Solid electrolytic capacitor element and solid electrolytic capacitor

Abstract

The present invention is provided with: an anode body; a dielectric layer formed on a surface of the anode body; and a cathode part covering at least a portion of the dielectric layer. The cathode part is provided with a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer contains: a first polymer component including a monomer unit that corresponds to a thiophene compound; and a second polymer component including a polymer anion. The initial ESR of the solid electrolytic capacitor can be kept low by using a solid electrolytic capacitor element in which a peak specific to the first polymer component is observed in a Raman spectrum in an outer layer of the solid electrolyte layer.

Description

[Technical Field]

[0001] The present disclosure relates to a solid electrolytic capacitor element and a solid electrolytic capacitor. [Background technology]

[0002] The solid electrolytic capacitor includes a solid electrolytic capacitor element, a resin outer casing or case that seals the solid electrolytic capacitor element, and external electrodes electrically connected to the solid electrolytic capacitor element. The solid electrolytic capacitor element includes an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion that covers at least a portion of the dielectric layer. The cathode portion includes a solid electrolyte layer that covers at least a portion of the dielectric layer and contains a conductive polymer and a dopant.

[0003] solid electrolyte quality From the viewpoint of easy layer formation, a method using a liquid dispersion containing a conductive polymer component is often used to form a solid electrolyte layer (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-58807 [Patent Document 2] International Publication No. 2014 / 155422 Summary of the Invention [Means for solving the problem]

[0005] A solid electrolytic capacitor element according to one aspect of the present disclosure includes an anode body, a dielectric layer formed on a surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer, the cathode portion including a solid electrolyte layer covering at least a portion of the dielectric layer, the solid electrolyte layer including a first polymer component including a monomer unit corresponding to a thiophene compound and a second polymer component including a polymer anion, and a peak specific to the first polymer component is observed in a Raman spectrum of a surface layer of the solid electrolyte layer.

[0006] A solid electrolytic capacitor according to another aspect of the present disclosure includes at least one of the above solid electrolytic capacitor elements.

[0007] According to the present disclosure, the initial increase in ESR of a solid electrolytic capacitor can be kept low. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic front view of the solid electrolytic capacitor element as viewed from one main surface side. [Figure 3] FIG. 3 is a schematic cross-sectional view of the solid electrolytic capacitor element taken along line III-III in FIG. 2, viewed in the direction of the arrows. [Figure 4] FIG. 4 shows the Raman spectrum of the solid electrolyte layer of the solid electrolytic capacitor A1. [Figure 5] FIG. 5 shows the Raman spectrum of the solid electrolyte layer of solid electrolytic capacitor B1. DETAILED DESCRIPTION OF THE INVENTION

[0009] Before describing the embodiments, the problems in the prior art will be briefly described below. The method of forming a solid electrolyte layer using a dispersion is simple and has become the mainstream method of forming a solid electrolyte layer in recent years. Meanwhile, in a solid electrolytic capacitor element, a porous portion is formed in at least the surface layer of the anode body. The dielectric layer is formed along the inner wall surfaces of the holes and depressions (sometimes called pits) on the surface of the anode body, including the inner wall surfaces of the holes in the porous portion. Therefore, the surface of the dielectric layer has fine irregularities corresponding to the surface shape of the anode body. The dispersion contains a conductive polymer component (e.g., a conjugated polymer such as a polythiophene-based polymer and a dopant) with a relatively high molecular weight. Therefore, when a dispersion is used, it is difficult to densely fill the fine depressions on the surface of the dielectric layer with the conductive polymer component. If the fine depressions in the dielectric layer cannot be densely filled with the conductive polymer component, the conductivity of the solid electrolyte layer will be low. Furthermore, because the orientation of the conjugated polymer is random in the dispersion, it is difficult to enhance the orientation of the conjugated polymer in the formed solid electrolyte layer. This also tends to result in low conductivity of the solid electrolyte layer. A decrease in the conductivity of the solid electrolyte layer leads to a decrease in the performance of the solid electrolytic capacitor, such as an increase in ESR, a decrease in capacitance, or an increase in tan δ of the solid electrolytic capacitor.

[0010] Polymer anions are preferred as dopants because they can easily ensure high stability and high heat resistance. Polymer anions have a high affinity for conjugated polymers and can easily ensure high conductivity of the solid electrolyte layer. Polymer anions are typically added to dispersions and used to form solid electrolyte layers. However, it has been found that when dispersions containing polymer anions are used, the polymer anions segregate at and near the surface of the solid electrolyte layer. Because the polymer anions themselves are insulating, their segregation increases the resistance of the solid electrolyte layer. Typically, a cathode extraction layer is formed on the surface of the solid electrolyte layer to cover this surface. However, the presence of segregated polymer anions in the surface layer reduces the physical and electrical connectivity between the solid electrolyte layer and the cathode extraction layer. This results in increased contact resistance between the solid electrolyte layer and the cathode extraction layer, leading to reduced initial capacitor performance, such as an increased initial ESR.

[0011] Another method, which predates dispersion technology, is to form a solid electrolyte layer using in-situ polymerization, such as chemical polymerization. In-situ polymerization allows for dense filling of conductive polymer components into the recesses of the dielectric layer. However, in-situ polymerization makes it difficult to control the polymerization reaction, resulting in large variations in the thickness of the solid electrolyte layer formed. This makes it difficult to ensure high conductivity of the solid electrolyte layer. Furthermore, because it is difficult to control the polymerization reaction in in-situ polymerization, the types of raw monomers and dopants that can be used for conjugated polymers are limited. In fact, in-situ polymerization employs pyrrole compounds, and only low-molecular-weight dopants are used.

[0012] In some cases, a first solid electrolyte layer is formed on the surface of a dielectric layer by chemical polymerization, followed by the formation of an outer second solid electrolyte layer using a dispersion. However, in the outer second solid electrolyte layer formed using a dispersion, polymer anions segregate on the surface and the orientation of the conjugated polymer is low, resulting in low conductivity. In addition, the types of raw material monomers and dopants used for the inner first solid electrolyte layer are limited.

[0013] When air penetrates into a solid electrolytic capacitor, the moisture or oxygen in the air can cause oxidative degradation of the conjugated polymer or dedoping of the dopants contained in the solid electrolyte layer due to decomposition, resulting in degradation of the solid electrolyte layer and a decrease in the conductivity of the solid electrolyte layer. For example, when a solid electrolyte layer is formed using a dispersion, as described above, segregation of polymer anions weakens the physical bond between the solid electrolyte layer and the cathode extraction layer, making it easier for air to penetrate. Furthermore, when a dispersion is used, it is difficult to densely fill the minute recesses on the surface of the dielectric layer with a conductive polymer component, which tends to form air channels in the recesses. This can lead to deterioration of the solid electrolyte layer. Depending on the application, solid electrolytic capacitors may be used in high-temperature environments. Furthermore, solid electrolytic capacitors are generally soldered to a substrate through a reflow process that exposes them to high temperatures. When solid electrolytic capacitors are exposed to high temperatures or used for long periods of time, the above-mentioned degradation of the solid electrolyte layer becomes more pronounced, resulting in a significant decrease in conductivity and a significant decrease in capacitor performance. For example, when a low-molecular-weight dopant is used, such as a chemically polymerized dopant, the low stability of the dopant makes it prone to dedoping, which results in a significant increase in ESR when the solid electrolytic capacitor is exposed to high temperatures or used for a long period of time.

[0014] In view of the above-mentioned problems, in a solid electrolytic capacitor element and a solid electrolytic capacitor according to one aspect of the present disclosure, the solid electrolyte layer includes a first polymer component containing a monomer unit corresponding to a thiophene compound and a second polymer component containing a polymer anion. A peak specific to the first polymer component is observed in the Raman spectrum of the surface layer of the solid electrolyte layer. In the solid electrolytic capacitor element, segregation of the polymer anion in the solid electrolyte layer is suppressed, resulting in a more uniform dispersion of the polymer anion in the solid electrolyte layer. Such a solid electrolyte layer can be formed by electrolytic polymerization of a precursor of the first polymer component in the presence of the second polymer component.

[0015] In the solid electrolytic capacitor element of the present disclosure, the first polymer component and polymer anions can be dispersed with high dispersibility in the solid electrolyte layer. This not only increases the electronic conductivity of the conductive polymer component but also suppresses an increase in the resistance of the solid electrolyte layer due to segregation of the polymer anions. Furthermore, the conductive polymer component can be densely filled into the fine recesses on the surface of the dielectric layer, and the orientation of the conjugated polymer in the solid electrolyte layer is also high. This suppresses an increase in the overall resistance of the solid electrolyte layer and ensures high conductivity of the solid electrolyte layer. Furthermore, suppressing segregation of the polymer anions improves the physical and electrical bonding between the solid electrolyte layer and the cathode extraction layer. This reduces the initial ESR of the solid electrolytic capacitor. Furthermore, high initial capacitance and low initial tan δ can be ensured, ensuring excellent initial capacitor performance.

[0016] Furthermore, in the solid electrolytic capacitor element and solid electrolytic capacitor of the present disclosure, despite the presence of a polymer anion, a rigid solid electrolyte layer with excellent film quality is formed due to the high orientation of the conjugated polymer. Therefore, even when the solid electrolytic capacitor is exposed to high temperatures or used for a long period of time, cracking in the solid electrolyte layer can be suppressed. In addition to suppressing cracking, the recesses on the surface of the dielectric layer are densely filled with the conductive polymer component, and the solid electrolyte layer and the cathode extraction layer have high adhesion, reducing air penetration into the solid electrolyte layer even when the solid electrolytic capacitor is exposed to high temperatures or used for a long period of time. Furthermore, the high stability and heat resistance of the polymer anion also reduce dedoping. As a result, even when the solid electrolytic capacitor is exposed to high temperatures or used for a long period of time, deterioration of the solid electrolyte layer and degradation of capacitor performance, such as an increase in ESR, can be suppressed. Therefore, a solid electrolytic capacitor element and solid electrolytic capacitor with excellent stability (including thermal stability) can be obtained. The increased stability can improve the reliability of the solid electrolytic capacitor element and solid electrolytic capacitor.

[0017] In the solid electrolytic capacitor element and solid electrolytic capacitor of the present disclosure, the recesses on the surface of the dielectric layer can be densely filled with a conductive polymer component, while the variation in thickness of the solid electrolyte layer can be reduced, thereby ensuring high conductivity of the solid electrolyte layer and suppressing the occurrence of short circuits or increases in leakage current, thereby ensuring stable capacitor performance.

[0018] When polymer anions segregate in the solid electrolyte layer, the fluorescence response of the segregated polymer anions prevents the observation of the spectral waveform of the first polymer component in the Raman spectrum of the surface layer of the solid electrolyte layer formed using the dispersion.

[0019] In this specification, the Raman spectrum of the surface layer of the solid electrolyte layer is measured under the following conditions: The surface layer of the solid electrolyte layer refers to the portion from the surface of the solid electrolyte layer to a depth of 100 nm.

[0020] Raman spectrometer: NanoPhoton RamanFORCE PAV Irradiation laser light wavelength: 532nm Laser power density: 870W / cm 2 Diffraction grating: 300 / cm Exposure time: 10 seconds Measurement wave number range: 0cm -1 More than 4700cm -1 below Temperature: 25℃

[0021] A sample obtained by the following procedure can be used to measure the Raman spectrum. First, the solid electrolytic capacitor is embedded in a curable resin, and the curable resin is cured. The cured product is polished or processed with a cross-section polisher to expose a cross section parallel to the thickness direction of the solid electrolyte layer (e.g., cross section G, described below). In this way, a sample for measurement (sample A) is obtained. The Raman spectrum can be measured for the surface layer of the cross section of the exposed solid electrolyte layer of sample A.

[0022] Hereinafter, the solid electrolytic capacitor and solid electrolytic capacitor element (hereinafter sometimes simply referred to as capacitor element) of the present disclosure will be described in more detail with reference to the drawings as necessary.

[0023] [Solid electrolytic capacitor] A solid electrolytic capacitor includes one or more capacitor elements. At least one of the capacitor elements included in the solid electrolytic capacitor has a solid electrolyte layer that includes a first polymer component and a second polymer component, and in which a peak specific to the first polymer component is observed in the Raman spectrum of the surface layer. Preferably, 50% or more (more preferably 75% or more) of the capacitor elements included in the solid electrolytic capacitor have the above-mentioned solid electrolyte layer, and more preferably, all of the capacitor elements have the above-mentioned solid electrolyte layer.

[0024] (Capacitor element) (anode body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials can be used alone or in combination. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode bodies having a porous surface can be obtained by roughening the surface of a substrate containing a valve metal (such as a sheet-like (e.g., foil-like, plate-like) substrate) by etching or the like. Surface roughening can be achieved by etching or the like. The anode body can also be a compact or sintered body of particles containing a valve metal. The compact and sintered body each have a porous structure. The compact and sintered body each can be in the form of a sheet, a rectangular parallelepiped, a cube, or similar shapes.

[0025] The anode body typically has an anode lead-out portion including a first end and a cathode formation portion including a second end. The cathode portion is typically formed on the cathode formation portion of the anode body via a dielectric layer. An anode terminal is connected to the anode lead-out portion.

[0026] (dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric and is formed so as to cover at least a portion of the surface of the anode body. The dielectric layer is formed by anodizing the valve metal on the surface of the anode body using a chemical conversion treatment or the like. The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Because the dielectric layer is formed on the porous surface of the anode body, the surface of the dielectric layer has a fine uneven shape as described above.

[0027] The dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these and may be any material that functions as a dielectric.

[0028] (cathode) The cathode section includes a solid electrolyte layer that covers at least a portion of the dielectric layer. The cathode section may further include a cathode extraction layer that covers at least a portion of the solid electrolyte layer. The cathode section is usually formed on at least a portion of the surface of the anode body via a dielectric layer. The solid electrolyte layer and the cathode extraction layer are described below.

[0029] (solid electrolyte layer) The solid electrolyte layer is formed on the surface of the anode body via the dielectric layer so as to cover the dielectric layer. The solid electrolyte layer does not necessarily have to cover the entire dielectric layer (the entire surface), but only needs to cover at least a portion of the dielectric layer. The solid electrolyte layer constitutes at least a portion of the cathode part of the solid electrolytic capacitor.

[0030] The solid electrolyte layer includes a first polymer component containing a monomer unit corresponding to a thiophene compound and a second polymer component containing a polymer anion. The monomer unit corresponding to the thiophene compound may be referred to as the "first monomer unit" below. The first polymer component is a π-conjugated polymer, and functions as a conductive polymer when the second polymer component acts as a dopant.

[0031] (First polymer component) Thiophene compounds corresponding to the first monomer unit include compounds having a thiophene ring and capable of forming a repeating structure of the first monomer unit. Thiophene compounds can be linked at the 2- and 5-positions of the thiophene ring to form a repeating structure of the first monomer unit, thereby making it possible to form a polymer in which the π-electron cloud is spread throughout the molecule. Thiophene compounds also include those having a substituent. The substituent may be, for example, at least one of the 3- and 4-positions of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring fused to the thiophene ring. Examples of thiophene compounds include thiophenes having a substituent at at least one of the 3- and 4-positions, alkylenedioxythiophene compounds (C such as ethylenedioxythiophene compounds), etc. 2-4The alkylenedioxythiophene compounds include those having a substituent in the alkylene group. The substituent in the thiophene compound is an alkyl group (C 10 group such as a methyl group or an ethyl group). 1-4 alkyl groups, alkoxy groups (methoxy groups, ethoxy groups, etc.) 1-4 Alkoxy groups, hydroxy groups, hydroxyalkyl groups (hydroxy C groups such as hydroxymethyl groups) 1-4 Preferred examples of the thiophene compound include, but are not limited to, alkyl groups. When the thiophene compound has two or more substituents, the substituents may be the same or different.

[0032] Among these, it is preferable to use a first polymer component containing at least a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound, since this not only makes it easier to obtain high heat resistance but also makes it easier to ensure higher conductivity of the solid electrolyte layer.

[0033] Thiophene compounds generally have a higher polymerization potential than pyrrole compounds and are therefore less likely to polymerize. The use of at least a thiophene compound in which an electron-donating group, such as an alkylenedioxythiophene or an alkoxy group, is substituted on the thiophene ring reduces the polymerization potential, allowing the polymerization reaction of the thiophene compound to proceed rapidly even in the presence of a polymer anion. Therefore, despite the use of a polymer anion, a conductive polymer component comprising a first polymer component and a second polymer component containing a polymer anion can be densely filled into minute recesses on the surface of a dielectric layer with each polymer component more uniformly dispersed.

[0034] The first polymer component may contain one type of first monomer unit or two or more types of first monomer units, and the solid electrolyte layer may contain one type of first polymer component or two or more types of first polymer components.

[0035] The first polymer component may contain a second monomer unit other than the first monomer unit, if necessary. From the viewpoint of easily ensuring a higher capacitance, the molar ratio of the first monomer unit in the first polymer component is preferably 90 mol % or more. The molar ratio of the first monomer unit in the first polymer component is 100 mol % or less. The first polymer component may be composed only of a repeating structure of the first monomer unit.

[0036] The weight average molecular weight (Mw) of the first polymer component is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0037] (Second polymer component) The polymer anion contained in the second polymer component may be, for example, a polymer having a plurality of anionic groups, such as a polymer containing a monomer unit having an anionic group.

[0038] Examples of the anionic group include a sulfonic acid group and a carboxy group. In the solid electrolyte layer, the anionic group may be contained in a free form, an anionic form, or a salt form, or may be contained in a form bonded to or interacting with the first polymer component. In this specification, all of these forms may be simply referred to as an "anionic group," "sulfonic acid group," or "carboxy group."

[0039] The second polymer component may contain one type of polymer anion or two or more types of polymer anions, but the second polymer component is assumed to contain only polymer anions.

[0040] Examples of polymer anions having a carboxy group include, but are not limited to, polyacrylic acid, polymethacrylic acid, and copolymers using at least one of acrylic acid and methacrylic acid.

[0041] From the viewpoints of ensuring higher conductivity of the solid electrolyte layer and easily suppressing dedoping from the solid electrolyte layer, the second polymer component preferably contains a polymer anion having at least a sulfonic acid group.

[0042] The polymer anion having a sulfonic acid group includes an anion containing a monomer unit M1 corresponding to an organic sulfonic acid compound. The organic sulfonic acid compound may be aliphatic, alicyclic, aromatic, or heterocyclic. The polymer anion may be a homopolymer containing only the monomer unit M1, or a copolymer containing the monomer unit M1 and other monomer units.

[0043] Specific examples of polymer anions having sulfonic acid groups include, but are not limited to, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid, and phenolsulfonic acid novolac resin.

[0044] In particular, when the polymer anion has an aromatic ring, high heat resistance is achieved, suppressing dedoping even when the solid electrolytic capacitor is exposed to high temperatures, thereby maintaining high conductivity of the solid electrolyte layer. However, when the polymer anion aggregates, it tends to emit strong fluorescence. Therefore, if the polymer anion segregates at the surface of the solid electrolyte layer, the peaks of the first polymer component and the second polymer component cannot be observed in the Raman spectrum of the surface of the solid electrolyte layer. In the capacitor element disclosed herein, even when a polymer anion having an aromatic ring is used, segregation of the polymer anion at the surface of the solid electrolyte layer is suppressed, ensuring a more uniform dispersion of the first polymer component and the second polymer component in the solid electrolyte layer. This excellent dispersion can be confirmed by Raman spectroscopy.

[0045] Examples of polymer anions having an aromatic ring include polymer anions containing a monomer unit M1 corresponding to an organic sulfonic acid compound, which also contains an aromatic ring. Such polymer anions are preferably those containing at least a monomer unit (sometimes referred to as a monomer unit M2) corresponding to the aromatic sulfonic acid compound as the monomer unit M1. Examples of such polymer anions include, but are not limited to, polystyrene sulfonic acid (including copolymers and substituted derivatives thereof), aromatic polyester sulfonic acid, and phenol sulfonic acid novolac resin, among the above-mentioned polymer anions.

[0046] The weight-average molecular weight (Mw) of the polymer anion is, for example, 300 or more, preferably 500 or more, and more preferably 1000 or more. When a dispersion containing a polymer anion with a large Mw is used, segregation of the polymer anion tends to become significant in the surface layer of the solid electrolyte layer. In the present disclosure, even when the Mw of the polymer anion is relatively large (e.g., 500 or more or 1000 or more), the first polymer component and the second polymer component can be more uniformly dispersed in the solid electrolyte layer. This can further reduce the increase in ESR and improve other capacitor performance. The Mw of the polymer anion is, for example, 250,000 or less, preferably 200,000 or less, and may be 160,000 or less. When the Mw is within this range, polymerization of the raw material monomer of the first polymer component tends to proceed smoothly, further improving the dispersibility of the first polymer component and the second polymer component in the solid electrolyte layer. These lower and upper limits can be combined arbitrarily.

[0047] The weight-average molecular weight (Mw) of the polymer anion is a value calculated as polystyrene by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0048] The Mw of the polymer anion can be determined for a sample taken from a solid electrolytic capacitor element. More specifically, GPC measurement can be performed using a sample taken using the following procedure. First, a cured product obtained using the same procedure as for the sample used for Raman spectroscopy is polished or cross-section polished to expose the solid electrolyte layer. The solid electrolyte layer is then scraped off, and the polymer anion is extracted with hot water at 80°C to 100°C. The extract is concentrated to obtain a sample for measurement (Sample B).

[0049] The amount of the second polymer component contained in the solid electrolyte layer is, for example, 10 to 1000 parts by mass, and may be 50 to 200 parts by mass, relative to 100 parts by mass of the first polymer component.

[0050] (Raman spectrum) In the capacitor element and solid electrolytic capacitor of the present disclosure, segregation of polymer anions in the surface layer of the solid electrolyte layer is suppressed. Therefore, when Raman spectroscopy of the surface layer of the solid electrolyte layer is performed, a peak specific to the first polymer component is observed without being disturbed by the fluorescence emission of the segregated polymer anions. This indicates that the first polymer component and the second polymer component are highly dispersed in the solid electrolyte.

[0051] When segregation of the polymer anion occurs, the waveform of the Raman spectrum of the first polymer component cannot be confirmed due to fluorescence emission. Therefore, the wave number of the peak specific to the first polymer component is not particularly limited as long as it is a peak derived from the first polymer component in the Raman spectrum. In the Raman spectrum of the first polymer component, the highest peak usually occurs at 1200 cm. -1 More than 1600cm -1 or less (preferably 1550cm -1 Therefore, it is preferable that the peak specific to the first polymer component includes a peak observed in such a wavenumber range (sometimes referred to as the first peak). The wavenumber range in which the first peak is observed is 1300 cm-1 More than 1600cm -1 or less (preferably 1550cm -1 less than 1300cm -1 More than 1500cm -1 It may be the following:

[0052] The Raman spectrum of the first polymer component shows a peak at 2750 cm -1 More than 3000cm -1 A peak (sometimes referred to as the second peak) may also be observed in the following wavenumber range. The second peak is smaller in height than the first peak, but it can be clearly observed because it is not obstructed by the fluorescence emission of the segregated polymer anion. Therefore, the second peak can also be said to be one of the peaks specific to the first polymer component. The wavenumber range in which the second peak is observed is 2800 cm -1 More than 3000cm -1 or less than 2800cm -1 More than 2900cm -1 It may be the following:

[0053] For example, when poly(3,4-ethylenedioxythiophene) (PEDOT) is used as the first polymer component, the first peak appears at 1350 cm -1 More than 1500cm -1 A second peak is observed in the range below 2800 cm -1 More than 2900cm -1 The following ranges are observed:

[0054] In the Raman spectrum of the surface layer of the solid electrolyte layer, peaks specific to polymer anions can be observed. For example, when the solid electrolyte layer is made of monomer units corresponding to aromatic sulfonic acid compounds, M When the polymer anion containing 2 is included, the Raman spectrum shows a peak at 800 cm -1 More than 1050cm -1 A peak due to the polymer anion (sometimes referred to as the third peak) can be observed in the following range.

[0055] Intensity of the first peak I p1Intensity of the third peak I p3 Ratio to (=I p1 / I p3 ) is, for example, 2 or more, or may be 3 or more, 4 or more, or 5 or more, or 6 or more. p1 / I p3 When the ratio is in this range, the first polymer component and the second polymer component are dispersed more uniformly in the solid electrolyte, ensuring higher electrical conductivity. p1 / I p3 The upper limit of the ratio is not particularly limited, but is, for example, 50 or less.

[0056] The solid electrolyte layer is a monomer unit corresponding to an aromatic sulfonic acid compound. M When the polymer anion containing 2 is included, the Raman spectrum of the solid electrolyte layer shows a peak at 1050 cm -1 Over 1200cm -1 Range less than 1550cm -1 Over 1750cm -1 Peaks due to polymer anions (sometimes referred to as the fourth peak and the fifth peak, respectively) can be observed in the following ranges.

[0057] (Thickness of solid electrolyte layer) The average thickness of the solid electrolyte layer is, for example, 5 μm or more and 20 μm or less, and may be 10 μm or more and 15 μm or less.

[0058] The average thickness of the solid electrolyte layer is determined by measuring the thickness at any number of points (for example, 10 points) on a cross section perpendicular to the longitudinal direction of the capacitor element and passing through the center of the cathode part in a direction parallel to the longitudinal direction of the capacitor element, and averaging the measured values.

[0059] In the solid electrolytic capacitor of the present disclosure, it is possible to reduce the variation in thickness of the solid electrolyte layer, thereby ensuring high conductivity of the solid electrolyte layer and reducing the occurrence of leakage current and short circuits, thereby ensuring stable capacitor performance.

[0060] The ratio T1 / T2 of the thickness T1 of the solid electrolyte layer formed at the corners of the anode body to the thickness T2 of the solid electrolyte layer formed at the center of the main surface of the anode body is, for example, 0.8 to 1.7, or alternatively, 0.8 to 1.5, or 0.9 to 1.4. When the ratio T1 / T2 is within this range, the thickness of the solid electrolyte layer at the corners is prevented from becoming thinner, thereby preventing product defects due to short circuits. Furthermore, a decrease in capacitance, an increase in ESR, or an increase in dielectric loss tangent tanδ is prevented, further stabilizing the quality of the solid electrolytic capacitor.

[0061] When forming a solid electrolyte layer using a dispersion, the dispersion is easily repelled at the corners of the anode body, making it difficult to increase the thickness of the solid electrolyte layer at the corners. Therefore, a solid electrolyte layer formed using a dispersion containing a first polymer component and a second polymer component typically does not achieve the above-mentioned T1 / T2 ratio. Furthermore, when forming a solid electrolyte layer by chemical polymerization, aggregates of the first polymer component generated in the treatment solution randomly adhere to the surface of the anode body, resulting in increased thickness variation of the solid electrolyte layer. In contrast, when forming a solid electrolyte layer by electropolymerization, the first polymer component is formed over the entire surface of the anode body by the electrolytic reaction, thereby reducing thickness variation of the solid electrolyte layer. This is because current tends to concentrate at corners during the electrolytic reaction. In particular, controlling the polymerization voltage during electropolymerization during solid electrolyte layer formation within the range described below makes it easier to control the T1 / T2 ratio within the above-mentioned range.

[0062] The thicknesses T1 and T2 are determined in a cross section perpendicular to the direction from the first end to the second end of the capacitor element at an arbitrary position on the first end side of the cathode section. This cross section may be simply referred to as cross section G. More specifically, thickness T1 is determined by measuring and averaging the thicknesses of the solid electrolyte layer formed at the four corners of the anode body in cross section G. First, a line is drawn through the corners of the anode body at a 45° angle relative to a line extending outward from a line segment corresponding to the main surface of the anode body. The distance between the point where this line intersects the outer edge of the solid electrolyte layer and the point where this line intersects the corresponding corner is defined as the thickness of the solid electrolyte layer formed at each corner. Thickness T2 is determined by measuring and averaging the thicknesses of the solid electrolyte layer formed at the center of each of the pair of main surfaces of the anode body in cross section G. First, a center line is drawn through the midpoints of the line segments corresponding to the main surfaces of the anode body in cross section G. The distance between the intersection of this center line and the outer edge of the solid electrolyte layer and the corresponding midpoint is defined as the thickness of the solid electrolyte layer formed at the center of each main surface.

[0063] If the anode body is in a sheet shape, thickness T2 can be determined by finding the average value for a pair of main surfaces (the main surfaces) that occupy most of the surface of the anode body, as described above. If the anode body is in a rectangular parallelepiped, cubic, or similar shape, thickness T2 can be determined by averaging the thicknesses at the center of each surface.

[0064] The direction from the first end toward the second end is a direction parallel to the line connecting the center of the end face of the first end and the center of the end face of the second end. This direction may be referred to as the longitudinal direction of the anode body or capacitor element. Cross section G is a cross section perpendicular to the longitudinal direction of the capacitor element at any position between the halfway point of the cathode portion in the direction parallel to the longitudinal direction of the capacitor element and the end of the cathode portion on the first end side in the portion where the cathode portion of the capacitor element is formed. The cross section of the capacitor element can be observed, for example, using an optical microscope.

[0065] (others) The solid electrolyte layer may be a single layer or may be composed of multiple layers. For example, the solid electrolyte layer may be composed of a first solid electrolyte layer covering at least a portion of the dielectric layer and a second solid electrolyte layer covering at least a portion of the first solid electrolyte layer. When the solid electrolyte layer is composed of multiple layers, it is preferable that all layers contain a first polymer component and a second polymer component. However, the type, composition, and content of the first polymer component and the second polymer component contained in each layer may be different or the same for each layer. When at least the layer covering the dielectric layer (i.e., the inner layer), such as the first solid electrolyte layer, contains the first polymer component and the second polymer component, the conductive polymer component can be highly filled into the minute recesses on the surface of the dielectric layer despite the inclusion of the second polymer component. When the outer layer, such as the second solid electrolyte layer, contains the first polymer component and the second polymer component, the Raman spectrum as described above can be obtained, thereby suppressing segregation of the first polymer component in the surface layer and improving the effect of reducing the thickness variation of the solid electrolyte layer. Therefore, stable capacitor performance can be obtained, and the occurrence of leakage current and short circuits can be reduced.

[0066] In addition to the first polymer component and the second polymer component, the solid electrolyte layer may contain at least one selected from the group consisting of other dopants, additives (such as known additives), and known conductive materials other than the first polymer component.

[0067] Examples of other dopants include anions other than polymer anions. Examples of anions include, but are not limited to, sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include paratoluenesulfonic acid and naphthalenesulfonic acid.

[0068] The conductive material may be at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0069] A layer for enhancing adhesion may be interposed between the dielectric layer and the solid electrolyte layer.

[0070] (Method for forming a solid electrolyte layer) The solid electrolyte layer can be formed on the surface of the dielectric layer by electropolymerizing a precursor of a first polymer component in the presence of a second polymer component. For example, electropolymerization is performed while immersing the cathode-forming portion of an anode body with a dielectric layer formed on its surface in a liquid mixture containing a precursor of the first polymer component and a second polymer component. Unlike the case of using a dispersion, this type of electropolymerization allows the conductive polymer component to be densely filled into the fine recesses on the surface of the dielectric layer. Furthermore, the orientation of the first polymer component can be improved in the solid electrolyte layer. The first polymer component and the second polymer component can be dispersed in the solid electrolyte with high dispersibility. Because the precursor of the first polymer component has a relatively low molecular weight, the liquid component can be easily attached not only to the center of the anode body but also to the corners, allowing polymerization to proceed even in the corners, thereby reducing thickness variation.

[0071] Examples of precursors of the first polymer component include raw material monomers of the first polymer component, oligomers and prepolymers formed by linking multiple molecular chains of the raw material monomers, etc. One type of precursor may be used, or two or more types may be used in combination. From the viewpoints of easily adhering to the corners of the anode body, smoothly progressing polymerization even at the corners, and easily increasing the thickness of the solid electrolyte layer at the corners, it is preferable to use at least one type (particularly a monomer) selected from the group consisting of monomers and oligomers as the precursor.

[0072] The liquid mixture usually contains a solvent, such as water, an organic solvent, or a mixed solvent of water and an organic solvent (such as a water-soluble organic solvent).

[0073] The temperature at which electropolymerization is carried out is, for example, 5°C or higher and 60°C or lower, and may be 15°C or higher and 35°C or lower.

[0074] If other dopants, other conductive materials, additives, etc. are used, they may be added to the liquid mixture.

[0075] The liquid component may contain an oxidizing agent, if necessary. The oxidizing agent may be applied to the anode body before or after contacting the liquid mixture with the anode body on which the dielectric layer has been formed. Examples of such oxidizing agents include sulfates, sulfonic acids, and salts thereof. The oxidizing agents may be used singly or in combination of two or more. Examples of sulfates include salts of metals with sulfuric acid, such as ferric sulfate and sodium persulfate, and salts of sulfates such as persulfates. Examples of metals constituting the salts include alkali metals (sodium, potassium, etc.), iron, copper, chromium, and zinc. Sulfonic acids and salts thereof function not only as oxidizing agents but also as dopants. Examples of sulfonic acids and salts thereof include low-molecular-weight sulfonic acids and salts thereof listed as examples of other dopants.

[0076] In electrolytic polymerization, the voltage (polymerization voltage) applied to the anode body is, for example, 0.8 V or more and 2.0 V or less, and may be 1.0 V or more and 1.5 V or less. By setting the polymerization voltage in this range, polymerization of the precursor of the first polymer component can proceed smoothly even though the polymerization is carried out in the presence of the second polymer component. The polymerization voltage is set at a value measured using a silver reference electrode (silver / silver chloride electrode (Ag / Ag + ) is the polymerization potential relative to

[0077] (Cathode extraction layer) The cathode extraction layer may include at least a first layer that is in contact with the solid electrolyte layer and covers at least a portion of the solid electrolyte layer, and may also include a first layer and a second layer that covers the first layer. Examples of the first layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be formed of a first layer containing conductive carbon (also referred to as a carbon layer) and a second layer containing metal powder or metal foil. When metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil.

[0078] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0079] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such second layers include metal paste layers formed using a composition containing metal powder such as silver particles and a resin (binder resin). While thermoplastic resins can be used as the resin, it is preferable to use thermosetting resins such as imide resins and epoxy resins.

[0080] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0081] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0082] (separator) When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode foil. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0083] (others) The solid electrolytic capacitor may be a wound type, a chip type, or a laminate type. For example, the solid electrolytic capacitor may include a laminate of two or more capacitor elements. The configuration of the capacitor elements may be selected depending on the type of solid electrolytic capacitor.

[0084] In the capacitor element, one end of a cathode terminal is electrically connected to the cathode extraction layer. The cathode terminal is bonded to the cathode extraction layer, for example, by applying a conductive adhesive to the cathode extraction layer and bonding the cathode terminal to the cathode extraction layer via the conductive adhesive. One end of the anode terminal is electrically connected to the anode body. The other end of the anode terminal and the other end of the cathode terminal are each extended from the resin exterior body or the case. The other end of each terminal exposed from the resin exterior body or the case is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted, for example.

[0085] The capacitor element is sealed using a resin outer casing or case. For example, the capacitor element and the resin material of the outer casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin outer casing by transfer molding, compression molding, or the like. At this time, the other end portions of the anode terminal and cathode terminal connected to the anode lead drawn from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be placed in a bottomed case so that the other end portions of the anode terminal and cathode terminal are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor.

[0086] Fig. 1 is a cross-sectional view schematically illustrating the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure. As shown in Fig. 1, solid electrolytic capacitor 1 includes a capacitor element 2, a resin outer casing 3 that seals capacitor element 2, and an anode terminal 4 and a cathode terminal 5, at least a portion of which is exposed to the outside of resin outer casing 3. Anode terminal 4 and cathode terminal 5 may be made of a metal such as copper or a copper alloy. Resin outer casing 3 has a substantially rectangular parallelepiped outer shape, and solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0087] The capacitor element 2 includes an anode body 6, a dielectric layer 7 covering the anode body 6, and a cathode section 8 covering the dielectric layer 7. The cathode section 8 includes a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode extraction layer 10 covering the solid electrolyte layer 9. In the illustrated example, the solid electrolyte layer 9 includes a first polymer component and a second polymer component, and the Raman spectrum of the surface layer shows a peak specific to the first polymer component. This configuration ensures high conductivity of the solid electrolyte layer 9 and high physical and electrical adhesion between the solid electrolyte layer 9 and the carbon layer 11. Therefore, the solid electrolytic capacitor 1 can maintain a low initial ESR. Furthermore, the intrusion of air into the solid electrolyte layer 9 can be suppressed. Therefore, even when the solid electrolytic capacitor 1 is used for a long period of time or exposed to high temperatures, the increase in ESR can be kept low.

[0088] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. Of the region of the anode body 6 not facing the cathode portion 8, an insulating separation layer 13 is formed in a strip-like shape on the surface of the anode body 6 in a portion adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode body 6. Of the region of the anode body 6 not facing the cathode portion 8, another part is electrically connected to the anode terminal 4 by welding. The cathode terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0089] Fig. 2 is a schematic front view of capacitor element 2 as viewed from one main surface side. Fig. 3 is a schematic cross-sectional view of capacitor element 2 taken along line III-III (cross-section G) in Fig. 2 as viewed in the direction of the arrow. Thicknesses T1 and T2 of solid electrolyte layer 9 can be determined, for example, by the following procedure.

[0090] The ratio T1 / T2 is determined in a cross section G of the cathode section 8 perpendicular to the direction from the first end E1 toward the second end E2 of the capacitor element 2 (sometimes referred to as the longitudinal direction of the anode body 6 or the capacitor element 2). Here, the cross section G is formed at an arbitrary position in the portion of the cathode section 8 on the first end E1 side. The portion of the cathode section 8 on the first end E1 side is a portion from the end of the cathode section 8 on the first end E1 side to a position at a distance of length L / 2, where L is the length of the cathode section 8 in the longitudinal direction of the capacitor element 2. In FIG. 2 , the portion of the cathode section 8 on the first end E1 side corresponds to the upper half of the cathode section 8.

[0091] 3 shows a cross section G of the capacitor element 2 taken along line III-III of the portion on the first end E1 side of the cathode portion 8, the cross section G being perpendicular to the longitudinal direction of the capacitor element 2. Line III-III corresponds to an arbitrarily selected position on the portion on the first end E1 side of the cathode portion 8. Note that hatching indicating a cross section is omitted in FIG.

[0092] In the cross section G, a pair of main surfaces Ms of the sheet-like anode body 6 and a pair of end surfaces Es located at the ends of the pair of main surfaces Ms can be seen. Since there are corners between each of the main surfaces Ms and each of the end surfaces Es, four corners can be seen in the cross section G of the anode body 6. Parallel Extend the line outward to draw imaginary straight lines L1 and L2, and then draw a straight line that passes through the corner that forms a 45° angle with line L1 or L2. Distances D11, D12, D13, and D14 between the point where this line intersects with the outer edge of solid electrolyte layer 9 and the point where this line intersects with the corresponding corner are defined as the thickness of solid electrolyte layer 9 at each corner. Then, T1 is calculated by averaging the values ​​of these four distances.

[0093] In the cross section G, when the width of the anode body 6, which corresponds to the length of the line segment corresponding to the main surface Ms, is W, a center line CL is drawn at a position W / 2 from each end face Es. The center line CL passes through the midpoint of the line segment corresponding to each main surface Ms of the anode body 6. Distances D21 and D22 between the intersection of the center line CL with the outer edge of the solid electrolyte layer 9 and the midpoint of the line segment are defined as the thickness of the solid electrolyte layer 9 at the center of the main surface Ms. T2 is calculated by averaging the values ​​of these two distances.

[0094] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0095] <Solid electrolytic capacitor A1> A solid electrolytic capacitor 1 (solid electrolytic capacitor A1) shown in FIG. 1 was fabricated in the following manner, and its characteristics were evaluated.

[0096] (1) Preparation of anode body 6 Anode body 6 was produced by roughening both surfaces of an aluminum foil (thickness: 100 μm) used as a substrate by etching.

[0097] (2) Formation of dielectric layer 7 The other end of the anode body 6 was immersed in a chemical conversion solution, and a direct current voltage of 70 V was applied for 20 minutes to form a dielectric layer 7 containing aluminum oxide.

[0098] (3) Formation of solid electrolyte layer 9 3,4-ethylenedioxythiophene monomer and the polymer anion polystyrene sulfonate (PSS, Mw: 160 × 10 3 ) was dissolved in ion-exchanged water to prepare a mixed solution. Iron (III) sulfate (oxidizing agent) dissolved in ion-exchanged water was added to the mixed solution while stirring, to prepare a polymerization liquid.

[0099] The anode body 6 on which the dielectric layer 7 was formed in (2) above and a counter electrode were immersed in the obtained polymerization solution, and electrolytic polymerization was carried out at 25°C and a polymerization voltage of 1.0 V (polymerization potential relative to the silver reference electrode), thereby forming a solid electrolyte layer 9.

[0100] (4) Formation of the cathode extraction layer 10 Anode body 6 obtained in (3) above was immersed in a dispersion liquid in which graphite particles were dispersed in water, and then removed from the dispersion liquid and dried, thereby forming carbon layer 11 at least on the surface of solid electrolyte layer 9. Drying was carried out at 130 to 180°C for 10 to 30 minutes.

[0101] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of carbon layer 11, and the binder resin was cured by heating at 150 to 200°C for 10 to 60 minutes to form metal paste layer 12. In this way, cathode extraction layer 10 composed of carbon layer 11 and metal paste layer 12 was formed, and cathode part 8 composed of solid electrolyte layer 9 and cathode extraction layer 10 was formed. Capacitor element 2 was fabricated in the manner described above.

[0102] (5) Assembly of solid electrolytic capacitors Cathode part 8 of capacitor element 2 obtained in (4) above was joined to one end of cathode terminal 5 with adhesive layer 14 of a conductive adhesive. One end of anode body 6 protruding from capacitor element 2 was joined to one end of anode terminal 4 by laser welding.

[0103] Next, a resin outer casing 3 made of insulating resin was formed around the capacitor element 2 by molding. At this time, the other end of the anode terminal 4 and the other end of the cathode terminal 5 were left pulled out from the resin outer casing 3.

[0104] In this way, the solid electrolytic capacitor 1 (A1) was completed. In the same manner as above, a total of 20 solid electrolytic capacitors 1 were produced.

[0105] (6) Evaluation The solid electrolytic capacitors were evaluated as follows.

[0106] (a) Capacitance, tanδ, and ESR Using a four-terminal LCR meter at 20°C, the initial capacitance (μF) and initial tanδ of each solid electrolytic capacitor at a frequency of 120 kHz were measured, as well as the initial ESR (mΩ) at a frequency of 100 kHz. The average values ​​for 20 solid electrolytic capacitors were then calculated.

[0107] Next, an accelerated test was performed on the solid electrolytic capacitors by applying the rated voltage to them for 1,000 hours in an environment of 145°C. After that, the capacitance, tanδ, and ESR after the accelerated test were measured in an environment of 20°C using the same procedure as for the initial capacitance, tanδ, and ESR, and the average values ​​for 20 solid electrolytic capacitors were calculated.

[0108] (b) Leakage current (LC) A 1 kΩ resistor was connected in series to the solid electrolytic capacitor, and the leakage current (initial leakage current) (μA) was measured after applying a rated voltage of 25 V from a DC power supply for 1 minute, and the average value for 20 solid electrolytic capacitors was calculated. After the same accelerated test as in (a) above, the average leakage current after the accelerated test was calculated in the same way as for the initial leakage current.

[0109] (c) Raman spectrum measurement of the solid electrolyte layer solid The surface layer of the solid electrolyte layer of the capacitor element 2 taken out from the solid electrolytic capacitor was subjected to Raman spectrum measurement according to the procedure described above.

[0110] The Raman spectrum of the solid electrolyte layer of the solid electrolytic capacitor A1 is shown in Figure 4. As shown in Figure 4, the Raman spectrum of the surface layer of the solid electrolyte layer of the solid electrolytic capacitor A1 shows a wavenumber of 1423 cm -1 and 2800 cm -1 The peaks (first and second peaks) characteristic of the first polymer component, PEDOT, were observed at the wavenumber of 990 cm.-1 A peak (third peak) due to the PSS of the second polymer component was observed. The ratio of the height of the first peak to the height of the third peak (=I p1 / I p3 ) was sought.

[0111] (d) Thickness ratio of solid electrolyte layer T1 / T2 The thickness ratio T1 / T2 of the solid electrolyte layer 9 in each solid electrolytic capacitor was determined using the procedure described above. Then, the ratios T1 / T2 of the 20 solid electrolytic capacitors were averaged to determine an average value.

[0112] <Solid electrolytic capacitor B1> A liquid dispersion containing poly(3,4-ethylenedioxythiophene) (PEDOT) and PSS as a dopant was prepared according to the following procedure.

[0113] First, under stirring, PSS (Mw: 150 × 10 3 3,4-ethylenedioxythiophene monomer was added to an aqueous solution of PEDOT (PEDOT) and then oxidizing agents (iron(III) sulfate and sodium persulfate) were added to carry out chemical oxidative polymerization. The resulting polymerization solution was filtered through an ion exchanger to remove impurities, yielding a solution containing PEDOT and PSS. Purified water was added to the resulting solution, which was then homogenized using a high-pressure homogenizer and filtered to prepare a liquid dispersion.

[0114] The anode body 6 having the dielectric layer 7 formed thereon obtained in (2) of the solid electrolytic capacitor A1 was immersed in a liquid dispersion, then removed and further dried at 120°C for 10 to 30 minutes. The immersion in the first treatment liquid and drying were repeated four more times, thereby forming a solid electrolyte layer 9 containing PEDOT and PSS so as to cover the surface of the dielectric layer 7. A solid electrolytic capacitor B1 was fabricated and evaluated in the same manner as the solid electrolytic capacitor A1, except that the anode body 6 having the solid electrolyte layer 9 thus formed was used.

[0115] The initial evaluation results and the evaluation results after the accelerated test are shown in Tables 1 and 2. In each table, the evaluation results for solid electrolytic capacitor A1 are relative values ​​when the measured value for solid electrolytic capacitor B1 after the accelerated test is set to 100%.

[0116] [Table 1]

[0117] [Table 2]

[0118] Figure 5 shows the Raman spectrum of the surface layer of the solid electrolyte layer of solid electrolytic capacitor B1, measured using the procedure described above. As shown in Figure 5, no distinctive peaks were observed in the Raman spectrum of the surface layer of the solid electrolyte layer of solid electrolytic capacitor B1. In contrast, the Raman spectrum of the surface layer of the solid electrolyte layer of solid electrolytic capacitor A1 showed the first and second peaks characteristic of PEDOT, as well as the third to fifth peaks characteristic of PSS (Figure 4). Since no peaks were observed in Figure 5, it is believed that the fluorescence was blocking the observation of Raman scattered light. On the other hand, in Figure 4, the peaks of PEDOT and PSS were clearly observed, indicating that the fluorescence emission observed in B1 was not occurring. In B1, PSS segregated to the extent that significant fluorescence was observed, whereas in A1, no PSS segregation was observed, suggesting that PSS was more uniformly dispersed in the solid electrolyte layer.

[0119] Furthermore, corresponding to the difference in the Raman spectra in Figures 4 and 5, A1 has lower initial ESR, tan δ, and leakage current, and higher capacitance, compared to B1, as shown in Table 1. Furthermore, as shown in Table 2, A1 has less increase in ESR, tan δ, and leakage current after the accelerated test, and less decrease in capacitance, compared to B1.

[0120] In addition, when the solid electrolyte layer comprises an inner first solid electrolyte layer formed by chemical polymerization and an outer second solid electrolyte layer formed from a dispersion, a Raman spectrum similar to that of solid electrolytic capacitor B1 is obtained at the surface layer of the solid electrolyte layer. [Industrial Applicability]

[0121] According to the present disclosure, the initial ESR of a solid electrolytic capacitor can be kept low. Furthermore, even when the solid electrolytic capacitor is used for a long period of time or when the solid electrolytic capacitor is exposed to high temperatures, the increase in ESR can be kept low. Therefore, the solid electrolytic capacitor element and the solid electrolytic capacitor can be used in a variety of applications requiring high reliability. [Explanation of symbols]

[0122] 1: solid electrolytic capacitor, 2: capacitor element, 3: resin outer casing, 4: anode terminal, 5: cathode terminal, 6: anode body, 7: dielectric layer, 8: cathode portion, 9: solid electrolyte layer, 10: cathode lead layer, 11: carbon layer, 12: metal paste layer, 13: separation layer, 14: adhesive layer, E1: first end of anode body, E2: second end of anode body, Ms: main surface of anode body, Es: end surface of anode body, L1, L2: straight lines extending line segments corresponding to a pair of main surfaces of the anode body, CL: center line of each main surface of the anode body

Claims

1. an anode body, a dielectric layer formed on a surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer, the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, the solid electrolyte layer includes a first polymer component including a monomer unit corresponding to a thiophene compound and a second polymer component including a polymer anion; peaks characteristic of the first polymer component and the polymer anion are observed in a Raman spectrum of the surface layer of the solid electrolyte layer; the peak specific to the first polymer component includes a first peak observed in a wave number range of 1200 cm −1 or more and 1600 cm −1 or less; The polymeric anion comprises a monomer unit M2 corresponding to an aromatic sulfonic acid compound; the peaks specific to the polymer anion include a third peak observed in a wave number range of 800 cm −1 to 1050 cm −1 , A solid electrolytic capacitor element, wherein a ratio of the intensity I p1 of the first peak to the intensity I p3 of the third peak (=I p1 / I p3 ) is 5 or more.

2. The peak characteristic of the first polymer component is at 2750 cm －１ More than 3000cm －１ 2. The solid electrolytic capacitor element according to claim 1, which comprises a second peak observed in the following wavenumber range:

3. 3. The solid electrolytic capacitor element according to claim 1, wherein the weight average molecular weight of the polymer anion is 300 or more and 250,000 or less.

4. The polymer anion is a monomer unit M corresponding to an organic sulfonic acid compound. １ The solid electrolytic capacitor element according to any one of claims 1 to 3, comprising:

5. 5. The solid electrolytic capacitor element according to claim 1, wherein the first polymer component contains at least a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound as the monomer unit corresponding to the thiophene compound.

6. the anode body has an anode lead portion including a first end of the anode body and a cathode forming portion including a second end of the anode body, 6. The solid electrolytic capacitor element according to claim 1, wherein, in a cross section perpendicular to a direction from the first end toward the second end of the solid electrolytic capacitor element at an arbitrary position in a portion on the first end side of the cathode portion, a ratio T1 / T2 of a thickness T1 of the solid electrolyte layer formed in a corner portion of the anode body to a thickness T2 of the solid electrolyte layer formed in a central portion of a main surface of the anode body is 0.8 or more and 1.7 or less.

7. A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element according to any one of claims 1 to 6.

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