Electrolytic capacitor

Abstract

An electrolytic capacitor 1 comprises: a body case 2 that is provided with an opening section; a capacitor element 10 that is accommodated inside the body case 2; and a sealing body 5 that seals the opening section in the body case 2. The capacitor element 10 is such that a positive electrode foil 11, which has an oxide film 16, and negative electrode foil 12, which faces the positive electrode foil 11 across a separator 13, are wound on a surface thereof, and has an electrolyte layer 19, which includes a solid electrolyte 17 containing a conductive polymer and a liquid electrolyte 18 covering at least a portion of the solid electrolyte 17, between the positive electrode foil 11 and the negative electrode foil 12. The liquid electrolyte 18 contains at least an unsaturated fatty acid salt. The unsaturated fatty acid salt alone or a mixture that is the unsaturated fatty acid salt with an unsaturated fatty acid added thereto accounts for 50 wt% or greater of the liquid electrolyte 17.

Description

electrolytic capacitor

[0001] The present invention relates to electrolytic capacitors having a solid electrolyte and a liquid electrolyte.

[0002] A conventional electrolytic capacitor is disclosed in Patent Document 1. This electrolytic capacitor has a capacitor element in which an anode foil with an oxide film formed thereon and an opposing cathode foil are wound together with a separator interposed therebetween. The capacitor element is housed in an outer case, which is sealed with a sealing member. Lead terminals are connected to the anode foil and the cathode foil, respectively, and the lead terminals penetrate the sealing member and extend to the outside of the outer case. The capacitor element contains a solid electrolyte layer made of a conductive polymer and is impregnated with an electrolyte solution.

[0003] The solute of the electrolyte contains 3 to 30 wt % of at least one selected from the group consisting of aliphatic hydroxy acids and their salts. This reduces the equivalent series resistance (ESR) of the electrolytic capacitor in high-temperature environments. In addition, the aliphatic hydroxy acid itself has the ability to prevent oxidation and degradation, thereby suppressing oxidation of the conductive polymer.

[0004] JP 2018-198248 A (pages 3 to 9, Figure 1)

[0005] However, with the conventional electrolytic capacitors described above, during extended use (especially at high temperatures), the solvent in the gasified electrolyte evaporates from the lead terminals or the gap between the outer case and the sealing body. This reduces the amount of electrolyte in the capacitor element, exposing the conductive polymer to the air inside the outer case. When the conductive polymer is oxidized by oxygen in the air in a high-temperature environment, it loses its conductivity and its electrical conductivity decreases. This increases the ESR of the electrolytic capacitor, preventing the electrolytic capacitor from having a long life.

[0006] An object of the present invention is to extend the life of an electrolytic capacitor.

[0007] In order to achieve the above object, the present invention provides an electrolytic capacitor comprising a main case having an opening, a capacitor element housed in the main case, and a sealing member that seals the opening of the main case, wherein the capacitor element comprises an anode foil having an oxide film on its surface and a cathode foil facing the anode foil with a separator interposed therebetween, and an electrolyte layer is disposed between the anode foil and the cathode foil, the electrolyte layer containing a solid electrolyte containing a conductive polymer and a liquid electrolyte that covers at least a portion of the solid electrolyte, and the liquid electrolyte contains at least an unsaturated fatty acid salt, and the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte.

[0008] In the electrolytic capacitor of the present invention having the above-mentioned structure, the unsaturated fatty acid salt is in a liquid state at 20° C. or higher.

[0009] Furthermore, in the electrolytic capacitor of the present invention having the above configuration, the liquid electrolyte contains the mixture, and the unsaturated fatty acid is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenedioic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid.

[0010] Furthermore, in the electrolytic capacitor having the above configuration, the present invention is characterized in that the base of the unsaturated fatty acid salt is at least one selected from the group consisting of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, and derivatives thereof.

[0011] Furthermore, in the electrolytic capacitor of the present invention having the above-described configuration, the liquid electrolyte contains a fat-soluble antioxidant.

[0012] Furthermore, in the electrolytic capacitor of the present invention having the above-described structure, the fat-soluble antioxidant is contained in an amount of 30% by weight or less of the liquid electrolyte.

[0013] According to the present invention, the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and the unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte. This prevents evaporation of the liquid electrolyte for a long period of time, and inhibits oxidative degradation of the conductive polymer. This prevents an increase in the ESR of the electrolytic capacitor, thereby extending the life of the electrolytic capacitor.

[0014] 1 is a longitudinal sectional view showing an electrolytic capacitor according to an embodiment of the present invention; 2 is a perspective view showing a capacitor element of an electrolytic capacitor according to an embodiment of the present invention; 3 is a partially enlarged sectional view showing a capacitor element of an electrolytic capacitor according to an embodiment of the present invention; 4 is an enlarged view showing the ESR change over time in the examples and comparative examples of the present invention; and 5 is an enlarged view showing the ESR range of 10 to 1000 mΩ in FIG.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a longitudinal cross-sectional view of an electrolytic capacitor 1 according to one embodiment. The electrolytic capacitor 1 includes a main case 2, a capacitor element 10, and a sealing member 5.

[0016] The main body case 2 is made of a metal such as aluminum or resin and has a cylindrical shape with a circular cross section and a closed bottom, with one axial end closed by a blocking surface 2a and the other end having an opening 2b. From the viewpoints of workability and sealing performance, it is preferable to form the main body case 2 from aluminum.

[0017] Sealing body 5 is formed into a disk shape from a molded insulating elastic body such as butyl rubber or ethylene propylene rubber, and has a pair of through holes 5a. Lead terminals 7 and 8 of capacitor element 10 are inserted into the pair of through holes 5a by press-fitting. As a result, lead terminals 7 and 8 are pulled out of the sealing body and connected to a circuit board (not shown) by soldering or the like.

[0018] Capacitor element 10 is housed in main case 2, and sealing body 5 is placed in opening 2b. With sealing body 5 placed in opening 2b of main case 2, main case 2 is subjected to a drawing process that presses the outer peripheral surface. As a result, a drawn portion 2c that protrudes toward the inner surface of main case 2 is formed. The drawn portion 2c compresses the outer peripheral surface of sealing body 5 in the inward direction, so that it adheres closely to the inner peripheral surface of main case 2. Furthermore, compression of sealing body 5 causes the inner surface of through hole 5a to adhere closely to lead terminals 7 and 8. As a result, opening 2b of main case 2 is sealed by sealing body 5.

[0019] The end of the main body case 2 on the opening 2b side is bent to form a bent portion 2d toward the sealing body 5. The bent portion 2d and the drawn portion 2c prevent the sealing body 5 from slipping out of the main body case 2.

[0020] To improve the ease of mounting on a circuit board, a well-known base plate may be provided. The lead terminals 7 and 8 pass through the base plate and are bent radially, and the bent portions can be used as soldering points for the circuit board.

[0021] 2 shows a perspective view of capacitor element 10. Capacitor element 10 has anode foil 11, cathode foil 12, and separator 13, which are formed in the shape of long strips. Capacitor element 10 is formed by winding a pair of electrode foils, consisting of anode foil 11 and cathode foil 12, which face each other with separator 13 interposed therebetween, into a substantially cylindrical shape. The ends of anode foil 11 or separator 13 are fixed with adhesive tape 14.

[0022] The width of separator 13 in the short side direction (axial direction) is formed to be larger than the width of anode foil 11 and cathode foil 12. As a result, separator 13 protrudes toward closed surface 2 a and opening 2 b relative to anode foil 11 and cathode foil 12, thereby preventing short-circuiting between anode foil 11 and cathode foil 12.

[0023] The anode foil 11 is made of a valve metal such as aluminum, tantalum, niobium, or titanium, and its surface is roughened by etching. An oxide film 16 (see FIG. 3) is formed on the anode foil 11 by applying a voltage in a chemical conversion solution.

[0024] The cathode foil 12 is made of a metal such as aluminum, and its surface is roughened by etching. A conductive coating layer of carbon, titanium, or the like may be formed on the surface of the anode foil 11. Alternatively, a natural oxide film or a chemical oxide film formed by applying a voltage in a chemical solution may be formed on the surface of the cathode foil 12.

[0025] The separator 13 is made of paper made from natural cellulose fibers or nonwoven fabric made from chemical fibers such as rayon, polyethylene terephthalate, or polyamide. The separator 13 is porous and can retain an electrolyte in the gaps between the fibers inside. The thickness of the separator 13 is preferably thicker than the size of protrusions such as burrs on the anode foil 11 and the cathode foil 12, and is formed to a thickness of, for example, 20 μm to 60 μm.

[0026] 3 is an enlarged cross-sectional view showing the anode foil 11 of the capacitor element 10. An electrolyte layer 19 containing a solid electrolyte 17 and a liquid electrolyte 18 is provided between the anode foil 11 and the cathode foil 12. The liquid electrolyte 18 covers at least a portion of the solid electrolyte 17. The electrolyte layer 19 is disposed on the surface of the oxide film 16 of the anode foil 11, on the surface of the cathode foil 12, and on the fiber surface of the separator 13. The solid electrolyte 17 of the electrolyte layer 19 held in the separator 13 is formed in the form of a layer on the surface of the fibers, and the liquid electrolyte 18 is held in the voids between the fibers or within the fibers.

[0027] The solid electrolyte 17 is made of a conductive polymer doped with a dopant. Examples of the conductive polymer that can be used include polypyrrole, polythiophene, polyaniline, and derivatives thereof. Examples of the dopant that can be used include p-toluenesulfonic acid and polystyrenesulfonic acid. The conductive polymer can be formed by a polymerization reaction within the capacitor element 10. The conductive polymer may be retained within the capacitor element 10 by impregnating the capacitor element 10 with a dispersion in which a conductive polymer that has been polymerized in advance is dispersed in water and then drying the dispersion.

[0028] It is preferable to use polyethylenedioxythiophene (hereinafter, PEDOT) as the polythiophene derivative and polystyrene sulfonic acid (hereinafter, PSS) as the dopant, which allows the solid electrolyte 17 to be formed from a conductive polymer dispersion that has excellent conductivity and stability.

[0029] Furthermore, when a sulfonic acid group is provided in the molecule of a polythiophene derivative, the polythiophene derivative can be used as a self-doping conductive polymer that is soluble in solvents such as water. Like the conductive polymer dispersion, the self-doping conductive polymer can be retained within the capacitor element 10 by impregnating the capacitor element 10 and then drying. Such a self-doping conductive polymer does not redissolve in the liquid electrolyte 18 containing the unsaturated fatty acid salt described below. Furthermore, the liquid electrolyte 18 suppresses moisture absorption of the self-doping conductive polymer, thereby improving the moisture resistance of the electrolytic capacitor 1.

[0030] Liquid electrolyte 18 contains at least an unsaturated fatty acid salt and covers at least a portion of solid electrolyte 17. The unsaturated fatty acid salt is formed by neutralizing at least a portion of the unsaturated fatty acid contained in capacitor element 10 with a base. As a result, liquid electrolyte 18 contains an unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid. In this case, liquid electrolyte 18 contains 50 mass% or more of the unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid.

[0031] Because unsaturated fatty acid salts react more readily with oxygen than conductive polymers and absorb surrounding oxygen, it is possible to maintain a state in which there is little oxygen around the conductive polymer covered with liquid electrolyte 18. Furthermore, unsaturated fatty acid salts evaporate much less than solvents used in ordinary electrolyte solutions. As a result, oxidative degradation of solid electrolyte 17, which is made of conductive polymer covered with liquid electrolyte 18, can be suppressed for a long period of time.

[0032] Furthermore, the unsaturated fatty acid salt is less likely to permeate into sealing member 5 than the unsaturated fatty acid, and can be retained for a long period of time within capacitor element 10. Furthermore, the inclusion of the unsaturated fatty acid salt in liquid electrolyte 18 can improve the compatibility between the unneutralized unsaturated fatty acid and the other components of liquid electrolyte 18, which will be described later.

[0033] Furthermore, when the liquid electrolyte 18 contains a solvent component, the evaporation of the solvent component can be suppressed by including 50% by weight or more of an unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid. In addition, even if the solvent component evaporates, the surface of the conductive polymer can be maintained in a state where it is covered with unsaturated fatty acid, resulting in a long-life electrolytic capacitor 1. Furthermore, when the liquid electrolyte 18 contains 80% by weight or more of an unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid, the electrolytic capacitor 1 can have an even longer life.

[0034] Unsaturated fatty acids are aliphatic compounds containing a carboxy group and at least one double bond between two carbon atoms in the molecule, such as palmitoleic acid, oleic acid, erucic acid, linoleic acid, eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenedioic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. Many of these unsaturated fatty acids have a boiling point of over 250° C. at normal pressure and evaporate very little, which allows the electrolytic capacitor 1 to have a long life.

[0035] Among unsaturated fatty acids, compounds with multiple double bonds between two carbon atoms in the molecule can react with more oxygen and stabilize the ESR characteristics for a long period of time, which is preferable because it is highly effective in extending the life of the electrolytic capacitor 1.

[0036] In particular, unsaturated fatty acids containing many double bonds in the molecule and unsaturated fatty acids having a branched structure with side chains attached to the main chain of the molecule often exist as liquids from room temperature (20°C) to their respective boiling points or decomposition points, and their salts, i.e., unsaturated fatty acid salts, are also preferred because they tend to become liquid at room temperature (20°C) or higher.

[0037] Examples of such unsaturated fatty acids include palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenedioic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid.

[0038] Furthermore, compounds having a 1,4-pentadiene structure in the molecule are more preferred because the hydrogen of the methylene group sandwiched between two double bonds is easily abstracted and easily reacts with oxygen. Examples of such compounds include linoleic acid, eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, adrenic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, and docosahexaenoic acid.

[0039] Because unsaturated fatty acids are weakly acidic, a weakly basic organic amine is used as the base for the unsaturated fatty acid salt. Unsaturated fatty acid salts neutralized with an unsaturated fatty acid and a weak base have low volatility like ionic liquids and are capable of repairing the oxide film 16. Furthermore, because a base with a weaker basicity than that used in general ionic liquids is used, dedoping of the conductive polymer can be suppressed. This allows the properties to be maintained over a long period of time, making it possible to use the liquid electrolyte 18 as a high-voltage, low-volatility liquid electrolyte. To suppress dedoping of the conductive polymer, the base preferably has a pKb of 4 or higher, and more preferably a pKb of 8 or higher.

[0040] In addition, fat-soluble organic amines that are highly compatible with unsaturated fatty acids are preferred because they easily form salts with unsaturated fatty acids. Specifically, trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2′-bipyridyl, acetanilide, acetamide, caffeine, or derivatives thereof can be used.

[0041] Furthermore, since unsaturated fatty acids are weakly acidic, it is preferable that the amount of the base substance is small relative to the unsaturated fatty acid, and more preferably, it is half or less.

[0042] Compared to the state of unsaturated fatty acids, unsaturated fatty acid salts tend to exist in a highly polar state as unsaturated fatty acid ions. Therefore, trace amounts of moisture, etc., in the capacitor element 10 can be used to repair defects in the oxide film 16 of the anode foil 11, thereby reducing leakage current over a long period of time. This reduces deterioration in the characteristics of the electrolytic capacitor 1, resulting in an electrolytic capacitor 1 with a long life.

[0043] The liquid electrolyte 18 may contain, as additives, a solvent for adjusting viscosity, an electrolytic solution for facilitating repair of defects in the oxide film 16, a gas absorbent for absorbing hydrogen gas generated by the repair action, an antioxidant for suppressing oxidative degradation of the conductive polymer, a voltage resistance improver for acting on the surface of the oxide film 16 to improve the voltage resistance, a dissolution aid for making the unsaturated fatty acid salt and the additive compatible, and the like.

[0044] Adding a solvent to the liquid electrolyte 18 can reduce the viscosity of the liquid electrolyte 18 and improve its impregnation. Using a high-boiling polar solvent as the solvent can enhance the repairability of the oxide film 16, improve the withstand voltage, and reduce leakage current. In addition, the solvent penetrates the conductive polymer layer to improve electrical conductivity, thereby reducing the ESR of the electrolytic capacitor 1. Examples of such solvents that can be used include high-boiling polar solvents such as γ-butyrolactone, sulfolane, ethylene glycol, and diethylene glycol.

[0045] The solvent does not need to be completely compatible with the unsaturated fatty acid salt alone or the mixture of the unsaturated fatty acid salt and the unsaturated fatty acid. The solvent can be used by covering at least a portion of the solid electrolyte 17 with the unsaturated fatty acid salt alone or the mixture of the unsaturated fatty acid salt and the unsaturated fatty acid.

[0046] It is more preferable that the liquid electrolyte 18 contains an electrolytic solution in which a solute is dissolved in a solvent and ionically dissociated. This further enhances the repairability of the oxide film 16, and further reduces the leakage current of the electrolytic capacitor 1.

[0047] The antioxidant added to the liquid electrolyte 18 may be a water-soluble antioxidant and / or a fat-soluble antioxidant.

[0048] The water-soluble antioxidant is easily soluble in high-boiling polar solvents and is thought to directly suppress oxidation of the conductive polymer. However, if the amount of the water-soluble antioxidant added is too large, it is likely to have an adverse effect, such as causing significant changes in characteristics such as voltage resistance and durability. For this reason, the amount of the water-soluble antioxidant is preferably 3 wt % or less of the liquid electrolyte 18, and more preferably 2 wt % or less.

[0049] In order to maximize the antioxidant effect of the water-soluble antioxidant, the water-soluble antioxidant is preferably contained in an amount of 0.1% by weight or more of the liquid electrolyte 18. Examples of the water-soluble antioxidant include catechol, hydroquinone, resorcinol, pyrogallol, protocatechuic acid, and gallic acid.

[0050] The fat-soluble antioxidant contained in the liquid electrolyte 18 is easily soluble in the unsaturated fatty acid salt alone or in a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid. The fat-soluble antioxidant can receive free radicals generated by the reaction of the unsaturated fatty acid salt or the unsaturated fatty acid with oxygen or by thermal cleavage, and can suppress or eliminate the activity of the free radicals.

[0051] This suppresses oxidation degradation of the unsaturated fatty acid and the conductive polymer due to free radicals. This dramatically improves the anti-oxidation effect of the conductive polymer through both the absorption of oxygen gas around the conductive polymer and the suppression of oxidation. This reduces the deterioration of the characteristics of the electrolytic capacitor 1 over a long period of time.

[0052] Furthermore, even if the amount of the fat-soluble antioxidant is increased, it does not inhibit the repair of defects in the oxide film 16 of the anode foil 11. This allows for greater freedom in designing the composition of the liquid electrolyte 18. Compared to water-soluble antioxidants, fat-soluble antioxidants have less impact on changes in voltage resistance and durability, and the amount added to the liquid electrolyte 18 can be 30 wt % or less. To obtain the oxidation-inhibiting effect of the fat-soluble antioxidant, it is preferable for the liquid electrolyte 18 to contain the fat-soluble antioxidant in an amount of 1 wt % or more.

[0053] Furthermore, a portion of the fat-soluble antioxidant permeates into the sealing member 5, thereby suppressing deterioration of the sealing member 5. Fat-soluble antioxidants are highly compatible with unsaturated fatty acid salts. Therefore, the balance between the fat-soluble antioxidant in the liquid electrolyte 18 and the fat-soluble antioxidant that permeates into the sealing member 5 can be adjusted by adjusting the amount of unsaturated fatty acid salt in the liquid electrolyte 18.

[0054] Furthermore, because the unsaturated fatty acid salt or a mixture of unsaturated fatty acid salt and unsaturated fatty acid is 50% by weight or more in liquid electrolyte 18, an excessive amount of fat-soluble antioxidant is not supplied to permeate sealing member 5. This makes it possible to suppress deterioration of sealing member 5 over the long term, thereby extending the life of electrolytic capacitor 1. It is also believed that some of the unsaturated fatty acid in liquid electrolyte 18 also permeates sealing member 5, thereby suppressing deterioration of sealing member 5.

[0055] Examples of fat-soluble antioxidants include retinol, β-carotene, α-carotene, β-cryptoxanthin, astaxanthin, tocopherols (α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol), tocotrienols (α-tocotrienol, β-tocotrienol, γ-tocotrienol, δ-tocotrienol), etc. From the viewpoint of suppressing deterioration of the sealing body 5, tocopherol is particularly preferred because of its excellent permeability and antioxidant effect.

[0056] In this embodiment, the unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte 18. This prevents evaporation of the liquid electrolyte 18 for a long period of time, and inhibits oxidation degradation of the solid electrolyte 17 made of a conductive polymer. This prevents an increase in the ESR of the electrolytic capacitor 1, thereby extending the life of the electrolytic capacitor 1.

[0057] Furthermore, since the unsaturated fatty acid salt contained in the liquid electrolyte 18 is liquid at temperatures above 20° C., the liquid electrolyte 18 can be easily realized.

[0058] The unsaturated fatty acid contained in the liquid electrolyte 18 is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenedioic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. This makes it possible to easily obtain a liquid unsaturated fatty acid salt at temperatures above 20°C.

[0059] Furthermore, at least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, or a derivative thereof is used as the base of the unsaturated fatty acid salt contained in the liquid electrolyte 18. This makes it possible to easily realize a liquid electrolyte 18 that has low transpiration properties and can suppress dedoping of the conductive polymer.

[0060] Furthermore, if the liquid electrolyte 18 contains a fat-soluble antioxidant, it is possible to suppress oxidative degradation of the unsaturated fatty acid and the conductive polymer due to free radicals, thereby minimizing deterioration of the characteristics of the electrolytic capacitor 1 for a longer period of time.

[0061] Furthermore, if the fat-soluble antioxidant is contained in an amount of 30% by weight or less of the liquid electrolyte 18, oxidative degradation of the unsaturated fatty acid and the conductive polymer can be more reliably suppressed.

[0062] The following describes examples formed to evaluate the electrolytic capacitor 1 of this embodiment. The compositions of the liquid electrolytes 18 in Examples 1 to 13 and Comparative Examples 1 and 2 are shown in Table 1.

[0063]

[0064] In the electrolytic capacitor 1 of Example 1, first, lead terminals 7 and 8 were connected to anode foil 11 and cathode foil 12, each having an oxide film 16 formed on its surface. Next, both electrode foils were wound with separator 13 interposed therebetween to form capacitor element 10 having an element shape of φ6.3 mm x L7.7 mm. Then, this capacitor element 10 was immersed in an ammonium adipate aqueous solution for 30 minutes, and a voltage was applied to perform repair formation.

[0065] Next, the capacitor element 10 was immersed in a conductive polymer compound dispersion in which a complex of PEDOT and PSS was dispersed in water, and then the capacitor element 10 was pulled out and dried at about 125°C to form a layer of solid electrolyte 17 made of a conductive polymer.

[0066] Next, the capacitor element 10 was impregnated with a liquid mixture of 76% by weight of oleic acid and 24% by weight of 1.10-phenanthroline. Oleic acid is an unsaturated fatty acid, and 1.10-phenanthroline is a weak base. This formed a liquid electrolyte 18 containing an unsaturated fatty acid salt. The boiling point of oleic acid is 203-205°C (5 mmHg).

[0067] Then, capacitor element 10 was inserted into bottomed cylindrical main case 2, and sealing body 5 was attached and crimped. After that, aging was performed by applying a voltage to form electrolytic capacitor 1. This electrolytic capacitor 1 had a rated voltage of 25 WV and a rated capacity of 100 μF.

[0068] In the electrolytic capacitor 1 of Example 2, the capacitor element 10 was impregnated with a liquid mixture of 74% by weight of oleic acid and 26% by weight of caffeine when forming the liquid electrolyte 18. The oleic acid is an unsaturated fatty acid, and the caffeine is a weak base. Other than that, the electrolytic capacitor 1 was the same as Example 1.

[0069] In the electrolytic capacitor 1 of Example 3, when the liquid electrolyte 18 was formed, the capacitor element 10 was impregnated with a liquid mixture of 76% by weight of linoleic acid and 24% by weight of 1.10-phenanthroline. Linoleic acid is an unsaturated fatty acid, and 1.10-phenanthroline is a weak base. The boiling point of linoleic acid is 229 to 230°C (16 mmHg). Other than that, the electrolytic capacitor was the same as Example 1.

[0070] In the electrolytic capacitor 1 of Example 4, the capacitor element 10 was impregnated with a liquid mixture of 74% by weight of linoleic acid and 26% by weight of caffeine when forming the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, and caffeine is a weak base. Other than that, the electrolytic capacitor 1 of Example 4 was the same as Example 1.

[0071] In the electrolytic capacitor 1 of Example 5, the capacitor element 10 was impregnated with a liquid mixture of 77% by weight of arachidonic acid and 23% by weight of 1.10-phenanthroline when the liquid electrolyte 18 was formed. Arachidonic acid is an unsaturated fatty acid, and 1.10-phenanthroline is a weak base. The boiling point of arachidonic acid is 169 to 171°C (0.15 mmHg). Other than that, the electrolytic capacitor was the same as Example 1.

[0072] In the electrolytic capacitor 1 of Example 6, a liquid mixture of 75% by weight of arachidonic acid and 25% by weight of caffeine was impregnated into the capacitor element 10 when the liquid electrolyte 18 was formed. Arachidonic acid is an unsaturated fatty acid, and caffeine is a weak base. Other than that, the electrolytic capacitor 1 of Example 6 was the same as Example 1.

[0073] For the electrolytic capacitor 1 of Example 7, when the liquid electrolyte 18 was formed, the capacitor element 10 was impregnated with a liquid mixture of 42.7 wt % linoleic acid, 14.5 wt % 1.10-phenanthroline, and 42.7 wt % diethylene glycol. Linoleic acid is an unsaturated fatty acid, 1.10-phenanthroline is a weak base, and ethylene glycol is a high-boiling-point polar solvent. The dimensions of the electrolytic capacitor 1 are φ6.3 mm x L7.7 mm, the rated voltage is 35 V, and the rated capacity is 47 μF. Other than that, it was the same as Example 1.

[0074] In the electrolytic capacitor 1 of Example 8, the capacitor element 10 was impregnated with a liquid mixture of 43.1 wt % linoleic acid, 13.8 wt % caffeine, and 43.1 wt % diethylene glycol when forming the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, caffeine is a weak base, and ethylene glycol is a high-boiling-point polar solvent. Other than that, the electrolytic capacitor 1 of Example 8 was the same as Example 7.

[0075] In the electrolytic capacitor 1 of Example 9, when forming the liquid electrolyte 18, the capacitor element 10 was impregnated with a liquid mixture of 50% by weight of oleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borodisalicylic acid, and 1% by weight of trimethylamine. Oleic acid is the unsaturated fatty acid, trimethylamine is the weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are the solvent of the electrolyte, and borodisalicylic acid is the solute of the electrolyte. Other than that, the electrolytic capacitor was the same as Example 1.

[0076] Since the electrolyte and the unsaturated fatty acid were not completely compatible with each other, the capacitor element 10 was impregnated with the electrolyte and then further impregnated with the unsaturated fatty acid to produce the electrolytic capacitor 1 .

[0077] For electrolytic capacitor 1 of Example 10, when liquid electrolyte 18 was formed, capacitor element 10 was impregnated with a liquid mixture of 50% by weight of linoleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borodisalicylic acid, and 1% by weight of trimethylamine. Linoleic acid is the unsaturated fatty acid, trimethylamine is the weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are the solvent of the electrolyte, and borodisalicylic acid is the solute of the electrolyte. Other than that, the electrolytic capacitor was the same as Example 9.

[0078] In the electrolytic capacitor 1 of Example 11, when the liquid electrolyte 18 was formed, the capacitor element 10 was impregnated with a liquid mixture of 25% by weight of oleic acid, 25% by weight of linoleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borodisalicylic acid, and 1% by weight of trimethylamine. Oleic acid and linoleic acid are unsaturated fatty acids, trimethylamine is a weak base and a solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, and borodisalicylic acid is a solute of the electrolyte. Other than that, the electrolytic capacitor 1 was the same as Example 9.

[0079] For the electrolytic capacitor 1 of Example 12, the liquid electrolyte 18 was formed by impregnating the capacitor element 10 with a liquid mixture of 50% by weight of oleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borodisalicylic acid, 1% by weight of trimethylamine, and 4% by weight of d-α-tocopherol. Oleic acid is an unsaturated fatty acid, trimethylamine is a weak base and a solute for the electrolyte, γ-butyrolactone and sulfolane are solvents for the electrolyte, borodisalicylic acid is a solute for the electrolyte, and d-α-tocopherol is a fat-soluble antioxidant. The boiling point of d-α-tocopherol is 220°C (0.1 mmHg). Other than that, the process was the same as in Example 9.

[0080] In the electrolytic capacitor 1 of Example 13, when the liquid electrolyte 18 was formed, the capacitor element 10 was impregnated with a liquid mixture of 50% by weight of linoleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borodisalicylic acid, 1% by weight of trimethylamine, and 4% by weight of D-α-tocopherol.

[0081] Linoleic acid is the unsaturated fatty acid, trimethylamine is the weak base and the solute of the electrolyte, γ-butyrolactone and sulfolane are the solvent of the electrolyte, borodisalicylic acid is the solute of the electrolyte, and D-α-tocopherol is the fat-soluble antioxidant.

[0082] [Comparative Example 1] A comparative example was also prepared for comparison. In Comparative Example 1, when forming the liquid electrolyte 18, the capacitor element 10 was impregnated with a liquid mixture of 76% by weight of isostearic acid and 24% by weight of 1.10-phenanthroline. 1.10-phenanthroline is a weak base, while isostearic acid is a saturated fatty acid. The boiling point of isostearic acid is 183°C (5 mmHg). Other than that, the comparative example was the same as Example 1.

[0083] In Comparative Example 2, the liquid electrolyte 18 was formed by impregnating the capacitor element 10 with an electrolyte solution containing 36 wt % γ-butyrolactone, 54 wt % sulfolane, 8 wt % borodisalicylic acid, and 2 wt % trimethylamine. γ-butyrolactone and sulfolane were the solvents of the electrolyte solution, and borodisalicylic acid and trimethylamine were the solutes of the electrolyte solution. The rest of the procedure was the same as in Example 1.

[0084] The above examples and comparative examples were subjected to a durability test in which the rated voltage was applied at 150°C for 10,000 hours, and the changes in ESR over time are shown in Table 2, Figures 4 and 5. The vertical axis of Figures 4 and 5 represents ESR (unit: mΩ), and the horizontal axis represents time (unit: Hrs). For ease of understanding, Figure 5 shows an enlarged view of the ESR range of 10 to 1,000 mΩ in Figure 4.

[0085]

[0086] 4 and 5, Examples 1 to 13, which contain 50% by weight or more of an unsaturated fatty acid salt or a mixture of an unsaturated fatty acid and an unsaturated fatty acid salt in the liquid electrolyte 18, maintain a low ESR in the durability test. This allows the ESR characteristics to be kept stable for a long period of time even in a high-temperature environment of 150°C.

[0087] Furthermore, even when a high-boiling polar solvent is added (Examples 7 and 8) or when an electrolytic solution is included (Examples 9 to 13), the ESR characteristics can be maintained stable for a long period of time.

[0088] Furthermore, it was confirmed that liquid electrolyte 18 remained in capacitor element 10 of each of electrolytic capacitors 1 of Examples 1 to 13 after the durability test. Therefore, liquid electrolyte 18 covers conductive polymer solid electrolyte 17, thereby suppressing deterioration of the conductive polymer and providing electrolytic capacitor 1 with a long life.

[0089] In contrast, Comparative Examples 1 and 2, which do not contain unsaturated fatty acids, show a significant deterioration in ESR characteristics after 3,000 to 4,000 hours in a high temperature environment of 150°C.

[0090] The present invention can be used in automobiles, electronic devices, etc., in which electrolytic capacitors are mounted in circuits.

[0091] REFERENCE SIGNS LIST 1 electrolytic capacitor 2 main body case 2a closed surface 2b opening 2c drawn portion 2d folded portion 5 sealing body 5a through hole 6 separator 7, 8 lead terminal 10 capacitor element 11 anode foil 12 cathode foil 13 separator 14 adhesive tape 16 oxide film 17 solid electrolyte 18 liquid electrolyte 19 electrolyte layer

Claims

1. An electrolytic capacitor comprising a main case having an opening, a capacitor element housed within the main case, and a sealing body which seals the opening of the main case, wherein the capacitor element is formed by winding an anode foil having an oxide film on its surface and a cathode foil facing the anode foil with a separator interposed therebetween, and an electrolyte layer is provided between the anode foil and the cathode foil, the electrolyte layer including a solid electrolyte containing a conductive polymer and a liquid electrolyte which covers at least a part of the solid electrolyte, the liquid electrolyte including at least an unsaturated fatty acid salt, and the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte.

2. The electrolytic capacitor according to claim 1, wherein the unsaturated fatty acid salt is in a liquid state at a temperature of 20° C. or higher.

3. The electrolytic capacitor according to claim 2, wherein the liquid electrolyte contains the mixture, and the unsaturated fatty acid is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenedioic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid.

4. The electrolytic capacitor according to claim 2, characterized in that the base of the unsaturated fatty acid salt is at least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, and derivatives thereof.

5. The electrolytic capacitor according to any one of claims 1 to 4, characterized in that the liquid electrolyte contains a fat-soluble antioxidant.

6. The electrolytic capacitor according to claim 5, wherein the fat-soluble antioxidant is contained in an amount of 30% by weight or less of the liquid electrolyte.

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