JPH0376573B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to solid electrolytic capacitors. A solid electrolytic capacitor has a structure in which a solid electrolyte is attached to a film-forming metal such as aluminum having an anodized film. In this type of capacitor, which has traditionally been mass-produced, the solid electrolyte that makes up the capacitor is mostly manganese dioxide, but in recent years, the weak points of manganese dioxide, namely, the anodization of the film-forming metal during thermal decomposition to form manganese dioxide, have been discovered. Organic semiconductors, mainly used as solid electrolytes to improve the damage to the film and the poor repairability of the anodic oxide film with manganese dioxide.
It was proposed to use TCNQ salt. Here,
TCNQ means 7,7,8,8 tetracyanoquinodimethane. However, TCNQ salt is usually a powdered crystal, and although the crystal itself exhibits high electrical conductivity and good repairability of the above-mentioned film, it is difficult to process because it is a powdered crystal. That is, film-forming metals
The problem is how to attach TCNQ salt crystals. In particular, film-forming metals used in fixed electrolytic capacitors are often porous, but it is extremely difficult to uniformly impregnate TCNQ salt onto such porous metals. What is more important is that TCNQ salt itself always carries the risk of deterioration due to alteration during the adhesion process. Conventionally proposed methods for attaching TCNQ salt can be classified into the following three types. (1) In solvents such as DMF (dimethylformamide)
Apply a solution of TCNQ salt to the above metal,
The method is then dried to remove the solvent by scattering. (2) A method in which fine crystals of TCNQ salt are made using a ball mill or the like and dispersed in alcohol, etc., and then applied to the above metal and dried. (3) A method of vacuum evaporating TCNQ salt onto the above metal. In method (1) above, DMF, which has high solubility for TCNQ salt, is used as a solvent, and such a solvent is
Even when heated to ℃, its solubility is limited to 10%. This means that it is necessary to apply and dry the solid electrolyte many times in order to adhere the necessary thickness of solid electrolyte to the foil-shaped metal, or to adhere the solid electrolyte to the porous metal in a sufficient impregnation manner. It means something. For example, in the case of a porous metal with a rating of 1 μF, the impregnation rate achieved by applying 5 to 10 times and drying is at most 30%, assuming the impregnation rate when manganese dioxide is used as the solid electrolyte as 100%. At such a low impregnation rate, the capacitance value of the capacitor cannot be increased even though the metal is porous. Furthermore, the metal coated with a solvent is left in a high temperature during each drying process, and at this time more or less TCNQ
Deterioration of the salt occurs, leading to deterioration of the conductivity of the solid electrolyte. In addition, since the solid electrolyte that is formed on the metal in this way consists of fine crystals of TCNQ salt, a coagulating resin such as polyvinylpyrrolidone is actually added to the coating solution to increase the adhesion strength of the fine crystals. However, since the coagulating resin is an electrical insulator, the electrical conductivity deteriorates as described above, and the electrical conductivity of the solid electrolyte is lowered (800Ω).
cm (25℃)). In method (2) above, there is a limit to the miniaturization of the TCNQ salt, and the adhesion strength to the above metal is particularly weak, so the solid electrolyte made of TCNQ salt may peel off from the above metal during the capacitor life test. , deterioration of characteristics, such as an increase in tanδ and a decrease in capacity, is observed. Although the above-mentioned enhancement of adhesive strength can be improved to some extent by employing a coagulating resin as described above, it also causes a decrease in the electrolyte of the solid electrolyte.
Furthermore, since a dispersion solution of microcrystals made of TCNQ salt is used, the impregnation rate is particularly poor for porous metals, and even if an ultrasonic diffusion impregnation method is used, the impregnation rate is at most the same as method (1) above. It is. In the method (3) above, not only is the vacuum evaporation work complicated, but it is also completely unsuitable for adhesion to porous metals. The present invention provides a completely new solid electrolytic capacitor, more specifically, a solid electrolytic capacitor including a capacitor element and a solid electrolyte made of a TCNQ complex salt impregnated into the element in a melted and liquefied state by heating. be. When carrying out the present invention, it is necessary to melt and liquefy TCNQ salt, but until now it has not been considered at all to melt and liquefy TCNQ salt in this way for forming a solid electrolyte. The most practical way to obtain a liquid consisting only of TCNQ salt is to liquefy the powdered TCNQ salt in its original form by heating and melting it. However, simply heating and melting the TCNQ salt thermally decomposes the TCNQ salt and turns it into almost an electrical insulator, completely eliminating the function of a solid electrolyte for a capacitor. The present invention shows that even if some TCNQ salts are heated and melted, it takes a short time to thermally decompose, but there is sufficient time for adhesion, and therefore it is possible to cool and solidify within such a time. maintains high conductivity if
This is based on the completely new knowledge that a solid electrolyte made of TCNQ salt can be obtained. TCNQ and its various salts, as well as its production process, are described in, for example, J.Am.Chem.Soc., Vol.84,
P3374-3387 (1962). TCNQ
Salts include a single salt represented by M ⁿ⁺ (TCNQ ^- )n and a complex salt represented by M ⁿ⁺ (TCNQ ^- )n (TCNQ)m. In addition, the above M is an organic cation, n is the value of the cation, and m is the neutrality contained in 1 mol of the complex salt.
Each term means a positive number corresponding to the number of moles of TCNQ. In the present invention, however, the use of complex salts is more preferable in terms of capacitor properties. The above m of the complex salt is preferably 0.5 to 1.5, more preferably about 1. Examples of TCNQ salts used in the present invention include:
Quinoline and isoquinoline substituted at N-position
TCNQ salt is mentioned. In addition, the substituent at the N position is
_C2 - _C13 (2-18 carbon atoms) alkyl (e.g. ethylene, propyl, butyl, pentyl, octyl,
decyl, octadecyl), _C5 - _C8 cycloalkyl (e.g. cyclopentyl, cyclohexyl), _C3
~ _C18 alkene (e.g. allyl), phenyl or phenyl( _C1 - _C18 )alkyl (e.g. phenethyl)
It is a hydrocarbon group such as. More preferred examples of the TCNQ salt used in the present invention include TCNQ salt of N-n-propylquinoline,
TCNQ salt of N-ethylisoquinoline, TCNQ salt of N-isopropylquinoline, TCNQ salt of N-n-hesysylquinoline, TCNQ salt of N-n-propylisoquinoline, TCNQ salt of N-isopropylisoquinoline, TCNQ salt of N-n-butylisoquinoline It is TCNQ salt. The melting points of various TCNQ salts used in the present invention are described below for nine types of salts shown as P-1 to P-9. P-1...N-n-propylquinoline ⁺
(TCNQ ^- ) (TCNQ) P-2...N-isopropylquinoline ⁺
(TCNQ ^- ) (TCNQ) P-3...N-n-propylisoquinoline ⁺
(TCNQ ^- ) (TCNQ) P-4...N-isopropylisoquinoline ⁺
(TCNQ ^- ) (TCNQ) P-5...N-n butylisoquinoline ⁺
(TCNQ ^- ) (TCNQ) P-6...N-ethylquinoline ⁺ (TCNQ ^- )
(TCNQ) P-7...N-ethylisoquinoline ⁺
(TCNQ ^- ) (TCNQ) P-8...N-n-hexylquinoline ⁺
(TCNQ ^- ) (TCNQ) P-9...N-n-hexylisoquinoline ⁺
(TCNQ ^- ) (TCNQ)

[Table] The production of each of the above salts is, for example, as follows. N-
Alkyl iodo and quinoline (or isoquinoline)
A TCNQ salt is prepared by reacting N-alkylquinoline (or isoquinoline) iodide obtained by reacting with TCNQ in a suitable solvent (for example, acetonitrile) at a suitable molar ratio (for example, 3:4). Since this salt contains many impurities, the purity of the salt can be increased by repeating a recrystallization operation consisting of heating, dissolving, cooling, and crystallizing at a temperature of 82° C. or lower in a suitable solvent (eg, acetonitrile). The resulting crystals are needle-shaped or rod-shaped powders. Depending on the type of solvent used in the above reaction or high purification, the quinoline (or isoquinoline) moiety and
The molar ratio with the TCNQ portion varies slightly. for example,
If the solvent used during the reaction and during the purification process is acetonityl, a TCNQ salt in the form of a complex salt with m of 1 is usually obtained, but if methanol is used during the purification process, m becomes smaller than 1. . The above molar ratio changes even if TCNQ is mixed in fine powder with TCNQ salt. For example, 5% of TCNQ salt with m=1
In the melt-solidified salt mixed with TCNQ, m is approximately 1.14. In this way, it can be used even if m changes slightly from 1. TCNQ salts not included in the present invention, such as TCNQ salts of H-quinoline (or isoquinoline) and TCNQ salts of N-methylquinoline (or isoquinoline), decompose without melting when heated, or decompose at the same time as they dissolve. . In contrast, the objects of the present invention as described above
When TCNQ salt is heated, it melts and becomes liquefied, but it takes a substantial amount of time for it to thermally decompose in that state. Thermal decomposition in this case occurs suddenly and the salt becomes an electrical insulator. The time required for insulation after complete melting is as follows.

[Table] However, heating was performed by filling an aluminum case with TCNQ salt crystal powder and bringing it into contact with a metal plate at the above temperature. Therefore, TCNQ salt in liquefied state must be cooled and solidified before its decomposition. Thereby, a solid electrolyte with high electrical conductivity is obtained. For example, P-
In the case of 1 and P-2, it is heated to a temperature above the melting point and below about 300°C, and cooling at room temperature or cooling in a refrigerant such as water is started within 1 minute, preferably within 20 seconds after completion of liquefaction. be done. P-3 and P-4, P
-5, it is heated to a temperature above the melting point and below about 320° C., and cooling at room temperature or cooling in a coolant such as water is started within about 4 minutes, preferably within 1 minute after completion of liquefaction. In this way, it is obtained by cooling and solidifying before decomposition.
The conductivity of TCNQ salt is as follows.

[Table] The solid electrolyte obtained by the present invention is obtained by the above conventional method.
It is not a collection of microcrystals of TCNQ salt like in cases (1) and (2), but is almost in the state of a polycrystalline mass. Furthermore, the solid electrolyte obtained by the present invention maintains the inherent properties of TCNQ salt, such as excellent repairability for oxide films on film-forming metal surfaces. According to the present invention, it is the same as attaching TCNQ salt to a film-forming metal using a solution containing 100% TCNQ salt. During the adhesion process, the required amount of solid electrolyte can be formed not only when the metal is in the form of a foil but also when it is porous, which not only improves mass productivity but also eliminates the conventional problem of TCNQ salt deteriorating each time it is dried. disadvantages are overcome. Further, according to the present invention, since the solid electrolyte is close to a polycrystalline state, the adhesion force to the metal is sufficiently large, so there is no need to use a conventional coagulating resin, and the undesirable conductivity of the solid electrolyte is eliminated. can be avoided. Examples of the present invention will be described below. A capacitor element is prepared by winding processed aluminum foil as an anode foil and etched aluminum foil as a cathode foil together with a separator made of manila paper. This element is then left in a constant temperature bath at 250° C. for about 4 hours to carbonize the separator. This treatment is intended to further increase the degree of impregnation of the solid electrolyte into the element.
It can be omitted. After that, the above element is heated to 250℃.
Preheat to a certain degree. On the other hand, powdered
TCNQ salt (in this example, the above P-1, P-3,
P-5) was filled into a bottomed cylindrical aluminum case, and the case was placed on a heated metal plate to melt and liquefy the TCNQ salt inside the case. As a subsequent step, immediately after the melting and liquefaction, the preheated capacitor element is inserted into the liquefied TCNQ salt in the case, and then the case is immersed in water to be rapidly cooled. As a result, the separator of the capacitor element is impregnated with TCNQ salt and solidified, and this TCNQ salt forms a solid electrolyte that exhibits high conductivity. Finally, the opening of the case is sealed with resin with the tips of the anode and cathode leads exposed, and the intended solid electrolytic capacitor is completed by aging.The table below shows the characteristics of the solid electrolytic capacitor of this example. . In the table, Cap and tanδ are the capacitance at 120Hz, respectively.
Loss, ESR is equivalent series resistance at 100KHz, △cap is capacitance change rate with respect to cap at +25℃, Lc is 25V
Each means the wetting current 15 seconds after application.

[Table] In the above embodiments, the foil metal constituting the capacitor element was aluminum, but other film-forming metals such as tantalum or niobium may be used. As is clear from the above description, according to the present invention, in a solid electrolytic capacitor using a solid electrolyte made of an organic semiconductor, impregnating and adhering the solid electrolyte to a film-forming metal can be performed with a simple operation, and Since the solid electrolyte has little deterioration and the solid electrolyte has excellent conductivity, it has excellent temperature characteristics, frequency characteristics, especially ESR at high frequencies, and is fully practical.

Claims (1)

[Scope of Claims] 1. A capacitor element, and a solid electrolyte made of a TCNQ complex salt impregnated into the element in a melted and liquefied state without containing a solvent, wherein the TCNQ complex salt is thermally decomposed for a predetermined period of time after being melted and liquefied by heating. A solid electrolytic capacitor that is characterized by maintaining a stable state without causing any damage. 2 In claim 1, the TCNQ complex salt is N-hexylquinoline, N-ethylisoquinoline, or N-butylisoquinoline.
A solid electrolytic capacitor characterized by being a TCNQ complex salt. 3 In claim 1, the above
A fixed electrolytic capacitor characterized in that the TCNQ complex salt is a TCNQ complex salt of quinoline or isoquinoline whose N position is substituted with a hydrocarbon group. 4. The solid electrolytic capacitor according to claim 3, wherein the hydrocarbon group is an alkyl group having 2 to 18 carbon atoms. 5 In claim 4, neutral
N with TCNQ and an alkyl group with 2 to 18 carbon atoms
The molar ratio with the isoquinoline substituted at the position is approximately 1:
1. A solid electrolytic capacitor characterized by: