JPH0666237B2 - 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: TCNQ below
The use of a complex) is proposed. This organic semiconductor can be dissolved in an organic solvent or can be impregnated and applied to the oxide film 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 property, has good high-frequency characteristics, and enables a large-capacity capacitor. For example, Shinichi Niwa has applied for an invention using an organic semiconductor composed of Nn-prolyl or N-isopropylisoquinoline and TCNQ as a solid electrolyte (Japanese Patent Laid-Open No. 58-17609). According to the above 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. It is said that the aluminum capacitor having significantly improved frequency characteristics and temperature characteristics will be manufactured with the help of the above. The use of such an organic semiconductor based on a TCNQ salt as a solid electrolyte has been disclosed by the same applicant as the invention (Japanese Patent Publication No. 56-10777).
Since the CNQ salt has higher conductivity and higher anodic oxidation ability (restoring action) than manganese dioxide, 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, isoquinolium having an N-position substituted with an alkyl group is used as a cation for T
The CNQ salt is supposed to be 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 the TCNQ salt is a substance having a high crystallinity, it has to be rapidly cooled after the melt impregnation to be in an amorphous state.

Regarding the capacitor characteristics, when TCNQ salt is oxidatively decomposed or has high crystallinity, the electrical conductivity is particularly lowered 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 formed on the surface thereof, and a first electrode provided so as to face the first electrode. 2 electrodes and a solid electrolyte layer provided between the first electrode and the second electrode, wherein the solid electrolyte layer uses isoquinolium in which the N-position is substituted with an alkyl group as a cation, A solid electrolytic capacitor containing an ion radical complex salt having 7,7,8,8-tetracyanoquinodimethane as an anion, wherein the alkyl group is an isobutyl group.

Action The present invention uses the cation of the TCNQ salt, which is a solid electrolyte that is melted by heat, in which the N-position of isoquinolium is replaced with an isobutyl group, so that the heat melting property and heat stability are improved, and the impregnation property into the oxide film is improved. And the adhesion are improved so that the capacitance and loss (tan δ) characteristics and reliability of the capacitor 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. A solid electrolyte composed of a TCNQ salt is provided between the (counter electrode) and the first electrode.

A feature of the present invention is that a complex salt of isoquinolium in which the N-position is substituted with an isobutyl group and TCNQ is used as a solid electrolyte.

N-n-butylisoquinolium (TCNQ) ₂ is used in the practically used solid electrolytic capacitor, and the present invention uses Nn-butylisoquinolium (TCNQ).
Q) It has the following features as compared with ₂ .

The melting point of Nn-butylisoquinolium (TCNQ) ₂ is 215 to 220 ° C. according to the DTA measurement, and if the temperature is higher than the melting point, it is easily oxidized and decomposed depending on the environment in the figure.

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 is 45 to 6
Lean for 0 seconds.

N-isobutylisoquinolium (TCNQ) _{2 of the} present invention
Has a melting point of 217 ° C. according to DTA measurement,
When heat-melted under the same conditions as in the case of n-butylisoquinolium (TCNQ) ₂ , the time required for complete melting is 2
It takes about 0 seconds, which is 7 as a stable molten liquid state.
Lean for 0 to 100 seconds.

In the present invention, the N-alkyl group is changed from an n-butyl group to an isobutyl group, so that the surface condition is improved in the impregnation property to the oxide film etched into many fine pores and the adhesion property with the oxide film. Further, since the isobutyl group is more amorphous, the capacitor characteristics equivalent to those obtained by rapid cooling can be obtained even after the hot melt impregnation without intentionally using the cooling medium to perform the rapid cooling treatment.

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

TCNQ of N-isobutylisoquinolium which is an electrolyte
The complex salt was pulverized into a fine powder, and then an aluminum can case (diameter: 10 mm, height: 11 mm) was filled with a required amount and melted on a hot plate at 250 ° C. to be in a liquid state.

Winding unit of winding type aluminum electrolytic capacitor (for rating 3μF, 16V, rating 100μF, 16V)
Was soaked and fully air-cooled in air.

The impregnation was performed after placing an aluminum can case filled with electrolyte on a hot plate for 40 seconds.

The aluminum end surface of the winding unit of the capacitor was one that had been previously subjected to chemical conversion treatment. Finally, the unit was placed in an aluminum case, epoxy resin was injected from above, and heat treatment (80-100 ° C, 2H) was performed to seal the unit.

The results of measuring the initial characteristics of the capacitor at frequencies of 120Hz and 1KHz and the change in capacitance after leaving it unloaded at 85 ° C and 100H are shown below. The value in the table is 10 for each capacitor.
It is the average value of K.

As is clear from the table, it has become possible to reduce tan δ and reduce the capacitance change ΔC to 1% or less.

EFFECTS OF THE INVENTION In summary, according to the present invention, by using the TCNQ complex salt of N-isobutylisoquinolium as the solid electrolyte, the capacitor characteristics and life reliability are improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Yoshimura 3-10-10 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Matsushita Giken Co., Ltd. (56) Reference JP-A-58-17609 (JP, A) Kosho 56-10777 (JP, B2)

Claims (1)

[Claims] 1. A first electrode having an oxide film formed on its surface, a second electrode provided so as to face the first electrode, and between the first electrode and the second electrode. And a solid electrolyte layer provided in the solid electrolyte layer, wherein the solid electrolyte layer has isoquinolium in which the N-position is substituted with an alkyl group as a cation,
A solid electrolytic capacitor comprising an ion radical complex salt having 7,7,8,8-tetracyanoquinodimethane as an anion, wherein the alkyl group is an isobutyl group.