JP2007273926A - Electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic capacitor having long service life characteristics, low impedance characteristics and proper low-temperature characteristics. <P>SOLUTION: This electrolytic capacitor employs an electrolyte containing a salt having dicyanamide as anion and 20-80 wt.% sulfolane; and as a cathode electrode foil, at least a foil having electrode potential in the electrolyte, exhibiting noble potential higher than that of a cathode extracting means. The electrolyte contains not more than 75 wt.% γ-butyrolactone. Since the decrease in dicyanamide anion during service life test is suppressed, even if absorption of humidity occurs during manufacturing process, the electrolytic capacitor described will have proper service life characteristics, low impedance characteristics, low-temperature characteristics and superior stability of electrostatic capacitance, as well. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrolytic capacitor, and more particularly to an electrolytic capacitor having long life characteristics and low impedance characteristics.

  Electrolytic capacitors are chemically or electrochemically etched on high-purity aluminum foil to enlarge the surface of the aluminum foil, and this aluminum foil is chemically treated in a chemical conversion solution such as an adipic acid aqueous solution. A capacitor element is formed by winding an anode electrode foil on which an oxide film layer is formed and a cathode electrode foil made of high-purity aluminum foil that has been subjected only to an etching process through a separator made of manila paper or the like. The capacitor element is then impregnated with an electrolytic solution for driving an electrolytic capacitor and then stored in a bottomed cylindrical outer case made of aluminum or the like. A sealing body made of elastic rubber is attached to the opening of the outer case, and the outer case is sealed by drawing.

Here, as an electrolytic solution for driving an electrolytic capacitor having high conductivity impregnated in a capacitor element, an imidazolinium cation, which is a cation obtained by quaternizing a cyclic amidine compound as a solute, with γ-butyrolactone as a solvent, as a cation component Further, a salt in which a conjugate base of an acid such as phthalate ion is used as an anion component, and a salt in which an aluminum tetrafluoride anion having high conductivity characteristics is used as an anion component are used.

On the other hand, among electrolytic capacitors, there is a strong demand for extending the life of electrolytic capacitors that have difficulties in life characteristics. Such a deterioration of the life of the electrolytic capacitor is largely caused by evaporation of the solvent of the electrolytic solution through the sealing member. Therefore, there is an attempt to extend the life by using a non-volatile ionic liquid as an electrolytic solution for an electrolytic capacitor (Patent Document 1).
JP 2005-353568 A

  However, when such an ionic liquid is used as an electrolytic solution for an electrolytic capacitor, it has been found that the impedance rises in the life test and long life characteristics cannot be obtained. Therefore, an object of the present invention is to provide an electrolytic solution for an electrolytic capacitor having a long-life characteristic and a high conductivity characteristic that have not been conventionally provided.

  The present inventors have investigated the cause of the deterioration of the life characteristics when an ionic liquid having dicyanamide as an anion is used. As a result, it is considered that the dicyanamide anion decomposes even when the moisture content of the electrolytic capacitor is 3 wt% or less, and further 0.2 to 0.3 wt%. It has been found that the lifetime decreases and the life characteristics deteriorate.

  Therefore, as a result of studies to suppress this decrease in conductivity, 20 to 80 wt% of sulfolane is contained, and at least the electrode potential in the electrolyte as a cathode electrode foil shows a more noble potential than the cathode extraction means. It has been found that the use of the foil suppresses the decrease in conductivity during the life test and also keeps the conductivity at the initial and low temperatures high. In addition, the stability of the capacitance after the life test is also good.

Furthermore, when γ-butyrolactone is contained in an amount of 75 wt% or less, an electrolytic solution having higher conductivity than an electrolytic solution containing a salt having aluminum tetrafluoride as an anion can be obtained.

As described above, the electrolytic solution for an electrolytic capacitor used in the present invention comprises a salt having dicyanamide represented by the following general formula (1) as an anion and 20 to 80 wt% of sulfolane.

Furthermore, the electrolytic solution for electrolytic capacitors contains 75 wt% or less of γ-butyrolactone in the electrolytic solution.

And the electrolytic capacitor of the present invention uses the electrolytic solution for electrolytic capacitor containing water, and uses a foil whose electrode potential in the electrolytic solution is more noble than the cathode extraction means as the cathode electrode foil. Features.

Here, the water content is 0.1 wt% to 3 wt%, preferably 0.1 to 1 wt%, and more preferably 0.1 to 0.5 wt%.

    As described above, at least the electrode potential in the electrolyte solution as the cathode electrode foil is higher than the cathode extraction means as the cathode electrode foil, the electrolyte solution containing the dicyanamide salt of the present invention and 20 to 80 wt% sulfolane. The electrolytic capacitor using the foil shown has unprecedented long life characteristics and high electrical conductivity. Moreover, the liquid leakage characteristic seen in the quaternary ammonium salt is good due to the synergistic effect of the electrochemical characteristics of the cathode electrode foil used in the present invention and the characteristics of the electrolytic solution used in the present invention. Furthermore, when γ-butyrolactone of 75 wt% or less is contained in the electrolytic solution, it can have unprecedented high conductivity characteristics and low temperature characteristics.

  And even if the electrolytic capacitor using these electrolyte solutions for electrolytic capacitors contains 3 wt% or less of moisture due to moisture absorption during the manufacturing process of the electrolytic capacitor, the impedance characteristics do not deteriorate during the life test. Furthermore, the capacitance is more stable than in the past.

  The electrolytic capacitor of the present invention is manufactured as follows. The anode electrode foil and the cathode electrode foil are wound through a separator to form a capacitor element. The anode electrode foil and the cathode electrode foil are connected to lead wires as an anode drawing means and a cathode drawing means, respectively. These lead wires are composed of a connection part connected to each foil, a round bar part continuous with the connection part, and an external connection part welded to the round bar part.

The anode electrode foil was subjected to surface expansion treatment by chemically or electrochemically etching an aluminum foil having a purity of 99% or more in an acidic solution, followed by chemical conversion treatment in an aqueous solution of ammonium adipate or the like, What formed the oxide film layer is used.

Then, the capacitor element impregnated with the electrolytic solution is housed in an outer case made of bottomed cylindrical aluminum, and a sealing body having a through hole for leading out a lead wire is inserted into the opening end of the outer case, and further the outer case The electrolytic capacitor is sealed by crimping the end of the capacitor.

  In the present invention, a foil in which at least the electrode potential in the electrolytic solution shows a noble potential as compared with the cathode drawing means is used as the cathode electrode foil. Examples of the embodiment include the following.

  In the first embodiment, the cathode electrode foil is obtained by etching an aluminum foil having a purity of 99% or more in the same manner as the anode electrode foil. The cathode electrode foil is formed with a 0.02-0.1 μm film made of metal nitride or metal on part or all of the surface. Examples of the metal nitride include titanium nitride, zirconium nitride, tantalum nitride, niobium nitride, and the like, and examples of the metal include titanium, zirconium, tantalum, niobium, and the like. Furthermore, it is preferable to use high-purity aluminum having a purity of 99% or more as the cathode extraction means.

  As a 2nd aspect, the purity which contains one or two or more among copper, iron, manganese, tin, titanium provided with the cathode extraction means which consists of aluminum with a purity of 99.9% or more as a cathode electrode foil. An electrode foil made of less than 9% aluminum is used. Furthermore, it is preferable to form an aluminum oxide layer formed by anodizing treatment with an aqueous ammonium borate solution, an aqueous ammonium phosphate solution, an aqueous ammonium adipate solution, or the like on at least the surface of the round bar portion of the lead wire.

  In a third aspect, as the cathode electrode foil, an electrode foil made of aluminum which is provided with a cathode drawing means made of aluminum having a purity of 99.9% or more and subjected to chemical conversion treatment is used. The electrode foil of the present invention can be obtained by subjecting an aluminum foil subjected to etching treatment such as AC etching to a chemical conversion treatment of 0.05 to 5 V, preferably 0.5 to 3 V. Furthermore, it is preferable to form an aluminum oxide layer formed by anodizing treatment with an aqueous ammonium borate solution, an aqueous ammonium phosphate solution, an aqueous ammonium adipate solution, or the like on at least the surface of the round bar portion of the lead wire.

  The electrolytic solution used in the present invention contains sulfolane, but the content is 20 to 80 wt%, preferably 30 to 70 wt% in the electrolytic solution. Within this range, the impedance characteristics after the life test are good. Furthermore, the low temperature characteristics are improved, and the change in capacitance after the life test is reduced. In the range of 20 to 50 wt%, the initial impedance characteristics and low temperature characteristics are good. When the sulfolane content was less than 20 wt%, the desired life characteristics could not be obtained, but the impedance characteristics were good.

  Further, the electrolytic solution contains γ-butyrolactone, and the content thereof is 75 wt% or less, preferably 20 to 70 wt% in the electrolytic solution. Above the lower limit of this range, high conductivity can be obtained, and below the upper limit, the low temperature characteristics are improved. In addition, if it is 20 wt% or less, the life characteristics are improved.

  Furthermore, although the electrolytic solution of the present invention contains water, the content is 0.1 to 3 wt%, preferably 0.1 to 1 wt%, more preferably 0.1 to 0.5 wt% in the electrolytic solution. is there. It is difficult in the process to suppress the water content below this range, and if it exceeds this range, the life characteristics will deteriorate.

Although containing the sulfolane and γ-butyrolactone of the present invention, the following solvents can be used in addition to these solvents. That is, a protic polar solvent, an aprotic solvent, and a mixture thereof can be used. Protic polar solvents include 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 polar solvents include amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethylacetamide, hexamethylphosphoricamide, etc.), lactones (δ-valerolactone, γ-valerolactone, etc.), sulfolanes (3-methylsulfolane, 2,4-dimethylsulfolane, etc.) ), Cyclic amides (such as N-methyl-2-pyrrolidone), nitriles (such as acetonitrile), and sulfoxides (such as dimethyl sulfoxide).

    Although the electrolytic solution for electrolytic capacitors of the present invention uses a salt having dicyanamide as an anion, an asymmetric cation represented by the following formula can be used as a cation forming an ionic liquid.

R1 and R2 are alkyl groups, preferably R1 is a methyl group, R2 is an ethyl group, a butyl group

R1 to R4 are alkyl groups, preferably R1 is a pentyl group, R2 to R4 are ethyl groups, R1 is a hexyl group, and R2 to R4 are ethyl groups or butyl groups.

R1 to R4 are alkyl groups, preferably R1 is a propyl group, a butyl group, or a hexyl group, and R2 is a methyl group

R1 to R4 are alkyl groups, preferably R1 to R3 are hexyl groups and R2 is a decyl group

  Of these, 1-ethyl-3-methylimidazolium, which has good electrical conductivity and liquid leakage characteristics, is most preferable.

In addition, in order to stabilize the life characteristics of electrolytic capacitors, fragrances such as nitrophenol, nitrobenzoic acid, nitroacetophenone, nitrobenzyl alcohol, 2- (nitrophenoxy) ethanol, nitroanisole, nitrophenetol, nitrotoluene, dinitrobenzene, etc. Phosphorus compounds such as group nitro compounds, phosphoric acid, phosphorous acid, polyphosphoric acid, and acidic phosphoric acid ester compounds can be added.

In addition, for the purpose of improving the safety of electrolytic capacitors, nonionic surfactants that can improve the withstand voltage of electrolytic solutions, polyoxygens obtained by addition polymerization of polyhydric alcohols and ethylene oxide and / or propylene oxide An alkylene polyhydric alcohol ether compound and polyvinyl alcohol can also be added.

Further, the withstand voltage can be further improved by adding boric acid, polysaccharides (mannit, sorbit, pentaerythritol, etc.), complex compounds of boric acid and polysaccharides, colloidal silica, etc. to the electrolytic solution for electrolytic capacitors of the present invention. Can be measured.

In addition, an oxycarboxylic acid compound or the like can be added for the purpose of reducing leakage current.

The present invention will be described more specifically with reference to the following examples. The capacitor element is formed by winding an anode electrode foil and a cathode electrode foil through a separator. The anode electrode foil and the cathode electrode foil are connected to lead wires for anode extraction and lead wires for cathode extraction, respectively.

These lead wires are composed of a connection portion that comes into contact with the electrode foil, a round bar portion formed integrally with the connection portion, and an external connection portion fixed to the tip of the round bar portion. The connecting part and the round bar part are made of 99% aluminum, and the external connecting part is made of a copper-plated steel wire (hereinafter referred to as CP wire). An anodized film made of aluminum oxide is formed on the surface of at least the round bar portion of the lead wire by chemical conversion treatment with an aqueous ammonium phosphate solution. This lead wire is electrically connected to the bipolar electrode foil by means such as stitching or ultrasonic welding at the connection portion.

The anode electrode foil was obtained by subjecting an aluminum foil of 99.9% purity to chemical or electrochemical etching in an acidic solution to enlarge the surface, followed by chemical conversion treatment in an aqueous solution of ammonium adipate. What formed the oxide film layer is used.

Then, the capacitor element impregnated with the electrolytic solution is housed in an outer case made of bottomed cylindrical aluminum, and a sealing body is attached to the opening of the outer case, and the end of the outer case is subjected to a drawing process and the outer case Seal the case. The sealing body is provided with through holes through which the lead wires are led out.

The electrolytic solution for the electrolytic capacitor used here is electrolytic solution A: 1-ethyl-3-methylimidazolium dicyanamide 25 wt%, sulfolane 45 wt%, γ-butyrolactone 30 wt%, electrolytic solution B: 1-ethyl-3-methyl. It is 100 wt% of imidazolium dicyanamide, electrolyte C: 1-ethyl-2,3-dimethylimidazolinium aluminum tetrafluoride 25 wt%, sulfolane 45 wt%, and γ-butyrolactone 30 wt%.

And in Example 1, the cathode electrode foil used what etched the aluminum foil of purity 99.9% similarly to the anode electrode foil. The entire surface of the cathode electrode foil is coated with 0.1 μm titanium nitride or titanium by vapor deposition. In this embodiment, the coating layer of titanium nitride or the like covers the entire surface of the cathode electrode foil. However, if necessary, a part of the cathode electrode foil, for example, only one surface of the cathode electrode foil is coated with metal nitride. May be.

In Example 2, an electrode foil obtained by etching a 99.6% purity aluminum alloy foil containing 0.3% copper and having a cathode drawing means made of aluminum having a purity of 99.9% or more was used as the cathode electrode foil. An aluminum oxide layer was formed on the surface of at least the round bar portion of the lead wire by anodizing with an aqueous ammonium phosphate solution.

In Example 3, the cathode electrode foil was provided with cathode extraction means made of aluminum having a purity of 99.9% or more, and an electrode foil made of aluminum that was subjected to chemical conversion treatment at 2 V after AC etching was used. An aluminum oxide layer was formed on the surface of at least the round bar portion of the lead wire by anodizing with an aqueous ammonium phosphate solution.

The rating of the electrolytic capacitor configured as described above is 35 WV-47 μF.

  The characteristics of the above electrolytic capacitor are shown in (Table 1). The water content of the electrolytic solution after producing these electrolytic capacitors was 0.3 wt%.

ΔCap: As can be seen from the capacitance change rate (Table 1), the impedance after the life test of the electrolytic capacitor of the example is much more stable than Comparative Example 2. Moreover, impedance, low temperature characteristics, and the capacitance change rate after the test are also better than those of Comparative Examples 2 and 3. Further, the life characteristics are better than those of Comparative Example 1. Furthermore, the leakage characteristics are good.

Claims (6)

Capacitor elements formed by winding an anode electrode foil and a cathode electrode foil, to which anode extraction means and cathode extraction means are respectively connected, through a separator, are impregnated with an electrolytic solution, and the capacitor element is covered with a bottomed cylindrical outer case In the electrolytic capacitor formed by sealing the open end of the outer case with a sealing body, an electrolytic solution containing a salt having dicyanamide as an anion and 20 to 80 wt% sulfolane is used as the electrolytic solution. 2. An electrolytic capacitor characterized in that a foil having at least an electrode potential in the electrolytic solution that is nobler than the cathode drawing means is used as the electrode foil. As the cathode electrode foil, 0.02 to 0.02 made of a metal nitride selected from titanium nitride, zirconium nitride, tantalum nitride, niobium nitride, or a metal selected from titanium, zirconium, tantalum, niobium on the surface of the aluminum foil 2. The electrolytic capacitor according to claim 1, wherein a foil provided with a 0.1 [mu] m layer is used. The cathode extraction means is made of aluminum having a purity of 99.9% or more, and the cathode electrode foil is made of aluminum having a purity of less than 99.9% containing one or more of copper, iron, manganese, tin, and titanium. The electrolytic capacitor according to claim 1. 2. The electrolytic capacitor according to claim 1, wherein the cathode drawing means is made of aluminum having a purity of 99.9% or more, and the cathode electrode foil is made of aluminum subjected to chemical conversion treatment. The electrolytic capacitor according to claim 1, wherein an electrolytic solution containing 75 wt% of the following γ-butyrolactone is used. The electrolytic capacitor according to claim 1, wherein an electrolytic solution having a water content of 3.0 wt% or less in the electrolytic solution is used.