Electrolytic capacitor

Abstract

To provide an electrolytic capacitor capable of suppressing leakage current, an electrode, and a manufacturing method thereof.SOLUTION: An electrolytic capacitor 100 includes: a metal material 111 including a valve-acting metal; an oxide film 113 formed over the surface of the metal material; and a solid electrolyte layer 131 covering at least part of the oxide film. The oxide film contains a tantalum oxide. In the spectrum obtained by electron energy loss spectroscopy of the oxide film, the difference between the average intensity of first peak I1A observed between 530 eV and 550 eV and the average intensity of second peak I2A observed between 560 eV and 570 eV is 10% or less of the average intensity of first peak I1A. The average intensity of first peak I1A is greater than the average intensity of second peak I2A.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrode for an electrolytic capacitor, a method for manufacturing the same, and an electrolytic capacitor. [Background technology]

[0002] A metal foil or porous sintered body containing a valve metal is used as the anode of the capacitor element. An oxide film is formed on the surface of the metal foil or porous sintered body by chemical conversion treatment. An aqueous solution of phosphoric acid is usually used for the chemical conversion treatment (Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-77257 Summary of the Invention [Problem to be solved by the invention]

[0004] Electrolytic capacitors having an oxide film formed using an aqueous phosphoric acid solution may have a high leakage current. [Means for solving the problem]

[0005] A first aspect of the present invention relates to a method for manufacturing an electrode for an electrolytic capacitor, comprising a chemical conversion step of passing an electric current through a metallic material containing a valve action metal in a chemical conversion solution containing an electrolyte to form an oxide film on the surface of the metallic material, wherein the chemical conversion solution contains a nitric acid compound as the electrolyte at a concentration of 0.03 mass % or more, and the concentration of a phosphorus compound in the chemical conversion solution is less than 0.01 mass %.

[0006] A second aspect of the present invention relates to a method for manufacturing an electrode for an electrolytic capacitor, comprising a chemical conversion step of passing an electric current through a metallic material containing a valve action metal in a chemical conversion solution containing an electrolyte to form an oxide film on a surface of the metallic material, wherein the chemical conversion solution contains a nitric acid compound as the electrolyte, the concentration of a phosphorus compound in the chemical conversion solution is less than 0.01 mass%, and the temperature of the chemical conversion solution in the chemical conversion step is 40°C or higher.

[0007] A third aspect of the present invention relates to an electrode for an electrolytic capacitor, comprising: a metal material containing a valve action metal; and an oxide film formed on a surface of the metal material, wherein a phosphorus concentration of the oxide film measured by energy dispersive X-ray spectroscopy is below the detection limit.

[0008] A fourth aspect of the present invention relates to an electrode for an electrolytic capacitor, comprising: a metal material containing a valve action metal; and an oxide film formed on a surface of the metal material, wherein the oxide film exhibits a phosphate ion fragment peak intensity obtained by time-of-flight secondary ion mass spectrometry below the detection limit.

[0009] A fifth aspect of the present invention provides a method for producing a metal material including a valve metal and an oxide film formed on a surface of the metal material, the oxide film including an oxide of tantalum, the oxide film having an average intensity I of a first peak observed between 530 eV and 550 eV in a spectrum obtained by electron energy loss spectroscopy of the oxide film. 1A and the average intensity I of the second peak observed between 560 eV and 570 eV 2A is 10% or less of the average intensity I1 of the first peak.

[0010] A sixth aspect of the present invention relates to an electrode for an electrolytic capacitor, comprising: a metallic material containing a valve action metal; and an oxide film formed on a surface of the metallic material, wherein the oxide film contains an oxide of tantalum; and in a spectrum of the oxide film obtained by electron energy loss spectroscopy, an intensity I1 of a first peak observed between 530 eV and 550 eV decreases with increasing proximity to the surface of the metallic material.

[0011] A seventh aspect of the present invention relates to an electrode for an electrolytic capacitor, comprising: a metallic material containing a valve action metal; and an oxide film formed on a surface of the metallic material, wherein the oxide film contains an oxide of tantalum; and in a spectrum obtained by electron energy loss spectroscopy of the oxide film, a fourth peak adjacent to the higher energy side of a third peak assigned to the Ta-N1 edge is observed at 570 eV or higher. Yet another aspect of the present invention is a method for manufacturing a semiconductor device comprising: an oxide film formed on the surface of the metal material; a solid electrolyte layer covering at least a portion of the oxide film, the oxide film includes an oxide of tantalum; In the spectrum obtained by electron energy loss spectroscopy of the oxide film, the average intensity I of the first peak observed between 530 eV and 550 eV 1A and the average intensity I of the second peak observed between 560 eV and 570 eV 2A The difference between the average intensity of the first peak, I 1A is less than 10% of The average intensity of the first peak I 1A is the average intensity of the second peak I 2A greater than Electrolytic capacitors. [Effects of the Invention]

[0012] According to the present invention, an electrolytic capacitor with reduced leakage current can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically showing a capacitor element according to one embodiment of the present invention. [Figure 2]1 is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] When using a phosphoric acid solution, traces of phosphorus atoms are mixed into the oxide film that is formed. The presence of phosphorus atoms creates a conductive path in the insulating oxide film. Furthermore, impurity levels are created in the band gap, making it easier for electrons to be released into the oxide film. This is thought to be the cause of leakage current in electrolytic capacitors.

[0015] When nitric acid compounds are used as the chemical conversion solution, it has been found that the properties of the oxide film formed change when nitrogen is mixed in instead of phosphorus. In particular, leakage current can be further suppressed by controlling the concentration of nitric acid compounds or the temperature of the chemical conversion solution.

[0016] That is, the method for manufacturing an electrode for an electrolytic capacitor according to this embodiment includes a chemical conversion step in which an electric current is passed through a metallic material containing a valve metal in a chemical conversion solution containing an electrolyte to form an oxide film on the surface of the metallic material, and the chemical conversion solution contains a nitrate compound as the electrolyte. In a first embodiment, the nitrate compound is contained in the chemical conversion solution at a concentration of 0.03 mass% or more. In a second embodiment, the chemical conversion step is carried out in a chemical conversion solution at a temperature of 45°C or more.

[0017] The oxide film formed using a nitric acid compound has characteristics different from those formed using other chemical conversion solutions. These characteristics become more pronounced when the concentration of the nitric acid compound or the temperature of the chemical conversion solution is controlled as described above.

[0018] That is, the electrode for an electrolytic capacitor according to this embodiment comprises a metal material containing a valve metal and an oxide film formed on the surface of the metal material. The oxide film is an oxide of a metal containing a valve metal, such as tantalum pentoxide.

[0019] [Method of manufacturing electrodes for electrolytic capacitors] A-1. First aspect In the chemical conversion step according to this embodiment, the chemical conversion solution contains the nitric acid compound as an electrolyte at a concentration of 0.03 mass % or more, which allows the formation of an oxide film while suppressing the incorporation of phosphorus.

[0020] The concentration of the nitrate compound is preferably 15% by mass or less, since this makes it easier to suppress corrosion of production equipment and to control the thickness of the oxide film. The concentration of the nitrate compound may be 0.04% by mass or more, or 0.08% by mass or more. The concentration of the nitrate compound may be 10% by mass or less, or 5% by mass or less.

[0021] The chemical conversion solution may contain electrolytes other than nitric acid compounds. However, it is desirable that the concentration of the electrolytes be low. In particular, it is desirable that the concentration of phosphorus-containing compounds be low. The concentration of the other electrolytes is preferably 0.01 mass% or less, more preferably 0.005 mass% or less. Examples of the other electrolytes include conventionally known electrolytes used in chemical conversion treatments. Examples of the other electrolytes include inorganic acids such as phosphoric acid and their salts, organic acids such as adipic acid and their salts, and basic substances such as ammonia.

[0022] When compared at the same concentration and temperature, the conductivity of an aqueous solution containing a nitric acid compound is higher than that of an aqueous solution containing other electrolytes, so chemical conversion treatment is performed efficiently when a nitric acid compound is used.

[0023] In this embodiment, the temperature of the chemical conversion solution during treatment is not particularly limited. From the viewpoint of productivity, the temperature of the chemical conversion solution may be 25°C or higher, 40°C or higher, or 45°C or higher. The temperature of the chemical conversion solution may be 75°C or lower, since this suppresses liquid evaporation and thus corrosion of production equipment. When the concentration of the nitrate compound is sufficiently low, for example, when the concentration of the nitrate compound is 1% by mass or lower, the temperature of the chemical conversion solution may be 70°C or lower. When the concentration of the nitrate compound exceeds 1% by mass, the temperature of the chemical conversion solution may be 55°C or lower.

[0024] A-2. Second mode In the chemical conversion step according to this embodiment, the temperature of the chemical conversion solution containing the nitric acid compound during treatment is 40°C or higher. This allows the formation of an oxide film while suppressing the incorporation of phosphorus. The temperature of the chemical conversion solution during treatment is preferably 75°C or lower, since this suppresses liquid evaporation, which makes it easier to suppress corrosion of production equipment and to control the thickness of the oxide film. When the concentration of the nitric acid compound is 1% by mass or lower, the temperature of the chemical conversion solution may be 60°C or higher. When the concentration of the nitric acid compound is greater than 1% by mass, the temperature of the chemical conversion solution during treatment may be 43°C or higher, or may be 45°C or higher. The temperature of the chemical conversion solution during treatment may be 70°C or lower, or may be 68°C or lower.

[0025] In this embodiment, the concentration of the nitrate compound is not particularly limited. From the viewpoint of productivity, the concentration of the nitrate compound may be 0.03 mass% or more, or 0.05 mass% or more. From the viewpoint of easily suppressing corrosion of production equipment, the concentration of the nitrate compound may be 15 mass% or less, or 10 mass% or less.

[0026] In this embodiment, the chemical conversion solution may also contain an electrolyte other than the nitric acid compound, provided that the concentration thereof is preferably 0.01% by mass or less, and more preferably 0.005% by mass or less.

[0027] (Nitrate compound) The nitric acid compound is not particularly limited. Examples of the nitric acid compound include nitric acid, nitrous acid, nitrates, nitrites, nitrate esters, and nitrite esters. Examples of salts of nitrates and nitrites include strontium, magnesium, calcium, barium, aluminum, zirconium, sodium, and lithium. Examples of functional groups of nitrate esters and nitrite esters include methyl, ethyl, and butyl groups. Among these, nitric acid is preferred because it is easily available and inexpensive.

[0028] (metallic material) The metal material includes a porous sintered body or foil (metal foil) containing a valve metal. When a metal foil is used, its main surface may be roughened by electrolytic etching or the like. This increases the capacitance of the electrolytic capacitor. When a porous sintered body is used, an electrode wire is embedded in one surface of the porous sintered body. The electrode wire is used to connect to a lead terminal.

[0029] Examples of valve metals include titanium, tantalum, aluminum, and niobium. The metal material may contain one or more of the above valve metals. The metal material may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. In terms of chemical stability, the metal material is preferably a porous sintered body containing tantalum.

[0030] The thickness of the metal foil is not particularly limited, and is, for example, 15 μm to 300 μm. The thickness of the porous sintered body is not particularly limited, and is, for example, 15 μm to 5 mm.

[0031] (Other chemical conditions) The formation voltage is the maximum voltage applied between the metal material and the counter electrode. The formation voltage affects the thickness of the oxide film and further the withstand voltage of the electrolytic capacitor. Therefore, the formation voltage may be set appropriately according to the rated voltage of the electrolytic capacitor, and is not particularly limited. The formation voltage may be, for example, 5 V or more. The formation voltage may be, for example, 100 V or less.

[0032] The time for which the above-mentioned chemical formation voltage is maintained (chemical formation time) is not particularly limited and may be appropriately set in consideration of the thickness of the oxide film, productivity, etc. The chemical formation time may be, for example, 1 hour or more. The chemical formation time may be, for example, 20 hours or less.

[0033] The current density flowing through the metal material is not particularly limited and may be set appropriately taking into consideration the chemical formation time, etc. The maximum current density is, for example, 0.001 mA / cm 2 The maximum current density may be, for example, 100 mA / cm 2It may be the following:

[0034] [Electrodes for electrolytic capacitors] The electrode according to this embodiment has an oxide film on its surface. The oxide film is formed by oxidizing the surface of a metal material. Therefore, the oxide film contains an oxide of the valve metal contained in the metal material.

[0035] The thickness of the oxide film is not particularly limited and is set appropriately taking into consideration the rated voltage of the electrolytic capacitor, etc. The thickness of the oxide film is, for example, 10 nm or more and 300 nm or less.

[0036] B-1. First mode In the oxide film according to this embodiment, the phosphorus concentration measured by energy dispersive X-ray spectroscopy (EDX) is below the detection limit. Such an oxide film can be formed on a metal material that has been subjected to a chemical conversion treatment using a chemical conversion solution containing a nitric acid compound (hereinafter referred to as nitric acid conversion).

[0037] EDX is used in combination with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM).

[0038] Phosphorus is detected in oxide films formed with phosphoric acid aqueous solutions commonly used in chemical conversion treatments (hereinafter referred to as phosphate conversion films). In other words, phosphate conversion films contain a relatively large number of atoms that form conductive paths. On the other hand, nitrogen atoms are barely detected (below the detection limit). Phosphorus is detected in large amounts near the surface of other oxide films.

[0039] The oxide film according to this embodiment contains almost no phosphorus atoms and only a small amount of nitrogen atoms mixed in. This means that it has properties different from those of a phosphate conversion film, and it is easier to suppress leakage current in electrolytic capacitors.

[0040] B-2. Second mode In the oxide film according to this embodiment, the phosphate ion fragment peak intensity obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is below the detection limit. This means that the oxide film contains little phosphorus. On the other hand, in the oxide film according to this embodiment, peaks presumably corresponding to nitrogen ion fragments are observed. This suggests the possibility of nitrogen being mixed into the oxide film. The slight incorporation of nitrogen in place of phosphorus changes the properties of the oxide film, suppressing leakage current in electrolytic capacitors. Such an oxide film can be formed on a metal material that has been subjected to nitrate conversion.

[0041] Similar to the EDX analysis results, when other oxide films are analyzed by TOF-SIMS, phosphate ion fragment peaks are detected. The ion fragment peaks are obtained by evaluating the surface of the oxide film. The oxide film may also be etched to evaluate its interior. The results of the interior evaluation show the same tendency as the surface evaluation results.

[0042] B-3. ​​Third aspect The oxide film according to this embodiment contains an oxide of tantalum. In the oxide film according to this embodiment, the average intensity I of the first peak observed between 530 eV and 550 eV in the spectrum obtained by electron energy loss spectroscopy (EELS) 1A and the average intensity I of the second peak observed between 560 eV and 570 eV 2A The difference between (=|I 1A -I 2A |) is the average intensity of the first peak, I 1A That is, 100×|I 1A -I 2A | / I 1A ≦10(%). Such an oxide film can be formed on a metal material that has been subjected to nitrate conversion.

[0043] The first peak is attributed to the OK edge (OK edge; an excitation process by oxygen K shell electrons). The second peak is attributed to the Ta-N1 edge (Ta-N1 edge; an excitation process by tantalum N1 shell electrons). The relationship between the first and second peaks indicates the oxidation state of the tantalum atoms.

[0044] When a chemical conversion solution containing an electrolyte other than the conventionally used nitric acid compound, for example, an inorganic acid such as phosphoric acid and its salt, an organic acid such as adipic acid and its salt, or a basic substance such as ammonia, is used, the relationship between the first peak and the second peak in the formed oxide film (hereinafter referred to as the other oxide film) is 100×|I 1A -I 2A | / I 1A ≦10(%) is not met. In other words, the oxidation state of tantalum atoms is different between the oxide film formed by nitric acid formation and other oxide films. The reason for this is not clear at present, but it is thought that this difference affects the electronic structure of the oxide film and is effective in suppressing leakage current in capacitors.

[0045] I 1A >I 2A I may 1A 2A I may 1A =I 2A may be.

[0046] Average intensity of the first peak I 1A is calculated as follows: The intensity of the peak observed between 530 eV and 550 eV is measured at a total of six points, including an arbitrary point on the surface of the oxide film, four points on a line drawn from this point toward the metal material that divide the thickness of the oxide film into five equal parts, and the intersection of this line with the surface of the metal material. Furthermore, the intensity of the peak observed between 530 eV and 550 eV is measured at four other arbitrary points at different depths in the same manner. The average intensity I of the first peak is 1A is the average of these 30 points.

[0047] Average intensity of the second peak I 2A ​is the average intensity of the peaks observed between 560 eV and 570 eV at the same 30 points where the intensity of the first peak was measured. If there are multiple peaks observed between 530 eV and 550 eV, the peak on the lowest energy side should be used. If there are multiple peaks observed between 560 eV and 570 eV, the peak on the lowest energy side should be used.

[0048] EELS is used in combination with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM).

[0049] B-4. Fourth mode The oxide film according to this embodiment contains an oxide of tantalum. In the oxide film according to this embodiment, the intensity I1 of the first peak observed between 530 eV and 550 eV in the EELS spectrum decreases toward the surface of the metal material. This means that the electronic structure of the oxide film changes in the same manner along the thickness direction. Such an oxide film can be formed on a metal material that has been subjected to nitrate conversion.

[0050] In other oxide films, it cannot be said that the intensity of the first peak I1 decreases the closer to the surface of the metal material. For example, in other oxide films, the intensity of the first peak on the surface of the metal material may be greater than the intensity of the first peak inside. In other oxide films, the oxygen bonding state changes randomly in the thickness direction. Although the reason for this is currently unclear, it is thought that this difference affects the electronic structure of the oxide film and is effective in suppressing the leakage current of capacitors.

[0051] The intensity I1 of the first peak is measured at six points, including an arbitrary point (depth zero) on the surface of the oxide film, four points (depths 1 to 4) on a line drawn from this point toward the metal material that divide the thickness of the oxide film into five equal parts, and the intersection point (depth 5) of this line with the surface of the metal material. The intensity of the first peak is then measured at four other arbitrary locations, for a total of six different depths. The five intensities measured at the same depth in different locations are averaged to determine the intensity of the first peak at that depth. If multiple peaks are observed between 530 eV and 550 eV, the lowest-energy peak should be used.

[0052] The intensity I1 of the first peak may be smaller as a whole, as long as it is closer to the surface of the metal material. For example, among two adjacent points among the six points from depth zero to depth 5, the intensity of the shallower point may be greater than or equal to the intensity of the deeper point. However, the intensity I1 at depth zero 10 is the intensity I at depth 5 15 Greater than.

[0053] In terms of the uniformity of the oxide layer quality, the intensity at zero depth I 10 and the intensity I at depth 5 15 It is desirable that the difference between the strength I and the strength I is not too large. 10 and intensity I 15 The difference between (=(I 10 -I 15 )) is the intensity I 10 It is preferable that the value is 30% or less of 100×(I 10 -I 15 ) / I 10 It is preferable that the ratio satisfies 100×(I 10 -I 15 ) / I 10 It is more preferable that the ratio is ≦20(%).

[0054] From a similar perspective, the intensity I at depth 1 11 is the intensity at zero depth I 10 Preferably, it is smaller than the intensity I 10 and intensity I 11It is desirable that the difference between the strength I and the strength I is large enough. 10 and intensity I 11 The difference between (=I 10 -I 11 ) is the intensity I 10 It is preferable that the ratio is 3% or more and 20% or less of the above. In other words, 3(%)≦100×(I 10 -I 11 ) / I 10 It is preferable that 5(%)≦100×(I 10 -I 11 ) / I 10 It is more preferable that the ratio is ≦20(%).

[0055] B-5. Fifth mode The oxide film according to this embodiment contains an oxide of tantalum. In the oxide film according to this embodiment, a fourth peak adjacent to the higher energy side of the third peak assigned to the Ta-N1 edge is observed at 570 eV or higher in the EELS spectrum. Such an oxide film can be formed on a metal material that has been subjected to nitrate conversion.

[0056] The third peak is attributed to the Ta-N1 edge (excitation process by the N1 shell electrons of tantalum). The position of the fourth peak indicates the state of the distance between oxygen atoms. The shift of the fourth peak to the high energy side means that the distance between oxygen atoms is reduced. In other words, it is inferred that the density of the oxide film is improved. The third peak coincides with the second peak in the third aspect.

[0057] The fourth peak in other oxide layers is observed on the lower energy side than 570 eV. This means that the oxidation state of tantalum atoms differs between the oxide layer formed by nitric acid formation and other oxide layers. The reason for this is currently unclear, but it is thought that this difference affects the electronic structure of the oxide layer and is effective in suppressing leakage current in capacitors.

[0058] The third and fourth peaks are identified as follows: An EELS spectrum is obtained at a point within 10 nm (e.g., 5 nm deep) from the surface of the oxide film toward the metal material. The third peak, which is attributed to the Ta-N1 edge, is then identified. The third peak typically appears between 563 eV and 567 eV. The fourth peak adjacent to this third peak is then identified. The location of the fourth peak is preferably confirmed by further evaluating EELS at nine other arbitrary points within 10 nm of the oxide film. If the fourth peak is observed at 570 eV or higher at eight of the ten arbitrary points, the oxide film may be considered to satisfy the fifth aspect.

[0059] (others) In the third to fifth aspects, it is desirable to satisfy the following: a) In the spectrum obtained by EELS of the oxide coating film according to this embodiment, the average intensity I of the fifth peak observed between 1770 eV and 1790 eV 5A is the average intensity of the fifth peak in other oxide layers, I 5R Lower.

[0060] In particular, the average intensity I 5A and the average intensity I 5R The difference between (=I 5R -I 5A ) is the average intensity I 5R It is preferable that the value is 10% or more of (I 5R -I 5A ) / I 5R It is preferable that ≧0.1 is satisfied.

[0061] The fifth peak is attributed to the Ta-M5 edge (excitation process by the M5 shell electrons of tantalum).

[0062] b) The average intensity I of the sixth peak observed between 1830 eV and 1850 eV in the spectrum obtained by EELS of the oxide coating film according to this embodiment 6A is the average intensity of the sixth peak in other oxide layers, I 6R Lower.

[0063] In particular, the average intensity I 6A and the average intensity I 6R The difference between (=I 6R -I 6A ) is the average intensity I 6R It is preferable that the value is 5% or more of (I 6R -I 6A ) / I 6R It is preferable that ≧0.05 is satisfied.

[0064] The sixth peak is attributed to the Ta-M4 edge (excitation process by the M4 shell electrons of tantalum).

[0065] average intensity I 5A and the mean intensity I 6A is the mean intensity I 1A The average strength of the oxide film to be compared, I 5R and the mean intensity I 6R is the mean intensity I 1A can be calculated in the same way.

[0066] In the first to fourth aspects, it is desirable to satisfy the following. c) The value of the current (leakage current) flowing through the electrode having the oxide film according to this embodiment is at least 10% lower than the leakage current value of electrodes having other oxide films, thereby further suppressing the leakage current of the electrolytic capacitor.

[0067] The leakage current value of the electrode according to this embodiment is preferably at least 15% lower, and more preferably at least 30% lower, than the leakage current value of electrodes having other oxide films.

[0068] The leakage current of an electrode is the current value when the electrode and the counter electrode are immersed in an aqueous electrolyte solution and a voltage that is 70% of the formation voltage is applied.

[0069] The oxide film for comparison was formed using a chemical conversion solution containing, for example, 0.1% by mass of phosphoric acid. The chemical conversion conditions, other than the composition of the chemical conversion solution, were the same as those for the oxide film of this embodiment. The chemical conversion conditions were, for example, a chemical conversion voltage of 15 V, a temperature of 60°C, and a treatment time of 10 hours.

[0070] [Electrolytic capacitor] The electrode obtained by chemically treating the metal foil as described above is used in a capacitor element. The capacitor element includes a first electrode, which is the electrode described above, and a second electrode. The second electrode includes, for example, a solid electrolyte layer and a cathode extraction layer. The leakage current of the electrolytic capacitor according to this embodiment is at least 30% lower than the leakage current of electrolytic capacitors including electrodes having other oxide films.

[0071] An electrolytic capacitor includes, for example, one or more of the capacitor elements described above, an exterior case that encapsulates the capacitor elements, and first and second lead terminals. At least a portion of each lead terminal is exposed from the exterior case. Such a capacitor element may be, for example, sheet-shaped or flat.

[0072] (1st electrode) The first electrode is a metal material having an oxide film formed as described above, and is, for example, an anode.

[0073] (2nd electrode) The second electrode includes a solid electrolyte layer and an electrode lead layer, and is, for example, a cathode.

[0074] (Solid electrolyte layer) The solid electrolyte layer is formed so as to cover at least a portion of the oxide film, or may be formed so as to cover the entire surface of the oxide film, and the thickness of the solid electrolyte layer is not particularly limited.

[0075] The solid electrolyte layer includes one or more solid electrolyte layers. The solid electrolyte layer is formed, for example, from a manganese compound or a conductive polymer. Examples of conductive polymers that can be used include polypyrrole, polyaniline, polythiophene, polyacetylene, and derivatives thereof. A solid electrolyte layer including a conductive polymer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing raw material monomers on an oxide film. Alternatively, the solid electrolyte layer can be formed by applying a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed to the oxide film.

[0076] (Cathode extraction layer) The cathode extraction layer may be formed so as to cover at least a portion of the solid electrolyte layer, or may be formed so as to cover the entire surface of the solid electrolyte layer.

[0077] The cathode extraction layer includes, for example, a carbon layer and a metal paste layer formed on the surface of the carbon layer. The carbon layer is made of a composition containing a conductive carbon material such as graphite. The metal paste layer is made of a composition containing silver particles and a resin. However, the configuration of the cathode extraction layer is not limited thereto and may be any configuration that has a current collecting function.

[0078] (Lead terminal) The material of the first lead terminal and the second lead terminal is not particularly limited as long as it is electrochemically and chemically stable and conductive, and may be metallic or non-metallic. The shapes of these terminals are also not particularly limited.

[0079] The first lead terminal is connected to the first electrode, and the second lead terminal is connected to the second electrode. The first electrode and the first lead terminal are electrically connected by, for example, welding them together. The second electrode and the second lead terminal are electrically connected by, for example, bonding them together via a conductive adhesive layer.

[0080] (exterior body) The exterior body covers the capacitor element and a portion of the lead terminal. This electrically insulates the first lead terminal from the second lead terminal and protects the capacitor element. The exterior body is made of an insulating material (exterior body material). Examples of exterior body materials include cured thermosetting resins and engineering plastics.

[0081] FIG. 1 is a cross-sectional view schematically showing a capacitor element according to this embodiment. The capacitor element 10 includes a first electrode 11 and a second electrode 13. The first electrode 11 includes a porous sintered body 111, an electrode wire 112 extending from the porous sintered body 111, and an oxide film 113 covering at least a portion of the porous sintered body 111. The second electrode 13 includes a solid electrolyte layer 131, a carbon layer 132, and a metal paste layer 133. The carbon layer 132 and the metal paste layer 133 function as cathode extraction layers. The capacitor element 10 has a generally cubic shape.

[0082] FIG. 2 is a cross-sectional view schematically illustrating the structure of the electrolytic capacitor according to this embodiment. Electrolytic capacitor 100 includes a capacitor element, an exterior body 20 that seals the capacitor element, and first and second lead terminals 30 and 40, at least a portion of which is exposed to the outside of exterior body 20.

[0083] The electrode wire 112 and the first lead terminal 30 are electrically connected by, for example, welding. The metal paste layer 133 and the second lead terminal 40 are electrically connected via an adhesive layer 50 formed of, for example, a conductive adhesive (a mixture of thermosetting resin with carbon particles or metal particles, etc.).

[0084] In this embodiment, an electrolytic capacitor using a solid electrolyte and having a capacitor element sealed in an outer casing has been described, but the present invention is not limited thereto. The electrode according to this embodiment can be applied to, for example, an electrolytic capacitor including a capacitor element in which a first electrode and a second electrode are wound with a separator interposed therebetween, and an electrolytic solution. In this case, the electrode according to this embodiment is used for at least one of the first electrode and the second electrode. (Addendum) This specification discloses the following techniques. (Technology 1) a metallic material including a valve metal; an oxide film formed on the surface of the metal material; a solid electrolyte layer covering at least a portion of the oxide film, the oxide film includes an oxide of tantalum; In the spectrum obtained by electron energy loss spectroscopy of the oxide film, the average intensity I of the first peak observed between 530 eV and 550 eV 1A and the average intensity I of the second peak observed between 560 eV and 570 eV 2A The difference between the average intensity of the first peak, I 1A is less than 10% of The average intensity of the first peak I 1A is the average intensity of the second peak I 2A greater than Electrolytic capacitor. (Technology 2) In a spectrum obtained by electron energy loss spectroscopy of the oxide coating, a third peak attributed to the Ta-N1 edge is observed at 566 eV or higher, and a fourth peak adjacent to the third peak on the higher energy side is observed at 570 eV or higher. The electrolytic capacitor according to claim 1. (Technology 3) In a spectrum obtained by electron energy loss spectroscopy of the oxide film, the intensity I1 of the first peak decreases as the oxide film approaches the surface of the metal material. Electrolytic capacitor according to Art. 1 or 2. (Technology 4) The phosphorus concentration of the oxide film measured by energy dispersive X-ray spectroscopy is below the detection limit. The electrolytic capacitor according to claim 3. (Technology 5) the intensity of a phosphate ion fragment peak obtained by time-of-flight secondary ion mass spectrometry of the oxide film is below the detection limit; The electrolytic capacitor according to claim 4.

[0085] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0086] Example 1 Twenty electrolytic capacitors shown in Figure 2 were fabricated using the following procedure, and their characteristics were evaluated.

[0087] (i) Fabrication of capacitor elements (ii) Preparation of the first electrode Tantalum metal particles were used as the valve metal. The tantalum metal particles were molded into a rectangular parallelepiped so that one end of an electrode wire made of tantalum was embedded in the tantalum metal particles, and the molded body was then sintered in a vacuum. This resulted in a precursor for a first electrode, which included a porous tantalum sintered body and an electrode wire with one end embedded in the porous sintered body and the other end extending from one surface of the porous sintered body.

[0088] (i-ii) Formation of oxide film A 0.06% by mass aqueous solution of nitric acid was prepared as the chemical conversion solution. A chemical conversion tank was filled with this chemical conversion solution, and the porous sintered body and a portion of the electrode wire were immersed in it. The temperature of the chemical conversion solution was 60°C. The other end of the electrode wire was connected to a counter electrode, and anodization was performed for 10 hours at a chemical conversion voltage of 15 V. In this way, a uniform oxide film (approximately 30 nm thick) of tantalum oxide (Ta2O5) was formed on the surface of the porous sintered body and on the surface of a portion of the electrode wire, and 20 first electrodes X1 were obtained.

[0089] (i-iii) Formation of solid electrolyte layer The porous sintered body on which the oxide film had been formed was impregnated with a dispersion containing polypyrrole for 5 minutes, and then dried at 150°C for 30 minutes to form a solid electrolyte layer on the oxide film.

[0090] (i-iv) Formation of carbon layer A dispersion liquid (carbon paste) in which carbon particles were dispersed in water was applied to the solid electrolyte layer, and then heated at 200°C to form a carbon layer on the surface of the solid electrolyte layer.

[0091] (iv) Formation of a metal paste layer A metal paste containing silver particles, a binder resin, and a solvent was applied to the surface of the carbon layer, and then heated at 200°C to form a metal paste layer, thereby obtaining a capacitor element.

[0092] (ii) Fabrication of electrolytic capacitors A conductive adhesive was applied to the metal paste layer, and the second lead terminal was bonded to the metal paste layer. The electrode wire was then resistance-welded to the first lead terminal. Next, the capacitor element with the bonded lead terminals and the exterior body material (uncured thermosetting resin and filler) were placed in a mold, and the capacitor element was sealed using transfer molding to produce an electrolytic capacitor.

[0093] Example 2 Twenty first electrodes X2 were fabricated in the same manner as in Example 1, except that the concentration of nitric acid in the chemical conversion solution was set to 10 mass % and the temperature of the chemical conversion solution was set to 45°C, and electrolytic capacitors were fabricated.

[0094] Comparative Example 1 Twenty first electrodes Y1 were fabricated and electrolytic capacitors were fabricated in the same manner as in Example 1, except that a chemical conversion solution containing phosphoric acid (concentration: 0.1% by mass) was used instead of nitric acid.

[0095] Comparative Example 2 Twenty first electrodes Y2 were fabricated and electrolytic capacitors were fabricated in the same manner as in Example 1, except that a chemical conversion solution containing diammonium adipate (concentration: 0.2 mass %) was used instead of nitric acid.

[0096] Comparative Example 3 Twenty first electrodes Y3 were fabricated and electrolytic capacitors were fabricated in the same manner as in Example 1, except that a chemical conversion solution containing ammonia (concentration: 2.5 mass %) was used instead of nitric acid.

[0097] [evaluation] (1) Analysis of oxide film After the formation of the oxide film (i-ii), the first electrodes X1, Y1 to Y3 were analyzed. (1-1)EELS analysis Spectral analysis was performed using a TEM-EELS instrument, and the results are shown in Table 1.

[0098] [Table 1]

[0099] (1-2)EDX analysis The oxide film surfaces of the first electrodes X1 and Y1 were subjected to elemental analysis using a TEM-EDX device. The results are shown in Table 2.

[0100] [Table 2]

[0101] (1-3)TOF-SIMS analysis The oxide film was analyzed using a TOF-SIMS system at the surface and its interior (1 to 10 nm deep). The oxide film was etched using an Ar gas cluster ion beam.

[0102] For the first electrodes X1 and X2, no phosphate ions were detected (below the detection limit) on either the surface or inside of the oxide film. For the first electrodes Y1 to Y3, phosphate ions were detected on either the surface or inside of the oxide film.

[0103] (2) Leakage current After the formation of the coating (i-ii), the leakage current values ​​of the first electrodes X1, Y2 and Y3 were measured. The prepared first electrode and counter electrode (SUS316L) were immersed in 0.1 wt % phosphoric acid. A voltage of 70% of the chemical conversion voltage was applied between each electrode, and the current flowing through the first electrode was measured and averaged. The average current value (leakage current value) for each first electrode was calculated, with the average current value for first electrode Y1 being set at 100%. The results are shown in Table 3. For reference, Table 3 also shows the average current value for first electrode X2.

[0104] [Table 3] [Industrial Applicability]

[0105] The electrodes produced by the method according to the present invention can be used in electrolytic capacitors for various applications because they suppress leakage current. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0106] 100: Electrolytic capacitor 10: Capacitor element 11: 1st electrode 111: Metal material (porous sintered body) 112: Electrode wire 113: Oxide film 13:Second electrode 131: Solid electrolyte layer 132: Carbon layer 133: Metal paste layer 20: Exterior body 30: First lead terminal 40: Second lead terminal 50: next layer

Claims

1. a metallic material including a valve metal; an oxide film formed on the surface of the metal material; a solid electrolyte layer covering at least a portion of the oxide film, the oxide film includes an oxide of tantalum; In the spectrum obtained by electron energy loss spectroscopy of the oxide film, the average intensity I of the first peak observed between 530 eV and 550 eV １Ａ and the average intensity I of the second peak observed between 560 eV and 570 eV. ２Ａ The difference between the average intensity of the first peak I １Ａ is 10% or less of The average intensity I of the first peak １Ａ is the average intensity I of the second peak ２Ａ greater than Electrolytic capacitor.

2. In a spectrum obtained by electron energy loss spectroscopy of the oxide coating, a third peak attributed to the Ta-N1 edge is observed at 566 eV or higher, and a fourth peak adjacent to the third peak on the higher energy side is observed at 570 eV or higher.

2. The electrolytic capacitor according to claim 1.

3. In the spectrum obtained by electron energy loss spectroscopy of the oxide film, the intensity I of the first peak １ is smaller closer to the surface of the metal material, 3. The electrolytic capacitor according to claim 1.

4. The phosphorus concentration of the oxide film measured by energy dispersive X-ray spectroscopy is below the detection limit.

4. The electrolytic capacitor according to claim 3.

5. the intensity of a phosphate ion fragment peak obtained by time-of-flight secondary ion mass spectrometry of the oxide film is below the detection limit; 5. The electrolytic capacitor according to claim 4.

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