JPH026210B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and particularly to improvements in a solid electrolyte layer made of an organic semiconductor and a method for forming the same. Solid electrolytic capacitors use a film-forming metal such as aluminum or tantalum for the anode, and in order to enlarge the surface of the anode, it is made porous by etching or sintering, and an oxide film layer that serves as a dielectric is formed on the surface. A solid electrolyte layer is formed on the surface of the solid electrolyte layer, and a conductive cathode extraction layer is further formed on the outside of the solid electrolyte layer. Conventionally, manganese dioxide has been used as this solid electrolyte layer. As a means of forming this manganese dioxide on the dielectric oxide film layer, the anode electrode is impregnated in liquid manganese nitrate, and then,
Manganese nitrate was thermally decomposed at a temperature of around 300°C and denatured into manganese dioxide. However, according to this method, only a small amount of manganese dioxide is deposited in one process, so it is necessary to repeat the same process several to more than ten times. As a result, the manufacturing process becomes extremely complicated, and the dielectric oxide film deteriorates due to the high temperature and gas generated during thermal decomposition. Therefore, recently, instead of this manganese dioxide,
It has been proposed to use conductive organic materials in this electrolyte layer. This organic electrolyte is known as
Tetracyanoquinodimethane (hereinafter referred to as TCNQ)
This method uses various complex salts of Since TCNQ complex salt is a solid substance at room temperature, the conventional method of attaching it to capacitor elements using it as an electrolyte is to impregnate the anode body in a solution of TCNQ complex salt dissolved in an organic solvent. After that, the anode is removed from the solution and an organic solvent is dispersed to form a TCNQ complex salt layer on the surface of the anode. However, in this method, the concentration of TCNQ complex salt in the solvent is low, so
It is not possible to deposit enough TCNQ complex salt in a single impregnation, and as with the formation of the manganese dioxide layer, it is necessary to repeat this process several to ten times, which again complicates the manufacturing process. Furthermore, since the TCNQ complex salt crystallizes after the solvent evaporates, sufficient contact with the dielectric oxide film on the surface of the anode body cannot be obtained, resulting in the drawback that a predetermined capacitance cannot be obtained. Recently, a method has been proposed in which only the TCNQ complex salt is heated above its melting point to liquefy, the anode body is impregnated with it, and then the liquefied TCNQ complex salt is pulled out and cooled to adhere the TCNQ complex salt. According to this method, since the highly concentrated TCNQ complex salt itself is deposited on the anode body, sufficient TCNQ complex salt can be deposited in one impregnation step. However, TCNQ complex salts are sensitive to heating, and many TCNQ complex salts are
Some substances decompose before they reach a melting point, making it virtually impossible to use this method. For example, methylisoquinolinium and TCNQ
An example of this is complex salts with .If heated below 200℃, they will emit smoke and decompose before melting, becoming an insulator. This invention improves on these drawbacks, and it is possible to improve TCNQ, which has conventionally been impossible to heat-melt and impregnate.
The aim is to make it possible to impregnate complex salts by heating and melting, and to obtain solid electrolytic capacitors with excellent characteristics. This invention relates to methylisoquinolinium TCNQ
A mixture formed by adding a lactone compound to a complex salt is liquefied by heating to a temperature lower than the melting point or decomposition temperature of the TCNQ complex salt, a capacitor element is impregnated into this liquid mixture, and after the impregnation, it is cooled and solidified. Focusing on the phenomenon that the melting point (freezing point) of a mixture is lower than that of a pure substance, this method heats and melts a mixture of TCNQ complex salt and additives and impregnates it into the anode body. This invention will be explained in detail based on the following examples. First, the manufacturing procedure of the solid electrolytic capacitor according to the present invention will be explained. FIG. 1 shows the capacitor element used in this example. This capacitor element 1 is formed by winding a band-shaped electrode body, and the anode 2 is made of high-purity aluminum foil. A dielectric oxide film is formed on the surface of this anode 2 by anodizing treatment. This strip-shaped anode 2 has a collector electrode 3 of approximately the same size disposed oppositely, and a separator paper 4, which is slightly wider than the electrodes 2 and 3, is sandwiched between the anode 2 and the collector electrode 3. The stuffed material is wound from one end to form a cylindrical capacitor element 1. Note that tabs 5 and 6 for obtaining electrical connection with the outside are connected to each of the anode 2 and the collector electrode 3 by means such as welding, and protrude in parallel from one end surface. Furthermore, external leads 7 and 8 are connected to the tips of these tabs by welding. FIG. 2 shows a method of impregnating the capacitor element 1 with a solid electrolyte layer, and a preheating block 10 is placed on the left side of the figure. This preheating block 10 has a heating heater embedded inside and a recess 11 on the top surface.
The capacitor element 1 is placed in the recess 11, and the capacitor element 1 is heated in advance to maintain a high temperature state. Next, an impregnating block 12 is placed on the right side of the figure, and this impregnating block 12 also has a heating heater embedded therein and a recess 13 formed in its upper surface. And in this recess 13,
Powder mixture 1 consisting of TCNQ complex salt and additives
4 is injected and the mixture 14 is melted by heating. The capacitor element 1, which has been kept on standby in the preheating block 10, is moved here and impregnated for a predetermined period of time.Then, the capacitor element 1 is pulled up from the recess 13, and the liquid mixture 14 is solidified by natural cooling to form a solid electrolyte layer. form. As shown in FIG. 3, the capacitor element 1 with the solid electrolyte layer formed thereon is housed in a cylindrical outer case 20 with a bottom, and the open end of the outer case 20 is sealed with an elastic sealing member 21. Closed, outer case 2
Tighten the open end of 0 to seal it. Note that the external leads 7 and 8 drawn out from the capacitor element 1 protrude to the outside from the through hole provided in the elastic sealing body 21, so that an electrical connection between the capacitor element 1 and the outside can be established. Next, we will show the results of fabricating an actual solid electrolytic capacitor using the procedure described above and determining its characteristics. Conventional examples include a normal dry electrolytic capacitor using a liquid electrolyte, a solid electrolytic capacitor made using isopropyl-isoquinolinium TCNQ complex salt that can be melted and impregnated with only TCNQ complex salt, and methylisoquinolinium TCNQ complex salt. As a conventional example, a method obtained by heating and melting only the present invention is shown in comparison with the present invention. First, the capacitor element used was made of high-purity aluminum (purity
99.99%) was prepared as an anode, and after enlarging the surface of this anode by electrolytic etching using alternating current, a dielectric oxide film with a withstand voltage of 9 V was formed on the surface by anodizing treatment. Aluminum (purity 99.94%) of the same size as the anode is placed oppositely as a current collecting electrode, and an aluminum tab for external extraction is connected approximately at the center of both electrodes by cold welding. It is wound into a cylindrical shape with a separator paper interposed between them. Next, for Conventional Example 1, this capacitor element was impregnated with an ethylene glycol-ammonium adipate based electrolyte. Also, conventional example 2,
4 and Invention Examples 1 to 7, using the impregnation apparatus shown in FIG. 2, the capacitor element was heated to 190°C in a preheating block and kept on standby. Inject the mixture with additives, heat and melt it,
The capacitor element was immersed in this solution for 10 seconds, then taken out of the melting tank and allowed to cool naturally to impregnate the solid electrolyte. Then, the impregnated capacitor element is stored in an aluminum exterior case, the opening is closed with a rubber sealing body, and the opening end of the exterior case is wrapped tightly to seal the rated voltage of 6.3V. capacity
Completed a 10μF electrolytic capacitor. At this time, the external dimensions of the capacitor main body were 3 mm in diameter and 5 mm in length. Among these capacitors, 15 minutes for conventional example 1 and 15 minutes for those using solid electrolyte.
Each capacitor was aged by applying a rated voltage for a period of time, and then its electrical characteristics were examined. The electrical characteristics were determined by measuring capacitance (μF), tangent of loss angle at 120Hz, equivalent series resistance [ESR] (Ω) at 100KHz, and leakage current value (μA/2 minute value), as shown in the table below. The results were obtained.

【table】

[Table] Looking at the results of these examples, methylisoquinolinium, which could not be used as a solid electrolyte due to thermal decomposition before melting when heated and melted, shows that
It can be seen that by adding and heating a lactone-based compound, the TCNQ complex salt can be liquefied at a temperature that does not lead to decomposition, and can be impregnated into capacitor elements. As mentioned above, even if an attempt is made to heat and melt the methylisoquinolinium TCNQ complex salt, it will undergo thermal decomposition before melting. Therefore, it cannot be used in the conventional method of heating and melting only the TCNQ complex salt to impregnate it. Incidentally, when only the methylisoquinolinium TCNQ complex salt is heated, it is observed that it gradually thermally decomposes with smoke emitting from around 200℃. However, as can be seen from the examples, although there are differences depending on the type of additive and the mixing ratio, in the examples of the present invention in which a lactone compound was added, in all cases, the mixture melted and liquefied at a temperature of 190°C or lower, It can be seen that impregnation into capacitor elements is now possible. In addition, when comparing the characteristics of solid electrolytic capacitors after impregnation, it is found that in conventional dry electrolytic capacitors using a liquid electrolyte as shown in Conventional Example 1, the electrolyte is held in a liquid state inside the solid electrolytic capacitor element, so the anode The electrolyte penetrates into the fine etching holes (pits) created by the etching process to enlarge the surface of the capacitor, making sufficient contact with the dielectric oxide film, resulting in a high capacitance value. However, the specific resistance value of the electrolyte is that of the TCNQ complex salt, which is several tens of Ωcm.
However, it is high at around 200-300Ωcm, which means that the loss or equivalent series resistance value of the product is high. In addition, in the solid electrolytic capacitor manufactured by heating and melting only the isopropyl-isoquinolinium TCNQ complex salt and impregnating it into the capacitor element, as shown in Conventional Example 2, the loss and equivalent series resistance value are lower than that of the TCNQ complex salt, as described above. Since the resistance value is lower than that of the electrolytic solution, excellent characteristics are obtained, but sufficient capacitance is not obtained. Although the reason for this is not clear, the molten isopropyl-isoquinolinium TCNQ complex salt
Although it penetrates into the etching pit of the anode, during subsequent cooling and solidification, the isopropyl-isoquinolinium TCNQ complex crystallizes into needles.
This is thought to be because contact with the dielectric oxide film in the etching pit occurs only partially. On the other hand, all of the solid electrolytic capacitors manufactured by the method of the present invention exhibit larger capacitance values than Conventional Example 2. This is because the solid electrolyte of this invention is a mixture of a TCNQ complex salt and a lactone compound, so crystallization is prevented during cooling after melting and impregnation, and it remains in the etching pit in an amorphous state, resulting in dielectric oxidation. This is thought to be due to sufficient contact with the film being maintained. Also, some
Whether the TCNQ complex salt crystallizes or not, it is thought that the presence of the lactone compound between the crystals provides intercrystalline conductivity and ensures capacitance. In this example, a capacitor element is constructed in which foil-shaped aluminum is used for the anode, and a dielectric oxide film is formed on the surface after surface expansion treatment, and a current collecting electrode is wound with a separator paper interposed. I used
The capacitor element is not limited to such a structure, and the metal constituting the anode may be other film-forming metals such as tantalum or alloys thereof. Further, the structure is not limited to such a wound structure, but may be a porous body obtained by sintering film-forming metal powder. In addition, even if it is a wound structure,
The separator paper may be omitted, the collecting electrode may be made of a metal other than aluminum, or a heat-resistant conductive resin film may be used. In addition, regarding the exterior structure, in this example, the case is housed in a metal exterior case, but the exterior body may be a resin case, a resin dip or mold, a laminate film exterior, etc. However, this does not deviate from the scope of this invention. Regarding the lactone compounds to be added,
Lactone compounds other than those exemplified in this example may also be used. Furthermore, in the examples, only one type of additive was used, but the same effect can be expected even if two or more types of lactone compounds are mixed and added. As described above, according to the present invention, methylisoquinolinium TCNQ
Capacitor elements can be impregnated by heating and melting the complex salt. Further, according to the present invention, the impregnation rate of TCNQ complex salt can be improved and the capacitance value per unit volume can be increased, which contributes to miniaturization of solid electrolytic capacitors. Furthermore, since it becomes liquid at a temperature lower than the decomposition temperature of the TCNQ complex salt, sufficient time can be secured for thermal decomposition. In addition, since sufficient characteristics can be obtained with one-time impregnation, the impregnation work becomes easier, and expensive TCNQ complex salts can be used without wasting them. This has the effect of improving the characteristics of solid electrolytic capacitors and improving workability. It is extremely useful for improving

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the structure of a capacitor element used in an embodiment of the present invention, FIG. 2 is a sectional view showing a solid electrolyte impregnation device of the present invention, and FIG. FIG. 2 is a cross-sectional view showing a completed state of the solid electrolytic capacitor. 1... Capacitor element, 2... Anode, 3... Collector electrode, 4... Separator paper, 5, 6... Tab,
7, 8... External lead, 10... Preheating block, 11, 13... Recess, 12... Impregnation block, 14... Mixture, 20... Exterior case, 21
...Elastic sealant.

Claims (1)

[Scope of Claims] 1. A solid electrolytic capacitor in which a dielectric oxide film is formed on a metal surface of an anode, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer, the solid electrolyte layer comprising tetracyanoquinodimethane and methyl isochloride. A solid electrolytic capacitor comprising a mixture of a quinolinium complex salt and a lactone compound. 2 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone. 3. In a solid electrolytic capacitor formed by forming a dielectric oxide film on the surface of the anode metal and further forming a solid electrolyte layer on the upper surface thereof, the solid electrolyte layer is formed using tetracyanoquinodimethane and methylisoquinolinium. A mixture obtained by adding a lactone compound to a complex salt of is liquefied by heating to a temperature lower than the decomposition temperature of the tetracyanoquinodimethane complex salt, a capacitor element is impregnated into this liquid mixture, and after the impregnation, it is cooled and solidified. A method for manufacturing a solid electrolytic capacitor, characterized in that the manufacturing method is carried out in a single step. 4 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The method for manufacturing a solid electrolytic capacitor according to claim 3, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone.