JP2007273928A - Electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic capacitor having long service life characteristic, low impedance characteristic and proper low-temperature characteristic. <P>SOLUTION: This electrolytic capacitor consists of a salt having dicyanamide as anion, an electrolyte containing 20-80 wt.% sulfolane and is provided with a sealing structure, consisting of a material of low moisture transparency selected from among rubber and polyphenylene sulfide, polyimide, polyamide, polyamideimide, polypropylene, polyetheretherketon, polyparaxylylene, urea resin, melamine resin, epoxy resin and metal, or is provided with a water-absorbing agent in the exterior case. The electrolyte contains γ-butyrolactone of not more than 75 wt.%. 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 has the proper service life characteristic, has low impedance characteristic, low-temperature characteristic 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 is used 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 conducting studies to suppress this decrease in conductivity, 20 to 80 wt% of sulfolane is contained, rubber and polyphenylene sulfide, polyimide, polyamide, polyamideimide, polypropylene, polyetheretherketone, polyparaxylylene, When equipped with a sealing structure made of a material with low moisture permeability selected from urea resin, melamine resin, epoxy resin, or metal, or provided with a water-absorbing agent in the exterior case, a decrease in conductivity during the life test is suppressed, It was also found that the electrical conductivity at the initial and low temperatures was kept 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, rubber and polyphenylene sulfide, polyimide, polyamide, polyamideimide, polypropylene, polyetheretherketone, polyparaxylylene, urea resin, melamine resin. It is characterized by having a sealing structure made of a material having low moisture permeability selected from epoxy resin and metal, or having a water absorbing agent in the outer case.

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, an electrolyte containing the salt of the present invention having dicyanamide as an anion and 20-80 wt% sulfolane, rubber, polyphenylene sulfide, polyimide, polyamide, polyamideimide, polypropylene, polyetheretherketone, polyparaxylylene Electrolytic capacitors that have a sealing structure made of a material with low moisture permeability selected from urea resin, melamine resin, epoxy resin, and metal, or that have a water absorbing agent in the outer case, have moisture penetration in the moisture resistance test. Suppressed or permeated moisture is absorbed and has unprecedented long life characteristics and high electrical conductivity. 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 1st electrolytic capacitor of this invention, it can be set as the sealing structure of this invention using the laminated body of rubber | gum and a material with low moisture permeability as a sealing body. The laminate may have a two-layer structure or a multilayer structure of three or more layers. Further, after drawing with the sealing rubber, a material having low moisture permeability may be coated and bonded to the upper surface of the sealing rubber. Furthermore, a plate-like material having low moisture permeability may be placed on the upper surface or the lower surface of the sealing rubber. Further, a layer made of a material having low moisture permeability may be formed on the surface including the through hole of the sealing body.

  here. Materials with low moisture permeability include fluoro rubber, polyphenylene sulfide, polyimide, polyamide, polyamide imide, polypropylene, polyether ether ketone, polyparaxylylene, urea resin, melamine resin, epoxy resin or polysulfide modified epoxy resin, epoxy resin Mention may be made of mixtures of phenolic resins, metals and the like. Here, the effects of the present invention cannot be obtained because polycarbonate, polystyrene, polyvinyl chloride, and the like have high moisture permeability. In addition, when the upper surface of the sealing rubber is coated and bonded after being drawn with the sealing rubber, a liquid resin is applied to the upper surface of the sealing rubber and then coated and bonded by thermosetting. Urea resin and melamine resin are preferred.

Further, as the rubber used in the present invention, a rubber usually used as a sealing rubber for electrolytic capacitors can be used. Examples of such rubber include isobutylene, isoprene copolymer, isobutylene, isoprene and divinylbenzene three-component copolymer, ethylene, propylene copolymer peroxide vulcanized rubber, and resin vulcanized rubber. it can.

  In the second electrolytic capacitor of the present invention, a water absorbing agent is provided in a bottomed cylindrical aluminum case. The water-absorbing agent may be placed in a case such as a film, plate or sphere, or a powder or fine powder placed in the case or the end face of the capacitor element, or a separator, electrode foil It may be attached to. Moreover, you may disperse | distribute to the electrolyte solution for electrolytic capacitors. Furthermore, you may mix in a sealing body.

here. Examples of the water absorbing agent include an inorganic water absorbing agent and an organic water absorbing agent. Examples of inorganic water-absorbing agents include activated carbon, zeolite, molecular sieves, silica gel, activated alumina and other large surface areas, water-absorbing particles such as calcium alginate beads, transition metal dichalcogenite such as NbS ₃ , NbSe ₂ , and TaSe ₂ Layered material such as graphite, unsaturated oxides such as GeO, oxides of alkaline earth metals such as CaO and BaO, crystal water such as NiSO4, LiClO4, sodium paratoluenesulfonate, sodium acetate, sodium citrate Compounds, inorganic compounds such as phosphorus pentoxide, calcium sulfate, zinc oxide, zinc bromide, and anhydrous copper sulfate, metals such as lithium, beryllium, potassium, sodium, magnesium, rubidium, strontium, calcium, and TiO ₂ , diatomaceous earth , Activated carbon, hemihydrate It can be mentioned.

Organic water-absorbing agents include starch, cellulose (graft polymerization, carboxymethyl: starch / polyacrylate, bridged carboxymethylated cellulose), synthetic polymer (acrylic, acrylamide, polyoxyethylene) -Based, methacrylic: bridged polyacrylate, acrylic fiber hydrolyzate), isobutylene / maleate, bridged polyvinyl alcohol, etc., super absorbent polymer, acetylcellulose, butylacetylcellulose, polyamide , Urea resin, polyester surrin A (ionomer), organic substances such as chlorinated rubber, ion exchange resin, polyvinyl alcohol, nylon, etc., in the molecule -NH2, -OH, -COOH, -SO3H, -OH, -NH-, etc. It has a hydrophilic group that absorbs and retains a lot of moisture. Resin, naphthylene diisocyanate, 4,4-diphenylmethane diisocyanate, paraphenylene diisocyanate, isopropylidenebis (4-cyclohexyl isocyanate), cyclohexyl diisocyanate, tolidine diisocyanate, lysine diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate , Hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, a copolymer of vinyl alcohol and acrylic acid, a copolymer of starch and acrylonitrile, and C60 (fullerene).

  Of these, zeolite, molecular sieves, silica gel, activated alumina, and superabsorbent polymer are preferable.

  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%.

  In Example 1, a peroxide vulcanized rubber of a ternary copolymer of isobutylene, isoprene and divinylbenzene was used as the sealing rubber, and a softened epoxy resin was injected into the upper surface of the sealing rubber, and cured by heating to cure the epoxy. A resin layer was formed. In Example 2, a molecular sieve was placed in the outer case of the electrolytic capacitor.

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 of the electrolytic capacitor of the example after the moisture resistance test is better than that of the comparative example.

Claims (4)

A capacitor element in which an anode electrode foil, a cathode electrode foil and a separator are wound and impregnated with an electrolytic solution, an exterior case for storing the capacitor element, and a sealing body for sealing an opening of the exterior case, Using an electrolyte containing a salt having dicyanamide as an anion and 20 to 80 wt% of sulfolane as an electrolyte, and rubber and polyphenylene sulfide, polyimide, polyamide, polyamideimide, polypropylene, polyetheretherketone, polyparaxylylene, An electrolytic capacitor having a sealing structure made of a material having low moisture permeability selected from urea resin, melamine resin, epoxy resin, and metal. A capacitor element in which an anode electrode foil, a cathode electrode foil and a separator are wound and impregnated with an electrolytic solution, an exterior case for storing the capacitor element, and a sealing body for sealing an opening of the exterior case, An electrolytic capacitor using, as an electrolytic solution, an electrolytic solution containing a salt having dicyanamide as an anion and 20 to 80 wt% sulfolane, and having a water absorbing agent in an outer case. 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.