JPH0423814B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a solid electrolyte for a solid electrolytic capacitor. 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 solid electrolyte is mostly manganese dioxide. However, in recent years, manganese dioxide's weak points, namely its film-forming properties during thermal decomposition from manganese nitrate to form manganese dioxide, have been discovered. It has been proposed to use organic semiconductors, mainly TCNQ salts, as solid electrolytes to improve the damage to metal anodic oxide films and the poor repairability of anodic oxide films with manganese dioxide. Here, TCNQ is 7, 7, 8, 8
means 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 solid 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 material, it may cause the solid electrolyte to have an even lower conductivity (800 Ωcm
(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 reinforcement of the adhesion strength can be improved to some extent by employing the coagulating resin as described above, it also causes a decrease in the electrical conductivity 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 liquefied state. When carrying out the present invention, it is necessary to liquefy TCNQ salt, but liquefying TCNQ salt in this way for forming a solid electrolyte layer has not been considered at all in the past. 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,
Disclosed in p. 3374-3387 (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 preferred for 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:
Examples include TCNQ salts of pyridine substituted at the N-position. Although various N-position substituents can be considered, those that can be melted, cooled, and solidified and are versatile are preferable, such as
C2-C18 (2-18 carbon atoms) alkyl, such as eryl, propyl, butyl, bentyl, octyl,
decyl, octadecyl), C5-C8 cycloalkyl (e.g. cyclobentyl, cyclohexyl), C3
-A hydrocarbon group such as a C18 alkene (eg allyl), phenyl or phenyl(C7-C18) alkyl (eg phenethyl). More preferred examples of the TCNQ salt used in the present invention include TCNQ salt of N-n-propylpyridine,
It is TCNQ salt of N-n-butylpyridine. The production of each of the above salts is, for example, as follows. N-
N-alkylpyridine iodide obtained by reacting an alkyl iodo and pyridine is reacted with TCNQ in an appropriate molar ratio (e.g. 3:4) in an appropriate solvent (e.g. acetonitrile).
Make TCNQ salt. This salt has many impurities, so
The purity of the salt can be increased by repeating a recrystallization operation consisting of heating, melting, cooling, and crystallization in a suitable solvent (eg, acetonitrile). The resulting crystals are needle-shaped or rod-shaped powders. The molar ratio of the pyridine part and the TCNQ part changes slightly depending on the type of solvent used in the above reaction or high purification. TCNQ salts not included in the present invention, such as H.pyridine TCNQ salt and N-methylpyridine
When TCNQ salt is heated, it decomposes without melting or decomposes simultaneously with melting. In contrast, the object of the present invention as described above is
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 insulating after complete dissolution is
19 seconds (290℃) and 60 seconds (260℃). However, the heating was carried out 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 a liquefied state must be cooled and solidified before its decomposition. Thereby, a solid electrolyte with high electrical conductivity is obtained. For example, n-
In the case of the TCNQ salt of butylpyridine, it is heated to a temperature above the melting point and below about 300°C, and then cooled at room temperature or in a cooling medium such as water within about 30 seconds, preferably within 10 seconds after completion of liquefaction. Begins. The electrical conductivity of the TCNQ salt obtained by cooling and solidifying before decomposition was as follows. N-n-propyl pyridine (TCNQ-)
TCNQ 1500Ωcm (25℃) N-n-butyl pyridine (TCNQ-)
TCNQ 330Ωcm (25℃) The solid electrolyte obtained by the present invention is
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. In addition, the solid electrolyte obtained by the present invention has the inherent properties of TCNQ salt,
For example, it maintains excellent repairability against 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. Furthermore, 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 an undesirable decrease in the electrical conductivity of the solid electrolyte can be avoided. Examples of the present invention will be described below. A capacitor element is prepared by winding up a chemically formed aluminum foil as an anode foil and an etched aluminum foil as a cathode foil together with a separator made of manila paper. This element is then subjected to a chemical conversion treatment at the cut end, and then left in a constant temperature bath at 250° C. for about 4 hours to carry out the carbonization treatment of the separator. Note that this treatment is for increasing the degree of impregnation of the solid electrolyte into the element, and can be omitted.
Thereafter, the above device was preheated to about 250°C. Meanwhile, powdered TCNQ salt (in this example, N-butylpyridine) prepared by the method described above was prepared.
TCNQ salt) is filled in a cylindrical aluminum case with a bottom, and the case is placed on a heated metal plate to melt and liquefy the TCNQ salt inside the case. As a subsequent step, immediately after such 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 TCNQ salt impregnates the separator of the capacitor element and solidifies, and the 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 lead and cathode lead exposed, and aging is performed to complete the intended solid electrolytic capacitor. The table below shows the characteristics of the solid electrolytic capacitor of this example. In the table, cap and tanδ are capacitance and loss at 120Hz, ESR is equivalent series resistance at 100KHz, respectively.
△cap means the capacitance change rate with respect to cap at +25°C, and LC means the leakage current after 15 seconds of applying 25V. For comparison, as a conventional product, a product using the same winding element as used in the present invention and impregnated with an ethylene glycol-based electrolyte is listed.

【table】

[Table] In the above embodiments, the foil metal constituting the capacitor element was aluminum, but other film-forming metals such as tantalum and 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 Furthermore, the solid electrolyte has high conductivity and is stable against temperature, so it has better temperature and frequency characteristics than conventional winding elements impregnated with electrolyte. Significantly improved.

Claims (1)

[Claims] 1 Pyridine substituted with a hydrocarbon group at the N position
A method for producing a solid electrolyte for a solid electrolytic capacitor, characterized in that TCNQ complex salt is heated and melted, impregnated into a capacitor element made of a film-forming metal on which an anodized film is formed, and then cooled and solidified. 2. The method for producing a solid electrolyte for a solid electrolytic capacitor according to claim 1, wherein the hydrocarbon group is n-propyl or n-butyl.