JP2005109054A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for an electrolytic capacitor having a high withstand voltage and also excellent high-temperature lifetime characteristics. <P>SOLUTION: In the electrolyte for the electrolytic capacitor, 3,5,5-trimethyl-hexanoic acid or 2,2,5,5-tetramethyl-hexanoic acid or these salts are added to the electrolyte in which one kind or more of the polyvalent alcohol complex compound of boric acid obtained from boric acid and polyvalent alcohol or its salt is dissolved in a solvent using ethylene glycol as a main body. The electrolyte has high withstand-voltage characteristics, and also has high-temperature lifetime characteristics. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrolytic solution for electrolytic capacitors, and more particularly to an electrolytic solution for medium to high pressure.

  The electrolytic solution for the electrolytic capacitor uses a valve metal having an insulating oxide film formed on the surface of aluminum or tantalum as an anode electrode, and the oxide film layer is a dielectric, and an electrolyte layer is formed on the surface of the oxide film layer. And an electrode for current collection, usually called a cathode, is arranged.

  The electrolytic solution for electrolytic capacitors directly contacts the dielectric layer as described above and acts as a true cathode. That is, the electrolytic solution is interposed between the dielectric of the electrolytic capacitor and the current collecting cathode, and the resistance component of the electrolytic solution is inserted in series with the electrolytic capacitor. Therefore, the characteristics of the electrolytic solution are a major factor that affects the characteristics of the electrolytic capacitor.

In the prior art of electrolytic capacitors, examples of using butyloctanedioic acid as a solute as an electrolyte for medium and high pressure (Patent Document 1) and examples using 1,7-octanedicarboxylic acid as a solute (Patent Document 2) is there. Electrolytic solutions using these organic carboxylic acids or their salts have high spark voltage and electrical conductivity, and high solubility, so that they have good low-temperature characteristics.
Japanese Patent Publication No. 60-13296 Japanese Patent Publication No. 63-15738

  However, in these electrolytic solutions, the esterification reaction proceeds between the hydroxyl group of ethylene glycol and the carboxyl group of the organic carboxylic acid, hydration deterioration proceeds due to the generation of water, and tan δ of the electrolytic capacitor increases. Furthermore, the organic carboxylic acid forms a complex with aluminum on the surface of the electrode foil, resulting in a decrease in the effective area of the electrode foil, resulting in a phenomenon that the capacitance decreases. For this reason, there exists a problem that the lifetime characteristic in the high temperature of an electrolytic capacitor is not enough.

  Therefore, an object of the present invention is to provide an electrolyte for medium and high pressures having high withstand voltage characteristics and good high-temperature life characteristics.

  In order to solve the above-mentioned problems, the electrolytic solution for electrolytic capacitors of the present invention is a kind of a polyhydric alcohol complex compound of boric acid or a salt thereof obtained from boric acid and a polyhydric alcohol in a solvent mainly composed of ethylene glycol. 3,5,5-trimethylhexanoic acid, 2,2,5,5-tetramethylhexanoic acid or a salt thereof is added to the electrolytic solution thus dissolved.

  Furthermore, the polyhydric alcohol in the polyhydric alcohol complex compound of boric acid in the electrolytic solution is a sugar alcohol selected from erythrite, arabit, adnit, sorbit, mannitol, dulcit, and tarit.

  In addition, one or more aromatic nitro compounds are added to the electrolytic solution.

（式中、Ｒ₁ 、Ｒ₂ は、炭素数１〜１８の同一または異なってよいアルキル基または水素原子を表わし、少なとも一つはアルキルである。）で示される酸性アルキル燐酸エステルあるいは、燐酸、亜燐酸を一種又は二種以上添加したことを特徴とする。 Furthermore, the electrolyte has the general formula:

(Wherein R ₁ and R ₂ represent the same or different alkyl group having 1 to 18 carbon atoms or a hydrogen atom, and at least one is alkyl), or an acidic alkyl phosphate ester or phosphoric acid 1 or 2 or more types of phosphorous acid were added.

  The electrolytic solution for electrolytic capacitors of the present invention contains, as a main solute, a polyhydric alcohol complex compound of boric acid or a salt thereof (hereinafter referred to as a polyhydric alcohol complex compound of boric acid) obtained from boric acid and a polyhydric alcohol. The polyhydric alcohol in the polyhydric alcohol complex compound of boric acid includes ethylene glycol, propylene glycol, trimethylol propane, trimethylol ethane, pentaerythritol, polyvinyl alcohol, etc., and further, trit, tetrit, pentite, hexit, Examples thereof include sugar alcohols such as petite, octet, nonit, decite, and dodecite.

  Here, the polyhydric alcohol complex compounds of boric acid are obtained by synthesizing boric acid and polyhydric alcohol. When mixing and preparing the electrolytic solution, a predetermined amount of boric acid and polyhydric alcohol are mixed in ethylene glycol. It can also be obtained by heating and dissolving and synthesizing in an electrolytic solution. In the latter method, water is formed (3 mol of water per 1 mol of boric acid) during the formation of the polyhydric alcohol complex compound of boric acid. Therefore, if necessary, the water is removed by heating and stirring in an open system.

  Then, 3,5,5-trimethylhexanoic acid or 2,2,5,5-tetramethylhexanoic acid or a salt thereof is added. The total amount of boric acid is 5 to 100% by weight, preferably 30 to 100% by weight. Here, the total amount of boric acid is, as described above, the polyhydric alcohol complex compounds of boric acid are prepared from boric acid and polyhydric alcohol. The total amount of boric acid used at that time is shown.

  The electrolytic solution of the present invention described above has good withstand voltage characteristics and good life characteristics. That is, the conventional electrolyte solution has a problem that the characteristics deteriorate due to an esterification reaction or the like during a high-voltage high-temperature test, but the electrolyte solution of the present invention solves such a problem, and withstand voltage characteristics, life The characteristics are also good.

  The electrolytic solution of the present invention is obtained by adding organic carboxylic acids in an amount of 5 to 100% by weight, preferably 30 to 100% by weight, based on the total amount of boric acid. If it falls and exceeds this range, the capacitance change rate will rise.

  And the content in the electrolyte solution of the solute which consists of these polyhydric alcohol complex compounds of boric acid and organic carboxylic acids is 3 to 50 weight%, Preferably it is 5 to 20 weight%. If it is less than this range, the ion concentration is low, and if it exceeds this range, the mobility of the electrolyte is increased due to the increase in the viscosity of the electrolyte solution, so that the conductivity is significantly reduced.

  And ammonia gas is inject | poured and added to the electrolyte solution formed in this way, pH is adjusted, and the electrolyte solution of this invention is formed.

  Here, as the polyhydric alcohol in the polyhydric alcohol complex compound of boric acid, a sugar alcohol having a hydroxyl group at the cis position such as erythrite, arabit, adnit, sorbit, mannitol, dulcite, and tarit is used, and further, at a high temperature. It is possible to suppress a decrease in electrical conductivity. This is presumably because, when a sugar alcohol having a hydroxyl group at the cis position is used, the two hydroxyl groups at the cis position are bonded to boric acid to form a more stable boric acid complex compound at high temperatures. Moreover, although the reason is not clear, the spark voltage can be increased. Of these sugar alcohols having a hydroxyl group at the cis position, mannitol is most preferred. And content of the sugar alcohol which has a hydroxyl group of a cis-position is 0.4-3.0 with respect to boric acid 1 by weight ratio, Preferably, it is the range of 1.0-2.0. If it is less than this range, the rate of decrease in capacitance at high temperatures will increase, and if this range is exceeded, the initial conductivity will decrease.

  Examples of the salt of the polyhydric alcohol complex compound of boric acid and the salt of the organic carboxylic acid compound in the present invention include ammonium salt, amine salt, quaternary ammonium salt and quaternary ammonium salt of cyclic amidine compound. As amines constituting the amine salt, primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, monoethanolamine, etc.), secondary amines (dimethylamine, diethylamine, dipropylamine, ethylmethylamine, diphenylamine, diethanolamine) Etc.), tertiary amines (trimethylamine, triethylamine, tributylamine, triethanolamine, ethyldimethylamine, etc.), 1,8-diazabicyclo (5,4,0) -undecene-7, and the like. Of these, ammonium salts are preferred.

  Although the solvent is mainly ethylene glycol, a protic polar solvent, an aprotic solvent, or water can be added for the purpose of improving low temperature characteristics and reducing specific resistance. Protic polar solvents include monohydric alcohols (methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, cyclopentanol, benzyl alcohol, etc.), polyhydric alcohols and oxyalcohol compounds (propylene glycol, glycerin, methyl cellosolve) Ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol, etc.). Examples of aprotic solvents include amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-dimethylformamide, N-methylacetamide, hexamethylphosphoric amide, etc.), lactones, Typical examples include cyclic amides, carbonates (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, etc.), nitriles (acetonitrile) oxides (dimethyl sulfoxide, etc.), and the like.

  Further, by adding an aromatic nitro compound to the electrolytic solution, an increase in the internal pressure of the capacitor can be suppressed, and the life characteristics of the capacitor can be improved. This seems to be due to the reduction reaction of the nitro group with the hydrogen gas generated inside the capacitor. The amount of the aromatic nitro compound added is 0.01 to 7.0% by weight, preferably 0.1 to 5.0% by weight. If it is less than this range, an effect will fall, and if it exceeds this range, the electrical conductivity of electrolyte solution will fall.

  Specific examples of aromatic nitro compounds include nitrophenol, dinitrophenol, nitrobenzoic acid, nitrotoluene, dinitrotoluene, nitroxylene, nitrobenzene, dinitrobenzene, nitrobenzyl alcohol, nitroacetophenone, nitroanisole, dimethoxynitrobenzene, nitroaniline, nitro Examples include phenetole, nitrophthalic acid, 2- (4-nitrophenoxy) ethanol, and the like.

  Further, by adding an acidic alkyl phosphate compound represented by (Chemical Formula 2), phosphoric acid, and phosphorous acid to the electrolytic solution, an increase in leakage current at a high temperature of the capacitor can be suppressed. This seems to be due to the effect of these additives to suppress the hydration deterioration of the anodized film that occurs when the capacitor is left for a long time. The addition amount of phosphoric acid and phosphorous acid is 0.01 to 1.0% by weight, preferably 0.1 to 0.5% by weight. The addition amount of the acidic alkyl phosphate compound is 0.01 to 5.0% by weight, preferably 0.1 to 3.0% by weight. Below this range, the effect decreases, and beyond this range, the spark voltage decreases.

As described above, the electrolytic solution for electrolytic capacitors of the present invention is obtained by dissolving at least one polyhydric alcohol complex compound of boric acid or a salt thereof obtained from boric acid and polyhydric alcohol in a solvent mainly composed of ethylene glycol. An electrolytic solution for an electrolytic capacitor in which 3,5,5-trimethylhexanoic acid, 2,2,5,5-tetramethylhexanoic acid or a salt thereof is added to the electrolytic solution, and has high withstand voltage characteristics. Good high-temperature life characteristics.

  Examples of the present invention will be described below.

  (Table 1) shows the spark voltage for the composition of the electrolytic solution for electrolytic capacitors and the electrolytic capacitor of 750V-90 μA for the examples of the present invention and comparative examples. Here, the electrolytic solution was prepared by a conventional method, and ammonia gas was injected to adjust the pH.

（表１）から分かるように、実施例の火花電圧は比較例より良好であることが分かる。また、（表２）から分かるように、高温寿命特性も良好である。
And (Table 2) shows the initial characteristics of a 400V-220 μF electrolytic capacitor using the electrolytic solution of the example in (Table 1), and the characteristics after 500 hours of applying the rated voltage at 105 ° C. Show.

As can be seen from Table 1, the spark voltage of the example is better than that of the comparative example. Moreover, as can be seen from (Table 2), the high-temperature life characteristics are also good.

Claims (4)

  3,5,5-trimethylhexanoic acid or 2 in an electrolytic solution in which at least one polyhydric alcohol complex compound of boric acid or a salt thereof obtained from boric acid and polyhydric alcohol is dissolved in a solvent mainly composed of ethylene glycol. Electrolytic solution for electrolytic capacitors to which 2,5,5-tetramethylhexanoic acid or a salt thereof is added.   2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the polyhydric alcohol in the polyhydric alcohol complex compound of boric acid is a sugar alcohol in the cis position selected from erythrite, arabit, adnit, sorbit, mannitol, dulcite, and tarit. .   The electrolytic solution for electrolytic capacitors according to claim 1, wherein one or more aromatic nitro compounds are added. General formula:

(Wherein R ₁ and R ₂ represent the same or different alkyl group having 1 to 18 carbon atoms or a hydrogen atom, and at least one is alkyl), or an acidic alkyl phosphate ester represented by: The electrolytic solution for electrolytic capacitors according to claim 1, wherein one or more types of phosphorous acid are added.