JP2017027992A - Solid electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor where change in capacitance is less even under a high temperature atmosphere of 125°C or more, a low ESR is maintained, and temperature cycle characteristics are excellent.SOLUTION: An electrolyte is formed on the surface of a dielectric oxide film by impregnating a capacitor element, having the dielectric oxide film formed thereon, with a dispersion solution having a basic composition of polyethylene dioxythiophene/polystyrene sulfonate and then drying. In the capacitor element, polyethyleneglycol and a compound including a chemical structure of (-CH-CH(R)-O-)(where, R represents an alkyl radical of 1C-4C, and n indicates an integer) are contained. A manufacturing method therefor is also provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

  As a solid electrolytic capacitor, a conductive polymer layer is formed on an anode foil of a capacitor element in which an anode foil having a dielectric oxide film formed on a surface and a cathode foil are wound through a separator, After forming a conductive polymer layer on the anode foil on which the body oxide film is formed, the conductive polymer is applied to the capacitor element on which the laminated capacitor element and the valve action metal powder are sintered, and then the capacitor element on which the dielectric oxide film is formed. What formed the layer is known.

  A solid electrolytic capacitor is generally made of a valve metal such as aluminum, tantalum, or niobium, and includes an anode body (anode foil or sintered body) having etching pits and fine holes formed on the surface. A dielectric oxide film is formed on the surface, a conductive polymer layer is formed on the dielectric oxide film, and electrodes are drawn out. This conductive polymer layer plays a role as a true cathode in the electrolytic capacitor, and greatly affects the electrical characteristics of the electrolytic capacitor.

  A conductive polymer layer is a layer containing a solid electrolyte that is electronically conductive, and a conductive polymer such as polyethylenedioxythiophene (PEDOT), polythiophene, polyaniline, or polypyrrole, which is a derivative of polythiophene, is a solid electrolyte. It is known to use as (patent document 1).

As a method for forming such a conductive polymer layer, a mixed solution of an oxidizing agent and a monomer is prepared in advance, and a capacitor element is immersed in the mixed solution and impregnated, or the oxidizing agent and the monomer are separately provided. There is a method of sequentially impregnating capacitor elements. For example, in the solid electrolytic capacitor described in Patent Document 2, a capacitor element is immersed in a mixed solution in which a polymerizable monomer and an oxidizing agent are mixed, and a polymerization reaction of a conductive polymer is generated in the capacitor element. Then, after forming the solid electrolyte layer, the capacitor element is immersed in a predetermined ion conductive material, and the void portion in the capacitor element is filled with the ion conductive material. Prevents deterioration.
Each of the above methods forms a conductive polymer layer while a polymerization reaction proceeds on a capacitor element. These methods include changes in solution viscosity accompanying the progress of polymerization, It has also been known that there are difficulties in process control such as insufficient mixing with monomers.

  On the other hand, a method of forming a conductive polymer layer by impregnating and drying a dispersion liquid containing a conductive polymer that has been polymerized in advance to form a coating film is also known. Since this method does not require a polymerization reaction on the dielectric oxide film, the process is relatively easy to control and is advantageous in terms of mass productivity (Patent Document 3).

  The invention of Patent Document 3 is a trade name Baytron-P (BAYTRON is a registered trademark, manufactured by Starck, Germany), which is an aqueous dispersion of polyethylenedioxythiophene (PEDOT), which is a conductive polymer, and polystyrenesulfonic acid (PSS). ) Is used to form a conductive polymer layer, and is intended to improve conductivity in the conductive polymer layer (avoidance of an increase in equivalent series resistance (ESR)) and long-term reliability of electrical characteristics. In the invention of Patent Document 3, an anodic oxide film is first formed, and a precoat layer (layer obtained by applying and drying polystyrene sulfonic acid) and an internal conductive polymer layer (formed by chemical oxidative polymerization, having a relatively molecular weight formed on the surface thereof. An anode body having a small conductive polymer film) is prepared. Next, a solution containing naphthalene sulfonic acids, high molecular weight PSS, boric acid, mannitol, glycols and water is mixed with an aqueous dispersion containing PEDOT and PSS, thereby preparing a polymer polymerization solution. The polymer solution is applied or impregnated into the anode body and dried to provide a conductive polymer layer.

By the way, as the use of solid electrolytic capacitors expands, there is a demand for capacitors that can be used without problems even in harsher environments.
Accordingly, it has been proposed to impregnate the capacitor element with a high boiling point solvent such as polyethylene glycol (boiling point: about 250 ° C.) in order to reduce the change in electrical characteristics under high temperature and high humidity. However, when impregnated only with polyethylene glycol as a high boiling point solvent, it exhibits good characteristics in a high humidity atmosphere such as 85 ° C.-85% RH, but in a high temperature atmosphere of 125 ° C. or higher and a temperature required recently. Under severe conditions of the cycle test, there has been a problem that the characteristic change due to oxidative degradation becomes large.

JP-A-2-15611 Japanese Patent No. 4779277 JP 2008-311582 A

  The present invention solves such problems in the prior art, and provides a solid electrolytic capacitor excellent in temperature cycle characteristics with little change in capacitance even under a high temperature atmosphere of 125 ° C. or higher, low ESR maintained. The task is to do.

The solid electrolytic capacitor of the present invention capable of solving the above problems is impregnated with a dispersion solution having a basic composition of polyethylenedioxythiophene / polystyrenesulfonic acid at least once on a capacitor element on which a dielectric oxide film is formed and dried. In the solid electrolytic capacitor in which the electrolyte is formed on the surface of the dielectric oxide film, in the capacitor element,
Polyethylene glycol,
(—CH ₂ —CH (R) —O—) is a compound having a chemical structure of _n (where R represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer). In this case, n is preferably 1 to 50.

Further, the present invention provides the solid electrolytic capacitor having the above characteristics, wherein the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is polyoxypropylene glyceryl ether, polyoxypropylene Or a derivative thereof (polyoxypropylene trimethylolpropane ether, polyoxypropylene sorbitol ether).

Further, according to the present invention, in the solid electrolytic capacitor having the above characteristics, the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is 0.5 to 5 in weight of polyethylene glycol. It is also characterized by being contained in double weight.

In the solid electrolytic capacitor having the above characteristics according to the present invention, the number average molecular weight of the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is 400 to 4000. It is also a feature.

The present invention is also a method for manufacturing a solid electrolytic capacitor having the above characteristics,
Impregnating and drying a capacitor element on which a dielectric oxide film is formed in a dispersion solution having a basic composition of PEDOT / PSS, chemistry of polyethylene glycol, and (—CH ₂ —CH (R) —O—) _n Compound containing structure (wherein R represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer)
A step of impregnating a mixed solution containing

  In the solid electrolytic capacitor of the present invention, polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) is applied to a capacitor element in which an anode foil on which a dielectric oxide film is formed and a cathode foil are wound through a separator. The conductive polymer layer is formed by impregnating and drying the dispersion solution having the basic composition at least once, and the conductive polymer layer composed of the layer made of PEDOT / PSS is used to perform solid electrolysis with high conductivity. A capacitor is obtained.

In the present invention, in order to suppress the swelling of the conductive polymer layer due to the influence of moisture and improve the moisture resistance of the solid electrolytic capacitor, polythiophene, polypyrrole, polyaniline or It is preferable to form a first conductive polymer layer by impregnating and drying a solution containing the derivative, and a PEDOT / PSS layer is formed thereon as the second conductive polymer layer.
Further, as the separator in the solid electrolytic capacitor of the present invention, a separator having no hydrolyzability, for example, a separator mainly composed of polyacrylonitrile or aramid is preferable. In the region, a solid electrolytic capacitor having higher durability can be obtained.

In the solid electrolytic capacitor of the present invention, a polyethylene glycol and a compound containing a chemical structure of (—CH ₂ —CH (R) —O—) _n (where R is 1 to 4 carbon atoms) in the capacitor element. A compound containing a chemical structure of (—CH ₂ —CH (R) —O—) _{n which} is preferable in the present invention, R is a methyl group, Examples include polyoxypropylene glyceryl ether in which the oxypropylene repeating structure is bonded to the OH group of glycerin, and polyoxypropylene in which the chemical structural formula is represented by HO (—CH ₂ —CH (CH ₃ ) —O—) _n H. It is done. In the present invention, the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is preferably mixed in a weight of 0.5 to 5 times the weight of polyethylene glycol. preferable.

Next, the production method of the present invention for producing the solid electrolytic capacitor of the present invention will be described. In the first step in the production method of the present invention, a capacitor element obtained by winding an anode foil with a dielectric oxide film and a cathode foil wound through a separator is impregnated with a solution in which a conductive polymer is dissolved. A first conductive polymer layer is formed on the dielectric oxide film by drying. At this time, the solution in which the conductive polymer is dissolved is preferably a solution in which any of polythiophene, polypyrrole, polyaniline or a derivative thereof is dissolved, and the separator of the solid electrolytic capacitor has hydrolyzability. It is preferable that there is no separator.
In the present invention, by using the above-mentioned solution in which the conductive polymer is dissolved, it is possible to form a single layer of the conductive polymer layer on the anode foil surface by a general method. Also, by using a conductive polymer solution, it is possible to form a conductive polymer layer more uniformly than when a polymerization reaction is carried out on the anodized film, and unreacted monomers in the capacitor element. Since unnecessary substances such as oxidants and oxidants do not remain, it is possible to improve the moisture resistance of the solid electrolytic capacitor and improve the electrical characteristics.

  In the next step of the production method of the present invention, the capacitor element is impregnated and dried with a dispersion liquid containing polyethylenedioxythiophene and polystyrenesulfonic acid, so that the second conductive material is formed on the first conductive polymer layer. The conductive polymer layer (PEDOT / PSS layer) is formed. When such a dispersion of polyethylene dioxythiophene and polystyrene sulfonic acid is used, the oxidizer and monomer components are less likely to remain in the capacitor element, and deterioration of the dielectric film particularly at high temperatures. Thus, it is possible to obtain a solid electrolytic capacitor in which the capacitance change in the low temperature region is small and the capacitor characteristic change is small even at a high temperature.

In the final step in the production method of the present invention, a capacitor element is impregnated with a mixed solution containing polyethylene glycol and a compound containing a chemical structure of (—CH ₂ —CH (R) —O—) _n for a certain period of time under reduced pressure. Let When polyethylene glycol is impregnated alone, the properties deteriorate in a short time due to auto-oxidation degradation during a temperature cycle test in a high temperature atmosphere, but the chemistry of (—CH ₂ —CH (R) —O—) _n By mixing with a compound containing a structure, the reactivity of thermal oxidative degradation is suppressed, and the high temperature resistance and temperature cycle characteristics are improved.

  According to the present invention, it is possible to obtain a solid electrolytic capacitor that has little change in capacitance even under a high temperature atmosphere of 125 ° C. or higher, maintains low ESR, and has excellent temperature cycle characteristics.

It is an exploded perspective view showing an outline of a capacitor element.

  FIG. 1 is an exploded perspective view showing an outline of a capacitor element. In the capacitor element 4, an anode foil 1 and a cathode foil 3 are wound and accommodated via a separator 2, and an anode lead wire 5 connected to the anode foil and a cathode lead wire 6 connected to the cathode foil. Has been pulled out.

  The anode foil of the solid electrolytic capacitor of the present invention was formed by subjecting the surface of a plate-like valve action metal having a predetermined width to a rough surface by etching treatment, followed by chemical oxidation treatment to form a dielectric oxide film on the surface. Use things. As the valve metal action, a metal containing at least one selected from aluminum, tantalum, niobium, and titanium is preferable, and aluminum is particularly preferable.

  Etching treatment and chemical oxidation treatment can be performed by known methods, and purchased products can also be used. For example, the chemical conversion liquid used for the chemical conversion treatment may be a chemical conversion liquid in which a solute of an organic acid salt having a carboxylic acid group or an inorganic acid salt such as phosphoric acid is dissolved in an organic solvent or an inorganic solvent.

  As described above, the anode foil is wound together with the separator and the cathode foil, and after the winding, restoration conversion is performed in order to repair the dielectric oxide film that is lost when the cut end of the anode foil or the external lead electrode is attached. As a chemical conversion liquid for restoration chemical conversion, a chemical conversion liquid in which a solute of an organic acid salt having a carboxylic acid group or an inorganic acid salt such as phosphoric acid is dissolved in an organic solvent or an inorganic solvent can be used.

  Next, a first conductive polymer layer is formed on the dielectric oxide film. The first conductive polymer layer is preferably formed by impregnating and drying a solution type conductive polymer solution. The first conductive polymer layer is formed using a solution mainly composed of polythiophene, polypyrrole, polyaniline or a derivative thereof, that is, a conductive polymer layer mainly composed of polythiophene, polypyrrole, polyaniline or a derivative thereof. It is preferable that The concentration of the conductive polymer in the solution is preferably 0.1 to 2.0% by weight, and the solvent dissolves the conductive polymer regardless of alcohol, ethers or aromatic solvent, and the drying temperature is less than 250 ° C. A solvent capable of being evaporated at a temperature can be used. The drying conditions are not limited as long as the solvent can be removed and the capacitor element is not adversely affected. For example, the drying can be performed at 100 to 250 ° C. for 30 to 120 minutes. Particularly preferably, the solution for forming the first conductive polymer layer can be formed by using a polyaniline / ethanol solution of 0.5 to 1.5 wt% and drying at 150 ° C. for 30 minutes. As the polyaniline dopant, for example, a sulfosuccinate can be used.

  A second conductive polymer layer is formed on the first conductive polymer layer thus formed. The second conductive polymer layer is formed by immersing and impregnating the capacitor element in a polymer dispersion containing polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS), and then removing moisture by drying. Preferably it is formed. As the PEDOT / PSS dispersion, those using water as the solvent are preferable, and those prepared with the concentration of PEDOT / PSS in the dispersion being 0.5 to 3.0 wt% may be used. When forming the second conductive polymer layer, the impregnation may be performed under normal pressure, but it is also preferable to perform it under reduced pressure. The impregnation and drying can be repeated twice or more. The drying conditions are not limited as long as the solvent can be removed and the capacitor element is not adversely affected. For example, drying can be performed at 85 to 150 ° C. for 30 to 120 minutes. Particularly preferably, by repeating the step of immersing and impregnating for 15 minutes under a reduced pressure of 10 kPa using a polymer dispersion solution containing 1.0 wt% PEDOT / PSS and drying at 100 ° C. for 60 minutes, A second conductive polymer layer can be formed.

Then, the capacitor element in which the conductive polymer layer is formed by the above process is reduced in pressure with respect to a mixed solution containing polyethylene glycol and a compound containing a chemical structure of (—CH ₂ —CH (R) —O—) _n. The capacitor element is impregnated for a certain period of time (for example, 30 minutes) at a lower temperature (for example, 10 kPa), and then the capacitor element is housed in a metal case, the opening of the metal case is curled, and the capacitor is heated at about 150 ° C. The solid electrolytic capacitor of the present invention can be obtained by applying an aging treatment by applying a rated voltage to the capacitor.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[Example 1]
A tab terminal for an external lead electrode was connected to the anode foil and the cathode foil cut to a predetermined width. As the anode foil, an aluminum foil was used as a valve metal, and the surface of the valve metal was subjected to an etching treatment and a chemical conversion treatment to form a dielectric oxide film.
The anode foil and the cathode foil having titanium oxide formed on the surface were wound through a separator mainly composed of polyacrylonitrile, thereby completing a wound element.
Subsequently, a so-called chemical conversion treatment was performed to repair the dielectric oxide film that was missing when the anode foil was cut or the external lead electrode was attached. Using a 0.5 to 3 wt% chemical conversion solution in which ammonium adipate was dissolved in an aqueous solvent, a voltage approximate to the chemical conversion voltage value of the dielectric oxide film was applied to perform chemical conversion treatment.

Next, a conductive polymer layer that is a cathode layer of the solid electrolytic capacitor was formed.
First, the wound element was impregnated with a 1.0 wt% polyaniline / ethanol solution and dried at 150 ° C. for 30 minutes to form a first conductive polymer layer.
Thereafter, a polymer dispersion solution containing 1.0 wt% PEDOT / PSS was immersed and impregnated under a reduced pressure of 10 kPa for 15 minutes, and the water was removed by heating at 100 ° C. for 60 minutes. This impregnation and drying were repeated three times to form a second conductive polymer layer.
Further, polyethylene glycol (PEG-600 manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight determined from hydroxyl value: 600) and polyoxypropylene glyceryl ether (Sanix GP-400 manufactured by Sanyo Chemical Industries, Ltd., determined from hydroxyl values) Number average molecular weight: 400) was mixed at a weight ratio of 40:60, and this mixed solution was impregnated with the above wound element under a reduced pressure of 10 kPa for 30 minutes.

  The capacitor element on which the conductive polymer layer was formed by the above method was housed in a metal case, and the opening of the metal case was curled. Subsequently, an aging treatment was performed by applying a rated voltage to the capacitor under a temperature condition of about 150 ° C. to complete a solid electrolytic capacitor.

[Example 2]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that a solution obtained by mixing PEG-600 and GP-400 at a weight ratio of 30:70 was used as a post-treatment solution to be impregnated into the capacitor element.

[Example 3]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that a solution obtained by mixing PEG-600 and GP-400 at a weight ratio of 70:30 was used as a post-treatment solution to be impregnated into the capacitor element.

[Example 4]
A solid electrolytic capacitor is produced in the same manner as in Example 1 except that a solution obtained by mixing PEG-600, GP-400, and pure water at a weight ratio of 30:20:50 is used as a post-treatment solution to be impregnated into the capacitor element. did.

[Conventional example]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that a 50% aqueous solution of PEG-600 was used as a post-treatment solution to be impregnated into the capacitor element.

[Evaluation of Solid Electrolytic Capacitors of Examples and Conventional Examples]
The solid electrolytic capacitors of Examples and Conventional Examples were evaluated by the following evaluation methods.
Products to be examined: φ8 × 10L 35WV-150μF
1. Temperature cycle test Test conditions: −55 ° C./+125° C. Each 30 min is one cycle, and the capacitance (Cap), tan δ and equivalent series resistance (ESR) after 1,000 cycles are measured. The rate of change was calculated. The results are shown in Table 1 below.
2. Reliability test Test condition: Test atmosphere: 145 ° C
Applied voltage / elapsed time: 35 V applied, 2,000 hours 145 ° C., 35 V applied, 2,000 hours later, the capacitance (Cap), tan δ, and equivalent series resistance (ESR) were measured and changed from the values before the test. The rate was calculated. The results are shown in Table 2 below.

Polymer solutions used in Examples 1 to 4 and the conventional example Conventional example: PEG-600 50% aq after-treatment solution Example 1: PEG-600 40% and GP-400 60% mixed after-treatment solution Example 2 : PEG-600 30%, GP-400 70% after-treatment solution Example 3: PEG-600 70%, GP-400 30% after-treatment solution Example 4: PEG-600 30%, GP -400 20% post-treatment solution mixed with pure water 50%

As shown in the experimental results of Table 1 and Table 2 above, the rate of change in capacitance (Cap), tan δ, and equivalent series resistance (ESR) in the above-described temperature cycle test and high-temperature reliability test are shown in Examples 1-4. Is smaller and more stable than the conventional example. Table 2 also shows that in the high temperature reliability test, the rate of change in capacitance (Cap), tan δ, and equivalent series resistance (ESR) in Examples 1 to 4 is smaller than that in the conventional example, and the high temperature region (145 (° C.), it is also shown that the stability is excellent, particularly when the weight of GP-400 exceeds 0.5 times the weight of PEG-600 (Examples 1, 2, 4). It has been found that good high temperature stability can be obtained. In addition, since the withstand voltage characteristics are improved by making the weight of GP-400 5 times or less than the weight of PEG-600, from the viewpoint of achieving both high temperature stability and withstand voltage characteristics, the weight of GP-400 is More preferably, it is 0.5 to 5 times the weight of PEG-600. Further, when a compound having a number average molecular weight of (—CH ₂ —CH (R) —O—) _n of 400 to 4000 is used, the impregnation property to the capacitor element can be improved.

In the above embodiment, the present invention uses polyoxypropylene glyceryl ether as the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n . The same effect can be obtained by using polyoxypropylene trimethylolpropane ether or polyoxypropylene sorbitol ether.

Furthermore, the present invention provides a winding element impregnated with a mixed solution of polyethylene glycol and polyoxypropylene glyceryl ether after the formation of the conductive polymer layer in the above embodiment. The element is impregnated with a solution obtained by mixing a polymer dispersion solution containing PEDOT / PSS with a compound containing a chemical structure of (—CH ₂ —CH (R) —O—) _n such as polyethylene glycol and polyoxypropylene glyceryl ether. Even if it makes it, the same effect is acquired.

In the present invention, as the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n , those in which R is a methyl group are used, but in addition, an ethyl group, a propyl group, a butyl group The same effect can be obtained even if one is used. And when R is a C1-C4 alkyl group, since the synthesis | combination of a compound is comparatively easy, R is a C1-C4 alkyl group.

  In the above embodiment, the capacitor element is formed by winding the anode foil and the cathode foil on which the dielectric oxide film is formed through the separator, but the capacitor is formed by stacking the anode foil on which the dielectric oxide film is formed. A capacitor element in which a dielectric oxide film is formed after sintering the element or valve action metal powder may be used.

1 Anode foil 2 Separator 3 Cathode foil 4 Capacitor element 5 Anode lead wire 6 Cathode lead wire

Claims (5)

In a solid electrolytic capacitor in which an electrolyte is formed on the surface of a dielectric oxide film by impregnating and drying a dispersion solution having a basic composition of polyethylenedioxythiophene / polystyrenesulfonic acid on a capacitor element on which the dielectric oxide film is formed In the capacitor element,
Polyethylene glycol,
(—CH ₂ —CH (R) —O—) and a compound having a chemical structure of _n (where R represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer), Solid electrolytic capacitor. _2. The solid according to claim 1, wherein the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is polyoxypropylene glyceryl ether, polyoxypropylene, or a derivative thereof. Electrolytic capacitor. Compounds containing the above _{(-CH 2 -CH (R) -O-} ) n in chemical structure, according to claim 1 or, characterized in that it is contained in 0.5 to 5 times the weight of the polyethylene glycol by weight 2. The solid electrolytic capacitor according to 2. 4. The number average molecular weight of the compound containing the chemical structure of (—CH ₂ —CH (R) —O—) _n is 400 to 4000. 5. Solid electrolytic capacitor. Impregnating and drying the capacitor element on which the dielectric oxide film is formed in a dispersion solution having a basic composition of polyethylenedioxythiophene / polystyrenesulfonic acid, polyethylene glycol, (—CH ₂ —CH (R) —O) -) Compound having a chemical structure of _n (wherein R represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer)
A method for producing a solid electrolytic capacitor comprising a step of impregnating a mixed solution containing

Images