WO2024204630A1 - Conductive polymer dispersion liquid, method for producing conductive polymer dispersion liquid, and method for producing solid electrolytic capacitor - Google Patents

Abstract

Provided are a conductive polymer dispersion liquid for achieving lower ESR of a solid electrolytic capacitor, a method for producing the conductive polymer dispersion liquid, and a method for producing the solid electrolytic capacitor. The conductive polymer dispersion liquid contains: a conductive polymer which is polyethylene dioxythiophene doped with polystyrene sulfonate; a dispersion medium; and an additive. The amount x (wt%) of the conductive polymer and the amount y (vol%) of the additive are within the range surrounded by the following relational formulae (1)-(4) in an additive addition step.　(1): y=-29x+100 (2): y=-34x+83 (3): x=1 (4): y=5

Description

Conductive polymer dispersion, method for producing conductive polymer dispersion, and method for producing solid electrolytic capacitor

The present invention relates to a conductive polymer dispersion for forming a solid electrolyte in a solid electrolytic capacitor, a method for producing a conductive polymer dispersion, and a method for producing a solid electrolytic capacitor.

An electrolytic capacitor has anode and cathode foils made of valve metals such as tantalum or aluminum. The anode foil is enlarged by forming the valve metal into a sintered or etched foil, and the enlarged surface has a dielectric film formed by a process such as anodizing. An electrolyte is interposed between the anode and cathode foils.

The advantage of electrolytic capacitors is that the specific surface area can be increased by expanding the surface area of the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors. Electrolytic capacitors contain electrolyte in the form of an electrolyte solution. The contact area of the electrolyte with the dielectric film on the anode foil increases. This makes it easier to further increase the capacitance of electrolytic capacitors.

In recent years, solid electrolytic capacitors, which use a solid electrolyte with higher conductivity than the electrolyte, have also been attracting attention. Solid electrolytic capacitors use a solid electrolyte with higher conductivity than the electrolyte, and can achieve low equivalent series resistance (ESR). Known examples of solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes.

In addition, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which has excellent adhesion to dielectric films, are rapidly becoming popular as solid electrolytes. Conductive polymers use acid compounds such as polyanions as dopants to achieve high conductivity. Therefore, solid electrolytic capacitors have the advantage of low equivalent series resistance (ESR).

A solid electrolyte containing a conductive polymer is formed by applying or impregnating a conductive polymer dispersion between an anode body and a cathode body and then drying the dispersion medium. A conductive polymer dispersion is a dispersion of a conductive polymer, and for example, water is used as the dispersion medium to disperse the conductive polymer in water.

JP 2011-60980 A JP 2014-152320 A

In this way, solid electrolytic capacitors are easier to achieve a low ESR than electrolytic capacitors that use an electrolyte. However, electrolytic capacitors are increasingly being used in digital devices where information processing in the high frequency range of over several tens of kHz is becoming commonplace, and solid electrolytic capacitors that use conductive polymers as the electrolyte are also attracting attention. As solid electrolytic capacitors become more versatile, there is an even greater demand for them to have a lower ESR.

The present invention has been proposed to solve the above problems, and its purpose is to provide a conductive polymer dispersion liquid for achieving a lower ESR in solid electrolytic capacitors, a method for producing the conductive polymer dispersion liquid, and a method for producing solid electrolytic capacitors.

In order to solve the above problems, the conductive polymer dispersion of the present embodiment contains polyethylenedioxythiophene doped with polystyrenesulfonic acid as a conductive polymer, a dispersion medium for the conductive polymer, and an additive added to the dispersion medium, and the amount x (wt %) of the conductive polymer and the amount y (Vol %) of the additive fall within the range surrounded by the following relational expressions (1) to (4).
y=-29x+100...(1)
y=-34x+83...(2)
x=1...(3)
y=5...(4)

The additive may be a polyhydric alcohol.

The pH may be between 3 and 6.

The mass ratio of the polystyrene sulfonic acid (PSS) to the polyethylenedioxythiophene (PEDOT) may be PEDOT:PSS=less than 1:3.

In order to solve the above problem, the method for producing a conductive polymer of this embodiment includes an additive addition step of adding an additive, or an additive and an additional dispersion medium, to a conductive polymer dispersion liquid in which a conductive polymer is dispersed in a dispersion medium, the conductive polymer being polyethylenedioxythiophene doped with polystyrenesulfonic acid, and in the additive addition step, the amount x (wt %) of the conductive polymer added and the amount y (Vol %) of the additive added are within the range surrounded by the relational expressions (1) to (4).

The mass ratio of the polystyrene sulfonic acid (PSS) to the polyethylenedioxythiophene (PEDOT) may be PEDOT:PSS=less than 1:3.

The method may include a pH adjustment step of adjusting the pH of the conductive polymer dispersion to 3 or more and 6 or less, and a concentration step of concentrating the conductive polymer dispersion after the pH adjustment step, and after the concentration step, in the additive addition step, the amount x (wt %) of the conductive polymer added and the amount y (Vol %) of the additive added may be adjusted to fall within the range enclosed by the relational expressions (1) to (4).

The concentration step is a second concentration step, and may include a first concentration step before the pH adjustment step in which the conductive polymer dispersion is concentrated to a range in which the conductive polymer concentration is less than 2.6 wt%, and the pH adjustment step is performed after the first concentration step, and in the second concentration step, the conductive polymer dispersion is further concentrated to a range in which the conductive polymer concentration is 3.5 wt% or less.

The additive may be a polyhydric alcohol.

In addition, to solve the above problem, the method for producing a conductive polymer in this embodiment uses the conductive polymer dispersion liquid to form a solid electrolyte layer between the anode body and the cathode body.

The present invention makes it possible to realize a solid electrolytic capacitor with low ESR.

1 is a graph showing the relationship between the amount of PEDOT:PSS and the amount of additive contained in a conductive polymer dispersion. FIG. 2 is a scatter diagram showing the results of relational expressions (1) to (4) and each of the examples and comparative examples.

The following describes the embodiment of the present invention. Note that the present invention is not limited to the embodiment described below.

(Conductive polymer dispersion)
The conductive polymer dispersion liquid is a dispersion liquid for forming a solid electrolyte layer in a solid electrolytic capacitor. A solid electrolytic capacitor is a passive element that stores and discharges electric charge by electrostatic capacitance, and is made of a dielectric film. The anode foil and the cathode foil on which the conductive layer is formed are arranged to face each other, and a solid electrolyte layer is interposed between the anode foil and the cathode foil. The solid electrolyte layer contains a conductive polymer. The solid electrolyte In addition to the layer, the foil may be impregnated with an electrolyte. A separator is inserted between the anode foil and the cathode foil to prevent short circuits between the anode foil and the cathode foil and to maintain the solid electrolyte layer. Good too.

The conductive polymer dispersion is a dispersion in which particles or powder of the conductive polymer to be contained in the solid electrolyte layer are dispersed. The conductive polymer is attached between the anode foil and the cathode foil by immersing each of the anode foil, cathode foil, and separator in the conductive polymer dispersion and drying them. Alternatively, the conductive polymer may be attached by producing a capacitor element by winding or stacking the anode foil and cathode foil with the separator in between, and then immersing the capacitor element in the conductive polymer dispersion and drying it. In addition to immersion, the conductive polymer dispersion may be applied by dripping or spraying. The drying process may be repeated multiple times, and drying may be performed under reduced pressure.

The conductive polymer used is polyethylenedioxythiophene, also known as PEDOT, which is represented by the following chemical formula (1).

This PEDOT is doped with polystyrene sulfonic acid, also known as PSS. In other words, the conductive polymer is polyethylene dioxythiophene doped with polystyrene sulfonic acid. Hereinafter, polyethylene dioxythiophene doped with polystyrene sulfonic acid will be referred to as PEDOT:PSS.

The number average molecular weight of PSS is 1,000 to 2,000,000, preferably 10,000 to 500,000. If the number average molecular weight is less than 1,000, the resulting conductive polymer will have insufficient conductivity and reduced dispersibility, which is undesirable, and if the number average molecular weight exceeds 2,000,000, the viscosity of the mixture will increase, which is undesirable.

If the weight ratio of PSS to PEDOT is less than PEDOT:PSS = 1:3, the initial ESR can be reduced. If the weight ratio of PEDOT:PSS is 1:1.5 or more, the increase in viscosity of the conductive polymer dispersion can be suppressed, and if the weight ratio of PEDOT:PSS is 1:2.5 or more, the initial ESR can be reduced while suppressing the increase in viscosity of the conductive polymer dispersion.

The dispersion medium of the conductive polymer dispersion liquid may be any medium that disperses conductive polymer particles or powder. The dispersion medium of the conductive polymer dispersion liquid is typically water, but it may also be an organic solvent or a mixture of an organic solvent and water. Examples of organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

Polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, etc. Alcohols include methanol, ethanol, propanol, butanol, etc. Esters include ethyl acetate, propyl acetate, butyl acetate, etc. Hydrocarbons include hexane, heptane, benzene, toluene, xylene, etc. Carbonate compounds include ethylene carbonate, propylene carbonate, etc. Ether compounds include dioxane, diethyl ether, etc. Chain ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, etc. Heterocyclic compounds include 3-methyl-2-oxazolidinone, etc. Nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, benzonitrile, etc.

The dispersion medium further contains an additive such as a polyhydric alcohol. Examples of polyhydric alcohols include polyethylene glycol, 1-hexanol, ethylene glycol, diethylene glycol, triethylene glycol, glycerin, or a combination of two or more of these. Since polyhydric alcohols have a high boiling point, they remain in the solid electrolyte layer even after the conductive polymer dispersion is dried.

Here, in the conductive polymer dispersion, the amount x (wt%) of the conductive polymer and the amount y (Vol%) of the additive are within the range Er surrounded by the following relational expressions (1) to (4), as shown in Figure 1. The amount x (wt%) of the conductive polymer is the percentage of the weight of the conductive polymer relative to the total weight of the conductive polymer dispersion, and the amount y (Vol%) of the additive is the percentage of the volume of the conductive polymer relative to the total volume of the conductive polymer dispersion.

(Relationship)
y=-29x+100 (5≦y≦71, 1≦x≦3.3) ... (1)
y=-34x+83 (5≦y≦49, 1≦x≦2.3) ... (2)
x=1 (49≦y≦71) ... (3)
y=5 (2.3≦x≦3.3) ... (4)

In Figure 1, the lines indicated by relational expressions (2), (3), and (4) are the boundaries of the range in which the initial ESR of a solid electrolytic capacitor is good. The initial ESR refers to the value when a solid electrolytic capacitor is manufactured, aged to repair defects by applying a voltage, and then not energized and not exposed to a high-temperature or low-temperature environment. The line indicated by relational expression (1) is the boundary at which aggregation occurs in the conductive polymer dispersion, even if the pH of the conductive polymer dispersion is 3 to 6. If there is a larger amount of ethylene glycol or a larger amount of PEDOT:PSS than the line indicated by relational expression (1), aggregation occurs in the conductive polymer dispersion and gels.

In addition, it is more preferable to set the amount x (wt %) of the conductive polymer and the amount y (Vol %) of the additive within the range Er surrounded by the following relational expressions (2a), (4a), (1), and (3) instead of the line segments shown by relational expressions (2) and (4).

(Relationship)

In order to keep the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) within the range Er enclosed by the relational expressions (1) to (4), it is sufficient to add an additive addition process to the manufacturing method of conductive polymer dispersion, in which an additive, or an additive and an additional dispersion medium, are added to the initial conductive polymer dispersion consisting of a conductive polymer and a dispersion medium. In this additive addition process, the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) are adjusted by adding the additive, or the additive and an additional dispersion medium.

However, in order to carry out this additive addition process, it may first be necessary to concentrate the initial PEDOT:PSS concentration of the conductive polymer dispersion. If the pH of the conductive polymer dispersion is 3 or less, concentrating the PEDOT:PSS concentration of the conductive polymer dispersion to 2.6 wt% or more will cause aggregation in the conductive polymer dispersion. Also, even if the pH of the conductive polymer dispersion is 3 to 6, concentrating the PEDOT:PSS concentration of the conductive polymer dispersion to 3.5 wt% or more will cause aggregation in the conductive polymer dispersion, as shown in relational formula (1).

Therefore, when concentrating the PEDOT:PSS concentration of the conductive polymer dispersion, a pH adjustment step is carried out before the concentration step, in which the pH of the conductive polymer dispersion is adjusted to 3 or more and 6 or less. In the pH adjustment step, for example, ammonia is blown into the conductive polymer dispersion. The concentration step may be carried out by any known method as long as it is possible to concentrate the conductive polymer dispersion, and one example of such a method is ultrafiltration. In other words, the conductive polymer dispersion is passed through a semipermeable membrane by pressure or the like.

Preferably, before the pH adjustment step, a concentration step is added to concentrate the conductive polymer dispersion to a PEDOT:PSS concentration below 2.6 wt%. That is, the first concentration step is performed, then the pH adjustment step is performed, and then a second concentration step is performed. In the first concentration step, the PEDOT:PSS concentration of the conductive polymer dispersion is suppressed to less than 2.6 wt% so that the initial conductive polymer dispersion at about pH = 1.9 does not gel, even if the pH adjustment step has not been performed. In the second concentration step, the PEDOT:PSS concentration of the conductive polymer dispersion is concentrated to a range of 3.5 wt% or less, because the pH adjustment step prevents gelation if the PEDOT:PSS concentration of the conductive polymer dispersion is 3.5 wt% or less.

By carrying out the first concentration process, then the pH adjustment process, and then carrying out another concentration process, it is possible to suppress de-doping of polystyrene sulfonic acid that may occur during the pH adjustment process. This makes it possible to maintain the high conductivity of the conductive polymer and further reduce the initial ESR of the solid electrolytic capacitor.

The process for preparing the initial conductive polymer dispersion before adjusting the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) is, for example, as follows. First, the monomer that constitutes the conductive polymer and an acid or its alkali metal salt that releases the dopant that constitutes the conductive polymer are added, an oxidizing agent is added, and the mixture is stirred until chemical oxidation polymerization is completed. Next, residual monomers and impurities are removed by purification means such as ultrafiltration, cation exchange, and anion exchange. This results in a conductive polymer dispersion.

In the process of preparing the conductive polymer dispersion, for example, a monomer constituting the conductive polymer and an acid or its alkali metal salt that releases a dopant constituting the conductive polymer are added, a supporting electrolyte is added, and electrolytic oxidation polymerization is carried out using either the constant potential method, the constant current method, or the potential sweep method while stirring, and then impurities and residual monomers are removed by purification means such as ultrafiltration, cation exchange, and anion exchange. The conductive polymer is dispersed using, for example, ultrasound.

In addition, the conductive polymer dispersion may contain organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, ultraviolet absorbers, etc.

Solid electrolytic capacitors in which the solid electrolyte layer is formed from such conductive polymer dispersion liquid improve the initial ESR regardless of the specific configuration. For example, the anode and cathode bodies are arranged in a laminated configuration in which they are alternately stacked with a separator in between. In the laminated type, in addition to using a flat plate type that omits the exterior, for example, the capacitor element is covered with a laminate film, or sealed by molding, dip coating, or printing with a resin such as a heat-resistant resin or insulating resin.

Alternatively, the anode and cathode bodies are wound in a wound arrangement, stacked alternately with a separator in between. In the wound arrangement, for example, the capacitor element is inserted into a cylindrical exterior case with a bottom, and the open end of the exterior case is sealed with a sealing body by crimping. The sealing body is made of rubber, for example, or a laminate of rubber and a hard substrate. Examples of rubber include ethylene propylene rubber and butyl rubber.

The anode and cathode bodies are foils made of valve metal. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity is preferably 99.9% or more for the anode foil and 99% or more for the cathode foil, but impurities such as silicon, iron, copper, magnesium, and zinc may be included. In addition, when the solid electrolytic capacitor is a flat type, a solid electrolyte layer may be formed on the anode foil so as to cover the dielectric film, and then a metal paste such as silver paste may be printed and dried. This silver layer corresponds to the cathode of the solid electrolytic capacitor.

The anode body has a porous structure on its surface, either as a sintered body made by sintering valve metal powder, or as an etched foil made by etching a stretched foil. The porous structure is made up of tunnel-like pits, spongy pits, or voids between densely packed powder particles. The porous structure is typically formed by direct current etching or alternating current etching, in which direct current or alternating current is applied in an acidic aqueous solution containing halogen ions such as hydrochloric acid, or by vapor deposition or sintering metal particles or the like on the core. The cathode body may also have a porous structure on its surface if necessary.

The dielectric film is the dielectric layer of a solid electrolytic capacitor, and is typically an oxide film formed on the surface of the anode body. If the anode body is an aluminum foil, the dielectric film is an aluminum oxide layer formed by oxidizing the porous structure region. This dielectric film is formed by applying a voltage in a solution that does not contain halogen ions, such as an aqueous solution of adipic acid or boric acid. A dielectric film may also be formed on the cathode foil as necessary, and further a layer made of metal nitride, metal carbide, or metal carbonitride formed by vapor deposition, or one containing carbon on the surface, may also be used.

Separators include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixtures thereof; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins; and these resins can be used alone or in combination. If the shape of the solid electrolyte layer can be maintained by itself and the pair of electrodes can be isolated by the solid electrolyte layer, the separator can be omitted from the capacitor element.

In addition to the solid electrolyte layer, an electrolyte solution may be used. The solvent for the electrolyte solution is not particularly limited, but a protic organic polar solvent or an aprotic organic polar solvent can be used. Representative examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds, such as ethylene glycol or propylene glycol. Representative examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides, such as sulfolane, γ-butyrolactone, ethylene carbonate, and propylene carbonate.

The solutes contained in the electrolyte include anionic and cationic components, and are typically organic acids such as adipic acid or benzoic acid or their salts, inorganic acids such as boric acid or phosphoric acid or their salts, or complex compounds of organic acids such as borodisalicylic acid and inorganic acids or their ionically dissociable salts, and are used alone or in combination of two or more. Examples of at least one salt of these organic acid salts, inorganic acid salts, and complex compounds of organic acids and inorganic acids include ammonium salts, quaternary ammonium salts, quaternary amidinium salts, amine salts, sodium salts, potassium salts, etc. Anionic acids and cationic bases may be added separately to the electrolyte as solute components.

The present invention will be described in more detail below based on examples. Note that the present invention is not limited to the following examples.

(Examples 1 to 16)
Conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 11 were prepared as follows. First, a conductive polymer dispersion composed of 1.2 wt% PEDOT:PSS and 98.8 wt% water was subjected to a dispersion treatment using ultrasonic waves to disperse the conductive polymer. The weight ratio of PSS to PEDOT was PEDOT:PSS=1:2.5. After the dispersion treatment, a first concentration step was performed using an ultrafiltration device. In the first concentration step, the conductive polymer dispersion was concentrated until the PEDOT:PSS was 2 wt% relative to the conductive polymer dispersion.

After the first concentration step, the pH was adjusted and ammonia was added until the pH of the conductive polymer dispersion reached 4. After the pH adjustment step, the conductive polymer dispersion was concentrated again using an ultrafiltration device until the PEDOT:PSS reached 3.4 wt % relative to the conductive polymer dispersion. Here, the conductive polymer dispersion of Comparative Example 11 was concentrated in the first concentration step without going through the pH adjustment step to pH = 4, until the PEDOT:PSS reached 2.6 wt % relative to the conductive polymer dispersion, but the conductive polymer dispersion of Comparative Example 11 gelled.

The conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 10 that remained liquid without gelling were moved to the additive addition process. In the additive addition process, ethylene glycol was used as the additive. In the additive addition process, ethylene glycol or ethylene glycol and water were added to the conductive polymer dispersion, and the amount x (wt%) of the conductive polymer and the amount y (Vol%) of the additive were adjusted for each of Examples 1 to 16 and Comparative Examples 1 to 10 to achieve various combinations.

The conductive polymer dispersions of Examples 1, 4, 9, 12, and 14 to 16 were prepared by adding ethylene glycol, while the conductive polymer dispersions of Examples 2, 3, 5 to 8, 10, 11, and 13 and Comparative Examples 1 to 10 were prepared by adding ethylene glycol and water. For Comparative Example 11, 10 vol. % ethylene glycol was added to the gelled conductive polymer dispersion and stirred, but it remained gelled.

Solid electrolytic capacitors were produced using the conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 10, and the initial ESR was measured. Aluminum foil was prepared as the anode foil and cathode foil of the solid electrolytic capacitor. Both sides of the anode foil were subjected to surface enlargement treatment by AC etching. The anode foil was transferred to a chemical conversion treatment process, and a dielectric film was formed on the anode foil.

Lead wires were connected to the anode foil and cathode foil, and the anode and cathode bodies were wound facing each other with a cellulose-based separator in between. Repair formation was performed on the wound body. This wound body has a diameter of 8 mm, a height along the winding axis of 10 mm, a product rated voltage of 35 WV, and a capacitance of 150 μF.

The conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 10 were impregnated into each wound body and dried at 125°C for 30 minutes. A solid electrolyte layer containing a conductive polymer was formed by drying the impregnated conductive polymer dispersion. Furthermore, the capacitor element with the solid electrolyte layer formed was impregnated with an electrolyte. The solvent for the electrolyte was ethylene glycol, and 0.16 mol of ammonium azelaate was added to the electrolyte as a solute per 1 kg of electrolyte.

The capacitor element, with the solid electrolyte layer formed and impregnated with the electrolyte, was housed in a cylindrical exterior case with a bottom. A rubber seal was attached to the open end of the exterior case, and the case was sealed by crimping. Each solid electrolytic capacitor was aged by applying a voltage.

The initial ESR of the solid electrolytic capacitors using the conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 10 was measured using an LCR meter (Agilent Technologies, E4980A) with an AC current level set to 1.0 Vrms and a measurement frequency set to 100 kHz.

The amount x (wt%) of conductive polymer, the amount y (Vol%) of additive, and the ESR measurement results for the conductive polymer dispersions of Examples 1 to 16 and Comparative Examples 1 to 10 are shown in Tables 1 and 2 below. In the tables, the PEDOT:PSS concentration is the concentration of conductive polymer relative to the conductive polymer dispersion, i.e., the amount x of conductive polymer dispersion, and the EG ratio is the ratio of additive relative to the conductive polymer dispersion, i.e., the amount y of additive.

(Table 1)

(Table 2)

The results of Tables 1 and 2 above were plotted in Figure 2, which was created in Figure 1. Figure 2 is a scatter plot showing the results of relational expressions (1) to (4) and each example and comparative example. In Figure 2, the plots of black squares are examples, and the plots of white squares are comparative examples. The numbers in parentheses next to each plot are ESR values.

As shown in Figure 2, the conductive polymer dispersions of Examples 1 to 16 were prepared so that the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) fell within the range Er enclosed by the relational expressions (1) to (4). On the other hand, the conductive polymer dispersions of Comparative Examples 1 to 10 were prepared so that the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) fell below the line segment of the relational expression (3) and fell outside the range Er. Examples 2, 3, 6, 8, 11, 13, and 16 were adjusted so that they fell on the line segment of the relational expressions (2a) and (4a) or were located in the vicinity of said line segment.

As a result, as shown in Tables 1, 2, and Figure 2, it was confirmed that the solid electrolytic capacitors produced using the conductive polymer dispersions of Examples 1 to 16 had an overall lower initial ESR than the solid electrolytic capacitors produced using the conductive polymer dispersions of Comparative Examples 1 to 10. In other words, it was confirmed that a conductive polymer dispersion in which the amount x (wt%) of conductive polymer and the amount y (Vol%) of additive are within the range Er surrounded by the relational expressions (1) to (4) reduces the initial ESR of a solid electrolytic capacitor.

In addition, for the conductive polymer dispersions of Comparative Examples 1 to 7, the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) were small, so similar to Comparative Example 11, gelation did not occur even when the initial conductive polymer dispersion was not concentrated, i.e., the concentration process and pH adjustment process were omitted, and the additive addition process was performed and the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) were adjusted.

In the conductive polymer dispersions of Comparative Examples 8 to 10, the line segment indicated by relational formula (1) was exceeded, and aggregation occurred in the conductive polymer dispersions, causing a significant deterioration in the initial ESR of the solid electrolytic capacitor. It was confirmed that the conductive polymer dispersions of Comparative Examples 8 to 10 gelled within a few minutes when left to stand.

On the other hand, when the amount of conductive polymer x (wt%) and the amount of additive y (Vol%) are within the range Er, as in the conductive polymer dispersions of Examples 1 to 16, it is necessary to concentrate the initial conductive polymer dispersion. Therefore, unless the pH adjustment process is carried out before the concentration process, the conductive polymer dispersion will gel, and it is not possible to reduce the ESR of the solid electrolytic capacitor. A solid electrolytic capacitor was produced using the gelled conductive polymer dispersion of Comparative Example 7, and the initial ESR was measured, and the ESR was found to be 1.5 Ω.

(Examples 17 to 24)
In addition, solid electrolytic capacitors were produced using the conductive polymer dispersions of Examples 17 to 24. The conductive polymer dispersions of Examples 17 to 24 differ from Examples 8, 9, 13, and 16 in the weight ratio of PSS to PEDOT in the conductive polymer dispersion. The weight ratio of PSS to PEDOT in Examples 8, 9, 13, and 16 was PEDOT:PSS=1:2.5, whereas the weight ratio of PSS to PEDOT in Examples 17 to 20 was PEDOT:PSS=1:2.7. In addition, the weight ratio of PSS to PEDOT in Examples 21 to 24 was PEDOT:PSS=1:3.

Other than the difference in the weight ratio of PSS to PEDOT, the conductive polymer dispersions of Examples 17 and 21 have the same composition as Example 8 and are produced by the same manufacturing method and under the same manufacturing conditions, the conductive polymer dispersions of Examples 18 and 22 have the same composition as Example 9 and are produced by the same manufacturing method and under the same manufacturing conditions, the conductive polymer dispersions of Examples 19 and 23 have the same composition as Example 13 and are produced by the same manufacturing method and under the same manufacturing conditions, and the conductive polymer dispersions of Examples 20 and 24 have the same composition as Example 16 and are produced by the same manufacturing method and under the same manufacturing conditions.

Then, using the conductive polymer dispersions of Examples 17 to 24, solid electrolytic capacitors having the same configuration as Examples 8, 9, 13, and 16 were produced using the same manufacturing method and under the same manufacturing conditions as Examples 8, 9, 13, and 16. The initial ESR of the solid electrolytic capacitors using the conductive polymer dispersions of Examples 17 to 24 was also measured under the same conditions as Examples 8, 9, 13, and 16. The ESR measurement results for Examples 17 to 24, as well as Examples 8, 9, 13, and 16, are shown in Table 3 below.

(Table 3)

The results of Experiments 8, 9, 13, 16, and 17-24 confirmed that the initial ESR could be reduced even by changing the weight ratio of PSS to PEDOT. In particular, there was a tendency for the ESR reduction effect to be greater by making the PEDOT:PSS ratio less than 1:3.

Claims (10)

As a conductive polymer, polyethylenedioxythiophene doped with polystyrenesulfonic acid;
A dispersion medium;
Additives and
Including,
The amount x (wt%) of the conductive polymer and the amount y (Vol%) of the additive fall within the range surrounded by the following relational expressions (1) to (4):
A conductive polymer dispersion comprising:
y=-29x+100...(1)
y=-34x+83...(2)
x=1...(3)
y=5...(4) The additive is a polyhydric alcohol;
The conductive polymer dispersion according to claim 1 , The pH is 3 or more and 6 or less.
3. The conductive polymer dispersion according to claim 1 or 2, a mass ratio of the polystyrene sulfonic acid (PSS) to the polyethylene dioxythiophene (PEDOT) is less than PEDOT:PSS=1:3;
3. The conductive polymer dispersion according to claim 1 or 2, The method includes an additive addition step of adding an additive, or an additive and an additional dispersion medium, to a conductive polymer dispersion liquid in which a conductive polymer is dispersed in a dispersion medium,
the conductive polymer is polyethylenedioxythiophene doped with polystyrenesulfonic acid;
In the additive addition step, the amount x (wt %) of the conductive polymer and the amount y (Vol %) of the additive are within the range surrounded by the following relational expressions (1) to (4):
A method for producing a conductive polymer dispersion, comprising:
y=-29x+100...(1)
y=-34x+83...(2)
x=1...(3)
y=5...(4) a mass ratio of the polystyrene sulfonic acid (PSS) to the polyethylene dioxythiophene (PEDOT) is less than PEDOT:PSS=1:3;
6. The method for producing the conductive polymer dispersion according to claim 5, a pH adjustment step of adjusting the pH of the conductive polymer dispersion to 3 or more and 6 or less;
a concentrating step of concentrating the conductive polymer dispersion after the pH adjusting step;
Including,
After the concentrating step, in the additive adding step, the amount x (wt%) of the conductive polymer and the amount y (Vol%) of the additive are adjusted to be within the range surrounded by the relational expressions (1) to (4);
6. The method for producing the conductive polymer dispersion according to claim 5, The concentration step is a second concentration step,
a first concentration step of concentrating the conductive polymer dispersion to a concentration of the conductive polymer of less than 2.6 wt % prior to the pH adjustment step,
the pH adjustment step is carried out after the first concentration step;
In the second concentrating step, the conductive polymer dispersion is further concentrated so that the concentration of the conductive polymer is in the range of 3.5 wt % or less.
The method for producing the conductive polymer dispersion according to claim 7, characterized by: The additive is a polyhydric alcohol;
9. The method for producing the conductive polymer dispersion according to claim 5, wherein forming a solid electrolyte layer between an anode body and a cathode body by using the conductive polymer dispersion liquid according to any one of claims 5 to 8;
A method for producing a solid electrolytic capacitor comprising the steps of:

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