JP6767527B2 - Electrolyte for hybrid electrolytic capacitors - Google Patents

Description

The present invention relates to an electrolytic solution applied to a so-called hybrid type electrolytic capacitor in which a solid electrolyte and an electrolytic solution are used in combination, and a hybrid type aluminum electrolytic capacitor impregnated with this electrolytic solution.

With the digitization of electronic devices, capacitors with a small equivalent series resistance (hereinafter abbreviated as ESR) in the high frequency region are required 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 that uses only an electrolytic solution as a conductive material, but a solid electrolytic capacitor that uses a solid electrolyte of a conductive polymer such as polypyrrole, polyaniline, or polythiophene so as to have a lower ESR. Is coming to be applied.

A solid electrolytic capacitor is superior to a liquid type electrolytic capacitor in that it has a particularly low ESR, but it does not have a function of repairing a defective portion of an anodized film which is a dielectric. Therefore, there is a risk that the leakage current will increase, leading to a short circuit.

On the other hand, in AV equipment and automobile electrical equipment, the demand for high reliability is increasing, so it is necessary to improve the low leakage current and short circuit resistance performance in addition to the performance such as low ESR in solid electrolytic capacitors. It's coming.
In response to these demands, a so-called hybrid electrolytic capacitor has been proposed as an electrolyte material, which uses a solid electrolyte such as a conductive polymer and an electrolytic solution having an excellent repairing effect on a defect portion of an anodic oxide film which is a dielectric. (For example, Patent Documents 1 and 2).

In these hybrid type 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. Therefore, the capacitance is increased, the ESR is reduced, 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 a short circuit does not occur.

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 period of 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 a low molecular weight polyethylene glycol.
However, polyethylene glycol does not volatilize when the molecular weight is high, but since it is a solid state, it is difficult to apply it to a hybrid capacitor, and polyethylene glycol is limited to those having a low molecular weight. Therefore, when these low molecular weight polyethylene glycol-containing electrolytic capacitors are exposed to a high temperature environment, these volatile components gradually volatilize from the gap between the sealant and the case and the gap between the sealant 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 becomes large, and a short circuit occurs.

JP-A-11-186110A Japanese Unexamined Patent Publication No. 2014-195116

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

The present inventors have arrived at the present invention as a result of studies for achieving the above object.
That is, the present invention is an electrolytic solution (A) for a hybrid electrolytic capacitor, which contains an alkylene oxide (b) adduct (C) of a trihydric polyhydric alcohol (a).

The electrolytic solution for a hybrid type electrolytic capacitor of the present invention has an effect that the leakage current can be reduced and a short circuit does not occur because the electrolytic solution does not volatilize even when exposed to a high temperature environment.
Further, 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 it has a high molecular weight. For example, it is liquid at room temperature even if it has a molecular weight of 3000 or more. Further, since the leakage current can be reduced when the molecular weight is large, the present invention using the alkylene oxide adduct of the polyhydric alcohol is different from the electrolytic solution using ordinary 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 trihydric polyhydric alcohol (a).

The electrolytic solution (A) of the present invention contains an alkylene oxide (a) adduct (C) as an essential component, and the alkylene oxide (a) adduct (C) is a trihydric to octavalent polyhydric alcohol ( It is a compound in which an alkylene oxide (b) is added to a).
Examples of the alkylene oxide (b) to be added include ethylene oxide (hereinafter, may be abbreviated as EO), propylene oxide (hereinafter, may be abbreviated as PO), butylene oxide, and the like. Two or more types may be used in combination.
The type of alkylene oxide to be added is preferably ethylene oxide alone or a combination of ethylene oxide and other alkylene oxides from the viewpoint of easily penetrating into the electrode.
In the case of using ethylene oxide in combination with other alkylene oxides, random addition or block addition may be used, but the random addition is preferable from the viewpoint of not attacking the sealing rubber of the capacitor.
When ethylene oxide is used in combination with other alkylene oxides, it is preferable that 60 to 95 mol% of the total alkylene oxide is ethylene oxide, and more preferably 65 to 90 mol, from the viewpoint of facilitating penetration into the electrode. %.
When the content of ethioxide with respect to the total alkylene oxide is less than 60 mol% or more than 95 mol%, the initial value of ESR (equivalent series resistance) becomes high. In addition, the rate of change in ESR also increases.

Examples of the trihydric / octavalent polyhydric alcohol (a) include trihydric alcohols such as trimethylolpropane and glycerin; tetrahydric alcohols such as pentaerythritol; pentahydric alcohols such as xylitol; sorbitol, mannitol, dipentaerythritol and the like. The hexahydric alcohol of.
Of these, as (a), trihydric, tetravalent and hexavalent polyhydric alcohols are preferable, glycerin, pentaerythritol and sorbitol are more preferable, and glycerin is most preferable.
On the other hand, in the case of a monohydric to divalent alcohol alkylene oxide adduct, if the molecular weight is small, it volatilizes, and if the molecular weight is large, it becomes a solid and does not function as a capacitor.

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

As a method for synthesizing the alkylene oxide adduct (C) of a 3- to 8-valent polyhydric alcohol, it is common to react the polyhydric alcohol with potassium hydroxide or ethylene oxide or propylene oxide under a sodium hydroxide catalyst. is there.
In the aluminum electrolytic capacitor application, which is the present application, metal ions cause a short circuit of the capacitor. Therefore, potassium or sodium needs to be 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.

It is preferable that the electrolytic solution (A) of the present invention further contains an electrolyte (D) in addition to (C).
The electrolyte (D) is composed of a cationic component (D1) and an anionic component (D2), and the cationic component (D1) includes 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-decandicarboxylic acid, phthalic acid, maleic acid, benzoic acid, phosphoric acid and its derivatives, boric acid and its derivatives, and the like. Is preferable.
The ratio of (D1) to (D2) is preferably 0.3 to 1.0, preferably 0.5, from the viewpoint of not dedoping the dopant incorporated in the conductive polymer. ~ 1.0 is more preferable.

It is preferable that the electrolytic solution (A) of the present invention also contains an organic solvent (E) 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.

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

The hybrid electrolytic capacitor of the present invention is formed of a capacitor element having a layer of a solid electrolyte (B) in contact with a dielectric layer of an anode foil, and the solid electrolyte (B) is a polythiophene or a derivative thereof, for example. , Poly 3,4-ethylenedioxythiophene, polypyrrole and other conductive polymers.
A dopant is incorporated in this conductive polymer, and the dopant plays a role of exhibiting conductivity. Typical dopants are acids such as p-toluenesulfonic acid and polystyrene sulfonic 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 body 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 tubular case and a sealing body. A capacitor element impregnated with an electrolytic solution is housed in this case, and the sealing body is passed through a through hole through which a lead wire is inserted to pass through the case. It is sealed by compressing with a drawing part provided on the outer peripheral surface of the above.

The capacitor element of the present invention has an anode foil having a dielectric layer on its surface and a layer of a solid electrolyte (B) in contact with the dielectric layer of the anode foil.
The anodic foil is made by roughening an aluminum foil by edging treatment, and further forming an anodic oxide film, which is a dielectric, by chemical conversion treatment on the surface thereof.
In addition to the anode foil, the condenser element also has a cathode foil and a separator, and the condenser element is configured by laminating and winding the anode foil, the cathode foil, and the separator. Then, a layer of a solid electrolyte made of a conductive polymer is formed between the anode foil and the cathode foil. As a production method, there are a method of impregnating with a conductive polymer solution and then drying, and a method of electrolytically polymerizing the conductive polymer.
The electrolytic solution enters the gap of the solid electrolyte formed in the capacitor element formed as described above, and a hybrid type capacitor is produced.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified,% indicates a weight% and a part indicates a weight part.

Production Example 1 Sorbitol EO24 molar 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., and the end point was reached when pressure equilibrium was reached.
After that, 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 on the proton nuclear magnetic resonance apparatus (H-NMR) chart that a 24 molar adduct of ethylene oxide (C-1) of sorbitol was obtained. The number average molecular weight (Mn) in terms of hydroxyl value was 1,240.

Production Example 2 Random adduct of glycerin with 11 mol / PO 5 mol (C-2)
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was used as a mixture of 92 parts by weight (1 mol) of glycerin, and 1,056 parts by weight (24 mol) of EO was used as a mixture of 484 parts by weight (11 mol) of EO and 290 parts by weight (5 mol) of PO. Random additions of 11 mol of EO and 5 mol of PO of glycerin were obtained in the same manner as in Production Example 1. Mn was 960.

Production Example 3 Random adduct of glycerin with 50 mol / PO 3 mol (C-3)
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was used as a mixture of 92 parts by weight (1 mol) of glycerin, and 1,056 parts by weight (24 mol) of EO was used as a mixture of 2200 parts by weight (50 mol) of EO and 165 parts by weight (3 mol) of PO. Random additions of 50 mol EO and 3 mol PO of glycerin were obtained in the same manner as in Production Example 1. Mn was 2,300.

Production Example 4 Random adduct of pentaerythritol with 55 mol / PO 40 mol (C-4)
In Production Example 1, 182 parts by weight (1 mol) of sorbitol was used as a mixture of 136 parts by weight (1 mol) of pentaerythritol, and 1,056 parts by weight (24 mol) of EO was used as a mixture of 2420 parts by weight (55 mol) and PO2320 parts by weight (40 mol). Random additions of pentaerythritol in an amount of 55 mol and 40 mol of EO were obtained in the same manner as in Production Example 1. Mn was 2,560.

Production Example 5 Random adduct (C-5) of 44 mol EO / 14 mol PO of EO12 mol adduct of glycerin
To 92 parts by weight (1 mol) of glycerin, 1.1 parts by weight (0.02 mol) of potassium hydroxide was added, and 528 parts by weight (12 mol) of EO was reacted at 170 ° C. until pressure equilibrium was reached. Then, a liquid in which EO1936 parts by weight (44 mol) and PO812 parts by weight (14 mol) were made uniform in a cylinder was reacted in advance, and when the pressure equilibrium was reached, the end point was set. Then, in order to remove potassium hydroxide, Kyoward 600 and Kyoward 700 (manufactured by Kyowa Chemical Industry Co., Ltd.) were used as adsorbents to reduce potassium hydroxide to 1 ppm or less.
Random adducts of 44 mol of EO and 14 mol of PO to the 12 mol adduct of glycerin were obtained on the H-NMR chart of the sampled product and the H-NMR chart of the final product at the end of the first stage reaction. It was confirmed. Mn was 3,370.

Production Example 6 Random adduct of sorbitol with 80 mol / PO 10 mol (C-6)
In Production Example 1, 1,056 parts by weight (24 mol) of ethylene oxide was used as a mixture of 3520 parts by weight (80 mol) of EO and 580 parts by weight (10 mol) of PO, except that 80 mol of sorbitol was used in the same manner as in Production Example 1. A random adduct with 10 mol 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., and the end point was set when pressure equilibrium was reached. After that, 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 manufacturing 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 EO1,188 parts by weight was 176 parts by weight (4 mol).

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

Next, using the above electrolyte and the solid electrolyte layer, a wound hybrid capacitor having a rated voltage of 50 V and a capacitance of 30 μF is produced by the following procedure.
(1) The anode foil, the cathode foil, and the separator having a dielectric layer of an aluminum oxide film on the surface are cut into a constant width and length. Then, the lead wire is connected to the anode and the cathode by caulking.
After that, it is rolled into a cylindrical shape. Further, the outer peripheral side surface is fixed with insulating tape to complete the capacitor element. Next, the sealing rubber and the lead wire are passed through and attached.

(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 liquid 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. In addition, polystyrene sulfonic acid is applied as a dopant.
Then, the capacitor element was impregnated with the above electrolytic solution (A), stored in a case and crimped to complete the capacitor.
Since (A'-1) in the comparative example was solid at room temperature, it could not be impregnated into the capacitor element.
In all of Examples and Comparative Examples, PEDOT (B-1) was used as the solid electrolyte layer.

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

<Evaluation after accelerated test>
In order to accelerate the volatility and evaluate it, the same evaluation as the initial evaluation was performed after leaving the capacitor element open at 125 ° C. for 200 hours without storing it in the case.

The hybrid type capacitor of the embodiment of the present invention has good initial characteristics, and good results are obtained in an accelerated test.
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 type 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) volatilizes in the accelerated test, resulting in a change in capacitance. The rate, ESR rate of change, leakage current and all items deteriorated.

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

Claims (4)

An electrolytic solution (A) for a hybrid electrolytic capacitor, characterized in that it contains an adduct (C) of an alkylene oxide (b) of glycerin, wherein the alkylene oxide (b) of the alkylene oxide adduct (C) is Ri Oh ethylene oxide and propylene oxide, the alkylene oxide adduct (C) hydroxyl value hybrid electrolytic capacitor electrolytic solution for a number average molecular weight of 960～4,000 by conversion. 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 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 of a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (B) in contact with the dielectric layer of the anode foil, and the capacitor element is impregnated. A hybrid electrolytic capacitor in which the electrolytic solution (A) contains an alkylene oxide (b) adduct (C) of glycerin, wherein the alkylene oxide (b) of the alkylene oxide adduct (C) is Ri Oh ethylene oxide and propylene oxide, the hybrid electrolytic capacitor is the number average molecular weight by hydroxyl value in terms of alkylene oxide adduct (C) is 960～4,000.