Electrode foil, wound capacitor, method for manufacturing electrode foil, and method for manufacturing wound capacitor

Abstract

To provide an electrode foil that is resistant to cracks during winding while increasing the surface area of a dielectric film, a wound capacitor obtained by winding the electrode foil, a method for manufacturing the electrode foil, and a method for manufacturing a wound capacitor.SOLUTION: An electrode foil 1 is made of strip-shaped foil, and includes an enlarged surface portion 3, a core portion 2, and a plurality of dividing portions 4. The enlarged surface portion 3 is formed on the surface of the foil, and the core portion 2 is the remainder of the foil excluding the enlarged surface portion 3. The dividing portion 4 extends in the enlarged surface portion 3 in the width direction of the band and divides the enlarged surface portion 3. The plurality of dividing portions 4 share the bending stress when the electrode foil 1 is wound, and prevent stress concentration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode foil used in a wound capacitor. [Background technology]

[0002] Electrolytic capacitors are constructed by filling the gaps with an electrolyte to ensure close contact between the dielectric film of the anode and the counter electrode, and include non-solid electrolytic capacitors with a liquid electrolyte, solid electrolytic capacitors with a solid electrolyte, hybrid electrolytic capacitors with both liquid and solid electrolytes, and bipolar electrolytic capacitors with a dielectric film formed on both electrodes. These electrolytic capacitors are constructed by impregnating a capacitor element with an electrolyte, and the capacitor element consists of an anode foil made of a valve metal foil such as aluminum with a dielectric film formed on it, and a cathode foil made of the same or another metal, with a separator interposed between the anode foil and the cathode foil.

[0003] The capacitance of an electrolytic capacitor is proportional to the surface area of ​​the dielectric film. Typically, the electrode foil of an electrolytic capacitor undergoes a surface-enlarging process such as etching, and the enlarged surface is then subjected to a chemical conversion treatment, resulting in a dielectric film with a large surface area. In recent years, efforts have been made to enlarge the surface area of ​​the electrode foil, extending from the surface to deeper areas, in order to further increase the capacitance of electrolytic capacitors.

[0004] In other words, the core portion of the electrode foil in electrolytic capacitors tends to become thinner. The expanded surface portion with the dielectric coating has lower flexibility and extensibility than the core portion. Therefore, electrode foils with a large surface area of ​​the dielectric coating have reduced flexibility and extensibility due to the thinning of the remaining core portion, which is highly flexible and extensible.

[0005] In order to achieve both compactness and large capacitance, electrolytic capacitors using such electrode foils are sometimes constructed as wound capacitors. The capacitor element of a wound capacitor is formed by stacking an anode foil and a cathode foil with a separator sandwiched between them and rolling them into a cylindrical shape. However, recent efforts to increase the surface area of ​​the dielectric film have caused significant problems with the winding properties of wound capacitors.

[0006] That is, by forming a dielectric coating on the expanded surface by chemical conversion treatment, the flexibility and extensibility of the electrode foil are reduced. As a result, the electrode foil is unable to bend smoothly into a bow shape, and numerous fine cracks occur. These fine cracks expose unoxidized metal portions on the inner surface of the cracks.

[0007] In the case of wound capacitors, aging is performed after the capacitor element is immersed in the electrolyte in the case of electrolytic capacitors, or before the electrolyte is formed in the case of solid electrolytic capacitors. If the aging process is performed with the unoxidized metal parts exposed, the aging time will be longer.

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-149759 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0009] In order to solve the problems of the prior art as described above, the present invention provides an electrode foil that has a large surface area for a dielectric film and is less likely to crack when wound, a wound capacitor formed by winding the electrode foil, a method for manufacturing the electrode foil, and a method for manufacturing the wound capacitor. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the electrode foil of the present invention is characterized in that it is made of a strip-shaped foil, and comprises an enlarged surface portion formed on the surface of the foil and consisting of a number of tunnel-shaped pits, a core portion which is the remaining part of the foil excluding the enlarged surface portion, a plurality of dividing portions which divide the enlarged surface portion, and a dielectric coating formed on the surface of the enlarged surface portion or on the surface of the enlarged surface portion and the dividing portions.

[0011] The dividing portion may be formed so as to connect or straddle at least a plurality of the tunnel-shaped pits.

[0012] The dividing portion may have a groove width of 50 μm or less, including 0 μm, when the foil is flattened.

[0013] Some of the numerous tunnel-shaped pits may penetrate through the core portion.

[0014] A wound capacitor having this electrode foil wound around is also one aspect of the present invention.

[0015] This wound capacitor may comprise a capacitor element formed by winding the electrode foil, the capacitor element having a winding core portion at the center of the winding, the electrode foil being wound around the winding core portion, and the dividing portion being formed at least on the winding center side within a predetermined radius including the start of winding onto the winding core portion.

[0016] In addition, in order to achieve the above-mentioned object, the manufacturing method of the electrode foil according to the present invention is characterized by having the steps of forming an enlarged surface portion consisting of a large number of tunnel-shaped pits on the surface of a strip-shaped foil, extending a plurality of dividing sections that divide the enlarged surface portion, and chemically treating the foil to form a dielectric coating on the surface of the enlarged surface portion or on the surfaces of the enlarged surface portion and the dividing sections.

[0017] After the division portions are formed, the foil may be subjected to the chemical conversion treatment.

[0018] After the formation of the enlarged surface portion, the foil may be subjected to the chemical conversion treatment before the formation of the dividing portion.

[0019] The method may further include a step of subjecting the foil to the chemical conversion treatment after the formation of the enlarged surface portion and before the formation of the dividing portion, and a step of subjecting the foil to a chemical conversion treatment again after the formation of the dividing portion.

[0020] Furthermore, in order to achieve the above object, the method for manufacturing a wound capacitor according to the present invention comprises an element formation step of forming a capacitor element by winding the electrode foil, an electrolyte formation step of forming an electrolyte in the capacitor element, and an aging step of aging the capacitor element, characterized in that the aging step is carried out after the electrolyte is formed in the electrolyte formation step, or the electrolyte is formed in the aged capacitor element in the electrolyte formation step after the aging step. [Effects of the Invention]

[0021] According to the present invention, the dividing portion disperses the bending stress during winding, making it less likely that cracks that expose unoxidized metal parts will occur during winding, reducing the amount of electricity required for the aging process and shortening the time required for the aging process. [Brief explanation of the drawings]

[0022] [Figure 1] 1A and 1B show the structure of an electrode foil according to this embodiment, where FIG. 1A is a cross-sectional view taken along the longitudinal direction, and FIG. 1B is a top view. [Figure 2] FIG. 2 is a perspective view showing a capacitor element included in the wound capacitor according to the embodiment. [Figure 3] FIG. 2 is a schematic diagram of a transfer device. [Figure 4] 1 is a cross-sectional view taken along the longitudinal direction of an electrode foil having a divided portion according to the present embodiment. [Figure 5] 1 is a photograph of a cross section along the longitudinal direction of an electrode foil having a divided portion according to the present embodiment, according to Example 1. [Figure 6] 1 is a photograph showing the surface of an electrode foil having a dividing portion according to the present embodiment, according to Example 1, in which the long side of the photograph corresponds to the width direction of the electrode foil, and the short side of the photograph corresponds to the longitudinal direction of the electrode foil. [Figure 7] 1 is a photograph showing the surface of an electrode foil according to Comparative Example 1, in which the long side direction of the photograph is the width direction of the electrode foil and the short side direction of the photograph is the longitudinal direction of the electrode foil. [Figure 8] 1 is a graph showing the results of the Erichsen test for Example 1 and Comparative Example 1. [Figure 9] 1 is a graph showing the integrated values ​​of the amounts of electricity in the aging treatment of the wound capacitors of Example 1, Example 2, and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the electrode foil and wound capacitor according to the present invention will be described in detail, but the present invention is not limited to the embodiments described below.

[0024] (electrode foil) 1 is used as the anode foil of a wound capacitor, the cathode foil on which a dielectric film 5 is formed, or both. A typical example of a wound capacitor is an electrolytic capacitor, and examples of electrolytic capacitors include non-solid electrolytic capacitors in which the electrolyte is liquid and a dielectric film is formed on the anode foil, solid electrolytic capacitors in which the electrolyte is solid and a dielectric film is formed on the anode foil, hybrid electrolytic capacitors that have both liquid and solid electrolytes, and bipolar electrolytic capacitors in which a dielectric film is formed on both the anode and cathode foils.

[0025] The electrode foil 1 is made of a valve metal such as aluminum, tantalum, titanium, niobium, or niobium oxide. The purity is preferably about 99.9% or higher for anode foils and about 99% or higher for cathode foils, but impurities such as silicon, iron, copper, magnesium, and zinc may be included. As shown in Figure 1, the electrode foil 1 is long and has an expanded surface portion 3 formed on both sides, leaving a core portion 2 in the center of the thickness direction. Multiple divided portions 4 are formed on one or both of the expanded surface portion 3, and a dielectric coating 5 is formed on the surfaces of the expanded surface portion 3 and the divided portions 4.

[0026] The surface expansion portion 3 has a porous structure. The porous structure is made up of tunnel-shaped pits. The surface expansion portion 3 is typically formed by direct current etching, which applies a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0027] This electrode foil 1 includes a high-voltage electrode foil. The remaining portion of the valve metal excluding the expanded surface portion 3 corresponds to the core portion 2. In other words, for example, an unetched layer corresponds to the core portion 2. However, the core portion 2 does not need to be understood as a layer where all of the tunnel-shaped pits have not reached, as long as it is a layer where most of the tunnel-shaped pits have not reached. In other words, some of the tunnel-shaped pits may penetrate the core portion 2. The thicknesses of the expanded surface portion 3 and the core portion 2 are not particularly limited, but it is preferable that the thickness of the expanded surface portion 3 combined on both sides is 40 to 200 μm, and that of the core portion 2 is 8 to 60 μm.

[0028] The dividing portions 4 divide the expanded surface portion 3 in the depth direction from the surface of the electrode foil 1 toward the core portion 2. The dividing portions 4 need not completely divide the core portion 2, and may be deep enough not to reach the core portion 2, deep enough that the deepest portion just reaches the core portion 2, or deep enough that the deepest portion bites into the core portion 2. Furthermore, the depth of all dividing portions 4 does not need to be uniform.

[0029] Specifically, the dividing portions 4 extend discontinuously across the electrode foil 1. The dividing portions 4 connect or span multiple tunnel-shaped pits that make up the expanded surface portion 3. The position, length, and extension direction of each dividing portion 4 vary. They may extend in the longitudinal direction or width direction of the electrode foil 1, or a mixture of these directions may form a random orientation. Linear and curved dividing portions 4 may also be present, and the dividing portions 4 may branch or be single lines. The separation distance between the ends of a single dividing portion 4 is between 40 μm and 150 μm on average, with some dividing portions as short as about 10 μm and others as long as about 600 μm. Dividing portions 4 with lengths within this range improve the flexibility and extensibility of the electrode foil 1.

[0030] Such dividing portions 4 are formed by cracking the enlarged surface portion 3, splitting the enlarged surface portion 3, making cuts in the enlarged surface portion 3 along the thickness direction of the electrode foil 1, cutting out the enlarged surface portion 3, or digging out the enlarged surface portion 3 along the thickness direction of the electrode foil 1. Therefore, actual examples of dividing portions 4 are cracks, fissures, cuts, notches, or digging out. However, the form of dividing portion 4 is not particularly limited as long as it divides the enlarged surface portion 3.

[0031] The groove width of the dividing portions 4 is 50 μm or less (including 0) when the electrode foil 1 is flattened without bending. The groove width of the dividing portions 4 is the length along the longitudinal direction of the electrode foil 1 measured near the surface layer of the electrode foil 1. If the dividing portions 4 are formed by splitting, tearing, or slitting, the groove width of the dividing portions 4 will be substantially zero. "Substantially zero" refers to a state in which the interfaces of the dividing portions 4 are at least partially in contact when the electrode foil 1 is flattened without bending. If the groove width of the dividing portions 4 is 50 μm or less, a significant decrease in the capacitance of the wound capacitor due to a decrease in the surface area of ​​the dielectric coating 5 can be prevented without impairing the flexibility and extensibility of the electrode foil 1.

[0032] Here, the dividing portions 4 can be formed by physical means, such as pressing the electrode foil 1 against a round bar. In a forming method using a round bar, the core portion 2 of the electrode foil 1 stretches in the longitudinal direction, resulting in a thinner core portion 2. However, by setting the groove width of the dividing portions 4 to 50 μm or less, the thickness of the core portion 2 is less likely to become thin, improving the flexibility and extensibility of the electrode foil 1. From this perspective, it is preferable to set the groove width of the dividing portions 4 to 50 μm or less.

[0033] The dividing portions 4 may be formed at a uniform average pitch or at a number within a unit range along the longitudinal direction of the electrode foil 1. The average pitch or the number within a unit range can also be changed taking into account the curvature at the location where the dividing portions 4 are formed when the electrode foil 1 is wound. This is because the smaller the curvature, i.e., the closer to the outer periphery when wound, the smaller the bending stress, which leads to the suppression of cracks during winding.

[0034] For example, dividing portions 4 may be formed only at the beginning of winding electrode foil 1 around the reel. The beginning of winding electrode foil 1 has a large curvature and is prone to cracking. Alternatively, the average pitch may be increased in proportion to the winding radius at the location where dividing portions 4 are located, or the number of dividing portions within a unit range may be reduced in inverse proportion to that radius. The fewer the number of dividing portions 4, the less impact they have on the capacitance of the wound capacitor.

[0035] It is desirable that this dividing portion 4 be formed on each of the enlarged surface portions 3 on both sides, but from the viewpoint of the stretching of the electrode foil 1 during winding, it is preferable that it be formed at least on the enlarged surface portion 3 that is on the outside of the foil and receives tension when the electrode foil 1 is wound.

[0036] The dielectric film 5 is formed by chemically treating the surface enlarged portion 3, and typically uses an oxide film formed by applying a voltage in a solution containing no halogen ions, such as an aqueous solution of adipic acid or boric acid.

[0037] Here, it is preferable to form the dielectric coating 5 also on the inner surface of the groove in the dividing portion 4. This is because it has been found that if the dielectric coating 5 is also formed on the inner surface of the groove in the dividing portion 4, the amount of electricity (C) required for the aging process to repair the dielectric coating 5 can be reduced.

[0038] Although this is speculation, if the dividing sections 4 are formed, each dividing section 4 shares the bending stress, making it less likely for the bending stress to concentrate and suppressing the occurrence of fine cracks during winding. Suppressing the occurrence of cracks during winding also makes it less likely for the unoxidized metal portion (aluminum) to be exposed from the inner surface of the crack. That is, if chemical conversion treatment is performed after forming the dividing sections 4, the dielectric coating 5 is also formed on the inner surface of the dividing sections 4. In other words, the unoxidized metal portion is not exposed from the inner surface of the dividing sections 4, and the amount of electricity required for the aging treatment is reduced.

[0039] Furthermore, forming the dividing portions 4 before the chemical conversion treatment allows for a smooth manufacturing process of the electrode foil 1. Therefore, preferably, the dividing portions 4 are formed after the formation of the enlarged surface portions 3 and before the chemical conversion treatment. In this case, forming a thin oxide before forming the dividing portions 4 makes it easier to form the dividing portions 4.

[0040] Incidentally, even if the dividing portions 4 are formed after the chemical conversion treatment, the effect of dispersing stress during winding by the dividing portions 4 can be obtained. Furthermore, by performing chemical conversion treatment before forming the dividing portions 4 and then performing chemical conversion treatment again after forming the dividing portions 4, it is also possible to form the dielectric coating 5 on the surface of the dividing portions 4.

[0041] (wound capacitor) 2 is a schematic diagram showing a capacitor element 6 of a wound capacitor using this electrode foil 1, and is an example of an aluminum electrolytic capacitor. In the capacitor element 6, the electrode foil 1, which is an anode foil, and the cathode foil 7 are overlapped with a separator 8 made of paper, synthetic fiber, or the like interposed therebetween. The separator 8 is overlapped so that one end protrudes beyond the other ends of the electrode foil 1 and the cathode foil 7. Then, the protruding separator 8 is wound first to create a winding core 9, and the layers of the electrode foil 1, the cathode foil 7, and the separator 8 are wound around the winding core 9.

[0042] The process of stacking the electrode foil 1 (which is an anode foil), the cathode foil 7, and the separator 8, and the process of winding the electrode foil 1, the cathode foil 7, and the separator 8 are typically performed by a transfer device provided with multiple rollers. As shown in Fig. 3, for example, this transfer device has four individual transfer paths Tr1, Tr2, and Tr3, and one collective transfer path Tr4 where the four transfer paths are gathered.

[0043] The individual transport paths Tr1, Tr2, and Tr3 and the collective transport path Tr4 are formed by multiple rollers R. The four individual transport paths Tr1, Tr2, and Tr3 carry the anode foil electrode foil 1, cathode foil 7, and separator 8, respectively. All of the electrode foil 1, cathode foil 7, and separator 8 that have traveled on the individual transport paths Tr1, Tr2, and Tr3 are hung on the roller R at the head of the collective transport path Tr4, and the electrode foil 1, cathode foil 7, and separator 8 are overlapped at the head of the collective transport path Tr4.

[0044] In order to reduce the size of the transfer device, each of the individual transfer paths Tr1, Tr2, and Tr3 and the collective transfer path Tr4 has multiple bending points C. At rollers R at the bending points C, the electrode foil 1, cathode foil 7, and separator 8 are bent so as to change their running direction along rollers R at the bending points C. Furthermore, the transfer device has a winding roller Rw at the end of the collective transfer path Tr4. The winding roller Rw winds up the overlapping electrode foil 1, cathode foil 7, and separator 8 by rotating around its axis.

[0045] When an electrolytic capacitor is produced from the capacitor element 6 thus produced, it is impregnated with an electrolyte, housed in a cylindrical outer case with a bottom, the anode and cathode terminals are drawn out, sealed with a seal, and subjected to an aging treatment to form a wound capacitor.When a solid electrolytic capacitor is produced from the capacitor element 6 thus produced, it is aged, an electrolyte is formed, it is housed in a cylindrical outer case with a bottom, the anode and cathode terminals are drawn out, and sealed with a seal, to form a wound capacitor.

[0046] 4 is a schematic diagram showing the state of the electrode foil 1 wound around a capacitor element 6. In the electrode foil 1 of this embodiment, the multiple divided portions 4 share and bear the bending stress, and the bending stress is distributed to each divided portion 4. As a result, new fine cracks are less likely to occur in the expanded surface portion 3, and stress that would lead to the destruction of the core portion 2 is prevented from being applied to the electrode foil 1. Therefore, destruction of the core portion 2 is avoided, and the electrode foil 1 is wound in a smooth curve without bending. In other words, the occurrence of cracks that would expose unoxidized metal portions during winding can be suppressed.

[0047] Furthermore, even when the electrode foil 1 is transferred by rollers using a transfer device, the rollers R at the bending point C bend the electrode foil 1, but the multiple divided portions 4 of the electrode foil 1 share and bear the bending stress, thereby preventing the electrode foil 1 from bending.

[0048] Example 1 The electrode foil 1 representing this embodiment was produced as follows. First, an aluminum foil having a thickness of 130 μm, a width of 10 mm, a length of 55 mm, and a purity of 98% by weight or more was used as the substrate. Then, on both sides of this aluminum foil, an enlarged surface portion 3 consisting of tunnel-shaped pits for medium to high voltage use was formed. Specifically, the process involves a first step of forming pits and a second step of enlarging the pits. In the first step, the aluminum foil was electrochemically etched with a direct current in an aqueous solution containing chloride ions. The etching in the first step was carried out at a current density of 400 mA / cm. 2 In the second step, in order to enlarge the pits formed in the aluminum foil after the first step, an electrochemical etching treatment was carried out using a direct current in an aqueous solution containing nitrate ions. The current density of the etching treatment in the second step was 300 mA / cm. 2 This was done for about 2 minutes.

[0049] After the etching treatment, dividing sections 4 were formed in the aluminum foil whose both surfaces had been etched. The dividing sections 4 were generated perpendicular to the longitudinal direction of the aluminum foil. Specifically, as a physical treatment method, the aluminum foil was pressed against a φ4 mm round bar at a wrap angle of 180 degrees, which indicates the area of ​​contact between the round bar and the aluminum foil, to form the dividing sections 4. This physical treatment method formed a plurality of dividing sections 4 that connected or spanned a plurality of tunnel-shaped pits and divided the expanded surface section 3.

[0050] Furthermore, after forming the dividing portion 4, a chemical conversion treatment was carried out to form a dielectric film 5 on the surfaces of the enlarged surface portion 3 and the dividing portion 4. Specifically, a voltage of 650 V was applied in a chemical conversion solution of 4 wt % boric acid at a liquid temperature of 85°C.

[0051] FIG. 5 is a longitudinal cross-sectional photograph of the electrode foil 1 according to Example 1. FIG. 6(a) is a 200x SEM photograph showing the surface of the electrode foil 1 according to Example 1. The long side of the photograph corresponds to the width direction of the electrode foil, and the short side of the photograph corresponds to the longitudinal direction of the electrode foil. FIG. 6(b) shows the divided portions shown in the photograph of FIG. 6(a) after digital processing to highlight them. As shown in FIGS. 5 and 6(a) and 6(b), 24 divided portions 4 were observed within an observation area of ​​10 mm × 10 mm in the electrode foil 1 according to Example 1. When 10 divided portions 4 were randomly selected from the 200x SEM photograph, the average distance between both ends of the selected divided portions 4 was approximately 120 μm. The distance between both ends of the divided portions 4 was approximately 40 μm for the shortest divided portions 4 and approximately 250 μm for the longest divided portions 4. In the electrode foil 1 of Example 1, the expanded surface portions 3 having the dielectric coating 5 were present on both sides of the core portion 2, each having a thickness of 55 μm, and the core portion 2 had a thickness of 10 μm.

[0052] (Comparative Example 1) The same substrate as in Example 1 was used, and the same etching treatment and chemical conversion treatment as in Example 1 were carried out. However, the process of forming dividing portions 4 was omitted, and dividing portions 4 were not formed. Fig. 7 is a 200x SEM photograph showing the surface of electrode foil 1 according to Comparative Example 1, with the long side of the photograph corresponding to the width direction of the electrode foil and the short side of the photograph corresponding to the longitudinal direction of the electrode foil.

[0053] As shown in Fig. 7, like Example 1, the electrode foil of Comparative Example 1 had an expanded surface portion 3 on each side of a core portion 2, and each expanded surface portion 3 had a dielectric coating 5. The expanded surface portions 3 with the dielectric coating 5 each had a thickness of 55 µm, and the core portion 2 had a thickness of 10 µm. However, even after SEM observation at 200x magnification, no lines connecting adjacent tunnel-shaped pits were observed on the surface of the electrode foil. In other words, no dividing portions 4 were formed.

[0054] To make the state of the dividing portions 4 more visible, the electrode foil 1 may be subjected to a surface treatment, such as a P-Cr treatment. Specifically, the electrode foil 1 is immersed in an aqueous solution of chromic anhydride (21 g / L) and phosphoric acid (53 g / L) at a liquid temperature of 85°C for about 1 hour, which removes fine oxides from the surface of the electrode foil 1 and makes it easier to observe the dividing portions 4. However, in Comparative Example 1, even when the electrode foil was subjected to the P-Cr treatment, no lines connecting adjacent tunnel-shaped pits were observed on the surface of the electrode foil.

[0055] (Erichsen test) An Erichsen test was performed on the electrode foil 1 of Example 1 and the electrode foil of Comparative Example 1. In the Erichsen test, the electrode foil 1 of Example 1 and the electrode foil of Comparative Example 1 were clamped with a pressure of 10 kN between a die and blank holder having an inner diameter of 33 mm, and pressed with a chisel-shaped punch. The chisel-shaped punch was 30 mm wide and had a spherical tip with a cross-sectional diameter of 4 mm. The chisel portion of the punch was pressed into the electrode foil 1 so as to be perpendicular to the longitudinal direction of the strip. The pressing speed of the punch was 0.5 mm / min.

[0056] The results of this Erichsen test are shown in Figure 8. Figure 8 is a graph with the punch stroke on the horizontal axis and the punch load on the vertical axis. The punch stroke is the distance the punch is pressed, and the punch load is the load required to achieve each punch stroke. As shown in Figure 8, the electrode foil of Comparative Example 1 broke before the punch stroke reached 1.1 mm, whereas the electrode foil 1 of Example 1 broke after the punch stroke exceeded 1.1 mm. In other words, the electrode foil 1 of Example 1 has improved extensibility due to the provision of the dividing portion 4.

[0057] 8, the electrode foil of Comparative Example 1 required a load of 1.8 N to achieve a punch stroke of 0.7 mm, while the electrode foil 1 of Example 1 achieved a punch stroke of 0.7 mm with a load of 1.6 N. That is, the electrode foil 1 of Example 1 had approximately 11% improved flexibility due to the provision of the dividing portion 4. That is, it was confirmed that Example 1, which had improved stretchability and flexibility, was less likely to develop cracks during winding and less likely to expose unoxidized metal portions compared to Comparative Example 1.

[0058] (Aging evaluation) The electrode foil 1 of Example 1 and the electrode foil of Comparative Example 1 were wound together as anode foils to produce a capacitor element 6. The electrode foil 1 of Example 1 and the electrode foil of Comparative Example 1 were both modified to have a width of 50 mm and a length of 3,300 mm. Furthermore, the electrode foil 1 of Example 2 was prepared using the same substrate as Example 1 and by carrying out the same etching treatment, dividing portion 4 formation treatment, and chemical conversion treatment as Example 1. However, before producing the capacitor element 6, the electrode foil 1 of Example 2 was subjected to the etching treatment, chemical conversion treatment, and dividing portion 4 formation treatment in that order, and the dielectric coating 5 was not formed on the surface of the dividing portion 4. Aluminum foil was used for the cathode foil 7. The cathode foil 7 had an enlarged surface portion 3 formed thereon, but the dielectric coating 5 was not formed thereon. Cellulose fiber was used for the separator 8.

[0059] Capacitor element 6 using electrode foil 1 of Example 1, capacitor element 6 using electrode foil 1 of Example 2, and capacitor element 6 using electrode foil 1 of Comparative Example 1 were impregnated with an electrolyte and housed in a bottomed cylindrical outer case, and the anode and cathode terminals were pulled out and sealed with a sealer. The electrolyte was an ethylene glycol solution of 1-7-octanedicarboxylic acid to which mannitol borate had been added. In this way, a wound capacitor using electrode foil 1 of Example 1, a wound capacitor using electrode foil 1 of Example 2, and a wound capacitor using electrode foil 1 of Comparative Example 1 were fabricated.

[0060] Both wound capacitors were subjected to an aging treatment, and the amount of electricity required for the aging treatment was measured. This aging treatment also served as a chemical conversion treatment for the electrode foil 1 of Example 2, and a dielectric film 5 was formed on the electrode foil 1 of Example 2 during this aging treatment. The aging treatment was performed by applying a rated voltage at a temperature of 100°C. During this aging treatment, the change in current flowing over time between the anode and cathode terminals was measured. Note that the current values ​​flowing through the three wound capacitors at the start of the aging treatment were the same. Figure 9 is a graph showing the integrated amount of electricity from the start of the aging treatment.

[0061] As shown in FIG. 9 , the current value of the wound capacitor using the electrode foil 1 of Example 1 leveled off around 36 minutes. In contrast, the current value of the wound capacitor using the electrode foil of Comparative Example 1 leveled off around 48 minutes. Furthermore, the current value of the wound capacitor using the electrode foil 1 of Example 2 leveled off around 131 minutes. This indicates that the wound capacitor using the electrode foil 1 of Example 1, which includes the divided portions 4 in the electrode foil 1, requires a significantly shorter time for the aging process and reduces the amount of electricity compared to the wound capacitor using the electrode foil of Comparative Example 1. Furthermore, the wound capacitor using the electrode foil 1 of Example 1 requires a significantly shorter time for the aging process and reduces the amount of electricity compared to the wound capacitor using the electrode foil of Example 2, which requires a significantly shorter time for the aging process and reduces the amount of electricity compared to the wound capacitor using the electrode foil of Example 2, due to the dielectric film 5 formed on the surfaces of the enlarged surface portion 3 and the divided portions 4 before assembly into the wound capacitor. [Explanation of symbols]

[0062] 1 Electrode foil 2 core 3 Enlarged surface area 4. Divided section 5 Dielectric coating 6 Capacitor elements 7 Cathode foil 8 Separator 9 Winding core

Claims

1. An electrode foil before being incorporated into a wound capacitor, It consists of a strip of foil, an enlarged surface portion formed on the surface of the foil; A core portion which is the remaining portion of the foil excluding the expanded surface portion; A plurality of dividing portions that divide the enlarged surface portion; a dielectric coating formed on the surface of the enlarged surface portion and the dividing portion; Equipped with the dividing portion is formed on both surfaces of the electrode foil or on the surface that will be on the outside when wound, When the wire is assembled into the wound capacitor, the wire is wound in a state where the dividing portion is present. An electrode foil characterized by:

2. The dividing portion is a crack, a fissure, a notch, a notch, or a recess, The plurality of dividing portions have different positions, lengths, and extending directions; The electrode foil according to claim 1,

3. Some of the plurality of dividing portions are branched midway along their extension; The electrode foil according to claim 1,

4. the dividing portion has a groove width of 50 μm or less when the foil is flattened, which is a width substantially equal to 0 μm, in which the interfaces of the dividing portions are at least partially in contact with each other; 4. The electrode foil according to claim 1, wherein:

5. 5. The electrode foil according to claim 1, which is a high voltage electrode foil.

6. The capacitor element is formed by winding an electrode foil. The electrode foil is It consists of a strip of foil, an enlarged surface portion formed on the surface of the foil; A core portion which is the remaining portion of the foil excluding the expanded surface portion; A plurality of dividing portions that divide the enlarged surface portion; a dielectric coating formed on the surface of the enlarged surface portion and the dividing portion; Equipped with the dividing portion is formed on both surfaces of the electrode foil or on the outer surface of the winding, the capacitor element is formed by winding the electrode foil in which the divided portion is present; A wound capacitor characterized by:

7. A method for manufacturing an electrode foil before it is incorporated into a wound capacitor, comprising the steps of: forming an enlarged surface portion on the surface of the strip-shaped foil; extending a plurality of dividing portions that divide the enlarged surface portion; a step of chemically treating the foil to form a dielectric coating on the surfaces of the enlarged surface portion and the divided portion; and the dividing portion is formed on both surfaces of the electrode foil or on the surface that will be on the outside when wound, the electrode foil is wound in a state where the dividing portion is present when the electrode foil is incorporated into the wound capacitor; A method for manufacturing an electrode foil, characterized by:

8. a foil forming step of forming an electrode foil; an element forming step of forming a capacitor element by winding the electrode foil; an electrolyte formation step of forming an electrolyte in the capacitor element; an aging step of aging the capacitor element; and The foil forming step includes: forming an enlarged surface portion on the surface of the strip-shaped foil; extending a plurality of dividing portions that divide the enlarged surface portion; a step of chemically treating the foil to form a dielectric coating on the surfaces of the enlarged surface portion and the divided portion; and In the foil forming step, the dividing portion is formed on both surfaces of the electrode foil or on a surface that will be on the outside when the electrode foil is wound, In the element forming step, The electrode foil having the divided portion is wound to form the capacitor element; performing the aging step after forming the electrolyte by the electrolyte forming step, or forming the electrolyte on the aged capacitor element by the electrolyte forming step after the aging step; A method for manufacturing a wound capacitor, characterized by:

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