. 2012 / 115050 Japanese Published Patent Application Japanese Published Patent Application No. 2004-281223, Japanese Published Patent Application No. 2012-195527, Japanese Published Patent Application No. 2011-192924, Japanese Published Patent Application No. 2021-145135, Specification of U.S. Patent Application Publication No. 2009 / 0161299, Specification of European Patent Application Publication No. 3817020, Specification of U.S. Patent Application Publication No. 2014 / 0036416, Specification of U.S. Patent Application Publication No. 2021 / 0383981, Japanese Published Patent Application No. 2005-294500, International Publication No. 2010 / 029598, Japanese Published Patent Application No. 2006-190878, Japanese Published Patent Application No. 2022-057601, Japanese Published Patent Application No. 2022-057985 The problem to be solved

[0022] Taking the above into consideration, the present invention comprises the following (1) to (7):

[0023] (1) It should have good adhesion to the solid electrolyte and low contact resistance at the interface.

[0024] (2) It shall have a solid electrolyte and a layer (geometric structure and surface modification) to retain the electrolyte.

[0025] (3) Excellent heat resistance to solid electrolytes, chemical polymerization solutions, electrolytes, and moisture.

[0026] (4) It shall act as a conductor that has no capacitance component, or has a low capacitance component and low resistance.

[0027] (5) Park Hyung-hwa will be able to realize it.

[0028] (6) It should be low cost.

[0029] (7) It will not cause misalignment of the coil.

[0030] The objective is to realize an electrolytic capacitor having an electrode material that can be used for a cathode foil for an electrolytic capacitor, having at least one of the following advantages, or a cathode foil using such an electrode material. means of solving the problem

[0031] To solve the above problem, the present invention provides an electrode material having an oxide layer on a smooth substrate and an inorganic conductive layer on the oxide layer, wherein the inorganic conductive layer comprises a first conductive layer comprising a metal and / or a metal compound and a second conductive layer comprising carbon, wherein the first conductive layer has an uneven portion on its surface side and the second conductive layer is located on the outermost layer of the inorganic conductive layer. In this context, "smooth substrate" refers to a substrate that has not undergone surface roughening treatment such as etching, but the surface of the substrate does not need to be completely flat. The smooth substrate includes, for example, a substrate having minute roughness or undulations on its surface caused by unavoidable rolling streaks or scratches that occur slightly during a foil manufacturing process such as rolling (naturally, the surface of the substrate may be completely smooth). Furthermore, "oxide layer" may be an oxide layer formed without special treatment, such as a natural oxide film, or an oxide layer intentionally formed by treatment such as chemical conversion treatment. The oxide layer may completely cover the smooth substrate or partially cover it, and, for example, the smooth substrate and the first conductive layer may be in direct contact by the material of the dense layer of the first conductive layer penetrating a portion of the oxide layer (forming the dense layer by the arc ion plating (AIP) method described later, etc.). 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 said uneven portion (refer to FIG. 1, etc. relating to an embodiment described later), but the "layer" in the above substrate and subsequent substrates may be a "layer" formed by being divided into multiple parts in such a way (not limited to the second conductive layer, but applies equally to any layer).

[0032] The smooth substrate and the first conductive layer may be composed of different materials.

[0033] The second conductive layer may substantially be a layer made of carbon.

[0034] Furthermore, among the descriptions above, the phrases "substantially composed of carbon" or "composed of carbon" do not necessarily mean that the second conductive layer contains absolutely no components other than carbon. The actual composition of the components may vary depending on the control of component purity within the layer, technical limitations regarding the incorporation of impurities, or the degree of resistance as an allowable error for the electrode material in individual products (components other than carbon may be included in the second conductive layer within a range where the function of the electrode material is maintained to an acceptable level). This point applies equally to descriptions such as "substantially composed of ~," "composed of ~," "substantially containing only ~," and "containing only ~."

[0035] The inorganic conductive layer may additionally have a dense layer in which a metal and / or metal compound is densely present, and the dense layer may be formed between the oxide layer and the first conductive layer. In addition, the term "densely present" as used herein means that (the metal and / or metal compound) is present more densely than in the "uneven portion."

[0036] Among the inorganic conductive layers, both the first conductive layer and the second conductive layer, or at least the first conductive layer may be a layer composed of a particle deposition layer, and the first conductive layer may be a layer comprising at least one of titanium, aluminum, their nitrides, oxides, oxynitrides, carbides, and carbonitrides. The materials that can be used for the first conductive layer are not limited to these, but when using an aluminum substrate as the substrate, it is particularly preferable to use a metal including titanium (Ti) and aluminum (Al) (which may include multiple components such as alloys, provided that it does not impair adhesion to the substrate or conductivity in the first conductive layer).

[0037] The oxide layer may be an oxide layer containing phosphorus.

[0038] The smooth substrate may be a substrate containing aluminum or an aluminum alloy. In addition, the material that can be used as a substrate is not limited to aluminum, and any other material such as tantalum (Ta), titanium (Ti), niobium (Nb), hafnium (Hf), zirconium (Zr), zinc (Zn), tungsten (W), which are valve metals, or an aluminum alloy in which any of these materials are added to aluminum may be used.

[0039] The maximum value of the current of the cyclic voltamogram obtained by the cyclic voltammetry method under conditions where the working electrode is made of the above electrode material, with a sweep range of ±0.3 VvsPt, a sweep rate of 500 mV / sec, an electrolyte of 30 ℃, a reference electrode of Pt, a counter electrode of stainless steel, and the working electrode is made of the above electrode material, may be 6.5 times or more the maximum value of the current of the cyclic voltamogram when the working electrode is made of the above smoothing substrate under the above conditions.

[0040] Between the first conductive layer and the second conductive layer, a mixed layer is formed in which the material constituting the first conductive layer and the material constituting the second conductive layer are mixed. The composition of the mixed layer may be configured to change from a component substantially containing only the material constituting the first conductive layer to a component substantially containing only the material constituting the second conductive layer as it extends from the first conductive layer to the second conductive layer. As previously described, "substantially containing only the material constituting the first conductive layer" and "substantially containing only the material constituting the first conductive layer" do not necessarily mean that no components other than the "material constituting the first conductive layer" are included at all, and "substantially containing only the material constituting the second conductive layer" and "substantially containing only the material constituting the second conductive layer" do not necessarily mean that no components other than the "material constituting the second conductive layer" are included at all (other components may be included within a range where the function of the electrode material is maintained to an acceptable degree).

[0041] In addition, the phrase “changes from a component containing only the material constituting the first conductive layer to a component containing only the material constituting the second conductive layer as it moves from the first conductive layer to the second conductive layer” in the description above does not necessarily mean that the content of the material constituting the second conductive layer within the mixed layer increases monotonically with respect to the direction from the first conductive layer to the second conductive layer. Depending on variations in the concentration of each component caused by limitations in manufacturing technology, the actual components at each location within the mixed layer may vary in various ways. However, preferably, the mixed layer is formed such that the content of the material constituting the second conductive layer continuously increases as it moves from the first conductive layer to the second conductive layer.

[0042] Between the first conductive layer and the second conductive layer, a mixed layer is formed in which the material constituting the first conductive layer and the material constituting the second conductive layer are mixed, and the composition of the mixed layer is configured to change from a component containing only the material constituting the first conductive layer to a component containing only the material constituting the second conductive layer as it moves from the first conductive layer to the second conductive layer, and when the amount of each C bond state is analyzed in the depth direction from the surface layer of the second conductive layer by XPS (X-ray photoelectron spectroscopy), the ratio of the amount of bonds between the metal element atoms constituting the first conductive layer and carbon atoms to the sum of the amounts of each C bond state according to the C1s spectrum may be 5% or more.

[0043] With respect to the full width at half maximum of the G band peak obtained by peak separation in the Raman spectrum by Raman spectroscopy, the full width at half maximum of the carbon included in the second conductive layer may be 3.8 times or more than the full width at half maximum of the graphite crystal.

[0044] The material constituting the first conductive layer and the material constituting the second conductive layer may be different from each other.

[0045] The BET specific surface area using krypton (Kr) as the adsorbed gas may be 1.5 times or more the BET specific surface area of ​​the smooth substrate.

[0046] The average diameter of the convex portion of the uneven portion on the surface side of the inorganic conductive layer may be 210 nm or less.

[0047] The carbon can be graphite-like carbon.

[0048] Although there are no specific restrictions on which material to use as carbon, it is preferable to use graphite-like carbon, which exhibits particularly excellent electrical conductivity among carbon materials, in order to reduce the ESR of the electrolytic capacitor. It is also desirable in terms of manufacturing cost. Here, graphite-like carbon refers to diamond bonding (sp of carbon atoms). 3 Hybrid orbital bonding) and graphite bonding (sp bonding between carbons) 2 It refers to carbons having an amorphous structure in which both directions of hybrid orbital bonding are intermingled, wherein the proportion of graphite bonds exceeds 50% (where the number of graphite bonds is greater than the number of diamond bonds). However, in addition to the amorphous structure, crystal structures consisting partially of a graphite structure (i.e., sp²) 2 It also includes having a phase consisting of a hexagonal crystal structure formed by hybrid orbital bonding. sp in carbon 3 Bonding and sp 2 The ratio of the bonding states can be interpreted by Raman spectroscopy or XPS (X-ray photoelectron spectroscopy (another name for ESCA)).

[0049] In an electrode material of one embodiment of the present invention, the static friction coefficient and the dynamic friction coefficient with respect to the separator sheet on the surface of the surface side may each be higher than the static friction coefficient and the dynamic friction coefficient with respect to the separator sheet on the surface of the electrode material having a conductive layer on the outermost surface side made of carbon on a smooth substrate and not having an uneven portion on the surface side.

[0050] Furthermore, the present invention provides a cathode foil for an electrolytic capacitor in which at least a solid electrolyte is interposed between an anode foil and a cathode foil, using the electrode material of the present invention described above.

[0051] In addition, the present invention provides an electrolytic capacitor having the cathode foil of the present invention described above, wherein at least a solid electrolyte is interposed between the anode foil and the cathode foil. In one example, a solid electrolytic capacitor is provided.

[0052] The above electrolytic capacitor may be an electrolytic capacitor in which an additional electrolyte is interposed between the positive electrode foil and the negative electrode foil. In one example, a hybrid capacitor is provided. Effects of the invention

[0053] By the present invention, an electrode material that can be used for a negative electrode foil for an electrolytic capacitor, etc., having at least one of the advantages of (1) to (7) described above regarding the problem to be solved by the invention, or an electrolytic capacitor having a negative electrode foil using such electrode material is realized. Specifically, for example, it is as follows.

[0054] By using a smooth foil instead of an etched substrate, there is no concern about residual chlorine, and since it is difficult for the material of the inorganic conductive layer to penetrate into the etched layer, there is no risk of the aluminum being exposed. As a result, it is possible to achieve excellent heat resistance (chemical resistance and durability) against solid electrolytes, chemical polymerization agents, electrolytes, and moisture ((3)), and it is possible to make it thin while maintaining strength ((5)). Additionally, since the etching process can be eliminated, it is possible to reduce costs, including the issue of waste liquid equipment ((6)).

[0055] · On a smooth foil, in one example, by depositing an inorganic conductive layer having an uneven surface on the surface side, it is possible to have a layer with a geometric structure suitable for holding a solid electrolyte and an electrolyte ((2)).

[0056] · Adhesion with solid electrolyte is improved by the geometric irregular structure applied to the surface side ((1)).

[0057] · Due to the geometric irregular structure applied to the surface side, the stopping and dynamic friction force (angular friction coefficient) with the separator is increased, thereby suppressing the occurrence of the winding misalignment problem that is prone to occur during the drawing of the winding core jig in the element winding process of the electrolytic capacitor ((7)).

[0058] · By forming a layer containing carbon on the outermost layer of the inorganic conductive layer, it becomes possible to make a cathode foil that has low resistance and no capacitance component (the formation of a depletion layer due to contact between the solid electrolyte and, for example, an aluminum oxide film is suppressed by forming a first conductive layer containing a metal and / or a metal compound and a second conductive layer containing carbon on the aluminum oxide layer, thereby significantly reducing the contact resistance with the solid electrolyte) ((1) and (4)). Brief explanation of the drawing

[0059] FIG. 1 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention. FIG. 2 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention (Variation Example 1). FIG. 3 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention (Variation Example 2). FIG. 4 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention (Variation Example 3). FIG. 5 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 the substrate, unlike FIG. 1, in one embodiment of the present invention. FIG. 6 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 the substrate, unlike FIG. 2, in one embodiment of the present invention. FIG. 7 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 the substrate, unlike FIG. 3, in one embodiment of the present invention. FIG. 8 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 the substrate, unlike FIG. 4, in one embodiment of the present invention. FIG. 9 is an exploded view showing the structure of a wound-type solid electrolytic capacitor and a wound-type hybrid capacitor, which are embodiments of the present invention. FIG. 10 is a TEM (Transmission Electron Microscopy) photograph (cross-sectional image) of a cathode foil using an electrode material according to one embodiment of the present invention (Example 2 described below). FIG. 11 is a TEM photograph (cross-sectional image) of a cathode foil using an electrode material which is another embodiment of the present invention (Example 4 described below). FIG. 12 is a STEM (Scanning Transmission Electron Microscopy) photograph (cross-sectional image) of the same cathode foil (Example 2) as FIG. 10. FIG. 13 is a STEM photograph (cross-sectional image) of the same cathode foil (Example 4) as FIG. 11. FIG. 14 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil (Example 2) as FIG. 10. FIG. 15 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil (Example 4) as FIG. 11. FIG. 16 is a graph showing the analysis results by ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) of the cathode foil (Example 2) as in FIG. 10 (showing the profile distribution of the chemical bonding state). FIG. 17 is a graph showing the results of analysis by ToF-SIMS of the same cathode foil as FIG. 11 (Example 4) (showing the profile distribution of the chemical bonding state). FIG. 18 is a graph (wave frequency region) of the Raman scattering spectrum obtained by laser micro Raman spectroscopy of the same cathode foil (Examples 2 and 4) as FIG. 10 and 11. FIG. 19 is a graph (CC coupling region) of the Raman scattering spectrum obtained by laser micro Raman spectroscopy of the same cathode foil (Examples 2 and 4) as FIG. 10 and 11. FIG. 20 is a table showing the results of ESR measurements performed on each of Examples 1 to 11 of the hybrid capacitor and Comparative Examples 1 to 3 of the hybrid capacitor. FIG. 21 is a table showing the results of ESR measurements performed on each of Examples 1 to 11 of solid electrolytic capacitors and Comparative Examples 1 to 3 of solid electrolytic capacitors. Figure 22 shows the elemental profile distribution obtained by TEM-EDS (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy) on the same cathode foil as in Figure 10. FIG. 23 is the elemental profile distribution obtained by TEM-EDS of the same cathode foil (Example 4) as FIG. 11. FIG. 24 shows the elemental profile distribution obtained by STEM-EELS (Scanning Transmission Electron Microscopy-Electron Energy Loss Spectroscopy) of the same cathode foil as FIG. 10 (Example 2) (carbon conductive layer side than FIG. 25). FIG. 25 shows the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 10 (Example 2) (see Figure 24). FIG. 26 shows the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 11 (Example 4) (carbon conductive layer side than FIG. 27). FIG. 27 shows the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 11 (Example 4) (see FIG. 26). FIG. 28 is a table showing the results of a tape adhesion test performed on each of the cathode foils of Examples 1, 2, 4, and 5 and the cathode foil of Comparative Example 1. FIG. 29 is a table showing the results of contact angle measurements performed on each of the cathode foils identical to FIG. 10 and FIG. 11 (Examples 2 and 4) and the cathode foil of Comparative Example 1, and the details of the surface free energy calculated therefrom (hydrogen bonding component and dispersion force component). FIG. 30a) is a Scanning Electron Microscopy (SEM) image (surface image) of the same cathode foil as FIG. 10 (Example 2). FIG. 30b) is an SEM image (surface image) of the same cathode foil as FIG. 11 (Example 4). FIG. 30c) is an SEM image (surface image) of the cathode foil of Example 5. FIG. 30d) is an SEM image (surface image) of the cathode foil of Example 6. FIG. 31 is a table showing the average diameter (Pere diameter) of Examples 1 to 6 and 8. FIG. 32a) is a graph showing the abundance of each element in the depth direction obtained by XPS (X-ray photoelectron spectroscopy) of the same cathode foil (Example 2) as FIG. 10. FIG. 32b) is a graph showing the sum of each C bond state in the depth direction and the abundance of TiC bonds obtained by XPS of the same cathode foil (Example 2) as FIG. 10. FIG. 33 is a narrow scan spectrum resulting from the C-bond state obtained by XPS of the same cathode foil (Examples 2 and 4) as FIG. 10 and 11. FIG. 34 is a table showing the static friction coefficient and average dynamic friction coefficient of the cathode foils of Examples 2, 4, and 5 and Comparative Example 1. FIG. 35 is a diagram showing the separation of the G band peak from the spectrum obtained by Raman spectroscopy of the same cathode foil (Example 2) as FIG. 10. FIG. 36 is a table showing the ratio of the BET specific surface area by the Kr adsorption method to the BET specific surface area of ​​the smooth substrate for the cathode foils of Examples 1 to 8. Specific details for implementing the invention

[0060] Hereinafter, as an embodiment of the present invention, a negative electrode foil for an electrolytic capacitor using an electrode material and an electrolytic capacitor using the negative electrode foil will be described. However, as previously described, the aluminum foil used as a substrate in the following description, and titanium (Ti) or aluminum (Al) for forming the first conductive layer, can be replaced with other materials. For example, materials for forming the first conductive layer may include 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 first conductive layer may include any material other than these. The same applies to other layers). Carbon is not limited to graphite-like carbon, but may be any carbon material. Furthermore, the use of the electrode material of the present invention is not limited to negative electrode foils for solid-state electrolytic capacitors or hybrid capacitors, but the electrode material may be used for electrodes (any electrodes such as negative electrodes, positive electrodes, positive electrodes, negative electrodes, etc.) of any other capacitor elements, such as secondary batteries, electric double-layer capacitors, and lithium-ion capacitors. The electrolytic capacitor of the present invention is not limited to the wound-type electrolytic capacitor described below, but may be any type, such as a stacked type or a chip type. The uneven surface of the first conductive layer shown in FIG. 1, etc., described below does not need to be formed on the entire surface of the first conductive layer on the surface side, and may be formed only partially on the surface side of the first conductive layer (naturally, the uneven surface may be formed on the entire surface side of the first conductive layer).The “smooth” substrate mentioned in Fig. 1, etc., described below, does not necessarily have to have a smooth surface on its entire surface, and even if there are minute roughness or undulations on the surface caused by unavoidable rolling streaks or scratches that occur slightly during a thin sheet manufacturing process, such as rolling, for example, it is included in the “smooth substrate” (naturally, the surface of the substrate may be completely smooth in the smooth substrate). The “second conductive layer” described in relation to Fig. 1, etc., described below may be a layer consisting (substantially) of carbon only, but may also be a layer containing any of other components other than 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 content. Furthermore, it is not mandatory for the electrode material, the negative electrode foil for an electrolytic capacitor, or the electrolytic capacitor of the present invention to possess all of the layers, components, and structures described in the following embodiments, and the electrode material and the negative electrode foil for an electrolytic capacitor may not possess at least one layer among a dense layer and a mixed layer. In FIG. 1 and others described later, the first conductive layer, etc. is formed on both sides of the smooth substrate, but various layers or elements such as uneven parts may be formed only on one side of the smooth substrate or on both sides. It is also possible to construct an electrolytic capacitor having an electrode material or a negative electrode foil using the electrode material, such that an oxide layer is formed on the first side (the surface side) of the smooth substrate but an oxide layer is not formed on the second side (the surface side), and different layer structures are formed on the first and second sides of the substrate, and the presence or absence and arrangement of elements such as uneven parts are different from the present invention on one side.Other layers, elements, structures, features, etc. may also be appropriately omitted as long as the electrode material, cathode foil for an electrolytic capacitor, or electrolytic capacitor of the present invention can perform its function. Furthermore, as long as the electrode material or electrolytic capacitor of the present invention can perform its function, the electrode material, cathode foil for an electrolytic capacitor, or electrolytic capacitor of the present invention may possess layers, elements, structures, features, etc., other than those described in the following embodiments. Additionally, in the electrolytic capacitor of the present invention, any of the electrode materials of the present invention may be used as the cathode foil. Each of the described layers, elements, structures, features, etc. may be arbitrarily selected and appropriately combined, and the electrode material, cathode foil for an electrolytic capacitor, electrolytic capacitor, etc. obtained after such selection and combination are all included within the scope of the present invention.

[0061] In addition, the heat resistance to the solid electrolyte, chemical polymerization solution, electrolyte, and moisture described above can be further improved by doing as follows.

[0062] If the adhesion at the interface between the smooth foil and the deposited layer is insufficient, the deposited layer may be applied after covering with a dense inorganic conductive layer; by covering the smooth foil with a dense inorganic conductive layer, the exposed portion of aluminum can be completely eliminated in one example, and chemical resistance and durability can be improved.

[0063] · It is possible to further improve chemical resistance and durability by applying an oxide film containing phosphorus (P) to a smooth foil and then covering it with a dense inorganic conductive layer (even without forming a dense layer, it is possible to improve chemical resistance and durability by applying an oxide film containing phosphorus to a smooth substrate through chemical treatment, etc.).

[0064] Cathode foil using the electrode material of the present invention

[0065] FIG. 1 is a cross-sectional view showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention. The cathode foil (electrode material) (1) has a substrate (smooth aluminum foil) (2) that has not been roughened by etching treatment, etc., 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) with irregularities formed by Ti or Al, and a second conductive layer (5) formed on the first conductive layer (4).

[0066] Commercially available high-purity aluminum sheets can be used as the smooth aluminum foil (2). The thickness of the aluminum sheet is not particularly limited, but if used as a negative electrode foil for a wound-type electrolytic capacitor (solid electrolytic capacitor, hybrid capacitor, etc.), it is preferable that the thickness be 10 μm or more and 50 μm or less.

[0067] The oxide layer (3) is an oxide layer such as a natural oxide film, or an oxide film intentionally formed by a chemical treatment such as an anodic oxidation or immersion treatment containing phosphorus, and is formed by exposing the smooth aluminum foil (2) to air, performing an anodic oxidation treatment with an ammonium dihydrogen phosphate solution, or heat treating after immersion in an aqueous phosphoric acid solution or an aqueous aluminum phosphate solution.

[0068] The first conductive layer (4) is formed by placing a smooth aluminum foil (2) with an oxide layer (3) formed thereon in a vacuum chamber, or, in the case of forming a dense layer (6) as described later, additionally by placing a smooth aluminum foil (2) with a dense layer (6) formed thereon on the oxide layer (3) by an arc ion plating method or the like in a vacuum chamber, and a metal material of Ti or Al as an evaporation source, then evaporating the metal material, and attaching the evaporated metal material onto the oxide layer (3) (or onto the dense layer (6) in the case of forming the dense layer (6)) (deposition method). As for the deposition method, in addition to the vacuum deposition method described above, a chemical vapor deposition (CVD) method, a sputtering method, etc., can be used, but among vacuum deposition methods, an electron beam deposition method is preferred in terms of controlling the geometric structure. The electron beam deposition method is a method of irradiating a deposition material with an accelerated electron beam to heat and vaporize it, and depositing it onto 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 attached. The particle size of the metal material can be appropriately controlled by adjusting conditions such as the type of gas introduced, the vacuum level, and the temperature of the substrate during deposition. In addition, in the case where an oxide layer (3) is formed and a dense layer (6) is also formed, in the embodiment in which a first conductive layer (4) made of a nitride, oxide, or carbide of a metal such as Ti or Al is additionally formed on a smooth aluminum foil (2) on which the dense layer (6) is formed, the above method can be carried out, for example, in an atmosphere of nitrogen gas, oxygen gas, or hydrocarbon gas such as acetylene gas or methane gas to form the first conductive layer (4).In addition, in the embodiment of forming the first conductive layer (4) made of an oxynitride or carbonitride of a metal such as Ti or Al, 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.

[0069] The second conductive layer (5) is preferably formed using a deposition method, such as ion plating, rather than by dispersing carbon particles in a binder such as a resin binder and then applying it. This is because, in a layer of carbon particles formed by mixing with a binder, the carbon content decreases by the amount of binder actually mixed, and the contact between the material of the first conductive layer in the lower layer and the carbon particles becomes point contact, making it difficult to form a mixed layer. Furthermore, with the coating method described above, it is difficult to increase the electrical conductivity of the interface, the interfacial resistance increases, adhesion deteriorates, and it is difficult to apply a thin and uniform coating. The second conductive layer (5) is preferably formed as a smooth and tight GLC (Graphite-Like Carbon) film. Additionally, carbon is measured by Raman spectroscopy, and the G band peak (sp 2The larger the half-width obtained by separating the bonding portion, the higher the degree of amorphousness, and generally, the density, hardness, and Young's modulus increase. Therefore, it is desirable to make the half-width of the carbon used in the second conductive layer (5) at least 3.8 times the half-width of the crystalline graphite. By doing so, the second conductive layer (5) becomes a film with a high degree of amorphousness and excellent heat resistance (chemical resistance and durability) against solid electrolytes, chemical polymerization solutions, electrolytes, and moisture. In addition, when the second conductive layer (5) is formed on the uneven portion of the first conductive layer (4), since the shape of the second conductive layer (5) depends on the shape of the uneven portion of the first conductive layer (4), the second conductive layer (5) does not necessarily need to have unevenness (its thickness is substantially constant) and may be a smooth and dense film. As shown in FIGS. 1 to 8, the surface of the electrode material (1) has irregularities (however, having irregularities on the surface is not mandatory for the electrode material (1)), so the static friction coefficient and dynamic friction coefficient for the separator sheet on the surface of the electrode material (1) are thought to be higher than the static friction coefficient and dynamic friction coefficient for the separator sheet on the surface of the electrode material that has a conductive layer on the outermost surface of the electrode material made of carbon on a smooth substrate and does not have irregularities on the surface.

[0070] The second conductive layer (5) is obtained in the same way as the dense layer (6), but among them, an ion plating method such as an arc ion plating method, which has a high ionization rate and attachment energy of the film-forming material, is one of the preferred methods because it is easy to form a mutual diffusion state with the first conductive layer and thus has a high effect of reducing interfacial resistance. Specifically, the second conductive layer (5) is formed by placing a laminate in a vacuum chamber in which an oxide layer (3) and a first conductive layer (4) are formed on a smooth aluminum foil (2) (in the case of forming a dense layer (6), a dense layer (6) is additionally formed between the oxide layer (3) and the first conductive layer (4)), and a carbon material that is an evaporation source (for example, a graphite material in the case of forming the second conductive layer (5) as a GLC film), and then evaporating and ionizing the carbon material by generating a vacuum arc discharge between the evaporation source target and the anode, and inducing the carbon cations generated by this into the laminate. Arc ion plating is desirable for the formation of high-melting-point compound films such as carbides or nitrides, as it can locally generate high Joule heat from the arc current on the target and also increase the ionization rate of the evaporated film material due to the high plasma density. At this time, a negative bias voltage may be applied to the laminate to accelerate carbon cations toward the laminate. When imparting an uneven geometric shape to the second conductive layer (5), carbon material (for example, graphite material when the second conductive layer (5) is formed as a GLC film) may be induced using the same electron beam deposition method as the uneven part of the first conductive layer (4). The second conductive layer (5) may contain any component other than carbon, but when forming the second conductive layer (5) containing a component other than carbon, any other material may be prepared in addition to the carbon material as an evaporation source, and the other material may be evaporated and ionized in the same way as the carbon material and induced into the laminate.

[0071] FIG. 2 is a cross-sectional view (Variation Example 1) showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention. Unlike the layer structure of FIG. 1, a dense layer (6) is formed between the oxide layer (3) and the first conductive layer (4).

[0072] The dense layer (6) is formed by placing a smooth aluminum foil (2) with an oxide layer (3) formed thereon and a metal material of Ti or Al, which is an evaporation source, inside a vacuum chamber, then evaporating and ionizing Ti or Al by means of an electron beam and a plasma generating electrode, and inducing the metal cations ionized by the arc discharge generated therefrom to the smooth aluminum foil (2). At this time, a negative bias voltage may be applied to the smooth aluminum foil (2) to accelerate the metal cations toward the smooth aluminum foil (2). Because of this, the Ti or Al ions penetrate the oxide layer (3) formed on the surface of the smooth aluminum foil (2) and adhere strongly to the smooth aluminum foil (2). However, it is not necessary for the material of the first conductive layer (4) and the smooth aluminum foil (2) to adhere to each other by penetrating the oxide layer (3), and the oxide layer (3), such as a natural oxide film or an oxide film formed by an anodic oxidation treatment containing phosphorus, may exist between the first conductive layer (4) and the smooth aluminum foil (2) without having any holes, etc. In addition, in the embodiment of forming a dense layer (6) made of a nitride, oxide, or carbide of a metal such as Ti or Al on the smooth aluminum foil (2) on which the oxide layer (3) is 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 hydrocarbon gas such as acetylene gas or methane gas. In addition, in the embodiment of forming a dense layer (6) made of an oxynitride or carbonitride of a metal such as Ti or Al, for example, the dense layer (6) can be formed in an atmosphere of nitrogen gas and oxygen gas, or nitrogen gas and a hydrocarbon gas such as acetylene gas or methane gas.

[0073] In addition, as a method for forming the dense layer (6), in addition to ion plating methods such as arc ion plating, vacuum deposition, chemical vapor deposition, sputtering, atomic layer deposition, sol-gel method, plating method, coating method, printing method, etc., can be used. In one example, the ion plating method can be used because the ESR of the capacitor is suppressed to a low level by the dense layer (6) and the smooth aluminum foil (2) penetrating the oxide layer (3) and adhering firmly to each other, and because it is easy to form a smooth metal film.

[0074] FIG. 3 is a cross-sectional view (modified example 2) showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention. Unlike the layer structure of FIG. 1, a mixed layer (7) is formed between the first conductive layer (4) and the second conductive layer (5).

[0075] In one example, the mixed layer (7) can be formed by performing both processes such that the process of forming the first conductive layer (4) by a deposition method such as vacuum deposition and the process of forming the second conductive layer (5) by arc ion plating are not completely separated in time as described above, and the process of forming the first conductive layer (4) and the process of forming the second conductive layer (5) are performed simultaneously. By introducing this mixed layer (7), the adhesion and chemical stability between the material constituting the first conductive layer (4) (metal, or any material including metal nitride, oxide, oxynitride, carbide, or carbonitride as described above) and the material constituting the second conductive layer (5) (carbon such as GLC, and any other material included in the second conductive layer (5) if the second conductive layer (5) also includes materials other than carbon) are increased, thereby preventing deterioration of the metal due to chemical reactions.

[0076] In addition, it is preferable that the mixed layer (7) be configured such that, in the boundary region with the first conductive layer (4), it substantially contains only the material constituting the first conductive layer (4), and in the boundary region with the second conductive layer (5), it substantially contains only the material constituting the second conductive layer (5), and in particular, the content of the material constituting the second conductive layer (5) increases continuously as it moves from the first conductive layer (4) to the second conductive layer (5). As an example, such a mixed layer (7) is configured such that,

[0077] (i) When the film formation of the mixed layer (7) begins, only the deposition method, 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, if the second conductive layer (5) includes a material other than carbon, any other material of the second conductive layer (5)),

[0078] (ii) gradually lowering the electron beam irradiation amount for the material constituting the first conductive layer (4) over time, thereby lowering the amount of metal material evaporated in the deposition method which is the process of forming the first conductive layer (4), and at the same time increasing the electron beam irradiation amount for a carbon material such as a graphite material (and, if the second conductive layer (5) also includes a material other than carbon, any other material of the second conductive layer (5)), thereby forming a mixed film 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 as it moves toward the upper layer, and

[0079] (iii) When the film formation process is finished, the deposition method, which is the process for forming the first conductive layer (4), is finished, and only the arc ion plating method, which is the process for forming the second conductive layer (5), is performed, so that a film of only the material constituting the second conductive layer is formed.

[0080] In addition, when forming a mixed layer (7) by a deposition method (first conductive layer (4)) and a sputtering method (second conductive layer (5)), the amount of evaporation of the material of the first conductive layer (4) is reduced over time, and the voltage applied to a carbon target such as a graphite target (and, if the second conductive layer (5) includes a material other than carbon, any other target of the second conductive layer material) is increased (increasing the sputtering rate of the graphite target and, if used, any other target of the second conductive layer material). Such a preferred mixed layer (7) can be formed by any method. In addition, (i) to (iii) are processes mainly suitable for batch-type single-wafer processing, but separately, a mixed layer can also be formed by carrying out a continuous film deposition process in the order of the first to the second while conveying the foil in a chamber in which a material target constituting the first conductive layer and a material target constituting the second conductive layer are arranged in order by a roll-to-roll method. A mixed layer is formed by arranging the first and second evaporation source targets adjacent to each other so that the vapor or ions of each deposition material, which are radiated in a conical shape from each of the first and second evaporation source targets toward the substrate, overlap (come into contact) with each other before they reach the substrate. By appropriately controlling the distance between each deposition source target and the distance between each deposition source target and the substrate, the mixing and diffusion state or bonding state of the mixed layer is adjusted to an optimal state. In this case, adjustment of the electron beam irradiation dose as described above is not performed, and each can always be kept constant, making it a process more suitable for mass production. In addition, regardless of the distance between each deposition source target or the distance between each deposition source target and the substrate, a mixed layer may be obtained by heating the substrate temperature to, for example, several hundred degrees Celsius.

[0081] FIG. 4 is a cross-sectional view (modified example 3) showing the layer structure of a cathode foil using an electrode material in one embodiment of the present invention. Unlike the layer structure of 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).

[0082] In addition, as previously described, it is not mandatory to laminate each layer on both sides of the substrate (2) as shown in FIGS. 1 to 4, and as shown in FIGS. 5 to 8, each layer may be laminated only on one side of the substrate (2), and different layer structures may be formed on the surface side and the back side of the substrate (2), such as 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).

[0083] In addition, the thickness of the oxide layer (3), the dense layer (6), the first conductive layer (4), the mixed layer (7), and the second conductive layer (5) is sufficient to be at least 0.005 μm and at least 1 μm, and if the sum of the thicknesses of each layer excluding the substrate (2) is at least 0.05 μm on the side of the substrate (2), good characteristics as a cathode foil are obtained. However, it does not matter whether each layer is formed thicker or thinner. The thicknesses of each layer in FIGS. 1 to 8 are merely examples, and the thickness of each layer can be determined arbitrarily.

[0084] Determining the actual surface area of ​​the electrode material (1) by the BET specific surface area method, which adsorbs nitrogen gas or krypton gas, is important as an indicator of the retention of solid electrolytes or electrolytes. However, in one embodiment of the present invention, prioritizing this, the electrochemical effective surface area, which includes the ease of electric flow such as the interfacial resistance that becomes important when making an actual capacitor, is evaluated by the cyclic voltammetry method. Under conditions in which 1 M tetraethylammonium hexafluorophosphate with propylene carbonate as the solvent is the electrolyte, a Pt electrode as the reference electrode, stainless steel as the counter electrode, an electrolyte temperature of 30 ℃, a shrinking range of ±0.3 V vs Pt electrode, and a shrinking speed of 500 mV / sec, the voltage was linearly shrunk, and the maximum value of the current in the cyclic voltamogram measured when the electrode material in one embodiment of the present invention is used as the working electrode was compared with the maximum value of the current measured when a smooth substrate is used as the working electrode, thereby serving as an indicator of the electrochemical effective surface area. Furthermore, it is preferable that the maximum value of the current when the electrode material in one embodiment of the present invention is used as the working electrode be at least 6.5 times the maximum value of the current when a smooth substrate is used as the working electrode. By using an electrode material that is at least 6.5 times the value when a smooth substrate is used as the working electrode, an effect of reducing ESR can be obtained through improved retention of the solid electrolyte and the electrolyte.

[0085] As a method for evaluating the bonding between atoms of metal elements constituting the first conductive layer and carbon atoms, the amount of each element in the depth direction and the bonding state can be analyzed by XPS. By repeating etching and measurement at intervals of several nanometers, the ratio of the amount of bonding between atoms of metal elements constituting the first conductive layer and carbon atoms to the sum of the amounts of all bonds involving detected carbon atoms can be interpreted. Therefore, it is desirable that the ratio of the amount of bonding between atoms of metal elements constituting the first conductive layer and carbon atoms to the sum of the amounts of all bonds involving detected carbon atoms be 5% or more, as this ratio results in a low-resistance conductor and an ESR reduction effect can be obtained.

[0086] In addition, when the electrode material in one embodiment of the present invention, in which a valve-acting metal is used as the substrate (2), is used as the negative electrode foil of an electrolytic capacitor, the potential corresponding to the current when a current flows that falls within the range of the leakage current density of the electrolytic capacitor due to electrochemical polarization may be lower than the natural immersion potential of a control negative electrode foil that is of the same type as the valve-acting metal used in the substrate (2) and has a purity of 99.99% or higher, and the natural immersion potential when immersed in the electrolyte may also be lower than the natural immersion potential when a control negative electrode foil that is of the same type as the valve-acting metal used in the substrate (2) and has a purity of 99.99% or higher is immersed in the same electrolyte (Patent Documents 26, 27). By doing so, the generation of hydrogen gas on the negative side can be suppressed when the dielectric oxide film formed on the anode foil is restored by the leakage current. To further explain this point, the control cathode foil has a natural oxide film formed thereon, and possesses a natural immersion potential in which the cathode reaction reducing hydrogen ions occurs predominantly. Furthermore, the cathode foil in one embodiment of the present invention has a natural immersion potential that is more favorable than that of the control cathode foil. Therefore, when the cathode foil in one embodiment of the present invention is embedded in an electrolytic capacitor and leakage current occurs, the potential of the cathode foil in one embodiment of the present invention can be maintained more favorable than that of the control cathode foil. Consequently, when leakage current occurs in the electrolytic capacitor, the potential of the cathode foil in one embodiment of the present invention is within the range of potentials in which the cathode reaction reducing dissolved oxygen occurs predominantly, and the cathode reaction reducing hydrogen ions is suppressed. As a result, since the rise in the internal pressure of the electrolytic capacitor caused by the generation of hydrogen gas is suppressed, the risk of the case housing the capacitor element expanding can be reduced.

[0087] As described above, as a method for determining the actual surface area required to maintain a solid electrolyte and an electrolyte solution in an inorganic conductive layer having an uneven surface portion on the surface side including a first conductive layer and a second conductive layer, the BET specific surface area method using adsorbed nitrogen gas or krypton gas can be cited. Among these, if krypton gas, which has a lower saturated vapor pressure than nitrogen gas, is used as the adsorbed gas, high-precision measurement is possible even in regions with a small specific surface area. It is preferable to set the expansion ratio (BET specific surface area of ​​the electrode material / BET specific surface area of ​​the smooth substrate) calculated from the BET specific surface area using krypton gas as the adsorbed gas to 1.5 or more. By making this expansion ratio 1.5 or more, the retention capacity of the solid electrolyte and an electrolyte solution is further improved, and an additional ESR reduction effect can be obtained. However, while it is possible to increase the surface area by making the first conductive layer thicker, making it excessively thick reduces the volumetric efficiency of the capacitor and also increases manufacturing costs. Therefore, it is more desirable to have a surface area ratio of 1.5 times or more and 200 times or less, calculated from the BET specific surface area using krypton gas as the adsorption gas.

[0088] FIGS. 30a) to d) are scanning electron microscope (SEM) surface photographs of the cathode foils of Examples 2, 4, 5, and 6. Here, although particles are captured in the SEM photographs, these are the convex portions of the uneven surface on the surface side of the electrode material, that is, on the surface side of the inorganic conductive layer. As described above, the electrode material (1) has an oxide layer (3), a first conductive layer (4), a mixed layer (7), and a second conductive layer (5) formed sequentially on a smooth substrate (2), and has an uneven portion on the surface side of the first conductive layer (4). In Examples 2, 4, 5, and 6, the first conductive layer is a particle deposition layer formed by deposition, and the mixed layer and the second conductive layer are formed thereon, but both the mixed layer and the second conductive layer are thin. In this way, when the surface of the cathode foil of each example is observed with an SEM, as shown in FIGS. 30a) to 30d), it appears as if the sample in which only the first conductive layer, which is a particle deposition layer, is formed is being observed. That is, each individual particle identified in the SEM surface image corresponds to each individual convex part of the inorganic conductive layer. Therefore, in Examples 2, 4, 5, and 6, the particle diameter of the particles identified in the SEM surface image was defined as the diameter of the convex part of the uneven portion on the surface side of the inorganic conductive layer. Specifically, the surface of the cathode foil of each example was observed at an observation magnification of 100,000x using a scanning electron microscope (JSM-7401F) manufactured by Nippon Electronics at that time, the Pere diameter of the particles present in the field of view was measured, and that Pere diameter was defined as the diameter of the convex part. In addition, the Peret diameter here is the distance between the left and right tangents of the particle that are parallel to the vertical direction of the field of view, as shown in Fig. 30a).If the diameter of this convex portion is excessively large, the surface area of ​​the uneven portion on the surface side of the electrode material becomes small, making it impossible to obtain the geometric structure necessary for maintaining the solid electrolyte and electrolyte solution. Therefore, it is desirable to make the average diameter of the convex portion of the uneven portion on the surface side of the inorganic conductive layer 210 nm or less. Furthermore, the average diameter here refers to the average of the Pere diameters measured for 50 particles (convex portions) present in the field of view. However, if the number of particles in one field of view is less than 50, measurements are taken for another field of view until the number of particles reaches 50.

[0089] Electrolytic capacitor of the present invention

[0090] Hereinafter, solid electrolytic capacitors and hybrid capacitors are described as examples of electrolytic capacitors that can be manufactured using the cathode foil of the present invention. Here, we describe the case where a cathode foil (1) having a layer structure of FIGS. 1 to FIGS. 4, in which each layer is stacked on both sides of the substrate (2), is used, but an electrolytic capacitor of the present invention can also be manufactured using a cathode foil (1) having a layer structure in which each layer is stacked only on one side of the substrate (2).

[0091] (Solid Electrolytic Capacitor)

[0092] FIG. 9 is an exploded view of a wound-type solid electrolytic capacitor (8) made using a cathode foil (1) having a layer structure of any of FIGS. 1 to 4. The solid electrolytic capacitor (8) is,

[0093] (i) An anode foil (9) formed by forming an oxide film on an anode aluminum foil by an anode oxidation treatment, and a cathode foil (10) having a layer structure of any of the ones shown in FIGS. 1 to 4 are overlapped with a separator paper (11) interposed, and an anode terminal (13) is connected to the anode foil (9) and a cathode terminal (14) is connected to the cathode foil (10), and then the two are wound to produce a capacitor element (12).

[0094] (ii) A condenser element (12) is immersed in a mixed solution of 3,4-ethylenedioxythiophene containing n-butyl alcohol as a diluent and p-toluenesulfonate (II) as an oxidizing agent, and then heated to form a solid electrolyte layer of polyethylenedioxythiophene (PEDOT) by thermal polymerization. Alternatively, a solid electrolyte layer may be formed by immersing and impregnating the condenser element in a PEDOT / PSS aqueous dispersion solution mixed with polystyrenesulfonic acid (PSS) to disperse polyethylenedioxythiophene in an aqueous solution, and then drying.

[0095] (iii) A capacitor element (12) having a solid electrolyte layer is housed in an aluminum case (15) and sealed with a sealing rubber (16).

[0096] It is manufactured by the method described above. In addition, a solid electrolyte layer may be formed by a conductive polymer such as a polypyrrole-based, polyaniline-based, polyacene-based, polyparaphenylenevinylene-based, or polyisothianaphthene-based polymer, or by manganese dioxide (MnO2) or TCNQ (tetracyanoquinodimethane) complex salt.

[0097] (Hybrid Capacitor)

[0098] A hybrid capacitor is produced by performing the processes of (i) and (ii) in the same way as when producing a solid electrolytic capacitor (8),

[0099] (ii-2) A capacitor element having a solid electrolyte layer is impregnated with an electrolyte solution comprising at least one of γ-butylactone, ethylene glycol, and water as a solvent.

[0100] (iii) A solid electrolyte layer is formed, and a capacitor element impregnated with the electrolyte is housed in an aluminum case and sealed with a sealing rubber.

[0101] It is manufactured by the method described above. In addition, a solid electrolyte layer may be formed by a conductive polymer such as a polypyrrole-based, polyaniline-based, polyacene-based, polyparaphenylenevinylene-based, or polyisothianaphthene-based polymer, or by manganese dioxide (MnO2) or TCNQ (tetracyanoquinodimethane) complex salt.

[0102] Examples

[0103] Hereinafter, the structure, analysis results, performance test results, etc. of various cathode foils and electrolytic capacitors fabricated as embodiments of the present invention will be described.

[0104] FIG. 10 is a TEM (transmission electron microscope) photograph (cross-sectional image) of a cathode foil using an electrode material that is an embodiment of the present invention (Example 2 described below). The cathode foil of FIG. 10 has a layer structure shown in FIG. 8 (a layer structure on the one-sided side shown in FIG. 4) (it is presumed that a natural oxide film is formed between the smooth substrate and the dense layer), and is manufactured by forming a dense layer (6) of Ti by an arc ion plating method on an aluminum smooth substrate (2) (on which a natural oxide film (3) is formed), forming a first conductive layer (4) of Ti by a vacuum deposition method, and forming a carbon layer (second conductive layer (5)) of GLC by an arc ion plating method. Such a cathode foil,

[0105] · By using a smooth substrate as the substrate (2), the surface of Al can be coated with Ti without gaps.

[0106] · By making it a granular sedimentation structure, it is possible to adhere to and maintain the polymer or electrolyte.

[0107] Ti pretreatment by arc ion plating can eliminate the influence of residues or oxides on the substrate surface.

[0108] It has the advantage of being different from the cathode foil shown in FIG. 10 (Example 4 described later). FIG. 11 also shows a TEM photograph (cross-sectional image) of a cathode foil different from the cathode foil shown in FIG. 10. The cathode foils shown in FIG. 10 and FIG. 11 are all common in that they are manufactured by forming a dense layer (6) of Ti by arc ion plating on an aluminum smooth substrate (2) (on which a natural oxide film (3) is 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, but the particle size of the metal material (Ti in the samples of FIG. 10 and FIG. 11) included in the first conductive layer (4) is different from each other, and therefore the fineness of the irregularities in the first conductive layer (4) is different from each other.

[0109] FIG. 12 is a STEM (scanning transmission electron microscope) image (cross-sectional image) of the same cathode foil (Example 2) as FIG. 10, and FIG. 13 is a STEM image (cross-sectional image) of the same cathode foil (Example 4) as FIG. 11. As described above, in the first conductive layer (4), the particle size of the metal material can be appropriately controlled by adjusting conditions such as the type of gas introduced, vacuum level, and temperature of the substrate during deposition, so the first conductive layer (4) can be formed with various particle sizes, that is, with various fine irregularities.

[0110] FIG. 14 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil as FIG. 10 (Example 2), and FIG. 15 is a TEM photograph (bright-field image, cross-sectional image) of the same cathode foil as FIG. 11 (Example 4). In either sample of Example 2 or Example 4, a natural oxide film (about a few nm) on the substrate can be identified.

[0111] FIG. 16 is a graph showing the analysis results by ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) of the same cathode foil as FIG. 10 (Example 2) (showing the profile distribution of the chemical bonding state), and FIG. 17 is a graph showing the analysis results by ToF-SIMS of the same cathode foil as FIG. 11 (Example 4) (showing the profile distribution of the chemical bonding state). In the graphs of FIG. 16 and FIG. 17, the vertical axis represents the secondary ion intensity, and the unit is [counts], which represents the number of each secondary ion detected at each measurement depth point. Among the graphs in FIGS. 16 and 17, carbon C6 derived from carbon deposition is a fragment (lump) ion consisting of 6 C atoms and is a monovalent negative ion, metallic titanium Ti2 ion is a monovalent negative ion consisting of 2 Ti atoms, metallic aluminum Al5 ion is a monovalent negative ion consisting of 5 Al atoms, and other TiC2 / TiO2 / TiN / TiNO / Al2O3, etc. are negative ions in their respective molecular bonding states. For example, in Example 4 shown in FIG. 17, it can be seen that the presence of metallic Ti is slight at the substrate interface, and most of it exists as carbide / oxide / nitride / oxynitride. In addition, in both samples of Example 2 and Example 4, a mixed layer of oxide and Ti compound on an aluminum substrate and a mixed layer of Ti compound and C are formed, respectively, and it can be seen that a mixed layer is formed as a gradient film in which the proportion of C increases toward the outermost layer (carbon layer).

[0112] FIG. 18 is a graph (wave frequency region) of the Raman scattering spectrum obtained by laser micro Raman spectroscopy of a cathode foil prepared under the same conditions as the samples shown in FIG. 10 and 11, and FIG. 19 is a graph (CC coupling region) of the Raman scattering spectrum obtained by laser micro Raman spectroscopy of a cathode foil prepared under the same conditions as the samples shown in FIG. 10 and 11. In the graph of FIG. 18, the Raman shift on the horizontal axis is 1500 cm⁻¹ -1 Near the point where the graph with a greater 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 -1 Near the point where the Raman intensity [counts] on the vertical axis is smaller, the graph corresponds to the sample of Example 4. In the graph of Fig. 19, the Raman shift on the horizontal axis is 1100 cm -1 Near the point where the Raman intensity [counts] on the vertical axis is smaller, the graph corresponds to the sample of Example 2, and the Raman shift on the horizontal axis is 1100 cm -1 The graph where the Raman intensity [counts] on the vertical axis is greater in the vicinity corresponds to the sample of Example 4. In particular, from the graph shown in FIG. 19, for both samples of Example 2 and Example 4, sp 3 sp than the Raman intensity in the (D band) 2 It can be seen that the Raman intensity in the (G band) is high, and that the carbon layer (second conductive layer) in both samples is formed including GLC.

[0113] FIG. 33 is a narrow-range scan spectrum of the 280–290 eV range at a point etched 36 nm from the surface layer, obtained by XPS for a cathode foil fabricated under the same conditions as the samples shown in FIG. 10 and 11. When peak separation is performed on the peak originating from the C bond state observed around 280–290 eV, sp² is found around 284.5 eV. 2 The peak originating from is sp near 285.5 eV 3 Peaks originating from each appear. Therefore, it can be seen that the carbon layer in both samples of Example 2 and Example 4 has an amorphous structure (amorphous structure) having a bidirectional bond of graphite and diamond. In addition, when comparing the peak areas, sp 3 See sp 2 It can be seen that the peak area has increased. Therefore, it can be seen from both laser micro Raman spectroscopy as well as XPS that the carbon layer in both samples is formed containing graphite-like carbon in which the ratio of graphite bonds exceeds 50%.

[0114] FIG. 32a) is a graph showing the ratio of atoms in the depth direction obtained by XPS of a sample prepared under the same conditions as the sample shown in FIG. 10. By repeating etching and measurement in nanometer increments from the surface layer, the depth-direction abundance shown in FIG. 32a) is obtained. FIG. 32b) is a graph showing the sum of all C bond states and TiC bonds when the sample shown in FIG. 10 is subjected to peak separation attributable to C bond states as in FIG. 33 until C is no longer detected, with the horizontal axis representing the depth converted to SiO2 and the vertical axis representing the peak area of ​​each C bond state (also, in the sample under analysis in FIG. 32, since the metal element constituting the first conductive layer is titanium, "TiC bond" corresponds to "bonding between atoms of the metal element constituting the first conductive layer and carbon atoms"). For each curve, the integral value was calculated, and the amount of the TiC bonding state (around 282 eV) was divided by the amount of the total C bonding state to determine the ratio of the abundance of the TiC bond. For other metal carbides, the ratio can be calculated from peaks such as the Al4C3 bonding state (around 282.4 eV), TaC bonding state (around 281.9 eV), NbC bonding state (around 281.9 eV), VC bonding state (around 282.5 eV), and WC bonding state (around 283.0 eV).

[0115] Performance test of the hybrid capacitor of the present invention

[0116] In one embodiment of the present invention, the cathode foils of Examples 1 to 11 were prepared as the cathode foils, and the cathode foils of Comparative Examples 1 to 3 were prepared as the cathode foils of Comparative Examples. Hybrid capacitors of Examples 1 to 11 were each fabricated using the cathode foils of Examples 1 to 11, and hybrid capacitors of Comparative Examples 1 to 3 were each fabricated using the cathode foils of Comparative Examples 1 to 3, 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.

[0117] Example 1: Ar gas is introduced into a chamber container that has been vacuumed to 0.003 Pa, and a first target made of Ti material and a second target made of graphite material are arranged adjacent to each other in sequence so that the vapor or ions of each deposition material radiated in a conical shape from each of the first and second targets toward the substrate overlap (contact) each other before reaching the substrate. During this process, a smooth aluminum foil is transported in this sequence, and an uneven Ti layer of 200 nm is imparted by electron beam deposition, and then a carbon film is deposited by arc ion plating. By continuous film deposition using this roll-to-roll method, a mixed layer was obtained at the interface between the oxide layer and the first conductive layer on the smooth substrate, and at the interface between the first conductive layer and the second conductive layer, respectively (in addition, the mixed layer formed at the interface between the oxide layer and the first conductive layer is composed of a mixture of the material constituting the oxide layer and the material constituting the first conductive layer, and is different from a mixture of the material constituting the first conductive layer and the material constituting the second conductive layer). Using the foil as the cathode, a hybrid capacitor was fabricated by combining it with an anode foil (etched aluminum phosphide foil anodic oxidized at 53 V), the initial ESR (100 kHz) was measured, and the ESR (100 kHz) was measured after being left at 125 ℃ for 2000 hr (1 hr is 60 minutes). In addition, the hybrid capacitor was fabricated as follows. That is, first, an anode foil and a cathode foil prepared as described above were overlapped with a separator paper interposed, and after connecting the anode terminal to the anode foil and the cathode terminal to the cathode foil, the two were wound to produce a capacitor element. Next, the capacitor element was immersed in a polymer dispersion solution in an aqueous solution in a container under vacuum of about 7000 Pa, and then a solid electrolyte layer was formed by drying at 150°C for 30 minutes under an atmospheric environment.In addition, the capacitor element was impregnated with an electrolyte containing ethylene glycol as a solvent in a container under vacuum of about 5000 Pa. Finally, the capacitor element was housed in an aluminum case and sealed with a sealing rubber.

[0118] Example 2: An amount of Ar gas equal to that of Example 1 is introduced into a chamber vessel with a vacuum reduced to 0.003 Pa, and a smooth aluminum foil is transported to deposit a 10 nm Ti film by arc ion plating. Then, during the same film deposition process as in Example 1, the aluminum foil with the Ti layer formed by arc ion plating is transported to deposit a 200 nm uneven Ti layer by deposition, and carbon is deposited by arc ion plating. The subsequent steps are the same as in Example 1.

[0119] Example 3: The same treatment as in Example 2 was performed, except that a smooth substrate was used that had been anodic oxidized with an ammonium dihydrogen phosphate solution at an applied voltage of 5 V.

[0120] Example 4: It is identical to Example 2 except that the two types of gases introduced are Ar and N2.

[0121] Example 5: Same as Example 2 except that the Ti layer with irregularities imparted by deposition is 70 nm.

[0122] Example 6: It is identical to Example 2 except that Al is deposited instead of Ti by arc ion plating, and then an Al layer with irregularities is imparted instead of an irregular Ti layer by deposition.

[0123] Example 7: The conditions are the same as in Example 2, except that the amount of Ar gas introduced is 1 / 40th of that in Example 2.

[0124] Example 8: The conditions are the same as in Example 6, except that the amount of Ar gas introduced is one-tenth of that in Example 6.

[0125] Example 9: Same as Example 2 except that the Ti layer with irregularities imparted by deposition is 30 nm.

[0126] Example 10: Same as Example 1 except that an Al layer is imparted instead of a Ti layer with irregularities by deposition.

[0127] Example 11: It is identical to Example 2 except that the introduced gas is only N2 gas.

[0128] Comparative Example 1: A smooth substrate was used, and an amount of Ar gas equal to that of Examples 1 to 3 was introduced. After depositing a Ti film by arc ion plating, a carbon film was deposited by arc ion plating and used as the cathode. Other conditions were the same as in Example 1.

[0129] Comparative Example 2: An etched foil anodic-oxidized at 2 V was used on a substrate, and an amount of Ar gas equal to that of Examples 1 to 3 was introduced to deposit Ti by arc ion plating, and then a carbon film was deposited by arc ion plating and used as the cathode. Other conditions were the same as in Example 1.

[0130] Comparative Example 3: A (dense) Ti layer was formed by vacuum deposition without introducing gas into a smooth substrate, 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 and used as the cathode. Other conditions are the same as those in Example 1. In addition, the film composition of the cathode foil of Comparative Example 3 is the same as the film composition disclosed in the specification of Japanese Patent Publication No. 2014-022707.

[0131] In addition, in the cathode foils of Examples 1 to 11 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 exist in a mixed state. In addition, the carbon layer in Examples 1 to 11 and Comparative Examples 1 and 2 contains GLC.

[0132] For the cathode foils of the examples and comparative examples, the current flowing through them was measured by cyclic voltammetry. The measurements were performed under a nitrogen atmosphere using a glove box. As the measurement solution, 1 M tetraethylammonium hexafluorophosphate with propylene carbonate as the solvent was prepared. The measurement was performed using a three-electrode method, with stainless steel as the counter electrode, a Pt electrode as the reference electrode, and the cathode foil of each example or comparative example as the working electrode. The cyclic voltammetry measurement conditions were set as a measurement solution temperature of 30 °C, a sweep range of ±0.3 V, and a sweep speed of 500 mV / sec. The current and voltage were recorded for 1 to 5 cycles, the maximum current value for each cycle was calculated, and their average value was taken as the maximum current value of the cathode foil of the corresponding example or comparative example. Similarly, the maximum current value was measured for the smooth substrate unit, and the maximum current value was set to 1 to indicate the maximum current value of the cathode foil of each example and comparative example.

[0133] For the cathode foils of the examples and comparative examples, etching and measurement were repeated in increments of 2.5 nm in SiO2 equivalent by XPS to confirm the bonding state in the depth direction. A JPS-9010TR manufactured by Nippon Electronics Co., Ltd. was used as the XPS device, and measurements were taken under the following conditions.

[0134] · X-ray Source: AlKα, Tube Voltage: 10 kV, Tube Current: 10 mA, Microanalysis: None, Dwell: 100 msec, Flood Gun: 3.0 V 4.0 mA

[0135] · Step: Wide range 1.0 eV / Narrow range 0.05 eV

[0136] · Pass : Wide range 50 eV / Narrow range 20 eV

[0137] · Scans : Wide Range 1 / Narrow Range 2

[0138] For the peaks originating from the C bonding state observed at around 270 eV to 290 eV measured at a measurement range of 0.05 eV, peak separation was performed, and the peak area for each C bonding state was calculated. An integral value was calculated for the curve plotted with the horizontal axis representing the depth converted to SiO2 and the vertical axis representing the peak area of ​​each C bonding state, and this was taken as the amount of each C bonding state. The value obtained by dividing the amount of the TiC bonding state (around 282 eV) or the Al4C3 bonding state (around 282.4 eV) by the total amount of the C bonding state was taken as the ratio of the bonding between metal element atoms and carbon atoms in the cathode foils of each example and comparative example.

[0139] For the cathode foils of the examples and comparative examples, sp² obtained by isolating the peaks originating from CC bonds measured by Raman spectroscopy 2 The full width at half maximum (FWHM) of the band (G band) peak was measured. As an example, Fig. 35 shows the spectrum originating from CC bonds obtained by Raman spectroscopy of the sample shown in Fig. 10; this was peak-separated, and the FWHM of the G band peak was measured. For the measurement, a Renishaw-manufactured inVia Qontor was used, a laser with a wavelength of 532 nm was irradiated, and the range was 100–3200 cm⁻¹. -1 A spectrum of the range was used. The full width at half maximum of the crystalline graphite was measured in the same way, and this was set to 1 as the ratio of the full width at half maximum of each example and comparative example.

[0140] FIG. 20 is a table showing the results of ESR measurements performed on the hybrid capacitors of Examples 1 to 11 and the hybrid capacitors of Comparative Examples 1 to 3, respectively. In FIG. 20, "after 2000 hr degradation" indicates that the ESR was measured after the hybrid capacitors were degraded for 2000 hours in an atmospheric environment at 125°C. As can be seen from the ESR measurement results in FIG. 20, first, in the initial state, the ESR of the hybrid capacitors of Examples 1 to 3, 6, and 7 is lower than the ESR of the hybrid capacitors of Comparative Examples 1 to 3, and the ESR of the hybrid capacitors of Examples 4, 5, and 8 to 11 is lower than the ESR of the hybrid capacitors of Comparative Examples 1 and 3 (also nearly equivalent to the ESR of the hybrid capacitor of Comparative Example 2). After 2000 hours of degradation, the ESR of the hybrid capacitors of Examples 1 to 11 is lower than the ESR of the hybrid capacitors of Comparative Examples 1 to 3. That is, on a smooth substrate, an oxide layer, a first conductive layer containing metal, a mixed layer formed by mixing the material constituting the first conductive layer and the material constituting the second conductive layer, and a second conductive layer containing carbon are formed in this order, and by using an electrode material having an uneven portion on the surface side of the first conductive layer as a negative electrode foil, the ESR of the hybrid capacitor at the beginning and after 2000 hours of degradation can be reduced. In addition, Comparative Example 1 is identical to Examples 1 to 11 in that, on a smooth substrate, an oxide layer, a first conductive layer containing metal, a mixed layer formed by mixing the material constituting the first conductive layer and the material constituting the second conductive layer, and a second conductive layer containing carbon are formed in this order; however, unlike Examples 1 to 11, there is no unevenness on the surface side of the first conductive layer. Therefore, it does not have a geometric structure suitable for holding solid electrolyte and electrolyte solution, and both the initial ESR and the ESR after 2000 hours of degradation are high.Comparative Example 2 is identical to Examples 1 to 11 in that, on a substrate, an oxide layer, a first conductive layer containing a metal, a mixed layer formed by mixing the material constituting the first conductive layer and the material constituting the second conductive layer, and a second conductive layer containing carbon are formed in this order; however, unlike Examples 1 to 11, an etched substrate is used as the substrate instead of a smooth substrate. Consequently, the entire surface of the substrate (especially the inner wall of the etching pit) cannot be covered during film formation and is partially exposed, resulting in a high ESR after 2000 hours of degradation. Comparative Example 3 is identical to Examples 1 to 11 in that a first conductive layer containing an oxide layer and a metal is formed in this order on a smooth substrate, and there is an uneven portion on the surface side of the first conductive layer; however, unlike Examples 1 to 11, neither a mixed layer formed by mixing the material constituting the first conductive layer and the material constituting the second conductive layer, nor a second conductive layer containing carbon, is formed on the first conductive layer. Consequently, the first conductive layer comes into direct contact with the solid electrolyte, increasing the interfacial resistance, and both the initial ESR and the ESR after 2000 hours of deterioration are high.

[0141] In addition, FIG. 20 also shows the measurement results by cyclic voltammetry, XPS, and Raman spectroscopy for the cathode foils of Examples 1 to 11 and Comparative Examples 1 to 3. For Examples 1 to 11, initially, the ESR of the hybrid capacitor of Example 9 is nearly equivalent to the ESR of the hybrid capacitors of Examples 1 to 8, 10, and 11, but after 2000 hours of degradation, the ESR of the hybrid capacitor of Example 9 is higher than the ESR of the hybrid capacitors of Examples 1 to 8, 10, and 11. Regarding this point, the multiplier of the maximum current value by cyclic voltammetry is 6.5 times or more for the cathode foils of Examples 1 to 8, 10, and 11, whereas it is only 6.0 times for the cathode foil of Example 9. Therefore, compared to other examples, Example 9 has an insufficient electrochemical effective surface area with ease of electrical flow, so the effect of reducing ESR by improving the retention capacity of the solid electrolyte and electrolyte is not fully exerted, and the ESR after 2000 hours of degradation is high. Therefore, it is desirable that the multiplier of the maximum current value by cyclic voltammetry be 6.5 times or more.

[0142] For Examples 1 to 8, 10, and 11, initially, the ESR of the hybrid capacitor of Example 10 is nearly equivalent to the ESR of the hybrid capacitors of Examples 1 to 8 and 11, but after 2000 hours of degradation, the ESR of the hybrid capacitor of Example 10 is higher than the ESR of the hybrid capacitors of Examples 1 to 8 and 11. In this regard, the proportion of metal carbides by XPS is 5% or more in the cathode foils of Examples 1 to 8 and 11, whereas it is only 3% in the cathode foil of Example 10. Accordingly, in Example 10, compared to other examples, the increase in interfacial resistance caused by the rapid change in the composition of the electrode material between the first conductive layer containing metal and the second conductive layer containing carbon cannot be suppressed, and since it is not a sufficiently low-resistance conductor, the ESR after 2000 hours of degradation is high. In addition, the metal carbides detected by XPS include those in the mixed layer. Therefore, in addition to the magnification of the maximum current value by cyclic voltammetry being 6.5 times or more, it is more preferable that a mixed layer is additionally formed between the first conductive layer and the second conductive layer, and that the ratio of metal carbides by XPS is 5% or more.

[0143] For Examples 1 to 8 and 11, initially, the ESR of the hybrid capacitor in Example 11 is nearly equivalent to that of the hybrid capacitors in Examples 1 to 8, but after 2000 hours of degradation, the ESR of the hybrid capacitor in Example 11 is higher than that of the hybrid capacitors in Examples 1 to 8. In this regard, the magnification of the full width at half maximum of the G band peak by Raman spectroscopy is 3.8 times or more for the cathode foils in Examples 1 to 8, whereas it is only 3.5 times for the cathode foil in Example 11. Therefore, in Example 11, compared to other examples, the degree of amorphousness of the carbon is lower and the degradation resistance is poor, resulting in a higher ESR after 2000 hours of degradation. Accordingly, it is more desirable that the magnification of the maximum current value by cyclic voltammetry is 6.5 times or more, a mixed layer is formed between the first conductive layer and the second conductive layer, and the ratio of metal carbides by XPS is 5% or more, in addition to the magnification of the full width at half maximum of the G band peak by Raman spectroscopy being 3.8 times or more.

[0144] FIG. 36 shows the magnification (expanding magnification) of the BET specific surface area by Kr adsorption method relative to the smooth substrate and the ESR after 2000 hours of degradation for the cathode foils of Examples 1 to 8. Examples 1 to 6 and 8, in which the expanding magnification by Kr adsorption method is 1.5 times or more, had a lower ESR after 2000 hours of degradation than Example 7, in which the expanding magnification by Kr adsorption method is 1.4 times. Therefore, in addition to the magnification of the maximum current value by cyclic voltammetry being 6.5 times or more, a mixed layer being formed between the first conductive layer and the second conductive layer, the ratio of metal carbides by XPS being 5% or more, and the magnification of the full width at half maximum of the G band peak by Raman spectroscopy being 3.8 times or more, it is particularly desirable to additionally have the expanding magnification by Kr adsorption method being 1.5 times or more.

[0145] FIG. 31 shows the average diameter of the convex portion of the uneven part on the surface side of the inorganic conductive layer after carbon conductive layer application and the ESR after 2000 hours of degradation in the cathode foils of Examples 1 to 6 and 8. Examples 1 to 6, with an average diameter of 210 nm or less, had a lower ESR after 2000 hours of degradation than Example 8, with an average diameter of 230 nm. Accordingly, it is particularly desirable that the magnification of the maximum current value by cyclic voltammetry is 6.5 times or more, a mixed layer is formed between the first conductive layer and the second conductive layer, the ratio of metal carbides by XPS is 5% or more, the magnification of the full width at half maximum of the G band peak by Raman spectroscopy is 3.8 times or more, and the magnification of the expanded surface by Kr adsorption is 1.5 times or more, in addition, the average diameter of the convex portion of the uneven portion on the surface side of the inorganic conductive layer is 210 nm or less.

[0146] Each of the following relates to an ultrathin section sample in the thickness direction of the entire film portion, including the substrate portion near the film. FIG. 22 is an elemental profile distribution obtained by TEM-EDS (transmission electron microscopy-energy dispersive X-ray analysis) of the same cathode foil as FIG. 10 (Example 2), and FIG. 23 is an elemental profile distribution obtained by TEM-EDS of the same cathode foil as FIG. 11 (Example 4). FIG. 24 is the elemental profile distribution obtained by STEM-EELS (Scanning Transmission Electron Microscopy-Electron Energy Loss Spectroscopy) of the same cathode foil as FIG. 10 (Example 2) (carbon conductive layer side in FIG. 25), and FIG. 25 is the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 10 (Example 2) (substrate side in FIG. 24). FIG. 26 is the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 11 (Example 4) (carbon conductive layer side in FIG. 27), and FIG. 27 is the elemental profile distribution obtained by STEM-EELS of the same cathode foil as FIG. 11 (Example 4) (substrate side in FIG. 26). Here, in FIGS. 22 to 27, K represents the K shell of the electron shell, and in FIGS. 24 to 27, L represents the L shell of the electron shell. In both Examples 2 and 4, it can be seen that a mixed layer exists beneath the carbon conductive layer.

[0147] Performance test of the solid electrolytic capacitor of the present invention

[0148] In addition, solid electrolytic capacitors of Examples 1 to 11 and Comparative Examples 1 to 3 were fabricated using the cathode foils of Examples 1 to 11 and Comparative Examples 1 to 3 described above (they were fabricated using a method different only from the method of fabricating the hybrid capacitors of Examples 1 to 11 and Comparative Examples 1 to 3 in that the treatment of impregnating the capacitor element with an electrolyte after forming the solid electrolyte layer was not performed), and a performance test (ESR measurement) was performed on each of the fabricated solid electrolytic capacitors.

[0149] FIG. 21 is a table showing the results of ESR measurements performed on each of the solid electrolytic capacitors of Examples 1 to 11 and the solid electrolytic capacitors of Comparative Examples 1 to 3. In the initial state, the ESR of the solid electrolytic capacitors of Examples 1 to 11 is lower than the ESR of the solid electrolytic capacitors of Comparative Examples 1 and 3.

[0150] Evaluation of physical properties of the electrode material of the present invention

[0151] The adhesion mechanism between the solid electrolyte and the cathode foil is of the adhesive tape type, and FIG. 28 is comparative data on the degree of adhesion using industrial adhesive tape. For the adhesive tape, a 10 mm wide polypropylene adhesive tape manufactured by Nitto Electric Co., Ltd. was used. This tape was cut to a length of 15 cm with the adhesive side facing down and lightly placed parallel to the longitudinal direction on a test specimen cut to a width of 50 mm × a length of 200 mm. A press roller with a load of 20 N was reciprocated once over a length of 100 mm or more on the tape to apply a uniform load for adhesion. One end of the specimen was firmly pressed with a clamp, and the tape on the side opposite to the side adhered to the specimen was folded 180° near the clamp. The end was then fixed with a clip connected to a push-pull gauge and pulled at a constant speed of 10 mm / second. The average value of the tensile load (gf / cm) at which the tape peeled off was read, and this value was defined as the degree of tape adhesion. For Examples 1, 2, 4, and 5, reflecting the anchor adhesion effect caused by the uneven structure applied to the surface side, significantly stronger tape adhesion was obtained compared to Comparative Example 1, which did not have an uneven structure applied to the surface side. In other words, it was found that the effect of improving adhesion to the solid electrolyte could be obtained by the uneven structure applied to the surface side of the first conductive layer.

[0152] In recent hybrid capacitors, from the perspectives of heat resistance, conductivity, withstand voltage performance, and manufacturing costs, there are many cases where a solid electrolyte layer is formed by immersing and impregnating the capacitor in a PEDOT / PSS aqueous dispersion solution—in which polyethylenedioxythiophene (PEDOT) is mixed with polystyrenesulfonic acid (PSS) to disperse PEDOT in an aqueous solution—and then drying it. The adhesion and retention properties of the solid electrolyte 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, respectively, and the surface free energy (mJ / m²) calculated from them using the Owens and Wendt model equation. 2 The details of ) are (polar hydrogen bonding component and non-polar dispersion component). The polar hydrogen bonding component relates to the affinity with the aqueous solvent, and the non-polar dispersion component relates to the affinity with hydrocarbons, organic solvents, polymers, etc. 1 μL of each solvent, water and diiodomethane, was dropped onto a horizontally positioned sample, 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, due to the uneven structure imparted to the surface side, significantly lower contact angles (excellent wettability) for both solvents and high surface free energy values ​​with a good balance for both components were obtained compared to Comparative Example 1, which did not impart an uneven structure to the surface side.

[0153] In a wound-type capacitor element made by winding a separator sheet between short, book-shaped electrode sheets on the positive and negative sides, a type that starts winding with the negative sheet in between on the winding axis is particularly prone to causing a problem of winding misalignment. This is because if the friction coefficient between the separator sheet in contact with the negative sheet near the winding axis is small, when the winding axis is drawn after the wound-type element is formed, the gripping force (frictional force) between the negative sheet and the separator sheet is insufficient, causing the negative sheet in contact with the winding axis to move in the drawing direction of the winding axis.

[0154] Figure 34 is comparative data of the friction coefficient with the separator paper. The separator paper provided was a separator paper (RTZ3040) with a thickness of 40 μm, made mainly of natural cellulose, manufactured by Japan Kodoji Industry Co., Ltd. This was attached to the back side (the side in contact with the foil sample) of a sliding piece (projected dimension: □63 mm square) of a flat SUS plate with a mass of 200 g, which was connected to a load cell by a flexible SUS wire with a buffer spring interposed therein. The foil sample, which was fixed flatly on a smooth acrylic plate with a thickness of 10 mm installed horizontally, was slid horizontally at a constant speed of 100 mm / min, and the load at that time was sampled every 60 milliseconds. The maximum load generated immediately after the start of movement of the sliding piece was set as the maximum static friction force, and the average load in a stable motion state was set as the average dynamic friction force; by dividing each by the normal force (1.96 N) of the sliding piece, the static friction coefficient and the average dynamic friction coefficient were obtained. For Examples 2, 4, and 5, an improvement in friction force was obtained by the uneven structure applied to the surface side of the first conductive layer, and for Comparative Example 1, which did not have an uneven structure applied to the surface side, it was confirmed that both the static friction coefficient and the dynamic friction coefficient with the separator paper increased significantly. That is, it was found that the effect of improving adhesion with the solid electrolyte was obtained by the uneven structure applied to the surface side of the first conductive layer, and that it is possible to have a geometric structure suitable for holding the solid electrolyte and the electrolyte.

[0155] [bookkeeping]

[0156] The present disclosure discloses the following configuration.

[0157] [Composition 1]

[0158] On a smooth substrate, an oxide layer, and also having an inorganic conductive layer on the oxide layer,

[0159] The above-mentioned inorganic conductive layer comprises a first conductive layer comprising a metal and / or a metal compound, and a second conductive layer comprising carbon, and

[0160] The first conductive layer above has an uneven portion on its surface side, and

[0161] The second conductive layer is an electrode material located at the outermost layer of the inorganic conductive layer.

[0162] [Composition 2]

[0163] An electrode material described in Composition 1, wherein the smooth substrate and the first conductive layer are composed of different materials.

[0164] [Composition 3]

[0165] The electrode material described in configuration 1 or 2, wherein the second conductive layer is substantially composed of carbon.

[0166] [Composition 4]

[0167] An electrode material described in any one of configurations 1 to 3, wherein the inorganic conductive layer further comprises 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.

[0168] [Composition 5]

[0169] An electrode material described in any one of configurations 1 to 4, wherein both the first conductive layer and the second conductive layer among the above-mentioned inorganic conductive layers, or at least the first conductive layer is composed of a particle deposition layer, and the first conductive layer comprises at least one of titanium, aluminum, their nitrides, oxides, oxynitrides, carbides, and carbonitrides.

[0170] [Composition 6]

[0171] The electrode material described in any one of compositions 1 to 5, wherein the oxide layer is an oxide layer containing phosphorus.

[0172] [Composition 7]

[0173] An electrode material described in any one of configurations 1 to 6, wherein the above-mentioned smooth substrate comprises aluminum or an aluminum alloy.

[0174] [Composition 8]

[0175] An electrode material described in any one of configurations 1 to 7, having a shrinkage range ±0.3 VvsPt, a shrinkage rate of 500 mV / sec, an electrolyte of 30 ℃, a reference electrode Pt, a counter electrode stainless steel, and a maximum value of the current of a cyclic voltamogram obtained by cyclic voltammetry under conditions in which the working electrode is made of the above electrode material, which is 6.5 times or more the maximum value of the current of a cyclic voltamogram when the working electrode is made of the above smooth substrate under the above conditions.

[0176] [Composition 9]

[0177] An electrode material described in any one of configurations 1 to 8, wherein a mixed layer is formed between the first conductive layer and the second conductive layer, wherein the material constituting the first conductive layer and the material constituting the second conductive layer are mixed, and the composition of the mixed layer is configured to change from a composition substantially comprising only the material constituting the first conductive layer to a composition substantially comprising only the material constituting the second conductive layer, as it extends from the first conductive layer to the second conductive layer.

[0178] [Composition 10]

[0179] Between the first conductive layer and the second conductive layer, a mixed layer is formed in which a material constituting the first conductive layer and a material constituting the second conductive layer are mixed, and the composition of the mixed layer is configured to change from a composition substantially comprising only the material constituting the first conductive layer to a composition substantially comprising only the material constituting the second conductive layer as it moves from the first conductive layer to the second conductive layer.

[0180] An electrode material described in Composition 8, wherein, when the amount of each C bond state is analyzed in the depth direction from the surface layer of the second conductive layer by XPS (X-ray photoelectron spectroscopy), the ratio of the amount of bonds between a metal element atom and a carbon atom constituting the first conductive layer to the sum of the amounts of each C bond state according to the C1s spectrum is 5% or more.

[0181] [Composition 11]

[0182] An electrode material described in Composition 10, wherein, with respect to the full width at half maximum of the G band peak obtained by peak separation in a Raman spectrum by Raman spectroscopy, the full width at half maximum of the carbon included in the second conductive layer is 3.8 times or more than the full width at half maximum of the graphite crystal.

[0183] [Composition 12]

[0184] An electrode material described in configuration 11, wherein the material constituting the first conductive layer and the material constituting the second conductive layer are different from each other.

[0185] [Composition 13]

[0186] An electrode material described in configuration 11 or 12, wherein the BET specific surface area using krypton (Kr) as an adsorbed gas is 1.5 times or more the BET specific surface area of ​​the smooth substrate.

[0187] [Composition 14]

[0188] An electrode material described in Composition 13, wherein the average diameter of the convex portion of the uneven portion on the surface side of the above-mentioned inorganic conductive layer is 210 nm or less.

[0189] [Composition 15]

[0190] An electrode material described in any one of compositions 1 to 14, wherein the carbon is graphite-like carbon.

[0191] [Composition 16]

[0192] An electrode material described in any one of compositions 1 to 15, wherein the static friction coefficient and dynamic friction coefficient with respect to the separator sheet on the surface of the surface side are each higher than the static friction coefficient and dynamic friction coefficient with respect to the separator sheet on the surface of the surface side of an electrode material having a conductive layer on the outermost surface side made of carbon on a smooth substrate and not having an uneven portion on the surface side.

[0193] [Composition 17]

[0194] A cathode foil for an electrolytic capacitor having at least a solid electrolyte interposed between the anode foil and the cathode foil, using an electrode material described in any one of configurations 1 to 16.

[0195] [Composition 18]

[0196] An electrolytic capacitor having at least a solid electrolyte interposed between an anode foil and a cathode foil, and having a cathode foil described in configuration 17.

[0197] [Composition 19]

[0198] An electrolytic capacitor described in configuration 18, wherein an additional electrolyte is interposed between the positive electrode foil and the negative electrode foil.

[0199] Industrial applicability

[0200] The electrode material of the present invention can be used as a negative electrode foil for electrolytic capacitors, such as hybrid capacitors and solid-state electrolytic capacitors. In addition, the electrode material of the present invention can be used as various capacitors, various energy storage devices such as electric double-layer capacitors, lithium-ion capacitors, and lithium-ion batteries, and various power generation devices such as fuel cells, solar cells, thermal power generation devices, and vibration power generation devices. Explanation of the symbols

[0201] 1 : Cathode foil (electrode material) 2 : Entry 3: Oxide layer 4: 1st Challenge Layer 5: 2nd Challenge Layer 6: Compact layer 7 : Mixed layer 8 : Wound-type solid-state electrolytic capacitor, wound-type hybrid capacitor 9 : Anode foil 10 : Cathode foil 11 : Separator 12: Capacitor element 13: Positive terminal 14: Negative terminal 15: Aluminum case 16: Bag rubber

Claims

Claim 1 An electrode material having an oxide layer on a smooth substrate, and also having an inorganic conductive layer on the oxide layer, wherein the inorganic conductive layer comprises a first conductive layer comprising a metal and / or a metal compound and a second conductive layer comprising carbon, wherein the first conductive layer has an uneven portion on its surface side, and the second conductive layer is located on the outermost layer of the inorganic conductive layer. Claim 2 An electrode material according to claim 1, wherein the smooth substrate and the first conductive layer are composed of different materials. Claim 3 An electrode material according to claim 1 or 2, wherein the second conductive layer is substantially made of carbon. Claim 4 An electrode material according to claim 1 or 2, wherein the inorganic conductive layer further comprises 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. Claim 5 An electrode material according to claim 1 or 2, wherein both the first conductive layer and the second conductive layer among the inorganic conductive layers, or at least the first conductive layer is composed of a particle deposition layer, and the first conductive layer comprises at least one of titanium, aluminum, their nitrides, oxides, oxynitrides, carbides, and carbonitrides. Claim 6 An electrode material according to claim 1 or 2, wherein the oxide layer is an oxide layer containing phosphorus. Claim 7 An electrode material according to claim 1 or 2, wherein the smooth substrate comprises aluminum or an aluminum alloy. Claim 8 An electrode material according to claim 1, wherein the sweep range ±0.3 V vs Pt electrode, sweep speed 500 mV / sec, electrolyte 30 ℃, reference electrode Pt, counter electrode stainless steel, and the maximum value of the current of the cyclic voltamogram obtained by the cyclic voltammetry method under conditions in which the working electrode is the electrode material is at least 6.5 times the maximum value of the current of the cyclic voltamogram when the working electrode is the smooth substrate under the above conditions. Claim 9 An electrode material according to claim 1 or 2, wherein a mixed layer is formed between the first conductive layer and the second conductive layer, wherein the material constituting the first conductive layer and the material constituting the second conductive layer are mixed, and the composition of the mixed layer is configured to change from a composition substantially comprising only the material constituting the first conductive layer to a composition substantially comprising only the material constituting the second conductive layer as it extends from the first conductive layer to the second conductive layer. Claim 10 An electrode material according to claim 8, wherein a mixed layer is formed between the first conductive layer and the second conductive layer, wherein the material constituting the first conductive layer and the material constituting the second conductive layer are mixed, and the composition of the mixed layer is configured to change from a component substantially containing only the material constituting the first conductive layer to a component substantially containing only the material constituting the second conductive layer as it moves from the first conductive layer to the second conductive layer, and when the amount of each C bond state is analyzed in the depth direction from the surface layer of the second conductive layer by XPS (X-ray photoelectron spectroscopy), the ratio of the amount of bonding between a metal element atom and a carbon atom constituting the first conductive layer to the sum of the amounts of each C bond state according to the C1s spectrum is 5% or more. Claim 11 An electrode material according to claim 10, wherein, with respect to the full width at half maximum of the G band peak obtained by peak separation in a Raman spectrum by Raman spectroscopy, the full width at half maximum of the carbon included in the second conductive layer is 3.8 times or more than the full width at half maximum of the graphite crystal. Claim 12 An electrode material according to claim 11, wherein the material constituting the first conductive layer and the material constituting the second conductive layer are different from each other. Claim 13 An electrode material according to claim 11 or 12, wherein the BET specific surface area using krypton (Kr) as an adsorbent gas is 1.5 times or more the BET specific surface area of ​​the smooth substrate. Claim 14 An electrode material according to claim 13, wherein the average diameter of the convex portion of the uneven portion on the surface side of the inorganic conductive layer is 210 nm or less. Claim 15 An electrode material according to claim 1 or 2, wherein the carbon is graphite-like carbon. Claim 16 An electrode material described in claim 1 or 2, wherein the static friction coefficient and dynamic friction coefficient with respect to the separator sheet on the surface of the surface side are each higher than the static friction coefficient and dynamic friction coefficient with respect to the separator sheet on the surface of the surface side of an electrode material having a conductive layer which is the outermost layer on the surface side made of carbon on a smooth substrate and not having an uneven portion on the surface side. Claim 17 A cathode foil for an electrolytic capacitor using the electrode material described in claim 1 or 2. Claim 18 A cathode foil for an electrolytic capacitor according to claim 17, wherein at least a solid electrolyte is interposed between the anode foil and the cathode foil. Claim 19 An electrolytic capacitor having at least a solid electrolyte interposed between an anode foil and a cathode foil, and having the cathode foil described in claim 18. Claim 20 In claim 19, an electrolytic capacitor in which an electrolyte is additionally interposed between the positive electrode foil and the negative electrode foil.

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