Electrolytic capacitors

Abstract

An electrolytic capacitor (1) comprising a main body shell (2), a capacitor element (10), and a sealing body (5), wherein the main body shell (2) has an opening, the capacitor element (10) is housed within the main body shell (2), the sealing body (5) seals the opening of the main body shell (2), the capacitor element (10) is wound with an anode foil (11) having an oxide coating (16) on its surface and a cathode foil (12) opposite to the anode foil (11) separated by a spacer (13), and an electrolyte layer (19) is provided between the anode foil (11) and the cathode foil (12), the electrolyte layer comprising: a solid electrolyte (17) comprising a conductive polymer; and a liquid electrolyte (18) covering at least a portion of the solid electrolyte (17), the liquid electrolyte (18) comprising at least an unsaturated fatty acid salt, wherein the unsaturated fatty acid salt monomer or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt comprises more than 50% by weight of the liquid electrolyte (17).

Description

Technical Field

[0001] This invention relates to electrolytic capacitors having solid electrolytes and liquid electrolytes. Background Technology

[0002] A conventional electrolytic capacitor is disclosed in Patent Document 1. This electrolytic capacitor has a capacitor element formed by winding an anode foil with an oxide coating and an opposing cathode foil with a spacer between them. The capacitor element is housed in an outer casing, which is sealed by a sealing body. The anode foil and cathode foil are respectively connected to lead terminals, which penetrate the sealing body and extend out of the outer casing. The capacitor element internally has a solid electrolyte layer composed of a conductive polymer, impregnated with an electrolyte solution.

[0003] In addition, the solute in 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 at high temperatures. Furthermore, the oxidation of conductive polymers is suppressed by the inherent anti-oxidative degradation properties of aliphatic hydroxy acids.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-198248 (Pages 3-9) Figure 1 ). Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, according to the aforementioned conventional electrolytic capacitors, during long-term use (especially at high temperatures), the solvent from the vaporized electrolyte evaporates from the lead terminals or the gap between the outer casing and the seal. This reduces the amount of electrolyte within the capacitor element, exposing the conductive polymer to air inside the casing. At high temperatures, the conductive polymer is oxidized by oxygen in the air, losing its conductivity and decreasing its electrical conductivity. Therefore, the ESR of the electrolytic capacitor increases, hindering the extension of its lifespan.

[0009] The purpose of this invention is to extend the lifespan of electrolytic capacitors.

[0010] Methods for solving problems

[0011] To achieve the above objectives, the present invention provides an electrolytic capacitor comprising a main housing, a capacitor element, and a sealing body. The main housing has an opening, the capacitor element is housed within the main housing, and the sealing body seals the opening of the main housing. The electrolytic capacitor is characterized in that... The capacitor element is wound with an anode foil having an oxide coating on its surface and a cathode foil opposite to the anode foil, separated by a spacer. An electrolyte layer is provided between the anode foil and the cathode foil, the electrolyte layer comprising: a solid electrolyte containing a conductive polymer; and a liquid electrolyte covering at least a portion of the solid electrolyte. The liquid electrolyte contains at least an unsaturated fatty acid salt, and the unsaturated fatty acid salt monomer or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt accounts for more than 50% by weight of the liquid electrolyte.

[0012] Furthermore, the present invention is characterized in that, in the electrolytic capacitor configured as described above, the unsaturated fatty acid salt is in a liquid state at or above 20°C.

[0013] Furthermore, the present invention is characterized in that, in the electrolytic capacitor constructed as described above, the liquid electrolyte comprises the mixture, and the unsaturated fatty acid used is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosapentaenoic acid, linolenic acid, terpineic acid, ricinoleic acid, medelic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, octadecanotic tetraenoic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbond acid, cluanodonic acid, docosahexaenoic acid, 12-vinyl-8-octadecenoic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid.

[0014] Furthermore, the present invention is characterized in that, in the electrolytic capacitor constructed as described above, at least one of the following is used as the base for the unsaturated fatty acid salt: trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-o-phenanthroline, 2,2'-bipyridine, acetanilide, acetamide, a derivative of trimethylamine, a derivative of N,N-dimethylbenzylamine, a derivative of pyridine, a derivative of N,N-dimethylaniline, a derivative of aniline, a derivative of 2-mercaptobenzimidazole, a derivative of 1-naphthylamine, a derivative of morpholine, a derivative of 1,10-o-phenanthroline, a derivative of 2,2'-bipyridine, a derivative of acetanilide, and a derivative of acetamide.

[0015] Furthermore, the present invention is characterized in that, in the electrolytic capacitor configured as described above, the liquid electrolyte contains a fat-soluble antioxidant.

[0016] Furthermore, the present invention is characterized in that the electrolytic capacitor configured as described above contains the fat-soluble antioxidant at a weight percentage of less than 30% of the liquid electrolyte.

[0017] The effects of the invention

[0018] According to the present invention, the unsaturated fatty acid salt monomer or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt accounts for more than 50% by weight of the liquid electrolyte. Therefore, the evaporation of the liquid electrolyte can be prevented for a long period, and the oxidative degradation of the conductive polymer can be suppressed. Therefore, the increase in the ESR of the electrolytic capacitor can be suppressed, and the lifespan of the electrolytic capacitor can be extended. Attached Figure Description

[0019] Figure 1 This is a longitudinal sectional view of an electrolytic capacitor according to an embodiment of the present invention.

[0020] Figure 2 This is a perspective view of the capacitor element of an electrolytic capacitor according to an embodiment of the present invention.

[0021] Figure 3 This is a partially enlarged cross-sectional view of the capacitor element of an electrolytic capacitor according to an embodiment of the present invention.

[0022] Figure 4 This is a graph showing the change of ESR over time for embodiments and comparative examples of the present invention.

[0023] Figure 5 It is Figure 4 The graph is a magnified representation of the ESR range of 10 to 1000 mΩ. Detailed Implementation

[0024] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a longitudinal sectional view showing an electrolytic capacitor 1 according to one embodiment. The electrolytic capacitor 1 includes a main body housing 2, a capacitor element 10, and a sealing body 5.

[0025] The main body shell 2 is formed from a metal such as aluminum or resin into a bottomed cylindrical shape with a circular cross-section. One end is closed in the axial direction by a sealing surface 2a, and the other end has an opening 2b. From the perspective of processability and sealing performance, it is preferable to form the main body shell 2 from aluminum.

[0026] The sealing body 5 is formed into a circular plate shape from an elastomer with insulating materials such as butyl rubber and ethylene propylene rubber, and has a pair of through holes 5a. The lead terminals 7 and 8 of the capacitor element 10 are pressed through the pair of through holes 5a. Thus, the lead terminals 7 and 8 are led out to the outside of the sealing body and connected to the circuit board (not shown) by solder or the like.

[0027] A capacitor element 10 is housed within the main housing 2, and a sealing body 5 is disposed at the opening 2b. With the sealing body 5 disposed at the opening 2b of the main housing 2, the outer peripheral surface of the main housing 2 is narrowed by pressing. As a result, a narrowed portion 2c protruding inward is formed in the main housing 2. The narrowed portion 2c compresses the outer peripheral surface of the sealing body 5 in the inward peripheral direction, sealing it against the inner peripheral surface of the main housing 2. Furthermore, the compression of the sealing body 5 causes the inner peripheral surface of the through hole 5a to seal against the lead terminals 7 and 8. Thus, the opening 2b of the main housing 2 is sealed by the sealing body 5.

[0028] The end of the main body shell 2 on the opening 2b side has a bent portion 2d that bends and folds towards the sealing body 5. The bent portion 2d and the narrowing processing portion 2c are used to prevent the sealing body 5 from falling off the main body shell 2.

[0029] It should be noted that, in order to improve the mounting capability to the circuit board, a known mounting plate can also be provided. The lead terminals 7 and 8 pass through the mounting plate and are bent radially, so that the bent portion can be used as a soldering portion to the circuit board.

[0030] Figure 2 A perspective view of capacitor element 10 is shown. Capacitor element 10 has an anode foil 11, a cathode foil 12, and a spacer 13 formed as elongated strips. A pair of electrode foils, consisting of the anode foil 11 and the cathode foil 12 facing each other across the spacer 13, are wound into a generally cylindrical shape to form capacitor element 10. The tail end of the anode foil 11 or the spacer 13 is secured with adhesive tape 14.

[0031] The width of the spacer 13 in the short side direction (axial direction) is made larger than the width of the anode foil 11 and the cathode foil 12 in the short side direction. As a result, the spacer 13 protrudes from the anode foil 11 and the cathode foil 12 toward the closed surface 2a side and the opening 2b side, preventing short circuit between the anode foil 11 and the cathode foil 12.

[0032] The anode foil 11 is formed from valve metals such as aluminum, tantalum, niobium, and titanium, and its surface is roughened by etching. An oxide coating 16 is formed by applying a voltage to the anode foil 11 in the formation solution (see reference). Figure 3 ).

[0033] The cathode foil 12 is formed of a metal such as aluminum, and its surface is roughened by etching. A conductive coating such as carbon or titanium may also be formed on the surface of the anode foil 11. Alternatively, a natural oxide coating or a chemically formed oxide coating may be formed on the surface of the cathode foil 12 by applying voltage in a chemical forming solution.

[0034] The spacer 13 is made of nonwoven fabric composed of chemical fibers such as paper, rayon, polyethylene terephthalate, and polyamide, which are made from natural cellulose fibers. The spacer 13 is porous, which allows it to retain electrolyte in the gaps between the fibers. Preferably, the thickness of the spacer 13 is greater than the size of the protrusions such as burrs on the anode foil 11 and the cathode foil 12, for example, it is formed to be 20 μm to 60 μm.

[0035] Figure 3 This is an enlarged cross-sectional view showing the anode foil 11 of the capacitor element 10. An electrolyte layer 19, comprising 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 coating 16 of the anode foil 11, the surface of the cathode foil 12, and the fiber surface of the spacer 13. The solid electrolyte 17, held in the electrolyte layer 19 of the spacer 13, is formed in a layered manner on the surface of the fibers, and the liquid electrolyte 18 is held in the gaps between the fibers or within the fibers.

[0036] The solid electrolyte 17 uses a conductive polymer doped with a dopant. The conductive polymer can be polypyrrole, polythiophene, polyaniline, and their derivatives. The dopant can be p-toluenesulfonic acid, polystyrenesulfonic acid, etc. The conductive polymer can be formed by polymerization within the capacitor element 10. Alternatively, the conductive polymer can be retained within the capacitor element 10 by impregnating a dispersion of pre-polymerized conductive polymer in water into the capacitor element 10 and then drying it.

[0037] Preferably, polyethylene dioxythiophene (hereinafter PEDOT) is used as a derivative of polythiophene, and polystyrene sulfonic acid (hereinafter PSS) is used as a dopant. This allows a solid electrolyte 17 to be formed from a conductive polymer dispersion with excellent conductivity and stability.

[0038] Furthermore, as a derivative of polythiophene, if a sulfonic acid group is incorporated into the molecule, it can be used as a self-doped conductive polymer that is soluble in solvents such as water. Like conductive polymer dispersions, the self-doped conductive polymer can be retained within the capacitor element 10 by impregnation in the capacitor element 10 followed by drying. Such a self-doped conductive polymer will not dissolve in the liquid electrolyte 18 containing unsaturated fatty acid salts, as described later. Additionally, since the self-doped conductive polymer utilizes the liquid electrolyte 18 to suppress moisture absorption, the moisture resistance of the electrolytic capacitor 1 can be improved.

[0039] The liquid electrolyte 18 contains at least an unsaturated fatty acid salt, covering at least a portion of the solid electrolyte 17. The unsaturated fatty acid salt is formed by neutralizing at least a portion of the unsaturated fatty acids contained in the capacitor element 10 with an alkali. Thus, the liquid electrolyte 18 contains unsaturated fatty acid salt monomers or a mixture of unsaturated fatty acids added to an unsaturated fatty acid salt. In this case, the liquid electrolyte 18 contains 50% by mass or more of unsaturated fatty acid salt monomers or a mixture of unsaturated fatty acids added to an unsaturated fatty acid salt.

[0040] Unsaturated fatty acid salts react with oxygen and absorb surrounding oxygen more readily than conductive polymers, thus creating a state with less surrounding oxygen for the conductive polymers covered by the liquid electrolyte 18. Furthermore, the evaporation of unsaturated fatty acid salts is significantly less compared to solvents commonly used in electrolytes. Therefore, the oxidative degradation of the solid electrolyte 17 composed of conductive polymers covered by the liquid electrolyte 18 can be suppressed for a long period.

[0041] Furthermore, compared to unsaturated fatty acids, the penetration of unsaturated fatty acid salts into the sealing body 5 is suppressed, allowing them to remain within the capacitor element 10 for a longer period. Moreover, by including unsaturated fatty acid salts in the liquid electrolyte 18, the compatibility of unneutralized unsaturated fatty acids with the other components of the liquid electrolyte 18 (described later) can be improved.

[0042] Furthermore, when the liquid electrolyte 18 contains a solvent component, the evaporation of the solvent component can be suppressed by including 50% or more of unsaturated fatty acid salt monomers or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt. Moreover, even if the solvent component evaporates, the surface of the conductive polymer can be maintained by covering it with unsaturated fatty acids, resulting in a long-life electrolytic capacitor 1. Furthermore, if the liquid electrolyte 18 contains 80% or more of unsaturated fatty acid salt monomers or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt, it can become an electrolytic capacitor 1 with an even longer lifespan.

[0043] Unsaturated fatty acids are aliphatic compounds containing at least one carboxyl group and a double bond between two carbon atoms. Examples include palmitoleic acid, oleic acid, erucic acid, linoleic acid, eicosadienoic acid, docosahexaenoic acid, linolenic acid, terpineic acid, ricinoleic acid, medelic acid, dihomo-γ-linolenic acid, eicostrienoic acid, octadecanoic acid, arachidonic acid, eicosadienoic acid, docosahexaenoic acid, borsenoic acid, eicosalienoic acid, docosahexaenoic acid, squalene, docosahexaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenoic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. These unsaturated fatty acids generally have boiling points exceeding 250°C under normal pressure and exhibit very low evaporation, thus enabling the long lifespan of electrolytic capacitors.

[0044] Among unsaturated fatty acids, compounds with multiple double bonds between two carbon atoms within the molecule can react with more oxygen and maintain stable ESR characteristics over a long period. Therefore, electrolytic capacitor 1 has a high effect on extending its lifespan and is thus preferred.

[0045] In particular, unsaturated fatty acids containing a large number of double bonds in their molecules, and unsaturated fatty acids with side chains and branched structures on their main chain, mostly exist in liquid form from room temperature (20°C) up to their respective boiling points or decomposition points. Unsaturated fatty acid salts, as their salts, also readily turn into liquids above room temperature (20°C), and are therefore preferred.

[0046] Examples of such unsaturated fatty acids include palmitoleic acid, oleic acid, linoleic acid, eicosapentaenoic acid, linolenic acid, terpineic acid, ricinoleic acid, medelic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, octadecanoic acid, arachidonic acid, eicosapentaenoic acid, docosapentaenoic acid, borsenoic acid, eicosapentaenoic acid, docosapentaenoic acid, stigmacooleic acid, docosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenoic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid.

[0047] Furthermore, compounds with an intramolecular 1,4-pentadiene structure are preferred because the hydrogen atom of the methylene group sandwiched between the two double bonds is easily abstracted, making it more prone to reaction with oxygen. Examples of such compounds include linoleic acid, eicosadienoic acid, docosahexaenoic acid, linolenic acid, terpineic acid, medelic acid, dihomo-γ-linolenic acid, eicostrienoic acid, octadecanoic acid, arachidonic acid, eicostrienoic acid, adrenaline, borseopentanoic acid, eicosalienoic acid, docosahexaenoic acid, stigmacooleic acid, docosahexaenoic acid, stigmacooleic acid, stigmacooleic acid, stigmacooleic acid, stigmacooleic acid, and docosahexaenoic acid.

[0048] For the base used in unsaturated fatty acid salts, since unsaturated fatty acids are weakly acidic, a weakly basic organic amine is used. The unsaturated fatty acid salt formed by neutralizing the unsaturated fatty acid with a weak base exhibits low volatility, similar to an ionic liquid, and possesses the restorative properties of the oxide coating 16. Furthermore, since a base weaker than that used in typical ionic liquids is used, dedoping of the conductive polymer can be suppressed. Therefore, its properties can be maintained for a long period, allowing it to be used as a high-voltage-resistant and low-evaporation liquid electrolyte 18. To suppress dedoping of the conductive polymer, the base is particularly preferably pKb4 or higher, and more preferably pKb8 or higher.

[0049] Furthermore, fat-soluble organic amines that are highly compatible with unsaturated fatty acids readily form salts with them, and are therefore preferred. Specifically, trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-o-phenanthroline, 2,2'-bipyridine, acetanilide, acetamide, caffeine, or derivatives thereof are used.

[0050] Furthermore, since unsaturated fatty acids are weakly acidic, the smaller the amount of base relative to the unsaturated fatty acids, the better, and more preferably less than half.

[0051] Compared to unsaturated fatty acids, unsaturated fatty acid salts, as unsaturated fatty acid ions, tend to exist in a highly polar state. Therefore, trace amounts of moisture within the capacitor element 10 can be used to repair defects caused by the oxide coating 16 of the anode foil 11, reducing leakage current over the long term. Thus, the characteristic degradation of the electrolytic capacitor 1 can be reduced, resulting in a long-life electrolytic capacitor 1.

[0052] In the liquid electrolyte 18, as an additive, it may contain a solvent for adjusting viscosity, an electrolyte for easily repairing defects in the oxide coating 16, a gas absorbent for absorbing hydrogen generated by the repair process, an antioxidant for inhibiting the oxidative degradation of conductive polymers, a voltage enhancer for improving voltage resistance by acting on the surface of the oxide coating 16, and a solubilizer for making unsaturated fatty acid salts and additives miscible.

[0053] Adding a solvent to the liquid electrolyte 18 can reduce its viscosity and improve its impregnation. Using a high-boiling-point polar solvent improves the repairability of the oxide coating 16, increases its withstand voltage, and reduces leakage current. Furthermore, the solvent's penetration into the conductive polymer layer increases conductivity, thereby reducing the ESR of the electrolytic capacitor 1. High-boiling-point polar solvents such as γ-butyrolactone, sulfolane, ethylene glycol, and diethylene glycol can be used as such solvents.

[0054] It should be noted that the solvent may not be completely miscible with the unsaturated fatty acid salt monomer or the mixture of unsaturated fatty acids added to the unsaturated fatty acid salt. The solvent can be used to cover at least a portion of the solid electrolyte 17 by the unsaturated fatty acid salt monomer or the mixture of unsaturated fatty acids added to the unsaturated fatty acid salt.

[0055] Furthermore, it is preferable that the electrolyte in which the solute is dissolved in the solvent and the ions have dissociated is contained in the liquid electrolyte 18. As a result, the repairability of the oxide coating 16 is further improved, and the leakage current of the electrolytic capacitor 1 can be further reduced.

[0056] As an antioxidant added to the liquid electrolyte 18, water-soluble and / or fat-soluble antioxidants can be used.

[0057] It is believed that water-soluble antioxidants readily dissolve in high-boiling-point polar solvents, directly inhibiting the oxidation of conductive polymers. However, with water-soluble antioxidants, excessive increases in their dosage can lead to significant changes in voltage withstand properties and durability, potentially causing adverse effects. Therefore, the water-soluble antioxidant is preferably 3% by weight or less of the liquid electrolyte 18, more preferably 2% by weight or less.

[0058] To maximize the antioxidant effect of water-soluble antioxidants, it is preferable that the liquid electrolyte 18 contains at least 0.1% by weight of the water-soluble antioxidant. Examples of water-soluble antioxidants include catechol, hydroquinone, resorcinol, pyrogallol, protocatechuic acid, and gallic acid.

[0059] The lipid-soluble antioxidant contained in liquid electrolyte 18 is readily soluble in unsaturated fatty acid salt monomers or in mixtures of unsaturated fatty acid salts containing unsaturated fatty acids. The lipid-soluble antioxidant can accept free radicals generated by the reaction or thermal decomposition of unsaturated fatty acid salts or unsaturated fatty acids with oxygen, inhibiting or eliminating the activity of free radicals.

[0060] Therefore, it can inhibit oxidative degradation caused by free radicals of unsaturated fatty acids and conductive polymers. Thus, through the absorption of oxygen around the conductive polymer and the inhibition of oxidation, the antioxidant effect of the conductive polymer can be greatly improved. Therefore, the characteristic degradation of electrolytic capacitor 1 can be reduced over a long period.

[0061] Furthermore, even with increased addition, the lipid-soluble antioxidant does not hinder the repair of defects in the oxide coating 16 of the anode foil 11. Therefore, the freedom in designing the composition of the liquid electrolyte 18 can be increased. Compared to water-soluble antioxidants, lipid-soluble antioxidants have less impact on changes in voltage withstand characteristics and durability, allowing the addition amount to the liquid electrolyte 18 to be set to 30% by weight or less. To achieve the effect of inhibiting oxidation by the lipid-soluble antioxidant, it is preferable to contain 1% by weight or more of the liquid electrolyte 18.

[0062] Furthermore, a portion of the fat-soluble antioxidant permeates into the sealing body 5, inhibiting its deterioration. The fat-soluble antioxidant exhibits high compatibility with unsaturated fatty acid salts. Therefore, the balance between the fat-soluble antioxidants in the liquid electrolyte 18 and those permeating into the sealing body 5 can be adjusted based on the amount of unsaturated fatty acid salts in the liquid electrolyte 18.

[0063] Furthermore, since the unsaturated fatty acid salt in the liquid electrolyte 18, or a mixture of unsaturated fatty acids added to the unsaturated fatty acid salt, accounts for 50% or more by weight, the supply of fat-soluble antioxidants that permeate into the sealing body 5 is not excessive. Therefore, the deterioration of the sealing body 5 can be suppressed for a long time, thus extending the lifespan of the electrolytic capacitor 1. It should be noted that it is believed that some of the unsaturated fatty acids in the liquid electrolyte 18 also permeate into the sealing body 5, contributing to the effect of inhibiting the deterioration of the sealing body 5.

[0064] Examples of fat-soluble antioxidants include retinol, β-carotene, α-carotene, β-cryptoxanthin, astaxanthin, tocopherols (α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol), and tocotrienols (α-tocotrienol, β-tocotrienol, γ-tocotrienol, δ-tocotrienol). From the perspective of inhibiting the deterioration of the sealing body 5, tocopherols, with their excellent permeability and antioxidant effects, are particularly preferred.

[0065] According to this embodiment, the unsaturated fatty acid salt monomer or a mixture of unsaturated fatty acids added to an unsaturated fatty acid salt accounts for 50% or more of the liquid electrolyte 18. Therefore, the evaporation of the liquid electrolyte 18 can be prevented for a long time, and the oxidative degradation of the solid electrolyte 17 composed of conductive polymers can be suppressed. Therefore, the increase in the ESR of the electrolytic capacitor 1 can be suppressed, thereby achieving a long lifespan for the electrolytic capacitor 1.

[0066] In addition, the unsaturated fatty acid salts contained in the liquid electrolyte 18 are in a liquid state above 20°C, so the liquid electrolyte 18 can be easily realized.

[0067] Furthermore, as the unsaturated fatty acid contained in the liquid electrolyte 18, at least one of the following is used: palmitoleic acid, oleic acid, linoleic acid, eicosapentaenoic acid, linolenic acid, terpineic acid, ricinoleic acid, middica acid, dihomo-γ-linolenic acid, eicosatrienoic acid, octadecanoic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, borsenoic acid, eicosapentaenoic acid, docosahexaenoic acid, squalene, docosapentaenoic acid, herring acid, docosahexaenoic acid, 12-vinyl-8-octadecenoic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. Thus, unsaturated fatty acid salts that are liquid at temperatures above 20°C can be readily obtained.

[0068] Furthermore, as the base for the unsaturated fatty acid salt contained in the liquid electrolyte 18, at least one of the following is used: trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-o-phenanthroline, 2,2'-bipyridine, acetanilide, acetamide, a derivative of trimethylamine, a derivative of N,N-dimethylbenzylamine, a derivative of pyridine, a derivative of N,N-dimethylaniline, a derivative of aniline, a derivative of 2-mercaptobenzimidazole, a derivative of 1-naphthylamine, a derivative of morpholine, a derivative of 1,10-o-phenanthroline, a derivative of 2,2'-bipyridine, a derivative of acetanilide, and a derivative of acetamide. Thus, a liquid electrolyte 18 with low evaporability and the ability to suppress the dedoping of highly conductive molecules can be readily achieved.

[0069] Furthermore, if the liquid electrolyte 18 contains a fat-soluble antioxidant, it can inhibit oxidative degradation caused by free radicals of unsaturated fatty acids and conductive polymers. Therefore, the performance degradation of the electrolytic capacitor 1 can be reduced over a longer period.

[0070] In addition, if the liquid electrolyte 18 contains less than 30% by weight of a fat-soluble antioxidant, the oxidative degradation of unsaturated fatty acids and conductive polymers can be suppressed more reliably.

[0071] Hereinafter, embodiments formed for evaluating the electrolytic capacitor 1 of this embodiment will be described. It should be noted that the composition of the liquid electrolyte 18 in the following embodiments 1 to 13 and comparative examples 1 and 2 is shown in Table 1.

[0072] Table 1

[0073] Example 1

[0074] For the electrolytic capacitor 1 of Embodiment 1, firstly, the lead terminals 7 and 8 are connected to the anode foil 11 and cathode foil 12, whose surfaces are formed with an oxide coating 16. Then, the two electrode foils are wound around the spacer 13 to form an element shape. A capacitor element 10 with dimensions L = 6.3 mm × L = 7.7 mm was then subjected to repair formation by applying voltage while the capacitor element 10 was immersed in an ammonium adipate aqueous solution for 30 minutes.

[0075] Then, the capacitor element 10 is immersed in a conductive polymer compound dispersion formed by dispersing a composite of PEDOT and PSS in water. The capacitor element 10 is then lifted and dried at approximately 125°C to form a layer of solid electrolyte 17 composed of conductive polymers.

[0076] Then, a liquid containing 76% by weight of oleic acid and 24% by weight of 1,10-o-phenanthroline is impregnated into capacitor element 10. Oleic acid is an unsaturated fatty acid, and 1,10-o-phenanthroline is a weak base. This forms a liquid electrolyte 18 containing an unsaturated fatty acid salt. It should be noted that the boiling point of oleic acid is 203–205 °C (5 mmHg).

[0077] Then, the capacitor element 10 is inserted into the bottomed cylindrical main body housing 2, the sealing body 5 is installed, and a compression process is used to seal it. Then, it is aged by applying voltage to form the electrolytic capacitor 1. The electrolytic capacitor 1 has a rated voltage of 25WV and a rated capacitance of 100μF.

[0078] Example 2

[0079] For the electrolytic capacitor 1 of Example 2, when forming the liquid electrolyte 18, a liquid consisting of 74% by weight of oleic acid and 26% by weight of caffeine is impregnated in the capacitor element 10. Oleic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1.

[0080] Example 3

[0081] For the electrolytic capacitor 1 of Example 3, when forming the liquid electrolyte 18, a liquid consisting of 76% by weight of linoleic acid and 24% by weight of 1,10-o-phenanthroline was impregnated in the capacitor element 10. Linoleic acid is an unsaturated fatty acid, and 1,10-o-phenanthroline is a weak base. Furthermore, the boiling point of linoleic acid is 229–230°C (16 mmHg). Otherwise, it is the same as in Example 1.

[0082] Example 4

[0083] For the electrolytic capacitor 1 of Example 4, when forming the liquid electrolyte 18, a liquid consisting of 74% by weight linoleic acid and 26% by weight caffeine is impregnated in the capacitor element 10. Linoleic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1.

[0084] Example 5

[0085] For the electrolytic capacitor 1 of Example 5, when forming the liquid electrolyte 18, a liquid consisting of 77% by weight of arachidonic acid and 23% by weight of 1,10-o-phenanthroline was impregnated in the capacitor element 10. Arachidonic acid is an unsaturated fatty acid, and 1,10-o-phenanthroline is a weak base. Furthermore, the boiling point of arachidonic acid is 169–171°C (0.15 mmHg). Otherwise, it is the same as in Example 1.

[0086] Example 6

[0087] For the electrolytic capacitor 1 of Example 6, when forming the liquid electrolyte 18, a liquid consisting of 75% by weight of arachidonic acid and 25% by weight of caffeine is impregnated in the capacitor element 10. Arachidonic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1.

[0088] Example 7

[0089] For the electrolytic capacitor 1 of Example 7, when forming the liquid electrolyte 18, a liquid consisting of 42.7 wt% linoleic acid, 14.5 wt% 1,10-phenanthroline, and 42.7 wt% diethylene glycol is impregnated in the capacitor element 10. 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 as follows: It measures 6.3mm x 7.7mm, has a rated voltage of 35V, and a rated capacitance of 47μF. Otherwise, it is identical to Example 1.

[0090] Example 8

[0091] For the electrolytic capacitor 1 of Example 8, when forming the liquid electrolyte 18, a liquid consisting of 43.1% by weight of linoleic acid, 13.8% by weight of caffeine, and 43.1% by weight of diethylene glycol is impregnated in the capacitor element 10. Linoleic acid is an unsaturated fatty acid, caffeine is a weak base, and ethylene glycol is a high-boiling-point polar solvent. Otherwise, it is the same as in Example 7.

[0092] Example 9

[0093] For the electrolytic capacitor 1 of Example 9, when forming the liquid electrolyte 18, a liquid consisting of 50% by weight of oleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of boro-disalicilic acid, and 1% by weight of trimethylamine is impregnated in the capacitor element 10. Oleic acid is an unsaturated fatty acid, trimethylamine is a weak base and a solute in the electrolyte, γ-butyrolactone and sulfolane are solvents in the electrolyte, and boro-disalicilic acid is a solute in the electrolyte. Otherwise, it is the same as in Example 1.

[0094] It should be noted that the electrolyte and unsaturated fatty acids are not completely miscible. Therefore, the electrolytic capacitor 1 is made by first impregnating the capacitor element 10 with the electrolyte and then impregnating it with unsaturated fatty acids.

[0095] Example 10

[0096] For the electrolytic capacitor 1 of Example 10, when forming the liquid electrolyte 18, a liquid consisting of 50% by weight of linoleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borosilicate acid, and 1% by weight of trimethylamine is impregnated in the capacitor element 10. Linoleic acid is an unsaturated fatty acid, trimethylamine is a weak base and a solute in the electrolyte, γ-butyrolactone and sulfolane are solvents in the electrolyte, and borosilicate acid is a solute in the electrolyte. Otherwise, it is the same as in Example 9.

[0097] Example 11

[0098] For the electrolytic capacitor 1 of Example 11, when forming the liquid electrolyte 18, a liquid consisting 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 borosilicate acid, and 1% by weight of trimethylamine is impregnated in the capacitor element 10. Oleic acid and linoleic acid are unsaturated fatty acids, trimethylamine is a weak base and a solute in the electrolyte, γ-butyrolactone and sulfolane are solvents in the electrolyte, and borosilicate acid is a solute in the electrolyte. Otherwise, it is the same as in Example 9.

[0099] Example 12

[0100] For the electrolytic capacitor 1 of Example 12, when forming the liquid electrolyte 18, a liquid consisting of 50% by weight of oleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borosilicate acid, 1% by weight of trimethylamine, and 4% by weight of D-α-tocopherol was impregnated in the capacitor element 10. Oleic acid is an unsaturated fatty acid, trimethylamine is a weak base and a solute in the electrolyte, γ-butyrolactone and sulfolane are solvents in the electrolyte, borosilicate acid is a solute in the electrolyte, and D-α-tocopherol is a fat-soluble antioxidant. The boiling point of D-α-tocopherol is 220°C (0.1 mmHg). Otherwise, it is the same as in Example 9.

[0101] Example 13

[0102] For the electrolytic capacitor 1 of Example 13, when forming the liquid electrolyte 18, a liquid consisting of 50% by weight of linoleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borosilicate, 1% by weight of trimethylamine, and 4% by weight of D-α-tocopherol is impregnated in the capacitor element 10.

[0103] Linoleic acid is an unsaturated fatty acid; trimethylamine is a weak base and a solute in the electrolyte; γ-butyrolactone and sulfolane are solvents in the electrolyte; borosilicate acid is a solute in the electrolyte; and D-α-tocopherol is a fat-soluble antioxidant. Otherwise, it is the same as in Example 9.

[0104] [Comparative Example 1]

[0105] In addition, comparative examples were prepared for comparison. For Comparative Example 1, when forming the liquid electrolyte 18, a liquid consisting of 76% by weight of isostearic acid and 24% by weight of 1,10-phenanthroline was impregnated in the capacitor element 10. 1,10-phenanthroline is a weak base, and isostearic acid is a saturated fatty acid. The boiling point of isostearic acid is 183°C (5 mmHg). Otherwise, it was the same as in Example 1.

[0106] [Comparative Example 2]

[0107] For Comparative Example 2, when forming the liquid electrolyte 18, an electrolyte solution consisting of 36% by weight of γ-butyrolactone, 54% by weight of sulfolane, 8% by weight of borosilicate acid, and 2% by weight of trimethylamine was impregnated in the capacitor element 10. γ-butyrolactone and sulfolane were the solvents of the electrolyte solution, and borosilicate acid and trimethylamine were the solutes of the electrolyte solution. Otherwise, it was the same as in Example 1.

[0108] The ESR shift of the above embodiments and comparative examples during a 10,000-hour durability test at 150°C under rated voltage is shown in Table 2. Figure 4 as well as Figure 5 . Figure 4 , Figure 5 The vertical axis represents ESR (unit: mΩ), and the horizontal axis represents time (unit: hours). It should be noted that, for ease of understanding, Figure 5 Lieutenant General Figure 4 The ESR range of 10 to 1000 mΩ is shown in an expanded manner.

[0109] Table 2

[0110] According to Table 2, Figure 4 , Figure 5 In Examples 1 to 13, where the liquid electrolyte 18 contains 50% by weight or more of an unsaturated fatty acid salt or a mixture of unsaturated fatty acids added to an unsaturated fatty acid salt, the ESR in the durability test is maintained at a low level. Therefore, the ESR characteristics can be maintained stably for a long period even at a high temperature of 150°C.

[0111] In addition, the ESR properties can be maintained stably for a long time when a high-boiling-point polar solvent is added (Examples 7 and 8) or when an electrolyte is included (Examples 9 to 13).

[0112] Furthermore, for each of the electrolytic capacitors 1 in Examples 1 to 13 after the durability test, it was confirmed that liquid electrolyte 18 remained inside the capacitor element 10. Therefore, by covering the solid electrolyte 17 of the conductive polymer with liquid electrolyte 18, the deterioration of the conductive polymer was suppressed, thereby obtaining an electrolytic capacitor 1 with a long service life.

[0113] In contrast, in Comparative Examples 1 and 2, which do not contain unsaturated fatty acids, the ESR properties deteriorated significantly after 3000 to 4000 hours at a high temperature of 150°C.

[0114] Industrial applicability

[0115] This invention can be applied to automobiles, electronic devices, and the like, in which electrolytic capacitors are installed in the circuit.

[0116] Explanation of reference numerals in the attached figures

[0117] 1: Electrolytic capacitor.

[0118] 2: Main body shell.

[0119] 2a: Closed surface.

[0120] 2b: Opening.

[0121] 2c: Narrowing processing section.

[0122] 2d: Bending section.

[0123] 5: Sealing body.

[0124] 5a: Through hole.

[0125] 6: Spacer.

[0126] 7, 8: Lead terminals.

[0127] 10: Capacitor components.

[0128] 11: Anode foil.

[0129] 12: Cathode foil.

[0130] 13: Spacer.

[0131] 14: Adhesive tape.

[0132] 16: Oxidation coating.

[0133] 17: Solid electrolytes.

[0134] 18: Liquid electrolyte.

[0135] 19: Electrolyte layer.

Claims

1. An electrolytic capacitor having a main case, a capacitor element, and a sealing body, the main case having an opening portion, the capacitor element being housed in the main case, and the sealing body sealing the opening portion of the main case, the electrolytic capacitor being characterized in that the capacitor element has an anode foil having an oxide film on a surface, and a cathode foil facing the anode foil with a separator therebetween, and has an electrolyte layer between the anode foil and the cathode foil, the electrolyte layer containing a solid electrolyte containing an electrically conductive polymer, and a liquid electrolyte covering at least a part of the solid electrolyte, the liquid electrolyte containing at least an unsaturated fatty acid salt, a mixture of a monomer of the unsaturated fatty acid salt or an unsaturated fatty acid added to the unsaturated fatty acid salt being 50% by weight or more of the liquid electrolyte. The unsaturated fatty acid salt is liquid at 20°C or higher. The liquid electrolyte contains the mixture, and 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, paullinoleic acid, docosapentaenoic acid, eicosapentaenoic acid, tetracosapentaenoic acid, clupanodonic acid, docosahexaenoic acid, 12-vinyl-8-octadecene dioic acid, 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid is used as the unsaturated fatty acid.

2. The electrolytic capacitor as claimed in claim 1, wherein At least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridine, acetanilide, acetamide, a derivative of trimethylamine, a derivative of N,N-dimethylbenzylamine, a derivative of pyridine, a derivative of N,N-dimethylaniline, a derivative of aniline, a derivative of 2-mercaptobenzimidazole, a derivative of 1-naphthylamine, a derivative of morpholine, a derivative of 1,10-phenanthroline, a derivative of 2,2'-bipyridine, a derivative of acetanilide, a derivative of acetamide is used as the base of the unsaturated fatty acid salt.

3. The electrolytic capacitor as claimed in claim 2, wherein The liquid electrolyte contains a fat-soluble antioxidant.

4. The electrolytic capacitor as claimed in claim 2, wherein The fat-soluble antioxidant is contained at 30% by weight or less of the liquid electrolyte.

5. The electrolytic capacitor according to any one of claims 1 to 4, wherein ​ 6. The electrolytic capacitor as claimed in claim 5, wherein ​

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