Electrode body, electrolytic capacitor including electrode body, and method for manufacturing electrode body

Abstract

To provide an electrode body that produces excellent cathode side capacitance and an electrolytic capacitor including the same.SOLUTION: The electrode body used for a cathode of the electrolytic capacitor has a cathode foil and a carbon layer. The cathode foil is made of a valve action metal and has a spreading layer formed on its surface. The carbon layer is formed on the spreading layer. An interface between the spreading layer and the carbon layer has an irregular shape.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] An electrolytic capacitor has an anode foil and a cathode foil made of valve metal such as tantalum or aluminum. The anode foil is enlarged by forming the valve metal into a sintered or etched foil, etc., and has a dielectric oxide film layer on the enlarged surface. An electrolyte is interposed between the anode foil and the cathode foil. The electrolyte is in close contact with the uneven surface of the anode foil and functions as a true cathode. This electrolytic capacitor obtains its anode capacitance by the dielectric polarization action of the dielectric oxide film layer.

[0003] An electrolytic capacitor can be considered as a series capacitor with capacitance appearing on the anode and cathode sides. Therefore, the cathode capacitance is very important for efficient use of the anode capacitance. Therefore, the surface area of ​​the cathode foil is increased by, for example, etching, but there is a limit to how much the cathode foil can be enlarged from the viewpoint of its thickness.

[0004] Therefore, an electrolytic capacitor has been proposed in which a film of a metal nitride such as titanium nitride is formed on the cathode foil (see Patent Document 1). In a nitrogen gas environment, titanium is evaporated by vacuum arc deposition, a type of ion plating method, and titanium nitride is deposited on the surface of the cathode foil. Metal nitrides are inactive, and a natural oxide film is unlikely to form. In addition, the evaporated film has fine irregularities, which increases the surface area of ​​the cathode.

[0005] An electrolytic capacitor in which a porous carbon layer containing activated carbon is formed on a cathode foil is also known (see Patent Document 2). The cathode capacitance of this electrolytic capacitor is generated by the charge storage action of an electric double layer formed on the boundary surface between the polarizable electrode and the electrolyte. Cations of the electrolyte align at the interface with the porous carbon layer and pair with electrons in the porous carbon layer at an extremely short distance, forming a potential barrier at the cathode. The cathode foil with this porous carbon layer formed is produced by kneading a water-soluble binder solution in which porous carbon is dispersed to form a paste, applying the paste to the surface of the cathode foil, and drying it by exposing it to high temperatures. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-61109 [Patent Document 2] JP 2006-80111 A Summary of the Invention [Problem to be solved by the invention]

[0007] The deposition process of metal nitride is complicated and difficult to introduce industrially, which leads to high cost and poor yield of electrolytic capacitors. An electrolytic capacitor in which a porous carbon layer containing activated carbon is formed on a cathode foil by applying a paste has a lower capacitance at room temperature and at high temperatures compared to an electrolytic capacitor in which a metal nitride is deposited on a cathode foil. Therefore, a satisfactory capacitance has not yet been obtained in an electrolytic capacitor in which a porous carbon layer is formed on a cathode foil by applying a paste.

[0008] The present invention has been proposed to solve the above-mentioned problems, and its object is to provide an electrode body that exhibits good capacitance, an electrolytic capacitor including this electrode body, and a method for manufacturing the electrode body. [Means for solving the problem]

[0009] In order to solve the above problems, the electrode body of the present invention is an electrode body used as a cathode of an electrolytic capacitor, and is characterized in that it comprises a cathode foil made of a valve metal and having a surface expansion layer formed on its surface, and a carbon layer formed on the surface expansion layer, and the interface between the surface expansion layer and the carbon layer has an uneven shape.

[0010] The unevenness may have a depth of 0.5 μm or more.

[0011] The surface expansion layer is formed by carving out a plurality of etching pits, the diameter of the etching pits is 0.12 μm or more and 0.43 μm or less near the surface layer, and the depth of the etching pits is 1.5 μm or more and 5.0 μm or less, the uneven shape has a distance between both ends of a cross section obtained by cutting the convex region along the height direction of 1.5 μm or more and 8.0 μm or less, and the height of the convex region of the uneven shape is 0.15 μm or more and 0.80 μm or less.

[0012] The surface-expanding layer may be formed by carving out a plurality of etching pits, and the carbon layer may extend from the interface of the uneven shape into the etching pits.

[0013] The carbon layer which extends from the recessed region into the etching pit may extend to a position that is 0.5 μm or more in depth on average from the apex of the protruding region adjacent to the recessed region.

[0014] The carbon layer which extends from the recessed region into the etching pit may extend to a position that is 0.7 μm or more in depth on average from the apex of the protruding region adjacent to the recessed region.

[0015] The surface-expanding layer may be formed by digging a plurality of etching pits, and the ratio (Y / X×100) of the interface length Y to the range length X may be 110% or more. The interface length Y is the length along the interface between the surface-expanding layer and the carbon layer from an arbitrary starting point to an arbitrary end point, and includes the carbon layer that has entered the etching pits. The range length X is the length of the directional component perpendicular to the height direction of the uneven shape, of the vector that connects the starting point and the end point where the interface length Y is measured.

[0016] The uneven shape may be compressively deformed by pressure.

[0017] The carbon layer may include a scaly carbon material and a spherical carbon material.

[0018] An electrolytic capacitor having this electrode body as a cathode is also one aspect of the present invention.

[0019] A method for producing an electrode body used for a cathode of an electrolytic capacitor according to the present invention includes the steps of: The method includes a step of forming a carbon layer on a cathode foil made of a valve metal and having a surface-expanding layer formed on the surface, and a step of pressing the cathode foil with the carbon layer formed thereon, wherein the interface between the surface-expanding layer and the carbon layer has an uneven shape.

[0020] The cathode foil on which the carbon layer was formed had a resistance of 1.54 kNcm -1 It may be pressed to more than this extent.

[0021] The carbon layer may be formed by applying a slurry containing scaly carbon and spherical carbon to the cathode foil and drying it. Effect of the Invention

[0022] According to the present invention, even if a carbon layer is used for the cathode body, good capacitance can be achieved. [Brief description of the drawings]

[0023] [Figure 1] 4 is a schematic diagram showing an interface structure between a surface expansion layer and a carbon layer of the electrode body according to the present embodiment. FIG. [Diagram 2] 1 shows SEM images of Comparative Example 1, where (a) is without pressing and (b) is with a pressing linear pressure of 3.85 kNcm-1. [Diagram 3] 1 is an SEM image of Comparative Example 2. [Figure 4] 1 is a SEM image of Example 1. [Diagram 5] 1 is an SEM image of Example 2. [Figure 6] 1 is a SEM image of Example 3. [Figure 7] 1 is an SEM image of Example 5. [Figure 8] 1 is an SEM image of Example 8. [Figure 9] 1 is an SEM image of a cathode foil without a carbon layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described with reference to an embodiment of a cathode body and an electrolytic capacitor including the cathode body. In the present embodiment, an electrolytic capacitor having an electrolytic solution will be described as an example, but the present invention is not limited thereto. The present invention can be applied to any of electrolytic capacitors having an electrolyte, a solid electrolyte layer such as a conductive polymer, a gel electrolyte, or a combination of a solid electrolyte layer and a gel electrolyte with an electrolytic solution.

[0025] (Electrolytic capacitor) An electrolytic capacitor is a passive device that stores and discharges electric charge according to its capacitance. This electrolytic capacitor has a wound or laminated capacitor element. The capacitor element is made by placing an anode foil and a cathode body opposite each other with a separator interposed between them and impregnated with an electrolytic solution. In this electrolytic capacitor, a cathode capacitance is generated by the electric double layer action generated at the interface between the electrolyte and the cathode body, and an anode capacitance is generated by the dielectric polarization action.

[0026] That is, a dielectric oxide film layer that generates dielectric polarization is formed on the surface of the anode foil. A carbon layer that generates an electric double layer effect at the interface with the electrolyte is formed on the surface of the cathode body. The electrolyte is interposed between the anode foil and the cathode body, and is in close contact with the dielectric oxide film layer of the anode foil and the carbon layer of the cathode body. A separator is interposed between the anode foil and the cathode body to prevent shorting between the anode foil and the cathode body, and also holds the electrolyte.

[0027] When a solid electrolyte is used, the carbon layer in contact with the current collector provides electrical continuity with the solid electrolyte, and the capacitance of the electrolytic capacitor is determined by the anode capacitance due to dielectric polarization.

[0028] (cathode body) This cathode body has a two-layer structure consisting of a cathode foil and a carbon layer. The cathode foil acts as a current collector, and a surface-expanding layer is formed on its surface. The carbon layer contains carbon material and is in close contact with the surface-expanding layer of the cathode foil.

[0029] The cathode foil is a long foil made of a valve metal. The valve metal is aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. The purity is preferably about 99% or more, but impurities such as silicon, iron, copper, magnesium, zinc, etc. may be contained. For example, the cathode foil may be an aluminum material having a temper code H specified in JIS standard H0001, so-called H material, or an aluminum material having a temper code O specified in JIS standard H0001, so-called O material. If a metal foil made of H material with high rigidity is used, deformation of the cathode foil due to press processing described later can be suppressed.

[0030] This cathode foil is a metal foil made of an elongated valve metal that has been subjected to a surface-expanding process. The surface-expanding layer is formed by electrolytic etching, chemical etching, sandblasting, or the like, or by depositing or sintering metal particles or the like on the metal foil. Examples of electrolytic etching include direct current etching and alternating current etching. In chemical etching, the metal foil is immersed in an acid solution or an alkaline solution. The formed surface-expanding layer is a layer region having tunnel-shaped etching pits or spongy etching pits dug from the foil surface toward the foil core. The etching pits may be formed so as to penetrate the cathode foil.

[0031] In the carbon layer, the carbon material is fibrous carbon, carbon powder, or a mixture thereof. The fibrous carbon is carbon nanotubes, carbon nanofibers, etc. The carbon nanotubes may be single-walled carbon nanotubes with one graphene sheet, or multi-walled carbon nanotubes (MWCNTs) with two or more graphene sheets rolled coaxially to form multiple tube walls. The carbon powder may be activated carbon made from natural plant tissues such as coconut shells, synthetic resins such as phenol, fossil fuels such as coal, coke, and pitch, carbon blacks such as ketjen black, acetylene black, and channel black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, etc. In an electrolytic capacitor using an electrolytic solution as an electrolyte, the carbon material is preferably one that exhibits an electric double layer effect.

[0032] The fibrous carbon or carbon powder may be subjected to a porous treatment such as an activation treatment or an opening treatment to form holes. The activation method of the carbon powder varies depending on the raw material used, but generally, a conventionally known activation treatment such as a gas activation method or a chemical activation method can be used. Examples of the gas used in the gas activation method include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or a gas consisting of a mixture of these. Examples of the chemical used in the chemical activation method include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, inorganic acids such as boric acid, phosphoric acid, sulfuric acid, and hydrochloric acid, and inorganic salts such as zinc chloride. During this activation treatment, a heat treatment is performed as necessary.

[0033] Figure 1(a) is a schematic diagram showing the interface structure between the cathode foil and the carbon layer, that is, the surface expansion layer and the carbon layer. The carbon layer (2) penetrates into the etching pits (1), so that part of the interface between the surface expansion layer (3) and the carbon layer has a fine uneven shape that follows the etching pits. Hereinafter, the uneven shape where the carbon layer penetrates into the etching pits is referred to as the etching unevenness (4).

[0034] In addition to the etching unevenness, wavy unevenness, i.e., unevenness with a long wavelength, occurs at the interface between the surface expansion layer and the carbon layer. Hereinafter, this unevenness will be referred to as the outer surface unevenness (reference number 5 in the figure). In other words, assuming there are no etching pits, the surface of the surface expansion layer will be wavy with convex and concave areas connected with wide bases, and the carbon layer will adhere along this wavyness. The etching unevenness extends continuously from the convex and concave areas of the outer surface unevenness toward the depths. The outer surface unevenness brings a three-dimensional structure to the surface of the surface expansion layer, increasing the area of ​​adhesion with the carbon layer.

[0035] Here, in the aging process of the electrolytic capacitor, an oxide film is formed on the exposed surface area of ​​the surface expansion layer. Furthermore, an increase in the contact area between the surface expansion layer and the carbon layer leads to a decrease in the exposed surface area of ​​the surface expansion layer. As a result, the surface irregularities that increase the contact area between the surface expansion layer and the carbon layer reduce the area on which the oxide film is formed on the entire cathode foil during the aging process. Therefore, an electrolytic capacitor using a cathode body having an external irregularity at the interface between the surface expansion layer and the carbon layer increases the capacitance during charging and discharging in the high frequency range such as 10 kHz and also suppresses the rate of decrease in capacitance in a high heat environment such as 125°C, compared to an electrolytic capacitor using a cathode foil on which titanium nitride is vapor-deposited.

[0036] In particular, the moderate intertwining of the outer surface irregularities enhances the effect of increasing the contact area between the surface expansion layer and the carbon layer. First, an oxide film is formed on the surface of the surface expansion layer naturally or due to the electrolyte, but when the carbon layer is formed on the surface expansion layer and pressed, the carbon material of the carbon layer is thrust into the surface of the surface expansion layer, breaking the oxide film, and the unoxidized surface expansion layer and the carbon layer come into direct contact. Second, the force that pushes the carbon layer in the recessed area further into the etching pits is easily transmitted, and the carbon layer penetrates into the surface expansion layer by the depth of the recessed area and the etching pit, further increasing the contact area between the carbon layer and the surface expansion layer, thereby lowering the resistance of the cathode body.

[0037] On the other hand, when the intricacy becomes too complex to a certain extent, it becomes difficult to transmit the force that pushes the carbon layer that has entered the recessed area further into the etching pit. Therefore, although the capacitance improves when the intricacy becomes too complex to a certain extent, the degree of improvement is limited.

[0038] The outer surface irregularities having a moderately intricate pattern are as follows. First, the depth Hf of the outer surface irregularities is preferably 0.5 μm or more. This depth Hf of the outer surface irregularities indicates the distance to the deepest recess of the outer surface irregularities based on a flat line L, which is a line connecting two vertices of the outer surface irregularities. The cross section of the cathode body is photographed with a scanning electron microscope, and the distance to the deepest recess can be measured based on a flat line connecting the two highest protrusions of the outer surface irregularities in the SEM image. By making the depth Hf of the outer surface irregularities 0.5 μm or more, adhesion to the carbon layer is improved.

[0039] The length Lc of the convex region of the external surface unevenness is in the range of 1.5 μm to 8.0 μm, and is about 2.9 μm to 4.0 μm on average, and the height Hc of the convex region of the external surface unevenness is in the range of 0.15 μm to 0.80 μm, and is about 0.3 μm to 0.6 μm on average. The length Lc of the convex region is the distance between both ends of the cross section of the convex region cut along the height direction. The length Ld of the concave region is in the range of 2.0 μm to 7.7 μm, and is about 3.8 μm on average. Each numerical value representing the external surface unevenness may be measured by photographing the cross section of the cathode body with a scanning electron microscope and measuring the SEM image. The average may be measured by extracting five points.

[0040] However, even within this range, if the external surface unevenness is severe, i.e., if the length Lc of the convex region of the external surface unevenness is in the range of 3.77 μm or less, the advantage in terms of capacitance degradation when used in a high heat environment such as 125° C. and in a high frequency range such as 10 kHz becomes smaller compared to a cathode body vapor-deposited with titanium nitride. On the other hand, if the external surface unevenness is gentle, i.e., there is external surface unevenness but the length Lc of the convex region of the external surface unevenness is 3.78 μm or more, the advantage in terms of capacitance degradation when used in a high heat environment such as 125° C. and in a high frequency range such as 10 kHz is great compared to a cathode body vapor-deposited with titanium nitride.

[0041] Due to this external surface unevenness, the deepest distance Hd of the carbon layer pushed further into the etching pit from the interface in the concave region is 0.42 μm to 1.40 μm in the depth direction from the apex of the convex region adjacent to the concave region, and is approximately 0.54 μm to 0.96 μm on average. If the external surface unevenness is gentle, the average can be 0.7 μm or more. If it is 0.5 μm or less, the effect of improving the capacitance is small. If it is 0.7 μm or more, it has good capacitance and also high thermal stability. Thermal stability means that there is little deterioration of the capacitance in a high-temperature environment.

[0042] The etching pits have a diameter De in the range of 0.12 μm to 0.43 μm near the surface, with an average diameter of about 0.25 μm, and the etching pits caused by the etching process have a depth He in the range of 1.5 μm to 5.0 μm, with an average depth of about 3.3 μm.

[0043] Furthermore, another index is shown for the outer surface irregularities having a moderate intricacy. FIG. 1(b) is a cross-sectional view cut along the height direction of the irregularities, in other words, a cross-sectional view cut along the thickness direction of the cathode body from the surface to the depth. In this cross-section, the length along the interface between the surface expansion layer and the carbon layer from an arbitrary start point to an arbitrary end point is defined as the interface length Y. This interface includes the carbon layer that has entered the etching pits. In addition, the length of the directional component where the height of the irregularities is constant, that is, the directional component perpendicular to the height direction of the irregularities, of the vector that connects the start point and the end point where the interface length Y is measured, is defined as the range length X.

[0044] In this case, it is desirable that the ratio of the interface length Y to the range length X is 110% or more. If it is less than 110%, it indicates that almost no external surface irregularities are formed, and the capacitances at no load at 20°C and at 120 Hz and 10 kHz charge / discharge after a load of 2.4 V DC is continuously applied for 250 hours in a 125°C environment are inferior to those of an electrolytic capacitor made with a cathode body on which titanium nitride is vapor-deposited.

[0045] It is also preferable that most of the voids in the carbon layer have disappeared and the carbon layer is dense. The porosity of the carbon layer is preferably less than 18%. A small porosity of the carbon layer increases the adhesion between the carbon layer and the etched surface. The porosity of the carbon layer is calculated by (area of ​​voids in the carbon layer / area of ​​the entire carbon layer) x 100. The porosity can be calculated by analyzing each cross-sectional SEM image (observation magnification: 25,000 times) using image analysis software ImageJ (NIH, National Institutes of Health, USA).

[0046] A method for forming the interface structure having the outer surface unevenness and the etched unevenness will be exemplified below. However, as long as the interface structure is constituted by the outer surface unevenness and the etched unevenness, the method is not limited to the exemplified method. For example, the wavy unevenness may be formed by removing the etching pits on the surface of the surface-expanding layer using another method such as shot peening.

[0047] First, a surface-expanding layer is formed on the cathode foil. Typically, the surface-expanding layer is formed by DC etching or AC etching in which a DC or AC current is applied in an acidic aqueous solution such as nitric acid, sulfuric acid, or hydrochloric acid.

[0048] For the carbon layer, carbon powder is dispersed in a solvent and a binder is added to prepare a slurry. The solvent may be alcohol such as methanol, ethanol, or 2-propanol, a hydrocarbon solvent, an aromatic solvent, an amide solvent such as N-methyl-2-pyrrolidone (NMP) or N,N-dimethylformamide (DMF), water, or a mixture of these. Dispersion methods include a mixer, jet mixing (jet collision), ultracentrifugation, and ultrasonic treatment. In the dispersion process, the carbon powder and binder in the mixed solution are finely divided and homogenized, and dispersed in the solution. An example of the binder is styrene butadiene rubber.

[0049] Next, the slurry is applied to the surface-expanding layer, dried, and then pressed with a predetermined pressure to bond the cathode foil and the carbon layer together. It is believed that the interface structure between the surface-expanding layer and the carbon layer is formed during the pressing process to bond the cathode foil and the carbon layer together.

[0050] In this pressing process, the carbon material of the carbon layer is pressed against the surface-expanding layer, and the entire surface of the cathode foil is compressed and deformed. Furthermore, the dense areas of the etching pits are significantly compressed and deformed. This causes the smooth surface condition of the cathode foil to deform, and wavy irregularities are created at the interface between the surface-expanding layer and the carbon layer. At the same time as the irregularities appear, the surface-expanding layer and the carbon layer are tightly attached to each other. The carbon material also breaks through the natural oxide film present on the surface of the cathode foil and comes into direct contact with the cathode foil. In this way, when the pressing process is performed at a specified pressure, the formation of external surface irregularities and the close contact between the surface-expanding layer and the carbon layer are simultaneously achieved, and gaps are less likely to occur between the wavy surface-expanding layer and the carbon layer.

[0051] In this pressing step, for example, a press roller applies a linear pressure to the cathode foil coated with the carbon layer. At this time, a press roller heated to a temperature equal to or higher than the softening temperature of the binder contained in the carbon layer may be used. In this way, the fluidity of the carbon layer is increased. Therefore, the carbon layer easily penetrates into the etching pits, the contact area between the carbon layer and the cathode foil is increased, and the interface resistance is further reduced.

[0052] In addition, pressing at a predetermined pressure forms gentle unevenness on the outer surface, which makes it easier for the pressing pressure to be transmitted to the carbon layer in the recessed regions, making it easier for the carbon layer in the recessed regions to penetrate further into the etching pits. Furthermore, pressing compresses the carbon layer, making it easier to eliminate voids in the carbon layer. It is desirable for the linear pressure applied by pressing to be such that the carbon material breaks through the natural oxide film present on the surface of the cathode foil and comes into direct contact with the cathode foil, specifically, 1.54 kNcm. -1 More preferably, 3.85 kNcm -1 That's all. Press line pressure is 1.54kNcm -1 If the pressure is more than 3.85 kNcm, the outer surface will be uneven. -1 If this is the case, the outer surface irregularities will be gentle.

[0053] The carbon material that promotes the change in the interface structure is preferably a mixture of a scaly carbon material and a spherical carbon material. The scaly carbon material is easy to press against the surface-expanding layer, easy to spread out neatly at the interface with the surface-expanding layer, and easy to pierce the natural oxide film on the foil surface by press bonding, and easy to break through the natural oxide film. Therefore, the scaly carbon material is easy to mold the interface structure into an undulating uneven shape, and easy to adhere to the cathode foil at the interface. In addition, the scaly carbon material is easy to pile up neatly at the interface of the surface-expanding layer. Therefore, the scaly carbon material reduces voids in the carbon layer. The spherical carbon material fills voids in the carbon layer and is easy to get into etching pits during the bonding process with the cathode foil.

[0054] Examples of the scaly carbon material include natural graphite, artificial graphite, and graphitized Ketjen Black. It is preferable to use these scaly carbons with an aspect ratio of the short diameter to the long diameter in the range of 1:5 to 1:100. Examples of the spherical carbon material include carbon black such as Ketjen Black (hereinafter referred to as KB), acetylene black, and channel black. The primary particle diameter of carbon black is preferably 100 nm or less, and it is easy to penetrate deep into the etching pit. In general, these scaly carbon materials and spherical carbon materials have a smaller specific surface area and a smaller electric double layer capacity than activated carbon and carbon nanotubes, so they generally play the role of a conductive assistant rather than an active material. However, in this electrolytic capacitor, sufficient cathode side capacity is drawn out due to the interface structure between the surface expansion layer and the carbon layer, that is, the occurrence of external surface unevenness, or further the occurrence of etching unevenness.

[0055] Of course, in addition to these scaly carbon materials and spherical carbon materials, activated carbon, carbon nanotubes, etc. can be contained, or these scaly carbon materials and spherical carbon materials can be contained in the carbon layer as the active material alone. Activated carbon and carbon nanotubes have delocalized pi electrons and a large specific surface area. In this electrolytic capacitor, the interface between the surface expansion layer and the carbon layer has an outer surface unevenness, or further has etching unevenness, and sufficient cathode capacity is obtained, so the scaly carbon materials and spherical carbon materials may not be porous. Of course, the scaly carbon materials and spherical carbon materials may be porous before use.

[0056] (anode foil) Next, the anode foil is a long foil made of valve metal. The purity of the anode foil is preferably about 99.9% or more. This anode foil is made by etching a stretched foil, by sintering a powder of valve metal, or by depositing a film of metal particles or the like on the foil. The anode foil has a surface-expanding layer or a porous structure layer on the surface.

[0057] The dielectric oxide film layer formed on the anode foil is typically an oxide film formed on the surface layer of the anode foil, and if the anode foil is made of aluminum, it is an aluminum oxide layer formed by oxidizing the porous structure region. This dielectric oxide film layer is formed by chemical conversion treatment in which a voltage is applied in a solution free of halogen ions, such as an acid such as ammonium borate, ammonium phosphate, or ammonium adipate, or an aqueous solution of such an acid. Note that a natural oxide film layer may be formed on the cathode foil, or a dielectric oxide film layer may be intentionally provided.

[0058] (Separator) Examples of the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins, polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, and acrylic resins. These resins can be used alone or in combination.

[0059] (electrolyte) The electrolyte is a mixed solution in which a solute is dissolved in a solvent and additives are added as necessary. The solvent may be water, a protic organic polar solvent, or an aprotic organic polar solvent. Representative examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and oxides.

[0060] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutaronitrile. Examples of oxides include dimethyl sulfoxide. As the solvent, these may be used alone or in combination of two or more.

[0061] The solute contained in the electrolytic solution includes anion and cation components, and is typically an organic acid or its salt, an inorganic acid or its salt, or a composite compound of an organic acid and an inorganic acid or its ion-dissociable salt, and is used alone or in combination of two or more. An acid that becomes an anion and a base that becomes a cation may be added separately to the electrolytic solution as solute components.

[0062] Examples of organic acids that become anion components in the electrolyte include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanediacid, dodecanediacid, and tridecanediacid, phenols, and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic and inorganic acids include borodisalicylic acid, borodioxalic acid, and borodiglycolic acid.

[0063] In addition, examples of at least one salt of an organic acid, an inorganic acid, and a complex compound of an organic acid and an inorganic acid include ammonium salt, quaternary ammonium salt, quaternary amidinium salt, amine salt, sodium salt, potassium salt, etc. Examples of the quaternary ammonium ion of the quaternary ammonium salt include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of the quaternary amidinium include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of the amine of the amine salt include primary amine, secondary amine, and tertiary amine. Examples of the primary amine include methylamine, ethylamine, propylamine, etc., examples of the secondary amine include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc., and examples of the tertiary amine include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0064] Furthermore, other additives can be added to the electrolyte. Examples of additives include polyethylene glycol, complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, etc.), and phosphoric acid esters. These may be used alone or in combination of two or more.

[0065] When a solid electrolyte is used as the electrolyte, examples of the electrolyte include polythiophenes such as polyethylenedioxythiophene, and conductive polymers such as polypyrrole and polyaniline. EXAMPLES

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0067] (cathode body) First, various cathode bodies were prepared. The aluminum foils shown in Table 1 below were prepared as cathode foils. In Table 1, the etching ratio indicates the ratio of the surface area after etching to the surface area of ​​the plain surface, i.e., the surface area in an unetched state. The etched layer thickness indicates the average depth from the surface to the deepest part of the etching pit. The residual core thickness indicates the thickness of the layer that the etching pit does not reach. The oxide film is shown by the nominal chemical formation voltage. That is, for the cathode foils of foil type 1, foil type 2, and foil type 4, a voltage was applied with an aqueous solution of ammonium dihydrogen phosphate to intentionally form an oxide film layer. For the cathode foil of foil type 3, no chemical formation was performed.

[0068] [Table 1]

[0069] A slurry was prepared under common conditions for the carbon layer formed on each cathode foil of Table 1. 16.3 g of graphite was selected as the scaly carbon material, 5 g of carbon black was selected as the spherical carbon material, and 3.7 g of styrene-butadiene rubber was selected as the binder. These were then added to 75 ml of pure water adjusted to pH 8 with ammonia, and dispersed with a stirrer. This slurry was applied to each cathode foil and dried at 100°C. The graphite had a particle size of 4 μm, and the carbon black had a primary particle size of 35 nm, and neither had been activated or apertured.

[0070] Then, various cathode bodies with different etching treatments and press line pressures were produced by applying various press line pressures to each cathode foil coated with a carbon layer, as shown in Table 2 below. For the press line pressure, a press machine manufactured by Takumi Giken Co., Ltd. was used. In this pressing process, the diameter of the press roller was 180 mm, the press width was 130 mm, and the cathode body was transported once at 3 m / min.

[0071] [Table 2]

[0072] As shown in Table 2, an electrolytic capacitor using foil type 1 that has not been etched is called Comparative Example 1, regardless of the press line pressure. In electrolytic capacitors using foil type 2 with an etching ratio of 7 times, the unpressed one is called Comparative Example 2, and Examples 1 to 3 are called in ascending order of press line pressure, and the one with a press line pressure between Examples 2 and 3 is called Example 10. In electrolytic capacitors using foil type 3 with an etching ratio of 17 times and no oxide film formed thereon, the unpressed one is called Comparative Example 3, and Examples 4 to 6 are called in descending order of press line pressure. In electrolytic capacitors using foil type 4 with an etching ratio of 22 times, the unpressed one is called Comparative Example 4, and Examples 7 to 9 are called in descending order of press line pressure.

[0073] (Cross-section observation of cathode body) The cross sections of the cathode bodies of Comparative Example 1, Comparative Example 2, Examples 1 to 3, Examples 5 and Example 8 were photographed with a scanning electron microscope at 5,000 magnifications to obtain SEM images. The results are shown in Figures 2 to 8. Figure 2 is an SEM image of Comparative Example 1, and (a) is an SEM image of Comparative Example 1, where (a) is an SEM image of Comparative Example 1 when the pressing line pressure was 0 kNcm. -1 (b) is a cathode body with a press line pressure of 3.85 kNcm -1 FIG. 3 is an SEM image of Comparative Example 2. FIG. 4 is an SEM image of Example 1, FIG. 5 is an SEM image of Example 2, FIG. 6 is an SEM image of Example 3, FIG. 7 is an SEM image of Example 5, and FIG. 8 is an SEM image of Example 8. In FIGS. 4 to 8, (a) and (b) are the same image, but (a) shows the convex portion length Lc, and (b) shows the concave-convex depth Hf.

[0074] As shown in Figures 2 and 3, in the cathode bodies of Comparative Example 1 and Comparative Example 2, the interface between the surface-expanding layer and the carbon layer is located approximately along the flat line L. On the other hand, as can be seen by comparing Figures 4 to 8 with Figures 2 and 3, in the cathode bodies of Examples 1 to 3, Example 5 and Example 8, the interface between the surface-expanding layer and the carbon layer is not located along the flat line L, and it was confirmed that there were external surface irregularities, and etching irregularities were also confirmed.

[0075] The length Lc and height Hc of each of the convex regions No. 1 to No. 6, which were confirmed from the SEM images of Figures 4 to 8, were measured, and the porosity of the carbon layer was also measured, resulting in the results shown in Table 3 below. In the table, the units of length and height are μm.

[0076] [Table 3]

[0077] As shown in Table 3, in detail, the cathode body of Example 1 has an outer surface unevenness with severe undulations within a moderate range. The average length Lc of the convex region of the outer surface unevenness of Example 1 is short at 2.91 μm, and the unevenness is steep. In this Example 1, although the surface expansion layer is compressed overall, the degree of compressive deformation is sparse, and it can be said that there are areas that are significantly compressed and deformed and areas that are less compressed and deformed. In addition, gaps remain in places between the carbon layer and the surface expansion layer. Although etching unevenness is formed, many voids that are not filled with carbon material still remain in the etching pits, and the porosity of the carbon layer is also high.

[0078] On the other hand, in the cathode bodies of Examples 2, 3, 5 and 8, the waviness of the outer surface unevenness becomes gentle within a moderate range. The length LC of the convex region of the outer surface unevenness is long, at 3.99 μm, 3.86 μm, 3.78 μm and 3.82 μm. In Examples 2, 3, 5 and 8, the surface expansion layer is compressed overall, and the degree of compressive deformation is approaching uniformity, but it can be seen that it is sparse, and there remain areas that are greatly compressed and deformed and areas that are small in compressive deformation. There is almost no gap between the carbon layer and the surface expansion layer. In addition, the etching pits are filled with a lot of carbon material, the gaps are considerably reduced, and the porosity of the carbon layer is also small. As in Examples 5 and 8, the higher the etching ratio, the lower the porosity of the carbon. In addition, the higher the etching ratio, the larger the average height of the convex portion becomes, and the interface with the carbon layer is greatly wavy, which is considered to exhibit good adhesion.

[0079] Next, based on the photographs shown in Figs. 2 to 8, the press line pressure was 3.85 kNcm -1 The penetration depth Hd of the carbon layer was measured at five arbitrary points in the cathode bodies of Comparative Example 1, Examples 1 to 3, Example 5, and Example 8. That is, the difference in height from the deepest part of the carbon layer that penetrated from the recessed area into the etching pit to the apex of the protruding area adjacent to the recessed area was measured at five points. Also, based on the photographs shown in Figs. 2 to 8, the penetration depth Hd of the carbon layer was measured at five arbitrary points in the cathode bodies of Comparative Example 1, Examples 1 to 3, Example 5, and Example 8. -1 The depth of the unevenness of the uneven shape (outer surface unevenness) was measured for the cathode bodies of Comparative Example 1, Examples 1 to 3, Example 5, and Example 8. The results are shown in Table 4 below.

[0080] [Table 4]

[0081] As shown in Table 4, the press line pressure was 3.85 kNcm -1In Comparative Example 1, the penetration depth Hd was 0.28 μm on average. It was also found that the unevenness depth Hf of the outer surface unevenness was also small at 0.36 μm. This is because Comparative Example 1 is unetched, so there is no room for the metal to penetrate into the etching pits, and because it is unetched, it is difficult to compress and deform, and there are no concave areas. It also shows the degree of unevenness of a flat cathode foil.

[0082] On the other hand, in Example 1, the penetration depth is 0.54 μm or more on average. The depth of the unevenness of the outer surface is also 0.5 μm or more in all cases. In Examples 2, 3, 5 and 8, recessed areas corresponding to the density of the etching pits are generated, and the carbon material penetrates into the etching pits from these recessed areas, resulting in an average penetration depth of 0.7 μm or more. This shows that the outer surface unevenness with a moderate penetration promotes the generation of etching unevenness.

[0083] In addition, the cathode bodies of Examples 4 and 7 have a higher etching ratio of the cathode foil than Example 1, but the etching rate is the same as that of Example 1, 1.54 kNcm -1 In addition, the cathode bodies of Examples 6 and 9 had a higher etching ratio of the cathode foil than Example 1, and the etching ratio was 3.85 kNcm. -1 Because the above pressure was applied, the outer surface was unevenly formed with gentle undulations within a moderate range, and etching unevenness was also generated.

[0084] In addition, from the SEM images in Figs. 2 to 8, the press line pressure was 0 kNcm -1 Comparative Example 1: Press line pressure is 3.85 kNcm -1 The ratio of interface length Y to area length X was measured for the cathode bodies of Comparative Example 1, Comparative Example 2, and Examples 1 to 3, 5, and 8. The ratio of interface length Y to area length X was also measured for the cathode body of Example 10. The results are shown in Table 5.

[0085] [Table 5]

[0086] As shown by the ratio of interface length Y to range length X in Table 5, in Comparative Example 1 and Comparative Example 2, range length X and interface length Y are almost the same, and no external surface irregularities occur. On the other hand, as can be seen by comparing Comparative Example 2 with Examples 1, 2, 3, and 10, in Examples 1, 2, and 10, the ratio is 110% or more, external surface irregularities occur, and the surface area of ​​the cathode body is improved. Furthermore, as can be seen by comparing Example 5 and Example 8, external surface irregularities also occur in Examples 5 and 8, and the surface area of ​​the cathode body is improved.

[0087] In addition, in Comparative Example 1, no pressing was performed (press line pressure 0 kNcm -1 The cathode bodies of Comparative Example 1 and Comparative Example 2 had almost no depth of unevenness on the outer surface and had a substantially flat outer surface. Fig. 9 shows SEM photographs of a cathode foil of the same foil type as that of Comparative Example 2, but without a carbon layer, pressed. Fig. 9 (a) shows the cathode foil without pressing, and (b) shows the cathode foil with a pressing line pressure of 3.85 kNcm -1 , and (c) is press line pressure of 7.69 kNcm -1 As shown in Figure 9, even if the cathode foil is pressed, if the carbon layer is not present, the force is 1.54 kNcm -1 Even when the above pressure was applied, no irregularities were formed on the outer surface.

[0088] (Electrolytic capacitor) Next, in addition to the cathode bodies of Comparative Examples 1 to 4 and Examples 1 to 9, a cathode body was prepared by forming a titanium nitride layer by electron beam deposition using unetched plain foil as a base current collector, and the result was designated as Comparative Example 5. Electrolytic capacitors were prepared using the cathode bodies of Comparative Examples 1 to 5 and Examples 1 to 9.

[0089] For each electrolytic capacitor, an anode foil made under common conditions and various cathode bodies were placed opposite each other through the same separator, impregnated with an electrolyte made under common conditions, made into a laminate cell, and then subjected to a common re-chemical treatment. In detail, for all electrolytic capacitors, an etching treatment was applied to the aluminum foil, and the nominal chemical formation voltage was set to 4V. fsA dielectric oxide film is formed so that the projected area is 2.1 cm 2 An aluminum foil of a size of 100 mm was obtained and used as the anode foil. Rayon was used as the separator for all electrolytic capacitors. The electrolyte common to all electrolytic capacitors was prepared using tetramethylimidazolium phthalate as the solute and γ-butyl lactone as the solvent. During re-chemical formation, a voltage of 3.35 V was applied to all electrolytic capacitors for 60 minutes in an environment of 105°C.

[0090] (Capacitance test) The electrostatic capacitance (Cap) of the electrolytic capacitors of Comparative Examples 1 to 5 and Examples 1 to 9 was measured at 120 Hz and 10 kHz charge and discharge when no load was applied at 20°C (initial state) and after a load of 2.4 V DC was applied for 250 hours in a 125°C environment (load under high heat environment). The results are shown in Table 6.

[0091] [Table 6]

[0092] As can be seen from the comparison between Comparative Example 1 and Comparative Example 5 in Table 6, the electrolytic capacitor using the plain foil made of the carbon layer and cathode foil and not etched was inferior in capacitance in all combinations of initial characteristics, characteristics under load in a high heat environment, and low and high frequency regions, compared to the electrolytic capacitor made of the cathode body with titanium nitride vapor deposition, and the rate of change of capacitance was also not good. Also, when Comparative Example 5 was compared with Comparative Examples 2 to 4, even if etching was performed, when no external surface irregularities were formed at the interface between the surface expansion layer and the carbon layer, it was inferior in almost all measurement items to the electrolytic capacitor made of the cathode body with titanium nitride vapor deposition.

[0093] On the other hand, as can be seen by comparing Comparative Example 5 with Examples 1 to 9, in the initial characteristics, the electrolytic capacitor in which the outer surface irregularities are formed at the interface between the cathode foil and the carbon layer has improved capacitance during charging and discharging at 10 kHz compared to an electrolytic capacitor using a cathode body on which titanium nitride is vapor-deposited. Also, as can be seen by comparing Comparative Example 5 with Examples 8 and 9, due to the outer surface irregularities with gentle undulations and the etching irregularities that reach a sufficient depth due to this outer surface irregularities and the high etching ratio, the initial characteristics show a larger capacitance during charging and discharging at 120 Hz compared to an electrolytic capacitor using a cathode body on which titanium nitride is vapor-deposited.

[0094] Furthermore, when comparing Comparative Example 5 with Examples 1 to 9, all electrolytic capacitors in which an outer surface irregularity was formed at the interface between the carbon layer and the surface-expanding layer had a higher capacitance in the high heat environment load characteristics when the charge / discharge was 120 Hz, compared to an electrolytic capacitor using a cathode body on which titanium nitride was vapor-deposited. In particular, as can be seen when comparing Comparative Example 5 with Examples 1 to 9, with regard to the rate of increase / decrease in capacitance when a load is applied in a high temperature environment relative to the initial capacitance, when the outer surface irregularity was formed, the degree of decrease in capacitance was dramatically suppressed in the 120 Hz charge / discharge.

[0095] Furthermore, as can be seen by comparing Comparative Example 5 with Examples 2, 3, 5, 6, 8, and 9, the rate of increase or decrease in capacitance during charging and discharging at 10 kHz is dramatically suppressed by the outer surface unevenness that is gentle to a moderate range and the etching unevenness that reaches a sufficient depth promoted by this outer surface unevenness.

[0096] From the above, it was confirmed that the unevenness of the outer surface improves the adhesion between the carbon layer and the surface-expanded layer, and that the capacitance and thermal stability are improved in both the low-frequency and high-frequency regions, and in both the initial characteristics and the load characteristics under high-temperature environments. In particular, the presence of the unevenness of the outer surface provides thermal stability that exceeds that of a cathode foil in which titanium nitride is vapor-deposited, in the combination of a low-frequency region and a high-temperature thermal environment, and exhibits high capacitance.

[0097] Furthermore, if the external surface unevenness is gentle, the cathode foil has thermal stability and exhibits high capacitance, even in high frequency ranges and high temperature environments, which exceeds that of titanium nitride vapor-deposited on the cathode foil. Also, if the external surface unevenness is gentle and the etching ratio is high, the cathode foil exhibits capacitance greater than that of titanium nitride vapor-deposited on the cathode foil in all combinations of low frequency ranges, high frequency ranges, initial characteristics, and high temperature environments.

Claims

1. An electrode body used as a cathode of an electrolytic capacitor, A cathode foil made of an aluminum material having a temper code of H and having a surface-expanding layer formed on its surface; A carbon layer formed on the surface-expanding layer; Equipped with an interface between the surface-expanding layer and the carbon layer has a compressively deformed uneven shape; The surface expansion layer is formed by digging a plurality of etching pits separate from the uneven shape, the carbon layer extends from the interface of the uneven surface into the etching pit; An electrode body comprising:

2. The unevenness depth of the unevenness shape is 0.5 μm or more; The electrode assembly according to claim 1 ,

3. the carbon layer which has penetrated from the concave region of the concave-convex shape further into the etching pit penetrates to a position which is on average 0.5 μm or more in a depth direction from an apex of the convex region of the concave-convex shape adjacent to the concave region; 3. The electrode assembly according to claim 1 or 2,

4. the carbon layer extending from the recessed region into the etching pit extends to a position that is recessed by an average of 0.7 μm or more in a depth direction from an apex of a protruding region adjacent to the recessed region; 4. The electrode assembly according to claim 3,

5. Providing the electrode body according to any one of claims 1 to 4 as a cathode; An electrolytic capacitor characterized by:

6. A method for manufacturing an electrode body used for a cathode of an electrolytic capacitor, comprising the steps of: a step of forming a surface enlarging layer by digging a plurality of etching pits on a surface of a cathode foil made of an aluminum material having a temper code of H; forming a carbon layer on the surface expanding layer; a step of pressing the cathode foil on which the carbon layer is formed to form a compressively deformed uneven shape at the interface between the surface-expanding layer and the carbon layer, and causing the carbon layer to penetrate further into the etching pits from the interface of the uneven shape; To have A method for manufacturing an electrode assembly, comprising the steps of:

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