JP2017228738A - Electrolytic solution and electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower ESR even in a high-temperature environment and suppress dissolution of aluminum used as an electrode of a capacitor or the like.SOLUTION: The capacitor element is formed by winding an anode foil and a cathode foil in a cylindrical shape via a separator. The separator holds a conductive polymer and an electrolytic solution. The electrolytic solution includes a first solvent containing a lactone and a second solvent containing a compound represented by the following Chemical Formula 1. Here, n is an integer of 1 or more, Ris CH, X is an integer of 1 or more, R, R, R, R, R, and Rare H or CH, and Y is an integer of 1 or more.SELECTED DRAWING: None

Description

  The present invention relates to an electrolytic solution used for an electrolytic capacitor and an electrolytic capacitor using the electrolytic solution.

  In recent years, a hybrid electrolytic capacitor (hybrid capacitor) using a conductive polymer and an electrolyte as an electrolyte has been used in various fields. A low-viscosity solvent such as γ-butyrolactone, ethylene glycol, or sulfolane is used as a solvent for the electrolytic solution. However, the low viscosity solvent has volatility and gradually evaporates from the inside of the capacitor. In particular, when the capacitor is used in a high temperature environment, the solvent in the capacitor may evaporate and disappear completely. Therefore, in Patent Document 1, a hardly volatile solvent containing polyalkylene glycol or a derivative thereof is mixed with the low viscosity solvent. By mixing a low-viscosity solvent and a hardly volatile solvent, volatilization of the solvent is suppressed and reliability in a high temperature environment is improved.

JP 2014-195116 A

  In order to suppress the volatilization of the solvent, it is necessary to increase the blending ratio of the hardly volatile solvent. However, if the blending ratio of the hardly volatile solvent is increased, the blending ratio of the low-viscosity solvent is decreased. Becomes higher. If the blending ratio of the hardly volatile solvent is decreased so that the ESR at low temperature does not increase so much, the reliability in a high temperature environment is lowered. In addition, in automotive applications, use for circuit modules mounted in the engine room is being studied, and there is a need for further support for higher temperature regions. There has been a problem that dedoping is caused by the electrolytic solution and ESR is increased.

  In hybrid capacitors, aluminum is generally used for electrodes, lead tabs (connecting electrodes and lead wires), and the like. As a result of researches by the present inventors, when the hardly volatile solvent of Patent Document 1 is used, the aluminum contained in the electrode and the lead tab is dissolved in the electrolyte solution under high temperature and high humidity environment, and the lead wire is disconnected. I understood. When the lead wire is disconnected, the electrical characteristics deteriorate, for example, the capacitance is significantly reduced.

  Accordingly, an object of the present invention is to reduce the ESR from a low-temperature environment to a high-temperature environment, and in a high-temperature and high-humidity environment, aluminum used for electrodes and the like is difficult to elute into the electrolyte. It is to provide liquid and hybrid capacitors.

ここで、Ｒ¹はＣ_XＨ_2Xで表され、Ｘは１以上の整数であり、ｎは１以上の整数である。また、Ｒ²,Ｒ³,Ｒ⁴,Ｒ⁵,Ｒ⁶及びＲ⁷はＨ又はＣ_YＨ_2Yで表され、Ｙは１以上の整数である。 The electrolytic solution of the present invention is a capacitor comprising an anode and a cathode having a dielectric oxide film, a separator disposed between the anode and the cathode, a conductive polymer and an electrolytic solution held in the separator. The electrolytic solution used includes a first solvent containing a lactone and a second solvent containing a compound represented by the following chemical formula 1.

Here, R ¹ is represented by C _X H _2X , X is an integer of 1 or more, and n is an integer of 1 or more. R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are represented by H or C _Y H _2Y , and Y is an integer of 1 or more.

From the studies by the present inventors, it has been found that in the conventional non-volatile solvent, the solvent molecules are hydrogen-bonded by oxygen atoms contained in the solvent molecules. It has been found that as the blending ratio of the hardly volatile solvent increases, the number of solvent molecules that form hydrogen bonds increases, and the smooth movement of ions is hindered in a low temperature environment, which increases the ESR.
In the present invention, the second solvent containing the compound represented by Chemical Formula 1 is used as the hardly volatile solvent. In Chemical Formula 1, since an oxygen atom exists only at the end of the solvent molecule, hydrogen bonding is unlikely to occur between the solvent molecules. Therefore, even if the blending ratio of the hardly volatile solvent is increased, the hydrogen bond between the solvent molecules is weak. Therefore, ESR can be lowered even in a low temperature environment. In addition, when the hardly volatile solvent of the present invention is present in the electrolytic solution, it is considered that the reaction of the conductive polymer dopant eluting into the electrolytic solution hardly occurs even when the electrolytic solution is at a high temperature. Can be suppressed.
Further, in the above chemical formula 1, a stable structure is not formed even if aluminum contained in an electrode or the like is to be bonded. Therefore, even when moisture from the outside of the capacitor enters inside the capacitor as in a high-temperature and high-humidity environment, and the moisture is mixed with the electrolyte, the reaction of elution of aluminum into the electrolyte hardly occurs. Almost no elution occurs.
From the above, when the electrolytic solution of the present invention is used, ESR can be lowered from a low temperature environment to a high temperature environment, and aluminum used for electrodes and the like is not easily eluted into the electrolytic solution even under a high temperature and high humidity environment. .

  The second solvent is 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and derivatives thereof, and 1,3-butanediol, -At least one of methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, 2,4-diethyl-1,5-pentanediol and derivatives thereof It is preferable to contain one.

  The first solvent preferably contains at least one of γ-butyrolactone and γ-valerolactone.

  The electrolytic capacitor of the present invention includes a capacitor element in which an anode and a cathode having a dielectric oxide film are wound through a separator, and the separator holds a conductive polymer and the above-described electrolytic solution.

  According to the present invention, ESR can be lowered from a low temperature environment to a high temperature environment, and aluminum used for electrodes and the like is not easily eluted into the electrolyte even under high temperature and high humidity conditions.

It is a principal part cutting front view of the electrolytic capacitor which concerns on embodiment of this invention. FIG. 2 is an exploded perspective view of the capacitor element shown in FIG. 1.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the hybrid capacitor 1 includes an outer case 2, a capacitor element 3 accommodated in the outer case 2, and a sealing body 4 that seals an opening of the outer case 2.

  As shown in FIG. 2, the capacitor element 3 is formed by winding an anode foil (anode) 11 and a cathode foil (cathode) 12 in a cylindrical shape with a separator 13 therebetween, and a tape 14 attached to the outer peripheral surface. It is stopped by.

  The anode foil 11 is a valve metal foil such as aluminum having a derivative oxide film formed on the surface thereof. The derivative oxide film is formed by performing a chemical conversion treatment after roughening the surface of an aluminum foil or the like by an etching treatment.

  The cathode foil 12 is also formed using a valve action metal such as aluminum, and a surface roughened by etching (roughened foil) is used. As the cathode foil 12, a plain foil that is not subjected to other etching treatment can be used, and titanium, nickel, its carbide, nitride, carbonitride, or these can be used on the surface of the roughened foil or plain foil. A metal thin film made of a mixture or a coating foil formed with a carbon thin film can also be used.

  Lead tabs (not shown) are connected to the anode foil 11 and the cathode foil 12, respectively. The anode foil 11 and the cathode foil 12 are connected to the lead terminal 21 and the lead terminal 22 through lead tabs. As shown in FIG. 1, the lead terminal 21 and the lead terminal 22 are drawn out through a hole 31 and a hole 32 formed in the sealing body 4.

ここで、化学式１において、
Ｒ¹はＣ_XＨ_2Xで表され、Ｘは１以上の整数であり、ｎは１以上の整数である。
また、Ｒ²,Ｒ³,Ｒ⁴,Ｒ⁵,Ｒ⁶及びＲ⁷はＨ又はＣ_YＨ_2Yで表され、Ｙは１以上の整数である。 The separator 13 shown in FIG. 2 holds a conductive polymer and an electrolytic solution. The conductive polymer is made of polythiophene, polypyrrole, polyaniline or a derivative thereof, and polyethylene dioxythiophene (PEDOT) using p-toluenesulfonic acid, polystyrene sulfonic acid (PSS) or the like as a dopant is generally used. The electrolytic solution includes a first solvent containing a lactone and a second solvent containing a compound represented by the following chemical formula 1.

Here, in Chemical Formula 1,
R ¹ is represented by C _X H _2X , X is an integer of 1 or more, and n is an integer of 1 or more.
R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are represented by H or C _Y H _2Y , and Y is an integer of 1 or more.

  The lactone contained in the first solvent reduces ESR. As the first solvent, for example, a solvent containing at least one of γ-butyrolactone and γ-valerolactone can be used. The first solvent may contain other lactones.

  The second solvent is a hardly volatile solvent containing the compound represented by Formula 1 above.

化学式１において、Ｒ¹はＣ_XＨ_2Xで表され、Ｘは１以上の整数であり、ｎは１以上の整数である。
また、Ｒ²,Ｒ³,Ｒ⁴,Ｒ⁵,Ｒ⁶及びＲ⁷はＨ又はＣ_YＨ_2Yで表され、Ｙは１以上の整数である。 Based on the above, the present inventors have further studied, and have found that when a hardly volatile solvent containing a compound represented by the following chemical formula 1 is used, hydrogen bonds between solvent molecules are weak.

In Chemical Formula 1, R ¹ is represented by C _X H _2X , X is an integer of 1 or more, and n is an integer of 1 or more.
R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are represented by H or C _Y H _2Y , and Y is an integer of 1 or more.

The inventors have also obtained the following knowledge.
Since monoalcohols having one oxygen atom have high volatility, the solvent tends to evaporate. Therefore, the reliability of the electrical characteristics of the capacitor over a long period is low. In addition, polyols having 3 or more oxygen atoms tend to cause hydrogen bonding between solvent molecules, resulting in high ESR.
On the other hand, it was found that diols having two oxygen atoms represented by the above chemical formula 1 have low volatility and hardly cause hydrogen bonding between solvent molecules. Therefore, in the capacitor using the second solvent (non-volatile solvent) containing the compound represented by Chemical Formula 1, the reliability of electric characteristics over a long period is high. Moreover, even if it makes a highly volatile solvent a high compounding ratio required for long-term reliability, the raise of ESR can be suppressed from a low temperature range to a high temperature range.

The inventors obtained the following knowledge by further research.
In the hybrid capacitor 1, aluminum is used for the electrodes of the anode foil 11 and the cathode foil 12 and lead tabs (not shown), but an electrolytic solution containing a conventional non-volatile solvent (polyalkylene glycol or a derivative thereof) is used. It was found that the aluminum contained in the electrode and the lead tab was dissolved into the electrolyte under a high temperature and high humidity environment. The following reasons can be considered.

The polyalkylene glycol or a derivative thereof usually has a structure containing two carbon atoms between two oxygen atoms. When these two oxygen atoms are coordinated to aluminum, a stable pentagonal structure as shown in the following chemical formula 2 is formed, and aluminum is easily eluted into the electrolytic solution. It is thought that aluminum dissolved into the electrolyte due to this. However, when aluminum is melted, the electrode and the lead tab are dissolved (corroded), and the lead wire is disconnected.

  On the other hand, in the compound represented by the chemical formula 1, three or more carbon atoms are arranged between two oxygen atoms. Here, when aluminum is coordinated to two oxygen atoms, an m-gon (m is an integer of 6 or more) is formed, but the m-gon does not have a stable structure and thus collapses immediately. Therefore, it is thought that aluminum becomes difficult to elute into the electrolyte. Therefore, it was found that when a solvent containing the compound represented by the above chemical formula 1 was used, aluminum hardly dissolved in the electrolytic solution.

  From the above, when the hardly volatile solvent containing the compound represented by the chemical formula 1 is used, it is possible to prevent the aluminum used for the electrode, the lead tab and the like from being eluted into the electrolytic solution even under a high temperature and high humidity environment.

  Examples of the compound represented by Chemical Formula 1 include 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and derivatives thereof, and 1,3-butane. Diols, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, 2,4-diethyl-1,5-pentanediol and these Derivatives.

The derivative of 1,3-propylene glycol includes H of one OH group (R ^{4 in} Chemical Formula 1) of two OH groups of 1,3-propylene glycol (corresponding to OR ⁴ and OR ⁷ in Chemical Formula 1). Or R ⁷ ) is substituted with an alkyl group, and H of both OH groups (R ⁴ and R ^{7 in} Formula 1) is substituted with an alkyl group.

The same applies to the derivatives of the other compounds, and one of the two OH groups (corresponding to OR ⁴ and OR ⁷ in Chemical Formula 1) has H (R ⁴ or R ^{7 in} Chemical Formula 1) as an alkyl group. And those in which both H (R ⁴ and R ^{7 in} Formula 1) are substituted with alkyl groups.

  In addition, when the structure of Chemical Formula 1 is provided, the above-described actions and effects are generated, and thus the compound represented by Chemical Formula 1 is not limited to the above-described example, and includes various compounds. Moreover, although the upper limit of n in Chemical Formula 1 is not particularly limited, for example, n may be 5 or less.

  As described above, in the electrolytic capacitor 1 of the present embodiment, an electrolytic solution including the first solvent containing the lactone and the second solvent containing the compound represented by the chemical formula 1 is used. Thereby, low ESR can be maintained even under a high temperature environment, and dissolution of aluminum used in the anode foil 11 and the lead tab can be suppressed even under a high temperature and high humidity condition.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Manufacture of capacitors)
Lead tabs for external lead electrodes were connected to the anode foil and cathode foil cut to a predetermined width. The lead tab is formed of aluminum. As the anode foil, an aluminum foil, which is a valve action metal, was roughened by an etching process and then subjected to a chemical conversion treatment to form a dielectric oxide film. As the cathode foil, an aluminum foil which is a valve metal was roughened by etching. A winding element was produced by winding the anode foil and the cathode foil through a separator mainly composed of natural fibers such as esparto pulp.

Subsequently, since the dielectric oxide film was missing at the cut end face of the anode foil and the attachment portion with the lead tab, this portion was subjected to chemical conversion treatment and repaired. An aqueous solution of ammonium adipate was used as the chemical conversion solution used in the chemical conversion treatment.
Next, the polymer dispersion aqueous solution containing PEDOT / PSS was immersed and impregnated in the wound element for 30 minutes under reduced pressure, and then dried to remove moisture. As a result, a conductive polymer layer serving as a cathode layer of the capacitor was formed.

  Next, the electrolytic solutions shown in Table 1 and Table 2 were poured into a bottomed cylindrical case made of aluminum. In Examples 1 to 6, 1,4-butanediol or 1,5-pentanediol was used as the hardly volatile solvent, and γ-valerolactone (GVL) was used as the low viscosity solvent. In Comparative Example 1, polyethylene glycol (trade name “PEG-300”, manufactured by Toho Chemical Industry Co., Ltd.) was used as the hardly volatile solvent, and γ-butyrolactone (GBL) was used as the low viscosity solvent. In addition to the components described in Table 1, the electrolytic solution contains 0.5 wt% phosphorous acid and 1.0 wt% boric acid as a solute with respect to the electrolytic solution. The composition in the table is the amount of each solvent mixed with respect to the total amount of solvent.

  After inserting the lead terminal of the capacitor element in which the conductive polymer is formed into the hole of the sealing rubber (sealing body), the capacitor element is accommodated in the case, and the capacitor element is impregnated with the electrolytic solution in the case. The periphery of the case was curled. Then, a rated voltage was applied to the capacitor, and an aging treatment was performed to produce a hybrid capacitor having a diameter of 6.3 mm, a height of 6.1 mm, a rated voltage of 35 V, and a capacitance of 47 μF. In Experiment 2, the capacitor element impregnated with the electrolytic solution was taken out of the case and used for the experiment.

(Experiment 1)
The initial ESR (−55 ° C., 25 ° C.) of the capacitor was measured. Further, the capacitor was left at a high temperature of 135 ° C. for 500 hours, and the ESR (25 ° C.) of the capacitor was measured. Table 1 shows the measurement results. ESR is a value measured at a frequency of 100 kHz.

  From Table 1, in Examples 1-6, the ESR is almost the same in the initial stage (25 ° C.) and after being left at 135 ° C., and the increase in ESR is suppressed even in a high temperature environment. The ESR after standing at 135 ° C. increased more than 3 times compared to the initial ESR (25 ° C.). Moreover, in Examples 1-6, it turned out that ESR is lower than the comparative example 1 in a low temperature area or a high temperature area.

(Experiment 2)
An accelerated high-temperature and high-humidity load test (n = 10) was carried out in a state where the lead terminal was pulled out through a hole of a sealing rubber (sealing body). Thereafter, the end face of the aluminum foil of the anode and the lead tab (particularly, the portion protruding from the winding element) were visually observed using a magnifying glass, and the presence or absence of dissolution (corrosion) was confirmed. In the accelerated high-temperature and high-humidity load test, the rated voltage was applied to the capacitor for 12 hours under high-temperature and high-humidity conditions of 85 ° C. and relative humidity of 85%. Table 2 shows the number of dissolution (corrosion) confirmed among the 10 samples.

  From Table 2, in Examples 1-6, dissolution (corrosion) of the aluminum foil and lead tab of the anode did not occur even in a high temperature and high humidity environment. On the other hand, in Comparative Example 1, dissolution (corrosion) was confirmed in four samples.

  As mentioned above, although embodiment of this invention was described based on drawing, it should be thought that a specific structure is not limited to these embodiment. The scope of the present invention is defined by the terms of the claims, rather than the description above, and includes all modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Exterior case 3 Capacitor element 4 Sealing body 11 Anode foil (anode)
12 Cathode foil (cathode)
21,22 Lead terminal

Claims (4)

An electrolytic solution for use in an electrolytic capacitor comprising an anode and a cathode having a dielectric oxide film, a separator disposed between the anode and the cathode, and a conductive polymer and an electrolytic solution held in the separator. ,
An electrolytic solution comprising a first solvent containing a lactone and a second solvent containing a compound represented by the following chemical formula 1.

Here, R ¹ is represented by C _X H _2X , X is an integer of 1 or more,
n is an integer of 1 or more,
R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are represented by H or C _Y H _2Y , and Y is an integer of 1 or more.   The second solvent is 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and derivatives thereof, and 1,3-butanediol, 2-methyl. 1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, 2,4-diethyl-1,5-pentanediol and at least one of these derivatives The electrolytic solution according to claim 1, comprising:   3. The electrolytic solution according to claim 1, wherein the first solvent contains at least one of γ-butyrolactone and γ-valerolactone. A capacitor element in which an anode and a cathode having a dielectric oxide film are wound through a separator,
The said separator is an electrolytic capacitor which hold | maintains electroconductive polymer and the electrolyte solution of any one of Claims 1-3.

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