Electrolyte and electrolytic capacitor

Abstract

The present invention provides an electrolyte that can achieve both good low-temperature and high-temperature characteristics, and an electrolytic capacitor using the same. [Solution] An electrolyte characterized by containing 0.1 to 0.5% by weight of a uronic acid represented by formula I in a mixed solvent with γ-butyrolactone as the main solvent and ethylene glycol as a secondary solvent. Galacturonic acid and / or glucuronic acid are preferred as the uronic acid. An organic carboxylic acid or a salt thereof can be used as the solute of the electrolyte, and a linear saturated aliphatic carboxylic acid or a salt thereof with a molecular weight of 200 or more is particularly preferred. TIFF2026105971000005.tif34153

Description

Technical Field

[0001] The present invention relates to an electrolytic solution and an electrolytic capacitor using the same. More specifically, the present invention relates to an electrolytic solution capable of achieving both good low-temperature characteristics and high-temperature characteristics, and an electrolytic capacitor using the same.

Background Art

[0002] Medium- and high-voltage electrolytic capacitors are mounted in inverters for driving hybrid vehicles. As an electrolytic solution for such medium- and high-voltage electrolytic capacitors, for example, one using ethylene glycol as a solvent is known. Ethylene glycol is an excellent electrolytic solution solvent that can improve the ESR, high-temperature stability, etc. of an electrolytic capacitor. However, since the freezing point of ethylene glycol is -12.9°C, in a low-temperature environment such as -40°C, there are problems such as freezing and an increase in the specific resistance of the electrolytic solution.

[0003] For the purpose of improving low-temperature characteristics, Patent Document 1 discloses an electrolytic solution for a medium- and high-voltage electrolytic capacitor using a mixed solvent of ethylene glycol and γ-butyrolactone with a low freezing point (about -44°C).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in an electrolytic solution using a mixed solvent of γ-butyrolactone and ethylene glycol, there is a problem that the withstand voltage of the anodic oxide film decreases and the leakage current (LC) increases during no-load standing at a high temperature such as 125°C. Therefore, an object of the present invention is to improve this problem.

Means for Solving the Problems

[0006] As a result of repeated studies to solve the above-mentioned problems, the inventors of the present invention have found that by using an electrolyte solution obtained by adding a specific amount of uronic acid hexose to a mixed solvent of γ-butyrolactone and ethylene glycol, it is possible to suppress the deterioration of the anodic oxide film at high temperatures and under no load while maintaining good low-temperature characteristics, and have completed the present invention.

[0007] The electrolyte of the present invention is characterized by containing 0.1 to 0.5% by weight of a uronic acid represented by formula I in a mixed solvent consisting of γ-butyrolactone as the main solvent and ethylene glycol as a secondary solvent. [ka]

[0008] The electrolyte contains γ-butyrolactone as the main solvent and ethylene glycol as a secondary solvent, so it does not freeze even at low temperatures such as -40°C, and can achieve good low-temperature characteristics. Furthermore, because it contains the uronic acid (e.g., galacturonic acid and / or glucuronic acid), the anodic oxide film is less likely to deteriorate even when left unloaded at high temperatures, thus it also has excellent high-temperature characteristics. In addition, by setting the concentration of the uronic acid in the range of 0.1 to 0.5% by weight, it is possible to achieve both leakage current suppression and high voltage resistance.

[0009] The electrolyte preferably contains an organic carboxylic acid (excluding uronic acid of formula I) or a salt thereof as a solute, and more preferably, a linear saturated aliphatic carboxylic acid with a molecular weight of 200 or more is used as the organic carboxylic acid. By using such an organic carboxylic acid as a solute, the voltage withstand capability of the electrolytic capacitor can be increased. [Effects of the Invention]

[0010] By using the electrolyte of the present invention in an electrolytic capacitor, it is possible to provide an electrolytic capacitor that exhibits excellent characteristics not only at low temperatures but also at high temperatures. [Modes for carrying out the invention]

[0011] The electrolyte of the present invention contains γ-butyrolactone as the main solvent and ethylene glycol as the secondary solvent. The main solvent refers to a solvent whose proportion to the total weight of the solvent exceeds 50% by weight, and the secondary solvent refers to a solvent whose proportion is lower than that of the main solvent. For example, the weight ratio of γ-butyrolactone to ethylene glycol is preferably 60:40 to 90:10, and more preferably 65:35 to 85:15.

[0012] A preferred electrolyte is one in which, when the total amount of the electrolyte is 100% by weight, the concentration of γ-butyrolactone is 55-85% by weight (particularly 60-80% by weight) and the concentration of ethylene glycol is 10-35% by weight (more preferably 12-33% by weight, or 15-30% by weight). In addition to γ-butyrolactone and ethylene glycol, other solvents may be used as the solvent for the electrolyte of the present invention, but the amount is preferably 5% by weight or less of the total amount of the electrolyte, and more preferably 3% by weight or less. The solvent used in the electrolyte of the present invention may consist only of γ-butyrolactone and ethylene glycol.

[0013] The electrolyte of the present invention contains a uronic acid represented by formula I. [ka] Examples of uronic acids that fit into formula I include galacturonic acid, glucuronic acid, iduronic acid, mannuronic acid, and guluronic acid. Galacturonic acid and glucuronic acid are more preferred.

[0014] The electrolyte of the present invention contains 0.1 to 0.5% by weight of the uronic acid. By using the electrolyte containing the uronic acid, leakage current can be significantly suppressed even when the electrolytic capacitor is in a high-temperature, no-load state. If the concentration of the uronic acid is less than 0.1% by weight, the leakage current suppression effect is insufficient, and if it exceeds 0.5% by weight, the withstand voltage characteristics deteriorate. Therefore, in order to achieve both the suppression of leakage current at high temperatures and no loads and high withstand voltage, it is preferable to use 0.1 to 0.5% by weight of the uronic acid.

[0015] In the present invention, organic carboxylic acids used as solutes (excluding uronic acid of formula I) include aromatic carboxylic acids and aliphatic carboxylic acids. Aliphatic carboxylic acids are preferred, saturated aliphatic carboxylic acids are more preferred, and linear saturated aliphatic carboxylic acids are particularly preferred. Examples of linear saturated aliphatic carboxylic acids include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanoic acid, undecanedic acid, dodecanoic acid, and dodecanedic acid. From the viewpoint of increasing voltage resistance, linear saturated aliphatic carboxylic acids with a molecular weight of 200 or more are preferred, and dicarboxylic acids are particularly preferred. Examples of linear saturated aliphatic dicarboxylic acids with a molecular weight of 200 or more include sebacic acid, undecanedic acid, and dodecanedic acid, with sebacic acid being particularly preferred.

[0016] The electrolyte of the present invention preferably contains 1 to 5% by weight of the organic carboxylic acid, more preferably 2 to 4% by weight, and particularly preferably 2.5 to 3.5% by weight.

[0017] The electrolyte of the present invention may contain a salt of an organic carboxylic acid. Preferred salts are amine salts of the organic carboxylic acids mentioned above. Examples of such amines include primary amines such as methylamine, ethylamine, and t-butylamine; secondary amines such as dimethylamine, ethylmethylamine, and diethylamine; tertiary amines such as trimethylamine, diethylmethylamine, ethyldimethylamine, triethylamine, tripropylamine, and diisopropylethylamine; and quaternary ammonium cations such as tetramethylammonium, triethylmethylammonium, and tetraethylammonium. More preferred amines are tripropylamine and diisopropylethylamine, with tripropylamine being a particularly preferred amine.

[0018] The electrolyte of the present invention preferably contains 1 to 5% by weight of the amine, more preferably 2 to 4% by weight, and particularly preferably 2.5 to 3.5% by weight. The amine may be added to the electrolyte as an amine salt of an organic carboxylic acid, or it may be added to the electrolyte separately from the organic carboxylic acid.

[0019] The electrolytic solution of the present invention may contain colloidal silica. As the colloidal silica, commercially available ones with a particle size of about 10 to 20 nm can be used. The concentration of colloidal silica in the electrolytic solution is preferably 0.3 to 5% by weight, more preferably 0.5 to 3% by weight, and particularly preferably 0.7 to 2% by weight.

[0020] In the electrolytic solution of the present invention, the water content is preferably 5% by weight or less. For example, after preparing the electrolytic solution, by heating and stirring at 100°C or higher for 1 hour or more, the condensed water formed by ethylene glycol and organic carboxylic acid can be evaporated to make the water content 5% by weight or less. The water content is more preferably 3% by weight or less, and particularly preferably 1% by weight or less. The water content of the electrolytic solution can be measured, for example, by a Karl Fischer moisture measuring device.

[0021] The electrolytic solution of the present invention may contain additional components other than the above components. Examples of the additional components include phosphoric acid compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, polyphosphoric acid, methyl phosphate, ethyl phosphate, butyl phosphate, isopropyl phosphate, dibutyl phosphate, dioctyl phosphate; boric acid compounds such as boric acid and its complex compounds; polyhydric alcohols such as mannitol, sorbitol, xylitol, pentaerythritol, polyvinyl alcohol; nitro compounds such as p-nitrobenzoic acid, m-nitroacetophenone; silicon compounds such as aluminosilicate, silicone compound, silane coupling agent.

[0022] The electrolytic solution of the present invention can be used, for example, in a wound aluminum electrolytic capacitor. A capacitor using the electrolytic solution according to the present invention can be manufactured by a normal method. For example, an anode foil having a dielectric oxide film formed by anodic oxidation on the surface of an aluminum foil with an effective surface area enlarged by etching, and a cathode foil made of an etched aluminum foil are wound through a separator to form a capacitor element. After impregnating the capacitor element with the electrolytic solution, it can be manufactured by a method of housing it in a bottomed cylindrical exterior case. As the separator, kraft paper, manila paper, etc. can be used.

[0023] The electrolytic solution of the present invention is particularly suitable for use as a driving electrolytic solution for medium and high voltage aluminum electrolytic capacitors.

[0024] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to the examples.

[0025] As the uronic acid of Formula I, galacturonic acid or glucuronic acid was used to prepare each electrolytic solution shown in Table 1. After preparation, the electrolytic solution was heated and stirred to reduce the water content to 5% by weight or less.

[0026] An anode lead and a cathode lead with a formed chemical conversion film were respectively connected to an aluminum anode foil subjected to an etching treatment and an oxide film formation treatment and an aluminum cathode foil subjected to an etching treatment, and then wound through a separator to form a capacitor element. After impregnating this capacitor element with each electrolytic solution for an electrolytic capacitor in Table 1, it was housed in a bottomed cylindrical exterior case made of aluminum, and a substrate self-supporting aluminum electrolytic capacitor with a rated voltage of 600 V, a capacitance of 100 μF, and a size of φ35×50L (mm) was produced.

[0027] The specific resistance was measured at -40°C and 30°C, and the specific resistance ratio was calculated. Also, the leakage current after 125°C·1000 hours and the product withstand voltage characteristics at 65°C were measured. The results are shown in Table 1.

Table 1

[0028] Conventional Example 2, in which the solvent consists solely of ethylene glycol (EG), exhibits poor low-temperature characteristics and a high resistivity ratio at -40°C / 30°C. In contrast, Conventional Example 1, which uses a mixed solvent of γ-butyrolactone (GBL) and EG, shows a significant decrease in resistivity ratio due to improved resistivity at -40°C, but the leakage current after high-temperature storage (125°C / 1000h) deteriorates significantly. In contrast, in Examples 1-4, by adding 0.1-0.5% by weight of galacturonic acid or glucuronic acid to the mixed solvent of GBL and EG, it was possible to significantly suppress leakage current after high-temperature storage while maintaining a low resistivity ratio of the electrolyte. As is clear from the comparison between Example 1 and Example 4, the effects of galacturonic acid and glucuronic acid were almost equivalent.

[0029] Comparative Example 1, in which the galacturonic acid concentration was less than 0.1% by weight, was able to suppress leakage current more effectively than Conventional Example 1, but the effect was not sufficient. On the other hand, in Comparative Example 2, where the concentration of galacturonic acid exceeded 0.5% by weight, the leakage current suppression effect was sufficient, but the product's withstand voltage characteristics deteriorated. Similar properties were also observed with uronic acids other than galacturonic acid and glucuronic acid, as shown in Formula I.

[0030] From the above examples, it was confirmed that by using an electrolyte containing γ-butyrolactone as the main solvent, ethylene glycol as a secondary solvent, and 0.1 to 0.5% by weight of uronic acid of formula I, an electrolytic capacitor can be obtained that maintains good low-temperature characteristics and voltage withstand characteristics while exhibiting low leakage current even when left unloaded at high temperatures.

Claims

1. An electrolyte characterized by containing 0.1 to 0.5% by weight of a uronic acid represented by formula I in a mixed solvent, with γ-butyrolactone as the main solvent and ethylene glycol as the secondary solvent. 【Chemistry 1】

2. The electrolyte according to claim 1, wherein the uronic acid is galacturonic acid and / or glucuronic acid.

3. The electrolyte according to claim 1, comprising an organic carboxylic acid (excluding uronic acid of formula I) or a salt thereof as a solute.

4. The electrolyte according to claim 3, wherein the organic carboxylic acid is a linear saturated aliphatic carboxylic acid with a molecular weight of 200 or more.

5. An electrolytic capacitor comprising the electrolyte according to any one of claims 1 to 4.

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