JPH02125410A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To increase an available temperature range by employing 1,6- or 2,5-decanedicarboxylic acid in anionic part as nonproton solvent containing no water in electrolyte for driving an aluminum electrolytic capacitor, and dissolving salt made of cationic part selected from a specific group. CONSTITUTION:A cationic part is selected from a group consisting of spirobycyclic ammonium such as 1,1'-spirobipyrrolizinium (1=m=4); N-N- dialkyltetrahydroxazinium such as N-N-ethylmethylmorphonium; 1-azabicyclo[r,l, g]alkanium such as N-methylpyrrolizinium (q=0,l=r=3), and an anionic part is desirably dissolved with salt formed as 1,6-or 2,5-decanedicarboxylic acid in such a manner that its concentration is 0.5-30wt.%. When nonproton solvent such as N,N-dimethylformamide, gamma-butylolactone, etc., is employed as main solvent, and ethyleneglycol, ethyl cellosolve, etc., is employed as sub solvent, excellent electrolyte for an electrolytic capacitor is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to improvement of an electrolytic solution for electrolytic capacitors, and more specifically, to expanding the operating temperature range by dissolving a compound with a unique structure in the electrolytic solution. The present invention relates to an improvement of an electrolytic capacitor that can achieve the following.

[Prior art] Electrolytic capacitors are small, large-capacity, inexpensive, and have excellent properties such as smoothing rectified output, and are one of the important components of various electrical and electronic devices. The aluminum film, which has been changed into an oxide film, is used as an anode.
This oxide film is used as a dielectric and an electrolytic solution is interposed between it and the current collecting cathode.

Electrolytic capacitors are used while constantly regenerating the dielectric oxide film while undergoing chemical reactions during use, so the steady state of the chemical reaction that occurs between the aluminum electrode with an oxide film on the surface and the electrolyte. It is important to maintain the aluminum oxide film that serves as a dielectric in order to stabilize the performance.

In the chemical reactions that occur during the use of electrolytic capacitors,
The electrolyte forms an ionic conductor that is a medium for the movement of ions. Charges move at the interface between the electrolyte and Ti as the electrode reaction progresses, an oxidation reaction progresses at the anode surface, and a reduction reaction progresses at the cathode surface, and at the same time, ions move through the electrolyte, which is an ionic conductor. Current flows. Therefore, the specific resistance, which is the reciprocal of the electrical conductivity of the electrolyte, reflects the properties of the electrolyte as an ionic conductor in the chemical reactions that occur during use of the electrolytic capacitor.

Scintillation is a phenomenon in which the electrochemical state fluctuates as a result of a change in the physical properties of the dielectric due to the high voltage load that occurs when the load voltage of the capacitor increases, resulting in a temporal change in dielectric constant.The voltage at which this phenomenon is observed is The scintillation voltage (spark voltage) can be used as a measure of the voltage resistance of the capacitor, and the higher the scintillation voltage (spark voltage), the greater the voltage resistance of the capacitor.
The spark voltage can be conveniently measured without assembling a final capacitor product by immersing an unformed aluminum foil of an appropriate size in the electrolyte to be measured.

Since the capacitance of a capacitor is proportional to the dielectric constant of the dielectric material, it is necessary to use a dielectric material with a high dielectric constant and maintain the dielectric constant high while avoiding physical and chemical changes in the dielectric material during use. The loss angle tangent, or dielectric loss tangent, which is the difference between the phase of the charging current and the phase of the external electric field, is used as a guideline for the power consumption of a capacitor, and a small value indicates low power consumption. It is highly dependent on changes in frequency, and for a constant frequency, for example, 1 on the high temperature side compared to the value at room temperature.
Although it does not change much even around 00℃, it increases geometrically as the temperature decreases on the low temperature side, for example, -2
At around 0°C, it becomes 4 to 5 times the normal temperature, and at around -50°C, it becomes about 100 times the normal temperature. The difference between the impedance and resistance of a capacitor is inversely proportional to capacitance, so as capacitance decreases, impedance increases. Leakage current, which is the current that flows when a certain value is reached after the start of charging, is due to the steady movement of charge carriers in the dielectric, and the charge carriers are mainly ions generated by dissociation of impurities in the dielectric. It is believed that the magnitude of change in leakage current reflects the stability of the electrochemical state of the dielectric.

The main cause of poor appearance of electrolytic capacitors is the generation of gas due to the progress of unfavorable chemical reactions other than the specified chemical reactions.Since the rate of chemical reactions depends on temperature, it is often not a problem at low temperatures, but at high temperatures. This is one of the important indicators for evaluating the overall performance of a capacitor, as it progresses rapidly and may involve the risk of explosion.

Conventional electrolytic capacitors have widely used ammonium pentaborate dissolved in ethylene glycol.
0, t, etc., which had the disadvantage that the characteristics of the capacitor reflected in impedance etc. deteriorate significantly especially at low temperatures.
For example, the electrolyte for electrolytic capacitors disclosed in U.S. Pat. No. 3,546,119 uses γ-
Boric acid and tri-n-butylamine are dissolved in a solvent in which butyrolactone is the main solvent and ethylene glycol is added as a subsolvent.Although electrolytic capacitors using this have fairly good low-temperature characteristics,
Poor life characteristics at 30°C, greatly lacking in high temperature stability,
The characteristics of capacitors cannot be maintained constant over a wide temperature range, and a solution to these problems has been desired.

[Problems to be Solved by the Invention] The aim of the present invention is to provide an electrolytic solution for medium and high voltages of electrolytic capacitors that exhibits stable characteristics over a wide operating temperature range.

[Means for Solving the Problems] According to the present invention, in an electrolytic solution for driving an aluminum electrolytic capacitor, the main solvent is an aprotic solvent and does not substantially contain water, and an anion moiety is added to the solvent by 1. 6-decanedicarboxylic acid is 2,5-decanedicarboxylic acid, and the cation moiety is spirobicyclic ammonium, N, N
-dialkyltetrahydroxazinium, and 1-
Azabicyclo [r, 1. There is provided an electrolytic solution for medium and high voltage electrolytic capacitors, which is characterized by dissolving a salt selected from the group consisting of ql alkanium.

The spirobicyclic ammonium of the present invention can be represented by the following general formula: (wherein n is an integer of 4 to 8, m is an integer of 3 to 6) includes, for example, the following molecular species: one spirobivirolidinium 1=m= one spirobipiperidinium=m= spiro[piperidine 1.1-one pyrrolidinium] (l=
4, m=5), spiro[azetidine-1,1-piveridinium] (
1=5, m=3).

The N,N-dialkyltetrahydroxazinium of the present invention can be represented by the following general formula: [wherein R1 and R2 are alkyl groups C, H2°++ (p=1 to 6) and are the same. R3 and R4 may be present or different;
is a hydrogen atom or an alkoxy group, s+t=4, s
= 2 to 4, t = 2 to 0].

The N,N-dialkyltetrahydroxazinium of the present invention includes, for example, the following molecular species: N.

N-ethylmethylmorporinium, N,N-dimethyltetrahydro-1,3-oxazinium, N.

N-diethyl tetra and draw 1° 2-Oki sadinium, N.

N.

-dimethyl-2-methylmorpholinium Mu, N.

N-diethyl-5-methoxytetrahydro-1.

3-Oxazinium.

of the present invention 1-Azabicyclo [r.

q] Alkanium can be represented by the following general formula: [wherein R1 is an alkyl group Cp H3p+l (P'' 1~
6), q=0.1.2.3, when q=Q, I=3 to 6 and r=3 to 6, and when q=1.2.3]=2. 3 and r=2°3].

1-Azabicyclo[r, 1. q] Alkanium includes, for example, the following molecular species: H3 N-methylpyrrolizidinium (q=0. 1=r=3) N-ethylquinolizidinium (q=0, = r = 4) N-n-propylpyrocollidinium (q = 0. 1 = 4, r = 3), N-methyl-1-azabicyclo[5゜3゜0] decanium (q = 0. 1 = 3) , r=5) CH.

N-Methyl-1-azabicyclo[2゜2゜] Pentanium (q = ! = r = 2 s N-ethyl-1-azabicyclo[3,3,1] nonanium (q = 1.1 = r = 3) Mi C2H.

N-ethylquinuclidinium (q=2, l=m=2).

The anion moiety described above is 1,6-decanedicarboxylic acid or 2,5-decanedicarboxylic acid, and the cation moiety is subirobicyclic ammonium, N,N-dialkyltetrahydroxazinium, and 1-azabicyclo[ r,
1. q] When dissolving the salt selected from the group consisting of alkanium, it is preferable to set the concentration to 0.5 to 30% by weight, and it is more preferable to set the concentration to 1.0 to 10% by weight. It is.

The aprotic solvent was N-methylformamide, N,N-
dimethylformamide, N-ethylformamide, N,
N-diethylformamide, N-methylacetamide,
Preferably selected from the group consisting of N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethylsulfoxide and acetonitrile. An electrolytic solution for electrolytic capacitors can be obtained.

Subsolvents include ethylene glycol, propylene glycol,
Polyhydric alcohol solvents selected from the group consisting of diethylene glycol, hexylene glycol, phenyl glycol, glycerin, erythritol, and hexitol, or alcohol ether solvents selected from methyl cellosolve and ethyl cellosolve, are excellent for electrolytic capacitors. An electrolyte can be obtained.

[Function] The anion moiety disclosed in the present invention is converted into 1,6-decanedicarbone #! i, t or 2,5-decanedicarboxylic acid,
The cationic moieties include spirobicyclic ammonium, N,N-dialkyltetrahydroxazinium, and 1-azabicyclo[r.

1.9] The mechanism of action of a salt selected from the group consisting of alkanium is not clear as to how it acts in a solvent where the main solvent is an aprotic solvent and does not substantially contain water. However, even if the electrolytic solution is a conventional electrolytic solution in which ammonium pentaborate is dissolved in ethylene glycol or an aprotic solvent, it contains a salt consisting of a specific anionic moiety and a cationic moiety disclosed in the present invention. Unlike electrolytes that do not have any effect, the electrolyte for electrolytic capacitors of the present invention has some effect on stabilizing the chemical steady state of the electrochemical reaction system consisting of the anode, cathode, aluminum oxide film dielectric, and electrolyte of the electrolytic capacitor. It is estimated that this contributes to

Regarding the improvement of low-temperature characteristics, the electrolytic solution for electrolytic capacitors of the present invention is an aprotic electrolytic solution that does not solidify even at around -50°C, unlike conventional ethylene glycol-based electrolytes, which solidify at around -10°C. The anionic part of the electrolyte is 1,6-decanedicarboxylic acid or 2,5-decanedicarboxylic acid, and the cationic part is spirobicyclic ammonium, N,N-dialkyltetrahydroxa. Zinium, as well as 1-azabicyclo[r
, 1. q] A freezing point lowering effect is realized with the contribution of a salt selected from the group consisting of alkane.
Even if the temperature is below C, solidification does not occur, the dissociation state of the electrolyte is stabilized, and low-temperature characteristics are improved.

Regarding the occurrence of appearance defects when used at high temperatures, it is effective to ultimately suppress the generation of water or hydrogen gas. Since it does not contain water and hydration deterioration does not occur, even if cracks occur in the aluminum oxide film, they are quickly repaired during use, and the reaction to generate aluminum hydroxide, which originally involves hydrogen generation, proceeds on the electrode. However, it is presumed that this property is further enhanced by the action of the specific salts disclosed in the present invention.

[Effects of the Invention] An electrolytic capacitor using the electrolytic solution for electrolytic capacitors of the present invention exhibits stable characteristics over a wide operating temperature range, and the decrease in capacitance is small at low temperatures, and the increase in dielectric loss tangent, that is, the increase in power consumption, is small. Capacitance hardly changes even at high temperatures, and changes in dielectric loss tangent, that is, power consumption and leakage current, are small. Since no gas is generated, no appearance defects occur even when used at high temperatures for long periods of time.

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited only to the following Examples.

The composition of the electrolytic solution for electrolytic capacitors prepared according to the present invention is shown in Table 1. As a comparative example, the composition of the conventional typical electrolytic solution for electrolytic capacitors is also shown in Table 1. The electrolyte consists of a solvent consisting of an aprotic solvent alone or a mixture of an aprotic solvent and a polyhydric alcohol solvent, an anion portion of which is 1,6-decanedicarboxylic acid or 2,5-decanedicarboxylic acid, and a cationic portion. and a salt selected from the group consisting of subirobicyclic ammonium, N,N-dialkyltetrahydroxazinium, and 1-azabicyclo[r,1°9]alkanium. Typical conventional electrolytic solutions for electrolytic capacitors include a polyhydric alcohol solvent alone or a borate solution dissolved in a solvent consisting mainly of an aprotic solvent and a polyhydric alcohol solvent, as described in U.S. Pat. No. 3,546,119. This is what I did. The values of conductivity and spark voltage measured by conventional methods are also shown in Table 1.

Table 2 shows the test results regarding the low-temperature characteristics of the electrolytic capacitor made using the electrolytic solution of the present invention. , the increase in the dielectric loss tangent (tan δ), which is a measure of the consumed power, is suppressed to a low level, and the impedance does not increase (Examples 1 to 15). Electrolytic capacitors that use liquid have a temperature of 96% of normal temperature at low temperatures (-55℃).
The capacitance is lost, the dielectric loss tangent (tan δ) is approximately 80 times larger, and the impedance value is also large (Comparative Example 1). An electrolytic capacitor using a conventional electrolytic solution in which a borate is dissolved in a solvent mainly composed of an aprotic solvent and a polyhydric alcohol solvent gives relatively good results in terms of low-temperature characteristics (Comparative Example 2).

The life evaluation results of electrolytic capacitors made using the electrolyte of the present invention at high temperatures (130°C) are shown in the third section.
The electrolytic capacitor using the electrolyte of the present invention shown in the table is as follows:
Even after 1000 hours of use at 130°C, there is almost no loss in capacitance, only a slight increase in dielectric loss tangent (tan δ), and almost no change in leakage current value reflecting the electrochemical state of the dielectric. No defects occur at all (Example 1)
~15), an electrolytic capacitor using an electrolyte in which a borate is dissolved in a conventional polyhydric alcohol solvent alone, and a borate dissolved in a conventional solvent consisting mainly of an aprotic solvent and a polyhydric alcohol solvent. For electrolytic cone capacitors that use electrolytic solution, during the high-temperature test at 130'C, all test specimens suffered from liquid leakage due to internal pressure increase due to gas generation, and appearance defects such as safety valve activation, and tests W and R were rejected. It became possible (Comparative Examples 1 and 2).

Claims (3)

[Claims] (1) In an electrolytic solution for driving an aluminum electrolytic capacitor, the main solvent is an aprotic solvent and does not substantially contain water, and the anion moiety is added to 1,6-decanedicarboxylic acid or 2,5-decanedicarboxylic acid. acid, and the cation moiety is spirobicyclic ammonium, N,N-dialkyltetrahydroxazinium, and 1-azabicyclo[r. l. q] An electrolytic solution for medium-high voltage electrolytic capacitors, characterized by dissolving a salt selected from the group consisting of alkanium. (2) The aprotic solvent is N-methylformamide, N
, N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, γ-butyrolactone, N-methyl- The electrolytic solution for an electrolytic capacitor according to claim 1, which is selected from the group consisting of 2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, and acetonitrile. (3) Subsolvent: ethylene glycol, propylene glycol, diethylene glycol, hexylene glycol,
Claim 1: The solvent is a polyhydric alcohol solvent selected from the group consisting of phenyl glycol, glycerin, erythritol, and hexitol, or an alcohol ether solvent selected from methylcellosolve and ethylcellosolve.
Electrolyte for electrolytic capacitors as described.