JPH0666236B2 - Solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor using an improved organic semiconductor as a solid electrolyte.

2. Description of the Related Art In recent years, along with the digitization of electric device circuits, the capacitors used therein have low impedance in the high frequency region, and there is an increasing demand for small and large capacity capacitors.
Conventionally, plastic film capacitors, mica capacitors, and monolithic ceramic capacitors have been used as capacitors for the high frequency region.However, film capacitors and mica capacitors are difficult to increase in capacity due to their large size. The capacitor has the drawback that the smaller the size and the larger the capacity, the worse the temperature characteristics and the cost becomes very high.
On the other hand, known as large-capacity type capacitors include an aluminum dry electrolytic capacitor or an aluminum or tantalum solid electrolytic capacitor. These capacitors can realize a large capacity because the anodic oxide film that serves as a dielectric can be made very thin, but on the other hand, damage to the oxide film is likely to occur, so damage between the oxide film and the cathode can be repaired. It is necessary to provide an electrolyte for this purpose. In an aluminum dry electrolytic capacitor, an etched positive and negative aluminum foil is wound around a paper separator and a liquid electrolyte is impregnated into the separator to be used. For this reason, there is a decrease in capacitance and an increase in loss (tan δ) over time due to electrolyte leakage and evaporation, and at the same time, high-frequency characteristics and low-temperature characteristics are markedly deteriorated due to the ionic conductivity of the electrolyte. It has drawbacks. Further, in the aluminum / tantalum solid electrolytic capacitor, manganese dioxide is used as a solid electrolyte in order to improve the drawbacks of the aluminum dry electrolytic capacitor. This solid electrolyte is obtained by immersing an anode element in an aqueous solution of manganese nitrate and thermally decomposing it at a temperature of around 350 ° C. In the case of this capacitor, since the electrolyte is a solid, there are no drawbacks such as electrolyte outflow at high temperature and deterioration of performance caused by solidification at low temperature, and it has better frequency and temperature characteristics than a capacitor using a liquid electrolyte. , But
Due to the damage of the oxide film due to the thermal decomposition of manganese nitrate and the high specific resistance of manganese dioxide, the impedance or loss in the high frequency range is one digit or more higher than that of multilayer ceramic capacitors or plastic film capacitors. There is.

In order to solve the above-mentioned problems, an organic semiconductor (7,7,8,8-tetracyanoquinodimethane complex) having a high conductivity and an excellent anodic oxidation property, that is, a repair property of a dielectric film is used as a solid electrolyte. Proposed to be used. This organic semiconductor can be dissolved in an organic solvent, or an oxide film can be impregnated and applied by means such as melting by heating to prevent damage to the oxide film due to thermal decomposition that occurs when impregnating MnO _2. You can The TCNQ complex has high conductivity and excellent anodic oxidation properties, has good high-frequency characteristics, and enables large-capacity capacitors. For example, Shinichi Niwa has applied for an invention using an organic semiconductor composed of Nn-propyl or N-ist-propylisoquinoline and TCNQ as a solid electrolyte (Japanese Patent Laid-Open No. 58-17609). According to the invention, the wound aluminum electrolytic capacitor is impregnated with the TCNQ salt by heating and melting the TCNQ salt, whereby a strong bond between the TCNQ salt and the oxide film is achieved, and the high conductivity of the TCNQ salt is achieved. Helped by
It is said that an aluminum capacitor with significantly improved frequency characteristics and temperature characteristics will be manufactured. TC like this
The use of an organic semiconductor based on NQ salt as a solid electrolyte has been shown in the invention (Japanese Patent Publication No. 56-10777) to which the same applicant has already been applied, and TCNQ salt has higher conductivity than manganese dioxide. Since it has a high anodic oxidation ability (restoring action), it enables excellent performance in both frequency characteristics and temperature characteristics as compared with a solid electrolytic capacitor using manganese dioxide. According to the invention, the TCNQ salt having cation of isoquinolium whose N-position is substituted with an alkyl group is impregnated by heating and melting the oxide film.

Problems to be Solved by the Invention However, the TCNQ salt using isoquinolium in which the N-position is substituted with an alkyl group has different thermal melting properties and thermal stability due to the difference in the alkyl group. Further, since the impregnating property to the oxide film and the electric conductivity are different, the usable alkyl groups are limited. If the alkyl is shorter than the ethyl group, it will not melt by heat. In the examples, the inventor refers to propyl, isopropyl and butyl groups. These also undergo oxidative decomposition when left in a heat-melted state for a certain time or longer. Further, since TCNQ salt is a substance having high crystallinity, it must be quenched by melt-impregnation and then made into an amorphous state.

As for the capacitor characteristics, if TCNQ salt is oxidized and decomposed, or if it has high crystallinity, the electrical conductivity is reduced and the loss becomes large. The capacity characteristic also varies depending on the length of the alkyl group, but there is a problem that the capacity achievement rate is about 80% for the butyl group.

The present invention solves these problems, and an object of the present invention is to improve the heat melting property of an electrolyte and the impregnation property into an oxide film to improve the capacity characteristics and the reliability of life.

Means for Solving the Problems The present invention has been made to achieve the above object, and includes a first electrode having an oxide film on its surface and a second electrode provided so as to face the first electrode. An electrode and a solid electrolyte provided between the first and second electrodes, wherein the solid electrolyte uses isoquinolium having an N-position substituted with an isoamyl group as a cation, and 7,7,8,8-tetracyano A first ion radical complex salt having quinodimethane as an anion and a cation in which the N-position of quinoline or isoquinoline is substituted with a decyl group or a dodecyl group;
A second ion radical complex salt having 8,8-tetracyanoquinodimethane as an anion is used in a weight ratio of 10
The present invention provides a solid electrolytic capacitor comprising a mixture of 0 to 10 to 100.

Action The present invention mixes the cation of the TCNQ salt, which is a solid electrolyte that is melted by heat, with the isoquinolium having the N-position substituted with an isoamyl group and the N-position substituted with a decyl group or a dodecyl group. It is improved and the impregnation property into the oxide film is also improved so that the capacity characteristics and the reliability of the life can be improved.

The basic configuration of the solid electrolytic capacitor according to the present invention is such that a valve metal (for example, aluminum, tantalum, titanium and alloys thereof) having an anodized film on the surface by anodic oxidation (formation) is used as a first electrode and a second electrode is used. A solid electrolyte composed of a TCNQ salt is provided between the (counter electrode) and the first electrode.

The features of the present invention are: a complex salt consisting of TCNQ in which the N-position of isoquinoline is substituted with an isoamyl group, and a complex salt consisting of TCNQ in which the N-position of quinoline or isoquinoline is substituted with a decyl group or dodecyl group The feature is that a mixture of 10 to 100 (weight ratio) is used as the solid electrolyte. What is used in the practically used solid electrolytic capacitor is N-n.
-Butylisoquinolium (TCNQ) ₂ , but a TCNQ salt is presented here which can remedy the above mentioned problems.

The melting point of Nn-butylisoquinolium (TCNQ) ₂ is DT
According to A measurement, the temperature is 215 to 220 ° C., and when the temperature is higher than the melting point, it is easily oxidized and decomposed, though it depends on the surrounding environment.

When this salt is melted in the atmosphere in an aluminum block tank at a constant temperature of 250 ° C, it takes about 30 seconds to completely melt it, and a stable heat-melted state lasts for 45 to 60 seconds. Be beaten

The melting point of N-isoamylisoquinolium (TCNQ) ₂ was 225 to 230 ° C. according to DTA measurement, and when it was melted under the same conditions as Nn-butylisoquinolium (TCNQ) ₂ , it was completely It takes 30 to 35 seconds to melt, and it takes 90 to 120 seconds as a stable molten liquid state.

By changing the N-alkyl group from an n-butyl group to an isoamyl group, the surface state is improved in the impregnating property with respect to the oxide film etched into many fine pores and the adhesion with the oxide film. However, it is still 100% in terms of capacity achievement rate.
The characteristics reaching up to% have not been obtained.

A quinoline or isoquinoline having a long alkyl group at the N-position, for example, GnH _{2n + 1-} substituted with n of 10,12,14,16, etc., has a melting point that decreases as n increases, resulting in thermal melting. Is easily performed, and the fine pores of the oxide film are easily impregnated, so that the capacity characteristics are improved. The capacity achievement rate is almost 100% when n = 16. However, the N position of quinoline or isoquinoline is actually
In the case of substituting with a larger n, the larger the value of n is, the worse the substitution rate is and the more easily by-products are formed. Regarding the capacitor characteristics, the capacitance increases as n increases, but tan
The characteristic of δ becomes worse.

Further, since the melting point is low (200 ° C. or lower), the heat resistance characteristics of the capacitor are deteriorated, and the characteristics are deteriorated in the solder dipping process.

Here, it is possible to easily carry out the alkyl substitution reaction at the N-position and obtain a highly pure product. By mixing it with Nn-isoamylisoquinolium (TCNQ) ₂ , it has solder heat resistance, and , Capacity characteristics and life can be improved, n
TCNQ of quinoline or isoquinoline for 10 and 12
I decided to use salt.

The mixing ratio is N-isoamylisoquinolium (TCNQ)
₂ 10 to 100 parts (weight ratio) is suitable for 100 parts.

Mixtures of up to 10 parts show almost no N-isoamylisoquinolium (TCNQ) ₂ properties. On the contrary, if 100 parts or more are mixed, heat resistance and tan δ characteristics deteriorate.

Examples Hereinafter, examples of the present invention will be described in detail.

<Example 1> N-isoamylisoquinolium (TCNQ) ₂ as an electrolyte
And Nn-decylisoquinolium (TCNQ) ₂ were mixed and the characteristics were compared by changing the mixing ratio. The electrolyte was pulverized into a fine powder, which was then filled in an aluminum can case (diameter 6.5 mm, height 6 mm) with the required amount, and melted into a liquid state on a 250 ° C. hot plate. A winding unit (for rating 3 μF, 50 V) of a wound type aluminum electrolytic capacitor was dipped and sufficiently impregnated, and then rapidly cooled using liquid N ₂ as a refrigerant.

The impregnation was performed after placing an electrolyte-filled aluminum can case on a hot plate for 60 seconds.

The aluminum end surface of the winding unit of the capacitor was one that had been previously subjected to chemical conversion treatment. Finally,
Exterior processing was performed using an epoxy resin.

Next, the capacitor characteristics at a frequency of 120Hz and 1KHz and 85 ℃
Table 1 shows the results of measuring the change in capacity after leaving for 1000 H. The values in the table are average values of 10 capacitors using each electrolyte.

Instead of <Example 2> Next N-n-decyl isoquinolizinyloxy helium (TCNQ) _2, shows the results obtained by using the N-n-dodecyl isoquinolizinyloxy helium (TCNQ) ₂ in Table 2. The same tendency of characteristics as in Example 1 was obtained.

The number of parts of the electrolyte is the same as that in Example 1.

As the mixing ratio of Nn-decyl (or dodecyl) isoquinolium (TCNQ) ₂ increases, the melting point of the electrolyte decreases. Although impregnation was carried out at 250 ° C. in Examples 1 and 2, good impregnation can be performed even at about 220 ° C. when the mixing ratio is about 50 parts or more. Therefore, oxidative deterioration of the electrolyte can be prevented, and the capacitor characteristic (tan δ) is improved accordingly.

Or the effect of the invention In brief the present invention, by using a mixture of a solid electrolyte N- isoamyl isoquinolizinyloxy helium (TCNQ) ₂ and N-n-decyl (or dodecyl) isoquinolium (TCNQ) _2, in practical use so far The characteristics of the capacitor and the reliability of the life are improved compared to the capacitor using TCNQ salt.

Claims (1)

[Claims] 1. A first electrode having an oxide film on its surface, a second electrode provided opposite to the first electrode, and a solid electrolyte provided between the first and second electrodes. The solid electrolyte comprises a first ion radical complex salt having isoquinolium having an N-position substituted with an isoamyl group as a cation and 7,7,8,8-tetracyanoquinodimethane as an anion, and quinoline or A cation in which the N-position of isoquinoline is substituted with a decyl group or a dodecyl group, and a second ion radical complex salt having 7,7,8,8-tetracyanoquinodimethane as an anion in a weight ratio of 100: 10 to 100 A solid electrolytic capacitor, characterized in that it is composed of a mixture in a ratio.