JPH0265115A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain capacitors with stable characteristics under a wide range of usable temperature by using an electrolyte of spiro bicyclic ammonium salt, melted in an organic solvent, of hydrated silica having a specified composition. CONSTITUTION:An electrolyte for driving aluminum electrolytic capacitors is spiro ring ammonium salt of hydrated silica shown by the equation, melted in an organic solvent. In the equation, x and y are arbitrary integers; l is an integer of 4 to 8; and m is an integer of 3 to 6. Besides, it is desirable that the inorganic solvent should consist of a non-proton solvent and a polyhydric alcohol solvent. Electrolytic capacitors using this electrolyte can diminish the decrease of the capacitance, and suppress the increase of the power dissipation to a low level on the low temperature side. On the high temperature side also, the capacitance hardly changes; the power dissipation and leakage current are almost constant; and gas production does not occur together. Accordingly, the external appearances do not become bed even if the capacitors are used under a high temperature for a long time.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an improvement of an electrolytic solution for electrolytic capacitors, and more particularly, to an electrolytic solution for medium and high voltages of electrolytic capacitors that exhibits stable characteristics over a wide operating temperature range. .

[Conventional technology]

Electrolytic capacitors are small, large capacity, inexpensive, and have excellent characteristics such as smoothing rectified output, and are one of the important components of various electrical and electronic devices.They are generally made of aluminum whose surface has been changed into an oxide film by electrolytic oxidation. It is created by using a film as an anode, this oxide film as a dielectric, and an electrolyte interposed between it and a current collecting cathode. During use, the oxide film is constantly regenerated, so it is stable, but if it is not used for a long time, for example, regeneration becomes insufficient and it deteriorates. Since electrolytic capacitors are used while undergoing chemical reactions, their characteristics largely depend on the properties of the electrolyte. Maintaining a steady state of the chemical reaction that occurs between the aluminum electrode, which has an oxide film on its surface, and the electrolyte, and maintaining the aluminum oxide film, which serves as a dielectric, in good condition is important for stabilizing performance. If the chemical steady state is disturbed due to an incorrect method, for example due to an excessive high voltage load, the aluminum oxide film will be destroyed and the insulation will eventually break, but even if it does not reach that point, it may cause problems other than the prescribed chemical reactions during use. A chemical reaction progresses, which can lead to poor appearance of the capacitor, opening of explosion-proof safety valves, etc., especially when accompanied by gas generation.

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 the electrode as the electrode reaction progresses, an oxidation reaction progresses at the anode surface, 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 electrical conductivity of the electrolytic solution reflects the characteristics of the electrolytic solution as an ionic conductor in the chemical reactions that occur during use of the electrolytic capacitor, and is one of the important indicators for evaluating the overall performance of the capacitor. 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 depends largely on the change in wavenumber, and at a constant frequency, it does not change much compared to the value at room temperature on the high temperature side, even around 100℃, but on the low temperature side it increases geometrically as the temperature decreases, for example. At around -20°C, it becomes 4 to 5 times as much as normal temperature, and around -50°C, it becomes about 100 times as much as normal temperature. The difference between the impedance and the resistance of a capacitor is inversely proportional to the capacitance, so when the capacitance decreases, the impedance increases, but the absolute value at that time is also defined in correlation with the resistance value. 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 causes of poor appearance of electrolytic capacitors are gas (mainly hydrogen) generation due to predetermined chemical reactions such as oxide film repair, and internal pressure increase due to vaporization of water contained in the electrolyte.

Conventional electrolytic capacitors generally use an electrolyte solution in which boric acid or ammonium borate is dissolved in a polyhydric alcohol solvent mainly composed of ethylene glycol. The capacitor's characteristics, reflected in tangent, impedance, etc., deteriorate significantly, especially at low temperatures.Furthermore, when a high-temperature life test at, for example, 130°C is performed, noticeable appearance defects occur and high-temperature stability is greatly lacking, resulting in the capacitor's The characteristics cannot be maintained constant over a wide temperature range, and a solution to these problems has been desired.

[Problem to be solved by the invention]

An object of the present invention is to provide an electrolytic solution for medium and high voltages in electrolytic capacitors that exhibits stable characteristics over a wide temperature range.

[Means to solve the problem]

According to the present invention, an electrolytic solution for driving an aluminum electrolytic capacitor has the following general formula of silicon 1.1''-spirobipiveridinium (l=m=5) (where X and y are arbitrary l is an integer of 4 to 8, and m is an integer of 3 to 6) is dissolved in an organic solvent.

The spirobicyclic ammonium of this QIJI includes, for example, the following compounds: Nispiro [piperidine-1,1'-pyrrolidinium] C1=4. m=5) Spiro[azetidine-1,1″-piperidinium] (j2=5.m=3) 1.1′-spirobivirolidinium (f=m=4) Spirobicyclic ammonium of the present invention Among them, the smallest one is l-4 and m=3, and the largest one is 2-8 and mw5.If the number of carbon atoms constituting the spiro ring is too small, the ring structure will be highly distorted. If it is too large, the molecule becomes thick (and the ratio of positive charges to the entire molecule becomes small), which is not preferable.

Spirobicyclic ammonium is manufactured by Example Itt:, J-■
, Brown, Berichte, Volume 49, Page 466 (191
For example, pyrrolidine can be synthesized by the method described in 6). 1,1-Spirobipyrrolidinium bromide can be obtained on the action of 4-dibromobutane: the obtained 1,1'-spirobipyrrolidinium bromide can be purified by electrodialysis using e.g. an ion exchange membrane. By performing anion exchange, an aqueous solution of 1,1゛-subirobipyrrolidinium hydroxide is obtained, and 5
By dissolving i02, silicic acid can be introduced into the anion moiety to obtain a 1,1'-spirobipyrrolidinium salt of silicic acid. However, the method is not limited to the above method.

In the general formula of the spirobicyclic ammonium salt of silicic acid, the form in which x=y=1 is the most common, but salts in other forms or mixtures thereof may also be used as the spirobicyclic ammonium salt of the present invention. It can be used as

The electrolytic solution for electrolytic capacitors of the present invention is prepared by dissolving spirobicyclic ammonium salt of silicic acid in an organic solvent, but it is preferable that the organic solvent is a mixed solvent consisting of an aprotic solvent and a polyhydric alcohol solvent. be. Such a solvent is substantially non-aqueous and is unlikely to cause hydration deterioration of the electrolytic capacitor.

Although polyhydric alcohol solvents should be avoided from the viewpoint of hydration deterioration because they may react with acids and produce condensed water, their addition can reduce the spirometry of silicic acid, which is an ionic compound. The solubility of the bicyclic ammonium salt increases and the chemical stability of the electrolyte improves.

The electrolytic solution for electrolytic capacitors of the present invention is prepared by dissolving 0.1% to 20% by weight, preferably 1% to 10% by weight, of a subirobicyclic ammonium salt of silicic acid in such an organic solvent. It is suitable if

The aprotic solvents were N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N
-diethylformamide, N-methylacetamide, N
, N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, T-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethyl sulfoxide and acetonitrile. An electrolytic solution for electrolytic capacitors can be obtained.

Suitable electrolysis is achieved if the polyhydric alcohol solvent is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, hexylene glycol, phenyl glycol, glycerin, erythritol, hexitol and alcohol ethers such as methyl cellosolve and ethyl cellosolve. An electrolytic solution for capacitors can be obtained.

[Effect]

How does the subirobicyclic ammonium salt of silicic acid disclosed by the present invention act in an organic solvent, particularly in a mixed solvent consisting of an aprotic solvent and a polyhydric alcohol solvent, when driving an electrolytic capacitor? The mechanism itself is not clear.

However, unlike the conventional electrolytic solution in which boric acid or ammonium borate is dissolved in a polyhydric alcohol solvent mainly composed of ethylene glycol, the electrolytic solution for electrolytic capacitors of the present invention can be used for electrolytic capacitor anodes, cathodes, aluminum oxide film dielectric It is presumed that this contributes in some way to stabilizing the chemical steady state of the electrochemical reaction system composed of the body and electrolyte.

The electrolytic solution for an electrolytic capacitor in which the spirobicyclic ammonium salt of silicic acid of the present invention is dissolved in an organic solvent as an electrolyte exhibits good electrical conductivity even when the solute concentration is relatively low. High conductivity is a basic condition required for an electrolytic solution for electrolytic capacitors, and its quality depends mainly on the properties of the electrolyte, but the spirobicyclic ammonium salt of silicic acid used in the present invention has at least It has characteristics that satisfy this basic condition.

Regarding the improvement of low-temperature characteristics, in addition to conventional polyhydric alcohol solvents such as ethylene glycol, which mostly solidify at around -10°C, the electrolytic solution for electrolytic capacitors of the present invention does not solidify even at around -50°C. Because it contains an aprotic solvent, it achieves a freezing point lowering effect with the contribution of the subirobicyclic ammonium salt of electrolytic silicic acid, and does not solidify even below 150°C, stabilizing the dissociation state of the electrolyte and improving low-temperature properties. be able to. Note that it is preferable to use a polyhydric alcohol solvent in combination with the spirobicyclic ammonium salt of silicic acid rather than using only an aprotic solvent as the solubility increases.

Since the electrolytic solution for electrolytic capacitors of the present invention is substantially non-aqueous, internal pressure does not increase due to water.

〔Effect of the invention〕

The electrolytic capacitor using the electrolytic solution for electrolytic capacitors of the present invention exhibits stable characteristics over a wide range of operating temperatures, and the decrease in capacitance is small at low temperatures, and the increase in dielectric loss tangent, that is, the increase in power consumption, can be suppressed to a low level. Even at high temperatures, the capacitance hardly changes, and the dielectric loss tangent, that is, the power consumption and leakage current, remain almost constant.Since no gas is generated, no appearance defects occur even when used at high temperatures for long periods of time.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to the following examples.

Composition and Conductivity of Electrolyte The composition and conductivity of the electrolyte for electrolytic capacitors prepared according to the present invention are shown in Table 1. As a comparative example, the composition of a typical conventional electrolytic solution for an electrolytic capacitor is also shown in Table 1. The electrolytic solution for electrolytic capacitors of the present invention is made by dissolving a spirobicyclic ammonium salt of silicic acid in an organic solvent, particularly in a mixed solvent of an aprotic solvent and a polyhydric alcohol solvent, and is made by dissolving a spirobicyclic ammonium salt of silicic acid in a mixed solvent of an aprotic solvent and a polyhydric alcohol solvent. The electrolyte for capacitors consists of ethylene glycol (polyhydric alcohol) and ammonium pentaborate. The conductivity of the electrolytic solution is an index to measure the performance of the electrolytic solution prepared before assembling the electrolytic capacitor as an electrolytic solution for an electrolytic capacitor. 22μF
created an electrolytic capacitor. Table 2 shows the test results regarding the low temperature characteristics of the produced electrolytic capacitor. Electrolytic capacitors using the electrolyte of the present invention can be used at low temperatures (-55°C).
However, the capacitance ti loss is small, the increase in dielectric loss tangent (tan δ), which is a measure of power consumption, is suppressed to a low level, and the impedance does not increase (Examples 1 to 6), but electrolytic capacitors using conventional electrolytes At a low temperature (-55° C.), 96% of the capacitance at room temperature is lost, the dielectric loss tangent (tan δ) becomes about 80 times, and the impedance value is also large (comparative example).

Product Life Characteristics Table 3 shows the product life characteristics of an electrolytic capacitor (rated 250 V, 22 μF) prepared by a conventional method using the above-mentioned electrolytic solution, as a result of a use test at a high temperature (130° C.). An electrolytic capacitor using the electrolyte of the present invention has a temperature of 10
Even after 00 hours of use, there is almost no loss in capacitance, only a slight increase in dielectric loss tangent (tan δ), almost no change in leakage current value that reflects the electrochemical state of the dielectric, and no appearance defects. Examples 1 to 6)
When an electrolytic capacitor using a conventional electrolytic solution was used for 500 hours at 130°C, all of the test specimens developed poor appearance, making it impossible to continue the test due to the danger (comparative example).

As explained above, by using the electrolytic solution for electrolytic capacitors of the present invention, it is possible to obtain an electrolytic capacitor for medium and high voltages that exhibits stable characteristics over a wide operating temperature range.

Claims (5)

[Claims] (1) In the electrolyte for driving aluminum electrolytic capacitors, spirobicyclic ammonium salt of silicic acid with the following general formula: ▲There are numerical formulas, chemical formulas, tables, etc.▼ (In the formula, x and y are arbitrary integers. 1 is an integer of 4 to 8, and m is an integer of 3 to 6) in an organic solvent. (2) The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the organic solvent comprises an aprotic solvent and a polyhydric alcohol solvent. (3) 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- 3. The electrolytic solution for an electrolytic capacitor according to claim 2, wherein the electrolytic solution is selected from the group consisting of 2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, and acetonitrile. (4) The polyhydric alcohol solvent is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, hexylene glycol, phenyl glycol, glycerin, erythritol, hexitol, and alcohol ethers such as methyl cellosolve and ethyl cellosolve. The electrolytic solution for an electrolytic capacitor according to claim 2. (5) The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 4, wherein in the general formula of the spirobicyclic ammonium salt of silicic acid, x=y=1.