Electrolytic capacitor and method for manufacturing electrolytic capacitor

Abstract

Provided is an electrolytic capacitor in which the connection between a cathode body including a carbon layer and a lead terminal is improved, and a method for manufacturing the electrolytic capacitor. The electrolytic capacitor (1) includes: an anode body (2) having a dielectric oxide film (5) formed on a surface; a cathode body (3) having a cathode foil (31) and a carbon layer (32) formed on the cathode foil (31); an electrolyte (6) interposed between the anode body (2) and the cathode body (3); and lead terminals (7) for each electrode cold-pressed to the anode body (2) and the cathode body (3). The maximum static friction coefficient of the surface of the carbon layer (32) of the cathode body (3) is 0.6 or more.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolytic capacitor and a manufacturing method of an electrolytic capacitor. BACKGROUND

[0002] The electrolytic capacitor includes a valve action metal such as tantalum or aluminum as an anode foil and a cathode foil. The anode foil is surface-enlarged by making a sintered body or an etching foil of the valve action metal, and has a dielectric oxide film layer on the surface-enlarged surface. An electrolyte is interposed between the anode foil and the cathode foil. The electrolyte is in close contact with the concave-convex surface of the anode foil, and functions as a true cathode. The electrolytic capacitor obtains an anode-side capacitance by dielectric polarization of the dielectric oxide film layer.

[0003] The electrolytic capacitor can be regarded as a series capacitor that exhibits capacitances on the anode side and the cathode side. Therefore, in order to efficiently utilize the anode-side capacitance, the cathode-side capacitance is also very important. The cathode foil is also surface-enlarged by etching processing, but the surface enlargement of the cathode foil is limited in view of the thickness of the cathode foil.

[0004] Therefore, an electrolytic capacitor in which a metal nitride such as titanium nitride is formed on the cathode foil has been proposed (see Patent Document 1). In a nitrogen atmosphere, titanium is evaporated by a vacuum arc deposition method which is one of ion plating methods, and titanium nitride is deposited on the surface of the cathode foil. The metal nitride is inert, and it is difficult to form a natural oxide film. In addition, the deposited film forms fine concave-convex, and the surface area of the cathode is enlarged. However, the deposition process of the metal nitride is complicated, resulting in high cost of the electrolytic capacitor.

[0005] Therefore, the present inventors and others have considered forming a carbon layer on the cathode foil. The carbon layer is located on the outermost surface of the cathode body. The cathode-side capacitance of the electrolytic capacitor is exhibited by the electric double layer of the boundary surface between the polarized electrode and the electrolyte.

[0006] [Related Art Documents]

[0007] [Patent Documents]

[0008] Patent Document 1: Japanese Patent Laid-Open No. 4-61109 SUMMARY

[0009] [Problems to be Solved by the Invention]

[0010] A lead terminal is drawn from the electrolytic capacitor, and the electrolytic capacitor is electrically connected to a circuit via the lead terminal. The lead terminal is, for example, a joint shape including a flat portion made of aluminum. The flat portion is connected to each of the anode body and the cathode body of the capacitor element by various connection methods, and the lead terminal is drawn from the main body of the electrolytic capacitor.

[0011] As a connection method of the lead terminal to the anode body or the cathode body, cold press bonding is known. The cold press bonding is to overlap the anode body or the cathode body with the flat portion of the lead terminal, and to press the anode body or the cathode body with the flat portion of the lead terminal in the stacking direction in a non-heated state. Thereby, it can be said that the anode body or the cathode body and the flat portion of the lead terminal cause atomic bonding between each other.

[0012] By the cold press bonding, it is confirmed that if the cathode body in which the carbon layer is formed on the cathode foil is connected to the lead terminal, the connection is poor compared to the case where the cathode body in which the carbon layer is not formed is cold press bonded to the lead terminal. That is, it is confirmed that the physical connection strength of the cathode body to the lead terminal is low, and in addition, the electrical resistance between the cathode body and the lead terminal is high.

[0013] The present application is proposed to solve the problem, and aims to provide an electrolytic capacitor in which the connection of the cathode body including the carbon layer to the lead terminal is improved, and a manufacturing method of the electrolytic capacitor.

[0014] [Technical means to solve the problem]

[0015] To solve the problem, the electrolytic capacitor of the embodiment is characterized by including: an anode body in which a dielectric layer is formed on a surface; a cathode body having a cathode foil and a carbon layer formed on the cathode foil; an electrolyte interposed between the anode body and the cathode body; and a lead terminal of each electrode cold press bonded to the anode body and the cathode body, and the maximum static friction coefficient of the surface of the carbon layer of the cathode body is 0.6 or more.

[0016] In addition, to solve the problem, the manufacturing method of the electrolytic capacitor of the embodiment is characterized by including: a cold press bonding process of cold press bonding a lead terminal to the cathode body in which a carbon layer having a maximum static friction coefficient of 0.6 or more is formed on a cathode foil.

[0017] When the lead terminal is cold press bonded to the cathode body, the cathode foil of the cathode body is made of metal such as aluminum foil, and thus is stretchable, and is easily stretched by pressing. On the other hand, the carbon layer inherently lacks stretchability compared to the cathode foil, but if the maximum static friction coefficient further reaches 0.6 or more, the carbon layer is caught by the pressing member, and in the cold press bonding, increasingly fails to follow the stretching of the cathode foil. In this way, the carbon layer is easily cracked, and the cathode foil is exposed from the cracks. Therefore, the flat portion of the lead terminal and the surface of the cathode foil are press bonded via the cracks of the carbon layer, and thus the connection of the lead terminal to the cathode body is improved.

[0018] In addition, if the friction of the surface of the carbon layer is low, the surface of the pressing member and the surface of the carbon layer slide at the time of cold press bonding. At the time of cold press bonding, a pressing region in which the cathode foil and the carbon layer are pressed by the pressing member is formed, but in a region outside the pressing region, a force to move to the outside of the pressing region acts by the surface of the pressing member and the surface of the carbon layer sliding. Therefore, the region outside the pressing region does not become thin by pressing, and the pressing region easily becomes a shape in which the thickness of the region outside and the other central region sharply changes. In this shape, stress easily concentrates in the portion in which the thickness sharply changes, and the connection of the cathode body and the lead terminal can be insufficient. However, if the maximum static friction coefficient of the surface of the carbon layer is set to 0.6 or more, the pressing member does not slide on the surface of the carbon layer, and the pressing region of the carbon layer and the cathode foil becomes thin in the entire region by pressing. Therefore, a structure in which stress does not concentrate is formed, and the connection force of the cathode body and the lead terminal can be improved.

[0019] The carbon layer can also contain graphite in a proportion of 18% by weight or less including no addition, with respect to the total amount of the entire carbon raw material in the carbon layer. Graphite has sliding properties, and therefore, if the content of graphite is set to no addition or 18% by weight or less, the maximum static friction coefficient of the surface of the carbon layer can be increased to 0.6 or more. Further, the carbon layer can also contain spherical carbon as the carbon raw material.

[0020] In the cold press bonding process, the cathode body and the lead terminal are overlapped and pressed by a pressing member, and the pressing member can have a flat surface and a side surface inclined at an angle of 120 degrees or more with respect to the flat surface. In addition, a cold press bonding region having a flat surface and an inclined surface at an angle of 120 degrees or more with respect to the flat surface can be formed at the boundary surface of the cathode body and the lead terminal.

[0021] If the cathode body and the lead terminal are pressed by a pressing member in which the side surface is inclined at an angle of 120 degrees or more, the cathode body is difficult to be sheared, and the connection of the cathode body and the lead terminal is improved. In addition, the cold press bonding region has a flat surface and an inclined surface at an angle of 120 degrees or more, and the region becomes wide, and the joining area becomes large, and therefore, the connection of the cathode body and the lead terminal is improved.

[0022] [Effects of the Invention]

[0023] According to the present application, the connection of the cathode body and the lead terminal is improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a model diagram of an electrolytic capacitor.

[0025] Figure 2 is a schematic view showing a cross section of a cathode body.

[0026] Figure 3 is a schematic view showing a connection process using cold press bonding.

[0027] Figure 4 is a graph showing the connection strength of each maximum static friction coefficient when cold press bonding is performed using a pressing member having a trapezoidal shape with a side surface having a 120-degree inclination angle.

[0028] Figure 5 is a graph showing the contact resistance of each maximum static friction coefficient when cold press bonding is performed using a pressing member having a trapezoidal shape with a side surface having a 120-degree inclination angle.

[0029] Figure 6 is a graph showing the connection strength of each maximum static friction coefficient when cold press bonding is performed using a pressing member having a trapezoidal shape with a side surface having a 150-degree inclination angle.

[0030] Figure 7 is a graph showing the contact resistance of each maximum static friction coefficient when cold press bonding is performed using a pressing member having a trapezoidal shape with a side surface having a 150-degree inclination angle. DETAILED DESCRIPTION

[0031] An electrode body of an embodiment of the present application and an electrolytic capacitor using the electrode body as a cathode will be described. In the present embodiment, a wound-type electrolytic capacitor having an electrolyte will be exemplified and described, but is not limited thereto. As the electrolyte, a solid electrolyte layer such as a conductive polymer, a gel electrolyte, or an electrolyte using both a solid electrolyte layer and a gel electrolyte, any of electrolytic capacitors having various electrolytes can be applied, and for example, can also be applied to a laminated-type electrolytic capacitor.

[0032] (Summary of electrolytic capacitor)

[0033] Figure 1 is a model view of an electrolytic capacitor of the present embodiment. The electrolytic capacitor 1 is a passive element that performs charge accumulation and discharge of electric charges corresponding to electrostatic capacitance. The electrolytic capacitor 1 includes an anode body 2 on which a dielectric oxide film 5 is formed on a surface, a cathode body 3 formed by forming a carbon layer 32 on a surface of a cathode foil 31, and a separator 4. Further, the carbon layer 32 is formed on both surfaces of the cathode foil 31. In addition, the anode body 2 and the cathode body 3 are in a band shape, are arranged facing each other with the separator 4 interposed therebetween, and are wound in a spiral shape in a length direction of the band.

[0034] The electrolytic solution 6 is in contact with the dielectric oxide film 5 of the anode body 2, and also in contact with the carbon layer 32 of the cathode body 3. The electrolytic capacitor 1 generates a cathode-side capacitance by the electric double layer action at the interface between the carbon layer 32 of the cathode body 3 and the electrolytic solution 6, and also generates an anode-side capacitance by the dielectric polarization action at the anode body 2.

[0035] Figure 2 is a sectional view of the cathode body 3. As shown in Figure 2 , the cathode body 3 is electrically and mechanically connected by cold press bonding to the lead terminal 7. The anode body 2 is also electrically and mechanically connected by cold press bonding to another lead terminal 7. The electrolytic capacitor 1 is mounted to an electric circuit or an electronic circuit by the lead terminal 7.

[0036] The lead terminal 7 is a metal member, for example, made of aluminum, having a flat plate shape or a flat wire shape, and including a flat portion 71. One end side of the lead terminal 7 is brought into surface contact with the cathode body 3 with the flat portion 71. The lead terminal 7 is caused to protrude from the cathode body 3 in a direction orthogonal to the long side of the cathode body 3. The lead terminal 7 is then connected to the cathode body 3 by cold press bonding. The connection method of the anode body 2 to another lead terminal 7 is the same. Further, the lead terminal 7 can be formed by crushing one end portion of a round bar portion to form the flat portion 71 by press working, and connecting a metal wire to the other end portion of the round bar portion by arc welding or the like.

[0037] (cathode body)

[0038] The cathode body 3 has a laminated structure of a cathode foil 31 and a carbon layer 32. The cathode foil 31 serves as a current collector, and preferably has a surface expansion layer formed on a surface thereof. The carbon layer 32 contains a carbon raw material as a main material. The laminated structure of the cathode foil 31 and the carbon layer 32 is formed by the carbon layer 32 being in contact with the surface expansion layer. The carbon layer 32 is located at the outermost surface of the cathode body 3.

[0039] The cathode foil 31 is a long strip-shaped foil made of a valve action metal. The valve action metal is aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, or the like. The purity is desirably substantially 99% or more, and can contain impurities such as silicon, iron, copper, magnesium, zinc, or the like. As the cathode foil 31, for example, an aluminum material having a temper symbol of H as defined by Japanese Industrial Standard (JIS) specification H0001, so-called H material, or an aluminum material having a temper symbol of O as defined by JIS specification H0001, so-called O material can be used. If a metal foil having high rigidity including the H material is used, deformation of the cathode foil 31 caused by press working can be suppressed.

[0040] The cathode foil 31 is subjected to surface expansion treatment on a metal foil to which valve action metal is applied. The surface expansion layer is formed by electrolytic etching or chemical etching, sandblasting, or the like, or by vapor deposition or sintering of metal particles or the like on the metal foil. As the electrolytic etching, direct current etching or alternating current etching or the like can be cited. In the chemical etching, the metal foil is immersed in an acid solution or an alkali solution. The surface expansion layer formed is a layer region having tunnel-like etching pits or sponge-like etching pits engraved from the foil surface toward the foil core. Further, the etching pits can be formed so as to penetrate the cathode foil 31.

[0041] In the surface expansion layer, a natural oxide film can also be intentionally or naturally formed. The natural oxide film is formed by reaction of the cathode foil 31 with oxygen in the air, and the chemical film is an intentionally formed oxide film by chemical conversion treatment in which a voltage is applied in a solution in which halogen ions are not present, such as an aqueous solution of adipic acid or boric acid. In the case where the metal foil is, for example, an aluminum foil, the oxide film obtained by the method described above is aluminum oxide formed by oxidation of the surface expansion layer.

[0042] The carbon layer 32 contains a carbon raw material that generates an electric double layer effect as a main material. The surface of the carbon layer 32 is adjusted so that the maximum static friction coefficient is 0.6 or more. By setting the maximum static friction coefficient of the surface of the carbon layer 32 to 0.6 or more, the connectivity of the cathode body 3 having the carbon layer 32 to the lead terminal 7 is improved. The following mechanism is presumed and is not limited to the mechanism, but it is considered that the connectivity of the cathode body 3 having the carbon layer 32 to the lead terminal 7 will be improved based on the following reasons.

[0043] That is, when the lead terminal 7 and the cathode body 3 are pressed by cold press bonding, the cathode foil 31 of the cathode body 3 is made of metal such as aluminum foil and is therefore highly extensible and easily stretched by pressing. On the other hand, the carbon layer 32 inherently lacks extensibility compared to the cathode foil 31, but if the maximum static friction coefficient further reaches 0.6 or more, the carbon layer 32 will be caught by the pressing member and will increasingly fail to follow the extension of the cathode foil 31 at the time of cold press bonding. In this way, the carbon layer 32 generates a large number of cracks, and the cathode foil 31 is exposed from the cracks of the carbon layer 32. Therefore, the flat portion 71 of the lead terminal 7 and the surface of the cathode foil 31 can be joined through the cracks of the carbon layer 32, thereby improving the connectivity of the lead terminal 7 to the cathode body 3. In this way, in order to make the surface of the carbon layer 32 easily caught by the lead terminal 7, the carbon layer 32 is adjusted so that the maximum static friction coefficient of the surface of the carbon layer 32 reaches 0.6 or more.

[0044] Further, if the frictional force of the surface of the carbon layer 32 is low, the surface of the pressing member and the surface of the carbon layer 32 can slip at the time of cold press bonding. At the time of cold press bonding, a pressing region in which the carbon layer 32 and the cathode foil 31 are pressed by the pressing member is generated, but outside the pressing region, a force to move to the outside of the pressing region acts by the surface of the pressing member and the surface of the carbon layer 32 slipping. Therefore, the outside of the pressing region does not become thin by pressing, and the pressing region easily becomes a shape in which the thickness of the outside and the other central region sharply changes. In the shape, stress easily concentrates in the portion in which the thickness sharply changes, and the connection of the cathode body 3 and the lead terminal 7 can not be sufficient. However, if the maximum static friction coefficient of the surface of the carbon layer 32 is 0.6 or more, the pressing member does not slip on the surface of the carbon layer 32, and the pressing region of the carbon layer 32 and the cathode foil 31 becomes thin in the entire region by pressing. Therefore, a structure in which stress does not easily concentrate is obtained, and the connection force of the cathode body 3 and the lead terminal 7 can be improved.

[0045] The carbon raw material contained in the carbon layer 32 is fibrous carbon, carbon powder, or a mixture of these. It can also be fibrous carbon or carbon powder subjected to a porous treatment such as an activation treatment or an opening treatment to form pores. The fibrous carbon is carbon nanotubes, carbon nanofibers, or the like. The carbon nanotubes can be single-walled carbon nanotubes in which a graphene sheet is one layer, or multi-walled carbon nanotubes (multi-wall carbon nanotubes (MWCNT)) in which two or more graphene sheets are coiled in a coaxial manner and the tube wall is multi-layered. The carbon powder is activated carbon using a powder derived from natural plant tissues such as coconut shells, synthetic resins such as phenol, fossil fuels such as coal, coke, pitch, or the like as a raw material, carbon black such as ketjen black, acetylene black, channel black, or the like, carbon nanohorns, amorphous carbon, mesoporous carbon, or the like. In the electrolytic capacitor 1 using the electrolytic solution 6 as an electrolyte, the carbon raw material is preferably a carbon raw material that exhibits an electric double layer effect.

[0046] As the carbon raw material, spherical carbon is particularly preferable. It is preferable to include one or two or more kinds of spherical carbon as the carbon raw material in the carbon layer 32. The spherical carbon has a small particle diameter and easily enters a deeper portion of the expanded layer formed in the cathode foil 31, and the carbon layer 32 is closely attached to the cathode foil 31. As the spherical carbon, for example, carbon black can be cited. As the carbon black, ketjen black, acetylene black, channel black, thermal black, or the like can be cited, and it is preferable that the primary particle diameter be 100 nm or less on average, and it is further preferable that the specific surface area (hereinafter referred to as the BET specific surface area) calculated according to the Brunauer-Emmett-Teller (BET) theory be 200 m 2 2 ​Carbon black having a particle size of 1 μm or less, for example, is acetylene black.

[0047] As the carbon raw material, graphite can also be added to the carbon layer 32 together with other carbon raw materials. As the other carbon raw materials to be added together with graphite, spherical carbon is preferable. As the graphite, scale-like or scaly graphite having an aspect ratio of the short diameter to the long diameter in the range of 1 : 5 to 1 : 100 is preferable. In the case where the carbon layer 32 containing the combination of the carbon raw materials is layered on the cathode foil 31, the spherical carbon is easily rubbed into the fine pores of the expanded layer by the graphite. The graphite is easily deformed along the concave-convex surface of the expanded layer and easily accumulates on the concave-convex surface. Then, the graphite becomes a pressing lid that presses the spherical carbon rubbed into the fine pores. Thus, the adhesion and the fixation of the carbon layer 32 to the cathode foil 31 are further improved.

[0048] Here, the graphite has high sliding properties, and thus the maximum static friction coefficient of the surface of the carbon layer 32 can be adjusted by adjusting the content of the graphite. The graphite is provided at a content of 18 wt% or less with respect to the carbon layer 32, or at a content of 18 wt% or less with respect to the total amount of all the carbon raw materials contained in the carbon layer 32. Thus, the maximum static friction coefficient of the surface of the carbon layer 32 becomes 0.6 or more.

[0049] Such a cathode body 3 is produced through a cathode body production process. In the cathode body production process, only a slurry of the material containing the carbon layer 32 is produced, and, in addition, the expanded layer is formed in advance on the cathode foil 31, and the slurry is applied to the expanded layer, and then dried and pressed. As for the carbon layer 32, the carbon raw materials are dispersed in a solvent, and a binder is added, and a slurry is produced. Before producing the slurry, the average particle diameter of the carbon raw materials can also be adjusted in advance by pulverization using a bead mill or a ball mill or the like. The solvent is alcohol such as methanol, ethanol or 2-propanol, a hydrocarbon-based solvent, an aromatic-based solvent, an amide-based solvent such as N-methyl-2-pyrrolidone (NMP) or N, N-dimethyl formamide (DMF), water, or a mixture of these. As the dispersion method, a mixer, jet mixing, or ultracentrifugal processing, or other ultrasonic processing is used. In the dispersion process, the graphite, the spherical carbon and the binder in the mixed solution are finely divided and homogenized and dispersed in the solution. As the binder, for example, styrene butadiene rubber, polyvinylidene fluoride, or polytetrafluoroethylene can be cited.

[0050] The slurry is applied to the cathode foil 31 by a slurry casting method, a doctor blade method, or a spray method or the like. After the application, the solvent is volatilized by drying. Alternatively, the carbon layer 32 is sheet-formed by papermaking and placed on the cathode foil 31. The sheet-formed paper is produced by dispersing the carbon raw materials contained in the carbon layer 32 in a dispersion solvent, adding a binder as necessary, and then peeling the accumulated material from the filter paper after pressure filtration and drying.

[0051] In addition to this, as a method of forming the carbon layer 32 on the cathode foil 31, vacuum evaporation, sputtering method, ion plating, chemical vapor deposition (CVD) method, electrolytic plating, non-electrolytic plating, and the like can be listed. In the case of using the evaporation method, the carbon raw material is evaporated by electrically heating it in a vacuum, or an electron beam is irradiated to the carbon raw material in a vacuum to evaporate it, and the carbon raw material is deposited on the cathode foil. In the case of using the sputtering method, a target containing the carbon raw material is disposed in a vacuum container together with the cathode foil, an inert gas is introduced into the vacuum container and a voltage is applied, whereby the plasma of the inert gas collides with the target, and the particles of the carbon raw material knocked out of the target are deposited on the cathode foil.

[0052] After the carbon layer 32 is formed on the cathode foil 31, the cathode foil 31 and the carbon layer 32 are pressure-bonded at a prescribed pressurizing pressure. In the pressurizing process, the cathode body 3 including the carbon layer 32 and the cathode foil 31, for example, is gripped by a pressurizing roller, and a pressurizing line pressure is applied. The pressurizing pressure is desirably about 0.01 t / cm to 100 t / cm. By the pressurizing, if the carbon raw material of the carbon layer 32 is graphite and spherical carbon, the graphite and the spherical carbon are spread and aligned. In addition, by the pressurizing, the graphite of the carbon layer 32 is deformed in a manner following the concave-convex surface of the expanded surface layer. In addition, by the pressurizing, stress of pressure bonding is applied to the graphite deformed following the concave-convex surface of the expanded surface layer, and the spherical carbon between the graphite and the expanded surface layer is pressed into the fine pores. Thus, the adhesion of the carbon layer 32 to the cathode foil 31 is improved.

[0053] The obtained cathode body 3 is connected to the lead terminal 7 through a cold pressure bonding process. Figure 3 is a schematic view showing the cold pressure bonding of the obtained cathode body 3 to the lead terminal 7. As shown in Figure 3 The obtained cathode body 3 is overlapped with the flat portion 71 of the lead terminal 7. Then, in a non-heated state, the flat portion 71 of the cathode body 3 and the lead terminal 7 is pressed from the cathode body 3 side by the pressing member 200, and the flat portion 71 of the cathode body 3 and the lead terminal 7 is pressed in the stacking direction by the pressing member 200.

[0054] The pressing member 200 preferably has a trapezoidal shape at the front end. That is, the front end of the pressing member 200 is divided by a flat surface 210 and a side surface 220. The side surface 220 is connected to the flat surface 210 and inclines to the outside of the pressing member 200, and the angle a formed by the flat surface 210 and the side surface 220 is preferably inclined at 120 degrees or more. If the side surface 220 is inclined at 120 degrees or more, the shear stress to the cold pressure bonding region 33 pressed by the pressing member 200 is reduced. That is, the cathode body 3 does not break partially or entirely between the cold pressure bonding region 33 and the surrounding thereof, and the connection of the cathode body 3 to the lead terminal 7 can be favorably maintained.

[0055] Further, the cold pressure bonding region 33 is a region in the boundary of the cathode body 3 and the lead terminal 7 that is bonded by cold pressure bonding, and is a region in which the pressing member 200 projects in the boundary of the cathode body 3 and the lead terminal 7.

[0056] The cold pressure bonding region 33 has a flat surface 33a and an inclined surface 33b by the pressing member 200 having a trapezoidal shape with an inclination angle of 120 degrees or more. The flat surface 33a is a region formed by the flat surface 210 of the pressing member 200 colliding, and the inclined surface 33b is a region formed by the side surface 220 of the pressing member 200 colliding. Therefore, the inclined surface 33b is inclined outward, and the angle formed with the flat surface 33a becomes an angle α of 120 degrees or more, which is the same as the pressing member 200. Therefore, the area of the cold pressure bonding region 33 is expanded, and the connectivity of the cathode body 3 and the lead terminal 7 is further improved.

[0057] (anode body 2)

[0058] Next, the anode body 2 is a long strip-shaped foil body made of a valve action metal. The purity of the anode body 2 is desirably 99.9% or more. The anode body 2 is formed by performing etching processing on an extended foil, or is formed by sintering a powder of a valve action metal, or is formed by forming a film by evaporating a film of a metal particle or the like on a foil. The anode body 2 has an etching layer or a porous structure layer on the surface.

[0059] The dielectric oxide film 5 formed on the anode body 2 is typically an oxide film formed on the surface layer of the anode body 2, and is an aluminum oxide layer obtained by oxidizing the porous structure region if the anode body 2 is made of aluminum. The dielectric oxide film 5 is formed by chemical conversion processing by applying a voltage in a solution in which halogen ions are not present, such as an aqueous solution of an acid such as ammonium borate, ammonium phosphate, ammonium adipate, or the like.

[0060] (separators)

[0061] The separators 4 can be cellulose such as kraft, Manila hemp, esparto, hemp, rayon, and a mixed paper of these; a polyester resin such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and a derivative of these; a polytetrafluoroethylene resin; a polyvinylidene fluoride resin; a vinylon resin; a polyamide resin such as aliphatic polyamide, semi-aromatic polyamide, and wholly aromatic polyamide; a polyimide resin; a polyethylene resin; a polypropylene resin; a trimethylpentene resin; a polyphenylene sulfide resin; an acrylic resin, and the like, and these resins can be used alone or in combination, and can be used in combination with cellulose.

[0062] (electrolyte solution)

[0063] The electrolytic solution 6 is a mixture obtained by dissolving a solute in a solvent and adding an additive as needed. The solvent can be either one of a protic polar solvent or an aprotic polar solvent. As the protic polar solvent, monohydric alcohols, polyhydric alcohols, oxy alcohol compounds, water, and the like can be exemplified as representatives. As the aprotic polar solvent, sulfone-based, amide-based, lactone-based, cyclic amide-based, nitrile-based, sulfoxide-based, and the like can be exemplified as representatives.

[0064] The solute contained in the electrolytic solution 6 contains components of anions and cations, and is typically an organic acid or a salt thereof, an inorganic acid or a salt thereof, or a complex compound of an organic acid and an inorganic acid or a salt having ion dissociability thereof, and two or more thereof can be used alone or in combination. An acid that becomes an anion and a base that becomes a cation can also be added to the electrolytic solution as the solute components, respectively.

[0065] Further, other additives can also be added to the electrolytic solution. As the additives, polyethylene glycol, complex compounds of boric acid and polysaccharides (mannitol, sorbitol, and the like), complex compounds of boric acid and polyhydric alcohols, borate esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, and the like), phosphate esters, colloidal silica, and the like can be exemplified. These can be used alone or two or more thereof can be used in combination.

[0066] Hereinabove, the electrolytic capacitor using the electrolytic solution 6 has been described, and in the case of using a solid electrolyte, the static capacitance of the electrolytic capacitor is constituted by the anode-side capacitance generated by dielectric polarization, with the carbon layer 32 being in conduction with the solid electrolyte. In the case of using a solid electrolyte, a conductive polymer such as polythiophene such as polyethylene dioxythiophene, or polypyrrole, polyaniline, and the like can be exemplified.

[0067] [Examples]

[0068] Hereinafter, the present application will be described in more detail based on examples. Further, the present application is not limited to the following examples.

[0069] (Examples 1 and 2)

[0070] (Production of the Cathode Body)

[0071] The cathode body 3 for the electrolytic capacitor 1 of Comparative Examples 1 to 3 and Examples 1 and 2 was produced in the following manner. First, the carbon raw material contained in the carbon layer 32 was a mixture of graphite and carbon black, which is one of the spherical carbons, or only carbon black. The powder of the graphite, the carbon black, and styrene butadiene rubber (SBR) as a binder were added to an aqueous solution of sodium carboxymethylcellulose (CMC-Na) as a dispersant-containing aqueous solution, and kneaded, thereby producing a slurry. The blending ratio of the carbon raw material, the binder, and the dispersant-containing aqueous solution was set to 84:10:6 in terms of weight ratio.

[0072] An aluminum foil was prepared separately as the cathode foil 31, and the slurry was uniformly applied to the cathode foil 31. For the aluminum foil, an extended surface layer was formed in advance by applying a voltage in hydrochloric acid. The surface area of the cathode foil 31 was enlarged by 22 times by the extended surface layer. The depth of the extended surface layer was 4 μm on a single surface, and 8 μm in total for both surfaces, and the foil core portion on which the extended surface layer was not formed remained with a thickness of 12 μm. Further, the depth of the extended surface layer was the average of the depth from the surface of the cathode foil 31 to the deepest portion of the etching pits. The thickness of the foil core portion was the average of the thickness of the layer on which the etching pits did not reach.

[0073] The slurry containing graphite and carbon black, or the slurry of only carbon black was applied to the cathode foil 31. The slurry was applied to the extended surface layer of the cathode foil 31. After the slurry was dried, vertical pressing was performed at a pressure of 150 kNcm -2 to fix the carbon layer 32 to the cathode foil 31.

[0074] The mixing ratio of graphite and carbon black in the cathode body 3 of Comparative Examples 1 to 3 and Examples 1 and 2 was different as shown in Table 1 below. Further, the carbon raw material contained in the carbon layer 32 of Comparative Examples 1 to 3 and Examples 1 and 2 was only graphite and carbon black, and the values of graphite in Table 1 can be said to be the weight proportion based on the total carbon raw material contained in the carbon layer 32.

[0075] (Table 1)

[0076] Graphite Carbon black Comparative Example 1 75 25 Comparative Example 2 56.25 43.75 Comparative Example 3 37.5 62.5 Example 1 18.75 81.25 Example 2 0 100

[0077] (Measurement of maximum friction coefficient)

[0078] The maximum static friction coefficient μ of the surface of each carbon layer 32 of the cathode body 3 of Comparative Examples 1 to 3 and Examples 1 and 2 was measured in the following manner. That is, the maximum static friction coefficient μ was measured by the horizontal straight line reciprocating sliding method in accordance with JIS Standard P-8147 "Test Method for Friction Coefficient of Paper and Paperboard". Specifically, a solvent-spun rayon (manufactured by Nippon High Paper Co., Ltd.; TEF (thickness 40 μm and density 0.40 g / cm3 )), felt, 200 g of a weight, and the solvent-spun rayon was stretched at a speed of 100 mm / min. The force at the moment when the solvent-spun rayon was moved by the slow increase of the pulling force was detected as the maximum static friction force (N) by a load cell (Okada Electric Co., Ltd.; Model LUX-B). The maximum static friction coefficient of the surface of the carbon layer 32 of each cathode body 3 was calculated from the vertical resistance (N) of the solvent-spun rayon from the cathode body 3 by the weight divided by the maximum static friction force (N).

[0079] The maximum static friction coefficient μ of the surface of each carbon layer 32 of the cathode bodies 3 of Comparative Examples 1 to 3 and Examples 1 and 2 is shown in Table 2 below.

[0080] (Table 2)

[0081] Maximum static friction force (N) Maximum static friction coefficient μ Comparative Example 1 0.65 0.33 Comparative Example 2 0.81 0.41 Comparative Example 3 0.99 0.51 Example 1 1.16 0.60 Example 2 1.40 0.71

[0082] As shown in Table 2 above, the maximum static friction coefficient μ of Examples 1 and 2 was 0.6 or more. In Example 1, the content of graphite was 18.75 wt% based on the total of graphite and carbon black, i.e., the entire carbon raw material, and in Example 2, no graphite was added. Therefore, it was confirmed that if the content of graphite with respect to the carbon layer 32 was set to 18 wt% or less based on the entire carbon raw material, the maximum static friction coefficient μ of the surface of the carbon layer 32 could be made 0.6 or more.

[0083] (Cold Press Bonding)

[0084] Next, the cathode bodies 3 of Comparative Examples 1 to 3 and Examples 1 and 2 were connected by cold press bonding of the lead-out terminals 7. The cathode body 3 was overlapped with the flat portion 71 of the lead-out terminal 7, and pressure was applied from the cathode body 3 side in the stacking direction by a pressing member 200. The front end of the pressing member 200 had a trapezoidal shape, and the angle between the flat surface 210 and the side surface 220 was 120 degrees.

[0085] (Strength of Connection Test)

[0086] With the lead-out terminal 7 on the upper side, the cathode body 3 was fixed, and the front end side of the lead-out terminal 7 projecting from the cathode body 3 was pulled up. Also, the maximum tensile stress generated before the flat portion 71 of the lead-out terminal 7 was peeled from each cathode body 3 was measured as the strength of connection by a load cell (Okada Electric Co., Ltd.; Model LUX-B). Furthermore, the positions of the points of force were all the same.

[0087] The results of the strength of connection test are shown in Table 3 below. In addition, the results of the average values of Table 3 are shown in Table 4 below. Figure 4In addition, as shown in the graph of FIG. 6, it was confirmed that the connection strength was different between Comparative Example 1 to Comparative Example 3 in which the maximum static friction coefficient was 0.51 or less and Example 1 and Example 2 in which the maximum static friction coefficient was 0.6 or more. When the maximum static friction coefficient was at least 0.51 or less, even if the maximum static friction coefficient was increased, the connection strength was not improved. However, when the maximum static friction coefficient was at least 0.6 or more, the connection strength was greatly improved compared to when the maximum static friction coefficient was at least 0.51 or less.

[0088] (Table 3)

[0089]

[0090] First, the cathode body 3 of Comparative Example 1 in which the maximum static friction coefficient was 0.33 was cold-pressed using the pressing member 200 having a side surface 220 inclined at 120 degrees, and the cathode body 3 was completely sheared and could not be connected to the lead terminal 7. In the cathode body 3 of Comparative Example 2 in which the maximum static friction coefficient was 0.41, only one of the three was not sheared and was connected to the lead terminal 7.

[0091] In addition, as shown in Table 3 and Figure 4 , it was confirmed that the connection strength was different between Comparative Example 1 to Comparative Example 3 in which the maximum static friction coefficient was 0.51 or less and Example 1 and Example 2 in which the maximum static friction coefficient was 0.6 or more. When the maximum static friction coefficient was at least 0.51 or less, even if the maximum static friction coefficient was increased, the connection strength was not improved. However, when the maximum static friction coefficient was at least 0.6 or more, the connection strength was greatly improved compared to when the maximum static friction coefficient was at least 0.51 or less.

[0092] (Contact Resistance Test)

[0093] The portion of the lead terminal 7 protruding from the cathode body 3 was connected to each terminal of the ohmmeter on the cathode body 3. The cathode body 3 was fixed with the lead terminal 7 on the upper side, and the contact resistance was measured in a state in which the lead terminal 7 was raised by 0.8 mm and in a state in which the lead terminal 7 was not raised, that is, in a state in which the lead terminal 7 was not raised by 0.0 mm. As the ohmmeter, Model RM3545 manufactured by Soken Denki Co., Ltd. was used. The measurement results showed the total value of the resistance value of the cathode body 3, the resistance value of the lead terminal 7, and the connection resistance. The resistance value of the cathode body 3 and the resistance value of the lead terminal 7 were the same values in Comparative Example 1 to Comparative Example 3 and Example 1 and Example 2.

[0094] The results of the contact resistance test are shown in Table 4 below. In addition, the results of the average values of Table 4 are shown in the graph of FIG. 7. Further, three of each of the cathode bodies 3 were produced, and for each of them, the contact resistance test was performed in a state in which the lead terminal 7 was raised by 0.0 mm and in a state in which the lead terminal 7 was raised by 0.8 mm, and the average values of three times were calculated. In Table 3 below, the × mark indicates that connection was not possible due to shearing, and it was not possible to measure, and each value is the resistance value (mΩ) obtained by the test. Figure 5

[0095] (Table 4) ​

[0096]

[0097] The resistance value of the cathode body 3 and the resistance value of the lead terminal 7 were the same value in Comparative Examples 1 to 3 and Examples 1 and 2, and therefore the difference in the results of the measurement shown in Table 4 and Figure 5 was the difference in the contact resistance. As shown in Table 4 and Figure 5 Example 3, the difference in the connection resistance was large in the state of being lifted by 0.0 mm and the state of being lifted by 0.8 mm. However, it was confirmed that if the maximum static friction coefficient reached 0.6 or more, the contact resistance in the state of being lifted by 0.8 mm decreased, and the difference from the contact resistance in the state of being lifted by 0.0 mm became small. Thus, if the maximum static friction coefficient of the surface of the carbon layer 32 was 0.6 or more, the contact resistance was greatly improved compared to the case where the maximum static friction coefficient was at least 0.51 or less.

[0098] (Modified example of pressing member)

[0099] The cathode body 3 for the electrolytic capacitor 1 of Comparative Examples 1 to 3 and Examples 1 and 2 was connected to the lead terminal 7 by cold press bonding using the pressing member 200 in which the inclination angle of the side surface 220 was different. The cathode body 3 was made to coincide with the flat portion 71 of the lead terminal 7, and the trapezoidal-shaped pressing member 200 in which the angle formed by the flat surface 210 and the side surface 220 was 150 degrees was pressed from the cathode body 3 side in the stacking direction.

[0100] After the cathode body 3 was connected to the lead terminal 7 by cold press bonding using the pressing member 200 having the side surface 220 inclined at 150 degrees, the connection strength test and the contact resistance test were performed. The method and the conditions of the connection strength test and the contact resistance test were the same as when the cathode body 3 was connected to the lead terminal 7 by cold press bonding using the pressing member 200 having the side surface 220 inclined at 120 degrees. The results of the connection strength test are shown in Table 5 below, and the results of the average value of the contact resistance test are shown in Table 6 below. In addition, the results of the average value of Table 5 are shown in the graph of Figure 6 , and the results of Table 6 are shown in the graph of Figure 7 . In Table 5 and Table 6 below, the symbol x indicates that connection was not possible due to shearing, and measurement was not possible, and in Table 6, each value is the resistance value (mΩ) obtained by the test.

[0101] (Table 5)

[0102]

[0103] (Table 6)

[0104]

[0105] In Comparative Example 2, where some cathode bodies 3 were sheared during cold pressing using a pressing member 200 with a side surface 220 inclined at 120 degrees, three out of three cathode bodies 3 did not experience shearing, and the cathode bodies 3 could be connected to the lead-out terminals 7. In Comparative Example 1, where all cathode bodies 3 were sheared during cold pressing using a pressing member 200 with a side surface 220 inclined at 120 degrees, two out of three cathode bodies 3 did not experience shearing, and the cathode bodies 3 could be connected to the lead-out terminals 7.

[0106] On the other hand, for the cathode bodies 3 of Comparative Examples 1 to 3 and Examples 1 and 2, attempts were made to connect the lead-out terminals 7 by cold pressing with a pressing member 200 whose angle between the side surface 220 and the flat surface 210 is 90 degrees. However, the cathode bodies 3 of each of the three individuals in Comparative Examples 1 to 3 and Examples 1 and 2 were sheared, and it was impossible to connect the cathode body 3 to the lead-out terminals 7.

[0107] That is, it is confirmed that by using a pressing member 200 with a side 220 inclined at 120 degrees or more for cold pressing, the cathode body 3 with a maximum static friction coefficient of 0.6 or more on the surface of the carbon layer 32 is not sheared and is connected to the lead-out terminal 7.

[0108] Moreover, as shown in Table 5 and Figure 6 As shown, when a pressing member 200 with a side surface 220 inclined at 150 degrees is used, the connection strength is also improved for Comparative Examples 1 to 3, where the maximum static friction coefficient is 0.51 or less. Furthermore, compared to the case where a pressing member 200 with a side surface 220 inclined at 120 degrees is used, the connection strength in Examples 1 and 2, where the maximum static friction coefficient is 0.6 or more, is further improved.

[0109] As shown in Table 5 and Figure 7 As shown, it can be confirmed that if a pressing member 200 with a side 220 inclined at 150 degrees is used, the maximum static friction coefficient increases, and the difference in connection resistance between the state with the tip raised by 0.0 mm and the state with the tip raised by 0.8 mm decreases. Moreover, if a pressing member 200 with a side 220 inclined at 150 degrees is used, and the maximum static friction coefficient reaches 0.6 or more, the difference in connection resistance between the state with the tip raised by 0.0 mm and the state with the tip raised by 0.8 mm almost disappears.

[0110] [Explanation of Symbols]

[0111] 1: Electrolytic capacitor

[0112] 2: Anode body

[0113] 3: Cathode

[0114] 31: Cathode foil

[0115] 32: Carbon layer

[0116] 33: Cold press bonding region

[0117] 33a: Flat surface

[0118] 33b: Inclined surface

[0119] 4: Separator

[0120] 5: Dielectric oxide film

[0121] 6: Electrolyte

[0122] 7: Lead terminal

[0123] 71: Flat portion

[0124] 200: Pressing member

[0125] 210: Flat surface

[0126] 220: Side surface

Claims

1. An electrolytic capacitor characterized by Comprising: an anode body having a dielectric layer formed on a surface; a cathode body having a cathode foil and a carbon layer formed on the cathode foil; an electrolyte interposed between the anode body and the cathode body; and an extraction terminal of each electrode cold-press bonded to the anode body and the cathode body, and the carbon layer and the cathode foil are press processed to adjust the maximum static friction coefficient of the surface of the carbon layer of the cathode body to 0.6 or more, the extraction terminal and the surface of the cathode foil are cold-press bonded via a crack in the carbon layer.

2. The electrolytic capacitor according to claim 1, characterized in that the carbon layer does not add graphite or contains graphite at a ratio of 18 wt% or less with respect to the total amount of all carbon raw materials in the carbon layer.

3. The electrolytic capacitor according to claim 2, characterized in that the carbon layer contains spherical carbon as the carbon raw material.

4. The electrolytic capacitor according to any one of claims 1 to 3, characterized in that a cold-press bonding region is present at the boundary surface of the cathode body and the extraction terminal, the cold-press bonding region has a flat surface and an inclined surface having an angle of 120 degrees or more with respect to the flat surface.

5. A method of manufacturing an electrolytic capacitor in which an anode body having a dielectric layer formed on a surface and a cathode body are opposed with an electrolyte interposed therebetween, the method of manufacturing an electrolytic capacitor characterized by comprising: a cathode body production step of forming a carbon layer on a cathode foil, the carbon layer and the cathode foil being press processed to adjust the maximum static friction coefficient of the surface of the carbon layer to 0.6 or more, a cold-press bonding step of cold-press bonding an extraction terminal to the cathode body, the cathode body having a carbon layer with a maximum static friction coefficient of the surface of 0.6 or more, in the cold-press bonding step, the surface of the carbon layer is pressed against the surface of a pressing member.

6. The method of manufacturing an electrolytic capacitor according to claim 5, characterized in that in the cold-press bonding step, the cathode body and the extraction terminal are overlapped and pressed using a pressing member, the pressing member has a flat surface and a side surface inclined at an angle of 120 degrees or more with respect to the flat surface.

7. The method of manufacturing an electrolytic capacitor according to claim 5 or 6, characterized in that in the cathode body production step, the carbon layer does not add graphite or contains graphite at a ratio of 18 wt% or less with respect to the total amount of all carbon raw materials in the carbon layer.

8. The method of manufacturing an electrolytic capacitor according to claim 7, characterized in that in the cathode body production step, spherical carbon is contained as the carbon raw material in the carbon layer.

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