JPH11238651A - Electrolytic solution for electrolytic capacitor and electrolytic capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the high-temperature life characteristic of an electrolytic capacitor and to prevent the occurrence of defective soldering in the capacitor by using a specific sulfolane as the solvent for the capacitor. SOLUTION: A capacitor element 1 is formed by winding an anode foil 2 and a cathode foil 3 with a separator 11 in between. A lead wire 4 for leading out anode and a lead wire 5 for leading out cathode are respectively connected to the two pieces of foil 2 and 3. Each lead wires 4 and 5 is constituted of a connecting section 7 which is brought into contact with the foil, a round bar section 6 integrally formed with the section 7, and an external connecting section 8 fixed to the front end of the section 6. Then the capacitor element 1 thus constituted is impregnated with an electrolytic solution for driving aluminum electrolytic capacitor by the use of 2,4-dimethyl sulfolane as the solvent of the electrolytic solution. The capacitor element 1 impregnated with the electrolytic solution is housed in an outer package case 10 and the case 10 is sealed by attaching a sealing body 9 to the opening of the case 10 and, at the same time, drawing the end section of the case 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for electrolytic capacitors, and more particularly to an electrolytic solution having good high-temperature life characteristics and an electrolytic capacitor using the same.

[0002]

2. Description of the Related Art Generally, an electrolytic capacitor is formed by chemically or electrochemically etching a strip-shaped foil of a valve metal such as aluminum or the like so as to enlarge the foil surface. An anode electrode foil having an oxide film layer formed on its surface by chemical conversion treatment in a chemical conversion solution such as an aqueous ammonium borate solution, and a cathode electrode foil made of a high-purity foil subjected to etching treatment only, And the like to form a capacitor element. Then, this capacitor element is impregnated with an electrolytic solution for driving an electrolytic capacitor, and then stored in a bottomed cylindrical outer case.
A sealing body made of elastic rubber is attached to the opening of the outer case, and the outer case is sealed by drawing.

[0003] Lead wires, which are electrode lead-out means for drawing out electrodes of both electrodes to the outside, are connected to the anode electrode foil and the cathode electrode foil by means such as stitching and ultrasonic welding. The lead wire as each electrode lead-out means has a round bar portion, a connection portion that comes into contact with the bipolar electrode foil, and an external connection made of a solderable metal fixed to the tip of the round bar portion by welding or the like. Department.

There are various electrolytic solutions for driving an electrolytic capacitor impregnated in a capacitor element, depending on the performance of the electrolytic capacitor to be used. Among them, an electrolytic solution for a low pressure, particularly having a high temperature and a long life characteristic is used. As an example, a solution in which adipic acid is dissolved in ethylene glycol is known.

[0005]

However, in recent years,
In the field of in-vehicle applications, demands for use of electronic components in a high-temperature engine room have been increasing in accordance with higher performance of automobile performance.Electrolytic capacitors using the electrolytic solution can withstand this high-temperature use. could not. Also,
At the time of soldering when mounting this electrolytic capacitor on a circuit board, depending on the heat treatment conditions, due to the rise in internal pressure,
There is a problem that the appearance is deformed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic capacitor having good high-temperature life characteristics and improved soldering failure, and an electrolytic solution used for the electrolytic capacitor.

[0007]

An electrolytic solution for an electrolytic capacitor according to the present invention is characterized in that 2,4-dimethylsulfolane is used as a solvent.

Further, the electrolytic capacitor of the present invention has a
-It is characterized in that an electrolytic solution using dimethylsulfolane as a solvent is used.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an aluminum electrolytic capacitor according to the present invention has the same structure as that of the prior art, as shown in FIGS. The capacitor element 1 is formed by winding an anode electrode foil 2 and a cathode electrode foil 3 with a separator 11 interposed therebetween.
As shown in FIG. 2, the anode electrode foil 2 and the cathode electrode foil 3 have a lead wire 4 for leading the anode and a lead wire 5 for leading the cathode.
Are connected respectively. These leads 4,5
Is composed of a connecting portion 7 in contact with the electrode foil, a round bar portion 6 formed integrally with the connecting portion 7, and an external connecting portion 8 fixed to the tip of the round bar portion 6. The connecting portion 7 and the round bar portion 6 are made of high-purity aluminum, and the external connecting portion 8 is made of a copper-plated steel wire plated with solder. These lead wires 4, 5
Are electrically connected to the bipolar electrode foils 2 and 3 at the connection portion 7 by means such as stitching or ultrasonic welding.

The anode electrode foil 2 is formed by etching an aluminum foil having a purity of 99% or more chemically or electrochemically in an acidic solution and expanding the surface of the foil, and then forming an ammonium borate, ammonium phosphate or ammonium adipate. A chemical conversion treatment is performed in an aqueous solution, and an anodic oxide film layer is formed on the surface.

The capacitor element 1 constructed as described above
Is impregnated with an electrolytic solution for driving an aluminum electrolytic capacitor.

The capacitor element 1 impregnated with the electrolytic solution as described above is housed in an outer case 10 made of aluminum having a bottomed cylindrical shape, and a sealing body 9 is attached to an opening of the outer case 10. Is subjected to a drawing process to seal the outer case 10. The sealing body 9 is made of an elastic rubber such as butyl rubber, for example, and has through holes for leading the lead wires 4 and 5, respectively.

In the present invention, 2,4-dimethylsulfolane is used as a solvent for the electrolytic solution. Further, it can be used as a mixed solvent with another solvent.

As the solvent to be mixed, monohydric alcohols (ethanol, propanol, butanol, pentanol, hexanol,
Cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and oxyalcohol compounds (ethylene glycol,
Propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.). Examples of aprotic organic polar solvents include amides (N-methylformamide, N, N─dimethylformamide, N─ethylformamide, N, N─diethylformamide, N─methylacetamide, N, N─dimethylacetamide , N-ethylacetamide, N, N-diethylacetamide, hexamethylphosphoramide, lactones (γ-butyrolactone, δ-valerolactone, etc.), cyclic amides (N-methyl-2-pyrrolidone, ethylene carbonate, Propylene carbonate,
Isobutylene carbonate, etc.), nitrile type (acetonitrile, etc.), oxide type (dimethylsulfoxide, etc.),
2-imidazolidinone [1,3-dialkyl-2-imidazolidinone (1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,
3-di (n-propyl) -2-imidazolidinone),
1,3,4-trialkyl-2-imidazolidinone (1,3,4-trimethyl-2-imidazolidinone and the like)] and the like.

The solute contained in the electrolytic solution includes ammonium salts, amine salts, quaternary ammonium salts and quaternary cyclic amidine compounds which are usually used in electrolytic solutions for driving electrolytic capacitors and have an anionic component of a conjugate base of an acid. Salts. Examples of the amine constituting the amine salt include primary amines (eg, methylamine, ethylamine, propylamine, butylamine, ethylenediamine), secondary amines (eg, dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine), and tertiary amines (eg, trimethylamine). , Triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo (5,4,0) undene 7 and the like. As the quaternary ammonium constituting the quaternary ammonium salt, tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), pyridium (1-methylpyridium) 1,1-ethylpyridium, 1,3-diethylpyridium, etc.). In addition, examples of the cation constituting the quaternary salt of the cyclic amidine compound include cations obtained by quaternizing the following compounds. That is, the imidazole monocyclic compound (1─
Methylimidazole, 1,2-dimethylimidazole,
Imidazole homologues such as 1,4-dimethyl-2-ethylimidazole, 1-phenylimidazole, oxyalkyl derivatives such as 1-methyl-2-oxymethylimidazole, 1-methyl-2-oxyethylimidazole, 1
Nitro and amino derivatives such as -methyl-4 (5) -nitroimidazole, 1,2-dimethyl-5 (4) -aminoimidazole, etc., benzimidazole (1-methylbenzimidazole, 1-methyl-2-benzylbenzimidazole) Etc.), compounds having a 2-imidazoline ring (1 @ -methylimidazoline, 1,2-dimethylimidazoline, 1,2,4-trimethylimidazoline, 1,4-
Dimethyl-2-ethylimidazoline, 1-methyl-2-
Phenylimidazoline, etc.), compounds having a tetrahydropyrimidine ring (1-methyl-1,4,5,6-tetrahydropyrimidine, 1,2-dimethyl-1,4,5,6)
-Tetrahydropyrimidine, 1,8-diazabicyclo [5.4.0] undecene-7, 1,5-diazabicyclo [4.3.0] nonene-5, and the like.

Examples of the anionic component include carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, phenols, boric acid, phosphoric acid, carbonic acid, and silicic acid. Illustrated are conjugate bases of acids.

Further, in the electrolytic solution for electrolytic capacitors of the present invention, boric acid compounds such as boric acid, complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), boric acid and polyhydric alcohols (ethylene glycol, glycerin, etc.) By adding a complex compound such as a surfactant, colloidal silica and the like, the withstand voltage can be improved.

Various additives can be added for the purpose of reducing leakage current and absorbing hydrogen gas. Examples of the additive include an aromatic nitro compound, (p-nitrobenzoic acid, p-nitrophenol, etc.), a phosphorus compound (phosphoric acid, phosphorous acid, polyphosphoric acid, acidic phosphoric acid ester compound), oxycarboxylic acid And the like.

The aluminum electrolytic capacitor using the electrolytic solution of the present invention as described above has good high-temperature life characteristics and can prevent poor soldering.

Further, in a conventional electrolytic solution using a quaternized cyclic amidinium salt such as a quaternized imidazolinium salt and a quaternized pyrimidinium salt as a solute, γ ラ ク ト butyrolactone is used as a solvent. With the liquid, there was a problem that the electrolyte leaked from between the sealing body 9 and the round bar portion 6 of the lead wire during the life test, but the use of the solvent of the present invention can also prevent this leak. The reason is presumed to be as follows.

The mechanism by which the electrolyte in which the quaternized cyclic amidinium salt is dissolved leaks from the cathode lead portion is considered as follows. In other words, when left unloaded, in a conventional electrolytic capacitor, the spontaneous immersion potential of the cathode lead shows a more noble potential than the spontaneous immersion potential of the cathode foil. Is configured. As a result, a reduction reaction of dissolved oxygen or hydrogen ions occurs on the cathode lead wire side, and the concentration of hydroxyl ions at the cathode-electrode-electrolyte interface portion increases.

The hydroxyl ion generated by the reduction reaction of the dissolved oxygen or hydrogen ion reacts with the quaternized cyclic amidinium, and the quaternized cyclic amidinium is opened to form a secondary amine. Since this secondary amine has high volatility and low hygroscopicity, it is expected that even if it is formed between the round bar portion of the cathode lead wire and the sealing body, it will evaporate quickly and will not be in a liquid leakage state. You.

However, when hydroxyl ions are generated,
Γ-butyrolactone, which is a solvent, also reacts with this hydroxyl ion to form γ-hydroxybutyric acid. Then, the above-mentioned secondary amine and this γ-hydroxybutyric acid are mixed, and the pH-lowering effect of γ-hydroxybutyric acid causes the quaternized cyclic amidinium to be opened and the secondary amine to be closed. Thus, it again becomes a quaternized cyclic amidinium salt. And since this quaternized cyclic amidinium salt has no volatility and high hygroscopicity, when it is formed between the round bar portion of the cathode lead wire and the sealing body, it absorbs moisture and becomes a liquid leakage state. The above was inferred from the results of analysis that the leak consisted of most of the water and the quaternized cyclic amidinium salt.

On the other hand, in the present invention, 2,4-dimethylsulfolane is used as a solvent, and since this 2,4-dimethylsulfolane does not react with hydroxyl ions, it reacts with the above-mentioned secondary amine. Is not produced. Therefore, the generated secondary amine is volatilized, and the liquid does not leak.

As described above, according to the configuration of the present invention,
Hydroxide ions generated in the vicinity of the cathode lead wire react with the quaternized cyclic amidinium and disappear, and the generated secondary amine is volatilized, so that the liquid does not leak.

In a conventional electrolytic capacitor,
If the cathode lead and the anode lead come into contact with each other when no load is left, a local battery will be composed of the anode lead and the cathode foil, and the reduction reaction of dissolved oxygen or hydrogen ions on the anode lead side Was generated to generate hydroxyl ions, and the liquid was in a leak state for the same reason as in the cathode lead portion.

However, also in this case, according to the configuration of the present invention, liquid leakage is prevented for the same reason that liquid leakage is prevented at the cathode lead portion.

For the reasons described above, it is considered that liquid leakage is prevented in the present invention.

As the cathode electrode foil 3, titanium nitride,
Coating a metal nitride selected from zirconium nitride, tantalum nitride, and niobium nitride, or a metal selected from titanium, zirconium, tantalum, and niobium by a conventionally known method such as an evaporation method, a plating method, or a coating method. Can be. Here, the portion to be coated may cover the entire surface of the cathode electrode foil 3 or, if necessary, a portion of the cathode electrode foil 3, for example, only one surface of the cathode electrode foil 3 may be coated with metal nitride or metal. You may. As a result, the natural immersion potential of the cathode lead wire is lower than the natural immersion potential of the cathode foil, and when an overvoltage is applied, the generation of hydroxyl ions is suppressed. Is more preferable.

An aluminum oxide layer formed by anodic oxidation with an aqueous solution of ammonium borate, an aqueous solution of ammonium phosphate or an aqueous solution of ammonium adipate is formed on at least the surface of the round bar portion 6 of the lead wires 4 and 5. Al ₂ O ₃ , SiO ₂ , ZrO ₂
It is possible to form an insulating layer such as a ceramic coating layer made of such as. As a result, the area of the cathode lead wire and the cathode foil constituting the local battery is reduced, and the generation of hydroxyl ions is suppressed, so that the effect of preventing liquid leakage is further improved.

[0031]

Embodiments of the present invention will be described below.

Table 1 shows the compositions of the electrolytic solutions for electrolytic capacitors of the examples of the present invention and the conventional examples.

[0033]

[Table 1] * 2,4-DMSL: 2,4-dimethylsulfolane EG: ethylene glycol EDMIP: 1-ethyl-2,3-dimethylimidazolinium phthalate TMAP: tetramethylammonium phthalate AAd: ammonium adipate

Further, as Embodiment 3, Embodiments 1 and 100
The mixture was prepared by adding p-nitrobenzoic acid, 1 part, phosphoric acid and 0.3 part to each part.

Then, in order to evaluate the defective soldering rate and the high-temperature life characteristics, an aluminum electrolytic capacitor was prepared using these electrolytic solutions. The rating of the aluminum electrolytic capacitor prepared here is 16 V-47 μF, and the case size is φ6.3 mm × 5 mm.

In order to evaluate the defective soldering rate, 100 electrolytic capacitors were mounted on an epoxy board, and
It passed through a solder reflow furnace. The heating conditions of the reflow furnace were peak 250 ° C., 5 seconds hold, 200 ° C., 60 seconds hold, 180
° C and 240 seconds. The number of appearance defects at this time is shown in (Table 2).

[0037]

[Table 2]

As is apparent from Table 2, the appearance defect at the time of soldering of the electrolytic capacitor of the embodiment of the present invention is improved as compared with the conventional example, and the defect rate is 0.

Next, in order to evaluate the high temperature life characteristics, a rated voltage was applied to 125 samples at 125 ° C.
The change rate of the capacitance after 0 hour and 4000 hours (Δ
C), the tangent (tan) of the loss angle was measured. The results are shown in (Table 3).

[0040]

[Table 3] * Cap (μF), ΔC (%), LC (μA)

As is clear from Table 3, the high-temperature life characteristics of the electrolytic capacitors of the examples are better than those of the conventional example, and it is possible to guarantee at 125 ° C. for 4000 hours.

Next, in order to evaluate the leakage characteristics, electrolytic capacitors using the electrolytic solutions of Examples 1 and 3 and 75% of γ─butyrolactone and 1-ethyl-2,3-dimethylimidazophthalate as comparative examples were used. For an electrolytic capacitor using a 25% lithium solution, 85
The rated voltage is applied at 85 ° C. and 85% RH for 500 hours.
The presence or absence of liquid leakage after 1000 hours and 2000 hours was visually observed. The results are shown in (Table 4).

[0043]

[Table 4]

As is clear from Table 4, in the comparative example using γ─butyrolactone as a solvent, 500 to 10
Although liquid leakage occurred after 00 hours, the electrolytic capacitors using the electrolytic solutions of Examples 1 and 2 of the present invention did not leak even after 2000 hours, and thus obtained good results.

[0045]

As described above, the electrolytic solution for an electrolytic capacitor according to the present invention uses 2,4-dimethylsulfolane as a solvent.

An electrolytic capacitor using this electrolytic solution has a good high-temperature life characteristic and also prevents poor soldering.

Further, by using the electrolytic solution of the present invention, liquid leakage can be prevented.

[Brief description of the drawings]

FIG. 1 is an internal sectional view showing the structure of an aluminum electrolytic capacitor.

FIG. 2 is an exploded perspective view showing the structure of the capacitor element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Anode electrode foil 3 Cathode electrode foil 4 Lead wire for anode drawing 5 Lead wire for cathode drawing 6 Round bar part 7 Connection part 8 External connection part 9 Sealing body 10 Exterior case 11 Separator

[Procedure amendment]

[Submission date] March 13, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Electrolytic solution for electrolytic capacitor
Electrolytic capacitor used

Claims (2)

[Claims] 1. An electrolytic solution for an electrolytic capacitor using 2,4-dimethylsulfolane as a solvent. 2. An electrolytic capacitor comprising 2,4-dimethylsulfolane as a solvent and using an electrolytic solution for an electrolytic capacitor.