Electrolytic capacitor

Abstract

Provided is an electrolytic capacitor that makes it possible to improve an initial characteristic by a simple method and maintain the initial characteristic after use for a long period of time. An electrolytic capacitor according to the present invention is characterized by comprising: a capacitor element which has a positive electrode foil that has a positive electrode oxide film on a surface thereof, a negative electrode foil, and a separator that is inserted between the positive electrode foil and the negative electrode foil; a conductive polymer layer which is impregnated into the capacitor element; and an electrolytic solution which is impregnated into the capacitor element, wherein the mass E2 per unit volume of the electrolytic solution impregnated into the center part of the separator is larger than the mass E1 per unit volume of the electrolytic solution impregnated into the end part of the separator.

Description

electrolytic capacitor

[0001] The present invention relates to an electrolytic capacitor.

[0002] As a small, high-capacity electrolytic capacitor with low ESR (equivalent series resistance), an electrolytic capacitor including an anode foil with a dielectric layer, a highly electrically conductive polymer layer formed to cover at least a portion of the dielectric layer, and an electrolyte capable of repairing the oxide film that forms the anode's dielectric layer is considered promising. Examples of such electrolytic capacitors include a capacitor in which a capacitor element is impregnated with a solution containing undoped soluble polyaniline to form a polyaniline layer, followed by the formation of a conductive polymer layer (see, for example, Patent Document 1). Also disclosed is a capacitor that uses an electrolyte containing a glycerin compound and γ-butyrolactone (see, for example, Patent Document 2).

[0003] JP 2014-93417 A JP 2016-82053 A

[0004] Electrolytic capacitors used in automotive electrical equipment are used for long periods of time in high-temperature environments, so they are required to maintain their initial capacity more than ever before. Patent Document 1 provides an electrolytic capacitor with improved reliability by immersing a capacitor element in a polyaniline solution to form a polyaniline layer, and then forming a conductive polymer layer. Patent Document 2 provides an electrolytic capacitor with high reliability by using an electrolyte solution containing γ-butyrolactone and a glycerin compound such as glycerin. However, neither method meets the requirement for maintaining the initial capacity.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electrolytic capacitor capable of maintaining its initial capacitance.

[0006] The electrolytic capacitor according to the present invention comprises a capacitor element having an anode foil having an anodized coating on its surface, a cathode foil, and a separator inserted between the anode foil and the cathode foil, a conductive polymer impregnated in the capacitor element, and an electrolyte impregnated in the capacitor element, wherein a mass E2 per unit volume of the electrolyte impregnated in the center portion of the separator is greater than a mass E1 per unit volume of the electrolyte impregnated in the end portion of the separator.

[0007] According to the present invention, a large amount of electrolyte is retained in the central portion of the separator, thereby improving the coating repair effect of the dielectric layer and improving the initial capacity. Furthermore, even if the electrolyte evaporates from the ends of the element, the electrolyte retained in the central portion of the element can be supplied to the ends, thereby maintaining the initial capacity.

[0008] FIG. 1 is a schematic diagram of an electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a simplified diagram of a partial cross section of a capacitor element (before conductive polymer impregnation) according to an embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing the state of conductive polymer impregnation of a capacitor element according to an embodiment of the present invention. FIG. 4 is a view showing an image of the surface of a separator according to an embodiment of the present invention. FIG. 5 is a view showing surface images of an anode foil and a cathode foil according to an embodiment of the present invention. FIG. 6 is a view showing an image of the surface of a separator according to a comparative example. FIG. 7 is a view showing surface images of an anode foil and a cathode foil according to a comparative example. FIG. 8 is a cross-sectional view schematically showing the state of formation of a conductive polymer layer in an electrolytic capacitor according to a comparative example.

[0009] Hereinafter, embodiments will be described with reference to the drawings.

[0010] (Embodiments of the Present Invention) FIG. 1 is a schematic diagram of an electrolytic capacitor 1 according to an embodiment of the present invention. FIG. 2 is a simplified diagram of a partial cross section of a capacitor element 20 (before conductive polymer impregnation) according to an embodiment of the present invention. FIG. 3 is a cross-sectional view schematically illustrating the state of conductive polymer impregnation of the capacitor element 20 according to an embodiment of the present invention. The electrolytic capacitor 1 includes a metal case 10 that functions as an exterior body, a capacitor element 20 inserted in the metal case 10, and a sealing body 30. The metal case 10 is a cylindrical aluminum case with a bottom and an opening 11 at one end. In this embodiment, the metal case 10 has a cylindrical shape as an example, but may also have a rectangular cylindrical shape.

[0011] Capacitor element 20 includes a pair of electrode foils. The pair of electrode foils is an anode foil 21 and a cathode foil 22. Capacitor element 20 is a wound type in which a first separator 23a, anode foil 21, second separator 23b, and cathode foil 22 are layered in this order and wound. The shape of capacitor element 20 roughly matches the internal shape of metal case 10. Therefore, capacitor element 20 has a columnar shape. In this embodiment, capacitor element 20 is used as a wound type (approximately cylindrical) that can effectively demonstrate the short-circuit path effect in electron transfer, but it may also be used as a stacked type capacitor element (approximately rectangular column) in which an anode foil and a cathode foil are layered in order with a separator interposed therebetween.

[0012] The anode foil 21 and the cathode foil 22 can be made of valve metals such as aluminum, tantalum, titanium, and niobium, as well as alloy foils and vapor-deposited foils. The entire surface of the anode foil 21 is covered with an oxide film. Therefore, the anode foil 21 is insulated from other components. This oxide film functions as a dielectric, allowing the capacitor element 20 to function as a capacitor. The surfaces of the anode foil 21 and the cathode foil 22 have porous portions 21a and 22a formed by etching or other methods. The cathode foil 22 may have an inorganic layer or a carbon layer formed on its surface. In this case, the conductive polymer layer described below is also formed on the surface of the inorganic layer or carbon layer. An anode lead terminal 24a is connected to the anode foil 21. A cathode lead terminal 24b is connected to the cathode foil 22.

[0013] The sealing body 30 is a rubber sealing body having a pair of lead insertion holes 31a, 31b through which the anode lead terminal 24a and the cathode lead terminal 24b are inserted. The sealing body 30 is fitted into the opening 11 of the metal case 10 and is firmly and airtightly attached by a horizontally drawn groove 12 formed around the outer periphery of the opening 11 using a crimping piece or the like. For example, butyl rubber, which has a low swelling rate in the electrolyte solvent described below, can be used for the sealing body 30. This reduces the impact of impurities extracted by ethylene glycol on the capacitor characteristics when the electrolyte contains ethylene glycol. Specifically, it is preferable to use butyl rubber that has a swelling rate of less than 0.4% by mass even when immersed in ethylene glycol solvent at 125°C for 2000 hours or more and a swelling rate of less than 2% by mass even when similarly immersed in gamma-butyrolactone solvent for 2000 hours or more.

[0014] The capacitor element 20 is impregnated with a conductive polymer. Examples of conductive polymers include polythiophene, polypyrrole, polyaniline, polyacetylene, polyfuran, polyacetylene, polyparaphenylene, polyparaphenylenevinylene, polyacene, and polythiophenevinylene. The above-mentioned conductive polymers may be used alone or in combination of two or more. Furthermore, the above-mentioned conductive polymer may be a polymer containing at least 50% by mass of a basic monomer constituting the conductive polymer, such as thiophene or pyrrole, preferably 70% by mass or more, and more preferably 90% by mass. A suitable conductive polymer is poly(3,4-ethylenedioxythiophene) containing 3,4-ethylenedioxythiophene as a monomer unit.

[0015] The conductive polymer preferably contains a dopant. Examples of the dopant include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. The above-mentioned dopants may be used alone or in combination of two or more.

[0016] The first separator 23a and the second separator 23b may be made of the same material or different materials. Examples of materials that can be used for the first separator 23a and the second separator 23b include glass fiber, cellulose, rayon, polyethylene terephthalate, vinylon, aliphatic polyamide, and aromatic polyamide. A blend of cellulose, rayon, and glass fiber is preferably used for the first separator 23a and the second separator 23b.

[0017] The capacitor element 20 is impregnated with an electrolytic solution. There are no limitations on the electrolytic solution as long as it is usable for electrolytic capacitors, but either a γ-butyllactone-based non-aqueous electrolytic solution or an ethylene glycol-based aqueous electrolytic solution can be used. Examples of solute components contained in the electrolytic solution include aliphatic carboxylic acids such as adipic acid, aromatic carboxylic acids such as phthalic acid, ammonia, amines such as triethylamine, and amidines such as tetramethylimidazolinium.

[0018] 2 and 3 , the anode foil 21 and the cathode foil 22 are configured to face each other with insulating first and second separators 23a and 23b interposed therebetween, and the first and second separators 23a and 23b prevent short circuits between the anode foil 21 and the cathode foil 22. In the electrolytic capacitor 1, the first and second separators 23a and 23b separating the anode foil 21 and the cathode foil 22 are impregnated with a conductive polymer dispersion, and the dispersion medium is dried to form a conductive polymer layer in the porous portions and on the surfaces of the anode foil 21, the cathode foil 22, and the separators. This allows for a low ESR.

[0019] As shown in FIG. 3 , in the electrolytic capacitor 1 according to the embodiment of the present invention, a band-shaped agglomerate 25 made of a conductive polymer is formed at the end of the capacitor element 20. In this specification, the end 20a of the capacitor element 20 refers to the end in the direction (width direction) perpendicular to the winding direction of the capacitor element 20. The end 20a of the capacitor element 20 occupies 15% of the length in the direction perpendicular to the winding direction. The central portion 20b of the capacitor element 20 is the center of the length perpendicular to the winding direction, and occupies 70% of the length in the direction perpendicular to the winding direction. In the case of a laminated capacitor element, the end of the capacitor element is within 15% of the length from each rectangular end face, and the central portion is within 70% of the length excluding the end.

[0020] In electrolytic capacitor 1, band-shaped agglomerates 25 of conductive polymer are formed at end portions 20a of capacitor element 20. Therefore, the conductive polymer impregnates the porous portions at end portions 20a of capacitor element 20, while the amount of conductive polymer impregnated into the porous portions at center portion 20b is reduced. Therefore, the proportion of voids in the center portions of first separator 23a and second separator 23b (S2) is greater than the proportion of voids in the end portions (S1). The volume of voids in first separator 23a and second separator 23b increases from the end portions toward the center. The amount of conductive polymer impregnation and porosity of first separator 23a and second separator 23b can be calculated from the change in mass before and after impregnation with the conductive polymer, as described below, or can be measured by SEM-EDS of a cross section perpendicular to the winding direction of the separator.

[0021] When the conductive polymer band-like agglomerates 25 are formed mainly at the end 20a of the capacitor element 20, the conductive polymer band-like agglomerates 25 can be seen from the end of the capacitor element 20. The width of the conductive polymer band-like agglomerates 25 formed on the first separator 23a and the second separator 23b varies depending on the size of the capacitor element 20, but is preferably 0.1 to 3 mm. By forming the conductive polymer band-like agglomerates 25 at the end of the first separator 23a and the second separator 23b over the above width, the proportion of voids in the center is relatively higher than that at the end, and the amount of electrolyte that can be retained is increased.

[0022] The electrolyte is held in the voids of the first separator 23 a and the second separator 23 b. The average void ratio S2 in the central portions of the first separator 23 a and the second separator 23 b is greater than the average void ratio S1 in the end portions, and therefore the average mass E2 per unit volume of the electrolyte impregnated in the central portions of the first separator 23 a and the second separator 23 b is greater than the average mass E1 per unit volume of the electrolyte impregnated in the end portions.

[0023] In capacitor element 20, the retention of a large amount of electrolyte in center portion 20b improves the coating repair effect of the aluminum dielectric layer in the center of the anode foil, reducing the number of coating defects and improving the initial characteristics. Furthermore, because a large amount of electrolyte is retained in center portion 20b, even if the electrolyte evaporates from the ends of capacitor element 20, it is possible to supply electrolyte from center portion 20b, thereby providing an electrolytic capacitor that maintains its initial characteristics for a long period of time.

[0024] The liquid volume ratio E2 / E1 of the mass E1 (average) per unit volume of the electrolyte solution impregnated into the ends of the first separator 23a and the second separator 23b to the mass E2 (average) per unit volume of the electrolyte solution impregnated into the central parts of the first separator 23a and the second separator 23b is preferably 1.05 or more, more preferably 1.10 or more, even more preferably 1.20 or more, and particularly preferably 1.67 or more.

[0025] FIG. 4 is an image of the surface of a separator according to an embodiment of the present invention. FIG. 5 is a surface image of an anode foil ( FIG. 5(A) ) and a cathode foil ( FIG. 5(B) ) according to an embodiment of the present invention. As shown in FIG. 4 , strip-shaped agglomerates 25 (black portions) of conductive molecules are primarily formed at the edges of separator 23, while a white portion exists in the center where strip-shaped agglomerates 25 of conductive polymer are not formed. The white portion in the center is less impregnated with conductive polymer, making it an area capable of holding more electrolyte. Strip-shaped agglomerates 25 of conductive polymer are formed at the edges to block this area, creating a dam-like central portion where electrolyte accumulates. Similarly, as shown in FIGS. 5(A) and 5(B) , anode foil 21 and cathode foil 22 are also heavily impregnated with conductive polymer black portions at the edges, while the center is less impregnated with conductive polymer.

[0026] FIG. 6 is an image of the separator surface of a comparative example. FIG. 7 is a surface image of an anode foil ( FIG. 7(A) ) and a cathode foil ( FIG. 7(B) ) of a comparative example. As shown in FIG. 6 , the separator 23 of the capacitor element of the comparative example is almost uniformly impregnated with conductive polymer. Because there is little white space (void) in the center where the conductive polymer is not impregnated and no band-like agglomerates of conductive polymer are formed at the edges, the dam effect is lost and the amount of electrolyte retained in the central void (white space) is reduced. The small amount of electrolyte retained reduces the film repair effect, making it difficult to maintain initial characteristics. Furthermore, if electrolyte evaporates from the edges of the capacitor element, there is no surplus electrolyte to replenish the evaporated electrolyte, resulting in electrode bonding at the evaporated area and causing performance degradation. Furthermore, as shown in FIGS. 7(A) and 7(B) , the anode foil 21 and the cathode foil 22 also have almost uniformly formed conductive polymer.

[0027] 8 is a cross-sectional view showing a schematic diagram of the impregnation state of the conductive polymer in an electrolytic capacitor according to a comparative example. In FIG. 8, the conductive polymer dispersion is impregnated from the bottom side of the page, and the amount of impregnated conductive polymer gradually decreases from the bottom end of the capacitor element 20 to the center and top end. When the conductive polymer is formed as shown in FIG. 8, there is no portion that can hold a large amount of electrolyte, which reduces the coating repair effect and prevents improvement in initial characteristics. Furthermore, there is no electrolyte to make up for the shortage that has evaporated from the edges, which causes a corresponding deterioration in characteristics.

[0028] A method for forming band-shaped agglomerates 25 made of conductive polymer in electrolytic capacitor 1 according to an embodiment of the present invention will be described. In order to form band-shaped agglomerates 25 made of conductive polymer mainly on end portion 20a of capacitor element 20, it is important to adjust the conductive polymer molecular weight in the conductive polymer dispersion with which capacitor element 20 is impregnated, the viscosity of the conductive polymer dispersion, and to control the impregnation conditions.

[0029] The conductive polymer dispersion impregnated into the capacitor element preferably has a conductive polymer mass ratio of 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 1.5 mass% or more. The conductive polymer dispersion impregnated into the capacitor element preferably has a conductive polymer mass ratio of 2.2 mass% or less, more preferably 2.1 mass% or less, and even more preferably 2.0 mass% or less. The viscosity of the conductive polymer dispersion at 20°C is preferably 10 mPa·s or more, and even more preferably 15 mPa·s or more. The viscosity of the conductive polymer dispersion at 20°C is preferably 30 mPa·s or less, and even more preferably 25 mPa·s or more.

[0030] The impregnation of the capacitor element with the conductive polymer dispersion is carried out by first reducing the pressure inside a box containing the conductive polymer dispersion and the capacitor element to remove the air from inside the capacitor element, and then immersing the capacitor element in the conductive polymer dispersion. The impregnation of the capacitor element with the conductive polymer is carried out under reduced pressure of -100 kPa or more and -81 kPa or less. The impregnation time varies depending on the pressure atmosphere, but it is preferable to impregnate for 500 seconds or more and 1000 seconds or less. The impregnation of the capacitor element with the conductive polymer is preferably carried out under reduced pressure of -100 kPa or more and less than -91 kPa.

[0031] The present invention will be described in more detail below with reference to examples, in which the measurement methods for the properties are as follows.

[0032] <Porosity of Separator and Amount of Electrolyte Impregnated> In each Example and Comparative Example, a capacitor element was impregnated with a conductive polymer dispersion and dried at 150°C for 60 minutes to remove the solvent. The capacitor element was then disassembled, and the separator was cut into end portions (15% from the longitudinal end) and a central portion (70% of the central portion), and the mass of each portion was measured. Similarly, a separator not impregnated with the conductive polymer was used as a reference, and cut into end portions and a central portion, and its mass was measured. The mass of the reference was subtracted from the mass of the end portions and central portion of the separator in each Example and Comparative Example to calculate the conductive polymer formed in each portion (conductive polymer per unit area). The density (1 g / cm) of the conductive polymer ３ The volume of the conductive polymer was calculated from the initial void volume of the separator, and the porosity after the formation of the conductive polymer layer was calculated from the initial void volume of the separator. The amount of the electrolyte solution was calculated assuming that the calculated void volume of the separator was impregnated with the electrolyte solution.

[0033] <Capacitance> Using a four-terminal LCR meter, the capacitance (initial capacitance) (μF) of the electrolytic capacitors of each Example and Comparative Example was measured at a frequency of 120 Hz. After that, each electrolytic capacitor was left at 125°C for 500 hours with various rated voltages applied, and the capacitance (post-test capacitance) (μF) was measured.

[0034] <Visual confirmation of band-shaped agglomerates of conductive polymer> When the electrolytic capacitors of each Example and Comparative Example were observed from the edge direction, it was confirmed whether the conductive polymer was visible. <Width of band-shaped agglomerates of conductive polymer> In each Example and Comparative Example, the capacitor element was impregnated with the conductive polymer dispersion and dried at 150°C for 60 minutes to remove the solvent. After that, the capacitor element was disassembled and the width of the band-shaped agglomerates of conductive polymer formed at the edge of the separator was measured. For each sample, measurements were taken at five locations on each side, for a total of 10 locations, and the average value was calculated.

[0035] Example 1 In Example 1, a wound electrolytic capacitor (diameter 8.0 mm × length 10.0 mm) with a rated voltage of 63 V and a rated capacitance of 33 μF was fabricated. A specific method for fabricating the electrolytic capacitor is described below. (Fabrication of a Wound Body) An anode lead terminal was connected to an aluminum anode foil on which an oxide film had been formed. A cathode lead terminal was connected to an aluminum cathode foil having a conductor layer on its end surface and subjected to a pretreatment for improving wettability. A first separator, cathode foil, second separator, and anode foil were then laminated in this order, wound around the lead terminal, and secured to the outer surface with a stop tape to fabricate a wound body. The fabricated wound body was immersed in an ammonium phosphate aqueous solution, and the anode foil was again subjected to chemical conversion treatment at 85°C while a voltage was applied to the anode foil, thereby forming a dielectric layer mainly on the end surface of the anode foil.

[0036] (Preparation of Capacitor Element) The wound body was immersed in a conductive polymer dispersion contained in a designated container in a reduced pressure (-81 kPa). The impregnation conditions for the conductive polymer dispersion were a vacuum impregnation time of 500 seconds and an atmospheric exposure time of 72 seconds. The wound body impregnated with the conductive polymer was then dried in a drying oven at 150°C for 60 minutes to impregnate the capacitor element with the conductive polymer. (Electrolyte Impregnation) The capacitor element was impregnated with the electrolyte for 30 seconds in a reduced pressure (-93 kPa). The commercially available Teica ESE2 electrolyte was used as the electrolyte. (Sealing of Capacitor Element) The impregnated capacitor element was sealed in a metal case 10 to complete the electrolytic capacitor. Subsequently, an aging treatment was performed at 85°C for 1 hour while applying the rated voltage. The initial capacitance and post-test capacitance of the fabricated electrolytic capacitor were measured. The results are shown in Table 1.

[0037] Example 2 An electrolytic capacitor was produced in the same manner as in Example 1, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and an impregnation time of 700 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 1. Example 3 An electrolytic capacitor was produced in the same manner as in Example 1, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and an impregnation time of 700 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 1.

[0038] Example 4: An electrolytic capacitor was fabricated in the same manner as in Example 1, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and the impregnation time was 900 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 1. Example 5: An electrolytic capacitor was fabricated in the same manner as in Example 1, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and the impregnation time was 900 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 1. Example 6: In Example 6, a wound-type electrolytic capacitor (diameter 12.5 mm x length 16.5 mm) with a rated voltage of 25 V and a rated capacitance of 1000 μF was fabricated under the same conditions as in Example 1, except that the other conditions were the same as in Example 1, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2.

[0039] Example 7 An electrolytic capacitor was fabricated in the same manner as in Example 6, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and the impregnation time was 700 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2. Example 8 An electrolytic capacitor was fabricated in the same manner as in Example 6, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and the impregnation time was 700 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2. Example 9 An electrolytic capacitor was fabricated in the same manner as in Example 6, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and the impregnation time was 900 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2.

[0040] Example 10 An electrolytic capacitor was prepared in the same manner as in Example 6, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and an impregnation time of 900 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2. Comparative Example 1 An electrolytic capacitor was prepared in the same manner as in Example 1, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and an impregnation time of 300 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 1. Comparative Example 2 An electrolytic capacitor was prepared in the same manner as in Example 6, except that the impregnation conditions for the conductive polymer dispersion were a reduced pressure atmosphere (-93 kPa) and an impregnation time of 300 seconds, and the initial capacitance and post-test capacitance were measured. The results are shown in Table 2.

[0041]

[0042]

[0043] It was confirmed that Comparative Example 1 had a lower initial capacity and a lower capacity retention rate after 500 hours of storage compared to Examples 1 to 5. Comparative Example 2 had lower initial characteristics and a lower capacity retention rate after 500 hours of storage compared to Examples 6 to 10. It is believed that the electrolytic capacitors of Comparative Examples 1 and 2 had a low amount of electrolyte retained in the center of the separator, resulting in insufficient film repair and a lower initial capacity. Furthermore, during testing in a 125°C environment, electrolyte evaporated from the capacitor edges, but there was no electrolyte to compensate for this, reducing the contact area with the electrode foil required for capacity development, which is thought to have resulted in a lower capacity retention rate. Furthermore, the products of each Example and Comparative Example were disassembled after testing to confirm the amount of electrolyte retained by the separator. In Examples 1 to 10, the amount of electrolyte in the center decreased, while the amount at the edges decreased only slightly. This is due to evaporation of the electrolyte from the edges, and in Examples 1 to 10, the amount of electrolyte in the center decreased easily due to the supply of electrolyte from the center, while the amount at the edges was maintained. In contrast, the amount of electrolyte at the ends was significantly reduced in Comparative Examples 1 and 2. This is because in Comparative Examples 1 and 2, no electrolyte was supplied, and therefore evaporation of the electrolyte from the ends was evident.

[0044] The electrolytic capacitor according to the present embodiment has excellent initial characteristics and can maintain the initial characteristics even after long-term use, and therefore can be suitably used as an electrolytic capacitor for vehicles.

[0045] REFERENCE SIGNS LIST 1 electrolytic capacitor 10 metal case 11 opening 12 horizontal drawing groove 20 capacitor element 21 anode foil 21a porous portion 22 cathode foil 22a porous portion 23a first separator 23b second separator 24a anode lead terminal 24b cathode lead terminal 25 strip-shaped agglomerate made of conductive polymer 30 sealing body 31a, 31b lead insertion hole

Claims

1. An electrolytic capacitor comprising: a capacitor element having an anode foil having an anodized coating on its surface, a cathode foil, and a separator inserted between the anode foil and the cathode foil; a conductive polymer impregnated in the capacitor element; and an electrolyte impregnated in the capacitor element, wherein a mass E2 per unit volume of the electrolyte impregnated in the center of the separator is greater than a mass E1 per unit volume of the electrolyte impregnated in the end portion of the separator.

2. The electrolytic capacitor according to claim 1, wherein a band-shaped agglomerate of the conductive polymer is formed at an end of the capacitor element.

3. The electrolytic capacitor according to claim 1 or 2, wherein the width of the band-like agglomerate is 0.1 to 3.0 mm.

4. The electrolytic capacitor according to claim 1 or 2, characterized in that the separator and the anode foil, and / or the separator and the cathode foil are bonded together with the conductive polymer.

5. The electrolytic capacitor according to claim 1 or 2, characterized in that E2 / E1 is 1.05 or more.

6. The electrolytic capacitor according to claim 1 or 2, characterized in that E2 / E1 is 1.10 or more.

7. The electrolytic capacitor according to claim 1 or 2, characterized in that E2 / E1 is 1.20 or more.

8. The electrolytic capacitor according to claim 1 or 2, characterized in that E2 / E1 is 1.67 or more.

9. The electrolytic capacitor according to claim 1 or 2, wherein the capacitor element is of a wound type.

10. The electrolytic capacitor according to claim 1 or 2, wherein the capacitor element is a laminated type.

11. An electrolytic capacitor comprising: a capacitor element having an anode foil having an anodized coating on its surface, a cathode foil, and a separator inserted between the anode foil and the cathode foil; a conductive polymer impregnated in the capacitor element; and an electrolyte impregnated in the capacitor element, wherein a proportion S2 of voids in the center of the separator is greater than a proportion S1 of voids at the ends of the separator.

12. The electrolytic capacitor according to claim 11, wherein the separator has an increased ratio of voids from the ends toward the center.

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