Solid electrolytic capacitor element and solid electrolytic capacitor

Abstract

A solid electrolytic capacitor element included in a solid electrolytic capacitor includes: an anode body including a porous portion in at least a surface layer; a dielectric layer covering at least a part of the surface of the anode body; and a solid electrolyte covering at least a part of the dielectric layer. The anode body contains a tantalum element, and the solid electrolyte contains a sulfur element. The solid electrolyte has: a first portion disposed in the pores of the porous portion; and a second portion disposed from the main surface of the anode body having the dielectric layer to the outside of the porous portion. In an element mapping in a predetermined region of a cross-section of the porous part using an electron probe microanalyzer, the abundance ratio of elemental sulfur is 0.17% or more when the abundance ratio of elemental tantalum is 100%.

Description

Technical Field

[0001] This disclosure relates to solid electrolytic capacitor elements and solid electrolytic capacitors. Background Technology

[0002] A solid electrolytic capacitor comprises: a solid electrolytic capacitor element, a resin casing or housing that seals the solid electrolytic capacitor element, and external electrodes electrically connected to the solid electrolytic capacitor element. The solid electrolytic capacitor element, for example, comprises: an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes a conductive polymer (e.g., a conjugated polymer and a dopant) covering at least a portion of the dielectric layer. The conductive polymer is also referred to as a solid electrolyte.

[0003] From the perspective of being able to easily form solid electrolytes, the formation of solid electrolytes mostly utilizes methods that use liquid dispersions containing conjugated polymers and dopants.

[0004] For example, Patent Document 1 discloses a method for manufacturing an electrolytic capacitor, which includes the following steps: impregnating an anode body on which a dielectric coating is formed on the surface with a first dispersion solution containing particles of a first conductive polymer and a first solvent, and then impregnating it with a second dispersion solution containing particles of a second conductive polymer and a second solvent, wherein the pH of the first dispersion solution is closer to 7 than the pH of the second dispersion solution.

[0005] Patent document 2 proposes a conductive polymer composite composed of PEDOT (poly(3,4-ethylenedioxythiophene)) and polyanions, which can detect the Raman spectrum at 1260 cm⁻¹. -1 The peak intensity at 1420 cm⁻¹ is set to I1. -1 When the peak intensity at a wavelength of 950 nm is set to I2, the absorbance at a wavelength of 950 nm is set to A1, and the absorbance at a wavelength of 2300 nm is set to A2, the conductive potential α derived from the following formula (I) is greater than -0.23.

[0006] α=(I1 / I2)-0.135×(A2 / A1)…(1)

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-58807

[0010] Patent Document 2: Japanese Patent Application Publication No. 2021-134331 Summary of the Invention

[0011] The first aspect of this disclosure relates to a solid electrolytic capacitor element. The solid electrolytic capacitor element comprises: an anode body having a porous portion at least in its surface layer; a dielectric layer covering at least a portion of the surface of the anode body; and a solid electrolyte covering at least a portion of the dielectric layer. The anode body comprises tantalum, and the solid electrolyte comprises sulfur. The solid electrolyte has: a first portion disposed within the pores of the porous portion; and a second portion disposed from the main surface of the anode body having the dielectric layer to the outer side of the porous portion. In elemental mapping of a defined region of the cross-section of the porous portion using an electron probe microanalyzer, the sulfur content is 0.17% or higher when the tantalum content is set to 100%.

[0012] A second aspect of this disclosure relates to a solid electrolytic capacitor comprising at least one of the aforementioned solid electrolytic capacitor elements.

[0013] In solid electrolytic capacitors, the change in equivalent series resistance (ESR) when exposed to high temperatures can be reduced. Attached Figure Description

[0014] Figure 1 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to one embodiment of the present disclosure. Detailed Implementation

[0015] From the perspective of increasing surface area to ensure high capacity, a porous structure with fine pores is formed at least on the surface of the anode. Liquid dispersions comprise particulate conductive polymers composed of conjugated polymers and polymer dopants (such as polymeric anions). Therefore, if a dispersion is used to form a solid electrolyte, the particulate conductive polymers are difficult to fill deep into the fine pores, making it difficult to improve the filling rate of the conductive polymer in the porous structure. In this case, the equivalent series resistance (ESR) of the solid electrolytic capacitor easily changes significantly when exposed to high temperatures.

[0016] The method of forming solid electrolytes using liquid dispersions is simple, and therefore has become the mainstream method for forming solid electrolytes in recent years. On the other hand, in solid electrolytic capacitor elements, a porous portion with fine pores is formed at least on the surface of the anode. The dielectric layer includes the inner wall surface of the pores of the porous portion and is formed along the inner wall surface of the depressions (sometimes called pits) on the surface of the anode. Therefore, fine irregularities are formed on the surface of the dielectric layer according to the shape of the surface of the anode. The liquid dispersion contains particulate conductive polymers (conjugated polymers and dopants, etc.) with relatively high molecular weight. Moreover, in the liquid dispersion, from the viewpoint of high affinity for conjugated polymers, easy assurance of high stability, and high heat resistance, high molecular weight polymer anions are preferred as dopants.

[0017] When using liquid dispersions to form solid electrolytes, there is a tendency for high ESR. The reasons are presumably as follows: Although the conductive polymer particles contained in the liquid dispersion fill the micro-recesses on the surface of the dielectric layer within the porous region, they struggle to penetrate deeply, making it difficult to increase the filling rate of the conductive polymer. Consequently, the resistance between the dielectric layer and the solid electrolyte increases, leading to a tendency for an initially high ESR. Furthermore, with a low filling rate of the conductive polymer in the porous region, the pores easily become air passageways. Due to the effects of moisture or oxygen in the air, the conjugated polymer undergoes oxidation and deterioration, or dopants decompose and dedoped, resulting in a decrease in the conductivity of the conductive polymer. This deterioration is particularly pronounced under high-temperature or high-temperature, high-humidity environments. Additionally, high-temperature or high-temperature, high-humidity environments cause volume changes in the conductive polymer. The movement of the first part, contained within the pores, is restricted by the porous metal framework. In contrast, the second part is more prone to movement due to volume changes under high temperature or high temperature and high humidity conditions, leading to deformation between the first and second parts. This deformation causes cracks to form between the surface of the first or porous part and the second part, reducing the number of contact points. Consequently, the resistance between the first or porous part and the second part is considered to increase. As a result, the ESR of the solid electrolytic capacitor is considered to change significantly when exposed to high temperature or high temperature and high humidity environments.

[0018] Besides using liquid dispersions, other methods for forming solid electrolytes include in-situ polymerization, such as chemical polymerization on the surface of an anode with a dielectric layer. However, in-situ polymerization is difficult to control, often resulting in a homogeneous solid electrolyte, and the types of conjugated polymer monomers and dopants that can be used are limited. In practice, pyrrole compounds are often used as dopants in in-situ polymerization, along with low-molecular-weight compounds such as aromatic sulfonic acids. Therefore, the dopants and conductive polymers have low stability, are prone to dedoping or degradation, and their ESR is easily altered when exposed to high temperatures or high-temperature, high-humidity environments.

[0019] In view of the above, (1) the solid electrolytic capacitor element of this disclosure comprises: an anode body having a porous portion at least in its surface layer; a dielectric layer covering at least a portion of the surface of the anode body; and a solid electrolyte covering at least a portion of the dielectric layer. The anode body comprises tantalum (Ta) and the solid electrolyte comprises sulfur (S). The solid electrolyte has: a first portion disposed within the pores of the porous portion; and a second portion disposed from the main surface of the anode body having the dielectric layer to the outside of the porous portion. In elemental mapping of a defined region of the cross-section of the porous portion using an electron probe microanalyzer, the presence rate of S is 0.17% or more when the presence rate of Ta is set to 100%. Hereinafter, the solid electrolytic capacitor element will sometimes be simply referred to as a capacitor element.

[0020] In this disclosure, the presence ratio of sulfur (S) is relatively high, exceeding 0.17%, relative to the presence ratio of Ta in the porous portion. This reduces the ESR variation of the solid electrolytic capacitor when exposed to high temperatures. The S element primarily originates from the conjugated polymers and dopants constituting the solid electrolyte. For example, polythiophene-based conjugated polymers contain S elements from thiophene rings, and dopants contain S elements derived from anionic groups such as sulfonyl groups. On the other hand, the anode containing Ta is primarily composed of Ta or Ta alloys, and the dielectric layer is composed of Ta oxides. Therefore, a relatively high presence ratio of S relative to the presence ratio of Ta in the porous portion means a relatively high proportion of solid electrolyte contained in the porous portion (in other words, a higher filling rate of solid electrolyte in the pores of the porous portion). In this disclosure, it is believed that by maintaining the presence ratio of S in the porous portion within the aforementioned range, a relatively high filling rate of the solid electrolyte can be obtained, reducing air flow and thus hindering the deterioration of the solid electrolyte. Furthermore, since the solid electrolyte is disposed in the pores of the porous portion with a high filling rate, it is believed that even if the solid electrolyte undergoes volume changes due to exposure of the solid electrolytic capacitor to high temperature or high humidity environments, a relatively large number of contact points will be maintained between the first part or the porous portion and the second part. Therefore, it is believed that the change in ESR of the solid electrolytic capacitor when exposed to high temperature or high temperature and high humidity environments can be reduced.

[0021] The relatively high sulfur content in the porous portion, as described above, is obtained, for example, by the following method. First, a dielectric layer is formed on the surface of an anode containing Ta and at least in the porous portion on the surface. After pre-coating the resulting anode with the dielectric layer on the surface, it is immersed in a polymerization solution containing a precursor of a conjugated polymer and polymer anions containing sulfur, and electrolytic polymerization is carried out in a three-electrode manner. Through the pre-coating treatment, the surface of the dielectric layer is covered with a conductive material to a certain extent, forming a pre-coating of the conductive material. Most of the surface area of ​​the dielectric layer is covered by the pre-coating, thereby facilitating electrolytic polymerization. Thus, it is believed that by utilizing the coverage of the pre-coating and the three-electrode electrolytic polymerization, even within the fine pores of the anode with the dielectric layer, in the presence of polymer anions with relatively high stability as dopants, the polymerization of the precursor of the conjugated polymer gradually proceeds, generating a conductive polymer formed by the interaction of the conjugated polymer and the polymer anions, forming a dense solid electrolyte. Most of the dielectric layer, including the inner surface of the fine pores of the porous portion, is pre-coated. Furthermore, since the precursor and polymer anions are dissolved in the polymerization solution, they can easily penetrate deep into the fine pores of the porous portion. Therefore, polymerization is easily achieved not only near the pore openings but also deep within the pores. Thus, a high filling rate of the solid electrolyte within the pores is considered achievable. Within the pores of the porous portion, the polymerization of the conjugated polymer precursor occurs while interacting with the polymer anions, resulting in a high orientation of the formed conjugated polymer and a relatively uniform dispersion of the polymer anions, facilitating a relatively high doping rate. Therefore, the conductivity of the solid electrolyte in the first part can be improved, and dedoping or degradation of the conjugated polymer is less likely to occur when the solid electrolytic capacitor is exposed to high temperature or high humidity environments. Additionally, due to the high filling rate of the solid electrolyte in the porous portion, even if the solid electrolyte undergoes volume changes when the solid electrolytic capacitor is exposed to high temperature or high humidity environments, the contact point between the first part or the porous portion and the second part can be maintained. Therefore, the excellent effects described above are considered achievable. Furthermore, in this disclosure, by achieving a high filling rate of solid electrolyte in the porous portion, the resistance of the first part can be suppressed to a low level from the initial stage, thereby reducing the initial ESR. Because the resistance of the first part is low, a relatively high initial capacity can be ensured.

[0022] It should be noted that even when the first part is formed using a liquid dispersion containing conjugated polymers with sulfur (PEDOT) and polymeric anions with sulfur (PSS), the sulfur content in the porous portion is low. As mentioned above, this is believed to be because the filling rate of the solid electrolyte in the porous portion is low even when using a liquid dispersion. Furthermore, the sulfur content in the porous portion is low, less than 0.17%, even without pre-coating or when the pre-coating layer has low coverage.

[0023] Three-electrode electrolytic polymerization uses three electrodes: an anode, a counter electrode, and a reference electrode, all with a dielectric layer formed on their surface. In three-electrode electrolytic polymerization, the anode potential can be precisely controlled using the reference electrode, unaffected by changes in the natural potential of the counter electrode. It is believed that, compared to the two-electrode method using an anode and a counter electrode, the electrolytic polymerization reaction is more precisely controlled in the three-electrode case, with polymer chains growing slowly while interacting with polymer anions. Therefore, it is believed that the orientation of the resulting conjugated polymer system is improved, and the dispersion of polymer anions is enhanced, resulting in a more uniform and denser solid electrolyte. Furthermore, due to the high coverage of the pre-coating, the polymerization reaction easily proceeds within the pores of the porous portion. Therefore, it is believed that a more uniform and denser solid electrolyte is formed with a high filling rate within the pores of the porous portion. Additionally, it is believed that by highly dispersing the polymer anions, a relatively high doping rate can be easily obtained, thus easily improving the conductivity of the solid electrolyte itself.

[0024] It should be noted that if the volume of the pores in the porous section is taken into account, the presence rate of sulfur element is, for example, less than 5%.

[0025] Analysis using an Electron Probe Micro Analyzer (EPMA) was performed on a sample in a capacitor element with a porous section containing a cathode portion and a platinum film, exposed in cross-section. In the cross-sectional image of the porous section containing the solid electrolyte, for a region 450 μm deep and 450 μm wide from one main face of the anode, elemental mapping was performed based on the wavelength differences of characteristic X-rays from EPMA, and the net intensity of the contained elements was determined. The net intensity is the measured value of each element after removing background (noise). The percentage of the net intensity of S element was calculated when the net intensity of Ta element was set to 100%. For multiple regions (e.g., 5 regions), the percentage of the net intensity of S element was calculated, and the average value was taken as the percentage of S element present when the presence rate of Ta element in the porous section was set to 100%.

[0026] The conditions for EPMA analysis are as follows.

[0027] The environment during the measurement: 25℃, atmospheric pressure

[0028] Accelerating voltage: 15.0kV

[0029] Beam current: 50.4 nA

[0030] Integrating time: 50.0ms / point (12-minute mode)

[0031] Spectroscopic crystals: AP / CH1, PbST / CH2, PET / CH3, LiF / CH4, LSA80 / CH5

[0032] The analytical sample can be prepared, for example, according to the following steps. First, a solid electrolytic capacitor or capacitor element is embedded in a curable resin, and the resin is cured. The anode has a first end and a second end opposite to the first end, and a solid electrolyte is formed on the portion of the anode on the second end side. At a predetermined position in the direction from the first end of the anode toward the second end (in other words, the length direction of the anode or capacitor element), the cured material obtained above is wet-ground or dry-ground in such a way that a cross-section perpendicular to the length direction of the capacitor element and parallel to the thickness direction is exposed. The exposed cross-section is smoothed by ion milling. Platinum (Pt) is sputtered onto the smoothed cross-section using a sputtering device, thereby forming a platinum film with a thickness of 1 nm to 2 nm. The analytical sample is thus obtained. It should be noted that when the length of the region where the solid electrolyte is formed in the direction parallel to the length direction of the capacitor element is set to 1, the cross-section is set at a position exceeding 0 and less than 0.05 from the end on the second end side of the region where the solid electrolyte is formed.

[0033] (2) In the configuration described in (1) above, the first part may include: a first polymer component equivalent to a conjugated polymer; and a second polymer component equivalent to a polymer anion containing sulfur. When the first part contains these polymer components (especially the second polymer component), it is difficult to increase the filling rate of the solid electrolyte in the first part. In this disclosure, the first part is formed by pre-coating and tripolar electrolytic polymerization, therefore, even when the first part contains the aforementioned polymer components, the presence ratio of S element in the porous portion can be increased, ensuring a high filling rate of the solid electrolyte.

[0034] (3) In the configuration described in (2) above, the first polymer component may contain sulfur (S). In this case, it is easier to increase the proportion of sulfur in the porous portion. In addition, it is easier to obtain higher conductivity in the first portion.

[0035] (4) Regarding the composition of (2) or (3) above, in the Raman spectrum of the first part, the intensity I of the first peak characteristic of the first polymer component is... p1 The intensity I relative to the second peak characteristic of the second polymer component p2 The ratio of I p1 / I p2 It can be more than 2. In this case, since the orientation and crystallinity of the conjugated polymer in the first part are relatively high, it is easy to ensure the high conductivity of the solid electrolyte.

[0036] (5) In the above (4) configuration, compared to I p1 / I p2 It can also be below 7. In this case, it is easy to obtain a relatively high doping rate, resulting in higher conductivity of the solid electrolyte, which is advantageous in suppressing ESR.

[0037] (6) Regarding the composition of any one of (2) to (5) above, in the first part, the conjugated polymer may contain monomer units corresponding to the thiophene compound. The polymer anion may contain monomer units corresponding to the aromatic sulfonic acid compound. In the Raman spectrum of the first part, it is possible to detect the Raman spectrum at 1200 cm⁻¹. -1 Above and 1600cm -1 The first peak characteristic of the first polymer component was observed in the following range. Additionally, in the Raman spectrum of the first part, a peak could be observed at 800 cm⁻¹. -1 Above and 1100cm -1 The following range shows a second peak characteristic of the second polymer component. In this case, high conductivity of the solid electrolyte is readily obtained in the first part, which is advantageous in terms of suppressing ESR to a lower level.

[0038] (7) In any of the configurations in (2) to (6) above, the weight-average molecular weight of the polymer anion can be 100 or more and 500,000 or less. Even if the weight-average molecular weight of the polymer anion is in such a range, a solid electrolyte can be configured with a high filling rate in the pores of the porous portion through pre-coating treatment and three-electrode electrolytic polymerization, and the high conductivity of the first part can be easily obtained. In addition, higher stability of the conductive polymer can be obtained. Therefore, it is possible to further reduce the change in ESR of the solid electrolytic capacitor when exposed to high temperature or high temperature and high humidity environments.

[0039] (8) In any of the configurations in (1) to (7) above, the anode body may also be a porous sintered body. In the case of an anode foil having a dielectric layer, the average depth of the pores in the porous portion is about tens of μm. In contrast, in a porous sintered body, the average depth of the pores in the porous portion of the anode body having a dielectric layer is, for example, 100 μm or more, and usually 300 μm or more. Therefore, in a porous sintered body, it is difficult to configure a solid electrolyte in the porous portion with a high filling rate compared to the case of an anode foil. In this disclosure, even when the anode body is a porous sintered body, a solid electrolyte can be configured in the porous portion with a high filling rate by pre-coating treatment and tripolar electrolytic polymerization, thus obtaining high conductivity and reducing the flow of air in the pores, thereby suppressing the deterioration of the conductive polymer. Therefore, even when the anode body is a porous sintered body, it is possible to suppress the change in ESR of the solid electrolytic capacitor when exposed to high temperature or high temperature and high humidity environments.

[0040] (9) This disclosure also includes a solid electrolytic capacitor element comprising at least one capacitor element as described in any one of (1) to (8) above.

[0041] The capacitor element and solid electrolytic capacitor of this disclosure will be described in more detail below, including the configurations described in (1) to (9) above. To the extent that there is no technical inconsistency, at least one of the configurations described in (1) to (9) above may be combined with at least one of the elements described below.

[0042] [Capacitor Components]

[0043] A capacitor element consists of an anode and a cathode.

[0044] (Anode section)

[0045] The anode section includes the anode body. The anode section may include the anode body and the anode wire.

[0046] (Anode)

[0047] The anode contains Ta (Ta). Ta functions as a valve-like metal. The anode can contain Ta metal, Ta alloys, or both.

[0048] The anode body has a porous portion, at least on its surface. This porous portion contains multiple fine pores. Through this porous portion, the anode body has a finely textured, uneven shape.

[0049] Examples of anode bodies include porous molded bodies or porous sintered bodies (such as sintered bodies of porous molded bodies) containing Ta particles. These anode bodies are generally porous. Both porous molded bodies and porous sintered bodies can be sheet-like, cuboid, cubic, or similar shapes. An anode body with porous portions on its surface is obtained, for example, by roughening the surface of a Ta-containing substrate (sheet-like (e.g., foil-like, plate-like) substrate). Roughening can be performed, for example, by etching (e.g., electrolytic etching, chemical etching, etc.). Such an anode body, for example, has a core and porous portions integrally formed with the core on both surfaces. A porous sintered body containing Ta is preferred as an anode body.

[0050] The anode body may have: an anode lead-out portion including a first end; and a cathode forming portion including a second end opposite to the first end. A cathode portion containing a solid electrolyte is formed on the surface of the cathode forming portion of the anode body. The anode lead-out portion is used, for example, for electrical connection to an external electrode on the anode side. Anode lead terminals may also be connected to the anode lead-out portion.

[0051] (Anode wire)

[0052] When the anode body is a porous sintered body or a porous molded body, the anode portion may include an anode wire. The anode wire may also be a wire formed of metal. Examples of materials for the anode wire are valve-acting metals, copper, or copper alloys. Examples of valve-acting metals include aluminum, tantalum, niobium, and titanium. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from one end of the anode body. The end of the anode wire protruding outward corresponds to the first end, and the end of the anode body opposite the first end corresponds to the second end.

[0053] (Dielectric layer)

[0054] The dielectric layer is formed in such a way that it covers at least a portion of the surface of the anode body (e.g., at least a portion of the surface of the porous portion). The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing tantalum (Ta) on the surface of the anode body. When the dielectric layer is formed on the surface of the porous portion of the anode body, the surface of the dielectric layer has a finely textured surface following the shape of the porous portion.

[0055] As described above, compared to the case of anode foil, in porous molded bodies or porous sintered bodies (especially porous sintered bodies), it is difficult to configure a solid electrolyte with a high filling rate within the pores due to the average depth of the pores in the porous portion. If the filling rate of the solid electrolyte in the porous portion is low, air can easily penetrate, and due to the effects of moisture or oxygen, the solid electrolyte will deteriorate due to the degradation of the conjugated polymer system and the dedoping of dopants. In addition, due to the degradation of the solid electrolyte and the stress caused by exposure to high temperature (or high temperature and high humidity environment), the first part may peel off from the second part and fall into the pores. These situations lead to a decrease in the conductivity of the solid electrolyte. The degradation of the solid electrolyte is particularly significant when solid electrolytic capacitors are exposed to high temperature or high temperature and high humidity environments. Therefore, in solid electrolytic capacitors using anode bodies that are porous as a whole, such as porous molded bodies or porous sintered bodies (especially porous sintered bodies), the ESR change when exposed to high temperature or high temperature and high humidity environments tends to become significant. In this disclosure, even when the anode body is porous as a whole (when a porous sintered body is used), the presence ratio of sulfur in the porous portion can be increased, enabling the solid electrolyte to be configured with a high filling rate within the fine pores. Therefore, it is possible to reduce the ESR change of solid electrolytic capacitors when exposed to high temperatures or high-temperature, high-humidity environments.

[0056] The dielectric layer can also be formed from a material that functions as a dielectric layer. Such a material includes, for example, an oxide of a valve-acting metal. Since the anode contains Ta, the dielectric layer formed through chemical conversion typically contains Ta₂O₅. However, the dielectric layer is not limited to such specific examples.

[0057] (Cathode section)

[0058] The cathode portion includes at least a solid electrolyte covering at least a portion of the dielectric layer. The portion of the solid electrolyte on the second end side of the anode body (in other words, the cathode forming portion) is formed across the dielectric layer. The cathode portion typically includes a solid electrolyte covering at least a portion of the dielectric layer and a cathode lead-out layer covering at least a portion of the solid electrolyte. The solid electrolyte and the cathode lead-out layer will be described below.

[0059] (Solid electrolyte)

[0060] In this disclosure, the solid electrolyte contains sulfur (S). Furthermore, the solid electrolyte in the anode body having a dielectric layer has: a first portion disposed within the pores of the porous portion; and a second portion disposed from the main surface of the anode body having the dielectric layer to the outer side of the porous portion.

[0061] Solid electrolytes are composed of conductive polymers. These conductive polymers include non-self-doped conductive polymers (conjugated polymers and dopants, etc.). Solid electrolytes may further include self-doped conductive polymers. Additionally, solid electrolytes may further include additives as needed. The sulfur (S) element in solid electrolytes primarily originates from the conductive polymers. More specifically, S is present at least in the dopants, and may also be present in both the dopants and the conjugated polymers. Furthermore, S is present at least in the first part, and typically in both the first and second parts.

[0062] (Part 1)

[0063] At least a portion of the first solid electrolyte is formed by three-electrode electrolytic polymerization as described above. The first portion may contain: a first polymer component corresponding to a conjugated polymer; and a second polymer component corresponding to a polymer anion containing an S element. The first solid electrolyte may contain a pre-coating of a conductive polymer as a conductive material.

[0064] Examples of conjugated polymers that are equivalent to the first polymer component include well-known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. The conjugated polymer that is equivalent to the first polymer component is typically a non-self-doped conjugated polymer (e.g., a conjugated polymer without anionic groups). Examples of such conjugated polymers include those with a basic backbone of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, poly(p-phenyleneacetylene), poly(phenylene oxide), and polythiophene vinylidene. These polymers only need to contain at least one monomer unit constituting the basic backbone. Monomer units also include monomer units with substituents. These polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophene includes PEDOT (poly(3,4-ethylenedioxythiophene)).

[0065] From the viewpoint of easily increasing the content ratio of sulfur (S), the first polymer component may contain sulfur. The conjugated polymer constituting such a first polymer component contains, for example, monomer units corresponding to thiophene compounds (preferably repeating monomer units). When using a thiophene compound as a precursor, electropolymerization can be easily carried out even in the presence of a polymer anion containing sulfur by adjusting the electropolymerization conditions, which is more advantageous in increasing the content ratio of sulfur. Examples of thiophene compounds include compounds having a thiophene ring and capable of forming repeating monomer units. The thiophene compound can form repeating monomer units by linking the 2 and 5 positions of the thiophene ring.

[0066] Thiophene compounds may, for example, have substituents at 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 can be linked to form a ring fused with the thiophene ring. Examples of thiophene compounds include thiophenes and alkylene dioxothiophene compounds (such as ethylene dioxothiophene compounds C) that may have substituents at at least one of the 3 and 4 positions. 2-4 Alkylene dioxothiophene compounds, etc.). Alkylene dioxothiophene compounds also include compounds with substituents in the alkylene moiety.

[0067] As a substituent, alkyl groups (methyl, ethyl, etc. C4) are preferred. 1-4 Alkyl groups, etc.), alkoxy groups (methoxy, ethoxy, etc. C 1-4 alkoxy, hydroxyl, hydroxyalkyl (hydroxymethyl, etc. hydroxy C 1-4 Alkyl groups, etc., but not limited to these. When a thiophene compound has two or more substituents, the substituents may be the same or different.

[0068] Alternatively, a conjugated polymer (PEDOT, etc.) may be used that contains at least a monomer unit (preferably a repeating structure of the monomer unit) corresponding to a 3,4-ethylenedioxythiophene compound (3,4-ethylenedioxythiophene (EDOT), etc.). The conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only the monomer unit corresponding to EDOT, or it may contain monomer units corresponding to thiophene compounds other than EDOT in addition to the monomer unit.

[0069] There is no particular limitation on the weight-average molecular weight (Mw) of conjugated polymers; for example, it can be above 1,000 and below 1,000,000.

[0070] It should be noted that, in this specification, the weight-average molecular weight (Mw) is a converted value for polystyrene determined using gel permeation chromatography (GPC). It should also be noted that GPC is typically performed using a polystyrene gel column and a water / methanol (8 / 2, v / v) mobile phase.

[0071] The first part may contain a second polymer component as a dopant, equivalent to a polymer anion containing sulfur (S). Examples of polymer anions constituting the second polymer component include polymers having multiple sulfonyl groups. By using the second polymer component, the presence ratio of S in the first part can be easily increased. In addition to sulfonyl groups, the polymer anion may also have other anionic groups (e.g., carboxyl groups).

[0072] In solid electrolytes, the anionic groups (sulfonyl, carboxyl, etc.) of dopants can be contained in free form, anionic form, or salt form, or in form that is bonded to or interacts with conjugated polymers. In this specification, all of these forms are sometimes simply referred to as "anionic group," "sulfonyl," or "carboxyl," etc.

[0073] Examples of polymeric anions containing sulfonyl groups include high-molecular-weight polysulfonic acids. Specific examples of polymeric anions include polyvinylsulfonic acid, polystyrene sulfonic acid (including copolymers and substituted derivatives), polyallyl sulfonic acid, polyacrylamide sulfonic acid, polymethacrylamide sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (aromatic polyester sulfonic acid, etc.), and phenol sulfonic acid phenolic varnish resins. However, polymeric anions are not limited to these specific examples. Solid electrolytes may contain one polymeric anion or a combination of two or more.

[0074] The Mw of the polymer anion is, for example, 100 or more and 500,000 or less. Even with such a range of weight-average molecular weight of the polymer anion, a solid electrolyte can be configured with a high filling rate within the pores of the porous portion through pre-coating treatment and tripolar electrolytic polymerization, easily achieving high conductivity in the first part. Furthermore, higher stability of the conductive polymer can be obtained. Therefore, the ESR change of the solid electrolytic capacitor when exposed to high temperature or high temperature and high humidity environments can be further mitigated. From the viewpoint of easily configuring the conductive polymer with a high filling rate within the pores of the porous portion, the Mw of the polymer anion included in at least the first part is preferably 100,000 or less, more preferably 1,000 or more and 100,000 or less, or 10,000 or more and 100,000 or less. In addition, when the Mw of the polymer anion is in this range, higher dispersibility and a relatively high doping rate of the polymer anion are easily obtained in the first part, which is advantageous in ensuring higher conductivity. Furthermore, high stability of the dopant and the conductive polymer is easily obtained.

[0075] In the first part, the amount of dopant contained in the solid electrolyte can be 10 parts by mass or more and 1000 parts by mass or less, or 20 parts by mass or more and 500 parts by mass, relative to 100 parts by mass of the conjugated polymer. From the viewpoint of easily obtaining higher dispersibility of polymer anions and a relatively high doping rate, it can be 50 parts by mass or more and 200 parts by mass or less.

[0076] The pre-coating may, for example, contain a conductive material (conductive polymer, etc.). The conductive polymer constituting the pre-coating preferably contains at least a self-doped conductive polymer, and may also contain a non-self-doped conductive polymer in addition to a self-doped conductive polymer. The pre-coating may, for example, be formed using a liquid composition (liquid dispersion, solution, etc.) containing a self-doped conductive polymer.

[0077] Self-doped conductive polymers, for example, have: a conjugated polymer backbone; and functional groups (anionic groups, etc.) that function as dopants and are directly or indirectly bonded to the backbone via covalent bonds. Examples of conjugated polymers corresponding to the backbone include conjugated polymers (π-conjugated polymers, etc.) that are equivalent to the first polymer component. From the viewpoint of easily obtaining high conductivity, etc., a polymer having a conjugated polymer backbone containing repeating structures of monomer units corresponding to thiophene compounds and anionic groups introduced into the backbone is preferred as a self-doped conductive polymer.

[0078] Self-doped conductive polymers can have a backbone of conjugated polymers (such as PEDOT) that includes at least repeating monomer units corresponding to 3,4-ethylenedioxythiophene compounds (such as EDOT). The backbone of a conjugated polymer that includes at least repeating monomer units corresponding to EDOT can contain only monomer units corresponding to EDOT, or it can contain monomer units corresponding to thiophene compounds other than EDOT in addition to those monomer units.

[0079] Examples of anionic groups include sulfonyl, carboxyl, phosphate, and phosphonic acid groups. Self-doped conductive polymers can contain one or more anionic groups. From the viewpoint of easily ensuring higher conductivity in self-doped conductive polymers, they can contain at least a sulfonyl group.

[0080] Anionic groups can be directly introduced into the backbone of conjugated polymers, or they can be introduced through linking groups. Preferably, the linking group is a polyvalent group (divalent group) containing an alkylene group. Examples of linking groups include aliphatic polyvalent groups (divalent groups, etc.) such as alkylene groups, and -R groups. 1 -XR 2 - Group (X is oxygen or sulfur, R) 1 and R 2(Whether the same or different, they are alkylene groups). The number of carbon atoms in each alkylene group contained in the linking group is, for example, 1 or more and 10 or less, or 1 or more and 6 or less. The alkylene group can be linear or branched. The linking group can, for example, contain at least alkylene groups with 2 or more carbon atoms. Such alkylene groups can have 2 or more (or 3 or more) and 10 or less carbon atoms, or 2 or more (or 3 or more) and 6 or less. For example, R 1 It can be an alkylene group with 1 or more but less than 6 carbon atoms, R 2 It can be an alkylene group with 2 or more (or 3 or more) carbon atoms and less than 10. However, the linking group is not limited to this.

[0081] In the pre-coating or the first part, the anionic groups of the self-doped conductive polymer may be included in any of the following forms: anionic, free, ester, and salt, or in a form that interacts with or is complexed with the components included in the first part. In this specification, all of these forms are simply referred to as anionic groups.

[0082] The Mw of self-doped conductive polymers can be above 1,000 and below 1,000,000, or above 1,000 and below 50,000.

[0083] The pre-coating may contain one self-doped conductive polymer, or a combination of two or more.

[0084] (Raman spectroscopy)

[0085] In the capacitor element of this disclosure, at least a first peak characteristic of the first polymer component (conjugated polymer) and a second peak characteristic of the second polymer component are observed in the Raman spectrum of the first part. The main component of the solid electrolyte is a conjugated polymer, and in the Raman spectrum of the solid electrolyte, the peak attributable to the C-S stretching vibration originating from the conjugated polymer (the first peak) is the highest and most characteristic. In the first part, the solid electrolyte exhibits high crystallinity due to the high orientation of the conjugated polymer. Furthermore, in the first part, the conjugated polymer is in an energy-stabilized state. Therefore, the first part displays the characteristic Raman spectrum of the first and second peaks as described above.

[0086] For example, in the first part, if the conjugated polymer contains monomer units corresponding to thiophene compounds and the polymer anion contains monomer units corresponding to aromatic sulfonic acid compounds, then in the Raman spectrum of the first part, at 1200 cm⁻¹... -1 Above and 1600cm -1 The first peak was observed in the following range, at 800cm. -1 Above and 1100cm -1A second peak was observed in the following range. The first peak is attributed to the C=C stretching vibration of the thiophene ring in the monomer unit corresponding to the thiophene compound. The second peak is attributed to the CS stretching vibration between the aromatic ring and the sulfur element of the sulfonate group in the monomer unit corresponding to the aromatic sulfonic acid compound. For example, in the case where the conjugated polymer contains at least the monomer unit corresponding to EDOT, the position of the first peak is, for example, 1400 cm⁻¹. -1 Above and 1450cm -1 The following can also be 1410cm -1 Above and 1435cm -1 Below. When the polymeric anion contains at least polystyrene sulfonic acid, the position of the second peak is, for example, 900 cm⁻¹. -1 Above and 1050cm -1 The following can also be 950cm -1 Above and 1050cm -1 the following.

[0087] On the other hand, the characteristic peaks described above were not observed in the Raman spectrum of the first part of the solid electrolyte formed using a liquid dispersion. This is believed to be because fluorescence emission hinders the observation of Raman scattered light. In the preparation of the liquid dispersion, since polymerization occurs in the liquid phase, it is believed that, compared to the conjugated polymer precursor, high molecular weight polymer anions tend to segregate on the surface of the resulting conductive polymer particles. In the case of using a liquid dispersion, it is believed that the conductive polymer particles with surface polymer anion segregation are disposed in porous sections; therefore, in the Raman spectrum of the first part, the characteristic peaks described above are not observed due to the fluorescence emission generated by the segregated polymer anions.

[0088] In the capacitor element of this disclosure, the intensity I of the first peak characteristic of the first polymer component (conjugated polymer) in the Raman spectrum of the first part is... p1 The intensity I relative to the second peak characteristic of the second polymer component (polymer anion) p2 The ratio of I p1 / I p2 It can be 2 or more, or 3 or more, or 4 or more. In comparison to I... p1 / I p2 Within this range, the orientation and crystallinity of the conjugated polymer in the first part are relatively high. Therefore, it is easy to ensure high conductivity of the solid electrolyte in the first part. From the viewpoint of easily ensuring higher crystallinity and conductivity, compared to I... p1 / I p2 It can be 5 or higher, or 5.5 or higher. Compared to I... p1 / I p2For example, below 10. From the viewpoint that higher conductivity can be easily ensured by obtaining a relatively high doping rate, it is better than I. p1 / I p2 Preferably 7 or less. Compared to I p1 / I p2 For example, it can be 2 or higher and 10 or lower (or 7 or lower), or 4 or higher and 10 or lower (or 7 or lower). Within these numerical ranges, the lower limit can be replaced with the values ​​mentioned above. It should be noted that the intensity of each peak is equivalent to the peak height obtained by subtracting the background height from the height of each peak.

[0089] In this specification, the Raman spectrum of the solid electrolyte in Part I is measured under the following conditions on the cross-section of the porous portion of the solid electrolyte present at a specified location in the solid electrolytic capacitor element.

[0090] Raman spectroscopy apparatus: NanoPhoton RamanFORCE PAV

[0091] Diffraction grating: 600gr / cm

[0092] Wavenumber range for measurement: 0 cm -1 Above and 2500cm -1 the following

[0093] Temperature: 25℃

[0094] The laser wavelength, laser output density, and exposure time are determined based on the type of conjugated polymer. For example, when the conjugated polymer is PEDOT, the laser wavelength is 784.73 nm, and the laser output density is 870 W / cm². 2 The exposure time is 60 seconds.

[0095] In Raman spectroscopy measurements, a sample acquired according to the following steps can be used. First, a solid electrolytic capacitor or capacitor element is embedded in a curing resin, and the resin is cured. The cured material is then ground or its cross-section is polished to expose a cross-section of the capacitor element that is perpendicular to its length direction and parallel to its thickness direction. The cross-section is set as follows: with the length of the region containing the solid electrolyte in the direction parallel to the length direction of the capacitor element set to 1, the cross-section is located at a position exceeding 0 and less than 0.05 from the end of the region containing the solid electrolyte on the opposite side of the anode lead (the end on the second end side). This process yields a sample for measurement. In the exposed cross-section of the sample, the Raman spectrum is measured for an 8μm × 8μm region of the solid electrolyte (first part) formed within the pits on the porous surface. The intensities of the first and second peaks are obtained by averaging the measured values ​​at 12 positions within the 8μm × 8μm region of the first part formed within the pits of the porous portion.

[0096] (Methods for forming solid electrolytes)

[0097] At least the first part of the solid electrolyte can be formed by pre-coating the surface of the dielectric layer and then electrolyzing a conjugated polymer precursor in the presence of a dopant in a three-electrode manner. For example, after pre-coating an anode having a dielectric layer in a liquid composition (polymerization solution) containing a conjugated polymer precursor and a dopant, electrolyzing is performed with the cathode forming portion of the anode impregnated. By adjusting the conditions of the pre-coating treatment and the electrolyzing conditions, a solid electrolyte can be configured with a high filling rate in the fine pores of the porous portion of the anode containing Ta, thereby increasing the presence ratio of S. In addition, the dopant can be doped at a relatively high doping rate, ensuring high conductivity of the solid electrolyte and enabling energy stabilization of the conjugated polymer. Therefore, the degradation of the solid electrolyte when the solid electrolytic capacitor is exposed to high temperature or high temperature and high humidity environments can be suppressed, high conductivity can be maintained, and thus changes in ESR can be reduced.

[0098] Precursors for conjugated polymers include raw material monomers, oligomers formed by linking multiple molecular chains of raw material monomers, and prepolymers. One type of precursor can be used, or two or more can be used in combination. From the viewpoint of easily obtaining higher orientation of the conjugated polymer, at least one (especially a monomer) selected from the group consisting of monomers and oligomers is preferred as a precursor.

[0099] Liquid compositions typically contain a solvent. Examples of solvents include water, organic solvents, and mixtures of water and organic solvents (such as water-soluble organic solvents).

[0100] It can also be added to liquid compositions when using other conductive materials, additives, etc.

[0101] The liquid composition may contain an oxidizing agent as needed. Additionally, the oxidizing agent may be applied to the anode body before or after contacting the liquid composition with the anode body having a dielectric layer formed. Examples of such oxidizing agents include those capable of generating Fe. 3+ Compounds (such as ferric sulfate), persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. Oxidizing agents can be used alone or in combination of two or more.

[0102] The three-electrode electrolytic polymerization is carried out while the anode, counter electrode, and reference electrode are immersed in a liquid composition. For example, a Ti electrode is used as the counter electrode, but it is not limited to this. As the reference electrode, a silver / silver chloride electrode (Ag / Ag) is preferably used. + ).

[0103] In electrolytic polymerization, the voltage applied to the anode (polymerization voltage) is, for example, 0.6V or higher and 1.5V or lower. From the viewpoint of easily configuring the anode within the pores of the porous section with a high filling rate and easily ensuring a relatively high crystallinity of the solid electrolyte, the polymerization voltage is preferably greater than 0.9V and less than 1.2V (or less than 1.1V), and can be greater than 1.0V and less than 1.2V, or greater than 1.0V and less than 1.1V. By performing electrolytic polymerization in a triode manner at such a polymerization voltage, the polymerization reaction within the pores can be precisely controlled. Therefore, within the pores, the polymer chains of the conjugated polymer can grow in a state of highly dispersed dopant, and the solid electrolyte can be configured within the pores with a high filling rate. In addition, since the polymerization can proceed slowly, the orientation and crystallinity of the conjugated polymer can be further improved, and a relatively high doping rate can be obtained, easily ensuring a relatively high conductivity. It should be noted that the polymerization voltage is the voltage applied to the anode relative to the reference electrode (silver / silver chloride electrode (Ag / Ag)). + )) of potential.

[0104] The temperature for electrolytic polymerization can be, for example, above 5°C and below 60°C, or above 15°C and below 35°C.

[0105] Before electrolytic polymerization, the surface of the dielectric layer is pre-coated. This pre-coating can be performed using a conductive material (conductive polymer, etc.). The pre-coating can be performed using either self-doped or non-self-doped conductive polymers. Alternatively, the pre-coating can be formed using a liquid composition (liquid dispersion, solution, etc.) containing at least a self-doped conductive polymer.

[0106] Compared to the liquid dispersion used in forming the solid electrolyte constituting the cathode, the conductive polymer in the liquid dispersion used in the pre-coating process has a smaller particle size and lower concentration. For example, the average primary particle size of the conductive polymer particles contained in the liquid dispersion used in the pre-coating process can be 100 nm or less, or 60 nm or less. Furthermore, the dry solids content of the liquid dispersion is, for example, 1.2% by mass or less. It should be noted that in the liquid dispersion used in forming the solid electrolyte constituting the cathode, the average primary particle size of the conductive polymer particles is typically 200 nm or more, and the dry solids content is 2% by mass or more. The conjugated polymer used in the pre-coating process (or the conjugated polymer forming the backbone of the self-doped conductive polymer) can be the same type or a different type of conjugated polymer formed by electrolytic polymerization. The dopant used in the pre-coating process can be the same type or a different type of dopant used in the electrolytic polymerization.

[0107] The pre-coating process is performed by applying a liquid composition containing a conductive material (such as a conductive polymer) to an anode body having a dielectric layer (specifically, a cathode forming portion) and then drying it. It is preferable to repeat the application and drying of the liquid composition two or more times. Even when the anode body is a porous molded body or a porous sintered body, by repeatedly applying and drying the liquid composition multiple times, the coverage of the pre-coating-based layer on the surface, including the inner walls of the pores in the porous portion, can be improved. Therefore, through electrolytic polymerization, a more uniform and dense solid electrolyte can be formed with a high filling rate, easily ensuring high stability and high conductivity of the first part. By forming the first part with a high filling rate within the pores, airflow can be reduced. Consequently, since the degradation of the solid electrolyte in the first part when the solid electrolytic capacitor is exposed to high temperature or high temperature and high humidity environments is suppressed, ESR changes can be reduced.

[0108] (Part Two)

[0109] The second part can be a single constituent layer (solid electrolyte layer). The second part may differ from the first part in at least one of the composition of the solid electrolyte and the membrane material, or it may have the same composition and membrane material. The second part may also consist of multiple layers. At least two of these multiple layers may differ in at least one of the composition and the membrane material, or they may have the same composition and membrane material.

[0110] The second part of the solid electrolyte can be formed by chemical polymerization, general two-electrode electrolytic polymerization or liquid dispersion. However, from the viewpoint that the dopant is highly dispersed in the solid electrolyte as a whole, it is easy to ensure high conductivity and easy to suppress the deterioration of the solid electrolyte, the second part is also preferably formed by three-electrode electrolytic polymerization.

[0111] As the conjugated polymer included in the second part, it can be selected from the conjugated polymers described in the first part, for example. The Mw of the conjugated polymer can be selected from the range described in the first part. As a dopant, at least one selected from the group consisting of polymer anions and anions described in the first part can be used. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, carboxylate ions, etc., but there are no particular limitations. Examples of dopants that generate organic sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid. From the viewpoint of easily obtaining higher stability, polymer anions are preferred.

[0112] In the second part, the amount of dopant contained in the solid electrolyte may be, for example, more than 10 parts by mass and less than 1000 parts by mass, more than 20 parts by mass and less than 500 parts by mass, or more than 50 parts by mass and less than 200 parts by mass relative to 100 parts by mass of the conjugated polymer.

[0113] The second part can be formed using a liquid dispersion (or solution) containing a conjugated polymer and a dopant. When the second part is formed by electrolytic polymerization, it can be formed in the same manner as described for the first part. The polymerization voltage for electrolytic polymerization can be within the range described for the first part, and can be 0.6V or higher and 1.5V or lower, or 0.7V or higher and 1.2V or lower.

[0114] (other)

[0115] The first and second parts may, as needed, further comprise at least one selected from the group consisting of known additives and known conductive materials other than conductive polymers. Examples of such conductive materials include at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0116] Examples of additives that can be added to solid electrolytes include known additives (e.g., coupling agents, silane compounds), known conductive materials other than conductive polymers, and water-soluble polymers. The first and second parts (or the layers constituting the parts) may each contain one of these additives, or a combination of two or more. In the case where each part is composed of multiple layers, the additives contained in each layer may be the same or different.

[0117] The first and second parts can each be a single layer or composed of multiple layers. When each part is composed of multiple layers, the types, composition, and content of conductive polymers, additives, etc., contained in each layer can be the same or different. A layer to improve adhesion can also be sandwiched between the dielectric layer and the solid electrolyte.

[0118] The differences between the individual solid electrolytes constituting the first or second part can be determined, for example, by cross-sectional image analysis using an electron probe microanalyzer (EPMA). For instance, EPMA analysis can be performed at equal intervals within a cross-sectional image of the entire solid electrolyte layer, and the interfaces between adjacent solid electrolytes can be determined based on the differences in the wavelengths of characteristic X-rays at each measurement point. The samples used for the measurement are prepared following the same procedures as those used for Raman spectroscopy measurements.

[0119] (Cathode lead-out layer)

[0120] The cathode lead-out layer may have at least a first layer that contacts and covers at least a portion of the solid electrolyte, or it may have a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles, a metal foil, etc. Examples of conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode lead-out layer may be composed of a layer containing conductive carbon (also called a carbon layer) as the first layer and a layer containing metal powder or a metal foil as the second layer. When a metal foil is used as the first layer, the cathode lead-out layer may also be composed of that metal foil.

[0121] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0122] The second layer, containing metal powder, can be formed, for example, by laminating a composition containing metal powder onto the surface of the first layer. Examples of such a second layer include a metal paste layer formed using a composition containing metal powder such as silver particles and a resin (binder resin). Thermoplastic resins can also be used as the resin component, but thermosetting resins such as imide resins and epoxy resins are preferred.

[0123] When using metal foil as the first layer, the type of metal is not particularly limited. Valve-acting metals (aluminum, tantalum, niobium, etc.) or alloys containing valve-acting metals are preferred. The surface of the metal foil may be roughened as needed. A chemical conversion film may be formed on the surface of the metal foil, or a coating of a different metal (dissimilar metal) or non-metal may be formed. Examples of dissimilar metals and non-metals include metals such as titanium and non-metals such as carbon (conductive carbon, etc.).

[0124] Alternatively, the coating of the aforementioned dissimilar metal or non-metal (e.g., conductive carbon) can be used as the first layer, and the aforementioned metal foil can be used as the second layer.

[0125] (other)

[0126] A solid electrolytic capacitor comprises at least one capacitor element. Solid electrolytic capacitors can be wound, chip-type, or multilayered. For example, a solid electrolytic capacitor may also comprise multiple stacked capacitor elements. Additionally, a solid electrolytic capacitor may comprise two or more wound capacitor elements. The configuration of the capacitor elements depends on the type of solid electrolytic capacitor.

[0127] In capacitor elements, one end of a cathode lead terminal can be electrically connected to the cathode lead layer. The cathode lead terminal is bonded to the cathode lead layer, for example, by coating the cathode lead layer with a conductive adhesive. Alternatively, one end of an anode lead terminal can be electrically connected to the anode lead portion of the anode body. The other ends of the anode and cathode leads extend from the resin housing or case, respectively. The other ends of each terminal exposed from the resin housing or case are used for soldering to the substrate on which the solid electrolytic capacitor is mounted. Furthermore, not limited to cases with extended lead terminals, at least one end face of the anode and cathode portions can be exposed from the outer surface of the sealing body for electrical connection to external electrodes.

[0128] The capacitor element is sealed using a resin housing or casing. For example, the capacitor element and the resin material of the housing (e.g., uncured thermosetting resin and filler) can be housed in a mold, and the capacitor element can be sealed with a resin housing by transfer molding, compression molding, or similar methods. In this case, the portions of the anode lead terminals and cathode lead terminals connected to the anode lead leading from the capacitor element are exposed from the mold. Alternatively, the capacitor element can be housed in a bottomed housing with the portions of the anode lead terminals and cathode lead terminals located at the opening of the bottomed housing, and the opening of the bottomed housing can be sealed with a sealing body, thereby forming a solid electrolytic capacitor. The leads can be wire-shaped or frame-shaped (lead frame, etc.).

[0129] Figure 1 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to one embodiment of the present disclosure.

[0130] The solid electrolytic capacitor 20 includes: a capacitor element 10 containing an anode portion 6 and a cathode portion 7; a casing 11 sealing the capacitor element 10; an anode lead frame 13 electrically connected to the anode portion 6; and a cathode lead frame 14 electrically connected to the cathode portion 7.

[0131] The anode portion 6 has an anode body 1 and an anode wire 2. A portion of the anode wire 2 is embedded within the anode body 1, while the remaining portion protrudes outward from the outer surface of the anode body 1. A portion of the first part of the anode lead frame 13 is electrically connected to the protruding portion of the anode wire 2 by means of welding or the like.

[0132] A dielectric layer 3 is formed on the surface of the anode body 1. The cathode portion 7 has a solid electrolyte layer 4 covering at least a portion of the dielectric layer 3 and a cathode lead-out layer 5 covering at least a portion of the surface of the solid electrolyte layer 4. The cathode lead-out layer 5 has: a carbon layer formed to cover at least a portion of the surface of the solid electrolyte layer 4, and a layer containing metal particles formed to cover at least a portion of the carbon layer. Furthermore, a portion of the first part of the cathode lead frame 14 is electrically connected to the cathode lead-out layer 5 by bonding it with a conductive adhesive layer 8.

[0133] [Example]

[0134] The present invention will now be described in detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0135] Examples 1-2 and Comparative Example 1

[0136] Construct capacitor components according to the following guidelines and evaluate their characteristics.

[0137] (1) Preparation of an anode with a dielectric layer

[0138] As the anode body, a tantalum sintered body (porous body) with a portion of the anode wire embedded is prepared. The tantalum sintered body is immersed in a chemical conversion solution, and anodizing is performed by applying a DC voltage of 70V for 20 minutes. In this way, a dielectric layer containing tantalum oxide is formed on the surface of the anode body.

[0139] (2) Formation of solid electrolyte layer

[0140] (2-1) Pre-coating treatment

[0141] An aqueous dispersion containing a self-doped polythiophene polymer was prepared. The tantalum sintered body portion (cathode forming portion) of the anode body with the dielectric layer obtained in (1) above was immersed in the aqueous dispersion for approximately 30–60 seconds, then removed and dried under reduced pressure. This immersion and drying process was repeated multiple times in the aqueous dispersion in solid electrolytic capacitors E1 and E2. A pre-coating was formed, similar to that of solid electrolytic capacitors. It should be noted that the concentration of the polythiophene polymer in the aqueous dispersion was 1% by mass. As the self-doped polythiophene polymer, PEDOT (Mw: approximately 10,000) with sulfonyl groups bonded to the PEDOT backbone via butylene linking groups was used.

[0142] (2-2) Electrolytic polymerization

[0143] A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene monomer and polystyrene sulfonic acid (PSS, Mw: 100,000) as the polymer anion in ion-exchanged water. Ferric(III) sulfate (oxidant) dissolved in the ion-exchanged water was added while stirring the mixed solution to prepare a polymerization solution. Electrolytic polymerization was carried out using the resulting polymerization solution in a three-electrode configuration. More specifically, a pre-coated anode, counter electrode, and reference electrode (silver / silver chloride reference electrode) were impregnated in the polymerization solution. A voltage was applied to the anode such that the potential of the anode relative to the reference electrode was 1.1V, and electrolytic polymerization was carried out at 25°C.

[0144] This process was repeated, resulting in the formation of a solid electrolyte layer.

[0145] (3) Formation of the cathode lead-out layer

[0146] The anode obtained in (2) above is immersed in a dispersion in which graphite particles are dispersed in water. After being removed from the dispersion, it is dried, thereby forming at least a first layer (carbon layer) on the surface of the solid electrolyte layer. The drying is carried out at 130°C to 180°C for 10 to 30 minutes.

[0147] Next, a silver paste containing silver particles and an adhesive resin (epoxy resin) is applied to the surface of the first layer, and heated at 150–200°C for 10–60 minutes to cure the adhesive resin, forming the second layer (the layer containing metal particles). Thus, a cathode lead-out layer consisting of the first layer (carbon layer) and the second layer (the layer containing metal particles) is formed, and a cathode portion consisting of a solid electrolyte layer and the cathode lead-out layer is formed.

[0148] In this way, a total of 20 capacitor elements were produced.

[0149] Reference Example 1

[0150] The solid electrolyte layer is formed according to the steps described below. Otherwise, the capacitor element is fabricated in the same manner as in Example 1.

[0151] In the pre-coating treatment, similar to Comparative Example 1, immersion in the aqueous dispersion and drying were performed once each. Using the pre-coated anode, the electrolytic polymerization of pyrrole was carried out according to the following steps.

[0152] A polymerization solution comprising pyrrole (a monomer of a conjugated polymer), naphthalenesulfonic acid (a dopant), and distilled water was prepared. Electrolytic polymerization was carried out using the obtained polymerization solution in a three-electrode configuration. More specifically, a pre-coated anode, counter electrode, and reference electrode (silver / silver chloride reference electrode) were impregnated in the polymerization solution. A voltage was applied to the anode with a potential of 0.9 V relative to the reference electrode, and electrolytic polymerization was carried out at 25 °C to form a solid electrolyte layer. The concentration of pyrrole in the polymerization solution was approximately 1.3% by mass, and the concentration of the dopant was approximately 4% by mass.

[0153] [evaluate]

[0154] The following evaluation was conducted using solid electrolytic capacitors.

[0155] (a) Presence ratio of sulfur in the porous section

[0156] Using a capacitor element, following the steps described above, perform EPMA analysis on the cross-section of the porous portion of the anode body, and determine the net intensities of Ta and S elements using element mapping. Then, determine the presence ratio of S element from these net intensities using the steps described above.

[0157] (b) Raman spectroscopy determination of solid electrolytes

[0158] Using the capacitor element of Example 1, the Raman spectrum of the first section of the solid electrolyte was measured according to the steps described above. In the Raman spectrum of the first section, the value at 1420 cm⁻¹... -1 The characteristic peak (first peak) of the five-membered ring of PEDOT was observed at 1000 cm⁻¹. -1 A peak characteristic of the aromatic ring -S element bond in PSS (the second peak) was observed. The intensity I of the first peak was determined. p1 and the intensity of the second peak I p2 Calculate the ratio I p1 / I p2 Result I p1 For 3545, I p2 It is 659, compared to I p1 / I p2 It is 5.38.

[0159] (c)ESR

[0160] At 20°C, the initial ESR (mΩ) of the capacitor elements was measured at a frequency of 100kHz using a 4-terminal LCR meter. Then, the average value (R0) of 20 capacitor elements was calculated for the initial ESR.

[0161] Ten of the 20 capacitor elements for which the initial ESR was measured were placed at 145°C for 600 hours and then cooled to 20°C. The ESR (mΩ) of the cooled capacitor elements was measured under the same conditions as the initial ESR measurement, and the average value (R1) of the 10 elements was calculated. The change in ESR 1 (mΩ) was obtained by subtracting R0 from R1.

[0162] The remaining 10 capacitor elements were placed at 85°C and 85% RH for 600 hours, then cooled to 20°C. The ESR (mΩ) of the cooled capacitor elements was measured under the same conditions as the initial ESR measurement, and the average value (R2) of the 10 elements was calculated. The change in ESR 2 (mΩ) was obtained by subtracting R0 from R2.

[0163] The evaluation results are shown in Table 1. Capacitor elements E1 to E2 are Examples 1 and 2, capacitor element C1 is Comparative Example 1, and capacitor element R1 is Reference Example 1. The changes in ESR 1 and 2 are expressed as relative values ​​when the change in Comparative Example 1 is set to 1.00.

[0164] [Table 1]

[0165]

[0166] As shown in Table 1, in capacitor elements formed by the electrolytic polymerization of pyrrole in the solid electrolyte layer, the ESR change when exposed to high temperature (or high temperature and high humidity environment) is very large (capacitor element R1). In capacitor element C1, where the sulfur content in the first part is less than 0.17%, the ESR change is smaller compared to capacitor element R1, but the change is still large. In contrast, it can be seen that in embodiments where the sulfur content in the first part is 0.17% or more (capacitor elements E1 to E2), the ESR change is significantly reduced, and excellent reliability can be obtained. It should be noted that when using a liquid dispersion containing PEDOT and PSS to form the first and second parts, it is difficult to configure the solid electrolyte with a high filling rate in the pores of the porous portion. Therefore, the sulfur content in the first part is lower than 0.14% in capacitor element C1, and the ESR changes 1 and 2 are larger than those in capacitor element C1.

[0167] Industrial availability

[0168] According to this disclosure, the ESR variation of solid electrolytic capacitors exposed to high temperatures (or high-temperature, high-humidity environments) can be reduced. The capacitor elements and solid electrolytic capacitors of this disclosure consistently ensure low ESR even when exposed to high temperatures (or high-temperature, high-humidity environments), and therefore can be used in various applications requiring heat resistance, moisture resistance, or reliability. However, the applications of the capacitor elements and solid electrolytic capacitors are not limited to this.

[0169] Explanation of reference numerals in the attached figures

[0170] 20: Solid electrolytic capacitors

[0171] 10: Capacitor Components

[0172] 1: Anode body

[0173] 2: Anode wire

[0174] 3: Dielectric layer

[0175] 4: Solid electrolyte layer

[0176] 5: Cathode lead-out layer

[0177] 6: Anode section

[0178] 7: Cathode section

[0179] 8: Conductive adhesive layer

[0180] 11: Outer shell

[0181] 13: Anode lead frame

[0182] 14: Cathode lead frame.

Claims

1. A solid electrolytic capacitor element comprising: an anode body having at least a porous portion on its surface; a dielectric layer covering at least a portion of the surface of the anode body; and a solid electrolyte covering at least a portion of the dielectric layer. The anode contains tantalum. The solid electrolyte contains sulfur. The solid electrolyte has: a first portion disposed within the pores of the porous portion; and a second portion disposed from the main surface of the anode having the dielectric layer to the outer side of the porous portion. In the elemental mapping of a specified region of the cross-section of the porous portion using an electron probe microanalyzer, the sulfur content is 0.17% or higher when the tantalum content is set to 100%.

2. The solid electrolytic capacitor element according to claim 1, wherein, The first part comprises: a first polymer component equivalent to a conjugated polymer; and a second polymer component equivalent to a polymer anion containing sulfur.

3. The solid electrolytic capacitor element according to claim 2, wherein, The first polymer component contains sulfur.

4. The solid electrolytic capacitor element according to claim 2, wherein, In the Raman spectrum of the first part, the intensity I of the first peak characteristic of the first polymer component is... p1 The intensity I relative to the second peak characteristic of the second polymer component p2 The ratio of I p1 / I p2 It is 2 or higher.

5. The solid electrolytic capacitor element according to claim 4, wherein, The ratio I p1 / I p2 It is below 7.

6. The solid electrolytic capacitor element according to any one of claims 2 to 5, wherein, In the first part, the conjugated polymer contains monomer units corresponding to thiophene compounds, and the polymer anion contains monomer units corresponding to aromatic sulfonic acid compounds. In the Raman spectrum of the first part, at 1200 cm⁻¹ -1 Above and 1600cm -1 The first peak characteristic of the first polymer component was observed in the following range, at 800 cm⁻¹. -1 Above and 1100cm -1 The second peak characteristic of the second polymer component was observed in the following range.

7. The solid electrolytic capacitor element according to any one of claims 2 to 5, wherein, The weight-average molecular weight of the polymer anion is above 100 and below 500,000.

8. The solid electrolytic capacitor element according to claim 1 or 2, wherein, The anode body is a porous sintered body.

9. A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element as described in claim 1 or 2.

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