JP4849701B2 - Electrolytic solution for electrolytic capacitor and electrolytic capacitor using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolytic solution for an electrolytic capacitor, in particular, an electrolytic solution for an electrolytic capacitor having good high-temperature life characteristics, and an electrolytic capacitor using the same.
[0002]
[Prior art]
Electrolytic capacitors are generally obtained by chemically or electrochemically etching a strip of high-purity aluminum or other valve metal foil to enlarge the surface of the foil, and using this foil as an aqueous solution of ammonium borate. A separator made of manila paper or the like is formed of an anode electrode foil formed by chemical conversion treatment in a chemical conversion solution such as an oxide film layer on the surface, and a cathode electrode foil made of high-purity foil subjected only to etching treatment. To form a capacitor element. The 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 pulling out 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 is an external connection composed of a round bar part, a connection part that contacts the bipolar electrode foil, and a solderable metal fixed to the tip of the round bar part by welding or the like. It consists of parts.
[0004]
There are various electrolytic solutions for driving an electrolytic capacitor impregnated in a capacitor element depending on the performance of the electrolytic capacitor used. Among them, ethylene is used as an electrolytic solution for low pressure, particularly having high temperature and long life characteristics. A solution in which adipic acid is dissolved in glycol is known.
[0005]
[Problems to be solved by the invention]
However, in recent years, in the in-vehicle field, there has been an increasing demand for the use of electronic components in an engine room that is at a high temperature as the performance of automobiles becomes higher. Could not withstand. Further, the low temperature characteristics were not good, and the minimum use temperature was limited to use at -25 ° C.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic capacitor having good high-temperature life characteristics and good low-temperature characteristics, and an electrolytic solution used for the electrolytic capacitor.
[0007]
[Means for Solving the Problems]
The electrolytic solution for an electrolytic capacitor of the present invention uses, as a solvent, a solvent selected from two kinds of 3-methylsulfolane and 2,4-dimethylsulfolane, and a mixed solvent with sulfolane, and a quaternized cyclic amidinium as a solute. It is characterized by using salt.
[0008]
Moreover, the electrolyte solution is characterized in that the content of sulfolane is 20 to 70% by weight in the mixed solvent.
[0010]
The electrolytic capacitor of the present invention is characterized by using these electrolytic solutions.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The structure of the aluminum electrolytic capacitor of the present invention is the same as that of the prior art as shown in FIGS. Capacitor element 1 is formed by winding anode electrode foil 2 and cathode electrode foil 3 with separator 11 interposed therebetween. Further, as shown in FIG. 2, anode lead foil 2 and cathode electrode foil 3 are connected to lead wire 4 for anode lead and lead wire 5 for cathode lead, respectively. These lead wires 4 and 5 include a connection portion 7 that contacts the electrode foil, a round bar portion 6 that is formed integrally with the connection portion 7, and an external connection portion 8 that is fixed to the tip of the round bar portion 6. Further, 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. The lead wires 4 and 5 are electrically connected to the bipolar electrode foils 2 and 3 at the connecting portion 7 by means such as stitching or ultrasonic welding.
[0012]
Anode electrode foil 2 is an aluminum foil having a purity of 99% or more subjected to surface expansion treatment by etching chemically or electrochemically in an acidic solution, and then in an aqueous solution such as ammonium borate, ammonium phosphate or ammonium adipate. A chemical conversion treatment is performed and an anodized film layer is formed on the surface.
[0013]
The capacitor element 1 configured as described above is impregnated with an electrolytic solution for driving an aluminum electrolytic capacitor.
[0014]
The capacitor element 1 impregnated with the electrolytic solution as described above is housed in an outer case 10 made of bottomed cylindrical aluminum, and the sealing body 9 is attached to the opening of the outer case 10, and the end of the outer case 10 The outer case 10 is sealed by drawing. The sealing body 9 is made of, for example, an elastic rubber such as butyl rubber, and has through holes through which the lead wires 4 and 5 are led out.
[0015]
In the present invention, as the solvent of the electrolytic solution, one kind selected from 2-methyl sulfolane and 2,4-dimethyl sulfolane, and a mixed solvent with sulfolane are used.
[0016]
As a solvent to be mixed, as a protic organic polar solvent, monohydric alcohols (ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and Examples include oxyalcohol compounds (ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and the like). 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, hexamethylphosphoric amide, etc.), lactones (γ-butyrolactone, δ-valerolactone, γ-valerolactone, etc.), cyclic amides (N-methyl-2- Pyrrolidone, ethylene carbonate, propylene carbonate, isobutylene carbonate, etc.), nitrile (acetonitrile, etc.), oxide (dimethyl sulfoxide, etc.), 2-imidazolidinone [1,3-dialkyl-2-imidazolidinone (1,3 -Dimethyl-2-imidazolide 1,3-diethyl-2-imidazolidinone, 1,3-di (n-propyl) -2-imidazolidinone, etc.), 1,3,4-trialkyl-2-imidazolidinone (1,1, 3,4-trimethyl-2-imidazolidinone etc.)] and the like.
[0017]
As the solute contained in the electrolytic solution, a quaternary salt of a cyclic amidine compound having an acid conjugate base as an anionic component, which is usually used in an electrolytic solution for driving an electrolytic capacitor, is used. Examples of the cation constituting the quaternary salt of the cyclic amidine compound include cations obtained by quaternizing the following compounds. That is, imidazole monocyclic compounds (1-methylimidazole, 1,2-dimethylimidazole, 1,4-dimethyl-2-ethylimidazole, imidazole homologues such as 1-phenylimidazole, 1-methyl-2-oxymethylimidazole, Oxyalkyl derivatives such as 1-methyl-2-oxyethylimidazole, nitro and amino derivatives such as 1-methyl-4 (5) -nitroimidazole, 1,2-dimethyl-5 (4) -aminoimidazole), 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-ethylimidazoli , 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.
[0018]
Anionic components include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, benzoic acid, toluic acid, enanthic acid, malonic acid and other carboxylic acids, phenols, boric acid, phosphoric acid, carbonic acid, silicic acid and other acid conjugates. Examples are bases.
[0019]
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, sorbit, etc.), complexes of boric acid and polyhydric alcohols (ethylene glycol, glycerin, etc.) are used. The withstand voltage can be improved by adding a compound, a surfactant, colloidal silica or the like.
[0020]
Various additives can be added for the purpose of reducing leakage current or absorbing hydrogen gas. Examples of additives include aromatic nitro compounds, (p-nitrobenzoic acid, p-nitrophenol, etc.), phosphorus compounds (phosphoric acid, phosphorous acid, polyphosphoric acid, acidic phosphoric acid ester compounds), oxycarboxylic acids A compound etc. can be mentioned.
[0021]
The aluminum electrolytic capacitor using the electrolytic solution of the present invention as described above has good high-temperature life characteristics and also good low-temperature characteristics.
[0022]
Moreover, in the said electrolyte solution, when the content rate in the mixed solvent of sulfolane is 20 to 70%, a low temperature characteristic is still more favorable.
[0023]
Here, when a quaternized cyclic amidinium salt is used as the solute, the low-temperature characteristics become better. Examples of the quaternized cyclic amidinium salt include salts using the above-mentioned anion component and quaternized imidazolinium, quaternized pyrimidinium, or the like as a cation component.
[0024]
Further, as quaternized imidazolinium, 1,3-dimethylimidazolinium, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1-ethyl-3 -Methyl imidazolinium, 1-ethyl-2,3-dimethyl imidazolinium, etc. are mentioned.
[0025]
The quaternized pyrimidinium includes 1,3-dimethyl-4,5,6-trihydropyrimidinium, 1,2,3-trimethyl-4,5,6-trihydropyrimidinium, 1,2 , 3,4-tetramethyl-5,6-dihydropyrimidinium, 1-ethyl-3-methyl-4,5,6-trihydropyrimidinium, 1-ethyl-2,3-dimethyl-4,5 , 6-trihydropyrimidinium and the like.
[0026]
Here, in the conventional electrolytic solution using a quaternized cyclic amidinium salt such as a quaternized imidazolinium salt and a quaternized pyrimidinium salt as a solute, γ-butyrolactone or the like was used as a solvent. Then, there was a problem that the electrolyte leaked from between the sealing member 9 and the round bar portion 6 of the lead wire during the life test, but no leak occurred in the electrolyte of the present invention. The reason is assumed to be as follows.
[0027]
The mechanism by which the electrolyte solution in which the quaternized cyclic amidinium salt is dissolved leaks from the cathode lead portion is considered as follows. That is, in the conventional electrolytic capacitor, the natural immersion potential of the cathode lead wire 5 shows a higher potential than the natural immersion potential of the cathode electrode foil 3, so that when left unloaded, the cathode lead wire and the cathode foil. Thus, a local battery is formed, and a cathode current flows through the cathode lead wire. In a DC load state, more cathode current flows through the cathode lead wire than the cathode foil. In this way, in both cases of load and no load, a cathode current flows through the cathode lead wire. As a result, a reduction reaction of dissolved oxygen or hydrogen ions occurs on the cathode lead wire side, and the cathode lead wire becomes round. Hydroxide ions are generated at the electrolyte solution interface portion of the rod portion 6 and the connecting portion 7.
[0028]
And the hydroxide ion produced | generated by the reduction reaction of such dissolved oxygen or a hydrogen ion reacts with quaternized cyclic | annular amidinium, As a result, quaternized cyclic | annular amidinium opens a ring and becomes a secondary amine. Since this secondary amine has high volatility and low hygroscopicity, it is expected that even if it is generated between the round part of the cathode lead wire and the sealing body, it will quickly evaporate and not leak. The
[0029]
However, when hydroxyl ions are generated, γ-butyrolactone, which is a solvent, also reacts with the hydroxide ions to become γ-hydroxybutyric acid, which is a substance having a pH lowering effect. And the secondary amine mentioned above and this γ-hydroxybutyric acid are mixed, and the secondary amine produced by ring opening of the quaternized cyclic amidinium is closed by the pH lowering action of γ-hydroxybutyric acid. Then, it becomes a quaternized cyclic amidinium salt again. Since this quaternized cyclic amidinium salt is not volatile and has a high hygroscopic property, the quaternized cyclic amidinium salt regenerated between the round part of the cathode lead and the sealing body absorbs moisture and leaks. It becomes a liquid state. The above was inferred from the analysis results that the liquid leakage consisted of most of the water and the quaternized cyclic amidinium salt.
[0030]
On the other hand, in the present invention, as a solvent, one kind selected from 2-methylsulfolane and 2,4-dimethylsulfolane, and a mixed solvent with sulfolane are used, and these 3-methylsulfolanes are used. Since 2,4-dimethylsulfolane and sulfolane do not react with hydroxide ions, a substance having a pH lowering action such as γ-hydroxybutyric acid is not produced. Therefore, the quaternized cyclic amidinium salt is not regenerated, and the generated secondary amine volatilizes, so that the liquid leakage state does not occur.
[0031]
Furthermore, no leakage occurs even when a reverse voltage is applied to the electrolytic capacitor of the present invention. That is, when a reverse voltage is applied, a cathode current flows to the anode side. However, since the polarization resistance of the anode foil is extremely larger than that of the cathode foil, most of the cathode current on the anode side flows to the anode tab. It will be. Therefore, in the conventional electrolytic capacitor, liquid leakage may occur at the initial stage of the reverse voltage test. However, in the electrolytic capacitor of the present invention, it seems that the behavior is similar to the behavior on the cathode side as described above, but also in this case, the liquid leakage state is prevented. As described above, the leakage preventing effect of the present invention is extremely strong.
[0032]
As described above, according to the configuration of the present invention, the hydroxide ions generated in the vicinity of the round bar portion of the cathode lead wire disappear by reacting with the quaternized cyclic amidinium, and the generated secondary amine volatilizes. Therefore, it does not become a leak state.
[0033]
In the conventional electrolytic capacitor, when the cathode lead wire 4 and the anode lead wire 5 are in contact with each other when left unloaded, a local battery is constituted by the anode lead wire and the cathode electrode foil 3. A reduction reaction of dissolved oxygen or hydrogen ions occurred on the anode lead wire side, and hydroxide ions were generated, resulting in a liquid leakage state for the same reason as in the cathode lead portion.
[0034]
However, also in this case, according to the configuration of the present invention, the leakage is prevented for the same reason as the leakage is prevented in the cathode lead portion.
[0035]
For the reasons as described above, it is considered that liquid leakage is prevented in the present invention.
[0036]
Further, as the cathode electrode foil 3, a metal nitride selected from titanium nitride, zirconium nitride, tantalum nitride, niobium nitride, or a metal selected from titanium, zirconium, tantalum, niobium is deposited, plated, or coated. A cathode electrode foil coated by a conventionally known method can be used. Here, the part to be coated may be coated on the entire surface of the cathode electrode foil, or a part of the cathode electrode foil, for example, only one surface of the cathode electrode foil may be coated with metal nitride or metal as necessary. . As a result, the natural immersion potential of the cathode foil is nobler than the natural immersion potential of the cathode lead wire, and the cathode polarization resistance is also reduced. Therefore, when an overvoltage is applied, the cathode current of the cathode lead wire becomes minute and the generation of hydroxide ions on the cathode lead wire side is suppressed, which is more suitable for preventing leakage.
[0037]
In addition, an aluminum oxide layer formed by anodizing treatment with an aqueous solution of ammonium borate, an aqueous solution of ammonium phosphate, an aqueous solution of ammonium adipate or the like is formed on at least the surface of the round bar portion 6 of the lead wires 4 and 5, An insulating layer such as a ceramic coating layer made of ₂ O ₃ , SiO ₂ , ZrO ₂ or the like can be formed. As a result, in the case of no load, the area constituting the local battery of the cathode lead wire and the cathode foil is reduced, and in the case of the load, the cathode current flowing through the cathode lead wire is reduced, and in both cases Since the production of hydroxide ions on the cathode lead wire side is suppressed, the liquid leakage preventing effect is further improved.
[0038]
【Example】
Examples of the present invention will be described below.
[0039]
(Table 1) and (Table 2) show the composition of the electrolytic solution for electrolytic capacitors and the specific resistance at 30 ° C. and −40 ° C. of each example of the present invention.
[0040]
[Table 1]
* 3-MSL: 3-methylsulfolane
SL: sulfolane
EG: Ethylene glycol
EDMIP: 1-ethyl-2,3-dimethylimidazolinium phthalate
TMAP: Tetramethylammonium phthalate
AAd: Ammonium adipate
() In SL column:% by weight of sulfolane in the mixed solvent
[0041]
[Table 2]
* 2,4-DMSL: 2,4-dimethylsulfolane
() In SL column:% by weight of sulfolane in the mixed solvent
[0042]
Further, as Example 8, the specific resistance of 100 parts of Example 4, 100 parts of p-nitrobenzoic acid, 1 part, phosphoric acid, and 0.3 parts was measured. It was 14 kΩ-cm at ° C. As Example 16, the specific resistance of 100 parts of Example 12, 100 parts of p-nitrobenzoic acid, 1 part, phosphoric acid and 0.3 part was measured. It was 11 kΩ-cm at ° C.
[0043]
As is clear from (Table 1) and (Table 2), the specific resistance at 30 ° C. and −40 ° C. of Examples 2 to 13 of the present invention is sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane alone. In Comparative Examples 1 to 3 and the conventional example using ethylene glycol and ammonium adipate, which are used in the above, are equal to or better than the conventional examples, and good values are obtained. In particular, Examples 2 to 5, 8, 10 to 13 and 16 having a sulfolane content of 20 to 70% maintain a low specific resistance even at −40 ° C., and can be used at −40 ° C. Recognize. On the other hand, in Comparative Examples 1-3 and the conventional example, it solidifies at -40 degreeC and cannot be used at -40 degreeC. Here, the specific resistance at −25 ° C. of the conventional example was 9 kΩ-cm.
[0044]
Moreover, Examples 4 and 12 using 1-ethyl-2,3-dimethylimidazolinium phthalate as a solute are both 30 ° C. and −40 ° C. from Comparative Examples 6 and 9 using tetramethylammonium phthalate. The specific resistance is kept low.
[0045]
Next, in order to evaluate the high-temperature life characteristics, aluminum electrolytic capacitors were prepared using the electrolytic solutions of Examples 2, 5, 10, and 13 and the electrolytic solution of the conventional example. The rating of the aluminum electrolytic capacitor used here is 16V-47 μF, and the case size is φ6.3 mm × 5 mm. Then, a rated voltage was applied to each of 25 samples of these electrolytic capacitors at 125 ° C., and the rate of change in capacitance (ΔC) and loss tangent (tan δ) after 2000 hours and 4000 hours had elapsed. Measurements were made. The results are shown in (Table 3).
[0046]
[Table 3]
[0047]
As is clear from Table 3, the high-temperature life characteristics of the electrolytic capacitors of Examples 2, 5, 10, and 13 are better than those of the conventional examples, and the initial tan δ is kept low. 4000 hours guarantee is possible.
[0048]
Next, in order to evaluate the leakage characteristics, electrolytic capacitors using the electrolytic solutions of Examples 4 and 11, and 75% by weight of γ-butyrolactone and 1-ethyl-2,3-dimethylimidazole phthalate as Comparative Example 4 were used. Regarding electrolytic capacitors using 25% by weight of electrolytic solution of nickel, the rated voltage was applied to each of 25 samples at 85 ° C. and 85% RH, and there was no leakage after 500 hours, 1000 hours, and 2000 hours Was visually observed. The results are shown in (Table 4). Furthermore, using the same electrolytic capacitor, a reverse voltage of -1.5 V was applied to 25 samples at 85 ° C. and 85% RH, and there was no leakage after 250 hours, 500 hours, and 1000 hours. Was visually observed. The results are shown in (Table 5).
[0049]
[Table 4]
[0050]
[Table 5]
[0051]
As apparent from (Table 4), in Comparative Example 4, leakage occurred after 1000 hours, but the electrolytic capacitors using the electrolytic solutions of Examples 4 and 11 of the present invention also leaked after 2000 hours. Not getting good results. Further, as is clear from Table 5, also in the reverse voltage test, leakage occurred in 250 hours in Comparative Example 4, but no leakage occurred in 1000 hours in the examples of the present invention. The leakage prevention effect is extremely strong. As described above, it can be seen that liquid leakage prevention is realized by the electrolytic solution of the present invention.
[0052]
【The invention's effect】
As described above, the electrolytic solution for an electrolytic capacitor of the present invention uses, as a solvent, a solvent selected from two types selected from two types of 3-methylsulfolane and 2,4-dimethylsulfolane, and sulfolane. A quaternized cyclic amidinium salt such as a quaternized imidazolinium salt or a quaternized pyrimidinium salt is used.
[0053]
The electrolyte electrolytic capacitor using the excellent high-temperature life characteristics, further low-temperature characteristics Ri excellent der, is not to be leakage.
[0054]
Moreover, in the said electrolyte solution, a favorable low-temperature characteristic can be acquired by making sulfolane in a mixed solvent into 20 to 70 weight% of the whole solvent.
[Brief description of the drawings]
FIG. 1 is an internal cross-sectional view showing the structure of an aluminum electrolytic capacitor.
FIG. 2 is an exploded perspective view showing a structure of a capacitor element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Anode electrode foil 3 Cathode electrode foil 4 Lead wire for anode extraction 5 Lead wire for cathode extraction 6 Round bar portion 7 Connection portion 8 External connection portion 9 Sealing body 10 Exterior case 11 Separator

Claims (2)

As the solvent, 3-methyl sulfolane, 2,4-dimethyl sulphoxide one selected from the two kinds of the run, and a mixed solvent of sulfolane, as a solute, the electrolytic solution for an electrolytic capacitor using the quaternized cyclic amidinium salt An electrolytic solution for an electrolytic capacitor, wherein the content of sulfolane is 20 to 70% by weight in the mixed solvent . An electrolytic capacitor using the electrolytic solution for an electrolytic capacitor according to claim 1 .