Cathode foil for electrolytic capacitor, electrolytic capacitor, and method for manufacturing the same

Abstract

The cathode foil for an electrolytic capacitor has: a metal porous part, a metal core part connected to the metal porous part, and a coating film covering the metal porous part. On the first main surface of the cathode foil for an electrolytic capacitor, the pores in the metal porous part are open. In the thickness direction of the metal porous part, the coating film is formed from the first main surface to a depth of 10% or more of the thickness of the metal porous part.

Description

Technical Field

[0001] The present invention relates to a cathode foil for an electrolytic capacitor, an electrolytic capacitor, and methods for manufacturing them. Background Art

[0002] For the anode body of an electrolytic capacitor, a metal foil containing a valve - acting metal is used. From the viewpoint of increasing the electrostatic capacitance, at least a part of the main surface of the metal material is subjected to treatment such as etching to form a porous body. Thereafter, the porous body is subjected to a chemical conversion treatment, thereby forming a layer of metal oxide (dielectric) on the surface of the pores or irregularities of the porous body.

[0003] On the other hand, as the configuration of the cathode body, depending on the use, a roughened metal foil, a chemical conversion foil obtained by further subjecting the roughened metal foil to chemical conversion, or one obtained by forming a non - valve metal such as titanium on the surface layer of the metal foil is used.

[0004] Patent Document 1 describes a cathode foil for a solid electrolytic capacitor, which is formed on an unroughened electrode substrate with: a first conductive layer, a mixed - presence layer in which the substance constituting the first conductive layer and carbon are mixed and present, and a second conductive layer substantially composed of carbon. Here, as approaching from the first conductive layer to the second conductive layer, the component concentration of the mixed - presence layer changes from a component composition substantially only containing the substance constituting the first conductive layer to a component composition substantially only containing carbon, thereby obtaining a high capacitance and being able to improve characteristics of the electrolytic capacitor such as low ESR.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Laid - Open No. 2012 - 174865 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] To provide a cathode foil for an electrolytic capacitor and a method for manufacturing the same that can achieve excellent characteristics.

[0010] Solutions to the Problems

[0011] The cathode foil for an electrolytic capacitor according to one aspect of the present invention has: a metal porous part, a metal core part connected to the metal porous part, and a coating film covering the metal porous part. On the first main surface of the cathode foil for an electrolytic capacitor, the pores in the metal porous part are open. In the thickness direction of the metal porous part, the coating film is formed from the first main surface to a depth of 10% or more of the thickness of the metal porous part.

[0012] Another aspect of the present invention relates to an electrolytic capacitor including: the above-mentioned cathode foil, an anode body having a dielectric layer formed on its surface, and an electrolyte.

[0013] A method for manufacturing a cathode foil for an electrolytic capacitor according to another aspect of the present invention includes: a step of preparing a metal substrate having a metal porous part and a metal core part connected to the metal porous part; and a step of forming a coating film on the surface of the metal part constituting the metal porous part of the metal substrate. The coating film is formed by atomic layer deposition (ALD).

[0014] A method for manufacturing an electrolytic capacitor according to another aspect of the present invention includes: a step of obtaining a cathode foil by using the above-mentioned method for manufacturing a cathode foil; a step of preparing an anode body having a dielectric layer on its surface; and a step of forming a capacitor element by using the anode body and the cathode foil for an electrolytic capacitor.

[0015] Effects of the Invention

[0016] By using the cathode foil of the present invention, the characteristics of the electrolytic capacitor can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A cross-sectional view schematically showing the structure of a cathode foil for an electrolytic capacitor according to an embodiment of the present invention.

[0018] Figure 2 A cross-sectional schematic view showing an enlarged part of the metal porous part of the cathode foil for an electrolytic capacitor.

[0019] Figure 3 To show Figure 2 A cross-sectional schematic view showing another example of the cathode foil for an electrolytic capacitor shown.

[0020] Figure 4 To show Figure 2 A cross-sectional schematic view showing yet another example of the cathode foil for an electrolytic capacitor shown.

[0021] Figure 5 A cross-sectional view schematically showing an electrolytic capacitor according to an embodiment of the present invention.

[0022] Figure 6 A schematic diagram showing a part of a wound body included in the same electrolytic capacitor unfolded. DETAILED DESCRIPTION

[0023] [Cathode Foil for Electrolytic Capacitor]

[0024] One embodiment of the present invention relates to a cathode foil for an electrolytic capacitor having: a metal porous portion, a metal core portion connected to the metal porous portion, a first main surface where the pores of the metal porous portion open, and a coating film covering the metal porous portion. More specifically, the coating film covers the surface of the metal skeleton constituting the metal porous portion. The coating film may include a conductive first layer and / or a second layer, the conductive first layer contains a first element, and the second layer is an oxide film containing a second element. The coating film may include both the first layer and the second layer. In this case, the first layer covers at least a part of the second layer.

[0025] In this embodiment, at least one main surface (the first main surface) of the cathode foil is roughened to form pores in such a manner that they open on the first main surface of the cathode foil. The portion with pores formed on the first main surface side of the cathode foil is the metal porous portion, and the inside of the cathode foil where no pores are formed is the metal core portion.

[0026] It should be noted that the main surfaces of the cathode foil (cathode body) and the anode foil (anode body) are the two surfaces that macroscopically (by visual observation) occupy the largest area among the surfaces of these electrode foils. The end faces of the cathode foil and the anode foil are the faces that exist at the ends other than the main surfaces of these electrode foils, and also include the cut surfaces in the case of cutting a large sheet of electrode foil. In a wound body, the faces of the electrode foil disposed on the top surface and the bottom surface other than the circumferential surface are end faces.

[0027] Generally, a natural oxide film is formed on the surface of the cathode foil. The natural oxide film has the function of protecting the metal portion of the cathode foil from the influence of the electrolyte. However, the thickness of the natural oxide film is sometimes insufficient to protect the metal portion from the influence of the electrolyte, and with the application of voltage, the reaction between the metal portion and the electrolyte easily proceeds. In addition, through the portion where the thickness of the natural oxide film is thin, the reaction between the metal portion and the electrolyte easily proceeds. As a result, gas is generated and the deterioration due to the oxidation of the cathode foil becomes larger. Moreover, sometimes the natural oxide film does not have sufficient water resistance, and in the case where the electrolyte contains moisture, the deterioration of the foil easily proceeds due to the hydration reaction. As a result, the ESR tends to increase.

[0028] In order to suppress the deterioration of the cathode foil, chemical conversion treatment of the cathode foil is also considered to form a thick oxide coating film. In this case, capacitance is also generated on the cathode side. If capacitance is generated not only on the anode but also on the cathode side, the capacitance (synthetic capacitance) of the electrolytic capacitor as a whole decreases. However, by forming an oxide coating film (corresponding to the second layer described later) with an appropriate thickness on the roughened cathode foil, the capacitance on the cathode side is deliberately increased, thereby suppressing the decrease in the capacitance of the electrolytic capacitor as a whole.

[0029] By using a roughened cathode foil, the contact area between the electrolyte and the cathode foil becomes larger, and it is easy to reduce the ESR. In addition, the capacitance on the cathode side can be increased. On the other hand, if the surface area of the cathode foil becomes larger, the reaction with the electrolyte is likely to occur on the surface of the cathode foil, and the cathode foil is likely to deteriorate.

[0030] Therefore, for the electrode foil for an electrolytic capacitor according to the present embodiment, in one aspect, the surface of the cathode foil can be covered with a conductive first layer. Thereby, the capacitance appearing on the cathode side can be suppressed. By electrically connecting the conductive first layer to the metal core portion, the cathode foil substantially functions as a conductor, and a decrease in the capacitance of the electrolytic capacitor can be suppressed. In addition, in the case of an electrolytic capacitor using a solid electrolyte such as a conductive polymer, the conductive polymer is formed so as to fill the pores deep inside the metal porous portion. In this case, by covering the inner side wall of the pores with the first layer, the adhesion between the solid electrolyte and the cathode foil is improved, and the ESR can be reduced. The first layer contains a first element. The first element can be at least one element selected from carbon, nickel, silver, and gold.

[0031] In addition, in one aspect, the surface of the cathode foil of the electrode foil for an electrolytic capacitor according to the present embodiment can be covered with a second layer which is an oxide film. The capacitance generated on the cathode side can be moderately increased to suppress a decrease in the capacitance of the electrolytic capacitor as a whole. In addition, by using the second layer, the reaction between the metal portion and the electrolyte is suppressed, so that the deterioration of the cathode foil is suppressed, and the ESR can be maintained at a low level. In addition, an electrolytic capacitor with excellent withstand voltage is obtained. The second layer contains a second element. The second element can be at least one element selected from aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium.

[0032] The thickness of the second layer is set to a desired thickness according to the characteristics of the electrolytic capacitor. From the viewpoint of maintaining the capacitance, the thickness of the second layer may be equal to or less than the thickness of the oxide coating film obtained by chemical conversion of the metal containing the second element at 4V. For example, when the second element is aluminum, the thickness of the second layer may be 5 nm or less. On the other hand, from the viewpoint of improving the withstand voltage, the thickness of the second layer can be made thicker than the thickness of the oxide coating film obtained by chemical conversion of the metal containing the second element at 4V. It should be noted that the above description does not necessarily mean that the second layer is formed by a chemical conversion treatment. For example, it includes a case where the second layer is formed by deposition to a thickness that can be obtained by chemical conversion at 4V.

[0033] Note that when the second element is aluminum, titanium, silicon, tantalum, niobium, hafnium, or zirconium, the thicknesses obtained by chemical conversion of the metal containing the second element at 4V are provided below. Note that, below, the thickness in the case of silicon corresponds to the thickness of a silicon oxide film that can achieve the same breakdown voltage as the aluminum oxide film formed by 4V chemical conversion.

[0034] Aluminum: 5nm

[0035] Titanium: 12nm

[0036] Silicon: 2nm

[0037] Tantalum: 6nm

[0038] Niobium: 9nm

[0039] Hafnium: 11nm

[0040] Zirconium: 8nm

[0041] The coating film including the first layer and / or the second layer may be formed in a region from the first main surface of the metal porous part to a depth of 10% or more, 20% or more, 30% or more, or 50% or more of the thickness of the metal porous part in the thickness direction of the metal porous part.

[0042] The first layer and / or the second layer can be formed by the ALD (Atomic Layer Deposition) method. According to the ALD method, the source gas (precursor material) diffuses in the voids formed by the pores of the metal porous part and can penetrate deep into the tortuous pores. As a result, the first layer and / or the second layer can also adhere to the inner sidewalls of the pores that are not exposed from the first main surface of the metal porous part and are blocked by the metal framework of the metal porous part. Therefore, by using the ALD method, the first layer and / or the second layer can be formed in a region from the first main surface to the deep part of the metal porous part. However, in the ALD method, although the source gas (precursor material) can reach the deep part of the metal porous part far from the outer surface (the first main surface) through the pores, the precursor material becomes more difficult to reach as it gets farther from the first main surface. As a result, the thickness of the coating film can have a distribution where it becomes thicker closer to the first main surface side (more precisely, the shorter the diffusion distance of the source gas supplied through the pores from the first main surface), and thinner farther from the first main surface (closer to the side of the metal core).

[0043] The second layer can be formed by chemical conversion treatment. However, when the second layer is formed by chemical conversion treatment, the state of chemical conversion cannot be stabilized by applying a chemical conversion voltage of 4 V or less, and it is difficult to form a thin chemical conversion coating film with a uniform film thickness, few defects, and in a dense manner. Sometimes, portions where the second layer is not formed or portions with a thin thickness of the second layer are generated on a part of the surface of the metal skeleton of the metal porous portion. As a result, the foil is liable to deteriorate due to the reaction with the electrolyte. In contrast, when the second layer is formed by the ALD method, if the thickness of the cathode foil exceeds, for example, 50 μm, the thickness of the second layer sometimes depends on the distance from the first main surface, but a uniform and dense film with few defects can be formed. Therefore, by using the ALD method, the surface of the metal skeleton can be easily covered with a dense and defect-free second layer.

[0044] In the thickness direction of the metal porous portion, in a region at a depth exceeding 10% of the thickness of the metal porous portion, a third layer containing at least any one of phosphorus and nitrogen may be attached. The third layer may also be attached to the deep part on the metal core side of the metal porous portion where the coating film containing the first layer and / or the second layer is not formed. By containing phosphorus and / or nitrogen, the third layer has high solvent resistance to various solvents (especially moisture) constituting the liquid component (such as the electrolyte). In addition, when the first layer and / or the second layer is formed by the ALD method, the adhesion between the first layer and / or the second layer and the metal skeleton and the coverage of the first layer and / or the second layer are improved.

[0045] In particular, when the pH of the liquid component is less than 7 and acidic, if the acidic liquid component comes into contact with the metal skeleton portion or the metal core of the metal porous portion, the cathode foil will corrode, for example, and deterioration is likely to occur. However, by providing the third layer, deterioration of the cathode foil can be suppressed. By providing the third layer, an excellent deterioration suppression effect of the cathode body can be obtained even when the pH of the liquid component is less than 5. In addition, even when used in a high-temperature and high-humidity environment of, for example, 85 °C or higher and a humidity of 85% or higher, the moisture resistance can be improved.

[0046] In addition, even when the liquid component contains water, the hydration reaction of the metal skeleton portion or the metal core can be suppressed. For example, the liquid component may contain moisture in the range of 3 to 15% by mass. Even in this case, since the third layer contains phosphorus and / or nitrogen, the hydration reaction is suppressed. Therefore, by providing the third layer, deterioration of the cathode foil can be suppressed even when the liquid component contains moisture.

[0047] The third layer can further be interposed between the above-mentioned film layer including the first layer and / or the second layer and the metal porous part. Even when cracks or the like occur in the film layer, the surface of the metal porous part is covered by the third layer, so that exposure of the metal skeleton part of the metal porous part and contact with the liquid component can be suppressed. Therefore, deterioration of the cathode foil can be suppressed, and an increase in ESR can be suppressed.

[0048] When the film layer includes the second layer, the second layer can also contain phosphorus and / or nitrogen. When the third layer is also interposed between the above-mentioned film layer and the metal porous part, the third layer can constitute part or all of the second layer in the above-mentioned film layer.

[0049] For example, by infiltrating a solution containing a compound containing phosphorus and / or nitrogen (for example, ammonium phosphate solution) into the roughened cathode foil, and then drying it by heat treatment, the third layer can be attached to the inner side wall of the pores. For the infiltration of the solution, when the chemical conversion solution contains a phosphorus compound and / or a nitrogen compound, it can be carried out simultaneously or in parallel with the chemical conversion treatment. The chemical conversion treatment can be carried out before the formation of the first layer and / or the second layer, or after the formation of the first layer and / or the second layer.

[0050] Figure 1 A cross-sectional schematic view of a cathode foil according to an embodiment of the present invention is shown. The cathode foil 22 is an integrated body of a metal core part 31 and a metal porous part 32. In the first main surface S1, the pores of the metal porous part 32 are open. The metal porous part 32 has a second main surface S2 at the boundary with the metal core part 31. The thickness of the metal porous part 32 (the depth from the first main surface S1) (that is, the distance between the first main surface S1 and the second main surface S2) is represented by T0.

[0051] The metal porous part 32 has pits or pores surrounded by a metal skeleton. In the region of the metal porous part 32 at a specified thickness (depth) from the first main surface S1, a film layer 33 is formed so as to cover the surface of the metal skeleton of the metal porous part 32 (refer to Figures 2 to 4 ). The film layer 33 can include the first layer 35 and / or the second layer 36. The thickness T1 of the region of the metal porous part 32 where the film layer 33 is formed is 10% or more of the thickness TO of the metal porous part 32 (T1≥0.1TO). The thickness T1 can be 30% or more of the thickness T0.

[0052] In the present embodiment, both the first layer 35 and the second layer 36 may be formed from the first main surface S1 to a depth exceeding 10% or more of the thickness T0 of the metal porous portion 32. However, it is sufficient that at least one of the first layer 35 and the second layer 36 is formed from the first main surface S1 to a depth exceeding 10% or more of the thickness TO of the metal porous portion 32. Preferably, at least the first layer 35 is formed from the first main surface S1 to a depth exceeding 10% or more of the thickness T0 of the metal porous portion 32.

[0053] The thickness of the metal porous portion is not particularly limited and may be appropriately selected according to the use of the electrolytic capacitor, the required withstand voltage, etc. The thickness of the metal porous portion may be, for example, 1 μm to 60 μm. In addition, the thickness T0 of the metal porous portion may be, for example, 1 / 10 or more and less than 5 / 10 of the thickness of the cathode foil. It should be noted that for the thickness T0 of the metal porous portion, the cathode foil is cut in a manner to obtain a cross-section in the thickness direction of the metal core portion and the metal porous portion, an electron microscope photograph of the cross-section is taken, and it can be obtained in the form of the average value of the thicknesses of any 10 points of the metal porous portion. For the thickness T1, it is obtained in the form of the average value of the thicknesses of any 10 points in the region of the metal porous portion of the coating film 33 having a thickness of 1 nm or more that can be confirmed in the above electron microscope photograph.

[0054] Figure 2 shows a schematic cross-sectional view of an enlarged area near the first main surface S1 of the metal porous portion 32 in the cathode foil 22. It should be noted that Figure 2 in, for the sake of explanation, the pores of the metal porous portion, the first layer 35, and the third layer 37 are emphasized and shown. The scale of each component in the figure (especially the film thicknesses of the first layer 35 and the third layer 37) does not match the actual scale. This is the same in Figure 3 and Figure 4 shown later.

[0055] As Figure 2 shown, in the cathode foil 22, the first main surface S1 is roughened, and pores 38 are formed on the roughened main surface. The pores 38 are tortuous and branched, and extend from the first main surface S1 toward the inner depth of the metal porous portion 32. The inner sidewall of the pores 38 is covered with the coating film 33 including the first layer 35.

[0056] The thickness of the first layer 35 is substantially constant, but it may be thicker as it is closer to the first main surface S1 side (more precisely, the shorter the shortest distance via the pores 38 to the first main surface S1). In addition, the first layer 35 also adheres to the regions that are not exposed from the first main surface S1 and are shielded from the outside by the metal skeleton of the metal porous portion 32 ( Figure 2 regions X1 and Y1). Such a coating film 33 can be obtained by forming the first layer 35 using the ALD method.

[0057] A third layer 37 is formed between the coating film 33 and the metal framework of the metal porous portion 32. The third layer 37 contains phosphorus and / or nitrogen and has water resistance. In addition, although not shown, the third layer 37 may also be formed to a deep part of the metal porous portion 32 where the coating film 33 is not formed (a region where the depth from the first main surface S1 exceeds T1).

[0058] Figure 3 Another example of the cathode foil according to one embodiment of the present invention is shown. Figure 3 Similar to Figure 2 is also a schematic cross-sectional view of an enlarged area near the first main surface S1 of the metal porous portion 32. It should be noted that Figure 3 in, for the sake of illustration, the pores of the metal porous portion, the second layer 36, and the third layer 37 are emphasized and shown. The scale of each component in the figure (especially the film thicknesses of the second layer 36 and the third layer 37) does not match the actual scale. This is the same in Figure 4 shown later.

[0059] Similar to Figure 2 is also the same. Figure 3 In the cathode foil 22A shown, the first main surface S1 is roughened, and pores 38 are formed on the roughened main surface. The inner wall of the pores 38 is covered with a coating film 33 containing the second layer 36.

[0060] The thickness of the second layer 36 is substantially constant, but it may be thicker as it is closer to the first main surface S1 side (more precisely, the shorter the shortest distance from the pores 38 to the first main surface S1). In addition, the second layer 36 also adheres to regions that are not exposed from the first main surface S1 and are shielded from the outside by the metal framework of the metal porous portion 32 ( Figure 3 regions X2 and Y2). Such a coating film 33 can be obtained by forming the second layer 36 using the ALD method. Similar to Figure 2 a third layer 37 is formed between the coating film 33 and the metal framework of the metal porous portion 32. Although not shown, the third layer 37 may also be formed to a deep part of the metal porous portion 32 where the coating film 33 is not formed (a region where the depth from the first main surface S1 exceeds T1).

[0061] Figure 4 Another example of the cathode foil according to one embodiment of the present invention is shown. Figure 4 Similar to Figure 2 and Figure 3 is also a schematic cross-sectional view of an enlarged area near the first main surface S1 of the metal porous portion 32. Figure 4 In the cathode foil 22B shown, the inner wall of the pores 38 is covered with a coating film 33 containing the first layer 35 and the second layer 36. The first layer 35 covers the second layer 36.

[0062] The thicknesses of the first layer 35 and the second layer 36 are formed to be thicker as they are closer to the first main surface S1 side (more precisely, the shorter the shortest distance through the fine pores 38 to the first main surface S1). In addition, the first layer 35 and the second layer 36 also adhere to the regions ( Figure 4 regions X3 and Y3) that are not exposed from the first main surface S1 and are shielded from the outside by the metal skeleton of the metal porous part 32. Figure 2 and Figure 3 Similarly, a third layer 37 is formed between the coating film 33 and the metal skeleton of the metal porous part 32. Although not shown, the third layer 37 can also be formed to the deep part of the metal porous part 32 where the coating film 33 is not formed (the region where the depth from the first main surface S1 exceeds T1).

[0063] The film thickness of the first layer 35 is, for example, 1 nm to 50 nm, and can be 1 nm to 30 nm. The film thickness of the second layer 36 is, for example, 1 nm to 10 nm. The film thickness of the coating film 33 (the sum of the film thicknesses of the first layer and the second layer) is, for example, 2 nm to 60 nm. It should be noted that for these film thicknesses, they are obtained in the form of the average value of the film thicknesses of any 10 points in the surface layer region where the depth from the first main surface S1 is 100 nm or less in the electron microscope photograph of the cross-section in the thickness direction of the metal porous part 32.

[0064] The film thickness of the third layer 37 is, for example, 2 nm or less, and can be 0.08 nm to 2 nm. The film thickness of the third layer 37 is obtained in the form of the average value of the film thicknesses of any 10 points in the electron microscope photograph of the cross-section in the thickness direction of the metal porous part 32.

[0065] From the viewpoint of suppressing the deterioration of the cathode foil, the concentration of phosphorus or nitrogen contained in the third layer is, for example, preferably 0.5 at% or more and 7.0 at% or less, and more preferably 1.0 at% or more and 5.0 at% or less.

[0066] It should be noted that the concentration of phosphorus or nitrogen contained in the third layer is obtained by observing the cross-section obtained by cutting the cathode foil in the thickness direction using a transmission electron microscope (TEM) and performing a composition analysis in a desired region of the cathode foil using an X-ray microanalyzer (XMA). The concentration of phosphorus or nitrogen is obtained by taking the average value of the measurement values of any 10 points.

[0067] The type of metal constituting the metal core part and the metal porous part is not particularly limited, and a metal having a valve action is preferred, such as aluminum, tantalum, niobium, etc.

[0068] The roughening of the cathode foil (formation of a metal porous portion) is preferably carried out by etching the metal foil. Additionally, a chemical conversion treatment can be performed on the cathode foil as needed to form an oxide coating film (second layer) on the surface of the cathode foil.

[0069] The peak of the pore diameter of the pits or pores in the metal porous portion is not particularly limited. From the viewpoints of increasing the surface area and enabling the formation of the first layer or the second layer to the deep part of the metal porous portion, for example, it can be set to 50 nm to 2000 nm, or it can also be set to 100 nm to 300 nm. The peak of the pore diameter is, for example, the most probable pore diameter (the most frequent pore diameter) of the volume-based pore diameter distribution measured by a mercury porosimeter.

[0070] As the conductive material for forming the first layer, as a material that can be formed into a film by the ALD method, in addition to amorphous carbon, metals or conductive metal compounds, etc. can also be cited. As the metal and the metal compound, those that are not easily formed into a passivation film by contact with air, etc. are preferred. As the metal, for example, silver, gold, titanium, titanium alloy, nickel, nickel alloy, etc. can be cited. As the metal compound, for example, nitrides, carbides, etc. can be cited, and nitrides are preferred. As the metal constituting the metal compound, titanium and / or nickel, etc. can be exemplified. The first layer can contain one of these materials or can contain two or more of them.

[0071] When forming the first layer and the second layer, if the thickness of the region where the second layer is formed is 10% or more of the thickness T0 of the metal porous portion 32, the first layer can be formed in a shallow region near the first main surface S1. In this case, the film formation method of the first layer is not limited to the ALD method, and vapor phase methods such as chemical vapor deposition, vacuum evaporation, sputtering, and ion plating can also be used.

[0072] The element other than oxygen (second element) contained in the oxide film constituting the second layer can be the same as or different from the metal element constituting the metal porous portion.

[0073] When forming the coating film including the first layer and the second layer, the thickness (depth) of the region where the first layer is formed in the metal porous portion can be made thicker than the thickness (depth) of the region where the second layer is formed. In this case, the first layer can also be electrically connected to the metal skeleton portion on the metal core side of the metal porous portion. Thereby, it is easy not to exhibit the cathode-side capacitance caused by the second layer.

[0074] [Electrolytic capacitor]

[0075] The electrolytic capacitor according to this embodiment includes: the above-mentioned cathode foil for an electrolytic capacitor, an anode body having a dielectric layer formed on its surface, and an electrolyte. Hereinafter, the components of the electrolytic capacitor other than the cathode foil will be described in detail.

[0076] (Anode body)

[0077] The anode body can use metal foil. The type of metal contained in the metal foil is not particularly limited. From the aspect of easy formation of the dielectric layer, it is preferably a valve metal such as aluminum, tantalum, niobium, titanium, etc. Among them, those containing a second metal as the main component are preferred. For example, elemental metals such as aluminum and alloys such as aluminum alloy. The surface of the anode body is roughened, and a dielectric layer is formed on the surface of the roughened metal foil.

[0078] (Spacer)

[0079] In an electrolytic capacitor using an electrolytic solution as the electrolyte, a spacer can be used to isolate the anode body from the cathode foil. As the material of the spacer, for example, a non-woven fabric or film containing cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, glassy material, etc. as the main component can be used.

[0080] (Electrolyte)

[0081] The electrolyte may contain a liquid component and / or a solid electrolyte. When the electrolyte does not contain a solid electrolyte, the liquid component is an electrolytic solution. When the electrolyte contains a solid electrolyte, the liquid component can be an electrolytic solution or not. The liquid component can have the function of improving the reparability of the dielectric layer formed on the surface of the anode body on the anode side of the electrolytic capacitor. As the solid electrolyte, a conductive polymer can be used.

[0082] (Conductive polymer)

[0083] As the conductive polymer, polypyrrole, polythiophene, polyaniline, etc. are preferred. They can be used alone, two or more kinds can be used in combination, or they can be copolymers of two or more kinds of monomers. The weight-average molecular weight of the conductive polymer is not particularly limited, for example, it is 1000 to 100000.

[0084] It should be noted that in this specification, polypyrrole, polythiophene, polyaniline, etc. respectively refer to polymers with polypyrrole, polythiophene, polyaniline, etc. as the basic skeleton. Therefore, polypyrrole, polythiophene, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT), etc.

[0085] A dopant can be added to a conductive polymer. From the viewpoint of suppressing the de-doping of the conductive polymer, it is ideal to use a polymer dopant. Examples of the polymer dopant include anions such as polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylic acid-based sulfonic acid, polymethacrylic acid-based sulfonic acid, poly(2-acrylamide-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic acid. They can be used alone or in combination of two or more. In addition, they can be homopolymers or copolymers of two or more monomers. Among them, polystyrenesulfonic acid (PSS) is preferred.

[0086] The weight-average molecular weight of the dopant is not particularly limited, and from the aspect of easily forming a homogeneous solid electrolyte layer, it is preferably 1000 to 100000, for example.

[0087] (Liquid component)

[0088] As the liquid component, it can be a non-aqueous solvent or a mixture of a non-aqueous solvent and an ionic substance (solute, such as an organic salt) dissolved therein (i.e., an electrolyte solution). The non-aqueous solvent can be an organic solvent or an ionic liquid. As the non-aqueous solvent, a high-boiling solvent is preferred. For example, polyols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (GBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate (PC), ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde can be used. In addition, as the high-boiling solvent, a polymer-based solvent can be used.

[0089] Examples of the polymer solvent include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group of a polyol is replaced by a polyalkylene glycol (including derivatives). Specifically, polyethylene glycol (PEG), polyethylene glycol glycerol ether, polyethylene glycol diglycerol ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glycerol ether, polypropylene glycol diglycerol ether, polypropylene glycol sorbitol ether, and polybutylene glycol can be cited. They can be used alone or in combination of two or more. In addition, the polymer-based solvent can be, for example, a copolymer of ethylene glycol - propylene glycol, a copolymer of ethylene glycol - butylene glycol, a copolymer of propylene glycol - butylene glycol, etc. The copolymer can be a random copolymer.

[0090] The liquid component can contain an acid component and a base component.

[0091] As the acid component, polycarboxylic acids and monocarboxylic acids can be used.

[0092] Examples of the above-mentioned polycarboxylic acids include aliphatic polycarboxylic acids ([saturated polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid]), aromatic polycarboxylic acids (such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (such as cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.).

[0093] Examples of the above-mentioned monocarboxylic acids include aliphatic monocarboxylic acids (having 1 to 30 carbon atoms) ([saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, naphthoic acid), and hydroxycarboxylic acids (such as salicylic acid, mandelic acid, m-dihydroxybenzoic acid).

[0094] Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and m-dihydroxybenzoic acid have high conductivity and thermal stability and are preferably used.

[0095] Examples of inorganic acids include carbon compounds, hydrogen compounds, boron compounds, sulfur compounds, nitrogen compounds, and phosphorus compounds. Examples of representative inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, fluoboric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, naphthalenesulfonic acid, etc.

[0096] In addition, a composite compound of an organic acid and an inorganic acid can be used as the acid component. For example, boron diglycolic acid, boron dioxylic acid, boron disalicylic acid, etc. can be cited.

[0097] The base component is a compound having an alkyl-substituted amidino group, and examples thereof include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds). Specifically, 1,8-diazabicyclo[5,4,0]undec-7-ene, 1,5-diazabicyclo[4,3,0]non-5-ene, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'-heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole, which can preferably provide a capacitor with high conductivity and excellent impedance performance, are preferred.

[0098] A quaternary salt of a compound having an alkyl-substituted amidine group can also be used as the base component. Examples thereof include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) quaternized with an alkyl group or an arylalkyl group having 1 to 11 carbon atoms. Specifically, 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethylimidazolinium, 1,3 , 4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, 1,3-dimethylbenzimidazolium.

[0099] In addition, tertiary amines can also be used as the base component, and examples thereof include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.), and phenyl-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among them, trialkylamines are preferred due to their high conductivity, and more preferably, the base component contains at least one selected from trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. In addition, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia can be used as the base component.

[0100] The liquid component may contain an acid component, an alkaline component, and / or a salt of an acid component and an alkaline component. The salt may be an inorganic salt or an organic salt. An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, 1,2,3,4-tetramethylimidazolinium phthalate, and 1,3-dimethyl-2-ethylimidazolinium phthalate.

[0101] The pH of the liquid component can be less than 7, or can be below 5. By setting the pH of the liquid component within the above range, the dedoping of the dopant of the conductive polymer can be suppressed. On the other hand, when the pH of the liquid component is less than 7, the cathode foil tends to deteriorate. In this case, it is preferable to form the above-mentioned third layer on the surface of the metal porous portion of the cathode foil. By making the third layer contain phosphorus and / or nitrogen, the deterioration of the cathode foil can be suppressed. In addition, even when boric acid dioxalate, boric acid diglycolate, or boric acid disalicylate, which easily corrodes the metal of the cathode foil such as aluminum, is added to the liquid component, the deterioration of the cathode foil can be suppressed.

[0102] Figure 5 FIG. is a schematic cross-sectional view of the electrolytic capacitor according to this embodiment, Figure 6 is a schematic view of unfolding a part of the wound body included in the same electrolytic capacitor. However, the following embodiments do not limit the present invention.

[0103] As Figure 5 shown, the electrolytic capacitor includes, for example: a capacitor element 10, a bottomed case 11 that houses the capacitor element 10, a sealing member 12 that closes the opening of the bottomed case 11, a base plate 13 that covers the sealing member 12, leads 14A, 14B that are led out from the sealing member 12 and penetrate the base plate 13, lead connectors 15A, 15B that connect the leads to the electrodes of the capacitor element 10, and a liquid component (not shown). The capacitor element 10 and the liquid component are housed in an outer package case together. The opening end of the bottomed case 11 is necked inward, and the opening end is curled so as to be riveted to the sealing member 12.

[0104] The capacitor element 10 is produced, for example, by attaching a conductive polymer to a wound body as Figure 6 shown. The wound body includes: an anode body 21 having a dielectric layer, a cathode body (cathode foil) 22 containing a first metal having a valve action, and a spacer 23 interposed therebetween. The conductive polymer is attached so as to cover at least a part of the surface of the dielectric layer of the anode body 21. The capacitor element 10 further includes a lead connector 15A connected to the anode body 21 and a lead connector 15B connected to the cathode body 22.

[0105] The anode body 21 and the cathode body 22 are wound with the spacer 23 interposed therebetween. The outermost periphery of the wound body is fixed by a stop tape 24. It should be noted that, Figure 6 shows a state in which a part is unfolded before stopping the outermost periphery of the wound body. The anode body 21 includes a metal foil whose surface is roughened so as to have irregularities, and a dielectric layer is formed on the main surface of the metal foil having irregularities.

[0106] In the above-described embodiments, the wound type electrolytic capacitor has been described. However, the application scope of the present invention is not limited to the above, and it can also be applied to other electrolytic capacitors, such as chip type electrolytic capacitors using a sintered body of a metal as the anode body, and stacked type electrolytic capacitors using a metal plate as the anode body.

[0107] [Cathode Foil for Electrolytic Capacitor and Method for Manufacturing Electrolytic Capacitor]

[0108] Hereinafter, an example of the above-described cathode foil for electrolytic capacitor and the method for manufacturing an electrolytic capacitor will be described for each process.

[0109] The method for manufacturing a cathode foil for an electrolytic capacitor according to the present embodiment includes, for example: (i) a step of preparing a metal substrate having a metal porous portion and a metal core portion connected to the metal porous portion; and (ii) a step of forming a coating film on the surface of the metal portion constituting the metal porous portion of the metal substrate. In step (ii), the coating film is formed by atomic layer deposition (ALD). The manufacturing method may further include (iii) a step of causing at least one of phosphorus and nitrogen to adhere to a region having a depth exceeding 10% of the thickness of the metal porous portion in the thickness direction of the metal porous portion.

[0110] Then, an electrolytic capacitor can be manufactured by a method including the following steps: a step of obtaining a cathode foil for an electrolytic capacitor using the above-described steps, (iv) a step of preparing an anode body having a dielectric layer on its surface, and (v) a step of forming a capacitor element using the anode body and the cathode foil for an electrolytic capacitor.

[0111] Step (i)

[0112] The step (i) of preparing a metal substrate may be, for example, a step of roughening a metal foil. By roughening, a metal porous portion having a plurality of pits or pores is formed on the surface side of the metal foil. At the same time, a metal core portion integrated with the metal porous portion is formed in the inner portion of the metal foil. Roughening can be performed by a known method. For example, roughening can be performed by etching. Etching can be performed, for example, by direct current etching using a direct current or alternating current etching using an alternating current.

[0113] The type of metal constituting the metal foil is not particularly limited, and valve action metals such as aluminum (Al), tantalum (Ta), niobium (Nb), or alloys containing valve action metals can be used. The thickness of the metal foil is not particularly limited, and is, for example, 15 μm or more and 100 μm or less.

[0114] Step (ii)

[0115] The process (ii) of forming the coating film may include: a process of forming a first layer having the conductivity of the first element, and / or a process of forming a second layer, which is an oxide film containing the second element. The first element may be at least one selected from carbon, nickel, silver, and gold. The second element may be at least one selected from aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium.

[0116] Both the first layer and the second layer can be formed. In this case, the formation of the first layer is carried out after the formation of the second layer.

[0117] The first layer and the second layer can be formed, for example, by atomic layer deposition (ALD). By using the ALD method, it is possible to form a dense coating film with few defects up to the deep inside of the tortuous pores in the metal porous part. In addition, the first layer and the second layer can also adhere to the inner sidewalls of the pores that are not exposed from the outer surface of the foil (i.e., shielded from the outside by the metal skeleton of the metal porous part). In contrast, when forming a coating film containing the first layer and / or the second layer by a vapor phase method such as vacuum evaporation or sputtering, although the coating film can be formed in a shallow area near the outer surface of the foil so as to cover the inner sidewalls of the pores, it is difficult to form in the deep part of the metal porous part that is not exposed from the outer surface of the metal porous part.

[0118] In the ALD method, the precursor material for forming the coating film can reach a region a certain distance away from the outer surface through the pores of the metal porous part. However, the farther away from the outer surface of the foil, the more difficult it is for the precursor material to reach. Therefore, the film thickness of the coating film formed in the metal porous part can have a distribution that is thicker on the outer surface side of the foil and thinner as it gets farther away from the outer surface. The film thickness of the coating film (the film thickness of the first layer and / or the second layer) at any position in the metal porous part depends on the length of the shortest path through the pores of the metal porous part to the outer surface, and does not necessarily depend on the shortest distance to the outer surface, but is generally formed to be thicker the closer it is to the outer surface of the foil.

[0119] According to the ALD method, by supplying a raw material gas containing the first element or the second element to the reaction chamber in which the object is arranged, it is possible to form a first layer having the conductivity of the first element or a second layer that is an oxide film of the second element on the surface of the object. In the ALD method, the self-limiting effect functions, so the first element or the second element is deposited on the surface of the object in atomic layer units. Therefore, the thicknesses of the first layer and the second layer can be respectively controlled by the number of cycles including the supply of the raw material gas → the exhaust (purge) of the raw material gas in one cycle. That is, by using the ALD method, the thickness of the first layer and / or the second layer can be easily controlled.

[0120] The first element or the second element is supplied to the reaction chamber in the form of a gas containing a precursor of the first element or the second element, respectively. The precursor is, for example, a metal organic compound containing the first element or the second element, whereby each element is easily chemisorbed onto the object. As the precursor, various metal organic compounds conventionally used in the ALD method can be used.

[0121] When forming the second layer by the ALD method, a source gas containing the second element and an oxidizing agent are alternately supplied to the reaction chamber. By setting the supply of the source gas → the exhaust of the source gas (purge) → the supply of the oxidizing agent → the exhaust of the oxidizing agent (purge) as one cycle, the number of cycles can control the thickness of the second layer. As the oxidizing agent, for example, water, oxygen, ozone, etc. can be cited. The oxidizing agent can be supplied to the reaction chamber in the form of a plasma using the oxidizing agent as a raw material.

[0122] It should be noted that, compared with CVD which is usually carried out under temperature conditions of 400 to 900 °C, the ALD method can be carried out under temperature conditions of 100 to 400 °C. That is, the ALD method is excellent in terms of suppressing thermal damage to the metal foil.

[0123] As the precursor containing C (carbon) that can be used in the formation of the first layer, for example, alkanes having 5 to 11 carbon atoms such as hexane can be cited.

[0124] In addition, as the precursor containing Ni, for example, bis(cyclopentadienyl)nickel (Ni(C5H5)2), bis(isopropylcyclopentadienyl)nickel (Ni(i-C3H7C4H5)2), bis(ethylcyclopentadienyl)nickel (Ni(C2H5C4H5)2), nickel tetrakis(trifluorophosphine) (Ni(PF3)4), etc. can be cited.

[0125] In addition, as the precursor containing Ag, for example, silver(I) 2,2,6,6-tetramethylheptane-3,5-dione (Ag(C 11 H 19 O2)) etc., and as the precursor containing Au, gold(III) dimethyl(acetylacetonate) (Au((CH3)2)C5H7O2) etc. can be cited.

[0126] As the precursor containing Al that can be used in the formation of the second layer, for example, trimethylaluminum ((CH3)3Al) etc. can be cited.

[0127] In addition, as the precursor containing Ti, for example, bis(tert-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26bis(cyclopentadienyl)titanium dichloride (Cl2Ti), tetrakis(dimethylamino)titanium(IV) ([(CH3)2N]4Ti, TDMAT), tetrakis(diethylamino)titanium(IV) ([(C2H5)2N]4Ti), tetrakis(ethylmethylamino)titanium(IV) (Ti[N(C2H5)(CH3)]4), diisopropoxybis(2,2,6,6-tetramethyl-3,5-heptanedionato)titanium(IV) (Ti[OCC(CH3)3CHCOC(CH3)3]2(OC3H7)2), titanium tetrachloride (TiCl4), titanium(IV) isopropoxide (Ti[OCH(CH3)2]4), titanium(IV) ethoxide (Ti[O(C2H5)]4), etc.

[0128] In addition, as a precursor containing Si, for example, N-sec-butyl(trimethylsilyl)amine (C7H 19 NSi), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C8H 23 NSi2), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(isopropoxy)silanol ([(H3C)2CHO]3SiOH), chloropentamethyldisilane ((CH3)3SiSi(CH3)2Cl), dichlorosilane (SiH2Cl2), tris(dimethylamino)silane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), silicon tetrabromide (SiBr4), etc.

[0129] In addition, as a precursor containing Ta, for example, (tert-butylimido)tris(ethylmethylamino)tantalum(V) (C 13 H 33 N4Ta, TBTEMT), pentaethoxytantalum(V) (Ta(OC2H5)5), (tert-butylimido)tris(diethylamino)tantalum(V) ((CH3)3CNTa(N(C2H5)2)3), pentakis(dimethylamino)tantalum(V) (Ta(N(CH3)2)5), etc.

[0130] In addition, as a precursor containing Nb, for example, niobium(V) ethoxide (Nb(OCH2CH3)5, tris(diethylamide)(tert-butylimido)niobium(V) (C 16 H 39 N4Nb), etc.

[0131] As a precursor containing Hf, for example, hafnium tetrachloride (HfC14), hafnium tetrakis(dimethylamino) (Hf[N(CH3)2]4), hafnium tetrakis(ethylmethylamino) (Hf[N(C2H5)(CH3)]4), hafnium tetrakis(diethylamino) (Hf[N(C2H5)2]4), hafnium tert-butoxide (Hf[OC(CH3)3]4), etc. can be cited.

[0132] In addition, as a precursor containing Zr, for example, bis(methyl-η 5 cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), zirconium(IV) tetrakis(dimethylamide) ([(CH3)2N]4Zr), zirconium(IV) tetrakis(ethylmethylamide) (Zr(NCH3C2H5)4), zirconium(IV) tert-butoxide (Zr[OC(CH3)3]4), etc. can be cited.

[0133] By using the ALD method, a coating film including the first layer and / or the second layer can be formed to a depth of 10% or more of the thickness of the metal porous portion in the thickness direction of the metal porous portion.

[0134] When the first layer is formed by the ALD method, the second layer can be formed by chemical conversion treatment of the cathode foil. Details of the chemical conversion treatment will be described later.

[0135] Step (iii)

[0136] Step (iii) of attaching at least one of phosphorus and nitrogen to the surface of the metal porous portion is performed, for example, by infiltrating a solution containing at least one of phosphorus and nitrogen into the metal porous portion. By subsequent heat treatment, phosphorus and / or nitrogen attached to the inner wall of the pores diffuses into the metal porous portion, and a layer (third layer) containing at least one of phosphorus and nitrogen can be formed on the surface of the metal porous portion. By using the third layer, the water resistance of the electrolytic capacitor can be improved.

[0137] Infiltration of the solution containing at least one of phosphorus and nitrogen can be performed in the chemical conversion process of the cathode foil. If the chemical conversion solution contains phosphorus or nitrogen, a solution containing a phosphorus compound or a nitrogen compound can be infiltrated into the pores in parallel with the growth of the oxide coating film on the inner wall of the pores. In this case, the oxide coating film grows on the inner wall of the pores, and at the same time, phosphorus and / or nitrogen diffuses into the oxide coating film, and an oxide coating film containing phosphorus and / or nitrogen grows.

[0138] In addition, the third layer can be formed by infiltrating a solution containing at least one of phosphorus and nitrogen into the cathode foil after chemical conversion. By subsequent heat treatment, phosphorus and / or nitrogen attached to the inner wall of the pores diffuses into the interior of the chemically converted oxide coating film, and the third layer containing phosphorus and / or nitrogen grows at least on the surface layer of the oxide coating film.

[0139] The chemically converted cathode foil can be chemically converted again using a chemical conversion solution containing at least one of phosphorus and nitrogen. In this case, the voltage applied to the cathode during the re-chemical conversion can be higher or lower than the voltage applied during the previous chemical conversion treatment. When the re-chemical conversion is performed at a voltage lower than the voltage applied during the previous chemical conversion treatment, the oxide film will not grow further, but the diffusion of phosphorus and / or nitrogen into the oxide film can be promoted. Thereby, the third layer can be formed thicker. In addition, the content ratio of phosphorus and / or nitrogen in the third layer can be increased.

[0140] The chemical conversion treatment can be carried out, for example, by applying a positive voltage to the metal foil while the cathode foil is immersed in the chemical conversion solution. At this time, the chemical conversion treatment can be carried out under temperature conditions of, for example, 50 to 85 °C as needed.

[0141] As the chemical conversion solution, an aqueous solution containing phosphoric acid, adipic acid, boric acid, oxalic acid, sulfuric acid, and / or their salts can be cited. Among them, since the phosphate salt contains phosphorus, the third layer containing phosphorus can be grown by the chemical conversion treatment. As the phosphate salt, ammonium phosphate salts, potassium phosphate salts, sodium phosphate salts, etc. can be exemplified.

[0142] As the chemical conversion solution containing nitrogen, an aqueous solution containing an ammonium salt can be cited. The ammonium salt can be a primary ammonium salt, secondary ammonium salt, tertiary ammonium salt, or quaternary ammonium salt obtained by substituting one or more hydrogen atoms of the ammonium cation with an organic functional group.

[0143] Among them, ammonium phosphate salt is preferred because it contains both phosphorus and nitrogen, and the third layer containing phosphorus and nitrogen can be easily formed. As the ammonium phosphate salt, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, etc. can be exemplified.

[0144] The chemical conversion solution can contain one salt containing phosphorus and / or nitrogen, or can contain two or more salts containing phosphorus and / or nitrogen. The chemical conversion solution can contain salts such as adipate salts, borate salts, or salts such as potassium salts and sodium salts that do not contain either phosphorus or nitrogen. From the viewpoints of operability, etc., it is preferable to use an ammonium phosphate aqueous solution such as an ammonium dihydrogen phosphate aqueous solution, an ammonium adipate aqueous solution, etc.

[0145] The formation of the third layer (impregnation with a solution containing phosphorus and / or nitrogen) can be carried out before the formation of the first layer (and / or the second layer) based on the ALD method, or after the formation of the first layer (and / or the second layer) based on the ALD method. In the former case, the third layer is formed in the entire depth region of the metal porous part, and the third layer can be interposed between the first layer and the second layer and the metal porous part. On the other hand, in the latter case, it is difficult for phosphorus or nitrogen to diffuse from the outer surface of the metal porous part on which the first layer has been formed into the metal porous part. Therefore, the third layer can be specifically formed in the deep part on the metal core side of the metal porous part where the first layer is not formed. In any case, the third layer can be attached to a region having a depth exceeding 10% of the thickness of the metal porous part in the thickness direction of the metal porous part.

[0146] The cathode foil after chemical conversion treatment can be washed and dried as needed.

[0147] The content of the phosphorus compound (e.g., PO4 3- ) attached to the cathode foil can be analyzed by ion chromatography. The content of the phosphorus compound attached to the cathode foil is, for example, 3 mg / m 2 or more and 300 mg / m 2 or less, preferably 5 mg / m 2 or more and 100 mg / m 2 or less.

[0148] From the viewpoint of mass productivity, roughening treatment and chemical conversion treatment are usually carried out on a large metal foil. In this case, the cathode foil can be prepared by cutting the treated metal foil into a desired size.

[0149] Process (iv)

[0150] In process (iv) of preparing an anode body having a dielectric layer on its surface, a metal foil containing a valve action metal as a raw material for the anode body is prepared, and the surface of the metal foil is roughened. By roughening, a plurality of irregularities are formed on the surface of the metal foil. The roughening is preferably carried out by etching the metal foil. The etching treatment can be carried out, for example, by a direct current electrolysis method or an alternating current electrolysis method.

[0151] Next, a dielectric layer is formed on the surface of the roughened metal foil. The formation method is not particularly limited, and it can be formed by chemically converting the metal foil. By chemically converting the metal foil, the surface of the metal foil is oxidized to form a dielectric layer as an oxide film.

[0152] Chemical conversion treatment can be carried out, for example, using a chemical conversion solution. The chemical conversion treatment can be carried out by immersing the metal foil in the chemical conversion solution and performing heat treatment. The temperature at this time is, for example, 50 to 80 °C. In addition, the chemical conversion treatment can also be carried out by immersing the metal foil in the chemical conversion solution and applying a voltage. When carrying out the chemical conversion treatment, both heat treatment and voltage application can be carried out. The chemical conversion solution can be appropriately determined according to the content described for the chemical conversion of the cathode body.

[0153] The anode body after chemical conversion treatment can be washed and dried as needed.

[0154] Generally, from the viewpoint of mass productivity, roughening treatment and chemical conversion treatment are carried out on a large sheet of metal foil. In this case, the anode body is prepared by cutting the treated metal foil into a desired size. The cut anode body has a dielectric layer on the main surface.

[0155] Process (v)

[0156] Next, a capacitor element is formed using the anode body and the cathode foil for electrolytic capacitors (process (v)).

[0157] First, a wound body is made using the cathode foil obtained in processes (i) to (iii) and the anode body prepared in process (iv).

[0158] The anode body 21 and the cathode foil are wound with a spacer 23 in between. At this time, by winding while inserting the lead connectors 15A, 15B, as Figure 6 shown, the lead connectors 15A, 15B can be made to stand up from the wound body.

[0159] The materials of the lead connectors 15A, 15B are not particularly limited and can be conductive materials. The materials of the leads 14A, 14B respectively connected to the lead connectors 15A, 15B are also not particularly limited and can be conductive materials.

[0160] Next, a stop winding tape 24 is disposed on the outer surface of the cathode foil that is outermost among the wound anode body 21, cathode foil, and spacer 23, and the end of the cathode foil is fixed with the stop winding tape 24.

[0161] The formation of the third layer can be performed on the cathode foil after forming the wound body. In this case, for example, a solution containing at least one of phosphorus and nitrogen is infiltrated into the wound body, and at least one of phosphorus and nitrogen adheres to the surface of the metal porous portion of the cathode foil. By subsequent heat treatment, phosphorus and / or nitrogen adhering to the inner side wall of the pores diffuses into the metal porous portion, and the third layer can be formed on the surface of the metal porous portion. When performing the chemical conversion treatment, the chemical conversion treatment can be performed by performing heat treatment in a state where the wound body is immersed in the chemical conversion solution. Alternatively, it can also be performed by applying a positive voltage to the anode body of the wound body with the third electrode as the counter electrode in a state where the third electrode and the wound body are immersed in the chemical conversion solution together. Both heat treatment and voltage application can be performed. The temperature conditions of the chemical conversion solution and the chemical conversion treatment can be appropriately determined respectively according to the content described in the process (iii). The chemical conversion treatment can be performed in a state where the entire wound body is immersed in the chemical conversion solution, or in a state where at least the top surface and the bottom surface of the wound body are immersed in the chemical conversion solution. It should be noted that the wound body after the chemical conversion treatment is washed and dried as needed.

[0162] When performing the formation treatment of the third layer on the wound body, phosphorus and / or nitrogen can also adhere to the surface of the first layer or the second layer. Thus, cracks that may exist on the surface of the first layer or the second layer can be covered by the layer containing phosphorus and / or nitrogen.

[0163] If cracks are generated in the first layer or the second layer, the liquid component will invade the metal core part through the cracks, and it is easy to deteriorate the cathode foil. As a result, the ESR sometimes increases. However, by forming the third layer containing phosphorus and / or nitrogen after the formation of the first layer or the second layer, it is possible to cover the inner side wall of the deep pores of the metal porous portion with the third layer, and cover the cracks generated in the first layer or the second layer with the third layer. Thus, it is possible to suppress the increase in ESR caused by the deterioration of the foil and maintain the ESR at a low level. In this case, the third layer can be formed in such a way as to fill the cracks that may exist in the first layer and / or the second layer.

[0164] In particular, in the manufacture of an electrolytic capacitor, when the anode body and the cathode foil are laminated with a spacer in between to form a wound body, cracks are likely to occur in the first layer after the wound body is formed. By performing the treatment of forming the third layer after the formation of the wound body, the cracks generated in the first layer are filled with the third layer, and the deterioration of the cathode foil and the increase in ESR can be suppressed.

[0165] In the case of an electrolytic capacitor including a solid electrolyte such as a conductive polymer in the electrolyte, a step of attaching the conductive polymer to the wound body can be performed. The conductive polymer is attached so as to cover at least a part of the dielectric layer of the anode body 21. Between the anode body 21 and the cathode body (cathode foil) 22, the conductive polymer can be attached in a layer form to the surface of the dielectric layer of the anode body 21 to form a conductive polymer layer (or solid electrolyte layer), but it is not limited to this case. In addition, the conductive polymer can cover at least a part of the surface of the spacer 23. In addition, the conductive polymer can be formed so as to fill the pores of the cathode body. As the conductive polymer, the above-mentioned substances can be used.

[0166] A solution containing a monomer, a dopant, an oxidizing agent, etc. can be applied to the capacitor element, and the conductive polymer can be attached to the wound body on the spot by a method of chemical polymerization or electrolytic polymerization. In addition, the conductive polymer can be attached to the wound body by a method of applying a treatment liquid containing the conductive polymer (hereinafter, also simply referred to as a polymer dispersion) to the wound body. By forming an oxide film on the main surface of the cathode body or forming a dielectric layer on the anode body, the polymer dispersion can be quickly infiltrated.

[0167] The concentration of the conductive polymer contained in the polymer dispersion is preferably 0.5 to 10% by mass. In addition, the average particle diameter D50 of the conductive polymer is preferably 0.01 to 0.5 μm, for example. Here, the average particle diameter D50 is the median particle diameter in the volume particle size distribution obtained by a particle size distribution measuring device based on the dynamic light scattering method.

[0168] The polymer dispersion contains a liquid dispersion medium and a conductive polymer dispersed in the liquid dispersion medium. The polymer dispersion can be a solution in which the conductive polymer is dissolved in the liquid dispersion medium, or a dispersion liquid in which the particles of the conductive polymer are dispersed in the liquid dispersion medium. After the treatment liquid is infiltrated into the wound body, it is usually dried to volatilize at least a part of the liquid dispersion medium.

[0169] In order to suppress the dedoping of the conductive polymer, an acid can be dissolved in the liquid dispersion medium. As the acid, phosphoric acid, sulfuric acid, phthalic acid, benzoic acid, nitrobenzoic acid, salicylic acid, trimellitic acid, pyromellitic acid, etc. are preferable.

[0170] A polymer dispersion can be obtained by, for example, a method of dispersing a conductive polymer in a liquid dispersion medium; a method of polymerizing a precursor monomer in a liquid dispersion medium to form particles of a conductive polymer, etc. As a preferred polymer dispersion, for example, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS), i.e., PEDOT / PSS, is preferred. It should be noted that an antioxidant for the conductive polymer can be added, but PEDOT / PSS hardly oxidizes, so an antioxidant does not have to be used.

[0171] The liquid dispersion medium can be water, a mixture of water and a non-aqueous solvent, or a non-aqueous solvent. The non-aqueous solvent is not particularly limited. For example, a protic solvent or an aprotic solvent can be used. As protic solvents, alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol, ethers such as formaldehyde and 1,4-dioxane, etc. can be exemplified. As aprotic solvents, amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, and ketones such as methyl ethyl ketone, etc. can be exemplified.

[0172] As a method of imparting (impregnating) the polymer dispersion to the wound body, for example, a method of immersing the wound body in the polymer dispersion stored in a container is simple and preferred. In addition, ultrasonic vibration can be imparted to the wound body or the polymer dispersion while being immersed in the polymer dispersion. Drying after lifting the wound body from the polymer dispersion is preferably carried out at 50 to 300 °C. The step of imparting the polymer dispersion to the wound body and the step of drying the wound body can be repeated two or more times. By performing these steps multiple times, the coverage rate of the conductive polymer in the wound body can be increased.

[0173] Through the above, a capacitor element 10 can be obtained in which a conductive polymer is attached so as to cover at least a part of the dielectric layer. It should be noted that the conductive polymer formed on the surface of the dielectric layer functions as a de facto cathode material.

[0174] Next, by further impregnating a liquid component (electrolyte) into the capacitor element 10, an electrolytic capacitor with excellent repair function of the dielectric layer can be obtained.

[0175] The method of impregnating the liquid component into the capacitor element 10 is not particularly limited. For example, a method of immersing the capacitor element 10 in the liquid component stored in a container is simple and preferred. The impregnation is preferably carried out under reduced pressure, for example, in an atmosphere of 10 to 100 kPa. As the liquid component, the above-mentioned materials can be cited.

[0176] Next, the capacitor element 10 is sealed. Specifically, first, the capacitor element 10 is housed in the bottomed case 11 such that the leads 14A and 14B are located on the upper surface of the opening of the bottomed case 11. As the material of the bottomed case 11, metals such as aluminum, stainless steel, copper, iron, brass, or their alloys can be used.

[0177] Next, the sealing member 12 formed so as to penetrate the leads 14A and 14B is disposed above the capacitor element 10, and the capacitor element 10 is sealed within the bottomed case 11. Next, a lateral necking process is performed on the vicinity of the open end of the bottomed case 11, and the open end is riveted to the sealing member 12 for crimping. Then, the seat plate 13 is disposed at the crimped portion, thereby completing the electrolytic capacitor as Figure 5 shown. Thereafter, an aging process can be performed while applying the rated voltage.

[0178] The sealing member 12 is formed of an elastic material containing a rubber component. As the rubber component, butyl rubber (IIR), nitrile rubber (NBR), ethylene propylene rubber, ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), isoprene rubber (IR), Hypalon rubber, silicone rubber, fluororubber, etc. can be used. The sealing member 12 may contain fillers such as carbon black and silica.

[0179] It should be noted that after the capacitor element 10 is sealed, if necessary, a chemical conversion process can be further performed to form a dielectric layer on the anode body or an oxide film on the cathode body. The chemical conversion process at this time can be performed using an electrolytic solution. The chemical conversion process can be performed, for example, by applying a positive voltage to the anode body and the cathode body while the capacitor element 10 is immersed in the electrolytic solution. At this time, usually, a heat treatment is also performed together. The temperature of the heat treatment is, for example, 80 to 150°C.

[0180] Industrial Applicability

[0181] The present invention can be used for electrolytic capacitors.

[0182] Description of Reference Numerals

[0183] 10: Capacitor element

[0184] 11: Bottomed case

[0185] 12: Sealing member

[0186] 13: Seat plate

[0187] 14A, 14B: Leads

[0188] 15A, 15B: Lead connectors

[0189] 21: Anode body

[0190] 22, 22A, 22B: Cathode foil

[0191] 31: Metal core

[0192] 32: Metal porous part

[0193] 33: Coating film

[0194] 35: First layer

[0195] 36: Second layer

[0196] 37: Third layer

[0197] 38: Pore

[0198] 23: Spacer

[0199] 24: Anti-unwinding tape

Claims

1. A cathode foil for an electrolytic capacitor, which has: a metal porous part, a metal core part connected to the metal porous part, and a coating film covering the metal porous part, Among them, on the first main surface of the cathode foil, pores in the metal porous part are open, the coating film includes: a conductive first layer and a second layer, the conductive first layer contains a first element, and the second layer is an oxide film containing a second element, the first element is at least one element selected from carbon, nickel, titanium, silver, and gold, the second element is at least one selected from aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium, in the thickness direction of the metal porous part, the first layer is formed in a region from the first main surface to a depth of 10% or more of the thickness of the metal porous part, the first layer covers at least a part of the second layer, the first layer also adheres to the inner sidewalls of pores that are not exposed on the first main surface where the pores of the metal porous part open and are blocked by the metal skeleton of the metal porous part.

2. The cathode foil for electrolytic capacitors according to claim 1, wherein, The film thickness of the second layer is not more than the thickness of the oxide coating film obtained by chemical conversion of the metal containing the second element at 4V.

3. The cathode foil for electrolytic capacitors according to claim 1, wherein, The film thickness of the second layer is greater than the thickness of the oxide coating film obtained by chemical conversion of the metal containing the second element at 4V.

4. The cathode foil for an electrolytic capacitor according to any one of claims 1 to 3, which further has a third layer, the third layer contains at least one of phosphorus and nitrogen, and adheres to a region in the thickness direction of the metal porous part that is deeper than 10% of the thickness of the metal porous part from the first main surface.

5. The cathode foil for electrolytic capacitors according to any one of claims 1 to 3, wherein, The coating film is thicker on the side closer to the first main surface of the metal porous part and thinner on the side closer to the metal core part.

6. The cathode foil for electrolytic capacitors according to any one of claims 1 to 3, wherein, At least a part of the coating film adheres to the inside of the metal porous part in a manner that is not exposed from the first main surface.

7. An electrolytic capacitor, which includes: the cathode foil for an electrolytic capacitor according to any one of claims 1 to 6, an anode body having a dielectric layer formed on its surface, and an electrolyte.

8. A method for manufacturing a cathode foil for an electrolytic capacitor, which includes: a step of preparing a metal substrate, the metal substrate having a metal porous part and a metal core part connected to the metal porous part; and a step of forming a coating film on the surface of the metal part of the metal porous part that constitutes the metal substrate; the coating film is formed by atomic layer deposition (ALD), The process of forming the coating film includes: a step of forming a conductive first layer, the conductive first layer contains a first element; and a step of forming a second layer, the second layer is an oxide film containing a second element, the first element is at least one selected from carbon, nickel, silver, and gold, the second element is at least one selected from aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium, after the step of forming the second layer, the step of forming the first layer is performed, by atomic layer deposition (ALD), the first layer also adheres to the inner sidewalls of pores that are not exposed on the first main surface where the pores of the metal porous part open and are blocked by the metal skeleton of the metal porous part.

9. The manufacturing method of the cathode foil for electrolytic capacitors according to claim 8 further includes the following steps: a step of causing at least any one of phosphorus and nitrogen to adhere to a region having a depth exceeding 10% of the thickness of the metal porous portion in the thickness direction of the metal porous portion.

10. A manufacturing method of an electrolytic capacitor, comprising: a step of obtaining a cathode foil for electrolytic capacitors by using the manufacturing method of the cathode foil for electrolytic capacitors according to claim 8 or 9; a step of preparing an anode body having a dielectric layer on its surface; and a step of forming a capacitor element by using the anode body and the cathode foil for electrolytic capacitors.

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