Electrolyte for electrolytic capacitor and electrolytic capacitor

Abstract

The purpose of the present invention is to provide: an electrolyte solution which is not susceptible to evaporation and volatilization with respect to a butyl rubber that is used as a sealing member; and an electrolytic capacitor which is suppressed in evaporation and volatilization of an electrolyte solution, thereby having a long service life. An electrolytic capacitor according to the present invention is provided with: a capacitor element that comprises a positive electrode foil, a negative electrode foil and a separator; an electrolyte solution that contains a solvent and a solute; a case that contains the capacitor element; and a butyl rubber that seals the case. With respect to this electrolytic capacitor, the distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of the butyl rubber is 26.5 or more; and the boiling point of the solvent is 160°C or higher.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for an electrolytic capacitor and an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor contains a capacitor element coated with an electrolyte solution in a bottomed case, the opening of which is sealed with a sealing material such as butyl rubber. The electrolyte has chemical properties that repair deterioration, such as deterioration or damage, of the dielectric film formed on the anode foil, affecting the leakage current and life characteristics of the electrolytic capacitor. However, over time, the electrolyte permeates the sealing material and evaporates to the outside of the electrolytic capacitor. As a result, the capacitance of the electrolytic capacitor decreases over time, and the tangent of the loss angle (tanδ) increases over time, eventually reaching the end of its life.

[0003] Patent Documents 1 and 2 disclose a technique for suppressing evaporation of an electrolyte solution by adding a polymer compound to the electrolyte solution to increase the viscosity. However, increasing the amount of polymer compound added can deteriorate the electrical characteristics of the capacitor, and there is a limit to how much the addition of a polymer compound can suppress evaporation.

[0004] Patent Document 3 discloses that evaporation is suppressed by using the Hildebrand solubility parameter (SP) to identify the difference in SP between an organic solvent and a sealing material. SP is a physical property defined as the square root of the cohesive energy density, and is a numerical value that indicates the dissolution behavior of a solvent. However, the accuracy of predicting dissolution behavior is not sufficient, and it has been difficult to use SP to find an optimal solvent for an electrolyte for an electrolytic capacitor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-73922 [Patent Document 2] International Publication No. WO2011 / 099261 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-214637 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been proposed to solve the above problems, and its purpose is to provide an electrolyte solution that is less likely to evaporate from butyl rubber used as a sealing material. It also provides an electrolytic capacitor that suppresses the evaporation of the electrolyte solution and has a long life. Furthermore, it is possible to easily find a solvent suitable for an electrolyte solution for an electrolytic capacitor from among many solvents. [Means for solving the problem]

[0007] The inventors have focused on the Hansen solubility parameter (HSP) and investigated the affinity between the butyl rubber used as the sealing material and the solvent contained in the electrolyte. HSP is a function of the dispersion component (δ D ), polar component (δ P ) and hydrogen bond components (δ H ) is represented by a single point in a three-dimensional space. The affinity between two substances can be evaluated by the distance between the two HSPs (HSP distance), and it can be estimated that the larger the HSP distance, the lower the affinity (the less compatible they are). The HSP distance (Δδ) can be calculated using the following formula:

[0008]

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[0009] As a result, it was found that when the distance between the HSPs of the butyl rubber and the electrolyte solvent is 26.2 or more, the evaporation of the electrolyte is significantly suppressed, making it possible to produce an electrolytic capacitor with a long life.

[0010] The present invention was made based on this finding, and the electrolyte for an electrolytic capacitor of the present invention contains a solvent having a boiling point of 160°C or higher, and the distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of the butyl rubber used as a sealing material is 26.2 or more.

[0011] The solvent of the electrolyte for an electrolytic capacitor may be one or more selected from glycerol carbonate, methanamide, and glycerin.

[0012] The electrolytic capacitor of the present invention includes a capacitor element having an anode foil having a dielectric film on its surface, a cathode foil, and a separator interposed between the anode foil and the cathode foil, an electrolyte solution contained in the capacitor element and containing a solvent and a solute, a case that houses the capacitor element, and butyl rubber that seals the case, wherein the distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of the butyl rubber is 26.2 or more, and the boiling point of the solvent is 160°C or more.

[0013] In another embodiment, the electrolytic capacitor of the present invention includes a capacitor element having an anode foil having a dielectric film on its surface, a cathode foil, and a separator interposed between the anode foil and the cathode foil, a solid electrolyte layer containing a conductive polymer formed on the capacitor element, a solvent contained in the capacitor element, a case that houses the capacitor element, and butyl rubber that seals the case, wherein the distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of the butyl rubber is 26.2 or more, and the boiling point of the solvent is 160°C or more. [Effects of the Invention]

[0014] The electrolyte for electrolytic capacitors of the present invention has the property of being less likely to evaporate from the butyl rubber used as a sealing material. By suppressing the evaporation of the electrolyte, electrolytic capacitors with long life can be obtained. Furthermore, evaluation using HSP distance has a high predictive accuracy, making it easy to select the optimal solvent for the electrolyte for electrolytic capacitors. DETAILED DESCRIPTION OF THE INVENTION

[0015] The electrolytic solution and electrolytic capacitor according to the embodiments of the present invention will be described below.

[0016] The electrolytic capacitor of the present invention includes a liquid electrolytic capacitor having only an electrolytic solution, and a solid electrolytic capacitor using both an electrolytic solution and a solid electrolyte layer containing a conductive polymer.

[0017] An electrolytic capacitor has a capacitor element, a case, and butyl rubber as a sealing material. The case houses the capacitor element. The butyl rubber is attached to the opening of the case by crimping, sealing the opening. The capacitor element includes an anode foil, a cathode foil, a separator, and an electrolyte. The electrolyte contains a solvent and a solute. The anode foil and the cathode foil face each other via the separator. A dielectric coating is formed on the surface of the anode foil. A dielectric coating is also formed on the cathode foil as needed.

[0018] When the distance between the HSP of the solvent contained in the electrolyte and the HSP of the butyl rubber is 26.2 or more, the affinity between the solvent and the butyl rubber is low, making it difficult for the electrolyte to permeate the butyl rubber and suppressing evaporation and evaporation of the electrolyte. In particular, when the distance between the HSP of the solvent contained in the electrolyte and the HSP of the butyl rubber is 26.5 or more, this is preferable because it effectively suppresses evaporation and evaporation of the electrolyte. Furthermore, when the boiling point of the solvent is 160°C or more, the electrolyte is less likely to evaporate when the electrolytic capacitor is used in a high-temperature environment or during the reflow process, so swelling of the butyl rubber and opening of the valve due to increased internal pressure of the electrolytic capacitor can be suppressed.

[0019] Such solvents include, for example, methanamide, glycerol carbonate, glycerin, and the like.

[0020] Here, an example of a solvent having an HSP distance from butyl rubber of 26.2 or more and a boiling point of less than 160°C is methyl hydroperoxide (boiling point 78.1°C). When methyl hydroperoxide is used as a solvent for an electrolyte solution, it vaporizes in a high-temperature environment, causing swelling of the butyl rubber and an increase in the internal pressure of the electrolytic capacitor. Therefore, even if the HSP distance from butyl rubber is 26.2 or more, a solvent having a boiling point of less than 160°C cannot be used as a solvent for an electrolyte solution for an electrolytic capacitor.

[0021] The electrolyte may contain a solute or an additive.

[0022] Examples of the acid component of the solute include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols, sulfonic acid, boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, and borodisalicylic acid.

[0023] Examples of salts composed of an acid component and a base component of the solute include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, potassium salts, etc. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of quaternized amidinium salts include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, propylamine, etc.; examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc.; and examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0024] Examples of additives include complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.), phosphate esters, etc. These may be used alone or in combination of two or more.

[0025] Butyl rubber is used as a sealing material for electrolytic capacitors. Compared to other elastomers, butyl rubber can suppress the evaporation and evaporation of the electrolyte.

[0026] The electrolytic capacitor may have a solid electrolyte layer containing a conductive polymer in the capacitor element. Such an electrolytic capacitor functions as a capacitor without adding a solute to the electrolyte solution. In other words, an electrolytic capacitor having a solid electrolyte layer containing a conductive polymer only needs to have an electrolyte solution containing at least a solvent.

[0027] When a solid electrolyte layer containing a conductive polymer is formed in a capacitor element, the conductive polymer is a conjugated polymer or a doped conjugated polymer. The conjugated polymer is preferably one obtained by polymerizing thiophene or its derivatives. Among these, poly(3,4-ethylenedioxythiophene) (PEDOT) is the most preferred. Any known dopant can be used without particular limitation, and polystyrene sulfonate (PSS) is preferred from the viewpoint of electrical conductivity.

[0028] By providing a capacitor element with a solid electrolyte layer containing a conductive polymer, an electrolytic capacitor with a lower equivalent series resistance (ESR) and a higher capacitance (Cap) can be obtained compared to when only an electrolyte solution is used.

[0029] When glycerol carbonate, methanamide, or glycerin is included in the solvent of the electrolyte used in solid electrolytic capacitors, it has the effect of improving the electrical conductivity of the conductive polymer attached to the capacitor element. As a result, the initial ESR of the solid electrolytic capacitor can be further suppressed. The reason for this is unclear, but it is thought that glycerol carbonate, methanamide, and glycerin probably change the structure of the conductive polymer PEDOT / PSS, improving carrier mobility. [Example]

[0030] (Example 1) Methanamide was used as a solvent. Methanamide has an HSP distance of 30.7 with butyl rubber and a boiling point of 210° C. This was used as an electrolyte.

[0031] Example 2 The electrolyte was made of glycerol carbonate, which has an HSP distance of 29.3 with butyl rubber and a boiling point of 160°C.

[0032] Example 3 A mixed solvent of ethylene glycol and glycerin was used as the solvent. The mixing ratio in the solvent was 40 wt% ethylene glycol and 60 wt% glycerin. This mixed solvent was used as the electrolyte. The HSP distance of this solvent with butyl rubber was 26.2. Since it is a mixed solvent of ethylene glycol and glycerin, the boiling point is above 160°C.

[0033] Example 4 A mixed solvent of ethylene glycol and glycerin was used as the solvent. The mixing ratio in the solvent was 20 wt% ethylene glycol and 80 wt% glycerin. This mixed solvent was used as the electrolyte. The HSP distance of this solvent with butyl rubber was 26.5. Since it is a mixed solvent of ethylene glycol and glycerin, the boiling point is above 160°C.

[0034] Example 5 A mixed solvent of ethylene glycol and glycerin was used as the solvent. The mixing ratio in the solvent was 10 wt% ethylene glycol and 90 wt% glycerin. This mixed solvent was used as the electrolyte. The HSP distance of this solvent with butyl rubber was 26.6. Since it is a mixed solvent of ethylene glycol and glycerin, the boiling point is above 160°C.

[0035] Example 6 The electrolyte was prepared using glycerin as a solvent. Glycerin has an HSP distance of 26.7 with butyl rubber and a boiling point of 265°C.

[0036] (Comparative Example 1) Diethylene glycol was used as the solvent for the electrolyte. Diethylene glycol has an HSP distance of 20.0 with butyl rubber and a boiling point of 244°C.

[0037] (Comparative Example 2) Ethylene glycol was used as the solvent for the electrolyte. Ethylene glycol has an HSP distance of 25.5 with butyl rubber and a boiling point of 197°C.

[0038] (Comparative Example 3) A mixed solvent of ethylene glycol and glycerin was used as the solvent. The mixing ratio in the solvent was 50 wt% ethylene glycol and 50 wt% glycerin. This mixed solvent was used as the electrolyte. The HSP distance of this solvent with butyl rubber was 26.0. Since it is a mixed solvent of ethylene glycol and glycerin, the boiling point is above 160°C.

[0039] (Evaluation of the amount of evaporation of electrolyte) Five grams of the prepared electrolyte was placed in a cylindrical aluminum case with a bottom, the open end of the aluminum case was sealed with butyl rubber, and the initial weight was measured. After leaving the case in an environment at 170°C for 500 hours, the weight was measured and the difference in weight before and after the high-temperature storage test was calculated. The results are shown in Table 1.

[0040] The type of solvent, the distance between the HSP of the solvent and the HSP of the butyl rubber, and the amount of evaporation of the electrolyte are shown in Table 1. The amount of evaporation of the electrolyte is shown as the weight difference before and after the load test in Examples 1 to 6 and Comparative Examples 2 and 3, with the weight difference before and after the high-temperature storage test in Comparative Example 1 set as the reference (100). [Table 1]

[0041] Table 1 shows that the amount of electrolyte evaporation is not correlated with the boiling point of the solvent, but is correlated with the HSP distance from the butyl rubber. When the HSP distance from the butyl rubber is 26.2 or more, the evaporation of the electrolyte is significantly suppressed. In particular, in Examples 1, 2, and 6, the electrolyte was hardly evaporated.

[0042] When the HSP distance with butyl rubber was 26.2 or more, evaporation of the electrolyte was significantly suppressed. By using such an electrolyte for electrolytic capacitors, electrolytic capacitors with long life can be manufactured.

Claims

1. a capacitor element including an anode foil having a dielectric film on its surface, a cathode foil, and a separator interposed between the anode foil and the cathode foil; an electrolyte solution contained in the capacitor element and including a solvent and a solute; a case that houses the capacitor element; butyl rubber sealing the case, The distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of butyl rubber is 26.2 or more; The boiling point of the solvent is 160°C or higher. Electrolytic capacitor.

2. a capacitor element including an anode foil having a dielectric film on its surface, a cathode foil, and a separator interposed between the anode foil and the cathode foil; a solid electrolyte layer containing a conductive polymer formed on the capacitor element; a solvent contained in the capacitor element; a case that houses the capacitor element; butyl rubber sealing the case, The distance between the Hansen solubility parameter of the solvent and the Hansen solubility parameter of butyl rubber is 26.2 or more; The boiling point of the solvent is 160°C or higher. Electrolytic capacitor.

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