Method for manufacturing capacitor member, capacitor, electric circuit, circuit board, equipment, and electricity storage device

Abstract

A method for manufacturing a capacitor member according to the present disclosure includes forming, on a valve metal, a modified layer containing a metal other than the valve metal by a cathodic reaction. In this manufacturing method, εH / KH [V / nm] > εL / KL [V / nm] is satisfied. εH is the dielectric constant of oxide of the metal other than the valve metal. KH [nm / V] is the thickness of the first oxide film of the metal per 1 V of anode potential when the first oxide film is formed by anodic oxidation. εL is the dielectric constant of the oxide of the valve metal. KL [nm / V] is the thickness of the second oxide film including the oxide of the valve metal per 1 V of anode potential when the second oxide film is formed by anodic oxidation.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a capacitor member, a capacitor, an electric circuit, a circuit board, an apparatus, and an electricity storage device. [Background technology]

[0002] Conventionally, metals such as Al, Ta, Nb, Zr, and Hf are known as valve metals. An insulating oxide film is formed by anodizing valve metals in a specific solution. For example, Al and Ta can be used to fabricate porous bodies with large surface areas, and Al electrolytic capacitors and Ta electrolytic capacitors are widely used.

[0003] Table 1 in Non-Patent Document 1 lists the dielectric constants of anodic oxide films of valve metals. In this table, the dielectric constant of Al2O3 is the second lowest after that of SiO2. Non-Patent Document 1 describes the formation of thin films of SiO2, Ta2O5, Nb2O5, ZrO2, TiO2, and BaTiO2 on an Al plate by a sol-gel method. It also describes the production of a composite barrier anodic oxide film (BAOF) by anodization in a neutral solution.

[0004] Non-Patent Document 2 describes the anodization of an Al-Ce alloy. The Al-Ce alloy is prepared by sputtering. The film formed on the Al-Ce alloy by anodization of the Al-Ce alloy has an inner oxide layer and an outer oxide layer. The inner oxide layer accounts for the majority of the film thickness and contains alumina and cerium oxide. The outer oxide layer is a layer rich in cerium species. According to Non-Patent Document 2, cerium species can function as an anodic inhibitor that inhibits aluminum corrosion in weakly alkaline and strongly alkaline solutions. It is understood that the description in Non-Patent Document 2 is based on the investigation of an alternative wet process that can impart corrosion resistance to aluminum alloys and form a substrate for subsequent surface treatments such as painting, in order to reduce the use of chromate. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Tanaka, Atsuo, and Takahashi, Hideaki: “Structure and formation mechanism of barrier-type anodic oxide coating on aluminum” Surface Technology, 69, 12 (2018) [Non-patent document 2] Crossland, AC, Thompson, GE, Skeldon, P., Wood, GC,Smith, CJE, Habazaki, H., & Shimizu, K. (1998). Aanodic oxidation of Al-Ce alloys and inhibitory behavior of cerium species. Corrosion science, 40(6), 871-885. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure provides a novel method for manufacturing a capacitor element having a dielectric containing a selected metal, such as cerium. [Means for solving the problem]

[0007] The method for manufacturing a capacitor member according to the present disclosure includes: forming a modified layer containing a metal other than the valve metal on the valve metal by a cathodic reaction; ε H / K H [V / nm]>ε L / K L The condition [V / nm] is met, In the above conditions, ε H is the relative dielectric constant of the oxide of the metal, K H [nm / V] is the thickness of the first oxide film per 1 V of anode potential when the first oxide film of the metal is formed by anodizing the metal, ε L is the relative dielectric constant of the oxide of the valve metal, K L [nm / V] is the thickness of the second oxide film containing an oxide of the valve metal per 1 V of anode potential when the second oxide film is formed by anodization. [Effects of the Invention]

[0008] According to the present disclosure, a novel capacitor member having a dielectric containing a predetermined metal such as cerium can be produced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flowchart showing an example of a method for manufacturing a capacitor member. [Figure 2A] FIG. 2A is a cross-sectional view showing an example of a capacitor according to the present disclosure. [Figure 2B] FIG. 2B is a cross-sectional view showing another example of a capacitor according to the present disclosure. [Figure 2C] FIG. 2C is a cross-sectional view showing a modification of the capacitor shown in FIG. 2B. [Figure 3A] FIG. 3A is a diagram schematically illustrating an example of an electric circuit according to the present disclosure. [Figure 3B] FIG. 3B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. [Figure 3C] FIG. 3C is a diagram schematically illustrating an example of the device of the present disclosure. [Figure 3D] FIG. 3D is a diagram schematically illustrating an example of an electricity storage device according to the present disclosure. [Figure 4] FIG. 4 is a potential-pH diagram showing the state of cerium in water. [Figure 5] FIG. 5 is a flowchart showing another example of a method for manufacturing a capacitor member. [Figure 6] FIG. 6 is a graph showing the X-ray diffraction (XRD) pattern of the capacitor member according to the example and the calculation results of the XRD patterns of Al and CeO2. [Figure 7]FIG. 7 is a graph showing the relationship between the signal intensity of AlO + , CeO + , and C + in time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the capacitor member according to the example and the depth of the capacitor member. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) In the technology described in Non-Patent Document 1, thin films of SiO2, Ta2O5, Nb2O5, ZrO2, TiO2, and BaTiO2 are formed on an Al plate by a sol-gel method that does not involve an electrochemical oxidation-reduction reaction. Therefore, it is considered difficult to uniformly coat a porous body with these thin films to a thickness suitable for a capacitor. Non-Patent Document 2 does not anticipate the application of an article obtained by anodizing an Al-Ce alloy to a capacitor. In the technology described in Non-Patent Document 2, an Al-Ce alloy is used as the substrate, and it is considered difficult to make the surface of the substrate porous. Therefore, the technology described in Non-Patent Document 2 is disadvantageous from the perspective of application to a capacitor.

[0011] The amount of charge Q [C] stored in a capacitor is generally expressed by equation (1). In equation (1), C is the capacitance and V is the applied voltage. In addition, ε0 is the permittivity of a vacuum, ε is the relative permittivity of the dielectric between the capacitor's electrodes, S is the surface area of ​​the capacitor's electrodes, and t is the distance between the electrodes, which corresponds to the thickness of the dielectric. Q=C·V=ε0·ε·(S / t)·V Formula (1)

[0012] When a dielectric layer such as a valve metal oxide is formed by an electrochemical reaction of a valve metal, the thickness of the dielectric layer increases roughly in proportion to the applied voltage. When a voltage exceeding the applied voltage at which the electrochemical reaction is possible is applied to the valve metal, film growth occurs due to the passage of current. Therefore, when a capacitor is used, the withstand voltage of the film obtained by the electrochemical reaction is determined by the applied voltage at which the electrochemical reaction is possible to form the dielectric layer.

[0013] The maximum capacitance Q of a capacitor with a dielectric layer formed by an electrochemical reaction max is expressed by equation (2) based on equation (1). In equation (2), V max is the applied voltage when forming the dielectric layer, and K is the applied voltage V max is the proportionality constant [nm / V] between the dielectric layer thickness t and the dielectric layer thickness t. Q max =ε0 ε (S / t) V max =ε0·S·(ε / K) Equation (2)

[0014] In equation (2), S is determined by the structure of the capacitor. On the other hand, ε and K are specific values ​​determined by the material used for the dielectric layer. ε is the relative permittivity of the material that forms the dielectric layer, and K is the dielectric constant of the material. Thickness of is the proportional constant between ε / K and the applied voltage when forming the dielectric layer. It is understood that using a material with a large ε / K as the dielectric of a capacitor is important from the perspective of increasing the capacitance of the capacitor.

[0015] The values ​​of ε, K, and ε / K in equation (2) for valve metal oxides and CeO2 are shown in Table 1.

[0016] [Table 1]

[0017] As shown in Table 1, for example, the ε / K of CeO2 is greater than the ε / K of Al2O3 and Ta2O5, which are commonly used as dielectrics in electrolytic capacitors. Therefore, if a layer containing a specific metal such as cerium could be formed on a layer containing an oxide of a valve metal, such as Al or Ta, which can make the surface porous, the performance of the capacitor is expected to improve. On the other hand, when forming an insulating film on a valve metal by anodization, anodization can be performed under neutral conditions around pH 7. Under neutral conditions, specific metals such as cerium are water-soluble. Therefore, it is difficult to form a layer containing a specific metal such as cerium on a layer containing a valve metal oxide using the aqueous solution used for anodization.

[0018] In view of these circumstances, the present inventors have conducted extensive trial and error and finally discovered a new method for forming a layer containing a predetermined metal such as cerium on a layer containing a valve metal oxide. Based on this new finding, the present inventors have devised the method for manufacturing a capacitor member of the present disclosure.

[0019] (Summary of one aspect of the present disclosure) A method for manufacturing a capacitor member according to a first aspect of the present disclosure includes: forming a modified layer containing a metal other than the valve metal on the valve metal by a cathodic reaction; ε H / K H [V / nm]>ε L / K L The condition [V / nm] is met, In the above conditions, ε H is the relative dielectric constant of the oxide of the metal, K H [nm / V] is the thickness of the first oxide film per 1 V of anode potential when the first oxide film of the metal is formed by anodizing the metal, ε L is the relative dielectric constant of the oxide of the valve metal, K L [nm / V] is the thickness of the second oxide film containing an oxide of the valve metal per 1 V of anode potential when the second oxide film is formed by anodization.

[0020] According to the first aspect, a predetermined altered layer can be formed on the valve metal by a cathodic reaction, so that a layer containing a predetermined metal such as cerium can be formed on a layer containing a valve metal oxide, which is advantageous in terms of increasing the capacitance of the capacitor.

[0021] In a second aspect of the present disclosure, for example, the method for manufacturing a capacitor member according to the first aspect may further include forming a first layer containing the substance and a second layer containing an oxide of the valve metal by anodizing the valve metal and the altered layer. According to the second aspect, a layer containing a predetermined metal such as cerium can be formed on the layer containing a valve metal oxide by anodizing the valve metal and the altered layer.

[0022] In a third aspect of the present disclosure, for example, in the method for manufacturing a capacitor member according to the first or second aspect, the metal may be cerium. According to the third aspect, the ε / K of CeO2 is larger than the ε / K of Al2O3 and Ta2O5, which are generally used as dielectrics in electrolytic capacitors, and therefore, a capacitor member that is more advantageous in terms of increasing the capacitance of the capacitor can be easily obtained.

[0023] A method for producing a capacitor member according to a fourth aspect of the present disclosure includes: forming a cerium-containing layer containing cerium on the valve metal by a cathodic reaction of the valve metal in a solution containing cerium; anodizing the valve metal and the cerium-containing layer to form a first layer comprising cerium and a second layer comprising a valve metal oxide; The second layer is in contact with the valve metal between the first layer and the valve metal in the thickness direction of the first layer.

[0024] According to the fourth aspect, a capacitor member can be provided that includes a first layer containing cerium and a second layer containing a valve metal oxide, even though cerium is water-soluble under neutral conditions. Additionally, in the capacitor member, the second layer is in contact with the valve metal between the second layer and the valve metal in the thickness direction of the first layer. Therefore, a capacitor member that is advantageous in terms of increasing the capacitance of the capacitor can be provided.

[0025] In a fifth aspect of the present disclosure, for example, in the method for producing a capacitor member according to the fourth aspect, the cerium-containing solution may contain hydrogen peroxide. According to the fifth aspect, a desired cerium-containing layer is easily formed in a cathodic reaction of a valve metal in the cerium-containing solution.

[0026] In a sixth aspect of the present disclosure, for example, in the method for manufacturing a capacitor member according to the fourth or fifth aspect, an electrolytic solution containing an organic solvent may be used in the anodization. According to the sixth aspect, in the anodization of the valve metal and the cerium-containing layer, cerium is less likely to dissolve in the electrolytic solution, and the concentration of cerium in the first layer is likely to be high.

[0027] A capacitor according to a seventh aspect of the present disclosure comprises: A first electrode; a second electrode comprising a valve metal and having a cerium content of less than 0.1% by atomic number; a dielectric disposed between the first electrode and the second electrode; The dielectric material is a first layer comprising cerium; a second layer including a valve metal oxide and in contact with the second electrode between the first layer and the second electrode in the thickness direction of the first layer;

[0028] According to the seventh aspect, a novel capacitor having a dielectric containing cerium can be provided. In this capacitor, the dielectric includes a first layer containing cerium and a second layer containing a valve metal oxide, and the second layer is in contact with the second electrode between the first layer and the second electrode in the thickness direction of the first layer. Therefore, in the capacitor according to the seventh aspect, the ε / K of the dielectric tends to be large. As a result, as can be seen from the above formula (2), the maximum capacitance Q of the capacitor max is likely to be large, and the capacitor is likely to have a high capacitance.

[0029] In an eighth aspect of the present disclosure, for example, in the capacitor according to the seventh aspect, the first layer may further contain a valve metal oxide. According to the eighth aspect, even if the first layer contains a valve metal oxide, the first layer also contains cerium, so the capacitor is likely to have a high capacitance.

[0030] In a ninth aspect of the present disclosure, for example, in the capacitor according to the seventh or eighth aspect, the valve metal in the second electrode may be aluminum. According to the ninth aspect, the surface of the second electrode is easily made porous, and the surface area of ​​the capacitor electrode is easily increased. Therefore, the capacitor is more likely to have a high capacitance.

[0031] In a tenth aspect of the present disclosure, for example, in the capacitor according to the ninth aspect, the valve metal oxide in the second layer may be aluminum oxide. According to the tenth aspect, the surface of the second electrode is easily made porous, and the surface area of ​​the capacitor electrode is easily increased. Therefore, the capacitor is more likely to have a high capacitance.

[0032] In an eleventh aspect of the present disclosure, for example, in the capacitor according to any one of the seventh to tenth aspects, the cerium concentration at a second position in the first layer that is closer to the second layer than the first position in the thickness direction of the first layer may be lower than the cerium concentration at the first position. According to the eleventh aspect, the cerium concentration in the first layer is likely to be in a desired state, and the capacitor is likely to have a high capacitance.

[0033] In a twelfth aspect of the present disclosure, for example, in the capacitor according to any one of the seventh to eleventh aspects, the first electrode may form at least a part of a cathode, and the second electrode may form an anode. In this case, a capacitor can be provided in which the second electrode containing a valve metal functions as an anode.

[0034] An electric circuit according to a thirteenth aspect of the present disclosure includes the capacitor according to any one of the seventh to twelfth aspects. According to the thirteenth aspect, the capacitor is likely to have a high capacitance, and the electric circuit is likely to exhibit desired performance.

[0035] A circuit board according to a fourteenth aspect of the present disclosure includes the capacitor according to any one of the seventh to twelfth aspects. According to the fourteenth aspect, the capacitor is likely to have a high capacitance, and the circuit board is likely to exhibit desired performance.

[0036] A device according to a fifteenth aspect of the present disclosure includes the capacitor according to any one of the seventh to twelfth aspects. According to the fifteenth aspect, the capacitor is likely to have a high capacitance, and the device is likely to exhibit desired performance.

[0037] An electricity storage device according to a sixteenth aspect of the present disclosure includes the capacitor according to any one of the seventh to twelfth aspects. According to the sixteenth aspect, the capacitor is likely to have a high capacitance, and the electricity storage device is likely to exhibit desired performance.

[0038] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0039] FIG. 1 is a flowchart showing an example of a method for manufacturing a capacitor member. The method for manufacturing a capacitor member includes forming an altered layer containing a metal other than the valve metal on the valve metal by a cathodic reaction. In this manufacturing method, ε H / K H [V / nm]>ε L / K L[V / nm] is satisfied. By forming such an altered layer by a cathodic reaction, a metal-containing layer derived from the altered layer can be formed on the layer containing a valve metal oxide by a predetermined treatment after the cathodic reaction. Therefore, the capacitor member produced is advantageous from the viewpoint of increasing the capacitance of the capacitor. The metal contained in the altered layer may be a valve metal other than the valve metal. Under the above conditions, ε H is the relative permittivity of the oxide of the above metal contained in the altered layer, and K H [nm / V] is the thickness of the first oxide film of the metal per 1 V of anode potential when the first oxide film of the metal is formed by anodizing the metal. L is the relative permittivity of the oxide of the valve metal, and K L [nm / V] is the thickness of the second oxide film containing the oxide of the valve metal per 1 V of anode potential when the second oxide film is formed by anodic oxidation.

[0040] In the above manufacturing method, the combination of the valve metal and the metal contained in the affected layer is ε H / K H [V / nm]>ε L / K L As long as the condition of [V / nm] is satisfied, the combination is not limited to a specific one. Examples of such combinations are a combination of aluminum (Al) and cerium (Ce), a combination of Al and tungsten (W), a combination of tantalum (Ta) and Ce, and a combination of Ta and W. In addition, with reference to the ε / K values ​​of each metal oxide listed in Table 1, ε H / K H [V / nm]>ε L / K L A combination of the valve metal and the metal contained in the altered layer that satisfies the condition [V / nm] may be determined.

[0041] 1, for example, in step S11, oxides on the surface of the valve metal are removed. Next, in step S12, the above-mentioned altered layer is formed on the valve metal by a cathodic reaction in the valve metal in a solution containing a predetermined metal other than the valve metal.

[0042] As shown in FIG. 1, this method for manufacturing a capacitor member further includes, for example, anodizing the valve metal and the altered layer to form a first layer containing a predetermined metal and a second layer containing an oxide of the valve metal (see step S13). The first layer contains the metal contained in the altered layer. In this case, anodizing the valve metal and the altered layer allows the first layer derived from the altered layer to be formed on the layer containing the valve metal oxide. This is advantageous in terms of increasing the capacitance of the capacitor.

[0043] During the anodization of a valve metal, an outer oxide layer is formed by the migration of valve metal ions, and an inner oxide layer is formed by the migration of oxide ions. Here, the inner oxide layer is an oxide layer formed in contact with the valve metal, and the outer oxide layer is an oxide layer formed on the inner oxide layer without contacting the valve metal. Components contained in the solution used for anodization may be mixed into the outer oxide layer. On the other hand, the inner oxide layer is formed as a dense layer composed of an oxide of the valve metal and contains almost no components contained in the solution used for anodization. The ratio of the thickness of the outer oxide layer to the total thickness of the oxide layer formed by anodization of a valve metal depends on the type of valve metal. Table 2 shows this ratio for aluminum (Al), niobium (Nb), and tantalum (Ta). As shown in Table 2, this ratio is less than 0.5, and it is understood that it is difficult to form a layer containing a specific metal on a layer containing valve metal oxide to a thickness of 50% or more of the total thickness by anodization of the valve metal alone.

[0044] [Table 2]

[0045] On the other hand, in the method for manufacturing a capacitor member described above, the first layer can be formed by anodizing the altered layer formed by the cathodic reaction. This tends to increase the ratio of the thickness of the first layer to the total thickness of the resulting dielectric layer. For example, the ratio of the thickness of the first layer to the sum of the thicknesses of the first layer and the second layer can be adjusted to 50% or more.

[0046] The metal contained in the above-mentioned altered layer is ε H / K H [V / nm]>ε L / K L As long as the condition of [V / nm] is satisfied, the metal is not limited to a specific one. This metal is, for example, cerium. As described above, the ε / K of CeO2 is larger than the ε / K of Al2O3 and Ta2O5, which are commonly used as dielectrics in electrolytic capacitors, so the manufactured capacitor member is more advantageous in terms of increasing the capacitance of the capacitor. The metal contained in the above-mentioned altered layer may be tungsten.

[0047] FIG. 2A is a cross-sectional view showing an example of a capacitor according to the present disclosure. As shown in FIG. 2A, capacitor 1a includes first electrode 11, second electrode 12, and dielectric 20. Second electrode 12 contains a valve metal. Additionally, the cerium content in second electrode 12 is less than 0.1% by atomic number. Dielectric 20 is disposed between first electrode 11 and second electrode 12. Dielectric 20 includes a first layer 21 containing cerium and a second layer 22 containing a valve metal oxide. First layer 21 is disposed between second layer 22 and first electrode 11 in the thickness direction of first layer 21. Second layer 22 contacts second electrode 12 between first layer 21 and second electrode 22 in the thickness direction of first layer 21. Because dielectric 20 includes first layer 21 containing cerium, ε / K of dielectric 20 is likely to be large, and capacitor 1a is likely to have a high capacitance.

[0048] The valve metal contained in the second electrode 12 is not limited to a specific valve metal. The valve metal contained in the second electrode 12 is, for example, aluminum. Aluminum is a metal that is relatively easy to obtain, making it easy to manufacture the capacitor 1a. In addition, the aluminum contained in the second electrode 12 can be recovered as a recycled resource after the capacitor 1a is used. The valve metal contained in the second electrode 12 may be a valve metal other than aluminum, such as tantalum.

[0049] The surface of the valve metal can be made porous by etching or the like. In this case, impurities contained in the valve metal can have a significant effect on the porosity. In addition, impurities contained in the valve metal can have a significant effect on the electrical properties of the dielectric film obtained by chemical conversion treatment of the valve metal. As described above, the cerium content in the second electrode 12 is less than 0.1% based on the number of atoms, and when the surface of the second electrode 12 is made porous, the influence of cerium is unlikely to extend to the porosity. Therefore, the capacitor 1a is likely to have a high capacitance. The cerium content in the second electrode 12 may be 0.01% or less, or even 0.001% or less, based on the number of atoms. The second electrode 12 may not contain any cerium.

[0050] In the first layer 21, cerium exists, for example, as cerium oxide. This tends to increase ε / K of the dielectric 20, and tends to give the capacitor 1a a high capacitance. The cerium oxide may be amorphous or polycrystalline.

[0051] First layer 21 may further contain, for example, a valve metal oxide. The valve metal oxide contained in first layer 21 is not limited to a specific valve metal oxide. When second electrode 12 contains aluminum as the valve metal, first layer 21 may contain aluminum oxide. The valve metal oxide contained in layer 21 may be a valve metal oxide other than aluminum oxide, such as tantalum oxide.

[0052] The valve metal oxide contained in second layer 22 is not limited to a specific valve metal oxide. When the valve metal contained in second electrode 12 is aluminum, the valve metal oxide contained in second layer 22 may be aluminum oxide. The valve metal oxide contained in second layer 22 may be a valve metal oxide other than aluminum oxide, such as tantalum oxide.

[0053] The thickness of the dielectric 20 is not limited to a specific value. The thickness of the dielectric 20 is, for example, 5 nm to 800 nm. In this case, the capacitor 1a is likely to have a high capacitance, and the dielectric 20 is likely to be formed uniformly. The thickness of the dielectric 20 may be 10 nm to 400 nm, or may be 20 nm to 100 nm.

[0054] The thickness of the first layer 21 is not limited to a specific value. The thickness of the first layer 21 is, for example, 2 nm to 800 nm. In this case, the capacitor 1a is likely to have a high capacitance, and the first layer 21 is likely to be formed uniformly. The thickness of the first layer 21 may be 4 nm to 400 nm, or may be 10 nm to 100 nm.

[0055] The ratio of the thickness of the first layer 21 to the sum of the thickness of the first layer 21 and the thickness of the second layer 22 is not limited to a specific value. This ratio is, for example, 50% or more. This makes it easier for the capacitor 1a to have a high capacitance. This ratio may be 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, or 80% or more. This ratio is, for example, 99% or less.

[0056] The thickness of the second layer 22 is not limited to a specific value. The thickness of the second layer 22 is, for example, 5 nm to 200 nm. In this case, the capacitor 1a tends to have a high capacitance, and the first layer 21 tends to be formed uniformly.

[0057] The cerium concentration distribution in the first layer 21 is not limited to a specific distribution. For example, the cerium concentration at the second position 21b of the first layer 21 is lower than the cerium concentration at the first position 21a of the first layer 21. The second position 21b is closer to the second layer 22 in the thickness direction of the first layer 21 than the first position 21a of the first layer 21. With this configuration, the cerium concentration in the first layer 21 is more likely to be in a desired state, and the capacitor 1a is more likely to have a high capacitance. The cerium concentration in the first layer 21 can be determined based on, for example, the results of TOF-SIMS measurements.

[0058] The concentration of cerium in n layer-like portions obtained by dividing the first layer 21 into n equal parts in the thickness direction is, for example, C i+1 <C i In this relationship, C i+1 is the cerium concentration based on the number of atoms at the (i+1)th site toward the second electrode 12, where the site farthest from the second electrode 12 among the n layered sites is the first site, where i=1. i is the cerium concentration based on the number of atoms at the i-th site toward second electrode 12, where the site farthest from second electrode 12 among the n layered sites is designated as the first site, where i=1. i is a consecutive integer ranging from 1 to n-1. n is an integer equal to or greater than 2. In this case, the thickness of each of the n layered sites obtained by dividing first layer 21 into n equal parts in the thickness direction is, for example, 5 nm to 20 nm.

[0059] The material forming the first electrode 11 is not limited to a specific material. The first electrode 11 may contain a valve metal or a metal other than a valve metal. The metal other than a valve metal may be a noble metal such as gold or platinum, or may be nickel. The first electrode 11 may contain a carbon material such as graphite. The first electrode 11 may contain a conductive polymer. In this case, the conductive polymer may be polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), or a mixture of these materials.

[0060] In the capacitor 1a, for example, the first electrode 11 forms at least a part of the cathode. In addition, the second electrode 12 forms the anode. With this configuration, a capacitor can be provided in which the second electrode 12 containing a valve metal functions as the anode. In the capacitor 1a, the first electrode 11 may form the anode, and the second electrode 12 may form the cathode.

[0061] 2B is a cross-sectional view showing another example of a capacitor according to the present disclosure. Capacitor 1b shown in FIG. 2B has the same configuration as capacitor 1a, except for portions that will be specifically described. Components of capacitor 1b that are the same as or correspond to those of capacitor 1a are designated by the same reference numerals, and detailed description thereof will be omitted. The description of capacitor 1a also applies to capacitor 1b, unless technically inconsistent.

[0062] 2B, in capacitor 1b, at least a portion of second electrode 12 is porous. This configuration tends to increase the surface area of ​​second electrode 12, and tends to increase the capacitance of capacitor 1b. Such a porous structure can be formed, for example, by etching a metal foil and sintering a powder.

[0063] 2B, a dielectric 20 is disposed on the surface of the porous portion of the second electrode 12. In the capacitor 1b, the first electrode 11 is disposed so as to fill the voids around the porous portion of the second electrode 12, for example.

[0064] Capacitors 1a and 1b may be electrolytic capacitors. In this case, an electrolyte 13 is disposed between first electrode 11 and dielectric 20. FIG. 2C shows a modified example of capacitor 1b configured as an electrolytic capacitor. In capacitor 1b according to the modified example, electrolyte 13 is disposed so as to fill, for example, voids around the porous portion of second electrode 12. In capacitor 1b, for example, first electrode 11 and electrolyte 13 form cathode 15.

[0065] The electrolyte includes, for example, at least one selected from the group consisting of an electrolytic solution and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte may be a manganese compound such as manganese oxide. The electrolyte may include a solid electrolyte.

[0066] For example, an electric circuit including capacitor 1a or 1b can be provided. FIG. 3A is a diagram schematically showing an example of an electric circuit of the present disclosure. Electric circuit 3 includes capacitor 1a. Electric circuit 3 may be an active circuit or a passive circuit. Electric circuit 3 may be a discharge circuit, a smoothing circuit, a decoupling circuit, or a coupling circuit. Because electric circuit 3 includes capacitor 1a, electric circuit 3 is likely to exhibit desired performance.

[0067] For example, a circuit board including capacitor 1a or 1b can be provided. FIG. 3B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. As shown in FIG. 3B, circuit board 5 includes capacitor 1a. For example, electric circuit 3 including capacitor 1a is formed on circuit board 5. Since circuit board 5 includes capacitor 1a, circuit board 5 is likely to exhibit the desired performance.

[0068] For example, a device including capacitor 1a or 1b can be provided. FIG. 3C is a diagram schematically illustrating an example of a device according to the present disclosure. As illustrated in FIG. 3C, device 7 includes capacitor 1a. Device 7 includes, for example, circuit board 5 including capacitor 1a. Because device 7 includes capacitor 1a, device 7 is likely to exhibit desired performance. Device 7 may be an electronic device, a communication device, a signal processing device, or a power supply. Device 7 may be a server, an AC adapter, an accelerator, or a flat panel display such as a liquid crystal display (LCD). Device 7 may be a USB charger, a solid-state drive (SSD), an information terminal such as a PC, a smartphone, or a tablet PC, or an Ethernet switch.

[0069] For example, an electricity storage device including capacitor 1a or 1b can be provided. FIG. 3D is a diagram schematically showing an example of an electricity storage device of the present disclosure. As shown in FIG. 3D, an electricity storage device 9 includes capacitor 1a. This makes it easier for the electricity storage device 9 to exhibit desired performance. As shown in FIG. 3D, for example, an electricity storage system 50 can be provided using the electricity storage device 9. The electricity storage system 50 includes the electricity storage device 9 and a power generation device 2. In the electricity storage system 50, electricity obtained as a result of power generation in the power generation device 2 is stored in the electricity storage device 9. The power generation device 2 is, for example, a device for solar power generation or wind power generation. The electricity storage device 9 includes, for example, a secondary battery such as a lithium-ion battery or a lead-acid battery.

[0070] The method for manufacturing the capacitor 1a or 1b is not limited to a specific method. The capacitor 1a or 1b can be manufactured using, for example, a capacitor member 25. As shown in Figures 2A, 2B, and 2C, the capacitor member 25 includes a second electrode 12 and a dielectric 20.

[0071] There is no particular limitation on the method for producing the capacitor member 25. The capacitor member 25 can be produced, for example, by a method including the following (I) and (II). (I) A cerium-containing layer containing cerium is formed on a valve metal by a cathodic reaction of the valve metal in a solution containing cerium. (II) Anodizing the valve metal and cerium-containing layer to form a first layer 21 containing cerium and a second layer 22 containing a valve metal oxide.

[0072] FIG. 4 is a potential-pH diagram showing the state of cerium in water. As shown in FIG. 4, under neutral conditions with a pH of approximately 7, cerium exists as a trivalent or tetravalent ion in water and is water-soluble. For example, when forming a dielectric layer on Al by anodization, the pH can be adjusted to 5 to 7 (Sulka, Grzegorz D. "Highly ordered anodic porous alumina formation by self-organized anodizing." Nanostructured materials in electrochemistry (2008): 1-116). For this reason, it is difficult to form a layer containing cerium using an aqueous solution for anodization. On the other hand, in the above (I), a cerium-containing layer can be formed on a valve metal by a cathodic reaction in the valve metal in a solution containing cerium.

[0073] 5 is a flowchart showing an example of a method for manufacturing a capacitor member 25. In step S101, oxides on the surface of the valve metal are removed. Next, in step S102, a cerium-containing layer containing cerium is formed on the valve metal by a cathodic reaction of the valve metal in a solution containing cerium. Next, in step S103, a first layer 21 containing cerium and a second layer 22 containing a valve metal oxide are formed by anodizing the valve metal and the cerium-containing layer.

[0074] As shown in Figure 4, when the pH of the cerium-containing solution is adjusted to about 8.5, cerium can be deposited on the valve metal as Ce(OH)3. The cerium-containing solution in (I) above contains, for example, hydrogen peroxide. In this case, the hydrogen peroxide contained in the cerium-containing solution participates in the reaction of the following formula (3) during the cathode reaction. In formula (3), *OH is a hydroxyl radical. H2O2+ e - → *OH + OH - Formula (3)

[0075] The reaction of formula (3) is an electrochemical reaction that occurs near the cathode, and it is relatively easy to adjust the amount of the reaction product of formula (3). - In the cathodic reaction, the pH of the cerium-containing solution around the cathode increases. Therefore, referring to FIG. 4, Ce(OH)3 can be precipitated on the valve metal, which is the cathode, in accordance with the reaction of formula (3). Ce(OH)3 is an insulator and has low conductivity. Therefore, in the cathodic reaction, a reaction in which Ce(OH)3 precipitates easily occurs in areas of the valve metal surface that are not covered with Ce(OH)3. As a result, the entire surface of the valve metal is covered with Ce(OH)3, forming a cerium-containing layer. The mechanism of Ce(OH)3 precipitation also applies when porous portions are formed on the surface of the valve metal. Therefore, when porous portions are formed on the surface of the valve metal, Ce(OH)3 can be precipitated to uniformly cover the porous portions on the surface of the valve metal.

[0076] By the anodic oxidation of the valve metal and the cerium-containing layer in the above (II), Ce(OH)3 is oxidized and converted to CeO2. In addition, oxide ions O 2- The valve metal present near the boundary is oxidized and converted into a valve metal oxide, thereby forming a first layer 21 containing cerium and a second layer 22 containing a valve metal oxide, thereby obtaining a capacitor member 25.

[0077] In the anodization in (II) above, for example, an electrolyte containing an organic solvent is used. As described above, Ce is water-soluble under neutral conditions. On the other hand, tetravalent cerium has low solubility in organic solvents. Therefore, by using an electrolyte containing an organic solvent in the anodization, cerium is less likely to dissolve in the electrolyte, and the cerium concentration in the first layer 21 is likely to be high.

[0078] The organic solvent in the electrolyte is not limited to a specific organic solvent, and may be a polyhydric alcohol such as ethylene glycol, ethylene glycol monomethyl ether, γ-butyrolactone, or N-methylformamide.

[0079] By disposing the first electrode 11 on the capacitor member 25 so that the dielectric 20 is located between the second electrode 12 and the first electrode 11, the capacitor 1a or 1b is obtained. [Example]

[0080] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are illustrative and the present disclosure is not limited to the following examples.

[0081] <Example> Electropolishing was performed to remove the native oxide film from the surface of a Nilaco aluminum plate (99% purity). The polishing solution used was a mixture of perchloric acid (Fujifilm Wako Pure Chemical Industries, Ltd.) and an ethanol aqueous solution. The HClO4 concentration in the perchloric acid was 70% by mass. The ethanol concentration in the ethanol aqueous solution was 96% by mass. Approximately 80 ml of the polishing solution was placed in a beaker, and both the cathode and anode were immersed in the polishing solution to a depth of approximately 3 cm. A Teccio Technology PSF-L DC power supply was connected to the aluminum plate using alligator clips, and a 2 A current was applied for 10 seconds to remove the oxide film from the anode side of the aluminum plate. The aluminum plate, from which the oxide film had been removed, was rinsed twice with pure water and then immersed in a pH 7 phosphate buffer solution for 3 minutes to prevent native oxidation. The solution was then rinsed off with running water for 10 minutes to obtain an aluminum plate for capacitors.

[0082] Next, a cerium-containing layer was formed on the aluminum plate for the capacitor by a cathodic reaction of the aluminum plate for the capacitor. Cerium (III) acetate monohydrate (Ce(CH3COO)3·H2O) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and hydrogen peroxide solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were dissolved in water to obtain a cerium-containing solution. The concentration of H2O2 in the hydrogen peroxide solution was 30 mass%. The concentration of Ce in the cerium-containing solution was 5 millimoles per cubic decimeter (mmol / dm 3 ) and the concentration of H2O2 in the cerium-containing solution is 4.9 mol / dm 3 Approximately 80 ml of the cerium-containing solution was poured into a beaker, and the aluminum plate was fixed in the cerium-containing solution as the cathode and the porous carbon as the anode. The cathode and anode were each connected to a current source, and a current of 0.01 A was passed through them for 60 seconds. A yellow layer (cerium-containing layer) was formed on the entire surface of the aluminum plate that had been immersed in the cerium-containing solution. The cerium-containing layer was then washed with running water without damaging it.

[0083] Next, an anodization treatment was performed. Dipotassium hydrogen phosphate (KHPO) was dissolved in ethylene glycol (HO-CH-CH-OH) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. to obtain an electrolyte. The concentration of dipotassium hydrogen phosphate in this electrolyte was 0.1 mol / dm 3 Approximately 80 ml of electrolyte was placed in a beaker, and the aluminum plate with the cerium-containing layer formed thereon was fixed as the anode and the metal tantalum plate as the cathode in the electrolyte. The anode and cathode were each connected to a current source, and a voltage of 80 V was applied for 1.5 hours. This resulted in the formation of an oxide film on the aluminum plate. The aluminum plate with the oxide film formed thereon was washed with running water for 10 minutes and air-dried to obtain a capacitor member according to the example.

[0084] (Crystallinity evaluation) An XRD pattern of the capacitor material according to the example was obtained by 2θ / θ scanning using an X-ray diffraction (XRD) device, X'pert Pro, manufactured by Panalytical. The capacitor material according to the example was placed on the sample stage of the XRD device, and the XRD pattern was obtained. Cu-Kα radiation was used as the X-ray source, and the voltage was adjusted to 45 kV, the current to 40 mA, and the scan rate to 12 deg. / min. Using RIETAN-FP (F. Izumi and K. Momma, Solid State Phenom., 130, 15-20 (2007)), the XRD pattern of aluminum (Al) and the powder XRD pattern of CeO2 were calculated to confirm the positions of the X-ray diffraction peaks.

[0085] FIG. 6 is a graph showing the XRD pattern of the capacitor member according to the example and the calculation results of the XRD patterns of Al and CeO2. The top XRD pattern in FIG. 6 is the XRD pattern of the capacitor member according to the example. The second XRD pattern from the top in FIG. 6 is the calculation result of the XRD pattern of Al. The bottom XRD pattern in FIG. 6 is the calculation result of the XRD pattern of crystalline CeO2. The vertical axis in FIG. 6 represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ. The vertical axis in FIG. 6 represents the relative relationship of the diffraction intensity in each XRD pattern, but does not represent the relative relationship of the diffraction intensity in different XRD patterns. A peak identified as Al is observed in the XRD pattern of the capacitor member according to the example. On the other hand, no peak derived from crystalline CeO2 is observed. Therefore, it is believed that amorphous CeO2 is present in the oxide film of the capacitor member according to the example.

[0086] (Composition analysis in the depth direction) Using a TOF-SIMS device TOF.SIMS5 manufactured by ION-TOF, TOF-SIMS was performed on the oxide film formed on the capacitor member according to the example, and the composition of the oxide film in the depth direction was analyzed. In the TOF-SIMS, Bi accelerated at 30 kV was used as the primary ion beam. 3+ The beam was used. The sputtering ion species was O2, which is highly sensitive to Al. + was used.

[0087] FIG. 7 shows the aluminum oxide ions (AlO ) in the TOF-SIMS of the capacitor member according to the example. + ), cerium oxide ions (CeO + ), and carbon ions (C + 7 is a graph showing the relationship between the signal intensity of CeO and the depth of the capacitor material. This indicates that Al, Ce, or C is present at the depth where the signal intensity is generated. The signal intensity in TOF-SIMS is semi-quantitative with respect to the amount of element present. According to FIG. 7, CeO + It can be seen that the signal intensity of AlO decreases exponentially from the surface of the oxide film.+ The signal intensity of the AlO film hardly changes up to a depth of 130 nm. On the other hand, the signal intensity decreases at depths of 130 nm or more. This is because the oxide film continues to a depth of 130 nm and reaches the aluminum plate at depths greater than 130 nm. + It is understood that the intensity of is small at depths of 130 nm or more.

[0088] 7, it can be seen that the majority of the oxide film is occupied by aluminum oxide, and that a layer with a distribution in which the Ce concentration decreases toward the inside is formed on the outside of the oxide film. In other words, the oxide film of the capacitor member according to the example has an outer layer containing cerium and aluminum oxide, and an inner layer containing aluminum oxide. The reason for the distribution in which the Ce concentration decreases toward the inside in the outer layer of the oxide film is thought to be that Al migrates into the cerium-containing layer as the oxide film grows due to anodization. TOF-SIMS was performed on multiple locations of the capacitor member according to the example, and the average thickness of the oxide film was 95 nm, which was the sum of the thickness of the outer layer and the thickness of the inner layer.

[0089] Figure 7C + Focusing on the signal intensity of , it can be seen that C is present in the outer layer containing cerium and aluminum oxide, while C is almost absent in the inner layer containing aluminum oxide. The presence of C in the outer layer is thought to be derived from cerium (III) acetate monohydrate used in the cathodic reaction of the aluminum plate for the capacitor. Therefore, it is thought that the outer layer is a layer derived from the cerium-containing layer formed by the cathodic reaction. From Figure 7, it can be seen that the ratio of the thickness of the outer layer to the sum of the thickness of the outer layer and the thickness of the inner layer is approximately 80%.

[0090] (AC impedance measurement) To measure the leakage current and evaluate the capacitance, the AC conductivity of the capacitor member according to the example was measured using an impedance analyzer. The impedance analyzer was constructed by combining a frequency response analyzer Model 1260A manufactured by Solartron Analytical and a potentiostat Model 1287A. Using this impedance analyzer, a 0.5 mol / dm 3 The capacitor material was combined with an ammonium adipate ((NH4)2(CH2)4(COO)2) solution having a concentration of 1000 ppm as the cathode and AC conductivity measurements were carried out. The relative permittivity ε of the oxide film was calculated based on the capacitance value obtained by this measurement, the thickness of the oxide film calculated by the cross-sectional structure analysis, and the measurement area in the AC conductivity measurement.

[0091] Table 3 shows the relative permittivity ε of the oxide film calculated from the capacitance obtained by AC conductivity measurement, the proportionality constant K [nm / V] between the oxide film thickness and the applied voltage during oxide film formation, and ε / K [V / nm]. For comparison, the corresponding values ​​for Al2O3 described in Non-Patent Document 1 are also listed. These comparisons reveal that the oxide film of the capacitor member according to the example has an outer layer containing cerium, which increases the relative permittivity of the oxide film and decreases the proportionality constant K. As a result, the oxide film of the capacitor member according to the example had a large ε / K.

[0092] [Table 3] [Industrial Applicability]

[0093] The capacitor according to the present disclosure is useful as it tends to have a high capacitance.

Claims

1. forming a modified layer containing a metal other than the valve metal on the valve metal by a cathodic reaction; ε H / K H [V / nm]>ε L / K L The condition [V / nm] is met, In the above conditions, ε H is the relative dielectric constant of the oxide of the metal, K H [nm / V] is the thickness of the first oxide film per 1 V of anode potential when the first oxide film of the metal is formed by anodizing the metal, ε L is the relative dielectric constant of the oxide of the valve metal, K L [nm / V] is the thickness of the second oxide film containing the oxide of the valve metal per 1 V of anode potential when the second oxide film is formed by anodizing. A method for manufacturing a capacitor member.

2. The method further includes anodizing the valve metal and the altered layer to form a first layer including the metal and a second layer including an oxide of the valve metal. A method for producing the capacitor member according to claim 1 .

3. The metal is cerium. A method for producing the capacitor member according to claim 1 .

4. forming a cerium-containing layer containing cerium on the valve metal by a cathodic reaction of the valve metal in a solution containing cerium; anodizing the valve metal and the cerium-containing layer to form a first layer comprising cerium and a second layer comprising a valve metal oxide; the second layer is in contact with the valve metal between the first layer and the valve metal in a thickness direction of the first layer; A method for manufacturing a capacitor member.

5. The cerium-containing solution contains hydrogen peroxide. The method for producing a capacitor member according to claim 4 .

6. In the anodization, an electrolytic solution containing an organic solvent is used. The method for producing the capacitor member according to claim 5 .

7. A first electrode; a second electrode comprising a valve metal and having a cerium content of less than 0.1% by atomic number; a dielectric disposed between the first electrode and the second electrode; The dielectric material is a first layer comprising cerium; a second layer including a valve metal oxide and in contact with the second electrode between the first layer and the second electrode in a thickness direction of the first layer; Capacitor.

8. the first layer further comprises a valve metal oxide; The capacitor of claim 7.

9. In the second electrode, the valve metal is aluminum. The capacitor of claim 7.

10. In the second layer, the valve metal oxide is aluminum oxide. The capacitor of claim 7.

11. a concentration of cerium at a second position of the first layer that is closer to the second layer than a first position of the first layer in a thickness direction of the first layer is lower than a concentration of cerium at the first position; The capacitor of claim 7.

12. the first electrode forms at least a part of a cathode; The second electrode serves as an anode. The capacitor of claim 7.

13. An electric circuit comprising a capacitor according to any one of claims 7 to 12.

14. A circuit board comprising the capacitor according to any one of claims 7 to 12.

15. An apparatus comprising a capacitor according to any one of claims 7 to 12.

16. An electricity storage device comprising the capacitor according to any one of claims 7 to 12.

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