JP6479725B2 - Electrolyte for hybrid electrolytic capacitors - Google Patents

Description

The present invention relates to an electrolytic solution applied to a so-called hybrid electrolytic capacitor using a solid electrolyte and an electrolytic solution in combination, and a hybrid aluminum electrolytic capacitor impregnated with the electrolytic solution.

Along with the digitization of electronic devices, capacitors having a low equivalent series resistance (hereinafter abbreviated as ESR) are required in a high frequency region as capacitors used in circuits on the power supply output side such as smoothing circuits and control circuits. .
As such a capacitor, there is a so-called aluminum electrolytic capacitor using only an electrolytic solution as a conductive material, but a solid electrolytic capacitor using a solid electrolyte of a conductive polymer such as polypyrrole, polyaniline, polythiophene so as to further reduce the ESR. Has been applied.

  A solid electrolytic capacitor is particularly excellent in terms of low ESR compared to a liquid electrolytic capacitor, but does not have a function of repairing a defective portion of an anodic oxide film that is a dielectric. For this reason, there is a risk that the leakage current increases, leading to a short circuit.

On the other hand, the demand for higher reliability is increasing in AV equipment and automotive electrical equipment. Therefore, in addition to the performance of lowering ESR in solid electrolytic capacitors, it is necessary to improve low leakage current and short circuit resistance. It is coming.
In response to these demands, so-called hybrid electrolytic capacitors have been proposed as electrolyte materials that use a solid electrolyte such as a conductive polymer in addition to an electrolyte solution that is excellent in the repairing of defective portions of the anodic oxide film, which is a dielectric. (For example, Patent Documents 1 and 2).

In these hybrid electrolytic capacitors, the electrolytic solution enters the gaps between the solid electrolytes of the conductive polymer, and the contact between the dielectric oxide film and the electrolyte is improved. As a result, the capacitance increases and ESR decreases, and the defective portion of the dielectric oxide film can be repaired by the action of the electrolytic solution, the leakage current is small, and no short circuit occurs.

By the way, electrolytic capacitors applied to AV equipment and automobile electrical equipment are exposed to a high temperature environment such as 105 ° C. for a long time. Since the opening of the case containing the capacitor element and the electrolytic solution is sealed with a rubber sealing material, the life of the capacitor is particularly important from the viewpoint of volatilization of the electrolytic solution.

However, the solvent of the electrolytic solution used in the conventional hybrid capacitor is a volatile organic solvent such as γ-butyrolactone, ethylene glycol, or sulfolane, or low molecular weight polyethylene glycol.
However, polyethylene glycol does not volatilize when the molecular weight is high, but since it is solid, it is difficult to apply to a hybrid capacitor, and polyethylene glycol is limited to low molecular weight. Therefore, when these electrolytic capacitors containing low molecular weight polyethylene glycol are exposed to a high temperature environment, these volatile components gradually evaporate from the gap between the sealing body and the case and the gap between the sealing body and the lead wire. To go. As a result, the action of the electrolytic solution for repairing the defective portion of the dielectric oxide film is lost, the leakage current is increased, and a short circuit is caused.

Japanese Patent Laid-Open No. 11-186110 JP 2014-195116 A

  An object of the present invention is to provide an electrolytic solution for an electrolytic capacitor that can reduce a leakage current and does not cause a short circuit in a hybrid aluminum electrolytic capacitor because the electrolytic solution does not evaporate even when exposed to a high temperature environment. To do.

The inventors of the present invention have reached the present invention as a result of studies to achieve the above object.
That is, the present invention is an electrolytic solution (A) for a hybrid electrolytic capacitor comprising an alkylene oxide (b) adduct (C) of a tri- to octavalent polyhydric alcohol (a).

The electrolytic solution for a hybrid electrolytic capacitor of the present invention has an effect that even when exposed to a high temperature environment, the electrolytic solution does not evaporate, so that leakage current can be reduced and no short circuit occurs.
Furthermore, since the electrolytic capacitor using the electrolytic solution of the present invention is an alkylene oxide adduct of a polyhydric alcohol, it is liquid at room temperature even if the molecular weight is high, for example, it is liquid at room temperature even if the molecular weight is 3000 or more. In addition, since the leakage current can be reduced with a higher molecular weight, the present invention using an alkylene oxide adduct of a polyhydric alcohol is different from an electrolytic solution using a normal polyalkylene glycol.

The electrolytic solution for a hybrid electrolytic capacitor of the present invention is characterized by containing an alkylene oxide (b) adduct (C) of a tri- to octavalent polyhydric alcohol (a).

The electrolytic solution (A) of the present invention contains an alkylene oxide (a) adduct (C) as an essential component. The alkylene oxide (a) adduct (C) is a trivalent to octavalent polyhydric alcohol ( It is a compound obtained by adding an alkylene oxide (b) to a).
Examples of the alkylene oxide (b) to be added include ethylene oxide (hereinafter sometimes abbreviated as EO), propylene oxide (hereinafter sometimes abbreviated as PO), butylene oxide, and the like. Two or more kinds may be used in combination.
The kind of alkylene oxide to be added is preferably ethylene oxide alone or a combination of ethylene oxide and another alkylene oxide from the viewpoint of easy penetration into the electrode.
When ethylene oxide and other alkylene oxides are used in combination, random addition or block addition may be used, but the random form is preferable from the viewpoint of not invading the capacitor sealing rubber.
When ethylene oxide is used in combination with other alkylene oxides, 60 to 95 mol% of the entire alkylene oxide is preferably ethylene oxide, and more preferably 65 to 90 mol from the viewpoint of facilitating penetration into the electrode. %.
When the content of ethoxide on the whole alkylene oxide is less than 60 mol% or exceeds 95 mol%, the initial value of ESR (equivalent series resistance) increases. Also, the rate of change of ESR increases.

Examples of the tri- to 8-valent polyhydric alcohol (a) include trihydric alcohols such as trimethylolpropane and glycerol; tetrahydric alcohols such as pentaerythritol; pentahydric alcohols such as xylitol; sorbitol, mannitol, dipentaerythritol, and the like. Of 6-valent alcohol.
Among these, as (a), trivalent, tetravalent and hexavalent polyhydric alcohols are preferable, glycerin, pentaerythritol and sorbitol are more preferable, and glycerin is most preferable.
On the other hand, the alkylene oxide adduct of monohydric to dihydric alcohols volatilizes when the molecular weight is small, and becomes solid when the molecular weight is large and does not function as a capacitor.

The number average molecular weight in terms of hydroxyl value of the alkylene oxide adduct (C) of the 3-8 valent polyhydric alcohol (a) is preferably 1,000 to 4,000, more preferably 1 from the viewpoint of volatility and viscosity. , 400-3,600. If it is less than 1,000, it has volatility, and if it exceeds 4,000, the viscosity increases, and it becomes difficult for the separator to soak the electrolyte when assembling the capacitor, and even if soaked, the electrode foil Adhesion to the surface may deteriorate and capacity may be difficult to develop.

As a method for synthesizing the alkylene oxide adduct (C) of a tri- to octavalent polyhydric alcohol, it is common to react polyhydric alcohol with ethylene oxide or propylene oxide under a potassium hydroxide or sodium hydroxide catalyst. is there.
In an aluminum electrolytic capacitor application, which is the present application, metal ions cause a short circuit of the capacitor. Therefore, potassium or sodium is preferably adsorbed to 20 ppm or less, more preferably 1 ppm or less.

The content of (C) contained in the electrolytic solution (A) is preferably 20 to 99.9% by weight, more preferably 50 to 99.9% by weight.

The electrolyte solution (A) of the present invention preferably further contains an electrolyte (D) in addition to (C).
The electrolyte (D) is composed of a cation component (D1) and an anion component (D2). Examples of the cation component (D1) include ammonia, triethylamine, dimethylethylamine, diethylmethylamine, dimethylamine, diethylamine, and 1-methylimidazole. 1,2,3,4-tetramethylimidazolinium, 1-ethyl-3-methylimidazolinium and the like, and triethylamine is preferable.
On the other hand, examples of the anionic component (D2) include adipic acid, azelaic acid, 1,6-decanedicarboxylic acid, phthalic acid, maleic acid, benzoic acid, phosphoric acid and derivatives thereof, boric acid and derivatives thereof, and the like. It is preferable.
The ratio of (D1) to (D2) is preferably (D1) / (D2) of 0.3 to 1.0 from the viewpoint that the dopant incorporated in the conductive polymer is not dedoped. -1.0 is more preferable.

In the electrolytic solution (A) of the present invention, it is more preferable to use an organic solvent (E) in combination for adjusting the viscosity.
Examples of the organic solvent (E) used for this purpose include ethylene glycol, γ-butyrolactone, sulfolane and the like, and ethylene glycol is most preferable.

Furthermore, various additives can be added to the electrolytic solution (A) as necessary.
Examples of additives include nitro compounds (for example, o-nitrobenzoic acid, p-nitrobenzoic acid, m-nitrobenzoic acid, o-nitrophenol, p-nitrophenol, etc.), boric acid, poval, and the like. . The added amount is preferably 5% by weight or less, particularly preferably 0.1 to 2% by weight based on the weight of the electrolytic solution from the viewpoint of solubility in the electrolytic solution.

The hybrid electrolytic capacitor of the present invention is formed from a capacitor element having a layer of a solid electrolyte (B) in contact with a dielectric layer of an anode foil. This solid electrolyte (B) is composed of polythiophene or a derivative thereof, for example, , Conductive polymers such as poly 3,4-ethylenedioxythiophene and polypyrrole.
This conductive polymer incorporates a dopant, and the dopant plays a role of developing conductivity. Typical dopants are acids such as p-toluenesulfonic acid and polystyrenesulfonic acid.

The hybrid capacitor of the present invention has a capacitor element, a pair of lead wires, and an exterior body. Each of the pair of lead wires is connected to a capacitor element. The outer package encloses the capacitor element so that the lead wire is led out to the outside at the other end.
The exterior body is composed of a cylindrical case and a sealing body. In this case, a capacitor element impregnated with an electrolytic solution is accommodated, and the sealing body is passed through through holes for inserting lead wires. It seals by compressing with the drawing process part provided in the outer peripheral surface of this.

The capacitor element of the present invention has an anode foil having a dielectric layer on the surface, and a solid electrolyte (B) layer in contact with the dielectric layer of the anode foil.
The anode foil is formed by roughening an aluminum foil by an edging process and further forming an anodic oxide film as a dielectric on the surface thereof by a chemical conversion process.
In addition to the anode foil, the capacitor element further includes a cathode foil and a separator. The capacitor element is configured by stacking and winding the anode foil, the cathode foil, and the separator. Then, a solid electrolyte layer made of a conductive polymer is formed between the anode foil and the cathode foil. As a preparation method, there are a method in which a conductive polymer solution is impregnated and then dried, and a method in which a conductive polymer is electrolytically polymerized.
The electrolyte enters the gap between the solid electrolytes formed in the capacitor element formed as described above, and a hybrid capacitor is created.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

Production Example 1 sorbitol EO 24 mol adduct (C-1)
1.1 parts by weight (0.02 mol) of potassium hydroxide was added to 182 parts by weight (1 mol) of sorbitol, and 1,056 parts by weight (24 mol) of EO was reacted at 170 ° C. When the pressure equilibrium was reached, the end point was reached.
Thereafter, an adsorption treatment was performed using Kyoward 600 and Kyoward 700 (manufactured by Kyowa Chemical Industry Co., Ltd.) to remove potassium, and it was also confirmed that the potassium content was 1 ppm or less.
It was confirmed by a proton nuclear magnetic resonance apparatus (H-NMR) chart that an ethylene oxide 24-mole adduct (C-1) of sorbitol was obtained. The number average molecular weight (Mn) in terms of hydroxyl value was 1,240.

Production Example 2 Glycerin random adduct (C-2) with EO 11 mol / PO 5 mol
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was changed to 92 parts by weight (1 mol) of glycerin, 1,056 parts by weight (24 mol) of EO was changed to a mixture of 484 parts by weight of EO (11 mol) and 290 parts by weight of PO (5 mol). Except that, a random adduct of 11 mol of glycerol and 5 mol of PO was obtained in the same manner as in Production Example 1. Mn was 960.

Production Example 3 Random adduct of glycerin with EO 50 mol / PO 3 mol (C-3)
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was changed to 92 parts by weight (1 mol) of glycerin, and 1,056 parts by weight (24 mol) of EO was changed to a mixture of 200 parts by weight of EO (50 mol) and 165 parts by weight of PO (3 mol). In the same manner as in Production Example 1, a random adduct of 50 mol EO and 3 mol PO of glycerin was obtained. Mn was 2,300.

Production Example 4 Random adduct of pentaerythritol with 55 mol of EO / 40 mol of PO (C-4)
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was changed to 136 parts by weight (1 mol) of pentaerythritol, and 1,056 parts by weight (24 mol) of EO was changed to a mixture of 2420 parts by weight (55 mol) and 2320 parts by weight (40 mol) of PO. A random adduct of pentaerythritol with EO 55 mol and EO 40 mol was obtained in the same manner as in Production Example 1 except that Mn was 2,560.

Production Example 5 EO44 mol adduct of glycerin EO44 mol / PO14 mol of random adduct (C-5)
To 92 parts by weight (1 mol) of glycerin, 1.1 parts by weight (0.02 mol) of potassium hydroxide was added and reacted at 170 ° C. until 528 parts by weight (12 mol) of EO reached pressure equilibrium. Then, the liquid which made EO1936 weight part (44 mol) and PO812 weight part (14 mol) uniform in the cylinder previously was made to react, and it was set as the end point when pressure equilibrium was reached. Thereafter, potassium hydroxide was adjusted to 1 ppm or less using Kiyoward 600 and Kiyoward 700 (manufactured by Kyowa Chemical Industry Co., Ltd.) as adsorbents for removing potassium hydroxide.
The random adduct of 44 mol of EO and 14 mol of PO to the EO12 mol adduct of glycerin was obtained from the H-NMR chart of the sample and the H-NMR chart of the final product when the first stage reaction was completed. It was confirmed. Mn was 3,370.

Production Example 6 Random adduct of sorbitol with EO 80 mol / PO 10 mol (C-6)
In Production Example 1, 80 mol of sorbitol EO in the same manner as in Production Example 1 except that 1,056 parts by weight (24 mol) of ethylene oxide was changed to a mixture of 3520 parts by weight of EO (80 mol) and 580 parts by weight of PO (10 mol). A random adduct with 10 moles of PO was obtained. Mn was 4,280.

Comparative Production Example 1 Polyethylene glycol (C′-1)
1.1 parts by weight (0.02 mol) of potassium hydroxide was added to 62 parts by weight (1 mol) of ethylene glycol, and 1,188 parts by weight (27 mol) of EO was reacted at 170 ° C. When the pressure equilibrium was reached, the end point was reached. Thereafter, an adsorption treatment was performed using Kyoward 600 and Kyoward 700 (manufactured by Kyowa Chemical Industry Co., Ltd.) to remove potassium, and it was also confirmed that the potassium content was 1 ppm or less. It was confirmed that polyethylene glycol (C′-1) having a number average molecular weight of 1,200 was obtained.

Comparative production example 2
In Comparative Production Example 1, polyethylene glycol (C′-2) having a number average molecular weight of 200 was obtained in the same manner as in Comparative Production Example 1, except that 188 parts by weight of EO was changed to 176 parts by weight (4 mol).

In accordance with the number of parts (parts by weight) in Table 1, triethylamine as an electrolyte, phthalic acid and ethylene glycol as a solvent were added, and electrolytic solutions (A1) to (A-8), (A′-1) of Examples and Comparative Examples, (A'-2) was created.

Next, a wound type hybrid capacitor having a rated voltage of 50 V and a capacitance of 30 μF is prepared by the following procedure using the electrolytic solution and the solid electrolyte layer.
(1) An anode foil, a cathode foil, and a separator having a dielectric layer of an aluminum oxide film on the surface are cut into a certain width and length. Then, the lead wire is connected to the anode and the cathode by caulking.
Then, it rolls up in roll shape and makes it cylindrical shape. Further, the outer peripheral side surface is fixed with an insulating tape to complete the capacitor element. Next, the sealing rubber and the lead wire are passed through.

(2) A solid electrolyte layer made of poly3,4-ethylenedioxidethiophene (PEDOT) (B-1) is formed on the capacitor element.
After impregnating the prepared capacitor element in a dispersion in which PEDOT is dispersed in an aqueous solution, the capacitor element is dried in a constant temperature bath at 120 ° C. for 1 hour. Note that polystyrene sulfonic acid is applied as the dopant.
Thereafter, the capacitor element was impregnated with the electrolytic solution (A), stored in a case, and caulked to complete the capacitor.
In addition, since (A′-1) of the comparative example was solid at room temperature, the capacitor element could not be impregnated.
In all of the examples and comparative examples, PEDOT (B-1) was used as the solid electrolyte layer.

Initial characteristics and post-test characteristics were measured and evaluated by the following methods.
<Initial evaluation>
As an initial evaluation, capacitance, ESR, and leakage current values were measured.
The electrostatic capacity is measured at 120 Hz, the ESR value is measured at 100 kHz, and the leakage current is measured after applying the rated voltage for 1 minute.

<Evaluation after accelerated test>
In order to be able to evaluate by accelerating volatility, the capacitor element was opened without being stored in the case, and the sample was left in a constant temperature bath at 125 ° C. for 200 hours.

The hybrid type capacitor of the example of the present invention had good initial characteristics, and the acceleration test also showed good results.
On the other hand, in Comparative Example 1, since the molecular weight of (C′-1) contained in the electrolytic solution is large, the electrolytic solution is solid and the capacitor element cannot be impregnated with the electrolytic solution, so that it cannot be assembled as a hybrid capacitor. .
Further, in Comparative Example 2, since the molecular weight of (C′-2) contained in the electrolytic solution is low, the leakage current becomes large in the initial characteristics, and (C′-2) is volatilized in the acceleration test, resulting in a change in capacity. Rate, ESR change rate, leakage current and all items worsened.

Since the hybrid capacitor of the present invention is excellent in terms of low ESR, low leakage current, and long life, it can be suitably used.
Furthermore, it is suitable for applications that require long life and reliability, such as home appliances and on-vehicle equipment.

Claims (5)

Additive of alkylene oxide (b) to 3-8 valent polyhydric alcohol (a) ( excluding polyoxyethylene glycerin or its derivative) (C) Electrolytic solution (A). The electrolytic solution for an electrolytic capacitor according to claim 1, wherein 60 to 95 mol% or more of the alkylene oxide (b) of the alkylene oxide adduct (C) is ethylene oxide. The electrolytic solution for an electrolytic capacitor according to claim 1 or 2, wherein the 3 to 8 valent polyhydric alcohol (a) is at least one selected from the group consisting of glycerin, sorbitol, pentaerythritol, trimethylolpropane, and mannitol. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 3, wherein the alkylene oxide adduct (C) has a number average molecular weight of 1,000 to 4,000 in terms of hydroxyl value. An electrolytic capacitor formed from a capacitor element having an anode foil having a dielectric layer on the surface and a layer of a solid electrolyte (B) in contact with the dielectric layer of the anode foil, the capacitor element being impregnated The electrolyte solution (A) contains an alkylene oxide (b) adduct (excluding polyoxyethylene glycerin or a derivative thereof) (C) of a tri- to octavalent polyhydric alcohol (a ) (C). Hybrid electrolytic capacitor.